EP3237648A1 - Method for surface treatment of a steel component by nitriding or nitrocarburising, oxidising and then impregnating - Google Patents

Method for surface treatment of a steel component by nitriding or nitrocarburising, oxidising and then impregnating

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Publication number
EP3237648A1
EP3237648A1 EP15821125.0A EP15821125A EP3237648A1 EP 3237648 A1 EP3237648 A1 EP 3237648A1 EP 15821125 A EP15821125 A EP 15821125A EP 3237648 A1 EP3237648 A1 EP 3237648A1
Authority
EP
European Patent Office
Prior art keywords
nitriding
minutes
process according
carried out
nitrocarburizing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP15821125.0A
Other languages
German (de)
French (fr)
Other versions
EP3237648B1 (en
Inventor
Pierre-Louis MAGDINIER
Marie-Noëlle DESBOUCHE-JANNY
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hydromecanique et Frottement SAS
Original Assignee
HEF SAS
Hydromecanique et Frottement SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by HEF SAS, Hydromecanique et Frottement SAS filed Critical HEF SAS
Priority to PL15821125T priority Critical patent/PL3237648T3/en
Priority to SI201531209T priority patent/SI3237648T1/en
Publication of EP3237648A1 publication Critical patent/EP3237648A1/en
Application granted granted Critical
Publication of EP3237648B1 publication Critical patent/EP3237648B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • 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
    • C23C8/80—After-treatment
    • 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
    • C23C8/34—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in more than one step
    • 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
    • C23C8/40—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 liquids, e.g. salt baths, liquid suspensions
    • C23C8/58—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 liquids, e.g. salt baths, liquid suspensions more than one element being applied in more than one step
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening

Definitions

  • the invention relates to a method for surface treatment of a ferrous metal part, in practice made of alloy steel or not, having a good resistance to corrosion due to an impregnation treatment.
  • the invention applies to any type of mechanical parts intended to ensure in service a mechanical function and having a high hardness, a long resistance to corrosion and wear. This is for example the case of many parts used in the field of automotive or aeronautics.
  • nitriding and nitrocarburizing are thermochemical treatments of nitrogen (respectively nitrogen and carbon) by combination-diffusion: it forms on the surface a combination layer formed of nitrides of iron (there exists several possible phases), under which nitrogen is present by diffusion.
  • the document EP-0 053 521 proposed, mainly for piston pins whose corrosion resistance and / or coefficient of friction was to be improved, a nitrocarburizing treatment adapted to form an Epsilon phase layer and a finishing treatment consisting in covering the Epsilon layer with a topcoat made of a resin
  • a resin the document mentions a very wide range, including acrylic resins, alkyds, maleic esters, epoxides, formaldehyde, phenolics, butyral-polyvinyl, polyvinyl chlorides, polyamides, polyimides, polyurethanes, silicones, polyvinyl ethers and urea-formaldehyde, advantageously loaded with additives chosen from phosphates and zinc chromates (to improve corrosion resistance), and / or silicone, waxes, poly-tetrafluoroethylenes, molybdenum diesulfite, graphite or zinc stearate (for reduce the coefficient of friction).
  • Document EP-0 122 762 describes a method of manufacturing corrosion-resistant steel parts, comprising nitriding steps (in the Epsilon phase, as above), then gas-phase oxidation, and then application of waxy material (Castrai V425) containing aliphatic hydrocarbons and Group 2a metal soaps, preferably calcium and / or barium soaps.
  • the resistance to salt spray corrosion was of the order of 250 hours.
  • the Applicant has itself proposed treatment processes to obtain even better outfits to corrosion.
  • EP-0 497 663 it has proposed a method of subjecting ferrous metal parts to nitriding, typically to a molten salt bath consisting of cyanates and sodium, potassium and lithium, followed by bath oxidation. of molten salts or in an oxidizing ionizing atmosphere, so as to obtain a nitrided layer comprising a deep and compact underlayer and a well-controlled surface layer of porosity and finally to deposit a polymer with a thickness of between 3 and 20 ⁇ , fluoroethylene-propylene (FEP), or even polytetrafluoroethylene (PTFE), or even polymers or copolymers of fluorinated or silicone polyurethanes, or polyamide-polyimides.
  • FEP fluoroethylene-propylene
  • PTFE polytetrafluoroethylene
  • the impregnating wax is an organic compound with a high molecular weight of between 500 and 10,000 and a surface tension in the liquid state of between 10 and 73 mN / m.
  • the contact angle between the solid phase and the surface layer and the wax in the liquid state is between 0 and 75 degrees.
  • the wax is chosen from natural waxes, synthetic waxes polyethylenes, polypropylenes, polyesters, fluorinated or modified petroleum residues.
  • EP-0 560 641 discloses a process for the phosphating of steel parts to improve the corrosion and wear resistance, making it possible to obtain specific surface characteristics resulting from a phosphating treatment preceded by a nitriding in a bath of molten salts containing sulfur species, a nitriding operation in a molten salt bath followed by a conventional sulfurization treatment, or a metal deposition followed by a conventional sulfurization operation.
  • the corrosion resistance values of the parts thus treated, after exposure to salt spray, are of the order of 900 to 1200 hours.
  • the patent EP-1,180,552 relates to a method of surface treatment of mechanical parts subjected to both wear and corrosion having a roughness conducive to good lubrication and according to which nitriding is carried out by immersion between 500 ° C and 700 ° C parts in a molten salt nitriding bath containing cyanates and alkaline carbonates in precise ranges but free of species sulfurized, then oxidation is carried out in an oxidizing aqueous solution below 200 ° C.
  • WO2012 / 146839 has aimed a nitriding treatment leading to an appropriate roughness without requiring finishing treatment; he has described a bath of molten salts for the nitriding of mechanical steel parts having specific contents of alkali metal chloride, alkali metal carbonate, alkali metal cyanate and cyanide ions.
  • the corrosion resistance measured in salt spray was between 240 and 650 hours.
  • finishing treatment deposition of a varnish or a wax, or phosphating treatment
  • oxidation of mechanical parts made of ferrous material makes it possible to often to improve the corrosion resistance, but usually involving a surcharge complicating obtaining, at the end of treatment, the desired dimensional dimensions.
  • certain finishing treatments result in the fact that the surface of the parts thus treated tends to transfer a little oil to the surfaces with which it can come into contact and tends to pick up the dust. the surrounding environment; this is hardly compatible with a complementary step such as overmolding.
  • the object of the invention is to remedy these disadvantages in a simple, safe, effective and rational manner, while achieving very high levels of resistance to corrosion and to wear, better than with baths. current impregnation.
  • a method of surface treatment of a mechanical part made of steel to give it a high resistance to wear and corrosion comprising: a nitriding or nitrocarburizing step adapted to form a combination layer at least 8 micrometers thick formed of iron nitrides of ⁇ and / or ⁇ phases,
  • an oxidation step suitable for generating a layer of oxides with a thickness of between 0.1 micrometer and 3 micrometers
  • the impregnation in a bath according to the invention leads to a substantial improvement in the corrosion resistance compared to a conventional bath, based on oils, acids and ethanol.
  • the parts are dry to the touch (this is understood to mean the absence of oil transfer on an opposing surface), hence the absence of a tendency to capture surrounding dust and the ability to undergo post-treatment such as overmolding.
  • a part according to the invention obtained by the method of the invention, namely a steel part having a high resistance to wear and corrosion, comprising a combination layer at least 8 microns, a layer of oxides with a thickness between 0.1 and 3 microns and an impregnation layer which is dry to the touch.
  • ambient temperature does not mean a precise temperature but the fact that the treatment is done without control of the temperature (it is thus neither necessary to heat the bath nor to cool it), and that it can be at the temperature induced by the environment, although it varies in proportions that can be significant during the year, for example between 15 ° C and 50 ° C.
  • the nitriding / nitrocarburizing step is conducted in such a way that the thickness of the resulting combination layer is at least 10 microns.
  • the synthetic phenolic additive is a compound of formula Ci 5 H 24 0.
  • the impregnation bath further comprises at least one additive selected from the group consisting of calcium or sodium sulfonate, phosphites, diphenylamines, zinc dithiophosphate, nitrites, phosphoramides.
  • the content of such additives is advantageously at most equal to 5%.
  • the bath is preferably formed of 90% +/- 0.5% by weight of solvent, 10% +/- 0.5% by weight of paraffin oils and between 0.01% and not more of 1% +/- 0.1% of synthetic phenolic additive of formula Ci 5 H 24 0.
  • the impregnation is carried out by soaking for a period of about 15 minutes.
  • This soaking step is advantageously followed by a natural drying operation or accelerated by steaming.
  • the nitriding / nitrocarburizing step is carried out in a bath of molten salts containing from 14% to 44% by weight of alkaline cyanates at a temperature of 550 ° C. to 650 ° C. for at least 45 minutes; preferably, this nitriding / nitrocarburizing bath contains from 14% to 18% by weight of alkaline cyanates.
  • this treatment is carried out at a temperature of 590 ° C for 90 minutes to 100 minutes; according to a variant which is also advantageous, the nitriding / nitrocarburizing treatment in salt baths melting is carried out at a temperature of 630 ° C for about 45 minutes to 50 minutes.
  • the nitriding / nitrocarburizing step is carried out in a gaseous medium between 500 ° C. and 600 ° C. containing ammonia.
  • the nitriding / nitrocarburizing step is carried out in an ionic medium (plasma) in a medium comprising at least nitrogen and hydrogen under reduced pressure.
  • the oxidation step is carried out in a bath of molten salts containing carbonates, nitrates and alkali hydroxides.
  • the bath of molten oxidation salts contains alkaline nitrates, alkaline carbonates and alkali hydroxides.
  • the oxidation step is carried out at a temperature of 430 ° C to 470 ° C for 15 to 20 minutes.
  • the oxidation is carried out in an aqueous bath containing alkali hydroxides, alkaline nitrates and alkaline nitrites.
  • the oxidation step is carried out at a temperature of 110 ° C to 130 ° C for 15 to 20 minutes.
  • the oxidation step is carried out in a gaseous medium consisting predominantly of water vapor, at a temperature of 450 ° C to 550 ° C for 30 to 120 minutes.
  • NITRU1 to NITRU3 which correspond to nitrocarburizing examples in accordance with the nitrocarburizing treatment taught by document EP-1 180 552 with:
  • NITRU 1 1 to 3 14 to 18 590> 45 ⁇ 8
  • NITRU 2 1 to 3 14 to 18 590> 90> 8
  • NITRU 3 1 to 3 14 to 18 630> 45> 8 More generally, it may be noted that the NITRU1 treatment leads to a combination layer with a thickness of less than 8 micrometers, whereas the NITRU2 and NITRU3 treatments lead to a layer whose thickness exceeds this threshold, and is preferably even at least 10 micrometers. It seems pointless, in practice, to try to exceed 25 micrometers, so that an effective range for the thickness of the layer seems to be 10 to 25 microns.
  • these three treatments correspond to a treatment in a bath of molten salts containing from 14% to 44% by weight of alkaline cyanates (preferably from 14% to 18%) at a temperature of 550 ° C. to 650 ° C. (preferably from 590 ° C to 630 ° C) for at least 45 minutes (it does not seem useful to exceed 120 minutes, or even 90 minutes).
  • NITRU4 aiming a combination layer thickness of at least 8 ⁇ and advantageously between 10 and 25 ⁇
  • NITRU5 aiming a combination layer thickness of at least 8 ⁇ and advantageously between 10 and 25 ⁇
  • the NITRU4 treatment in gaseous medium was carried out in an oven between about 500 and 600 ° C under a controlled atmosphere comprising ammonia.
  • the treatment time has been established to ensure a combination layer thickness of at least 8 microns, preferably greater than 10 microns.
  • the NITRU5 treatment it was carried out in an ionic medium (plasma) in a mixture comprising at least nitrogen and hydrogen, under reduced pressure (that is to say at a pressure below atmospheric pressure). typically less than 0.1 atmosphere).
  • the treatment time has also been established to ensure a combination layer thickness of at least 8 microns, preferably at least 10 microns.
  • the indicated treatment layer thickness does not take into account the diffusion layer (for nitrogen as well as for carbon).
  • Oxidation "type 1" (or 0x1), that is to say in ionic liquid medium containing NaNO3 (between 35 and 40% by weight), carbonates (of Li, K, Na) (between 15 and 20% by weight), NaOH (between 40 and 45% by weight) - 450 ° C. temperature - treatment time of 15 minutes.
  • the oxidations 0x1 and 0x2 substantially correspond, respectively, to the salt bath oxidation and to the aqueous oxidation of the aforementioned EP1 180552 document, whereas the parameters of nitrocarburizing treatments (NITRU5) and of oxidation oxidation treatments, in an ionized medium. , correspond substantially to example 9 of EP0497663.
  • the oxidations were carried out so as to obtain oxidation layers with a thickness of between 0.1 and 3 microns.
  • Imp1 a new impregnation known as "impregnation 1" (or Imp1) in a bath containing mainly a solvent (90% +/- 0.5% by weight) formed of a mixture of hydrocarbons composed of a section of C9 alkanes; at C17, 10% +/- 0.5% by weight of a paraffin oil composed of a C16 to C32 alkane fraction and between 0.1% and 1% +/- 0.1% of a phenolic synthesis additive; the formula 5 H 24 O.
  • This impregnation was carried out by dipping for about 1 5 minutes of immersion, followed by natural drying or accelerated by stoving.
  • Imp2 A conventional impregnation called "impregnation 2" (or Imp2), in a bath containing mainly oils (between 60 and 85% by weight), acids (between 6 and 15% by weight) and ethanol (between 1 and 5% by weight). This impregnation was carried out by dipping for about 15 minutes immersion, followed by natural drying or accelerated by steaming.
  • the oxidation-impregnation treatment is of little importance when there is no nitriding / nitrocarburization (the corrosion resistance remains at 96h, in the first column).
  • the impregnation treatment 2 (conventional) results in a lower corrosion resistance to the case without any nitriding.
  • the interest of type 1 impregnation is particularly visible in the case of NITRU5 nitrocarburizing since, with the case of oxidation 3 (in a gaseous medium - treatments 5 and 6), the improvement is of the order of a tripling of the resistance to corrosion (increase of about fifty hours) compared to the case of a conventional impregnation; it is nevertheless the case where the oxidation has a particularly negative effect.
  • NITRU5 In all other cases NITRU5, the increase in corrosion resistance is at least of the order of 200 hours. Thus, in the case of NITRU5 combined with oxidation in an aqueous medium (oxidation 2 - treatments 3 and 4) or in the absence of oxidation (treatments 7 and 8), the new impregnation results in an increase in resistance to corrosion of the order of 300 hours; in the case of NITRU5 combined with oxidation in an ionic liquid medium (oxidation 1 - treatments 1 and 2), the increase is even of the order of 500 hours.
  • the beneficial effect of the new impregnation exists but is moderate, including in percentage, compared with the conventional impregnation (treatments 3 to 8, even if the suits at the corrosion, in absolute value, are better than with NITRU5).
  • a very important increase of 600 hours, in the case of an oxidation in ionic medium (treatments 1 and 2), with a resistance to the corrosion approaching threshold of 1000 hours. It can be inferred that the condition of a combination layer of at least 8 micrometers thick can be lowered in the case of type 1 oxidation.
  • the new impregnation brings an improvement, especially significant in the case of NITRU3.
  • the improvement in corrosion resistance is, for oxidation of type 2 and 3 (treatments 3 to 6) of at least 250 hours for the treatment NITRU3 and even 450 hours for the treatment NITRU2.
  • type 2 oxidation treatments 3 and 4
  • corrosion resistance exceeding the threshold of 1000 hours is obtained.
  • the increase brought by the new impregnation is surprisingly high, since it is 456 hours for NITRU2 and even 576h for NITRU3 to reach a particularly high threshold, of the order of 1370h.
  • the new impregnation brings about an improvement in the resistance to corrosion compared to a conventional impregnation, whatever the nitriding / nitrocarburizing and oxidation treatments,
  • This improvement is particularly notable and leads to particularly high corrosion resistance values for salt bath nitrocarburizing treatments resulting in a combination layer of at least 8 microns (NITRU2 and NITRU3), preferably between 10 and 25 microns, This improvement is particularly notable and leads to particularly high corrosion resistance values for nitrocarburations in salt baths (NITRU1 to NITRU3) or in the gas phase (NITRU4) in the case of oxidation in molten salt baths ( type 1),
  • the impregnating bath 1 has a surprising synergistic effect with nitriding / nitrocarburizing treatments NITRU2 and NITRU3 provided that nitriding / nitrocarburizing is followed by oxidation of type 1 or 2 , an optimum appearing to be obtained when the oxidation treatment is of type 1.
  • composition of the impregnation bath considered in the tests is part of a more general composition, namely a bath consisting of at least 70% by weight, to within 1%, of a solvent formed of a mixture of hydrocarbons. formed from a cut of C9 to C17 alkanes, from 10% to 30% by weight, to within 1%, of at least one paraffin oil composed of a section of C16 to C32 alkanes and from minus a synthetic phenolic additive additive at a concentration of between 0.01% and 3% by weight, at room temperature.
  • the solvent content is preferably between 80% and 90% by weight; likewise, the content of paraffin oil is preferably between 10% and 20% by weight.
  • the alkane section of the solvent is preferably C9 to C14.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Chemical Treatment Of Metals (AREA)

Abstract

The invention relates to a method for surface treatment of a steel component in order to grant same high resistance to wear and corrosion, including a step of nitriding or nitrocarburising suitable for forming a compound layer with a thickness of at least 8 micrometres made up of iron nitrides having phases ε and/or γ', an oxidising step suitable for generating a layer of oxides with a thickness of 0.1 to 3 micrometres, and a step of impregnating by soaking in an impregnation bath during at least 5 minutes at room temperature, said bath being made up of at least 70 wt %, plus or minus 1%, of a solvent made up of a mixture of hydrocarbons formed by a C9 to C17 alkane fraction, 10 to 30 wt %, plus or minus 1%, of at least one paraffin oil formed by a C16 to C32 alkane fraction, and at least one additive such as a synthetic phenolic additive with a concentration of 0.01 to 3 wt %, plus or minus 0.1%.

Description

PROCEDE DE TRAITEMENT SUPERFICIEL D'UNE PIECE EN ACIER PAR NITRURATION OU NITROCARBU RATION, OXYDATION PUIS IMPREGNATION  PROCESS FOR THE SUPERFICIAL TREATMENT OF A STEEL PART BY NITRURATION OR NITROCARBU RATION, OXIDATION THEN IMPREGNATION
L'invention concerne un procédé de traitement superficiel d'une pièce en métal ferreux, en pratique en acier allié ou non, ayant une bonne tenue à la corrosion grâce à un traitement d'imprégnation. The invention relates to a method for surface treatment of a ferrous metal part, in practice made of alloy steel or not, having a good resistance to corrosion due to an impregnation treatment.
Plus généralement, l'invention s'applique à tout type de pièces mécaniques destinées à assurer en service une fonction mécanique et devant avoir une dureté importante, une longue résistance à la corrosion et à l'usure. C'est par exemple le cas de nombreuses pièces utilisées dans le domaine de l'automobile ou de l'aéronautique. More generally, the invention applies to any type of mechanical parts intended to ensure in service a mechanical function and having a high hardness, a long resistance to corrosion and wear. This is for example the case of many parts used in the field of automotive or aeronautics.
Pour améliorer la tenue à la corrosion de pièces mécaniques en acier, divers traitements ont été proposés, qui comportent une étape de nitruration ou de nitrocarburation (en bains de sels fondus, ou en milieu gazeux), parfois suivie d'une étape d'oxydation et/ou du dépôt d'une couche de finition. Il est rappelé que la nitruration et la nitrocarburation sont des traitements thermochimiques d'apport d'azote (respectivement d'azote et de carbone) par combinaison-diffusion : il se forme en surface une couche de combinaison formée de nitrures de fer (il existe plusieurs phases possibles), sous laquelle l'azote est présent par diffusion. To improve the corrosion resistance of mechanical steel parts, various treatments have been proposed, which include a nitriding or nitrocarburizing step (in molten salt baths or in a gaseous medium), sometimes followed by an oxidation step. and / or the deposition of a topcoat. It is recalled that nitriding and nitrocarburizing are thermochemical treatments of nitrogen (respectively nitrogen and carbon) by combination-diffusion: it forms on the surface a combination layer formed of nitrides of iron (there exists several possible phases), under which nitrogen is present by diffusion.
Ainsi, le document EP- 0 053 521 a proposé, principalement pour des axes de piston dont on cherchait à améliorer la tenue à la corrosion et/ou le coefficient de frottement, un traitement de nitrocarburation adapté à former une couche de phase Epsilon et un traitement de finition consistant à recouvrir la couche en phase Epsilon d'une couche de finition formée d'une résine (le document mentionne une gamme très variée, englobant les résines acryliques, les alkydes, les esters maléiques, les époxy, les formaldéhydes, les phénoliques, le butyral-polyvinyle, les chlorures polyvinyle, les polyamides, les poly-imides, les polyuréthanes, les silicones, les éthers polyvinyle et les urée- formaldéhydes, avantageusement chargés en additifs choisis parmi les phosphates et les chromâtes de zinc (pour améliorer la résistance à la corrosion), et/ou du silicone, des cires, des poly-tétra-fluoro-éthylènes, du di- sulfite de molybdène, du graphite ou du stéarate de zinc (pour réduire le coefficient de frottement). Il n'y a pas de résultat précis ; il est simplement mentionné qu'un bon exemple est un système de résines acryliques/époxide/amino, contenant du chromate ou du stéarate de zinc ou une cire. Thus, the document EP-0 053 521 proposed, mainly for piston pins whose corrosion resistance and / or coefficient of friction was to be improved, a nitrocarburizing treatment adapted to form an Epsilon phase layer and a finishing treatment consisting in covering the Epsilon layer with a topcoat made of a resin (the document mentions a very wide range, including acrylic resins, alkyds, maleic esters, epoxides, formaldehyde, phenolics, butyral-polyvinyl, polyvinyl chlorides, polyamides, polyimides, polyurethanes, silicones, polyvinyl ethers and urea-formaldehyde, advantageously loaded with additives chosen from phosphates and zinc chromates (to improve corrosion resistance), and / or silicone, waxes, poly-tetrafluoroethylenes, molybdenum diesulfite, graphite or zinc stearate (for reduce the coefficient of friction). There is no precise result; it is simply mentioned that a good example is a system of acrylic / epoxy / amino resins, containing chromate or zinc stearate or a wax.
Quant au document EP - 0 122 762, il décrit un procédé de fabrication de pièces d'acier résistant à la corrosion, comprenant des étapes de nitruration (en phase Epsilon, comme précédemment), puis d'oxydation par voie gazeuse, puis d'application de matière cireuse (Castrai V425) contenant des hydrocarbures aliphatiques et des savons métalliques du groupe 2a, de préférence des savons au calcium et/ou au baryum. La tenue à la corrosion en brouillard salin a été de l'ordre de 250 heures. La Demanderesse a elle-même proposé des procédés de traitements visant à obtenir des tenues encore meilleures à la corrosion. Document EP-0 122 762 describes a method of manufacturing corrosion-resistant steel parts, comprising nitriding steps (in the Epsilon phase, as above), then gas-phase oxidation, and then application of waxy material (Castrai V425) containing aliphatic hydrocarbons and Group 2a metal soaps, preferably calcium and / or barium soaps. The resistance to salt spray corrosion was of the order of 250 hours. The Applicant has itself proposed treatment processes to obtain even better outfits to corrosion.
Dans le document EP - 0 497 663, elle a proposé un procédé consistant à soumettre des pièces en métal ferreux à une nitruration, typiquement en un bain de sels fondus constitué de cyanates et de sodium, potassium et lithium, puis à une oxydation en bains de sels fondus ou dans une atmosphère ionisante oxydante, en sorte d'obtenir une couche nitrurée comprenant une sous-couche profonde et compacte et une couche superficielle de porosité bien contrôlée et enfin au dépôt d'un polymère d'épaisseur comprise entre 3 et 20 μιτι, en fluoroéthylène-propylène (FEP), voire en polytetrafluoroéthylène, (PTFE), voire en polymères ou copolymères de polyuréthanes fluorés ou siliconés, ou en polyamides-polyimides. Avec ce procédé, des essais ont montré que la résistance à la corrosion était améliorée en permettant d'obtenir une exposition au brouillard salin (BS) pouvant aller de 500 à 1000 heures environ sans qu'apparaisse une manifestation de corrosion. Ensuite, par le document EP - 0 524 037, il a été proposé un procédé de traitement selon lequel les pièces sont nitrurées de préférence en bains de sels fondus à base d'ions cyanates puis oxydées et enfin imprégnées d'une cire hydrophobe. La nitruration suivie de l'oxydation conduit à la formation d'une couche constituée d'une sous-couche profonde compacte et d'une couche superficielle dont la porosité est bien contrôlée. La cire d'imprégnation est un composé organique à haut poids moléculaire compris entre 500 et 10000 et de tension superficielle, à l'état liquide, comprise entre 10 et 73 mN/m. L'angle de contact entre la phase solide et la couche superficielle et la cire à l'état liquide, est compris entre 0 et 75 degrés. Plus précisément, la cire est choisie parmi les cires naturelles, les cires synthétiques polyéthylènes, polypropylènes, polyesters, fluorés ou bien résidus pétroliers modifiés. Cette solution permet d'améliorer simultanément la résistance à la corrosion et les propriétés de friction des pièces en métal ferreux. Les pièces ainsi traitées ont une bonne résistance à la corrosion en brouillard salin normalisé combinée à de bonnes propriétés de friction. In EP-0 497 663, it has proposed a method of subjecting ferrous metal parts to nitriding, typically to a molten salt bath consisting of cyanates and sodium, potassium and lithium, followed by bath oxidation. of molten salts or in an oxidizing ionizing atmosphere, so as to obtain a nitrided layer comprising a deep and compact underlayer and a well-controlled surface layer of porosity and finally to deposit a polymer with a thickness of between 3 and 20 μιτι, fluoroethylene-propylene (FEP), or even polytetrafluoroethylene (PTFE), or even polymers or copolymers of fluorinated or silicone polyurethanes, or polyamide-polyimides. With this method, tests have shown that the resistance to corrosion was improved by obtaining exposure to salt spray (BS) ranging from 500 to about 1000 hours without showing a manifestation of corrosion. Then, by the document EP-0 524 037, it was proposed a treatment process according to which the parts are nitrided preferably in molten salt baths based on cyanate ions and then oxidized and finally impregnated with a hydrophobic wax. Nitriding followed by oxidation leads to the formation of a layer consisting of a compact deep sub-layer and a surface layer whose porosity is well controlled. The impregnating wax is an organic compound with a high molecular weight of between 500 and 10,000 and a surface tension in the liquid state of between 10 and 73 mN / m. The contact angle between the solid phase and the surface layer and the wax in the liquid state is between 0 and 75 degrees. More specifically, the wax is chosen from natural waxes, synthetic waxes polyethylenes, polypropylenes, polyesters, fluorinated or modified petroleum residues. This solution simultaneously improves the corrosion resistance and friction properties of ferrous metal parts. The parts thus treated have a good resistance to corrosion in standardized salt spray combined with good friction properties.
Le brevet EP - 0 560 641 décrit un procédé de phosphatation de pièces en acier pour améliorer la résistance à la corrosion et à l'usure permettant d'obtenir des caractéristiques spécifiques de surface résultant d'un traitement de phosphatation précédé d'une opération de nitruration dans un bain de sels fondus contenant des espèces soufrées, d'une opération de nitruration dans un bain de sels fondus suivie d'un traitement classique de sulfuration, ou d'un dépôt de métal suivi d'une opération classique de sulfuration. Les valeurs de résistance à la corrosion des pièces ainsi traitées, après exposition au brouillard salin, sont de l'ordre de 900 à 1200 heures. EP-0 560 641 discloses a process for the phosphating of steel parts to improve the corrosion and wear resistance, making it possible to obtain specific surface characteristics resulting from a phosphating treatment preceded by a nitriding in a bath of molten salts containing sulfur species, a nitriding operation in a molten salt bath followed by a conventional sulfurization treatment, or a metal deposition followed by a conventional sulfurization operation. The corrosion resistance values of the parts thus treated, after exposure to salt spray, are of the order of 900 to 1200 hours.
Le brevet EP - 1 180 552 concerne un procédé de traitement superficiel de pièces mécaniques soumises à la fois à l'usure et à la corrosion en ayant une rugosité propice à une bonne lubrification et selon lequel une nitruration est mise en œuvre par immersion entre 500 °C et 700 °C des pièces dans un bain de nitruration de sels fondus contenant des cyanates et carbonates alcalins dans des gammes précises mais exempt d'espèces soufrées, puis une oxydation est mise en œuvre dans une solution aqueuse oxydante en dessous de 200 °C. The patent EP-1,180,552 relates to a method of surface treatment of mechanical parts subjected to both wear and corrosion having a roughness conducive to good lubrication and according to which nitriding is carried out by immersion between 500 ° C and 700 ° C parts in a molten salt nitriding bath containing cyanates and alkaline carbonates in precise ranges but free of species sulfurized, then oxidation is carried out in an oxidizing aqueous solution below 200 ° C.
Le document WO2012/146839 a visé un traitement de nitruration conduisant à une rugosité appropriée sans nécessiter de traitement de finition ; il a décrit un bain de sels fondus pour la nitruration de pièces mécaniques en acier présentant des teneurs spécifiques en chlorure de métal alcalin, en carbonate de métal alcalin, en cyanate de métal alcalin et en ions cyanures. La résistance à la corrosion mesurée en brouillard salin a été comprise entre 240 et 650 heures. II est à noter que le fait d'ajouter un traitement de finition (dépôt d'un vernis ou d'une cire, ou traitement de phosphatation) à un traitement de nitruration ou de nitrocarburation puis d'oxydation de pièces mécaniques en matériau ferreux permet souvent d'améliorer la résistance à la corrosion, mais en impliquant généralement une surcote compliquant l'obtention, en fin de traitement, des cotes dimensionnelles souhaitées. A titre subsidiaire, il a été constaté que certains traitements de finition se traduisent par le fait que la surface des pièces ainsi traitées tend à transférer un peu d'huile sur les surfaces avec lesquelles elle peut venir en contact et a tendance à capter la poussière du milieu environnant ; cela est difficilement compatible avec une étape complémentaire telle qu'un surmoulage. WO2012 / 146839 has aimed a nitriding treatment leading to an appropriate roughness without requiring finishing treatment; he has described a bath of molten salts for the nitriding of mechanical steel parts having specific contents of alkali metal chloride, alkali metal carbonate, alkali metal cyanate and cyanide ions. The corrosion resistance measured in salt spray was between 240 and 650 hours. It should be noted that the fact of adding a finishing treatment (deposition of a varnish or a wax, or phosphating treatment) to a nitriding or nitrocarburizing treatment and then oxidation of mechanical parts made of ferrous material makes it possible to often to improve the corrosion resistance, but usually involving a surcharge complicating obtaining, at the end of treatment, the desired dimensional dimensions. In the alternative, it has been found that certain finishing treatments result in the fact that the surface of the parts thus treated tends to transfer a little oil to the surfaces with which it can come into contact and tends to pick up the dust. the surrounding environment; this is hardly compatible with a complementary step such as overmolding.
L'invention s'est fixée pour but de remédier à ces inconvénients de manière simple, sure, efficace et rationnelle, tout en atteignant des niveaux très élevés de résistance à la corrosion ainsi qu'à l'usure, meilleurs qu'avec les bains d'imprégnation actuels. The object of the invention is to remedy these disadvantages in a simple, safe, effective and rational manner, while achieving very high levels of resistance to corrosion and to wear, better than with baths. current impregnation.
Pour résoudre un tel problème, il a été conçu et mis au point un procédé de traitement superficiel d'une pièce mécanique en acier pour lui conférer une résistance élevée à l'usure et à la corrosion comportant : - une étape de nitruration ou de nitrocarburation adaptée à former une couche de combinaison d'au moins 8 micromètres d'épaisseur formée de nitrures de fer de phases ε et/ou γ', To solve such a problem, it has been designed and developed a method of surface treatment of a mechanical part made of steel to give it a high resistance to wear and corrosion comprising: a nitriding or nitrocarburizing step adapted to form a combination layer at least 8 micrometers thick formed of iron nitrides of ε and / or γ phases,
- une étape d'oxydation adaptée à générer une couche d'oxydes d'épaisseur comprise entre 0.1 micromètre et 3 micromètres et  an oxidation step suitable for generating a layer of oxides with a thickness of between 0.1 micrometer and 3 micrometers, and
- une étape d'imprégnation par trempage dans un bain d'imprégnation pendant au moins 5 minutes, ce bain étant formé d'au moins 70% en poids, à 1 % près, d'un solvant formé d'un mélange d'hydrocarbures formé d'une coupe d'alcanes de C9 à CM, de 10% à 30% en poids, à 1 % près, d'au moins une huile de paraffine composée d'une coupe d'alcanes C16 à C32 et d'au moins un additif du type additif phénolique de synthèse à une concentration comprise entre 0.01 % et 3% en poids, à 0.1 % près, à la température ambiante.  a step of impregnation by dipping in an impregnation bath for at least 5 minutes, this bath being formed of at least 70% by weight, to within 1%, of a solvent formed of a mixture of hydrocarbons formed from a cut of alkanes of C9 to CM, from 10% to 30% by weight, to within 1%, of at least one paraffin oil composed of a section of C16 to C32 alkanes and from minus an additive of the phenolic synthetic additive type at a concentration of between 0.01% and 3% by weight, to the nearest 0.1%, at room temperature.
Il est apparu que, sous réserve que la nitruration ou la nitrocarburation et l'oxydation aient été effectuées de manière suffisamment efficace pour former les couches définies ci-dessus, l'imprégnation dans un bain conforme à l'invention conduit à une amélioration substantielle de la résistance à la corrosion par rapport à un bain classique, à base d'huiles, d'acides et d'éthanol. En outre il a été constaté que, après le traitement d'imprégnation, les pièces sont sèches au toucher (on entend par là l'absence de transfert d'huile sur une surface antagoniste), d'où l'absence de tendance à capter la poussière environnante et l'aptitude à subir un post-traitement tel qu'un surmoulage.  It has been found that, provided that nitriding or nitrocarburizing and oxidation have been carried out sufficiently efficiently to form the layers defined above, the impregnation in a bath according to the invention leads to a substantial improvement in the corrosion resistance compared to a conventional bath, based on oils, acids and ethanol. In addition, it has been found that, after the impregnation treatment, the parts are dry to the touch (this is understood to mean the absence of oil transfer on an opposing surface), hence the absence of a tendency to capture surrounding dust and the ability to undergo post-treatment such as overmolding.
C'est ainsi qu'on peut reconnaître une pièce conforme à l'invention, obtenue par le procédé de l'invention, à savoir une pièce en acier ayant une résistance élevée à l'usure et à la corrosion, comportant une couche de combinaison d'au moins 8 micromètres, une couche d'oxydes d'épaisseur comprise entre 0.1 et 3 micromètres et une couche d'imprégnation qui est sèche au toucher.  Thus one can recognize a part according to the invention, obtained by the method of the invention, namely a steel part having a high resistance to wear and corrosion, comprising a combination layer at least 8 microns, a layer of oxides with a thickness between 0.1 and 3 microns and an impregnation layer which is dry to the touch.
La notion de température ambiante ne désigne pas une température précise mais le fait que le traitement se fait sans contrôle de la température (il n'est donc nécessaire ni de chauffer le bain ni de le refroidir), et qu'elle peut se faire à la température induite par l'environnement, même si elle varie dans des proportions pouvant être importantes au cours de l'année, par exemple entre 15°C et 50 °C. The notion of ambient temperature does not mean a precise temperature but the fact that the treatment is done without control of the temperature (it is thus neither necessary to heat the bath nor to cool it), and that it can be at the temperature induced by the environment, although it varies in proportions that can be significant during the year, for example between 15 ° C and 50 ° C.
De manière préférée, l'étape de nitruration/nitrocarburation est conduite de manière à ce que l'épaisseur de la couche de combinaison obtenue est d'au moins 10 micromètres.  Preferably, the nitriding / nitrocarburizing step is conducted in such a way that the thickness of the resulting combination layer is at least 10 microns.
De manière avantageuse, l'additif phénolique de synthèse est un composé de formule Ci5H240. Advantageously, the synthetic phenolic additive is a compound of formula Ci 5 H 24 0.
De manière également avantageuse, le bain d'imprégnation comporte en outre au moins un additif choisi dans le groupe constitué par le sulfonate de calcium ou de sodium, les phosphites, les diphénylamines, le dithiophosphate de zinc, les nitrites, les phosphoramides. La teneur en de tels additifs est avantageusement au plus égale à 5%. Also advantageously, the impregnation bath further comprises at least one additive selected from the group consisting of calcium or sodium sulfonate, phosphites, diphenylamines, zinc dithiophosphate, nitrites, phosphoramides. The content of such additives is advantageously at most equal to 5%.
Plus particulièrement, le bain est, de manière préférée, formé de 90%+/-0,5% en poids de solvant, 10% +/-0,5% en poids d'huiles de paraffine et entre 0.01 % et pas plus de 1 %+/-0.1 % d'additif phénolique de synthèse de formule Ci5H240. More particularly, the bath is preferably formed of 90% +/- 0.5% by weight of solvent, 10% +/- 0.5% by weight of paraffin oils and between 0.01% and not more of 1% +/- 0.1% of synthetic phenolic additive of formula Ci 5 H 24 0.
De manière avantageuse, l'imprégnation s'effectue par trempage pendant une durée d'environ 15 minutes. Cette étape de trempage est avantageusement suivie d'une opération de séchage naturel ou accéléré par étuvage. Advantageously, the impregnation is carried out by soaking for a period of about 15 minutes. This soaking step is advantageously followed by a natural drying operation or accelerated by steaming.
Selon une première option avantageuse, l'étape de nitruration/nitrocarburation est effectuée en un bain de sels fondus contenant de 14% à 44% en poids de cyanates alcalins à une température de 550 °C à 650 °C pendant au moins 45 minutes ; de préférence, ce bain de nitruration/nitrocarburation contient de 14% à 18% en poids de cyanates alcalins. De manière avantageuse, ce traitement est effectué à une température de 590 °C pendant 90 minutes à 100 minutes ; selon une variante, également avantageuse, le traitement de nitruration/nitrocarburation en bains de sels fondus est effectué à une température de 630 °C pendant environ 45 minutes à 50 minutes. According to a first advantageous option, the nitriding / nitrocarburizing step is carried out in a bath of molten salts containing from 14% to 44% by weight of alkaline cyanates at a temperature of 550 ° C. to 650 ° C. for at least 45 minutes; preferably, this nitriding / nitrocarburizing bath contains from 14% to 18% by weight of alkaline cyanates. Advantageously, this treatment is carried out at a temperature of 590 ° C for 90 minutes to 100 minutes; according to a variant which is also advantageous, the nitriding / nitrocarburizing treatment in salt baths melting is carried out at a temperature of 630 ° C for about 45 minutes to 50 minutes.
Selon une seconde option avantageuse, l'étape de nitruration/nitrocarburation est effectuée en un milieu gazeux entre 500 °C et 600°C contenant de l'ammoniac. According to a second advantageous option, the nitriding / nitrocarburizing step is carried out in a gaseous medium between 500 ° C. and 600 ° C. containing ammonia.
Selon une troisième option avantageuse, l'étape de nitruration/nitrocarburation est effectuée en milieu ionique (plasma) dans un milieu comprenant au moins de l'azote et de l'hydrogène sous pression réduite. According to a third advantageous option, the nitriding / nitrocarburizing step is carried out in an ionic medium (plasma) in a medium comprising at least nitrogen and hydrogen under reduced pressure.
De manière avantageuse, l'étape d'oxydation est effectuée dans un bain de sels fondus contenant des carbonates, des nitrates et des hydroxydes alcalins. Advantageously, the oxidation step is carried out in a bath of molten salts containing carbonates, nitrates and alkali hydroxides.
Selon une option particulièrement intéressante, le bain de sels fondus d'oxydation contient des nitrates alcalins, des carbonates alcalins et des hydroxydes alcalins. Dans ce cas, il est avantageux que l'étape d'oxydation soit réalisée à une température de 430 °C à 470 °C pendant de 15 à 20 minutes. According to a particularly interesting option, the bath of molten oxidation salts contains alkaline nitrates, alkaline carbonates and alkali hydroxides. In this case, it is advantageous that the oxidation step is carried out at a temperature of 430 ° C to 470 ° C for 15 to 20 minutes.
Selon une autre option intéressante, l'oxydation est conduite dans un bain aqueux contenant des hydroxydes alcalins, des nitrates alcalins et des nitrites alcalins. Dans ce cas, il est avantageux que l'étape d'oxydation soit réalisée à une température de 1 10°C à 130°C pendant de 15 à 20 minutes. En variante, l'étape d'oxydation est effectuée en un milieu gazeux majoritairement constitué de vapeur d'eau, à une température de 450°C à 550 °C pendant de 30 à 120 minutes. According to another interesting option, the oxidation is carried out in an aqueous bath containing alkali hydroxides, alkaline nitrates and alkaline nitrites. In this case, it is advantageous that the oxidation step is carried out at a temperature of 110 ° C to 130 ° C for 15 to 20 minutes. Alternatively, the oxidation step is carried out in a gaseous medium consisting predominantly of water vapor, at a temperature of 450 ° C to 550 ° C for 30 to 120 minutes.
Ces diverses préférences ressortent de divers essais qui ont été effectués, à titre d'exemple illustratif non limitatif. Plus précisément, ces essais ont été effectués en combinant plusieurs types de traitements de nitruration ou nitrocarburation, connus en soi, plusieurs types de traitement d'oxydation, connus en soi, et plusieurs types d'imprégnation. Ces essais ont été effectués sur des pièces en métal ferreux présentant des zones lisses et des arêtes vives. Plus particulièrement, des essais ont été effectués sur des axes cannelés en acier XC45 recuit et rectifié, présentant une portée lisse et une portée filetée. These various preferences are apparent from various tests that have been carried out, by way of nonlimiting illustrative example. More specifically, these tests were carried out by combining several types of nitriding or nitrocarburizing treatments, known per se, several types of oxidation treatment, known per se, and several types of impregnation. These tests were carried out on ferrous metal parts with smooth areas and sharp edges. More particularly, tests have been carried out on annealed and rectified XC45 steel splined shafts having a smooth bearing and a threaded bearing.
Au total, cinq traitements de nitruration ou de nitrocarburation ont été testés. Trois de ces traitements sont des traitements en bains de sels fondus, NITRU1 à NITRU3, qui correspondent à des exemples de nitrocarburation conformes au traitement de nitrocarburation enseigné par le document EP - 1 180 552 avec : In total, five nitriding or nitrocarburizing treatments were tested. Three of these treatments are molten salt bath treatments, NITRU1 to NITRU3, which correspond to nitrocarburizing examples in accordance with the nitrocarburizing treatment taught by document EP-1 180 552 with:
* le traitement NITRU1 situé en fourchette basse de température préférée et le temps moyen préféré de traitement (de 45 minutes à 50 minutes), * The treatment NITRU1 located in the lower range preferred temperature and the preferred average processing time (from 45 minutes to 50 minutes),
* le traitement NITRU2 situé en cette même fourchette basse de température préférée mais avec le temps de traitement maximum (en dehors de la zone préférée, soit de 90 minutes à 100 minutes) et * the NITRU2 treatment located in this same low temperature range preferred but with the maximum treatment time (outside the preferred zone, ie from 90 minutes to 100 minutes) and
* le traitement NITRU3 situé en fourchette haute de température préférée avec le temps moyen préféré de traitement (45 minutes à 50 minutes). Les paramètres de ces traitements sont récapitulés dans le tableau ci-dessous. * the NITRU3 treatment located in the preferred high temperature range with the preferred average treatment time (45 minutes to 50 minutes). The parameters of these treatments are summarized in the table below.
Teneur en Teneur en Température Temps de Epaisseur de couche CN" en % CNO" en % (en °C) traitement(en de traitement (en (en poids) (en poids) minutes) micromètres) Content in Temperature Temperature Time of layer thickness CN " in% CNO " in% (in ° C) treatment (in treatment (in (by weight) (in weight) minutes) micrometers)
NITRU 1 1 à 3 14 à 18 590 >=45 <8 NITRU 1 1 to 3 14 to 18 590> = 45 <8
NITRU 2 1 à 3 14 à 18 590 >= 90 >8 NITRU 2 1 to 3 14 to 18 590> = 90> 8
NITRU 3 1 à 3 14 à 18 630 >= 45 >8 Plus généralement, on peut noter que le traitement NITRU1 conduit à une couche de combinaison d'épaisseur inférieure à 8 micromètres, tandis que les traitements NITRU2 et NITRU3 conduisent à une couche dont l'épaisseur dépasse ce seuil, et soit même de préférence d'au moins 10 micromètres. Il semble inutile, en pratique, de chercher à dépasser 25 micromètres, de sorte qu'une plage efficace pour l'épaisseur de la couche semble être de 1 0 à 25 micromètres. NITRU 3 1 to 3 14 to 18 630> = 45> 8 More generally, it may be noted that the NITRU1 treatment leads to a combination layer with a thickness of less than 8 micrometers, whereas the NITRU2 and NITRU3 treatments lead to a layer whose thickness exceeds this threshold, and is preferably even at least 10 micrometers. It seems pointless, in practice, to try to exceed 25 micrometers, so that an effective range for the thickness of the layer seems to be 10 to 25 microns.
De manière générale, ces trois traitements correspondent à un traitement en un bain de sels fondus contenant de 14% à 44% en poids de cyanates alcalins (de préférence de 14% à 18%) à une température de 550 °C à 650 °C (de préférence, de 590 °C à 630 °C) pendant au moins 45 minutes (il ne semble pas utile de dépasser 120 minutes, voire 90 minutes). In general, these three treatments correspond to a treatment in a bath of molten salts containing from 14% to 44% by weight of alkaline cyanates (preferably from 14% to 18%) at a temperature of 550 ° C. to 650 ° C. (preferably from 590 ° C to 630 ° C) for at least 45 minutes (it does not seem useful to exceed 120 minutes, or even 90 minutes).
Un autre de ces traitements est un traitement classique en milieu gazeux, NITRU4 (en visant une épaisseur de couche de combinaison d'au moins 8 μιτι et avantageusement comprise entre 1 0 et 25 μιτι), et un autre de ces traitements est un traitement classique en milieu ionique (plasma), NITRU5 (en visant une épaisseur de couche de combinaison d'au moins 8 μιτι et avantageusement comprise entre 10 et 25 μιτι). Another of these treatments is a conventional gaseous treatment, NITRU4 (aiming a combination layer thickness of at least 8 μιτι and advantageously between 10 and 25 μιτι), and another of these treatments is a conventional treatment. in ionic medium (plasma), NITRU5 (aiming a combination layer thickness of at least 8 μιτι and advantageously between 10 and 25 μιτι).
Plus précisément, le traitement NITRU4 en milieu gazeux a été effectué dans un four entre environ 500 et 600 °C sous atmosphère contrôlée comprenant de l'ammoniac. Le temps de traitement a été établi pour garantir une épaisseur de couche de combinaison d'au moins 8 micromètres, de préférence supérieure à 10 micromètres. More specifically, the NITRU4 treatment in gaseous medium was carried out in an oven between about 500 and 600 ° C under a controlled atmosphere comprising ammonia. The treatment time has been established to ensure a combination layer thickness of at least 8 microns, preferably greater than 10 microns.
Quant au traitement NITRU5, il a été effectué en milieu ionique (plasma) dans un mélange comprenant au moins de l'azote et de l'hydrogène, sous pression réduite (c'est-à-dire sous une pression inférieure à la pression atmosphérique, typiquement moins de 0.1 atmosphère). Le temps de traitement a également été établi pour garantir une épaisseur de couche de combinaison d'au moins 8 micromètres, de préférence d'au moins 10 micromètres. Dans ce qui précède, l'épaisseur de couche de traitement indiquée ne tient pas compte de la couche de diffusion (pour l'azote ainsi que pour le carbone). As for the NITRU5 treatment, it was carried out in an ionic medium (plasma) in a mixture comprising at least nitrogen and hydrogen, under reduced pressure (that is to say at a pressure below atmospheric pressure). typically less than 0.1 atmosphere). The treatment time has also been established to ensure a combination layer thickness of at least 8 microns, preferably at least 10 microns. In the above, the indicated treatment layer thickness does not take into account the diffusion layer (for nitrogen as well as for carbon).
Selon ces divers traitements de nitruration/nitrocarburation, on a obtenu différentes couches de combinaison : According to these various nitriding / nitrocarburizing treatments, different combination layers have been obtained:
- soit des nitrures en phase ε (Fe2-3N), soit des nitrures en phases ε et Y' (Fe2-3N + Fe4N) avec les bains de sels NITRU1 à NITRU3, or ε (Fe 2 -3N) phase nitrides or ε and Y '(Fe 2 - 3 N + Fe 4 N) phase nitrides with NITRU1 to NITRU3 salt baths,
- des nitrures en phases ε et Y' (Fe2-3 + Fe4N) avec le traitement en phase gazeuse NITRU4, nitrides in ε and Y 'phases (Fe 2 -3 + Fe 4 N) with the gas phase treatment NITRU4,
- des nitrures en phases ε et Y' (Fe2-3N + Fe4N) avec le traitement en phase plasma NITRU5. nitrides in ε and Y 'phases (Fe 2 -3N + Fe 4 N) with the NITRU5 plasma phase treatment.
Seuls les traitements NITRU2 à NITRU5 ont abouti à des épaisseurs de couche de combinaison d'au moins 8 micromètres, avantageusement entre 10 et 25 micromètres. Only NITRU2 to NITRU5 treatments resulted in combination layer thicknesses of at least 8 microns, preferably between 10 and 25 microns.
Pour chacun des 5 traitements de nitruration NITRU1 à NITRU5, trois types de traitements d'oxydation ont été mis en œuvre : For each of the 5 nitriding treatments NITRU1 to NITRU5, three types of oxidation treatments were implemented:
1 ) Oxydation « type 1 » (ou 0x1 ), c'est-à-dire en milieu liquide ionique contenant du NaNO3 (entre 35 et 40% en poids), des carbonates (de Li, de K, de Na) (entre 15 et 20% en poids), du NaOH (entre 40 et 45% en poids) - température de 450°C - temps de traitement de 15 minutes. 1) Oxidation "type 1" (or 0x1), that is to say in ionic liquid medium containing NaNO3 (between 35 and 40% by weight), carbonates (of Li, K, Na) (between 15 and 20% by weight), NaOH (between 40 and 45% by weight) - 450 ° C. temperature - treatment time of 15 minutes.
2) Oxydation « type 2 » (ou Ox2, c'est-à-dire en milieu aqueux contenant du KOH (entre 80% et 85% en poids, du NaNO3 (entre 10% et 15% en poids et du NaNO2 (entre 1 et 6% en poids - température de 120°C - temps de traitement de 15 minutes. 3) Oxydation « type 3 » (ou 0x3) en milieu gazeux (traitement en vapeur d'eau) - température de 500 °C - temps de traitement de 60 minutes. 2) "Type 2" oxidation (or Ox2, that is to say in an aqueous medium containing KOH (between 80% and 85% by weight, NaNO3 (between 10% and 15% by weight and NaNO2 (between 1 and 6% by weight - temperature of 120 ° C - treatment time of 15 minutes. 3) Oxidation "type 3" (or 0x3) in a gaseous medium (steam treatment) - temperature of 500 ° C - treatment time of 60 minutes.
Les oxydations 0x1 et 0x2 correspondent sensiblement, respectivement, à l'oxydation en bain de sel et à l'oxydation aqueuse du document EP1 180552 précité, alors que les paramètres de traitements de nitrocarburation (NITRU5) et d'oxydation 0x3, en milieu ionisé, correspondent sensiblement à l'exemple 9 du document EP0497663.  The oxidations 0x1 and 0x2 substantially correspond, respectively, to the salt bath oxidation and to the aqueous oxidation of the aforementioned EP1 180552 document, whereas the parameters of nitrocarburizing treatments (NITRU5) and of oxidation oxidation treatments, in an ionized medium. , correspond substantially to example 9 of EP0497663.
Les oxydations ont été effectuées en sorte d'obtenir des couches d'oxydation d'épaisseur comprises entre 0.1 et 3 micromètres. The oxidations were carried out so as to obtain oxidation layers with a thickness of between 0.1 and 3 microns.
Enfin, après l'opération d'oxydation, deux types d'imprégnation ont été réalisés : Finally, after the oxidation operation, two types of impregnation have been carried out:
1 ) une imprégnation nouvelle dite « imprégnation 1 » (ou Imp1 ) dans un bain contenant principalement un solvant (90%+/-0.5% en poids) formé d'un mélange d'hydrocarbures composé d'une coupe d'alcanes de C9 à C17, 1 0% +/-0.5% en poids d'une huile de paraffine composée d'une coupe d'alcanes C16 à C32 et entre 0.1 % et 1 % +/- 0.1 % d'un additif phénolique de synthèse de formule Ci5H24O. Cette imprégnation a été réalisée par trempage pendant environ 1 5 minutes d'immersion, suivie d'un séchage naturel ou accéléré par étuvage. 1) a new impregnation known as "impregnation 1" (or Imp1) in a bath containing mainly a solvent (90% +/- 0.5% by weight) formed of a mixture of hydrocarbons composed of a section of C9 alkanes; at C17, 10% +/- 0.5% by weight of a paraffin oil composed of a C16 to C32 alkane fraction and between 0.1% and 1% +/- 0.1% of a phenolic synthesis additive; the formula 5 H 24 O. This impregnation was carried out by dipping for about 1 5 minutes of immersion, followed by natural drying or accelerated by stoving.
2) Une imprégnation classique dite « imprégnation 2 » (ou Imp2), dans un bain contenant principalement des huiles (entre 60 et 85% en poids), des acides (entre 6 et 15% en poids) et de l'éthanol (entre 1 et 5% en poids). Cette imprégnation a été réalisée par trempage pendant environ 15 minutes d'immersion, suivi d'un séchage naturel ou accéléré par étuvage.  2) A conventional impregnation called "impregnation 2" (or Imp2), in a bath containing mainly oils (between 60 and 85% by weight), acids (between 6 and 15% by weight) and ethanol (between 1 and 5% by weight). This impregnation was carried out by dipping for about 15 minutes immersion, followed by natural drying or accelerated by steaming.
En combinant les types d'oxydation et les types d'imprégnation, on a défini 8 traitements, notés 1 à 8, conformément au tableau suivant (on y désigne une absence d'oxydation par « OxO »). Type d'oxydation Type d'imprégnation By combining the types of oxidation and the types of impregnation, 8 treatments, denoted 1 to 8, were defined in accordance with the following table (it denotes an absence of oxidation by "OxO"). Type of oxidation Type of impregnation
Traitement 1 0x1 Imp2 Processing 1 0x1 Imp2
Traitement 2 0x1 Imp1 Processing 2 0x1 Imp1
Traitement 3 0x2 Imp2 Treatment 3 0x2 Imp2
Traitement 4 0x2 Imp1 Processing 4 0x2 Imp1
Traitement 5 0x3 Imp2 Processing 5 0x3 Imp2
Traitement 6 0x3 Imp1 Processing 6 0x3 Imp1
Traitement 7 Sans oxydation (OxO) Imp2 Treatment 7 Oxidation-free (OxO) Imp2
Traitement 8 Sans oxydation (OxO) Imp1 Treatment 8 Oxidation-free (OxO) Imp1
Des échantillons ont été préparés en combinant ces traitements 1 à 8 avec les traitements de nitruration/nitrocarburation précités. Des essais de tenue à la corrosion ont été effectués selon la norme ISO 9227 (2006) en brouillard salin. Les résultats sont résumés dans le tableau ci-dessous. Pour chaque essai, un minimum de 10 pièces a été testé. Le temps (indiqué en heures) correspond à une absence totale de trace de corrosion sur 100% des pièces. Samples were prepared by combining these treatments 1 to 8 with the aforementioned nitriding / nitrocarburizing treatments. Corrosion resistance tests were performed according to ISO 9227 (2006) in salt spray. The results are summarized in the table below. For each test, a minimum of 10 pieces has been tested. The time (indicated in hours) corresponds to a total absence of trace of corrosion on 100% of the parts.
II est apparu que le traitement d'imprégnation 1 n'induisait pas de variation dimensionnelle. De surcroît, la surface des pièces était sèche au toucher ; cela implique que, d'une part, la surface de ces pièces n'a pas tendance à capter la poussière et que, d'autre part, ces pièces sont compatibles avec un post-traitement tel qu'un surmoulage. Sans It appeared that the impregnation treatment 1 did not induce dimensional variation. In addition, the surface of the pieces was dry to the touch; this implies that, on the one hand, the surface of these parts does not have a tendency to capture the dust and that, on the other hand, these parts are compatible with a post-treatment such as overmolding. Without
NITRU 1 NITRU 2 NITRU 3 NITRU 4 NITRU 5 Nitruration  NITRU 1 NITRU 2 NITRU 3 NITRU 4 NITRU 5 Nitriding
Traitement 1  Treatment 1
96h 360h 912h 792h 384h 72h Ox1 +lmp2  96h 360h 912h 792h 384h 72h Ox1 + lmp2
Traitement 2  Treatment 2
96h 960h 1368h 1368h 1008h 576h Ox1 +lmp1  96h 960h 1368h 1368h 1008h 576h Ox1 + lmp1
Traitement 3  Treatment 3
96h 312h 576h 792h 504h 72h Ox2+lmp2  96h 312h 576h 792h 504h 72h Ox2 + lmp2
Traitement 4  Treatment 4
96h 360h 1056h 1056h 720h 360h Ox2+lmp1  96h 360h 1056h 1056h 720h 360h Ox2 + lmp1
Traitement 5  Treatment 5
96h 192h 456h 552h 312h 24h Ox3+lmp2  96h 192h 456h 552h 312h 24h Ox3 + lmp2
Traitement 6  Treatment 6
96h 264h 888h 792h 552h 72h Ox3+lmp1  96h 264h 888h 792h 552h 72h Ox3 + lmp1
Traitement 7  Treatment 7
96h 96h 456h 384h 48h 48h Ox0+lmp2  96h 96h 456h 384h 48h 48h Ox0 + lmp2
Traitement 8  Treatment 8
96h 120h 504h 624h 360h 336h OxO+lmp1  96h 120h 504h 624h 360h 336h OxO + lmp1
Il ressort tout d'abord de ce tableau que le traitement nouveau d'imprégnation (imprégnation 1 - traitements pairs) apporte une amélioration sensible par rapport au cas d'une imprégnation classique (imprégnation 2 - traitements impairs). It emerges first from this table that the new impregnation treatment (impregnation 1 - even treatments) provides a significant improvement over the case of a conventional impregnation (impregnation 2 - odd treatments).
On peut noter que le traitement d'oxydation-imprégnation importe peu lorsqu'il n'y a pas de nitruration/nitrocarburation (la résistance à la corrosion reste à 96h, dans la première colonne). It can be noted that the oxidation-impregnation treatment is of little importance when there is no nitriding / nitrocarburization (the corrosion resistance remains at 96h, in the first column).
Quant au traitement NITRU5, il tend à montrer que le traitement d'imprégnation 2 (classique) aboutit à une résistance à la corrosion inférieure au cas sans aucune nitruration. L'intérêt de l'imprégnation de type 1 est notamment visible dans le cas de la nitrocarburation NITRU5 puisque, avec le cas de l'oxydation 3 (en milieu gazeux - traitements 5 et 6), l'amélioration est de l'ordre d'un triplement de la tenue à la corrosion (augmentation d'une cinquantaine d'heures) par rapport au cas d'une imprégnation classique ; il s'agit pourtant du cas où l'oxydation a un effet particulièrement négatif. As for the NITRU5 treatment, it tends to show that the impregnation treatment 2 (conventional) results in a lower corrosion resistance to the case without any nitriding. The interest of type 1 impregnation is particularly visible in the case of NITRU5 nitrocarburizing since, with the case of oxidation 3 (in a gaseous medium - treatments 5 and 6), the improvement is of the order of a tripling of the resistance to corrosion (increase of about fifty hours) compared to the case of a conventional impregnation; it is nevertheless the case where the oxidation has a particularly negative effect.
Dans tous les autres cas NITRU5, l'augmentation de tenue à la corrosion est d'au moins de l'ordre de 200 heures. Ainsi, dans le cas de la NITRU5 combinée avec l'oxydation en milieu aqueux (oxydation 2 - traitements 3 et 4) ou en l'absence d'oxydation (traitements 7 et 8), l'imprégnation nouvelle aboutit à une augmentation de la tenue à la corrosion de l'ordre de 300 heures ; dans le cas de la NITRU5 combinée avec l'oxydation en milieu liquide ionique (oxydation 1 - traitements 1 et 2), l'augmentation est même de l'ordre de 500 heures. En ce qui concerne le traitement NITRU1 , on peut noter que l'effet bénéfique de l'imprégnation nouvelle existe mais est modéré, y compris en pourcentage, par rapport à l'imprégnation classique (traitements 3 à 8, même si les tenues à la corrosion, en valeur absolue, sont meilleures qu'avec NITRU5). Toutefois, on peut noter une augmentation très importante, de 600 heures, dans le cas d'une oxydation en milieu ionique (traitements 1 et 2), avec une tenue à la corrosion qui approche du seuil de 1000 heures. On croit pouvoir en déduire que la condition d'une couche de combinaison d'au moins 8 micromètres d'épaisseur peut être abaissé dans le cas d'une oxydation de type 1 . Si l'on considère maintenant le traitement NITRU4, il conduit au même commentaire que le traitement NITRU5 en l'absence d'oxydation (traitements 7 et 8). Par contre on constate une augmentation d'au moins 200 heures de la tenue à la corrosion dans le cas des oxydations de type 2 (en milieu aqueux - traitements 3 et 4) et de type 3 (en milieu gazeux - traitements 5 et 6). On observe toutefois une augmentation tout à fait remarquable dans le cas d'une oxydation de type 1 (oxydation en milieu ionique à haute température - traitements 1 et 2), puisque la tenue à la corrosion est améliorée de près de 600 heures en dépassant le seuil de 1000 heures. In all other cases NITRU5, the increase in corrosion resistance is at least of the order of 200 hours. Thus, in the case of NITRU5 combined with oxidation in an aqueous medium (oxidation 2 - treatments 3 and 4) or in the absence of oxidation (treatments 7 and 8), the new impregnation results in an increase in resistance to corrosion of the order of 300 hours; in the case of NITRU5 combined with oxidation in an ionic liquid medium (oxidation 1 - treatments 1 and 2), the increase is even of the order of 500 hours. With regard to the NITRU1 treatment, it can be noted that the beneficial effect of the new impregnation exists but is moderate, including in percentage, compared with the conventional impregnation (treatments 3 to 8, even if the suits at the corrosion, in absolute value, are better than with NITRU5). However, we can note a very important increase, of 600 hours, in the case of an oxidation in ionic medium (treatments 1 and 2), with a resistance to the corrosion approaching threshold of 1000 hours. It can be inferred that the condition of a combination layer of at least 8 micrometers thick can be lowered in the case of type 1 oxidation. If we now consider the NITRU4 treatment, it leads to the same comment as the NITRU5 treatment in the absence of oxidation (treatments 7 and 8). On the other hand, there is an increase of at least 200 hours of corrosion resistance in the case of oxidation type 2 (in aqueous medium - treatments 3 and 4) and type 3 (in gaseous medium - treatments 5 and 6) . However, an increase is quite remarkable in the case of a type 1 oxidation (oxidation in high temperature ionic medium). - treatments 1 and 2), since the corrosion resistance is improved by nearly 600 hours by exceeding the threshold of 1000 hours.
Si l'on considère maintenant les traitements de nitruration/nitrocarburation en bains de sels fondus dans lesquels on a pris soin d'obtenir une couche de combinaison d'au moins 8 micromètres d'épaisseur (voire 10 micromètres), on constate que l'imprégnation nouvelle conduit à des niveaux particulièrement élevés de la tenue à la corrosion. If one now considers nitriding / nitrocarburizing treatments in molten salt baths in which care has been taken to obtain a combination layer at least 8 micrometers thick (or even 10 micrometers), it can be seen that New impregnation leads to particularly high levels of corrosion resistance.
Dans le cas d'une absence d'oxydation, l'imprégnation nouvelle apporte une amélioration, surtout significative dans le cas de NITRU3. En présence d'une oxydation, l'amélioration de la tenue à la corrosion est, pour les oxydations de type 2 et 3 (traitements 3 à 6) d'au moins 250 heures pour le traitement NITRU3 et même de 450 heures pour le traitement NITRU2. Avec le type d'oxydation de type 2 (traitements 3 et 4) on obtient des tenues à la corrosion dépassant le seuil de 1000 heures. Avec l'oxydation de type 1 (traitements 1 et 2), l'augmentation apportée par l'imprégnation nouvelle est étonnamment élevée, puisqu'elle est de 456 heures pour NITRU2 et même de 576h pour NITRU3 pour atteindre un seuil particulièrement élevé, de l'ordre de 1370h. In the case of an absence of oxidation, the new impregnation brings an improvement, especially significant in the case of NITRU3. In the presence of oxidation, the improvement in corrosion resistance is, for oxidation of type 2 and 3 (treatments 3 to 6) of at least 250 hours for the treatment NITRU3 and even 450 hours for the treatment NITRU2. With type 2 oxidation (treatments 3 and 4), corrosion resistance exceeding the threshold of 1000 hours is obtained. With the oxidation of type 1 (treatments 1 and 2), the increase brought by the new impregnation is surprisingly high, since it is 456 hours for NITRU2 and even 576h for NITRU3 to reach a particularly high threshold, of the order of 1370h.
Ainsi, il apparaît que : Thus, it appears that:
• l'imprégnation nouvelle apporte une amélioration de la tenue à la corrosion par rapport à une imprégnation classique, quels que soient les traitements de nitruration/nitrocarburation et d'oxydation, The new impregnation brings about an improvement in the resistance to corrosion compared to a conventional impregnation, whatever the nitriding / nitrocarburizing and oxidation treatments,
• Cette amélioration est particulièrement notable et conduit à des valeurs de tenue à la corrosion particulièrement élevées pour les traitements de nitrocarburation en bains de sels conduisant à une couche de combinaison d'au moins 8 micromètres (NITRU2 et NITRU3), de préférence entre 10 et 25 micromètres, • Cette amélioration est particulièrement notable et conduit à des valeurs de tenue à la corrosion particulièrement élevées pour les nitrocarburations en bains de sels (NITRU1 à NITRU3) ou en phase gazeuse (NITRU4) dans le cas d'une oxydation en bains de sels fondus (type 1 ), This improvement is particularly notable and leads to particularly high corrosion resistance values for salt bath nitrocarburizing treatments resulting in a combination layer of at least 8 microns (NITRU2 and NITRU3), preferably between 10 and 25 microns, This improvement is particularly notable and leads to particularly high corrosion resistance values for nitrocarburations in salt baths (NITRU1 to NITRU3) or in the gas phase (NITRU4) in the case of oxidation in molten salt baths ( type 1),
• Cette amélioration aboutit à des niveaux particulièrement élevés de tenue à la corrosion en combinant les nitrocarburations en bains de sels conduisant à une couche d'au moins 8 micromètres d'épaisseur (NITRU2 et NITRU3) et une oxydation de type 1 ou 2, surtout dans le cas d'une oxydation en bains de sels (type 1 ).  • This improvement leads to particularly high levels of corrosion resistance by combining nitrocarburations in salt baths leading to a layer of at least 8 micrometers thick (NITRU2 and NITRU3) and oxidation of type 1 or 2, especially in the case of oxidation in salt baths (type 1).
Les résultats ci-dessus ont été mesurés sur des zones lisses des échantillons. The above results were measured on smooth areas of the samples.
Des mesures sur des zones présentant des aspérités (des zones filetées en l'occurrence) ont également montré que les meilleurs résultats sont obtenus avec les traitements d'oxydation en milieu liquide 1 et 2, combinés avec une imprégnation de type 1 et avec une nitrocarburation en bains de sels conduisant à des couches de combinaison d'au moins 8 micromètres, NITRU2 et NITRU3. Measurements on areas with asperities (threaded zones in this case) have also shown that the best results are obtained with the liquid oxidation treatments 1 and 2, combined with a type 1 impregnation and nitrocarburizing in salt baths leading to combination layers of at least 8 micrometers, NITRU2 and NITRU3.
Alors que l'imprégnation nouvelle aboutit à des résultats excellents, équivalents pour NITRU2 et NITRU3, avec les oxydations en milieu liquide, sur des surfaces lisses, il semble que, sur les zones non lisses, l'imprégnation nouvelle donne de très bons résultats pour ces deux mêmes types de nitrocarburation, un peu meilleurs avec NITRU3 qu'avec NITRU2. While the new impregnation results in excellent results, equivalent for NITRU2 and NITRU3, with the oxidations in liquid medium, on smooth surfaces, it seems that, on the non-smooth zones, the new impregnation gives very good results for these two same types of nitrocarburation, a little better with NITRU3 than with NITRU2.
En résumé, les résultats ci-dessus montrent que le bain d'imprégnation 1 présente un effet surprenant de synergie avec les traitements de nitruration/nitrocarburation NITRU2 et NITRU3 sous réserve que la nitruration/nitrocarburation soit suivie d'une oxydation de type 1 ou 2, un optimum semblant être obtenu lorsque le traitement d'oxydation est de type 1 . L'ampleur des augmentations de résistance à la corrosion constatées pour la combinaison du bain d'imprégnation 1 avec les traitements de nitruration/nitrocarburation en bains de sels fondus aboutissant à des couches de combinaison de plus de 8 micromètres d'épaisseur (NITRU2 et NITRU3) et le traitement d'oxydation 1 en bain de sels fondus traduit l'existence d'une synergie surprenante entre ces trois types de traitement qui reste incomprise. In summary, the above results show that the impregnating bath 1 has a surprising synergistic effect with nitriding / nitrocarburizing treatments NITRU2 and NITRU3 provided that nitriding / nitrocarburizing is followed by oxidation of type 1 or 2 , an optimum appearing to be obtained when the oxidation treatment is of type 1. The magnitude of the corrosion resistance increases noted for the combination of impregnation bath 1 with nitriding / nitrocarburizing treatments in molten salt baths resulting in combination layers of more than 8 micrometers thick (NITRU2 and NITRU3 ) and the oxidation treatment 1 molten salt bath reflects the existence of a surprising synergy between these three types of treatment that remains misunderstood.
La composition particulière du bain d'imprégnation considérée dans les essais rentre dans une composition plus générale, à savoir un bain formé d'au moins 70% en poids, à 1 % près, d'un solvant formé d'un mélange d'hydrocarbures formé d'une coupe d'alcanes de C9 à C17, de 10% à 30% en poids, à 1 % près, d'au moins une huile de paraffine composée d'une coupe d'alcanes C16 à C32 et d'au moins un additif du type additif phénolique de synthèse à une concentration comprise entre 0.01 % et 3% en poids, à la température ambiante. The particular composition of the impregnation bath considered in the tests is part of a more general composition, namely a bath consisting of at least 70% by weight, to within 1%, of a solvent formed of a mixture of hydrocarbons. formed from a cut of C9 to C17 alkanes, from 10% to 30% by weight, to within 1%, of at least one paraffin oil composed of a section of C16 to C32 alkanes and from minus a synthetic phenolic additive additive at a concentration of between 0.01% and 3% by weight, at room temperature.
La teneur en solvant est de préférence comprise entre 80% et 90% en poids ; de même, la teneur en huile de paraffine est de préférence comprise entre 10% et 20% en poids. La coupe d'alcanes du solvant est de préférence de C9 à C14. Les résultats précités ont été obtenus sur la base d'échantillons d'acier XC45, mais il est à la portée de l'homme de métier d'adapter les paramètres de traitement en fonction du matériau utilisé, et suivre ainsi l'enseignement précité. The solvent content is preferably between 80% and 90% by weight; likewise, the content of paraffin oil is preferably between 10% and 20% by weight. The alkane section of the solvent is preferably C9 to C14. The above results were obtained on the basis of XC45 steel samples, but it is within the abilities of those skilled in the art to adapt the processing parameters according to the material used, and thus follow the aforementioned teaching.

Claims

REVENDICATIONS
1 . Procédé de traitement superficiel d'une pièce en acier pour lui conférer une résistance élevée à l'usure et à la corrosion comportant  1. A method of surface treatment of a steel part to give it a high resistance to wear and corrosion including
* une étape de nitruration ou de nitrocarburation adaptée à former une couche de combinaison d'au moins 8 micromètres d'épaisseur formée de nitrures de fer de phases ε et/ou γ', * A step of nitriding or nitrocarburizing adapted to form a compound layer of at least 8 micrometers thick formed of iron nitride ε-phase and / or γ '
* une étape d'oxydation adaptée à générer une couche d'oxydes d'épaisseur comprise entre 0.1 et 3 micromètres et * An oxidation step adapted to generate a thick oxide layer of between 0.1 and 3 micrometers and
* une étape d'imprégnation par trempage dans un bain d'imprégnation pendant au moins 5 minutes, ce bain étant formé d'au moins * A step of impregnation by immersion in an impregnating bath for at least 5 minutes, said bath being formed at least
70% en poids, à 1 % près, d'un solvant formé d'un mélange d'hydrocarbures formé d'une coupe d'alcanes de C9 à C17, de 10% à 30% en poids, à 1 % près, d'au moins une huile de paraffine composée d'une coupe d'alcanes C16 à C32 et d'au moins un additif du type additif phénolique de synthèse à une concentration comprise entre 0.01 % et 3% en poids, à 0.1 % près, à la température ambiante. 70% by weight, to within 1%, of a solvent formed of a hydrocarbon mixture formed from a C9 to C17 alkane cut, from 10% to 30% by weight, to within 1%, of at least one paraffin oil composed of a section of C16 to C32 alkanes and at least one additive of the phenolic synthetic additive type at a concentration of between 0.01% and 3% by weight, to within 0.1%, at Room temperature.
2. Procédé selon la revendication 1 dans lequel l'additif phénolique de synthèse est un composé de formule Ci5H240. 2. The process according to claim 1 wherein the synthetic phenolic additive is a compound of formula Ci 5 H 24 0.
3. Procédé selon la revendication 2, dans lequel le bain d'imprégnation est formé de 90%+/-0,5% en poids de solvant, 10% +/-0,5% en poids d'huiles de paraffine et moins de 1 %+/-0.1 %, d'additif phénolique de synthèse de formule Ci5H24O. The method of claim 2, wherein the impregnating bath is formed of 90% +/- 0.5% by weight of solvent, 10% +/- 0.5% by weight of paraffin oils and less 1% +/- 0.1%, phenolic synthesis additive of formula Ci 5 H 24 O.
4. Procédé selon l'une quelconque des revendications 1 à 3, dont le bain d'imprégnation comporte en outre au moins un additif choisi dans le groupe constitué par le sulfonate de calcium ou de sodium, les phosphites, les diphénylamines, le dithiophosphate de zinc , les nitrites, les phosphoramides. 4. Method according to any one of claims 1 to 3, wherein the impregnating bath further comprises at least one additive selected from the group consisting of calcium or sodium sulfonate, phosphites, diphenylamines, sodium dithiophosphate. zinc, nitrites, phosphoramides.
5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel l'opération de trempage est suivie d'une opération de séchage naturel ou accéléré par étuvage. 5. A process according to any one of claims 1 to 4, wherein the soaking operation is followed by a natural drying operation or accelerated by steaming.
6. Procédé selon l'une quelconque des revendications 1 à 5, dont l'étape de nitruration ou de nitrocarburation est effectuée en un bain de sels fondus contenant de 14% à 44% en poids de cyanates alcalins à une température de 550 °C à 650 °C pendant au moins 45 minutes. 6. Process according to any one of claims 1 to 5, in which the nitriding or nitrocarburizing step is carried out in a bath of molten salts containing from 14% to 44% by weight of alkaline cyanates at a temperature of 550 ° C. at 650 ° C for at least 45 minutes.
7. Procédé selon la revendication 6, dans lequel le bain de nitruration/nitrocarburation contient de 14% à 18% en poids de cyanates alcalins. The process according to claim 6, wherein the nitriding / nitrocarburizing bath contains from 14% to 18% by weight of alkaline cyanates.
8. Procédé selon la revendication 6 ou la revendication 7, dans lequel le traitement de nitruration/nitrocarburation est effectué à une température de 590 °C pendant 90 minutes à 100 minutes. The process according to claim 6 or claim 7, wherein the nitriding / nitrocarburizing treatment is carried out at a temperature of 590 ° C for 90 minutes to 100 minutes.
9. Procédé selon la revendication 6 ou la revendication 7, dans lequel le traitement de nitruration/nitrocarburation est effectué à une température de 630 °C pendant environ 45 minutes à 50 minutes. The process of claim 6 or claim 7, wherein the nitriding / nitrocarburizing treatment is conducted at a temperature of 630 ° C for about 45 minutes to 50 minutes.
10. Procédé selon l'une quelconque des revendications 1 à 5, dans lequel l'étape de nitrocarburation est effectuée en un milieu gazeux entre 500°C et 600°C contenant de l'ammoniac. The process according to any one of claims 1 to 5, wherein the nitrocarburizing step is carried out in a gaseous medium between 500 ° C and 600 ° C containing ammonia.
1 1 . Procédé selon l'une quelconque des revendications 1 à 5, dont l'étape de nitruration ou de nitrocarburation est effectuée dans un milieu ionique formant un plasma, comprenant au moins de l'azote et de l'hydrogène sous pression réduite. 1 1. Process according to any one of claims 1 to 5, in which the nitriding or nitrocarburizing step is carried out in an ionic medium forming a plasma, comprising at least nitrogen and hydrogen under reduced pressure.
12. Procédé selon l'une quelconque des revendications 1 à 1 1 , dont l'étape de nitruration ou de nitrocarburation est effectuée en sorte de former une couche de combinaison d'épaisseur au moins égale à 10 micromètres. 12. A method according to any one of claims 1 to 1 1, the nitriding or nitrocarburizing step is performed so as to form a combination layer of thickness at least equal to 10 microns.
13. Procédé selon l'une quelconque des revendications 1 à 12, dont l'étape d'oxydation est effectuée dans un bain de sels fondus qui contient des nitrates alcalins, des carbonates alcalins et des hydroxydes alcalins. 13. A process according to any one of claims 1 to 12, wherein the oxidation step is carried out in a bath of molten salts which contains alkali nitrates, alkali carbonates and alkali hydroxides.
14. Procédé selon la revendication 13, dans lequel l'étape d'oxydation est réalisée à une température de 430 °C à 470 °C pendant de 15 àThe process according to claim 13, wherein the oxidation step is carried out at a temperature of from 430 ° C to 470 ° C for from 15 to 15 ° C.
20 minutes. 20 minutes.
15. Procédé selon l'une quelconque des revendications 1 à 12, dont l'étape d'oxydation est effectuée dans un bain aqueux qui contient des hydroxydes alcalins, des nitrates alcalins et des nitrites alcalins. 15. Process according to any one of claims 1 to 12, the oxidation step of which is carried out in an aqueous bath which contains alkali hydroxides, alkaline nitrates and alkaline nitrites.
16. Procédé selon la revendication 15, dans lequel l'étape d'oxydation est réalisée à une température de 1 10°C à 130°C pendant de 15 à 20 minutes. The process according to claim 15, wherein the oxidation step is carried out at a temperature of 110 ° C to 130 ° C for 15 to 20 minutes.
17. Procédé selon l'une quelconque des revendications 1 à 1 2, dans lequel l'étape d'oxydation est effectuée en un milieu gazeux majoritairement constitué de vapeur d'eau, à une température de 450 °C à 550 °C pendant de 30 à 120 minutes. 17. A process according to any one of claims 1 to 1 2, wherein the oxidation step is carried out in a gaseous medium consisting predominantly of water vapor, at a temperature of 450 ° C to 550 ° C for 30 to 120 minutes.
18. Pièce en acier ayant une résistance élevée à l'usure et à la corrosion obtenue par le procédé de l'une quelconque des revendications 1 à 17, comportant une couche de combinaison d'au moins 8 micromètres, une couche d'oxydes d'épaisseur comprise entre 0.1 et 3 micromètres et une couche d'imprégnation qui est sèche au toucher. 18. A steel piece having a high wear and corrosion resistance obtained by the process of any one of claims 1 to 17, having a combination layer of at least 8 micrometers, a layer of oxides of thickness between 0.1 and 3 micrometers and an impregnation layer which is dry to the touch.
EP15821125.0A 2014-12-23 2015-12-15 Method for surface treatment of a steel component by nitriding or nitrocarburising, oxidising and then impregnating Active EP3237648B1 (en)

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PCT/FR2015/053511 WO2016102813A1 (en) 2014-12-23 2015-12-15 Method for surface treatment of a steel component by nitriding or nitrocarburising, oxidising and then impregnating

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US20170349997A1 (en) 2017-12-07
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CN107109617A (en) 2017-08-29
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HUE049293T2 (en) 2020-09-28
ZA201704730B (en) 2018-05-30
BR112017011508B1 (en) 2021-08-10
PH12017500936A1 (en) 2017-11-20
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KR102455917B1 (en) 2022-10-17
WO2016102813A1 (en) 2016-06-30
EP3237648B1 (en) 2020-03-18
PT3237648T (en) 2020-05-27
FR3030578B1 (en) 2017-02-10
FR3030578A1 (en) 2016-06-24
TW201631183A (en) 2016-09-01
PH12017500936B1 (en) 2017-11-20
RU2017126188A3 (en) 2019-06-07
BR112017011508A2 (en) 2018-02-27
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