Practically the whole steel, including the free-cutting one, is casting by continuous casting machines (CCM). The technological parameters of the free-cutting steel continuous casting have their features, since the high content of Sulphur and phosphor in the free-cutting steel, necessary for its high machinability, increases the probability of fractures and emergency breach of metal. The purpose of the work was study of influence of temperature-speed mode of A12 free-cutting steel casting on cooling agent consumption in the secondary cooling zone of radial type billet CCM. The CCM mold was 900 long with supporting system on the mold frame of two rows of rollers. The secondary cooling (SC) zone comprised four zones of 340, 2360, 3460 and 3610 mm length. The cooling in the first zone is accomplished by water, in the others – by water-air mist. The study was carried out by application of mathematical simulation method to the process of billet secondary cooling, elaborated by V.N. Selivanov. The temperature of the free-cutting steel billet surface was calculated by zones of secondary cooling at various steel temperature in the tundish. The flow density and water consumption in various SC zones determined, necessary to reach the required variation of billet surface temperature. The dependence of total and specific water consumption for the billet cooling on the metal temperature in the CCM tundish determined.
The speed of billet withdrawal from a continuous caster (CC) mold has a decisive effect on the CC productivity. However, increase of the speed results in an increase of pollution of the CC metal by non-metallic inclusion and increase of surface defects of CC billet. Estimation of steel casting speed mode impact on the degree of different defects formation presented for long products CC billets, casted at a five-strand CC of radial type. Defects of CC billet from Ст3сп steel grade studied for a billet having section of 150×150 mm. The purpose of the study was to determine the degree of influence of withdrawal speed, metal chemical composition and billets cross section dimensions on billets quality. Array of industrial data of more than 550 billets studied, 80.4% of which were casted by an open stream and the balance – by a closed stream. As a result of the CC billets quality study it was confirmed, that during metal casting by an open stream the degree of evolution of form defect, like rhombic defects, internal and surface defects is higher comparing with those when casting by a closed stream. General tendency of increase of the CC metal pollution by non-metallic inclusions at the increase of billet withdrawal speed. The tendency is similar for both casting by an open and by a closed stream. However, during casting by an open stream the increase takes place rather evenly. During casting by a closed stream a sharp increase of billets with defects were observed at the billets withdrawal speed exceeding 2.4 m/min. Linear dependencies of billets withdrawal speed while casting by a closed stream on the degree of liquation cracks evolution and general strips, edge point pollutions and peripheral fine structure metal zone thickness determined. To improve the long products billets surface, casted by a closed stream, it was recommended to restrict the withdrawal speed of the billet from a carbon steel of general quality by the value of 2.4 m/min.
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