Pre-Alloyed Chromium Material with Consistent Properties for Medium Strenghth Applications
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.