A Framework for Life Prediction of 2.25Cr-1Mo Under Creep and Thermomechanical Fatigue

Low alloy steels are often utilized in components experiencing decades of usage under aggressive operating conditions. Even though there has been remarkable advancement in the development of modern alloys, however, these materials continue to be applied in boilers, heat exchanger tubes, and throttle valve bodies in both turbomachinery and pressure-vessel/piping applications. These steels display excellent resistance to deformation and damage under creep and/or fatigue at moderate temperatures. For example, the material 2.25Cr-1Mo has exceptional balance of ductility, corrosion resistance, and creep strength under temperatures up to 650□C. Both creep and non-isothermal fatigue conditions have been the limiting factor for most 2.25Cr-1Mo components; therefore, a life prediction approach is constructed with the capability of approximating the number of cycles to failure for conditions where the material is experiencing creep and fatigue with thermal cycling. Parameters for the approach are built on regression fits in comparison with a comprehensive experimental database. This database includes low cycle fatigue (LCF), creep fatigue (CF), and thermomechanical fatigue (TMF) experiments. The cumulative damage approach was utilized for the life prediction model where dominant damage maps can be used to determine primary microstructural mechanism associated with failure. 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.