Effect of Composition on Desulfurization Capacity in the CaO-SiO 2 -Al 2 O 3 -MgO-CaF 2 -BaO System

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SULFUR, as one of the harmful elements in steel, might worsen the performance of the steel product.[1–3] With the increasing demands on steel quality, sulfur must be lessened to the lowest possible level (even lower than 5 to 10 9 106 in some purity steel).[4] Theoretical studies on deep desulfurization in purity steel have been focused recently on meeting such a strict demand.[5–7] Slag refining is used to improve steel cleanliness by absorbing inclusion, decreasing sulfur, or adjusting inclusion composition and morphology.[8] Normally, lime-based slags are used in steelmaking, but they exhibit limited sulfur removal. It is possible that the addition of highly basic oxides to lime fluxes will increase the abilities of the flux to absorb sulfur without being too expensive. Barium oxide has received attention for this reason. In the past years, much research was carried out on such fluxes all over the world.[9–13] However, to the knowledge of the authors, only limited experimental data are available in the literature in the CaO-SiO2-Al2O3-MgO-CaF2-BaO system. In the current work, the flux composition is determined according to the updated reference: Al2O3/CaO ratio, 0.5 to 1.1 pct; MgO, 4 to 10 pct; CaF2, 6 to 10 pct; BaO, 0 to 15 pct; and SiO2, 6 pct. A mathematical model of the ability of the sulfur removal by CaO-SiO2-Al2O3-MgO-CaF2-BaO flux was established using experimental data by taking advantage of the method of quadratic orthogonal regression (4 factors, 3 levels),[14] and the influences of the flux composition on its desulfurization ability were investigated. YANHONG GAO, Lecturer, is with the College of Materials Science and Engineering, Chongqing University, Chongqing 400030, P.R. China, and with the School of Metallurgy and Materials Engineering, Chongqing University of Science and Technology, Chongqing 401331, P.R. China. Contact e-mail: gyh3636@hotmail. com QINGCAI LIU, Professor, is with the College of Materials Science and Engineering, Chongqing University. LINGTAO BIAN, Senior Engineer, is with Chongqing Industry Polytechnic College, Chongqing 401120, P.R. China. Manuscript submitted December 6, 2010. Article published online November 30, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B

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EXPERIMENTAL

The experimental fluxes were prepared by mixing the appropriate ratios of high-purity CaO, Al2O3, SiO2, MgO, CaF2, and BaCO3 and premelted in a Si-Mo furnace. Then the quenched slags were ground in an agate mortar. The experiments were performed using a vertical resistance furnace with MoSi2 heating elements and an Al2O3 working tube. The experimental setup is shown schematically in Figure 1. To measure the sample temperature accurately, a double Pt-Rh thermocouple placed in an alumina sheath was located adjacent to the sample. The furnace temperature was controlled within ±1 K. A corundum crucible containing approximately 1 kg steel sample was placed in the furnace chamber in the even temperature zone of the furnace. Argon gas was passed through the furnace during the entire experiment to avoid

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