Mathematical Model for Prediction of Composition of Inclusions Formed during Solidification of Liquid Steel

Non-metallic inclusions originate mainly during secondary steelmaking due to deoxidation and other exogenous sources. Additional inclusions form during cooling and subsequent freezing of liquid steel. Rejection of solutes by the solidifying dendrites causes segregation of solutes in the interdendritic liquid with consequent build-up of their thermodynamic supersaturation. The work reported in the present paper was undertaken to develop a computation procedure for prediction of inclusion compositions formed during cooling and solidification of liquid steel. The model has been applied to an inclusion sensitive grade of steel. Segregation of various solutes with progress of freezing has been calculated using the Clyne-Kurz microsegregation equation. A sequential computation procedure involving segregation equation and thermodynamic equilibrium calculations by the Factsage thermodynamic software has been developed. Compositions of inclusions at various solid fractions have been determined. Model predictions have been compared with literature as well as with inclusion compositions determined in continuously cast billet samples using SEM-EDS. Reasonably good correspondence between model predictions and observed inclusions have been obtained.