Effect of cooling conditions on the size evolution of typical inclusions in the Al-Ti deoxidised steel

Confocal laser scanning microscopy was used to perform experiments with various cooling rates for the solidification of Al-Ti deoxidised steel. The effects of cooling rate on the morphology, size distribution of observed with typical inclusions, Al2O3, TiS, and Al2O3-TiS in the steel were investigated. The experimental results demonstrate that the inclusion morphology is significantly influenced by the cooling rate. With an increase in cooling rate, the number of inclusions smaller than 3 μm rises while the number of inclusions bigger than 3 μm continues to fall. The number density of the inclusions increases gradually with the increase of the cooling rate. The nucleation and growth of inclusion were calculated using a combination of kinetics and thermodynamics. It was found that the cooling rate has no influence on the precipitation temperature of inclusions but has slightly influence on the segregation of solute elements during solidification. TiS inclusions can precipitate at the end of solidification while Al2O3 inclusions can precipitate in the liquid phase based on the thermodynamic calculations. As the cooling rate rises, the size of the inclusions decreases gradually and the effect of cooling rate on inclusion decreases.