Advanced Chamfered Mold Design for Reducing Slab Corner Cracks in High-Speed Steel Casting

Abstract Transverse corner cracks on the slab surface occur most frequently, particularly in hypo-peritectic steel cast by the vertical-bending casters. These defects require additional surface machining before rolling, along with compensating for temperature drops in the reheating furnace, which significantly increases steel production cost. To address this issue, POSCO developed a chamfered mold, which effectively reduced transverse corner cracks when operating at casting speeds below 1.0 m/min. At higher speeds, however, the chamfered mold exacerbated side effects such as longitudinal cracks on chamfered faces. With insights gained from a multiphysics model, it is revealed in this work that these longitudinal cracks are caused by uneven solidification due to excessive gap formation from insufficient taper at the corner in the mold top region. Consequently, a better chamfered mold has been designed to improve taper on both the wide and narrow faces, leading to a reduction in the gap size and associated problems. This new mold is currently being applied to specific high-speed casters with higher cracking rates, and is found to be effective in reducing transverse corner cracks without side effects of longitudinal cracks or excessive mold wear.