2002 年 42 巻 9 号 p. 1042-1048
Low carbon Cr-Mo steel (0.176C, 0.119Si, 1.014Cr, 0.387Mo) has been plasma carburized and its fatigue properties have been investigated. The effective case depth in plasma carburized steel at a lower temperature for a shorter time increased up to 50% in comparison to that of gas carburizing. In case of boost-diffuse carburizing, which cycles the carburization and diffusion period, the number of cycle times had more effect than carburizing time on the surface carbon content. High cycle fatigue properties of plasma carburized steel were assessed by comparing with those of gas carburized steel in reference to microstructure, effective case depth, amount of retained austenite and compressive residual stress near the surface. The fatigue limit of the plasma carburized steel was higher than that of gas carburized steel in the same effective case depth because the former had a higher compressive residual stress and had no internal oxidation layer. Transgranular fracture was in plasma carburized steel due to the fact that it had no grain boundary internal oxidation layer that initiated the crack.
