JPS6123702A - Raw material powder of powder metallurgy for producing ferrous parts - Google Patents

Abstract

PURPOSE:To provide raw material powder of powder metallurgy for producing ferrous parts having excellent sinterability and compressibility by mixing prealloy powders having specific different grain sizes at a specific ratio. CONSTITUTION:30-40wt% Iron powder or prealloy powder having 1-20mu grain size, <40wt% coarse prealloy particles having 10-500mu grin size and the bal- ance prealloy powder having 20-100mu grain size are mixed. The prealloy powder in this case denotes the alloy steel powder added with a small amt. of alloy elements such as Mn, Cr, Mo, V, B, Ni, Cu, Co, Nb, etc. The pulverous powder having 1-20mu grain size is so formed as to have <=1.5 shape index expressed by the equation. The powder raw material has the excellent sinterability and compressiblity and is excellent as the raw material for the case which high-strength mechanical parts are manufactured by a powder metallurgical method.

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 sinterability and compressibility, 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, the progress and development of metal and alloy powder manufacturing technology and powder metallurgy technology that uses these has been remarkable, and along with this, powder metallurgy products have expanded widely into various fields. I've come to do it.

However, sintered parts manufactured using powder metallurgy generally have a problem in that they have a low density due to many voids remaining inside, and therefore have lower mechanical strength than parts made from molten wood. This tendency was particularly pronounced for iron-based sintered machine parts.

For these reasons, 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. For example, demand for high-strength iron-based sintered parts with a tensile strength of about 100 to 120 Kti f /m4, such as automotive transmissions, engine parts, and steering parts, is increasing day by day.

However, the mixing method that has traditionally been used to manufacture iron-based sintered parts (pre-mix method diferon-based sintered materials use pure iron powder as the main raw material) is insufficient to meet these demands. Therefore, it has become desirable to use alloyed steel powder (pre-alloyed powder) which has excellent so-called "heat treatment properties" such as carburizing property and hardenability.
Alloy steel powder to which alloying elements such as V, B, Ni, Cu, Co, and Nb are added has been attracting attention as a raw material for powder metallurgy.

However, since pre-alloyed powder has been alloyed in advance, the hardness of the powder particles is higher than that of pure metal powder, and as a result, it has had the problem that its compressibility does not exhibit a sufficiently satisfactory value. Therefore, when a compacted body is made from pre-alloyed powder, the density and mechanical strength do not reach the desired values, and in the end, the density and mechanical strength of the sintered body obtained by firing do not improve as expected. There wasn't.

Therefore, in order to prevent the pre-alloy powder particles themselves from becoming too hard, we have tried to improve the compressibility by devising the chemical composition of the particles (Japanese Unexamined Patent Publication No. 55-621.01), or
Attempts have been made to improve sinterability and promote densification of sintered bodies by adding ultrafine powder C (particle size 0.1μ or less) to some high-grade powders as a sintering aid. (Industrial Materials J, Vol. 31, No. 7, pp. 50-54).

<Problems to be Solved by the Invention> However, with steel powder in which the chemical composition of pre-alloyed powder particles is devised (for example, the one described in the above-mentioned Japanese Patent Application Laid-open No. 55-62101), the resultant green compact is The density is only about 6.6 to 6.8 f/cTI (5t/cTI).
(under crl molding), it is difficult to achieve a value exceeding 6.8 f/crd, which is necessary for manufacturing high-strength sintered mechanical parts.On the other hand, ultrafine powder added as a sintering aid The cost of the powder itself is extremely high, and therefore the application of these powders to iron-based sintered machine parts is difficult to determine from a cost perspective, and none of them are fully satisfactory as iron-based raw material powders for the production of sintered machine parts. .

As mentioned above, the iron-based raw material powder for manufacturing sintered machine parts has the following characteristics: ■ It is desirable that the main powder is a pre-alloyed powder, and ■ Compressibility (compressibility) A material that simultaneously satisfies the following four points is needed: (1) excellent sinterability (evaluated by the degree of densification due to sintering); (2) low cost. ing.

Therefore, from this perspective, the present inventors have developed a powder metallurgy raw material powder for manufacturing iron-based parts that has both excellent sinterability and compressibility, and is suitable for the manufacturing of mechanical parts that require high strength. In order to provide this, we conducted research focusing on the particle size of the powder, which is thought to have a large impact on sinterability, and found the following (
The findings shown in al~fc) were obtained.

(a) Generally, although fine powder has excellent sinterability, the bulk density of the powder is low, and the green compact density is also low. Therefore, when compacting and sintering only fine powder, the density of the sintered body is excellent, but the rate of dimensional change during sintering is too high, making it difficult to apply it as sintered machine parts. .

Figure 1 is a graph showing the relationship between the particle diameter of raw material powder for powder metallurgy, green compact density, sintered compact density, and dimensional change rate. It can be seen that the rate of dimensional change that must occur becomes significantly larger as the powder particle size decreases.

(bl) In this way, it is not possible to avoid a decrease in green compact density with only fine powder, but when coarser powder is mixed with the fine powder, green compact density gradually increases, and the particle size Once the configuration is adjusted to a certain range,
A powder metallurgy raw material powder suitable for producing iron-based sintered parts can be obtained, in which the good sinterability of the fine powder is utilized while the green compact density is significantly improved.

(C) When used alone, the finer the fine powder, the better the sinterability, but when used in combination with coarser powder, this is not necessarily the case; The second graph shows the relationship between the average particle diameter and the rate of increase in sintered body density.
As is clear from the figure, when the particle size of the fine powder becomes 1 μm or less, the sinterability improvement effect is saturated. This phenomenon occurs because if the particle size of fine powder is too small, there is a strong tendency for fine powder to agglomerate with each other, and the efficiency of mixing and dispersing with coarser powder decreases, reducing the effect of improving sinterability. This is thought to be due to

This invention was made based on the above findings, and the raw material powder for producing iron-based sintered parts by powder metallurgy is: Fine powder with a particle size of 1 to 20 μm: 3 to 40% by weight.

Particle size], Coarse particles of more than OO ~ 500μ: 40% by weight or less.

By adjusting the particle size structure to the following: intermediate particles with a particle size of more than 20 to 100 μm, the main feature is that the sinterability and compressibility of the powder are greatly improved.

From the component composition, the powder targeted by this invention is as follows:
The type of powder is not critical as long as it is possible to manufacture iron-based sintered parts, and either premix powder or prealloy powder can be used.

However, when the purpose is to apply it to high-density, high-strength sintered machine parts, the effects of the present invention can be utilized more effectively by employing pre-alloyed alloy steel powder.

If so, as already mentioned, it is preferable to use pre-alloyed alloy steel powder for high-strength sintered machine parts.1!
However, since pre-alloyed steel powder has been alloyed in advance, it has a strong tendency to harden, resulting in a lower green compact density and, as a result, a decrease in sintered compact density. This is because when a predetermined proportion of fine powder is mixed according to the present invention, sinterability is improved and a high-density sintered body is obtained, which has a large effect of improving mechanical strength. Note that, in this case, it goes without saying that the fine powder may be a metal powder that is not alloyed.

Next, in this invention, the reason why the particle size of the powder and its blending ratio are numerically limited as described above will be explained.

■ Fine powder Fine powder is mixed in to improve the sinterability of the raw material powder, but as is clear from Figure 2 shown above, if the particle size of the fine powder is less than 1 μm, sintering will occur. The effect of improving cohesion becomes saturated. On the other hand, as can be seen from Figure 2, the effect of improving sinterability becomes remarkable when the particle size of the powder is 20.
It is less than μ.

Considering the above facts and the fact that ultrafine powder with a particle size of less than 1 μm is too expensive, the particle size of the fine powder added to improve sinterability was determined to be 1 to 20 μm.

In addition, Figure 3 shows the relationship between the amount of fine powder added, compression conditions, sinterability, and dimensional change rate when fine powder with a particle size of 1 to 20 μ is mixed with coarser powder. The graph shows that the effect of improving sinterability becomes remarkable when the amount of fine powder added is 3% by weight or more, and the greater the amount added, the better the sinterability is. - On the other hand, if the amount added is too large, the compressibility decreases significantly - and therefore the increase in the density of the sintered body becomes slow. Considering the dimensional change rate, the maximum amount of fine powder to be added is 40% by weight.

For this reason, the blending ratio of fine powder with a particle size of 1 to 20 μm was determined to be 3 to 40% by weight.

■ Coarse-grained fine powder alone cannot avoid a decrease in green compact density, so in this invention it is used in combination with coarser powder, but the particle size range of coarser powder is Spraying method (water atomization, gas atomization, oil atomization)
Coarse particles with a particle size of more than 500 μm, which are considered to have a very large adverse effect on compressibility, formability, and sinterability, were excluded.

However, even if the powder has a particle size of 500μ or less, it is generally considered that the coarse part of the powder deteriorates sinterability and compressibility, so it is not suitable as a powder for manufacturing sintered machine parts. , in the powder metallurgy industry, 150
It is customary to remove coarse particles by sieving with mesh C (particle size: 100 μm), 100' mesh C (particle size: 150 μm), or 60 mesh C (particle size: 250 μm). Based on the above, in this invention, according to the customary practice in the powder metallurgy industry, coarse particles with a particle size of 150 mesh or more (particle size of more than 100 μ) are considered, and the relationship between the blending ratio of coarse particles and sinterability and compressibility. was inspected.

FIG. 4 is a graph showing the relationship between the amount of coarse particles with a particle size of more than 100 μm and compressibility and sinterability when 20% by weight of fine powder with a particle size of 1 to 20 μm is added.

From Figure 4, it can be seen that the compressibility of the powder is slightly improved by adding coarse particles of more than 100μ, but it decreases when a large number of particles are added.Also, the sinterability decreases with the addition of coarse particles, It can be seen that the weight percentage is the limit.

For this reason, the blending ratio of coarse particles with a particle size of more than 100 to 500 μm was determined to be 40% by weight or less.

As described above, the present invention uses 3 to 40% by weight of fine powder with a particle size of 1 to 20μ, which has good sinterability, in powder metallurgy raw material powder for manufacturing iron-based parts, and which has good compressibility and sinterability. It is characterized by limiting the content to 40% by weight or less of coarse particles with a particle size of more than 100 μm.

In this case, ordinary metal powder for sintering (particularly powder obtained by the spraying method) does not contain fine powder with a particle size of 1 to 20 μm, or even if it does contain it, the amount is small. In such cases, it is better to separately prepare fine powder with a particle size of 1 to 20 μm and then mix and use it. In addition, particle size 1
~20μ fine powder can be obtained by reduction method, pulverization method, atomization method,
Of course, it may be produced by any other method.

Further, in addition to the modification of the particle size structure described above, if the particle shape of the powder is modified, further improvement in compressibility is possible. That is, by making the particle shape of the fine powder with a particle size of 1 to 20 microns spherical, the compressibility is further improved.

FIG. 5 is a graph showing the relationship between the shape index of fine powder blended at a ratio of 20% by weight and the green compact density and sintered compact density of the powder. Here, the shape index of the powder is the formula %Formula %As is clear from Figure 5, the shape index of fine powder affects the green compact density, and the compressibility is particularly good when the shape index is 1.5 or less. It becomes. It can also be seen that as a result, the density of the sintered body is improved.

This is thought to be because the fine spherical powder has the effect of reducing the internal friction of the copper powder, and therefore the fine spherical powder is efficiently filled into the gaps between the coarse particles during powder compaction.

In this way, by combining the particle size structure and making the fine powder spheroidal, it is possible to give the powder both good sinterability and better compressibility, and this effect is , is particularly effective in the case of pre-alloyed steel powder with hard powder hardness.

Next, the present invention will be explained using examples while comparing it with a conventional example.

<Example> First, powders P1 to P12 were prepared in which the sintered bodies were powders having chemical compositions as shown in Table 1 and particle size configurations as shown in Table 2.・°Note that powders P9 to P12 are conventional steel powders.

The sinterability (sintered compact density) and compressibility (green compact density under compression conditions of 5 t/ca) were measured for these steel powders, and the obtained results are also shown in Table 2.

As is clear from the results shown in Table 2, the steel powder of the present invention has particularly excellent sinterability by adjusting the particle size structure (
Conventional steel powder P9. PIO, pH and Pl2, and their improved steel powder P5. (This is clear from the comparison with P6°Pl and P8), and it can be seen that the compressibility is even more excellent by combining it with the particle shape.

Furthermore, those targeting pre-alloyed steel powder (Pl.

P2. It is clear that P3 and P4) have particularly excellent sintered body density and can be applied to high-density, high-strength mechanical parts.

As mentioned 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 sinterability and compressibility, and This brings about extremely useful effects in one industry, such as making it possible to mass produce high-strength mechanical parts on an industrial scale.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the particle size of powder metallurgy raw material powder, green compact density, sintered compact density, and dimensional change rate. Figure 2 is a graph showing the relationship between powder particle diameter and sintered compact density increase rate. Figure 3 is a graph showing the relationship between the amount of fine powder added and the green compact density, sintered compact density, and dimensional change rate of the powder. Figure 4 is a graph showing the relationship between the blending ratio of coarse particles and Graph showing the relationship between powder compact density, sintered compact density, and density increase rate. Figure 5 is a graph showing the relationship between fine powder shape index, powder compact density, and sintered compact density. It is. Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo Haka 1 person Figure 1 Tan n beast - Shinfusaizu 1 child diameter (p) Figure 3 JfEK Jf New 4 ;tsu D t ('A) Figure 4 $Bs aC/≦Toma (%) Figure 5 r, o 1.5 2.04tiXm
m'19ixtgt

Claims (4)

[Claims] (1) Fine powder with a particle size of 1 to 20μ: 3 to 40% by weight, Coarse particles with a particle size of more than 100 to 500μ: 40% by weight or less, Intermediate particles with a particle size of more than 20 to 100μ: the remainder, adjusted to the following particle size composition. Powder metallurgy raw material powder for manufacturing iron-based parts. (2) Powders of each particle size are prealloyed powders,
Powder metallurgy raw material powder for manufacturing iron-based parts according to claim 1. (3) The powder metallurgy raw material powder for manufacturing iron-based parts according to claim 1, wherein the coarse particles and intermediate particles are pre-alloyed powders, and the fine particles are single metal powders. (4) When the shape index of the powder is expressed by the formula shape index=surface area of powder particles/surface area of a sphere with the same volume as the powder particles, the shape index of the fine powder is 1.5 or less. Powder metallurgy raw material powder for manufacturing iron-based parts according to any one of items 1 to 3.