Formation mechanism of point-like defect in IF steel sheet during deep drawing process

Abstract

In the current study, the three-dimensional morphology of a typical point-like defect in deep drawing IF steel sheets was characterized by step machining method, and the corresponding casting parameters and stopper tip clogs were also analyzed. The results show that the defect contains two parts: single alumina refractory grain and alumina clusters. Furthermore, the actual size of inclusion in the defect using the 3D characterization was determined to about 1 mm, much larger than that only from surface evaluation (~ 0.1 mm). Based on clog analysis and tracing casting parameters, the formation mechanism of defect during the whole production process was proposed. The defect may originates from the occasional dislodging of stopper tip deposits in the tundish level rising period of ladle exchange process where the entrapped FeO rich ladle slag into the tundish and temperature drop worsen the clogging. Therefore, elimination of ladle slag entrapment and stabilization of steel temperature in the tundish during ladle change procedures help to eliminate the point-like defect of steel sheets for deep drawing purpose.