Variations in steel cleanness during transient continuous casting practices

Abstract

During sequenced continuous casting, concerns have been expressed about the density of nonmetallic inclusions present in steel slab produced during the transition period as successive ladles are teemed. Consequently, for critical applications such as thin wall tinplate products, with can wall thicknesses of ～0.26 mm, only steel cast during 'steady state' conditions is selected. In contrast, slab cast over defined lengths before and after a ladle change is downgraded to less demanding applications, irrespective of cleanness. To evaluate this practice, steel inclusion levels have been assessed during ladle change operations, when the steel reservoir in the tundish fell to below 20 t. This plant based study confirmed that, during the transition period, marked variations occur in the size and morphology of the nonmetallic inclusions, as well as in the oxygen content of the steel slab.