Effects of magnetic field and post-weld heat treatment on microstructure and properties of laser welded joints of 22MnB5-TRIP590 steel

Laser welding without and with an auxiliary magnetic field (B = 30 mT) is performed on 22MnB5-TRIP590 steel. Subsequently, post-weld heat treatment, involving quenching at 800 degrees C followed by tempering at 200 degrees C, is carried out on the welded joints prepared by these two welding processes (B = 0 mT, B = 30 mT). This study examines the improvement of microstructures and mechanical properties of the welded joints by applying the magnetic field (B = 30 mT). Furthermore, this research investigates whether these enhanced characteristics of the welded joints persist after post-weld heat treatment. When the magnetic field is applied, the overall width of the welded joint is significantly reduced, and the microstructure of the weld is changed mainly from proeutectoid ferrite, granular bainite, and upper bainite to lath martensite and lower bainite. Furthermore, the grains in the coarse grain zone are refined, and the plasticity and overall hardness of the welded joint are considerably improved. After post-weld heat treatment, the weld and coarse grain zone of both welded joints (B = 0 mT, B = 30 mT) are mainly tempered martensite, and the tensile strength and overall hardness are significantly improved compared to those without post-weld heat treatment. Although the plasticity of two welded joints is lower than that of two unheated-treated welded joints, the fracture positions are all at the base metal and are both ductile fractures. The improved characteristics, such as optimized macro-morphology, refined grain morphology, improved plasticity, welded joint efficiency, and weld hardness of magnetic field-assisted laser welded joint, are all retained after post-weld heat treatment. A thorough comparison reveals that the magnetic field-assisted laser welded joint with post-weld heat treatment has better comprehensive mechanical properties.