Laser Hybrid Welding of WAAM-Fabricated Dissimilar Steels: Microstructural Evolution and Mechanical Performance of AISI 308L and ER70S-6 Joints with 316L Filler

In this study, dissimilar stainless steel (AISI 308L stainless steel) and low-alloy steel (ER70S-6) plates fabricated via Wire Arc Additive Manufacturing were joined using Laser Hybrid Welding with AISI 316L stainless steel filler wire. Four welding parameter sets were tested by varying laser power (1000-1500 W) and Laser scanning speed (1000-1500 mm/min). Microstructural analysis using Scanning Electron Microscopy, Electron Backscatter Diffraction, and x-ray Diffraction revealed significant phase transformations in the weld zone, including the formation of δ-ferrite and γ-austenite, with retained δ-ferrite decreasing at higher laser powers. The welds exhibited refined grain structures, especially at the fusion boundaries and heat-affected zone, with Electron Backscatter Diffraction measured grain sizes of 5.13 ± 1 μm (ER70S-6 heat-affected zone), 16.33 ± 5 μm (316L weld), and 10.09 ± 6 μm (weld center). Maximum microhardness values reached 303 HV in the heat-affected zone of 308L, 297 HV in ER70S-6, and 245 HV in the weld center. Tensile testing showed a 43% increase in strength for the sample welded at 1500 W and 1000 mm/min compared to lower heat input conditions, confirming improved ductility and joint integrity. These findings demonstrate the feasibility and effectiveness of Laser Hybrid Welding for producing robust joints between wire arc additive manufacturing-fabricated dissimilar steels with enhanced mechanical and microstructural performance.