EP0452294A2 - Method and device for the continuous casting of a metal - Google Patents

Method and device for the continuous casting of a metal Download PDF

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Publication number
EP0452294A2
EP0452294A2 EP91870056A EP91870056A EP0452294A2 EP 0452294 A2 EP0452294 A2 EP 0452294A2 EP 91870056 A EP91870056 A EP 91870056A EP 91870056 A EP91870056 A EP 91870056A EP 0452294 A2 EP0452294 A2 EP 0452294A2
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EP
European Patent Office
Prior art keywords
metal
cast product
casting
temperature
cooling
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EP91870056A
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German (de)
French (fr)
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EP0452294B1 (en
EP0452294A3 (en
Inventor
Paul Naveau
Stéphan Wilmotte
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Centre de Recherches Metallurgiques CRM ASBL
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Centre de Recherches Metallurgiques CRM ASBL
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/112—Treating the molten metal by accelerated cooling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/124—Accessories for subsequent treating or working cast stock in situ for cooling

Definitions

  • the present invention relates to the continuous casting of a metal, such as liquid steel; it relates on the one hand to a process and on the other hand to an installation making it possible to carry out continuous casting with a high speed.
  • Continuous casting is a casting method which is now well known and widely used in the art, and in particular in the steel industry.
  • the description which follows is specially devoted to the continuous casting of steel, but it goes without saying that the present process could also find its application for the casting of other metals or metal alloys.
  • continuous casting consists in casting steel from a container, such as a ladle or a distribution basket, in a bottomless ingot mold whose side walls are energetically cooled. .
  • the steel undergoes a beginning of cooling in this ingot mold, and it is extracted therefrom by the bottom in the form of a continuous ingot which has a solidified skin surrounding a liquid core.
  • the ingot undergoes cooling by spraying water, called secondary cooling, while being mechanically supported to avoid breakthroughs, that is to say flows of liquid steel by tearing the skin. solidified.
  • the secondary cooling has the effect of increasing the thickness of the solidified skin to a value where there is no longer any risk of breakthrough.
  • the length of the ingot between the exit of the ingot mold and the point where the solidification is complete is called metallurgical length.
  • the steel is poured vertically and the ingot then follows, during its solidification, a curved trajectory which brings it to the horizontal.
  • the point of passage from the curved trajectory to the rectilinear horizontal trajectory is generally called the straightening point of the ingot, because its curvature becomes zero there.
  • the steel contained in the casting container has a temperature higher than its liquidus temperature, in order to avoid any risk of freezing due to localized cooling.
  • This temperature difference, called overheating is typically of the order of 25 to 35 ° C.
  • the object of the present invention is to provide a process for the continuous casting of a metal, in particular steel, which does not have the above-mentioned drawback and which therefore makes it possible to obtain cast products free from cracks. , both on the surface and inside the metal.
  • the temperature of the metal in the casting container is lowered to a value situated in the aforementioned temperature range, and the temperature of the metal is maintained at this value during casting .
  • This implementation may require heating of the metal to compensate for heat losses by radiation or convection.
  • Another particular implementation of the process of the invention consists in lowering the temperature of said metal by controlled cooling during casting, that is to say between the casting container and the mold.
  • a hollow jet of metal is formed, for example, which flows in a continuous layer along a cooled wall before entering the ingot mold.
  • the first means for lowering the temperature of the metal can consist of a device limiting the cooling of the metal caused by thermal losses in the pouring vessel, ladle or distributor basket; such a device can for example comprise a heat-insulating cover and / or burners.
  • Another embodiment of said first means consists of a vertical conduit disposed between the casting container and the ingot mold, comprising at its inlet end a metal distribution member which extends transversely to near the interior surface of said drove.
  • This vertical duct is preferably cooled externally, for example by circulation of water, over at least part of its length.
  • the second means which provide intense secondary cooling of the cast product, advantageously comprise a box surrounding at least partially and at a certain distance the cast product, and at least one wall of which faces towards said product is pierced with orifices for passage of the liquid. cooling.
  • Such cooling means make it possible to establish a continuous layer of pressurized coolant on the surface of the cast product and thus not only to cool it quickly but also to support it uniformly.
  • said second means could also be constituted, totally or partially, by any other secondary cooling device capable of ensuring the desired cooling.
  • this device may consist of a conventional set of water sprinklers alternating with rollers for supporting the cast product.
  • Another interesting way of ensuring the desired rapid cooling consists in using an enclosure surrounding the product poured over an appropriate length, the interior wall of this enclosure being pierced with orifices directed towards the product to be cooled.
  • This enclosure is supplied with pressurized water; this escapes through the orifices in the form of jets which strike the surface of the cast product to be cooled and ensure its rapid cooling.
  • said third means for the moderate cooling of the cast product comprise an enclosure situated under the aforementioned second means, which surrounds the cast product by defining at its lower end a slot of calibrated width with the poured product.
  • Means can also be provided for measuring the temperature of the product poured at the outlet of said enclosure and for adjusting the width of said slot as a function of the measured temperature.
  • the continuous casting installation is arranged essentially under a casting container, for example a distribution basket symbolized by its casting nozzle 1.
  • the first device encountered by steel is a distribution member 2, in the form of a dome, disposed in the inlet portion of a vertical duct 3, which is provided with a water cooling circuit 4.5. .
  • This vertical duct 3 is extended downwards by a pouring tube 6.
  • the path of the liquid steel is indicated in dotted lines in Figure 1. This first cooling eliminates part of the steel overheating.
  • the pouring tube 6 is introduced into a casting mold 7, of conventional type, and the lower end of this tube is immersed in the liquid steel 8 present in the ingot mold 7.
  • the steel undergoes cooling and a start of solidification in the ingot mold 7, and it leaves it in the form of a continuous ingot 9 having a solidified skin of a relatively small thickness.
  • the partially solidified ingot 9 then enters an intense cooling device 10; this essentially consists of a box surrounding the ingot 9 and whose wall facing the ingot is pierced with slots 11 inclined in the direction of progression of the ingot 9. These slots provide passage to a pressurized coolant, usually water, which forms a continuous layer between the ingot 9 and said wall and which cools and uniformly supports said ingot 9.
  • a pressurized coolant usually water
  • This water then flows along the ingot 9 and is collected in an enclosure 12 which surrounds the ingot under the box 10.
  • the lower end of this enclosure 12 is throttled so as to form an outlet slot 13 calibrated around the ingot 9. Due to this constriction, the water collected in the enclosure 12 forms a relatively calm bath where the ingot undergoes moderate cooling.
  • a pyrometer 14 measures the surface temperature of the ingot 9 at the outlet of the enclosure 12 and optionally controls the width of the slot 13.
  • the ingot is finally guided along a curved trajectory, in a manner known per se, to the straightening point where it takes a trajectory horizontal. Its temperature T R is also measured at the recovery point, because it is this which conditions certain subsequent operations, in particular the hot charging of the cast products.
  • Figure 3 illustrates the evolution of axial segregation as a function of overheating.
  • Axial segregation is expressed by the ratio (C max / C0) between the maximum carbon content, essentially in the axis, and the average carbon content in the cross section of the cast product.
  • Overheating ( ⁇ T) is expressed in degrees centigrade.
  • the products considered here are square billets of 220 mm side, with a nominal carbon content of 0.8%.
  • the Figure shows a curve (a) representing the variation of the aforementioned ratio in the case of products cast with conventional cooling and a casting speed of 0.85 m / min.
  • the set of points (b) corresponds to products obtained in accordance with the invention, cast with a speed of 1.5 m / min.
  • the C max / C0 ratio is much closer to 1 for these latter products, which translates into a marked reduction in axial segregation thanks to the two-stage low overheating and cooling casting provided by the present invention.
  • the method of the invention makes it possible to obtain products having optimal properties, in particular a very fine solidification structure, practically zero central segregation, a total absence of cracks both internal and surface and a very low porosity.
  • An additional advantage is that these properties are obtained with a substantially increased casting speed compared to conventional practice; the productivity of the installation and certain subsequent operations such as hot charging are thereby favored.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Continuous Casting (AREA)
  • Treatment Of Steel In Its Molten State (AREA)

Abstract

The present method for the continuous casting of a metal comprises the following successive operations: a) the temperature of the metal is lowered to a value between Tf and (Tf + 20 DEG C) before and/or during casting of the said metal in the ingot mould, Tf being the liquidus temperature of the said metal, for example by forming a hollow jet flowing along a cooled conduit; b) the cast product is subjected to an intense cooling by means of a continuous layer of cooling liquid under pressure formed at the surface of the said cast product; and c) a moderate cooling is then applied to the said cast product by means of a cooling liquid preferably coming from the preceding intense cooling. In this way, continuously cast products are obtained which have no internal or surface cracks. <IMAGE>

Description

La présente invention concerne la coulée continue d'un métal, tel que l'acier liquide; elle porte d'une part sur un procédé et d'autre part sur une installation permettant d'effectuer la coulée continue avec une vitesse élevée.The present invention relates to the continuous casting of a metal, such as liquid steel; it relates on the one hand to a process and on the other hand to an installation making it possible to carry out continuous casting with a high speed.

La coulée continue est une méthode de coulée qui est à présent bien connue et largement utilisée dans la technique, et en particulier dans l'industrie sidérurgique. La description qui va suivre est spécialement consacrée à la coulée continue de l'acier, mais il va de soi que le présent procédé pourrait également trouver son application pour la coulée d'autres métaux ou alliages métalliques.Continuous casting is a casting method which is now well known and widely used in the art, and in particular in the steel industry. The description which follows is specially devoted to the continuous casting of steel, but it goes without saying that the present process could also find its application for the casting of other metals or metal alloys.

On sait que, selon son principe bien connu, la coulée continue consiste à couler l'acier à partir d'un récipient, tel qu'une poche de coulée ou un panier répartiteur, dans une lingotière sans fond dont les parois latérales sont énergiquement refroidies. L'acier subit un début de refroidissement dans cette lingotière, et il en est extrait par le fond sous la forme d'un lingot continu qui présente une peau solidifiée entourant un coeur liquide. A la sortie de la lingotière, le lingot subit un refroidissement par projection d'eau, dit refroidissement secondaire, tout en étant supporté mécaniquement pour éviter des percées, c'est-à-dire des écoulements d'acier liquide par déchirure de la peau solidifiée. Le refroidissement secondaire a pour effet d'augmenter l'épaisseur de la peau solidifiée jusqu'à une valeur où il n'existe plus de risque de percée. La longueur du lingot entre la sortie de la lingotière et le point où la solidification est totale est appelée longueur métallurgique.We know that, according to its well-known principle, continuous casting consists in casting steel from a container, such as a ladle or a distribution basket, in a bottomless ingot mold whose side walls are energetically cooled. . The steel undergoes a beginning of cooling in this ingot mold, and it is extracted therefrom by the bottom in the form of a continuous ingot which has a solidified skin surrounding a liquid core. At the exit of the ingot mold, the ingot undergoes cooling by spraying water, called secondary cooling, while being mechanically supported to avoid breakthroughs, that is to say flows of liquid steel by tearing the skin. solidified. The secondary cooling has the effect of increasing the thickness of the solidified skin to a value where there is no longer any risk of breakthrough. The length of the ingot between the exit of the ingot mold and the point where the solidification is complete is called metallurgical length.

Habituellement, l'acier est coulé verticalement et le lingot suit ensuite, au cours de sa solidification, une trajectoire courbe qui l'amène à l'horizontale. Le point de passage de la trajectoire courbe à la trajectoire horizontale rectiligne est généralement appelé point de redressement du lingot, parce que sa courbure y devient nulle.Usually, the steel is poured vertically and the ingot then follows, during its solidification, a curved trajectory which brings it to the horizontal. The point of passage from the curved trajectory to the rectilinear horizontal trajectory is generally called the straightening point of the ingot, because its curvature becomes zero there.

Dans la pratique actuelle de la coulée continue, l'acier contenu dans le récipient de coulée présente une température supérieure à sa température de liquidus, afin d'éviter tout risque de figeage dû à un refroidissement localisé. Cette différence de température, appelée surchauffe, est typiquement de l'ordre de 25 à 35°C.In the current practice of continuous casting, the steel contained in the casting container has a temperature higher than its liquidus temperature, in order to avoid any risk of freezing due to localized cooling. This temperature difference, called overheating, is typically of the order of 25 to 35 ° C.

On a déjà proposé, en particulier par le brevet BE-A-08900414, un procédé de refroidissement secondaire d'un produit métallique coulé en continu, qui comprend une étape de refroidissement intense au moyen d'une couche d'eau continue sous pression, suivie d'une étape de refroidissement modéré au moyen de l'eau s'écoulant le long du produit coulé.There has already been proposed, in particular by patent BE-A-08900414, a process for the secondary cooling of a continuously cast metal product, which comprises a step of intense cooling by means of a layer of continuous water under pressure, followed by a moderate cooling step by means of the water flowing along the cast product.

Ce procédé permet d'obtenir des produits qui présentent une ségrégation axiale très faible, ainsi qu'une surface pratiquement exempte de fissures. Il subsiste cependant dans ces produits des fissures internes, fermées, qui apparaissent au front de solidification.This process makes it possible to obtain products which have very low axial segregation, as well as a surface practically free from cracks. In these products, however, there remain internal, closed cracks, which appear at the solidification front.

L'objet de la présente invention est de proposer un procédé pour la coulée continue d'un métal, en particulier de l'acier, qui ne présente pas l'inconvénient précité et qui permet dès lors d'obtenir des produits coulés exempts de fissures, tant en surface qu'à l'intérieur du métal.The object of the present invention is to provide a process for the continuous casting of a metal, in particular steel, which does not have the above-mentioned drawback and which therefore makes it possible to obtain cast products free from cracks. , both on the surface and inside the metal.

Conformément à la présente invention, un procédé pour la coulée continue d'un métal, dans lequel on coule ledit métal dans une lingotière sans fond et on soumet ensuite le produit coulé à un refroidissement secondaire au moyen d'un liquide de refroidissement, est caractérisé en ce qu'il comprend les opérations suivantes, en combinaison :

  • a) on abaisse la température du métal jusqu'à une valeur comprise entre Tf et (Tf + 20°C) avant et/ou pendant la coulée dudit métal dans la lingotière, Tf étant la température de liquidus dudit métal;
  • b) on soumet le produit coulé à une première étape de refroidissement secondaire consistant en un refroidissement intense au moyen d'une couche continue de liquide de refroidissement sous pression formée à la surface dudit produit coulé; et
  • c) on applique ensuite audit produit coulé une seconde étape de refroidissement secondaire consistant en un refroidissement modéré au moyen d'un liquide de refroidissement assurant un coefficient d'échange de chaleur inférieur ou égal à 50 % du coefficient d'échange de chaleur réalisé par le liquide de refroidissement utilisé dans ladite première étape de refroidissement secondaire.
According to the present invention, a method for the continuous casting of a metal, in which said metal is poured into a bottomless ingot mold and then the cast product is subjected to secondary cooling by means of a coolant, is characterized in that it comprises the following operations, in combination:
  • a) the temperature of the metal is lowered to a value between T f and (T f + 20 ° C) before and / or during the casting of said metal in the ingot mold, T f being the liquidus temperature of said metal;
  • b) subjecting the cast product to a first secondary cooling step consisting of intense cooling by means of a continuous layer of pressurized coolant formed on the surface of said cast product; and
  • c) there is then applied to said cast product a second secondary cooling step consisting of moderate cooling by means of a cooling liquid ensuring a heat exchange coefficient less than or equal to 50% of the heat exchange coefficient produced by the cooling liquid used in said first secondary cooling step.

Suivant une première mise en oeuvre du procédé de l'invention, on abaisse la température du métal dans le récipient de coulée jusqu'à une valeur située dans la gamme de températures précitée, et on maintient la température du métal à cette valeur pendant la coulée.According to a first implementation of the process of the invention, the temperature of the metal in the casting container is lowered to a value situated in the aforementioned temperature range, and the temperature of the metal is maintained at this value during casting .

Cette mise en oeuvre peut nécessiter un réchauffage du métal pour compenser les pertes thermiques par rayonnement ou convection.This implementation may require heating of the metal to compensate for heat losses by radiation or convection.

Une autre mise en oeuvre particulière du procédé de l'invention consiste à abaisser la température dudit métal par un refroidissement contrôlé pendant la coulée, c'est-à-dire entre le récipient de coulée et la lingotière.Another particular implementation of the process of the invention consists in lowering the temperature of said metal by controlled cooling during casting, that is to say between the casting container and the mold.

A cet effet, on forme par exemple un jet creux de métal qui s'écoule en une couche continue le long d'une paroi refroidie avant de pénétrer dans la lingotière.For this purpose, a hollow jet of metal is formed, for example, which flows in a continuous layer along a cooled wall before entering the ingot mold.

Il s'est cependant avéré intéressant d'opérer cet abaissement de la température en deux étapes, à savoir une diminution limitée dans le récipient de coulée et un refroidissement complémentaire pendant la coulée.However, it has proved advantageous to effect this lowering of the temperature in two stages, namely a limited decrease in the pouring vessel and additional cooling during the casting.

L'invention porte également sur une installation pour la coulée continue d'un métal, en particulier de l'acier, qui, en plus d'un récipient de coulée et d'une lingotière sans fond, comporte en combinaison :

  • a) des premiers moyens pour abaisser la température du métal jusqu'à une valeur comprise entre Tf et (Tf + 20°C) avant et/ou pendant la coulée dudit métal dans la lingotière, Tf étant la température de liquidus dudit métal;
  • b) des deuxièmes moyens pour soumettre le produit coulé à une première étape de refroidissement secondaire consistant en un refroidissement intense au moyen d'une couche continue de liquide de refroidissement sous pression formée à la surface dudit produit coulé; et
  • c) des troisièmes moyens pour appliquer audit produit coulé une deuxième étape de refroidissement secondaire consistant en un refroidissement modéré au moyen d'un liquide de refroidissement.
The invention also relates to an installation for the continuous casting of a metal, in particular steel, which, in addition to a casting container and a bottomless ingot mold, comprises in combination:
  • a) first means for lowering the temperature of the metal to a value between T f and (T f + 20 ° C) before and / or during the casting of said metal in the ingot mold, T f being the liquidus temperature of said metal;
  • b) second means for subjecting the cast product to a first secondary cooling step consisting of intense cooling by means of a continuous layer of pressurized coolant formed on the surface of said cast product; and
  • c) third means for applying to said cast product a second secondary cooling step consisting of cooling moderate with coolant.

Les premiers moyens pour abaisser la température du métal peuvent consister en un dispositif limitant le refroidissement du métal provoqué par des pertes thermiques dans le récipient de coulée, poche de coulée ou panier répartiteur; un tel dispositif peut par exemple comprendre un couvercle thermo-isolant et/ou des brûleurs.The first means for lowering the temperature of the metal can consist of a device limiting the cooling of the metal caused by thermal losses in the pouring vessel, ladle or distributor basket; such a device can for example comprise a heat-insulating cover and / or burners.

Une autre forme de réalisation desdits premiers moyens consiste en un conduit vertical disposé entre le récipient de coulée et la lingotière, comportant à son extrémité d'entrée un organe de distribution du métal qui s'étend transversalement jusqu'à proximité de la surface intérieure dudit conduit. Ce conduit vertical est de préférence refroidi extérieurement, par exemple par circulation d'eau, sur au moins une partie de sa longueur.Another embodiment of said first means consists of a vertical conduit disposed between the casting container and the ingot mold, comprising at its inlet end a metal distribution member which extends transversely to near the interior surface of said drove. This vertical duct is preferably cooled externally, for example by circulation of water, over at least part of its length.

Les deux formes précitées de réalisation de ces premiers moyens, ainsi que d'autres formes équivalentes, peuvent évidemment être combinées sans sortir du cadre de l'invention.The two aforementioned embodiments of these first means, as well as other equivalent forms, can obviously be combined without departing from the scope of the invention.

Les deuxièmes moyens, qui assurent un refroidissement secondaire intense du produit coulé, comprennent avantageusement un caisson entourant au moins partiellement et à une certaine distance le produit coulé, et dont au moins une paroi tournée vers ledit produit est percée d'orifices de passage du liquide de refroidissement.The second means, which provide intense secondary cooling of the cast product, advantageously comprise a box surrounding at least partially and at a certain distance the cast product, and at least one wall of which faces towards said product is pierced with orifices for passage of the liquid. cooling.

De tels moyens de refroidissement permettent d'établir une couche continue de liquide de refroidissement sous pression à la surface du produit coulé et ainsi non seulement de le refroidir rapidement mais aussi de le supporter uniformément.Such cooling means make it possible to establish a continuous layer of pressurized coolant on the surface of the cast product and thus not only to cool it quickly but also to support it uniformly.

On comprendra aisément que lesdits deuxièmes moyens pourraient également être constitués, totalement ou partiellement, par tout autre dispositif de refroidissement secondaire capable d'assurer le refroidissement désiré. Par exemple, ce dispositif peut être constitué par un ensemble classique de gicleurs à eau alternant avec des rouleaux de support du produit coulé.It will easily be understood that said second means could also be constituted, totally or partially, by any other secondary cooling device capable of ensuring the desired cooling. For example, this device may consist of a conventional set of water sprinklers alternating with rollers for supporting the cast product.

Une autre façon intéressante d'assurer le refroidissement rapide désiré consiste à utiliser une enceinte entourant le produit coulé sur une longueur appropriée, la paroi intérieure de cette enceinte étant percée d'orifices dirigés vers le produit à refroidir. Cette enceinte est alimentée en eau sous pression; celle-ci s'échappe par les orifices sous la forme de jets qui viennent frapper la surface du produit coulé à refroidir et assurent son refroidissement rapide.Another interesting way of ensuring the desired rapid cooling consists in using an enclosure surrounding the product poured over an appropriate length, the interior wall of this enclosure being pierced with orifices directed towards the product to be cooled. This enclosure is supplied with pressurized water; this escapes through the orifices in the form of jets which strike the surface of the cast product to be cooled and ensure its rapid cooling.

Selon une réalisation particulière de l'installation de l'invention, lesdits troisièmes moyens pour le refroidissement modéré du produit coulé, comprennent une enceinte située sous les deuxièmes moyens précités, qui entoure le produit coulé en définissant à son extrémité inférieure une fente de largeur calibrée avec le produit coulé. Il peut également être prévu des moyens pour mesurer la température du produit coulé à la sortie de ladite enceinte et pour régler la largeur de ladite fente en fonction de la température mesurée.According to a particular embodiment of the installation of the invention, said third means for the moderate cooling of the cast product, comprise an enclosure situated under the aforementioned second means, which surrounds the cast product by defining at its lower end a slot of calibrated width with the poured product. Means can also be provided for measuring the temperature of the product poured at the outlet of said enclosure and for adjusting the width of said slot as a function of the measured temperature.

On va maintenant décrire un mode de réalisation actuellement préféré du procédé et de l'installation de l'invention, en faisant référence aux dessins annexés, dans lesquels la

  • Figure 1 représente schématiquement une installation combinée conforme à la présente invention; et la
  • Figure 2 illustre graphiquement l'amélioration obtenue par le procédé de l'invention en ce qui concerne la fissuration interne des produits coulés; la
  • Figure 3 illustre graphiquement l'amélioration obtenue par le procédé de l'invention en ce qui concerne la ségrégation axiale dans les produits coulés.
We will now describe a currently preferred embodiment of the method and installation of the invention, with reference to the accompanying drawings, in which the
  • Figure 1 schematically shows a combined installation according to the present invention; and the
  • Figure 2 graphically illustrates the improvement obtained by the process of the invention with regard to the internal cracking of the cast products; the
  • Figure 3 graphically illustrates the improvement obtained by the method of the invention with regard to axial segregation in cast products.

L'installation de coulée continue, représentée schématiquement dans la Figure 1, est disposée essentiellement sous un récipient de coulée, par exemple un panier répartiteur symbolisé par sa busette de coulée 1.The continuous casting installation, represented diagrammatically in FIG. 1, is arranged essentially under a casting container, for example a distribution basket symbolized by its casting nozzle 1.

Les différents dispositifs constituant ladite installation seront décrits dans l'ordre suivant lequel ils sont traversés par le métal coulé, depuis l'état liquide jusqu'à l'état solide. Dans le cas présent, l'installation illustrée est destinée à la coulée de l'acier.The various devices constituting said installation will be described in the order in which they are traversed by the cast metal, from the liquid state to the solid state. In the present case, the illustrated installation is intended for the casting of steel.

Le premier dispositif rencontré par l'acier est un organe de distribution 2, en forme de dôme, disposé dans la portion d'entrée d'un conduit vertical 3, lequel est pourvu d'un circuit de refroidissement à l'eau 4,5. Ce conduit vertical 3 se prolonge vers le bas par un tube de coulée 6.The first device encountered by steel is a distribution member 2, in the form of a dome, disposed in the inlet portion of a vertical duct 3, which is provided with a water cooling circuit 4.5. . This vertical duct 3 is extended downwards by a pouring tube 6.

L'acier, dévié par le dôme 2, s'écoule en une couche mince le long de la surface intérieure du conduit vertical 3, et il subit de ce fait un premier refroidissement. Le trajet de l'acier liquide est indiqué en pointillé dans la Figure 1. Ce premier refroidissement élimine une partie de la surchauffe de l'acier.The steel, deflected by the dome 2, flows in a thin layer along the inner surface of the vertical duct 3, and it therefore undergoes a first cooling. The path of the liquid steel is indicated in dotted lines in Figure 1. This first cooling eliminates part of the steel overheating.

Le tube de coulée 6 est introduit dans une lingotière de coulée 7, de type conventionnel, et l'extrémité inférieure de ce tube est immergée dans l'acier liquide 8 présent dans la lingotière 7. L'acier subit un refroidissement et un début de solidification dans la lingotière 7, et il sort de celle-ci sous la forme d'un lingot continu 9 présentant une peau solidifiée d'une épaisseur relativement faible.The pouring tube 6 is introduced into a casting mold 7, of conventional type, and the lower end of this tube is immersed in the liquid steel 8 present in the ingot mold 7. The steel undergoes cooling and a start of solidification in the ingot mold 7, and it leaves it in the form of a continuous ingot 9 having a solidified skin of a relatively small thickness.

Le lingot 9 partiellement solidifié pénètre ensuite dans un dispositif de refroidissement intense 10; celui-ci est essentiellement constitué d'un caisson entourant le lingot 9 et dont la paroi tournée vers le lingot est percée de fentes 11 inclinées dans le sens de progression du lingot 9. Ces fentes livrent passage à un liquide de refroidissement sous pression, habituellement l'eau, qui forme une couche continue entre le lingot 9 et ladite paroi et qui refroidit et supporte uniformément ledit lingot 9.The partially solidified ingot 9 then enters an intense cooling device 10; this essentially consists of a box surrounding the ingot 9 and whose wall facing the ingot is pierced with slots 11 inclined in the direction of progression of the ingot 9. These slots provide passage to a pressurized coolant, usually water, which forms a continuous layer between the ingot 9 and said wall and which cools and uniformly supports said ingot 9.

Cette eau ruisselle ensuite le long du lingot 9 et est recueillie dans une enceinte 12 qui entoure le lingot sous le caisson 10. L'extrémité inférieure de cette enceinte 12 est étranglée de façon à former une fente de sortie 13 calibrée autour du lingot 9. Du fait de cet étranglement, l'eau recueillie dans l'enceinte 12 forme un bain relativement calme où le lingot subit un refroidissement modéré. Un pyromètre 14 mesure la température de surface du lingot 9 à la sortie de l'enceinte 12 et commande éventuellement un réglage de la largeur de la fente 13.This water then flows along the ingot 9 and is collected in an enclosure 12 which surrounds the ingot under the box 10. The lower end of this enclosure 12 is throttled so as to form an outlet slot 13 calibrated around the ingot 9. Due to this constriction, the water collected in the enclosure 12 forms a relatively calm bath where the ingot undergoes moderate cooling. A pyrometer 14 measures the surface temperature of the ingot 9 at the outlet of the enclosure 12 and optionally controls the width of the slot 13.

Le lingot est finalement guidé suivant une trajectoire courbe, de façon connue en soi, jusqu'au point de redressement où il prend une trajectoire horizontale. On mesure également sa température TR au point de redressement, car c'est elle qui conditionne certaines opérations ultérieures, en particulier l'enfournement chaud des produits coulés.The ingot is finally guided along a curved trajectory, in a manner known per se, to the straightening point where it takes a trajectory horizontal. Its temperature T R is also measured at the recovery point, because it is this which conditions certain subsequent operations, in particular the hot charging of the cast products.

Dans une installation du type représenté dans la Figure 1, on a coulé un acier à 0,8 % C en blooms carrés de 220 mm de côté, avec différentes valeurs de la surchauffe (ΔT). Celle-ci était comprise entre 31°C et 15°C; la température des blooms au point de redressement (TR) était comprise entre 870°C et 910°C.In an installation of the type shown in Figure 1, a 0.8% C steel was poured in square blooms of 220 mm side, with different values of overheating (ΔT). This was between 31 ° C and 15 ° C; the temperature of the blooms at the rectification point (T R ) was between 870 ° C and 910 ° C.

Pour le type de produit et la nuance d'acier précités, la vitesse de coulée est normalement de 0,85 m/min avec une température TR = 930°C. Dans les conditions de l'invention, la vitesse de coulée a pu être portée à des valeurs de 1,2 m/min à 1,6 m/min sans qu'il se produise de fissures superficielles, quelle que soit la surchauffe.For the aforementioned product type and steel grade, the casting speed is normally 0.85 m / min with a temperature T R = 930 ° C. Under the conditions of the invention, the casting speed could be brought to values from 1.2 m / min to 1.6 m / min without the occurrence of surface cracks, whatever the overheating.

Il est toutefois apparu que des surchauffes supérieures à 20°C conduisaient à une fissuration interne au front de solidification, alors que ces fissures internes ne se produisaient plus pour des surchauffes inférieures à 20°C.However, it appeared that overheating above 20 ° C led to internal cracking at the solidification front, while these internal cracks no longer occurred for overheating below 20 ° C.

Ce résultat est clairement illustré dans la Figure 2, où les points noirs représentent les coulées ayant donné lieu à des fissures internes, tandis que les points blancs représentent les coulées sans fissuration.This result is clearly illustrated in Figure 2, where the black dots represent the flows which gave rise to internal cracks, while the white points represent the flows without cracking.

La Figure 3 illustre l'évolution de la ségrégation axiale en fonction de la surchauffe. La ségrégation axiale est exprimée par le rapport (Cmax/C₀) entre la teneur en carbone maximale, essentiellement dans l'axe, et la teneur en carbone moyenne dans la section transversale du produit coulé. La surchauffe (ΔT) est exprimée en degrés centigrades. Les produits considérés ici sont des billettes carrées de 220 mm de côté, ayant une teneur en carbone nominale de 0,8 %. La Figure montre une courbe (a) représentant la variation du rapport précité dans le cas de produits coulés avec un refroidissement conventionnel et une vitesse de coulée de 0,85 m/min. L'ensemble de points (b) correspond à des produits obtenus conformément à l'invention, coulés avec une vitesse de 1,5 m/min. On voit clairement que le rapport Cmax/C₀ est beaucoup plus proche de 1 pour ces derniers produits, ce qui traduit une nette diminution de la ségrégation axiale grâce au procédé de coulée à surchauffe faible et de refroidissement en deux étapes proposé par la présente invention.Figure 3 illustrates the evolution of axial segregation as a function of overheating. Axial segregation is expressed by the ratio (C max / C₀) between the maximum carbon content, essentially in the axis, and the average carbon content in the cross section of the cast product. Overheating (ΔT) is expressed in degrees centigrade. The products considered here are square billets of 220 mm side, with a nominal carbon content of 0.8%. The Figure shows a curve (a) representing the variation of the aforementioned ratio in the case of products cast with conventional cooling and a casting speed of 0.85 m / min. The set of points (b) corresponds to products obtained in accordance with the invention, cast with a speed of 1.5 m / min. We can clearly see that the C max / C₀ ratio is much closer to 1 for these latter products, which translates into a marked reduction in axial segregation thanks to the two-stage low overheating and cooling casting provided by the present invention.

Le procédé de l'invention permet d'obtenir des produits présentant des propriétés optimales, en particulier une structure de solidification très fine, une ségrégation centrale pratiquement nulle, une absence totale de fissures tant internes que superficielles et une très faible porosité. Un avantage supplémentaire est que ces propriétés sont obtenues avec une vitesse de coulée sensiblement accrue par rapport à la pratique conventionnelle; la productivité de l'installation et certaines opérations ultérieures comme l'enfournement chaud s'en trouvent favorisées.The method of the invention makes it possible to obtain products having optimal properties, in particular a very fine solidification structure, practically zero central segregation, a total absence of cracks both internal and surface and a very low porosity. An additional advantage is that these properties are obtained with a substantially increased casting speed compared to conventional practice; the productivity of the installation and certain subsequent operations such as hot charging are thereby favored.

Il convient de souligner le caractère inattendu des améliorations apportées par le procédé de l'invention; il n'existe en effet pas de relation prévisible entre la diminution de la surchauffe du métal avant la coulée et le comportement de ce même métal pendant sa solidification.It should be emphasized that the improvements brought about by the process of the invention are unexpected; there is in fact no predictable relationship between the reduction in the overheating of the metal before casting and the behavior of this same metal during its solidification.

Bien que l'invention ait été décrite et illustrée en faisant référence à un produit et à un acier particuliers, il va de soi que son objet n'est pas limité à cette seule application. Au contraire, de nombreuses variantes peuvent être envisagées par un homme de métier, non seulement en ce qui concerne le type de métal mais aussi dans les moyens mis en oeuvre pour assurer les divers refroidissements requis par le procédé revendiqué.Although the invention has been described and illustrated with reference to a particular product and steel, it goes without saying that its object is not limited to this single application. On the contrary, many variants can be envisaged by a person skilled in the art, not only with regard to the type of metal but also in the means used to provide the various coolings required by the claimed process.

Claims (10)

Procédé pour la coulée continue d'un métal, dans lequel on coule ledit métal dans une lingotière sans fond et on soumet ensuite le produit coulé à un refroidissement secondaire au moyen d'un liquide de refroidissement, caractérisé en ce qu'il comprend les opérations suivantes, en combinaison : a) on abaisse la température du métal jusqu'à une valeur comprise entre Tf et (Tf + 20°C) avant et/ou pendant la coulée dudit métal dans la lingotière, Tf étant la température de liquidus dudit métal; b) on soumet le produit coulé à une première étape de refroidissement secondaire consistant en un refroidissement intense au moyen d'une couche continue de liquide de refroidissement sous pression formée à la surface dudit produit coulé; et c) on applique ensuite audit produit coulé une seconde étape de refroidissement secondaire consistant en un refroidissement modéré au moyen d'un liquide de refroidissement assurant un coefficient d'échange de chaleur inférieur ou égal à 50 % du coefficient d'échange de chaleur réalisé par le liquide de refroidissement utilisé dans ladite première étape de refroidissement secondaire. Process for the continuous casting of a metal, in which the said metal is poured into a bottomless ingot mold and the subdued product is then subjected to secondary cooling by means of a coolant, characterized in that it comprises the operations following, in combination: a) the temperature of the metal is lowered to a value between T f and (T f + 20 ° C) before and / or during the casting of said metal in the ingot mold, T f being the liquidus temperature of said metal; b) subjecting the cast product to a first secondary cooling step consisting of intense cooling by means of a continuous layer of pressurized coolant formed on the surface of said cast product; and c) there is then applied to said cast product a second secondary cooling step consisting of moderate cooling by means of a cooling liquid ensuring a heat exchange coefficient less than or equal to 50% of the heat exchange coefficient produced by the coolant used in said first secondary cooling step. Procédé suivant la revendication 1, caractérisé en ce que l'on abaisse la température du métal avant la coulée jusqu'à une valeur située dans la gamme de températures précitée, et on maintient la température dudit métal à cette valeur pendant la coulée.Process according to Claim 1, characterized in that the temperature of the metal is lowered before casting to a value situated in the above-mentioned temperature range, and the temperature of said metal is maintained at this value during casting. Procédé suivant la revendication 1, caractérisé en ce que l'on abaisse la température dudit métal pendant la coulée en formant un jet creux dudit métal et en faisant s'écouler ledit jet creux en une couche continue le long d'une paroi refroidie avant de pénétrer dans la lingotière.A method according to claim 1, characterized in that the temperature of said metal is lowered during casting by forming a hollow jet of said metal and causing said hollow jet to flow in a continuous layer along a cooled wall before enter the mold. Installation pour la coulée continue d'un métal suivant le procédé qui fait l'objet des revendications précédentes, caractérisée en ce qu'en plus d'un récipient de coulée (1) et d'une lingotière sans fond (7), elle comporte en combinaison : a) des premiers moyens (3) pour abaisser la température du métal jusqu'à une valeur comprise entre Tf et (Tf + 20°C) avant et/ou pendant la coulée dudit métal dans la lingotière, Tf étant la température de liquidus dudit métal; b) des deuxièmes moyens (10) pour soumettre le produit coulé à une première étape de refroidissement secondaire consistant en un refroidissement intense au moyen d'une couche continue de liquide de refroidissement sous pression formée à la surface dudit produit coulé (9); et c) des troisièmes moyens (12) pour appliquer audit produit coulé (9) une deuxième étape de refroidissement secondaire consistant en un refroidissement modéré au moyen d'un liquide de refroidissement. Installation for the continuous casting of a metal according to the process which is the subject of the preceding claims, characterized in that in addition to a casting container (1) and a bottomless ingot mold (7), it comprises in combination: a) first means (3) for lowering the temperature of the metal to a value between T f and (T f + 20 ° C) before and / or during the casting of said metal in the ingot mold, T f being the temperature of liquidus of said metal; b) second means (10) for subjecting the cast product to a first secondary cooling step consisting of intense cooling by means of a continuous layer of pressurized coolant formed on the surface of said cast product (9); and c) third means (12) for applying to said cast product (9) a second secondary cooling step consisting of moderate cooling by means of a coolant. Installation suivant la revendication 4, dans laquelle lesdits premiers moyens (3) pour abaisser la température du métal consistent en un conduit vertical (3) disposé entre le récipient de coulée (1) et la lingotière sans fond (7) et comportant à son extrémité d'entrée un organe (2) de distribution du métal qui s'étend transversalement jusqu'à proximité de la surface intérieure dudit conduit (3), ledit conduit vertical (3) étant de préférence refroidi extérieurement.Installation according to claim 4, in which said first means (3) for lowering the temperature of the metal consist of a vertical duct (3) disposed between the casting container (1) and the bottomless ingot mold (7) and comprising at its end from the input a metal distribution member (2) which extends transversely to near the interior surface of said duct (3), said vertical duct (3) being preferably cooled externally. Installation suivant l'une ou l'autre des revendications 4 et 5, dans laquelle lesdits deuxièmes moyens (10) comprennent un caisson (10) entourant au moins partiellement et à une certaine distance le produit coulé, et dont au moins une paroi tournée vers ledit produit est percée d'orifices (11) de passage du liquide de refroidissement.Installation according to either of Claims 4 and 5, in which said second means (10) comprise a box (10) at least partially and at a certain distance surrounding the cast product, and of which at least one wall faces towards said product is pierced with holes (11) for the passage of the coolant. Installation suivant l'une ou l'autre des revendications 4 à 6, dans laquelle lesdits troisièmes moyens (12) comprennent une enceinte (12) entourant le produit coulé (9) et située sous lesdits deuxièmes moyens de refroidissement (10).Installation according to either of claims 4 to 6, in which said third means (12) comprise an enclosure (12) surrounding the cast product (9) and located under said second cooling means (10). Installation suivant la revendication 7, dans laquelle ladite enceinte (12) présente une extrémité inférieure qui définit une fente (13) de largeur réglable avec le produit coulé (9).Installation according to claim 7, wherein said enclosure (12) has a lower end which defines a slot (13) of adjustable width with the cast product (9). Installation suivant l'une ou l'autre des revendications 4 à 8, dans laquelle le conduit vertical (3) est pourvu d'un tube de coulée (6) qui le prolonge verticalement vers le bas et qui pénètre dans la lingotière sans fond (7).Installation according to either of Claims 4 to 8, in which the vertical duct (3) is provided with a pouring tube (6) which extends it vertically downwards and which enters the bottomless ingot mold ( 7). Installation suivant l'une ou l'autre des revendications 6 à 9, dans laquelle lesdits orifices sont des fentes (11) de largeur réglable, inclinées dans le sens de progression dudit produit coulé (9).Installation according to either of Claims 6 to 9, in which the said orifices are slots (11) of adjustable width, inclined in the direction of progression of the said cast product (9).
EP91870056A 1990-04-11 1991-04-08 Method and device for the continuous casting of a metal Expired - Lifetime EP0452294B1 (en)

Applications Claiming Priority (2)

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LU87722A LU87722A1 (en) 1990-04-11 1990-04-11 PROCESS AND PLANT FOR CONTINUOUS CASTING OF METAL
LU87722 1990-04-11

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EP0452294A2 true EP0452294A2 (en) 1991-10-16
EP0452294A3 EP0452294A3 (en) 1994-01-19
EP0452294B1 EP0452294B1 (en) 1998-07-01

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AT (1) ATE167821T1 (en)
DE (1) DE69129671D1 (en)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000054909A1 (en) * 1999-03-17 2000-09-21 Corus Uk Limited Apparatus for removing superheat from liquid metal

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3771584A (en) * 1971-01-08 1973-11-13 Roblin Industries Method for continuously casting steel billet strands to minimize the porosity and chemical segregation along the center line of the strand
DE3048711C2 (en) * 1980-12-23 1991-08-01 Hamburger Stahlwerke Gmbh, 2103 Hamburg Process for cooling strands in the continuous casting of steel billets
DE3440235C2 (en) * 1984-11-03 1986-11-06 Mannesmann AG, 4000 Düsseldorf Method and device for continuous strip casting of metals, in particular steel
DE3775722D1 (en) * 1986-11-26 1992-02-13 Centre Rech Metallurgique DEVICE FOR CASTING A PASTE-LIKE METAL.
BE1003164A6 (en) * 1989-04-13 1991-12-17 Centre Rech Metallurgique METHOD AND DEVICE FOR COOLING A CONTINUOUSLY CAST METAL PRODUCT.

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000054909A1 (en) * 1999-03-17 2000-09-21 Corus Uk Limited Apparatus for removing superheat from liquid metal

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LU87722A1 (en) 1990-07-24
DE69129671D1 (en) 1998-08-06
EP0452294B1 (en) 1998-07-01
EP0452294A3 (en) 1994-01-19
ATE167821T1 (en) 1998-07-15

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