Distribution of Ca-oxide, Ca-sulfide and MnS in Ca-added CC slabs has been investigated by new X-ray microanalyser (CMA).Although the relation between the amount of MnS and ACR and ESSP which had been proposed as parameters indicating the degree of shape control was found, it was not quite satisfactory since MnS formation was observed to be suppressed by Ca addition even in the slab in which oxygen content was too high to form CaS according to the ACR or ESSP concept.
On the other hand, calcium-aluminate inclusions were found to be classified into the following two types:
i) Ca+O type ; Calcium-aluminate covered by thin S enriched zone.
ii) Ca+S type ; Calcium-aluminate enriched by S in the whole region.
The Ca+S type inclusions were mainly observed in the segregated area.
A thermodynamical consideration as well as the above experimental results revealed that the desulfurization by calcium-aluminate during the solidification had the dominent importance in the shape controlling mechanism.This desulfurization mechanism by calcium-aluminate inclusions qualitatively explains the above descrived deviation of the experimental results from the prediction by ACR or ESSP concept.