Microstructure and properties of steady magnetic field-assisted laser welded joints of CP780-TRIP590 steels

Tailored blank laser welding was performed on dissimilar automobile metals, i.e., CP780 and TRIP590 steels, by coupling laser welding with a steady-state magnetic field. Before magnetic field application, the weld seam center was mainly composed of proeutectoid ferrite, acicular ferrite, granular bainite, and upper bainite, whereas the heat-affected zone on both sides was mainly composed of lath martensite and lower bainite. Under the same heat-input conditions, magnetic field application makes the laser energy more concentrated and accelerates the crystallization process of the weld pool, reducing the width of welded joints. Therefore, lath martensite and lower bainite are generated in the weld seam center, and only martensite is generated in the heat-affected zone, while the grain size in the heat-affected zone on both sides is reduced. Under a heat input of 160 J mm(-1), the comprehensive mechanical properties of the welded joints exhibit the most significant improvement with a magnetic induction intensity of 20 mT.