Speaker
Description
Continuous casting of steel typically consists of primary, secondary, and air-cooling zones, whose intensity is weakened in sequence. It promotes the transition of columnar dendrites to equiaxed ones, especially for middle and high carbon steels. However, due to the weak cooling rate, the inner solidification structure is prone to become coarsened deteriorating the solidification quality. So, it is necessary to clarify influence mechanisms of casting parameters on the evolution of solidification structure of the steel strand. With cellular automaton (CA) method, we developed a simple and efficient approach to connect the temperature fields at the macroscopic scale and the dendrite evolution at the microscopic scale. First, the thermal history of a high carbon steel strand was predicted and validated through comparison with measured surface temperature and shell thickness. Second, a 2D CA model for the dendritic growth of steel was developed and evaluated through comparison with in situ observation experiments. Then, the thermal history of a 4 mm × 40 mm region near the centerline of the strand was extracted and imported into the CA model to predict the dendrite evolution from the strand surface to the center under the critical conditions for CET including the nucleation undercooling, the nucleation probability, and the temperature gradient. The predicted dendritic arm spacing and CET location agree well with the actual results in the strand. The primary dendrite arm spacing of columnar dendrites decreases with increasing secondary cooling intensity, or decreasing superheat and casting speed. The CET is promoted as the secondary cooling intensity and superheat decrease. At weak secondary cooling intensity, some inner dendrites develop with extremely long and asymmetrical primary arms. The CET is not influenced by the casting speed, owing to the adjusting of the flow rate of secondary spray water.