ガス浸炭焼入れを施したSCM420H鋼の回転曲げ疲労特性に及ぼす軟質微粒子ピーニングの影響

抄録

In order to examine the effects of soft-fine particle peening (Soft-FPP) on the fatigue properties of gas carburized SCM420H steel, rotating bending fatigue tests were conducted for carburized SCM420H steels treated with FPP using shot particles having different hardness. The Soft-FPP treated steels pre-treated with carburizing showed higher fatigue life and fatigue strength at 10⁷ cycles compared with the only-carburized steels. This is attributed to the increase of surface hardness and the generation of compressive residual stress induced by FPP. The carburized steels treated with FPP failed in the subsurface fracture mode from the singular microstructure beneath the carburized layer in the long life region. The transition stress for the carburized steels treated with FPP, at which the surface fracture mode changed to the subsurface one, tended to increase with the hardness of shot particles used in FPP. Furthermore, the release behavior of residual stress induced by FPP during fatigue tests was also examined. There were no noticeable differences in compressive residual stress after the fatigue tests between the two types of carburized specimens treated with FPP; therefore, the Soft-FPP treated steels exhibited same fatigue strength as the steels treated with FPP using hard shot particles. These results suggest that the effect of hardness of shot particles used in FPP on the fatigue properties of carburized steels is not observed.