CORROSION BEHAVIOR OF FE-CR AND FE-NI-BASE COMMERCIAL ALLOYS IN FLOWING AR-42.6-PERCENT-O-2-14.7-PERCENT-BR-2 GAS-MIXTURE AT 700-DEGREES-C

The corrosion behavior of Fe-Cr and Fe-Ni-Base commercial alloys has b een investigated in an argon-42.6% oxygen-14.7% bromine gas mixture at 700 degrees C which was one of the environments encountered in the UT -3 thermochemical water decomposition reaction process to produce hydr ogen. The test alloys were type 304 and 310 stainless steels, Incoloy 800, and Incoloy 825. Two-dimensional thermodynamic phase stability di agrams were constructed for iron, chromium, nickel, and titanium to pr edict the condensed corrosion products that are stable with respect to the representative alloying elements when the alloy is exposed to the argon-42.6% oxygen-14.7% bromine gas mixture at 700 degrees C. The ox ides were thermodynamically stable phases with respect to the correspo nding metals. Post-reaction treatment of test alloys included disconti nuous mass-change measurements, scanning electron microscopy (SEM), el ectron probe micro-analysis (EPMA) for morphological and compositional investigation of the corrosion products, and the X-ray diffraction (X RD) for phase identification. XRD identified oxides and spinels as cor rosion products but low-melting metal bromides were detected for all a lloys with deleterious effects on high-temperature properties of these alloys during exposure to the environment. The poor corrosion resista nce of the rest alloys was mainly caused by the cracking and spalling of iron and chromium-rich oxides and further growth of various metal b romides beneath the oxide scale following prolonged exposure. The high iron content of the test alloys had deleterious effects on the perfor mance of these alloys in the environment.