The application of thermodynamics to the oxidation behavior of mild steels in carbon dioxide-based atmospheres

Abstract

When steels oxidize in CO₂-based atmospheres, they frequently experience an enhanced form of attack known as “breakaway.” It has been suggested that for this to occur, the gas in contact with the metal must be not only oxidizing but also carburizing with respect to iron. This approach implies that as part of the breakaway process either carbon will be deposited in the oxide (a feature commonly observed with some mild steels) or carbides will form. The present work has tested this hypothesis by analyzing the thermodynamics of chemical equilibria between the individual gases in an AGR atmosphere and iron using techniques developed by other workers. The results have been used to predict the oxidizing and carburizing tendencies of various gas mixtures and thus to identify those conditions which are capable of supporting the breakaway process. This theoretical approach has been compared with experimental observations and found to show significant agreement.