Mixed powder for powder metallurgy

Abstract

This mixed powder for powder metallurgy contains an iron-based powder and a fatty acid amide as a lubricant. The fatty acid amide contains only saturated fatty acid bisamides and saturated fatty acid monoamides, and does not contain unsaturated fatty acid amides. The content of a saturated fatty acid bisamide (b1) present as the bonded lubricant, the content of a saturated fatty acid monoamide (b2) present as the bonded lubricant, the content of a saturated fatty acid bisamide (c1) present as the free lubricant and the content of a saturated fatty acid monoamide (c2) present as the free lubricant satisfy requirements (1) and (2).　(1): 0<(b1)+(b2)+(c1)+(c2)≤1.0. (2): 0<[(b1)+(c1)] / [(b2)+(c2)]<0.50.

Description

Mixed powder for powder metallurgy

[0001] The present invention relates to mixed powders for powder metallurgy.

[0002] Powder metallurgy is a technology that involves placing metal powder in a die, compressing it, and sintering it at high temperatures to create parts with high dimensional accuracy. Powder metallurgy allows parts with complex shapes to be formed with high dimensional accuracy, significantly reducing cutting costs compared to shaping processes such as machining. For this reason, powder metallurgy products are used in a wide range of applications, including in various machines and parts.

[0003] In powder metallurgy, a powder mixture for powder metallurgy (hereinafter sometimes simply referred to as "powder mixture") is used as the raw material powder, which is made by mixing an iron-based powder, which is the main raw material, with an alloying powder such as copper powder, graphite powder, or iron phosphide powder, a machinability improving powder such as MnS, and a lubricant as needed. In particular, the lubricant has the effect of reducing friction when the powder mixture is molded in a die and improving moldability, and therefore plays an extremely important role in manufacturing products using powder metallurgy.

[0004] The lubricant is primarily required to have the functions of reducing friction between particles contained in the mixed powder and between the particles and the mold used in compaction.

[0005] The effect of reducing interparticle friction is achieved, for example, by the presence of a lubricant between particles during compaction. Reducing interparticle friction promotes particle rearrangement, improving compactibility. The effect of reducing friction between a die and particles is achieved, for example, by the presence of a lubricant on the die surface between the die and particles. Reducing friction between the die and particles promotes particle rearrangement on the surface of the green compact, improving compactibility.

[0006] These two effects make it possible to compress the mixed powder to a high density during molding. Furthermore, the friction between the mold and the resulting compact when it is removed from the mold is reduced, improving the releasability of the compact from the mold. The compact is removed from the mold, for example, by pushing it out with a punch, but if the friction between the mold and the compact is high, it may be difficult to remove the compact from the mold or the surface of the compact may be damaged.

[0007] Although the lubricant plays an important role during compaction and removal from the die as described above, it is required that it does not remain in the final sintered body. Since the lubricant becomes unnecessary after the compact is removed from the die, it is desirable that the lubricant disappear during sintering of the compact, for example.

[0008] Powder metallurgy mixtures sometimes contain additional components that function as binders. Here, binders refer to components that adhere additive components, such as alloying powders, to the surfaces of the iron particles in the iron-based powder (the main component). Mixed powders obtained by simply mixing an iron-based powder with additive components, such as alloying powders, machinability-improving powders, and lubricants, can result in the segregation of each component after mixing. In particular, graphite powder, which is commonly used as an alloying powder, has a lower density than other components and therefore easily segregates when the mixed powder is fluidized or vibrated. To prevent this segregation, additive components may be attached to the particle surfaces of the iron-based powder via a binder. Such mixed powders are sometimes referred to as segregation prevention treatment powders. In segregation prevention treatment powders, the additive components adhere to the iron-based powder, preventing the aforementioned segregation of the components.

[0009] Generally, lubricants have stronger adhesive power than iron-based powders, which can lead to a problem of impairing the flowability of the mixed powder. However, this adhesive power can be utilized to use lubricants as binders.

[0010] Powder metallurgy mixed powders are generally press-molded at pressures of 300 MPa to 1000 MPa to obtain a desired part shape, and then sintered at high temperatures of 1000°C or higher to obtain the final part shape. The total amount of lubricant and binder contained in the mixed powder is generally about 0.1 to 2 parts by mass per 100 parts by mass of the iron-based powder. Because the density of lubricant and binder is lower than that of the iron-based powder, adding large amounts of them reduces the density of the compact, which in turn reduces the density of the sintered compact. Therefore, to increase the density of the compact, it is better to add less lubricant and binder. Therefore, by using a lubricant that also functions as a binder, the total amount of binder and lubricant added to the mixed powder can be reduced.

[0011] The lubricating performance of a lubricant is greatly affected by the types of compounds contained in the lubricant. For example, fatty acid amides and fatty acid metal soaps have excellent lubricating properties and are widely used as lubricants for powder metallurgy.

[0012] However, fatty acid metal soaps can produce metal oxides during sintering, which can contaminate the surface of the sintered body and the sintering furnace. In contrast, fatty acid amides decompose during sintering, volatilizing all of their components, preventing contamination. For this reason, fatty acid amides are used as clean lubricants.

[0013] For example, Patent Document 1 discloses the use of one or more selected from stearic acid, oleic acid monoamide, and stearic acid monoamide, and at least one selected from the group consisting of ethylene bisstearic acid amide and methylene bisstearic acid amide, as a "binder" and a "lubricant."

[0014] Furthermore, Patent Document 2 discloses the use of a primary or secondary fatty acid amide in combination with an alkylenebisfatty acid amide or a secondary or tertiary polyhydroxy fatty acid amide.

[0015] Patent Document 3 discloses the use of a linear fatty acid bisamide and a linear fatty acid monoamide with an unsaturated fatty acid bisamide or a branched fatty acid bisamide or an unsaturated fatty acid monoamide in a predetermined ratio.

[0016] Patent Document 4 discloses the use of a lubricant in which an unsaturated fatty acid bisamide and a saturated hydroxy fatty acid are combined.

[0017] Japanese Patent Laid-Open No. 05-148505 Japanese Patent Laid-Open No. 2011-184708 International Publication No. 2014 / 123106 Japanese Patent Laid-Open No. 2019-143200

[0018] In commercial powder metallurgy molding processes, hundreds to thousands of parts are molded continuously. During such continuous molding, the temperature of the mold gradually increases due to frictional heat. The degree of mold temperature increase varies depending on the mold and part shape, but for parts with large side surfaces, the mold temperature can rise to approximately 70 to 80°C. Therefore, powder metallurgy lubricants are required to exhibit high lubricity not only at room temperature during the initial molding process, but also after the mold temperature has increased.

[0019] However, Patent Documents 1 to 4 only evaluate the ejection property and compressibility at room temperature, and do not take into consideration the performance when the mold temperature is elevated.

[0020] The present invention has been made in view of the above circumstances, and has as its object to provide a mixed powder for powder metallurgy which uses a fatty acid amide, which is a clean lubricant, and which exhibits excellent ejection and compressibility of a molded product not only at room temperature but also after an increase in mold temperature.

[0021] The present invention has been made to solve the above problems, and the gist of the present invention is as follows.

[0022] 1. A mixed powder for powder metallurgy comprising an iron-based powder and a fatty acid amide as a lubricant, wherein the fatty acid amide contains only saturated fatty acid bisamide and saturated fatty acid monoamide, and does not contain unsaturated fatty acid amide, a portion of the lubricant is a bound lubricant (b) that adheres to the surface of the iron-based powder, and the remainder of the lubricant is a free lubricant (c) that does not adhere to the surface of the iron-based powder, and the contents of the saturated fatty acid bisamide (b1) present as the bound lubricant, the saturated fatty acid monoamide (b2) present as the bound lubricant, the saturated fatty acid bisamide (c1) present as the free lubricant, and the saturated fatty acid monoamide (c2) present as the free lubricant satisfy the following formulas (1) and (2): 0<(b1)+(b2)+(c1)+(c2)≦1.0 (1) 0<[(b1)+(c1)] / [(b2)+(c2)]<0.50 (2) Here, (b1), (b2), (c1), and (c2) in the above formulas (1) and (2) represent the content of each component expressed in parts by weight relative to 100 parts by mass of the iron-based powder.

[0023] 2. The mixed powder for powder metallurgy according to 1 above, wherein the saturated fatty acid bisamide (c1) present as the free lubricant has an average particle size of 20 to 60 μm, and the saturated fatty acid monoamide (c2) present as the free lubricant has an average particle size of 20 to 60 μm.

[0024] 3. The mixed powder for powder metallurgy according to item 1 or 2 above, wherein the fatty acid amide is a derivative of at least one selected from the group consisting of lauric acid, palmitic acid, stearic acid, and behenic acid.

[0025] 4. The mixed powder for powder metallurgy according to any one of 1 to 3 above, further comprising, as a flowability improver, at least one selected from the group consisting of carbon black, metal oxides, and metal soaps.

[0026] 5. The mixed powder for powder metallurgy according to any one of 1 to 4 above, further comprising an alloying powder.

[0027] 6. The mixed powder for powder metallurgy according to 5 above, wherein the alloying powder is adhered to the surfaces of the particles constituting the iron-based powder via the binding lubricant.

[0028] The mixed powder for powder metallurgy of the present invention can provide a molded product with excellent ejection and compressibility not only at room temperature but also after the mold temperature is elevated.

[0029] Hereinafter, an embodiment of the present invention will be specifically described. However, the present invention is not limited to this embodiment. In the following description, "%" refers to "% by mass" unless otherwise specified.

[0030] A mixed powder for powder metallurgy in one embodiment of the present invention contains, as essential components, an iron-based powder (a) and a fatty acid amide as a lubricant. A portion of the lubricant is a bound lubricant (b) adhering to the surface of the iron-based powder, and the remainder of the lubricant is a free lubricant (c) not adhering to the surface of the iron-based powder. In other words, the mixed powder in one embodiment of the present invention contains the following (a), (b), and (c). Furthermore, a mixed powder for powder metallurgy in another embodiment of the present invention can optionally contain at least one of the following (d), (e), and (f) in addition to the above components. Each of these components will be described below. (a) Iron-based powder (b) Bound lubricant (c) Free lubricant (d) Flowability improver (e) Alloying powder (f) Machinability improver

[0031] (a) Iron-based Powder The iron-based powder is not particularly limited, and any iron-based powder can be used. The iron-based powder may be one or both of iron powder and iron-based alloy powder. Here, "iron-based powder" refers to a metal powder containing 50 mass% or more of Fe. Furthermore, "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. "Iron-based alloy powder" refers to a powder consisting of at least one alloying element and the remainder consisting of Fe and unavoidable impurities, and is generally referred to as "alloyed steel powder" in this technical field.

[0032] The iron-based alloy powder (alloy steel powder) may be at least one selected from the group consisting of pre-alloyed steel powder (fully alloyed steel powder) in which alloying elements are pre-alloyed during melting, partially diffusion-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 element may be at least one selected from the group consisting of C, Cu, Ni, Mo, Mn, Cr, V, and Si.

[0033] The iron-based powder can be produced by a conventional method. For example, the iron-based powder may 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. Alternatively, a powder obtained by diffusing and adhering alloy elements to the surface of the reduced iron-based powder or the atomized iron-based powder can be used as the iron-based powder.

[0034] Although the particle size of the iron-based powder is not particularly limited, the average particle size of the iron-based powder is preferably 30 μm or more. Furthermore, the average particle size is preferably 150 μm or less. Here, the average particle size of the iron-based powder is defined as the median diameter D50 in the particle size distribution based on weight. The particle size distribution is measured by a sieving test.

[0035] The content of the iron-based powder in the mixed powder for powder metallurgy is not particularly limited, but is preferably 86% or more, more preferably 90% or more, in terms of percentage relative to the total mass of the mixed powder. Meanwhile, the upper limit of the content of the iron-based powder is also not particularly limited, but the remainder of the mixed powder other than the lubricant may be entirely iron-based powder. Therefore, the content of the iron-based powder in the mixed powder may be less than 100%, or may be 99.0% or less, or may be 97.0% or less.

[0036] (b) Bound lubricant (c) Free lubricant The mixed powder of the present invention contains a fatty acid amide as a lubricant. The fatty acid amide contains only saturated fatty acid bisamides and saturated fatty acid monoamides, and does not contain unsaturated fatty acid amides. In other words, the fatty acid amides contained in the mixed powder of the present invention consist of saturated fatty acid bisamides and saturated fatty acid monoamides, and the mixed powder does not substantially contain unsaturated fatty acid amides.

[0037] Because unsaturated fatty acid amides have double bonds, they are difficult to form an ideal layered structure. As a result, they have a lower melting point and are more likely to soften than saturated fatty acid amides with the same number of carbon atoms in the fatty chain. Therefore, in order to obtain excellent ejection and compressibility not only at room temperature but also at elevated mold temperatures, it is necessary to use only saturated fatty acid bisamides and saturated fatty acid monoamides as fatty acid amides.

[0038] Specifically, the fatty acid amide is preferably an amide made from at least one saturated fatty acid selected from the group consisting of lauric acid, palmitic acid, stearic acid, and behenic acid, or a derivative of at least one selected from the group consisting of lauric acid, palmitic acid, stearic acid, and behenic acid.

[0039] In one embodiment of the present invention, only the fatty acid amide can be used as the lubricant. In other words, the powder mixture for powder metallurgy in one embodiment of the present invention may be composed of an iron-based powder and a fatty acid amide as the lubricant. Even in this case, the powder mixture for powder metallurgy may further optionally contain at least one selected from the group consisting of a flowability improver, an alloying powder, and a machinability improver.

[0040] At least a portion of the lubricant adheres to the surface of the iron-based powder, and the remainder does not adhere to the surface of the iron-based powder. The lubricant adhered to the surface of the iron-based powder is defined as (b) a bonded lubricant, and the lubricant not adhered to the surface of the iron-based powder is defined as (c) a free lubricant. In other words, the lubricant consists of (b) a bonded lubricant adhered to the surface of the iron-based powder and (c) a free lubricant not adhered to the surface of the iron-based powder.

[0041] To adhere a lubricant to the surface of an iron-based powder to form a bonded lubricant, for example, the mixture may be heated to or above the melting point of the lubricant while stirring, and then gradually cooled while mixing. This results in the surface of the iron-based powder being coated with the molten lubricant. On the other hand, the free lubricant may be added and mixed separately after the bonded lubricant has been adhered to the surface of the iron-based powder. The addition and mixing of the free lubricant is carried out at a temperature lower than the melting point of the bonded lubricant so as not to melt the already adhered bonded lubricant.

[0042] In the mixed powder for powder metallurgy of the present invention, it is important that the contents of the saturated fatty acid bisamide (b1) present as the bound lubricant, the saturated fatty acid monoamide (b2) present as the bound lubricant, the saturated fatty acid bisamide (c1) present as the free lubricant, and the saturated fatty acid monoamide (c2) present as the free lubricant satisfy the following formulas (1) and (2): 0<(b1)+(b2)+(c1)+(c2)≦1.0 (1) 0<[(b1)+(c1)] / [(b2)+(c2)]<0.50 (2) In the formulas (1) and (2), (b1), (b2), (c1), and (c2) represent the contents of each component expressed in parts by weight relative to 100 parts by mass of the iron-based powder.

[0043] The above formula (1) indicates that the total amount of b1, b2, c1, and c2 is greater than 0 parts by mass and 1.0 parts by mass or less, relative to 100 parts by mass of the iron-based powder. By satisfying the condition of formula (1), the compressibility of the mixed powder is improved, and a high compact density can be obtained. If the total amount exceeds 1.0 part by mass, the compressibility decreases. The total amount is preferably 0.6 parts by mass or less. In other words, it is preferable to satisfy the condition of the following formula (1'): 0<(b1)+(b2)+(c1)+(c2)≦0.6 ... (1')

[0044] On the other hand, from the viewpoint of enhancing the effect of adding the lubricant, the total amount is preferably 0.2 parts by mass or more. In other words, it is preferable to satisfy the condition of the following formula (1"), and it is more preferable to satisfy the condition of the following formula (1"'): 0.2<(b1)+(b2)+(c1)+(c2)≦1.0 (1") 0.2<(b1)+(b2)+(c1)+(c2)≦0.6 (1"')

[0045] The above formula (2) indicates that the ratio of the total amount of b1 and c1 to the total amount of b2 and c2 is greater than 0 and less than 0.50. By satisfying the condition of formula (2), it is possible to reduce the ejection force of the molded body from the mold after the mold temperature has increased. The ratio of the total amounts is preferably 0.05 or more, and more preferably 0.10 or more.

[0046] The particle size of the lubricant is not particularly limited. However, if the particle size of the free lubricant is too small, the lubricating effect may be reduced. Therefore, from the viewpoint of further improving the extractability and flowability, it is preferable that the average particle size of the saturated fatty acid bisamide (c1) present as the free lubricant and the average particle size of the saturated fatty acid monoamide (c2) present as the free lubricant are each 20 μm or more. On the other hand, if the particle size of the free lubricant is too large, the flowability decreases. Therefore, from the viewpoint of improving the flowability, it is preferable that the average particle size of the saturated fatty acid bisamide (c1) present as the free lubricant and the average particle size of the saturated fatty acid monoamide (c2) present as the free lubricant are each 60 μm or less.

[0047] Here, the average particle size of the lubricant is the median diameter D50 in the volume-based particle size distribution, which is measured using a laser diffraction / scattering particle size distribution analyzer.

[0048] The saturated fatty acid bisamide (c1) present as a free lubricant and the saturated fatty acid monoamide (c2) present as a free lubricant may be contained in the mixed powder in an independent state, or may be contained in an integrated state. When the two are contained in the mixed powder in an integrated state, for example, a co-melt lubricant may be prepared by melt-mixing the saturated fatty acid bisamide and the saturated fatty acid monoamide in advance, and then the co-melt lubricant may be mixed with an iron-based powder or the like. When the co-melt lubricant is used, it is preferable that the average particle size of the co-melt lubricant is 20 to 60 μm.

[0049] (d) Flowability Improver The mixed powder in one embodiment of the present invention may further contain a flowability improver. Addition of the flowability improver improves the flowability of the mixed powder, making it easier to pour into a mold. It also improves moldability during compression molding. The flowability improver is preferably at least one selected from the group consisting of carbon black, metal oxides, and metal soaps. Examples of the metal oxides include titanium oxide and silicon oxide. Examples of the metal soaps include metal stearates such as zinc stearate and lithium stearate.

[0050] The amount of the flowability improver added is not particularly limited and may be any amount. However, from the viewpoint of enhancing the flowability improving effect, the amount of the flowability improver added is preferably 0.01 parts by mass or more, and more preferably 0.05 parts by mass or more, relative to 100 parts by mass of the iron-based powder. On the other hand, if the amount of the flowability improver added is excessive, the compressibility may decrease. Therefore, from the viewpoint of preventing a decrease in compressibility and ensuring higher compressibility, the amount of the flowability improver added is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.0 part by mass or less, and most preferably 0.5 parts by mass or less, relative to 100 parts by mass of the iron-based powder.

[0051] (e) Alloying Powder The mixed powder in one embodiment of the present invention can further contain an alloying powder. When a mixed powder containing an alloying powder is sintered, the alloying elements dissolve in iron to form an alloy. Therefore, the use of the alloying powder can improve the strength of the final sintered body. The alloying powder is not particularly limited, and any powder that can become an alloying component can be used. For example, the alloying powder can be at least one powder selected from the group consisting of C, Cu, Ni, Mo, Mn, Cr, V, and Si. When C is used as an alloying component, it is preferable to use graphite powder as the alloying powder.

[0052] The amount of the alloying powder added is not particularly limited and may be any amount. However, from the viewpoint of enhancing the effect of adding the alloying powder, the amount of the alloying powder added is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 parts by mass or more, per 100 parts by mass of the iron-based powder. On the other hand, if the amount of the alloying powder added is excessive, the density of the sintered body may decrease. Therefore, from the viewpoint of preventing a decrease in density and ensuring a higher strength of the sintered body, the amount of the alloying powder added is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the iron-based powder.

[0053] (f) Machinability Improver The mixed powder according to an embodiment of the present invention may further contain a machinability improver. Examples of the machinability improver include MnS and CaF. ２ At least one selected from the group consisting of tungsten, tungsten carbide ...

[0054] The amount of the machinability improver added is not particularly limited and may be any amount. However, from the viewpoint of enhancing the effect of adding the machinability improver, it is preferable to add the machinability improver in an amount of 0.01 parts by mass or more per 100 parts by mass of the iron-based powder. On the other hand, if the amount of the machinability improver added is excessive, the density of the sintered body may decrease. Therefore, from the viewpoint of preventing a decrease in density and ensuring a higher strength of the sintered body, it is preferable to add the machinability improver in an amount of 5 parts by mass or less per 100 parts by mass of the iron-based powder.

[0055] <Method for producing mixed powder> Next, a method for producing the mixed powder will be described. The mixed powder of the present invention can be produced by any method without any particular limitation. Typically, a general method for producing mixed powders for powder metallurgy can be applied.

[0056] For example, the components to be contained in the mixed powder can be mixed using a mixer to obtain the mixed powder. The addition and mixing of each component can be carried out in one go, or in two or more separate goes.

[0057] It is preferable to heat the mixture during mixing. For example, when mixing the iron-based powder and the lubricant, the mixture can be heated at a temperature higher than the melting point of the lubricant, so that the lubricant becomes a bonded lubricant adhered to the surface of the iron-based powder. After the lubricant has adhered to the surface of the iron-based powder, it is preferable to gradually cool the mixture to a temperature lower than the melting point of the lubricant while mixing. This allows the lubricant to be fixed in a state of being adhered to the surface of the iron-based powder.

[0058] Alternatively, the iron-based powder and the lubricant may be mixed at a temperature lower than the melting point of the lubricant, in which case the lubricant becomes a free lubricant that is not attached to the surface of the iron-based powder.

[0059] Therefore, to produce a mixed powder containing both bound and free lubricants, it is preferable to perform two or more mixing steps under different temperature conditions. For example, in the first mixing step, an iron-based powder and a lubricant are heated and mixed at a temperature higher than the melting point of the lubricant to obtain a mixed powder containing a bound lubricant. Then, a new lubricant is added to the mixed powder and mixed at a temperature lower than the melting point of the new lubricant to obtain a mixed powder containing both bound and free lubricants.

[0060] When adding and mixing the lubricant in two or more stages in this way, the type and amount of the lubricant added in each stage may be adjusted so that the amount of each component in the finally obtained mixed powder satisfies the above-mentioned formulas (1) and (2).

[0061] Furthermore, when using either or both of an alloying powder and a machinability improver, the alloying powder and the machinability improver can be adhered to the surface of the iron-based powder by heating during mixing. Specifically, first, the iron-based powder and a lubricant, and either or both of the alloying powder and the machinability improver, are mixed while being heated to a temperature equal to or higher than the melting point of the lubricant. This melts the lubricant, and the alloying powder and the machinability improver adhere to the surface of the iron-based powder via the lubricant. Then, by gradually cooling while mixing, the alloying powder and the machinability improver are fixed in a state of being adhered to the surface of the iron-based powder.

[0062] On the other hand, it is preferable that the flowability improver is not adhered to the surface of the iron-based powder in order to fully exert its function. Therefore, when adding the flowability improver, it is preferable to mix the powder at a temperature lower than the melting point of the lubricant. For example, when one or both of the alloying powder and the machinability improver are adhered to the surface of the iron-based powder, the flowability improver can be added and mixed after cooling to a temperature lower than the melting point of the lubricant.

[0063] There are no particular limitations on the mixing method and mixing device used to produce the mixed powder. Various known mixers can be used as the mixing device used to produce the mixed powder. Examples of the mixing device include a V-type mixer, a high-speed bottom stirring mixer, an inclined rotating pan mixer, a rotating hoe mixer, and a conical planetary screw mixer. A combination of multiple types of mixing devices can also be used.

[0064] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. In these examples, the content of each component contained in the mixed powder is expressed as the amount (parts by mass) relative to 100 parts by mass of the iron-based powder.

[0065] Example 1 A powder metallurgy mixture consisting of (a) an iron-based powder, (b) a bonded lubricant, (c) a free lubricant, and (e) an alloying powder was prepared by the following procedure.

[0066] (a) Iron-based Powder As the iron-based powder, iron powder (pure iron powder) (JIP304AS manufactured by JFE Steel Corporation) produced by atomization was used. The average particle size of the iron powder was 80 μm.

[0067] (b) Bound lubricant, (c) Free lubricant As the bound lubricant and free lubricant, the following saturated fatty acid bisamides and saturated fatty acid monoamides were used in combination. Saturated fatty acid bisamides: S1: ethylene bisstearic acid amide S2: ethylene bisbehenic acid amide S3: lauric acid amide S4: palmitic acid amide S5: stearic acid amide S6: behenic acid amide

[0068] For comparison, unsaturated fatty acid amides were used in some examples. As the unsaturated fatty acid amides, any of the following U1 to U4 was used: U1: oleic acid amide U2: erucic acid amide U3: ethylene bis-erucic acid amide U4: ethylene bis-oleic acid amide

[0069] The combinations of fatty acid amides used and their respective contents are shown in Table 1. The average particle size of each fatty acid amide used was 20 to 60 μm.

[0070] (e) Alloying Powder Copper powder and graphite powder were used as the alloying powder. The copper powder had an average particle size of 25 μm. The graphite powder had an average particle size of 4.2 μm. The amounts of the copper powder and graphite powder mixed were 2 parts by mass and 0.8 parts by mass, respectively, per 100 parts by mass of the iron-based powder.

[0071] The mixed powder was prepared as follows: First, the alloying powder and the bonded lubricant were added to the iron-based powder in the proportions shown in Table 1 into a high-speed bottom-stirring mixer. The mixture was heated and mixed for 20 minutes at a temperature higher than the melting points of all the bonded lubricants used, and then cooled to a temperature lower than the melting points. The free lubricant was then added in the proportions shown in Table 1, and the mixture was mixed at room temperature for 1 minute to obtain a mixed powder for powder metallurgy.

[0072] Next, the ejection property and compressibility of the obtained mixed powder were evaluated by the following method. The evaluation was carried out under two conditions of mold temperature: 30°C and 70°C. The evaluation at a mold temperature of 70°C simulated a case where the mold temperature rises due to frictional heat during continuous molding in a commercial powder metallurgy molding process. The evaluation results are also shown in Table 1.

[0073] (Ejectability) To evaluate ejectability, powder compaction was performed using a die, and then the ejection force required to eject the compact from the die was measured. Specifically, a cylindrical compact having a diameter of 25 mm and a height of 20 mm was first produced using the mixed powder. The compact was produced at a molding pressure of 686 MPa according to the method specified in JPMA P 13-2022. During this process, the die temperature was adjusted to 30°C or 70°C using a heater.

[0074] Next, the maximum load when the compact was ejected from the mold was measured and used as the ejection force. In this evaluation, the lower the ejection force, the better the ejection property.

[0075] (Compressibility) To evaluate compressibility, the density of the molded body obtained by the above procedure was measured. Specifically, the weight of the molded body was measured, and the density of the molded body was calculated using the measured weight and the volume calculated from the size of the molded body according to the method specified in JIS Z 2508:2020. The higher the density of the molded body, the better the compressibility.

[0076] As shown in Table 1, the mixed powders satisfying the conditions of the present invention had excellent ejection properties and compressibility at both 30° C. and 70° C. In contrast, the mixed powders not satisfying the conditions of the present invention were inferior to the mixed powders of the present invention in at least one of the ejection properties and compressibility.

[0077]

[0078] Example 2 A powder metallurgy mixture consisting of (a) an iron-based powder, (b) a bonded lubricant, (c) a free lubricant, (d) a flow improver, and (e) an alloying powder was prepared by the following procedure.

[0079] (d) Flowability Improver As the flowability improver, any of the following D1 to D5 was used. The flowability improvers used and their blending amounts are shown in Table 2. D1: Carbon black D2: Titanium oxide (TiO ２ ) D3: Silica (SiO ２ ) D4: Zinc stearate D5: Lithium stearate

[0080] The blending amounts of (b) bonded lubricant, (c) free lubricant, and (d) flow improver were as shown in Table 2. Other conditions were the same as in Example 1. The mixed powder was prepared in the same manner as in Example 1, except that the flow improver was added together with the free lubricant.

[0081] The properties of the resulting mixed powder were then evaluated by the following methods. The evaluation results are shown in Table 2.

[0082] (Apparent Density) The apparent density of the mixed powder was measured according to the method specified in JIS Z 2504:2020. A funnel with an orifice diameter of 2.5 mm was used for the measurement. The larger the apparent density value, the better the properties of the mixed powder.

[0083] (Fluidity) To evaluate the fluidity of the mixed powder, the flow rate was measured according to the method specified in JIS Z 2502:2020. The flow rate is the time it takes for 50 g of mixed powder to flow through the orifice of a funnel. A funnel with an orifice diameter of 2.5 mm was used to measure the flow rate. If the flow rate is insufficient, the mixed powder will not be discharged from the funnel, and the flow rate cannot be measured. In such cases, "does not flow" is recorded in Table 2. On the other hand, if the flow rate can be measured, it can be considered that the mixed powder has sufficient fluidity. The smaller the flow rate value, the better the fluidity of the mixed powder.

[0084] Furthermore, the extractability and compressibility of the resulting mixed powder were evaluated in the same manner as in Example 1. The evaluation results are also shown in Table 2.

[0085] As shown in Table 2, the mixed powders satisfying the conditions of the present invention had both excellent ejection properties and compressibility at both 30°C and 70°C. In addition, because they contained a flowability improver, they exhibited good apparent density and fluidity. In contrast, the mixed powders not satisfying the conditions of the present invention were inferior to the mixed powders of the present invention in at least one of ejection properties and compressibility. Furthermore, the mixed powders to which an unsaturated fatty acid amide was added as a free lubricant were also inferior in apparent density and fluidity.

[0086]

[0087] [Example 3] A mixed powder was prepared under the same conditions as in Example 2, except that fatty acid amides with different average particle sizes were used as the free lubricant. The fatty acid amides used and their average particle sizes are as follows. The blending amounts of each component were as shown in Table 3. S1n: Ethylene bis stearic acid amide: average particle size 30 μm S1f: Ethylene bis stearic acid amide (fine particles): average particle size 10 μm S1c: Ethylene bis stearic acid amide (coarse particles): average particle size 70 μm S5n: Stearic acid amide: average particle size 40 μm S5c: Stearic acid amide (coarse particles): average particle size 70 μm

[0088] The obtained mixed powder was subjected to the same evaluation as in Example 2. The results are shown in Table 3.

[0089] As shown in Table 3, the mixed powders satisfying the conditions of the present invention exhibited excellent ejection and compressibility at both 30°C and 70°C. In addition, because they contained a flowability improver, they exhibited good apparent density and fluidity. Among them, Inventive Example No. 38, which used a free lubricant of 20 to 60 μm, exhibited the best balance of fluidity and ejection. In contrast, mixed powders not satisfying the conditions of the present invention were inferior to the mixed powders of the present invention in at least one of ejection and compressibility.

[0090]

Claims

1. A mixed powder for powder metallurgy comprising an iron-based powder and a fatty acid amide as a lubricant, wherein the fatty acid amide contains only saturated fatty acid bisamide and saturated fatty acid monoamide, and does not contain unsaturated fatty acid amide, a portion of the lubricant is a bound lubricant (b) adhering to the surface of the iron-based powder, and the remainder of the lubricant is a free lubricant (c) not adhering to the surface of the iron-based powder, and the contents of the saturated fatty acid bisamide (b1) present as the bound lubricant, the saturated fatty acid monoamide (b2) present as the bound lubricant, the saturated fatty acid bisamide (c1) present as the free lubricant, and the saturated fatty acid monoamide (c2) present as the free lubricant satisfy the following formulas (1) and (2): 0<(b1)+(b2)+(c1)+(c2)≦1.0 (1) 0<[(b1)+(c1)] / [(b2)+(c2)]<0.50 (2) Here, (b1), (b2), (c1), and (c2) in the above formulas (1) and (2) represent the content of each component expressed in parts by weight relative to 100 parts by mass of the iron-based powder.

2. The mixed powder for powder metallurgy according to claim 1, wherein the saturated fatty acid bisamide (c1) present as the free lubricant has an average particle size of 20 to 60 μm, and the saturated fatty acid monoamide (c2) present as the free lubricant has an average particle size of 20 to 60 μm.

3. The mixed powder for powder metallurgy according to claim 1 or 2, wherein the fatty acid amide is a derivative of at least one selected from the group consisting of lauric acid, palmitic acid, stearic acid, and behenic acid.

4. The mixed powder for powder metallurgy according to any one of claims 1 to 3, further comprising at least one fluidity improver selected from the group consisting of carbon black, metal oxides, and metal soaps.

5. The mixed powder for powder metallurgy according to any one of claims 1 to 4, further comprising an alloying powder.

6. The mixed powder for powder metallurgy according to claim 5, wherein the alloying powder adheres to the surfaces of the particles constituting the iron-based powder via the binding lubricant.