Influence of Mold Flux Basicity on Surface Quality of Ultra-low Carbon Steel Slabs

Abstract

Mold flux has a large influence on the surface quality of ultra-low carbon steel slabs. Especially, its entrapment in the continuous casting mold must be prevented in order to reduce inclusions in the surface layer of the slabs. In this work, experimental casts with a pilot continuous caster were conducted and the influence of mold flux basicity on the surface quality of the slabs was researched.Spherical inclusions, which existed in the surface layer of the slabs and seem to be caused by the entrapment of molten flux in the mold, decreased in number or size, with the increase of mold flux basicity.The effect of basicity could be explained in terms of interfacial tension or wettability between mold flux and molten steel. Thus, the number and the size of spherical inclusions decreased with the increase of interfacial tension and contact angle of molten flux on the surface of molten steel. This effect was considered to be larger than that by the viscosity or density of mold flux.