The reaction behavior of Fe-C-S droplets in CaO-SiO 2 -MgO-FeO slags
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I. INTRODUCTION
(4) mass transfer of C through the metal, and
ONE of the fundamental steelmaking reactions is the reduction of FeO in the slag by carbon in the metal as follows: FeO ⫹ C ⫽ Fe (1) ⫹ CO (g)
[1]
The mechanisms influencing the rate of this reaction have been studied in great detail.1–7 Mulholland et al.[1] were the first to observe the presence of a gas halo surrounding FeC-S droplets (0.8 to 4.5 wt pct C, 0.04, and 1.0 wt pct S) while they reacted with a 47 wt pct CaO-38 wt pct SiO215 wt pct Al2O3-10-30 wt pct Fe2O3 slag between 1723 and 1873 K. The presence of the gas halo gave rise to theories in which gas-slag and gas-metal interfacial reactions influence the rate of Reaction [1]. In a more recent study, Min and Fruehan[4] developed a model to describe the mechanisms controlling the rate of Reaction [1] for CaO-SiO2-4.6 wt pct Al2O3 slags with a basicity (pct CaO/pct SiO2) of 1 containing 2 to 10 wt pct FeO. The Fe-C-S droplets contained 2.3 to 4.2 wt pct C and 0.001 to 0.08 wt pct S, and the temperature ranged from 1673 to 1723 K. In their study, they considered five possible mechanisms to be rate limiting: (1) gas-metal reaction: CO2 ⫹ C ⫽ 2CO,
[2]
(2) gas-slag reaction: CO ⫹ (FeO) ⫽ CO2 ⫹ Fe (1),
[3]
(3) mass transfer of FeO as Fe the slag,
2⫹
and O
2⫺
(5) mass transfer of CO-CO2 through the gas halo. These mechanisms are shown schematically in Figure 1. According to Min and Fruehan, it was found that step (1) was rate limiting if the sulfur content of the metal was ⱖ0.01 wt pct. Step (3) was also found to contribute to the overall rate. Steps (2), (4), and (5) were fast and therefore not considered to influence the rate of reaction [1]. Despite the extensive work that has been conducted on Reaction [1], limited work has been done on the behavior of Fe-C-S droplets in CaO-SiO2-MgO slags with FeO contents ⱖ20 wt pct at temperatures ranging from 1643 to 1798 K such as is experienced during the early stages of the oxygen steelmaking process. Understanding the behavior of Reaction [1] during this process may be critical to understanding slopping behavior, an unfavorable result of excessive slag foaming in steelmaking. Therefore, this study focuses on measuring the rate of Reaction [1] for Fe-C-S droplets containing approximately 2.9 wt pct C and 0.01 wt pct S and for slag FeO contents ranging from 3 to 35 wt pct FeO. In addition, the behavior of the metal droplets within the molten slag was studied using X-ray fluoroscopy. Finally, the effects of temperature, additions of Fe2O3 to the slag, and the sulfur content of the metal on the rate of Reaction [1] were investigated.
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C.L. MOLLOSEAU, formerly Graduate Student, Materials Science and Engineering, Department, Carnegie Mellon University, is Senior Process Engineer, Intel Corporation, Portland, OR 97229. R.J. FRUEHAN, Professor, is with the Materials and Engineering Department, Carnegie Mellon University, Pittsburgh, PA 15213. Contact e-mail: fruehan@andrew. cmu.edu Manuscript submitted April 18, 2001. METALLURGICAL AND MATERI
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