WO2017170540A1 - Carbonitrided component having excellent surface fatigue strength and bending fatigue strength, and method for manufacturing same - Google Patents

Carbonitrided component having excellent surface fatigue strength and bending fatigue strength, and method for manufacturing same Download PDF

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Publication number
WO2017170540A1
WO2017170540A1 PCT/JP2017/012621 JP2017012621W WO2017170540A1 WO 2017170540 A1 WO2017170540 A1 WO 2017170540A1 JP 2017012621 W JP2017012621 W JP 2017012621W WO 2017170540 A1 WO2017170540 A1 WO 2017170540A1
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fatigue strength
residual stress
amount
compressive residual
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PCT/JP2017/012621
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French (fr)
Japanese (ja)
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亮廣 松ヶ迫
武浩 酒道
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株式会社神戸製鋼所
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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
    • 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
    • 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
    • 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
    • C21D9/32—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for gear wheels, worm wheels, or the like
    • 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
    • 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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present disclosure relates to a carbonitrided component having excellent surface fatigue strength and bending fatigue strength, and a method for manufacturing the same.
  • AT automatic transmissions
  • a planetary gear mechanism In order to meet the needs of higher engine output, smaller parts and lighter parts, ATs are being multi-staged. However, if the load torque is the same with the unit size unchanged, the tooth width will be reduced and the gears will be reduced. The load on is increased. Therefore, it is strongly desired to provide a gear excellent in fatigue strength (both surface fatigue strength and bending fatigue strength).
  • Patent Document 1 discloses a carburized part in which fatigue strength (bending fatigue strength) in the “low to medium cycle range” is significantly improved and a method for manufacturing the same.
  • Patent Document 2 discloses a carburized part or a carbonitrided part having excellent surface fatigue strength.
  • Patent Document 1 does not consider the surface fatigue strength, and the surface roughness Rz [maximum height roughness Rz defined in JIS B 0601 (2001)] of the carburized part in the example is about 6 to 11 ⁇ m. And very big.
  • Patent Document 2 the value of internal compressive residual stress is insufficient, and the surface fatigue strength is not sufficiently strengthened.
  • Patent Documents 1 and 2 it is not possible to realize a component excellent in surface fatigue strength and bending fatigue strength that can sufficiently meet recent demands for downsizing and high stress load.
  • Embodiments of the present invention have been made in view of the above circumstances, and an object of the present invention is to provide a carbonitrided component excellent in both surface fatigue strength and bending fatigue strength, and a method for manufacturing the same.
  • a carbonitriding component excellent in surface fatigue strength and bending fatigue strength according to an embodiment of the present invention that has solved the above problems is a carbonitriding component having a carbonitriding layer on the surface of a steel material, and the steel material has a mass %, C: 0.15 to 0.25%, Si: 0.4 to 1%, Mn: 0.30 to 0.6%, P: more than 0%, 0.02% or less, S: 0% More than 0.02%, Cr: 1.2 to 2%, Mo: 0.3 to 0.5%, N: more than 0%, 0.015% or less, the balance from iron and inevitable impurities
  • the carbonitrided layer has a hardness of 850 HV or more at a depth of 25 ⁇ m from the surface, an absolute value of a compressive residual stress value of 200 MPa or more at a depth of 200 ⁇ m from the surface, and a depth of 200 ⁇ m from the surface.
  • the absolute value of the maximum compressive residual stress value is 850 MPa or more, and JIS
  • the steel material is further in mass%, V: more than 0%, 0.5% or less, Ti: more than 0%, 0.5% or less, Nb: more than 0%, 0.5 % Or less, and Al: at least one element selected from the group consisting of more than 0% and 0.5% or less.
  • the steel material further includes, in mass%, Cu: more than 0%, 0.3% or less, Ni: more than 0%, 0.3% or less, and B: more than 0%,. It contains at least one element selected from the group consisting of 01% or less.
  • a carbonitriding component manufacturing method that has solved the above problems is a method for manufacturing the carbonitriding component according to any one of the above, and after the steel material is carbonitriding
  • the gist is that the processing is performed in the order of shot peening using shot grains having a particle diameter of more than 300 ⁇ m, polishing, and shot peening using shot grains having a particle diameter of 300 ⁇ m or less.
  • FIG. 1A is a diagram showing the shape of a small roller among the roller pitching test pieces used in this example.
  • FIG. 1B is a diagram showing the shape of a large roller among the roller pitching test pieces used in this example.
  • FIG. 2 is a diagram showing the shape of a four-point bending test piece used in this example.
  • the Si, Cr, and Mo components are optimized to increase the temper softening resistance.
  • the surface hardness specifically, the hardness at a depth of 25 ⁇ m from the surface
  • the absolute value of the internal compressive residual stress is increased to 200 MPa or more to suppress breakage at the internal origin.
  • the absolute value of the surface compressive residual stress (specifically, the maximum compressive residual stress value from the surface to the 200 ⁇ m depth position) is increased to 850 MPa or more to suppress the fracture at the surface starting point.
  • the surface roughness (ten-point average roughness Rz in the embodiment of the present invention) is reduced to 2.5 ⁇ m or less to suppress the breakage at the surface starting point.
  • the part in order to obtain a part that satisfies all the requirements (i) to (v), the part was manufactured as follows. First, carbon steel was subjected to carbonitriding treatment to the steel material whose components were appropriately controlled as in (i) above, to ensure the surface hardness of (ii) above and to increase the softening resistance at the time of temperature rise.
  • a method of performing a polishing process during two-stage shot peening using shot grains having different particle diameters is effective. It has been found. Specifically, first, shot peening is performed with shot grains having a large particle diameter (projection material) to secure the internal compressive residual stress of (iii), and then polishing is performed to obtain the surface roughness (v) ( Rz) is reduced. Thereafter, it was found that if shot peening was performed with small-sized shot grains to ensure the surface compressive residual stress of (iv) above, a desired part could be obtained, and an embodiment of the present invention was completed.
  • Patent Document 1 described above also describes that it is preferable to perform two-stage shot peening, but it is disclosed that the polishing process is performed between the first stage and the second stage as in the embodiment of the present invention. It has not been. So far, there is a technique for performing shot peening twice as in Patent Document 1, but generally, shot peening is continuously performed from the viewpoint of productivity and the like, and as in the embodiment of the present invention, A polishing process is not interposed. As proved in the column of Examples described later, it is confirmed that when the polishing treatment is not performed, Rz defined in the embodiment of the present invention is not obtained and becomes high, and the surface fatigue strength is lowered.
  • a carbonitriding component has a carbonitriding layer on the surface of a steel material, and the steel material is C: 0.15 to 0.25%, Si: 0.4 to 1%, Mn: 0.30 to 0.6%, P: more than 0%, 0.02% or less, more than 0%, S: 0.02% or less, Cr: 1.2 to 2% , Mo: 0.3 to 0.5%, N: more than 0%, 0.015% or less, the balance is made of iron and inevitable impurities, and the carbonitrided layer has a depth of 25 ⁇ m from the surface.
  • the hardness is 850 HV or more
  • the absolute value of the compressive residual stress value at the 200 ⁇ m depth position from the surface is 200 MPa or more
  • the absolute value of the maximum compressive residual stress value from the surface to the 200 ⁇ m depth position is 850 MPa or more.
  • the ten-point average roughness Rz specified by B0601 (1994) is 2.5 ⁇ m or less. There is a feature in the point.
  • the hardness at a depth of 25 ⁇ m from the surface is simply the surface hardness
  • the absolute value of the compressive residual stress at the depth of 200 ⁇ m from the surface is simply the internal compressive residual stress value
  • the position of the depth of 200 ⁇ m from the surface is simply abbreviated as the surface compressive residual stress value.
  • the component according to the embodiment of the present invention is premised on having a carbonitriding layer on the surface. Thereby, surface hardness can be raised to 850 HV or more. On the other hand, it is demonstrated in the column of the example described later that the desired surface hardness cannot be obtained by a normal carburizing treatment.
  • the surface hardness is set to 850 HV or more in terms of Vickers hardness.
  • 850 HV or more is 875 HV or more, More preferably, it is 900 HV or more.
  • the upper limit is not particularly limited from the above viewpoint, but it is preferably 1100 HV or less in consideration of applying residual stress in shot peening.
  • the absolute value of the compressive residual stress value at 200 ⁇ m depth from the surface is 200 MPa or more
  • the application of internal compressive residual stress is useful for suppressing fracture at the internal starting point. That is, when the load increases due to surface fatigue, spalling failure that breaks at the internal origin may occur, but spalling failure can be suppressed by increasing the internal compressive residual stress value.
  • the absolute value (internal compressive residual stress value) of the compressive residual stress value at a depth of 200 ⁇ m from the surface is set to 200 MPa or more. Preferably it is 210 MPa or more, More preferably, it is 220 MPa or more. In order to give a high compressive residual stress to the inside, it is effective to perform shot peening using shot grains having a particle size of more than 300 ⁇ m and a large particle size, as will be described later.
  • the absolute value of the maximum compressive residual stress value from the surface to the 200 ⁇ m depth position is 850 MPa or more
  • the application of surface compressive residual stress is effective in improving bending fatigue strength and surface fatigue strength (pitting).
  • the absolute value of the maximum compressive residual stress value (surface compressive residual stress value) from the surface to the 200 ⁇ m depth position is set to 850 MPa or more.
  • it is 875 MPa or more, More preferably, it is 900 MPa or more.
  • the “maximum compressive residual stress value from the surface to a 200 ⁇ m depth position” is the maximum value of the compressive residual stress value up to the depth position, and the maximum value is obtained from the surface, generally less than 50 ⁇ m. Position.
  • it is effective to perform shot peening using shot grains having a grain size of 300 ⁇ m or less and a small grain size.
  • Rz is set to 2.5 ⁇ m or less.
  • Rz is set to 2.5 ⁇ m or less.
  • Rz is 2.3 micrometers or less, More preferably, it is 2.0 micrometers or less.
  • the lower limit is not particularly limited from the above viewpoint, but is preferably 0.5 ⁇ m or more in consideration of processing costs and the like. In order to reduce Rz, as described later, it is effective to perform a polishing process during shot peening.
  • C 0.15-0.25%
  • the C content is 0.15% or more.
  • the C content is preferably 0.16% or more, and more preferably 0.17% or more. However, if the amount of C becomes excessive, machinability and toughness deteriorate, so the amount of C is made 0.25% or less.
  • the C content is preferably 0.24% or less, and more preferably 0.23% or less.
  • Si 0.4 to 1% Si is useful as an element for improving temper softening resistance. Specifically, in a gear or the like, the temperature of the contact portion rises during driving and the hardness decreases, but by adding Si, softening at the time of temperature rise is suppressed and the surface hardness can be maintained. As a result, the surface fatigue strength such as pitting and the wear resistance are improved.
  • the Si amount is set to 0.4% or more.
  • the amount of Si is preferably 0.45% or more, and more preferably 0.50% or more. However, if the Si amount becomes excessive, the machinability deteriorates, so the Si amount is set to 1% or less.
  • the amount of Si is preferably 0.8% or less, and more preferably 0.7% or less.
  • Mn 0.30 to 0.6% Mn is a hardenability improving element, and when the amount of Mn is less than 0.30%, FeS is formed and productivity is lowered. Therefore, the amount of Mn is set to 0.30% or more.
  • the amount of Mn is preferably 0.33% or more, and more preferably 0.35% or more. However, if the amount of Mn becomes excessive, the machinability decreases, so the amount of Mn is set to 0.6% or less.
  • the amount of Mn is preferably 0.5% or less, and more preferably 0.45% or less.
  • P more than 0% and 0.02% or less
  • P is an element inevitably contained as an impurity in the manufacturing process, etc., segregating at the grain boundary, workability, fatigue characteristics (surface fatigue strength and bending fatigue strength), etc. Reduce. Therefore, the P content is 0.02% or less.
  • extremely reducing the amount of P causes an increase in steelmaking costs.
  • S more than 0% and 0.02% or less S is an element that is inevitably contained as an impurity in the production process, etc., as in the case of P, and precipitates as MnS to exhibit fatigue properties (surface fatigue strength and bending fatigue strength). Reduce impact characteristics. Therefore, the S content is 0.02% or less. The smaller the amount of S, the better. It is preferably 0.015% or less, and more preferably 0.010% or less. However, extremely reducing the amount of S causes an increase in steelmaking costs.
  • Cr acts as a hardenability improving element like Mn, and is also useful as a temper softening resistance improving element like Si.
  • the Cr content is set to 1.2% or more.
  • the amount of Cr is preferably 1.25% or more, and more preferably 1.30% or more. However, if the amount of Cr becomes excessive, the cost increases and the machinability decreases, so the Cr amount is set to 2% or less.
  • the amount of Cr is preferably 1.8% or less, and more preferably 1.5% or less.
  • Mo 0.3 to 0.5% Mo is useful as a hardenability improving element and a temper softening resistance element like Cr. In order to effectively exhibit these actions, the Mo amount is set to 0.3% or more.
  • the Mo amount is preferably 0.32% or more, and more preferably 0.35% or more. However, if the amount of Mo becomes excessive, the cost increases and the machinability decreases, so the amount of Mo is set to 0.5% or less.
  • the Mo amount is preferably 0.48% or less, and more preferably 0.45% or less.
  • N more than 0% and 0.015% or less N is an element that is inevitably contained as an impurity in the manufacturing process and the like, and lowers workability by strain aging. Therefore, the N content is 0.015% or less.
  • extremely reducing the amount of N causes an increase in steelmaking costs.
  • the steel material constituting the carbonitriding component according to the embodiment of the present invention satisfies the above components, and the balance is iron and unavoidable impurities.
  • the steel material can further contain the following selective components as required.
  • V more than 0%, 0.5% or less
  • Ti more than 0%, 0.5% or less
  • Nb more than 0%, 0.5% or less
  • Al more than 0%, 0.5% or less
  • At least one element selected from the group These elements are elements that improve toughness and improve fatigue strength (surface fatigue strength and bending fatigue strength) by grain refinement after carbonitriding.
  • the V amount 0.05% or more
  • the Nb amount 0.05% or more
  • Al 0.01% or more.
  • the above-mentioned action is saturated, but also coarse precipitates are formed and the strength is lowered.
  • V amount 0.5% or less, Ti amount: 0.5% or less, Nb amount: 0.5% or less, and Al amount: 0.5% or less. More preferably, the V amount is 0.45% or less, the Ti amount is 0.45% or less, the Nb amount is 0.45% or less, and the Al amount is 0.45% or less. 4% or less, Ti content: 0.4% or less, Nb content: 0.4% or less, Al content: 0.4% or less. These elements may be added alone or in combination of two or more.
  • Cu more than 0%, 0.3% or less
  • Ni more than 0%, 0.3% or less
  • B more than 0%, 0.01% or less.
  • the amount of Cu is 0.25% or less
  • the amount of Ni is 0.25% or less
  • the amount of B is 0.008% or less
  • the amount of Cu is 0.2% or less
  • the amount of Ni is 0.00. 2% or less
  • shot peening primary shot peening
  • polishing shot having a grain size of 300 ⁇ m or less. It has a gist in that it is processed in the order of shot peening (secondary shot peening) using grains.
  • carbon steel is carbonitrided with the above composition.
  • carbon potential for example, after carburizing under conditions of 900 to 980 ° C., carbon potential of 0.7 to 0.9 mass%, 100 to 500 minutes, 800 to 900 ° C., Nitriding was performed under conditions of carbon potential 0.7 to 0.9 mass%, ammonia 3 to 8 vol%, 100 to 500 minutes, and then oil-cooled at 60 to 100 ° C, 100 to 200 ° C, 60 to 180. It is preferable to perform carbonitriding under the condition of a minute tempering treatment.
  • shot peening using large grain size shot grains (primary shot grains) having a grain size of more than 300 ⁇ m is performed.
  • shot peening using large grain size shot grains (primary shot grains) having a grain size of more than 300 ⁇ m is performed.
  • a high residual stress is applied to the inside (at a depth of 200 ⁇ m from the surface).
  • the surface roughness Rz is large.
  • the particle size of the primary shot grains to be used is not particularly limited as long as it is in the above range, and is preferably 400 ⁇ m or more and 1200 ⁇ m or less, for example.
  • polish In the embodiment of the present invention, it is important to perform the polishing treatment before the next secondary shot peening, whereby the surface is removed by about 20 to 50 ⁇ m, and the surface roughness Rz after the polishing is the embodiment of the present invention. And the surface fatigue strength is improved.
  • the polishing may be mechanical polishing using a grindstone, sandpaper or the like. Further, electrolytic polishing or chemical polishing may be used.
  • shot peening using small grain size shot grains (secondary shot grains) having a grain size of 300 ⁇ m or less is performed.
  • the surface roughness Rz does not change much and remains reduced to the desired level, and a high maximum compressive residual stress is applied to the surface.
  • the particle size of the secondary shot particles to be used is not particularly limited as long as it is in the above range, and is preferably 20 ⁇ m or more and 200 ⁇ m or less, for example.
  • the hardness of the shot grains may be the same as in the examples described later, but in consideration of the residual stress application efficiency and the like, the secondary shot grains are preferably harder than the primary shot grains.
  • Steel type A in Table 1 is an SCr420H equivalent steel of conventional steel, and is a steel type that has a small amount of Si, Cr, Mo, and a large amount of Mn compared to the embodiment of the present invention.
  • roller pitching test pieces having the shapes shown in FIGS. 1A and 1B and 4-point bending test pieces having the shapes shown in FIG. 2 were prepared as follows.
  • test pieces thus obtained were subjected to heat treatment (carburizing treatment or carbonitriding treatment) and processing (primary shot peening, polishing, secondary shot peening) as shown in Table 2.
  • heat treatment carburizing treatment or carbonitriding treatment
  • processing primary shot peening, polishing, secondary shot peening
  • Carburization was carried out under the conditions of 950 ° C., carbon potential 0.8 mass%, 140 minutes, then held at 845 ° C., carbon potential 0.8 mass%, 30 minutes, then oil cooled at 80 ° C., 160 A tempering treatment at 120 ° C. for 120 minutes was performed.
  • Carburizing and nitriding Carburizing was performed under conditions of 940 ° C., carbon potential of 0.85 mass%, 300 minutes, and then nitriding was performed under conditions of 840 ° C., carbon potential of 0.85 mass%, ammonia 5 volume%, and 240 minutes. Then, oil cooling was performed at 80 ° C., and tempering treatment was performed at 160 ° C. for 120 minutes.
  • Primary shot peening Primary (large particle size) shot peening was performed using a projection material having a particle size of 1000 ⁇ m and an average hardness of 800 HV so that the arc height was 0.2 mmC and the coverage was 300% or more.
  • polishing For the small roller for roller pitching test, the surface of the test piece was polished by 50 ⁇ m by polishing using a grindstone, and finished to a diameter of 26.0 mm.
  • Secondary shot peening Secondary (fine particle) shot peening was performed using a projection material having a particle size of 300 ⁇ m and an average hardness of 800 HV so that the arc height was 0.2 mmA and the coverage was 300% or more.
  • the surface hardness, compressive residual stress, surface fatigue strength, and bending fatigue strength of each test piece subjected to the above treatment were measured by the following methods.
  • the surface Vickers hardness was measured based on “Vickers hardness test-test method” in JIS Z 2244 (2003) using the small roller for roller pitching test subjected to the above treatment. Specifically, the test portion of the small roller is cut by a plane perpendicular to the axial direction of the small roller, the cut surface is mirror-polished, and the test force is 1 at a depth of 25 ⁇ m from the surface of the test portion. .961N was measured at 10 points, and the arithmetic average value was defined as the surface Vickers hardness.
  • the compression residual stress in each depth position was measured by X-ray using the small roller for roller pitching test which performed said process. Specifically, using a Position-Sensitive Proportional Counter (PSPC) micro-part X-ray stress measurement apparatus, electrolysis is performed from the test part surface of the small roller to positions of 0 ⁇ m (surface), 10 ⁇ m, 25 ⁇ m, 50 ⁇ m, 100 ⁇ m, and 200 ⁇ m, respectively. The residual stress was measured after polishing.
  • the measurement conditions of the PSPC minute part X-ray stress measurement apparatus are collimator diameter: ⁇ 1 mm, measurement site: axial center position, measurement direction: circumferential direction.
  • the surface fatigue strength was measured by performing a roller pitching test with an “RP-201 type” roller pitching tester (manufactured by Komatsu Engineering Co., Ltd.). Specifically, the roller pitching test was performed using the small roller and the large roller for the roller pitching test, which were subjected to the above treatment, under the conditions of an oil for automatic as a lubricating oil, an oil temperature of 120 ° C., and a slip ratio of ⁇ 40%. An S-repetition number N diagram was prepared, and the pitching strength (surface fatigue strength) was evaluated by the strength of 10 million times (meaning the maximum stress that does not break when tested 10 million times).
  • the strength exceeding 4.0 GPa is not measured in consideration of the load on the testing machine.
  • the surface fatigue strength obtained in this way is 3.6 GPa or more [about 1.7 times higher than steel type A in Table 1 (SCR420H equivalent steel of conventional steel)]. The fatigue strength was evaluated as excellent.
  • No. in Table 3 Nos. 2 to 11 and 18 are examples manufactured using the steel types shown in Table 1 that satisfy the requirements of the embodiment of the present invention under the conditions of the embodiment of the present invention, and are excellent in both surface fatigue strength and bending fatigue strength. .
  • No. No. 12 is an example using the steel type L of Table 1 with a small amount of C and Si and no Mo, and the surface fatigue strength was lowered.
  • No. No. 13 is an example using the steel type M of Table 1 with a small amount of Mn, a large amount of S, and no Mo, and since no cracks occurred during the test, no measurement was performed (each of the values in Table 3). Items"-").
  • No. 14 is an example using the steel type N of Table 1 with a large amount of P, and the surface fatigue strength and the bending fatigue strength decreased.
  • No. 15 is an example using the steel type O of Table 1 with a small amount of Cr, and the surface fatigue strength was lowered.
  • No. 16 is an example using the steel type P of Table 1 with a small amount of Mo, and the surface fatigue strength decreased.
  • No. No. 17 is an example using the steel type Q in Table 1 with a large amount of N, and cracking occurred during the test, and thus no measurement was performed (each item in Table 3 is “ ⁇ ”).
  • No. Nos. 19 to 23 are examples in which the steel type R in Table 1 that satisfies the requirements of the embodiment of the present invention was used, but was manufactured under conditions that did not satisfy the requirements of the embodiment of the present invention.
  • No. 19 is an example in which carburizing was performed instead of carbonitriding, and the surface hardness decreased.
  • No. No. 20 is an example in which the first shot peening was not performed, and the internal compressive residual stress was lowered, and thus the surface fatigue strength was lowered.
  • No. No. 21 is an example in which the second shot peening was not performed, and since the surface compressive residual stress was reduced, both the surface fatigue strength and the bending fatigue strength were reduced.
  • No. No. 22 was an example in which shot peening was not performed at all, and both the internal compressive residual stress and the surface compressive residual stress were reduced, and both the surface fatigue strength and the bending fatigue strength were reduced.
  • No. No. 23 is an example in which the second shot peening was performed without polishing after the first shot peening, and the surface roughness Rz increased and the surface fatigue strength decreased.
  • a carbonitriding component having a carbonitriding layer on the surface of a steel material The steel material is mass%, C: 0.15-0.25%, Si: 0.4-1%, Mn: 0.30 to 0.6%, P: more than 0%, 0.020% or less, S: more than 0%, 0.02% or less, Cr: 1.2-2%, Mo: 0.3 to 0.5%, N: more than 0% and 0.015% or less, with the balance consisting of iron and inevitable impurities,
  • the carbonitriding layer is Hardness at a depth of 25 ⁇ m from the surface is 850 HV or more, The absolute value of the compressive residual stress value at a depth of 200 ⁇ m from the surface is 200 MPa or more, The absolute value of the maximum compressive residual stress value from the surface to the 200 ⁇ m depth position is 850 MPa or more,
  • the steel material is further in mass%, V: more than 0%, 0.5% or less, Ti: more than 0%, 0.5% or less,
  • the steel material is further in mass%, Cu: more than 0%, 0.3% or less,
  • the carbonitrided part according to aspect 1 or 2 comprising at least one element selected from the group consisting of Ni: more than 0% and not more than 0.3%, and B: more than 0% and not more than 0.01%.

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Abstract

The carbonitrided component pertaining to an embodiment of the present invention has a carbonitrided layer on the surface of a steel material, wherein the steel material contains a predetermined ingredient, and the carbonitrided layer has a hardness of 850 HV or greater at a position a depth of 25 µm from the surface thereof, the absolute value of the compressive residual stress thereof at a position a depth of 200 µm from the surface thereof is 200 MPa or greater, the absolute value of the maximum compressive residual stress to a position a depth of 200 µm from the surface thereof is 850 MPa or greater, and the ten-point average roughness Rz specified by JIS B0601 (1994) thereof satisfies a value of 2.5 µm or less.

Description

面疲労強度および曲げ疲労強度に優れた浸炭窒化部品、並びにその製造方法Carbonitrided parts excellent in surface fatigue strength and bending fatigue strength, and manufacturing method thereof
　本開示は、面疲労強度および曲げ疲労強度に優れた浸炭窒化部品、並びにその製造方法に関する。 The present disclosure relates to a carbonitrided component having excellent surface fatigue strength and bending fatigue strength, and a method for manufacturing the same.
　車両などに搭載される変速機は、プラネタリーギヤ（遊星歯車）機構で変速を行なうオートマチックトランスミッション（ＡＴ）が主流である。エンジンの高出力化、部品の小型軽量化などのニーズに対応するため、ＡＴの多段化が進められているが、ユニットサイズをそのままにして負荷トルクが同等の場合、歯幅が減少して歯車への負荷が増大する。そのため、疲労強度（面疲労強度および曲げ疲労強度の両方）に優れた歯車の提供が強く望まれている。 2. Description of the Related Art Transmissions mounted on vehicles and the like are mainly automatic transmissions (AT) in which a planetary gear mechanism is used. In order to meet the needs of higher engine output, smaller parts and lighter parts, ATs are being multi-staged. However, if the load torque is the same with the unit size unchanged, the tooth width will be reduced and the gears will be reduced. The load on is increased. Therefore, it is strongly desired to provide a gear excellent in fatigue strength (both surface fatigue strength and bending fatigue strength).
　例えば特許文献１には、「低～中サイクル域」における疲労強度（曲げ疲労強度）を大幅に向上させた浸炭部品とその製造方法が開示されている。また、特許文献２には、面疲労強度に優れた浸炭部品または浸炭窒化部品が開示されている。 For example, Patent Document 1 discloses a carburized part in which fatigue strength (bending fatigue strength) in the “low to medium cycle range” is significantly improved and a method for manufacturing the same. Patent Document 2 discloses a carburized part or a carbonitrided part having excellent surface fatigue strength.
ＷＯ２０１０／１３７６０７号パンフレットWO2010 / 137607 pamphlet 特開２００８－２６１０３７号公報JP 2008-261037 A
　しかしながら、上記特許文献１では面疲労強度について考慮しておらず、実施例における浸炭部品の表面粗さＲｚ［ＪＩＳ Ｂ ０６０１（２００１）に規定される最大高さ粗さＲｚ］は約６～１１μｍと、非常に大きい。 However, the above-mentioned Patent Document 1 does not consider the surface fatigue strength, and the surface roughness Rz [maximum height roughness Rz defined in JIS B 0601 (2001)] of the carburized part in the example is about 6 to 11 μm. And very big.
　また、上記特許文献２では、内部圧縮残留応力の値が不足しており、面疲労強度の強化が十分でない。 Further, in Patent Document 2, the value of internal compressive residual stress is insufficient, and the surface fatigue strength is not sufficiently strengthened.
　よって、上記特許文献１、２では、近年の小型化、高応力負荷などの要請に十分対応可能な、面疲労強度および曲げ疲労強度に優れた部品を実現できていない。 Therefore, in the above-mentioned Patent Documents 1 and 2, it is not possible to realize a component excellent in surface fatigue strength and bending fatigue strength that can sufficiently meet recent demands for downsizing and high stress load.
　本発明の実施形態は上記事情に鑑みてなされたものであり、その目的は、面疲労強度および曲げ疲労強度の両方に優れた浸炭窒化部品、並びにその製造方法を提供することにある。 Embodiments of the present invention have been made in view of the above circumstances, and an object of the present invention is to provide a carbonitrided component excellent in both surface fatigue strength and bending fatigue strength, and a method for manufacturing the same.
　上記課題を解決し得た本発明の実施形態に係る面疲労強度および曲げ疲労強度に優れた浸炭窒化部品は、鋼材の表面に浸炭窒化層を有する浸炭窒化部品であって、前記鋼材は、質量％で、Ｃ：０．１５～０．２５％、Ｓｉ：０．４～１％、Ｍｎ：０．３０～０．６％、Ｐ：０％超、０．０２％以下、Ｓ：０％超、０．０２％以下、Ｃｒ：１．２～２％、Ｍｏ：０．３～０．５％、Ｎ：０％超、０．０１５％以下を含有し、残部が鉄および不可避不純物からなり、前記浸炭窒化層は、表面から２５μｍ深さ位置での硬さが８５０ＨＶ以上、表面から２００μｍ深さ位置での圧縮残留応力値の絶対値が２００ＭＰａ以上、且つ、表面から２００μｍ深さ位置までの最大圧縮残留応力値の絶対値が８５０ＭＰａ以上であり、ＪＩＳ Ｂ０６０１（１９９４）で規定される十点平均粗さＲｚが２．５μｍ以下である点に要旨を有する。 A carbonitriding component excellent in surface fatigue strength and bending fatigue strength according to an embodiment of the present invention that has solved the above problems is a carbonitriding component having a carbonitriding layer on the surface of a steel material, and the steel material has a mass %, C: 0.15 to 0.25%, Si: 0.4 to 1%, Mn: 0.30 to 0.6%, P: more than 0%, 0.02% or less, S: 0% More than 0.02%, Cr: 1.2 to 2%, Mo: 0.3 to 0.5%, N: more than 0%, 0.015% or less, the balance from iron and inevitable impurities The carbonitrided layer has a hardness of 850 HV or more at a depth of 25 μm from the surface, an absolute value of a compressive residual stress value of 200 MPa or more at a depth of 200 μm from the surface, and a depth of 200 μm from the surface. The absolute value of the maximum compressive residual stress value is 850 MPa or more, and JIS B0601 (1 Ten-point average roughness Rz defined in 94) has a gist in that at 2.5μm or less.
　本発明の好ましい実施形態において、前記鋼材は更に、質量％で、Ｖ：０％超、０．５％以下、Ｔｉ：０％超、０．５％以下、Ｎｂ：０％超、０．５％以下、およびＡｌ：０％超、０．５％以下よりなる群から選択される少なくとも一種の元素を含む。 In a preferred embodiment of the present invention, the steel material is further in mass%, V: more than 0%, 0.5% or less, Ti: more than 0%, 0.5% or less, Nb: more than 0%, 0.5 % Or less, and Al: at least one element selected from the group consisting of more than 0% and 0.5% or less.
　本発明の好ましい実施形態において、前記鋼材は更に、質量％で、Ｃｕ：０％超、０．３％以下、Ｎｉ：０％超、０．３％以下、およびＢ：０％超、０．０１％以下よりなる群から選択される少なくとも一種の元素を含む。 In a preferred embodiment of the present invention, the steel material further includes, in mass%, Cu: more than 0%, 0.3% or less, Ni: more than 0%, 0.3% or less, and B: more than 0%,. It contains at least one element selected from the group consisting of 01% or less.
　また、上記課題を解決し得た本発明の実施形態に係る浸炭窒化部品の製造方法は、上記のいずれかに記載の浸炭窒化部品を製造する方法であって、前記鋼材を浸炭窒化処理した後、粒径３００μｍ超のショット粒を用いたショットピーニング、研磨、粒径３００μｍ以下のショット粒を用いたショットピーニングの順に加工する点に要旨を有する。 A carbonitriding component manufacturing method according to an embodiment of the present invention that has solved the above problems is a method for manufacturing the carbonitriding component according to any one of the above, and after the steel material is carbonitriding The gist is that the processing is performed in the order of shot peening using shot grains having a particle diameter of more than 300 μm, polishing, and shot peening using shot grains having a particle diameter of 300 μm or less.
　本発明の実施形態によれば、面疲労強度および曲げ疲労強度に優れた浸炭窒化部品を提供することができる。 According to the embodiment of the present invention, it is possible to provide a carbonitrided component having excellent surface fatigue strength and bending fatigue strength.
図１Ａは、本実施例に用いたローラーピッチング試験片のうち小ローラーの形状を示す図である。FIG. 1A is a diagram showing the shape of a small roller among the roller pitching test pieces used in this example. 図１Ｂは、本実施例に用いたローラーピッチング試験片のうち大ローラーの形状を示す図である。FIG. 1B is a diagram showing the shape of a large roller among the roller pitching test pieces used in this example. 図２は、本実施例に用いた４点曲げ試験片の形状を示す図である。FIG. 2 is a diagram showing the shape of a four-point bending test piece used in this example.
　本発明者らは上記課題（面疲労強度および曲げ疲労強度の向上）を解決するため、鋭意検討を行なった。 In order to solve the above problems (improvement of surface fatigue strength and bending fatigue strength), the present inventors have conducted intensive studies.
　その結果、面疲労強度の向上には、下記（ｉ）～（ｖ）の要件を全て満足することが必要であり、これらの一つでも満足しないと、所望とする面疲労強度が得られないことが判明した。
（ｉ）Ｓｉ、Ｃｒ、Ｍｏの成分を最適化して焼戻し軟化抵抗を増加させる。
（ｉｉ）表面硬さ（具体的には、表面から２５μｍ深さ位置での硬さ）を８５０ＨＶ以上に高めて表面起点での破壊を抑制する。
（ｉｉｉ）内部圧縮残留応力（具体的には、表面から２００μｍ深さ位置の圧縮残留応力）の絶対値を２００ＭＰａ以上に高めて内部起点での破壊を抑制する。
（ｉｖ）表面圧縮残留応力（具体的には、表面から２００μｍ深さ位置までの最大圧縮残留応力値）の絶対値を８５０ＭＰａ以上に高めて表面起点での破壊を抑制する。
（ｖ）表面粗さ（本発明の実施形態では十点平均粗さＲｚ）を２．５μｍ以下に低減して表面起点での破壊を抑制する。 As a result, in order to improve the surface fatigue strength, it is necessary to satisfy all the following requirements (i) to (v). If any one of these requirements is not satisfied, the desired surface fatigue strength cannot be obtained. It has been found.
(I) The Si, Cr, and Mo components are optimized to increase the temper softening resistance.
(Ii) The surface hardness (specifically, the hardness at a depth of 25 μm from the surface) is increased to 850 HV or more to suppress destruction at the surface starting point.
(Iii) The absolute value of the internal compressive residual stress (specifically, the compressive residual stress at a depth of 200 μm from the surface) is increased to 200 MPa or more to suppress breakage at the internal origin.
(Iv) The absolute value of the surface compressive residual stress (specifically, the maximum compressive residual stress value from the surface to the 200 μm depth position) is increased to 850 MPa or more to suppress the fracture at the surface starting point.
(V) The surface roughness (ten-point average roughness Rz in the embodiment of the present invention) is reduced to 2.5 μm or less to suppress the breakage at the surface starting point.
　更に曲げ疲労強度の向上には、上記（ｉｖ）のように表面圧縮残留応力の絶対値を８５０ＭＰａ以上に高めて表面起点での破壊を抑制することが重要であることが判明した。 Further, it has been found that, in order to improve the bending fatigue strength, it is important to increase the absolute value of the surface compressive residual stress to 850 MPa or more as described above (iv) to suppress the fracture at the surface starting point.
　そして本発明の実施形態では、上記（ｉ）～（ｖ）の要件を全て満足する部品を得るため、以下のようにして部品を製造した。まず、上記（ｉ）のように成分が適切に制御された鋼材に浸炭窒化処理を行なって、上記（ｉｉ）の表面硬さを確保すると共に、温度上昇時の軟化抵抗を高めることにした。 In the embodiment of the present invention, in order to obtain a part that satisfies all the requirements (i) to (v), the part was manufactured as follows. First, carbon steel was subjected to carbonitriding treatment to the steel material whose components were appropriately controlled as in (i) above, to ensure the surface hardness of (ii) above and to increase the softening resistance at the time of temperature rise.
　更に上記（ｉｉｉ）～（ｖ）の要件を備えた部品を得るため、粒径（投射材の直径）の異なるショット粒を用いた二段ショットピーニングの間に研磨処理を行なう方法が有効であることが判明した。具体的には、まず、大粒径のショット粒（投射材）でショットピーニングを行なって上記（ｉｉｉ）の内部圧縮残留応力を確保した後、研磨を行なって上記（ｖ）の表面粗さ（Ｒｚ）を低減する。その後、小粒径のショット粒でショットピーニングを行なって上記（ｉｖ）の表面圧縮残留応力を確保すれば、所望とする部品が得られることを見出し、本発明の実施形態を完成した。 Further, in order to obtain a part having the requirements (iii) to (v), a method of performing a polishing process during two-stage shot peening using shot grains having different particle diameters (projection material diameters) is effective. It has been found. Specifically, first, shot peening is performed with shot grains having a large particle diameter (projection material) to secure the internal compressive residual stress of (iii), and then polishing is performed to obtain the surface roughness (v) ( Rz) is reduced. Thereafter, it was found that if shot peening was performed with small-sized shot grains to ensure the surface compressive residual stress of (iv) above, a desired part could be obtained, and an embodiment of the present invention was completed.
　なお、前述した特許文献１にも二段ショットピーニングを行なうことが良い旨記載されているが、本発明の実施形態のように１段目と２段目の間に研磨処理を行なうことは開示されていない。これまで、特許文献１のようにショットピーニングを２回行なう技術は存在するが、一般には、生産性などの観点からショットピーニング連続的に行なっており、本発明の実施形態のように、その間に研磨処理を介在させることはしていない。後記する実施例の欄で実証したように、研磨処理を行なわない場合、本発明の実施形態で規定するＲｚが得られず高くなって、面疲労強度が低下することを確認している。 Note that Patent Document 1 described above also describes that it is preferable to perform two-stage shot peening, but it is disclosed that the polishing process is performed between the first stage and the second stage as in the embodiment of the present invention. It has not been. So far, there is a technique for performing shot peening twice as in Patent Document 1, but generally, shot peening is continuously performed from the viewpoint of productivity and the like, and as in the embodiment of the present invention, A polishing process is not interposed. As proved in the column of Examples described later, it is confirmed that when the polishing treatment is not performed, Rz defined in the embodiment of the present invention is not obtained and becomes high, and the surface fatigue strength is lowered.
　また、二段ショットピーニングを行なわずに、前述した特許文献２のように粒径の小さいショット粒を用いた一段ショットピーニングを行なうと、内部圧縮残留応力の絶対値が小さくなり、やはり、面疲労強度が低下することを確認している。 In addition, when one-stage shot peening is performed using shot grains having a small particle size as in Patent Document 2 described above without performing two-stage shot peening, the absolute value of internal compressive residual stress is reduced, and surface fatigue is also caused. It has been confirmed that the strength decreases.
　以下、本発明の実施形態に係る浸炭窒化部品について説明する。 Hereinafter, the carbonitriding component according to the embodiment of the present invention will be described.
　前述したとおり、本発明の実施形態に係る浸炭窒化部品は、鋼材の表面に浸炭窒化層を有しており、前記鋼材は、質量％で、Ｃ：０．１５～０．２５％、Ｓｉ：０．４～１％、Ｍｎ：０．３０～０．６％、Ｐ：０％超、０．０２％以下、０％超、Ｓ：０．０２％以下、Ｃｒ：１．２～２％、Ｍｏ：０．３～０．５％、Ｎ：０％超、０．０１５％以下を含有し、残部が鉄および不可避不純物からなり、前記浸炭窒化層は、表面から２５μｍ深さ位置での硬さが８５０ＨＶ以上、表面から２００μｍ深さ位置での圧縮残留応力値の絶対値が２００ＭＰａ以上、且つ、表面から２００μｍ深さ位置までの最大圧縮残留応力値の絶対値が８５０ＭＰａ以上であり、ＪＩＳ Ｂ０６０１（１９９４）で規定される十点平均粗さＲｚが２．５μｍ以下である点に特徴がある。 As described above, a carbonitriding component according to an embodiment of the present invention has a carbonitriding layer on the surface of a steel material, and the steel material is C: 0.15 to 0.25%, Si: 0.4 to 1%, Mn: 0.30 to 0.6%, P: more than 0%, 0.02% or less, more than 0%, S: 0.02% or less, Cr: 1.2 to 2% , Mo: 0.3 to 0.5%, N: more than 0%, 0.015% or less, the balance is made of iron and inevitable impurities, and the carbonitrided layer has a depth of 25 μm from the surface. The hardness is 850 HV or more, the absolute value of the compressive residual stress value at the 200 μm depth position from the surface is 200 MPa or more, and the absolute value of the maximum compressive residual stress value from the surface to the 200 μm depth position is 850 MPa or more. The ten-point average roughness Rz specified by B0601 (1994) is 2.5 μm or less. There is a feature in the point.
　本明細書では、表面から２５μｍ深さ位置での硬さを単に表面硬さ、表面から２００μｍ深さ位置での圧縮残留応力値の絶対値を単に内部圧縮残留応力値、表面から２００μｍ深さ位置までの最大圧縮残留応力値の絶対値を単に表面圧縮残留応力値と、それぞれ、略記する場合がある。 In this specification, the hardness at a depth of 25 μm from the surface is simply the surface hardness, the absolute value of the compressive residual stress at the depth of 200 μm from the surface is simply the internal compressive residual stress value, and the position of the depth of 200 μm from the surface. In some cases, the absolute value of the maximum compressive residual stress value is simply abbreviated as the surface compressive residual stress value.
　まず、本発明の実施形態を最も特徴付ける浸炭窒化層について説明する。 First, the carbonitriding layer that best characterizes the embodiment of the present invention will be described.
　本発明の実施形態に係る部品は、表面に浸炭窒化層を有することが前提である。これにより、表面硬さを８５０ＨＶ以上に高めることができる。これに対し、通常の浸炭処理では、所望とする表面硬さが得られないことを、後記する実施例の欄で実証している。 The component according to the embodiment of the present invention is premised on having a carbonitriding layer on the surface. Thereby, surface hardness can be raised to 850 HV or more. On the other hand, it is demonstrated in the column of the example described later that the desired surface hardness cannot be obtained by a normal carburizing treatment.
（表面から２５μｍ深さ位置での表面硬さが８５０ＨＶ以上）
　ピッチングなどの面疲労強度を高めるためには、表面の硬さ上昇が有効である。そのため、本発明の実施形態では表面硬さをビッカース硬さで８５０ＨＶ以上とする。好ましくは８７５ＨＶ以上であり、より好ましくは９００ＨＶ以上である。なお、その上限は、上記の観点からは特に限定されないが、ショットピーニングでの残留応力付与などを考慮すると、１１００ＨＶ以下であることが好ましい。 (Surface hardness at a depth of 25 μm from the surface is 850 HV or more)
In order to increase surface fatigue strength such as pitching, an increase in surface hardness is effective. Therefore, in the embodiment of the present invention, the surface hardness is set to 850 HV or more in terms of Vickers hardness. Preferably it is 875 HV or more, More preferably, it is 900 HV or more. The upper limit is not particularly limited from the above viewpoint, but it is preferably 1100 HV or less in consideration of applying residual stress in shot peening.
（表面から２００μｍ深さ位置での圧縮残留応力値の絶対値が２００ＭＰａ以上）
　内部圧縮残留応力の付与は、内部起点での破壊抑制に有用である。すなわち、面疲労において負荷が高まった場合、内部起点で破壊するスポーリング破壊が発生する虞があるが、内部圧縮残留応力値を高めることにより、スポーリング破壊を抑制できる。このような作用を有効に発揮させるため、本発明の実施形態では、表面から２００μｍ深さ位置での圧縮残留応力値の絶対値（内部圧縮残留応力値）を２００ＭＰａ以上とする。好ましくは２１０ＭＰａ以上であり、より好ましくは２２０ＭＰａ以上である。内部に高い圧縮残留応力を付与するためには、後述するように、粒径３００μｍ超と粒径の大きなショット粒を用いてショットピーニングを行うことが有効である。 (The absolute value of the compressive residual stress value at 200 μm depth from the surface is 200 MPa or more)
The application of internal compressive residual stress is useful for suppressing fracture at the internal starting point. That is, when the load increases due to surface fatigue, spalling failure that breaks at the internal origin may occur, but spalling failure can be suppressed by increasing the internal compressive residual stress value. In order to effectively exhibit such an action, in the embodiment of the present invention, the absolute value (internal compressive residual stress value) of the compressive residual stress value at a depth of 200 μm from the surface is set to 200 MPa or more. Preferably it is 210 MPa or more, More preferably, it is 220 MPa or more. In order to give a high compressive residual stress to the inside, it is effective to perform shot peening using shot grains having a particle size of more than 300 μm and a large particle size, as will be described later.
（表面から２００μｍ深さ位置までの最大圧縮残留応力値の絶対値が８５０ＭＰａ以上）
　表面圧縮残留応力の付与は、曲げ疲労強度および面疲労強度（ピッチング）の向上に有効である。これらの疲労強度を両方高めるため、本発明の実施形態では、表面から２００μｍ深さ位置までの最大圧縮残留応力値の絶対値（表面圧縮残留応力値）を８５０ＭＰａ以上とする。好ましくは８７５ＭＰａ以上であり、より好ましくは９００ＭＰａ以上である。ここで「表面から２００μｍ深さ位置までの最大圧縮残留応力値」とは、当該深さ位置までの圧縮残留応力値の最大値であり、最大値が得られるのは表面から、おおむね５０μｍ未満の位置である。表面に高い圧縮残留応力を付与するためには、後述するように、粒径３００μｍ以下と粒径の小さいショット粒を用いてショットピーニングを行うことが有効である。 (The absolute value of the maximum compressive residual stress value from the surface to the 200 μm depth position is 850 MPa or more)
The application of surface compressive residual stress is effective in improving bending fatigue strength and surface fatigue strength (pitting). In order to increase both of these fatigue strengths, in the embodiment of the present invention, the absolute value of the maximum compressive residual stress value (surface compressive residual stress value) from the surface to the 200 μm depth position is set to 850 MPa or more. Preferably it is 875 MPa or more, More preferably, it is 900 MPa or more. Here, the “maximum compressive residual stress value from the surface to a 200 μm depth position” is the maximum value of the compressive residual stress value up to the depth position, and the maximum value is obtained from the surface, generally less than 50 μm. Position. In order to give a high compressive residual stress to the surface, as will be described later, it is effective to perform shot peening using shot grains having a grain size of 300 μm or less and a small grain size.
（ＪＩＳ Ｂ０６０１（１９９４）で規定される十点平均粗さＲｚが２．５μｍ以下）
　面疲労（ピッチング）強度を高めるためには、表面粗さを低減して応力集中源を減らすことが有効である。このような作用を有効に発揮させるため、Ｒｚを２．５μｍ以下とする。好ましくは２．３μｍ以下であり、より好ましくは２．０μｍ以下である。なお、その下限は、上記の観点からは特に限定されないが、加工コストなどを考慮すると、０．５μｍ以上であることが好ましい。Ｒｚを低減するためには、後述するように、ショットピーニングの間に研磨処理を行うことが有効である。 (10-point average roughness Rz specified by JIS B0601 (1994) is 2.5 μm or less)
In order to increase the surface fatigue (pitting) strength, it is effective to reduce the surface roughness and reduce the stress concentration source. In order to effectively exhibit such an action, Rz is set to 2.5 μm or less. Preferably it is 2.3 micrometers or less, More preferably, it is 2.0 micrometers or less. The lower limit is not particularly limited from the above viewpoint, but is preferably 0.5 μm or more in consideration of processing costs and the like. In order to reduce Rz, as described later, it is effective to perform a polishing process during shot peening.
　次に、本発明の実施形態に係る浸炭窒化部品に用いられる鋼材について説明する。 Next, the steel material used for the carbonitriding component according to the embodiment of the present invention will be described.
Ｃ：０．１５～０．２５％
　Ｃは強度を確保するうえで有用な元素であり、そのためにＣ量を０．１５％以上とする。Ｃ量は０．１６％以上であることが好ましく、０．１７％以上であることがより好ましい。但し、Ｃ量が過剰になると被削性、靱性が低下するため、Ｃ量を０．２５％以下とする。Ｃ量は０．２４％以下であることが好ましく、０．２３％以下であることがより好ましい。 C: 0.15-0.25%
C is an element useful for ensuring strength, and for that purpose, the C content is 0.15% or more. The C content is preferably 0.16% or more, and more preferably 0.17% or more. However, if the amount of C becomes excessive, machinability and toughness deteriorate, so the amount of C is made 0.25% or less. The C content is preferably 0.24% or less, and more preferably 0.23% or less.
Ｓｉ：０．４～１％
　Ｓｉは、焼戻し軟化抵抗向上元素として有用である。詳細には歯車などでは、駆動中に接触部位の温度が上昇して硬さが低下するが、Ｓｉを添加することによって温度上昇時の軟化が抑制されて表面硬さを維持できる。その結果、ピッチングなどの面疲労強度、更には耐摩耗性が向上する。このような作用を有効に発揮させるため、Ｓｉ量を０．４％以上とする。Ｓｉ量は０．４５％以上であることが好ましく、０．５０％以上であることがより好ましい。但し、Ｓｉ量が過剰になると被削性が低下するため、Ｓｉ量を１％以下とする。Ｓｉ量は０．８％以下であることが好ましく、０．７％以下であることがより好ましい。 Si: 0.4 to 1%
Si is useful as an element for improving temper softening resistance. Specifically, in a gear or the like, the temperature of the contact portion rises during driving and the hardness decreases, but by adding Si, softening at the time of temperature rise is suppressed and the surface hardness can be maintained. As a result, the surface fatigue strength such as pitting and the wear resistance are improved. In order to effectively exhibit such an action, the Si amount is set to 0.4% or more. The amount of Si is preferably 0.45% or more, and more preferably 0.50% or more. However, if the Si amount becomes excessive, the machinability deteriorates, so the Si amount is set to 1% or less. The amount of Si is preferably 0.8% or less, and more preferably 0.7% or less.
Ｍｎ：０．３０～０．６％
　Ｍｎは、焼入れ性向上元素であり、Ｍｎ量が０．３０％を下回るとＦｅＳができて製造性が低下する。そのため、Ｍｎ量を０．３０％以上とする。Ｍｎ量は０．３３％以上であることが好ましく、０．３５％以上であることがより好ましい。但し、Ｍｎ量が過剰になると被削性が低下するため、Ｍｎ量を０．６％以下とする。Ｍｎ量は０．５％以下であることが好ましく、０．４５％以下であることがより好ましい。 Mn: 0.30 to 0.6%
Mn is a hardenability improving element, and when the amount of Mn is less than 0.30%, FeS is formed and productivity is lowered. Therefore, the amount of Mn is set to 0.30% or more. The amount of Mn is preferably 0.33% or more, and more preferably 0.35% or more. However, if the amount of Mn becomes excessive, the machinability decreases, so the amount of Mn is set to 0.6% or less. The amount of Mn is preferably 0.5% or less, and more preferably 0.45% or less.
Ｐ：０％超、０．０２％以下
　Ｐは、製造過程などで不可避的に不純物として含有する元素であり、粒界に偏析して加工性、疲労特性（面疲労強度および曲げ疲労強度）などを低下させる。そのため、Ｐ量を０．０２％以下とする。Ｐ量は、少ない程良く、０．０１５％以下であることが好ましく、０．０１０％以下であることがより好ましい。但し、Ｐ量を極端に低減することは製鋼コストの増大を招く。 P: more than 0% and 0.02% or less P is an element inevitably contained as an impurity in the manufacturing process, etc., segregating at the grain boundary, workability, fatigue characteristics (surface fatigue strength and bending fatigue strength), etc. Reduce. Therefore, the P content is 0.02% or less. The smaller the amount of P, the better. It is preferably 0.015% or less, and more preferably 0.010% or less. However, extremely reducing the amount of P causes an increase in steelmaking costs.
Ｓ：０％超、０．０２％以下
　Ｓも上記Ｐと同様、製造過程などで不可避的に不純物として含有する元素であり、ＭｎＳとして析出して疲労特性（面疲労強度および曲げ疲労強度）、衝撃特性などを低下させる。そのため、Ｓ量を０．０２％以下とする。Ｓ量は、少ない程良く、０．０１５％以下であることが好ましく、０．０１０％以下であることがより好ましい。但し、Ｓ量を極端に低減することは製鋼コストの増大を招く。 S: more than 0% and 0.02% or less S is an element that is inevitably contained as an impurity in the production process, etc., as in the case of P, and precipitates as MnS to exhibit fatigue properties (surface fatigue strength and bending fatigue strength). Reduce impact characteristics. Therefore, the S content is 0.02% or less. The smaller the amount of S, the better. It is preferably 0.015% or less, and more preferably 0.010% or less. However, extremely reducing the amount of S causes an increase in steelmaking costs.
Ｃｒ：１．２～２％
　Ｃｒは、Ｍｎと同様に焼入れ性向上元素として作用する他、Ｓｉと同様に焼戻し軟化抵抗向上元素としても有用である。これらの作用を有効に発揮させるため、Ｃｒ量を１．２％以上とする。Ｃｒ量は１．２５％以上であることが好ましく、１．３０％以上であることがより好ましい。但し、Ｃｒ量が過剰になるとコストが上昇する他、被削性が低下するため、Ｃｒ量を２％以下とする。Ｃｒ量は１．８％以下であることが好ましく、１．５％以下であることがより好ましい。 Cr: 1.2-2%
Cr acts as a hardenability improving element like Mn, and is also useful as a temper softening resistance improving element like Si. In order to exhibit these effects effectively, the Cr content is set to 1.2% or more. The amount of Cr is preferably 1.25% or more, and more preferably 1.30% or more. However, if the amount of Cr becomes excessive, the cost increases and the machinability decreases, so the Cr amount is set to 2% or less. The amount of Cr is preferably 1.8% or less, and more preferably 1.5% or less.
Ｍｏ：０．３～０．５％
　Ｍｏは、Ｃｒと同様に焼入れ性向上元素および焼戻し軟化抵抗元素として有用である。これらの作用を有効に発揮させるため、Ｍｏ量を０．３％以上とする。Ｍｏ量は０．３２％以上であることが好ましく、０．３５％以上であることがより好ましい。但し、Ｍｏ量が過剰になるとコストが上昇する他、被削性が低下するため、Ｍｏ量を０．５％以下とする。Ｍｏ量は０．４８％以下であることが好ましく、０．４５％以下であることがより好ましい。 Mo: 0.3 to 0.5%
Mo is useful as a hardenability improving element and a temper softening resistance element like Cr. In order to effectively exhibit these actions, the Mo amount is set to 0.3% or more. The Mo amount is preferably 0.32% or more, and more preferably 0.35% or more. However, if the amount of Mo becomes excessive, the cost increases and the machinability decreases, so the amount of Mo is set to 0.5% or less. The Mo amount is preferably 0.48% or less, and more preferably 0.45% or less.
Ｎ：０％超、０．０１５％以下
　Ｎは、製造過程などで不可避的に不純物として含有する元素であり、ひずみ時効により加工性を低下させる。そのため、Ｎ量を０．０１５％以下とする。Ｎ量は、少ない程良く、０．０１３％以下であることが好ましく、０．０１２％以下であることがより好ましい。但し、Ｎ量を極端に低減することは製鋼コストの増大を招く。 N: more than 0% and 0.015% or less N is an element that is inevitably contained as an impurity in the manufacturing process and the like, and lowers workability by strain aging. Therefore, the N content is 0.015% or less. The smaller the amount of N, the better. It is preferably 0.013% or less, and more preferably 0.012% or less. However, extremely reducing the amount of N causes an increase in steelmaking costs.
　本発明の実施形態に係る浸炭窒化部品を構成する鋼材は上記成分を満足し、残部：鉄および不可避的不純物である。 The steel material constituting the carbonitriding component according to the embodiment of the present invention satisfies the above components, and the balance is iron and unavoidable impurities.
　更に上記鋼材は、必要に応じて、更に以下の選択成分を含有することができる。 Furthermore, the steel material can further contain the following selective components as required.
Ｖ：０％超、０．５％以下、Ｔｉ：０％超、０．５％以下、Ｎｂ：０％超、０．５％以下、およびＡｌ：０％超、０．５％以下よりなる群から選択される少なくとも一種の元素
　これらの元素は、浸炭窒化後の結晶粒微細化により靭性を向上させると共に、疲労強度（面疲労強度および曲げ疲労強度）を向上させる元素である。このような作用を有効に発揮させるため、Ｖ量：０．０５％以上、Ｔｉ量：０．０５％以上、Ｎｂ量：０．０５％以上、Ａｌ量：０．０１％以上であることが好ましい。但し、多量に添加すると上記作用が飽和するだけでなく、粗大な析出物を形成して強度が低下する。そのため、Ｖ量：０．５％以下、Ｔｉ量：０．５％以下、Ｎｂ量：０．５％以下、Ａｌ量：０．５％以下であることが好ましい。より好ましくは、Ｖ量：０．４５％以下、Ｔｉ量：０．４５％以下、Ｎｂ量：０．４５％以下、Ａｌ量：０．４５％以下であり、更に好ましくはＶ量：０．４％以下、Ｔｉ量：０．４％以下、Ｎｂ量：０．４％以下、Ａｌ量：０．４％以下である。これらの元素は単独で添加しても良いし、二種以上を併用しても良い。 V: more than 0%, 0.5% or less, Ti: more than 0%, 0.5% or less, Nb: more than 0%, 0.5% or less, and Al: more than 0%, 0.5% or less At least one element selected from the group These elements are elements that improve toughness and improve fatigue strength (surface fatigue strength and bending fatigue strength) by grain refinement after carbonitriding. In order to effectively exhibit such an action, the V amount: 0.05% or more, the Ti amount: 0.05% or more, the Nb amount: 0.05% or more, and the Al amount: 0.01% or more. preferable. However, when added in a large amount, not only the above-mentioned action is saturated, but also coarse precipitates are formed and the strength is lowered. Therefore, it is preferable that V amount: 0.5% or less, Ti amount: 0.5% or less, Nb amount: 0.5% or less, and Al amount: 0.5% or less. More preferably, the V amount is 0.45% or less, the Ti amount is 0.45% or less, the Nb amount is 0.45% or less, and the Al amount is 0.45% or less. 4% or less, Ti content: 0.4% or less, Nb content: 0.4% or less, Al content: 0.4% or less. These elements may be added alone or in combination of two or more.
Ｃｕ：０％超、０．３％以下、Ｎｉ：０％超、０．３％以下、およびＢ：０％超、０．０１％以下よりなる群から選択される少なくとも一種の元素
　これらの元素は、焼入性向上元素として有用である。このような作用を有効に発揮させるため、Ｃｕ量：０．０５％以上、Ｎｉ量：０．０５％以上、Ｂ量：０．０００３％以上であることが好ましい。但し、多量に添加すると熱間加工性、冷間加工性が低下する。そのため、Ｃｕ量：０．３％以下、Ｎｉ量：０．３％以下、Ｂ量：０．０１％以下であることが好ましい。より好ましくは、Ｃｕ量：０．２５％以下、Ｎｉ量：０．２５％以下、Ｂ量：０．００８％以下であり、更に好ましくはＣｕ量：０．２％以下、Ｎｉ量：０．２％以下、Ｂ量：０．００５％以下である。これの元素は単独で添加しても良いし、二種以上を併用しても良い。 At least one element selected from the group consisting of Cu: more than 0%, 0.3% or less, Ni: more than 0%, 0.3% or less, and B: more than 0%, 0.01% or less. These elements Is useful as an element for improving hardenability. In order to effectively exhibit such actions, it is preferable that the Cu content is 0.05% or more, the Ni content is 0.05% or more, and the B content is 0.0003% or more. However, if it is added in a large amount, hot workability and cold workability are lowered. Therefore, it is preferable that Cu amount: 0.3% or less, Ni amount: 0.3% or less, and B amount: 0.01% or less. More preferably, the amount of Cu is 0.25% or less, the amount of Ni is 0.25% or less, the amount of B is 0.008% or less, and more preferably the amount of Cu is 0.2% or less, and the amount of Ni is 0.00. 2% or less, B amount: 0.005% or less. These elements may be added alone or in combination of two or more.
　次に、本発明の実施形態に係る浸炭窒化部品を製造する方法について説明する。前述したように本発明の実施形態に係る製造方法は、上記鋼材を浸炭窒化処理した後、粒径３００μｍ超のショット粒を用いたショットピーニング（一次ショットピーニング）、研磨、粒径３００μｍ以下のショット粒を用いたショットピーニング（二次ショットピーニング）の順に加工する点に要旨を有する。 Next, a method for producing a carbonitrided part according to an embodiment of the present invention will be described. As described above, in the manufacturing method according to the embodiment of the present invention, after the carbon steel is carbonitrided, shot peening (primary shot peening) using a shot grain having a grain size of more than 300 μm, polishing, shot having a grain size of 300 μm or less. It has a gist in that it is processed in the order of shot peening (secondary shot peening) using grains.
　まず、上記組成の鋼材を浸炭窒化処理する。所望とする表面硬さを確保するためには、例えば、９００～９８０℃、カーボンポテンシャル０．７～０．９質量％、１００～５００分の条件で浸炭を実施した後、８００～９００℃、カーボンポテンシャル０．７～０．９質量％、アンモニア３～８体積％、１００～５００分の条件で窒化を実施し、その後、６０～１００℃で油冷し、１００～２００℃、６０～１８０分の焼戻し処理の条件で浸炭窒化することが好ましい。 First, carbon steel is carbonitrided with the above composition. In order to ensure the desired surface hardness, for example, after carburizing under conditions of 900 to 980 ° C., carbon potential of 0.7 to 0.9 mass%, 100 to 500 minutes, 800 to 900 ° C., Nitriding was performed under conditions of carbon potential 0.7 to 0.9 mass%, ammonia 3 to 8 vol%, 100 to 500 minutes, and then oil-cooled at 60 to 100 ° C, 100 to 200 ° C, 60 to 180. It is preferable to perform carbonitriding under the condition of a minute tempering treatment.
　次に、ショットピーニングによる加工を行なう。具体的には、まず、粒径３００μｍ超の大粒径ショット粒（一次ショット粒）を用いたショットピーニング（一次ショットピーニング）を行なう。粒径の大きいショット粒でショットピーニングすることにより、内部（表面から２００μｍ深さ位置）に高い残留応力が付与される。但し、この時点では、表面粗さＲｚは大きくなっている。使用する一次ショット粒の粒径は、上記範囲であれば特に限定されず、例えば、４００μｍ以上、１２００μｍ以下であることが好ましい。 Next, processing by shot peening is performed. Specifically, first, shot peening (primary shot peening) using large grain size shot grains (primary shot grains) having a grain size of more than 300 μm is performed. By performing shot peening with shot grains having a large grain size, a high residual stress is applied to the inside (at a depth of 200 μm from the surface). However, at this time, the surface roughness Rz is large. The particle size of the primary shot grains to be used is not particularly limited as long as it is in the above range, and is preferably 400 μm or more and 1200 μm or less, for example.
　次いで、研磨する。本発明の実施形態では、次の二次ショットピーニングの前に研磨処理を行なうことが重要であり、これにより表面は２０～５０μｍ程度除去され、研磨後の表面粗さＲｚが本発明の実施形態に係る範囲（２．５μｍ以下）に低減されて面疲労強度が向上する。研磨は砥石、サンドペーパー等を用いる機械研磨であってよい。また、電解研磨または化学研磨であってもよい。 Next, polish. In the embodiment of the present invention, it is important to perform the polishing treatment before the next secondary shot peening, whereby the surface is removed by about 20 to 50 μm, and the surface roughness Rz after the polishing is the embodiment of the present invention. And the surface fatigue strength is improved. The polishing may be mechanical polishing using a grindstone, sandpaper or the like. Further, electrolytic polishing or chemical polishing may be used.
　その後、粒径３００μｍ以下の小粒径ショット粒（二次ショット粒）を用いたショットピーニング（二次ショットピーニング）を行なう。小粒径のショットピーニングでは、表面粗さＲｚはあまり変化せず所望レベルに低減されたままで、且つ、表面に高い最大圧縮残留応力が付与される。使用する二次ショット粒の粒径は、上記範囲であれば特に限定されず、例えば、２０μｍ以上、２００μｍ以下であることが好ましい。 Thereafter, shot peening (secondary shot peening) using small grain size shot grains (secondary shot grains) having a grain size of 300 μm or less is performed. In shot peening with a small particle size, the surface roughness Rz does not change much and remains reduced to the desired level, and a high maximum compressive residual stress is applied to the surface. The particle size of the secondary shot particles to be used is not particularly limited as long as it is in the above range, and is preferably 20 μm or more and 200 μm or less, for example.
　本発明の実施形態では、上記のように粒径が異なるショット粒（一次ショット粒および二次ショット粒）を用いて二段階ショットピーニングを行なうことが重要であり、その他の要件は特に限定されない。例えばショット粒の硬さは、後記する実施例のように同一であっても良いが、残留応力付与効率などを考慮すると、一次ショット粒に比べて二次ショット粒の方が硬い方が好ましい。 In the embodiment of the present invention, it is important to perform two-stage shot peening using shot grains having different grain sizes (primary shot grains and secondary shot grains) as described above, and other requirements are not particularly limited. For example, the hardness of the shot grains may be the same as in the examples described later, but in consideration of the residual stress application efficiency and the like, the secondary shot grains are preferably harder than the primary shot grains.
　以下、実施例を挙げて本発明の実施形態をより具体的に説明するが、本発明は下記実施例によって制限されず、前・後記の趣旨に適合し得る範囲で変更を加えて実施することも可能であり、それらはいずれも本発明の技術的範囲に包含される。 Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and may be implemented with modifications within a range that can meet the purpose described above and below. Are all possible and are within the scope of the present invention.
　表１に記載の種々の鋼Ａ～Ｒ（単位は質量％、残部：鉄および不可避的不純物）を溶製し、１２００℃に加熱して熱間鍛造し、直径３２ｍｍの熱間圧延材（棒鋼）を得た。鍛造後、１２５０℃で１時間加熱後、放冷する溶体化処理を行い、その後、９００℃で１時間加熱後、放冷する焼ならし処理を行った。なお、表１の鋼種Ａは、従来鋼のＳＣｒ４２０Ｈ相当鋼であり、本発明の実施形態に比べてＳｉ量、Ｃｒ量、Ｍｏ量が少なく、Ｍｎ量が多い鋼種である。 Various steels A to R (unit: mass%, balance: iron and unavoidable impurities) listed in Table 1 are melted, heated to 1200 ° C. and hot forged, and hot rolled (diameter bar) having a diameter of 32 mm ) After forging, it was heated at 1250 ° C. for 1 hour and then allowed to cool, and then heated at 900 ° C. for 1 hour and then allowed to cool. Steel type A in Table 1 is an SCr420H equivalent steel of conventional steel, and is a steel type that has a small amount of Si, Cr, Mo, and a large amount of Mn compared to the embodiment of the present invention.
　次いで、上記棒鋼を用い、以下のようにして図１Ａ、図１Ｂに示す各形状のローラーピッチング試験片、および図２に示す形状の４点曲げ試験片を作製した。 Next, using the above steel bars, roller pitching test pieces having the shapes shown in FIGS. 1A and 1B and 4-point bending test pieces having the shapes shown in FIG. 2 were prepared as follows.
（ローラーピッチング試験片の作製）
　上記の棒鋼から、機械加工により図１Ａに示す形状のローラーピッチング試験用小ローラー（研磨を行うときの直径２６．１ｍｍ、研磨を行わないときの直径２６．０ｍｍ）を作製した。 (Preparation of roller pitching specimen)
A small roller for roller pitching test having a shape shown in FIG. 1A (a diameter of 26.1 mm when polishing and a diameter of 26.0 mm when polishing is not performed) having the shape shown in FIG.
　更に、ＪＩＳ　Ｇ　４０５３（２００８）に規定されるＳＣＭ４３５を素材とし、一般的な製造工程（焼きならし、試験片加工、ガス浸炭炉による共析浸炭、低温焼戻し及び研磨）により、図１Ｂに示すように直径１３０ｍｍ、接触部のＲ形状が１５０ｍｍＲの形状のローラーピッチング試験用大ローラーを作製した。 Furthermore, using SCM435 defined in JIS G 4053 (2008) as a raw material, it is shown in FIG. 1B by a general manufacturing process (normalizing, specimen processing, eutectoid carburizing with a gas carburizing furnace, low temperature tempering and polishing). Thus, a large roller for roller pitching test having a diameter of 130 mm and an R shape of the contact portion of 150 mmR was produced.
（４点曲げ試験片の作製）
　上記棒鋼のｄ／４（ｄは直径）位置から、図２に示す形状の４点曲げ試験片を作製した。 (Preparation of 4-point bending specimen)
From the d / 4 (d is the diameter) position of the steel bar, a four-point bending test piece having the shape shown in FIG. 2 was produced.
　このようにして得られた各試験片に対し、表２に示すように熱処理（浸炭処理または浸炭窒化処理）、および加工処理（一次ショットピーニング、研磨、二次ショットピーニング）を行なった。本実施例に用いた熱処理および加工処理の詳細は以下のとおりである。 The test pieces thus obtained were subjected to heat treatment (carburizing treatment or carbonitriding treatment) and processing (primary shot peening, polishing, secondary shot peening) as shown in Table 2. The details of the heat treatment and processing used in this example are as follows.
（熱処理）
　浸炭：９５０℃、カーボンポテンシャル０．８質量％、１４０分の条件で浸炭を実施した後、８４５℃、カーボンポテンシャル０．８質量％、３０分保持し、その後、８０℃で油冷し、１６０℃、１２０分の焼戻し処理を施した。 (Heat treatment)
Carburization: Carburization was carried out under the conditions of 950 ° C., carbon potential 0.8 mass%, 140 minutes, then held at 845 ° C., carbon potential 0.8 mass%, 30 minutes, then oil cooled at 80 ° C., 160 A tempering treatment at 120 ° C. for 120 minutes was performed.
　浸炭窒化：９４０℃、カーボンポテンシャル０．８５質量％、３００分の条件で浸炭を実施した後、８４０℃、カーボンポテンシャル０．８５質量％、アンモニア５体積％、２４０分の条件で窒化を実施し、その後、８０℃で油冷し、１６０℃、１２０分の焼戻し処理を施した。 Carburizing and nitriding: Carburizing was performed under conditions of 940 ° C., carbon potential of 0.85 mass%, 300 minutes, and then nitriding was performed under conditions of 840 ° C., carbon potential of 0.85 mass%, ammonia 5 volume%, and 240 minutes. Then, oil cooling was performed at 80 ° C., and tempering treatment was performed at 160 ° C. for 120 minutes.
（加工処理）
　一次ショットピーニング
　粒径１０００μｍ、平均硬さ８００ＨＶの投射材を用い、アークハイト０．２ｍｍＣ、カバレージ３００％以上となるように一次（大粒径）ショットピーニングを実施した。 (Processing)
Primary shot peening Primary (large particle size) shot peening was performed using a projection material having a particle size of 1000 μm and an average hardness of 800 HV so that the arc height was 0.2 mmC and the coverage was 300% or more.
　研磨
　ローラーピッチング試験用小ローラーについては、砥石を用いた研磨により、試験片の表面を５０μｍ研磨し、直径２６．０ｍｍに仕上げた。 Polishing For the small roller for roller pitching test, the surface of the test piece was polished by 50 μm by polishing using a grindstone, and finished to a diameter of 26.0 mm.
　二次ショットピーニング
　粒径３００μｍ、平均硬さ８００ＨＶの投射材を用い、アークハイト０．２ｍｍＡ、カバレージ３００％以上となるよう二次（微粒子）ショットピーニングを実施した。 Secondary shot peening Secondary (fine particle) shot peening was performed using a projection material having a particle size of 300 μm and an average hardness of 800 HV so that the arc height was 0.2 mmA and the coverage was 300% or more.
　上記の処理を行なった各試験片について、以下の方法で表面硬さ、圧縮残留応力、面疲労強度、および曲げ疲労強度を測定した。 The surface hardness, compressive residual stress, surface fatigue strength, and bending fatigue strength of each test piece subjected to the above treatment were measured by the following methods.
（表面硬さの測定）
　上記の処理を行なったローラーピッチング試験用小ローラーを用いて、表面のビッカース硬さを、ＪＩＳ Ｚ ２２４４（２００３）における「ビッカース硬さ試験－試験方法」に基づいて測定した。詳細には、上記小ローラーの試験部を小ローラーの軸方向に垂直な面で切断し、その切断面を鏡面研磨して試験部の表面からの深さが２５μｍの位置で、試験力を１．９６１Ｎとして１０点測定し、その算術平均値を表面のビッカース硬さとした。 (Measurement of surface hardness)
The surface Vickers hardness was measured based on “Vickers hardness test-test method” in JIS Z 2244 (2003) using the small roller for roller pitching test subjected to the above treatment. Specifically, the test portion of the small roller is cut by a plane perpendicular to the axial direction of the small roller, the cut surface is mirror-polished, and the test force is 1 at a depth of 25 μm from the surface of the test portion. .961N was measured at 10 points, and the arithmetic average value was defined as the surface Vickers hardness.
（圧縮残留応力の測定）
　上記の処理を行なったローラーピッチング試験用小ローラーを用いて、各深さ位置における圧縮残留応力を、Ｘ線により測定した。詳細には、ＰＳＰＣ（Ｐｏｓｉｔｉｏｎ－Ｓｅｎｓｉｔｉｖｅ Ｐｒｏｐｏｒｔｉｏｎａｌ Ｃｏｕｎｔｅｒ）微小部Ｘ線応力測定装置を用いて、上記小ローラーの試験部表面からそれぞれ０μｍ（表面）、１０μｍ、２５μｍ、５０μｍ、１００μｍ、２００μｍの位置まで電解研磨して残留応力を測定した。ＰＳＰＣ微小部Ｘ線応力測定装置の測定条件は、コリメーター径：φ１ｍｍ、測定部位：軸方向中央位置、測定方向：円周方向である。 (Measurement of compressive residual stress)
The compression residual stress in each depth position was measured by X-ray using the small roller for roller pitching test which performed said process. Specifically, using a Position-Sensitive Proportional Counter (PSPC) micro-part X-ray stress measurement apparatus, electrolysis is performed from the test part surface of the small roller to positions of 0 μm (surface), 10 μm, 25 μm, 50 μm, 100 μm, and 200 μm, respectively. The residual stress was measured after polishing. The measurement conditions of the PSPC minute part X-ray stress measurement apparatus are collimator diameter: φ1 mm, measurement site: axial center position, measurement direction: circumferential direction.
（面疲労強度の測定）
　「ＲＰ－２０１型」ローラーピッチング試験機（コマツエンジニアリング株式会社製）にてローラーピッチング試験を行なって面疲労強度を測定した。詳細には、上記の処理を行なったローラーピッチング試験用小ローラーおよび大ローラーを用い、潤滑油としてオートマチック用油、油温１２０℃、すべり率－４０％の条件でローラーピッチング試験を行って、応力Ｓ－繰返し数Ｎ線図を作成し、１０００万回強度（１０００万回試験した際に破損しない最大の応力を意味する）によりピッチング強度（面疲労強度）を評価した。但し、本実施例では試験機の負荷を考慮して、４．０ＧＰａ超の強度は測定していない。本実施例では、このようにして得られた面疲労強度が３．６ＧＰａ以上のもの［表１の鋼種Ａ（従来鋼のＳＣｒ４２０Ｈ相当鋼）に比べて約１．７倍程度高いもの］を面疲労強度に優れると評価した。 (Measurement of surface fatigue strength)
The surface fatigue strength was measured by performing a roller pitching test with an “RP-201 type” roller pitching tester (manufactured by Komatsu Engineering Co., Ltd.). Specifically, the roller pitching test was performed using the small roller and the large roller for the roller pitching test, which were subjected to the above treatment, under the conditions of an oil for automatic as a lubricating oil, an oil temperature of 120 ° C., and a slip ratio of −40%. An S-repetition number N diagram was prepared, and the pitching strength (surface fatigue strength) was evaluated by the strength of 10 million times (meaning the maximum stress that does not break when tested 10 million times). However, in this embodiment, the strength exceeding 4.0 GPa is not measured in consideration of the load on the testing machine. In this example, the surface fatigue strength obtained in this way is 3.6 GPa or more [about 1.7 times higher than steel type A in Table 1 (SCR420H equivalent steel of conventional steel)]. The fatigue strength was evaluated as excellent.
（曲げ疲労特性の評価）
　油圧サーボ試験機（株式会社島津製作所製）を用いて、上記の処理を行なった４点曲げ試験片に周波数２０Ｈｚ、応力比（最大応力／最小応力）０．１で曲げ疲労試験を行い、応力Ｓ－繰返し数Ｎ線図を作成し、２００万回強度（２００万回試験した際に破損しない最大の応力を意味する）により曲げ疲労強度を評価した。本実施例では、このようにして得られた曲げ疲労強度が１２８０ＭＰａ以上のもの［表１の鋼種Ａ（従来鋼のＳＣｒ４２０Ｈ相当鋼）に比べて約１．７倍程度高いもの］を曲げ疲労強度に優れると評価した。 (Evaluation of bending fatigue characteristics)
Using a hydraulic servo tester (manufactured by Shimadzu Corporation), a bending fatigue test was performed on the four-point bending test piece subjected to the above-described treatment at a frequency of 20 Hz and a stress ratio (maximum stress / minimum stress) of 0.1. An S-repetition number N diagram was prepared, and the bending fatigue strength was evaluated based on the strength of 2 million times (meaning the maximum stress that does not break when tested 2 million times). In this example, the bending fatigue strength obtained in this way was 1280 MPa or more [about 1.7 times higher than steel type A (conventional steel of SCr420H equivalent steel) in Table 1]. It was evaluated as excellent.
（表面粗さ）
　上記の処理を行なったローラーピッチング試験用小ローラーを用い、ＪＩＳ Ｂ０６０１：１９９４に基づいてＲｚを測定した。詳細には、小ローラーの試験面を軸方向にして、測定速度０．２ｍｍ／ｓ、カットオフ値０．８ｍｍ、測定長さ４ｍｍにて測定した。 (Surface roughness)
Rz was measured based on JIS B0601: 1994 using the small roller for roller pitching test which performed said process. Specifically, the measurement was performed at a measurement speed of 0.2 mm / s, a cut-off value of 0.8 mm, and a measurement length of 4 mm with the test surface of the small roller in the axial direction.
　これらの結果を表３に記載する。 These results are shown in Table 3.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表３の結果より、以下のように考察することができる。 From the results in Table 3, it can be considered as follows.
　まず、表３のＮｏ．２～１１、１８は本発明の実施形態の要件を満足する表１の鋼種を用い、本発明の実施形態の条件で製造した例であり、面疲労強度および曲げ疲労強度の両方に優れている。 First, No. in Table 3 Nos. 2 to 11 and 18 are examples manufactured using the steel types shown in Table 1 that satisfy the requirements of the embodiment of the present invention under the conditions of the embodiment of the present invention, and are excellent in both surface fatigue strength and bending fatigue strength. .
　これに対し、表３の下記例は本発明の実施形態のいずれかの要件を満足しないため、以下の不具合を抱えている。 On the other hand, since the following example in Table 3 does not satisfy any of the requirements of the embodiment of the present invention, it has the following problems.
　Ｎｏ．１２は、Ｃ量およびＳｉ量が少なく、Ｍｏを含まない表１の鋼種Ｌを用いた例であり、面疲労強度が低下した。 No. No. 12 is an example using the steel type L of Table 1 with a small amount of C and Si and no Mo, and the surface fatigue strength was lowered.
　Ｎｏ．１３は、Ｍｎ量が少なく、Ｓ量が多く、Ｍｏを含まない表１の鋼種Ｍを用いた例であり、試験中に割れが生じたため、いずれの測定も行なわなかった（表３中の各項目は「－」）。 No. No. 13 is an example using the steel type M of Table 1 with a small amount of Mn, a large amount of S, and no Mo, and since no cracks occurred during the test, no measurement was performed (each of the values in Table 3). Items"-").
　Ｎｏ．１４は、Ｐ量が多い表１の鋼種Ｎを用いた例であり、面疲労強度および曲げ疲労強度が低下した。 No. 14 is an example using the steel type N of Table 1 with a large amount of P, and the surface fatigue strength and the bending fatigue strength decreased.
　Ｎｏ．１５は、Ｃｒ量が少ない表１の鋼種Ｏを用いた例であり、面疲労強度が低下した。 No. 15 is an example using the steel type O of Table 1 with a small amount of Cr, and the surface fatigue strength was lowered.
　Ｎｏ．１６は、Ｍｏ量が少ない表１の鋼種Ｐを用いた例であり、面疲労強度が低下した。 No. 16 is an example using the steel type P of Table 1 with a small amount of Mo, and the surface fatigue strength decreased.
　Ｎｏ．１７は、Ｎ量が多い表１の鋼種Ｑを用いた例であり、試験中に割れが生じたため、いずれの測定も行なわなかった（表３中の各項目は「－」）。 No. No. 17 is an example using the steel type Q in Table 1 with a large amount of N, and cracking occurred during the test, and thus no measurement was performed (each item in Table 3 is “−”).
　Ｎｏ．１９～２３は、本発明の実施形態の要件を満足する表１の鋼種Ｒを用いたが、本発明の実施形態の要件を満足しない条件で製造した例である。 No. Nos. 19 to 23 are examples in which the steel type R in Table 1 that satisfies the requirements of the embodiment of the present invention was used, but was manufactured under conditions that did not satisfy the requirements of the embodiment of the present invention.
　まず、Ｎｏ．１９は浸炭窒化の代わりに浸炭を行なった例であり、表面硬さが低下した。 First, No. 19 is an example in which carburizing was performed instead of carbonitriding, and the surface hardness decreased.
　Ｎｏ．２０は、１回目のショットピーニングを行なわなかった例であり、内部圧縮残留応力が低下したため、面疲労強度が低下した。 No. No. 20 is an example in which the first shot peening was not performed, and the internal compressive residual stress was lowered, and thus the surface fatigue strength was lowered.
　Ｎｏ．２１は、２回目のショットピーニングを行なわなかった例であり、表面圧縮残留応力が低下したため、面疲労強度および曲げ疲労強度の両方が低下した。 No. No. 21 is an example in which the second shot peening was not performed, and since the surface compressive residual stress was reduced, both the surface fatigue strength and the bending fatigue strength were reduced.
　Ｎｏ．２２は、ショットピーニングを全く行なわなかった例であり、内部圧縮残留応力および表面圧縮残留応力の両方が低下したため、面疲労強度および曲げ疲労強度の両方が低下した。 No. No. 22 was an example in which shot peening was not performed at all, and both the internal compressive residual stress and the surface compressive residual stress were reduced, and both the surface fatigue strength and the bending fatigue strength were reduced.
　Ｎｏ．２３は、１回目のショットピーニング後、研磨を行なわずに２回目のショットピーニングを行なった例であり、表面粗さＲｚが増加して面疲労強度が低下した。 No. No. 23 is an example in which the second shot peening was performed without polishing after the first shot peening, and the surface roughness Rz increased and the surface fatigue strength decreased.
　本明細書の開示内容は、以下の態様を含む。
（態様１）
　鋼材の表面に浸炭窒化層を有する浸炭窒化部品であって、
　前記鋼材は、質量％で、
Ｃ ：０．１５～０．２５％、
Ｓｉ：０．４～１％、
Ｍｎ：０．３０～０．６％、
Ｐ ：０％超、０．０２０％以下、
Ｓ ：０％超、０．０２％以下、
Ｃｒ：１．２～２％、
Ｍｏ：０．３～０．５％、
Ｎ ：０％超、０．０１５％以下
を含有し、残部が鉄および不可避不純物からなり、
　前記浸炭窒化層は、
　表面から２５μｍ深さ位置での硬さが８５０ＨＶ以上、
　表面から２００μｍ深さ位置での圧縮残留応力値の絶対値が２００ＭＰａ以上、
　表面から２００μｍ深さ位置までの最大圧縮残留応力値の絶対値が８５０ＭＰａ以上であり、
　ＪＩＳ Ｂ０６０１（１９９４）で規定される十点平均粗さＲｚが２．５μｍ以下であることを特徴とする面疲労強度および曲げ疲労強度に優れた浸炭窒化部品。
（態様２）
　前記鋼材は更に、質量％で、
Ｖ ：０％超、０．５％以下、
Ｔｉ：０％超、０．５％以下、
Ｎｂ：０％超、０．５％以下、および
Ａｌ：０％超、０．５％以下
よりなる群から選択される少なくとも一種の元素を含む態様１に記載の浸炭窒化部品。
（態様３）
　前記鋼材は更に、質量％で、
Ｃｕ：０％超、０．３％以下、
Ｎｉ：０％超、０．３％以下、および
Ｂ ：０％超、０．０１％以下
よりなる群から選択される少なくとも一種の元素を含む態様１または２に記載の浸炭窒化部品。
（態様４）
　態様１～３のいずれかに記載の浸炭窒化部品を製造する方法であって、
　前記鋼材を浸炭窒化処理した後、粒径３００μｍ超のショット粒を用いたショットピーニング、研磨、粒径３００μｍ以下のショット粒を用いたショットピーニングの順に加工することを特徴とする浸炭窒化部品の製造方法。 The disclosure of the present specification includes the following aspects.
(Aspect 1)
A carbonitriding component having a carbonitriding layer on the surface of a steel material,
The steel material is mass%,
C: 0.15-0.25%,
Si: 0.4-1%,
Mn: 0.30 to 0.6%,
P: more than 0%, 0.020% or less,
S: more than 0%, 0.02% or less,
Cr: 1.2-2%,
Mo: 0.3 to 0.5%,
N: more than 0% and 0.015% or less, with the balance consisting of iron and inevitable impurities,
The carbonitriding layer is
Hardness at a depth of 25 μm from the surface is 850 HV or more,
The absolute value of the compressive residual stress value at a depth of 200 μm from the surface is 200 MPa or more,
The absolute value of the maximum compressive residual stress value from the surface to the 200 μm depth position is 850 MPa or more,
A carbonitrided component excellent in surface fatigue strength and bending fatigue strength, characterized in that a ten-point average roughness Rz defined by JIS B0601 (1994) is 2.5 μm or less.
(Aspect 2)
The steel material is further in mass%,
V: more than 0%, 0.5% or less,
Ti: more than 0%, 0.5% or less,
The carbonitrided component according to aspect 1, comprising at least one element selected from the group consisting of Nb: more than 0%, 0.5% or less, and Al: more than 0%, 0.5% or less.
(Aspect 3)
The steel material is further in mass%,
Cu: more than 0%, 0.3% or less,
The carbonitrided part according to aspect 1 or 2, comprising at least one element selected from the group consisting of Ni: more than 0% and not more than 0.3%, and B: more than 0% and not more than 0.01%.
(Aspect 4)
A method for producing a carbonitrided part according to any one of aspects 1 to 3,
Carbonitriding of the steel material, followed by shot peening using shot grains having a grain size of more than 300 μm, polishing, and shot peening using shot grains having a grain size of 300 μm or less are performed in this order to produce a carbonitriding component Method.
　本出願は、出願日が２０１６年３月３０日である日本国特許出願、特願第２０１６－０６６９６０号を基礎出願とする優先権主張を伴う。特願第２０１６－０６６９６０号は参照することにより本明細書に取り込まれる。 This application is accompanied by a priority claim based on Japanese Patent Application No. 2016-0666960, whose application date is March 30, 2016. Japanese Patent Application No. 2016-066960 is incorporated herein by reference.

Claims (3)

  1. 　鋼材の表面に浸炭窒化層を有する浸炭窒化部品であって、
    　前記鋼材は、質量％で、
    Ｃ ：０．１５～０．２５％、
    Ｓｉ：０．４～１％、
    Ｍｎ：０．３０～０．６％、
    Ｐ ：０％超、０．０２０％以下、
    Ｓ ：０％超、０．０２％以下、
    Ｃｒ：１．２～２％、
    Ｍｏ：０．３～０．５％、
    Ｎ ：０％超、０．０１５％以下
    を含有し、残部が鉄および不可避不純物からなり、
    　前記浸炭窒化層は、
    　表面から２５μｍ深さ位置での硬さが８５０ＨＶ以上、
    　表面から２００μｍ深さ位置での圧縮残留応力値の絶対値が２００ＭＰａ以上、
    　表面から２００μｍ深さ位置までの最大圧縮残留応力値の絶対値が８５０ＭＰａ以上であり、
    　ＪＩＳ Ｂ０６０１（１９９４）で規定される十点平均粗さＲｚが２．５μｍ以下であることを特徴とする面疲労強度および曲げ疲労強度に優れた浸炭窒化部品。     A carbonitriding component having a carbonitriding layer on the surface of a steel material,
    The steel material is mass%,
    C: 0.15-0.25%,
    Si: 0.4-1%,
    Mn: 0.30 to 0.6%,
    P: more than 0%, 0.020% or less,
    S: more than 0%, 0.02% or less,
    Cr: 1.2-2%,
    Mo: 0.3 to 0.5%,
    N: more than 0% and 0.015% or less, with the balance consisting of iron and inevitable impurities,
    The carbonitriding layer is
    Hardness at a depth of 25 μm from the surface is 850 HV or more,
    The absolute value of the compressive residual stress value at a depth of 200 μm from the surface is 200 MPa or more,
    The absolute value of the maximum compressive residual stress value from the surface to the 200 μm depth position is 850 MPa or more,
    A carbonitrided component excellent in surface fatigue strength and bending fatigue strength, characterized in that a ten-point average roughness Rz defined by JIS B0601 (1994) is 2.5 μm or less.
  2. 　前記鋼材は更に、質量％で、以下の（ａ）～（ｂ）のいずれか１つ以上を含有する請求項１に記載の浸炭窒化部品。
    （ａ）Ｖ ：０％超、０．５％以下、Ｔｉ：０％超、０．５％以下、Ｎｂ：０％超、０．５％以下、およびＡｌ：０％超、０．５％以下よりなる群から選択される少なくとも一種の元素
    （ｂ）Ｃｕ：０％超、０．３％以下、Ｎｉ：０％超、０．３％以下、およびＢ ：０％超、０．０１％以下よりなる群から選択される少なくとも一種の元素     The carbonitrided part according to claim 1, wherein the steel material further contains at least one of the following (a) to (b) in mass%.
    (A) V: more than 0%, 0.5% or less, Ti: more than 0%, 0.5% or less, Nb: more than 0%, 0.5% or less, and Al: more than 0%, 0.5% At least one element selected from the group consisting of (b) Cu: more than 0%, 0.3% or less, Ni: more than 0%, 0.3% or less, and B: more than 0%, 0.01% At least one element selected from the group consisting of:
  3. 　請求項１～２のいずれかに記載の浸炭窒化部品を製造する方法であって、
    　前記鋼材を浸炭窒化処理した後、粒径３００μｍ超のショット粒を用いたショットピーニング、研磨、粒径３００μｍ以下のショット粒を用いたショットピーニングの順に加工することを特徴とする浸炭窒化部品の製造方法。     A method for producing a carbonitrided part according to any one of claims 1 to 2,
    Carbonitriding of the steel material, followed by shot peening using shot grains having a grain size of more than 300 μm, polishing, and shot peening using shot grains having a grain size of 300 μm or less are performed in this order to produce a carbonitriding component Method.
PCT/JP2017/012621 2016-03-30 2017-03-28 Carbonitrided component having excellent surface fatigue strength and bending fatigue strength, and method for manufacturing same WO2017170540A1 (en)

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JP2002327237A (en) * 2001-04-27 2002-11-15 Nippon Steel Corp Gear with long dedendum life and contact fatigue life, and manufacturing method therefor
JP2007262470A (en) * 2006-03-28 2007-10-11 Aichi Steel Works Ltd Pulley for belt type cvt
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