Change of Mold Slag Composition during Slab Casting of Steel with High Al Content

Abstract

Three different mold slags have been sampled in dependence of time during slab casting of TRIP steel, and compositional changes have been analyzed. Mass transfer coefficients governing the decrease of silica and increase of alumina have been determined. Moreover change of manganese content was investigated in dependence of the initial manganese content of the mold powder which was close to zero for one of the powders investigated. The following findings have been revealed: Mass transfer coefficients are rising with increasing elapsed time or decreasing silica content, respectively. An initial increase of manganese content by oxidation from the steel followed by later reduction has been observed for the manganese free mold powder. For interpretation of these findings, further simulation according to an effective equilibrium reaction zone model was performed. It was revealed that the primary impact of the steel flow at the steel/slag interface close to the mold wall followed by a stratified flow is of major importance for the phenomena observed. Further results make it possible to predict the steady state composition and show that steady state silica content is nonzero in any case. Moreover, for the mold powders investigated here, it was concluded that manganese content does not decrease silica reduction.