Effect of Carbon on the Long-Term Oxidation Behavior of Fe3Al Iron Aluminides

Electroslag, remelted-iron aluminides having the compositions: (1) Fe–16Al–0.05C, (2) Fe–16Al–0.14C, (3) Fe–16Al–0.5C, and (4) Fe–16Al–1.0C were investigated to understand the effect of carbon on their oxidation behavior in the temperature range 700–1000°C. The oxidation behavior of these aluminides was compared with that of 310 SS, a reference alloy used in the study. Regardless of carbon content, the iron aluminides exhibit marginally higher oxidation tendency than that of 310 SS at 700°C. However, between 800 and 1000°C, they exhibit better oxidation resistance than 310 SS. Although the oxidation resistance of aluminides at 1000°C is better than that of 310 SS, they suffer severe spallation during long-term exposure and C exacerbates this effect. Examination of the early stages of oxidation of the alloys at 800 and 900°C shows that they do not gain a corresponding weight as they do for a temperature rise from 700 to 800°C. A further rise to 1000°C leads to a marginal inversion in the oxidation tendency of the alloys. Based on the literature, this inversion is attributed to the possible dissolution and/or change in compo- sition of Fe₃AlC_0.69 carbide phase with temperature.