JPH06100902A - Pure iron powder for powder metallurgy manufactured by spraying method using water and method for manufacturing the same - Google Patents

Abstract

PURPOSE:To improve the strength of the sintered part by working the Fe having specified contents of Si, Mn and oxygen into the pure iron powder for powder metallurgy by water atomization. CONSTITUTION:The Fe contg. by weight, <0.08% Si, 0.01-0.3% Mn, <=0.15% oxygen and the balance essentially Fe is water-atomized to produce a pure iron powder for powder metallurgy. The powder is dried in a nitrogen atmosphere contg. <=7.5vol.% oxygen and then reduced in a reducing gas atmosphere. When Cu and graphite are added to the powder and the mixture is sintered, the strength is improved, and high-strength sintered parts are easily designed and produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pure iron-based iron powder for powder metallurgy produced by a spraying method using water and a method for producing 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 system contains some Mn (usually 0.1 to 0.5% by weight) and S
The balance is i, including C, etc., and 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 is usually used by adding and mixing pure iron powder with Cu powder, graphite powder, etc. and compacting in a mold, usually 5.0 to 7.2 g / cm. ^The purpose is to produce sintered parts with a density of ³ . When the pure iron powder is used as compared with the case where the alloy steel powder is used, the strength after sintering does not increase so much, but it is characterized in that the powder compacting is easier and the compacting density can be increased. And pure iron powder, Cu powder,
It is a conventionally used technique to improve the strength of the sintered body by adding graphite powder or the like. Its strength depends on the amount of added Cu powder and graphite powder, and is selected from the required strength characteristics and the cost required for alloying.

[0004]

Problems to be Solved by the Invention Without changing the alloy composition,
In order to further increase the strength of these sintered bodies, the compacting density and the final sintering density can be increased, the sintering temperature can be increased to strengthen the bond between iron powder particles, and There is a method to fully diffuse the However, the molding density at the same molding pressure is limited by the inherent compressibility of iron powder,
Further, there is a problem that an increase in molding pressure causes an increase in ejection force from the mold after molding and a decrease in mold life.

Further, the increase of the sintering temperature causes the installation of a high temperature sintering furnace, the shortening of the life of the sintering furnace body, the increase of the sintering cost, etc., and the economic burden at the time of sintering increases. The purpose of the present invention is to
While having the characteristics of pure iron powder as described above, it is possible to improve the strength of the pure iron powder sintered body without changing the molding and sintering conditions and without newly adding a special alloy component. is there.

[0006]

According to the present invention, the Si content is less than 0.008% by weight, the Mn content is 0.01% by weight or more and 0.30% by weight or less, and the oxygen content is 0.15% by weight or less. And, the balance is pure iron powder for powder metallurgy produced by a spraying method using water, wherein the balance is Fe and unavoidable impurities, and the present invention also has a Si content of less than 0.008% by weight, A water-sprayed raw powder having a Mn content of 0.01% by weight or more and 0.30% by weight or less and the balance being Fe and unavoidable impurities is dried in a nitrogen atmosphere having an oxygen concentration of 7.5% by volume or less and then reduced. It is a method for producing pure iron powder for powder metallurgy, which is produced by a spraying method using water, which is characterized by reducing in a gas atmosphere.

[0007]

The inventors have obtained iron powder having high strength without changing the molding and sintering conditions as described above and without requiring new addition of a special alloy component and having the characteristics of pure iron powder. As a result of diligent research for the purpose of producing, as shown in Table 1, it was found that by reducing the Si content in the iron powder, the strength is sharply improved above a certain graphite addition amount.

[0008]

[Table 1]

Conventionally, it has been known that when an impurity element in iron becomes a non-metallic inclusion, the increase thereof reduces the strength of the sintered body regardless of the amount of C in iron. The effect of reducing the Si content is obtained when the amount of added graphite is equal to or more than that of From this, it was found that the effect of reducing the Si content in the pure iron powder for powder metallurgy is a completely different effect from the effect of reducing the nonmetallic inclusions known in the related art.

Based on this finding, the present inventors have
Made the invention. Next, the reason for defining the components of the steel powder in the present invention will be described. The reason for limiting the Si content to less than 0.008% by weight is that if the Si content is 0.008% by weight or more, a sufficient increase in radial crushing strength cannot be obtained even if the amount of graphite added is increased. . The reason why the Mn content is limited to 0.01% by weight 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 the content thereof is reduced to less than 0.01% by weight. This is because it is relatively difficult and its achievement is not practical because it involves an increase in iron powder production cost.

The reason for limiting the Mn content to 0.30% by weight or less is that although Mn is an element that improves strength,
This is because if it is added in an amount of more than 0.30% by weight, the radial crushing strength cannot be sufficiently increased when the amount of graphite added is increased. The reason for limiting the oxygen content to 0.15 wt% or less is that if it exceeds 0.15 wt%, the radial crushing strength cannot be sufficiently increased when the amount of graphite added is increased.

On the other hand, water having a composition such that the Si content is less than 0.008% by weight, the Mn content is 0.01% by weight or more and 0.30% by weight or less, and the balance is Fe and inevitable impurities is used. The reason for limiting the oxygen concentration in the dry atmosphere to 7.5% by volume or less for the drying conditions of the water-sprayed raw powder, which is the raw material powder produced by the spraying method used, is that if it exceeds 7.5% by volume, annealing is performed. This is because the oxygen content in the subsequent iron powder exceeds 0.15% by weight and the radial crushing strength cannot be sufficiently increased when the amount of graphite added is increased.

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 like hydrogen even at low temperatures, and more economical than Ar. . Drying temperature is 100 ° C or higher, 200
It is sufficient that the temperature is not more than 0 ° C. and the drying time is not less than 30 minutes and not more than 120.

As the reducing conditions, ordinary reducing conditions of pure iron powder are sufficient. Hereinafter, the present invention will be described based on examples.

[0015]

Examples Table 2 shows the chemical composition of pure iron powder used in Examples and Comparative Examples. All iron powders have P and S contents of 0.0
1% by weight, Al is less than 0.01% by weight.

[0016]

[Table 2]

For these iron powders, raw powders obtained by spraying molten steel with water are dried at 140 ° C. for 60 minutes in a nitrogen atmosphere of various oxygen concentrations, and then reduced at 930 ° C. for 20 minutes in a pure hydrogen atmosphere, and then ground and classified. Manufactured. The radial crushing strength was 2% by weight of copper powder, 0.6 and 0.9% by weight of graphite powder, and 1% by weight of zinc stearate as a lubricant. A ring-shaped test piece having an outer diameter of 38 mm, an inner diameter of 25 mm and a height of 10 mm, which was compacted and molded to have a weight of 6.80 g / cm ³ , was sintered at 1130 ° C for 20 min in RX gas having a CO ₂ content of 0.3%. It measured using the tested test piece.

In Examples 1 to 6 according to the present invention, the radial crushing strength when the amount of graphite added was 1.0% by weight was as high as 900 N / mm ² or more, and the radial crushing strength when the amount of graphite added was 0.6% by weight was significantly improved. There is. However, in Comparative Example 1, since the Mn content is 0.35%, which exceeds the specified upper limit, the radial crushing strength when the graphite addition amount is 1% is 700 N / mm ^2, which is much lower than expected.

In Comparative Example 2, O was 0.18%, which exceeds the upper limit of the present invention, so that the radial crushing strength is 820 N / mm ² when the amount of graphite added is 1%, though not as much as in Comparative Example 1. And lower than expected. In Comparative Examples 3 and 4, since the Si content exceeds the upper limit of the present invention, the radial crushing strength when the graphite content is 1% is lower than expected. Furthermore, the amount of graphite added is 0.
The radial crushing strength of 6% by weight is also reduced.

From the above results, it is clear that the water atomized pure iron powder having the composition range specified in the present invention can remarkably increase in strength when the amount of graphite added increases. It is also clear that the drying condition of the water-sprayed raw powder for obtaining the composition within this specified range should be within the specified range.

[0021]

EFFECT OF THE INVENTION The pure iron powder for powder metallurgy of the present invention is different from the conventional pure iron powder for powder metallurgy in that when it is sintered with the addition of Cu and graphite, it has the same molding and sintering conditions and a special alloy. Since the strength is remarkably improved with the same amount of graphite as the amount of added graphite is increased without adding any component, it becomes easy to design and manufacture a high-strength sintered part.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiaki Maeda 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Takeo Omura 1 Kawasaki-cho, Chuo-ku, Chiba Chiba Chiba Steel Works, Ltd.

Claims (2)

[Claims] 1. A Si content of less than 0.008% by weight, Mn
Manufactured by a spraying method using water, which has a content of 0.01% by weight or more and 0.30% by weight or less and an oxygen content of 0.15% by weight or less, and the balance is Fe and inevitable impurities. Pure iron powder for powder metallurgy. 2. Si content less than 0.008% by weight, Mn
Oxygen concentration of water-sprayed raw powder containing 0.01% by weight or more and 0.30% by weight or less and the balance being Fe and inevitable impurities.
A method for producing pure iron powder for powder metallurgy, which is produced by a spraying method using water, which comprises drying in a nitrogen atmosphere of 5% by volume or less and then reducing in a reducing gas atmosphere.