Pulsed Nd: YAG laser welding and subsequent post-weld heat treatment on super duplex stainless steel

This study attempts to explore the weldability of super duplex stainless steel UNS S32750 (SDSS), using a pulsed Nd: YAG laser welding machine with an average power of 600 W. The process was performed by varying welding speeds (200 mm/min-400 mm/min in steps of 50 mm/min) and keeping the other parameters unchanged, so as to alter the heat input (75 J/mm-150 J/mm). Microstructural analysis on the joints reveal higher volume percentages of ferrite (>50%) affecting the phase equilibrium of base alloy. The as-weld joints were subjected to post weld heat treatment (PWHT) at 1050 °C for two hours to enhance the levels of the austenite phase. This alleviates the phase imbalance and improves the corrosion properties of SDSS laser welds. Vickers microhardness and tensile strength of as-weld joints were found to be higher than PWHT joints due to the higher ferritic phase in the weld zone.