EFFECT OF A MAGNETIC FIELD ON THE MICROSTRUCTURE AND PROPERTIES OF A 22MnB5-CP780 WELDED JOINT

A steady-state magnetic field-assisted laser welding test of 1-mm-thick automotive 22MnB5 and CP780 high-strength steel plates was carried out using a low-power fiber laser. The effects of different magnetic induction intensities on the microstructure and mechanical properties of welded joints were investigated under a heat input of 150 J/mm. When no magnetic field was applied, there was splashing on the welded joint surface, the width was wide and the main solid-state phase transitions in the weld center included ferrite transformation and bainite transformation. The application of a magnetic field resulted in an acceleration of the cooling rate of the molten pool due to the thermoelectric magnetic force. This, in turn, led to the predominance of the bainite transformation and martensite transformation as the primary solid-state phase transitions in the weld center. In a range of 5–25 mT, the welded joints were narrow, symmetrical, well-formed and free of defects such as splashing. The experiment proved that as the magnetic induction intensity increased, the laser energy became more concentrated. This led to an increase in the average hardness at the center of the weld, a gradual reduction of the softening in the heat-affected zone and an increase in both the yield strength and elongation of the welded joint. The optimal comprehensive mechanical properties of the welded joints were observed when B = 25 mT.