Influence of Mn and Al on the high-temperature oxidation behavior of austenitic stainless steels

Abstract In this study, the high-temperature oxidation behavior of three low-density austenitic stainless steels in the Fe–Mn–Al–Cr system, designated FMC, 1FMCAl, and 2FMCAl, was systematically investigated to clarify the influence of incremental Al and Mn additions on oxidation resistance. The alloys were produced via vacuum arc remelting, where FMC contained the baseline Fe–Mn–Cr composition, while 1FMCAl and 2FMCAl incorporated moderate and higher Al/Mn levels, respectively. All samples were oxidized at 900 °C for 648 h, and oxidation kinetics were quantified through weight-gain measurements. The parabolic oxidation rate constants of the FMC, 1FMCAl, and 2FMCAl alloys are 4.5 × 10 ⁻⁸ , 3.7 × 10 ⁻⁹ , and 4.6 × 10 ⁻¹⁰ g ² /(cm ⁴ /h), respectively. In contrast, both 1FMCAl and 2FMCAl follow a parabolic rate law, demonstrating significantly reduced weight gain and the development of protective, slowly growing oxide scales. Phase and microstructural analyses (XRD, SEM, EDS) revealed that FMC primarily forms Fe-rich oxides (Fe ₂ O ₃ and Fe ₃ O ₄ ) with limited MnCr ₂ O ₄ spinel, resulting in a non-protective and unstable scale. However, 1FMCAl and 2FMCAl develop adherent, multilayered scales composed of Al ₂ O ₃ , Mn ₂ O ₃ , Mn ₃ O ₄ , and MnCr ₂ O ₄ , with Al enrichment in the outer layers and Cr accumulation at the metal/oxide interface. The improved oxidation resistance in the Al- and Mn-containing alloys is attributed to the formation of dense Al-rich and Mn-rich protective phases that suppress rapid Fe oxidation. These results highlight the synergistic roles of Al and Mn in enhancing scale stability and demonstrate their effectiveness in designing lightweight, oxidation-resistant Fe–Mn–Cr steels for advanced high-temperature applications.