Effect of the thermal field on the microstructure of dissimilar welded joints between TWIP steel and 2205 duplex stainless steel

Abstract

This study reported a theoretical-experimental analysis of dissimilar metals duplex stainless steel (DSS) grade 2205 and twinning induced plasticity (TWIP) steel joined. Welded joints were performed in autogenous mode and using filler metal (ER2209) by the pulsed gas tungsten arc welding (GTAW-P) process. Critical weld regions were characterized metallographically using LOM and SEM. Microstructural changes such as the morphology and contents of ferritic and austenitic phases were correlated to the temperature ranges estimated numerically by a finite element (FE) model, which considered the variation of the percentage dilution in the fusion zone (FZ). The average variation between experimental and numerical results was up to 6.75%. SEM chemical analysis and line scanning analysis corroborated the diffusion of Al, Mn, Cr and Ni in the FZ of the autogenous joint. Small concentration gradients promoted a homogenous chemical composition of the ferritic and austenitic phases in the filler metal joint. The FZ exhibited an austenitic phase coarsening due to the elevated temperatures (1506°C–1803 °C, DSS 2205 side). Wetting problems were observed in both weldments producing prominent interfaces between the welded metal (WM) and the heat-affected zone (HAZ). Other weld defects such as underfilling, undercuts and lack of fusion were also detected. When a high TWIP steel volume was melted (filler metal joint), WM hardness increased compared to the autogenous joint. The hardness increment (2–5% in the DSS 2205) combined with the lack of fusion brought about the failure of the filler metal joint during the bend test.