EP1080243A1 - Low pressure carbonitriding method for metal alloy parts - Google Patents

Low pressure carbonitriding method for metal alloy parts

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Publication number
EP1080243A1
EP1080243A1 EP99915850A EP99915850A EP1080243A1 EP 1080243 A1 EP1080243 A1 EP 1080243A1 EP 99915850 A EP99915850 A EP 99915850A EP 99915850 A EP99915850 A EP 99915850A EP 1080243 A1 EP1080243 A1 EP 1080243A1
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Prior art keywords
parts
nitrogen
action
metal alloy
fuel mixture
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Granted
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EP99915850A
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German (de)
French (fr)
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EP1080243B1 (en
Inventor
Jacques Frey
Philippe Dubois
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Aubert and Duval SA
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Aubert and Duval SA
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/28—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in one step
    • C23C8/30—Carbo-nitriding
    • C23C8/32—Carbo-nitriding of ferrous surfaces

Definitions

  • the present invention relates to a process for carbonitriding metal alloy parts.
  • Carbonitriding is a thermochemical treatment of simultaneous diffusion of carbon and nitrogen from the surface of a ferrous alloy in the solid state. It is generally carried out in a sealed oven, in which a controlled atmosphere is maintained, consisting of a support gas to which is added if necessary, to achieve the desired carbon potential, a carbon enrichment gas, and in addition, a nitrogen gas.
  • the support gas is an endothermic generator gas comprising an alkane which is oxidized to carbon monoxide CO, since oxidation is carried out in the absence of air with respect to the stoichiometric reaction which would transform all the carbon into C0 2 .
  • the gases used can be nitrogen-methanol mixtures or endothermic mixtures based on hydrocarbon and ammonia, as described in "Engineering Techniques, M1226-8 to 14, July 1994, [1].
  • the conventional process uses atmospheres which all contain oxygen due to the presence or the formation of CO.
  • the oxygen released by the decomposition of CO leads to a surface oxidation of the steel which, on the one hand, slows down the absorption of carbon and, on the other hand, leads to structures harmful in terms of the mechanical characteristics of the treated part, contact fatigue for example.
  • the parts carbonitrided in this way are most often used in the state, without any mechanical retouching of the surface.
  • the present invention relates to a carbonitriding process which makes it possible to avoid the harmful presence of oxygen, during the thermochemical treatment of diffusion of carbon and nitrogen in the metal alloy part.
  • the process for carbonitriding metal alloy parts consists in subjecting said parts to the action of a fuel mixture consisting of ethylene and hydrogen, and to the action of a nitriding gas consisting of ammonia, under a pressure of less than 100 hPa and at a temperature of about 750 to about 1050 ° C.
  • the supply of carbon takes place by the direct dissociation of a hydrocarbon, in this case ethylene, in the enclosure of a vacuum furnace, and the supply of nitrogen comes from the dissociation ammonia gas, depending on the thermally activated reaction:
  • ammonia dissociation reaction is thermodynamically total, but its kinetics are low. Therefore, there is still at the room ammonia to dissociate, generating active nascent nitrogen. It is for this reason that ammonia can be used for nitrogen supply.
  • the pressure used can be in particular in the range of 10 to 100 hPa.
  • One of the other advantages of the process of the invention is that it can enrich the surface of the part with carbon and nitrogen in a much wider temperature range, from around 750 to around 1050 ° C., depending on the enrichment sequences. considered.
  • the use of the ethylene dissociation reaction at low pressure makes it possible to be able to supply carbon from 750 ° C. and therefore thus by reducing the temperature to benefit from a greater nitriding power of ammonia because the availability of atomic nitrogen useful for diffusion is greater. This increases the possibilities of surface enrichment of carbon and nitrogen.
  • carbonitriding can be carried out either by subjecting said parts to the simultaneous action of the fuel mixture and the nitriding gas, or by subjecting said parts to the successive action of the fuel mixture and of the nitriding gas.
  • the treatment can also be carried out by subjecting the parts to the simultaneous action of the fuel mixture and the nitriding gas, then by subjecting them to the action of the nitriding gas alone.
  • the method of the invention can comprise a complementary step of treatment of vacuum diffusion of the parts, after they have been subjected to the action of the fuel mixture and the nitriding gas.
  • Such treatment can be carried out at a temperature of about 750 to about 1050 ° C, under pressures not exceeding 100 hPa.
  • the metal alloys capable of being treated by the process of the invention can be of various types. In particular, steels and superalloys based on cobalt can be used.
  • the method advantageously applies to the treatment of passivable steels, containing for example 2 to 9% of chromium and to the treatment of stainless steels containing for example 9 to 18% of chromium, thanks to the low pressure technique .
  • the processing of such steels further enriches them with nitrogen to a high degree of up to 4%.
  • the process of the invention therefore makes it possible on these steels to obtain in the surface layer, the C / N ratio offering the best compromise for the desired properties of wear resistance and / or corrosion resistance, for example.
  • the process of the invention makes it possible, by widening the temperature range, by the possibility of linking in a simple manner different simultaneous or alternating enrichment sequences in carbon and / or nitrogen, to achieve gradients in carbon and nitrogen very varied and this on very diverse steels, even passive.
  • the invention also relates to steel parts obtained by this process.
  • These parts can be, for example, passivable steel parts comprising 2 to 9% chromium, which are enriched in nitrogen on their surface up to a content of 2% by mass, or stainless steel parts comprising 9 to 18 % chromium, which are enriched in nitrogen on their surface up to a content of 4% by mass.
  • a double-vacuum oven known as with hot walls or an oven with cold walls, such as the devices described in FR-A-2 663 953.
  • the method can include the following steps:
  • carbonitriding treatment which can be carried out in different ways: a) a carbon enrichment period by introduction of the ethylene fuel gas, followed by a nitrogen enrichment period by introduction of ammonia, or vice versa, or a ') carbon and nitrogen enrichment period by simultaneous introduction of ethylene and ammonia,
  • step 6 optionally an enrichment treatment analogous to that of step 6), or a diffusion treatment under vacuum at a temperature of 750 to 1050 ° C., under a pressure of 10 _1 hPa, for example, and
  • steps 6) and 7) can be repeated several times if necessary.
  • the pressure in the tank is preferably maintained at around 25 hPa.
  • steps 1 to 5 and 8 and steps 6 and 7 were carried out using flow rates of ethylene and ammonia and enrichment sequences and / or different diffusion.
  • a preliminary austenitization step is carried out under vacuum at 10 ⁇ 2 hPa, at a temperature of 850 ° C., for 30 minutes.
  • Steps 6) and 7) are then carried out under the conditions given in table 2.
  • the reference of the alloys used whose compositions are given in table 1 has also been specified.
  • step 6) corresponds to carbonitriding with simultaneous dispatch of ethylene and ammonia and step 7) is a diffusion diffusion treatment.
  • step 6) corresponds to carbonitriding with simultaneous dispatch of ethylene and ammonia (at a lower flow rate) and step 7) is a nitriding treatment with ammonia alone.
  • step 6) corresponds to carburetion and step 7) to nitriding.
  • step 6) corresponds to carbonitriding with simultaneous dispatch of ethylene and ammonia, but the flow rate of ammonia is very high and step 7) is a vacuum diffusion treatment.
  • step 6 is carried out, which corresponds to carbonitriding by simultaneous sending of ethylene and ammonia, for a duration greater than that of the preceding examples.
  • the process of the invention is therefore very advantageous since it leads to much higher degrees of nitrogen enrichment than those which can be obtained with conventional carbonitriding processes where the nitrogen contents at the surface are at most about 0.3% 10

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Carbon And Carbon Compounds (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Inorganic Fibers (AREA)
  • Ceramic Products (AREA)

Abstract

The invention concerns a method for carbonitriding metal alloy parts which consists in treating said parts with a fuel mixture consisting of ethylene and hydrogen and with a nitriding gas consisting of ammonia, under pressure less than 100 hPa and at a temperature of about 750 to 1050 DEG C. The invention is particularly advantageous for treating passivable and stainless steel since it enables to attain very high surface enrichment in nitrogen.

Description

1 1
PROCEDE DE CARBONITRURATION A BASSE PRESSION DE PIECESLOW PRESSURE CARBONITRURATION PROCESS FOR PARTS
EN ALLIAGE METALLIQUEMETALLIC ALLOY
DESCRIPTIONDESCRIPTION
Domaine techniqueTechnical area
La présente invention a pour objet un procédé de carbonitruration de pièces en alliage métallique.The present invention relates to a process for carbonitriding metal alloy parts.
Elle s'applique en particulier à la carbonitruration de pièces en acier, notamment d'aciers riches en chrome utilisables dans les industries de pointe et l'industrie automobile.It applies in particular to the carbonitriding of steel parts, in particular of steels rich in chromium usable in the advanced industries and the automobile industry.
Etat de la technique antérieureState of the art
La carbonitruration est un traitement thermochimique de diffusion simultanée de carbone et d'azote à partir de la surface d'un alliage ferreux à l'état solide. Elle s'effectue généralement dans un four étanche, dans lequel on maintient une atmosphère contrôlée, constituée d'un gaz support auquel on ajoute si nécessaire, pour atteindre le potentiel carbone souhaité, un gaz d'enrichissement en carbone, et en plus, un gaz azoté. Généralement, le gaz support est un gaz de générateur endothermique comprenant un alcane qui est oxydé en monoxyde de carbone CO, car on réalise l'oxydation en défaut d'air par rapport à la réaction stoechiométrique qui transformerait tout le carbone en C02. Les gaz utilisés peuvent être des mélanges azote- méthanol ou des mélanges endothermiques à base d'hydrocarbure et d'ammoniac, comme il est décrit dans « Les Techniques de l'Ingénieur, M1226-8 à 14, juillet 1994, [1].Carbonitriding is a thermochemical treatment of simultaneous diffusion of carbon and nitrogen from the surface of a ferrous alloy in the solid state. It is generally carried out in a sealed oven, in which a controlled atmosphere is maintained, consisting of a support gas to which is added if necessary, to achieve the desired carbon potential, a carbon enrichment gas, and in addition, a nitrogen gas. Generally, the support gas is an endothermic generator gas comprising an alkane which is oxidized to carbon monoxide CO, since oxidation is carried out in the absence of air with respect to the stoichiometric reaction which would transform all the carbon into C0 2 . The gases used can be nitrogen-methanol mixtures or endothermic mixtures based on hydrocarbon and ammonia, as described in "Engineering Techniques, M1226-8 to 14, July 1994, [1].
Ainsi, le procédé classique met en oeuvre des atmosphères qui contiennent toutes de l'oxygène dû à la présence ou à la formation de CO. L'oxygène libéré par la décomposition du CO conduit à une oxydation superficielle de l'acier qui, d'une part, freine l'absorption du carbone et, d'autre part, conduit à des structures néfastes au plan des caractéristiques mécaniques de la pièce traitée, fatigue de contact par exemple. Il faut signaler que les pièces carbonitrurées de cette façon sont le plus souvent utilisées en l'état, sans aucune retouche mécanique de la surface.Thus, the conventional process uses atmospheres which all contain oxygen due to the presence or the formation of CO. The oxygen released by the decomposition of CO leads to a surface oxidation of the steel which, on the one hand, slows down the absorption of carbon and, on the other hand, leads to structures harmful in terms of the mechanical characteristics of the treated part, contact fatigue for example. It should be noted that the parts carbonitrided in this way are most often used in the state, without any mechanical retouching of the surface.
Le document FR-A-2 663 953, [2] décrit un procédé et une installation de cémentation de pièces en alliage métallique à basse pression évitant la présence d'oxygène. Cette technique basse pression n'a toutefois jamais été envisagée pour réaliser des traitements de carbonitruration .Document FR-A-2 663 953, [2] describes a process and an installation for carburizing metal alloy parts at low pressure avoiding the presence of oxygen. This low pressure technique has however never been envisaged for carrying out carbonitriding treatments.
Exposé de l'inventionStatement of the invention
La présente invention a pour objet un procédé de carbonitruration qui permet d'éviter la présence néfaste d'oxygène, lors du traitement thermochimique de diffusion du carbone et de l'azote dans la pièce en alliage métallique.The present invention relates to a carbonitriding process which makes it possible to avoid the harmful presence of oxygen, during the thermochemical treatment of diffusion of carbon and nitrogen in the metal alloy part.
Selon l'invention, le procédé de carbonitruration de pièces en alliage métallique consiste à soumettre lesdites pièces à l'action d'un mélange carburant constitué d'éthylène et d'hydrogène, et à l'action d'un gaz nitrurant constitué d'ammoniac, sous une pression inférieure à 100 hPa et à une température d'environ 750 à environ 1050°C.According to the invention, the process for carbonitriding metal alloy parts consists in subjecting said parts to the action of a fuel mixture consisting of ethylene and hydrogen, and to the action of a nitriding gas consisting of ammonia, under a pressure of less than 100 hPa and at a temperature of about 750 to about 1050 ° C.
Dans ce procédé, l'apport de carbone se fait par la dissociation directe d'un hydrocarbure, en l'occurrence l'éthylène, dans l'enceinte d'un four à vide, et l'apport d'azote provient de la dissociation du gaz ammoniac, selon la réaction activée thermiquement :In this process, the supply of carbon takes place by the direct dissociation of a hydrocarbon, in this case ethylene, in the enclosure of a vacuum furnace, and the supply of nitrogen comes from the dissociation ammonia gas, depending on the thermally activated reaction:
2NH3 N2 + 3H2.2NH 3 N 2 + 3H 2 .
Selon l'invention, on utilise pour ce traitement de carbonitruration des températures plus élevées que celles utilisées habituellement pour ce type de réaction, qui se situaient généralement dans un domaine de 400 à 600°C.According to the invention, higher temperatures than those usually used for this type of reaction are used for this carbonitriding treatment, which were generally in the range 400 to 600 ° C.
Aux températures plus élevées utilisées dans l'invention, la réaction de dissociation de l'ammoniac est thermodynamiquement totale, mais sa cinétique est faible. De ce fait, il existe encore au niveau de la pièce de l'ammoniac à dissocier, générant de l'azote naissant actif. C'est pour cette raison que l'on peut utiliser l'ammoniac pour l'apport d'azote.At the higher temperatures used in the invention, the ammonia dissociation reaction is thermodynamically total, but its kinetics are low. Therefore, there is still at the room ammonia to dissociate, generating active nascent nitrogen. It is for this reason that ammonia can be used for nitrogen supply.
D'autre part, le fait de travailler sous pression réduite, permet de bénéficier d'une vitesse de passage du gaz dans la charge supérieure à la cinétique de dissociation.On the other hand, the fact of working under reduced pressure makes it possible to benefit from a speed of passage of the gas in the charge greater than the dissociation kinetics.
La pression utilisée peut être en particulier dans la gamme de 10 à 100 hPa.The pressure used can be in particular in the range of 10 to 100 hPa.
Un des autres avantages du procédé de l'invention est de pouvoir enrichir la surface de la pièce en carbone et en azote dans un domaine de température beaucoup plus large, depuis environ 750 à environ 1050°C, selon les séquences d'enrichissement envisagées. En effet, l'utilisation de la réaction de dissociation de l'éthylène à basse pression permet de pouvoir apporter du carbone dès 750 °C et donc ainsi en diminuant la température de bénéficier d'un pouvoir nitrurant plus important de l'ammoniac car la disponibilité en azote atomique utile pour la diffusion, est plus grande. Ceci permet d'accroître les possibilités d'enrichissement superficiel en carbone et en azote. Ainsi selon l'invention, on peut obtenir des degrés et des profondeurs d'enrichissement en carbone et en azote voulus en choisissant de façon appropriée les débits d'éthylène et d'ammoniac, la température et la durée du traitement par le mélange carburant et le gaz nitrurant en fonction de l'alliage constituant lesdites pièces.One of the other advantages of the process of the invention is that it can enrich the surface of the part with carbon and nitrogen in a much wider temperature range, from around 750 to around 1050 ° C., depending on the enrichment sequences. considered. Indeed, the use of the ethylene dissociation reaction at low pressure makes it possible to be able to supply carbon from 750 ° C. and therefore thus by reducing the temperature to benefit from a greater nitriding power of ammonia because the availability of atomic nitrogen useful for diffusion is greater. This increases the possibilities of surface enrichment of carbon and nitrogen. Thus, according to the invention, it is possible to obtain desired degrees and depths of carbon and nitrogen enrichment by appropriately choosing the flow rates of ethylene and ammonia, the temperature and the duration of the treatment with the fuel mixture and the nitriding gas as a function of the alloy constituting said parts.
Selon l'invention, on peut réaliser la carbonitruration, soit en soumettant lesdites pièces à l'action simultanée du mélange carburant et du gaz nitrurant, soit en soumettant lesdites pièces à l'action successive du mélange carburant et du gaz nitrurant.According to the invention, carbonitriding can be carried out either by subjecting said parts to the simultaneous action of the fuel mixture and the nitriding gas, or by subjecting said parts to the successive action of the fuel mixture and of the nitriding gas.
On peut encore effectuer le traitement en soumettant les pièces à l'action simultanée du mélange carburant et du gaz nitrurant, puis en les soumettant à l'action du gaz nitrurant seul.The treatment can also be carried out by subjecting the parts to the simultaneous action of the fuel mixture and the nitriding gas, then by subjecting them to the action of the nitriding gas alone.
Ces étapes peuvent être répétées et combinées entre elles en utilisant des débits, température et durées différentes, situées dans les gammes données ci-dessus.These steps can be repeated and combined with each other using different flow rates, temperatures and times, located in the ranges given above.
Enfin, le procédé de l'invention peut comprendre une étape complémentaire de traitement de diffusion sous vide des pièces, après qu'elles aient été soumises à l'action du mélange carburant et du gaz nitrurant. Un tel traitement peut être effectuée à une température d'environ 750 à environ 1050 °C, sous des pressions ne dépassant pas 100 hPa. Les alliages métalliques susceptibles d'être traités par le procédé de l'invention peuvent être de divers types. On peut en particulier utiliser des aciers et des superalliages à base de cobalt. Parmi les aciers, le procédé s'applique avantageusement au traitement des aciers passivables, contenant par exemple 2 à 9 % de chrome et au traitement d'aciers inoxydables contenant par exemple 9 à 18 % de chrome, grâce à la technique de la basse pression. Le traitement de tels aciers permet de plus de les enrichir en azote à un degré élevé pouvant atteindre 4 %.Finally, the method of the invention can comprise a complementary step of treatment of vacuum diffusion of the parts, after they have been subjected to the action of the fuel mixture and the nitriding gas. Such treatment can be carried out at a temperature of about 750 to about 1050 ° C, under pressures not exceeding 100 hPa. The metal alloys capable of being treated by the process of the invention can be of various types. In particular, steels and superalloys based on cobalt can be used. Among the steels, the method advantageously applies to the treatment of passivable steels, containing for example 2 to 9% of chromium and to the treatment of stainless steels containing for example 9 to 18% of chromium, thanks to the low pressure technique . The processing of such steels further enriches them with nitrogen to a high degree of up to 4%.
Actuellement, ces aciers inoxydables sont, pour certaines applications liées à l'usure, utilisés à l'état cémenté. Après cémentation et traitement d'emploi, la couche superficielle durcie est très riche en carbures de chrome, ce qui dégrade fortement la résistance à la corrosion de ces aciers naturellement inoxydables avant cémentation.Currently, these stainless steels are, for certain wear-related applications, used in the case hardened state. After case hardening and processing, the hardened surface layer is very rich in chromium carbides, which greatly degrades the corrosion resistance of these naturally stainless steels before case hardening.
Le fait de pouvoir substituer en surface une partie du carbone par de l'azote, permet de former des précipités de nature différente, et ainsi de consommer moins de chrome de la matrice. L'azote peut également entrer en partie en solution solide dans la matrice, son action bénéfique sous cette forme sur la tenue à la corrosion étant déjà reconnue.The fact of being able to replace part of the carbon with nitrogen at the surface makes it possible to form precipitates of different nature, and thus to consume less chromium from the matrix. Nitrogen can also partly enter into a solid solution in the matrix, its beneficial action in this form on corrosion resistance having already been recognized.
Par sa souplesse, le procédé de l'invention permet donc sur ces aciers d'obtenir dans la couche superficielle, le rapport C/N offrant le meilleur compromis pour les propriétés recherchées de résistance à l'usure et/ou de résistance à la corrosion, par exemple.By its flexibility, the process of the invention therefore makes it possible on these steels to obtain in the surface layer, the C / N ratio offering the best compromise for the desired properties of wear resistance and / or corrosion resistance, for example.
En fait, le procédé de l'invention permet, par l'élargissement du domaine de température, par la possibilité d'enchaîner de façon simple différentes séquences d'enrichissement simultanées ou alternées en carbone et/ou en azote, de réaliser des gradients en carbone et azote très variés et ceci sur des aciers très divers, même passifs.In fact, the process of the invention makes it possible, by widening the temperature range, by the possibility of linking in a simple manner different simultaneous or alternating enrichment sequences in carbon and / or nitrogen, to achieve gradients in carbon and nitrogen very varied and this on very diverse steels, even passive.
Aussi, l'invention a également pour objet des pièces en acier obtenues par ce procédé. Ces pièces peuvent être, par exemple, des pièces en acier passivable comprenant 2 à 9 % de chrome, qui sont enrichies en azote sur leur surface jusqu'à une teneur de 2 % en masse, ou des pièces en acier inoxydable comprenant 9 à 18 % de chrome, qui sont enrichies en azote sur leur surface jusqu'à une teneur de 4 % en masse. Pour mettre en oeuvre le procédé de l'invention, on peut utiliser un four à double vide dit à parois chaudes ou un four à parois froides, tels que les dispositifs décrits dans FR-A-2 663 953.Also, the invention also relates to steel parts obtained by this process. These parts can be, for example, passivable steel parts comprising 2 to 9% chromium, which are enriched in nitrogen on their surface up to a content of 2% by mass, or stainless steel parts comprising 9 to 18 % chromium, which are enriched in nitrogen on their surface up to a content of 4% by mass. To implement the method of the invention, it is possible to use a double-vacuum oven known as with hot walls or an oven with cold walls, such as the devices described in FR-A-2 663 953.
A titre d'exemple, le procédé peut comprendre les étapes suivantes :By way of example, the method can include the following steps:
1) prévidage de la cuve du four jusqu'à une pression de 10"1 hPa de façon à éliminer l'air,1) preheating of the oven tank to a pressure of 10 "1 hPa so as to eliminate the air,
2) remplissage de la cuve par de l'azote à la pression atmosphérique, 3) enfournement de la cuve contenant les pièces métalliques et mise sous vide de la cuve à environ 10"2 hPa, 72) filling the tank with nitrogen at atmospheric pressure, 3) charging the tank containing the metal parts and evacuating the tank at around 10 "2 hPa, 7
4) chauffage jusqu'à la température d' austénitisation avec des paliers si nécessaire, et maintien à cette température pendant 30 minutes pour l'homogénéisation des pièces, 5) introduction d'hydrogène jusqu'à 500 hPa, de préférence ou moins selon le type de four,4) heating to the austenitization temperature with stages if necessary, and maintaining at this temperature for 30 minutes for the homogenization of the parts, 5) introduction of hydrogen up to 500 hPa, preferably or less depending on the type of oven,
6) traitement de carbonitruration qui peut être effectué de différentes façons : a) une période d'enrichissement en carbone par introduction du gaz carburant éthylène, suivie d'une période d'enrichissement en azote par introduction d'ammoniac, ou l'inverse, ou a') période d'enrichissement en carbone et en azote par introduction simultanée d'éthylène et d'ammoniac,6) carbonitriding treatment which can be carried out in different ways: a) a carbon enrichment period by introduction of the ethylene fuel gas, followed by a nitrogen enrichment period by introduction of ammonia, or vice versa, or a ') carbon and nitrogen enrichment period by simultaneous introduction of ethylene and ammonia,
7) éventuellement un traitement d'enrichissement analogue à celui de l'étape 6), ou un traitement de diffusion sous vide à une température de 750 à 1050°C, sous une pression de 10_1 hPa, par exemple, et7) optionally an enrichment treatment analogous to that of step 6), or a diffusion treatment under vacuum at a temperature of 750 to 1050 ° C., under a pressure of 10 _1 hPa, for example, and
8) introduction d'azote dans le four en vue du défournement .8) introduction of nitrogen into the furnace with a view to charging.
Il est à noter que les étapes 6) et 7) peuvent être répétées plusieurs fois si nécessaire. Lors de l'envoi des gaz éthylène et ammoniac, la pression dans la cuve est de préférence maintenue à environ 25 hPa.It should be noted that steps 6) and 7) can be repeated several times if necessary. When sending the ethylene and ammonia gases, the pressure in the tank is preferably maintained at around 25 hPa.
Exposé détaillé des modes de réalisationDetailed description of the embodiments
D'autres caractéristiques et avantages de l'invention ressortiront des exemples de réalisations 8Other characteristics and advantages of the invention will emerge from examples of embodiments 8
qui suivent donnés bien entendu à titre illustratif et non limitatif.which follow given of course by way of illustration and not limitation.
Dans les exemples qui suivent on a utilisé les alliages répertoriés dans le tableau 1 dont les composition sont données également dans le tableau 1.In the following examples, the alloys listed in Table 1 were used, the compositions of which are also given in Table 1.
Dans ces exemples, on a suivi le mode opératoire général décrit ci-dessus, pour les étapes 1 à 5 et 8 et les étapes 6 et 7 ont été réalisées en utilisant des débits d'éthylène et d'ammoniac et des séquences d'enrichissement et/ou de diffusion différentes .In these examples, the general procedure described above was followed, for steps 1 to 5 and 8 and steps 6 and 7 were carried out using flow rates of ethylene and ammonia and enrichment sequences and / or different diffusion.
Dans tous les exemples, on réalise une étape préalable d' austénitisation sous vide à 10~2 hPa, à une température de 850°C, pendant 30 minutes. On effectue ensuite les étape 6) et 7) dans les conditions données dans le tableau 2. Dans ce tableau, on a spécifié également la référence des alliages utilisés dont les compositions sont données dans le tableau 1.In all the examples, a preliminary austenitization step is carried out under vacuum at 10 ~ 2 hPa, at a temperature of 850 ° C., for 30 minutes. Steps 6) and 7) are then carried out under the conditions given in table 2. In this table, the reference of the alloys used whose compositions are given in table 1 has also been specified.
Dans les exemples 1 et 2, l'étape 6) correspond à une carbonitruration avec envoi simultané d'éthylène et d'ammoniac et l'étape 7) est un traitement de diffusion sous vide.In Examples 1 and 2, step 6) corresponds to carbonitriding with simultaneous dispatch of ethylene and ammonia and step 7) is a diffusion diffusion treatment.
Dans les exemples 3 et 4, l'étape 6) correspond à une carbonitruration avec envoi simultané d'éthylène et d'ammoniac ( à un débit plus faible) et l'étape 7) est un traitement de nitruration par l'ammoniac seul.In Examples 3 and 4, step 6) corresponds to carbonitriding with simultaneous dispatch of ethylene and ammonia (at a lower flow rate) and step 7) is a nitriding treatment with ammonia alone.
Dans les exemples 5 et 6, l'étape 6) correspond à une carburation et l'étape 7) à une nitruration.In Examples 5 and 6, step 6) corresponds to carburetion and step 7) to nitriding.
Dans les exemples 7 à 9, l'étape 6) correspond à une carbonitruration avec envoi simultané d'éthylène et d'ammoniac, mais le débit d'ammoniac est très élevé et l'étape 7) est un traitement de diffusion sous vide.In Examples 7 to 9, step 6) corresponds to carbonitriding with simultaneous dispatch of ethylene and ammonia, but the flow rate of ammonia is very high and step 7) is a vacuum diffusion treatment.
Dans les exemples 10 à 16, on réalise seulement l'étape 6) qui correspond à une carbonitruration par envoi simultané d'éthylène et d'ammoniac, pendant une durée supérieure à celle des exemples précédents.In Examples 10 to 16, only step 6) is carried out, which corresponds to carbonitriding by simultaneous sending of ethylene and ammonia, for a duration greater than that of the preceding examples.
Les résultats obtenus dans chaque exemple, c'est-à-dire les profils d'enrichissement superficiel en carbone et en azote (en % en masse) pour chacun des alliages traités, sont donnés dans les tableaux 3 à 8.The results obtained in each example, that is to say the surface enrichment profiles of carbon and nitrogen (in% by mass) for each of the alloys treated, are given in Tables 3 to 8.
Les résultats obtenus dans les exemples 1 à 6 sur des nuances classiques de carbonitruration sont voisins de ceux que l'on peut obtenir en réalisant une carbonitruration gazeuse classique.The results obtained in Examples 1 to 6 on conventional grades of carbonitriding are similar to those which can be obtained by carrying out conventional gaseous carbonitriding.
Dans les exemples 7 à 9, on obtient de bons résultats en traitant des alliages plus riches en chrome, donc plus passifs.In Examples 7 to 9, good results are obtained by treating alloys which are richer in chromium and therefore more passive.
Dans les exemples 10 à 16, on observe que l'on peut atteindre superficiellement des valeurs très élevées en azote sur des aciers inoxydables riches en chrome où les taux d'azote atteignent respectivement 2,86 et 4 % d'azote dans les exemples 14 et 15. Ainsi, l'azote remplace en partie le carbone superficiel, ce qui permet d'obtenir des couches avec des propriétés particulières .In Examples 10 to 16, it can be seen that very high nitrogen values can be reached superficially on stainless steels rich in chromium where the nitrogen levels reach 2.86 and 4% of nitrogen respectively in Examples 14 and 15. Thus, nitrogen partially replaces surface carbon, which makes it possible to obtain layers with particular properties.
Le procédé de l'invention est donc très avantageux car il conduit à des degrés d'enrichissement en azote beaucoup plus élevés que ceux que l'on peut obtenir avec les procédés classiques de carbonitruration où les teneurs en azote en surface sont au plus d'environ 0,3 % 10The process of the invention is therefore very advantageous since it leads to much higher degrees of nitrogen enrichment than those which can be obtained with conventional carbonitriding processes where the nitrogen contents at the surface are at most about 0.3% 10
Références citéesReferences cited
[1] Techniques de l'Ingénieur M 1226-8 à 14, Juillet 1994[1] Engineering techniques M 1226-8 to 14, July 1994
[2] FR-A-2 663 953 [2] FR-A-2 663 953
1111
Tableau 1Table 1
Acier C Ni Cr Mo V AlSteel C Ni Cr Mo V Al
20 NC 6 0, 17 1,60 0,8520 NC 6 0.17 1.60 0.85
27 CD 4 0,27 1,0 0,227 CD 4 0.27 1.0 0.2
20 CD 12 0,25 3,0 0,420 CD 12 0.25 3.0 0.4
32 CDV 13 0,30 3,0 1,0 0,2032 CDV 13 0.30 3.0 1.0 0.20
40 CAD 6.12 0,40 1,8 0,25 1 ,040 CAD 6.12 0.40 1.8 0.25 1.0
20 DN 34.13 0,20 3,0 3,520 DN 34.13 0.20 3.0 3.5
Z 15 CN 17.03 0,16 2,0 17,0Z 15 CN 17.03 0.16 2.0 17.0
Z 12 CNDV 12 0,12 2,5 11,5 1,6 0,30 Z 12 CNDV 12 0.12 2.5 11.5 1.6 0.30
Tableau 2Table 2
Ex Acier Etape 6) Etape 7) t durée C2H4 NH3 P t durée NH3 PEx Steel Step 6) Step 7) t duration C 2 H 4 NH 3 P t duration NH 3 P
(°C) (min) 0/h) 0/h) (hPa) (°C) (min) (1/n) (hPa)(° C) (min) 0 / h) 0 / h) (hPa) (° C) (min) (1 / n) (hPa)
1 20NC6 850 45 50 300 25 850 45 - 0,11 20NC6 850 45 50 300 25 850 45 - 0.1
2 27CD42 27CD4
3 20NC6 850 45 50 100 25 850 45 100 253 20NC6 850 45 50 100 25 850 45 100 25
4 27CD44 27CD4
5 20NC6 850 45 50 - 25 850 45 100 255 20NC6 850 45 50 - 25 850 45 100 25
6 27CD46 27CD4
7 27CD47 27CD4
8 32CVD13 850 45 50 600 25 850 45 - 0,18 32CVD13 850 45 50 600 25 850 45 - 0.1
9 Z15CN17.039 Z15CN17.03
10 20NC610 20NC6
11 27D411 27D4
12 20CD1212 20CD12
13 40CAD6.12 850 360 50 300 2513 40 CAD 6.12 850 360 50 300 25
14 Z12CNDV1214 Z12CNDV12
15 Z15CN17.03 16 20DN34.13 1215 Z15CN17.03 16 20DN34.13 12
Tableau 3Table 3
Ex 1 2Ex 1 2
Alliage 20 NC 6 27 CD 4Alloy 20 NC 6 27 CD 4
Profondeur C % N % C % N % (mm)Depth C% N% C% N% (mm)
0,05 0,50 0,304 0,61 0,324 0,15 0,45 0,215 0,58 0,223 0,25 0,45 0,113 0,51 0,122 0,35 0,33 0,039 0,47 0,043 coeur 0,19 0,0059 0,27 0,00800.05 0.50 0.304 0.61 0.324 0.15 0.45 0.215 0.58 0.223 0.25 0.45 0.113 0.51 0.122 0.35 0.33 0.039 0.47 0.043 heart 0.19 0.0059 0.27 0.0080
Tableau 4Table 4
Ex 3 4Ex 3 4
Alliage 20 NC 6 27 CD 4Alloy 20 NC 6 27 CD 4
Profondeur C % N % C % N % (mm)Depth C% N% C% N% (mm)
0,05 0,72 0,297 0,75 0,279 0,15 0,66 0,203 0,69 0,189 0,25 0,57 0,114 0,61 0,102 0,35 0,46 0,049 0,51 0,037 coeur 0,19 0,0059 0,27 0,0081 0.05 0.72 0.297 0.75 0.279 0.15 0.66 0.203 0.69 0.189 0.25 0.57 0.114 0.61 0.102 0.35 0.46 0.049 0.51 0.037 heart 0.19 0.0059 0.27 0.0081
1313
Tableau 5Table 5
Ex 5 6Ex 5 6
Alliage 20NC6 27 CD 4Alloy 20NC6 27 CD 4
Profondeur C% N% C% N% (mm)Depth C% N% C% N% (mm)
0,05 0,79 0,148 0,82 0,165 0,15 0,71 0,094 0,72 0,078 0,25 0,56 0,029 0,57 0,028 0,35 0,37 0,0092 0,44 0,012 coeur 0,19 0,0059 0,27 0,0081 0.05 0.79 0.148 0.82 0.165 0.15 0.71 0.094 0.72 0.078 0.25 0.56 0.029 0.57 0.028 0.35 0.37 0.0092 0.44 0.012 heart 0.19 0.0059 0.27 0.0081
Tableau 6Table 6
Ex 7 8 9Ex 7 8 9
Alliage 27CD4 32CDV13 Z15CN17.03Alloy 27CD4 32CDV13 Z15CN17.03
Profondeur C % N % C % N % C % N % (mm)Depth C% N% C% N% C% N% (mm)
0,05 0,63 0,22 0,34 0,73 0,89 2,00 0,15 0,58 0,19 0,60 0,29 0,77 0,08 0,25 0,54 0,12 0,55 0,03 0,33 0,05 0,35 0,46 0,05 0,44 0,01 0,20 0,05 0.05 0.63 0.22 0.34 0.73 0.89 2.00 0.15 0.58 0.19 0.60 0.29 0.77 0.08 0.25 0.54 0, 12 0.55 0.03 0.33 0.05 0.35 0.46 0.05 0.44 0.01 0.20 0.05
1414
Tableau 7Table 7
Ex 10 11 12 13Ex 10 11 12 13
Alliage 20NC6 27CD4 20CD12 40CAD6.12Alloy 20NC6 27CD4 20CD12 40CAD6.12
Profondeur C % N % C % N % C % N % C % N % (mm)Depth C% N% C% N% C% N% C% N% (mm)
0,05 0,98 0,52 0,93 0,44 0,60 0,89 0,81 0,98 0, 15 0,86 0,51 0,86 0,44 0,54 0,80 0,77 0,84 0,25 0,81 0,45 0,79 0,41 0,54 0,55 0,89 0,48 0,35 0,73 0,31 0,77 0,31 0,73 0, 12 0,80 0,04 0,45 0,65 0,20 0,66 0,24 0,57 0,04 0,66 0,01 0,55 0,56 0,09 0,51 0, 15 0,46 0,02 0,57 0,01 0.05 0.98 0.52 0.93 0.44 0.60 0.89 0.81 0.98 0.15 0.86 0.51 0.86 0.44 0.54 0.80 0, 77 0.84 0.25 0.81 0.45 0.79 0.41 0.54 0.55 0.89 0.48 0.35 0.73 0.31 0.77 0.31 0.73 0 , 12 0.80 0.04 0.45 0.65 0.20 0.66 0.24 0.57 0.04 0.66 0.01 0.55 0.56 0.09 0.51 0.15 0.46 0.02 0.57 0.01
Tableau 8Table 8
Ex 14 15 16Ex 14 15 16
Alliage Z12CNDV12 Z15CN17.03 20DN34.13Alloy Z12CNDV12 Z15CN17.03 20DN34.13
Profondeur C % N % C % N % C % N % (mm)Depth C% N% C% N% C% N% (mm)
0,05 0,41 2,86 0,61 4,00 0,57 0,53 0,15 2,07 0,26 2,45 0,36 0,53 0,41 0,25 1,32 0,07 1,21 0,08 0,50 0,31 0,35 1,62 0,04 0,51 0,05 0,46 0,19 0,45 0,22 0,03 0,26 0,04 0,40 0, 11 0,55 0, 14 0,03 0,20 0,04 0,35 0,08 0.05 0.41 2.86 0.61 4.00 0.57 0.53 0.15 2.07 0.26 2.45 0.36 0.53 0.41 0.25 1.32 0, 07 1.21 0.08 0.50 0.31 0.35 1.62 0.04 0.51 0.05 0.46 0.19 0.45 0.22 0.03 0.26 0.04 0 , 40 0, 11 0.55 0.14 0.03 0.20 0.04 0.35 0.08

Claims

15REVENDICATIONS 15 CLAIMS
1. Procédé de carbonitruration de pièces en alliage métallique, dans lequel on soumet lesdites pièces à l'action d'un mélange carburant constitué d'éthylène et d'hydrogène et à l'action d'un gaz nitrurant constitué d'ammoniac, sous une pression inférieure à 100 hPa et à une température d'environ 750 à 1050°C. 1. A method of carbonitriding metal alloy parts, in which said parts are subjected to the action of a fuel mixture consisting of ethylene and hydrogen and to the action of a nitriding gas consisting of ammonia, under a pressure below 100 hPa and at a temperature of about 750 to 1050 ° C.
2. Procédé selon la revendication 1, dans lequel la pression est de 10 à 100 hPa.2. The method of claim 1, wherein the pressure is 10 to 100 hPa.
3. Procédé selon l'une quelconque des revendications 1 et 2, dans lequel l'alliage métallique est un acier. 3. Method according to any one of claims 1 and 2, wherein the metal alloy is a steel.
4. Procédé selon la revendication 3, dans lequel les débits d'éthylène et d'ammoniac, la température et la durée du traitement par le mélange carburant et le gaz nitrurant sont choisis de façon à obtenir un enrichissement en azote de la surface de la pièce pouvant aller jusqu'à 4 % en masse.4. The method of claim 3, wherein the flow rates of ethylene and ammonia, the temperature and the duration of the treatment with the fuel mixture and the nitriding gas are chosen so as to obtain a nitrogen enrichment of the surface of the part up to 4% by mass.
5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel l'alliage métallique est un acier passivable comprenant 2 à 9 % de chrome.5. Method according to any one of claims 1 to 4, wherein the metal alloy is a passivable steel comprising 2 to 9% chromium.
6. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel l'alliage métallique est un acier inoxydable comprenant 9 à 18 % de chrome.6. Method according to any one of claims 1 to 4, wherein the metal alloy is a stainless steel comprising 9 to 18% chromium.
7. Procédé selon l'une quelconque des revendications 1 à 6, dans lequel on soumet lesdites pièces à l'action simultanée du mélange carburant et du gaz nitrurant.7. Method according to any one of claims 1 to 6, wherein said parts are subjected to the simultaneous action of the fuel mixture and the nitriding gas.
8. Procédé selon l'une quelconque des revendications 1 à 6, dans lequel on soumet lesdites 168. Method according to any one of claims 1 to 6, wherein said subject is subjected 16
pièces successivement à l'action du mélange carburant, puis à l'action du gaz nitrurant.parts successively to the action of the fuel mixture, then to the action of the nitriding gas.
9. Procédé selon l'une quelconque des revendications 1 à 6, dans lequel on soumet les pièces 1) à l'action simultanée du mélange carburant et du gaz nitrurant, puis 2) à l'action du gaz nitrurant seul.9. Method according to any one of claims 1 to 6, wherein the parts are subjected 1) to the simultaneous action of the fuel mixture and the nitriding gas, then 2) to the action of the nitriding gas alone.
10. Procédé selon l'une quelconque des revendications 1 à 9, dans lequel après avoir soumis les pièces à l'action du mélange carburant et du gaz nitrurant, on soumet les pièces à un traitement de diffusion sous vide, à une température d'environ 750 à 1050°C.10. Method according to any one of claims 1 to 9, in which after having subjected the parts to the action of the fuel mixture and of the nitriding gas, the parts are subjected to a treatment of diffusion under vacuum, at a temperature of about 750-1050 ° C.
11. Procédé selon la revendication 5, dans lequel on enrichit en azote la surface de ladite pièce jusqu'à une teneur de 2 % en masse.11. The method of claim 5, wherein the surface of said part is enriched in nitrogen to a content of 2% by mass.
12. Procédé selon la revendication 6, dans lequel on enrichit en azote la surface de ladite pièce jusqu'à une teneur de 4 % en masse. 12. The method of claim 6, wherein the surface of said part is enriched in nitrogen to a content of 4% by mass.
EP99915850A 1998-04-28 1999-04-27 Low pressure carbonitriding method for metal alloy parts Expired - Lifetime EP1080243B1 (en)

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US10156006B2 (en) 2009-08-07 2018-12-18 Swagelok Company Low temperature carburization under soft vacuum

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US10934611B2 (en) 2009-08-07 2021-03-02 Swagelok Company Low temperature carburization under soft vacuum
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