Preliminary investigation on underwater wet welding of Inconel 625 alloy: microstructure, mechanical properties and corrosion resistance

Abstract

This paper aimed to investigate the feasibility of underwater wet welding for Inconel 625 alloy using Ni-based filler. The microstructure, elemental distribution, and properties of underwater wet welded Inconel 625 alloy joints were analyzed. The grain boundary type and grain growth orientation across the fusion boundary were particularly investigated. A continuous and smooth weld with no visible defects was obtained. The nickel based welds was fully austenite structure with extensive grain boundary migration. The heat-affected zone experienced obvious grain growth. A compositional transition zone with a width of 50 μm was observed across the fusion boundary. Apparent epitaxial growth across the fusion boundaries was found and the grain boundaries roughly perpendicular to the fusion boundaries are was mainly high angle grain boundaries. The density of low Σ CSL grain boundary in Inconel 625 base metal was higher than that in Ni-based weld metal. The ultimate tensile strength of underwater wet welded joints reached up to 83% that of Inconel 625 alloy. The impact toughness of HAZ was deteriorated because of the segregation of carbide and Laves phase in grain boundary. The corrosion resistance of Ni-based welds maintained at a high level based on the corrosion current density, although it was inferior to that of Inconel 625 alloy. The expected research results could enrich the underwater welding/repair technology of Ni-based alloy structures.