Rolling contact fatigue crack initiation in medium carbon bainitic steel

Rolling contact fatigue crack initiation and propagation were investigated to optimize the grinding and replacing techniques of medium carbon bainitic backup roll. The failure life curve was, measured using a rolling contact fatigue test machine JPM-lB with water lubrication by the pit occurrence and spalling on contact surface. The crack initiation life curve was measured by the turning parallel to crack surface on specimen section after different fatigue cycles. The results show that the two curves (the crack initiation life curve and the failure life curve) obviously deflect at a maximum contact pressure of 0.86 GPa and the initiation to failure life ratio is 70%-80%. The contact surface and the sections were observed using SEM. Perpendicular cracks dominates at lower stresses, while ratchetting cracks dominated at higher stresses. Both types of cracks have the same characteristics as general short cracks.