Temperature and water vapour effects on the cyclic oxidation behaviour of Fe–Cr alloys

Binary Fe–Cr alloys were subjected to cyclic oxidation at 600, 700 and 950 °C in flowing gases of Ar–20O2 and Ar–20O2–5H2O (vol.%). The minimum chromium concentration required to achieve protective scale growth decreased as temperature increased from 600 to 700 °C. This change is attributed to faster chromium diffusion at higher temperature. Conversely, this minimum chromium level increased when the temperature was raised from 700 to 950 °C. This is attributed to faster scale growth, leading to its rapid mechanical failure, along with formation of slow-diffusing austenite. Water vapour accelerated scaling, leading to a need for higher chromium concentrations to resist breakaway oxidation.