Microstructural and mechanical characterization of a Ti-containing TWIP steel welded joint through GTAW process

Abstract

The aim herein is to study the microstructural and mechanical changes generated in a welded joint of Ti-containing twinning-induced plasticity (TWIP) steel by the gas tungsten arc welding (GTAW) process. For this purpose, the welding parameters that allow the union of 5.6¿mm-thick butt plates with full penetration and without filler material are investigated. Microstructural changes are examined by light optical metallography. Segregation and second-phase precipitated particles are investigated by scanning electron microscopy and electron-dispersive spectroscopy. Phase transformations are evaluated using X-ray diffraction. Finally, the mechanical behavior is assessed by Vickers microhardness and microtensile tests. In general, the welded joint shows dendritic structure formations in the fusion zone (FZ) and equiaxed grain growth in the heat-affected zone (HAZ). The FZ shows a high degree of segregation, where Mn, Si, and C segregate in the interdendritic regions, whereas Al preferentially segregates in dendritic areas. In contrast, no effect on austenite stability is noticed. The welded joint shows an increase in microhardness, which is associated with the formation of precipitated particles. Finally, the microtensile results show a decrease in ultimate tensile strength (UTS) in the FZ, whereas the welding interface and HAZ show an increase in UTS compared with the base material.