Effect of laser beam position on mechanical properties of F82H/SUS316L butt-joint welded by fiber laser

A dissimilar butt-joint between reduced activation ferritic/martensitic steel F82H and SUS316L austenitic stainless steel was made by 4 kW fiber laser and the influence of laser beam position on its mechanical properties before and after post-weld heat treatment (PWHT) was examined at room temperature. From the nano-indentation measurements and the microstructural observations, it is found that the micro hardness of weld metal partially decreases after PWHT by shifting beam position to SUS316L because its phase seems to move from only the martensitic phase to the mixture of austenitic and martensitic phases. In addition, Charpy impact test suggests that the impact energy slightly increases by shifting beam position before PWHT and obviously increases after PWHT due to the release of residual stress. Moreover, the tensile test indicates that the tensile strength of weld metal is higher than that of SUS316L and the fracture occurs at the base metal of SUS316L regardless of laser beam position.