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.