Effect of Welding Parameters on Mechanical Performance and Microstructural Characterization of Fiber Laser Oscillation Welded Dissimilar TWIP/304L Steel Joints

A dissimilar TWIP/304L joint was produced using oscillation fiber laser welding with welding speeds of 80 mm/s and 120 mm/s, as well as different power levels. Tensile tests, hardness measurements, and SEM/EDS/EBSD analyses were conducted to reveal the characterization of dissimilar TWIP/304L steel joint. Oscillation of the laser beam resulted in layered marks in the fusion zone. These layered marks contain primary austenitic dendrites and inertinitic secondary austenite. Both steels exhibited narrow heat-affected zones. An interlayer of an unmixed zone was formed between the fusion zone and the heat-affected zone of 304L due to differences in their liquidus points. Some intergranular gaps were observed in the heat-affected zone of the TWIP steel. The maximum tensile strength, 561.3 MPa, was achieved at a laser power of 3600 W and a welding speed of 80 mm/s. All specimens failed from the fusion zone of the dissimilar joint due to high hardness difference and underfill induced notch effect. The hardness difference reached 51.4 Hv10 due to the heterogeneous composition of the fusion zone. This variation in the microstructure resulted in both ductile and brittle fractures.