Effect of Temperature on the Initial Oxidation Behavior and Kinetics of 5Cr Ferritic Steel in Air

The oxidation behavior of 5 wt pct Cr (5Cr) ferritic steel in air at high temperatures has been investigated. A connected Cu-rich layer adjacently forms in inner oxidation layer (IOL) at 500 °C to 600 °C in addition to the formation of a continuous Cr-rich and Si-rich ribbon. Their synergistic effects imped growth of the Fe-rich oxide film towards the outer oxidation layer (OOL) and thus improve the oxidation resistance of 5Cr steel. With increasing oxidation temperature, the Cr, Si, and Cu oxide scales are gradually damaged and spallation of the oxide scale occurs at 1000 °C. Regarding the reaction kinetics, oxidation is controlled by oxygen inward diffusion. A gas–solid model is used to describe the oxidation behavior of 5Cr steel at 500 °C to 900 °C and there is good agreement with the experimental data. In particular, this model can predict the oxidation behavior and the typical results at 750 °C and 850 °C are provided.