Some observations on the effects of sulfur and active elements on the oxidation of Fe−Cr−Al alloys

Abstract

A very-low-sulfur-content industrial Fe−Cr−Al alloy has been used both as a baseline and as a charge material for laboratory metlts with variable sulfur and rare-earth additions. No significant differences in behavior were observed in cyclic oxidation tests on 1-mm-thick coupons at 1100°C, except for an excessive rare-earth content, which led to accelerated scale growth. At 1300°C, alloys without rare-earth additions developed high growth stresses in the oxide, leading to large tensile strains in the substrate. The oxide-metal interface in the low-sulfur (<2ppm) material resisted these stresses and the oxide remained adherent. However, as little as 4ppm S was sufficient to cause considerable spalling. Rare-earth additions markedly reduced growth stresses and eliminated both dimensional instability and spalling.