EP0924305B1 - Metallurgical reactor for treating of molten metal under reduced pressure - Google Patents

Metallurgical reactor for treating of molten metal under reduced pressure Download PDF

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Publication number
EP0924305B1
EP0924305B1 EP98403021A EP98403021A EP0924305B1 EP 0924305 B1 EP0924305 B1 EP 0924305B1 EP 98403021 A EP98403021 A EP 98403021A EP 98403021 A EP98403021 A EP 98403021A EP 0924305 B1 EP0924305 B1 EP 0924305B1
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Prior art keywords
tank
enclosure
chamber
ladle
gas
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EP98403021A
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German (de)
French (fr)
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EP0924305A1 (en
Inventor
Didier Huin
Hubert Saint Raymond
François Stouvenot
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Sollac SA
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Sollac SA
Lorraine de Laminage Continu SA SOLLAC
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/04—Refining by applying a vacuum
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum

Definitions

  • the invention relates to the preparation of metals in the liquid state, in particular of steel. It is particularly applicable to the production of high purity steels, with grades extremely low in carbon, or even nitrogen, hydrogen and oxygen.
  • the circulation of metal between the pocket and the tank causes a gentle agitation of the metal in the pocket, favorable for good settling of non-metallic inclusions.
  • reactors from the type called "DH" differ from HR in that their tank is only connected to one single plunger, by which part of the liquid metal contained in the pocket is sucked into the tank to be subjected to reduced pressure.
  • the renewal of the metal present in the tank is provided discontinuously, either by temporary interruptions of the setting under reduced tank pressure, which returns the metal to the pocket liquid contained in the tank, either by a distance of the pocket from the tank to constant pressure in the tank; which also causes such a metal return in the pocket since the difference in level between the metal surfaces in the pocket and in the tank must remain constant.
  • gas insufflation is not necessary; it is nevertheless highly recommended if we want to promote the most effective metallurgical degassing and, possibly, decarburatiori reactions sought.
  • a time treatment time of 10 minutes may be enough to lower the carbon content in the steel by 300 ppm to 20 ppm.
  • Installations in which the steel pocket is simply placed in an enclosure under reduced pressure are not as good adapted for this purpose.
  • Very large quantities of gas cannot be injected into it to accelerate the decarburization kinetics, and the vacuum exposure of the refractories in the pocket, which often contain carbonaceous materials, accentuates the recarburations of the metal from of these refractories.
  • RH and DH reactors of conventional design Another disadvantage of the RH and DH reactors of conventional design is that their tightness compared to the ambient atmosphere is not always satisfactory at the level of the plungers (whose refractories have a certain porosity) and their connections at the bottom of the tank. .
  • the resulting air aspirations can be estimated at several hundred Nm 3 / h on large industrial installations. They cause an uncontrolled supply of oxygen and nitrogen to the liquid metal, which makes it more difficult to control decarburization and limits the extent of denitriding that can be carried out.
  • the aim of the invention is to propose a new type of metallurgical reactor, which, in particular, gives access to the carbon contents in liquid steel of the order of 10 ppm and less under satisfactory productivity conditions.
  • This reactor should also be capable of being used to produce steels with low or very low nitrogen contents as well in oxygen, just like the HR and DH of classic design.
  • the subject of the invention is a metallurgical reactor for treatment under reduced pressure of a liquid metal, such as steel, contained in a pocket, of the type comprising a tank connected to a gas suction installation capable of keeping it there reduced pressure and two tubular plungers with upper ends open into openings in the bottom of the tank, the ends of which lower can be immersed in said liquid metal contained in said pocket, one of said plungers, called “ascending plunger”, comprising means for blowing a gas in its interior space in order to create a movement of movement of the metal liquid between the bag and the tank during said treatment, characterized in that it comprises also an enclosure provided with means for blowing a gas into its interior space adapted to the creation in the enclosure of a pressure greater than atmospheric pressure, and in which the pocket is placed, the upper edge of said enclosure being provided for sealingly support the bottom of the tank during said treatment, and means to lift the pocket towards the tank during said treatment.
  • the invention also relates to a metallurgical reactor for treatment under reduced pressure of a liquid metal, such as steel, contained in a pocket, of the type comprising a tank connected to a gas suction installation capable of keeping it there reduced pressure and a tubular plunger whose upper end opens into a opening in the bottom of the tank, the lower end of which can be submerged in said liquid metal contained in said pocket, characterized in that it comprises also an enclosure provided with means for blowing a gas into its interior space adapted to the creation in the enclosure of a pressure greater than atmospheric pressure, and in which the pocket is placed, the upper edge of said enclosure being provided for sealingly support the bottom of the tank during said treatment, and means to lift the pocket towards the tank during said treatment.
  • the metallurgical reactor according to the invention is distinguished traditional vacuum reactor type RH or DH essentially in that the pocket, instead of just being in the open air, is placed in an enclosure on the edge upper part of which the bottom of the vacuum tank is made to seal.
  • the enclosure is inerted by a neutral gas which puts it under a pressure substantially higher than atmospheric pressure, so as to cause the rise in the tank vacuum of a maximum quantity of liquid metal.
  • the tank 5 is equipped with means for blowing argon into the liquid steel 1 which it contains, such as parietal nozzles 12 (only one has been shown, but there may be several) or submerged spears.
  • This blown argon the flow of which is generally of the same order of magnitude as the flow blown into the ascending plunger 7 or even a little higher, accelerates the degassing and also the decarburization reaction. This is due to a sweeping effect of the gases present or formed in the liquid bath 1, and also to the creation of projections of liquid steel 13 in the form of fine droplets.
  • These droplets 13 offer a large specific surface of exposure to the rarefied atmosphere of the tank 5, which also goes in the direction of an acceleration of decarburization.
  • the argon blown into the ascending plunger 7 has a similar effect of creating projections 13 in the tank 5.
  • the argon blown into the pocket 2 by the porous plug 14 to homogenize the liquid steel 1 which it contains may also contribute if the porous plug 14 is placed directly above the ascending plunger 7. It is also possible to provide the possibility of injecting oxygen into the liquid steel 1 present in the tank 5, by means of an emerged lance 15 or parietal nozzles, if necessary to increase its dissolved oxygen content to accentuate decarburization at the start of treatment. Insufflation of oxygen can also be used at certain stages of the treatment to heat the liquid metal 1 by aluminothermy.
  • This suction capacity would be more usefully used for the evacuation of a larger quantity of gases favoring the kinetics of decarburization, such as the argon blown through the pipe 11 and the nozzles 12.
  • a larger quantity of gases favoring the kinetics of decarburization, such as the argon blown through the pipe 11 and the nozzles 12.
  • the amount of argon that can be injected into the tank 5 is limited by the intensity of the projections 13 which it can tolerate: these projections 13 must not lead to too rapid fouling of the internal walls of the tank 5 by creating a layer 16 of solidified metal.
  • the installation of the type according to the invention has in common with the previous one the presence of a pocket 2 containing the steel liquid 1 to be treated, and equipped with a porous plug 14.
  • a pocket 2 containing the steel liquid 1 to be treated and equipped with a porous plug 14.
  • the vacuum treatment bag 2 is not exposed to the open air but placed in an enclosure vertical 17 of which, in the example shown, the height appreciably exceeds that of the pocket 2.
  • Pocket 2 is not placed directly on the bottom of the enclosure 17, but on the platform 18 of an elevating device 19.
  • the enclosure 17 includes means 20 for infuse large quantities of an inerting gas such as argon.
  • the enclosure 17 there is at least one hopper 21 containing elements addition that one may wish to add to the liquid steel 1 during its treatment, or mineral matter which may constitute a synthetic slag intended to cover the surface liquid steel 1 present in the pocket 2.
  • a retractable chute 22 makes it possible to produce these inputs of material into the pocket 2, at least when the latter is in the low position.
  • the upper edge of the enclosure 17 is constituted by a wide horizontal rim 23, comprising on its upper face a seal 24.
  • the installation according to the invention also comprises a tank 25, inside which is carried out the vacuum treatment of the liquid steel 1.
  • this tank 25 is similar to the tank 5 of the conventional RH of Figure 1. It comprises two plungers 26, 27 connected to the bottom 28 of the tank 25: an ascending plunger 26, comprising a pipe 29 for bringing argon into its interior space, and a descending plunger 27 by which the liquid steel returns to the pocket 2 after having passed through the interior of the tank 25.
  • a suction installation 30 makes it possible to maintain a tank pressure P of the order of approximately 1 torr inside the tank 25.
  • the tank passed through the interior space of the tank 25.
  • a suction installation 30 makes it possible to maintain a pressure P tank of the order of approximately 1 torr inside the tank 25.
  • the tank 25 is fitted, on its side wall, with parietal nozzles 31 for insufflati one argon, or even also a lance 32 for insufflation of oxygen.
  • parietal nozzles 31 and this lance 32 it is advantageous to have nozzles 33 for blowing argon and / or oxygen into the bottom 28 of the tank 25; thus, at a given instant, most of the liquid metal 1 present in the tank 25 can be directly subjected to the action of these gases, and not only the liquid metal 1 which would be located directly above the ascending plunger 26 or near the side wall of the tank 25.
  • the tank 25 is brought above the enclosure 17, and it is allowed to rest with its full weight on the rim 23, so as to obtain excellent sealing all around the rim 23, thanks to the seal 24.
  • the length plungers 26, 27 is chosen so that at this stage of processing where the elevator 19 on which the pocket 2 rests is in the low position, their lower ends do not not dip or weakly (as shown in Figure 2a) in the liquid steel 1 contained in the pocket 2.
  • the tank 25 After the installation of the tank 25, one begins to breathe massively of argon inside the enclosure 17 thanks to the means 20 provided for in this Indeed, in order to make the atmosphere of the enclosure 17 non-polluting for the liquid metal 1.
  • the bag 2 is raised by means of the device riser 19 so as to dip the plungers 26, 27 more deeply into the steel liquid 1, and simultaneously lowering the pressure in the tank 25 to suck steel therein liquid 1 from bag 2.
  • the rise in bag 2 continues, preferably up to that the lower ends of the plungers 26, 27 are close to the bottom of the pocket 2.
  • the circulation of the liquid metal between the bag 2 and the tank 25 is started thanks to a blowing argon into the ascending plunger 26 by means of the pipe 29.
  • the supply of this pipe 29 should preferably, for convenience, remain external to the enclosure 17. For this purpose, it is possible, as shown, to cross the pipe 29 the bottom 28 of the tank 25 to open it outside the installation.
  • a quantity of argon is injected into the enclosure 17 so that it creates therein an enclosure pressure P significantly higher than atmospheric pressure, for example from 2 to 3 bar (i.e. 2.10 5 to 3.10 5 Pa) .
  • P significantly higher than atmospheric pressure
  • this overpressure guarantees that the air cannot penetrate inside the enclosure 17 during the treatment, it has the very important advantage of increasing the difference in level ⁇ h between the surfaces of the baths of liquid steel 1 present in the pocket 2 and in tank 25.
  • the tank 25 of the installation according to the invention can have a very significantly greater capacity. Indeed, the diameter of its bottom 28 must be at least sufficient for the tank 25 to rest on the rim 23 of the enclosure 17, which implies that this diameter is significantly greater than that of pocket 2 (unless laterally extends the bottom 28 by a collar, and that it is this collar which rests on the rim 23 of the enclosure 17; but then we deprive our of the particular advantages related to a large diameter of the tank 25 which will be seen later).
  • a partition in refractory 34 disposed between the orifices 35, 36 through which the liquid metal arrives in the tank 25 and leaves, bars the bottom of the interior space of the tank 25 to prevent a significant portion of the liquid metal 1 which enters the tank 25 via the ascending plunger 26 does not then pass directly into the descending diver 27 after having stayed than a brief moment in the tank 25. This reduces the dispersion of the residence times in the tank 25 of the different portions of the liquid metal 1.
  • This partition 34 can, as shown, have a relatively small height, and thus allow the liquid steel 1 of the cross by overflow when it has reached its nominal level.
  • the tank 25 can also make these additions of alloying elements in the tank 25 itself, if it is equipped with devices for this purpose, as is generally the case with RH tanks conventional 5.
  • the hoppers can also be placed outside the enclosure 17, by associating with means of transporting materials passing through the wall of the enclosure 17.
  • a such an arrangement has the advantage of reducing the necessary internal volume of the enclosure 17, therefore to decrease the quantity of gas which it is necessary to breathe in to inert it or the To put under pressure.
  • the first advantage of the installation according to the invention over HR classic is to make the leaks that can be seen without consequences usually at the plungers and their connections to the tank. If such faults exist on the installation according to the invention, they only result in the aspiration of a part of the inerting argon present in the enclosure 17, and not by the air intake. There is therefore no oxygen and nitrogen pollution of the liquid metal 1 by atmospheric air.
  • the suction installation 30 can be used to the best of its ability. capacities, since all the gases it extracts from tank 25 or result from the degassing of liquid steel 1, or contributed to accelerating this degassing. This advantage can only be increased if, in addition, the enclosure 17 is maintained under a high inerting gas pressure.
  • the installation according to the invention makes it possible to increase very substantially the average residence time of a given portion of the liquid metal 1 in the tank 25, without increasing the total duration of the treatment. Metallurgical reactions related to stay of the liquid metal in the tank 25 under reduced pressure can therefore be carried out in more detail.
  • the need to have a tank 25 of relatively large diameter, of so as to completely close the enclosure 17, has the corollary of providing the liquid steel 1 present in the tank 25 a large specific surface of exposure to reduced pressure.
  • the elevator 19 and its platform 18 allow to control the relative positions of the bag 2 and the tank 25, as previously described.
  • the absence of the elevator 19 would oblige, during placing the tank 25, immediately immersing the plungers 26, 27 in the steel liquid 1 over almost their entire height, and the volume of liquid steel 1 they move would cause pocket 2 to overflow if used to capacity nominal.
  • a tank 25 whose internal diameter is 4.4 m (which corresponds to an area of 15 m 2 ) and plungers of length 2.45 m and internal diameter 0.7 m.
  • a pressure difference P enclosure - P tank ) of 2 bar (i.e. 2.10 5 Pa) to obtain the difference in level ⁇ h of 2.95 m necessary to obtain the target bath depth of 0.5 m in the tank 25. It corresponds to an amount of metal 1 present in the tank 25 and the plungers 26, 27 of 65.5 t.
  • the metal 1 found in the tank 25, by means of the nozzles 31, 33 a total quantity of argon of approximately 20,000 Nl / min (compared to the flow rate of around 5000 Nl / min that a conventional RH could tolerate without that excessive metal splashes occur on the walls of the tank).
  • An installation according to the invention is part of a production chain simply by replacing a vacuum treatment system of the RH or DH type conventional or empty in tank, without the need to modify the organization of the steelworks and the general production scheme in force for ultra-low grade steel grades carbon.
  • it can also, like conventional HR, deal with profit other grades than ultra-low carbon steels. They will benefit from the absence of pollution of the metal by aspirated air, as well as the increase in time means of exposure to reduced pressure and gas sweep for a period of treatment given. This will notably allow either to obtain dehydrogenations, carbon denitruration and deoxidation more than with RH conventional, or, for equal metallurgical performance, to reduce the processing time liquid steel.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
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  • Metallurgy (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
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Abstract

A metallurgical reactor for the treatment under reduced pressure of a liquid metal (1) contained in a ladle (2) incorporates a tank (25) connected to a gas blowing installation (30) and two tubular plungers (26, 27) of which the upper ends emerge in some orifices (35, 36) cut in the bottom (28) of the tank (25) and the lower ends may be immersed in the liquid metal (1). One of the plungers (26), the ascending plunger, incorporates some means (29) for blowing the gas into its inner space to create a circulation of the liquid metal (1) between the ladle (2) and the tank (25) during treatment. It also incorporates an enclosure (17) fitted with a means (20) for blowing gas into its inner space to create in the enclosure (17) a pressure greater than atmospheric pressure and in which the ladle (2) is placed, the upper edge (23) of the enclosure (17) being provided with some means of support in a sealed manner the bottom (28) of the tank (25) during treatment and some means for lifting the ladle (2) in the direction of the tank (25) during treatment.

Description

L'invention concerne l'élaboration des métaux à l'état liquide, notamment de l'acier. Elle s'applique particulièrement à l'élaboration d'aciers de haute pureté, à teneurs extrêmement faibles en carbone, voire également en azote, en hydrogène et en oxygène.The invention relates to the preparation of metals in the liquid state, in particular of steel. It is particularly applicable to the production of high purity steels, with grades extremely low in carbon, or even nitrogen, hydrogen and oxygen.

L'utilisation lors de l'élaboration de l'acier liquide de réacteurs sous vide du type appelé "RH" est aujourd'hui courante. On rappelle que ces réacteurs se composent :

  • d'une cuve de grande hauteur et de forme grossièrement cylindrique, revêtue intérieurement de réfractaires, et dont la partie supérieure est connectée à une installation d'aspiration des gaz capable de maintenir dans cette cuve une pression réduite, qui peut descendre jusqu'à 1 torr ou moins lorsque le réacteur est en fonctionnement (on rappelle que 1 torr ≈ 133 Pa ou 1,33.10-3 bar);
  • de deux plongeurs tubulaires en matériau réfractaire, de section circulaire ou ovale, connectés à la cuve par leur extrémité supérieure; l'un de ces plongeurs est muni d'un dispositif permettant d'insuffler un gaz dans son espace intérieur, habituellement de l'argon.
The use during the production of liquid steel of vacuum reactors of the type called "RH" is common today. Remember that these reactors are made up of:
  • a very tall and roughly cylindrical tank, lined with refractories, the upper part of which is connected to a gas extraction system capable of maintaining a reduced pressure in this tank, which can drop to 1 torr or less when the reactor is in operation (remember that 1 torr ≈ 133 Pa or 1.33.10 -3 bar);
  • two tubular plungers of refractory material, of circular or oval section, connected to the tank by their upper end; one of these plungers is fitted with a device allowing a gas to be blown into its interior space, usually argon.

Ces installations sont utilisées comme suit. La poche contenant le métal liquide à traiter est amenée sous le RH, et les extrémités inférieures des plongeurs y sont immergées. Après quoi, la cuve est mise sous vide, ce qui provoque l'aspiration dans la cuve d'une certaine quantité de métal qui, pour cela, remonte par l'intérieur des plongeurs. La dénivellation entre les surfaces du métal liquide dans la poche et dans la cuve est égale à la hauteur ferrostatique correspondant à la différence de pression entre le milieu extérieur et l'intérieur de la cuve. Enfin, l'insufflation de gaz dans le plongeur équipé à cet effet débute. La fonction de cette insufflation est d'entraíner en direction de la cuve le métal qui se trouve dans ce plongeur, appelé pour cette raison "plongeur ascendant". Le métal transitant par la cuve redescend ensuite dans la poche en passant par l'autre plongeur, dit "plongeur descendant". On obtient ainsi une circulation continue de métal entre la poche et la cuve. Pendant toute la durée du traitement (soit généralement une dizaine à une trentaine de minutes), une même portion de métal effectue donc plusieurs séjours à l'intérieur de la cuve. Leur durée moyenne est fonction du débit de circulation du métal dans les plongeurs et du rapport entre les capacités respectives de la cuve et de la poche (ce dernier est généralement de l'ordre de 1/10 à 1/20). Le passage du métal liquide dans la cuve maintenue sous vide permet principalement de diminuer ses teneurs en hydrogène dissous et, dans une moindre mesure, en azote dissous. Les autres opérations métallurgiques susceptibles de se produire dans la cuve sont :

  • une décarburation partielle, par combinaison sous forme de CO du carbone avec de l'oxygène déjà dissous dans le métal ou y étant insufflé à cet effet par une lance ou des tuyères insérées dans la paroi de la cuve ;
  • une addition d'éléments d'alliages qui est ainsi effectuée à l'abri de l'air et du laitier de poche, donc avec un rendement optimal ;
  • un réchauffage du métal par aluminothermie : on lui ajoute de l'aluminium, puis on y insuffle de l'oxygène, et l'oxydation de l'aluminium qui en résulte provoque ce réchauffage.
These facilities are used as follows. The pocket containing the liquid metal to be treated is brought under the RH, and the lower ends of the plungers are immersed there. After which, the tank is evacuated, which causes the suction into the tank of a certain amount of metal which, for this, rises from inside the plungers. The difference in level between the surfaces of the liquid metal in the pocket and in the tank is equal to the ferrostatic height corresponding to the pressure difference between the outside environment and the inside of the tank. Finally, the gas blowing into the diver equipped for this purpose begins. The function of this insufflation is to drive towards the tank the metal that is in this plunger, called for this reason "ascending plunger". The metal passing through the tank then descends into the pocket via the other plunger, called "descending plunger". A continuous circulation of metal is thus obtained between the pocket and the tank. Throughout the duration of the treatment (generally around ten to thirty minutes), the same portion of metal therefore makes several stays inside the tank. Their average duration is a function of the rate of circulation of the metal in the plungers and of the ratio between the respective capacities of the tank and the pocket (the latter is generally of the order of 1/10 to 1/20). The passage of the liquid metal in the tank maintained under vacuum makes it possible mainly to decrease its contents in dissolved hydrogen and, to a lesser extent, in dissolved nitrogen. The other metallurgical operations likely to occur in the tank are:
  • partial decarburization, by combining CO in the form of carbon with oxygen already dissolved in the metal or being blown into it for this purpose by a lance or nozzles inserted into the wall of the tank;
  • an addition of alloying elements which is thus carried out in the absence of air and pocket slag, therefore with optimum yield;
  • reheating of the metal by aluminothermy: aluminum is added thereto, then oxygen is blown into it, and the oxidation of the aluminum which results therefrom causes this reheating.

Parallèlement, la circulation du métal entre la poche et la cuve provoque une agitation douce du métal en poche, favorable à une bonne décantation des inclusions non-métalliques.At the same time, the circulation of metal between the pocket and the tank causes a gentle agitation of the metal in the pocket, favorable for good settling of non-metallic inclusions.

On utilise également, quoique moins couramment aujourd'hui, des réacteurs du type appelé "DH". Ils se distinguent des RH en ce que leur cuve n'est connectée qu'à un seul plongeur, par lequel une partie du métal liquide contenu dans la poche est aspirée dans la cuve pour y être soumise à la pression réduite. Le renouvellement du métal présent dans la cuve est assuré de manière discontinue, soit par des interruptions temporaires de la mise sous pression réduite de la cuve, ce qui a pour effet de renvoyer dans la poche le métal liquide que renferme la cuve, soit par un éloignement de la poche par rapport à la cuve à pression dans la cuve constante; qui entraíne également un tel renvoi de métal dans la poche puisque la dénivellation entre les surfaces du métal dans la poche et dans la cuve doit rester constante. Dans ces réacteurs DH, une insufflation de gaz n'est pas nécessaire ; elle est néanmoins très conseillée si on veut promouvoir de la manière la plus efficace les réactions métallurgiques de dégazage et, éventuellement, de décarburatiori recherchées.Although less commonly used today, reactors from the type called "DH". They differ from HR in that their tank is only connected to one single plunger, by which part of the liquid metal contained in the pocket is sucked into the tank to be subjected to reduced pressure. The renewal of the metal present in the tank is provided discontinuously, either by temporary interruptions of the setting under reduced tank pressure, which returns the metal to the pocket liquid contained in the tank, either by a distance of the pocket from the tank to constant pressure in the tank; which also causes such a metal return in the pocket since the difference in level between the metal surfaces in the pocket and in the tank must remain constant. In these DH reactors, gas insufflation is not necessary; it is nevertheless highly recommended if we want to promote the most effective metallurgical degassing and, possibly, decarburatiori reactions sought.

Les dernières années ont vu s'accroítre la demande des industries consommatrices d'acier en produits sidérurgiques à teneur extrêmement basse en carbone (moins de 50 ppm), en particulier pour les tôles laminées à froid à hautes ductilité et résistance à la traction, pour les aciers pour emboutissage profond et pour emballages, pour les aciers inoxydables ferritiques au chrome-molybdène, etc. Le RH est vite apparu comme le réacteur de métallurgie en poche le mieux adapté à l'obtention de tels aciers dans des conditions industrielles. En effet, la cinétique de décarburation y est favorablement influencée par l'insufflation massive de gaz qui est effectuée dans le plongeur ascendant, voire également à l'intérieur de la cuve. Ainsi, pour une poche contenant 300 t d'acier liquide, une cuve de RH en contenant 15 t, et un débit de circulation de 240 t/mn, un temps de traitement de 10 minutes peut suffire à abaisser la teneur en carbone dans l'acier de 300 ppm à 20 ppm. Les installations dans lesquelles la poche d'acier est simplement placée dans une enceinte sous pression réduite (installations dites de "vide en cuve"), ou coiffée d'un couvercle en dessous duquel on maintient une pression réduite, ne sont pas aussi bien adaptées à cet effet. On ne peut y insuffler de très grosses quantités de gaz pour accélérer la cinétique de décarburation, et l'exposition au vide des réfractaires de la poche, qui contiennent souvent des matières carbonées, accentue les recarburations du métal à partir de ces réfractaires. The last few years have seen an increase in demand from consumer industries steel into extremely low carbon steel products (less than 50 ppm), in particular for cold rolled sheets with high ductility and resistance to tensile, for steels for deep drawing and for packaging, for steels ferritic chromium-molybdenum stainless steels, etc. HR quickly emerged as the ladle metallurgy reactor best suited to obtaining such steels in industrial conditions. Indeed, the kinetics of decarburization is favorable there influenced by the massive insufflation of gas which is carried out in the ascending plunger, or even inside the tank. Thus, for a pocket containing 300 tonnes of steel liquid, an RH tank containing 15 t, and a circulation rate of 240 t / min, a time treatment time of 10 minutes may be enough to lower the carbon content in the steel by 300 ppm to 20 ppm. Installations in which the steel pocket is simply placed in an enclosure under reduced pressure (so-called "tank-empty" installations), or capped a cover below which a reduced pressure is maintained, are not as good adapted for this purpose. Very large quantities of gas cannot be injected into it to accelerate the decarburization kinetics, and the vacuum exposure of the refractories in the pocket, which often contain carbonaceous materials, accentuates the recarburations of the metal from of these refractories.

Les DH, si on insuffle de l'argon dans le plongeur, sont également assez bien adaptés à la production d'aciers à teneurs en carbone inférieure à 50 ppm.DH, if you blow argon into the plunger, are also pretty good suitable for the production of steels with carbon contents lower than 50 ppm.

L'accroissement de la demande en aciers d'une pureté de plus en plus poussée rendra probablement, dans un très proche avenir, nécessaire de pouvoir obtenir couramment des teneurs en carbone encore plus basses (5 à 10 ppm) avec une productivité au moins équivalente à celle des installations actuelles (environ 10 t/mn dans les grandes usines intégrées). Or, dans les RH et DH classiques, on constate un net ralentissement de la décarburation lorsque la teneur en carbone moyenne de l'acier liquide devient inférieure à 30 ppm. Une accélération sensible de cette cinétique dans le domaine des très basses teneurs en carbone permettrait d'obtenir les performances métallurgiques souhaitées dans un temps toujours compatible avec une marche optimale des autres ateliers de l'aciérie. Mais elle ne serait concevable qu'en augmentant considérablement la vitesse de circulation du métal et les quantités de gaz insufflées dans les diverses zones du réacteur. Il en résulterait un encrassement très rapide de l'intérieur de la cuve sous vide par les projections de métal et une usure exagérément accélérée des réfractaires des plongeurs, donc des arrêts plus fréquents et un fonctionnement moins fiable de l'installation. De plus, un accroissement substantiel de la quantité de gaz insufflée obligerait à augmenter la capacité de l'installation d'aspiration des gaz, qui est déjà considérable, sous peine de ne pouvoir atteindre des pressions suffisamment basses. En définitive, l'obtention en marche industrielle de teneurs en carbone sensiblement inférieures à 10 ppm dans des conditions techniques et économiques satisfaisantes paraít difficilement à la portée d'un RH ou d'un DH de conception traditionnelle.Increasing demand for increasingly high-purity steels will likely make it necessary in the very near future to be able to obtain commonly even lower carbon levels (5-10 ppm) with productivity at least equivalent to that of current installations (around 10 rpm in large integrated factories). However, in conventional HR and DH, there is a marked slowdown in the decarburization when the average carbon content of the liquid steel falls below 30 ppm. A significant acceleration of these kinetics in the very low range carbon content would achieve the desired metallurgical performance in a time always compatible with an optimal running of the other workshops of the steelworks. But it would be conceivable only by considerably increasing the speed of circulation of the metal and the quantities of gas blown into the various zones of the reactor. It would result in very rapid fouling of the interior of the vacuum tank by projections of metal and excessively accelerated wear of divers' refractories, thus stopping more frequent and less reliable operation of the installation. In addition, a substantial increase in the quantity of gas supplied would require an increase in capacity the gas extraction system, which is already considerable, on pain of being unable to achieve sufficiently low pressures. Ultimately, getting in motion industrial carbon content significantly below 10 ppm under conditions satisfactory techniques and economics are hardly within the reach of an HR or DH of traditional design.

L'obtention d'une teneur en carbone aussi basse que possible dans l'acier liquide est d'autant plus importante que, dans la suite des opérations d'élaboration et de coulée, l'acier aura de multiples occasions de se recarburer, par exemple lors de la coulée en continu au contact des réfractaires et des poudres de couverture du répartiteur et de la lingotière.Getting carbon content as low as possible in liquid steel is all the more important since, in the course of the preparation and casting operations, the steel will have multiple opportunities to re-bend, for example during casting in continuous in contact with refractories and covering powders of the distributor and the mold.

Un autre inconvénient des réacteurs RH et DH de conception classique est que leur étanchéité par rapport à l'atmosphère ambiante n'est pas toujours satisfaisante au niveau des plongeurs (dont les réfractaires présentent une certaine porosité) et de leurs connexions au fond de la cuve. Les aspirations d'air qui en résultent peuvent être estimées à plusieurs centaines de Nm3/h sur les installations industrielles de grandes dimensions. Elles entraínent un apport non contrôlé d'oxygène et d'azote au métal liquide, ce qui rend plus difficile le pilotage de la décarburation et limite l'ampleur de la dénitruration que l'on peut réaliser. De plus, une part non négligeable de la capacité de l'installation d'aspiration est consacrée à l'évacuation de ces gaz indésirables, alors qu'elle serait plus utilement employée à l'évacuation de gaz résultant du dégazage et de la décarburation de l'acier liquide, ou qui ont favorisé ce dégazage et cette décarburation. Another disadvantage of the RH and DH reactors of conventional design is that their tightness compared to the ambient atmosphere is not always satisfactory at the level of the plungers (whose refractories have a certain porosity) and their connections at the bottom of the tank. . The resulting air aspirations can be estimated at several hundred Nm 3 / h on large industrial installations. They cause an uncontrolled supply of oxygen and nitrogen to the liquid metal, which makes it more difficult to control decarburization and limits the extent of denitriding that can be carried out. In addition, a non-negligible part of the capacity of the suction installation is devoted to the evacuation of these undesirable gases, whereas it would be more usefully employed for the evacuation of gases resulting from the degassing and decarburization of liquid steel, or which favored this degassing and this decarburization.

Il a déjà été proposé (document JP-A-58181818) de réaliser une connexion étanche entre le rebord supérieur de la poche et un flasque solidaire de la cuve du RH. Une insufflation de gaz mettant sous pression la surface de l'acier liquide en poche permet d'augmenter le débit de recirculation du métal entre la poche et la cuve, ce qui améliore l'efficacité du dégazage. Les aspirations d'air au niveau des plongeurs sont aussi évitées. Toutefois ces modifications ne seraient pas suffisantes pour assurer une décarburation aussi poussée et rapide qu'on pourrait le souhaiter.It has already been proposed (document JP-A-58181818) to make a connection watertight between the upper rim of the pocket and a flange secured to the RH tank. A blowing gas pressurizing the surface of the liquid steel in the pocket allows increase the rate of metal recirculation between the pocket and the tank, which improves the efficiency of degassing. Air intake at the plungers is also avoided. However, these modifications would not be sufficient to ensure decarburization as well. push and fast as one might wish.

Le but de l'invention est de proposer un nouveau type de réacteur métallurgique, qui, notamment, donne accès aux teneurs en carbone dans l'acier liquide de l'ordre de 10 ppm et moins dans des conditions de productivité satisfaisantes. Ce réacteur devrait aussi pouvoir être utilisé pour produire des aciers à faibles ou très faibles teneurs en azote ainsi qu'en oxygène, tout comme les RH et DH de conception classique.The aim of the invention is to propose a new type of metallurgical reactor, which, in particular, gives access to the carbon contents in liquid steel of the order of 10 ppm and less under satisfactory productivity conditions. This reactor should also be capable of being used to produce steels with low or very low nitrogen contents as well in oxygen, just like the HR and DH of classic design.

A cet effet, l'invention a pour objet un réacteur métallurgique de traitement sous pression réduite d'un métal liquide, tel que de l'acier, contenu dans une poche, du type comportant une cuve connectée à une installation d'aspiration des gaz pouvant y maintenir une pression réduite et deux plongeurs tubulaires dont les extrémités supérieures débouchent dans des orifices ménagés dans le fond de la cuve et dont les extrémités inférieures peuvent être immergées dans ledit métal liquide contenu dans ladite poche, l'un desdits plongeurs, dit "plongeur ascendant", comportant des moyens pour insuffler un gaz dans son espace intérieur dans le but de créer un mouvement de circulation du métal liquide entre la poche et la cuve pendant ledit traitement, caractérisé en ce qu'il comporte également une enceinte munie de moyens d'insufflation d'un gaz dans son espace intérieur adaptés à la création dans l'enceinte d'une pression supérieure à la pression atmosphérique, et dans laquelle est placée la poche, le bord supérieur de ladite enceinte étant prévu pour supporter de manière étanche le fond de la cuve pendant ledit traitement, et des moyens pour soulever la poche en direction de la cuve pendant ledit traitement..To this end, the subject of the invention is a metallurgical reactor for treatment under reduced pressure of a liquid metal, such as steel, contained in a pocket, of the type comprising a tank connected to a gas suction installation capable of keeping it there reduced pressure and two tubular plungers with upper ends open into openings in the bottom of the tank, the ends of which lower can be immersed in said liquid metal contained in said pocket, one of said plungers, called "ascending plunger", comprising means for blowing a gas in its interior space in order to create a movement of movement of the metal liquid between the bag and the tank during said treatment, characterized in that it comprises also an enclosure provided with means for blowing a gas into its interior space adapted to the creation in the enclosure of a pressure greater than atmospheric pressure, and in which the pocket is placed, the upper edge of said enclosure being provided for sealingly support the bottom of the tank during said treatment, and means to lift the pocket towards the tank during said treatment.

L'invention a également pour objet un réacteur métallurgique de traitement sous pression réduite d'un métal liquide, tel que de l'acier, contenu dans une poche, du type comportant une cuve connectée à une installation d'aspiration des gaz pouvant y maintenir une pression réduite et un plongeur tubulaire dont l'extrémité supérieure débouche dans un orifice ménagé dans le fond de la cuve et dont l'extrémité inférieure peut être immergée dans ledit métal liquide contenu dans ladite poche, caractérisé en ce qu'il comporte également une enceinte munie de moyens d'insufflation d'un gaz dans son espace intérieur adaptés à la création dans l'enceinte d'une pression supérieure à la pression atmosphérique, et dans laquelle est placée la poche, le bord supérieur de ladite enceinte étant prévu pour supporter de manière étanche le fond de la cuve pendant ledit traitement, et des moyens pour soulever la poche en direction de la cuve pendant ledit traitement.The invention also relates to a metallurgical reactor for treatment under reduced pressure of a liquid metal, such as steel, contained in a pocket, of the type comprising a tank connected to a gas suction installation capable of keeping it there reduced pressure and a tubular plunger whose upper end opens into a opening in the bottom of the tank, the lower end of which can be submerged in said liquid metal contained in said pocket, characterized in that it comprises also an enclosure provided with means for blowing a gas into its interior space adapted to the creation in the enclosure of a pressure greater than atmospheric pressure, and in which the pocket is placed, the upper edge of said enclosure being provided for sealingly support the bottom of the tank during said treatment, and means to lift the pocket towards the tank during said treatment.

Comme on l'aura compris, le réacteur métallurgique selon l'invention se distingue des réacteurs traditionnels à cuve sous vide de type RH ou DH essentiellement en ce que la poche, au lieu d'être simplement à l'air libre, est placée dans une enceinte sur le bord supérieur de laquelle on fait reposer, de manière étanche, le fond de la cuve sous vide. L'enceinte est inertée par un gaz neutre qui la met sous une pression sensiblement supérieure à la pression atmosphérique, de manière à provoquer la montée dans la cuve sous vide d'une quantité maximale de métal liquide.As will be understood, the metallurgical reactor according to the invention is distinguished traditional vacuum reactor type RH or DH essentially in that the pocket, instead of just being in the open air, is placed in an enclosure on the edge upper part of which the bottom of the vacuum tank is made to seal. The enclosure is inerted by a neutral gas which puts it under a pressure substantially higher than atmospheric pressure, so as to cause the rise in the tank vacuum of a maximum quantity of liquid metal.

L'invention sera mieux comprise à la lecture de la description qui suit, donnée en référence aux figures annexées suivantes :

  • la figure 1 qui représente vue en coupe longitudinale, à titre de référence, une installation de traitement sous vide de l'acier liquide du type RH, représentative de l'art antérieur de l'invention;
  • la figure 2 qui représente une installation de traitement sous vide de l'acier liquide selon l'invention; la figure 2a la montre vue de face en coupe longitudinale selon IIa-IIa au stade initial du traitement; la figure 2b la montre de la même façon à un stade ultérieur du traitement; la figure 2c la montre en vue de dessus partielle en section selon IIc-IIc.
The invention will be better understood on reading the description which follows, given with reference to the following appended figures:
  • Figure 1 which shows a longitudinal sectional view, for reference, an installation for vacuum treatment of RH type liquid steel, representative of the prior art of the invention;
  • FIG. 2 which represents an installation for vacuum treatment of the liquid steel according to the invention; Figure 2a shows the front view in longitudinal section along IIa-IIa at the initial stage of treatment; FIG. 2b shows it in the same way at a later stage of the treatment; FIG. 2c shows it in partial top view in section along IIc-IIc.

Dans l'installation de traitement sous vide de type RH classique de la figure 1, l'acier liquide 1 est contenu dans une poche 2 revêtue intérieurement d'une couche de réfractaires 3 et exposée à la pression atmosphérique Patm. Une couche de laitier 4 sumage à la surface de l'acier liquide 1 et l'isole de l'atmosphère ambiante. Le RH lui-même se compose d'une cuve 5 revêtue intérieurement de réfractaires 6 et de deux plongeurs tubulaires 7, 8 en matériau réfractaire, de forme généralement cylindrique, connectés au fond 9 de la cuve 5. La cuve 5 est, à sa partie supérieure, connectée à une installation d'aspiration des gaz 10, telle qu'une batterie d'éjecteurs à vapeur. Au début du traitement, la cuve 5 est placée au dessus de la poche 1, et par un mouvement relatif de la cuve 5 et de la poche 2, on amène les extrémités inférieures des plongeurs 7, 8 à tremper dans l'acier liquide 1. Puis, à l'aide de l'installation d'aspiration 10, on instaure une pression réduite Pcuve à l'intérieur de la cuve 5, ce qui a pour effet d'y aspirer du métal liquide 1 à travers les plongeurs 7, 8. On pratique ensuite une insufflation d'un gaz à l'intérieur de l'un des plongeurs 7, au moyen d'une conduite 11 débouchant dans l'espace intérieur dudit plongeur 7. Ce gaz est, de préférence, un gaz neutre tel que de l'argon, insoluble dans l'acier liquide. Son débit est en général de l'ordre de 4 à 12 litres par minute et par tonne d'acier à traiter. Il crée un mouvement ascendant de circulation à l'intérieur du plongeur 7 (appelé pour cette raison "plongeur ascendant"). Ce mouvement a pour effet de faire redescendre depuis la cuve 5 dans la poche 2, à travers l'autre plongeur 8 (appelé "plongeur descendant"), une quantité de métal liquide 1 équivalente à celle qui pénètre dans la cuve 5 par le plongeur ascendant 7. On obtient ainsi une circulation continue de l'acier liquide 1 entre la poche 2 à la pression atmosphérique Patm et la cuve 5 sous pression réduite Pcuve, dans laquelle l'acier liquide subit les réactions métallurgiques désirées, notamment celles qui sont spécifiques aux traitements sous vide. Ces réactions sont essentiellement :

  • une déshydrogénation, relativement facile car sa cinétique est favorable ;
  • une dénitruration, dont l'ampleur est généralement limitée, du fait d'une cinétique peu favorable et étroitement dépendante de la composition du métal : la dénitruration est d'autant plus lente que les teneurs de l'acier en oxygène dissous et en soufre sont plus élevées ; le balayage de l'acier liquide par l'argon qui le traverse, et éventuellement par l'hydrogène qui s'en dégage, favorise, au contraire, la dénitruration ;
  • une décarburation, qui n'a lieu que si la teneur du bain en éléments désoxydants forts (aluminium, silicium, manganèse) et la pression partielle de CO dans la cuve 5 sont suffisamment faibles pour que l'oxygène dissous contenu dans l'acier liquide 1 présent dans la cuve 5 puisse se combiner au carbone, selon des lois thermodynamiques connues ; la cinétique de cette décarburation, lorsqu'elle est possible, est également favorisée par le balayage dû à l'argon et le dégagement de l'hydrogène.
In the conventional RH type vacuum treatment installation of FIG. 1, the liquid steel 1 is contained in a pocket 2 internally coated with a layer of refractories 3 and exposed to atmospheric pressure P atm . A layer of slag 4 sumage on the surface of the liquid steel 1 and isolates it from the ambient atmosphere. The RH itself consists of a tank 5 internally coated with refractories 6 and two tubular plungers 7, 8 made of refractory material, of generally cylindrical shape, connected to the bottom 9 of the tank 5. The tank 5 is, at its upper part, connected to a gas suction installation 10, such as a battery of steam ejectors. At the start of the treatment, the tank 5 is placed above the pocket 1, and by a relative movement of the tank 5 and the pocket 2, the lower ends of the plungers 7, 8 are brought to dip in the liquid steel 1 . Then, using the extraction system 10, it establishes a reduced pressure P vessel inside the tank 5, which has the effect of sucking liquid metal y 1 through the plungers 7 , 8. A gas is then blown inside one of the plungers 7, by means of a pipe 11 opening into the interior space of said plunger 7. This gas is preferably a gas neutral such as argon, insoluble in liquid steel. Its flow rate is generally around 4 to 12 liters per minute per tonne of steel to be treated. It creates an upward movement of circulation inside the plunger 7 (therefore called "upward plunger"). The effect of this movement is to bring down from the tank 5 in the pocket 2, through the other plunger 8 (called "descending plunger"), an amount of liquid metal 1 equivalent to that which enters the tank 5 by the plunger ascending 7. A continuous circulation of the liquid steel 1 is thus obtained between the pocket 2 at atmospheric pressure P atm and the tank 5 under reduced pressure P tank , in which the liquid steel undergoes the desired metallurgical reactions, in particular those which are specific to vacuum treatments. These reactions are essentially:
  • dehydrogenation, relatively easy because its kinetics are favorable;
  • denitriding, the extent of which is generally limited, due to an unfavorable kinetics and closely dependent on the composition of the metal: the denitriding is all the slower the higher the dissolved oxygen and sulfur contents of the steel higher; the sweeping of the liquid steel by the argon which passes through it, and possibly by the hydrogen which is released therefrom, promotes, on the contrary, denitriding;
  • decarburization, which takes place only if the content of strong deoxidizing elements in the bath (aluminum, silicon, manganese) and the partial pressure of CO in the tank 5 are sufficiently low that the dissolved oxygen contained in the liquid steel 1 present in the tank 5 can be combined with carbon, according to known thermodynamic laws; the kinetics of this decarburization, when possible, is also favored by the sweeping due to argon and the release of hydrogen.

La dénivellation Δh entre les surfaces des bains d'acier liquide 1 dans la poche 2 et dans la cuve 5 est fonction de la différence (Patm - Pcuve) selon l'équation : Δh = (Patm - Pcuve)ρ . g où ρ est la masse volumique de l'acier liquide (environ 6900 kg/m3 pour une température de 1600°C) et g l'accélération de la pesanteur (9,81 m/s2). Si, comme c'est généralement le cas, on maintient dans la cuve 5 une pression d'environ 1 torr (soit 133 Pa ou 1,33.10-3 bar), la dénivellation Δh est de l'ordre de 1,5 m.The difference in height Δh between the surfaces of the liquid steel baths 1 in the pocket 2 and in the tank 5 is a function of the difference (P atm - P tank ) according to the equation: Δh = (P ATM - P tank ) ρ. g where ρ is the density of the liquid steel (around 6900 kg / m 3 for a temperature of 1600 ° C) and g the acceleration of gravity (9.81 m / s 2 ). If, as is generally the case, there is maintained in the tank 5 a pressure of approximately 1 torr (ie 133 Pa or 1.33.10 -3 bar), the difference in height Δh is of the order of 1.5 m.

De préférence, la cuve 5 est équipée de moyens d'insufflation d'argon dans l'acier liquide 1 qu'elle renferme, tels que des tuyères pariétales 12 (on n'en a représenté qu'une, mais il peut y en avoir plusieurs) ou des lances immergées. Cet argon insufflé, dont le débit est généralement du même ordre de grandeur que le débit insufflé dans le plongeur ascendant 7 ou même un peu supérieur, accélère le dégazage et aussi la réaction de décarburation. Cela est dû à un effet de balayage des gaz présents ou formés dans le bain liquide 1, et également à la création de projections d'acier liquide 13 sous forme de fines gouttelettes. Ces gouttelettes 13 offrent une grande surface spécifique d'exposition à l'atmosphère raréfiée de la cuve 5, ce qui va aussi dans le sens d'une accélération de la décarburation. L'argon insufflé dans le plongeur ascendant 7 a un semblable effet de création de projections 13 dans la cuve 5. L'argon insufflé dans la poche 2 par le bouchon poreux 14 pour homogénéiser l'acier liquide 1 qu'elle renferme peut également y contribuer si le bouchon poreux 14 est placé à l'aplomb du plongeur ascendant 7. On peut également prévoir la possibilité d'insuffler de l'oxygène dans l'acier liquide 1 présent dans la cuve 5, au moyen d'un lance émergée 15 ou de tuyères pariétales, afin si nécessaire d'augmenter sa teneur en oxygène dissous pour accentuer la décarburation au début du traitement. Une insufflation d'oxygène peut également être utilisée à certaines étapes du traitement pour réchauffer le métal liquide 1 par aluminothermie. les porosités des réfractaires constituant les plongeurs 7, 8, et aussi à travers les joints séparant le fond 9 de la cuve 5 et les extrémités supérieures des plongeurs 7, 8 si leur étanchéité n'est pas parfaite. D'une part, cette aspiration d'air entraíne une pollution du métal liquide 1 par de l'azote et de l'oxygène, ce qui diminue les performances de l'installation pour la dénitruration et la propreté inclusionnaire, surtout si le métal est déjà désoxydé. D'autre part, les gaz aspirés doivent ensuite être évacués par l'installation d'aspiration 10. Celle-ci doit donc consacrer une part non négligeable de sa capacité d'aspiration à l'évacuation de ces gaz indésirés. Cette capacité d'aspiration serait plus utilement employée à l'évacuation d'une plus grande quantité de gaz favorisant la cinétique de décarburation, comme l'argon insufflé par la conduite 11 et les tuyères 12. De même, en l'absence de ces entrées d'air, on pourrait choisir de conserver la même quantité d'argon insufflée, mais d'obtenir une pression Pcuve plus faible, également favorable à un dégazage et une décarburation poussés. Enfin, la quantité d'argon que l'on peut insuffler dans la cuve 5 est limitée par l'intensité des projections 13 qu'elle peut tolérer : il ne faut pas que ces projections 13 conduisent à un encrassement trop rapide des parois internes de la cuve 5 par création d'une couche 16 de métal solidifié.Preferably, the tank 5 is equipped with means for blowing argon into the liquid steel 1 which it contains, such as parietal nozzles 12 (only one has been shown, but there may be several) or submerged spears. This blown argon, the flow of which is generally of the same order of magnitude as the flow blown into the ascending plunger 7 or even a little higher, accelerates the degassing and also the decarburization reaction. This is due to a sweeping effect of the gases present or formed in the liquid bath 1, and also to the creation of projections of liquid steel 13 in the form of fine droplets. These droplets 13 offer a large specific surface of exposure to the rarefied atmosphere of the tank 5, which also goes in the direction of an acceleration of decarburization. The argon blown into the ascending plunger 7 has a similar effect of creating projections 13 in the tank 5. The argon blown into the pocket 2 by the porous plug 14 to homogenize the liquid steel 1 which it contains may also contribute if the porous plug 14 is placed directly above the ascending plunger 7. It is also possible to provide the possibility of injecting oxygen into the liquid steel 1 present in the tank 5, by means of an emerged lance 15 or parietal nozzles, if necessary to increase its dissolved oxygen content to accentuate decarburization at the start of treatment. Insufflation of oxygen can also be used at certain stages of the treatment to heat the liquid metal 1 by aluminothermy. the porosities of the refractories constituting the plungers 7, 8, and also through the joints separating the bottom 9 of the tank 5 and the upper ends of the plungers 7, 8 if their tightness is not perfect. On the one hand, this air intake leads to pollution of the liquid metal 1 with nitrogen and oxygen, which decreases the performance of the installation for denitriding and inclusion cleanliness, especially if the metal is already deoxidized. On the other hand, the aspirated gases must then be evacuated by the suction installation 10. The latter must therefore devote a non-negligible part of its suction capacity to the evacuation of these unwanted gases. This suction capacity would be more usefully used for the evacuation of a larger quantity of gases favoring the kinetics of decarburization, such as the argon blown through the pipe 11 and the nozzles 12. Similarly, in the absence of these air inlets, one could choose to keep the same amount of argon blown in, but to obtain a lower tank pressure P, also favorable for high degassing and decarburization. Finally, the amount of argon that can be injected into the tank 5 is limited by the intensity of the projections 13 which it can tolerate: these projections 13 must not lead to too rapid fouling of the internal walls of the tank 5 by creating a layer 16 of solidified metal.

L'installation du type selon l'invention, dont un exemple est représenté sur la figure 2, a en commun avec la précédente la présence d'une poche 2 renfermant l'acier liquide 1 à traiter, et équipée d'un bouchon poreux 14. Selon l'invention, pendant le traitement sous vide la poche 2 n'est pas exposée à l'air libre mais mise dans une enceinte verticale 17 dont, dans l'exemple représenté, la hauteur excède sensiblement celle de la poche 2. La poche 2 n'est pas posée directement sur le fond de l'enceinte 17, mais sur la plate-forme 18 d'un dispositif élévateur 19. L'enceinte 17 comporte des moyens 20 pour y insuffler de grandes quantités d'un gaz d'inertage tel que de l'argon. Préférentiellement, à l'intérieur de l'enceinte 17 se trouve au moins une trémie 21 renfermant des éléments d'addition que l'on peut souhaiter ajouter à l'acier liquide 1 lors de son traitement, ou des matières minérales pouvant constituer un laitier synthétique destiné à recouvrir la surface de l'acier liquide 1 présent dans la poche 2. Une goulotte escamotable 22 permet de réaliser ces apports de matières dans la poche 2, au moins quand celle-ci est en position basse. Le bord supérieur de l'enceinte 17 est constitué par un large rebord horizontal 23, comportant sur sa face supérieure un joint d'étanchéité 24.The installation of the type according to the invention, an example of which is shown in the Figure 2, has in common with the previous one the presence of a pocket 2 containing the steel liquid 1 to be treated, and equipped with a porous plug 14. According to the invention, during the vacuum treatment bag 2 is not exposed to the open air but placed in an enclosure vertical 17 of which, in the example shown, the height appreciably exceeds that of the pocket 2. Pocket 2 is not placed directly on the bottom of the enclosure 17, but on the platform 18 of an elevating device 19. The enclosure 17 includes means 20 for infuse large quantities of an inerting gas such as argon. Preferably, to inside the enclosure 17 there is at least one hopper 21 containing elements addition that one may wish to add to the liquid steel 1 during its treatment, or mineral matter which may constitute a synthetic slag intended to cover the surface liquid steel 1 present in the pocket 2. A retractable chute 22 makes it possible to produce these inputs of material into the pocket 2, at least when the latter is in the low position. The upper edge of the enclosure 17 is constituted by a wide horizontal rim 23, comprising on its upper face a seal 24.

L'installation selon l'invention comporte également une cuve 25, à l'intérieur de laquelle est effectué le traitement sous vide de l'acier liquide 1. Dans son principe général, cette cuve 25 est semblable à la cuve 5 du RH classique de la figure 1. Elle comporte deux plongeurs 26, 27 connectés au fond 28 de la cuve 25 : un plongeur ascendant 26, comportant une conduite 29 permettant d'amener de l'argon dans son espace intérieur, et un plongeur descendant 27 par lequel l'acier liquide retourne dans la poche 2 après avoir transité par l'espace intérieur de la cuve 25. Une installation d'aspiration 30 permet de maintenir une pression Pcuve de l'ordre d'environ 1 torr à l'intérieur de la cuve 25. La cuve transité par l'espace intérieur de la cuve 25. Une installation d'aspiration 30 permet de maintenir une pression Pcuve de l'ordre d'environ 1 torr à l'intérieur de la cuve 25. La cuve 25 est équipée, sur sa paroi latérale, de tuyères pariétales 31 pour l'insufflation d'argon, voire également d'une lance 32 pour l'insufflation d'oxygène. A la place ou en plus de ces tuyères pariétales 31 et de cette lance 32, on peut avantageusement disposer des tuyères 33 d'insufflation d'argon et/ou d'oxygène dans le fond 28 de la cuve 25 ; ainsi, à un instant donné, la plus grande partie du métal liquide 1 présent dans la cuve 25 peut être directement soumise à l'action de ces gaz, et pas seulement le métal liquide 1 qui serait situé à l'aplomb du plongeur ascendant 26 ou à proximité de la paroi latérale de la cuve 25.The installation according to the invention also comprises a tank 25, inside which is carried out the vacuum treatment of the liquid steel 1. In its general principle, this tank 25 is similar to the tank 5 of the conventional RH of Figure 1. It comprises two plungers 26, 27 connected to the bottom 28 of the tank 25: an ascending plunger 26, comprising a pipe 29 for bringing argon into its interior space, and a descending plunger 27 by which the liquid steel returns to the pocket 2 after having passed through the interior of the tank 25. A suction installation 30 makes it possible to maintain a tank pressure P of the order of approximately 1 torr inside the tank 25. The tank passed through the interior space of the tank 25. A suction installation 30 makes it possible to maintain a pressure P tank of the order of approximately 1 torr inside the tank 25. The tank 25 is fitted, on its side wall, with parietal nozzles 31 for insufflati one argon, or even also a lance 32 for insufflation of oxygen. Instead of or in addition to these parietal nozzles 31 and this lance 32, it is advantageous to have nozzles 33 for blowing argon and / or oxygen into the bottom 28 of the tank 25; thus, at a given instant, most of the liquid metal 1 present in the tank 25 can be directly subjected to the action of these gases, and not only the liquid metal 1 which would be located directly above the ascending plunger 26 or near the side wall of the tank 25.

En début de traitement (cas de la figure 2a), la cuve 25 est amenée au dessus de l'enceinte 17, et on la laisse reposer de tout son poids sur le rebord 23, de manière à obtenir une excellente étanchéité sur tout le pourtour du rebord 23, grâce au joint 24. La longueur des plongeurs 26, 27 est choisie de telle manière qu'à ce stade du traitement où l'élévateur 19 sur lequel repose la poche 2 est en position basse, leurs extrémités inférieures ne plongent pas ou faiblement (comme montré sur la figure 2a) dans l'acier liquide 1 contenu dans la poche 2. Après la mise en place de la cuve 25, on commence à insuffler massivement de l'argon à l'intérieur de l'enceinte 17 grâce aux moyens 20 prévus à cet effet, afin de rendre l'atmosphère de l'enceinte 17 non polluante pour le métal liquide 1.At the start of treatment (case of FIG. 2a), the tank 25 is brought above the enclosure 17, and it is allowed to rest with its full weight on the rim 23, so as to obtain excellent sealing all around the rim 23, thanks to the seal 24. The length plungers 26, 27 is chosen so that at this stage of processing where the elevator 19 on which the pocket 2 rests is in the low position, their lower ends do not not dip or weakly (as shown in Figure 2a) in the liquid steel 1 contained in the pocket 2. After the installation of the tank 25, one begins to breathe massively of argon inside the enclosure 17 thanks to the means 20 provided for in this Indeed, in order to make the atmosphere of the enclosure 17 non-polluting for the liquid metal 1.

Une fois cette condition réalisée, on soulève la poche 2 au moyen du dispositif élévateur 19 de manière à faire tremper plus profondément les plongeurs 26, 27 dans l'acier liquide 1, et simultanément on abaisse la pression dans la cuve 25 pour y aspirer de l'acier liquide 1 à partir de la poche 2. L'élévation de la poche 2 se poursuit, de préférence jusqu'à ce que les extrémités inférieures des plongeurs 26, 27 soient proches du fond de la poche 2. Enfin on démarre la circulation du métal liquide entre la poche 2 et la cuve 25 grâce à une insufflation d'argon dans le plongeur ascendant 26 au moyen de la conduite 29. L'alimentation de cette conduite 29 doit de préférence, pour plus de commodité, demeurer externe à l'enceinte 17. A cet effet, on peut, comme représenté, faire traverser à la conduite 29 le fond 28 de la cuve 25 pour la faire déboucher à l'extérieur de l'installation.Once this condition is fulfilled, the bag 2 is raised by means of the device riser 19 so as to dip the plungers 26, 27 more deeply into the steel liquid 1, and simultaneously lowering the pressure in the tank 25 to suck steel therein liquid 1 from bag 2. The rise in bag 2 continues, preferably up to that the lower ends of the plungers 26, 27 are close to the bottom of the pocket 2. Finally, the circulation of the liquid metal between the bag 2 and the tank 25 is started thanks to a blowing argon into the ascending plunger 26 by means of the pipe 29. The supply of this pipe 29 should preferably, for convenience, remain external to the enclosure 17. For this purpose, it is possible, as shown, to cross the pipe 29 the bottom 28 of the tank 25 to open it outside the installation.

D'autre part, on insuffle dans l'enceinte 17 une quantité d'argon telle qu'elle y crée une pression Penceinte significativement supérieure à la pression atmosphérique, par exemple de 2 à 3 bar (soit 2.105 à 3.105 Pa). Outre que cette surpression garantit que l'air ne peut pénétrer à l'intérieur de l'enceinte 17 pendant le traitement, elle présente le très important avantage d'augmenter la dénivellation Δh entre les surfaces des bains d'acier liquide 1 présents dans la poche 2 et dans la cuve 25. Δh est calculée au moyen de la formule: Δh = (Penceinte - Pcuve)ρ . g On the other hand, a quantity of argon is injected into the enclosure 17 so that it creates therein an enclosure pressure P significantly higher than atmospheric pressure, for example from 2 to 3 bar (i.e. 2.10 5 to 3.10 5 Pa) . Besides that this overpressure guarantees that the air cannot penetrate inside the enclosure 17 during the treatment, it has the very important advantage of increasing the difference in level Δh between the surfaces of the baths of liquid steel 1 present in the pocket 2 and in tank 25. Δh is calculated using the formula: Δh = (P pregnant - P tank ) ρ. g

Toujours pour une pression de 1 torr (soit 133 Pa) dans la cuve 25, une pression de 2 bar dans l'enceinte 17 (soit 2.105 Pa) crée une dénivellation Δh de 2,95 m, et une pression de 3 bar une dénivellation de 4,43 m. On se donne ainsi la possibilité de faire une dénivellation Δh importante, à un instant donné, il ne subsiste dans la poche 2 que la moitié environ de l'acier liquide 1 qui y était initialement présent. L'autre moitié, qui circule entre la poche 2 et la cuve 25, se trouve soit à l'intérieur des plongeurs 26, 27, soit, surtout, à l'intérieur de la cuve 25 où elle est soumise à la pression réduite qui provoque son dégazage et, si sa composition s'y prête, sa décarburation.Still for a pressure of 1 torr (or 133 Pa) in the tank 25, a pressure of 2 bar in the enclosure 17 (or 2.10 5 Pa) creates a drop Δh of 2.95 m, and a pressure of 3 bar a drop of 4.43 m. This gives us the possibility of making a significant difference in Δh, at a given instant, there remains in the pocket 2 only about half of the liquid steel 1 which was initially present there. The other half, which circulates between the bag 2 and the tank 25, is either inside the plungers 26, 27, or, above all, inside the tank 25 where it is subjected to the reduced pressure which causes its degassing and, if its composition is suitable, its decarburization.

Par rapport aux RH classiques, la cuve 25 de l'installation selon l'invention peut avoir une capacité très sensiblement plus grande. En effet, le diamètre de son fond 28 doit être au moins suffisant pour que la cuve 25 repose sur le rebord 23 de l'enceinte 17, ce qui implique que ce diamètre soit sensiblement supérieur à celui de la poche 2 (à moins qu'on ne prolonge latéralement le fond 28 par une collerette, et que ce soit cette collerette qui repose sur le rebord 23 de l'enceinte 17 ; mais alors on se prive des avantages particuliers liés à un diamètre élevé de la cuve 25 qui seront vus plus loin). De préférence, une cloison en réfractaire 34, disposée entre les orifices 35, 36 par lesquels le métal liquide arrive dans la cuve 25 et en repart, barre le fond de l'espace intérieur de la cuve 25 pour éviter qu'une portion importante du métal liquide 1 qui pénètre dans la cuve 25 par le plongeur ascendant 26 ne passe ensuite directement dans le plongeur descendant 27 après n'avoir séjourné qu'un bref instant dans la cuve 25. On réduit ainsi la dispersion des temps de séjour dans la cuve 25 des différentes portions du métal liquide 1. Cette cloison 34 peut, comme représenté, avoir une hauteur relativement faible, et permettre ainsi à l'acier liquide 1 de la franchir par débordement lorsqu'il a atteint son niveau nominal. Elle peut aussi être suffisamment haute pour partager la cuve 25 en deux compartiments ne communicant entre eux que par des espaces libres ménagés entre la cloison 34 et la paroi interne de la cuve 25, et/ou des perforations ménagées dans la cloison 34. Comme représenté sur la figure 2c, de tels espaces libres 37, 38 et/ou perforations peuvent également exister dans le cas où la cloison 34 a une faible hauteur.Compared to conventional RH, the tank 25 of the installation according to the invention can have a very significantly greater capacity. Indeed, the diameter of its bottom 28 must be at least sufficient for the tank 25 to rest on the rim 23 of the enclosure 17, which implies that this diameter is significantly greater than that of pocket 2 (unless laterally extends the bottom 28 by a collar, and that it is this collar which rests on the rim 23 of the enclosure 17; but then we deprive ourselves of the particular advantages related to a large diameter of the tank 25 which will be seen later). Preferably, a partition in refractory 34, disposed between the orifices 35, 36 through which the liquid metal arrives in the tank 25 and leaves, bars the bottom of the interior space of the tank 25 to prevent a significant portion of the liquid metal 1 which enters the tank 25 via the ascending plunger 26 does not then pass directly into the descending diver 27 after having stayed than a brief moment in the tank 25. This reduces the dispersion of the residence times in the tank 25 of the different portions of the liquid metal 1. This partition 34 can, as shown, have a relatively small height, and thus allow the liquid steel 1 of the cross by overflow when it has reached its nominal level. It can also be high enough to divide the tank 25 into two compartments not communicating between them only by free spaces formed between the partition 34 and the internal wall of the tank 25, and / or perforations made in the partition 34. As shown in FIG. 2c, from such free spaces 37, 38 and / or perforations may also exist in the case where the partition 34 has a low height.

Si on vise à ne laisser dans la poche 2 qu'une faible quantité d'acier liquide 1 lorsque l'installation est en fonctionnement, le courant de circulation de l'acier liquide 1 dans la poche 2 y provoque une agitation très intense. Il n'est donc pas souhaitable que du laitier se trouve à la surface de l'acier liquide dans la poche 2 pendant le traitement, car ce laitier serait inévitablement entraíné au sein de l'acier liquide et détériorerait sa propreté inclusionnaire. Indépendamment de cela, le laitier peut se déposer sur les parois de la poche lors de la descente du niveau de métal en poche. Pour ces raisons, il est très conseillé que le laitier soit entièrement ôté avant que la poche ne soit mise dans l'enceinte 17. Une fois que le traitement sous vide est terminé, l'installation est remise dans sa configuration initiale telle que représentée sur la figure 2a. Mais avant de relever la cuve 25 pour remettre la poche 2 l'air libre afin de la transférer, par exemple, vers l'installation de coulée, il est préférable de reconstituer à la surface de l'acier liquide 1 une couche de laitier synthétique afin de protéger immédiatement le métal des réoxydations et renitrurations atmosphériques et de limiter ses pertes thermiques par rayonnement, lors des étapes ultérieures d'élaboration et de coulée. Cette couche de laitier synthétique peut être ajoutée, comme on l'a dit, à l'aide de la trémie 21 et de la goulotte 22. Si des additions d'éléments d'alliage doivent être effectuées au sein de l'acier liquide 1 pendant le traitement, elles peuvent l'être grâce à cette même trémie ou d'autres similaires, de préférence à un moment où une quantité d'acier liquide 1 relativement importante se trouve dans la poche 2. En variante, on peut aussi réaliser ces additions d'éléments d'alliage dans la cuve 25 elle-même, si elle est équipée de dispositifs à cet effet, comme c'est généralement le cas des cuves de RH classiques 5. On peut aussi disposer les trémies à l'extérieur de l'enceinte 17, en les associant à des moyens de transport des matières traversant la paroi de l'enceinte 17. Une telle disposition a pour avantage de réduire le volume intérieur nécessaire de l'enceinte 17, donc de diminuer la quantité de gaz qu'il est nécessaire d'y insuffler pour l'inerter ou la mettre sous pression.If we aim to leave in pocket 2 only a small amount of liquid steel 1 when the installation is in operation, the circulation current of the liquid steel 1 in pocket 2 causes very intense agitation. It is therefore not desirable that slag is on the surface of the liquid steel in pocket 2 during processing, because this slag would inevitably be entrained within the liquid steel and would deteriorate its cleanliness inclusions. Regardless of this, the slag can settle on the walls of the pocket when lowering the metal level in the pocket. For these reasons, it is highly recommended the slag is completely removed before the bag is placed in enclosure 17. A once the vacuum treatment is finished, the installation is reset to its configuration initial as shown in Figure 2a. But before raising the tank 25 to put back the pocket 2 in the open air in order to transfer it, for example, to the casting installation, it is preferable to reconstitute on the surface of the liquid steel 1 a layer of synthetic slag to immediately protect the metal from atmospheric reoxidation and renitruration and to limit its thermal losses by radiation, during the subsequent stages elaboration and casting. This layer of synthetic slag can be added as said it, using the hopper 21 and the chute 22. If additions of alloying elements must be carried out in liquid steel 1 during treatment, they can be carried out through this same hopper or others similar, preferably at a time when a relatively large quantity of liquid steel 1 is in the pocket 2. As a variant, can also make these additions of alloying elements in the tank 25 itself, if it is equipped with devices for this purpose, as is generally the case with RH tanks conventional 5. The hoppers can also be placed outside the enclosure 17, by associating with means of transporting materials passing through the wall of the enclosure 17. A such an arrangement has the advantage of reducing the necessary internal volume of the enclosure 17, therefore to decrease the quantity of gas which it is necessary to breathe in to inert it or the To put under pressure.

Comme il est déjà connu, pendant une partie du traitement on peut également insuffler de l'hydrogène dans l'acier liquide 1, que ce soit dans la poche 2, le plongeur ascendant 26 ou la cuve 25 à la place d'une partie ou de la totalité de l'argon destiné à agiter le métal liquide 1 et à accélérer la cinétique de décarburation, ou en plus de cet argon. L'insufflation d'hydrogène dans la poche 2 par le bouchon poreux 14 est particulièrement avantageuse si on maintient une surpression dans l'enceinte 17 : cette surpression augmente la quantité d'hydrogène qui peut être dissoute dans l'acier liquide 1 avant son passage dans la cuve 25, donc l'efficacité de l'insufflation d'hydrogène. On peut aussi envisager de mélanger de l'hydrogène à l'argon d'inertage/surpression de l'enceinte 17, voire même de réaliser temporairement cet inertage/surpression exclusivement à l'hydrogène. Sachant que l'hydrogène est un élément indésirable dans l'acier liquide au moment de sa coulée, l'introduction d'hydrogène dans l'installation devra être interrompue avant la fin du traitement sous vide, afin de donner à l'installation le temps de ramener la teneur en hydrogène de l'acier liquide 1 à un niveau acceptable, lors de la phase finale du traitement.As is already known, during part of the treatment it is also possible inject hydrogen into the liquid steel 1, whether in the pocket 2, the plunger upward 26 or tank 25 in place of some or all of the argon intended to stir liquid metal 1 and to accelerate the kinetics of decarburization, or in addition to this argon. The blowing of hydrogen into the bag 2 by the porous plug 14 is particularly advantageous if an overpressure is maintained in enclosure 17: this overpressure increases the amount of hydrogen that can be dissolved in liquid steel 1 before it passes through the tank 25, therefore the efficiency of the hydrogen insufflation. We can also consider mix hydrogen with the argon inerting / overpressure of enclosure 17, or even temporarily carry out this inerting / overpressure exclusively with hydrogen. Knowing that hydrogen is an undesirable element in liquid steel when it is poured, the introduction of hydrogen into the installation must be stopped before the end of the vacuum treatment, in order to give the installation time to reduce the content of hydrogen from liquid steel 1 at an acceptable level during the final treatment phase.

Le premier avantage de l'installation selon l'invention par rapport aux RH classiques est de rendre sans conséquences les défauts d'étanchéité que l'on peut constater habituellement au niveau des plongeurs et de leurs connexions à la cuve. Si de tels défauts existent sur l'installation selon l'invention, ils se traduisent seulement par l'aspiration d'une partie de l'argon d'inertage présent dans l'enceinte 17, et non par l'aspiration d'air. Il n'y a donc pas de pollution en oxygène et en azote du métal liquide 1 par de l'air atmosphérique. De plus, comme on l'a dit, l'installation d'aspiration 30 peut être utilisée au mieux de ses capacités, puisque tous les gaz qu'elle extrait de la cuve 25 soit résultent du dégazage de l'acier liquide 1, soit ont contribué à accélérer ce dégazage. Cet avantage ne peut qu'être accru si, de plus, on maintient l'enceinte 17 sous une pression de gaz d'inertage élevée.The first advantage of the installation according to the invention over HR classic is to make the leaks that can be seen without consequences usually at the plungers and their connections to the tank. If such faults exist on the installation according to the invention, they only result in the aspiration of a part of the inerting argon present in the enclosure 17, and not by the air intake. There is therefore no oxygen and nitrogen pollution of the liquid metal 1 by atmospheric air. In addition, as has been said, the suction installation 30 can be used to the best of its ability. capacities, since all the gases it extracts from tank 25 or result from the degassing of liquid steel 1, or contributed to accelerating this degassing. This advantage can only be increased if, in addition, the enclosure 17 is maintained under a high inerting gas pressure.

D'autre part, on a établi depuis peu que la différence de niveau entre le lieu d'injection d'argon dans le plongeur ascendant et le fond 28 de la cuve 25 est un paramètre particulièrement important pour le débit de circulation du métal liquide 1 entre la poche et la cuve. Ce débit est d'autant plus important que ladite différence de niveau est grande. L'installation selon l'invention, lorsqu'elle est équipée de plongeurs 26, 27 de grande longueur, dont les extrémités inférieures peuvent être placées très près du fond de la poche 2 et dont le point d'injection d'argon dans le plongeur ascendant 26 est situé très bas, permet d'optimiser ce paramètre. Par rapport à un RH classique que l'installation selon l'invention remplacerait, on peut choisir de conserver le même débit d'argon insufflé dans le plongeur ascendant 26, et augmenter ainsi le débit de circulation du métal liquide 1. On peut aussi choisir de conserver le même débit de circulation du métal liquide 1 en diminuant le débit d'argon insufflé, ce qui permet de diminuer l'usure des réfractaires du plongeur ascendant 26.On the other hand, it has recently been established that the difference in level between the place Argon injection into the ascending plunger and the bottom 28 of the tank 25 is a parameter particularly important for the flow rate of circulation of the liquid metal 1 between the bag and tank. This flow is all the more important that said level difference is large. The installation according to the invention, when equipped with plungers 26, 27 of large length, the lower ends of which can be placed very close to the bottom of the pocket 2 and whose point of injection of argon into the ascending plunger 26 is situated very low, optimizes this parameter. Compared to a conventional HR that the installation according to the invention would replace, one can choose to keep the same flow rate of argon blown into the ascending plunger 26, and thus increase the circulation rate of the liquid metal 1. can also choose to keep the same flow rate of liquid metal 1 in reducing the flow of injected argon, which reduces wear on the refractories of the ascending diver 26.

L'autre avantage important de l'installation est particulièrement sensible si on maintient une forte surpression dans l'enceinte 17 et si les extrémités inférieures des plongeurs 26, 27 peuvent être maintenues à proximité du fond de la poche 2 pendant le traitement. Il s'agit de la possibilité qu'à un instant donné du traitement sous vide, une très grande partie du métal liquide 1 (par exemple la moitié) se trouve dans la cuve 25 et dans le plongeur ascendant 26, donc soit soumise à la pression réduite et à l'intense balayage gazeux qui favorisent les réactions de dégazage et de décarburation. Par rapport à un RH classique qui traiterait des poches 2 identiques et dont la cuve ne pourrait renfermer que 1/10 à 1/20 de l'acier liquide 1 à traiter, l'installation selon l'invention permet d'augmenter très sensiblement le temps de séjour moyen d'une portion donnée du métal liquide 1 dans la cuve 25, sans augmenter la durée totale du traitement. Les réactions métallurgiques liées au séjour du métal liquide dans la cuve 25 sous pression réduite peuvent donc être effectuées de façon plus poussée.The other important advantage of the installation is particularly noticeable if one maintains a high overpressure in enclosure 17 and if the lower ends of the plungers 26, 27 can be kept close to the bottom of the pocket 2 during the treatment. It is the possibility that at some point in vacuum processing, a very large part of the liquid metal 1 (for example half) is in the tank 25 and in the ascending plunger 26, therefore be subjected to reduced pressure and intense scanning gases which promote degassing and decarburization reactions. Compared to an HR classic which would treat identical pockets 2 and the tank of which could only contain 1/10 to 1/20 of the liquid steel 1 to be treated, the installation according to the invention makes it possible to increase very substantially the average residence time of a given portion of the liquid metal 1 in the tank 25, without increasing the total duration of the treatment. Metallurgical reactions related to stay of the liquid metal in the tank 25 under reduced pressure can therefore be carried out in more detail.

D'autre part, la nécessité d'avoir une cuve 25 de relativement fort diamètre, de manière à obturer totalement l'enceinte 17, a pour corollaire de procurer à l'acier liquide 1 présent dans la cuve 25 une grande surface spécifique d'exposition à la pression réduite. De plus, on a la possibilité de multiplier les points d'insufflation d'argon à l'intérieur de la cuve 25, notamment à travers son fond 28. On peut ainsi créer pratiquement dans toute la cuve 25 d'intenses projections de gouttelettes de métal. Enfin, on peut choisir d'effectuer cette insufflation d'argon de manière privilégiée dans des zones relativement éloignées de la paroi interne de la cuve 25, afin d'éviter autant que possible que les projections 13 de métal liquide ne viennent encrasser trop vite ladite paroi en formant une couche de métal solidifié 16. Si la puissance de l'installation d'aspiration 30 le permet, on peut ainsi augmenter sensiblement la quantité d'argon insufflée dans la cuve sous vide par rapport à un RH classique sans pour autant accélérer de manière intolérable l'encrassement des parois. Tous ces facteurs contribuent à augmenter la surface réactionnelle de l'acier liquide 1 dans la cuve 25, ce qui est très favorable aux réactions de dégazage et de décarburation qui y sont recherchées, particulièrement lorsqu'on a déjà atteint des teneurs extrêmement basses en hydrogène, azote ou carbone. On peut ainsi atteindre des teneurs en carbone et en azote dans le métal liquide extrêmement basses en conservant la productivité habituelle des RH. Il est même possible d'obtenir des conditions cinétiques permettant une véritable désoxydation par le carbone sous vide, de manière à parvenir simultanément à de très basses teneurs en carbone et en oxygène. Cela facilite considérablement la dénitruration, qui n'est plus gênée par l'oxygène dissous.On the other hand, the need to have a tank 25 of relatively large diameter, of so as to completely close the enclosure 17, has the corollary of providing the liquid steel 1 present in the tank 25 a large specific surface of exposure to reduced pressure. Of more, we have the possibility of multiplying the argon insufflation points inside the tank 25, in particular through its bottom 28. It is thus possible to create practically throughout the tank 25 intense projections of metal droplets. Finally, we can choose to perform this blowing argon favorably in areas relatively far from the internal wall of the tank 25, in order to avoid as much as possible the projections 13 of metal liquid do not foul the wall too quickly, forming a layer of solidified metal 16. If the power of the suction installation 30 allows, we can increase appreciably the quantity of argon blown into the vacuum tank compared to an RH classic without intolerably accelerating the fouling of the walls. All these factors contribute to increasing the reaction surface of the liquid steel 1 in the tank 25, which is very favorable for degassing and decarburization reactions which are there sought after, particularly when extremely low levels of hydrogen, nitrogen or carbon. We can thus reach carbon and nitrogen contents in extremely low liquid metal while maintaining the usual productivity of HR. It is even possible to obtain kinetic conditions allowing true deoxidation by carbon under vacuum, so as to simultaneously achieve very low carbon and oxygen contents. This greatly facilitates denitriding, which is no longer hindered by dissolved oxygen.

Si on confère aux plongeurs 26, 27 une longueur telle que leurs extrémités inférieures avoisinent le fond de la poche 2 lorsque l'installation est en service, l'élévateur 19 et sa plate-forme 18 permettent de maítriser les positions relatives de la poche 2 et de la cuve 25, comme on l'a précédemment décrit. L'absence de l'élévateur 19 obligerait, lors de la mise en place de la cuve 25, à immerger immédiatement les plongeurs 26, 27 dans l'acier liquide 1 sur pratiquement toute leur hauteur, et le volume d'acier liquide 1 qu'ils déplaceraient provoquerait un débordement de la poche 2 si elle était utilisée à sa capacité nominale.If we give divers 26, 27 a length such that their ends lower around the bottom of the pocket 2 when the installation is in service, the elevator 19 and its platform 18 allow to control the relative positions of the bag 2 and the tank 25, as previously described. The absence of the elevator 19 would oblige, during placing the tank 25, immediately immersing the plungers 26, 27 in the steel liquid 1 over almost their entire height, and the volume of liquid steel 1 they move would cause pocket 2 to overflow if used to capacity nominal.

Par rapport au document JP-A-58181818 où la cuve du RH a une configuration classique, placer la poche dans une enceinte et pouvoir régler la profondeur d'immersion des plongeurs 26, 27 lorsque l'installation est en service permet d'augmenter considérablement le diamètre et la capacité de la cuve 25, et donc le débit de recirculation. Les ultra-basses teneurs en carbone sont ainsi plus aisément accessibles.Compared to document JP-A-58181818 where the RH tank has a configuration classic, place the bag in an enclosure and be able to adjust the immersion depth divers 26, 27 when the installation is in service increases considerably the diameter and the capacity of the tank 25, and therefore the recirculation flow. Ultra-low carbon contents are therefore more easily accessible.

On va donner à présent deux exemples de dimensionnement d'une installation selon l'invention. Ils sont applicables au cas où on veut traiter une poche 2 refermant 245 t d'acier liquide 1 et ayant un diamètre intérieur moyen de 3,5 m, ce qui correspond à une surface d'environ 10 m2 et une hauteur de métal de 3,5 m environ. Dans les deux exemples, on vise à apporter dans la cuve 25 mise sous vide une quantité de métal telle qu'elle y crée un bain d'une profondeur de 0,5 m. Le débit d'argon insufflé dans le plongeur ascendant 26 est comparable à ce qui se pratique dans le cas d'un traitement RH classique appliqué à la même poche, soit environ 2,4 Nm3/mn. Il assure une vitesse de circulation de métal dans les plongeurs 26, 27 d'environ 120 t/mn.We will now give two examples of sizing of an installation according to the invention. They are applicable in the case where it is desired to treat a pocket 2 enclosing 245 t of liquid steel 1 and having an average internal diameter of 3.5 m, which corresponds to an area of approximately 10 m 2 and a height of metal of 3.5 m approximately. In the two examples, the aim is to bring into the tank 25 placed under vacuum a quantity of metal such that it creates a bath therein with a depth of 0.5 m. The flow of argon blown into the ascending plunger 26 is comparable to what is practiced in the case of a conventional RH treatment applied to the same bag, that is to say approximately 2.4 Nm 3 / min. It ensures a metal circulation speed in the plungers 26, 27 of around 120 rpm.

Dans un premier exemple, on dispose d'une cuve 25 dont le diamètre intérieur est de 4,4 m (ce qui correspond à une surface de 15 m2) et de plongeurs de longueur 2,45 m et de diamètre intérieur 0,7 m. Dans ces conditions, pour une pression de l'ordre de 1 torr (133 Pa) dans la cuve 25, il faut créer une différence de pression (Penceinte - Pcuve) de 2 bar (soit 2.105 Pa) pour obtenir la dénivellation Δh de 2,95 m nécessaire à l'obtention de la profondeur de bain visée de 0,5 m dans la cuve 25. Elle correspond à une quantité de métal 1 présente dans la cuve 25 et les plongeurs 26, 27 de 65,5 t.In a first example, there is a tank 25 whose internal diameter is 4.4 m (which corresponds to an area of 15 m 2 ) and plungers of length 2.45 m and internal diameter 0.7 m. Under these conditions, for a pressure of the order of 1 torr (133 Pa) in the tank 25, it is necessary to create a pressure difference (P enclosure - P tank ) of 2 bar (i.e. 2.10 5 Pa) to obtain the difference in level Δh of 2.95 m necessary to obtain the target bath depth of 0.5 m in the tank 25. It corresponds to an amount of metal 1 present in the tank 25 and the plungers 26, 27 of 65.5 t.

Dans un deuxième exemple, on dispose d'une cuve 25 dont le diamètre intérieur est de 6,2 m (ce qui correspond à une surface de 30 m2) et de plongeurs de longueur 3,26 m et de diamètre intérieur 0,7 m. Dans ces conditions, pour une pression de l'ordre de 1 torr (133 Pa) dans la cuve 25, il faut créer une différence de pression (Penceinte - Pcuve) de 2,55 bar (soit 2,55.105 Pa) pour obtenir la dénivellation Δh de 3,76 m nécessaire à l'obtention de la profondeur de bain visée de 0,5 m dans la cuve 25. Elle correspond à une quantité de métal 1 présente dans la cuve 25 et les plongeurs 26, 27 de 121,5 t.In a second example, there is a tank 25 whose internal diameter is 6.2 m (which corresponds to an area of 30 m 2 ) and plungers of length 3.26 m and internal diameter 0.7 m. Under these conditions, for a pressure of the order of 1 torr (133 Pa) in tank 25, it is necessary to create a pressure difference (P enclosure - P tank ) of 2.55 bar (i.e. 2.55.10 5 Pa) to obtain the drop Δh of 3.76 m necessary to obtain the target bath depth of 0.5 m in the tank 25. It corresponds to a quantity of metal 1 present in the tank 25 and the plungers 26, 27 121.5 t.

Dans ces deux exemples, on peut insuffler à l'intérieur du métal 1 se trouvant dans la cuve 25, au moyen des tuyères 31, 33, une quantité totale d'argon d'environ 20000 Nl/mn (à comparer au débit de l'ordre de 5000 Nl/mn que pourrait tolérer un RH classique sans que ne s'y produisent des projections de métal excessives sur les parois de la cuve).In these two examples, the metal 1 found in the tank 25, by means of the nozzles 31, 33, a total quantity of argon of approximately 20,000 Nl / min (compared to the flow rate of around 5000 Nl / min that a conventional RH could tolerate without that excessive metal splashes occur on the walls of the tank).

Une variante de l'invention consiste à prévoir un réacteur métallurgique similaire au précédent, mais qui ne comporterait qu'un seul plongeur connecté à la cuve. Il ressemblerait donc à un réacteur de type DH. La circulation continue du métal liquide entre la poche et la cuve n'étant pas possible dans ces conditions (sauf, de manière limitée, par des mouvements de convection naturelle, suite au refroidissement subi par le métal dans la cuve), il faut donc :

  • soit calculer la géométrie de l'installation pour que la quasi-totalité du métal initialement présent dans la poche se retrouve dans la cuve lors du traitement, de manière à limiter autant que possible la quantité de métal qui ne sera pas significativement soumise au traitement sous vide ;
  • soit assurer le renouvellement du métal dans la cuve, par des réductions périodiques de la différence de pression (Penceinte - Pcuve), ou par des éloignements périodiques de la poche et de la cuve à l'aide du dispositif élévateur de la poche.
A variant of the invention consists in providing a metallurgical reactor similar to the previous one, but which would only comprise a single plunger connected to the tank. It would therefore look like a DH type reactor. The continuous circulation of liquid metal between the ladle and the tank is not possible under these conditions (except, to a limited extent, by natural convection movements, following the cooling undergone by the metal in the tank), it is therefore necessary:
  • either calculate the geometry of the installation so that almost all of the metal initially present in the pocket ends up in the tank during treatment, so as to limit as much as possible the quantity of metal which will not be significantly subjected to treatment under empty;
  • either ensure the renewal of the metal in the tank, by periodic reductions in the pressure difference (P enclosure - P tank ), or by periodic distances from the bag and the tank using the bag lifting device.

Si une décarburation très poussée du métal est recherchée, une insufflation d'argon dans le plongeur est très vivement conseillée, comme dans le cas des DH classiques.If a very strong decarburization of the metal is sought, an insufflation of argon in the diver is highly recommended, as in the case of classic DH.

Une installation selon l'invention s'insère dans une chaíne d'élaboration simplement en se substituant à une installation de traitement sous vide de type RH ou DH classique ou vide en cuve, sans nécessiter de modifier l'organisation de l'aciérie et le schéma d'élaboration général en vigueur pour les nuances d'acier à ultra-basses teneurs en carbone. Enfin, elle peut également, tout comme les RH classiques, traiter avec profit d'autres nuances que les aciers à ultra-basses teneurs en carbone. Elles bénéficieront de l'absence de pollution du métal par de l'air aspiré, ainsi que de l'augmentation du temps moyen d'exposition à la pression réduite et au balayage gazeux pour une durée de traitement donnée. Cela permettra notamment soit d'obtenir des déshydrogénations, dénitrurations et désoxydations par le carbone plus poussées qu'au moyen d'un RH classique, soit, à performances métallurgiques égales, de diminuer le temps de traitement de l'acier liquide.An installation according to the invention is part of a production chain simply by replacing a vacuum treatment system of the RH or DH type conventional or empty in tank, without the need to modify the organization of the steelworks and the general production scheme in force for ultra-low grade steel grades carbon. Finally, it can also, like conventional HR, deal with profit other grades than ultra-low carbon steels. They will benefit from the absence of pollution of the metal by aspirated air, as well as the increase in time means of exposure to reduced pressure and gas sweep for a period of treatment given. This will notably allow either to obtain dehydrogenations, carbon denitruration and deoxidation more than with RH conventional, or, for equal metallurgical performance, to reduce the processing time liquid steel.

Il va de soi que l'installation qui a été décrite peut être utilisée pour le traitement sous vide d'autres métaux que l'acier liquide.It goes without saying that the installation which has been described can be used for the treatment under vacuum other metals than liquid steel.

Claims (8)

  1. A metallurgical reactor for the treatment under reduced pressure of a liquid metal (1), such as steel, contained in a ladle (2), of the type comprising a chamber (25), connected to a gas-suction plant (30) which can maintain a reduced pressure therein, and two tubular snorkels (26, 27), the upper ends of which emerge in orifices (35, 36) made in the bottom (28) of the chamber (25) and the lower ends of which may be immersed in said liquid metal (1) contained in said ladle (2), one of said snorkels, called "ascending snorkel" (26), having means (29) for injecting a gas into its internal space for the purpose of creating a circulatory motion in the liquid metal (1) between the ladle (2) and the chamber (25) during said treatment, which also comprises an enclosure (17) which is provided with means (20) for injecting a gas into its internal space, these means being suitable for creating a pressure greater than atmospheric pressure in the enclosure (17), and the ladle (2) being placed in said latter, the upper edge (23) of the enclosure (17) being designed to support the bottom (28) of the chamber (25) in a sealed manner during said treatment, and means (18, 19) for raising the ladle (2) toward the chamber (25) during said treatment.
  2. A metallurgical reactor for the treatment under reduced pressure of a liquid metal, such as steel, contained in a ladle, of the type comprising a chamber connected to a gas-suction plant able to maintain a reduced pressure therein, and one tubular snorkel, the upper end of which emerges in an orifice made in the bottom of the chamber and the lower end of which may be immersed in said liquid metal contained in said ladle, which also comprises an enclosure which is provided with means for injecting a gas into its internal space, these means being suitable for creating a pressure greater than atmospheric pressure in the enclosure, and the ladle being placed in the latter, the upper edge of said enclosure being designed to support the bottom of the chamber in a sealed manner during said treatment, and means for raising the ladle toward the chamber during said treatment.
  3. The reactor as claimed in claim 1 or 2, wherein the chamber (25) includes means (31, 32, 33) for injecting gas into the liquid metal (1) that it contains.
  4. The reactor as claimed in claim 3, wherein such injection means (33) are provided in the bottom of the chamber (25).
  5. The reactor as claimed in claim 1, wherein the chamber (25) includes a partition (34) placed on the bottom of its internal space between said orifices (35, 36) made in the bottom of the chamber (25) and dividing the chamber (25) into two compartments.
  6. The reactor as claimed in claim 5, wherein it includes spaces (37, 38) separating the partition (34) from the internal wall of the chamber (25).
  7. The reactor as claimed in one of claims 1 to 6, wherein the enclosure (17) includes means (21, 22) for adding solid materials to the surface of or into the liquid metal (1) contained in the ladle (2).
  8. The reactor as claimed in one of claims 1 to 7, wherein the means (20) for injecting gas into the enclosure (17) can inject hydrogen or a gas mixture containing hydrogen.
EP98403021A 1997-12-22 1998-12-03 Metallurgical reactor for treating of molten metal under reduced pressure Expired - Lifetime EP0924305B1 (en)

Applications Claiming Priority (2)

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FR9716453A FR2772653B1 (en) 1997-12-22 1997-12-22 METALLURGICAL REACTOR FOR REDUCED PRESSURE TREATMENT OF A LIQUID METAL
FR9716453 1997-12-22

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DE10009898A1 (en) * 2000-03-01 2001-08-16 Bernd Feldhaus Process for blowing pure oxygen, combustible gases and solids onto molten metal, especially steel in an Ruhrstahl-Heraeus vessel comprises using a blow lance to blow an oxygen stream
FR2807066B1 (en) * 2000-03-29 2002-10-11 Usinor PNEUMATIC BREWING PROCESS FOR POUCHED LIQUID METAL
US20120198968A1 (en) * 2010-06-07 2012-08-09 Qiang Niu Method for producing metallic magnesium by vacuum circulating silicothermic process and apparatus thereof
CN102181658B (en) * 2011-03-23 2012-12-19 广西大学 Device and method for removing impurities in aluminum melt
EP2801627A1 (en) * 2013-05-06 2014-11-12 Siemens VAI Metals Technologies GmbH Vacuum treatment vessel for the treatment of molten metal, in particular for a RH installation
US20160052049A1 (en) * 2014-08-22 2016-02-25 Moltenideas Llc Apparatus and Process for delivering molten steel to a continuous casting mold
WO2016061423A1 (en) * 2014-10-17 2016-04-21 Nucor Corporation Method of continuous casting

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US3022059A (en) * 1958-03-10 1962-02-20 Hoerder Huettenunion Ag Apparatus for treating metal melts
LU62545A1 (en) * 1971-02-04 1972-12-05
US3798025A (en) * 1971-12-29 1974-03-19 Allegheny Ludlum Ind Inc Vacuum decarburization in rh and dh type degassing systems
US4298376A (en) * 1980-04-14 1981-11-03 Kobe Steel, Ltd. Method for treating molten steel and apparatus therefor
JPS58181818A (en) * 1982-04-19 1983-10-24 Nippon Steel Corp Vacuum degasifier
JPS5925919A (en) * 1982-08-02 1984-02-10 Kawasaki Steel Corp Method for adding additive element of high vapor pressure to molten steel
JPS61130415A (en) * 1984-11-29 1986-06-18 Kawasaki Steel Corp Heating method of molten steel in vacuum degassing device
US4950324A (en) * 1988-10-24 1990-08-21 A. Finkl & Sons Co. Tri-level method and apparatus for post melting treatment of molten steel

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ES2189113T3 (en) 2003-07-01
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US6162388A (en) 2000-12-19
FR2772653B1 (en) 2000-01-21
EP0924305A1 (en) 1999-06-23
FR2772653A1 (en) 1999-06-25
DE69810256D1 (en) 2003-01-30
ATE230035T1 (en) 2003-01-15
JPH11315315A (en) 1999-11-16
BR9805707A (en) 2000-01-04

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