Patent ID: 7909086

Claim:
A method for continuously casting a billet with a small cross section in which the billet has a cross sectional area of not more than 500 cm 2 and a cylindrical immersion nozzle with a single port of not less than 40 mm in inner diameter is used for pouring a molten steel into a mold, wherein: a surface level of molten steel is measured using an eddy current sensor for molten steel level control in a mold and the molten steel level is controlled based on the thus-measured value, and motion of molten steel in the mold is adjusted by applying electromagnetic stirring; a cooling zone during a final period of solidification, which is 3-8 m in length and continuous in the direction of casting, is provided in a region ranging from the meniscus of molten steel in the mold to an area that is 15-45 m away therefrom in the direction of casting, and a casting speed is adjusted so that a region in which the solid phase ratio at the billet center is 0.3-0.99 may be included in the cooling zone during the final period of solidification; the billet is cooled in a secondary cooling zone, located on a side upstream relative to the cooling zone during the final period of solidification, with a cooling water in a specific amount of 0.1-0.8 liter (L)/kg-steel to thereby adjust a billet surface temperature at the entrance to the cooling zone during the final period of solidification to 900-1200° C.; the billet is cooled in the cooling zone during the final period of solidification with the cooling water at a density of 20-300 liters (L)/(min·m 2 ) on the billet surface; and the billet is cut at a site of at least 1 m downstream relative to the exit of the cooling zone during the final period of solidification.