Primary stage of Fe-Cr-C alloy oxidation at 1100°C

Abstract

The oxidation of Fe-Cr-C alloys containing 13% Cr and carbon ranging from 0.15 to 1.63% was studied at 1100°C for 3 hr. It was found that the oxidation rate increased with increasing carbon content in the alloys. The measured time variation of CO₂ evolution showed that, during the first period of oxidation (0–40 min), a compact surface layer of FeO formed, which prohibited the free transfer of CO₂ into the streaming oxidation atmosphere. The measurable CO₂ evolution started between 40 and 50 min, and the most rapid evolution occurred in the interval t=60–90 min of oxidation. This effect corresponds well to scale-layer damage and to the maximum O₂ absorption. The measurements carried out by the combined thermobalance-Chromatograph equipment were supplemented by metallographic investigation of the oxide layers. The results enabled us to interpret the primary stage of the oxidation of Fe-Cr-C alloys and to discuss the relations between the cation diffusivities in the individual oxide sublayers, i.e., in wustite, magnetite, and hematite.