Desiliconization and decarburization behavior of molten Fe-C-Si(-S) alloy with CO 2 and O 2
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Desiliconization and Decarburization Behavior of Molten Fe-C-Si(-S) Alloy with CO2 and O2 KENJI TAGUCHI, HIDEKI ONO-NAKAZATO, TATEO USUI, and KATSUKIYO MARUKAWA One of the most important problems in the steelmaking process is an increase of the disposal slag mainly discharged from the dephosphorization process. In order to reduce the quantity of the disposal slag, the complete removal of silicon from molten pig iron is considered very effective before the dephosphorization in the pretreatment process. From this point of view, the desiliconization and the decarburization behavior of Fe-C-Si alloy with CO2 and O2 has been investigated in the present work. It is thermodynamically calculated that silicon should be oxidized in preference to carbon over 0.60 mass pct Si under the condition of aSiO2 aC 1 at 1573 K and is experimentally confirmed that silicon is only oxidized under the condition in actual. Even under the competitive region of desiliconizing and decarbonizing, under 0.60 mass pct Si, silicon is found to be oxidized down to about 0.1 mass pct Si in preference. The overall rate constants for the desiliconization and the decarburization are derived, and the value for the desiliconization is one order of magnitude larger than that for the decarburization. The influence of sulfur is also examined, and the retarding effect is not observed on the oxidation reactions.
II. THERMODYNAMIC CALCULATIONS OF OXIDATION EQUILIBRIA OF SILICON AND CARBON
I. INTRODUCTION
BECAUSE the demand for the superpurification of steel has been greater and greater, it is difficult to reduce the disposal slag, and its quantity has been unchanged or increased only slightly in recent years. Therefore, the development of an effective use of the disposal slag has become one of the most important themes in steelmaking. In order to reduce the quantity of the disposal slag, the complete removal of silicon from molten pig iron is considered very effective in the pretreatment process, because silicon is oxidized in preference to phosphorus in the succeeding dephosphorization process and the formed SiO2 lowers the basicity of slag. However, there is a desiliconization limit because the competitive decarburization reaction proceeds as the silicon content of metal decreases. Therefore, the development of an effective method to remove silicon in preference to carbon from the Fe-C-Si alloy is desired. Much research of the desiliconization with fluxes containing FeO has been reported.[1,2] On the other hand, the use of oxidizing gas may be effective for the desiliconization in order to minimize the disposal slag. However, the research considering the use of CO2 in refining processes has been limited.[3,4,5] In the present work, the simultaneous desiliconization and decarburization behavior of Fe-C-Si alloy with CO2 and O2 is thermodynamically and experimentally investigated at 1573 K. Moreover, the influence of sulfur on the oxidation behavior of the Fe-C-Si alloy is also investigated. KENJI TAGUCHI, Graduate Student,
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