Effect of Braze Clearance on Localized Corrosion of a Superaustenitic Stainless Steel Brazed with a Ni-Based Alloy (Ni-22Cr-6.3Si-3.8P)

Abstract The microstructural and local corrosion characteristics of a superaustenitic stainless steel (SASS) (Fe-24Ni-20.5Cr-6.3Mo-0.22N, UNS N08367), brazed with a commercially available Ni-based filler alloy (Ni-22Cr-6.5Si-3.5P), were investigated. The isolated SASS base material was intrinsically resistant to pitting and crevice corrosion in 0.6 M sodium chloride (NaCl) solution at room temperature. The isolated braze alloy, tested as a bead prepared at 1,150°C for 60 min in a vacuum furnace without the diffusive egress of melting point depressants (MPD), exhibited critical potentials for crevice corrosion in 0.6 M NaCl solution at ambient temperature well below that of the SASS. This is due to both the low localized corrosion resistance of the Ni-Cr solid solution and the further loss of beneficial Cr due to formation of silicide and phosphide phases, enabled by the presence of Si and P MPD. Further characterization was performed on a novel, tapered, brazed SASS joint sample that linearly increases th...