Numerical analysis of thermal cycle characteristics and prediction of microstructure in multi-pass UWW

Underwater wet welding process has been widely used in assembling and maintaining marine structures, due to its economy and versatility. However, it is difficult to understand the physical phenomenon during wet welding, especially when water environment makes this fleeting process even more complicated. It is necessary to get a deeper understanding of wet welding process by numerical analysis and thus provide theoretical references for process selection. A customized experiment platform was set up for multi-pass wet welding of the grooved butt joint of E36 steel. Besides, a hybrid heat source consisting of double ellipsoid heat source and Gaussian heat source was selected for numerical analysis of multi-pass underwater wet welding. This paper introduced the pool boiling heat transfer theory in numerical simulation of underwater wet welding process and proved to be applicable. The results of numerical analysis show that the profiles of calculated molten pools match well with those obtained by the experiment. A notable effect of water environment on thermal cycle characteristics is especially demonstrated by the comparison of cooling time t8/5. In this study, the calculated t8/5 values near the fusion zone are lowered so markedly that a result of full martensite transformation can be expected in E36 steel, which coincides well with the actual microstructure in its heat-affected zone.