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
  • 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
  • C21D7/00—Modifying the physical properties of iron or steel by deformation
  • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
  • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
• • 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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F17/00—Multi-step processes for surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by subclass C21D or C22F or class C25

Definitions

• the present invention relates to a method of surface treatment of steel or cast iron parts, in particular of cylindrical parts, with a view to giving these parts resistance to wear and corrosion.
• the main treatment processes currently used for this purpose are nitriding, chromium plating and other electrolytic deposits, boriding, chromizing, oxidation.
• the hard chromium plating often used in these applications exhibits a limited corrosion resistance due to the micro-cracks which characterize it. In addition, it requires complex and expensive operations with a final superfinishing operation.
• Variants have been proposed for nitriding in a salt bath, comprising in the final phase an oxidation in an oxidizing bath, followed by running in and a new oxidation.
• the corrosion resistance obtained is generally satisfactory, but the intermediate lapping is difficult to carry out and, moreover, the quantity of material extracted by lapping is not reproducible, which makes the results dispersed.
• the present invention aims to provide a surface treatment method which is easy to carry out and which makes it possible to obtain good resistance to corrosion.
• the subject of the present invention is a method of surface treatment of steel or cast iron parts to give these parts resistance to wear and corrosion, characterized in that the surface of the parts with ionic nitriding, ionic oxynitriding and ionic oxidation.
• the three successive operations can be carried out in the same ionization enclosure by successively using a nitriding gas, a mixture of nitriding gas and oxidizing gas and an oxidizing gas.
• the method according to the invention makes it possible to obtain a layer of iron nitrides (Fe 2-3 N) and a layer of iron oxide of Fe304 type, these layers being separated by a transition layer in which layers are progressively passed.
• iron nitrides with Fe 3 O 4 type oxide iron nitrides with Fe 3 O 4 type oxide.
• a surface hardening operation is advantageously carried out after the three operations under ion bombardment, which has the effect of compressing the layers formed by ion bombardment.
• This surface hardening can be carried out in particular by roller burnishing in the case of cylindrical parts.
• the method according to the present invention can be implemented on these annealed or tempered steel parts, in gray cast iron or in spheroidal graphite cast iron.
• the first phase of the process is ion nitriding.
• This phase can be carried out in a conventional manner in an enclosure containing a nitriding gas under reduced pressure.
• the parts to be treated are arranged in the heart of the enclosure which serves as an anode.
• the parts to be treated constitute the cathode.
• a voltage of a few hundred volts is applied between the anode and the cathode.
• the parts to be treated are bombarded with nitrogen ions.
• the nitriding gas can be a gaseous mixture based on nitrogen and hydrogen or ammonia, for example a gaseous mixture containing 80% by weight of nitrogen, 2 to 6% by weight of methane, the rest being l 'hydrogen.
• the pressure can be of the order of 1.5 to 4.10 2 Pa.
• the temperature can be from 550 to 600 ° C.
• the treatment time can be around 15 to 60 minutes depending on the parts to be treated and the desired nitriding thickness.
• the thickness of the nitride layer obtained can be approximately 10 to 30 microns.
• the procedure is the same as for the first phase, but an oxidizing gas can be added to the nitriding gas which can be 0 2 , C0 2 or H 2 0.
• the content of oxidizing gas is advantageously from 0.5 to 2% by weight (expressed in oxygen).
• the temperatures and pressures can be the same as for the first phase.
• the duration of treatment can vary from 30 to 120 minutes.
• the thickness of the intermediate layer obtained can be from 2 to 10 microns.
• an oxidizing gas is introduced into the enclosure.
• This gas can be 0 2 , CO 2 , H 2 0 or a mixture of these gases.
• This third phase can be carried out under glow discharge, the temperature conditions and pressure then being the same as for the first two phases.
• the duration of the treatment can be approximately 10 to 20 minutes.
• This third phase can also be carried out in the absence of glow discharge, under a pressure of 1.5 to 2.10 Pa for a period of 15 to 20 minutes, the oxidizing gas being introduced continuously and pumped continuously.
• the quantity of oxidizing gas used can represent from 50 to 100 Nl per m 2 of surface to be treated.
• the room temperature drops to around 450 ° C.
• the thickness of the Fe 3 0 4 type oxide layer obtained can be from 0.5 to 4 microns.
• the parts can then be cooled under a nitrogen atmosphere.
• the parts thus obtained can have a roughness less than or equal to 1 micron.
• the surface condition can be improved by the surface hardening operation.
• this work hardening can be carried out by roller burnishing at the pass under a pressure of 2 to 5.10 6 Pa and with an advance of 1 mm per revolution.
• This operation which maintains the entire coating layers compresses these layers and makes it possible to obtain a roughness of less than 0.4 microns.
• the work hardening pressure is adjusted according to the desired final roughness.
• XC38 steel cylinder rods having a diameter of 12 mm are treated by the method according to the invention.
• the rods are placed in an ionization enclosure, the rods being maintained under a voltage of -400 V relative to the walls of the enclosure.
• a gaseous mixture comprising 80% by weight of nitrogen, 3% by weight of methane and 17% by weight of hydrogen is introduced into the enclosure.
• the pressure is 2.10 2 P a.
• the temperature is 575 ° C.
• the duration of the treatment is 30 minutes.
• the duration of the treatment is 90 minutes.
• Water vapor is then introduced into the enclosure at a pressure of 1.5 ⁇ 10 3 Pa.
• the duration of the treatment is 20 minutes.
• a coating comprising a compact layer of iron nitride Fe 2-3 N with a thickness of about 18 microns, a porous layer consisting of a mixture of iron nitride and Fe 3 0 4 with a thickness d '' about 5 microns and a surface layer of black appearance of Fe 3 0 4 of 1 to 2 microns.
• the coating thus obtained has a roughness of the order of 1 micron.
• the parts are subjected to a corrosion test of the marine atmosphere type.
• the parts are treated by carrying out only the first nitriding phase.
• the parts thus treated exhibit generalized corrosion after 90 days.
• Example 2 The procedure is as in Example 1, but the cylinder rods thus treated are further subjected to roller burnishing on the parade under a pressure of 4.10 6 Pa with an advance of 1 mm per revolution. A surface roughness of about 0.2 microns is obtained.

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

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• 1984
  • 1984-03-12 FR FR8403768A patent/FR2560892B1/fr not_active Expired
• 1985
  • 1985-03-07 EP EP85400442A patent/EP0159222A1/de not_active Withdrawn

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