In rolling contact fatigue(RCF), cracks are usually initiated from inclusions under the surface and propagated to the contact surface. In the present study, RCF cracks was observed using synchrotron radiation computed laminography(SRCL) in SPring-8. The specimen with flaking damage was measured by SRCL. It was found that two types of cracks, vertical crack and horizontal crack under the contact surface, which is typically rolling fatigue crack, was measured by SRCL. The ex-situ fatigue tests and SRCL observation was conducted in SPring-8. It was found that the horizontal crack initiated after the vertical crack initiated and propagated along inclusion. It is considered that the vertical crack is an important factor of flaking process, and the shape and length of inclusion affect the initiation and propagation of vertical crack.
