EP0408168B1 - Verfahren zur Vorbehandlung von metallischen Werkstücken und zur Nitrierhärtung von Stahl - Google Patents

Verfahren zur Vorbehandlung von metallischen Werkstücken und zur Nitrierhärtung von Stahl Download PDF

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Publication number
EP0408168B1
EP0408168B1 EP90302232A EP90302232A EP0408168B1 EP 0408168 B1 EP0408168 B1 EP 0408168B1 EP 90302232 A EP90302232 A EP 90302232A EP 90302232 A EP90302232 A EP 90302232A EP 0408168 B1 EP0408168 B1 EP 0408168B1
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Prior art keywords
steel
layer
nitriding
works
furnace
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French (fr)
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EP0408168A1 (de
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Masaaki Tahara
Takakazu Tomoda
Kenzo Kitano
Teruo Minato
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Air Water Inc
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Daido Sanso Co Ltd
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Priority claimed from JP1177660A external-priority patent/JPH089766B2/ja
Priority claimed from JP1333424A external-priority patent/JP2501925B2/ja
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—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
    • C23C8/02—Pretreatment of the material to be coated

Definitions

  • This invention relates to (I) a method of pretreating metallic articles or works for the purpose of cleaning and activating the surface thereof prior to (1) diffusion/penetration processing, such as boronizing, carburization or nitriding, (2) hard ceramic coating formation, for example by physical vapor deposition or thermal spraying, or (3) plating, for example by hot dipping in a molten aluminum or zinc bath and (II) a method of nitriding steel for the improvement of wear resistance and other properties by forming a nitrided layer on the steel surface.
  • diffusion/penetration processing such as boronizing, carburization or nitriding
  • hard ceramic coating formation for example by physical vapor deposition or thermal spraying
  • plating for example by hot dipping in a molten aluminum or zinc bath
  • II a method of nitriding steel for the improvement of wear resistance and other properties by forming a nitrided layer on the steel surface.
  • thermal diffusion/penetration treatment Prior to being subjected to thermal diffusion/penetration treatment, coating treatment to form hard ceramic coatings, plating treatment or the like thermal surface treatment, metallic works made of steel, aluminum, titanium or nickel, for instance, are generally subjected to various types of pretreatment, for example cleaning, degreasing, acid pickling and treatment with a molten flux.
  • pretreatment for example cleaning, degreasing, acid pickling and treatment with a molten flux.
  • alkali degreasing and/or cleaning with an organic solvent is selectively applied to carbon steel works before such thermal treatment as carburization or nitriding.
  • a step of removing surface oxidized layers by washing with a hydrofluoric acid-nitric acid mixture is added to the above-mentioned pretreatment step or steps.
  • thermal treatment as physical vapor deposition (PVD) or chemical vapor deposition (CVD) for forming hard ceramic coating layers
  • intermediate processing as nickel plating is conducted as a pretreatment step in some instances for improving the adhesion of coating layers to substrate metallic works.
  • substrate works are pretreated with a molten flux following degreasing and acid pickling to thereby realize an increased surface activity, or substrate works are maintained at a temperature above the contemplated thermal treatment temperature for a certain period of time and then gaseous hydrogen or a gas containing a high concentration of hydrogen is introduced into the system for reducing the substrate work surface in the resulting reducing atmosphere to achieve the same purpose.
  • the primary object of these pretreatment processes is to activate the surface of substrate metallic works to thereby facilitate the thermal treatment proper and produce maximum treatment effects.
  • recent regulations against waste water discharge, regulations against the use of fluorocarbon species, aggravated working conditions and other factors have made it difficult to continue the commercial use of most of the above-mentioned pretreatment processes and have caused increases in pretreatment cost year by year.
  • the pretreatment process comprising maintaining substrate steel works in a reducing gas atmosphere at an elevated temperature prior to plating treatment using molten zinc or aluminum not only requires an expensive reducing gas in large quantities but also involves the problem that the efficiency of plating is impaired by selective oxidation of valuable elements contained in steel materials, for example Mn, Si and Al.
  • the methods of nitriding or carbonitriding steel articles or works for the formation of a nitrided layer on their surface which have been so far employed for the purpose of improving their mechanical properties, such as wear resistance, corrosion resistance and fatigue strength, include the following, among others:
  • method (a) which uses hazardous molten salts, has a dark future when evaluated from the labor environment, waste treatment and other viewpoints.
  • Method (b) which achieves nitriding by means of glow discharge in an N2 + H2 atmosphere under a low degree of vacuum, can indeed avoid, to a considerable extent, the staining of the steel surface or the influences of oxidized layer formation owing to some cleaning effect of sputtering but tends to allow occurrence of uneven nitriding due to local temperature differences.
  • this method is disadvantageous in that articles or works which can be nitrided are much limited in shape and size and that increases in cost result.
  • Method (c) also has problems, for instance, the treatment process is not very stable but tends to lead to uneven nitriding. Another problem lies in that deep nitriding requires a fairly long time.
  • steel is nitrided at temperatures not lower than 500°C.
  • the surface should be free not only of organic and inorganic contaminants but also of any oxidized layer or adsorbed O2 layer. It is also necessary that the steel surface layer itself should be highly active.
  • the above-mentioned oxidized layer if present, would unfavorably promote dissociation of the nitriding gas ammonia. In practice, however, it is impossible to prevent oxidized layer formation in gas nitriding.
  • the oxide formation on the steel surface varies in extent depending on the surface state, working conditions and other factors even in one and the same work, resulting in unevenly nitrided layer formation.
  • the means or methods so far proposed for solving the above-mentioned essential problems encountered in gas nitriding and gas soft nitriding include, among others, the one comprising charging a vinyl chloride resin into a furnace together with works, the one comprising sprinkling works with chlorine, CH3Cl or the like and heating at 200-300°C to thereby cause evolution of HCl and prevent oxide formation and remove oxides therewith, and the one comprising plating works in advance to thereby prevent oxide formation. Practically none of them have been put into practical use, however. Where chlorine or a chloride is used, chlorides such as FeCl2, FeCl3 and CrCl3 are formed on the steel surface.
  • EP 0 352 061 published after the priority date, but before the filing date of the present application discloses a metal material having on its surface a film passivated by fluorination, the film being composed mainly of a metal fluoride substantially satisfying stoichiometric ratio.
  • An apparatus comprising the metal material is also disclosed.
  • the first object of the invention to provide a method of pretreating metallic works for cleaning and activating the surface thereof to thereby facilitate the succeeding thermal treatment proper, without causing environmental pollution or increases in pretreatment cost and without impairing performance characteristics of metallic materials
  • the invention provides a method of pretreating metallic works which comprises holding a metallic work in a heated condition in a fluorine- or fluoride-containing gas atmosphere and then removing the resulting fluorinated layer to thereby clean and activate the surface of said metallic work and to accomplish the second object, the invention provides a method of nitriding steel by reacting the surface of steel articles or works with nitrogen for the formation of a hard nitrided layer thereon which comprises preliminarily holding a steel work in a fluorine- or fluoride-containing gas atmosphere and, after formation of a fluorinated layer on the surface of the work, heating the steel work in a nitriding atmosphere for the formation of a nitrided layer on the surface thereof.
  • this fluorinated layer is stable and continues covering and protecting the metallic work surface at temperature of about 300°C-600°C.
  • Such fluorinated layer is formed on the furnace inside wall surface as well and covers and protects said wall surface, so that corrosion and wear of the furnace inside wall surface can be prevented.
  • chloride gases such as CH3Cl (chloromethane) and HCl (hydrogen chloride).
  • CH3Cl chloromethane
  • HCl hydrogen chloride
  • the oxidized layer occurring on the metallic work surface is removed and a fluoride layer is formed instead.
  • This fluoride layer covers and protects the metallic work surface.
  • the fluorinated layer covering and protecting the metallic work surface in the above manner can be eliminated, prior to the step of thermal treatment proper, by, for example, introducing into the furnace, which is maintained at a temperature of about 480-700 °C, an H2-containing gas, such as an H2-containing inert gas or a mixture of a nitrogen source gas (e.g. NH3 gas) and H2 to thereby cause destruction of the fluorinated layer by means of H2 contained in said gas.
  • an H2-containing gas such as an H2-containing inert gas or a mixture of a nitrogen source gas (e.g. NH3 gas) and H2 to thereby cause destruction of the fluorinated layer by means of H2 contained in said gas.
  • a hard coating for instance, is formed thereon with good adhesion in the subsequent thermal treatment step.
  • the thermal treatment is a nitriding treatment of steel, uniform nitrided layer can be formed.
  • the metallic work surface is subjected to pretreatment with a fluorine- or fluoride-containing gas and subsequent thermal treatment such as treatment for nitriding steel.
  • fluorine- or fluoride-containing gas means a dilution of at least one fluorine source component selected from the group consisting of NF3, BF3, CF4 , HF, SF6, and F2 in an inert gas such as N2.
  • NF3, BF3, CF4 and F2 are gaseous at ordinary temperature while SF6 occurs as a liquid at ordinary temperature. They are admixed, either singly or in combination, with an inert gas, such as N2, to give fluorine- or fluoride-containing gases to be used in the practice of the invention.
  • NF3 is most suited for practical use since it is superior in safety, reactivity, controllability, ease of handling and other aspects to the other.
  • F2 is not so preferable since it has extremely high reactivity and toxicity, is inferior in ease of handling and makes it difficult to operate the furnace smoothly.
  • the fluorine- or fluoride-containing gases are used in an elevated temperature atmosphere and, therefore, even the fluorine source component SF6, which is liquid at ordinary temperature, is vaporized and mixed with the inert gas under the conditions of use.
  • the fluorine- or fluoride-containing gases should contain the fluorine source components, such as NF3, in a concentration within the range of 0.05% to 20% (on the weight basis; hereinafter the same shall apply), preferably from 0.1 to 10%, more preferably 2% to 7%, still more preferably 3% to 5%.
  • steel works As examples of the metallic works that can be pretreated in accordance with the invention, there may be mentioned steel works, aluminum works, titanium works and nickel works. Said steel works include works made of various steel species, for example carbon steel and stainless steel.
  • the metallic works may vary in shape or form and in dimensions. Thus, for example, they may be in the form of plates or sheets, coils, screws or some other machined articles.
  • the metallic works to which the method of the invention is applicable may be made not only of one of such metallic materials as mentioned above but also of an alloy derived from the above-mentioned materials by appropriate combination, with or without addition of another or other minor component metallic materials.
  • the metallic works mentioned above are pretreated, for example, as follows.
  • the metallic works are placed in a heating furnace and heated to a temperature of 150-600 °C, preferably 300-500°C.
  • a fluorine- or fluoride-containing gas is introduced into the heating furnace.
  • the metallic works are held at the above-mentioned temperature in an fluorine- or fluoride-containing gas atmosphere for about 10-120 minutes, preferably about 20-90 minutes, more preferably 30-60 minutes, whereby the oxidized layer on the metallic work surface is removed and a fluorinated layer is formed on said surface.
  • An H2-containing inert gas is then introduced into the heating furnace for decomposing and eliminating the fluorinated layer.
  • a cleaned and activated metallic material surface reveals itself.
  • This series of steps may be performed, for example, in a heat treatment furnace 1 such as the one shown in Fig. 1.
  • the furnace 1 is a pit furnace and has a heater 3 provided in the space between an outer shell 2 and an inner vessel 4, with a gas inlet pipe 5 being inserted in said vessel.
  • Gas supply is made from cylinders 15 and 16 via flow meters 17 and a valve 18.
  • the inside atmosphere is stirred by means of a fan 8 driven by a motor 7.
  • Works 10 placed in a wire net container 11 are charged into the furnace 1.
  • the furnace is provided with an exhaust pipe 6, a vacuum pump 13 for exhaustion, and a noxious substance eliminator 14.
  • the pretreatment procedure is carried out as follows.
  • the metallic works 10 charged in the furnace 1 as shown in Fig. 1 are heated by means of the heater 3 to a predetermined temperature.
  • a fluorine- or fluoride-containing gas for example a mixed gas composed of NF3 and N2 is introduced into the furnace 1 from the cylinder 15, whereby processing aids and the like adhering to the surface of the metallic woks 10 are removed and at the same time the oxidized layer possibly occurring on the surface of the metallic works 10 is removed and a fluorinated layer is formed instead.
  • the surface of the metallic works 10 is covered and protected by the fluorinated layer.
  • the fluorine- or fluoride-containing gas in the furnace 1 is discharged from the furnace through the exhaust pipe 6 by applying vacuum.
  • the metallic works 10 are then heated by the heater 3 to a further elevated temperature of 480-700 °C. In that state, a mixed gas composed of N2 and H2 is blown into the furnace from the cylinder 16, whereby the fluorinated layer is eliminated.
  • the metallic works 10 reveal a clean and active metallic surface. This surface undergoes various kinds of treatment process in the subsequent thermal treatment step. In this case, thermal treatment proper, for example diffusion/penetration treatment, can be applied to the surface of the metallic works 10 deeply and uniformly, since said surface has now been cleaned and activated.
  • a uniform and closely adhering coating layer or metal deposit layer can be formed.
  • the fluorinated layer may be eliminated simultaneously with thermal treatment proper.
  • pretreatment and thermal treatment proper are carried out simultaneously. That is, steel works are cleaned for degreasing, for instance, and then charged into a heat treatment furnace 1 such as shown in Fig. 1.
  • a fluorine- or fluoride-containing reaction gas for example a mixed gas composed of NF3 and N2, is introduced into this furnace.
  • the concentration of NF3 should amount to, for example, 10,000 ⁇ 100,000ppm, preferably 20,000 ⁇ 70, 000ppm, more preferably 30,000 ⁇ 50,000ppm.
  • the holding time of the works in such fluorine- or fluoride-containing gas atmosphere may appropriately be selected depending on the steel species, geometry and dimensions of the works, heating temperature and so forth, generally within the range of ten and odd minutes to scores of minutes.
  • the works are heated at a specified reaction temperature.
  • NF3 evolves fluorine in the nascent state, whereby the organic and inorganic contaminants on the steel work surface are eliminated therefrom and at the same time this fluorine rapidly reacts with the base elements Fe and chromium on the surface and/or with oxides occurring on the steel work surface, such as FeO, Fe3O2 and Cr2O3.
  • a very thin fluorinated layer containing such compounds as FeF2, FeF3, CrF2 and CrF4 in the metal structure is formed on the surface, for example as follows: FeO + 2 F ⁇ FeF2 + 1/2 O2; Cr2O3 + 4 F ⁇ 2 CrF2 + 3/2 O2.
  • active N atoms are adsorbed thereon, then enter the metal structure and diffuse the rein and, as a result, a layer (nitrided layer) containing such nitrides as CrN, Fe2N, Fe3N and Fe4N is formed on the surface.
  • a layer containing such compounds is formed in the prior art processes as well.
  • the surface activity of the works is reduced by oxidized layer formation and O2 adsorption during the period of temperature rise from ordinary temperature to the nitriding temperature. Therefore, in the nitriding step, the adsorption of N atoms on the surface is low in degree and uneven. Such unevenness in N adsorption is promoted by the fact that it is practically impossible to maintain a uniform extent or rate of decomposition of NH3 in the furnace.
  • N atoms are adsorbed on the work surface uniformly and rapidly, hence the problem mentioned above is never encountered.
  • the process is simplified, for example continuous treatment becomes possible, as compared with the processes which involve plating treatment or use of PVC, which is a solid, or a liquid chlorine source.
  • the tufftriding process can hardly be said to have a bright future since a great expenditure is required for work environment improvement and environmental pollution prevention, for instance, although it is excellent in promoting nitrided layer formation and increasing fatigue strength, among others.
  • the above-mentioned process according to the invention requires only a simple device for eliminating hazardous substances from the exhaust waste gas, and allows at least the same extent of nitrided layer formation as in the tufftriding process and thereby makes it possible to avoid uneven nitriding. While nitriding is accompanied by carburizing in the tufftriding process, it is possible to perform nitriding alone in the process according to the invention.
  • the subsequent thermal treatment is not limited to such nitriding.
  • the method of the invention is effective in performing such processing treatments as carbonitriding, physical vapor deposition (PVD) and chemical vapor deposition (CVD), which are to be carried out at or below 700°C.
  • the pretreatment for fluorinated layer formation should preferably be conducted in a furnace other than the furnace in which the thermal treatment proper is carried out.
  • Other examples of the subsequent thermal treatment for which the method of the invention is effective are plating treatments using molten zinc or aluminum. While these treatments generally include a complicated series of steps, namely alkali degreasing, acid pickling, molten flux treatment and dipping in molten aluminum or zinc, the pretreatment stage from alkali degreasing to molten flux treatment can be markedly simplified when the method of pretreatment according to the invention is employed. As a result, the length of the overall process can be shortened and the production cost can be reduced. Furthermore, particularly in plating works made of a high Si content steel species, the method of the invention can produce a favorable effect in that a metal deposit layer superior in adhesion can be formed.
  • the method of pretreating metallic works comprises holding metallic works in a heated state in a fluorine- or fluoride-containing gas atmosphere so that active fluorine atoms supplied by the fluorine- or fluoride-containing gas can act on the metallic work surface, cleaning the same by destructing and eliminating processing aids and other foreign matters adhering thereto and at the same time removing the surface oxidized layer therefrom and forming a fluorinated layer instead.
  • This fluorinated layer can serve as a protective coating on the surface of the metallic works.
  • the fluorinated layer can be decomposed and eliminated in a step just prior to or in the subsequent thermal treatment step by means of an H2-containing gas, whereby an uncoated and activated metallic work surface can appear.
  • the pretreatment method of this invention does not cause the unfavorable phenomenon that a new oxidized layer is formed on the pretreated metallic work surface. This is because the fluorinated layer formed after removal of the oxidized layer from the metallic work surface covers and protects said surface.
  • the oxide layer on the metallic work surface is converted to a fluorinated layer, which can be readily decomposable and removable, so that the metallic work surface can be converted to an uncovered and activated state. This is an outstanding feature of the invention.
  • the steel nitriding method according to the invention comprises holding steel works with heating in a fluorine- or fluoride-containing gas atmosphere to thereby eliminate organic and inorganic contaminants and at the same time cause the passive coat layer, such as an oxidized layer, on the steel work surface to be converted to a fluorinated layer, and then subjecting the works to nitriding treatment. Since the oxidized layer or the like passive coat layer on the steel work surface is converted to a fluorinated layer in that manner, the steel work surface is protected in a good state.
  • the fluorinated layer formed on the steel work surface remains in a good condition, still protecting the steel work surface remains in a good condition, still protecting the steel work surface.
  • no oxidized layer can be formed again on the steel work surface.
  • such fluorinated layer is decomposed and eliminated, whereby a new steel work surface appears.
  • This newly exposed metal surface is in an active condition, allowing N atoms to penetrate readily into the steel works subjected to nitriding treatment.
  • the resulting uniform penetration of N atoms from the steel work surface into the depth leads to formation of a favorable nitrided layer.
  • the fluorine- or fluoride-containing gas to be used in accordance with the invention in the pretreatment step prior to nitriding treatment is a gas which shows no reactivity at ordinary temperature and can be handled with ease, for example NF3, and therefore the pretreatment step can be simplified by carrying out the step in a continuous manner, for instance.
  • SUS 305 tapping screws were shaped and then cleaned with vaporized trichloroethylene. They were charged into such a furnace 1 as shown in Fig. 1 and heated to a temperature of 350 °C. In that state, a fluoride-containing gas composed of 7.0% of NF3 and 93.0% of N2 was introduced into the furnace 1 and the resulting system was maintained at 350°C for 20 minutes. Then, some of the above-mentioned samples were taken out and examined for their surface structure. It was confirmed that a fluorinated layer had been formed all over the surface.
  • the samples remaining in the furnace 1 were heated to 550 °C, held in an N2 + 90% H2 atmosphere for 30 minutes and then subjected to 5 hours of nitriding treatment by introducing into the furnace 1 a mixed gas composed of 50% NH3, 10% CO2 and 40% N2.
  • a mixed gas composed of 50% NH3, 10% CO2 and 40% N2.
  • the fluorinated layer was decomposed and eliminated and at the same time a nitrided layer was formed.
  • the thus-nitrided samples were air-cooled and taken out of the furnace.
  • Example 2 The same tapping screw samples as used in Example 1 were cleaned with vaporized trichloroethylene, pretreated by dipping in a hydrofluoric acid-nitric acid mixture for 30 minutes, charged into the same furnace 1 as used in Example 1, and subjected to nitriding treatment in a mixed gas composed of 50% NH3 and 50% RX (H2, CO) for 5 hours.
  • Example 1 Comparative Example 1 State of nitrided layer Nitrided layer uniform in thickness formed all over the surface.
  • a fragment of a very low carbon steel strip (Si content: 1.5%; Mn content: 0.5%) was used as a sample.
  • the sample was cleaned by alkali degreasing, washed with water and charged into a furnace as shown in Fig. 5.
  • the furnace body 20 including its heat insulating wall has a heating means 21 circumferentially embedded in the furnace body 20.
  • a sliding door 22 closes the bottom of the furnace body 20 is slidable in the left and right directions in the plane shown.
  • the ceiling of the furnace body 20 is equipped with a gas inlet pipe 23 which enables gas introduction into the furnace body 20 containing the sample 24 to be treated.
  • a zinc pot furnace 25 is disposed below the furnace body 20, with the sliding door 22 serving as a partition therebetween.
  • the zinc pot furnace 25 has an induction coil 26 embedded in the surrounding wall and contains a zinc bath 27 maintained at 450°C.
  • the sample charged in such a furnace was heated to 300 °C and then held, for pretreatment, at that temperature in a mixed gas composed of 1% NF3 and 99% N2 as introduced into the furnace for 30 minutes.
  • the sample was then heated to 500°C and held in a mixed gas (75% N2+25% H2) introduced into the furnace for 10 minutes, whereby the fluorinated layer formed in the pretreatment was eliminated.
  • the sliding door 22 was opened and the sample was transferred to the zinc pot furnace 25 and zinc-plated there.
  • a fragment of the same very low carbon steel strip as used in Example 2 was cleaned by alkali degreasing, acid pickling and washing with water, then charged into the furnace shown in Fig. 5, and heated to 700 °C. In that state, a mixed gas composed of 25% N2 and 75% H2 was blown into the furnace for 20 minutes. Then, the sliding door 22 was opened and the sample fragment was transferred to the zinc pot furnace situated below the furnace 20 and subjected to zinc plating under the same conditions as used in Example 2, followed by blowing N2 gas against the sample, cooling and drying.
  • Example 2 The thus-obtained two steel samples were tested for the adhesion of the zinc metal deposit layer by performing a bending test followed by obsevation of the bent portion.
  • the sample of Comparative Example 2 which had been heated at 700°C showed marked insufficiency of metal deposit layer adhesion in places. On the contrary, the sample of Example 2 did not show such a phenomenon.
  • the samples of Example 2 and Cpmparative Example 2 were subjected to surface analysis by means of an optical microscope, an X ray microanalyzer (EPMA) and an ion microanalyzer (IMA). Selective oxidation to Si m O n and Mn m O n was observed with the sample of Comparative Example 2 while such phenomenon was not found in the sample of Example 2.
  • EPMA X ray microanalyzer
  • IMA ion microanalyzer
  • An SKH 51 end mill was used as a sample. This was degreased, dried, further subjected to fluorocarbon cleaning and then charged into the furnace shown in Fig. 1.
  • the furnace was evacuated to 0.1-1.3 Pa (10 ⁇ 2 to 10 ⁇ 3 torr) using a vacuum pump while the furnace inside temperature was raised. Then, the temperature was maintained at 280 °C and the pressure at 2.0x104 to 2.7x104 Pa (150 to 200 torr). In that state, a mixed gas composed of 20% NF3 and 80% N2 was introduced into the furnace. The sample was held in that state in the mixed gas for 30 minutes, the furnace was then cooled, and the sample was taken out.
  • the thus-pretreated sample was placed in such a low temperature plasma CVD furnace as shown in Fig. 7 and subjected to TiN coating by heating at 480 °C for 60 minutes.
  • the reference numeral 30 stands for the sample, 31 for a pump, 32 for a thermometer and 33 for a power source.
  • the TiN coating layer on the thus-obtained sample had a thickness of 3 »m.
  • the adhesion of this coating layer as measured on a scratch tester was higher by 30% as compared with the adhesion attainable by the plasma CVD technique using the conventional pretreatment methods.
  • the durability of the sample end mill was at least 5 times higher as compared with an uncoated sample.
  • the nitrided layer of each work thus obtained was uniform in thickness.
  • the surface hardness was 1,100-1,300 Hv while the base material portion had a hardness of 360-380 Hv.
  • Comparative Example 3 the same works as used in Example 1 were cleaned with trichloroethylene, treated with a mixture of hydrofluoric acid and nitric acid, placed in the furnace mentioned above, and heated in 75% NH3 at 530°C or 570°C for 3 hours. In either case, great variations were found in the thickness of the nitrided layer formed. The proportion of portions having no nitrided layer at all was high.
  • a 40-50 »m thick nitrided layer was formed all over the screw surface.
  • the nitrided layer showed a corrosion resistance to 5% sulfuric acid which was not so inferior to that of the base material.
  • Example 6 The works used in Example 6 were hot-worked mold parts polished by emery cloth (SKD 61). They were charged into the furnace shown in Fig. 1, heated in an N2 atmosphere containing 3,000 ppm of NF3 at 300°C for 15-20 minutes, then heated to 570°C, and treated at that temperature with a mixed gas composed of 50% NH3 and 50% N2 for 3 hours. A uniform nitrided layer of a thickness of 120 »m was obtained with a surface hardness of 1,000-1,100 Hv (base material hardness 450-500 Hv).
  • Comparative Example 4 the same parts as used in Example 6 were cleaned with hydrofluoric acid-nitric acid and then subjected to nitriding treatment at 570°C for 3 hours.
  • the nitrided layer thickness was at most 90-100 »m and great variations were found in said thickness. Severe surface roughening was also observed.
  • Nitriding steel (SACM 1) parts were cleaned, charged into the furnace shown in Fig. 1, held in an N2 gas atmosphere containing 5,000 ppm of NF3 at 280 °C for 20 minutes and then heated in 75% NH3 at 550 °C for 12 hours.
  • the nitrided layer obtained had a thickness of 0.42mm.
  • Comparative Example 5 the same parts as above were nitrided in the conventional manner. The thickness of the nitrided layer was 0.28mm.
  • Structural carbon steel (S45C) mold parts were cleaned, held in an atmosphere containing 5,000 ppm of NF3 at 300 °C for 20 minutes, then treated at 530°C with 50% NH3 plus 50% RX for 4 hours, oil-quenched, and taken out.
  • the nitrided layer obtained had a hardness of 450-480 Hv.
  • the nitrided layer of each work thus obtained had a uniform thickness.
  • the depth of the nitrided layer was about 70 »m.
  • the nitrided layer was more compact than that obtained in Example 4.
  • the surface of the nitrided layer of the works thus obtained was polished and subjected to a corrosion test using sodium chloride and sulfuric acid. Still better results were obtained as compared with Example 4.
  • the NH3 concentration in the mixed gas used for nitriding was below 25% and this is presumably why better nitrided layer formation, resulted as compared with the case where the NH3 concentration exceeded 25%.
  • the nitrided layer comprised of a compound layer containing intermetallic compounds composed of N and Cr, Fe, etc., and a diffusion layer containing nitrogen atoms that have diffused shows a much higher diffusion layer/compound layer ratio, as shown by the curve A in Fig. 5, as compared with the corresponding ratio shown by the curve B for the conventional nitriding processes.
  • the works were charged into the nitriding furnace, heated at 530 °C and nitrided for 4 hours while feeding a mixed gas composed of 20% NH3 + 10% CO2 + N2 to the furnace.
  • Work-hardened SCM 440 works (shafts) contaminated with a cutting oil were degreased with an alkali. Without cleaning with any organic solvent, they were placed in the treatment furnace 1, such as shown in Fig. 1, heated to 330°C, and held at that temperature in an N2 gas atmosphere containing 30,000 ppm of NF3 for 3 hours. Then, the temperature was raised to 570 °C while feeding gaseous N2 in lieu of the mixed gas mentioned above. At that temperature, a mixed gas composed of 50% N2 + 50% H2 was fed to the furnace for 40 minutes and then a mixed gas composed of 50% NH3 + 10% CO2 + 40% N2 was introduced into the furnace for effecting nitriding for 3 hours.
  • Example 6 the same cutting oil-contaminated work-hardened works as used in Example 11 were subjected to alkali cleaning, then directly charged into the furnace shown in Fig. 1, heated to 570 °C, and nitrided at that temperature for 3 hours while feeding a mixed gas composed of 50% NH3 + 50% RX to the furnace.
  • Example 11 The nitrided layers of both lots of works thus obtained were compared with each other.
  • the nitrided layer had a micro Vickers hardness (Hv) of 350 and nitrided layer depth of 180»m whereas, in Comparative Example 6, the nitrided layer thickness was 40»m. It is thus evident that the nitrided layer of the works obtained in Example 11 had a greater depth.
  • the work-hardened sample works were subjected to alkali cleaning and then further to cleaning with trichloroethylene. Then, they were nitrided in the same manner as in Comparative Example 6 for 3 hours using a mixed gas composed of 50% NH3 + 50% RX. Even in this case, the nitrided layer thickness could not exceed 95»m.

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Claims (17)

  1. Verfahren zur Vorbehandlung von metallischen Werkstücken, welches umfaßt das Halten eines metallischen Werkstückes in einem erhitzten Zustand in einer Fluor oder Fluorid enthaltenden Gasatmosphäre und anschließende Entfernung der fluorierten Schicht, um hierdurch die Oberfläche des metallischen Werkstückes zu reinigen und zu aktivieren.
  2. Verfahren nach Anspruch 1, bei welchem das metallische Werkstück im wesentlichen aus Stahl, Aluminium, Titan oder Nickel besteht.
  3. Verfahren nach irgendeinem vorhergehenden Anspruch, bei welchem die fluorierte Schicht durch Behandlung mit Wasserstoffgas und wahlweise mit einem Gas aus einer Stickstoffquelle entfernt wird.
  4. Verfahren nach Anspruch 3, bei welchem die Behandlung bei einer Temperatur zwischen 480 und 700°C durchgeführt wird.
  5. Verfahren nach Anspruch 1, bei dem das Metall Stahl ist, weiterhin umfassend, nach der Bildung der fluorierenden Schicht an der Oberfläche des Stahls, Erhitzen des Stahls in einer nitrierenden Atmosphäre, um an dessen Oberfläche eine nitrierte Schicht zu bilden.
  6. Verfahren zur Nitrierung von Stahl durch Reagieren der Oberfläche des Stahls mit Stickstoff, um eine harte nitrierte Schicht darauf zu bilden, dadurch gekennzeichnet, daß das Verfahren das Halten des Stahls in einer Atmosphäre, die Fluor oder Fluoride enthält und nach der Bildung einer fluorierten Schicht an der Oberfläche des Stahls Erhitzen des Stahls in einer nitrierenden Atmosphäre umfaßt, um an dessen Oberfläche eine nitrierte Oberfläche zu bilden.
  7. Verfahren nach Anspruch 6, bei dem die nitrierende Atmosphäre Ammoniak enthält.
  8. Verfahren nach Anspruch 6 oder 7, dadurch gekennzeichnet, daß die nitrierende Oberfläche Ammoniak und eine gasförmige Kohlenstoffquelle enthält.
  9. Verfahren nach Anspruch 6, 7 oder 8, bei welchem die nitrierende Atmosphäre Ammoniak und Stickstoff enthält.
  10. Verfahren nach irgendeinem der Ansprüche 6 - 9, bei welchem der Stahl in der nitrierenden Atsmosphäre auf eine Temperatur zwischen 480 und 700°C erhitzt wird.
  11. Verfahren nach irgendeinem der Ansprüche 6 - 10, in welchem der fluorierte Stahl in einer Stickstoffatmosphäre gehalten wird, bevor er der nitrierenden Atmosphäre ausgesetzt wird.
  12. Verfahren nach irgendeinem vorhergehenden Anspruch, bei welchem das Fluor oder Fluorid enthaltende Gas eine Verdünnung in einem inerten Gas aus mindestens einem von NF₃, BF₃, CF₄, HF, SF₆ und F₂ ist.
  13. Verfahren nach irgendeinem der vorhergehenden Ansprüche, bei welchem die Fluor oder Fluorid enthaltenden Atmosphäre außerdem ein inertes Gas, wie Stickstoff, enthält.
  14. Verfahren nach irgendeinem der vorhergehenden Ansprüche, bei welchem das Fluor oder Fluorid enthaltende Gas in dieser Atmosphäre in einer Konzentration von 0,05 bis 20 Gew.%, vorzugsweise von 0,1 bis 10%, vorzugsweise von 2 bis 7 Gew.% und am bevorzugtesten von 3 bis 5 Gew.% gegenwärtig ist.
  15. Verfahren nach irgendeinem vorhergehenden Anspruch, bei dem die Bildung der fluorierten Schicht bei einer Temperatur zwischen 150 und 600°C, vorzugsweise zwischen 300 und 500°C, durchgeführt wird.
  16. Verfahren nach irgendeinem vorhergehenden Anspruch, bei dem die Bildung der fluorierten Schicht bei einer Temperatur zwischen 150 und 350°C durchgeführt wird.
  17. Verfahren nach irgendeinem vorhergehenden Anspruch, bei welchem das Metall in dem Fluor oder Fluorid enthaltenden Gas für von 10 bis 120 Minuten, vorzugsweise von 20 bis 90 Minuten, am bevorzugtesten von 30 bis 60 Minuten, gehalten wird.
EP90302232A 1989-07-10 1990-03-01 Verfahren zur Vorbehandlung von metallischen Werkstücken und zur Nitrierhärtung von Stahl Expired - Lifetime EP0408168B1 (de)

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JP177660/89 1989-07-10
JP1177660A JPH089766B2 (ja) 1989-07-10 1989-07-10 鋼の窒化方法
JP333424/89 1989-12-22
JP1333424A JP2501925B2 (ja) 1989-12-22 1989-12-22 金属材の前処理方法

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US6093303A (en) * 1998-08-12 2000-07-25 Swagelok Company Low temperature case hardening processes
US6165597A (en) * 1998-08-12 2000-12-26 Swagelok Company Selective case hardening processes at low temperature

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JP2633076B2 (ja) * 1990-10-04 1997-07-23 大同ほくさん株式会社 硬質オーステナイト系ステンレスねじおよびその製法
US5252145A (en) * 1989-07-10 1993-10-12 Daidousanso Co., Ltd. Method of nitriding nickel alloy
JP2501062B2 (ja) * 1992-01-14 1996-05-29 大同ほくさん株式会社 ニッケル合金の窒化方法
JP2842712B2 (ja) * 1990-11-30 1999-01-06 大同ほくさん株式会社 めつき方法
JP2862689B2 (ja) * 1991-01-22 1999-03-03 大同ほくさん株式会社 カラー金属板の製法
ATE129023T1 (de) * 1991-06-04 1995-10-15 Daido Hoxan Inc Verfahren der nitrierung von stahl.
EP0532806B1 (de) * 1991-09-20 1995-12-06 Daido Hoxan Inc. Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung
DE4208848C2 (de) * 1991-12-04 2001-08-30 Ald Vacuum Techn Ag Verfahren zur thermochemischen Nachbehandlung von Stählen und Metallen
DE4139975C2 (de) * 1991-12-04 2001-02-22 Ald Vacuum Techn Ag Verfahren zur Behandlung von legierten Stählen und Refraktärmetallen und Anwendung des Verfahrens
US5445683A (en) * 1992-05-13 1995-08-29 Daidousanso Co., Ltd. Nickel alloy products with their surfaces nitrided and hardened
JP3174422B2 (ja) * 1993-03-01 2001-06-11 エア・ウォーター株式会社 ステンレス窒化品
US5403409A (en) * 1993-03-01 1995-04-04 Daidousanso Co., Ltd. Nitrided stainless steel products
US5556483A (en) * 1994-04-18 1996-09-17 Daido Hoxan, Inc. Method of carburizing austenitic metal
EP0678589B1 (de) * 1994-04-18 1999-07-14 Daido Hoxan Inc. Verfahren zur Aufkohlung von austenitischem Metall
US5792282A (en) * 1995-04-17 1998-08-11 Daido Hoxan, Inc. Method of carburizing austenitic stainless steel and austenitic stainless steel products obtained thereby
JPH102336A (ja) * 1996-04-16 1998-01-06 Koyo Seiko Co Ltd 軸受用保持器とその製造方法
JP3699803B2 (ja) * 1997-05-09 2005-09-28 光洋精工株式会社 軸受の製造方法および軸受
US6547888B1 (en) 2000-01-28 2003-04-15 Swagelok Company Modified low temperature case hardening processes
AU2003266561A1 (en) * 2002-09-24 2004-04-19 Honda Giken Kogyo Kabushiki Kaisha Method of nitriding metal ring and apparatus therefor
JP2009516927A (ja) * 2005-11-23 2009-04-23 イー・アイ・デュポン・ドウ・ヌムール・アンド・カンパニー アルカン液浸液を再循環させるための装置、および使用方法
GB2497354B (en) 2011-12-07 2014-09-24 Solaris Holdings Ltd Method of improvement of mechanical properties of products made of metals and alloys
DE102014218488A1 (de) * 2014-09-15 2016-03-17 Robert Bosch Gmbh Verfahren zum Nitrieren eines Bauteils eines Kraftstoffeinspritzsystems
CN106637267A (zh) * 2015-10-28 2017-05-10 通用电气公司 用于从金属基材去除氧化物的方法和装置
CN110425824A (zh) * 2019-06-21 2019-11-08 广西电网有限责任公司电力科学研究院 能够对互感器绝缘层中水分进行干燥的现场处理方法

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US6093303A (en) * 1998-08-12 2000-07-25 Swagelok Company Low temperature case hardening processes
US6165597A (en) * 1998-08-12 2000-12-26 Swagelok Company Selective case hardening processes at low temperature

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