CONTROL OF INITIAL SOLIDIFICATION OF STEE L BY APPLICATION OF HIGH-FREQUENCY MAGNETIC-FIELD

This research work was conducted to find the possibility of controllin g the initial solidification in the continuous casting processes with the triple point by appling high frequency electromagnetic field. Some continuous casting processes such as the horizontal continuous castin g have the triple point defined as the intersection of a refractory, a mold and molten steel. Since the triple point has a role of initiatin g solidification shell, proper initiation of solidification at the poi nt is required. The imposition of high frequency electromagnetic field on the triple point was investigated to achieve the appropriate solid ification control. First of all, numerical calculations were done to e stimate the magnetic pressure and the joule heat. Then, bench scale ex periments and plant tests with the horizontal continuous easter in Kei hin Works were carried out. An induction coil was installed around the triple point and driven at 3kHz in both cases. For the bench scale ex periments, 250kg of plain carbon steel was cast into a round billet wi th 65mm in diameter, and for the plant tests 50t of high carbon steel was cast into billets with 330mm in diameter. The cast surface appeara nce and subsurface solidification structure were examined. Without ele ctromagnetic field, the triple point defects such as rough surface and irregular subsurface solidification structure appeared on the cast. O n the other hand, almost no such defects were observed. Better bonding between the shell tip and the molten metal near the triple point was supposed to be promoted by the electromagnetic field.