Microstructure and properties of magnetic field assisted laser wire-filled welded 22MnB5 steel joints

Abstract

Abstract The magnetic field-assisted laser wire-filled welding test of 1.5 mm automotive 22MnB5 steel is performed to investigate the influence of magnetic field on the microstructure and properties of the welded joints. When no magnetic field is applied, and the laser heat input is 190 J mm−1, the welded joint width and the grain size of the coarse grain region are large. Also, there is an obvious hump defect at the bottom of the weld. Under the same heat input conditions, when a 5 mT and 15 mT steady magnetic field is applied, the thermoelectric magnetic force generated by the magnetic field promoted the flow of molten pool and concentrated laser energy. It is found that the hump defect is eliminated, the width of the welded joint is reduced, the grain size of the coarse grain region is significantly reduced, and the overall hardness of the welded joint is improved. However, different magnetic induction intensities have different effects on the solid phase transformation of the weld. When no magnetic field is added, the weld center is mainly composed of granular bainite and polygonal ferrite due to the slow cooling rate of the molten pool. When the applied magnetic field is 5 mT, the center of the weld is mainly composed of brittle and hard upper bainite because the thermoelectric magnetic force stirs the molten pool and accelerates the cooling rate of the molten pool but the overall mechanical properties of the welded joint were relatively poor. At 15 mT, lath martensite and lower bainite predominate in the weld center due to the increased cooling rate of the molten pool, thereby increasing the overall mechanical properties of the welded joint. Therefore, choosing the appropriate magnetic induction intensity is critical for improving the microstructure and properties of welded joints.