Steel thermo-fluid-dynamics at tundish drainage and quality features

AUTHOR/S: V. Battaglia, M. De Santis (Centro Sviluppo Materiali SpA, V. Volponi, M. Zanforlin (ORI Martin Spa)

ABSTRACT

In steelmaking, transient operations are very critical for product quality and process regularity. This is especially true for the tundish, the steel buffer in the casting machine. Typical drawbacks can occur at ladle change and drainage at sequence end. At ladle change, tundish steel from ‘old’ and ‘new’ ladle has ‘intermixed’ composition, sometimes unacceptable leading to rejection and consequent lower yield. At ladle change, refilling high flow rates induce flow short-circuits risky for dispersed oxides (‘inclusions’) dragging towards the strands. Finally, at drainage, vortexes formation can affect steel cleanliness via slag entrapment. Such topics were investigated for an industrial tundish with Computational Fluid Dynamics validated tools. Focus was given on a multi-strand layout more prone to unevenness features. As a matter of fact, the different steel path to reach different strands causes often too high temperature differences and different strand cleanliness levels. Strands closer to the tundish center, are generally hotter and less clean; the others, slightly colder but cleaner. Multiphase models, together with advanced meshing techniques and validated boundary conditions, were used to describe tundish refilling and drainage. Thermal and fluid flow relevant features, together with the typical inclusions path in the steel, were achieved suggesting operating countermeasures to enhance steel quality.

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