JPS6123701A - Raw material powder of powder metallurgy for producing ferrous parts - Google Patents

Abstract

PURPOSE:To provide raw material powder for producing ferrous sintered parts having a excellent compressibility and compartibility by mixing iron powders having different grain sizes and characteristics at a specific ratio. CONSTITUTION:The iron powder A having <=350 mesh grain size and 3.2-6.0g/ cm<3> apparent density, the rion powder B having 60-350 mesh grain size, 2.0- 3.2g/cm<3> apparent density and <=150 micro-Vickers hardness in the average value of hardness and the iron powder C having >=60 mesh grain size are mixed so as to contain the iron powder A at 10-50%, the iron powder C at <=10% and the balance the iron powder B. Such iron powder mixture as a raw material is compacted and sintered by a powder metallurgical method to produce mechanical parts. The raw material of powder metallurgy has the excellent compressibility and compaclibility and the sintered mechanical parts produced from said material have the high-strength characteristics.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to powder metallurgy raw material powder for manufacturing iron-based parts that has particularly excellent compressibility and moldability, and is particularly suitable for application to the manufacturing of mechanical parts. The present invention relates to raw material powder for manufacturing iron-based sintered parts.

<Conventional technology> In recent years, there has been remarkable progress in manufacturing technology for metal and alloy powders, and in powder metallurgy technology that uses these. It has started to expand widely.

However, sintered parts manufactured using powder metallurgy generally have a low density with many voids remaining inside, and therefore have the problem of having low mechanical strength compared to parts made from melted lumber. This tendency was especially marked for iron-based sintered machine parts.

For these reasons5, up until now, the application of sintered materials has tended to be limited to medium-strength parts that do not require much strength, but against the backdrop of recent competition in the development of powder metallurgy technology that has become even more intense. As an example, demand for high-strength iron-based sintered parts such as automobile transmissions, engine parts, and steering parts, which have a tensile strength of about 100 to 130 kgf/mi, is increasing day by day.

By the way, 5. In general, to increase the strength of sintered parts.

The following four factors are said to be important in terms of the powder characteristics of raw material powder. That is, 1) Excellent compressibility (higher density of compacted powder).

■ Excellent moldability (high strength of compacted compact).

■ Excellent sinterability (high tendency for densification due to sintering)
, ■ High strength of the powder material itself.

In order to improve the "compressibility" shown in item 0 above, in addition to increasing the apparent density of the powder and appropriately selecting the particle size structure of the powder by 1/4, the hardness of the powder must be increased. It is necessary to keep it low. Still, the "moldability" shown in item 0 above
To improve this, it is necessary to have a powder with low apparent density.

In other words, improving "compressibility" and improving "moldability" require contradictory properties in terms of the "apparent density" of the powder.

FIG. 1 is a graph showing the relationship between the apparent density of copper powder, green compact density, and Rattler value (the green compact was obtained by pressure molding at 5t/cIl). From the figure, ○ The smaller the apparent density, the lower the compressibility and the lower the density of the green compact, but the moldability improves and the strength becomes higher. Q: The higher the apparent density, the lower the compaction becomes It was found that the moldability decreases and the strength of the compacted powder body decreases, but the compressibility improves and the density becomes high, and it appears that compressibility and moldability are contradictory in terms of density. That is clear.

Normally, apparently dense powder has a spherical particle shape.
It is believed that if the particle size structure is appropriately selected, a compacted powder with high density can be obtained by compaction. In addition, powders with apparently low density have irregular particle shapes, and the filling rate of the powder when compacted is low, but it is thought that the mechanical entanglement of the powders increases the strength of the compact.

In this way, the appearance of a powder is closely related to its density, and in other words, its particle shape is closely related to both compressibility and moldability, but satisfying both of them at the same time is mutually contradictory from the perspective of particle shape. This is a request to do so.

For this reason, when manufacturing high-strength sintered parts, the particle size structure of the raw material powder must be modified (Japanese Patent Laid-Open No. 58-819
No. 03), and the apparent density was adjusted
201, Japanese Patent Application Publication No. 58-81901), or by devising the chemical composition (Japanese Patent Publication No. 58-10962), or by reducing the hardness of the powder by annealing, to improve its compressibility and moldability. The current situation is to find a compromise between sexes.

<Problems to be solved by the invention> As mentioned above, even if attempts are made to manufacture high-strength mechanical parts using powder metallurgy with the hope of significantly reducing cutting work in the manufacturing process, the strength of the product will be significantly affected. Because the "compressibility" and "mouldability" of the raw material powder have contradictory properties, it has been extremely difficult to stably mass-produce fully satisfactory sintered products.

<Means to Solve the Problems> The present inventors have solved the above-mentioned problems and have developed a method with compressibility and moldability that is suitable for the manufacture of mechanical parts that particularly require high strength. In order to provide a raw material powder for powder metallurgy for manufacturing iron-based parts that has both excellent properties, the appearance of the powder as described above is
In other words, we conducted research focusing on the particle shape, which has a close relationship with the compressibility and moldability of the powder.
From the viewpoint of placing emphasis on improving moldability, we mainly use irregularly shaped powder, and we also mix spherical powder to improve filling properties (compressibility), and make the irregularly shaped powder relatively coarse. If the spherical powder is made up of relatively fine particles and the particle size distribution is changed depending on the particle shape,
During powder compaction, the skeletal structure formed by mechanically intertwining irregularly shaped coarse particles is maintained firmly, while the fine spherical particles smoothly enter and fill the gaps in the skeletal structure, improving formability and We obtained the knowledge that a compacted powder body with extremely excellent compressibility can be obtained, and that a high-strength sintered body can be stably manufactured.''

This invention was made based on the above knowledge, and the raw material powder for manufacturing iron-based sintered parts by powder metallurgy is A powder: particle size of 13'50 mesh and apparent density. 3.2-6. o&/d powder 5B powder 2 particle size is 060
~ ■ 350 mesh, and the apparent density is 2.0 to 3.
2111 cr & powder 5C powder 2 Powder with a particle size of +60 mesh Powder is composed of a mixed powder, and the weight proportion of the A powder is 10 to 50%, and the weight proportion of the C powder is suppressed to less than 10%, It is characterized by stably improving the compressibility and moldability of the powder.

From the component composition, the powder targeted by this invention is as follows:
As long as it is possible to manufacture iron-based sintered parts, the type does not matter; premixed powder (a mixture of powders of various components so as to achieve the desired composition through sintering; for example, iron-based sintered parts) For system machine parts, N is added to low-alloy steel powder.
1 powder, an appropriate mixture of metal powder such as Cu powder or Fe powder), or pre-alloyed powder (powder having a desired component composition in advance) may be employed.

Next, in this invention, the particle size of the powder, the apparent density,
The reason why the blending ratio is numerically limited as described above will be explained.

(a) Particle size and apparent density of powder As described above, this invention is applicable to particle size and apparent density.
By mixing powders of different shapes, the aim is to maintain the mechanical intertwining of the skeletal structure formed by irregularly shaped coarse particles while efficiently filling the gaps with fine powder. , Spherical powder with good filling properties on the fine powder side (
That is, a powder with apparently large density is selected, and irregularly shaped coarse particles with good moldability are selected on the coarse particle side.

In this case, the appropriate effect can be obtained no matter what particle size is selected for the boundary between the fine grain side and the coarse grain side, but it is said that it is preferable in terms of the balance between compressibility and formability in ordinary powder metallurgy raw material powder, and The customary “350 mesh”
is also defined as the grain size boundary in this invention, and the -350 mesh side (i.e., the side that passes through the 350 mesh sieve) is defined as the fine grain side, and the +350 mesh side (i.e., the side that remains on the 350 mesh sieve) is defined as the fine grain side. side) as the coarse grain side.

Of course, it goes without saying that if the powder is divided into fine particles and coarse particles using the above particle size as a boundary, the powder of the present invention will have the best balance between compressibility and moldability.

In addition, even on the coarse grain side, those with a grain size of +60 mesh do not have a negative effect on compressibility, moldability, sinterability, etc., so in accordance with the customary practice in the powder metallurgy industry, coarse grains with a mesh of 60 mesh or more was considered defective.

Now, to repeat, the raw material powder for manufacturing iron-based sintered parts of the present invention achieves both high compressibility and high moldability by mixing powders with different particle sizes and particle shapes. In this case, of course, the spherical fine powder as a powder component must have high compressibility, and the irregularly shaped powder must have high moldability. be done.

By the way, the present inventors have found that in order to obtain a sintered material with sufficient characteristics as a high-strength mechanical part, the compact density obtained by pressure molding of 5t/c11t should be approximately 6.61//cr& or more. It is necessary to use a raw material powder that has both compressibility such that the powder compact obtained by pressure molding at <5 t/d has a Rattler value of 1.0% or less or less. Check i~.

Therefore, from this point of view, the apparent lower limit of the density of the fine grain side with a grain size of 1350 mesh is 3,211/cr&
The particle size is determined to be a desired collection of spherical powder, while the particle size is set to 060 to
0 mesh) on the coarse grain side (5 grain size +60 mesh) is a defective part.

As will be described later, we suppressed the amount of contamination as much as possible and virtually eliminated its influence on the apparent density. cr/I was determined to obtain a desired collection of irregularly shaped powder.

In other words, from Figure 1 shown above, the apparent density of the powder is 3.
．． 2. ! When i'/cff1 or more, the compact density becomes 66
g/cut or more, and the apparent density of the powder is 3.1.
It is clear that the Rattler value: ], 0 or less can be achieved at g/cd or less.

Also, the apparent upper limit of the density of the fine grain side, which has a grain size of 1350 mesh, is 6. The reason why oE/cwt is defined is that with currently known technology, the apparent density is 6. This is because it is impossible to produce iron-based metal powder that exceeds o g lcr&.On the other hand, iron-based metal powder with an apparent density of less than 2.09/cr& has extremely poor fluidity, and when filled into molds, etc. Since smooth flow would not be achieved, the lower limit of the apparent density on the coarse grain side, which is 5060 to 350 mesh, was set as z, og/d.

(b) Blending ratio of powder of each particle size The blending ratio of 1350 mesh fine powder (apparently spherical powder with density: 3.zll/Clft or more) in the raw material powder for manufacturing iron-based sintered parts is less than 10% by weight. If it is present, the desired green compact density (i.e., about 6.6 Elcr& or higher) cannot be secured, while if it is blended in excess of 50% by weight, the desired low Rattler value (i.e.,

Since it was not possible to achieve a particle size of about 1.0 cm or less), the blending ratio of the fine spherical powder was set at 10 to 50% by weight.

Figure 2 shows 135% of the raw material powder for producing iron-based sintered parts.
0 mesh fine spherical powder (apparent density 3, aglCr
! This is a graph showing the relationship between the blending ratio (above), green compact density, and Rattler value (however, compact powder compacting is advantageous when pressure molded at 5t/cffl).

From Figure 2, if the amount of fine spherical powder blended is small,
Although the Rattler value improves, the green compact density is insufficient, resulting in a decrease in compressibility.Also, if the amount of fine spherical powder blended is too large, the green compact density improves, but the Rattler value deteriorates, making it difficult to form. It can be seen that this leads to a decline in sexual performance. This means that if there are too few fine spherical powders, the intertwining of the skeleton structure formed by the coarse irregularly shaped powders is sufficient, but the fine powder particles are not sufficient to fill the gaps; If it is too large, the mechanical intertwining of the skeletal structure formed by the coarse particles and irregular shapes tends to be destroyed, although the filling properties are improved.

In addition, in the raw material powder for manufacturing iron-based sintered parts of the present invention, the content of coarse particles that do not pass through a 60 mesh sieve is reduced to 1
Although the content is limited to less than 0% by weight, the -1-60 mesh coarse particles are compressible and moldable.

This is because it has been confirmed that the above-mentioned disadvantages can be almost suppressed by making the content less than 10% by weight, since it does not have an adverse effect on the sinterability.

It should be noted that it is natural that the particle shape and appearance of the powder are affected by the density depending on the method of manufacturing the powder for manufacturing iron-based sintered parts, but the powder of this invention may be manufactured by any method, and the particle size It is sufficient that the relationship between the appearance and the density satisfies the conditions of this invention. Well, if you use the oil atomization method.

This is preferable because powder having a particle structure that satisfies the conditions of the present invention can be produced all at once under certain production conditions.

As mentioned above, in this invention, powder components are used.

There are no restrictions on the manufacturing method, origin, etc., but in order to obtain more advantageous effects, it is preferable to make the hardness of the powder itself as soft as possible.

Figure 3 is a graph showing the relationship between powder hardness, green compact density, and Rattler value.From Figure 3, it can be seen that the hardness of 5 powders also affects compressibility and moldability. It is clear that the smaller the micro-Vickers hardness, the better the results for both, and it is also clear that it is ideal to have a micro Vickers hardness of 150 or less.

Of course, the hardness of powder usually shows different values for each particle, and considering that there is still a limit to the hardness measurement of fine powder, especially coarse grain powder of 060 to 350 mm. It is practical to set so that the average value of hardness is 150 or less in terms of micro Vickers hardness.

Furthermore, although the powder of the present invention has regulated conditions regarding particle size and apparent density, it is not possible to produce powder that satisfies the above conditions by a single manufacturing method, except for the oil atomization method mentioned above. is often difficult. For example, reduced powder, water atomized powder, etc. have irregular particle shapes over the entire particle size, and their apparent density is small. 3.
It is normal that it is 1 g/i or less. In the case of gas atomized powder, the particle shape is spherical over all 5 particle sizes, and both the +350 mesh coarse particles and -350 mesh fine particles have an apparent density of 3.2 g/cd or more -F.

In such a case, it is necessary to mix the coarse irregularly shaped powder and the fine spherical powder to meet the conditions of the present invention. Select a powder with a density of 2.0 to 3.2g/cm3.211/crl, or a metal powder with an average particle size of 44μ or less and an apparent density of 32 to 6.0g/cnt as fine spherical powder. is good.

As mentioned above, in this invention, the particle size is 350 mesh,
That is, coarse particles and fine particles are distinguished by the particle size of 44μ, but when coarse irregularly shaped powder and fine spherical powder are mixed to meet the conditions of the present invention, the coarse irregularly shaped powder is: 06
0~■350 mesh and the apparent density is 2.0~3.2. i
? /ci rather than.

The average particle size is 060 to ■350, including both coarse and fine particles.
It is better to select a powder with a mesh size (44 to 246μ) and an apparent density of 20 to 2g/air.
Similarly, fine spherical powder has an average particle size of 44μ or less (
-3!50 mesh) and the apparent density is 32 to 6.0g1
CR! It is natural to select a powder of

Next, the present invention will be explained using examples and comparing with comparative examples.

<Example> First, powders P1 to P19 were prepared in which the sintered bodies were powders having a chemical composition as shown in Table 1, and the particle size structure and apparent density were adjusted to be as shown in Table 2. prepared.

Note that powders P14 and PI3 are comparative examples in which the particle size structure is not appropriate, and powders P16 to P19 are comparative examples in which the apparent density is not appropriate.

For each of these powders, the green compact density and the Rattler value of the green compact were measured, and the obtained results are also shown in Table 2.

As is clear from the results shown in Table 2.

In the steel powders P1 to P9 of the present invention, the particle size structure and apparent density are appropriately adjusted, and the green compact density is 661! /d or more, and the Rattler value was 1.0 or less, indicating that good results were obtained in both compressibility and moldability. On the other hand, for comparative steel powders P14 and PI3, the apparent density adjustment is P1 to P3.
, but the particle size structure is not adjusted and PI3
P'15 has poor compressibility, and P'15 has poor moldability.

Regarding Comparative Examples P16 to P]9, the particle size structure has been adjusted, but the apparent density has not been adjusted, and P]7
and P'18 had poor compressibility, and P2O and PI3 had poor moldability.

Regarding the steel powder PLO-P13 of the present invention, the particle size structure and apparent density are adjusted to be almost the same, and the coarse powder 060
~ ■ The only difference is the hardness of the 350 mesh powder, but as the hardness of the powder increases, even if the particle size structure and apparent density are adjusted, both compressibility and moldability will be disadvantageous. It has become. Therefore, in order to obtain more advantageous powder properties, the hardness of the powder should be made as small as possible (preferably micro-Vickers hardness of 1.50 or less).

<Overall Effects> As described above, according to the present invention, it is possible to stably and reliably obtain powder metallurgy raw material powder for manufacturing iron-based parts that has excellent compressibility and moldability, and it is possible to obtain iron-based high-strength machinery. This brings about extremely useful effects industrially, such as making it possible to mass produce parts on an industrial scale.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the apparent density of copper powder, green compact density, and Rattler value. Figure 2 is a graph showing the relationship between -350 mesh fine spherical powder, green compact density, and Rattler value. Figure 3 is a graph showing the relationship between powder hardness, green compact density, and Rattler value. Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo and 1 other person (MHv)

Claims (3)

[Claims] (1) Powder A: Powder with a particle size of -350 mesh and an apparent density of 3.2 to 6.0 g/cm^3, Powder B: Powder with a particle size of 60 to 350 mesh and an apparent density of 2. Powder metallurgy raw material powder for manufacturing iron-based parts consisting of a mixed powder of 0 to 3.2 g/cm^3 powder, C powder: powder with particle size of +60 mesh, and the weight ratio of the A powder is 10 to 50. %, and the weight ratio of the C powder is suppressed to less than 10%. (2) The raw material powder for manufacturing iron-based sintered parts according to claim 1, wherein the B powder has an average particle hardness of 150 or less in terms of micro-Vickers hardness. (3) Production of iron-based sintered parts according to claim 1 or 2, wherein the average particle size of the A powder is 44 μm or less, and the average particle size of the B powder is more than 44 μm. Raw material powder for use.