Technischer Bericht

The intensifying electrification trend in the automotive industry along with calls for high-efficiency, low-cost industrial applications drive the demand for energy- and cost-efficient electromagnetic components. Electromagnetic components of soft magnetic composite (SMC) materials can play an important role in this trend, making it possible to manufacture more compact and cost-efficient motor and inductor solutions compared to using traditional designs.

SMC materials are made of iron powder particles coated with an electrically insulating layer and can be formed into complex shapes by means of powder metallurgy (PM), thereby allowing three-dimensional magnetic circuit design.

This study mainly evaluates and analyses a partial carbon footprint of a product (CFP), applied to SMC powder production including raw materials, atomizing, annealing and surface insulation coating. Some life cycle analyses (LCA) of component manufacturing and benefit in electromagnetic application are also presented. A primary investigation to recycle SMC part is reported in this study as well.

Electrification pushes the agenda of soft magnetic material development, with increased demands on efficient low loss materials with minimal environmental impact. Soft Magnetic Composites (SMC) challenges traditional magnetic materials such as soft ferrites and electrical steels in applications with alternating magnetic fields, and can many times offer a solution that is more efficient and with lower carbon footprint. In comparison to those traditional materials, however, the relatively higher hysteresis has so far limited wide application of SMC. This paper presents a new material which combines an improved base powder and a newly developed water-based coating, into a product with lower hysteresis losses than any previous SMC material, combined with improvements in processing and application.

This paper introduces Somaloy® 7P, discusses the effect of manufacturing process parameters, such as compaction, heat treatment atmosphere, on component performance. Furthermore, the effects of operating temperature on component properties are investigated.

The quality of drinking water is affected by metal ions introduced through leaching from materials that come in contact with it, such as pipes, fittings and heat exchangers. Regulatory authorities have established maximum permissible quantities of metal ions in drinking water. In brazed components, the leaching of metal ions can be observed due to the interaction of both the base material and the brazing filler metal in contact with the water. With the correct selection of base material and brazing filler metal this effect can be minimized. The metal ion leaching of AISI 316L components brazed with different filler metals, Cu-foil (99.9% Cu), BNi-5, BrazeLet^® Ni613, BrazeLet F300-20 and BrazeLet F86, was investigated and compared to suggest the best choice for minimizing the amount of metal ions leached into the water.

Ferritic stainless steels are gaining increasing interest for brazed components due to the combination of low cost, low thermal expansion and good high temperature scaling resistance, compared to the commonly used austenitic stainless steels. As a continuation of our recent work on the effect of gap clearance on joint strength for austenitic stainless steels, the same effect has been studied for ferritic stainless steels. Due to differences in diffusivity of elements in ferritic stainless steels compared to austenitic stainless steels, the data from austenitic stainless steels cannot easily be extrapolated to ferritic stainless steels. In this investigation, AISI 430 butt-joint specimens were brazed with different nominal gap clearances ranging up to 300 μm, and the effect on the joint tensile strength was measured.

Ferritic stainless steels are gaining interest due to the combination of low cost, low thermal expansion and good high temperature scaling resistance compared to the commonly used austenitic stainless steels. These materials are of special interest for exhaust gas system components in gasoline cars, where the service temperatures are higher than for diesel cars. Previous research on the corrosion resistance of brazed ferritic stainless steel components have focused largely on vacuum brazed components, while the focus on belt furnace brazing has been limited. The presence of nitrogen in the brazing atmosphere has been found to affect the corrosion resistance of the base materials and filler materials in studies with austenitic stainless steels, but the effect on ferritic stainless steels has not yet been studied. In this investigation, AISI 430 and AISI 441 test samples were brazed with the common Ni-base brazing filler metals BNi-2, BNi-7, BrazeLet^® Ni613 and Höganäs Fe-base brazing filler metal BrazeLet F300.

Overlay welding using PTA or laser cladding is a technique commonly used to hardface components exposed to wear. State-of-the-art materials for these applications are nickel-based alloys with tungsten carbide particles embedded. Iron-based materials offer a cost effective alternative with lower environmental impact. The iron-based system offers different challenges compared to the nickel based system in terms of hard phase formation and stability upon processing. To be able to optimize composition and fulfil final application properties, microstructure evolution during processing needs to be understood and predicted. This paper focuses on computational materials design using thermodynamic calculations applied to multicomponent systems to optimize alloy compositions.

The High Velocity Air Fuel (HVAF) Spray process is becoming more and more popular but despite off its long history, the industrial activities to work out differences of HVAF and classical Kerosene-fired High Velocity Oxygen Fuel (KF-HVOF) Spraying are still on a level of “collecting experience” and “not being understood completely”. This publication gives an explanation of the differences between HVAF and HVOF and their impact on the metallurgy and coating properties.

In 2008, Höganäs together with KBE+ redesigned the transmission for the smart fortwo car. The ambition was to create a powder metallergy (PM) friendly, reduced weight transmission that could be built into the original transmission housing whilst maintaining reliability. The reverse engineering analysis showed that this could be done without sacrificing service life, and with an accumulated weight reduction on the gears of 1 kg. In 2010, this transmission was built into a smart fortwo, driven to the PM World Congress in Florence and exhibited there. Since the congress, the smart car has been used as an everyday driver for eight years and accumulated 200 000 km.

In this paper, an evaluation of the PM gears will be presented. The gears are visually inspected after 200 000 km of real driving. The wear, as well as any other damage to gears and synchronizers will be investigated and discussed. Topography measurements before and after 200 000 km will be shown for quantification of wear, and pictures of the gear flanks will be shown to establish the general condition of the gears. From the design work the stress conditions are known, and from the logging system in the car, information on cycles and load can be estimated to further understand the load history of the gears.

The automotive electrification open doors for new powder materials, manufacturing methods and assembly routines that are found to be very cost-effective. Soft-magnetic composites (SMC) show great potential to fulfill these demands by both significant size- and weight reduction of the active parts in the electromagnetic circuit. The result will not appear by using traditional thinking but will require openness towards both new routes and new investments to deliver the desired values. The new SMC components must be designed to enhance both magnetic performance, as well as the production of components and assembly into applications and systems to improve productivity and save costs. This case study provides an analysis and overview of the route to produce an
SMC based electric motor for an automotive cooling water pump to fit in a hybrid or full electric car. The results of the study show a concurrent engineering approach for creating an optimized magnetic design combined with component and tooling design adapted for high-volume production. The SMC component is further matched to a dedicated press showing the way to a high efficient manufacturing line that can meet the demands of higher quality and cost-effectiveness. The performance of the motor is verified by prototypes made from net-shaped pressed SMC components. The outcome of the study is aimed to advise a state-of art SMC component process including design, manufacturing and assembly aspects for a potential automotive electrification application

In 2008, Höganäs together with KBE+ redesigned the transmission for the smart fortwo car. The ambition was to create a PM friendly, reduced weight transmission that could be built into the original transmission housing whilst maintaining reliability. The reverse engineering analysis showed that this could be done without sacrificing service life, and with an accumulated weight reduction on the gears of 1 kg. In 2010, this transmission was built into a smart fortwo, driven to the PM World Congress in Florence and exhibited there. Since the congress, the smart car has been used as an everyday driver for eight years and accumulated 200 000 km.

In this paper, an evaluation of the PM gears will be presented. The gears are visually inspected after 200 000 km of real driving. The wear, as well as any other damage to gears and synchronizers will be investigated and discussed. Topography measurements before and after 200 000 km will be shown for quantification of wear, and pictures of the gear flanks will be shown to establish the general condition of the gears. From the design work the stress conditions are known, and from the logging system in the car, information on cycles and load can be estimated to further understand the load history of the gears.

Machining is a tribological process which involves friction, lubrication and wear. It is important to understand the basic machining principles and link them to the actual machining of components. Powder metalallurgy (PM) components are commonly considered to be more difficult to machine compared to wrought steels due to their inherent porosity and differences in the material compositions required to achieve similar performance. Machinability enhancing additives are a commonly used solution to improve machining. However, to utilize the benefits provided by the additives for specific or multiple machining operations is a challenging subject due to the complexity of machining. Therefore, developing an effective laboratory testing procedure based on specific machining operations is critical to avoid failures in production trials when introducing a machining enhancer into the material. In this study, the basics of machining PM materials and the ways to improve machining are discussed. The effectiveness of recenttly developed machining enhancers is demonstrated for improving productivity and increasing tool life through application case studies.

Variable valve timing (VVT) systems have done much to improve fuel efficiency and to reduce emission levels of combustion engines. These factors are of increasing importance with stricter legislation and higher demands upon sustainable transportation. Components for VVT require a complex shape and make high demands on dimensional precision and machinability. Their complex
geometry makes VVT components very suitable applications for PM. In addition, commercial manufacturing of VVT parts require high productivity and a minimized scrap rate.

This paper describes a new powder mix concept that has been developed to meet the requirements of efficient manufacturing, and a trial of stator components under full production conditions validates the concept. Factors influencing the production efficiency and product precision such as die filling, compaction, and machinability have been investigated. Results from the tests show that this new concept enables improvement of dimensional precision and productivity, thus improving overall manufacturing effectiveness.

Sinter hardening is an established cost-effective process for producing high strength parts that combines sintering and accelerated cooling in one sintering cycle, and also removes the need for additional heat treatment. It is known that the cooling rate after sintering greatly influences the microstructure of PM steel through the formation of martensite, which strongly determines its final properties. Alloying elements such as molybdenum, chromium, nickel and copper all promote hardenability. By increasing the hardenability of the material, martensite can also be obtained at lower cooling rates.

In this study, a number of materials used for sinter hardening (Mo/Cu hybrid low alloy steel and Cr/(Mo) pre-alloyed low alloy steels) have been investigated utilizing various sintering temperatures and cooling rates in a new pusher/roller furnace. The mechanical properties and microstructures achieved for each individual PM material are described. By understanding how sintering temperatures and cooling rates influence microstructure and mechanical properties, it is possible to optimize the sintering cycle for each material and its applications.

Steel powder grades pre-alloyed with Cr are suitable for the manufacturing of high performance PM components, since Cr is a cost-efficient alloying element with excellent hardenability. Cr-alloyed PM steel parts are also fully recyclable, and this is increasingly important from a sustainability perspective. High fatigue strength is a key feature for many applications with high demands, such as synchronizer parts in automotive transmissions.

This paper presents fatigue properties for two Cr-alloyed powder grades after different sinter-hardening processes. Sintering trials were undertaken in a mesh belt furnace at 1120 °C, as well as a roller hearth high temperature furnace at 1250 °C. In both trials, rapid cooling was applied after sintering to obtain predominately martensitic microstructures. The fatigue strength of the sinter-hardened and tempered materials were evaluated by plane bending tests on standard test bars. Microstructures were identified and correlated with the fatigue performance of the Cr-alloyed materials.

Soft magnetic composites (SMC) are used for electromagnetic applications such as motors, inductors, actuators and pulse-transformers. The occurrence of corrosion in magnetic components in different environments can be a universal problem, and good corrosion protection is very important for many electromagnetic applications. This study investigated the effect of corrosion on the mechanical strength and magnetic properties of four types of SMC components when compared with Fe-Si laminated steel components. Several protection coatings were evaluated using both a Salt Spray Test and Electrochemical Impedance Spectroscopy (EIS) measurements. It was found
that corrosion might decrease the mechanical strength and magnetic properties of SMC. However, the stability of magnetic properties for SMC materials is better than laminated steel sheets in corrosive environments. A water-borne single coat of paint can offer good protective properties against corrosion.

To meet the need of improved properties, e.g. resistance against fatigue and wear, a variety of hardening treatments can be chosen on steel components. These improved properties are in fact the result of high hardness, the introduction of residual stresses and, with some diffusion treatment methods, a modified chemistry close to the component surface. To avoid larger changes of form and dimension, the hardening process temperature could be kept low, e.g. in the ferritic area. With this temperature restriction in mind, the nitriding diffusion hardening method is often a suitable alternative to achieve the improved properties in question on  conventionally wrought steel. The presence of porosity in a powder metallugy (PM) component could however affect the result. This paper will discuss how properties are influenced by different nitriding processes, PM material grade and component density.

The hardenability of steels is dependent on the type and amount of alloying elements present. Ni and Cu are commonly used in PM industry and can boost the hardenability of PM steels resulting in improved mechanical performance. In this study the effect of Cu or Ni additions on the hardenability of material grades pre-alloyed with Cr is investigated by generating and comparing the respective CCT diagrams. Results from mechanical testing from a previous study as well as metallographic investigation are used for getting a full picture regarding the hardenability of those steels. These results can be a useful tool for designing and controlling the heat treatment of PM steels.

Cost-effective material solutions with high performance will be required to continue to grow the PM industry and expand the use of PM into more demanding applications. Chromium alloyed PM steels combine excellent mechanical properties with good dimensional stability, as well as stable alloying costs when compared to traditional Mo/Ni alloyed material. Sustainability is also becoming a more important factor in the selection of material and processing conditions. Utilizing the PM process with chromium materials is proven to be a sustainable solution with less influence on the environment. The combination with the sinter-hardening process makes chromium material even more competitive. By
increasing the conventional sintering temperature of 1120 ºC to a higher temperature of 1250 ºC, the properties of chromium materials can be developed further. In this study, some chromium alloyed materials will be presented and the properties achieved after conventional sintering at both 1120 ºC and 1250 ºC are discussed. The environmental impact of chromium material and high performance applications which utilize chromium alloyed PM steels will also be described.

Metallographic investigations have always been useful to find out the reasons for failure. The present paper contains PM industrial examples where the problems have been solved with the help of microstructural analysis. This analyses will help PM customers to become more aware about microstructures and their importance in order to produce better quality products and taking PM to a higher level.

The layer by layer build-up of metal parts by selective laser melting puts specific requirements on the powder quality. The powder should be able to spread homogeneously throughout the layer, to melt and fuse without forming detrimental defects. Consequently, the clean, highly spherical gas atomized powders with excellent flowability are used in this process. However, little work has been published on water atomized powder since higher oxygen levels and lower apparent density can be expected and are believed to be detrimental to build quality. Several variants of water atomized powder was used to investigate the effects of higher levels of impurities and cohesivity on the properties of the built part. Powder properties were analyzed using traditional methods such as Hall flow, particle size distributions, and various density measurements in combination with a modern powder rheometer for characterization. The behavior during building was evaluated through metallographic investigations, mechanical properties and the chemistry of the printed parts. All of which were compared to the properties of built specimens with industry standard gas atomized powder and forged material. Results indicate that the experimental powders with poor flowability can be successfully spread out onto a bed and consolidated to full density when building with a small layer thickness. The resulting mechanical properties match closely the reference, except for significantly lower impact toughness. This is probably caused by increased numbers of spherical nano-sized oxides homogenously distributed in the structure. This is in turn caused by the higher oxygen contents in the experimental powder. It was also found that part integrity went down when increasing the build layer thickness for the experimental powders.

PM gear rolling densification is a post-sintering process in which the porosity is closed at the surface and at some depth into the flank of the gear. It results in improved mechanical properties such as higher contact strength, but can also be used to improve tolerances. The optimization of the rolling process, the design of the tool geometry, the gear preform and the overall process is time consuming. Therefore, FE simulations are used to optimize the overall process and reduce the development time.

Variable valve timing (VVT) systems allow for the perfect combination of performance
increase, better economy and improved emission control. The components used in a VVT system are typically highly complex in design and challenging to manufacture. Therefore, successful large volume production of high-tolerance VVT components requires a metal powder that continuously delivers high quality and consistent results. The powder solution has to be properly designed to optimize powder handling and processing conditions to fulfill product quality and performance requirements at the total lowest cost for the producers in their manufacturing.

The objective of this paper is to demonstrate properties achievable with Cr pre-alloyed powders. After different processing routes, materials based on these powders exhibit properties suitable for synchronizing hubs, cam lobes, gears and other challenging applications.

A high density is a prerequisite for making high strength PM components. By increasing the density, both strength, and in particular fatigue strength and ductility are improved. 

To achieve high density one of the key issues is to use as low amount of lubricant as possible in order to increase the theoretical density to which the mix can be compacted. However, the lubrication must be efficient enough to eject the pressed part from the tool without deteriorating the surface of the part due to friction. Insufficient lubrication may also lead to damage of the press tool.

Warm die compaction is a process route that is increasingly used for production of high density PM components. By heating the tool die the efficiency of the lubricant will be enhanced, thus allowing a lower amount of lubricant to be used.

Efficient lubrication does not only influence the ejection of the part but also the overall density, as well as the density
distribution inside the pressed component. Lower friction during the compaction results in less density gradients in the pressed part. 

In this paper results are presented from measurements of the lubrication during the compaction. The results include different lubricants and how heated tool die influences the lubrication as well as density of the parts.

Ring gears are used in a planetary gear system to transfer torque from one axis to another. During this transfer the resulting gear forces cause tensile, compressive and contact stresses, which must not exceed permitted values and fatigue stress limits of the material used. To reach necessary fatigue stress levels on gears, i.e., on flank and root, and also to improve tribological performance during gear contact, a number of wellknown processes such as heat treatments can be selected. However, this selection can be limited by the impact on possible distortion of the gear geometry. It is therefore important that both the strength and the geometry, such as dimensions, shape and runout can meet the given specifications. Today, ring gears are in general made from steel forged preforms and undergo a substantial number of expensive machining processes prior to heat treatment. The ring gear design and its critical tolerances, such as runout, are set in order to also minimize gear noise. Ring gears made from PM can be made near to net shape and help to substantially reduce the machining and total cost per unit. In this investigation, different hardening processes have been applied on gears and the influence on shape distortions and fatigue stress limits were determined.

The driving force for using PM compared to other manufacturing techniques is almost always due to its ability to produce structural components with close dimensional tolerances and the required performance in a cost-effective way. To further grow the PM market into new high challenging automotive applications, cost-effective PM material solutions combining higher precision with increased performance will be required. This can be achieved by different means.

The development of new cost-effective alloy systems, new compaction techniques enabling higher densities, sintering at higher temperatures in combination with increased cooling rates, carbon control and adoption of secondary heat treatments, are all examples of ways that either on
their own or in combination can be used to increase material performance. The growing awareness of sustainability also makes it important to select both material and manufacturing processes with the least impact on the environment.

In this paper some key aspects of the selection of suitable metal powder solutions and the processing conditions needed to meet performance requirements. These include costeffectiveness and sustainability for automotive applications like synchronizing hubs, cam lobes, sprockets, gears and other demanding applications that will be presented.

This study presents a novel soft magnetic composite powder that is suitable for the preparation of soft magnetic components working at high frequencies, such as inductors or reactors for power electronics. The material is a combination of Somaloy 110i 5P, a pure iron powder with a coating capable of withstanding heat treatments at 650°C or higher, and a low loss gas atomized Fe-6.5%Si.

Compared to pure Fe-6.5% Si, the advantages of this new material are higher magnetic saturation and high component density similar to that of pure Somaloy 110i 5P, as well as easy manufacturing procedures, i.e., the compaction pressure is low or moderate (800-1200 MPa vs. 1200-2000 MPa for pure FeSi) which reduces production costs. The material displays high frequency losses similar to that of Somaloy 110i 5P+Sendust, but due to the high saturation and density of the Somaloy 110i 5P/FeSi components, the low frequency core losses are further reduced. In this study, this new material concept will also be compared to other inductor materials.

Many new applications utilize the unique possibilities of PM to achieve high strength in combination with close dimensional tolerances and a minimum of manufacturing operations. However, there are many factors from the process, including materials, compaction and sintering, that influence the dimensional tolerances. The sintering process is one of the main factors, including sintering temperature, time, atmosphere and cooling rate. It has in many cases been overlooked or not seen as the primary focus for enabling higher quality PM component manufacturing. The need for a better understanding of the influence of sintering conditions on sinter-hardening materials is becoming more important for cost-effective manufacturing of PM components that combine high mechanical properties with high dimensional precision. 

In this paper, different low alloy PM materials sintered at different temperatures and cooling rates will be described. The influence of these sintering conditions on dimensional precision of a prototype gear will also be presented.

Sinter hardening has developed into a highly cost-effective method for the production of through hardened powder metallurgy (PM) components without the need for additional heat treatments. Over the last years, advances have been made in sinter-hardening materials, processing and with furnaces. Gas quenching can be realized when the cooling zone, directly added to the sintering furnace is prepared with the controlled cooling gas. The performance of the PM component is not only affected by the material and the process, but also by its mass and geometry. In this paper, the effect of mass and geometry on the performance of different PM components in different materials will be studied.

Vanadium is a commonly used alloying element in high strength low alloy (HSLA) steels because it improves strength and wear resistance through the precipitation of vanadium carbonitrides. The use of vanadium in powder metallurgy (PM) steels has so far been limited. A previous study demonstrated that by using a vanadium alloyed PM steel, the total alloying content could be reduced by 50% while maintaining similar or improved properties. This study will examine the effect of sintering conditions on vanadium prealloyed PM steels by varying the sintering atmosphere & temperature. Different material systems based upon prealloyed vanadium steel powders and plain iron powders were sintered in different sintering atmospheres. Mechanical properties and microstructure of each composition and sintering condition will be compared to understand the improvement in properties achieved through the use of vanadium alloying.

Tempering is a heat treatment technique used to improve the strength, ductility and toughness of hardened carbon steels. Tempering occurs by heating the steel to below its critical temperature in order to transform the metastable body-centered tetragonal martensite structure that is formed during quenching into a more stable structure of fine carbide particles. Choosing the correct parameters for tempering is critical to achieving the desired balance of properties. It is important to understand the role tempering has onstrength and toughness properties, as well as the microstructural changes experienced over a range of tempering temperatures. This study examined the mechanical performance of two different alloy systems, a prealloyed and a diffusion-bonded material, after being heat treated and tempered at various tempering parameters.

A successful PM part production process starts with a suitable powder mix with good properties such as good flow and AD, good lubrication, easy to handle, high productivity and precision. Efficiency and reliability of PM process as any other powder processing is depending upon behaviour of the powder composition during handling and processing. Starmix 500i is a bonded mix with excellent lubrication. It offers good powder properties and bonding. It works well for parts with complicated shapes requiring additional lubrication and by applying warm die compaction, its properties can be further improved. Good filling characteristics, of the Starmix 500i, enables higher compaction rates as well as improved productivity and tolerances simultaneously. As the Starmix 500i is free from zinc the staining tendency is low. Moreover, as there will be no zinc residues in the furnace, the need for furnace maintenance is reduced. A benchmark where Starmix 500i is compared to other mixes are presented in this paper.

Powder metallurgy is a cost-efficient process route for the production of net shape or near net shape Components. In many situations, secondary operations for instance, sizing or machining operations are required to meet the tolerance class of the application. Better tolerances of as sintered components will increase the competitiveness of PM technology by reducing the need for secondary operations. In this presentation, the benefits of advancements in material and mixing methods for dimensional control are discussed. In search of new applications for PM components, the industry has a need for ever higher performing lubricants in metal powder mixes. Over the years, several different paths have been taken to improve performance of mixes. Examples are bonded mixes, mixes for warm compaction and more recently mixes for use with heated tooling. Besides good lubrication during compaction there are several requirements on high performance mixes, such as stable powder behavior in terms of filling the tool, stability to variations in temperature and humidity. Some newly developed lubricants exhibit improved properties in key areas such as climate robustness, lubrication and the possibility to boost compaction performance by using heated tooling during compaction. Moreover these new lubricants are Zn-free, thus minimizing  the need for sintering furnace maintenance. Extensive testing has proven that lubrication is superior to amide wax, lubricant properties are not sensitive to humid climate conditions and that green density can be increased compared to conventional mixes.

The continued expansion of the PM market into new applications requires cost-effective materials with increased performance. This can be achieved by different means. The development of newcost effective alloy systems, new compaction techniques enabling higher densities, sintering combined with increased cooling rates and carbon control are all examples of means that either singly or in combination can be used to increase material performance. Alloying elements commonly used in PM materials intended for high performance applications are copper, nickel and molybdenum. However, raw material prices of these elements have been volatile in recent years, making material cost predictions difficult.

Variable valve timing (VVT) systems allow for the perfect combination of performance increase, better economy and improved emission control. The components used in a VVT system are typically highly complex in design and challenging to manufacture. Therefore, successful large volume production of high-tolerance VVT components requires a metal powder that continuously delivers high quality and consistent results. The powder solution has to be properly designed to optimize powder handling and processing conditions to fulfill product quality and performance requirements at the total lowest cost for the producers in their manufacturing.

With all these aspects in mind a metal powder mix concept specifically engineered for manufacturing of
high precision VVT components has been developed and will be presented in this paper.

Metallographic investigations have always been useful to find out the reasons for failure. The present paper contains PM industrial examples where the problems have been solved with the help of microstructural analysis. This analyses will help PM customers to become more aware about microstructures and their importance in order to produce better quality products and taking PM to a higher level.

There are many different types of possible joint configurations when brazing components or test specimens. In practice, the joints produced in a component are often very complex and thus it is difficult to know the strength of the bond without performing some sort of destructive testing.

Whenever designing a component it is important to properly take fatigue related phenomena into account, both to ensure safe operation, but also to allow PM to be used in ever more demanding applications. In previous papers it was shown how the endurance limit of PM steels can be modelled using a fracture mechanics approach combined with an extreme value statistics treatment of the porosity. With this approach it was possible to include both the influence of density and stress concentrations in one comprehensive model. In this paper it is investigated how the model can be extended to include also the short life portion of the SN-curve. This is accomplished by also including fatigue crack propagation in the fracture mechanics model. The use of the model is demonstrated on a chromium based PM steel for sinter hardening applications.

Gear rolling densification is a post sintering process in which the porosity is closed at the surface and in some depth into the flank surface of the gear. The rolling process improves the mechanical properties such as the contact strength. In order to optimize the gear rolling process and produce more accurate results, FE (Finite Element) simulations can be used for validation and thereafter optimization of tool, gear geometry and overall process. In this paper, FE simulations will be conducted with two plasticity material models to understand their behavior in compression. Moreover, experimental results from an indentation of a wrought steel ball to a PM material will be correlated to FE simulation results for different load levels. Furthermore, gear-rolling simulation results will be compared to experimental results for both material models in involute profile.

A cost-effective way to achieve high-performance PM low alloyed steel components is the sinter hardening process route. By controlling the cooling rate accordingly one can steer the microstructure and consequently the mechanical performance of the component. Therefore materials with sufficiently high hardenability are required which in turn can be controlled by optimising the chemical composition. In this study a number of materials suitable for sinter hardening applications have been evaluated with regard to their mechanical performance. The study was complemented with basic material data such as CCT diagrams and Jominy hardenability testing. Metallographic investigation was performed in order to correlate the respective microstructure with the obtained mechanical properties. Results show that using the suitable material data one has flexibility in choosing the appropriate material, over a broad range, for addressing challenging applications through the sinter-hardening process route.

By increasing the density of sintered steels, the attractive combination of both higher strength and higher ductility of the material is gained. One process route to achieve high density PM components is to use high performing lubricants in combination with heated tool die. The synergies of lubricant content, efficiency of the lubricant and tool die temperature are presented in this paper. Using the right combination of mix composition and compaction parameters is one of the keys to obtain higher density of PM components.

A cost-effective way to achieve high-performance PM low alloyed steel components is the sinter hardening process route. By controlling the cooling rate accordingly one can steer the microstructure and consequently the mechanical performance of the component. Therefore materials with sufficiently high hardenability are required which in turn can be controlled by optimising the chemical composition. In this study a number of materials suitable for sinter hardening applications have been evaluated with regard to their mechanical performance. The study was complemented with basic material data such as CCT diagrams and Jominy hardenability testing. Metallographic investigation was performed in order to correlate the respective microstructure with the obtained mechanical properties. Results show that using the suitable material data one has flexibility in choosing the appropriate material, over a broad range, for addressing challenging applications through the sinter-hardening process route.

A recently developed martensitic stainless steel powder designed for laser additive manufacturing was characterized. Mechanical as well as microstructural investigations were performed. It was concluded that the investigated powder is very robust and have a wide process window. The microstructural examination indicates that the powder has a martensitic structure possibly containing small amounts of ferrite in the grain boundaries, which is also supported by thermodynamic calculations.

Iron-based hardfacing alloys are widely used to counteract abrasive and impact wear of industrial components in soil, sand and mineral processing applications. These alloys show a high performance to cost ratio as well as a low environmental impact. The wear resistance of the components hardfaced with these alloys depends on achieved coating microstructure i.e. on the alloys chemical composition, the coating method and process parameters selected.

The wear of piston rings in large marine two-stroke diesel engines is a major maintenance cost. Applying coatings with good oxidation, corrosion resistance and high temperature strength, can lower the total maintenance cost. In the past nickel aluminide with chromium carbide have been applied to pistons by thermal spraying. Using laser cladding a suitable microstructure can be formed while at the same time avoiding cracks and bonding issues. In this report powders and coatings were manufactured in order to be able to investigate the dry-sliding wear behavior. Material with three levels of carbides was atomized. Wear test samples were manufactured by laser cladding. The dry sliding wear-mechanism maps are generated by using block on ring test setup where coated blocks slide against cast iron rings. All alloys exhibited regions of plasticity-dominated wear and oxidational wear with a transition region in-between. The carbide-containing alloys showed lower friction and wear in comparison to the carbide free nickel aluminide alloy.

The Fe-Cu-C family of steels are the most common materials used in producing powder metal components. After conventional sintering, these materials feature a microstructure composed of ferrite and pearlite with the diffused carbon content determining the ratio. The structure is also strengthened by copper as substitutional alloying element. As more than 95% of the matrix is constructed by the base iron powder, the chemistry (purity) and manufacturing method of the base iron powder are considered to play important role in the machinability. This study evaluated the machining responses of sintered Fe-Cu-C steels manufactured from different base iron powder grades and graphite additions to understand the contribution of the base iron and the ratio of ferrite and pearlite to the overall machinability. A commercial machining enhancing additive was selected to evaluate its effectiveness in improving the machining of such sintered materials made with the different grades of base iron powder.

Vanadium is a common alloying element used in wrought metallurgy to manufacture high strength low alloy (HSLA) materials. Vanadium provides improvement in strength and wear resistance through grain refinement and precipitation of vanadium carbonitrides. As PM steels typically utilize high amounts of carbon and are sintered in nitrogen containing atmospheres, potential exists to utilize the element. With small alloy additions and well controlled manufacturing conditions, it is interesting to evaluate the potential improvement in properties by the use of vanadium. In this study, prealloyed vanadium powders with differing vanadium levels were manufactured and evaluated in common ferrous PM material systems. As sintered and heat treated properties indicated the vanadium containing materials achieved identical or better mechanical properties with 50% of the total alloying content reduced.

Martensitic stainless steels are widely used for their superior mechanical properties and moderate corrosion resistance. Martensitic 400 series stainless steel can be heat treated to a wide range of hardness and strength levels. There are many different variations of martensitic 400 series stainless steel, each with its own unique property characteristics for corrosion resistance, mechanical and physical properties as well as surface aspects. Selecting the right martensitic stainless steel grade for a specific application is very important in order to achieve a workable solution. This paper will evaluate properties of common 400 series stainless grades to determine the optimum material and processing methods for required properties. As a comparison, properties of a precipitation-hardened (PH) steel were also examined.

Copper is a common alloying element used in powder metallurgy (PM) materials to achieve improved mechanical strength and hardness. Different amounts of copper with course or fine particle sizes can be admixed with iron to achieve desired properties. However, the addition of copper has a great effect on the dimensional change of PM components. Variation in dimensions and large pores are often caused by copper segregation when the copper is admixed. One way to minimize this drawback is to diffusion-bond the copper to the iron particles with homogeneous distributions of copper. The diffusion-bonding method can help further improve the dimensional stability during sintering. This study introduced a newly developed copper diffusion bonded iron powder aiming for better dimensional control and stability. The mechanical properties and dimensional changes were examined compared to current copper diffusionbonded iron powder and admixed powder containing elemental copper.

Higher density is required to obtain higher mechanical properties of PM components, in particular for the fatigue strength. Besides the compressibility of the base powder, the lubricant and compaction method plays an essential role for compaction of high density. The lubricant type and content are limiting factors to the compressibility due to their low theoretical density. However, by improving the efficiency of the lubricant, a lower added content of lubricant can be meet the requirement of during ejection and thus higher density can be achieved. In this paper, an increased density by using high performance lubricant in Fe-Cu-C mixes as well as excellent green strength and higher tensile strength after sintering, will be presented.

Water-atomized steel powder grades pre-alloyed with Cr are cost effective, robust and versatile materials which are suitable for PM steel parts in demanding structural applications. By choosing the right processing route, these materials enable efficient manufacturing of PM components with high mechanical performance. In this paper properties obtained after different sintering and heat treatment operations are presented for two different Cr-alloyed steel powder grades. Results from high temperature sintering, sinter-hardening and low pressure carburizing tests are reviewed with focus on static mechanical data, bending fatigue properties and microstructures.

When manufacturing powder metal (PM) gears lead crowning is not achievable in the compaction process. This has to be accomplished by either shaving, grinding or honing. Each of these processes have their merit and draw back. When employing rolling using a roll burnishing machine lead crowning can be accomplished but due to errors in profile a hard finishing operation such as grinding is used by the industry [1]. In this paper a helical PM gear that has sufficient tolerance class after rolling has been tested in a test rig for durability and the wear has been studied.

Machining of powder metal (PM) steels is often completed in order to meet final dimensions, provide a desired surface finish or impart features not possible during compaction. Understanding machinability is of increasing importance as more PM components are machined. Additionally, understanding the roles of machinability enhancing additives and their interaction with different material systems is critical in order to select the best additives for a given material system and machining conditions. This paper will detail the microstructure effects on machining and the effectiveness of machining additives. Production case studies will be presented for different material systems and operations. It will be shown that not all additives are effective in every material system and that pairing the microstructure to the machining additive and machining operation is key to maximizing the machinability.

Metal-matrix composite coatings consisting of a nickel based metal matrix and tungsten carbides are commonly used for hardfacing of components requiring resistance to abrasive wear. The nickel based matrix works as a binder providing toughness while the tungsten carbides provide wear resistance. The properties of metal matrix composite coatings depend on the volume fraction of carbides in the clad but also on the shape, particle size and microstructure of the carbide particles, the chemistry of the matrix material and the process parameters selected. In this paper, the properties of laser cladded and PTA welded nickel based coatings with different amounts of tungsten carbides are investigated.

Variable valve timing (VVT) systems allow for the perfect combination of performance increase, better economy and improved emission control. The components used in a VVT system are typically highly complex in design and challenging to manufacture as they require extremely tight tolerances and good machinability. PM has proven to be a robust and cost effective manufacturing technique to meet these demands. In this paper a newly developed mix concept specifically engineered for manufacturing of high precision VVT components will be described.

Fatigue is one of the most common failure mechanism for components subjected to mechanical load. Therefore it is of key importance to have reliable models to describe the fatigue strength of materials and components. This paper describes how a fracture mechanics based model can be used to take both density and notch effects into account. First the porosity is described using extreme value statistics, and then the largest pores linked to the fatigue strength by linear fracture mechanics. It is demonstrated how this concept can be used to estimate the fatigue strength for test bars with different densities and stress concentrations, requiring only a minimum of fatigue testing.

This paper presents the analysis of an Axial Flux Permanent Magnet (AFPM) Machine with 12 slots, 14 poles applied to a hermetic compressor. The motor is made of Soft Magnetic Composite with NdFeB permanent magnets. The simulations are calculated by 3D Finite Elements Analysis due to the 3D shape of the geometry. Motor performance results are presented including iron loss separation.

A key to high strength PM parts is to achieve high density of the parts. An attractive process route is to use high performing lubricants in combination with heated tool die. In this paper the synergies of lubricant content, efficiency of the lubricant and tool die temperature are reviewed and processing conditions for high density PM components are suggested.

Sinter hardening has been one of the ways to obtain high performance PM low alloyed steel components. The control of the final microstructure and consequently of the mechanical performance of the components is acquired by the suitable process route optimization, namely the cooling rate. The sinter hardening process therefore requires materials with sufficient hardenability which in turn is achieved by chemical composition optimization. This paper presents the properties of a number of materials suitable for sinter hardening processes with regard to mechanical performance as well as material characteristics such as Jominy hardenability tests and CCT diagrams. The materials composition and the respective mechanical properties are correlated by means of metallographic investigation.

Net shape manufacturing advantages and its cost effectiveness is well known for sintered structural parts for many automotive applications. Combined with cost effective material solutions, plus smart secondary processes, and finally leading to higher product performance, PM technology can add even more value to customer processes and end user applications. This paper describes the conversion study of a manual transmission component from wrought to pm steel, while presenting the results of comparing the wear performance when subjected to moderate forces and high sliding velocities. The authors analyzed the behavior of PM based Cr plus nitriding (gas or plasma) specimens in comparison with a wrought steel plus carburizing. The component lifetime and reliability was evaluated according to the IRG-diagram. The final conclusion is that the PM material has better wear performance than the current wrought steel component.

One of the modes in which a gear can fail is through sudden shock loads, caused by for instance abuse of the transmission. Therefore the question of how PM gears can take abuse loads compared to wrought materials often arises when looking at new application for sintered gears. In the paper the development of a new equipment to test impact strength of gears is described. It is also described how the staircase method, often used to determine for instance endurance limits in fatigue testing, can be employed to determine the impact strength of a gear. Finally results for different powder metal steels at different densities and heat treatments are presented, along with a comparison of a typical wrought steel.

Powder Metallurgy (PM) processes are the preferred net shape manufacturing technology for a number of automotive and non-automotive applications. While PM offers the ability to provide net shape components with higher material utilization compared to competing metal working technologies, often additional machining operations are required. Variable valve timing (VVT) components are an example of a PM component which has a number of machining operations required to meeting application requirements. In order to maximize productivity, machinability enhancers are often employed to improve the machinability of the PM component. However, most applications also have strict requirements for surface stains and rust eliminating the opportunity to utilize the common additive MnS. A new, advanced machining enhancing additive has been recently introduced which provide superior turning and drilling performance compared to other additives while providing stain free surfaces. This paper details the performance of the new additive in laboratory and production environments.

There are strong driving forces towards high-performance gear wheels which can handle higher engine outputs, or allow more compact designs of transmissions. Today the performance and life of conventionally manufactured gear wheels are limited by factors such as inhomogeneous microstructure and distribution of inclusions. Powder metallurgy (PM) can solve some of these problems but has so far had limitations caused by porosity. In this paper a cost effective way to eliminate porosity by HIP-ing without canister has been evaluated with encouraging results. Parameters such as powder particle size, lubricant and double pressing have been evaluated in the PM route in order to get a gas tight surface enabling effective post HIP-ing. So far double pressing has given promising results. Challenges such as open porosity, surface porosity and inclusions are addressed in the paper.

In high strength applications heat treatment is done to obtain the required mechanical properties. Low pressure carburizing + gas quench (LPC + GQ) is one case hardening method that gains interest in the PM industry. Inherent benefits from the LPC + GQ process are less distortions, possibility to case harden chromium alloys and good process control. A trend in the PM industry is to use low alloying content due to benefits in cost and compressibility. However, when comparing alloying content of conventional steel high strength components alloying contents of 2-3% is common. Even if the heat treatment is performed correctly, low hardenability will compromise the final properties of the component. In this paper the M32 PM transmission gear will be used as demonstrator when influence of alloying content will be presented in regards of processing, microstructure and case profiles. Fatigue strength of investigated materials will be presented and discussed.

Numerous applications utilize components manufactured from powder metallurgy (PM) stainless steels. While PM stainless steel components meet very demanding performance criteria, the overall PM stainless steel market is quite small compared to ferrous PM. Stainless steel powders often have poor powder properties which makes the manufacturing of stainless steel PM components challenging, often leading to lower productivity to meet quality goals. The components often require secondary machining in order to meet final dimensions or add features which couldn’t be achieved through PM compaction and sintering processes. The machining of PM stainless steel can be challenging due to the inherent microstructure of stainless steel and the resulting low particle hardness of matrix. Recent material advances in PM stainless steels now offer solutions to these common problems. This paper will discuss the recent advances detailing the improvements in powder properties and machinability which can be expected for common PM stainless steels.

A 6 speed manual transmission was redesigned and optimized for using powder metal steel as the gear material. The design work was very comprehensive and included deformations of housing, shaft, bearings, bolts and gears and varying temperature conditions. The analysis showed that powder metal (PM) gears would survive the durability cycle despite that no densification methods were used. In the second phase of the project, a SAAB 95 was equipped with a prototyped gear box according to the PM optimized design and 3 transmissions were built and tested in test rig for durability and vibrations. This paper will demonstrate the testing procedure and the results from testing. The transmission has also been benchmarked with the original transmission and comparisons have been made. Lessons learned will be discussed and how the design can be improved in future transmissions.

Today Low Pressure Carburizing (LPC) followed by High Pressure Gas Quenching (HPGQ) is an established process to produce high performance components for conventional steels in order to combine high surface hardness and fatigue strength. On the other hand, thanks to its ability to combine good quality and cost saving, PM process is more and more popular in the automotive industry (especially in the transmission applications as synchronizer hubs/rings, sliding sleeves…). In order to answer the increasing application performance requirements, chromium-alloyed grades are often used because they provide a cost-efficient way to reach high mechanical properties. However these materials need specific sintering conditions and cannot be surface hardened by conventional gas carburization and oil quenching. Thus, the alternative LPC & HPGQ applied to PM parts is a very promising, cost-efficient and is an environmental solution to produce high performance parts. This paper presents the last trends and results of this solution.

Heat treatment operations such as case and through hardening are commonly used for obtaining high performance PM components. Such operations require a number of specific material data in order to be successful. In the PM industry today, however, the material data are often inadequate and heat treatments are generally performed based on previous experience on solid steels. The latter may lead to poor heat treatment results and PM parts with deteriorated mechanical properties. This paper presents results from quench dilatometry experiments and, in connection with metallography, the respective CCT diagrams for pre-alloyed PM steel grades suitable for heat treatment. The hardenability of the same materials was also investigated by means of Jominy end quench test. The obtained results are a valuable tool for the design and control of a successful heat treatment of PM steels.

A lot of alloyed powders have been developed and are selected for PM parts. Recently, some lean alloyed powders can be used because of the cost effectiveness, however, the mechanical properties have not been clarified yet. In the past study, conventional diffusion bonded alloy powders and the lean alloyed powders were compared. As-sintered compact made from lean alloy powder didn’t show adequate mechanical properties. But the properties after heat treatment improved as almost equivalent as conventional diffusion bonded alloy powders. A typical lean alloy diffusion bonded 0.5%Ni and 0.5%Mo powder (AQ) revealed high performance. Prior investigations were done mainly by simple test specimen. In order to know the feasibility, in this study actual PM gears made from diffusion bonded lean alloy (AQ) were evaluated and the results are presented. Furthermore, the effect of surface rolling on tooth fatigue is also made clear.

Main benefits of the PM technology versus conventional steel making processes in the manufacture of structural steel parts are high material utilization, low energy consumption and short production time. These benefits are fully exploited by choosing the right combination of material and processing route to get the required mechanical properties at a low production cost. Powder grades pre-alloyed with Cr are robust and cost effective materials which are suitable for high performance PM steel components. This paper presents mechanical properties of Cr-alloyed PM steel obtained after different processing routes, including high temperature sintering, sinter-hardening and heat treatment by low pressure carburizing. Static mechanical data are presented as well as results from plane bending fatigue tests. Microstructures are also shown and correlated with the mechanical properties obtained for the respective processing routes.

Carburizing of PM‐steels is a relatively fast process and the main reason for it is the presence of porosity. In order to have good control of this process, it is of utmost importance that carbon potential, temperature, time at temperature and carbon source used is accurately controlled so no through carburization will occur in particular as the material consists of interconnected porosity. Porosity also has, due to its effect on thermal conductivity, influence on relative hardenability which further adds important considerations in how to perform the heat treatment process. The purpose of this paper is to guide those being involved in the heat treatment process of PM‐steels how to practically consider when planning carburizing of PM‐steels. Here, 2 common types of PM materials having different shapes and densities of 7.00‐ and 7.25 g/cc respectively are investigated with the purpose to achieve successful processing.

Powder metallurgy is a cost-efficient process route for the production of net shape or near net shape components. In many situations, secondary operations – for instance, sizing or machining operations – are required to meet the tolerance class of the application. Better tolerances of as-sintered components will increase the competitiveness of PM technology by reducing the need for secondary operations. In this presentation, the benefits of advancements in material for dimensional control are discussed. Experimental results are presented that demonstrate how the dimensional variability of components can be reduced.

Multi-layer coated pure Fe-based soft magnetic material is a recently developed new generation of Soft Magnetic Composite (SMC) which has low hysteresis core loss due to its thermally stable, high temperature electrical insulation coating. These SMC materials can preferably be used for various electrical machines and other inductive components designed for higher operating frequencies up to several kilo Hz. Both magnetic properties and other performance of a SMC component depends not only on the powder material itself, but also on the component manufacturing processes.

This paper investigate the effect of the manufacturing processes, including compaction pressure, die temperature, heat treatment
temperature, heat treatment time as well as heat treatment atmosphere, on the final properties of the SMC component. Finally, a proposal of an optimised process recommendation for the manufacturing of Somaloy^®5P components is made.

Axial field machines often have unusual three dimensional flux paths and as a result soft magnetic composites can be a key material in their production. Producing such machines using laminations is possible but in many cases is prohibitively difficult or expensive.

This paper investigates a single sided axial flux machine utilising a single stator iron component made from soft magnetic composite material. This stator can be combined with the use of preformed, bobbin wound coils and a surface mounted ferrite rotor to create a very simple to manufacture machine with very few components. A machine designed for a pump application is presented along with simulated data, this will then be verified by results from a constructed prototype. The results show that a machine constructed in such a way offers the possibility of a low cost manufacturing alternative to the more widespread radial flux machines.

A new application for plate heat exchangers used in cooling units are subjected to a very aggressive coolant. This means both base material and brazing alloy needs to have very high corrosion resistance to the coolant. As base material high alloyed austenitic stainless steels were identified as available with necessary corrosion resistance. The only braze material on the market with good enough corrosion resistance in these environments was BrazeLet® Ni613. However, when testing this alloy it was early recognized that the melting range of this alloy was not compatible with these base materials. High alloyed austenitic stainless steels may form excessive amounts of inter metallic phases if heat treated incorrectly. Therefore a rapid cooling from above the critical temperature range for the specific base material is necessary. A new alloy with corrosion resistance similar to BrazeLet® Ni613 but with higher melting range was developed and is presented in this paper.

A new application for plate heat exchangers used in cooling units are subjected to a very aggressive coolant. This means both base material and brazing alloy needs to have very high corrosion resistance to the coolant. As base material high alloyed austenitic stainless steels were identified as available with necessary corrosion resistance. The only braze material on the market with good enough corrosion resistance in these environments was BrazeLet® Ni613. However, when testing this alloy it was early recognized that the melting range of this alloy was not compatible with these base materials. High alloyed austenitic stainless steels may form excessive amounts of inter metallic phases if heat treated incorrectly. Therefore a rapid cooling from above the critical temperature range for the specific base material is necessary. A new alloy with corrosion resistance similar to BrazeLet® Ni613 but with higher melting range was developed and is presented in this paper.

Heat-treating is a secondary process that uses heating and rapid cooling to develop a martensitic microstructure. While heat treatment is utilized to achieve higher mechanical properties and improve overall part performance, the addition of secondary operations such as quenching increase overall fabrication costs compared to single operation sintering. Sinter hardening is an operation that combines both conventional sintering and secondary heat treatment into a single process by using accelerated cooling in the sintering furnace. Prealloyed material systems that yield high hardenability, such as those alloyed with chromium and molybdenum, are capable of developing small percentages of martensite during conventional sintering. By utilizing accelerated cooling during the sintering process, these materials are capable of achieving microstructures and mechanical properties equal to or greater than heat-treated components. However, one of the drawbacks to using prealloyed base iron is that they have lower compressibility compared to standard iron powder. Because of this, specially designed lubricants are an important development to achieve the highest densities possible. A new lubricant system has been developed which provides improved density and ejection performance. The mechanical properties of prealloyed chromium materials with the high performance lubricant will be compared to other sinter hardened materials and lubricant systems.

Components often require high strength, high hardness, or high wear resistance to meet the demands of high performance applications. To meet these requirements, a martensitic microstructure is required. In powder metallurgy (PM), the martensitic structure can be achieved through conventional heat treatment or through sinter hardening. PM offers unique alloying techniques which can be used to develop the desired microstructure. Even if the resulting microstructure is predominantly martensitic, differences in final performance are often observed. In this paper, common alloying systems are compared in the martensitic condition. The microstructure and resulting properties of the different alloys are compared and discussed.

One of the distinct features of powder metallurgy (PM) material is porosity. Depending on the application, this can be advantageous or a disadvantage. While density levels may be kept low in bearing applications, structural parts requiring high strength will maximize density in order to meet mechanical properties. The geometry of the component being compacted will influence not only the overall density level, but also the consistency of the density throughout the component. PM materials are considered more difficult to machine due to the porosity. While it is generally accepted that porosity negatively impacts machinability of PM steels, detailed works generally lack on the relationship between porosity and machinability, especially when a machinability enhancer is utilized. In this study, machinability of the popular iron-copper-carbon steel was evaluated at different density levels. Commercial machining enhancing additives were examined in the study to determine the effect of density (or porosity) level on their overall effectiveness.

HVOF and HVAF deposited coatings of three commercial Fe-based powder alloys have been ranked according to ASTM G76 solid particle erosion testing. The reference was electrolytic hard chrome (EHC) plating. The test results at 30 m/s abrasive particle velocity showed that 6AB powder alloy, when HVAF sprayed, Fe SP586 when both HVOF and HVAF sprayed meet the EHC plating reference erosion rate. 6AB HVOF sprayed and Fe SP529 both HVOF and HVAF sprayed powder alloys achieved two to three times higher erosion rate but were still at the same level of magnitude as the EHC plating reference.

One of the most widely accepted and versatile materials used with many coating deposition methods is austenitic stainless steel 316L. This is due to the combination of good corrosion and mechanical properties that are suitable for numerous varying applications. As a result of our familiarity with 316L we assume the properties achieved will be within the expected frame as described in the literature. Deposition techniques and component size and shape have an impact on the heating and cooling variations which will then effect the microstructure of the final coating. This will in turn result in variations in the properties achieved. Some of these numerous factors such as: deposition technique, component geometry and size, impurities in the substrate and chemistry of the substrate will be considered. The influence of these factors on the microstructure and the definitive properties of 316L will be presented.

In order for Powder Metal (PM) to increase market share there are two factors that have a significant influence. The two factors are strength and cost There are methods on the market such as Surface Densification by rolling, shot peening, powder forging and some other proprietary methods that will increase strength but the common denominator for all methods are increased cost and sometimes other draw backs. In this paper a method for Hot Isostatic Pressing (HIP) of PM parts is presented. The container needed for HIP of PM parts is very costly and impossible to make in the shape of a gear wheel. This paper will demonstrate a method for HIP:ing gears and components in PM without a container thus eliminating a big part of the cost for the HIP process. The strength benefits will be demonstrated as well as the cost situation for HIP:ing of a gear to full density.

Shock absorber parts like pistons, cylinder ends and rod guides are multi-level parts with rather complex geometry. These are preferably produced by means of PM due to their net shape and design freedom, in combination with the dimensional precision that is a critical requirement. The demand on sintered strength is not so high why the Fe+Cu+C system is mainly used with densities typically in the range of 6.3-6.7 g/cm3. The relatively low density in combination with the complex geometries and the demand for dimensional accuracy, make the sponge iron powders a natural choice. A new lubricant and mix system has been developed in order to improve dimensional stability and especially green strength even further. This system, Intralube S, is tailored to work with sponge powders at low densities. It is a Zn-free system.

Titanium based alloys show very high strength to density ratio, and could be the choice of material for a wide range of applications. By practicing press and sintering for production of Ti components, high materials utilization can be assured, and at the same time costly machining operations can be limited. Difficulties in processing and high cost for powders have been limiting factors for progress, but recent development indicates good possibilities on cost effective use of TiH2 powder in the press and sintering segment. In this paper, influence of processing parameters and powder properties on final sintered component properties are discussed.

Automotive exhaust flanges and HEGO bosses are common components manufactured by powder metallurgy (PM) using 400 series stainless steel powders. These components often require secondary machining in order to meet final dimensions or add features which couldn’t be achieved through PM compaction and sintering processes. The machining of PM stainless steel can be challenging due to the inherent microstructure of stainless steel and the resulting low particle hardness of matrix. Recently, Stainless Steel EZTM powders have been introduced to improve productivity when machining operations are necessary. In this study, a component manufactured from 400 series PM was selected to evaluate against a Stainless Steel EZTM version in a production environment to quantify machinability improvement. Since 400 series components are also typically welded into place, welding evaluation of the materials was also conducted.

The powder metal (PM) industry is constantly striving to increase the density in components in order to improve the mechanical performance. High density can be achieved with a variety of different manufacturing methods; however, warm die compaction has become popular due to the simplicity of the process. Using specially designed lubricants and heated tooling, high density can be achieved in a single compaction step. A new lubricant system has been developed which provides improved density and ejection performance. The optimal operating conditions and achievable properties of the lubricant system will be discussed.

Resin bonding of powder metal (PM) mixes has been shown to improve the flowability and fillability of the mix by bonding the fine particles to the larger iron particles. The improvement in powder properties results in the ability to obtain more consistent components and tighter tolerances. A new bonded mix has been developed which provides improved lubricity while maintaining other powder properties. With many bonding options available it is important to understand the benefits and optimum working conditions of each Starmix® bonding system. In this study, the properties of the new bonded mix will be compared to a conventional Starmix® and Starmix® Boost. Properties such as apparent density, flow rate, green strength, ejection, and filling performance will be compared for each system.

In the powder metal industry, machining of components is becoming more prevalent as tolerances and features become more demanding. The powder manufacturing processes provide easy and flexible capability in formulating alloying and additives to achieve desired properties including machinability. Manganese sulfide (MnS) has long been the dominant machinability enhancing additive due to its ability to provide improvement in turning and drilling of PM materials, especially in machining of iron-coppercarbon materials. The development of the SM3 machining additive overcame the negative effects of MnS such as stains and corrosion while providing superior performance of turning operations but its performance in drilling of the iron-copper-carbon materials is not as good as MnS. A newly developed machinability enhancing additive aiming for improved performance in both drilling and turning has been evaluated and compared to the commercial additives in machining of iron-copper-carbon materials based on laboratory testing and full scale production trials. Machinability data, mechanical properties and corrosion testing results are presented to demonstrate the effectiveness of the new machining additive named SM4 as a potential machinability improvement solution for replacing MnS without corrosion and stain concerns.

Recent research has indicated the good possibility to use TiH2 powder in press and sintering operations to obtain titanium components with high final density. In this work, compaction behavior of TiH2 powder treated with a lubricant is studied. The effect of compaction pressure on green density is investigated. Subsequent sintering trials show on the effect of green density and heat treatment parameters on final density and dimensional change.

Metal-matrix composite (MMC) coatings consisting of a nickel based metal matrix, providing toughness and tungsten carbides, providing wear resistance, are used in applications subjected to severe abrasive wear conditions. The aim of this work is to map the influence of typ, morphology and amount of tungsten carbides in a nickel based matrix on the wear resistance and microstructure of laser cladded MMC coatings. Abrasive wear, evaluated according to ASTM-G65, is mainly influenced by the volume fraction of the tungsten carbides in the coating. Shape and microstructure of the tungsten carbides have a minor impact on this property, for similar degree of melting or dilution from the substrate material and size of the tungsten carbides. Microstructure analysis shows that the dissolution of the tungsten carbides in the melt pool is influenced by the chemical composition of the liquid metal phase, the microstructure and the amount of tungsten carbides selected.

The powder metal (PM) industry is constantly striving to increase the density in components in order to improve the mechanical performance. High density can be achieved with a variety of different manufacturing methods; however, warm die compaction has become popular due to the simplicity of the process. Using specially designed lubricants and heated tooling, high density can be achieved in a single compaction step. A new lubricant system has been developed which provides improved density and ejection performance. The optimal operating conditions and achievable properties of the lubricant system will be discussed.

PTA cladding is a widespread means of thermal surfacing of structural components exposed to wear and corrosion. Traditional high performing cladding materials are based on cobalt or nickel, both of which are subject to relatively high prices on the raw metal market. Although the cost of the cladding material is small compared to the total cost of the application and the value it creates, it is nevertheless an important factor. Iron based cladding materials are present on the world consumable market and are less expensive but also not as well understood as cobalt or nickel based materials. This paper provides a comparison of PTA cladding using a well-known cobalt based and two iron based powder alloys.

This paper explores recent material development for Soft Magnetic Composites (SMC) which are based on pure iron metal powders combined with inorganic resistive coatings. SMC components are manufactured by compaction in a shaped tool followed by heat-treatment of the component for stress relaxation and to reach optimal magnetic and mechanical performance.

The recently developed Somaloy^® 5P SMC materials are presented and compared to former technology. The unique combination of material properties and manufacturing process is here concluded to enable possibilities to realize compact and efficient high-frequency electromagnets, a technique that can be an interesting opportunity for large volume, cost efficient magnetic bearings and bearingless applications.

The development of high speed electrical machines and the use of harmonic rich controls demand magnetic cores of good high frequency performance. Soft Magnetic Composite (SMC) can be a suitable alternative material for such applications because of its low eddy current loss. On the other hand, there is a variety of SMC materials with different magnetic properties such as, permeability, resistivity, and coercivity due to particle size variation, in addition, various insolation coating technologies may be utilized. Furthermore, the performance of a SMC core can be tailored by manufacturing processes such as compaction pressure, heat treatment temperature and atmosphere, etc.

In this work the hysteresis loss, particle eddy current loss and component bulk eddy current loss of SMC magnetic cores are analysed with the aim to facilitate the selection of suitable materials and manufacturing processes for different applications. A core loss model is proposed to estimate core losses in SMC cores for currents of sinus waveform. The parameters required for core loss calculation of several Somaloy^® materials are extracted from measured core losses of standard magnet rings. Finally, an attempt to position different Somaloy^® for different applications is made.

Sinter hardening of PM components is well known as a cost-effective and feasible alternative to secondary heat treatment. Lots of application progress has been made in recent years. Nickel and molybdenum containing materials are very commonly used for sinter hardening application while increases and fluctuations in prices of nickel and molybdenum make manufacturers facing increased cost pressure. From this point of view, chromium-containing alloys show favourable prices and good hardenability, but limitations of atmosphere type and quality have influenced its wide application. To extend sinter hardening application and enhance competitiveness of PM technology there is a strong need for cost effective alloys combined with robustness. In this paper, we present conventional and newly developed lean alloys including both Ni-Mo and Cr-Mo systems, and their achievable properties and consistency under industrial conditions for typical PM applications.

In order to improve final product quality and reduce expensive machining operations, part-makers are striving to improve process robustness and reduce dimensional variations of compacted components. In addition, better flow and cavity-fill characteristics of advanced powder concepts, as well as the latest improvements in press technology and control systems, are pushing the limits of achievable tolerances to new levels. This paper describes the relevant aspects, contributions and possible improvements for improved compact quality.

The Hall flowmeter funnel according to ISO 4490 is a well-established test method used in the PM industry for decades. The method is recommended and works well for metallic powders without organic additives such as lubricants and graphite. The Hall funnel is also widely used for determination of apparent density and flow of metallic powder mixes including organic additives. However, a problem is that powder mixes, especially mixes with high content of lubricant, graphite and/or other fine particulate additives, will not always flow freely through the funnel. To overcome this, a new funnel with a 30° cone angle has been developed. The new funnel enables mass flow so “rat holes” leading to flow stops can be eliminated. The new flowmeter funnel, called Gustavsson, is now standardized according to ISO 13517. In this paper a comparison between the Hall and Gustavsson funnels is presented. Different types of metal powders and metal powder mixes have been evaluated and will be reported.

Using sintered steels in ever more demanding applications require thorough understanding of the material behavior to be able to make reliable, optimal designs. One of the most common failure mechanisms of components in service is fatigue. Thus, reliable models for predicting fatigue strength is important, and one of the factors that need to be accounted for is stress concentrations. In this paper plane bending fatigue of a diffusion bonded alloy, Distaloy AQ, is investigated. Heat treated specimens with different notch sizes are tested, and the results evaluated using models based on critical distance, stress gradients, highly stressed volume and fracture mechanics. It was found that all models worked well but the models based on stress gradients and critical distance gave the lowest scatter compared to experimental data, whereas critical distance gave the highest scatter. The fracture mechanics model gave intermediate scatter, but used one less fitting parameter.

The driving force for using PM compared to other manufacturing techniques is almost always due to its ability to produce structural components with required performance in a cost effective way. Nowadays there is also a growing awareness of other aspects than cost on the selection of raw materials and production processes. Most manufacturing methods have an impact on the environment in the sense that it consumes energy and resources. It is thus necessary to select both material and process with the least impact on the environment. In this presentation some key aspects on the selection of raw materials, alloy compositions and processing conditions are discussed regarding performance requirements, cost effectiveness and environmental impact for some new challenging PM applications.

PM components are commonly used in applications where they are exposed to different degrees of wear. Often various heat treatments are used in order to increase the hardness and thereby the wear resistance. In this paper we will take a closer look at aspects of the thermochemical nitrocarburising process when used for PM materials. The porosity is having a very large influence on the formation of the compound layer. This can to some extent be controlled by applying a steam treatment before the nitrocarburising step. Chemical composition of the PM part is another factor having great importance for the surface hardness. Here the presence of chromium shows great benefits.

Tooth root bending fatigue is one of the failure mechanisms of gears. Thus by decreasing the stresses in the tooth root the strength of the gears can be increased. Here the PM technology is more flexible than traditional machining of gears, since the tooth root can be designed into whatever shape desired. In this paper it’s investigated how the tooth root of PM Gears can be optimized to reduce stresses. By two different methods, using a CAD software and a gear design software it’s demonstrated that bending stresses can be decreased with as much as 30% for gears in a six speed automotive gearbox.

High performance components are often case hardened to have high surface hardness and fatigue strength. Low pressure carburizing and gas quenching is an increasingly popular process method for conventional steels but so far not commonly used for PM steels. Besides the benefits offered for conventional steels, such as less distortion and clean parts after heat treatment, low pressure carburizing enables surface hardening of chromium alloyed PM steels which is not possible with conventional gas carburizing. This paper presents results for low pressure carburized and gas quenched PM steels. The control of the case profiles is demonstrated together with related micro structures and initial fatigue strength results are presented.

Powder metallurgy is known to be a cost effective technology to manufacture components with narrow tolerances in combination with required mechanical properties. A key aspect is the sintering process. Through control and creation of internal stresses guided by the sinter hardening atmosphere give you properties that even outperform sintered and case hardened properties at considerable lower cost. Creation and control of such atmosphere is essential to increase the competiveness of the PM technology. In this paper concepts for carbon control and carbon gradient are presented and described in terms of how to create it through addition and measurements. Influences of created internal stresses by the atmosphere on PM applications are presented.

The machinability of powder metal (PM) steels depends on the microstructure of the steel. With increasing carbon levels and alloying the machinability of PM steels decreases. Heat treatment only increases the difficulty of machining. To improve machinability of PM steels, machining enhancers are often admixed with the steel powder. In previous studies, the SM3 additive has been shown to greatly improve the machinability of different PM steels while not negatively affecting mechanical properties or corrosion resistance. In this study, the SM3 additive is evaluated in both carburized and sinterhardened materials. The additive will be evaluated on both laboratory and production components. The results of the study show SM3 offers an opportunity to improve both tool life and productivity when machining hardened materials.

Sinter hardening is commonly used in the powder metal (PM) industry as a cost effective method to produce components requiring high mechanical performance. Using accelerated cooling in combination with higher alloying contents, sinter hardening steels offer similar performance to conventional heat treated steels with reduced distortion. As demands on component precision increase, understanding the effects of processing and composition on the precision of the sinter harden steels will be required by component manufacturers to select the proper sinter hardening grade and composition for a given set of requirements. In this paper, common sinter hardening alloys are subjected to various processing conditions. The mechanical performance and precision of the different compositions under these processing conditions will be presented.

PM stainless steels present very different machinability behaviors from plain carbon and low alloy PM steels. Since they contain high alloy content without carbon addition, stainless steels become gummy and work harden during machining so that they are difficult to machine. To improve the machinability, conventional machinability enhancers such as MnS and MoS2, etc. may be applied into the materials but the sulfur containing additives can severely decrease corrosion resistance. Resin-impregnation is also a common solution for improving the machinability of stainless steel materials without detrimental effect on corrosion resistance. However, resin impregnation not only greatly increases operation cost but also lacks consistency in improving machining due to density gradients in the components. In order to provide an effective solution in a cost-effective way, an easy-machinable version of stainless steel powder has been developed based on a modified powder manufacturing technology. Previous study has demonstrated that components made with the newly developed 300 series easy machinable stainless steel powder provide superior machinability in comparison with their standard grade counterparts. In this paper results obtained from evaluations of 400 series stainless steels will be presented. Machinability, material properties, and corrosion resistance of materials made with the newly developed 400 series easy machinable stainless steel powder will be compared with those of their standard grade counterparts.

A number of common thermal surfacing materials for soil tillage applications were ranked for abrasive wear by dry–sand–rubber–wheel testing according to ASTM G65. Focus was on plasma transferred arc (PTA) and powder welding (PW) deposition consisting of a nickel based self-fluxing matrix with and without additions of 50 or 60% tungsten carbide. For comparison PTA coated M2 tool steel and the quenched and tempered wrought spring steels EN C75S and EN30MnB5 were also tested. PTA and PW deposition techniques produced coatings with a similar level of abrasive wear resistance. Hardfacing with M2 and a 60 HRC nickel based self-fluxing grade showed ~30% and ~15% wear respective compared to the reference steels while the grades with additions of 50% carbide phase showed ~5% wear compared to the reference steels. By increasing the amount of tungsten carbide from 50 to 60 wt% abrasive wear resistance was increased by 25%.

Hardfacing of components is widely used worldwide as a means of improving life of components and reducing operating costs. Numerous hardfacing techniques currently exist which utilize filler materials in wire/strip of powder form. One of the most commonly used techniques is the one referred to as GMAW/MIG (Gas Metal Arc Welding/Metal Inert Gas) and it uses wire. It is highly developed and it is used in a very wide range of applications. Modern powder utilizing techniques however, such as Laser Cladding or PTA, are rapidly gaining ground in the industry due to their technical but most importantly economical merits. In this study, a direct comparison will be conducted between the two technologies both in technical and economical terms in order to investigate the viability of the new method. Furthermore, advanced powder materials for wear prone applications will be tested in an effort to identify possible gains from the use of modern techniques.

The performance of conventional cladding techniques, on the coating of large industrial compponents, is analyzed and compared against a high end technique. A variety of criteria are used such as mechanical, metallographic and economic in order to obtain a more complete picture. The conventional technique under investigation is Gas Metal Arc Welding (GMAW/MIG) being one of the most established in the field, while the high end counterpart is an emerging technique referred to as Laser Cladding. The mechanical performance is judged in regard to tensile testing with marine classification society rules in mind. Furthermore, the economic aspects of the operation are examined considering capital investment, labour, welding consumable as well as post welding operation costs. A cladding material often used in such applications is compared, an austenitic stainless steel AISI 316L. In the case of the conventional tecnique, the filler material is in wire form while in the case of the laser technique, metal powder is used. Results indicate that the laser technique presents significant advantages in all respects as faster turnaround can be achieved with less material consumed and lower labour cost. While equivalent if not better mechanical and corrosion properties can be realised.

Powder metal gear manufacturing allows for a root design that may be optimized with respect to stress. Conventional gear cutting using a hob is a balance between tool wear, kinematics, hob tip geometry and achieved tooth root radius. With PM manufacturing technology a root design that reduces stresses from bending, compared to a machined root design, can be built into the compaction tool. This paper will give some examples between stress levels from conventional root design using a Hob and stress levels using an optimized root design possible with PM manufacturing. The paper will also investigate how PM can reduce stresses in the root from transient loads generated by abusive driving.

Distaloy AQ is a lean alloyed (Fe-0.5Ni-0.5Mo) cost effective alternative to the PM steels traditionally used for heat treatment applications; these are materials that often include copper, nickel, or molybdenum in quantities of totally 2-6%. Compared to the traditional materials the low alloying content of Distaloy AQ offers relatively low hardness in sintered state, allowing for excellent as-sintered machinability. After heat treatment, however, the material performs on the same level as the more highly alloyed materials. Performance of Distaloy AQ after different heat treatments, such as quench and tempering and case carburizing is investigated and compared to performance of materials traditionally used in heat treatments. The comparisons show on possibilities and limitations with the lean alloying route, and indicate application windows where the lean alloying route can be a competitive alternative to the traditional more costly high alloyed materials.

The design of Powder Metal (PM) gears can not be copied from the steel gear that it may be replacing in an automotive transmission. This paper deals with the implications of copying the micro geometry of the steel gear when rebuilding a 6 speed manual transmission for an Opel Insignia 4 cylinder turbocharged 2 litre engine delivering 220hp/320Nm. It will be showed that a different micro geometry of the PM gear teeth coupled with the lower Young’s modulus can theoretically enhance performance compared to the solid steel design. A thorough reverse engineering and redesign has been required in order to understand and map the performance of the Solid steel versus the PM gears and the findings from that work will be discussed in this paper. Weight reductions and inertia reductions will be demonstrated with maintained performance levels to put light on some of the advantages with PM technology.

Powder metallurgy is known to be a cost-effective technology for manufacturing components with narrow tolerances as well as the required mechanical properties. The selection of the material and process that gives the best cost/performance ratio is a very important factor in becoming the preferred technology to fulfil the requirements of an application. Sintering, sinter hardening with carbon control and different heat treatment operations is all processes of prime interest from this point of view. This paper evaluates the influence of both the material and process conditions used to produce a small engine connecting rod. A range of materials processed by different methods are compared regarding static and dynamic performance, tolerances and cost for each process condition.

Distaloy AQ is a rather new material suitable for heat treatments, whereas the new Astaloy CrA and Astaloy CrM are materials suited for sinter hardening. By combining these with warm compaction, mechanical properties can be lifted to the next level, due to increased density and improved pore morphology. This has a positive effect on all mechanical properties, especially properties such as impact energy and fatigue strength. These improved properties open up further potential to convert, challenging conventionally produced parts, such as helical gears and connecting rods to PM-technology.

A major advantage of powder metallurgy (PM) compared to other manufacturing technologies is the inherent near net shape capabilities. As PM continues to expand and material costs continue to rise, applications continue to increase in complexity. The increase in complexity will require PM component manufacturers to have an understanding of current lubrication technologies available in the industry to maximize productivity of complex components. In this paper, several lubricant systems are tested on current production components. Different component geometries are evaluated to show the limitations of each lubricant system on weight scatter, density, ejection, surface finish, and staining after sintering.

Stainless steels offer excellent corrosion resistance compared to other ferrous steels such as plain-carbon and low-alloy steels. Owing to their carbon and high alloying content, stainless steels are usually difficult to machine as they become gummy and work harden during machining. Since the machinability behavior of stainless steels is very different, machinability enhancers that work for other ferrous steels do not always have the same effect in stainless steels. Current additives such as MnS and MoS2 offer marginal improvement in machinability, while severely decreasing corrosion resistance and also are prone to decomposition if sintered in reducing atmosphere. Research efforts have been made in developing an easy-machinable version of stainless steel powder using powder manufacturing technology. This paper presented the results obtained on the newly developed 300 series easy-machinable stainless steel powders. The newly developed 300 series materials were found to have identical green and sintered properties to their standard grade counterparts while offing greater machinability without deteriorated effect on corrosion resistance.

Demands for better performance and cost competiveness of powder metallurgy (PM) parts have required a new insight to conventional warm compaction processing without heating the powder prior to die filling. It will eliminate the cost and temperature issues related to a separate powder heater. This paper will describe a new powder system designed for warm-die compaction at temperature ranges from 45 to 95 °C (110 to 200 °F). The objective is to achieve an increase of 0.1 g/cm³ over conventional single press/single sinter process and a minimum green strength of 13.8 MPa (2000 psi). Fundamentals of the warm-die compaction process as well as effect of temperature on lubrication and green properties will be presented to aid the parts producer in making high density, high green strength PM parts.

Sinterhardening is currently being used in the powder metal (PM) industry to meet the demands of high performance components. The alloys used for sinterhardening produce a predominately martensitic microstructure when subjected to rapid cooling. This martensitic microstructure can be challenging to machine due to the particle hardness of the martensite. If the cooling rate is not sufficient, a mix phase microstructure of bainite and martensite will be produced. This mixed phase structure can be equally challenging to machine due to the differences in particle hardness. In this paper, two common sinterhardening alloys (FL-5305 & FLC2-4808) are subjected to two different cooling rates (0.5 °C/s & 2 °C/s) to understand the effect of microstructure on turning and drilling performance. This effect along with options for improving the machinability of these alloys will be discussed.

The performance of conventional cladding techniques, on the coating of submerged propeller shafts, is analysed and compared against high end techniques. A variety of criteria are used such as mechanical, metallographic and economic in order to obtain a more complete picture. The conventional technique under investigation is Gas Metal Arc Welding (GMAW/MIG) being one of the most established in the field, while the high end counterpart is an emerging technique referred to as Laser Cladding. The mechanical performance is judged in regard to tensile testing with classification society rules in mind. Furthermore, the economic aspects of the operation are examined considering capital investment, labour, welding consumable as well as post welding operations costs. A cladding material often used in suc applications is compared, an austenitic stainles steel AISI 316L. In the case of the conventinal technique, the filler material is in wire form while in the case of the laser technique, metal powder is used. Results indicate that the laser technique presents significant advantages in all respects as faster turnaround can be achieved with less material consumed and lower labour cost. While equivalent if not better mechanical and corrosion properties can be realised.

In this paper it’s studied how density influences fatigue strength of two sintered steels; one standard, diffusion alloyed material and one sinter hardened pre alloyed chromium material. Fatigue testing on materials at different densities are performed and compared. Furthermore, extreme value statistics is applied to the pore structure to determine the size of the largest pore, and fracture mechanics is used to link fatigue strength to porosity. It’s found that there is a strong correlation between fatigue limit and largest pore size. For the sinter hardened material it’s found that a LEFM model can be used to predict fatigue crack initiation, whereas for the diffusion alloyed material with a complex microstructure initiation is a more complex interaction between porosity and the softer micro constituents.

The development of synchronizing hubs goes towards more complicated shapes and higher performance, at the same time as there is a strong pressure on costs. Today many high performance synchronizing hubs are produced using different diffusion bonded materials like Distaloy AE and Distaloy HP. With the new demands it is a desire to move to materials and processes with better cost/performance ratio. This means to move away from high and unstable costs for pure nickel and molybdenum to pre-alloyed materials preferable based on chromium with none or smaller additions of plain nickel. Astaloy CrA and Astaloy LH are pre-alloyed powders suitable for sinter hardening. By selecting different additions of copper or nickel as well as the carbon content the properties can be tailored for different strength requirements. The usage of CCT-diagrams can assist in the selection of the optimal composition depending on which cooling rate that can be applied.

Heat treatment of PM components is often used in order to meet requirements on high hardness and other mechanical properties. Traditional processes such as quench and temper, case carburizing and induction hardening are well known routes to meet these requirements. Traditional PM materials for heat treatment often include Copper, Nickel, or Molybdenum in quantities of totally 2-6%. In the light of recent cost increases for these alloying elements these materials are becoming less competitive compared to solid steel process routes. A new diffusion alloyed steel powder having a lean alloy composition has been designed to perform well in different heat treatment operations. This paper describes the performance of this new powder in commonly used heat treatment operations. Static and dynamic properties achieved both with test specimens and components will be presented.

The ferritic grades of stainless steel (400 series) undergo greater amounts of dimensional change (shrinkage) during sintering when compared to the austenitic grades (300 series) of stainless steel. Prediction and management of dimensional change is highly essential in order to meet the dimensional and density requirements of the sintered components. The most commonly utilized powder and process parameters for management of dimensional change are particle size distribution of the starting powder, green density, and sintering temperature. This study examines the relative influences of these three variables on the dimensional change of 434L stainless steel in 100% hydrogen atmosphere sintering. Sintering temperature was found to be the most significant variable controlling dimensional change and sintered density. Particle size distribution and green density were found to have less significant influence on dimensional change. 

In order to meet the increasing precision requirements of new applications, bonded mixes are required. Previous studies have shown that by bonding the finer particles to the base iron increased flow rates and tighter tolerances can be achieved. With a number of bonded material solutions available, understanding the relative performance of each is required. In this paper, different bonding systems are compared to a conventional premix for powder properties and final component performance. The precision of the components over a production run will be compared for each bonding system.

Diffusion alloyed steels are known worldwide for their robustness and mechanical property performance. These alloys contain significant amounts of nickel, copper, and molybdenum.

To achieve better machinability of powder metallurgy (PM) components, machinability enhancers are often added. Recently a newly developed machinability enhancer, SM3, was introduced. This enhancer was compared to the industry standard additive MnS and showed improved machinability and corrosion resistance in a conventionally cooled prealloyed material system. This paper continues the previous study by examining the heat treat response of the components with different machining additives. The machinability of prealloyed PM components sintered with an accelerated cooling rate is presented.

NiCrBSi alloys are often used in thermal spraying because of their good wear and corrosion resistance even at temperatures over 500° C. Experience has proved these alloys are a good choice for components in the presence of hard particles. The main wear mechanism here is abrasive wear caused by hard particles. Some examples are wear plates exposed to impact sliding; extruders, screw conveyors or mixer parts exposed to grooving; fans, rotor wheel blades or impellors transporting sand/granular material at temperatures over 500° C; or pump parts exposed to fluid containing sand. In spite of such widespread use of NiCrBSi alloys in thermal spraying, their abrasive wear resistance is still not fully understood. In order to better understand, a series of sprayed and fused NiCrBSi coatings with hardness from 36 to 62 HRC were tested for abrasive wear according to ASTM G65-4 norm and the wear volumes achieved are presented. Tribological and metallographic analysis of track wear was done in order to better understand how microstrcture and hardness of NiCrBSi coatings influence abrasive wear mechanisms. These results are compared to results previously published.

In this paper it is demonstrated how fine powder based materials can be used to improve fatigue strength. The increase in strength is accomplished by the smaller pores in the fine powder based materials. Also, a model linking pore size to fatigue strength is presented. This model is based on fracture mechanics in combination with an estimate of the largest pore sizes using extreme value statistics. Such a model can be used both to investigate the influence of different parameters on PM fatigue and to predict the fatigue strength of a material.

To maintain its competitiveness towards other manufacturing techniques, the PM industry must continue to offer solutions that combine high demands on both mechanical properties and close tolerances of the sintered components in a robust, reliable and productive cost effective way. One effective way to shorten time to market, reduce development costs and minimize risks to successfully implement new PM solutions into new applications is to combine unique competencies regarding powder concepts, tool design and powder compaction aspects to develop new offerings and advance the limits for PM parts manufacturing. It is most desirable, for both economic and technical reasons, to achieve the highest possible utilisation of powder, tooling and press technology. Experimental work for proper powder, tooling and pressing solution is performed utilising an integrated team approach. Improving tool wear resistance / reducing die-wall friction using proper combination of die material, powder and precision pressing is highlighted in this paper.

The load carrying capacities of 1P1S (Single Press Single Sinter) 1.5Cr-0.2Mo very high density (7.5 g/cc) sintered steel gear was tested and analyzed. The P/M gear specimens were machined from sintered packs and some were surface rolled. The bending durability was investigated by single tooth bending fatigue tests. The surface durability was evaluated using a power re-circulation type gear testing rig with a counter pinion gear made of standard grade Ni-Cr-Mo wrought steel. Both of P/M gears and counter pinion wrought steel gears were case carburized and finished by grinding. Failure modes of the tested gears in respect to tooth bending fatigue and rolling contact fatigue were analyzed. The test results show that the high density P/M gears with or without teeth surface densification have high enough durability to replace gears made of typical wrought Cr-Mo steel.

The strength of the PM manufacturing technology is the ability to manufacture net-shape or near net-shape components. Nevertheless there is a large share of PM components machined to improve tolerances or to make additional geometrical features which are not possible to press. The efficiency of the machining operations is of great importance to be cost competitive. A number of factors influence the efficiency of the machining operation. In this paper data for three alloying systems, Fe-Cu-C, Distaloy AE and Astaloy CrM are presented. The influence of machine enhancing additives and tool materials were investigated and based on the results guidelines for selection of additives and tool materials are outlined.

Higher density is a key route for higher performance of PM components. With higher density strength and ductility of the sintered materials are improved. There are a number of possible routes for higher density such as high temperature sintering, copper infiltration, liquid phase sintering and double pressing. It is however attractive if high density can be achieved by single press and single sintering process and thus avoiding large shrinkage during sintering in order to keep close tolerances. Recent developments with more efficient lubricants and powder mixing concepts open up new possibilities to compact components to high density. The possibilities by combining high performance lubricants with warm compaction or warm die compaction will be presented in this paper.

Powder metal technology is an alternative manufacturing method for the series-production of gears. But the properties of PM and regular steel gears differ. Especially the values for Young’s Modulus, Poisson’s Ratio and the hardness are smaller, the surface is densified and the tolerance zone is wider. Since PM gears are not state of the art yet, the properties for these gears are not taken into account by regular tooth contact analysis software.  In order to design gears for the manufacturing with PM technology which will show good noise and bearing behaviour, the design has to be tested by tooth contact analysis software that takes the PM characteristics into account. This paper shows the program ZaKo3D of WZL which is able to take the characteristics into account using a FE-based approach. Using ZaKo3D a case study for the design of the micro geometry of an automotive PM gear was carried out. This study, including the PM gear modelling, the sensitivity analysis and the derivation of flank modifications is presented in the paper.

The commonly used grades of austenitic stainless steels (303L, 304L and 316L) exhibit modest levels of mechanical strength, when sintered in a 100% hydrogen atmosphere. Hydrogen sintering is essential for the achievement of good corrosion resistance. Hence, despite having good corrosion and oxidation resistance, the usage of PM austenitic stainless steels is limited to applications that are less demanding from the mechanical strength point of view. The present work is aimed at enhancing the room and elevated temperature mechanical strengths of austenitic stainless steels, without compromising their corrosion resistance. These enhancements are achieved via modification of alloy composition and sintering practice.

The development of new materials and cost effective processes are two main factors that have contributed to the growth of PM during the last decades. Sinter hardening, which utilises high performance materials in combination with accelerated post sintering cooling rates, is one example of such material and process development. As this is a one step process it combines good manufacturing economy with the ability to achieve a unique combination of mechanical properties. However, materials for sinter hardening have been facing increased cost pressure due to the increases and fluctuations in the costs of the most commonly alloying elements molybdenum, nickel and copper. To extend the use of PM into new high performance applications there is a strong need for cost effective alloys that enable enhanced mechanical properties after sinter hardening. In this paper a newly developed cost effective low alloy steel powder containing leaner amount of nickel and copper will be described. Properties achieved after both conventional sintering at 1120 ºC and sinter hardening will be presented.

Powder metallurgy is inherently a net shape process and for cost reasons secondary operations should be avoided. However, in practice it is often necessary to perform at least some machining in the soft condition after sintering in order to create the desired geometry of the part. These parts can then be heat treated in order to reach high mechanical properties. Traditional materials for heat treatment often include Copper, Nickel, or Molybdenum in quantities of totally 2-6%. In the light of the recent cost increases for these alloying elements these materials are becoming less competitive compared to solid steel process routes. Recently a new iron powder was introduced that is designed to perform well in heat treatment and having a lean alloy composition. The present work compares the performance of this powder to some powders commonly used in heat treated applications.

The process of reconditioning a propeller shaft from a large ferry boat with the aid of a robotic "Laser Cladding" system is described. The shaft was damaged following a failure of the aft sealing system and the loss of lubrication. This resulted in an accumulation of considerable wear and cold cracking to significant depths. The propeller shaft, which measured 11.5 metres in length and weighed 26.2 tons, was transported to the workshop. The whole process, which was supervised by the classification society, was preceded by the conduction of a series of experiments such as tensile bar breaking test, Charpy impact testing, as well as metallographic imaging. Based on these results suitable filler materials were selected. The damaged section of the shaft was rebuilt utilising a Laser Cladding system to weld 100 hours continuously and deposit 300 kg of material.

Except for high–end gear applications in automotive and aerospace transmissions, high performance sintered steel gears meet wrought steel gears in respect to gear strength and geometrical quality. The performance increase has to thank advances in powder metallurgy in last two decades such as selective surface densification, new materials and lubricants for high density–, warm– and warm die pressing. This review lists results of a decade with high performance sintered steel gear prototypes development at Höganäs AB in Sweden.

Even though powder metallurgy (PM) offers near net-shape capability, often secondary machining is necessary to meet tolerance and surface finish requirements. Besides compositions of material itself, processing conditions and the resultant microstructures play a large role in determining the machinability of a component. Machinability enhancers are usually added to achieve better machinability. As alloying elements and content increase, machining of PM components becomes more difficult and traditional machinability enhancers become less effective. In this paper, a newly developed machinability enhancer with the potential of improving the machinability of prealloyed powder metal components while minimizing potential effects on material properties is examined. Results of this study demonstrate the benefits of the newly developed machinability enhancer, significantly improving the machinability without detrimental effect to sintered strength. This is accomplished without staining while maintaining the same corrosion resistance as the material without any additive.

While recently a large effort has been made to utilize sinter hardening for high performance components, a sizable portion still require the tradition quench and temper heat treatment process. Heat treatable alloys often contain high amounts of copper, molybdenum and nickel to achieve proper hardenability. With recent fluctuations in metal prices, these alloys have come under pressure from competing technologies. A newly developed lean diffusion alloyed material, D.AQ, has been developed to combine excellent properties in the heat treated condition with high compressibility, high workability and improved machinability in the sintered condition while maintaining the trademark stability and robustness of diffusion alloying. This paper will compare the newly developed diffusion alloyed material with other common PM heat treat alloys.

In order to achieve high performance, the powder metal (PM) industry has relied upon alloys containing high amounts of nickel and molybdenum. Recent volatility in the price of metals has spurred the development of leaner alloys. A newly developed chromium – nickel steel has been shown to provide exceptional mechanical properties. In this paper, the properties achievable with the newly developed steel will be compared against common PM material systems. Static and dynamic properties will be compared using both test bars and components.

This paper presents newly developed brazing filler metals for high temperature brazing of stainless steels. The development of the new alloys has been driven by the market demand to find low cost alternatives to Ni based brazing filler metals used in high end applications like heat exchangers and EGR coolers. High and fluctuating raw material costs for the Ni alloys resulted in that the new brazing filler metals are based on iron. The iron based brazing filler metals have been evaluated in several brazing trials. The evaluation included wetting and spreading investigations, metallographic examinations, joint strength and corrosion resistance. Results from the evaluation have been benchmarked against commercial available brazing filler metal and are presented in this paper. The conclusion is that the newly developed iron based brazing filler metals fulfil the requested properties for high end applications.

Powder metallurgy (PM) is a method known for producing components of great complexity i.e. to near net shape and to very close tolerances. Nevertheless, some components require at least some type of machining operation to fully obtain the definitive shape and geometry, e.g. holes perpendicular to powder pressing direction, bevels, slots and threads. Machining operations are also used to fulfil the demands of higher surface quality and to further improve tolerances. Once the decision to carry out a machining operation of a PM steel component has been made the need to understand the characteristic of machinability will be inevitable. However, machinability of PM steel will not be influenced by the material properties alone but by all parameters concerning the machining operation, i.e. tool grade and geometry, cutting speed and machine stability. This paper describes how machinability for some sintered PM steels can be improved by optimizing different parameters, e.g. tool material, additives and cutting fluid.

The iron-copper-carbon material system is well established in the manufacture of powder forged connecting rods. Utilizing this system takes advantage of the brittleness of the material to fracture split the large end of the connecting rod streamlining the shape and reducing the weight of the final component. Recent advancements by competing technologies have shown similar fracture splitting properties while increasing the fatigue strength. This paper explores new material systems for powder forged connecting rods which exhibit compressive yield strength and machinability properties similar to or better than the competing technologies.

Sinter-hardened and heat-treated PM materials are considered as the most difficult materials to be machined due to their martensitic structure and high hardness. Machining these types of materials is usually low productivity and/or short tool life. A new machining enhancement additive has been developed aiming to improve the machinability of sinter-hardened and heat-treated PM materials. The performance of the newly developed machinability enhancing additive has been evaluated through designated machinability tests with 6 different sinter-hardened and heat-treated materials that were prepared and tested in actual production conditions. It has been demonstrated as an effective machinability additive for sinter hardenable materials with enabling productive machining and/or extending tool life.

Traditionally, PM exhaust flanges and HEGO bosses are manufactured from 409L stainless steel powder by employing high temperature, hydrogen sintering. High temperature, hydrogen sintering is deemed essential for meeting the minimum specified sintered density of 7.20 g/cm3 set forth by OEMs. Compacting pressures employed typically range from 620 to 760 MPa (45 to 55 TSI), and the sintering temperatures range from 1288°C to 1388 °C (2350 °F to 2530 °F). A newly developed low chromium ferritic stainless steel, designated 410LV (patented), exhibits greater sinterability compared to the standard 409L. By selecting this alloy it is feasible to achieve a sintered density of 6.90 g/cm3 under mesh-belt sintering conditions (below 1177 °C, 2150 °F). This represents a significant reduction in the cost of manufacture. Low temperature sintered 410LV offers mechanical strength, corrosion resistance, and weldability that may satisfy the requirements of some of the exhaust flange and HEGO boss applications. This paper covers the properties of low temperature sintered 410LV, and compares those with the properties of similarly processed 409L. 

Alloy 440C is a high carbon, hardenable, martensitic grade of stainless steel, which offers   high wear resistance, combined with a moderate resistance to corrosion. A successful PM (powder metallurgy) version of the alloy should exhibit a high sintered density, at least greater than 7.60 g/cm3, i.e., above 98% of full theoretical density. Liquid phase sintering offers an attractive means of achieving this high density via single-press-single-sinter process. In addition, the sintered and heat treated material should have a predominantly martensitic matrix, with minimal amount of grain boundary carbides for achieving good impact strength.   The current paper covers the process parameters used, and the mechanical properties achieved, for a liquid phase sintered 440C alloy in both as-sintered and heat-treated conditions. The sintered density and hardness of this PM version of the alloy are comparable to those of the wrought and MIM (metal injection molding) processed 440C materials.  

Powder Metal materials that exhibit excellent heat treated properties and achieve good fatigue performance are needed to convert wrought components & gears to the PM process as well as to offer a cost effective alternate to existing the FN-020X PM material systems. North American Höganäs successfully demonstrated the excellent heat treated properties of the new developed prealloyed Cr-Ni steel (Astaloy® CMN). The purpose of this paper is to demonstrate the dynamic properties achievable with this material compared to wrought steels and FN-020X system.

Chromium pre-alloyed powders are used in an increasing number of PM applications. These pre-alloyed Cr-powders are attractive as they combine high mechanical strength with cost effectiveness. However, due to the solution hardening effect of the pre-alloying elements, mixes based on pre-alloyed powders obtain lower compressibility compared to mixes based on pure iron powders. Therefore, Cr alloyed powders can be more demanding to compact and require more efficient lubricants. The search for higher performance PM components calls for higher density of the sintered materials. To achieve this, a lower amount of lubricant is a prerequisite. To obtain sufficient lubrication, also at a lower amount of lubricant, heating of the tool die is an attractive approach. A new, highly efficient lubricant system for demanding applications has been developed. In this paper this new lubricant system is compared to amide wax as lubricant in mixes based on chromium alloyed powders. Data of the performance of the different mixes during compaction of components under production conditions is presented. Improved mechanical properties from the increase in density are also reported.

4th International Brazing & Soldering Conference (IBSC), in Orlando, Florida. Author: Ulrika Persson, M Sc, Höganäs AB. Nickel based brazing filler metals are commonly used in applications with high demands. Due to fluctuating raw material costs the performance of a low cost alternative to the Nickel based alloys was investigated. This paper presents an iron-chromium based brazing filler metal appropriate for brazing stainless steel. The alloy is suitable for brazing heat exchangers and EGR coolers with tough requirements on strength and corrosion resistance. The new brazing filler metal was tested in several brazing trials. The brazed joints were investigated by metallographic examinations, joint strength and corrosion resistance. The target was to benchmark against commercial available brazing filler metals. The investigations show that the alloy has excellent wetting and brazing on 316L stainless steel. The microstructure consists of a homogenous mixed matrix. The brazed joint has high strength and good corrosion resistance. The brazing temperature for the alloy is lower than for BNi5.

Currently PM exhaust flanges and HEGO bosses are manufactured from 409L or 434 L stainless steel powder by employing high temperature, hydrogen sintering. The high temperature sintering is necessary to achieve the large shrinkage needed to reach the specified sintered density set forth by OEM. Producers of exhaust components are today sintering between 1290 C to 1390 C to reach desired densities. 410LV is a newly developed low chromium ferritic stainless steel which exhibits greater sintering activity at lower temperatures compared to the standard 409L. By selecting this alloy it is feasible to achieve a sintered density of 6.9 g/cc under mesh-belt sintering conditions (below 1180 C). This permits a significant reduction in the manufacturing cost and allows possible production of exhaust components without investment in high temperature capability. 410LV sintered at reduced temperature may offer adequate  mechanical strength, corrosion resistance, and weldability for the exhaust flange and HEGO boss applications. This paper treats the properties of low temperature sintered 410LV, and compares those with the properties of low and high temperature sintered 409L.

The usage of steel powders prealloyed with chromium in PM components for high performance applications is steadily increasing. Excellent mechanical properties are achieved with these powder grades, provided that the processing into components is accurately done. Photoacoustic spectroscopy (PAS) technique has been used here to study oxide reduction during sintering in 90N2/10H2 atmosphere of test specimens based on 3%Cr-0.5%Mo prealloyed powders with 0.5% C added. Results from performed reduction trials show that Fe oxides on the powder surfaces are removed by H2 reduction early in the heating stage of the process. Carbothermal reduction is the main mechanism for reduction of stable Cr-containing oxides from 900°C and above. Efficient Cr oxide reduction requires a sintering temperature of at least around 1200°C. Therefore, small oxide particles remain in the material after sintering at 1120°C for 30 minutes. However, such oxides have earlier been shown to have no significant influence on mechanical properties.

Heat treatment of powder metallurgy components is often used in order to meet requirements on high hardness and other mechanical properties. Traditional processes such as quench and temper and case carburizing provide a well known route to meet these requirements. Sintered steels behave different compared to wrought steel due to its porous body. Interaction with the carburizing atmosphere for case depth control and decarburization of the surface is important as is the stress relief temperature to achieve required performance. However, sintered PM steels can also be sinter hardened where fast cooling is directly applied after the sintering process in order to form the martensite. In this paper suitable powder metallurgy materials when used at processing routes dedicated for the respective material are investigated with respect to achieved performance after sintering and subsequent heat treatment. Traditional processes such as carburizing and through hardening are selected as well as sinter hardening and low pressure carburizing.

As the major driver for the Powder Metallurgy (PM) industry is the automotive industry, the sintering process now has to be more cost effective than ever. One way to success here is to combine multiple processes and to control the processes by newer technological development as well as the deployment of processes with less energy and lower consumption of resources. The quality of PM parts is directly related to the control of process parameters of the individual production steps. The metallurgical properties and especially the microstructural changes in the case of a sintering component can only be regulated by controlling the furnace atmosphere accurately.  The carbon control of the sintering process has however always been somewhat out of control since no suitable control concept was available. It is therefore a primary objective of this paper to give detailed results of successful control of carbon potential in sintering processes and leveraging the advantage of the control to produce higher quality product and at the same time to facilitate a lower production cost.

To improve the performance of PM components higher density is one important approach. Lower amount of lubricant is often required to increase the compressibility of a mix. To obtain sufficient lubrication also at lower amount of lubricant, heating of the tool die is an attractive method. Chromium prealloyed powders are used in an increasing number of PM applications. These prealloyed Cr-powders are attractive as they combine high mechanical strength with cost effectiveness. However, due to the solution hardening effect of the prealloying elements, mixes based on prealloyed powders obtain lower compressibility compared to mixes based on pure iron powders. Therefore, Cr alloyed powder can be more demanding to compact and require more efficient lubricants. A new highly efficient lubricant system for demanding applications has  been developed. In this paper this new lubricant system is compared to amide wax as lubricant in mixes based on chromium alloyed powders. Data of the performance of the different mixes during compaction is presented including compaction of multi level components under production conditions.

Chromium, molybdenum and manganese are effective alloying elements suitable for low-alloyed structural steel components. Efficient use of these alloying elements in PM steels will make the PM technology more competitive in high performance applications. This study demonstrates mechanical properties obtained with prealloyed powder grades containing Cr, Mo and Mn after application of different press-sinter process routes. Astaloy CrL (Fe-1.5%Cr-0.2%Mo) with 0.7%C obtains tensile strength values of 714/880 MPa combined with elongations of 1.2/1.8% at density levels 7.0/7.2 g/cm3 after conventional sintering at 1120°C. Corresponding tensile strength and elongation values for two development grades with more ductile property profiles are 632/736 MPa combined with 2.2/3.0% for Fe-1.8%Cr, and 586/662 MPa combined with 3.3/4.0% for Fe-0.8%Cr-0.4%Mn, both with 0.7%C after sintering. Application of higher sintering temperature is beneficial for the mechanical performance of the studied materials. Sintering at 1250°C leads to increased tensile strength values by 15-25% compared to the properties obtained after sintering at 1120°C.

Sinter hardening of PM components is a well established and cost effective alternative to secondary heat treatment as one step in the manufacturing chain can be eliminated. However, during the last years alloys suitable for sinter hardening have been facing increased cost pressure due to increases and fluctuations in prices of nickel and molybdenum. Therefore, there is an increasing interest for availability of more cost effective low alloy steel powders that realize a compromise between compressibility and hardenability. The purpose of this paper is to present both static and dynamic properties achievable with a number of cost effective low alloy steel powders after sinter hardening.

Belt pulleys are commonly produced by the powder metallurgy process. The shape normally features a teeth section where a narrow and deep cavity is to be filled when the parts are pressed. With modern presses the performance of the powder mixes will often limit the productivity of the compaction process. Increased press rate will lead to distortion of shape due to uneven filling of the tool die. By using high a performance bonded mix filling is improved and the shape of the parts, e.g. parallelism and run-out, are improved in combination with increased productivity. In this paper results are presented from manufacturing of belt pulleys in a state-of-the-art hydraulic press. A high performance bonded mix is benchmarked with an elemental mix of the same nominal composition. Improvements in productivity as well as quality of sintered components are presented.

In search of new applications for PM components, the industry has a need for ever higher performing lubricants in metal powder mixes. Over the years, several different paths have been taken to improve performance of mixes. Examples are bonded mixes, mixes for warm compaction and more recently mixes for use with heated tooling. Sinter hardening has been more and more applied in the PM component manufactures worldwide, due to its pronounced advantages: good hardening effect, cost saving and better dimensional control. Some newly developed lubricants exhibit improved properties in key areas such as climate robustness, lubrication and the possibility to boost compaction performance by using heated tooling during compaction. Moreover these new lubricants are Zn-free, thus minimizing environmental impact and the need for sintering furnace maintenance. Extensive testing has proven that lubrication is superior to amide wax, lubricant properties are not sensitive to humid climate conditions and that green density can be increased compared to conventional mixes.

Sinter hardening is a well established industrial process which combines sintering and quenching in one step, and thereby avoiding re-heating and quenching of parts. It is getting an ever increasing interest thanks to availability of cost effective low alloy steel powders, which realize a compromise between compressibility and hardenability, on one side, and to the development of continuous furnaces which allow cooling rates high enough to transform austenite into martensite in these low alloyed steels. In this paper both static and dynamic properties obtained with a number of cost effective low alloy steel powders after sinter hardening will be presented.

Sinterhardening of PM components has been a successful and cost effective alternative to secondary heat treatment by eliminating the Heat Treatment manufacturing step. However, Sinterhardening alloys have been facing increased cost pressure due to the increases and fluctuations in the prices of molybdenum and nickel. Sinter-hardened components can also be susceptible to dimensional inconsistency due to the presence of admixed copper. The purpose of this paper will be to present the properties achievable with a newly developed sinter-hardening grade based on 0.9%Mo/0.9%Ni/0.25%Mn. The sinter-hardened material properties achieved on test pieces and production components will be evaluated. The new material is also manufactured in a version with 2% Cu diffusion alloyed. The dimensional consistency of the diffusion alloyed grade on production based components will be compared to traditional Sinter-hardened grades such as FLC-4608HT.

One area where powder metallurgy has proven to be superior to other means of manufacturing is wear resistant structures. Highly wear resistant high speed steel powders are commonly used in both HIPped and pressed and sintered forms. The carbide size and structure obtained depends both on production conditions and carbide type but the carbide types are fixed by the alloy composition. Alternative carbides have different properties and can be introduced in new alloy compositions. This paper presents the development of a new material where the carbides are designed to be of the most useful type for a sintered tool steel. A mix of small hard carbides and larger less hard carbides in a matrix capable of being hardened gives a good combination of properties. In some applications, the properties achieved are more effective than those obtained from the pressed and sintered M3/2 and M2 currently in use.

Powder metallurgy is a near net shape technology. Demand on high performance parts increases the demand for tight tolerances to be cost effective toward competing technologies. Heat treatment is commonly used for such parts. Tolerances will be affected by how these elements are added to the powder mix in such processes. The alloying elements can be added in many ways to a mix as either a premix, diffusion or organic bonded, or as pre alloyed. They will dependent on how they are added contribute in different ways to obtained tolerances. The effect of alloying element distribution on tolerances and tolerance correlated to microstructures in the heat treated condition will be presented.

Many PM applications requiring very good heat treated properties have utilized the FN-020X material system due to the relative economy of the system and ease of use. Recently, however, increases and wide fluctuations in the price of nickel have made the FN material systems less attractive. The FN system has also been challenging to use in applications requiring tight dimensional tolerances due to inconsistencies in dimensions related to negative dimensional change and segregation of admixed nickel. Many of the Cr-based systems introduced in the last few years have lower total alloy cost and excellent properties, but require careful sintering and heat treatment.  The purpose of this paper will be to demonstrate the properties achievable with a new prealloyed Cr-Ni steel (Astaloy CMN) that is suitable for sintering in endogas and for conventional atmosphere heat treatment. The heat treated properties of this new Cr-Ni prealloyed steel equal or exceed the FN-020X system while providing significantly lower total alloying cost. The focus of this paper is to present heat treated properties of test specimens sintered both in 90 v/oN2/10 v/oH2 and Endogas.

Sinterhardening of PM components has been a successful and cost effective alternative to secondary heat treatment by eliminating the Heat Treatment manufacturing step. However, Sinterhardening alloys have been facing increased cost pressure due to the increases and fluctuations in the prices of molybdenum and nickel. Sinter-hardened components can also be susceptible to dimensional inconsistency due to the presence of admixed copper. The purpose of this paper will be to present the properties achievable with a newly developed sinter-hardening grade based on 0.9%Mo/0.9%Ni/0.25%Mn. The sinter-hardened material properties achieved on test pieces and production components will be evaluated. The new material is also manufactured in a version with 2% Cu diffusion alloyed. The dimensional consistency of the diffusion alloyed grade on production based components will be compared to traditional Sinter-hardened grades such as FLC-4608HT.

Gas Nitriding treatment is proposed in combination with Shot Peening as a processing route to increase the wear performances of PM components made of prealloyed powder Astaloy CrL™. Porosity closure by surface densification allows limiting the depth of treatment and containing dimensional variations. 7,0 g/cm³ sintered density was considered. Pin on disk tests have been carried out at a constant load of 5N, sliding distance up to 7500m and sliding speed in the range of 0,2-2m/s. Disks in both as-sintered and gas nitrided condition, with and without Shot Peening, have been tested against a WC static counterface. An energetic interpretation of the wear rates is here presented. The different surfaces have been initially characterized through macro and microhardness profiles, LOM observations, X-ray diffraction and texture analysis.

One of the main strengths of PM technology is its ability to make near net shape components with a cost efficient process. There is, however, variability in the dimensions of the sintered parts that often calls for sizing or machining to reach the desired tolerance class.  High performance bonded mixes and state-of-the-art compaction presses are able to contribute to operational excellence. Precision in the dimensions of the pressed parts can be improved and parts can be made to higher tolerance classes. In this paper results are presented from compaction of a multi-level component in an advanced hydraulic press. A high performance bonded mix is benchmarked with elemental mixes of the same nominal alloying composition. Improvements in productivity as well as quality of sintered components are presented.

Ferritic and austenitic stainless steels exhibit moderate levels of strength which are adequate for a wide range of applications. Martensitic stainless steels offer significantly higher strengths, but have very low ductility. For applications requiring high levels of strength (typically, above 600 MPa, 87 KSI in tensile strength) and a moderate ductility, alloys from the precipitation strengthened family of stainless steels are often considered as potential candidates. The most popular alloy of this family is 17-4 PH. Full dense version of this alloy, produced via MIM route, has gained a high degree of acceptance in many demanding applications.  Conventional PM processing of 17-4 PH poses a number of challenges, the primary one being the achievement of a near-full theoretical density. This paper describes the optimum processing parameters, and properties of the alloy in both as-sintered and heat treated conditions. The effects of process parameters and the residual carbon content on the microstructure and mechanical properties are examined.

PM materials for gear applications have been reviewed based on results of own investigations of gear tooth bending strength of simple spur gears and rolling contact fatigue resistance of rollers. It was concluded that surface densified casehardened P/M gears reached gear tooth bending strength of reference casehardened machined wrought steel gears. Surface densified case-hardened PM rollers reached RCF-resistance of casehardened wrought machined rollers. Surface densification plays the main role in reaching high performance of PM components. Chromium low alloyed PM materials show a promising potential for a high performance/cost ratio.

The sinter hardening response of PM steels is affected by alloying system, cooling rate, density and mass of the component. In this paper the sinter hardening response of two chromium alloyed PM steels has been investigated when the mass and density are varied. Components of different size and green densities have been sinter hardened under production conditions for comparison. Macro hardness and micro structural transformations for each of the parts were evaluated to characterize the response. The objective of this work is to provide an aid for selecting correct sinter hardening material and processing conditions for a given application.

Precision parts tend to get more and more complex in geometry. For the production of P/M parts, cost efficiency is essential to remain viable and continue to be the process of choice versus other competing metal forming techniques. Production cost in combination with dimensional consistency play major roles in the design of the P/M process. Even with advanced equipment and controlled powder handling system the influence from filling characteristic for the material as such play an important role.  In this paper the influence of enhanced filling characteristic and segregation behavior by organically bonding of fine additives using the Starmix™ technique during a production period of more than 1 year for production parts are presented.

Austenitic stainless steels offer significantly superior corrosion resistance, when compared to ferritic and martensitic stainless steels. Austenitic stainless steels are however difficult to machine. Austenitic alloy 303L is formulated with a small sulfur addition, which leads to the formation of MnS precipitates in the matrix. Presence of MnS in the alloy does lead to improved machinability. Alternately, it is possible to add a machinability enhancing additive, such as MnS or MoS2 to a standard grade of stainless steel in the powder form in order to improve its machinability. Unfortunately, the presence of a sulfide in an austenitic stainless steel significantly lowers its corrosion resistance. Hence, neither of these options makes it possible to combine good corrosion resistance with good machinability.  This study evaluates a sulfur free additive for enhancing machinability of PM 316L, along with its effect on the corrosion resistance of the alloy. Two currently popular additives, namely MnSE and MoS2, are also included in the study for comparison. The new additive is found to offer enhanced machinability without any adverse effect on the alloy’s corrosion resistance. All sintering was carried out under conditions that maximize corrosion resistance. Machinability was determined by drilling.

The sinterhardening response of PM steel is affected by the alloying system, cooling rate, density and component mass. In this paper, the sinterhardening response of a chromium PM steels is investigated when the mass and density are varied. Three different sized components at two different green densities will be sinterhardened in a production furnace for comparison. The macrohardness and microstructural transformation for each of the parts will be evaluated to characterize the response. The goal is to provide an aid for selecting the correct sinterhardening material and processing conditions for a given application.

The past decades have seen a continuous growth of use of PM parts in automotive applications. However, the performance requirements future components must fulfill are becoming more and more demanding. Transmission gears for automotive applications are complex in shape and require both very high geometrical accuracy in terms of gear quality and very high mechanical performance in terms of durability of tooth flank and root. PM offers possibilities to produce complex shaped parts in a very cost effective way and by adding a selective densification of the gear teeth both accuracy and mechanical performance requirements can be met at a low added cost. In this paper a process route consisting of compaction, sintering, surface densification by rolling and finally heat treatment have been studied to assess the feasibility of producing high performance gears for automotive applications by powder metallurgy. Helical and spur gears were used in the study where the densification as well as the resulting gear quality and durability were tested.

The utilization of PM steel components in automotive has increased steadily during the last decades. Further growth is forecast based on new applications primarily in the engine and transmission systems. The designer of components for these automotive systems has to decide what type of material to use. The most common and established materials are wrought steels such as steel bar, forgings or castings. The steel bar has the advantage of reliable and well documented mechanical performance and the possibility to achieve almost any shape. The disadvantages on the other hand are often high machining cost and large material loss in the form of turnings. Both forgings and castings have since long been established materials for automotive applications requiring medium to high strength. Both technologies have the advantage of near-net shape and machining can be limited to just a few parts of the components. These manufacturing technologies, however, create an anisotropic material and therefore the mechanical performance of components made by forging and casting is strongly dependent on the specific processing steps used by the manufacturer of the components. A fourth alternative material for the designer is PM steel. In this case net shape is achievable and machining can be completely excluded or limited. This, in turn, reduces the manufacturing cost of the component. Due to the unique forming method of powder compaction the design of the components can often involve multiple functions or be designed to reduce size or weight. The decision by the designer, however, is also based on experience, track-record, availability of reliable material performance data, existence of material standards and supply opportunities. Due to the longer experience of machining, forging and casting and the more widespread use of these technologies as compared to powder metallurgy much effort is needed to serve the designer with such information to choose PM steel for a component. This paper discusses the situation today regarding potential new applications for PM steels and the opportunities to fulfil the designers’ demands for these with PM materials, component manufacturing knowledge and available data of the mechanical performance.

Sinter hardening has been more and more applied in the PM component manufactures worldwide, due to its pronounced advantages: good hardening effect, cost saving and better dimensional control. In this paper, the present situation of sinter hardening in mainland China is reviewed. The mechanism of sinter hardening is discussed in terms of both material and process effects. Among other sinter hardening materials, Cr-containing PM steels have shown a good market potential due to their high hardenability effect and low cost for raw materials. Combined with other technologies in PM such as warm compaction and high temperature sintering, Astaloy CrM can reach a tensile strength of 1400MPa, an elongation of 1.5%. A bending fatigue strength of 437MPa can also be reached after sinter hardening and tempering. In addition, sinter hardening gives a less dimensional change for this material. Finally, some suggestions are proposed regarding how to promote the sinter hardening technique in the Chinese PM market.

A preform of 1.5Cr-0.2Mo PM steel having density of 7.55 g/cc was surface rolled using a high precision transverse rolling machine to form a spur gear. The rolling was designed to get good surface densification and tight tolerances on the gear profile. After rolling, casehardening was conducted. Pore distribution and endurance limits in both bending fatigue and rolling contact fatigue were investigated. The results support the feasibility of using transverse rolling of high density P/M materials to obtain high precision spur gears with strength comparable to wrought steel.

Filling of the tool die directly influences dimensional tolerances and density variation. To minimize the variations in filling, both within different sections of the cavity and from part to part, are of great importance for produce high quality P/M parts. Filling of the tool die is also one of the limiting factors in the productivity in powder pressing. By using aeration filling in combination with bonded powder mixes, both weight scatter and productivity can be improved. In this presentation results are presented showing the benefit of using aeration filling for different types of powders

Organically bonded P/M mixes have been developed to improve the stability of dimensional properties by reducing the segregation of the mix constituents and improving the filling characteristics. Robustness and reliability are key factors for the promotion of P/M as cost effective substitute of competing manufacturing technologies. Based on the production of four different belt pulleys, this paper presents the achievement of reduced weight scatter and close dimensional control realizable by using a Starmix® that is organically bonded.

Powder grades pre-alloyed with 1.5-3 wt% chromium can be successfully sintered at the conventional temperature 1120 °C, although well-monitored sintering atmospheres are required to avoid oxidation. Mechanical properties of the Cr-alloyed PM grades are enhanced by a higher sintering temperature in the range 1120-1250 °C, due to positive effects from pore rounding, increased density and more effective oxide reduction. Astaloy CrM (Fe-3 wt% Cr-0.5 wt% Mo) with 0.6 wt% graphite added obtains an ultimate tensile strength of 1470 MPa and an impact strength of 31 J at density 7.1 g/cm³, after sintering at 1250 °C followed by cooling at 2.5 °C/s and tempering.

A comparative study is made on root bending fatigue performance of spur gears and plane bending fatigue performance of notched test bars. R = 0 root bending fatigue tests are made on small spur gears with critical root radius 1.0 mm. The results are compared to plane bending fatigue tests of 0.9 mm radius notched specimens. Results are presented for tests on 4%Ni/2%Cu/1.5%Mo prealloyed PM steel with addition of about 0.6% graphite. Predicted values from the test bars coincide well with the results obtained from the gear root fatigue tests.

New applications for PM have resulted in a substantial market growth during the last decades. The clue to these components lies in the utilization of new powders and component production processes. In order to reduce development time and increase the probability for success it is essential to work in close cooperation within the whole chain from powder supplier to component supplier and component user.

Optimized choice of material for two principally different types of PM components is presented. The first is characterized by high stresses in areas with high stress concentrations (for example synchronizer hubs with very sharp notches, typically <0.25mm in the pre-synchronizer slot and the inner splines). The second type has slightly larger notch radii (small spur gears and sprockets with typically notch radii between 1- 3mm). Diffusion alloyed materials are well suited for sharp notch components. Pre-alloyed materials are also well suited for applications with sharp notches if compressive residual stresses in the notch roots are created by appropriate process control. A free choice of material is available for components with the larger notch radii.

Improving the dimensional stability of PM components provides the opportunity to reduce overall cost by potentially eliminating secondary operation such as sizing. The ability to hold tight as-sintered tolerances becomes even more important when more difficult to size prealloyed materials are used. Dimensional stability is affected by many factors, including material handling and mix composition. This paper will investigate how Starmix® bonded mixes can improve dimensional stability by reducing the segregation of mix constituents. The investigations presented include conventional and bonded FC-0208 mixes in a simulated production environment.

Two important areas for the growth of PM are increased performance and improved cost effectiveness. Chromium is an alloying element that can help to achieve these goals. Chromium has positive effects on the final properties of steels while being historically less susceptible to fluctuations in cost. This paper will discuss the properties achievable using two chromium steels being standardized, FL-5208 and FL-5305. FL-5208 is a fully pre-alloyed PM steel based on 1.5% Cr and 0.2% Mo. FL-5305 is a fully pre-alloyed PM steel based on 3.0% Cr and 0.5% Mo. Both of these materials exhibit a combination of high material properties and versatility. Static and dynamic material properties achievable by these materials using conventional sintering and high temperature conditions as well as sinter hardening will be discussed.

In North America, legislative pressures to minimize pollution from motor vehicles are placing greater demands on the vehicle exhaust systems. Because of this, and the increasing market demand for long-term vehicle warranties, conversion to all stainless steel exhaust systems have been progressing steadily since mid-1990s. All stainless steel exhaust systems are expected to become more popular in Europe and Asia as well, in response to similar legislative agenda. In an all stainless steel exhaust system, PM stainless steel exhaust flanges and HEGO bosses are frequently selected over wrought (stamped and formed) stainless steel components. This is because PM stainless steel provides significant advantages in performance, cost and design flexibility, over their wrought counterparts. The improved performance is primarily due to the fact that PM stainless steel is more resistant to spalling of oxide scales in application-specific cyclic oxidation tests, compared to wrought stainless and wrought carbon steels. This paper investigates the cause of the superior resistance to scaling of PM stainless steels in these oxidation tests. Stainless steel flanges made of 400 series alloys, via PM and wrought processes, were investigated to determine the rate of the oxide scale build up, and the subsequent spalling of the scale. Microstructural examinations revealed major differences in the characteristics of the scale formed in these two types of materials. The lower coefficient of thermal expansion, combined with the beneficial effect of pore-scale interaction, are found to be responsible for stronger adherence of scale to the metal substrate in the case of PM, which in turn prevents spalling of the scale during thermal cycling.

The sinterhardening response of PM steels is affected by many factors, including the alloy system, the cooling rate, density, and component size. In this paper influence of mass and density on the response to sinter hardening has been investigated for some PM steels. Micro structural transformations, macro hardness and plane bending fatigue performance of un-notched and notched specimens have been evaluated. It is shown that the performance is highly depending on both surface hardness but also strongly on the martensite gradient in the part. Higher amount of martensite in the surface induces compressive residual stresses that are beneficial for the fatigue performance. The effect is more pronounced for notched materials compared to un-notched and this strongly compensates for the raised stress in the notch root. This information is of great value for selecting optimal sinter hardening material and processing parameters for a given application.

Case carburizing followed by quench and temper is a well established method of reaching very high properties for components like gears and sprockets. The well established materials on Fe-Cu-Mo-Ni base can all be case hardened using standard equipment and processes. Cr-containing PM materials, with their increased sensitivity to oxidation (and local carbon level), require special considerations.  In this paper an overview of how different methods to carburise low alloyed chromium alloyed PM steels will be presented. Among methods discussed are gas carburizing, carbonitriding and vacuum carburizing. Specific emphasis is on selection of appropriate process with regard to density of the components and the formation of carbides.

Surface densification is now a well-known technology for improving the performance of PM components. Chromium-alloyed powder grades have been developed in order to replace expensive alloying elements such as nickel and molybdenum with more cost beneficial chromium. Astaloy™ CrL (Fe-1.5Cr-0.2Mo) is a material with excellent formability in the as-sintered state, high hardenability and high fatigue performance and is therefore selected as a candidate material for surface densified gears in this study. Helical gears for the fifth gear in a manual gearbox have been investigated in this study. The response to surface densification by radial rolling is investigated and compared to the behaviour of Astaloy 85 Mo. The result after case hardening is also compared for the two materials using low pressure carburising for the Astaloy CrL and conventional gas carburising for Astaloy 85 Mo. The implications of these results are discussed in terms of tooth root bending fatigue and service life.

P/M is a net or near net shape process. Machining operations are used for many applications in order to reach final tolerances or shapes not possible to achieve in the compaction step. Chromium pre-alloyed high strength PM steels in sinter-hardening condition or in heat treat conditions have increased in recent time. Guidelines for insert choice and effect from additives are needed to improve the performance in the machining operation for these application areas. This paper describes the influence of material structure and selection of machining tool for bainitic and martensitic chromium pre-alloyed PM steels. Guidelines for cost effective machining of banitic and martensitic chromium pre-alloyed PM steels are presented.

A final-drive idle helical gear from a passenger car transmission was made of water atomized and fully pre-alloyed Fe-1.5Cr-0.2Mo powder. The gear samples were cold compacted to 7.1 g/cm³, sintered, surface densified by radial gear rolling and casehardened. A 3D gear meas-urement center was used to evaluate profile, alignment, pitch and runout deviations of the gears after the gear rolling and after the casehardening. The gears achieved an overall DIN 7 quality after rolling for all single deviations suggested in DIN 3961 to have general or particu-lar importance for uniformity of rotation, load capacity and noise reduction of gear. After the low-pressure casehardening, the overall gear quality for the deviations as above was DIN 7, except for the total profile deviation Fá, which achieved DIN 10 quality. To achieve DIN 7 gear quality after casehardening, further work should include activities on reduction of the tooth width contraction along the tooth height.

This study is a step towards of developing a means for predicting the performance of solid powder lubricant used in P/M process. Lubricant is an indispensable part of the P/M process. Lubricants are often used admixed with metal powders in order to reduce adhesion and friction between powder particles and between powder and the die-wall during the filling, compaction and the ejection process. The lubricants are often solid organic substances such as metallic stearates and amide wax. During compaction and ejection of a component the lubricant is exposed to high pressure and high shear stress. Experiments have been performed to evaluate tribological properties of lubricants from different aspects under such conditions. A powder friction-measuring device (PFMD) has been used to evaluate the friction of the powder die-wall contact. Results obtained from friction measurements using PFMD are shown to correlate well with the results from real pressing process. This paper will describe the performance of lubricants including Amide wax, Kenolube and Zinc stearate regarding friction properties.

The high structural performance of Chromium pre-alloyed PM steels have opened the possibility to replace high loaded components conventionally made of wrought steel with PM. Small notch radii, wear or high bending stresses characterize these components. A systematic investigation is made on bending fatigue performance and notch sensitivity of Chromium pre-alloyed PM steel. The results are benchmarked to other PM alloying systems.

Two material models for prediction of the fatigue performance of PM steels are compared. The Murakami model considers Vickers hardness and maximum defect (pore) size. The fracture mechanics model includes defect (crack) size and threshold stress intensity factor. Both models shall be considered simultaneously and the combination gives a good prediction of PM steel fatigue limit.

Chromium is an attractive alloying element in steels due to its positive effect on hardenability and low cost. Historically, the use of chromium has been limited in PM steels due to cost reasons and its high affinity for oxygen. In the pre-alloyed state, the lowered activity of chromium makes it possible to meet performance for highly loaded PM applications when sintering in conventional mesh belt furnaces. In this paper, considerations when sintering pre-alloyed chromium PM steels are presented. Influence of sintering temperature is treated and the need for well-controlled sintering atmosphere is emphasized. Mechanical properties and microstructures obtained for different sintering conditions are given.

Powder Metallurgy (PM) is a near net shape process. Since this process is “near net”, secondary operations, e.g. machining, are often required for many applications, in order to create shapes not possible to achieve through compaction only, or to reach demanded tolerances. The use of chromium alloyed PM steels, a high strength PM material, has increased in recent time. One of the features of the chromium alloyed PM steel material is the excellent hardenability. Machinability is related to the hardness of the component. To maintain the cost benefit for PM applications, machining of such parts is to be taken into account in material selection. Guidelines for tool choice, cutting data and the effect from additives are needed to improve the machining performance of chromium alloyed PM steels in their various applications. This paper describes the machinability of a high strength chromium alloyed PM steel. Optimal settings of inserts are established at which properties like life time and surface roughness are improved. The gains achieved when machining these PM steels by using machinability additives are also shown.

Powder metallurgy (PM) technology has a growth of 7% annually. Competing technologies set demand on the PM technology to convert more highly loaded components to maintain this growth rate. Development work up till today on both material and processes has proven to meet these demands. Chromium as an alloying element has opened up a cost efficient way to manufacture high performance parts. Compacting techniques, sintering concepts and improvements for secondary operations for such a material gives the opportunity for further strengthening of the growth for the PM technology. In this presentation development trends for high performance components are discussed. Potential for PM technology as such is set in relation towards precision casting and other competitive techniques. Potential material and potential processing techniques are discussed.

The demands on powder metal components for new automotive applications are placing more and more pressure on increased performance at reduced costs. This has created a demand for high performance and cost effective materials that can be used in a variety of applications. The growing interest for chromium as an alloying element for sintered steels is due to the excellent mechanical properties attainable both in the as sintered condition and after heat treatment, such as through hardening or case hardening. Among case hardening treatments, low pressure carburising is an attractive process aimed to improve fatigue strength and wear resistance of PM components.  In this paper properties achievable with a Cr-Mo pre-alloyed powder, Astaloy CrL, after processing by different conditions are described. Properties achieved at different density levels after conventional and high temperature sintering and low pressure carburising are compared. A case study of a production component is also described.

Steel powders pre-alloyed with chromium are successfully used in PM components for high performance applications. Good mechanical properties are obtained after conventional sintering and the properties can be further improved by the use of high temperature sintering and/or sinter-hardening. Case hardening operations may also be applied for applications where the PM component surfaces are highly loaded. This paper presents dynamic as well as static mechanical properties obtained for different Cr-Mo pre-alloyed powder grades after various process routes. Compaction pressure, sintering temperature and cooling rate have been varied and case hardening has been applied. Correlations between microstructures and mechanical properties are described for the different materials. The benefits of using case hardening are highlighted, which is demonstrated by the excellent fatigue properties obtained.

There are many factors that will help P/M continue to be a cost effective alternative to more traditional metal forming technologies. Among these factors are consistency of properties and dimensions during the manufacturing process. Material handling, mix composition, and manufacturing environment all affect the performance of P/M mixes. This paper will discuss how mixes bonded using the Starmix™ process can improve the consistency of dimensions and properties by reducing the possibility of segregation of mix constituents. The improvements in component consistency were analyzed during production of typical P/M.

Recent advances in powder manufacturing and processing have made chromium an attractive element in P/M manufacturing. In addition to chromium’s positive affects on strength and hardenability, it is also a cost effective alternative to traditional alloying elements, such as nickel and molybdenum. The purpose of this paper will be to demonstrate how a Cr-Mo alloy, Astaloy CrL, can be used to replace a more expensive, traditional alloy system,FLN2-4405. Sintered and heat treated properties will be presented.

Phosphorus is an extensively used additive in ferrous Powder Metallurgy components for magnetic applications. Changes in powders and /or sintering processes, however, occasionally lead to intergranular cracking in parts made from phosphorus-containing materials. The goal is to understand this detrimental phenomenon and develop robust processes to ensure ductile components. The results of the studies from the conventional metallographic evaluation and Auger analysis are presented. 

Diesel engine components conventionally made of wrought steel are identified as candidates to be replaced by high performance PM steel. An investigation is made on notch sensitivity and bending fatigue performance of as sintered Chromium/Molybdenum pre-alloyed Astaloy CrL and sintered-hardened Astaloy CrM. Best bending fatigue performance, 437 MPa at load ratio R=-1, is found for 1120 °C (2050 °F) sintered-hardened Astaloy CrM+0.4% graphite with addition of methane to the sintering atmosphere. Astaloy CrL+0.85% graphite sintered at 1250 °C (2280 °F) with regular cooling 0.8%C/sec have a fatigue limit of 296 MPa. Lowest notch sensitivity index in this investigation is found for Astaloy CrM+0.4% graphite followed by Astaloy CrL+0.85% graphite sintered at 1120 °C (2050 °F) and 1250°C(2280 °F) respectively.

Austenitic stainless steels are difficult to machine, and if a significant amount of machining is required in an application, one often has no choice but to use a sulfide containing grade, such as 303L, or 316L admixed with MnS. The presence of sulfides in an austenitic stainless steel, however, lowers its corrosion resistance significantly. Addition of a small amount of Sn and Cu has been reported in the literature to significantly improve corrosion resistance of austenitic stainless steels, including that of the sulfide containing grade. Addition of Sn and Cu is also reported to have a favorable influence on the machinability of sulfide free grades of P/M austenitic stainless steels.  This study evaluates the machinability and corrosion resistance of the standard grades, 303L and 304L, along with their Sn and Cu modified versions, 303LSC and 304LSC, and a Cu modified version of 303L, called 303LCu. In this study all sintering was carried out under conditions that are known to be ‘optimal’ from the corrosion resistance point of view. Machinability was determined by the use of a drilling test.

The past decades have seen a continuous growth of the use of PM parts in automotive applications. However, the performance requirements the components must meet are more and more demanding. Transmission gears for automotive applications are complex in shape and require very high geometrical accuracy in terms of gear quality (DIN, ISO, AGMA, etc) and also very high mechanical performance in terms of durability of tooth flank and root. Powder metallurgy is very cost effective for complex shaped parts and by adding a selective densification of the teeth the accuracy and mechanical performance requirements can be met at a very low added cost. A process route consisting of compaction, sintering, surface densification by rolling and finally heat treatment was used to assess the feasibility of producing transmission gears by powder metallurgy. Helical and spur gears were used in the study where the densification as well as the resulting gear quality and tooth root fatigue was tested.

The development of high performance materials and more efficient production methods makes a changeover from traditional manufacturing methods both possible and profitable. High temperature sintering is one potentially effective processing technique to capture future applications demanding high performance of the material system. In this paper, an analysis comparing conventional belt furnace sintering at 2050°F to high temperature sintering at 2280°F is presented. The study covers a comparison of sintering costs for a P/M gear made of two different low alloyed steels. Static and dynamic properties of these materials achieved at these temperatures are discussed.

Diffusion bonding is an effective method to obtain high fatigue performance in PM steels. The main characteristic of diffusion-bonded materials consists of a well-organized microstructural heterogeneity. This work gives reason of the mechanism underlying this fact by means of microstructural interpretation of dynamic performance. Four point bending fatigue tests have been performed on D.AE and D.HP powder metal steels at density close to 7.1 g/cm³, sintered at 1120 °C (2050°F); cooling rate was 0.8 °C/s (1.4°F/s). Notch sensitivity has been tested with 0.25, 0.9 and 3 mm notch radius.   Particular focus has been made on the interaction of the different phases. The effect of the Cu-rich network surrounding the base powder particles is considered to be the main factor responsible for the high fatigue performance of diffusion-bonded materials.

For more than 50 years, iron metal powders have been successfully applied in semi-metallic friction materials for OEM and aftermarket applications in North America. The advantages of using iron metal powders in brake formulations stems from its ability to enhance friction performance, to reduce brake/rotor wear, to make it easier to manufacture brake linings and to provide a cost-effective brake material. However, there are few publications exploring the roles of iron metal powders in friction materials due to manufacturing know-how reasons and/or lack knowledge in understanding powder characteristics of iron metal powders manufactured by different manufacturing methods and processes. On the other hand, more and more modified iron and alloyed iron powders have been developed in last 10 years. Many of them have unique chemical and physical properties and have been found wide applications in different industries including friction. However, the advantages of these modified iron-based powders have not been discussed in the past.  This paper investigates the roles of different types of iron metal powders manufactured today and discusses the effect of using various raw materials, production methods and processing technologies on the key characteristics of iron powder such as particle size, particle density, and particle morphology. In order to evaluate the effect of iron metal powders on friction noise and performance, dynamometer tests were performed based on a modified noise testing procedure. The testing results indicated that the difference in powder characteristics of iron metal powder could greatly affect the performance of brake materials, especially on co-efficient of friction and braking noise.

Powder metallurgy is a well-established technology for manufacturing a variety of complex shaped parts in the gearbox of a passenger car. However, using standard PM technology it is not possible to reach the mechanical properties necessary for gear components. Combining the net shape capability of powder metallurgy and cold forming by a burnishing operation provides a method of producing transmission gears for automotive gearboxes at a low cost with mechanical properties equivalent to conventionally produced gears. Powder and process selection is discussed, including the influence of core density on densification and quality. The mechanical performance of a helical and a spur gear are compared to their respective reference gears made of case hardening steels. The endurance limit in tooth root bending fatigue testing of the surface densified helical PM gear reaches 94% of the reference material, while the surface densified spur gear reaches 106% of its reference gear. The gear quality of the two gears is DIN class 8 after heat treatment and the surface roughness of the gear tooth and root is Ra=1,2 µm.

Over the last decades many new powder metallurgy components have been developed and the average growth has been around 6%/year. This is substantially higher than for other technologies such as casting, forging and machining of bar stock. This growth is expected to continue at least at the same pace if not higher. The prime reason for the increased use of PM components is the combination of strength and dimensional tolerances which in this paper is defined as “The Powder Metallurgy Playing Field”. Characteristics of different sections of this “playing field” are defined and typical materials representing these fields are presented. The paper presents four high strength materials and compares mechanical properties and dimensional tolerances of these. The four materials are alloyed with two or more of the alloying elements Cu, Ni, Mo and Cr and the alloying methods are diffusion alloying, pre-alloying respectively combinations thereof.

An overview of the plane bending fatigue performance of PM steels in as-sintered state is presented. Pre-alloyed Molybdenum and Chromium-Molybdenum materials, diffusion-bonded Ni-Cu-Mo and Fe-2%Cu pre-mixes are reviewed. The effect of varying density level and Carbon content upon fatigue performance is analyzed separately. Diffusion-bonded materials exhibit heterogeneous microstructures with high performance metallographic phases distributed along the sinter-necks and around the pores. Optimized carbon content in diffusion-alloyed materials is characterized by a well-distributed martensitic microstructure. Furthermore, fatigue crack initiation is found in the low yield stress phase in the base powder core. PM steels based on pre-alloyed powders exhibit one phase or random distribution of two or more phases with no systematic order in relation to the pores, hence fatigue crack initiation is related to sinter-neck failure. Influence of density is more pronounced for pre-alloyed materials than compared to diffusion-bonded materials.

The high dimensional and mechanical requirements have in the past limited or prohibited the use of gears produced by powder metallurgy for automotive transmissions. The introduction of a technique for selectively densifying the highly loaded regions of the gear provides a production route for high performance gears. The present work is part of a larger program that aims at demonstrating the feasibility, quality and economics of producing surface densified P/M gears for automotive gearboxes. The selected gear is the 5th gear (fixed) from a line of gearboxes for Renault passenger cars. It is characterised by a helical angle of 30°, it has 31 teeth and internal splines. In order to select a material a series of surface densified rollers were manufactured and tested for rolling contact fatigue strength. The results show that the Distaloy DC1 can match the solid steel reference material. The investigations were carried out as part of a project funded by the European Commission under the “Competitive and Sustainable Growth” program (Project No: GRD1-1999-10674).

Powder metallurgy a.k.a PM in combination with surface densification by radial cold rolling is a competitive manufacturing method for high performance gears compared to producing gears by turning, hobbing and shaving. This paper aims to give a deeper understanding regarding density and stress distribution in a surface densified and case hardened PM gear tooth. The results from the calculations are presented and the design aspect of surface densified components will be discussed.

A helical PM gear for a passenger car gear box was manufactured by pressing, sintering and selective surface densification using transverse rolling. The evolution of gear properties in terms of microstructure, geometry, surface roughness and DIN-quality is monitored at each step of the processing sequence. The geometry of the PM gear is compared to a conventional wrought steel gear being currently used in the gear box. It is shown that PM gears can be manufactured well within the DIN “quality 8” tolerance fields. Furthermore it is demonstrated that alignment and profile errors can be reduced in the sequence of processing. While wrought gears have less alignment and profile errors, PM gears are superior in terms of run-out and pitch errors as well as surface roughness.  These investigations were carried out as a part of a project funded by the European Community under the “Competitive and Sustainable Growth” Program (Project No.: GRD1-1999-10674).

Planetary gears in heavy truck gearboxes are normally manufactured by forging a blank, turning, hobbing, shaving and heat-treatment followed by grinding. Due to the size of the gear the net shape capability of PM methods can be cost effective alternatively to conventional manufacturing. Warm compaction and surface densification are two PM methods to reach high density and thereby high strength and fatigue properties. Typical characteristics for PM gears manufactured by these methods are outlined.

PM2004, in Vienna, Austria  Authors: Luigi Alzati, Anders Bergmark. The past decades have shown an increased use of P/M components in passenger cars. However, in order to continue this increase the mechanical and fatigue performance must be further improved. Furthermore, it is important that not only the average level of the critical properties improves, but also their consistency and robustness. The diffusion bonded iron powders exhibit superior properties in several areas, and the robustness to avoid segregation is very high. The present paper describes detailed aspects of microstructure in relation to the fatigue performance for some diffusion-alloyed powders sintered at 1120 °C and cooled at a cooling rate of 0.8°C/sec. Fractographic observations analyse difference in fatigue crack path among the materials.

PM2004, in Vienna, Austria.  Authors: Mats Larsson, Daniel Edman. Dimensional stability is a prerequisite to produce net-shape P/M components. Improved dimensional stability will make the P/M route even more cost competitive compared to competing manufacturing techniques.  Diffusion bonded powders and chemically bonded mixes are means to reduce dimensional scatter due to segregation of alloying elements. By utilizing specific bonding substances chemically bonded mixes exhibit superior flow properties that facilitate even filling of the die cavity in the press. In this presentation results are presented from a study comprising different mix compositions, type of alloying additives and use of bonded mixes, pointing out ways to improve dimensional stability.

PM2004, in Vienna, Austria. Authors: Koki Kanno, Yoshinobu Takeda, Anders Bergmark, Luigi Alzati, Björn Lindqvist, Y. Ueda, K. Kanda, A. Zandonati. The fatigue performance of as sintered PM steel is depending on microstructure and density. Additional increase of the fatigue performance can be achieved by the secondary operations case hardening and/or shot peening. Shot peening is a well-established secondary operation on homogeneous steels with the purpose to introduce compressive residual stresses in the surface and to increase the yield stress by work hardening. Two additional features of shot peening are utilized in PM. Local plastic deformation of the surface layer increases the relative stiffness of the cross-section and also eliminates the detrimental effect of pores open to the surface. The present study is made on 1.5%Chromium/0.2%Molybdenum pre-alloyed PM steel notched samples in plane bending load mode. Increase of the plane bending fatigue performance by about 70% is found in cases where all mechanisms are combined.

PM2004, in Vienna, Austria. Authors: Erik Hjortsberg, L. Nyborg, Hilmar Vidarsson. The use and effect of lubricants during compaction and ejection of metal powder has for a long time been studied from a macro perspective, assessing effects of different factors but ignoring the actual mechanisms through which they operate. Here, the intention is to explain the physical interaction between the metal powder, lubricant and tool wall on a microscopic level. With the development of a new compaction tool, the use of X-ray photoelectron spectroscopy and ion sputtering, it has been established that, for iron powder samples containing 0.5-3 wt% ethylene bis-stearamide, compressed with 400-800 MPa, both the compact surface and the tool wall are to a large extent covered by a film of monomolecular thickness. Through interference microscopy, the volume of pores at the surface of the compact have been determined to 0.4 (µm)³/(µm)². Several conclusions that deepen the understanding of the functionality of lubricants have been drawn from these observations.

PM2004, in Vienna, Austria. Authors: Hilmar Vidarsson, Björn Johansson, Per Knutsson. Warm compaction of Densmix™ powder mixes is an established technique to produce PM parts with uniform densities up to 7,4 g/cm³. This has opened new possibilities for cost efficient production of parts with high requirements on both mechanical strength and dimensional tolerances. This paper will address important properties of Densmix™ powder mixes and how these facilitate efficient and robust production of PM parts. Powder properties at elevated temperature, density levels, lubrication performance and mechanical properties will be described, together with process capability studies from simulation of full-scale production of PM components.

PM2004, in Vienna, Austria. Authors: Sigurd Berg, Barbara Maroli.  Increased mechanical properties of sintered steels are the major factor for the introduction of PM components as substitute for wrought steels. Materials based on grades pre-alloyed with chromium have proved to be an attractive choice for the production of high performance PM parts. Already in the as-sintered condition materials alloyed with 1.5% res. 3% chromium achieve high strength compared to PM steels alloyed with up to 4% Ni. Further improved mechanical performance is achieved utilizing increased cooling rate i.e. sinter-hardening has been the break-through.  In this paper the influence of process conditions on the static and dynamic properties of materials prealloyed with chromium is presented and explained through their microstructure. Alternative process routes such as for example high temperature sintering followed by rapid cooling are shown to give outstanding performance such as yield strength of 1250Mpa and bending fatigue strength of 445MPa.

PM²TEC 2004, in Chicago, USA. Authors: Sven Bengtsson, Linnéa Fordén, Magnus Bergström. The past decades have seen an increased use of P/M components in passenger cars and light trucks. However, only a limited number of applications have been found in heavy trucks. P/M technology have so far not met the performance requirements of transmission gears. Forging of a blank, followed by turning, hobbing, shaving, heat treatment and finally grinding are the manufacturing steps normally used for the planetary gear of a hub reduction unit of a heavy truck. The large size of the gear means that a lot of material is machined away before the component is finished.  Using a net shape process offers the potential of significant cost savings. Normally conventional cold compaction cannot deliver the fatigue performance and tolerances required, but other techniques can increase these properties to new levels.  Warm compaction improves the density and exhibits an excellent pore size distribution. This means that the fatigue properties improve at a moderate cost increase. Surface densification is an additional process step in the manufacture of a P/M component. By introducing this step the net shape capability of the P/M technology is utilized while at the same time the highly loaded regions benefit from increased density. Also tolerances of the densified regions can be improved.

PM²TEC 2004, in Chicago, USA. Authors: Anders Bergmark, Ola Bergman, Luigi Alzati. The use of PM materials in highly loaded components is continuously expanding. Fatigue properties on such parts are becoming more and more important. Pre-alloyed chromium materials enables cost efficient productions of highly fatigue loaded PM parts. In this paper fatigue performance of pre-alloyed chromium material sintered at 1120 °C(2050°F), 1250 °C(2280 °F) and 1280 °C(2340 °F) are presented. Cold compaction to 7.0 – 7.1 g/cm³ and warm compaction to 7.3 g/cm³ are used. The materials are processed to high performance microstructures obtained directly in as sintered state after normal cooling. Shot peening has been shown to be a very efficient process route on Chromium pre-alloyed materials with fine pearlite or tempered martensite microstructures. The results of the Chromium pre-alloyed materials are compared to diffusion alloyed high performance material D.HP1. Dynamic data are presented and correlations between microstructures and mechanical properties are stated.

PM²TEC 2004, in Chicago, USA. Authors: Daniel Edman, Paul Hofecker, Denis O'Keefe, Ulf Engström, Sigurd Berg. Many factors influence the productivity and efficiency of the powder metal process. Among these are segregation of the mix constituents and filling performance. STARMIX™ products address these issues by bonding ingredients to reduce segregation and increase filling performance. This paper describes the improvements in dimensional stability attainable with STARMIX™ products by using case studies comparing the performance of premixes made with conventional blending to STARMIX™ products. The results of laboratory based testing will also be discussed.

PM²TEC 2004, in Chicago, USA. Authors: Sigurd Berg, Barbara Maroli. Increased demand on high strength PM applications and cost reduction from the automotive industry has lead to introduction of chromium as an alloying element mainly due to its low cost and high hardenability. A common process for pre-alloyed material with 3% chromium has been sinter-hardening using normal sintering temperatures. Further increase in mechanical properties is achieved utilizing high sintering temperature or heat treatment operations like vacuum case hardening.  In this paper the influence of process conditions on the static and dynamic properties of materials pre-alloyed with chromium are presented and explained through their microstructure. After high temperature sintering with a carbon content of 0.7% a fatigue strength of 445 MPa (65 ksi) is obtained. Combining high temperature sintering with rapid cooling yield strength up to 1250 MPa (181 ksi) is obtained at 0.45% C. If high temperature sintering is followed by vacuum carburizing fatigue strength of 527 MPa (76 ksi) is achieved.

PM²TEC 2004, in Chicago, USA. Authors: Bo Hu, Alexander Klekovkin, Dave Milligan, Ulf Engström, Sigurd Berg, Barbara Maroli.  Chromium and molybdenum as pre-alloying elements in ferrous powders can offer potentials for achieving excellent sintered properties. The potential properties are further increased when the materials are compacted to high green density, and/or are sintered at high temperature and sinterhardening. This paper evaluated the properties achievable using Cr-Mo prealloyed materials compacted with different compacting techniques such as cold compaction, warm compaction and high velocity compaction to increase green density. Furthermore, the properties achieved after conventional / high temperature sintering as well as sinterhardening were compared.

PM²TEC 2004, in Chicago, USA. Authors: Prasan K. Samal, Owe Mårs, Ingrid Hauer. P/M ferritic stainless steels 409L and 434L are most commonly specified for automotive exhaust system components. A sintered density of 7.25 –7.30 g/cm³ is desired in these applications, in order to meet mechanical property, as well as, leak tightness, thermal fatigue, oxidation resistance and weldabilty criteria. With each of these two alloys, the desired sintered density of 7.25- 7.30 g/cm³ is achievable via various combinations of compaction and sintering parameters. This paper compares the room and elevated temperature mechanical properties, as well as the microstructure, of P/M 409L and 434L sintered to 7.25 – 7.30 g/cm³ using various combinations of process parameters. Sintering temperatures employed range from 1232°C (2250 °F) to 1366 °C (2490 °F). 

PM²TEC 2004, in Chicago, USA. Authors: Dave Milligan, Paul Hofecker, Ulf Engström, Mats Larsson, Sigurd Berg. It is well known that the properties of powder metal components increase as the density increases. There are many methods of increasing the density of green compacts, including lubricants, warm compaction and increased compaction pressures. The purpose of this paper will be to describe the properties achievable using elevated die and/or powder temperature to achieve increased green densities. Green densities achieved using elevated temperature processing will be compared to green.

PM² TEC 2004, in Chicago, USA.  Authors: Ulf Engström, Mary Schmidt, Sigurd Berg. It has long been known that diffusion bonding elements such as copper, nickel, and molybdenum to iron can offer excellent performance, high compressibility, and very stable dimensional performance. These characteristics are enhanced when copper and/or nickel are diffusion bonded to a 1.5% Mo prealloyed base. This paper describes the performance available from systems using 2% Ni and 4% Ni + 2% Cu diffusion bonded to a 1.5% Mo prealloyed base. Properties achieved by conventional compaction, conventional and high temperature sintering, and sinterhardening will be discussed.

PM² TEC 2004, in Chicago, USA. Authors: Mary Schmidt, Peter Thorne, Ulf Engström, Jason Gabler, Thomas J. Jesberger, Stephen Feldbauer. Sinter hardening is a cost-effective process that combines sintering and heat treatment in one step. It is known that the cooling rate following sintering greatly affects material microstructures, which determine the final properties of sinter hardened materials. This study investigates the properties of three sinter hardenable materials (two Cr/Mo prealloys and a Ni/Mo prealloy) under various sintering times and cooling rates. The objective is to understand how these sintering conditions influence the development of martensite in the microstructure and control the mechanical properties of the materials. By understanding how sintering and cooling affect these parameters, it is possible to optimize the sintering cycle for individual materials and applications.

PTECH2003, in Guarujá, São Paulo, Brazil. Authors: Mats Larsson, Sigurd Berg, Barbara Maroli. Chromium is an alloying element that is of increasing interest in P/M material. Low cost, recycling advantages and improved hardenability are benefits of using chromium as an alloying element. The combination of good mechanical properties and low alloying cost makes chromium-alloyed materials very competitive. In this paper, the static and dynamic properties of two materials pre-alloyed with chromium and molybdenum are compared with materials based on more traditional alloying systems for P/M materials, such as Fe-Cu-C and diffusion-alloyed materials. The good hardenability of chromium-alloyed materials also makes this type of material suitable for sinter hardening.

PTECH2003, in Guarujá, São Paulo, Brazil. Authors: Mats Larsson, Maria Ramstedt. In the production of P/M components admixed lubricant in the metal powder mix is the most common way to achieve the lubrication needed during compaction and ejection of the components. However, the type of lubricant not only influences the compaction, but also the properties of the powder mix, as well as the properties of the green component. In this paper a comparison is made between four types of lubricants; zinc stearate, amide wax, Kenolube® and Metallub®. The properties of GS-lube, a lubricant designed for high green strength, are also presented.

EURO PM2003, in Valencia, Spain. Author: Anders Bergmark  PM steels with excellent fatigue properties are characterized by high performance microstructures and high density. Much effort has been put on reaching high densities during the last years. High density is important to get high rolling contact fatigue properties. It is well known that a martensitic surface is of outmost importance to get a material that is resistant to high Herzian pressure in combination with sliding. When bending fatigue is considered, however, it must be pointed out that high density alone has a relatively low impact on the fatigue properties.  The two microstructure extremes from mechanical performance point of view are Ferrite and Martensite. A survey of data presented in the literature indicates a fatigue limit of 380 MPa in rotating bending for 100% martensite [2]. The alloying system and processing route to get through hardening seems not to be important [2]. The bending fatigue limit at density 7.1 g/cm³ is about 120 MPa for 100% ferrite and 210 MPa for Copper-Carbon PM steel with 2% Cu and 0.8%C. These values indicate that the fatigue performance of martensite is almost 3 times superior to ferrite and almost 2 times superior to Fe2Cu0.8C.  The influence of density is twofold. Increased density normally implies smaller pores that are favorable, as higher – critical - strains are needed to start crack initiation. Increased density also means a higher Young’s Modulus, which in turn demands higher stress to obtain the critical strain [3]. An evaluation from data in the literature [2] reveals that the influence of density in the density interval 7.0 – 7.4 g/cm³ on the fatigue performance is about 5 – 10% per 0.1 g/cm³ [3]. This indicates that density only has an impact of about plus 15 – 30% when the density is increased from 7.1 to 7.4 g/cm³. Microstructure is obviously much more important than density from the bending fatigue performance point of view. This paper presents an overview of the influence of microstructure on the fatigue performance of PM steel. The reference material is Astaloy Mo, 1.5%Mo pre-alloyed material with 0.6% sintered carbon and 100% upper bainitic microstructure. The influence on the fatigue performance is evaluated for systematic variations of the microstructure.

EURO PM2003, in Valencia, Spain. Authors: Linnéa Fordén, Sven Bengtsson, Klaus Lipp, C M Sonsino The PM industry is permanently expanding the applications into new and challenging fields. Sintered components are becoming more and more frequent for highly loaded components also under rolling contact conditions. Gears are successfully introduced for applications such as oil pumps. An important field of future expansion for PM materials are highly loaded gears in e.g. vehicle transmission and power train gears. To ensure that PM materials have the ability to compete with wrought steels, rolling contact fatigue investigations have been performed on molybdenum pre-alloyed PM materials. A summary of design aspects under rolling contact conditions for surface densified PM components will be discussed studying the surface and sub-surface stress distribution.

EURO PM2003, in Valencia, Spain. Author: Ricardo Canto Leyton At present, high sintering temperatures are essential in order to meet the density requirements of ferritic stainless steels intended for high performance applications. Use of high sintering temperatures leads to large dimensional changes, making close tolerances more difficult to achieve. By increasing compressibility of the powder, less shrinkage is necessary to meet the density requirements and closer tolerances can be achieved. This paper will give a general overview of advantages and disadvantages of different process routes available to reach a final density of 7,3 g/cm³ with ferritic stainless steel 409L. One of the processes discussed here is warm compaction, a technique already proven to increase compressibility of ferritic stainless steels by about 0,2 g/cm³. Green and sintered properties, including tensile test data, are compared.

EURO PM2003, in Valencia, Spain. Authors: Daniel Edman, Hilmar Vidarsson, Björn Johansson.  The geometrical complexity of many new PM applications in combination with higher capacity of presses for powder compaction requires metal powder mixes with even and faster die filling characteristics. This demand has led to development of the Starmix™ concept. In Starmix™ additives such as alloying elements, lubricants and machinability enhancing compounds are bonded to avoid segregation, dusting and to improve powder properties. Development work has made it possible to improve the powder flow more than 25%.  This paper presents the gain in productivity due to enhanced flow rate behaviour of Starmix™ in full-scale production tests.

EURO PM2003, in Valencia, Spain.  Author: Ola Bergman. Chromium is an attractive alloying element in steels due to its positive effect on the hardenability, its low cost and environmental benefits. These advantages are utilised in two recently developed pre-alloyed water-atomised PM grades. Astaloy CrL, which contains 1.5% Cr and 0.2% Mo, and Astaloy CrM, which contains 3% Cr and 0.5% Mo, are suitable for high-performance applications. This paper is focused on the fatigue properties of these materials. The bending fatigue limits at sintered density 7.1 g/cm³ are 261 MPa for Astaloy CrL + 0.8% graphite and 287 MPa for Astaloy CrM + 0.45% graphite after conventional sintering at 1120 ºC. High temperature sintering followed by rapid cooling increase the fatigue limits of the materials by 20-30% to 320 MPa and 372 MPa respectively. Moreover, Astaloy CrM + 0.45% graphite obtains a very high fatigue limit of 527 MPa at sintered density 7.3 g/cm³ after high temperature sintering and vacuum-carburising.

PM²TEC 2003, in Las Vegas, USA . Authors: Tom Luzier, Dave Milligan, Paul Hofecker, Owe Mårs. Segregation of alloying elements in powder mixes creates issues in final components such as increased dimensional variation and increased property variation. Material handling systems that promote mass flow have been shown to reduce segregation during powder handling, leading to improvements in consistency. This paper will describe the bulk bag handling system as a method to reduce the segregation of alloying elements. Case studies comparing the bulk bag system to traditional material handling systems will also be described.

PM²TEC 2003, in Las Vegas, USA. Author: Ricardo Canto Leyton  At present, most stainless steel materials are sintered at high temperatures to achieve the desired mechanical, corrosion and high-temperature properties through densification. Although this method of processing achieves the desired properties, the resulting dimensional change can be difficult to control. A potential alternative to reduce the amount of densification required would be stainless steel powders with higher compressibility, which can reach higher green densities at reasonable compaction pressures. The purpose of this paper will be to compare different techniques to attain the desired sintered properties. The mechanical properties and green and sintered densities reached with these techniques will also be discussed.

PM²TEC 2003, in Las Vegas, USA. Authors: Ulf Engström, Alexander Klekovkin, Sigurd Berg, Bill Edwards, Leonid Frayman, Gerd Hinzmann, Dax Whitehouse. The appearance of advanced forming technologies such as high velocity compaction as well as newly developed chromium-molybdenum P/M materials may promote powder metallurgy to challenge wrought materials, such as SAE-AISI 4135 and 4140. This study describes metallurgical and mechanical properties of sintered steels based on the chromium-molybdenum prealloyed material Astaloy CrL processed with various compaction, sintering, and heat treatment methods. In particular, the properties of Astaloy CrL powder material has been subjected to high velocity, warm, and conventional compaction and then being conventional and high temperature sintered as well as vacuum carburized will be discussed.

PM²TEC 2003, in Las Vegas, USA.  Authors: Senad Dizdar, Paul Skoglund, Sven Bengtsson. High-performance P/M test-gears made by a high-density manufacturing route and sinter-hardening have been experimentally investigated with respect to dimensional accuracy and mechanical properties. The properties of the gears, compacted to a density of 7.5 g/cm³, were compared to the properties of gears made of heat-treated wrought steel. Dimensional- and surface finish features of the P/M prototypes equal to that of conventionally manufactured gears made of wrought steel. The AGMA and DIN gear quality numbers for profile-, alignment- and pitch deviation of net shape sinter-hardened gears were comparable with hobbed gears. P/M gears can thus offer significant cost savings due to fewer costly machining operations such as turning and hobbing and due to better materials utilization compared to conventional gears. The endurance limit of the sinter-hardened P/M gears at a density of 7.5 g/cm³ was similar to that of a quenched and tempered (SAE4140) wrought steel material, commonly used for medium-duty gears.

PM²TEC 2003, in Las Vegas, USA. Authors: Dave Milligan, Ulf Engström, Jim Lingenfelter, Senad Dizdar, Ingalill Nyberg. Warm Compaction of Densmix™ powders provides means to produce P/M parts with densities in the range of 7.1 to 7.4 g/cm³. As most properties are improved by increased density, the warm compaction method offers possibilities to increase the competitiveness of P/M compared to other manufacturing techniques. In this paper a comparison of material properties obtained by two different manufacturing routes is presented. Heat treated properties of some P/M steels after double pressing/sintering are compared with properties obtained with sinterhardening and conventional heat treating of warm compacted Densmix™ powders. Additionally, the single tooth static rupture force and the single tooth bending fatigue strength will be presented.

PM²TEC 2003, in Las Vegas, USA. Authors: Hilmar Vidarsson, Sigurd Berg, Daniel Edman, Björn Johansson, Peter Thorne. In production of P/M parts, dimensional stability is one of the most important quality parameters. While the contributions from powder handling, pressing operation and sintering are known to influence dimensional stability, powder properties also play an important role. Bonding of powder mixes can be used to as a means to improve dimensional stability of green and sintered components. Although the primary reason for bonding is to avoid dusting and segregation, it also influences powder properties, especially the flow behaviour. The bonding system used in Starmix™ powders is optimised to achieve maximum bonding efficiency in combination with superior die filling performance and at high production rates. This is demonstrated by comparing Starmix™ powders with non-bonded powder mixes in both laboratory studies and full-scale production.

PM²TEC 2003, in Las Vegas, USA.  Authors: Ola Bergman, Anders Bergmark. The fatigue properties of PM steels are mainly depending on the microstructure and density. Focus of this article is to quantify the mechanical performance of PM steel materials based on mixed, pre-alloyed and diffusion-alloyed powders in relation to the microstructures. Fatigue performance is the target parameter and this has decided the amounts of graphite added to the base powders. With one exception, test samples were sintered for 30 minutes at 2050°F/1120°C in 90%N2/10%H2. Fatigue tests have been made in displacement controlled four-point plane bending on modified ISO 3928 specimens. No machining of the test bars was made. All materials have been tested at densities close to 7.1 g/cm³. The PM steel microstructures are classified according to their fatigue performance. Sinter-hardened Astaloy CrM + 0.35%C with its martensitic microstructure has the highest fatigue limit of the tested materials (54 ksi/370 MPa). The diffusion-alloyed materials exhibit somewhat lower bending fatigue limits with D.HP + 0.8%C (48 ksi/330 MPa) followed by D.AE + 0.8%C (40 ksi/280 MPa). These materials demonstrate pronounced heterogeneous microstructures characterized by a continuous network of martensite with islands of softer structures. The pre-alloyed Astaloy CrL + 0.8%C with its mainly lower bainitic microstructure reaches a fatigue limit of 38 ksi/260 MPa. Astaloy Mo + 0.8%C has a microstructure dominated by upper bainite and reaches a fatigue limit of 31 ksi/210 MPa. The FC-0208 has a fatigue limit of 32 ksi/220 MPa and the microstructure consists mainly of fine pearlite.

PM²TEC 2003, in Las Vegas, USA. Authors: Barbara Maroli, Sigurd Berg, Peter Thorne, Ulf Engström. Increased mechanical property of sintered steels is the major factor for the introduction of PM components as substitute for wrought steels. Materials based on the newly developed grades prealloyed with chromium, Astaloy CrM and Astaloy CrL, reach, depending on processing conditions, static and dynamic properties comparable to those of conventional fully dense steels.  In this paper the influence of the sintering temperature combined with increased post-sintering cooling rate or heat treatments such as low pressure carburizing, on the static and dynamic properties of materials based on Astaloy CrM is presented. If high temperature is followed by rapid cooling a tensile strength of 1400 MPa (200 ksi) is achieved, while by combining high temperature sintering with low pressure carburizing a fatigue limit over 500 MPa (72 ksi) can be obtained. A study of the dimensional stability of Astaloy CrM gears manufactured under production condition is also discussed.

PM²TEC 2003, in Las Vegas, USA.  Authors: Bo Hu, Alexander Klekovkin, Sigurd Berg, Rick Young. Powder metallurgy components are expected not only to have good mechanical properties but also to meet dimensional tolerances consistently. Chromium pre-alloyed materials have received great interest recently due to properties achievable, sinter hardening response and possibility in improving dimensional tolerances. An additional advantage of using chromium as an alloying element is its low cost when compared to other alloying elements. In this study, sintering production tests have been performed in order to evaluate dimensional capability using Cr-alloyed materials verses conventional P/M alloyed materials. The first part of the study compares the Cr-alloyed materials with Fe-Cu-C alloyed materials under conventional sintering conditions. The second part of the study compares the Cr-alloyed materials against traditional Ni/Mo alloyed materials under sinter hardening conditions.

PM²TEC 2003, in Las Vegas, 2003. Authors: Ingalill Nyberg, Mary Schmidt, Peter Thorne, J. Gabler, T. Jesberger, S. Feldbauer. Sinter hardening is a cost-effective process that combines sintering and heat treatment in one step. It is known that the cooling rate following sintering greatly affects material microstructures, which determine the final properties of sinter-hardened materials. This study investigated the properties of three sinter-hardenable materials (Cr/Mo pre-alloy, Cu/Mo diffusion bonded and Ni/Mo pre-alloy) at three sintering times and three cooling rates. The objective was to understand how these sintering conditions influence the development of martensite in the microstructure and thereby control the hardness and mechanical properties of materials. This was accomplished through examining the percentage of martensite and microstructural homogeneity.

PM²TEC 2002, in Orlando, USA. Authors: Ingrid Hauer, Mats Larsson, Ulf Engström. New applications for PM steels are continuously introduced on the market. Many of these new applications utilize the unique possibilities of PM to achieve high strength in combination with close dimensional tolerances and a minimum of manufacturing operations.  Materials like Astaloy CrM and Astaloy Mo +2%Ni are all aimed at applications combining high strength with close dimensional tolerances. These materials reach tensile strength levels in the range of 650 MPa to 1000 MPa after conventional compaction at room temperature and sintering in belt furnaces at 1120°C (2050°F). By applying high temperature sintering i.e. sintering at temperatures > 1200°C (2200°F), these strength levels can be further increased. By combining high temperature sintering with warm compaction or high velocity compaction (HVC) PM materials with even higher strength levels can be obtained. This paper describes the influence of sintering temperature on static and dynamic properties for conventionally pressed, warm compacted and high velocity compacted powder mixes based on Astaloy CrM and Astaloy Mo +2%Ni.

PM²TEC 2002, in Orlando, USA. Authors: David Milligan, Alain Marcotte, Jim Lingenfelter, Björn Johansson. Warm Compaction of Densmix™ powders provides means to produce P/M parts with densities in the range of 7.1 to 7.4 g/cc. As most properties are improved by increased density, the warm compaction method offers possibilities to increase the competitiveness of P/M compared to other manufacturing techniques.  In this paper a comparison of material properties obtained by two different manufacturing routes is presented. Heat treated properties of some P/M steels after double pressing/sintering are compared with properties obtained with sinterhardening of warm compacted Densmix™ powders.

PM²TEC 2002, in Orlando, USA. Authors: Sigurd Berg, Barbara Maroli. Chromium as an alloying element in PM steel is of great interest due to its low cost, positive effect on hardenability and recycling advantages in the scrap phase of PM parts. The conversion from conventional steels to PM steels for large-scale production of components is primarily based on cost advantages. Traditionally, however, the cost for alloying elements in PM steels is higher than that of wrought steel. By utilization of a low cost alloying element such as chromium in PM, competitiveness can be improved. This paper compares a new prealloyed powder containing chromium and molybdenum with conventional powders. Static and dynamic properties are evaluated after sintering at 2050 °F and 2280 °F (1120°C and 1250°C). Mechanical performance after cooling in the range 1.8 to 9oF/s will also be shown.

PM²TEC 2002, in Orlando, USA. Authors: Hilmar Vidarsson, Jeanette Lewenhagen, Björn Johansson. Several key factors dictate the quality and economical outcome of the pressing operation in P/M parts production. Among these, productivity, filling performance and dusting are influenced by the properties of the powder mix. The concept of Starmix powders makes it possible to improve all these key factors by utilization of organic binders and high quality lubricants. The versatility of these powders is demonstrated in this paper through case studies, where improvements in parameters such as weight scatter and dimensional tolerances are shown. Examples are also given of filling behavior and productivity of bonded mixes as compared with plain powder mixes.

PM²TEC 2002, in Orlando, USA. Authors: Björn Lindqvist, Koki Kanno. The majority of mass-produced PM steels are sintered in continuous belt furnaces operating at temperatures up to 1150 °C/2100 °F. The alloying elements Cu, Ni, Mo and C are normally used to obtain good material properties. However, environmental concerns and cost might restrict their use, especially Cu and Ni, as additives to PM steels, in the future. Chromium is commonly used in solid steels mainly due to low cost and good material performance, but is still rarely used for PM structural parts. One reason for this is oxidation sensitiveness. However, continuously improved sintering technology and the more frequent use of N2-based atmospheres now makes alloying with Cr more attractive for the production of high-performance PM components at a low cost. Considerations when sintering Cr-alloyed materials in different types of furnaces are given in this paper.

PM²TEC 2002, in Orlando, USA. Authors: Paul Skoglund, Mikael Kejzelman, Ingrid Hauer. High Velocity Compaction (HVC) is a compaction method that enables high density and the possibility to make large P/M parts weighing up to more than ten pounds. The powder is compacted in less than 20 milliseconds by high-energy impact. Further densification is possible by adding multiple impacts as short as 300 milliseconds after each other. High Velocity Compaction is a mass-production method that can expand the use of P/M beyond its present limitations. High Velocity Compaction can be used in cases where components would require such high compaction force that the tonnage of conventional presses is a limitation. This paper describes and discusses High Velocity Compaction. Properties of materials based on both pre-alloyed Astaloy powders and diffusion-alloyed grades at densities in the range of 7.4 -7.7 g/cm³ are presented. This new manufacturing technology was recently introduced for P/M and examples are given of components that can be produced

PM²TEC 2002, in Orlando, USA. Authors: Ulf Engström, John McLelland, Barbara Maroli. The development of new materials and cost-effective processes are two factors that have contributed to the strong growth of PM parts over the past decades. Sinter-hardening is one example of such development combining good manufacturing economy with the ability to achieve a unique combination of mechanical properties. By controlling the post-sintering cooling rate, the microstructure can be controlled to form the required amount of martensite to obtain the desired mechanical properties. By increasing the sintering temperature from 1120ºC (2048ºF) to 1250ºC (2282ºF) these properties can be further increased.  In this paper sinter-hardening of a number of PM materials is presented. The influence of alloying system, sintering temperature and cooling rate on both microstructure and mechanical properties will be discussed

PM²TEC 2002, in Orlando, USA. Authors: Pernilla Johansson, Sven Bengtsson, Senad Dizdar. Selective densification can be an appropriate way to fulfill high demands on rolling contact fatigue (RCF) resistance of P/M materials for gear applications. Pre–alloyed P/M materials were tested us-ing the ZF-RCF test. Reference material was low-alloyed case hardened steel DIN 16MnCr5 (AISI 5115) commonly used for gear applications. Test samples, rollers Ø 30X30 mm, were pressed from different test materials as cylinders, machined to an oversize compared to the finished roller, selectively densified on a rolling machine and finally heat treated in different ways. The tested roll-ers were characterized with respect to microstructure, mechanical properties, and surface character-istics. Damage mechanisms were examined and failure analyses were performed on the rollers in or-der to trace crack initiation and propagation.

Surface engineering is a topic of great relevance on today’s engineering. Surface features can be improved from the point of view of the material being deposited or from the point of view of the depositing process. The present work characterises coatings of a cobalt-based alloy, deposited by PTA welding on an AISI 304 stainless steel substrate. Samples were subjected to temperature cycling at 1050 8C. As-deposited features and their stability to high temperature were study, results are presented and compared with similar samples obtained by laser cladding. The performance of hardfaced material was evaluated by microstructure, chemical analysis and microhardness measurements. For the processing conditions tested, results showed that, for operating conditions that do not require elevated temperature, laser hardfacing shows the bests results, due to the refine solidification structure produced. However, for the high temperature tested, PTA deposits exhibited superior microstructural stability whereas laser deposits undergo significant changes.

The International Latin American Conference on Powder Technology in Florianópolis, Brazil 2001. Author: Olle Thornblad. The dimensional tolerance is a very important factor for manufacturing of powder compo-nents. It is essential to consider this point already as the first step of the calculation/quotation process. By choosing a composition of the mix that is designed to be the least sensitive to segregation in handling of the powder as well as variations in pressing and sintering, a lot of worry can be avoided at the end of the process. Also small modifications of the production line give large effects on the stability of the end product and important cost savings.

The International Latin American Conference on Powder Technology in Florianópolis, Brazil 2001. Author: Jeanette Lewenhagen. Chromium as an alloying element is of great interest due to its low cost, high hardenability and possibility to recycle. Use of pre-alloyed chromium powders has increased recently due to its accessibility at low cost. Low total cost is and has been the driving force to convert parts made from conventional steel to PM material. By use of pre-alloyed chromium material, the PM industry can further increase its market share, compared to conventional steel. Two pre-alloyed iron powders, one for high strength applications containing 3 % Cr and 0,5 % Mo and one for medium strength applications containing 1,5% Cr and 0,2% Mo are considered in this paper. The mechanical properties for mentioned materials in the carbon range from 0,2 to 0,8% are described.

EURO PM2001, in Nice, France. Authors: Barbara Maroli, Sigurd Berg, Jeanette Lewenhagen. Sinter-hardening is a cost-effective process, as it combines sintering and hardening operation in one step. Utilisation of the sinter-hardening process in combination with tailor made alloying system gives a unique combination of strength, toughness and hardness. A variety of microstructures are obtained by changing the post-sintering cooling rate, type and amount of alloying elements. Carbon, molybdenum, copper, nickel and chromium prealloyed and/or admixed with iron promote its hardenability. By using tailor made alloying system different amount of martensite and as a consequence different mechanical properties are obtained after sintering. This paper gives a general overview of the properties and microstructures that are obtained for sinter-hardening materials. Focus is paid on PM materials prealloyed with chromium, molybdenum and nickel with and without additions of copper.

EURO PM2001, in Nice, France. Author: Björn Lindqvist. The dominating part of mass produced PM- steels today are sintered in continuous furnaces operating at maximum 1150°C. The alloying elements Cu,Ni,Mo and C are normally used to obtain good material properties. However, environmental concerns and cost might restrict the use of especially Cu and Ni, as additives to PM-steels, in the future. Since many years, Cr-alloyed PM-steels are available as complement to the existing Cu/Ni-alloyed materials. This family of materials has many advantages and the most important are cost, the ability to be recycled and hardenability. However, still PM part production of Cr-steels is mainly limited to top performance applications sintered at high temperature. In the present paper focus is put on processing Cr-alloyed PM-steels in furnaces operating at maximum 1150°C. It shows necessary precautions to be taken for the successful sintering of PM-steels alloyed with Cr.

EURO PM2001, in Nice, France.  Höganäs Chair. For sintered steels prepared from prealloyed steel powder Astaloy CrM (Fe-3%Cr-0.5% Mo) various heat treatment techniques and their effect on properties and microstructure are described. It could be shown that steels with carbon contents between 0.2 and 0.5 mass% can be effectively hardened by oil or gas quenching, and regular martensitic microstructures are attained also after gas quenching. The quench hardness depends on carbon level, total porosity, and high temperature sintering. Tempering is recommended either in the range <200°C, for high hardness, or at 500-650°C for optimum strength / toughness. For surface hardening, low pressure carburising of sintered steels with <0.3%C, followed by gas quenching, has shown to be quite effective although carburizing temperature and carbon activity have to be carefully balanced to avoid excessive carbide formation. High sintered density, which can be obtained best by warm compaction combined with high temperature sintering, is beneficial for the formation of well defined hard surface layers with high wear and contact fatigue resistance.

EURO PM2001, in Nice, France. Author: Ola Bergman. Powders prealloyed with chromium have recently been introduced on the market for sintered steels. Due to chromium’s high affinity for oxygen, sintering is performed in nitrogen/hydrogen-based atmospheres with low oxygen partial pressures. However, chromium also has a high nitrogen affinity, which will lead to nitrogen uptake by the steel during the sintering process. The effects of nitrogen uptake during sintering have been studied for a water atomised iron powder fully prealloyed with 3% chromium and 0.5% molybdenum. Test specimens with varying graphite additions and green densities were sintered for 30 minutes at 1120°C in a mixture of nitrogen and hydrogen (90%N2/10%H2). Different cooling rates after sintering were applied. Evaluation of the sintered specimens included metallography, phase analysis, chemical analysis, and mechanical testing. Based on the evaluation results, conclusions are drawn regarding how nitrogen uptake and nitride formation during sintering affect the material properties.

EURO PM2001, in Nice, France. Author: Anders Bergkvist. Most new applications for sintered stainless steels depend on high sintered density. To achieve this with close tolerances, the manufacturing process depends on optimised powder properties and high green density. This means that the ability to fill the die uniformly and at the same time keep the compressibility high are important. In this experimental approach different lubrication systems have been evaluated to get high sintered density with good tolerances.

EURO PM2001, in Nice, France. Authors: Anders Bergmark, Sven Bengtsson. A full factor test of the axial fatigue properties of Cu + C alloyed PM steel is performed. The three variables are: density (approx 7.15 and 7.4 g/cm³ obtained by single and double compaction), Cu content (0 and 2%) and C content (0.2% and 0.8%). The greatest influence on the fatigue endurance limit was found for Cu (+53 MPa) followed by density (+33.5 MPa) and C (+25 MPa). The greatest combined influence was found for Cu and C (+12.5 MPa in addition to the individual effects). The high cycle fatigue properties of cold compacted double pressed and sintered Fe2Cu0.8C are compared with warm compacted material with the same composition. Fractography, displaying the sizes and origins of the initial faults, is performed on double pressed/sintered and warm compacted Fe2Cu0.8C.

EURO PM2001, in Nice, France. Author: Anders Bergkvist. Most new applications for sintered stainless steels depend on high sintered density. To achieve this with close tolerances, the manufacturing process depends on optimised powder properties and high green density. This means that the ability to fill the die uniformly and at the same time keep the compressibility high are important. In this experimental approach different lubrication systems have been evaluated to get high sintered density with good tolerances.

EURO PM2001, in Nice, France. Authors: Fredrik Vinnerborg, Ulf Engström, Hilmar Vidarsson, Johan Arvidsson. In order to expand the applications for sintered structural components there is a continuous demand for development of new powders and processes which result in improved mechanical properties and precision of tolerances at reduced processing costs.  A wide range of different alloying elements and ways to add these are used in PM. As the way of adding the alloying elements influences both the mechanical properties and the dimensional scatter of the components after sintering it is important that press ready powder mixes are made in such a manner that the required mechanical properties are achieved without losing the dimensional precision. One way to secure this is to bond the constituents to the iron or steel powder. By efficient bonding, powder mixes less prone to segregation and dusting and with improved filling of the press tools can be prepared In this paper, low alloy steel powder mixes prepared with this new bonding concept are compared with conventional premix, both regarding tool filling behaviour and scatter of dimensional tolerances after pressing and sintering. The results are obtained in mass production trials. 

The International Conference on Power Transmission Components, in Ypsilanti, Michigan, USA. Arranged by MPIF. Authors: Sven Bengtsson, Linnéa Fordén, Senad Dizdar, Pernilla Johansson. Progress in development of a surface densified P/M transmission gear is reviewed. The gear is the fifth gear of a manual transmission for a medium sized passenger car. Blanks were produced by hobbing of pressed and sintered slugs. Densification of both the root and the flanks of the P/M gear was achieved using gear rolling technique. The rolled gears were case hardened. At present the development stage, the quality of such the gear is close to AGMA class 10, which is considered to be the required level for automotive manual gearboxes. The surface roughness is better than for the shaved reference gear. The hardness profile in the flank region matches the hardness profile of the wrought reference gear; and finally, the desired density distribution was reached.

The International Conference on Power Transmission Components, in Ypsilanti, Michigan, USA. Arranged by MPIF. Author: Paul Skoglund. High Velocity Compaction (HVC) is a compaction method that enables high density and the possibility to make large P/M parts up to more than five kg (10 lbs). The powder is compacted in less than 20 milliseconds by high-energy impact. Further densification is possible by adding multiple impacts as short as 300 milliseconds after each other. HVC is a mass production method that can expand the use of P/M beyond its present limitations. In the case of components that would require such high compaction force that the tonnage of conventional presses is a limitation, HVC can be used. In this paper the HVC technology is described and discussed. Properties of materials based on both pre-alloyed Astaloy powders and diffusion alloyed grades at densities in the range of 7.4-7.7 g/cm³ are presented. This new manufacturing technology was recently introduced for PM and examples of components that can be produced are given.

PM²TEC 2001, in New Orleans, USA. Author: Sigurd Berg. Cost reduction for P/M application with maintained mechanical properties is one of the most important factors in order to preserve the strong growth for the P/M industry. Heat treatment has since long time been used in order to achieve increased properties. By tailor made alloying systems it is possible to include the hardening process. Pre-alloyed material like Astaloy CrM, Astaloy A diffusion bonded alloys as D.DH-1 and premixes based on Astaloy 85 Mo are all suitable for sinterhardening. In this paper mechanical properties achieved at different cooling rates and carbon contents are discussed. Cost comparison for evaluated materials combined with mechanical properties achievable by the sinterhardening process gives areas for use of these materials. Selection of material is of importance to benefit the most out of this process route.

PM²TEC 2001, in New Orleans, USA. Authors: Paul Skoglund, Sven Bengtsson. A con rod for a modern passenger car engine has been studied to show the performance of high-density PM-materials manufactured by warm compaction of high compressible low alloyed powders. The con rod design was optimized with respect to weight and fatigue performance by finite element analysis. Prototypes manufactured from the diffusion alloyed powder D.HP1 with 0.7%C have been tested and found to meet the design goal of a fatigue safety factor exceeding 1.5 at engine peak power. Results from the endurance tests on these warm-compacted con rods were used as a base for further improvements of mechanical strength and reliability of the manufacturing process. Fractographic investigations have led to both a better understanding of the probability for failure, as well as suggestions to design improvements for reduced scatter of fatigue strength. This paper presents a functional material design for warm compacted connecting rods with a performance similar to the currently used con rods. The design and the procedure for prototype manufacturing are described. Results from fatigue tests on both test samples and connecting rods are given. The results show that warm-compaction of robust low-alloyed powders offers the potential of reduced total cost due to less machining and fewer processing steps.

PM²TEC 2001, in New Orleans, USA. Authors: John McLelland, Owe Mårs, Thomas J. Jesberger. It is well known that the cooling rate influences the final microstructure and therefore the properties of sinter hardened steel parts. This investigation looked at the relationship between the sintering furnace cycle (time, temperature and atmosphere) and cooling rate to part microstructure. The objective was to identify how the above sintering variables influenced the development of martensite, hardness and strength. Tests were conducted varying the sintering cycle. The changes to the cycle were sintering time, sintering temperature, atmosphere composition (specifically hydrogen concentration), and cooling rate. The final microstructure was evaluated and correlated to the sintering cycle.

PM²TEC 2001, in New Orleans, USA. Authors: Olof Andersson, Andreas Benner. Powder metallurgy (P/M) is known for producing complex parts to very close tolerances. Due to technical limitations some parts are too complex to obtain, with regard to the final shape, merely with applying P/M technique. When P/M-technique is inadequate a secondary operation is a possible way to achieve the desired shape. Machining of sintered parts is comparatively well known but nevertheless, in some cases, a demanding operation due to sintered properties. However, machining of green parts often fails due to poor properties of the compacts (e.g. strength). Warm compaction is one way to achieve the necessary strength, without the disadvantage due to sintering. The following report summarise the experience of green drilling when using two warm compacted powder materials, D. AE + 0.5%C and Astaloy CrM + 0.5%C.

PM²TEC 2001, in New Orleans, USA. Authors: Olof Andersson, Andreas Benner. Powder metallurgy (P/M) is known for producing complex parts to very close tolerances. Due to technical limitations some parts are too complex to obtain, with regard to the final shape, merely with applying P/M technique. When P/M-technique is inadequate a secondary operation is a possible way to achieve the desired shape. Machining of sintered parts is comparatively well known but nevertheless, in some cases, a demanding operation due to sintered properties. However, machining of green parts often fails due to poor properties of the compacts (e.g. strength). Warm compaction is one way to achieve the necessary strength, without the disadvantage due to sintering. The following report summarise the experience of green drilling when using two warm compacted powder materials, D. AE + 0.5%C and Astaloy CrM + 0.5%C.

PM² TEC 2001, in New Orleans, USA. Author: Ulf Engström. New applications for PM steels are continuously introduced on the market. This is primarily due to development taking place within the PM industry but also a result of new designs of engines etc. Many of these new applications utilise the unique possibilities of PM to achieve high strength in combination with close dimensional tolerances with a minimum of manufacturing operations The diffusion alloyed materials D.AE and D.HP-1 and the completely prealloyed material Astaloy CrM are all aimed for applications combining high strength with close dimensional tolerances. These materials reach tensile strength levels in the range of 850 MPa to 1000 MPa after conventional compaction at room temperature and sintering in belt furnaces at1120°C/ 2048°F. By applying high temperature sintering i.e sintering at temperatures >1200°C/ 2200°F, these strength levels can be increased. By combining high temperature sintering with warm compaction PM materials with even higher strength levels can be obtained. In this paper the influence of sintering temperature on static properties for both convention-ally and warm compacted D.AE, D.HP-1 and Astaloy CrM is described. The effect of using higher sintering temperatures than 1120°C/2048°F on the dimensional change for these materials is also presented.

PM² TEC 2001, in New Orleans, USA. Authors: Ulf Engström, K Lipp, C M Sonsino. The ability of PM to achieve high mechanical properties opens up many possibilities to further extend the use of PM. As fatigue properties are becoming more and more important in the applications of PM parts the demand for high performance materials and data characterising these materials is continuously increasing. In this paper fatigue life curves of some high performance PM materials are compared at two different notch factors in as-sintered condition. The results are interpreted on the basis of microstructural features, porosity and extend notches. The paper presents statistically based design data about the different materials under different stress concentrations and loading modes.

PM² TEC 2001, in New Orleans, USA. Authors: Sven Bengtsson, Linnéa Fordén. The fatigue behaviour of a powder metallurgy component depends strongly on its density. By using selective densification, the local density can be improved to near full density. This procedure is well suited for components with a high stress near the surface. Rolling contact fatigue experiments have been conducted on selectively densified materials. The rolling contact fatigue endurance limit of the Astaloy Mo based material is approximately 1500 MPa that can be compared to the selected reference material, AISI 5115 (DIN 16MnCr5), 1600 MPa. For the diffusion alloyed material, D.DC-1, it was not possible to determine the endurance limit due to too few tests. However, the endurance limit is believed to be slightly lower than the Astaloy Mo material. The case depth is believed to be to low for both materials, but the effect to be more severe for the D.DC-1 material.  

PM² TEC 2001, in New Orleans, USA. Authors: Sigurd Berg, Owe Mårs. The choice of machinability enhancing additive depends on the machining conditions such as operations used, tool used, material machined and some others. This presentation describes the large variation in tool life when testing additives under different conditions. MnS ans MnX have been tested as additives in PM materials ranging from soft pure Iron to the complex structure of Distaloy AE containing ferrite, perlite, bainite and martensite. The effect of the additives has been compared in drilling and turning applications as well as using different tool materials and coatings.

EUROMAT 2001, in Rimini, Italy. Authors: Barbara Maroli, Sigurd Berg, Mats Larsson, Ingrid Hauer. Cost reduction with maintained mechanical properties is the key to preserve the strong growth of the P/M industry. Heat treatments have since long time been used to achieve a martensitic structure either at the surface or throughout a part. By combining tailor made alloying systems with sinter-hardening the required amount of martensite can be obtained directly after sintering. Pre-alloyed materials like Astaloy A, Astaloy Mo with copper additions and Astaloy CrM are suitable for sinter-hardening. In this paper mechanical properties and performance of sinter-hardened materials are discussed. It is found that different materials are to be used depending on the process route. Material selection is of importance to benefit the most from sinter-hardening.

PM2000, in Kyoto, Japan. Author: Mats Larsson. Alloying elements can be added in different ways to metal powders. Admixed, with or without addition of binder, pre-alloyed and diffusion bonded alloying elements are commonly used in the industry. The way of adding the alloying elements influences mechanical properties of the material. Dimensional scatter after sintering is another important characteristic of the material that is influenced. Good dimensional stability after sintering is a way to avoid the need for secondary operations such as sizing and machining. In this presentation, properties of materials with similar alloying content but utilizing different alloying techniques are presented. Both mechanical properties and dimensional stability are investigated and discussed.

PM2000, in Kyoto, Japan. Authors: Paul Skoglund, Sven Bengtsson. Warm compaction offers high density, favorable pore structure and as a result of this better fatigue properties combined with the robustness and shaping ability of the established compaction technology. This means that high performing parts, such as connecting rods, cam lobes and transmission gears etc., can be produced in a cost efficient way. In this investigation different high density P/M steels are evaluated concerning fatigue strength and a comparison is also made with powder forged and conventionally forged steels. Fatigue data on specimen are used as a base for the design of a P/M connecting rod. The connecting rod used for this comparison is for a modern mass produced four cylinder 2.2 liter gasoline engine. Its design has been optimized for the P/M route in order to minimize the weight. The dynamic performance of the warm compacted prototypes is discussed and a comparison with connecting rods made by the other manufacturing techniques is made.

PM2000, in Kyoto, Japan. Authors: Ulf Engström, Björn Johansson. Warm compaction of Densmix™ powders provides means to produce PM parts with uniform densities up to 7,4 g/cm³. As most properties are improved by increased density this compaction technology offers new possibilities of increasing the competitiveness of PM compared to other manufacturing techniques.  In this paper the experience of using warm compaction of Densmix™ powders in production is described. A number of different parts that have been developed during the last years and now are in production will be presented together with material properties and component performances. Process robustness and process capability as well as the benefits that have been experienced with warm compaction are also discussed. The economical advantage of warm compaction compared to other manufacturing methods is also considered.

PM2000, in Kyoto, Japan. Author: Jan Tengzelius. Two major environmental advantages with powder metallurgy are high utilisation of material and low energy consumption. A disadvantage as compared to most low-alloyed wrought steels is the use of other alloying elements such as copper and nickel. It is also common to use higher alloying contents. The systematic approach of LCA has been used to compare the PM process with other manufacturing methods. The paper also presents how LCA can be used to evaluate different powder metallurgical processing steps and alloys for the manufacture of components as a means to quantify the environmental influence.

PM2000, in Kyoto, Japan. Author: Yang Yu. The phase diagram and some other properties of Astaloy CrM have been calculated based on thermodynamics. Experimental investigations on microstructures of the sintered samples were performed by means of metallography, X-ray diffraction and TEM, which indicate a great deviation from the calculated phase diagram. A very strong kinetic behaviour of this material is conformed. The CCT diagrams of Astaloy CrM with different carbon content (0.3%, 0.4% and 0.5%) are determined. Factors influencing diffusion behaviours of carbon as well as chromium and molybdenum are discussed. The effects of chromium and molybdenum on the formation of carbides and on the sintered microstructure are also discussed. In addition, the oxidation state during sintering and its temperature dependence is calculated and discussed.

PM2000, in Kyoto, Japan. Author: Sigurd Berg. Chromium as an alloying element is of main interest due to its effect on hardenability. Compared to powder with nickel and molybdenum it is cost efficient and recycling causes no problem, which is the case for example with copper. In a pre-alloyed state the activity of chromium is low whereas the activity of chromium added in elemental form or as a master alloy is rather high, which enhances the possibility to use normal sintering conditions i.e. 1120°C, 90/10 N2/H2, 30 min. To prevent oxidation partial pressure of oxygen in the sintering atmosphere should be below 5*10-18 atm. when sintering chromium alloyed materials. A benefit from using a pre-alloyed powder with chromium for sintered parts is the enhanced dimensional tolerances. The paper describes a low alloyed powder with chromium as the major alloying element and comparison is made to Fe-Cu-C powder. The low amount of alloying element results in a total low cost for parts made thereof. The strength levels achieved with these two alloying systems are similar but the potential for close dimensional tolerances are substantially improved with the chromium alloyed powder.

PM2000, in Kyoto, Japan. Authors: Sven Bengtsson, Senad Dizdar, Martin Svensson. In order to increase the fatigue properties in the flank and the tooth root regions of PM gears a selective densification can be performed. Previous investigations have shown a substantial improvement of gear performance by utilising this technology and commercial production has been established. This paper describes the relation between material properties and densification as well as some results with powders of different types and alloying systems. The feasibility and influence on quality of the processing steps were also considered and the fatigue life of gears was discussed.

PM2000, in Kyoto, Japan. Authors: Hilmar Vidarsson, Johan Arvidsson. The quality of powder mixes in P/M is frequently studied using standardized techniques, such as Hall Flow, AD etc. These techniques are however limited in predicting the performance during production. For this purpose, a die-filling simulator has been developed. Filling of dies of rectangular shape was characterized to establish the importance of the die width and orientation on the filling density of powder mixes. Furthermore, the effect of bonding of the powder mixes on the die filling was studied, especially in terms of the maximum feed shoe rate possible for complete filling. The results are discussed in terms of impact on filling performance during pressing.

EURO PM2000, in Münich, Germany. Author: Ulf Engström. To increase the competitiveness of PM compared to other manufacturing techniques there is a demand for alloy systems as well as processes which result in improved mechnical properties with maintained precision of tolerance control at reduced processing costs. Warm compaction was developed to be one possible technique to meet this objective. By warm compaction of low alloy steel it has now become possible to produce PM parts with uniform densities up to 7.4 g/cc by single compaction and sintering. The higher and more even density results in improved static and dynamic mechanical properties. However, warm compaction not only improves the static mechanical properties which opens up new opportunities to use PM in high performance applications that up to now have not been technically and economically feasible. In this paper some of the merits that have been found with warm compaction both in laboratory scale and in production of complex parts are described. Material properties and process robustness obtained with warm compaction of Densmix powders are presented. Future potential high performance applications that might be realised by utilising the merits of warm compaction of Densmix powders will be discussed.

EURO PM2000, in Münich, Germany. Author: Mats Larsson. The strength of the P/M technique is to produce components to net shape. Even if the components are pressed to final shape additional machining or sizing operations are in many cases needed to achieve the desired tolerance class. These additional operations increase the production costs. If dimensional scatter can be reduced the P/M route to produce components becomes more competitive in comparison with other manufacturing techniques. Different alloying techniques are available in powder metallurgy. Alloying elements can be admixed, organically bonded in the mixes, diffusion bonded to the iron powders or pre-alloyed. Often combinations of these techniques are utilized. These techniques have different pros and cons with respect to compressibility, dimensional stability and mechanical properties of the sintered material. In this presentation a comparison of different alloying techniques is made focusing on dimensional stability.

PM² TEC 2000, in New York, USA. Authors: Caroline Lindberg, Björn Johansson, Barbara Maroli. The Astaloy CrM powder is a high strength prealloyed powder containing 3 % Cr and 0.5 % Mo. It reaches a very high strength in the range of 120 ksi (850 MPa) after conventional compaction at room temperature and sintering in belt furnaces at 2050°F (1120 °C). The strength can be improved further by applying high temperature sintering. Another way to improve the strength further is to utilise warm compaction. The compressibility of this high- and prealloyed powder is naturally lower compared to a plain iron powder. Due to optimisation of the composition and the production process it achieves a high compressibility of about 7.0 g/cm³ at a compacting pressure of 43 tsi (600 MPa) for the plain powder. The density is increased 0.15 g/cm³ by using warm compaction with the same compacting pressure. This density increase will of course improve the mechanical properties.

PM² TEC 2000, in New York, USA. Author: Sven Bengtsson. A common cause of failure in service is by fatigue fracture, especially of heavily loaded components subjected to dynamic stresses. The Fe-Ni-Cu-Mo steels have very high static mechanical properties and are becoming increasingly popular in highly stressed applications. This presentation deals with the fatigue behavior of warm-compacted Fe-Ni-Cu-Mo steels. The fatigue behavior has been investigated with respect to density and microstructure. The fatigue strength was determined for several density levels in the as sintered condition and in one case for a rapidly cooled material. Fracture surfaces have been characterized with respect to the origin of the fatigue crack and size of defect at the starting point.

PM² TEC 2000, in New York, USA. Authors: Paul Skoglund, Sven Bengtsson, Magnus Bergström. P/M steel synchronizing parts for automotive transmissions are commonly used in passenger cars today, but larger and more stressed parts such as those used in transmissions for heavy trucks can also be realized. A synchronizing latch cone aimed for the gear switch in a 500 bhp heavy truck is a highly stressed component. In a feasibility study prototype latch cones of Fe-Cu-Ni-Mo material were warm compacted to high density. The prototypes were evaluated with respect to material properties and dimensions.The warm compacted latch cone met all the requirements, including a gear box test and is therefore an interesting alternative offering cost savings compared to existing methods.

PM² TEC 2000, in New York, USA. Author: Mats Larsson, Hilmar Vidarsson. In production of P/M components sizing or machining operations are often used to meet the demands for narrow tolerances. These additional operations increase the production costs. By improving the dimensional stability after sintering more components will by possible to produce without these secondary operations. Bonding technique affects the dimensional stability by several mechanisms. Segregation of alloying elements, variation in fill weight and warping of component are factors that deteriorate the dimensional stability of P/M components. With efficient bonding technique mixes less inclined to segregate and with superior filling of press tools are obtained. Less dusting is another benefit of the bonding technique that improves the working environment in P/M production.Results are presented showing the improved dimensional stability obtained by efficient bonding technique.

PM² TEC 2000, in New York, USA. Author: Ulf Engström. The development of new materials and cost effective processes are two main factors that have contributed to the growth of PM parts during the last decade. Sinter-hardening , which utilises high performance materials in combination with an accelerated post sintering cooling rate, is one exampleof such material and process development. As this technique is a one step process it combines good manufacturing economy with the ability to achieve a unique combination of mechanical properties. By controlling the post sintering cooling rate, the microstructure can be manipulated to form the required amount of martensite to obtain the desired mechanical properties. Alloying elements such as molybdenum, chromium, nickel and copper all promote hardenability. By increasing the hardenability of the material still large amounts of martensite can be obtained also at slower cooling rates. In this paper a number of different PM materials are evaluated after sinter-hardening. The influence of alloying system and cooling rate on both microstructure and mechanical properties will be discussed

PM² TEC 2000, in New York, USA. Author: Anders Bergkvist. The performance of stainless steel powder metallurgy (P/M) materials in elevated temperature applications has become a subject of interest for automotive exhaust type applications. In this study a ferritic and a duplex sintered stainless steel has been evaluated for properties relevant for these applications, such as hot oxidation resistance, mechanical and corrosion properties. The relative performance of the stainless steels is reviewed and compared.