Effect of admixed alloying components on the properties of sintered steels based on Cr prealloyed powder

For highly loaded precision parts required in large numbers, the powder metallurgy route by pressing and sintering is attractive both economically and ecologically. To obtain the required mechanical properties, heat treatment is necessary. For this purpose, sinter hardening, that is, gas quenching of the parts immediately after leaving the high temperature zone of the furnace, is a highly cost-effective variant. Compared to standard oil quenching, however, the cooling rates are significantly lower, which means that alloying of the sintered steels plays a major role. In the present study, hybrid alloyed steels were investigated, based on Cr prealloyed powder with the addition of Ni or Mn elemental powder grades, as well as a fine Mn–Si masteralloy powder. The sinter hardening behaviour was investigated as a function of the alloy element and the carbon content, respectively, with moderate cooling in the range of 0.7 K/s (linearised) being applied. It showed that in this cooling regime, less Mn is required for sinter hardening than Ni or the masteralloy. However, the impact energy is significantly lowered by Mn addition, as a consequence of intergranular failure, while both Ni alloying and addition of the Mn–Si masteralloy offer an attractive combination of hardness and toughness. This underlines the importance of the alloying route, in particular when using Mn.