The effect of stress ratio in fatigue properties of bearing steel including long life region was experimentally examined under axial loading. As a result, the complicated S-Nproperty was, irrespective of stress ratio, well explained as duplex S-N characteristics obtained by superposition of S-N curves for surface induced fracture and interior inclusion induced fracture. Fish-eye marks were necessarily observed on the fracture surfaces failed in the latter fracture mode and an inclusion was found at the center of the fish-eye. It was finally found that the fatigue fracture of this steel in the long life region occurred through three different processes of (1) formation of the characteristic area of FGA, (2) crack propagation to form the fish-eye and (3) rapid crack propagation to cause the catastrophic fracture.
