Calculation Of Coupled Fluid Flow, Heat Transfer And Solidification In Mold For Wide And Thick Slab Continuous Casting

In the background of the highly competition of steel and increasing demand of the market, wide and thick slab with highly value-added production is being more and more concerned and valued, and it is widely used in off shore oil platforms, bridges, ships, heavy machinery manufacturing and other military industry. Compared with conventional slab, the casting process of wide and thick slab is different, and this is due to the special nature of steel section. Currently, the domestic casters of wide and thick slab mainly cast medium carbon steel, peritectic steel and alloy steel. But those steels are hard to cast, and highly sensitive to the crack excessively, high amount of the steel flux increases the thermal load of the mold. Crack and various types of surface defects restrict the production efficiency of wide and thick slab, for example, steel breakout and longitudinal crack. At the same time, the larger sections and dimensions of the generous slab would easily induce bonding, longitudinal crack and other Surface defects, especially excessive width, uniformity deterioration of slag inflows and shrinkage unevenness of initial shell. Moreover, the casting of wide and thick slab has low casting speed, and the temperature of exit of mold slab surface is decreased significantly. The service temperature range of slag in casting direction is significantly stretched. Thus, uniformity of the slag melts and inflows and stability of slag consume need higher stability. In continuous casting of steel, the initial solidification behavior of the molten steel is controlled by the mold. The velocity field of the steel significantly affects behaviors in the mold such as slag infiltration into the gap, float of inclusions, slag involvement, surface level fluctuations and the uniformity of the initial steel shell, especially for the wide and heavy slag which has a large section. So the reasonable design of the submerged entry nozzle (SEN) and optimization of flow pattern in the mold are of great significance in improving and stabilizing slab quality.A three-dimensional mathematical model has been developed based on the equipment parameters and process conditions of arc caster for wide and thick slab continuous casting. The model is established on the basis of Navier-Stokes momentum equation and low Reynolds number turbulence k-s equation. The flow of liquid steel with three different structures and sizes of submerged entry nozzles is calculated. The effects of structure and size on the flow field, the turbulent kinetic energy, velocity of free surface and level wave profiles of mold were analyzed and compared. These results provided some references for the optimization the flow field and SEN in mold of wide and thick slab continuous casting.Moreover, a three-dimensional mathematical model has been developed based on Navier-Stokes momentum equation and low Reynolds number turbulence k-ε equation. This model comprehensively considers energy conservation, solidification of molten steel and the influence of mushy zone on the flow process. The heat flux obtained through inverse heat transfer model combined with measured temperature is set as the boundary condition to the coupling model, to investigate the fluid flow, heat transfer and solidification in continuous casting mold. The results show that the liquid steel flow has an important influence on the distribution of temperature and heat flux, and the solidification process is governed by the synthetic action of fluid flow and heat flux. The proposed model and the result of non-uniform characteristic could provide reference for further investigation on longitudinal cracks and other surface defects during continuous casting.