Mechanical performance and formability of laser-welded dissimilar butt joints between medium-Mn stainless steel and high-strength carbon steel

The mechanical performance and stretch formability of dissimilar butt joints between medium-Mn stainless steel (MMn-SS) and high-strength carbon steel (HS-CS) processed by laser welding using different parameters were studied under uniaxial and biaxial loadings applied by tensile and Erichsen cupping tests, respectively. Laser scanning microscopy and electron backscatter diffraction (EBSD) were used to study the microstructural evolution. An electron probe microanalyzer (EPMA) was employed to analyse the distribution of alloying elements within the weld zone. The dominating deformation mechanisms operating in the paired metals during stretch-forming were identified through EBSD analysis. The study revealed that a fully martensitic microstructure is promoted in the fusion zones (FZs) of the weldments processed with low and high specific point energy (SPE 19, 25, and 30 J). Consequently, hardness values of the FZs were slightly decreased with SPE. Similarly, tensile properties were not affected since failure occurred at the softer base metal HS-CS. During stretch-forming deformation by Erichsen cupping tests, the dissimilar metals exhibited various operating deformation mechanisms. The formation of shear bands (SBs) and strain-induced martensite along the SBs were observed to be the biaxial strain-induced microstructural features in the MMn-SS. However, the HS-CS was deformed by the general deformation mode, i.e., dislocation-mediated plasticity.