Oxidation of low carbon steel in multicomponent gases: Part I. Reaction mechanisms during isothermal oxidation
- PDF / 239,454 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 30 Downloads / 198 Views
I.
INTRODUCTION
OXIDATION of steels in multicomponent gases is of great importance, especially during the reheating of steel stocks in reheat furnaces. In such furnaces, oxidation normally takes place in atmospheres consisting of various gaseous components such as free oxygen, carbon dioxide, water vapor, and nitrogen. There is no shortage of work done on the oxidation of pure iron under various conditions of oxidation. However, little work has been reported concerning the oxidation of low carbon steels in practical oxidation conditions. The oxidation of low carbon steel in binary gases of O2 and N2 was the subject of a previous article.[1] The rate controlling mechanism during the initial stages of oxidation in the temperature range 1000 7C to 1250 7C was found to be the rate of mass transfer of oxygen from the bulk of the gas to the steel surface, through a gas boundary layer at the reaction surface. In the case of the oxidation of iron in CO2-CO atmospheres, studies[2,3,4] have shown that the initial rates were a linear function of the partial pressure of CO2 in the gas phase, and that the rate controlling step was the dissociation of carbon dioxide to carbon monoxide and adsorbed oxygen ions on the oxide surface. This mechanism was also found to hold for oxidation of iron-nickel and iron-silicon alloys.[5,6] For the oxidation of iron in H2O-H2 atmospheres, Turkdogan et al.[7] concluded that the rate was also conH.T. ABULUWEFA, Postdoctoral Fellow, and R.I.L. GUTHRIE, Macdonald Professor, FRSC, and Director, MMPC, are with the McGill Metals Processing Centre, Department of Mining and Metallurgical Engineering, McGill University, Montreal, PQ, Canada H2A 2A7. F. AJERSCH, Professor, is with the Department of Metallurgy and Materials Engineering, Ecole Polytechnique, 2900 Edouard-Montpetit, Montreal, Quebec, Canada H3C 3A7. Manuscript submitted April 4, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
trolled by the rate of dissociation of water vapor on the surface of the wustite. In studies done by Selenz and Oeters[8] on the oxidation of Armco iron in ternary and quaternary gases of O2, CO2, H2O, and N2, in the temperature range 1000 7C to 1300 7C, it was concluded that the various gaseous components behave in an additive way with respect to initial oxidation. The objectives of this article are to examine the oxidation of low carbon steel in various gases of O2, CO2, H2O, and N2, in the temperature range 900 7C to 1150 7C. The measured oxidation rates were compared with those predicted on the basis of known oxidation mechanisms for pure iron at corresponding oxidation conditions. II.
OXIDATION MECHANISMS AND RATE EQUATIONS
As previously indicated, the initial rates of oxidation of pure iron in CO2 and H2O atmospheres can be interpreted in terms of the dissociation of CO2 or H2O to adsorbed oxygen at the oxide surface and the subsequent rate of oxygen incorporation into the oxide. Considering the initial oxidation period of pure iron in CO2 atmospheres, assuming that the initial oxide product is wusfite (Fex
Data Loading...
