The effect of carbon in slag on steel reoxidation and carbon analysis by x-ray photoelectron spectroscopy in the CaO-SiO
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I. INTRODUCTION
THERE has been an increasing demand for ultra-clean high-grade steels with minimum amounts of inclusions. The reduction of oxide inclusions is mainly performed by flotation into the slag phase and by prevention of Al reoxidation in steel during ladle refining operations. Steel reoxidation by reducible oxides in slag, such as FetO and MnO, induces the formation of fine inclusions, H, which are not easily floatable during the refining stage. Therefore, for the production of ultra-clean steels, it is important to decrease the activity of the reducible oxides causing the steel reoxidation. In ladle refining processes, (FetO MnO) content in slag should be lowered less than 1 wt pct for the effective desulfurization and the suppression of the steel reoxidation. This brings about the increment of production cost and processing time because of excessive injection of raw materials. Decreasing the activity coefficients of FetO and MnO is an alternative solution for controlling the activities of the reducible oxides while maintaining high (FetO MnO) content. Slag phase will inevitably contain a certain degree of carbon. Previous research confirms that carbon in Cr2O3 containing slag reduces the activity coefficients of FetO and MnO.[1] It is necessary to investigate in more detail the activity behaviors of reducible oxides in carbon containing slags to minimize steel reoxidation. However, studies on carbon containing slags have focused mainly on solubility and stable forms of carbon in slag.[2–6] To date there have been no reports on the effect of carbon in slag on the activities of FetO and MnO. So, in this work, the thermodynamic equiMIN-OH SUK, Graduate Student, SUNG-KOO JO, Research Associate, and SEON-HYO KIM, Professor, are with the Department of Materials Science and Engineering, POSTECH, Pohang, Kyung-buk, South Korea 790-784. Contact e-mail: [email protected] JEONG-SIK KIM, Plant Manager, Gwangyang Works, and SANG-CHUL SHIM, Senior Researcher, Technical Research Laboratories, are with POSCO, Pohang, Kyung-buk, South Korea 790-360. Manuscript submitted April 20, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
libria between CaO-SiO2-Al2O3-MgO-MnO-FetO slag systems and liquid iron were carried out in a MgO crucible at 1873 K varying the carbon content in slag. The activity coefficients of FetO and MnO, which affect the steel cleanliness, will be discussed, stressing the effect of carbon in slag. To clarify the stable form of carbon in slag, X-ray photoelectron spectroscopy (XPS) was introduced. Park et al. showed the possibility of XPS application for the analysis of carbon in iron ore.[7] From the XPS results, we will ascertain the dominant parameters affecting the activity coefficients of FetO and MnO. Finally, this article will suggest an application method of the present results to actual ladle refining processes in order to enhance the steel cleanliness under the condition of relatively high (FetO MnO) content. II. EXPERIMENTAL The equilibrium study between slag and metal was carried out
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