JPS6366362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an alloy steel powder for powder metallurgy used for manufacturing various sintered parts and a method for manufacturing the same. Sintered parts made from pure iron powder as a main raw material have been known for some time, but this type of sintered parts has a low strength level and has the disadvantage that its uses are limited. Therefore, recently, in order to compensate for the above-mentioned drawbacks, a technique has been developed in which alloy steel powder is used instead of pure iron powder. However, if alloy components are dissolved excessively in iron powder,
This often impairs the compressibility of the steel powder, in which case a high sintered body density cannot be obtained, resulting in a problem that no improvement in strength can be expected. On the other hand, a method of mixing pure iron powder with alloying component powder and causing the alloying component to react and form a solid solution during sintering has also been widely adopted. However, although compressibility is secured to some extent with this method, the formability may be reduced, the structure may become non-uniform due to powder segregation during compaction, and the structure may become non-uniform due to poor solid solution diffusion during sintering. There is a problem that this may occur. Therefore, as proposed in Japanese Patent Publication No. 45-9649, for example, the above-mentioned problem can be overcome by using powder manufactured by a method of partially diffusing and adhering alloying component powder to pure iron powder. is possible. In the above proposal, as a specific method for partially diffusing alloy component powder into pure iron powder, alloy components with low diffusivity into iron, e.g.
Regarding Mo, a method has been disclosed in which Mo is finely precipitated on the surface of pure iron powder by mixing Mo oxide with pure iron powder and heating it in a reducing atmosphere, but this method requires a complicated Mo addition process. ,Also
There is a possibility that the addition yield of Mo may decrease, and furthermore, it is difficult to apply it to an alloy component such as Mo whose oxide does not evaporate at a relatively low temperature. In addition, the above proposal involves soaking pure iron powder in a solution of soluble salts of alloying components such as Mo, drying and heating it to precipitate finely alloyed components such as Mo on the surface of the pure iron powder, and removing the alloying components from the iron powder. A method of diffusing the material into the interior has also been disclosed, but this method requires a drying step, which complicates the process and increases manufacturing costs. This invention was made in view of the above circumstances, and aims to overcome the above-mentioned problems and provide an alloy steel powder for powder metallurgy that has particularly excellent compressibility and a method for producing the same. be. That is, the alloyed steel powder for powder metallurgy of the present invention is an atomized steel powder obtained by prealloying Mo, which is an alloying component that has poor diffusivity into steel powder during sintering, within a composition range that does not adversely affect compressibility. On the surface of alloy steel powder,
It is characterized in that the remaining alloy components, Ni and/or Cu, are partially diffused and deposited in the form of powder. In addition, the alloyed steel powder for powder metallurgy of the present invention uses atomized alloyed steel powder that is prealloyed with Mo, which is an alloying component that has poor diffusivity into steel powder, in a range of 0.1 to 1.0% by weight. 2.5% by weight or less of Ni as an alloying component partially diffused and deposited in powder form on the surface of the atomized alloy steel powder.
and 2.0% by weight or less of Cu. Furthermore, the method for producing alloyed steel powder for powder metallurgy of the present invention uses alloying components that have poor diffusibility into steel powder during sintering of steel powder.
Atomized alloy steel powder is created by pulverizing molten alloy steel made by pre-alloying Mo within a composition range that does not adversely affect the compressibility of the powder using an atomization method.
Next, Ni and/or Cu as the remaining alloy components are diffused and adhered in the form of powder onto the surface of the atomized alloy steel powder. Hereinafter, the alloy steel powder for powder metallurgy of the present invention and the method for producing the same will be explained in more detail. In producing the alloyed steel powder for powder metallurgy of the present invention, first, as described above, Mo, which is an alloying component with poor diffusibility into the steel powder during sintering of the steel powder, is prealloyed during atomization. Atomized alloy steel powder containing the alloy components is created. That is,
A molten alloy steel containing Mo is melted, and the molten alloy steel is sprayed and rapidly cooled by a water atomization method or a gas atomization method to obtain an atomized alloy steel powder containing Mo. Then, on the surface of the atomized alloy steel powder, the remaining alloy components with good diffusivity are deposited on the surface of the atomized alloy steel powder.
Ni and Cu are partially diffused and deposited in powder form.
Here, partially diffusing and adhering means that the alloy component is not completely dissolved in the steel powder, but a portion of the alloy component is diffused into the steel powder, and a portion of the alloy component powder is not completely dissolved in the steel powder. This means that the parts are bonded to the steel powder. In order to partially diffuse and adhere the remaining alloy components to the steel powder surface in powder form,
For example, the atomized alloy steel powder and alloy component powder such as Ni powder or Cu powder may be mixed and heated to about 700 to 1000°C in a reducing atmosphere such as a hydrogen gas atmosphere. In this way, at the contact surface between the Ni powder or Cu powder and the atomized alloy steel powder, the Ni and Cu components partially diffuse into the steel powder, and the Ni powder and Cu powder are partially attached to the steel powder. becomes. When the partial diffusion adhesion treatment is performed in this way, the entire powder is usually in a solidified state, so it is crushed to the desired particle size, further annealed if necessary,
The final alloyed steel powder product is produced. X-ray microanalyzer (EPMA) of the cross section of the alloy steel powder of this invention obtained as described above
Figure 1 shows the secondary electron image photograph of the corresponding Mo
A characteristic X-ray image is shown in Figure 2. Also, EPMA of the cross section of powder with Mo attached to the surface by the conventional method.
Figure 3 shows the secondary electron image photograph of the corresponding Mo
A characteristic X-ray image is shown in FIG. As shown in Figs. 3 and 4, in the powder obtained by the conventional method, Mo powder 2 exists on the surface of steel powder 1, and it is clear that Mo is unevenly distributed. As shown in Fig. 2, in the alloy steel powder 3 of this invention, Mo
It is clear that Mo is not unevenly distributed and Mo is uniformly dissolved inside. As described above, the alloy steel powder of the present invention can be clearly distinguished from steel powder obtained by conventional methods by applying EPMA. As mentioned above, by pre-alloying Mo, which is an alloy component with particularly poor diffusivity, during atomization, the structure of the sintered body can be improved when performing powder metallurgy using the alloy steel powder of the present invention. Uniformity is improved, and the alloy component Mo, which has poor diffusivity, does not require partial diffusion adhesion treatment after atomization, so the addition yield of that alloy component is improved, and the process of adding the alloy component is simplified, making it possible to improve the alloy composition. The cost of adding ingredients is low. However, the composition range of the alloy components to be prealloyed during atomization should be within a range that does not adversely affect the compressibility of the powder. This is because if the compressibility of the atomized alloy steel sheet is impaired due to excessive solid solution of the alloy components, the green compact density will decrease, and the sintered compact density will also decrease, resulting in a decrease in the sintered compact strength. On the other hand, by pre-alloying MO, which is an alloy component with poor diffusivity, at the time of atomization, and by performing a partial diffusion adhesion treatment of Ni and/or Cu, which are other alloy components, steel powder It is possible to improve compressibility, eliminate non-uniformity in the sintered body due to component segregation during molding, and eliminate non-uniformity in the structure of the sintered body due to poor diffusion during sintering. The alloy components used in the alloy steel powder of this invention are:
Mo is used as a pre-alloying component during atomization, and Ni and/or Cu are used as alloying components for subsequent partial diffusion adhesion treatment. The reason is as follows. In other words, Mo has poor diffusibility into the steel base, but adding a small amount of 1% by weight or less increases hardenability and hardness. Therefore, pre-alloying Mo during atomization improves the compressibility of steel powder. It is possible to improve hardenability and increase hardness without damaging the properties. On the other hand, Ni has the effect of improving toughness and hardenability and has good diffusion into the steel base, while Cu has the effect of improving strength and corrosion resistance and can easily diffuse into the steel base. because there is,
These effects can be brought out by partially diffusing and adhering Ni and/or Cu to the atomized alloy powder. However, the pre-alloy amount of Mo during atomization is 0.1 to 1.0.
within the range of 0.1 to 1.0% by weight.
It is desirable that the upper limits of Ni and/or Cu to be partially diffused and adhered to the atomized alloy steel powder containing Mo are 2.5% by weight and 2.0% by weight, respectively. The reason for limiting these ingredients is as follows. Mo: The above-mentioned effect of adding Mo can usually be obtained when the amount added is 0.1% by weight or more, but when the amount added is 1.0% by weight
If this value is exceeded, the compressibility of the steel powder will drop sharply, and the cost of the steel powder will increase, impairing economic efficiency.
The lower limit was set to 0.1% by weight, and the upper limit was set to 1.0% by weight. Ni: As the amount of Ni added increases, the above-mentioned
The effect of Ni addition is further increased, but if it is added in excess of 2.5% by weight, the hardening of the steel powder surface due to partially diffused Ni cannot be ignored, resulting in a decrease in compressibility, and the economic efficiency of the steel powder. You will lose money, so set the upper limit.
The content was 2.5% by weight. Cu: Similar to Ni, the more the amount of Cu added, the more
The above-mentioned effect of Cu addition increases, but since Cu has excellent diffusion into the steel base, especially to grain boundaries, if the amount added exceeds 2.0%, it will partially diffuse.
Since Cu reduces the compressibility of the steel powder and also impairs the economic efficiency of the steel powder, the upper limit was set at 2.0% by weight. Next, the present invention will be explained in more detail with reference to preliminary test examples and examples. Preliminary test example Atomized alloy steel powder with three types of Mo pre-alloyed amount was created by changing the Mo content to three levels using the water atomization method, and the steel powder was placed in a hydrogen gas atmosphere.
Reduction annealing was performed at 1000℃. 1.0 to alloy steel powder after annealing
% of zinc stearate was added and mixed, and powder molding was performed using two types of molding pressure. The chemical composition and compact density of the alloy steel powder are shown in Table 1.

[Table] From Table 1, in sample A with Mo prealloy content of 0.58% by weight, a high green compact density of 7.21 g/cm ³ could be obtained at a molding pressure of 7 t/cm ² , but Mo prealloy As the amount increases, the density of the green compact decreases.In particular, if the prealloy amount exceeds 1.0% by weight, the residual amount of C, which has a strong affinity with Mo, increases, and the hardness of the steel powder increases rapidly. It became clear that the powder density decreased rapidly. Example 1 Atomized alloy steel powder was prepared by pre-alloying a certain amount of Mo using the water atomization method, and the steel powder was
After mixing and adding three levels of Ni powder, reduction annealing was performed at 1000° C. for 1 hour in an H ₂ atmosphere to partially diffuse and adhere Ni. 1.0% to the obtained alloy steel powder
Zinc stearate was added and mixed, and powder molding was performed under two types of molding pressures. Table 2 shows the chemical composition and green compact density of the steel powder in this example.

[Table] As is clear from Table 2, when the amount of Ni added was 2.06% by weight, a high green compact density of 7.17g/cm ³ was obtained at a molding pressure of 7t/cm ² , but when the amount of Ni added was 2.5% %, it can be seen that the green compact density sharply decreased due to an increase in the amount of partial diffusion of the added Ni powder into the steel powder surface layer. Example 2 Atomized alloy steel powder was prepared by pre-alloying a certain amount of Mo using the water atomization method, and the steel powder was
After mixing and adding three levels of Cu powder, reduction annealing was performed at 1000°C for 1 hour in an H ₂ atmosphere to partially diffuse and adhere Cu. 1.0 to the obtained alloy steel powder
% of zinc stearate was added and mixed, and powder molding was performed at two types of molding pressure. Table 3 shows the chemical composition of the steel powder and the green compact density in this example.

[Table] From Table 3, a high compact density of 7.20 g/cm ³ was obtained at a compacting pressure of 7 t/cm ² when the Cu addition amount was 1.51% by weight, but if the Cu addition amount exceeded 2.0%, the Cu into powder
It is clear that the density of the green compact decreases rapidly due to the increase in the amount of partial diffusion of . Example 3 Atomized alloy steel powder was prepared by pre-alloying a certain amount of Mo using the water atomization method, and the steel powder was
After adding and mixing Ni powder and Cu powder, reduction annealing was performed at 1000° C. for 1 hour in an H ₂ atmosphere to partially diffuse and adhere Ni and Cu to the surface of the steel powder. Add 1.0% zinc stearate to the obtained alloy steel powder and mix it.
It was compacted using a seed pressure. The chemical composition and green compact density of the alloy steel powder according to this example were
Shown in the table.

[Table] As shown in Table 4, Ni1.48% by weight and
The steel powder of this example with 0.93% Cu added is 7t/
A high compact density of 7.18 g/cm was obtained at a compacting pressure of cm ² . Example 4 1.0% zinc stearate and graphite powder were added to the same steel powder (sample code J) as that obtained in Example 3.
0.9% was added and mixed, compacted into a JSPM standard tensile test piece at a molding pressure of 7t/ ^cm2 , and further sintered at 1150°C for 50 minutes in an AX gas atmosphere. For comparison, Mo powder, Ni powder, and Cu powder were added to pure iron powder with sample code J.
0.9% graphite powder and zinc stearate as above.
1.0% was added and mixed, and the powder was compacted and sintered under the same conditions as above (Comparative Example 1). Also, special public service in 1977-
9649, graphite 0.9
% and zinc stearate 1.0% are added and mixed,
Powder compacting and sintering were carried out under the same conditions as above (Comparative Example 2). Table 5 shows the chemical composition of each of the obtained sintered bodies, the density of the compacted powder body, and the tensile strength of the sintered body.

[Table] As is clear from Table 5, the tensile strength of the sintered body (Comparative Example 1) using the alloy steel powder of the present invention (sample code J) Since the uniformity of the sintered body structure was superior to that of the sintered body (Comparative Example 1), a value as high as about 5 Kg/mm ² was obtained. Furthermore, the sintered body (Comparative Example 2) made using steel powder with alloy components partially diffused and adhered by the method of Japanese Patent Publication No. 45-9649 is different from the sintered body made by the conventional mixed powder method. Although the tensile strength was improved compared to (Comparative Example 1), when compared with the sintered body using steel powder according to the example of this invention (sample code J), despite the large amount of alloy, the tensile strength was Therefore, it is clear that by using the steel powder of the present invention, a sintered body with higher strength can be obtained. As is clear from the above description, the alloy steel powder for powder metallurgy of the present invention is an atomized alloy steel made by pre-alloying alloy components that have poor diffusivity to steel powder in a sintered body within a range that does not impair compressibility. The alloy steel powder of the present invention has excellent compressibility because the remaining alloy components are partially diffused and adhered to the surface of the atomized alloy steel powder in the form of powder using a powder. It is possible to obtain a high-density and high-strength sintered body using this method, and it also has several advantages such as there is no risk of non-uniform structure of the sintered body due to powder segregation during molding or poor diffusion during sintering. . In addition, the method for producing alloy steel powder of the present invention has a simpler manufacturing process and a much higher yield of alloying components than the previously proposed method of Japanese Patent Publication No. 45-9649, and is superior at low cost. We can provide alloy steel powder with specific properties, etc.
It has various advantages.

[Brief explanation of drawings]

Figures 1 and 2 show the cross section of the alloy steel powder of this invention.
In the EPMA photographs, Figure 1 is a secondary electron image photograph, and Figure 2 is a secondary electron image photograph.
The figure is a Mo characteristic X-ray image, and Figures 3 and 4 are EPMA photographs of alloyed steel powder obtained by the conventional method.
Figure 3 is a secondary electron image photograph, and Figure 4 is a Mo characteristic X-ray image.

Claims (1)

[Claims] 1. Atomized alloy steel powder in which Mo is prealloyed within a composition range that does not adversely affect the compressibility of the powder as an alloying component with poor diffusibility into the steel powder during sintering of the steel powder. Ni as the remaining alloying component on the surface of
An alloy steel powder for powder metallurgy, characterized in that one or more of Cu and Cu is partially diffused and adhered in powder form. 2. The pre-alloyed amount of Mo is within the range of 0.1 to 1.0% by weight, and the added amount of Ni and/or Cu is set to an upper limit of 2.5% by weight for Ni and an upper limit of 2.0% by weight for Cu. Alloy steel powder for powder metallurgy according to claim 1. 3. Molten alloy steel is made by pre-alloying Mo, which is an alloy component with poor diffusivity into steel powder during sintering of steel powder, within a composition range that does not adversely affect the compressibility of the powder, and is pulverized by the atomization method. Create alloy steel powder, then add Ni as the remaining alloying component
A method for producing alloy steel powder for powder metallurgy, characterized in that one or more of Cu and Cu is diffused and adhered in powder form to the surface of the atomized alloy steel powder.