New approaches of the initial solidified shell formation mechanisms in the continuous casting mould

One of the main industrial objective for the continuous casting people is to improve the surface quality of the as cast products, in order to spare the cost of surface inspection and repairing or to increase the casting speed without degradation of the surface quality. In accordance with these industrial objectives the work carried out in the frame of this ECSC project (July 1999 - June 2002) focussed on the first shell solidification. The objectives of the works of the five partners (BFI, CSM, IEVB, ACERALIA and IRSID) was to have a better insight on the phenomena occurring at the meniscus and to propose new tools to have a better control of the shell solidification. This work aimed to have a wide insight of the solidification in mold. Hence works were carried out as well for flat products as for long products, as well for lubrication with mould powders as for lubrication with oil. The work done during this ECSC project allowed to develop new numerical or experimental tools and to extend our knowledges of the mechanisms in order to have a good interpretation and use of the results coming out of these tools. Some operational indications have been proposed, especially in the field of the fluid flow. These tools have now to be used more systematically, in accordance with the aims and stakes of the steel producers. The main way could be the implementation of data bases to fit the models and to have a feed-back of the model predictions. The main difficulty will be the necessity to have an extensive instrumentation at meniscus because the phenomena involved are both transient and very localized. Considering oil lubrication, a new insight was achieved and a step was made in order to better understand and to have keys to improve oil lubrication as it was extensively made in the past for powder lubrication. Lubrication with powder and modeling of slag infiltration, shell solidification and oscillation mark (CSM, ACERALIA, IRSID) The characterizations of slag rims (Aviles, Fos sur Mer, Dunkirk, Ugine Savoie) underline there is no general and stable case. As a consequence for the shell formation and heat extraction near the meniscus, mean values for the heat flux and casting parameters will give mean values for shell growth and oscillation mark formation. To know at each time the solidification conditions, with possible consequences on the product surface quality, it is necessary to know the physical-chemistry conditions at each time near the meniscus, at least knowing the thermal heat flux. The thermal field and solidification modeling at meniscus was fitted to measurements made by Aceralia. It has been shown, for the investigated cases that the temperature near the meniscus is higher at the narrow face than at the broad face. This is due to the different cooling performance of the water channels. The flux thickness at the narrow face is higher than at the wide face. The liquid layer in the case of medium carbon disappears at the wide face before the mould end (this is due to the higher flux melting temperature). The downward velocity of the solid layer is much higher in the case of the powder for low carbon steels than for the powder for medium carbon steels. This could be a consequence of the much lower flux viscosity when casting the low carbon steel. The radiation contribution of the powder used for medium carbon steels is lower than that of the powder used for low carbon steels (this is in agreement with the physical properties of the two powders, being the one used for medium carbon steels adequately designed to develop higher crystalline fractions). For the modeling of the meniscus shape, oscillation mark and flux infiltration, assumptions have been requested, relative to not well known conditions as: the geometry of the gap, the heat transfer through the flux layer, the velocity of the solid flux layer and so on. Sensitive analyses on the effect of variation of some process parameters over relevant casting aspects have been d