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Article Dans Une Revue Revue de Métallurgie Année : 2000

Study of the formation of the skin in meniscus free continuous casting. I. Surface features on continuous casting products

Etude de la formation de la peau en coulée continue sans solidification au ménisque. I. Caractéristiques de surface des produits de coulée continue

Résumé

In vertical continuous casting, the formation of the linear horizontal marks observed all around the products is known to be due to the partial solidification of the meniscus of the free surface of the liquid metal. On the contrary, in the case of horizontal continuous casting or meniscus free continuous casting, the origin of transverse corrugations or marks on the surface of the cast products is not yet fully understood. In fact, the initial solidification against the cold mold occurs far from the free surface of the liquid metal. In order to better identify the solidification mechanisms that are responsible of the corrugated appearance on the surface of the horizontal continuous casting products (for example), we have built two experimental devices. With the so-called « hot » device, it is possible to obtain spheroidal graphite cast iron (SG iron) samples that have been solidified like the steel products in meniscus free continuous casting (as far as the formation of the skin is concerned). The « cold » device allows the direct observation of the solidification of organic compounds that are transparent in the liquid state and opaque in the solid state. First, in order to verify the good conception of our devices, we looked for and found the values of the casting parameters which result in the formation of marks like those that are present at the surface of the products which are continuously cast in practice. We then studied the modifications of these marks when the value of one casting parameter or another is changed, with both the « hot » and the « cold » devices. We saw that the type, number, width and depth of the marks depend on the extraction speed and the temperature of the cooling liquid. At the lowest extraction rates, we can see a lot of corrugations on the skin of the cast iron samples. On the other hand, for higher extraction rates, we can see only two types of transverse marks. With the cold device, the organic compound samples present different marks on their surface : longitudinal fibres at low extraction speed, transverse corrugations at high extraction speed. For cast iron and for one of the two organic compounds that have been used here, unusual figures like vortices have been observed for the lowest extraction rates. In the case of the cast iron samples obtained with high extraction speeds, the microstructure has been observed. The evolution of the sub-surface microstructure along the outer side of the cast iron sample appears very particular. For example, we can find more pearlite near the marks of the second type than near those of the first type. On the other hand, the marks of the second type are related to a severe discontinuity in the orientation of the austenite dendrites. More generally, it appears that there is a good correspondence between the microstructure evolution and the location of the two principal marks. All these observations are precious indications to further understand how the skin solidifies and finally how corrugations and marks form in a meniscus free continuous casting process. Later, in a second paper, we will present the results of the direct observation of the solidification of the skin with organic transparent compound inside the cold device. Then, we shall be able to propose hypotheses about the solidification phenomena that are responsible of the appearance of corrugations and transverse marks.
En coulée continue horizontale ou en coulée continue verticale en charge, l'apparition de certaines marques sur la surface externe des produits ne peut pas être mise en relation avec la solidification partielle du ménisque de la surface libre du liquide comme dans le cas de la coulée continue verticale classique. Pour comprendre leur formation, un travail expérimental a été mené avec deux maquettes de simulation permettant : avec la première, d'obtenir des échantillons métalliques solidifiés à examiner post mortem, avec la seconde, d'observer directement la solidification de la peau avec des alliages transparents. Dans ce premier article, nous exposons les résultats de l'observation de la surface des échantillons réalisés dans des conditions de tirage variées. Dans un deuxième article, nous proposons une description de la formation des marques observées en termes de phénomènes élémentaires se déroulant pendant la solidification.

Domaines

Matériaux
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Dates et versions

hal-02108829 , version 1 (02-05-2019)

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Patrice Berthod, Gérard Lesoult. Etude de la formation de la peau en coulée continue sans solidification au ménisque. I. Caractéristiques de surface des produits de coulée continue. Revue de Métallurgie, 2000, 97 (12), pp.1441-1453. ⟨10.1051/metal:2000120⟩. ⟨hal-02108829⟩
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