Kinetics of oxidation of carbon in liquid iron-carbon-silicon-manganese-sulfur alloys by carbon dioxide in nitrogen
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INTRODUCTION
C o 2 , 02, and H 2 0 gases are considered to be the major gaseous components oxidizing liquid iron in the cupola. Reactions between liquid iron and these oxidizing gases occur in the melting zones, liquid flow zone, and combustion zone in a cupola, while liquid iron descends through the coke bed. Greater understanding of these reactions has been recognized as an important factor in improving cupola operations and extending computer applications to cupola modeling. Oxidizing gas-molten iron reactions were studied in many investigations 11-61 during the 1960s and 1970s. In these studies, however, the effort was focused on the oxidation of a single element (carbon, silicon, manganese, etc.) in molten iron by these oxidizing gases. The kinetic analyses in these studies generally were without thermochemical considerations. Nevertheless, valuable information can be drawn from these studies about the oxidation mechanism for a single element. For higher concentrations of carbon 12'7-9'121and silicon 14,j~ J21 in molten iron, such as the composition of cast iron charged in the cupola, the oxidation rates of these elements were found to be controlled by diffusion in the gas phase. The oxidation of manganese has been studied by Kawai and Mori l~2] and Baker, [~u but the rate-limiting HAIPING SUN, formerly Visiting Assistant Research Scientist, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, is Research Associate, Department of Materials Science and Engineering, Kyushu University, Fukuoka 813, Japan. ROBERT D. PEHLKE, Professor, is with the Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109. Manuscript submitted December 8, 1992. METALLURGICALAND MATERIALS TRANSACTIONS B
step for this reaction was not reported. As the products of silicon or manganese oxidation reactions, an oxide layer was formed at the surface of the liquid metal, and diffusion in the oxide layer could become the ratelimiting step for the reactions. Emi and Pehlke, l~~ Baker, It'] and Sano and Matsushita t4] have observed the effect of formation of an oxide layer on the reaction rate. They found that above 3.5 pct silicon in the metal, the oxide scale became progressively richer in silica and less oxidizing to the metal and formed a passive layer that inhibited further reaction. However, the oxide layer did not affect the reaction rate when the initial silicon concentration in the metal was less than 3 pct at 1600 ~ Our knowledge about the mechanisms of competition between oxidation of carbon, silicon, manganese, and iron in liquid iron by these oxidizing gases is still insufficient to describe the reaction phenomena that occur in the cupola. Unlike single element oxidation, oxidation of more than one element in liquid iron involves thermochemical relations that play an important role in the reaction rates, even though the reaction system is far away from the equilibrium states for these elements. In previous w o r k , It31 the study concentrated on O2/
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