As cast CC slabs of microalloyed steels are prone to surface cracking. Precipitation phenomena, initiated during solidification, reduce ductility at high temperature. The size, morphology and distribution of precipitates in as cast semis depend on solidification rate, on secondary cooling, straightening and cooling off the caster. Microsegregation of the microalloying additions to the interdendritic boundaries during solidification increases precipitation temperature. Results are presented concerning the effect of solidification and cooling on precipitates characteristics in semis. The characterization of precipitates is quite satisfactory although it could not be clearly correlated with surface quality.