EBSD observations of microstructural features and mechanical assessment of INCOLOY 825 alloy/AISI 321 stainless steel dissimilar welds

Abstract

In this research the microstructure evolution and mechanical behavior of dissimilar weld between AISI 321 stainless steel (SS) and INCOLOY 825 using ERNiCrMo-3 (Inconel 625) filler wire were investigated. Electron back scattered diffraction (EBSD) analysis was used to characterize the weld substructure. The microstructural examination exhibited an austenitic matrix in either of the two base materials in which formation of Ti-bearing precipitates, more often with cubic morphology, were unveiled. An incomplete transformation of ferrite to austenite led to a significant accumulation of δ-ferrite at the heat affected zone (HAZ) of AISI 321 SS. An entirely austenitic structure accompanied by evidences of secondary phases, rich in Mo and Nb, at the inter-dendritic spaces in the weld metal were observed. Some columnar grains showed the <001> direction parallel to the normal direction relationship. The grain orientation spread map indicated that misorientation variations within the weld metal grains were significantly higher than those of the base metals and HAZs. Texture intensities of HAZs were relatively low. The abnormal grain growth observed in INCOLOY 825 HAZ had a significant effect on orientations of the austenite grains. However, it did not weaken the tensile strength of the weldment. Tensile specimen failure from SS side indicated that this material was more feeble comparing to the INCOLOY one and the weld area. Presence of brittle phases at the inter-dendritic spaces led to a fall in the weld impact toughness in comparison with the parent materials.