The Mechanism of the High-Temperature Oxidation of Iron-Chromium Alloys in Water Vapor

Oxidation studies of Fe‐Cr alloys show that a characteristic layered scale is formed on alloys containing 15 w/o (weight per cent) Cr or less when oxidized in atmospheres of in the temperature range 800°–1100°C. Though the outer wüstite layer is extensively detached from the inner wüstite‐spinel layer, a linear oxidation rate is observed. For the continued high rate of oxidation a dissociative mode of scale development is necessary, and hydrogen appears to play an important role in this process as an oxygen carrier in the internal voids. Since the oxidation rate is linear, is virtually independent of Cr content, is approximately proportional to , and shows a modest activation energy of 22 kcal/mole, the rate‐controlling process occurs at the gas: oxide interface.