The effect of water vapor on the oxidation behavior of 9%Cr steels in simulated combustion gases

The effect of the O(2) and H(2)O content on the oxidation behavior of the 9%Cr steel P91 was studied in the temperature range of 600-800 degrees C. The oxidation rates under the various experimental conditions were determined by in-situ thermogravimetry. In dry oxygen a protective scale growth occurs with an oxidation rate controlled by diffusion in the scale. In presence of water vapor, after an incubation period, the scales become non-protective, as a result of a change of the oxidation limiting process. The water vapor effect is especially apparent in the temperature range of 600-700 degrees C, whereas at higher temperatures hardly any effect was found. The destruction of the protective scale by water vapor does not only depend on the H(2)O content but also on the H(2)O/O(2)-ratio.