Improving the oxidation resistance by forming continuous Al2O3 protective layer in alumina-forming austenitic stainless steel

The effect of varying aluminum (Al) levels on the high-temperature oxidation resistance of Alumina-Forming Austenitic stainless steels (AFA) has been investigated under dry air conditions at 800 °C and 900 °C. Mass gain assessments indicate that AFA stainless steel containing a higher concentration of Al, with a composition of Fe-20Ni-15Cr-2.4Al-1.6Mn, demonstrates enhanced resistance to oxidation when contrasted with steel of lower Al content, characterized as Fe-23Ni-15Cr-1.9Al. This phenomenon is attributed to the development of a compact CrMn 1.5 O 4 layer on the exterior and an Al 2 O 3 layer on the interior. The dense oxide layers that form on the high-Al steel impede the permeation of oxygen and deter the peeling of the oxide layer, thus preserving structural stability of the material upon exposure to high temperatures. Conversely, the steel with a lower Al content undergoes considerable chipping of its oxide layer. The morphology and distribution of Al 2 O 3 are determined by the relative rates of oxygen inward movement and aluminum outward movement. In the case of the Fe-20Ni-15Cr-2.4Al-1.6Mn steel, the tight oxide film significantly reduces the inward movement of oxygen and increases the outward movement of Al, leading to a denser Al 2 O 3 layer underneath the Cr 2 O 3 . • Al2O3 layer's compactness in high-Al AFA steels reduces oxygen permeation. • Oxide scale's adherence in 20Ni-15Cr-2.4Al-1.6Mn alloy deters spallation. • Oxidation studies identify Al's critical role in forming stable protective scales. • Comparative study unveils Al's impact on AFA steel's oxidation kinetics