Surface Hardening Vs. Surface Embrittlement in Carburizing of Porous Steels

Carburizing increases the contact fatigue resistance of sintered steels, but the surface hardening may result the formation of surface brittle cracks due to the combined effect of high hardness and porosity. The effect of carburizing on the embrittlement of the case of a 7.3 g/cm³ 1.5%Mo - 0.25%C sintered steel was studied. The phenomenon was analyzed theoretically and verified by experiments. The resistance of the carburized steel to surface brittle cracking increases with the load bearing surface and the decrease of the maximum pore size, of the surface microhardness and the friction coefficient. The theoretical analysis was implemented in a design procedure for parts subject to contact stresses.