Effects of Single-Layer Versus Three-Layer Flux-Cored Arc Welding Deposition on Dilution, Microstructure, Bending Integrity, and Corrosion Resistance of Inconel 625 Overlays on AH36 Steel

This study investigated the effects of repeated flux-cored arc welding deposition on the dilution, microstructure, bending integrity, and electrochemical corrosion behavior of Inconel 625 weld overlays on AH36 steel by comparing single-layer and three-layer multipass conditions. Both overlays exhibited dendritic solidification structures; however, qualitative SEM observations indicated differences in the morphology and spatial distribution of the interdendritic constituents, with a relatively continuous or semi-continuous network observed in the single-layer overlay and a more discontinuous and dispersed distribution in the topmost multipass layer. These qualitative morphological differences coincided with substantial compositional recovery; the Fe content decreased from 36.29 wt.% in the single-layer overlay to 4.77 wt.% in the third multipass layer, whereas the Ni, Cr, and Mo contents increased toward nominal Inconel 625 filler-metal values. Local Nb and Mo enrichment persisted within interdendritic regions under both conditions, with no consistent reduction in local Nb enrichment following multipass deposition. The spatial distribution of the interdendritic constituents also differed between the two conditions, while Mo exhibited a more uniform overall distribution at the mapping scale in the multipass third layer. One of the three single-layer specimens developed a large open crack after 180° side bending, whereas none of the three multipass specimens exhibited visible open cracking or fracture. The multipass overlay further exhibited a lower anodic current density, and higher film and charge-transfer resistance, consistent with a more stable passive electrochemical response.