The tensile, creep and fatigue tests were carried out on stress aged SUS316 stainless steel in order to clarify the effect of creep damage on fatigue strength. The interaction between creep damage and high temperature strength, especially fatigue life, was discussed.
The precipitates of M23C6, χ-phase and Laves-phase were observed, and σ-phase precipitated mainly along grain boundaries in the long-term stress aged material. In the long-term stress aged material the creep cavities were found to exist along the grain boundary particles and non-metallic inclusions in grain.
The fatigue life of the stress aged material decreased with increasing ageing time. On the other hand, the fatigue life of the thermal aged material increased by ageing. It was considered that the increase of fatigue life of the thermal aged material was related to structural change, especially the precipitation of carbides, etc., and that the decrease of fatigue life of the stress aged material was related to creep cavities which accelerate fatigue-crack initiation and propagation.
The creep damage of the stress aged material accompanies structural change as well as formation of creep cavities. Therefore, the fatigue life of the stress aged material is affected by these two factors; deceleration of fatigue crack propagation due to the precipitation and acceleration of fatigue crack initiation and propagation due to the creep cavities.