New insights into thermomechanical fatigue behavior of AISI Type 316 LN SS weld joint

Abstract

AbstractCyclic deformation and fracture behavior of a type 316 LN austenitic stainless steel (SS) weld joint (WJ) were investigated under thermomechanical fatigue (TMF) and isothermal low cycle fatigue (IF) cycling at the maximum temperature (Tmax) of TMF. A higher cyclic stress response (CSR) and reduced cyclic softening were observed under TMF compared with IF tests. In‐phase (IP) TMF resulted in lower lives compared with IF cycling at the Tmax and out‐of‐phase (OP) TMF, which was attributed to the more pronounced creep‐induced intergranular damage. Characterization of microstructural features and microhardness variations revealed that the accumulation of damage and associated failure depends on the strength and microstructural gradient, together with the deformation incompatibility. The crack propagation is found to depend on the individual and synergistic interactions of the microstructural transformations, creep, and oxidation, depending on the type of fatigue cycle (IF and IP/OP TMF), strain amplitude, and thermal cycling effects.