The results of industrial research on the end-to-end quality evaluation of continuous cast slabs made of SS400 steel and hot-rolled sheet rolled products made from them, in the context of ship consignment, are presented. The performed evaluation of the frequency distribution of defects for each of the CCM revealed that, despite the fact, that during the control fire cleaning the surface quality of slabs from CCM #1 was slightly worse (1,1-2,0 %) than from CCM #2, the finished sheets from slabs casted on CCM #1 have a better quality than from slabs casted on CCM #2. At the same time, in the conditions of both machines, the quality of slabs from stream #2 is better than from stream #1. A consequence of the unstable internal quality of the sheet with a thickness of 30-45 mm was the fact that restrictions were imposed on the maximum thickness of the sheet: no more than 25.0 mm. In the course of microstructural analysis of the causes of cracks and the nature of segregation, it was found that the presence of non-metallic inclusions in the internal structure of the sheet is, in fact, the source of the crack development. Analysis using energy-dispersive x-ray spectroscopy (EDX) showed that nonmetallic inclusions in the dominant mass are manganese sulfides MnS.