Abstract
We studied high Mn-substituted-for-Ni AFA steel (Fe-14Cr-(6–12) Mn-10Ni-2.5Al-3Cu-Nb-C AFA steel) oxidation behaviors at 800 °C in air. (6–12) Mn AFA steel formed a three-layered scale: the outer layer is (Mn, Fe)-rich oxide, such as (Mn0·983Fe0.017)2O3, the intermediate is Cr-rich oxide, and the inner layer is Al2O3. (6–8) Mn-AFA steels formed a protective Al2O3 layer with stronger oxidation resistance than (10–12) Mn-AFA steels. The oxidation rate constants of 6Mn- and 8Mn-AFA steels are 1.7 × 10−3 and 2.4 × 10−3 mg2/(cm4·h), respectively, approximately 10 times higher oxidation resistance than that of 10Mn- and 12Mn-AFA steels. (10–12) Mn-AFA steels cannot form a continuous Al2O3 layer. The discontinuous Al2O3 layer allows the elements to diffuse outward, eventually forming Mn-Fe-Nb-rich oxide nodules on the surface of the steel. Mn concentrations with the potential to form protective alumina at 800 °C were identified.
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