Prevention of corner cracks in slab continuous casting

Abstract

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