Abstract
During the year 2000, billets of several steel grades produced in the billet caster of Sidetur Casima works presented a defect classified a priori as slag entrapment. A study was carried out to define the root cause of the problem and take action to solve the problem. A metallographic study of the defects in the billets is presented, revealing that the defect was not only pure slag entrapment, but that it was associated with cold drops and porosity. Various etching techniques were used for microscopic examination; also, SEM analysis was conducted. The mechanism for scum formation and entrapment is discussed, based on the literature and on a thermodynamic model of the Fe-Si-Mn-O system. A mechanism for formation and entrapment of cold drops is suggested, based on the findings of the metallographic study. The actions taken in the plant to cope with the problem are summarised. The results in terms of billet rejection before and after the actions had been taken are detailed.
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