Influence of the intensity of ultrasonic rolling on surface strengthening features of 25CrMo4 axle steel

In order to improve the service life of train axle. The work aims to research the surface morphology and roughness, surface hardness and its depth, surface residual stress and surface microstructure of the specimen after different treatment. The influence of rolling and ultrasonic rolling treatment with different loads on the surface strengthening characteristics of 25CrMo4 axle steel was explored. The results show that compared to grinding specimen, both rolling and ultrasonic rolling reinforcement improve the surface flatness of the specimen, the surface roughness of low-load ultrasonic rolling specimen was the lowest, reaching 0.2 μm; After high-load ultrasonic rolling, the plastic deformation layer obtained on the surface of the specimen is the deepest. The surface hardness of high-load ultrasonic rolling specimen is the largest, reaching 370 HV_0.1 and forming a hardened layer with a depth of about 150 μm. Both the surface of the rolling specimen and the ultrasonic rolling specimen produce high residual compressive stress. Conclusion: rolling and ultrasonic rolling treatment increase the surface hardness and its gradient, produce high residual compressive stress and reduce the surface roughness of 25CrMo4 axle steel, which will have a favorable effect on the improvement of fatigue performance. However, excessive load will increase the axle roughness, which has an adverse impact on the improvement of its fatigue performance.