Effect of compressive residual stress introduced by cavitation peening and shot peening on the improvement of fatigue strength of stainless steel

One of the traditional methods used to improve the fatigue properties of metallic materials is shot peening. More recently, cavitation peening, in which the surface is treated using cavitation impact, has been developed, and the improvements this makes to the fatigue life and the strength of metallic materials have been reported. In order to clarify the difference between these two methods, stainless steel SUS316 L samples were treated by shot peening and cavitation peening, and the fatigue properties of the samples were evaluated utilizing a displacement controlled plane bending fatigue test. The residual stress and hardness before and after the fatigue test were measured, and the surface roughness of each specimen was also measured. It was concluded that the fatigue life of shot peened specimens at bending stress a > 450 MPa was longer than that of cavitation peened specimens; however, the fatigue strength of the cavitation peened specimens was slightly larger than that of the shot peened specimens. The compressive residual stress introduced by both peening methods decreased during the fatigue test. The reduction in the compressive residual stress in the shot peened specimens was greater than in the cavitation peened specimens, and after the fatigue test, the compressive residual stress in the shot peened specimens was greater than that in the cavitation peened specimens. It was found that the fatigue strength corresponded well with the yield stress estimated from the Vickers hardness corrected by the residual stress obtained after the fatigue test.