Characteristic S-N properties of high-carbon-chromium-bearing steel under axial loading in long-life fatigue

Owing to difficult economical conditions, machines and structures often have to be used beyond the design lifetime. In this study, fatigue properties of a bearing steel in the long-life region were experimentally examined under cyclic axial loading. The complicated S-N behaviour was well explained as a combination of S-N curves for surface-induced fracture and interior inclusion-induced fracture. Fish-eye marks were always observed on the fracture surfaces of specimens, which failed in the latter fracture mode, and an inclusion was found at the center of the fish-eye. Finally, it was found that the fatigue fracture of this steel in the long-life region occurred through the following three processes: (i) formation of the characteristic area as a fine granular area (FGA), (ii) crack propagation to form the fish-eye and (iii) rapid crack propagation to cause the catastrophic fracture.