Sliver defects in an ultra-low carbon Al-killed steel caused by low steel level in the tundish

Abstract

Sliver defects were detected in galvanized and uncoated cold-rolled strips, and their causes were investigated. Most of these strips were produced from transition ladle slabs, which were obtained in a sequence of twenty heats of an ultra-low carbon Al-killed steel. A significant reduction in the steel level in tundish occurred during these slabs’ casting. The strip defects, and as a comparative, a mould flux inclusion found in a first slab of the sequence, were analysed with a scanning electron microscope (SEM). Also, each of the twenty heats was sampled in tundish, quenched in water, and manually analysed with SEM to characterize its dominant inclusions. Regarding the sliver defects, mainly silica together with alumina or Al–Ti–O systems particles were found in them. The primary sources for these particles are likely tundish flux and reoxidation products. Finally, a mechanism was proposed for the formation of these inclusions.