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

Abstract

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 CrMn1.5O4 layer on the exterior and an Al2O3 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 Al2O3 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 Al2O3 layer underneath the Cr2O3.