Modeling and experimental study of gaseous oxidation of liquid iron alloys
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I.
INTRODUCTION
M A J O R components in the gas phase of a coke-fueled shaft furnace, such as a cupola, include oxygen and nitrogen blown through the tuyeres, as well as carbon dioxide and carbon monoxide produced by the reaction between oxygen and coke. The partial pressures of oxygen and carbon dioxide vary from 0 to 0.2 atm in an air-blast cupola, and although the partial pressures decrease at higher positions in the cupola, there is still a high partial pressure of CO2 (0.1 atm) remaining in the outlet gas of a cupola furnace. The liquid metal contacts these oxidizing gases until it reaches the slag layer. The lower the position in the cupola, the stronger the oxidizing potential in the gas phase. Carbon, silicon, and manganese in the melt react with these gases, resulting in the loss of alloying elements. The mechanisms of competing oxidation of carbon, silicon, manganese, and iron in the liquid iron by 02 or CO2 gases have been experimentally determined in previous studies.E~.z~ It was found that the thermochemical relations play an important role in the reactions of this system, although these reactions are far away from the equilibrium states, as is the situation in the coke bed of a cupola where the alloying element contents in the melt are much higher than those in equilibrium with the gas phase. The oxidation of carbon, silicon, and manganese was found to be limited by diffusion in the gas phase when the contents of these elements are higher, and the oxidation of these elements occurs in a thermochemically favored order. In the present study, the aforementioned reactions have
HAIPING SUN, formerly Visiting Assistant Research Scientist, the Department of Materials Science and Engineering, the University of Michigan, is Research Associate, Department of Materials Science and Engineering, Kyushu University, Fukuoka 812, Japan. ROBERT D. PEHLKE, Professor, is with the Department of Materials Science and Engineering, the University of Michigan, Ann Arbor, MI 48109-2236. Manuscript submitted July 26, I994. 854--VOLUME 27B, OCTOBER 1996
been considered, and a system reaction model has been developed for liquid iron reacting with 02/COJCO/N2 gases. Experiments on liquid iron-OjCO2/CO/N 2 gas reactions have been carried out varying gas composition, carbon concentration in the metal, gas flow rate, and temperature to verify this reaction model.
II.
REACTION MODEL
A. Reaction Mechanism In previous studies,V.21 the simultaneous oxidation of carbon, silicon, and manganese in cast irons was studied using 1-g liquid iron droplets levitated in streams of Oz/N 2 or CO2/N2 gases at 1813 to 1993 K. Oxidation of carbon was favored over oxidation of silicon and manganese when cast iron reacted with these gases at higher temperature ( > 1873 K). Diffusion in the gas phase was found to be the ratelimiting step for these reactions when the content of the element being oxidized was relatively higher and as the content of the element decreased during the later period of the reaction; however, diffusion in the metal phase c
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