JPH044363B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a nickel alloy powder for sintering that is added to iron powder when manufacturing iron-based sintered machine parts, etc. The present invention relates to a nickel alloy powder for additives that can improve properties, reduce variations in dimensional change of sintered bodies, and improve tensile strength through subsequent heat treatment.

[Conventional technology]

For example, sintered machine parts manufactured by sintering iron-based powder are made by alloying to strengthen the material.
It is manufactured by adding various elements to iron powder and going through processes such as mixing, molding, and sintering. In alloying for such sintered machine parts, two or more types of C, Cu, Ni, Mo, etc. are added to iron powder to form Fe-Cu-C, Fe-
Alloy systems such as Ni-C, Fe-Ni-Cu-C, and Fe-Ni-Mo-C have been adopted and put into practical use (Ni,
Cu, Mo: 1-10%, C: 0.2-2%). In this case, the strength of Fe-Ni-Cu-C alloys in particular can be improved by heat treatment after forming and sintering.
In recent years, it has been used as a high-strength sintered material.

By the way, when adding elements to the above iron powder, in addition to the intended alloy strengthening items, ease of alloying,
That is, it is necessary to consider formability, sinterability, stability against dimensional changes of the sintered body, diffusibility into iron, oxidation resistance during the sintering process, etc. Conventionally, methods for adding such alloying elements include the premix method, in which individual powders of Fe, Ni, Cu, C, etc. are mixed individually, or the premix method, in which Fe-Ni
- There is a pre-alloy method in which C powder is mixed with Cu alloy powder.

[Problem that the invention seeks to solve]

However, Fe
-Ni-Cu-C alloys have the following problems.

When using the above premix method, Ni to Fe,
Since the alloying of Cu is non-uniform, the dimensional changes of the sintered body vary widely, and the strength improvement effect of heat treatment is also small.

In addition, when using the pre-alloy method, the variation in dimensional changes can be reduced because the alloying is homogeneous, but due to the high hardness of the Fe-Ni-Cu alloy powder, the compressibility during molding is poor, and the Although the density is low and the alloying is homogeneous, the strength improvement effect of heat treatment is small. As a result, special manufacturing processes such as remolding, resintering or powder forging are required.

The purpose of the present invention is to improve compressibility and sinterability, and to reduce variations in dimensional changes of sintered bodies, in view of the problems of the conventional element addition method described above.
Moreover, it is an object of the present invention to provide a nickel alloy powder for sintering whose tensile strength can be greatly improved by heat treatment after sintering.

[Means for solving problems]

In order to achieve the above purpose, the inventors of the present invention
As a result of extensive experimental research, we have developed a base powder for iron powder, etc.
Focusing on adding Ni-Cu alloy powder, the Ni
-If you find the conditions for the content of Cu in the Cu alloy powder and the particle size of the alloy powder, it will be difficult to alloy it alone.
Homogeneous alloying of Ni, Cu, etc. with Fe becomes possible,
In addition, the compressibility during molding is improved, furthermore, the variation in dimensional change of the sintered body is reduced, and the strength improvement effect of post-sintering heat treatment is also significant, which led to the creation of the present invention. be.

Therefore, the present invention provides a nickel alloy powder for sintering that is added to iron powder for iron-based sintered parts, which has a Cu content of 10 to 50% by weight, the remainder being Ni and unavoidable impurities, and has an average content of 10 to 50% by weight. This is a sintering nickel alloy powder characterized by a particle size of 30 μm or less.

Here, in the present invention, the reason why Ni and Cu are alloyed in advance and the reason why the content of Cu and the average grain size are limited will be explained.

In the powder produced by the conventional premix method, Ni
It is well known that due to the poor diffusibility of Fe into Fe, it is necessary to perform sintering at high temperatures and for a long time in order to achieve sufficient diffusion and improve the tensile strength. On the other hand, since Cu generates a liquid phase during sintering, alloying with Fe is partially easy, but on the other hand, alloying occurs rapidly, and as a result, Cu invades into Fe. Due to this, the dimensional change due to so-called Cu-growth becomes large, and its dispersion inevitably becomes large. This problem can be solved if Fe powder and Cu powder are ideally and uniformly mixed, but this is difficult in practice.
In addition, although alloying is ideal for pre-alloyed powder materials, the compact density and sintered density are low, so the original alloy strengthening feature is not fully exhibited.

In contrast, in the present invention, alloyed
Since we added Ni-Cu alloy powder,
This method can simultaneously solve the problems in the conventional premix method and prealloy method. In other words, since the melting point of Ni-Cu alloy powder is between that of pure Ni powder and pure Cu powder, it not only promotes the diffusion of Ni into Fe, but also promotes the diffusion of Ni into Fe.
It has a great effect of slowing down the diffusion of Cu, and as a result, Ni, Cu, etc. are homogeneously alloyed during sintering.
Furthermore, since the mother powder is pure iron powder, the compressibility is better than in the pre-alloy method which uses a hard alloy powder as the mother powder, and the green compact density can be greatly improved.

In this way, by adding Ni-Cu alloy powder to iron powder, the compressibility during molding is improved, and furthermore, the alloying of Ni and Cu in Fe powder during sintering is carried out homogeneously and appropriately. This greatly improves tensile strength.

The content of Cu in Ni-Cu alloy powder is 10~
Reason for setting it at 50% First, an experiment conducted to find the above-mentioned Cu content range will be explained.

(b) Cu content is 5%, 10%, 20%, respectively.
Ni-Cu alloy powders of 50%, 70%, and the balance Ni were produced by water atomization and classified to 30 μm or less using a microsieve. In addition, as a result of measuring the particle size distribution of these various alloy powders by a sedimentation method, the average particle size was 15 to 20 μm. Experimental sample powders were prepared by adding and mixing 5% of each of the Ni--Cu alloy powders and 0.5% of commercially available C powders to commercially available iron powders.

(b) In addition, in order to compare the performance with the above Ni-Cu alloy powder, a comparative example powder having the same composition as the case using the above Ni-20% Cu powder was prepared using the premix method and prealloy method described below. .

Premix powder: Commercially available iron powder, commercially available Ni,
Each powder of Cu and C was 4.0, 1.0,
A premix powder was prepared by adding and mixing 0.5%.

Pre-alloyed powder: C powder is added to Fe-4%Ni-1%Cu powder produced by water atomization method.
A pre-alloyed powder was prepared by adding and mixing 0.5%.

(c) Each of the above sample powders and comparative example powders were molded, annealed and heat treated under the following conditions.

Each of the powders described above was compression molded into each part under a pressure of 6 tons/cm ² , and the density of the green compact was measured.

Next, the above green compact is placed in an RX gas atmosphere.
Sintering was carried out at 1120°C for 30 minutes, and dimensional changes during this sintering were measured.

After heating the above sintered parts at 900℃ for 20 minutes, oil quenching is performed, and then heated at 250℃ for 60 minutes.
The tensile strength of the parts was measured.

Figures 1a to 1c are characteristic diagrams showing the green compact density, dimensional change, and tensile strength in the above experimental results, respectively. In the figures, ○ marks are Ni-Cu alloy powders, □ marks are pre-alloy powders, The x mark indicates the characteristics when premix powder is added.

As is clear from each figure, the Cu content is
It can be seen that when it is less than 10%, the tensile strength is low, and when it is more than 50%, the variation in dimensional change is large and the tensile strength is decreased. From this point of view, in the present invention, the Cu content is set to 10 to 50%, and the green compact density, dimensional change, and tensile strength will be explained in detail below.

() First, looking at the green compact density (see Figure 1 a), Ni-Cu alloy powder ○ shows a relatively high value as well as premix powder material ×, and as the Cu content increases, it slightly decreases. It is increasing. On the other hand, since the individual powder particles of the prealloy powder □ are hard, there is little plastic deformation of the powder during compression, and the value is low. As described above, although the green compact density is improved by using the Ni-Cu alloy powder, it does not change much depending on the Cu content.

() Next, looking at the dimensional changes (see Figure 1b), in Ni-Cu alloy powder ○,
A tendency to expand as the Cu content increases is observed. This occurs during sintering.
This is caused by an expansion phenomenon called Cu-growth, which is caused by the penetration of Cu from the Ni-Cu powder into the Fe powder. Incidentally, although it is important that the absolute value of the dimensional change of sintered mechanical parts is small, it is most important in practical terms that the variation be small. As is clear from Figure b, the variation in dimensional change is small at about 0.1% for the prealloy powder □, but it is large at about 0.2% for the premix powder x. On the other hand, in Ni-Cu alloy powder ○,
When Cu is 50% or less, it is in the range of around 0.1%, and there is relatively little variation, but when it reaches 70%, it tends to increase by about twice (about 0.2%). From the viewpoint of this dimensional change, it is desirable that the Cu content be 50% or less.

The reason why the variation in dimensional changes differs in this way is deeply related to the expansion phenomenon of Cu-growth. That is, Ni−Cu or Fe−Ni−
Although Cu-growth is basically suppressed by adding Cu in the form of an alloy powder such as Cu, it is thought that this is because the suppressing effect decreases when the Cu content in the alloy powder is too large.

() Finally, looking at the tensile strength after the above heat treatment (see Figure 1c), in Ni-Cu alloy powder ○, the tensile strength increases significantly as the Cu content increases, and at 10% Cu or more, the premix Powder × and prealloy powder □ greatly exceed it, and it shows a tendency to be saturated at 20% or more, and a tendency to decrease considerably when it exceeds 50%. In this way, the Cu of Ni-Cu alloy powder
If the content is less than 10%, the diffusivity of Ni to Fe will be insufficient and the strength improvement effect will be small.
Above 50%, the Ni content decreases.
The effect of adding Ni is small. Therefore, from the perspective of tensile strength, the Cu content is 10
It is desirable to set it to ~50%.

From the above experimental results of green compact density, dimensional change, and tensile strength, it is desirable to limit the Cu content to 10 to 50%.

Reason for setting the average particle size to 30 μm or less First, an experiment conducted to find the above particle size will be explained.

(b) Ni-20% generated by water atomization
Cu alloy powder less than 10μm, 10μm or more 20μm
less than, 20μm or more and less than 44μm, 44μm or more and less than 53μm
Fe-4%Ni-
A sintered body having a composition of 1% Cu-0.5% C was produced.
After heat-treating the sintered body, the tensile strength was measured.

FIG. 2 is a characteristic diagram showing the above experimental results.
As is clear from the figure, when the particle size of the Ni--Cu alloy powder becomes 30 μm or more, the alloying of Ni and Cu with Fe becomes non-uniform, resulting in a decrease in tensile strength. From this result, the above Ni
- It is desirable that the upper limit of the average particle size of the Cu alloy powder is 30 μm.

〔Example〕

Examples of the present invention will be described below.

Example 1 Ni-Cu alloy powder with Cu content of 20% and remaining Ni,
Water atomization method (water pressure as a condition: 200Kg/cm ² ,
water amount; 200/min), and the average particle size is
The powder was classified to 15 μm to produce Ni-Cu alloy powder.

Then, 5% of the above Ni-Cu alloy powder and 0.5% of C powder were added and mixed to commercially available iron powder, and the mixture was mixed at 6 ton/cm ^{2 .}
molded under the pressure of
Sintering was performed at 1120°C for 30 minutes. Next, this sintered body
After heating at 900℃ for 20 minutes, quenching in oil and then heating at 250℃
Tempering treatment was performed at ℃ for 60 minutes.

The sintered body thus obtained has a density of 7.08 g/cm ³ ,
It was recognized that it exhibited excellent mechanical properties with a tensile strength of 63Kg/ ^mm2 .

Example 2 5% of the Ni-20% Cu alloy powder produced by water atomization was added to and mixed with commercially available iron powder, heated in a hydrogen gas atmosphere at 850°C for 30 minutes, and then disintegrated to form a partially diffused powder. Alloy steel powder was produced.

Then, 0.5% of commercially available C powder was added to the above alloy steel powder.
% and mixed, molded under a pressure of 6 ton/cm ² , and sintered at 1120° C. for 30 minutes in an RX gas atmosphere.
Next, this was heated at 900℃ for 20 minutes, then oil quenched.
Thereafter, a tempering treatment was performed at 250°C for 60 minutes.

The sintered body thus obtained has a density of 7.14 g/cm ³ ,
It was confirmed that it exhibited excellent mechanical properties with a tensile strength of 72 Kg/mm ² .

〔Effect of the invention〕

As described above, according to the nickel alloy powder for sintering added to the iron powder for iron-based sintered parts according to the present invention,
The Cu content is 10-50% by weight and the average particle size is
Since the thickness is set to 30 μm or less, it is possible to reduce variations in dimensional change of the sintered body, improve compressibility and sinterability, and improve strength due to heat treatment.

[Brief explanation of drawings]

Figures 1 and 2 are characteristic diagrams for explaining the experimental results for determining the Cu content and average particle size conditions of the present invention, and Figure 1 a, b, and c are respectively
Figure 2 is a characteristic diagram showing the relationship between Cu content of Ni-Cu alloy powder, green compact density, dimensional change, and tensile strength.
FIG. 2 is a characteristic diagram showing the relationship between the particle size of Ni--Cu alloy powder and the tensile strength of a heat-treated sintered body.

Claims (1)

[Claims] 1 Nickel alloy powder for sintering added to iron powder for iron-based sintered parts, consisting of 10 to 50% by weight of Cu (hereinafter simply referred to as %), the balance being Ni and unavoidable impurities, and having an average particle size of 30 μm A nickel alloy powder for sintering, characterized by the following: