Sinter Hardening of Cr-Mo Pre-Alloyed Steels as a Function of the Carbon Content

Sinter hardening is a technique that is frequently employed in powder metallurgy parts production since it is an economical, clean, and environmentally friendly procedure. Since the cooling rates are however significantly lower than e.g. in water or oil quenching, alloy systems have to be used that ensure martensite formation already at moderate cooling rates. In the present study, quenching dilatometry was used to investigate the hardenability of two types of Cr pre-alloyed steels, Fe-3Cr-0.5Mo and Fe-1.5Cr-0.2Mo, the carbon content being varied, and sinter hardening diagrams were plotted. It showed that this parameter has a pronounced influence on the hardenability of the 3 % Cr alloy; in particular in the range 0.3…0.4 % combined C. For the lower alloyed system, in contrast, even 0.52 % combined C was insufficient to ensure martensite formation at the cooling rates typical for industrial sinter hardening. Finally, impact test specimens were prepared by sinter hardening at cooling rates typical for industry, and hardness, as well as impact energy, were determined.