JP5949952B2 - Method for producing iron-based sintered body - Google Patents

Description

The present invention relates to an alloy steel powder for powder metallurgy suitable for use in powder metallurgy technology, and in particular, intends to improve the strength and toughness of a sintered material using the alloy steel powder for powder metallurgy .
Moreover, this invention relates to the manufacturing method of the iron-based sintered compact excellent in the intensity | strength and toughness manufactured using said alloy steel powder for powder metallurgy.

The powder metallurgy technique can manufacture parts having a complicated shape in a shape very close to a product shape (so-called near net shape) and with high dimensional accuracy, so that the cutting cost can be greatly reduced. For this reason, powder metallurgy products are used in various fields as various mechanical structures and parts thereof.
Furthermore, recently, there has been a strong demand for improving the strength of powder metallurgy products in order to reduce the size and weight of parts. In particular, there is a demand for higher strength of iron-based powder products (iron-based sintered bodies). strong.

  The iron-based powder compact for powder metallurgy, which is the pre-stage of the iron-based sintered body, is generally made of an alloy powder such as copper powder and graphite powder, and a lubricant such as stearic acid and zinc stearate with respect to the iron-based powder. Are mixed to obtain an iron-based powder mixed powder, which is filled into a mold and pressure-molded. And iron base powder is classified into iron powder (for example, pure iron powder etc.), alloy steel powder, etc. according to a component. Moreover, in the classification | category by a manufacturing method, there exist atomized iron powder, reduced iron powder, etc., and the word iron powder in these classification | category is used by the wide meaning containing alloy steel powder.

The density of the iron-based powder compact for powder metallurgy obtained by a normal powder metallurgy process is generally about 6.8 to 7.3 Mg / m ³ . This iron-based powder molded body is subsequently subjected to a sintering process to be an iron-based sintered body, and further subjected to sizing, cutting, or the like as necessary to obtain a powder metallurgy product. Further, when higher strength is required, carburizing heat treatment or bright heat treatment may be performed after sintering.

Conventionally, as a powder to which alloying elements are added at the raw material powder stage,
(1) Mixed powder in which each alloy element powder is mixed with pure iron powder,
(2) Pre-alloyed steel powder that completely alloyed each element,
(3) Diffusion-bonded alloy steel powder or the like in which each alloy element powder is partially diffused on the surface of pure iron powder or prealloyed steel powder is known.

The mixed powder in which each alloy element powder is mixed with the pure iron powder shown in the above (1) has an advantage that high compressibility as high as that of the pure iron powder can be secured. However, because the segregation of each alloy element powder is large, there is a large variation in characteristics, and the alloy elements do not diffuse sufficiently in Fe, and the inhomogeneous structure remains and effective base strengthening cannot be achieved. was there.
For this reason, the amount of use of the mixed powder in which each alloy element powder is blended with the above pure iron powder has not been able to meet the recent demands for characteristic stabilization and high strength.

  In addition, the prealloyed steel powder that completely alloyes each element shown in (2) above is manufactured by atomizing molten steel, which can achieve base strengthening with a homogeneous structure, but by solid solution hardening action Decrease in compressibility is a problem.

Furthermore, the diffusion-adhesive alloy steel powder shown in (3) above contains pure iron powder and pre-alloy steel powder mixed with metal powders of each element, heated in a non-oxidizing or reducing atmosphere, Since each metal powder is partially diffusion bonded on the surface of iron powder or prealloyed steel powder, the advantages of the iron-based mixed powder of (1) above and the prealloyed steel powder of (2) above are combined be able to.
Therefore, while preventing segregation of alloy elements, it is possible to ensure high compressibility equivalent to that of pure iron powder, and at the same time, a composite structure in which a partial alloy concentrated phase is dispersed. It is being developed as a diffusion-bonded alloy steel powder for strength.

  Thus, in order to improve the strength and toughness of the powder metallurgy product, high alloying can be considered. However, this alloying has a problem that the alloy steel powder as a raw material is hardened and compressibility is lowered, and the equipment burden in pressure forming is increased. In addition, a decrease in compressibility of the alloy steel powder causes a decrease in the density of the sintered body and offsets the increase in strength. That is, in order to improve the strength and toughness of the powder metallurgy product, a technique for increasing the strength of the sintered body while suppressing the decrease in compressibility as much as possible is required.

  As described above, as a technique for increasing the strength of a sintered body while maintaining compressibility, it is common to add alloy elements such as Ni, Cu and Mo that improve hardenability to iron-based powders. Has been done. As an element effective for this purpose, for example, in Patent Document 1, Mo is added to the iron powder as a pre-alloying element in a range where the compressibility is not impaired (Mo: 0.1 to 1.0% by mass). A technique has been disclosed in which Cu and Ni are diffused and adhered to the particle surface in the form of powder to achieve both compressibility during compacting and strength of the sintered member.

Patent Document 2 proposes an alloy steel powder for powder metallurgy for high-strength sintered bodies in which two or more kinds of alloy elements, particularly Mo and Ni, or further Cu are diffused and adhered to the surface of steel powder. .
In this technology, furthermore, for each diffusion adhesion element, it is possible to control so that the diffusion adhesion concentration with respect to the fine powder having a particle diameter of 44 μm or less is within a range of 0.9 to 1.9 times the diffusion adhesion concentration with respect to the entire steel powder. It has been proposed that the impact toughness of the sintered body is ensured by this limitation to a relatively wide range.

  On the other hand, Mo-based alloy steel powders that do not contain Ni or Cu as the main alloying element have been proposed. For example, in Patent Document 3, in order to promote the sintering by forming an α single phase of Fe having a high self-diffusion rate, Mo as a ferrite stabilizing element is included as a prealloy in the range of 1.5 to 20% by mass. Alloy steel powder has been proposed. This alloy steel powder is said to have a high-density sintered body by adapting the particle size distribution to the process of pressure sintering, and it is homogeneous by not using a diffusion adhesion type alloy element. It is said that a stable tissue can be obtained.

  Similarly, there is a technique disclosed in Patent Document 4 as an alloy steel powder for powder metallurgy containing Mo as a main alloy element. This technology proposes an alloy steel powder in which Mo: 0.2-10.0% by mass is diffused and adhered to the surface of an iron-based powder containing Mn of 1.0% by mass or less or less than 0.2% by mass of Mo as a pre-alloy. Is. As the iron-based powder, atomized iron powder or reduced iron powder may be used, and the average particle size is preferably 30 to 120 μm. And this alloy steel powder is not only excellent in compressibility but is said to be able to obtain a high-density and high-strength sintered part.

Japanese Patent Publication No.63-66362 JP 61-130401 A Japanese Patent Publication No. 6-89365 JP 2002-146403 A

  However, in the techniques described in Patent Documents 1 and 2, Ni is an essential additive component, but since Ni diffuses slowly during sintering, in order to sufficiently diffuse Ni into iron powder and steel powder. Requires long-time sintering.

Further, the technique described in Patent Document 3 has a disadvantage that a high molding density cannot be obtained because the Mo addition amount is relatively high at 1.8% by mass or more and the compressibility is low.
For this reason, when a normal sintering process (single sintering without pressing) is applied, only a low sintered density can be obtained, and sufficient strength and toughness cannot be obtained.

Furthermore, the technique described in Patent Document 4 is adapted to a powder metallurgy process including recompression and re-sintering of a sintered body. That is, the usual sintering method has a problem that the above-described effects are not so much exhibited.
As a result, the inventors' research shows that it is difficult to achieve both strength and toughness at a high level in any sintered body using any of the alloy steel powders described in Patent Documents 1 to 4 above. I understood.

  The present invention has been developed in view of the above-described current situation, overcomes the problems of the prior art described above, and is an alloy steel for powder metallurgy capable of achieving both high strength and toughness of a sintered body using the same. The purpose is to propose powder.

Now, in order to achieve the above object, the inventors have made various studies on the alloy components of the iron-based powder and the means for adding the same, and as a result, have obtained the following knowledge.
That is, a composite alloy steel powder in which Mo-containing alloy powder is adhered to the iron-based powder surface, the specific surface area of this composite alloy steel powder is 0.100 m ² / g or more, and Mo is further in the composite alloy steel powder, By using a composite alloy steel powder containing 0.2 to 1.5% by mass, when the alloy steel powder for powder metallurgy obtained from this composite alloy steel powder is molded and sintered, its sinterability is excellent. It was found that the pores of the sintered body were appropriately refined and the toughness of the sintered body was improved along with the strength of the sintered body.
The present invention has been made based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. An alloy steel powder for powder metallurgy comprising a composite alloy steel powder having a mean particle size of 76-96 μm and a Mo-containing alloy powder adhered to the surface of an iron-based powder and a graphite powder, the specific surface area of the composite alloy steel powder there in 0.100M ² / g or more 0.5 m ² / g or less, and a range Mo amount of 0.2 to 1.5 mass% of the composite alloy steel powder in further the powder metallurgy alloy steel powder: 100 wt% powder metallurgy alloy steel powder content of the graphite powder is in the range of 0.1 to 1.0% by weight against to, after adding and mixing a lubricant, pressing process, carried out once the sintering process A method for producing an iron-based sintered body as an iron-based sintered body .

2. The iron-based firing according to 1, wherein the alloy steel powder for powder metallurgy further contains Cu powder in a range of 0.5 to 4.0% by mass with respect to 100% by mass of the alloy steel powder for powder metallurgy. A method for producing a knot.

3. 3. The method for producing an iron-based sintered body according to 1 or 2 above, wherein in the alloy steel powder for powder metallurgy, the iron-based powder includes reduced iron powder, and the average particle size of the iron-based powder is 80 μm or less. .

4). 4. The method for producing an iron-based sintered body according to any one of 1 to 3, wherein in the alloy steel powder for powder metallurgy, the oxygen content of the iron-based powder is 0.3% by mass or less.

Delete

  According to the alloy steel powder for powder metallurgy according to the present invention, it is not necessary to use Ni, and since the compressibility is high, a sintered material having both high strength and high toughness can be obtained at low cost even with a normal sintering method. Can get to.

Hereinafter, the present invention will be specifically described.
Powder metallurgy alloy steel powder of the present invention, the surface of the iron-based powder was deposited Mo-containing alloy powder, and a specific surface area of 0.100M ² / g or more, the range M o amount of 0.2 to 1.5 mass% It is characterized by containing a composite alloy steel powder .
The composite alloy steel powder described above is mixed with an appropriate amount of graphite powder shown below to obtain an alloy steel powder for powder metallurgy , which is then formed into a compact and sintered, whereby the pores of the sintered body are effective. Thus, it is possible to obtain a sintered part that is refined and improved in both strength and toughness.

The inventors consider the mechanism by which the pores of the sintered body can be effectively refined and a sintered part with improved strength and toughness can be obtained by the present invention as follows.
Generally, since there are many pores in a sintered body, stress concentrates on the pores, and the strength and toughness of the sintered body tend to decrease. However, in the alloy steel powder for powder metallurgy according to the present invention, by setting the specific surface area of the composite alloy steel powder to 0.100 m ² / g or more, the pores of the sintered body are refined and the degree of stress concentration is reduced. At the same time, the sintered neck portion is toughened.

In addition, by making Mo in the composite alloy steel powder in the range of 0.2 to 1.5% by mass, Mo concentrates around the pores of the sintered body, and the sintered body is further strengthened. In the alloy steel powder for powder metallurgy according to the invention, Mo-containing alloy powder adheres to the surface of the iron-based powder, and Mo is not contained in the base part, so that it is difficult to generate carbide compared to the sintered neck part. And a tough structure.
That is, by controlling the pore distribution and the Mo distribution of the sintered body, it is considered that the present invention makes it possible to achieve both high strength and high toughness of the sintered body.

Hereinafter, the reasons for the limitation of the present invention will be described.
First, the manufacturing method of the alloy steel powder for powder metallurgy of this invention is demonstrated.
In the present invention, iron powder such as atomized iron powder and reduced iron powder, and Mo raw material powder that is a raw material of Mo-containing alloy powder are prepared as iron-based powder.

  The iron-based powder is not particularly limited as long as it is an iron-based powder usually used in powder metallurgy, but so-called atomized raw powder, atomized iron powder, or reduced iron powder is preferable. The atomized iron-based powder may be any of atomized raw powder obtained by atomizing molten steel, dried and classified, and atomized iron powder obtained by reducing the atomized raw powder in a reducing atmosphere.

The reduced iron powder is preferably a reduced iron powder obtained by reducing mill scale or iron ore generated during the production of steel. The apparent density of the reduced iron powder may be about 1.7 Mg / m ³ to 3.0 Mg / m ³ . More preferably, it is 2.2 to 2.8 Mg / m ³ . Here, the apparent density is measured by the test method of JIS Z 2504.

  On the other hand, as the Mo raw material powder, the target Mo-containing alloy powder itself may be used, or a Mo compound that can be reduced to the Mo-containing alloy powder may be used. The average particle diameter of the Mo raw material powder is 50 μm or less, preferably 20 μm or less. Here, the average particle diameter is a volume-based median diameter (so-called d50).

  As the Mo-containing alloy powder, Mo alloy powder such as Mo pure metal powder, oxidized Mo powder, or Fe-Mo (ferromolybdenum) powder is advantageously suitable. On the other hand, examples of the Mo compound include Mo carbide, Mo sulfide, and Mo nitride.

Next, the iron-based powder and the Mo raw material powder are mixed at a predetermined ratio to obtain a mixed powder. This ratio is finally obtained when the Mo amount in the composite alloy steel powder is 0.2 to 1.5 mass%. Adjust to be within range. In mixing, the mixing method and the mixing equipment are not particularly limited, and can be performed according to a conventional method using, for example, a Henschel mixer or a corn mixer.

Furthermore, by holding this mixed powder at a high temperature and diffusing Mo into iron at the contact surface between the iron-based powder and the Mo raw material powder and bonding (diffusion adhesion treatment), a composite alloy steel powder used in the present invention is obtained. It is done.
As the atmosphere for the diffusion adhesion treatment, a reducing atmosphere or a hydrogen-containing atmosphere is suitable, and a hydrogen atmosphere is particularly suitable. Note that heat treatment may be applied under vacuum. Moreover, the temperature of a suitable diffusion adhesion process is the range of 800-1000 degreeC.

When the diffusion adhesion treatment is performed as described above, the iron-based powder and the Mo-containing alloy powder are usually sintered and solidified, and thus pulverized and classified to a desired particle size. Furthermore, you may anneal as needed. The particle diameter of the composite alloy steel powder is preferably 180 μm or less.

In the present invention, it is preferable that the Mo-containing alloy powder is uniformly attached to the surface of the iron-based powder. When not uniformly adhered, when the composite alloy steel powder is pulverized or transported after the diffusion adhesion treatment, it is easy to fall off from the iron-based powder surface, and thus the Mo-containing alloy powder in the free state is particularly likely to increase. When the alloy steel powder for powder metallurgy obtained from the composite alloy steel powder in such a state is molded and sintered, the dispersion state of carbides is segregated. Therefore, in order to increase the strength and toughness of the sintered body, it is preferable to uniformly attach the Mo-containing alloy powder to the surface of the iron-based powder, and to reduce the free Mo-containing alloy powder generated by dropping or the like.

The amount of Mo to be diffused and deposited is in the range of 0.2 to 1.5 mass% (inner number) in the composite alloy steel powder. When the content is less than 0.2% by mass, the effect of improving the hardenability is small and the effect of improving the strength is small. This is because high strength and toughness cannot be obtained. Therefore, the amount of Mo to be diffused and deposited is in the range of 0.2 to 1.5 mass% in the composite alloy steel powder. Preferably it is the range of 0.3-1.0 mass%.

On the other hand, the specific surface area of the composite alloy steel powder to which Mo is diffused and attached used in the present invention is limited to 0.100 m ² / g or more. Preferably it is 0.150 m ² / g or more. When the specific surface area is less than 0.100 m ² / g, coarse pores exist, the reactivity during sintering is insufficient, or the reasons are compounded. First, it is because toughness falls. The upper limit of the specific surface area, although not particularly limited, taken to contain a large amount of fine powder exceeds 0.5 m ² / g, for compressibility is lowered, 0.5 m ² / g or less.

In addition, since the specific surface area of the powder is reduced by subjecting Mo to the surface of the iron-based powder by diffusion, the specific surface area of the base iron-based powder is preferably 0.150 m ² / g or more. The specific surface area in the present invention is measured by a gas adsorption method (BET method).

In the present invention, the balance of the composite alloy steel powder is iron and inevitable impurities. Examples of impurities contained in the composite alloy steel powder include C, O, N, and S. These contents are C: 0.02% by mass or less and O: 0.3 in the composite alloy steel powder, respectively. There is no particular problem as long as it is not more than% by mass, N: not more than 0.004% by mass, and S: not more than 0.03% by mass, but O is more preferably not more than 0.25% by mass. When the amount of inevitable impurities exceeds these ranges, the compressibility of the alloy steel powder for powder metallurgy obtained from the composite alloy steel powder will be reduced, and it will be difficult to compress the preform into a preform having a sufficient density. Because.

To the alloy steel powder for powder metallurgy mainly composed of the above composite alloy steel powder, graphite powder should be added in the range of 0.1 to 1.0% by mass in a ratio to the whole alloy steel powder for powder metallurgy (100% by mass). Is essential. Moreover, in this invention, 0.5-4.0 mass% of Cu powder can be added by the ratio with respect to the whole alloy steel powder for powder metallurgy (100 mass%).
C, which is the main component of the graphite powder, is a useful element for increasing the strength of the sintered part because it can be dissolved in iron during sintering to enhance solid solution and improve hardenability. In the present invention, when carburizing the sintered body from the outside by carburizing heat treatment or the like after sintering, the amount of graphite to be added may be small, but if the amount is less than 0.1% by mass, the above-described addition effect is poor. On the other hand, when carburizing heat treatment is not performed at the time of sintering, graphite powder is added, but when it exceeds 1.0 mass%, it becomes hypereutectoid, so that cementite is precipitated and the strength is reduced. Therefore, the graphite powder is limited to the range of 0.1 to 1.0% by mass. The average particle size of the graphite powder is preferably 50 μm or less.

  On the other hand, Cu is a useful element that has the effect of increasing the strength of sintered parts by solid solution strengthening and hardenability improvement of iron-based powder, and melts into a liquid phase during sintering of iron-based powder. There is also an effect of fixing the particles of the iron-based powder to each other. However, if the addition amount is less than 0.5% by mass, the effect of addition is poor. On the other hand, if it exceeds 4.0% by mass, the effect of improving the strength of the sintered part is not only saturated but also machinability is reduced. Accordingly, the Cu powder is preferably in the range of 0.5 to 4.0 mass%. More preferably, it is the range of 1.0-3.0 mass%. The average particle size of the Cu powder is preferably 50 μm or less.

The iron-based powder used in the present invention contains reduced iron powder and preferably has an average particle size of 80 μm or less. This is because if the average particle size is larger than 80 μm, that is, if a powder with a large particle size is included, the driving force during sintering becomes weak, and coarse iron-based powder is surrounded by coarse voids. This is because holes are formed. And this coarse hole becomes the cause which reduces the intensity | strength and toughness of a sintered compact.
Here, the average particle diameter is a mass-based median diameter (so-called d50). Specifically, sieving was performed using a sieve specified in JIS Z 8801, and the mass of the sample remaining on each sieve was measured to obtain a particle size in which the smaller side and the larger side were equivalent.

In this invention, the additive for improving a characteristic can be added according to the objective. For example, for the purpose of improving the strength of the sintered body, Ni powder can be added, and for the purpose of improving the machinability of the sintered body, addition of a machinability improving powder such as MnS can be appropriately performed. In addition, it is preferable to make Ni powder into the range of 0.5-5 mass% in the ratio with respect to the whole alloy steel powder for powder metallurgy (100 mass%).

On the other hand, the amount of the machinability improving powder such as MnS added may be about 0.1 to 1% by mass in a conventionally known amount, that is, a ratio to the whole alloy steel powder for powder metallurgy (100% by mass).

Further, the molding conditions and sintering conditions suitable for producing a sintered body using the alloy steel powder for powder metallurgy of the present invention will be described.
In the press molding using the alloy steel powder for powder metallurgy according to the present invention, a powdery lubricant can be mixed. It can also be molded by applying or adhering a lubricant to the mold. In any case, as the lubricant, any of metal soaps such as zinc stearate and lithium stearate, amide waxes such as ethylenebisstearic acid amide, and other known lubricants can be suitably used. . In addition, when mixing a lubrication agent, it is preferable to set it as about 0.1-1.2 mass part (external addition) with respect to 100 mass parts of alloy steel powder for powder metallurgy.

  When press-molding the alloy steel powder for powder metallurgy of the present invention, it is preferably performed with a pressure of 400 to 1000 MPa. This is because if the applied pressure is less than 400 MPa, the density of the resulting molded product will be low, and the properties of the sintered body will be reduced.On the other hand, if it exceeds 1000 MPa, the life of the mold will be shortened, which is economical. It is because it becomes disadvantageous. In addition, it is preferable that the temperature at the time of pressurization shall be the range of normal temperature (about 20 degreeC)-about 160 degreeC.

  Moreover, it is preferable to sinter the alloy steel powder for powder metallurgy of the present invention in a temperature range of 1100 to 1300 ° C. This is because if the sintering temperature is less than 1100 ° C., the sintering does not proceed and the characteristics of the sintered body deteriorate, whereas if it exceeds 1300 ° C., the life of the sintering furnace is shortened. Because it becomes economically disadvantageous. The sintering time is preferably in the range of 10 to 180 minutes.

  The obtained sintered body can be subjected to strengthening treatment such as carburizing quenching, bright quenching, induction quenching, and carbonitriding as required, but according to the present invention even when the strengthening treatment is not performed. The sintered body using the alloy steel powder for powder metallurgy has improved strength and toughness compared to a conventional sintered body (one not subjected to strengthening treatment). In addition, what is necessary is just to give each reinforcement | strengthening process according to a conventional method.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the following examples at all.
In this example, the iron-based powder includes an atomized raw powder having an apparent density of 2.65 Mg / m ³ or an apparent density of 2.80 Mg / m ³ and an apparent density of 3.25 Mg / m ³ , and an apparent density. : 2.60Mg / m ³ or apparent density: 2.75Mg / m ³ reduced iron powder, apparent density: 2.60Mg / m ³ or apparent density: 2.80Mg / m ³ , apparent density: 3.30Mg / m ³ atomized iron powder was used.
Mo oxide powder (average particle size: 10 μm) was added to these iron-based powders at a predetermined ratio, mixed for 15 minutes with a V-type mixer to form mixed powders, and then heat-treated in a hydrogen atmosphere with a dew point of 30 ° C ( Holding temperature: 880 ° C., holding time: 1 h), a composite alloy steel powder was produced in which a predetermined amount of Mo shown in Table 1 was diffused and adhered to the surface of the iron-based powder.
Next, copper powder (average particle size: 30 μm) and graphite powder (average particle size: 5 μm) in the amounts shown in Table 1 are added to these composite alloy steel powders (Mo diffusion adhesion alloy steel powders) , and powder Alloy steel powder for metallurgy was obtained. Further, 0.6 parts by mass of ethylenebisstearic acid amide was added to 100 parts by mass of these alloy steel powders for powder metallurgy, and then mixed for 15 minutes with a V-type mixer. Subsequently, press molding was performed so that the density of the molded body was 7.0 Mg / m ^3, and a tablet-shaped molded body having a length of 55 mm, a width of 10 mm, and a thickness of 10 mm was produced.
The tablet-like molded body was sintered to obtain a sintered body. This sintering was performed in a propane modified gas atmosphere under conditions of sintering temperature: 1130 ° C. and sintering time: 20 minutes.
Subsequently, the obtained sintered body was processed into a round bar tensile test piece having a parallel part diameter of 5 mm for a tensile test specified by JIS Z 2241. In addition, for Charpy impact test specified in JIS Z 2242, the obtained sintered body is in the as-sintered shape and is carburized with carbon potential: 0.8 mass% (holding temperature: 870 ° C, holding time) : 60 minutes), and then subjected to quenching (60 ° C., oil quenching) and tempering (180 ° C., 60 minutes).
These sintered bodies were measured for tensile strength (MPa) and impact value (J / cm ² ) by a tensile test specified by JIS Z 2241 and a Charpy impact test specified by JIS Z 2242. The respective measurement results are also shown in Table 1.

As shown in Table 1, when the tensile strength and impact value of the inventive example and the comparative example were compared, all of the inventive examples showed a tensile strength of 1000 MPa or more and an impact value of 14.0 J / cm ² or more. While both strength and toughness could be achieved at a high level, the comparative examples all had impact values of less than 14.0 J / cm ² and were inferior to the inventive examples in at least one of tensile strength and impact value. It was.

Table 1 also shows the results of a 4Ni material (4Ni-1.5Cu-0.5Mo, maximum particle size of raw material powder: 180 μm) as a conventional material. It turns out that the example of an invention can obtain the characteristic more than conventional 4Ni material.

Claims (4)

An alloy steel powder for powder metallurgy comprising a composite alloy steel powder having a mean particle size of 76-96 μm and a Mo-containing alloy powder adhered to the surface of an iron-based powder and a graphite powder, the specific surface area of the composite alloy steel powder there in 0.100M ² / g or more 0.5 m ² / g or less, and a range Mo amount of 0.2 to 1.5 mass% of the composite alloy steel powder in further the powder metallurgy alloy steel powder: 100 wt% After adding a lubricant to the alloy powder for powder metallurgy having a graphite powder content of 0.1 to 1.0% by mass with respect to the iron powder, the pressure forming treatment and the sintering treatment are carried out once and the iron base A method for producing an iron-based sintered body as a sintered body. The iron base according to claim 1, wherein the alloy steel powder for powder metallurgy further contains Cu powder in a range of 0.5 to 4.0% by mass with respect to 100% by mass of the alloy steel powder for powder metallurgy. A method for producing a sintered body . The iron-based sintered body according to claim 1 or 2, wherein in the alloy steel powder for powder metallurgy, the iron-based powder includes reduced iron powder, and the average particle size of the iron-based powder is 80 µm or less. Method. The method for producing an iron-based sintered body according to any one of claims 1 to 3, wherein in the alloy steel powder for powder metallurgy, the oxygen content of the iron-based powder is 0.3 mass% or less.