Water Vapour Effects on Fe–Cr Alloy Oxidation (original) (raw)

Isothermal oxidation at 700°C of binary Fe-Cr alloys containing 9, 17 and 25 wt% chromium was measured using continuous thermogravimetric analysis. All alloys developed thin, protective chromia scales in Ar-20O 2 (vol%). Chromia scale growth on the 17 and 25 Cr alloys was faster in Ar-20O 2 -5H 2 O and Ar-5O 2 -20H 2 O. In these gases, the Fe-9Cr failed to form a chromia scale and suffered rapid breakaway oxidation, growing iron-rich oxides instead. A low oxygen potential gas, Ar-10H 2 -5H 2 O caused chromia scaling on Fe-17Cr and Fe-25Cr, but internal oxidation of Fe-9Cr. Application of Wagner's criterion for sustaining external scale growth is shown to account satisfactorily for these observations.