Thermochemical treatment of Fe–Cr–Mo alloys

Thermochemical treatment in different atmospheres containing nitrogen, sulfur and oxygen was applied to the sintered prealloyed powder Astaloy CrM containing 3 wt.% Cr and 0.5 wt.% Mo. The base material was modified by boron and carbon addition. In this paper, special attention was paid to explaining the influence of the microstructure of the base material on the formation of a compound layer and the wear resistance of surface-treated sintered components. A bainitic–martensitic microstructure was obtained after sintering. Depending on the nitriding atmosphere, nitriding (N), oxynitriding (NO), sulfonitriding (NS) or oxysulfonitriding (NSO), the compound layer of the surface-treated specimen has a different constitution and compactness. Wear resistance investigations under dry sliding conditions show that sulfonitriding, due to the presence of iron sulfide, which possesses excellent friction properties against steel, particularly improves the wear resistance of the sintered Astaloy CrM.