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

ABSTRACT 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.