Statistical characteristics of relaxation behavior of compressive residual stresses with time, about in 1500 days after quenching, was investigated for two kind of induction hardened carbon steel S45C quenched into city water (W specimen) or the water containing 3 % polyvinil-alcohol (S specimen). The longitudinal and circumferential stresses at two points on the surface of specimen were measured by X ray sin^2 ψ method again after some intervals. A little relaxation of compressive residual stresses with time in room temperature (mean temperature 21℃) was recognized for S specimen and W specimen. Relaxation behavior of median value with time may be expressed by an equation which was almost equivalent with the relaxation behavior during creep process.
