WO2021181570A1 - Gas soft-nitriding processed article and method of producing same - Google Patents

Gas soft-nitriding processed article and method of producing same Download PDF

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WO2021181570A1
WO2021181570A1 PCT/JP2020/010585 JP2020010585W WO2021181570A1 WO 2021181570 A1 WO2021181570 A1 WO 2021181570A1 JP 2020010585 W JP2020010585 W JP 2020010585W WO 2021181570 A1 WO2021181570 A1 WO 2021181570A1
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gas
less
compound layer
steel
nitriding
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PCT/JP2020/010585
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French (fr)
Japanese (ja)
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崇秀 梅原
将人 祐谷
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日本製鉄株式会社
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Priority to DE112020006870.6T priority Critical patent/DE112020006870T5/en
Priority to JP2022507086A priority patent/JP7277859B2/en
Priority to PCT/JP2020/010585 priority patent/WO2021181570A1/en
Publication of WO2021181570A1 publication Critical patent/WO2021181570A1/en

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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
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • 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
    • 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
    • C21D9/30—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for crankshafts; for camshafts
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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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    • 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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    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment

Definitions

  • the present invention relates to a steel part subjected to gas soft nitriding treatment and a method for manufacturing the same.
  • Some steel parts used in automobiles and various industrial machines require surface fatigue strength.
  • CVT pulleys and camshafts in transmissions are required to have abrasion resistance and bending fatigue strength, and gears are required to have fatigue characteristics such as surface fatigue strength and bending fatigue strength. It is said that improvement of surface hardness is effective for improving these characteristics. Therefore, nitriding and soft nitriding treatments are being applied to these steel parts.
  • the nitriding treatment and the soft nitriding treatment have the advantages that high surface hardness can be obtained and heat treatment strain is small.
  • Nitriding is a surface hardening heat treatment that allows nitrogen to penetrate the surface of steel
  • soft nitriding is a surface hardening heat treatment that allows nitrogen and carbon to penetrate the surface of steel.
  • the medium used for nitriding and soft nitriding includes gas, salt bath, plasma and the like. Gas nitriding and gas nitrocarburizing, which are excellent in productivity, are mainly applied to transmission parts of automobiles.
  • the cured layer produced by gas nitriding and gas nitrocarburizing consists of a nitrogen diffusion layer (hereinafter, may be abbreviated as a diffusion layer) and a compound layer having a thickness of several to several tens of ⁇ m formed on the surface side of the diffusion layer. be.
  • the diffusion layer is a layer cured by a solid solution strengthening mechanism by penetrating nitrogen and carbon, and a particle dispersion strengthening mechanism of nitride. It is known that improving the hardness and depth of the diffusion layer improves the bending fatigue strength and surface fatigue strength of parts. Many studies have been conducted on the improvement of the hardness and depth of the diffusion layer.
  • the compound layer is mainly composed of iron nitrides of Fe 2 N to Fe 3 N ( ⁇ phase) and Fe 4 N ( ⁇ 'phase), and has extremely high hardness as compared with the matrix phase. Therefore, the compound layer is effective in improving the wear resistance.
  • the ⁇ phase has a larger solid solution range of C and a higher growth rate than the ⁇ 'phase. For this reason, in soft nitriding in which a carburizing gas is mixed, a compound layer mainly composed of the ⁇ phase is likely to be formed. Therefore, soft nitriding can obtain a thick compound layer in a shorter time than nitriding, regardless of the steel type of the component. Therefore, soft nitriding has been used for a long time for the purpose of improving the wear resistance of parts.
  • Patent Document 1 describes nitriding or nitriding or characterized in that the thickness of the ⁇ single-phase compound layer is 8 to 30 ⁇ m, the Vickers hardness is 680 HV or more, and the volume ratio of the voids in the compound layer is less than 10%. Soft nitride components are disclosed.
  • Patent Document 2 the compound layer thickness after nitriding is 1 to 5 ⁇ m, the surface roughness after nitriding is Rz 1.6 or less, and the compound layer is ⁇ 'phase or ⁇ 'phase and ⁇ .
  • Patent Document 3 discloses that a nitriding component is produced under nitriding potential control by adjusting the content of steel components, particularly C, Mn, Cr, V, and Mo, according to a target property. There is.
  • Patent Document 4 describes a component having excellent rotational bending fatigue strength in addition to surface fatigue strength, which is made of a steel material having a predetermined chemical composition and contains iron, nitrogen and carbon formed on the surface of the steel material. It has a compound layer with a thickness of 3 ⁇ m or more and less than 20 ⁇ m, and the phase structure of the compound layer in the range from the surface to a depth of 5 ⁇ m contains ⁇ 'phase in an area ratio of 50% or more, and in a range from the surface to a depth of 3 ⁇ m.
  • a nitriding component characterized in that the void area ratio is less than 1% and the compressive residual stress on the surface of the compound layer is 500 MPa or more is disclosed.
  • Patent Document 5 describes that when low alloy steel is heated to 550 to 620 ° C. and gas nitrocarburizing treatment is performed with a treatment time A of 1.5 to 10 hours, the nitriding potential Kn X is 0.10 to 1.00. , The average value Kn Xave is 0.20 to 0.55, and after high Kn value processing with the processing time as X hours, the nitriding potential Kn Y is in the range of 0.01 to 0.20, and the average value.
  • the void ratio in the outermost surface to the lowermost surface (the interface between the compound layer and the diffusion layer) of the compound layer is suppressed.
  • the voids are often concentrated in the area from the surface of the steel to about 3 ⁇ m. If there are many voids in this region, good bending fatigue strength cannot be obtained.
  • the pores of the compound layer were concentrated in the surface layer region of the component, and the volume fraction of the pores in this surface layer region exceeded 40%. rice field. Therefore, there is room for improvement in the technique of Patent Document 1 regarding the steel component for suppressing the void ratio at the surface to 3 ⁇ m and the nitriding control method.
  • the nitrided part of Patent Document 2 has a very thin compound layer of at least 1 ⁇ m, and has a phase structure mainly composed of a ⁇ 'phase having a hardness lower than that of the ⁇ phase. Therefore, according to the technique of Patent Document 2, good wear resistance may not be obtained.
  • the structure of the compound layer is mainly composed of the ⁇ 'phase having a low hardness.
  • the nitriding potential is set to a value lower than usual. Therefore, it is considered that the nitrided parts of Patent Documents 3 to 5 have room for improvement in terms of wear resistance.
  • An object of the present invention is to provide a part having excellent wear resistance as well as rotational bending fatigue strength and a method for manufacturing the same.
  • the gist of the present invention is as follows.
  • the gas nitrocarburizing component according to one aspect of the present invention includes a steel core portion, a compound layer, and a nitrogen diffusion layer existing between the steel core portion and the compound layer, and the steel.
  • the composition of the core is C: 0.05% to 0.60%, Si: 0.05% to 1.50%, Mn: 0.20% to 2.50%, P: 0.
  • the balance contains Fe and impurities, the content of C, Mn, Cr, V, Mo in the composition of the steel core portion satisfies the formula 1, and the thickness of the compound layer is 3 to 20 ⁇ m.
  • the compound layer contains more than 50% of the ⁇ phase in terms of area ratio, the balance is the ⁇ 'phase, and the area ratio of the voids is less than 12% in the region from the surface of the compound layer to a depth of 3 ⁇ m. Is.
  • the element symbol in the formula 1 indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
  • the composition of the steel core portion is C: 0.05% to 0.60% and Si: 0.05% to 1 in mass%.
  • Mn 0.20% to 2.50%, P: 0.025% or less
  • S 0.050% or less
  • Cr 0.50% to 2.50%
  • V 0.05% ⁇ 1.30%
  • Al 0.050% or less
  • N 0.0250% or less
  • Mo 0 to 1.50%
  • Cu 0 to 1.00%
  • W 0 to 0.50%
  • Co 0 to 0.50%
  • Nb 0 to 0.300%
  • Ti 0 to 0.250%
  • B 0 to 0.0100%
  • Ca 0 to 0. It may contain 010%, Mg: 0 to 0.010%, and REM: 0 to 0.010%, with the balance consisting of Fe and impurities.
  • the ⁇ phase in the compound layer may have an area ratio of 90% or less.
  • the thickness of the compound layer may be 6 ⁇ m or more.
  • the method for manufacturing a gas nitriding-treated part according to another aspect of the present invention is the method for manufacturing a gas nitriding-treated part according to any one of (1) to (5) above.
  • the gas nitrocarburizing treatment comprises steps and, in which the gas containing at least one of CO 2 , CO and hydrocarbon gas is contained in a carburable gas input ratio represented by the formula 2 in an amount of 2% by volume or more and less than 10% by volume.
  • the balance is maintained at a temperature of 550 ° C. or higher and 630 ° C. or lower for 1 hour or more and 7 hours or less.
  • the required nitriding potential K N is within the range of 0.15 or more and 0.40 or less through the step of performing the gas soft nitriding treatment, and the average value K Nave of the nitriding potential K N is 0.18 or more and 0.30. Is less than.
  • Carburizing gas input ratio (volume%) CO 2 , CO, total input flow rate of hydrocarbon gas (l / min) / total input flow rate of atmospheric gas (l / min) ⁇ 100 ... Equation 2
  • K N (NH 3 partial pressure) / [(H 2 partial pressure) 3/2 ] (atm- 1 / 2 ) ⁇ ⁇ ⁇ Equation 3
  • the present inventors focused on the morphology of the compound layer formed on the surface of the steel material by soft nitriding, and investigated the relationship between the morphology of the compound layer and the fatigue strength.
  • the voids generated on the surface side of the compound layer can be suppressed by soft nitriding the steel material whose composition has been adjusted while controlling the nitriding potential in a constant atmosphere. Furthermore, it has been found that by setting the thickness of the compound layer within a certain range and the hardness of the compound layer to a certain value or more, a soft nitrided part having excellent wear resistance and rotational bending fatigue strength can be produced.
  • the gas nitrocarburizing component 1 (hereinafter, may be simply referred to as “part”) according to the present embodiment is referred to as a steel core portion 11 (hereinafter, simply referred to as “steel”). There is), and a nitrogen diffusion layer 13 (hereinafter, may be simply referred to as a “diffusion layer”) existing between the compound layer 12 and the steel core portion 11 and the compound layer 12.
  • a nitrogen diffusion layer 13 (hereinafter, may be simply referred to as a “diffusion layer”) existing between the compound layer 12 and the steel core portion 11 and the compound layer 12.
  • C stabilizes the formation of the ⁇ phase. Therefore, C is an element effective for increasing the thickness of the compound layer after nitriding and the volume ratio of the ⁇ phase and enhancing the wear resistance of the component. In addition, C is an element necessary for ensuring the hardness of the core of the component. In order to obtain these effects, C needs to be 0.05% or more. On the other hand, if the C content exceeds 0.60%, the hardness of the steel bars and wires used as raw materials after hot forging becomes too high. Therefore, the machinability of the material is greatly reduced.
  • the C content may be 0.08% or more, 0.10% or more, or 0.15% or more.
  • the C content may be 0.55% or less, 0.50% or less, 0.40% or less, or 0.35% or less.
  • Si 0.05 to 1.50%
  • Si is an element that increases the hardness of the core by strengthening the solid solution. Further, since Si increases the softening resistance due to high temperature, the wear resistance is improved when the component becomes high temperature in a contact friction environment. In order to exert these effects, Si needs to be 0.05% or more. On the other hand, if the Si content exceeds 1.50%, the hardness of the steel bars and wires used as raw materials after hot forging becomes too high. Therefore, the machinability of the material is greatly reduced.
  • the Si content may be 0.08% or more, 0.10% or more, or 0.20% or more.
  • the Si content may be 1.30% or less, 1.10% or less, or 1.00% or less.
  • Mn is an element that forms fine soft nitrides (Mn 3 N 2 ) in the compound layer and diffusion layer by soft nitriding treatment to enhance wear resistance and bending fatigue strength. Further, Mn increases the hardness of the core portion by strengthening the solid solution. In order to obtain these effects, Mn needs to be 0.20% or more. On the other hand, when the Mn content exceeds 2.50%, not only the effect of increasing wear resistance and bending fatigue strength is saturated, but also the hardness of the steel bars and wires used as raw materials after hot forging becomes high. Too much. Therefore, the machinability of the material is greatly reduced.
  • the Mn content may be 0.40% or more, 0.60% or more, or 1.00% or more.
  • the Mn content may be 2.30% or less, 2.00% or less, or 1.80% or less.
  • P is an impurity that segregates the grain boundaries and embrittles the part. Therefore, it is preferable that the P content is low. If the P content exceeds 0.025%, the wear resistance and bending fatigue strength may decrease. The preferable upper limit of the P content for preventing a decrease in wear resistance and bending fatigue strength is 0.018%, 0.015%, or 0.010%. The P content may be 0%, but the P content may be 0.001% or more, 0.005% or more, or 0.008% or more in consideration of the economic efficiency of refining.
  • S is an element that combines with Mn to form MnS and improves machinability. However, when the S content exceeds 0.050%, coarse MnS is likely to be generated, and the wear resistance and bending fatigue strength are greatly reduced.
  • the preferable upper limit of the S content for preventing a decrease in wear resistance and bending fatigue strength is 0.030%, 0.025%, or 0.020%.
  • the S content may be 0%, but the S content may be 0.001% or more, 0.002%% or more, or 0.005% or more in consideration of the economic efficiency of refining.
  • Cr is an element that forms fine soft nitrides (CrN) in the compound layer and the diffusion layer by soft nitriding treatment to enhance wear resistance and bending fatigue strength.
  • Cr needs to be 0.50% or more.
  • the Cr content may be 0.70% or more, 0.80% or more, or 1.00% or more.
  • the Cr content may be 2.20% or less, 2.00% or less, or 1.80% or less.
  • V 0.05 to 1.30%
  • V is an element that forms fine soft nitrides (VN) in the compound layer and the diffusion layer by the soft nitriding treatment to enhance wear resistance and bending fatigue strength. In order to obtain these effects, V needs to be 0.05% or more.
  • V content exceeds 1.30%, not only the effect of improving wear resistance and bending fatigue strength is saturated, but also the hardness of the steel bars and wire rods as raw materials after hot forging becomes high. Too much. Therefore, the machinability of the material is significantly reduced.
  • the V content may be 0.10% or more, 0.20% or more, or 0.40% or more.
  • the V content may be 1.10% or less, 1.00% or less, or 0.80% or less.
  • Al 0.050% or less
  • Al is not essential in the parts according to this embodiment.
  • Al is a deoxidizing element. Further, Al combines with N to form AlN, and the pinning action of the austenite grains has the effect of refining the structure of the steel material before the soft nitriding treatment and reducing variations in the mechanical properties of the soft nitriding treated parts. In order to obtain this effect, Al needs to be 0.005% or more. On the other hand, Al tends to form hard oxide-based inclusions. If the Al content exceeds 0.050%, the bending fatigue strength is significantly reduced, and the desired bending fatigue strength cannot be obtained even if other requirements are satisfied.
  • the preferable upper limit of the Al content for preventing a decrease in bending fatigue strength is 0.040%, 0.030%, or 0.020%.
  • the Al content may be 0%, but in order to obtain the above-mentioned effects, the Al content may be 0.001% or more, 0.002% or more, or 0.005% or more.
  • N is not essential in the parts according to the present embodiment, and the N content may be 0%.
  • N combines with Mn, Cr, Al, and V to form Mn 3 N 2 , CrN, AlN, and VN.
  • Al and V which have a high tendency to form nitrides, refine the structure of the steel material before the soft nitriding treatment by the pinning action of the austenite grains, and reduce the variation in the mechanical properties of the soft nitriding treated parts.
  • the N content may be 0.0030% or more, 0.0035% or more, or 0.0040% or more.
  • the content of N exceeds 0.0250%, coarse AlN and VN are likely to be formed, so that the above effect is difficult to obtain.
  • the N content may be 0.0220% or less, 0.0200% or less, or 0.0100% or less.
  • the chemical composition of the steel core portion of the gas soft nitriding treated part according to the present embodiment contains the above elements, and the balance contains Fe and impurities.
  • Impurities refer to components contained in raw materials, components mixed in during the manufacturing process, and the like, which do not impair the characteristics of the parts according to the present embodiment.
  • the impurities are, for example, O (oxygen) of 0.0040% or less.
  • the part that mainly contributes to solve the problem is the compound layer.
  • the steel core portion contains a component other than the above-mentioned components.
  • the following elements can be exemplified as components that can be further contained in the steel core portion.
  • the parts according to the present embodiment can solve the problem without containing the elements exemplified below. Therefore, the lower limit of the content of the elements exemplified below is 0%.
  • Mo stabilizes the ⁇ phase in the compound layer.
  • Mo forms fine nitrides (Mo 2 N) in the compound layer and the diffusion layer to increase the hardness. Therefore, Mo is an element effective for improving wear resistance and bending fatigue strength.
  • Mo is preferably contained in an amount of 0.01% or more.
  • the Mo content is 1.50% or less, the hardness of the steel bars and wire rods as raw materials after hot forging can be suppressed, and the machinability of the raw materials can be ensured, which is preferable.
  • a more preferable lower limit of the Mo content is 0.05% or 0.10%.
  • a more preferred upper limit for Mo is less than 1.20%, 1.10%, or 1.00%.
  • Cu improves the hardness of the core of the component and the hardness of the nitrogen diffusion layer as a solid solution strengthening element.
  • the content is preferably 0.01% or more.
  • the Cu content is 1.00% or less, the hardness of the steel bars and wire rods as raw materials after hot forging can be suppressed, and the machinability of the raw materials can be ensured, which is preferable.
  • the Cu content is 1.00% or less, the hot ductility of the material can be improved, and the occurrence of surface scratches during hot rolling and hot forging can be further suppressed, which is preferable.
  • the Cu content may be 0.05% or more, 0.10% or more, or 0.20% or more.
  • the content may be 0.90% or less, 0.80% or less, or 0.60% or less.
  • Ni improves core hardness and surface hardness by solid solution strengthening.
  • the content is preferably 0.01% or more.
  • the Ni content when the Ni content is 1.00% or less, the hardness of the steel bar and the wire rod after hot forging can be suppressed, and the machinability of the material can be further improved, which is preferable.
  • the Ni content may be 0.05% or more, 0.10% or more, or 0.20% or more.
  • the Ni content may be less than 0.90%, 0.80% or less, or 0.70% or less.
  • W improves the core hardness and surface hardness by precipitation of solid solution strengthening and carbide (WC or W 2 C).
  • the content of W is preferably 0.01% or more.
  • the W content may be 0.05% or more, 0.10% or more, or 0.20% or more.
  • the W content may be 0.40% or less, 0.35% or less, or 0.30% or less.
  • Co improves core hardness and surface hardness by solid solution strengthening. Moreover, in order to surely exert the action of Co, the content of Co of 0.01% or more is preferable. On the other hand, when the Co content is 0.50% or less, the hardness of the steel bar and the wire rod after hot forging can be suppressed and the machinability can be ensured, which is preferable.
  • the Co content may be 0.05% or more, 0.10% or more, or 0.20% or more.
  • the Co content may be 0.40% or less, 0.35% or less, or 0.30% or less.
  • Nb 0 to 0.300%
  • Nb combines with N that has penetrated into the surface layer of steel during nitriding and C of the matrix phase to form fine nitrides and carbonitrides.
  • Nb improves the surface hardness and the core hardness.
  • the content of Nb of 0.010% or more is preferable.
  • the Nb content may be 0.015% or more, 0.020% or more, or 0.050% or more.
  • the Nb content may be less than 0.250%, 0.200% or less, or 0.180% or less.
  • Ti 0 to 0.250%
  • Ti combines with N that has penetrated into the surface layer of steel during nitriding and C of the parent phase to form fine nitrides and carbonitrides.
  • the content of Ti 0.005% or more is preferable.
  • the Ti content is 0.250% or less, the formation of coarse nitrides and carbonitrides can be suppressed, which is preferable.
  • the Ti content may be 0.007% or more, 0.010% or more, or 0.020% or more.
  • the Ti content may be 0.200% or less, 0.150% or less, or 0.100% or less.
  • the solid solution B has the effect of suppressing the grain boundary segregation of P and improving the toughness. Further, the BN that binds to N and precipitates improves machinability. In order to surely obtain these effects, B is preferably 0.0005% (5 ppm) or more.
  • B content may be 0.0008% or more, 0.0010% or more, or 0.0020% or more. The content may be 0.0080% or less, 0.0070% or less, or 0.0060% or less.
  • Ca has a function of refining MnS and improving surface fatigue strength.
  • the content of Ca is preferably 0.001% or more.
  • the Ca content may be 0.002% or more, 0.003% or more, or 0.004% or more.
  • the Ca content may be 0.009% or less, 0.008% or less, or 0.007% or less.
  • Mg has a function of refining MnS and improving surface fatigue strength.
  • the content of Mg is preferably 0.001% or more.
  • the Mg content may be 0.002% or more, 0.003% or more, or 0.004% or more.
  • the Mg content may be 0.009% or less, 0.008% or less, or 0.007% or less.
  • REM 0 to 0.010%
  • the term "REM” refers to a total of 17 elements consisting of Sc, Y and lanthanoids, and the REM content means the total content of these 17 elements.
  • lanthanoids are used as REMs, industrially, REMs are added in the form of mischmetal.
  • the REM has the function of refining MnS to improve surface fatigue strength.
  • the content of REM is preferably 0.001% or more.
  • the REM content may be 0.002% or more, 0.003% or more, or 0.004% or more.
  • the REM content may be 0.009% or less, 0.008% or less, or 0.007% or less.
  • the components of the steel core portion of the gas soft nitriding-treated component according to the present embodiment further satisfy the following formula (1) in terms of the content (mass%) of C, Mn, Cr, V, and Mo.
  • the element symbol in the formula (1) indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
  • C, Mn, Cr, V and Mo are elements that affect the thickness of the compound layer.
  • C and Mo have the effect of stabilizing the ⁇ phase and increasing the thickness.
  • Mn, Cr and V have the effect of thinning the compound layer. Therefore, by controlling the content of these elements within a certain range, the thickness of the compound layer can be stably controlled, and the wear resistance and bending fatigue strength can be improved.
  • the value of ⁇ -2.1 ⁇ C + 0.04 ⁇ Mn + 0.5 ⁇ Cr + 1.8 ⁇ V-1.5 ⁇ Mo ⁇ in the formula (1) is preferably 0.00 or more. ..
  • the value of ⁇ -2.1 ⁇ C + 0.04 ⁇ Mn + 0.5 ⁇ Cr + 1.8 ⁇ V-1.5 ⁇ Mo ⁇ exceeds 0.50, the compound layer becomes thin, and the desired surface fatigue strength and desired surface fatigue strength and Bending fatigue strength may not be obtained.
  • the preferable lower limit of the value of ⁇ 2.1 ⁇ C + 0.04 ⁇ Mn + 0.5 ⁇ Cr + 1.8 ⁇ V-1.5 ⁇ Mo ⁇ is 0.03%, 0.05%, or 0.10%.
  • the preferred upper limit of the value of ⁇ 2.1 ⁇ C + 0.04 ⁇ Mn + 0.5 ⁇ Cr + 1.8 ⁇ V-1.5 ⁇ Mo ⁇ is 0.45%, 0.40%, or 0.30%.
  • the measurement location of the chemical composition of the steel core shall be 5.0 mm or more deep from the surface of the part. This is due to the following reasons. It is difficult to strictly identify the boundary between the nitrogen diffusion layer in which nitrogen has penetrated by the nitriding treatment and the steel core portion in which nitrogen has not penetrated. Under the nitriding conditions according to the present embodiment, there is almost no influence of nitrogen intrusion by the nitriding treatment at a position deeper than 5.0 mm from the surface. Therefore, by measuring the chemical composition at a depth of 5.0 mm or more from the surface of the component, the chemical composition of the steel core can be measured without being affected by the chemical composition due to nitriding.
  • the gas soft nitriding part according to the present embodiment is manufactured by processing a steel material (Steel Material) into a basic steel (Roug Sharped Steel) and then performing a soft nitriding treatment under predetermined conditions.
  • the gas nitrocarburizing component 1 according to the present embodiment includes a steel core portion (Core Steel) 11, a nitrogen diffusion layer (Nitrogen Diffusion Layer) 13 formed on the steel core portion 11, and a nitrogen diffusion layer 13. It includes a compound layer 12 formed on the nitrogen diffusion layer 13. That is, the gas nitrocarburizing component 1 according to the present embodiment has a structure in which the compound layer 12 is provided on the surface, the nitrogen diffusion layer 13 is provided inside the compound layer 12, and the steel core portion 11 is provided inside the nitrogen diffusion layer 13. Has.
  • the compound layer is a layer containing iron nitride as a main component, which is formed by combining a nitrogen atom that has penetrated into the structural steel by a nitriding treatment and an iron atom contained in the structural steel.
  • the compound layer is mainly composed of iron nitride, but in addition to iron and nitrogen, oxygen mixed from the outside air and each element contained in the structural steel (that is, each element contained in the steel core). Elements) are also included in the compound layer. Generally, 90% or more (mass%) of the elements contained in the compound layer are nitrogen and iron.
  • the iron nitride contained in the compound layer is mainly Fe 2-3 N ( ⁇ phase) or Fe 4 N ( ⁇ 'phase).
  • the thickness of the compound layer affects the wear resistance and bending strength of gas nitrocarburizing parts.
  • the compound layer 12 has a smaller deformability than the diffusion layer 13. Therefore, if the compound layer is too thick, the compound layer tends to be a fracture starting point due to bending. Further, if the compound layer is too thin, a surface without the compound layer may be present in a part of the component, and the wear resistance and bending strength are lowered.
  • the thickness of the compound layer is 3 ⁇ m or more and 20 ⁇ m or less from the viewpoint of wear resistance and bending strength.
  • the compound layer thickness may be 5 ⁇ m or more, 6 ⁇ m or more, or 8 ⁇ m or more.
  • the compound layer thickness may be 15 ⁇ m or less, 14 ⁇ m or less, or 12 ⁇ m or less.
  • the thickness of the compound layer can be measured by a secondary electron image of a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • the cross section perpendicular to the surface of the gas soft nitriding part is polished and etched with a 3% nital solution for 20 to 30 seconds.
  • the compound layer 12 is observed as an uncorroded layer without unevenness on the surface layer of the component 1, and the diffusion layer 13 is observed as a corroded layer directly under the compound layer.
  • the compound layer 12 in 10 visual fields (area per visual field: 6.6 ⁇ 10 2 ⁇ m 2) of the tissue photograph taken at 4000 times is specified. Then, in each photograph, the thickness of the compound layer 12 is measured at three points every 10 ⁇ m in the horizontal direction. The 10 fields of view are designed so that they do not overlap each other. Then, the average value of the thickness of the compound layer 12 at the measured 30 points is defined as the thickness ( ⁇ m) of the compound layer of the gas soft nitriding processed component.
  • the constituent phase of the compound layer affects the wear resistance and bending strength of the gas nitrocarburizing component.
  • the ⁇ phase has an hcp structure and has a smaller deformability than the ⁇ 'phase, which has an fcc structure.
  • the ⁇ phase has a wider solid solution range of N and C and higher hardness than the ⁇ 'phase.
  • the area ratio of the ⁇ phase is low, the hardness of the compound layer tends to be small, and the wear resistance may be lowered.
  • the area ratio of the ⁇ phase in the compound layer is more than 50%.
  • the preferred range of the area ratio of the ⁇ phase is more than 70%, 75% or more, or 80% or more.
  • the area ratio of the ⁇ phase may be 100%.
  • the upper limit of the area ratio of the ⁇ phase is not particularly limited, but for example, from the viewpoint of further increasing the rotational fatigue bending strength, the area ratio of the ⁇ phase may be 95% or less, 92% or less, 90% or less, or 88% or less. ..
  • the area ratio of the ⁇ phase may be 100% and therefore the balance may be absent. If the balance of the compound layer is present, the balance is mainly composed of the ⁇ 'phase. In addition, a singular phase that does not apply to either the ⁇ phase or the ⁇ 'phase may be included.
  • the compound layer in which the ⁇ phase has an area ratio of more than 50% and the total value of the area ratios of the ⁇ phase and the ⁇ 'phase exceeds 95% contains the ⁇ phase in an area ratio of more than 50%, and the balance. Is considered to be a compound layer in the ⁇ 'phase.
  • the area ratio of the ⁇ phase is obtained by image processing the tissue photograph. Specifically, the ⁇ 'phase in the compound layer was taken with respect to 10 microstructure photographs of the cross section perpendicular to the surface of the nitrided part taken at 4000 times by the backscattered electron diffraction method (Electron Backscatter Diffraction: EBSD). , ⁇ phase is discriminated. Then, the area ratio of the ⁇ phase in the compound layer is obtained by image-processing the tissue photograph and binarizing it. Then, the average value of the measured area ratios of the ⁇ phases in the 10 visual fields is defined as the area ratio (%) of the ⁇ phases.
  • the void area ratio can be measured by SEM.
  • the nitriding parts are Ni-plated.
  • the Ni-plated nitriding part is then cut perpendicular to its surface and its cross section polished. Ni plating is provided before polishing in order to prevent the compound layer from being deformed during polishing.
  • a secondary electron image of a rectangular region (area 90 ⁇ m 2 ) consisting of a product of a depth from the outermost surface to 3 ⁇ m and a length of 30 ⁇ m along the outermost surface is photographed.
  • the black part in the secondary electron image in the above region can be regarded as a void.
  • the outermost surface of the component may have irregularities.
  • the integrated average of the outermost surface is regarded as the outermost surface.
  • the ratio of the total area of the voids to the photograph of each secondary electron image (void area ratio, unit is%) is obtained by an image processing application.
  • the average value of the void area ratio in the measured 10 visual fields is defined as the void area ratio (%) of the component.
  • the measurement target is similarly up to a depth of 3 ⁇ m from the surface.
  • the 10 fields of view are designed so that they do not overlap each other.
  • the size of the void to be measured is 0.3 ⁇ m or more in the equivalent circle diameter in terms of area. That is, in measuring the void area ratio, voids having a diameter equivalent to a circle and less than 0.3 ⁇ m are ignored. Normally, the circle-equivalent diameter of the void is about 1 ⁇ m at the maximum.
  • the void area ratio is preferably less than 11%, less than 10%, less than 9%, less than 7%, or less than 3%, and may be 0%.
  • the lower limit of the void area ratio is not particularly limited, but for example, the void area ratio may be 0% or more, 1% or more, 2% or more, or 4% or more.
  • Hardness of compound layer preferably 740 HV or more
  • the hardness of the compound layer can be increased by increasing the area ratio of the ⁇ phase, precipitating nitrides such as CrN and VN in the compound layer, and dissolving the substituted element in the compound layer. On the other hand, it also changes depending on the nitriding temperature.
  • the gas nitrocarburizing component according to the present embodiment is preferable because the compound layer has a hardness of 740 HV or more and thus has excellent wear resistance and rotational bending fatigue strength.
  • the hardness of the compound layer is more preferably 770 HV or more. By controlling the composition of the compound layer as described above, the hardness of the compound layer can be set to 740 HV or more.
  • a steel material having the above-mentioned steel core component is formed into a predetermined shape by processing such as hot forging, and it is necessary.
  • a shaped steel is obtained by cutting or grinding according to the above conditions.
  • the structural steel is subjected to gas soft nitriding treatment to obtain a gas soft nitriding treated component.
  • a total of 99 volumes of hydrocarbon gas such as CO 2 , CO, or CH 4 or C 3 H 8 is added for the purpose of allowing C to penetrate the surface of the steel. It is applied under the condition that the nitriding potential is controlled in a gas atmosphere containing% or more.
  • the balance may contain an impurity gas such as O 2.
  • NH 3 , H 2 , N 2 , CO 2 , CO, CH 4 , and C 3 H 8 are 99.5% by volume or more in total.
  • the gas added for the purpose of invading C (CO 2 , CO, or a hydrocarbon gas such as CH 4 or C 3 H 8 ) is hereinafter referred to as a carburizing gas.
  • the temperature of the gas nitrocarburizing treatment mainly correlates with the diffusion rate of nitrogen and affects the surface hardness and the depth of the hardened layer. If the treatment temperature is too low, the diffusion rate of nitrogen will be low, and the thickness of the compound layer and the depth of the cured layer will be small. On the other hand, if the soft nitriding treatment temperature is too high, voids are likely to be generated from the surface side of the compound layer, and the hardness of the compound layer is lowered.
  • the soft nitriding treatment temperature in this embodiment is 550 to 630 ° C. around the ferrite temperature range. In this case, it is possible to suppress the hardness of the compound layer from becoming low, and it is possible to suppress the depth of the cured layer from becoming shallow.
  • the total time of the gas soft nitriding treatment that is, the time from the start to the end of the soft nitriding treatment (retention time) correlates with the formation and decomposition of the compound layer and the diffusion and permeation of nitrogen, and the surface hardness and the depth of the hardened layer. Affects the gas. If the treatment time is too short, the thickness of the compound layer and the depth of the cured layer become small. On the other hand, if the treatment time is too long, the void area ratio on the surface of the compound layer increases and the bending fatigue strength decreases. If the processing time is too long, the manufacturing cost will be higher. Therefore, the processing time (holding time) of the gas soft nitriding treatment is preferably 1.0 hour or more and 7.0 hours or less. The lower limit of the holding time is preferably 1.5 hours, more preferably 2.0 hours.
  • a carburized gas represented by the formula (2) is a single or mixed gas containing at least one of CO 2 , CO, or a hydrocarbon gas such as CH 4 or C 3 H 8. It is managed by the input ratio (volume%).
  • Carburizing gas input ratio (volume%) CO 2 , CO, and hydrocarbon gas total input flow rate (l / min) / atmospheric gas total input flow rate (l / min) x 100 ... Equation (2)
  • the input ratio of the carburizing gas in the production method according to the present embodiment is 2% by volume or more and less than 10% by volume.
  • the carburizing gas input ratio may be 3% by volume or more or 4% by volume or more.
  • the carburizing gas input ratio may be 9% by volume or less, or less than 8% by volume.
  • the nitriding potential in gas nitrocarburizing treatment is controlled.
  • the nitriding potential is controlled.
  • it has a compound layer with a thickness of 3 to 20 ⁇ m, and the area ratio of voids is less than 12% in the region from the surface of the compound layer to a depth of 3 ⁇ m. Gas soft nitriding processed parts can be obtained.
  • the nitriding potential K N of the gas soft nitriding treatment is defined by the following equation (3).
  • K N (NH 3 partial pressure) / [(H 2 partial pressure) 3/2 ] (atm- 1 / 2 ) ⁇ ⁇ ⁇ Equation ( 3)
  • the average value K Nave nitride potential K N is the average value of the recorded the nitriding potential K N every 10 minutes from the start to the end of the gas nitrocarburizing treatment.
  • the partial pressure of NH 3 and H 2 uses the value in the unit (atm).
  • the partial pressure of NH 3 and H 2 in the atmosphere of gas nitrocarburizing treatment can be controlled by adjusting the flow rate of the gas.
  • the nitriding potential of the gas nitrocarburizing treatment affects the thickness of the compound layer and the void area ratio.
  • the nitriding potential K N obtained by the formula (3) is maintained within the range of 0.15 or more and 0.40 or less through the gas nitrocarburizing treatment step, and the average value K Nave of the nitriding potential K N during the gas nitrocarburizing treatment step is maintained. It was found that the optimum nitriding potential is set to 0.18 or more and less than 0.30.
  • a compound layer having a thickness of 3 to 20 ⁇ m is stably provided, and the area ratio of voids is 12 in the region from the surface to the depth of 3 ⁇ m. It can be a gas nitriding-treated part having a compound layer of less than%.
  • Steels a to ab having the chemical components shown in Table 1 were melted in a 50 kg vacuum melting furnace to produce molten steel, and the molten steel was cast to produce an ingot.
  • a to t in Table 2-1 and Table 2-2 are steels having a chemical composition specified in this invention.
  • steels u to ab are comparative steels having at least one element or more that deviates from the chemical composition specified in the present invention.
  • "X" indicates a value of "-2.1 x C + 0.04 x Mn + 0.5 x Cr + 1.8 x V-1.5 x Mo".
  • the underline indicates that the composition is outside the scope of the present invention, and the blank indicates that the alloying element is not intentionally added.
  • components (remaining portions) other than the components shown in Table 1 are Fe and impurities. In all steels, O was contained as an impurity in about 10 ppm.
  • Each ingot of the steels a to ab was hot forged to obtain a round bar having a diameter of 40 mm. Subsequently, after each round bar was annealed, it was cut to produce a small roller for a roller pitting test for evaluating the wear resistance shown in FIG. 3 and a large roller shown in FIG. Further, a cylindrical test piece for evaluating the rotational bending fatigue strength shown in FIG. 5 was prepared.
  • test pieces were subjected to gas nitrocarburizing treatment under the following conditions.
  • the test piece was charged into a gas soft nitriding furnace, NH 3 , H 2 , N 2 , and CO 2 gases were introduced into the furnace, and the soft nitriding treatment was performed under the conditions shown in Table 2-1 and Table 2-2. Was carried out.
  • the total input flow rate of NH 3 , H 2 , and N 2 gas and the input flow rate of CO 2 gas were not changed during the treatment so that the input ratio of CO 2 gas was constant.
  • the test piece after the soft nitriding treatment was oil-cooled using oil at 80 ° C.
  • the H 2 partial pressure in the atmosphere was measured using a heat conduction type H 2 sensor directly mounted on the gas soft nitride furnace body. The difference in thermal conductivity between the standard gas and the measured gas was converted into gas concentration and measured. H 2 partial pressure during the gas nitrocarburizing treatment, was continuously measured.
  • the NH 3 partial pressure was measured every 10 minutes using a glass tube type NH 3 analyzer mounted outside the furnace.
  • the NH 3 flow rate, the H 2 flow rate, and the N 2 flow rate were adjusted so that the nitriding potential K N converged to the target value. Record the nitriding potential K N every 10 minutes, the minimum value being processed to derive the maximum value and average value.
  • the compound layer can be confirmed as an uncorroded layer existing on the surface layer of steel.
  • the ratio of the total area of voids (void area ratio, unit is%) to the area 90 ⁇ m 2 in the range of 3 ⁇ m depth from the outermost surface can be determined by an image processing application (manufactured by JEOL Ltd .; Anallysis Station). Obtained by. Then, the average value of the measured 10 visual fields was defined as the void area ratio (%). Even when the compound layer was less than 3 ⁇ m, the measurement target was similarly up to a depth of 3 ⁇ m from the surface.
  • the hardness of the compound layer was measured by the following method using a nanoindentation device (manufactured by Hysiron; TI950).
  • the Vickers hardness HV was measured from the obtained load-displacement curve by randomly pushing 50 points of the indenter with a pushing load of 10 mN at a position near the center in the thickness direction of the compound layer.
  • Indenter is triangular pyramid (Berkovich) shape, hardness derivation complies with ISO14577-1, the conversion from nanoindentation hardness H IT to Vickers hardness HV, was performed by the following equation.
  • HV 0.0924 x H IT (MPa)
  • HV hardness
  • roller pitting test was performed under the conditions shown in Table 4 by combining the above-mentioned small roller for the roller pitting test and the large roller for the roller pitting test having the shape shown in FIG.
  • the unit of dimensions in FIGS. 3 and 4 is "mm".
  • the large roller for roller peening test uses steel that meets the SCM420 standard of JIS G 4053 (2016), and is used in the general manufacturing process, that is, "normalizing-> test piece processing-> co-deposit carburizing by gas carburizing furnace-> After being produced by the process of "low temperature tempering ⁇ polishing", shot peening treatment with a projection pressure of 0.2 MPa was performed using a steel ball with a particle size of 0.8 mm for the purpose of imparting fine irregularities to the surface.
  • the Vickers hardness HV at a position of 0.05 mm from the surface, that is, at a depth of 0.05 mm is 740 to 760, and the depth of the Vickers hardness Hv of 550 or more is 0.8 to 1.0 mm.
  • the Vickers hardness HV at a position of 0.05 mm from the surface, that is, at a depth of 0.05 mm is 740 to 760, and the depth of the Vickers hardness Hv of 550 or more is 0.8 to 1.0 mm.
  • Table 3 shows the test conditions for which the wear resistance was evaluated.
  • the test was completed with 5 ⁇ 10 6 repetitions, and the wear depth of the small roller after the test was measured.
  • a surface roughness shape measuring machine (manufactured by Tokyo Seimitsu Co., Ltd .; SURFCOM FLEX) scans the worn part of the small roller after the test along the spindle direction to acquire the cross-sectional shape profile, and the maximum of the obtained cross-sectional shape profile. The difference between the depth (wear part) and the minimum depth (non-wear part) was measured as the maximum wear depth.
  • the value of the wear depth was calculated by measuring and averaging the maximum wear depths at five measurement positions on the same test piece (small roller). In the parts of the present invention, it was aimed that the wear depth was 10 ⁇ m or less.
  • the goal was to have a maximum stress of 500 MPa or more in the fatigue limit.
  • Test results The results are shown in Table 2-1 and Table 2-2.
  • the steel composition and the conditions of the gas soft nitriding treatment were within the range of the present invention, the compound layer thickness was 3 ⁇ m or more and 20 ⁇ m or less, and the compound layer void area ratio was less than 12%.
  • good results were obtained with a wear depth of less than 10 ⁇ m and a rotational bending fatigue strength of 500 MPa or more.
  • test numbers 27 to 45 the composition of the steel and some of the conditions for the gas soft nitriding treatment are outside the scope of the present invention, and any one of the thickness of the compound layer, the area ratio of the ⁇ phase, and the void area ratio is determined. Alternatively, a plurality of characteristics did not reach the target value in the present invention. As a result, wear resistance or rotational bending fatigue strength did not meet the object of the present invention.
  • Test number 27 is a comparative example in which the gas nitrocarburizing treatment temperature was too high during production. As a result, in Test No. 27, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Test number 28 is a comparative example in which the gas nitrocarburizing treatment temperature was too low during production. As a result, in Test No. 28, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Test number 29 is a comparative example in which the gas nitrocarburizing treatment time was too long during production. As a result, in Test No. 29, the thickness of the compound layer became excessive, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Test number 30 is a comparative example in which the gas nitrocarburizing treatment time was too short at the time of production. As a result, in Test No.
  • Test number 31 is a comparative example in which the nitriding potential K N becomes too high during manufacturing. As a result, in Test No. 31, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Test number 32 is a comparative example in which the nitriding potential K N was too low during production. As a result, in Test No. 32, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Test number 33 is a comparative example in which the gas nitrocarburizing treatment time was too long during production. As a result, in Test No.
  • Test number 34 is a comparative example in which the average nitriding potential K Nave was too low at the time of manufacture. As a result, in Test No. 34, the thickness of the compound layer was insufficient, the ⁇ area ratio was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Test number 35 is a comparative example in which the carburizing gas input ratio was too high at the time of production. As a result, in Test No. 35, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Test number 36 is a comparative example in which the carburizing gas input ratio was too low at the time of production (that is, nitriding was performed instead of soft nitriding). As a result, in test number 36, the ⁇ area ratio was insufficient and the wear resistance was insufficient.
  • Serial number 37 (steel u) is a comparative example in which ⁇ 2.1 ⁇ C + 0.04 ⁇ Mn + 0.5 ⁇ Cr + 1.8 ⁇ V-1.5 ⁇ Mo was too high in the chemical composition of the steel core portion. As a result, in Test No. 37, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • Serial number 38 (steel v) is a comparative example in which ⁇ 2.1 ⁇ C + 0.04 ⁇ Mn + 0.5 ⁇ Cr + 1.8 ⁇ V-1.5 ⁇ Mo was too low in the chemical composition of the steel core portion. As a result, in Test No. 38, the thickness of the compound layer became excessive, and the rotational bending fatigue strength was insufficient.
  • Serial number 39 (steel w) is a comparative example in which the amount of C in the steel core is too low. As a result, the wear resistance of test number 39 was insufficient.
  • Serial number 40 (steel x) is a comparative example in which the amount of Mn in the steel core is too low. As a result, in Test No.
  • Serial number 41 (steel y) is a comparative example in which the amount of Cr in the steel core is too low. As a result, in Test No. 41, the wear resistance and the rotational bending fatigue strength were insufficient.
  • Serial number 42 (steel z) is a comparative example in which the amount of V in the steel core is too low. As a result, in Test No. 42, the wear resistance and the rotational bending fatigue strength were insufficient.
  • Serial number 43 (steel aa) is a comparative example in which the P amount of the steel core portion is too high. As a result, in Test No. 43, the wear resistance and the rotational bending fatigue strength were insufficient.
  • Serial number 44 (steel ab) is a comparative example in which the S amount of the steel core portion is too high. As a result, in Test No. 44, the wear resistance and the rotational bending fatigue strength were insufficient.
  • Production number 45 is a comparative example in which the nitriding potential K N and the average nitriding potential K Nave were too high at the time of production. As a result, in Test No. 45, the thickness of the compound layer became excessive, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
  • a soft nitriding-treated part having excellent wear resistance and rotational bending fatigue strength and a method for manufacturing the same, and a continuously variable transmission (CVT) having particularly excellent wear resistance and bending fatigue strength.
  • CVT continuously variable transmission

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Abstract

A gas soft-nitriding processed article according to an aspect of the present invention comprises a steel core part, a compound layer, and a nitrogen diffusion layer that exists between the steel core part and the compound layer, wherein: the steel core part contains, in terms of mass%, 0.05%-0.60% of C, 0.05%-1.50% of Si, 0.20%-2.50% of Mn, not more than 0.025% of P, not more than 0.050% of S, 0.50%-2.50% of Cr, 0.05%-1.30% of V, not more than 0.050% of Al, and not more than 0.0250% of N, with the remainder being Fe and impurities; the amounts of C, Mn, Cr, V, and Mo in the composition of the steel core part satisfy 0.00≤-2.1×C+0.04×Mn+0.5×Cr+1.8×V-1.5×Mo≤0.50; the thickness of the compound layer is 3-20 μm; the compound layer contains an ε phase in an amount of more than 50% in terms of area, with the remainder being a γ' phase; and in a region of the compound layer up to a depth of 3 μm from the surface thereof, the area ratio of voids is less than 12%.

Description

ガス軟窒化処理部品及びその製造方法Gas soft nitriding parts and their manufacturing methods
　本発明は、ガス軟窒化処理を施された鋼部品とその製造方法に関する。 The present invention relates to a steel part subjected to gas soft nitriding treatment and a method for manufacturing the same.
　自動車や各種産業機械などに使用される鋼部品には、表面の疲労強度が要求されるものがある。例えばトランスミッション中のＣＶＴプーリやカムシャフトには、耐摩耗性や曲げ疲労強度が要求され、歯車には、面疲労強度や曲げ疲労強度などの疲労特性が要求される。これらの特性の改善には、表面硬度の向上が有効とされている。そのため、これらの鋼部品には、窒化および軟窒化処理の適用が進められている。窒化処理および軟窒化処理には、高い表面硬度が得られ、かつ熱処理ひずみが小さいという利点がある。 Some steel parts used in automobiles and various industrial machines require surface fatigue strength. For example, CVT pulleys and camshafts in transmissions are required to have abrasion resistance and bending fatigue strength, and gears are required to have fatigue characteristics such as surface fatigue strength and bending fatigue strength. It is said that improvement of surface hardness is effective for improving these characteristics. Therefore, nitriding and soft nitriding treatments are being applied to these steel parts. The nitriding treatment and the soft nitriding treatment have the advantages that high surface hardness can be obtained and heat treatment strain is small.
　窒化は、鋼の表面に窒素を侵入させる表面硬化熱処理であり、軟窒化は、鋼の表面に窒素と炭素を侵入させる表面硬化熱処理である。窒化および軟窒化に用いる媒体には、ガス、塩浴、プラズマなどがある。自動車のトランスミッション部品には、主に、生産性に優れるガス窒化およびガス軟窒化が適用されている。 Nitriding is a surface hardening heat treatment that allows nitrogen to penetrate the surface of steel, and soft nitriding is a surface hardening heat treatment that allows nitrogen and carbon to penetrate the surface of steel. The medium used for nitriding and soft nitriding includes gas, salt bath, plasma and the like. Gas nitriding and gas nitrocarburizing, which are excellent in productivity, are mainly applied to transmission parts of automobiles.
　ガス窒化およびガス軟窒化によって生成される硬化層は、窒素拡散層（以下、拡散層と略す場合がある）と、拡散層よりも表面側に生成する厚さ数～数十μｍの化合物層である。 The cured layer produced by gas nitriding and gas nitrocarburizing consists of a nitrogen diffusion layer (hereinafter, may be abbreviated as a diffusion layer) and a compound layer having a thickness of several to several tens of μm formed on the surface side of the diffusion layer. be.
　拡散層は、侵入窒素及び炭素による固溶強化機構、並びに窒化物の粒子分散強化機構により硬化された層である。拡散層の硬さおよび深さを向上することで、部品の曲げ疲労強度や面疲労強度が向上することが知られている。従来から、拡散層の硬さや深さの向上については多くの研究がなされてきた。 The diffusion layer is a layer cured by a solid solution strengthening mechanism by penetrating nitrogen and carbon, and a particle dispersion strengthening mechanism of nitride. It is known that improving the hardness and depth of the diffusion layer improves the bending fatigue strength and surface fatigue strength of parts. Many studies have been conducted on the improvement of the hardness and depth of the diffusion layer.
　化合物層は主に、Ｆｅ２Ｎ～Ｆｅ３Ｎ（ε相）とＦｅ４Ｎ（γ’相）の鉄窒化物で構成されており、母相に比べて硬さが極めて高い。そのため、化合物層は耐摩耗性の向上に有効である。ε相は、γ’相に比べＣの固溶範囲が大きく、成長速度も大きい。このことから、浸炭性ガスを混合させる軟窒化では、ε相主体の化合物層が形成されやすい。そのため軟窒化は、窒化に比べて短時間で、さらに部品の鋼種を問わず、厚い化合物層を得ることができる。そのため軟窒化は、部品の耐摩耗性を向上させる目的で古くから利用されてきた。 The compound layer is mainly composed of iron nitrides of Fe 2 N to Fe 3 N (ε phase) and Fe 4 N (γ'phase), and has extremely high hardness as compared with the matrix phase. Therefore, the compound layer is effective in improving the wear resistance. The ε phase has a larger solid solution range of C and a higher growth rate than the γ'phase. For this reason, in soft nitriding in which a carburizing gas is mixed, a compound layer mainly composed of the ε phase is likely to be formed. Therefore, soft nitriding can obtain a thick compound layer in a shorter time than nitriding, regardless of the steel type of the component. Therefore, soft nitriding has been used for a long time for the purpose of improving the wear resistance of parts.
　化合物層と、耐摩耗性および疲労強度との関係についての従来知見として、以下が挙げられる。 The following are examples of conventional findings regarding the relationship between the compound layer and wear resistance and fatigue strength.
　特許文献１には、ε単相の化合物層の厚さが８～３０μｍ、ビッカース硬さが６８０ＨＶ以上であり、化合物層中の空隙の体積率が１０％未満であることを特徴とする窒化または軟窒化部品が開示されている。 Patent Document 1 describes nitriding or nitriding or characterized in that the thickness of the ε single-phase compound layer is 8 to 30 μm, the Vickers hardness is 680 HV or more, and the volume ratio of the voids in the compound layer is less than 10%. Soft nitride components are disclosed.
　また、特許文献２には、窒化後における化合物層厚さが１～５μｍであり、且つ、窒化後の面粗度がＲｚ１．６以下であり、化合物層はγ’相またはγ’相とε相の混相であり、空隙比率が５％以下であることを特徴とする回転圧縮機用ベーンが開示されている。
　特許文献３には、目的とする特性に応じて、鋼の成分、特にＣ、Ｍｎ、Ｃｒ、Ｖ、Ｍｏの含有量を調整し、窒化ポテンシャル制御下で窒化部品を作製することが開示されている。
　特許文献４には、面疲労強度に加え回転曲げ疲労強度に優れた部品であって、所定の化学組成を有する鋼材を素材とし、鋼材の表面に形成された、鉄、窒素及び炭素を含有する厚さ３μｍ以上２０μｍ未満の化合物層を有し、表面から５μｍの深さまでの範囲の化合物層における相構造がγ’相を面積率で５０％以上含有し、表面から３μｍの深さまでの範囲において空隙面積率が１％未満であり、化合物層表面の圧縮残留応力が５００ＭＰａ以上であることを特徴とする窒化処理部品が開示されている。
　特許文献５には、低合金鋼を５５０～６２０℃に加熱し、処理時間Ａを１．５～１０時間とするガス軟窒化処理を行うに際し、窒化ポテンシャルＫｎＸが０．１０～１．００、平均値ＫｎＸａｖｅが０．２０～０．５５であり、処理時間をＸ時間とする高Ｋｎ値処理の後、窒化ポテンシャルＫｎＹが０．０１～０．２０の範囲内であり、平均値ＫｎＹａｖｅが０．０２～０．１５であり、処理時間をＹ時間とする低Ｋｎ値処理を行い、前記平均値ＫｎＸａｖｅと、前記平均値ＫｎＹａｖｅと、前記処理時間Ａと、前記高Ｋｎ値処理及び前記低Ｋｎ値処理の処理時間Ｘ及びＹとから、軟窒化処理の窒化ポテンシャルの平均値Ｋｎａｖｅが０．０５～０．２０であることを特徴とする低合金鋼のガス軟窒化処理方法が開示されている。 Further, in Patent Document 2, the compound layer thickness after nitriding is 1 to 5 μm, the surface roughness after nitriding is Rz 1.6 or less, and the compound layer is γ'phase or γ'phase and ε. A vane for a rotary compressor, which is a mixed phase of phases and has a void ratio of 5% or less, is disclosed.
Patent Document 3 discloses that a nitriding component is produced under nitriding potential control by adjusting the content of steel components, particularly C, Mn, Cr, V, and Mo, according to a target property. There is.
Patent Document 4 describes a component having excellent rotational bending fatigue strength in addition to surface fatigue strength, which is made of a steel material having a predetermined chemical composition and contains iron, nitrogen and carbon formed on the surface of the steel material. It has a compound layer with a thickness of 3 μm or more and less than 20 μm, and the phase structure of the compound layer in the range from the surface to a depth of 5 μm contains γ'phase in an area ratio of 50% or more, and in a range from the surface to a depth of 3 μm. A nitriding component characterized in that the void area ratio is less than 1% and the compressive residual stress on the surface of the compound layer is 500 MPa or more is disclosed.
Patent Document 5 describes that when low alloy steel is heated to 550 to 620 ° C. and gas nitrocarburizing treatment is performed with a treatment time A of 1.5 to 10 hours, the nitriding potential Kn X is 0.10 to 1.00. , The average value Kn Xave is 0.20 to 0.55, and after high Kn value processing with the processing time as X hours, the nitriding potential Kn Y is in the range of 0.01 to 0.20, and the average value. Low Kn value processing in which Kn Yave is 0.02 to 0.15 and the processing time is Y time is performed, and the average value Kn Xave , the average value Kn Yave , the processing time A, and the high Kn From the processing times X and Y of the value treatment and the low Kn value treatment, gas nitrocarburizing of a low alloy steel characterized in that the average value Kn ave of the nitriding potential of the soft nitriding treatment is 0.05 to 0.20. The processing method is disclosed.
国際公開第２０１６／１５３００９号International Publication No. 2016/15309 日本国特開２００５－１６３８６号公報Japanese Patent Application Laid-Open No. 2005-16386 国際公開第２０１９／０９８３４０号International Publication No. 2019/098340 国際公開第２０１８／０６６６６６号International Publication No. 2018/0666666 日本国特開２０１５－１７５００９号公報Japanese Patent Application Laid-Open No. 2015-17509
　特許文献１の窒化部品または軟窒化部品では、化合物層の最表面から最下面（化合物層と拡散層の界面）中の空隙比率を抑制している。しかし実際には、空隙は鋼の表面～約３μｍまでの領域に集中することが多い。この領域において空隙が多いと、良好な曲げ疲労強度が得られない。本発明者らが特許文献３の窒化処理部品を評価したところ、化合物層の空孔は部品の表層領域に集中的に生じており、この表層領域における空孔の体積率は４０％を超えていた。そのため、表面～３μｍにおける空隙比率を抑制するための鋼の成分、及び窒化制御方法に関し、特許文献１の技術には改善の余地がある。 In the nitrided component or soft nitrided component of Patent Document 1, the void ratio in the outermost surface to the lowermost surface (the interface between the compound layer and the diffusion layer) of the compound layer is suppressed. However, in practice, the voids are often concentrated in the area from the surface of the steel to about 3 μm. If there are many voids in this region, good bending fatigue strength cannot be obtained. When the present inventors evaluated the nitrided component of Patent Document 3, the pores of the compound layer were concentrated in the surface layer region of the component, and the volume fraction of the pores in this surface layer region exceeded 40%. rice field. Therefore, there is room for improvement in the technique of Patent Document 1 regarding the steel component for suppressing the void ratio at the surface to 3 μm and the nitriding control method.
　特許文献２の窒化部品では、化合物層が最小１μｍと非常に薄く、ε相よりも低硬度のγ’相を主体とした相構造である。そのため、特許文献２の技術によれば、良好な耐摩耗性が得られない可能性がある。 The nitrided part of Patent Document 2 has a very thin compound layer of at least 1 μm, and has a phase structure mainly composed of a γ'phase having a hardness lower than that of the ε phase. Therefore, according to the technique of Patent Document 2, good wear resistance may not be obtained.
　特許文献３及び特許文献４の窒化部品では、化合物層の組織が、硬度が低いγ’相を主体とするものとされている。特許文献５に記載の技術では、化合物層の生成を抑制することを課題とし、このために窒化ポテンシャルを通常より低い値としている。そのため、特許文献３～５の窒化部品は、耐摩耗性に関して改善の余地があると考えられる。 In the nitrided parts of Patent Documents 3 and 4, the structure of the compound layer is mainly composed of the γ'phase having a low hardness. In the technique described in Patent Document 5, it is an object to suppress the formation of a compound layer, and for this reason, the nitriding potential is set to a value lower than usual. Therefore, it is considered that the nitrided parts of Patent Documents 3 to 5 have room for improvement in terms of wear resistance.
　本発明の目的は、良好な耐摩耗性に加え、回転曲げ疲労強度にも優れた部品及びその製造方法を提供することである。 An object of the present invention is to provide a part having excellent wear resistance as well as rotational bending fatigue strength and a method for manufacturing the same.
　本発明の要旨は以下のとおりである。
（１）本発明の一態様に係るガス軟窒化処理部品は、鋼芯部と、化合物層と、前記鋼芯部と前記化合物層との間に存在する窒素拡散層と、を備え、前記鋼芯部の組成が、質量％で、Ｃ：０．０５％～０．６０％、Ｓｉ：０．０５％～１．５０％、Ｍｎ：０．２０％～２．５０％、Ｐ：０．０２５％以下、Ｓ：０．０５０％以下、Ｃｒ：０．５０％～２．５０％、Ｖ：０．０５％～１．３０％、Ａｌ：０．０５０％以下、及びＮ：０．０２５０％以下を含有し、残部はＦｅ及び不純物を含み、前記鋼芯部の前記組成におけるＣ、Ｍｎ、Ｃｒ、Ｖ、Ｍｏの含有量が式１を満たし、前記化合物層の厚さが３～２０μｍであり、前記化合物層は、ε相を面積率で５０％超含有し、残部がγ’相であり、前記化合物層の表面から深さ３μｍまでの領域において、空隙の面積比率が１２％未満である。
　０．００≦－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ≦０．５０・・・式１
　ただし、式１中の元素記号は当該元素の含有量（質量％）を示し、含有しない場合は０を代入する。
（２）上記（１）に記載のガス軟窒化処理部品では、前記鋼芯部の前記組成が、質量％で、Ｃ：０．０５％～０．６０％、Ｓｉ：０．０５％～１．５０％、Ｍｎ：０．２０％～２．５０％、Ｐ：０．０２５％以下、Ｓ：０．０５０％以下、Ｃｒ：０．５０％～２．５０％、Ｖ：０．０５％～１．３０％、Ａｌ：０．０５０％以下、Ｎ：０．０２５０％以下、Ｍｏ：０～１．５０％、Ｃｕ：０～１．００％、Ｎｉ：０～１．００％、Ｗ：０～０．５０％、Ｃｏ：０～０．５０％、Ｎｂ：０～０．３００％、Ｔｉ：０～０．２５０％、Ｂ：０～０．０１００％、Ｃａ：０～０．０１０％、Ｍｇ：０～０．０１０％、及びＲＥＭ：０～０．０１０％を含有し、残部はＦｅ及び不純物からなってもよい。
（３）上記（１）又は（２）に記載のガス軟窒化処理部品では、前記鋼芯部の前記組成において、Ｃ：０．０５％～０．３５％であってもよい。
（４）上記（１）～（３）のいずれか一項に記載のガス軟窒化処理部品前記化合物層における前記ε相が面積率で９０％以下であってもよい。
（５）上記（１）～（４）のいずれか一項に記載のガス軟窒化処理部品では、前記化合物層の厚さが６μｍ以上であってもよい。
（６）本発明の別の態様に係るガス軟窒化処理部品の製造方法は、上記（１）～（５）のいずれか一項に記載のガス軟窒化処理部品の製造方法であって、上記（１）～（３）のいずれか一項に記載の鋼芯部の組成を有する鋼材を所定の形状に加工して素形鋼を得る工程と、前記素形鋼にガス軟窒化処理を施す工程と、を有し、前記ガス軟窒化処理は、ＣＯ２、ＣＯ、炭化水素ガスのうち少なくとも１種を含むガスを、式２で表す浸炭性ガス投入比率で２体積％以上１０体積％未満含み、残部はＮＨ３、Ｈ２、Ｎ２及び不純物ガスであるガス雰囲気中において、温度５５０℃以上６３０℃以下で、１時間以上７時間以下保持して行い、前記ガス雰囲気は、式３によって求められる窒化ポテンシャルＫＮが、前記ガス軟窒化処理を施す工程を通じて０．１５以上０．４０以下の範囲内であって、前記窒化ポテンシャルＫＮの平均値ＫNａｖｅが０．１８以上０．３０未満である。
　浸炭性ガス投入比率（体積％）＝ＣＯ２、ＣＯ、炭化水素ガスの総投入流量（ｌ／ｍｉｎ）／雰囲気ガスの総投入流量（ｌ／ｍｉｎ）×１００・・・式２
　ＫＮ＝（ＮＨ３分圧）／［（Ｈ２分圧）3/2］（ａｔｍ－１／２）・・・式３ The gist of the present invention is as follows.
(1) The gas nitrocarburizing component according to one aspect of the present invention includes a steel core portion, a compound layer, and a nitrogen diffusion layer existing between the steel core portion and the compound layer, and the steel. The composition of the core is C: 0.05% to 0.60%, Si: 0.05% to 1.50%, Mn: 0.20% to 2.50%, P: 0. 025% or less, S: 0.050% or less, Cr: 0.50% to 2.50%, V: 0.05% to 1.30%, Al: 0.050% or less, and N: 0.0250 % Or less, the balance contains Fe and impurities, the content of C, Mn, Cr, V, Mo in the composition of the steel core portion satisfies the formula 1, and the thickness of the compound layer is 3 to 20 μm. The compound layer contains more than 50% of the ε phase in terms of area ratio, the balance is the γ'phase, and the area ratio of the voids is less than 12% in the region from the surface of the compound layer to a depth of 3 μm. Is.
0.00 ≦ -2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo ≦ 0.50 ・ ・ ・ Equation 1
However, the element symbol in the formula 1 indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
(2) In the gas soft nitrided component according to (1) above, the composition of the steel core portion is C: 0.05% to 0.60% and Si: 0.05% to 1 in mass%. .50%, Mn: 0.20% to 2.50%, P: 0.025% or less, S: 0.050% or less, Cr: 0.50% to 2.50%, V: 0.05% ~ 1.30%, Al: 0.050% or less, N: 0.0250% or less, Mo: 0 to 1.50%, Cu: 0 to 1.00%, Ni: 0 to 1.00%, W : 0 to 0.50%, Co: 0 to 0.50%, Nb: 0 to 0.300%, Ti: 0 to 0.250%, B: 0 to 0.0100%, Ca: 0 to 0. It may contain 010%, Mg: 0 to 0.010%, and REM: 0 to 0.010%, with the balance consisting of Fe and impurities.
(3) In the gas nitrocarburizing component according to (1) or (2) above, C: 0.05% to 0.35% may be used in the composition of the steel core portion.
(4) The gas soft nitriding treatment component according to any one of (1) to (3) above. The ε phase in the compound layer may have an area ratio of 90% or less.
(5) In the gas nitrocarburizing component according to any one of (1) to (4) above, the thickness of the compound layer may be 6 μm or more.
(6) The method for manufacturing a gas nitriding-treated part according to another aspect of the present invention is the method for manufacturing a gas nitriding-treated part according to any one of (1) to (5) above. A step of processing a steel material having the composition of the steel core portion according to any one of (1) to (3) into a predetermined shape to obtain a raw steel, and performing gas nitrocarburizing treatment on the raw steel. The gas nitrocarburizing treatment comprises steps and, in which the gas containing at least one of CO 2 , CO and hydrocarbon gas is contained in a carburable gas input ratio represented by the formula 2 in an amount of 2% by volume or more and less than 10% by volume. In a gas atmosphere containing NH 3 , H 2 , N 2 and impurity gas, the balance is maintained at a temperature of 550 ° C. or higher and 630 ° C. or lower for 1 hour or more and 7 hours or less. The required nitriding potential K N is within the range of 0.15 or more and 0.40 or less through the step of performing the gas soft nitriding treatment, and the average value K Nave of the nitriding potential K N is 0.18 or more and 0.30. Is less than.
Carburizing gas input ratio (volume%) = CO 2 , CO, total input flow rate of hydrocarbon gas (l / min) / total input flow rate of atmospheric gas (l / min) × 100 ... Equation 2
K N = (NH 3 partial pressure) / [(H 2 partial pressure) 3/2 ] (atm- 1 / 2 ) ・ ・ ・ Equation 3
　本発明によれば、耐摩耗性に加え回転曲げ疲労強度に優れた軟窒化処理部品を得ることができる。 According to the present invention, it is possible to obtain a soft nitriding-treated component having excellent rotational bending fatigue strength in addition to wear resistance.
本実施形態に係るガス軟窒化処理部品の表面の拡大図である。It is an enlarged view of the surface of the gas soft nitriding processed component which concerns on this embodiment. 本実施形態に係るガス軟窒化処理部品の製造方法を説明するフローチャートである。It is a flowchart explaining the manufacturing method of the gas nitrocarburizing part which concerns on this embodiment. ローラピッティング試験用小ローラの形状を示す図である。なお、図中の寸法の単位は「ｍｍ」である。It is a figure which shows the shape of the small roller for a roller pitting test. The unit of dimensions in the figure is "mm". ローラピッティング試験用大ローラの形状を示す図である。なお、図中の寸法の単位は「ｍｍ」である。It is a figure which shows the shape of the large roller for a roller pitting test. The unit of dimensions in the figure is "mm". 回転曲げ疲労試験用円柱試験片の形状を示す図である。なお、図中の寸法の単位は「ｍｍ」である。It is a figure which shows the shape of the cylindrical test piece for a rotary bending fatigue test. The unit of dimensions in the figure is "mm".
　本発明者らは、軟窒化によって鋼材の表面に形成される化合物層の形態に着目し、化合物層の形態と疲労強度との関係を調査した。 The present inventors focused on the morphology of the compound layer formed on the surface of the steel material by soft nitriding, and investigated the relationship between the morphology of the compound layer and the fatigue strength.
　その結果、成分を調整した鋼材を、一定の雰囲気下で窒化ポテンシャル制御しながら軟窒化することにより、化合物層の表面側に生成される空隙を抑制可能であることを知見した。さらに、化合物層の厚さを一定の範囲とし、化合物層の硬さを一定値以上とすることにより、優れた耐摩耗性、及び回転曲げ疲労強度を有する軟窒化部品を作製できることを見出した。 As a result, it was found that the voids generated on the surface side of the compound layer can be suppressed by soft nitriding the steel material whose composition has been adjusted while controlling the nitriding potential in a constant atmosphere. Furthermore, it has been found that by setting the thickness of the compound layer within a certain range and the hardness of the compound layer to a certain value or more, a soft nitrided part having excellent wear resistance and rotational bending fatigue strength can be produced.
　以上の知見により得られた、本実施形態に係るガス軟窒化処理部品について詳しく説明する。本実施形態に係るガス軟窒化処理部品１（以下、単に「部品」と記載する場合がある）は、図１に示されるように、鋼芯部１１（以下、単に「鋼」と記載する場合がある）と、化合物層１２と、鋼芯部１１と化合物層１２との間に存在する窒素拡散層１３（以下、単に「拡散層」と記載する場合がある）とを備える。
［鋼の組成］
　以下、鋼の組成について説明する。以下に述べる各成分元素の含有量は、特に断りがない限り、鋼の組成に関するものである。化合物層及び拡散層の組成は、以下に説明される範囲内に限定されない。また、鋼における各成分元素の含有量及び部品表面における元素の濃度の「％」は、特に断りのない限り「質量％」を意味する。 The gas nitrocarburizing component according to the present embodiment obtained from the above findings will be described in detail. As shown in FIG. 1, the gas nitrocarburizing component 1 (hereinafter, may be simply referred to as “part”) according to the present embodiment is referred to as a steel core portion 11 (hereinafter, simply referred to as “steel”). There is), and a nitrogen diffusion layer 13 (hereinafter, may be simply referred to as a “diffusion layer”) existing between the compound layer 12 and the steel core portion 11 and the compound layer 12.
[Steel composition]
Hereinafter, the composition of the steel will be described. Unless otherwise specified, the content of each component element described below relates to the composition of steel. The composition of the compound layer and the diffusion layer is not limited to the range described below. Further, "%" of the content of each component element in steel and the concentration of the element on the surface of the component means "mass%" unless otherwise specified.
　［Ｃ：０．０５～０．６０％］
　Ｃは、ε相の形成を安定化させる。そのため、Ｃは、窒化後の化合物層の厚さおよびε相の体積比率を高め、部品の耐摩耗性を高めるのに有効な元素である。この他、Ｃは、部品の芯部硬さを確保するために必要な元素である。これらの効果を得るため、Ｃは０．０５％以上が必要である。一方、Ｃの含有量が０．６０％を超えると、素材となる棒鋼及び線材等の熱間鍛造後の硬さが高くなりすぎる。そのため、素材の切削加工性が大きく低下する。Ｃ含有量を０．０８％以上、０．１０％以上、又は０．１５％以上としてもよい。Ｃ含有量を０．５５％以下、０．５０％以下、０．４０％以下、又は０．３５％以下としてもよい。 [C: 0.05 to 0.60%]
C stabilizes the formation of the ε phase. Therefore, C is an element effective for increasing the thickness of the compound layer after nitriding and the volume ratio of the ε phase and enhancing the wear resistance of the component. In addition, C is an element necessary for ensuring the hardness of the core of the component. In order to obtain these effects, C needs to be 0.05% or more. On the other hand, if the C content exceeds 0.60%, the hardness of the steel bars and wires used as raw materials after hot forging becomes too high. Therefore, the machinability of the material is greatly reduced. The C content may be 0.08% or more, 0.10% or more, or 0.15% or more. The C content may be 0.55% or less, 0.50% or less, 0.40% or less, or 0.35% or less.
　［Ｓｉ：０．０５～１．５０％］
　Ｓｉは、固溶強化によって、芯部硬さを高める元素である。また、Ｓｉは高温による軟化抵抗を高めるため、部品が接触摩擦環境下で高温となる際に耐摩耗性を高める。これらの効果を発揮させるために、Ｓｉは０．０５％以上が必要である。一方、Ｓｉの含有量が１．５０％を超えると、素材となる棒鋼及び線材等の熱間鍛造後の硬さが高くなりすぎる。そのため、素材の切削加工性が大きく低下する。Ｓｉ含有量を０．０８％以上、０．１０％以上、又は０．２０％以上としてもよい。Ｓｉ含有量を１．３０％以下、１．１０％以下、又は１．００％以下としてもよい。 [Si: 0.05 to 1.50%]
Si is an element that increases the hardness of the core by strengthening the solid solution. Further, since Si increases the softening resistance due to high temperature, the wear resistance is improved when the component becomes high temperature in a contact friction environment. In order to exert these effects, Si needs to be 0.05% or more. On the other hand, if the Si content exceeds 1.50%, the hardness of the steel bars and wires used as raw materials after hot forging becomes too high. Therefore, the machinability of the material is greatly reduced. The Si content may be 0.08% or more, 0.10% or more, or 0.20% or more. The Si content may be 1.30% or less, 1.10% or less, or 1.00% or less.
　［Ｍｎ：０．２０～２．５０％］
　Ｍｎは、軟窒化処理によって、化合物層や拡散層中に微細な軟窒化物（Ｍｎ３Ｎ２）を形成し、耐摩耗性や曲げ疲労強度を高める元素である。またＭｎは、固溶強化によって、芯部硬さを高める。これらの効果を得るために、Ｍｎは０．２０％以上が必要である。一方、Ｍｎの含有量が２．５０％を超えると、耐摩耗性や曲げ疲労強度を高める効果が飽和するだけでなく、素材となる棒鋼及び線材等の熱間鍛造後の硬さが高くなりすぎる。そのため、素材の切削加工性が大きく低下する。Ｍｎ含有量を０．４０％以上、０．６０％以上、又は１．００％以上としてもよい。Ｍｎ含有量を２．３０％以下、２．００％以下、又は１．８０％以下としてもよい。 [Mn: 0.20 to 2.50%]
Mn is an element that forms fine soft nitrides (Mn 3 N 2 ) in the compound layer and diffusion layer by soft nitriding treatment to enhance wear resistance and bending fatigue strength. Further, Mn increases the hardness of the core portion by strengthening the solid solution. In order to obtain these effects, Mn needs to be 0.20% or more. On the other hand, when the Mn content exceeds 2.50%, not only the effect of increasing wear resistance and bending fatigue strength is saturated, but also the hardness of the steel bars and wires used as raw materials after hot forging becomes high. Too much. Therefore, the machinability of the material is greatly reduced. The Mn content may be 0.40% or more, 0.60% or more, or 1.00% or more. The Mn content may be 2.30% or less, 2.00% or less, or 1.80% or less.
　［Ｐ：０．０２５％以下］
　Ｐは不純物であって、粒界偏析して部品を脆化させる。そのため、Ｐ含有量は少ない方が好ましい。Ｐの含有量が０．０２５％を超えると、耐摩耗性や曲げ疲労強度が低下する場合がある。耐摩耗性や曲げ疲労強度の低下を防止するためのＰ含有量の好ましい上限は０．０１８％、０．０１５％、又は０．０１０％である。Ｐの含有量は０％でもよいが、精錬の経済性を考慮し、Ｐ含有量を０．００１％以上、０．００５％以上、又は０．００８％以上としてもよい。 [P: 0.025% or less]
P is an impurity that segregates the grain boundaries and embrittles the part. Therefore, it is preferable that the P content is low. If the P content exceeds 0.025%, the wear resistance and bending fatigue strength may decrease. The preferable upper limit of the P content for preventing a decrease in wear resistance and bending fatigue strength is 0.018%, 0.015%, or 0.010%. The P content may be 0%, but the P content may be 0.001% or more, 0.005% or more, or 0.008% or more in consideration of the economic efficiency of refining.
　［Ｓ：０．０５０％以下］
　Ｓは、Ｍｎと結合してＭｎＳを形成し、切削加工性を向上させる元素である。しかし、Ｓの含有量が０．０５０％を超えると、粗大なＭｎＳを生成しやすくなり、耐摩耗性や曲げ疲労強度が大きく低下する。耐摩耗性や曲げ疲労強度の低下を防止するためのＳ含有量の好ましい上限は０．０３０％、０．０２５％、又は０．０２０％である。Ｓの含有量は０％でもよいが、精錬の経済性を考慮し、Ｓ含有量を０．００１％以上、０．００２％％以上、又は０．００５％以上としてもよい。 [S: 0.050% or less]
S is an element that combines with Mn to form MnS and improves machinability. However, when the S content exceeds 0.050%, coarse MnS is likely to be generated, and the wear resistance and bending fatigue strength are greatly reduced. The preferable upper limit of the S content for preventing a decrease in wear resistance and bending fatigue strength is 0.030%, 0.025%, or 0.020%. The S content may be 0%, but the S content may be 0.001% or more, 0.002%% or more, or 0.005% or more in consideration of the economic efficiency of refining.
　［Ｃｒ：０．５０～２．５０％］
　Ｃｒは、軟窒化処理によって、化合物層や拡散層中に微細な軟窒化物（ＣｒＮ）を形成し、耐摩耗性や曲げ疲労強度を高める元素である。これらの効果を得るため、Ｃｒは０．５０％以上が必要である。一方、Ｃｒの含有量が２．５０％を超えると、耐摩耗性や曲げ疲労強度を向上させる効果が飽和するだけでなく、素材となる棒鋼及び線材の熱間鍛造後の硬さが高くなりすぎる。そのため、素材の切削加工性が著しく低下する。Ｃｒ含有量を０．７０％以上、０．８０％以上、又は１．００％以上としてもよい。Ｃｒ含有量を２．２０％以下、２．００％以下、又は１．８０％以下としてもよい。 [Cr: 0.50 to 2.50%]
Cr is an element that forms fine soft nitrides (CrN) in the compound layer and the diffusion layer by soft nitriding treatment to enhance wear resistance and bending fatigue strength. In order to obtain these effects, Cr needs to be 0.50% or more. On the other hand, when the Cr content exceeds 2.50%, not only the effect of improving wear resistance and bending fatigue strength is saturated, but also the hardness of the steel bars and wire rods as raw materials after hot forging becomes high. Too much. Therefore, the machinability of the material is significantly reduced. The Cr content may be 0.70% or more, 0.80% or more, or 1.00% or more. The Cr content may be 2.20% or less, 2.00% or less, or 1.80% or less.
　［Ｖ：０．０５～１．３０％］
　Ｖは、軟窒化処理によって、化合物層や拡散層中に微細な軟窒化物（ＶＮ）を形成し、耐摩耗性や曲げ疲労強度を高める元素である。これらの効果を得るため、Ｖは０．０５％以上が必要である。一方、Ｖの含有量が１．３０％を超えると、耐摩耗性や曲げ疲労強度を向上させる効果が飽和するだけでなく、素材となる棒鋼及び線材の熱間鍛造後の硬さが高くなりすぎる。そのため、素材の切削加工性が著しく低下する。Ｖ含有量を０．１０％以上、０．２０％以上、又は０．４０％以上としてもよい。Ｖ含有量を１．１０％以下、１．００％以下、又は０．８０％以下としてもよい。
　［Ａｌ：０．０５０％以下］
　Ａｌは本実施形態に係る部品において必須ではない。一方、Ａｌは、脱酸元素である。また、ＡｌはＮと結合してＡｌＮを形成し、オーステナイト粒のピンニング作用により、軟窒化処理前の鋼材の組織を微細化し、軟窒化処理部品の機械的特性のばらつきを低減する効果を持つ。この効果を得るためには、Ａｌは０．００５％以上が必要である。一方で、Ａｌは硬質な酸化物系介在物を形成しやすい。Ａｌの含有量が０．０５０％を超えると、曲げ疲労強度の低下が著しくなり、他の要件を満たしていても所望の曲げ疲労強度が得られなくなる。曲げ疲労強度の低下を防止するためのＡｌ含有量の好ましい上限は０．０４０％、０．０３０％、又は０．０２０％である。Ａｌの含有量は０％でもよいが、上述の効果を得るために、Ａｌ含有量を０．００１％以上、０．００２％以上、又は０．００５％以上としてもよい。 [V: 0.05 to 1.30%]
V is an element that forms fine soft nitrides (VN) in the compound layer and the diffusion layer by the soft nitriding treatment to enhance wear resistance and bending fatigue strength. In order to obtain these effects, V needs to be 0.05% or more. On the other hand, when the V content exceeds 1.30%, not only the effect of improving wear resistance and bending fatigue strength is saturated, but also the hardness of the steel bars and wire rods as raw materials after hot forging becomes high. Too much. Therefore, the machinability of the material is significantly reduced. The V content may be 0.10% or more, 0.20% or more, or 0.40% or more. The V content may be 1.10% or less, 1.00% or less, or 0.80% or less.
[Al: 0.050% or less]
Al is not essential in the parts according to this embodiment. On the other hand, Al is a deoxidizing element. Further, Al combines with N to form AlN, and the pinning action of the austenite grains has the effect of refining the structure of the steel material before the soft nitriding treatment and reducing variations in the mechanical properties of the soft nitriding treated parts. In order to obtain this effect, Al needs to be 0.005% or more. On the other hand, Al tends to form hard oxide-based inclusions. If the Al content exceeds 0.050%, the bending fatigue strength is significantly reduced, and the desired bending fatigue strength cannot be obtained even if other requirements are satisfied. The preferable upper limit of the Al content for preventing a decrease in bending fatigue strength is 0.040%, 0.030%, or 0.020%. The Al content may be 0%, but in order to obtain the above-mentioned effects, the Al content may be 0.001% or more, 0.002% or more, or 0.005% or more.
　［Ｎ：０．０２５０％以下］
　Ｎは本実施形態に係る部品において必須ではなく、Ｎ含有量が０％であってもよい。一方、Ｎは、Ｍｎ、Ｃｒ、Ａｌ、Ｖと結合してＭｎ３Ｎ２、ＣｒＮ、ＡｌＮ、ＶＮを形成する。これら窒化物形成元素の中でも、窒化物形成傾向の高いＡｌ、Ｖは、オーステナイト粒のピンニング作用により、軟窒化処理前の鋼材の組織を微細化し、軟窒化処理部品の機械的特性のばらつきを低減する効果を持つ。上述の効果を得る観点から、Ｎの含有量を０．００３０％以上、０．００３５％以上、又は０．００４０％以上としてもよい。一方で、Ｎの含有量が０．０２５０％を超えると、粗大なＡｌＮやＶＮが形成されやすくなるため、上記の効果は得難くなる。Ｎ含有量を０．０２２０％以下、０．０２００％以下、又は０．０１００％以下としてもよい。 [N: 0.0250% or less]
N is not essential in the parts according to the present embodiment, and the N content may be 0%. On the other hand, N combines with Mn, Cr, Al, and V to form Mn 3 N 2 , CrN, AlN, and VN. Among these nitride-forming elements, Al and V, which have a high tendency to form nitrides, refine the structure of the steel material before the soft nitriding treatment by the pinning action of the austenite grains, and reduce the variation in the mechanical properties of the soft nitriding treated parts. Has the effect of From the viewpoint of obtaining the above-mentioned effects, the N content may be 0.0030% or more, 0.0035% or more, or 0.0040% or more. On the other hand, when the content of N exceeds 0.0250%, coarse AlN and VN are likely to be formed, so that the above effect is difficult to obtain. The N content may be 0.0220% or less, 0.0200% or less, or 0.0100% or less.
　本実施形態に係るガス軟窒化処理部品の鋼芯部の化学成分は、上記の元素を含有し、残部はＦｅ及び不純物を含む。不純物とは、原材料に含まれる成分、あるいは製造の過程で混入する成分等であって、本実施形態に係る部品の特性を損なわない成分のことをいう。不純物とは、例えば、０．００４０％以下のＯ（酸素）等である。 The chemical composition of the steel core portion of the gas soft nitriding treated part according to the present embodiment contains the above elements, and the balance contains Fe and impurities. Impurities refer to components contained in raw materials, components mixed in during the manufacturing process, and the like, which do not impair the characteristics of the parts according to the present embodiment. The impurities are, for example, O (oxygen) of 0.0040% or less.
　ただし、本実施形態に係るガス軟窒化処理部品において、その課題を解決するために主に貢献する箇所は化合物層である。化合物層が後述するものとされる限り、鋼芯部が上述の成分以外の成分を含有することは妨げられない。鋼芯部がさらに含有しうる成分として、以下の元素を例示することができる。ただし、以下に例示される元素を含むことなく、本実施形態に係る部品はその課題を解決することができる。従って、以下に例示される元素の含有量の下限値は０％である。 However, in the gas nitrocarburizing component according to the present embodiment, the part that mainly contributes to solve the problem is the compound layer. As long as the compound layer is described later, it is not prevented that the steel core portion contains a component other than the above-mentioned components. The following elements can be exemplified as components that can be further contained in the steel core portion. However, the parts according to the present embodiment can solve the problem without containing the elements exemplified below. Therefore, the lower limit of the content of the elements exemplified below is 0%.
　［Ｍｏ：０～１．５０％］
　Ｍｏは、化合物層中のε相を安定化させる。また、Ｍｏは化合物層や拡散層中に微細な窒化物（Ｍｏ２Ｎ）を形成し、硬さを高める。そのため、Ｍｏは耐摩耗性や曲げ疲労強度の向上に有効な元素である。これらの効果を確実に得るため、Ｍｏは０．０１％以上の含有が好ましい。一方、Ｍｏの含有量が１．５０％以下とすると、素材となる棒鋼及び線材の熱間鍛造後の硬さを抑制し、素材の切削加工性を担保できるので好ましい。Ｍｏ含有量のさらに好ましい下限は０．０５％、又は０．１０％である。Ｍｏのさらに好ましい上限は１．２０％未満、１．１０％、又は１．００％である。 [Mo: 0 to 1.50%]
Mo stabilizes the ε phase in the compound layer. In addition, Mo forms fine nitrides (Mo 2 N) in the compound layer and the diffusion layer to increase the hardness. Therefore, Mo is an element effective for improving wear resistance and bending fatigue strength. In order to surely obtain these effects, Mo is preferably contained in an amount of 0.01% or more. On the other hand, when the Mo content is 1.50% or less, the hardness of the steel bars and wire rods as raw materials after hot forging can be suppressed, and the machinability of the raw materials can be ensured, which is preferable. A more preferable lower limit of the Mo content is 0.05% or 0.10%. A more preferred upper limit for Mo is less than 1.20%, 1.10%, or 1.00%.
　［Ｃｕ：０～１．００％］
　Ｃｕは、固溶強化元素として部品の芯部硬さならびに窒素拡散層の硬さを向上させる。Ｃｕの固溶強化の作用を確実に発揮させるためには、０．０１％以上の含有が好ましい。一方、Ｃｕの含有量を１．００％以下とすると、素材となる棒鋼及び線材の熱間鍛造後の硬さを抑制し、素材の切削加工性を担保できるので好ましい。また、Ｃｕの含有量を１．００％以下とすると、素材の熱間延性を向上させ、熱間圧延時、及び熱間鍛造時の表面傷発生を一層抑制することができるので好ましい。Ｃｕ含有量を０．０５％以上、０．１０％以上、又は０．２０％以上としてもよい。含有量を０．９０％以下、０．８０％以下、又は０．６０％以下としてもよい。 [Cu: 0 to 1.00%]
Cu improves the hardness of the core of the component and the hardness of the nitrogen diffusion layer as a solid solution strengthening element. In order to surely exert the action of strengthening the solid solution of Cu, the content is preferably 0.01% or more. On the other hand, when the Cu content is 1.00% or less, the hardness of the steel bars and wire rods as raw materials after hot forging can be suppressed, and the machinability of the raw materials can be ensured, which is preferable. Further, when the Cu content is 1.00% or less, the hot ductility of the material can be improved, and the occurrence of surface scratches during hot rolling and hot forging can be further suppressed, which is preferable. The Cu content may be 0.05% or more, 0.10% or more, or 0.20% or more. The content may be 0.90% or less, 0.80% or less, or 0.60% or less.
　［Ｎｉ：０～１．００％］
　Ｎｉは、固溶強化により芯部硬さ及び表面硬さを向上させる。Ｎｉの固溶強化の作用を確実に発揮させるためには、０．０１％以上の含有が好ましい。一方、Ｎｉの含有量を１．００％以下とすると、棒鋼及び線材の熱間鍛造後の硬さを抑制し、素材の切削加工性を一層向上させることができるので好ましい。Ｎｉ含有量を０．０５％以上、０．１０％以上、又は０．２０％以上としてもよい。Ｎｉ含有量を０．９０％未満、０．８０％以下、又は０．７０％以下としてもよい。 [Ni: 0 to 1.00%]
Ni improves core hardness and surface hardness by solid solution strengthening. In order to surely exert the action of strengthening the solid solution of Ni, the content is preferably 0.01% or more. On the other hand, when the Ni content is 1.00% or less, the hardness of the steel bar and the wire rod after hot forging can be suppressed, and the machinability of the material can be further improved, which is preferable. The Ni content may be 0.05% or more, 0.10% or more, or 0.20% or more. The Ni content may be less than 0.90%, 0.80% or less, or 0.70% or less.
　［Ｗ：０～０．５０％］
　Ｗは、固溶強化や炭化物（ＷＣやＷ２Ｃ）の析出により芯部硬さおよび表面硬さを向上させる。Ｗの作用を確実に発揮させるためには、０．０１％以上のＷの含有が好ましい。一方、Ｗの含有量を０．５０％以下とすると、棒鋼および線材の熱間鍛造後の硬さを抑制し、切削加工性を担保できるので好ましい。Ｗ含有量を０．０５％以上、０．１０％以上、又は０．２０％以上としてもよい。Ｗ含有量を０．４０％以下、０．３５％以下、又は０．３０％以下としてもよい。 [W: 0 to 0.50%]
W improves the core hardness and surface hardness by precipitation of solid solution strengthening and carbide (WC or W 2 C). In order to ensure the action of W, the content of W is preferably 0.01% or more. On the other hand, when the W content is 0.50% or less, the hardness of the steel bar and the wire rod after hot forging can be suppressed and the machinability can be ensured, which is preferable. The W content may be 0.05% or more, 0.10% or more, or 0.20% or more. The W content may be 0.40% or less, 0.35% or less, or 0.30% or less.
　［Ｃｏ：０～０．５０％］
　Ｃｏは、固溶強化により芯部硬さ及び表面硬さを向上させる。また、Ｃｏの作用を確実に発揮させるためには、０．０１％以上のＣｏの含有が好ましい。一方、Ｃｏの含有量を０．５０％以下とすると、棒鋼および線材の熱間鍛造後の硬さを抑制し、切削加工性を担保できるので好ましい。Ｃｏ含有量を０．０５％以上、０．１０％以上、又は０．２０％以上としてもよい。Ｃｏ含有量を０．４０％以下、０．３５％以下、又は０．３０％以下としてもよい。 [Co: 0 to 0.50%]
Co improves core hardness and surface hardness by solid solution strengthening. Moreover, in order to surely exert the action of Co, the content of Co of 0.01% or more is preferable. On the other hand, when the Co content is 0.50% or less, the hardness of the steel bar and the wire rod after hot forging can be suppressed and the machinability can be ensured, which is preferable. The Co content may be 0.05% or more, 0.10% or more, or 0.20% or more. The Co content may be 0.40% or less, 0.35% or less, or 0.30% or less.
　［Ｎｂ：０～０．３００％］
　Ｎｂは、窒化時に鋼の表層に侵入したＮや、母相のＣと結合し、微細な窒化物や炭窒化物を形成する。これにより、Ｎｂは表面硬さや芯部硬さを向上させる。この効果を確実に発揮させるためには、０．０１０％以上のＮｂの含有が好ましい。一方、Ｎｂの含有量を０．３００％以下とすることにより、粗大な窒化物、炭窒化物の生成を抑制することができるので、好ましい。Ｎｂ含有量を０．０１５％以上、０．０２０％以上、又は０．０５０％以上としてもよい。Ｎｂ含有量を０．２５０％未満、０．２００％以下、又は０．１８０％以下としてもよい。 [Nb: 0 to 0.300%]
Nb combines with N that has penetrated into the surface layer of steel during nitriding and C of the matrix phase to form fine nitrides and carbonitrides. As a result, Nb improves the surface hardness and the core hardness. In order to surely exert this effect, the content of Nb of 0.010% or more is preferable. On the other hand, by setting the Nb content to 0.300% or less, the formation of coarse nitrides and carbonitrides can be suppressed, which is preferable. The Nb content may be 0.015% or more, 0.020% or more, or 0.050% or more. The Nb content may be less than 0.250%, 0.200% or less, or 0.180% or less.
　［Ｔｉ：０～０．２５０％］
　Ｔｉは、窒化時に鋼の表層に侵入したＮや、母相のＣと結合し、微細な窒化物や炭窒化物を形成する。これにより、Ｔｉは表面硬さや芯部硬さを向上させる。この効果を確実に発揮させるためには、０．００５％以上のＴｉの含有が好ましい。一方、Ｔｉの含有量を０．２５０％以下とすることにより、粗大な窒化物、炭窒化物の生成を抑制することができるので、好ましい。Ｔｉ含有量を０．００７％以上、０．０１０％以上、又は０．０２０％以上としてもよい。Ｔｉ含有量を０．２００％以下、０．１５０％以下、又は０．１００％以下としてもよい。 [Ti: 0 to 0.250%]
Ti combines with N that has penetrated into the surface layer of steel during nitriding and C of the parent phase to form fine nitrides and carbonitrides. As a result, Ti improves the surface hardness and the core hardness. In order to surely exert this effect, the content of Ti of 0.005% or more is preferable. On the other hand, when the Ti content is 0.250% or less, the formation of coarse nitrides and carbonitrides can be suppressed, which is preferable. The Ti content may be 0.007% or more, 0.010% or more, or 0.020% or more. The Ti content may be 0.200% or less, 0.150% or less, or 0.100% or less.
　［Ｂ：０～０．０１００％］
　固溶Ｂは、Ｐの粒界偏析を抑制し、靭性を向上させる効果を持つ。また、Ｎと結合して析出するＢＮは、切削性を向上させる。これらの作用を確実に得るため、Ｂは０．０００５％（５ｐｐｍ）以上とすることが好ましい。一方、Ｂの含有量を０．０１００％以下とすることにより、多量なＢＮの偏析を抑制し、鋼材の割れを抑制することができるので、好ましい。Ｂ含有量を０．０００８％以上、０．００１０％以上、又は０．００２０％以上としてもよい。含有量を０．００８０％以下、０．００７０％以下、又は０．００６０％以下としてもよい。 [B: 0 to 0.0100%]
The solid solution B has the effect of suppressing the grain boundary segregation of P and improving the toughness. Further, the BN that binds to N and precipitates improves machinability. In order to surely obtain these effects, B is preferably 0.0005% (5 ppm) or more. On the other hand, by setting the B content to 0.0100% or less, segregation of a large amount of BN can be suppressed and cracking of the steel material can be suppressed, which is preferable. The B content may be 0.0008% or more, 0.0010% or more, or 0.0020% or more. The content may be 0.0080% or less, 0.0070% or less, or 0.0060% or less.
　［Ｃａ：０～０．０１０％］
　Ｃａは、ＭｎＳを微細化して面疲労強度を向上させる働きがある。Ｃａの作用を確実に発揮させるためには、０．００１％以上のＣａの含有が好ましい。一方、Ｃａの含有量を０．０１０％以下とすることで、経済性を損なうことなくＣａの作用を効果的に発揮できる。Ｃａ含有量を０．００２％以上、０．００３％以上、又は０．００４％以上としてもよい。Ｃａ含有量を０．００９％以下、０．００８％以下、又は０．００７％以下としてもよい。 [Ca: 0 to 0.010%]
Ca has a function of refining MnS and improving surface fatigue strength. In order to ensure the action of Ca, the content of Ca is preferably 0.001% or more. On the other hand, by setting the Ca content to 0.010% or less, the action of Ca can be effectively exerted without impairing economic efficiency. The Ca content may be 0.002% or more, 0.003% or more, or 0.004% or more. The Ca content may be 0.009% or less, 0.008% or less, or 0.007% or less.
　［Ｍｇ：０～０．０１０％］
　Ｍｇは、ＭｎＳを微細化して面疲労強度を向上させる働きがある。Ｍｇの作用を確実に発揮させるためには、０．００１％以上のＭｇの含有が好ましい。一方、Ｍｇの含有量を０．０１０％以下とすることで、経済性を損なうことなくＭｇの作用を効果的に発揮できる。Ｍｇ含有量を０．００２％以上、０．００３％以上、又は０．００４％以上としてもよい。Ｍｇ含有量を０．００９％以下、０．００８％以下、又は０．００７％以下としてもよい。 [Mg: 0 to 0.010%]
Mg has a function of refining MnS and improving surface fatigue strength. In order to ensure the action of Mg, the content of Mg is preferably 0.001% or more. On the other hand, by setting the Mg content to 0.010% or less, the action of Mg can be effectively exhibited without impairing economic efficiency. The Mg content may be 0.002% or more, 0.003% or more, or 0.004% or more. The Mg content may be 0.009% or less, 0.008% or less, or 0.007% or less.
　［ＲＥＭ：０～０．０１０％］
　「ＲＥＭ」との用語は、Ｓｃ、Ｙおよびランタノイドからなる合計１７元素を指し、ＲＥＭの含有量とは、これらの１７元素の合計含有量を意味する。ランタノイドをＲＥＭとして用いる場合、工業的には、ＲＥＭはミッシュメタルの形で添加される。 [REM: 0 to 0.010%]
The term "REM" refers to a total of 17 elements consisting of Sc, Y and lanthanoids, and the REM content means the total content of these 17 elements. When lanthanoids are used as REMs, industrially, REMs are added in the form of mischmetal.
　ＲＥＭは、ＭｎＳを微細化して面疲労強度を向上させる働きがある。ＲＥＭの作用を確実に発揮させるためには、０．００１％以上のＲＥＭの含有が好ましい。一方、ＲＥＭの含有量を０．０１０％以下とすることで、経済性を損なうことなくＲＥＭの作用を効果的に発揮できる。ＲＥＭ含有量を０．００２％以上、０．００３％以上、又は０．００４％以上としてもよい。ＲＥＭ含有量を０．００９％以下、０．００８％以下、又は０．００７％以下としてもよい。 REM has the function of refining MnS to improve surface fatigue strength. In order to ensure the action of REM, the content of REM is preferably 0.001% or more. On the other hand, by setting the content of REM to 0.010% or less, the action of REM can be effectively exhibited without impairing economic efficiency. The REM content may be 0.002% or more, 0.003% or more, or 0.004% or more. The REM content may be 0.009% or less, 0.008% or less, or 0.007% or less.
［０．００≦－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ≦０．５０］
　本実施形態に係るガス軟窒化処理部品の鋼芯部の成分は、さらに、Ｃ、Ｍｎ、Ｃｒ、Ｖ、Ｍｏの含有量（質量％）が以下の式（１）を満たす。
　０．００≦－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ≦０．５０・・・式（１）
　ただし、式（１）中の元素記号は当該元素の含有量（質量％）を示し、含有しない場合は０を代入する。 [0.00 ≦ -2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo ≦ 0.50]
The components of the steel core portion of the gas soft nitriding-treated component according to the present embodiment further satisfy the following formula (1) in terms of the content (mass%) of C, Mn, Cr, V, and Mo.
0.00 ≦ -2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo ≦ 0.50 ・ ・ ・ Equation (1)
However, the element symbol in the formula (1) indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
　Ｃ、Ｍｎ、Ｃｒ、ＶおよびＭｏは、化合物層の厚さに影響を及ぼす元素である。Ｃ及びＭｏにはε相を安定化させ、厚さを高める効果がある。一方Ｍｎ、ＣｒおよびＶには、化合物層を薄くする効果がある。そのため、これらの元素の含有量を一定の範囲に制御することで、化合物層の厚さを安定して制御でき、耐摩耗性および曲げ疲労強度を向上させることができる。 C, Mn, Cr, V and Mo are elements that affect the thickness of the compound layer. C and Mo have the effect of stabilizing the ε phase and increasing the thickness. On the other hand, Mn, Cr and V have the effect of thinning the compound layer. Therefore, by controlling the content of these elements within a certain range, the thickness of the compound layer can be stably controlled, and the wear resistance and bending fatigue strength can be improved.
　これらの効果を得るため、式（１）中の｛－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ｝の値は０．００以上であるとよい。一方、｛－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ｝の値が０．５０を超えると、化合物層が薄くなり、所望の面疲労強度及び曲げ疲労強度が得られないことがある。｛－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ｝の値の好ましい下限は０．０３％、０．０５％、又は０．１０％である。｛－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ｝の値の好ましい上限は０．４５％、０．４０％、又は０．３０％である。 In order to obtain these effects, the value of {-2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo} in the formula (1) is preferably 0.00 or more. .. On the other hand, when the value of {-2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo} exceeds 0.50, the compound layer becomes thin, and the desired surface fatigue strength and desired surface fatigue strength and Bending fatigue strength may not be obtained. The preferable lower limit of the value of {−2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo} is 0.03%, 0.05%, or 0.10%. The preferred upper limit of the value of {−2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo} is 0.45%, 0.40%, or 0.30%.
　鋼芯部の化学成分の測定箇所は、部品の表面から５．０ｍｍ以上深い箇所とする。これは、以下の理由による。
　窒化処理により窒素が侵入した窒素拡散層と、窒素の侵入が及ばなかった鋼芯部との境界を厳密に特定することは困難である。本実施の形態にかかる窒化条件であれば、表面から５．０ｍｍ以上深い位置では窒化処理による窒素の侵入の影響がほとんどない。このため、部品の表面から５．０ｍｍ以上深い箇所において化学組成を測定することにより、窒化による化学成分への影響を受けることなく、鋼芯部の化学成分を測定することができる。 The measurement location of the chemical composition of the steel core shall be 5.0 mm or more deep from the surface of the part. This is due to the following reasons.
It is difficult to strictly identify the boundary between the nitrogen diffusion layer in which nitrogen has penetrated by the nitriding treatment and the steel core portion in which nitrogen has not penetrated. Under the nitriding conditions according to the present embodiment, there is almost no influence of nitrogen intrusion by the nitriding treatment at a position deeper than 5.0 mm from the surface. Therefore, by measuring the chemical composition at a depth of 5.0 mm or more from the surface of the component, the chemical composition of the steel core can be measured without being affected by the chemical composition due to nitriding.
　次に、本実施形態に係るガス軟窒化処理部品の化合物層について説明する。 Next, the compound layer of the gas nitrocarburizing component according to the present embodiment will be described.
　本実施形態に係るガス軟窒化処理部品は、鋼材（Ｓｔｅｅｌ　Ｍａｔｅｒｉａｌ）を素形鋼（Ｒｏｕｇｈ　Ｓｈａｐｅｄ　Ｓｔｅｅｌ）に加工したうえで、所定の条件下で軟窒化処理を行うことによって製造される。上述されたように、本実施形態に係るガス軟窒化処理部品１は、鋼芯部（Ｃｏｒｅ　Ｓｔｅｅｌ）１１と、鋼芯部１１の上に形成された窒素拡散層（Ｎｉｔｒｏｇｅｎ　Ｄｉｆｆｕｓｉｏｎ　Ｌａｙｅｒ）１３と、窒素拡散層１３の上に形成された化合物層（Ｃｏｍｐｏｕｎｄ　Ｌａｙｅｒ）１２とを備える。すなわち、本実施形態に係るガス軟窒化処理部品１は、表面に化合物層１２があり、化合物層１２の内側に窒素拡散層１３があり、窒素拡散層１３の内側に鋼芯部１１がある構造を有する。 The gas soft nitriding part according to the present embodiment is manufactured by processing a steel material (Steel Material) into a basic steel (Roug Sharped Steel) and then performing a soft nitriding treatment under predetermined conditions. As described above, the gas nitrocarburizing component 1 according to the present embodiment includes a steel core portion (Core Steel) 11, a nitrogen diffusion layer (Nitrogen Diffusion Layer) 13 formed on the steel core portion 11, and a nitrogen diffusion layer 13. It includes a compound layer 12 formed on the nitrogen diffusion layer 13. That is, the gas nitrocarburizing component 1 according to the present embodiment has a structure in which the compound layer 12 is provided on the surface, the nitrogen diffusion layer 13 is provided inside the compound layer 12, and the steel core portion 11 is provided inside the nitrogen diffusion layer 13. Has.
　化合物層は、窒化処理により素形鋼に侵入した窒素原子と、素形鋼に含まれる鉄原子とが結合して形成した鉄窒化物を、主成分として含む層である。化合物層は、主として鉄窒化物により構成されるが、鉄及び窒素のほかに、外気から混入する酸素、および、素形鋼に含有されている各元素（すなわち、鋼芯部に含有される各元素）も化合物層に含まれる。一般に、化合物層に含まれる元素の９０％以上（質量％）は窒素および鉄である。化合物層に含まれる鉄窒化物は、主にＦｅ２～３Ｎ（ε相）、又はＦｅ４Ｎ（γ’相）である。 The compound layer is a layer containing iron nitride as a main component, which is formed by combining a nitrogen atom that has penetrated into the structural steel by a nitriding treatment and an iron atom contained in the structural steel. The compound layer is mainly composed of iron nitride, but in addition to iron and nitrogen, oxygen mixed from the outside air and each element contained in the structural steel (that is, each element contained in the steel core). Elements) are also included in the compound layer. Generally, 90% or more (mass%) of the elements contained in the compound layer are nitrogen and iron. The iron nitride contained in the compound layer is mainly Fe 2-3 N (ε phase) or Fe 4 N (γ'phase).
　［化合物層の厚さ：３μｍ以上２０μｍ以下］
　化合物層の厚さは、ガス軟窒化処理部品の耐摩耗性や曲げ強度に影響する。化合物層１２は、拡散層１３に比べて変形能が小さい。そのため、化合物層が厚すぎると、化合物層が曲げによる破壊起点となりやすい。また、化合物層が薄すぎると、化合物層のない表面が部品の一部に存在する場合があり、耐摩耗性や曲げ強度が低下する。本実施形態に係るガス軟窒化処理部品においては、耐摩耗性や曲げ強度の観点から、化合物層の厚さは３μｍ以上２０μｍ以下とする。化合物層厚さを５μｍ以上、６μｍ以上、又は８μｍ以上としてもよい。化合物層厚さを１５μｍ以下、１４μｍ以下、又は１２μｍ以下としてもよい。 [Thickness of compound layer: 3 μm or more and 20 μm or less]
The thickness of the compound layer affects the wear resistance and bending strength of gas nitrocarburizing parts. The compound layer 12 has a smaller deformability than the diffusion layer 13. Therefore, if the compound layer is too thick, the compound layer tends to be a fracture starting point due to bending. Further, if the compound layer is too thin, a surface without the compound layer may be present in a part of the component, and the wear resistance and bending strength are lowered. In the gas nitrocarburizing component according to the present embodiment, the thickness of the compound layer is 3 μm or more and 20 μm or less from the viewpoint of wear resistance and bending strength. The compound layer thickness may be 5 μm or more, 6 μm or more, or 8 μm or more. The compound layer thickness may be 15 μm or less, 14 μm or less, or 12 μm or less.
　化合物層の厚さは、走査型電子顕微鏡（Ｓｃａｎｎｎｉｇ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ：ＳＥＭ）の二次電子像によって測定することができる。ガス軟窒化処理した部品の表面に垂直な断面を、研磨し、３％ナイタール溶液で２０～３０秒間エッチングを行う。化合物層１２は、部品１の表層に、凹凸の無い未腐食の層として観察され、拡散層１３は、腐食された層として化合物層の直下に観察される。４０００倍で撮影した組織写真１０視野（１視野当たりの面積：６．６×１０２μｍ２）における化合物層１２を特定する。そして、それぞれの写真において、水平方向に１０μｍ毎に３点で、化合物層１２の厚さを測定する。前記１０視野は、互いに重複しないようにされる。そして、測定された３０点における化合物層１２の厚さの平均値を、ガス軟窒化処理部品の化合物層の厚さ（μｍ）と定義する。 The thickness of the compound layer can be measured by a secondary electron image of a scanning electron microscope (SEM). The cross section perpendicular to the surface of the gas soft nitriding part is polished and etched with a 3% nital solution for 20 to 30 seconds. The compound layer 12 is observed as an uncorroded layer without unevenness on the surface layer of the component 1, and the diffusion layer 13 is observed as a corroded layer directly under the compound layer. The compound layer 12 in 10 visual fields (area per visual field: 6.6 × 10 2 μm 2) of the tissue photograph taken at 4000 times is specified. Then, in each photograph, the thickness of the compound layer 12 is measured at three points every 10 μm in the horizontal direction. The 10 fields of view are designed so that they do not overlap each other. Then, the average value of the thickness of the compound layer 12 at the measured 30 points is defined as the thickness (μm) of the compound layer of the gas soft nitriding processed component.
　［化合物層中のε相の面積率：５０％超］
　化合物層の構成相は、ガス軟窒化処理部品の耐摩耗性や曲げ強度に影響する。ε相はｈｃｐ構造であり、ｆｃｃ構造であるγ’相に比べ変形能が小さい。一方で、ε相はγ’相に比べ、ＮおよびＣの固溶範囲が広く、高硬度である。ε相の面積率が低いと、化合物層の硬さが小さくなりやすく、耐摩耗性が低下することがある。本実施形態に係るガス軟窒化処理部品においては、化合物層中のε相の面積率は５０％超とする。ε相の面積比率の好ましい範囲は７０％超、７５％以上、又は８０％以上である。ε相の面積比率が１００％であってもよい。ε相の面積比率の上限値は特に限定されないが、例えば回転疲労曲げ強度を一層高める観点から、ε相の面積比率を９５％以下、９２％以下、９０％以下、又は８８％以下としてもよい。
　ε相の面積率は１００％であってもよく、従って残部が存在しなくともよい。化合物層の残部が存在する場合、残部は主にγ’相から構成される。なお、ε相及びγ’相のいずれにも当てはまらない特異相が含まれる場合がある。しかし、ε相が面積率で５０％超であり、且つε相及びγ’相の面積率の合計値が９５％超である化合物層は、ε相を面積率で５０％超含有し、残部がγ’相である化合物層であるとみなす。 [Area ratio of ε phase in compound layer: over 50%]
The constituent phase of the compound layer affects the wear resistance and bending strength of the gas nitrocarburizing component. The ε phase has an hcp structure and has a smaller deformability than the γ'phase, which has an fcc structure. On the other hand, the ε phase has a wider solid solution range of N and C and higher hardness than the γ'phase. When the area ratio of the ε phase is low, the hardness of the compound layer tends to be small, and the wear resistance may be lowered. In the gas nitrocarburizing component according to the present embodiment, the area ratio of the ε phase in the compound layer is more than 50%. The preferred range of the area ratio of the ε phase is more than 70%, 75% or more, or 80% or more. The area ratio of the ε phase may be 100%. The upper limit of the area ratio of the ε phase is not particularly limited, but for example, from the viewpoint of further increasing the rotational fatigue bending strength, the area ratio of the ε phase may be 95% or less, 92% or less, 90% or less, or 88% or less. ..
The area ratio of the ε phase may be 100% and therefore the balance may be absent. If the balance of the compound layer is present, the balance is mainly composed of the γ'phase. In addition, a singular phase that does not apply to either the ε phase or the γ'phase may be included. However, the compound layer in which the ε phase has an area ratio of more than 50% and the total value of the area ratios of the ε phase and the γ'phase exceeds 95% contains the ε phase in an area ratio of more than 50%, and the balance. Is considered to be a compound layer in the γ'phase.
　ε相の面積率は、組織写真を画像処理することにより求める。具体的には、後方散乱電子回折法（Ｅｌｅｃｔｒｏｎ　ＢａｃｋＳｃａｔｔｅｒ　Ｄｉｆｆｒａｃｔｉｏｎ：ＥＢＳＤ）により、４０００倍で撮影した、窒化処理部品の表面に垂直な断面の組織写真１０枚に対して、化合物層中のγ’相、ε相を判別する。そして、化合物層中に占めるε相の面積比率を、組織写真を画像処理して２値化することにより求める。そして、測定された１０視野のε相の面積比率の平均値を、ε相の面積率（％）と定義する。 The area ratio of the ε phase is obtained by image processing the tissue photograph. Specifically, the γ'phase in the compound layer was taken with respect to 10 microstructure photographs of the cross section perpendicular to the surface of the nitrided part taken at 4000 times by the backscattered electron diffraction method (Electron Backscatter Diffraction: EBSD). , Ε phase is discriminated. Then, the area ratio of the ε phase in the compound layer is obtained by image-processing the tissue photograph and binarizing it. Then, the average value of the measured area ratios of the ε phases in the 10 visual fields is defined as the area ratio (%) of the ε phases.
　［化合物層の表面から３μｍの深さの範囲における空隙の面積比率：１２％未満］
　化合物層の表面から３μｍの深さの範囲に空隙が存在すると応力集中が生じ、耐摩耗性が低下したり、曲げ疲労における破壊の起点となる。そのため、化合物層の表面から３μｍの深さの範囲における空隙の面積比率（空隙面積率）は１２％未満とする必要がある。 [Area ratio of voids in a depth range of 3 μm from the surface of the compound layer: less than 12%]
If voids are present in the depth range of 3 μm from the surface of the compound layer, stress concentration occurs, wear resistance is lowered, and it becomes a starting point of fracture in bending fatigue. Therefore, the area ratio of the voids (void area ratio) in the depth range of 3 μm from the surface of the compound layer needs to be less than 12%.
　空隙面積率は、ＳＥＭによって測定することができる。まず、窒化処理部品をＮｉめっきする。次いで、Ｎｉめっきされた窒化処理部品を、その表面に垂直に切断し、この断面を研磨する。Ｎｉめっきは、研磨の際に化合物層が変形することを防止するために、研磨の前に設けられる。そして、研磨された断面において、最表面から３μｍまでの深さと最表面に沿った長さ３０μｍとの積からなる長方形の領域（面積９０μｍ２）の二次電子像を撮影する。上記領域の二次電子像における黒色部位を、空隙とみなすことができる。なお、二次電子像において、部品の最表面に凹凸が含まれる場合がある。この場合は、最表面の積分平均を最表面とみなす。
　そして、各二次電子像の写真に占める空隙の総面積の比（空隙面積率、単位は％）を、画像処理アプリケーションにより求める。そして、測定された１０視野での空隙面積率の平均値を、部品の空隙面積率（％）と定義する。化合物層の厚さが３μｍ未満の場合においても、同様に表面から３μｍ深さまでを測定対象とする。前記１０視野は、互いに重複しないようにされる。測定する空隙の大きさは、面積換算による円相当径で０．３μｍ以上のものを対象とする。即ち、空隙面積率の測定にあたり、円相当径で０．３μｍ未満の空隙は無視される。なお、通常、空隙の円相当径は最大で１μｍ程度である。 The void area ratio can be measured by SEM. First, the nitriding parts are Ni-plated. The Ni-plated nitriding part is then cut perpendicular to its surface and its cross section polished. Ni plating is provided before polishing in order to prevent the compound layer from being deformed during polishing. Then, in the polished cross section, a secondary electron image of a rectangular region (area 90 μm 2 ) consisting of a product of a depth from the outermost surface to 3 μm and a length of 30 μm along the outermost surface is photographed. The black part in the secondary electron image in the above region can be regarded as a void. In the secondary electron image, the outermost surface of the component may have irregularities. In this case, the integrated average of the outermost surface is regarded as the outermost surface.
Then, the ratio of the total area of the voids to the photograph of each secondary electron image (void area ratio, unit is%) is obtained by an image processing application. Then, the average value of the void area ratio in the measured 10 visual fields is defined as the void area ratio (%) of the component. Even when the thickness of the compound layer is less than 3 μm, the measurement target is similarly up to a depth of 3 μm from the surface. The 10 fields of view are designed so that they do not overlap each other. The size of the void to be measured is 0.3 μm or more in the equivalent circle diameter in terms of area. That is, in measuring the void area ratio, voids having a diameter equivalent to a circle and less than 0.3 μm are ignored. Normally, the circle-equivalent diameter of the void is about 1 μm at the maximum.
　空隙面積率は好ましくは１１％未満、１０％未満、９％未満、７％未満、又は３％未満であり、０％であってもよい。空隙面積率の下限値は特に限定されないが、例えば空隙面積率を０％以上、１％以上、２％以上、又は４％以上としてもよい。 The void area ratio is preferably less than 11%, less than 10%, less than 9%, less than 7%, or less than 3%, and may be 0%. The lower limit of the void area ratio is not particularly limited, but for example, the void area ratio may be 0% or more, 1% or more, 2% or more, or 4% or more.
　［化合物層の硬さ：好ましくは７４０ＨＶ以上］
　化合物層の硬さが高くなると、部品の耐摩耗性や回転曲げ疲労強度が向上する。化合物層の硬さは、ε相の面積率を高めたり、ＣｒＮやＶＮなどの窒化物を化合物層中に析出させたり、置換型元素を化合物層に固溶させることで高めることができる。その一方で窒化温度によっても変化する。本実施形態に係るガス軟窒化処理部品は、化合物層の硬さを７４０ＨＶ以上とすることにより、優れた耐摩耗性、回転曲げ疲労強度を有するものとなるので好ましい。化合物層の硬さは、一層好ましくは７７０ＨＶ以上である。化合物層の構成を上述のように制御することにより、化合物層の硬さを７４０ＨＶ以上とすることができる。 [Hardness of compound layer: preferably 740 HV or more]
When the hardness of the compound layer is increased, the wear resistance of the component and the rotational bending fatigue strength are improved. The hardness of the compound layer can be increased by increasing the area ratio of the ε phase, precipitating nitrides such as CrN and VN in the compound layer, and dissolving the substituted element in the compound layer. On the other hand, it also changes depending on the nitriding temperature. The gas nitrocarburizing component according to the present embodiment is preferable because the compound layer has a hardness of 740 HV or more and thus has excellent wear resistance and rotational bending fatigue strength. The hardness of the compound layer is more preferably 770 HV or more. By controlling the composition of the compound layer as described above, the hardness of the compound layer can be set to 740 HV or more.
　次に、本実施形態に係るガス軟窒化処理部品の製造方法の一例を説明する。 Next, an example of a method for manufacturing a gas nitriding-treated part according to the present embodiment will be described.
　図２に示されるように、本実施形態に係るガス軟窒化処理部品の製造方法では、まず上述された鋼芯部の成分を有する鋼材を、熱間鍛造などの加工によって所定の形状とし、必要に応じて切削加工や研削加工を施して、素形鋼を得る。そして、素形鋼にガス軟窒化処理を施して、ガス軟窒化処理部品を得る。 As shown in FIG. 2, in the method for manufacturing a gas soft nitriding part according to the present embodiment, first, a steel material having the above-mentioned steel core component is formed into a predetermined shape by processing such as hot forging, and it is necessary. A shaped steel is obtained by cutting or grinding according to the above conditions. Then, the structural steel is subjected to gas soft nitriding treatment to obtain a gas soft nitriding treated component.
　［ガス軟窒化処理］
　ガス軟窒化処理は、ＮＨ３、Ｈ２、Ｎ２に加え、鋼の表面にＣを侵入させる目的でＣＯ２、ＣＯ、もしくはＣＨ４やＣ３Ｈ８などの炭化水素ガスを合計で９９体積％以上含むガス雰囲気中で窒化ポテンシャルを制御した条件で施される。なお、残部はＯ２などの不純物ガスを含んでもよい。好ましくは、ＮＨ３、Ｈ２、Ｎ２、ＣＯ２、ＣＯ、ＣＨ４、Ｃ３Ｈ８が合計で９９．５体積％以上であるとよい。なお、Ｃを侵入させる目的で加えられる気体（ＣＯ２、ＣＯ、もしくはＣＨ４やＣ３Ｈ８などの炭化水素ガス）を、以降では浸炭性ガスと表記する。 [Gas soft nitriding treatment]
In the gas nitrocarburizing treatment, in addition to NH 3 , H 2 , and N 2 , a total of 99 volumes of hydrocarbon gas such as CO 2 , CO, or CH 4 or C 3 H 8 is added for the purpose of allowing C to penetrate the surface of the steel. It is applied under the condition that the nitriding potential is controlled in a gas atmosphere containing% or more. The balance may contain an impurity gas such as O 2. Preferably, NH 3 , H 2 , N 2 , CO 2 , CO, CH 4 , and C 3 H 8 are 99.5% by volume or more in total. The gas added for the purpose of invading C (CO 2 , CO, or a hydrocarbon gas such as CH 4 or C 3 H 8 ) is hereinafter referred to as a carburizing gas.
　［処理温度：５５０～６３０℃］
　ガス軟窒化処理の温度は、主に、窒素の拡散速度と相関があり、表面硬さ及び硬化層深さに影響を及ぼす。処理温度が低すぎれば、窒素の拡散速度が小さく、化合物層の厚さや硬化層深さが小さくなる。一方、軟窒化処理温度が高すぎると化合物層表面側から空隙が生成されやすくなる他、化合物層の硬さが低下する。加えて、処理温度がＡＣ１点を超えれば、フェライト相（α相）よりも窒素の拡散速度が小さいオーステナイト相（γ相）が化合物層と拡散層との界面から生成され、硬化層深さが浅くなる。したがって、本実施形態における軟窒化処理温度はフェライト温度域周囲の５５０～６３０℃である。この場合、化合物層の硬さが低くなるのを抑制でき、かつ、硬化層深さが浅くなるのを抑制できる。 [Treatment temperature: 550 to 630 ° C]
The temperature of the gas nitrocarburizing treatment mainly correlates with the diffusion rate of nitrogen and affects the surface hardness and the depth of the hardened layer. If the treatment temperature is too low, the diffusion rate of nitrogen will be low, and the thickness of the compound layer and the depth of the cured layer will be small. On the other hand, if the soft nitriding treatment temperature is too high, voids are likely to be generated from the surface side of the compound layer, and the hardness of the compound layer is lowered. In addition, if the treatment temperature is exceeds the C1 point A, ferrite phase (alpha phase) the diffusion rate of nitrogen than smaller austenite phase (gamma-phase) is generated from the interface between the compound layer and the diffusion layer, hardening depth Becomes shallower. Therefore, the soft nitriding treatment temperature in this embodiment is 550 to 630 ° C. around the ferrite temperature range. In this case, it is possible to suppress the hardness of the compound layer from becoming low, and it is possible to suppress the depth of the cured layer from becoming shallow.
　［ガス窒化処理全体の処理時間（保持時間）］
　ガス軟窒化処理全体の時間、つまり、軟窒化処理の開始から終了までの時間（保持時間）は、化合物層の形成及び分解、及び窒素の拡散浸透と相関があり、表面硬さ及び硬化層深さに影響を及ぼす。処理時間が短すぎると化合物層の厚さや、硬化層深さが小さくなる。一方、処理時間が長すぎれば、化合物層表面の空隙面積率が増加し、曲げ疲労強度が低下する。処理時間が長すぎればさらに、製造コストが高くなる。したがって、ガス軟窒化処理の処理時間（保持時間）は１．０時間以上７．０時間以下であるとよい。保持時間の下限は、好ましくは１．５時間、さらに好ましくは２．０時間にするとよい。 [Processing time (holding time) of the entire gas nitriding process]
The total time of the gas soft nitriding treatment, that is, the time from the start to the end of the soft nitriding treatment (retention time) correlates with the formation and decomposition of the compound layer and the diffusion and permeation of nitrogen, and the surface hardness and the depth of the hardened layer. Affects the gas. If the treatment time is too short, the thickness of the compound layer and the depth of the cured layer become small. On the other hand, if the treatment time is too long, the void area ratio on the surface of the compound layer increases and the bending fatigue strength decreases. If the processing time is too long, the manufacturing cost will be higher. Therefore, the processing time (holding time) of the gas soft nitriding treatment is preferably 1.0 hour or more and 7.0 hours or less. The lower limit of the holding time is preferably 1.5 hours, more preferably 2.0 hours.
　［ガス軟窒化処理における浸炭性ガスの投入比率］
　本発明におけるガス軟窒化処理では、ＣＯ２、ＣＯ、若しくはＣＨ４やＣ３Ｈ８などの炭化水素ガスのうち、少なくとも１種を含む単独もしくは混合ガスを、式（２）で示す浸炭性ガス投入比率（体積％）で管理する。
　浸炭性ガス投入比率（体積％）＝ＣＯ２、ＣＯ、及び炭化水素ガスの総投入流量（ｌ／ｍｉｎ）／雰囲気ガスの総投入流量（ｌ／ｍｉｎ）×１００・・・式（２） [Carburizing gas input ratio in gas nitrocarburizing treatment]
In the gas nitrocarburizing treatment in the present invention, a carburized gas represented by the formula (2) is a single or mixed gas containing at least one of CO 2 , CO, or a hydrocarbon gas such as CH 4 or C 3 H 8. It is managed by the input ratio (volume%).
Carburizing gas input ratio (volume%) = CO 2 , CO, and hydrocarbon gas total input flow rate (l / min) / atmospheric gas total input flow rate (l / min) x 100 ... Equation (2)
　浸炭性ガス投入比率が２体積％未満だと、均一なε相が形成されず、耐摩耗性が下がることがある。一方、浸炭性ガス投入比率が１０体積％以上だと、相対的にＮＨ３、Ｈ２などの窒化反応ガスの分圧が低くなることで、化合物層の生成速度が小さくなり、化合物層が薄くなったり、化合物層厚さのバラつきが大きくなることで耐摩耗性や曲げ疲労強度が低下する。したがって本実施形態に係る製造方法における浸炭性ガスの投入比率は、２体積％以上１０体積％未満とする。浸炭性ガスの投入比率を３体積％以上又は４体積％以上としてもよい。浸炭性ガスの投入比率を９体積％以下、又は８体積％未満としてもよい。 If the carburizing gas input ratio is less than 2% by volume, a uniform ε phase is not formed, and the wear resistance may decrease. On the other hand, when the carburizing gas input ratio is 10% by volume or more, the partial pressure of the nitriding reaction gas such as NH 3 and H 2 becomes relatively low, so that the formation rate of the compound layer becomes low and the compound layer becomes thin. Abrasion resistance and bending fatigue strength are reduced due to the increase in the thickness of the compound layer and the increase in the thickness of the compound layer. Therefore, the input ratio of the carburizing gas in the production method according to the present embodiment is 2% by volume or more and less than 10% by volume. The carburizing gas input ratio may be 3% by volume or more or 4% by volume or more. The carburizing gas input ratio may be 9% by volume or less, or less than 8% by volume.
　［ガス軟窒化処理における窒化ポテンシャル］
　本実施形態に係るガス軟窒化処理部品の製造方法では、窒化ポテンシャルを制御する。上述した素形鋼を以下の条件で軟窒化することにより、厚さ３～２０μｍの化合物層を有し、上記化合物層の表面から深さ３μｍまでの領域において空隙の面積比率が１２％未満のガス軟窒化処理部品を得ることができる。 [Nitriding potential in gas nitrocarburizing treatment]
In the method for manufacturing a gas soft nitriding processed component according to the present embodiment, the nitriding potential is controlled. By soft nitriding the above-mentioned structural steel under the following conditions, it has a compound layer with a thickness of 3 to 20 μm, and the area ratio of voids is less than 12% in the region from the surface of the compound layer to a depth of 3 μm. Gas soft nitriding processed parts can be obtained.
　ガス軟窒化処理の窒化ポテンシャルＫＮは下記式（３）で定義される。
　　ＫＮ＝（ＮＨ３分圧）／［（Ｈ２分圧）3/2］（ａｔｍ－１／２）　　・・・　式（
３）
　また、窒化ポテンシャルＫＮの平均値ＫＮａｖｅは、ガス軟窒化処理の開始から終了まで１０分毎に記録された上記窒化ポテンシャルＫＮの平均値である。上記式の通り、ＮＨ３およびＨ２の分圧は、単位（ａｔｍ）での値を用いる。 The nitriding potential K N of the gas soft nitriding treatment is defined by the following equation (3).
K N = (NH 3 partial pressure) / [(H 2 partial pressure) 3/2 ] (atm- 1 / 2 ) ・ ・ ・ Equation (
3)
The average value K Nave nitride potential K N is the average value of the recorded the nitriding potential K N every 10 minutes from the start to the end of the gas nitrocarburizing treatment. As shown in the above formula, the partial pressure of NH 3 and H 2 uses the value in the unit (atm).
　ガス軟窒化処理の雰囲気のＮＨ３及びＨ２の分圧は、ガスの流量を調整することにより制御することができる。 The partial pressure of NH 3 and H 2 in the atmosphere of gas nitrocarburizing treatment can be controlled by adjusting the flow rate of the gas.
　本発明者らの検討の結果、ガス軟窒化処理の窒化ポテンシャルは、化合物層の厚さ、空隙面積率に影響する。式（３）によって求められる窒化ポテンシャルＫＮを、ガス軟窒化処理工程を通じて０．１５以上０．４０以下の範囲内に維持し、ガス軟窒化処理工程中の窒化ポテンシャルＫＮの平均値ＫNａｖｅを０．１８以上０．３０未満とすることが、最適な窒化ポテンシャルであることを見出した。 As a result of the study by the present inventors, the nitriding potential of the gas nitrocarburizing treatment affects the thickness of the compound layer and the void area ratio. The nitriding potential K N obtained by the formula (3) is maintained within the range of 0.15 or more and 0.40 or less through the gas nitrocarburizing treatment step, and the average value K Nave of the nitriding potential K N during the gas nitrocarburizing treatment step is maintained. It was found that the optimum nitriding potential is set to 0.18 or more and less than 0.30.
　このような条件で、本発明における成分系の鋼を軟窒化することにより、安定的に厚さ３～２０μｍの化合物層を有し、表面から深さ３μｍまでの領域において空隙の面積比率が１２％未満の化合物層を有するガス軟窒化処理部品とすることができる。 By soft nitriding the component-based steel of the present invention under such conditions, a compound layer having a thickness of 3 to 20 μm is stably provided, and the area ratio of voids is 12 in the region from the surface to the depth of 3 μm. It can be a gas nitriding-treated part having a compound layer of less than%.
　表１に示す化学成分を有する鋼ａ～ａｂを、５０ｋｇ真空溶解炉で溶解して溶鋼を製造し、前記溶鋼を鋳造してインゴットを製造した。なお、表２－１及び表２－２中のａ～ｔは、本発明で規定する化学成分を有する鋼である。一方、鋼ｕ～ａｂは、少なくとも１元素以上、本発明で規定する化学成分から外れた比較例の鋼である。尚、表１において、「Ｘ」は、“－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ”の値を示す。また、下線は本発明の範囲外の組成であることを示し、空欄は合金元素を意図的に添加しないことを示す。また、表１に示す鋼ａ～ａｂの組成のうち、表１に示す成分以外の成分（残部）は、Ｆｅ及び不純物である。なお、全ての鋼において、Ｏが不純物として約１０ｐｐｍ含まれていた。 Steels a to ab having the chemical components shown in Table 1 were melted in a 50 kg vacuum melting furnace to produce molten steel, and the molten steel was cast to produce an ingot. In addition, a to t in Table 2-1 and Table 2-2 are steels having a chemical composition specified in this invention. On the other hand, steels u to ab are comparative steels having at least one element or more that deviates from the chemical composition specified in the present invention. In Table 1, "X" indicates a value of "-2.1 x C + 0.04 x Mn + 0.5 x Cr + 1.8 x V-1.5 x Mo". Further, the underline indicates that the composition is outside the scope of the present invention, and the blank indicates that the alloying element is not intentionally added. Further, among the compositions of steels a to ab shown in Table 1, components (remaining portions) other than the components shown in Table 1 are Fe and impurities. In all steels, O was contained as an impurity in about 10 ppm.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　前記鋼ａ～ａｂのそれぞれのインゴットを熱間鍛造して直径４０ｍｍの丸棒とした。続いて、各丸棒を焼鈍した後、切削加工を施し、図３に示す耐摩耗性を評価するためのローラピッティング試験用の小ローラ、図４に示す大ローラを作製した。さらに、図５に示す回転曲げ疲労強度を評価するための円柱試験片を作製した。 Each ingot of the steels a to ab was hot forged to obtain a round bar having a diameter of 40 mm. Subsequently, after each round bar was annealed, it was cut to produce a small roller for a roller pitting test for evaluating the wear resistance shown in FIG. 3 and a large roller shown in FIG. Further, a cylindrical test piece for evaluating the rotational bending fatigue strength shown in FIG. 5 was prepared.
　採取された試験片に対して、次の条件でガス軟窒化処理を実施した。試験片をガス軟窒化炉に装入し、炉内にＮＨ３、Ｈ２、Ｎ２、ＣＯ２の各ガスを導入して、表２－１及び表２－２に示す条件で軟窒化処理を実施した。なお、ＣＯ２ガスの投入比率が一定となるよう、ＮＨ３、Ｈ２、Ｎ２ガスの総投入流量およびＣＯ２ガスの投入流量は処理中に変化させないようにした。軟窒化処理後の試験片に対して、８０℃の油を用いて油冷を実施した。 The collected test pieces were subjected to gas nitrocarburizing treatment under the following conditions. The test piece was charged into a gas soft nitriding furnace, NH 3 , H 2 , N 2 , and CO 2 gases were introduced into the furnace, and the soft nitriding treatment was performed under the conditions shown in Table 2-1 and Table 2-2. Was carried out. The total input flow rate of NH 3 , H 2 , and N 2 gas and the input flow rate of CO 2 gas were not changed during the treatment so that the input ratio of CO 2 gas was constant. The test piece after the soft nitriding treatment was oil-cooled using oil at 80 ° C.
　雰囲気中のＨ２分圧は、ガス軟窒化炉体に直接装着した熱伝導式Ｈ２センサを用いて測定した。標準ガスと測定ガスとの熱伝導度の違いをガス濃度に換算して測定した。Ｈ２分圧は、ガス軟窒化処理の間、継続して測定した。 The H 2 partial pressure in the atmosphere was measured using a heat conduction type H 2 sensor directly mounted on the gas soft nitride furnace body. The difference in thermal conductivity between the standard gas and the measured gas was converted into gas concentration and measured. H 2 partial pressure during the gas nitrocarburizing treatment, was continuously measured.
　また、ＮＨ３分圧は、炉外に取り付けたガラス管式ＮＨ３分析計を用いて、１０分毎に測定した。 The NH 3 partial pressure was measured every 10 minutes using a glass tube type NH 3 analyzer mounted outside the furnace.
　窒化ポテンシャルＫＮが目標値に収束するように、ＮＨ３流量、Ｈ２流量及びＮ２流量を調整した。１０分毎に窒化ポテンシャルＫＮを記録し、処理中の最小値、最大値および平均値を導出した。 The NH 3 flow rate, the H 2 flow rate, and the N 2 flow rate were adjusted so that the nitriding potential K N converged to the target value. Record the nitriding potential K N every 10 minutes, the minimum value being processed to derive the maximum value and average value.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　［化合物層厚さ及び空隙面積率の測定］
　ガス軟窒化処理後の小ローラの、長手方向に垂直な方向の断面を鏡面研磨し、エッチングした。走査型電子顕微鏡（Ｓｃａｎｎｎｉｇ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ：ＳＥＭ）、日本電子社製；ＪＳＭ－７１００Ｆ）を用いてエッチングされた断面を観察し、化合物層厚さの測定及び化合物層表層の空隙の有無の確認を行った。エッチングは、３％ナイタール溶液で２０～３０秒間行った。 [Measurement of compound layer thickness and void area ratio]
The cross section of the small roller after the gas nitrocarburizing treatment in the direction perpendicular to the longitudinal direction was mirror-polished and etched. Observe the etched cross section using a scanning electron microscope (Scanning Electron Microscope: SEM), manufactured by JEOL Ltd .; JSM-7100F), measure the thickness of the compound layer, and confirm the presence or absence of voids on the surface layer of the compound layer. rice field. Etching was performed with a 3% nital solution for 20-30 seconds.
　化合物層は、鋼の表層に存在する未腐食の層として確認可能である。４０００倍で撮影した組織写真１０視野（１視野面積：横３０μｍ×縦２２μｍ＝６．６×１０２μｍ２）から化合物層を観察し、それぞれ１０μｍ毎に３点の化合物層の厚さを測定した。そして、測定された３０点の平均値を、化合物層厚さ（μｍ）と定義した。 The compound layer can be confirmed as an uncorroded layer existing on the surface layer of steel. The compound layer was observed from 10 visual fields (1 visual field area: width 30 μm × length 22 μm = 6.6 × 10 2 μm 2 ) taken at 4000 times, and the thickness of 3 compound layers was measured every 10 μm. bottom. Then, the average value of the measured 30 points was defined as the compound layer thickness (μm).
　また、同じ組織写真から、最表面から３μｍ深さの範囲の面積９０μｍ２中に占める空隙の総面積の比（空隙面積率、単位は％）を、画像処理アプリケーション（日本電子社製；ＡｎａｌｙｓｉｓＳｔａｔｉｏｎ）により求めた。そして、測定された１０視野の平均値を、空隙面積率（％）と定義した。化合物層が３μｍ未満の場合においても、同様に表面から３μｍ深さまでを測定対象とした。 In addition, from the same tissue photograph, the ratio of the total area of voids (void area ratio, unit is%) to the area 90 μm 2 in the range of 3 μm depth from the outermost surface can be determined by an image processing application (manufactured by JEOL Ltd .; Anallysis Station). Obtained by. Then, the average value of the measured 10 visual fields was defined as the void area ratio (%). Even when the compound layer was less than 3 μm, the measurement target was similarly up to a depth of 3 μm from the surface.
　［化合物層の硬さ］
　化合物層の硬さは、ナノインデンテーション装置（Ｈｙｓｉｔｒｏｎ社製；ＴＩ９５０）により、次の方法で測定した。化合物層の厚さ方向中央近傍位置において、圧子を押込み荷重１０ｍＮにてランダムに５０点押し込むことによって、得られた荷重－変位曲線からビッカース硬さＨＶを測定した。圧子は三角錐（バーコビッチ）形状であり、硬さ導出はＩＳＯ１４５７７－１に準拠し、ナノインデンテーション硬さＨＩＴからビッカース硬さＨＶへの換算を、次式により行った。 [Hardness of compound layer]
The hardness of the compound layer was measured by the following method using a nanoindentation device (manufactured by Hysiron; TI950). The Vickers hardness HV was measured from the obtained load-displacement curve by randomly pushing 50 points of the indenter with a pushing load of 10 mN at a position near the center in the thickness direction of the compound layer. Indenter is triangular pyramid (Berkovich) shape, hardness derivation complies with ISO14577-1, the conversion from nanoindentation hardness H IT to Vickers hardness HV, was performed by the following equation.
　　ＨＶ＝０．０９２４×ＨＩＴ（ＭＰａ）
測定した５０点の平均値を、化合物層の硬さ（ＨＶ）と定義した。 HV = 0.0924 x H IT (MPa)
The average value of the measured 50 points was defined as the hardness (HV) of the compound layer.
　［耐摩耗性評価試験］
　耐摩耗性は、ローラピッティング試験機（小松設備社製；ＲＰ１０２）により、次の方法で評価した。ローラピッティング試験用小ローラを、熱処理ひずみを除く目的で掴み部の仕上げ加工を行った後、それぞれローラピッティング試験片に供した。仕上げ加工後の形状を図３に示す。 [Abrasion resistance evaluation test]
The wear resistance was evaluated by a roller pitting tester (manufactured by Komatsu Kikai Co., Ltd .; RP102) by the following method. The small rollers for the roller pitting test were subjected to finishing processing of the grip portion for the purpose of removing heat treatment strain, and then subjected to each roller pitting test piece. The shape after finishing is shown in FIG.
　ローラピッティング試験は、上記のローラピッティング試験用小ローラと図４に示す形状のローラピッティング試験用大ローラの組み合わせで、表４に示す条件で行った。 The roller pitting test was performed under the conditions shown in Table 4 by combining the above-mentioned small roller for the roller pitting test and the large roller for the roller pitting test having the shape shown in FIG.
　なお、図３、４における寸法の単位は「ｍｍ」である。上記ローラピッティング試験用大ローラは、ＪＩＳ　Ｇ　４０５３（２０１６）のＳＣＭ４２０規格を満たす鋼を用いて、一般的な製造工程、つまり「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→研磨」の工程によって作製した後、表面に微細な凹凸を付与する目的で、粒子径が０．８ｍｍの鋼球を用いて投射圧０．２ＭＰａのショットピーニング処理を行ったものであり、表面から０．０５ｍｍの位置、すなわち、深さ０．０５ｍｍの位置におけるビッカース硬さＨＶは７４０～７６０で、また、ビッカース硬さＨｖが５５０以上の深さは、０．８～１．０ｍｍの範囲にあった。 The unit of dimensions in FIGS. 3 and 4 is "mm". The large roller for roller peening test uses steel that meets the SCM420 standard of JIS G 4053 (2016), and is used in the general manufacturing process, that is, "normalizing-> test piece processing-> co-deposit carburizing by gas carburizing furnace-> After being produced by the process of "low temperature tempering → polishing", shot peening treatment with a projection pressure of 0.2 MPa was performed using a steel ball with a particle size of 0.8 mm for the purpose of imparting fine irregularities to the surface. The Vickers hardness HV at a position of 0.05 mm from the surface, that is, at a depth of 0.05 mm is 740 to 760, and the depth of the Vickers hardness Hv of 550 or more is 0.8 to 1.0 mm. Was in the range of.
　表３に、耐摩耗性の評価を行った試験条件を示す。試験は繰返し数５×１０6回で終了し、試験後の小ローラの摩耗深さを測定した。表面粗さ形状測定機（東京精密社製；ＳＵＲＦＣＯＭ　ＦＬＥＸ）により、試験後の小ローラの摩耗部を主軸方向に沿って走査して、断面形状プロファイルを取得し、取得された断面形状プロファイルの最大深さ（摩耗部）と最小深さ（非摩耗部）との差分を、最大摩耗深さとして計測した。同一の試験片（小ローラ）において、５か所の測定位置において最大摩耗深さを測定して平均することにより、摩耗深さの値を算出した。本発明部品においては、摩耗深さが１０μｍ以下であることを目標とした。 Table 3 shows the test conditions for which the wear resistance was evaluated. The test was completed with 5 × 10 6 repetitions, and the wear depth of the small roller after the test was measured. A surface roughness shape measuring machine (manufactured by Tokyo Seimitsu Co., Ltd .; SURFCOM FLEX) scans the worn part of the small roller after the test along the spindle direction to acquire the cross-sectional shape profile, and the maximum of the obtained cross-sectional shape profile. The difference between the depth (wear part) and the minimum depth (non-wear part) was measured as the maximum wear depth. The value of the wear depth was calculated by measuring and averaging the maximum wear depths at five measurement positions on the same test piece (small roller). In the parts of the present invention, it was aimed that the wear depth was 10 μm or less.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　［回転曲げ疲労強度評価試験］
　ガス軟窒化処理に供した円柱試験片に対し、ＪＩＳ　Ｚ　２２７４（１９７８）に準拠した小野式回転曲げ疲労試験を実施した。回転数は３０００ｒｐｍ、試験打ち切り回数は、一般的な鋼の疲労限を示す１×１０７回とし、回転曲げ疲労試験片において、破断が生じずに１×１０７回に達した最大応力を回転曲げ疲労試験片の疲労限とした。 [Rotary bending fatigue strength evaluation test]
An Ono-type rotary bending fatigue test based on JIS Z 2274 (1978) was carried out on a cylindrical test piece subjected to gas nitrocarburizing treatment. The number of rotations is 3000 rpm, the number of test censoring is 1 × 10 7 times, which indicates the fatigue limit of general steel, and the maximum stress that reaches 1 × 10 7 times without fracture occurs in the rotary bending fatigue test piece. The fatigue limit of the bending fatigue test piece was used.
　本発明部品においては、疲労限における最大応力が５００ＭＰａ以上であることを目標にした。 In the parts of the present invention, the goal was to have a maximum stress of 500 MPa or more in the fatigue limit.
　［試験結果］
　結果を表２－１及び表２－２に示す。試験番号１～２６は、鋼の成分及びガス軟窒化処理の条件が本発明の範囲内であり、化合物層厚さが３μｍ以上２０μｍ以下、化合物層空隙面積率が１２％未満となった。その結果、摩耗深さが１０μｍ未満、回転曲げ疲労強度が５００ＭＰａ以上と良好な結果が得られた。 [Test results]
The results are shown in Table 2-1 and Table 2-2. In Test Nos. 1 to 26, the steel composition and the conditions of the gas soft nitriding treatment were within the range of the present invention, the compound layer thickness was 3 μm or more and 20 μm or less, and the compound layer void area ratio was less than 12%. As a result, good results were obtained with a wear depth of less than 10 μm and a rotational bending fatigue strength of 500 MPa or more.
　試験番号２７～４５は、鋼の成分、およびガス軟窒化処理の条件の一部が本発明の範囲外であり、化合物層の厚さ、ε相の面積率、空隙面積率のうちいずれか、もしくは複数の特性が、本発明における目標値に届かなかった。その結果、耐摩耗性もしくは回転曲げ疲労強度が本発明の目標を満たさなかった。
　試験番号２７は、製造時にガス軟窒化処理温度が高すぎた比較例である。これにより、試験番号２７では空隙面積率が過剰となり、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号２８は、製造時にガス軟窒化処理温度が低すぎた比較例である。これにより、試験番号２８では化合物層の厚さが不足し、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号２９は、製造時にガス軟窒化処理時間が長すぎた比較例である。これにより、試験番号２９では化合物層の厚さが過剰となり、且つ空隙面積率が過剰となり、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号３０は、製造時にガス軟窒化処理時間が短すぎた比較例である。これにより、試験番号３０では化合物層の厚さが不足し、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号３１は、製造時に窒化ポテンシャルＫＮが高くなりすぎた比較例である。これにより、試験番号３１では空隙面積率が過剰となり、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号３２は、製造時に窒化ポテンシャルＫＮが低くなりすぎた比較例である。これにより、試験番号３２では化合物層の厚さが不足し、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号３３は、製造時にガス軟窒化処理時間が長すぎた比較例である。これにより、試験番号３３では化合物層の厚さが過剰となり、且つ空隙面積率が過剰となり、耐摩耗性が不足した。
　試験番号３４は、製造時に平均窒化ポテンシャルＫＮａｖｅが低すぎた比較例である。これにより、試験番号３４では化合物層の厚さが不足し、且つε面積率が不足し、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号３５は、製造時に浸炭性ガス投入比率が高すぎた比較例である。これにより、試験番号３５では化合物層の厚さが不足し、耐摩耗性及び回転曲げ疲労強度が不足した。
　試験番号３６は、製造時に浸炭性ガス投入比率が低すぎた（すなわち軟窒化でなく窒化処理がなされた）比較例である。これにより、試験番号３６ではε面積率が不足し、耐摩耗性が不足した。
　製造番号３７（鋼ｕ）は、鋼芯部の化学成分において、－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏが高すぎた比較例である。これにより、試験番号３７では化合物層の厚さが不足し、耐摩耗性と回転曲げ疲労強度が不足した。
　製造番号３８（鋼ｖ）は、鋼芯部の化学成分において、－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏが低すぎた比較例である。これにより、試験番号３８では化合物層の厚さが過剰となり、回転曲げ疲労強度が不足した。
　製造番号３９（鋼ｗ）は、鋼芯部のＣ量が低すぎた比較例である。これにより、試験番号３９では耐摩耗性が不足した。
　製造番号４０（鋼ｘ）は、鋼芯部のＭｎ量が低すぎた比較例である。これにより、試験番号４０では耐摩耗性及び回転曲げ疲労強度が不足した。
　製造番号４１（鋼ｙ）は、鋼芯部のＣｒ量が低すぎた比較例である。これにより、試験番号４１では耐摩耗性及び回転曲げ疲労強度が不足した。
　製造番号４２（鋼ｚ）は、鋼芯部のＶ量が低すぎた比較例である。これにより、試験番号４２では耐摩耗性及び回転曲げ疲労強度が不足した。
　製造番号４３（鋼ａａ）は、鋼芯部のＰ量が高すぎた比較例である。これにより、試験番号４３では耐摩耗性及び回転曲げ疲労強度が不足した。
　製造番号４４（鋼ａｂ）は、鋼芯部のＳ量が高すぎた比較例である。これにより、試験番号４４では耐摩耗性及び回転曲げ疲労強度が不足した。
　製造番号４５は、製造時に窒化ポテンシャルＫＮ及び平均窒化ポテンシャルＫＮａｖｅが高すぎた比較例である。これにより、試験番号４５では化合物層の厚さが過剰となり、且つ空隙面積率が過剰となり、耐摩耗性及び回転曲げ疲労強度が不足した。 In test numbers 27 to 45, the composition of the steel and some of the conditions for the gas soft nitriding treatment are outside the scope of the present invention, and any one of the thickness of the compound layer, the area ratio of the ε phase, and the void area ratio is determined. Alternatively, a plurality of characteristics did not reach the target value in the present invention. As a result, wear resistance or rotational bending fatigue strength did not meet the object of the present invention.
Test number 27 is a comparative example in which the gas nitrocarburizing treatment temperature was too high during production. As a result, in Test No. 27, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 28 is a comparative example in which the gas nitrocarburizing treatment temperature was too low during production. As a result, in Test No. 28, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 29 is a comparative example in which the gas nitrocarburizing treatment time was too long during production. As a result, in Test No. 29, the thickness of the compound layer became excessive, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 30 is a comparative example in which the gas nitrocarburizing treatment time was too short at the time of production. As a result, in Test No. 30, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 31 is a comparative example in which the nitriding potential K N becomes too high during manufacturing. As a result, in Test No. 31, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 32 is a comparative example in which the nitriding potential K N was too low during production. As a result, in Test No. 32, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 33 is a comparative example in which the gas nitrocarburizing treatment time was too long during production. As a result, in Test No. 33, the thickness of the compound layer became excessive, the void area ratio became excessive, and the wear resistance was insufficient.
Test number 34 is a comparative example in which the average nitriding potential K Nave was too low at the time of manufacture. As a result, in Test No. 34, the thickness of the compound layer was insufficient, the ε area ratio was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 35 is a comparative example in which the carburizing gas input ratio was too high at the time of production. As a result, in Test No. 35, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
Test number 36 is a comparative example in which the carburizing gas input ratio was too low at the time of production (that is, nitriding was performed instead of soft nitriding). As a result, in test number 36, the ε area ratio was insufficient and the wear resistance was insufficient.
Serial number 37 (steel u) is a comparative example in which −2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo was too high in the chemical composition of the steel core portion. As a result, in Test No. 37, the thickness of the compound layer was insufficient, and the wear resistance and the rotational bending fatigue strength were insufficient.
Serial number 38 (steel v) is a comparative example in which −2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo was too low in the chemical composition of the steel core portion. As a result, in Test No. 38, the thickness of the compound layer became excessive, and the rotational bending fatigue strength was insufficient.
Serial number 39 (steel w) is a comparative example in which the amount of C in the steel core is too low. As a result, the wear resistance of test number 39 was insufficient.
Serial number 40 (steel x) is a comparative example in which the amount of Mn in the steel core is too low. As a result, in Test No. 40, the wear resistance and the rotational bending fatigue strength were insufficient.
Serial number 41 (steel y) is a comparative example in which the amount of Cr in the steel core is too low. As a result, in Test No. 41, the wear resistance and the rotational bending fatigue strength were insufficient.
Serial number 42 (steel z) is a comparative example in which the amount of V in the steel core is too low. As a result, in Test No. 42, the wear resistance and the rotational bending fatigue strength were insufficient.
Serial number 43 (steel aa) is a comparative example in which the P amount of the steel core portion is too high. As a result, in Test No. 43, the wear resistance and the rotational bending fatigue strength were insufficient.
Serial number 44 (steel ab) is a comparative example in which the S amount of the steel core portion is too high. As a result, in Test No. 44, the wear resistance and the rotational bending fatigue strength were insufficient.
Production number 45 is a comparative example in which the nitriding potential K N and the average nitriding potential K Nave were too high at the time of production. As a result, in Test No. 45, the thickness of the compound layer became excessive, the void area ratio became excessive, and the wear resistance and the rotational bending fatigue strength were insufficient.
　以上、本発明の実施の形態を説明した。しかしながら、上述した実施の形態は本発明を実施するための例示にすぎない。したがって、本発明は上述した実施の形態に限定されることなく、その趣旨を逸脱しない範囲内で上述した実施の形態を適宜変更して実施することができる。 The embodiment of the present invention has been described above. However, the embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.
　本発明によれば、耐摩耗性に加え回転曲げ疲労強度に優れた軟窒化処理部品とその製造方法を提供することができ、特に耐摩耗性及び曲げ疲労強度に優れる連続可変トランスミッション（ＣＶＴ）、カムシャフト部品等を提供することができる。 According to the present invention, it is possible to provide a soft nitriding-treated part having excellent wear resistance and rotational bending fatigue strength and a method for manufacturing the same, and a continuously variable transmission (CVT) having particularly excellent wear resistance and bending fatigue strength. Cam shaft parts and the like can be provided.
１　　ガス軟窒化処理部品（部品）
１１　鋼芯部（鋼）
１２　化合物層
１３　窒素拡散層（拡散層） 1 Gas soft nitriding parts (parts)
11 Steel core (steel)
12 Compound layer 13 Nitrogen diffusion layer (diffusion layer)

Claims (6)

  1. 　鋼芯部と、化合物層と、前記鋼芯部と前記化合物層との間に存在する窒素拡散層と、を備え、
    　前記鋼芯部の組成が、質量％で、
    Ｃ：０．０５％～０．６０％、
    Ｓｉ：０．０５％～１．５０％、
    Ｍｎ：０．２０％～２．５０％、
    Ｐ：０．０２５％以下、
    Ｓ：０．０５０％以下、
    Ｃｒ：０．５０％～２．５０％、
    Ｖ：０．０５％～１．３０％、
    Ａｌ：０．０５０％以下、及び
    Ｎ：０．０２５０％以下
    を含有し、残部はＦｅ及び不純物を含み、
    　前記鋼芯部の前記組成におけるＣ、Ｍｎ、Ｃｒ、Ｖ、Ｍｏの含有量が式（１）を満たし、
    　前記化合物層の厚さが３～２０μｍであり、
    　前記化合物層は、ε相を面積率で５０％超含有し、残部がγ’相であり、
    　前記化合物層の表面から深さ３μｍまでの領域において、空隙の面積比率が１２％未満である
    ことを特徴とするガス軟窒化処理部品。
    　０．００≦－２．１×Ｃ＋０．０４×Ｍｎ＋０．５×Ｃｒ＋１．８×Ｖ－１．５×Ｍｏ≦０．５０・・・式（１）
    　ただし、式（１）中の元素記号は当該元素の含有量（質量％）を示し、含有しない場合は０を代入する。     A steel core portion, a compound layer, and a nitrogen diffusion layer existing between the steel core portion and the compound layer are provided.
    The composition of the steel core is mass%.
    C: 0.05% to 0.60%,
    Si: 0.05% to 1.50%,
    Mn: 0.20% to 2.50%,
    P: 0.025% or less,
    S: 0.050% or less,
    Cr: 0.50% to 2.50%,
    V: 0.05% to 1.30%,
    Al: 0.050% or less, N: 0.0250% or less, the balance contains Fe and impurities,
    The contents of C, Mn, Cr, V, and Mo in the composition of the steel core portion satisfy the formula (1).
    The thickness of the compound layer is 3 to 20 μm, and the thickness of the compound layer is 3 to 20 μm.
    The compound layer contains the ε phase in an area ratio of more than 50%, and the balance is the γ'phase.
    A gas soft nitriding-treated component, characterized in that the area ratio of voids is less than 12% in a region from the surface of the compound layer to a depth of 3 μm.
    0.00 ≦ -2.1 × C + 0.04 × Mn + 0.5 × Cr + 1.8 × V-1.5 × Mo ≦ 0.50 ・ ・ ・ Equation (1)
    However, the element symbol in the formula (1) indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
  2. 　前記鋼芯部の前記組成が、質量％で、
    Ｃ：０．０５％～０．６０％、
    Ｓｉ：０．０５％～１．５０％、
    Ｍｎ：０．２０％～２．５０％、
    Ｐ：０．０２５％以下、
    Ｓ：０．０５０％以下、
    Ｃｒ：０．５０％～２．５０％、
    Ｖ：０．０５％～１．３０％、
    Ａｌ：０．０５０％以下、
    Ｎ：０．０２５０％以下、
    Ｍｏ：０～１．５０％、
    Ｃｕ：０～１．００％、
    Ｎｉ：０～１．００％、
    Ｗ：０～０．５０％、
    Ｃｏ：０～０．５０％、
    Ｎｂ：０～０．３００％、
    Ｔｉ：０～０．２５０％、
    Ｂ：０～０．０１００％、
    Ｃａ：０～０．０１０％、
    Ｍｇ：０～０．０１０％、及び
    ＲＥＭ：０～０．０１０％
    を含有し、残部はＦｅ及び不純物からなることを特徴とする請求項１に記載のガス軟窒化処理部品。     When the composition of the steel core portion is mass%,
    C: 0.05% to 0.60%,
    Si: 0.05% to 1.50%,
    Mn: 0.20% to 2.50%,
    P: 0.025% or less,
    S: 0.050% or less,
    Cr: 0.50% to 2.50%,
    V: 0.05% to 1.30%,
    Al: 0.050% or less,
    N: 0.0250% or less,
    Mo: 0 to 1.50%,
    Cu: 0 to 1.00%,
    Ni: 0 to 1.00%,
    W: 0 to 0.50%,
    Co: 0 to 0.50%,
    Nb: 0 to 0.300%,
    Ti: 0 to 0.250%,
    B: 0 to 0.0100%,
    Ca: 0 to 0.010%,
    Mg: 0 to 0.010%, and REM: 0 to 0.010%
    The gas nitrocarburizing treatment component according to claim 1, wherein the gas soft nitriding component is composed of Fe and impurities in the balance.
  3. 　前記鋼芯部の前記組成において、
    Ｃ：０．０５％～０．３５％
    であることを特徴とする請求項１又は２に記載のガス軟窒化処理部品。     In the composition of the steel core portion
    C: 0.05% to 0.35%
    The gas nitrocarburizing treatment component according to claim 1 or 2, wherein the gas nitrocarburizing component is characterized by the above.
  4. 　前記化合物層における前記ε相が面積率で９０％以下であることを特徴とする請求項１～３のいずれか一項に記載のガス軟窒化処理部品。 The gas soft nitriding treatment component according to any one of claims 1 to 3, wherein the ε phase in the compound layer has an area ratio of 90% or less.
  5. 　前記化合物層の厚さが６μｍ以上であることを特徴とする請求項１～４のいずれか一項に記載のガス軟窒化処理部品。 The gas soft nitriding component according to any one of claims 1 to 4, wherein the compound layer has a thickness of 6 μm or more.
  6. 　請求項１～５のいずれか一項に記載のガス軟窒化処理部品の製造方法であって、
    　請求項１～３のいずれか一項に記載の鋼芯部の組成を有する鋼材を所定の形状に加工して素形鋼を得る工程と、
    　前記素形鋼にガス軟窒化処理を施す工程と、
    を有し、
    　前記ガス軟窒化処理は、ＣＯ２、ＣＯ、炭化水素ガスのうち少なくとも１種を含むガスを、式（２）で表す浸炭性ガス投入比率で２体積％以上１０体積％未満含み、
    　残部はＮＨ３、Ｈ２、Ｎ２及び不純物ガスであるガス雰囲気中において、
    　温度５５０℃以上６３０℃以下で、１．０時間以上７．０時間以下保持して行い、
    　前記ガス雰囲気は、式（３）によって求められる窒化ポテンシャルＫＮが、前記ガス軟窒化処理を施す工程を通じて０．１５以上０．４０以下の範囲内であって、
    　前記窒化ポテンシャルＫＮの平均値ＫNａｖｅが０．１８以上０．３０未満であることを特徴とするガス軟窒化処理部品の製造方法。
    　浸炭性ガス投入比率（体積％）＝ＣＯ２、ＣＯ、炭化水素ガスの総投入流量（ｌ／ｍｉｎ）／雰囲気ガスの総投入流量（ｌ／ｍｉｎ）×１００・・・式（２）
    　ＫＮ＝（ＮＨ３分圧）／［（Ｈ２分圧）3/2］（ａｔｍ－１／２）・・・式（３）     The method for manufacturing a gas soft nitriding processed component according to any one of claims 1 to 5.
    A step of processing a steel material having the composition of the steel core portion according to any one of claims 1 to 3 into a predetermined shape to obtain a shaped steel.
    The process of applying gas nitrocarburizing treatment to the structural steel and
    Have,
    The gas nitrocarburizing treatment contains a gas containing at least one of CO 2 , CO, and a hydrocarbon gas in an amount of 2% by volume or more and less than 10% by volume in a carburizing gas input ratio represented by the formula (2).
    The rest is NH 3 , H 2 , N 2 and impurity gas in a gas atmosphere.
    Hold the temperature at 550 ° C or higher and 630 ° C or lower for 1.0 hour or longer and 7.0 hours or lower.
    In the gas atmosphere, the nitriding potential K N obtained by the formula (3) is in the range of 0.15 or more and 0.40 or less through the step of performing the gas nitrocarburizing treatment.
    A method for manufacturing a gas soft nitriding processed component, wherein the average value K Nave of the nitriding potential K N is 0.18 or more and less than 0.30.
    Carburizing gas input ratio (volume%) = CO 2 , CO, total input flow rate of hydrocarbon gas (l / min) / total input flow rate of atmospheric gas (l / min) x 100 ... Equation (2)
    K N = (NH 3 partial pressure) / [(H 2 partial pressure) 3/2 ] (atm- 1 / 2 ) ・ ・ ・ Equation (3)
PCT/JP2020/010585 2020-03-11 2020-03-11 Gas soft-nitriding processed article and method of producing same WO2021181570A1 (en)

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