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the melts containing 10, 20, and 30 mass pct Al2O3 were determined to be 6950, 2715, and 12092 J/mol, respectively. Iso-activity contours for MnO in the five component system were calculated using the quadratic formalism, and they showed a good agreement with the experimental data. DOI: 10.1007/s11663-016-0859-7  The Minerals, Metals & Materials Society and ASM International 2016

I.

INTRODUCTION

HIGH-MN twinning-induced plasticity (TWIP) steels have gained great attention due to their outstanding material properties, such as ultra-high strength, toughness, and excellent ductility.[1,2] For the production of high-Mn TWIP steels, Mn metal and ferromanganese alloys can be used as an Mn source and added to liquid steels. However, the less expensive MnO ore is more desirable as the Mn source. MnO ore can be added, together with SiMn and slag-forming components (CaO, MgO, etc.), to the liquid metal after deslagging in the BOF, and then the formed slag containing high MnO is reduced through silico-thermic reaction to increase the Mn content in the liquid metal.[3] In this regard, the thermodynamic properties of MnO in the MnO-CaO-SiO2-Al2O3-MgO slags, especially in the slags containing high MnO, are necessary for controlling and optimizing the process. Concerning the thermodynamic activity of MnO in slags, the activity data of MnO in the SiO2-MnO,[4–6] SiO2-MnO-CaO[4] and SiO2-Al2O3-CaO-MnO (MnO < 10 mass pct)[4,5,7–10] systems were measured. Besides, numerous investigations dealt with the slags containing FetO with the aim to utilize Mn resource in the steelmaking process effectively.[11–17] For example, the activities of MnO in CaO-SiO2-FetO-MnO[11] and FeO-MnO-MgO-P2O5-SiO2(-CaO)[12] slags were measured by equilibrating Ag with slags under controlled atmosphere at 1673 K (1400 C). The activities of MnO BAIJUN YAN, XUEXIN CHEN, and JUN TAO are with the Department of Physical Chemistry of Metallurgy, University of Science and Technology Beijing, Beijing 100083, PR China. Contact e-mail: [email protected] Manuscript submitted August 1, 2016. Article published online December 22, 2016. 1100—VOLUME 48B, APRIL 2017

in CaO-MnO-SiO2-PO2.5(-MgO, FetO) slags[13] were measured through the equilibrium between Cu and slags under controlled atmosphere in the temperature range of 1573 K to 1673 K (1300 C to 1400 C). The activities of MnO in the CaO-SiO2-MnO-FetO-P2O5MgOsat slags with high MnO content were measured by equilibrating with liquid iron[14] under Ar atmosphere at 1873 K (1600 C). However, regarding the thermodynamic properties of MnO in the FetO-free slags with high MnO content, only a few systems were investigated. For example, the activity of MnO in MnO-CaO-SiO2[4] slag at 1773 K (1500 C) and 1923 K (1650 C) with the molar fraction of MnO as high as 0.5, the activity of MnO in MnO-SiO2-Al2O3 slags[18] at 1823 K (1550 C) with the molar fraction of MnO ranging from 0.232 to 0.705, and the activity of MnO in MnO-SiO2-Al2O3-MnS slags[19] at 1773 K (1500 C) with the molar fraction of MnO less than 0.55 were meas