Effect of tensile dwell on low cycle fatigue cyclic stress response and damage mechanism of 316L austenitic stainless steel welding joint

Continuous and tensile dwell low cycle fatigue tests of 316 L austenitic stainless steel base metal and weldment were carried out at 873 K temperature. The dislocation microstructure and crack propagation evolution in the specimens were examined using optical microscope(OM) and transmission electron microscopy(TEM). The effect of tensile dwell on the low cycle fatigue cyclic stress response and damage mechanism of base and weld metal was experimentally investigated. Cyclic hardening was observed in the base metal during both continuous and tensile dwell low cycle fatigue tests. However, continuous cyclic softening was observed during continuous low cycle fatigue in the weldment whereas clear cyclic saturation stage occurred during tensile dwell test. The fatigue life during tensile dwell low cycle fatigue was much shorter than that during continuous low cycle fatigue. Transgranular propagation of crack was the main character during continuous low cycle fatigue for both base metal and weldment. However, the crack propagated intergranularly or in mixed mode during tensile dwell low cycle fatigue test.