Effect of Shot-Peening on Super-Long-Life Fatigue Behavior in High Carbon-Chromium Bearing Steel

Effect of shot-peening on fatigue behavior in gigacycle regime was investigated in order to clarify the duplex S-N curve characteristics. A cantilever-type rotating-bending fatigue tests were performed in laboratory air at room temperature using hour-glass-shaped specimen of high carbon-chromium bearing steel, JIS SUJ2. Fatigue crack initiation site was transited from surface on untreated specimen to subsurface of the specimen due to hardening and compressive residual stress with shot-peening in the region of high stress amplitude. On the other hand, no difference in fatigue life controlled by subsurface crack initiation between untreated specimen and shot peening one was observed in high cycle region. It is suggested that the S-N curve corresponding to internal failure mode is an inherent in the material, as compared with that the S-N curve of surface failure mode is affected by surface conditions, environmental conditions and so on. Subsurface crack initiation and propagation behavior were discussed under the detailed measurement of crack initiation area and shape of fish-eye. And also, S-N characteristics of case-hardened material was discussed.