Structural integrity and corrosion behavior assessment of the dissimilar gas tungsten arc welded joint of sDSS 2507/ IN625 superalloy

Abstract

This study investigates the effect of filler materials on the structural integrity of dissimilar welded joints (sDSS 2507/IN625) employed in marine subsea manifold applications. Multi-pass gas tungsten arc welding (GTAW) using ER2594 and ERNiCrMo-3 fillers investigates microstructure evolution, solidification mechanisms, mechanical characteristics, residual stresses, and corrosion behavior. Optical and scanning electron microscopy revealed an unmixed zone (peninsula/island-shaped) at the weld interface and weld zone (WZ) in both filler weldments. Segregation of Mo, Nb, and Ni was observed in the interdendritic region of ERNiCrMo-3 filler WZ, whereas the skeletal ferrite matrix of ER2594 filler WZ revealed the existence of the Laves phase (Fe2Nb form). Electron beam scattered diffraction (EBSD) investigation showed austenitic solidification for ERNiCrMo-3 and fully ferritic solidification for ER2594 with distinct dendrite formations. Inhomogeneity has been observed in microhardness maps, with ER2594 and ERNiCrMo-3 WZ averaging 310 ± 7 Hv0.5 and 270 ± 10 Hv0.5, respectively. ERNiCrMo-3 (165 ± 5 J and 180 ± 3 J) and ER2594 (100 ± 3 J and 110 ± 6 J) fillers exhibited distinct effects on toughness in the weld cap and root due to laves phase precipitation. Additionally, ER2594 (750 ± 6 MPa) and ERNiCrMo-3 (790 ± 7 MPa) fillers exhibited lower tensile strength than base metals. The structural integrity of WZ can be better understood by residual stress analysis, which showed compressive cap pass and tensile root pass residual stresses for both fillers. In a 3.5 wt% NaCl solution, both fillers exhibited outstanding corrosion resistance in marine conditions. These findings improve subsea manifold structure integrity and performance in corrosive marine environments.