Prevention of Scum Formation and Entrapment in High Carbon Steel Billets

Gradual build-up of scum over the liquid steel surface in the mould gives rise to entrapped exogenous inclusions and slag patch in the cast billets. The problem is more commonly observed during the open stream casting of continuous casting of high carbon (C > 0.6 mass%) steel billets. This problem has been quite commonly observed at Tata Steel during its billet casting. Present work aimed at eliminating the problem of scum formation during open stream billet casting of high carbon steel billets. This work involved experiments in the laboratory as well as in the plant. In addition, based on liquid steel composition thermodynamic calculations were carried out for predicting the possible oxide inclusions in Mn-Si deoxidised steels. Water model experiments were carried out in a full-scale billet caster physical model for investigating the influence of tundish outlet nozzle alignment on the entrapment of scum as slag patch over the billet surface. Based on these, cause of scum formation and its exact mechanism of entrapment in cast billets were established. Finally, countermeasures were recommended to the plant. Adequacy of the proposed countermeasures was established through a series of trials in the plant before implementation. Improvement obtained from the implementation over a period of time has been reported in the paper.