2021 年 107 巻 1 号 p. 64-72
Continuous casting of high-carbon steel containing 1% carbon tends to be operated with low mold flux consumption, resulting in insufficient lubricity. In this study, a mold flux was developed by increasing the viscosity to form a glassy film easily and improve the lubricity between the mold and the solidified shell. In the casting with the developed mold flux, a film with a thickness of 3 mm was stably formed inside the mold to cover the meniscus, bleeding was prevented, and the frequency of surface crack defects on the bloom was reduced by 80%. In the film of the developed mold flux, a 1.2 mm liquid layer lubricated the initial solidification shell.The increased thermal resistance at the film-mold interface reduced the heat flux in the mold, which contributed to the uniform initial solidification. The formation and the growth mechanisms of the crystalline layer in the film were as follows. Firstly, the mold flux flows into the gap between the mold and the initial solidification shell and forms a glassy film. Subsequently, crystallization of the glassy film starts from the mold plate side. Thereafter, the crystallization progresses in the thickness direction of the film until the position of the solidification temperature of the mold flux. The existence of two phases, a liquid layer and a solid layer, played an important role to achieve high lubricity and uniform initial solidification.
