Microstructure and Properties of Local Dry Underwater TIG Welded 304L Stainless Steel

To address the need for in‐service repair of underwater facilities, this study developed a double‐chamber local dry underwater TIG patch welding system for 304L stainless steel. The microstructures and properties of welds produced in air and underwater environments were systematically compared. The results showed that both welds exhibited continuous, defect‐free bead appearances, whereas the underwater weld exhibited reduced surface oxidation compared with the air‐environment weld. Rapid underwater cooling promoted the transformation of δ‐ferrite from a coarse skeletal morphology to a fine lath‐like structure. Meanwhile, the proportion of austenitic columnar grains increased, whereas the fraction of equiaxed grains decreased. The average grain size was refined to 39.54 μm, the fraction of low‐angle grain boundaries increased to 35.7%, and the average kernel average misorientation value increased to 0.265°. The texture intensity of ferrite increased to 23.71, whereas that of austenite decreased to 13.34. Furthermore, rapid underwater cooling enhanced weld hardness and suppressed elemental redistribution, while reducing Mo volatilization. The underwater weld exhibited a corrosion current density of 2.12 × 10 −6 A cm −2 and a corrosion potential of −0.262 V. A smaller capacitive arc radius in the electrochemical impedance spectrum indicated lower corrosion resistance compared with the air‐environment weld. This study elucidates the process–microstructure–property relationships in local dry underwater TIG patch welding, providing experimental evidence and mechanistic insight into the welding metallurgy of 304L stainless steel.