Investigation of the Oxidation Kinetics of Fe-Cr and Fe-Cr-C Melts under Controlled Oxygen Partial Pressures
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DUCTION
DURING the production of high alloy steels containing Cr, it is desirable to minimize the loss of chromium to the slag phase, in view of the economic and environmental impacts. In this case, an understanding of the mechanism of the oxidation process of Fe-Cr alloy in liquid state is very important. A survey of the published literature reveals that a great deal of efforts have been laid on the oxidation of iron chromium alloys in the solid state. Rhys-Jones et al.[1] have studied the isothermal oxidation kinetics of solid Fe-10 mass pct Cr alloy at 1273 K (1000 °C) and have shown that the oxidation rate follows a parabolic rate law. These authors also pointed out that during the oxidation of Fe-20 mass pct Cr alloy for 70 hours, the products were identified as Fe2O3 and Fe3O4. Wood et al.[2] reported
HAIJUAN WANG, formerly Ph.D. Student, Division of Materials Process Science, Royal Institute of Technology, Stockholm, Sweden, is now Lecturer, University of Science and Technology Beijing, 100083 Beijing, P.R. China. Contact e-mail: wanghaijuan@ ustb.edu.cn LIDONG TENG, Docent, and SESHADRI SEETHARAMAN, Professor, are with the Division of Materials Process Science, Royal Institute of Technology, Stockholm, SE-10044, Sweden. Manuscript submitted February 1, 2010. Article published online August 23, 2012. 1476—VOLUME 43B, DECEMBER 2012
that there is a spallation oxidation of Fe-Cr alloys, and the oxidation rate shows a quick increase after a protective induction period. Only Cr2O3 was formed in the case of the alloy with 14 to 25 mass pct Cr. Mortimer and Sharp[3] reported that the oxidation of alloys with high Cr content of 16 to 19 mass pct results in the formation of the oxide solid solution (Cr, Fe)2O3 in the product layer. It is seen that the earlier investigations on the oxidation of Fe-Cr alloys were focused on the solid state oxidation in oxygen or air. A number of scientists have devoted extensive research efforts towards slag systems containing the oxides of chromium. Holappa et al.[4] have shown that the higher the oxygen partial pressure prevailing, the more Cr3+(CrO1.5) is present in the slag and the melting point increased correspondingly. The oxide phases in equilibrium with liquid Fe-Cr alloys were studied by Hilty et al.[5] at 1823 K, 1873 K, and 1923 K (1550 °C, 1600 °C, 1650 °C). These authors point out that besides chromite (FeOÆCr2O3) and Cr2O3, the product layer consists of two unknown oxide phases, one being Cr3O4 with tetragonal crystal structure and the other a distorted spinel with the composition between FeOÆCr2O3 and Cr3O4. Richards and White[6] and Woodhouse and White[7] have also studied the equilibria in the Fe-Cr-O system from 1693 K to 1923 K (1420 °C to 1650 °C) in air. Muan and S omiya[8] have identified the phases in Fe-Cr-O system in the METALLURGICAL AND MATERIALS TRANSACTIONS B
temperature range 1673 K to 2323 K (1400 °C to 2050 °C) in air. In the current group, Dong et al.[9] investigated the activity of chromium oxide in CaO-SiO2-MgO-Al2O3CrOx slags in the temperature rang
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