Thermomechanical fatigue behavior and lifetime prediction of niobium-bearing ferritic stainless steels

In this study, the thermomechanical fatigue (TMF) and isothermal low-cycle-fatigue (LCF) behaviors of niobium-containing ferritic stainless steels are presented for the temperature range from 100 °C to the maximum temperatures between 500 and 800 °C; furthermore, we propose a new fatigue failure criterion to predict the fatigue lives of the components for different thermal cycle ranges using the TMF condition. Higher maximum temperatures during TMF cycle resulted in shorter TMF life. By modifying the Coffin–Manson equation using the temperature factor, we obtained a new parameter that was successfully correlated with the life under different maximum temperatures. The deformation responses during fatigue cycling and the fatigue microstructure were compared to elucidate the different fatigue behaviors under the TMF and LCF conditions.

► Out-of-phase thermomechanical fatigue (OP-TMF) of Nb-added ferritic stainless steels. ► Higher maximum temperature of thermal cycle induces shorter fatigue life. ► We model TMF failure criterion which normalizes life change with temperature variation. ► Hysteresis loops are characterized by severe dynamic stress relaxation. ► OP-TMF significantly enhances dislocation recovery and formation of coarse subgrains.