Effect of Hook Formation During Initial Solidification on Distribution of Subsurface Inclusions in Ultralow Carbon Steel Slabs

摘要

Entrapment of macro-inclusions under the shell surface would lead to the surface quality of final steel products, which is closely related to the formation of oscillation mark hooks during the initial shell solidification. In this study, the distribution of inclusions at different depths beneath the shell surface was analyzed by auto-SEM. Water simulations and particle image velocimetry (PIV) measurements were conducted to reveal the mechanism of inclusions captured by hooks. The results shown that the inclusions were maximizing at 1 mm depth from the slab surface. Three kinds of inclusion movements in hook region were found: being captured by the meniscus; being captured below the meniscus; and some of captured inclusions returned to liquid steel. Most of the inclusions were captured near the meniscus which might lead to the highest inclusion amount near the surface of slab. Additionally, the number of inclusions captured by hooks would be reduced with increasing the casting speed.