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

Technical Field

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

Background Art

[0002] Powder metallurgy is a technique in which metal powder is placed in a die, compressed and solidified, and sintered at a high temperature to produce parts with high dimensional accuracy. According to powder metallurgy, even parts with complex shapes can be formed with high dimensional accuracy, so the cutting cost can be significantly reduced compared to shape processing by cutting or the like. Therefore, powder metallurgy products are used in various fields as various machines and parts.

[0003] In powder metallurgy, a mixed powder for powder metallurgy (hereinafter sometimes simply referred to as "mixed powder"), which is obtained by mixing an iron-based powder as a main raw material with alloying powders such as copper powder, graphite powder, and iron phosphide powder as required, a machinability improving powder such as MnS, and a lubricant, is used as a raw material powder. Among them, the lubricant has the effect of reducing the friction between the particles contained in the mixed powder and the effect of reducing the friction between the die used for molding and the particles, and plays an extremely important role in manufacturing products by powder metallurgy.

[0004] This lubricant is mainly required to have the effect of reducing the friction between the particles contained in the mixed powder and the effect of reducing the friction between the die used for molding and the particles.

[0005] The effect of reducing friction between particles occurs, for example, when a lubricant is interposed between particles during molding. Reducing friction between particles promotes particle rearrangement, improving moldability. Similarly, the effect of reducing friction between the mold and particles occurs, for example, when a lubricant present on the mold surface interposes between the mold and the particles. Reducing friction between the mold and particles promotes particle rearrangement on the surface of the molded body (green compact), improving moldability.

[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 molded body when removing the resulting molded body from the mold is reduced, resulting in improved release properties of the molded body from the mold. Removal of the molded body from the mold is done, for example, by pushing it out with a punch, but if the friction between the mold and the molded body is high, it may become difficult to remove the molded body from the mold, or the surface of the molded body may be damaged.

[0007] As mentioned above, lubricants play a significant role during molding and removal from the mold, but it is required that they do not remain in the final sintered body. Since lubricants are no longer needed after the molded body is removed from the mold, it is desirable that the lubricant disappears during the sintering process of the molded body.

[0008] Incidentally, powder metallurgy mixtures sometimes contain additional components that function as binders. Here, a binder is a component that adheres alloying powders and other additives to the surface of the iron particles of the iron-based powder, which is the main component. In a mixture of iron-based powder and additives such as alloying powder, machinability-improving powder, and lubricants, segregation of each component may occur after mixing. In particular, graphite powder, which is commonly used as an alloying powder, has a lower density than other components, so it easily segregates when the mixture is subjected to flow or vibration. To prevent such segregation, additives are sometimes attached to the surface of the iron-based powder particles via a binder. Such a mixture is sometimes specifically called segregation prevention treatment powder. In segregation prevention treatment powder, the additives are attached to the iron-based powder, thus preventing the segregation of the components as described above.

[0009] Generally, lubricants have a stronger adhesive force than iron-based powders, which can worsen the fluidity of the mixed powder. However, this adhesive force can sometimes be utilized, and lubricants are used as binders.

[0010] Powder metallurgy mixes are generally press-molded at a pressure of 300 MPa to 1000 MPa to form a predetermined part shape, and then sintered at a high temperature of 1000°C or higher to obtain the final part shape. In this process, the total amount of lubricant and binder contained in the mix is ​​generally about 0.1 to 2 parts by mass per 100 parts by mass of iron-based powder. Since lubricants and binders have a lower density than iron-based powder, adding a large amount will reduce the density of the molded body, and consequently, the density of the sintered body will decrease. Therefore, to increase the density of the molded body, it is better to use less lubricant and binder. Thus, by using a lubricant that also functions as a binder, the total amount of binder and lubricant added to the mix can be reduced.

[0011] The lubrication performance of a lubricant is greatly influenced by the types of compounds it contains. For example, fatty acid amides and fatty acid metal soaps possess excellent lubrication properties and are widely used as lubricants for powder metallurgy.

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

[0013] For example, Patent Document 1 discloses using one or more selected from stearic acid, oleic acid monoamide, and stearic acid monoamide, and at least one selected from the group consisting of ethylenebisstearamide and methylenebisstearamide, as both 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 alkylenebis fatty acid amide or a secondary or tertiary polyhydroxy fatty acid amide.

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

[0016] Patent Document 4 discloses the use of a lubricant that is a compound of an unsaturated fatty acid bisamide and a saturated hydroxy fatty acid. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] Japanese Patent Application Publication No. 05-148505 [Patent Document 2] Japanese Patent Publication No. 2011-184708 [Patent Document 3] International Publication No. 2014 / 123106 [Patent Document 4] Japanese Patent Publication No. 2019-143200 [Overview of the project]

Problems to be Solved by the Invention

[0018] In a commercial powder metallurgy forming process, hundreds to thousands of parts are continuously formed. In such a continuous forming process, the temperature of the mold gradually rises due to frictional heat. The degree of mold temperature rise varies depending on the shape of the mold and the parts, but in the case of parts with a large side area, the mold temperature may rise to about 70 to 80 °C. Therefore, for the powder metallurgy lubricant, it is required to exhibit high lubricity not only at room temperature in the initial stage of forming but also after the mold temperature rises.

[0019] However, in Patent Documents 1 to 4, only the extractability and compressibility at room temperature are evaluated, and the performance when the mold temperature rises is not considered.

[0020] The present invention has been made in view of such a situation, and an object thereof is to provide a mixed powder for powder metallurgy that uses a fatty acid amide, which is a clean lubricant, and exhibits excellent extractability and compressibility of formed products not only at room temperature but also after the mold temperature rises.

Means for Solving the Problems

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

[0022] 1. A mixed powder for powder metallurgy containing an iron-based powder and a fatty acid amide as a lubricant, wherein the fatty acid amide contains only a saturated fatty acid bisamide and a saturated fatty acid monoamide, and does not contain an unsaturated fatty acid amide, a part of the lubricant is a binding 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, the saturated fatty acid bisamide (b1) present as the binding lubricant, The saturated fatty acid monoamide (b2) present as the binding lubricant, the saturated fatty acid bisamide (c1) present as the free lubricant, and the saturated fatty acid monoamide (c2) present as the free lubricant The content of which satisfies the following formulas (1) and (2), a mixed powder for powder metallurgy. 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 values obtained by expressing the content of each component in parts by weight based on 100 parts by mass of the iron-based powder.

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

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

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

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

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

Advantages of the Invention

[0028] The powder metallurgy mixture of the present invention can achieve excellent ejectability and compressibility of molded products not only at room temperature but also after the mold temperature rises. [Modes for carrying out the invention]

[0029] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, "%" refers to "mass%".

[0030] The powder metallurgy mixed powder 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 binding 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 powder mixed powder in one embodiment of the present invention includes the following (a), (b), and (c). Furthermore, the powder metallurgy mixed powder in other embodiments of the present invention may 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) binding lubricant (c) Free lubricant (d) Fluidity improvers (e) Powder for alloys (f) Machining performance improving agent

[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 iron powder and / or iron-based alloy powder. Here, "iron-based powder" refers to metal powder containing 50% by mass or more of Fe. "Iron powder" refers to powder consisting of Fe and unavoidable impurities, and is generally referred to as "pure iron powder" in this art. "Iron-based alloy powder" refers to powder consisting of at least one alloying element and the remainder being Fe and unavoidable impurities, and is generally referred to as "alloyed steel powder" in this art.

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

[0033] The iron-based powder can be manufactured by conventional methods. For example, the iron-based powder may be reduced iron-based powder, atomized iron-based powder, or a mixture thereof. Reduced iron-based powder is iron-based powder produced by reducing iron oxide. Atomized iron-based powder is iron-based powder produced by the atomization method. Alternatively, a powder in which alloying elements are diffusely deposited on the surface of reduced iron-based powder or atomized iron-based powder can be used as the iron-based powder.

[0034] The particle size of the iron-based powder is not particularly limited, but 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 weight-based particle size distribution. The particle size distribution shall be measured by a sieving test.

[0035] The content of the iron-based powder in the powder metallurgy mixed powder is not particularly limited, but it is preferably 86% or more, and more preferably 90% or more, as a percentage of the total mass of the mixed powder. On the other hand, there is no particular upper limit to the content of the iron-based powder, but the remainder of the mixed powder other than the lubricant may all be iron-based powder. Therefore, the content of the iron-based powder in the mixed powder may be less than 100%, 99.0% or less, or 97.0% or less.

[0036] (b) binding lubricant (c) Free lubricant The mixed powder of the present invention contains fatty acid amides as lubricants. Furthermore, the fatty acid amides consist only of saturated fatty acid bisamides and saturated fatty acid monoamides, and do 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 substantially does not contain unsaturated fatty acid amides.

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

[0038] The fatty acid amide is preferably an amide derived from at least one saturated fatty acid selected from the group consisting of lauric acid, palmitic acid, stearic acid, and behenic acid. In other words, the fatty acid amide is preferably at least one derivative selected from the group consisting of lauric acid, palmitic acid, stearic acid, and behenic acid.

[0039] In one embodiment of the present invention, only fatty acid amides can be used as lubricants. In other words, the powder metallurgy mixture in one embodiment of the present invention may consist of iron-based powder and fatty acid amides as lubricants. In this case as well, the powder metallurgy mixture may further optionally include at least one selected from the group consisting of flowability improvers, alloy powders, and machinability improvers.

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

[0041] To attach a lubricant to the surface of iron-based powder to form a binding lubricant, for example, the mixture can be heated above the melting point of the lubricant while stirring, and then gradually cooled while mixing. This coats the surface of the iron-based powder with the molten lubricant. On the other hand, the free lubricant can be added and mixed separately after the binding lubricant has been fixed to the surface of the iron-based powder. The addition and mixing of the free lubricant should be carried out at a temperature lower than the melting point of the binding lubricant so as not to melt the already fixed binding lubricant.

[0042] In the powder metallurgy mixed powder of the present invention, The saturated fatty acid bisamide (b1) present as the binding lubricant, The saturated fatty acid monoamide (b2) present as the binding lubricant, The saturated fatty acid bisamide (c1) present as the free lubricant, and The saturated fatty acid monoamide (c2) present as the free lubricant It is important that the content satisfies the following equations (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 equations (1) and (2) above represent the content of each component expressed in parts by weight per 100 parts by mass of the iron-based powder.

[0043] Equation (1) above 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 per 100 parts by mass of iron-based powder. By satisfying the conditions of equation (1), the compressibility of the mixed powder is improved and a high molded article density can be obtained. If the total amount exceeds 1.0 part by mass, the compressibility decreases. It is preferable that the total amount is 0.6 parts by mass or less. In other words, it is preferable to satisfy the conditions of equation (1') below. 0<(b1)+(b2)+(c1)+(c2)≦0.6 …(1')

[0044] On the other hand, from the viewpoint of enhancing the lubricant addition effect, it is preferable that the total amount is 0.2 parts by mass or more. In other words, it is preferable that the conditions of equation (1'') below be satisfied, and it is more preferable that the conditions of equation (1''') below be satisfied. 0.2<(b1)+(b2)+(c1)+(c2)≦1.0 …(1'') 0.2<(b1)+(b2)+(c1)+(c2)≦0.6 …(1''')

[0045] Equation (2) above 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 conditions of equation (2), the extraction force of the molded product from the mold after the mold temperature rises can be reduced. 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 excessively small, the lubrication effect may be reduced. Therefore, from the viewpoint of further improving extraction and fluidity, it is preferable that the average particle size of the saturated fatty acid bisamide (c1) and the saturated fatty acid monoamide (c2) present as free lubricants be 20 μm or larger. On the other hand, if the particle size of the free lubricant is excessively large, fluidity decreases. Therefore, from the viewpoint of improving flowability, it is preferable that the average particle size of the saturated fatty acid bisamide (c1) and the saturated fatty acid monoamide (c2) present as free lubricants be 60 μm or smaller.

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

[0048] The saturated fatty acid bisamide (c1) and saturated fatty acid monoamide (c2) present as free lubricants may be included in the mixed powder in separate states or in an integrated state. When both are included in the mixed powder in an integrated state, for example, a co-meltable lubricant can be prepared by pre-melting and mixing saturated fatty acid bisamide and saturated fatty acid monoamide, and then mixing the co-meltable lubricant with iron-based powder or the like. When using the co-meltable lubricant, it is preferable that the average particle size of the co-meltable lubricant is 20 to 60 μm.

[0049] (d) Fluidity improving material The mixed powder in one embodiment of the present invention may further contain a flowability improver. By adding a flowability improver, the flowability of the mixed powder is improved, making it easier to pour into the mold. It also improves the moldability during compression molding. Preferably, the flowability improver is 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 stearate salts such as zinc stearate and lithium stearate.

[0050] The amount of the above-mentioned fluidity improving agent added is not particularly limited and may be any amount. However, from the viewpoint of enhancing the fluidity improving effect, it is preferable to add 0.01 parts by mass or more, and more preferably 0.05 parts by mass or more, per 100 parts by mass of iron-based powder. On the other hand, if the amount of fluidity improving agent added is excessive, compressibility may decrease. Therefore, from the viewpoint of preventing a decrease in compressibility and ensuring higher compressibility, it is preferable to add 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, per 100 parts by mass of iron-based powder.

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

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

[0053] (f) Machining performance improving agent The mixed powder in one embodiment of the present invention may further contain a machinability improving agent. For example, at least one selected from the group consisting of MnS, CaF2, and talc can be used as the machinability improving agent. By adding a machinability improving agent, the machinability (processability) of the final sintered body can be improved.

[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 at least 0.01 parts by mass of the machinability improver per 100 parts by mass of iron-based powder. On the other hand, if the amount of 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 higher strength of the sintered body, it is preferable to add at least 5 parts by mass of the machinability improver per 100 parts by mass of iron-based powder.

[0055] <Method for manufacturing mixed powder> Next, a method for producing the above-mentioned mixed powder will be described. The mixed powder of the present invention is not particularly limited and can be produced by any method. Typically, a general method for producing mixed powders for powder metallurgy can be applied.

[0056] For example, a mixed powder can be created by mixing the components to be included in the mixed powder using a mixer. The addition and mixing of each component can be done in one step, or it can be done in two or more steps.

[0057] When mixing, heating is preferable. For example, when mixing iron-based powder and lubricant, heating at a temperature higher than the melting point of the lubricant allows the lubricant to adhere to the surface of the iron-based powder as a binding lubricant. After the lubricant has adhered to the surface of the iron-based powder, it is preferable to gradually cool it to a temperature lower than the melting point of the lubricant while mixing. This fixes the lubricant in place on the surface of the iron-based powder.

[0058] Alternatively, the iron-based powder and lubricant can be mixed at a temperature lower than the melting point of the lubricant. In this case, the lubricant becomes a free lubricant that does not adhere to the surface of the iron-based powder.

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

[0060] When adding and mixing lubricants in two or more stages in this manner, the type and amount of lubricant added at each stage should be adjusted so that the amount of each component in the final mixed powder satisfies equations (1) and (2) described above.

[0061] Furthermore, when using either or both alloy powder and machinability improver, heating during mixing can cause the alloy powder and machinability improver to adhere to the surface of the iron-based powder. Specifically, first, the iron-based powder and lubricant, along with either or both of the alloy powder and machinability improver, are mixed while being heated to a temperature above the melting point of the lubricant. This causes the lubricant to melt, and the alloy powder and machinability improver adhere to the surface of the iron-based powder via the lubricant. Subsequently, by gradually cooling while mixing, the alloy powder and machinability improver are fixed in place on the surface of the iron-based powder.

[0062] On the other hand, in order to fully utilize the function of the fluidity improver, it is preferable not to allow it to adhere to the surface of the iron-based powder. Therefore, when adding a fluidity improver, it is preferable to mix it at a temperature lower than the melting point of the lubricant. For example, if one or both of the alloy powder and the machinability improver are attached to the surface of the iron-based powder, the fluidity improver should be added and mixed after cooling to a temperature lower than the melting point of the lubricant.

[0063] There are no particular restrictions on the mixing method and mixing apparatus used in the production of mixed powders. Various known mixers can be used as mixing apparatus for the production of mixed powders. Examples of mixing apparatus include V-type mixers, high-speed bottom-stirring mixers, inclined rotary pan-type mixers, rotary hoe-type mixers, and conical planetary screw-type mixers. Multiple types of mixing apparatus can also be used in combination. [Examples]

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

[0065] [Example 1] A powder metallurgy mixed powder consisting of (a) iron-based powder, (b) a binding 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) manufactured by the atomization method (JIP304AS, manufactured by JFE Steel Corporation) was used. The average particle size of the iron powder was 80 μm.

[0067] (b) binding lubricant, (c) free lubricant The following saturated fatty acid bisamides and saturated fatty acid monoamides were used as the binding lubricant and free lubricant. • Saturated fatty acid bisamide: S1: Ethylene bis-stearamide S2: Ethylene bisbehenamide • Saturated fatty acid monoamide S3: Lauric acid amide S4: Palmitic acid amide S5: Stearic acid amide S6: Behenamide

[0068] Furthermore, for comparison, unsaturated fatty acid amides were used in some of the examples. The unsaturated fatty acid amides used were any of the following U1 to U4. U1: Oleamide U2: Erucic acid amide U3: Ethylenebiserucic acid amide U4: Ethylene bisoleamide

[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 20-60 μm.

[0070] (e) Powder for alloys Copper powder and graphite powder were used as the alloy powders. The average particle size of the copper powder was 25 μm. The average particle size of the graphite powder was 4.2 μm. The blending amounts of copper powder and graphite powder were 2 parts by mass and 0.8 parts by mass, respectively, per 100 parts by mass of iron-based powder.

[0071] The mixed powder was prepared using the following procedure. First, the iron-based powder was mixed with the alloy powder and binder lubricant in the proportions shown in Table 1 using 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 binder lubricants used, and then cooled to a temperature lower than the melting points. After that, the free lubricant was added in the proportions shown in Table 1 and mixed at room temperature for 1 minute to obtain a mixed powder for powder metallurgy.

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

[0073] (Evacuation) To evaluate the ejectability, the ejection force required to remove the molded body from the mold after compacting it using a mold was measured. Specifically, first, a cylindrical molded body with a diameter of 25 mm and a height of 20 mm was made using the aforementioned powder mixture. The molded body was made at a molding pressure of 686 MPa according to the method specified in JPMA P 13-2022. At this time, the mold temperature was adjusted to 30°C or 70°C using a heater.

[0074] Next, the maximum load applied when removing the molded body from the mold was measured and defined as the extraction force. In this evaluation, a lower extraction force indicates better extraction performance.

[0075] (Compressibility) To evaluate compressibility, the density of the molded body obtained using 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 obtained 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 powder that met the conditions of the present invention exhibited excellent extraction and compressibility at both 30°C and 70°C. In contrast, the mixed powder that did not meet the conditions of the present invention was inferior to the mixed powder of the present invention in at least one of the extraction and compressibility.

[0077] [Table 1]

[0078] [Example 2] A powder metallurgy mixed powder consisting of (a) iron-based powder, (b) binding lubricant, (c) free lubricant, (d) fluidity improver, and (e) alloy powder was prepared by the following procedure.

[0079] (d) Fluidity improvers As the aforementioned fluidity improving agent, one of the following D1 to D5 was used. The fluidity improving agents used and their respective amounts are shown in Table 2. D1: Carbon Black D2: Titanium oxide (TiO2) D3: Silica (SiO2) D4: Zinc stearate D5: Lithium stearate

[0080] The amounts of (b) binding lubricant, (c) free lubricant, and (d) fluidity improver were as shown in Table 2. All other conditions were the same as in Example 1 above. The preparation of the mixed powder was carried out in the same procedure as in Example 1 above, except that the fluidity improver was added together with the free lubricant.

[0081] Next, the properties of the resulting mixed powder were evaluated using the following method. 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. A higher apparent density value indicates better properties of the mixed powder.

[0083] (Liquidity) To evaluate the fluidity of the mixed powder, the fluidity was measured according to the method specified in JIS Z 2502:2020. The fluidity was defined as the time it took for 50g of the mixed powder to flow through the orifice of a funnel. A funnel with an orifice diameter of 2.5mm was used to measure the fluidity. If the fluidity was insufficient, the mixed powder would not be discharged from the funnel, and therefore the fluidity could not be measured. In that case, "did not flow" was indicated in Table 2. On the other hand, if the fluidity could be measured, it could be considered that the powder had sufficient fluidity. The smaller the fluidity value, the better the fluidity of the mixed powder.

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

[0085] As shown in Table 2, the mixed powder that met the conditions of the present invention exhibited excellent extraction and compressibility at both 30°C and 70°C. In addition, because it contained a flowability improver, it showed good apparent density and flowability. In contrast, the mixed powder that did not meet the conditions of the present invention was inferior to the mixed powder of the present invention in at least one of the extraction and compressibility. Furthermore, the mixed powder to which unsaturated fatty acid amide was added as a free lubricant was also inferior in apparent density and flowability.

[0086] [Table 2]

[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 free lubricants. The fatty acid amides used and their average particle sizes are as follows. The amounts of each component are shown in Table 3. S1n: Ethylene bis-stearamide: Average particle size 30 μm S1f: Ethylene bis-stearamide (fine particles): Average particle size 10 μm • S1c: Ethylene bis-stearamide (coarse grain): Average particle size 70 μm S5n: Stearic acid amide: Average particle size 40 μm S5c: Stearic acid amide (coarse grain): Average particle size: 70 μm

[0088] The resulting mixed powder was evaluated in the same manner 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 extractability and compressibility at both 30°C and 70°C. In addition, because they contained a fluidity improver, they showed good apparent density and fluidity. Among them, Invention Example No. 38, which used a free lubricant of 20-60 μm, showed the best balance between fluidity and extractability. In contrast, the mixed powders that did not satisfy the conditions of the present invention were inferior to the mixed powders of the present invention in at least one of the extractability and compressibility.

[0090] [Table 3]

Claims

1. A powder metallurgy mixed powder containing iron-based powder and fatty acid amide as a lubricant, The aforementioned fatty acid amides consist only of saturated fatty acid bisamides and saturated fatty acid monoamides, and do not contain unsaturated fatty acid amides. The lubricant is a binding lubricant (b) in which a portion of the lubricant adheres to the surface of the iron-based powder, and the remaining portion of the lubricant is a free lubricant (c) that does not adhere to the surface of the iron-based powder. The saturated fatty acid bisamide (b1) present as the binding lubricant, The saturated fatty acid monoamide (b2) present as the binding lubricant, The saturated fatty acid bisamide (c1) present as the free lubricant, and It contains saturated fatty acid monoamide (c2) present as the free lubricant, and The contents of b1, b2, c1, and c2 satisfy the following equations (1) and (2): The average particle size of the saturated fatty acid bisamide (c1) present as the free lubricant is 20 to 60 μm. A mixed powder for powder metallurgy, wherein the average particle size of the saturated fatty acid monoamide (c2) present as the free lubricant is 20 to 60 μm. 0<(b1)+(b2)+(c1)+(c2)≦1.0…(1) 0<[(b1)+(c1)] / [(b2)+(c2)]<0.50...(2) Here, (b1), (b2), (c1), and (c2) in equations (1) and (2) above represent the content of each component expressed in parts by weight relative to 100 parts by mass of the iron-based powder.

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

3. The powder metallurgy mixture according to claim 1 or 2, further comprising at least one selected from the group consisting of carbon black, metal oxides, and metal soaps as a fluidity improver.

4. The powder metallurgy mixture according to claim 1 or 2, further comprising alloying powder.

5. The powder metallurgy mixture according to claim 3, further comprising alloying powder.

6. The powder metallurgy mixed powder according to claim 4, wherein the alloy powder is attached to the surface of the particles constituting the iron-based powder via the binding lubricant.

7. The powder metallurgy mixed powder according to claim 5, wherein the alloy powder is attached to the surface of the particles constituting the iron-based powder via the binding lubricant.

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