Impact of surface ultrasonic rolling on cavitation erosion behavior of 304 stainless steel

Surface ultrasonic rolling process (SURF) is a prior self-nano-technology of surface strengthening to improve the cavitation resistance of metal materials. In the paper, the 304 stainless steel (304SS) specimens were processed into 5 times, 10 times, 15 times and 20 times by SURP, then were cut into pieces along the SURP surface. In order to investigate impact of SURF on cavitation erosion behavior of 304SS, microstructure, mechanical properties and phase distribution of 304SS with difference SURP times were characterized firstly. Subsequently, ultrasonic cavitation erosion process and electrochemical measurements was experimented respectively: the specimens with different SURP times were subjected to 3 h in ore pulp solution (The mass fraction of 3.5% NaCl and 5% plumbum-zinc) by ultrasonic cavitation erosion process (UCEP), meanwhile, the electrochemical behaviors of the 304SS specimens with difference SURP times, such as open circuit potential (OCP), polarization curves and electrochemical impedance spectroscopy (EIS) were measured successively. Finally, the influences of the mechanical properties and corrosion characteristics of the 304SS with different microstructures after SURP on cavitation corrosion resistance were discussed in details, in the meantime, the microscopic mechanisms of the cavitation resistance for 304SS with different SURP times were investigated. The result shows that SURP is significantly beneficial to protect 304SS from the cavitation erosion behavior via introduction of deformation layers, transformation between martensite and austenitic, formation of passivation film, grain refinement and the surface hardness as well as residual stress of the 304SS were enhanced accordingly. However, the energy transfer of SURP is not only used to surface hardening, grain refinement, slip bands establishment but also defects formation, overmuch energy transfer plays the opposite role. Therefore SURP 10 times is a suitable SURP times that makes 304SS achieved optimal cavitation resistance.