Effects of spatial welding positions on arc bubble behavior, droplet transfer process, and weld microstructure and properties in underwater wet welding

With the growth of the marine economy, underwater wet welding has become increasingly essential in marine engineering, especially for repairing large, thick-walled structures in non-horizontal positions. However, research on underwater welding in non-horizontal orientations remains limited. This study used high-speed imaging to observe the dynamic behavior of the arc and arc bubble, as well as the molten droplet transfer under various spatial positions, with the angle between the base metal and the horizontal plane as the variable. Results showed that, compared to flat welding, vertical welding significantly reduced arc stability, while overhead welding maintained higher stability due to sustained arc bubble protection. The change in spatial position introduced gravity as a resistance, causing molten droplets to fall off during vertical and overhead welding process, preventing them from entering the molten pool. This resulted in a loss of Cr and Ni elements from the filler material, transforming the weld metal from duplex stainless steel to ferritic steel. Vertical downward welding increased the weld metal hardness to 398.23 HV, while overhead welding formed a diffusion layer between the weld and heat-affected zone, consisting of martensite and ferrite, with a hardness exceeding 500 HV, but also numerous cracks. The results indicate that by appropriately adjusting the proportion of filler materials, it is possible to achieve underwater repair coatings or welded joints with a desirable combination of high hardness and corrosion resistance. This study reveals the droplet transfer processes and microstructural characteristics of welds in underwater wet welding at different spatial positions, providing valuable guidelines for underwater wet welding techniques under multi-positional welding conditions.