WO2023162515A1 - Method for producing steel member - Google Patents

Method for producing steel member Download PDF

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Publication number
WO2023162515A1
WO2023162515A1 PCT/JP2023/001183 JP2023001183W WO2023162515A1 WO 2023162515 A1 WO2023162515 A1 WO 2023162515A1 JP 2023001183 W JP2023001183 W JP 2023001183W WO 2023162515 A1 WO2023162515 A1 WO 2023162515A1
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Prior art keywords
steel member
temperature
manufacturing
carbon
steel
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PCT/JP2023/001183
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French (fr)
Japanese (ja)
Inventor
一晃 岡田
将芝 榊原
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株式会社アイシン
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Priority to JP2024502903A priority Critical patent/JPWO2023162515A1/ja
Priority to CN202380023388.4A priority patent/CN118786227A/en
Publication of WO2023162515A1 publication Critical patent/WO2023162515A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • 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
    • C21D9/28—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for plain shafts
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/32—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for gear wheels, worm wheels, or the like
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces
    • 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
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/34—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in more than one step

Definitions

  • the present invention relates to a method for manufacturing steel members.
  • Japanese Patent Application Laid-Open No. 2019-127624 discloses a method for manufacturing a steel member that includes a carburizing step of infiltrating carbon into a steel member in an austenitized state.
  • a carburizing step of infiltrating carbon into a steel member in an austenitized state.
  • carbon is introduced into the austenitized steel member at a carbon concentration at which the steel member and carbon have a hyper-eutectoid composition.
  • the hardness of a steel member is generally approximately proportional to the carbon concentration of the surface (carburized layer) of the steel member.
  • the hardness of a steel member is generally inversely proportional to the toughness of the steel member. That is, in manufacturing the steel member described in JP-A-2019-127624, the hardness of the steel member tends to be excessively high and the toughness of the steel member tends to be excessively low. When the toughness of the steel member becomes low, the steel member becomes vulnerable to impact. Therefore, there is a demand for a method of manufacturing a steel member that can improve the hardness and toughness of the steel member in a well-balanced manner.
  • the present invention has been made to solve the above problems, and one object of the present invention is to provide a method for manufacturing a steel member capable of improving the hardness and toughness of the steel member in a well-balanced manner. to provide.
  • a steel member manufacturing method in one aspect of the present invention provides a steel member in an austenitized state by heating the steel member to a temperature equal to or higher than the austenitizing transformation completion temperature.
  • a carburizing process in which carbon is infiltrated at a carbon concentration that makes the sub-eutectoid composition, and the steel member into which carbon is infiltrated is slowly cooled, and after the carburizing process, the steel member is heated to a temperature equal to or higher than the austenitizing transformation completion temperature. and a quenching step of heating again and quenching the heated steel member.
  • carbon is added to the austenitized steel member at a carbon concentration such that the steel member and carbon have a hypo-eutectoid composition. infiltrate.
  • the carbon concentration penetrating into the steel member is excessive. never get higher.
  • the hardness of the steel member does not become excessively high, and the toughness of the steel member does not become excessively low.
  • the hardness and toughness of the steel member can be improved in a well-balanced manner.
  • FIG. 4 is a diagram showing temperature changes of the steel member in the steel member manufacturing method according to the embodiment of the present invention. It is a state diagram of S20C as an example of a steel member. 5 is a diagram showing temperature changes of a steel member in a steel member manufacturing method according to Comparative Example 1.
  • FIG. FIG. 4 is a diagram showing temperature changes of the steel member in the steel member manufacturing method according to the embodiment of the present invention. It is a state diagram of S20C as an example of a steel member. 5 is a diagram showing temperature changes of a steel member in a steel member manufacturing method according to Comparative Example 1.
  • FIG. 10 is a diagram showing temperature changes of a steel member in a method for manufacturing a steel member according to Comparative Example 2;
  • a steel member in a method for manufacturing a steel member according to an embodiment of the present invention a steel member in a method for manufacturing a steel member according to a first modification, a steel member in a method for manufacturing a steel member according to a second modification, and a steel member according to Comparative Example 1
  • FIG. 2 is a diagram showing the bending fatigue strength and toughness of a steel member in the steel member manufacturing method; Fig.
  • FIG. 3 shows the bending fatigue strength of the steel member in the steel member manufacturing method according to the embodiment of the present invention, the steel member in the steel member manufacturing method according to the first modified example, and the steel member in the steel member manufacturing method according to Comparative Example 2; It is a diagram. Torsional fatigue strength of the steel member in the steel member manufacturing method according to the embodiment of the present invention, the steel member in the steel member manufacturing method according to the first modified example, and the steel member in the steel member manufacturing method according to Comparative Example 3 It is a figure which shows.
  • FIG. 5 is a diagram showing the grain boundary oxidation depth and average grain size of a steel member in a steel member manufacturing method according to an embodiment of the present invention and a steel member in a steel member manufacturing method according to Comparative Example 2;
  • FIG. 1 A method for manufacturing a steel member according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.
  • FIG. The method for manufacturing a steel member according to one embodiment of the present invention can be applied to steel members such as gears, bearings, and shafts.
  • the cold forging step (S1) is a step of forging a steel member into a desired shape (for example, the shape of a gear, bearing, shaft, etc.) at room temperature.
  • a desired shape for example, the shape of a gear, bearing, shaft, etc.
  • case-hardening steel for example, SCM420
  • SCM420 case-hardening steel
  • step S2 a carburizing process is performed.
  • the steel member in the carburizing step (S2), the steel member is heated to a temperature T1 (for example, about 1000° C.) equal to or higher than the austenitizing transformation completion temperature A3, and carbon is introduced into the steel member in the austenitized state. It is a step of slowly cooling the steel member into which carbon is impregnated.
  • the austenitized steel member is a steel member made of austenite ( ⁇ -iron).
  • the austenitizing transformation completion temperature A3 is the temperature at which the steel member is heated and the austenitizing transformation of the steel member is completed. Specifically, as shown in FIG. 2, the steel member is placed in the first heat treatment chamber.
  • the steel member is then heated to temperature T1 so that the steel member is austenitized.
  • a carburizing gas for example, C 2 H 2
  • C 2 H 2 a carburizing gas
  • the carburizing gas is decomposed on the surface of the austenitized steel member to produce carbon.
  • a carburized layer is formed on the surface layer of the steel member by the generated carbon diffusing from the surface of the steel member toward the inside.
  • the steel member is slowly cooled so that the steel member becomes pearlitic. Slow cooling of the steel member is performed at a cooling rate at which the steel member becomes pearlitic.
  • the slow cooling of the steel member is performed at a cooling rate at which the steel member does not turn into martensite.
  • slow cooling of the steel member is performed in an inert gas (for example, Ar, N 2 , He, etc.) atmosphere in order to prevent the formation of an oxide film on the steel member.
  • the carburizing step (S2) is performed while the pressure inside the first heat treatment chamber is reduced by a vacuum pump.
  • the steel member In the case of a carbon concentration (less than about 0.77%) where the steel member and carbon have a hypo-eutectoid composition, at a temperature lower than the austenitizing transformation start temperature A1, the steel member It is a state consisting of ferrite ( ⁇ -iron) and pearlite. Further, when the carbon concentration of the steel member and carbon is less than the concentration of hypo-eutectoid composition, at a temperature higher than the austenitization transformation start temperature A1 and lower than the austenitization transformation completion temperature A3, the steel member It is a state of austenite ( ⁇ -iron) and ferrite ( ⁇ -iron).
  • the steel member when the carbon concentration of the steel member and carbon is less than the carbon concentration where the steel member and carbon have a hypo-eutectoid composition, the steel member is in a state of austenite ( ⁇ iron) at a temperature higher than the austenitizing transformation completion temperature A3.
  • the carburizing step (S2) carbon is infiltrated into the austenitized steel member at a carbon concentration such that the steel member and carbon have a hypo-eutectoid composition.
  • the continuous introduction of the carburizing gas into the first heat treatment chamber increases the carbon concentration of the surface (carburized layer) of the steel member.
  • the carbon concentration of the surface (carburized layer) of the steel member is less than the carbon concentration at which the steel member and carbon have a eutectoid composition (for example, about 0.77% when the steel member is SCM420, which is case-hardened steel).
  • the hardness of a steel member is generally approximately proportional to the carbon concentration of the surface (carburized layer) of the steel member.
  • the hardness of a steel member is generally inversely proportional to the toughness of the steel member.
  • the hardness and toughness of the steel member can be improved in a well-balanced manner.
  • a nitriding process is performed in step S3.
  • the nitriding step (S3) is a step of infiltrating nitrogen into the steel member heated to a temperature T2 (for example, about 810° C.) lower than the austenitizing transformation completion temperature A3. .
  • the steel member is placed in the second heat treatment chamber.
  • the pearlitic steel member is heated to a temperature T2.
  • the steel member is in a state in which ferrite ( ⁇ -iron) and austenite ( ⁇ -iron) are mixed.
  • a nitriding gas ( NH 3 ) is introduced in a predetermined amount (eg 0.8 m 3 /h). Then, nitrogen is generated by decomposition of the nitriding gas on the surface of the steel member. As the generated carbon diffuses from the surface of the steel member toward the inside, nitrogen enters the carburized layer on the surface layer of the steel member, forming a carbo-nitrided layer.
  • the nitriding step (S3) is performed while adjusting the carbon concentration inside the second heat treatment chamber so that the carbon concentration of the carburized layer does not decrease.
  • the amount of nitrogen that penetrates into the surface layer of the steel member is generally inversely proportional to the temperature of the steel member at a temperature equal to or higher than the austenitizing transformation start temperature A1 (described later).
  • the higher the carbon concentration of the carburized layer the more easily voids are generated in the steel member.
  • the higher the temperature of the steel member the more easily the grain boundary oxide layer is formed in the steel member.
  • the hardness of the steel member is improved as the amount of nitrogen that penetrates into the surface layer of the steel member increases.
  • a temperature T3 e.g., about 850° C.
  • nitriding is performed in which nitrogen enters the steel member. It is possible to increase the amount of nitrogen to be used and to suppress the generation of voids and the formation of grain boundary oxide layers in the steel member. As a result, the hardness of the steel member can be effectively improved. hardness can be ensured.
  • the time for introducing the nitriding gas and the amount of the nitriding gas are adjusted so that the nitrogen concentration on the surface of the steel member (carbonitriding layer) reaches a predetermined concentration.
  • the nitriding step (S3) is a step of infiltrating nitrogen into the steel member so that the nitrogen concentration on the surface of the steel member reaches a predetermined concentration.
  • the predetermined concentration is at least about 0.5% or less.
  • the predetermined concentration is preferably greater than or equal to about 0.05% and less than or equal to 0.35%.
  • the nitriding step (S3) is a step of infiltrating nitrogen into the steel member at a temperature T2 (for example, about 810°C) that is equal to or higher than the austenitizing transformation start temperature A1 and lower than the austenitizing transformation completion temperature A3.
  • the austenitizing transformation start temperature A1 is the temperature at which the austenitizing transformation of the steel member starts.
  • the amount of nitrogen that penetrates into the steel member is significantly reduced. This makes it possible to increase the amount of nitrogen that penetrates into the steel member compared to the case where nitriding is performed by introducing nitrogen into the steel member at a temperature below the austenitizing transformation start temperature A1.
  • the cold forging process is performed in step S1. That is, the carburizing step (S2) is performed on the cold-forged steel member.
  • the carburizing step (S2) the steel member is heated and slowly cooled, so that residual stress generated in the steel member by cold forging can be removed from the steel member.
  • the quenching step (S4) is a step of reheating the steel member to a temperature T3 (for example, about 850° C.) equal to or higher than the austenitizing transformation completion temperature A3, and rapidly cooling the heated steel member. .
  • T3 for example, about 850° C.
  • the steel member is placed in the second heat treatment chamber.
  • the steel member is then heated again to temperature T3 so that the steel member austenites.
  • the steel member is transported from the heat treatment chamber into the cooling device, where the steel member is martensitic.
  • the steel member is quenched so as to The steel member is quenched at a cooling rate that martensites the steel member. That is, the steel member is quenched at a cooling rate that does not cause pearlitization of the steel member. Also, the steel member is quenched using water or oil.
  • the steel member is heated from a temperature T2 (for example, about 810° C.) below the austenitization completion temperature A3 to a temperature T3 (for example, , about 850° C.) and rapidly cooling the heated steel member. That is, the nitriding step (S3) and the quenching step (S4) are continuously performed in this order.
  • the steel member heated to a temperature T2 (for example, about 810° C.) lower than the austenitization completion temperature A3 in the nitriding step (S3) is heated from the temperature T2 (for example, about 810° C.) to the austenitization completion temperature.
  • the steel member can be heated Energy consumption can be suppressed.
  • the tempering step (S5) is a step of reheating and cooling the martensitic steel member. As a result, the steel member, which has become martensitic and temporarily excessively hardened and excessively reduced in toughness, is tempered to have appropriate fatigue strength and toughness.
  • a steel member was produced by using the steel member as a gear on the basis of the steel member manufacturing method according to the above-described embodiment (Example 1). Specifically, first, a cold forging step of cold forging a steel member was performed. SCM420 of case hardening steel was used for the steel member. Then, the steel member is heated to a temperature T1 (1000° C.) equal to or higher than the austenitization transformation completion temperature A3 to infiltrate carbon into the steel member in the austenitized state, and carburize the steel member into which carbon has been infiltrated and slowly cool it. did the process.
  • T1 1000° C.
  • the carburizing step carbon was infiltrated into the austenitized steel member at a carbon concentration (less than 0.77%) at which the steel member and carbon had a hypo-eutectoid composition.
  • the carburizing process was performed while reducing the pressure inside the first heat treatment chamber with a vacuum pump.
  • a nitriding step was performed in which nitrogen was introduced into the steel member in a state where the steel member was heated to a temperature T2 (810° C.) lower than the austenitizing transformation completion temperature A3.
  • the steel member was again heated to a temperature T3 (850° C.) higher than the austenitization transformation completion temperature A3, and a quenching step was performed to rapidly cool the heated steel member. Then, a tempering process of heating and cooling the martensitic steel member again was performed.
  • T3 850° C.
  • a steel member was manufactured by omitting the nitriding step from the steel member manufacturing method according to the above-described embodiment (Example 2). Further, as a second modification of the above embodiment, the nitriding step is omitted from the steel member manufacturing method according to the above embodiment, and the steel member in the steel member manufacturing method according to the above embodiment is changed from case hardened steel to sintered material. Instead, a steel member was produced (Example 3).
  • a steel member was produced using the steel member as a shaft based on the method for manufacturing a steel member according to the above embodiment (Example 4). Further, a steel member was produced using the steel member as a shaft based on the method for manufacturing a steel member according to the first modified example (Example 5).
  • a steel member was produced using the steel member as a gear, based on the steel member manufacturing method according to Comparative Example 1 shown in FIG. Specifically, first, a cold forging step was performed in the same manner as in the steel member manufacturing method according to the above embodiment. SCM420 of case-hardened steel was used for the steel member in the same manner as in the method for manufacturing the steel member according to the above-described embodiment. Then, in the same manner as in the method for manufacturing a steel member according to the above-described embodiment, the steel member is heated to a temperature T1 (1000° C.) equal to or higher than the austenitization transformation completion temperature A3, and carbon is introduced into the steel member in the austenitized state.
  • T1 1000° C.
  • a carburizing step was carried out to slowly cool the steel member infiltrated with carbon.
  • the steel member is cooled to a temperature lower than the austenitization transformation start temperature A1 so that only part of the austenite is pearlitic while the steel member is slowly cooled.
  • the temperature was maintained at T4 (710° C.) for a predetermined time. That is, the steel member stays in a high temperature state (a state other than room temperature) longer than in the steel member manufacturing method according to the above-described embodiment by the time that the steel member is maintained at temperature T4 (710° C.).
  • the steel member in the austenitized state has a carbon concentration (0.77% or more) at which the steel member and carbon have a hyper-eutectoid composition, Infiltrated with carbon.
  • the carburizing process was performed while reducing the pressure inside the heat treatment chamber with a vacuum pump, as in the steel member manufacturing method according to the above-described embodiment. Then, the steel member was heated to a temperature T3 (850° C.) higher than the austenitizing transformation completion temperature A3, and after the steel member was maintained at the temperature T3 (850° C.) for a while, a quenching process was performed to rapidly cool the steel member.
  • a carburizing step was carried out to slowly cool the steel member infiltrated with carbon.
  • the slow cooling in the carburizing process was performed until the temperature of the steel member reached the temperature T3 (850°C) for the quenching process.
  • carbon is added to the austenitized steel member at a carbon concentration (0.77%) at which the steel member and carbon have a eutectoid composition. infiltrated.
  • the carburizing step was performed without depressurizing the inside of the heat treatment chamber.
  • the steel member was subjected to a quenching step of quenching. That is, unlike the steel member manufacturing method according to the above-described embodiment, the steel member was not pearliticized after the carburizing step, and the quenching step was performed immediately after the carburizing step. In addition, unlike the steel member manufacturing method according to the above-described embodiment, the nitriding process was not performed. Then, a tempering step was performed in the same manner as in the steel member manufacturing method according to the above embodiment.
  • the steel member of Example 1 (SCM (with nitriding) in the figure), the steel member of Example 2 (SCM (without nitriding) in the figure), and the steel member of Example 3 ( All of the sintered materials (no nitriding) in the figure have crack initiation energy E i (J/cm 2 ) and bending fatigue strength ⁇ (MPa) during the impact test, both of which are the same as those of the steel member of Comparative Example 1.
  • SCM420 (Comparative Example 1) in the figure).
  • the crack initiation energy E i of the steel member of Example 1 was greater than the crack initiation energy E i of the steel member of Comparative Example 1.
  • the crack initiation energy Ei of the steel member of Example 2 was larger than the crack initiation energy Ei of the steel member.
  • the crack initiation energy E i of the steel member of Example 3 was larger than the crack initiation energy E i of the steel member of Example 2.
  • the bending fatigue strength ⁇ of the steel member of Example 3 was greater than the bending fatigue strength ⁇ of the steel member of Comparative Example 1.
  • the bending fatigue strength ⁇ of the steel member of Example 2 was greater than the bending fatigue strength ⁇ of the steel member of Example 3.
  • the bending fatigue strength ⁇ of the steel member of Example 1 was greater than the bending fatigue strength ⁇ of the steel member of Example 2.
  • the magnitude of the crack initiation energy Ei during the impact test is approximately proportional to the magnitude of toughness.
  • the bending fatigue strength ⁇ means the magnitude of strength against bending.
  • the bending fatigue strength ⁇ is generally approximately proportional to hardness.
  • the crack initiation energy Ei during the impact test was measured using the Charpy impact test.
  • the bending fatigue strength ⁇ was measured using the Ono rotating bending fatigue test.
  • both the steel member of Example 1 (SCM (with nitriding) in the figure) and the steel member of Example 2 (SCM (without nitriding) in the figure) have bending fatigue strength ⁇ (MPa) was larger than that of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure).
  • both the steel member of Example 4 (SCM (with nitriding) in the figure) and the steel member of Example 5 (SCM (without nitriding) in the figure) have a torque amplitude T a (N ⁇ m) was larger than that of the steel member of Comparative Example 3 (SCM420 (Comparative Example 3) in the figure).
  • the torque amplitude Ta is an index representing the torsional fatigue strength. Torque amplitude Ta was measured using a torsional fatigue test.
  • the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure) had a surface hardness of 760 HV
  • the steel member of Example 1 (SCM (Comparative Example 2) in the figure) had a surface hardness of 760 HV.
  • the surface hardness of the steel member of Example 2 (SCM in the figure (without nitriding)) was 771. That is, the steel member of Example 1 and the steel member of Example 2 had higher surface hardness than the steel member of Comparative Example 2.
  • the surface hardness was measured using a Vickers hardness test conforming to JIS Z 2244.
  • the surface hardened layer depth of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure) was 0.77 mm, whereas the steel member of Example 1 (SCM (with nitriding) in the figure) was 0.77 mm. )) had a hardened surface layer depth of 0.82 mm, and the steel member of Example 2 (SCM (no nitriding) in the figure) had a hardened surface layer depth of 0.80 mm. That is, the steel member of Example 1 and the steel member of Example 2 had a greater surface hardening layer depth than the steel member of Comparative Example 2.
  • the surface carbon concentration of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure) was 0.70 wt%, whereas the steel member of Example 1 (SCM (with nitriding) in the figure) was 0.70 wt%. )) was 0.54 wt%, and the carbon concentration of the surface of the steel member of Example 2 (SCM (no nitriding) in the figure) was 0.57 wt%. That is, the steel member of Example 1 and the steel member of Example 2 had a significantly lower carbon concentration on the surface than the steel member of Comparative Example 2.
  • the total carburization depth of the steel member of Example 1 (SCM (with nitriding) in the figure), the total carburization depth of the steel member of Example 2 (SCM (without nitriding) in the figure), and the comparative example 2 steel members (SCM420 (Comparative Example 2) in the drawing) had a total carburizing depth of 1.4 mm. This is because the steel member of Example 1, the steel portion of Example 2, and the steel member of Comparative Example 2 are all heated to a temperature T1 (1000° C.) to austenite, and carbon is introduced into the steel members. This is probably due to the fact that
  • the nitrogen concentration on the surface of the steel member of Example 1 was 0.34 wt%. That is, in the steel member of Example 1, the surface nitrogen concentration was lower than the surface carbon concentration. Further, the total nitriding depth of the steel member of Example 1 (SCM (with nitriding) in the figure) was 0.3 mm. That is, in the steel member of Example 1, the total carburization depth was smaller than the total carburization depth of the surface.
  • the grain boundary oxidation depth of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the drawing) was 14 ⁇ m, whereas the steel member of Example 1 (SCM420 in the drawing (Comparative Example 2)
  • the grain boundary oxidation depth of SCM was 5 ⁇ m. That is, the steel member of Example 1 had a smaller grain boundary oxidation depth than the steel member of Comparative Example 2. Therefore, in the steel member of Example 1, the formation of a grain boundary oxide layer during the manufacturing process was greatly suppressed.
  • the minimum crystal grain size of the steel member of Example 1 (MIN in the figure) and the minimum crystal grain size of the steel member of Comparative Example 2 were both 10 ⁇ m.
  • the maximum grain size (MAX in the drawing) of the steel member of Comparative Example 2 was 170 ⁇ m, while the maximum grain size of the steel member of Example 1 was 22 ⁇ m.
  • the average grain size of the steel member of Comparative Example 2 was 38 ⁇ m, while the average grain size of the steel member of Example 1 was 14 ⁇ m. That is, the steel member of Example 1 had a smaller average grain size than the steel member of Comparative Example 2. Therefore, in the steel member of Example 1, coarsening of the crystal grain size during the manufacturing process was greatly suppressed.
  • the steel members of Examples were shown to have relatively high toughness, bending fatigue strength, surface hardness, surface hardened layer depth, etc. Therefore, the steel member manufacturing method according to the above embodiment, the steel member manufacturing method according to the first modified example of the above embodiment, and the steel member manufacturing method according to the second modified example of the above embodiment have high hardness and high toughness. It is suitable as a method of manufacturing steel members (for example, gears, bearings, shafts, etc.) that require both
  • the carburizing step (S2) is performed on a cold-forged steel member, but the present invention is not limited to this. In the present invention, the carburizing process may be performed on hot forged steel members.
  • the nitriding step (S3) is a step of infiltrating nitrogen into the steel member at a temperature T2 that is equal to or higher than the austenitizing transformation start temperature A1 and lower than the austenitizing transformation completion temperature A3.
  • the invention is not so limited.
  • the nitriding step may be a step of impregnating the steel member with nitrogen at a temperature lower than the austenitizing transformation start temperature.
  • the nitriding step (S3) is a step of introducing nitrogen into the steel member heated to the temperature T2 below the austenitizing transformation completion temperature A3.
  • the nitriding step may be a step of introducing nitrogen into the steel member heated to a temperature equal to or higher than the austenitizing transformation completion temperature. In that case, as in Comparative Example 1, the nitriding step may be performed simultaneously with the heating in the quenching step.
  • the present invention is not limited to this.
  • the nitriding step of infiltrating nitrogen into the steel member need not be performed.
  • case-hardened steel is used as the steel member, but the present invention is not limited to this.
  • a sintered material may be used for the steel member as in the above-described second modification.
  • Austenitization transformation start temperature For Austenitization transformation start temperature...A1, austenitization transformation completion temperature...A3, temperature (above austenitization transformation completion temperature).
  • austenitization transformation completion temperature For austenitization transformation completion temperature.
  • T1, T3, temperature below austenitization transformation completion temperature.

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Abstract

This method for producing a steel member includes: a carburizing step in which an austenitized steel member obtained by heating a steel member to at least an austenization completion temperature is subjected to carbon infiltration at a carbon concentration at which the steel member and carbon form a hypoeuctectic composition, and the carbon-infiltrated steel member is subjected to annealing; and a quenching step in which, after the carburizing step, the steel member is reheated to at least the austenization completion temperature and the heated steel member is rapidly cooled.

Description

鋼部材の製造方法Steel member manufacturing method
　本発明は、鋼部材の製造方法に関する。 The present invention relates to a method for manufacturing steel members.
　従来、オーステナイト化した状態の鋼部材に炭素を浸入させる浸炭工程を備える鋼部材の製造方法が知られている。このような鋼部材の製造方法は、たとえば、特開２０１９－１２７６２４公報に開示されている。 Conventionally, there has been known a method of manufacturing steel members that includes a carburizing process in which carbon is infiltrated into steel members in an austenitic state. A method for manufacturing such a steel member is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2019-127624.
　特開２０１９－１２７６２４公報には、オーステナイト化した状態の鋼部材に炭素を浸入させる浸炭工程を備える鋼部材の製造方法が開示されている。特開２０１９－１２７６２４公報に記載されている鋼部材の製造方法では、浸炭工程において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが過共析組成となる炭素濃度で、炭素を浸入させる。 Japanese Patent Application Laid-Open No. 2019-127624 discloses a method for manufacturing a steel member that includes a carburizing step of infiltrating carbon into a steel member in an austenitized state. In the method for manufacturing a steel member described in JP-A-2019-127624, in the carburizing step, carbon is introduced into the austenitized steel member at a carbon concentration at which the steel member and carbon have a hyper-eutectoid composition. Let
特開２０１９－１２７６２４号公報JP 2019-127624 A
　しかしながら、特開２０１９－１２７６２４公報に記載されている鋼部材の製造では、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが過共析組成となる炭素濃度で、炭素を浸入させるので、鋼部材に侵入する炭素濃度が過度に高くなり易い。ここで、鋼部材の硬さは、一般的に、鋼部材の表面（浸炭層）の炭素濃度に略比例する。また、鋼部材の硬さは、一般的に、鋼部材の靭性と略反比例する。すなわち、特開２０１９－１２７６２４公報に記載の鋼部材の製造では、鋼部材の硬さが過度に高くなるとともに鋼部材の靭性が過度に低くなり易い。鋼部材の靭性が低くなると、鋼部材は、衝撃に弱くなる。このため、鋼部材の硬さと靭性とをバランスよく向上させることが可能な鋼部材の製造方法が望まれている。 However, in the production of the steel member described in JP-A-2019-127624, carbon is introduced into the austenitized steel member at a carbon concentration at which the steel member and carbon have a hyper-eutectoid composition, The concentration of carbon penetrating into the steel member tends to become excessively high. Here, the hardness of a steel member is generally approximately proportional to the carbon concentration of the surface (carburized layer) of the steel member. Moreover, the hardness of a steel member is generally inversely proportional to the toughness of the steel member. That is, in manufacturing the steel member described in JP-A-2019-127624, the hardness of the steel member tends to be excessively high and the toughness of the steel member tends to be excessively low. When the toughness of the steel member becomes low, the steel member becomes vulnerable to impact. Therefore, there is a demand for a method of manufacturing a steel member that can improve the hardness and toughness of the steel member in a well-balanced manner.
　この発明は、上記のような課題を解決するためになされたものであり、この発明の１つの目的は、鋼部材の硬さと靭性とをバランスよく向上させることが可能な鋼部材の製造方法を提供することである。 The present invention has been made to solve the above problems, and one object of the present invention is to provide a method for manufacturing a steel member capable of improving the hardness and toughness of the steel member in a well-balanced manner. to provide.
　上記目的を達成するために、この発明の一の局面における鋼部材の製造方法は、鋼部材をオーステナイト化変態完了温度以上の温度まで加熱してオーステナイト化した状態の鋼部材に、鋼部材と炭素とが亜共析組成となる炭素濃度で、炭素を浸入させるとともに、炭素を浸入させた鋼部材を徐冷する浸炭工程と、浸炭工程の後に、鋼部材をオーステナイト化変態完了温度以上の温度まで再度加熱するとともに、加熱した鋼部材を急冷する焼入れ工程と、を備える。 In order to achieve the above object, a steel member manufacturing method in one aspect of the present invention provides a steel member in an austenitized state by heating the steel member to a temperature equal to or higher than the austenitizing transformation completion temperature. A carburizing process in which carbon is infiltrated at a carbon concentration that makes the sub-eutectoid composition, and the steel member into which carbon is infiltrated is slowly cooled, and after the carburizing process, the steel member is heated to a temperature equal to or higher than the austenitizing transformation completion temperature. and a quenching step of heating again and quenching the heated steel member.
　この発明の一の局面における鋼部材の製造方法では、上記のように、浸炭工程において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが亜共析組成となる炭素濃度で、炭素を浸入させる。これにより、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが過共析組成となる炭素濃度で、炭素を浸入させる浸炭が行われる場合と異なり、鋼部材に侵入する炭素濃度が過度に高くなることがない。これにより、鋼部材の硬さが過度に高くならないとともに、鋼部材の靭性が過度に低くならない。その結果、鋼部材の硬さと靭性とをバランスよく向上させることができる。これにより、硬さの向上により曲げ疲労強度などを向上させることができるとともに、靭性の向上により衝撃に対する強度を向上させることができる。 In the steel member manufacturing method according to one aspect of the present invention, as described above, in the carburizing step, carbon is added to the austenitized steel member at a carbon concentration such that the steel member and carbon have a hypo-eutectoid composition. infiltrate. As a result, unlike the case where carburization is performed by infiltrating carbon into a steel member in an austenitized state at a carbon concentration at which the steel member and carbon have a hyper-eutectoid composition, the carbon concentration penetrating into the steel member is excessive. never get higher. As a result, the hardness of the steel member does not become excessively high, and the toughness of the steel member does not become excessively low. As a result, the hardness and toughness of the steel member can be improved in a well-balanced manner. As a result, it is possible to improve the bending fatigue strength and the like by improving the hardness, and it is possible to improve the strength against impact by improving the toughness.
　本発明によれば、上記のように、鋼部材の硬さと靭性とをバランスよく向上させることが可能な鋼部材の製造方法を提供することができる。 According to the present invention, as described above, it is possible to provide a method for manufacturing a steel member capable of improving the hardness and toughness of the steel member in a well-balanced manner.
本発明の一実施形態による鋼部材の製造フローを示す図である。It is a figure which shows the manufacturing flow of the steel member by one Embodiment of this invention. 本発明の一実施形態による鋼部材の製造方法における鋼部材の温度変化を示す図である。FIG. 4 is a diagram showing temperature changes of the steel member in the steel member manufacturing method according to the embodiment of the present invention; 鋼部材の一例としてＳ２０Ｃの状態図である。It is a state diagram of S20C as an example of a steel member. 比較例１による鋼部材の製造方法における鋼部材の温度変化を示す図である。5 is a diagram showing temperature changes of a steel member in a steel member manufacturing method according to Comparative Example 1. FIG. 比較例２による鋼部材の製造方法における鋼部材の温度変化を示す図である。FIG. 10 is a diagram showing temperature changes of a steel member in a method for manufacturing a steel member according to Comparative Example 2; 本発明の一実施形態による鋼部材の製造方法における鋼部材、第１変形例による鋼部材の製造方法における鋼部材、第２変形例による鋼部材の製造方法における鋼部材、および、比較例１による鋼部材の製造方法における鋼部材の曲げ疲労強度および靭性を示す図である。A steel member in a method for manufacturing a steel member according to an embodiment of the present invention, a steel member in a method for manufacturing a steel member according to a first modification, a steel member in a method for manufacturing a steel member according to a second modification, and a steel member according to Comparative Example 1 FIG. 2 is a diagram showing the bending fatigue strength and toughness of a steel member in the steel member manufacturing method; 本発明の一実施形態による鋼部材の製造方法における鋼部材、第１変形例による鋼部材の製造方法における鋼部材、および、比較例２による鋼部材の製造方法における鋼部材の曲げ疲労強度を示す図である。Fig. 3 shows the bending fatigue strength of the steel member in the steel member manufacturing method according to the embodiment of the present invention, the steel member in the steel member manufacturing method according to the first modified example, and the steel member in the steel member manufacturing method according to Comparative Example 2; It is a diagram. 本発明の一実施形態による鋼部材の製造方法における鋼部材、第１変形例による鋼部材の製造方法における鋼部材、および、比較例３による鋼部材の製造方法における鋼部材の捩じり疲労強度を示す図である。Torsional fatigue strength of the steel member in the steel member manufacturing method according to the embodiment of the present invention, the steel member in the steel member manufacturing method according to the first modified example, and the steel member in the steel member manufacturing method according to Comparative Example 3 It is a figure which shows. 本発明の一実施形態による鋼部材の製造方法における鋼部材、第１変形例による鋼部材の製造方法における鋼部材、および、比較例２による鋼部材の製造方法における鋼部材の表面硬さ、表面硬化層深さ、表面の炭素濃度等を示す図である。Surface hardness and surface of the steel member in the steel member manufacturing method according to the embodiment of the present invention, the steel member in the steel member manufacturing method according to the first modified example, and the steel member in the steel member manufacturing method according to Comparative Example 2 It is a figure which shows the hardened layer depth, the carbon concentration of a surface, etc. FIG. 本発明の一実施形態による鋼部材の製造方法における鋼部材、および、比較例２による鋼部材の製造方法における鋼部材の粒界酸化深さおよび平均結晶粒径を示す図である。FIG. 5 is a diagram showing the grain boundary oxidation depth and average grain size of a steel member in a steel member manufacturing method according to an embodiment of the present invention and a steel member in a steel member manufacturing method according to Comparative Example 2;
　以下、本発明の実施形態を図面に基づいて説明する。 Hereinafter, embodiments of the present invention will be described based on the drawings.
　［鋼部材の製造方法］
　図１～図３を参照して、本発明の一実施形態による鋼部材の製造方法について説明する。なお、本発明の一実施形態による鋼部材の製造方法は、たとえば、歯車、軸受け、シャフト等の鋼部材に適用することができる。 [Manufacturing method of steel member]
A method for manufacturing a steel member according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. The method for manufacturing a steel member according to one embodiment of the present invention can be applied to steel members such as gears, bearings, and shafts.
　（冷間鍛造工程）
　まず、図１に示すように、ステップＳ１において、冷間鍛造工程が行われる。冷間鍛造工程（Ｓ１）は、常温において鋼部材を所望の形状（たとえば、歯車、軸受け、シャフト等の形状）となるように鍛造する工程である。鋼部材には、表面に熱処理等を行って硬化層を生成するための肌焼鋼（たとえば、ＳＣＭ４２０）が用いられる。 (Cold forging process)
First, as shown in FIG. 1, a cold forging process is performed in step S1. The cold forging step (S1) is a step of forging a steel member into a desired shape (for example, the shape of a gear, bearing, shaft, etc.) at room temperature. For the steel member, case-hardening steel (for example, SCM420) is used for generating a hardened layer by heat treatment or the like on the surface.
　（浸炭工程）
　次に、ステップＳ２において、浸炭工程が行われる。図２に示すように、浸炭工程（Ｓ２）は、鋼部材をオーステナイト化変態完了温度Ａ３以上の温度Ｔ１（たとえば、約１０００℃）まで加熱してオーステナイト化した状態の鋼部材に、炭素を浸入させるとともに、炭素を浸入させた鋼部材を徐冷する工程である。図３に示すように、オーステナイト化した状態の鋼部材とは、オーステナイト（γ鉄）からなる鋼部材である。オーステナイト化変態完了温度Ａ３は、鋼部材が加熱されて、鋼部材のオーステナイト化変態が完了する温度である。具体的には、図２に示すように、鋼部材が、第１熱処理室に配置される。そして、鋼部材がオーステナイト化するように、鋼部材が温度Ｔ１まで加熱される。そして、鋼部材が温度Ｔ１に保持された状態（すなわち、鋼部材がオーステナイト化した状態）で、第１熱処理室の内部に浸炭用のガス（たとえば、Ｃ２Ｈ２）が導入される。そして、オーステナイト化した状態の鋼部材の表面において浸炭用のガスが分解して炭素が生成される。そして、生成された炭素が鋼部材の表面から内部に向かって拡散することによって、鋼部材の表層部に浸炭層が形成される。そして、鋼部材がパーライト化するように、鋼部材が徐冷される。鋼部材の徐冷は、鋼部材がパーライト化する冷却速度で行われる。すなわち、鋼部材の徐冷は、鋼部材がマルテンサイト化しない冷却速度で行われる。また、鋼部材の徐冷は、鋼部材に酸化膜が形成されるのを防止するために、不活性ガス（たとえば、Ａｒ、Ｎ２、Ｈｅ等）雰囲気により行われる。なお、浸炭工程（Ｓ２）は、第１熱処理室の内部が真空ポンプによって減圧されながら行われる。 (Carburizing process)
Next, in step S2, a carburizing process is performed. As shown in FIG. 2, in the carburizing step (S2), the steel member is heated to a temperature T1 (for example, about 1000° C.) equal to or higher than the austenitizing transformation completion temperature A3, and carbon is introduced into the steel member in the austenitized state. It is a step of slowly cooling the steel member into which carbon is impregnated. As shown in FIG. 3, the austenitized steel member is a steel member made of austenite (γ-iron). The austenitizing transformation completion temperature A3 is the temperature at which the steel member is heated and the austenitizing transformation of the steel member is completed. Specifically, as shown in FIG. 2, the steel member is placed in the first heat treatment chamber. The steel member is then heated to temperature T1 so that the steel member is austenitized. Then, a carburizing gas (for example, C 2 H 2 ) is introduced into the first heat treatment chamber while the steel member is maintained at temperature T1 (that is, the steel member is austenitized). Then, the carburizing gas is decomposed on the surface of the austenitized steel member to produce carbon. A carburized layer is formed on the surface layer of the steel member by the generated carbon diffusing from the surface of the steel member toward the inside. Then, the steel member is slowly cooled so that the steel member becomes pearlitic. Slow cooling of the steel member is performed at a cooling rate at which the steel member becomes pearlitic. That is, the slow cooling of the steel member is performed at a cooling rate at which the steel member does not turn into martensite. In addition, slow cooling of the steel member is performed in an inert gas (for example, Ar, N 2 , He, etc.) atmosphere in order to prevent the formation of an oxide film on the steel member. The carburizing step (S2) is performed while the pressure inside the first heat treatment chamber is reduced by a vacuum pump.
　図３に示すように、鋼部材と炭素とが亜共析組成となる炭素濃度（約０．７７％未満の濃度）の場合、オーステナイト化変態開始温度Ａ１よりも低い温度では、鋼部材は、フェライト（α鉄）とパーライトとからなる状態である。また、鋼部材と炭素とが亜共析組成となる炭素濃度未満の濃度の場合、オーステナイト化変態開始温度Ａ１よりも高い、かつ、オーステナイト化変態完了温度Ａ３よりも低い温度では、鋼部材は、オーステナイト（γ鉄）とフェライト（α鉄）とからなる状態である。また、鋼部材と炭素とが亜共析組成となる炭素濃度未満の炭素濃度の場合、オーステナイト化変態完了温度Ａ３よりも高い温度では、鋼部材は、オーステナイト（γ鉄）からなる状態である。 As shown in FIG. 3, in the case of a carbon concentration (less than about 0.77%) where the steel member and carbon have a hypo-eutectoid composition, at a temperature lower than the austenitizing transformation start temperature A1, the steel member It is a state consisting of ferrite (α-iron) and pearlite. Further, when the carbon concentration of the steel member and carbon is less than the concentration of hypo-eutectoid composition, at a temperature higher than the austenitization transformation start temperature A1 and lower than the austenitization transformation completion temperature A3, the steel member It is a state of austenite (γ-iron) and ferrite (α-iron). In addition, when the carbon concentration of the steel member and carbon is less than the carbon concentration where the steel member and carbon have a hypo-eutectoid composition, the steel member is in a state of austenite (γ iron) at a temperature higher than the austenitizing transformation completion temperature A3.
　図２に示すように、浸炭工程（Ｓ２）において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが亜共析組成となる炭素濃度で、炭素を浸入させる。具体的には、第１熱処理室の内部に浸炭用のガスが導入され続けることによって、鋼部材の表面（浸炭層）の炭素濃度が上昇する。そして、鋼部材の表面（浸炭層）の炭素濃度が、鋼部材と炭素とが共析組成となる炭素濃度（たとえば、鋼部材が肌焼鋼のＳＣＭ４２０の場合、約０．７７％）未満となるように、浸炭用のガスを導入する時間が調整される。ここで、鋼部材の硬さは、一般的に、鋼部材の表面（浸炭層）の炭素濃度に略比例する。また、鋼部材の硬さは、一般的に、鋼部材の靭性と略反比例する。これにより、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが過共析組成となる炭素濃度（約０．７７％以上の濃度）で、炭素を浸入させる浸炭が行われる場合と異なり、鋼部材に侵入する炭素濃度が過度に高くなることがない。これにより、鋼部材の硬さが過度に高くならないとともに、鋼部材の靭性が過度に低くならない。その結果、鋼部材の硬さと靭性とをバランスよく向上させることができる。これにより、硬さの向上により曲げ疲労強度などを向上させることができるとともに、靭性の向上により衝撃に対する強度を向上させることができる。 As shown in FIG. 2, in the carburizing step (S2), carbon is infiltrated into the austenitized steel member at a carbon concentration such that the steel member and carbon have a hypo-eutectoid composition. Specifically, the continuous introduction of the carburizing gas into the first heat treatment chamber increases the carbon concentration of the surface (carburized layer) of the steel member. Then, the carbon concentration of the surface (carburized layer) of the steel member is less than the carbon concentration at which the steel member and carbon have a eutectoid composition (for example, about 0.77% when the steel member is SCM420, which is case-hardened steel). The time for introducing the carburizing gas is adjusted so that the Here, the hardness of a steel member is generally approximately proportional to the carbon concentration of the surface (carburized layer) of the steel member. Moreover, the hardness of a steel member is generally inversely proportional to the toughness of the steel member. As a result, unlike the case where carburization is performed by infiltrating carbon into the austenitized steel member at a carbon concentration (concentration of about 0.77% or more) at which the steel member and carbon have a hyper-eutectoid composition, The concentration of carbon penetrating into the steel member does not become excessively high. As a result, the hardness of the steel member does not become excessively high, and the toughness of the steel member does not become excessively low. As a result, the hardness and toughness of the steel member can be improved in a well-balanced manner. As a result, it is possible to improve the bending fatigue strength and the like by improving the hardness, and it is possible to improve the strength against impact by improving the toughness.
　（浸窒工程）
　次に、図１に示すように、ステップＳ３において、浸窒工程が行われる。図２に示すように、浸窒工程（Ｓ３）は、鋼部材をオーステナイト化変態完了温度Ａ３未満の温度Ｔ２（たとえば、約８１０℃）まで加熱した状態の鋼部材に窒素を浸入させる工程である。具体的には、鋼部材が、第２熱処理室に配置される。そして、浸炭工程（Ｓ２）においてパーライト化した状態の鋼部材が温度Ｔ２まで加熱される。このとき、鋼部材は、フェライト（α鉄）とオーステナイト（γ鉄）とが混ざった状態となっている。そして、鋼部材が温度Ｔ２に保持された状態（すなわち、鋼部材がフェライト（α鉄）とオーステナイト（γ鉄）とが混ざった状態）で、第２熱処理室の内部に浸窒用のガス（たとえば、ＮＨ３）が所定の量（たとえば、０．８ｍ３／時）だけ導入される。そして、鋼部材の表面において浸窒用のガスが分解して窒素が生成される。そして、生成された炭素が鋼部材の表面から内部に向かって拡散することによって、鋼部材の表層部の浸炭層に窒素が侵入して、浸炭浸窒層が形成される。なお、浸窒工程（Ｓ３）は、浸炭層の炭素濃度が低下しないように、第２熱処理室の内部の炭素濃度が調整されながら行われる。ここで、鋼部材の表層部に侵入する窒素量は、一般的に、オーステナイト化変態開始温度Ａ１（後述する）以上の温度において、鋼部材の温度に略反比例する。また、鋼部材の表層部の浸炭層に窒素を侵入させる場合、一般的に、浸炭層の炭素濃度が高い程、鋼部材にボイドが発生し易い。また、鋼部材の温度が高くなる程、一般的に、鋼部材に粒界酸化層が形成され易い。また、鋼部材の表層部に侵入する窒素量が増える程、鋼部材の硬さが向上する。これにより、鋼部材をオーステナイト化変態完了温度Ａ３以上の温度Ｔ３（たとえば、約８５０℃）まで加熱した状態の鋼部材に窒素を浸入させる浸窒が行われる場合と比較して、鋼部材に侵入する窒素量を多くすることができるとともに、鋼部材にボイドが発生したり粒界酸化層が形成されたりするのを抑制することができる。その結果、鋼部材の硬さを効果的に向上させることができるので、浸炭工程（Ｓ２）において鋼部材の靭性を向上させた分だけ鋼部材の硬さが低下した場合でも、鋼部材の十分な硬さを確保することができる。 (Nitriding process)
Next, as shown in FIG. 1, a nitriding process is performed in step S3. As shown in FIG. 2, the nitriding step (S3) is a step of infiltrating nitrogen into the steel member heated to a temperature T2 (for example, about 810° C.) lower than the austenitizing transformation completion temperature A3. . Specifically, the steel member is placed in the second heat treatment chamber. Then, in the carburizing step (S2), the pearlitic steel member is heated to a temperature T2. At this time, the steel member is in a state in which ferrite (α-iron) and austenite (γ-iron) are mixed. Then, in a state in which the steel member is held at temperature T2 (that is, a state in which ferrite (α-iron) and austenite (γ-iron) are mixed in the steel member), a nitriding gas ( NH 3 ) is introduced in a predetermined amount (eg 0.8 m 3 /h). Then, nitrogen is generated by decomposition of the nitriding gas on the surface of the steel member. As the generated carbon diffuses from the surface of the steel member toward the inside, nitrogen enters the carburized layer on the surface layer of the steel member, forming a carbo-nitrided layer. The nitriding step (S3) is performed while adjusting the carbon concentration inside the second heat treatment chamber so that the carbon concentration of the carburized layer does not decrease. Here, the amount of nitrogen that penetrates into the surface layer of the steel member is generally inversely proportional to the temperature of the steel member at a temperature equal to or higher than the austenitizing transformation start temperature A1 (described later). Further, when nitrogen is introduced into the carburized layer on the surface of the steel member, generally, the higher the carbon concentration of the carburized layer, the more easily voids are generated in the steel member. Generally, the higher the temperature of the steel member, the more easily the grain boundary oxide layer is formed in the steel member. Further, the hardness of the steel member is improved as the amount of nitrogen that penetrates into the surface layer of the steel member increases. As a result, compared to the case where the steel member is heated to a temperature T3 (e.g., about 850° C.) equal to or higher than the austenitizing transformation completion temperature A3, nitriding is performed in which nitrogen enters the steel member. It is possible to increase the amount of nitrogen to be used and to suppress the generation of voids and the formation of grain boundary oxide layers in the steel member. As a result, the hardness of the steel member can be effectively improved. hardness can be ensured.
　浸窒工程（Ｓ３）では、鋼部材の表面（浸炭浸窒層）の窒素濃度が、所定の濃度となるように、浸窒用のガスを導入する時間および浸窒用のガスの量が調整される。すなわち、浸窒工程（Ｓ３）は、鋼部材の表面の窒素濃度が、所定の濃度となるように、鋼部材に窒素を浸入させる工程である。所定の濃度は、少なくとも、約０．５％以下である。所定の濃度は、好ましくは、約０．０５％以上かつ０．３５％以下である。これにより、鋼部材の硬さと靭性とをバランスよく向上させるように、浸窒を行うことができる。 In the nitriding step (S3), the time for introducing the nitriding gas and the amount of the nitriding gas are adjusted so that the nitrogen concentration on the surface of the steel member (carbonitriding layer) reaches a predetermined concentration. be done. That is, the nitriding step (S3) is a step of infiltrating nitrogen into the steel member so that the nitrogen concentration on the surface of the steel member reaches a predetermined concentration. The predetermined concentration is at least about 0.5% or less. The predetermined concentration is preferably greater than or equal to about 0.05% and less than or equal to 0.35%. Thereby, nitriding can be performed so as to improve the hardness and toughness of the steel member in a well-balanced manner.
　浸窒工程（Ｓ３）は、オーステナイト化変態開始温度Ａ１以上で、かつ、オーステナイト化変態完了温度Ａ３未満の温度Ｔ２（たとえば、約８１０℃）で、鋼部材に窒素を浸入させる工程である。オーステナイト化変態開始温度Ａ１は、鋼部材のオーステナイト化変態が開始する温度である。ここで、オーステナイト化変態開始温度Ａ１未満で鋼部材に窒素を浸入させる浸窒が行わる場合、オーステナイト化変態開始温度Ａ１以上で鋼部材に窒素を浸入させる浸窒が行わる場合と比較して、一般的に、鋼部材に侵入する窒素量が著しく少なくなる。これにより、オーステナイト化変態開始温度Ａ１未満で、鋼部材に窒素を浸入させる浸窒が行わる場合と比較して、鋼部材に侵入する窒素量を多くすることができる。 The nitriding step (S3) is a step of infiltrating nitrogen into the steel member at a temperature T2 (for example, about 810°C) that is equal to or higher than the austenitizing transformation start temperature A1 and lower than the austenitizing transformation completion temperature A3. The austenitizing transformation start temperature A1 is the temperature at which the austenitizing transformation of the steel member starts. Here, when nitriding is performed by infiltrating nitrogen into the steel member at a temperature lower than the austenitizing transformation start temperature A1, compared with the case where nitriding is performed by infiltrating nitrogen into the steel member at the austenitizing transformation start temperature A1 or higher. , generally, the amount of nitrogen that penetrates into the steel member is significantly reduced. This makes it possible to increase the amount of nitrogen that penetrates into the steel member compared to the case where nitriding is performed by introducing nitrogen into the steel member at a temperature below the austenitizing transformation start temperature A1.
　上述したように、ステップＳ１において、冷間鍛造工程が行われている。すなわち、浸炭工程（Ｓ２）は、冷間鍛造された鋼部材に対して行われる。これにより、浸炭工程（Ｓ２）において、鋼部材が加熱されるとともに徐冷されることによって、冷間鍛造されることによって鋼部材に生じた残留応力を鋼部材から取り除くことができる。その結果、後工程（後述する焼入れ工程（Ｓ４）等）において、残留応力に起因して鋼部材の結晶粒が粗大化するのを抑制することができる。すなわち、結晶粒の粗大化に起因して鋼部材の強度が低下するのを抑制することができる。また、結晶粒が粗大化するのを抑制して、後工程において、鋼部材の部位毎の寸法変化が大きくなるのを抑制することができる。また、冷間鍛造された鋼部材に結晶粒の粗大化が生じるのを抑制するためにＮｂ、Ｔｉ、Ｖ等を添加した特殊な鋼部材を用いることなく、鋼部材として一般的に用いられる肌焼鋼（たとえば、ＳＣＭ４２０）を用いることができる。 As described above, the cold forging process is performed in step S1. That is, the carburizing step (S2) is performed on the cold-forged steel member. As a result, in the carburizing step (S2), the steel member is heated and slowly cooled, so that residual stress generated in the steel member by cold forging can be removed from the steel member. As a result, it is possible to suppress the coarsening of the crystal grains of the steel member due to the residual stress in the subsequent steps (quenching step (S4), etc., which will be described later). That is, it is possible to suppress the deterioration of the strength of the steel member due to the coarsening of the crystal grains. In addition, it is possible to suppress the coarsening of crystal grains, and to suppress the increase in dimensional change in each part of the steel member in the subsequent process. In addition, without using a special steel member to which Nb, Ti, V, etc. are added in order to suppress the occurrence of coarsening of crystal grains in the cold forged steel member, the surface that is generally used as a steel member Tempered steel (eg, SCM420) can be used.
　（焼入れ工程）
　次に、図１に示すように、ステップＳ４において、焼入れ工程が行われる。図２に示すように、焼入れ工程（Ｓ４）は、鋼部材をオーステナイト化変態完了温度Ａ３以上の温度Ｔ３（たとえば、約８５０℃）まで再度加熱するとともに、加熱した鋼部材を急冷する工程である。具体的には、鋼部材が、第２熱処理室に配置される。そして、鋼部材がオーステナイト化するように、鋼部材が温度Ｔ３まで再度加熱される。そして、鋼部材が温度Ｔ３に保持された状態（すなわち、鋼部材がオーステナイト化した状態）が暫く維持された後、鋼部材が熱処理室から冷却装置の内部に搬送され、鋼部材がマルテンサイト化するように、鋼部材が急冷される。鋼部材の急冷は、鋼部材がマルテンサイト化する冷却速度で行われる。すなわち、鋼部材の急冷は、鋼部材がパーライト化しない冷却速度で行われる。また、鋼部材の急冷は、水または油を用いて行われる。 (Quenching process)
Next, as shown in FIG. 1, a hardening process is performed in step S4. As shown in FIG. 2, the quenching step (S4) is a step of reheating the steel member to a temperature T3 (for example, about 850° C.) equal to or higher than the austenitizing transformation completion temperature A3, and rapidly cooling the heated steel member. . Specifically, the steel member is placed in the second heat treatment chamber. The steel member is then heated again to temperature T3 so that the steel member austenites. After the steel member is maintained at temperature T3 (that is, the steel member is austenitized) for a while, the steel member is transported from the heat treatment chamber into the cooling device, where the steel member is martensitic. The steel member is quenched so as to The steel member is quenched at a cooling rate that martensites the steel member. That is, the steel member is quenched at a cooling rate that does not cause pearlitization of the steel member. Also, the steel member is quenched using water or oil.
　焼入れ工程（Ｓ４）は、浸窒工程（Ｓ３）の直後に、鋼部材をオーステナイト化変態完了温度Ａ３未満の温度Ｔ２（たとえば、約８１０℃）からオーステナイト化変態完了温度Ａ３以上の温度Ｔ３（たとえば、約８５０℃）に加熱するとともに、加熱した鋼部材を急冷する工程である。すなわち、浸窒工程（Ｓ３）と焼入れ工程（Ｓ４）とが、この順に、連続して行われる。これにより、浸窒工程（Ｓ３）においてオーステナイト化変態完了温度Ａ３未満の温度Ｔ２（たとえば、約８１０℃）まで加熱した状態の鋼部材を、温度Ｔ２（たとえば、約８１０℃）からオーステナイト化変態完了温度Ａ３以上の温度Ｔ３（たとえば、約８５０℃）まで加熱するだけでよいので、焼入れ工程（Ｓ４）が浸窒工程（Ｓ３）の直後に行われない場合と比較して、鋼部材の加熱における消費エネルギーを抑制することができる。 In the quenching step (S4), immediately after the nitriding step (S3), the steel member is heated from a temperature T2 (for example, about 810° C.) below the austenitization completion temperature A3 to a temperature T3 (for example, , about 850° C.) and rapidly cooling the heated steel member. That is, the nitriding step (S3) and the quenching step (S4) are continuously performed in this order. As a result, the steel member heated to a temperature T2 (for example, about 810° C.) lower than the austenitization completion temperature A3 in the nitriding step (S3) is heated from the temperature T2 (for example, about 810° C.) to the austenitization completion temperature. Since it is only necessary to heat to a temperature T3 (for example, about 850 ° C.) that is higher than the temperature A3, compared to the case where the quenching step (S4) is not performed immediately after the nitriding step (S3), the steel member can be heated Energy consumption can be suppressed.
　（焼戻し工程）
　次に、図１に示すように、ステップＳ５において、焼戻し工程が行われる。焼戻し工程（Ｓ５）は、マルテンサイト化した鋼部材を再度加熱して冷却する工程である。これにより、マルテンサイト化して一時的に硬さが過度に大きくなるとともに靭性が過度に低下した状態の鋼部材が、焼戻しされることによって、適切な疲労強度および靭性を有する状態となる。 (Tempering process)
Next, as shown in FIG. 1, a tempering process is performed in step S5. The tempering step (S5) is a step of reheating and cooling the martensitic steel member. As a result, the steel member, which has become martensitic and temporarily excessively hardened and excessively reduced in toughness, is tempered to have appropriate fatigue strength and toughness.
　［実施例］
　図４～図１０を参照して、上記実施形態による鋼部材の製造方法の実施例について、比較例１による鋼部材の製造方法および比較例２による鋼部材の製造方法と比較しながら説明する。 [Example]
An example of the steel member manufacturing method according to the above embodiment will be described in comparison with the steel member manufacturing method according to Comparative Example 1 and the steel member manufacturing method according to Comparative Example 2 with reference to FIGS.
　（上記実施形態による鋼部材の製造）
　上記実施形態による鋼部材の製造方法に基づいて、鋼部材を歯車として、鋼部材を作製した（実施例１）。具体的には、まず、鋼部材に対して冷間鍛造する冷間鍛造工程を行った。鋼部材には、肌焼鋼のＳＣＭ４２０を用いた。そして、鋼部材をオーステナイト化変態完了温度Ａ３以上の温度Ｔ１（１０００℃）まで加熱してオーステナイト化した状態の鋼部材に、炭素を浸入させるとともに、炭素を浸入させた鋼部材を徐冷する浸炭工程を行った。浸炭工程において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが亜共析組成となる炭素濃度（０．７７％未満）で、炭素を浸入させた。浸炭工程は、第１熱処理室の内部を真空ポンプによって減圧しながら行った。そして、鋼部材をオーステナイト化変態完了温度Ａ３未満の温度Ｔ２（８１０℃）まで加熱した状態の鋼部材に窒素を浸入させる浸窒工程を行った。そして、浸窒工程の直後に、鋼部材をオーステナイト化変態完了温度Ａ３以上の温度Ｔ３（８５０℃）まで再度加熱するとともに、加熱した鋼部材を急冷する焼入れ工程を行った。そして、マルテンサイト化した鋼部材を再度加熱して冷却する焼戻し工程を行った。 (Manufacture of steel members according to the above embodiment)
A steel member was produced by using the steel member as a gear on the basis of the steel member manufacturing method according to the above-described embodiment (Example 1). Specifically, first, a cold forging step of cold forging a steel member was performed. SCM420 of case hardening steel was used for the steel member. Then, the steel member is heated to a temperature T1 (1000° C.) equal to or higher than the austenitization transformation completion temperature A3 to infiltrate carbon into the steel member in the austenitized state, and carburize the steel member into which carbon has been infiltrated and slowly cool it. did the process. In the carburizing step, carbon was infiltrated into the austenitized steel member at a carbon concentration (less than 0.77%) at which the steel member and carbon had a hypo-eutectoid composition. The carburizing process was performed while reducing the pressure inside the first heat treatment chamber with a vacuum pump. Then, a nitriding step was performed in which nitrogen was introduced into the steel member in a state where the steel member was heated to a temperature T2 (810° C.) lower than the austenitizing transformation completion temperature A3. Then, immediately after the nitriding step, the steel member was again heated to a temperature T3 (850° C.) higher than the austenitization transformation completion temperature A3, and a quenching step was performed to rapidly cool the heated steel member. Then, a tempering process of heating and cooling the martensitic steel member again was performed.
　（第１変形例および第２変形例による鋼部材の製造）
　上記実施形態の第１変形例として、上記実施形態による鋼部材の製造方法から浸窒工程を省いて、鋼部材を作製した（実施例２）。また、上記実施形態の第２変形例として、上記実施形態による鋼部材の製造方法から浸窒工程を省くとともに、上記実施形態による鋼部材の製造方法における鋼部材を肌焼鋼から焼結材に置き換えて、鋼部材を作製した（実施例３）。 (Manufacturing of steel members according to the first and second modifications)
As a first modified example of the above-described embodiment, a steel member was manufactured by omitting the nitriding step from the steel member manufacturing method according to the above-described embodiment (Example 2). Further, as a second modification of the above embodiment, the nitriding step is omitted from the steel member manufacturing method according to the above embodiment, and the steel member in the steel member manufacturing method according to the above embodiment is changed from case hardened steel to sintered material. Instead, a steel member was produced (Example 3).
　（上記実施形態および第１変形例による別の鋼部材の製造）
　上記実施形態による鋼部材の製造方法に基づいて、鋼部材をシャフトとして、鋼部材を作製した（実施例４）。また、第１変形例による鋼部材の製造方法に基づいて、鋼部材をシャフトとして、鋼部材を作製した（実施例５）。 (Manufacture of another steel member according to the above embodiment and first modification)
A steel member was produced using the steel member as a shaft based on the method for manufacturing a steel member according to the above embodiment (Example 4). Further, a steel member was produced using the steel member as a shaft based on the method for manufacturing a steel member according to the first modified example (Example 5).
　（比較例１による鋼部材の製造）
　図４に示す比較例１による鋼部材の製造方法に基づいて、鋼部材を歯車として、鋼部材を作製した。具体的には、まず、上記実施形態による鋼部材の製造方法と同様に、冷間鍛造工程を行った。鋼部材には、上記実施形態による鋼部材の製造方法と同様に、肌焼鋼のＳＣＭ４２０を用いた。そして、上記実施形態による鋼部材の製造方法と同様に、鋼部材をオーステナイト化変態完了温度Ａ３以上の温度Ｔ１（１０００℃）まで加熱してオーステナイト化した状態の鋼部材に、炭素を浸入させるとともに、炭素を浸入させた鋼部材を徐冷する浸炭工程を行った。上記実施形態による鋼部材の製造方法と異なり、浸炭工程において、鋼部材が徐冷される途中で、オーステナイトの一部のみがパーライト化されるように、鋼部材がオーステナイト化変態開始温度Ａ１未満の温度Ｔ４（７１０℃）に保持された状態で所定の時間だけ維持した。すなわち、鋼部材が温度Ｔ４（７１０℃）に保持された状態で維持される時間だけ、上記実施形態による鋼部材の製造方法よりも鋼部材が高温の状態（常温でない状態）が長くなる。また、上記実施形態による鋼部材の製造方法と異なり、浸炭工程において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが過共析組成となる炭素濃度（０．７７％以上）で、炭素を浸入させた。なお、浸炭工程は、上記実施形態による鋼部材の製造方法と同様に、熱処理室の内部を真空ポンプによって減圧しながら行った。そして、鋼部材がオーステナイト化変態完了温度Ａ３以上の温度Ｔ３（８５０℃）に加熱され、鋼部材が温度Ｔ３（８５０℃）に暫く維持された後、鋼部材を急冷する焼入れ工程を行った。なお、焼入れ工程において、鋼部材が温度Ｔ３（８５０℃）に保持された状態（すなわち、鋼部材がオーステナイト化した状態）が暫く維持される際に、鋼部材に窒素を浸入させる浸窒工程も行った。そして、上記実施形態による鋼部材の製造方法と同様に、焼戻し工程を行った。 (Production of steel members according to Comparative Example 1)
A steel member was produced using the steel member as a gear, based on the steel member manufacturing method according to Comparative Example 1 shown in FIG. Specifically, first, a cold forging step was performed in the same manner as in the steel member manufacturing method according to the above embodiment. SCM420 of case-hardened steel was used for the steel member in the same manner as in the method for manufacturing the steel member according to the above-described embodiment. Then, in the same manner as in the method for manufacturing a steel member according to the above-described embodiment, the steel member is heated to a temperature T1 (1000° C.) equal to or higher than the austenitization transformation completion temperature A3, and carbon is introduced into the steel member in the austenitized state. , a carburizing step was carried out to slowly cool the steel member infiltrated with carbon. Unlike the steel member manufacturing method according to the above-described embodiment, in the carburizing step, the steel member is cooled to a temperature lower than the austenitization transformation start temperature A1 so that only part of the austenite is pearlitic while the steel member is slowly cooled. The temperature was maintained at T4 (710° C.) for a predetermined time. That is, the steel member stays in a high temperature state (a state other than room temperature) longer than in the steel member manufacturing method according to the above-described embodiment by the time that the steel member is maintained at temperature T4 (710° C.). In addition, unlike the steel member manufacturing method according to the above embodiment, in the carburizing step, the steel member in the austenitized state has a carbon concentration (0.77% or more) at which the steel member and carbon have a hyper-eutectoid composition, Infiltrated with carbon. The carburizing process was performed while reducing the pressure inside the heat treatment chamber with a vacuum pump, as in the steel member manufacturing method according to the above-described embodiment. Then, the steel member was heated to a temperature T3 (850° C.) higher than the austenitizing transformation completion temperature A3, and after the steel member was maintained at the temperature T3 (850° C.) for a while, a quenching process was performed to rapidly cool the steel member. In the quenching process, when the steel member is maintained at the temperature T3 (850°C) (that is, the steel member is austenitized) for a while, there is also a nitriding step of infiltrating nitrogen into the steel member. went. Then, a tempering step was performed in the same manner as in the steel member manufacturing method according to the above embodiment.
　（比較例２による鋼部材の製造）
　図５に示す比較例２による鋼部材の製造方法に基づいて、鋼部材を歯車として、鋼部材を作製した。具体的には、まず、上記実施形態による鋼部材の製造方法と同様に、冷間鍛造工程を行った。鋼部材には、上記実施形態による鋼部材の製造方法と同様に、肌焼鋼のＳＣＭ４２０を用いた。そして、上記実施形態による鋼部材の製造方法と同様に、鋼部材をオーステナイト化変態完了温度Ａ３以上の温度Ｔ１（１０００℃）まで加熱してオーステナイト化した状態の鋼部材に、炭素を浸入させるとともに、炭素を浸入させた鋼部材を徐冷する浸炭工程を行った。なお、浸炭工程における徐冷は、鋼部材の温度が焼入れ工程のための温度Ｔ３（８５０℃）となるまで行った。また、上記実施形態による鋼部材の製造方法と異なり、浸炭工程において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが共析組成となる炭素濃度（０．７７％）で、炭素を浸入させた。なお、上記実施形態による鋼部材の製造方法と異なり、浸炭工程において、熱処理室の内部を減圧せずに行った。そして、鋼部材がオーステナイト化変態完了温度Ａ３以上の温度Ｔ３（８５０℃）に暫く維持された後、鋼部材を急冷する焼入れ工程を行った。すなわち、上記実施形態による鋼部材の製造方法と異なり、浸炭工程の後に鋼部材をパーライト化させずに、浸炭工程の直後に焼入れ工程を行った。なお、上記実施形態による鋼部材の製造方法と異なり、浸窒工程を行わなかった。そして、上記実施形態による鋼部材の製造方法と同様に、焼戻し工程を行った。 (Production of steel members according to Comparative Example 2)
Based on the steel member manufacturing method according to Comparative Example 2 shown in FIG. 5, a steel member was produced using the steel member as a gear. Specifically, first, a cold forging step was performed in the same manner as in the steel member manufacturing method according to the above embodiment. SCM420 of case-hardened steel was used for the steel member in the same manner as in the method for manufacturing the steel member according to the above-described embodiment. Then, in the same manner as in the method for manufacturing a steel member according to the above-described embodiment, the steel member is heated to a temperature T1 (1000° C.) equal to or higher than the austenitization transformation completion temperature A3, and carbon is introduced into the steel member in the austenitized state. , a carburizing step was carried out to slowly cool the steel member infiltrated with carbon. The slow cooling in the carburizing process was performed until the temperature of the steel member reached the temperature T3 (850°C) for the quenching process. In addition, unlike the steel member manufacturing method according to the above embodiment, in the carburizing step, carbon is added to the austenitized steel member at a carbon concentration (0.77%) at which the steel member and carbon have a eutectoid composition. infiltrated. Note that unlike the steel member manufacturing method according to the above-described embodiment, the carburizing step was performed without depressurizing the inside of the heat treatment chamber. Then, after the steel member was kept at temperature T3 (850° C.) equal to or higher than the austenitizing transformation completion temperature A3 for a while, the steel member was subjected to a quenching step of quenching. That is, unlike the steel member manufacturing method according to the above-described embodiment, the steel member was not pearliticized after the carburizing step, and the quenching step was performed immediately after the carburizing step. In addition, unlike the steel member manufacturing method according to the above-described embodiment, the nitriding process was not performed. Then, a tempering step was performed in the same manner as in the steel member manufacturing method according to the above embodiment.
　（比較例３による鋼部材の製造）
　比較例３として、比較例２による鋼部材の製造方法における鋼部材を歯車からシャフトに置き換えて、鋼部材を作製した。 (Production of steel members according to Comparative Example 3)
As Comparative Example 3, a steel member was produced by replacing the steel member in the steel member manufacturing method according to Comparative Example 2 with a shaft instead of the gear.
　（鋼部材の性能の試験結果）
　以下に、上記実施形態による鋼部材の製造方法を用いた鋼部材（実施例１の鋼部材および実施例４の鋼部材）、上記第１変形例による鋼部材の製造方法を用いた鋼部材（実施例２の鋼部材および実施例５の鋼部材）、上記第２変形例による鋼部材の製造方法を用いた鋼部材（実施例３の鋼部材）、比較例１による鋼部材の製造方法を用いた鋼部材（比較例１の鋼部材）、比較例２による鋼部材の製造方法を用いた鋼部材（比較例２の鋼部材）、および、比較例３による鋼部材の製造方法を用いた鋼部材（比較例３の鋼部材）の性能の試験結果について説明する。 (Test result of steel member performance)
Steel members using the steel member manufacturing method according to the above embodiment (steel member of Example 1 and steel member of Example 4), steel members using the steel member manufacturing method according to the first modification ( The steel member of Example 2 and the steel member of Example 5), the steel member using the method of manufacturing the steel member according to the second modification (the steel member of Example 3), and the method of manufacturing the steel member according to Comparative Example 1 The steel member used (steel member of Comparative Example 1), the steel member using the method of manufacturing the steel member according to Comparative Example 2 (steel member of Comparative Example 2), and the method of manufacturing the steel member according to Comparative Example 3 were used. The test results of the performance of the steel member (steel member of Comparative Example 3) will be described.
　図６に示すように、実施例１の鋼部材（図中のＳＣＭ（浸窒有り））、実施例２の鋼部材（図中のＳＣＭ（浸窒無し））および実施例３の鋼部材（図中の焼結材（浸窒無し））は、いずれも、衝撃試験時の亀裂発生エネルギーＥｉ（Ｊ／ｃｍ２）および曲げ疲労強度σ（ＭＰａ）が、共に、比較例１の鋼部材（図中のＳＣＭ４２０（比較例１））よりも大きかった。具体的には、実施例１の鋼部材の亀裂発生エネルギーＥｉは、比較例１の鋼部材の亀裂発生エネルギーＥｉよりも大きかった。実施例２の鋼部材の亀裂発生エネルギーＥｉは、鋼部材の亀裂発生エネルギーＥｉよりも大きかった。実施例３の鋼部材の亀裂発生エネルギーＥｉは、実施例２の鋼部材の亀裂発生エネルギーＥｉよりも大きかった。実施例３の鋼部材の曲げ疲労強度σは、比較例１の鋼部材の曲げ疲労強度σよりも大きかった。実施例２の鋼部材の曲げ疲労強度σは、実施例３の鋼部材の曲げ疲労強度σよりも大きかった。実施例１の鋼部材の曲げ疲労強度σは、実施例２の鋼部材の曲げ疲労強度σよりも大きかった。なお、衝撃試験時の亀裂発生エネルギーＥｉの大きさは、靭性の大きさと略比例する。また、曲げ疲労強度σは、曲げに対する強度の大きさを意味する。曲げ疲労強度σは、一般的に、硬さと略比例する。衝撃試験時の亀裂発生エネルギーＥｉは、シャルピー衝撃試験を用いて測定した。また、曲げ疲労強度σは、小野式回転曲げ疲労試験を用いて測定した。 As shown in FIG. 6, the steel member of Example 1 (SCM (with nitriding) in the figure), the steel member of Example 2 (SCM (without nitriding) in the figure), and the steel member of Example 3 ( All of the sintered materials (no nitriding) in the figure have crack initiation energy E i (J/cm 2 ) and bending fatigue strength σ (MPa) during the impact test, both of which are the same as those of the steel member of Comparative Example 1. (SCM420 (Comparative Example 1) in the figure). Specifically, the crack initiation energy E i of the steel member of Example 1 was greater than the crack initiation energy E i of the steel member of Comparative Example 1. The crack initiation energy Ei of the steel member of Example 2 was larger than the crack initiation energy Ei of the steel member. The crack initiation energy E i of the steel member of Example 3 was larger than the crack initiation energy E i of the steel member of Example 2. The bending fatigue strength σ of the steel member of Example 3 was greater than the bending fatigue strength σ of the steel member of Comparative Example 1. The bending fatigue strength σ of the steel member of Example 2 was greater than the bending fatigue strength σ of the steel member of Example 3. The bending fatigue strength σ of the steel member of Example 1 was greater than the bending fatigue strength σ of the steel member of Example 2. The magnitude of the crack initiation energy Ei during the impact test is approximately proportional to the magnitude of toughness. Also, the bending fatigue strength σ means the magnitude of strength against bending. The bending fatigue strength σ is generally approximately proportional to hardness. The crack initiation energy Ei during the impact test was measured using the Charpy impact test. The bending fatigue strength σ was measured using the Ono rotating bending fatigue test.
　図７に示すように、実施例１の鋼部材（図中のＳＣＭ（浸窒有り））および実施例２の鋼部材（図中のＳＣＭ（浸窒無し））は、いずれも、曲げ疲労強度σ（ＭＰａ）が、比較例２の鋼部材（図中のＳＣＭ４２０（比較例２））よりも大きかった。 As shown in FIG. 7, both the steel member of Example 1 (SCM (with nitriding) in the figure) and the steel member of Example 2 (SCM (without nitriding) in the figure) have bending fatigue strength σ (MPa) was larger than that of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure).
　図８に示すように、実施例４の鋼部材（図中のＳＣＭ（浸窒有り））および実施例５の鋼部材（図中のＳＣＭ（浸窒無し））は、いずれも、トルク振幅Ｔａ（Ｎ・ｍ）が、比較例３の鋼部材（図中のＳＣＭ４２０（比較例３））よりも大きかった。なお、トルク振幅Ｔａは、捩じり疲労強度を表す指標である。トルク振幅Ｔａは、捩じり疲労試験を用いて測定した。 As shown in FIG. 8, both the steel member of Example 4 (SCM (with nitriding) in the figure) and the steel member of Example 5 (SCM (without nitriding) in the figure) have a torque amplitude T a (N·m) was larger than that of the steel member of Comparative Example 3 (SCM420 (Comparative Example 3) in the figure). Note that the torque amplitude Ta is an index representing the torsional fatigue strength. Torque amplitude Ta was measured using a torsional fatigue test.
　図９に示すように、比較例２の鋼部材（図中のＳＣＭ４２０（比較例２））の表面硬さが７６０ＨＶであったのに対して、実施例１の鋼部材（図中のＳＣＭ（浸窒有り））の表面硬さは７７０であり、実施例２の鋼部材（図中のＳＣＭ（浸窒無し））の表面硬さは７７１であった。すなわち、実施例１の鋼部材および実施例２の鋼部材は、表面硬さが、比較例２の鋼部材よりも大きかった。なお、表面硬さは、ＪＩＳ　Ｚ　２２４４に準拠したビッカース硬さ試験を用いて測定した。 As shown in FIG. 9, the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure) had a surface hardness of 760 HV, whereas the steel member of Example 1 (SCM (Comparative Example 2) in the figure) had a surface hardness of 760 HV. The surface hardness of the steel member of Example 2 (SCM in the figure (without nitriding)) was 771. That is, the steel member of Example 1 and the steel member of Example 2 had higher surface hardness than the steel member of Comparative Example 2. The surface hardness was measured using a Vickers hardness test conforming to JIS Z 2244.
　比較例２の鋼部材（図中のＳＣＭ４２０（比較例２））の表面硬化層深さが０．７７ｍｍであったのに対して、実施例１の鋼部材（図中のＳＣＭ（浸窒有り））の表面硬化層深さは０．８２ｍｍであり、実施例２の鋼部材（図中のＳＣＭ（浸窒無し））の表面硬化層深さは０．８０ｍｍであった。すなわち、実施例１の鋼部材および実施例２の鋼部材は、表面硬化層深さが、比較例２の鋼部材よりも大きかった。 The surface hardened layer depth of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure) was 0.77 mm, whereas the steel member of Example 1 (SCM (with nitriding) in the figure) was 0.77 mm. )) had a hardened surface layer depth of 0.82 mm, and the steel member of Example 2 (SCM (no nitriding) in the figure) had a hardened surface layer depth of 0.80 mm. That is, the steel member of Example 1 and the steel member of Example 2 had a greater surface hardening layer depth than the steel member of Comparative Example 2.
　比較例２の鋼部材（図中のＳＣＭ４２０（比較例２））の表面の炭素濃度が０．７０ｗｔ％であったのに対して、実施例１の鋼部材（図中のＳＣＭ（浸窒有り））の表面の炭素濃度は０．５４ｗｔ％であり、実施例２の鋼部材（図中のＳＣＭ（浸窒無し））の表面の炭素濃度は０．５７ｗｔ％であった。すなわち、実施例１の鋼部材および実施例２の鋼部材は、表面の炭素濃度が、比較例２の鋼部材よりも著しく小さかった。これは、比較例２の鋼部材が、浸炭工程において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが共析組成となる炭素濃度（０．７７％）で、炭素を浸入させたのに対して、実施例１の鋼部材および実施例２の鋼部材は、浸炭工程において、オーステナイト化した状態の鋼部材に、鋼部材と炭素とが亜共析組成となる炭素濃度（０．７７％未満）で、炭素を浸入させたことに起因すると考えられる。 The surface carbon concentration of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the figure) was 0.70 wt%, whereas the steel member of Example 1 (SCM (with nitriding) in the figure) was 0.70 wt%. )) was 0.54 wt%, and the carbon concentration of the surface of the steel member of Example 2 (SCM (no nitriding) in the figure) was 0.57 wt%. That is, the steel member of Example 1 and the steel member of Example 2 had a significantly lower carbon concentration on the surface than the steel member of Comparative Example 2. This is because the steel member of Comparative Example 2 was infiltrated with carbon at a carbon concentration (0.77%) at which the steel member and carbon had a eutectoid composition in the austenitized steel member in the carburizing process. On the other hand, in the steel member of Example 1 and the steel member of Example 2, in the carburizing process, the steel member in the austenitized state has a carbon concentration (0. less than 77%), which is attributed to the infiltration of carbon.
　実施例１の鋼部材（図中のＳＣＭ（浸窒有り））の全浸炭深さ、実施例２の鋼部材（図中のＳＣＭ（浸窒無し））の全浸炭深さ、および、比較例２の鋼部材（図中のＳＣＭ４２０（比較例２））全浸炭深さは、いずれも、１．４ｍｍであった。これは、実施例１の鋼部材、実施例２の鋼部および比較例２の鋼部材は、いずれも、温度Ｔ１（１０００℃）まで加熱してオーステナイト化した状態の鋼部材に、炭素を浸入させたことに起因すると考えられる。 The total carburization depth of the steel member of Example 1 (SCM (with nitriding) in the figure), the total carburization depth of the steel member of Example 2 (SCM (without nitriding) in the figure), and the comparative example 2 steel members (SCM420 (Comparative Example 2) in the drawing) had a total carburizing depth of 1.4 mm. This is because the steel member of Example 1, the steel portion of Example 2, and the steel member of Comparative Example 2 are all heated to a temperature T1 (1000° C.) to austenite, and carbon is introduced into the steel members. This is probably due to the fact that
　実施例１の鋼部材（図中のＳＣＭ（浸窒有り））の表面の窒素濃度は、０．３４ｗｔ％であった。すなわち、実施例１の鋼部材は、表面の窒素濃度が表面の炭素濃度よりも小さかった。また、実施例１の鋼部材（図中のＳＣＭ（浸窒有り））の全浸窒深さは、０．３ｍｍであった。すなわち、実施例１の鋼部材は、全浸窒深さが表面の全浸炭深さよりも小さかった。 The nitrogen concentration on the surface of the steel member of Example 1 (SCM (with nitriding) in the figure) was 0.34 wt%. That is, in the steel member of Example 1, the surface nitrogen concentration was lower than the surface carbon concentration. Further, the total nitriding depth of the steel member of Example 1 (SCM (with nitriding) in the figure) was 0.3 mm. That is, in the steel member of Example 1, the total carburization depth was smaller than the total carburization depth of the surface.
　図１０に示すように、比較例２の鋼部材（図中のＳＣＭ４２０（比較例２））の粒界酸化深さが１４μｍであったのに対して、実施例１の鋼部材（図中のＳＣＭ（浸窒有り））の粒界酸化深さは５μｍであった。すなわち、実施例１の鋼部材は、粒界酸化深さが、比較例２の鋼部材よりも小さかった。したがって、実施例１の鋼部材は、製造工程における粒界酸化層の形成が大きく抑制されていた。 As shown in FIG. 10, the grain boundary oxidation depth of the steel member of Comparative Example 2 (SCM420 (Comparative Example 2) in the drawing) was 14 μm, whereas the steel member of Example 1 (SCM420 in the drawing (Comparative Example 2) The grain boundary oxidation depth of SCM (with nitriding) was 5 μm. That is, the steel member of Example 1 had a smaller grain boundary oxidation depth than the steel member of Comparative Example 2. Therefore, in the steel member of Example 1, the formation of a grain boundary oxide layer during the manufacturing process was greatly suppressed.
　実施例１の鋼部材の結晶粒径の最小値（図中のＭＩＮ）および比較例２の鋼部材の結晶粒径の最小値は、共に１０μｍであった。一方、比較例２の鋼部材の結晶粒径の最大値（図中のＭＡＸ）が１７０μｍであったのに対して、実施例１の鋼部材の結晶粒径の最大値は２２μｍであった。そして、比較例２の鋼部材の平均結晶粒径が３８μｍであったのに対して、実施例１の鋼部材の平均結晶粒径は１４μｍであった。すなわち、実施例１の鋼部材は、平均結晶粒径が、比較例２の鋼部材よりも小さかった。したがって、実施例１の鋼部材は、製造工程における結晶粒径の粗大化が大きく抑制されていた。 The minimum crystal grain size of the steel member of Example 1 (MIN in the figure) and the minimum crystal grain size of the steel member of Comparative Example 2 were both 10 μm. On the other hand, the maximum grain size (MAX in the drawing) of the steel member of Comparative Example 2 was 170 μm, while the maximum grain size of the steel member of Example 1 was 22 μm. The average grain size of the steel member of Comparative Example 2 was 38 μm, while the average grain size of the steel member of Example 1 was 14 μm. That is, the steel member of Example 1 had a smaller average grain size than the steel member of Comparative Example 2. Therefore, in the steel member of Example 1, coarsening of the crystal grain size during the manufacturing process was greatly suppressed.
　以上のように、実施例（実施例１～５）の鋼部材は、靭性、曲げ疲労強度、表面硬さ、表面硬化層深さ等が、比較的高いことが示された。したがって、上記実施形態による鋼部材の製造方法、上記実施形態の第１変形例による鋼部材の製造方法、および、上記実施形態の第２変形例による鋼部材の製造方法は、高い硬さと高い靭性とが共に要求される鋼部材（たとえば、歯車、軸受け、シャフト等）の製造方法として好適である。 As described above, the steel members of Examples (Examples 1 to 5) were shown to have relatively high toughness, bending fatigue strength, surface hardness, surface hardened layer depth, etc. Therefore, the steel member manufacturing method according to the above embodiment, the steel member manufacturing method according to the first modified example of the above embodiment, and the steel member manufacturing method according to the second modified example of the above embodiment have high hardness and high toughness. It is suitable as a method of manufacturing steel members (for example, gears, bearings, shafts, etc.) that require both
　［変形例］
　なお、今回開示された実施形態は、すべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は、上記した実施形態の説明ではなく請求の範囲によって示され、さらに請求の範囲と均等の意味および範囲内でのすべての変更（変形例）が含まれる。 [Modification]
It should be noted that the embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present invention is indicated by the scope of the claims rather than the above description of the embodiments, and includes all modifications (modifications) within the scope and meaning equivalent to the scope of the claims.
　たとえば、上記実施形態では、浸炭工程（Ｓ２）が、冷間鍛造された鋼部材に対して行われる例を示したが、本発明はこれに限られない。本発明では、浸炭工程が、熱間鍛造された鋼部材に対して行われてもよい。 For example, in the above embodiment, the carburizing step (S2) is performed on a cold-forged steel member, but the present invention is not limited to this. In the present invention, the carburizing process may be performed on hot forged steel members.
　また、上記実施形態では、浸窒工程（Ｓ３）が、オーステナイト化変態開始温度Ａ１以上で、かつ、オーステナイト化変態完了温度Ａ３未満の温度Ｔ２で、鋼部材に窒素を浸入させる工程である例を示したが、本発明はこれに限られない。本発明では、浸窒工程が、オーステナイト化変態開始温度未満の温度で、鋼部材に窒素を浸入させる工程であってもよい。 Further, in the above embodiment, the nitriding step (S3) is a step of infiltrating nitrogen into the steel member at a temperature T2 that is equal to or higher than the austenitizing transformation start temperature A1 and lower than the austenitizing transformation completion temperature A3. Although shown, the invention is not so limited. In the present invention, the nitriding step may be a step of impregnating the steel member with nitrogen at a temperature lower than the austenitizing transformation start temperature.
　また、上記実施形態では、浸窒工程（Ｓ３）が、鋼部材をオーステナイト化変態完了温度Ａ３未満の温度Ｔ２まで加熱した状態の鋼部材に窒素を浸入させる工程である例を示したが、本発明はこれに限られない。本発明では、比較例１のように、浸窒工程が、鋼部材をオーステナイト化変態完了温度以上の温度まで加熱した状態の鋼部材に窒素を浸入させる工程であってもよい。その場合、比較例１のように、焼入れ工程における加熱と同時に浸窒工程が行われてもよい。 Further, in the above embodiment, the nitriding step (S3) is a step of introducing nitrogen into the steel member heated to the temperature T2 below the austenitizing transformation completion temperature A3. The invention is not limited to this. In the present invention, as in Comparative Example 1, the nitriding step may be a step of introducing nitrogen into the steel member heated to a temperature equal to or higher than the austenitizing transformation completion temperature. In that case, as in Comparative Example 1, the nitriding step may be performed simultaneously with the heating in the quenching step.
　また、上記実施形態では、鋼部材に窒素を浸入させる浸窒工程（Ｓ３）が行われる例を示したが、本発明はこれに限られない。本発明では、上述した第１変形例および第２変形例のように、鋼部材に窒素を浸入させる浸窒工程が行われなくてもよい。 Further, in the above embodiment, an example was shown in which the nitriding step (S3) of impregnating the steel member with nitrogen was performed, but the present invention is not limited to this. In the present invention, unlike the above-described first and second modifications, the nitriding step of infiltrating nitrogen into the steel member need not be performed.
　また、上記実施形態では、鋼部材には、肌焼鋼が用いられる例を示したが、本発明はこれに限られない。本発明では、上述した第２変形例のように、鋼部材には、焼結材が用いられてもよい。 Further, in the above embodiment, an example in which case-hardened steel is used as the steel member is shown, but the present invention is not limited to this. In the present invention, a sintered material may be used for the steel member as in the above-described second modification.
　オーステナイト化変態開始温度…Ａ１、オーステナイト化変態完了温度…Ａ３、（オーステナイト化変態完了温度以上の）温度…Ｔ１、Ｔ３、（オーステナイト化変態完了温度未満の）温度…Ｔ２
  Austenitization transformation start temperature...A1, austenitization transformation completion temperature...A3, temperature (above austenitization transformation completion temperature)...T1, T3, temperature (below austenitization transformation completion temperature)...T2

Claims (6)

  1. 　鋼部材をオーステナイト化変態完了温度以上の温度まで加熱してオーステナイト化した状態の前記鋼部材に、前記鋼部材と前記炭素とが亜共析組成となる炭素濃度で、炭素を浸入させるとともに、前記炭素を浸入させた前記鋼部材を徐冷する浸炭工程と、
    　前記浸炭工程の後に、前記鋼部材を前記オーステナイト化変態完了温度以上の温度まで再度加熱するとともに、加熱した前記鋼部材を急冷する焼入れ工程と、を備える、鋼部材の製造方法。     The steel member is heated to a temperature equal to or higher than the austenitizing transformation completion temperature, and carbon is introduced into the steel member in an austenitized state at a carbon concentration at which the steel member and the carbon have a hypo-eutectoid composition, and a carburizing step of slowly cooling the steel member infiltrated with carbon;
    A method of manufacturing a steel member, comprising: after the carburizing step, reheating the steel member to a temperature equal to or higher than the austenitizing transformation completion temperature, and quenching the heated steel member.
  2. 　前記浸炭工程の後に、かつ、前記焼入れ工程の前に、前記鋼部材を前記オーステナイト化変態完了温度未満の温度まで加熱した状態の前記鋼部材に窒素を浸入させる浸窒工程をさらに備える、請求項１に記載の鋼部材の製造方法。 After the carburizing step and before the quenching step, the steel member is heated to a temperature lower than the austenitizing transformation completion temperature, further comprising a nitriding step of infiltrating nitrogen into the steel member. 2. The method for manufacturing the steel member according to 1.
  3. 　前記焼入れ工程は、前記浸窒工程の直後に、前記鋼部材を前記オーステナイト化変態完了温度未満の温度から前記オーステナイト化変態完了温度以上の温度に加熱するとともに、加熱した前記鋼部材を急冷する工程である、請求項２に記載の鋼部材の製造方法。 In the quenching step, immediately after the nitriding step, the steel member is heated from a temperature below the austenitizing transformation completion temperature to a temperature above the austenitizing transformation completion temperature, and the heated steel member is rapidly cooled. The method for manufacturing a steel member according to claim 2, wherein
  4. 　前記浸窒工程は、オーステナイト化変態開始温度以上で、かつ、前記オーステナイト化変態完了温度未満の温度で、前記鋼部材に窒素を浸入させる工程である、請求項２に記載の鋼部材の製造方法。 3. The method of manufacturing a steel member according to claim 2, wherein the nitriding step is a step of introducing nitrogen into the steel member at a temperature equal to or higher than the austenitization transformation start temperature and lower than the austenitization transformation completion temperature. .
  5. 　前記浸窒工程は、前記鋼部材の表面の窒素濃度が０．５％以下となるように、前記鋼部材に窒素を浸入させる工程である、請求項２に記載の鋼部材の製造方法。 The method for manufacturing a steel member according to claim 2, wherein the nitriding step is a step of impregnating the steel member with nitrogen so that the nitrogen concentration on the surface of the steel member is 0.5% or less.
  6. 　前記浸炭工程は、冷間鍛造された前記鋼部材に対して行われる、請求項１に記載の鋼部材の製造方法。 The method for manufacturing a steel member according to claim 1, wherein the carburizing step is performed on the cold forged steel member.
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JPH1099937A (en) * 1996-08-06 1998-04-21 Nissan Motor Co Ltd Gear forming method and forming device
WO2005068862A1 (en) * 2004-01-15 2005-07-28 Ntn Corporation Rolling bearing and method for heat treatment of steel
WO2009131202A1 (en) * 2008-04-25 2009-10-29 アイシン・エィ・ダブリュ株式会社 Method for producing steel parts
JP2017137518A (en) * 2016-02-01 2017-08-10 アイシン・エィ・ダブリュ株式会社 Method for manufacturing case hardened component
JP2019127624A (en) 2018-01-25 2019-08-01 トヨタ自動車株式会社 Production method of steel member

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH1099937A (en) * 1996-08-06 1998-04-21 Nissan Motor Co Ltd Gear forming method and forming device
WO2005068862A1 (en) * 2004-01-15 2005-07-28 Ntn Corporation Rolling bearing and method for heat treatment of steel
WO2009131202A1 (en) * 2008-04-25 2009-10-29 アイシン・エィ・ダブリュ株式会社 Method for producing steel parts
JP2017137518A (en) * 2016-02-01 2017-08-10 アイシン・エィ・ダブリュ株式会社 Method for manufacturing case hardened component
JP2019127624A (en) 2018-01-25 2019-08-01 トヨタ自動車株式会社 Production method of steel member

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