Development of a multicomponent reaction rate model coupling thermodynamics and kinetics for reaction between high Mn-high Al steel and CaO-SiO2-type molten mold flux

Abstract

A new multi-component reaction model was developed in order to describe complex reaction phenomena between a high Mn-high Al steel and a CaO-SiO2-type molten mold flux. This model is an extension of Robertson's multicomponent mixed-transport-control theory (Robertson et al., 1984) [7], where rate controlling step is assumed to be a mass transport of diffusing species in a boundary layer, while chemical equilibrium is assumed at the reaction interface. This model also employs a CALPHAD type multicomponent-multiphase thermodynamic calculations for chemical equilibria at the interface. By explicitly taking into account 1) local equilibrium at the liquid steel-liquid flux interface, 2) flux density equations for each diffusing species in the steel and the flux phases, and 3) instantaneous change of mass transfer coefficients of all diffusing species in the flux phase by varying viscosity of the flux, previous laboratory scale experimental data could be well explained under various [pet Al](0), [pct Si](0) in the liquid steel, (pet CaO)/(pct SiO2), (pct Al2O3)(0), (pet MgO)(0) in the liquid flux, and reaction temperature. From the model calculations under the various [pet Al](0), it was concluded that the present reaction model can be successfully applicable from low [pct Al] to high [pct Al] conditions in liquid steel. The present model was further extended in simulating composition change in a mold flux in a continuous casting mold, where the steel and the flux continuously enter and leave. The model calculations show good agreement with pilot plant scale data available in literature. From the calculation results under different casting variables such as [pct Al](0), mold flux pool depth, and mold flux consumption rate, the Al2O3 accumulation in the CaO-SiO2-type mold flux during the continuous casting was discussed.