Effect of Non-metallic Inclusion on Rolling Contact Fatigue Damage in High-strength Steel by Synchrotron Radiation Laminography

Abstract

In rolling contact fatigue (RCF), cracks are initiated and propagate from inclusions beneath the surface. In the present study, crack propagation behavior under RCF was observed by laminography using ultra-bright synchrotron radiation, which is suitable for thin plates, at SPring-8 (Super Photon Ring - 8 GeV). The material had intentionally contains a high concentration of sulfur to enable the observation of crack initiation from MnS inclusion. Fatigue tests were interrupted to conduct laminography by a new developed compact RCF test machine. In the present study, we observed specimens with inclusions which is oriented parallel to the sample surface and parallel to the rolling direction (L-type specimen). The crack growth behavior of the L-type specimen is different from the other types, vertical cracks propagated perpendicular to the rolling direction after vertical cracks were appeared parallel to the rolling direction in the sample surface. In addition, the L-type specimen has a longer life than the other types.