Rate of decarburization of Fe-C sat melts by H 2 O at 1523 and 1873 K
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I.
INTRODUCTION
THE reaction
of water vapor with liquid iron plays an important role in several metallurgical reactions. For example, the dissociation of H20 on liquid steel during ladle processing can cause significant hydrogen pickup in the metal according to the reaction: H20 (g) = 2H + O
[1]
I f the steel is deoxidized, such as in the ladle, the driving force for Reaction [ 1] is enhanced and hydrogen pickup can be significant. Another example of the importance of this reaction is in the new bath-smelting processes to produce iron. [11 In these processes, coal, ore, and oxygen are reacted in a liquid iron bath. The off gases, CO and Hz, are partially postcombusted to CO2 and H20 in order to provide energy for the process. Using a medium volatile coal, the H20 would typically be of the order of 19 to 23 pct after postcombustion. This H20 will react with iron drops containing carbon according to the reactions: C + H20 = H 2 + CO
[2]
Fe + H 2 0 = H2 + FeO
[3]
marily controlled by chemical kinetics and kinetic rates have been determined. Despite the importance of this reaction, no conclusive work has been reported on the chemical kinetics of Reaction [1]. Shigeno et al. 121 studied the decarburization of iron by H20 from 1573 to 1773 K. However, their measurements were strongly influenced by gas phase mass transfer. Sasaki and Belton [3] used a mixed control model for gas phase mass transfer and chemical kinetics to estimate the chemical rate constant for high sulfur melts from Shigeno et a l . ' s results. However, the correction for mass transfer was not precise and excessively large, thereby making the calculated chemical rate constant, at best, a first-order estimation. The rate of dissociation of H20 was determined at the University of Newcastle (UN) and Carnegie Mellon University (CMU) by measuring the rate of the decarburization of iron in independent investigations. The authors concluded that rather than have two separate publications on the same subject, more definitive conclusions could be drawn by combining the two studies into a single publication.
or
Reaction [2] is endothermic, taking energy from the system, whereas Reaction [3] causes iron oxidation which reduces the overall rate of reduction for the process. In addition to the practical significance of establishing the kinetics of the reaction of H 2 0 o n iron, such information would extend our theoretical understanding of the dissociation of gases on liquid metal surfaces. For liquid iron, only the reactions of nitrogen and carbon dioxide have been studied under conditions when the rate is pri-
R.J. FRUEHAN, Professor, is with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. G.R. BELTON, Director, is with the Broken Hill Proprietary/Central Laboratory, Wallsend, New South Wales, Australia. F.J. MANNION, Senior Research Engineer, is with the US Steel Division, USX, Monroeville, PA 15146. Y. SASAKI, Senior Research Engineer, is with Nisshin Steel, Tokyo, Japan. Manuscrip
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