A novel approach of ultra-low diffusible hydrogen welding wire for underwater wet flux-cored arc welding: a spontaneous barrier of molten slag

In underwater wet welding, a hydrogen-rich arc atmosphere generated by the thermal decomposition of water leads to extremely high diffusible hydrogen content and defects such as pores and cracks in the weld. In the present study, a neutral slag system was designed and verified for its protection in underwater wet flux-cored arc welding. This neutral slag system forms a stable protective layer of molten salt on the surface of the molten pool, mechanically isolating the molten metal from the water environment and effectively delaying heat loss. More crucially, it also retained the chemical metallurgical dehydrogenation component. When pure Ni belt was used as the outer metal, weld joints free of porosity were obtained, and the diffusible hydrogen content of the deposited metal was 3.61 mL/100 g, close to the level of onshore welding. This neutral slag system was further extended to the use of a pure Fe belt, where the diffused hydrogen content of the molten metal was 10.40 mL/100 g.