A Thermodynamic Model to Predict the Composition of Inclusions in Al‐Killed Ca‐Treated Steels

Abstract

Based on the principle of minimum Gibbs free energy, a thermodynamic model is established to predict the composition of inclusions in the Al‐killed steel during the calcium treatment process. The Wagner model combined with coexistence theory is applied to calculate the Gibbs free energy of the steel‐inclusion system. The composition evolution of inclusions is accurately predicted through the current thermodynamic model which is widely applied to predict the modification of inclusions by the calcium treatment process with different contents of total oxygen (T.O), total sulfur (T.S), and total calcium (T.Ca) in the molten steel. Alumina inclusions can be modified to liquid calcium aluminate inclusions with appropriate T.Ca contents. Solid CaS or CaO inclusions can be formed as a result of the excessive calcium addition to molten steel, while the insufficient calcium addition can hardly modify alumina inclusions to liquid ones. The effect of the T.O and T.S contents on the liquid window is also discussed. The relationship between the value of T.S/T.O in the molten steel and the composition of inclusions is also studied. Based on the established thermodynamic model, a software for the precise control of inclusions is also developed to guide the calcium treatment operation timely in the accrual refining process.