WO2014042066A1 - 圧縮コイルばねおよびその製造方法 - Google Patents
圧縮コイルばねおよびその製造方法 Download PDFInfo
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- WO2014042066A1 WO2014042066A1 PCT/JP2013/073937 JP2013073937W WO2014042066A1 WO 2014042066 A1 WO2014042066 A1 WO 2014042066A1 JP 2013073937 W JP2013073937 W JP 2013073937W WO 2014042066 A1 WO2014042066 A1 WO 2014042066A1
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- wire
- coil spring
- steel wire
- residual stress
- coiling
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F1/00—Springs
- F16F1/02—Springs made of steel or other material having low internal friction; Wound, torsion, leaf, cup, ring or the like springs, the material of the spring not being relevant
- F16F1/021—Springs made of steel or other material having low internal friction; Wound, torsion, leaf, cup, ring or the like springs, the material of the spring not being relevant characterised by their composition, e.g. comprising materials providing for particular spring properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21F—WORKING OR PROCESSING OF METAL WIRE
- B21F3/00—Coiling wire into particular forms
- B21F3/02—Coiling wire into particular forms helically
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21F—WORKING OR PROCESSING OF METAL WIRE
- B21F35/00—Making springs from wire
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
- B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
- B24C1/10—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for compacting surfaces, e.g. shot-peening
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/06—Surface hardening
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- 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
- C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
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- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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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
- C23C8/02—Pretreatment of the material to be coated
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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
- C23C8/20—Carburising
- C23C8/22—Carburising of ferrous surfaces
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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
- C23C8/80—After-treatment
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F1/00—Springs
- F16F1/02—Springs made of steel or other material having low internal friction; Wound, torsion, leaf, cup, ring or the like springs, the material of the spring not being relevant
- F16F1/04—Wound springs
- F16F1/06—Wound springs with turns lying in cylindrical surfaces
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F2224/00—Materials; Material properties
- F16F2224/02—Materials; Material properties solids
- F16F2224/0216—Materials; Material properties solids bimetallic
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F2226/00—Manufacturing; Treatments
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F2236/00—Mode of stressing of basic spring or damper elements or devices incorporating such elements
- F16F2236/04—Compression
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F2238/00—Type of springs or dampers
- F16F2238/02—Springs
- F16F2238/026—Springs wound- or coil-like
Definitions
- the present invention relates to a compression coil spring used in, for example, an automobile engine or clutch, and more particularly to a compression coil spring having excellent fatigue resistance even in a use environment under high stress and a method for manufacturing the same.
- the hot forming method is a coil spring in which cold forming is difficult due to its poor workability such as a large wire diameter d and a small spring index D / d which is a ratio of the coil average diameter D to the wire diameter d.
- Carbon steel or spring steel is used as the coil spring wire.
- the wire is heated to a high temperature so as to be easily processed, wound around a cored bar, coiled into a coil spring shape, and further subjected to shot peening and setting after quenching and tempering.
- the fatigue resistance and sag resistance which are the main characteristics of the coil spring, are obtained.
- coiling with a coreless metal is technically very difficult, so that it has not been put into practical use so far. Therefore, in the hot forming method, it is indispensable in the prior art to use a cored bar, and as a coil spring that can be molded, the degree of freedom of shape is low compared to the cold forming method that can be coiled with a coreless bar.
- valve springs and clutch damper spring class compression coil springs can be cold formed because of their relatively small wire diameter.
- a cold forming method has been adopted.
- a coreless metal forming technique has been established, and the high degree of freedom in the shape of the coil spring is also a major factor in the use of the cold forming method.
- the production technology of compression coil springs of the valve springs and clutch damper spring class by has never existed.
- a hard wire such as a carbon steel wire, a hard steel wire, a piano wire, or a spring steel wire has been conventionally used as the coil spring wire.
- a hard wire such as a carbon steel wire, a hard steel wire, a piano wire, or a spring steel wire has been conventionally used as the coil spring wire.
- the wire is cold coiled into a coil spring shape, and after annealing, shot peening and setting are performed as necessary.
- the purpose of annealing is to remove the residual stress caused by the processing that hinders the improvement of the fatigue resistance of the coil spring. Together with the application of compressive residual stress to the surface by shot peening, Contributes to improved fatigue resistance.
- the surface hardening process by a nitriding process is performed as needed before shot peening.
- Patent Document 1 describes an oil tempered wire for cold forming, and discloses a technique for improving fatigue resistance by utilizing a processing-induced transformation of retained austenite.
- Patent Document 2 discloses a technique for improving fatigue resistance by applying a large compressive residual stress to a surface of a wire subjected to nitriding treatment by multistage shot peening at different projection speeds.
- Patent Document 1 residual stress is generated in the coil spring after coiling.
- This residual stress particularly the tensile residual stress in the direction of the linear axis generated on the inner surface of the coil, is an impediment to improving fatigue resistance as a coil spring.
- annealing is performed to remove the residual stress due to this processing, but even with the wire in Patent Document 1 having a high resistance to temper softening, the residual stress is completely maintained while maintaining the strength of the desired wire. This is difficult to remove and is well known to those skilled in the art.
- the compression residual stress of the wire spring surface vicinity (henceforth "surface") of a coil spring is about 1400 MPa
- the compressive residual stress is sufficient for suppressing crack initiation on the surface.
- the compressive residual stress inside the wire is reduced, and the effect of the compressive residual stress is poor on cracks inside the wire starting from inclusions.
- the energy given by shot peening is limited, that is, although the change in compressive residual stress distribution is given, it is difficult to greatly improve the sum of compressive residual stresses. It is not considered to eliminate the influence of the residual stress caused by the above-described processing. Therefore, the effect of improving the fatigue resistance is poor with respect to the wire having the same strength.
- depth the depth from the surface of the wire
- the maximum value of the combined stress which is the sum of the applied stress and the residual stress due to the external load, exists in the range of 0.1 to 0.4 mm, and the highest part of the combined stress is the starting point of fracture. Is the actual situation. Therefore, securing a large compressive residual stress in the depth range of 0.1 to 0.4 mm is important for fatigue resistance.
- the present invention eliminates the tensile residual stress due to the coiling process and forms a C-concentrated layer on the surface of the wire, thereby providing an appropriate compressive residual stress distribution to the formed wire.
- An object of the present invention is to provide a highly durable compression coil spring and a method for manufacturing the same using a simple wire.
- the present inventors conducted extensive research on the fatigue resistance of coil springs.
- the tensile residual stress at the time of coiling can be eliminated, and the effects of shot peening and setting performed later can be effectively obtained.
- a method for eliminating the tensile residual stress of the spring wire before the shot peening process was studied. As a result, focusing on the fact that the residual stress can be eliminated by heating the coil spring wire to the austenite region, coiling is performed while the coil spring wire is heated to the austenite region, thereby eliminating the residual stress caused by the processing. It was found that the effects of shot peening and setting performed later can be obtained efficiently.
- crystal grain size In the heating stage up to the austenite region, performing the heating in a shorter time leads to suppression of coarsening or refinement of the prior austenite crystal grain size (hereinafter referred to as “crystal grain size”).
- the crystal grain size is closely related to the fatigue resistance, and the refinement of the crystal grain size is effective for improving the fatigue resistance. Therefore, by heating the coil spring wire in a short time and performing hot processing, it becomes possible to manufacture a spring with more excellent fatigue resistance in combination with eliminating residual stress caused by processing.
- the yield stress can be improved by making the vicinity of the surface high in hardness, and the effect of shot peening performed later can be efficiently obtained.
- the carburizing process is performed during hot coiling, the carburizing process can be performed efficiently.
- the effect of shot peening and setting performed later can be obtained efficiently by heating the coil spring wire to the austenite region after cold coiling to eliminate the residual stress caused by the processing.
- the carburizing process can be efficiently performed by performing the carburizing process simultaneously with heating after coiling.
- the compression coil spring of the present invention contains, by weight%, C in a range of 0.45 to 0.80%, Si in a range of 0.15 to 2.50%, Mn in a range of 0.3 to 1.0%, and the balance remaining.
- the internal hardness in an arbitrary wire cross section is 570 to 700 HV
- the surface layer portion is made of steel wire. It has a C-enriched layer that exceeds the average concentration of C contained, and is approximately 0. 0 from the surface of the wire when there is no load in the direction of the maximum principal stress that occurs when a compression load is applied to the coil spring inner diameter side of the wire.
- the compressive residual stress at a depth of 2 mm is 200 MPa or more, and the compressive residual stress at a depth of 0.4 mm from the surface is 60 MPa or more.
- the substantially maximum principal stress direction generated when a compressive load is applied to the spring indicates a direction of approximately + 45 ° with respect to the axial direction of the wire.
- the maximum principal stress direction changes depending on the coil spring shape (particularly, the relationship with the pitch angle), and the direction exists in the range of + 45 ° to + 60 ° with respect to the axial direction.
- the compression coil spring of the present invention contains, by weight%, C in a range of 0.45 to 0.80%, Si in a range of 0.15 to 2.50%, Mn in a range of 0.3 to 1.0%, and the balance remaining.
- C in a range of 0.45 to 0.80%
- Si in a range of 0.15 to 2.50%
- Mn in a range of 0.3 to 1.0%
- the internal hardness in an arbitrary wire cross section is 570 to 700 HV
- the surface layer portion is made of steel wire. It has a C-enriched layer exceeding the average concentration of C contained, and I- ⁇ R is 160 MPa ⁇ mm or more on the coil spring inner diameter side of the wire .
- I ⁇ R is the crossing point, which is the depth from the surface of the wire where the value of the compressive residual stress at no load becomes zero in the direction of the substantially maximum principal stress generated when a compression load is applied to the spring,
- the integrated value from the surface to the crossing point in the residual stress distribution curve where the vertical axis is the residual stress and the horizontal axis is the wire radius.
- a large crossing point suggests that compressive residual stress is deep from the surface.
- the compression coil spring of the present invention contains, by weight%, C in a range of 0.45 to 0.80%, Si in a range of 0.15 to 2.50%, Mn in a range of 0.3 to 1.0%, and the balance remaining.
- the internal hardness in an arbitrary wire cross section is 570 to 700 HV
- the surface layer portion is made of steel wire It has a C-enriched layer that exceeds the average concentration of C contained, and is approximately 0. 0 from the surface of the wire when there is no load in the direction of the maximum principal stress that occurs when a compression load is applied to the coil spring inner diameter side of the wire.
- the compressive residual stress at a depth of 15 mm is 300 MPa or more, and the compressive residual stress at a depth of 0.3 mm from the surface is 50 MPa or more.
- the compression coil spring of the present invention contains, by weight%, C in a range of 0.45 to 0.80%, Si in a range of 0.15 to 2.50%, Mn in a range of 0.3 to 1.0%, and the balance being
- C in a range of 0.45 to 0.80%
- Si in a range of 0.15 to 2.50%
- Mn in a range of 0.3 to 1.0%
- the balance being
- the internal hardness in an arbitrary wire cross-section is 570 to 700 HV
- the surface layer portion is made of steel wire It has a C-concentrated layer exceeding the average concentration of C contained, and I ⁇ R is 130 MPa ⁇ mm or more on the inner diameter side of the coil spring of the wire.
- Material component C 0.45 to 0.80% C contributes to strength improvement. If the C content is less than 0.45%, the effect of improving the strength cannot be obtained sufficiently, so that the fatigue resistance and sag resistance are insufficient. On the other hand, when the content of C exceeds 0.80%, the toughness is lowered and cracking is likely to occur. Therefore, the C content is set to 0.45 to 0.80%.
- Si 0.15 to 2.50% Si is effective for deoxidation of steel and contributes to improvement of strength and resistance to temper softening. If the Si content is less than 0.15%, these effects cannot be obtained sufficiently. On the other hand, if the Si content exceeds 2.50%, the toughness is lowered and cracks are likely to occur, and decarburization is promoted to cause a reduction in the wire surface strength. Therefore, the Si content is 0.15 to 2.50%.
- Mn 0.3 to 1.0% Mn contributes to improvement of hardenability.
- Mn content is less than 0.3%, it becomes difficult to ensure sufficient hardenability, and the effect of S fixing (MnS generation) that is harmful to ductility becomes poor.
- MnS generation S fixing
- the content of Mn exceeds 1.0%, ductility is lowered, and cracks and surface scratches are likely to occur. Therefore, the Mn content is set to 0.3 to 1.0%.
- additive elements are the minimum elements necessary for configuring the present invention, and other elements may be further added. That is, in the present invention, one or more elements of Cr, B, Ni, Ti, Cu, Nb, V, Mo, W, etc., which are generally used as the component composition of spring steel, are set to 0. 0.005 to 4.5% can be appropriately added depending on the purpose, and as a result, it is possible to produce a coil spring having higher performance or more suitable for use. For example, the case where Cr is added will be described below.
- Cr 0.5-2.0% Cr is effective in preventing decarburization, contributes to improvement in strength and resistance to temper softening, and is effective in improving fatigue resistance. It is also effective in improving warm sag resistance. Therefore, in the present invention, it is preferable to further contain 0.5 to 2.0% of Cr. If the Cr content is less than 0.5%, these effects cannot be obtained sufficiently. On the other hand, if the Cr content exceeds 2.0%, the toughness is lowered, and cracks and surface scratches are likely to occur.
- the coil springs have the compressive residual stress described later in order to satisfy the required fatigue resistance and sag resistance.
- the strength of the wire itself is important as well as the distribution. That is, the internal hardness of the wire in an arbitrary cross section needs to be in the range of 570 to 700 HV, and when it is less than 570 HV, sufficient fatigue resistance and sag resistance are obtained due to the low material strength. I can't get it.
- C concentrated layer In order to improve the yield stress by increasing the hardness of the surface of the wire, a C concentrated layer is formed on the surface layer portion of the wire by carburizing treatment. By improving the yield stress, a large surface compressive residual stress can be applied by shot peening performed later. Moreover, the surface roughness of the wire can be improved. For this reason, there exists an effect which improves a fatigue resistance further.
- the C-enriched layer contains C having a concentration exceeding the average concentration of C contained in the wire. Further, in order to sufficiently obtain these effects, the maximum C concentration in the C concentrated layer is 0.7 to 0.9% by weight, and the C concentrated layer (carburized depth) is 0.01 to 0 from the surface of the wire. It is preferable to be formed to a depth of 1 mm.
- the treatment When the maximum C concentration of the C concentrated layer exceeds 0.9% by weight or when the thickness of the C concentrated layer exceeds 0.1 mm, the treatment must be performed at a high temperature in order to efficiently perform the carburizing reaction. Therefore, the crystal grain size is deteriorated and the fatigue resistance is likely to be lowered. In addition, when the C concentration exceeds 0.9% by weight, toughness is reduced because a large amount of C that cannot be dissolved in the matrix phase is precipitated as carbides at the grain boundaries, and in this case, fatigue resistance is also reduced. easy.
- the hardness of the C concentrated layer is 50 HV or more higher than the internal hardness of the wire. This is because the C-concentrated layer on the surface of the wire is higher than the internal hardness, so that a higher compressive residual stress can be obtained in the vicinity of the surface and fatigue cracks starting from the vicinity of the surface (including the outermost surface) can be generated. This is because it can be prevented.
- the above numerical value is less than 50 HV, these effects do not appear remarkably.
- the inventors of the present invention have applied stress required for valve springs and clutch damper springs and various factors that can become fatigue fracture starting points (toughness, non-metallic inclusions, incompletely quenched structures, etc. Fracture mechanics calculation in relation to abnormal structure, surface roughness, surface scratches, etc.), and verification by actual endurance test, etc., the following conclusion was obtained regarding the compressive residual stress required near the wire surface of the coil spring It was.
- the compressive residual stress in the present invention is in the direction of the substantially maximum principal stress when a compressive load is applied to the spring, that is, in the + 45 ° direction with respect to the axial direction of the wire.
- Compressive residual stress distribution from the surface of the wire to the inside of the spring is given by shot peening and setting.
- it is necessary not only to improve the compressive residual stress on the surface of the wire, but also to introduce the compressive residual stress in the interior larger and deeper. It is important to further increase the compressive residual stress in the range of a depth of about 0.1 to 0.4 mm.
- As an index indicating the distribution of compressive residual stress inside the wire in the case of a steel wire having an equivalent circle diameter of 2.5 mm or more and 10 mm or less, it is approximately the maximum that occurs when a compression load is applied to the spring on the spring inner diameter side.
- a steel wire rod having a compressive residual stress of 200 MPa or more at a depth of 0.2 mm and a compressive residual stress of 60 MPa or more at a depth of 0.4 mm and an equivalent circle diameter of 1.5 mm to 3 mm in the principal stress direction.
- the compression residual stress at a depth of 0.15 mm is 300 MPa or more, and the compression residual stress at a depth of 0.3 mm is 50 MPa or more. When these values are not satisfied, it is insufficient to suppress fatigue fracture at the internal origin.
- I- ⁇ R which is another index indicating the magnitude or depth of the compressive residual stress
- I- ⁇ R which is another index indicating the magnitude or depth of the compressive residual stress
- I- ⁇ R In the direction of the substantially maximum principal stress that occurs when a compressive load is applied, in the case of a steel wire having an I- ⁇ R of 160 MPa ⁇ mm or more at no load and an equivalent circle diameter of 1.5 mm or more and 3 mm or less, 130 MPa ⁇ mm or more To do.
- the maximum compression residual stress when the surface is unloaded is targeted for valve springs and clutch damper springs that are subject to high load stress. In the case, it is preferably 900 MPa or more.
- Compressive residual stress distribution in the present invention is preferably formed by shot peening treatment.
- a sphere equivalent diameter of a shot used for shot peening performed later is smaller than a sphere equivalent diameter of a shot used for shot peening performed earlier.
- the shot peening process includes a first shot peening process using a shot having a particle diameter of 0.6 to 1.2 mm, a second shot peening process using a shot having a particle diameter of 0.2 to 0.8 mm, A multi-stage shot peening process including a third shot peening process using shots having a particle diameter of 0.02 to 0.30 mm is preferable. Thereby, the surface roughness increased by the shot peening performed previously can be reduced by the shot peening performed later.
- the shot diameter and the number of steps in the shot peening process are not limited to the above, and it is only necessary to obtain the necessary residual stress distribution, surface roughness, and the like according to the required performance. Therefore, the shot diameter, material, number of steps, etc. are selected as appropriate. Moreover, since the compressive residual stress distribution to be introduced varies depending on the projection speed and the projection time, these are also set as necessary.
- the present invention is suitable for a compression coil spring having the following specifications that require a high degree of processing during coiling and require high fatigue resistance.
- the present invention has a wire equivalent diameter of 1.5 to 10 mm (including a diameter of a perfect circle calculated from the cross-sectional area of the wire, including non-circular cross sections including a square shape and an oval shape), and a spring index of 3 to It can be used for a compression coil spring which is 20 and is generally cold formed.
- valve springs and clutch damper springs that require a high degree of workability during coiling (that is, a large tensile residual stress on the inner diameter side of the coil caused by coiling in cold forming) and that require high fatigue resistance.
- a compression coil spring having a circle equivalent diameter of 1.5 to 9.0 mm and a spring index of 3 to 8.
- the compression coil spring of the present invention can be obtained by a hot forming method or a cold forming method. Even in the case of producing by the hot forming method, unlike the conventional hot forming method, a coil spring forming machine, which will be described later, is used. Therefore, the degree of freedom of the spring shape that can be formed is high. That is, the coil spring shape in the present invention can be applied to a coil spring having a shape other than this, including a cylindrical shape in which the outer diameter of the coil is not substantially changed in the entire winding as a typical coil spring. For example, a deformed spring such as a cone shape, a bell shape, a hourglass shape, or a barrel shape can be formed.
- the grain size measurement method is defined in JIS G0551, and the prior austenite grain average grain size number G is preferably 10 or more for improving fatigue resistance.
- the prior austenite crystal grains are fine, it is possible to prevent the movement of the slip at the stress concentrated portion at the tip of the fatigue crack, so that the effect of suppressing the crack growth is great and the desired fatigue resistance can be obtained. .
- it is less than 10 the effect of suppressing crack growth is poor and it is difficult to obtain sufficient fatigue resistance.
- the average crystal grain size (using a boundary having an orientation angle difference of 5 ° or more as a grain boundary) measured by using a SEM / EBSD (Electron Back Scatter Diffraction) method is 2.0 ⁇ m or less.
- SEM / EBSD Electro Back Scatter Diffraction
- a method for manufacturing the compression coil spring of the present invention will be described.
- the coil spring forming machine is continuously supplied from the rear after a feed roller for continuously supplying the steel wire, a coiling portion for forming the steel wire into a coil shape, and coiling the steel wire with a predetermined number of turns.
- Cutting means for cutting the incoming steel wire.
- the coiling unit includes a wire guide for guiding the steel wire supplied by the feed roller to an appropriate position of the processing unit, and a coiling pin for processing the steel wire supplied via the wire guide into a coil shape.
- a coiling tool including a coiling roller and a pitch tool for adding a pitch are provided.
- the coil spring forming machine has a heating means for raising the temperature of the steel wire to the austenite region within 2.5 seconds between the feed roller outlet and the coiling tool.
- the 1st manufacturing method of the compression coil spring of this invention is characterized by performing the carburizing process which sprays hydrocarbon-type gas directly on the steel wire rod surface between during heating and quenching.
- the heating means is high frequency heating, and is concentric with the steel wire on the passage of the steel wire in the wire guide or on the passage of the steel wire in the space between the steel wire outlet end and the coiling tool in the wire guide.
- a high frequency heating coil is preferably arranged.
- heating may be performed by energization heating or laser heating other than high-frequency heating.
- the carburizing process which forms C concentrating layer in the surface layer part of steel wire, the coiling process which hot-forms steel wire with a coil spring forming machine, and coiling After that, the quenching process in which the coil that has been separated and the temperature is still in the austenite region is quenched as it is, the tempering process in which the coil is tempered, the shot peening process in which compressive residual stress is applied to the wire surface, and the setting process are performed in order.
- Formation of the C concentrated layer in the carburizing process is performed by a method in which a hydrocarbon-based gas is directly sprayed onto the surface of the heated steel wire.
- the coil spring forming machine used in the coiling process is the same as that used in the first manufacturing method of the compression coil spring of the present invention.
- the heating means uses high-frequency heating and is concentric with the steel wire on the passage of the steel wire in the wire guide or on the passage of the steel wire in the space between the steel wire outlet end and the coiling tool in the wire guide.
- a high-frequency heating coil is arranged.
- the 2nd manufacturing method of the compression coil spring of this invention is a continuous process in which the carburizing process and the coiling process do not have separation of a steel wire in the middle.
- a coiling step of forming a steel wire by a coil spring forming machine, a heating and quenching step of heating and quenching the coil to an austenite region within 20 seconds, A tempering step for tempering the coil, a shot peening step for imparting compressive residual stress to the surface of the wire, and a setting step are sequentially performed.
- the heating means in the heating and quenching step is high-frequency heating, and a carburizing step in which a hydrocarbon-based gas is directly sprayed on the surface of the steel wire during heating to quenching is performed.
- the surface temperature of the steel wire at the time when the hydrocarbon-based gas is sprayed is 850 to 1150 ° C., and the movement of the hydrocarbon-based gas on the surface of the wire
- the pressure is preferably 0.1 to 5.0 kPa. According to this carburizing condition, carburizing can be performed efficiently in a short time while preventing a significant decrease in the crystal grain size of the wire.
- the main component of the hydrocarbon gas is any one of methane, butane, propane, and acetylene.
- the tempering step is performed in order to temper the coil cured by the quenching step into a coil having appropriate hardness and toughness. Therefore, when desired hardness and toughness can be obtained with quenching, the tempering step may be omitted.
- the shot peening process multi-stage shot peening may be performed, and furthermore, low temperature aging treatment for the purpose of recovering the surface elasticity limit may be combined as necessary.
- the low temperature aging treatment can be performed after the shot peening process or between each stage of the multi-stage shot peening, and shot peening with a shot having a particle diameter of 0.02 to 0.30 mm is performed as the final stage in the multi-stage shot peening.
- the pretreatment When applied, it is preferable to perform the pretreatment to further increase the compressive residual stress on the outermost surface.
- various methods such as cold setting and hot setting as the setting applied to the coil as a settling prevention process in the setting process, it is selected as appropriate according to desired characteristics.
- the compression coil spring of the present invention since hot coiling is performed by the coil spring molding machine, it is possible to prevent generation of residual stress due to processing. And since a steel wire is heated up to an austenite area within 2.5 seconds, the coarsening of a crystal grain can be prevented and the outstanding fatigue resistance can be acquired. Moreover, since the carburizing treatment is performed, the surface of the steel wire can be made high in hardness, and compressive residual stress can be effectively applied by shot peening performed later. Particularly, in the first manufacturing method of the compression coil spring of the present invention, the carburizing process is performed using the heat at the time of hot coiling, and therefore the carburizing process can be performed efficiently.
- the third manufacturing method of the compression coil spring of the present invention since the coil is heated to the austenite region within 20 seconds and quenched, the tensile force generated by cold coiling while preventing coarsening of crystal grains is prevented. Residual stress can be eliminated. Moreover, since the carburizing process is performed using the heat at the time of heating and quenching, the carburizing process can be performed efficiently. From these, compressive residual stress can be effectively applied by shot peening performed later, and excellent fatigue resistance can be obtained.
- the present invention is a carbon steel wire, hard steel wire, piano wire, spring steel wire, carbon steel oil temper wire, chrome vanadium steel oil temper wire, silicon chrome steel oil temper wire, silicon chrome vanadium steel oil temper used as a spring. Applicable to lines. In particular, it is preferable to apply to inexpensive carbon steel wires, hard steel wires, piano wires, and spring steel wires. This makes it possible to obtain a fatigue-resistant spring superior to a conventional cold-formed spring using an expensive oil tempered wire to which a high-level element is added even if an inexpensive wire is used. Because.
- a highly durable compression coil spring is obtained using an inexpensive wire by eliminating tensile residual stress due to coiling and imparting an appropriate compressive residual stress distribution to the formed wire. be able to.
- SYMBOLS 1 Coiling machine shaping
- FIG. 1 shows each manufacturing process. 1A to 1C show a manufacturing process for obtaining the compression coil spring of the present invention
- FIGS. 1D and 1E show a conventional example.
- the manufacturing process shown in FIGS. 1A and 1B is a hot forming method using the following coiling machine
- the manufacturing process shown in FIG. 1C is a cold forming method using any coiling machine. is there.
- FIG. 2 shows an outline of a molding part of a coiling machine used in the manufacturing process shown in FIGS. 1 (A) and 1 (B).
- the coiling machine forming unit 1 includes a feed roller 10 for continuously supplying the steel wire M, a coiling unit 20 for forming the steel wire M into a coil shape, and a rear after coiling a predetermined number of turns.
- a heating coil 40 is a heating coil 40.
- the coiling unit 20 is for guiding the steel wire M supplied by the feed roller 10 to an appropriate position, and for processing the steel wire M supplied via the wire guide 21 into a coil shape.
- a coiling tool 22 including a coiling pin (or coiling roller) 22a and a pitch tool 23 for adding a pitch are provided.
- the rapid heating in the coiling machine is performed by the high-frequency heating coil 40, and the temperature of the steel wire is raised to the austenite region within 2.5 seconds.
- the installation position of the high frequency heating coil 40 is as shown in FIG.
- the high-frequency heating coil 40 is installed in the vicinity of the wire guide 21, and the coiling portion 20 is provided so that the steel wire M can be formed immediately after heating.
- the installation position of a high frequency heating coil should just be able to shape
- the steel wire M passed through the wire guide 21 is brought into contact with the coiling pin 22a and bent with a predetermined curvature, and further brought into contact with the downstream coiling pin 22a and bent with a predetermined curvature. Then, the steel wire M is brought into contact with the pitch tool 23 to give a pitch so as to obtain a desired coil shape.
- the cutting blade 30a of the cutting means 30 is cut by shearing with the straight portion of the inner mold 30b to separate the steel wire M supplied from the rear and the spring-shaped steel wire M from each other. .
- FIG. 1 The manufacturing process of 1st Embodiment is shown to FIG. 1 (A). First, it is equivalent to a circle consisting of 0.45 to 0.80% C, 0.15 to 2.50% Si, 0.3 to 1.0% Mn, with the balance being iron and inevitable impurities.
- a steel wire M having a diameter of 1.5 to 10 mm is prepared. The steel wire M is supplied to the feed roller 10 by a wire drawing machine (not shown), and the steel wire M is heated to the austenite region within 2.5 seconds by the high-frequency heating coil 40, and then coiling is performed in the coiling section 20 (coiling). Process).
- a hydrocarbon gas is directly blown onto the surface of the steel wire M to perform carburizing treatment simultaneously (carburizing process).
- a gas spray nozzle 50 as shown in FIG. 3 is used.
- the position of the nozzle only needs to be downstream from the high-frequency heating coil 40, and may be other than the position shown in FIG.
- Carburization is performed at a gas spray pressure (dynamic pressure on the surface of the steel wire M) of 0.1 to 5.0 kPa and a wire temperature of 850 to 1150 ° C., and the maximum C concentration on the surface of the steel wire M is 0.7 to 0.9.
- a C concentrated layer having a thickness of 0.01 to 0.1 mm is formed. Thereby, the surface layer part 50HV or more higher than wire internal hardness can be obtained.
- the coil that has been separated after coiling and is still in the austenite region is quenched as it is in a quenching tank (not shown) (for example, an oil of about 60 ° C. as a quenching solvent) (quenching step), and further tempered (for example, 150 to 450 ° C.) (tempering step).
- a quenching tank for example, an oil of about 60 ° C. as a quenching solvent
- further tempered for example, 150 to 450 ° C.
- a general method may be used for quenching / tempering, and the heating temperature of the wire before quenching, the type and temperature of the quenching solvent, and the temperature and time of tempering are appropriately set according to the material of the steel wire M. .
- desired fatigue resistance can be obtained by subjecting the steel wire M to shot peening treatment (shot peening process) and setting treatment (setting process). Since coiling is performed in a state heated to the austenite region, it is possible to prevent the generation of residual stress due to processing. For this reason, it is easy to apply compressive residual stress by shot peening, and deep and large compressive residual stress can be effectively applied on the inner diameter side of the spring. Furthermore, by performing the setting process, a deep compressive residual stress distribution is formed in the maximum principal stress direction when used as a spring, and fatigue resistance can be improved.
- the shot peening process to be performed later since the shot smaller than the shot peening process to be performed earlier is used, the surface roughness of the wire can be smoothed.
- steel cut wires, steel beads, FeCrB-based high hardness particles, or the like can be used. Further, the compressive residual stress can be adjusted by a shot equivalent sphere diameter, a projection speed, a projection time, and a multi-stage projection method.
- hot setting is performed as a setting process, heating is performed at 100 to 300 ° C., and the shear strain acting on the surface of the wire is greater than or equal to the shear strain in the working stress when actually used as a spring.
- plastic strain is applied to the spring-shaped steel material.
- the compression coil spring of the present invention produced by the process as described above has an internal hardness of 570 to 700 HV in an arbitrary cross section of the spring element wire, and has a C concentrated layer in the surface layer portion.
- compression is performed at a depth of 0.2 mm from the surface under no load in the direction of approximately the maximum principal stress that occurs when a compression load is applied to the spring on the inner diameter side of the spring.
- the residual stress is 200 MPa or more, and the compressive residual stress at a depth of 0.4 mm from the surface is 60 MPa or more.
- the compressive residual stress at a depth of 0.15 mm from the surface is 300 MPa or more and the compressive residual stress at a depth of 0.3 mm from the surface is 50 MPa or more. is there.
- the compression coil spring of the present invention produced by the above steps has an internal hardness of 570 to 700 HV in an arbitrary cross section of the spring element wire, and has a C-concentrated layer in the surface layer portion.
- I -Shigumaaru at no load is equivalent circle diameter of 2.5mm or more 10mm or less of the steel wire rod, 160 MPa ⁇ mm
- it is 130 MPa ⁇ mm or more.
- the C-concentrated layer has a maximum C concentration of 0.7 to 0.9% by weight, a thickness of 0.01 to 0.1 mm, and a hardness higher than the internal hardness by 50 HV or more. Therefore, the compression coil spring of the present invention is excellent in fatigue resistance because the compressive residual stress is deep and large.
- the carburizing process was performed during hot coiling.
- the compression coil of the present invention can be used even if the carburizing process is performed before hot coiling.
- a spring can be obtained.
- a carburizing process is performed by installing a gas blowing nozzle 50 in front of the feed roller 10. The position of the nozzle may be upstream from the feed roller 10, and may be other than the position shown in FIG.
- the carburizing conditions are the same as in the first embodiment.
- the steel wire M is not cut off and used as it is in the coiling process.
- the coiling process, quenching process, tempering process, shot peening process, and setting process are performed in the same manner as in the first embodiment.
- a compression coil spring equivalent to the first embodiment can be obtained.
- the carburizing time can be freely set as compared with the first embodiment.
- the compression coil spring of the present invention can be obtained using a cold forming method as shown in FIG.
- Cold coiling is performed on the steel wire M used in the first embodiment by an arbitrary coiling machine (coiling process). Then, the steel wire M after coiling is heated to the austenite region within 20 seconds and quenched (heat quenching step). At this time, high-frequency heating means is used for heating, and a carburizing process (carburizing process) is performed simultaneously by spraying a hydrocarbon-based gas directly on the surface of the steel wire M during heating and quenching. For example, as shown in FIG.
- a steel wire M is fixed to a rotatable jig 60, and a high frequency heating coil 40 is installed around the steel wire M, and a nozzle 50 having a gas supply hole inside a spring is installed. Then, while rotating the steel wire M by rotating the jig 60, gas is supplied through the nozzle 50 so that the surface of the coil spring is uniformly quenched and carburized.
- the carburizing conditions are the same as in the first embodiment.
- a quenching process, a tempering process, a shot peening process, and a setting process are sequentially performed. Since heating is performed up to the austenite region in the heating and quenching step, the tensile residual stress generated by cold forming can be eliminated, and the effects of shot peening and setting can be obtained effectively. Thus, a compression coil spring having the same performance as that of the first embodiment can be obtained.
- the third embodiment performs high-frequency heating on the coil-shaped steel wire M, so it is necessary to consider soaking.
- the heating time is relatively long, the effect of crystal grain refinement is inferior to that of the first and second embodiments.
- a large processing strain remains in the coil spring after forming, and the processing strain is not uniform within the individual. For this reason, in the heating and quenching process, when the processing strain is released, the shape tends to be distorted.
- the manufacturing method in the first and second embodiments is more preferable than that in the third embodiment.
- Sample Preparation Method Samples of coil springs were prepared by each manufacturing process, and fatigue resistance was evaluated. First, a hard drawn wire and an oil tempered wire having the chemical components shown in Table 1 and the balance being iron and inevitable impurities were prepared. The wire diameter of each wire is as shown in Table 2. Then, for the hard drawn wire or the oil tempered wire, the spring is formed by a hot forming method or a cold forming method in accordance with the manufacturing steps shown in FIGS. 1A to 1E (respectively indicated as manufacturing steps A to E). A coil spring having an index of 6, an effective portion pitch angle of 9 °, and an effective portion winding number of 4.25 was produced.
- coiling is performed by heating a steel wire with a coiling machine (see FIG. 3) equipped with a high-frequency heating coil and a gas spray nozzle, and after carburizing under the conditions shown in Table 2, oil at 60 ° C. Quenched by.
- the carburizing temperature is the surface temperature of the steel wire
- the dynamic pressure represents the dynamic pressure of propane gas on the surface of the steel wire.
- a tempering treatment was performed under the conditions shown in Table 2 (Invention Examples 1 to 23, 26 to 29, Comparative Examples 9 and 10).
- the manufacturing process B after performing carburizing treatment using the coiling machine shown in FIG. 4 under the carburizing treatment conditions shown in Table 2, the steel wire is heated to 900 ° C. and coiled, and quenched with oil at 60 ° C. did. Thereafter, a tempering treatment was performed at 350 ° C. (Invention Example 24).
- shot peening processing and setting processing were performed on each sample.
- a first shot peening process using a steel round cut wire having a sphere equivalent diameter of 1.0 mm a first shot peening process using a steel round cut wire having a sphere equivalent diameter of 1.0 mm
- a second shot peening process using a steel round cut wire having a sphere equivalent diameter of 0.5 mm and a sphere equivalent diameter.
- a third shot peening treatment with 0.1 mm steel beads was sequentially performed.
- the setting was hot setting, and the heating was performed at a coil spring heating temperature of 200 ° C. and a load stress of 1500 MPa.
- HV Hardness
- Compressive residual stress ( ⁇ R0.15 , ⁇ R0.2 , ⁇ R0.3 , ⁇ R0.4 ) having a depth of 0.15, 0.2 , 0.3 , 0.4 mm , Maximum compressive residual stress ( ⁇ Rmax ), integrated compressive residual stress (I ⁇ R ), crossing point (CP)
- ⁇ Rmax Maximum compressive residual stress
- I ⁇ R integrated compressive residual stress
- CP crossing point
- an X-ray diffraction type residual stress measuring device manufactured by Rigaku
- the measurement was performed with a tube: Cr and a collimator diameter: 0.5 mm.
- the above measurement was performed after the entire surface of the wire was chemically polished using hydrochloric acid with respect to the coil spring, and the residual stress distribution in the depth direction was obtained by repeating this, and from the result, 0.15, 0.2 , 0.3, and 0.4 mm depths of no-load compressive residual stress, maximum compressive residual stress, and crossing point were obtained.
- the integrated compressive residual stress value was calculated by integrating the compressive residual stress from the surface to the crossing point in the relationship diagram of depth and residual stress.
- the residual stress distribution of Invention Example 12 is shown in FIG.
- Average crystal grain size The average crystal grain size was measured by JEOL JSM-7000F (TSL Solutions OIM-Analysis Ver. 4.6) by FE-SEM / EBSD (Electron Back Scatter Diffraction) method. Here, the measurement was performed at the position of the depth d / 4 of the cross section of the coil spring, the observation magnification was 10,000 times, and the average crystal grain size was calculated with the boundary having an azimuth angle difference of 5 ° or more as the grain boundary.
- Fatigue resistance breakage rate
- the test stress was 735 ⁇ 662 MPa, the frequency was 20 Hz, the number of tests was 8 each, and the fatigue resistance was evaluated by the breakage rate (number of breaks / number of tests) at the time of vibration 20 million times.
- the hardness of the surface is higher by 50 HV or more than the internal hardness by carburizing treatment.
- - ⁇ Rmax is 900 MPa or more, and a large maximum compressive residual stress is obtained. This is thought to be due to the improvement in compressive residual stress due to shot peening due to the improvement in yield stress in the vicinity of the surface due to carburization.
- I ⁇ R is 160 MPa ⁇ mm or more
- CP is 0.43 mm or more
- I ⁇ R is 130 MPa ⁇ mm.
- CP was 0.38 mm or more, deep and large compressive residual stress was obtained, and fatigue resistance was good.
- Invention Example 25 by the manufacturing process C as a result of heating for a short time by high frequency heating, G is 10.1 and fine crystal grains can be obtained.
- the reason why the crystal grain size is slightly deteriorated in the manufacturing process C compared to the invention example 12 of the manufacturing process A is that the coil in the manufacturing process C is in a coil shape compared to the case of heating the wire as in the manufacturing process A. This is because the heating time is increased in order to heat uniformly because the high frequency heating is performed. Therefore, depending on the wire diameter and shape of the coil spring, the manufacturing process A is more preferable than the manufacturing process C from the viewpoint of crystal grain refinement.
- the surface roughness Rz (maximum height) was 9.0 ⁇ m or less, sufficiently satisfying the desired surface roughness Rz of 20 ⁇ m or less. ing.
- This surface roughness is formed by rubbing with tools during coiling or by shot peening.
- the surface roughness formed by the shot peening process is determined by the combination of the hardness of the wire and the conditions such as the shot particle size, hardness, and projection speed. Therefore, it is necessary to appropriately set the conditions for shot peening so that Rz does not exceed 20 ⁇ m.
- Inventive Examples 7 to 19 have a smaller surface roughness than Comparative Example 9 having the same internal hardness. This is because a C-concentrated layer having high hardness is formed on the surface. Since the surface is hard, it is considered that the surface roughness is difficult to decrease during the shot peening process, and a good surface roughness is obtained. Therefore, the improvement of the surface hardness due to the formation of the C-concentrated layer suppresses the generation of valleys on the surface that are likely to be fracture starting points, and is effective for improving the fatigue resistance (improving the reliability).
- the wire diameter is more preferably 1.5 to 9.0 mm.
- the gas blowing pressure is preferably 0.1 kPa to 5.0 kPa, and the wire temperature during gas blowing is preferably 850 to 1150 ° C. According to these conditions, as shown in Invention Examples 7 to 19, a surface C concentration of 0.7% by weight or more and a C concentrated layer thickness of 10 ⁇ m or more can be obtained.
- a compression coil spring of the present invention it is possible to obtain a compression coil spring that is more excellent in fatigue resistance than a conventional cold-formed spring using high-grade steel, even if an inexpensive wire is used. it can.
Abstract
Description
C:0.45~0.80%
Cは、強度向上に寄与する。Cの含有量が0.45%未満では、強度向上の効果が十分に得られないため、耐疲労性、耐へたり性が不十分となる。一方、Cの含有量が0.80%を超えると、靭性が低下して割れが発生し易くなる。このため、Cの含有量は0.45~0.80%とする。
Siは、鋼の脱酸に有効であると共に、強度向上や焼戻し軟化抵抗向上に寄与する。Siの含有量が0.15%未満では、これらの効果が十分に得られない。一方、Siの含有量が2.50%を超えると靭性が低下して割れが発生し易くなると共に、脱炭を助長し線材表面強度の低下を招く。このため、Siの含有量は0.15~2.50%とする。
Mnは焼入れ性の向上に寄与する。Mnの含有量が0.3%未満では、十分な焼入れ性を確保し難くなり、また、延靭性に有害となるSの固着(MnS生成)の効果も乏しくなる。一方、Mnの含有量が1.0%を超えると、延性が低下し、割れや表面キズが発生し易くなる。このため、Mnの含有量は0.3~1.0%とする。
Crは脱炭を防止するのに有効であると共に、強度向上や焼戻し軟化抵抗向上に寄与し、耐疲労性の向上に有効である。また、温間での耐へたり性向上にも有効である。このため、本発明においてはさらに、Crを0.5~2.0%含有することが好ましい。Crの含有量が0.5%未満では、これらの効果を十分に得られない。一方、Crの含有量が2.0%を超えると、靭性が低下し、割れや表面キズが発生し易くなる。
高負荷応力下で使用されるバルブスプリングやクラッチダンパースプリング等としては、要求される耐疲労性と耐へたり性を満足するために、コイルばねとしては後述の圧縮残留応力分布と共に線材自体の強度も重要である。すなわち、任意の横断面における線材内部硬さが、570~700HVの範囲であることが必要であり、570HV未満の場合は、その材料強度の低さから十分な耐疲労性と耐へたり性が得られない。また、700HVを超えた場合は、靭性の低下に伴う切欠き感受性の高まりから、コイリング時にツール類との擦れにより発生した表面キズや、ショットピーニングで形成される線材表面粗さの谷部を起点とした亀裂発生による早期折損の危険性が増大し、信頼性が重要な自動車部品として用いるには不適となる。
線材表面の硬度を高めて降伏応力を向上させるため、線材の表層部に浸炭処理によってC濃化層を形成する。降伏応力を向上させることにより、後に行うショットピーニングによって大きな表面圧縮残留応力を付与することができる。また、線材の表面粗さを改善することができる。このため、耐疲労性をさらに向上させる効果がある。このC濃化層には線材に含有されるCの平均濃度を超える濃度のCを含有させる。また、これらの効果を十分に得るため、C濃化層における最大C濃度が0.7~0.9重量%であり、C濃化層(浸炭深さ)は線材表面から0.01~0.1mmの深さまで形成されていることが好ましい。C濃化層の最大C濃度が0.9重量%を超える場合やC濃化層の厚さが0.1mmを超える場合は、浸炭反応を効率的に行うために高温で処理を行わなければならないため、結晶粒度が悪化し、耐疲労性の低下を招き易い。また、C濃度が0.9重量%を超えた場合は、母相に固溶できないCが炭化物として結晶粒界に多く析出することで靭性が低下し、この場合も耐疲労性の低下を招き易い。
本発明者等は、バルブスプリングやクラッチダンパースプリングとして要求される作用応力と、疲労折損起点と成りうる様々な要因(延靭性、非金属系介在物、不完全焼入れ組織等の異常組織、表面粗さ、表面キズ等々)との関係における破壊力学的計算、及び、実際の耐久試験等による検証から、コイルばねの線材表面近傍に必要な圧縮残留応力について次の結論を得た。なお、本発明における圧縮残留応力は、ばねに圧縮荷重を負荷した場合の略最大主応力方向、すなわち、線材の軸方向に対し+45°方向におけるものである。
本発明は、コイリング時の加工度が大きく、高い耐疲労性が必要とされる、次に挙げる仕様の圧縮コイルばねに好適である。本発明は、線材の円相当直径(線材横断面積から算出した真円とした場合の直径、角形や卵形をはじめとした非円形断面も含む)が1.5~10mm、ばね指数が3~20である、一般的に冷間成形されている圧縮コイルばねに利用できる。
粒度測定方法はJIS G0551に規定されており、耐疲労性向上には旧オーステナイト粒平均結晶粒度番号Gが10番以上であることが好ましい。この場合、旧オーステナイト結晶粒が微細であることから疲労亀裂先端の応力集中部におけるすべりの移動を防ぐことができるため、亀裂進展を抑制する効果が大きく、所望の耐疲労性を得ることができる。一方、10番未満の場合には、亀裂進展抑制効果が乏しく、十分な耐疲労性を得難くなる。
高負荷応力下で使用されるバルブスプリングやクラッチダンパースプリング等としては、要求される耐疲労性を満足するために、上述の圧縮残留応力分布と共に表面粗さも重要である。本発明者らが破壊力学的計算とその検証実験を行った結果、表面起点による亀裂の発生・進展に対しては、表面キズの深さ(すなわち、表面粗さRz(最大高さ))を20μm以下とすることで、その影響を無害化できることが判明している。このため、表面粗さRzが、20μm以下であることが好ましい。Rzが20μmを超える場合、表面の谷部が応力集中源となり、その谷部を起点とした亀裂の発生・進展が起こり易くなるため、早期折損を招き易い。
図1(A)に第1実施形態の製造工程を示す。まず、重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%含み、残部が鉄および不可避不純物からなる円相当直径が1.5~10mmの鋼線材Mを用意する。この鋼線材Mを線出機(図示省略)によりフィードローラ10へ供給し、高周波加熱コイル40によって鋼線材Mを2.5秒以内でオーステナイト域に加熱後、コイリング部20においてコイリングを行う(コイリング工程)。
第1実施形態においては熱間コイリング時に浸炭処理を施したが、図1(B)に示すように、熱間コイリング前に浸炭工程を行っても本発明の圧縮コイルばねを得ることができる。たとえば、図4に示すように、フィードローラ10の手前にガス吹付けノズル50を設置して浸炭処理を行う。ノズルの位置はフィードローラ10よりも上流であれば良く、図4に示した位置以外でも良い。浸炭条件は第1実施形態と同様である。浸炭工程後は、鋼線材Mを切離さずにそのままコイリング工程に供する。なお、コイリング工程、焼入れ工程、焼戻し工程、ショットピーニング工程、およびセッチング工程は第1実施形態と同様に行う。
また、図1(C)に示すような冷間成形法を用いて本発明の圧縮コイルばねを得ることもできる。第1実施形態において用いた鋼線材Mを任意のコイリングマシンによって冷間コイリングを行う(コイリング工程)。そして、コイリング後の鋼線材Mを20秒以内でオーステナイト域まで昇温し焼入れを行う(加熱焼入れ工程)。このとき、加熱は高周波加熱手段を用い、加熱中から焼入れまでの間に鋼線材Mの表面に炭化水素系ガスを直接吹付けて浸炭処理(浸炭工程)を同時に行う。たとえば、図5に示すように、鋼線材Mを回転可能な冶具60に固定し、鋼線材Mの周囲に高周波加熱コイル40、ばねの内側にガス供給穴を備えたノズル50を設置する。そして、冶具60を回転させることにより鋼線材Mを回転させながら、ノズル50を通してガスを供給して、コイルばねの表面が均一に焼入れおよび浸炭されるように行う。浸炭条件は第1実施形態と同様である。
各製造工程によってコイルばねのサンプルを作製し、耐疲労性の評価を行った。まず、表1に記載の化学成分を有し、残部が鉄および不可避不純物からなる硬引線およびオイルテンパー線を用意した。各線材の線径は表2に示す通りである。そして、硬引線またはオイルテンパー線に対して、図1(A)~(E)に示す製造工程(それぞれ、製造工程A~Eと表す)にしたがって、熱間成形法または冷間成形法によりばね指数6、有効部ピッチ角9°、有効部巻数4.25巻のコイルばねを作製した。
このようにして得たサンプルに対し、以下の通り諸性質を調査した。その結果を表3に示す。なお、比較例1については、コイリングは可能であったが、コイリング中に線材の座屈が生じ所定のばね形状が得られなかったため、評価を行わなかった。
ビッカース硬さ試験機(フューチャテック FM-600)を用いてコイルばねの線材横断面におけるコイル内径側で測定を行った。測定荷重は表面から深さ0.05mmまでは10gf、深さ0.05~0.1mmまでは25gf、深さ0.2mm以上の位置では200gfとした。
コイルばねの内径側表面において、線材の線軸方向に対し+45°方向(ばねに圧縮荷重を負荷した場合の略最大主応力方向)の圧縮残留応力を、X線回折型残留応力測定装置(リガク製)を用いて測定した。測定は、管球:Cr、コリメータ径:0.5mmとして行った。また、コイルばねに対して塩酸を用いて線材表面の全面化学研磨後上記測定を行い、これを繰返すことで深さ方向の残留応力分布を求め、その結果から表面から0.15、0.2、0.3、0.4mmの深さにおける無負荷時の圧縮残留応力、最大圧縮残留応力、クロッシングポイントを求めた。また、圧縮残留応力積分値は、深さと残留応力の関係図における、表面からクロッシングポイントまでの圧縮残留応力を積分することにより算出した。なお、一例として発明例12の残留応力分布を図6に示す。
コイルばねの線材横断面における内径側において表面C濃度およびC濃化層の厚さを測定した。測定にはEPMA(島津製作所 EPMA-1600)を用い、ビーム径1μm、測定ピッチ1μmとしてライン分析を行った。C濃化層厚さは、線材内部と同じC濃度となるまでの表面からの深さとした。なお、比較例9ではC濃化層を得られなかったため、表3にこれらの数値を記載していない。
前処理として、コイルばねのサンプルを500℃で1時間加熱した。そして、コイルばねの横断面の深さd/4の位置において、視野数を10箇所として、光学顕微鏡(NiKON ME600)を用いて倍率:1000倍でJIS G0551に準拠して測定を行い、旧オーステナイト粒平均結晶粒度番号Gを算出した。
非接触三次元形状測定装置(MITAKA NH-3)を用いてJIS B0601に準拠して表面粗さの測定を行った。測定条件は、測定倍率:100倍、測定距離:4mm、測定ピッチ:0.002mm、カットオフ値:0.8mmとした。
FE-SEM/EBSD(Electron Back Scatter Diffraction)法により、JEOL JSM-7000F(TSLソリューションズ OIM-Analysys Ver.4.6)を用いて、平均結晶粒径を測定した。ここで、測定はコイルばねの横断面の深さd/4の位置において行い、観察倍率10000倍で行い、方位角度差5°以上の境界を粒界として平均結晶粒径を算出した。
油圧サーボ型疲労試験機(鷺宮製作所)を用いて室温(大気中)において疲労試験を行った。試験応力:735±662MPa、周波数:20Hz、試験数:各8本であり、2千万回加振時の折損率(折損数/試験本数)で耐疲労性を評価した。
(1)硬さ
表3から分かるように、本発明では、内部硬さが570~700HVであると、高い耐疲労性を得ることができる。また、570~690HVであるとより好ましい。硬さがこのような範囲であると、破壊起点となる0.1~0.4mmの深さにおける圧縮残留応力を十分に得ることができる。このため、内部起点の破壊が防止され、高い耐疲労性が得られたと考えられる。また、比較例10の結果から、熱間成形法によって作製したコイルばねでも、硬さが570HV未満の場合は耐力が乏しく、十分な耐疲労性が得られない。したがって、本発明においては、硬さは570~700HVが好ましく、570~690HVがより好ましい。
同様の組成の線材を用い製造工程Aにより作製した発明例12、製造工程Bにより作製した発明例24、および製造工程Cにより作製した発明例25は、製造工程Dで作製し、焼鈍処理を行った比較例12と比べて、表面から深い位置での圧縮残留応力(-σR0.4)が大きい。これは、製造工程AまたはBによって作製した発明例では、冷間コイリングにおいて発生する引張残留応力(コイル内径側に残存)が、熱間コイリングにおいてはほとんど発生しないためである。また、製造工程Cにより作製した発明例25では、冷間コイリングにおいて発生した引張残留応力が、その後オーステナイト域まで加熱することで完全に解消するためである。つまり、冷間コイリングによる引張残留応力が残存したままの比較例12と比べ、発明例12、24、25では、ショットピーニングによって圧縮残留応力が表面から深くまで入り易い。このため、破壊起点となり易い0.1~0.4mm深さにおける圧縮残留応力が大きいため、耐疲労性を向上させることができる。
比較例9や10と比べ、発明例7~19では表面C濃度0.7~0.9重量%、C濃化層厚さ10μm以上の浸炭が施されており、それにより表面近傍での硬さが高いことから、表面近傍で高い圧縮残留応力が得られ、また、表面粗さも改善されるため高い耐疲労性を得ることができた。
単純組成の材質A、B、C、またはDからなる、製造工程Aによる発明例1、2、12および26では、Gは10番以上であり、結晶粒微細化効果のあるV量が多い高級鋼の材質Eを用いた比較例12、13と同等程度の微細結晶粒が得られている。単純組成からなる材質を用いてこのような微細結晶粒が得られたのは、高周波加熱による急速加熱によるものである。すなわち、高周波加熱によって短時間で加熱を行うことで旧オーステナイト粒の粗大化抑制、或いは微細化効果が得られた。このため、単純組成からなる発明例1、2、12および26において微細結晶粒を得ることができ、耐疲労性が良好である。
高い耐疲労性の得られた発明例1~29について、表面粗さRz(最大高さ)は9.0μm以下であり、所望する表面粗さRz20μm以下を十分に満足している。この表面粗さは、コイリング時におけるツール類との擦れや、ショットピーニング処理により形成されるものである。そしてショットピーニング処理により形成される表面粗さについては、線材の硬さと、ショットの粒径・硬さ・投射速度といった条件との組み合わせによりその大きさが決まる。よって、Rzが20μmを超えないようにショットピーニングの条件は適宜設定する必要がある。
単純組成の材質A、B、C、またはDからなる発明例1、2、12および26では、dGSは0.73~0.95μmであり、高級鋼である材質Eを用いた比較例12、13と同程度の平均結晶粒径であった。これは、前述のように、高周波加熱によって短時間で加熱を行うことが組織の粗大化抑制、あるいは微細化に繋がったためであり、その結果、発明例1、2、12および26では微細な平均結晶粒径が得られ耐疲労性が向上している。
線径を1.5~10mmの範囲で変えた発明例3~6、12、20~22では、製造工程Aでの熱間成形に際し異常変形等が無く、略円形のコイルばねを製作できた。線径を1.2mmとした比較例1ではコイリング中に線材が座屈し、コイリングツールから脱離し、コイルの製作が不可能であった。なお、線径を10mmとした発明例22では、線材中心近傍(具体的には、中心から2mm程度の範囲)において、完全なマルテンサイト組織が得られず、不完全焼入れ組織となっていた。これは、コイリング中に浸炭処理を行うため、高周波加熱の時間が短くなり、線材の径方向の均熱化に十分な加熱時間が得られなかったためである。ただし、中心近傍はコイルばねとしての使用上、ほとんど応力が掛らない範囲であり、その結果、発明例22においても高い耐久性が得られている。このことから、線径が10mmを超えると、前述した不完全焼入れ組織がコイルばねとしての使用上問題となる領域に達してしまうと分かる。したがって、本発明においては、線径は1.5~9.0mmがより好ましい。
線材表面での浸炭反応を効率的に行うためには、一定以上のガス吹付圧(線材表面での動圧)が必要であり、ガス吹付圧が低すぎるとC濃化層を得ることが出来ない。一方、ガス吹付圧が高すぎても線材表面温度が低下することによる浸炭反応性の低下を招くため好ましくない。また、線材温度が800℃である比較例9ではC濃化層が生成しなかった。したがって、浸炭反応の速度の観点から短時間での浸炭には線材温度は850℃以上が必要である。なお、線材温度が1150℃を超えると、加熱温度が高いため結晶粒度が悪化し、耐疲労性が低化し易くなる。これらのことから、ガス吹付圧は0.1kPa~5.0kPa、ガス吹付け時の線材温度は850~1150℃であることが好ましい。この条件によれば、発明例7~19が示す通りいずれも表面C濃度0.7重量%以上、かつC濃化層厚さ10μm以上が得られる。
Claims (24)
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%含み、残部が鉄および不可避不純物からなる円相当直径が2.5mm以上10mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の前記線材の表面から0.2mm深さでの圧縮残留応力が200MPa以上であると共に表面から0.4mm深さでの圧縮残留応力が60MPa以上であることを特徴とする圧縮コイルばね。
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%含み、残部が鉄および不可避不純物からなる円相当直径が2.5mm以上10mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の圧縮残留応力の値がゼロとなる前記線材の表面からの深さをクロッシングポイントとし、縦軸を残留応力、横軸を素線半径とした残留応力分布曲線において表面からクロッシングポイントまでの積分値をI-σRと表したとき、I-σRが160MPa・mm以上であることを特徴とする圧縮コイルばね。
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%含み、残部が鉄および不可避不純物からなる円相当直径が1.5mm以上3mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の前記線材の表面から0.15mm深さでの圧縮残留応力が300MPa以上であると共に表面から0.3mm深さでの圧縮残留応力が50MPa以上であることを特徴とする圧縮コイルばね。
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%含み、残部が鉄および不可避不純物からなる円相当直径が1.5mm以上3mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の圧縮残留応力の値がゼロとなる前記線材の表面からの深さをクロッシングポイントとし、縦軸を残留応力、横軸を素線半径とした残留応力分布曲線において表面からクロッシングポイントまでの積分値をI-σRと表したとき、I-σRが130MPa・mm以上であることを特徴とする圧縮コイルばね。
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%、Cr、B、Ni、Ti、Cu、Nb、V、Mo、Wのうち1種または2種以上を0.005~4.5%含み、残部が鉄および不可避不純物からなる円相当直径が2.5mm以上10mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の前記線材の表面から0.2mm深さでの圧縮残留応力が200MPa以上であると共に表面から0.4mm深さでの圧縮残留応力が60MPa以上であることを特徴とする圧縮コイルばね。
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%、Cr、B、Ni、Ti、Cu、Nb、V、Mo、Wのうち1種または2種以上を0.005~4.5%含み、残部が鉄および不可避不純物からなる円相当直径が2.5mm以上10mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の圧縮残留応力の値がゼロとなる前記線材の表面からの深さをクロッシングポイントとし、縦軸を残留応力、横軸を素線半径とした残留応力分布曲線において表面からクロッシングポイントまでの積分値をI-σRと表したとき、I-σRが160MPa・mm以上であることを特徴とする圧縮コイルばね。
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%、Cr、B、Ni、Ti、Cu、Nb、V、Mo、Wのうち1種または2種以上を0.005~4.5%含み、残部が鉄および不可避不純物からなる円相当直径が1.5mm以上3mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の前記線材の表面から0.15mm深さでの圧縮残留応力が300MPa以上であると共に表面から0.3mm深さでの圧縮残留応力が50MPa以上であることを特徴とする圧縮コイルばね。
- 重量%で、Cを0.45~0.80%、Siを0.15~2.50%、Mnを0.3~1.0%、Cr、B、Ni、Ti、Cu、Nb、V、Mo、Wのうち1種または2種以上を0.005~4.5%含み、残部が鉄および不可避不純物からなる円相当直径が1.5mm以上3mm以下である鋼線材を用いた圧縮コイルばねにおいて、任意の線材横断面における内部硬さが570~700HVであり、表層部に前記鋼線材に含まれるCの平均濃度を超えるC濃化層を有し、前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の圧縮残留応力の値がゼロとなる前記線材の表面からの深さをクロッシングポイントとし、縦軸を残留応力、横軸を素線半径とした残留応力分布曲線において表面からクロッシングポイントまでの積分値をI-σRと表したとき、I-σRが130MPa・mm以上であることを特徴とする圧縮コイルばね。
- 前記線材のコイルばね内径側のばねに圧縮荷重を負荷した場合に生じる略最大主応力方向において、無負荷時の最大圧縮残留応力が900MPa以上であることを特徴とする請求項1~8のいずれかに記載の圧縮コイルばね。
- JIS G0551に規定される旧オーステナイト粒平均結晶粒度番号が10番以上であることを特徴とする請求項1~9のいずれかに記載の圧縮コイルばね。
- SEM/EBSD法を用いて測定した平均結晶粒径(方位角度差5°以上の境界を粒界とする)が2.0μm以下であることを特徴とする請求項1~10のいずれかに記載の圧縮コイルばね。
- 前記C濃化層の硬さが内部硬さよりも50HV以上高いことを特徴とする請求項1~11のいずれかに記載の圧縮コイルばね。
- 前記C濃化層における最大C濃度が0.7~0.9重量%であり、前記C濃化層の厚さが0.01~0.1mmであることを特徴とする請求項1~12のいずれかに記載の圧縮コイルばね。
- Crを0.5~2.0重量%含むことを特徴とする請求項5~8のいずれかに記載の圧縮コイルばね。
- 表面粗さRz(最大高さ)が20μm以下であることを特徴とする請求項1~14のいずれかに記載の圧縮コイルばね。
- 前記圧縮残留応力がショットピーニング処理により付与されていることを特徴とする請求項1~15のいずれかに記載の圧縮コイルばね。
- 前記ショットピーニング処理が、粒径0.6~1.2mmのショットによる第1のショットピーニング処理と、粒径0.2~0.8mmのショットによる第2のショットピーニング処理と、粒径0.02~0.30mmのショットによる第3のショットピーニング処理からなる多段ショットピーニング処理であることを特徴とする請求項16に記載の圧縮コイルばね。
- ばね形状が、円筒形、または、円錐形、釣鐘形、鼓形、樽形等の異形であることを特徴とする請求項1~17のいずれかに記載の圧縮コイルばね。
- コイルばね成形機により鋼線材を熱間成形するコイリング工程と、コイリングした後に切離され温度が未だオーステナイト域にあるコイルをそのまま焼入れする焼入れ工程と、コイルを調質する焼戻し工程と、線材表面に圧縮残留応力を付与するショットピーニング工程と、セッチング工程とを順に行う圧縮コイルばねの製造方法において、
前記コイルばね成形機は、連続的に鋼線材を供給するためのフィードローラと、鋼線材をコイル状に成形するコイリング部と、鋼線材を所定巻数コイリングした後に後方より連続して供給されてくる鋼線材とを切断するための切断手段とを有し、
前記コイリング部は、前記フィードローラにより供給された鋼線材を加工部の適切な位置へ誘導するためのワイヤガイドと、前記ワイヤガイドを経由して供給された鋼線材をコイル形状に加工するためのコイリングピンもしくはコイリングローラからなるコイリングツールと、ピッチを付けるためのピッチツールとを備えており、
前記コイルばね成形機は、さらに、前記フィードローラの出口から前記コイリングツールの間に鋼線材を2.5秒以内でオーステナイト域まで昇温する加熱手段を有し、
加熱中から焼入れまでの間に鋼線材表面に炭化水素系ガスを直接吹付ける浸炭工程を行うことを特徴とする圧縮コイルばねの製造方法。 - 前記加熱手段が高周波加熱であり、前記ワイヤガイド内における鋼線材の通過経路上若しくは前記ワイヤガイドにおける鋼線材出口側末端と前記コイリングツールとの空間における鋼線材の通路経路上に鋼線材と同心となるように高周波加熱コイルが配置されていることを特徴とする請求項19に記載の圧縮コイルばねの製造方法。
- 鋼線材の表層部にC濃化層を形成する浸炭工程と、コイルばね成形機により鋼線材を熱間成形するコイリング工程と、コイリングした後に切離され温度が未だオーステナイト域にあるコイルをそのまま焼入れする焼入れ工程と、コイルを調質する焼戻し工程と、線材表面に圧縮残留応力を付与するショットピーニング工程と、セッチング工程とを順に行う圧縮コイルばねの製造方法において、
前記浸炭工程におけるC濃化層を形成する手段が、加熱した鋼線材表面に炭化水素系ガスを直接吹付ける方法であり、
前記コイリング工程に用いる前記コイルばね成形機が、連続的に鋼線材を供給するためのフィードローラと、鋼線材をコイル状に成形するコイリング部と、鋼線材を所定巻数コイリングした後に後方より連続して供給されてくる鋼線材とを切断するための切断手段とを有し、
前記コイリング部は、前記フィードローラにより供給された鋼線材を加工部の適切な位置へ誘導するためのワイヤガイドと、前記ワイヤガイドを経由して供給された鋼線材をコイル形状に加工するためのコイリングピンもしくはコイリングローラからなるコイリングツールと、ピッチを付けるためのピッチツールとを備え、
前記コイルばね成形機は、さらに、前記フィードローラの出口から前記コイリングツールの間に鋼線材を2.5秒以内でオーステナイト域まで昇温する加熱手段を有し、
前記加熱手段は高周波加熱であり、前記ワイヤガイド内における鋼線材の通過経路上若しくは前記ワイヤガイドにおける鋼線材出口側末端と前記コイリングツールとの空間における鋼線材の通過経路上に鋼線材と同心となるように高周波加熱コイルが配置されており、
前記浸炭工程と前記コイリング工程が途中で鋼線材の切離がない連続した工程であることを特徴とする請求項1~18のいずれかに記載の圧縮コイルばねの製造方法。 - コイルばね成形機により鋼線材を成形するコイリング工程と、コイルを20秒以内でオーステナイト域まで昇温し焼入れを行う加熱焼入れ工程と、コイルを調質する焼戻し工程と、線材表面に圧縮残留応力を付与するショットピーニング工程と、セッチング工程とを順に行う圧縮コイルばねの製造方法において、
前記加熱焼入れ工程における加熱手段が高周波加熱であり、
加熱中から焼入れまでの間に鋼線材表面に炭化水素系ガスを直接吹付ける浸炭工程を行うことを特徴とする請求項1~18のいずれかに記載の圧縮コイルばねの製造方法。 - 前記炭化水素系ガスを吹付ける時点の鋼線材表面温度が850~1150℃であり、且つ、鋼線材表面部における前記炭化水素系ガスの動圧が0.1~5.0kPaであることを特徴とする請求項19~22のいずれかに記載の圧縮コイルばねの製造方法。
- 前記炭化水素系ガスの主成分は、メタン、ブタン、プロパン、アセチレンのいずれかであることを特徴とする請求項19~23のいずれかに記載の圧縮コイルばねの製造方法。
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Also Published As
Publication number | Publication date |
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JP5361098B1 (ja) | 2013-12-04 |
EP2896712B1 (en) | 2019-08-07 |
JP2014055343A (ja) | 2014-03-27 |
KR20150054969A (ko) | 2015-05-20 |
US20150252863A1 (en) | 2015-09-10 |
CN104619878B (zh) | 2016-11-16 |
KR102191407B1 (ko) | 2020-12-15 |
EP2896712A4 (en) | 2016-04-27 |
KR20200010619A (ko) | 2020-01-30 |
EP2896712A1 (en) | 2015-07-22 |
US9752636B2 (en) | 2017-09-05 |
CN104619878A (zh) | 2015-05-13 |
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