Effect of microstructure on the hardness heterogeneity of dissimilar metal joints between 316L stainless steel and SS400 steel

The dissimilar weld joints between 316L austenitic stainless steel and SS400 ferritic steel were used to investigate the effect that microstructure exerts on hardness heterogeneity in weld joints. In order to identify the constituent phases and deformation mechanisms in the dissimilar weld joints, microstructure characterization of undeformed and deformed specimens was conducted via optical microscope (OM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) techniques. Micro-hardness measurements across the different weld regions and mini-tension testing combined with digital image correlation (DIC) were conducted to evaluate the mechanical properties of the base metals (BMs), the weld zone (WZ), and the heat-affected zone (HAZ). Local strain heterogeneity on deformed specimens was also explained by microstructure heterogeneity in terms of grain morphology and constituent phases. Non-uniform enhancements of the strain distributions were distinct in the WZ, which consisted of a dendritic structure with a irregular morphologies. Uneven patterns of a martensite transformation from γ to α′ in the 316L contributed to localized heterogeneity in the strain distribution.