| Summary: | Since the introduction of continuous casting, concerns exist about the suitability of slabs cast during the transitional periods as successive ladle are teemed. Consequently, for critical applications such as thin-wall tinplate products, 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 the steel cleanness during ladle changes, inclusions levels were assessed when the steel reservoir level in the tundish fell to predefined weights. This plant based research project found marked variations in oxygen levels and inclusion morphology over the transitional period. However, individual inclusions sizes remained consistent over the period. The study concluded that steel cleanness that steel cleanness levels improve towards the end of a heat and current grading rules are unnecessarily downgrading clean steel. The deteriorations in cleanness levels are ladle changes were primarily due to the presence of reoxidation products, caused by the practice of opening ‘new’ ladles with the steel stream unshrouded i.e. exposed to the atmosphere.
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