Investigation on high Mn austenitic lightweight steels weldability via GTAW overlay welding and butt-welding operations

Abstract

Lightweight steels are currently under development for potential applications in the transportation sector. These alloys are characterized by high manganese (Mn) and aluminium (Al) content, exceptional mechanical properties (yield strength up to 800 MPa and elongation at break up to 55 %), and reduced density (approximately 16 % lower than conventional stainless steel). Due to the demands of the application sector, a thorough assessment of the alloy’s weldability is crucial. The high concentration of chemical elements in these steels leads to critical phenomena, notably Mn evaporation and κ-carbide precipitation, both of which can significantly influence the microstructure. Mn evaporation may result in an inhomogeneous chemical composition, leading to variations in microstructure and mechanical properties. κ-carbide precipitation, while typically utilized as a strengthening mechanism, may cause an undesirable reduction in ductility. A lightweight austenitic steel alloy with high Mn content was evaluated using Gas Tungsten Arc Welding (GTAW) under various configurations and material conditions. The microstructure and mechanical properties of the welded joints were analysed. Sound welded joints free from porosity and hot cracking were achieved. In the fusion zone, a duplex structure with dendritic morphology was observed, while the heat-affected zone (HAZ) exhibited coarse grains. The fusion zone demonstrated low hardness values, and no hardness peaks associated with κ-carbides were detected in the HAZ. Despite similarities in microstructure and welding parameters, mechanical testing revealed that direct current (DC) samples exhibited superior ductility compared to alternating current (AC) samples.