Effect of longitudinal magnetic fields on the grain growth of hollow stud welded joints

In this study, a drawing arc stud welding method combined with a longitudinal magnetic field was used for welding a 30CrNi3MoV low-alloy super strong steel substrate and Q235 hollow steel, and the effects of a longitudinal magnetic field on the microstructure growth process and mechanical properties of stud welds were studied. The results show that an arc controlled by a longitudinal magnetic field stirred the molten pool continuously, reducing the number of coarse proeutectoid ferrite, increasing the proportion of acicular ferrite, and smoothing the transition of alloyed elements near the weld joint fusion line within a certain range of excitation current. Under the action of the magnetic field, the weld grain size was refined from 4.30 μm to 3.14 μm, and the proportion of large-angle grain boundaries in the weld area increased from 24.27% to 34.2%. After the magnetic field application, the toughness of the welded joint was significantly improved. With an increase in the excitation current, the shear strength of the joint first increased and then decreased to 312 Mpa. Similarly, the impact toughness of the joint first increased and then decreased to 31.88 J·cm−2