Low alloy steels remain to be the materials of choice for large structural components at elevated temperature for extended periods of time. The material 2.25Cr-lMo is frequently used in boilers, heat exchanger tubes, and throttle valve bodies in both turbomachinery and pressure-vessel/piping applications alike. The resistance of this alloy to deformation and damage under creep and/or fatigue at elevated temperature make it suitable for components expected to endure decades of service. In the present work, a life prediction approach is developed for cases where the material is experiencing conditions where creep and fatigue exist. Parameters for the approach are based on regression fits in comparison with a broad collection experimental data. The data are comprised of low cycle fatigue (LCF) and creep fatigue (CF) experiments. The form of the life prediction model follows the cumulative damage approach where dominant damage maps can be used to identify primary microstructural mechanism associated with failure. The total damage is divided between three different modules in this approach: fatigue, creep, and environmental fatigue. Life calculations are facilitated by the usage of a non-interacting creep-plasticity constitutive model capable of representing not only the temperature- and rate-dependence, but also the history-dependence of the material.
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