Metallographic, structural and mechanical characterization of welded plates of an austenitic Fe-31Mn-8Al-1.9C low-density steel

The automotive industry has made significant efforts reducing component weight to improve fuel efficiency. Recently, low-density (LD) steels have gained importance due to their lower density and good combination of high strength and elongation. However, the welding of these steels implies challenges due to concurrent phase transformations, second-phase precipitation and chemical segregation which generate hot-cracking and embrittlement. Accordingly, this work examines the microstructural changes in different welding zones of an austenitic Fe-31Mn-8Al-1.9C LD steel welded by gas tungsten arc welding (GTAW) process and their impact on the mechanical behavior. Characterization techniques included light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness Vickers (HV), and micro-tensile tests. Results showed a dendritic structure in the fusion zone (FZ); and equiaxed/deformed grains and \(\kappa\) $\kappa$ -carbides in the heat-affected zones (HAZ-1 and HAZ-2). The lowest and highest yield strength (YS) and ultimate tensile strength (UTS) values were found in the FZ and HAZ-2 zones, respectively. The lowest elongation was found in the HAZ-1 zone and the highest microhardness values were found near the fracture zone.