WO2017047100A1 - 粉末冶金用混合粉、焼結体および焼結体の製造方法 - Google Patents
粉末冶金用混合粉、焼結体および焼結体の製造方法 Download PDFInfo
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
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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
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
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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
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/09—Mixtures of metallic powders
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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
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/12—Metallic powder containing non-metallic particles
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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
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/17—Metallic particles coated with metal
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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
- 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
- B22F3/12—Both compacting and sintering
- B22F3/16—Both compacting and sintering in successive or repeated steps
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- 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
- C22C33/0207—Using a mixture of prealloyed powders or a master alloy
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- 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%
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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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
- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/10—Copper
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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
- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/35—Iron
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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
- B22F2302/00—Metal Compound, non-Metallic compound or non-metal composition of the powder or its coating
- B22F2302/40—Carbon, graphite
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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
- B22F2304/00—Physical aspects of the powder
- B22F2304/10—Micron size particles, i.e. above 1 micrometer up to 500 micrometer
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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
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
Definitions
- the present invention relates to a powder mixture for powder metallurgy, particularly a powder mixture for powder metallurgy suitable for the production of high-strength sintered parts for automobiles, and the density of a sintered body obtained by molding and sintering the alloy steel powder,
- the present invention relates to a mixed powder for powder metallurgy and a sintered body produced by using the same, in which the tensile strength and toughness (impact value) after carburizing, quenching and tempering of the sintered body are surely improved.
- the present invention also relates to a method for producing the sintered body.
- Powder metallurgy technology is a technology that enables a drastic reduction in cutting costs because parts with complicated shapes can be manufactured in a shape very close to the product shape (so-called near net shape) and with high dimensional accuracy. For this reason, powder metallurgy products are used in various fields as various machines and parts.
- the compact before sintering is a mixed powder obtained by mixing an iron-based powder, an alloy powder such as copper powder or graphite powder, and a lubricant such as stearic acid or lithium stearate. It is manufactured by filling in and pressure molding.
- the density of the molded body obtained by a normal powder metallurgy process is generally about 6.6 to 7.1 Mg / m 3 .
- the formed body is subsequently subjected to a sintering process to be a sintered body, and further subjected to sizing and cutting as necessary to obtain a powder metallurgy product.
- carburizing heat treatment or bright heat treatment may be performed after sintering.
- the iron-based powder used here is classified into iron powder (for example, pure iron powder) and alloy steel powder according to the components. Moreover, as classification according to the manufacturing method of iron-based powder, there are atomized iron powder and reduced iron powder. Iron powder in the classification according to this manufacturing method is used in a broad sense including pure iron powder and alloy steel powder.
- the mixed powder (1) has the advantage of having high compressibility comparable to that of pure iron powder.
- each alloy element does not sufficiently diffuse into Fe to form a heterogeneous structure, and as a result, the strength of the finally obtained sintered body may be inferior.
- Mn, Cr, V, Si, etc. are used as alloy elements, these elements are oxidized more easily than Fe, so that the sintered body finally obtained by oxidation during sintering There was a problem that the strength of the steel was lowered.
- the prealloyed steel powder (2) which is completely alloyed with each element, is used, the segregation of the alloy elements is completely prevented and the structure of the sintered body can be made uniform, so that the mechanical properties are stabilized. To do.
- Mn, Cr, V, Si, or the like is used as an alloy element, there is an advantage that the oxygen content of the sintered body can be reduced by limiting the type and amount of the alloy element.
- pre-alloyed steel powder is produced from molten steel by the atomizing method, oxidation in the atomizing process of molten steel and solid solution hardening of the steel powder due to complete alloying are likely to occur. There was a problem that it was difficult to increase.
- the density of the molded body is low, the toughness of the sintered body is low when the molded body is sintered. Therefore, even when pre-alloyed steel powder is used, it cannot meet the recent demands for high strength and high toughness.
- the partially diffused alloy steel powder (3) above is prepared by mixing each alloy element powder with pure iron powder or prealloyed steel powder and heating it in a non-oxidizing or reducing atmosphere to obtain pure iron powder or prealloyed steel powder.
- Each alloy element powder is partially diffusion bonded to the surface of the alloy steel powder particles. Therefore, the advantages of the iron-based mixed powder (1) and the prealloyed steel powder (2) can be obtained.
- Ni and Mo are frequently used as basic alloy components used in the partially diffused alloy steel powder.
- Ni has the effect of improving the toughness of the sintered body. This is because the addition of Ni stabilizes austenite, and as a result, more austenite remains as retained austenite without being transformed into martensite after quenching. Moreover, Ni has the effect
- Mo has the effect of improving hardenability. Therefore, Mo strengthens the matrix of the sintered body by suppressing the formation of ferrite during the quenching process and facilitating the formation of bainite or martensite. Mo has both the effect of solid solution strengthening by solid solution in the matrix and the effect of precipitation strengthening the matrix by forming fine carbides.
- Patent Document 1 discloses an alloy in which Ni: 0.5 to 4 mass% and Mo: 0.5 to 5 mass% are partially alloyed. Further disclosed is a mixed powder for high-strength sintered parts in which Ni: 1 to 5 mass%, Cu: 0.5 to 4 mass%, and graphite powder: 0.2 to 0.9% mass% are further mixed with steel powder.
- the sintered material described in Patent Document 1 contains at least 1.5 mass% Ni, and in the examples, it substantially contains 3 mass% or more of Ni.
- Ni such as 3 mass% or more is required to obtain a high strength of 800 MPa or more in the sintered body. Furthermore, in order to obtain a high-strength material of 1000 MPa or higher by carburizing, quenching, and tempering the sintered body, a large amount of Ni such as 3 mass% or 4 mass% is similarly required.
- Ni is a disadvantageous element from the viewpoint of dealing with recent environmental problems and recycling, and it is desirable to avoid using it as much as possible. In terms of cost, the addition of several mass% of Ni is extremely disadvantageous. Furthermore, when Ni is used as an alloy element, there is also a problem that long-time sintering is required to sufficiently diffuse Ni into iron powder and steel powder. Furthermore, when the diffusion of Ni, which is an austenite phase stabilizing element, is insufficient, the high Ni region is stabilized as an austenite phase (hereinafter also referred to as ⁇ phase), and the Ni dilute region is stabilized by other phases. As a result, the metal structure of the sintered body becomes non-uniform.
- Patent Document 2 discloses a technique related to Mo partially-diffused alloy steel powder that does not contain Ni. That is, by optimizing the amount of Mo, a sintered body having high ductility and toughness that can withstand re-pressurization after sintering can be obtained.
- Patent Document 3 discloses that iron powder having an average particle diameter of 1 to 18 ⁇ m and copper powder having an average particle diameter of 1 to 18 ⁇ m are 100: (0.2 to 5 ) Are mixed and molded and sintered at a weight ratio.
- an extremely high density sintered body having a sintered body density of 7.42 g / cm 3 or more is obtained by using an iron-based powder having an average particle diameter extremely smaller than usual. Is possible.
- Patent Document 4 a high-strength and high-toughness sintered body is obtained by using Ni-free powder in which Mo is diffused and adhered to the surface of an iron-based powder and the specific surface area is 0.1 m 2 / g or more. It is described.
- Patent Document 5 describes that a sintered body having high strength and high toughness is obtained by using a powder obtained by diffusing and adhering Mo to an iron-based powder containing reduced iron powder.
- Patent Document 2 Patent Document 3
- Patent Document 4 Patent Document 5
- Patent Document 2 assumes that high strength is obtained by re-compression after sintering, although there is no addition of Ni, and when manufactured by a normal powder metallurgy process, sufficient strength, Establishing toughness and hardness is difficult.
- the average particle size of the iron-based powder used is 1 to 18 ⁇ m, which is smaller than usual.
- the particle size is small as described above, the fluidity of the mixed powder is deteriorated, and there is a problem that the working efficiency when filling the mixed powder with a mold at the time of pressure molding is lowered.
- Patent Document 4 since the powder described in Patent Document 4 has a very large specific surface area, when such a powder is used, the fluidity of the powder is lowered, and the handling of the powder becomes difficult.
- the object of the present invention is a component system that does not use any Ni (hereinafter also referred to as Ni-free) which causes non-uniformity of the metal structure in the sintered body and is the largest factor in increasing the cost of the alloy powder.
- an object of the present invention is to provide a powder mixture for powder metallurgy, which can sinter a molded body of alloy steel powder and further make the mechanical properties of the carburized, quenched and tempered parts equal to or higher than those of Ni-added products.
- the objective of this invention is providing the iron-based sintered compact excellent in the mechanical characteristic produced using the mixed powder.
- the inventors have made various studies on the alloy component of the powder mixture for powder metallurgy not containing Ni, its addition means, and powder characteristics.
- the mixed powder for powder metallurgy controlled the average particle size, specific surface area and circularity of partially diffused alloy steel powder partially alloyed with Mo instead of using Ni at all.
- I came up with the idea of mixing Cu powder with graphite powder. That is, Mo acts as a ferrite stabilizing element during the sintering heat treatment. As a result, a ferrite phase is generated in the vicinity of the portion where the amount of Mo is large, the sintering of the iron powders is promoted, and the density of the sintered body is improved.
- the circularity of the partially diffused alloy steel powder by controlling the circularity of the partially diffused alloy steel powder to have a low circularity, coarse pores that reduce toughness in the sintered body can be reduced. Furthermore, it has also been found that the compressibility at the time of molding is improved by setting the specific surface area of the partially diffused alloy steel powder to a certain value or less. Furthermore, it has been found that when the average particle size of the partially diffused alloy steel powder is controlled to 30 ⁇ m or more, the fluidity of the alloy steel powder can be improved.
- the present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows. 1. It has a partial diffusion alloy steel powder in which Mo is diffused and adhered to the particle surface of the iron-based powder, Cu powder and graphite powder, and Mo: 0.2 to 1.5 mass%, Cu: 0.5 to 4.0 mass%, C: 0.1 to A powder mixture for powder metallurgy having a composition containing 1.0 mass% and the balance consisting of Fe and inevitable impurities, The partially diffused alloy steel powder has an average particle size of 30 to 120 ⁇ m, a specific surface area of less than 0.10 m 2 / g, and a circularity of particles having a diameter in the range of 50 to 100 ⁇ m is 0.65 or less. Mixed powder for powder metallurgy.
- the sintered compact which is a sintered compact of the molded object containing the mixed powder for powder metallurgy in any one of said 1-3.
- It has a partial diffusion alloy steel powder in which Mo is diffused and adhered to the particle surface of the iron-based powder, Cu powder and graphite powder, and Mo: 0.2 to 1.5 mass%, Cu: 0.5 to 4.0 mass%, C: 0.1 to A mixed powder for powder metallurgy having a composition of 1.0 mass%, the balance being composed of Fe and inevitable impurities, wherein the partial diffusion alloy steel powder has an average particle size of 30 to 120 ⁇ m and a specific surface area of 0.10 m A method for producing a sintered body for sintering a compact of a powder mixture for powder metallurgy, wherein the circularity of particles having a diameter of less than 2 / g and a diameter in the range of 50 to 100 ⁇ m is 0.65 or less.
- a mixed powder for powder metallurgy that can produce a sintered body having excellent characteristics equivalent to or better than the case of containing Ni while being a Ni-free component system that does not use any Ni. can get. Moreover, since the mixed powder for powder metallurgy of the present invention has high fluidity, it is excellent in work efficiency when filling the mixed powder for powder metallurgy into a mold for pressure molding. Furthermore, according to the present invention, a sintered body having both excellent strength and toughness can be produced at low cost even by a normal sintering method.
- the mixed powder for powder metallurgy according to the present invention is obtained by adding Cu to the surface of an iron-based powder, partially diffused alloy steel powder having an appropriate average particle diameter and specific surface area (hereinafter also referred to as partial alloy steel powder), Cu It is a mixed powder for powder metallurgy in which powder and graphite powder are mixed.
- the partially diffused alloy steel powder has an average particle size of 30 to 120 ⁇ m and a specific surface area of less than 0.10 m 2 / g, and the circularity of the powder having a diameter in the range of 50 to 100 ⁇ m is 0.65 or less, is required.
- the mixed powder for powder metallurgy needs to contain Mo: 0.2 to 1.5 mass%, Cu: 0.5 to 4.0 mass%, C: 0.1 to 1.0 mass%, with the balance being composed of Fe and inevitable impurities. There is.
- the mixed powder for powder metallurgy is formed into a molded body by a conventional pressure molding, and further sintered by a conventional method to obtain a sintered body according to the present invention.
- the entanglement between the powders at the time of molding due to the formation of Mo enriched parts at the sintering neck between the iron-based powder particles of the compact and the low circularity of the partially diffused alloy steel powder As a result, the subsequent sintering is promoted.
- the density of the sintered body increases in this way, both the strength and toughness of the sintered body improve, but unlike the sintered body using Ni as in the conventional material, the machine of the sintered body of the present invention Since the metal structure is uniform, the characteristics are small and stable.
- the mixed powder for powder metallurgy according to the present invention will be described in detail.
- the “%” shown below means “mass%” unless otherwise specified, and the Mo amount, Cu amount and graphite powder amount represent the respective ratios in the entire powder mixture for powder metallurgy (100% mass%). ing.
- the partially diffused alloy steel powder has Mo diffused on the surface of the iron-based powder, has an average particle size of 30 to 120 ⁇ m, a specific surface area of less than 0.10 m 2 / g, and a diameter of 50 It is important that the circularity of the powder in the range of ⁇ 100 ⁇ m is 0.65 or less.
- the particle size and the circularity hardly change. Accordingly, an iron-based powder within the same range as the average particle diameter and circularity of the partially diffused alloy steel powder is used.
- the iron-based powder has an average particle diameter of 30 to 120 ⁇ m and a powder having a diameter of 50 to 100 ⁇ m having a circularity (cross-sectional circularity) of 0.65 or less. That is, for the reasons described later, the average particle size of the partially alloyed steel powder must be 30 to 120 ⁇ m and the circularity of the powder in the range of 50 to 100 ⁇ m must be 0.65 or less. It is necessary to satisfy the conditions.
- the average particle diameter of the iron-base powder and the partially alloyed steel powder is the median diameter D50 of the weight cumulative distribution, and is obtained by measuring the particle size distribution using a sieve specified in JIS Z 8801-1.
- the particle size is such that the weight above and below the sieve is 50%.
- the circularity of the iron-based powder and the partially alloyed steel powder can be determined according to the following.
- iron-based powder will be described as an example, but in the case of partially alloyed steel powder, the circularity is obtained in the same procedure.
- iron-based powder is embedded in a thermosetting resin.
- the iron-based powder is uniformly embedded in the thermosetting resin with a thickness of 0.5 mm or more so that a sufficient amount of iron-based powder cross section can be observed on the observation surface where the embedded resin is polished and exposed.
- a cross section of the iron-based powder is revealed by polishing, the cross section is mirror-polished, and the cross section is magnified with an optical microscope and photographed.
- the cross-sectional area A and the outer peripheral length Lp of each iron-based powder in the cross-sectional photograph are obtained by image analysis.
- image analysis for example, Image J (Open Source, National Institutes of Health) is available.
- the equivalent circle diameter dc is calculated from the obtained cross-sectional area A.
- dc is obtained by the following equation (I).
- the circular approximate outer circumference Lc is calculated by multiplying the particle diameter dc by the circumference ratio ⁇ .
- the circularity C is calculated from the obtained Lc and the outer peripheral length Lp of the iron-based powder cross section.
- the circularity C is a value defined by the following formula (II).
- the iron-based powder means a powder having an Fe content of 50% or more.
- the iron-based powder include atomized raw powder (atomized iron powder as atomized), atomized iron powder (reduced atomized raw powder in a reducing atmosphere), reduced iron powder, and the like.
- the iron-based powder used in the present invention is preferably atomized raw powder or atomized iron powder. This is because the reduced iron powder contains a large number of pores in the particles, so that there is a possibility that a sufficient density cannot be obtained during pressure molding. Further, the reduced iron powder contains more inclusions in the particles as starting points of fracture than the atomized iron powder, and there is a risk that fatigue strength, which is an important mechanical property of the sintered body, is reduced.
- a suitable iron-based powder used in the present invention is atomized raw powder that is obtained by atomizing molten steel, drying, classifying, and not performing heat treatment for deoxidation treatment (reduction treatment) or decarburization treatment, or Any atomized iron powder obtained by reducing atomized raw powder in a reducing atmosphere.
- the iron-based powder according to the circularity described above can be obtained by appropriately adjusting the spraying conditions during atomization and the conditions of additional processing performed after spraying. Further, iron-base powders having different circularities may be mixed and adjusted so that the circularity of the iron-base powder having a particle diameter in the range of 50 to 100 ⁇ m falls within the above range.
- Partially diffused alloy steel powder is obtained by diffusing and adhering Mo to the surface of the iron-based powder described above, having an average particle size of 30 to 120 ⁇ m, a specific surface area of less than 0.10 m 2 / g, and a diameter of 50 to 100 ⁇ m. It is necessary that the circularity of the powder in the range is 0.65 or less.
- the partial diffusion alloy steel powder is produced by diffusing and adhering Mo to the above-mentioned iron-based powder.
- the amount of Mo at that time shall be a ratio of 0.2 to 1.5% in the entire powder mixture for powder metallurgy (100%).
- the amount of Mo is less than 0.2%, in the sintered body produced using the powder mixture for powder metallurgy, the effect of improving hardenability is small and the effect of improving strength is also small.
- the amount of Mo to be diffused is 0.2 to 1.5%.
- it is 0.3 to 1.0%, more preferably 0.4 to 0.8%.
- examples of the Mo supply source include Mo-containing powder.
- examples of the Mo-containing powder include Mo pure powder, Mo oxide powder, and Mo alloy powder such as Fe-Mo (ferromolybdenum) powder.
- Mo compound Mo carbide, Mo sulfide, Mo nitride, and the like can be used as suitable Mo-containing powders. These may be used alone or as a mixture of a plurality of substances.
- the iron-based powder and the Mo-containing powder are mixed at the above-described ratio (Mo amount is 0.2 to 1.5% in the entire powder mixture for powder metallurgy (100%)).
- Mo amount is 0.2 to 1.5% in the entire powder mixture for powder metallurgy (100%).
- the mixing method For example, it can carry out in accordance with a conventional method using a Henschel mixer, a corn type mixer, etc.
- the mixed powder of the iron-based powder and the Mo-containing powder is heated, and Mo is diffused into the iron-based powder through the contact surface between the iron-based powder and the Mo-containing powder to join Mo to the iron-based powder.
- partial alloy steel powder containing Mo is obtained.
- the atmosphere for the heat treatment a reducing atmosphere or a hydrogen-containing atmosphere is suitable, and a hydrogen-containing atmosphere is particularly suitable.
- heat treatment may be applied under vacuum.
- the heat treatment temperature is preferably in the range of 800 to 1100 ° C. when a Mo compound such as oxidized Mo powder is used as the Mo-containing powder.
- the heat treatment temperature is less than 800 ° C.
- the Mo compound is not sufficiently decomposed, and Mo does not diffuse into the iron-based powder, making it difficult to adhere Mo.
- the temperature exceeds 1100 ° C. sintering between the iron-based powders during the heat treatment proceeds, and the circularity of the iron-based powder exceeds the specified range.
- a preferable heat treatment temperature is in the range of 600 to 1100 ° C.
- the temperature of the heat treatment is less than 600 ° C.
- the diffusion of Mo into the iron-based powder is insufficient and it becomes difficult to adhere the Mo.
- the temperature exceeds 1100 ° C. the sintering of the iron-based powders during the heat treatment proceeds, and the circularity of the partially alloyed steel powder exceeds the specified range.
- the partially alloyed steel powders are in a sintered and solidified state. Do. That is, if necessary, the pulverization conditions are strengthened or coarse powder is removed by classification with a sieve having a predetermined opening so that the prescribed particle size is obtained. Furthermore, you may anneal as needed.
- the average particle size of the partially alloyed steel powder is in the range of 30 to 120 ⁇ m.
- the lower limit of the average particle diameter is 40 ⁇ m, more preferably 50 ⁇ m.
- the upper limit of the average particle diameter is 100 ⁇ m, more preferably 80 ⁇ m.
- the average particle size of the partially alloyed steel powder is the median diameter D50 of the weight cumulative distribution as described above, and is obtained by measuring the particle size distribution using a sieve specified in JIS Z 8801-1. When the cumulative particle size distribution is created from the measured particle size distribution, the particle diameter is such that the weight of the sieve top and the sieve bottom is 50%.
- the average particle size of the partial alloy steel powder is less than 30 ⁇ m, the fluidity of the partial alloy steel powder is deteriorated, which hinders the production efficiency at the time of compression molding in a mold.
- the average particle diameter of the partial alloy steel powder exceeds 120 ⁇ m, the driving force during the sintering becomes weak, and coarse pores are formed around the coarse partial alloy steel powder in the sintering process, and the sintering is performed. This results in a decrease in the density of the sintered body and causes a decrease in strength and toughness after carburizing, quenching, and tempering the sintered body.
- the maximum particle size of the partially alloyed steel powder is preferably 180 ⁇ m or less.
- the specific surface area of the partially alloyed steel powder is set to less than 0.10 m 2 / g.
- the specific surface area of the partial alloy steel powder refers to the specific surface area of the powder of the partial alloy steel powder excluding additives (Cu powder, graphite powder, lubricant).
- the specific surface area of the partially alloyed steel powder exceeds 0.10 m 2 / g, the fluidity of the mixed powder for powder metallurgy is lowered.
- the specific surface area can be arbitrarily controlled by adjusting the particle size of coarse particles of more than 100 ⁇ m and fine particles of less than 50 ⁇ m after diffusing adhesion treatment by sieving. That is, the specific surface area decreases by reducing the proportion of fine particles or increasing the proportion of coarse particles.
- the degree of circularity of particles having a partial alloy steel powder diameter of 50 to 100 ⁇ m needs to be 0.65 or less.
- the circularity is preferably 0.60 or less, more preferably 0.58 or less.
- the entanglement between the powders during pressure molding is strengthened and the compressibility of the powder mixture for powder metallurgy is improved, so that coarse pores in the compact and sintered body are eliminated. Decrease.
- the circularity is excessively reduced, the compressibility of the powder mixture for powder metallurgy is reduced, so the circularity is preferably 0.40 or more.
- the circularity of the particles having a partial alloy steel powder diameter of 50 to 100 ⁇ m can be measured as follows. First, with the particle diameter of the partial alloy steel powder calculated in the same manner as the iron-based powder described above as dc, the partial alloy steel powder having this dc in the range of 50 to 100 ⁇ m is extracted. At this time, an optical microscope image sufficient to extract at least 150 particles of partially alloyed steel powder in the range of 50 to 100 ⁇ m is performed. And the degree of circularity is calculated about the extracted partial alloy steel powder similarly to the case of the above-mentioned iron base powder.
- the reason for limiting the particle diameter of the partially alloyed steel powder to 50 to 100 ⁇ m is that reducing the circularity of the powder in the left range is the most effective in promoting the sintering. That is, since particles smaller than 50 ⁇ m are fine particles, the sintering promoting effect is originally high, and even if the circularity of the particles smaller than 50 ⁇ m is lowered, the sintering promoting effect is small. In addition, particles having a particle diameter exceeding 100 ⁇ m are extremely coarse, and even if the circularity is lowered, the sintering promoting effect is small. In addition, the circularity of the partial alloy steel powder can be obtained by the same method as the circularity of the iron-based powder described above.
- the remaining composition in the partially alloyed steel powder is iron and inevitable impurities.
- impurities contained in the partial alloy steel powder include C (excluding graphite), O, N, S, and the like. %: O: 0.3% or less, N: 0.004% or less, S: 0.03% or less, Si: 0.2% or less, Mn: 0.5% or less, P: 0.1% or less. % Or less is more preferable.
- the amount of inevitable impurities exceeds these ranges, the compressibility in forming using the partially alloyed steel powder is lowered, and it becomes difficult to form a compact having a sufficient density.
- Cu powder is added to the partial alloy steel powder obtained above. And add graphite powder.
- Cu is a useful element that enhances the solid solution strengthening and hardenability of the iron-based powder and increases the strength of the sintered part, and is added in the range of 0.5% to 4.0%.
- the amount of Cu powder added is less than 0.5%, the above-mentioned useful effects of Cu addition hardly appear, while if it exceeds 4.0%, not only the strength improvement effect of sintered parts is saturated, but also sintering. It causes a drop in body density. Therefore, the amount of Cu powder added is limited to the range of 0.5 to 4.0%. Preferably it is 1.0 to 3.0% of range.
- the average particle size of the Cu powder is preferably 50 ⁇ m or less. More preferably, it is 40 ⁇ m or less, and further preferably 30 ⁇ m or less.
- the average particle size of the Cu powder is preferably 50 ⁇ m or less. More preferably, it is 40 ⁇ m or less, and further preferably 30 ⁇ m or less.
- the minimum of the average particle diameter of Cu powder In order not to raise the manufacturing cost of Cu powder unnecessarily, about 0.5 micrometer is preferable.
- the average particle diameter of Cu powder can be obtained by the following method. Since powder having an average particle size of 45 ⁇ m or less is difficult to measure the average particle size by sieving, the particle size is measured with a laser diffraction / scattering particle size distribution analyzer. As a laser diffraction / scattering type particle size distribution measuring apparatus, there is LA-950V2 manufactured by Horiba. Of course, other laser diffraction / scattering particle size distribution measuring devices may be used, but in order to perform accurate measurement, the lower limit of the measurable particle diameter range is 0.1 ⁇ m or less and the upper limit is 45 ⁇ m or more. Is preferred.
- the solvent in which the Cu powder is dispersed is irradiated with laser light, and the particle size distribution and average particle diameter of the Cu powder are measured from the diffraction and scattering intensity of the laser light.
- the solvent for dispersing the Cu powder it is preferable to use ethanol, which has good particle dispersibility and is easy to handle.
- Use of a solvent having a high van der Waals force such as water and low dispersibility is not preferable because particles aggregate during measurement and a measurement result coarser than the original average particle diameter is obtained. Therefore, it is preferable to carry out an ultrasonic dispersion treatment on the ethanol solution into which Cu powder has been added before measurement.
- the dispersion treatment time is carried out in 7 steps of 10 min intervals between 0 to 60 min, and the average particle diameter of Cu powder is measured after each dispersion treatment. Do. During each measurement, measurement is performed while stirring the solvent in order to prevent particle aggregation. And the smallest value is used as an average particle diameter of Cu powder among the particle diameters obtained by seven measurements performed by changing the dispersion treatment time at intervals of 10 min.
- graphite powder Since graphite powder is effective for increasing strength and fatigue strength, 0.1 to 1.0% is added to and mixed with partially alloyed steel powder. The above effects cannot be obtained unless the amount of graphite powder added is less than 0.1%. On the other hand, if it exceeds 1.0%, it becomes hypereutectoid, so that cementite is precipitated and the strength is lowered. Therefore, the amount of graphite powder added is limited to the range of 0.1 to 1.0%. Preferably, it is 0.2 to 0.8%.
- the average particle size of the graphite powder to be added is preferably in the range of about 1 to 50 ⁇ m.
- the above-mentioned Cu powder and graphite powder are mixed with the partial diffusion alloy steel powder to which Mo is diffused and adhered to form a mixed powder for powder metallurgy of the Fe—Mo—Cu—C system. What is necessary is just to perform the mixing method according to the conventional method of powder mixing.
- a powdery lubricant can be further mixed. It can also be molded by applying or adhering a lubricant to the mold.
- a lubricant any of metal soaps such as zinc stearate and lithium stearate, amide waxes such as ethylenebisstearic acid amide, and other known lubricants can be suitably used.
- the amount is preferably about 0.1 to 1.2 parts by mass with respect to 100 parts by mass of the mixed powder for powder metallurgy.
- the pressure-molding is preferably performed at a pressure of 400 to 1000 MPa.
- the pressure molding temperature is preferably in the range of room temperature (about 20 ° C.) to about 160 ° C.
- the sintering temperature is less than 1100 ° C., the sintering does not proceed and it becomes difficult to obtain a desired tensile strength of 1000 MPa or more. On the other hand, if it exceeds 1300 ° C, the life of the sintering furnace is shortened, which is economically disadvantageous.
- the sintering time is preferably in the range of 10 to 180 minutes.
- the sintered compact obtained using the powder metallurgy mixed powder according to the present invention under the above sintering conditions has the same compact density as compared with the case where the alloy steel powder out of the above range is used.
- a high sintered body density can be obtained after sintering.
- the obtained sintered body can be subjected to strengthening treatment such as carburizing quenching, bright quenching, induction quenching, carbonitriding treatment, etc., if necessary.
- strengthening treatment such as carburizing quenching, bright quenching, induction quenching, carbonitriding treatment, etc.
- the sintered body using the mixed powder for powder metallurgy according to the present invention has improved strength and toughness as compared with the conventional sintered body not subjected to the strengthening treatment.
- strengthening process should just be performed according to a conventional method.
- Example 1 As the iron-based powder, atomized raw powder having different circularity was used. The circularity of the atomized raw powder was varied by giving the atomized raw powder a pulverization process using a high-speed mixer (LFS-GS-2J type, manufactured by Fukae Pautech Co., Ltd.). To this iron-based powder, oxidized Mo powder (average particle size: 10 ⁇ m) was added at a predetermined ratio, mixed for 15 minutes with a V-type mixer, and then heat-treated in a hydrogen atmosphere with a dew point of 30 ° C. (holding temperature: 880).
- LFS-GS-2J type high-speed mixer
- a partial alloy steel powder in which a predetermined amount of Mo shown in Table 1 was diffused and adhered to the particle surface of the iron-based powder was produced at a temperature of 1 ° C. for 1 hour.
- the amount of Mo was variously changed as shown in Sample Nos. 1 to 8 in Table 1.
- the produced partial alloy steel powder was embedded in a resin and polished so that a cross section of the partial alloy steel powder was exposed.
- the partial alloy steel powder was evenly embedded in the thermosetting resin with a thickness of 0.5 mm or more so that a sufficient amount of the partial alloy steel powder cross section could be observed on the polished surface, that is, the observation surface. After polishing, the polished surface was magnified with an optical microscope and photographed, and the circularity was calculated by image analysis according to the above. In addition, specific surface area measurement by BET method was performed on partially alloyed steel powder. All the partial alloy steel powders were confirmed to have a specific surface area of less than 0.10 m 2 / g.
- the obtained powder mixture for powder metallurgy 0.6 parts by mass of ethylenebisstearic acid amide added to 100 parts by mass and mixed for 15 minutes with a V-type mixer is pressed to a density of 7.0 g / cm 3 Molded to produce rod-shaped compacts (length: 55 mm, width: 10 mm and thickness: 10 mm each), and ring-shaped compacts of outer diameter: 38 mm, inner diameter: 25 mm and thickness: 10 mm .
- the rod-shaped molded body and the ring-shaped molded body were sintered to obtain a sintered body. This sintering was performed in a propane modified gas atmosphere under conditions of sintering temperature: 1130 ° C. and sintering time: 20 minutes.
- sintering temperature 1130 ° C.
- sintering time 20 minutes.
- the outer diameter, inner diameter and thickness were measured and the mass was measured, and the sintered body density (Mg / m 3 ) was calculated.
- 5 pieces each were processed into round bar tensile test pieces (JIS No. 2) with a parallel part diameter of 5 mm in order to be subjected to the tensile test specified in JIS Z2241.
- the above measurement results are also shown in Table 1.
- the criteria for determination are as follows. (1) Flowability Mixed powder for powder metallurgy: 100 g passed through a nozzle with a diameter of 2.5 mm ⁇ , which passed within a total amount of 80 s without stopping ( ⁇ ), one that took more than 80 s, or A sample which did not flow because the whole amount or a part of it was stopped was judged as rejected (x). (2) Sintered body density The sintered body density is equal to or greater than the conventional 4Ni material (4Ni-1.5Cu-0.5Mo, maximum particle size of raw material powder: 180 ⁇ m), 6.95 Mg / m 3 or more The case was determined to be acceptable.
- samples No. 1 to 8 are affected by the amount of Mo
- Nos. 9 to 14 are affected by the amount of Cu
- Nos. 15 to 19 are affected by the amount of graphite
- Nos. 20 to 25 are affected by the Cu particle size
- No. Nos. 26 to 31 are the results of the examination of the influence of the alloy particle size
- Nos. 32 to 38 are the results of the examination of the influence of the circularity and average particle size of the partially alloyed steel powder.
- Table 1 also shows the results of a 4Ni material (4Ni-1.5Cu-0.5Mo, maximum particle size of raw material powder: 180 ⁇ m) as a conventional material. It turns out that the example of an invention can obtain the characteristic more than the conventional 4Ni material.
- Example 2 In order to clarify the technical difference between the present invention example and Patent Document 3, the following experiment was performed. Three types of atomized iron powders having different specific surface areas and roundnesses were prepared. The specific surface area and circularity can be adjusted by applying a high-speed mixer (LFS-GS-2J type, manufactured by Fukae Powtech Co., Ltd.) to atomized iron powder, and blending coarse powder with a particle size of 100 ⁇ m or more and fine powder with a particle size of 45 ⁇ m or less. This was done by adjusting the ratio.
- LFS-GS-2J type manufactured by Fukae Powtech Co., Ltd.
- oxidized Mo powder (average particle size: 10 ⁇ m) was added at a predetermined ratio, mixed for 15 minutes with a V-type mixer, and then heat-treated in a hydrogen atmosphere with a dew point of 30 ° C. (holding temperature: 880).
- a partial alloy steel powder in which a predetermined amount of Mo shown in Table 2 was diffused and adhered to the particle surface of the iron-based powder was produced by heating at 1 ° C. for 1 hour.
- These partial alloy steel powders were embedded in a resin and polished so that the cross section of the partial alloy steel powder was exposed, and then an enlarged upper photograph was taken with an optical microscope, and the circularity was calculated by image analysis. Moreover, the specific surface area was measured for the partially alloyed steel powder by the BET method.
- the rod-shaped body and the ring-shaped body were sintered to obtain a sintered body.
- This sintering was performed in a propane modified gas atmosphere under conditions of sintering temperature: 1130 ° C. and sintering time: 20 minutes.
- sintering temperature 1130 ° C.
- sintering time 20 minutes.
- the outer diameter, inner diameter and thickness were measured and the mass was measured, and the sintered body density (Mg / m 3 ) was calculated.
- the rod-shaped sintered bodies As for the rod-shaped sintered bodies, 5 pieces each were processed into round bar tensile test pieces (JIS No. 2) with a parallel part diameter of 5 mm in order to be subjected to the tensile test specified in JIS Z2241, and 5 pieces each were JIS Z2242.
- the size of the rod is as-sintered (no notch), and all are carburized with carbon potential of 0.8 mass% (holding temperature: 870 ° C) , Holding time: 60 minutes), followed by quenching (60 ° C., oil quenching) and tempering (holding temperature: 180 ° C., holding time: 60 minutes).
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Abstract
Description
通常の粉末冶金工程で得られる成形体の密度は、6.6~7.1 Mg/m3程度が一般的である。成形体は、その後に焼結処理が行われて焼結体とされ、さらに必要に応じてサイジングや切削加工が行われて、粉末冶金製品とされる。また、さらに高い強度が必要な場合は、焼結後に浸炭熱処理や光輝熱処理が行われることもある。
まず、鉄基粉末の合金化手段としては、
(1) 純鉄粉に各合金元素粉末を配合した混合粉、
(2) 各合金元素を完全に合金化した予合金鋼粉、
(3) 純鉄粉や予合金鋼粉の表面に各合金元素粉末を部分的に付着拡散させた部分拡散合金鋼粉(複合合金鋼粉ともいう)
等が知られている。
Niは、焼結体の靭性を向上させる効果を有している。これは、Niの添加により、オーステナイトが安定化され、その結果、より多くのオーステナイトが焼入れ後もマルテンサイトへ変態せずに残留オーステナイトとして残るためである。また、Niは、固溶強化によって焼結体のマトリックスを強化する作用を有している。
すなわち、Moは、焼結熱処理の際にはフェライト安定化元素として働く。その結果、Mo量が多い部分の近傍ではフェライト相を生じて鉄粉同士の焼結が促進され、焼結体の密度を向上する。また、上記部分拡散合金鋼粉の円形度を制御し、低い円形度とすることにより、焼結体において靭性を低下させる粗大な空孔を低減できる。さらに、部分拡散合金鋼粉の比表面積を一定の値以下とすることにより、成形時の圧縮性が改善されることも同時に見出した。さらにまた、部分拡散合金鋼粉の平均粒径を30μm以上に制御すると、合金鋼粉の流動性の向上が併せて実現できることが分った。
1.鉄基粉末の粒子表面にMoが拡散付着した部分拡散合金鋼粉と、Cu粉および黒鉛粉とを有し、かつMo:0.2~1.5mass%、Cu:0.5~4.0mass%、C:0.1~1.0mass%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有する粉末冶金用混合粉であって、
前記部分拡散合金鋼粉は、平均粒径が30~120μmおよび比表面積が0.10m2/g未満であり、径が50~100μmの範囲にある粒子の円形度が0.65以下であることを特徴とする粉末冶金用混合粉。
本発明の粉末冶金用混合粉は、鉄基粉末の表面にMoが拡散付着した、適正な平均粒径および比表面積を有する部分拡散合金鋼粉(以下、部分合金鋼粉ともいう)に、Cu粉および黒鉛粉を混合した粉末冶金用混合粉である。
特に、部分拡散合金鋼粉は、平均粒径が30~120μmおよび比表面積が0.10m2/g未満であること並びに径が50~100μmの範囲にある粉末の円形度が0.65以下であること、が必要である。さらに、粉末冶金用混合粉は、Mo:0.2~1.5mass%、Cu:0.5~4.0mass%、C:0.1~1.0mass%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有する必要がある。
この様に焼結体での密度が増加すると、焼結体の強度および靭性はともに向上するが、従来材のようなNiを使用した焼結体とは異なり、本発明の焼結体の機械特性は、金属組織が均一なために、ばらつきが小さく安定したものとなる。
上記のとおり、部分拡散合金鋼粉は、鉄基粉末の表面にMoが拡散付着したものであり、平均粒径が30~120μmおよび比表面積が0.10m2/g未満であること並びに径が50~100μmの範囲にある粉末の円形度が0.65以下であること、が肝要である。ここで、鉄基粉末に部分合金化を施した際、粒径および円形度はほとんど変化しない。従って、部分拡散合金鋼粉の平均粒径および円形度と同じ範囲内の鉄基粉末を用いる。
まずは、鉄基粉末を熱硬化性樹脂に埋め込む。このとき、埋込樹脂を研磨して現出させる観察面において、十分な量の鉄基粉末断面が観察できるように、0.5mm以上の厚みで満遍なく鉄基粉末を熱硬化性樹脂に埋め込む。その後、研磨により鉄基粉末の断面を現出させ、その断面を鏡面研磨し、該断面を光学顕微鏡で拡大して写真撮影する。得られた断面写真から画像解析により該断面写真における各鉄基粉末の断面積Aおよび外周長さLpを求める。このような画像解析が可能なソフトとしては、例えばImage J(オープンソース,アメリカ国立衛生研究所)などがある。求めた断面積Aより円相当径dcを算出する。ここで、dcは以下の式(I)によって求められる。
この円形度Cが1の場合、断面形状は真円となり、値Cが小さくなるにつれて不定形な断面となる。
上記した円形度に従う鉄基粉末は、アトマイズ時の噴霧条件や噴霧後に行う追加工の条件を適宜に調整することによって得ることが出来る。また、円形度の異なる鉄基粉末を混合し、粒子径が50~100μmの範囲にある鉄基粉末の円形度が上記の範囲内に納まるように調整しても構わない。
部分拡散合金鋼粉は、上記した鉄基粉末の表面にMoが拡散付着したものであり、平均粒径が30~120μmおよび比表面積が0.10m2/g未満であること並びに径が50~100μmの範囲にある粉末の円形度が0.65以下である、必要がある。
上記熱処理の雰囲気としては、還元性雰囲気や水素含有雰囲気が好適であり、とりわけ水素含有雰囲気が適している。或いは、真空下で熱処理を加えても良い。
また、熱処理の温度は、例えば、Mo含有粉末として酸化Mo粉末等のMo化合物を用いた場合、800~1100℃の範囲が好適である。熱処理の温度が800℃未満であると、Mo化合物の分解が不十分になってMoが鉄基粉末中へ拡散せず、Moの付着が困難となる。また、1100℃超えると、熱処理中の鉄基粉末同士の焼結が進み、鉄基粉末の円形度が規定の範囲を超えてしまう。一方、Mo含有粉末として、Mo純金属やFe-Moなどの金属および合金を用いる場合、好適な熱処理温度は600~1100℃の範囲である。熱処理の温度が600℃未満であると、鉄基粉末へのMoの拡散が不十分となりMoの付着が困難となる。一方、1100℃を超えると、熱処理中の鉄基粉末同士の焼結が進み、部分合金鋼粉の円形度が規定の範囲を超えてしまう。
なお、部分合金鋼粉の平均粒径は、上述のとおり、重量累積分布のメジアン径D50のことであって、JIS Z 8801-1に規定される篩を用いて粒度分布を測定し、得られた粒度分布から積算粒度分布を作成したときに、篩上および篩下の重量が50%となる粒子径のことである。
ここで、部分合金鋼粉の平均粒径が30μmを下回ると、部分合金鋼粉の流動性が悪くなって、金型での圧縮成形時の製造効率などの点に支障をきたす。一方、部分合金鋼粉の平均粒径が120μmを超えると、焼結の際の駆動力が弱くなって、焼結工程において粗大な部分合金鋼粉の周囲に粗大な空孔が形成され、焼結密度の低下をもたらし、焼結体やこの焼結体に浸炭・焼入れ・焼戻しを施した後の、強度や靭性を低下させる原因となる。なお、部分合金鋼粉の最大粒径は、180μm以下であることが好ましい。
なお、部分合金鋼粉の粒子径を50~100μmに限定する理由は、左記範囲の粉末の円形度を下げることが、焼結促進には最も効果的であるためである。すなわち、50μm未満の粒子は微粒であることから元々焼結促進効果が高く、50μm未満の粒子の円形度を低下させたとしてもその焼結促進効果は小さい。また、粒子径100μm超の粒子は、きわめて粗大であり、例え円形度を低下させたとしても焼結促進効果は小さい。
なお、部分合金鋼粉の円形度は、前述の鉄基粉末の円形度と同じ方法で求めることができる。
Cuは、鉄基粉末の固溶強化および焼入れ性向上を促し、焼結部品の強度を高める有用元素であり、0.5%以上4.0%以下で添加する。すなわち、Cu粉の添加量が0.5%に満たないと、上記したCu添加の有用な効果が現れにくく、一方4.0%を超えると、焼結部品の強度向上効果が飽和するばかりでなく、焼結体密度の低下を招く。したがって、Cu粉の添加量を0.5~4.0%の範囲に限定する。好ましくは1.0~3.0%の範囲である。
平均粒子径が45μm以下の粉末は篩分けによる平均粒子径の測定が困難なため、レーザー回折/散乱式粒度分布測定装置による粒子径の測定を行う。レーザー回折/散乱式粒度分布測定装置としては、堀場製作所製:LA-950V2などがある。もちろん、他のレーザー回折/散乱式粒度分布測定装置を使用しても構わないが、正確な測定を行う為に測定可能粒子径範囲の下限が0.1μm以下、上限が45μm以上のものを用いることが好ましい。前記装置では、Cu粉を分散させた溶媒に対してレーザー光を照射し、レーザー光の回折、散乱強度からCu粉の粒度分布および平均粒子径を測定する。Cu粉を分散させる溶媒として、粒子の分散性が良く、扱いが容易であるエタノールを用いるのが好ましい。水などのファンデルワールス力が高く、分散性の低い溶媒を用いると、測定中に粒子が凝集し、本来の平均粒子径よりも粗い測定結果が得られるので好ましくない。従って、Cu粉を投入したエタノール溶液に対して、測定前に超音波による分散処理を実施することが好ましい。なお、対象とする粉末によって、適正な分散処理時間が異なるため、前記分散処理時間を0~60minの間で10min間隔の7段階で実施し、各分散処理後にCu粉の平均粒子径の測定を行う。各測定中は粒子の凝集を防ぐために、溶媒を攪拌しながら測定を行う。そして、分散処理時間を10min間隔で変更して行った7回の測定で得られた粒子径のうち、最も小さい値をCu粉の平均粒子径として用いる。
黒鉛粉は、強度並びに疲労強度を高めるために有効であるため、部分合金鋼粉に0.1~1.0%を添加し、混合する。黒鉛粉の添加量が0.1%に満たないと上記の効果を得ることができない。一方、1.0%を超えると過共析になるため、セメンタイトが析出して強度の低下を招く。したがって、黒鉛粉の添加量を0.1~1.0%の範囲に限定する。好ましくは、0.2~0.8%である。なお、添加する黒鉛粉の平均粒径は、1~50μm程度の範囲が好ましい。
本発明の粉末冶金用混合粉を用いた加圧成形では、さらに、粉末状の潤滑剤を混合することができる。また、金型に潤滑剤を塗布あるいは付着させて成形することもできる。いずれの場合であっても、潤滑剤として、ステアリン酸亜鉛やステアリン酸リチウムなどの金属石鹸、エチレンビスステアリン酸アミドなどのアミド系ワックスおよびその他公知の潤滑剤のいずれもが好適に用いることができる。なお、潤滑剤を混合する場合は、粉末冶金用混合粉:100質量部に対して、0.1~1.2質量部程度とすることが好ましい。
[実施例1]
鉄基粉末には、円形度の異なるアトマイズ生粉を用いた。アトマイズ生粉の円形度を、ハイスピードミキサー(深江パウテック社製 LFS-GS-2J型)による粉砕加工をアトマイズ生粉へ与えることによって種々異なるようにした。
この鉄基粉末に、酸化Mo粉末(平均粒径:10μm)を所定の比率で添加し、V型混合機で15分間混合したのち、露点:30℃の水素雰囲気中で熱処理(保持温度:880℃、保持時間:1h)して、鉄基粉末の粒子表面に表1に示す所定量のMoを拡散付着させた部分合金鋼粉を作製した。なお、Mo量を表1の試料No.1~8に示すように種々に変更した。
また、BET法による比表面積測定を部分合金鋼粉に実施した。いずれの部分合金鋼粉も比表面積が0.10m2/g未満であることを確認した。
ちなみに、試料No.9~25は、試料No.5と同等の部分合金鋼粉を用いており、添加するCu粉や黒鉛粉の量を種々に変更している。試料No.26~31は、試料No.5の部分合金鋼粉をベースとして、篩分により平均粒子径を調整している。また、試料No.32~38は部分合金鋼粉の円形度が種々に異なっている。
リング状焼結体については、外径、内径および厚さの測定および質量測定を行い、焼結体密度(Mg/m3)を算出した。
棒状状焼結体については、各々5個をJIS Z2241で規定される引張試験に供するために、平行部径:5mmの丸棒引張試験片(JIS 2号) に加工し、また、各々5個をJIS Z2242で規定されるシャルピー衝撃試験に供するため、JIS Z2242に規定された大きさの焼結したままの棒形状(ノッチ無し)で、いずれもカーボンポテンシャル:0.8mass%のガス浸炭(保持温度:870℃、保持時間:60分)を行い、続いて焼入れ(60℃、油焼入れ)および焼戻し(保持温度:180℃、保持時間:60分)を行った。
これらの浸炭・焼入れ・焼戻し処理を施した丸棒引張試験片およびシャルピー衝撃試験用棒状試験片を、JIS Z2241で規定される引張試験およびJIS Z2242で規定されるシャルピー衝撃試験に供して、引張強さ(MPa)および衝撃値(J/cm2)を測定し、試験数n=5での平均値を求めた。
なお、判定基準は以下のとおりである。
(1)流動性
粉末冶金用混合粉:100gを径:2.5mmφのノズルを通して、停止することなく全量80s以内に流れきったものを合格(○)、80sを超える時間を要したもの、もしくは全量あるいは一部が停止して流れなかったものを不合格(×)と判定した。
(2)焼結体密度
焼結体密度は、従来材である4Ni材(4Ni-1.5Cu-0.5Mo、原料粉の最大粒径:180μm)と同等以上である、6.95Mg/m3以上の場合を合格と判定した。
(3)引張強さ
浸炭・焼入れ・焼戻し処理を施した丸棒引張試験片についての引張強さが1000MPa以上の場合を合格と判定した。
(4)衝撃値
浸炭・焼入れ・焼戻し処理を施したシャルピー衝撃試験用棒状状試験片についての衝撃値が14.5J/cm2以上の場合を合格と判定した。
表1に示すように、発明例はいずれも、Niを一切使用しない成分系でありながら、Ni添加材を用いた場合と同等以上の引張強さと靭性をもつ焼結体を得ることができる、粉末冶金用混合粉が得られていることが分かる。
本発明例と特許文献3との技術的差異を明確にするため、以下のような実験を実施した。
比表面積および円形度の異なる3種類のアトマイズ鉄粉を準備した。比表面積および円形度の調整は、ハイスピードミキサー(深江パウテック社製 LFS-GS-2J型)による粉砕加工をアトマイズ鉄粉へ与えることと、粒度100μm以上の粗粉および45μm以下の微粉との配合割合を調整することによって行った。
リング状焼結体については、外径、内径および厚さの測定および質量測定を行い、焼結体密度(Mg/m3)を算出した。
これらの浸炭・焼入れ・焼戻し処理を施した丸棒引張試験片およびシャルピー衝撃試験用棒状試験片を、JIS Z2241で規定される引張試験およびJIS Z2242で規定されるシャルピー衝撃試験に供して、引張強さ(MPa)および衝撃値(J/cm2)を測定し、試験数n=5での平均値を求めた。
測定結果を表2に併記する。また、各種特性値の合格基準は実施例1と同じである。
Claims (7)
- 鉄基粉末の粒子表面にMoが拡散付着した部分拡散合金鋼粉と、Cu粉および黒鉛粉とを有し、かつMo:0.2~1.5mass%、Cu:0.5~4.0mass%、C:0.1~1.0mass%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有する粉末冶金用混合粉であって、
前記部分拡散合金鋼粉は、平均粒径が30~120μmおよび比表面積が0.10m2/g未満であり、径が50~100μmの範囲にある粒子の円形度が0.65以下であることを特徴とする粉末冶金用混合粉。 - 前記Cu粉の平均粒径が50μm以下であることを特徴とする請求項1に記載の粉末冶金用混合粉。
- 前記鉄基粉末がアトマイズ生粉およびアトマイズ鉄粉のいずれか一方または両方であることを特徴とする請求項1または2に記載の粉末冶金用混合粉。
- 請求項1から3のいずれかに記載の粉末冶金用混合粉を含む成形体の焼結体である焼結体。
- 鉄基粉末の粒子表面にMoが拡散付着した部分拡散合金鋼粉と、Cu粉および黒鉛粉とを有し、かつMo:0.2~1.5mass%、Cu:0.5~4.0mass%、C:0.1~1.0mass%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有する粉末冶金用混合粉であって、前記部分拡散合金鋼粉は、平均粒径が30~120μmおよび比表面積が0.10m2/g未満であり、径が50~100μmの範囲にある粒子の円形度が0.65以下である、粉末冶金用混合粉の成形体を焼結する焼結体の製造方法。
- 前記Cu粉の平均粒径が50μm以下であることを特徴とする請求項5に記載の焼結体の製造方法。
- 前記鉄基粉末がアトマイズ生粉およびアトマイズ鉄粉のいずれか一方または両方であることを特徴とする請求項5または6に記載の焼結体の製造方法。
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- 2016-09-16 WO PCT/JP2016/004258 patent/WO2017047100A1/ja active Application Filing
- 2016-09-16 CN CN201680049635.8A patent/CN108025357B/zh active Active
- 2016-09-16 CA CA2992092A patent/CA2992092C/en active Active
- 2016-09-16 JP JP2017500097A patent/JP6160792B1/ja active Active
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CN111902556B (zh) * | 2018-03-26 | 2021-11-19 | 杰富意钢铁株式会社 | 粉末冶金用合金钢粉及粉末冶金用铁基混合粉末 |
US11236411B2 (en) | 2018-03-26 | 2022-02-01 | Jfe Steel Corporation | Alloyed steel powder for powder metallurgy and iron-based mixed powder for powder metallurgy |
JPWO2020202805A1 (ja) * | 2019-04-05 | 2021-04-30 | Jfeスチール株式会社 | 粉末冶金用鉄基混合粉末および鉄基焼結体 |
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JPWO2017047100A1 (ja) | 2017-09-14 |
CA2992092C (en) | 2020-04-07 |
CA2992092A1 (en) | 2017-03-23 |
JP6160792B1 (ja) | 2017-07-12 |
CN108025357A (zh) | 2018-05-11 |
CN108025357B (zh) | 2020-03-03 |
US10710155B2 (en) | 2020-07-14 |
KR102097956B1 (ko) | 2020-04-07 |
SE1850096A1 (en) | 2018-01-29 |
KR20180031750A (ko) | 2018-03-28 |
SE541269C2 (en) | 2019-05-28 |
US20180193908A1 (en) | 2018-07-12 |
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