Iron-based mixed powders for powder metallurgy, iron-based sintered bodies, and sintered machine parts

Abstract

To provide an iron-based powder mix for powder metallurgy that is superior in both compressibility and ejectability.SOLUTION: An iron-based powder mix for powder metallurgy includes iron-based powder, alloy powder, a lubricant, and particulate matter. The particulate matter has a specific surface area of 6 m2 / g or more. The content of the particulate matter is 0.01-1.0 pts.mass relative to the total of 100 pts.mass of the iron-based powder and the alloy powder.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an iron-based mixed powder for powder metallurgy, in particular to an iron-based mixed powder for powder metallurgy having both excellent compressibility and ejectability, and also to an iron-based sintered body made from said iron-based mixed powder for powder metallurgy as a raw material, and a sintered machine part made from said iron-based sintered body. [Background technology]

[0002] In powder metallurgy, a mixed powder (hereinafter referred to as "mixed powder for powder metallurgy" or simply "mixed powder") is used in which an iron-based powder, which is the main raw material, is mixed with components such as alloying powder and lubricants as necessary. Examples of the alloying powder that are used include copper powder, graphite powder, and iron phosphide powder. Examples of the lubricant that are widely used include fatty acids and metal soaps.

[0003] Such mixed powders for powder metallurgy are required to have various excellent properties such as flowability, compressibility, extractability, etc. Generally, lubricants are responsible for improving these properties.

[0004] For example, the lubricant has the effect of reducing friction between particles contained in the mixed powder, which promotes rearrangement of the particles during compaction, making it possible to compress the mixed powder to a high density.

[0005] Lubricants also exert a lubricating effect when the mixed powder (green compact) compressed in a die is removed (ejected) from the die. Generally, green compacts are pushed out of a die by a punch, but during this process, a large frictional resistance occurs due to friction between the green compact and the die surface. However, by adding a lubricant, the friction between the green compact and the die surface is reduced, allowing the green compact to be ejected with a small ejection force.

[0006] Thus, in the field of mixed powders for powder metallurgy, the performance of the mixed powders has been improved by using lubricants. However, further performance improvements are required for mixed powders for powder metallurgy, and various new technologies have been proposed to achieve this.

[0007] For example, Patent Document 1 proposes a technique for improving the fluidity and extractability of a mixed powder by adding metal carbonate porous particles containing a lubricant. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2010-059517 A Summary of the Invention [Problem to be solved by the invention]

[0009] According to the conventional technology as described in Patent Document 1, a certain degree of improvement in the compressibility and extractability of the mixed powder is observed, but further improvement in performance is required.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide an iron-based mixed powder for powder metallurgy which has both excellent compressibility and extractability. [Means for solving the problem]

[0011] The present invention has been made to solve the above problems, and the gist of the present invention is as follows.

[0012] 1. An iron-based mixed powder for powder metallurgy, comprising an iron-based powder, an alloying powder, a lubricant, and a particulate material, The specific surface area of ​​the particulate matter is 6 m 2 / g or more, The iron-based mixed powder for powder metallurgy, wherein the content of the fine particle material is 0.01 to 1.0 part by mass per 100 parts by mass of the total of the iron-based powder and the alloying powder.

[0013] 2. The iron-based mixed powder for powder metallurgy according to claim 1, wherein at least a portion of said particulate matter is directly attached to the surface of said iron-based powder.

[0014] 3. The iron-based mixed powder for powder metallurgy according to the above 1 or 2, wherein the iron-based powder is at least one of a reduced iron-based powder and an atomized iron-based powder.

[0015] 4. The iron-based mixed powder for powder metallurgy according to any one of 1 to 3 above, wherein the fine particle material is at least one selected from the group consisting of calcium carbonate, magnesium aluminometasilicate, talc, melamine cyanurate, molybdenum disulfide, graphite, and carbon black.

[0016] 5. The iron-based mixed powder for powder metallurgy according to any one of 1 to 4 above, wherein the content of the fine particle material is 0.01 parts by mass or more and less than 0.05 parts by mass per 100 parts by mass of the iron-based mixed powder for powder metallurgy.

[0017] 6. An iron-based sintered body obtained by using as a raw material the iron-based mixed powder for powder metallurgy according to any one of 1 to 5 above.

[0018] 7. A sintered machine part using the iron-based sintered body described in 6 above. Effect of the Invention

[0019] According to the present invention, it is possible to provide an iron-based mixed powder for powder metallurgy having both excellent compressibility and extractability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A method for carrying out the present invention will be specifically described below. Note that the following description shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto.

[0021] [Iron-based mixed powder for powder metallurgy] The iron-based mixed powder for powder metallurgy of the present invention contains an iron-based powder, an alloying powder, a lubricant, and a particulate material as essential components. Here, the iron-based mixed powder for powder metallurgy refers to a mixed powder for powder metallurgy in which the proportion of Fe in the whole is 50 mass % or more.

[0022] [Iron-based powder] The iron-based powder is not particularly limited and any iron-based powder can be used. Examples of the iron-based powder include iron powder and alloyed steel powder. The alloyed steel powder can be, for example, one or more selected from the group consisting of pre-alloyed steel powder (fully alloyed steel powder) in which alloying elements are pre-alloyed during melting, partially diffused alloyed steel powder in which alloying elements are partially diffused into iron powder, and hybrid steel powder in which alloying elements are further partially diffused into pre-alloyed steel powder. The alloying elements can be, for example, one or more selected from the group consisting of C, Cu, Ni, Mo, Mn, Cr, V, and Si. Here, the term "iron-based powder" refers to a metal powder containing 50% by mass or more of Fe. The term "iron powder" refers to a powder consisting of Fe and unavoidable impurities, and is generally referred to as "pure iron powder" in this technical field.

[0023] The iron-based powder can be produced by any method. For example, the iron-based powder can be a reduced iron-based powder, an atomized iron-based powder, or a mixture thereof. The reduced iron-based powder is an iron-based powder produced by reducing iron oxide. The atomized iron-based powder is an iron-based powder produced by an atomization method. In addition, a powder in which alloy elements are diffused and attached to the surface of the reduced iron-based powder or the atomized iron-based powder can also be used as the iron-based powder.

[0024] The proportion of the mass of the iron-based powder relative to the total mass of the powder mixture for powder metallurgy is not particularly limited, but is preferably 86 mass % or more, and more preferably 90 mass % or more.

[0025] The average particle size of the iron-based powder is not particularly limited and may be any particle size. However, if the particle size of the iron-based powder is too small, it is likely to generate dust, making it difficult to handle. From the viewpoint of ease of handling, the average particle size of the iron-based powder is preferably 1 μm or more, and more preferably 10 μm or more. On the other hand, if the particle size of the iron-based powder is too large, it may adversely affect the strength of the sintered body. Therefore, from the viewpoint of improving the strength of the sintered body, the average particle size of the iron-based powder is preferably 200 μm or less. Here, the average particle size of the iron-based powder is the median diameter D50 in the particle size distribution based on weight. The particle size distribution is measured by a sieving test.

[0026] [Alloy powder] When a mixed powder containing an alloying powder is sintered, the alloying elements dissolve in the iron to form an alloy, and therefore the strength of the final sintered body can be improved by using the alloying powder.

[0027] The alloy powder is not particularly limited, and any powder that can be an alloy component can be used. For example, one or more powders selected from the group consisting of C, Cu, Ni, Mo, Mn, Cr, V, and Si can be used as the alloy powder. When C is used as an alloy component, it is preferable to use graphite powder as the alloy powder.

[0028] The particle size of the alloy powder is not particularly limited, and powders of any size can be used. However, if the particle size of the alloy powder is too small, the alloy powder may aggregate in the mixed powder, which may cause problems in handling. From the viewpoint of ease of handling, the average particle size of the alloy powder is preferably 1 μm or more. On the other hand, if the particle size of the alloy powder is too large, it may adversely affect the strength of the sintered body. Therefore, from the viewpoint of improving the strength of the sintered body, the average particle size is preferably 100 μm or less. Here, the average particle size of the alloy powder is the median diameter D50 in the volume-based particle size distribution. The particle size distribution is measured by a laser diffraction / scattering type particle size distribution analyzer.

[0029] As mentioned above, alloy powders function as alloy components, and are added for a different purpose than the fine particle substances described below. 2 / g or more, and therefore the specific surface area of ​​the alloy powder is 6 m 2 / g.

[0030] [Lubricant] The lubricant is not particularly limited and any lubricant can be used. As the lubricant, it is preferable to use one or more selected from the group consisting of metal soap, bisamide, fatty acid amide, fatty acid, liquid lubricant, and thermoplastic resin.

[0031] Examples of the metal soap include zinc stearate, manganese stearate, and lithium stearate. Examples of the bisamide include ethylene bisstearamide. Examples of the fatty acid amide include stearic acid monoamide and erucic acid amide. Examples of the fatty acid include oleic acid and stearic acid. Examples of the liquid lubricant include phosphoric acid ester, polyol ester, mineral oil, and polyglycol. Examples of the thermoplastic resin include polyamide, polyethylene, and polyacetal.

[0032] The amount of the lubricant contained is not particularly limited, but is preferably 0.5 to 1.5 parts by mass relative to 100 parts by mass of the iron-based powder and the alloying powder combined.

[0033] The state of the lubricant in the mixed powder is not particularly limited. For example, the lubricant may be one or both of a free lubricant and a bound lubricant. Here, the free lubricant is a lubricant that is not bound to particles of other components such as iron-based powder and exists in a free state in the mixed powder. Also, the bound lubricant is a lubricant that exists in a state of adhering to the surface of the iron-based powder. When at least a part of the lubricant exists as a bound lubricant, the alloy powder can be fixed to the surface of the iron-based powder via the bound lubricant. As a result, the segregation of the components in the mixed powder can be suppressed.

[0034] [Particulate matter] In the present invention, a fine particle material is added to further improve the compressibility and extractability of the powder mixture for powder metallurgy. To achieve this effect, the fine particle material should have a specific surface area of ​​6 m 2 / g or more. The reason for this is unclear, but 2 It is believed that the friction between the iron-based powder particles and between the iron-based powder and the die surface is reduced by the very fine particles, with a particle size of 1 / g or more, adhering in a dispersed state to the surface of the iron-based powder.

[0035] In addition, the median diameter D50 is generally used to limit the particle size. However, when the particles are extremely fine, the primary particles aggregate to form pseudo particles (secondary particles), and the median diameter obtained by a general measurement is the particle size of these secondary particles. However, according to the study by the present inventors, the compressibility when a compressive force for molding is applied to the mixed powder and the extractability of the green compact are more significantly affected by the size of the primary particles than by the size of the secondary particles. Therefore, in the present invention, the specific surface area of ​​the particulate material is limited as described above as a parameter that is an index of the size of the primary particles. In other words, the higher the specific surface area, the finer the primary particles of the particulate material are.

[0036] On the other hand, from the viewpoint of compressibility and extractability, the higher the specific surface area, the better, so there is no particular upper limit to the specific surface area. However, even if the primary particles are made too fine, the effect becomes saturated, and handling of the fine particle material may become difficult. Therefore, the specific surface area is set to 1000 m 2 / g or less, and 2 / g or less is more preferable. Note that, as the specific surface area, a BET specific surface area measured by a gas adsorption method using nitrogen gas is used.

[0037] As described above, the fine particles of the present invention improve the compressibility and extractability by utilizing the physical effect of the fine particles adhering to the surface of the iron-based powder. 2 Any particles can be used regardless of their material as long as they have a molecular weight of at least 1.0 μm / g.

[0038] Therefore, the particulate material may be particulates made of one or both of an inorganic material and an organic material. The particulate material is not intended to supply an alloy metal element. Therefore, the particulate material may be particles made of a non-metallic material. Here, non-metallic materials refer to materials other than metallic materials (metals and alloys), and metal compounds are included in non-metallic materials.

[0039] Examples of the inorganic material include graphite, graphite fluoride, boron nitride, molybdenum disulfide, tungsten disulfide, titanium oxide, carbon black, calcium carbonate, and silicate compounds. As the boron nitride, it is preferable to use hexagonal boron nitride. As the silicate compound, it is preferable to use magnesium aluminometasilicate and phyllosilicates (layered silicates). As the phyllosilicates, it is preferable to use talc, mica, vermiculite, and kaolin. Among these inorganic materials, graphite, graphite fluoride, hexagonal boron nitride, molybdenum disulfide, tungsten disulfide, and phyllosilicates have a layered structure, and therefore are considered to have an excellent effect of reducing friction.

[0040] Examples of the organic material include various organic resins and melamine cyanurate. Examples of the organic resin include PMMA (polymethyl methacrylate resin). Melamine cyanurate has a layered structure similar to that of graphite, and is therefore considered to have an excellent effect of reducing friction.

[0041] In one embodiment of the present invention, the particulate material may be at least one selected from the group consisting of calcium carbonate, magnesium aluminometasilicate, talc, melamine cyanurate, molybdenum disulfide, graphite, and carbon black.

[0042] The content of the fine particle material is 0.01 to 1.0 parts by mass relative to 100 parts by mass of the total of the iron-based powder and the alloy powder. If the content is less than 0.01 parts by mass, the desired compressibility and ejection force cannot be obtained. On the other hand, if the content is more than 1.0 parts by mass, the green density decreases, and as a result, the strength of the finally obtained sintered body also decreases. This is considered to be because the effect of improving compressibility by the fine particle material becomes saturated, and the proportion of the iron-based powder relatively decreases with the increase in the fine particle material.

[0043] Furthermore, when a substance that is not dewaxed in the sintering step is used as the particulate material, the particulate material adversely affects the sintering characteristics, and therefore, from the viewpoint of achieving a higher level of compatibility between the characteristics of the green compact and the sintered compact even when the particulate material is not dewaxed, it is preferable that the content of the particulate material be 0.01 parts by mass or more and less than 0.05 parts by mass relative to 100 parts by mass of the total of the iron-based powder and the alloying powder.

[0044] The particulate material is not particularly limited and may be present in the mixed powder in any state, but it is preferable that at least a part of the particulate material is directly attached to the surface of the iron-based powder. By having the particulate material directly attached to the surface of the iron-based powder, the effect of reducing friction between the iron-based powder particles and between the iron-based powder and the die can be further enhanced. Here, the particulate material is directly attached to the surface of the iron-based powder when no lubricant is present between the iron-based powder and the particulate material. In other words, it is preferable that at least a part of the particulate material is directly attached to the surface of the iron-based powder without the lubricant.

[0045] [Method of manufacturing mixed powder] The mixed powder of the present invention is not particularly limited and can be produced by any method. In one embodiment of the present invention, the above-mentioned components can be mixed using a mixer to produce an iron-based mixed powder for powder metallurgy. The addition and mixing of the components can be carried out in one go, or in two or more separate gos.

[0046] In order to make the lubricant adhere to the surface of the iron-based powder to form a bound lubricant, for example, the mixture is stirred while being heated to the melting point of the lubricant or higher during mixing, and then gradually cooled while being mixed. As a result, the surface of the iron-based powder is covered with the molten lubricant. When using an alloying powder and a machinability improver, it is preferable to add them simultaneously with the lubricant used as the bound lubricant. As a result, the components of the alloying powder, the machinability improver, etc. are fixed to the surface of the iron-based powder through the bound lubricant attached to the surface of the iron-based powder. On the other hand, the free lubricant may be added and mixed separately after the bound lubricant is fixed to the surface of the iron-based powder as described above. The addition and mixing of the free lubricant is carried out at a temperature lower than the melting point of the bound lubricant so that the already-fixed bound lubricant does not melt. The particulate material may be added simultaneously with the bound lubricant, simultaneously with the free lubricant, or separately from the free lubricant.

[0047] As described above, in the iron-based mixed powder for powder metallurgy of the present invention, it is preferable that at least a part of the particulate material is directly attached to the surface of the iron-based powder. In order to directly attach at least a part of the particulate material to the surface of the iron-based powder, the iron-based powder, the lubricant, and the particulate material may be heated to a temperature equal to or higher than the melting point of the lubricant while being mixed. At the initial stage of the temperature increase, the temperature is still low and the lubricant is not melted. Therefore, the particulate material can be directly attached to the surface of the iron-based powder. In this case, if the particulate material is a secondary particle (agglomerated particle), it is considered that a part of the particulate material is crushed into primary particles by being mixed with the iron-based powder in the mixer, and the primary particles are attached to the surface of the iron-based powder. After that, when the temperature reaches a temperature equal to or higher than the melting point of the lubricant, the lubricant is further attached to the surface of the iron-based powder to which the particulate material is attached by the molten lubricant. As a result, at least a part of the particulate material is directly attached to the surface of the iron-based powder without the lubricant.

[0048] In the above process, the alloying powder can be mixed at any timing. For example, the alloying powder may be mixed when the iron-based powder, the lubricant, and the particulate material are mixed. Alternatively, the iron-based powder, the lubricant, and the particulate material may be mixed in the above procedure, cooled, and then the alloying powder may be mixed.

[0049] The mixer is not particularly limited and any mixer can be used, but it is preferable to use a mixer equipped with a heating device. From the viewpoint of easy heating, it is preferable to use one or more mixers selected from the group consisting of a high-speed bottom stirring mixer, an inclined rotating pan type mixer, a rotating hoe type mixer, and a conical planetary screw type mixer.

[0050] [Iron-based sintered body] The iron-based sintered body in one embodiment of the present invention is an iron-based sintered body made from the iron-based mixed powder for powder metallurgy. Also, the sintered mechanical part in one embodiment of the present invention is a sintered mechanical part using the iron-based sintered body. The manufacturing method of the iron-based sintered body is not particularly limited, but it can be manufactured by pressurizing the iron-based mixed powder for powder metallurgy to form a molded body and sintering the molded body. Each step will be described below.

[0051] (Pressure molding) First, the iron-based mixed powder for powder metallurgy is pressure-molded into a desired shape to obtain a molded body. In the pressure molding, the iron-based mixed powder for powder metallurgy may be optionally mixed with auxiliary materials, lubricants, powders for improving machinability, etc. The method of the pressure molding is not particularly limited, and any method can be used, for example, a method in which the mixed powder is filled in a die and pressure molded. The pressure of the pressure molding is not particularly limited, and can be, for example, 400 MPa or more and 1000 MPa or less.

[0052] (Sintering) The sintering method is not particularly limited, and can be performed by any method. The sintering temperature can be 1100°C or higher, preferably 1120°C or higher, from the viewpoint of sufficiently advancing the sintering. On the other hand, the higher the sintering temperature, the more uniform the distribution of the alloy elements in the sintered body becomes, so the upper limit of the sintering temperature is not particularly limited, but from the viewpoint of suppressing the manufacturing cost, the sintering temperature is preferably 1250°C or lower, more preferably 1180°C or lower. EXAMPLES

[0053] An iron-based mixed powder for powder metallurgy was prepared according to the following procedure, and the properties of the obtained iron-based mixed powder for powder metallurgy and the properties of a green compact and a sintered compact produced using the iron-based mixed powder for powder metallurgy were evaluated.

[0054] First, an iron-based powder, an alloying powder, a particulate material, and a lubricant were mixed and heated to a temperature equal to or higher than the melting point of the lubricant. An atomized iron powder (JIP-301A, manufactured by JFE Steel Corporation) was used as the iron-based powder. An electrolytic copper powder and an ion exchange resin with a specific surface area of ​​2.3 m were used as the alloying powder.2 / g of natural graphite powder was used. The iron-based powder, alloying powder, and particulate matter contents were as follows: ·Iron-based powder: 97.2% by mass ·Electrolytic copper powder: 2.0% by mass Natural graphite powder: 0.8% by mass Here, the content is a ratio to the total mass of the iron-based powder and the alloying powder.

[0055] The particulate material used was that shown in Table 1, in the amounts shown in Table 1. The amount of particulate material shown in Table 1 is based on 100 parts by mass of the iron-based powder and the alloying powder combined. However, for comparison, no particulate material was added in some examples (Comparative Example No. 1).

[0056] The lubricants used were stearic acid amide and ethylene bis stearic acid amide, with the lubricant contents being 0.1 parts by mass of stearic acid amide and 0.1 parts by mass of ethylene bis stearic acid amide per 100 parts by mass of the iron-based powder and the alloying powder combined.

[0057] After the above mixing, the mixture was cooled to a temperature below the melting point of the free lubricant to be added next, and further, stearic acid amide, ethylene bisstearic acid amide, and zinc stearate were added as free lubricants. The content of the free lubricants was 0.25 parts by mass of stearic acid amide, 0.25 parts by mass of ethylene bisstearic acid amide, and 0.1 parts by mass of zinc stearate, relative to a total of 100 parts by mass of the iron-based powder and the alloy powder. For comparison, in some examples (No. 14), instead of adding the particulate material before heating and mixing, the particulate material was added together with the free lubricant after cooling.

[0058] The iron-based mixed powder for powder metallurgy was obtained by the above procedure. When the obtained iron-based mixed powder for powder metallurgy was observed with a scanning electron microscope (SEM), it was found that in all the iron-based mixed powders for powder metallurgy except for Comparative Example No. 14, some of the fine particles were directly attached to the surface of the iron-based powder. In the iron-based mixed powder for powder metallurgy of Comparative Example No. 14, the fine particles were added after cooling, so the fine particles were not directly attached to the surface of the iron-based powder, but were attached to the surface of the lubricant attached to the surface of the iron-based powder.

[0059] (Green density, ejection force) A powder compact was produced using each of the iron-based mixed powders for powder metallurgy obtained by the above procedure, and the density of the powder compact (green density) and the ejection force when the powder compact was ejected from a die were measured. The powder compact was produced by filling 55 g of the iron-based mixed powder for powder metallurgy into a die having a diameter of 25 mm and pressing at room temperature. The pressure during the pressing was 686 MPa. The green density was calculated from the dimensions and weight of the obtained cylindrical green compact. The measurement results are shown in Table 1.

[0060] (Ring crushing strength) In addition, an iron-based sintered body was prepared using each of the iron-based mixed powders for powder metallurgy, and the strength of the iron-based sintered body was measured. Specifically, the mixed powder was first filled into an annular die having an outer diameter of 38 mm and an inner diameter of 14 mm, and molded to a height of 10 mm under a molding pressure of 686 MPa to obtain an annular green compact. The green compact was sintered in an RX gas atmosphere at 1130°C in a mesh belt furnace having a belt width of 6 inches to obtain an annular iron-based sintered body. The strength (radial crushing strength) of the obtained iron-based sintered body was measured according to JIS Z 2507-2000. The measurement results are shown in Table 1.

[0061] As can be seen from the results shown in Table 1, the iron-based mixed powder for powder metallurgy that satisfied the conditions of the present invention had both excellent compressibility and extractability. In contrast, the iron-based mixed powder for powder metallurgy that did not satisfy the conditions of the present invention was inferior in at least one of the compressibility and extractability.

[0062] [Table 1]

Claims

1. An iron-based powder mixture for powder metallurgy comprising an iron-based powder, an alloying powder, a lubricant, and a particulate material, the particulate material is at least one selected from the group consisting of calcium carbonate, magnesium aluminometasilicate, talc, melamine cyanurate, molybdenum disulfide, and graphite; The specific surface area of ​​the particulate matter is 6 m ２ / g or more, The iron-based mixed powder for powder metallurgy, wherein the content of the fine particle material is 0.01 to 0.04 parts by mass per 100 parts by mass of the total of the iron-based powder and the alloying powder.

2. 2. The iron-based powder mixture for powder metallurgy according to claim 1, wherein at least a portion of said particulate matter is directly attached to a surface of said iron-based powder.

3. 3. The iron-based mixed powder for powder metallurgy according to claim 1, wherein the iron-based powder is at least one of a reduced iron-based powder and an atomized iron-based powder.

4. 3. An iron-based sintered body using the iron-based mixed powder for powder metallurgy according to claim 1 or 2 as a raw material.

5. A sintered machine part using the iron-based sintered body according to claim 4.

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