EP0076745B1 - Process for treating the surfaces of steels against wear, and coating obtained - Google Patents

Process for treating the surfaces of steels against wear, and coating obtained Download PDF

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Publication number
EP0076745B1
EP0076745B1 EP82401774A EP82401774A EP0076745B1 EP 0076745 B1 EP0076745 B1 EP 0076745B1 EP 82401774 A EP82401774 A EP 82401774A EP 82401774 A EP82401774 A EP 82401774A EP 0076745 B1 EP0076745 B1 EP 0076745B1
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Prior art keywords
molybdenum
chromium
layer
iron
sulfur
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German (de)
French (fr)
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EP0076745A1 (en
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Guy Nicolas
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Nicolas Guy
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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
    • C23C12/00—Solid state diffusion of at least one non-metal element other than silicon and at least one metal element or silicon into metallic material surfaces
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12576—Boride, carbide or nitride component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12597—Noncrystalline silica or noncrystalline plural-oxide component [e.g., glass, etc.]
    • Y10T428/12604—Film [e.g., glaze, etc.]

Definitions

  • the technical sector of the present invention is that of surface treatments of the surface layers of steel parts in order to improve their mechanical properties. More particularly, the technical sector of the present invention relates to treatments which aim to increase the resistance to wear of structural steel parts and tool steel subjected to friction.
  • coatings having good wear resistance are obtained.
  • These coatings generally consist of layers based on chromium carbides M 23 C 6 and M 7 C 3 , M denoting a metal which apart from the chromium (Cr) can be iron (Fe), molybdenum (Mo) vanadium (V) etc.
  • the layers obtained have a limited thickness; for example the layers obtained by chromizing treatment on steels having a carbon content of at least 0.15% have a total thickness of carbides of the order of 10 to 15 ⁇ m.
  • the lifetime of a system, thus treated, and subjected to friction depends on the kinetics of wear of this layer of carbides. For a given stressing mode, this lifetime is linked, on the one hand, to the total thickness of the hard surface layer, on the other hand, to the crystallization morphology of the carbides M 7 C 3 .
  • M 7 C 3 has a columnar structure which is harmful to good wear resistance. Furthermore, in the case of dry friction contact with antagonists of lesser hardness, these undergo very significant wear.
  • the aim of the present invention is to produce a surface coating of steel parts which improves the wear resistance of the part subjected to friction and makes it possible to increase the service life of systems subjected to friction while limiting the wear of the antagonists in contact by friction with said parts.
  • the subject of the present invention is a method of treatment against surface wear of steel parts with a carbon content of at least 0.15%, characterized in that a supply of sulfur is successively carried out on this surface of a metallic sulfide and chromium-plating in the vapor phase.
  • the addition of sulfur, by depositing the metal sulphide on the surface of the steel, is preferably done by depositing a varnish based on molybdenum disulphide or by depositing an iron-molybdenum alloy sulphide of formulation ( fe Mo) 3 S 4 .
  • an iron-molybdenum deposition is carried out prior to the deposition of iron-molybdenum sulfide.
  • Chromization is carried out at 950 ° C for 15 hours and without the flow of hydrogen.
  • hydrogen can desulfurize the deposit by the formation of H 2 S and thus prevent the formation of chromium sulfide on the surface of the substrate.
  • the coating obtained by the process according to the invention is characterized in that it consists of a surface layer of chromium-molybdenum sulfide, the molybdenum being substituted in the hexagonal network of chromium sulfide at the rate of a mass content less than 18% and a layer underlying the surface layer consisting of chromium carbides M 23 C 6 and M 7 C 3 .
  • the carbide layer is made up of two sublayers consisting successively of chromium carbide M 23 C 6 and chromium carbide M 7 C 3 .
  • the chromium carbide underlay M 7 C 3 is recrystallized over part of its thickness at from the substrate.
  • the steel used for this description is the low alloy steel 35CD4, widely used in industrial manufacturing. Any other steel with a carbon content of at least 0.15% could be used.
  • the sequenced processing according to the invention comprises two parts, the order of which must be respected.
  • the first part of this treatment consists of a treatment making it possible to deposit a sulphide of the iron-molybdenum sulphide or molybdenum sulphide type.
  • the treatment mode only matters with regard to the uniformity in thickness and distribution of the deposit. It is thus possible to carry out deposits of the varnish type based on molybdenum disulphide or to carry out deposits by the “sprettering-magnetron” technique of (Fe-Mo) 3 S 4 .
  • the latter technique allows good control of the thickness and distribution of the initial deposit.
  • a deposit of at least 5 ⁇ m is necessary to obtain good results.
  • a thickness of 8 to 15 ⁇ m is best suited to the conditions of subsequent chromization.
  • the chromizing treatment is carried out according to average parameters such as:
  • the external sulphide layer formed from the (Cr, Mo) S phase which crystallizes in the hexagonal system, is quite heterogeneous as regards its distribution of molybdenum and sulfur.
  • the iron is almost zero in content and molybdenum at a rate of at most 18%.
  • the underlying carbide layer is divided into two carbide sublayers M 23 C 6 and M 7 C 3 .
  • the latter carbide, rich in molybdenum, is partially recrystallized.
  • the iron was therefore pumped from the initial deposit of iron-molybdenum-sulfur, to give rise to deposit of chromium.
  • This last element diffusing through the whole of the initial deposit, has migrated to the substrate interface to form there with the carbon of the steel, the sequence of carbides obtained in conventional chromization, with however some different characteristics.
  • the M 23 C 6 carbide sublayer is much larger here and the M 7 C 3 carbide is partially recrystallized.
  • the general morphology of the layers is in the form of crystals with a spherular front. These crystals are distributed in domains separated by fairly shallow "channels".
  • the coating is divided into two main layers A and B with respective thicknesses of 9 ⁇ m, for a total thickness of 18 ⁇ m.
  • Layer A has a two-phase appearance with basaltic domains. These areas are generally set back from the outside surface. They correspond to channels.
  • Layer B consists of two sublayers Bi and B 2 ; revealed after basic attack, these sub-layers correspond to carbides; the sublayer 8 2 has the typical morphology of the carbide M 7 C 3 with recrystallization.
  • Layer A consists essentially of the elements chromium, sulfur, molybdenum.
  • the two-phase aspect observed in metallography seems to be due only to relative variations in sulfur and molybdenum.
  • the iron is almost zero in content, and molybdenum up to 18%.
  • the hardness of this phase is 777 ⁇ 50 Hv0.02.
  • Layer B is made up of two layers formed of carbides where no sulfur is detected.
  • the chromium concentration levels and the shape of the carbon distribution profiles indicate that the sublayers B i and B 2 correspond respectively to the carbides M 23 C 6 and M 7 C 3 . It should be noted that the molybdenum content in these carbides is high. But molybdenum can largely replace this type of phase.
  • the carbide M 7 C 3 is in this case partially recrystallized, which ensures an increase in toughness to this layer of carbide.
  • the hardness of carbide M 23 C 6 is 1400 ⁇ 200 Hv0.02, that of carbide M 7 C 3 is 2700 ⁇ 500 Hv0.02, for the recrystallized domain.
  • the advantage of the invention resides in the fact that it is possible to increase the overall performance of wear resistance of systems subjected to dry friction or poorly lubricated. Furthermore, this gain in quality can be acquired from various implementation techniques without fundamentally modifying the characteristics obtained. A change in technology for carrying out the conventional chromization treatment requires only a fine-tuning of the parameters, which is of obvious interest from an economic point of view.
  • the economic benefit also lies in improving the service lives and reliability of the parts.
  • the invention can be applied to any moving mechanical system, made of steel, in particular weapon mechanisms or engine transmission mechanisms, etc.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physical Vapour Deposition (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)

Description

Le secteur technique de la présente invention est celui des traitements de surface des couches superficielles de pièces en acier en vue d'améliorer leurs propriétés mécaniques. Plus particulièrement le secteur technique de la présente invention concerne les traitements qui visent à accroître la résistance à l'usure de pièces en acier de construction et acier à outils soumises à frottement.The technical sector of the present invention is that of surface treatments of the surface layers of steel parts in order to improve their mechanical properties. More particularly, the technical sector of the present invention relates to treatments which aim to increase the resistance to wear of structural steel parts and tool steel subjected to friction.

Les principaux traitements de ce type actuellement pratiqués sur les aciers à outils sont la nitruration, l'oxydation, la chromisation, le chromage dur et la boruration. La sulfuration directe d'un substrat n'a jamais été employée pour des traitements de ce type car cet élément conduit à la fragilisation des aciers. Le soufre est utilisé sous forme combinée au molybdène ou au fer en vue d'application antifriction comme lubrifiant solide et non pas en résistance à l'usure.The main treatments of this type currently practiced on tool steels are nitriding, oxidation, chromium plating, hard chromium plating and boriding. Direct sulfurization of a substrate has never been used for treatments of this type because this element leads to the embrittlement of steels. Sulfur is used in combined form with molybdenum or iron for antifriction application as a solid lubricant and not for wear resistance.

Par les traitements de chromisation connus, on obtient des revêtements ayant une bonne résistance à l'usure. Ces revêtements se composent généralement de couches à base de carbures de chrome M23C6 et M7C3, M désignant un métal qui à part le chrome (Cr) peut être le fer (Fe), le molybdène (Mo) le vanadium (V) etc. Les couches obtenues ont une épaisseur limitée; par exemple les couches obtenues par traitement de chromisation sur des aciers ayant une teneur en carbone d'au moins 0,15% ont une épaisseur totale de carbures de l'ordre de 10 à 15 µm.By the known chromium-plating treatments, coatings having good wear resistance are obtained. These coatings generally consist of layers based on chromium carbides M 23 C 6 and M 7 C 3 , M denoting a metal which apart from the chromium (Cr) can be iron (Fe), molybdenum (Mo) vanadium (V) etc. The layers obtained have a limited thickness; for example the layers obtained by chromizing treatment on steels having a carbon content of at least 0.15% have a total thickness of carbides of the order of 10 to 15 μm.

Or, la durée de vie d'un système, ainsi traité, et sollicité en frottement, dépend de la cinétique d'usure de cette couche de carbures. Pour un mode de sollicitation donné, cette durée de vie est liée, d'une part, à l'épaisseur totale de la couche dure superficielle, d'autre part, à la morphologie de cristallisation des carbures M7C3. Dans ces traitements de chromisation connus, M7C3 a une structure colonnaire néfaste à une bonne résistance à l'usure. Par ailleurs, dans le cas de contact en frottement sec avec des antagonistes de moindre dureté, ceux-ci subissent une usure très importante.However, the lifetime of a system, thus treated, and subjected to friction, depends on the kinetics of wear of this layer of carbides. For a given stressing mode, this lifetime is linked, on the one hand, to the total thickness of the hard surface layer, on the other hand, to the crystallization morphology of the carbides M 7 C 3 . In these known chromizing treatments, M 7 C 3 has a columnar structure which is harmful to good wear resistance. Furthermore, in the case of dry friction contact with antagonists of lesser hardness, these undergo very significant wear.

Le but de la présente invention est la réalisation d'un revêtement de surface de pièces en acier qui améliore la résistance à l'usure de la pièce soumise à frottement et permette d'augmenter la durée de vie des systèmes sollicités en frottement tout en limitant l'usure des antagonistes en contact par frottement avec lesdites pièces.The aim of the present invention is to produce a surface coating of steel parts which improves the wear resistance of the part subjected to friction and makes it possible to increase the service life of systems subjected to friction while limiting the wear of the antagonists in contact by friction with said parts.

La présente invention a pour objet un procédé de traitement contre l'usure de surface de pièces en acier à teneur en carbone d'au moins 0,15%, caractérisé en ce qu'on effectue successivement sur cette surface un apport de soufre par dépôt d'un sulfure métallique et une chromisation en phase vapeur.The subject of the present invention is a method of treatment against surface wear of steel parts with a carbon content of at least 0.15%, characterized in that a supply of sulfur is successively carried out on this surface of a metallic sulfide and chromium-plating in the vapor phase.

Par apport préalable de soufre sur l'acier de base, on modifie les conditions d'échange entre le chrome déposé au cours de la chromisation ultérieure et les éléments du substrat et on permet ainsi au soufre de se combiner avec le chrome. On obtient en effet une couche superficielle originale composée de sulfure de chrome. La surface ainsi traitée présente une résistance à l'usure satisfaisante et offre en outre l'avantage de réduire très largement l'usure de l'antagoniste en acier non revêtu. Au cours du frottement, le soufre réagit par contact avec l'antagoniste et forme sur ce dernier des couches de transfert riches en espèces soufrées favorisant sa moindre usure. Ce traitement permet d'autre part d'augmenter l'épaisseur totale de la couche dure en surface. La teneur en carbone supérieure ou égale à 0,15% est nécessaire pour la constitution de sous-couches de carbures qui participent à la résistance à l'usure.By prior supply of sulfur on the base steel, the exchange conditions between the chromium deposited during the subsequent chromization and the elements of the substrate are modified and the sulfur is thus allowed to combine with the chromium. An original surface layer composed of chromium sulfide is obtained. The surface thus treated has satisfactory wear resistance and also offers the advantage of greatly reducing the wear of the antagonist in uncoated steel. During friction, the sulfur reacts by contact with the antagonist and forms on the latter transfer layers rich in sulfur species favoring its least wear. This treatment also makes it possible to increase the total thickness of the hard layer on the surface. The carbon content greater than or equal to 0.15% is necessary for the constitution of sublayers of carbides which participate in the resistance to wear.

L'apport de soufre, par dépôt en surface de l'acier du sulfure métallique, se fait préférentiellement par dépôt d'un vernis à base de bisulfure de molybdène ou par dépôt d'un sulfure d'alliage de fer-molybdène de formulation (fe­ Mo)3S4.The addition of sulfur, by depositing the metal sulphide on the surface of the steel, is preferably done by depositing a varnish based on molybdenum disulphide or by depositing an iron-molybdenum alloy sulphide of formulation ( fe Mo) 3 S 4 .

La sulfuration directe du substrat est en effet à éviter car le soufre conduit à la fragilisation des aciers. D'autre part, par réaction d'échange avec les éléments métalliques, il est possible d'assurer le transport du chrome à partir d'un halogénure de chrome en phase vapeur.Direct sulfurization of the substrate is indeed to be avoided since sulfur leads to the embrittlement of steels. On the other hand, by exchange reaction with the metallic elements, it is possible to transport chromium from a chromium halide in the vapor phase.

Avantageusement, on effectue préalablement au dépôt de sulfure de fer-molybdène, un dépôt de fer-molybdène.Advantageously, an iron-molybdenum deposition is carried out prior to the deposition of iron-molybdenum sulfide.

Si le dépôt de sulfure de fer-molybdène est mis en oeuvre directement sur la pièce, son adhérence dans le temps est assez faible. Par contre, und dépôt préalable sans soufre accroît notablement l'adhérence.If the deposit of iron-molybdenum sulphide is applied directly to the part, its adhesion over time is quite weak. On the other hand, a sulfur-free pre-deposit significantly increases adhesion.

La chromisation est effectuée à 950° C pendant 15 heures et sans débit d'hydrogène.Chromization is carried out at 950 ° C for 15 hours and without the flow of hydrogen.

En effet, l'hydrogène peut désulfurer le dépôt par formation de H2S et ainsi empêcher la formation de sulfure de chrome en surface du substrat.Indeed, hydrogen can desulfurize the deposit by the formation of H 2 S and thus prevent the formation of chromium sulfide on the surface of the substrate.

Les traitements thermiques usuels peuvent être pratiqués sur les aciers traités par ce procédé. Cependant, la trempe à l'eau est déconseillée, car elle peut introduire des fissurations dans le revêtement effectué selon l'invention.The usual heat treatments can be practiced on steels treated by this process. However, water quenching is not recommended, as it can introduce cracks in the coating made according to the invention.

Dans la suite de la description, tous les pourcentages sont des pourcentages en masse.In the following description, all the percentages are percentages by mass.

Le revêtement obtenu par le procédé selon l'invention est caractérisé en ce qu'il est constitué par une couche superficielle de sulfure de chrome-molybdène, le molybdène étant substitué dans le réseau hexagonal de sulfure de chrome à raison d'une teneur en masse inférieure à 18% et une couche sous-jacente à la couche superficielle constituée de carbures de chrome M23C6 et M7C3.The coating obtained by the process according to the invention is characterized in that it consists of a surface layer of chromium-molybdenum sulfide, the molybdenum being substituted in the hexagonal network of chromium sulfide at the rate of a mass content less than 18% and a layer underlying the surface layer consisting of chromium carbides M 23 C 6 and M 7 C 3 .

La couche de carbure se compose de deux sous-couches constituées successivement par du carbure de chrome M23C6 et du carbure de chrome M7C3.The carbide layer is made up of two sublayers consisting successively of chromium carbide M 23 C 6 and chromium carbide M 7 C 3 .

La sous-couche de carbure de chrome M7C3 est recristallisée sur une partie de son épaisseur à partir du substrat.The chromium carbide underlay M 7 C 3 is recrystallized over part of its thickness at from the substrate.

On constate en effet une modification du mode de cristallisation des carbures M7C3. Le molybdène codiffuse avec le chrome dans les carbures M7C3 permettant ainsi de réduire la quantité de chrome dans cette phase et d'atteindre la teneur critique de 60% de chrome pour laquelle se produit la recristallisation de M7C3. Celle-ci accroît la ténacité de la couche de carbures et par ce fait sa résistance à l'usure.There is indeed a change in the crystallization mode of M 7 C 3 carbides. Molybdenum codiffuses with chromium in M 7 C 3 carbides, thereby reducing the amount of chromium in this phase and reaching the critical content of 60% chromium for which recrystallization of M 7 C 3 occurs. This increases the toughness of the carbide layer and thereby its resistance to wear.

D'autres avantages et caractéristiques de l'invention apparaîtront dans la description d'un mode de réalisation de l'invention non limitatif qui va suivre.Other advantages and characteristics of the invention will appear in the description of an embodiment of the invention which is not limiting, which follows.

L'acier retenu pour cette description est l'acier faiblement allié 35CD4, largement utilisé dans les fabrications industrielles. Tout autre acier dont la teneur en carbone serait d'au moins 0,15%, pourrait être employé.The steel used for this description is the low alloy steel 35CD4, widely used in industrial manufacturing. Any other steel with a carbon content of at least 0.15% could be used.

Le traitement séquencé selon l'invention comprend deux parties, dont l'ordre doit être respecté. La première partie de ce traitement consiste en un traitement permettant d'effectuer un dépôt de sulfure du type sulfure de fer-molybdène ou sulfure de molybdène. Le mode de traitement n'a d'importance que vis-à-vis de l'homogénéité en épaisseur et en répartition du dépôt. On peut ainsi effectuer des dépôts du type vernis à base de bisulfure de molybdène ou procéder à des dépôts par la technique »sprettering-magnetron« de (Fe-Mo)3S4. Cette dernière technique permet une bonne maîtrise de l'épaisseur et de la répartition du dépôt initial.The sequenced processing according to the invention comprises two parts, the order of which must be respected. The first part of this treatment consists of a treatment making it possible to deposit a sulphide of the iron-molybdenum sulphide or molybdenum sulphide type. The treatment mode only matters with regard to the uniformity in thickness and distribution of the deposit. It is thus possible to carry out deposits of the varnish type based on molybdenum disulphide or to carry out deposits by the “sprettering-magnetron” technique of (Fe-Mo) 3 S 4 . The latter technique allows good control of the thickness and distribution of the initial deposit.

Un dépôt d'au moins 5 µm est nécessaire pour obtenir de bons résultats. Une épaisseur de 8 à 15 µm est la mieux adaptée aux conditions de chromisation ultérieure.A deposit of at least 5 µm is necessary to obtain good results. A thickness of 8 to 15 µm is best suited to the conditions of subsequent chromization.

Quand les pièces sont traitées sans dépôt préalable de fer-molybdène, on observe des faïençages de dépôt, avant chromisation. Des traitements avec dépôt préalable de fer-molybdène ont donc été effectués. Ils n'ont pas présenté de défaut d'adhérence.When the parts are treated without prior deposition of iron-molybdenum, deposit cracks are observed before chromization. Treatments with prior deposition of iron-molybdenum were therefore carried out. They did not exhibit any adhesion defect.

Après dépôt de la couche de sulfure, on procède au traitement de chromisation selon des paramètres moyens tels que:

Figure imgb0001
After depositing the sulphide layer, the chromizing treatment is carried out according to average parameters such as:
Figure imgb0001

Si l'on veut éviter la formation superficielle d'une couche de chrome exempte de soufre, il est nécessaire dans ce cas de supprimer le débit d'hydrogène habituellement assuré dans ces types de traitement.If one wishes to avoid the surface formation of a sulfur-free chromium layer, it is necessary in this case to suppress the flow of hydrogen usually provided in these types of treatment.

Il est à noter que le type de cément et le mode statique ou dynamique de transport ne conditionnent pas ici la nature du revêtement; ils n'en modulent que les épaisseurs de couches relatives.It should be noted that the type of cement and the static or dynamic mode of transport do not condition the nature of the coating here; they only modulate the thicknesses of relative layers.

Deux couches principales d'égales épaisseurs, respectivement à base de sulfure et de carbures de chrome, composent le revêtement obtenu après chromisation.Two main layers of equal thicknesses, respectively based on sulfide and chromium carbides, make up the coating obtained after chromization.

La couche externe de sulfure, formée de la phase (Cr, Mo)S qui cristallise dans le système hexagonal, est assez hétérogène quant à sa répartition en molybdène et en soufre. Le fer y est en teneur quasiment nulle et le molybdène à raison d'au plus 18%.The external sulphide layer, formed from the (Cr, Mo) S phase which crystallizes in the hexagonal system, is quite heterogeneous as regards its distribution of molybdenum and sulfur. The iron is almost zero in content and molybdenum at a rate of at most 18%.

La couche sous-jacente de carbures se répartit en deux sous-couches de carbures M23C6 et M7C3. Ce dernier carbure riche en molybdène, est partiellement recristallisé.The underlying carbide layer is divided into two carbide sublayers M 23 C 6 and M 7 C 3 . The latter carbide, rich in molybdenum, is partially recrystallized.

Au cours des échanges, le fer a donc été pompé du dépôt initial de fer-molybdène-soufre, pour donner lieu à dépôt de chrome. Ce dernier élément, diffusant à travers l'ensemble du dépôt initial, a migré jusqu'à l'interface de substrat pour y former avec le carbone de l'acier, la séquence de carbures obtenue en chromisation classique, avec toutefois quelques caractéristiques différentes. La sous-couche de carbure M23C6 est ici beaucoup plus importante et le carbure M7C3 est partiellement recristallisé.During the exchanges, the iron was therefore pumped from the initial deposit of iron-molybdenum-sulfur, to give rise to deposit of chromium. This last element, diffusing through the whole of the initial deposit, has migrated to the substrate interface to form there with the carbon of the steel, the sequence of carbides obtained in conventional chromization, with however some different characteristics. The M 23 C 6 carbide sublayer is much larger here and the M 7 C 3 carbide is partially recrystallized.

En surface, la morphologie générale des couches se présente sous la forme de cristaux à front sphérulaire. Ces cristaux sont répartis en domaines séparés par des »canaux« assez peu profonds.On the surface, the general morphology of the layers is in the form of crystals with a spherular front. These crystals are distributed in domains separated by fairly shallow "channels".

En coupe, le revêtement se répartit en deux couches principales A et B d'épaisseurs respectives de 9 µm, soit une épaisseur totale de 18 µm.In section, the coating is divided into two main layers A and B with respective thicknesses of 9 µm, for a total thickness of 18 µm.

La couche A a un aspect biphasé avec des domaines à caractère basaltique. Ces domaines sont en général en retrait par rapport à la surface extérieure. Ils correspondent à des canaux.Layer A has a two-phase appearance with basaltic domains. These areas are generally set back from the outside surface. They correspond to channels.

La couche B se compose de deux sous-couches Bi et B2; révélées après attaque basique, ces sous-couches correspondent à des carbures; la sous-couche 82 a la morphologie typique du carbure M7C3 avec recristallisation.Layer B consists of two sublayers Bi and B 2 ; revealed after basic attack, these sub-layers correspond to carbides; the sublayer 8 2 has the typical morphology of the carbide M 7 C 3 with recrystallization.

La couche A se compose essentiellement des éléments chrome, soufre, molybdène. L'aspect biphasé observé en métallographie ne semble dû qu'à des variations relatives du soufre et du molybdène. Le fer y est en teneur quasiment nulle, et le molybdène jusqu'à 18%. La dureté de cette phase est de 777±50 Hv0,02.Layer A consists essentially of the elements chromium, sulfur, molybdenum. The two-phase aspect observed in metallography seems to be due only to relative variations in sulfur and molybdenum. The iron is almost zero in content, and molybdenum up to 18%. The hardness of this phase is 777 ± 50 Hv0.02.

Sur la base des données du diagramme binaire chrome-soufre, il apparaît d'après le niveau de concentration du chrome dans une couche que la phase dont elle se compose, est celle du sulfure de chrome CrS. Cette phase cristallise dans le système hexagonal (a=3,45 Å, c=5,76 Å c/a=1,67).Based on the data of the chromium-sulfur binary diagram, it appears from the level of concentration of chromium in a layer that the phase of which it is composed is that of chromium sulfide CrS. This phase crystallizes in the hexagonal system (a = 3.45 Å, c = 5.76 Å c / a = 1.67).

La couche B se compose de deux couches formées de carbures où l'on ne détecte pas de soufre. Les niveaux de concentration en chrome et l'allure des profils de répartition du carbone indiquent que les sous-couches Bi et B2 correspondent respectivement aux carbures M23C6 et M7C3. Il est à remarquer que la teneur en molybdène dans ces carbures est élevée. Mais le molybdène peut se substituer largement dans ce type de phase.Layer B is made up of two layers formed of carbides where no sulfur is detected. The chromium concentration levels and the shape of the carbon distribution profiles indicate that the sublayers B i and B 2 correspond respectively to the carbides M 23 C 6 and M 7 C 3 . It should be noted that the molybdenum content in these carbides is high. But molybdenum can largely replace this type of phase.

Le carbure M7C3 est dans ce cas partiellement recristallisé, ce qui assure un accroissement de ténacité à cette couche de carbure. La dureté du carbure M23C6 est de 1400±200 Hv0,02, celle du carbure M7C3 est de 2700 ±500 Hv0,02, pour le domaine recristallisé.The carbide M 7 C 3 is in this case partially recrystallized, which ensures an increase in toughness to this layer of carbide. The hardness of carbide M 23 C 6 is 1400 ± 200 Hv0.02, that of carbide M 7 C 3 is 2700 ± 500 Hv0.02, for the recrystallized domain.

A l'inverse des résultats enregistrés lors des précédentes analyses, on s'aperçoit ici que le molybdène au lieu d'être pompé dans le substrat pour migrer vers les carbures en formation, a en fait diffusé jusque dans celui-ci à partir du dépôt initial.Contrary to the results recorded during the previous analyzes, we notice here that the molybdenum instead of being pumped in the substrate to migrate towards the carbides in formation, in fact diffused until in this one from the deposit initial.

Il est à noter que par chromisation directe avec des paramètres identiques de traitement la couche avait une épaisseur totale de carbure de 13 µm.It should be noted that by direct chromization with identical treatment parameters the layer had a total thickness of carbide of 13 μm.

Une caractérisation tribologique de cette couche a été effectuée. En essai standard d'usure sur tribomètre en configuration pion-disques, les paramètres d'essai étaient les suivants:

  • - disque plan en acier 35CD4,
  • - pions cylindriques à bout plat de diamètre 1,5 mm en acier 35CD4, traités thermiquement pour une dureté de 310 H vo.5,
  • - effort normal 1 N, soit une contrainte statique normale de 0,56 MPa,
  • - vitesse circonférentielle: 500 tr. mn-1
  • - vitesse linéaire de contact: 41 m . mn-1
  • - température de laboratoire: 20° C,
  • - frottement sec,
  • - distance de sollicitation: 50 km
A tribological characterization of this layer was carried out. In the standard wear test on a tribometer in disc-disc configuration, the test parameters were as follows:
  • - 35CD4 steel flat disc,
  • - cylindrical pins with flat ends, diameter 1.5 mm, made of 35CD4 steel, heat treated for a hardness of 310 H v o . 5 ,
  • - normal force 1 N, i.e. a normal static stress of 0.56 MPa,
  • - circumferential speed: 500 rpm. mn- 1
  • - linear contact speed: 41 m. mn- 1
  • - laboratory temperature: 20 ° C,
  • - dry friction,
  • - operating distance: 50 km

Des essais identiques étant effectués sur disques 35CD4 chromisés directement avec les mêmes paramètres de traitement, les résultats du tableau montrent que:

  • a) la couche composée de sulfure de chrome est moins usée que la couche obtenue par chromisation directe;
  • b) le pion antagoniste, qui n'a pas de traitement spécifique anti-usure, est ici très peu endommagé. Cette usure particulièrement faible est assurée par un film transfert à base de soufre, oxygène et carbone mis en évidence par spectrométrie Auger.
    Figure imgb0002
Identical tests being carried out on 35CD4 chromized discs directly with the same processing parameters, the results of the table show that:
  • a) the layer composed of chromium sulfide is less used than the layer obtained by direct chromization;
  • b) the antagonist counter, which has no specific anti-wear treatment, is very little damaged here. This particularly low wear is ensured by a transfer film based on sulfur, oxygen and carbon highlighted by Auger spectrometry.
    Figure imgb0002

L'intérêt de l'invention réside dans le fait qu'il est possible d'accroître les performances globales de résistance à l'usure des systèmes sollicités en frottement à sec ou mal lubrifiés. Par ailleurs, ce gain de qualité peut être acquis à partir de techniques de mise en oeuvre diverses sans pour autant modifier d'une façon fondamentale les caractéristiques obtenues. Un changement de technologie de réalisation du traitement de chromisation classique ne nécessite qu'une mise au point des paramètres ce qui est d'un intérêt évident du point de vue économique.The advantage of the invention resides in the fact that it is possible to increase the overall performance of wear resistance of systems subjected to dry friction or poorly lubricated. Furthermore, this gain in quality can be acquired from various implementation techniques without fundamentally modifying the characteristics obtained. A change in technology for carrying out the conventional chromization treatment requires only a fine-tuning of the parameters, which is of obvious interest from an economic point of view.

L'intérêt économique réside en outre dans l'amélioration des durées de vie et de la fiabilité des pièces.The economic benefit also lies in improving the service lives and reliability of the parts.

L'invention peut s'appliquer à tout système mécanique en mouvement, réalisé en acier, notamment les mécanismes d'armes ou les mécanismes de transmission de moteurs etc.The invention can be applied to any moving mechanical system, made of steel, in particular weapon mechanisms or engine transmission mechanisms, etc.

Claims (10)

1. A method for treating steel parts having a carbon content of at least 0.15%, said treatment providing said steel parts with protection against surface wear, characterised by the fact that, suc- cevely one realises addition of sulfur on this surface by depositing a metal sulfid and a vapor phase chromizing.
2. The method of claim 1, wherein the addition of sulfur is effected by depositing a varnish of molybdenum disulfide.
3. The method of claim 1, wherein the addition of sulfur is effected by depositing a sulfide of an iron-molybdenum alloy having the formula (Fe-Mo)3S4.
4. The method according to claim 2 or 3, wherein prior to depositing the iron-molybdenum sulfide, iron-molybdenum is deposited on the surface of the steel.
5. The method of claim 4, wherein a first layer of iron-molybdenum or at least 1 µm in thickness is deposited, followed by a second layer consisting essentially of iron-molybdenum of at least 4 µm in thickness.
6. The method according to claims 1-5, wherein the chromizing is effected at 950° C for 15 hours without flow of hydrogen.
7. The method according to claims 1-6, additionally comprising a thermal hardening-tempering treatment without water quenching.
8. An anti-wear surface coating for steel parts obtained by the method according to claims 1-7, characterised in that it is constitued by a surface layer of chromium-molybdenum sulfide, the molybdenum being substituted in a hexagonal lattice of the chromium sulfide in an amount by weight of at most 18%, and an inner layer underlying the surface layer and consisting essentially of chromium carbides M23C6 and M7C3.
9. The surface coating according to claim 8, wherein said layer of carbides comprises two sublayers formed in succession by chromium carbide M23C6 and chromium carbide M7C3, respectively.
10. The surface coating according to claim 9, wherein said chromium carbide M7C3 sublayer is recrystallised over a portion of its thickness, starting from the substrate.
EP82401774A 1981-10-06 1982-09-30 Process for treating the surfaces of steels against wear, and coating obtained Expired EP0076745B1 (en)

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FR8118780 1981-10-06
FR8118780A FR2514034A1 (en) 1981-10-06 1981-10-06 PROCESS FOR TREATING THE SURFACE OF STEELS AGAINST WEAR AND COATING OBTAINED

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US6042949A (en) * 1998-01-21 2000-03-28 Materials Innovation, Inc. High strength steel powder, method for the production thereof and method for producing parts therefrom
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US2243787A (en) 1938-06-30 1941-05-27 Allegheny Ludlum Steel Colored steel
CH365921A (en) * 1958-11-04 1962-11-30 Berghaus Elektrophysik Anst Process for treating the surface of metal bodies
FR1535457A (en) * 1966-11-30 1968-08-09 Applic Des Traitements De Surf Igneous baths for the treatment of metal surfaces
GB1356268A (en) * 1970-05-21 1974-06-12 Kito Kk Preparation of fine powders
US3769098A (en) 1971-05-19 1973-10-30 Kito Kk Process of manufacturing fine powders of metal halide
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FR2514034A1 (en) 1983-04-08

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