Mixed Oxidation of Iron–Chromium Alloys in Gases Containing Oxygen and Chlorine at 900 to 1200°K

Abstract

Abstract The mixed oxidation of three binary Fe-Cr alloys containing 1, 5, and 20 wt% Cr in Ar-50%O2−1%Cl2 and in Ar-50%O2−0.25%Cl2 at temperatures between 900 and 1200 K has been investigated using thermogravimetric analysis and examination of the corrosion products by scanning electron microscopy. At 1000 K and above, the alloys experience accelerated corrosion associated with the formation of a porous two-layered oxide scale. Iron oxide is concentrated in the outer layer and chromium oxide in the inner layer. Iron chloride deposits are detected near the scale-metal interface at 1000 K, but not at higher temperatures. Although the 20% Cr alloy is much more resistant to oxidation than the other alloys in uncontaminated O2, the rates of corrosion of all three alloys are very similar in the chlorine-containing environments at 1000 K. A mechanism proposed for the accelerated oxidation in these environments is based on the formation, diffusion, and reoxidation of volatile iron chlorides.