Creep-fatigue evaluation by hysteresis energy in modified 9Cr-1Mo steel

Nagae, Yuji ; Takaya, Shigeru  ; Asayama, Tai 

Researchers have proposed the methods of creep-fatigue evaluation, such as time fraction rules or ductility exhaustion rules. However, the microstructure change during creep-fatigue should not be directly considered in these methods. The hysteresis energy contributes the microstructure change related to the damage and the crack initiation. We have evaluated the creep-fatigue based on the hysteresis energy in modified 9Cr-1Mo steel as a candidate for structural material in Fast Breeder Reactor (FBR) plant. Creep-fatigue and fatigue tests were carried out at 723873 K in air. We converted the hysteresis energy a cycle at the middle of life (N/2, N is the number of cycles to failure) into that of an hour, and the number of cycles into the time to failure. The relationship can be expressed by the power-law function. We have concluded that the creep-fatigue life can be evaluated based on the hysteresis energy an hour at N/2.