Process Optimization of Ultrasonic Rolling Treatment for G20Cr2Ni4A Bearing Race

The influence of surface ultrasonic rolling process（SURP） on surface morphology, surface microstructure and rolling contact fatigue（RCF） performance of G20 Cr2 Ni4A carburized bearing steel was studied. The results show that the main factor affecting the surface roughness and surface hardnes is static pressure, followed by current, and the minimum is feed rate.The main factor affecting surface residual stress is feed rate, followed by current and static pressure. The correlation coefficient of the response surface prediction model of surface roughness, hardness and surface residual stress is high. The second-order response surface prediction model optimizes the ultrasonic rolling process. The optimized process parameters are as follows:the feed is 0.05 mm/r, the current is 1.5 A, the static pressure is 200 kg. After SURP with optimized process parameters, the fatigue life of the sample is increased to 7.3 times. In the RCF test, the surface of the sample without SURP forms flake spalling and gradually fails. The fatigue spalling pit of SURP sample appears in SURP plastic deformation zone, and then gradually develops into tongue tip spalling pit, and the tongue tip points to the rolling direction, resulting in fatigue failure.