ショットピーニング加工したマルエージング鋼における表層組織と疲労特性

抄録

Rotating bending fatigue tests were carried out to investigate the effect of microstructure in subsurface on the fatigue properties of a shot peened maraging steel. The steel had a fine-grained microstructure formed at the surface layer with 50-70 μm in depth. Especially a thin surface layer showed a nano-size structure. A surface fracture occurred at high stress levels, while the combined fracture occurred due to coalescence of a surface crack and an internal one initiated independently with decreasing in stress level until 108 cycles. In all of the macroscopic fracture surfaces in the shot-peened specimen, a ring-shaped flat area was observed at the surface layer irrespective of the fracture mode and the depth of the area nearly corresponded to the one of the fine-grained microstructure. The formation mechanism of the ring-shaped area was explained from the initiation and propagation properties of a surface crack in the surface layer in connection with the microstructure.