GTAW feasibility study on medium-Mn lightweight steel via overlay welding and butt-welding operations

Lightweight steels are under development aiming to application in automotive sector. Such alloys are featured by high Mn and Al content, high mechanical properties (up to 800 MPa of yield strength and up to 55 % of elongation at break) and low density (13 % lower than conventional stainless steel). Especially because of the application sector, the alloy weldability assessment is compelling. Due to the high content chemical elements different criticalities are expected, as Mn evaporation and κ-carbides precipitation. The former may lead to inhomogeneous chemical composition and so different microstructure and mechanical properties. The latter is usually exploit as strengthening method, but it may lead to excessive ductility loss. A novel austenitic with medium Mn lightweight steel alloy has been tested for the first time with Gas Tungsten Arc Welding with different configuration and different material conditions. Microstructure and mechanical properties of the welded joints has been investigated. Solid welded joints were obtained without porosity or hot-cracking. In the WZ, a dendritic duplex microstructure has been observed, while in the HAZ coarse fully austenitic grains have been detected. In the WZ a limited softening has been observed in the material after solubilization while in the hot rolled one, the difference is more marked. Uniaxial tensile test has highlighted the microporosity effect in the HR samples while it has provided good results in the SOL samples.