In this contribution, we will present recent advances in the CFD modelling of the continuous casting process in the framework of K1-MET projects in Austria. Physical phenomena on both microscopic and macroscopic scales have been investigated, and the resulting dynamics in the metallurgical process sequence of continuous casting has been modelled.
Non-metallic inclusions (NMIs), their microscopic dynamics and their interaction with macroscopic flows in casting vessels have strong impact on the final steel quality. If NMIs are not properly treated in the tundish of a continuous caster, e.g., captured by or dissolved in the covering slag, these particles can cause clogging in the submerged entry nozzle (SEN) and lead to harmful defects in the cast steel slab. Therefore, K1-MET has made great effort to model the NMI behavior using CFD tools to depict their behavior in a multiphase fluid flow, i.e., their removal from the steel into the slag phase in a tundish, their subsequent advance into the SEN and impact on clogging, as well as their behaviour in the mold during the casting and solidification.
Detailed simulations of the NMI behaviour have been developed, characterizing their tendencies of dissolving into a slag phase at the steel-slag interface or adhering to the vessel walls. Considering the wettability and size of the particles, as well as local capillary motion and Marangoni convection, an effective removal rate of NMIs from steel into a slag phase has been derived. These simulations have been validated with laboratory experiments determining separation dynamics as well as material properties, for different combinations of NMI and slag materials.
Subsequently, transport of NMIs in the SEN, nozzle clogging considering the transient clog growth and its interaction with the multiphase flow are modelled. Laboratory investigations of clogged SENs with different material compositions have been compared to the simulations for a validation of the CFD model.
Based on these detailed simulations, effective models for the NMI behaviour in tundish and SEN have been developed, and effective NMI removal rates and clogging rates, respectively, have been incorporated into larger-scale simulations to simulate a realistic flow behaviour in vessels like tundish and SEN. Ultimately, the SEN clogging model has been used as a boundary condition for the effective flow behaviour of steel into the mold, and the resulting impact on the solidification and potential casting defects in the steel slab has been investigated.
The different modelling approaches and their respective validation by experiments have been successfully brought together to achieve a comprehensive image of the dynamics governing the complete continuous casting process and are an impressive showcase of the insights into complex industrial processes that can be gained with CFD modelling.