Control of nucleation on the surface of solidified shell is of importance to establish the whole structure of continuously-cast products. In the conventional continuous casting of steel, the nucleation of steel takes place on the molten state of mold flux. Lab-scale dipping tests have been carried out, where the solidification satisfied the above-mentioned condition. Changing the material of chill block and mold flux, the cooling rates of initial solidification have been varied systematically. The detailed observations of the surfaces and cross section of solidified shells have been made.
The grain size was affected by cooling rate and decreased monotonously with increasing cooling rate. Many small protrusions have been found on the surface of the solidified shell. They resembled discs as Biloni et al. named. The density of discs was affected by cooling rate and increased with increasing cooling rate. The effective nucleation ratio was defined as the ratio between the number of grains and that of discs. The effective nucleation ratio obtained was a few percent and indicated small dependence on cooling rate in the range of this study.