Study on Microstructure-Property Relationship of Inconel 617 Alloy/304L SS Steel Dissimilar Welds Joint

Abstract

Welding of Inconel 617 (IN617) alloy and austenitic 304L SS steel has been attempted using the autogenous Laser Beam Welding (LBW) process. Characterization of dissimilar weldments was performed on either side of the fusion boundaries. The metallographic results showed that the inhomogeneous microstructure formation for weld metal contained columnar and cellular dendrites near the interface, whilst the columnar, cellular, and equiaxed types of dendrites were in the weld center. The energy dispersive spectroscopy (EDS) and electron probe microanalysis (EPMA) studies revealed the white layer near the interface on both sides of the fusion line, as well as a significant change in the concentration of alloying elements (Fe, Cr, Ni, Co, and Mo). The weld metal accompanied by Cr, Ti, and Mo precipitates evolved in the inter-dendritic spaces. The Cr and Mo-rich M23C6 and Mo-rich M6C phases in IN617 heat-affected zone (HAZ) were found in SEM/EDS and EPMA studies. The 304L SS side showed a distinct HAZ, whilst, on the IN617 side, no distinct HAZ was seen. Samples were prepared from the dissimilar weldments to evaluate their mechanical properties, such as tensile strength and hardness. The microhardness plot showed the non-uniformity in hardness along the weldments. The weld metal hardness was 253 ± 10 HV. The tensile test of the welded joint results was compared with the base metals. The tested results exhibited that the failure of the specimen from 304L SS base metal (BM) or from weld metal with tensile strength was marginally lower than the Inconel 617 base metal but significantly higher than the 304L SS BM. The fracture surface study revealed the presence of Mo and Cr segregation in inter-dendritic spaces, which impoverished the tensile properties. The order of impact toughness was measured as follows: 304L SS BM > 304L SS HAZ > IN617 BM > weld metal > IN617 HAZ. The IN617 HAZ was recognized as the weakest area of the weldments in terms of impact strength. The welded joint was considered safe for AUSC application because the stress-rupture properties were evaluated in between base metals data.