Mechanical properties of sinter hardened sintered steels prepared by hybrid alloying

Abstract

For PM steel precision parts, high mechanical loading is very common in service. In particular for automotive applications, fatigue up to very high loading cycle num-bers may be encountered. Advanced alloying concepts for sintered steels are required, involving also alloy ele-ments with high oxygen affinity. In the present study, hybrid alloyed sintered steels based on prealloyed steel powder Fe-1.8%Cr were prepared by the press-and-sinter route. Mn and Ni, respectively, were admixed as well as a masteralloy containing Mn and Si, the alloy element content being varied, and the combination hardness vs. impact energy was assessed. From the most promising variants, fatigue test specimens were prepared, sinter hardened and characterized, fatigue testing being done by ultrasonic resonance up to Nmax = 10E10 cycles. Ni alloying proved to be positive both for the impact energy and the gigacycle fatigue strength while Mn resulted in high hardenability but low impact and fatigue strength, in part because of intergranular embrittlement. The grade with Mn-Si mas-teralloy was slightly less ductile than the Ni alloyed variant, but in particular at N > 10E8 the fatigue endur-ance strength was similar to that of the Ni alloyed type, however with significantly lower scatter.