Theoretical Study And Its Application On The General Dynamics Of Inclusion Particle In Metallurgical Melts

With the increasing demands for the quality of steel product, much attention has been drawn to the production of pure steel in metallurgical enterprises throughout the world. It is key to how to control the level of impurity, especially the inclusion, which mainly responsible for the defect of most steel products. Therefore, it is of significance to investigate the law of dynamics, such as growth, transfer and removal of inclusions in molten melts, and further improve the conventional process or develop new techniques regarding pure steel.The paper is divided into four parts. In the first part, the experimental and theoretical studies are carried out from several aspects involving the dynamics of inclusions as follows:The modification coefficients of motion resistance, Cs, of inclusion particles of different shape to the ideal spherical particle are measured by model experiments using polystyrene particle of radius 1-2.6mm. It is found that the order of increasing Cs is the rod-like particle oriented its long axis, the spherical particle, the flake-like particle oriented its plane, the cluster-type particle, the flake-like particle oriented the normal to its plane, and the rod-like particles oriented its radial axis. Commonly, Cs=1.5-2.8 for real inclusion particles.The mechanical condition that an inclusion adheres stably to the rough wall of vessel exposed to a shear flow is analyzed theoretically, then a relationship of the adhesion efficiency is formulated, and the mass transfer coefficient, , of inclusion to the wall due to turbulence fluctuation and field force effect is obtained which is the function of wall friction force of fluid. It indicates that there exists a peak for the mass transfer coefficient over the wall friction force, and in most cases, the turbulence promotes the transfer of inclusion to wall.A theory on inclusion growth of single particle in molten melts is developed. Two main growth modes, diffusion-reaction-precipitation and collision-coalescence, of inclusion are simplified physically and modeled mathematically, and some analyticsolutions or relationships for the growth rate of inclusion are derived, which give an general physical picture of inclusion growth. The theoretical growth rate of diffusion is supported by the experimental results early reported by Japanese scholar. This theory shows that the early growth of inclusion depends on diffusion-reaction-precipitation and Braunian motion collision, and the former is decisive, while the latter growth depends on turbulence shear collision and Stokes' collision, and the former is dominant; The collision and coalescence proceeds quickly during smelting process, and is negligible in continuous casting process, moreover, a transition state exists in the refining process. Further, the micro- structure of inclusion aggregate is simulated by methods of Monte-Carlo, the resultant aggregates agree with the cluster inclusions reported in literatures. The Fractal theory is introduced to interpret the structure of the aggregate, the simulation shows that the cluster inclusion has a Fractal dimension of 2.25.Based on above studies, a general dynamic model of inclusion coupling the nucleation, growth, coalescence and transfer has been developed firstly, which is expected to lay a foundation to further investigate widely and profoundly the basic behavior of inclusion in metallurgical vessels.In the second part, foregoing theory has been utilized to build a comprehensive mathematical model within the Lagrangian framework to study the transport of inclusion in some continuous casting tundish. The results demonstrate that the floatout by buoyancy is the main path of removal of inclusion, and the coalescence and adhesion to wall provide a secondary aid. In present tundish, a removal efficiency of 20%-75% can be obtained for inclusion of radius from 10m to 30m. The coalescence helps the removal of inclusion, but seems not notable, restricted by the practical condition of tundish.In the third part, as another application, the only-by-current ele...