WO2022176878A1 - 鋼部材の窒化処理方法 - Google Patents

鋼部材の窒化処理方法 Download PDF

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Publication number
WO2022176878A1
WO2022176878A1 PCT/JP2022/006065 JP2022006065W WO2022176878A1 WO 2022176878 A1 WO2022176878 A1 WO 2022176878A1 JP 2022006065 W JP2022006065 W JP 2022006065W WO 2022176878 A1 WO2022176878 A1 WO 2022176878A1
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Prior art keywords
nitriding
gas
potential
gases
controlled
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PCT/JP2022/006065
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English (en)
French (fr)
Japanese (ja)
Inventor
泰 平岡
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パーカー熱処理工業株式会社
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Application filed by パーカー熱処理工業株式会社 filed Critical パーカー熱処理工業株式会社
Priority to MX2023009143A priority Critical patent/MX2023009143A/es
Priority to KR1020237030522A priority patent/KR20230145118A/ko
Priority to EP22756196.6A priority patent/EP4296383A4/en
Priority to US18/546,438 priority patent/US20240132985A1/en
Priority to CN202280014939.6A priority patent/CN116917529A/zh
Publication of WO2022176878A1 publication Critical patent/WO2022176878A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/02—Pretreatment of the material to be coated
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D9/32—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
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment
    • 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 nitriding a steel member comprising at least two stages of nitriding.
  • Carburizing treatment and nitriding treatment are known as techniques for strengthening steel members such as gears in order to meet such demands.
  • Patent Document 1 in order to improve the pitting resistance and bending fatigue strength of steel members, iron containing ⁇ ' phase as a main component is applied to the surface of steel members by nitriding treatment. It is disclosed that the formation of a nitride layer is effective.
  • Patent Document 2 in order to suppress variations during mass production, the steel member is heated in a nitriding gas atmosphere with a nitriding potential that generates a ⁇ ' phase or ⁇ phase nitride compound layer. and then performing a second nitriding step of nitriding the steel member in a nitriding gas atmosphere with a nitriding potential lower than that of the first nitriding step.
  • a nitriding method for precipitating a ⁇ ' phase in a compound layer is disclosed. Specifically, a gas nitriding treatment performed at a temperature of 600° C.
  • NH 3 gas and H 2 gas are described as an example. More specifically, at a temperature of 600° C., a range of 0.6 to 1.51 is adopted for the nitriding potential in the first nitriding process, and a range of 0.16 to 1.51 is adopted for the nitriding potential in the second nitriding process. A range of 0.25 has been adopted.
  • Patent Document 2 Japanese Patent No. 6378189
  • the action (reaction) in which the ⁇ ' phase precipitates in the nitride compound layer is affected by both the nitriding potential and the furnace temperature. If the nitriding potential in the nitriding treatment step is set to 0.25 or less, the ⁇ phase, which is lower in hardness than the ⁇ ' phase, is also precipitated, resulting in insufficient pitting resistance and bending fatigue strength.
  • An object of the present invention is to enable the ⁇ ' phase to be favorably precipitated in the nitride compound layer in the nitriding treatment performed in the temperature range of 500° C. to 590° C., thereby realizing high pitting resistance and bending fatigue strength. It is to provide a nitriding method capable of
  • the present invention A nitriding method for a steel member comprising at least two stages of nitriding treatment, a first nitriding step of nitriding the steel member in a nitriding gas atmosphere of a first nitriding potential; a second nitriding step of further nitriding the steel member in a nitriding gas atmosphere having a second nitriding potential lower than the first nitriding potential after the first nitriding step; with The first nitriding treatment step is performed at a temperature of 500° C. to 590° C., The second nitriding treatment step is also performed at a temperature of 500° C.
  • the first nitriding potential is a value within the range of 0.300 to 10.000
  • the second nitriding potential is a value within the range of 0.253 to 0.600
  • a nitride compound layer of ⁇ ' phase, ⁇ phase, or a mixture of ⁇ ' phase and ⁇ phase is generated
  • a ⁇ ' phase is precipitated in the nitride compound layer in the second nitriding step.
  • the second nitriding potential is set to a value within the range of 0.253 to 0.600. It is possible to suppress the precipitation of the ⁇ phase, which is lower in hardness than the other phases, to favorably precipitate the ⁇ ' phase in the nitride compound layer, and to realize high pitting resistance and bending fatigue strength.
  • the first nitriding step and the second nitriding step are sequentially performed in, for example, the same batch-type heat treatment furnace, and in the first nitriding step, NH 3 gas and AX gas are used. N 2 gas and three kinds of gases are used, and by changing the introduction amount of each of NH 3 gas and AX gas while keeping the total flow rate thereof constant, the nitriding potential during the first nitriding treatment step can be changed to the above-mentioned It is controlled to have a nitriding potential of 1.
  • the second nitriding step two kinds of gases, NH 3 gas and AX gas, are used. Thereby, the nitriding potential during the second nitriding treatment step is controlled to be the second nitriding potential.
  • the first nitriding treatment step is performed at a temperature of 500° C. to 590° C.
  • the second nitriding treatment step is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is 0.5° C. Effectiveness of the present invention characterized in that the value is in the range of 300 to 10.000, and the second nitriding potential is lower than the first nitriding potential and is in the range of 0.253 to 0.600. was demonstrated.
  • the first nitriding step and the second nitriding step are sequentially performed in, for example, the same single-chamber heat treatment furnace, and in the first nitriding step, NH 3 gas and Three kinds of gases, AX gas and N 2 gas, are used, and by changing the introduction amount of each of NH 3 gas and AX gas while keeping the total flow rate thereof constant, the nitriding potential during the first nitriding treatment step is controlled to be the first nitriding potential, and in the second nitriding step, two kinds of gases, NH 3 gas and AX gas, are used, and their total flow rates are kept constant while introducing each of them By varying the amount, the nitriding potential during the second nitriding step is controlled to be the second nitriding potential.
  • the first nitriding process is performed at a temperature of 500° C. to 590° C.
  • the second nitriding process is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is 0. 0.300 to 10.000
  • the second nitriding potential is lower than the first nitriding potential and has a value in the range of 0.253 to 0.600. sex has been demonstrated.
  • the first nitriding step and the second nitriding step are sequentially performed in the same batch-type heat treatment furnace, and in the first nitriding step, NH 3 gas and AX By changing the introduction amount of each of them while keeping the total flow rate thereof constant, the nitriding potential during the first nitriding treatment step is adjusted to the first nitriding potential.
  • Two types of gases, NH 3 gas and AX gas, are also used in the second nitriding treatment step, and the second nitriding process is performed by changing the introduction amount of each while keeping the total flow rate thereof constant.
  • the nitriding potential during the treatment process is controlled to be the second nitriding potential.
  • the first nitriding process is performed at a temperature of 500° C. to 590° C.
  • the second nitriding process is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is 0. 0.300 to 10.000
  • the second nitriding potential is lower than the first nitriding potential and has a value in the range of 0.253 to 0.600. sex has been demonstrated.
  • the first nitriding step and the second nitriding step are sequentially performed in, for example, the same single-chamber heat treatment furnace, and in the first nitriding step, NH 3 gas and Two kinds of gases, AX gas and AX gas, are used, and by changing the introduction amount of each while keeping the total flow rate thereof constant, the nitriding potential during the first nitriding treatment step is adjusted to the first nitriding potential. Also in the second nitriding process, two kinds of gases, NH 3 gas and AX gas, are used. The nitriding potential during the nitriding process is controlled to be the second nitriding potential.
  • the first nitriding process is performed at a temperature of 500° C. to 590° C.
  • the second nitriding process is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is 0. 0.300 to 10.000
  • the second nitriding potential is lower than the first nitriding potential and has a value in the range of 0.253 to 0.600. sex has been demonstrated.
  • the first nitriding step and the second nitriding step are sequentially performed in the same single-chamber heat treatment furnace.
  • the first nitriding process two kinds of gases, NH 3 gas and AX gas, are used, and by changing the amount of one introduced while keeping the amount of one introduced constant, the first nitriding
  • the nitriding potential during the treatment process is controlled to be the first nitriding potential
  • the second nitriding treatment process as well two kinds of gases, NH 3 gas and AX gas, are used, and the introduction amount of one of them is changed to By changing the introduction amount of the other while keeping it constant, the nitriding potential during the second nitriding treatment step is controlled to be the second nitriding potential.
  • the first nitriding process is performed at a temperature of 500° C. to 590° C.
  • the second nitriding process is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is 0. 0.300 to 10.000
  • the second nitriding potential is lower than the first nitriding potential and has a value in the range of 0.253 to 0.600. sex has been demonstrated.
  • the first nitriding step and the second nitriding step are sequentially performed in the same single-chamber heat treatment furnace.
  • the first nitriding step three kinds of gases, NH 3 gas, AX gas, and N 2 gas, are used, and the introduction amount of one of the NH 3 gas and the AX gas is kept constant while the introduction amount of the other is changed.
  • the nitriding potential during the first nitriding process is controlled to be the first nitriding potential
  • two kinds of gases, NH 3 gas and AX gas are used.
  • the introduction amount of one of the NH 3 gas and the AX gas while keeping the introduction amount of the other gas constant, the nitriding potential during the second nitriding treatment step is controlled to be the second nitriding potential.
  • the first nitriding process is performed at a temperature of 500° C. to 590° C.
  • the second nitriding process is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is 0. 0.300 to 10.000
  • the second nitriding potential is lower than the first nitriding potential and has a value in the range of 0.253 to 0.600. sex has been demonstrated.
  • the one-chamber heat treatment furnace is a heat treatment furnace that does not have a separate cooling chamber from the heating chamber like the batch heat treatment furnace (see FIG. 1), and performs heating and cooling in only one chamber.
  • Pit furnaces see Fig. 3
  • horizontal furnaces see Fig. 5 are generally used.
  • the time for the first nitriding process is longer than the time for the second nitriding process.
  • the thickness of the compound layer after nitriding can be adjusted to an arbitrary thickness by performing the first nitriding process longer than the second nitriding process.
  • the second nitriding potential is set to a value within the range of 0.253 to 0.600. It is possible to suppress the precipitation of the ⁇ phase, which is lower in hardness than the other phases, to favorably precipitate the ⁇ ' phase in the nitride compound layer, and to realize high pitting resistance and bending fatigue strength.
  • FIG. 1 is a schematic diagram of the configuration of a batch-type heat treatment furnace used in the nitriding method of the present invention.
  • FIG. 1. It is process drawing of one Embodiment of the nitriding treatment method of this invention using the heat treatment furnace of FIG. 1 is a schematic diagram showing the configuration of a pit-type (single-chamber type) heat treatment furnace used in the nitriding method of the present invention.
  • FIG. FIG. 4 is a process diagram of one embodiment of the nitriding treatment method of the present invention using the heat treatment furnace of FIG. 3 ;
  • 1 is a schematic diagram showing the configuration of a horizontal (single-chamber) heat treatment furnace used in the nitriding method of the present invention.
  • 1 is a table showing nitriding conditions and treatment results of examples and comparative examples of the present invention.
  • 1 is a table showing nitriding conditions and treatment results of examples and comparative examples of the present invention.
  • 1 is a table showing nitriding conditions and treatment results of examples and comparative examples of the present invention.
  • 1 is a table showing nitriding conditions and treatment results of examples and comparative examples of the present invention.
  • 1 is a table showing nitriding conditions and treatment results of examples and comparative examples of the present invention.
  • 1 is a table showing nitriding conditions and treatment results of examples and comparative examples of the present invention.
  • the object to be processed (work) is a steel member. Specifically, it is a steel member made of a carbon steel material for machine structural use or an alloy steel material for machine structural use, such as a gear used in an automatic transmission.
  • a cylindrical ring gear or a bottomed cylindrical ring gear is mounted on a multistage jig and placed flat in a case (to be described later) for nitriding.
  • pre-clean steel members it is preferable to pre-clean steel members to remove dirt and oil before nitriding.
  • the pre-cleaning is preferably, for example, vacuum cleaning for degreasing and drying by dissolving and replacing oil or the like with a hydrocarbon-based cleaning liquid and evaporating it, or alkali cleaning for degreasing with an alkaline-based cleaning liquid.
  • FIG. 1 is a schematic diagram of the configuration of a batch-type heat treatment furnace 1 used in the nitriding method of the present invention.
  • the batch-type heat treatment furnace 1 includes a loading section 10, a heating chamber 11, a transfer chamber 12, and an unloading conveyor 13.
  • a case 20 is placed in the carry-in section 10, and a steel member as an object to be processed (work) is accommodated in the case 20.
  • the maximum processed weight is 700 kg gross.
  • An entrance hood 22 having a door 21 that can be freely opened and closed is attached to the entrance side of the heating chamber 11 (left side in FIG. 1).
  • the heating chamber 11 has a retort structure, and the temperature inside the furnace is controlled to a predetermined temperature by heating the outer periphery of the retort with a heater (not shown).
  • a plurality of types of gases for nitriding are introduced into the heating chamber 11 while being controlled as described later.
  • a fan 26 is attached to the ceiling of the heating chamber 11 to stir the gas introduced into the heating chamber 11 to uniformize the heating temperature of the steel member.
  • An openable and closable intermediate door 27 is attached to the exit side of the heating chamber 11 (on the right side in FIG. 1).
  • the transfer chamber 12 is provided with an elevator 30 that raises and lowers the case 20 containing the steel members.
  • a cooling chamber (oil tank) 32 in which cooling oil 31 is stored is provided in the lower portion of the transfer chamber 12 .
  • An outlet hood 36 having an openable/closable door 35 is attached to the outlet side (right side in FIG. 1) of the transfer chamber 12 .
  • the heating chamber 11 and the transfer chamber 12 may be the same processing chamber, and a configuration may be adopted in which the steel member after the heat treatment is air-cooled by gas.
  • the heating chamber 11 may be divided into two chambers, and a two-stage nitriding treatment process, which will be described later, may be performed in each of the heating chambers.
  • the case 20 containing the steel member is carried into the heating chamber 11 from the carry-in section 10 by a pusher or the like. Then, after the steel member (the case 20 containing the steel member) is carried into the heating chamber 11, the processing gas is introduced into the heating chamber 11, the processing gas is heated to a predetermined temperature by the heater, and the fan 26 The nitriding treatment of the steel member carried into the heating chamber 11 is performed while being stirred at (for example, rotating at 1500 rpm).
  • FIG. 2 is a process diagram of one embodiment of the nitriding method of the present invention using the heat treatment furnace 1 of FIG.
  • the inside of the heating chamber 11 is preheated to 550° C. before the steel member (work) is loaded.
  • N 2 gas is introduced at a constant flow rate of 70 (L/min) and NH 3 gas is introduced at a constant flow rate of 90 (L/min).
  • a steel member (work) is then loaded into the heating chamber 11 .
  • the temperature in the heating chamber 11 is temporarily lowered as shown in FIG.
  • the door 21 is closed and the temperature inside the heating chamber 11 is heated up to 550° C. again.
  • a two-step nitriding process is carried out. Specifically, first, a value of, for example, 1.500 (0.300 to 10.000) is adopted as the first nitriding potential, and the first nitriding treatment step is performed at a temperature of 550.degree.
  • K N P( NH3 ) / P(H2) 3/2
  • the partial pressure P (NH 3 ) of NH 3 gas or the partial pressure P (H 2 ) of H 2 gas in the heating chamber 11 is measured, and the nitriding potential value calculated from the measured value. is within the vicinity of the target first nitriding potential, the amount of the processing gas introduced is feedback-controlled.
  • such a first nitriding process is performed for 240 minutes.
  • a nitride compound layer of ⁇ ' phase, ⁇ phase, or a mixture of ⁇ ' phase and ⁇ phase is formed on the steel member.
  • a value of, for example, 0.300 (0.253 to 0.600) is adopted as the second nitriding potential, and the second nitriding process is performed at a temperature of 550°C.
  • the partial pressure P (NH 3 ) of NH 3 gas or the partial pressure P (H 2 ) of H 2 gas in the heating chamber 11 is measured, and the nitriding potential calculated from the measured value is The amount of the processing gas introduced is feedback-controlled so that the value is within the vicinity of the target second nitriding potential.
  • the partial pressure P (H 2 ) of H 2 gas in the heating chamber 11 is measured by a thermal conductivity type H 2 sensor (not shown), and the measured value is analyzed online (the measurement While calculating the nitriding potential from the value), the introduction amount of the processing gas is feedback-controlled. Specifically, NH 3 gas and AX gas are each increased or decreased under the condition of a total flow rate of 160 (L/min).
  • the cooling process is performed.
  • the cooling step is performed for 15 minutes (oil bath with stirrer, held in oil (100° C.) for 15 minutes).
  • the case 20 containing the steel member is carried out to the carry-out conveyor 13 .
  • FIG. 3 is a schematic diagram of the configuration of a pit-type heat treatment furnace 201 used in the nitriding method of the present invention.
  • the pit-type heat treatment furnace 201 includes a bottomed cylindrical furnace wall 211 and a furnace lid 212 .
  • a fan 213 is provided on the lower side (inside) of the furnace lid 212, and the rotation shaft of the fan 213 passes through the furnace lid 212, and a fan motor 214 is provided on the upper side (outside) of the furnace lid 212. It is connected to the.
  • a retort 221 is provided inside the furnace wall 211 , and a gas guide cylinder 222 is provided further inside the retort 221 .
  • the temperature inside the furnace (inside the retort 221) is controlled to a predetermined temperature by heating the outer peripheral portion of the retort 221 with a heater (not shown).
  • a case 20 is placed in the gas guide tube 222, and a steel member as an object to be processed (work) is accommodated in the case 20. As shown in FIG.
  • the maximum processed weight is 700 kg gross.
  • a plurality of types of gases for nitriding are introduced into the retort 221 while being controlled as described later.
  • the outer periphery of the retort 221 also has a cooling function by a blower (not shown), and during cooling, the work in the furnace is cooled by lowering the temperature of the retort 221 itself (furnace cooling).
  • the furnace cover 212 is opened, and the case 20 containing the steel members is carried into the gas guide tube 222 .
  • the processing gas is introduced into the gas guide cylinder 222, the processing gas is heated to a predetermined temperature by the heater, and further The steel member carried into the gas guide cylinder 222 is nitrided while being stirred by the fan 213 (rotating at 1500 rpm, for example).
  • FIG. 4 is a process diagram of one embodiment of the nitriding method of the present invention using the heat treatment furnace 201 of FIG.
  • a two-step nitriding process is carried out. Specifically, first, a value of, for example, 1.500 (0.300 to 10.000) is adopted as the first nitriding potential, and the first nitriding treatment step is performed at a temperature of 550.degree.
  • K N P( NH3 ) / P(H2) 3/2
  • the partial pressure P (NH 3 ) of NH 3 gas or the partial pressure P (H 2 ) of H 2 gas in the gas guide tube 222 is measured (the partial pressure P of NH 3 gas in the exhaust gas). (NH 3 ) or H 2 gas partial pressure P (H 2 ) may be measured), so that the nitriding potential value calculated from the measured value is within the vicinity of the target first nitriding potential. Also, the amount of processing gas introduced is feedback-controlled.
  • the partial pressure P (H 2 ) of H 2 gas in the gas guide tube 222 is measured by a thermal conductivity type H 2 sensor (not shown), and the measured value is analyzed online (the While calculating the nitriding potential from the measured value), the introduction amount of the processing gas is feedback-controlled. Specifically, the NH 3 gas is increased or decreased while the AX gas is introduced at a constant flow rate of 20 (L/min). The total flow will also fluctuate.
  • such a first nitriding process is performed for 240 minutes.
  • a nitride compound layer of ⁇ ' phase, ⁇ phase, or a mixture of ⁇ ' phase and ⁇ phase is formed on the steel member.
  • a value of, for example, 0.300 (0.253 to 0.600) is adopted as the second nitriding potential, and the second nitriding process is performed at a temperature of 550°C.
  • the partial pressure P (NH 3 ) of NH 3 gas or the partial pressure P (H 2 ) of H 2 gas in the gas guide tube 222 is measured, and the nitriding potential calculated from the measured value.
  • the amount of the processing gas introduced is feedback-controlled so that the value of is within the vicinity of the target second nitriding potential.
  • the partial pressure P (H 2 ) of H 2 gas in the gas guide tube 222 is measured by a thermal conductivity type H 2 sensor (not shown), and the measured value is analyzed online (the While calculating the nitriding potential from the measured value), the introduction amount of the processing gas is feedback-controlled. Specifically, the NH 3 gas is increased or decreased while the AX gas is introduced at a constant flow rate of 30 (L/min). The total flow will also fluctuate.
  • a cooling process is performed.
  • the processing gas introduction amount is controlled in the same manner as in the second nitriding process. That is, while the AX gas is introduced at a constant flow rate of 30 (L/min), the NH 3 gas is increased or decreased. In the latter half of the cooling process (about 400° C. to 100° C.), N 2 gas is introduced at a constant flow rate of 20 (L/min).
  • the furnace lid 212 is opened and the case 20 containing the steel member is carried out from the gas guide cylinder 222 .
  • FIG. 5 is a schematic diagram of the configuration of a horizontal heat treatment furnace used in the nitriding method of the present invention.
  • a horizontal heat treatment furnace is basically a furnace in which a pit-type heat treatment furnace is oriented horizontally, but as shown in FIG. A configuration provided on the wall surface of the furnace wall 211 facing the .
  • the furnace cover 212 is opened and the case 20 containing the steel member is carried into the gas guide tube 222 .
  • the processing gas is introduced into the retort 211, the processing gas is heated to a predetermined temperature by the heater, and the fan 213
  • the nitriding treatment of the steel member carried into the gas guide tube 222 is performed while being stirred at (for example, rotating at 1500 rpm).
  • the process chart in FIG. 4 is effective even when a horizontal heat treatment furnace is used. Specifically, a heating process (the gas introduction mode differs between the first half and the second half), a first nitriding process, a second nitriding process, and a cooling process can be performed. After the cooling process is completed, the furnace lid 212 is opened and the case 20 containing the steel member is carried out from the gas guide cylinder 222 .
  • the surface has an iron nitride compound layer mainly composed of the ⁇ ' phase.
  • a nitrided steel member can be obtained.
  • the steel member obtained by each embodiment has a nitrogen diffusion layer and nitrides formed inside and is reinforced, and a ⁇ ' phase-rich iron nitride compound layer is formed on the surface, so that sufficient pitting resistance and bending fatigue strength can be realized.
  • the nitriding of the present invention is performed at a temperature below the austenite transformation temperature, so the amount of strain is small.
  • the quenching step which is an essential step in carburizing and carbonitriding, can be omitted, the amount of strain variation is small. As a result, a high-strength, low-strain nitrided steel member can be obtained.
  • the temperature of each nitriding process is set to 500.degree. C. to 590.degree. It is said that the higher the temperature of the nitriding treatment, the better the productivity. However, according to the inventor's verification, if the temperature is higher than 590°C, the amount of hardening decreases and an austenite layer is formed on the surface, so 590°C is the upper limit. On the other hand, according to the inventor's verification, if the nitriding temperature is lower than 500.degree.
  • the temperature difference between the two nitriding processes is preferably controlled within 50°C, more preferably within 30°C.
  • Examples 1-1 to 1-9, Comparative Examples 1-1 to 1-4 Two-stage nitriding treatment was performed on a plurality of cylindrical ring gears (of which the steel type may be different) using a batch-type heat treatment furnace 1 according to the conditions in Table 1 shown in FIG.
  • Example 1-1 to 1-9 and Comparative Examples 1-1 to 1-4 the first nitriding process and the second nitriding process were sequentially performed in the same batch-type heat treatment furnace 1.
  • nitriding potential during the second nitriding step was controlled to the target second nitriding potential (K N ) by changing the introduction amount of each of them while keeping them constant.
  • each step described with reference to FIG. 2 was performed before and after the first nitriding step and the second nitriding step. .
  • the phase identification method is based on the X-ray diffraction pattern obtained by performing X-ray diffraction measurement by the 2 ⁇ - ⁇ scanning method (Rigaku MiniFlex 600, Cu tube, 40 kV-15 mA) from the steel surface. It was conducted.
  • the thickness of the compound layer was obtained by cutting the nitriding-treated steel material in the depth direction and measuring the thickness of the surface compound layer from the results of observing the structure of the cross section.
  • the thickness of the ⁇ ' phase-rich compound layer is preferably 4 to 16 ⁇ m. If it is less than 4 ⁇ m, it is too thin and the fatigue strength is not sufficiently improved. The porous layer of the compound layer becomes thicker and the fatigue strength decreases.
  • the first nitriding treatment step was performed at a temperature of 500 ° C. to 590 ° C.
  • the second nitriding treatment step is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is a value within the range of 0.300 to 10.000
  • the second nitriding potential is the first nitriding
  • Examples 2-1 to 2-9, Comparative Examples 2-1 to 2-4 A plurality of cylindrical ring gears (of different steel types) were subjected to two-stage nitriding treatment using a pit-type heat treatment furnace 201 according to the conditions in Table 2 shown in FIG.
  • Example 2-1 to 2-9 and Comparative Examples 2-1 to 2-4 the first nitriding process and the second nitriding process were sequentially performed in the same pit-shaped heat treatment furnace 201 .
  • each step described with reference to FIG. 4 was performed before and after the first nitriding step and the second nitriding step. .
  • phase identification method and compound layer thickness in Table 2 were determined in the same manner as those in Table 1.
  • the first nitriding treatment step was performed at a temperature of 500 ° C. to 590 ° C.
  • the second nitriding treatment step is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is a value within the range of 0.300 to 10.000
  • the second nitriding potential is the first nitriding
  • Examples 3-1 to 3-9, Comparative Examples 3-1 to 3-4 Two-stage nitriding treatment was performed on a plurality of cylindrical ring gears (steel types may differ) using a batch-type heat treatment furnace 1 according to the conditions in Table 3 shown in FIG.
  • Example 3-1 to 3-9 and Comparative Examples 3-1 to 3-4 the first nitriding process and the second nitriding process were sequentially performed in the same batch-type heat treatment furnace 1.
  • nitriding potential during the first nitriding step was controlled to the target first nitriding potential (K N ) by changing the introduced amount of each of them while keeping them constant.
  • nitriding potential during the second nitriding step was controlled to the target second nitriding potential (K N ) by changing the introduction amount of each of them while keeping them constant.
  • each step described with reference to FIG. 2 was performed before and after the first nitriding step and the second nitriding step. .
  • phase identification method and compound layer thickness in Table 3 were determined in the same manner as those in Tables 1 and 2.
  • the first nitriding process was performed at a temperature of 500 ° C. to 590 ° C.
  • the second nitriding treatment step is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is a value within the range of 0.300 to 10.000
  • the second nitriding potential is the first nitriding
  • Examples 4-1 to 4-9, Comparative Examples 4-1 to 4-4 A plurality of cylindrical ring gears (of different steel types) were subjected to two-stage nitriding treatment using a pit-type heat treatment furnace 201 according to the conditions in Table 4 shown in FIG.
  • Example 4-1 to 4-9 and Comparative Examples 4-1 to 4-4 the first nitriding process and the second nitriding process were sequentially performed in the same pit-shaped heat treatment furnace 201 .
  • nitriding potential during the first nitriding step was controlled to the target first nitriding potential (K N ) by changing the introduced amount of each of them while keeping them constant.
  • nitriding potential during the second nitriding step was controlled to the target second nitriding potential (K N ) by changing the introduction amount of each of them while keeping them constant.
  • each step described with reference to FIG. 4 was performed before and after the first nitriding step and the second nitriding step. .
  • phase identification method and compound layer thickness in Table 4 were determined in the same manner as those in Tables 1 to 3.
  • the first nitriding process was performed at a temperature of 500 ° C. to 590 ° C.
  • the second nitriding treatment step is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is a value within the range of 0.300 to 10.000
  • the second nitriding potential is the first nitriding
  • Examples 5-1 to 5-9, Comparative Examples 5-1 to 5-4 A plurality of cylindrical ring gears (of different steel types) were subjected to two-stage nitriding treatment using a pit-type heat treatment furnace 201 according to the conditions in Table 5 shown in FIG.
  • Example 5-1 to 5-9 and Comparative Examples 5-1 to 5-4 the first nitriding process and the second nitriding process were sequentially performed in the same pit-shaped heat treatment furnace 201 .
  • each step described with reference to FIG. 4 was performed before and after the first nitriding step and the second nitriding step. .
  • phase identification method and compound layer thickness in Table 5 were determined in the same manner as those in Tables 1 to 4.
  • the first nitriding treatment step was performed at a temperature of 500 ° C. to 590 ° C.
  • the second nitriding treatment step is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is a value within the range of 0.300 to 10.000
  • the second nitriding potential is the first nitriding
  • Examples 6-1 to 6-9, Comparative Examples 6-1 to 6-4 A plurality of cylindrical ring gears (of different steel types) were subjected to two-stage nitriding treatment using a pit-type heat treatment furnace 201 according to the conditions in Table 6 shown in FIG.
  • Example 6-1 to 6-9 and Comparative Examples 6-1 to 6-4 the first nitriding process and the second nitriding process were sequentially performed in the same pit-shaped heat treatment furnace 201 .
  • each step described with reference to FIG. 4 was performed before and after the first nitriding step and the second nitriding step. .
  • phase identification method and compound layer thickness in Table 6 were determined in the same manner as those in Tables 1 to 5.
  • the first nitriding process was performed at a temperature of 500 ° C. to 590 ° C.
  • the second nitriding treatment step is also performed at a temperature of 500° C. to 590° C.
  • the first nitriding potential is a value within the range of 0.300 to 10.000
  • the second nitriding potential is the first nitriding

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EP22756196.6A EP4296383A4 (en) 2021-02-17 2022-02-16 NITRIDING PROCESS FOR STEEL ELEMENT
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