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.