Microstructure and Properties of 2205 Duplex Stainless Steel Welded by Local Dry Underwater Laser with Adjustable Ring-Mode

To address the issues of rapid cooling rate during the solidification in underwater welding and the deterioration of the microstructure and properties, this work conducted local dry underwater welding experiments on 2205 duplex stainless steel using adjustable ring-mode laser. Meanwhile, compared with in-air welds, the effects of the power ratio between center and ring lasers on weld formation, microstructure and mechanical properties were investigated. The results show that the center laser mainly affects the penetration depth. With the increase in proportion of central power, the oxidation degree and surface roughness of the weld become more severe. In terms of microstructure, the underwater weld exhibits an increase in Widmanstätten austenite content, but a decrease in or even disappearance of intragranular austenite, compared to welds produced with the same parameters in air. With the increase in proportion of ring laser, the austenite content in the weld shows no significant change, the grain size and aspect ratio of the weld decrease, the directionality of columnar crystal growth on both sides of the weld weakens, and the number of low-angle grain boundary increases. In terms of performance, the underwater joints exhibit slightly higher tensile strength but lower elongation than those welds in air. As the proportion of ring laser power increases from 1/3 to 2/3, the elongation of underwater joints increases by about 50%.