Effects of dwell time on the isothermal and thermomechanical fatigue behavior of 316LN stainless steel

Isothermal fatigue (IF) and thermomechanical fatigue (TMF) tests with and without tensile dwell time at various strain amplitudes were conducted on 316LN stainless steel. The results showed that the inelastic relaxation strain rate is more appropriate to characterize creep damage than the amount of stress relaxation. The introduction of tensile strain hold imparted a more deleterious effect on the TMF than the IF performance based on a statistical analysis of the number of secondary cracks and their size distribution, which was primarily attributed to the more severe oxidation-assisted cracking at the interface between the oxide scale and substrate. Most importantly, the lowest fatigue life occurred in the TMF test with tensile dwell time at the low strain amplitude of 0.4% rather than in the creep-fatigue test at the isothermal maximum temperature, indicating that it was not always conservative to predict the life of engineering components based on the IF data.