Relationship between Microstructure and Corrodibility of Local Dry Underwater Laser Welded 304 Stainless Steel

To understand the relationship between microstructure and corrosion, in this study, underwater bead-on-plate laser welding was compared with the in-air laser welding of 10-mm-thick 304 stainless steel plates at different laser powers (2, 4, and 6 kW). Welding was performed via local dry underwater laser welding (UWLW) using a custom-designed nozzle and a fiber laser at a water depth of 70 mm. The best weld quality was obtained in both underwater and in-air environments using 2 kW of laser power. To understand the relationship between the microstructure and corrosion resistance of 304ss in underwater laser welding (UWLW), this study was conducted using a custom-designed nozzle. The grain boundary analysis revealed that the specimen prepared by UWLW had high-angle grain boundaries content approximately 1.5 times higher than that of the specimen produced by in-air laser welding, and the fraction of the coincidence site lattice (CSL) boundaries was increased remarkably. High residual stress and microchromium precipitation were observed in the UWLW specimen, and the corrosion rate of the same at 2 kW laser power was considerably similar to that of the in-air laser weld specimen.