JPH10317012A - Production of metal porous powder sintered body by hot isostatic pressing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make net shape forming possible, in particular to improve a yield of a thin sintered body and to reduce the production cost by efficiently conducting capsule removal after hot isostatic pressing(HIP) when producing of a porous sintered body, which is subjected to HIP with filling a metal powder in a metal capsule. SOLUTION: Metal capsule removal after HIP treatment is conducted by chemical dissolving (a dissolving solution can dissolve the capsule but does not have dissolving capability for a product sintered body). When the capsule is changed to a non-dissolvable composition by diffusion reaction of a boundary between the capsule and a metal powder, a ceramic powder layer of non-binding as a barrier layer is interposed. The ceramic powder layer is fallen off from a sinterd body surface by capsule dissolving treatment after HIP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal-based porous sintered body in which metal powder is sealed in a metal capsule and subjected to hot isostatic pressing, and more particularly to a method for removing a metal capsule after the treatment. This enables simplification, cost reduction, and net shape molding of a sintered product.

[0002]

2. Description of the Related Art The hot isostatic pressing method (HIP method) is one of the typical methods for producing a sintered body using powder as a raw material. Generally, a raw material powder is formed in a metal capsule (mild steel can). The metal capsule HIP is heated under the action of a hydrostatic pressure medium to cause a sintering reaction (hereinafter referred to as “metal capsule HIP”).
Law "). In addition, HI using glass capsule
There are P method (glass capsule HIP method) and HIP method without capsule (capsuleless HIP method).
In the glass capsule HIP method, it is difficult to select an appropriate glass material. In the case of the capsuleless HIP method, a step of preforming the raw material powder is required, and the steps are complicated. It has hardly been put to practical use.

[0003]

The metal capsule HIP method requires a capsule removing process for removing the sintered body from the capsule after the treatment. The removal process is conventionally performed by machining. However, since the interface between the metal capsule and the sintered body is joined by solid phase diffusion inevitably occurring during the HIP process, the metal capsule alone cannot be removed by machining, and the product sintered body cannot be removed. The surface layer will be removed at the same time. For this reason, in the metal capsule HIP method, even if the product sintered body has a relatively simple shape, net shape molding is impossible, and the yield is reduced due to cutting and removal of the surface layer of the sintered body. Inevitable. In particular, when the product sintered body is a porous sintered body to be used for a filter member or a permeable member constituting a molding die (a resin molding die or a non-ferrous metal casting die), It is difficult to remove the capsule without damaging the product sintered body. When the porous sintered body is a thin-walled body, the difficulty of processing and the disadvantage of lowering the yield become more remarkable.
The present invention is intended to solve the above-mentioned problem relating to the production of a metal-based porous sintered body using a metal capsule HIP.

[0004]

[MEANS FOR SOLVING THE PROBLEMS] Metal capsule H of the present invention
The first method for producing a metal-based porous sintered body by IP is characterized in that the metal capsule after the treatment is removed by chemical dissolution. According to the second production method of the present invention, the metal powder is sealed as a barrier layer for preventing solid phase diffusion at the interface between the metal powder and the metal capsule with a ceramic powder layer interposed therebetween, and hot isostatic pressing is performed. The method is characterized in that the metal capsule after the treatment is removed by chemical dissolution.

[0005] The metal capsule in the HIP of the present invention is:
This is a mild steel can container or the like used as a capsule material for ordinary HIP processing, and is dissolved using an acid solution or the like as a processing liquid. By dissolving the capsule and selecting and using a solution that does not have a dissolving effect on the sintered body or has a weak dissolving effect as the treatment liquid, the sintered body can be removed from the capsule with almost no corrosion damage to the sintered body. Can be taken out. Depending on the metal material of the sintered body, during the HIP process,
In the case where the metal capsule changes to a chemically insoluble composition due to a diffusion reaction at the interface between the metal powder and the metal capsule (diffusion of the metal powder component into the capsule),
The problem can be avoided by interposing a barrier layer that prevents the diffusion reaction.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The dissolving solution used for the chemical dissolving treatment of metal capsules after the HIP treatment is, for example, an acid solution such as nitric acid, hydrochloric acid, or various mixed acids. Is appropriately selected and used according to the metal material type.
When the capsule is hardly dissolved due to the diffusion reaction at the interface between the capsule and the metal powder in the HIP process due to the type of the metal powder encapsulated in the capsule (for example, the capsule is made of carbon steel such as S25C, When the metal powder is SUS 316L stainless steel, the diffusion of Cr from the metal powder into the capsule makes the capsule hardly soluble in nitric acid, and a barrier layer for preventing the diffusion is provided. ). The barrier layer has a high melting point that does not cause sintering during the HIP process, and is formed of a powder that maintains a non-consolidated state that can be collapsed after HIP. The material type is, for example, silica powder (SiO ₂ ), alumina (Al ₂ O ₃ ), silicon nitride (S
iO ₂ ), boron nitride (BN) and the like, and can be appropriately selected from common ceramics. The thickness of the barrier layer may be, for example, ○ to ○ mm, and the particle diameter of the ceramic powder may be, for example, about the same as that of the metal powder, or may be finer than that.

The barrier layer is formed by applying a slurry of ceramics powder to the inner surface of the metal capsule (surface in contact with the metal powder) and drying the slurry, a method of forming the ceramics powder layer by a cold isostatic pressing method, It is performed by other appropriate methods. FIG. 1 shows an example of the form of a metal capsule used for manufacturing a pipe-shaped sintered body and a barrier layer on the inner surface side (the surface facing the metal powder).
(11) is an outer can member, (12) is an inner can member, (13) and (14) are lids, and (20) is a barrier layer formed on the inner surface of each member. As an example of the case where the barrier layer (20) is formed by applying a slurry of ceramic powder, the barrier layer of the outer can member (11) is formed by rotating the outer can member around an axis while rotating the slurry. The inner peripheral surface is coated with a slurry layer by the action of centrifugal force and then dried by heating (centrifugal molding). The barrier layer (20) of the inner can member (12) is formed by removing the inner can member (12). It is formed by applying a slurry to the outer peripheral surface by spraying and drying while rotating about an axis.

[0008] H performed by encapsulating metal powder in a metal capsule
The IP processing is performed by using ordinary H for high-density sintered products.
Unlike IP processing, low temperature and low temperature
Low pressure processing conditions apply. For encapsulation of metal powder, instead of vacuum (reduced pressure) encapsulation in normal HIP processing, normal pressure (if necessary, an inert atmosphere of N ₂ , Ar, etc.)
You may go to. The low-temperature / low-pressure HIP treatment is preferably performed at a temperature of 0.35 to 0.85 mpK (mpK is the melting point of the metal powder,
(Absolute temperature), pressure: 5 to 150 MPa. At a lower temperature and a lower pressure, the sintering reaction of the metal powder is insufficient, and at a higher temperature and a higher pressure, the porosity of the obtained sintered body is impaired. The porous sintered body obtained by the HIP treatment is subjected to a heat treatment for strengthening the interparticle bonding, if desired. The heat treatment temperature is suitably in the range of about 0.6 to 0.95 mpK, and by maintaining the temperature in the same temperature range for an appropriate time, the strength of the sintered body can be increased without impairing the porosity of the sintered body. This heat treatment may be performed in the HIP device in a state where the pressurizing action of the hydrostatic medium is released.

After the HIP treatment (and the optional heat treatment), the metal capsules are chemically dissolved and removed. When the barrier layer (ceramics powder layer) does not intervene at the boundary between the metal capsule and the metal powder-filled layer, the boundary surface is bonded by solid phase diffusion during HIP processing. By selecting the kind, the capsule can be dissolved and removed without damaging the sintered body such as corrosion. The sintered body taken out of the capsule is washed with water to remove the acid solution remaining on the surface. On the other hand, when a barrier layer is interposed at the boundary between the metal capsule and the metal powder layer, the barrier layer (having a collapsible non-consolidated state) is formed by melting and removing the metal capsule. Fall off the surface. On the surface of the obtained sintered body, a small amount of ceramic powder may adhere and remain,
This can be easily removed by lightly rubbing the surface with a brush when washing the sintered body with water.

In the melting process of the metal capsule, if necessary, a partial region (one or a plurality of portions) of the capsule solid-phase bonded to the surface of the sintered body is left unmelted as a part of the product sintered body. Then, a composite of a sintered body (porous material) and a metal member (non-porous material) can be obtained (claims 2 and 4). This complex is coated (masked) with an acid-resistant paint, resin, etc. on a desired portion of the capsule surface,
It is obtained by preventing capsule dissolution in that part. FIG. 2 shows that, for the pipe-shaped sintered body (A), the circumferential portions at both ends of the outer can material (11) of the capsule are left, and a flange-shaped metal member (outer can material 11) is formed on the sintered body (A). (B) shows an example of a composite having undissolved residue (B). The sintered body manufactured by the HIP processing with the barrier layer (20)
If it is desired to form a composite, the formation of the barrier layer may be partially omitted, and the solid-phase bonding of the interface between the metal powder and the capsule in that portion may be performed by HIP treatment. A composite having a metal member (part of a capsule) in a desired portion of a sintered body can be obtained by a dissolution treatment in which masking is applied to the above. Due to such a combination, when assembling a product sintered body to an apparatus / equipment, the metal member (B) is used as a joining margin to join the sintered bodies or to join the sintered body and other members. (It is almost impossible to weld a porous sintered body),
The handleability of the porous sintered body is improved.

The removal of the metal capsule after the HIP is performed as follows.
In the present invention performed by chemical dissolution as described above, for example, when the metal material type of the sintered body is a high Cr-containing alloy such as SUS 316L, and nitric acid is used for dissolving the metal capsule, When the treatment liquid comes into contact with the surface of the sintered body as the capsule is dissolved and removed, a passive film is formed on the surface of the sintered body, and the corrosion resistance (pitting corrosion resistance, etc.) of the sintered body is significantly enhanced. Is also obtained.

[0012]

EXAMPLE A hollow cylindrical sintered body (outer diameter 114, wall thickness 2, length 1000, mm) is manufactured by the following steps. [1] Metal capsule A hollow cylindrical can container consisting of an outer can, an inner can, and upper and lower lids (see Fig. 1) (1) Grade: S25C carbon steel (2) Size: inner can 109 mm outside diameter Outer can inner diameter 115 mm, wall thickness 3 mm, length 1000 mm [2] Formation of barrier layer A slurry prepared by suspending silica (SiO ₂ ) powder (particle size-10 μm) in water. The barrier layer of the outer can is formed by injecting slurry inside, rotating the outer can about the axis, coating the inner peripheral surface with a slurry layer by the action of centrifugal force, and drying the inner can. The barrier layer is formed by setting the inner can on a lathe and rotating it and applying it by spraying to the outer peripheral surface, and applying the lid material to the inner surface by spraying and drying. The thickness (dry) of each barrier layer is about 0.5 mm.

[3] Formation of porous sintered body (1) Sintering raw material (metal powder) and encapsulation stainless steel SUS 316 L (JIS G 4303), particle size: -500 /
+ 300μm The outer can (11) and the inner can (12) are concentrically placed on the lower lid (13) and welded, and the space defined by the outer can (11) and the inner can (12)
(S) is filled with metal powder and the upper lid (13) is welded. (2) HIP treatment Temperature: 600 ° C (0.45 mpK) Pressure: 108 MPa Time: 2 Hr (3) Enhanced heat treatment After HIP treatment, heat treatment is performed by releasing the pressure of the hydrostatic medium in the device. . Temperature: 1140 ° C (0.85 mpK) Time: 4 Hr

[4] Dissolution and Removal of Metal Capsules The capsule body is immersed in the treatment liquid. Treatment solution: nitric acid solution (25% concentration) Solution temperature: normal temperature Time: 24 hours Due to dissolution and disappearance of the capsule, the barrier layer (silica powder layer) almost dropped off the surface of the sintered body. A small amount of ceramic powder adhered to the surface of the sintered body taken out of the liquid, but was completely removed by gently rubbing with a brush during the water washing process.

Table 1 shows the powder yield of the sintered product.
This is shown in comparison with a product sintered body from which capsules have been removed by conventional machining.

[Table 1]

In the sintered body of the above-mentioned invention, the treatment liquid (nitric acid solution) comes into contact with the surface during the dissolution treatment of the capsule, and is made inactive. The pitting corrosion resistance is as follows when compared with the conventional material from which the capsule has been removed by machining. Measurement of pitting potential Test solution: 3.5% NaCl solution (solution temperature 25 ° C), degassed with argon Sweep speed: 20mV / min

[Table 2]

[0017]

According to the present invention, the cost of removing capsules in the production of a metal-based porous sintered body by hot isostatic pressing can be reduced, and net-shape molding can be performed, and the yield of raw materials can be improved. Thus, the effect of reducing the processing cost is obtained. Furthermore, the combination of the metal component of the sintered body and the grade of the solution for dissolving the capsule can enhance the corrosion resistance of the sintered body without taking additional measures to enhance the corrosion resistance. It is also easy to obtain a composite member composed of a porous material of a sintered body and a non-porous metal member while leaving.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of assembling a metal capsule used in the HIP processing of the present invention.

FIG. 2 is a sectional view showing an example of a form of a sintered body manufactured according to the present invention.

[Explanation of symbols]

 10: Metal capsule 11: Outer can member 12: Inner can member 13, 14: Lid material 20: Barrier layer (ceramics powder layer) A: Sintered body (porous material) B: Metal member (non-porous material)

Claims (4)

[Claims] In a method of manufacturing a porous metal powder sintered body in which a metal powder is sealed in a metal capsule and hot isostatic pressing is performed, the metal capsule after the treatment is removed by chemical dissolution. A method for producing a metal-based porous powder sintered body. 2. A masking is formed on a desired portion of the outer surface of the metal capsule after the hot isostatic pressure treatment, and the metal capsule is subjected to a chemical dissolution treatment. 2. The method according to claim 1, wherein the adhesive is left on the surface.
3. The method for producing a metal-based porous powder sintered body according to item 1. 3. A method for producing a porous metal powder sintered body in which a metal powder is encapsulated in a metal capsule and subjected to hot isostatic pressing, wherein a barrier for preventing solid phase diffusion at an interface between the metal powder and the metal capsule. As a layer, a metal powder is sealed with a ceramic powder layer interposed, hot isostatic pressing is performed, and the metal capsule after the treatment is removed by chemical dissolution. The method of manufacturing the aggregate. 4. The formation of a barrier layer at a desired portion of the interface between the metal capsule and the metal powder-filled layer is omitted, and after hot isostatic pressing, the outside of the metal capsule at the portion where the formation of the barrier layer is omitted. 4. The metal-based porous powder firing according to claim 3, wherein a masking is formed on the surface to perform a chemical dissolution treatment of the metal capsule, and the metal capsule piece in the region is left on the surface of the sintered body. The method of manufacturing the aggregate.