SLIVER EVOLUTION IN THE ROLLED MATERIAL FOR AUTOMOTIVE APPLICATION IN ARCELOR MITTAL TUBARAO/VEGA

In 2009 it was carried out an investigation in the Arcelor Mittal Tubarao steelmaking process to identify the origins of sliver index rejection for cold rolled ultra-low carbon material for automotive application, focusing on cleanliness. It was analyzed the main refining and continuous casting process variables and correlated with the liquid steel cleanliness using the Spark-DAT and total oxygen (TOS) methods. Correlation with the defect in the final product was conducted as well. The results showed an increase in the inclusions level from refining to the continuous casting, as well as the cleanliness evolution along the tundish sequence. The most sensitive variables correlated with the final defect were the cast speed and the alumina clogging. Furthermore, there was the necessity to review the quality model for critical applications. The main variables control and the quality model revision led to a sliver index reduction in order of 95 % in the exposed material.