Sulfide Capacities of CaO-MgO-Al 2 O 3 -SiO 2 -CrO x Slags
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HROMIUM-CONTAINING slags play a predominant role in production of stainless steel and high alloy steels. It is important to understand the chemistry of chromium-containing slags with special reference to the phase equilibria,[1–5] oxidation states of chromium in slag phase[6–11] and distribution of Cr between the steel melt and slag phases.[6,12–14] These studies provide invaluable information for the optimization of the processes for high alloy steels. However, experimental data on the properties of slags containing CrOX are scarce in literature as the melting points of these slags are quite high. Drakaliysky et al.[15] reported sulfide capacities of CaO-MgO-SiO2-Al2O3 slags containing small amounts of Cr2O3. Their results indicate that adding 5 wt pct Cr2O3 to a high-MgO (25 wt pct) slag could cause a 4-fold decrease in sulfide capacities. Wang et al.[16] studied sulfide capacities of CaO-SiO2-CrOx system in the temperature range from 1823 K to 1923 K (1550 °C to 1650 °C). These authors noticed that, when the SiO2 content was fixed in the slag, the increasing content of CrO would initially decrease the sulfide capacity and increase it subsequently. In the current study, experimental determinations of the sulfide capacities of chromium slags of 12 different compositions were carried out in the temperature range from 1823 K to 1898 K (1550 °C to 1625 °C);
CaO-MgO-Al2O3-SiO2 was adopted as basic system and the chromium-oxide contents were varied.
II.
EARLIER WORK
A. Distribution of Cr(II)/Cr(III) In order to understand the chemistry of Cr-bearing slag, it is imperative that the distribution of the two valence states of chromium in the slag viz. Cr(II) and Cr(III) as functions of basicity, oxygen potential and temperature is clarified. While a number of publications are available in the literature on the valence states of Cr in the slags, a significant discrepancy has been found between the results reported. Recently X-ray Near edge Spectroscopy (XANES) and high-temperature Knudsen cell mass spectrometry were employed to determine the influence of temperature, oxygen partial pressure as well as slag chemistry on the Cr(II) and Cr(III) ratio in the slag by the present authors.[17] By combining the results, a relationship could be established enabling the estimation of the ratio of Cr(II)/Cr(III) as a function of the above-mentioned variables. Cr(II) was found to be stable at high temperature, low oxygen partial pressure, and low basicity environment, while Cr(III) had the opposite tendency. B. Sulfide Capacities as Structure Indicator
LIJUN WANG, Associate Professor, and KUO-CHIH CHOU, Professor, are with the State Key Laboratory of Advanced Metallurgy and Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] YAXIAN WANG, formerly Master Student with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China, is now Ph.D. Student with the Department of Ma
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