Thermodynamics of Mn in Cu-Mn Melts
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anese is one of the most important elements in alloy steel as it can significantly improve the mechanical properties of steel, such as strength, hardenability, and toughness.[1] For some advanced high strength steel, such as TRIP and TWIP aided steels, the content of manganese is even up to about 30 wt pct.[2–4] Manganese alloying in steel is done by adding ferromanganese in ladle, or adding less expensive manganese ore in an oxygen steelmaking converter directly. Therefore, the redox equilibrium between Mn in liquid steel and MnOcontaining slag, especially for the high Mn content steel and high MnO-containing slag, is important for the optimization of alloying process. To determine the activity of one component in slags, copper is an appropriate reference metal to equilibrate with slags.[5–7] The merit of copper as reference metallic phase is that it does not reduce the component in slag, so the composition of slag phase is easy to be controlled. Therefore, the information on the activity coefficient of manganese in liquid copper is useful and required for determining the activity of MnO in slags. Considering the activity coefficient of manganese in liquid copper, some investigations have been carried
out. Hultgren et al.,[8] Spencer and Pratt[9] and Uchida et al.[10] have reported the Henry’s constant of manganese in liquid copper, c0MnðlÞ , at 1500 K, 1573 K, and 1673 K (1227 C, 1300 C, and 1400 C), respectively. Jung et al.[11] have reported the temperature dependence of the Henry’s constant of manganese in liquid copper in the temperature range from 1623 K to 1773 K (1350 C to 1500 C). However, these thermodynamic data are not enough for measuring the thermodynamic properties of MnO in high MnO-containing slag. First, there were no data of 1873 K (1600 C), reported, this temperature is close to the steelmaking temperature. Second, the content of manganese in liquid copper investigated in the literature is less than 0.2 wt pct,[11] this concentration range is not broad enough. If copper is used as reference metallic phase to equilibrate with high MnO-containing slag, the concentration of manganese in liquid copper will be high correspondingly. When the content of manganese in liquid copper exceeds the concentration range in which the activity coefficient is independent on composition, the Henry’s constant will no longer be used. That is to say, a relationship to correlate the activity coefficient to composition is necessary. To express the activity coefficients of solute in solution, the equation proposed by Wagner[12] has been widely used. However, the quadratic formalism proposed by Darken can be applied to higher solute content. Therefore, in this study, the activity coefficient of manganese in liquid copper was measured over a broad concentration (0.48–2.53 wt pct) in the temperature range from 1673 K to 1873 K (1400 C to 1600 C), and Darken’s quadratic formalism was employed to correlate the activity coefficient of Mn in liquid copper to composition. Simultaneously, the linear relationship between the Henry’s con
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