Effect of Shot Peening on the Rolling Contact Fatigue Behavior of Carburized High-Strength Bearing Steel

In this study, the high-strength bearing steel after carburizing treatment was shot peened with different strengths. The microstructure, hardness gradient, residual stress, surface roughness and rolling contact fatigue behavior of carburized and carburized + shot peening composite bearing steels of different strength were studied. The results showed that after carburizing treatment, the surface layer of the bearing steel was mainly composed of high-carbon martensitic and worm-like carbides, and the worm-like carbides were mainly M23C6, M6C, M7C3 carbides, the surface layer of carburized bearing steel undergoes plastic deformation after shot peening, resulting in the increase of the density of geometric necessary dislocation (GND) in the surface matrix (BCC phase). Under the effect of and dislocation strengthening, the microhardness of the surface layer of the bearing steel was slightly increased. Compared with carburized bearing steel, the surface residual compressive stress of carburized + shot peening bearing steel was significantly increased, while the surface residual stress of carburized + shot peening bearing steel decreased with the increase of shot peening strength. The median life of rolling contact fatigue (L50) of carburized bearing steel after shot peening treatment with different strengths decreased with the increased of shot peening strength, which was lower than that of carburized bearing steel without shot peening treatment (L50), which was mainly attributed to the significant increase in surface roughness, the number of surface convex or depressions in the surface layer after shot peening, and the appearance of microcracks of different sizes on the surface, resulted in an increase in the position of surface stress concentration, and the transformation of the initiation mechanism of rolling contact fatigue cracks. Surface fatigue cracks were preferential to subsurface fatigue crack initiation, and after the surface eruption of rolling contact fatigue cracks dominates, the crack would propagate with a faster propagation rate and a shorter propagation path, resulting in a reduction in the initiation life of rolling contact fatigue crack of carburized + shot peening bearing steel.