08257 Corrosion of A Super-Austenitic Stainless Steel (Fe-24Ni-20Cr-6.3Mo-0.22N) When Brazed with a Ni-Cr Braze Material (Ni-22Cr-6.3Si-3.8P): Corrosion Behavior of Isolated and Combined Materials

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Product Number: 51300-08257-SG

ISBN: 08257 2008 CP

Author: Sara Hebb, Joshua James, Jim Gerald, George Young, and John Scully

Publication Date: 2008

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The corrosion of a super-austenitic stainless steel (SASS) Al-6XN (Fe-24Ni-20Cr-6.3Mo-0.22N in wt.%, UNS N08367) when brazed with a commercial Nicrobraze alloy (Nicrobraze 31: Ni-22Cr-6.3Si-3.8P) in 0.6 M NaCl at 25oC is reported. The SASS sheet material was intrinsically resistant to pitting and crevice corrosion in marine environments at room temperature, as indicated by its performance in both multiple crevice assembly exposures and electrochemical polarization testing in 0.6 M NaCl. The open circuit potential of isolated AL-6XN fell roughly 900 mV below the critical potential for crevice corrosion repassivation (Ecrev,r). Isolated beads of complex multiphase Nicrobraze 31 exhibited an open circuit potential equal to or greater than the measured Ecrev,r of -0.200 VSCE when prepared at 1150°C for 60 minutes in a vacuum furnace. This was related to both the low PRE number of the solid solution phase and the segregation of beneficial chromium due to the complex microstructure of the alloy in a bead form, representative of a brazed joint of infinite clearance.