Anomalous temperature dependence of oxidation kinetics during steam oxidation of ferritic steels in the temperature range 550-650°C

The oxidation behavior of a number of selected ferritic steels in a simulated steam environment at temperatures between 550 and 650 degreesC was studied. In the prevailing test gas, some of the studied 9-12% Cr steels tended to exhibit an anomalous temperature dependence of the oxidation behavior. This means, that the oxidation rates do not steadily increase with increasing temperature. At higher temperatures, some of the studied steels tend to form a very thin and protective oxide scale whereas at lower temperature rapidly growing, less-protective oxides are being developed. The anomalous temperature dependence is related to differences in chromium distribution in the inner part of the oxide scale. The effect is observed for steels with intermediate-Cr contents (similar to10-12%) whereas steels with either lower or higher Cr contents exhibit an increasing oxidation rate with increasing temperature. (C) 2004 Elsevier Ltd. All rights reserved.