In order for Cr-steels to have oxidation resistance, the Cr content in the alloy must be above a critical limit. Since the recently developed 9 percent Cr steels are close to that limit their oxidation behavior is of critical importance concerning service lifetime and reliability of structural components. In the present paper the influence of water vapor and the alloying elements Si and W on the oxidation behavior of 9 percent Cr steels was investigated. Four different alloys of the ferritic-martensitic 9 percent Cr steel type were discontinously oxidized at 650 deg C in dry air and air containing 4 and 10 percent water vapor for up to 3500 h. The results indicate that water vapor significantly accelerates oxidation of these steels and that the Si- content of the alloys is critical for the oxidation performance, especially under wet conditions.
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