Patent ID: 7677070

Claim:
A shot-peening process to be applied on a grain boundary oxidation layer that is formed on a metal surface that has been treated by a carburization and quenching process, or a carbonitriding and quenching process, said shot-peening process comprising the steps of: providing shot particles and a projection device for projecting the shot particles, wherein a size of the shot particles is greater than 0.2 mm but 1.0 mm or less, and wherein a hardness of the shot particles is greater than or equal to that of the metal surface; projecting the shot particles against the metal surface to reach 100% to 500% in coverage by adjusting a speed of the projected shot, under shot-peening conditions for projecting the shot particles by said projecting device, to be from 30 to 100 m/s, or by adjusting a pressure, under shot-peening conditions for projecting the shot particles by said projecting device, to be from 0.1 to 0.5 MPa, whereby at least a part of the grain boundary oxidation layer is ablated; and determining the existence or non-existence of any remaining grain boundary oxidation layer that may remain after the ablation by measuring the full-width at half maximum on the surface that has been peened by the shot.