A model of a tundish has been developed that takes into account the steel, slag, and refractory phases. Predicted temperatures and velocities in the steel and refractory from the model were earlier found to agree well with measured velocities and temperatures. The model was also used to determine the optimal location of flow devices, making the temperature distribution in the steel more even and enhancing the removal of inclusions to the slag. In this study, the focus was on using the model to study the slag/steel interface in the tundish. Predictions showed that slag is dispersed into the steel close to the interface as well as close to the ladle shroud. In order to confirm these predictions, the momentary interfacial solidification sampling (MISS) method was developed. Using this method, a sample of the steel/slag interface could be taken that represented almost an instantaneous picture of the interface. The MISS sampler was used for sampling low-carbon steel in the tundish. Samples were analyzed using ultrasonic testing, optical microscopy, and scanning electron microscopy (SEM). Analysis results confirmed the presence of nonmetallic particles close to the slag/steel interface and close to the ladle shroud, as suggested by the modeling results. The analyses also showed that the slag/steel interface is very irregular, despite the low velocities.
Some aspects of inclusion behaviour in the tundish have been investigated both theoretically and experimentally. Good agreement was obtained between measured and predicted temperature and flow fields for 1-to 6-strand continuouscasting tundishes. In this study the flow field was redesigned with weirs, resulting in the addition of a vertical component to Stoke's equation. The results indicate an increase in the velocity that cause a rise of inclusions (smaller inclusions (<20 µm)). Consideration of slag, flux and refractory in the model has also made it possible to simulate the mixing of steel and slag. Special sampling techniques were used to gather information. Samples were analysed using ultrasonic testing, LOM, SEM and Atomic Force Microscopy (AFM). The analysis results were used to verify the predictions regarding steel/slag mixing and understanding of physical conditions at the interfaces. As a result, the casting praxis was improved (cleaner steel) and the products were of higher quality.Key words: clean steel, fluid flow, microscope studies, mixing, models, sampling, slag, steel, theory, tundish. C Blackwell Munksgaard, 2003Accepted for publication 24 May 2002 Extensive efforts have been made in academia and industry over the past decades to exploit and enhance continuous-casting-tundish systems with respect to their metallurgical performance. As a consequence, numerous physical and mathematical modelling studies embodying both industrial and water-model tundishes have been carried out and reported in the literature. Recently, Mazumdar & Guthrie [1] reviewed these modelling efforts of continuous-casting systems. They pointed out that a modern-day steel-making tundish should be designed to provide maximum opportunity for carrying out various metallurgical operations such as inclusion separation, flotation, alloy trimming, inclusion modification, superheat control, as well as thermal and particulate homogenisation. Furthermore, they concluded that mathematical studies indicate that flow conditions conducive to the removal of non-metallic inclusions from tundishes can be created by inserting appropriate flow-modification devices. The optimal design and location of flow modifiers, with respect to clean steel, clearly depend on tundish geometry [2], the operating conditions and very much on the steel inclusions' size range.In the models reported on, however, the refractory has rarely been included and, to the knowledge of the authors, neither the flux nor liquid slag have so far been included in any modelling efforts. It is obvious though that both the refractory and the slag layer preferably should be the integrated parts of the model for appropriate understanding of many metallurgical issues such as thermal and inclusion behaviour because the slag and the refractory are both potential sources, sinks and modifiers for inclusions. Furthermore, a useful approach to modelling fluid flow in the slag phase enables studies of heat and fluid-flow conditions coupled with thermodynamics in the very important steel/...
It is very important to understand the underlying physical phenomena at the steel/slag interface in a continuous casting tundish in order to control reoxidation and deoxidation phenomena that can occur. Aiming to investigate probable sources of exogenous inclusions originating from the covering slag, an existing mathematical model of the tundish was augmented to include key physical parameters needed for the prediction of the physical behaviour of steel/slag mixing phenomena. Results showed a recirculation flow in the inlet region to be responsible for both the entrainment of steel drops into the slag and slag fragments into the steel. The highest concentration of slag in the steel was found to be in the area behind the inlet where slag fragment sizes are smaller due to a high degree of turbulent energy dissipation. Likewise, higher concentrations of steel in the slag, consisting of smaller steel droplets, were only found in the inlet region and along the walls. The results indicate that only small slag fragments of approximately 10‐50 microns from the covering slag reach the outlet.
Since the early 1990s, mathematical modelling has supported metallurgical research at MEFOS. In addition to thermodynamic calculations and trials in various scales, the commercial software PHOENICS has been used to describe the transport of mass and heat. Steady‐state models, as well as transient models, have been developed for single‐, 2‐ and 3‐phase systems. In some applications, chemical reactions between the phases are also incorporated. Modelling activities have focused on the process route of steelmaking, including melting, secondary metallurgy and continuous casting. In this paper, highlights from some of these modelling activities are presented, including verification measurements. Process improvements are suggested, as well as some implications for treatment strategies and practices. Finally, future work and planned research are discussed.
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