Microstructural characterization of welded plates of austenitic low-density Fe-Mn-Al-C steels microalloyed with Ti/B and Ce/La

Abstract

The excellent combination of tensile strength and elongation of low-density (LD) steels of the Fe-Mn-Al-C system has generated great interest in the metallurgical field. The need to understand the effects produced by welding processes has increased the studies carried out on the weldability of LD steels. Researchers have focused their attention on the weldability issues of LD steels, which occur due to the high Mn, Al, and C contents and their harmful effects in welded joints, such as segregation, hot cracking, and phase transformations, which, in turn, may decrease mechanical resistance. The main objective of this research work is to study the microstructural and mechanical behavior of the fusion zone (FZ) and different heat-affected zones (HAZs) generated by the welding of Fe-31Mn-8Al-1.9 C, Fe-31Mn-8Al-1.9C-Ce/La, and Fe-27Mn-7Al-1.2C-Ti/B austenitic LD steels in 3.5 mm thickness plates through an autogenous GTAW process. The welded plates were mechanically, metallographicaly, and structurally characterized by means of Vickers microhardness (HV), light optical microscopy (LOM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results exhibited strong variations in the microhardness profile of the welded joint, particularly in the heat-affected zones. The lowest hardness values (≈ 250 HV) were found in the FZ, which was associated with the dendritic structure. The HAZ-1 near to the FZ showed hardness values in the range of 300–375 HV, whereas HAZ-2 furthest from the FZ showed the highest hardness values (up to 430 HV), which could be associated with moderate and high κ-carbide precipitation with modulated structure, respectively. The welded joints of the LD steels under study did not exhibit cracking and showed austenite as the main phase, as well as low presence of α-ferrite, κ-carbides, and β-Mn.