Modeling the cyclic softening and lifetime of ferritic-martensitic steels under creep-fatigue loading

摘要

Ferritic-martensitic (F/M) steels are a common choice for high-pressure, high-temperature boilers and steam piping in power plants, but cyclic softening without saturation is a major degradation mechanism of F/M steels. This degradation mechanism is more pronounced and complex under creep-fatigue loadings. For reliable, but not overly conservative design a better understanding of this phenomenon is necessary. The intent of this work is to characterize and model the softening and lifetime behavior under creep-fatigue conditions at high temperature. Therefore, low-cycle fatigue (LCF) tests with hold time were performed at 550 degrees C.