JPS6036602A - Iron powder for powder metallurgy - Google Patents

Abstract

PURPOSE:To manufacture inexpensively iron powder with superior compressibility and moldability by specifying the upper limit of the grain sizes of iron powder for powder metallurgy and the percentage of iron powder of certain grain sizes. CONSTITUTION:Iron powder is prepd. so as to adjust the upper limit of the grain sizes to 32 mesh and the content of iron powder of 32-80 mesh grain sizes to 2-30wt%. The prepd. iron powder is filled into the cavity of a metallic mold, compression-molded, and sintered to obtain a molded body of high density.

Description

[Detailed description of the invention] The present invention relates to iron powder for powder metallurgy, and more particularly.

It relates to iron powder for powder metallurgy that has excellent compressibility and formability and can be manufactured at low cost.

Traditionally, iron powder for powder metallurgy has been mainly produced using the reduction method and the injection method. Below, we will discuss the manufacturing considerations necessary to ensure the required properties of iron powder for powder metallurgy, as well as the current status and problems of conventional iron powder for powder metallurgy. Let's take the law as an example.

Among the many properties required for iron powder for powder metallurgy (hereinafter simply referred to as iron powder), which are the most important properties?

■ The density of the molded product can easily rise by -(1) during powder compaction. So-called good compressibility.

■ High strength molded product. So-called good moldability.

It is.

Here, compressibility mainly refers to the hardness of the iron powder.

Formability is greatly influenced by the shape of the iron powder.

It is desirable that the hardness be low and that the shape be irregular.

As is well known, the water spray method is a method of manufacturing iron powder in which high-pressure water is sprayed over one piece of falling molten metal, and after shaping, the metal is dehydrated, dried, reduced, crushed, and sieved to become a product.

In these processes, it is necessary to control the hardness of the iron powder so that the iron powder, which has been annealed and softened in the reduction process, does not undergo work hardening by giving a radical impact during the crushing process. It is necessary to aim for irregularity in the process and, in particular, to promote sintering of the fine powders in the reduction process, thereby increasing the ratio of the formation of secondary particles and the formation of regular shapes.

On the other hand, with conventional iron powder, the upper limit of the sieving process is 80 to 100 meshes, which is cut through the wire mesh with narrow sieve mesh, making it difficult to produce iron powder that satisfies the characteristic values of iron powder as described above. Not yet.

For this reason, conventional iron powder has nine drawbacks in terms of quality and cost as described below.

First of all, from 9 quality 1m, the upper limit of iron powder particle size is 80 to 100.
Since the iron powder is regulated to be fine (wire mesh sieve size 149-177μ) and fine powder, it is necessary to crush it strongly in the crushing process to ensure the yield of product iron powder. The iron powder becomes hard due to work hardening, and the irregularly shaped powder obtained in the spraying process and reduction process is destroyed, and the iron powder shape becomes close to a simple shape.

As mentioned above, such iron powder has low compressibility and moldability, and has the disadvantage that it is not satisfactory as an iron powder in terms of quality.

Generally, in water spray iron powder, coarse iron powder of 1 grain size is used.
Many have irregular shapes (as the particle size becomes finer, the proportion of simple shapes tends to increase).

From this point of view as well, making the upper limit of the iron powder particle size fine is a factor in reducing formability.

In addition, from the aspect of manufacturing cost of iron powder, as mentioned above, the sieve mesh is narrow, so even if 1-strong crushing is applied, the residual iron powder on the sieve mesh is small.
Occurs in a large area.

This residual iron powder can only be disposed of or used for low value-added purposes.

As a result, the yield as a product iron powder decreases.

This results in increased depreciation costs, raw material costs, and running costs, and has the drawback of significantly increasing the cost of producing iron powder.

In the present invention, iron powder is filled into a mold cavity.

After forming a molded body by compression molding, it is sintered. By controlling the particle size composition of iron powder for powder metallurgy.

The purpose of this invention is to provide iron powder for powder metallurgy that has excellent compressibility and formability and is inexpensive to produce.

According to the present invention, iron powder is filled into a mold cavity and formed by compression molding.

An iron powder for powder metallurgy that is sintered after being formed into a shape, with an upper limit of iron powder particle size of 32 mesh, and a particle size ratio in the range of 32 to 80 mesh at a weight ratio of 2% or more and 30% or less. This is achieved by using iron powder for powder metallurgy, which is characterized by the following.

In this way, in the iron powder for powder metallurgy according to the present invention,
Particle size ratio ranging from 32 to 80 mesh.

The reason why the weight ratio is set at 2% to 30% is because if it exceeds 30%, the powder properties such as fluidity and sintering properties such as tensile properties deteriorate compared to conventional iron powders. ,
If it is less than 2%, the iron powder for powder metallurgy, which is the object of the present invention,
Good for compressibility and moldability.

In addition, reduction in manufacturing costs cannot be expected.

Hereinafter, the present invention will be described in detail based on the accompanying drawings.

As an example, it was manufactured by a water spray method. Powder 5 - Metallurgical iron powder (hereinafter simply referred to as iron powder) will be described below as an example.

Figure 1 shows the influence of the ratio of 32 to 80 mesh in the iron powder on the bending strength of the molded product, which is a property substitute for the formability of the iron powder.
The results are shown when molding to a molded body density of 68 using Ml composition.

As is clear from this figure, compared to conventional iron powder which has a low ratio of 32 to 80 mesh powder in iron powder,
The iron powder of the present invention has a high ratio of mesh powder.

It is understood that the molded product clearly has high bending strength and therefore has excellent moldability.

In addition, Figure 2 shows the influence of the ratio of 32 to 80 mesh in iron powder on compact density, which is a substitute characteristic for the compressibility of iron powder, for Fe-2Cu-0,8Gr-1,8t, Zn The results are shown by molding at a molding pressure of 5 ton/d with the composition.

Similar to Figure 1, this figure shows that compared to conventional iron powder, which has a low ratio of 32 to 80 mesh powder in iron powder,
It is understood that the iron 6 of the present invention, which has a high proportion of 0 mesh powder, has a clearly high compact density and therefore has excellent compressibility.

Next, the iron powder cake obtained by reducing the iron powder produced by the water fountain scarlet method is crushed using a Hammer Milk Eve crusher (the crushing energy in the crushing process (specifically, the number of rotations of the hammer)
6 levels were set, and for iron powder crushed under each condition,
The characteristics of the fibers were evaluated.

Figure 3 shows the results obtained at each grinding energy level. Among the particle size composition of iron powder, the ratio of 32 to 80 mesh, 32
The ratio of residual iron powder in the mesh mesh (hereinafter simply referred to as 1132 mesh iron powder) is shown.

Moreover, FIG. 4 shows the apparent density and fluidity of iron powder obtained at each grinding energy level.

From Figures 3 and 4, it can be seen that as the crushing energy increases, the +32 mesh iron powder ratio and the 32-80 mesh iron powder ratio decrease, the apparent density increases, and the fluidity decreases. .

Here, when the crushing energy falls below a certain level, coarse powder (+32 mesh iron powder) that is not crushed remains, and in particular,
There is an F limit to the grinding energy level because it lowers the fluidity.

On the other hand, even if the crushing energy is increased, the 32 to 80 mesh size does not decrease significantly.

This is because primary particles exist during the spraying process and are not completely destroyed.For this reason, when the upper limit of the particle size of the product iron powder is set to 80 to ioo mesh, as with conventional iron powder,
It can be seen that a certain amount of residual iron powder is definitely generated in the sieving process.

For example, when grinding at the conventional level of iron powder.

If the upper limit of product iron powder particle size is 80 mesh, then 17
% will be discarded or redirected to low value-added uses.

Figure 5 shows the results using the iron powder produced in the two examples.

A tensile test piece of a material equivalent to SMF 4040 was manufactured, and the tensile strength of the sintered body was actually measured.

From this figure, it can be seen that the iron powder containing 32 to 80 mesh powder has exactly the same tensile strength as the conventional iron powder.

However, if 30% is 32-80 mesh powder.

There is a tendency to decrease slightly.

Table 1 shows conventional iron powders and those produced according to this example. Using iron powder containing 30% of 32-80 mesh,
A plate-shaped test piece of Fe-C-CIJ-based sintered alloy was prepared by sintering and forging, and its fatigue strength was evaluated.

Table 1 As is clear from Table 1, the durability limit of the sintered forged product using the iron powder of the present invention is equivalent to that of the sintered forged product using the conventional iron powder.

Next, the iron powder produced by the above water spray method.

Table 2 shows a comparison of yields between conventional iron powder and iron powder of the present invention.

Table 2 9- As is clear from Table 2, compared to conventional iron powder.

The product yield of the iron powder of the present invention is significantly improved.

According to the iron powder of the present invention, it goes without saying that the yield of the product iron powder affects the manufacturing cost.

This shows that compared to conventional iron powder, it is possible to achieve a significant manufacturing cost reduction of nearly 20%.

As is clear from the following, the iron powder for powder molding according to the present invention has excellent compressibility and moldability by controlling the particle size structure of the iron powder.

It has the advantage of low manufacturing cost.

The above explanation has been about pure iron powder produced by the water spray method, but the present invention also focuses on the final process of pulverization and iron powder production.
Since the invention relates to the h1j process, it is equally applicable to other iron powder manufacturing methods, for example, iron powder manufacturing methods such as reduction methods, within the scope of the present invention.

It goes without saying that it is not affected by the type of iron powder.

[Brief explanation of the drawing]

FIG. 1 is a diagram comparing the formability of conventional iron powder and iron powder of the present invention. FIG. 2 is a diagram comparing the compressibility of conventional iron powder and iron powder of the present invention. FIG. 3 is a diagram showing the relationship between crushing energy and the ratio of +32 mesh iron powder and 32 to 80 mesh iron powder in the iron powder. FIG. 4 is a diagram showing the relationship between crushing energy and the apparent density and fluidity of iron powder. FIG. 5 is a diagram showing the relationship between the ratio of 32 to 80 mesh powder and the tensile strength of the sintered body. Applicant Toyota Motor Corporation

Claims (1)

[Claims] (1) Iron powder for powder metallurgy that is filled into a mold cavity and formed into a compact by compression molding and then sintered, with an upper limit of iron powder particle size of 32 mesh and 32 to 80 mesh.
The particle size ratio in the mesh range is 1% by weight or more, 3
An iron powder for powder metallurgy characterized by having a content of 0% or less.