Effects of water vapour and oxygen partial pressures on low carbon steel oxidation in N2-H2-H2O mixtures

AbstractA low carbon, low silicon steel was oxidised at temperatures of 900–1000 °C in flowing N2–H2–H2O gas mixtures in which oxygen and water vapour partial pressures were varied independently. Scales of dense, single‐phase, coarse grained wüstite grew rapidly, according to parabolic kinetics. Both the scaling rate and the oxide grain growth increased with $p_{{\rm O}_{2} } $ at constant $p_{{\rm H}_{2} {\rm O}} $, and also with $p_{{\rm H}_{2} {\rm O}} $ at constant $p_{{\rm O}_{2} } $. An inert marker experiment showed that significant oxygen transport but majority metal transport supported scale growth. Gas composition effects are interpreted using point defect models involving formation of hydroxyl species on anion sites as well as cation vacancies.