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.