The advantages of low pressure carburising

Chromium-alloyed powders provide a cost-efficient way to manufacture high-performance applications. However, PM components produced from such powders cannot be surface hardened by conventional gas carburising and oil quenching. To meet the stringent requirements on quality and dimensional accuracy, an alternative is to use low pressure carburising (LPC) with pressurised gas quenching.

LPC is a well proven heat treatment technology already globally applied by many OEMs. The well-known and proven advantages over traditional atmospheric carburising are manifold. For instance, the unlimited process design flexibility including high temperature sintering, the precisely monitored process control, the well-defined uniform and tailored case-depths as well as the elimination of any risk for oxidation.

Additionally, LPC results in reduced distortions during the heat treatment process and consequently improves the overall dimensional quality and tolerances of PM components. As opposed to traditional methods, the processing under vacuum vs. atmospheric, also reduces the risk of contaminants and delivers clean and bright surfaces.

Finally, due to the overall reduced process chain and reduced time for the handling of parts, the one-cycle batch vacuum sintering combined with low pressure carburising & gas quenching, leads to lower total factor cost for heat treated components.

With its new maintenance friendly furnace technology in place and through a close collaboration with ECM Technologies France, the Höganäs PoP Centre is now ready to support customers and OEMs during the development of new PM applications and processes. The new furnace concept will be exposed and presented to the PM industry community and public for the first time during the forthcoming PoP Day on the 18th of September in Höganäs, Sweden.

How the furnace works

By alternate injection of acetylene (for carburising) and nitrogen (for diffusion) at low pressure (5-10 mbar), the parts get carburised by decomposition of acetylene at the surface, followed by diffusion of carbon to an appropriate carburising depth. After the carburisation the parts are moved to the quench cell where they are quenched in nitrogen at pressure up to 20 bar. The high pressure nitrogen in the quench cell is circulated by turbines through heat exchangers to obtain high cooling rates.

- The furnace allows a very precise control of the carbon profile and, thanks to the gas cooling, also reduced distortion compared to oil quench, says Magnus Dahlström, Development Engineer.

The furnace can also be used to combine de-lubrication and sintering of the parts with heat treatment into one single process cycle, starting with green parts and resulting in heat treated and surface hardened parts.

Bringing benefits to the industry

The benefits with the combined sintering and heat treatment technology are lower total costs as well as better quality and performance as the strength of the sintered components is increased.   Moreover, there is less distortion of the parts as well as energy savings and elimination of oil and chemical .

– With the new furnace in the PoP Centre we can offer state-of-the-art technology for sintering and hardening of PM parts in pilot scale, says Mats Larsson, Manager PM Components – Process development. Our intention is to work closely with customers and end-users to develop attractive PM solutions, both from a cost and functional perspective, and ultimately to help reduce time to market and grow the market for PM parts in high strength applications, with load carrying gears as the main target.