EP0067098A1 - Method of ionitriding a steel article which has been plastically deformed in advance - Google Patents

Method of ionitriding a steel article which has been plastically deformed in advance Download PDF

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Publication number
EP0067098A1
EP0067098A1 EP82400928A EP82400928A EP0067098A1 EP 0067098 A1 EP0067098 A1 EP 0067098A1 EP 82400928 A EP82400928 A EP 82400928A EP 82400928 A EP82400928 A EP 82400928A EP 0067098 A1 EP0067098 A1 EP 0067098A1
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Prior art keywords
nitrogen
pascal
sequence
hours
temperature
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German (de)
French (fr)
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EP0067098B1 (en
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Robert Leveque
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Creusot Loire SA
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Creusot Loire SA
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/02—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
    • C23C8/36—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 using ionised gases, e.g. ionitriding
    • C23C8/38—Treatment of ferrous surfaces

Definitions

  • the present invention relates to ion nitriding of steels.
  • the combination layer because of the appearance of cracks at the limit of the two categories of nitrides, and the rapid spalling of the most superficial compounds
  • the diffusion layer because of carbonitride precipitation, poorly resistant to the mechanical and thermal stresses to which the two nitrided layers are subjected.
  • the nature and size of the diffusion zone have effects on the greater or lesser increase in the set of resistance properties of the part, in particular on its dynamic resistance to alternating forces, and, to a lesser extent, on its resistance to wear and on its sliding properties.
  • this base material under the diffusion zone is the base material, not reached by the diffusion of nitrogen, and therefore which must remain unchanged by the nitriding treatment.
  • this base material must of itself have as high a resistance as possible, which is not likely to be compromised by the thermal conditions of nitriding.
  • this base material is then capable of providing sufficient mechanical support to all of the two nitriding layers, relatively thin, so that the total resistance of the part is satisfactory.
  • Ion nitriding of steel parts uses an electrical discharge created by a potential difference between 400 and 700 volts between the part to be treated, constituting the cathode, and the reactor wall, constituting the anode, in a pressure vessel. reduced, generally between 100 and 1000 Pascal, of a gas consisting of a mixture of nitrogen and hydrogen, which may contain between 1% and 35% of nitrogen by volume depending on the case, with possibly a little hydrocarbon gaseous, at temperatures between 430 ° and 600 ° G.
  • the parts thus treated by ionic nitriding are characterized in that they have an outer combination layer free of pores and of single-phase composition, with a thickness of 10 micrometers at most, and a diffusion zone free to a large extent of networks. and nitride lines.
  • One of the essential advantages of ionic nitriding is to achieve independence between the treatment temperature, which is a function of the parameters of the electrical discharge (voltage, intensity, gas pressure), and the activity of the reaction medium, which depends on the mixture. gas used.
  • the aim of the present invention is to take advantage of the beneficial effect of a prior work hardening on the growth kinetics of the nitrided layers, while avoiding any risk of excessive brittleness, and yet without practicing any special stress relieving treatment. .
  • the duration of the first sequence of ionic nitriding and the duration of the second sequence are all the longer as the steel to be treated is no longer loaded with alloying elements. This is due to the fact that, in steels which are more loaded with alloying elements, such as stainless steels or refractory steels, the restoration of the structure after work hardening is slower.
  • the part having first undergone a final work hardening rate of between 10% and 40%, for example close to 30% by cold hammering, is then subjected to a first sequence of ionic nitriding during a duration between 2 and 4 hours, at a temperature between 490 ° and 510 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial pressure of nitrogen is between 10 and 15 Pascal, the gas pressure total being between 200 and 650 Pascal.
  • the part is subjected to a second sequence of ionic nitriding for a period of between 25 and 40 hours, at a temperature between 510 ° and 560 ° C, in a gaseous mixture of nitrogen and hydrogen such as pressure partial nitrogen is of the order of 60 Pascal, the total gas pressure remaining between 200 and 650 Pascal.
  • a gaseous mixture of nitrogen and hydrogen such as pressure partial nitrogen is of the order of 60 Pascal, the total gas pressure remaining between 200 and 650 Pascal.
  • the part, having undergone the same work hardening as previously is then subjected to a first sequence of nitriding for a period of between 6 and 10 hours, at a temperature between 500 ° and 520 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial pressure of nitrogen is between 30 and 35 Pascal, the total gas pressure being between 200 and 650 Pascal.
  • the part is subjected to a second sequence of ionic nitriding, for a period of between 40 and 70 hours, at a temperature of between 500 and 580 ° C., in a mixture of nitrogen and hydrogen such as partial pressure nitrogen is between 60 and 80 Pascal, and preferably close to 70 Pascal, the total gas pressure remaining between 200 and 650 Pascal.
  • a second sequence of ionic nitriding for a period of between 40 and 70 hours, at a temperature of between 500 and 580 ° C., in a mixture of nitrogen and hydrogen such as partial pressure nitrogen is between 60 and 80 Pascal, and preferably close to 70 Pascal, the total gas pressure remaining between 200 and 650 Pascal.
  • the gaseous mixture used always consists of nitrogen and hydrogen
  • the relative proportions of these two gases, at least in the first sequence of ionic nitriding must be regulated according to the composition of the steel, and more particularly to its contents in elements of alloys avid of nitrogen, such as: chromium, vanadium, titanium and aluminum.
  • elements of alloys avid of nitrogen such as: chromium, vanadium, titanium and aluminum.
  • the length of the first sequence is very important.
  • the surface decarburization which is caused by this phase of the treatment can lead, if it is continued for too long, to modifications in the mechanical properties of the nitrided layers.
  • the penetration of nitrogen into the steel is facilitated by the reduction in the quantity of carbides, and this can result in a significant reduction in the surface hardness, with, as a consequence, a reduction in the following properties: resistance to 'sinking, wear, and mechanical or thermal fatigue.
  • This first sequence is then followed by a second sequence, in which the activity of the reaction medium is modified as a function of the thickness of the combination layer which it is desired to obtain at the surface.
  • the temperature and the holding time must be adjusted taking into account the beneficial influence of the preliminary work hardening on the growth kinetics of the nitrided layers.
  • This phenomenon controlled by the diffusion of nitrogen in the treated room, can be visualized by a graph representing the evolution of the ratio (e being the thickness of the layers in micrometers and t being the holding time in hours) as a function of the inverse of the absolute temperature.
  • This representation makes it possible to determine in the second sequence of the treatment, the holding time necessary to produce a nitrided layer of given thickness at a given temperature, which characterizes the growth kinetics.
  • the gain on the total treatment time of the second part (according to the invention) compared to the first is significant, and that it is understood between 10% and 50% depending on the case.
  • This first tube then undergoes conventional ionic nitriding, under the conditions indicated above.
  • the second tube undergoes ionic nitriding in two successive sequences according to the invention, under the conditions indicated above.
  • the kinetics of growth of the layers by this ionic nitriding according to the invention is represented by curve 2 of FIG. 1.
  • FIG. 2 Another way of considering the previous comparison is shown in FIG. 2, on which we have plotted on the abscissa, on a linear scale, the ion nitriding temperatures (that of the second sequence in the case of the invention) and on the ordinate , on a logarithmic scale, the nitriding times, by representing by two bundles of lines the nitriding depths reached on the one hand for the first tube (straight lines in solid lines) and on the other hand for the second tube, according to the invention (dashed lines, for respective values of 200, 300, 400 500 and 600 micrometers.

Abstract

1. A method for the ionic nitriding of pieces of steel of any type, which comprises the following four stages in succession : a) a prior cold-working operation on the piece, the final degree of cold-working of which is between 10% and 40% ; b) a first ionic nitriding sequence with a duration of between one hour and 10 hours, carried out at a temperature t1 of between 450 degrees and 520 degrees, in a gaseous mixture consisting of nitrogen and hydrogen, which is such that the nitrogen partial pressure p1 is between 10 and 35 Pascal and such that the total gas pressure is between 200 and 650 Pascal ; c) a second ionic nitriding sequence the duration of which is between 40 and 70 hours, carried out at a temperature t2 of between 500 degrees and 580 degrees C and at least 10 degrees C and at most 50 degrees C above t1 in a gaseous mixture consisting of nitrogen and hydrogen, which is such that the nitrogen partial pressure p2 is between 60 and 80 Pascal, and that the total gas pressure remains between 200 and 650 Pascal ; and d) a final cooling in vacuo.

Description

La présente invention concerne la nitruration ionique des aciers.The present invention relates to ion nitriding of steels.

On sait que la nitruration ionique des aciers est un procédé distinct de la nitruration gazeuse.It is known that ionic nitriding of steels is a process distinct from gas nitriding.

Cette dernière, de nature thermo-chimique, s'effectue classiquement entre 500 et 550° C dans une atmosphère d'ammoniac, diluée éventuellement par de l'azote. Il en résulte un durcissement superficiel de l'acier qui est important, par suite de la présence de deux couches nitrurées successives :

  • (a) En surface, une couche de combinaison, réalisée en raison de la sursaturation en azote, constituée de nitrures de fer de deux natures différentes (Fe2,3N et Fe4N), les premiers se trouvant plus en surface et les seconds plus en profondeur.
  • (b) Juste au-dessous de la couche de combinaison, une couche de diffusion d'azote, beaucoup plus épaisse que la précédente, et fortement marquée par de fines précipitations en réseau de carbonitrures de fer et d'autres métaux résultant de l'action combinée de l'azote en insertion et du carbone de l'acier.
The latter, of thermochemical nature, is conventionally carried out between 500 and 550 ° C. in an ammonia atmosphere, optionally diluted with nitrogen. This results in a surface hardening of the steel which is significant, due to the presence of two successive nitrided layers:
  • (a) On the surface, a combination layer, produced due to the nitrogen supersaturation, consisting of iron nitrides of two different natures (Fe2.3N and Fe 4 N), the former being more on the surface and the latter more in depth.
  • (b) Just below the combination layer, a nitrogen diffusion layer, much thicker than the previous one, and strongly marked by fine network precipitation of carbonitrides of iron and other metals resulting from the combined action of nitrogen in insertion and carbon of steel.

Ces deux couches sont sensibles à l'amorçage et à la propagation des fissures : la couche de combinaison, à cause de l'apparition de fissures à la limite des deux catégories de nitrures, et de l'écaillage rapide des composés les plus superficiels ; la couche de diffusion,à cause des précipitations de carbonitrures, résistant mal aux contraintes mécaniques et thermiques auxquelles sont soumises les deux couches nitrurées.These two layers are sensitive to the initiation and propagation of cracks: the combination layer, because of the appearance of cracks at the limit of the two categories of nitrides, and the rapid spalling of the most superficial compounds; the diffusion layer, because of carbonitride precipitation, poorly resistant to the mechanical and thermal stresses to which the two nitrided layers are subjected.

La nature et l'importance de la zone de diffusion ont des effets sur le plus ou moins grand accroissement de l'ensemble des propriétés de résistance de la pièce, notamment sur sa résistance dynamique aux efforts alternés, et, dans une plus faible mesure, sur sa résistance à l'usure et sur ses propriétés de glissement.The nature and size of the diffusion zone have effects on the greater or lesser increase in the set of resistance properties of the part, in particular on its dynamic resistance to alternating forces, and, to a lesser extent, on its resistance to wear and on its sliding properties.

Enfin, sous la zone de diffusion se trouve la matière de base, non atteinte par la diffusion de l'azote, et par conséquent qui doit rester inchangée par le traitement de nitruration. Pour cela, cette matière de base doit avoir d'elle-même une résistance aussi élevée que possible, qui ne risque pas d'être compromise par les conditions thermiques de la nitruration. Ainsi, cette matière de base est alors capable d'apporter un soutien mécanique suffisant à l'ensemble des deux couches de nitruration, relativement minces, afin que la résistance totale de la pièce soit satisfaisante.Finally, under the diffusion zone is the base material, not reached by the diffusion of nitrogen, and therefore which must remain unchanged by the nitriding treatment. For this, this base material must of itself have as high a resistance as possible, which is not likely to be compromised by the thermal conditions of nitriding. Thus, this base material is then capable of providing sufficient mechanical support to all of the two nitriding layers, relatively thin, so that the total resistance of the part is satisfactory.

Les inconvénients de fissuration et d'écaillage dus à la nitruration gazeuse, qui viennent d'être exposés, peuvent être évités dans une large mesure par la nitruration ionique, qui est de nature électro-thermo-chimique.The disadvantages of cracking and flaking due to gaseous nitriding, which have just been exposed, can be largely avoided by ionic nitriding, which is of an electro-thermo-chemical nature.

La nitruration ionique de pièces en acier utilise une décharge électrique créée par une différence de potentiel comprise entre 400 et 700 volts entre la pièce à traiter, constituant la cathode, et la paroi du réacteur, constituant l'anode, dans une enceinte placée sous pression réduite, généralement comprise entre 100 et 1000 Pascal, d'un gaz constitué par un mélange d'azote et d'hydrogène, pouvant contenir entre 1 % et 35 % d'azote en volume selon les cas, avec éventuellement un peu d'hydrocarbures gazeux, à des températures comprises entre 430° et 600°G.Ion nitriding of steel parts uses an electrical discharge created by a potential difference between 400 and 700 volts between the part to be treated, constituting the cathode, and the reactor wall, constituting the anode, in a pressure vessel. reduced, generally between 100 and 1000 Pascal, of a gas consisting of a mixture of nitrogen and hydrogen, which may contain between 1% and 35% of nitrogen by volume depending on the case, with possibly a little hydrocarbon gaseous, at temperatures between 430 ° and 600 ° G.

Les pièces ainsi traitées par nitruration ionique sont caractérisées en ce qu'elles présentent une couche de combinaison extérieure exempte de pores et à composition monophasée, d'une épaisseur de 10 micromètres au maximum, et une zone de diffusion exempte dans une large mesure de réseaux et de lignes de nitrures.The parts thus treated by ionic nitriding are characterized in that they have an outer combination layer free of pores and of single-phase composition, with a thickness of 10 micrometers at most, and a diffusion zone free to a large extent of networks. and nitride lines.

Elles sont donc beaucoup moins sensibles à la fissuration et à l'écaillage que les pièces traitées par nitruration gazeuse.They are therefore much less sensitive to cracking and chipping than parts treated by gas nitriding.

Un des avantages essentiels de la nitruration ionique est de réaliser l'indépendance entre la température de traitement, qui est fonction des paramètres de la décharge électrique (tension, intensité, pression gazeuse), et l'activité du milieu réactionnel, qui dépend du mélange gazeux utilisé.One of the essential advantages of ionic nitriding is to achieve independence between the treatment temperature, which is a function of the parameters of the electrical discharge (voltage, intensity, gas pressure), and the activity of the reaction medium, which depends on the mixture. gas used.

Tout ce qui précède est bien connu des spécialistes.All of the above is well known to specialists.

D'autre part, il est également connu que, dans le cas de traitements thermo-chimiques, une déformation plastique préliminaire de l'acier a une très forte influence sur les processus de diffusion des éléments in- tersticiels, comme le carbone et l'azote. C'est ainsi que, dans le cas d'une nitruration, la déformation à froid ou à température modérée, au plus égale à 6000C, de l'acier entraine une augmentation sensible de l'épaisseur des couches nitrurées, pour une température et un temps de maintien donnés.On the other hand, it is also known that, in the case of thermochemical treatments, a preliminary plastic deformation of the steel has a very strong influence on the diffusion processes of the interstitial elements, such as carbon and nitrogen. Thus, in the case of nitriding, the cold or moderate temperature deformation, at most equal to 600 ° C., of the steel results in a significant increase in the thickness of the nitrided layers, for a temperature and a given hold time.

Mais cette influence favorable d'une déformation plastique préliminaire de l'acier sur la cinétique de croissance des couches nitrurées s'accompagne toutefois d'un inconvénient majeur dans les conditions habituelles de nitruration. En effet, les précipités de cémentite ou de carbu- res alliés présents dans l'acier écroui sont partiellement remis en solution lors du maintien en température du traitement de nitruration (430° à 600°C), et le carbone présent dans la solution solide facilite la croissance des carbonitrures aussi bien dans la couche de combinaison que dans la couche de diffusion d'azote. Il en résulte alors des pénétrations de la couche de combinaison dans la couche de diffusion, soit le long des joints de grains, soit le long des lignes d'écrouissage. Ces composés, qui sont naturellement fragiles, détériorent la ténacité et la tenue à la fatigue aussi bien mécanique que thermique des couches nitrurées.However, this favorable influence of a preliminary plastic deformation of the steel on the growth kinetics of the nitrided layers is however accompanied by a major drawback under the usual nitriding conditions. Indeed, the precipitates of cementite or carburetor res alloys present in the work hardened steel are partially redissolved during the maintenance of the temperature of the nitriding treatment (430 ° to 600 ° C), and the carbon present in the solid solution facilitates the growth of carbonitrides as well in the layer of combination as in the nitrogen diffusion layer. This then results in penetrations of the combination layer into the diffusion layer, either along the grain boundaries, or along the work hardening lines. These compounds, which are naturally fragile, deteriorate the toughness and the resistance to fatigue, both mechanical and thermal, of the nitrided layers.

Le but de la présente invention est de tirer parti de l'effet bénéfique d'un écrouissage préalable sur la cinétique de croissance des ·couches nitrurées, tout en évitant tout risque de fragilité excessive, et pourtant sans pratiquer aucun traitement spécial de détensionnement des contraintes.The aim of the present invention is to take advantage of the beneficial effect of a prior work hardening on the growth kinetics of the nitrided layers, while avoiding any risk of excessive brittleness, and yet without practicing any special stress relieving treatment. .

A cet effet, la présente invention a pour objet une méthode de nitruration ionique des pièces en aciers, de toutes nuances, depuis les aciers peu alliés jusqu'aux aciers inoxydables et aux aciers réfractaires, caractérisée par la succession des quatre phases suivantes :

  • (a) Une opération d'écrouissage préalable de la pièce, dont le taux final d'écrouissage est compris entre 10 % et 40 %, et de préférence voisin de 30 % ;
  • (b) Une première séquence de nitruration ionique, de durée limitée, c'est-à-dire comprise entre une heure et 10 heures selon la nature de l'acier à traiter, et plus précisément comprise entre une et 5 heures pour les aciers faiblement alliés, et entre 5 et 10 heures pour les aciers fortement alliés, réalisée à une température tl comprise entre 450° et 520°C dans un mélange gazeux constitué par de l'azote et de l'hydrogène, tel que la pression partielle d'azote pl soit comprise entre 10 et 35 Pascal, et que la pression gazeuse totale soit comprise entre 200 et 650 Pascal ;
  • (c) Une deuxième séquence de nitruration ionique, dont la durée et la température sont ajustées en fonction de l'influence bénéfique de l'écrouissage préalable selon (a) sur la cinétique de croissance des couches nitrurées, dont la durée est ainsi comprise entre 20 et 70 heures selon la nature de l'acier à traiter, dont la température t2 est comprise entre 500 et 580°C, et est supérieure à tl d'au moins 10°C et d'au plus 50°C, cette deuxième séquence étant réalisée dans un mélange gazeux constitué par de l'azote et de l'hydrogène, tel que la pression partielle d'azote p2 soit comprise entre 20 et 100 Pascal, et soit supérieure à pl, tandis que la pression gazeuse totale reste comprise entre 200 et 650 Pascal ;
  • (d)Un refroidissement final sous vide.
To this end, the subject of the present invention is a method of ionic nitriding of steel parts, of all shades, from low alloyed steels to stainless steels and refractory steels, characterized by the succession of the following four phases:
  • (a) A prior work hardening operation, the final work hardening rate of which is between 10% and 40%, and preferably close to 30%;
  • (b) A first sequence of ionic nitriding, of limited duration, that is to say between one hour and 10 hours depending on the nature of the steel to be treated, and more precisely between one and 5 hours for steels weakly alloyed, and between 5 and 10 hours for highly alloyed steels, carried out at a temperature tl between 450 ° and 520 ° C in a gas mixture consisting of nitrogen and hydrogen, such as the partial pressure d 'nitrogen pl is between 10 and 35 Pascal, and that the total gas pressure is between 200 and 650 Pascal;
  • (c) A second sequence of ionic nitriding, the duration and the temperature of which are adjusted as a function of the beneficial influence of the previous work hardening according to (a) on the growth kinetics of the nitrided layers, the duration of which is thus between 20 and 70 hours depending on the nature of the steel to be treated, whose temperature t2 is between 500 and 580 ° C, and is greater than tl by at least 10 ° C and at most 50 ° C, this second sequence being carried out in a gaseous mixture consisting of nitrogen and hydrogen, such that the partial pressure of nitrogen p2 is between 20 and 100 Pascal, and is greater than pl, while the total gas pressure remains included between 200 and 650 Pascal;
  • (d) Final vacuum cooling.

Suivant une caractéristique particulière de la présente invention, la durée de la première séquence de nitruration ionique et la durée de la deuxième séquence, tout en restant dans le cadre des durées indiquées précédemment, sont d'autant plus longues que l'acier à traiter est plus chargé en éléments d'alliages. Ceci provient du fait que, dans les aciers pluschar- gés en éléments d'alliages, tels que les aciers inoxydables ou les aciers réfractaires, la restauration de la structure après écrouissage est plus lente.According to a particular characteristic of the present invention, the duration of the first sequence of ionic nitriding and the duration of the second sequence, while remaining within the framework of the durations indicated previously, are all the longer as the steel to be treated is no longer loaded with alloying elements. This is due to the fact that, in steels which are more loaded with alloying elements, such as stainless steels or refractory steels, the restoration of the structure after work hardening is slower.

Ainsi, dans une variante particulière de l'invention applicable aux aciers au chrome-molybdène et aux aciers au chrome-nickel-molybdène faiblement alliés, c'est-à-dire aux aciers contenant entre 0,5 % et 4 % de chrome, au plus 4 % de nickel, et entre 0,10 % et 1 % de molybdène, par exemple dans le cas de la nuanne 35 CD 12, à 0,35 % de carbone, 3 % de chrome, 0,80 % de molybdène, et sans nickel, la pièce, ayant subi d'abord un taux d'écrouissage final compris entre 10 % et 40 %, par exemple voisin de 30 % par martelage à froid, est ensuite soumise à une première séquence de nitruration ionique pendant une durée comprise entre 2 et 4 heures, à une température comprise entre 490° et 510°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote soit comprise entre 10 et 15 Pascal, la pression gazeuse totale étant comprise entre 200 et 650 Pascal. Ensuite, la pièce est soumise à une deuxième séquence de nitruration ionique pendant une durée comprise entre 25 et 40 heures, à une température comprise entre 510 ° et 560°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote soit de l'ordre de 60 Pascal, la pression gazeuse totale restant comprise entre 200 et 650 Pascal.Thus, in a particular variant of the invention applicable to chromium-molybdenum steels and to low-alloy chromium-nickel-molybdenum steels, that is to say steels containing between 0.5% and 4% of chromium, at most 4% nickel, and between 0.10% and 1% molybdenum, for example in the case of nuane 35 CD 12, with 0.35% carbon, 3% chromium, 0.80% molybdenum , and without nickel, the part, having first undergone a final work hardening rate of between 10% and 40%, for example close to 30% by cold hammering, is then subjected to a first sequence of ionic nitriding during a duration between 2 and 4 hours, at a temperature between 490 ° and 510 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial pressure of nitrogen is between 10 and 15 Pascal, the gas pressure total being between 200 and 650 Pascal. Then, the part is subjected to a second sequence of ionic nitriding for a period of between 25 and 40 hours, at a temperature between 510 ° and 560 ° C, in a gaseous mixture of nitrogen and hydrogen such as pressure partial nitrogen is of the order of 60 Pascal, the total gas pressure remaining between 200 and 650 Pascal.

Dans une autre variante particulière de linvention , applicable aux aciers inoxydables au chrome, avec ou sans nickel, et aux aciers réfractaires, donc aux aciers fortement alliés, la pièce, ayant subi le même écrouissage que précédemment, est ensuite soumise à une première séquence de nitruration pendant une durée comprise entre 6 et 10 heures, à une température comprise entre 500° et 520°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote soit comprise entre 30 et 35 Pascal, la pression gazeuse totale étant comprise entre 200 et 650 Pascal. Ensuite, la pièce est soumise à une deuxième séquence de nitruration ionique, pendant une durée comprise entre 40 et 70 heures, à une température comprise entre 500 et 580°C, dans un mélange d'azote et d'hydrogène tel que la pression partielle d'azote soit comprise entre 60 et 80 Pascal, et de préférence voisine de 70 Pascal, la pression gazeuse totale restant comprise entre 200 et 650 Pascal.In another particular variant of the invention, applicable to chrome stainless steels, with or without nickel, and to refractory steels, therefore to highly alloyed steels, the part, having undergone the same work hardening as previously, is then subjected to a first sequence of nitriding for a period of between 6 and 10 hours, at a temperature between 500 ° and 520 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial pressure of nitrogen is between 30 and 35 Pascal, the total gas pressure being between 200 and 650 Pascal. Then, the part is subjected to a second sequence of ionic nitriding, for a period of between 40 and 70 hours, at a temperature of between 500 and 580 ° C., in a mixture of nitrogen and hydrogen such as partial pressure nitrogen is between 60 and 80 Pascal, and preferably close to 70 Pascal, the total gas pressure remaining between 200 and 650 Pascal.

Il faut remarquer que si, dans tous les cas d'application de la méthode selon l'invention, le mélange gazeux utilisé est toujours constitué d'azote et d'hydrogène, les proportions relatives de ces deux gaz, au moins dans la première séquence de nitruration ionique, doivent être réglées en fonction de la composition de l'acier, et plus particulièrement de ses teneurs en éléments d'alliages avides d'azote, tels que : le chrome, le vanadium, le titane et l'aluminium. Plus les teneurs en ces éléments sont élevées, et plus la pression partielle d'azote doit être importante pour une même pression totale de travail.It should be noted that if, in all cases of application of the method according to the invention, the gaseous mixture used always consists of nitrogen and hydrogen, the relative proportions of these two gases, at least in the first sequence of ionic nitriding, must be regulated according to the composition of the steel, and more particularly to its contents in elements of alloys avid of nitrogen, such as: chromium, vanadium, titanium and aluminum. The higher the contents of these elements, the higher the partial nitrogen pressure must be for the same total working pressure.

La durée de la première séquence a beaucoup d'importance. La décarburation superficielle qui est provoquée par cette phase du traitement peut entraîner, si elle est poursuivie trop longtemps, des modifications dans les propriétés mécaniques des couches nitrurées. En particulier, la pénétration d'azote dans l'acier est facilitée par la diminution de la quantité de carbures, et il peut en résulter un abaissement sensible de la dureté superficielle, avec, comme conséquence, une diminution des propriétés suivantes : résistance à l'enfoncement, à l'usure, et à la fatigue mécanique ou thermique.The length of the first sequence is very important. The surface decarburization which is caused by this phase of the treatment can lead, if it is continued for too long, to modifications in the mechanical properties of the nitrided layers. In particular, the penetration of nitrogen into the steel is facilitated by the reduction in the quantity of carbides, and this can result in a significant reduction in the surface hardness, with, as a consequence, a reduction in the following properties: resistance to 'sinking, wear, and mechanical or thermal fatigue.

Afin d'éviter ce risque, il est nécessaire de ne pas poursuivre trop longtemps la première séquence de nitruration ionique, et c'est pourquoi la durée du maintien en température au cours de cette séquence ne doit pas dépasser 10 heures.In order to avoid this risk, it is necessary not to continue the first ion nitriding sequence for too long, and this is why the duration of the temperature maintenance during this sequence must not exceed 10 hours.

Cette première séquence est alors suivie d'une deuxième séquence, dans laquelle l'activité du milieu réactionnel est modifiée en fonction de l'épaisseur de la couche de combinaison que l'on désire obtenir en surface. Dans cette deuxième séquence, la température et le temps de maintien doivent être ajustés en tenant compte de l'influence bénéfique de l'écrouissage préliminaire sur la cinétique de croissance des couches nitrurées. Ce phénomène, contrôlé par la diffusion de l'azote dans la pièce traitée, peut être visualisé par un graphique représentant l'évolution du rapport

Figure imgb0001
(e étant l'épaisseur des couches en micromètres et t étant le temps de maintien en heures) en fonction de l'inverse de la température absolue. Cette représentation permet de déterminer dans la deuxième séquence du traitement, le temps de maintien nécessaire pour réaliser une couche nitrurée d'épaisseur donnée à une température donnée, ce qui caractérise la cinétique de croissance.This first sequence is then followed by a second sequence, in which the activity of the reaction medium is modified as a function of the thickness of the combination layer which it is desired to obtain at the surface. In this second sequence, the temperature and the holding time must be adjusted taking into account the beneficial influence of the preliminary work hardening on the growth kinetics of the nitrided layers. This phenomenon, controlled by the diffusion of nitrogen in the treated room, can be visualized by a graph representing the evolution of the ratio
Figure imgb0001
 (e being the thickness of the layers in micrometers and t being the holding time in hours) as a function of the inverse of the absolute temperature. This representation makes it possible to determine in the second sequence of the treatment, the holding time necessary to produce a nitrided layer of given thickness at a given temperature, which characterizes the growth kinetics.

Lors de la première séquence du traitement de nitruration ionique la restauration de la structure déformée par l'écrouissage a été fortement ralentie par l'insertion d'azote dans le réseau, car les dislocations qui servent de sites favorables pour la pénétration de l'azote ont été gênées dans leur déplacement par les précipités de nitrures formés. Mais la deuxième séquence, bien ajustée comme il vient d'être dit, complète, en un temps raccourci, la restauration de la structure déformée par l'écrouissage.During the first sequence of the ion nitriding treatment, the restoration of the structure deformed by work hardening was greatly slowed down by the insertion of nitrogen into the network, because the dislocations which serve as favorable sites for the penetration of nitrogen were embarrassed in their displacement by the precipitates of nitrides formed. But the second sequence, well adjusted as it has just been said, completes, in a shortened time, the restoration of the structure deformed by hardening.

Il est d'ailleurs fort intéressant, pour bien juger de l'intérêt de la méthode selon l'invention, de procéder à la comparaison suivante sur deux pièces d'acier semblables, ayant toutes les deux subi la même déformation plastique préliminaire, par martelage à froid, avec un taux d'écrouissage final égal à 30 % :

  • - d'une part, la première pièce subit d'abord un traitement de détensionnement à 500°C pendant 2 à 4 heures dans un four classique à atmosphère contrôlée, pour restauration partielle de la structure écrouie, puis une nitruration ionique de type classique, à des températures comprises entre 500 et 560°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote soit égale à 60 Pascal.
  • - d'autre part, la deuxième pièce subit les deux séquences successives de nitruration ionique selon l'invention, la première séquence étant une nitruration ionique pendant 2 à 4 heures, aux environs de 500°C dans un mélange gazeux d'azote et d'ydrogène tel que la pression partielle d'azote soit comprise entre 10 et 15 Pascal, la deuxième séquence étant, comme dans le cas précédent, réalisée entre 500° et 56OC, dans le même mélange gazeux, sous une pression partielle d'azote de 60 Pascal.
It is moreover very interesting, in order to judge the advantage of the method according to the invention, to carry out the following comparison on two similar pieces of steel, both having undergone the same preliminary plastic deformation, by hammering cold, with a final hardening rate equal to 30%:
  • on the one hand, the first part is first subjected to a stress relieving treatment at 500 ° C. for 2 to 4 hours in a conventional oven with controlled atmosphere, for partial restoration of the work hardened structure, then an ion nitriding of conventional type, at temperatures between 500 and 560 ° C., in a gaseous mixture of nitrogen and hydrogen such that the partial pressure of nitrogen is equal to 60 Pascal.
  • - on the other hand, the second part undergoes the two successive sequences of ionic nitriding according to the invention, the first sequence being an ionic nitriding for 2 to 4 hours, around 500 ° C. in a gaseous mixture of nitrogen and d hydrogen such that the partial pressure of nitrogen is between 10 and 15 Pascal, the second sequence being, as in the previous case, carried out between 500 ° and 56OC, in the same gas mixture, under a partial pressure of nitrogen of 60 Pascal.

Dans une telle comparaison, on observe que, pour une même épaisseur de couche nitrurée, le gain sur le temps total de traitement de la deuxième pièce (selon l'invention) par rapport à la première, est notable, et qu'il est compris entre 10 % et 50 % suivant les cas.In such a comparison, it is observed that, for the same thickness of nitrided layer, the gain on the total treatment time of the second part (according to the invention) compared to the first, is significant, and that it is understood between 10% and 50% depending on the case.

AFin d'illustrer cette comparaison, voici le cas, à titre d'exemple non limitatif, de deux tubes en acier 35 CD 12 (à 0,35 % C, 3 % Cr, 0,80 % Mo), dont la mise en forme a été faite par martelage à froid avec un taux d'écrouissage final de 30 %.In order to illustrate this comparison, here is the case, by way of nonlimiting example, of two 35 CD 12 steel tubes (at 0.35% C, 3% Cr, 0.80% Mo), the setting of which shape was made by cold hammering with a final hardening rate of 30%.

Les contraintes mesurées par radiocristallographie sur la surface de chacun de ces deux tubes dans un tel état sont les suivantes (en désignant par

Figure imgb0002
L la contrainte longitudinale, c'est-à-dire dans l'axe de la pièce, et par
Figure imgb0003
θ la contrainte circonférentielle, c'est-à-dire perpendiculaire à l'axe de la pièce) :

  • σL = 750 MPa
  • σ θ = - 400 MPa
The stresses measured by X-ray crystallography on the surface of each of these two tubes in such a state are as follows (by designating by
Figure imgb0002
L the longitudinal stress, that is to say in the axis of the part, and by
Figure imgb0003
θ the circumferential stress, that is to say perpendicular to the axis of the part):
  • σ L = 750 MPa
  • σ θ = - 400 MPa

Le premier tube subit alors un détensionnement à 500°C pendant trois heures dans un four classique à atmosphère contr8lée. Les contraintes se trouvent alors abaissées aux valeurs suivantes :

  • σL = - 210 MPa
  • σθ = - 170 MPa
  • Il y a donc bien restauration partielle de la structure écrouie.
The first tube then undergoes stress relieving at 500 ° C. for three hours in a conventional oven with controlled atmosphere. Constraints are then lowered to the following values:
  • σ L = - 210 MPa
  • σ θ = - 170 MPa
  • There is therefore a partial restoration of the work hardened structure.

Ce premier tube subit ensuite une nitruration ionique classique, dans les conditions indiquées précédemment.This first tube then undergoes conventional ionic nitriding, under the conditions indicated above.

La cinétique de croissance des couches nitrurées par cette nitruration ionique classique, telle qu'elle a été précédemment définie, est représentée par la courbe 1 de la figure 1 (voir plus loin).The growth kinetics of the layers nitrided by this conventional ionic nitriding, as previously defined, are represented by curve 1 in FIG. 1 (see below).

Le deuxième tube subit la nitruration ionique en deux séquences successives selon l'invention, dans les conditions indiquées précédemment. La cinétique de croissance des couches par cette nitruration ionique selon l'invention est représentée par la courbe 2 de la figure 1.The second tube undergoes ionic nitriding in two successive sequences according to the invention, under the conditions indicated above. The kinetics of growth of the layers by this ionic nitriding according to the invention is represented by curve 2 of FIG. 1.

Sur cette figure 1 on a porté en abscisses l'inverse de la température absolue du traitement, (celle de la deuxième séquence dans le cas de l'invention) et en ordonnées le rapport entre l'épaisseur nitrurée et la racine carrée du temps de nitruration ionique. On voit nettement que, pour une température donnée, supérieure à 490°C, la courbe 2 est constamment située au-dessus de la courbe 1. Pour un même temps de nitruration, on observe par exemple, pour un traitement à 520°C, que l'épaisseur nitrurée est environ 1,25 fois plus forte selon la courbe 2 que selon la courbe 1, et que ce coefficient augmente avec la température de traitement. La cinétique de croissance des couches nitrurées se trouve donc nettement améliorée par la méthode selon l'invention.In this FIG. 1, we have plotted on the abscissa the inverse of the absolute temperature of the treatment (that of the second sequence in the case of the invention) and on the ordinate the ratio between the nitrided thickness and the square root of the time of ionic nitriding. It is clearly seen that, for a given temperature, greater than 490 ° C., the curve 2 is constantly located above the curve 1. For the same nitriding time, for example, for a treatment at 520 ° C., that the nitrided thickness is approximately 1.25 times greater according to curve 2 than according to curve 1, and that this coefficient increases with the treatment temperature. The growth kinetics of the nitrided layers is therefore significantly improved by the method according to the invention.

Une autre manière d'envisager la précédente comparaison est représentée sur la figure 2, sur laquelle on a porté en abscisses, en échelle linéaire, les températures de nitruration ionique (celle de la deuxième séquence dans le cas de l'invention) et en ordonnées, en échelle logarithmique, les temps de nitruration, en représentant par deux faisceaux de droites les profondeurs de nitruration atteintes d'une part pour le premier tube (droites en traits pleins) et d'autre part pour le deuxième tube, selon l'invention (droites en tiretés, pour des valeurs respectives de 200, 300, 400 500 et 600 micromètres.Another way of considering the previous comparison is shown in FIG. 2, on which we have plotted on the abscissa, on a linear scale, the ion nitriding temperatures (that of the second sequence in the case of the invention) and on the ordinate , on a logarithmic scale, the nitriding times, by representing by two bundles of lines the nitriding depths reached on the one hand for the first tube (straight lines in solid lines) and on the other hand for the second tube, according to the invention (dashed lines, for respective values of 200, 300, 400 500 and 600 micrometers.

Sur cette figure 2, on voit par exemple que, pour obtenir des épaisseurs de couche nitrurée voisines de 500 micromètres avec un traitement de nitruration voisin de 540°C, il faut :

  • - 60 heures de maintien à cette température pour le traitement classique après détensionnement des contraintes,
  • - seulement 42 heures de maintien à cette température pour le traitement selon l'invention.
In this FIG. 2, we see for example that, to obtain thicknesses of nitrided layer close to 500 micrometers with a nitriding treatment close to 540 ° C., it is necessary:
  • - 60 hours of maintenance at this temperature for conventional treatment after stress relieving,
  • - only 42 hours of maintenance at this temperature for the treatment according to the invention.

Ainsi, la méthode de nitruration ionique selon l'invention introduit un progrès très notable.Thus, the method of ionic nitriding according to the invention introduces very significant progress.

Ce progrès est également marqué si l'on règle l'atmosphère réactive de façon à n'obtenir en surface de la pièce nitrurée qu'une couche de diffusion d'azote, sans couche de combinaison. Ce résultat peut être atteint en réglant de la manière suivante les deux séquences de nitruration ionique :

  • - Une première séquence, de durée comprise entre 4 et 10 heures, selon la nature de l'acier à traiter, réalisée à une température tl comprise entre 500° et 520°C, dans un mélange gazeux, constitué par de l'azote et de l'hydrogène, tel que la pression partielle d'azote pl soit comprise entre 10 et 30 Pascal, et que la pression gazeuse totale soit comprise entre 200 et 650 Pascal ;
  • - Une deuxième séquence, de durée comprise entre 20 et 40 heures, selon la nature & l'acier à traiter, réalisée à une température t2 comprise entre 530° et 550°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote p2 soit comprise entre 20 et 60 Pascal et soit supérieure à pl.
This progress is also marked if the reactive atmosphere is adjusted so as to obtain on the surface of the nitrided part only a nitrogen diffusion layer, without a combination layer. This result can be achieved by adjusting the two ion nitriding sequences as follows:
  • - A first sequence, lasting between 4 and 10 hours, depending on the nature of the steel to be treated, carried out at a temperature tl between 500 ° and 520 ° C, in a gas mixture, consisting of nitrogen and hydrogen, such that the partial pressure of nitrogen pl is between 10 and 30 Pascal, and that the total gas pressure is between 200 and 650 Pascal;
  • - A second sequence, of duration between 20 and 40 hours, depending on the nature & the steel to be treated, carried out at a temperature t2 between 530 ° and 550 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial pressure of nitrogen p2 is between 20 and 60 Pascal and is greater than pl.

Pour un acier peu allié, par exemple du type 35 CD 12 déjà mentionné ci-dessus à titre d'exemple, on utilise des pressions partielles d'azote pl et p2 qui sont basses : pl = 10 à 15 Pascal, p2 = 20 à 25 Pascal, tandis que, pour un acier inoxydable, par exemple un acier austénitique à 18 % de chrome et 10 % de nickel, on utilise des pressions partielles d'azote pl et p2 qui sont plus élevées : pl = 30 Pascal, p2 = 40 à 60 Pascal. Ces conditions particulières bien précises des deux séquences de nitruration permettent d'obtenir en surface de la pièce nitrurée une couche de diffusion d'azote, sans couche de combinaison.For a low-alloy steel, for example of the 35 CD 12 type already mentioned above by way of example, partial pressures of nitrogen pl and p2 are used which are low: pl = 10 to 15 Pascal, p2 = 20 to 25 Pascal, while for a stainless steel, for example an austenitic steel with 18% chromium and 10% nickel, partial pressures of nitrogen pl and p2 are used which are higher: pl = 30 Pascal, p2 = 40 to 60 Pascal. These very specific particular conditions of the two nitriding sequences make it possible to obtain on the surface of the nitrided part a nitrogen diffusion layer, without a combination layer.

Il est bien entendu que l'on peut, sans sortir du cadre de l'invention, imaginer des variantes et perfectionnements de détails, de même qu'envisager l'emploi de moyens équivalents.It is understood that it is possible, without departing from the scope of the invention, to imagine variants and refinements of details, as well as to envisage the use of equivalent means.

Claims (7)

1.- Méthode de nitruration ionique de pièces en aciers de toutes nuances, depuis les aciers peu alliés jusqu'aux aciers inoxydables et aux aciers réfractaires,
caractérisé par la succession des quatre phases suivantes : (a) une opération d'écrouissage préalable de la pièce, dont le taux final d'écrouissage est compris entre 10 % et 40 % ; (b) une première séquence de nitruration ionique, de durée limitée, c'est-à-dire comprise entre une heure et 10 heures selon la nature de l'acier à traiter, et plus précisément comprise entre une et 5 heures pour les aciers faiblement alliés, et entre 5 et 10 heures pour les aciers fortement alliés, réalisée à une température tl comprise entre 450° et 520° dans un mélange gazeux constitué par de l'azote et de l'hydrogène, tel que la pression partielle d'azote p1 soit comprise entre 10 et 35 Pascal, et que la pression gazeuse totale soit comprise entre 200 et 650 Pascal ; (c) une deuxième séquence de nitruration ionique dont la durée et la température sont ajustées en fonction de l'influence bénéfique de l'écrouissage préalable selon (a) sur la cinétique de croissance des couches nitrurées, dont la durée est ainsi comprise entre 20 et 70 heures selon la nature de l'acier à traiter, dont la température t2 est comprise entre 500° et 580°C et est supérieure à tl d'au moins 10°C et d'au plus 50°C, cette deuxième séquence étant réalisée dans un mélange gazeux constitué par de l'azote et de l'hydrogène, tel que la pression partielle d'azote p2 soit comprise entre 20 et 100 Pascal, et soit supérieure à pl, tandis que la pression gazeuse totale reste comprise entre 20 et 650 Pascal ; (d) un refroidissement final sous vide. 1.- Method of ionic nitriding of steel parts of all grades, from low alloyed steels to stainless steels and refractory steels,
characterized by the succession of the following four phases: (a) a prior work hardening operation, the final work hardening rate of which is between 10% and 40 % ; (b) a first sequence of ionic nitriding, of limited duration, that is to say between one hour and 10 hours depending on the nature of the steel to be treated, and more precisely between one and 5 hours for steels weakly alloyed, and between 5 and 10 hours for highly alloyed steels, produced at a temperature tl of between 450 ° and 520 ° in a gas mixture consisting of nitrogen and hydrogen, such as the partial pressure of nitrogen p1 is between 10 and 35 Pascal, and the total gas pressure is between 200 and 650 Pascal; (c) a second sequence of ionic nitriding, the duration and the temperature of which are adjusted as a function of the beneficial influence of the previous work hardening according to (a) on the growth kinetics of the nitrided layers, the duration of which is thus between 20 and 70 hours depending on the nature of the steel to be treated, the temperature t2 of which is between 500 ° and 580 ° C and is greater than tl by at least 10 ° C and at most 50 ° C, this second sequence being produced in a gaseous mixture consisting of nitrogen and hydrogen, such that the partial pressure of nitrogen p2 is between 20 and 100 Pascal, and is greater than pl, while the total gas pressure remains between 20 and 650 Pascal; (d) final cooling under vacuum. 2.- Méthode de nitruration ionique selon la revendication 1, caractérisée en ce que le taux final d'écrouissage préalable de la pièce à traiter est de l'ordre de 30 %.2. A method of ionic nitriding according to claim 1, characterized in that the final rate of prior work hardening of the part to be treated is of the order of 30%. 3.- Méthode de nitruration ionique selon l'une quelconque des revendications 1 et 2, caractérisée en ce que la durée de la première séquence de nitruration ionique et celle de la deuxième séquence sont d'autant plus longues que l'acier à traiter est plus chargé en éléments d'alliages.3. A method of ionic nitriding according to any one of claims 1 and 2, characterized in that the duration of the first sequence of ionic nitriding and that of the second sequence are all the longer as the steel to be treated is no longer loaded with alloying elements. 4.- Méthode de nitruration ionique selon l'une quelconque des revendications 1, 2 et 3, applicable aux pièces en aciers faiblement alliés, tels que les aciers au chrome-molybdène et les aciers au chrome-nickel-molybdène,
caractérisée en ce que la première séquence de nitruration ionique a une durée comprise entre 2 et 4 heures, qu'elle s'effectue à une température comprise entre 490° et 510°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote soit comprise entre 10 et 15 Pascal, et en ce que la deuxième séquence a une durée comprise entre 25 et 40 heures, qu'elle s'effectue à une température comprise entre 510° et 560°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote soit de l'ordre de 60 Pascal.4. A method of ionic nitriding according to any one of claims 1, 2 and 3, applicable to parts made of low-alloy steels, such as chromium-molybdenum steels and chromium-nickel-molybdenum steels,
characterized in that the first ion nitriding sequence has a between 2 and 4 hours, that it takes place at a temperature between 490 ° and 510 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial pressure of nitrogen is between 10 and 15 Pascal, and in that the second sequence has a duration between 25 and 40 hours, that it is carried out at a temperature between 510 ° and 560 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial nitrogen pressure is of the order of 60 Pascal. 5.- Méthode de nitruration ionique selon l'une quelconque des revendications 1, 2 et 3, applicable aux pièces en -aciers fortement alliés, tels que les aciers inoxydables au chrome, avec ou sans nickel, et les aciers réfractaires,
caractérisée en ce que la première séquence de nitruration ionique a une durée comprise entre 6 et 10 heures, qu'elle s'effectue à une température comprise entre 500° et 520°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote soit comprise entre 30 et 35 Pascal, et en ce que la deuxième séquence a une durée comprise entre 40 et 70 heures, qu'elle s'effectue à une température comprise entre 500° et 580°C, dans un mélange d'azote et d'hydrogène tel que la pression partielle d'azote soit comprise entre 60 et 80 Pascal.5. An ion nitriding method according to any one of claims 1, 2 and 3, applicable to parts made of highly alloyed steels, such as chromium stainless steels, with or without nickel, and refractory steels,
characterized in that the first ionic nitriding sequence has a duration of between 6 and 10 hours, that it takes place at a temperature of between 500 ° and 520 ° C, in a gaseous mixture of nitrogen and hydrogen such that the partial nitrogen pressure is between 30 and 35 Pascal, and that the second sequence has a duration between 40 and 70 hours, that it takes place at a temperature between 500 ° and 580 ° C, in a mixture of nitrogen and hydrogen such that the partial pressure of nitrogen is between 60 and 80 Pascal. 6.- Méthode de nitruration ionique selon l'une quelconque des revendications 1 à 5, caractérisée en ce que l'atmosphère réactive de nitruration est réglée, en fonction de la nature de l'acier à traiter, de manière que la couche de diffusion se trouve directement en surface de la: pièce, sans aucune couche de combinaison.6.- Method of ionic nitriding according to any one of claims 1 to 5, characterized in that the reactive nitriding atmosphere is adjusted, depending on the nature of the steel to be treated, so that the diffusion layer is directly on the surface of the: part, without any combination layer. 7.- Méthode de nitruration ionique selon la revendication 6, caractérisée en ce que la première séquence de nitruration ionique est d'une durée comprise entre 4 et 10 heures, est réalisée à une température tl comprise entre 500° et 520°C, dans un mélange gazeux, constitué d'azote et d'hydrogène, tel que la pression partielle d'azote pl soit comprise entre 10 et 30 Pascal, la pression gazeuse totale étant comprise entre 200 et 650 Pascal, et en ce que la deuxième séquence de nitruration ionique est d'une durée comprise entre 20 et 40 heures, et est réalisée à une température t2 comprise entre 530° et 550°C, dans un mélange gazeux d'azote et d'hydrogène tel que la pression partielle d'azote p2 supérieure à pl soit comprise entre 20 et 60 Pascal, la pression gazeuse totale restant comprise entre 200 et 650 Pascal.7.- Method of ionic nitriding according to claim 6, characterized in that the first sequence of ionic nitriding is of a duration between 4 and 10 hours, is carried out at a temperature tl between 500 ° and 520 ° C, in a gas mixture, consisting of nitrogen and hydrogen, such that the partial pressure of nitrogen pl is between 10 and 30 Pascal, the total gas pressure being between 200 and 650 Pascal, and in that the second sequence of ionic nitriding lasts between 20 and 40 hours, and is carried out at a temperature t2 between 530 ° and 550 ° C, in a gaseous mixture of nitrogen and hydrogen such as the partial pressure of nitrogen p2 greater than pl is between 20 and 60 Pascal, the total gas pressure remaining between 200 and 650 Pascal.
EP82400928A 1981-05-21 1982-05-19 Method of ionitriding a steel article which has been plastically deformed in advance Expired EP0067098B1 (en)

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AT82400928T ATE16293T1 (en) 1981-05-21 1982-05-19 METHOD OF IONIZING A STEEL WORKPIECE THAT HAS BEEN PLASTIC DEFORMED.

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FR8110129 1981-05-21
FR8110129A FR2506339A1 (en) 1981-05-21 1981-05-21 METHOD FOR THE ION NITRURATION OF A PLASTICALLY PREFORMED DEFORMED STEEL PART

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EP0067098A1 true EP0067098A1 (en) 1982-12-15
EP0067098B1 EP0067098B1 (en) 1985-10-30

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ZA (1) ZA823472B (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2193732A (en) * 1986-08-08 1988-02-17 Verdict Ion Technology Limited Improvements in tooling
US5658394A (en) * 1994-08-24 1997-08-19 Lindauer Dornier Gesellschaft Mbh Method for increasing the surface hardness of loom components exposed to friction
WO2007137557A2 (en) * 2006-05-30 2007-12-06 Schaeffler Kg Method for hardening running surfaces of roller bearing components
WO2016020384A1 (en) * 2014-08-08 2016-02-11 Plasma Metal S.A. Method for surface treatment of a stainless steel part
CN105695922A (en) * 2014-11-25 2016-06-22 上海新力动力设备研究所 Surface glow ion nitriding method of 30Cr3SiNiMoVA steel

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008060161B4 (en) * 2008-12-02 2012-07-19 Benteler Automobiltechnik Gmbh Method for producing a suspension component with increased fatigue strength and chassis component

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FR86012E (en) * 1963-12-11 1965-11-26 Berliet Automobiles friction elements particularly resistant to abrasion wear
DE2845757A1 (en) * 1977-10-20 1979-04-26 Kawasaki Heavy Ind Ltd ION NITRATION HARDENING PROCESS
DE2845756A1 (en) * 1977-10-20 1979-04-26 Kawasaki Heavy Ind Ltd ION NITRATION CURING PROCESS
GB2030600A (en) * 1978-07-14 1980-04-10 Kawasaki Heavy Ind Ltd Ion nitriding process
FR2446326A1 (en) * 1979-01-10 1980-08-08 Creusot Loire IMPROVEMENT IN ION NITRURATION OF ELONGATED HOLLOW BODIES, IN STEEL

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FR86012E (en) * 1963-12-11 1965-11-26 Berliet Automobiles friction elements particularly resistant to abrasion wear
DE2845757A1 (en) * 1977-10-20 1979-04-26 Kawasaki Heavy Ind Ltd ION NITRATION HARDENING PROCESS
DE2845756A1 (en) * 1977-10-20 1979-04-26 Kawasaki Heavy Ind Ltd ION NITRATION CURING PROCESS
GB2030600A (en) * 1978-07-14 1980-04-10 Kawasaki Heavy Ind Ltd Ion nitriding process
FR2446326A1 (en) * 1979-01-10 1980-08-08 Creusot Loire IMPROVEMENT IN ION NITRURATION OF ELONGATED HOLLOW BODIES, IN STEEL

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Title
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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2193732A (en) * 1986-08-08 1988-02-17 Verdict Ion Technology Limited Improvements in tooling
US5658394A (en) * 1994-08-24 1997-08-19 Lindauer Dornier Gesellschaft Mbh Method for increasing the surface hardness of loom components exposed to friction
WO2007137557A2 (en) * 2006-05-30 2007-12-06 Schaeffler Kg Method for hardening running surfaces of roller bearing components
WO2007137557A3 (en) * 2006-05-30 2008-12-11 Schaeffler Kg Method for hardening running surfaces of roller bearing components
US8479396B2 (en) 2006-05-30 2013-07-09 Schaeffler Technologies AG & Co. KG Method for hardening running surfaces of roller bearing components
WO2016020384A1 (en) * 2014-08-08 2016-02-11 Plasma Metal S.A. Method for surface treatment of a stainless steel part
CN105695922A (en) * 2014-11-25 2016-06-22 上海新力动力设备研究所 Surface glow ion nitriding method of 30Cr3SiNiMoVA steel

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DK157691C (en) 1990-07-02
DK157691B (en) 1990-02-05
ATE16293T1 (en) 1985-11-15
PT74775B (en) 1983-11-08
GR75839B (en) 1984-08-02
ZA823472B (en) 1983-03-30
EP0067098B1 (en) 1985-10-30
DE3267120D1 (en) 1985-12-05
ES8304613A1 (en) 1983-03-01
FR2506339B1 (en) 1983-12-23
DK228982A (en) 1982-11-22
FR2506339A1 (en) 1982-11-26
ES512331A0 (en) 1983-03-01
PT74775A (en) 1982-05-01

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