Microstructure Distribution and Mechanical Properties of Ultra-High Power Laser-Mig Hybrid Weld of 316l Stainless Steel Thick Plate

Ultra-high power laser-MIG hybrid welding is adopted to weld thick 316L stainless steel plates using single-pass under the optimized process parameters. The microstructure distribution and mechanical properties along the thickness direction are investigated. Three parts has been divided along the thickness, including the upper layer (UL), middle layer (ML) and lower layer (LL). Results show that the growth direction and morphollogical features of grains will change significantly along the thickness direction. The grains size of ML and LL are significantly refined when compared with UL. Interestingly, a “teardrop-like” morphology is formed in LL and the growth direction of dendrites start at the “teardrop-like” boundary and eventually point to weld center. Besides, the refinement of average grain size and increasement of δ-ferrite in weld center along the thickness direction will enhance the micro-hardness. UL exhibits the highest tensile strength (551.57 MPa) when compares with ML (536.85 MPa) and LL (527.39 MPa). Although tiny shrinkage cavity will be formed in LL, the joints efficiency still can reach more than 95% of base metal (BM). Additionally, the LL presents excellent toughness because the smaller grain size will produce the greater resistance to crack formation and propagation. All specimens exhibit qualified mechanical performance, which indicates that ultra-high power laser-MIG hybrid welding can achieve high-quality welding of thick plates and meet the industry requirements.