A novel underwater submerged-arc welding acquires sound quality joints for high strength marine steel

[Display omitted] •The underwater submerged-arc welding (USAW) process was innovatively developed.•A mixture of epoxy resin and submerged-arc flux was employed.•The process stability and weld formation was enhanced.•Weld metal microstructure consists of pro-eutectoid ferrite and acicular ferrite.•The comprehensive mechanical properties of joints were greatly improved. The serious interferences from the surrounding water severely limit the process stability and joint quality of the current underwater welding technologies. To effectively isolate the welding area, a mixture of epoxy resin and submerged-arc flux was innovatively prepositioned in the welding area during underwater welding process. Butt welding experiments of a typical high strength marine steel were conducted to verify the advantages of this technique. Compared with the traditional underwater wet welding, underwater submerged-arc welding significantly optimized the arc burning environment due to the covering and isolation, which effectively improved the stability of welding process. Defectless joints with microstructure that full of fine acicular ferrite and high-quality mechanical properties, especially, outstanding performance of ultimate strength and plasticity were obtained. The results are expected to positively widen the practical application of underwater welding in many water related industries.