JPH08218102A - Production of metallic porous body - Google Patents

Abstract

PURPOSE: To provide a method for producing a metallic porous body excellent in porous characteristics and mechanical properties. CONSTITUTION: Metal powder is sealed in a capsule and is subjected to temporary sintering of executing low pressure-low temp. heating in a hydrostatic medium to form a porous temporarily sintered body. After the removal of the capsule or without removing the capsule, this temporarily sintered body is subjected to heating treatment to strengthen the boning of the grains without damaging the distribution of the pares. Preferably, the temporary sintering treatment is executed at 0.35 to 0.85mpK [mpK denotes the m.p. (absolute temp.) of the metal powder] under 5 to 150MPa, and the heating treatment for the temporarily sintered body is executed at 0.6 to 0.95mpK.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a mold, a filter,
The present invention relates to a method for producing a metal porous body which is useful as a heat insulating material, a soundproofing material, a vibration damping material, a catalyst carrier, a diaphragm material and the like.

[0002]

2. Description of the Related Art A metal porous body is useful as a constituent material of a mold used for, for example, thermoforming of resin (injection molding, blow molding, etc.) and metal casting (low pressure casting, die casting, etc.). The efficiency of molding and casting operations is improved by applying porous metal to the entire mold or a part of it, or by assembling it in the mold as an accessory to improve the degassing, heat insulation and heat retention of the mold. And molding of products with complex shapes
It is possible to improve casting quality. In the engineering application of the metal porous body to the mold, the filter, the heat insulating material, and other various members, the porosity and the pore diameter required according to the application, the mode of use, etc. are provided, and the mechanical properties are It is necessary to satisfy. Therefore, as a method of manufacturing a porous metal body, for example, a mixture of metal fibers such as stainless steel adjusted to a predetermined size and a metal powder is used as a raw material, which is pressure-molded, and then the powder molded body is vacuumed. Alternatively, a method of sintering in a reducing atmosphere, a method of increasing the strength or hardness by subjecting the obtained sintered body to a nitriding treatment after the sintering treatment of the powder compact, or the raw material powder at a low pressure Various proposals have been made, such as a method of subjecting a powder compact to a two-stage pressure compaction of a pressure compaction at a higher temperature and a pressure compaction at a higher pressure, and then sintering the powder compact in a predetermined atmosphere. (Japanese Patent Laid-Open Nos. 3-239509, 4-72004, 4-30
8048, JP-A-6-33112, etc.).

[0003]

In the conventional manufacturing method in which a powder compact obtained by pressure-molding a raw material powder is sintered (atmospheric pressure sintering) in a vacuum or in an atmosphere of a predetermined composition, the pores of a metal porous body are used. It is difficult to control the porosity and pore diameter, and the porosity and pore diameter are likely to be non-uniform. The defects will increase as the product size increases and the shape becomes more complex. In addition, it is difficult to secure mechanical strength with a metal material that is difficult to form and sinter. The mechanical strength of the sintered body can be increased by applying a high temperature to the sintering process to promote the sintering reaction. On the other hand, on the other hand, the sintered body is densified (porosity). Rate and pore diameter decrease), the function as a porous body is unavoidably deteriorated. The present invention has been made for the purpose of solving the above-mentioned problems relating to the production of a metal porous body.

[0004]

The method for producing a porous metal body according to the present invention comprises encapsulating a metal powder in a capsule and performing a temporary sintering treatment of low pressure and low temperature heating in a hydrostatic medium to obtain a porous temporary body. It is characterized in that after forming the sintered body, the pre-sintered body is heat-treated without removing the capsule or without removing the capsule.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A porous pre-sintered body is formed by a hot isostatic pressing process of low pressure and low temperature heating performed by encapsulating metal powder in a capsule. As a result of the uniform pressure action of the hydrostatic medium, this pre-sintered body has a uniform porosity regardless of shape or size. This temporary sintered body is poor in bonding force between particles as it is, but by being subjected to heat treatment, bonding between particles is promoted while maintaining the pore distribution of the temporary sintered body, resulting in high porosity. It is finished into a porous metal body having good mechanical properties. Hot isotropic pressure treatment (HIP treatment) of metal powder is known as an industrial method for producing a sintered alloy product, which is used for producing a sintered product having a high density close to the true density. Done for the purpose,
High temperature heating and high pressure are applied to the HIP process.
The present invention utilizes this HIP treatment as a means for forming a porous body, and under the treatment conditions of low pressure and low temperature heating different from the original application form of the HIP treatment, temporary sintering having high porosity. As a result of the formation of the body and the combination of the HIP treatment and the subsequent heat treatment, it is possible to combine the improved porous characteristics and mechanical properties desired for various structural members and functional members in a wide range of applications.

The encapsulation operation for encapsulating the metal powder in the HIP treatment (temporary sintering treatment) is carried out in the same manner as in the ordinary case by filling a capsule of an appropriate material type (for example, mild steel) and degassing. It is performed by sealing (for example, 1 × 10 ^-1 to 1 × 10 ^-3 Torr). In the HIP treatment of the metal powder for forming the temporary sintered body, the heating temperature is 0.35 mp
Range of 0.85mpK (mpK is melting point of metal powder in absolute temperature) [eg, 0.35 × 1700 for melting point 1700K]
K to 0.85 × 1700K (= 595 to 1445K)], and the applied pressure is preferably controlled to a range of 5 to 150 MPa.
Under the processing conditions where the heating temperature is lower than 0.35 mpK and the applied pressure is less than 5 MPa, it takes a long time to form the pre-sintered body, and even if the processing is carried out for a long time depending on the type of metal powder, handling is possible. This is because it is difficult to form a temporary sintered body that can withstand the above conditions. On the other hand, under the processing conditions where the heating temperature is higher than 0.85 mpK and the applied pressure exceeds 150 MPa, the fusion of the particles of the metal powder progresses unnecessarily, making it difficult to obtain a temporary sintered body with high porosity. Because it will be. By holding for a suitable time (about 0.5 to 8 hours) under the conditions of low temperature and low pressure controlled as described above, the metal powder is appropriately softened to form a bond between the particle sizes, and the metal powder has a high porosity. A sintered body is formed.

After the above HIP treatment, heat treatment (strengthening heat treatment) of the pre-sintered body is carried out for the purpose of improving the strength of the pre-sintered body.
Is preferably controlled to a temperature range of 0.6 mp to 0.95 mpK [mpK has the same meaning as above]. Processing temperature is 0.6
If it is lower than mpK, it is difficult to efficiently carry out the diffusion bonding reaction at the contact interface between particles, while 0.95 mpK
This is because if a high temperature exceeding 1.0 is applied, the agglomeration reaction between particles is promoted and the pore distribution of the pre-sintered body is impaired.
The processing time is about 5 to 15 hours. This heat treatment is performed after taking out the pre-sintered body from the capsule or in a state of being encapsulated in the capsule. Since the inter-particle bonding force of the temporary sintered body is low, the temporary sintered body is fragile when the raw material powder is a material that is difficult to sinter, and the capsule for removing the temporary sintered body from the capsule is weak. During the machining process or the handling process of the removed pre-sintered body, the pre-sintered body is likely to be damaged or collapsed. In such a case, the above-mentioned trouble can be prevented by carrying out heat treatment while encapsulating the capsule to strengthen the interparticle bond and then taking out the capsule. Further, even when the raw material powder is an active material, if the heat treatment of the pre-sintered body is performed in a state of being encapsulated, it is not necessary to use a vacuum furnace or an atmosphere furnace, Processing can be achieved.

The selection of the type of metal powder is arbitrary, and stainless steel (for example, SUS304, SUS630), tool steel (for example, SKD61, SKD11), maraging steel (for example, 18Ni system, 20Ni system), high speed steel (for example, SKH51, SKH55), non-ferrous metal (for example, aluminum or its alloy, titanium or its alloy, copper or its alloy), etc. are selected and used according to the intended use of the porous metal body and the required material properties. .

The metal powder has, as its particle size constitution, a cumulative frequency of 5 on the weight-based particle size cumulative distribution curve (see FIG. 1).
% Particle size R ₅ , 50% particle size R ₅₀ , and 95% particle size R ₉₅ satisfy the following formula: (R ₉₅ −R ₅ ) / R ₅₀ ≦ 2.5 ... [1] Those having a particle size distribution are preferably used.
For particle size R ₅₀ (average particle diameter), the ratio of the width of the particle size R ₉₅ and particle size R ₅ (R ₉₅ -R ₅₎ value large particle size distribution _{"(R 95 -R 5) / R} 50 " In the powder having, the coarse voids are likely to be generated between the particles in the powder packed layer, and the voids are likely to be blocked due to the intrusion of the fine particles into the voids between the particles. The former increases the distribution of coarse pores in the sintered body, and the latter reduces the distribution of open pores, which lowers the porous performance of the product porous body. The ratio of _{(R 95 -R 5) / R} 50, be adjusted to about 2.5 or less is effective in inhibiting alleviate such a problem, more preferably, 1.
It is 5 or less. The particle size R ₅₀ of the powder is about 10 to 10
A range of 00 μm is suitable. When a product porous body having a large distribution of open pores with a relatively small pore size (suitable for a mold etc.) is desired, a particle size R _{50 of} about 10 to 75 μ
If it is advantageous to use a powder having a relatively small diameter of about m, on the other hand, if one wishes to have a large distribution of open pores having a large pore diameter (suitable for a filter etc.), then a particle diameter R _{50 of} about 300 to 10
A coarse powder of 00 μm is preferably used.

Using a metal powder having the above grain size constitution,
The porous metal body produced through the preliminary sintering treatment and the heat treatment process of the present invention has a porosity of about 7 to 50%, a pore diameter of about 500 μm or less, and a pore diameter distribution satisfying the following formula. (D ₉₅ −D ₅ ) / D ₅₀ ≦ 2.5 ... [2] [wherein, D ₉₅ : pore diameter of cumulative frequency 95% in cumulative distribution curve of pore diameter, D ₅ : pore diameter of 5%, D ₅₀ : Same as 50
% Pore size (average pore size)]. Such pore distribution characteristics imparted to the metal porous body enhances the usefulness of the metal porous body as various structural members / functional members in various fields,
For example, molds and filters that require gas / particle permeability, heat insulation, mechanical strength, etc., catalyst carriers and sensors that require permeability and a large specific surface area, or high vibration damping characteristics are required. It increases the possibility of engineering application to damping materials and soundproofing materials.

[0011]

[Raw material powder]

A: Atomized powder of stainless steel (JIS G4303 SUS 310S equivalent) (C: 0.02, Si: 1.0, Mn: 0.1, Cr: 18.3, Ni: 10.8,%) B: Alloy tool steel (JIS G4404 SKD 61 equivalent) Atomized powder (C: 0.38, Si: 0.9, Mn: 0.01, Cr: 5.25, Mo: 1.20, V: 1.0,
%)

Table 1 shows the production conditions, and Table 2 shows various characteristics of the obtained porous metal body. Specimen Nos. 1 to 5 are invention examples, No. 11
Is a comparative example corresponding to the conventional material. In the table, the numerical value in the "Gas release" column indicates the air pressure (Kgf / cm ² ) required to allow the air to permeate, and the "Bending strength" column indicates the JIS B1601
Shows the 3-point bending strength (Kgf / mm ² ) by the bending test method (span distance: 30 mm). The metal porous body of the invention example is N
As shown in o.1 to 3, even though the average pore diameter is the same as that of Comparative Example No. 11, the open porosity is high, the gas permeability is excellent, and the mechanical strength is remarkably high. No.4, No.5
As described above, while maintaining the same strength level as that of the comparative example, it has a rich pore distribution of open pores.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

Industrial Applicability The metal porous body produced by the hot isostatic pressing of the raw material powder and the heat treatment of the pre-sintered body according to the present invention has various porosity and mechanical properties. It is useful as a structural member and a functional member of, for example, in resin molding dies and metal casting dies, damping members, heat insulating members, sound absorbing members, catalyst carriers, filters, diaphragms, and various other fields. It is possible to expand and diversify engineering applications of porous metal.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a particle size distribution curve of metal powder.

Claims (3)

[Claims] 1. Encapsulating a metal powder in a capsule, performing a low pressure / low temperature heating pre-sintering treatment in a hydrostatic medium to form a porous pre-sintered body, and then removing or removing the capsule. A method for producing a porous metal body, which comprises heat-treating the pre-sintered body without heat treatment. 2. The pre-sintering treatment of the encapsulated metal powder is carried out at a temperature of 0.35 to 0.85 mpK [where mpK is
Melting point of metal powder (absolute temperature)], pressure: 5 to 150M
The heat treatment of the pre-sintered body is performed at a temperature of 0.6 to
The method for producing a metal porous body according to claim 1, wherein the method is performed at 0.95 mpK (mpK is as defined above). 3. The metal powder has a particle size cumulative particle diameter R _{5 of} 5%, a particle diameter R _{50 of} 50%, and a particle diameter R _{95 of} 95% in a cumulative distribution curve (weight basis) of particle diameters, The following formula: (R ₉₅
-R ₅ ) / R ₅₀ ≦ 2.5 is satisfied, and the particle size R ₅₀ is 1
It has a particle size distribution which is 0-1000 micrometers, The manufacturing method of the metal porous body of Claim 1 or Claim 2 characterized by the above-mentioned.