Effect of heat input on microstructure and mechanical properties in underwater wet flux-cored arc welding of structural steels

In recent years, the researches have been leaning towards the use of the wet welding process using the self-shielded flux-cored arc welding (FCAW-S) due to its higher productivity. Processing parameters such as welding current (I), arc voltage (E) and welding speed (v) notably determine the final microstructure and resulting mechanical properties of underwater wet welds. In this research work, the effect of the heat input generated by experimental underwater wet welding using the FCAW-S process on the microstructure and microhardness of weld beads made on ASTM A36 steel plates is investigated. For this purpose, experimental underwater welding tests were carried out in a special tank containing 30 cm of water column using three levels of heat input (578, 694 and 1074 J/mm) and a commercial filler metal (AWS E71T-GS). The microstructure and mechanical properties of the weld beads obtained were characterized by scanning electron microscopy (SEM) and Vickers hardness tests, respectively. In general, the experimental results show that the microstructure in both heat-affected zone (HAZ) and fusion zone (FZ) is basically constituted by martensite (M) for the three energy levels studied, which is related to the high cooling rates involved in the underwater welding processes. In addition, the mechanical properties reveal that the hardness values decrease with the increase in heat input due that increasing the ratio decreases the cooling rate and the martensite resulting is less hard. Finally, it is concluded that it is necessary to change the filler metal or looking for better parameters configuration to obtain higher heat input and change de microstructure in the fusion zone (FZ) to improve the mechanical properties in the welded component. Graphical abstract: [Figure not available: see fulltext.]