Effect of Multi-pass Ultrasonic Surface Rolling Process on Surface Properties and Microstructure of GCr15 Steel

This paper investigates the effect of different rolling times of ultrasonic surface rolling process (USRP) on the surface properties of GCr15 steel. A finite element model was established to investigate the effect of different rolling times on the residual stress and equivalent plastic strain distribution in the surface layer of the specimen. Based on scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), friction and wear test, laser confocal microscopy and electrochemistry, wear resistance, corrosion resistance, hardness, surface roughness, and microstructure of USRP multi-pass treated specimens were analyzed. The results show that with the increase of the number of ultrasonic rolling, the intense plastic deformation of the GCr15 surface layer intensifies, and the surface grain refinement becomes more obvious. The thickness of the grain refinement layer reaches 36 μm, and the proportion of low-angle grain boundaries (LAGBs) increases significantly, reaching 53% in the USRP-9(9-pass USRP machining) treated specimens. The microhardness increased by 7.96%, 11.25%, 14.07% and 16.57%, respectively, compared to the untreated specimens. The surface roughness of the specimens after the USRP treatment decreased and then increased with the increase in the number of rolling passes and the optimum value was achieved at USRP-3. Similarly, the USRP-3 treated GCr15 specimens showed the minimum width and depth of wear and the best wear and corrosion resistance.