Effect of microstructure and microtexture modified by magnetic field on as-weld notch bending performance

Abstract

Abstract A 10 mm 316 L stainless steel, filled by 1.2 mm 316 LSi, was joined using multi-layer laser-GMAW in the presence of a constant magnetic field. Results suggested that the addition of a 18 m T magnetic field resulted in an optimized weld bead formation with asymmetrical fusion line and grain growth by stabilizing the arc morphology and droplet transfer in the narrow gap. The interaction of arc current and magnetic field differed in central and columnar zones with a moving heat source such that refinement was relatively obvious in the columnar zone. These two zones were dominated by high angle grain boundaries (HAGBs: 15°-60°) and the magnetic field potentially strengthen both the fraction and density. Due to the induced rotation and deflection behavior in austenite (γ) grain growth, the applied magnetic field progressively decreased the texture density of (010)[101] in columnar zones while altered (051)[6 1 - 5] , (032)[6 2 - 3] and (011)[3 2 - 2] to (001)[3 1 - 0] and (001)[1 2 - 0] in central zones. Refinement of γ grains was attributable to the fragment, rotation and deflection of ferrite and associated γ assemblies under axial torques induced by the magnetic field and arc current. Also, γ grain refinement and texture alternation of the central and columnar zones decrease the notch sensitivity of the weld bead. These results and findings suggested a novel means for improving the weld quality of thick plates with favorable microstructure and microtexture using an external magnetic field.