The first shell formation in meniscus free casting

The meniscus free casting technology was jointly developed by CRM (Centre de Recherches Métallurgiques) and Irsid (Central Research Laboratory of Usinor) in order to significantly improve the surface and subsurface quality of continuously cast long products. This technology realizes a shifting of the meniscus zone upstream of the solidification area by means of a refractory feed‐head located above the mould. In this way, the hydrodynamical perturbations of the meniscus and the meniscus shape do not affect anymore the shell solidification. An important part of the development work was dedicated to the understanding of the solidification mechanisms at the very top of the mould, where the first solidified shell is formed. For that purpose, EMN (Ecole des Mines de Nancy) and Irsid have developed a physical and numerical model of the shell solidification in the new concept. This model takes into account the relative motion between the mould and the product together with two stages of solidification: static near the upper edge of the copper mould and dynamic at the contact of the skin of the cast product. During the casting trials realized at CRM and Irsid, the temperature of the copper on the first 50 mm of the mould and the heat flux extracted were recorded. These values were used to determine the boundary conditions entered into the model. The model calculates the location of the isotherms and the iso‐fraction of solid along the mould wall at each moment of the oscillation cycle. It can predict whether or not the skin is sufficiently solid at the end of the negative strip to be extracted without any damage. When the casting speed increases, the resistance of the skin decreases. In order to alleviate this effect, the influence of the oscillation parameters was studied during continuous casting trials. Sinusoidal and non‐sinusoidal oscillation cycles were investigated. A triangular cycle brings good surface quality for the high carbon grades while a sinusoidal cycle is better suited to the casting of the peritectic and low carbon steel grades. These results are discussed and a guide for the choice of the best oscillation parameters is provided. Die Technik des meniskusfreien Gießens wurde vom CRM (Centre de Recherches Métallurgiques) und Irsid (Central Research Laboratory of Usinor) gemeinsam entwickelt. Damit sollten sowohl die Qualität an als auch direkt unter der Oberfläche von stranggegossenen Langprodukten verbessert werden. Bei diesem Verfahren sitzt ein