JPH062007A - Pure iron powder for powder metallurgy excellent in compressibility and magnetic characteristic - Google Patents

Abstract

PURPOSE:To obtain a pure iron powder for powder metallurgy capable of producing a high-density and strength sintered part by specifying the impurity element content of the pure iron powder, grain size distribution, grain shape and diameter of the ferrite crystal grain. CONSTITUTION:The pure iron powder for powder metallurgy contains, by weight, <=0.005% C, <=0.010% Si, <=0.050% Mn, <=0.010% P, <=0.010% S, <=0.10% O, <=0.0020% N and the balance Fe. The content of the grains of -60/+80 mesh screened by a screen stipulated in JIS Z8801 is controlled to <=5wt.%, that of grains of -83/+100 mesh to 4-10wt.%, that of grains of -100/+140 mesh to 10-25wt.%, and that of grains of -330 mesh to 10-30wt.%. The average diameter of the coarse crystal grains of -60/+120 mesh measured according to JIS G0052 is controlled to <=6.0, 0.75wt.% of zinc stearate is added as a lubricant, the mixture is compacted in a mold at 5T/cm<2> pressure, and a green compact having >=7.05g/cm<3> density is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a pure iron powder for powder metallurgy which has excellent compressibility and exhibits excellent soft magnetic properties when used in the production of magnetic parts.

[0002]

2. Description of the Related Art The powder metallurgy method is a method in which a powder, which has been adjusted to have a desired grain size by physical crushing or a chemical phenomenon, is compression-molded using a metal mold as a raw material, and then sintered to obtain a product. It is a method for obtaining various products, which are obtained or kneaded with a binder such as a resin and then molded with a mold to obtain products with excellent industrial productivity.

When the powder metallurgical product thus produced is applied to parts requiring strength such as machine structural parts or soft magnetic parts, the product density is one of the factors that have an important influence on these characteristics. Is known to be.

Japanese Patent Publication No. 49-28101, for example, is known as one of iron powders for powder metallurgy used as a raw material for such parts. High-pressure water is made to collide with a falling trickle of molten iron at a predetermined angle. An iron powder for powder metallurgy by a so-called water atomizing method, in which the iron powder is pulverized to obtain an iron powder, and a manufacturing method thereof are disclosed.

[0005]

The iron powder for powder metallurgy disclosed in JP-B-49-28101 has certain characteristics suitable as a raw material for powder metallurgy. However, from the viewpoint of the economical manufacturing process of the sintered parts considering the durability of the molding die, since the compressibility is not yet sufficient, a large amount of voids remain in the product after sintering, Therefore, the mechanical properties of the sintered material are generally inferior to those of the ingot material.

Furthermore, even when pure iron powder is mixed only with a lubricant such as zinc stearate, and the mixture is die-molded and then sintered to produce a so-called sintered soft magnetic part, voids remaining in the product Due to the influence, there is a problem that it is not sufficient as compared with the magnetic characteristics of the ingot made of the same composition.

Conventionally, in order to solve these problems, after molding with a mold, sintering (temporary sintering) is performed at a relatively low temperature of about 600 to 900 ° C., and the temporary sintered body is molded with another mold. The method of performing the second compression and then sintering (main sintering) at a sintering temperature of 1100 ° C to 1250 ° C, that is, the 2P2S method involving two pressing steps and two sintering steps is adopted. To improve the density,
Alternatively, a method has been taken in which an alloy element having a matrix modifying effect is excessively added to obtain a desired characteristic value. However, these methods cannot fully utilize the advantage of the powder metallurgy method that the manufacturing cost is low.

The present invention has been made in view of such circumstances, and an object thereof is to remedy the above problems caused by the drawback of the conventional steel powder for powder metallurgy that the compressibility is not yet sufficient. An object of the present invention is to provide an iron powder for powder metallurgy, which can manufacture a sintered part at low cost and can manufacture a product excellent in compressibility and magnetic properties.

[0009]

From the viewpoint that it is necessary to improve the compressibility of the raw material powder in order to increase the density of the sintered parts, the present inventors (1) pure iron Amount of chemical components in powder (2) Particle size composition and particle shape of pure iron powder (3) Ferrite grain size of iron powder particles was studied. As a result, reduce the impurity elements such as C, Si, Mn, P, S, O, N, etc. For the particle size distribution of iron powder, aim to utilize coarse powder that has a dense and irregular shape. It was found that increasing the grain size is effective for facilitating the compositional deformation of powder particles during molding.

The specific configuration of the present invention is as follows. That is, the impurity content is C ≦ 0.005%, Si ≦ 0.010
%, Mn ≦ 0.050%, P ≦ 0.010%, S ≦ 0.010%, O
≤0.10%, N≤0.0020%, the balance consisting essentially of Fe and unavoidable impurities, and the particle size composition is JIS Z 8801.
Sieving weight ratio (%) using the sieve specified in No. -60 / +
83 mesh is 5% or less, −83 / + 100 mesh is 4% or more and 10% or less, −100 / + 140 mesh is 10% or more and 25% or less, 330 mesh passing amount is 10% or more and 30% or less, −
The average crystal grain size of 60 / + 200 mesh is JIS G 0052
No. 6, which is a coarse crystal grain of 6.0 or less according to the ferrite crystal grain size measuring method specified in No. 1, and which is compounded with 0.75% of zinc stearate as a lubricant for powder metallurgy and molded with a molding pressure of 5 T / cm ^2. It is a pure iron powder for powder metallurgy excellent in compression and magnetic properties, characterized in that a green compact density of 7.05 g / cm ³ or more can be obtained.

[0011]

Now, the reasons for limiting the respective constituents of the present invention will be described. (1) Composition of pure iron powder: Impurity content in iron powder is C ≦ 0.005
%, Si ≦ 0.010%, Mn ≦ 0.050%, P ≦ 0.010%,
The reason why S ≦ 0.010%, O ≦ 0.10%, N ≦ 0.0020% and the balance of Fe and unavoidable impurities are defined is to ensure excellent compressibility, and each element will be described as follows. is there.

Si, Mn: These are added for the purpose of deoxidizing in the production process of pure iron powder, but these elements having a strong affinity for oxygen are oxidized at the time of water atomization and remain in the iron powder as oxidation inclusions, resulting in compressibility. Inhibit. Therefore, when Si and Mn increase, the amount of inclusions also increases, and even in the subsequent reduction step, these oxidized inclusions remain without being reduced and reduce the compressibility. Therefore, it was concluded that it is desirable to reduce Si to 0.010% or less and Mn to 0.050% or less as much as possible.

P, S: If P, S remain during the refining of molten steel, the iron powder particles are hardened and the compressibility is lowered. Also, P,
If the amount of S is large, the particles will not become soft even after the reduction treatment. From these, in order to prevent the hardening of the particles, both P and S were reduced to 0.010% or less as much as possible.

C, O, N: C, O can be reduced by decarburization and deoxidation reaction in the heating and reduction step in a reducing atmosphere, but a large amount of C remains in the iron powder after reduction. Doing so hardens the iron powder particles and significantly reduces the compressibility, so the amount was made as small as 0.005% or less. Further, if the amount of O is large, not only the compressibility is lowered, but also the yield of the graphite powder mixed and used in the powder metallurgy method is lowered, and the variation of the structure is caused.
% Or less. N is also set to 0.0020% or less, which is as small as possible in order to significantly reduce the compressibility. Also these C,
It is desirable that O and N are as small as possible in terms of magnetic characteristics.

(2) Grain size composition: -60 / + 83 mesh 5%
Below, -83 / + 100 mesh 4% to 10%, -100
/ + 140 mesh is defined as 10% or more and 25% or less, and 330 mesh passage amount is defined as 10% or more and 30% or less for the following reasons. It is not preferable to set the upper limit of the size to 60 mesh or less because if the coarse particles that do not pass through the 60 mesh are mixed, the homogeneity of the compression molded product is impaired and the cause of the strength defect is included.

Further, from the results of various experiments of the present invention, the coarse particles show a dense and irregular shape as their characteristics,
It was also found that it is effective in improving the compressibility because it has a large grain size and is soft. -60 / + 83 mesh 5%
The following is effective when the particle size range is for improving the compressibility, but when 5% or more of the particles are mixed, and when chipping or the like occurs at the tip of the molded product, chipping occurs, It is not preferable because it causes a defect in strength and also deteriorates the homogeneity inside the product and causes a defect in strength.

The reason why the -80 / + 100 mesh is 4% or more is that if it is less than 4%, the effect of improving compression cannot be sufficiently obtained, and
The reason why it is set to 10% or less is that the amount of coarse particles becomes too much and causes defects in strength. The same is true for -100 / + 140 mesh. If it is 10% or more, the effect of improving the compressibility is insufficient if it is less than 10%, and if it is 25% or less, the strength defect is caused if too much coarse powder is added. This is because there is a fear of inclusion.

Also, the amount of fine powder passing through -330 mesh is
The reason why the content is set to 10% or more and 30% or less is that if the content is less than 10%, the sinterability is good, and therefore, the fine powder that improves the sintering strength is too small, resulting in deterioration of the strength. The reason why the content is 30% or less is that when the amount of fine powder increases, the compressibility decreases and the purpose of the present invention is not improved.

(3) Ferrite crystal grain size: Regarding the crystal grain size, the larger the crystal grain size, the shorter the grain boundary length per unit area. Therefore, the mean free path of dislocations when a plastic deformation force is applied. In addition to the long length, the deformation resistance due to pile-up of dislocations is small and it is effective for improving the compressibility. Also, in terms of soft magnetic properties, the small number of grain boundaries has an advantageous effect in terms of suppressing the formation of magnetic domains and internal loss. And this characteristic is strongly exhibited in the iron powder of -60 / + 200 mesh. Therefore, the particles having the above particle size range are specifically taken up. And the pure iron powder that satisfies the above characteristics is 5T
The green compact density when molding with a molding pressure of / cm ² is 7.
In order to obtain an excellent magnetic property of 05 g / cm ³ or more, the grain size was determined to be 6.0 or less by the ferrite grain size measuring method defined in JIS (the smaller the number, the larger the grain size).

[0020]

EXAMPLES Examples embodying the present invention will be described below. Compressibility and formability are obtained by compounding 0.75% zinc stearate as a lubricant into the raw iron powder, and molding density with a tablet test piece with a diameter of 11.3 mmφ, which was molded at a molding pressure of 5 T / cm ³ (g
/ cm ³ ). Example 1 The content of impurities in iron powder was C ≦ 0.005%, Si ≦ 0.010
%, Mn ≦ 0.050%, P ≦ 0.010%, S ≦ 0.010%, O
The reasons for defining ≦ 0.10% and N ≦ 0.0020% will be described with reference to Tables 1 and 2.

[0021]

[Table 1]

[0022]

[Table 2]

It is known that any of the impurity elements specified in the present invention deteriorates the compressibility of steel powder. Of these, Si and P are sometimes added in order to improve the soft magnetic properties, but in a very small amount range, the deterioration of the properties of the sintered product due to the deterioration of the compressibility rather than the effect of modifying the matrix. Since it becomes dominant, it is ideally desired to be completely removed like other impurity elements. The compressibility is 0.75% zinc stearate as a lubricant.
The added pure iron powder was evaluated by the green compact density (g / cm ³ ) when it was molded at a molding pressure of 5 T / cm ² using a mold having a diameter of 11.3 mmφ. As shown in the invention examples in the table, the content of impurity elements in pure iron powder is C ≦ 0.005%, Si ≦ 0.010%, Mn ≦ 0.050
%, P ≦ 0.010%, S ≦ 0.010%, O ≦ 0.10%, N ≦ 0.
If it is limited to 0020%, a green compact density of 7.05 g / cm ³ or more could be achieved.

Example 2 A weight ratio (%) of -60 / + 83 mesh of 5% or less of a mesh having a particle size constitution defined in JIS Z 8801 was used.
83 / + 100 mesh 4% to 10%, -100 / + 14
Table 3, Table 4 and Table 5 show the reasons for defining 0 mesh as 10% or more and 25% or less and +330 mesh passing amount as 10% or more and 30% or less.
Will be explained.

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

Tables 3 and 4 show the properties of the reference material, and Table 5 shows the influence on the compressibility when the weight ratio of the steel powder of a specific grain size is changed. M in the table indicates a mesh. The weight ratio between the remaining particle sizes excluding the specific particle size changed here maintains a constant composition ratio. That is, the particle size composition (%) of the basic iron powder is (-60M / + 80M): (-80M / + 100M): (-100M / + 140M): ...: (-330M) = a : B: c: ...: When expressed by g, for example, a weight ratio b of −80 M / + 100 M
When changing, the weight ratio of other particle sizes is Maintain a relationship. The figures below the number of digits shown in the table are truncated.

The influence of the particle size composition on the compressibility is -60 /
The effect of each weight ratio of the coarse powder in the range of +140 mesh and the fine powder of −330 mesh in the total steel powder is remarkable,
It was found that the effect of the weight ratio of the middle part of −140 / + 330 mesh is not clear. More specifically, -60 /
When the particle size in the range of +140 mesh increases, the green density also increases, but when the particle size of -330 mesh increases, the compressibility decreases, and when it exceeds 30%, 7.05g / cm
The green compact density of ³ cannot be achieved. Therefore, the range of particle size composition that can improve the compressibility is -60 / + 83 mesh is 5
% Or less, -83 / + 100 mesh 4% or more and 10% or less,-
100 / + 140 mesh must be 10% or more and 25% or less, and 330 mesh passage must be 10% or more and 30% or less.

Example 3 The effect of the particle size of iron powder on the soft magnetic properties was measured for each particle size. The test piece for magnetic measurement has an outer diameter of 45 mmφ and an inner diameter of 33 mmφ.
The ring-shaped molded body of 1 was manufactured by die molding and was sintered in an ammonia decomposition gas atmosphere at 1180 ° C. for 60 minutes. FIG. 1 shows the maximum magnetic permeability for each grain size. It was found that the coarser the maximum magnetic permeability, the more suitable the properties as a soft magnetic material are expressed, and the fine powder having a mesh size of 200 or less deteriorates the above properties. The reason for this is that the finer the powder, the larger the specific surface area, so the grain boundary length per unit area after sintering is larger than that of the coarse powder, and it is considered that a large number of magnetic domains are formed and loss occurs. To be Therefore, the weight ratio of coarse powder in iron powder, especially -60 / + 200
Increasing the weight ratio of the coarse powder in the range of the mesh is essential for developing good magnetic properties.

Example 4 The average crystal grain size of -60 / + 200 mesh is JIS G 00.
The reasons for defining coarse crystal grains of 6.0 or less by the ferrite crystal grain size measuring method defined in No. 52 will be described with reference to Tables 6 and 7. In the table, compressibility is the compact density (g / cm ³ ) at a molding pressure of 5 T / cm ² , and maximum permeability is the sintered body density of 7.1 g.
The values in / cm ³ are shown.

[0032]

[Table 6]

[0033]

[Table 7]

The influence of the crystal grain size is known as one of the factors affecting the soft magnetic properties, and there is a correlation between the coarsening of the crystal grain size and the improvement of the soft magnetic properties. Example 3
Based on the findings obtained by the above, the relationship between the crystal grain size of the coarse powder and the soft magnetic property in the range of −60 / + 200 mesh was examined, and the average crystal grain size in the range was determined to be ferrite specified in JIS G 0052. Iron powder with coarse grains showing less than or equal to 6.0 according to the grain size measurement method showed significant improvement in maximum permeability.

Embodiment 5 By combining the above-mentioned Embodiments 1 to 4, the compressibility and soft magnetic characteristics can be remarkably improved as compared with the conventional commercially available powder. Tables 8 and 9 show the characteristics of the examples of the present invention and conventional commercial powders.

[0036]

[Table 8]

[0037]

[Table 9]

[0038]

According to the pure iron powder for powder metallurgy having the constitution of the present invention, the following effects can be expected as compared with the conventional iron powder for powder metallurgy. Due to its excellent compressibility, it is possible to achieve high density even with the same mold forming pressure. Therefore, it is inexpensive to manufacture high-strength parts that require complicated steps or addition of excessive alloy elements with conventional iron powder. And it becomes easy. Due to its excellent compressibility, large parts can be manufactured even by using a powder molding press having the same pressurizing ability. By reducing the impurities contained in the pure iron powder and coarsening the grain size composition and the crystal grain size, it becomes easy to manufacture a sintered part exhibiting excellent soft magnetic characteristics.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the density of a sintered body and the maximum magnetic permeability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaaki Sato, 2 Nadahama Higashi-cho, Nada-ku, Kobe City Kobe Steel Works, Ltd. Kobe Steel Works (72) Inei Takaei, No. 2 Nadahama-cho, Nada-ku, Kobe City Kobe Steel, Ltd. Tokoro Steel Works

Claims (1)

[Claims] 1. The impurity content is C ≦ 0.005%, Si ≦
0.010%, Mn ≦ 0.050%, P ≦ 0.010%, S ≦ 0.010
%, O ≦ 0.10%, N ≦ 0.0020%, the balance substantially consisting of Fe and unavoidable impurities, and the particle size composition is JIS Z
Sieving weight ratio (%) using the sieve specified in No. 8801, −
60 / + 83 mesh is 5% or less, −83 / + 100 mesh is 4% or more and 10% or less, −100 / + 140 mesh is 10% or more
25% or less, 330 mesh passing amount is 10% or more and 30% or less, and the average crystal grain size of -60 / + 200 mesh is JIS G
6.0 according to the ferrite grain size measurement method specified in No. 0052
The following coarse grains, 0.75% of zinc stearate was added as a lubricant for powder metallurgy, and a green compact density of 7.05 g / cm ³ or more was obtained when molding with a molding pressure of 5 T / cm ^2. Pure iron powder for powder metallurgy with excellent compressibility and magnetic properties.