Kinetics and mechanisms of calcium dissolution and modification of oxide and sulphide inclusions in steel

Steel clad calcium wire was fed into 40 kg heats of AISI 1045 steel with various sulphur and aluminium contents under argon atmosphere. Samples were taken frequently during and after calcium injection for chemical and inclusion analysis from 12 experiments. Calcium absorption was found to be enhanced by higher sulphur and oxygen contents in steel. The enhancement was explained by countercurrent diffusion of calcium against sulphur and oxygen in the boundary layer at the injection point. Calcium diffuses through the boundary layer into the melt where it modifies oxide and sulphide inclusions. The overall interaction between oxides and sulphides with the bulk drives towards the equilibrium between lime, calcium sulphide, and dissolved oxygen and sulphur. The rate of approach to equilibrium was interpreted using a mathematical model for the multiphase kinetics of calcium absorption, deoxidation, desulphurisation, and oxide and sulphide inclusion modification during and after injection. The implications for full scale operation are discussed.