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

Cyclic 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 (T-max) 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 T-max 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.

Automated summary

The study investigated the cyclic deformation and fracture behavior of a type 316 LN austenitic stainless steel weld joint under thermomechanical fatigue (TMF) and isothermal low cycle fatigue (IF) cycling. It was found that TMF resulted in higher cyclic stress response and reduced cyclic softening compared to IF tests, with in-phase (IP) TMF leading to lower lives than IF cycling at the maximum temperature. The accumulation of damage and failure depended on strength, microstructural gradient, and deformation incompatibility, with crack propagation influenced by microstructural transformations, creep, and oxidation.