In order to examine the mechanism of the change of CaO and CaS content in inclusion during and after Ca addition, experiments were made with 180Kg of molten steel in MgO crucible at 1873K. Effect of initial sulfer content, Ca consumption and Ca addition pattern on the change of inclusion composition were verified in the experiments.
A mathematical model, in which the kinetics of Ca evaporation and the reaction between inclusion and molten steel were considered, was developed to calculate the change of CaO and CaS content in inclusion as function of time. The calculated results coincided with the experimental results.
The following reaction mechanism was, thus, estimated:
(1) The change of inclusion composition during Ca addition (a) was in the completely reverse way of the change after Ca addition (b) in which [Ca] was vaporized.
Al₂O₃_??_CaO-Al₂O₃-low CaS_??_CaO-Al₂O₃-high CaS
(2) The way of the change of inclusion composition was influenced by [%S] in spite of no effect of Ca consumption and Ca addition pattern.
(3) The above mentioned phenomena depend on the following reversible reaction:
CaO_inclusion=Ca+O
CaO_inclusion+S=CaS_inclusion+O