Microstructural and mechanical performance of underwater wet welded S355 steel

Underwater wet shielded metal-arc welding using three heat inputs were investigated. The columnar microstructures in weld metal contain large amounts of ferrite with second phase aligned and grain boundary ferrite, and some polygonal ferrite and acicular ferrite. The coarse grain heat affected zone (CGHAZ) is dominated by lath martensite and some bainite. The microstructure evolution of the reheated columnar region and CGHAZ is discussed to explain the beneficial effect of temper bead. The unaltered CGHAZ in the top layer is the most preferential sites for cold cracks due to the lack of tempering. Although large heat input can reduce the hardness and the susceptibility of cold cracking, it also degrades the mechanical performance of weld metal owing to the microstructure coarsening and less reheated regions.