Effect of microstructure tailoring on the deformation coordination of welded duplex stainless steel

With the improvement of the strength of stainless steel, the proportion of stainless steel used for structural components has increased significantly, and the welding problem has become increasingly important. In this study, the microstructure features of gas tungsten arc welding (GTAW) welded duplex stainless steel (DSS) before and after deformation were characterized by scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and nanoindentation. The results show that base metal (BM) consists of bimodal ferrite grains and fine austenite grains while weld zone (WZ) features fine acicular austenite grains scatter between irregularly shaped ferrite. Coarse equiaxed ferrite grains were observed in heat affected zone (HAZ) which have a relatively poor capacity for dislocation multiplication and storage. The appropriate distribution of fine delta-ferrite and gamma-austenite and almost no precipitate together guarantee the high yield strength (768.6 MPa), ultimate tensile strength (935 MPa), and enough plasticity (total elongation 32.6%) for the welded DSS. Fractography presents that welded DSS is in ductile rupture mode composed of various dimple patterns in the different regions. The drop in the elongation of welded DSS is attributed to the weakened deformation coordination involving dislo-cation slipping and multiplication. Investigating the microstructure origin related to the mechanical properties of welded joint may provide ideas for improving the welding process from the microstructure design level.