JPH0297602A - Composite alloy steel powder and sintered alloy steel - Google Patents

Abstract

PURPOSE:To obtain composite alloy steel powder for powder metallurgy of a high density and high strength sintered alloy steel by partially diffusing and sticking the alloy component as powder state on surface of iron powder particles and specifying the composition composed of Ni, Mo and Fe. CONSTITUTION:In the composite alloy steel powder partially dispersing and sticking the alloy component as the powder state on the surface of iron powder particles, the above alloy composition is composed of 0.50-3.50wt.% Ni, 0.65-3.50% Mo and if necessary, a part or the whole of the above Mo is displaced to the prescribed quantity of W and the balance of Fe with inevitable impurities. Further, the contents of Ni and Mo having <=45mum particle size in the above steel powder is made in the range of 2.0-4.2 times of the average content of the whole steel powder. After sintering by using the composite alloy steel powder for powder metallurgy having the above composition, quenching and tempering are executed and high strength sintered alloy having >=7.0g/cm<3> density and >=130kgf/mm<2> tensile strength can be obtd.

Description

Detailed Description of the Invention [Industrial Application Fields] This invention relates to alloy steel powder used in the production of sintered parts by powder metallurgy, and high-strength sintered alloy steel used after heat treatment after sintering. It is related to.

[Background technology J Iron-based sintered materials are widely used in automobile parts.

Recently, efforts have been made to reduce the weight of these parts, and there is a demand for increased strength.

It is a well-known technique to use various alloyed steel powders to increase the strength of sintered parts. These high strength sintered parts are
Completely uniform alloyed steel powder, which is often required to have a high density, makes the steel powder particles hard, so composite alloy steel is made by partially diffusing and adhering alloying element powder to the surface of the iron powder particles. Efforts have been made to improve the compressibility of steel powder as a powder.

However, even in a method using such a composite alloy steel powder, if the alloy composition, manufacturing method, and usage method are not appropriate, sufficient sintered body properties cannot be expected.

JP-A-61-231102 attempts to increase the strength of a sintered material by increasing the alloy composition. However, since it has a high alloy composition containing 7% or more Ni, it is not only expensive, but also has high hardness in the sintered state, making sizing and cutting impossible. This increases the amount of austenite, and in order to achieve a high tensile strength of 130 kg f/mm2 or more, special heat treatment such as sub-zero treatment is required, which causes many problems, such as increasing costs.

In addition, residual austenite decomposes over time and
Another problem is that it causes changes over time such as deformation of parts.

Japanese Patent Publication No. 45-9649 discloses a low-alloy steel powder that exhibits little dimensional change during heat treatment after forming and provides a high-strength sintered body. This low alloy steel powder contains iron powder and Ni,
It is obtained by heating a mixture of Mo and Cu compounds to allow the alloy components to diffuse and adhere, pulverizing the aggregated particles, and further annealing.However,
This low alloy steel powder has a CI-1 of 0.50 to 2. OOm
This is not preferable because Cu is polarized at grain boundaries and forms an ε-Cu embrittlement layer, deteriorating mechanical properties.

Keita, one of the present inventors, has proposed a composition of composite alloy steel powder that is particularly suitable for use as sintered without any subsequent heat treatment (Japanese Patent Application Laid-Open No. 6''1-89601). >.

This alloy steel powder contains Nig and/or OLl and ~10, and has an alloy composition that provides high sintered body hardness and dimensional stability during sintering. However, the tensile strength of the sintered body is 1
30kgf/mm'-L or more cannot be achieved.

Furthermore, one of the present inventors has discovered that two or more types of alloy components are diffused and adhered to the surface of the steel powder, and that the content of each alloy component in the particle size of 44 g m or less is the average content of the entire steel powder. has proposed a composite alloy steel powder in the range of 0.9 to 1.9 times (Japanese Unexamined Patent Publication No. 130401/1983). However, the sintered body manufactured using this alloy steel powder does not undergo strain-induced transformation from austenite to martenite during tension, and has insufficient compressibility and density, resulting in a bow tensile strength of 130 kg+'/m. It is impossible to achieve more than Go.

Sintered parts subjected to carburizing and quenching have high toughness inside the part, and the surface is hard and has high wear resistance and scratch resistance.
-V also has high fatigue strength. Therefore, it has the highest practical value as a high-strength part such as Southeast.
It is difficult to obtain high strength above 0 kgf/mm'' toss.

One of the problems is that the sintered body has pores.

The carburizing behavior is different from normal steel materials, making it difficult to obtain an appropriate carbon concentration distribution. Therefore, the strength becomes less than 1-min. 1: In order to solve this problem, an attempt was made to sufficiently increase the density of the sintered body and then carburize it. Sintered steel is one of them, and is a high-strength material.

However, this method requires special equipment and is often costly due to the short lifespan of the mold used for hot-working steel foil.
Application is limited.

On the other hand, cold preparation or coining of sintered bodies! 7.: Above 7.6~7.8 g/c rr? Attempts were also made to obtain high-strength materials by increasing the
4''; Publication), this method has the advantage of not requiring hot processing equipment, but it requires a high density of 7.6 g/cn3 or more.Secondly, it requires high pressure during cold processing or coining. The problem is that there is a need to apply pressure, and Kim's J4 life is short.

Furthermore, in sintered parts that undergo heat treatment, there are many examples of high strength being obtained by increasing the alloy and density. However, the tensile strength of the heat-treated sintered body disclosed in JP-A-62-146203 is less than 120 kgf/mrrI'', and cannot satisfy the demand for higher strength.

In Maj-1 JP-A-54-50409, the density is 7, 6
A technique for producing a sintered heat-treated material with a tensile strength of 160 kgf/mm'' has been disclosed.
The impact value is 2.5 kg f-m/cm" or less.
The toughness is low. Recently, there has been an increasing demand for higher strength of sintered parts, and as a result, the use of heat treatment after sintering has become increasingly important. In this case, the sintered body becomes extremely hard after heat treatment, making it difficult to correct the dimensions by cutting or sizing.

Therefore, since we will add about 1 of these before heat treatment, we will make cutting and sizing as easy as possible.
It is necessary to keep the hardness and therefore the strength of the sintered body low before heat treatment, and increase the strength (product hardness) through subsequent heat treatment.

For conventional composite alloy steel powders, the specifications suitable for these conditions have not been sufficiently studied, and the appearance of alloy steel powders with new specifications has been awaited.

The object of the present invention is to obtain a composite alloy for powder metallurgy to obtain a sintered alloy steel with a relatively low alloy composition and high strength and high toughness without requiring a high alloy composition or special equipment. Our objective is to provide steel powder and heat-treated sintered steel. This makes it possible to facilitate the cutting or sizing of the sintered body before heat treatment, and to simultaneously realize the contradictory techniques of obtaining a sintered body with high strength and high toughness after the sintering treatment.

Disclosure of the Invention 1 As a result of intensive research into increasing the strength and toughness of a sintered body, the present inventors have found that both the composition of the steel powder used and the density of the sintered body can increase the strength and toughness of the sintered body. It has been found that this has a significant effect on increasing toughness.

The focus of the present inventors is to optimize the composition of Ni-Mo composite alloy steel powder when carburizing and quenching is performed subsequent to sintering. Sunawa.

Carburizing and quenching is a method of quenching low carbon sintered steel without diffusing carbon. Therefore, in order to give machinability and sizing properties before heat treatment, a composition is selected as a low carbon alloy steel, and its composition is It may be any material as long as it provides the desired strength in a state containing carbon after heat treatment.

According to the findings of the present inventors, in a state where carbon does not coexist, the sintered body becomes harder than Mo or Ni. On the other hand, Mo contributes more than Ni to the increase in strength after carburizing, so the composition of the existing Ni-Mo composite alloy steel powder (M
It was thought that extremely good results could be obtained by using Mo more frequently than Ni (including the case where o was replaced with W).

The relationship between the strength and toughness and the composition and density of the sintered body obtained by the present inventors will be described.

The content of Ni and Mo, respectively, (X) 0.58%Ni-3, 21%M.

(Yl, 07%Ni-3,42%Mo (Z) 1.09%Ni-0.6%M.

Graphite and a lubricant (zinc stearate) were added to this composite alloy steel powder, which was pre-sintered, and then recompressed by changing the compacting pressure to change the density.

Thereafter, main sintering (1250°C x 30 minutes, in ammonia decomposition gas) was performed, oil quenching (870°C x 60 minutes, heating in inert gas), and tempering at tSO°C x 60 minutes. The relationship between the density, tensile strength, and Charpy impact value of these sintered bodies is shown in Figures 1 and 2. 6 Density 7.0 g/c
Above (X) if tn' or more.

It can be seen that the sintered body of (Y) has a tensile strength of 130 kgf/mm' or more and high toughness.6 Furthermore, when the density is increased to 7.3 g/c try' or more, the tensile strength is 150 kgf/mm2. You can do more than that.

The present invention is constructed based on the above findings. That is, the present invention.

(1) A composite alloy steel powder in which an alloying component is partially diffused and attached to the surface of iron powder particles in powder form, and N as an alloying component.
i and at least one of Mo or W,
The alloy composition is: Ni: 0.50 to 3.50% by weight Mo + 1/2 W: 0.65 to 3.50
In terms of weight%, the balance consists of Fe and unavoidable impurities, and the content of Ni and Mo + 1 / 2 W in the particle size of 45 μm or less of the steel powder is 2.0% of the average content of the entire steel powder, respectively. Composite alloy steel powder for powder metallurgy 6 (2) Final product characterized by being in the range of ~4.2 times Ni and at least one of Mo or W as alloy components. : 0.50 to 3.50% by weight Mo + 1/2 W : 0.65 to 3.50
i amount%, the balance consists of Fe, C and unavoidable impurities, the density is 7.0 g/crd or more, and the tensile strength after carburizing, quenching and tempering is 130 kgf/mm2 or more. Strength sintered alloy steel.

(3) C, Ni, and M as final product alloy components.

or W: C: 0.3 to 0.8 wt% Ni: 0.50 to 3.50 wt% Mo + 1/2 W: 0.65 to 3 .50
Weight%, the balance consists of Fe and unavoidable impurities, the density is 7.0 g/cn3 or more, and the tensile strength after quenching and tempering is 13. A high-strength, high-toughness sintered alloy steel characterized by having a sintered alloy steel having a sintered alloy steel having a sintered alloy steel having a sintered alloy with a high strength and a high toughness.

(4) A sintered alloy steel manufactured using the composite alloy steel powder according to invention (1), which contains Ni and at least one of Mo or W as a final product alloy component, and has an alloy composition. Ni: 0.50 to 3.50% by weight Mo + 1/2 W: 0.65 to 3.50
Weight%, the balance consists of Fe, CG and unavoidable impurities, and the density is 7.0 g/crry' or more, and the tensile strength after carburizing, quenching and tempering is 130 kgf/mtti.
A high-strength sintered alloy steel characterized by having more than '.

(5) A sintered alloy steel manufactured using the composite alloy steel powder according to invention (1), wherein the final product alloy components include C and N.
i and at least one of Mo or W,
The alloy composition is: C: 0.3 to 0.8 wt% Ni: 0.50 to 3.50 wt% Mo + 1/2 W: 0.65 to 3.50
A high-strength, high-toughness sintered material having a density of 7.0 g/c- or more and a tensile strength of 130 kgf/mrrf' or more after quenching and tempering, with the remainder consisting of Fe and unavoidable impurities in weight%. Combined metal steel.

It is.

In the present invention, composite alloy steel powder refers to steel powder in which alloying elements such as Ni, Mo, and W are partially diffused and adhered to the surface of iron powder particles.

The significance of the above numerical limitation will be explained.

Ni: 0.50 to 3.50% by weight Ni is dissolved in the Fe base to strengthen the sintered body and is useful for improving toughness. If it is less than 0.50% by weight, it is not possible to obtain high strength due to solid solution strengthening and hardenability improvement, and the effect of improving matrix toughness. On the other hand, 3.50% by weight
If it exceeds this, excessive austenite phase will be generated, resulting in a decrease in strength.

Mo: 0.65-3.50% by weight Mo solidly dissolves in the Fe base, strengthens the sintered body, and
In addition to forming carbides to improve strength and hardness, it is also highly effective in increasing hardenability.

If it is less than 0.65% by weight, high strength due to solid solution strengthening and hardenability improvement cannot be obtained. On the other hand, 3.50% by weight
Exceeding this will impede toughness. Note that M o '4 is 0
．． High strength can be obtained at 65mM% or more, but at 0.85if
When it is f1% or more, high strength of the negative layer can be achieved, which is preferable.

Above, we have mentioned Ni and Mo as the basic alloy components, but in 6 cases where part or all of Mo can be replaced with twice the weight of W, doubling the amount of W is ,
This is because the effect of W on the change in properties of sintered steel is equal to the effect of its 172 weight Mo.

C: 0.3 to 0.8% by weight C is an inexpensive reinforcing element, but if the amount of C in the heat-treated sintered body is 0.
．． If it is less than 3% by weight, the tensile strength I300kgf/mrr
A high strength higher than r' cannot be obtained. If it is contained in a large amount, it will form carbides, reduce strength and toughness, and cause austenite formation, so Cffi of the heat-treated sintered body should be set to 0.3
The range was 0.8% by weight. The results obtained by the present inventors regarding the influence of Cff1 will be described below.

For composite alloy steel powder with Ni and Mo in the above range, graphite is added in varying amounts so that the product C content is 0.1 to 1.0% by weight, and 1% by weight of zinc stearate is added as a lubricant. was added to produce a mixed powder. These steel powders were molded and sintered, then oil quenched (870° C. for 30 minutes) and then tempered at 180° C. for 60 minutes to produce heat-treated sintered steel, which was then subjected to a tensile test and a Charpy impact test. The results are shown in FIGS. 3 and 4. High strength and high toughness can be obtained when the CM content is in the range of 0.3 to 0.8% by weight.

Depending on the intended use of the part, C may be added by mixing graphite phase with alloy steel powder during sintering, or may be added by carburizing and quenching after sintering.

In the case of carburizing and quenching, a distribution of C content occurs in the cross section of the part, but the C content does not necessarily have to be within the above range in the entire cross section, and it is sufficient that it is satisfied in the carburized part.

In order to obtain a sintered product with high density, the raw material alloy steel powder must have high compressibility.

For this purpose, a so-called composite alloy steel powder in which Ni, Mo and/or W are diffused and adhered to the surface of iron powder particles is suitable. Completely homogeneous Brialloy steel powder generally has low compressibility and is disadvantageous for high density production.

With a mixed powder of ordinary iron powder, Ni powder, Mo powder, and/or W powder, the diffusion of alloying elements during sintering is insufficient, and the increase in strength is insufficient. Even if it is a composite alloy steel powder, if the degree of diffusion alloying is low.

The strength of the sintered body is still insufficient. In order to see the progress of diffusion alloying, the content of Ni or Mo + 1/2 W in one alloy steel powder with a particle size of 45 um or less was compared to the average content of Ni or Mo + 1/2 W in the entire steel powder. Find out how many times each is.

This is used as an index as the "degree of diffusion segregation."

When the degree of diffusion segregation for Ni and Mo+1/2W each exceeds 4.2, the strength and compressibility of the heat-treated sintered body decrease. Moreover, as mentioned above, the degree of diffusion segregation is 2.
Even if it is less than 0, compressibility is insufficient and furthermore, austenite does not undergo strain-induced transformation into martensite, resulting in insufficient tensile strength.

Therefore, the range of the degree of diffusion segregation is set to 2.0 to 4.2.

This is achieved by adjusting the particle size of the iron powder and alloy components and the temperature at which they are heated.

The composite alloy steel powder composition is adapted to the composition of the sintered body, and Ni
is 0.50 to 3.50% by weight, Mo+l/2W is 0.6
5 to 3.50% by weight, the remainder being Fe and unavoidable impurities.

What is the acceptable range of impurities?

C: within 0-03% by weight, preferably within 0.01% by weight Si: O, within 1% by weight, preferably within 0.05% by weight Mn: within 0.4% by weight, preferably 0.15% by weight Cr: within 0.3 wt% Cu: within 0.3 wt% Aβ: within 0.1 wt% P: within 0.02 wt% S: within 0.02 wt% 0: within 0.25 wt% , preferably within 0.15% by weight N: within 0.01% by weight, preferably within 0.002% by weight Among the above elements, Mn, Cr, etc., if within the allowable range, rather improve the strength. It is not always a good idea to lower the value unnecessarily.

In addition, to ensure the strength of the sintered body, the particle size of the composite alloy steel powder is
It is preferable that the weight proportion of particles with a particle size of 180 μm or more is within 10%.

Next, heat treatment will be explained. To obtain high strength, heat treatment is performed after sintering.

For heat treatment, carburizing, quenching, and tempering are used when high hardness is desired near the surface. If uniform strength is desired, carbon is added to the composite alloy steel powder using graphite powder during sintering, and the steel is subjected to normal quenching and tempering treatment.

This heat treatment turns one structure into tempered martensite, resulting in high strength and high toughness steel. Quenching temperature is 800~
The temperature is preferably 930°C, and if it is less than 800°C, a uniform austenite structure will not be formed during heating, resulting in a decrease in strength and toughness.

In addition, when the temperature exceeds 930℃, austenite becomes coarse,
Strength and toughness decrease.

The tempering temperature is preferably 100 to 250°C; if it is less than 100°C, the toughness is low (and if it exceeds 250°C, the strength is reduced). The molding and sintering may be repeated one or more times to improve the density.

That is, a recompression method such as molding-sintering-coining (sizing) or molding-preliminary sintering-coining (sizing)-main sintering is useful.

[BEST MODE FOR CARRYING OUT THE INVENTION 1 Examples 1 to 3, Comparative Examples 1 to 3 First, examples and comparative examples will be shown regarding the production of composite alloy steel powder as a raw material.

First, add -325 to the atomized pure iron powder of -80 mesh.
A predetermined amount of mesh nickel oxide powder and -325 mesh molybdenum dioxide powder were mixed and heated to 800°C in hydrogen gas.
was heated for 120 minutes to reduce nickel oxide and molybdenum trioxide to obtain a composite alloy steel powder in which Ni and Mo were diffused and adhered around iron powder particles.

In order to investigate the influence of "diffusion segregation degree", the above pure iron powder was
- A predetermined amount of metallic Ni powder and metallic Mo powder of 325 mesh were mixed, and the heating temperature in hydrogen gas was set to 700 °C and 75 °C.
By changing the temperature to 0℃, 800℃, 850℃, 1050℃,
Composite alloy steel powder was produced.

The composition of this composite alloy steel powder is: Ni: 2.10-2.18% by weight Mo: 1.12-1.23% by weight, and in addition, C: 0.002% by weight, 5ilo-04% by weight, Mn : 0.07% by weight Cu: 0.01% by weight P: 0.006% by weight S: 0.006% by weight 0: 0.07-0.13% by weight N: 0.0007-0.0019% by weight It contained. Moreover, the content of particle size of 180 μm or more in each steel powder was 0.9 to 2.5% by weight.

To these alloy steel powders, 0.9% by weight of zinc stearate was added as a lubricant, molded with a pressure cuff t/crn'', pre-sintered in hydrogen gas at 900°C for 30 minutes, and
After coining at t/crn'', main sintering was performed in hydrogen gas at 1250°C for 90 minutes, resulting in a density of 7.28-7.
A sintered body weighing 51 g/crn' was obtained.

This was carburized with a carbon potential of 0.8% by weight at 900°C for 6.5 hours, immediately oil quenched, and heated to 120°C at 180°C.
Tempered for a minute. The strength was measured using a tensile test piece with a parallel portion of 5 mmφ. The results are summarized in Table 1.

As seen in Table 1, the degree of diffusion segregation is between 2.0 and 4.2.
If it is within the range of , the strength is high.

Examples 4 to 16, Comparative Examples 4 to 6 Nickel oxide and molybdenum dioxide were blended with atomized pure iron powder to produce Ni and M as shown in Table 2.

And/or 15 types of composite alloy steel powders having different amounts of W were prepared. The heating temperature during the production of alloy steel powder was 800°C.

Furthermore, alloy steel powder containing Ni%Mo and Cu was produced at a heating temperature of 850°C (Comparative Example 6). Alloy steel powder 180
The content of particles coarser than gm is 0.5 to 3.0.
It was within the range of % by weight. The sintering, carburizing and quenching and tempering conditions were the same as in Examples 1-3. The test results are summarized in Table 2.

As shown in Table 2, if the chemical composition is within the range of Ni: 0.50 to 3.50% by weight and Mo: 0.65 to 3.50% by weight and the degree of diffusion segregation is appropriate, the weight of 130 kg
It exhibited a tensile strength of f/mm3 or more. Especially Mo is 085
More than % by weight showed more favorable results.

Examples 17 to 24, Comparative Example 7 Here, Examples and Comparative Examples will be shown regarding the relationship between sintered density and tensile strength.

As the alloy steel powder, the 2.15% Ni used in Example 1 was used.
-1,18% Mo composite alloy steel powder was used.

To this alloy steel powder, 0.9% by weight of zinc stearate was added with or without graphite powder, and primary molding (normal molding) was performed at a predetermined pressure. Primary sintering (preliminary sintering or normal sintering) is performed at a temperature of The next sintering (main sintering) was performed at 1300°C in H2 gas.
Carburizing, quenching and tempering were carried out under the same conditions as in Example 1, and the tensile strength was measured. The results are summarized in Table 3.

In this way, if the density is 7.0 g/crn" or more, the tensile strength is 130 kgf/mrn", which is 7.3 g/crn".
cm'' or more, even higher strength was obtained.

Examples 25 to 31, Comparative Examples 8 to 14 Composite alloy steel powders were prepared according to the following procedure. As raw iron powder,
Water atomized pure iron powder was used. Particle size is 180 mesh.
The chemical composition is C: 0.002% by weight Si: 0.03% by weight Mn: 0.04% by weight Cu: O, 01% by weight P: 0.005% by weight S: 0.007% by weight 0:0.086 Weight % N: 0.0008 weight %. As alloy raw materials, carbonyl nickel powder is used for Ni, and molybdenum dioxide (M
oOa ), W is tungsten trioxide (WO
3) was used. All alloy component raw materials were 1325 mesh.

Iron powder and alloy component raw materials are uniformly mixed so as to have a predetermined composition shown later, and heated in a hydrogen gas atmosphere at 850°C for 60 minutes to partially diffuse and adhere the alloy element powder to the iron powder particles. Thereafter, it was crushed to obtain composite alloy steel powder. To these alloy steel powders, 1% by weight of zinc stearate was added and molded at a molding pressure of 6 t/crrr in the entire mold. Subsequently, sintering was performed at 1250° C. for 60 minutes in an ammonia decomposition gas atmosphere to obtain a sintered body. The tensile strength of these sintered bodies was determined as an indicator of workability before heat treatment.

Next, the sintered body was heat treated. This was carburized for 200 minutes at 880° C. with a carbon potential of 0.85% and quenched in oil. Thereafter, tempering was performed at 180° C. for 60 minutes. Tensile strength was determined as an index of strength after heat treatment.

The composition of the composite alloy steel powder prepared is summarized in Table 4.
Examples 25 to 31 and Comparative Examples 8 to 13 selected compositions in and around the composition range of the present invention, and Comparative Example 14
is the conventional standard composite alloy steel powder composition.

Table 5 shows the results of testing these steel powders.

Compressibility is 7.05 at a molding pressure of 6 t/c rn”
The density of the high-Mo, low-Ni composition of the present invention after heat treatment is desired as a steel powder for high-density sintered bodies having a density of about 107 to 12 g/crn' at a compacting pressure of 6 t/crn'.
It showed a tensile strength of 6 kgf/mrn'. Further, if the tensile strength of the sintered body before heat treatment is within about 40 kg f/m, cutting and sizing can be performed without difficulty.

In both Examples A-E and Comparative Example F-, 1325 mesh Ni layer and Mo oxide layer (Mo
Oa) was mixed with -80 mesh Fe powder at a predetermined ratio, and after reduction annealing at 1000° C. for 1 hour in a hydrogen gas atmosphere, it was crushed to produce a composite alloy steel powder. The chemical composition and degree of diffusion segregation at this time are shown in Table 6 together with comparative examples.

0.75% by weight of graphite powder and 1% by weight of zinc stearate as a lubricant were added to these steel powders to produce 7 t/w.
It was molded at a pressure of cr'.

Next, it was sintered at 850°C for 30 minutes in an ammonia decomposition gas atmosphere, and recompression molded at a pressure of 7t/crn'.

Thereafter, it was sintered at 1250° C. for 30 minutes in an ammonia decomposition gas atmosphere. Further, it was subjected to oil quenching by heating at 870°C for 60 minutes in an inert gas, followed by quenching and tempering by heating at 180°C for 60 minutes in an oil bath and cooling in air, and subjected to a tensile test and a Charpy impact test. The experimental results of the chemical composition, density, tensile strength and impact value of the sintered bodies are shown in Table 7.

150 kgf at the chemical composition and density within the range of the present invention
/mm2 or more tensile strength and 4kgf-m/cr
It can be seen that the Charpy impact value is n' or more.

Examples LP, Comparative Examples Q~■ 0.75% by weight of graphite powder and 1% by weight of zinc stearate as a lubricant were added to the composite alloy steel powder shown in Table 6, and 7 t/c was added. Molded at a pressure of rn', 1250℃
The sample was sintered for 30 minutes in an ammonia decomposition gas atmosphere. Further, it was subjected to a quenching and tempering treatment by heating at 870°C for 60 minutes in an inert gas bath, followed by heating at 180°C for 60 minutes in an oil bath and cooling in air, and subjected to a tensile test and a Charpy impact test.

The experimental results are shown in Table 8. Tensile strength of 130 kgf/mm2 or more and 3.5 k within the chemical composition range of the present invention
It shows a Charpy impact value of g f -m/cm' or more.

Chemical composition of composite alloy steel powder [Industrial applicability] As is clear from the above explanation, the heat-treated sintered steel of the present invention has extremely high strength and toughness. Useful for required sintered parts. The alloy steel powder according to the present invention meets the future trend of increasing the strength of sintered parts, and can be used when both high density and workability are required.
This indicates extremely high aptitude. Therefore, it is thought that it will be easier to manufacture mechanical parts with higher loads and complicated shapes by powder metallurgy than ever before, and great effects can be expected.

[Brief explanation of drawings]

Figure 1 is a graph explaining the relationship between density and tensile strength for the composition of the heat-treated sintered body obtained by the present inventors, and Figure 2 is the density and Charpy impact value for the same composition of the sintered body as in Figure 1. Figure 3 is a graph explaining the relationship between C content and tensile strength of a heat-treated sintered body whose Ni and Mo contents are within the range of the present invention. It is a graph explaining the relationship between the amount of C and the Charpy impact value of the same sintered compact as the figure.

Claims (1)

[Claims] 1. In a composite alloy steel powder in which an alloy component is partially diffused and adhered to the surface of iron powder particles in powder form, Ni as an alloy component
and Mo, the alloy composition is Ni: 0.50 to 3.50% by weight, Mo: 0.65 to 3.50% by weight, the balance is Fe and unavoidable impurities, and the steel powder has a diameter of 45 μm or less. The content of Ni and Mo in the particle size of is 2.0 to 4 of the average content of the whole steel powder, respectively.
．． Composite alloy steel powder for powder metallurgy, characterized in that it is in a double range. 2. The final product contains Ni and Mo as alloy components, and the alloy composition is Ni: 0.50 to 3.50% by weight, Mo: 0.65 to 3.50% by weight, and the balance is Fe, C, and unavoidable impurities. A high-strength sintered alloy steel having a density of 7.0 g/cm^3 or more and a tensile strength after quenching and tempering of 130 kgf/mm^2 or more. 3. Contains C, Ni and Mo as final product alloy components,
The alloy composition is C: 0.3 to 0.8% by weight, Ni: 0.50 to 3.50% by weight, Mo: 0.65 to 3.50% by weight, with the balance consisting of Fe and unavoidable impurities, and the density is A high-strength, high-toughness sintered alloy steel characterized by having a tensile strength of 7.0 g/cm^3 or more and a tensile strength after quenching and tempering of 130 kgf/mm^3 or more. 4. A sintered alloy steel manufactured using the composite alloy steel powder according to claim 1, which contains Ni and M as the final product alloy components.
o, the alloy composition is Ni: 0.50 to 3.50% by weight, Mo: 0.65 to 3.50% by weight, the balance consists of Fe, C and unavoidable impurities, and the density is 7.0g/ A high-strength sintered alloy steel having a tensile strength of 130 kgf/mm^3 or more after carburizing, quenching and tempering at cm^3 or more. 5. A sintered alloy steel manufactured using the composite alloy steel powder according to claim 1, which contains C and Ni as the final product alloy components.
and Mo, and the alloy composition is C: 0.3 to 0.8% by weight, Ni: 0.50 to 3.50% by weight, Mo: 0.65 to 3.50% by weight, and the balance is Fe and unavoidable impurities. A high-strength, high-toughness sintered alloy steel, characterized in that it has a density of 7.0 g/cm^2 or more and a tensile strength of 130 kgf/mm^2 or more after quenching and tempering. 6. Composite alloy steel powder in which alloy components are partially diffused and attached to the surface of iron powder particles in the form of powder, which contains Ni, Mo and W as alloy components, and has an alloy composition of Ni: 0.50 to 3.50. Weight% Mo + 1/2W: 0.65 to 3.50% by weight, the balance consisting of Fe and unavoidable impurities, and Ni in the steel powder with a particle size of 45 μm or less
A composite alloy steel powder for powder metallurgy, characterized in that the content of Mo and Mo+1/2W is in a range of 2.0 to 4.2 times the average content of the entire steel powder. 7. The final product alloy component contains Ni, Mo and W,
The alloy composition is Ni: 0.50 to 3.50% by weight, Mo+1/2W: 0.65 to 3.50% by weight, the balance is Fe, C, and inevitable impurities, and the density is 7.
A high-strength sintered alloy steel having a tensile strength of 0 g/cm^3 or more and a tensile strength of 130 kgf/mm^2 or more after carburizing and quenching and tempering. 8. Final product alloy components include C, Ni, Mo and W, alloy composition: C: 0.3-0.8% by weight Ni: 0.50-3.50% by weight Mo+1/2W: 0.65 ~3.50% by weight, with the remainder consisting of Fe and unavoidable impurities, and has a density of 7.0g/cm^3 or more and a tensile strength of 130kgf/mm^2 or more after quenching and tempering. High strength, high toughness sintered alloy steel. 9. A sintered alloy steel manufactured using the composite alloy steel powder according to claim 6, which contains Ni and M as final product alloy components.
o and W, the balance is Fe and unavoidable impurities, and the alloy composition is Ni: 0.50 to 3.50% by weight, Mo+1/2W: 0.65 to 3.50% by weight, and the balance is Fe and C. and unavoidable impurities, and has a density of 7.
A high-strength sintered alloy steel having a tensile strength of 0 g/cm^3 or more and a tensile strength of 130 kgf/mm^2 or more after carburizing and quenching and tempering. 10. A sintered alloy steel manufactured using the composite alloy steel powder according to claim 6, which contains C and N as the final product alloy components.
i, Mo and W, and the alloy composition is C: 0.3 to 0.8% by weight, Ni: 0.50 to 3.50% by weight, Mo+1/2W: 0.65 to 3.50% by weight, and the balance is composed of Fe and inevitable impurities, has a density of 7.0 g/cm^3 or more, and has a tensile strength of 130 kgf/mm^2 or more after quenching and tempering. . 11. In a composite alloy steel powder in which alloy components are partially diffused and adhered to the surface of iron powder particles in powder form, N as an alloy component
i and W, the alloy composition is Ni: 0.50 to 3.50% by weight, W: 1.30 to 7.00% by weight, the balance is Fe and unavoidable impurities, and 45 μm of the steel powder The Ni and W contents in the following grain sizes are respectively 2.0 to 4.0% of the average content of the steel powder as a whole.
Composite alloy steel powder for powder metallurgy, characterized in that it is in a double range. 12. The final product contains Ni and W as alloy components, and the alloy composition is Ni: 0.50 to 3.50% by weight, W: 1.30 to 7.00% by weight, and the balance is Fe, C, and unavoidable impurities. A high-strength sintered alloy steel having a density of 7.0 g/cm^3 or more and a tensile strength of 130 kgf/mm^2 or more after carburizing and quenching and tempering. 13. Contains C, Ni and W as final product alloy components,
The alloy composition is C: 0.3 to 0.8% by weight, Ni: 0.50 to 3.50% by weight, W: 1.30 to 7.00% by weight, with the balance consisting of Fe and unavoidable impurities, and the density is A high-strength, high-toughness sintered alloy steel having a tensile strength of 7.0 g/cm^3 or more and a tensile strength after quenching and tempering of 130 kgf/mm^2 or more. 14. A sintered alloy steel manufactured using the composite alloy steel powder according to claim 11, which contains Ni as the final product alloy component.
and W, the alloy composition is Ni: 0.50-3.50% by weight, W: 1.30-7.00% by weight, the balance consists of Fe, C and unavoidable impurities, and the density is 7.0g. /cm^3 or more, and has a tensile strength of 130 kgf/mm^2 or more after carburizing, quenching and tempering. 15. A sintered alloy steel manufactured using the composite alloy steel powder according to claim 11, which contains Ni as the final product alloy component.
and W, and the alloy composition is C: 0.3-0.8% by weight, Ni: 0.50-3.50% by weight, W: 1.30-7.00% by weight, and the balance is Fe and unavoidable impurities. A high-strength, high-toughness sintered alloy steel characterized by having a density of 7.0 g/cm^3 or more and a tensile strength of 130 kgf/mm^2 or more after quenching and tempering.