Distribution of surface residual stress and fatigue property of gas carburized JIS SCM420 with double shot peening were investigated. Developed FeCrB media with 0.1 mm diameter and high hardness of HV 1200 was used as secondary shot peening media, while conventional cast steel media of 0.8 mm diameter was used as primary one. As a reference, the specimen with double shot peening by high speed steel media of 0.1 mm diameter as secondary shot peening media was also examined.
Distribution of surface residual stress of double shot peened specimen had two peaks, which corresponded with the primary and secondary shot peening. The peak value at near-surface region of the specimen shot peened using FeCrB media was 170 MPa higher than that of the specimen using high speed steel media. Fatigue strength was improved by double shot peeing. It was related to integral value of compressive residual stress both of the ranges from the surface to 30 μm and from 30 to 400 μm in depth. Furthermore, the integral value of compressive residual stress in the range from the surface to 30 μm strongly contributed to fatigue strength.