EBSD study on magnetic field altering crystal texture and grain growth during laser-hybrid welding

Abstract

In this study, evolutions of austenite and ferrite microstructures and relevant variations of performances were analyzed during laser-arc welding 316L austenitic stainless steel with a magnetic field. For austenite grains, the magnetic field gave rise to grain refinement in columnar zones, grain coarsening in central zones and discontinuous grain growth at interfacial zones. For ferrite dendrites, the magnetic field suppressed the concentrated growth, side-branched irregular morphology as well as orientation deflections across the weld. Results indicated that grain refinement, increased boundary disorientation and reduced residual strain enhanced the tensile strength, lowered brittleness and cracking susceptibility. Furthermore, variations of current, supercooling and electromagnetic stirring were analyzed at 0mT and 18mT magnetic intensities. At 0mT, current first increased and then decreased, attaining the highest in the columnar zone while supercooling rose in a steady form. At 18mT, the enhanced heat diffusion induced by fusion line variation lowered the supercooling and inhibited the columnar-to-equiaxed behavior while electromagnetic stirring reached the highest in columnar zones. Therefore, grain refinement was observed in columnar zones while coarsening in central zones at 18mT. In the interfacial zone, continuous and directional growth was achieved by the current at 0mT while grain refinement and growth deflection by electromagnetic stirring.