JPWO2017043094A1 - Method for producing mixed powder for powder metallurgy, method for producing sintered body, and sintered body - Google Patents

Abstract

Provided is a powder mixture for powder metallurgy that can obtain a sintered body having an excellent tensile strength and toughness equivalent to or higher than that of the case of containing Ni, although it does not contain Ni.
A first mixing step in which an iron-based powder is mixed with a Mo-containing powder and a Cu-containing powder to form a raw material mixed powder, and heat treatment of the raw material mixed powder diffuses Mo and Cu on the surface of the iron-based powder. A mixed powder for powder metallurgy comprising: a diffusion adhesion step for adhering to a partially diffused alloy steel powder; and a second mixing step for mixing the partially diffused alloy steel powder with graphite powder to obtain a mixed powder for powder metallurgy. In the production method, the iron-based powder has an average particle size of 30 to 120 μm, cuprous oxide powder is used as the Cu-containing powder, and the component composition of the powder metallurgy mixed powder is Mo: 0.2 -1.5mass%, Cu: 0.5-4.0mass%, C: 0.1-1.0mass%, and the manufacturing method of the mixed powder for powder metallurgy made into the component composition which consists of remainder Fe and an unavoidable impurity .

Description

  The present invention relates to a method for producing a powder mixture for powder metallurgy, and more particularly, to a method for producing a powder mixture for powder metallurgy having characteristics suitable for the production of high-strength sintered parts for automobiles, etc., despite not containing Ni. . Moreover, this invention relates to the sintered compact obtained by the manufacturing method of the sintered compact, and the said manufacturing method.

  The powder metallurgy technique can manufacture a component having a complicated shape in a shape very close to a product shape (so-called near net shape) and with high dimensional accuracy. Therefore, if a part is produced using powder metallurgy technology, the cutting cost can be greatly reduced. For this reason, powder metallurgy products to which powder metallurgy technology is applied are used in various fields as various machine parts.

  For such powder metallurgy, iron-based powders are mainly used. Iron-based powders are classified into iron powder (for example, pure iron powder), alloy steel powder, and the like depending on the components. Iron-based powders are classified into atomized iron powder, reduced iron powder, and the like based on the production method. And when using the classification | category by a manufacturing method, iron powder is used by the wide meaning containing not only pure iron powder but alloy steel powder.

  In the powder metallurgy technique, a sintered body is manufactured by producing a molded body using the iron-based powder as described above and sintering the molded body. The molded body is generally mixed with iron-based powder, alloy powder such as Cu powder and graphite powder, and a lubricant such as stearic acid and lithium stearate, and then filled into a mold. Then, it is manufactured by pressure molding.

Here, the density of the molded body obtained by a normal powder metallurgy process is about 6.6 to 7.1 Mg / m ³ . These molded bodies are converted into sintered bodies by a subsequent sintering process, and further subjected to sizing and cutting as necessary to form powder metallurgy parts (parts). When higher strength is required, carburizing heat treatment or bright heat treatment may be performed after sintering.

  Recently, there has been a strong demand for improving the strength of powder metallurgy parts in order to reduce the size and weight of the parts. In particular, there is a strong demand for higher strength for iron-based powder parts (iron-based sintered bodies) made from iron-based powders.

Here, as the iron-based powder, mainly the following powders obtained by adding alloy elements to raw powder (pure iron powder) are known;
(1) Mixed powder in which each alloy element powder is mixed with pure iron powder,
(2) Pre-alloyed steel powder in which each alloy element and pure iron powder are completely alloyed,
(3) Partial diffusion alloy steel powder (also referred to as composite alloy steel powder) in which each alloy element powder is partially adhered and diffused on the surface of pure iron powder or pre-alloy steel powder.

The mixed powder (1) has the advantage of having high compressibility comparable to that of pure iron powder. However, at the time of sintering, each alloy element does not sufficiently diffuse into Fe to form a heterogeneous structure, and as a result, the strength of the finally obtained sintered body may be inferior. Also, when Mn, Cr, V, Si, etc. are used as alloy elements, these elements are oxidized more easily than Fe, so that the sintered body finally obtained by oxidation during sintering There was a problem that the strength of the steel was lowered. In order to suppress the oxidation and reduce the oxygen content of the sintered body, it is necessary to strictly control the atmosphere during sintering and, when carburizing after sintering, the CO ₂ concentration and dew point in the carburizing atmosphere. There is. For this reason, the mixed powder of the above (1) cannot meet the recent demand for higher strength and has not been used.

  If the prealloyed steel powder (2) is used, segregation of the alloy elements can be completely prevented, so that the structure of the sintered body can be made uniform. Therefore, in addition to stabilizing the mechanical properties of the sintered body, even when Mn, Cr, V, Si, etc. are used as alloy elements, by limiting the type and amount of alloy elements, It is possible to achieve a low oxygen content in the body. However, since prealloyed steel powder is manufactured by atomizing molten steel, it tends to cause solid solution hardening of the steel powder due to oxidation and complete alloying in the atomizing process of the molten steel. There was a problem that the density of the body was difficult to increase.

  The partially diffused alloy steel powder of (3) above is a mixture of pure iron powder or pre-alloyed steel powder with metal powder of each alloy element, heated in a non-oxidizing or reducing atmosphere, In addition, the metal powder is partially diffusion bonded to the surface of the prealloyed steel powder. Therefore, by using the partial diffusion alloy steel powder, while avoiding the problem of the iron-based mixed powder of (1) and the pre-alloyed steel powder of (2), the iron-based mixed powder of (1) and the above ( The advantage of the prealloyed steel powder of 2) can be obtained.

  That is, by using partially diffused alloy steel powder, it is possible to achieve both low oxygen content and high compressibility comparable to pure iron powder. Furthermore, since the structure of the sintered body can be a composite structure composed of a complete alloy phase and a partially concentrated phase, the strength of the sintered body is further improved. Therefore, the partially diffused alloy steel powder can meet the recent demand for higher strength of parts, and its development is widely performed.

  Ni and Mo are mentioned as a basic alloy component generally used for manufacture of the said partial diffusion alloy steel powder.

  Ni has the effect of improving the toughness of the sintered body. This is because austenite is stabilized by the addition of Ni, and as a result, more austenite remains as retained austenite without being transformed into martensite after quenching. Moreover, Ni has the effect | action which strengthens the matrix of a sintered compact by solid solution strengthening.

  On the other hand, Mo has the effect of improving hardenability. Therefore, Mo suppresses the formation of ferrite during the quenching process and facilitates the formation of bainite or martensite, thereby strengthening the matrix of the sintered body by transformation. Mo has both an effect of solid-solution strengthening by solid solution in the matrix and an effect of precipitation strengthening the matrix by forming fine carbides. Furthermore, since Mo has good gas carburizing properties and is a non-grain boundary oxidizing element, it also has an effect of carburizing and strengthening the sintered body.

  As a mixed powder for high-strength sintered parts using partially diffusion alloy steel powder containing these alloy components, for example, in Patent Document 1, Ni: 0.5-4 mass%, Mo: 0.5-5 mass% A high strength sintered part in which Ni: 1 to 5 mass%, Cu: 0.5 to 4 mass%, and graphite powder: 0.2 to 0.9 mass% are further mixed with the alloy steel powder partially alloyed so that The mixed powder is shown.

In addition, as a high-density iron-based sintered body that does not contain Ni, Patent Document 2 discloses that an iron-based powder having an average particle diameter of 1 to 18 μm and Cu powder having an average particle diameter of 1 to 18 μm are 100: A method for producing an iron-based sintered body that is mixed and molded and sintered at a weight ratio of (0.2 to 5) is disclosed. In the technique described in Patent Document 2, by using an iron-based powder having an average particle size extremely smaller than usual, the sintered body density is 7.42 g / cm ³ or more, which is not normally high. This makes it possible to obtain a sintered body having a high density.

  Furthermore, as mixed powder for high-strength sintered parts using partially diffused alloy steel powder, for example, in Patent Document 3, metal Cu powder and graphite powder are mixed with alloy steel powder to which Ni and Mo are diffused and adhered. A mixed powder for high strength sintered parts is disclosed.

Japanese Patent No. 3663929 JP-A-4-285141 Japanese Patent No. 4484595

  However, as a result of consideration by the inventors, the sintered material using the mixed powder described in Patent Document 1 and Patent Document 3 described above and the sintered material obtained by the method described in Patent Document 2 include the following: It turns out that there is a problem like this.

  In other words, the sintered material described in Patent Document 1 requires at least 1.5 mass% Ni, and, as can be seen from the examples thereof, substantially contains 3 mass% or more of Ni. Therefore, in order to obtain a high strength of 800 MPa or more with the sintered material described in Patent Document 1, a large amount of Ni such as 3 mass% or more is required. Furthermore, in order to obtain a sintered body having a strength of 1000 MPa or more after carburizing, quenching, and tempering treatment, a larger amount of Ni is considered necessary.

  However, Ni is an element which is disadvantageous from the viewpoint of dealing with environmental problems in recent years and from the viewpoint of recycling, and is an element which should be avoided as much as possible. Further, the addition of several mass% of Ni is extremely disadvantageous in terms of cost. Furthermore, when Ni is used as an alloy element, there is also a problem that long-time sintering is required in order to sufficiently diffuse Ni into iron powder or alloy steel powder.

  Further, in the sintered material described in Patent Document 2, although Ni is not added, the average particle size of the iron-based powder used is 1 to 18 μm, which is smaller than usual. Thus, when the particle size is small, the fluidity of the mixed powder is deteriorated, and there is a problem that the working efficiency when filling the powder with a die is reduced when performing press molding.

  Furthermore, in the sintered material described in Patent Document 3, the mixed powder contains metallic Cu powder. This metal Cu powder melts during the sintering process and penetrates between the iron powder grains, thereby expanding the inter-particle distance of the iron powder and increasing the size of the sintered body compared to the size of the compact. . Therefore, the density of the sintered body is lower than that of the molded body. This phenomenon is generally known as Cu expansion. When the density reduction due to the Cu expansion is large, there is a disadvantage that the strength and toughness of the sintered body are reduced.

  In view of the above-described present situation, the present invention has excellent characteristics equivalent to or better than those in the case of containing Ni (for example, tensile strength and toughness after carburizing, quenching, and tempering in spite of not containing Ni (Ni-free)). It is an object of the present invention to provide a method for producing a powder mixture for powder metallurgy, which can obtain a sintered body having a). Moreover, this invention aims at providing the sintered compact obtained by the manufacturing method of the sintered compact using the said mixed powder for powder metallurgy, and the said manufacturing method.

  In order to achieve the above-mentioned object, the inventors have made various studies on the alloy components of the powder mixture for powder metallurgy not containing Ni and the means for adding them. As a result, the following findings (1) to (6) were obtained.

(1) Mo and Cu are partially diffused into an iron-based powder to obtain a partially-diffused alloy steel powder, and Ni is obtained by using a mixed powder for powder metallurgy obtained by mixing the partially-diffused alloy steel powder with graphite powder. In some cases, a sintered body having characteristics equal to or higher than that in the case of including Ni may be obtained although it is not included.

(2) In the case of (1) above, Mo works as a ferrite stabilizing element during sintering. As a result, in the vicinity of the portion where the Mo content is high, the ferrite phase is generated, the sintering of the iron powders is promoted, and the density of the sintered body is improved.

(3) In the case of the above (1), when carburizing and quenching the sintered body, Cu moves the temperature at which martensitic transformation starts to the low temperature side and strengthens the sintered body.

(4) In the case of (1) above, in order to obtain a sintered body having excellent characteristics, the composition of the mixed powder for powder metallurgy is controlled to be within a specific range, and the iron group It is necessary to use a powder of cuprous oxide (Cu ₂ O) instead of metal Cu powder as the Cu source used when producing the partial diffusion alloy steel powder by setting the average particle size of the powder to 30 to 120 μm.

(5) By using cuprous oxide powder, it is possible to avoid Cu expansion that occurs when metal Cu powder is used, and to suppress density reduction of the sintered body.

(6) The fluidity of the powder mixture for powder metallurgy can be improved by using an iron-based powder having an average particle size of 30 to 120 μm.

  This invention is made | formed based on the said knowledge, The summary structure is as follows.

1. A first mixing step of mixing a Mo-containing powder and a Cu-containing powder with an iron-based powder to obtain a raw material mixed powder;
A diffusion adhesion process in which Mo and Cu are diffused and adhered to the surface of the iron-based powder to form a partial diffusion alloy steel powder by heat-treating the raw material mixed powder;
A method of producing a mixed powder for powder metallurgy comprising a second mixing step of mixing the partially diffused alloy steel powder with graphite powder to obtain a mixed powder for powder metallurgy,
The iron-based powder has an average particle size of 30 to 120 μm,
Using cuprous oxide powder as the Cu-containing powder,
The composition of the mixed powder for powder metallurgy includes Mo: 0.2 to 1.5 mass%, Cu: 0.5 to 4.0 mass%, C: 0.1 to 1.0 mass%, and the balance of Fe and inevitable. A method for producing a mixed powder for powder metallurgy having a component composition comprising impurities.

2. 2. The method for producing a mixed powder for powder metallurgy according to 1 above, wherein the Cu-containing powder has an average particle size of 5 μm or less.

3. A method for producing a sintered body, comprising molding and sintering a powder mixture for powder metallurgy obtained by the method for producing a powder mixture for powder metallurgy described in 1 or 2 above.

4). 4. A sintered body obtained by the method for producing a sintered body according to 3 above.

  ADVANTAGE OF THE INVENTION According to this invention, although it does not contain Ni, the mixed powder for powder metallurgy which can manufacture the sintered compact which has the same or more excellent characteristic as the case where it contains Ni is obtained. Moreover, since the mixed powder for powder metallurgy according to the present invention has high fluidity, it is excellent in work efficiency when filling the mold with the mixed powder for powder metallurgy for press molding. Furthermore, according to the present invention, a sintered body having both excellent strength and toughness can be produced at low cost even by a normal sintering method.

  Next, a method for carrying out the present invention will be specifically described.

The method for producing a mixed powder for powder metallurgy according to an embodiment of the present invention includes the following steps (1) to (3);
(1) A first mixing step in which an iron-based powder is mixed with a Mo-containing powder and a Cu-containing powder to obtain a raw material mixed powder;
(2) A diffusion adhesion step in which Mo and Cu are diffused and adhered to the surface of the iron-based powder to form a partially-diffusion alloy steel powder by heat-treating the raw material mixed powder, and (3) A second mixing step in which graphite powder is mixed to obtain a mixed powder for powder metallurgy.

  And as said iron-based powder, the iron-based powder whose average particle diameter is 30-120 micrometers is used. Moreover, cuprous oxide powder is used as the Cu-containing powder. Furthermore, the component composition of the powder mixture for powder metallurgy includes Mo: 0.2 to 1.5 mass%, Cu: 0.5 to 4.0 mass%, C: 0.1 to 1.0 mass%, and the balance of Fe. And consisting of inevitable impurities.

  As described above, in the conventional method, a mixed powder for powder metallurgy is manufactured by mixing metal Cu powder and graphite powder with partially diffused alloy steel powder to which Mo is diffused and adhered. In contrast, in the method of the present invention, cuprous oxide powder is used as a Cu source for diffusing and adhering Cu in addition to diffusing and adhering Cu to the iron-based powder together with Mo.

  Next, each process of said (1)-(3) is demonstrated. In the following description, “%” means mass% unless otherwise specified. Moreover, the amount of Mo, the amount of Cu, and the amount of graphite powder shall mean each content with respect to the whole mixed powder for powder metallurgy.

[First mixing step]
In the first mixing step, an iron-based powder is mixed with a Mo-containing powder and a Cu-containing powder to obtain a raw material mixed powder. There is no restriction | limiting in particular about the mixing method used at the said 1st mixing process, For example, it can carry out in accordance with a conventional method using a Henschel mixer, a cone type mixer, etc. Moreover, what is necessary is just to adjust the compounding ratio of the iron-based powder mixed, the Mo containing powder, and the Cu containing powder so that the component composition of the powder mixture for powder metallurgy finally obtained may become the range mentioned later. That is, it mixes with the mixed powder for powder metallurgy so that Mo amount may be 0.2-1.5% and Cu amount may be 0.5-4.0% with respect to the whole.

(Iron-based powder)
Average particle size: 30-120 μm
In the present invention, the average particle size of the iron-based powder used is 30 to 120 μm. When the average particle size of the iron-based powder is less than 30 μm, the fluidity of the iron-based powder itself or a raw material mixed powder obtained using the iron-based powder is deteriorated, and work efficiency such as mold filling is reduced. Therefore, the average particle diameter of the iron-based powder is set to 30 μm or more. The average particle diameter is preferably 40 μm or more, and more preferably 50 μm or more. On the other hand, if the average particle size exceeds 120 μm, the driving force for densification during sintering becomes small, and coarse pores are formed around coarse iron powder particles, resulting in a decrease in the density of the sintered body. . As a result, the strength and toughness of the sintered body are reduced. Therefore, the average particle size of the iron-based powder is set to 120 μm or less. The average particle diameter is preferably 100 μm or less, and more preferably 80 μm or less. Incidentally, the average particle diameter in the present invention is intended to mean a median diameter (d ₅₀₎ in volume.

  Here, “iron-based powder” means a powder having an Fe content of 50% by mass or more. Examples of the iron-based powder include pure iron powder and alloy steel powder. It is preferable to use iron powder (pure iron powder) as the iron-based powder.

  The iron-based powder is not particularly limited, and any iron-based powder produced by any method can be used. From the viewpoint of availability, an iron-based powder produced by the atomization method or the reduction method. Is preferably used. As the iron-based powder produced by the atomization method, both so-called atomized powder (as-atomized powder) and atomized powder (atomized powder) can be used. Here, the atomized raw powder means a powder obtained by atomizing molten steel, arbitrarily dried and classified, and not subjected to heat treatment for deoxidation (reduction) or decarburization. The atomized powder means a powder reduced by treating the atomized raw powder in a reducing atmosphere. As the iron-based powder produced by the reduction method, it is preferable to use reduced iron powder obtained by reducing mill scale or iron ore produced during the production of steel.

The apparent density of the iron-based powder is not particularly limited, but is preferably 1.7 to 3.5 Mg / m ³ . When using an iron-based powder produced by an atomizing method as the iron-based powder, the apparent density of the iron-based powder is preferably about 2.0 to 3.5 Mg / m ³ , 2.5 It is more preferable to set it to -3.2Mg / m < ³ >. Moreover, when using the iron-based powder produced by the reduction method as the iron-based powder, the apparent density of the iron-based powder is preferably about 1.7 to 3.0 Mg / m ^3. More preferably, it is 2 to 2.8 Mg / m ³ . Here, the apparent density is measured by the test method of JIS Z 2504.

The specific surface area of the iron-based powder is not particularly limited, but is preferably 0.002 to 0.5 m ² / g. When the iron-based powder produced by the atomization method is used as the iron-based powder, the specific surface area of the iron-based powder is preferably about 0.005 m ² / g or more, 0.01 m ² / g or more More preferably. On the other hand, the upper limit of the specific surface area is preferably 0.1 m ² / g. Moreover, when using the iron-base powder manufactured by the reduction method as said iron-base powder, it is preferable that the specific surface area of this iron-base powder shall be about 0.01 m < ² > / g or more, 0.02 m < ² > / g g or more is more preferable. On the other hand, the upper limit of the specific surface area is preferably 0.3 m ² / g.

(Mo-containing powder)
The Mo-containing powder is a powder that functions as a Mo source in the diffusion adhesion step described later. Any powder can be used as the Mo-containing powder as long as it contains Mo as an element. Therefore, any one of metal Mo powder (pure Mo powder), Mo alloy powder, and Mo compound powder can be used. Can also be used. As the Mo alloy powder, for example, Fe-Mo (ferromolybdenum) powder can be used. Examples of the Mo compound powder include powders of Mo compounds such as Mo oxide, Mo carbide, Mo sulfide, and Mo nitride. These Mo-containing powders may be used alone or in combination.

(Cu-containing powder)
The Cu-containing powder is a powder that functions as a Cu source in the diffusion adhesion step described later. In the present invention, it is important to use cuprous oxide powder as the Cu-containing powder. Since the cuprous oxide powder is reduced to metal Cu in the diffusion adhesion step described later, it is possible to obtain partially diffused alloy steel powder in which Mo and Cu are diffused and adhered to the surface of the iron-based powder.

By using cuprous oxide powder as the Cu-containing powder, Cu expansion that occurs when metal Cu powder is used can be avoided, and density reduction of the sintered body can be suppressed. Further, cuprous oxide is chemically stable and does not oxidize (rust) like metal Cu, so that it is easy to handle. Furthermore, since cuprous oxide (Cu ₂ O) has a smaller oxidation number than copper oxide (CuO), it can be easily reduced to metal Cu in the diffusion adhesion step described later. For example, in the diffusion adhesion process, when the raw material mixed powder is heat-treated in a hydrogen atmosphere, by using cuprous oxide, in addition to reducing the amount of hydrogen required for reduction, the heating temperature can be lowered, Processing time can also be shortened.

  The average particle size of the Cu-containing powder is not particularly limited, but is preferably 5 μm or less. By making the average particle size 5 μm or less, the effect of improving the strength and toughness by Cu can be further improved. The average particle size is more preferably 4.5 μm or less. On the other hand, the lower limit of the average particle diameter of the Cu-containing powder is not particularly limited, but if the average particle diameter is excessively lowered, the production cost of the Cu-containing powder increases. Therefore, the average particle size of the Cu-containing powder is preferably 0.2 μm or more, and more preferably 1.0 μm or more.

  In addition, in the case of the metal Cu powder conventionally used, the average particle diameter of a general commercially available metal Cu powder is about 20-40 micrometers.

[Diffusion adhesion process]
Next, the raw material mixed powder is heat-treated. Due to the heat treatment, Mo contained in the Mo-containing powder and Cu contained in the Cu-containing powder diffuse into the iron-based powder at the contact surface between the iron-based powder and the Mo-containing powder and between the iron-based powder and the Cu-containing powder. Thus, partially diffused alloy steel powder in which Mo and Cu are diffused and adhered to the surface of the iron-based powder is obtained.

  The heat treatment can be performed in any atmosphere, but is preferably performed in a reducing atmosphere, and more preferably in a hydrogen-containing atmosphere. A hydrogen gas atmosphere can also be used as the hydrogen-containing atmosphere. The heat treatment may be performed at atmospheric pressure or under reduced pressure, and may be performed under vacuum.

  Although the temperature of the said heat processing is not specifically limited, It is preferable to set it as 800-1000 degreeC.

[Crushing / Classification]
The partial diffusion alloy steel powder obtained as described above is usually in a state in which iron-based powder particles contained in the partial diffusion alloy steel powder are sintered and solidified. Therefore, it is preferable to provide a pulverization / classification step of pulverizing and classifying the partially diffused alloy steel powder after the diffusion adhesion step and prior to the next second mixing step. For example, after pulverizing to a desired particle size, the coarse powder can be removed by classification with a sieve having a predetermined opening. The maximum particle size of the partially diffused alloy steel powder is preferably 180 μm or less.

  Moreover, prior to the next second mixing step, the partially diffused alloy steel powder can be optionally annealed.

  It is preferable that the said partial diffusion alloy steel powder contains Mo and Cu, and has a component composition which consists of remainder Fe and an unavoidable impurity. Examples of inevitable impurities contained in the partially diffused alloy steel powder include C, O, N, and S. These contents are each an internal number of the partially alloyed steel powder, and C: 0.02% Hereinafter, it is preferable that O: 0.3% or less, N: 0.004% or less, and S: 0.03% or less. In particular, the O content is more preferably 0.25% or less. When the amount of inevitable impurities exceeds the above range, the compressibility of the powder mixture for powder metallurgy, which is the result of the following second mixing step, is reduced, and compression molding can be performed on a molded body having sufficient density. It can be difficult.

[Second mixing step]
Subsequently, graphite powder is mixed with the partial diffusion alloy steel powder obtained as described above to obtain a mixed powder for powder metallurgy. C, which is the main component of the graphite powder, has the effect of improving the strength of the sintered body by precipitation strengthening with carbide and improving hardenability. Therefore, especially in order to obtain an excellent tensile strength of 1000 MPa or more after carburizing, quenching, and tempering the sintered body, addition of graphite is essential.

  The graphite powder may be mixed according to a conventional method, for example, by a method used for general powder mixing. Moreover, what is necessary is just to adjust the compounding ratio of the partial diffusion alloy steel powder and graphite powder to mix so that the component composition of the mixed powder for powder metallurgy finally obtained may become the range mentioned later. That is, it mixes with the mixed powder for powder metallurgy so that C amount may be 0.1-1.0% with respect to the whole.

(Graphite powder)
The graphite powder is not particularly limited, and an arbitrary one can be used. The average particle size of the graphite powder is not particularly limited, but is preferably about 1 to 50 μm.

[Component composition of mixed powder]
In the present invention, the component composition of the finally obtained mixed powder for powder metallurgy is Mo: 0.2-1.5%, Cu: 0.5-4.0%, C: 0.1-1. The component composition consists of 0% and the balance Fe and inevitable impurities. As will be described later, an additive such as a lubricant can be added to the powder metallurgy alloy steel powder. Here, the “component composition of the mixed powder for powder metallurgy” refers to the mixed powder, The component composition of the part except the said additive material, ie, the part which consists of a partial diffusion alloy steel powder and graphite powder shall be pointed out.

  Hereinafter, the reasons for limiting the component composition of the mixed powder will be described.

Mo: 0.2 to 1.5%
When the Mo content is less than 0.2%, the effect of improving the hardenability and the effect of improving the strength of the sintered body become insufficient. Therefore, the Mo content is 0.2% or more. The Mo content is preferably 0.3% or more, and more preferably 0.4% or more. On the other hand, if the Mo content exceeds 1.5%, the effect of improving the hardenability is saturated, and the non-uniformity of the structure of the sintered body is increased. Therefore, the Mo content is 1.5% or less. The Mo content is preferably 1.0% or less, and more preferably 0.8% or less.

Cu: 0.5 to 4.0%
If the Cu content is less than 0.5%, the effects of solid solution strengthening and hardenability improvement that Cu has cannot be sufficiently obtained, and the strength and toughness of the sintered parts are lowered. Therefore, the Cu content is 0.5% or more. The Cu content is preferably 1.0% or more, and more preferably 1.5% or more. On the other hand, when the Cu content exceeds 4.0%, the strength improvement effect of the sintered part is saturated. Therefore, the Cu content is 4.0% or less. The Cu content is preferably 3.0% or less, and more preferably 2.5% or less.

C: 0.1 to 1.0%
C is an element having an effect of improving the strength and fatigue strength of the sintered body. In order to acquire the said effect, C content shall be 0.1% or more. On the other hand, if the C content exceeds 1.0%, it becomes hypereutectoid, so that a lot of cementite is precipitated, and the strength of the sintered body is lowered. Therefore, the C content is 1.0% or less.

  Next, the manufacturing method of the sintered compact in one Embodiment of this invention is demonstrated. In the present invention, a sintered body can be obtained by molding and sintering the powder mixture for powder metallurgy.

[Molding]
The molding is not particularly limited and can be performed by any method as long as it is a method capable of molding a powder mixture for powder metallurgy. As a general molding method, a mixed powder for powder metallurgy is filled in a mold and pressure-molded. The pressing force in the pressure molding is preferably 400 to 1000 MPa. When the applied pressure is less than 400 MPa, the density of the obtained molded body is lowered, and the properties of the sintered body are deteriorated. On the other hand, when the applied pressure exceeds 1000 MPa, the life of the mold becomes extremely short, which is economically disadvantageous. Moreover, it is preferable that the temperature at the time of the said pressure molding shall be normal temperature (about 20 degreeC)-about 160 degreeC.

  In addition, when it is necessary to cut the final sintered body to create a part shape, prior to the above molding, the powder for metallurgy powder is used to improve machinability. Can be mixed. As the machinability improving powder, for example, MnS or the like can be used. The addition of the machinability improving powder can be performed according to a conventional method.

  Prior to the molding, a lubricant can be further added to the powder mixture for powder metallurgy. As the lubricant, a powdery lubricant is preferably used. Further, the molding can be performed by applying or attaching a lubricant to the mold. In any case, as the lubricant, any lubricant such as a metal soap such as zinc stearate or lithium stearate, or an amide wax such as ethylenebisstearic acid amide can be used. In addition, when mixing a lubricant with the powder mixture for powder metallurgy, the amount of lubricant is preferably about 0.1 to 1.2 parts by mass with respect to 100 parts by mass of powder mixture for powder metallurgy.

[Sintering]
Next, the molded body obtained as described above is sintered. The sintering is preferably performed in a temperature range of 1100 to 1300 ° C. If the sintering temperature is less than 1100 ° C., the sintering does not proceed sufficiently, so it is difficult to obtain a sintered body having excellent tensile strength (1000 MPa or more). On the other hand, if the sintering temperature exceeds 1300 ° C., the life of the sintering furnace is shortened, which is economically disadvantageous. The sintering time is preferably 10 to 180 minutes.

  According to such a procedure, the sintered body obtained by using the mixed powder for powder metallurgy according to the present invention has an excellent tensile strength compared to a sintered body obtained by molding and sintering a conventional powder under the same conditions. It has toughness.

  Further, the obtained sintered body can be further optionally subjected to a strengthening treatment. Examples of the strengthening treatment include carburizing quenching, bright quenching, induction quenching, and carbonitriding. However, even when these strengthening treatments are not performed, the sintered body using the powder metallurgy mixed powder according to the present invention has improved strength and toughness compared to the conventional sintered body without the strengthening treatment. Yes. In addition, each reinforcement | strengthening process should just be performed according to a conventional method.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to the following examples.

  A mixed powder for powder metallurgy was produced by the following procedure.

(First mixing step)
The iron-based powder was mixed with a Mo-containing powder and a Cu-containing powder to obtain a raw material mixed powder. As the iron-based powder, atomized raw powder having an apparent density shown in Table 1 was used. The specific surface area of the iron-based powder was 0.39 m ² / g. As the Mo-containing powder, oxidized Mo powder having an average particle size of 10 μm was used. As the Cu-containing powder, cuprous oxide powder having an average particle size shown in Table 1 was used. The mixing was performed for 15 minutes using a V-type mixer. In addition, the compounding quantity of each powder was adjusted so that content of Mo and Cu in the mixed powder for powder metallurgy finally obtained might become the value shown in Table 1.

(Diffusion adhesion process)
Next, by heat-treating the obtained raw material mixed powder, Mo and Cu were diffused and adhered to the surface of the iron-based powder to obtain a partially diffused alloy steel powder. The heat treatment was performed in a hydrogen atmosphere with a dew point of 30 ° C. under conditions of a temperature of 880 ° C. and a time of 1 hour.

  In some comparative examples (No. 1, 3), instead of adding the Cu-containing powder in the first mixing step, the metal Cu powder is added in the second mixing step, and the first In the mixing step, only the Mo-containing powder was added, and then the diffusion adhesion step was performed. For comparison, no. 29, in the first mixing step, to the iron-based powder, a metal Ni powder having an average particle size of 8 μm, a metal Cu powder having an average particle size of 28 μm (the same metal Cu powder as in Comparative Examples No. 1 and 3), And the oxidation Mo powder (the same oxidation Mo powder as the example of this invention) with an average particle diameter of 10 micrometers was mixed, and the said diffusion adhesion process was implemented. No. The composition of the partially diffused alloy steel powder in 29 was 4% Ni-1.5% Cu-0.5% Mo-Fe.

(Crushing and classification)
The obtained partial diffusion alloy steel powder was pulverized and classified by the following procedure. First, since the partial diffusion alloy steel powder may be hardened by the heat treatment, pulverization with a hammer mill was performed three times in order to pulverize the powder. At this time, the opening of the hammer mill rostral was reduced in order of 3 mm (first time), 2 mm (second time), and 1 mm (third time). Next, the pulverized powder is passed through a vibrating sieve having an opening of 180 μm, and the coarse powder remaining on the sieve is removed and discarded, and only the portion of the particle size of 180 μm or less under the sieve is collected, and the next second mixing step It was used for.

(Second mixing step)
Subsequently, graphite powder (average particle diameter: 5 μm) was added to the partially diffused alloy steel powder so as to have the content shown in Table 1. Subsequently, ethylene bis-stearic acid amide was further added so that it might become 0.6 mass part with respect to 100 mass parts of mixed powder for powder metallurgy, Then, it mixed for 15 minutes with the V-type mixer.

  The balance of the alloy steel powder in the table is iron and inevitable impurities, but the amount of inevitable impurities in the alloy steel powder used in the present invention is 0.2% or less with respect to the amount of partial alloy steel powder. . No. In 1 and 3, the metal Cu powder was mixed with the graphite powder so that the Cu content in the mixed powder for powder metallurgy would be the value shown in Table 1.

(Molding)
Thereafter, the mixed powder for powder metallurgy was pressure-molded to produce a rod-shaped compact having a length: 55 mm, a width: 10 mm, and a thickness: 10 mm. Ten compacts were prepared from each powder metallurgy mixed powder. The density of the molded body was 7.0 Mg / m ³ .

(Sintering)
The rod-shaped molded body was sintered to obtain a rod-shaped sintered body. The sintering was performed in a propane modified gas atmosphere, which is a reducing atmosphere, under conditions of temperature: 1130 ° C. and time: 20 minutes.

  Next, the characteristics of the mixed powder for powder metallurgy obtained by the above procedure and the rod-shaped sintered body were evaluated by the following methods. The obtained results are as shown in Table 1.

(Fluidity of mixed powder for powder metallurgy)
100 g of test powder was sampled from the powder mixture for powder metallurgy and passed through a 5 mmφ nozzle. At that time, it was determined that a sample that completely flowed without stopping was passed (◯), and a sample that did not flow because all or part of the sample flowed was determined to be rejected (x).

(Tensile strength)
A total of five tensile test pieces each having a parallel part diameter of 5 mm and a distance between scores of 15 mm were cut out from five of the ten rod-shaped sintered bodies. The obtained tensile test piece was sequentially subjected to gas carburizing, quenching, and tempering under the following conditions.
-Gas carburization: Carbon potential: 0.8 mass%, Temperature: 870 ° C, Time: 60 minutes · Quenching: Temperature: 60 ° C, Oil quenching and tempering: Temperature: 180 ° C, Time: 60 minutes

  Using the tensile test piece obtained by the above procedure, a tensile test was performed by the method specified in JIS Z 2241 to measure the tensile strength. The value of the tensile strength was the average value of the measured values of the five test pieces. Furthermore, the case where the measured tensile strength was 1000 MPa or more was determined to be acceptable (◯), and the case where it was less than 1000 MPa was determined to be unacceptable (x).

(Toughness)
In order to evaluate the toughness of the sintered body, a Charpy impact test was performed. In the Charpy impact test, the remaining five of the ten rod-shaped sintered bodies were used as they were as test pieces, and the impact value was measured by the method defined in JIS Z 2242. Prior to the Charpy impact test, the rod-shaped sintered body was subjected to gas carburization, quenching, and tempering under the same conditions as the tensile test piece. The impact value was an average value of measured values of five test pieces. Furthermore, the case where the measured impact value was 14.5 J / cm ² or more was determined to be acceptable (◯), and the case where it was less than 14.5 J / cm ² was determined to be unacceptable (x).

  As can be seen from the results shown in Table 1, in the examples satisfying the conditions of the invention example, the tensile strength equal to or higher than that of the comparative example (No. 29) using Ni, although Ni is not used. And the sintered compact which has toughness was able to be obtained. Furthermore, the alloy steel powder for powder metallurgy of the above example had excellent fluidity.

Claims (4)

A first mixing step of mixing a Mo-containing powder and a Cu-containing powder with an iron-based powder to obtain a raw material mixed powder;
A diffusion adhesion process in which Mo and Cu are diffused and adhered to the surface of the iron-based powder to form a partial diffusion alloy steel powder by heat-treating the raw material mixed powder;
A method of producing a mixed powder for powder metallurgy comprising a second mixing step of mixing the partially diffused alloy steel powder with graphite powder to obtain a mixed powder for powder metallurgy,
The iron-based powder has an average particle size of 30 to 120 μm,
Using cuprous oxide powder as the Cu-containing powder,
The composition of the mixed powder for powder metallurgy includes Mo: 0.2 to 1.5 mass%, Cu: 0.5 to 4.0 mass%, C: 0.1 to 1.0 mass%, and the balance of Fe and inevitable. A method for producing a mixed powder for powder metallurgy having a component composition comprising impurities.   The manufacturing method of the mixed powder for powder metallurgy of Claim 1 whose average particle diameter of the said Cu containing powder is 5 micrometers or less.   The manufacturing method of the sintered compact which shape | molds and sinters the mixed powder for powder metallurgy obtained by the manufacturing method of the mixed powder for powder metallurgy of Claim 1 or 2.   The sintered compact obtained by the manufacturing method of the sintered compact of Claim 3.