鋳造時に鋳型内で凝固シェルに捕捉された介在物や気泡はブローホールやスリバーといった表面欠陥の原因となることがある。近年，自動車用外板に要求される表面品質は厳格になってきており，鋳型内での凝固シェルへの介在物や気泡の捕捉を低減するため，Fig．1に示すような鋳型内の介在物や気泡に働く力について，これまで様々な研究が行われてきた。%In order to clarify the effect of compositions on the surface quality of ultra low carbon steel slabs, a model experiment investigating the effect of compositions on entrapment of inclusions was performed using molten steel with various concentrations of S, which is a surface active element between molten steel and inclusions, while varying the velocity of the molten steel flow at the solidification interface to obtain clear changes in the interfacial tension between the inclusions and the molten steel.rnAs a result, entrapment of inclusions was enhanced with increasing S concentration, and the effect of S concentration on entrapment of inclusions depended on the velocity of the molten steel flow at the solidification interface.rnIn the case of a large inclusion, the effect of S concentration on entrapment of inclusions is considered to be affected by the various thicknesses of the concentration boundary layer.
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