Effect of Shot Peening on Fatigue Strength of 18%Ni Maraging Steel

Rotating bending fatigue tests were carried out on an 18%Ni maraging steel to investigate the effect of shot peening on fatigue strength. Fatigue strength was increased markedly by shot peening. The increase in fatigue strength due to shot peening depended on shot size and stress level. Fracture mode changed from surface fracture in the short-life region to interior fracture, i.e., fish-eye fracture, in the long-life region. In the middle-life region, however, cracks initiated from both the surface and the inside of the material individually coalesced and led to the final fracture. These results were discussed on the basis of the effects of shot size on surface roughness, the depth and magnitude of compressive residual stress and work hardening.