Effect of V on the strengthening and fatigue behavior of a high-strength low-alloy steel welded joint

The development of high-strength low-alloy (HSLA) steels for structural applications, including wind towers, offshore structures and shipbuilding, requires a continuous effort to achieve the balance between high strength, toughness and weldability. During a multiple-pass welding, the intercritically reheated grain coarsened heat-affected zone (IC GC HAZ) represents the most brittle section of HSLA steels welds. The presence of microalloying elements in HSLA steels induces the formation of microstructural constituents, capable of improving the mechanical performance of welded joints, such as fatigue resistance and toughness. The scope of this study is to investigate the influence of vanadium addition on the behaviour of IC GC HAZ in S355 steel grade. Different welded samples were carried out by robotic Gas Metal Arc Welding (GMAW) process, involving multiple passes on high-thickness S355 steel plates, varying the addition of vanadium as a microalloying element. The results of the microstructural analysis reveal diverse microstructures, including bainite, martensite and pearlite-ferrite, present in both the heat-affected zone (HAZ) and the weld zone (WZ). Additionally, a discernible change in grain size is observed in the intercritical HAZ. Regarding the microhardness evaluation, it is evident that the presence of vanadium influences the behavior of this property, even showing minimal variation in the vanadium-enhanced weld root.