JPH0633101A - Production of high-strength alloy steel powder for powder metallurgy - Google Patents

Abstract

PURPOSE:To obtain the steel powder for powder metallurgy having high compressibility and high strength by separately mixing iron powder and respective fine particulate powders of Cu, Ni and Mo, subjecting the respective powders to a diffusion treatment at respectively specific temps. to disintegrate the grains thereof, then mixing the powders so as to have specified components. CONSTITUTION:The fine powders of the respective metals Cu, Ni and Mo are separately mixed with the iron powder or only the Cu is separated and is mixed with the iron powder. The powder mixture is subjected to the diffusion treatment at 700 to 850 deg.C in the case of mixing of the Cu and the iron powder, is subjected to the diffusion treatment at 850 to 950 deg.C in the case of mixing of the Mo and the iron powder, is subjected to the diffusion treatment at 900 to 1000 deg.C in the case of mixing of the Mo and the iron powder and is subjected to the diffusion treatment at 900 to 950 deg.C in the case of mixing of the Ni and the Mo and the iron powder, by which the Cu, the Ni and the Mo are respectively stuck to the iron power surface. After the powder mixture is disintegrated, the powders are so mixed as to have the specified component compounding. The powders are preferably so mixed that the compsn. of the alloy steel powder after the mixing contains 1 to 2% Cu, 2 to 8% Ni and 0.5 to 1.0% Mo.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing alloy steel powder for powder metallurgy having high compressibility and high strength, which is used for manufacturing various sintered machine parts such as gears and bearing parts.
The alloy steel powder produced according to the present invention is formed into a desired shape, then sintered, and then processed into various parts by HIP (hot isostatic pressing) or the like.

[0002]

2. Description of the Related Art The powder metallurgy method is a method in which conventional manufacturing processes such as rolling, forging, casting, etc. are largely rewritten, and a metal powder as a raw material is compression molded and then sintered to obtain a product. Therefore, according to the powder metallurgy method, it is difficult to manufacture by a conventional melting method such as high melting point metal materials such as W and Mo, porous materials such as oil-impregnated bearings and filters, cemented carbide and cermet. Can be manufactured. Not only that,
There are various advantages that can not be obtained with ingot materials such as improvement in material yield due to non-cutting, advantages in manufacturing such as high dimensional accuracy, and advantages in material aspects such as segregation and anisotropy that are less likely to occur in ingot materials. Due to its advantages, various members conventionally manufactured by the melting method are replaced with the powder metallurgy method and manufactured.

In recent years, there has been an increasing demand for higher strength of these sintered parts, and various high-strength sintered members have been developed by methods such as alloying and densification in response to this request. Is coming.

The premix method and the prealloy method are known as typical methods for obtaining a high-strength sintered member by the powder metallurgy method. In the premix method, pure iron powder is used as a main raw material, and fine powders for alloys such as Ni, Cu, Mo, etc. are mixed with the powder, and the powder is compacted and heated and sintered to solidify the alloy elements during sintering. It is a method of melting. However, this premix method has a drawback that the iron powder and the fine powder for alloy are separated and segregated due to the difference in specific gravity in the stage until compaction molding, or the diffusion of the alloy powder during sintering does not proceed sufficiently. ,
As a result, there is a quality problem that variations in strength and dimensions occur.

On the other hand, the pre-alloy method uses alloy steel powder in which alloy elements such as Ni, Cu, Mo, etc. are dissolved in Fe in advance, and the problem of nonuniform structure as in the premix method is solved. I can do it now. However, in this method, the alloy steel powder is much harder than pure Fe,
Compressibility at the time of compacting is reduced, and a high-density sintered member cannot be obtained. As a result, there arises a problem that a sintered member having sufficient strength cannot be obtained.

Therefore, as another method for solving the above problems and obtaining a sintered member having high density and high strength, for example, Japanese Patent Publication No.
As disclosed in Japanese Patent Application Laid-Open No. 5-9649 and Japanese Patent Application Laid-Open No. 63-297502, a so-called diffusion adhesion method has been proposed, in which other metal or alloy powder is diffusely adhered to iron powder. According to this method, the compressibility is hardly reduced, and the problem of uneven strength and dimensional accuracy due to segregation can be prevented to some extent.

[0007]

In the conventional diffusion deposition method as described above, iron powder is mixed with metal powder of Ni, Cu, Mo or the like, or alloy powder of these metals, and then in a reducing gas atmosphere. By heating at a temperature in the range of 700 to 1000 ° C., Ni, Cu, Mo, etc. are diffused and adhered to the iron powder surface. However, in this method, since Cu has a relatively low melting point (1083 ° C.), diffusion into the iron powder proceeds too much, and the compressibility of the alloy steel powder obtained is decreased because the entire iron powder is hardened. On the contrary, since Ni and Mo have high melting points (Ni: 1453 ° C, Mo: 2610 ° C), they diffuse slowly into the iron powder and are dissociated from the iron powder or peeled off in the disintegration step after the diffusion treatment. As a result, segregation and reduction in strength are caused. In addition, high-temperature sintering for a long time is required for sufficient diffusion.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for inexpensively and efficiently producing a steel powder for powder metallurgy having high compressibility and high strength. Is what you are trying to do.

[0009]

The present invention, which has been able to solve the above-mentioned problems, provides a method for producing alloy steel powder in which fine metal powders of Cu, Ni and Mo are diffused and adhered to the surface of iron powder.
After mixing the fine metal powders of Cu, Ni, and Mo separately, or separately with Cu, and mixing with the iron powder, each is subjected to diffusion treatment at the following diffusion treatment temperature, and after pulverization, the predetermined components are blended. It has the gist to mix so that. Diffusion treatment temperature; When Cu and iron powder are mixed: 700 to 850 ° C. When Ni and iron powder are mixed: 850 to 950 ° C. When Mo and iron powder are mixed: 900 to 1000 ° C. Ni and Mo are iron powder When mixed: 900-950 ° C

[0010]

The composition of the pure iron powder used as the mother powder in the present invention is
C: 0.01% (wt%, the same applies hereinafter), Si: 0.
02% or less, Mn: 0.10% or less, P: 0.010%
Hereinafter, S: 0.010% or less, O: 0.15% or less, and the balance Fe and inevitable impurities are preferable. This is to ensure excellent compressibility.

Si, Mn: A small amount of Si or Mn is added in order to deoxidize molten steel in the process of producing pure iron powder. However, when the amount of the element having a strong affinity with O is large, the production is performed. It is oxidized in the process and becomes an oxidation inclusion, which remains in the iron powder and impairs compressibility. Therefore, it is desirable that Si is 0.02% or less and Mn is 0.10% or less.

P, S: If P, S remain during the refining of molten steel, the iron powder particles are hardened and the compressibility is lowered. When the amount of P and S is large, the particles do not become soft even after the reduction treatment. In order to prevent the iron powder particles from hardening, P,
S is preferably 0.010% or less.

C, O: This C, O can be reduced by decarburization and deoxidation in the reducing step of heating in a reducing atmosphere, but a large amount of C is contained in the iron powder after reduction. When it remains in C, the compressibility is remarkably reduced, so that C
Is preferably 0.01% or less. Further, if O is large, not only the compressibility is lowered, but also the yield of the graphite powder mixed and used in the usual powder metallurgy is lowered, and further it causes the variation of the structure, so O is 0.15. % Or less is preferable.

Next, elemental elements for alloys added to iron powder or alloys thereof in the present invention will be described. That is, Ni
Has the effect of improving toughness and hardenability, and Mo enhances hardenability and prevents softening during quenching and tempering. Also Cu
Has the effect of improving the strength or hardness of the sintered member. However, when these elemental elements for alloys are simultaneously solid-dissolved in iron powder, the diffusion rate differs due to the difference in melting point of each element, resulting in non-uniform structure, and high strength alloy steel powder is obtained. Absent.

Therefore, in the present invention, each alloying element is mixed with iron powder separately or only with Cu, and each is subjected to diffusion treatment at an optimum temperature to be disintegrated, and then mixed so as to have a predetermined composition. I decided.

Cu alone is mixed with iron powder to obtain 700-85
By performing the diffusion treatment in the temperature range of 0 ° C., excessive diffusion of Cu into the iron powder particles is suppressed, and the hardness of the alloy steel powder does not become too high, so that the compressibility is improved. If the diffusion treatment temperature is lower than 700 ° C., Cu does not sufficiently diffuse and adhere, causing peeling in the disintegration step and causing segregation. On the other hand, if the temperature exceeds 850 ° C., the diffusion of Cu into the iron powder proceeds too much, resulting in a decrease in compressibility.

In addition, Ni and Mo are mixed with iron powder separately or together, and when Ni alone is used, 850 to 950.
C., diffusion treatment is performed in the temperature range of 900 to 1000.degree. C. for Mo alone and 900 to 950.degree. C. for Ni + Mo.

In the case of Ni, if the diffusion treatment temperature is lower than 850 ° C., diffusion adhesion becomes insufficient, which causes peeling in the disintegration step, resulting in segregation and reduction in strength. On the other hand, if the temperature exceeds 950 ° C., the diffusion of Ni into the iron powder proceeds too much and the compressibility decreases. In the case of Mo, when the diffusion treatment temperature is lower than 900 ° C., diffusion adhesion becomes insufficient, which causes separation in the disintegration step and causes segregation and strength reduction. If it exceeds 1000 ° C, M
O spreads too much and the compressibility decreases, and the sintering of iron powders also progresses, making it difficult to disintegrate. Further, when Ni and Mo are mixed together, it is necessary to satisfy the diffusion treatment temperature conditions of both elements, so it is necessary to perform the diffusion treatment within the range of 900 to 950 ° C.

The Cu diffusion-adhered steel powder and Ni thus obtained
The high-strength powder metallurgical steel powder is obtained by mixing the diffusion-adhesion steel powder and the Mo diffusion-adhesion steel powder or the Ni + Mo diffusion-adhesion steel powder after the granulation so as to have a predetermined composition.

The particle size of the Cu, Ni and Mo powders used in the present invention is not particularly limited, but the maximum particle size is preferably 45 μm or less and the average particle size is preferably 15 μm or less. This is because when the average particle diameter is 20 μm or more, alloying during sintering is deteriorated, a uniform structure cannot be obtained, and variations in strength, hardness and the like are likely to occur.

The amounts of Cu, Ni and Mo added to the iron powder may be appropriately determined according to the intended composition of the alloy steel powder. In addition, Cu diffusion adhesion steel powder, Ni diffusion adhesion steel powder, M
o The mixing ratio of the diffusion-adhesion steel powder or the Ni + Mo diffusion-adhesion steel powder may be appropriately determined in consideration of the required characteristics of the final product, etc., but the composition of the alloy steel powder after mixing is 1 to Cu.
It is desirable to mix 2%, Ni 2 to 8%, and Mo 0.5 to 1.0%. In this case, Ni is 2%
When it is less than 8%, the strength is insufficient, while when it exceeds 8%, the strength deteriorates due to an increase in retained austenite. Mo
If less than 0.5%, the effect of improving hardenability cannot be obtained, and
If it exceeds 0%, the toughness decreases. When Cu is less than 1%, sufficient strength cannot be obtained, and when it exceeds 2%, the dimensional accuracy during sintering deteriorates.

[0022]

The present invention will be described in more detail with reference to the following examples, but the following examples do not limit the present invention.
Modifications and implementations without departing from the spirit of the above and below are all included in the technical scope of the present invention.

Example 1 Cu, Ni and Mo simple substance powders were used as high purity pure iron powders (C: 0.01% or less, Si: Si:
0.02% or less, Mn: 0.10% or less, P: 0.01
% Or less, S: 0.01% or less, O: 0.15% or less and mixed with the balance Fe and unavoidable impurities), and then mixed with AX gas (7
In a 5% H ₂ + 25% N ₂ ) atmosphere, diffusion treatment was performed for 30 minutes at each temperature shown in Table 1 to disintegrate.

[0024]

[Table 1]

As shown in Table 2, the disintegrated steel powder contained 4% N
i-1.5% Cu-0.5% Mo were mixed so as to have an alloy composition to obtain steel powders 1 and 2 of the present invention.

[0026]

[Table 2]

Steel powders 1 and 2 and steel powder L as a comparative example were used as test materials, and 0.6% graphite powder and 0.75 were added to steel powder (various).
% Zinc stearate powder was added and mixed in a V-type mixer for 30 minutes, and this mixed powder was used in a mold to obtain 6 tons /
The powder was compacted at a cm ² to obtain a compact having a size of 10 × 10 × 50 mm. The molded body was heated at 1120 ° C. × 3 in an AX gas atmosphere.
Sintered for 0 minutes. A tensile test piece having a parallel portion 6Φ was cut out from this sintered body, and the tensile strength was measured. The above measurement results are shown in Table 3 and FIG.

[0028]

[Table 3]

As is clear from Table 3 and FIG. 1, Cu,
The compressibility of Ni and Mo improves as the diffusion treatment temperature decreases, but the diffusion adhesiveness decreases, so that the content of Ni and Mo in the steel powder decreases due to peeling or the like. On the contrary, when the diffusion processing temperature becomes high, the compressibility is lowered. Therefore, the steel powders 1 and 2 that have been subjected to the diffusion treatment at the optimum diffusion treatment temperature of each element and then mixed have higher compressibility and higher tensile strength than the steel powder L that has undergone the diffusion treatment of all alloy powders at once. . Further, it can be seen that the steel powders 1 and 2 of the examples of the present invention have little component loss in the diffusion and disintegration steps of Ni and Mo.

[0030]

The present invention is configured as described above,
According to the manufacturing method of the present invention, highly compressible and high-strength steel powder for powder metallurgy can be provided inexpensively and efficiently.

[Brief description of drawings]

FIG. 1 is a graph showing the tensile strength of sintered bodies using the steel powders of the present invention and comparative examples.

Claims (1)

[Claims] 1. In the production of an alloy steel powder in which fine metal powders of Cu, Ni and Mo are diffused and adhered to the surface of iron powder, C
After mixing the fine metal powders of u, Ni, Mo separately or only Cu and mixing with the iron powder, diffusion treatment is performed at the following diffusion treatment temperature, and after the disintegration, predetermined components are blended. A method for producing a high-strength alloy steel powder for powder metallurgy, comprising: Diffusion treatment temperature; When Cu and iron powder are mixed: 700 to 850 ° C. When Ni and iron powder are mixed: 850 to 950 ° C. When Mo and iron powder are mixed: 900 to 1000 ° C. Ni and Mo are iron powder When mixed: 900-950 ° C