Local dry underwater welding of 304 stainless steel based on a microdrain cover

To improve the performance of the underwater dry welding repair process in nuclear spent fuel pools, a microdrain cover based on the shrinkage nozzle principle with a dual air curtain structure was designed, and a welding process was performed for investigation. American Iron and Steel Institute (AISI) 304 stainless steel was used as the base metal, and 14 sets of direct current (DC) pulse gas-shielded underwater welding experiments with different parameters were conducted. The water depth of the welding experiment was 40 cm. The main analysis included the weld formation, microstructure and microhardness as well as the mechanical properties of the weld, and the best experimental parameters were selected. A stable underwater welding process was achieved by using the microdrain cover combined with the optimized welding parameters. The weld width was uniform, the reinforcement height was moderate, there were almost no defects, and no porosity were observed. Austenite was the matrix structure of the weld zone, and the grain boundary was mixed with a certain amount of delta-ferrite, thereby showing a good corrosion resistance. Tensile fracturing occurred in the heat-affected zone (HAZ), the average yield strength exceeded 500 MPa, and the fracture displayed dimples.