JPH0257613A - Production of sintered metallic material and its raw powder - Google Patents

Abstract

PURPOSE:To produce the title high-density sintered metallic material at a low cost by forming raw powder having specified particle size, degreasing the formed product, sintering the product, and then further pressure-sintering the sintered product at specified temp. and pressure in a nonoxidizing atmosphere. CONSTITUTION:The raw powder of stainless steel, etc., having 9-30mu mean particle diameter is formed. The spherical raw powder obtained by the atomization process is preferably used. The forming can be carried out by injection molding. The obtained formed product is degreased, and then sintered to obtain a primary sintered product. The primary sintering is preferably performed at a reduced pressure of <=0.1Torr or in a nonoxidizing atmosphere. The primary sintered product is then pressure-sintered at 1,000-1,400 deg.C and at 30-150atm pressure in a nonoxidizing atmosphere. By this method, a high- density sintered metallic material having >=97.0% density ratio can be obtained at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a sintered metal material and a raw material powder thereof.

<Prior Art> In recent years, the production of sintered metal materials by powder metallurgy has shown remarkable growth, and the range of applications of sintered metal materials is expanding.

Among these, automotive parts, electronics, and
What is the shape of metal materials such as electrical parts and office parts? As manufacturing methods become more complex, the cutting method is being replaced by the powder metallurgy method.

However, the sintered metal material produced by the powder metallurgy method has pores, which has the disadvantage that the density of the sintered metal material is low, and the presence of the pores impairs corrosion resistance and mechanical properties. Since the properties of such sintered metal materials are proportional to their density, various studies are being conducted to increase the density of sintered metal materials.

There are two main approaches to increasing density: one is by improving the sinterability of raw material powder, and the other is by improving the manufacturing process. Among the various approaches, the ones that are attracting particular attention are the former, which uses fine metal powder (the deterioration of compressibility when using fine powder is solved by introducing injection molding), and the latter, which uses HIP (hot, etc.). One example is the use of directional pressure. moreover,
Regarding HIP technology, the pressure sintering method (US, Pat, No. 4591482) has significantly reduced equipment costs.
, Japanese Patent Publication No. 63-500874), and this method has high industrial value.

<Problems to be Solved by the Invention> As mentioned above, the pressure sintering method is a method of high industrial value as a method for producing sintered metal materials. However, in this pressure sintering method, no consideration was given to the particle size of the raw material powder.

Therefore, the primary sintered body obtained by using powder with a large particle size as the raw material powder, molding it by a method such as injection molding, and sintering it is not a closed-pore sintered body, so pressure sintering is used. Even after re-sintering, the density did not increase and the pitting corrosion resistance was poor.
Further, if a fine powder is used as the raw material powder, a closed-pore primary sintered body can be easily obtained, but the smaller the average particle size of the raw material powder, the higher the price, which poses a problem in terms of cost. Furthermore, when fine powder was used, the effect of improving the density of the sintered body was small even if it was re-sintered by the pressure sintering method.

The present invention has been made in view of the above circumstances, and provides a low-cost manufacturing method for a sintered metal material with a density ratio of 97.0% or more, and a low-cost raw material powder used in manufacturing the sintered metal material. Means for Solving the Problems> The present inventors have investigated the effect of pressure sintering conditions on the sintered density of raw material powders having various particle sizes during the production of sintered metal materials. Detailed experiments were conducted to examine the effects, and the present invention was completed.

In the present invention, a powder having an average particle size of 9 to 30 μm is used as a raw material powder, the powder is molded, the obtained molded body is subjected to a degreasing treatment, and then sintered to obtain a primary sintered body. After that, the temperature was 1000-1400℃ and the pressure was 30℃ in a non-oxidizing atmosphere.
The present invention provides a method for producing a sintered metal material, characterized in that pressure sintering is performed at a pressure of ~150 atmospheres.

Preferably, the molding is injection molding.

Furthermore, the present invention involves molding the raw material powder, degreasing the resulting molded body, and then sintering it to obtain a primary sintered body. 1400℃,
The present invention provides a raw material powder characterized by having an average particle size of 9 to 30 μm and used when producing a sintered metal material by performing pressure sintering at a pressure of 30 to 150 atmospheres.

In each of the above inventions, the raw material powder is preferably a powder obtained by an atomization method.

Similarly, in each of the above inventions, stainless steel powder can be used as a preferable raw material powder.

The present invention will be explained in detail below.

The raw material powder of the present invention has an average particle size of 9 to 30 μm.

When the average particle size is more than 30 μm, the primary sintered body with closed pores (
In the particle size range of the present invention, a sintered density ratio of 90% or more cannot be obtained. These non-closed pore primary sintered bodies cannot be densified by pressure without a special container filling process (generally called canning) or a special pore sealing process. On the other hand, as the average particle size decreases, the sinterability of the powder itself improves, so it is easy to obtain a primary sintered body with a sintered density ratio of 90% or more, which has only closed pores. On the other hand, despite the rise in powder prices, the effect of improving the density ratio by pressure sintering the secondary sintered body becomes smaller. Therefore, the average diameter of the raw material powder is 9~
It is set to 30 μm.

The raw material powder of the present invention may be manufactured by any method, but for example, metal fine powders manufactured by high-pressure water atomization method, water atomization method, reduction method, carbonyl method, crushing and classification, and fine metal powders thereof. Mixed powder can be used.

Among these, powder produced by the atomization method is preferable because the alloy composition can be easily obtained and a shape close to a spherical shape can be obtained, but high-pressure water atomization is preferable because powder with an average particle size of 30 μm or less can be easily obtained. Law is most preferred.

Further, the raw material powder of the present invention may be made of any metal, such as stainless steel, Ni, C
r, Mo, V, Mn.

Examples include iron alloys containing St, Co, etc.

Further, in the present invention, the raw material powder is molded, degreased, and sintered to obtain a primary sintered body.

The molding may be performed by any known molding method, including conventional mold press molding, extrusion molding, powder rolling molding, injection molding, and the like. Injection molding is particularly preferred when molding a metal material into a complicated shape.

Injection molding of powder is carried out after adding and mixing a binder in order to impart injection fluidity and strength to the molded body, as is known when performing injection molding using only powder. The binder for injection molding is mainly composed of thermoplastic resin and/or wax, and if necessary, a plasticizer, lubricant, degreasing accelerator, etc. are added thereto.

Thermoplastic resins include acrylic, polyethylene,
There are polypropylene-based and polystyrene-based waxes, and waxes include natural waxes such as beeswax, Japanese wax, and montan wax, and low-molecular polyethylene, microclostalin wax, paraffin wax, etc. There are many synthetic waxes, and one or more types selected from these are used.

The plasticizer is selected depending on the combination with the main resin or wax, but specifically, di-2-ethylhexyl phthalate (DOP), diethyl phthalate (DEP)
Examples include di-n-butyl phthalate (DHP).

Examples of the lubricant include higher fatty acids, fatty acid amides, fatty acid esters, etc. In some cases, waxes are also used as the lubricant.

Moreover, a sublimable substance such as camphor can also be added as a degreasing accelerator.

The amount of the injection molding binder is usually about 10% by weight.

For mixing and kneading powder and binder, batch method or
A continuous type kneader can be used, and among the batch type kneaders, a pressure kneader, a Banbury mixer, etc. are advantageously suited, and among the continuous type kneaders, a 2IjiIII extruder and the like are advantageously suited. After kneading, granulation is performed using a pelletizer or a pulverizer as needed to obtain a compound for molding.

Injection molding may be performed using a normal plastic injection molding machine or the like. At this time, the injection pressure is usually 0.
．． It is about 3 to 3 t/cm2.

After injection molding, heating is performed to remove the binder. The temperature increase rate at this time is 5 to bhr, -numerically, 4
Maintain at 50 to 700°C for about 0 to 4 hours. In addition,
If the temperature increase rate at this time is too high, cracks or swelling will occur in the obtained molded product, which is not preferable. Further, the removal of the binder is preferably carried out in a non-oxidizing atmosphere that suppresses oxidation of the powder and does not contribute to the decomposition reaction of the binder.

After removing the binder, a second sintering is performed. At the end of the heat treatment in the previous step, some of the binder remains, but in the next sintering, the carbon in the residual binder reacts with the oxygen in the oxide film on the surface of the metal powder, - Decrease C and Oi in the secondary sintered body. Therefore, it is necessary to adjust the degree of removal of the binder, or perform oxidation treatment after removal, and C10
Primary sintering is performed after adjusting the molar ratio to an optimum value, preferably 0.3 to 3.0.

Although it is necessary to obtain a sintered body with closed pores through primary sintering, if the raw material powder of the present invention is used, a general sintering method can be applied.

Primary sintering is 0. It is carried out under reduced pressure of ITorr or less and/or in a non-oxidizing atmosphere.

For example, if the raw material powder is stainless steel, 0, IT
After general sintering is performed at 1050 to 1300°C for about 2 hours, two-stage sintering is performed in Ar at 1250 to 1370°C for about 1 hour. In addition, the raw material powder is Cr, Mo,
V.

In the case of alloys containing reducing elements such as Mn and Si,
Can be sintered like stainless steel. Note that the sintering conditions can be easily determined from the above range through trial experiments. Furthermore, the raw material powder is Fe, Ni, Co, Cu, Mo.
, Sn, and other easily reducible elements, sintering is performed at 800 to 1400° C. for about 2 hours in a reducing gas such as hydrogen.

In the present invention, the primary sintered body obtained by the above method is heated at a temperature of 1000 to 1400 t and a pressure of 30 t in a non-oxidizing atmosphere.
Pressure sintering is performed at ~150 atmospheres.

Since this step is a step of densifying the primary sintered body whose pores were closed in the previous step (density ratio of 97.0% or more), there is no need to use a reactive gas. Therefore, sintering is performed in a non-oxidizing atmosphere. However, inert gas is preferable for handling because it has low risk of explosion even when pressurized.

The higher the temperature, the greater the effect of improving the density ratio by pressure sintering, but if the temperature exceeds 1400°C, the crystal grain size may become coarser than necessary, and the metal may start to melt.
If it is less than this, there is no effect of improving the density ratio by pressure sintering, and a sintered metal material with a density ratio of 97.0% or more cannot be obtained, which is not preferable.

Furthermore, when secondary sintering is performed under reduced pressure, a compositional distribution occurs on the surface of the sintered body due to the difference in vapor pressure of the constituent elements, and
Even when the process is carried out in a reducing gas atmosphere, a compositional distribution may occur between the surface of the sintered body or powder that is in contact with the gas and the inside thereof. This compositional distribution deteriorates the properties of the sintered body and is not preferable.

Therefore, after the second sintering, under pressure above atmospheric pressure, in an atmosphere in which the constituent elements do not evaporate, the sintering is carried out at a temperature higher than that at which the diffusion rate of atoms is higher, in an atmosphere in which no chemical reactions occur. It is necessary to sinter the area and uniformize the composition quickly.
It needs to be at least ℃.

In addition, when the pressure is less than 30 atm, the effect of improving the density ratio by pressure sintering is not significantly different from that when no pressure is applied, and a sintered metal material with a density ratio of 97.0% or more is obtained. I can't. On the other hand, in order to use a gas medium exceeding 150 atmospheres,
Because equipment costs have skyrocketed and are inconsistent with the purpose of the present invention,
The pressure shall be 30 to 150 atmospheres.

In the steps up to this point, gases used to create a non-oxidizing atmosphere include inert gases such as Ar and He', reducing gases such as CHa, CsHa, N2, combustion exhaust gas, and the like.

<Example> The present invention will be specifically explained based on examples.

(Example I) As raw material powder, average particle size of 5US316 composition is 7.5~
A water atomized powder of 35.0 μm and a water atomized powder of 5US304 composition with an average particle size of 7.5 to 16.5 μm were prepared.
Adding a thermoplastic binder mainly made of acrylic,
After kneading with a pressure kneader, the mixture was pulverized to obtain an injection molding compound.

This was injection molded at 160°C and It/cm2.
It was made into a molded body of 0 mm x l l mm x 5 mm.

Next, in a N2 atmosphere, the heating rate was 15°C/h.
The temperature was raised to 0°C and held for 0.5 hours to remove the binder. Furthermore, the temperature was raised to 1160°C and the pressure was 1xlO-3
After holding at Torr for 2 hours, the temperature was raised to 1365°C and held in Ar7 atmosphere (pressure 1 atm) for 2 hours,
A next sintered body was obtained.

These secondary sintered bodies were maintained at a temperature of 1300°C and a pressure of 150 atm for 1 hour in an Ar atmosphere as shown in Table 1, or were heated at a temperature of 1300°C and a pressure of 1100°C in an Ar atmosphere.
A secondary sintered body was obtained by holding at at for 2 hours.

For each of the primary sintered body and the secondary sintered body, the density ratio was determined from the density and true density by the Archimedes method.

The results are shown in Table 1.

(Example I+) As a raw material powder, the average particle size of 5O5316 composition was 12.5
A water atomized powder of .mu.m was prepared and a primary sintered body was obtained in the same manner as in Example (2).

This was carried out in an Ar atmosphere at a temperature and pressure of 15% as shown in Table 2.
A secondary sintered body was obtained by maintaining the temperature at 0 atm for 1 hour.

The density ratio was determined in the same manner as in Example r, and the results are shown in Table 2.

(Example I11) As a raw material powder, the average particle size of 5US316 composition was 12.5
A water atomized powder of .mu.m was prepared and a primary sintered body was obtained in the same manner as in Example (2).

This was maintained in an Ar atmosphere at a temperature of 1350°C and a pressure shown in Table 3 for 1 hour to obtain a secondary sintered body.

The density ratio was determined in the same manner as in Example I, and the results are shown in Table 3.

A primary sintered body was obtained in the same manner as in Example I.

Further, using the same raw material powder, 3% by weight of camphor was dissolved in acetone, and the raw material powder was mixed while drying and removing the acetone in a mortar to obtain a raw material for mold forming. This is 3
Mold forming is performed at a pressure of t/cm2, and the length of 40m
It was made into a molded body of mX 10mmX5mm.

Next, the temperature was raised to 600°C at a temperature increase rate of 5°C/m t n in dry hydrogen and maintained for 0.5 hours to remove camphor.

This was sintered in the same manner as in Example (2) to obtain a subsequent sintered body.

These were maintained under the conditions shown in Table 4 for 1 hour to obtain secondary sintered bodies.

The density ratio was determined in the same manner as in Example 2, and the results are shown in Table 4.

(Example IV) As a raw material powder, the average particle size of 5US316 composition was 12.5
Example 2 of Table 1 examines the relationship between the average particle diameter of the raw material powder and the density ratio of the sintered metal material by preparing water atomized powder of .mu.m.

The density ratio of the primary sintered body becomes smaller as the average grain size increases, and the average grain size exceeds 30 μm (Comparative Example 2)
Therefore, the density ratio of 90% at which the sintered body becomes closed pores cannot be achieved,
Therefore, no increase in density was observed due to secondary (pressure) sintering.

On the other hand, raw material powder with a relatively small average particle size (Comparative Example 1.
When 3) was used, the final density ratio after secondary sintering did not increase much, although the secondary sintered body had a high density ratio. It can be assumed that this is because the surface area of the powder is large, so the contact resistance between the powders during pressurization is large, and the effect of pressurization is not improved.

When the powder of the present invention (Invention Examples 1 to 8) is used, the density ratio of the secondary sintered body decreases to some extent due to the increase in the average particle size, but the contact resistance between the powders during secondary sintering decreases. The effect on the increase in density ratio of the final sintered body after secondary sintering was well balanced, and a sintered metal material with a high density ratio (density ratio of 97.0% or more) was obtained.

Example 11 examines the relationship between the temperature during secondary sintering and the density ratio of the sintered metal material.

When the temperature is less than 1000°C (Comparative Example 4), the density ratio improvement effect is small, and when the temperature is less than 1000°C to 1300°C (Invention Example 3.
9), the density ratio could be effectively improved, and a sintered metal material with a density ratio of 97.0% or more was obtained.

Example (2) examines the relationship between the pressure during secondary sintering and the density ratio of the sintered metal material.

When the pressure is less than 30 atm (Comparative Example 5), the effect of improving the density ratio is small;
t t ), a sintered metal material with a density ratio of 97.0% or more was obtained.

Example IV examines the method of forming the raw material powder during the production of the secondary sintered body and the atmospheric gas during the secondary sintering.

When producing a sintered metal material using the raw material powder of the present invention by the method of the present invention, the raw material powder may be molded not only by injection molding (Invention Example 3.11) but also by mold molding (Invention Example 13). It has become clear that it can be applied.

In addition, the atmosphere during secondary sintering is non-oxidizing, and Ar (Invention Example 3, 11.13
) It is clear that not only N2 (Invention Example 12) can also be applied.

<Effects of the Invention> The present invention provides a low-cost manufacturing method for a sintered metal material with a density ratio of 97.0% or more, and a method for manufacturing a sintered metal material with a density ratio of 97.0% or more using this method. A low cost raw material powder is provided.

Therefore, the sintered metal material can be used in a wider range of fields.

Claims (7)

[Claims] (1) Powder with an average particle size of 9 to 30 μm was used as the raw material powder, the powder was molded, the resulting molded body was subjected to degreasing treatment, and then sintered to obtain a primary sintered body. After that, in a non-oxidizing atmosphere at a temperature of 1000~1400℃ and a pressure of 30~1
A method for producing a sintered metal material, characterized by pressure sintering at 50 atmospheres. (2) The method for producing a sintered metal material according to claim 1, wherein the raw material powder is a powder obtained by an atomization method. (3) The method for producing a sintered metal material according to claim 1 or 2, wherein the raw material powder is stainless steel powder. (4) The method for manufacturing a sintered metal material according to any one of claims 1 to 3, wherein the molding is injection molding. (5) After molding the raw material powder, degreasing the obtained molded body, and then sintering it to obtain a primary sintered body, in a non-oxidizing atmosphere at a temperature of 1000 to 1400°C and a pressure of 30～
A raw material powder characterized in that it has an average particle size of 9 to 30 μm and is used when producing a sintered metal material by performing pressure sintering at 150 atmospheres. (6) The raw material powder according to claim 5, wherein the raw material powder is a powder obtained by an atomization method. (7) The raw material powder according to claim 5 or 6, wherein the raw material powder is stainless steel powder.