The aims of this work were the classification and investigation of surface defects on rolled billet material by using an automatic surface inspection system (SIAS - Surface Inspection Automated System). Besides the influence of the carbon content on the crack sensitivity it also could be shown that first cast blooms of every sequence show more surface defects after re-rolling than the other blooms. The careful metallographic investigation of the appeared surface defects in the face centre was a further focus of the work. Most defects appearing at the re-rolled billet surface seem to have their origin in the continuous casting process. Now, ten months after the start-up, the installation works reliable. Only some fine adjustments of the software are still necessary to eliminate the disturbing influence of the scale at the surface.