Rotational bending fatigue tests were carried out using ferrite-pearlite steel modified by the WPC process, which is one of the shotpeening processes. To clarify the high cycle fatigue properties, measurements of residual stress and hardness distribution were performed. Fatigue strength of the specimen with a WPC-treated surface was higher than that of an untreated one. This is because (i) the WPC process forms an extremely shallow hardened layer with high compressive residual stress, and (ii) the compressive residual stress generated by the WPC process was very stable under cyclic loading ; after 107 cycles of stress loading, the reduction of compressive residual stress was very small. A comparison with fatigue properties of the specimen hardened by conventional shotpeening was also conducted with special focus on the difference in fatigue strength and fatigue crack initiation behavior.
