24.10.2001 Pressing & Sintering

Heat Treatment of Cr-Mo Sintered Steels Based on Astaloy CrM

EURO PM2001, in Nice, France.  Höganäs Chair. For sintered steels prepared from prealloyed steel powder Astaloy CrM (Fe-3%Cr-0.5% Mo) various heat treatment techniques and their effect on properties and microstructure are described. It could be shown that steels with carbon contents between 0.2 and 0.5 mass% can be effectively hardened by oil or gas quenching, and regular martensitic microstructures are attained also after gas quenching. The quench hardness depends on carbon level, total porosity, and high temperature sintering. Tempering is recommended either in the range <200°C, for high hardness, or at 500-650°C for optimum strength / toughness. For surface hardening, low pressure carburising of sintered steels with <0.3%C, followed by gas quenching, has shown to be quite effective although carburizing temperature and carbon activity have to be carefully balanced to avoid excessive carbide formation. High sintered density, which can be obtained best by warm compaction combined with high temperature sintering, is beneficial for the formation of well defined hard surface layers with high wear and contact fatigue resistance.