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 700-1000degreesC. 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 700degreesC. However, between 800 and 1000degreesC, they exhibit better oxidation resistance than 310 SS. Although the oxidation resistance of aluminides at 1000degreesC 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 900degreesC shows that they do not gain a corresponding weight as they do for a temperature rise from 700 to 800degreesC. A further rise to 1000degreesC 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 Fe3AlC0.69 carbide phase with temperature.