Solidification behaviours in the continuously cast slabs of mild steel were determined by addition of radioactive gold and solute distribution in the slabs under various casting conditions was analysed, comparing with the solidification structures.
From these experimental data, the flow velocity in the liquid pool and solute segregation in the center of the slabs were estimated mathematically, using the boundary layer theory and partial mixing model in liquid.
The liquid flow along the shell is composed of the nozzle jet, the natural convection and the bulging flow, the amount of its velocity being 10-40 cm/sec, 1-2.5 cm/sec and2-4 cm/sec. The center segregation is mainly caused of solute redistribution during uni-directional solidification in columnar crystal region, which intensity is strongly dependent on the rate of solidification and the liquid flow, especially the bulging flow.
To reduce the center segregation, increasing the equiaxed crystals and minimizing the bulging were effective, which are related to the amount of cooling water, casting speed, casting temperature, slab thickness and the machine arrangement.