Welding of S960QL High-Strength Steel by the Manual–Automated MAG Technique—A Study of Mechanical Properties, Residual Stresses and Fracture Mechanisms in the Heat-Affected Zone

This paper presents results of investigations of a V-type welded joint made of S960QL high-strength steel made using a mixed technique: the root was welded manually and the face automatically. Although high-strength steels have been available on the market for many years, they are still the subject of research due to their increasingly widespread usage. For this reason, detailed investigations of welded joints of S960QL steel were carried out in terms of microstructure, microhardness, impact toughness and residual stresses, in order to expand knowledge in this area. The obtained results made it possible to determine their changes in heat-affected zone (HAZ) as a function of the distance from the fusion line. One of the most important findings is that during the tensile tests, the rupture occurred in the sub-zone of HAZ, which is characterized by increased strength and low ductility. This was due to the fact that an unfavorable residual stress distribution occurred in this area, causing the highest initial local strain of the material. Furthermore, different fracture mechanisms, both ductile and brittle, as well as mixed, were observed and described in detail for each sub-zone of the HAZ and in the weld.