Microstructural and mechanical analysis of double pass dissimilar welds of twinning induced plasticity steel to austenitic/duplex stainless steels

Double pass dissimilar welds between the twinning induced plasticity (TWIP) steel and austenitic stainless steel (ASS) AISI 304 L and duplex stainless steel (DSS) 2205 were studied theoretically and experimentally. A finite element (FE) thermal model linked to the liquid fraction calculation was used to estimate the optimal heat input level. The metallographic characterization of dissimilar weldments TWIP-SS 304 L and TWIP-DSS 2205 disclosed a priori the lack of hot cracking in the fusion zone (FZ) and liquation cracks in the heat-affected zone (HAZ). Later, the root bend test results corroborated a lack of fusion in the FZ-HAZ interface of the TWIP-DSS 2205 weld (TWIP steel side). The FE model predicted the heat accumulation in the SS 304 L and DSS 2205, which produced variation in the thermal gradient. The thermal gradient changes induced the ferritic-austenitic (FA) solidification mode in TWIP steel and SS 304 L and the massive austenite formation by epitaxial growth in the FZ-HAZ interface of the DSS 2205 side. Microhardness profiles corroborated the formation of homogenous FZs in both dissimilar welded joints. The microhardness increase/decrease was related to the solidification mode change in the FZ-HAZ interface. The mechanical strength and ductility of the TWIP-SS 304 L weld decreased 26% and 40%, respectively, compared to the reference autogenous similar weldment SS 304 L. The planar solidification growth detected in the FZ-HAZ interface was responsible for mechanical properties loss.