WO2003000947A1 - Method for carburizing and carbonitriding steel by carbon oxide - Google Patents

Method for carburizing and carbonitriding steel by carbon oxide Download PDF

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Publication number
WO2003000947A1
WO2003000947A1 PCT/FR2002/002151 FR0202151W WO03000947A1 WO 2003000947 A1 WO2003000947 A1 WO 2003000947A1 FR 0202151 W FR0202151 W FR 0202151W WO 03000947 A1 WO03000947 A1 WO 03000947A1
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Prior art keywords
carbon
enrichment
steel
atomic hydrogen
ammonia
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PCT/FR2002/002151
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French (fr)
Inventor
Michel Gantois
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Serthel
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Priority to US10/481,737 priority Critical patent/US20040231753A1/en
Priority to EP02751277A priority patent/EP1409761A1/en
Publication of WO2003000947A1 publication Critical patent/WO2003000947A1/en

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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
    • C23C8/02—Pretreatment of the material to be coated
    • 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
    • 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 invention relates to the field of metallurgy and relates to a process for carburizing and carbonitriding steels with carbon monoxide ensuring an improved speed of transfer of carbon in steel and avoiding the surface oxidation of the cemented and carbonitrided layers. .
  • the object of the invention is to reduce the adsorbed oxygen layer in order on the one hand to obtain the maximum carbon transfer speed, by reducing the transfer resistance, and on the other hand to avoid any super-granular surface oxidation .
  • the invention therefore aims to make the initial transient phase as short as possible and to implement it on a steel surface where the adsorbed oxygen is removed by a powerfully reducing agent.
  • This objective is achieved, in accordance with the invention, by the introduction of atomic hydrogen into the atmosphere at the start of the treatment, before the carbon potential of the atmosphere has reached a very high value.
  • atomic hydrogen is obtained by the thermal decomposition of a gaseous molecule with at least transient formation of atomic hydrogen. This decomposition occurs at the temperature chosen for carbon enrichment and on condition that the other species resulting from the decomposition of the molecule do not react with steel.
  • atomic hydrogen is obtained by the decomposition of gas mixtures containing molecular hydrogen in an electric or electromagnetic field in the form of cold plasmas or hot plasmas obtained using various modes of excitation, arc, microwave, radio frequency for example and this in discharge or post discharge.
  • the steel parts are introduced into the furnace where they are heated to the carbon enrichment temperature. This is at least equal to 920 ° C.
  • the atmosphere of the furnace consists of nitrogen chemically inert with respect to the steel during this heating phase,
  • the fuel mixture carbon monoxide - hydrogen
  • the fuel mixture carbon monoxide - hydrogen
  • This concentration makes it possible to regulate the carbon potential of the atmosphere to a value equal to the saturated carbon concentration of the austenite corresponding to the chosen enrichment temperature, - at the end of the enrichment phase, we replace the furnace atmosphere with nitrogen.
  • the carbon flux transferred to the interface is then zero.
  • the temperature and the duration of this diffusion phase in the steel with zero transferred flow are chosen to obtain the desired surface carbon concentration profile.
  • This diffusion phase ends at the temperature chosen for quenching the parts.
  • This mixture is highly reducing at these temperatures. It makes it possible to avoid the formation of oxides during the short period of growth of the carbon potential at the time of the introduction of the CO - H2 mixture used for enrichment.
  • the processing of the invention makes it possible to control the transfer of material in a rigorous manner, and therefore to control and simulate in real time the profiles of concentration obtained.
  • each phase of the treatment corresponds to rigorous boundary conditions: during the heating the carbon flux is naked, during the enrichment phase the carbon transfer is at a constant surface concentration equal to the saturation concentration of the austenite , during the diffusion phase the carbon flux is zero.
  • the process of the invention has the following advantages: the carbon is transferred at the maximum speed, there is no surface oxidation, it allows rigorous control of the transfer of carbon by controlling and regulating the carbon potential of the atmosphere, it simulates and controls carbon concentration profiles at all times thanks to the control of interface boundary conditions for each phase of the treatment.
  • the analyzes show that there is no nitrogen introduced into the steel, the concentrations measured over the first 100 microns are less than 0.02% which is in accordance with thermodynamic forecasts.
  • a controlled flow of ammonia is introduced at a temperature below 880 ° C. during the diffusion phase with zero carbon flow so as to create a nitrogen concentration gradient.
  • This operation is carried out in accordance with the usual practices of carbonitriding according to the following operating mode:

Abstract

The method for enriching steel with carbon by carbon oxide comprises a step involving heating to a temperature of enrichment in a furnace in a gaseous phase, then an enrichment step involving the introduction of a gas containing carbon oxide. According to the invention, atomic hydrogen is formed in said gaseous phase prior to the enrichment phase, said atomic hydrogen being of a sufficient amount to suppress interface resistance to the transfer of carbon and to avoid surface oxidation of said steel.

Description

Procédé de cémentation et de carbonitruration des aciers par l'oxyde de carbone Process for carburizing and carbonitriding steels with carbon monoxide
L'invention se rapporte au domaine de la métallurgie et vise un procédé de cémentation et de carbonitruration des aciers par l'oxyde de carbone assurant une vitesse améliorée du transfert du carbone dans l'acier et évitant l'oxydation superficielle des couches cémentées et carbonitrurées.The invention relates to the field of metallurgy and relates to a process for carburizing and carbonitriding steels with carbon monoxide ensuring an improved speed of transfer of carbon in steel and avoiding the surface oxidation of the cemented and carbonitrided layers. .
La cémentation des aciers par une réaction gaz-solide utilisant l'oxyde de carbone est un procédé ancien dont les modalités de mise en œuvre sont bien connues, c'est actuellement le procédé le plus utilisé à l'échelle industrielle dans des fours à charge ou des fours continus fonctionnant à la pression atmosphérique avec des atmosphères gazeuses constituées principalement d'oxyde de carbone et d'hydrogène. Le pouvoir carburant potentiel de ces mélanges gazeux est défini par le potentiel carbone de l'atmosphère, grandeur qui caractérise l'état d'équilibre thermodynamique entre l'atmosphère et l'acier à la température de traitement. Ce potentiel carbone qui est une caractéristique fondamentale permettant d'assurer le contrôle de l'atmosphère vis-à-vis de sa capacité carburante, permet aussi le contrôle de réactions secondaires souvent indésirables telle que l'oxydation superficielle des couches cémentées ou carbonitrurées. En effet, le transfert du carbone entre l'atmosphère gazeuse et l'acier s'effectue à partir de la décomposition à l'interface gaz-solide de la molécule d'oxyde de carbone. Le carbone libéré par cette décomposition diffuse dans la solution solide austénitique en y créant un gradient de concentration en carbone.The case hardening of steels by a gas-solid reaction using carbon monoxide is an old process whose methods of implementation are well known, it is currently the process most used on an industrial scale in charge ovens or continuous ovens operating at atmospheric pressure with gaseous atmospheres mainly consisting of carbon monoxide and hydrogen. The potential fuel power of these gas mixtures is defined by the carbon potential of the atmosphere, a quantity which characterizes the state of thermodynamic equilibrium between the atmosphere and the steel at the treatment temperature. This carbon potential which is a fundamental characteristic making it possible to ensure the control of the atmosphere with respect to its fuel capacity, also allows the control of often undesirable secondary reactions such as the surface oxidation of the cemented or carbonitrided layers. In fact, the transfer of carbon between the gaseous atmosphere and the steel takes place from the decomposition at the gas-solid interface of the carbon monoxide molecule. The carbon released by this decomposition diffuses into the austenitic solid solution, creating a carbon concentration gradient there.
L'oxygène libéré de façon concomitante reste d'abord adsorbé à la surface de l'acier puis, selon les caractéristiques spécifiques de l'atmosphère et du réacteur de traitement (four) se combine, soit avec l'hydrogène moléculaire de l'atmosphère avec formation dans l'atmosphère de molécules d'eau, soit avec l'oxyde de carbone pour former des molécules de gaz carbonique, soit avec d'autres atomes d'oxygène pour foπner des molécules d'oxygène.The oxygen released concomitantly remains first adsorbed on the surface of the steel and then, depending on the specific characteristics of the atmosphere and the treatment reactor (furnace) combines, either with the molecular hydrogen in the atmosphere with the formation of water molecules in the atmosphere, either with carbon monoxide to form carbon dioxide molecules, or with other oxygen atoms to form oxygen molecules.
Toutes ces réactions ne sont pas instantanées. Il en résulte que l'oxygène libéré par la décomposition de l'oxyde de carbone n'est que partiellement éliminé de la surface et qu'il subsiste donc une couche d'oxygène adsorbé sur cette surface qui se comporte comme une résistance au transfert du carbone entre l'atmosphère et l'acier et qui, lorsque l'acier contient des éléments d'alliage ayant une forte affinité pour l'oxygène, tels que le chrome, le manganèse et le silicium, conduit à une oxydation superficielle inter-granulaire d'autant plus importante que le potentiel carbone est faible. Dans ce cas, la concentration en carbone de la surface est faible, et la pression partielle d'oxygène de l'atmosphère est élevéeAll of these reactions are not instantaneous. As a result, the oxygen released by the decomposition of carbon monoxide is only partially removed from the surface and there therefore remains a layer of adsorbed oxygen. on this surface which behaves as a resistance to the transfer of carbon between the atmosphere and the steel and which, when the steel contains alloying elements having a strong affinity for oxygen, such as chromium, manganese and silicon, leads to an inter-granular surface oxidation which is all the more important as the carbon potential is low. In this case, the carbon concentration of the surface is low, and the partial pressure of oxygen in the atmosphere is high
L'objet de l'invention est de réduire la couche d'oxygène adsorbée afin d'une part obtenir la vitesse de transfert du carbone maximale, par réduction de la résistance de transfert, et d'autre part éviter toute oxydation inter-granulaire superficielle.The object of the invention is to reduce the adsorbed oxygen layer in order on the one hand to obtain the maximum carbon transfer speed, by reducing the transfer resistance, and on the other hand to avoid any super-granular surface oxidation .
Les considérations développées précédemment montrent que l'enrichissement en carbone doit être conduit au potentiel carbone le plus élevé car la pression partielle d'oxygène de l'atmosphère est alors la plus faible et la concentration en carbone de la surface de l'acier la plus élevée.The considerations developed above show that carbon enrichment must be carried out at the highest carbon potential since the partial pressure of oxygen in the atmosphere is then the lowest and the carbon concentration of the steel surface the most high.
Cependant, il existe une phase initiale du traitement pendant laquelle le potentiel carbone de l'atmosphère est faible. La concentration superficielle en carbone de l'acier est limitée en début de traitement à la teneur en carbone de l'acier choisi (0,10 à 0,3% de carbone). C'est pendant cette phase initiale que la couche d'oxygène adsorbé s'établit et peut conduire à une oxydation de la surface et à une résistance de transfert pratiquement irréversibles.However, there is an initial phase of treatment during which the carbon potential of the atmosphere is low. The surface carbon concentration of the steel is limited at the start of treatment to the carbon content of the chosen steel (0.10 to 0.3% carbon). It is during this initial phase that the adsorbed oxygen layer is established and can lead to surface oxidation and practically irreversible transfer resistance.
Ce phénomène est caractéristique de tous les procédés de cémentation par l'oxyde de carbone utilisés traditionnellement.This phenomenon is characteristic of all the carbon monoxide cementation processes traditionally used.
L'invention a donc pour objectif de rendre la phase transitoire initiale la plus courte possible et de la mettre en œuvre sur une surface d'acier où l'oxygène adsorbé est éliminé par un agent puissamment réducteur.The invention therefore aims to make the initial transient phase as short as possible and to implement it on a steel surface where the adsorbed oxygen is removed by a powerfully reducing agent.
Cet objectif est réalisé, conformément à l'invention, par l'introduction d'hydrogène atomique dans l'atmosphère au début du traitement, avant que le potentiel carbone de l'atmosphère ait atteint une valeur très élevée.This objective is achieved, in accordance with the invention, by the introduction of atomic hydrogen into the atmosphere at the start of the treatment, before the carbon potential of the atmosphere has reached a very high value.
Selon un premier mode de réalisation, l'hydrogène atomique est obtenu par la décomposition thermique d'une molécule gazeuse avec formation au moins transitoire d'hydrogène atomique. Cette décomposition se produit à la température choisie pour l'enrichissement en carbone et à la condition que les autres espèces résultant de la décomposition de la molécule ne réagissent pas avec l'acier.According to a first embodiment, atomic hydrogen is obtained by the thermal decomposition of a gaseous molecule with at least transient formation of atomic hydrogen. This decomposition occurs at the temperature chosen for carbon enrichment and on condition that the other species resulting from the decomposition of the molecule do not react with steel.
Selon un second mode de réalisation, l'hydrogène atomique est obtenu par la décomposition de mélanges gazeux contenant de l'hydrogène moléculaire dans un champ électrique ou électromagnétique sous forme de plasmas froids ou de plasmas chauds obtenus à l'aide de divers modes d'excitation, arc, micro-onde, radio fréquence par exemple et ceci en décharge ou post décharge.According to a second embodiment, atomic hydrogen is obtained by the decomposition of gas mixtures containing molecular hydrogen in an electric or electromagnetic field in the form of cold plasmas or hot plasmas obtained using various modes of excitation, arc, microwave, radio frequency for example and this in discharge or post discharge.
On décrit ci-après un exemple de procédé conforme à l'invention dans le cas de la cémentation par l'oxyde de carbone à la pression atmosphérique :An example of a process according to the invention is described below in the case of carburizing with carbon monoxide at atmospheric pressure:
- on introduit les pièces en acier dans le four où elles sont chauffées jusqu'à la température d'enrichissement en carbone. Celle-ci est au moins égale à 920°C. L'atmosphère du four est constituée d'azote chimiquement inerte vis à vis de l'acier pendant cette phase de chauffage,- the steel parts are introduced into the furnace where they are heated to the carbon enrichment temperature. This is at least equal to 920 ° C. The atmosphere of the furnace consists of nitrogen chemically inert with respect to the steel during this heating phase,
- on introduit à partir de 920°C, un débit d'ammoniac correspondant à un taux de renouvellement de l'atmosphère d'environ 3 dans le four et ceci pendant une durée pouvant atteindre 30 minutes. On introduit l'ammoniac pendant que la température de la charge continue à croître jusqu'à atteindre la température d'enrichissement en carbone effectivement choisie. Elle est comprise entre 930 à 980°C,- Introducing from 920 ° C, a flow of ammonia corresponding to a rate of renewal of the atmosphere of about 3 in the oven and this for a period of up to 30 minutes. Ammonia is introduced while the temperature of the feed continues to increase until it reaches the actually chosen carbon enrichment temperature. It is between 930 to 980 ° C,
- lorsque la température est atteinte, on introduit le mélange carburant (oxyde de carbone - hydrogène) avec un débit suffisant pour que la concentration en oxyde de carbone du mélange gazeux atteigne 24% en quelques minutes (5 à 10 minutes). Cette concentration permet de réguler le potentiel carbone de l'atmosphère à une valeur égale à la concentration en carbone à saturation de l'austénite correspondant à la température d'enrichissement choisie, - à la fin de la phase d'enrichissement, on remplace l'atmosphère du four par de l'azote. Le flux de carbone transféré à l'interface est alors nul. La température et la durée de cette phase de diffusion dans l'acier à flux transféré nul sont choisies pour obtenir le profil de concentration en carbone superficiel souhaité.- when the temperature is reached, the fuel mixture (carbon monoxide - hydrogen) is introduced with a sufficient flow rate so that the carbon monoxide concentration of the gaseous mixture reaches 24% in a few minutes (5 to 10 minutes). This concentration makes it possible to regulate the carbon potential of the atmosphere to a value equal to the saturated carbon concentration of the austenite corresponding to the chosen enrichment temperature, - at the end of the enrichment phase, we replace the furnace atmosphere with nitrogen. The carbon flux transferred to the interface is then zero. The temperature and the duration of this diffusion phase in the steel with zero transferred flow are chosen to obtain the desired surface carbon concentration profile.
Cette phase de diffusion se termine à la température choisie pour la trempe des pièces.This diffusion phase ends at the temperature chosen for quenching the parts.
L'introduction d'ammoniac immédiatement avant le début de l'enrichissement en carbone permet de disposer d'une surface parfaitement désoxydée par les atomes d'hydrogène résultant de la décomposition de la molécule d'ammoniac à la surface de l'acier :The introduction of ammonia immediately before the start of carbon enrichment provides a perfectly surface deoxidized by hydrogen atoms resulting from the decomposition of the ammonia molecule on the steel surface:
NH3 =>" N° + 3H°. Cette réaction transitoire se poursuit avec la formation d'azote et d'hydrogène moléculaire conduisant à un mélange contenant 75% d'hydrogène et 25% d'azote.NH3 =>" N ° + 3H °. This transient reaction continues with the formation of nitrogen and molecular hydrogen leading to a mixture containing 75% hydrogen and 25% nitrogen.
2 N°=> N2 2 H°=> H2.2 N ° => N2 2 H ° => H2.
Ce mélange est fortement réducteur à ces températures. Il permet d'éviter la formation d'oxydes pendant la courte période de croissance du potentiel carbone au moment de l'introduction du mélange CO - H2 utilisé pour l'enrichissement.This mixture is highly reducing at these temperatures. It makes it possible to avoid the formation of oxides during the short period of growth of the carbon potential at the time of the introduction of the CO - H2 mixture used for enrichment.
L'absence d'oxygène adsorbé et de couche oxydée permet de supprimer la résistance inter faciale au transfert du carbone. Cette absence d'oxygène associée à une circulation efficace du mélange gazeux à la surface des pièces (on assure une agitation des gaz à l'intérieur du four), permet à la concentration superficielle en carbone de la surface d'atteindre la concentration correspondant au potentiel carbone d'enrichissement en moins de trois minutes après que celui-ci a été atteint par l'atmosphère.The absence of adsorbed oxygen and oxidized layer makes it possible to suppress the inter-facial resistance to the transfer of carbon. This absence of oxygen associated with an efficient circulation of the gaseous mixture on the surface of the parts (agitation of the gases is ensured inside the furnace), allows the surface carbon concentration of the surface to reach the concentration corresponding to the carbon enrichment potential in less than three minutes after it has been reached by the atmosphere.
Outre l'intérêt présenté par cette vitesse d'enrichissement maximum et par l'absence d'oxydation, le traitement de l'invention permet de contrôler le transfert de matière de façon rigoureuse, et donc de piloter et simuler en temps réel les profils de concentration obtenus. En effet, chaque phase du traitement correspond à des conditions limites rigoureuses : pendant le chauffage le flux de carbone est nu, pendant la phase d'enrichissement le transfert du carbone est à une concentration superficielle constante égale à la concentration à saturation de l'austénite, pendant la phase de diffusion le flux de carbone est nul.In addition to the advantage presented by this maximum enrichment speed and by the absence of oxidation, the processing of the invention makes it possible to control the transfer of material in a rigorous manner, and therefore to control and simulate in real time the profiles of concentration obtained. Indeed, each phase of the treatment corresponds to rigorous boundary conditions: during the heating the carbon flux is naked, during the enrichment phase the carbon transfer is at a constant surface concentration equal to the saturation concentration of the austenite , during the diffusion phase the carbon flux is zero.
En résumé le procédé de l'invention présente les avantages suivants : le carbone est transféré à la vitesse maximale, on ne constate pas d'oxydation superficielle, il permet un contrôle rigoureux du transfert du carbone par le pilotage et la régulation du potentiel carbone de l'atmosphère, il permet de simuler et de contrôler les profils de concentration en carbone à chaque instant grâce à la maîtrise des conditions limites d'interface pour chaque phase du traitement. Les analyses montrent qu'il n'y a pas d'azote introduit dans l'acier, les concentrations mesurées sur les 100 premiers microns sont inférieures à 0,02% ce qui est conforme aux prévisions thermodynamiques.In summary, the process of the invention has the following advantages: the carbon is transferred at the maximum speed, there is no surface oxidation, it allows rigorous control of the transfer of carbon by controlling and regulating the carbon potential of the atmosphere, it simulates and controls carbon concentration profiles at all times thanks to the control of interface boundary conditions for each phase of the treatment. The analyzes show that there is no nitrogen introduced into the steel, the concentrations measured over the first 100 microns are less than 0.02% which is in accordance with thermodynamic forecasts.
Conformément à des modes particuliers de réalisation, on introduit simultanément à l'ammoniac d'autres produits renforçant le caractère réducteur de l'atmosphère, des hydrocarbures, par exemple du méthane. Une telle addition permet un pré enrichissement de la surface en carbone avant l'introduction du mélange CO - H2. Enfin, toute source d'hydrogène atomique dans l'atmosphère avant enrichissement en carbone conduit aux phénomènes décrits.In accordance with particular embodiments, other products are added simultaneously to the ammonia which reinforce the reducing nature of the atmosphere, hydrocarbons, for example methane. Such an addition allows a pre-enrichment of the carbon surface before the introduction of the CO - H2 mixture. Finally, any source of atomic hydrogen in the atmosphere before carbon enrichment leads to the phenomena described.
Conformément à une autre caractéristique de l'invention, dans une application à la carbonitruration des aciers, on introduit un débit contrôlé d'ammoniac, à une température inférieure à 880°C pendant la phase de diffusion à flux de carbone nul de manière à créer un gradient de concentration en azote. Cette opération est effectuée conformément aux pratiques habituelles de la carbonitruration selon le mode opératoire suivant :According to another characteristic of the invention, in an application to the carbonitriding of steels, a controlled flow of ammonia is introduced at a temperature below 880 ° C. during the diffusion phase with zero carbon flow so as to create a nitrogen concentration gradient. This operation is carried out in accordance with the usual practices of carbonitriding according to the following operating mode:
- chauffage des pièces jusqu'à 920°C sous azote suivi d'introduction d'ammoniac, - enrichissement en carbone entre 930 et 980°C,- heating of rooms up to 920 ° C under nitrogen followed by introduction of ammonia, - carbon enrichment between 930 and 980 ° C,
- diffusion du carbone dans une atmosphère d'azote,- diffusion of carbon in a nitrogen atmosphere,
- diminution de la température jusque 880°C,- decrease in temperature to 880 ° C,
- maintien en température à 880°C avec introduction d'ammoniac,- temperature maintenance at 880 ° C with introduction of ammonia,
- trempe de l'acier. - hardening of steel.

Claims

REVENDICATIONS
1.- Procédé d'enrichissement en carbone des aciers par l'oxyde de carbone comportant une étape de chauffage dans un four en phase gazeuse jusqu'à la température d'enrichissement, puis une étape d'enrichissement par introduction d'un gaz contenant de l'oxyde de carbone, caractérisé par le fait que l'on forme de l'hydrogène atomique dans ladite phase gazeuse avant ladite étape d'enrichissement, en quantité suffisante pour supprimer la résistance d'interface au transfert du carbone et éviter l'oxydation superficielle de l'acier.1.- Process for the carbon enrichment of steels with carbon monoxide comprising a stage of heating in an oven in gas phase until the temperature of enrichment, then a stage of enrichment by introduction of a gas containing carbon monoxide, characterized in that atomic hydrogen is formed in said gas phase before said enrichment step, in an amount sufficient to suppress the interface resistance to carbon transfer and avoid surface oxidation of steel.
2.- Procédé selon la revendication 1, caractérisé par le fait que l'on introduit dans la dite phase gazeuse des composés chimiques dont la décomposition thermique conduit à la formation au moins transitoire d'hydrogène atomique.2.- Method according to claim 1, characterized in that one introduces into said gas phase chemical compounds whose thermal decomposition leads to the formation of at least transient atomic hydrogen.
3.- Procédé selon la revendication 2, caractérisé par le fait que l'on introduit de l'ammoniac3.- Method according to claim 2, characterized in that one introduces ammonia
4.- Procédé selon la revendication 3, caractérisé par le fait que l'on introduit simultanément à l'ammoniac un hydrocarbure, par exemple le méthane.4.- Method according to claim 3, characterized in that one simultaneously introduces ammonia a hydrocarbon, for example methane.
5.- Procédé selon les revendications 1 à 4, comportant une étape de carbonitruration, caractérisé par le fait- que l'on introduit un débit contrôlé d'ammoniac, à une température inférieure à 880°C pendant la phase de diffusion à flux de carbone nul de manière à créer un gradient de concentration en azote.5.- Method according to claims 1 to 4, comprising a carbonitriding step, characterized by the fact that a controlled flow of ammonia is introduced at a temperature below 880 ° C during the diffusion phase with flow of zero carbon so as to create a nitrogen concentration gradient.
6.- Procédé selon la revendication 1, caractérisé par le fait que l'on forme l'hydrogène atomique par voie physique sous forme de plasmas froids ou de plasmas chauds, en décharges ou en post décharges.6.- Method according to claim 1, characterized in that the atomic hydrogen is physically formed in the form of cold plasmas or hot plasmas, in discharges or in post discharges.
7.- Procédé selon l'une des revendications 1 à 5, caractérisé par le fait que l'on contrôle, en temps réel, les profils de concentration en carbone.7.- Method according to one of claims 1 to 5, characterized in that one controls, in real time, the carbon concentration profiles.
8.- Procédé selon l'une des revendications 1 à 6, caractérisé par le fait que l'on simule en temps réel les profils de concentration en carbone. 8.- Method according to one of claims 1 to 6, characterized in that the carbon concentration profiles are simulated in real time.
PCT/FR2002/002151 2001-06-25 2002-06-20 Method for carburizing and carbonitriding steel by carbon oxide WO2003000947A1 (en)

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US10/481,737 US20040231753A1 (en) 2001-06-25 2002-06-20 Method for carburizing and carbonitriding steel by carbon oxide
EP02751277A EP1409761A1 (en) 2001-06-25 2002-06-20 Method for carburizing and carbonitriding steel by carbon oxide

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FR01/08329 2001-06-25
FR0108329A FR2826376B1 (en) 2001-06-25 2001-06-25 CARBONITRURATION AND CARBONITRURATION PROCESS OF STEELS WITH CARBON OXIDE

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DE10254846B4 (en) * 2002-11-25 2011-06-16 Robert Bosch Gmbh Method for case-hardening components made of hot-work steels by means of vacuum carburizing
EP3168314A1 (en) * 2015-11-13 2017-05-17 Air Liquide Deutschland GmbH Method for heat treating metallic work pieces

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CH427073A (en) * 1964-06-16 1966-12-31 Berghaus Elektrophysik Anst Process for the treatment of workpieces under the action of an electric glow discharge at elevated temperatures
US5372655A (en) * 1991-12-04 1994-12-13 Leybold Durferrit Gmbh Method for the treatment of alloy steels and refractory metals
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GB2324539A (en) * 1997-04-26 1998-10-28 Daimler Benz Ag Aluminium nitride coating of cylinder running surface

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EP1409761A1 (en) 2004-04-21
US20040231753A1 (en) 2004-11-25
FR2826376B1 (en) 2003-09-26
FR2826376A1 (en) 2002-12-27

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