Kinetics, mechanisms and modelling of calcium treatment of steel

Abstract

<p>Steel-clad calcium wire was fed into 40 kg heats of AISI steel with various sulphur and aluminum contents under argon atmosphere. Samples were taken continuously during and after calcium injection for chemical and inclusion analysis from more than twelve heats of injection. Calcium dissolution was found to be enhanced by instantaneous reactions with oxygen and sulfur in the boundary layer. The unreacted calcium diffuses through the gas-liquid film into the melt for oxide and sulfide inclusion modification. The overall interaction between oxides and sulfides with the bulk drives towards the equilibrium of (CaO) + S = (CaS) + O. The system paths from the initial state to the final state were kinetically studied with the assistance of a_CaS-a_MnS diagrams, which were calculated by applying a regular solution model to the solid phase and an ideal model to the liquid phase of the CaS-MnS phase diagram at various steelmaking temperatures. A mathematical model for the multiphase kinetics was developed to interpret the calcium dissolution, deoxidation, desulphurization, oxide and sulfide inclusion modification during and after calcium injection. The implications for full-scale operation were discussed.</p>