Structure and Viscosity of Molten CaO-SiO 2 -Fe x O Slag During the Early Period of Basic Oxygen Steelmaking
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INTRODUCTION
BASIC oxygen steelmaking is widely used in the primary smelting process of steel because of the better smelting effect and the shorter smelting cycle. The core task of basic oxygen steelmaking is to control the appropriate chemical composition and temperature of molten steel by desiliconization, dephosphorization and decarburization. However, the different smelting periods have different functions during basic oxygen steelmaking. The main task of the initial smelting period is to promote the dephosphorization reaction by rapid slagging. At this period, molten slag plays an irreplaceable metallurgical role in fixing phosphorus transferred from molten steel and controlling the slag-steel reaction rate.
RUI ZHANG, YU WANG, XUAN ZHAO, and CHENGJUN LIU are with the Key Laboratory for Ecological Metallurgy of Multimetallic Ores (Ministry of Education), Shenyang 110819, Liaoning, P.R. China, and also with the School of Metallurgy, Northeastern University, Shenyang 110819, Liaoning, P.R. China. JIXIANG JIA is with the State Key Laboratory of Metal Material for Marine Equipment and Application, Anshan 114021, Liaoning, P.R. China. YI MIN is with the Key Laboratory for Ecological Metallurgy of Multimetallic Ores (Ministry of Education), Shenyang 110819, Liaoning, P.R. China, and also with the School of Metallurgy, Northeastern University, Shenyang 110819, Liaoning, P.R. China, and also with the Key Laboratory for Ecological Metallurgy of Multimetallic Ores (Ministry of Education), Shenyang 110819, Liaoning, P.R. China. Contact e-mail: [email protected] Manuscript submitted July 31, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
These metallurgical functions are closely related to the viscosity of the converter slag. The suitable viscous flow of molten slag can facilitate the chemical reaction to eliminate impurity elements and control the heat transfer, mass transfer and smelting stability related to the active multiphase reaction among molten slag, liquid steel and gas.[1,2] To adjust the viscosity of molten slag, the relationship of the viscosity-structure-composition of converter slag was investigated in previous studies,[3–7] which showed that the increasing CaO/SiO2 ratio and MgO resulted in lower viscosity of the converter slag because of a decrease in the complex structures of the [SiO4] tetrahedron. The structural role of MgO is similar to that of CaO, which could cut off the bridging oxygen of the [SiO4] tetrahedron. Therefore, investigations on the structures of molten slag are essential to gain a thorough comprehension of the viscosity of metallurgical slag systems. Considering the structure of the converter slag, the structural behaviors of silicon as a network-forming ion are explicit, and it can form the tetrahedral unit by combining oxygen to construct a three-dimensional network structure.[8] The structural behaviors of alkali and alkaline earth metals in converter slag are also clear. For example, as typical network modifiers, calcia and magnesia can dissociate into Ca2+, Mg2+ and O2 [9]
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