Effect of water flow on the microstructure, mechanical performance, and cracking susceptibility of underwater wet welded Q235 and E40 steel

Underwater wet flux-cored arc welding was investigated varying water flow velocities. Q235 and E40 steel, which have different carbon equivalent (CE) values, were used for these experiments. At the same flow conditions, the joint with E40 (a higher CE value steel) contained more side plate ferrite, acicular ferrite, and even martensite microstructures in the weld metal. The coarse grain heat-affected zone (CGHAZ) in the Q235 joints was dominated by Widmanstatten ferrite and some bainite, while lath martensite and acicular martensite were dominant in E40 joints. The side plate ferrite in the weld metal and acicular martensite in the CGHAZ were the most probable locations for the formation of cold cracks owing to their brittle characteristics. In the E40 weld joints, the mechanical properties showed a slight increase initially and then decreased dramatically with increasing flow velocity. In this study, the joints with higher CE values demonstrated a higher susceptibility for cold cracking, resulting in narrower process parameter ranges limited by cold cracking in the underwater environment.