Control of centerline segregation in slab casting

Abstract

A complex mathematical model characterizing the centerline segregation level in the midregion of continuously cast slabs was developed. The basic heat transfer and solidification model connected to the semi-empirical liquid feeding model (LMI - Liquid Motion Intensity model) gives the possibility to estimate the centerline segregation parameters of slab cast under industrial circumstances. Solid shell deformation changes the volume of the space available for the liquid inside the slab and hereby also changes the conditions of liquid supply. In modelling slab casting in practical industrial cases the deformation of the solid shell cannot be ignored, especially from the point of view of centerline segregation formation. From this aspect, the most important effects resulting in deformation of the solid shell are as follows: shrinkage of the solid shell due to solidification and cooling; setting of the supporting rolls along the length of the casting machine i.e. decreasing the roll gaps as a function of cast length; bulging of the solid shell between successive supporting rolls; positioning errors and wear of rolls; eccentricity of individual rolls; etc. The critical parameter to describe the inhomogeneity in the center area of slabs is the porosity level in the mushy region. As a result of calculations performed by the model, ISD Dunaferr Co. Ltd. has changed the strategy of supporting roll settings in their continuous casting. After the modification had been implemented on casting machines, the quality problems due to centerline segregation of slabs decreased to a great extent.