JP5663974B2 - Iron-based mixed powder for powder metallurgy - Google Patents

Description

  The present invention relates to an iron-based mixed powder suitable for use in powder metallurgy technology, and in particular to increase the density of a green compact and to advantageously reduce the extraction output when the green compact is extracted from a mold after compacting. It is intended to be illustrated.

In the powder metallurgy process, after mixing raw material powders, the mixed powder is transferred and filled into a mold, and a molded body (referred to as a green compact) produced by pressure molding is taken out of the mold and sintered as necessary. After-treatment is performed.
In such a powder metallurgy process, in order to improve product quality and reduce manufacturing costs, high powder flowability in the transfer process, high compressibility in the pressure molding process, and further, the green compact is extracted from the mold. It is required to simultaneously achieve a low output in the process.

As means for improving the fluidity of the iron-based mixed powder, Patent Document 1 discloses that the fluidity of the iron-based mixed powder can be improved by adding fullerenes.
Patent Document 2 discloses a technique for improving the fluidity of a powder by adding a granular inorganic oxide having an average particle diameter of less than 500 nm.
However, even if these means are used, it is insufficient to realize high compressibility and low output power while maintaining fluidity.

In order to increase the green compacting density or reduce the punching power, it is effective to use a soft and extensible lubricant at the temperature at which the iron-based mixed powder is pressure-molded. The reason is that the lubricant oozes out from the iron-based mixed powder by pressure molding and adheres to the mold surface, thereby reducing the frictional force between the mold and the green compact.
However, since such a lubricant has stretchability, it easily adheres to the particles of iron powder and alloy powder, so that the fluidity and filling properties of the iron-based mixed powder are hindered. .
Furthermore, blending the carbon material, fine particles, and lubricant as described above reduces the theoretical density of the iron-based mixed powder (assuming that the porosity is zero) and causes a reduction in molding density. Too much addition is not preferable.
Thus, conventionally, it has been extremely difficult to establish the fluidity of the iron-based mixed powder, the high molding density, and the low punching power.

In addition, as a technique regarding the additive to the iron-based mixed powder, Patent Document 3 describes that the dimensional change rate of the sintered body can be controlled by adding a mill scale that is an iron oxide.
Further, Patent Document 4 discloses a method for synthesizing mica-like iron oxide having an aspect ratio of 5 to 30 with respect to a technique for producing α-iron oxide used as a pigment for a rust-proof paint for steel.

JP 2007-31744 A JP-T-2002-515542 JP-A-8-325667 Japanese Patent Laid-Open No. 3-131526

  The present invention has been developed in view of the above-mentioned present situation, and by improving the fluidity of the iron-based mixed powder, the compacting density of the compact is improved and at the same time the output power after compacting is greatly increased. An object of the present invention is to propose an iron-based mixed powder for powder metallurgy that can be reduced, thereby achieving both improvement in product quality and reduction in manufacturing cost.

Now, in order to achieve the above object, the inventors have conducted various studies on the additive in the iron-based mixed powder.
As a result, by adding an appropriate amount of oxide particles having an average particle diameter of 0.5 μm or more to the iron-based mixed powder, the fluidity is greatly improved, and the molding density and the output power are also improved. Obtained knowledge.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. An iron-based mixed powder for powder metallurgy mainly comprising an iron-based powder having an average particle size of 10 to 200 μm (but not including rare earth elements) , and the average particle size is 0 in the iron-based mixed powder 0.01 to 5.0% by mass of oxide particles (not including rare earth elements) containing 5 μm or more and 100 μm or less and an aspect ratio of less than 5 and containing at least one selected from iron, aluminum, and silicon An iron-based mixed powder for powder metallurgy, characterized by containing in the range of

2 . The iron-based mixed powder, 0.1-10 wt% of the alloy powder, powder according to the 1, characterized in that it contains a state attached to the surface of the iron-based powder through an organic binder Iron-based mixed powder for metallurgy.

3 . 3. The iron-based mixed powder for powder metallurgy according to 1 or 2 , wherein the iron-based mixed powder contains 0.02 to 0.8% by mass of an organic lubricant .

4 . 4. The iron-based mixed powder for powder metallurgy according to any one of 1 to 3 , wherein the iron-based mixed powder contains 0.01 to 1.0% by mass of a free lubricant.

  According to the present invention, by adding an appropriate amount of oxide particles having an average particle diameter of 0.5 μm or more to the iron-based mixed powder, not only the fluidity is improved, but also a high molding density and a low output power are achieved. As a result, an improvement in productivity and a reduction in manufacturing costs are realized.

It is a schematic diagram explaining the aspect ratio of powder.

Hereinafter, the present invention will be specifically described.
In the present invention, oxide particles are utilized as a fluidity improving component of the iron-based powder.
In a general iron-based mixed powder, an organic lubricant is blended in an amount of about 1% by mass in order to increase the fluidity of the powder or reduce the output of the molded body. The specific gravity of this organic lubricant is around 1.0, which is significantly lower than the specific gravity of iron powder 7.8. In general, when mixing powders having a large difference in specific gravity, segregation occurs during mixing, which causes a decrease in fluidity and variation in characteristics within a lot.
Therefore, when mixing different types of powders, it is important to minimize the difference in specific gravity between them.

If the oxide particles used in the present invention are, for example, iron oxide (hematite), the specific gravity is 5.3, which is higher than that of the organic lubricant. Therefore, the oxide particles are less susceptible to the air flow in the powder layer during powder flow than the organic lubricant.
Therefore, in the iron-based mixed powder of the present invention, which is replaced with an organic lubricant or a part of which is replaced with oxide particles, segregation of various additives is suppressed, resulting in improved fluidity of the iron-based mixed powder. It is considered to be done.
In addition, when the particle size of the oxide particles to be added is increased as in the present invention, the oxide particles are like fluidity improving powder having a primary particle size of nanometer order as disclosed in Patent Document 2. It is presumed that the space between the iron-based powders is preferably filled in rather than coating the surface of the iron-based powder. Therefore, in the molding process, it is presumed that the effective contact area between the green compact and the mold is increased and the springback stress is dispersed, and as a result, a reduction in the extraction force can be realized.

In order to exhibit the above effect, the average particle diameter of the oxide particles needs to be 0.5 μm or more. When the average particle diameter of the oxide particles is smaller than 0.5 μm, a sufficient effect of reducing the output power cannot be obtained. However, when the average particle size of the oxide particles exceeds 100 μm, uniform mixing with the iron-based mixed powder (average particle size: around 100 μm) commonly used in powder metallurgy cannot be performed, and the above effect can also be exhibited. because eliminated, the particle diameter of the oxide particles shall be the 100μm or less on average. More preferably, the average particle size of the oxide particles is 40 μm or less, and more preferably 20 μm or less.
In addition, it is permissible for the oxide particles to contain impurities other than oxide in an amount of about 20% by mass or less (ratio to the total oxide particles). However, it is preferable to use a material having less impurities (for example, 10% by mass or less, or 2% by mass or less) if there is no problem in industrial availability. The impurities are not particularly limited, and there are no particular problems as long as they are impurities (for example, metals and other inorganic compounds) that are mixed into oxide particles produced by a known industrial means.

In the present invention, as the oxide particles, an oxide containing at least one selected from iron, aluminum and silicon is advantageously suitable. Specific examples of such oxides include Fe ₂ O ₃ , Al ₂ O _3, and SiO ₂ , but the components and crystal structure are not particularly specified. The total content of at least one oxide selected from iron, aluminum, and silicon in the oxide particles is preferably about 80% by mass or more (ratio to the total oxide particles), and 98% by mass. % Or more is more preferable.

Further, in order to enable the present invention to be implemented at low cost, it is preferable that the oxide particles are inexpensive and easily available. From the viewpoint of availability, iron oxides or iron-based oxides mainly composed of iron oxides are particularly preferable. Among such iron-based oxides, those that are relatively easily available industrially contain about 70 to 95% by mass of iron oxide (ratio to the total oxide particles), and in addition to Al What contains a total of about 5-30 mass% of an oxide and / or the oxide of Si is mentioned.
By the way, from the viewpoint of the aspect ratio, the particles having a high aspect ratio can be artificially synthesized. For example, Patent Document 4 discloses a method for synthesizing α-iron oxide having an aspect ratio of 5 to 30. However, such a method requires long-time heating and pressurization during the synthesis process, resulting in an unavoidably high manufacturing cost and is not easily available. Accordingly, the aspect ratio you less than 5.
In the present invention, the aspect ratio means the ratio of the major axis 1 to the powder thickness 2 as shown in FIG. The aspect ratio of the oxide particles is preferably determined by the method described in the examples described later.

  Moreover, in this invention, when the compounding quantity with respect to the iron-based mixed powder of an oxide particle is less than 0.01 mass%, the addition effect of an oxide particle will not appear. On the other hand, if it exceeds 5.0 mass%, it is not preferable because it causes a significant increase in the unplugging power. Therefore, the compounding quantity of oxide particles shall be 0.01-5.0 mass%. More preferably, it is the range of 0.05-1.0 mass%.

In the present invention, the iron-based powder that is the main component of the iron-based mixed powder includes pure iron powder such as atomized iron powder and reduced iron powder, or partially diffusion alloyed steel powder and fully alloyed steel powder, and also a complete alloy Examples thereof include hybrid steel powder in which alloy components are partially diffused in chemical steel powder. The average particle diameter of such iron-based powder, and 10 to 200 [mu] m.
In the present invention, the “main component” means that the content of the iron-based powder in the iron-based mixed powder is 50% by mass or more.

Examples of the type of alloy powder include graphite powder, metal powders such as Cu, Mo, and Ni, and metal compound powders. It goes without saying that other known alloy powders can also be used. The strength of the sintered body can be increased by mixing at least one of these alloy powders with the iron-based powder.
The total blending amount of the above-described alloy powder is preferably about 0.1 to 10% by mass in the iron-based mixed powder. This is because when the alloy powder is blended in an amount of 0.1% by mass or more, the strength of the obtained sintered body is advantageously improved, whereas when it exceeds 10% by mass, the dimensional accuracy of the sintered body is lowered. Because.

  The above-described alloy powder is preferably in a state of being adhered to the surface of the iron-based powder via an organic binder (hereinafter referred to as alloy component exterior iron powder). Thereby, segregation of the powder for alloy can be prevented and the component distribution in the powder can be made uniform.

  Here, fatty acid amides, metal soaps and the like are particularly advantageously suitable as organic binders, but other known organic binders such as polyolefins, polyesters, (meth) acrylic polymers and vinyl acetate polymers can also be used. it can. These organic binders may be used alone or in combination of two or more. When using 2 or more types of organic binders together, you may use at least one part as a co-melt. When the amount of the organic binder added is less than 0.01% by mass, the alloy powder cannot be uniformly and sufficiently adhered to the surface of the iron powder. On the other hand, when it exceeds 1.0 mass%, iron powder adheres and aggregates, and there exists a possibility that fluidity | liquidity may fall. Therefore, the amount of organic binder added is preferably in the range of 0.01 to 1.0% by mass. In addition, the addition amount (mass%) of an organic binder points out the ratio of the organic binder which occupies for the whole iron-base mixed powder for powder metallurgy.

  Furthermore, in order to improve the fluidity and formability of the iron-based mixed powder for powder metallurgy, a free lubricant can be added. The amount of the free lubricant added is preferably 1.0% by mass or less as a proportion of the entire iron-based mixed powder for powder metallurgy. On the other hand, it is preferable to add 0.01% by mass or more of the free lubricant. Free lubricants include metal soaps (for example, zinc stearate, manganese stearate, lithium stearate, etc.), bisamides (for example, ethylene bisstearic acid amide), fatty acid amides containing monoamides (for example, stearic acid monoamide, erucic acid amide, etc.) ), Fatty acids (for example, oleic acid, stearic acid, etc.) and thermoplastic resins (for example, polyamide, polyethylene, polyacetal, etc.) are preferred because they have the effect of reducing the output of the green compact. Other known free lubricants other than those described above can also be used.

In the present invention, the blending amount of the organic lubricant is reduced as compared with the conventional one, and this is replaced with oxide particles, whereby the fluidity and the molding density can be improved while ensuring excellent output power. That is, normally, when the organic lubricant is reduced, the output is increased, but in the present invention, this adverse effect can be avoided by the addition of oxide particles. On the other hand, the molding density is improved by containing oxide particles instead of the organic lubricant. In addition, the fluidity is improved by the presence of the oxide particles. From the viewpoint of enjoying the advantages described above, the blending amount of the organic lubricant is preferably 0.8% by mass or less as a proportion of the entire iron-based mixed powder. More preferably, it is 0.7 mass% or less, More preferably, it is 0.6 mass% or less. The lower limit amount of the organic lubricant is preferably 0.02% by mass, which is the sum of the lower limit values of the organic binder and the free lubricant.
The organic lubricant is composed of at least one of an organic binder, an organic free lubricant, and an organic non-free lubricant (an organic lubricant adhered to the iron powder surface with a binder). Since an organic binder often substitutes its function, the total amount of the organic binder and the organic free lubricant is usually the amount of the organic lubricant.

Next, the manufacturing method of the iron-based mixed powder of the present invention will be described.
Additives such as oxide particles, a binder, and a lubricant according to the present invention and, if necessary, an alloy powder are added to the iron-based powder and mixed. In addition, it is not always necessary to add all of the above-mentioned additives such as binders and lubricants at the same time. After adding only a part and performing primary mixing, the remainder is added and secondarily mixed. You can also.

  The mixing means is not particularly limited, and any conventionally known mixer can be used. For example, conventionally known stirring blade type mixers (for example, Henschel mixers) and container rotation type mixers (for example, V type mixers, double cone mixers, etc.) can be used. When heating is required, a high-speed bottom-stirring mixer, an inclined rotary van mixer, a rotary mulberry mixer, a conical planetary screw mixer, etc., which are easy to heat, are particularly advantageously adapted.

  In addition, in this invention, it cannot be overemphasized that the additive for improving a characteristic can be added according to the objective other than the above-mentioned additive. For example, for the purpose of improving the machinability of the sintered body, the addition of a machinability improving powder such as MnS is exemplified.

Pure iron powder A (atomized iron powder, average particle size: 80 μm) as an iron-based powder, and an alloy component exterior iron powder B in which an alloy powder is attached to the surface of the pure iron powder via an organic binder Prepared the kind. The alloy powder used for B was Cu powder (average particle size: 25 μm): 2.0 mass% and graphite powder (average particle diameter: 5.0 μm): 0.8 mass%. As organic binders, stearic acid monoamide: 0.05% by mass and ethylenebisstearic acid amide: 0.05% by mass were used. In addition, all of these addition ratios are ratios which occupy for the whole iron-based mixed powder.
To the pure iron powder A and the alloy component exterior iron powder B, oxide particles having an aspect ratio of less than 5 and a free lubricant are added in various ratios, and then mixed to obtain an iron-based mixed powder for powder metallurgy. did. As oxide particles, JC (Fe ₂ O ₃ , manufactured by JFE Chemical), MIOX (mixture of Fe ₂ O ₃ , SiO ₂ and Al ₂ O ₃ : Fe ₂ O ₃ = 90 mass%, SiO ₂ = 5) Mass%, Al ₂ O ₃ = 3 mass%, the remaining impurities (both approximate values), Karntner Montanindustrie Gesellschaft mbH) and A31 (Al ₂ O ₃ , Nippon Light Metal) were used. Further, as the free lubricant, in addition to lithium stearate: 0.1% by mass, zinc stearate, ethylenebisstearic acid amide, erucic acid amide and the like were used. The average particle size of the iron powder and oxide particles was determined by measuring the particle size distribution by a laser diffraction / scattering method in accordance with JIS R 1629, and adopting a 50% diameter in a volume-based integrated fraction. The oxide particles were observed with a scanning electron microscope, and the average value of the aspect ratios of 50 randomly selected particles was defined as the aspect ratio.
Table 1 shows the blending ratio of these mixed powders. This blending ratio is the ratio of the entire iron-based mixed powder for powder metallurgy.

Next, each obtained iron-based mixed powder was filled in a mold and pressure-molded at a pressure of 980 MPa at room temperature to obtain a cylindrical green compact having an outer diameter of 11 mm and a height of 11 mm. Table 1 also shows the results of measurement of the fluidity of the iron-based mixed powder, the output when the green compact is extracted from the mold, and the green density of the obtained green compact. The fluidity of the iron-based mixed powder was evaluated according to JIS Z 2502.
Here, if the fluidity is a flow rate of 30 sec / 50 g or less, and the compressibility is a molding density of 7.35 Mg / m ³ or more, then the drawability is more than 25 MPa or less, respectively. It can be said that it is good.

As is apparent from Table 1, it can be seen that by adding an appropriate amount of the oxide particles according to the present invention, an iron-based mixed powder having excellent compressibility and punching power as well as fluidity can be obtained.
In contrast, all of the comparative examples were inferior in at least one of fluidity, molding density, and punching power.
From Table 1, for example, iron-based oxide particles (Fe ₂ O ₃ , SiO _2, and Al ₂ O ₃ are compared with the iron-based mixed powder of Comparative Example 9 containing only 0.8% by mass of the organic lubricant in total. The iron-based mixed powders of Invention Examples 9 and 10 in which the organic lubricant is reduced to 0.4 to 0.5% by mass by blending the mixture particles), while ensuring the same output power, the molding density and fluidity It can be seen that is significantly improved. Of course, as can be seen from Invention Example 8, even if the organic lubricant is further reduced, good fluidity, molding density, and extraction power can be obtained.
In addition, when organic binders, free lubricants, alloy powders and oxide particles (especially oxide particles containing iron, aluminum and / or silicon) are variously changed, and further machinability improving powders are added. In this case, the same results as in the above invention examples were obtained.

  By adding an appropriate amount of the oxide particles according to the present invention to the iron-based mixed powder, not only the fluidity but also the molding density and the unloading power can be improved, and not only the productivity is improved, Manufacturing cost can be reduced.

1 Major axis 2 Thickness

Claims (4)

An iron-based mixed powder for powder metallurgy mainly comprising an iron-based powder having an average particle size of 10 to 200 μm (but not including rare earth elements) , and the average particle size is 0 in the iron-based mixed powder 0.01 to 5.0% by mass of oxide particles (not including rare earth elements) containing 5 μm or more and 100 μm or less and an aspect ratio of less than 5 and containing at least one selected from iron, aluminum, and silicon An iron-based mixed powder for powder metallurgy, characterized by containing in the range of The iron-based mixed powder is 0.1 to 10 wt% alloy powders, according to claim 1, characterized in that it contains a state attached to the surface of the iron-based powder through an organic binder Iron-based mixed powder for powder metallurgy. The iron-based mixed powder for powder metallurgy according to claim 1 or 2 , wherein the iron-based mixed powder contains 0.02 to 0.8 mass% of an organic lubricant . The iron-based mixed powder for powder metallurgy according to any one of claims 1 to 3 , wherein the iron-based mixed powder contains 0.01 to 1.0 mass% of a free lubricant.

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