Youn-Bae Kang

Modeling short-range ordering in solutions

Abstract Various aspects of the modeling of short-range order in binary and ternary solutions using the Bragg – Williams (random mixing), associate, and quasichemical models are examined. The models are compared with respect to their ability to predict properties of ternary solutions from optimized binary model parameters in the presence of short-range order. It is shown how introducing short-range order through the quasichemical model can explain the observed flattened shape of most miscibility gaps. The combination of the quasichemical model for nearest-neighbor short-range order with the Bragg – Williams model for the remaining lattice interactions is described.

Thermodynamic assessment of the Ce–Si, Y–Si, Mg–Ce–Si and Mg–Y–Si systems

Abstract The binary Ce – Si and Y – Si systems have been critically evaluated based upon available phase equilibrium and thermodynamic data, and optimized model parameters have been obtained giving the Gibbs energies of all phases as functions of temperature and composition. The liquid solution has been modeled with the Modified Quasichemical Model to account for the short-range ordering. The results have been combined with those of our previous optimizations of the Mg – Si, Mg – Ce and Mg – Y systems to predict the phase diagrams of the Mg – Ce – Si and Mg – Y – Si systems. The predictions have been compared with available data.

Dissolution behavior of alumina in mold fluxes for steel continuous casting

Dissolution of alumina in various mold fluxes for steel continuous casting has been investigated by employing the rotating cylinder method. The weight loss of the rod, the dipping area and the immersed time were measured to determine dissolution rate of Al2O3. The dissolution rate increased with temperature of molten fluxes, the rotating speed of the rod and the addition of MgO, CaF2 and Na2O components in the mold flux. When the Na2O content exceeded 5%mass, the dissolution rate was found to decrease. Intermediate compounds such as CaO·6Al2O3, CaO·2Al2O3 and 2CaO·Al2O·SiO2 formed at the Al2O3/flux interface and formation of three compounds was found to play important roles in the dissolution rate. In conclusion, the dissolution of Al2O3 was controlled not only by the mass transfer in the molten flux also by the formation of intermediate compounds on the interface.

Effects of MnO on Crystallization, Melting, and Heat Transfer of CaO-Al2O3-Based Mold Flux Used for High Al-TRIP Steel Casting

An investigation was carried out to study the effect of MnO on crystallization, melting, and heat transfer of lime-alumina-based mold flux used for high Al-TRIP steel casting, through applying the infrared emitter technique (IET) and the double hot thermocouple technique (DHTT). The results of IET tests showed that MnO could improve the general heat transfer rate through promoting the melting and inhibiting the crystallization of mold flux; meanwhile the radiative heat flux was being attenuated. DHTT experiments indicated that the crystallization fraction, melting temperature of mold flux decreased with the addition of MnO. The results of this study can further elucidate the properties of the CaO-Al2O3 slag system and reinforce the basis for the application of lime-alumina system mold fluxes for casting high Al steels.

Modeling surface tension of multicomponent liquid steel using Modified Quasichemical Model and Constrained Gibbs Energy Minimization

Surface tension of multicomponent liquid steel was calculated based on the concept proposed by Butler, which assumes a chemical equilibrium between a bulk phase and a surface phase of a monolayer. Requirement for the calculation of the surface tension was categorized as: 1) accurate description of partial excess Gibbs energies of solutes in the liquid steel, in particular for those of non-metallic solutes such as S, C, etc., 2) physical properties of pure components, such as surface tension and molar volume, and 3) possibility of solving a series of Butler equations for multicomponent liquid steel. In the present study, it is proposed to use the Modified Quasichemical Model in order to describe the partial excess Gibbs energies of solutes, and to use the Constrained Gibbs Energy Minimization in order to solve equilibrium between the bulk and the surface phases of the multicomponent liquid steel. Physical properties of non-stable pure components such as S, C, were treated as variables to reproduce known experimental data in binary systems. The proposed method can be easily extended into multicomponent liquid steel. Examples of the surface tension calculations are presented.

Simultaneous Evaporation of Cu and Sn from Liquid Steel

In order to understand evaporation refining of tramp elements in molten ferrous scrap, Cu and Sn, a series of experiments were carried out using liquid–gas reaction in a levitation melting equipment. Effect of S and C, which are abundant in hot metal from ironmaking process, was examined and analyzed by employing a comprehensive evaporation kinetic model developed by the present authors (Jung et al. in Metall Mater Trans B 46B:250–258, 2014; Jung et al. in Metall Mater Trans B 46B:259–266, 2014; Jung et al. in Metall Mater Trans B 46B:267–277, 2014; Jung and Kang in Metall Mater Trans B 10.1007/s11663-016-0601-5, 2016). Evaporation of Cu and Sn were treated by evaporation of individual species such as Cu(g), CuS(g), Sn(g), and SnS(g), along with CS2(g). Decrease of Cu and Sn content in liquid steel was in good agreement with the model prediction. Optimum conditions of steel composition for the rapid evaporation of Cu and Sn were proposed by utilizing the model predictions.

Aluminum Deoxidation Equilibria in Liquid Iron: Part III—Experiments and Thermodynamic Modeling of the Fe-Mn-Al-O System

Deoxidation equilibria in high-Mn- and high-Al-alloyed liquid steels were studied over the entire Fe-Mn-Al composition range by both experiments and thermodynamic modeling. Effect of Mn on the Al deoxidation equilibria in liquid iron was measured by the different experimental techniques depending on the Al content. In order to confirm the reproducibility of the experimental results, the deoxidation experiments were carried out reversibly from high oxygen state by addition of Al as a deoxidizer, and from low oxygen state by addition of Fe2O3 or MnO as an oxygen source. For the Al-rich side, CaO flux was added on top of liquid iron in order to remove suspended Al2O3 inclusions in the melt. Based on the present experimental result and available critically evaluated literature data, the Al deoxidation equilibria in Fe-Mn-Al-O liquid alloy were thermodynamically modeled. The Modified Quasichemical Model was used in order to take into account a strong short-range ordering of atoms in molten state. Deoxidation equilibria and inclusion stability diagram for entire Fe-Mn-Al melt were successfully reproduced by the present model.

Thermodynamic Modeling of Oxide Phases in the Mn-O System

A critical evaluation and thermodynamic modeling for thermodynamic properties of all oxide phases and phase diagrams in the Mn-O system are presented. Optimized Gibbs energy parameters for the thermodynamic models of the oxide phases were obtained which reproduce all available and reliable experimental data within error limits from 298 K (25 °C) to above the liquidus temperature at compositions covering from MnO to MnO2, and oxygen partial pressure from 10−15 to 102 (bar). The optimized thermodynamic properties and phase diagrams are believed to be the best estimates presently available. Two spinel phases (

On the Evaporation of S from Liquid Fe–C–S Alloy

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