Role of vanadium in welding of flat products in high strength low alloyed steels: microstructure and mechanical properties

The use of High Strength Low-Alloy (HSLA) steels in structural applications requires detailed analysis of their microstructure to optimize the strength and toughness of welded joints. During multi-pass welding, thermal cycling generates a complex heat-affected zone (HAZ) with subregions containing brittle phases that can compromise mechanical strength. This study evaluates the effect of vanadium and niobium additions on the HAZ microstructure in 15 mm thick S355 steel welds produced by robotic GMAW welding. The results reveal a heterogeneous microstructure with ferrite of several morphologies, bainite, and martensite/austenite (M/A) islands. The presence of vanadium reduces the solubility of carbon during phase transformations, favoring the formation of ultrafine precipitates (∼11 nm) and reducing the M/A phase in the high vanadium (0.1 wt%) variant. Nevertheless, the micro-alloyed variants improve mechanical strength (yield and ultimate strength) without loss of ductility or fatigue resistance, exhibiting a stress dissipation behavior that favors resistance to crack propagation.