Internal Oxidation of a Fe-Cr Binary Alloy at 700-900 degrees C: The Role of Hydrogen and Water Vapor

Internal oxidation of Fe-2.25Cr has been studied in Fe/FeO Rhines pack (RP) and H-2/H2O gas mixtures at 700-900 degrees C. A novel exposure technique allowing RP experiments in dual atmosphere conditions was developed. No measurable effect of hydrogen on lattice oxygen permeability in ferrite could be detected: neither in single nor in dual atmosphere conditions. The H-2/H2O atmosphere was found to induce stronger oxidation attack at alloy grain boundaries resulting in a morphology similar to intergranular stress corrosion cracking often reported in nuclear technology. The intergranular oxidation attack was demonstrated to be independent of the dual atmosphere effect, i.e., hydrogen dissolved in the alloy