A study was made on the desulfurization rate of steel by CaO-CaF2 powder injected into a 150 t ladle.
EPMA analysis of suspending particles taken from an Al-Si killed steel melt during powder injection was made, and two types of particles contributing to desulfurization were found. The one formed by coalescense of injected powder with deoxidized Al2O3 particles showed a high sulfur partition ratio of 1 000 to 6 000. The other type of suspending particles formed by coalescense of injected powder with entrained top slag and Al2O3 showed a lower sulfur partition ratio. Observed sulfur partition ratios of both types of particles agree with those estimated from thermodynamic calculation, which indicates that the reaction between suspending particles and sulfur in a steel melt is in equilibrium.
A model was proposed, which took account of resulfurization from top slag. Calculation based on the model shows that the contribution of transitory reaction to overall amount of desulfurization is approximately 46% under this experimental condition.
