Classifications

• • 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
  • B22F1/09—Mixtures of metallic powders
• • 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
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
• • 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
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0264—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements the maximum content of each alloying element not exceeding 5%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
• • 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
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
  • B22F2003/248—Thermal after-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
  • B22F2301/00—Metallic composition of the powder or its coating
  • B22F2301/35—Iron
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/008—Heat treatment of ferrous alloys containing Si

Definitions

• JP H01-142002 A proposes an alloyed steel powder pre-alloyed with at least one of Mo: 1.5 mass % to 2.0 mass % and W: 3.0 mass % to 20 mass %.
• JP S61-295302 A (PTL 2) proposes an alloyed steel powder pre-alloyed with Mo: 0.2% to 1.5% and Mn: 0.05% to 0.25% in weight ratio.
• JP S59-215401 A proposes an alloyed steel powder obtained by diffusion-bonding Cu and Ni in powder form to the surface of an iron powder pre-alloyed with Mo: 0.1 mass % to 1.0 mass %.
• WO 2020/202805 A1 proposes an iron-based mixed powder for powder metallurgy containing: an alloyed steel powder containing 0.2 mass % to 1.5 mass % of Mo; and a copper powder having an average particle size of 25 ⁇ m or less and a specific surface area of 0.30 m 2 /g or more.
• the alloyed steel powder proposed in PTL 1 at least one of Mo and W, which are ferrite-stabilizing elements, is added to form a single phase with a high self-diffusion rate of Fe, as a result of which sintering can be accelerated.
• the addition amount of Mo is relatively large, so that the compressibility of the alloyed steel powder is low and high forming density cannot be achieved.
• a decrease in density tends to cause a decrease in the impact resistance of the sintered body.
• powder metallurgical products are used in various mechanical and structural parts such as automotive parts as mentioned above, excellent impact resistance is also required.
• the Mo content is 1.5 mass % or less, so that a single phase is not formed. Sintering between particles is therefore not accelerated. Hence, sufficient strength of the sintered neck part cannot be obtained with sintering temperatures (1120° C. to 1140° C.) of mesh belt furnaces commonly used.
• Mn is added as a pre-alloying element in the alloyed steel powder proposed in PTL 2, if the addition amount of Mn is increased in order to improve hardenability, the compressibility of the powder decreases, making it impossible to achieve a sufficient strength improving effect.
• the mixed powder proposed in PTL 4 enables obtaining high-strength sintered parts through sintering using an ordinary belt furnace and carburizing, quenching, and tempering.
• the compressibility of the mixed powder is roughly equal to that of a typical iron-based alloy powder, compacting at a high pressure of 688 MPa is needed in order to achieve high tensile strength. This severely wears the die.
• the mixed powder proposed in PTL 5 enables obtaining a sintered body having a tensile strength of 1300 MPa or more. However, since pressing at a high pressure of 690 MPa is needed, the die wears severely as in PTL 4.
• an iron-based mixed powder for powder metallurgy that has excellent compressibility and, even in a typical production process with a compacting pressure of less than 600 MPa, enables production of a sintered body having a tensile strength of 1200 MPa or more and excellent impact resistance with an impact value of 13 J/cm 2 or more.
• compressionibility herein means how easy the mixed powder can be compressed when it is charged into a die and pressed. As an index of compressibility, the density of a green compact obtained as a result of compacting at a certain pressure can be used, where higher density indicates better compressibility.
• An iron-based mixed powder for powder metallurgy consisting of: a partially diffusion-alloyed steel powder comprising an iron-based powder and Mo diffusionally adhered to a surface of the iron-based powder; and an alloying metal powder, wherein the iron-based powder has a chemical composition containing (consisting of) Mn: 0.04 mass % or more and 0.15 mass % or less and Si: 0.01 mass % or more and 0.10 mass % or less with a balance consisting of Fe and inevitable impurities, the partially diffusion-alloyed steel powder has a Mo content of 0.20 mass % or more and 1.5 mass % or less, and an apparent density of 2.8 g/cm 3 or more and 3.6 g/cm 3 or less, the alloying metal powder contains one or both of a Cu powder with an apparent density of 0.5 g/cm 3 to 2.0 g/cm 3 and a Ni powder with an apparent density of 0.5 g/cm 3 to 2.0 g/cm 3 , and an addition amount of
• An iron-based sintered body obtainable by carburizing, quenching, and tempering a sintered body produced using the iron-based mixed powder for powder metallurgy according to 1, or 2.
• the iron-based mixed powder for powder metallurgy according to the present disclosure has excellent compressibility, and thus can be used to produce a high-density sintered body. Moreover, the iron-based mixed powder for powder metallurgy according to the present disclosure enables production of a sintered body having high tensile strength and excellent impact resistance even in a typical production process with a compacting pressure of less than 600 MPa.
• the iron-based mixed powder for powder metallurgy according to the present disclosure has these excellent properties while being inexpensive because it does not contain Ni or, even if it contains Ni, the Ni content is 3.0 mass % or less.
• An iron-based mixed powder for powder metallurgy (hereafter also simply referred to as “mixed powder”) in one embodiment of the present disclosure comprises a partially diffusion-alloyed steel powder and an alloying metal powder.
• the term “iron-based mixed powder” herein refers to a mixed powder in which the mass proportion of Fe contained is 50% or more with respect to the total mass of the partially diffusion-alloyed steel powder and the alloying metal powder.
• the partially diffusion-alloyed steel powder (hereafter also referred to as “alloyed steel powder”), a partially diffusion-alloyed steel powder comprising an iron-based powder and Mo diffusionally adhered to a surface of the iron-based powder is used.
• the “partially diffusion-alloyed steel powder” is a technical term commonly used in this technical field, and typically refers to a powder that consists of an iron-based powder as a core and the particles of at least one alloying element adhering to the surface of the iron-based powder and in which the iron-based powder and the alloying element particles are diffusion-bonded.
• the “iron-based powder” refers to a powder in which the mass proportion of Fe contained is 50% or more.
• iron-based powder an iron-based powder having a chemical composition containing Mn: 0.04% or more and 0.15% or less and Si: 0.01% or more and 0.10% or less with the balance consisting of Fe and inevitable impurities is used.
• Mn 0.04% or more and 0.15% or less
• Si 0.01% or more and 0.10% or less with the balance consisting of Fe and inevitable impurities.
• Mn is an element contained as an inevitable impurity in iron-based powder. If the Mn content is more than 0.15%, a large amount of Mn oxide forms. Mn oxide not only lowers the compressibility of the iron-based mixed powder for powder metallurgy, but also serves as a fracture origin inside the sintered body and causes a decrease in the strength of the sintered body.
• the Mn content is therefore 0.15% or less, and preferably 0.10% or less.
• low Mn content is desirable from the viewpoint of improving compressibility, excessive reduction leads to a longer time required for Mo removal treatment and resulting higher production costs.
• the Mn content is therefore 0.04% or more.
• Si is an element contained as an inevitable impurity in iron-based powder. If the Si content is more than 0.10%, a large amount of Si oxide forms. Si oxide not only lowers the compressibility of the iron-based mixed powder for powder metallurgy, but also serves as a fracture origin inside the sintered body and causes a decrease in the strength of the sintered body.
• the Si content is therefore 0.10% or less, and preferably 0.05% or less. Although low Si content is desirable from the viewpoint of improving compressibility, excessive reduction leads to a longer time required for Si removal treatment and resulting higher production costs. The Si content is therefore 0.01% or more.
• the iron-based powder is preferably an atomized powder, without being limited thereto.
• the atomized powder may be any of gas atomized powder and water atomized powder, but is more preferably water atomized powder.
• the atomized powder is preferably a powder that has been, after atomization, heat-treated by heating in a reducing atmosphere (for example, hydrogen atmosphere) to reduce C and O.
• a reducing atmosphere for example, hydrogen atmosphere
• the atomized powder may be an as-atomized iron-based powder not subjected to such heat treatment.
• Mo is diffusion-bonded to the particle surface of the iron-based powder.
• the Mo content in the partially diffusion-alloyed steel powder is 0.20% or more and 1.5% or less. The reasons for this limitation will be explained below.
• Mo is an element that has the effect of improving hardenability and thus improving the strength of the sintered body. Adding a small amount of Mo as compared with Ni can achieve a sufficient hardenability improving effect. If the Mo content in the partially diffusion-alloyed steel powder is less than 0.20%, the strength improving effect by Mo is insufficient. The Mo content in the partially diffusion-alloyed steel powder is therefore 0.20% or more, and preferably 0.40% or more. If the Mo content is more than 1.5%, the effect of improving the strength of the sintered body by Mo is saturated, and also the compressibility of the partially diffusion-alloyed steel powder decreases and the compacting die tends to wear. The Mo content in the partially diffusion-alloyed steel powder is therefore 1.5% or less, and preferably 1.0% or less.
• the partially diffusion-alloyed steel powder comprising an iron-based powder having the above-described chemical composition and 0.20% to 1.5% of Mo diffusionally adhered to a surface of the iron-based powder is used.
• the partially diffusion-alloyed steel powder in one embodiment of the present disclosure has a chemical composition containing Mn derived from the iron-based powder, Si derived from the iron-based powder, and diffusion-bonded Mo, with the balance consisting of Fe and inevitable impurities.
• the components contained as the inevitable impurities and their amounts are not limited, but it is desirable to reduce the amounts of the inevitable impurities as much as possible.
• the inevitable impurities include Ni
• the Ni content is preferably 0.1% or less because Ni causes an increase in material costs.
• the contents of C, O, P, S, and N as the inevitable impurities are preferably in the following ranges:
• the O content herein includes the amount of oxygen contained in oxides that inevitably form in the alloyed steel powder.
• the total amount of elements contained as the inevitable impurities other than those listed above is preferably limited to 0.01% or less.
• the apparent density of the partially diffusion-alloyed steel powder is a parameter that depends on, for example, the shape and particle size distribution of the particles forming the alloyed steel powder, and greatly influences the compressibility of the iron-based mixed powder for powder metallurgy.
• the apparent density of the alloyed steel powder is lower, the volume of the iron-based mixed powder for powder metallurgy charged into the die is larger. This increases the work hardening of the particles of the alloyed steel powder during press forming and hinders plastic deformation of the particles, resulting in lower green density. This decrease in green density is particularly noticeable when the apparent density of the partially diffusion-alloyed steel powder is less than 2.8 g/cm 3 .
• the apparent density of the partially diffusion-alloyed steel powder is therefore 2.8 g/cm 3 or more, and preferably 2.9 g/cm 3 or more. If the apparent density of the partially diffusion-alloyed steel powder is more than 3.6 g/cm 3 , not only the compressibility improving effect is saturated but also the strength of the green compact decreases and as a result the green compact tends to crack when taken out of the die after press forming. Moreover, excessively increasing the apparent density of the partially diffusion-alloyed steel powder requires treatment for making the shape of the particles forming the partially diffusion-alloyed steel powder closer to a spherical shape or treatment for making the particle size distribution of the alloyed steel powder a bimodal distribution, thus leading to higher production costs.
• the apparent density of the alloyed steel powder is therefore 3.6 g/cm 3 or less, and preferably 3.3 g/cm 3 or less. The apparent density can be measured in accordance with JIS Z 2504:2012.
• the particle size of the partially diffusion-alloyed steel powder is not limited and may be any particle size. From the viewpoint of ease of production, the average particle size of the partially diffusion-alloyed steel powder is preferably 30 ⁇ m or more and 150 ⁇ m or less.
• the alloyed steel powder having such average particle size can be produced industrially at low cost by using the water atomizing method.
• the term “average particle size” herein refers to a mass-based median size (D50). The average particle size can be determined from the particle size distribution measured by the dry sieving method described in JIS-Z 2510.
• a mass-based cumulative particle size distribution is calculated from the obtained particle size distribution, the particle size (D50) at which the cumulative proportion is 50% in the cumulative particle size distribution is determined by interpolation, and the determined particle size (D50) is taken to be the average particle size.
• the method of producing the partially diffusion-alloyed steel powder is not limited.
• the partially diffusion-alloyed steel powder can be produced by mixing the foregoing iron-based powder and Mo raw material powder and then holding the mixture at a high temperature to diffusion-bond Mo to the surface of the iron-based powder.
• the Mo raw material powder is a powder that functions as a Mo source in the below-described diffusion bonding process.
• the Mo raw material powder any powder that contains Mo as an element can be used.
• the Mo raw material powder may be any of metallic Mo powder (powder consisting only of Mo), Mo alloy powder, and Mo compound powder.
• Mo alloy powder for example, Fe—Mo (ferromolybdenum) powder is preferably used.
• Fe—Mo powder atomized Fe—Mo powder containing 5% or more of Mo is preferably used.
• the atomized powder may be any of gas atomized powder and water atomized powder.
• Mo compound powder Mo oxide is preferably used for its easy availability and ease of reduction reaction. These Mo raw material powders may be used alone or in a mixture of two or more.
• the foregoing iron-based powder and Mo raw material powder are mixed.
• the mixing amounts of the iron-based powder and Mo-containing powder are adjusted so that the Mo content in the resulting partially diffusion-alloyed steel powder will be in the foregoing range.
• the mixing method is not limited, and the mixing may be performed according to a conventional method using, for example, a Henschel mixer or a cone mixer. In the mixing, 0.1 mass % or less of machine oil or the like may be added in order to improve the bonding between the iron-based powder and the Mo raw material powder.
• the obtained mixture is then heat-treated at 800° C. to 1000° C. in a reducing atmosphere such as a hydrogen atmosphere to obtain an alloyed steel powder to which Mo is diffusion-bonded as metallic Mo or a Mo-containing alloy.
• a reducing atmosphere such as a hydrogen atmosphere
• an as-atomized iron-based powder is used as the iron-based powder
• a large amount of C and O contained in the iron-based powder can be reduced by the heat treatment.
• Such heat treatment normally causes the iron-based powder and the metallic Mo or Mo-containing alloy to be in a sintered state.
• the sintered material is then ground and classified into a desired particle size. Annealing may be optionally further performed.
• the iron-based mixed powder for powder metallurgy in one embodiment of the present disclosure contains, as the alloying metal powder, one or both of a Cu powder with an apparent density of 0.5 g/cm 3 to 2.0 g/cm 3 and a Ni powder with an apparent density of 0.5 g/cm 3 to 2.0 g/cm 3 .
• the expression “the alloying metal powder contains a Cu powder with an apparent density of 0.5 g/cm 3 to 2.0 g/cm 3 ” means that the apparent density of a Cu powder contained in the alloying metal powder is 0.5 g/cm 3 to 2.0 g/cm 3 .
• the expression “the alloying metal powder contains a Ni powder with an apparent density of 0.5 g/cm 3 to 2.0 g/cm 3 ” means that the apparent density of a Ni powder contained in the alloying metal powder is 0.5 g/cm 3 to 2.0 g/cm 3 .
• the machinability improving powder is not limited and any machinability improving powder may be used.
• the machinability improving powder for example, one or both of MnS powder and oxide powder may be used.
• the addition amount of the machinability improving powder is preferably 0.1 parts by mass or more with respect to 100 parts by mass of the total of the partially diffusion-alloyed steel powder and the alloying metal powder.
• the addition amount of the machinability improving powder is preferably 0.7 parts by mass or less with respect to 100 parts by mass of the total of the partially diffusion-alloyed steel powder and the alloying metal powder.
• the iron-based mixed powder for powder metallurgy is pressed in a desired shape to obtain a green compact.
• An auxiliary raw material, a lubricant, a machinability improving powder, etc. may be optionally added to the iron-based mixed powder for powder metallurgy before the pressing.
• the pressing method is not limited and any method may be used.
• the mixed powder may be charged into a die and pressed.
• a lubricant may be applied or adhered to the die.
• the amount of the lubricant is preferably 0.3 parts by mass or more with respect to 100 parts by mass of the total of the partially diffusion-alloyed steel powder and the alloying metal powder.
• the amount of the lubricant is preferably 1.0 part by mass or less with respect to 100 parts by mass of the total of the partially diffusion-alloyed steel powder and the alloying metal powder.
• the sintering method is not limited and any method may be used.
• the sintering temperature may be 1100° C. or more and is preferably 1120° C. or more, from the viewpoint of sufficient progress of sintering. Since a higher sintering temperature contributes to a more uniform distribution of Cu and Mo in the sintered body, no upper limit is placed on the sintering temperature. From the viewpoint of reducing production costs, however, the sintering temperature is preferably 1250° C. or less and more preferably 1180° C. or less.
• the sintering time may be 15 minutes or more and 50 minutes or less. If the sintering time is in this range, insufficient sintering and resulting insufficient strength can be prevented, and production costs can be reduced.
• the cooling rate when cooling the sintered body after sintering may be 20° C./min or more and 40° C./min or less. If the cooling rate is less than 20° C./min, quenching is insufficient, which can cause a decrease in tensile strength. If the cooling rate is more than 40° C./min, equipment for increasing the cooling rate is needed, causing an increase in production costs.
• a degreasing process of holding the green compact at a temperature of 400° C. or more and 700° C. or less for a certain time may be performed to decompose and remove the lubricant before sintering.
• production conditions, equipment, and the like for the sintered body are not limited and any production conditions, equipment, and the like may be used.
• the obtained iron-based sintered body may be further subjected to heat treatment.
• the heat treatment can further enhance the strength of the sintered body.
• treatment involving rapid cooling is preferable.
• strengthening treatment such as carburizing-quenching, bright quenching, induction hardening, and carbonitriding heat treatment may be performed.
• the sintered body after rapid cooling may be subjected to impact resistance recovery treatment such as tempering.
• the tempering temperature is preferably about 100° C. to 300° C.
• the iron-based sintered body in one embodiment of the present disclosure can be obtained by pressing the iron-based mixed powder for powder metallurgy in a desired shape to obtain a green compact, sintering the green compact to obtain a sintered body, and subjecting the sintered body to carburizing, quenching, and tempering sequentially.
• Iron-based mixed powders for powder metallurgy were produced in the following manner.
• iron-based powders having the chemical compositions shown in Tables 1 to 3 were each produced by the water atomizing method.
• the amounts of P and S contained in the iron-based powder as inevitable impurities were as follows: P: less than 0.025 mass % and S: less than 0.025 mass %.
• MoO 3 powder as Mo raw material powder was added to the obtained iron-based powder and mixed for 15 minutes in a V-type mixer. The mixture was then heat-treated in a hydrogen atmosphere to reduce the MoO 3 powder and diffusion-bond Mo to the particle surface of the iron-based powder. The heat treatment was performed at a temperature of 900° C. for 60 minutes.
• the heat-treated body of particles in lump form as a result of sintering was ground using a hammer mill, classified using a sieve with an opening of 180 ⁇ m, and the undersize powder was collected to thus obtain a partially diffusion-alloyed steel powder.
• the amounts of C, O, and N contained in the partially diffusion-alloyed steel powder as impurities were as follows: C: less than 0.01 mass %, O: less than 0.20 mass %, and N: less than 0.05 mass %.
• the alloying metal powder shown in Tables 1 to 3, graphite powder, and lubricant were added to the obtained partially diffusion-alloyed steel powder and mixed using a double-cone mixer to obtain an iron-based mixed powder for powder metallurgy.
• the addition amount of the graphite powder was 0.3 parts by mass with respect to 100 parts by mass of the total of the partially diffusion-alloyed steel powder and the alloying metal powder.
• Zinc stearate was used as the lubricant, and the addition amount of the lubricant was 0.5 parts by mass with respect to 100 parts by mass of the total of the partially diffusion-alloyed steel powder and the alloying metal powder.
• the apparent density of each of the partially diffusion-alloyed steel powder, Cu powder, and Ni powder used was as shown in Tables 1 to 3.
• the apparent density was measured in accordance with JIS Z 2504:2012.
• the iron-based mixed powder for powder metallurgy was compacted at a compacting pressure of 588 MPa into a green compact of a 10 mm ⁇ 10 mm ⁇ 55 mm rectangular parallelepiped shape.
• the weight of the obtained green compact was measured, and the measured weight was divided by the volume of the green compact to yield the density of the green compact.
• the density of the green compact was as shown in Tables 1 to 3.
• the obtained green compact was then sintered (holding temperature: 1130° C., holding time: 20 minutes) in a RX atmosphere (N 2-32 vol % H 2 -24 vol % CO-0.3 vol % CO 2 ) to obtain a sintered body.
• the obtained sintered body was subjected to gas carburizing (holding temperature: 870° C., holding time: 60 minutes) at a carbon potential of 0.8 mass %, and then subjected to quenching (temperature: 60° C., oil quenching) and tempering (holding temperature: 200° C., holding time: 60 minutes).
• the carbon potential is an index indicating the carburizing ability of the atmosphere for heating steel, and is expressed by the carbon concentration on the surface of the steel upon reaching equilibrium with the gas atmosphere at the temperature.
• the density of the obtained sintered body was measured in accordance with JIS Z 2501.
• the tensile strength and impact value were measured in order to evaluate the strength and impact resistance of the sintered body.
• the tensile strength was measured by the tensile test prescribed in JIS Z 2241.
• the tensile test was conducted at room temperature using a test piece taken from the sintered body and having a parallel portion diameter of 5 mm.
• the maximum stress before breaking measured in the tensile test was taken to be the tensile strength.
• the impact value was measured by measuring the absorbed energy at room temperature in accordance with JIS Z 2242 and dividing the absorbed energy by the cross-sectional area of the test piece. The measurement results were as shown in Tables 1 to 3.
• the green compact and the sintered body had high density and the powder had excellent compressibility.
• the sintered body had high tensile strength and impact value. Specifically, the tensile strength was 1200 MPa or more and the impact value was 13 J/cm 2 or more.
• a sintered body having excellent properties can be produced in a typical production process with a compacting pressure of less than 600 MPa.
• at least one of compressibility, strength, and impact resistance was inferior.

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  • 2022-10-27 KR KR1020247017612A patent/KR20240095297A/ko unknown
  • 2022-10-27 WO PCT/JP2022/040258 patent/WO2023157386A1/ja active Application Filing

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