ピーニング処理された浸炭鋼の回転曲げ疲労特性に及ぼす圧縮残留応力分布の影響

抄録

In order to investigate the effect of residual stress distribution pattern in the specimen on the fatigue crack initiation behavior and fatigue strength at 2×10⁷ cycles, rotating bending fatigue tests were conducted for carburized SCM420H steels treated with several shot peening conditions. In the case of a specimen having a S-type residual stress distribution in which a peak residual stress exists inside the specimen and the surface residual stress is smaller than the peak residual stress, the specimen fractures in surface fracture type under high stress load and in internal fracture type under low stress load. The boundary stress between surface and internal fracture type is the lower limit stress at which the surface crack can proceed through the depth where the peak of the residual stress exists. On the other hand, most of the SP-treated specimen fractures in internal fracture type and clear fish-eye pattern was observed on the fracture surface. And the crack initiation site was at the location of transgranular cracking that occurred in a region deeper than the hardened layer. It was predicted that the fatigue strength at 2×10⁷ cycles of SP treated specimen corresponds to the crack generation limit when the residual stress peak position is relatively shallow. Furthermore, it was predicted that the fatigue strength at 2×10⁷ cycles corresponds to the crack propagation limit when the residual stress peak position is relatively deep.