Rate of decarburization of iron-carbon melts: Part I. experimental determination of the effect of sulfur
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INTRODUCTION
D E C A R B U R I Z A T I O N is undoubtedly one of the most important heterogeneous reactions occurring in the steelmaking processes. It is believed that the production of the refined metal is largely governed by the rate of the decarburization reaction. Understandably there has been a great deal of interest in the kinetics of decarburization and numerous studies have been conducted on this subject. The gaseous oxidants CO2 (or gases containing CO2) and 02 (or gases containing 02) have found frequent application in the study of decarburization of Fe-C melts. Most of the previous studies 1-t5'17-25have been carried out using either the crucible method ~-~2'22or the electromagnetic levitation method. ~3-~5'23The experimental findings of the previous investigators may be summarized as follows: (i) At carbon concentrations higher than a critical value, the rate of decarburization is independent of carbon concentration. This critical value was found to vary between 0.05 and 0.2 wt pct C depending on the experimental conditions employed. (ii) At carbon concentrations lower than the critical value, the rate decreases with carbon concentration. (iii) The rate increases with increase in the partial pressure of oxidant, its flow rate, and the temperature of the melt. (iv) No clear consensus has emerged with respect to the effect of surface-active elements such as sulfur on the decarburization rate. The foregoing observations are consistent with the common belief that at elevated temperatures the mass-transfer in the gas-phase exercises a particularly strong influence on the rate of decarburization. As far as the effect of surface-active elements like sulfur on the rate of decarburization is concerned, however, the published experimental results are in considerable disagreement. Hayer et a122 have studied the effect of sulfur on the rate of decarburization of molten iron containing 1 to 3 wt pct C and up to 3 wt pet S. The melt H.G. LEE, Graduate Research Assistant, and Y. K. RAO, Professor, are both with Metallurgical Engineering, FB-10, University of Washing-' ton, Seattle, WA 98195. Manuscript submitted August 3, 1981. METALLURGICAL TRANSACTIONS B
was contained in an alumina crucible and was decarburized in an argon-oxygen atmosphere at 1450 ~ They observed that sulfur itself was not removed from the melt, but its presence decreased the rate of decarburization, the retarding effect being greatest in the range 0 to 0.3 wt pct S and becoming less noticeable at higher sulfur contents. Hayer e t a122 suggested that sulfur occupies surface sites on the melt and thereby interferes with the activated adsorption of CO2. However, Goto et a l 2 have found in their study of the decarburization using the crucible method that the addition of sulfur to the liquid Fe-C system did not produce any significant retardation of the rate of decarburization. In fact, these authors 2 report that the decarburization rates were essentially the same for solid graphite, liquid Fe-C, Fe-C-S, Co-C, and Ni-C alloys. Nomura et a l 6 have
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