Numerical Modelling of Non-metallic Inclusion Separation in a Continuous Casting Tundish

Abstract

Nowadays the cleanliness of steel plays a major role for steel producers. It is defined by the size and number of non-metallic inclusions in the final product. Today, the dominating method of global steel production is continuous casting. A continuous casting plant includes the ladle turret, several steel ladles, a tundish, and mould/moulds. Tundish buffers steel melt during the ladle change and distributes the steel melt to several strands. Tundish plays also an important role in removing non-metallic inclusions (i.e. Al2O3 or SiO2), to the slag layer due to buoyancy force. The aluminium oxides are very hard and destroy steel structure during plastic formation process. Therefore strict steel quality conditions require a steady increase in the purity of steels and thus reducing the number and size of non-metallic inclusions is necessary. Measurements of the melt flow and inclusions transport and separation in a steel mill, at working conditions, are nearly impossible due to the high temperatures and opacity of the fluid. The solution is using the physical and numerical simulations in this field of investigation. Water can be used for the physical simulation because the kinematic viscosities of liquid steel and water are comparable (νst,1536°C = 8.26⋅10-7 m2/s, νw,20°C = 10.0⋅10-7 m2/s), thus the flows of both fluids are similar. A wide review of such investigation was first done by Mazumdar and Guthrie (Mazumdar & Guthrie, 1999) and lately by Chattopadhyay et al. (Chattopadhyay et al., 2010). From this reviews it can be seen, that experimental measurements using water models are widely used, and considering the similarity laws, the results from water modelling can be transferred to the real process. Though, many publications are available with water model experiments, only a few experimental studies were done on particle separation in the tundish. Tundish flow and accompanying inclusion separation process are strongly investigated with Computational Fluid Dynamics (CFD) models as well. Numerous studies can be found in literature. Present state of the CFD techniques allow to calculate the fluid flow in tundish with the satisfying accuracy. This is confirmed by a good agreement in flow fields predicted mathematically and measured by laser-optical method using water models (Braun et al., 2010). For turbulence modelling, the standard or realizable k-e models are mostly used, rather than Reynolds Stress Model (RSM) or Large-Eddy Simulations (LES). Results show that in many engineering problems, flow field is well described by steady-state numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equations combined with the realizable k-e model.