Prevention of corner cracks in slab continuous casting 499

摘要

Surface corner cracks are sometimes observed on slabs of high strength low alloyed steel grades, requiring expensive scarfing. To avoid surface crack formation, we can act on the steel intrinsic ductility loss through the limitation of S and N contents: S < 30 ppm and N < 40 ppm are well adapted thresholds. A Ti/N ratio higher than 3.6 and a limitation of Al*N product lead to a significant improvement of the quality results. In addition, the continuous casting process must be optimized. It aims at limiting the thermomechanical strains faced by the slab surface during solidification and cooling, particularly when the slab corner temperature is in the range of the ductility trough. The main process actuators are the mould powder, the secondary cooling curves and the limitation of the misalignments in the top part of the caster, especially the transitions between the mould foot-rolls, the vertical and the bending segments.