Grain refinement and orientation alternation of 10 mm 316L welds prepared by magnetic field assisted narrow gap laser-MIG hybrid welding

Abstract

The effect of vertical magnetic field on grain size and orientation of ferrite (δ) and austenite (γ) in welds of 10 mm 316L stainless steel were investigated during multilayer narrow gap laser-MIG hybrid welding. Results show that shapes of weld beads are changed by the ampere force from “T” to “V” and “▪”, which results from arc current and magnetic field. The optimized fusion boundary accelerates thermal diffusion and raises temperature gradient, which reduces duration of high temperature of δ-γ solid phase transition and heat affected zone (HAZ). As a result, δ-islands and reduction of HAZ are observed. At the meantime, the growth direction of γ grains are altered from preferred 〈100〉-crystal direction to maximum temperature gradient with the increase of temperature gradient. Moreover, vermicular, continuous and reticular δ dendrites are changed to be skeletal, deflected and seaweed-like in the interface and columnar zone under the effect of magnetic field. The occurrence of this phenomenon is associated with the joint effect of ampere force, viscous resistance and hot metal liquid. And the fragment of primary δ dendrites leads to the refinement of γ grains and increase of central zone.