Study on mechanical properties of high-strength steel butt-welded joints

Compared with normal-strength steel butt-welded joint, high-strength steel butt-welded joint has more complicated mechanical properties. Four different material zones, including hardened heat-affected zone (HHAZ), softened heat-affected zone (SHAZ), welding material zone (WM), and base metal zone (BM) might be generated after welding, exhibiting different material properties. The global performance of the high-strength steel butt-welded joint is influenced by the material properties of these four zones. However, because of the limited size of these zones in a butt-welded joint, it is difficult to obtain their material behavior and determine their effects on the global mechanical properties of the butt-welded joint. In this research, using the notched tensile specimens, the loading and deformation capacities of HHAZ, SHAZ, WM, and BM in the butt-welded joint made of Q550 and Q690 steels respectively and their strength-matching welding materials were first experimentally studied. Then, the stress-strain behaviors of different zones were obtained using the numerical approach together with notched specimen test data. The obtained material properties of each zone in the steel butt-welded joint were used to numerically determine the strength of high-strength steel butt-welded joints. The numerically predicted strengths of the butt-welded joints were further validated by the experiment results. According to this research, for a given heat input energy and geometry, the strength of SHAZ in high-strength steel butt-welded joint were deteriorated, compared with that of base metal. Due to the constraining effects from WM and HHAZ, the strength of the high-strength butt-welded joint was lower than that of the base metal but higher than that of SHAZ.