Distribution Ratios of Phosphorus Between CaO-FeO-SiO 2 -Al 2 O 3 /Na 2 O/TiO 2 Slags and Carbon-Saturated Iron
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e Minerals, Metals & Materials Society and ASM International 2017
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INTRODUCTION
THE demand for high-quality steel with fewer impurities such as phosphorus is increasing. As is known, CaO-FeO-SiO2-based slag tends to form during the dephosphorization process. While this slag generally has a high melting point, lower temperatures thermodynamically aid the removal of phosphorus from the metal melt. Therefore, fluxes are usually added to the slag to decrease its melting point, to improve the solubility of lime, and to enhance the kinetic efficiency of the dephosphorization process. CaF2 was used widely
FENGSHAN LI, XIANPENG LI, and YANLING ZHANG are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China. Contact e-mail: [email protected] SHUFENG YANG is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China. Manuscript submitted October 24, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
in the past as an additive to reduce the melting point of the slag. However, these days, its use has been significantly restricted because of its toxic effects on human health. Increasing the FeO content is another common way of decreasing the melting point of the slag. However, this causes large iron losses. The effects of other additives such as Al2O3, Na2O, MnO, and MgO on the properties of CaO-FeO-SiO2 slag as well as its dephosphorization ability have been studied previously.[1–5] For instance, Diao[1] measured the melting temperature of CaF2-free CaO-Fe2O3-Na2O-Al2O3 dephosphorization slag using the hemisphere method. The results showed that both Na2O and Al2O3 can decrease the melting temperature to less than 1473 K (1200 °C). Li et al.[2] reported the results of the dephosphorization of molten steel using MgO-saturated CaO-FeOt-SiO2 slag at 1823 K and 1873 K (1550 °C and 1600 °C). It was found that the addition of Na2O to the MgO-saturated CaO-FeOt-SiO2 system increased the phosphorus distribution ratio in the slag. The addition of Al2O3 to the slag, in contrast, decreased the phosphorus distribution ratio. The phosphorus
distribution ratio for slags containing 0 to 5 mass pct Al2O3 and 0 to 1.75 mass pct Na2O at 1873 K was 147 to 629 while that for slags containing 4.1 to 5.0 mass pct Al2O3 and 0 to 2.37 mass pct Na2O at 1823 K was 202 to 247. For slags containing 21.28 to 23.59 mass pct Al2O3 and 0 to 4.25 mass pct Na2O at 1823 K, the ratio was 41.5 to 84.8. Pak and Fruehan[3] reported that the addition of small amounts of Na2O to conventional steelmaking slags greatly improved the dephosphorization rate. In the case of the CaO-Al2O3-SiO2 slag used in ladle metallurgy for Al-killed steels, the addition of as little as 3 mass pct Na2O increased the phosphorus distribution ratio at 1873 K (1600 °C) by a factor of 100. Jung et al.[4] reported that the phosphorus distribution ratio between CaO-MgOsat-SiO2-Al2O3-FetOMnO-P2O5 ladle slag and liquid iron increased with increase
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