JPH09287002A - Mixed powder for powder metallurgy - Google Patents

Abstract

(57) Abstract: An Fe-Cu-based or Fe-Cu-C-based mixed powder for powder metallurgy is proposed, which can produce a sintered part with small dimensional fluctuation and high dimensional accuracy. SOLUTION: This is an Fe-Cu-based or Fe-Cu-C-based powder metallurgical mixed powder obtained by mixing iron-based powder, copper powder, and further graphite powder, and the Pb content in the copper powder is 0.05 wt. By using the copper powder limited to not more than%, the dimensional fluctuation during sintering can be reduced. The composition of the mixed powder consists of copper powder: 0.1 to 5 wt% or further graphite powder: 2 wt% or less and the balance iron-based powder, and the iron-based powder is preferably one in which the copper powder is diffused and adhered to the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder mixture for powder metallurgy used for the production of machine parts and the like, and more particularly to a raw material mixture powder suitable for the production of sintered parts having excellent dimensional stability.

[0002]

2. Description of the Related Art In the manufacture of machine structural parts and the like, it is required to reduce the amount of finishing cutting as much as possible and process the final part shape to improve productivity. For that purpose, dimensional stability is important from the molded body formed from powder to the component material that has undergone sintering and heat treatment. In particular, it is the most important point to improve the dimensional stability of parts by making the dimensional change during sintering close to zero.

In iron-based sintered materials, Cu is the most common alloying element from the viewpoint of excellent mechanical properties and high economic efficiency.
Is used. However, it is known that the Fe-Cu system undergoes significant expansion called "copper expansion phenomenon" during sintering. This "copper expansion phenomenon" is an expansion phenomenon that occurs when the copper powder contained in the mixed powder is melted during sintering and infiltrates and diffuses into the gaps between the surrounding iron particles.

When C is added to the Fe-Cu system, it has a certain expansion suppressing effect in the range where the amount of Cu is small.
Although many C-based sintered materials have been used, when the amount of Cu is large, the dimensional change cannot be suppressed. Several attempts have been made in the past to suppress dimensional changes during sintering. For example, Japanese Patent Laid-Open No. 56-20142 discloses an iron-based sintered alloy containing B in an amount of 0.03 wt% or more so as to suppress the copper expansion phenomenon due to melting of copper during sintering. A method for producing a copper-based high-density sintered alloy has been proposed. Further, in Japanese Patent Laid-Open No. 55-2791, by containing 0.15 to 1.0 wt% of P in Fe-Cu system powder or Fe-Cu-C system powder, expansion due to melting of copper during sintering is suppressed. However, it is disclosed that good dimensional accuracy can be obtained. Further, in JP-A-59-123740, Fe-Cu-P is disclosed.
-A method for manufacturing C-based sintered alloy members is shown, and as a raw material powder
It is disclosed that the use of Cu-P alloy powder causes generation of Cu-P liquid phase little by little and reduces the dimensional change of the sintered body.

Further, JP-A-53-92306 and JP-A-53-1
Japanese Patent No. 28513 and Japanese Patent Laid-Open No. 1-290702 disclose that copper is segregated and adhered to the surface of iron powder to prevent copper segregation and to produce a sintered part having excellent dimensional accuracy. ing. However, even with the above-mentioned technique, it is not possible to sufficiently suppress the dimensional change during sintering of the Fe-Cu-based or Fe-Cu-C-based sintered mechanical parts, and it is possible to correct the sizing or the like when manufacturing high-precision mechanical parts. It was essential.

[0006]

[Problems to be Solved by the Invention] Fe-Cu system or Fe-
The Cu-C-based raw material mixed powder undergoes expansion and contraction behavior intricately entangled with solid-phase diffusion of Cu and C into Fe, melting of Cu, phase transformation of Fe, etc. during sintering, resulting in a sintered body. Results in complex dimensional changes.
An object of the present invention is to solve the above problems advantageously and to propose a powder mixture for powder metallurgy capable of producing a sintered part having a small dimensional variation.

[0007]

Means for Solving the Problems The present inventor has
Occurring in Fe-Cu-based or Fe-Cu-C-based raw material mixed powder,
The factors that influence such expansion and contraction behavior have been thoroughly studied. The expansion behavior of the Fe-Cu-based or Fe-Cu-C-based raw material mixed powder during sintering is that the copper powder contained in the mixed powder melts and rapidly infiltrates into the gaps between the surrounding iron particles. It is an expansion phenomenon caused by diffusion. Since it is a phenomenon between the copper liquid phase and the iron solid phase, it is considered that the trace elements in the copper liquid phase and the trace elements present in the iron solid phase have a great influence, and especially the trace elements contained in the copper powder. As a result of investigating the influence of Pb, it was found that a small amount of Pb contained in the copper powder used in the mixed powder had a great influence on the dimensional variation of the sintered body. First, the experiment on which the present invention is based will be described.

Atomized iron-based powders A, B, and C having slightly different apparent densities, Mn, and Si contents were prepared by adding 2.0 wt% of copper powder having different Pb contents and 0.8 wt% of graphite powder to zinc stearate. After mixing with 0.75 wt% and molding, sintering was performed at 1130 ° C for 20 min in a reducing atmosphere. The outer diameter dimension after sintering was measured, the rate of change with respect to the outer diameter dimension of the molding die was determined, and the result is shown in FIG.

From FIG. 1, when the Pb content in the copper powder exceeds 0.05 wt%, the dimensional change rate becomes large, and further, the difference in the dimensional change rate among the iron-based powders A, B and C becomes large. I understand. That is, by setting the Pb content in the copper powder to be 0.05 wt% or less, it is possible to suppress the dimensional change rate and the variation in the dimensional change due to the difference in the iron-based powder brand and lot.

The present invention is based on the above findings. That is, the present invention is a raw material mixed powder for producing sintered parts, which is prepared by mixing iron-based powder and copper powder or further graphite powder, wherein the copper powder has a Pb content of 0.05 wt% or less. The mixed powder for powder metallurgy is preferably characterized in that the mixed powder is composed of copper powder: 0.1 to 5 wt% or further graphite powder: 2 wt% or less, and the balance iron-based powder,
Furthermore, it is preferable that the iron-based powder is obtained by diffusing and adhering a part or all of the copper powder on the surface.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, iron-based powder and copper powder or further graphite powder are blended as a raw material mixed powder for producing sintered parts. In the present invention, the Pb content contained in the copper powder to be blended is limited to 0.05 wt% or less. Pb content in copper powder is 0.05
By setting it to wt% or less, it is within the allowable range of dimensional change during sintering of the mixed powder compact (preferably 0.40% or less)
Can be In addition, variations in dimensional changes during sintering of mixed powder compacts due to variations in iron-based powders mixed in mixed powders, for example, variations in trace elements due to differences in brand of iron-based powders, lots, etc. can be tolerated. It can be within the range. When the Pb content in the copper powder exceeds 0.05 wt%, the melting point is lowered, the surface tension of the copper liquid phase is lowered, the wettability to the iron particle surface is increased, and copper expansion is promoted. Therefore, it is considered that the dimensional change becomes large. Also,
It is presumed that the reduction of Pb contained in the copper powder reduces the influence of various factors on the wettability of the copper liquid phase to the iron particles. Therefore, the Pb content in the copper powder is 0.05 wt% or less.

The blending amount of copper powder in the mixed powder is 0.1 to 5% by weight.
It is preferable that The copper powder mixed into the mixed powder becomes a liquid phase during sintering, diffuses into the iron powder, and has the effect of increasing the strength of the sintered part and preventing sintering shrinkage. If the content of the copper powder in the mixed powder is less than 0.1 wt%, the effect is not recognized, and if it exceeds 5 wt%, the dimensional change during sintering becomes large, and the dimensional accuracy of the sintered part deteriorates. Therefore, the blending amount of the copper powder is set in the range of 0.1 to 5 wt%.

The blending amount of the graphite powder in the mixed powder is preferably 2 wt% or less. The graphite powder can be easily diffused into the iron powder during sintering and alloyed to increase the strength of the sintered body. When graphite powder is added in excess of 2 wt%, the dimensional accuracy of the sintered body deteriorates. The graphite powder is preferably flaky natural graphite powder.

As the iron-based powder used in the present invention, any of reduced iron powder, atomized iron powder, electrolytic iron powder and the like can be suitably applied and it is not particularly limited, but atomized iron powder capable of containing an alloying element is preferred. Is. Further, in the present invention, an iron-based powder in which a part or all of the copper powder is preliminarily diffused and adhered to the surface of the iron powder particles is preferable from the viewpoint of preventing Cu segregation and reducing variation in dimensional change. The diffusion and adhesion of the copper powder on the surface of the iron powder particles can be achieved by mixing the iron-based powder and the copper powder and heat-treating them in a reducing atmosphere. The diffusive adhesion amount of copper powder on the surface of iron powder particles is 0.1
Effective over the entire range of ~ 5%.

In addition, a lubricant and a machinability improving substance may be added to the mixed powder. As the lubricant, zinc stearate, wax and the like are suitable. It is preferable that the raw material mixed powder having the above-mentioned composition is formed into a compact having a predetermined size by compression molding and sintered in a non-oxidizing atmosphere.

[0016]

【Example】

(Example 1) 0.013 wt% S with grain size # 80 or less
Iron-based powder (A) with an apparent density of 2.98 containing 0.17 wt% Mn, 0.020 wt% Si, iron-based powder with an apparent density of 2.79 containing 0.25 wt% Mn (B) and 0.025 wt% Si, 0.22 wt % Mn
Containing 3 types of atomized iron powder (C) with an apparent density of 2.68, copper powder having a particle size of # 200 or less and a Pb content of 0.002 to 0.10 wt%, or even 0.8 to 2.
After mixing 3 wt% of natural graphite powder with 0.75 wt% of zinc stearate at the ratio shown in Table 1, a mixed powder was prepared.
It was formed into a ring shape of φ35 × φ14 × 10 mm by pressing. The molding density of the molded body was 6.85 g / cm ³ . These compacts were sintered in an RX gas atmosphere with a CO ₂ concentration of 0.3 vol%. After sintering, the outer diameter dimension of the sintered body was measured, and the rate of change with respect to the outer diameter dimension of the molding die and the standard deviation of the outer diameter dimension change rate were calculated. Table 1 shows the measurement results of the change rate of the outer diameter dimension.

[0017]

[Table 1]

In the sample Nos. 1 to 6 of the present invention example, the change rate of the outer diameter dimension is low, and even if the iron-based powders having different contents of Mn, Si, etc. are used, the change rate of the outer diameter dimension is changed. Is few. Also, the standard deviation of the dimensional change rate between the same mixed test pieces is small. On the other hand, specimens with high Pb content in copper powder No. 10, 12, 12, 15
In the comparative example, the outer diameter dimensional change rate is large and the standard deviation is also large. Further, the outer diameter dimensional change rate varies depending on the type of iron-based powder. In addition, a sample No. 1 in which the amount of copper powder or the amount of graphite powder is outside the scope of the present invention
Also in Comparative Examples 1 and 13, the outer diameter dimensional change rate is large, and the standard deviation of the outer diameter dimensional change rate is also large.

(Example 2) Particle size of # 80 mesh or less,
Atomized iron powder containing 0.013 wt% Si, 0.17 wt% Mn and copper powder containing 0.03 wt% Pb with a grain size of # 250 mesh or less (2 wt%) were mixed and heat treated in a reducing atmosphere.
Copper powder was diffused and adhered to the iron powder surface. The iron-based powder with the copper powder diffused and adhered to the surface had a particle size of # 250 mesh or less.
Copper powder containing 03wt% Pb 1.0wt%, graphite powder
1.0 wt% was mixed to obtain a raw material mixed powder. This raw material mixed powder was formed into a ring shape of φ35 × φ14 × 10 mm by a press. The molding density of the molded body was 6.85 g / cm ³ . These compacts were sintered in an RX gas atmosphere with a CO ₂ concentration of 0.3 vol%. After sintering, the outer diameter of the sintered body was measured, and the rate of change of the outer diameter of the molding die was calculated. As a result, the change rate of the outer diameter was 0.25%, which was very low.

[0020]

According to the present invention, dimensional fluctuations during sintering can be effectively suppressed, and it becomes possible to manufacture a sintered machine part having a high degree of dimensional accuracy without correction such as sizing.・ Economic efficiency is greatly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the dimensional change rate and the Pb content in copper powder.

Claims (3)

[Claims] 1. A raw material mixed powder for producing a sintered part, which comprises a mixture of iron-based powder and copper powder or graphite powder, wherein the copper powder is a copper powder having a Pb content of 0.05 wt% or less. A powder mixture for powder metallurgy, characterized by being present. 2. The mixed powder for powder metallurgy according to claim 1, wherein the mixed powder comprises copper powder: 0.1 to 5 wt% or further graphite powder 2 wt% or less and the balance iron-based powder. 3. The mixed powder for powder metallurgy according to claim 1 or 2, wherein the iron-based powder is obtained by diffusing and adhering a part or all of the copper powder on the surface.