EP0089885A2 - Method of surface-hardening metallic parts - Google Patents

Method of surface-hardening metallic parts Download PDF

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Publication number
EP0089885A2
EP0089885A2 EP83400541A EP83400541A EP0089885A2 EP 0089885 A2 EP0089885 A2 EP 0089885A2 EP 83400541 A EP83400541 A EP 83400541A EP 83400541 A EP83400541 A EP 83400541A EP 0089885 A2 EP0089885 A2 EP 0089885A2
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EP
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Prior art keywords
parts
volume
gas
ammonia
gas mixture
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EP83400541A
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German (de)
French (fr)
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EP0089885A3 (en
EP0089885B1 (en
Inventor
Michel Madsac
Thierry Hiron
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Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Priority to AT83400541T priority Critical patent/ATE29154T1/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
    • C23C8/06—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
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding 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

  • nitriding or nitrocarburizing treatments in the gas phase are intended to improve the resistance to fatigue and seizure and to increase the resistance to wear and to corrosion of steels.
  • the nitriding atmospheres used at present consist either of gaseous ammonia or of gaseous ammonia diluted in nitrogen, or of gaseous ammonia, optionally diluted in nitrogen, in mixture with a compound capable of increasing the degree of dissociation of the amnoniac in contact with the part and therefore the kinetics of nitriding; this compound is, for example, an oxidizing compound such as oxygen, carbon dioxide, water vapor, or else a hydrocarbon.
  • a mixture of amino-gas and a carbon-bearing gas for example an endothemical gas (CO-H 2 -CO 2 - H 2 O-CH 4 -N 2 ), is used or a hydrocarbon; then there is nitrocarburization with the formation of carbonitrides ⁇ .
  • a carbon-bearing gas for example an endothemical gas (CO-H 2 -CO 2 - H 2 O-CH 4 -N 2 )
  • CO-H 2 -CO 2 - H 2 O-CH 4 -N 2 an endothemical gas
  • the subject of the invention is a method of surface hardening of metal parts, in particular of steel parts, by nitriding or nitrocarburizing which makes it possible to remedy the disadvantages mentioned above.
  • the process according to the invention consists in placing the parts in an oven and in maintaining them, at a temperature between 490 ° C and 750 ° C, in an atmosphere formed by the introduction into said oven of a gaseous mixture comprising in particular of the amimmor and a compound accelerating the catalytic dissociation of the armoniac in contact with said parts consisting of an oxidizing gas.
  • a gaseous mixture comprising in particular of the amimmor and a compound accelerating the catalytic dissociation of the armoniac in contact with said parts consisting of an oxidizing gas.
  • said oxidizing gas is nitrous oxide, said gaseous mixture containing approximately 0.1% to 10% by volume of said nitrous oxide.
  • said gaseous mixture can contain approximately 10% to 99% by volume of ammonia and at most 90% by volume of nitrogen.
  • said gaseous mixture also contains hydrogen in a concentration of at most 25% by volume.
  • said gaseous mixture also contains a carbon-bearing gas.
  • This carbon-bearing gas is constituted, for example, either by a hydrocarbon, such as methane or propane, in a concentration of at most 25% by volume, or by methanol in a concentration of at most 54% by volume , or by a mixture of these two compounds.
  • the treatment is carried out in an oven of the "well" type shown diagrammatically in the attached figure.
  • This oven (1) is made of refractory material (2) coated internally with a steel jacket (3); it is fitted with heating resistors (4) and a cover (5).
  • the steel part to be treated represented in the form of a block (6), is placed inside the oven in a basket (7) which rests on a grid (8) supported by a base (9) placed on the bottom of the oven (1).
  • a turbine (10) the function of which is to continuously stir the atmosphere of the oven, is placed at a distance above the basket (7).
  • the constituents of the treatment gas mixture are fed continuously into the oven (1), either from a mixer (11), or separately, by one or more conduits (12), provided with one or more valves (13), passing through the cover (5).
  • This gaseous mixture is discharged from the oven, also continuously, through the conduit (14).
  • the treated parts are then cooled by quenching in an oil bath (not shown in the figure).
  • steel parts of grade 35CD4 are treated, and on the other hand, parts of nitriding steel of grade 40CAD612, with a gas mixture consisting of 40% NH 3 , 3% N 2 0 and 57% N 2 at a temperature of 570 ° C.
  • the oven (1) is previously heated to a temperature of 570 ° C.
  • the gaseous mixture (40% NH 3 - 3% N 2 0 - 57% N 2 ) ' from the mixer (11) is then brought into the oven (1) and it is circulated there for a certain time.
  • the part to be treated is then placed in the basket (7) which is placed in the oven (1).
  • the NH 3 - N 2 0 - N 2 gas mixture is then continuously circulated in the oven at a flow rate of 0.25 m 3 / hour.
  • the rate of renewal of the furnace atmosphere is 5 times per hour.
  • Steel parts of grade 35CD4 are treated with a gas mixture consisting of 40% NH 3 , 3% N 2 0, 10% H 2 and 37% N 2 , respectively for three hours and four hours, under conditions identical to those of example 1 (same temperature, same flow rate of the gas mixture, same rate of renewal of the furnace atmosphere).
  • Steel parts of grade 35CD4 are treated with a gas mixture consisting of 40% NH 3 , 3% N 2 0, 5% C 3 H 8 and 5 2 % N 2 , p for four hours, under identical conditions. to those of Example 1 (temperature, flow rate, renewal rate).
  • a first treatment was carried out for three hours with a gaseous mixture consisting of 40% NH 3 , 10% CO 2 and 50% N 2 , on the one hand on steel parts 35CD4, on the other hand on steel parts. 40CAD612 steel.
  • the thickness and hardness measurements of the nitrided layers of the parts thus treated gave the following results:
  • a third treatment was carried out for three hours with a gas mixture consisting of 40% NH 3 , 24% H 2 , 12% CO, 24% N 2 , 1.7% CO 2 and 2% H 2 0, of a part on steel parts 35CD4, on the other hand on steel parts 40CAD612.
  • the thickness and hardness measurements of the nitrided layers of the parts thus treated gave the following results:

Abstract

In a surface hardening process for metal parts by nitriding or carbonitriding, the parts to be treated are placed in a furnace and maintained at a temperature of between 490 DEG C. and 750 DEG C., in a nitrogen bearing atmosphere, such atmosphere formed by introducing into the furnace a gaseous mixture comprising in particular ammonia and an oxidizing gas for accelerating the catalytic dissociation of ammonia in contact with said parts. The oxidizing gas is nitrous oxide and the gaseous mixture contains about 0.1% to 10% by volume of nitrous oxide. The invention is well suited for the surface hardening of steel parts.

Description

Comme on le sait, les traitements de nitruration ou de nitrocarburation en phase gazeuse sont destinés à améliorer la tenue à la fatigue et au grippage et à augmenter la résistance à l'usure et à la corrosion des aciers.As is known, nitriding or nitrocarburizing treatments in the gas phase are intended to improve the resistance to fatigue and seizure and to increase the resistance to wear and to corrosion of steels.

Ces traitements consistent à maintenir les pièces en acier dans une atmosphère contenant 50 % à 100 % d'ammniac gazeux à une température de 490°C à 750°C. Les pièces ainsi traitées sont ensuite refroidies par trempe en phase gazeuse ou liquide. Aux températures de traitement utilisées, l'ammoniac gazeux se décompose partiellement au contact des pièces en acier et l'azote naissant ainsi créé entre en solution solide et diffuse sur une certaine profondeur dans l'acier. Il se forme ainsi, à la surface de la pièce, une couche nitrurée qui est constituée d'une couche dite "couche de combinaison" ou "couche blanche" supportée par une couche dite "couche de diffusion". La structure et la composition de ces couches est la suivante :

  • - la couche blanche, située à l'extrême surface de la pièce, est constituée d'un mélange de nitrures ε (Fe2N - Fe3N) et de nitrures α ' (Fe4N).
  • - la couche de diffusion, sous-jacente à la couche blanche, est moins dure et plus épaisse que cette dernière ; dans cette couche de diffusion, l'azote est en solution solide d'insertion et forme des nitrures par combinaison avec certains des éléments constituant l'acier.
These treatments consist in maintaining the steel parts in an atmosphere containing 50% to 100% of gaseous ammonia at a temperature of 490 ° C to 750 ° C. The parts thus treated are then cooled by quenching in the gas or liquid phase. At the treatment temperatures used, the gaseous ammonia partially decomposes on contact with the steel parts and the nascent nitrogen thus created enters into solid solution and diffuses over a certain depth in the steel. There is thus formed, on the surface of the part, a nitrided layer which consists of a layer called "combination layer" or "white layer" supported by a layer called "diffusion layer". The structure and composition of these layers is as follows:
  • - The white layer, located at the extreme surface of the part, consists of a mixture of nitrides ε (Fe 2 N - Fe 3 N) and nitrides α '(Fe4N).
  • - the diffusion layer, underlying the white layer, is less hard and thicker than the latter; in this diffusion layer, the nitrogen is in solid insertion solution and forms nitrides by combination with some of the elements constituting the steel.

Les atmosphères de nitruration utilisées à l'heure actuelle sont constituées, soit d'ammoniac gazeux, soit d'ammoniac gazeux dilué dans de l'azote, soit d'ammoniac gazeux, le cas échéant dilué dans de l'azote, en mélange avec un composé susceptible d'augmenter le degré de dissociation de l'amnoniac au contact de la pièce et donc la cinétique de nitruration ; ce composé est, par exemple, un composé oxydant tel que l'oxygène, le gaz carbonique, la vapeur d'eau, ou bien un hydrocarbure. Selon certains procédés, on utilise un mélange d'amro- niac gazeux et d'un gaz porteur de carbone, par exemple un gaz endo- thezmique (CO-H2-CO2 - H2O-CH4-N2) ou un hydrocarbure ; il y a alors nitrocarburation avec formation de carbonitrures ε. Dans tous les cas, selon les procédés utilisés jusqu'à présent, il est préférable d'avoir une concentration initiale d'ammoniac dans l'atmosphère utilisée d'au moins 50 %.The nitriding atmospheres used at present consist either of gaseous ammonia or of gaseous ammonia diluted in nitrogen, or of gaseous ammonia, optionally diluted in nitrogen, in mixture with a compound capable of increasing the degree of dissociation of the amnoniac in contact with the part and therefore the kinetics of nitriding; this compound is, for example, an oxidizing compound such as oxygen, carbon dioxide, water vapor, or else a hydrocarbon. According to certain methods, a mixture of amino-gas and a carbon-bearing gas, for example an endothemical gas (CO-H 2 -CO 2 - H 2 O-CH 4 -N 2 ), is used or a hydrocarbon; then there is nitrocarburization with the formation of carbonitrides ε. In all cases, according to the methods used until now, it is preferable to have an initial concentration of ammonia in the atmosphere used of at least 50%.

Parmi les procédés de nitruration utilisant de l'ammoniac en mélange avec un composé oxydant, mis en oeuvre jusqu'à présent, on peut citer plus particulièrement le procédé décrit dans le brevet anglais n° 2.049.740. Ce procédé consiste à maintenir des pièces en acier, à une température de 550°C à 600°C, dans une atmosphère gazeuse constituée d'au moins 50 % en volume d'ammoniac, de gaz carbonique et d'azote (par exemple 70 % de NH3, 7 % de CO2 et 23 % de N2; pendant une durée de 12 à 20 heures.Among the nitriding processes using ammonia in admixture with an oxidizing compound, used up to now, there may be mentioned more particularly the process described in English Patent No. 2,049,740. This process consists in maintaining steel parts, at a temperature of 550 ° C to 600 ° C, in a gas atmosphere consisting of at least 50% by volume of ammonia, carbon dioxide and nitrogen (for example 70 % NH 3 , 7% CO 2 and 23% N 2 ; for a period of 12 to 20 hours.

Tous ces procédés permettent d'obtenir un durcissaient superficiel des pièces traitées mais présentent toutefois certains inconvénients relatifs à la couche blanche. En effet :

  • - la couche blanche se développe de façon hétérogène et présente don une épaisseur inégale sur toute la surface de la pièce. la couche blanche est fragile et peu adhérente du fait qu'elle es constituée d'un mélange intime des deux pièces ε (Fe2N - Fe3N) et α' (Fe4N).
  • - la couche blanche se présente sous la forme d'une zone compacte recouverte d'une zone poreuse, ce qui dans certains cas peut présenter quelques inconvénients. Or, à partir d'une certaine durée traitement, la zone compacte atteint une épaisseur maximale limi (20µm) et, seule, la zone poreuse se développe.
  • - le temps d'incubation nécessaire à la nucléation des nitrures est assez long et la formation de la couche blanche exige donc un cer tain temps.
All these methods make it possible to obtain a surface hardening of the treated parts but nevertheless have certain drawbacks relating to the white layer. Indeed :
  • - the white layer develops in a heterogeneous way and presents an uneven thickness over the entire surface of the room. the white layer is fragile and not very adherent because it consists of an intimate mixture of the two parts ε (Fe 2 N - Fe 3 N) and α '(Fe 4 N).
  • - The white layer is in the form of a compact area covered with a porous area, which in some cases can have some drawbacks. However, from a certain treatment duration, the compact zone reaches a limited maximum thickness (20 μm) and, alone, the porous zone develops.
  • - the incubation time necessary for the nucleation of nitrides is quite long and the formation of the white layer therefore requires a certain time.

L'invention a pour objet un procédé de durcissement super ficiel de pièces métalliques, notanment de pièces en acier, par nitruration ou nitrocarburation qui permet de remédier aux inconvénie rappelés ci-dessus.The subject of the invention is a method of surface hardening of metal parts, in particular of steel parts, by nitriding or nitrocarburizing which makes it possible to remedy the disadvantages mentioned above.

Le procédé conforme à l'invention consiste à placer lesdj pièces dans un four et à les maintenir, à une température comprise entre 490°C et 750°C, dans une atmosphère formée par introduction dans ledit four d'un mélange gazeux comprenant notamment de l'aimmor et un composé accélérateur de la dissociation catalytique de l'armo- niac au contact desdites pièces constitué par un gaz oxydant. Ce procédé se caractérise en ce que ledit gaz oxydant est du protoxyde d'azote, ledit mélange gazeux contenant environ 0,1 % à 10 % en volume dudit protoxyde d'azote.The process according to the invention consists in placing the parts in an oven and in maintaining them, at a temperature between 490 ° C and 750 ° C, in an atmosphere formed by the introduction into said oven of a gaseous mixture comprising in particular of the amimmor and a compound accelerating the catalytic dissociation of the armoniac in contact with said parts consisting of an oxidizing gas. This process is characterized in that said oxidizing gas is nitrous oxide, said gaseous mixture containing approximately 0.1% to 10% by volume of said nitrous oxide.

Selon une caractéristique de l'invention, ledit mélange gazeux peut contenir environ 10 % à 99 % en volume d' ammoniac et au plus 90 % en volume d'azote.According to a characteristic of the invention, said gaseous mixture can contain approximately 10% to 99% by volume of ammonia and at most 90% by volume of nitrogen.

Selon une variante de l'invention, ledit mélange gazeux contient en outre de l'hydrogène dans une concentration d'au plus 25 % en volume.According to a variant of the invention, said gaseous mixture also contains hydrogen in a concentration of at most 25% by volume.

Selon une autre caractéristique de l'invention, dans le cas d'une nitrocarburation, ledit mélange gazeux contient en outre un gaz porteur de carbone. Ce gaz porteur de carbone est constitué par exemple, soit par un hydrocarbure, tel que du méthane ou du propane, dans une concentration d'au plus 25 % en volume, soit par du méthanol dans une concentration d'au plus 54 % en volume, soit par un mélange de ces deux composés.According to another characteristic of the invention, in the case of nitrocarburization, said gaseous mixture also contains a carbon-bearing gas. This carbon-bearing gas is constituted, for example, either by a hydrocarbon, such as methane or propane, in a concentration of at most 25% by volume, or by methanol in a concentration of at most 54% by volume , or by a mixture of these two compounds.

A partir de 400°C, le protoxyde d'azote N20 se décompose catalytiquement facilement, libérant ainsi de l'oxygène sous forme atomique. Cet oxygène actif favorise la dissociation de l'ammoniac au contact de la pièce à traiter et permet donc une nitruration rapide et efficace de ladite pièce. Ainsi, l'utilisation d'un mélange gazeux contenant du protoxyde d'azote conforme à ..l'invention permet d'obtenir, du point de vue de la nitruration, des résultats nettement améliorés par rapport à l'utilisation de composés oxydants classiques tel que O2, C02 ou H20. En effet :

  • - la couche blanche formée présente une épaisseur constante sur toute la surface de la pièce à traiter.
  • - la couche blanche n'est en générale constituée que de la phase ε (Fe2N - Fe3N), et est donc plus résistante. Si, parfois, pour certaines durées de traitement et teneurs en ammoniac de l'atmosphère utilisée, la phase Y' (Fe4N) apparaît, cette dernière ne se mélange pas à la phase ε mais se présente conme une zone mince prise en sandwich entre la zone ε et la couche de diffusion ; dans ces conditions, la présence de la phase α' n'affecte pas la résistance de la couche nitrurée.
  • - la zone poreuse de la couche blanche est extrêmement mince, et peut même être inexistante dans le cas de traitements de faible durée.
  • - du fait que les cinétiques de réaction sont augmentées par rapport à celles des traitements classiques, le temps d'incubation nécessaire pour la nucléation des nitrures est plus court ; ceci permet, si on le désire, d'une part de pouvoir diminuer la concentration initiale du mélange gazeux en ammoniac jusqu'à 10 %, d'autre part de raccourcir la durée du traitement, et également de diminuer le débit et le taux de renouvellement de l'atmosphère dans le four de traitement.
From 400 ° C, nitrous oxide N 2 0 decomposes catalytically easily, thereby releasing oxygen in atomic form. This active oxygen promotes the dissociation of ammonia on contact with the part to be treated and therefore allows rapid and effective nitriding of said part. Thus, the use of a gas mixture containing nitrous oxide in accordance with .. the invention makes it possible to obtain, from the point of view of nitriding, markedly improved results compared to the use of conventional oxidizing compounds. such as O 2 , C0 2 or H 2 0. Indeed:
  • - The white layer formed has a constant thickness over the entire surface of the part to be treated.
  • - The white layer generally consists only of the ε phase (Fe 2 N - Fe 3 N), and is therefore more resistant. If, sometimes, for certain treatment times and ammonia contents of the atmosphere used, the Y 'phase (Fe 4 N) appears, the latter does not mix with the ε phase but occurs as a thin sandwiched area between the zone ε and the diffusion layer; under these conditions, the presence of the α 'phase does not affect the resistance of the nitrided layer.
  • - the porous zone of the white layer is extremely thin, and may even be nonexistent in the case of treatments of short duration.
  • - the fact that the reaction kinetics are increased compared to those of conventional treatments, the incubation time necessary for the nucleation of nitrides is shorter; this allows, if desired, on the one hand to be able to decrease the initial concentration of the gaseous mixture of ammonia up to 10%, on the other hand to shorten the duration of the treatment, and also to decrease the flow rate and the rate of renewal of the atmosphere in the treatment furnace.

Les caractéristiques et avantages de l'invention apparaîtront dans la description qui suit d'exemples de réalisation, donnés à titre non limitatif, du procédé de l'invention.The characteristics and advantages of the invention will appear in the description which follows of embodiments, given without limitation, of the process of the invention.

Dans tous les exemples décrits ci-après, le traitement est effectué dans un four du type "puits" représenté schématiquement sur la figure jointe. Ce four (1) est en matériau réfractaire (2) revêtu intérieurement d'un chemisage en acier (3) ; il est muni de résistances chauffantes (4) et d'un couvercle (5). La pièce en acier à traiter, représentée sous la forme d'un bloc (6), est placée à l'intérieur du four dans un panier (7) qui repose sur une grille (8) supportée par un socle (9) placé sur le fond du four (1). Une turbine (10), dont la fonction est de brasser en permanence l'atmosphère du four, est placée à distance au-dessus du panier (7). Les constituants du mélange gazeux de traitement sont amenés en continu dans le four (1), soit d'un mélangeur (11), soit séparément, par un ou des conduits (12) , munis d'une ou de vannes (13), traversant le couvercle (5). Ce mélange gazeux est évacué du four, également en continu, par le conduit (14). Les pièces traitées sont ensuite refroidies par trempe dans un bain d'huile (non représenté sur la figure).In all the examples described below, the treatment is carried out in an oven of the "well" type shown diagrammatically in the attached figure. This oven (1) is made of refractory material (2) coated internally with a steel jacket (3); it is fitted with heating resistors (4) and a cover (5). The steel part to be treated, represented in the form of a block (6), is placed inside the oven in a basket (7) which rests on a grid (8) supported by a base (9) placed on the bottom of the oven (1). A turbine (10), the function of which is to continuously stir the atmosphere of the oven, is placed at a distance above the basket (7). The constituents of the treatment gas mixture are fed continuously into the oven (1), either from a mixer (11), or separately, by one or more conduits (12), provided with one or more valves (13), passing through the cover (5). This gaseous mixture is discharged from the oven, also continuously, through the conduit (14). The treated parts are then cooled by quenching in an oil bath (not shown in the figure).

Le même traitement a également été effectué dans un four du type "batch" avec un bain d'huile incorporé, comportant un sas entrée- sortie d'amenée des pièces dans l'enceinte de traitement, sas muni d'un bac de trempe à l'huile.The same treatment was also carried out in an oven of the "batch" type with an incorporated oil bath, comprising an airlock entry-exit for bringing the parts into the treatment enclosure, airlock provided with a quenching tank at oil.

Bien entendu, on effectue une purge préalable du four par de l'azote gazeux avant chaque changement d'atmosphère.Of course, a preliminary purge of the oven is carried out with nitrogen gas before each change of atmosphere.

Exemple 1.Example 1.

On traite, d'une part des pièces en acier de nuance 35CD4, et d'autre part, des pièces en acier de nitruration de nuance 40CAD612, avec un mélange gazeux constitué de 40 % NH3, 3 % N20 et 57 % N2 à une température de 570°C.On the one hand, steel parts of grade 35CD4 are treated, and on the other hand, parts of nitriding steel of grade 40CAD612, with a gas mixture consisting of 40% NH 3 , 3% N 2 0 and 57% N 2 at a temperature of 570 ° C.

De façon plus précise, on chauffe préalablement le four (1) à une température de 570°C. On amène alors le mélange gazeux (40 % NH3 - 3 % N20 - 57 % N2)' provenant du mélangeur (11) dans le four (1) et on l'y fait circuler un certain temps. On place ensuite la pièce à traiter dans le panier (7) que l'on met dans le four (1). On fait alors circuler en continu le mélange gazeux NH3 - N20 - N2 dans le four à un débit de 0,25 m3/heure. Le taux de renouvellement de l'atmosphère du four est de 5 fois par heure.More specifically, the oven (1) is previously heated to a temperature of 570 ° C. The gaseous mixture (40% NH 3 - 3% N 2 0 - 57% N 2 ) ' from the mixer (11) is then brought into the oven (1) and it is circulated there for a certain time. The part to be treated is then placed in the basket (7) which is placed in the oven (1). The NH 3 - N 2 0 - N 2 gas mixture is then continuously circulated in the oven at a flow rate of 0.25 m 3 / hour. The rate of renewal of the furnace atmosphere is 5 times per hour.

On effectue ce traitement :

  • - d'une part, sur des pièces d'acier 35CD4, respectivement pendant deux heures, trois heures et quatre heures,
  • - d'autre part, sur des pièces d'acier 40CAD612, respectivement pendant deux heures, trois heures et quatre heures.
We perform this treatment:
  • - on the one hand, on pieces of steel 35CD4, respectively for two hours, three hours and four hours,
  • - on the other hand, on pieces of steel 40CAD612, respectively for two hours, three hours and four hours.

Après trempe des pièces ainsi traitées dans un bain d'huile, on effectue les mesures d'épaisseur et de dureté des couches nitrurées. Les résultats obtenus sont donnés dans le tableau ci-après :

Figure imgb0001
After soaking the parts thus treated in an oil bath, the thickness and hardness measurements of the nitrided layers are carried out. The results obtained are given in the table below:
Figure imgb0001

Exemple 2.Example 2.

On traite des pièces en acier de nuance 35CD4 avec un mélange gazeux constitué de 40 % NH3, 3 % N20, 10 % H2 et 37 % N2, respectivement pendant trois heures et quatre heures, dans des conditions identiques à celles de l'exemple 1 (même température, même débit du mélange gazeux, même taux de renouvellement de l'atmosphère du four).Steel parts of grade 35CD4 are treated with a gas mixture consisting of 40% NH 3 , 3% N 2 0, 10% H 2 and 37% N 2 , respectively for three hours and four hours, under conditions identical to those of example 1 (same temperature, same flow rate of the gas mixture, same rate of renewal of the furnace atmosphere).

Après trempe des pièces ainsi traitées dans un bain d'huile, on effectue les mesures d'épaisseur et de dureté des couches nitrurées. Les résultats obtenus sont donnés dans le tableau ci-après :

Figure imgb0002
After soaking the parts thus treated in an oil bath, the thickness and hardness measurements of the nitrided layers are carried out. The results obtained are given in the table below:
Figure imgb0002

Exemple 3.Example 3.

On traite des pièces en acier de nuance 35CD4 avec un mélange gazeux constitué de 40 % NH3, 3 % N20, 5 % C3H8 et 52 % N2, pen- dant quatre heures, dans des conditions identiques à celles de l'exemple 1 (tenpérature, débit, taux de renouvellement).Steel parts of grade 35CD4 are treated with a gas mixture consisting of 40% NH 3 , 3% N 2 0, 5% C 3 H 8 and 5 2 % N 2 , p for four hours, under identical conditions. to those of Example 1 (temperature, flow rate, renewal rate).

Après trempe des pièces ainsi traitées dans un bain d'huile, on effectue les mesures d'épaisseur et de dureté des couches nitro- carburées. Les résultats obtenus sont donnés dans le tableau ci-après :

Figure imgb0003
After soaking the parts thus treated in an oil bath, the thickness and hardness measurements of the nitro-carburetted layers are carried out. The results obtained are given in the table below:
Figure imgb0003

Exemple 4.Example 4.

On traite, d'une part des pièces en acier de nuance 35CD4, d'autre part, des pièces en acier de nuance 40CAD612, avec un mélange gazeux constitué de 40 % NH3, 3 % N20, 11 % CH3OH et 46 % N2, pendant deux heures et demie, dans des conditions indentiques à celles de l'exemple 1 (température, débit, taux de renouvellement).On the one hand, we process steel parts of grade 35CD4, on the other hand, steel parts of grade 40CAD612, with a gas mixture consisting of 40% NH 3 , 3% N 2 0, 11% CH 3 OH and 46% N 2 , for two and a half hours, under conditions identical to those of Example 1 (temperature, flow rate, renewal rate).

Après trempe des pièces ainsi traitées dans un bain d'huile, on effectue les mesures d'épaisseur et de dureté des couches nitro- carburées. Les résultats obtenus sont donnés dans le tableau ci-après :

Figure imgb0004
After soaking the parts thus treated in an oil bath, the thickness and hardness measurements of the nitro-carburetted layers are carried out. The results obtained are given in the table below:
Figure imgb0004

A titre de comparaison, on a effectué trois traitements de nitruration et de nitrocarburation, à l'aide d'atmosphères gazeuses classiques dans lesquelles le composé oxydant est du gaz carbonique, sur des pièces en acier identiques et dans les mêmes conditions que celles des exemples de l'invention décrits ci-dessus ( température 570°C ; débit : 0,25 m3/heure ; taux de renouvellement de l'atmosphère du four : 5 fois par heure).For comparison, three nitriding and nitrocarburizing treatments were carried out, using conventional gas atmospheres in which the oxidizing compound is carbon dioxide, on identical steel parts and under the same conditions as those of the examples. of the invention described above (temperature 570 ° C; flow rate: 0.25 m 3 / hour; renewal rate of the furnace atmosphere: 5 times per hour).

Traitement I. (comparaison nitruration)Treatment I. (nitriding comparison)

Un premier traitement a été effectué pendant trois heures avec un mélange gazeux constitué de 40 % NH3, 10 % CO2 et 50 % N2, d'une part sur des pièces d'acier 35CD4, d'autre part sur des pièces d'acier 40CAD612. Les mesures d'épaisseur et de dureté des couches nitrurées des pièces ainsi traitées ont donné les résultats suivants :

Figure imgb0005
A first treatment was carried out for three hours with a gaseous mixture consisting of 40% NH 3 , 10% CO 2 and 50% N 2 , on the one hand on steel parts 35CD4, on the other hand on steel parts. 40CAD612 steel. The thickness and hardness measurements of the nitrided layers of the parts thus treated gave the following results:
Figure imgb0005

Traitement II. (comparaison nitrocarburation)Treatment II. (nitrocarburization comparison)

Un deuxième traitement a été effectué pendant quatre heures avec un mélange gazeux constitué de 50 % NH3, 5 % CO2, 15 % CH4 et 30 % N2 sur des pièces d'acier 35CD4. Les mesures d'épaisseur et de lureté des couches nitrurées des pièces ainsi traitées ont donné les résultats suivants :

Figure imgb0006
A second treatment was carried out for four hours with a gas mixture consisting of 50% NH 3 , 5% CO 2 , 15% CH 4 and 30% N 2 on steel parts 35CD4. The thickness and luster measurements of the nitrided layers of the parts thus treated gave the following results:
Figure imgb0006

Traitement III. (comparaison nitrocarburation)Treatment III. (nitrocarburization comparison)

Un troisième traitement a été effectué pendant trois heures avec un mélange gazeux constitué de 40 % NH3, 24 % H2, 12 % CO, 24 % N2, 1,7 % CO2 et 2 % H20, d'une part sur des pièces d'acier 35CD4, d'autre part sur des pièces d'acier 40CAD612. Les mesures d'épaisseur et de dureté des couches nitrurées des pièces ainsi traitées ont donné les résultats suivants :

Figure imgb0007
A third treatment was carried out for three hours with a gas mixture consisting of 40% NH 3 , 24% H 2 , 12% CO, 24% N 2 , 1.7% CO 2 and 2% H 2 0, of a part on steel parts 35CD4, on the other hand on steel parts 40CAD612. The thickness and hardness measurements of the nitrided layers of the parts thus treated gave the following results:
Figure imgb0007

Comme on le voit, grâce au procédé de l'invention, on obtient des couches nitrurées plus épaisses et une couche blanche beaucoup plus dure que par les traitements classiques.As can be seen, thanks to the process of the invention, thicker nitrided layers and a much harder white layer are obtained than by conventional treatments.

Claims (9)

1. - Procédé de durcissement superficiel de pièces métalliques, notanment de pièces en acier, par nitruration selon lequel on place lesdites pièces dans un four et on les maintient, à une température comprise entre 490°C et 750°C, dans une atmosphère formée par introduction dans ledit four d'un mélange gazeux comprenant notamment de l'amroniac et un composé accélérateur de la dissociation catalytique de l'ammoniac au contact desdites pièces constitué par un gaz oxydant, caractérisé en ce que ledit gaz oxydant est du protoxyde d'azote, ledit mélange gazeux contenant environ 0,1 % à 10 % en volume dudit protoxyde d'azote.1. - Method of surface hardening of metal parts, in particular of steel parts, by nitriding according to which said parts are placed in an oven and kept at a temperature between 490 ° C and 750 ° C, in a formed atmosphere by introducing into said furnace a gaseous mixture comprising in particular ammonia and a compound accelerating the catalytic dissociation of ammonia in contact with said parts consisting of an oxidizing gas, characterized in that said oxidizing gas is protoxide nitrogen, said gas mixture containing about 0.1% to 10% by volume of said nitrous oxide. 2. - Procédé selon la revendication 1, caractérisé en ce que ledit mélange gazeux oontient environ 10 % à 99 % en volume d'ammoniac.2. - Method according to claim 1, characterized in that said gas mixture oontient about 10% to 99% by volume of ammonia. 3. - Procédé selon l'une des revendications 1 ou 2, caractérisé en ce que ledit mélange gazeux contient au plus 90 % en volume d'azote.3. - Method according to one of claims 1 or 2, characterized in that said gas mixture contains at most 90% by volume of nitrogen. 4. - Procédé selon l'une des revendications 1 à 3, caractérisé en ce que ledit mélange gazeux contient au plus 25 % en volume d'hydrogène.4. - Method according to one of claims 1 to 3, characterized in that said gas mixture contains at most 25% by volume of hydrogen. 5. - Procédé selon l'une des revendications 1 à 4, caractérisé en ce que, dans le cas d'une nitrocarburation, ledit mélange gazeux contient en outre un gaz porteur de carbone.5. - Method according to one of claims 1 to 4, characterized in that, in the case of a nitrocarburization, said gaseous mixture further contains a carbon carrier gas. 6. - Procédé selon la revendication 5, caractérisé en ce que ledit mélange gazeux contient au plus 25 % en volume d'un hydrocarbure tel que du méthane ou du propane.6. - Method according to claim 5, characterized in that said gas mixture contains at most 25% by volume of a hydrocarbon such as methane or propane. 7. - Procédé selon l'une des revendications 5 ou 6, caractérisé en ce que ledit mélange gazeux contient au plus 54 % en volume de méthanol.7. - Method according to one of claims 5 or 6, characterized in that said gas mixture contains at most 54% by volume of methanol. 8. - Procédé selon l'une des revendications 1 à 7, caractérisé en ce que l'on renouvelle l'atmosphère du four au moins 2 à 10 fois par heure.8. - Method according to one of claims 1 to 7, characterized in that the atmosphere of the oven is renewed at least 2 to 10 times per hour. 9. - Procédé selon l'une des revendications 1 à 8, caractérisé en ce que l'on maintient lesdites pièces dans ladite atmosphère pendant au moins une heure.9. - Method according to one of claims 1 to 8, characterized in that said parts are kept in said atmosphere for at least one hour.
EP83400541A 1982-03-23 1983-03-16 Method of surface-hardening metallic parts Expired EP0089885B1 (en)

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WO1995029269A1 (en) * 1994-04-22 1995-11-02 Innovatique S.A. Method of low pressure nitriding a metal workpiece and oven for carrying out said method
DE10003526A1 (en) * 2000-01-27 2001-08-09 Messer Griesheim Gmbh Frankfur Process for the carbonitriding of high-carbon and high-alloy steels
FR2999609A1 (en) * 2012-12-13 2014-06-20 Peugeot Citroen Automobiles Sa Thermochemically treating steel part i.e. gear train that is used in gear box, comprises performing first thermochemical enrichment process in steel with carbon and a second thermochemical enrichment process in steel with nitrogen

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