WO2017056512A1 - Production method for alloy steel powder for powder metallurgy - Google Patents

Production method for alloy steel powder for powder metallurgy Download PDF

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Publication number
WO2017056512A1
WO2017056512A1 PCT/JP2016/004441 JP2016004441W WO2017056512A1 WO 2017056512 A1 WO2017056512 A1 WO 2017056512A1 JP 2016004441 W JP2016004441 W JP 2016004441W WO 2017056512 A1 WO2017056512 A1 WO 2017056512A1
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powder
atomized iron
based powder
content
moving bed
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PCT/JP2016/004441
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French (fr)
Japanese (ja)
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小林　聡雄
中村　尚道
伊都也 佐藤
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Ｊｆｅスチール株式会社
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Priority to JP2017500094A priority Critical patent/JP6112283B1/en
Priority to KR1020187008471A priority patent/KR102090035B1/en
Publication of WO2017056512A1 publication Critical patent/WO2017056512A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/14—Treatment of metallic powder
    • B22F1/142—Thermal or thermo-mechanical treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2201/00—Treatment under specific atmosphere
    • B22F2201/01—Reducing atmosphere
    • B22F2201/013—Hydrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2203/00—Controlling
    • B22F2203/11—Controlling temperature, temperature profile

Definitions

  • the present invention relates to a method for producing an alloy steel powder for powder metallurgy by reducing atomized iron base powder to produce an alloy steel powder for powder metallurgy, and in particular, the atomized iron base powder contains an easily oxidizable alloy element such as Cr.
  • the present invention relates to a method for producing alloy steel powder for powder metallurgy that can effectively reduce the C (carbon) content and the O (oxygen) content in the alloy steel powder even if contained.
  • Powder metallurgy technology allows parts with complex shapes to be manufactured in a shape very close to the product shape (so-called near net shape) and with high dimensional accuracy. Therefore, if a part is produced using powder metallurgy technology, the cutting cost can be greatly reduced. For this reason, powder metallurgy products to which powder metallurgy technology is applied are used in various fields as various machine parts. Recently, there has been a strong demand for improving the strength of powder metallurgy products in order to reduce the size and weight of parts. In particular, there is a demand for higher strength in iron-based powder metallurgy products (iron-based sintered bodies). Is strong.
  • an alloy element is added to the iron-based powder used in powder metallurgy.
  • the alloy element for example, Cr, Mn, and Mo are used because they have a high effect of improving hardenability and are relatively inexpensive.
  • V is used as an alloy element in order to improve high temperature strength and wear resistance.
  • Examples of the alloy powder for powder metallurgy containing the above alloy elements include Cr—Mo alloy steel powder (Patent Document 1), Cr—Mn—Mo alloy steel powder (Patent Document 2, Patent Document 3), Cr—Mn—Mo—V alloy steel powder (Patent Document 4) is known.
  • heat treatment is performed to reduce the C content and O content in the iron-based powder as a raw material.
  • the heat treatment is generally carried out continuously using a moving bed furnace (moving bed furnace).
  • the iron-based powder include a crude iron-based powder that has been atomized and a roughly reduced iron obtained by roughly reducing a mill scale.
  • a crude iron-based powder such as a base powder is used.
  • at least one treatment of decarburization, deoxidation, and denitrification is performed according to the use of the powder.
  • an apparatus described in Patent Document 5 As an apparatus for performing the above heat treatment, for example, an apparatus described in Patent Document 5 is known.
  • the space in the moving bed furnace is divided into a plurality of partitions by a partition wall provided so as to be perpendicular to the traveling direction of the raw material powder.
  • the flow path for flowing atmospheric gas is provided in the upper part of each divided
  • the heat treatment is continuously performed while flowing the atmospheric gas countercurrently, that is, in a direction opposite to the traveling direction of the raw material powder.
  • Patent Document 5 a heat treatment method as described in Patent Document 5 is used to reduce the C content and O content.
  • it contains elements such as Cr and Mn (hereinafter referred to as “easily oxidizable elements”) that are more easily oxidized than Fe. Therefore, when an iron-based powder containing Cr or Mn is produced by an atomizing method (particularly, a water atomizing method), the obtained iron-based powder contains an oxide formed by oxidation of Cr or Mn during atomization. It will be. The oxide remains without being sufficiently reduced even in the heat treatment.
  • Cr and Mn are further oxidized during the heat treatment, and the amount of oxide is increased.
  • the C content and the O content are large, the compressibility of the alloy steel powder at the time of pressure forming is lowered, so that a large amount of oxide remains is a problem.
  • V used as an alloy element in Patent Document 4 has a property of being more easily oxidized than Cr and Mn. Therefore, V oxide contained in the atomized iron-based powder is removed by a normal heat treatment. It is difficult. Therefore, in Patent Document 4, costly vacuum reduction is performed.
  • Patent Document 6 and Patent Document 7 propose a method that enables decarburization and deoxidation in the production of alloy steel powder containing easily oxidizable elements such as Cr and Mn.
  • the method proposed in Patent Document 7 is a method in which heat treatment is continuously performed using a belt furnace, and thus is suitable for mass production.
  • it is essential to continuously measure the CO or CO 2 concentration or the oxygen potential (O 2 concentration or H 2 / H 2 O concentration ratio) in the atmospheric gas during the heat treatment, Furthermore, it is necessary to adjust the amount of water vapor injected into the furnace so that these measured values become target values.
  • the sensor part is soiled and the gas intake port is clogged, making it impossible to perform measurement normally. There's a problem. Therefore, when the method of Patent Document 7 is continuously performed, maintenance of the analyzer is a heavy burden.
  • the present invention has been made in view of the above circumstances, and is a method for producing alloy steel powder for powder metallurgy using a moving bed furnace, without requiring gas analysis that requires complicated maintenance management, To provide a method for producing an alloy steel powder for powder metallurgy that can heat-treat an iron-based powder containing an easily oxidizable element such as Cr, Mn, V, and stably reduce the C content and the O content. With the goal.
  • the gist of the present invention is as follows. 1. % By mass C: 0.8% or less, O: 1.0% or less, S: 0.3% or less, P: 0.03% or less, and as an alloy element, Mn: more than 0.08% and 1.0% or less, Cr: 0.3 to 3.5%, 1 or 2 or more selected from the group consisting of Mo: 0.1-2% and V: 0.1-0.5%, Prepare the remaining Fe and atomized iron-based powder which is an inevitable impurity, Supplying the atomized iron-based powder into a moving bed furnace so as to form a packed bed of thickness d (mm); In the moving bed furnace, an inert gas is supplied so as to have an average gas flow velocity v (mm / s), The atomized iron-based powder is reduced by heat treatment in the moving bed furnace to obtain an alloy steel powder for powder metallurgy, a method for producing an alloy steel powder for powder metallurgy, Said d and v satisfy
  • an alloy steel powder containing oxidizable elements such as Cr, Mn, and V is heat-treated using a moving bed furnace without performing gas analysis that requires complicated maintenance and management. , C content and O content can be stably reduced. As a result, it is possible to produce alloy steel powder that is low in cost and excellent in compressibility during pressure forming.
  • sintered parts produced using the alloy steel powder for powder metallurgy obtained by the production method of the present invention have excellent mechanical properties such as strength, toughness and fatigue properties. Applications of powders and sintered bodies can be expanded.
  • FIG. 1 It is side sectional drawing which shows the example of the heat processing apparatus which can be used in one Embodiment of this invention. It is a figure which shows the example of the temperature pattern in the heat processing apparatus described in patent document 5.
  • FIG. 1 It is side sectional drawing which shows the example of the heat processing apparatus which can be used in one Embodiment of this invention. It is a figure which shows the example of the temperature pattern in the heat processing apparatus described in patent document 5.
  • alloy steel powder for powder metallurgy (hereinafter sometimes simply referred to as “alloy steel powder”) is produced by heat-treating atomized iron-based powder as a raw material using a moving bed furnace.
  • the production method of the present invention includes the following treatments; (1) Prepare atomized iron-based powder. (2) supplying the atomized iron-based powder into a moving bed furnace so as to form a packed bed having a thickness of d (mm); (3) by supplying an inert gas in the moving bed furnace so as to have an average gas flow velocity v (mm / s); and (4) by heat-treating the atomized iron-based powder in the moving bed furnace. Reduce to alloy steel powder for powder metallurgy.
  • Each of the above processes can be performed independently at an arbitrary timing, and a plurality of processes can be performed simultaneously.
  • the thickness d of the packed bed and the average gas flow velocity v must satisfy the above-described conditions.
  • the atomized iron-based powder is further mixed with a carbon component according to the C content and O content of the atomized iron-based powder, and then the moving bed Supply to the furnace.
  • atomized iron-based powder is used as a raw material.
  • the manufacturing method of the atomized iron-based powder is not particularly limited, and can be manufactured according to a conventional method.
  • “Atomized iron-based powder” means an iron-based powder produced by the atomizing method.
  • the “iron-based powder” means a powder containing 50% by mass or more of Fe.
  • the atomized iron-based powder either a gas atomized iron-based powder obtained by a gas atomizing method or a water atomized iron-based powder obtained by a water atomizing method can be used.
  • the gas atomization method it is preferable to use an inert gas such as nitrogen or argon.
  • gas since gas is inferior in cooling capacity compared to water, it is necessary to use a large amount of gas when producing iron-based powder by the gas atomization method. Therefore, it is preferable to use the water atomization method from the viewpoint of mass productivity and manufacturing cost.
  • the water atomization method is normally performed in an atmosphere in which air is mixed, the iron-based powder is more easily oxidized in the production process than the gas atomization method. Therefore, the method of the present invention is particularly effective when a water atomized iron-based powder is used.
  • C and O are elements to be reduced by a heat treatment described later. And from the viewpoint of improving the compressibility of the finally obtained alloy steel powder for powder metallurgy, it is desirable to reduce the C content and O content of the alloy steel powder as much as possible, specifically, C: 0.1% or less, O: 0.28% or less are preferable. In order to achieve these appropriate amounts of C and O, the amount that can be reduced by the heat treatment according to the present invention is anticipated, and the appropriate ranges of the C content and O content of the atomized iron-based powder are determined as follows.
  • C 0.8% or less C is present in the atomized iron-based powder mainly as a precipitate such as cementite or in a solid solution state.
  • the C content in the atomized iron-based powder exceeds 0.8%, it becomes difficult to lower the C content to 0.1% or less in the heat treatment of the present invention, and an alloy powder having excellent compressibility is obtained. I can't. Therefore, the C content of the atomized iron-based powder is set to 0.8% or less.
  • the lower the C content the easier the reduction (decarburization) of the C content during heat treatment. Therefore, the lower limit of the C content is not particularly limited, and may be 0% or industrially greater than 0%.
  • O 1.0% or less O is mainly present on the surface of the iron-based powder as Cr oxide, Mn oxide, V oxide, and Fe oxide. If the O content in the atomized iron-based powder exceeds 1.0%, it becomes difficult to reduce the O content to 0.28% or less during heat treatment, and an alloy powder having excellent compressibility cannot be obtained. Therefore, the O content of the atomized iron-based powder is set to 1.0% or less. The O content is preferably 0.9% or less. On the other hand, the lower the O content, the easier the reduction (deoxidation) of the O content during heat treatment. Therefore, the lower limit of the O content is not particularly limited, but excessive reduction leads to an increase in manufacturing cost, so the O content is preferably 0.4% or more.
  • the contents of S, P, Cr, Mn, Mo, and V are not changed by the heat treatment of the present invention. Therefore, these elements contained in the atomized iron-based powder remain as they are in the alloy steel powder for powder metallurgy after the heat treatment. Based on this, the contents of these elements in the atomized iron-based powder are respectively defined as follows.
  • the S content in the alloy steel powder is 0.3% or less.
  • the S content in the atomized iron-based powder stage is made 0.3% or less.
  • the S content is preferably set to 0.25% or less.
  • the lower limit of the S content is not particularly limited and may be 0%, but industrially it may be more than 0%. From the viewpoint of improving the machinability after sintering, the S content is preferably 0.05% or more.
  • P 0.03% or less
  • P is an element contained as one of inevitable impurities.
  • the P content of the atomized iron-based powder is set to 0.03% or less.
  • the lower limit of the P content is not particularly limited and may be 0%, but industrially it may be more than 0%. However, excessive reduction leads to an increase in manufacturing cost, so the P content is preferably 0.0005% or more.
  • the atomized iron-based powder in the present invention contains one or more selected from the group consisting of Mn, Cr, Mo, and V in addition to the above components.
  • Mn more than 0.08% and not more than 1.0% Mn is an element having an action of improving the strength of the sintered body by improving hardenability and strengthening solid solution.
  • Mn content shall be over 0.08%.
  • the Mn content is preferably 0.10% or more.
  • the Mn content is higher than 1.0%, the amount of Mn oxide generated increases, and the compressibility of the alloy steel powder decreases. Further, the Mn oxide serves as a starting point for destruction inside the sintered body, and reduces fatigue strength and toughness. Therefore, the Mn content is 1.0% or less.
  • the Mn content is preferably 0.95% or less, and more preferably 0.80% or less.
  • Cr 0.3-3.5%
  • Cr is an element that has the effect of improving hardenability and improving the tensile strength and fatigue strength of the sintered body. Further, Cr has the effect of increasing the hardness after heat treatment such as quenching and tempering of the sintered body and improving the wear resistance. When adding Cr, in order to acquire these effects, Cr content shall be 0.3% or more. On the other hand, when the Cr content exceeds 3.5%, the amount of Cr oxide generated increases. Since the Cr oxide serves as a starting point for fatigue failure inside the sintered body, the fatigue strength of the sintered body is reduced. Therefore, the Cr content is 3.5% or less.
  • Mo 0.1-2%
  • Mo is an element having an action of improving the strength of the sintered body by improving hardenability, solid solution strengthening, precipitation strengthening, and the like.
  • Mo content shall be 0.1% or more.
  • the content of Mo exceeds 2%, the toughness of the sintered body decreases. Therefore, the Mo content is 2% or less.
  • V 0.1-0.5%
  • V is an element having an action of improving the strength of the sintered body by improving hardenability, solid solution strengthening, precipitation strengthening, and the like.
  • V content shall be 0.1% or more.
  • the V content exceeds 0.5%, the toughness of the sintered body decreases. Therefore, the V content is 0.5% or less.
  • the component composition of the atomized iron-based powder in the present invention is composed of the above elements, the remainder Fe and inevitable impurities.
  • the C content [C] (mass%) of the atomized iron base powder and the O content [O] (mass%) of the atomized iron base powder satisfy the following formula (2). There is a need. [O] ⁇ 4/3 [C] -2/15 (2)
  • the C content [C] (mass%) of the atomized iron-based powder and the O content [O] (mass%) of the atomized iron-based powder satisfy the following formula (2):
  • the amount of C in the powder can be reduced to a sufficiently low amount, for example, 0.1% by mass or less.
  • a carbon component is further mixed with the atomized iron-based powder as necessary.
  • the atomized iron base powder is used as it is in the moving bed furnace.
  • “Supply as it is” means that only the atomized iron-based powder is supplied to the moving bed furnace without being mixed with other components such as a carbon component. 4/3 [C] + 0.28 ⁇ [O] (3)
  • the method of adjusting C content and O content of atomized iron-based powder is not specifically limited, Arbitrary methods can be used. For example, what is necessary is just to adjust the component composition of the molten steel used for manufacture of an atomized iron base powder so that C content and O content of atomized iron base powder may satisfy the said conditions. Adjustment of the composition of the molten steel can be performed by a steel refining and steelmaking technique using a general converter.
  • the atomized iron-based powder if the atomized iron-based powder is as-atomized and satisfies the conditions of the above formulas (2) and (3), the atomized iron-based powder can be directly subjected to heat treatment. This is preferable because it is possible. However, if the C content in the atomized iron-based powder becomes excessive and the condition of the formula (2) is not satisfied, the adjustment before the heat treatment cannot be performed to satisfy the formula (2). Therefore, when producing atomized iron-based powder, it is necessary to satisfy the formula (2), and oxygen is allowed to be excessive for that purpose. This is because even if oxygen is excessive and the formula (3) is not satisfied, the amount of C and O in the final alloy steel powder can be reduced by adding the carbon component as described above.
  • the average particle size of the atomized iron-based powder is not particularly limited, and any particle size can be used as long as it is an iron-based powder obtained by the atomization method.
  • the average particle size of the atomized iron-based powder is less than 30 ⁇ m, the fluidity of the atomized iron-based powder is lowered, and it may be difficult to supply to the moving bed furnace using a hopper or the like.
  • the average particle size of the atomized iron-based powder is less than 30 ⁇ m, the fluidity of the alloy steel powder after heat treatment also decreases, so the work efficiency of filling the mold when the alloy steel powder is press-formed decreases. There is a case.
  • the average particle size of the atomized iron-based powder is preferably 30 ⁇ m or more, more preferably 40 ⁇ m or more, and even more preferably 50 ⁇ m or more.
  • the average particle size of the atomized iron-based powder is preferably 120 ⁇ m or less, more preferably 100 ⁇ m or less, and even more preferably 90 ⁇ m or less.
  • the average particle diameter means a median diameter (so-called d50, volume basis).
  • the apparent density of the atomized iron-based powder is not particularly limited, but is preferably 2.0 to 3.5 Mg / m 3 , more preferably 2.4 to 3.2 Mg / m 3 .
  • Atomized iron-based powder having the above component composition is supplied to a moving bed furnace, and a packed bed having a thickness d (mm) is formed on the moving bed of the moving bed furnace.
  • a moving bed furnace any one can be used as long as it can heat treat the atomized iron-based powder, but a moving bed furnace (hereinafter referred to as a “belt type moving bed furnace” or “ It is preferable to use a belt furnace).
  • a moving bed furnace hereinafter referred to as a “belt type moving bed furnace” or “ It is preferable to use a belt furnace).
  • an atomized iron-based powder can be supplied onto the belt to form a packed bed.
  • the atomized iron-based powder can be supplied by any method, but it is preferable to use a hopper.
  • the conveyance direction of the atomized iron-based powder in the moving bed furnace is not particularly limited, but it is generally conveyed linearly from the inlet side to the outlet side of the moving bed furnace. The thickness of the fill
  • the heating system of the moving bed furnace is not particularly limited, and any system can be used as long as it can heat the atomized iron-based powder.
  • the indirect heating system is used. It is preferable to use heating using a radiant tube.
  • a muffle furnace can also be suitably used as an indirect heating furnace.
  • Patent Document 5 As the moving bed furnace, a moving bed furnace as described in Patent Document 5 can be used. Therefore, the moving bed furnace in Patent Document 5 will be described below for reference. However, the atomized iron-based powder and the atmospheric gas used in the present invention are different from the processing in Patent Document 5 described below. The atomized iron-based powder and atmospheric gas used in the present invention will be described later.
  • Patent Document 5 it is assumed that one or more processes of decarburization, deoxidation, or denitrification are continuously performed by using a continuous moving bed furnace to heat-treat the iron-based powder. Further, in the description of Patent Document 5, each of the decarburization, deoxidation, and denitrification treatment steps is made independent using the divided space of the moving bed furnace, and the decarburization step is performed at 600 to 1100 ° C. In the denitrification process, the iron-base powder is heat-treated by controlling the temperature independently at 450 to 750 ° C.
  • Patent Document 5 as an atmospheric gas, a reducing gas such as H 2 or AX gas at decarburization zone or an inert gas such as N 2 or Ar, reduction such as H 2 or AX gas in deoxidation zone It is said that gas mainly composed of H 2 is used in the denitrification zone.
  • FIG. 1 A heat treatment apparatus 100 shown in FIG. 1 is provided on a furnace body 30 divided into a plurality of zones by a partition wall 1, that is, a decarburization zone 2, a deoxidation zone 3, and a denitrification zone 4, and an entrance side of the furnace body 30.
  • the hopper 8 is provided, a wheel 10 provided on the entrance / exit side of the furnace body 30, a belt 9 that continuously rotates by the wheel 10 and circulates in each zone in the furnace body 30, and a radiant tube 11.
  • the product powder 13 is stored in the product tank 14.
  • the reaction in each zone is considered as follows.
  • the ambient temperature is controlled to 600 to 1100 ° C. by the radiant tube 11, and water vapor (H 2 O gas) introduced from the water vapor inlet 12 provided on the downstream side of the decarburization zone 2
  • water vapor H 2 O gas
  • decarburization is performed from the crude iron-based powder while adjusting the atmospheric gas in the deoxidation zone 3 as the next zone to a dew point of 30 to 60 ° C.
  • an atmospheric gas discharge port 6 is provided to discharge the atmospheric gas to the outside of the apparatus.
  • the decarburization reaction formula is represented by the following formula (I).
  • C (in Fe) + H 2 O (g) CO (g) + H 2 (g) (I)
  • the ambient temperature is controlled to 700 to 1100 ° C. by the radiant tube 11, and deoxidation is performed from the crude iron-based powder using the atmospheric gas from the denitrification zone 4 (dew point: hydrogen gas of 40 ° C. or less). Is going to do.
  • the ambient temperature is controlled to 450 to 750 ° C. by the radiant tube 11, and hydrogen gas (dew point: 40 ° C.) as a reaction gas is supplied from the atmosphere gas inlet 5 provided on the downstream side of the denitrification zone 4.
  • hydrogen gas dew point: 40 ° C.
  • the following is introduced to denitrify the crude iron-based powder.
  • the water sealing tank 15 functions to block the mixing of the outside gas into the furnace gas and the leakage of the inside gas to the outside of the furnace.
  • FIG. 5 a typical example of a heat treatment temperature pattern by a belt furnace type heat treatment apparatus described in Patent Document 5 is shown in FIG.
  • the iron-based powder to be treated is first heated in the decarburization zone, then soaked in the deoxidation zone, and finally in the denitrification zone.
  • the hydrogen gas introduced in the direction opposite to the flow of the iron-based powder first enters the denitrification zone, denitrifies the iron-based powder while being heated, and then enters the deoxidation zone and is kept at a constant temperature.
  • the iron-base powder is deoxidized while finally entering the decarburization zone together with a predetermined amount of water vapor, and the iron-base powder is decarburized while being cooled.
  • the inert gas is not particularly limited, and any inert gas can be used.
  • the inert gas that can be suitably used include argon (Ar) gas, nitrogen (N 2 ) gas, and a mixed gas thereof.
  • the inert gas is supplied into the moving bed furnace so as to have an average gas flow velocity v (mm / s) during the heat treatment of the atomized iron-based powder in the moving bed furnace.
  • the inert gas is preferably flowed in the moving bed furnace in a direction opposite to the moving direction of the raw material powder.
  • a conveying means such as a belt
  • the inert gas is introduced from the other end (downstream side) and exhausted from the one end (upstream side). Therefore, it is preferable that the moving bed furnace is provided with an atomized iron-based powder supply port and an atmosphere gas discharge port at one end, and a discharge port and an inert gas supply port for treated powder (alloy steel powder) at the other end.
  • the alloy steel powder for powder metallurgy can be obtained by heat-treating the atomized iron-based powder in the moving bed furnace with the inert gas supplied as described above. By the heat treatment, C and O contained in the atomized iron-based powder are removed by a decarburization and deoxidation (reduction) reaction described later.
  • both the thickness d (mm) of the packed bed and the average gas flow velocity v (mm / s) are controlled so as to satisfy the following expression (1).
  • the heat treatment By performing the heat treatment under the above conditions, it is possible to stably reduce C and O contained in the atomized iron-based powder in spite of the fact that the atomized iron-based powder contains oxidizable elements such as Cr, Mn, and V. it can. As a result, the C content and the O content in the alloy steel powder after the heat treatment can be set to extremely low values such as C ⁇ 0.1% and O ⁇ 0.28%. The reason will be described below.
  • the thickness d of the packed bed and the average gas flow velocity v in the furnace when the inert gas is introduced into the furnace are controlled so as to satisfy the above formula (1).
  • a velocity boundary layer of the flowing inert gas is formed in the space above the surface of the packed bed. It is derived from the theory regarding the boundary layer that the thickness of the velocity boundary layer is inversely proportional to ⁇ v. Further, since the diffusion rate of CO generated by the reduction reaction is considered to be constant regardless of the thickness of the velocity boundary layer, the diffusion time is proportional to the thickness of the velocity boundary layer. Therefore, if the velocity boundary layer thickness is halved and the same diffusion time is given, it is considered that the concentration of CO on the surface of the packed layer is halved. Then, even if the thickness of the packed layer is doubled, It is estimated that the CO concentration in the lowermost layer can be made the same.
  • the packed layer thickness and the velocity boundary layer thickness are inversely proportional, that is, it is estimated that the packed layer thickness and ⁇ v are in a proportional relationship. Therefore, as in the present invention, in the heat treatment, if the packed layer thickness and the gas flow rate are adjusted so that the condition of d / ⁇ v ⁇ 3.0 is satisfied, a gas analyzer that requires complicated maintenance management is required. Even if it is not used, the state in which the CO partial pressure in the furnace atmosphere is lower than the equilibrium CO partial pressure determined by the reactions of the above formulas (a) to (d) is maintained.
  • the lower limit of d / ⁇ v is not particularly limited. The lower the better, the lower the better. However, if d is excessively decreased, the production efficiency decreases, and if v is excessively increased, the cost increases. It is preferable to set it as the above, and it is more preferable to set it as 0.3 or more.
  • the atomized iron-based powder reduced by the heat treatment is further cooled using hydrogen gas or a hydrogen-containing gas.
  • the reason is as follows.
  • the reduced atomized iron-based powder may contain N as an impurity.
  • the N content of the finally obtained alloy steel powder for powder metallurgy may be as high as exceeding 0.005% by mass. .
  • the alloy steel powder contains N, the compressibility is lowered. Therefore, it is preferable to reduce the N content of the alloy steel powder as much as possible. Therefore, if the reduced atomized iron-based powder is cooled using hydrogen gas or a hydrogen-containing gas, N contained in the powder can be removed by the reaction of the following formula (e).
  • N content of the alloy steel powder for powder metallurgy finally obtained shall be 0.005 mass% or less.
  • the gas used for the cooling may be supplied by any method.
  • the inert gas in the moving bed furnace is exhausted at the position where the reduction of the iron-based powder in the moving bed furnace is completed, or at the downstream side in the transport direction from the position, and the cooling gas is transferred to the moving bed furnace. It can be introduced into the furnace.
  • the timing exhaust and introduction position in the moving bed furnace
  • the atmosphere gas can be replaced.
  • C that should be used for reduction of Cr 2 O 3 and MnO reacts with water vapor in the atmosphere and is consumed, or once reduced Cr and Mn are in the atmosphere This is because it is reoxidized by water vapor. In order to efficiently advance the reduction reaction in the heat treatment, it is necessary to suppress such wasteful consumption of C and reoxidation of Cr and Mn.
  • the dew point of the inert gas is set to 5 ° C. or less.
  • the dew point of the inert gas is preferably 5 ° C. or less, more preferably ⁇ 10 ° C. or less as described above.
  • the dew point of the inert gas The lower the dew point of the inert gas, the better the deoxidation reaction will proceed.
  • a gas with a low dew point is expensive, and the use of a gas with an excessively low dew point causes an increase in production cost. Therefore, it is usually preferable to set the dew point to ⁇ 40 ° C. or higher.
  • the moving bed furnace includes a sealing unit for preventing gas leakage and intrusion.
  • a sealing unit for example, a water-sealed tank (15 in FIG. 1) as described in Patent Document 5 can be used, but it is more preferable to use a system that does not use water such as a seal roll.
  • the sealing means is preferably provided at both ends on the upstream side and the downstream side in the transport direction.
  • the atmospheric temperature is preferably set to 1080 ° C. or higher.
  • the upper limit of the ambient temperature is not particularly limited, but is preferably about 1200 ° C. in consideration of the heat resistance performance of the apparatus, the manufacturing cost, and the like.
  • the “atmosphere temperature” is a temperature measured by a thermocouple at a position 20 mm immediately above the surface of the iron-based powder (packed bed) in the moving bed furnace.
  • Holding time t 10 4 -0.0037 ⁇ T (h) or more If the holding time t is 10 4 -0.0037 ⁇ T (h) or more according to the ambient temperature T (° C.), O Since it can reduce more, it is preferable.
  • the relationship between the said t and T was determined from the result of having conducted the experiment which manufactures alloy steel powder with various T and t. Specifically, the O content of the obtained alloy steel powder was plotted on a Tt diagram, and a curve (contour line) connecting the same oxygen content was determined as an approximate expression.
  • the upper limit of the retention time is not particularly limited, but the retention time is preferably 4 hours or less because the production cost only increases even if the retention time is longer than the time required for completion of the deoxidation reaction.
  • Example 1 An atomized iron-based powder having the component composition shown in Table 1 was produced by the water atomization method. Atomized iron-based powder symbols: A, B, F, I, and M satisfy [O] ⁇ 4/3 [C] ⁇ 2/15, but 4/3 [C] + 0.28 ⁇ [ O] is not satisfied, and O is excessive. Therefore, in order to adjust the C amount and O amount after heat treatment to an appropriate range, an appropriate amount of carbon component, for example, carbon powder such as graphite powder is adjusted before heat treatment. Mixing is necessary.
  • Atomized iron-based powder symbols C to E, G, H, and J satisfy both [O] ⁇ 4/3 [C] ⁇ 2/15 and 4/3 [C] + 0.28 ⁇ [O] It is not necessary to mix carbon powder before heat treatment.
  • the atomized iron-based powder is supplied into the moving bed furnace so as to have the packed bed thickness d shown in Tables 2 and 3, and the average gas flow velocity v shown in Tables 2 and 3 is obtained.
  • the heat treatment was continuously performed while supplying the inert gas.
  • the component composition of the obtained alloy steel powder for powder metallurgy was as shown in Tables 2 and 3.
  • surface and the following description means vol%.
  • Table 2 is an example at the time of using Ar containing gas as an inert gas.
  • powder symbols: A and I that are not mixed with carbon powder (powder symbols: A10, I10), the atomized iron-based powder is O-excess, so these can be obtained even after the heat treatment conditions are adjusted appropriately. The amount of O after heat-treating is out of the proper value. Therefore, for the atomized iron-based powder symbols: A and I, it is necessary to mix an appropriate amount of carbon powder that satisfies 4/3 ([C] + [MXC]) + 0.28 ⁇ [O].
  • the inert gas is 100% Ar and d / ⁇ v ⁇ 2.6 (powder symbols: A11 to A13, A16, B13 to B15, C11 to C14, D11 to D14, E11 to E13, F11, G11, For H11, I11, J11), the C content is 0.1% by mass or less and the O content is 0.23% by mass or less. Since the O content is further reduced, d / ⁇ v ⁇ 2.6. It is preferable that
  • the introduced gas was changed from 100% Ar to 50% Ar-50% N 2 , and in each case, the O amount was 0.28% by mass or less.
  • powder symbols: C11 to C14 good values were obtained with a dew point of 5 ° C. or less (powder symbols: C12 to C14) and an O amount of 0.20 mass% or less. Further, when the dew point is ⁇ 10 ° C. or lower (powder symbol: C14), the amount of O is 0.15% by mass or lower, which is a much better value. Further, for powder symbols D11 to D13 and E11 to E13, the soaking temperature is 1080 ° C. or higher and t ⁇ 10 4 ⁇ 0.0037 ⁇ T is satisfied (powder symbols: D13 to D14, E13) and the amount of O is An even better value of 0.20% by mass or less is obtained.
  • the amount of C and O in the atomized iron-based powder is [O] ⁇ 4/3 [C] ⁇ 2 / Since both 15 and 4/3 [C] + 0.28 ⁇ [O] are satisfied, the heat treatment can be performed by treating in an inert gas atmosphere using appropriate heat treatment conditions without mixing the carbon powder before the heat treatment. It shows that appropriate values are obtained for the subsequent C and O amounts.
  • the amount of C and O in the atomized iron-based powder does not satisfy [O] ⁇ 4/3 [C] ⁇ 2/15 and is excessive C. This shows that the amount of C after the heat treatment is out of the proper range even if the treatment is performed under the conditions.
  • the C amount or O amount of the atomized iron-based powder is too high, and therefore the C amount or O amount cannot be reduced to the specified amount even by heat treatment.
  • ⁇ N 2 containing case Table 3 using the gas is an example of a case of performing heat treatment in an N 2 containing atmosphere.
  • Atomized iron-based powder symbol: A, B, F and I are O-excessive, so an appropriate amount of carbon powder satisfying 4/3 ([C] + [MXC]) + 0.28 ⁇ [O] Mixing is necessary.
  • examples of mixing graphite powder as shown in Table 3 and treating under various heat treatment conditions are powder symbols: A21 to A28, B21 to B25, C21 to C24, D21 to D24, E21 to E23, F21. , G21, H21, I21, J21.
  • the relationship between the packed bed thickness d (mm) of the iron powder and the flow velocity v (mm / s) of the inert gas satisfies d / ⁇ v ⁇ 3.0 (powder symbol: A21 -A24, A26-A28, B22-B25, C21-C24, D21-D24, E21-E23, F21, G21, H21, I21, J21), the amount of O is 0.28% by mass or less. In addition, for those not satisfying d / ⁇ v ⁇ 3.0 (powder symbols: A25, B21), the amount of O exceeds 0.28% by mass.
  • the introduced gas is 100% N 2 and d / ⁇ v ⁇ 2.6 (powder symbols: A21 to A23, A26, B23 to B25, C21 to C24, D21 to D24, E21 to E23, F21, G21, For H21, I21, J21), the C amount is 0.1% by mass or less, the O amount is 0.23% by mass or less, and the O amount is further reduced. It can be seen that the relationship with the flow velocity v (mm / s) of the inert gas is preferably d / ⁇ v ⁇ 2.6.
  • the introduced gas was changed from 100% N 2 to 90% N 2 -10% He, and in each case, the O amount was 0.28% by mass or less. .
  • powder symbols: C21 to C24 those having a dew point of 5 ° C. or less (powder symbols: C22 to C24) and an O amount of 0.20% by mass or less are good values. Further, when the dew point is ⁇ 10 ° C. or less (powder symbol: C24), the amount of O is 0.15% by mass or less, which is a much better value. Furthermore, powder symbols: D21 to D24 and E21 to E23 satisfy the condition of t ⁇ 10 4 ⁇ 0.0037 ⁇ T when the soaking temperature is 1080 ° C. or more (powder symbols: D23 to D24, E23). An even better value of 0.20% by mass or less is obtained.
  • the amount of C and O in the atomized iron-based powder is [O] ⁇ 4/3 [C] -2 / Since both 15 and 4/3 [C] + 0.28 ⁇ [O] are satisfied, it is possible to reduce the C amount and O after the heat treatment by reducing the carbon powder before the heat treatment under appropriate heat treatment conditions. It shows that an appropriate value is obtained for the amount.
  • Example 2 Of the atomized iron-based powders in Table 1, A and J were reduced by heat treatment using N 2 as an inert gas. Table 4 shows the processing conditions. At that time, the atomized iron-based powder A was mixed with the amount of graphite powder shown in Table 4 and then supplied to the moving bed furnace. On the other hand, the atomized iron-based powder J was supplied as it was (only the atomized iron-based powder J) to the moving bed furnace without being mixed with the graphite powder.
  • the inert gas in the moving bed furnace was exhausted and H 2 gas was supplied, and the reduced powder was cooled in the H 2 gas atmosphere (A31, J31). After cooling, the obtained powder was crushed to obtain alloy steel powder for powder metallurgy.
  • the component composition of the obtained alloy steel powder is shown in Table 4.
  • the heat treatment conditions of A23 and J21 in Example 1 and the component composition of the alloy steel powder are also shown in Table 4. In A23 and J21, the cooling after the reduction is performed in an N 2 atmosphere.
  • N as an impurity contained in the alloy steel powder can be further reduced by cooling the reduced atomized iron-based powder using hydrogen gas or a hydrogen-containing gas.

Abstract

Provided is a method for producing an alloy steel powder for powder metallurgy. The method uses a moving bed furnace and, without the need for gas analysis, which makes cumbersome maintenance necessary, makes it possible to heat treat an iron-based powder that contains easily-oxidized elements such as Cr, Mn, and V and stably reduce C content and O content. A production method for an alloy steel powder for powder metallurgy wherein an atomized iron-based powder that has a specific component composition is prepared, wherein the atomized iron-based powder, after being mixed with a carbon component as necessary, is supplied to the inside of a moving bed furnace such that a filling layer that has a thickness of d (mm) is formed, wherein an inert gas is supplied to the inside of the moving bed furnace such that the inert gas has an average gas flow velocity of v (mm/s), and wherein the atomized iron-based powder is reduced by being heat treated inside the moving bed furnace and an alloy steel powder for powder metallurgy is produced, wherein d and v satisfy the expression d/√v ≤ 3.0 (mm1/2∙s1/2).

Description

粉末冶金用合金鋼粉の製造方法Method for producing alloy steel powder for powder metallurgy
　本発明は、アトマイズ鉄基粉末を還元して粉末冶金用合金鋼粉とする、粉末冶金用合金鋼粉の製造方法に関し、特に、前記アトマイズ鉄基粉末が、Ｃｒなどの酸化されやすい合金元素を含有していても、合金鋼粉中のＣ（炭素）含有量およびＯ（酸素）含有量を効果的に下げることができる粉末冶金用合金鋼粉の製造方法に関する。 The present invention relates to a method for producing an alloy steel powder for powder metallurgy by reducing atomized iron base powder to produce an alloy steel powder for powder metallurgy, and in particular, the atomized iron base powder contains an easily oxidizable alloy element such as Cr. The present invention relates to a method for producing alloy steel powder for powder metallurgy that can effectively reduce the C (carbon) content and the O (oxygen) content in the alloy steel powder even if contained.
　粉末冶金技術は、複雑な形状の部品を、製品形状に極めて近い形状（いわゆるニアネット形状）で、しかも高い寸法精度で製造することができる。よって、粉末冶金技術を用いて部品を作製すると、大幅な切削コストの低減が可能となる。このため、粉末冶金技術を適用した粉末冶金製品は、各種の機械用部品として、多方面に利用されている。さらに、最近では、部品の小型化、軽量化のために、粉末冶金製品の強度の向上が強く要望されており、特に、鉄基粉末冶金製品（鉄基焼結体）に対する高強度化の要求が強い。 Powder metallurgy technology allows parts with complex shapes to be manufactured in a shape very close to the product shape (so-called near net shape) and with high dimensional accuracy. Therefore, if a part is produced using powder metallurgy technology, the cutting cost can be greatly reduced. For this reason, powder metallurgy products to which powder metallurgy technology is applied are used in various fields as various machine parts. Recently, there has been a strong demand for improving the strength of powder metallurgy products in order to reduce the size and weight of parts. In particular, there is a demand for higher strength in iron-based powder metallurgy products (iron-based sintered bodies). Is strong.
　この高強度化の要求に応じるため、粉末冶金に用いられる鉄基粉末に対して合金元素が添加される。前記合金元素としては、例えば、焼入れ性向上効果が高く、比較的安価であることから、Ｃｒ、Ｍｎ、Ｍｏが使用される。また、高温強度や耐摩耗性を向上させるためには、Ｖが合金元素として使用される。 In order to meet this demand for higher strength, an alloy element is added to the iron-based powder used in powder metallurgy. As the alloy element, for example, Cr, Mn, and Mo are used because they have a high effect of improving hardenability and are relatively inexpensive. In addition, V is used as an alloy element in order to improve high temperature strength and wear resistance.
　上記のような合金元素を含む粉末冶金用合金粉としては、例えば、Ｃｒ－Ｍｏ系合金鋼粉（特許文献１）、Ｃｒ－Ｍｎ－Ｍｏ系合金鋼粉（特許文献２、特許文献３）、Ｃｒ－Ｍｎ－Ｍｏ－Ｖ系合金鋼粉（特許文献４）が知られている。 Examples of the alloy powder for powder metallurgy containing the above alloy elements include Cr—Mo alloy steel powder (Patent Document 1), Cr—Mn—Mo alloy steel powder (Patent Document 2, Patent Document 3), Cr—Mn—Mo—V alloy steel powder (Patent Document 4) is known.
　また、粉末冶金用鉄基粉末の製造においては、原料としての鉄基粉末中のＣ含有量およびＯ含有量を低減するために熱処理が行われる。前記熱処理は、一般的に移動床炉（moving bed furnace）を用いて連続的に実施され、前記鉄基粉末としては、アトマイズしたままの粗鉄基粉末や、ミルスケールを粗還元した粗還元鉄基粉末などの粗鉄基粉末が用いられる。そして、前記熱処理においては、粉末の用途に応じて、脱炭、脱酸、および脱窒の少なくとも１つの処理が行われる。 Also, in the production of iron-based powder for powder metallurgy, heat treatment is performed to reduce the C content and O content in the iron-based powder as a raw material. The heat treatment is generally carried out continuously using a moving bed furnace (moving bed furnace). Examples of the iron-based powder include a crude iron-based powder that has been atomized and a roughly reduced iron obtained by roughly reducing a mill scale. A crude iron-based powder such as a base powder is used. In the heat treatment, at least one treatment of decarburization, deoxidation, and denitrification is performed according to the use of the powder.
　上記熱処理を行うための装置としては、例えば、特許文献５に記載された装置が知られている。特許文献５に記載の装置では、原料粉末の走行方向に垂直となるように設けられた仕切壁によって、移動床炉内の空間が複数に分割されている。そして、分割された各空間の上部には、雰囲気ガスを流すための流路が設けられている。熱処理は、前記流路に、向流的に（countercurrently）、すなわち、原料粉末の走行方向と反対の方向に、雰囲気ガスを流しながら、連続的に行われる。 As an apparatus for performing the above heat treatment, for example, an apparatus described in Patent Document 5 is known. In the apparatus described in Patent Document 5, the space in the moving bed furnace is divided into a plurality of partitions by a partition wall provided so as to be perpendicular to the traveling direction of the raw material powder. And the flow path for flowing atmospheric gas is provided in the upper part of each divided | segmented space. The heat treatment is continuously performed while flowing the atmospheric gas countercurrently, that is, in a direction opposite to the traveling direction of the raw material powder.
特許第３２２４４１７号公報Japanese Patent No. 3224417 特許第５１２５１５８号公報Japanese Patent No. 5125158 特許第５３８９５７７号公報Japanese Patent No. 5,389,577 特開昭５５－０６２１０１号公報Japanese Patent Laid-Open No. 55-062101 特公平０１－４０８８１号公報Japanese Patent Publication No. 01-40881 特表２００２－５０１１２３号公報JP-T-2002-501123 特許第４２２５５７４号公報Japanese Patent No. 4225574
特許文献１～３に記載されているような合金元素を含む粉末冶金用合金粉の製造において、Ｃ含有量やＯ含有量を低減するために特許文献５に記載されているような熱処理法を用いた場合、次のような問題があった。すなわち、Ｆｅに比べて酸化されやすい性質を有するＣｒやＭｎといった元素（以下、「易酸化性元素」という）が含まれている。そのため、アトマイズ法（特に水アトマイズ法）によりＣｒやＭｎを含有する鉄基粉末を製造すると、得られた鉄基粉末にはアトマイズの際にＣｒやＭｎが酸化されてできた酸化物が含まれることとなる。前記酸化物は、前記熱処理においても十分に還元されることなく残留する。また、場合によっては、熱処理の際にさらにＣｒやＭｎが酸化され、かえって酸化物の量が増加する。一般にＣ含有量やＯ含有量が多いと加圧成形時における前記合金鋼粉の圧縮性が低下するので、酸化物が多く残留するのは問題である。 In the production of alloy powders for powder metallurgy containing alloy elements as described in Patent Documents 1 to 3, a heat treatment method as described in Patent Document 5 is used to reduce the C content and O content. When used, there were the following problems. That is, it contains elements such as Cr and Mn (hereinafter referred to as “easily oxidizable elements”) that are more easily oxidized than Fe. Therefore, when an iron-based powder containing Cr or Mn is produced by an atomizing method (particularly, a water atomizing method), the obtained iron-based powder contains an oxide formed by oxidation of Cr or Mn during atomization. It will be. The oxide remains without being sufficiently reduced even in the heat treatment. In some cases, Cr and Mn are further oxidized during the heat treatment, and the amount of oxide is increased. In general, when the C content and the O content are large, the compressibility of the alloy steel powder at the time of pressure forming is lowered, so that a large amount of oxide remains is a problem.
また、特許文献４において合金元素として用いられているＶは、ＣｒおよびＭｎよりもさらに酸化されやすい性質を有しているため、アトマイズ鉄基粉末に含まれるＶ酸化物を通常の熱処理によって除去することは困難である。そのため、特許文献４では、コストのかかる真空還元を行っていた。 In addition, V used as an alloy element in Patent Document 4 has a property of being more easily oxidized than Cr and Mn. Therefore, V oxide contained in the atomized iron-based powder is removed by a normal heat treatment. It is difficult. Therefore, in Patent Document 4, costly vacuum reduction is performed.
　そこで、特許文献６および特許文献７では、ＣｒおよびＭｎなどの易酸化性元素を含む合金鋼粉の製造の際に、脱炭や脱酸を可能とする方法が提案されている。 Therefore, Patent Document 6 and Patent Document 7 propose a method that enables decarburization and deoxidation in the production of alloy steel powder containing easily oxidizable elements such as Cr and Mn.
　しかし、特許文献６で提案されている処理方法では、気密性のバッチ炉を使用して、不活性ガス雰囲気下で熱処理が行われる。前記方法ではバッチ炉が用いられるため、ベルト炉を含む移動床炉を用いて連続的に熱処理を行う場合に比べて生産性が低く、したがって大量生産に不向きである。 However, in the treatment method proposed in Patent Document 6, heat treatment is performed in an inert gas atmosphere using an airtight batch furnace. Since a batch furnace is used in the method, the productivity is low as compared with the case where continuous heat treatment is performed using a moving bed furnace including a belt furnace, and thus is not suitable for mass production.
　一方、特許文献７で提案されている方法は、ベルト炉を用いて連続的に熱処理を行う方法であるため、量産に適している。しかし、前記方法では、熱処理を行う間、雰囲気ガス中のＣＯまたはＣＯ２濃度、あるいは酸素ポテンシャル（Ｏ２濃度またはＨ２／Ｈ２Ｏ濃度比）を連続的に測定することが必須であり、さらにこれらの測定値が目標の値になるよう炉内に注入する水蒸気量を調節する必要がある。このようなガス分析のための装置を、実際に、鉄粉等を製造する工場において連続的に使用する場合、センサー部分の汚れやガス取り込み口の詰まりが発生し、測定が正常に行えなくなるという問題がある。そのため、特許文献７の方法を連続的に実施する上で、分析装置の維持管理が大きな負担となる。 On the other hand, the method proposed in Patent Document 7 is a method in which heat treatment is continuously performed using a belt furnace, and thus is suitable for mass production. However, in the above method, it is essential to continuously measure the CO or CO 2 concentration or the oxygen potential (O 2 concentration or H 2 / H 2 O concentration ratio) in the atmospheric gas during the heat treatment, Furthermore, it is necessary to adjust the amount of water vapor injected into the furnace so that these measured values become target values. When such a device for gas analysis is actually used continuously in a factory that manufactures iron powder, etc., the sensor part is soiled and the gas intake port is clogged, making it impossible to perform measurement normally. There's a problem. Therefore, when the method of Patent Document 7 is continuously performed, maintenance of the analyzer is a heavy burden.
　本発明は、上記実状に鑑みてなされたものであり、移動床炉を用いた粉末冶金用合金鋼粉の製造方法であって、煩雑な維持管理が必要となるガス分析を必要とせずに、Ｃｒ、Ｍｎ、Ｖなどの易酸化性元素を含有する鉄基粉末を熱処理し、Ｃ含有量およびＯ含有量を安定して低減することができる粉末冶金用合金鋼粉の製造方法を提供することを目的とする。 The present invention has been made in view of the above circumstances, and is a method for producing alloy steel powder for powder metallurgy using a moving bed furnace, without requiring gas analysis that requires complicated maintenance management, To provide a method for producing an alloy steel powder for powder metallurgy that can heat-treat an iron-based powder containing an easily oxidizable element such as Cr, Mn, V, and stably reduce the C content and the O content. With the goal.
　本発明の要旨構成は次のとおりである。
１．質量％で、
　　Ｃ　：０．８％以下、
　　Ｏ　：１．０％以下、
　　Ｓ　：０．３％以下、
　　Ｐ　：０．０３％以下、ならびに
　　合金元素として、
　　　Ｍｎ：０．０８％超１．０％以下、
　　　Ｃｒ：０．３～３．５％、
　　　Ｍｏ：０．１～２％、および
　　　Ｖ　：０．１～０．５％、からなる群より選択される１または２以上
　を含有し、
　　残部Ｆｅおよび不可避不純物であるアトマイズ鉄基粉末を用意し、
　前記アトマイズ鉄基粉末を、厚さｄ（ｍｍ）の充填層を形成するように移動床炉内へ供給し、
　前記移動床炉内に、不活性ガスを平均ガス流速ｖ（ｍｍ／ｓ）となるように供給し、
　前記アトマイズ鉄基粉末を前記移動床炉内で熱処理することによって還元し、粉末冶金用合金鋼粉とする、粉末冶金用合金鋼粉の製造方法であって、
　前記ｄおよびｖが、下記（１）式を満足し
　前記アトマイズ鉄基粉末のＣ含有量［Ｃ］（質量％）と前記アトマイズ鉄基粉末のＯ含有量［Ｏ］（質量％）とが、下記（２）式を満足し、
　前記アトマイズ鉄基粉末の移動床炉への供給において、前記アトマイズ鉄基粉末のＣ含有量［Ｃ］およびＯ含有量［Ｏ］が下記（３）式を満たす場合には、該アトマイズ鉄基粉末をそのまま前記移動床炉に供給し、下記（３）式を満たさない場合には、下記（４）式を満足するように該アトマイズ鉄基粉末に炭素成分をさらに混合したのち、前記移動床炉に供給する、粉末冶金用合金鋼粉の製造方法。
　　　　　　　　　　　　記
　ｄ／√ｖ≦３．０（ｍｍ１／２・ｓ１／２）…（１）
　［Ｏ］≧４／３［Ｃ］－２／１５…（２）
　４／３［Ｃ］＋０．２８≧［Ｏ］…（３）
　４／３（［Ｃ］＋［ＭＸＣ］）＋０．２８≧［Ｏ］…（４）
（ここで、［ＭＸＣ］は、（前記アトマイズ鉄基粉末に混合される炭素成分の質量／該アトマイズ鉄基粉末の質量）×１００（質量％）とする） The gist of the present invention is as follows.
1. % By mass
C: 0.8% or less,
O: 1.0% or less,
S: 0.3% or less,
P: 0.03% or less, and as an alloy element,
Mn: more than 0.08% and 1.0% or less,
Cr: 0.3 to 3.5%,
1 or 2 or more selected from the group consisting of Mo: 0.1-2% and V: 0.1-0.5%,
Prepare the remaining Fe and atomized iron-based powder which is an inevitable impurity,
Supplying the atomized iron-based powder into a moving bed furnace so as to form a packed bed of thickness d (mm);
In the moving bed furnace, an inert gas is supplied so as to have an average gas flow velocity v (mm / s),
The atomized iron-based powder is reduced by heat treatment in the moving bed furnace to obtain an alloy steel powder for powder metallurgy, a method for producing an alloy steel powder for powder metallurgy,
Said d and v satisfy | fill following (1) Formula, C content [C] (mass%) of the said atomized iron base powder, and O content [O] (mass%) of the said atomized iron base powder, The following equation (2) is satisfied,
In the supply of the atomized iron-based powder to the moving bed furnace, when the C content [C] and the O content [O] of the atomized iron-based powder satisfy the following formula (3), the atomized iron-based powder Is supplied to the moving bed furnace as it is, and if the following formula (3) is not satisfied, the atomized iron-based powder is further mixed with a carbon component so as to satisfy the following formula (4), and then the moving bed furnace A method for producing alloy steel powder for powder metallurgy, which is supplied to the company.
D / √v ≦ 3.0 (mm 1/2 · s 1/2 ) (1)
[O] ≧ 4/3 [C] -2/15 (2)
4/3 [C] + 0.28 ≧ [O] (3)
4/3 ([C] + [MXC]) + 0.28 ≧ [O] (4)
(Here, [MXC] is (mass of carbon component mixed with the atomized iron-based powder / mass of the atomized iron-based powder) × 100 (mass%))
２．前記還元されたアトマイズ鉄基粉末を、水素ガスまたは水素含有気体を用いて冷却する、上記１に記載の粉末冶金用合金鋼粉の製造方法。 2. 2. The method for producing alloy steel powder for powder metallurgy according to 1 above, wherein the reduced atomized iron-based powder is cooled using hydrogen gas or a hydrogen-containing gas.
３．前記不活性ガスの露点を５℃以下とする、上記１または２に記載の粉末冶金用合金鋼粉の製造方法。 3. 3. The method for producing alloy steel powder for powder metallurgy according to 1 or 2 above, wherein a dew point of the inert gas is 5 ° C. or less.
４．前記熱処理において、雰囲気温度Ｔ：１０８０℃以上、保持時間ｔ：１０４－０．００３７・Ｔ（ｈ）以上の条件で脱酸が行われる、上記１～３のいずれか一項に記載の粉末冶金用合金鋼粉の製造方法。 4). 4. The powder according to any one of 1 to 3 above, wherein deoxidation is performed in the heat treatment under conditions of an atmospheric temperature T: 1080 ° C. or more and a holding time t: 10 4−0.0037 · T (h) or more. Manufacturing method of alloy steel powder for metallurgy.
　本発明によれば、Ｃｒ、Ｍｎ、Ｖなどの易酸化性元素を含有する合金鋼粉であっても、煩雑な維持管理が必要となるガス分析を行うことなく移動床炉を用いて熱処理し、Ｃ含有量およびＯ含有量を安定して低減することができる。そしてその結果、低コストで、かつ加圧成形時の圧縮性に優れた合金鋼粉を製造することができる。また、本発明の製造方法によって得られる粉末冶金用合金鋼粉を用いて製造される焼結部品は、優れた強度、靭性、疲労特性などの機械的特性を有することから、粉末冶金用合金鋼粉および焼結体の用途を拡大できる。 According to the present invention, even an alloy steel powder containing oxidizable elements such as Cr, Mn, and V is heat-treated using a moving bed furnace without performing gas analysis that requires complicated maintenance and management. , C content and O content can be stably reduced. As a result, it is possible to produce alloy steel powder that is low in cost and excellent in compressibility during pressure forming. In addition, sintered parts produced using the alloy steel powder for powder metallurgy obtained by the production method of the present invention have excellent mechanical properties such as strength, toughness and fatigue properties. Applications of powders and sintered bodies can be expanded.
本発明の一実施形態において用いることのできる熱処理装置の例を示す側断面図である。It is side sectional drawing which shows the example of the heat processing apparatus which can be used in one Embodiment of this invention. 特許文献５に記載された熱処理装置における温度パターンの例を示す図である。It is a figure which shows the example of the temperature pattern in the heat processing apparatus described in patent document 5. FIG.
　以下、本発明を具体的に説明する。本発明においては、原料となるアトマイズ鉄基粉末を、移動床炉を用いて熱処理することによって粉末冶金用合金鋼粉（以下、単に「合金鋼粉」という場合がある）が製造される。具体的には、本発明の製造方法は、次の各処理を含む；
（１）アトマイズ鉄基粉末を用意する、
（２）前記アトマイズ鉄基粉末を、厚さｄ（ｍｍ）の充填層を形成するように移動床炉内へ供給する、
（３）前記移動床炉内に、不活性ガスを平均ガス流速ｖ（ｍｍ／ｓ）となるように供給する、および
（４）前記アトマイズ鉄基粉末を前記移動床炉内で熱処理することによって還元し、粉末冶金用合金鋼粉とする。 Hereinafter, the present invention will be specifically described. In the present invention, alloy steel powder for powder metallurgy (hereinafter sometimes simply referred to as “alloy steel powder”) is produced by heat-treating atomized iron-based powder as a raw material using a moving bed furnace. Specifically, the production method of the present invention includes the following treatments;
(1) Prepare atomized iron-based powder.
(2) supplying the atomized iron-based powder into a moving bed furnace so as to form a packed bed having a thickness of d (mm);
(3) by supplying an inert gas in the moving bed furnace so as to have an average gas flow velocity v (mm / s); and (4) by heat-treating the atomized iron-based powder in the moving bed furnace. Reduce to alloy steel powder for powder metallurgy.
　上記各処理は、それぞれ独立して、任意のタイミングで行うことができ、複数の処理を同時に行うこともできる。 Each of the above processes can be performed independently at an arbitrary timing, and a plurality of processes can be performed simultaneously.
　さらに、本発明においては、前記充填層の厚さｄおよび前記平均ガス流速ｖが上述した条件を満たす必要がある。また、アトマイズ鉄基粉末を移動床炉内へ供給する際、該アトマイズ鉄基粉末のＣ含有量およびＯ含有量に応じて、該アトマイズ鉄基粉末に炭素成分をさらに混合したのち、前記移動床炉に供給する。 Furthermore, in the present invention, the thickness d of the packed bed and the average gas flow velocity v must satisfy the above-described conditions. In addition, when supplying the atomized iron-based powder into the moving bed furnace, the atomized iron-based powder is further mixed with a carbon component according to the C content and O content of the atomized iron-based powder, and then the moving bed Supply to the furnace.
　以下、各処理の詳細と、上記条件の限定理由について説明する。 The details of each process and the reasons for limiting the above conditions are described below.
［アトマイズ鉄基粉末］
　本発明においては、原料としてアトマイズ鉄基粉末を使用する。アトマイズ鉄基粉末の製造方法は特に限定されず、常法に従って製造することができる。なお、「アトマイズ鉄基粉末」とは、アトマイズ法によって製造された鉄基粉末を意味する。また、「鉄基粉末」とは、Ｆｅを５０質量％以上含有する粉末を意味する。 [Atomized iron-based powder]
In the present invention, atomized iron-based powder is used as a raw material. The manufacturing method of the atomized iron-based powder is not particularly limited, and can be manufactured according to a conventional method. “Atomized iron-based powder” means an iron-based powder produced by the atomizing method. The “iron-based powder” means a powder containing 50% by mass or more of Fe.
　前記アトマイズ鉄基粉末としては、ガスアトマイズ法によって得られるガスアトマイズ鉄基粉末と、水アトマイズ法によって得られる水アトマイズ鉄基粉末の、いずれをも使用することができる。前記ガスアトマイズ法では、窒素、アルゴンなどの不活性ガスを用いることが好ましい。ただし、ガスは水に比べて冷却能力に劣るため、ガスアトマイズ法で鉄基粉末を製造する場合には、多量のガスを使用する必要がある。そのため、量産性や製造コストの観点からは、水アトマイズ法を用いることが好ましい。また、水アトマイズ法は、通常大気が混入するような雰囲気でアトマイズが行われるため、ガスアトマイズ法に比べて製造過程における鉄基粉末の酸化が生じやすい。そのため、本発明の方法は、水アトマイズ鉄基粉末を用いる場合に特に有効である。 As the atomized iron-based powder, either a gas atomized iron-based powder obtained by a gas atomizing method or a water atomized iron-based powder obtained by a water atomizing method can be used. In the gas atomization method, it is preferable to use an inert gas such as nitrogen or argon. However, since gas is inferior in cooling capacity compared to water, it is necessary to use a large amount of gas when producing iron-based powder by the gas atomization method. Therefore, it is preferable to use the water atomization method from the viewpoint of mass productivity and manufacturing cost. In addition, since the water atomization method is normally performed in an atmosphere in which air is mixed, the iron-based powder is more easily oxidized in the production process than the gas atomization method. Therefore, the method of the present invention is particularly effective when a water atomized iron-based powder is used.
（成分組成）
　次に、本発明においてアトマイズ鉄基粉末の成分組成を上記のように限定する理由について説明する。なお、特に断らない限り、以下の説明において「％」は「質量％」を意味するものとする。 (Component composition)
Next, the reason for limiting the component composition of the atomized iron-based powder in the present invention as described above will be described. Unless otherwise specified, “%” in the following description means “mass%”.
　本発明において、ＣおよびＯは、後述する熱処理によって低減させるべき元素である。そして、最終的に得られる粉末冶金用合金鋼粉の圧縮性を向上させるという観点からは、該合金鋼粉のＣ含有量およびＯ含有量を可能な限り低減することが望ましく、具体的には、Ｃ：０．１％以下、Ｏ：０．２８％以下とすることが好ましい。これらＣおよびＯの適正量を達成するために、本発明に従う熱処理で低減できる量を見込み、アトマイズ鉄基粉末のＣ含有量およびＯ含有量の適正範囲を以下のように定める。 In the present invention, C and O are elements to be reduced by a heat treatment described later. And from the viewpoint of improving the compressibility of the finally obtained alloy steel powder for powder metallurgy, it is desirable to reduce the C content and O content of the alloy steel powder as much as possible, specifically, C: 0.1% or less, O: 0.28% or less are preferable. In order to achieve these appropriate amounts of C and O, the amount that can be reduced by the heat treatment according to the present invention is anticipated, and the appropriate ranges of the C content and O content of the atomized iron-based powder are determined as follows.
Ｃ：０．８％以下
　Ｃは、主にセメンタイトなどの析出物として、あるいは固溶状態でアトマイズ鉄基粉末中に存在する。アトマイズ鉄基粉末中のＣ含有量が０．８％を超えると、本発明の熱処理においてＣ含有量を０．１％以下まで下げることが困難となり、優れた圧縮性を有する合金粉末を得ることができない。そのため、アトマイズ鉄基粉末のＣ含有量を０．８％以下とする。一方、Ｃ含有量が低ければ低いほど、熱処理時のＣ含有量の低減（脱炭）が容易になる。そのため、Ｃ含有量の下限は特に限定されず、０％であって良く、工業的には０％超であってよい。 C: 0.8% or less C is present in the atomized iron-based powder mainly as a precipitate such as cementite or in a solid solution state. When the C content in the atomized iron-based powder exceeds 0.8%, it becomes difficult to lower the C content to 0.1% or less in the heat treatment of the present invention, and an alloy powder having excellent compressibility is obtained. I can't. Therefore, the C content of the atomized iron-based powder is set to 0.8% or less. On the other hand, the lower the C content, the easier the reduction (decarburization) of the C content during heat treatment. Therefore, the lower limit of the C content is not particularly limited, and may be 0% or industrially greater than 0%.
Ｏ：１．０％以下
　Ｏは、主にＣｒ酸化物、Ｍｎ酸化物、Ｖ酸化物、およびＦｅ酸化物として鉄基粉末表面に存在する。アトマイズ鉄基粉末中のＯ含有量が１．０％を超えると、熱処理においてＯ含有量を０．２８％以下まで下げることが困難となり、優れた圧縮性を有する合金粉末を得ることができない。そのため、アトマイズ鉄基粉末のＯ含有量を１．０％以下とする。Ｏ含有量は、０．９％以下とすることが好ましい。一方、Ｏ含有量が低ければ低いほど、熱処理時のＯ含有量の低減（脱酸）が容易になる。そのため、Ｏ含有量の下限は特に限定されないが、過度の低減は製造コストの増加を招くため、Ｏ含有量は０．４％以上とすることが好ましい。 O: 1.0% or less O is mainly present on the surface of the iron-based powder as Cr oxide, Mn oxide, V oxide, and Fe oxide. If the O content in the atomized iron-based powder exceeds 1.0%, it becomes difficult to reduce the O content to 0.28% or less during heat treatment, and an alloy powder having excellent compressibility cannot be obtained. Therefore, the O content of the atomized iron-based powder is set to 1.0% or less. The O content is preferably 0.9% or less. On the other hand, the lower the O content, the easier the reduction (deoxidation) of the O content during heat treatment. Therefore, the lower limit of the O content is not particularly limited, but excessive reduction leads to an increase in manufacturing cost, so the O content is preferably 0.4% or more.
　また、Ｓ、Ｐ、Ｃｒ、Ｍｎ、Ｍｏ、およびＶの含有量は、いずれも本発明の熱処理によって変化はしない。したがって、アトマイズ鉄基粉末中に含まれるこれらの元素は、熱処理後の粉末冶金用合金鋼粉中にそのまま残留する。このことを踏まえ、アトマイズ鉄基粉末におけるこれらの元素の含有量を、それぞれ以下のように規定する。 Further, the contents of S, P, Cr, Mn, Mo, and V are not changed by the heat treatment of the present invention. Therefore, these elements contained in the atomized iron-based powder remain as they are in the alloy steel powder for powder metallurgy after the heat treatment. Based on this, the contents of these elements in the atomized iron-based powder are respectively defined as follows.
Ｓ：０．３％以下
　合金鋼粉に含まれるＳの一部はＭｎと結合してＭｎＳを形成し、焼結後の切削性を向上させる。しかし、合金鋼粉中のＳ含有量が０．３％を超えると固溶Ｓが増え、粒界強度が低下する。そのため、合金鋼粉中のＳ含有量を０．３％以下とするために、アトマイズ鉄基粉末の段階でのＳ含有量を０．３％以下とする。粒界強度の低下を確実に回避するためには、Ｓ含有量を０．２５％以下とすることが好ましい。一方、Ｓ含有量の下限は特に限定されず、０％であって良いが、工業的には０％超であってよい。焼結後の切削性を改善するという観点からは、Ｓ含有量を０．０５％以上とすることが好ましい。 S: 0.3% or less Part of S contained in the alloy steel powder combines with Mn to form MnS, thereby improving the machinability after sintering. However, if the S content in the alloy steel powder exceeds 0.3%, the solid solution S increases and the grain boundary strength decreases. Therefore, in order to make the S content in the alloy steel powder 0.3% or less, the S content in the atomized iron-based powder stage is made 0.3% or less. In order to reliably avoid a decrease in grain boundary strength, the S content is preferably set to 0.25% or less. On the other hand, the lower limit of the S content is not particularly limited and may be 0%, but industrially it may be more than 0%. From the viewpoint of improving the machinability after sintering, the S content is preferably 0.05% or more.
Ｐ：０．０３％以下
　Ｐは不可避不純物の１つとして含まれる元素である。Ｐ含有量を０．０３％以下とすることによって、粒界強度が増加し、靭性が向上する。そのため、アトマイズ鉄基粉末のＰ含有量を０．０３％以下とする。一方、Ｐ含有量は低ければ低いほど粒界強度が増加し、靭性が向上するため好ましい。そのため、Ｐ含有量の下限は特に限定されず、０％であってよいが、工業的には０％超であってよい。しかし、過度の低減は製造コストの増加を招くため、Ｐ含有量は０．０００５％以上とすることが好ましい。 P: 0.03% or less P is an element contained as one of inevitable impurities. By setting the P content to 0.03% or less, the grain boundary strength is increased and the toughness is improved. Therefore, the P content of the atomized iron-based powder is set to 0.03% or less. On the other hand, the lower the P content, the greater the grain boundary strength and the better the toughness. Therefore, the lower limit of the P content is not particularly limited and may be 0%, but industrially it may be more than 0%. However, excessive reduction leads to an increase in manufacturing cost, so the P content is preferably 0.0005% or more.
　本発明におけるアトマイズ鉄基粉末は、以上の成分に加えて、Ｍｎ、Ｃｒ、Ｍｏ、およびＶからなる群より選択される１または２以上を含有する。 The atomized iron-based powder in the present invention contains one or more selected from the group consisting of Mn, Cr, Mo, and V in addition to the above components.
Ｍｎ：０．０８％超１．０％以下
　Ｍｎは、焼入性向上、固溶強化などによって、焼結体の強度を向上させる作用を有する元素である。Ｍｎを添加する場合は、前記効果を得るためにＭｎ含有量を０．０８％超とする。Ｍｎ含有量は０．１０％以上とすることが好ましい。一方、Ｍｎ含有量が１．０％より高いと、Ｍｎ酸化物の生成量が多くなり、合金鋼粉の圧縮性が低下する。また、Ｍｎ酸化物が、焼結体内部の破壊の起点となって、疲労強度および靱性を低下させる。そのため、Ｍｎ含有量を１．０％以下とする。Ｍｎ含有量は０．９５％以下とすることが好ましく、０．８０％以下とすることがより好ましい。 Mn: more than 0.08% and not more than 1.0% Mn is an element having an action of improving the strength of the sintered body by improving hardenability and strengthening solid solution. When adding Mn, in order to acquire the said effect, Mn content shall be over 0.08%. The Mn content is preferably 0.10% or more. On the other hand, if the Mn content is higher than 1.0%, the amount of Mn oxide generated increases, and the compressibility of the alloy steel powder decreases. Further, the Mn oxide serves as a starting point for destruction inside the sintered body, and reduces fatigue strength and toughness. Therefore, the Mn content is 1.0% or less. The Mn content is preferably 0.95% or less, and more preferably 0.80% or less.
Ｃｒ：０．３～３．５％
　Ｃｒは、焼入性を向上させて、焼結体の引張強度および疲労強度を向上させる作用を有する元素である。さらにＣｒは、焼結体の焼入れ・焼き戻しなどの熱処理後の硬さを高め、耐摩耗性を向上させる効果を有している。Ｃｒを添加する場合は、これらの効果を得るためにＣｒ含有量を０．３％以上とする。一方、Ｃｒ含有量が３．５％を超えると、Ｃｒ酸化物の生成量が多くなる。Ｃｒ酸化物は、焼結体内部の疲労破壊の起点となるため、焼結体の疲労強度を低下させる。したがって、Ｃｒ含有量を３．５％以下とする。 Cr: 0.3-3.5%
Cr is an element that has the effect of improving hardenability and improving the tensile strength and fatigue strength of the sintered body. Further, Cr has the effect of increasing the hardness after heat treatment such as quenching and tempering of the sintered body and improving the wear resistance. When adding Cr, in order to acquire these effects, Cr content shall be 0.3% or more. On the other hand, when the Cr content exceeds 3.5%, the amount of Cr oxide generated increases. Since the Cr oxide serves as a starting point for fatigue failure inside the sintered body, the fatigue strength of the sintered body is reduced. Therefore, the Cr content is 3.5% or less.
Ｍｏ：０．１～２％
　Ｍｏは、焼入性向上、固溶強化、析出強化などによって、焼結体の強度を向上させる作用を有する元素である。Ｍｏを添加する場合は、前記効果を得るために、Ｍｏ含有量を０．１％以上とする。一方、Ｍｏの含有量が２％を超えると、焼結体の靭性が低下する。したがって、Ｍｏ含有量を２％以下とする。 Mo: 0.1-2%
Mo is an element having an action of improving the strength of the sintered body by improving hardenability, solid solution strengthening, precipitation strengthening, and the like. When adding Mo, in order to acquire the said effect, Mo content shall be 0.1% or more. On the other hand, when the content of Mo exceeds 2%, the toughness of the sintered body decreases. Therefore, the Mo content is 2% or less.
Ｖ：０．１～０．５％
　Ｖは、焼入性向上、固溶強化、析出強化などによって、焼結体の強度を向上させる作用を有する元素である。Ｖを添加する場合は、前記効果を得るためにＶ含有量を０．１％以上とする。一方、Ｖ含有量が０．５％を超えると、焼結体の靭性が低下する。そのため、Ｖ含有量を０．５％以下とする。 V: 0.1-0.5%
V is an element having an action of improving the strength of the sintered body by improving hardenability, solid solution strengthening, precipitation strengthening, and the like. When adding V, in order to acquire the said effect, V content shall be 0.1% or more. On the other hand, if the V content exceeds 0.5%, the toughness of the sintered body decreases. Therefore, the V content is 0.5% or less.
　本発明におけるアトマイズ鉄基粉末の成分組成は、上記元素と、残部Ｆｅおよび不可避不純物からなる。 The component composition of the atomized iron-based powder in the present invention is composed of the above elements, the remainder Fe and inevitable impurities.
　さらに本発明においては、上記アトマイズ鉄基粉末のＣ含有量［Ｃ］（質量％）と前記アトマイズ鉄基粉末のＯ含有量［Ｏ］（質量％）とが、下記（２）式を満足する必要がある。
　［Ｏ］≧４／３［Ｃ］－２／１５…（２） Furthermore, in the present invention, the C content [C] (mass%) of the atomized iron base powder and the O content [O] (mass%) of the atomized iron base powder satisfy the following formula (2). There is a need.
[O] ≧ 4/3 [C] -2/15 (2)
 アトマイズ鉄基粉末に含まれるＣとＯは、主にＣ＋Ｏ＝ＣＯの反応によって一酸化炭素ガスとなって鉄基粉末から除去される。その際、前記アトマイズ鉄基粉末のＣ含有量［Ｃ］（質量％）と前記アトマイズ鉄基粉末のＯ含有量［Ｏ］（質量％）とが、下記（２）式を満足していれば、熱処理によって粉末中のＣ量を、例えば、０．１質量％以下といった十分に低い量まで低減することができる。 C and O contained in the atomized iron-based powder are removed from the iron-based powder as carbon monoxide gas mainly by the reaction of C + O = CO. At that time, if the C content [C] (mass%) of the atomized iron-based powder and the O content [O] (mass%) of the atomized iron-based powder satisfy the following formula (2): By the heat treatment, the amount of C in the powder can be reduced to a sufficiently low amount, for example, 0.1% by mass or less.
　さらに本発明においては、以下に述べるように、必要に応じて前記アトマイズ鉄基粉末に炭素成分をさらに混合して用いる。 Furthermore, in the present invention, as described below, a carbon component is further mixed with the atomized iron-based powder as necessary.
・（３）式を満たす場合
　前記アトマイズ鉄基粉末のＣ含有量［Ｃ］およびＯ含有量［Ｏ］が下記（３）式を満たす場合には、該アトマイズ鉄基粉末をそのまま前記移動床炉に供給する。なお、「そのまま供給する」とは、炭素成分などの他の成分と混合することなく、アトマイズ鉄基粉末のみを移動床炉へ供給することを意味する。
　４／３［Ｃ］＋０．２８≧［Ｏ］…（３） When the formula (3) is satisfied When the C content [C] and the O content [O] of the atomized iron base powder satisfy the following formula (3), the atomized iron base powder is used as it is in the moving bed furnace. To supply. “Supply as it is” means that only the atomized iron-based powder is supplied to the moving bed furnace without being mixed with other components such as a carbon component.
4/3 [C] + 0.28 ≧ [O] (3)
　アトマイズ鉄基粉末の［Ｃ］および［Ｏ］が（３）式の条件を満たしている場合には、酸素に対して十分な量の炭素が存在しているため、熱処理によって粉末中のＯ量を、例えば、０．２８質量％以下といった十分に低い量まで低減することができる。 When [C] and [O] of the atomized iron-based powder satisfy the condition of the formula (3), a sufficient amount of carbon is present with respect to oxygen, so the amount of O in the powder by heat treatment Can be reduced to a sufficiently low amount, for example, 0.28 mass% or less.
・（３）式を満たさない場合
　一方、アトマイズ鉄基粉末の［Ｃ］および［Ｏ］が（３）式の条件を満たしていない場合には、熱処理によって粉末中のＯ量を十分に低減することができない。そこで、下記（４）式を満足するように該アトマイズ鉄基粉末に炭素成分をさらに混合したのち、移動床炉に供給する。
　４／３（［Ｃ］＋［ＭＸＣ］）＋０．２８≧［Ｏ］…（４）
（ここで、［ＭＸＣ］は、（前記アトマイズ鉄基粉末に混合される炭素成分の質量／該アトマイズ鉄基粉末の質量）×１００（質量％）とする） -When the formula (3) is not satisfied On the other hand, when [C] and [O] of the atomized iron-based powder do not satisfy the condition of the formula (3), the amount of O in the powder is sufficiently reduced by heat treatment. I can't. Therefore, the atomized iron-based powder is further mixed with a carbon component so as to satisfy the following expression (4), and then supplied to the moving bed furnace.
4/3 ([C] + [MXC]) + 0.28 ≧ [O] (4)
(Here, [MXC] is (mass of carbon component mixed with the atomized iron-based powder / mass of the atomized iron-based powder) × 100 (mass%))
　このように炭素成分を混合することによって、アトマイズ鉄基粉末に含まれる炭素の不足を補うことができる。そしてその結果、熱処理によって粉末中のＯ量を、例えば、０．２８質量％以下といった十分に低い量まで低減することができる。 混合 By mixing the carbon components in this way, the shortage of carbon contained in the atomized iron-based powder can be compensated. As a result, the amount of O in the powder can be reduced to a sufficiently low amount such as 0.28% by mass or less by heat treatment.
　なお、炭素成分を添加する場合、次の（５）式をさらに満足することが、より好ましい。
　［Ｏ］≧４／３（［Ｃ］＋［ＭＸＣ］）－２／１５…（５） In addition, when adding a carbon component, it is more preferable that the following formula (5) is further satisfied.
[O] ≧ 4/3 ([C] + [MXC]) − 2/15 (5)
　なお、アトマイズ鉄基粉末のＣ含有量とＯ含有量を調整する方法は、特に限定されず、任意の方法を用いることができる。例えば、アトマイズ鉄基粉末のＣ含有量およびＯ含有量が上記条件を満たすように、アトマイズ鉄基粉末の製造に用いる溶鋼の成分組成を調整すればよい。溶鋼の成分組成の調整は、一般的な転炉を使用した鉄鋼の精錬・製鋼技術によって行うことができる。 In addition, the method of adjusting C content and O content of atomized iron-based powder is not specifically limited, Arbitrary methods can be used. For example, what is necessary is just to adjust the component composition of the molten steel used for manufacture of an atomized iron base powder so that C content and O content of atomized iron base powder may satisfy the said conditions. Adjustment of the composition of the molten steel can be performed by a steel refining and steelmaking technique using a general converter.
　なお、本発明では、アトマイズ鉄基粉末が、アトマイズまま（as-atomized）で、上記（２）および（３）式の条件を満たしていれば、該アトマイズ鉄基粉末をそのまま熱処理に供することができるため、好ましい。ただし、アトマイズ鉄基粉末におけるＣ含有量が過剰となり、（２）式の条件を満たさなくなると、熱処理前の調整を行って（２）式を満足するようにすることができない。したがって、アトマイズ鉄基粉末を製造する際には、必ず（２）式を満足するようにする必要があり、そのためには酸素が過剰となることも許容される。酸素が過剰であり、（３）式を満たさない場合であっても、上述したように炭素成分を添加することによって、最終的な合金鋼粉におけるＣ量とＯ量を低減できるためである。 In the present invention, if the atomized iron-based powder is as-atomized and satisfies the conditions of the above formulas (2) and (3), the atomized iron-based powder can be directly subjected to heat treatment. This is preferable because it is possible. However, if the C content in the atomized iron-based powder becomes excessive and the condition of the formula (2) is not satisfied, the adjustment before the heat treatment cannot be performed to satisfy the formula (2). Therefore, when producing atomized iron-based powder, it is necessary to satisfy the formula (2), and oxygen is allowed to be excessive for that purpose. This is because even if oxygen is excessive and the formula (3) is not satisfied, the amount of C and O in the final alloy steel powder can be reduced by adding the carbon component as described above.
（平均粒径）
　アトマイズ鉄基粉末の平均粒径は特に限定されず、アトマイズ法によって得られた鉄基粉末であれば、任意の粒径のものを用いることができる。しかし、アトマイズ鉄基粉末の平均粒径が３０μｍを下回ると、アトマイズ鉄基粉末の流動性が低下し、ホッパなどを用いて移動床炉へ供給することが困難となる場合がある。また、アトマイズ鉄基粉末の平均粒径が３０μｍを下回ると、熱処理後の合金鋼粉の流動性も低下するため、該合金鋼粉をプレス成形する際の金型への充填の作業効率が低下する場合がある。そのため、アトマイズ鉄基粉末の平均粒径を３０μｍ以上とすることが好ましく、４０μｍ以上とすることがより好ましく、５０μｍ以上とすることがさらに好ましい。 (Average particle size)
The average particle size of the atomized iron-based powder is not particularly limited, and any particle size can be used as long as it is an iron-based powder obtained by the atomization method. However, when the average particle size of the atomized iron-based powder is less than 30 μm, the fluidity of the atomized iron-based powder is lowered, and it may be difficult to supply to the moving bed furnace using a hopper or the like. In addition, if the average particle size of the atomized iron-based powder is less than 30 μm, the fluidity of the alloy steel powder after heat treatment also decreases, so the work efficiency of filling the mold when the alloy steel powder is press-formed decreases. There is a case. For this reason, the average particle size of the atomized iron-based powder is preferably 30 μm or more, more preferably 40 μm or more, and even more preferably 50 μm or more.
　一方、アトマイズ鉄基粉末の平均粒径が１２０μｍより大きいと、得られた合金粉末を用いて得られる焼結体に粗大な空孔が生じて焼結体の密度が低下し、強度や靭性が不足する場合がある。そのため、アトマイズ鉄基粉末の平均粒径を１２０μｍ以下とすることが好ましく、１００μｍ以下とすることがより好ましく、９０μｍ以下とすることがさらに好ましい。なお、ここで平均粒径とは、メジアン径（いわゆるd50、体積基準）を指すものとする。 On the other hand, if the average particle size of the atomized iron-based powder is larger than 120 μm, coarse pores are generated in the sintered body obtained using the obtained alloy powder, the density of the sintered body is lowered, and the strength and toughness are reduced. There may be a shortage. Therefore, the average particle size of the atomized iron-based powder is preferably 120 μm or less, more preferably 100 μm or less, and even more preferably 90 μm or less. Here, the average particle diameter means a median diameter (so-called d50, volume basis).
（見掛密度）
　アトマイズ鉄基粉末の見掛密度は、特に限定しないが、２．０～３．５Ｍｇ／ｍ３とすることが好ましく、２．４～３．２Ｍｇ／ｍ３とすることがより好ましい。　 (Apparent density)
The apparent density of the atomized iron-based powder is not particularly limited, but is preferably 2.0 to 3.5 Mg / m 3 , more preferably 2.4 to 3.2 Mg / m 3 .
［移動床炉］
　上記成分組成を有するアトマイズ鉄基粉末を、移動床炉に供給し、該移動床炉の移動床上に厚さｄ（ｍｍ）の充填層を形成する。前記移動床炉としては、アトマイズ鉄基粉末を熱処理できるものであれば任意のものを用いることができるが、搬送用のベルトを備えた移動床炉（以下、「ベルト式移動床炉」または「ベルト炉」ともいう）を用いることが好ましい。ベルト炉を用いて熱処理を行う場合には、ベルト上にアトマイズ鉄基粉末を供給して、充填層を形成することができる。アトマイズ鉄基粉末の供給は、任意の方法で行うことができるが、ホッパを用いて行うことが好ましい。また、移動床炉におけるアトマイズ鉄基粉末の搬送方向は特に限定されないが、移動床炉の入り口側から出口側へ直線的に搬送することが一般的である。なお、充填層の厚さについては後述する。 [Moving floor furnace]
Atomized iron-based powder having the above component composition is supplied to a moving bed furnace, and a packed bed having a thickness d (mm) is formed on the moving bed of the moving bed furnace. As the moving bed furnace, any one can be used as long as it can heat treat the atomized iron-based powder, but a moving bed furnace (hereinafter referred to as a “belt type moving bed furnace” or “ It is preferable to use a belt furnace). When heat treatment is performed using a belt furnace, an atomized iron-based powder can be supplied onto the belt to form a packed bed. The atomized iron-based powder can be supplied by any method, but it is preferable to use a hopper. Moreover, the conveyance direction of the atomized iron-based powder in the moving bed furnace is not particularly limited, but it is generally conveyed linearly from the inlet side to the outlet side of the moving bed furnace. The thickness of the filling layer will be described later.
　上記移動床炉の加熱方式は特に限定されず、アトマイズ鉄基粉末を加熱することができるものであれば、任意の方式を用いることができるが、雰囲気制御の観点からは、間接加熱式とすることが好ましく、ラジアントチューブを用いた加熱を用いることがより好ましい。また、マッフル炉も、間接加熱式の炉として好適に用いることができる。 The heating system of the moving bed furnace is not particularly limited, and any system can be used as long as it can heat the atomized iron-based powder. However, from the viewpoint of atmosphere control, the indirect heating system is used. It is preferable to use heating using a radiant tube. A muffle furnace can also be suitably used as an indirect heating furnace.
　なお、上記移動床炉としては、特許文献５に記載されているような移動床炉を用いることができる。そこで、参考のために、特許文献５における移動床炉について、以下に説明する。ただし、本願発明で用いられるアトマイズ鉄基粉末や雰囲気ガスは、以下に説明する特許文献５における処理とは異なる。本発明で用いられるアトマイズ鉄基粉末や雰囲気ガスについては後述する。 As the moving bed furnace, a moving bed furnace as described in Patent Document 5 can be used. Therefore, the moving bed furnace in Patent Document 5 will be described below for reference. However, the atomized iron-based powder and the atmospheric gas used in the present invention are different from the processing in Patent Document 5 described below. The atomized iron-based powder and atmospheric gas used in the present invention will be described later.
　特許文献５の記載では、連続式移動床炉を用いて、脱炭、脱酸または脱窒のうちの１種以上の処理を連続的に行い、鉄基粉末の熱処理を行うとされている。また、特許文献５の記載では、移動床炉の分割された空間を利用して、脱炭、脱酸、脱窒の各処理工程を独立させ、脱炭工程では６００～１１００℃、脱酸工程では７００～１１００℃、脱窒工程では４５０～７５０℃に独立に温度制御して、鉄基粉末の熱処理を行うとされている。さらに、特許文献５では、雰囲気ガスとして、脱炭ゾーンではＨ２やＡＸガスなどの還元性ガス、または、Ｎ２やＡｒなどの不活性ガス、脱酸ゾーンではＨ２やＡＸガスなどの還元性ガス、さらに脱窒ゾーンではＨ２主体のガスが用いられる、とされている。 In the description of Patent Document 5, it is assumed that one or more processes of decarburization, deoxidation, or denitrification are continuously performed by using a continuous moving bed furnace to heat-treat the iron-based powder. Further, in the description of Patent Document 5, each of the decarburization, deoxidation, and denitrification treatment steps is made independent using the divided space of the moving bed furnace, and the decarburization step is performed at 600 to 1100 ° C. In the denitrification process, the iron-base powder is heat-treated by controlling the temperature independently at 450 to 750 ° C. Further, Patent Document 5, as an atmospheric gas, a reducing gas such as H 2 or AX gas at decarburization zone or an inert gas such as N 2 or Ar, reduction such as H 2 or AX gas in deoxidation zone It is said that gas mainly composed of H 2 is used in the denitrification zone.
　ここで、特許文献５に記載された連続式移動床炉と同型の熱処理装置を、図１に示す。図１に示した熱処理装置１００は、仕切壁１により複数のゾーン、すなわち脱炭ゾーン２、脱酸ゾーン３、脱窒ゾーン４に分割された炉体３０と、炉体３０の入側に設けられたホッパ８と、炉体３０の入出側に設けられたホイール１０と、該ホイール１０により連続回転し、炉体３０内の各ゾーンを巡回するベルト９と、ラジアントチューブ１１と、を有する。ホッパ８から、ホイール１０の連続回転により連続的に移動するベルト９上に所定の充填層厚（ベルト上に積載される粗製鉄基粉末の厚み）にて供給された粗製鉄基粉末７は、ラジアントチューブ１１により適正温度に加熱された各ゾーン２，３，４を移動しながら熱処理され、脱炭、脱酸、脱窒されて製品粉１３とされる。なお、製品粉１３は製品タンク１４に貯められる。 Here, a heat treatment apparatus of the same type as the continuous moving bed furnace described in Patent Document 5 is shown in FIG. A heat treatment apparatus 100 shown in FIG. 1 is provided on a furnace body 30 divided into a plurality of zones by a partition wall 1, that is, a decarburization zone 2, a deoxidation zone 3, and a denitrification zone 4, and an entrance side of the furnace body 30. The hopper 8 is provided, a wheel 10 provided on the entrance / exit side of the furnace body 30, a belt 9 that continuously rotates by the wheel 10 and circulates in each zone in the furnace body 30, and a radiant tube 11. The crude iron-based powder 7 supplied from the hopper 8 on the belt 9 continuously moved by the continuous rotation of the wheel 10 with a predetermined packed bed thickness (thickness of the crude iron-based powder loaded on the belt), It is heat-treated while moving through the zones 2, 3 and 4 heated to an appropriate temperature by the radiant tube 11, and decarburized, deoxidized and denitrified to obtain the product powder 13. The product powder 13 is stored in the product tank 14.
　そして、特許文献５に記載された技術において、各ゾーンでの反応はつぎのように考えられている。　脱炭ゾーン２では、ラジアントチューブ１１により雰囲気温度を６００～１１００℃に制御し、脱炭ゾーン２の下流側に設けられた水蒸気吹込み口１２から導入された水蒸気（Ｈ２Ｏガス）により、次ゾーンである脱酸ゾーン３の雰囲気ガスを露点：３０～６０℃に調整しつつ、粗製鉄基粉末から脱炭を行うとしている。
　脱炭ゾーン２の上流側には、雰囲気ガスの排出口６が設けられ、雰囲気ガスを装置外に排出している。なお、脱炭の反応式は、次式（Ｉ）で表される。
　　　Ｃ（ｉｎ　Ｆｅ）＋　Ｈ２Ｏ（ｇ）＝ＣＯ（ｇ）＋Ｈ２（ｇ）…（Ｉ） And in the technique described in Patent Document 5, the reaction in each zone is considered as follows. In the decarburization zone 2, the ambient temperature is controlled to 600 to 1100 ° C. by the radiant tube 11, and water vapor (H 2 O gas) introduced from the water vapor inlet 12 provided on the downstream side of the decarburization zone 2 It is supposed that decarburization is performed from the crude iron-based powder while adjusting the atmospheric gas in the deoxidation zone 3 as the next zone to a dew point of 30 to 60 ° C.
At the upstream side of the decarburization zone 2, an atmospheric gas discharge port 6 is provided to discharge the atmospheric gas to the outside of the apparatus. The decarburization reaction formula is represented by the following formula (I).
C (in Fe) + H 2 O (g) = CO (g) + H 2 (g) (I)
　脱酸ゾーン３では、ラジアントチューブ１１により雰囲気温度を７００～１１００℃に制御し、脱窒ゾーン４からの雰囲気ガス（露点：４０℃以下の水素ガス）を用いて、粗製鉄基粉末から脱酸を行うとしている。なお、脱酸の反応式は、次式（ＩＩ）で表される。
　　　ＦｅＯ（ｓ）＋　Ｈ２（ｇ）＝Ｆｅ（ｓ）＋Ｈ２Ｏ（ｇ）…（ＩＩ） In the deoxidation zone 3, the ambient temperature is controlled to 700 to 1100 ° C. by the radiant tube 11, and deoxidation is performed from the crude iron-based powder using the atmospheric gas from the denitrification zone 4 (dew point: hydrogen gas of 40 ° C. or less). Is going to do. The reaction formula for deoxidation is represented by the following formula (II).
FeO (s) + H 2 (g) = Fe (s) + H 2 O (g) (II)
　脱窒ゾーン４では、ラジアントチューブ１１により雰囲気温度を４５０～７５０℃に制御し、この脱窒ゾーン４の下流側に設けられた雰囲気ガス導入口５から反応ガスである水素ガス（露点：４０℃以下）を導入して、粗製鉄基粉末から脱窒するとしている。なお、脱窒の反応式は、次式（ＩＩＩ）で表される。
　　　Ｎ（ｉｎ　Ｆｅ）＋　３／２Ｈ２（ｇ）＝ＮＨ３（ｇ）…（ＩＩＩ）
　水封槽１５は、炉外ガスの炉内ガスへの混入や炉内ガスの炉外への漏洩を遮断する働きを果たしている。 In the denitrification zone 4, the ambient temperature is controlled to 450 to 750 ° C. by the radiant tube 11, and hydrogen gas (dew point: 40 ° C.) as a reaction gas is supplied from the atmosphere gas inlet 5 provided on the downstream side of the denitrification zone 4. The following is introduced to denitrify the crude iron-based powder. The denitrification reaction formula is represented by the following formula (III).
N (in Fe) + 3 / 2H 2 (g) = NH 3 (g) (III)
The water sealing tank 15 functions to block the mixing of the outside gas into the furnace gas and the leakage of the inside gas to the outside of the furnace.
　また、特許文献５に記載されたベルト炉タイプの熱処理装置による熱処理温度パターンの典型例を図２に示す。処理される鉄基粉末は、（イ）または（ロ）に示したように、炉に入るとまず脱炭ゾーンで昇温され、続いて脱酸ゾーンで均熱され、最後に脱窒ゾーンで冷却される。鉄基粉末の流れと逆向きに導入される水素ガスは、まず脱窒ゾーンに入って昇温されながら鉄基粉末の脱窒を行い、次に脱酸ゾーンに入って一定の温度に保たれながら鉄基粉末の脱酸を行い、最後に脱炭ゾーンに所定量の水蒸気とともに入り、冷却されながら鉄基粉末の脱炭を行う。 Further, a typical example of a heat treatment temperature pattern by a belt furnace type heat treatment apparatus described in Patent Document 5 is shown in FIG. As shown in (a) or (b), the iron-based powder to be treated is first heated in the decarburization zone, then soaked in the deoxidation zone, and finally in the denitrification zone. To be cooled. The hydrogen gas introduced in the direction opposite to the flow of the iron-based powder first enters the denitrification zone, denitrifies the iron-based powder while being heated, and then enters the deoxidation zone and is kept at a constant temperature. The iron-base powder is deoxidized while finally entering the decarburization zone together with a predetermined amount of water vapor, and the iron-base powder is decarburized while being cooled.
［不活性ガス］
　本発明において、上記不活性ガスとしては、特に限定されず、任意の不活性ガスを用いることができる。好適に用いることのできる不活性ガスの例としては、アルゴン（Ａｒ）ガス、窒素（Ｎ２）ガス、およびそれらの混合ガスが挙げられる。 [Inert gas]
In the present invention, the inert gas is not particularly limited, and any inert gas can be used. Examples of the inert gas that can be suitably used include argon (Ar) gas, nitrogen (N 2 ) gas, and a mixed gas thereof.
　前記不活性ガスは、上記移動床炉においてアトマイズ鉄基粉末の熱処理を行う間、平均ガス流速ｖ（ｍｍ／ｓ）となるように該移動床炉内へ供給される。不活性ガスは、移動床炉内に、原料粉末の移動方向と反対の方向に流すことが好ましい。例えば、移動床炉の一端（上流側）からアトマイズ鉄基粉末を供給し、該アトマイズ鉄基粉末をベルト等の搬送手段により該移動床炉の他端（下流側）へ搬送する場合には、不活性ガスを前記他端（下流側）から導入し、前記一端（上流側）より排気することが好ましい。そのため、移動床炉は、一端にアトマイズ鉄基粉末供給口および雰囲気ガス排出口を備え、他端に処理済みの粉末（合金鋼粉）の排出口および不活性ガス供給口を備えることが好ましい。 The inert gas is supplied into the moving bed furnace so as to have an average gas flow velocity v (mm / s) during the heat treatment of the atomized iron-based powder in the moving bed furnace. The inert gas is preferably flowed in the moving bed furnace in a direction opposite to the moving direction of the raw material powder. For example, when supplying atomized iron-based powder from one end (upstream side) of the moving bed furnace, and transporting the atomized iron-based powder to the other end (downstream side) of the moving bed furnace by a conveying means such as a belt, It is preferable that the inert gas is introduced from the other end (downstream side) and exhausted from the one end (upstream side). Therefore, it is preferable that the moving bed furnace is provided with an atomized iron-based powder supply port and an atmosphere gas discharge port at one end, and a discharge port and an inert gas supply port for treated powder (alloy steel powder) at the other end.
［熱処理］
　上記のように不活性ガスを供給した状態で、前記アトマイズ鉄基粉末を前記移動床炉内で熱処理することにより、粉末冶金用合金鋼粉を得ることができる。前記熱処理により、アトマイズ鉄基粉末に含まれるＣおよびＯは、後述する脱炭および脱酸（還元）の反応により、除去される。 [Heat treatment]
The alloy steel powder for powder metallurgy can be obtained by heat-treating the atomized iron-based powder in the moving bed furnace with the inert gas supplied as described above. By the heat treatment, C and O contained in the atomized iron-based powder are removed by a decarburization and deoxidation (reduction) reaction described later.
・ｄ／√ｖ≦３．０
　本発明においては、上記熱処理を行う間、前記充填層の厚さｄ（ｍｍ）および平均ガス流速ｖ（ｍｍ／ｓ）の両者を、下記（１）式を満足するように制御する。
　ｄ／√ｖ≦３．０（ｍｍ１／２・ｓ１／２）…（１） ・ D / √v ≦ 3.0
In the present invention, during the heat treatment, both the thickness d (mm) of the packed bed and the average gas flow velocity v (mm / s) are controlled so as to satisfy the following expression (1).
d / √v ≦ 3.0 (mm 1/2 · s 1/2 ) (1)
　上記条件で熱処理を行うことにより、アトマイズ鉄基粉末がＣｒ、Ｍｎ、Ｖなどの易酸化性元素を含むにもかかわらず、アトマイズ鉄基粉末に含まれるＣおよびＯを安定して低減することができる。そしてその結果、熱処理後の合金鋼粉におけるＣ含有量およびＯ含有量を、例えば、Ｃ≦０．１％、Ｏ≦０．２８％といった極めて低い値とすることができる。以下、その理由について説明する。 By performing the heat treatment under the above conditions, it is possible to stably reduce C and O contained in the atomized iron-based powder in spite of the fact that the atomized iron-based powder contains oxidizable elements such as Cr, Mn, and V. it can. As a result, the C content and the O content in the alloy steel powder after the heat treatment can be set to extremely low values such as C ≦ 0.1% and O ≦ 0.28%. The reason will be described below.
　アトマイズ鉄基粉末に含まれるＦｅ、Ｃｒ、Ｍｎ、およびＶの酸化物と炭素との反応（脱酸反応）は、次の（ａ）～（ｄ）式で表される。
　ＦｅＯ（ｓ）＋Ｃ＝Ｆｅ（ｓ）＋ＣＯ（ｇ）…（ａ）
　Ｃｒ２Ｏ３（ｓ）＋３Ｃ＝２Ｃｒ（ｉｎ　Ｆｅ）＋３ＣＯ（ｇ）…（ｂ）
　ＭｎＯ（ｓ）＋Ｃ＝Ｍｎ（ｉｎ　Ｆｅ）＋ＣＯ（ｇ）…（ｃ）
　ＶＯ（ｓ）＋　Ｈ２（ｇ）＝　Ｖ（ｉｎ　Ｆｅ）＋Ｈ２Ｏ（ｇ）…（ｄ） The reaction (deoxidation reaction) of the oxides of Fe, Cr, Mn, and V contained in the atomized iron-based powder with carbon is represented by the following equations (a) to (d).
FeO (s) + C = Fe (s) + CO (g) (a)
Cr 2 O 3 (s) + 3C = 2Cr (in Fe) + 3CO (g) (b)
MnO (s) + C = Mn (in Fe) + CO (g) (c)
VO (s) + H 2 (g) = V (in Fe) + H 2 O (g) (d)
　上記反応ではＣＯガスが生成するため、脱酸反応を効率よく進めるためには、炉内雰囲気におけるＣＯ分圧を低く保つ必要がある。 Since CO gas is generated in the above reaction, it is necessary to keep the CO partial pressure in the furnace atmosphere low in order to advance the deoxidation reaction efficiently.
　そのためには、移動床炉内へ装入する鉄基粉末の量すなわち充填層厚を抑制することが考えられる。また、上記反応により発生したＣＯガスを除去する、あるいは移動床炉に導入する不活性ガスで希釈することによってＣＯ分圧を低下させることが考えられる。そこで、本発明では、充填層の厚さｄと、不活性ガスを炉内へ導入したときの炉内での平均ガス流速ｖを、上記（１）式を満たすように制御することとした。 Therefore, it is conceivable to suppress the amount of iron-based powder charged into the moving bed furnace, that is, the packed bed thickness. It is also conceivable to reduce the CO partial pressure by removing the CO gas generated by the reaction or diluting with an inert gas introduced into the moving bed furnace. Therefore, in the present invention, the thickness d of the packed bed and the average gas flow velocity v in the furnace when the inert gas is introduced into the furnace are controlled so as to satisfy the above formula (1).
　上記（１）式を満たすように充填層厚ｄと平均ガス流速ｖを制御することにより、脱酸が効率的に進む理由については、必ずしも明確ではないものの、次のように推定される。 The reason why the deoxidation proceeds efficiently by controlling the packed bed thickness d and the average gas flow velocity v so as to satisfy the above expression (1) is not necessarily clear, but is estimated as follows.
　すなわち、移動床炉内での熱処理中、充填層の表面上部の空間には流している不活性ガスの速度境界層ができる。この速度境界層の厚さは√ｖに反比例することが境界層に関する理論から導かれる。また、還元反応により発生したＣＯの拡散速度は、速度境界層の厚さによらず一定であると考えられるので、拡散時間は速度境界層の厚さに比例する。したがって、速度境界層厚さを半分にして同じ拡散時間を与えると充填層表面でのＣＯの濃度は１／２になると考えられ、そうすると、充填層の厚さを２倍にしても充填層の最下層でのＣＯの濃度を同じ濃度にできると推定される。したがって、濃度を一定と仮定すれば充填層厚と速度境界層の厚さは反比例することになり、つまりは、充填層厚と√ｖが比例関係にあると推定される。よって、本発明のように、熱処理において、ｄ／√ｖ≦３．０の条件が満たされるように充填層厚とガス流速の調整を行えば、煩雑な維持管理が必要となるガス分析装置を使わなくても、上記（ａ）～（ｄ）式の反応によって決まる平衡ＣＯ分圧よりも炉内雰囲気におけるＣＯ分圧が低い状態が維持されることになる。 That is, during the heat treatment in the moving bed furnace, a velocity boundary layer of the flowing inert gas is formed in the space above the surface of the packed bed. It is derived from the theory regarding the boundary layer that the thickness of the velocity boundary layer is inversely proportional to √v. Further, since the diffusion rate of CO generated by the reduction reaction is considered to be constant regardless of the thickness of the velocity boundary layer, the diffusion time is proportional to the thickness of the velocity boundary layer. Therefore, if the velocity boundary layer thickness is halved and the same diffusion time is given, it is considered that the concentration of CO on the surface of the packed layer is halved. Then, even if the thickness of the packed layer is doubled, It is estimated that the CO concentration in the lowermost layer can be made the same. Therefore, assuming that the concentration is constant, the packed layer thickness and the velocity boundary layer thickness are inversely proportional, that is, it is estimated that the packed layer thickness and √v are in a proportional relationship. Therefore, as in the present invention, in the heat treatment, if the packed layer thickness and the gas flow rate are adjusted so that the condition of d / √v ≦ 3.0 is satisfied, a gas analyzer that requires complicated maintenance management is required. Even if it is not used, the state in which the CO partial pressure in the furnace atmosphere is lower than the equilibrium CO partial pressure determined by the reactions of the above formulas (a) to (d) is maintained.
　なお、粉末冶金用合金鋼粉におけるＯ含有量をさらに低減するという観点からは、ｄ／√ｖ≦２．６（ｍｍ１／２・ｓ１／２）とすることがより好ましい。一方、ｄ／√ｖの下限は特に限定されず、低ければ低いほどよいが、ｄを過度に小さくすると生産効率が低下し、また、ｖを過度に大きくするとコストが増大するため、０．１以上とすることが好ましく、０．３以上とすることがより好ましい。 From the viewpoint of further reducing the O content in the powder metallurgical alloy steel powder, it is more preferable that the d / √v ≦ 2.6 (mm 1/2 · s 1/2). On the other hand, the lower limit of d / √v is not particularly limited. The lower the better, the lower the better. However, if d is excessively decreased, the production efficiency decreases, and if v is excessively increased, the cost increases. It is preferable to set it as the above, and it is more preferable to set it as 0.3 or more.
［冷却］
　本発明の一実施形態においては、前記熱処理によって還元されたアトマイズ鉄基粉末を、さらに、水素ガスまたは水素含有気体を用いて冷却することが好ましい。その理由は次の通りである。 [cooling]
In one embodiment of the present invention, it is preferable that the atomized iron-based powder reduced by the heat treatment is further cooled using hydrogen gas or a hydrogen-containing gas. The reason is as follows.
　還元されたアトマイズ鉄基粉末には、不純物としてＮが含まれている場合がある。特に、上記還元を、Ｎ２含有雰囲気中で行った場合、最終的に得られる粉末冶金用合金鋼粉のＮ含有量が、０．００５質量％を超えるような、高濃度となる場合がある。合金鋼粉にＮが含まれていると圧縮性が低下するため、合金鋼粉のＮ含有量をできるだけ低減することが好ましい。そこで、還元されたアトマイズ鉄基粉末を、水素ガスまたは水素含有気体を用いて冷却すれば、下記（ｅ）式の反応により、粉末中に含まれるＮを除去することができる。なお、最終的に得られる粉末冶金用合金鋼粉のＮ含有量は、０．００５質量％以下とすることが好ましい。
　２Ｎ（ｉｎ　Ｆｅ）＋３Ｈ２（ｇ）＝２ＮＨ３（ｇ）…（ｅ） The reduced atomized iron-based powder may contain N as an impurity. In particular, when the above reduction is performed in an N 2 -containing atmosphere, the N content of the finally obtained alloy steel powder for powder metallurgy may be as high as exceeding 0.005% by mass. . When the alloy steel powder contains N, the compressibility is lowered. Therefore, it is preferable to reduce the N content of the alloy steel powder as much as possible. Therefore, if the reduced atomized iron-based powder is cooled using hydrogen gas or a hydrogen-containing gas, N contained in the powder can be removed by the reaction of the following formula (e). In addition, it is preferable that N content of the alloy steel powder for powder metallurgy finally obtained shall be 0.005 mass% or less.
2N (in Fe) + 3H 2 (g) = 2NH 3 (g) (e)
　上記（ｅ）式の反応を効果的に進めるという観点からは、上記冷却を、水素ガスを用いて行うことがより好ましい。 From the viewpoint of effectively advancing the reaction of the above formula (e), it is more preferable to perform the cooling using hydrogen gas.
　上記冷却に用いるガスは、任意の方法で供給すればよい。例えば、移動床炉内の、鉄基粉末の還元が完了した位置、または前記位置よりも搬送方向の下流側において、移動床炉内の不活性ガスを排気するとともに、冷却用のガスを移動床炉内へ導入することができる。上記タイミング（移動床炉中の排気および導入位置）については、厳密に冷却が始まる位置でなくともよく、均熱中であっても鉄粉の還元が完了している位置以降であれば問題はない。また、反対に、冷却（粉末の温度低下）が始まった後に、上記雰囲気ガスの入れ替えを行うこともできる。ただし、反応効率の観点からは、上記（ｅ）式の反応を、４５０～７５０℃の温度域で進行させることが望ましいため、粉末の温度が４５０℃未満となる前、言い換えれば、粉末の温度が４５０℃以上である時点で、上記不活性ガスの排気と冷却用ガスの導入を行うことが好ましい。 The gas used for the cooling may be supplied by any method. For example, the inert gas in the moving bed furnace is exhausted at the position where the reduction of the iron-based powder in the moving bed furnace is completed, or at the downstream side in the transport direction from the position, and the cooling gas is transferred to the moving bed furnace. It can be introduced into the furnace. The timing (exhaust and introduction position in the moving bed furnace) does not have to be strictly the position where cooling starts, and there is no problem as long as it is after the position where the reduction of iron powder is completed even during soaking. . On the other hand, after the cooling (powder temperature decrease) starts, the atmosphere gas can be replaced. However, from the viewpoint of reaction efficiency, it is desirable to proceed the reaction of the above formula (e) in a temperature range of 450 to 750 ° C., so before the temperature of the powder becomes less than 450 ° C., in other words, the temperature of the powder When the temperature is 450 ° C. or higher, it is preferable to exhaust the inert gas and introduce a cooling gas.
（露点）
・不活性ガスの露点：５℃以下
　炉内に導入する不活性ガスの露点を５℃以下とすることが好ましい。不活性ガスの露点があまりに高いと、脱酸反応（還元反応）が進みにくくなる。本来、上式（ｂ）および（ｃ）の反応においてＣｒ２Ｏ３およびＭｎＯの還元に使われるはずのＣが雰囲気中の水蒸気と反応して消費されたり、一旦還元されたＣｒやＭｎが雰囲気の水蒸気によって再酸化されたりするためである。熱処理での還元反応を効率よく進めるためには、このようなＣの無駄な消費や、ＣｒおよびＭｎの再酸化を抑制することが必要である。上記観点で、本発明者らが検討を行った結果、充填層厚ｄと不活性ガスの平均ガス流速ｖが上記の条件を満足する場合においては、不活性ガスの露点を５℃以下とすることにより、還元反応を効率的に進めることができることを見出した。 (Dew point)
Inert gas dew point: 5 ° C. or less It is preferable that the dew point of the inert gas introduced into the furnace is 5 ° C. or less. If the dew point of the inert gas is too high, the deoxidation reaction (reduction reaction) is difficult to proceed. Originally, in the reaction of the above formulas (b) and (c), C that should be used for reduction of Cr 2 O 3 and MnO reacts with water vapor in the atmosphere and is consumed, or once reduced Cr and Mn are in the atmosphere This is because it is reoxidized by water vapor. In order to efficiently advance the reduction reaction in the heat treatment, it is necessary to suppress such wasteful consumption of C and reoxidation of Cr and Mn. From the above viewpoint, as a result of investigations by the present inventors, when the packed layer thickness d and the average gas flow velocity v of the inert gas satisfy the above conditions, the dew point of the inert gas is set to 5 ° C. or less. Thus, it has been found that the reduction reaction can proceed efficiently.
　なお、従来のように、Ｃｒなどの易酸化性元素を含まない鉄基粉末では、特許文献５にあるように、露点を４０℃以下とすれば問題はない。しかし、本発明では易酸化性元素を含む鉄基粉末を用いるため、上記のように不活性ガスの露点を５℃以下とすることが好ましく、－１０℃以下とすることがより好ましい。 In addition, as in the conventional art, there is no problem if the dew point is set to 40 ° C. or less, as in Patent Document 5, in the conventional iron-based powder that does not contain an easily oxidizable element such as Cr. However, since an iron-based powder containing an easily oxidizable element is used in the present invention, the dew point of the inert gas is preferably 5 ° C. or less, more preferably −10 ° C. or less as described above.
　脱酸反応の進みやすさの点では、不活性ガスの露点は低いほどよい。しかし、露点が低いガスは高価であり、過度に露点が低いガス使用することは製造コストの増加を招くため、通常は前記露点を－４０℃以上とすることが好ましい。 The lower the dew point of the inert gas, the better the deoxidation reaction will proceed. However, a gas with a low dew point is expensive, and the use of a gas with an excessively low dew point causes an increase in production cost. Therefore, it is usually preferable to set the dew point to −40 ° C. or higher.
　上記のような低い露点を達成するためには、炉外ガスの炉内への侵入や炉内ガスの炉外への漏洩を遮断することが好ましい。そのため、上記移動床炉は、ガスの漏洩および侵入を防止するための封止手段を備えることが好ましい。前記封止手段としては、例えば、特許文献５に記載されているような水封槽（図１の１５）を用いることができるが、シールロールなどの水を使わない方式とすることがより好ましい。前記封止手段は、搬送方向の上流側と下流側の両端に設けることが好ましい。 In order to achieve the low dew point as described above, it is preferable to block intrusion of out-of-furnace gas into the furnace and leakage of out-of-furnace gas to the outside of the furnace. Therefore, it is preferable that the moving bed furnace includes a sealing unit for preventing gas leakage and intrusion. As the sealing means, for example, a water-sealed tank (15 in FIG. 1) as described in Patent Document 5 can be used, but it is more preferable to use a system that does not use water such as a seal roll. . The sealing means is preferably provided at both ends on the upstream side and the downstream side in the transport direction.
（雰囲気温度、保持時間）
　さらに、上記熱処理では、雰囲気温度Ｔ：１０８０℃以上、保持時間ｔ：１０４－０．００３７・Ｔ（ｈ）以上の条件で脱酸を行うことが好ましい。言い換えれば、上記熱処理では、雰囲気温度Ｔ：１０８０℃以上で、保持時間ｔ：１０４－０．００３７・Ｔ（ｈ）以上保持する時間を設けることが好ましい。以下、その理由について説明する。 (Atmosphere temperature, holding time)
Further, in the above heat treatment, it is preferable to perform deoxidation under conditions of an atmospheric temperature T: 1080 ° C. or more and a holding time t: 10 4−0.0037 · T (h) or more. In other words, in the heat treatment, it is preferable to provide a time for holding at an atmospheric temperature T: 1080 ° C. or more and a holding time t: 10 4−0.0037 · T (h) or more. The reason will be described below.
・雰囲気温度Ｔ：１０８０℃以上
　従来のように、Ｃｒ、Ｍｎ、Ｖなどの易酸化性元素を含まない鉄基粉末を還元する場合には、還元すべき酸化物はＦｅＯのみである。そのため、特許文献５に記載されているように脱酸ゾーンにおける雰囲気温度を７００℃以上とすれば、上式（２）の平衡反応から決まる平衡露点は７０℃以上と高い温度になる。このとき、導入する不活性ガスの露点を特許文献５にあるように４０℃以下とすれば、十分な速度で脱酸反応（還元反応）が進むために問題は発生しなかった。 -Atmospheric temperature T: 1080 degreeC or more As usual, when reducing the iron-based powder which does not contain oxidizable elements, such as Cr, Mn, and V, the oxide which should be reduced is only FeO. Therefore, as described in Patent Document 5, when the atmospheric temperature in the deoxidation zone is set to 700 ° C. or higher, the equilibrium dew point determined from the equilibrium reaction of the above formula (2) is as high as 70 ° C. or higher. At this time, if the dew point of the inert gas to be introduced was set to 40 ° C. or less as described in Patent Document 5, no problem occurred because the deoxidation reaction (reduction reaction) proceeded at a sufficient rate.
　これに対して、Ｃｒ、Ｍｎ、Ｖなどの易酸化性元素を含む鉄基粉末を還元する場合、雰囲気温度を１０８０℃以上とすることが好ましい。一方、雰囲気温度の上限は、特に限定されないが、装置の耐熱性能、製造コスト等を考慮すれば、１２００℃程度とすることが好ましい。なお、ここで「雰囲気温度」とは、移動床炉内の鉄基粉末（充填層）の表面から直上２０ｍｍの位置で、熱電対により測定した温度とする。 In contrast, when reducing an iron-based powder containing an easily oxidizable element such as Cr, Mn, or V, the atmospheric temperature is preferably set to 1080 ° C. or higher. On the other hand, the upper limit of the ambient temperature is not particularly limited, but is preferably about 1200 ° C. in consideration of the heat resistance performance of the apparatus, the manufacturing cost, and the like. Here, the “atmosphere temperature” is a temperature measured by a thermocouple at a position 20 mm immediately above the surface of the iron-based powder (packed bed) in the moving bed furnace.
・保持時間ｔ：１０４－０．００３７・Ｔ（ｈ）以上
　保持時間ｔを、雰囲気温度Ｔ（℃）に応じて、１０４－０．００３７・Ｔ（ｈ）以上とすれば、Ｏをより低減することができるため好ましい。なお、前記ｔおよびＴの間の関係は、様々なＴおよびｔで合金鋼粉を製造する実験を行った結果から決定した。具体的には、得られた合金鋼粉のＯ含有量を、Ｔ－ｔ図上へプロットし、同一酸素量を結ぶ曲線（等高線）を近似式として定めた。一方、保持時間の上限は特に限定されないが、脱酸反応完了に必要な時間以上に保持を行っても製造コストが増加するだけであるため、　前記保持時間は４時間以下とすることが好ましい。 Holding time t: 10 4 -0.0037 · T (h) or more If the holding time t is 10 4 -0.0037 · T (h) or more according to the ambient temperature T (° C.), O Since it can reduce more, it is preferable. In addition, the relationship between the said t and T was determined from the result of having conducted the experiment which manufactures alloy steel powder with various T and t. Specifically, the O content of the obtained alloy steel powder was plotted on a Tt diagram, and a curve (contour line) connecting the same oxygen content was determined as an approximate expression. On the other hand, the upper limit of the retention time is not particularly limited, but the retention time is preferably 4 hours or less because the production cost only increases even if the retention time is longer than the time required for completion of the deoxidation reaction.
　以下、実施例により本発明をさらに詳細に説明するが、本発明は以下の例に何ら限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.
（実施例１）
　水アトマイズ法にて、表１に示す成分組成を有するアトマイズ鉄基粉末を製造した。アトマイズ鉄基粉末記号：Ａ、Ｂ、Ｆ、Ｉ、およびＭについては、［Ｏ］≧４／３［Ｃ］－２／１５を満たしているが、４／３［Ｃ］＋０．２８≧［Ｏ］を満たしておらずＯ過剰であるため、熱処理後のＣ量およびＯ量を適正範囲に調整するためには、熱処理前に、適正量の炭素成分、例えば、黒鉛粉などの炭素粉末の混合が必要である。アトマイズ鉄基粉末記号：Ｃ～Ｅ、Ｇ、Ｈ、およびＪについては、［Ｏ］≧４／３［Ｃ］－２／１５および４／３［Ｃ］＋０．２８≧［Ｏ］をともに満たしており、熱処理前での炭素粉末の混合は必要ない。アトマイズ鉄基粉末記号：ＫおよびＬについては、［Ｏ］≧４／３［Ｃ］－２／１５を満たしておらずＣ過剰である。アトマイズ鉄基粉末記号：ＬおよびＭについては、Ｃ量またはＯ量がアトマイズ鉄基粉末での適正範囲を外れている。 Example 1
An atomized iron-based powder having the component composition shown in Table 1 was produced by the water atomization method. Atomized iron-based powder symbols: A, B, F, I, and M satisfy [O] ≧ 4/3 [C] −2/15, but 4/3 [C] + 0.28 ≧ [ O] is not satisfied, and O is excessive. Therefore, in order to adjust the C amount and O amount after heat treatment to an appropriate range, an appropriate amount of carbon component, for example, carbon powder such as graphite powder is adjusted before heat treatment. Mixing is necessary. Atomized iron-based powder symbols: C to E, G, H, and J satisfy both [O] ≧ 4/3 [C] −2/15 and 4/3 [C] + 0.28 ≧ [O] It is not necessary to mix carbon powder before heat treatment. Atomized iron-based powder symbols: K and L do not satisfy [O] ≧ 4/3 [C] −2/15 and are C-excessive. Atomized iron-based powder symbol: For L and M, the amount of C or O is outside the appropriate range for the atomized iron-based powder.
　これらのアトマイズ鉄基粉末を、移動床炉を用いて熱処理し、解砕して粉末冶金用合金鋼粉を得た。使用したアトマイズ鉄基粉末と、熱処理条件を表２、３に示す。一部の例においては、炭素成分としての黒鉛粉を前記アトマイズ鉄基粉末に混合した後に、移動床炉へ供給した。前記炭素成分の混合量を、表２、３に合わせて示した。 These atomized iron-based powders were heat-treated using a moving bed furnace and crushed to obtain alloy steel powder for powder metallurgy. The used atomized iron-based powder and heat treatment conditions are shown in Tables 2 and 3. In some examples, graphite powder as a carbon component was mixed with the atomized iron-based powder and then supplied to the moving bed furnace. The mixing amounts of the carbon components are shown in Tables 2 and 3.
　また、前記熱処理においては、前記アトマイズ鉄基粉末を表２、３に示した充填層厚さｄとなるように移動床炉内へ供給し、表２、３に示した平均ガス流速ｖとなるように不活性ガスを供給しながら、連続的に熱処理を実施した。得られた粉末冶金用合金鋼粉の成分組成は表２、３に示した通りであった。なお、各表および以下の説明における不活性ガスの組成における％表示は、ｖｏｌ％を意味する。 In the heat treatment, the atomized iron-based powder is supplied into the moving bed furnace so as to have the packed bed thickness d shown in Tables 2 and 3, and the average gas flow velocity v shown in Tables 2 and 3 is obtained. Thus, the heat treatment was continuously performed while supplying the inert gas. The component composition of the obtained alloy steel powder for powder metallurgy was as shown in Tables 2 and 3. In addition,% display in the composition of the inert gas in each table | surface and the following description means vol%.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
・Ａｒ含有ガスを用いた場合
　表２は、不活性ガスとしてＡｒ含有ガスを用いた場合の例である。粉末記号：ＡおよびＩを使用し、炭素粉末を混合していないもの（粉末記号：Ａ１０、Ｉ１０）については、アトマイズ鉄基粉末がＯ過剰であるため、熱処理条件を適正に調整した上でもこれらを熱処理した後のＯ量が適正値を外れている。したがって、アトマイズ鉄基粉末記号：ＡおよびＩについては、４／３（［Ｃ］＋［ＭＸＣ］）＋０．２８≧［Ｏ］を満たすような適正量の炭素粉末の混合が必要である。アトマイズ鉄基粉末記号：Ｂ、Ｆ、Ｍについても、アトマイズ鉄基粉末がＯ過剰であるため、同様である。これらについて、４／３（［Ｃ］＋［ＭＸＣ］）＋０．２８≧［Ｏ］を満たすように表２に示したような黒鉛粉の混合を行った例が、粉末記号：Ａ１１～Ａ１８、Ｂ１１～Ｂ１５、Ｆ１１、Ｉ１１、およびＭ１１に示されている。 -When Ar containing gas is used Table 2 is an example at the time of using Ar containing gas as an inert gas. For powder symbols: A and I that are not mixed with carbon powder (powder symbols: A10, I10), the atomized iron-based powder is O-excess, so these can be obtained even after the heat treatment conditions are adjusted appropriately. The amount of O after heat-treating is out of the proper value. Therefore, for the atomized iron-based powder symbols: A and I, it is necessary to mix an appropriate amount of carbon powder that satisfies 4/3 ([C] + [MXC]) + 0.28 ≧ [O]. The same applies to the atomized iron-based powder symbols: B, F, and M because the atomized iron-based powder is O-excessive. Regarding these, examples of mixing graphite powder as shown in Table 2 so as to satisfy 4/3 ([C] + [MXC]) + 0.28 ≧ [O] are powder symbols: A11 to A18, B11 to B15, F11, I11, and M11.
　同表から明らかなように、鉄粉の充填層厚ｄ（ｍｍ）と不活性ガスの流速ｖ（ｍｍ／ｓ）との関係がｄ／√ｖ≦３．０を満たすもの（粉末記号：Ａ１１～Ａ１５、Ａ１７～Ａ１９、Ｂ１２～Ｂ１５、Ｃ１１～Ｃ１４、Ｄ１１～Ｄ１３、Ｅ１１～Ｅ１３、Ｆ１１、Ｇ１１、Ｈ１１、Ｉ１１、Ｊ１１）についてはＯ量が０．２８質量％以下となっており、逆にｄ／√ｖ≦３．０を満たさないもの（粉末記号：Ａ１５、Ｂ１１）についてはＯ量が０．２８質量％を超えている。さらに、不活性ガスが１００％Ａｒでｄ／√ｖ≦２．６のもの（粉末記号：Ａ１１～Ａ１３、Ａ１６、Ｂ１３～Ｂ１５、Ｃ１１～Ｃ１４、Ｄ１１～Ｄ１４、Ｅ１１～Ｅ１３、Ｆ１１、Ｇ１１、Ｈ１１、Ｉ１１、Ｊ１１）についてはＣ量が０．１質量％以下、Ｏ量が０．２３質量％以下となっており、Ｏ量がより低減されているので、ｄ／√ｖ≦２．６とすることが好ましい。 As is apparent from the table, the relationship between the packed bed thickness d (mm) of the iron powder and the flow velocity v (mm / s) of the inert gas satisfies d / √v ≦ 3.0 (powder symbol: A11 -A15, A17-A19, B12-B15, C11-C14, D11-D13, E11-E13, F11, G11, H11, I11, J11) have an O content of 0.28% by mass or less. In addition, for those not satisfying d / √v ≦ 3.0 (powder symbols: A15, B11), the amount of O exceeds 0.28 mass%. Further, the inert gas is 100% Ar and d / √v ≦ 2.6 (powder symbols: A11 to A13, A16, B13 to B15, C11 to C14, D11 to D14, E11 to E13, F11, G11, For H11, I11, J11), the C content is 0.1% by mass or less and the O content is 0.23% by mass or less. Since the O content is further reduced, d / √v ≦ 2.6. It is preferable that
　また、粉末記号：Ａ１６～Ａ１８については、導入ガスを１００％Ａｒから５０％Ａｒ－５０％Ｎ２まで変化させているが、いずれもＯ量で０．２８質量％以下が得られている。 In addition, regarding the powder symbols: A16 to A18, the introduced gas was changed from 100% Ar to 50% Ar-50% N 2 , and in each case, the O amount was 0.28% by mass or less.
　さらに、粉末記号：Ｃ１１～Ｃ１４については、露点が５℃以下のもの（粉末記号：Ｃ１２～Ｃ１４）でＯ量が０．２０質量％以下と、良好な値が得られている。また、露点が－１０℃以下のもの（粉末記号：Ｃ１４）ではＯ量が０．１５質量％以下と、一段と良好な値が得られている。さらに、粉末記号：Ｄ１１～Ｄ１３およびＥ１１～Ｅ１３については、均熱温度が１０８０℃以上でｔ≧１０４－０．００３７・Ｔを満たすもの（粉末記号：Ｄ１３～Ｄ１４、Ｅ１３）でＯ量が０．２０質量％以下と、一段と良好な値が得られている。 Further, regarding powder symbols: C11 to C14, good values were obtained with a dew point of 5 ° C. or less (powder symbols: C12 to C14) and an O amount of 0.20 mass% or less. Further, when the dew point is −10 ° C. or lower (powder symbol: C14), the amount of O is 0.15% by mass or lower, which is a much better value. Further, for powder symbols D11 to D13 and E11 to E13, the soaking temperature is 1080 ° C. or higher and t ≧ 10 4−0.0037 · T is satisfied (powder symbols: D13 to D14, E13) and the amount of O is An even better value of 0.20% by mass or less is obtained.
　さらに、粉末記号：Ｃ１１～Ｃ１４、Ｄ１１～Ｄ１４、Ｅ１１～Ｅ１３、Ｇ１１、Ｈ１１、Ｊ１１については、アトマイズ鉄基粉末でのＣ量およびＯ量が［Ｏ］≧４／３［Ｃ］－２／１５および４／３［Ｃ］＋０．２８≧［Ｏ］をともに満たしているので、熱処理前で炭素粉末を混合しなくとも、適正な熱処理条件を用い不活性ガス雰囲気で処理することで、熱処理後のＣ量およびＯ量について適正値が得られることを示している。 Further, for powder symbols: C11 to C14, D11 to D14, E11 to E13, G11, H11, and J11, the amount of C and O in the atomized iron-based powder is [O] ≧ 4/3 [C] −2 / Since both 15 and 4/3 [C] + 0.28 ≧ [O] are satisfied, the heat treatment can be performed by treating in an inert gas atmosphere using appropriate heat treatment conditions without mixing the carbon powder before the heat treatment. It shows that appropriate values are obtained for the subsequent C and O amounts.
　他方、粉末記号：Ｋ１１については、アトマイズ鉄基粉末でのＣ量およびＯ量が［Ｏ］≧４／３［Ｃ］－２／１５を満たしておらず、Ｃ過剰であるため、適正な熱処理条件で処理しても、熱処理後のＣ量が適正範囲を外れていることを示している。 On the other hand, for the powder symbol K11, the amount of C and O in the atomized iron-based powder does not satisfy [O] ≧ 4/3 [C] −2/15 and is excessive C. This shows that the amount of C after the heat treatment is out of the proper range even if the treatment is performed under the conditions.
　また、粉末記号：Ｌ１１およびＭ１１については、アトマイズ鉄基粉末のＣ量またはＯ量が高過ぎたために、熱処理によってもＣ量またはＯ量が規定の量まで低減できていない。 In addition, regarding the powder symbols L11 and M11, the C amount or O amount of the atomized iron-based powder is too high, and therefore the C amount or O amount cannot be reduced to the specified amount even by heat treatment.
・Ｎ２含有ガスを用いた場合
　表３は、Ｎ２含有雰囲気で熱処理を行った場合の例である。アトマイズ鉄基粉末記号：Ａ、Ｂ、ＦおよびＩについてはＯ過剰であるため、４／３（［Ｃ］＋［ＭＸＣ］）＋０．２８≧［Ｏ］を満たすような適正量の炭素粉末の混合が必要である。そこで、表３に示したような黒鉛粉の混合を行い、種々の熱処理条件で処理した例が、粉末記号：Ａ２１～Ａ２８、Ｂ２１～Ｂ２５、Ｃ２１～Ｃ２４、Ｄ２１～Ｄ２４、Ｅ２１～Ｅ２３、Ｆ２１、Ｇ２１、Ｈ２１、Ｉ２１、Ｊ２１に示されている。 · N 2 containing case Table 3 using the gas is an example of a case of performing heat treatment in an N 2 containing atmosphere. Atomized iron-based powder symbol: A, B, F and I are O-excessive, so an appropriate amount of carbon powder satisfying 4/3 ([C] + [MXC]) + 0.28 ≧ [O] Mixing is necessary. Accordingly, examples of mixing graphite powder as shown in Table 3 and treating under various heat treatment conditions are powder symbols: A21 to A28, B21 to B25, C21 to C24, D21 to D24, E21 to E23, F21. , G21, H21, I21, J21.
　同表から明らかなように、鉄粉の充填層厚ｄ（ｍｍ）と不活性ガスの流速ｖ（ｍｍ／ｓ）との関係がｄ／√ｖ≦３．０を満たすもの（粉末記号：Ａ２１～Ａ２４、Ａ２６～Ａ２８、Ｂ２２～Ｂ２５、Ｃ２１～Ｃ２４、Ｄ２１～Ｄ２４、Ｅ２１～Ｅ２３、Ｆ２１、Ｇ２１、Ｈ２１、Ｉ２１、Ｊ２１）についてはＯ量が０．２８質量％以下となっており、逆にｄ／√ｖ≦３．０を満たさないもの（粉末記号：Ａ２５、Ｂ２１）についてはＯ量が０．２８質量％を超えている。さらに、導入ガスが１００％Ｎ２でｄ／√ｖ≦２．６のもの（粉末記号：Ａ２１～Ａ２３、Ａ２６、Ｂ２３～Ｂ２５、Ｃ２１～Ｃ２４、Ｄ２１～Ｄ２４、Ｅ２１～Ｅ２３、Ｆ２１、Ｇ２１、Ｈ２１、Ｉ２１、Ｊ２１）についてはＣ量が０．１質量％以下、Ｏ量が０．２３質量％以下となっており、Ｏ量がより低減されているので、充填層厚ｄ（ｍｍ）と不活性ガスの流速ｖ（ｍｍ／ｓ）との関係は、ｄ／√ｖ≦２．６とすることが好ましいことが分かる。 As apparent from the table, the relationship between the packed bed thickness d (mm) of the iron powder and the flow velocity v (mm / s) of the inert gas satisfies d / √v ≦ 3.0 (powder symbol: A21 -A24, A26-A28, B22-B25, C21-C24, D21-D24, E21-E23, F21, G21, H21, I21, J21), the amount of O is 0.28% by mass or less. In addition, for those not satisfying d / √v ≦ 3.0 (powder symbols: A25, B21), the amount of O exceeds 0.28% by mass. Further, the introduced gas is 100% N 2 and d / √v ≦ 2.6 (powder symbols: A21 to A23, A26, B23 to B25, C21 to C24, D21 to D24, E21 to E23, F21, G21, For H21, I21, J21), the C amount is 0.1% by mass or less, the O amount is 0.23% by mass or less, and the O amount is further reduced. It can be seen that the relationship with the flow velocity v (mm / s) of the inert gas is preferably d / √v ≦ 2.6.
　また、粉末記号：Ａ２６～Ａ２８については、導入ガスを１００％Ｎ２から９０％Ｎ２－１０％Ｈｅまで変化させているが、いずれもＯ量で０．２８質量％以下が得られている。 In addition, regarding the powder symbols: A26 to A28, the introduced gas was changed from 100% N 2 to 90% N 2 -10% He, and in each case, the O amount was 0.28% by mass or less. .
　さらに、粉末記号：Ｃ２１～Ｃ２４については、露点が５℃以下のもの（粉末記号：Ｃ２２～Ｃ２４）でＯ量が０．２０質量％以下と、良好な値が得られている。また、露点が－１０℃以下のもの（粉末記号：Ｃ２４）ではＯ量が０．１５質量％以下と、一段と良好な値が得られている。さらに、粉末記号：Ｄ２１～Ｄ２４およびＥ２１～Ｅ２３については、均熱温度が１０８０℃以上でｔ≧１０４－０．００３７・Ｔを満たすもの（粉末記号：Ｄ２３～Ｄ２４、Ｅ２３）でＯ量が０．２０質量％以下と、一段と良好な値が得られている。 Further, regarding the powder symbols: C21 to C24, those having a dew point of 5 ° C. or less (powder symbols: C22 to C24) and an O amount of 0.20% by mass or less are good values. Further, when the dew point is −10 ° C. or less (powder symbol: C24), the amount of O is 0.15% by mass or less, which is a much better value. Furthermore, powder symbols: D21 to D24 and E21 to E23 satisfy the condition of t ≧ 10 4−0.0037 · T when the soaking temperature is 1080 ° C. or more (powder symbols: D23 to D24, E23). An even better value of 0.20% by mass or less is obtained.
　また、粉末記号：Ｃ２１～Ｃ２４、Ｄ２１～Ｄ２４、Ｅ２１～Ｅ２３、Ｇ２１、Ｈ２１、Ｊ２１については、アトマイズ鉄基粉末でのＣ量およびＯ量が［Ｏ］≧４／３［Ｃ］－２／１５および４／３［Ｃ］＋０．２８≧［Ｏ］をともに満たしているので、熱処理前で炭素粉末を混合しなくとも、適正な熱処理条件で還元することで、熱処理後のＣ量およびＯ量について適正値が得られることを示している。 In addition, regarding powder symbols: C21 to C24, D21 to D24, E21 to E23, G21, H21, and J21, the amount of C and O in the atomized iron-based powder is [O] ≧ 4/3 [C] -2 / Since both 15 and 4/3 [C] + 0.28 ≧ [O] are satisfied, it is possible to reduce the C amount and O after the heat treatment by reducing the carbon powder before the heat treatment under appropriate heat treatment conditions. It shows that an appropriate value is obtained for the amount.
（実施例２）
　表１のアトマイズ鉄基粉末のうち、ＡおよびＪを、不活性ガスとしてＮ２を用いて熱処理することによって還元した。処理条件を表４に示す。その際、アトマイズ鉄基粉末Ａについては、表４に示した量の黒鉛粉と混合した後に、移動床炉へ供給した。一方、アトマイズ鉄基粉末Ｊについては、黒鉛粉と混合することなく、そのまま（アトマイズ鉄基粉末Ｊのみを）移動床炉へ供給した。 (Example 2)
Of the atomized iron-based powders in Table 1, A and J were reduced by heat treatment using N 2 as an inert gas. Table 4 shows the processing conditions. At that time, the atomized iron-based powder A was mixed with the amount of graphite powder shown in Table 4 and then supplied to the moving bed furnace. On the other hand, the atomized iron-based powder J was supplied as it was (only the atomized iron-based powder J) to the moving bed furnace without being mixed with the graphite powder.
　さらに、上記還元終了後、移動床炉内の不活性ガスを排気するとともにＨ２ガスを供給し、還元された粉末を前記Ｈ２ガス雰囲気中で冷却した（Ａ３１、Ｊ３１）。冷却後、得られた粉末を解砕して粉末冶金用合金鋼粉を得た。得られた合金鋼粉の成分組成を表４に示す。なお、比較のために、実施例１におけるＡ２３、Ｊ２１の熱処理条件と合金鋼粉の成分組成を表４に併記した。前記Ａ２３、Ｊ２１では、還元後の冷却が、Ｎ２雰囲気中で行われている。 Further, after the reduction, the inert gas in the moving bed furnace was exhausted and H 2 gas was supplied, and the reduced powder was cooled in the H 2 gas atmosphere (A31, J31). After cooling, the obtained powder was crushed to obtain alloy steel powder for powder metallurgy. The component composition of the obtained alloy steel powder is shown in Table 4. For comparison, the heat treatment conditions of A23 and J21 in Example 1 and the component composition of the alloy steel powder are also shown in Table 4. In A23 and J21, the cooling after the reduction is performed in an N 2 atmosphere.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　Ｈ２雰囲気で冷却を行ったＡ３１およびＪ３１では、Ｃ量およびＯ量がそれぞれ０．１質量％以下、０．２８質量％以下まで低減できているとともに、Ｎ量は０．００２質量％（２０質量ｐｐｍ）以下であった。これに対して、Ｎ２雰囲気で冷却を行ったＡ２３およびＪ２１では、Ｎ量が０．００７質量％（７０質量ｐｐｍ）よりも高かった。 In A31 and J31 cooled in an H 2 atmosphere, the C amount and the O amount were reduced to 0.1% by mass or less and 0.28% by mass or less, respectively, and the N amount was 0.002% by mass (20 Mass ppm) or less. On the other hand, in A23 and J21 cooled in an N 2 atmosphere, the N amount was higher than 0.007 mass% (70 mass ppm).
　以上の結果から、還元されたアトマイズ鉄基粉末を、水素ガスまたは水素含有気体を用いて冷却することにより、合金鋼粉に含まれる不純物としてのＮをさらに低減できることがわかる。 From the above results, it is understood that N as an impurity contained in the alloy steel powder can be further reduced by cooling the reduced atomized iron-based powder using hydrogen gas or a hydrogen-containing gas.
　１　仕切り壁
　２　脱炭ゾーン
　３　脱酸ゾーン
　４　脱窒ゾーン
　５　雰囲気ガス供給口（供給雰囲気ガス）
　６　雰囲気ガス排出口（排出雰囲気ガス）
　７　粗製鉄基粉末
　８　ホッパ
　９　ベルト
　10　ホイール
　11　ラジアントチューブ
　12　水蒸気吹込み管
　13　製品粉
　14　製品タンク
　15　水封槽
　20　製品粉粉砕用装置
　21　冷却器
　22　循環ファン
　30　炉体（加熱炉）
 100　熱処理装置 1 Partition Wall 2 Decarburization Zone 3 Deoxidation Zone 4 Denitrification Zone 5 Atmosphere Gas Supply Port (Supply Atmosphere Gas)
6 Atmosphere gas outlet (exhaust gas)
7 Crude iron-based powder 8 Hopper 9 Belt 10 Wheel 11 Radiant tube 12 Steam blowing tube 13 Product powder 14 Product tank 15 Water seal tank 20 Product powder grinding device 21 Cooler 22 Circulating fan 30 Furnace (heating furnace)
100 Heat treatment equipment

Claims (4)

  1. 　質量％で、
    　　Ｃ　：０．８％以下、
    　　Ｏ　：１．０％以下、
    　　Ｓ　：０．３％以下、
    　　Ｐ　：０．０３％以下、ならびに
    　　合金元素として、
    　　　Ｍｎ：０．０８％超１．０％以下、
    　　　Ｃｒ：０．３～３．５％、
    　　　Ｍｏ：０．１～２％、および
    　　　Ｖ　：０．１～０．５％、からなる群より選択される１または２以上
    　を含有し、
    　　残部Ｆｅおよび不可避不純物であるアトマイズ鉄基粉末を用意し、
    　前記アトマイズ鉄基粉末を、厚さｄ（ｍｍ）の充填層を形成するように移動床炉内へ供給し、
    　前記移動床炉内に、不活性ガスを平均ガス流速ｖ（ｍｍ／ｓ）となるように供給し、
    　前記アトマイズ鉄基粉末を前記移動床炉内で熱処理することによって還元し、粉末冶金用合金鋼粉とする、粉末冶金用合金鋼粉の製造方法であって、
    　前記ｄおよびｖが、下記（１）式を満足し
    　前記アトマイズ鉄基粉末のＣ含有量［Ｃ］（質量％）と前記アトマイズ鉄基粉末のＯ含有量［Ｏ］（質量％）とが、下記（２）式を満足し、
    　前記アトマイズ鉄基粉末の移動床炉への供給において、前記アトマイズ鉄基粉末のＣ含有量［Ｃ］およびＯ含有量［Ｏ］が下記（３）式を満たす場合には、該アトマイズ鉄基粉末をそのまま前記移動床炉に供給し、下記（３）式を満たさない場合には、下記（４）式を満足するように該アトマイズ鉄基粉末に炭素成分をさらに混合したのち、前記移動床炉に供給する、粉末冶金用合金鋼粉の製造方法。
    　　　　　　　　　　　　記
    　ｄ／√ｖ≦３．０（ｍｍ１／２・ｓ１／２）…（１）
    　［Ｏ］≧４／３［Ｃ］－２／１５…（２）
    　４／３［Ｃ］＋０．２８≧［Ｏ］…（３）
    　４／３（［Ｃ］＋［ＭＸＣ］）＋０．２８≧［Ｏ］…（４）
    （ここで、［ＭＸＣ］は、（前記アトマイズ鉄基粉末に混合される炭素成分の質量／該アトマイズ鉄基粉末の質量）×１００（質量％）とする）     % By mass
    C: 0.8% or less,
    O: 1.0% or less,
    S: 0.3% or less,
    P: 0.03% or less, and as an alloy element,
    Mn: more than 0.08% and 1.0% or less,
    Cr: 0.3 to 3.5%,
    1 or 2 or more selected from the group consisting of Mo: 0.1-2% and V: 0.1-0.5%,
    Prepare the remaining Fe and atomized iron-based powder which is an inevitable impurity,
    Supplying the atomized iron-based powder into a moving bed furnace so as to form a packed bed of thickness d (mm);
    In the moving bed furnace, an inert gas is supplied so as to have an average gas flow velocity v (mm / s),
    The atomized iron-based powder is reduced by heat treatment in the moving bed furnace to obtain an alloy steel powder for powder metallurgy, a method for producing an alloy steel powder for powder metallurgy,
    Said d and v satisfy | fill following (1) Formula, C content [C] (mass%) of the said atomized iron base powder, and O content [O] (mass%) of the said atomized iron base powder, The following equation (2) is satisfied,
    In the supply of the atomized iron-based powder to the moving bed furnace, when the C content [C] and the O content [O] of the atomized iron-based powder satisfy the following formula (3), the atomized iron-based powder Is supplied to the moving bed furnace as it is, and if the following formula (3) is not satisfied, the atomized iron-based powder is further mixed with a carbon component so as to satisfy the following formula (4), and then the moving bed furnace A method for producing alloy steel powder for powder metallurgy, which is supplied to the company.
    D / √v ≦ 3.0 (mm 1/2 · s 1/2 ) (1)
    [O] ≧ 4/3 [C] -2/15 (2)
    4/3 [C] + 0.28 ≧ [O] (3)
    4/3 ([C] + [MXC]) + 0.28 ≧ [O] (4)
    (Here, [MXC] is (mass of carbon component mixed with the atomized iron-based powder / mass of the atomized iron-based powder) × 100 (mass%))
  2. 　前記還元されたアトマイズ鉄基粉末を、水素ガスまたは水素含有気体を用いて冷却する、請求項１に記載の粉末冶金用合金鋼粉の製造方法。 The method for producing alloy steel powder for powder metallurgy according to claim 1, wherein the reduced atomized iron-based powder is cooled using hydrogen gas or a hydrogen-containing gas.
  3. 　前記不活性ガスの露点を５℃以下とする、請求項１または２に記載の粉末冶金用合金鋼粉の製造方法。 The method for producing alloy steel powder for powder metallurgy according to claim 1 or 2, wherein the dew point of the inert gas is 5 ° C or lower.
  4. 　前記熱処理において、雰囲気温度Ｔ：１０８０℃以上、保持時間ｔ：１０４－０．００３７・Ｔ（ｈ）以上の条件で脱酸が行われる、請求項１～３のいずれか一項に記載の粉末冶金用合金鋼粉の製造方法。 The deoxidation is performed in the heat treatment under conditions of an atmospheric temperature T: 1080 ° C. or more and a holding time t: 10 4−0.0037 · T (h) or more. A method for producing alloy steel powder for powder metallurgy.
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