Effect of Microstructure on Surface Integrity of 45CrNiMoVA Steel by Ultrasonic Surface Rolling Process

To solve the problem that the effect of microstructure on the surface integrity of ultrasonic surface rolling process (USRP) is unclear, USRP tests were carried out on 45CrNiMoVA steel with ferrite + pearlite and tempered martensite respectively. The surface morphology, surface roughness, surface microhardness, residual stress, and surface microstructure were analyzed. The results show that the material with a soft phase is easier to achieve surface finishing effect under USRP, and the surface material is more prone to plastic deformation, resulting in a more obvious surface hardening effect, but it is difficult to form higher amplitude residual compressive stress. The results show that the magnitude of residual compressive stress introduced by USRP on the surface of 45CrNiMoVA steel is proportional to its microstructure strength. The residual compressive stress on the surface of 45CrNiMoVA steel is easy to be "spoon-shaped" under tempered martensitic structure, and the maximum residual compressive stress appears on the subsurface, reaching - 1 272 MPa. The residual compressive stress on the surface of 45CrNiMoVA steel is easy to be "gradient" under ferrite + pearlite structure, the maximum residual compressive stress is -694 MPa on the surface. The results show that the structure of BCT crystal is more prone to grain refinement under the action of USRP, while the structure of BCC crystal is mainly plastic deformation under the action of USRP. The above rules can be used to guide the accurate regulation of material processing surface integrity under different microstructure states.