Evaluation of creep–fatigue life based on fracture energy for modified 9Cr–1Mo steel

Preventing creep–fatigue damage is a major consideration in nuclear power plants, which operate at high temperatures. Energy absorbed during creep–fatigue loading is focused on for predicting long-term creep–fatigue life for modified 9Cr–1Mo steel. Fracture energy decreases with time owing to creep deformation localization. Change in fracture energy is described by a power law function of hysteresis energy density rate and time to fracture. Hysteresis energy density is approximately expressed as a function of the total strain range. Then, hysteresis energy density rate is determined by dividing hysteresis energy density by time per cycle. The function gives a good fit of data for creep–fatigue and low strain-rate fatigue. The creep–fatigue life can be predicted using the power law function. According to microstructure observation, change in fracture energy is due to annihilation of block and packet boundary.