Abnormal Growth Transport in Oxide Scales on Fe-16Cr Steels in Water Vapor

The oxidation behavior of Fe-16Cr steels in N-2-12 vol pct H2O was studied at 850 degrees C. The oxide scale was compact and had excellent adhesion to the substrate; moreover, there were three layers of different compositions existing in the scale. To gain an insight into the transport mechanism, two-stage oxidation was carried out in N-2-12 vol pct (H2O)-O-16 and followed in N-2-12 vol pct (H2O)-O-18 gas mixtures. The oxygen isotope profiles in oxide scales were determined by secondary ion mass spectrometry. The results showed that oxidation in water vapor proceeded by outward chromium transport, especially, the oxidation involved inward transport of water molecules.