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EP1141422B1 - Method for denitriding molten steel during its production - Google Patents

Method for denitriding molten steel during its production Download PDF

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Publication number
EP1141422B1
EP1141422B1 EP99959490A EP99959490A EP1141422B1 EP 1141422 B1 EP1141422 B1 EP 1141422B1 EP 99959490 A EP99959490 A EP 99959490A EP 99959490 A EP99959490 A EP 99959490A EP 1141422 B1 EP1141422 B1 EP 1141422B1
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EP
European Patent Office
Prior art keywords
carbon
denitriding
bath
oxygen
nitrogen
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EP99959490A
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German (de)
French (fr)
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EP1141422A1 (en
Inventor
Jean-Christophe Mailhan
Daniel Pernet
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USINOR SA
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USINOR SA
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    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04Removing impurities by adding a treating agent
    • C21C7/072Treatment with gases
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0025Adding carbon material
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0037Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 by injecting powdered material
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27DDETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00Charging; Discharging; Manipulation of charge
    • F27D3/0025Charging or loading melting furnaces with material in the solid state
    • F27D3/0026Introducing additives into the melt
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27DDETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00Charging; Discharging; Manipulation of charge
    • F27D3/18Charging particulate material using a fluid carrier

Definitions

  • the present invention relates to the field of production of low steels nitrogen contents. It is advantageously applied to the development of shades at low and very low carbon.
  • the manufacturing processes, or the nuance of certain steels therefore sometimes require very low nitrogen contents on the final product obtained, for example, to fix ideas, from 15 to 25 ppm for sheets intended for automobile construction or for steels for packaging, around 50 ppm for plates on offshore platforms, or from 40 to 60 ppm for tire reinforcement wires, etc.
  • These nitrogen contents are expected at the steelworks, at all stages of the development of molten metal, from the furnace electric, or from the converter until it solidifies with continuous casting.
  • the elaboration in the electric oven in particular, is distinguished by a strong contamination in nitrogen of the metal, due to the cracking of the nitrogen molecule from the air in the thermal zone of the electric arc which facilitates its transfer to the liquid metal.
  • a N is the dissolved nitrogen activity, which can be assimilated to the nitrogen content of the metal in the case of low-alloy carbon steels
  • P N2 is the partial nitrogen pressure of the gas in contact with the liquid metal. This means that in the presence of atmospheric N 2 , the nitrogen content of the metal will continuously increase towards its solubility limit, which is in the vicinity of 430 ppm at the temperature of the molten steel (approximately 1600 ° C.).
  • this gas can be argon or helium injected, but at low flow rate and with a high cost, or carbon monoxide formed in situ by the decarburization of the metal during the injection of oxygen, which is conventionally practiced in gaseous or particulate form (see for example the article by K. Shinme and T. Matsuo, "Acceleration of nitrogen removal with decarburization by powdered oxidizer blowing under reduced pressure", published in the Japanese journal ISIJ in 1987).
  • JP-A-63 206 421 relates to a process for advanced denitriding of a steel bath by means of a simultaneous and separate injection of gaseous hydrocarbon and powdery oxide.
  • the purpose of the present invention is precisely to promote denitriding of molten metal which exploits the denitriding potential of the washing gas on the one hand, and which allows, on the other hand, to control the final nitrogen content independently of the content initial carbon of the metallic bath, whereas this is currently the case with a classic decarburization.
  • the invention relates to a process for denitriding molten steel being developed by oxygen blowing as defined in claim 1.
  • carbon and oxygen are injected jointly but separately and side by side at the same level of the metal bath (at a distance of about 20 cm from each other for example).
  • the carbon content of the metal bath is not modified.
  • the co-injection technique according to the invention has been tested and implemented under industrial conditions in a small oven with a capacity of 6 tonnes, by simultaneously supplying carbon and oxygen by two independent injection lances whose outlet ends were placed side by side at the same level within the molten steel bath to be treated, about twenty centimeters from each other.
  • the carbon was supplied by a coal with low sulfur and nitrogen contents (weight contents lower than 0.1% for these two elements), and using either argon or nitrogen as carrier gas .
  • the oxygen was supplied either by injection of gaseous O 2 or by injection of iron ore (equivalent to 0.2 Nm 3 of O 2 per 1 kg of ore).
  • the denitriding method of the invention turns out to be flexible enough to realization to allow multiple variants of implementation, which are mentioned below some examples:
  • Any oxidizing gas, or any oxidizing powder iron ore, but also manganese ore, silica powder, etc.
  • any type of carbon product can be used for the purpose of adding carbon.
  • Co-injection according to the invention can be carried out without particular difficulties in the electric furnace, but also in the O 2 blowing converter from the top (type LD, AOD) or from the bottom (type OBM, LWS); in a pocket oven or in vacuum systems, type RH, where one can also benefit from the effect of vacuum on denitriding (P N2 low above the metal bath).
  • This technique can be particularly interesting in the case of an oven electric double-tank, where the denitriding phase by simultaneous supply of carbon and oxygen can be done in masked time while the merger of a new metallic charge in the other tank energized. For this, the denitriding operation will be done at the end of the development of a load, without electric voltage, the electric power being transferred to the other tank for the fusion of the next charge, without loss of productivity for the steelworks.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Abstract

The invention concerns a method which consists in injecting into a molten metal bath to be treated, jointly but separately into the same bath zone, oxygen and carbon in a form capable of being blown (powder carbon preferably) so as to generate locally in the bath CO bubbles from those two elements, which will then be loaded in denitriding nitrogen. A stoichiometric adjustment of the carbon and oxygen inputs enable a constant carbon denitriding in the bath. The method is preferably applicable to the production of low-carbon steel grades, in particular in an electric oven.

Description

La présente invention se rapporte au domaine de l'élaboration d'aciers à basses teneurs en azote. Elle s'applique avantageusement à l'élaboration des nuances à bas et très bas carbone.The present invention relates to the field of production of low steels nitrogen contents. It is advantageously applied to the development of shades at low and very low carbon.

On sait que la présence d'azote dans l'acier peut s'avérer indésirable pour différentes raisons. L'une d'entre-elles est l'impact de cet élément sur les propriétés d'emploi des aciers, par suite d'une diminution de la ductilité du métal et donc de son aptitude à l'emboutissage, ou, si l'azote est présent sous forme de nitrures d'aluminium, par suite d'une limitation de la soudabilité due à une remise en solution de l'azote dans la ZAC (zone affectée par la chaleur) et de la fragilisation mécanique locale résultante. Mais, la présence d'azote peut aussi être indésirable en raison de son impact sur les étapes même des filières de production, tel qu'une augmentation des criques liées à la poche de ductilité à la coulée continue, ou la diminution de l'aptitude du produit obtenu à être tréfilé.We know that the presence of nitrogen in steel can be undesirable for different reasons. One of them is the impact of this element on the properties of use of steels, as a result of a decrease in the ductility of the metal and therefore in its ability to stamp, or, if the nitrogen is present in the form of aluminum nitrides, due to a limitation of the weldability due to re-solution of nitrogen in the ZAC (zone affected by the heat) and the resulting local mechanical embrittlement. However, the presence of nitrogen can also be undesirable because of its impact on the very stages of the production chains, such as an increase in cracks associated with the ductility ladle in continuous casting, or the decrease in the ability of the product obtained to be drawn.

Les processus de fabrication, ou la nuance de certains aciers, nécessitent donc parfois de très basses teneurs en azote sur le produit final obtenu, par exemple, pour fixer les idées, de 15 à 25 ppm pour les tôles destinées à la construction automobile ou pour les aciers pour emballage, de 50 ppm environ pour les plaques des plates-formes off-shore, ou de 40 à 60 ppm pour les fils de renforcement des pneumatiques, etc... Ces teneurs en azote sont attendues à l'aciérie, à toutes les étapes de l'élaboration du métal en fusion, depuis le four électrique, ou depuis le convertisseur jusqu'à sa solidification à la coulée continue. On sait que l'élaboration au four électrique, notamment, se distingue par une forte contamination en azote du métal, due au cracking de la molécule d'azote de l'air dans la zone thermique de l'arc électrique qui facilite son transfert au métal liquide. Ce phénomène est connu pour être un facteur important qui empêche l'élaboration par la "filière électrique" d'une partie des nuances réalisées aujourd'hui par la "filière fonte" (réduction-fusion des minerais de fer en fonte au haut fourneau puis affinage à l'oxygène dans un convertisseur pneumatique) par laquelle des teneurs en azote plus basses, de l'ordre de 20 ppm, sont couramment obtenues.The manufacturing processes, or the nuance of certain steels, therefore sometimes require very low nitrogen contents on the final product obtained, for example, to fix ideas, from 15 to 25 ppm for sheets intended for automobile construction or for steels for packaging, around 50 ppm for plates on offshore platforms, or from 40 to 60 ppm for tire reinforcement wires, etc. These nitrogen contents are expected at the steelworks, at all stages of the development of molten metal, from the furnace electric, or from the converter until it solidifies with continuous casting. We know that the elaboration in the electric oven, in particular, is distinguished by a strong contamination in nitrogen of the metal, due to the cracking of the nitrogen molecule from the air in the thermal zone of the electric arc which facilitates its transfer to the liquid metal. This phenomenon is known to be an important factor which prevents the development by the "electrical sector" of a part of grades produced today by the "cast iron industry" (reduction-smelting of iron ores in blast furnace then refining with oxygen in a pneumatic converter) by which lower nitrogen contents, of the order of 20 ppm, are commonly obtained.

Les mécanismes physico-chimiques qui régissent l'évolution de la teneur en azote de l'acier liquide sont bien connus (voir par exemple l'article de Ch. Gatellier et H. Gaye paru dans la REVUE de METALLURGIE, CIT de Janvier 1986, p. 25 à 42). L'azote suit un équilibre chimique "métal-gaz" qui peut s'exprimer par la formule N ⇄ ½ N2(gaz),. La constante d'équilibre de cette réaction, qui s'écrit KN = aN /(PN2)½, dépend faiblement de la température dans le domaine de fonctionnement des réacteurs concernés (1550 à 1700°C). aN est l'activité en azote dissous, laquelle peut être assimilée à la teneur en azote du métal dans le cas des aciers au carbone faiblement alliés, et PN2 est la pression partielle d'azote du gaz en contact avec le métal liquide. Ceci signifie qu'en présence de N2 atmosphérique, la teneur en azote du métal va continuellement augmenter vers sa limite de solubilité, laquelle se situe au voisinage de 430 ppm à la température de l'acier en fusion (1600°C environ).The physicochemical mechanisms which govern the evolution of the nitrogen content of liquid steel are well known (see for example the article by Ch. Gatellier and H. Gaye published in the REVUE de METALLURGIE, CIT of January 1986, p. 25 to 42). Nitrogen follows a chemical "metal-gas" balance which can be expressed by the formula N ⇄ ½ N 2 (gas) ,. The equilibrium constant of this reaction, which is written K N = a N / (P N2 ) ½ , depends weakly on the temperature in the operating range of the reactors concerned (1550 to 1700 ° C). a N is the dissolved nitrogen activity, which can be assimilated to the nitrogen content of the metal in the case of low-alloy carbon steels, and P N2 is the partial nitrogen pressure of the gas in contact with the liquid metal. This means that in the presence of atmospheric N 2 , the nitrogen content of the metal will continuously increase towards its solubility limit, which is in the vicinity of 430 ppm at the temperature of the molten steel (approximately 1600 ° C.).

La dénitruration du métal est, quant à elle, obtenue en faisant circuler dans le métal liquide un gaz de lavage ne comportant pas d'azote (PN2 = 0) afin de déplacer la réaction ci-avant vers la droite (effet de lavage). Industriellement, ce gaz peut être de l'argon ou de l'hélium injecté, mais à faible débit et avec un coût élevé, ou du monoxyde de carbone formé in situ par la décarburation du métal lors de l'injection d'oxygène, laquelle se pratique classiquement sous forme gazeuse ou particulaire (voir par exemple l'article de K.Shinme et T. Matsuo, "Acceleration of nitrogen removal with decarburization by powdered oxidizer blowing under reduced pressure", paru dans la revue japonaise ISIJ en 1987). La limite à cette pratique d'injection d'O2 est liée à la teneur en carbone du métal en début de décarburation, qui va imposer le volume de CO émis au cours temps et donc la dénitruration possible, et ce quelque soient les teneurs en azote initiale et visée du métal à élaborer.The denitriding of the metal is obtained by circulating in the liquid metal a washing gas containing no nitrogen (P N2 = 0) in order to move the above reaction to the right (washing effect) . Industrially, this gas can be argon or helium injected, but at low flow rate and with a high cost, or carbon monoxide formed in situ by the decarburization of the metal during the injection of oxygen, which is conventionally practiced in gaseous or particulate form (see for example the article by K. Shinme and T. Matsuo, "Acceleration of nitrogen removal with decarburization by powdered oxidizer blowing under reduced pressure", published in the Japanese journal ISIJ in 1987). The limit to this practice of injecting O 2 is linked to the carbon content of the metal at the start of decarburization, which will impose the volume of CO emitted over time and therefore the possible denitriding, whatever the contents are. initial and target nitrogen of the metal to be produced.

JP-A-63 206 421 concerne un procédé de dénitruration poussée d'un bain d'acier au moyen d'une injection simultanée et séparée d'hydrocarbure gazeux et d'oxyde pulvérulent.JP-A-63 206 421 relates to a process for advanced denitriding of a steel bath by means of a simultaneous and separate injection of gaseous hydrocarbon and powdery oxide.

Cette approche physico-chimique doit être complétée par le rôle joué par les éléments tensio-actifs du métal, à savoir l'oxygène et le soufre, qui ont tous deux pour effet de bloquer les transferts d'azote entre métal et gaz. De ce fait, au-delà d'une certaine activité en oxygène dissous, correspondant à une limite supérieure de la teneur en carbone qui est de l'ordre de 0,1% pondéraux pour les aciers au carbone), la dénitruration par gaz de lavage peut être totalement inhibée.This physico-chemical approach must be supplemented by the role played by metal surfactants, namely oxygen and sulfur, both of which have the effect to block nitrogen transfers between metal and gas. Therefore, beyond a certain activity in dissolved oxygen, corresponding to an upper limit of the carbon content which is 0.1% by weight for carbon steels), denitriding by washing gas can be totally inhibited.

On comprend ainsi tout l'intérêt à pouvoir développer une technique de dénitruration du métal liquide permettant notamment d'élaborer par la filière "électrique" des aciers dont les teneurs en azote soient similaires à celles obtenues par la filière "fonte", c'est-à-dire de l'ordre de 20 ppm, voire moins sur le produit final obtenu.We can therefore understand the advantage of being able to develop a denitriding technique liquid metal, making it possible in particular to develop steels with the "electrical" sector the nitrogen contents are similar to those obtained by the "pig iron" process, that is to say from around 20 ppm or less on the final product obtained.

Le but de la présente invention est précisément de promouvoir une dénitruration du métal en fusion qui exploite au mieux le potentiel dénitrurant du gaz de lavage d'une part, et qui permette, d'autre part, de contrôler la teneur finale en azote indépendamment de la teneur initiale en carbone du bain métallique, alors que c'est actuellement le cas avec une décarburation classique.The purpose of the present invention is precisely to promote denitriding of molten metal which exploits the denitriding potential of the washing gas on the one hand, and which allows, on the other hand, to control the final nitrogen content independently of the content initial carbon of the metallic bath, whereas this is currently the case with a classic decarburization.

A cet effet, l'invention a pour objet un procédé de dénitruration de l'acier en fusion en cours d'élaboration par insufflation d'oxygène comme défini dans la revendication 1. Notamment, le carbone et l'oxygène sont injectés conjointement mais séparément et côte à côte au même niveau du bain métallique (à quelques 20 cm de distance l'un de l'autre par exemple).To this end, the invention relates to a process for denitriding molten steel being developed by oxygen blowing as defined in claim 1. In particular, carbon and oxygen are injected jointly but separately and side by side at the same level of the metal bath (at a distance of about 20 cm from each other for example).

Ainsi, dans la zone d'apport du carbone et de l'oxygène, on crée localement des conditions favorables à la dénitruration. En effet, dans le cas d'une injection simple d'oxygène (cas de la décarburation classique), la zone d'injection (nez de lance) va se traduire rapidement par un appauvrissement en carbone qui va retarder la formation de CO, et par une activité en oxygène dissous corrélativement élevée qui, on le sait, va contrarier la dénitruration du métal par les bulles de CO formées. Thus, in the carbon and oxygen supply zone, locally created favorable conditions for denitriding. Indeed, in the case of a simple injection oxygen (in the case of conventional decarburization), the injection area (lance nose) will quickly translate into carbon depletion which will delay the formation of CO, and by a correspondingly high dissolved oxygen activity which, as we know, will thwart the denitriding of the metal by the CO bubbles formed.

L'apport conjoint de carbone dans cette même zone va permettre une formation plus rapide des bulles de CO par réaction entre carbone et oxygène apportés, et une réduction de l'activité locale en oxygène dissous. On obtient de ce fait une meilleure efficacité de la dénitruration par le CO émis, laquelle va ainsi supplanter la tendance naturelle de l'acier à se nitrurer au contact de l'azote de l'air en surface et conduire donc globalement à une diminution de la teneur en azote du métal.The joint contribution of carbon in this same area will allow more training CO bubbles quickly by reaction between carbon and oxygen supplied, and a reduction in local dissolved oxygen activity. This results in better efficiency of the denitriding by the CO emitted, which will thus supplant the natural tendency of steel to nitriding on contact with nitrogen from the surface air and therefore overall leading to a decrease in the nitrogen content of the metal.

On rappelle en effet que dans un four à arcs, comme d'ailleurs dans tout réacteur sidérurgique qui compose la filière d'élaboration du métal, l'enceinte n'est pas et ne peut pas être rigoureusement étanche à l'égard de l'atmosphère extérieure. En conséquence, la teneur finale en azote du produit obtenu résulte nécessairement d'un compromis entre les reprises en azote (contamination par l'air par exemple) et la dénitruration mise en oeuvre lors de l'élaboration à l'état liquide.It is indeed recalled that in an arc furnace, as elsewhere in any reactor iron and steel making up the metal production chain, the enclosure is not and cannot be strictly airtight with respect to the outside atmosphere. Consequently, the content final nitrogen of the product obtained necessarily results from a compromise between recoveries in nitrogen (contamination by air for example) and the denitriding implemented during working out in the liquid state.

Par ailleurs, en réglant de préférence les apports de façon stoechiométrique (à savoir 1kg de C pour 0,9Nm3 d'O2), on ne modifie pas la teneur en carbone du bain métallique. On réalise ainsi une émission de CO à "teneur en carbone du bain constante", et dont la durée peut alors être adaptée à la dénitruration souhaitée (teneur en azote visée par rapport à la teneur en azote initiale).Furthermore, by preferably adjusting the intakes stoichiometrically (namely 1 kg of C for 0.9Nm3 of O 2 ), the carbon content of the metal bath is not modified. This produces a CO emission with "constant carbon content in the bath", the duration of which can then be adapted to the desired denitriding (targeted nitrogen content relative to the initial nitrogen content).

L'invention sera bien comprise, et d'autres aspects et avantages apparaítront au vu de la description qui suit donnée en référence aux planches de dessins jointes sur lesquelles:

  • la figure 1 est un graphique montrant l'évolution comparée de la teneur pondérale en azote d'un bain d'acier au four électrique contenant plus de 0.15% de carbone en poids, en fonction du volume de CO émis dans le bain, à partir d'une injection solitaire d'oxygène (courbe a) et à partir d'une co-injection carbone-oxygène selon l'invention (courbe b);
  • la figure 2 est un graphique analogue à celui de la figure précédente, mais sur bain décarburé, c'est-à-dire dans le cas où la teneur pondérale en carbone du bain métallique est faible, à savoir inférieur à 0.1%;
  • la figure 3 est un graphe montrant l'évolution comparée de la teneur pondérale en azote en fonction du volume de CO émis dans le bain par co-injection carbone-oxygène selon la nature du gaz de de transport du carbone injecté.
The invention will be well understood, and other aspects and advantages will appear on reading the following description given with reference to the accompanying drawing plates in which:
  • FIG. 1 is a graph showing the comparative evolution of the nitrogen content by weight of a steel bath in an electric oven containing more than 0.15% of carbon by weight, as a function of the volume of CO emitted in the bath, from a solitary injection of oxygen (curve a) and from a carbon-oxygen co-injection according to the invention (curve b);
  • Figure 2 is a graph similar to that of the previous figure, but on a decarburized bath, that is to say in the case where the carbon content by weight of the metal bath is low, namely less than 0.1%;
  • FIG. 3 is a graph showing the comparative evolution of the nitrogen content by weight as a function of the volume of CO emitted in the bath by carbon-oxygen co-injection according to the nature of the transport gas of the carbon injected.

La technique de co-injection selon l'invention a été testée et mise en oeuvre dans des conditions industrielles dans un petit four de 6 tonnes de capacité, en apportant simultanément carbone et oxygène par deux lances d'injection indépendantes dont les extrémités de sortie étaient placées cote à cote au même niveau au sein du bain d'acier en fusion à traiter, à un vingtaine de centimètres l'une de l'autre. L'apport de carbone a été réalisé par un charbon à basses teneurs en soufre et azote (teneurs pondérales inférieures à 0,1% pour ces deux éléments), et en utilisant soit de l'argon, soit de l'azote comme gaz porteur. L'apport d'oxygène s'est fait soit par injection d'O2 gazeux, soit par injection de minerai de fer (équivalent de 0,2 Nm3 d'O2 pour 1kg de minerai).The co-injection technique according to the invention has been tested and implemented under industrial conditions in a small oven with a capacity of 6 tonnes, by simultaneously supplying carbon and oxygen by two independent injection lances whose outlet ends were placed side by side at the same level within the molten steel bath to be treated, about twenty centimeters from each other. The carbon was supplied by a coal with low sulfur and nitrogen contents (weight contents lower than 0.1% for these two elements), and using either argon or nitrogen as carrier gas . The oxygen was supplied either by injection of gaseous O 2 or by injection of iron ore (equivalent to 0.2 Nm 3 of O 2 per 1 kg of ore).

Les résultats quantitatifs obtenus sont d'abord ceux présentés aux figures 1 et 2 où l'on compare la co-injection de carbone et d'oxygène (courbe b) à une décarburation simple (courbe a) et ce, en représentant l'évolution de la teneur en azote du métal en fonction du volume de CO émis dans le bain, pour un acier respectivement à plus de 0,15 % en carbone (fig.1) et à moins de 0.10 % (fig.2).The quantitative results obtained are first of all those presented in Figures 1 and 2 where we compare the co-injection of carbon and oxygen (curve b) to a simple decarburization (curve a), by representing the change in the nitrogen content of the metal as a function of volume of CO emitted into the bath, for a steel with more than 0.15% carbon respectively (fig.1) and less than 0.10% (fig.2).

Comme on peut le voir, pour les aciers relativement peu décarburés, la teneur en O2 dissous est toujours trop faible pour parvenir à bloquer la diffusion de l'azote dissous vers les bulles de gaz de lavage, et ce, que ce soit du CO de décarburation du bain (courbe a) ou du CO généré par réaction entre le carbone et l'oxygène apportés au bain conformément à l'invention (courbe b). On observe en effet une allure tout à fait similaire de ces deux courbes de cinétique de dénitruration, d'ailleurs voisines l'une de l'autre, données en fonction de la quantité cumulée de CO qui se dégage du bain avec le temps, encore que l'on peut noter une efficacité légèrement meilleure, de l'ordre de 5 ppm, en faveur de l'injection mixte selon l'invention.As can be seen, for relatively poorly decarburized steels, the dissolved O 2 content is always too low to succeed in blocking the diffusion of the dissolved nitrogen towards the bubbles of washing gases, and this, whether CO decarburization of the bath (curve a) or of the CO generated by reaction between the carbon and the oxygen supplied to the bath in accordance with the invention (curve b). We observe indeed a very similar appearance of these two kinetics of denitriding curves, which are also close to each other, given as a function of the cumulative amount of CO which emerges from the bath over time, again that a slightly better efficiency can be noted, of the order of 5 ppm, in favor of the mixed injection according to the invention.

En revanche, pour les aciers décarburés ou à bas carbone -dont on placera la frontière à 0.10 % en poids pour fixer les idées, car on sait qu'en dessous de ce seuil on ne parvient plus à dénitrurer par le simple jeu habituel de la décarburation-, on observe sur la figure 3 que la cinétique de dénitruration en cas de co-injection (courbe b) a bien même allure que dans le cas précédent, et qu'elle est donc indépendante de la teneur initiale en carbone du bain. En revanche, dans le cas classique de la mono-injection d'O2 seul (courbe a), on constate une reprise systématique d'azote qui croít régulièrement tout au long de l'émission du CO de décarburation. Ce phénomène de reprise d'azote qui, comme déjà explicité auparavant, est la résultante de deux mécanismes agissant simultanément mais en sens contraire, montre clairement que dans le cas des bas carbone, la dénitruration par le CO de décarburation est bloquée par la formation locale, au voisinage des bulles de gaz, de phases oxydées à activité élevée, et qu'en conséquence les reprises d'azote atmosphérique sont le mécanisme dominant, d'autant plus puissant d'ailleurs que la surface du bain est alors agitée par les bulles qui viennent y crever (courbe a). Par contre, à l'instar de ce que montre la courbe b de la fig. 1, dans le cas de la co-injection selon l'invention (courbe b de la fig.2), le mécanisme dominant est toujours celui de la dénitruration par le CO de lavage, indépendamment de la teneur initiale en carbone, donc même pour les très bas carbone.On the other hand, for decarburized or low carbon steels - which we will place the border at 0.10% by weight to fix ideas, because we know that below this threshold we can no longer denitritrate by the simple usual game of decarburization, it can be seen in FIG. 3 that the kinetics of denitriding in the event of co-injection (curve b) has the same appearance as in the previous case, and that it is therefore independent of the initial carbon content of the bath. On the other hand, in the classic case of mono-injection of O 2 alone (curve a), there is a systematic uptake of nitrogen which increases regularly throughout the emission of decarburization CO. This nitrogen uptake phenomenon, which, as already explained above, is the result of two mechanisms acting simultaneously but in opposite directions, clearly shows that in the case of low carbon, the denitriding by decarburization CO is blocked by local formation. , in the vicinity of gas bubbles, of oxidized phases with high activity, and that consequently the recovery of atmospheric nitrogen is the dominant mechanism, all the more powerful since the surface of the bath is then agitated by the bubbles who die there (curve a). On the other hand, like what curve b in fig. 1, in the case of co-injection according to the invention (curve b of FIG. 2), the dominant mechanism is always that of denitriding by the washing CO, independently of the initial carbon content, therefore even for very low carbon.

L'influence du gaz de transport du carbone sur les résultats obtenus est donnée sur la figure 3. On peut y voir qu'avec une injection du charbon sous flux d'azote (courbe 1), la cinétique de dénitruration est plus lente et conduit à une teneur en azote du métal limite (palier p) en-dessous de laquelle on ne peut accéder, plus élevée que dans le cas d'une injection sous flux d'argon. Il est néanmoins possible d'obtenir une dénitruration dans ce cas là, qui peut être compatible avec un objectif "moyen" sur la teneur en azote visée (palier p à 35 ppm dans le cas présent par exemple).The influence of the carbon transport gas on the results obtained is given on the figure 3. We can see there that with an injection of coal under nitrogen flow (curve 1), the kinetics of denitriding is slower and leads to a limit nitrogen content of the metal (level p) below which one cannot access, higher only in the case of a injection under argon flow. It is nevertheless possible to obtain denitriding in this case there, which can be compatible with an "average" objective on the targeted nitrogen content (level p to 35 ppm in this case for example).

La méthode de dénitruration de l'invention s'avère être suffisamment souple de réalisation pour permettre de multiples variantes de mise en oeuvre, dont on mentionne ci-après quelques exemples: The denitriding method of the invention turns out to be flexible enough to realization to allow multiple variants of implementation, which are mentioned below some examples:

- Utilisation de tout type d'apport de carbone et d'oxygène. - Use of any type of carbon and oxygen supply.

On pourra en effet utiliser comme apporteur d'oxygène tout gaz oxydant, ou toute poudre oxydante (minerai de fer, mais aussi minerai de Manganèse, poudre de Silice, etc...) De même on pourra utiliser tout type de produit carboné aux fins de l'apport de carbone.Any oxidizing gas, or any oxidizing powder (iron ore, but also manganese ore, silica powder, etc.) Similarly, any type of carbon product can be used for the purpose of adding carbon.

On pourra également utiliser des produits contenant à la fois ces deux éléments, pour lesquels l'apport local est alors effectué de manière connues par des moyens automatisés, voire des mélanges préparés à l'avance (mélange Charbon/Minerai de fer par exemple).We can also use products containing both of these elements, to which the local supply is then carried out in a known manner by automated means, or even mixtures prepared in advance (Coal / Iron Ore mixture for example).

- Utilisation de toute technologie d'apport assurant les conditions "locales" visées ici. - Use of any input technology ensuring the "local" conditions referred to here.

On pourra utiliser en effet des lances d'injection classiques, refroidies ou non; des tuyères pariétales immergées, ou toute autre forme d'injecteurs, qu'il soient du type "à injections séparées" pour l'oxygène et le carbone, ou du type à "injection unique", à tubes concentriques, ou adjacents.It will be possible in fact to use conventional injection lances, cooled or not; of the immersed parietal nozzles, or any other form of injectors, whether of the "to separate injections "for oxygen and carbon, or of the" single injection "type, with tubes concentric, or adjacent.

- Utilisation de cette technique dans tout type de réacteur sidérurgique: - Use of this technique in any type of steel reactor:

La co-injection selon l'invention peut se pratiquer sans difficultés particulières au four électrique, mais également au convertisseur à soufflage d'O2 par le haut (type LD, AOD) ou par le fond (type OBM, LWS); au four-poche ou dans les installations sous vide, type RH, où l'on pourra de surcroít bénéficier de l'effet du vide sur la dénitruration (PN2 faible au dessus du bain métallique).Co-injection according to the invention can be carried out without particular difficulties in the electric furnace, but also in the O 2 blowing converter from the top (type LD, AOD) or from the bottom (type OBM, LWS); in a pocket oven or in vacuum systems, type RH, where one can also benefit from the effect of vacuum on denitriding (P N2 low above the metal bath).

- Modification du rapport carbone/oxygène par rapport à la stoechiométrie. - Modification of the carbon / oxygen ratio compared to stoichiometry.

On a vu précemment l'avantage de régler les apports d'O2 et de C à la stoechiométrie. Comme on le comprend, il est en donc également possible de maintenir des conditions dénitrurantes en nez de lance, tout en modifiant légèrement ce rapport carbone/oxygène, afin par exemple de poursuivre une décarburation du métal en même temps qu'a lieu la phase dénitrurante.We have already seen the advantage of regulating the contributions of O 2 and C to stoichiometry. As we understand, it is therefore also possible to maintain denitriding conditions at the nose, while slightly modifying this carbon / oxygen ratio, in order for example to continue decarburization of the metal at the same time as the denitriding phase takes place. .

Parmi les avantages marquants de l'invention, on notera en particulier:Among the significant advantages of the invention, it will be noted in particular:

- la possibilité de dénitruration à basses teneurs en carbone. - the possibility of denitriding at low carbon contents.

Du fait de la modification des conditions locales (teneur en carbone, activité en oxygène dissous), cette technique permet, comme on l'a vu, de dénitrurer le métal alors que la teneur moyenne en carbone du bain métallique y est inférieure à 0,1% (limite en-dessous de laquelle on ne dénitrure plus avec une simple décarburation). Des phases de dénitruration par émission de CO à "teneur en carbone du bain constante" ont pu être ainsi réalisées pour une teneur en carbone moyenne du bain comprise entre 0,05 et 0,1% en poids.Due to the modification of local conditions (carbon content, activity in dissolved oxygen), this technique allows, as we have seen, to denitride the metal while the average carbon content of the metal bath is less than 0.1% (limit below which we no longer denitrit with a simple decarburization). Denitriding phases by emission of CO at "constant carbon content of the bath" could thus be achieved for an average carbon content of the bath of between 0.05 and 0.1% by weight.

- la facilité et souplesse de mise en oeuvre du procédé. - the ease and flexibility of implementing the process.

La technique ne nécessite pas d'investissement lourd. Dans le cas du four électrique notamment, les installations nécessaires sont généralement déjà disponible en usine, à savoir: un réseau d'alimentation en oxygène couplé à un dispositif d'injection dans le métal (ordinairement déjà présent pour la décarburation), et un distributeur de poudre associé à un dispositif d'injection du charbon dans le métal (déjà présent généralement pour l'injection de charbon dans le laitier). Ce dernier dispositif devra néanmoins être dédoublé si l'on veut réaliser une injection simultanée de carbone et d'oxygène dans le métal, alors que l'on développe dans le même temps un laitier moussant sur le bain métallique. Dans le cas des autres réacteurs d'élaboration, il peut être nécessaire de prévoir un dispositif d'apport du carbone dans la même zone que l'oxygène injecté.The technique does not require heavy investment. In the case of the electric oven in particular, the necessary installations are generally already available in the factory, at know: an oxygen supply network coupled to a metal injection device (usually already present for decarburization), and a powder distributor associated with a device for injecting carbon into the metal (already generally present for the injection of coal in the slag). This last device will nevertheless have to be split if you want carry out a simultaneous injection of carbon and oxygen into the metal, while at the same time develops a foaming slag on the metal bath. In the case of other production reactors, it may be necessary to provide a device for supplying the carbon in the same area as the injected oxygen.

Le coût de la pratique de cette technique de dénitruration se résume alors à celui des consommables: produits d'apport du carbone et de l'oxygène, et gaz de transport dans le cas d'une injection de produits solides.The cost of practicing this denitriding technique then comes down to that of consumables: carbon and oxygen supply products, and transport gases in the case injection of solid products.

-- une dénitruration possible en"temps masqué",possible denitriding in "masked time",

Cette technique peut être particulièrement intéressante dans le cas d'un four électrique à double-cuve, où la phase de dénitruration par apport simultané de carbone et d'oxygène pourra se faire en temps masqué pendant que s'opère la fusion d'une nouvelle charge métallique dans l'autre cuve mise sous tension. Pour cela, l'opération de dénitruration se fera en fin d'élaboration d'une charge, hors tension électrique, la puissance électrique étant transférée sur l'autre cuve pour la fusion de la charge suivante, sans perte de productivité pour l'aciérie.This technique can be particularly interesting in the case of an oven electric double-tank, where the denitriding phase by simultaneous supply of carbon and oxygen can be done in masked time while the merger of a new metallic charge in the other tank energized. For this, the denitriding operation will be done at the end of the development of a load, without electric voltage, the electric power being transferred to the other tank for the fusion of the next charge, without loss of productivity for the steelworks.

Il va de soi que la méthode selon l'invention peut présenter de multiples équivalents ou variantes de réalisation dans la mesure où est respectée sa définition donnée dans les revendications jointes.It goes without saying that the method according to the invention can have multiple equivalents or variant embodiments insofar as its definition given in the attached claims.

Claims (4)

  1. Method for denitriding a bath of molten steel during its production by the introduction of oxygen, wherein carbon in a form capable of being blown is likewise introduced into the bath, the carbon and the oxygen being injected jointly but separately into the bath of molten steel to be treated, characterized in that the carbon and the oxygen are injected side by side at the same level of the bath of molten steel, so as to generate a reaction between the injected carbon and oxygen.
  2. Method according to Claim 1, characterized in that the inputs of carbon and oxygen are adjusted in a stoichiometric manner.
  3. Method according to claim 1 or 2, characterized in that the carbon is injected in the powdery solid state with the aid of a transport gas.
  4. Method according to any one of claims 1 to 3, characterized in that it is carried out in an electrical steelworks installation with double vat.
EP99959490A 1998-12-18 1999-12-17 Method for denitriding molten steel during its production Expired - Lifetime EP1141422B1 (en)

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FR9816082A FR2787468B1 (en) 1998-12-18 1998-12-18 PROCESS FOR DENITRURATION OF MOLTEN STEEL DURING DEVELOPMENT
FR9816082 1998-12-18
PCT/FR1999/003176 WO2000037688A1 (en) 1998-12-18 1999-12-17 Method for denitriding molten steel during its production

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US20050050767A1 (en) * 2003-06-06 2005-03-10 Hanson Kyle M. Wet chemical processing chambers for processing microfeature workpieces
CN112342400A (en) * 2020-10-14 2021-02-09 潘玉霞 Precise bubble-eliminating casting process for hardware casting
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JPH0819456B2 (en) * 1987-02-24 1996-02-28 新日本製鐵株式会社 Manufacturing method of ultra low nitrogen steel
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