JPH05279713A - Pure iron powder for powder metallurgy produced by atomization method using water and its production - Google Patents

Abstract

PURPOSE:To produce the iron powder for iron metallurgy which decreases the width of fluctuations in dimensional change at the time of sintering by pulverizing molten iron of a low Si content and low Mn content by a water atomization method, then drying the powder in an oxygen-contg. gaseous nitrogen atmosphere and, in succession, reducing the powder in a reducing gaseous atmosphere. CONSTITUTION:The molten iron of the compsn. contg., by weight % 0.008 to 0.025% Si, 0.01 to 0.30% Mn and <0.25% O2 and consisting of the balance Fe is pulverized by the water atomization method to produce the iron powder as the raw material for iron metallurgy. This powder is dried in the atmosphere having 2.5 to 7.5vol.% oxygen concn. and consisting the balance the gaseous nitrogen to decrease the width in the fluctuations in the ratio of the Si content constituting the oxide in the Si contained in the iron powder to <=50%. The powder is then subjected to the reduction under heating in the reducing gaseous atmosphere of hydrogen, etc., by which the iron powder for the iron metallurgy having the decreased width in the fluctuations of the dimensional changes of the sintering member at the time of sintering is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron powder for pure iron powder metallurgy manufactured by a spray method using water and a method for manufacturing the same.

[0002]

2. Description of the Related Art Iron powder used for powder metallurgy is roughly classified into two types, pure iron powder type and alloy steel powder type. Pure iron powder composition is a little Mn (usually 0.1 to 0.5% by weight)
And Si, C, etc., and the balance is iron. On the other hand, the alloy steel powder system contains necessary amounts of Ni, Cr, Mo, etc., respectively. The present invention relates to the former pure iron powder system.

The pure iron powder-based powder of the present invention can be used by adding and mixing pure iron powder with Cu powder, graphite powder, etc., compacting in a mold, sintering and then correcting the dimensions as necessary. Sizing is performed to produce a sintered part having a density of usually 5.0 to 7.2 g / cm ³ .

[0004]

[Problems to be Solved by the Invention] However, pure iron powder contains Cu.
A sintered body produced by adding powder, graphite powder or the like has a high strength, and even if sizing is performed for dimensional correction, the sintered body cannot be sufficiently sized because of spring back. Therefore, in order to secure the accuracy of dimensional change without relying on sizing, the Japanese Patent Publication No.
A technique for improving dimensional accuracy from a powder particle size distribution as disclosed in Japanese Patent Publication No. 04-04, and a dimensional change during sintering based on the shape of powder as disclosed in Japanese Patent Application Laid-Open No. 3-142342. Technology etc. are proposed. But,
Iron powder for powder metallurgy has properties such as particle size distribution and shape in the process from powder production to molding by adding lubricants and alloy component powders, mixing operation for homogenizing properties, and transfer operation for replacing containers. Tended to change, and dimensional changes during sintering tended to change.

In view of the above drawbacks of the prior art, it is an object of the present invention to provide a pure iron powder for powder metallurgy with a stable dimensional change during sintering and a method for producing the same, within a range that does not impair the compressibility. It is what The target of variation width of dimensional change is within 0.06%.

[0006]

According to the present invention, the first invention is
Si content is 0.008 to 0.025% by weight, Mn content is 0.01 to 0.30% by weight, and oxygen content is 0.25.
A spraying method using water, characterized in that the balance is less than 50% by weight, the balance is Fe and unavoidable impurities, and the variation width of the ratio of the amount of Si in the contained Si is 50% or less. According to the second invention, the Si content is 0.008 to 0.025% by weight, the Mn content is 0.01 to 0.30% by weight, and the balance is Fe. And water spray raw iron powder, which is an unavoidable impurity, are dried in a nitrogen atmosphere with an oxygen concentration of 2.5 to 7.5% by volume and contain S
In the method for producing pure iron powder for powder metallurgy, the variation width of the ratio of Si, which is an oxide of i, is set to 50% or less and then reduction is performed in a reducing gas atmosphere.

[0007]

The reason why the composition of the iron powder is limited in the present invention will be described below. The inventors of the present invention obtained a trace element in pure iron powder and a dimensional change during sintering for the purpose of reducing variation in dimensional change during sintering so that sufficient dimensional accuracy can be obtained without depending on sizing. As a result of diligent research on the relationship with the variation, the following findings shown in Table 1 were obtained.

[0008]

[Table 1]

Table 1 shows the Si content and (a) the variation width of the ratio of oxidized Si to the contained Si, (b)
The relationship between the variation width of the dimensional change during sintering and (c) the green compact density is shown. From the results in Table 1, from the viewpoint of stability of dimensional change during sintering, the Si content is 0.008% by weight or more,
From the viewpoint of compressibility, it is derived that the Si content is preferably 0.025% by weight or less.

The materials used for the sintering dimensional change test were all pure iron powders having various Si contents and the dew point of the reducing atmosphere of water atomized iron powders being 10 to 60 ° C. which is usually used. 2% by weight of Cu powder, 0.8% by weight of graphite powder and 1% by weight of zinc stearate as a lubricant, and mixed, and compacted to a density of 6.9 g / cm ^3. Is. Sintering was performed at 1130 ° C. for 20 minutes in RX gas having a CO ₂ content of 0.3%. Variations in dimensional changes are 60 mm outer diameter, 25 mm inner diameter, and 10 mm height.
It is the result of measuring the variation width of the dimensional change at the time of sintering based on the green compact of the outer diameter of 100 ring-shaped test pieces. Further, 1% by weight of zinc stearate, which is a lubricant, was added to and mixed with pure iron powder having the same green compact density, and the molding pressure was 5 t.
/ Cm ² and is molded.

By the way, from Table 1, the Si content is 0.0
When it is 04%, the ratio of oxidized Si contained is 5
% To 100%, and the variation width is 100-5 = 95%, but the Si content is 0.016.
When%, the variation width is 45-35 = 10%.
At this time, the variation width of the dimensional change before and after sintering is 0.60% in the former, while it is significantly reduced to 0.06% in the latter.

As described above, it was found that the variation width of the dimensional change at the time of sintering varies corresponding to the variation width of the ratio of the amount of Si which is an oxide in the Si contained in the iron powder. The reason why the variation width of the ratio of the amount of Si that is an oxide in the contained Si is limited to 50% or less is that when it exceeds 50%, the variation width of the dimensional change during sintering is not reduced to 0.06% or less. Because.

Si content 0.008% by weight or more 0.0
The reason for limiting the content to 25% by weight or less is that the Si content is 0.0
If it is less than 08% by weight, the effect of reducing the variation width of the dimensional change during sintering cannot be obtained, and if it exceeds 0.025% by weight,
This is because the compressibility drops sharply. If the Mn content is 0.
The reason for limiting the content to 01 wt% or more is that Mn is an element that can enter as an impurity element in the usual industrial manufacturing process of iron powder, and it is relatively difficult to reduce the content thereof to less than 0.01 wt%. This is because the achievement is not practical because it involves a considerable increase in iron powder manufacturing cost. The reason for limiting the Mn content to 0.30% by weight or less is that Mn is an element that improves the strength, but when it is added in excess of 0.30% by weight, it becomes an oxide in the Si content. S
This is because the variation width of the sintering dimension change is not reduced to 0.06% or less even if the variation width of the ratio of i is 50% or less.

The reason why the oxygen content is limited to 0.25% by weight or less is that, when the oxygen content exceeds 0.25% by weight, the variation range of the Si content as an oxide in the Si content is 5%.
Even if it is 0% or less, the variation width of the sintering dimension change is 0.06%
This is because it is not reduced below. In the second invention,
The reason for limiting the oxygen concentration in the dry atmosphere to 2.5% by volume or more and 7.5% by volume or less is that, as shown in Comparative Example 4 in Table 4, when the content of Si is less than 2.5% by volume, This is because the lower limit of the ratio of the amount of Si, which is an oxide, decreases, and as a result, the variation width does not become 50% or less, and the variation width of the sintering dimensional change is not reduced to 0.06% or less. Four
As shown in Comparative Example 3 of No. 3, when the content exceeds 7.5% by volume, Si
This is because even if the variation width of the ratio of the amount of Si that is an oxide in the content is 50% or less, the variation width of the sintering dimension change is not reduced to 0.06% or less.

The nitrogen atmosphere is used as the dry atmosphere because it is easy to control the oxygen concentration in the atmosphere, there is no danger of explosion such as hydrogen even at low temperature, and more economical than Ar. .. Drying temperature, time is 100 ℃ or more 20
It is sufficient if the temperature is 0 ° C. or lower for 30 minutes or more and 120 minutes or less.

As the reducing condition, the ordinary reducing condition of pure iron powder is sufficient. Examples of the present invention will be described below.

[0017]

Example 1 Pure iron powder having a Si content of the present invention of 0.008 to 0.025 wt% and a Si content of a comparative example of 0.008 wt%
The variation in dimensional change during sintering of less than and more than 0.025% by weight of pure iron powder was compared.

The variation in the dimensional change during sintering was obtained by adding 1.5% by weight of Cu powder, 0.5% by weight of graphite powder, and 1% by weight of zinc stearate as a lubricant to pure iron powder. , A ring-shaped test piece having an outer diameter of 60 mm, an inner diameter of 25 mm, and a height of 10 mm, and 100 pieces of the test piece compacted so that the compact density was 6.9 g / cm ³ , the compact standard of the contour The change in the sintered dimension was measured and compared.
Sintered at 1130 ° C in RX gas with CO ₂ content of 0.3%
X 20 minutes.

Table 2 shows the results of measuring the variation in the sintering dimension change based on the green compact. As can be seen from this, although stable sizing dimensional changes were obtained in the examples, the dimensional changes during sintering became large in the comparative examples due to the inappropriate Si content.

[0020]

[Table 2]

Example 2 Pure iron powder having a Si content of 0.008 to 0.025% by weight of the present invention and a Si content of Comparative Example of 0.008% by weight.
The variation in dimensional change during sintering of less than and more than 0.025% by weight of pure iron powder was compared. The variation in dimensional change during sintering was as follows: pure iron powder, Cu powder 2.0% by weight, graphite powder 0.8% by weight, and zinc stearate 1% by weight as a lubricant were mixed. 60 mm, inner diameter 25 mm,
A ring-shaped test piece with a height of 10 mm and a green density of 6.9 g
For 100 test pieces that were compacted to give a powder / cm ³ , the change in the sintering dimension of the outer shape of the compact was measured and compared. Sintering is 1250 ° C x 20 in AX gas
I went for a minute.

Table 3 shows the results of measuring the variation in the sintering dimension change based on the green compact. As can be seen from this, although stable sizing dimensional changes were obtained in the examples, the dimensional changes during sintering became large in the comparative examples due to the inappropriate Si content.

[0023]

[Table 3]

Example 3 Table 4 shows the chemical composition of pure iron powder used in Examples and Comparative Examples. The content of P and S in each iron powder is 0.01% by weight,
Al is less than 0.01% by weight. These iron powders were produced by drying raw steel powder sprayed with molten steel in various nitrogen atmospheres at 140 ° C. for 60 minutes, reducing it in a pure hydrogen atmosphere at 930 ° C. for 20 minutes, and then pulverizing and classifying.

[0025]

[Table 4]

The variation of the sintering dimensional change was obtained by adding 1.5% by weight of copper powder, 0.5% by weight of graphite powder, and 1% by weight of zinc stearate as a lubricant to the iron powder, Using the mixed powder, 10 ring-shaped test pieces each having a density of 6.9 g / cm ³ , an outer diameter of 60 mm, an inner diameter of 25 mm, and a height of 10 mm were used.
Obtained by molding 0 pieces, sintering at 1130 ° C. for 20 min in propane metamorphic gas with a CO ₂ content of 0.3%, and measuring the variation width of the sintering dimension change of the outer diameter based on the green compact. It was

The green compact density was obtained by adding and mixing 1% by weight of zinc stearate, which is a lubricant, to these pure iron powders and molding them at a pressure of 5 t / cm ³ . The variation width of the proportion of Si that is an oxide in the Si content was calculated from the fluctuation width of each proportion by analyzing the total Si content and the SiO ₂ content in the reduced iron powder 10 times. ..

In Examples 1 to 7 according to the present invention, the variation width of the proportion of Si which is an oxide in the Si content is 50% or less, and represents the dimensional accuracy after the dimensional change correction by the conventional sizing. An excellent range of variation in sintering dimensional change of 0.06% or less of the lower limit was obtained together with high compressibility. However, in the comparative example, Si which is an oxide
Since the amount ratio or Si, Mn, 0, or the dry atmosphere was insufficient, only 0.5% or more of the inferior sintering dimensional change variation or low compressibility was obtained.

[0029]

EFFECTS OF THE INVENTION The pure iron powder for powder metallurgy of the present invention has less variation in dimensional change after sintering when sintered with addition of Cu and graphite, as compared with the conventional pure iron powder for powder metallurgy. Since excellent dimensional accuracy equal to or higher than that after the sizing step can be obtained, it becomes possible to manufacture a sintered body with high dimensional accuracy without adding the sizing step.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takeo Omura Inventor 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside the Chiba Works, Kawasaki Steel Co., Ltd. (72) Yoshiaki Maeda 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Works Co., Ltd. Chiba Works (72) Minor Nitta Minoru Nitta 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Yutaka Yoshii 1 Kawasaki-cho, Chuo-ku, Chiba Address Kawasaki Iron & Steel Co., Ltd. Technical Research Headquarters (72) Inventor Hiroshi Otsubo 1 Kawasaki-cho, Chuo-ku, Chiba City Chiba Prefecture Kawasaki Steel & Co. Technical Research Headquarters

Claims (2)

[Claims] 1. A Si content of 0.008 to 0.025% by weight, a Mn content of 0.01 to 0.30% by weight, an oxygen content of 0.25% by weight or less, and a balance of Fe and unavoidable. Which is a static impurity and is an oxide of the contained Si
Pure iron powder for powder metallurgy produced by a spraying method using water, characterized in that the variation width of the amount of i is 50% or less. 2. The Si content is 0.008 to 0.025.
%, Mn content is 0.01 to 0.30% by weight, and the balance is F
e and water spray raw iron powder which is an unavoidable impurity are dried in a nitrogen atmosphere having an oxygen concentration of 2.5 to 7.5% by volume to contain S.
A method for producing a pure iron powder for powder metallurgy, which comprises setting the variation width of the amount of Si, which is an oxide of i, to 50% or less, and then reducing in a reducing gas atmosphere.