Deformation and Damage Mechanisms of 316L Stainless Steel Under Various Dwell Times and Modes of Creep‐Thermomechanical Fatigue Interaction

ABSTRACT The creep‐thermomechanical fatigue (CTMF) behavior and microscopic damage mechanisms of 316L austenitic stainless steel are investigated under in‐phase loading conditions with different dwell times and dwell modes. The results show that increasing dwell time intensifies stress relaxation, reduces the stabilized peak tensile and compressive stresses, and broadens the hysteresis loops, leading to an increase in the inelastic strain range. Microstructural characterization indicates that the observed cyclic softening is mainly associated with thermally activated dynamic recovery, during which dense dislocation tangles progressively rearrange into lower‐energy subgrain structures. The reduction in fatigue life is governed by the coupled effects of dwell‐enhanced inelastic deformation, creep cavitation, and oxidation‐related damage, with their relative contributions depending on dwell mode. Under tensile dwell, fatigue life decreases rapidly at short dwell times and then becomes less sensitive to further dwell extension, which is attributed to the competition between enhanced inelastic deformation/cavity formation and the crack‐tip blunting effect of a thickened oxide layer. Under compressive dwell, brittle rupture of the oxide layer exposes fresh metal and thereby facilitates crack propagation, although the dwell‐time sensitivity of fatigue life also weakens at longer hold times. In contrast, symmetric dwell causes the most severe degradation because the largest inelastic deformation is coupled with oxidation during tensile holding and oxide rupture during compressive holding.