EP2490842B1 - Method for manufacturing a metal ingot comprising a bore, and associated ingot and molding device - Google Patents

Description

The present invention relates to the manufacture of a metal ingot having a longitudinal bore and in particular a steel ingot for producing forged annular parts.

To produce forged annular parts, such as ferrules, for example for the construction of nuclear power plant tanks or for the construction of petrochemical reactors, it is known to use ingots which are either solid ingots, which must then be the object of a forging operation having the drilling of an axial hole, the direct casting of ingots having a central bore which can be transformed directly in the form of ferrule.

These two types of ingots are distinguished in particular in the casting conditions which result in particular in the hydrogen content retained in the liquid state and which may affect both the properties of the parts obtained and the manufacturing conditions. .

Indeed, the solid ingots can be cast under vacuum, which allows them to be made of steel which was degassed at the time of vacuum casting, to obtain guaranteed hydrogen contents of less than 1 ppm.

On the other hand, ingots having a central bore are cast in air source. These ingots are cast using metal or liquid steel which has been degassed during the pocket metallurgy operations, and which generally have a guaranteed hydrogen content of less than 1.5 ppm. However, during the spring casting, through the passage through the air and the contact with the refractories that constitute the source, the steel takes up a quantity of hydrogen of the order of 0.3 ppm, it is therefore difficult to obtain ingots which can be guaranteed, when the steel is in the liquid state in the mold, a hydrogen content of less than 1.8 ppm.

However, for certain applications, and particularly for applications in the field of construction of nuclear reactors, it is necessary to obtain parts whose hydrogen content on finished parts is less than 0.8 ppm. Such contents can be obtained with solid ingots cast under vacuum when in particular the pressure in the vacuum casting chamber is of the order of 0.1 Torr. However, with ingots cast in a source, and in particular ingots having a longitudinal bore, this guarantee can not be obtained by subjecting the parts during their forging to a succession of long and expensive thermal treatments intended in particular to diffuse hydrogen. It therefore follows from these differences that if the ingots having a longitudinal bore can be forged with a simplified forging process compared to the solid ingot, they require on the other hand very long and very expensive degassing treatments which make the process more complicated.

In contrast, solid ingots, although having a low hydrogen content and therefore do not require degassing treatments, require a more complicated forging process. Indeed, this process must include at least one step for making a central hole that requires several forging and reheating operations in furnaces.

An object of the present invention is to overcome these disadvantages by providing a means for obtaining forging ingots having a longitudinal bore, while having a sufficiently low hydrogen content from the beginning, in order to be able to guarantee conditions of hydrogen content. low on the finished parts, without many thermal degassing treatments being necessary.

To this end, the subject of the invention is a method for producing a metal ingot having a longitudinal bore, by casting of liquid metal in a mold comprising a generally annular molding cavity, defined by an ingot mold extending vertically above the mold. a support, the mold having an upwardly open cavity, a vertical core disposed within the cavity of the mold, and a bottom.

• le moule est disposé à l'intérieur d'une enceinte de coulée sous vide comprenant, à sa partie supérieure, un moyen d'introduction de métal liquide ;
• un moyen de réception et de répartition de métal liquide adapté pour recevoir l'acier liquide introduit dans l'enceinte de coulée sous vide et pour redistribuer le métal liquide dans la cavité de moulage, est disposé à la partie supérieure de la cavité de moulage, et :
• on introduit le métal liquide dans l'enceinte de coulée sous vide de façon à former un premier jet d'acier liquide sous vide pour déverser le métal liquide sur le moyen de réception et de répartition et à former au moins un deuxième jet d'acier liquide sous vide provenant du moyen de réception et de répartition et aboutissant dans la cavité de moulage de façon à couler le métal liquide dans la cavité de moulage.

According to this method:

• the mold is disposed inside a vacuum casting chamber comprising, at its upper part, a liquid metal introduction means;
• a liquid metal receiving and distributing means adapted to receive the liquid steel introduced into the vacuum casting chamber and to redistribute the liquid metal in the molding cavity, is disposed at the upper part of the molding cavity, and
• the liquid metal is introduced into the vacuum casting chamber so as to form a first liquid steel jet under vacuum to discharge the liquid metal onto the receiving and distributing means and forming at least a second vacuum liquid steel jet from the receiving and distributing means and terminating in the molding cavity so as to flow the liquid metal into the molding cavity.

• le moyen de réception et de répartition du métal liquide est un répartiteur en forme de cuvette comprenant au moins un canal d'évacuation, débouchant dans la cavité de moulage. Le canal d'évacuation peut avoir différentes formes (tube, coude....) et différentes positions (horizontale, inclinée ...)
• le moyen de réception et de répartition du métal liquide est un cône en matériau réfractaire dont la pointe est adaptée pour recevoir le premier jet d'acier liquide ;
• le moyen de réception et de répartition du métal liquide est en appui sur l'extrémité supérieure du noyau ;
• le noyau est constitué d'un corps généralement cylindrique en matériau réfractaire comprenant une armature axiale métallique ;
• l'armature du noyau est un tube métallique, par exemple en acier, dont la paroi comporte une pluralité de trous ;
• le moule est généralement de révolution ;
• le métal liquide est de l'acier liquide ;
• la pression dans l'enceinte sous vide est inférieure à 0,2 Torr.

The method according to the invention may comprise one or more of the following characteristics:

• the means for receiving and distributing the liquid metal is a cup-shaped distributor comprising at least one evacuation channel, opening into the mold cavity. The evacuation channel can have different shapes (tube, elbow ....) and different positions (horizontal, inclined ...)
• the means for receiving and distributing the liquid metal is a cone made of refractory material whose tip is adapted to receive the first liquid steel jet;
• the means for receiving and distributing the liquid metal bears on the upper end of the core;
• the core consists of a generally cylindrical body of refractory material comprising a metal axial armature;
• the core reinforcement is a metal tube, for example steel, whose wall comprises a plurality of holes;
• the mold is generally of revolution;
• the liquid metal is liquid steel;
• the pressure in the vacuum chamber is less than 0.2 Torr.

The invention further relates to a steel ingot comprising a longitudinal bore has been obtained by vacuum casting. The ingot may for example have a generally rotational shape.

The ingot may have a hydrogen content of less than 1.2 ppm, preferably less than or equal to 1 ppm and more preferably less than or equal to 0.8 ppm.

• une lingotière ;
• un noyau en matériau réfractaire armé disposé verticalement dans la lingotière ; et
• un fond,
• et un moyen de réception et de répartition de métal liquide disposé en appui sur l'extrémité supérieure du noyau.

The invention also relates to an apparatus for vacuum casting a metal ingot comprising a longitudinal bore, comprising a molding cavity defined by:

• an ingot mold;
• a core of reinforced refractory material disposed vertically in the mold; and
• a fund,
• and liquid metal receiving and distributing means disposed in abutment on the upper end of the core.

• le moyen de réception et de répartition du métal liquide est un répartiteur en forme de cuvette comprenant au moins un canal d'évacuation débouchant dans la cavité de moulage ;
• le moyen de réception et de répartition du métal liquide est un cône en matériau réfractaire dont la pointe est adaptée pour recevoir le premier jet d'acier liquide.

According to variants:

• the means for receiving and distributing the liquid metal is a dish-shaped distributor comprising at least one evacuation channel opening into the molding cavity;
• the means for receiving and distributing the liquid metal is a cone made of refractory material whose tip is adapted to receive the first liquid steel jet.

• la figure 1 représente en coupe une installation de coulée sous vide d'un lingot métallique comportant un alésage longitudinal ;
• la figure 2 est une vue de dessus d'une lingotière pour la coulée d'un lingot comportant un alésage longitudinal muni d'un moyen de réception et de répartition du métal liquide ;
• la figure 3 est une représentation schématique en coupe d'un deuxième mode de réalisation de dispositif de répartition de métal liquide au sommet de la lingotière de coulée de lingot comportant un alésage longitudinal ;
• la figure 4 est une vue éclatée agrandie du dispositif de réception et de répartition de métal liquide représenté à la figure 3.

The invention will now be described more precisely, but not limitatively, with reference to the appended figures in which:

• the figure 1 shows in section a vacuum casting installation of a metal ingot having a longitudinal bore;
• the figure 2 is a plan view of an ingot mold for casting an ingot having a longitudinal bore provided with means for receiving and distributing the liquid metal;
• the figure 3 is a schematic sectional representation of a second embodiment of a liquid metal distribution device at the top of the ingot casting mold having a longitudinal bore;
• the figure 4 is an enlarged exploded view of the liquid metal receiving and distribution device shown in FIG. figure 3 .

To the figure 1 , there is shown an installation for vacuum casting a metal ingot, and in particular a steel ingot, generally of revolution shape and having a longitudinal central bore.

This installation comprises a mold 1 intended to mold the metal ingot, consisting of a cast iron mold 2 known in itself which delimits a cavity 3 inside which is disposed a vertical core 4. The whole is arranged in a vacuum casting chamber 5 consisting of a tank 6 closed by a cover 8 having a pipe 7 pumping connected to a pump installation not shown. The cover 8 has a means 9 introduction of the liquid metal inside the vacuum chamber which consists of an intermediate pocket 10 closed by a drawer nozzle 11 arranged at the junction between the intermediate bag 10 and the vacuum chamber 5.

Such a vacuum casting installation is known in itself and it makes it possible to pour liquid metal and in particular steel which is first poured into the intermediate bag 10, then which can be penetrated into the vacuum chamber 5 by opening the drawer nozzle 11 without breaking vacuum.

The mold 1 rests on a wedge 17 whose height is adapted so that the mold is completely disposed inside the vacuum casting chamber 5, which vacuum casting chamber 5 rests under the ground 16.

At its lower part, the mold 1 comprises a bottom marked generally by 27 comprising a wedging means 18 and a cast iron counterplate 20. The bottom is adapted to obtain the desired ingot height. The wedging means is for example cast iron. The space between the wedging means and the side wall of the mold is filled with dry sand 19.

The counterplate cast iron 20 for receiving the lower portion of the vertical core 4, is surrounded by chromite gaskets.

Thus, the mold 2, the core 4 and the bottom 27 define a generally annular mold cavity 3A intended to receive the liquid metal.

The vertical core 4, of generally cylindrical shape, is constituted, in its outer part, chromite surrounding a metal frame consisting of a steel tube 42 extending over the entire height and whose wall may optionally have holes. This metal reinforcement is intended on the one hand, to ensure the rigidity and strength of the vertical core 4 and on the other hand, to form a chimney through which can evacuate the gases resulting from degassing of the chromite core. The chromite core may advantageously be coated with a refractory lining based on zirconium silicate or any equivalent product.

At the upper part of the molding cavity 3A, grinding plates 22 are arranged on the inner wall of the mold and on the wall external of the kernel. Such grinding plates are known in themselves to those skilled in the art.

At the upper part of the mold, is disposed a means 11A for receiving and distributing the liquid steel which is introduced into the vacuum chamber. This means 11A for receiving and distributing the liquids is constituted by a cup-shaped distributor 12 consisting of tabular alumina, which comprises at its periphery channels 13 opening vertically above the molding cavity 3A. The channels 13 are intended to drive the liquid steel which is contained inside the distributor 12 in the molding cavity 3A. These channels 13. are of refractory material and are contained in housings 14 filled with sand. They rest on a support plate 15 which bears on the upper part of the vertical core 4 and on the upper face of the mold 2.

As can be seen on the figure 2 , which is a view from above, the distributor 12 comprises an inner bowl 121 from which four channels 13 which are contained in four holding boxes containing sand 14 and which are supported by the arms 122 of the support plate 15. These arms 122, which are arranged in a cross, rest on the top of the mold 2.

Finally, at the upper part of the molding cavity 3A and near the outlet of the channels 13 which allow the liquid steel to be poured into the molding cavity 3A, the mold 1 comprises massaging plates 22 which surround a on the other hand, the mold 2. Such massing plates are known in themselves to those skilled in the art.

A method of casting a metal ingot, and in particular a generally revolving steel ingot with a central bore also of revolution, will now be described.

After having closed the tank 6 with the cover 8, the vacuum casting chamber 5 is evacuated by pumping through the pipe 7 using a vacuum pumping installation known in itself. even of the skilled person. Thus, the pressure of the atmosphere within the vacuum chamber 5 is lowered to a value that can fall below 0.5 Torr, and better below 0.2 Torr, and better still below 0.1 Torr. Once the vacuum is achieved in the enclosure, there is a steel pocket above the intermediate pocket 10, it pours liquid steel in the pocket intermediate 10. When the intermediate bag 10 is sufficiently filled with steel, the drawer nozzle 11 is opened, which makes it possible to introduce liquid steel inside the vacuum enclosure 5. This liquid steel forms a first jet 50 which forms a reserve 51 of liquid steel in the bowl 121 of the distributor 12.

The reserve 51 of liquid steel then flows through the channels 13 to form secondary jets 52 which introduce liquid steel inside the molding cavity 3A and which gradually fill this molding cavity 3 forming a volume of liquid steel 53 inside the molding cavity 3A.

Due to the formation of a plurality of jets 50, 52 of liquid steel in a vacuum chamber 5, which are on the one hand, the jet 50 located between the spool nozzle and the distributor 12 and secondly the filling jets 52 of the molding cavity 3A, the degassing of the steel is particularly effective. Indeed, both the first jet 50, the other jets 52 are exploded and the bursting of these jets 50, 52 in the vacuum promotes the evacuation of hydrogen.

Thus, by using a liquid steel which has been previously degassed statically in a static degassing ladle or during a secondary metallurgy operation, so as to have a hydrogen content of between 1.2 and 1.5 ppm of Preferably, an ingot may be obtained having a longitudinal bore which, when still in the liquid state inside the mold, may have a hydrogen content substantially less than 0.8 ppm.

In an alternative embodiment, it may, however, from a liquid steel having a hydrogen content greater than 1.5 ppm, while still obtaining an ingot whose hydrogen content will be substantially less than 0.8 ppm.

Once the molding cavity 3A filled with liquid steel, it proceeds in a known manner by allowing the ingot to solidify inside the vacuum casting chamber 5.

It is then possible to open the vacuum casting chamber 5 by removing the cover 8, then removing the receiving and distribution means 11, and then demolding the ingot in a manner known in itself to those skilled in the art. .

Thus, a metal ingot, in particular a steel ingot, and in particular low alloy steel, having high metal properties, which can be used to manufacture forgings for heavy equipment, such as plant vessels, is obtained. nuclear or petrochemical equipment. The ingot has a very low hydrogen content, which can be guaranteed less than 1, 2 ppm and even less than 1 ppm, and better still, possibly lower than 0.8 ppm.

Such an ingot has the advantage of subsequently allowing very simplified forging operations to obtain parts having very high qualities. In the embodiment which has been shown here, the means 11A for receiving and distributing the liquid metal consists of a distributor 12 comprising a bowl and which bears on the central core 4. Other embodiments are possible, the essential is to achieve at least the formation of two successive streams of liquid metal, under vacuum, which can burst to ensure two successive degassing operations.

To the figure 3 another alternative embodiment is shown in which the mold 2 is surmounted by a receiving and distributing means 11 'of the jet 50 of liquid metal which is introduced into the vacuum casting chamber. This means 11 'is constituted by a cone 110 bearing on the central core 4. The liquid metal which comes from the jet 50 flows on an area 51' which is on the outer periphery of the cone 110, then opens into the cavity of molding 3A forming jets 52 'which are exploded and which can ensure a very good degassing.

To the figure 4 the cone 110 of the liquid steel receiving and distributing means is shown, which is completed by a U-shaped jumper 111 which is intended to hold the cone 110.

In the foregoing description, the manufacture of an ingot generally of revolution having an axial bore also of revolution has been described. But, the skilled person will understand that the ingot and the bore may not be of revolution and that the bore may not be axial. In all cases, the molding cavity is said to be generally annular.

Likewise, a generally cylindrical core and mold have been described, but it will be understood by those skilled in the art that the core and / or the mold may also be slightly tapered. In general, it will be understood by those skilled in the art that the molding cavity may have undercuts intended to facilitate demolding.

Finally, in a manner known per se, the mold may consist of several assembled segments.

Claims (13)

1. Process for production of a metal ingot comprising a longitudinal bore, by casting of liquid metal in a mould (1) comprising a moulding cavity (3A) which is generally annular, delimited by an ingot mould (2) which extends vertically above a support (17), the ingot mould comprising a cavity (3) which is open at the top, by a vertical core (4) which is arranged inside the cavity (3) and by a base (27),
   characterised in that:

   - the mould (1) is arranged inside a casting enclosure under vacuum (5), comprising in its upper part a means (9) for introduction of liquid metal;

   - a means (11A, 11') for receipt and distribution of liquid metal, which is designed to receive the liquid steel introduced into the casting enclosure under vacuum (5) and to redistribute the liquid metal in the moulding cavity (3A), and being arranged in the upper part of the moulding cavity (3A),

   and in that:

   - the liquid metal is introduced into the casting enclosure under vacuum (5) such as to form a first jet of liquid steel (50) under vacuum, in order to pour the liquid metal onto the means (11A, 11') for receipt and distribution and to form at least one second jet of liquid steel (52) under vacuum obtained from the means (11A, 11') for receipt and distribution, and leading into the moulding cavity (3A), such as to fill the moulding cavity (3A) with liquid metal.
2. Process according to claim 1, characterised in that the means (11A) for receipt and distribution of the liquid metal is a distributor (12) in the form of a dish comprising at least one discharge channel (13) which opens out into the moulding cavity (3A).
3. Process according to claim 1, characterised in that the means (11') for receipt and distribution of the liquid metal is a cone (110) made of refractory material, the tip of which is designed to receive the first jet of liquid steel.
4. Process according to any one of claims 1 to 3, characterised in that the means (11A, 11') for receipt and distribution of the liquid metal is supported on the upper end of the core (4).
5. Process according to any one of claims 1 to 4, characterised in that the core (4) is constituted by a generally cylindrical body (41) made of refractory material comprising an axial metal reinforcement (42).
6. Process according to claim 5, characterised in that the reinforcement of the core is a metal tube (42), for example made of steel, the wall of which comprises a plurality of holes.
7. Process according to any one of claims 1 to 6, characterised in that the mould is generally of revolution.
8. Process according to any one of claims 1 to 7, characterised in that the liquid metal is liquid steel.
9. Process according to any one of claims 1 to 8, characterised in that the pressure in the casting enclosure under vacuum (5) is lower than 0.5 Torr.
10. Steel ingot comprising a longitudinal bore, characterised in that it has been obtained by casting under vacuum, and it that it has a hydrogen content of less than 1.2 ppm.
11. Moulding device (1) for casting under vacuum of a metal ingot comprising a longitudinal bore, characterised in that it comprises:

    - a mould (1) comprising a moulding cavity (3A) delimited by:

    - an ingot mould (2);

    - a core (4) made of reinforced refractory material which is arranged in the ingot mould (2); and

    - a base (27);

    - and a means (11A, 11') for receipt and distribution of liquid metal arranged such as to be supported on the upper end of the core.
12. Moulding device according to claim 11, characterised in that the means (11) for receipt and distribution of the liquid metal is a distributor (12) in the form of a dish comprising at least one discharge channel (13) which opens out into the moulding cavity (3A).
13. Moulding device (1) according to claim 11, characterised in that the means (11') for receipt and distribution of the liquid metal is a cone (110) made of refractory material, the tip of which is designed to receive the first jet of liquid steel.

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