Thermodynamic Relation between Silicon and Aluminum in Liquid Iron
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AN accurate control of complex deoxidation by Si-Al in liquid steel is very important in view of high deoxidation efficiency and inclusion controls in many grades of steels. Despite its importance, the reported data on the interaction parameter between silicon and aluminum in liquid iron are very limited. Chipman and Floridis[1] determined the first-order interaction parameter between aluminum and silicon in the Fe-Al-Si-C system as eSi Al ¼ 6:9 at 1873 K (1600 C) using a silver bath isoactivity method for the four alloys containing silicon in the range of XSi = 0.13 to 0.38. They estimated the activity coefficient of Al, cAl in Fe-Al melts at 1873 K (1600 C) using the extrapolated activity data of the solid binary Ag-Al system[2] based on the phase diagram[3] and the assumption that logcAl is inversely proportional to absolute temperature. Later, Wilder and Elliott[4] determined the activity of aluminum in liquid binary Ag-Al alloys at higher temperatures up to 1223 K (950 C). They reexamined Chipman and Floridis’ data and recalculated the eSi Al value as 7.0 at can be converted to 1873 K (1600 C). The value of eSi Al value as 0.056 at 1873 K (1600 C) using the the eSi Al Lupis’ conversion relationship.[5] This eSi Al value is the only data compiled as the recommended value by the Japan Society for the Promotion of Science.[6] There is no information on the temperature effect for this important parameter value. DO-HYEONG KIM and MIN-KYU PAEK, Graduate Students, and JONG-JIN PAK, Professor, are with the Department of Metallurgical and Materials Engineering, Hanyang University, Ansan 426-791, Korea. Contact e-mail: [email protected] MOON-SIC JUNG, formerly Graduate Student, Department of Metallurgical and Materials Engineering, Hanyang University, is now Engineer with POSCO, Seoul 135-777, Korea. HAE NAM, formerly Graduate Student, Department of Metallurgical and Materials Engineering, Hanyang University, is now Engineer with Hyundai Steel Co., Dangjin 343-823, Korea. Manuscript submitted December 7, 2011. Article published online May 17, 2012. 1106—VOLUME 43B, OCTOBER 2012
The interaction parameter, by its definition, is the effect of one solute on the activity coefficient of another solute in the dilute solution. Aluminum and silicon contents in liquid steel during the Al-Si codeoxidation process are normally less than 1 mass pct. In some special grades such as transformation-induced plasticity steels, their contents are as high as 2 mass pct.[7–9] In the authors’ recent study,[10] the effect of aluminum content on nitrogen solubility in liquid iron and the solubility product of aluminum and nitrogen in liquid iron saturated with pure solid AlN were measured as a function of temperature. In the current study, the thermodynamic interaction between silicon and aluminum in liquid iron was determined by measuring the effect of silicon on the solubility product of AlN in Fe-Si melts in the temperature range from 1823 K to 1923 K (1550 C to 1650 C). The effect of silicon on nitrogen solubility was separately determi
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