Evolution of Oxide Film of T91 Steel in Water Vapor Atmosphere at 750 A°C

In order to investigate the evolution of oxide film on T91 steel, oxidation tests were conducted in water vapor atmosphere at 750 A degrees C. The phase compositions and microstructures of the oxide scales for early stage oxidation were investigated by using glancing angle XRD and SEM equipped with EDS. The results showed that during the initial oxidation stage Cr-rich oxide film formed and then it covered the sample surface rapidly. The initial Cr-rich oxide film was mainly composed of FeCr2O4, (Fe,Cr)(2)O-3 and Fe2O3. This oxide film acted as a barrier against outward diffusion of iron and inward diffusion of oxygen. During the initial oxidation stage, chromium in the sample surface was consumed gradually, and then a large amount of iron ions penetrated the oxide film and diffused rapidly to the sample surface, resulting in forming an outer non-protective Fe2O3 layer.