Fatigue Damage Evolution and Short Crack Behavior of the Fusion Zone of SUS301L-HT Stainless Steel Laser-Arc Hybrid Welding Joints

Abstract

Many approaches have been developed to estimate fatigue damage for alloys and welding joints. In this study, a parameter, i.e., fractal dimension, characterized fatigue damage caused by persistent slip bands (PSBs) in the fusion zone of SUS301L-HT laser-arc hybrid welding (LAHW) joints. The fractal dimension first increased and then tended to be stable for different stress levels. The saturation values for stress levels of 328.5, 342, and 352.8 MPa were found to be 2.4938, 2.5640, and 2.5949, respectively. The goodness of fit was larger than 0.84 for all stress levels when a power function was used for fitting. Unified curves were obtained, but the saturation level of the fractal dimension at a stress level of 342 MPa did not match well with others. At the inner wall of a notch, PSBs were likely to provide natural nucleation sources for crack initiation. Some short cracks merged directly at the tips or indirectly by interaction between the tip of one crack with another crack, thereby developing larger cracks. At the sample surface, only a few short cracks were adjacent to the notch. One of these cracks merged with the developing crack at the inner wall of the notch, thereby forming a dominant crack. The fracture showed quasi-cleavage features with dendrites.