Microstructural Evolution of Multilayered Oxide Scales on Stainless Steels

Abstract

ABSTRACTSi containing stainless steels form complex oxide scales during high temperature oxidation at 900°C. These scales consist of an outer iron chromium manganese spinel layer, an intermediate Cr2O3 (chromia) layer and an inner SiO2 (silica) layer. During isothermal oxidation, alloys exhibit minimum weight gain when the inner silica layer is continuous, due to its effectiveness as a diffusion barrier. This continuous silica scale can be formed in a short time only by a combination of fine alloy grain size and high silicon content. However, formation of a continuous silica layer may lead to scale spallation on cooling, thus having a deleterious effect on the oxidation resistance of the alloy.