Contribution a l'etude de la cristallisation des poudres de coulee pour la coulee continue des aciers.

摘要

During the continuous casting of steel, several surface defects may occur and are related to the continuous casting parameters and to the behavior of mold powder, which in turn affect the lubrication and the level of heat transfer. The control of such defects is crucial for the improvement of the continuous casting process. This can be achieved by a proper selection of a continuous casting powder adapted to the continuous casting conditions. The usual selection criteria based on viscosity and on solidification temperature are not able to give an accurate estimation of the mold powder performance because these two characteristics do not fully reflect the powder behavior during the continuous casting. Neither melting nor crystallization temperature are suitable for the evaluation of this performance due to the complexity of the phenomena in the mold.; The two major characteristics in terms of mold powder behavior and performance are the melting rate and the crystallization rate. Melting rate controls the ability of a powder to produce enough liquid flux and to provide a sufficient lubrication. The crystallization rate has a major influence on the rate of heat transfer, as the nature and the structure of the solid slag layer controls the mechanisms by which the heat is transferred from the liquid steel to the copper mold. To evaluate the performance of mold powders, these two parameters must be known.; The objectives of this study were to develop experimental methods to determine the melting rate and the crystallization rate, and to evaluate with these two characteristics the performance of mold powder. The work has been carried mainly on mold powders for the continuous casting of slabs.; From the experimental results on melting and solidification, two indices, IL and ITC, have been calculated. These two indices give an indication of the lubrication capability and of the ability of the mold powder to control the heat transfer to the mold. Using these indices, it is possible to evaluate the performance of mold powder and to compare different materials. These indices give a more reliable estimation of performance than viscosity at 1300°C and solidification temperature. This approach could be used to improve the selection of mold powder, and in turn the quality of the continuous cast products. (Abstract shortened by UMI.)