Solute segregation, and constitution and distribution of inclusions in Ca and/or RE treated continuously cast steel slabs have been investigated as a function of concentrations of Ca, RE, S, and 0. Derivation of an atomic concentration ratio, ACR, of effective Ca or RE to S has been made on the basis of commercial scale experiments. Sulfide shape control is insufficient throughout the slabs at ACR of 0.2 and becomes satisfactory at 0.4 except for center-line segregates. This is in accordance with the previous observation for large ingots. Also, sulfide shape control in the center-line segregates has been found to become insufficient with increasing degree of segregation, because the amount of MnS in the segregates increases with increasing solute segregation ratio. This observation is interpreted quantitatively by the decrease due to the precipitation of CaS and/or RES of concentrations of effective Ca and/or RE in the interdendritic melts in the mushy zone during solidification.
