EP0532806A1 - Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung - Google Patents

Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung Download PDF

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Publication number
EP0532806A1
EP0532806A1 EP91308660A EP91308660A EP0532806A1 EP 0532806 A1 EP0532806 A1 EP 0532806A1 EP 91308660 A EP91308660 A EP 91308660A EP 91308660 A EP91308660 A EP 91308660A EP 0532806 A1 EP0532806 A1 EP 0532806A1
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EP
European Patent Office
Prior art keywords
screw
stainless steel
austenitic stainless
nitrided
layer
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
EP91308660A
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English (en)
French (fr)
Other versions
EP0532806B1 (de
Inventor
Akira Yoshino
Haruo Senbokuya
Masaaki Tahara
Kenzo Kitano
Teruo Minato
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.)
Air Water Inc
Original Assignee
Daido Sanso Co Ltd
Daido Hoxan Inc
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 Daido Sanso Co Ltd, Daido Hoxan Inc filed Critical Daido Sanso Co Ltd
Priority to ES91308660T priority Critical patent/ES2082151T3/es
Priority to AT91308660T priority patent/ATE131217T1/de
Priority to DE69115274T priority patent/DE69115274T2/de
Priority to DK91308660.9T priority patent/DK0532806T3/da
Priority to EP91308660A priority patent/EP0532806B1/de
Publication of EP0532806A1 publication Critical patent/EP0532806A1/de
Application granted granted Critical
Publication of EP0532806B1 publication Critical patent/EP0532806B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • C23C8/08—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 only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding 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
    • C23C8/80—After-treatment

Definitions

  • This invention relates to a hard austenitic stainless steel screw which has excellent corrosion resistance and to a method for manufacturing the same.
  • an austenitic stainless steel is higher in corrosion resistance against acid or salt compared than a carbon steel.
  • it is inferior to carbon steel. Therefore, it has not been proper to use austenitic stainless steel for a screw which particularly needs to be able to tighten to an iron-based plate by self-tapping, such as a tapping screw, a self-drilling screw or a dry wall screw.
  • plated carburized iron articles or 13 Cr stainless steel articles are used.
  • these articles are not only inferior in oxidation resistance (rust resistance) to austenitic stainless steel articles but are also weak in their tightening function because of corrosion of their base material by acid rain, which is a major environmental problem of today.
  • Austenitic stainless steel articles are far superior in acid resistance. Accordingly, the present inventors provided new technology for maintaining the tapping property as well as carburized iron articles by nitriding-hardening the austenitic stainless steel screw (Japanese Patent Application No. 177660/1989).
  • a nitrided hard layer with which even a thick iron plate can be drilled and tapped self-forcedly is formed over the entire surface of the austenitic stainless steel screw.
  • this new technology has a serious defect in that the so formed nitrided hard layer lacks the corrosion resistance characteristic of austenitic stainless steel.
  • the screw head exposed to the atmosphere, readily rusts.
  • its head and the neighbourhood of the head are visible, and are exposed to the atmosphere.
  • An austenitic stainless steel screw is devalued as commercial goods by even a bit of change in the color of its head because of rust. It is possible to conduct plating or color-painting on the surface of a nitrided hard layer after nitriding in order to prevent rust from being generated there. However, this is only a temporary solution, not a fundamental one. So as to protect the screw head or the like against nitriding, it was proposed to apply some methods, such as copper-plating and a masking by flame coating, to these parts prior to nitriding. Even if such methods are employed, it is difficult to completely prevent nitriding on the surface of the portion of the austenitic stainless steel base.
  • the invention provides a hard austenitic stainless steel screw, in a first aspect, characterized in that a nitrided hard layer is formed on the surface of the austenitic stainless steel screw, and that the nitrided layer of predetermined parts of the nitrided screw is removed, and in a second aspect, a method for manufacturing a hard austenitic stainless steel screw comprising steps of heating an austenitic stainless steel screw in a nitriding atmosphere to form a nitrided hard layer on the screw surface, and removing the nitrided hard layer of predetermined parts of the austenitic stainless steel screw partially.
  • the nitrided layer formed on the screw head, a neck portion, and the like of the screw which are in contact with the atmosphere when tightened is removed.
  • Austenitic stainless steel base is exposed where the nitrided layer, is removed to achieve rust prevention and corrosion resistance characteristic of austenitic stainless steel per se .
  • the nitrided hard layer comprising an alloy layer and a diffused layer of the screw head portion and the like is removed from part of the surface of the screw.
  • Methods of removal include a chemical method such as a dipping treatment in which the screw head and the like of the austenitic stainless steel screw is dipped in a mixed acid, for example, HCl + HNO3 or HF + HNO3, or in a single acid solution of HNO3 heated to about 60°C, and a mechanical method such as scouring.
  • a chemical method such as a dipping treatment in which the screw head and the like of the austenitic stainless steel screw is dipped in a mixed acid, for example, HCl + HNO3 or HF + HNO3, or in a single acid solution of HNO3 heated to about 60°C, and a mechanical method such as scouring.
  • the diameter of some portions of the austenitic stainless steel screw, such as the screw head and the neck part, from which the nitrided hard layer is removed, are relatively small.
  • the diameter of the screw head and the neck part connected thereto are advantageously designed to be larger by thickness of the nitrided hard layer. In this way, there is no deterioration in the breaking torque and thus no decrease in the tightening function of the screw.
  • An austenitic stainless screw is held preliminarily in a fluorine- or fluoride-containing gas atmosphere to form a fluorinated layer on the steel surface, then heated in a nitriding atmosphere to remove the fluorinated layer and at the same time to convert the surface (the surface layer of the screw) to a nitrided layer.
  • the nitrided layer over predetermined parts of the screw is removed to prevent rust on those parts.
  • fluorine- or fluoride-containing gas used in the pretreatement prior to nitriding means a dilution of at least one fluorine source component selected from NF3, BF3, CF4, HF, SF6, F2, CH2F2, CH3F, C2F6, WF6, CHF3, SiF4 and the like in an inert gas such as N2.
  • fluorine source components NF3 is most suitable for practical use since it is superior in reactivity, ease of handling and other aspects to the others.
  • the screws are held in the above-mentioned fluorine- or fluoride-containing gas atmosphere at a temperature of, for example, 250 to 400°C in the case of NF3, for a preliminary treatment of the surface of an austenitic stainless screw and then subjected to nitriding (or carbonitriding) using a known nitriding gas such as ammonia.
  • a known nitriding gas such as ammonia.
  • F2 gas alone or a mixed gas composed of F2 gas and an inert gas is used as the fluorine- or fluoride-containing gas the above-mentioned holding temperature is arranged in the range of 100°C to 250°C.
  • the concentration of the fluorine source component, such as NF3, in such fluorine- or fluoride-containing gas should amount to, for example, 1,000-100,000ppm, preferably 20,000-70,000ppm, more preferably 30,000-50,000ppm.
  • the holding time in such a fluorine- or fluoride-containing gas atmosphere may appropriately be selected depending on the steel species, geometry and dimensions of screws, heating temperature and so forth, and is generally within the range of ten and odd minutes or scores of minutes.
  • austenitic stainless screws X having a head portion A, a neck portion B and a thread portion C as shown in Fig. 1, for instance, are degreased and then charged into a heat treatment furnace 1 such as shown in Fig. 2.
  • This furnace 1 is a pit furnace comprising an inner vessel 4 surrounded by a heater 3 disposed within an outer shell 2, with a gas inlet pipe 5 and an exhaust pipe 6 therein. Gas is supplied from cylinders 15 and 16 via flow meters 17, a valve 18 and the like into the gas inlet pipe 5. The inside atmosphere is stirred by means of a fan 8 driven by a motor 7.
  • the screws X placed in a metallic container 11 are charged into the furnace.
  • the reference numeral 13 indicates a vacuum pump and 14 a noxious substance eliminator.
  • a fluorine- or fluoride-containing reaction gas for example, a mixed gas composed of NF3 and N2 is introduced into this furnace and heated, together with the works, at a predetermined reaction temperature.
  • NF3 evolves fluorine in the nascent state, whereby the organic and inorganic contaminants on the surface of the screws 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 on the steel work surface, such as FeO, Fe3O4 and Cr2O3.
  • a very thin fluorinated layer containing such compounds as FeF2, FeF3, CrF2, CrF4 and the like in the metal composition is formed on the surface, for example as follows: FeO + 2F FeF2 + 1/2 O2 Cr2O3 + 4F 2CrF2 + 3/2 O2
  • FeO + 2F FeF2 + 1/2 O2 Cr2O3 + 4F 2CrF2 + 3/2 O2 These reactions convert the oxidized layer on the surface of the screws X to a fluorinated layer.
  • O2 adsorbed on the surface is removed therefrom.
  • such fluorinated layer is stable at temperature up to 600°C and it is considered that the stable fluorinated layer prevents oxidized layer formation on the metal bases and absorption of O2 thereon until the subsequent step of nitriding.
  • a fluorinated layer which is similarly stable, is formed on the furnace material surface as well and minimizes damages to the furnace material surface.
  • the screws X thus treated with such fluorine- or fluoride-containing reaction gas are then heated at a nitriding temperature of 480°C-700°C.
  • a nitriding temperature 480°C-700°C.
  • NH3 or a mixed gas composed of NH3 and a carbon source gas e.g.
  • the fluorinated layer undergoes reduction or destruction by means of H2 or a trace amount of water to give an active metal base comprised of austenitic stainless steel, as shown, for example, by the following reaction equations: CrF4 + 2H3 Cr + 4HF 2FeF3 + 3H2 2 Fe + 6HF
  • active metal base comprised of austenitic stainless steel
  • active N atoms are adsorbed thereon, then enter the metal structure and diffuse therein and, as a result, a chemical compound layer (a nitrided hard layer) containing such nitrides as CrN, Fe2N, Fe3N and Fe4N is formed on the surface.
  • the obtained nitrided hard layer comprises an alloy layer and a diffused layer and covers all the screw X shown in Fig. 1.
  • This invention allows removal of a nitrided hard layer on, for example, the whole head portion A and a part of the neck portion B of the screw X shown in Fig. 1, while leaving the nitrided hard layer on the thread portion C and rest of the neck portion B as they are.
  • the removal is, for example, conducted by heating HNO3-HF solution at about 50 °C, dipping the whole head portion A and a part of the neck portion B of the screw therein for about 10 to 120 minutes to melt and remove the nitrided hard layer.
  • the nitrided layer of the whole head portion and a part of the neck portion is removed in this way to expose austenitic stainless steel.
  • the screw X has sufficient corrosion resistance, resulting from that of austenitic stainless steel per se .
  • the remaining nitrided hard layer of part of the neck portion B and the thread portion C has significantly improved hardness compared with that of austenitic stainless steel, giving the screw the same excellent tapping and tightening functions as carburized iron articles.
  • nitriding is conducted by using NH3 or a mixed gas comprising NH3 and a gas containing a carbon source, but nitriding by glow discharge or by salt bath may be substituted for this type of nitriding.
  • Cross recessed head tapping screws of SUS305, austenitic stainelss steel (4.2mm ⁇ x 19mm) were cleaned with trichloroethylene, then charged into a treatment furnace 1 as shown in Fig. 2, and held at 380°C for 15 minutes in an N2 gas atmosphere containing 5,000ppm of NF3 for fluoriding, then heated at 530°C, and nitriding treatment was carried out at that temperature for 3 hours while a mixed gas composed of 50% NH3 plus 50% N2 (hereinafter: % by volume) was introduced into the furnace.
  • the works were then air-cooled and taken out of the furnace.
  • the thus obtained screws had a nitrided hard layer with thickness of 40 ⁇ m overall.
  • the nitrided screw except for the head portion and a part of the neck portion to 4mm below the head was coated with vinyl choloride resin liquid and dried, to cover the screw with the coating.
  • the screw was then dipped in 10% solution of HNO3 at 63°C for 15 minutes, taken out, washed with water and dried.
  • the surface hardness (Hv) of the part of the tapping screw masked by the coating was 1000 to 1100.
  • the head of the tapping screw from which the nitrided hard layer had been removed by the acid treatment had a surface hardness of 340 to 380.
  • a salt spray test (Corrosion acceleration test) was conducted on the tapping screw and it was found that rust was not caused even after 2000 hours on the head and the part of the neck portion on which the austenitic stainless steel base was exposed. On the contrary, it was found that rust was caused after 6 hours on the part (mainly the thread) from which the nitrided hard layer was not removed.
  • a drilling test was conducted on the above-mentioned screw and it was found that it had the same property as a conventional tapping screw (carburized iron steel works).
  • Self drilling screws of SUS 305, austenitic stainless steel (hexagon head, 4.8mm ⁇ x 25mm) were nitrided as in Example 1.
  • the nitrided hard layer was formed over the entire self-drilling screw; its thickness was 55 ⁇ m.
  • the nitrided screw, except for the head and a part of the neck to 5mm below the head was dipped in vinyl chloride resin liquid and dried to cover the screw with a coating. Then a plurality of the screws were screwed into a polystyrene resin plate having a thickness of 30mm as shown in Fig. 3.
  • Self-drilling screws of austenitic stainless steel (hexagon head, 6.3mm ⁇ x 150mm) as shown in Fig. 1 were nitrided as in Example 1.
  • the thus obtained self-drilling screw was covered with a nitrided hard layer overall; the thickness thereof was 75 ⁇ m.
  • Example 2 A salt spray test was conducted on the thus treated screw and the same result as in Example 1 was obtained, and the result of drilling test was the same as in Example 2.
  • the breaking torque value of the thus obtained austenitic stainless self-drilling screw was examined. The value was lower by 7% than the austenitic stainless steel self-drilling screw the whole surface of which was covered by a nitrided hard layer, without the acid dipping treatment.
  • austenitic stainless steel self drilling screws of which the diameter of the screw head and the neck portion was relatively large (about 150 ⁇ m) were manufactured. They were nitrided and then dipped in acid to remove the nitrided hard layer of the screw head portion and neck portion. After eliminating the nitrided hard layer of the head and neck portions, the diameters of the head and neck portions, the diameters of the head and neck portions were decreased.
  • the breaking torque value of such screws was equal to an austenitic stainless steel self-drilling screw the whole surface of which was covered with a nitrided hard layer and the whole part has diameter as previously designed respectively.
  • a nitrided hard layer is removed from predetermined portions such as the head and neck portion, so that the austenitic stainless steel base is exposed on these portions.
  • the head portion is exposed to the atmosphere in a tightened state and is affected by acid rain and the like, and the neck portion is in contact with acid rain and the like penetrating from outside.
  • the portions from which the nitrided layer is removed maintain a good anti-corrosion property comparible with that of the austenitic stainless steel itself.
  • the thread portion the hardness and the like are greatly improved by the nitrided hard layer, so that surface hardness and strength becomes approximately equal to those of carbon steel products, so that they are able to tap and tighten by itself.
  • the screw prior to nitriding the above-mentioned austenitic stainless steel screw, the screw is advantageously held in a fluorine- or fluoride-containing gas atmosphere to form a fluoride layer on the surface thereof. In that state the screw is nitrided, so that the formed nitrided layer is uniform and deep to give a hard austenitic stainless steel screw having good surface properties.

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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)
  • Forging (AREA)
  • Heat Treatment Of Articles (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Dental Tools And Instruments Or Auxiliary Dental Instruments (AREA)
  • Extrusion Moulding Of Plastics Or The Like (AREA)
EP91308660A 1991-09-20 1991-09-20 Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung Expired - Lifetime EP0532806B1 (de)

Priority Applications (5)

Application Number Priority Date Filing Date Title
ES91308660T ES2082151T3 (es) 1991-09-20 1991-09-20 Tornillo de acero inoxidable austenitico duro y un metodo para fabricarlo.
AT91308660T ATE131217T1 (de) 1991-09-20 1991-09-20 Eine harte, austenitische rostfreie stahlschraube und verfahren zu ihrer herstellung.
DE69115274T DE69115274T2 (de) 1991-09-20 1991-09-20 Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung.
DK91308660.9T DK0532806T3 (da) 1991-09-20 1991-09-20 Hård austenitisk rustfri stålskrue og en fremgangsmåde til fremstilling heraf
EP91308660A EP0532806B1 (de) 1991-09-20 1991-09-20 Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP91308660A EP0532806B1 (de) 1991-09-20 1991-09-20 Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung

Publications (2)

Publication Number Publication Date
EP0532806A1 true EP0532806A1 (de) 1993-03-24
EP0532806B1 EP0532806B1 (de) 1995-12-06

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EP91308660A Expired - Lifetime EP0532806B1 (de) 1991-09-20 1991-09-20 Eine harte, austenitische rostfreie Stahlschraube und Verfahren zu ihrer Herstellung

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EP (1) EP0532806B1 (de)
AT (1) ATE131217T1 (de)
DE (1) DE69115274T2 (de)
DK (1) DK0532806T3 (de)
ES (1) ES2082151T3 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014122367A (ja) * 2012-12-20 2014-07-03 Daido Steel Co Ltd 真空浸窒処理方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2155078A5 (en) * 1971-10-06 1973-05-18 Kolomensky Teplovozostro Spheroidal cast irons - strengthening by thermal and nitriding processes
FR2404142A1 (fr) * 1977-09-27 1979-04-20 Deutsher Pty Ltd Procede de fabrication d'une vis autoperforante et autotaraudeuse, et cette vis
EP0166847A1 (de) * 1984-02-14 1986-01-08 International Business Machines Corporation Verfahren zum Aufkohlen und zur Wärmebehandlung von einem Maschinenteil, beispielsweise einem Druckhammer
EP0408168A1 (de) * 1989-07-10 1991-01-16 Daidousanso Co., Ltd. Verfahren zur Vorbehandlung von metallischen Werkstücken und zur Nitrierhärtung von Stahl

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2155078A5 (en) * 1971-10-06 1973-05-18 Kolomensky Teplovozostro Spheroidal cast irons - strengthening by thermal and nitriding processes
FR2404142A1 (fr) * 1977-09-27 1979-04-20 Deutsher Pty Ltd Procede de fabrication d'une vis autoperforante et autotaraudeuse, et cette vis
EP0166847A1 (de) * 1984-02-14 1986-01-08 International Business Machines Corporation Verfahren zum Aufkohlen und zur Wärmebehandlung von einem Maschinenteil, beispielsweise einem Druckhammer
EP0408168A1 (de) * 1989-07-10 1991-01-16 Daidousanso Co., Ltd. Verfahren zur Vorbehandlung von metallischen Werkstücken und zur Nitrierhärtung von Stahl

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
high nitrogen steels, p.174-179,18-20-05-88, lille,fr. so. institute of metallurgy swiss fed. inst. of technology. zurich,ch. p. uggowitzer strenthening of austenitic stainless steel by n2 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014122367A (ja) * 2012-12-20 2014-07-03 Daido Steel Co Ltd 真空浸窒処理方法

Also Published As

Publication number Publication date
ES2082151T3 (es) 1996-03-16
ATE131217T1 (de) 1995-12-15
DE69115274D1 (de) 1996-01-18
DK0532806T3 (da) 1996-03-04
DE69115274T2 (de) 1996-05-30
EP0532806B1 (de) 1995-12-06

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