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
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/36—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases using ionised gases, e.g. ionitriding
  • C23C8/38—Treatment of ferrous surfaces
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/36—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases using ionised gases, e.g. ionitriding

Definitions

• the present invention relates to a method of surface treatment of a metal part, and more particularly, to a method of surface hardening by enriching with carbon or boron a surface layer located in the vicinity of a surface of the part.
• a surface treatment of a metal part has been described in which a gas atmosphere containing an element is brought into contact with a surface of the part brought to a temperature between 270 and 550 ° C. interstitial such as carbon or nitrogen, in the ionized state, at a pressure less than 10 mtorr. Due to the low pressure of the gaseous atmosphere, the content of the layer interstitial surface remains low even for treatment times of several hours.
• interstitial such as carbon or nitrogen
• these compounds In the case of the surface treatment of a stainless steel part, these compounds contain chromium which is taken from the surface layer of the stainless steel part. This results in a degradation of the part's resistance to corrosion.
• An object of the present invention is to remedy this drawback by proposing a method for hardening the surface of a metal part which does not deteriorate its resistance to corrosion.
• Another object of the present invention is to provide a surface treatment of a metal part which can be implemented industrially, under favorable conditions with regard to the costs and the duration of the treatment.
• the gaseous compound can be constituted by an aliphatic or aromatic hydrocarbon or by a cyclane.
• the gaseous compound can also consist of methane and in this case, the gaseous atmosphere can contain from 5 to 30% by volume of methane.
• the gaseous compound can also be constituted by a gaseous derivative of boron, for example, a diborane.
• the gaseous atmosphere may also contain nitrogen or a gaseous derivative of nitrogen such as ammonia.
• the method applies, in particular, to parts of metal alloy whose structure is cubic with centered face, cubic centered or tetragonal, more particularly, to parts of austenitic or martensitic stainless steel, to parts of nickel-based alloy and to parts made of cobalt-based alloy.
• the process can also be applied to metal alloy parts based on aluminum or based on titanium.
• the metallic part obtained has a hardened surface layer consisting of a homogeneous solid solution of carbon or boron in the metal matrix of the part whose carbon or boron content is between 5 and 50 atom% and preferably between 10% and 30%.
• the part is placed in the enclosure of a plasma surface treatment oven.
• the enclosure is placed under vacuum and then a mixture of gases is introduced into the enclosure, the pressure of which is less than atmospheric pressure may be between 0.5 and 200 mbar.
• the gas mixture consists of a reactive gas on the one hand, and dilution gases on the other hand which are, for example, hydrogen and argon.
• the reactive gas is a gaseous compound either of carbon or of boron; for example, an aliphatic hydrocarbon, an aromatic hydrocarbon or a cyclane, and in particular methane, or, for example, a diborane.
• the gas mixture can also comprise a small proportion of a gaseous nitrogen compound.
• the gas mixture is ionized, at least partially, by creating a cold plasma.
• the ionization of the gas mixture creates ions which, by bombarding the surface of the part, can passivate it to make it reactive and heat it, and, on the other hand, creates very reactive species of carbon or boron, which are atoms in which certain electronic layers are excited.
• the highly reactive carbon or boron species react with the surface and penetrate inside by diffusion to form an interstitial solid solution free of precipitates.
• the temperature of the surface must be sufficient, and preferably greater than 300 ° C. But to avoid the formation of precipitated the surface temperature must remain below 460 ° C.
• the production of active element on the surface of the part is not too great. In fact, with carbon, for example, if the production of active carbon is too rapid, a deposit of carbon black harmful to the treatment is formed on the surface of the part. To avoid this, the active gas content of the gas mixture is limited in order to balance the kinetics of production of active element on the surface of the part, and the kinetics of penetration of the active element in the part.
• the active gas when the active gas is methane, its content in the gas mixture is between 5 and 30% and, preferably, of the order of 10%.
• the gaseous atmosphere in contact with the surface of the part is maintained at a pressure which must be greater than 0.5 and which can range up to 200 mbar.
• the plasma can be a so-called “discharge plasma", that is to say a plasma generated by an electric discharge between an anode and a cathode, the part to be treated being brought to a cathodic potential and being able itself to be the In this case, the ions are accelerated, they bombard the surface of the part which heats it up sufficiently so that there is no need to provide additional heating means.
• discharge plasma that is to say a plasma generated by an electric discharge between an anode and a cathode, the part to be treated being brought to a cathodic potential and being able itself to be the In this case, the ions are accelerated, they bombard the surface of the part which heats it up sufficiently so that there is no need to provide additional heating means.
• the plasma can also be a plasma generated by an electromagnetic wave generator, or a microwave generator, or a "post-discharge" plasma, that is to say a plasma transferred from a plasma generator. to the enclosure in which the room is located.
• the bombardment of the surface of the part may be insufficient to cause the necessary heating.
• the surface of the room is heated, for example, by radiation.
• the duration of the treatment depends on the thickness of the treated layer that one wants to obtain, this duration can vary between 1 hour and a few tens of hours.
• the solid solution contains a high proportion of interstitial element, between 5 and 50 atom% and, generally between 10 and 30 atom%. Depending on the conditions of implementation of the treatment and in particular, depending on the duration of the treatment, it is possible to obtain a hardened surface layer with a thickness of 1 to 60 ⁇ m.
• the surface layer of the part may have, after treatment, a Vickers Hv hardness greater than 800.
• This treatment which is applicable to a very wide variety of metallic alloys and, in particular, to alloys having a cubic structure with centered face, cubic centered or tetragonal (for example, austenitic, ferritic or martensitic stainless steels), makes it possible to '' obtain a layer 1 to 60 ⁇ m thick, of a solid saturated, or even supersaturated, solution of carbon or boron, homogeneous, that is to say free of precipitates of carbides or borides, the hardness can be greater than 800 Vickers or even 1000 Vickers and which is very resistant to corrosion. Carbon can be combined with nitrogen to form the solid solution layer.
• the alloy is an austenitic steel, the carburetted layer cannot be attacked by chemical reagents usually used in metallography and has a resistance to attack by salt spray greater than 1000 hours.
• the parts are subjected to an atmosphere containing carbon in activated form at a temperature generally lower than the treatment temperature during the first phase and for example, between 300 and 350 ° C.
• the surface layer of the parts is loaded with carbon, so that a solid solution of carbon in the steel of the part loaded with nitrogen is formed in the surface layer during the first phase.
• the martensitic steel parts then exhibit both high wear resistance and very good corrosion resistance.
• This treatment in two successive phases applies in particular to mechanical parts made of highly stressed martensitic steel such as the parts used in the field of oil drilling or to tools or cutting blades.
• austenitic stainless steel nuts for the nuclear industry were treated for 12 hours at a temperature of about 420 ° C.
• the nuts thus treated had remarkable anti-seizing characteristics due to the level of hardness obtained on the threads (Hv> 800).
• the treatment according to the invention which makes it possible to obtain very hard surface layers, very resistant to wear and very resistant to corrosion, can be carried out on all kinds of parts, and in particular on any mechanical part subject to wear in a corrosive environment (for example: food industry, chemical industry, nuclear industry, marine environment, biomedical applications); on any austenitic steel container which must resist scratches, for example flat austenitic stainless steel which can be coated before forming; on the blades of martensitic stainless steel cutting objects such as knives and scalpels; on orthopedic implants; on valves; on turbine or condenser parts subject to pitting corrosion.
• the treatment can also be carried out on a strip or on a metal blank, implemented after treatment.
• the treatment applies in particular, in the case of decorative austenitic stainless steel panels, for example, to polished and / or colored panels by a process such as anodization.
• the hardening of the surface of the panels by forming a homogeneous solid solution of carbon in a surface layer of the panels makes it possible to avoid risks of scratches and degradation of the aesthetic appearance of the panels.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Heat Treatment Of Articles (AREA)

Applications Claiming Priority (2)

Publications (3)

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Family Applications (1)

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Cited By (9)

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Family Cites Families (12)

• 1996
  • 1996-04-12 FR FR9604561A patent/FR2747398B1/fr not_active Expired - Lifetime
• 1997
  • 1997-04-09 EP EP19970400816 patent/EP0801142B1/de not_active Expired - Lifetime
  • 1997-04-09 DE DE1997613662 patent/DE69713662T2/de not_active Expired - Lifetime

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