Phosphorus Partition between Liquid Steel and CaO-SiO 2 -FeO x -P 2 O 5 -MgO Slag Containing 15 to 25 Pct FeO
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RODUCTION
THE CaO-SiO2-FeOx-P2O5-MgO slags are very commonly encountered in primary steel making processes, e.g., the basic oxygen furnace (BOF). It is widely known that the quality of the steel produced depends strongly on the refining capacity of the slag. The necessity of reducing the phosphorus content in steel and the means of achieving this objective in commercial steelmaking processes have been discussed widely.[1–4] Investigations on the phosphate capacity of steelmaking slag date back to the first half of the twentieth century,[5–8] and a detailed literature review has been covered in a recent work.[9] Most of the published data on phosphorus partition relate to steelmaking slags containing at least one, or more, of Al2O3, MnO, or CaF2. However, precise information on the equilibrium phosphorus partition ratio for CaO-SiO2-FeOx-P2O5-MgO slag, free of Al2O3, MnO, CaF2, etc., is not readily available. The phosphorus partition behavior for such slag, containing low FeOx (less than 15 mass pct), was recently investigated.[9] However, the FeOx concentration in the slag is often in the range of 15 to 25 mass pct, particularly during the beginning and the final part of the basic oxygen steelmaking (BOS) process. The phosphorus holding capacity of such a slag plays a critical role in achieving efficient dephosphorization in the BOF.[10,11] It was therefore felt necessary to extend the investigations to FeOx contents in the range of 15 to 25 mass pct. SOMNATH BASU, Researcher, is with the Research & Development, Tata Steel, Jamshedpur 831 001, India. Contact e-mail: somnath [email protected]. ASHOK KUMAR LAHIRI, is a former Professor, Indian Institute of Science, Bangalore 560 012, India. SESHADRI SEETHARAMAN, Professor, is with the Royal Institute of Technology, Stockholm 100 44, Sweden. Manuscript submitted September 13, 2006. Article published online June 28, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
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EXPERIMENTATION
A. Choice of Chemical Compositions The composition of the actual slag in the BOF varies over a range of basicity and iron oxide (FeOx) concentration.[10–13] The present investigation was focused on slags containing iron oxide (FeOx) in the range of 15 to 25 mass pct, which is typically encountered before the onset of the ‘‘dry slag’’ period and also toward the later part of the blow in the BOF. The FeOx contents in the slag were taken as 15, 20, and 25 mass pct, and the basicities (mass pct CaO/mass pct SiO2) as 1.5, 2.0, 2.5, 3.0, and 3.5. This led to 15 discrete combinations of basicity and iron oxide content, for a specific temperature. B. Preparation of Raw Materials The methodology for preparation of raw materials, which has been described in a recent work by the authors,[9] was adopted for the present set of experiments. Table I provides a comprehensive summary of the starting materials used in the experiments. C. Slag-Metal Equilibration Dense-sintered magnesia (>98 pct MgO) crucibles were selected for carrying out all the experiments. The reasons for this choice, and the details of th
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