Numerical investigation of unsteady molten steel flow and inclusion behavior in the tundish in the ladle change period

Abstract

Prevention of defects caused by inclusions is an important technical issue in the production of highgrade steel products. In particular, inclusion removal in the continuous casting tundish is an essential technology for production of high-grade steels. It is well known that inclusion removal in the ladle change period is more difficult than during steady state casting. However, the unsteady phenomena of molten steel flow and inclusion motion in the ladle change period have not been studied in detail. To clarify these phenomena, unsteady molten steel flow and inclusion particle motion in the tundish in the ladle change period were investigated by numerical approaches. First, a numerical simulation of the unsteady molten steel flow and unsteady inclusion particle motion was carried out. As a result, it is found that the outflow rate of inclusions to the mold increases sharply immediately after the start of pouring from the new ladle. Second, flow characterization of the molten steel flow in the tundish in the ladle change period was carried out. A new method using a combined model was proposed to evaluate the flow characteristics of unsteady state tundishes in the ladle change period. The method was applied to the numerical simulation results, and showed that sharp increases in the well-mixed volume and dead volume occur simultaneously with inclusion outflow. This result indicates that flow control at the start of pouring from a new ladle is an effective approach to improve the inclusion removal performance of tundishes. © 2014 ISIJ.