A Novel Control Technique for Longitudinal Off-Corner Depressions on Wide Faces of Continuous Casting Slabs: Effect of the Mold Design on Controlling LOCDs

Associated with uneven heat transfer in molds, longitudinal off-corner depressions (LOCDs) have been identified as a general defect on wide–thick slabs during continuous casting. Additionally, the concurrent surface and subsurface cracks accompanying LOCDs consistently undermine the quality of high-end steel production. To control LOCDs and crack defects, a multibody and multifield coupling model is developed, upon which a convex-structure mold (CSM) is designed and optimized. In this work, the model is extended to cover the mold, secondary cooling zones, and reduction segments. Thus, the shell deformation can be described during the full process of continuous casting. Based on the model, the CSM is thoroughly compared with a traditional flat-plate mold (FPM) in terms of contact status, air gap expansion, interfacial heat transfer, shell growth, shell deformation, and LOCD formation. The results show that shell shrinkage in the FPM causes a larger contact gap at the corners. Consequently, thick slag layers and air gaps forming around shell corners lead to a hot (thin) spot at the wide face off-corner. With the corner gaps being closed in the CSM, the shell growth at the off-corner is homogenized, and the local hot spot disappears. In secondary cooling zones, the solidifying shell cast by the FPM undergoes larger deformation due to the thin spot. However, uniform shell growth in the CSM could avoid concentrated stress and increase the resistance to deformation. Therefore, the width and depth of the LOCD are greatly reduced throughout the continuous casting process. At the end of mechanical reduction, the depths of the LOCDs in the FPM and CSM cases are 1.77 and 1.1 mm, which correspond to heavy and slight defect levels, respectively. Through these numerical comparisons, the advantages of CSMs in controlling LOCDs are finally confirmed.