Formation of a Solidified Hook-like Structure at the Subsurface in Ultra Low Carbon Steel.

Influence of carbon content on a solidified shell structure at meniscus is examined by investigating continuous cast slabs and by mold dip experiments. Large hook-like structures are frequently observed on oscillation marks of continuous cast slab subsurfaces and are created in a solidified shell in mold dip tests in ultra low carbon steel. Shapes of the solidified shell structure formed in dip tests are analyzed in detail. The surface of molten steel solidifies and is maintained by the static balance of interfacial tension and gravity force. Shape of the hook-like structure of solidified shell is a result of deformation resulting from the balance of bending force toward the molten steel side and reverse force by static pressure and shell strength. Solidification of the molten steel surface at meniscus part is numerically calculated. This solidification far from the mold wall caused by high solidification temperature and a thin mushy zone generates a large hook like structure in ultra low carbon steel.