Among many properties of continuous-casting powders, chemical composition, melting rate introduced by the present authors (1/tf), and viscosity (η) have been found to give most significant influences on longitudinal facial cracks and scums on continuously-cast wide slabs for plate use. Laboratory-and industry-scale experiments exhibit that, under the experimental conditions the following properties are required for the powders to make the slabs free from the two surface defects:(1) composition of CaO/SiO2 0.6-1.1, Al2O3 7-10%, F-<3%, F-<+CO32-<5%, freeC≤5%, S≤4%, and (2)η, tf., andη/tf of 48 poises, 20 sec., 2.4±0.2 at 1250°C, and llpoises, 11sec., 1.0±0.1 at 1400±C, respectively.
