EP0213011B1 - Process for speedily and homogeneously carburizing a charge in a furnace - Google Patents

Process for speedily and homogeneously carburizing a charge in a furnace Download PDF

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EP0213011B1
EP0213011B1 EP86401585A EP86401585A EP0213011B1 EP 0213011 B1 EP0213011 B1 EP 0213011B1 EP 86401585 A EP86401585 A EP 86401585A EP 86401585 A EP86401585 A EP 86401585A EP 0213011 B1 EP0213011 B1 EP 0213011B1
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Prior art keywords
furnace
casehardening
flow rate
diffusion
charge
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German (de)
French (fr)
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EP0213011A1 (en
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Philippe Queille
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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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
    • C23C8/08—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 only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces

Definitions

  • the present invention relates to a cementation-diffusion process in a charge oven, in which the oven door is opened, a charge is introduced into the oven previously conditioned to the case temperature, the oven door is closed, the charge in a first phase known as carburizing during which the speed of transfer of carbon from the atmosphere to the surface of the part is preponderant compared to the speed of diffusion of carbon from the surface of the part towards the interior of this, then in a second so-called diffusion phase during which said diffusion speed becomes preponderant with respect to said transfer speed, the temperature of the furnace possibly possibly decreasing during this second phase, the load possibly being cooled before the opening of the oven door to allow its extraction and the introduction of a new charge, a carrier gas, possibly supplemented with hydrocarbon being introduced in the oven for the duration of the process.
  • a carrier gas possibly supplemented with hydrocarbon being introduced in the oven for the duration of the process.
  • a charge oven has a charge entry door, which door is closed for the duration of the treatment so as to maintain a controlled atmosphere in the oven and avoid air entry.
  • the atmosphere of a charge furnace, during case hardening generally comprises the following components:
  • a low gas flow rate in the oven results in an even longer reconditioning thereof.
  • a large quantity of air is introduced at ambient temperature.
  • the atmosphere is thus "deconditioned", the concentration of oxidizing species (CO 2 , O 2 , H 2 O) becoming much too high for the cementation process to take place correctly.
  • the temperature of the oven generally between 850 ° C and 1050 ° C, decreases due to the introduction of the load at room temperature. This decrease in temperature is accompanied by a transition to a temperature below the safety temperature, below which the atmosphere becomes explosive. To reduce this risk, nitrogen is injected into the oven so as to dilute the atmosphere to stay within safety standards.
  • the invention makes it possible to avoid these drawbacks.
  • the method according to the invention is characterized in that the flow D1 of carrier gas during the carburizing phase is linked to the flow D2 of carrier gas during the diffusion phase by the relation 1.2 D2 ⁇ D1 ⁇ 2 x D2, the flow rate D 2 being greater than or equal to the minimum safety threshold of the furnace used.
  • D l will be greater than or equal to 1.5 D 2 -
  • the gas flow will be equal to the value D 1 . If, on the contrary, the gas is to be saved as much as possible, while slightly lengthening the carburizing cycle, the gas flow will be equal to D 2 .
  • the gas flow will be equal to D 3 > D, and preferably greater than 1.2 D, but less than 2 x D l .
  • This flow D 3 can be maintained, in the case of an automatic regulation of the gas flows as a function of the temperature, until the return to the temperature T of carburizing of the charge introduced.
  • the desired atmosphere can therefore be assimilated to a so-called protective atmosphere, neutral vis-à-vis the surface of the parts (no carburizing or decarburization).
  • composition of the atmosphere can also be varied according to the teaching of US Pat. No. 4,519,853, but also according to the teaching of US Patent 4,306,918.
  • an atmosphere generated from methanol sprayed with nitrogen will be chosen.
  • at least 20% nitrogen and the balance of methanol will generally be used.
  • An injection rod as described in US Patent 4,279,406 is suitable, for example for this operation.
  • This example represents the known art with a "conventional" carrier gas flow rate.
  • the quality of the load is good.
  • the quality of the filler is excellent, superior to that of Example 1.
  • Example 3 shows that it is possible to obtain a treatment of excellent quality (equivalent to or better than that of Example 1) while minimizing the total gas consumption.
  • the atmosphere injected during the cementation phase included 80% methanol and 20% nitrogen while the atmosphere injected during the diffusion phase included about 30% methanol and 70% nitrogen, while the carbon potentials of these atmospheres were kept within the usual limits for the cementation and diffusion phases, but identical in the three examples.

Abstract

The process comprises opening the door of the furnace, introducing a charge into the furnace which was previously conditioned at the carburization temperature, closing the door of the furnace, subjecting the charge to a first phase, termed carburization phase, in the course of which the rate of transfer of the carbon of the atmosphere to the surface of the workpiece is preponderant relative to the rate of diffusion of the carbon from the surface of the workpiece to the interior of the workpiece, then to a second phase, termed diffusion phase, in the course of which said rate of diffusion becomes preponderant relative to said rate of transfer, the charge being possibly cooled before the opening of the door of the furnace so as to permit its extraction and the introduction of a new charge, a carrier gas, to which hydrocarbon may be added, being introduced into the furnace throughout the duration of the process. According to the invention, the flow rate D1 of carrier gas during the carburization phase is related to the flow rate D2 of carrier gas during the diffusion phase by the relation 1.2 D2</=D1</=2xD2, the flow rate D2 being higher than or equal to the minimum safety limit of the considered furnace.

Description

La présente invention concerne un procédé de cémentation-diffusion dans un four à charge, dans lequel on ouvre la porte du four, on introduit une charge dans le four préalablement conditionné à la température de cémentation, on ferme la porte du four, on soumet la charge à une première phase dite de cémentation au cours de laquelle la vitesse de transfert du carbone de l'atmosphère à la surface de la pièce est prépondérante par rapport à la vitesse de diffusion du carbone de la surface de la pièce vers l'intérieur de celle-ci, puis à une seconde phase dite de diffusion au cours de laquelle ladite vitesse de diffusion devient prépondérante par rapport à ladite vitesse de transfert, la température du four pouvant éventuellement diminuer au cours de cette seconde phase, la charge étant éventuellement refroidie avant l'ouverture de la porte du four pour permettre son extraction et l'introduction d'une nouvelle charge, un gaz porteur, éventuellement additionné d'hydrocarbure étant introduit dans le four pendant toute la durée du procédé.The present invention relates to a cementation-diffusion process in a charge oven, in which the oven door is opened, a charge is introduced into the oven previously conditioned to the case temperature, the oven door is closed, the charge in a first phase known as carburizing during which the speed of transfer of carbon from the atmosphere to the surface of the part is preponderant compared to the speed of diffusion of carbon from the surface of the part towards the interior of this, then in a second so-called diffusion phase during which said diffusion speed becomes preponderant with respect to said transfer speed, the temperature of the furnace possibly possibly decreasing during this second phase, the load possibly being cooled before the opening of the oven door to allow its extraction and the introduction of a new charge, a carrier gas, possibly supplemented with hydrocarbon being introduced in the oven for the duration of the process.

Un four à charge comporte une porte d'entrée de la charge, porte qui est fermée pendant toute la durée du traitement de manière à maintenir une atmosphère contrôlée dans le four et éviter les entrées d'air.A charge oven has a charge entry door, which door is closed for the duration of the treatment so as to maintain a controlled atmosphere in the oven and avoid air entry.

L'atmosphère d'un four à charge, lors d'une cémentation (voir par exemple le brevet américain US 4.145.232) comporte généralement les composants suivants:

Figure imgb0001
The atmosphere of a charge furnace, during case hardening (see for example US Pat. No. 4,145,232) generally comprises the following components:
Figure imgb0001

Afin de diminuer le coût du traitement de cémentation d'une charge de pièces, l'homme de métier cherche à diminuer les débits de gaz introduits dans le four.In order to reduce the cost of the case-hardening treatment of a charge of parts, the skilled person seeks to reduce the gas flow rates introduced into the furnace.

Autrefois, on utilisait des générateurs dit "endothermiques" pour créer l'atmosphère de cémentation requise. Les générateurs utilisant du gaz naturel engendrent ainsi une atmosphère contenant principalement environ 20 % de CO, 40 % de H2 et 40 % de N2, à débit constant.In the past, so-called "endothermic" generators were used to create the required carburizing atmosphere. Generators using natural gas thus generate an atmosphere containing mainly about 20% CO, 40% H 2 and 40% N 2 , at constant flow.

Plus récemment, on a remplacé les générateurs endothermiques par l'injection d'un mélange de méthanol et d'azote, permettant de faire varier la composition de l'atmosphère dans les limites décrites plus haut. On sait en effet que le méthanol se décompose, au-delà d'une température de 750°C, principalement en monoxyde de carbone et en hydrogène selon la réaction:

Figure imgb0002
More recently, endothermic generators have been replaced by the injection of a mixture of methanol and nitrogen, making it possible to vary the composition of the atmosphere within the limits described above. We know that methanol decomposes, above a temperature of 750 ° C, mainly into carbon monoxide and hydrogen according to the reaction:
Figure imgb0002

La simple substitution du générateur par des sources de gaz à débit constant à permis de réduire ceux-ci et réaliser une économie, tout en obtenant une charge de qualité identique. Un exemple de réalisation d'un procédé de ce type est décrit dans le brevet US 4.519.853.The simple substitution of the generator by gas sources at constant flow has made it possible to reduce these and save money, while obtaining a charge of identical quality. An exemplary embodiment of a process of this type is described in US Patent 4,519,853.

A l'heure actuelle, on cherche encore à réduire ces débits de gaz de manière à obtenir un bilan économique encore plus favorable.At present, efforts are still being made to reduce these gas flow rates so as to obtain an even more favorable economic balance.

Toutefois, l'homme de métier sait que l'on ne peut réduire le débit de gaz au-dessous d'un seuil minimum, sous lequel on doit faire face à différents problèmes:

  • Lorsque les portes du four sont fermées et si le débit des gaz injectés est inférieur au seuil minimum (detérminé expérimentalement et qui dépend du four et des conditions de traitement), ceci engendre des entrées d'air dues à l'absence d'étanchéité des fours de traitement thermique. Pour compenser ces entrées d'espèces oxydantes, l'homme de métier procède à une injection supplémentaire d'hydrocarbures de manière à maintenir le potentiel carbone au-dessus d'une valeur désirée. Or, cette injection supplémentaire d'hydrocarbures augmente considérablement les risques de dépôt de suie, d'une part et provoque d'autre part une dilution des concentrations de monoxyde de carbone et d'hydrogène, ce qui va à l'encontre du but recherché, ces concentrations devant être maintenues aussi élevées que possible pour une bonne cémentation: on sait en effet (voir par exemple J. Heat Treating - 14 - Vol. 1 N° 13- "Basic Requirements for reducing the consumption of carburizing gases" U. Wss - R. Hoffman and P. Neumann) que le coefficient de transfert du carbone de l'atmosphère cémentante sur la pièce à cémenter dépend du produit pH2 x pCO (pressions partielles de H2 et CO dans le four).
However, those skilled in the art know that one cannot reduce the gas flow below a minimum threshold, under which one must face various problems:
  • When the oven doors are closed and the flow rate of the injected gases is below the minimum threshold (determined experimentally and which depends on the oven and the treatment conditions), this generates air intakes due to the lack of airtightness of the heat treatment furnaces. To compensate for these inputs of oxidizing species, the skilled person proceeds with an additional injection of hydrocarbons so as to maintain the carbon potential above a desired value. However, this additional injection of hydrocarbons considerably increases the risks of soot deposition, on the one hand and causes on the other hand a dilution of the concentrations of carbon monoxide and hydrogen, which goes against the desired objective. , these concentrations having to be kept as high as possible for a good carburizing: we know indeed (see for example J. Heat Treating - 14 - Vol. 1 N ° 13- "Basic Requirements for reducing the consumption of carburizing gases" U. Wss - R. Hoffman and P. Neumann) that the carbon transfer coefficient from the cementing atmosphere to the part to be cemented depends on the product pH 2 x pCO (partial pressures of H 2 and CO in the furnace).

Par ailleurs, un faible débit de gaz dans le four engendre un reconditionnement d'autant plus long de celui-ci. Lors de l'ouverture de la porte du four pour l'introduction de la charge, on introduit une quantité importante d'air, à température ambiante. L'atmosphère est ainsi "déconditionnée", la concentration en espèce oxydante (CO2, O2, H2O) devenant beaucoup trop importante pour que le procédé de cémentation se déroule correctement. Par ailleurs, la température du four, généralement comprise entre 850°C et 1050°C, diminue du fait de l'introduction de la charge à température ambiante. Cette diminution de la température est accompagnée d'un passage à une température inférieure à la température de sécurité, en-dessous de laquelle l'atmosphère devient explosive. Pour diminuer ce risque, on injecte de l'azote dans le four de manière à diluer l'atmosphère pour rester dans les normes de sécurite. Ceci engendre une diminution de la concentration en monoxyde de carbone et en hydrogène de l'atmosphère. Il n'est donc pas possible, simultanément, de se maintenir au seuil minimal de débit dans le four et de conserver une qualité identique aux charges traitées sous un débit de gaz "conventionnel", c'est-à-dire supérieur au débit minimal. (Par qualité de charge, on entend l'aspect visuel de surface de la pièce, la profondeur cémentée obtenue pour une durée de cémentation déterminée ainsi que l'homogénéité de ces deux paramètres dans la charge.)In addition, a low gas flow rate in the oven results in an even longer reconditioning thereof. When the oven door is opened for the introduction of the charge, a large quantity of air is introduced at ambient temperature. The atmosphere is thus "deconditioned", the concentration of oxidizing species (CO 2 , O 2 , H 2 O) becoming much too high for the cementation process to take place correctly. Furthermore, the temperature of the oven, generally between 850 ° C and 1050 ° C, decreases due to the introduction of the load at room temperature. This decrease in temperature is accompanied by a transition to a temperature below the safety temperature, below which the atmosphere becomes explosive. To reduce this risk, nitrogen is injected into the oven so as to dilute the atmosphere to stay within safety standards. This results in a decrease in the concentration of carbon monoxide and hydrogen in the atmosphere. It is therefore not possible, simultaneously, to maintain the minimum flow threshold in the furnace and to maintain a quality identical to the charges treated under a "conventional" gas flow, that is to say greater than the minimum flow. (By load quality, we mean the visual appearance of the workpiece surface, the cemented depth obtained for a determined carburizing duration as well as the homogeneity of these two parameters in the load.)

L'invention permet d'éviter ces inconvénients.The invention makes it possible to avoid these drawbacks.

On a constaté que, de manière inattendeu, pour une même qualité de pièces traitées, on pouvait diminuer le débit des gaz pendant la phase de diffusion. Cette constatation est surprenante car l'homme de métier a toujours considéré que les débits de gaz devaient être les mêmes pendant les phases de cémentation et de diffusion.It has been found that, unexpectedly, for the same quality of treated parts, it was possible to reduce the gas flow rate during the diffusion phase. This finding is surprising because the person skilled in the art has always considered that the gas flow rates should be the same during the cementation and diffusion phases.

Le procédé selon l'invention est caractérisé en ce que le débit D1 de gaz porteur pendant la phase de cémentation est lié au débit D2 de gaz porteur pendant la phase de diffussion par la relation
1,2 D2 < D1 < 2 x D2,
le débit D2 étant supérieur ou égal au seuil minimal de sécurité du four utilisé. De préférence, Dl sera supérieur ou égal à 1,5 D2-The method according to the invention is characterized in that the flow D1 of carrier gas during the carburizing phase is linked to the flow D2 of carrier gas during the diffusion phase by the relation
1.2 D2 <D1 <2 x D2,
the flow rate D 2 being greater than or equal to the minimum safety threshold of the furnace used. Preferably, D l will be greater than or equal to 1.5 D 2 -

De l'ouverture à la fermeture de la porte du four, c'est-à-dire pendant l'introduction de la charge à cémenter dans le four, plusierus variantes préférentielles sont possibles. Si l'on veut obtenir de pièces d'excellentes qualité et le plus rapidement possible, le débit de gaz sera égal à la valeur D1. Si l'on veut, au contraire, économiser au maximum le gaz, tout en allongeant faiblement le cycle de cémentation, le débit de gaz sera égal à D2.From the opening to the closing of the oven door, that is to say during the introduction of the charge to be cemented into the oven, several preferential variants are possible. If you want to obtain excellent quality parts and as quickly as possible, the gas flow will be equal to the value D 1 . If, on the contrary, the gas is to be saved as much as possible, while slightly lengthening the carburizing cycle, the gas flow will be equal to D 2 .

Si l'on veut enfin diminuer au maximum la durée des cycles de cémentation, le débit de gaz sera égal à D3 > D, et de préférence supérieur à 1,2 D, mais inférieur à 2 x Dl. Ce débit D3 peut être maintenu, dans le cas d'une régulation automatique des débits de gaz en fonction de la température, jusqu'au retour à la température T de cémentation de la charge introduite.If we finally want to minimize the duration of the carburizing cycles, the gas flow will be equal to D 3 > D, and preferably greater than 1.2 D, but less than 2 x D l . This flow D 3 can be maintained, in the case of an automatic regulation of the gas flows as a function of the temperature, until the return to the temperature T of carburizing of the charge introduced.

Généralement, le débit D2 de gaz porteur sera inférieur au débit "conventionnel", le débit Dl étant supérieur ou égal au débit "conventionnel". Par débit "conventionnel", on entend le débit constant cémentation-diffusion permettant d'obtenir les mêmes qualités de pièces traitées. Le procédé selon l'invention permet d'atteindre une qualité des pièces traitées identique ou meilleure à celle obtenue avec le procédé conventionnel tout en permettant une diminution de consommation de gaz porteuur. En effet, dans la phase de fort débit D, (cémentation), on constate:

  • - qui ce fort débit D, permet un chauffage accéléré de la charge par convection;
  • - qu'il permet de conserver un potentiel carbone élevé sans addition excessive d'hydrocarbure. Ceci est important car les hydrocarbures additionnels étant toujours partiellement craqués, on engendre de la suie (réaction hors d'équilibre, non contrôlable). Moins on on injecte d'hydrocarbure, moins le dépôt de suie dans le four est important;
  • - que le taux de CO dans l'atmosphère, dont dépend la vitesse de transfert du carbone de l'atmosphère vers la pièce, est augmenté rapidement, ce qui permet de réduire la durée du cycle de cémentation.
Generally, the flow rate D 2 of carrier gas will be less than the "conventional" flow rate, the flow rate D l being greater than or equal to the "conventional" flow rate. By "conventional" flow means the constant cementation-diffusion flow allowing the same qualities of treated parts to be obtained. The method according to the invention makes it possible to achieve a quality of the treated parts identical or better than that obtained with the conventional method while allowing a reduction in consumption of carrier gas. Indeed, in the high flow phase D, (case hardening), we note:
  • - which this high flow D, allows accelerated heating of the charge by convection;
  • - it makes it possible to maintain a high carbon potential without excessive addition of hydrocarbon. This is important because the additional hydrocarbons being always partially cracked, soot is generated (out of equilibrium reaction, not controllable). The less hydrocarbon is injected, the less the deposit of soot in the oven;
  • - that the rate of CO in the atmosphere, on which the speed of transfer of carbon from the atmosphere to the part depends, is increased rapidly, which makes it possible to reduce the duration of the carburizing cycle.

Au cours de la phase de diffusion il suffit généralement de maintenir un potentiel carbone de l'atmosphère sensiblement égal à la concentration finale désirée de carbone à la surface de la pièce.During the diffusion phase, it is generally sufficient to maintain a carbon potential of the atmosphere substantially equal to the desired final concentration of carbon on the surface of the part.

On peut donc ainsi réduire le débit de gaz porteur au cours de la phase de diffusion d'un facteur de 1,2 à 2 par rapport au débit au cours de la phase de cémetation de minière à rendre l'atmosphère moins active, diminuer le potentiel carbone moyen aux environs de 0,6 à 0,8, réalisant ainsi un balayage moins important des pièces et en tolérant les entrées d'air dans les limites de sécurité de fonctionnement.We can therefore reduce the flow rate of carrier gas during the diffusion phase by a factor of 1.2 to 2 compared to the flow rate during the mining phase of rendering the atmosphere less active, decrease the average carbon potential around 0.6 to 0.8, thus achieving less sweeping of the parts and tolerating the ingress of air within the limits of operating safety.

L'atmosphère recherchée peut donc s'assimiler à une atmosphère dite de protection, neutre vis- à-vis de la surface des pièces (ni cémentation, ni décarburation).The desired atmosphere can therefore be assimilated to a so-called protective atmosphere, neutral vis-à-vis the surface of the parts (no carburizing or decarburization).

Selon une autre variante de réalisation de l'invention, on peut également faire varier la composition de l'atmosphère selon l'enseignement du brevet US 4.519.853, mais également selon l'enseignement du brevet US 4.306.918.According to another alternative embodiment of the invention, the composition of the atmosphere can also be varied according to the teaching of US Pat. No. 4,519,853, but also according to the teaching of US Patent 4,306,918.

De préférence, cependant, on choisira une atmosphère engendrée à partir de méthanol pulvérisé à l'aide d'azote. Dans la première phase du procédé, on utilisera généralement au moins 20 % d'azote et le complément de méthanol. En effet, on a constaté que pour un fonctionnement fiable du procédé selon l'invention, il était tout à fait approprié de pulvériser pneumatiquement le méthanol, la quantité minimale d'azote étant alors de 10 % mais de préférence 20 %. On évite ainsi les risques importants de suie dans le four pour des atmosphères ne contenant que du méthanol, comme décrit dans le brevet US 4.306.918, ainsi qu'un bouchage prématuré de l'orifice d'injection du méthanol. Une canne d'injection telle que décrite dans le brevet US 4.279.406 convient, par exemple pour cette opération. L'utilisation d'une atmosphère engendrée à l'aide de méthanol (ou tout autre alcool équivalent) permet de maintenir un ratio pCO/pH2 sensiblement constant. Dans la seconde phase du procédé, on utilisera de préférence un mélange comportant environ 70 % d'azote et 30 % de méthanol, le débit de gaz injecté dans le four au cours de la phase de cémentation étant environ 1,5 fois supérieur au débit de gaz injecté au cours de la phase de diffusion. Cependant, la dilution du méthanol par l'azote dans cette phase de diffusion peut varier assez sensiblement dans les limites décrites dans le brevet US 4.519.853.Preferably, however, an atmosphere generated from methanol sprayed with nitrogen will be chosen. In the first phase of the process, at least 20% nitrogen and the balance of methanol will generally be used. In fact, it has been found that for reliable operation of the process according to the invention, it was entirely appropriate to spray methanol pneumatically, the minimum amount of nitrogen then being 10% but preferably 20%. This avoids the significant risks of soot in the furnace for atmospheres containing only methanol, as described in US Pat. No. 4,306,918, as well as premature plugging of the methanol injection orifice. An injection rod as described in US Patent 4,279,406 is suitable, for example for this operation. The use of an atmosphere generated using methanol (or any other equivalent alcohol) makes it possible to maintain a substantially constant pCO / pH 2 ratio. In the second phase of the process, a mixture preferably comprising approximately 70% nitrogen and 30% methanol will be used, the flow rate of gas injected into the furnace during the carburizing phase being approximately 1.5 times greater than the flow rate of gas injected during the diffusion phase. However, the dilution of methanol with nitrogen in this diffusion phase can vary quite appreciably within the limits described in US Patent 4,519,853.

L'invention sera mieux comprise à l'aide des exemples de réalisation suivants, donnés à titre non limitatif, conjointement avec les figures qui représentent:

  • - les figures 1 et 2, des illustrations de l'art antérieur;
  • - la figure 3, une illustration du procédé selon l'invention.
The invention will be better understood with the aid of the following embodiments, given without limitation, together with the figures which represent:
  • - Figures 1 and 2, illustrations of the prior art;
  • - Figure 3, an illustration of the method according to the invention.

Exemple 1:Example 1:

Dans un four à charge à bac de trempe incorporé, on introduit une charge de 350 kg de pièce en acier de nuance 20 MC5. Le débit de gaz porteur de composition fixe est constant (8 m3/h) pendant toute la durée de la cémentation et de la diffusion. La température de cémentation T1 est de 920°C, celle de diffusion passant rapidement à la valeur T2 870° C, selon le profil de température représenté sur la figure 1. Les résultats obtenus sur l'ensemble des pièces de la charge sont les suivants:

  • . épaisseur cémentée à 550 HV1 = 0,95 à 1,05 mm
  • . aspect gris pale
  • . légère austénite résiduelle
Into a charge oven with incorporated quench tank, a load of 350 kg of steel piece of grade 20 MC5 is introduced. The flow rate of carrier gas of fixed composition is constant (8 m 3 / h) throughout the duration of the carburizing and the diffusion. The cementation temperature T1 is 920 ° C, that of diffusion rapidly passing to the value T2 870 ° C, according to the temperature profile shown in Figure 1. The results obtained on all the parts of the load are as follows :
  • . case-hardened thickness at 550 HV1 = 0.95 to 1.05 mm
  • . pale gray appearance
  • . slight residual austenite

Cet exemple représente l'art connu avec un débit de gaz porteur "conventionnel". La qualité de la charge est bonne.This example represents the known art with a "conventional" carrier gas flow rate. The quality of the load is good.

Exemple 2:Example 2:

Dans les mêmes conditions que précédemment (figure 2), mais sous un débit constant faible (limite de sécurité) de 5 m3/h de gaz porteur, on obtient les résultat suivants:

  • . épaisseur céméntée à 550 HV1 = 0,80 à 1,00 mm
  • . aspect gris foncé,
  • . dépôt de suie par endroits
Under the same conditions as above (Figure 2), but under a low constant flow (safety limit) of 5 m 3 / h of carrier gas, the following results are obtained:
  • . thickened at 550 HV1 = 0.80 to 1.00 mm
  • . dark gray appearance,
  • . deposits of soot in places

La qualité de la charge est médiocre:

  • l'épaisseur cémentée obtenue a diminué pour des durées et des témperatures identiques, l'hétérogénéité a nettement augmenté et l'aspect de surface est mauvais.
The quality of the load is poor:
  • the cemented thickness obtained has decreased for identical durations and temperatures, the heterogeneity has clearly increased and the surface appearance is poor.

Exemple 3:Example 3:

Dans les mêmes conditions que dans l'exemple 1 mais avec un débit de gaz porteur de 8 m3/h pendant la phase de cémentation ("débit conventionnel") et de 5 m3/h pendant la phase de diffusion (figure 3), on obtient les résultats suivants:

  • . épaisseur cémentée à 550 HV1 = 0,95 à 1,05 mm
  • - aspect gris clair
  • . pas d'austénite résiduelle observable
Under the same conditions as in Example 1 but with a carrier gas flow rate of 8 m 3 / h during the carburizing phase ("conventional flow") and 5 m 3 / h during the diffusion phase (Figure 3) , we obtain the following results:
  • . case-hardened thickness at 550 HV1 = 0.95 to 1.05 mm
  • - light gray appearance
  • . no observable residual austenite

La qualité de la charge est excellente, supérieure à celle de l'exemple 1.The quality of the filler is excellent, superior to that of Example 1.

D'une manière générale, l'exemple 3 montre qu'il est possible d'obtenir un traitement d'excellente qualité (équivalente ou supérieure à celle de l'exemple 1) tout en minimisant la consommation gazeuse totale.In general, Example 3 shows that it is possible to obtain a treatment of excellent quality (equivalent to or better than that of Example 1) while minimizing the total gas consumption.

Dans les trois exemples ci-dessus, l'atmosphère injectée au cours de la phase de cémentation comportait 80 % de méthanol et 20 % d'azote tandis que l'atmosphère injectée au cours de la phase de diffusion comportait environ 30 % de méthanol et 70 % d'azote, tandis que les potentiels carbones de ces atmosphères étaient maintenus dans les limites habituelles pour les phases de cémentation et de diffusion, mais identiques dans les trois exemples.In the three examples above, the atmosphere injected during the cementation phase included 80% methanol and 20% nitrogen while the atmosphere injected during the diffusion phase included about 30% methanol and 70% nitrogen, while the carbon potentials of these atmospheres were kept within the usual limits for the cementation and diffusion phases, but identical in the three examples.

Bien entendu, on pourra substituer au méthanol tous les corps bien connus (en particulier, les alcools) qui sont susceptibles d'engendrer aux températures habituelles de cémentation et de diffusion du monoxyde de carbone et de l'hydrogène.Of course, it is possible to substitute for methanol all the well-known bodies (in particular, alcohols) which are capable of generating at the usual carburizing and diffusion temperatures of carbon monoxide and hydrogen.

D'une manière connue en soi également, on pourra ajouter éventuellement de l'ammoniac auxdites atmosphères pour réaliser des traitements de nitro-carburation.In a manner also known per se, it is possible optionally to add ammonia to said atmospheres in order to carry out nitro-carburization treatments.

Claims (9)

1. Casehardening-diffusion process in a batch furnace, in which the furnace door is opened, a charge is introduced to the furnace previously brought to the casehardening temperature, the furnace door is closed, the charge is subjected to a first so-called casehardening stage during which the speed of carbon transfer from the atmosphere to the surface of the workpiece is preponderant relative to the speed of diffusion of the carbon from the surface of the workpiece towards the inside thereof, then to a second so-called diffusion stage during which the said diffusion speed becomes preponderant relative to the said transfer speed, the furnace temperature possibly being able to fall during this second stage, the charge possibly being cooled before opening the furnace door to allow its extraction and the introduction of another charge, a carrier gas, possibly incorporating added hydrocarbon, being fed into the furnace throughout the duration of the process, characterised in that the flow rate D1 of carrier gas during the casehardening stage is linked with the flow rate D2 of carrier gas during the diffusion stage by the relationship
1.2 D2 ≤ D1 ≤ 2 x D2,
the flow rate D2 being higher than or equal to the minimum safety threshold of the furnace in question.
2. Casehardening-diffusion process in a batch furnace according to claim 1, characterised in that D, is greater than or equal to 1.5 D2.
3. Casehardening-diffusion process in a batch furnace according to claim 1 or 2, characterised in that the flow rate of gas injected into the furnace from the opening to the closing of the door is equal to D1.
4. Casehardening-diffusion process in a batch furnace according to claim 1 or 2, characterised in that the flow rate of gas injected into the furnace from the opening to the closing of the door is equal to D2.
5. Casehardening-diffusion process in a batch furnace according to claim 1 or 2, characterised in that the flow rate of gas injected into the furnace from the opening to the closing of the door is equal to D3, exceeding D1.
6. Casehardening-diffusion process in a batch furnace according to claim 5, in which the casehardening takes place at a predetermined temperature T1, characterised in that the flow rate D3 of gas injected into the furnace remains higher than D, until the return to temperature TI.
7. Casehardening-diffusion process in a batch furnace according to one of the claims 5 or 6, characterised in that D, and D3 are linked by the relationship;
1.2xD1 ≤ D3 < 2 x D1
8. Casehardening-diffusion process in a batch furnace according to one of claims 1 to 7, characterised in that the composition of the atmosphere injected into the furnace is caused to vary during at least one of the flow rate variations.
9. Process according to one of the preceding claims, characterised in that the atmosphere injected into the furnace is produced from a mixture of nitrogen and methanol.
EP86401585A 1985-08-14 1986-07-16 Process for speedily and homogeneously carburizing a charge in a furnace Expired EP0213011B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86401585T ATE40415T1 (en) 1985-08-14 1986-07-16 PROCESS FOR FAST AND HOMOGENEOUS CARBURIZING OF WORKPIECES IN A FURNACE.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8512379A FR2586258B1 (en) 1985-08-14 1985-08-14 PROCESS FOR THE QUICK AND HOMOGENEOUS CEMENTING OF A LOAD IN AN OVEN
FR8512379 1985-08-14

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EP0213011A1 EP0213011A1 (en) 1987-03-04
EP0213011B1 true EP0213011B1 (en) 1989-01-25

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EP (1) EP0213011B1 (en)
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ZA (1) ZA865391B (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2586259B1 (en) * 1985-08-14 1987-10-30 Air Liquide QUICK CEMENTATION PROCESS IN A CONTINUOUS OVEN
WO1992005295A1 (en) * 1986-08-12 1992-04-02 Nobuo Nishioka Gas carburizing process and apparatus
DE3707003A1 (en) * 1987-03-05 1988-09-15 Ewald Schwing METHOD FOR CARBONING A STEEL WORKPIECE
DE3714283C1 (en) * 1987-04-29 1988-11-24 Ipsen Ind Internat Gmbh Process for gas carburizing steel
US5168200A (en) * 1989-12-18 1992-12-01 Payne Kenneth R Automatic powered flowmeter valves and control thereof
US6547888B1 (en) 2000-01-28 2003-04-15 Swagelok Company Modified low temperature case hardening processes
JP6773411B2 (en) * 2015-12-08 2020-10-21 日本エア・リキード合同会社 Carburizing system and manufacturing method of surface hardened steel
CN113957228A (en) * 2021-10-09 2022-01-21 上海丰东热处理工程有限公司 Heat treatment process for transmission motor shaft

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US26935A (en) * 1860-01-24 Attaching bonnets to sails
US2955062A (en) * 1952-02-27 1960-10-04 Midland Ross Corp Method for carburizing in a continuous furnace
US3356541A (en) * 1965-08-20 1967-12-05 Midland Ross Corp Carburizing method and apparatus
GB1471880A (en) * 1973-10-26 1977-04-27 Air Prod & Chem Furnace atmosphere for the heat treatment of ferrous metal
US3950192A (en) * 1974-10-30 1976-04-13 Monsanto Company Continuous carburizing method
US4049472A (en) * 1975-12-22 1977-09-20 Air Products And Chemicals, Inc. Atmosphere compositions and methods of using same for surface treating ferrous metals
US4145232A (en) * 1977-06-03 1979-03-20 Union Carbide Corporation Process for carburizing steel
CH632013A5 (en) * 1977-09-22 1982-09-15 Ipsen Ind Int Gmbh METHOD FOR GAS CARBONING WORKPIECE FROM STEEL.
US4175986A (en) * 1978-10-19 1979-11-27 Trw Inc. Inert carrier gas heat treating control process
US4306918A (en) * 1980-04-22 1981-12-22 Air Products And Chemicals, Inc. Process for carburizing ferrous metals
FR2527641A1 (en) * 1982-05-28 1983-12-02 Air Liquide PROCESS FOR THERMALLY TREATING METALLIC PARTS THROUGH CARBURATION
FR2586259B1 (en) * 1985-08-14 1987-10-30 Air Liquide QUICK CEMENTATION PROCESS IN A CONTINUOUS OVEN

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BR8603866A (en) 1987-03-24
JPS6240358A (en) 1987-02-21
JPS644583B2 (en) 1989-01-26
ES8707310A1 (en) 1987-07-16
ZA865391B (en) 1987-03-25
EP0213011A1 (en) 1987-03-04
DE3661942D1 (en) 1989-03-02
US4744839A (en) 1988-05-17
CA1281266C (en) 1991-03-12
ES556250A0 (en) 1987-07-16
FR2586258A1 (en) 1987-02-20
AU6045986A (en) 1987-02-19
FR2586258B1 (en) 1987-10-30
AU589202B2 (en) 1989-10-05
ATE40415T1 (en) 1989-02-15

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