Development and Application of the Mixing Model to Predict the Composition Concentration of Intermixed As-Cast Steel

Abstract

Although there have been studies on models for predicting the mixing concentration of elements between old and new molten steel with different chemical components during continuous casting, there is limited information about the concentration of the mixed portion in the cross-sectional and the longitudinal directions of the intermixed bloom. In the present study, the concentration of the intermixed bloom generated by the different-grade continuous casting is measured in the cross-sectional and the longitudinal directions. A significant difference in the concentration of the mixed portion is noticed at different heights along the thickness direction of the intermixed bloom. Based on the measurement results, we propose a new mixing prediction model that can accurately predict the concentration of the mixed portion at the subsurface and the center in the intermixed bloom along the longitudinal direction. The present results show that each height which has the minimum and the maximum concentrations of the mixed portion in the cross-section varies along the longitudinal direction of the intermixed bloom. This implies that the maximum and the minimum concentrations of the mixed portion in the cross-section do not necessarily occur only at the surface and the center of the intermixed bloom. The newly proposed mixing prediction model can be employed to cut off the mixed portion by predicting the minimum and maximum concentrations of the mixed portion in the cross-section along the length direction of the intermixed bloom. The newly proposed mixing model is also applied to predict the concentration of the mixed portion of the intermixed slab. The concentration of the mixed portion is measured along the width direction of the intermixed slab in order to determine the location with the maximum and minimum concentrations in the slab with a large cross-sectional aspect ratio. The concentration of the mixed portion in the thickness direction not only at the center of the slab in the width direction but also the edge of the slab in the width direction shows a large difference. However, at the 1/4 and the 3/4 positions in the width direction, the difference in concentration of the mixed portion in the thickness direction was not large. The newly proposed mixing model can also be employed to cut off the mixed portion by predicting the minimum and maximum concentrations of the mixed portion in the cross-section along the length direction of the intermixed slab. As a result of applying the new mixing model to the on-site online process, the annual average reduction rate are 52.5% for the scrapped intermixed blooms, 29.5-32.6% for the scrapped intermixed slabs, respectively. In addition, all hot-rolled steels, rolled from the adjacent slabs produced before and after the intermixed as-cast steel, satisfied the allowable concentration range of each steel. In this study, the methods for reducing the mixed portion were also considered, and the possibility of reducing the mixed portion is confirmed through experiments.