Rolling Contact Fatigue Failure Mechanism of Martensitic Bearing Steel after Carbonitriding

Carbonitriding is widely used, it is necessary to further reveal the rolling contact fatigue performance of modified parts. The surface of martensitic bearing steel is treated by gas carbonitriding method. Rolling contact fatigue tests are carried on carbonitrided specimens. The effect of carbonitriding on the rolling contact fatigue property and failure mechanism are studied. The results show that the carbonitrided specimens display significantly increase fatigue lives in contrast to the conventional specimens. This is due to the increase in the hardness, residual stress and content of retained austenite. Fatigue cracks of originate from both the surface and sub-surface. The parallel surface cracks are mainly caused by hardness gradient change in white etch layer. The surface is subjected to severe plastic deformation induced grain refinement The sub-surface cracks are greatly influenced by the distribution of the maximum stress and the carbonitriding thickness. The surface and subsurface crack propagation and coalescence leads to shallow spalling and delamination.