Investigation On The Growth And Removal Of Inclusions In The Molten Steel In A Continuous Casting Tundish

Steel cleanliness has a direct influence on the property of the steel. One of the factors affecting the steel cleanliness is the amount, size, composition and morphology of non-metallic inclusions in the steel. The nucleation, growth and removal of inclusions are closely related to the flow of the molten steel and the collision of inclusions. Many investigations on the collision, growth and removal of inclusions are reported. But the following several aspects have not been systematically studied. Firstly, there has been a lack of fully coupling calculation between the 3-Dimensional (3D) macroscopic flow and the collision of different size inclusions. Secondly, the removal theory of inclusions at the interface between the molten steel and the slag combining with 3D flow has not been established yet. Thirdly, the effect of composition of inclusions on the collision of inclusions arid the removal at the interface between the molten steel and the slag has been neglected in previous investigations.In the current study, the theory of the collision and growth of inclusions, the floating removal and adhesion to the lining refractory were elaborated systematically. Meanwhile, the corresponding mathematical models and the solution methods were also introduced.Mathematical models were developed to predict the transient concentration and size distribution of inclusions in a two-strand continuous casting tundish, and validated by the measured results using automated SEM-EDS system, called ASPEX1020 system. The Stokes and turbulent collision were the dominant factors for the collision and coalescence of inclusion particles. The removal of inclusions at the interface between the molten steel and the slag was modeled by considering the turbulent fluctuation velocity, wettability, interfacial tension, density and size. The effect of composition of inclusions on the collision of inclusions was included through the Hamaker constant. For 12CaO·7Al2O3, MgO·Al2O3, Al2O3 and SiO2 inclusions, their coagulation coefficients are ?StO2> ?At2O2> ?At2O2>?12((?))7 Al2O2>?M8O·At2O3It was found that the growth and removal of inclusions in the current tundish was always in an unsteady state during continuous casting. The equilibrium time when the simulation reached the steady state was 2440 seconds, but the mean residence time of the molten steel was only 625 s. It indicated that the transport processes in the current tundish were always in transient state during the casting time of each heat. The removal fraction of inclusions was 16.3%. With the collision of inclusions proceeding, the small size inclusions gradually collided with each other to form big size inclusions and the contribution of number density of the former to total volume or mass of inclusions decreased, but for big size inclusions, their contribution was enhanced. It was much easier for Al2O3 and SiO2 inclusions with a larger contact angle to remove from the interface between the molten steel and the slag, and their removal fraction were 39.2% and 36.5%, respectively. However, it was only 26.6% for liquid 12CaO·7Al2O3 inclusions.Due to a short residence time of the molten steel and a large volume of dead zone in the current tundish, the optimization design of tundish capacity was conducted. The mean residence time of the molten steel after optimization was 3.5 minutes longer than that before optimization. Besides, the volume of dead zone was decreased by 15.3% and the removal fraction of inclusions was increased by 16.5%.