Effect of in-situ transverse magnetic field on the fluid flow, microstructure evolution and corrosion resistance of GMAW 316L stainless steel

Abstract

In order to modify heat and mass transfer, alter crystal orientation and suppress elemental segregation of the molten pool by electromagnetic stirring effect, a new in-situ transverse magnetic field generated by clamp-type electromagnet integrated with a 6-axis robot was firstly applied to real-time control the arc characteristic and fluid flow when welding 316L stainless steel by GMAW-CMT. As the magnetic field intensity at the end point of the wire increases from 0 mT to 14.6 mT and then 20.7 mT, the 316L welding bead morphology becomes flatter, and their cross sections clearly exhibit a lower welding reinforcement, a wider welding width and a smaller welding penetration. Microstructure observations show that the application of in-situ transverse magnetic field in GMAW-CMT process can contribute to the lower inner porosity, the smaller stress concentration, the more dispersed austenite grain orientation and the elimination of residual skeletal ferrite distributed in the austenite matrix. CPP and EIS tests indicate that 14.6 mT molten pool exhibits the highest pitting corrosion resistance and the most compact passive film, which is related with the finer cellular γ grain with dispersed orientation and less Cr-Mo atomic segregation on the boundary. The deflection of arc column and the fragmentation of dendritic tips induced by the Lorentz force under the appropriate transverse magnetic field are verified, which provides great potential for optimizing weldment performance.