JPH1046283A - Composite powder for high strength sintered steel, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve tensile strength and fatigue strength by specifying a composition and also specifying the degree of adhesion of Ni to iron powder. SOLUTION: This composite powder is composed of Ni powder, graphite powder, solid binder, and iron powder. As to the Ni powder, an Ni powder of <=5μm average grain size is incorporated by 0.2-8wt.% and diffused into the iron powder to improve the mechanical properties of a sintered compact. The graphite powder is useful for the improvement of strength and incorporated by 0.2-1.0wt.%. The solid binder is added by 0.05-0.5wt.% in order to obtain sufficient adhesion ratio, though its kind is not particularly limited as long as it can make the Ni powder adhere to the surface of the iron powder. As to the iron powder, an iron powder in which grains of 45-150μm grain size comprise >=50% is used in order to increase the strength of a sintered steel. It is necessary that, in the iron powder with the above composition, the degree of Ni adhesion to the iron powder, computed by equation, is regulated to >=90%. Because of the above-mentioned high degree of adhesion, excellent mechanical caracteristics can be provided and also the dispersion of the mechanical caracteristics caused by the segregation of Ni can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw material powder for various sintered parts requiring high strength and a method for efficiently producing the powder. The composite powder for high-strength sintered steel of the present invention is very useful in that the tensile strength and fatigue strength of sintered steel to which Ni powder is added can be significantly improved.

[0002]

2. Description of the Related Art Conventionally, Ni has been added to steel in order to improve the mechanical properties of sintered steel. However, simply adding Ni powder to iron powder and mixing the same results in Ni. Is known to segregate, resulting in large variations in mechanical properties. Therefore, various proposals have been made as a method of adding Ni.

As a first method, there is a method using a so-called prealloyed iron powder in which Ni is dissolved in iron powder in advance. This method is excellent in that, when it is made into a sintered body, the Ni concentration is uniform, but the compressibility of the powder is reduced due to solid solution hardening, so that the density of the molded body is reduced and mechanical Deterioration of properties; good quenchability, often resulting in uniform martensite structure after quenching, excellent tensile strength, but with toughness, non-uniform structure of residual γ phase and martensite structure There is a problem that it is inferior to the above method.

As a second method, there has been proposed a method of diffusing and adhering a single element of Ni, Cu and Mo, or an alloy fine powder obtained by pre-alloying two or more of these elements (Japanese Patent Application Laid-Open No. 2-145703). Gazette). Although this method is superior in compressibility as compared with the method using the first pre-alloyed iron powder, the reduction in compressibility due to alloying of Ni is still unavoidable, and the production cost is increased due to the diffusion adhesion treatment. There is also.

[0005] To prevent such a decrease in compressibility due to the addition of Ni, Japanese Patent Publication No. 7-4568.
No. 3 discloses Ni, C having a particle size of 45 μm or less.
A method has been proposed in which alloy element powders of u and Mo are attached by a co-melt of a lubricant and a binder.

However, the above method has the following problems. According to the publication, it is described that when the proportion of Ni powder of 45 μm or less (more preferably, 15 μm or less) is 60% or more, the degree of adhesion of the Ni powder to iron powder particles is improved. However, according to the study results of the present inventors, when using such fine Ni powder (and thus easily agglomerated), a lubricant and a binder are mixed and heated, and an alloy such as Ni is mixed with the obtained co-melt. It has been found that it is difficult to uniformly disintegrate and agglomerate Ni by using the method of this publication in which the elemental powder is adhered to the iron powder, and the mechanical properties vary greatly. . Furthermore, according to this method, after quenching, the residual γ
It was also found that the phase was coarsened, which adversely affected the mechanical strength.

Although it has been suggested that the use of fine Ni powder is effective for the purpose of increasing the mechanical strength of sintered steel, any of the methods disclosed so far has been proposed. It cannot be said that the effect of adding Ni is effectively exhibited, and conversely, there is a problem that variation in mechanical strength is caused.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain excellent mechanical properties such as tensile strength and fatigue strength, and to reduce variations in the properties. An object of the present invention is to provide a composite powder for high-strength sintered steel with a small amount, and also provide a method capable of efficiently producing such a powder.

[0009]

Means for Solving the Problems The first composite powder for high-strength sintered steel according to the present invention which can solve the above-mentioned problems is a Ni powder having an average particle size of 5 μm or less: 0.2 to 8%. , Graphite powder: 0.2 to 1.0%, solid binder: 0.05 to 0.5%, balance: iron powder containing 50% or more in the range of particle size of 45 to 150 μm. The gist lies in that the degree of adhesion of Ni to the iron powder shown in the formula (1) is adjusted to 90% or more.

[0010]

(Equation 2)

Further, the second composite powder for a high-strength sintered steel of the present invention which can solve the above-mentioned problems is as follows: Ni powder having an average particle size of 5 μm or less: 0.2 to 8%, graphite powder: 0 0.2 to 1.0%, solid binder: 0.05 to 0.5%, Cu: 0.5 to 4% and / or Mo: 0.2 to 5%, balance: particle size in the range of 45 to 150 μm And the gist is that the iron powder containing 50% or more is satisfied and the degree of adhesion of Ni to the iron powder shown in the above formula (1) is adjusted to 90% or more.

In order to obtain more excellent mechanical properties, in the first and second composite powders for high-strength sintered steel, the iron powder has a particle size distribution of Rosin Ramler represented by the following formula (2). with distribution index n satisfy the 1.5 to 5.0 in the equation, that median diameter dp ₅₀ particle size in the R = 50 satisfies the 50.0~90μm in formula (2) is preferably of the present invention It is an aspect. log {log (100 / R)} = log β '+ nlog (dp) (2) In the formula, R is a ratio (%) of particles larger than a certain particle size (on a sieve) to the whole. , N is the distribution index, and dp is the particle size (μm) β ′ = β / In10 (where β is the particle size characteristic coefficient).

In producing the first composite powder, Ni powder having an average particle diameter of 5 μm or less; graphite powder; (Cu powder and / or Mo powder in producing the second composite powder); After adding a 1 to 16% solvent solution of a solid binder to a mixed powder composed of iron powder containing 50% or more in a diameter of 45 to 150 µm and mixing, the solvent is evaporated. . Here, the iron powder used in the above method has a distribution index n of 1. in the particle size distribution formula of Rosin Ramler shown in the above equation (2).
5 to 5.0, and in the formula (2), R =
The median diameter dp50 of the particle size at ₅₀ is 50.0-9.
Those satisfying 0 μm are very useful because more excellent mechanical properties can be obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on the relationship between the size and mechanical properties of Ni powder in a Ni-added sintered steel. As a result, by adding a solid binder by a wet mixing method. The present inventors have found that even with a very fine Ni powder, the degree of adhesion to iron powder can be significantly increased and good mechanical properties can be obtained, and the present invention has been completed.

First, the first composite powder for high-strength sintered steel of the present invention (which may be simply abbreviated as sintering powder) is a Ni powder having an average particle size of 5 μm or less: 0.2 to 8%, Graphite powder: 0.2 to 1.0%, solid binder: 0.05 to 0.5%, balance: It is necessary to satisfy iron powder containing 50% or more in the range of particle size of 45 to 150 μm. is there. Hereinafter, each component will be described in detail.

Ni powder having an average particle size of 5 μm or less: 0.2
In 8% as described above, when the addition of Ni powder compacting and sintering in the iron powder, Ni is gradually diffused into the iron powder, which contributes to improving mechanical properties of the sintered body knowledge Have been. Ni like this
The effect of adding less than 0.2% is insufficient. It is preferably at least 1.0%, more preferably at least 1.5%. Conversely, if the content exceeds 8%, the residual γ phase in the sintered body increases more than necessary, and the mechanical properties deteriorate. Preferably 4%
Or less, more preferably 3% or less.

On the other hand, since the diffusion rate of Ni into the iron powder is not very high, it is difficult to make the Ni concentration completely uniform under ordinary sintering conditions, and the Ni-rich phase is contained in the sintered body. Is formed. When Ni locally exceeds a certain ratio with respect to the iron powder, a residual γ phase is formed when heat treatment such as quenching is performed. According to Japanese Patent Application Laid-Open No. 2-254137, it is reported that this residual γ phase is effective for increasing the strength of a sintered body because it transforms into a martensite structure when strain is applied. The present inventors have studied and found that if the size of the residual γ phase is too large, the strength of the sintered body as a whole decreases because the strength of the sintered body itself is low. Accordingly, in order to obtain excellent mechanical strength, it is necessary to uniformly disperse the finer residual γ phase as much as possible.
m or less. It is preferably 3 μm or less, and if it is desired to obtain higher strength, it is recommended to be 1 μm or less. Furthermore, as described later, the smaller the particle size of the Ni powder, the more significantly the degree of adhesion of the solid binder to the iron powder can be significantly increased.
It is preferable to use one having the smallest possible particle size.

Graphite powder: 0.2-1.0% Graphite powder is useful for increasing the strength, and for that purpose, it is necessary to add 0.2% or more. It is preferably at least 0.4%, more preferably at least 0.5%. However, if it exceeds 1.0%, excessive C is precipitated, and sufficient strength cannot be obtained. Preferably it is 0.8% or less, more preferably 0.7% or less.

Solid binder: 0.05 to 0.5% The solid binder needs to be added in an amount sufficient to allow the Ni powder to sufficiently adhere to the iron powder.
If it is less than 5%, the adhesion rate is insufficient. Preferably 0.0
8% or more, more preferably 0.12% or more. On the other hand, when the content exceeds 0.5%, the flowability of the powder becomes poor, and the dispersion of the mechanical properties becomes rather large. Preferably it is 0.4% or less, more preferably 0.3% or less.

The solid binder used in the present invention is not particularly limited as long as it can adhere Ni powder to the surface of iron powder. For example, a solid binder containing styrene, butadiene and / or isoprene as a monomer component can be used. Polymers; copolymers containing ethylene and propylene as monomer components; and fatty acid esters.

The balance: 50 in the range of 45 to 150 μm in particle size.
% Or more iron powder The iron powder used in the present invention may be a pure iron powder having a purity of 99% or more, or a powder having a purity of less than 99% for the purpose of further improving the strength of the sintered body. Iron powder, Ni, Mo,
It may be a material to which an alloy element such as Cr or Mn is added, or a material containing another element as an impurity.

In order to increase the strength of the sintered steel, 45 to 1
It is necessary to use iron powder such that 50% or more is contained in the range of 50 μm. Less than 45 μm, especially 25
If a large amount of particles of less than μm
Not only is it impossible to obtain a sufficient degree of adhesion by antagonizing the size of the powder, but also the compressibility is reduced and the density of the molded body is reduced,
There are problems such as a decrease in strength. On the other hand, when a large portion exceeding 150 μm is contained, the crystal grains are coarsened when sintered, and the strength is reduced. Preferably 45 to 150
It is preferable to use iron powder containing 70% or more in the range of μm. The second powder for sintered steel of the present invention is intended to further improve the mechanical properties by adding the following in addition to the above powders and making the remainder iron powder.

Cu: 0.5-4% and / or Mo:
0.2 to 5% Cu and Mo are added to improve the physical properties of the sintered body. Among them, Cu is an element which generates a liquid phase during sintering to promote sintering and improve strength. If it is less than 0.5%, a sufficient effect cannot be obtained. It is more preferably at least 0.8%. On the other hand, even if added over 4%, the improvement effect is saturated,
It is economically useless. It is more preferably at most 2.5%. At the time of use, it is recommended to use electrolytic copper powder or atomized copper powder.

Mo is an element that enhances solid solution strengthening and hardenability in iron powder and contributes to improvement of mechanical properties. 0.2
%, The effect cannot be exhibited effectively.
More preferably, it is 0.5% or more. On the other hand, even if it exceeds 5%, the effect is saturated. It is more preferably at most 3.0%. At the time of use, iron powder obtained by alloying Mo in advance by a pre-alloy method may be used, or Mo powder or Fe-Mo alloy powder may be used.

In order to obtain a sintered steel having more excellent strength, the iron powder is further required to have a distribution index n of 1.5 to 1.5 in the particle size distribution formula of Rosin-Rammler shown in the above formula (2).
5.0 and R = 50 in the formula (2).
Median diameter dp ₅₀ of 50.0 to 90 μm
It is recommended that m be satisfied. Hereinafter, the reason for setting such requirements will be described using a Rosin-Rammler distribution equation.

The Rosin-Rammler distribution formula is a distribution formula usually used to express the particle size distribution of the powdery granules, and is represented by the following formula (3). R = 100 exp {−β (dp) ⁿ } (3) In the formula, R, β, n and dp have the same meaning as before. By transforming this equation as follows, the above equation (2) is obtained. First, the common logarithm of the above equation (3) is as follows.

Log R = log 100 + log [exp ｛−β (dp) ⁿ ｝] log (R / 100) = log [exp ｛−β (dp) ⁿ ｝] where log [exp ｛−β (dp) ⁿ ｝] = In [exp ｛−β (d
p) ⁿ }] / In10, so that log (R / 100) = In [exp {-β (dp) ⁿ }] / In10 = -β (dp) ⁿ / In10. Therefore, log (100 / R) = β (dp) ⁿ / In10 Here, if β ′ = β / In10, then log (100 / R) = β ′ (dp) ^n, and taking the common logarithm, log ｛ log (100 / R)｝ = log {β ′ (dp) ⁿ } = log β ′ + nlog (dp) (2), and the above equation (2) is obtained.

For the equation (2) thus obtained, log (dp) is plotted on the horizontal axis and log β ′ (= β / In10) on the vertical axis.
, A linear cumulative particle size distribution equation shown in FIG. 1 is obtained. The slope (gradient) of the equation is the distribution index n, and the particle size distribution becomes wider when the value of n is small, and the particle size distribution becomes narrow when the value of n is large. Also, the y-intercept of the equation (that is, dp = 1μ)
β can be calculated from m), but the particle diameter when R = 50, that is, the median diameter dp ₅₀ (central cumulative value, 50%
Particle size) can be calculated by β = In2 / (dp ₅₀ ) ⁿ .

First, in the present invention, the median diameter dp₅₀5
The thickness is preferably set to 0.0 to 90 μm. dp₅₀Is small
Fine iron powder and graphite are not sufficient for excessive iron powder.
Does not adhere, and the apparent density and compact density of iron powder increase.
Because it is difficult. Preferably at least 50.0 μm
More preferably, it is 60 μm or more. On the other hand, dp
₅₀Is too large, the added Ni powder is
Does not diffuse to the center, so sufficient strength improvement cannot be obtained
No. It is preferably 90 μm or less, and more preferably
It is 80 μm or less.

On the other hand, even if the median diameter dp ₅₀ is the same, if the distribution index n is small, the variation in particle size becomes large, and a large amount of coarse iron powder is mixed. From such a viewpoint, in the present invention, the distribution index n is preferably set to 1.5 to 5.0. For a coarse iron powder having an n value smaller than 1.5, the added Ni powder does not diffuse to the center of the iron powder, so that the effect of improving the strength cannot be sufficiently obtained. More preferably, it is 2.0 or more. On the other hand, a large value of n means that the particle size distribution is narrow, that is, the particle size is uniform. However, if the value of n exceeds 5.0, both the apparent density and the compact density of the iron powder decrease. I will. More preferably, it is 3.0 or less.

The powder for sintered steel of the present invention basically has the above-mentioned first and second component compositions. It is also possible to add in the range of%. Lubricants are very useful in that they facilitate press molding and can effectively prevent the occurrence of mold galling and the like during die molding. By adding in advance as a part of the above, such an effect can be effectively exerted. Of course, it can be used in press molding and die molding without being added during the production of powder for sintered steel. Examples of the lubricant include commonly used lubricants such as zinc stearate, calcium stearate, and wax-based lubricant.

Further, in the sintered steel powder of the present invention, the degree of adhesion of Ni to iron powder calculated by the following equation (1) needs to be 90% or more. Those having such a high degree of adhesion have excellent mechanical properties and can significantly suppress variations in mechanical properties due to segregation of Ni. Further, in the case of 95% or more, the variation in strength can be remarkably suppressed.

[0033]

(Equation 3)

The above formula (1) indicates that what percentage of the added Ni powder is
Is evaluated using a 100-mesh and a 200-mesh sieve in order to calculate whether or not Ni has adhered to the iron powder. That is, according to this evaluation method, 90% or more (preferably 95% or more) of iron powder to which Ni powder is attached exists in a region where a 100-mesh sieve passes but a 200-mesh sieve does not pass. On the other hand, the free Ni powder not adhering to the iron powder is very fine with an average particle diameter of 5 μm or less, so that it passed through a 200-mesh sieve, while the Ni powders aggregated to form a coarse powder. The objects are sieved such that they do not pass through a 100 mesh screen. Next, a method for producing a composite powder for high-strength sintered steel having the Ni adhesion shown by the above formula (1) of 90% or more using the above raw material powder will be described.

In the present invention, when attaching the Ni powder to the iron powder, it is necessary to first dissolve the solid binder in the solvent. As described above, the most significant feature of the present invention is that a wet mixing method is used in which the solid binder is dissolved in a solvent in advance, adjusted to a predetermined concentration, and then added to the raw material powder.

That is, in the present invention, an extremely fine Ni powder having an average particle size of 5 μm or less is used. As described above, when the size of Ni becomes fine, N
The i-powder segregates, resulting in a large variation in mechanical strength of the resulting sintered part. Therefore, in order to avoid such a problem and effectively exert the effect of increasing mechanical strength by adding Ni, a solid binder having a predetermined concentration diluted with a solvent is used. ) Could be efficiently attached to the iron powder surface.

As the solvent used in the present invention, 200 solvents such as hexane, acetone, toluene and alcohols are used.
There is no particular limitation as long as it is an organic solvent that volatilizes at a temperature of not more than ° C.
Further, the amount of the solvent to be added must be sufficient to dissolve the solid binder and to penetrate into the whole powder, but if it is too much, it takes time to evaporate and the production efficiency is deteriorated. Therefore, the concentration of the solid binder with respect to the solvent is 1-16.
% (Preferably 5-12%).

Next, Ni powder, graphite powder, and iron powder are used for producing the first sintered steel powder, and Ni powder, graphite powder and iron powder are used for producing the second sintered steel powder. Prepare graphite powder, Cu powder and / or Mo powder, and iron powder, put them together with the solid binder in a mixer that can be mixed in a wet state, and mix under a wet state.
The solvent is evaporated, for example, by heating at 140 ° C.

The wet mixer is not particularly limited as long as the solid binder and the raw material powder having the above-mentioned concentrations can be mixed in a wet manner. For example, in addition to a container-fixed mixer with blades, a container-fixed mixer is also used. Screw-type mixer and ribbon-type mixer. A rotary mixer, which does not have a stirring blade and cannot be mixed in a wet system, is not suitable as a mixer used in the present invention.

The wet mixer is used for the following reasons. In general, when the average particle size of the Ni powder is 5 μm or less, agglomeration becomes severe. In this case, a sufficiently uniform mixing state cannot be obtained by dry mixing using a usual container-type mixer such as a V-type mixer or a double cone mixer. This is because, in a container rotating type mixer, the aggregating of Ni powder cannot be broken because the shearing force applied to the powder is insufficient, and the fine Ni powder is contained in the gas present in the container. The main cause is that they are easily dispersed and cannot be mixed uniformly. On the other hand, in the present invention, the raw material powder is placed in a mixer with a fixed-type blade and mixed under a wet method, so that a larger shearing force can be applied to disintegrate the agglomeration of the Ni powder and to reduce the gas. Since scattering into the inside can also be prevented, even a fine Ni powder can be uniformly mixed.

By subjecting the mixed powder thus obtained to molding and sintering heat treatment in a usual manner, a powder for sintering having excellent mechanical strength and little variation thereof can be obtained. Specifically, the molding pressure is 4 t / cm ²
Ｔ8 t / cm ^2, and the sintering temperature is 10
It is recommended that the temperature be 00 to 1300 ° C., and as the heat treatment, quenching and tempering from a vacuum or carburizing treatment can be performed.

Here, in order to further clarify the features of the present invention, a description will be given in comparison with Japanese Patent Publication No. 7-45683. First, in the above publication, a co-melt of a binder and a lubricant (a material having a considerably high viscosity) is used, and the co-melt is mixed with a powder such as iron powder and then heated. After using a solid binder previously dissolved in a solvent and mixing with other powders without heating, the mixture is heated to evaporate and remove the used solvent. That is, in the present invention,
(1) The lubricant is not an essential raw material, and (2) the solvent is added to such an extent that all the powder used penetrates, and the mixture is mixed under wet conditions (therefore, the concentration is considerably low). They are clearly distinguished.

First, regarding (1), in the above-mentioned publication, Ni powder is adhered by a co-melt of a binder and a lubricant, whereas in the present invention, a lubricant is basically unnecessary. The difference is that, if necessary, it can be added when it is desired to effectively exert the above-mentioned action of the lubricant.
The present inventors have studied and found that according to the above-mentioned publication, since the co-melt of the lubricant and the binder is used, the original effect of the lubricant cannot be effectively exhibited.

Next, as for (2), in the above-mentioned publication, since the molten binder and the lubricant are only present as liquids, the uniform effect by wet mixing as in the present invention cannot be obtained. It is unsuitable when a fine Ni powder of 5 μm or less is used. On the other hand, in the present invention, the concentration of the solid binder is as extremely low as 1 to 16%, and a sufficient amount of solvent is added to penetrate all the used raw material powders, so that fine Ni powder which is easy to aggregate is added. Is used, the uniform effect of wet mixing can be effectively exhibited, and as a result, the degree of adhesion of the Ni powder to the iron powder can be significantly increased to 90% or more.

Hereinafter, the present invention will be described in detail with reference to examples.
However, the following examples do not limit the present invention,
All modifications and alterations without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

[0046]

【Example】

Example 1 Iron powder, Ni powder and graphite powder having composition ratios shown in Tables 1 to 5, and further, if necessary, Cu powder and / or M powder
o The powder is added to a high-speed mixer with wings, dry-mixed for 10 minutes (mixed for 30 minutes in the case of a V-type mixer), and then a solid binder (10% toluene solution) dissolved in toluene is added to the raw material powder. , And mixed under a wet method, and then the solvent is evaporated by heating, and if necessary, a lubricant (zinc stearate) is added to obtain mixed powders of the present invention and comparative examples. Was. In the table, No.
Nos. 1 to 33 are examples in which a lubricant was added.
* Is an example in which no lubricant is added. Here, for example, No.
No. 2 * has exactly the same composition and method as No. 2 except that no lubricant is added, and the same applies to those marked with other *.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

[Table 4]

[0051]

[Table 5]

The following characteristics were evaluated for each of the powders thus obtained. [Adhesion of Ni to Iron Powder] Measured according to the above equation. [Tensile strength] M04-199 of JPMA (Japan Powder Metallurgy Association) using the above mixed powder under a pressure of 6 t / cm ^2.
After forming a tensile test piece in accordance with No. ₂ , [N ₂ + 10%
[H ₂ ] sintering was performed at 1120 ° C. in an atmosphere. However, in the case of a powder to which no lubricant was added, an appropriate amount of zinc stearate was applied to a mold and molded. 850 ° C in vacuum
After quenching in oil at 60 ° C, heating to 200 ° C
After performing tempering for × 30 minutes, a tensile test was performed to measure the tensile strength. The tensile test was performed five times for each test piece, and [maximum value-minimum value] was defined as a range of variation in tensile strength.

[Fatigue strength] Using the above mixed powder, 6t /
12.5mm × 12.5mm × 100 under pressure of cm ²
mm and then in an atmosphere of [N ₂ + 10% H ₂ ]
After sintering at 120 ° C, JIS Z2274-1
Machined according to No. test specimen. However, in the case of a powder to which no lubricant was added, an appropriate amount of zinc stearate was applied to a mold and molded. The rotary bending fatigue test piece thus obtained was heated to 850 ° C. in a vacuum, then quenched in oil at 60 ° C., and then tempered at 200 ° C. for 30 minutes.
The fatigue strength of the Ono-type rotating bending was measured. Tables 6 to 8 show these results.

[0054]

[Table 6]

[0055]

[Table 7]

[0056]

[Table 8]

Nos. 1 to 18 and 2 * to 13 * are examples satisfying the requirements of the present invention. It can be seen that the tensile strength and fatigue strength are excellent and the variation in tensile strength is small. Among them, those in which the particle size of Ni is controlled to 3 μm or less have a Ni adhesion of 95% or more, and those in which the particle size is controlled to 1 μm or less have a Ni adhesion of 99% or more, and the variation in tensile strength is further reduced. ing.
Nos. 5 to 6 are examples in which a prealloyed low alloy powder is used as the base iron powder. However, in order to satisfy the requirements of the present invention, the alloy has excellent mechanical properties as in the case of the pure iron powder. doing. Nos. 14 to 18 are characteristic improvement powders such as Cu and Mo.
Is an example in which an appropriate amount of is added, and further excellent mechanical properties can be obtained.

On the other hand, Nos. 19 and 20 are comparative examples in which the particle size of the Ni powder is large, and the mechanical properties are larger than those of the present invention (for example, Nos. 1 and 2) having an appropriate Ni size. And the variation in tensile strength is large. No.2
1 to 22 are comparative examples in which the amount of added Ni is small / large,
The tensile strength and the fatigue strength are lower than those of the examples of the present invention (for example, Nos. 7 to 8).

Nos. 23 to 24 are comparative examples in which the amount of added graphite is small / large, and are examples of the present invention (for example, Nos. 9 to 1).
The mechanical properties are inferior to 1). No. 25-27
Is a comparative example in which a solid binder is not added / a small amount / a large amount, and the variation in mechanical properties is larger than that of the present invention examples (for example, Nos. 12 to 13).

No. 32 is a comparative example in which dry mixing was performed with a V-type mixer without using a solid binder, but fine Ni powder could not be uniformly adhered to iron powder, and tensile strength was low. The variation is large. No.33 is Tokuhei 7
Although this is a conventional example using the co-melting method described in Japanese Patent No. 45683, the variation in tensile strength is large due to insufficient mixing ability.

Nos. 28 to 31 are reference examples in which the added amount of the property improving powder is out of the preferable range specified in the present invention, and it can be seen that the addition of these powders cannot effectively exert the effect of improving the mechanical properties.

Example 2 In this example, the effect of the particle size distribution of the iron powder on the characteristics such as the Ni adhesion and the tensile strength was examined. First, the iron powder was classified, and the iron powder was classified using a V-type mixer to a particle size distribution shown in Table 9.
Blend for minutes. Incidentally, FIG. 2, of the iron powder in Table 9, distribution index n (slope) is approximately the same (about 2.0 to 2.5) is different median diameter dp ₅₀ (Min 48.1μm~ up to 96 .8Myuemu) is a diagram showing a graph of the particle size distribution of iron powder, Fig. 3, of the iron powder in Table 9, the median diameter dp ₅₀ is approximately the same (about 70～74Myuemu) is distribution index n (slope) It is the figure which graphed the particle size distribution of iron powder with different (1.41-5.24 micrometer of maximum). The plot method of these figures is based on Example No. 2 of FIG. 2 (“− △
-) Will be described as an example.

For example, (a) in the figure shows [log ｛l when dp = 45 μm [that is, log (dp) = 1.65].
og (100 / R)}]. d
When p = 45 μm, R (the ratio of particles larger than a certain particle size to the whole) is 100−23 = 77 from Table 9. That is, it means that the ratio of particles having a particle size larger than 45 μm is 77%. When R is 77, lo
g {log (100 / R)} = − 0.94, and this is plotted in FIG.

On the other hand, (b) in the drawing indicates that dp = 150 μm
[Ie, log (dp) = 2.18]
{Log (100 / R)}]. When dp = 150 μm, R is 100− (23 + 15 + 18 + 25 + 16) = 3 from Table 9. That is, the ratio of particles having a particle size larger than 150 μm is 3%. When R is 150, l
og {log (100 / R)} = 0.18, and this is plotted as (b) in FIG.

Next, each of the iron powders thus obtained was mixed with N
i powder and graphite powder were added in a mixing ratio shown in Table 10 in a high-speed mixer with wings and dry-mixed for 10 minutes, and then a solid binder (10% toluene solution) dissolved in toluene was added to a desired amount of the raw material powder. The mixture was added in the amount to be added and mixed under a wet method, then the solvent was evaporated by heating, and a lubricant (zinc stearate) was further added to obtain mixed powders of the present invention and comparative examples.

For each of the powders thus obtained, the degree of adhesion of Ni to the iron powder was measured, and molding, sintering, machining, and heat treatment were performed in the same manner as in Example 1 to obtain a tensile test and a fatigue test. , And the tensile strength, the range of variation in the tensile strength, and the fatigue strength were measured. The evaluation of these characteristics was performed in the same manner as in Example 1. Table 11 shows the obtained results.

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[Table 9]

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[Table 10]

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[Table 11]

The following can be considered from the results in Table 11. Nos. 1 to 5 are all examples in which the particle size distribution of the iron powder satisfies the preferable requirements of the present invention, and has a good Ni adhesion rate, excellent tensile strength and fatigue strength, and little variation in tensile strength. I understand.

On the other hand, Nos. 6 and 7 are examples in which the median diameter is large / small, and Nos. 8 and 9 are examples in which the distribution index is large / small. Low strength and fatigue strength. Among them, No. 8 has a large distribution index and the particle size distribution of the iron powder is too narrow, so that a sufficiently large density cannot be obtained at the time of molding. No. 9 has a small distribution index and conversely a coarse particle size. Because of the large amount of iron powder, the effect of adding Ni powder was not sufficiently obtained.
The degree of adhesion is small.

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Industrial Applicability The present invention is constituted as described above, and it is possible to efficiently obtain a powder for sintered steel which is excellent in tensile strength and fatigue strength and has little variation in tensile strength.

[Brief description of the drawings]

FIG. 1 is a graph showing a Rosin-Rammler distribution equation represented by equation (2).

FIG. 2 is a graph showing a particle size distribution of iron powders having substantially the same distribution index but different median diameters among iron powders used in Example 2.

FIG. 3 is a graph showing the particle size distribution of iron powder having the same median diameter but different distribution index among the iron powders used in Example 2.

Claims (6)

[Claims] 1. Ni powder having an average particle size of 5 μm or less: 0.2 to 8% (% by weight, the same applies hereinafter); graphite powder: 0.2 to 1.0%; solid binder: 0.05 to 0.1%. 5%, balance: iron powder containing 50% or more in the range of particle diameter of 45 to 150 μm is satisfied, and the degree of adhesion of Ni to the iron powder represented by the following formula (1) is adjusted to 90% or more. A composite powder for high-strength sintered steel, characterized in that: (Equation 1) 2. The iron powder according to claim 1, wherein a distribution index n satisfies 1.5 to 5.0 in a particle size distribution formula of Rosin-Rammler shown in the following formula (2), and R = 50 in the formula (2). Median diameter d
high-strength sintered steel composite powder according to claim 1 p ₅₀ is achieved, thereby satisfying the 50.0～90Myuemu. log {log (100 / R)} = log β '+ nlog (dp) (2) where R is the ratio (%) of particles larger than a certain particle size to the whole, and n is distribution The index, dp, mean the particle size (μm) β ′ = β / In10 (where β is the particle size characteristic coefficient). 3. The composite powder for a high-strength sintered steel according to claim 1, further comprising: Cu: 0.5 to 4% and / or Mo: 0.2 to 5%. 4. Ni powder having an average particle size of 5 μm or less; graphite powder; balance: 50 particles in the range of 45 to 150 μm.
The composite for high-strength sintered steel according to claim 1, wherein a 1 to 16% solvent solution of a solid binder is added to and mixed with a mixed powder composed of iron powder containing at least 1% by weight, and then the solvent is evaporated. A method for producing a composite powder for high-strength sintered steel, which comprises producing a powder. 5. Ni powder having an average particle size of 5 μm or less; graphite powder; balance: 50 to 50 to 150 μm.
% Or more, wherein the distribution index n satisfies 1.5 to 5.0 in the particle size distribution formula of Rosin-Rammler shown in the following formula (2), and R in the formula (2) = Median diameter dp _{50 at 50} = 50.0
To a mixed powder of iron powder satisfying 90 μm, a 1-16% solvent solution of a solid binder is added and mixed.
A method for producing a composite powder for high-strength sintered steel, comprising producing the composite powder for high-strength sintered steel according to claim 2 by evaporating the solvent. log {log (100 / R)} = log β '+ nlog (dp) (2) where R is the ratio (%) of particles larger than a certain particle size to the whole, and n is distribution The index, dp, mean the particle size (μm) β ′ = β / In10 (where β is the particle size characteristic coefficient). 6. The manufacturing method according to claim 4, wherein the composite powder for high-strength sintered steel according to claim 3 is manufactured by using a mixed powder containing Cu and / or Mo. Method for producing composite powder for high-strength sintered steel.