Microstructure evolution and mechanical performance of underwater local dry welded DSS metals at various simulated water depths

The phase balance, interface boundaries, and grain types were characterized in the local dry underwater welded DSS metals. The results showed that the austenite content of the weld metals decreased first, then increased and then decreased with the increase in the simulated water depth from 0.1 m to 75 m. The fractions of Sigma 3 austenite twin grain boundaries and recrystallized ferrite and austenite grains had a similar trend with the austenite content, while the change in the proportion of special ferrite-austenite interphase boundaries showed an opposite trend. The microstructure changes in the weld metal from 15 m to 45 m were more dramatic than those from 45 m to 75 m. The resultant mechanical performance was in good agreement with the microstructure evolution. More austenite content, Sigma 3 austenite twin grain boundaries and recrystallized grains made the plasticity and toughness of the weld metals better at 45 m and 75 m. The best plasticity and toughness performance was obtained in the weld metal at 45 m.