The metallurgical behaviors and crystallographic characteristic on macro deformation mechanism of 316 L laser-MIG hybrid welded joint

A 10 mm 316 L stainless steel plate was joined using multi-layer laser-MIG hybrid welding. Results showed that unmixed zone and real fusion zone (FZ) existed near the fusion line. Frequently met dendritic ferrite (delta) and newly encountered spherical nanoscale particles trapped in austenite (gamma) were only observed in the latter region. Chemically, these particles turned out a SiO2 phase. From base metal to FZ, delta morphology was altered from originally linear to relatively diversely dendritic. Meantime, gamma exhibited a converse manner where previously randomly oriented equiaxed was replaced by coarse, columnar and textured. Accordingly, a comparably high Schmidt factor in gamma phase was obtained in FZ. Moreover, delta exhibited a relatively higher stress level than gamma which presented a decrease in residual stress with grain coarsening in heat affected zone. In FZ, delta fraction displayed a dramatical increase with special BCC-FCC orientation relations established. Finally, tensile test and fracture appearance implied that FZ was exactly the weakest link of the whole welded joint in spite of a qualified strength achieved. In summary, lack in Sigma 3, largely increased delta fraction, high Schmidt factor in gamma and especially being rich in SiO2 particles collectively led to the micro-void coalescence fracture in FZ. (C) 2020 The Authors. Published by Elsevier Ltd.