UST rejection ratio of heavy plates was relatively high sincethe 300 mm thickness slab caster has been operated atPohang Works. An internal quality prediction system for slabwas developed that can evaluate the center segregationlevel of slabs within 5 minutes after cutting. The rejectionratio of heavy plate thicker than 70 mm could be reducedeffectively from 5% down to below 0.5% by applying thistechnology.