Development of high speed continuous casting techniques of high silicon steel

At Yawata Steel Works, using Bow type continuous casting machine, the high Si content (more than 3%) steel plates are manufactured with thicknesses up to 250 mm. To improve the productivity and as a cost reduction measure the line speed was increased from 1.2 m /min to 1.6 m/min, which has resulted in appearance of internal fractures and cracks in the product. Authors report on their findings and countermeasures to eliminate such defects. A secondary cooling method is applied for the purpose. At 1.6 m/min the defects are formed in the form of blisters occurring on the Looses Side as shown in illustrations, especially at approx50 mm from Loose Side, the number of pillar-shaped crystal structures also distinctively increase. On the Fixed Side, the occurrence of blisters are quite rare. Using secondary cooling at 1.2 m/min the maximum bulging between the rolls was 0.2%, however at 1.6 m/min this is increased to 0.9% with significant defects in the material. The slab edge cooling at III to IV zones show drastic reduction in the internal cracks. The roll gap at horizontal zone in continuing cast machine and the effects of electromagnetic stirrer on equi-mixed zone ratio are plotted. Also, experiment results for compression casting (CPC) reveal reduction in the number of internal cracks.