THE OXIDATION SULFIDATION BEHAVIOR OF IRON-ALLOYS CONTAINING 16-40 AT-DEGREES ALUMINUM

Iron aluminide alloys containing 16-40 at% aluminum and 0-5 at% chromium were tested in H2S-H-2-H2O gas mixtures at 800-degrees-C and in air at 800-1000-degrees-C. Results were compared with those for developmental Fe-Cr-Al alloys. Alloys containing 18% or more aluminum were highly resistant to H2S-H-2-H2O gas mixtures, and the corrosion behavior did not change significantly with aluminum concentrations above 18%. A 20 at% Al level was found to be critical for sustained oxidation resistance of binary Fe-Al alloys in air at 900-degrees-C and above. However, the addition of 5 at% Cr at the 16 at% Al level reduced the oxidation rate in air to that of alloys containing greater-than-or-equal-to 20% Al. Corrosion rates of iron aluminides were comparable to Fe-Cr-Al alloys in air but were significantly lower than Cr-containing alloys in H2S-H-2-H2O. The respective corrosion processes operative for iron aluminides in mixed gas and air are discussed in terms of the observed alloying effects.