Mechanical and microstructural evaluation of resistance spot welded dissimilar TWIP/martensitic steel joints
Abstract
AHSS grade dissimilar TWIP/martensitic steel joints were produced with resistance spot welding with different welding times and welding currents under 4-kN electrode force. The microstructures were examined with EDS, SEM, and XRD analyses. Fusion zone especially at high heat inputs exhibited considerable amount of shrinkage gaps and high Mn content-induced voids. (Fe, Mn)(x)C segregation behavior in heat-affected zone (HAZ) of TWIP was coincided. Segregation behavior adversely affected HAZ and limited tensile-shear force bearing capacity. Failure mode change from interfacial failure to nugget pullout failure mode was mainly controlled by the nugget size diameter. Tearing-type failure mode was not observed in all experiments. All nugget pullout separations were failed from the TWIP side due to segregation-induced intergranular gaps. Tensile-shear fracture surfaces were examined and MxC segregation-induced gaps were observed. The weld lobe was determined according to mechanical and geometrical calculations.