Research on fusion regulation mechanism of dissimilar steel welds based on compound magnetic field

Due to significant differences in the mechanical and physical properties of materials, low-alloy steel/stainless-steel joints by gas tungsten arc welding (GTAW) have welding quality problems such as incomplete penetration and cracking, which are caused by large variations in base metal fusion ratio. To address such issues, in this study, the effect of the regulation mechanism by a compound magnetic field approach (longitudinal magnetic field (LMF) + cusp magnetic field (CMF)) on the base metal fusion ratio in Q345/316L dissimilar metal welds was investigated, through arc behavior, weld formation, and microstructure evolution. The suppression methods of weld defects such as incomplete penetration are also discussed. It was found that compound magnetic field-assisted dissimilar steel welding can be used to control the base metal fusion ratio, effectively avoid defects due to incomplete weld penetration, and significantly improve the quality of dissimilar steel weldments. Compared with the sample without external magnetic field (EMF), as the exciting currents increased, the fusion ratio of Q345 in the dissimilar steel weld FR_Q345 gradually diminished from 34.15 % to 11.99 %; The fusion ratio of base metals FR_BMs gradually diminished from 46.55 % to 26.55 %; The content of brittle-phase martensite in the weld metal gradually decreased, and the content of residual austenite phase significantly increased. The dendrite arm spacing (DAS) was significantly reduced under the influence of the compound magnetic field, resulting in the refinement degree ranging from 32.58 % to 46.83 %. These results provide guidance for heat energy regulation in dissimilar steel welding and a new solution for improving the welding quality of dissimilar metals with asymmetric material properties.