JPS6152201B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention significantly shortens the cycle time compared to the hot isostatic press treatment method (hereinafter abbreviated as HIP treatment method) that uses inert gas, and allows the use of relatively simple hydraulic pressure equipment. In particular, it relates to a HIP treatment method using heat-resistant grease as a pressure medium. The HIP treatment method has recently been attracting a lot of attention as a method that exhibits excellent effects on densifying metal powder, producing defect-free sintered bodies of large size or various shapes, and removing defects from cast products. . Conventionally, this method uses an inert gas such as argon gas as a pressure medium to apply high temperature and three-dimensional hydrostatic pressure to the object to be treated, and it solves various problems that were considered almost impossible with conventional technology. As the most powerful sintering or bonding technology among existing industrial technologies, it is rapidly being industrialized in advanced technology fields centered on the aircraft industry. However, this HIP treatment method uses a high-pressure HIP device and uses argon gas or
Because _N2 gas is used, there are technical difficulties in loading and unloading the object to be processed into the high-pressure equipment, raising the temperature within the high-pressure equipment, ensuring a high-temperature, high-pressure atmosphere, heating equipment, insulation structure, sealing structure, etc. In addition, it takes a considerable amount of time to raise the temperature and pressure within the high-pressure device, and the cycle time of the treatment is extremely long, 3 to 7 hours, resulting in low productivity. In view of this situation, the inventors of the present invention have been conducting various studies to shorten the cycle time, but as long as the above-mentioned gas pressure is used as the pressure medium, there is a limit to the cycle time. In fact, it has come to be known that such shortening is nearly impossible. After further investigation, including the selection of the pressure medium, we discovered that the HIP treatment method using hydraulic pressure has the potential to shorten the cycle time to some extent, as well as the simplicity of the equipment. . Of course, such hydraulic HIP processing is already known (a).
JP-A-55-120499, (b) JP-A-54-19405, (c) JP-A-55-75970, (d) JP-A-55-
Including Publication No. 7596, (E) Iron and Steel International (Iron and Steel
Related technologies are introduced in the February 1981 issue of International), but (a) the stamp process described in the publication uses talc and pyroferite as pressure media, and (c) and (d) The ones described in each publication use BN powder for the former, and zirconium oxide and magnesium oxide for the latter, and both are used in powder form, so 30 to 40% of voids remain during filling. , it becomes necessary to increase the pressure stroke during pressurization, which increases the size of the pressure vessel and increases the processing time.In addition, when processing products with poor mold release properties and complex shapes, There is a problem that the concave portion cannot be completely filled with the pressure medium powder, and there is a defect that inhibits isotropy of pressure transmission. In addition, the method described in the (b) publication uses molten salt as the pressure medium, and is excellent in terms of isotropic pressure transmission, but requires preheating of the salt, and moreover, the high-temperature molten salt is not heated inside the pressure vessel. inject into
In addition, it is not only dangerous to discharge from the container, but there are also problems such as generation of harmful gas, increase in container temperature, difficulty in high-pressure sealing, and corrosion of the pressure container. Therefore, based on such prior art, the present inventors continued to conduct further extensive studies in order to resolve the deficiencies of each of these technologies, and as a result, the present inventors found that the present invention has excellent filling properties, easy filling, mold releasability, and isotropic compressibility. We have discovered that heat-resistant grease is extremely suitable as a good pressure medium, and have arrived at the present invention. That is, the present invention uses such a heat-resistant grease as a pressure medium to heat a metal powder-filled capsule structure or a metal molded structure housed in a pressure vessel.
It is characterized by HIP treatment under pressure conditions below atmospheric pressure, preferably 1,000 to 10,000 atmospheres. Hereinafter, specific embodiments of the method of the present invention will be described in detail. First, the object structure to be processed in the method of the present invention is a capsule structure filled with metal powder or a metal molded structure pre-formed into a desired shape, and the former metal powder-filled capsule is especially preferred. Structures are the most common. Although this is not necessarily impossible in the case of ceramic powder, it remains difficult because the processing temperature exceeds 2000°C. Therefore, the present invention is limited to metals. The metal powder used is various metals used in powder metallurgy, and includes powder used to make general sintered components, cemented carbide powder, ferrite powder, etc.; It is made by gas atomization method etc. This powder is then filled into a metal capsule consisting of a lid 1 having an opening 2 shown in FIG. 1 and a container body 3, and the lid 1 is welded to form a metal powder-filled capsule. It is formed. The capsule is made of steel, copper, aluminum, etc., but mild steel or stainless steel is most commonly used, and the capsule is usually filled with powder at a filling rate of about 60 to 70%. . When the metal powder to be treated is filled into the capsule,
This capsule is then subjected to HIP pretreatment and molded into a capsule structure as a preform for hydraulic HIP according to the present invention. This molding is almost the same as the degassing and sealing performed in conventional HIP processing, by connecting to a vacuum device, heating and exhausting the air gas remaining inside the capsule through the opening 2, and then sealing the opening 2. However, after filling the container body 3 with the metal powder A to be treated, the lid 1 may be welded to seal the container as it is without evacuating the container with air remaining inside. In any of these cases, in order to promote the densification of the powder filled in the capsule, it is recommended to enclose getter powder A' such as Ti or Zr in advance as shown in Figure 2A. This is extremely effective in completely absorbing residual gas or in omitting the degassing step. Particularly in the hydraulic HIP process of the present invention, residual gas is particularly useful since it is a major obstacle to densification. After the above vacuum heating, degassing, and sealing are completed and the structure is formed as a preform for hydraulic HIP, it is then heat treated for the required time prior to HIP treatment, and the structure is soaked to a temperature suitable for HIP treatment. do. This is usually carried out in N ₂ gas at a temperature suitable for HIP treatment of each structure, for example, about 1050°C. At this time, if any gas remains in the capsule container, this gas is absorbed and eliminated. In general, it is desirable that this heating temperature be below the solidus temperature of the metal material to be treated, but depending on the material to be treated, it may be acceptable for some liquid phase to occur, so It is preferable that the temperature is below the solidus temperature of , and a temperature range of 400 to 1250°C is used. The thus heat-treated hydraulic HIP preform is then stored in a pressure vessel and subjected to a hydraulic HIP process, which is an important step of the present invention. This HIP process is performed, for example, using a press machine as shown in FIG. Of course, it is possible to use not only this press machine but also various other press machines with similar functions, but
A heating device such as a HIP device and a heat insulating layer structure are not particularly required. In the apparatus shown in FIG. 3, a preform structure 5 for hydraulic HIP is obtained by accommodating heat-resistant grease in a pressure vessel 4 and filling and molding the metal powder material into a capsule.
When stored, one side is closed by the blind lid 6, so when the stem 7 is appropriately moved from the other side along the inner wall of the pressure vessel 4 by a reciprocating mechanism (not shown) and compressed, heat-resistant grease is filled in the sealed space. The structure 5 is filled with three-dimensional isotropic compression from the periphery of the structure as shown by the arrow. At this time, the heat-resistant grease has extremely good fluidity and applies appropriate isotropic compression to the structure. Of course, the pressure medium in this case may be any liquid with good fluidity, and oil can also be used, but since oil has a low ignition temperature, it poses a problem in terms of operation, so the heat-resistant grease is not suitable. Most suitable for practical use. In addition, as for the pressure during the hydraulic HIP, compared to gas compression, the volume reduction rate corresponding to the pressure increase is much smaller, so the equipment can fully handle up to 20,000 atmospheres. Considering the lifetime of the pressure and capacity, it is industrially preferable to set the pressure to 10,000 atmospheres or less, and it is usually advantageous to carry out the process within the range of 1,000 to 10,000 atmospheres. Next, the holding time during this hydraulic pressure HIP may be any suitable time after the pressure is increased, but generally the processing time for this isotropic compression is only a few minutes, and in most cases it is only a few minutes.
About a minute is sufficient, thereby achieving the desired densification effect and molding the product into the desired external shape. At this time, the temperature of the preform structure or the temperature of the capsule has an influence on the densification effect during processing, so as shown in FIGS. It is also a preferred design to provide a heat insulating layer 8, 8' on the outer periphery. In this way, it is possible to prevent the temperature of the capsule from falling and also to prevent the temperature of the inner wall of the pressure vessel from rising, and the retention time of the structure in the pressure vessel can be extended, and a further densification effect can be expected. Another method is to provide a sleeve inside the pressure vessel to prevent direct contact between the capsule and the inner wall of the pressure vessel. Note that the above describes the case where metal powder is used as the material to be treated, and therefore the case where a capsule is used. However, when removing inherent pores such as removing casting defects, a capsule is not used. There is also. At this time, the metal molded structure formed into the required shape is heat treated as described above, preheated to a temperature appropriate for hydraulic HIP treatment, and then stored in the pressure vessel of the press machine to form the required shape. HIPing under pressure conditions can achieve the purpose of densification and eliminate casting defects. Of course, in this case as well, since heat-resistant grease is used as the pressure medium, the conditions of temperature and pressure described above apply. As described above, HIP treatment is performed using heat-resistant grease as a pressure medium, and then, through appropriate heat treatment, densification is achieved as in conventional HIP treatment.Next, we will clarify the effects of the method of the present invention in more detail. Therefore, examples are listed below. (Example) Using grease as a pressure medium, the gas atomized steel powder for rolls shown in Table 1 below was molded in the following manner.

[Table] First, the filling rate was determined by using the above sample powder in a 65φ x 100 capsule with the structure shown in Figure 1.
Filled with 15Kg metal powder at 65%. Next, this capsule was vacuum heated and degassed at 1050°C for 3 hours, sealed, and a preform structure for hydraulic HIP was prototyped, which was further heated at 1050°C for 2 hours in N ₂ gas.
It was preheated and soaked. The resulting 1050℃ soaked foam structure was then pressed into a second press using a 400-ton press with the structure shown in Figure 3.
Hydraulic HIP treatment was performed under each setting condition shown in the table to obtain HIP treated materials.

[Table] The appearance and shape of the thus obtained HIP billet were observed and the dimensions were measured. Subsequently, the above HIP pillar was divided into two equal parts and subjected to the following heat treatments to prepare each test piece material, and a mini-size tensile test piece (total length 40 mm) and a test piece for density measurement were taken. (1) 700℃×3HrFC……test piece 455L, 456L (2) 1000℃×3HrFC→700℃×3HrFC……test piece
455H, 456H And density measurement based on each test piece above,
Inspections were conducted on the microstructure, tensile test (n = 3), and observation of the fracture surface of the test material.
The results were as follows. (A) External shape and dimensional measurement of hydraulic HIP billet When we observed the external shape of the above HIP billet, we found that it was not much different from the shape of conventional gas pressure HIP billet, and even in hydraulic HIP material, the initial preform structure was isotropic. It was recognized that the pressure was on. In addition, as a result of measuring the external dimensions of the hydraulic billet, it was found that due to the hydraulic HIP, the original structure was approximately
It was found that the shrinkage was approximately 20% in the 12% axial direction. (B) Density Determination Next, the density was measured based on the test piece, and the results were as shown in Table 3. The table also shows the density of conventional HIP treated materials using Ar gas for comparison.

[Table] As is clear from the table above, in the case of hydraulic HIP,
Even when pressurized at a pressure of 1000 Kg/ ^cm2 , some pores remained with a porosity of about 0.5%, and these did not decrease even with heat treatment after HIP, but when the pressure was increased
When pressurized at a pressure of 5000Kg/ ^cm2 , a density ratio of 100% is obtained, and although the required pressure is higher, it is sufficient to achieve the same true density as the conventional HIP treatment method. is approved. (C) Microstructure Figure 4 A and B show the microstructure of the hydraulic HIP material according to the present invention (1050℃ x 5000Kg/cm ² x 1 minute) and the conventional HIP material using Ar gas (1050℃ x 1000
Kg/cm ² ×1Hr). As is clear from the same micrograph, no particular difference is observed between the microstructures of the two. (D) Tensile test The results of the tensile test are shown in Table 4. In addition, conventional HIP materials using Ar gas (1050℃×1000Kg/
cm ² ×1Hr).

[Table] From the table above, the hydraulic HIP material according to the present invention is
It is found that there is no inferiority to HIP material and that it has almost the same characteristics. In addition, the area near the fracture origin of the above tensile test piece
SEM fracture surface photographs are shown in Figure 5 A and B. (a) is a SEM photograph of the raw material powder. When observed in comparison with the SEM fracture surface photograph of the tensile test piece (b), no fracture along the original powder grain boundaries is observed in the fracture surface photograph of the test piece, and no fracture is observed between the powder particles. It can be seen that the bonding is complete. As is clear from the above examples, the method of the present invention uses the heat-resistant grease as described above as a pressure medium, and
By performing HIP treatment, true density HIP material can be obtained in about 5 minutes per cycle, and
It has been confirmed that the tensile properties of HIP material are comparable to those of conventional gas pressure HIP material.
It was recognized that the HIP cycle time was significantly shortened and significantly contributed to improving productivity. In other words, the hydraulic HIP treatment method of the present invention has the remarkable effect of dramatically shortening the conventional HIP treatment cycle time as described above and can be expected to play a major role in industrial applications. By being a liquid, (1) the HIP failure rate due to capsule defects such as small holes due to poor welding can be significantly reduced; (2) Even if a pressure vessel breakage accident were to occur, the damage caused by the explosion would be smaller than with conventional HIP treatment. (3) Unlike gas, the device is not subject to the regulations of the High Pressure Gas Control Act, so it is easy to install and maintain, and a simple compression device can be used without requiring complicated mechanisms like conventional HIP devices. It has various advantages and will have a great effect on improving the quality of various powder metallurgy products due to the spread of HIP processing technology in the future.

[Brief explanation of the drawing]

Fig. 1 is an exploded explanatory view of a capsule used in the method of the present invention, and Fig. 2 A, B, and C are examples of embodiments of the method of the present invention. C shows examples of insulation structures for pressure vessels and capsules. Figure 3 is a schematic diagram of the hydraulic HIP treatment apparatus of the present invention, and Figures 4A and 4B are micrographs (400x magnification) showing each microstructure of the HIP treated material.
A is a conventional HIP material, and B is a hydraulic HIP material of the present invention.
In addition, Figure 5 A and B are SEM fracture surface micrographs (×330
A is the case of the raw material powder, and B is the case of the liquid HIP material test piece of the present invention. 1... Capsule container lid, 2... Opening, 3...
Capsule container body, 4... pressure vessel, 5... metal powder filled capsule structure.

Claims (1)

[Scope of Claims] 1. A metal powder-filled capsule structure formed by filling a metal powder into a metal capsule container having an opening, and then evacuating or sealing the capsule without evacuating, or a metal powder-filled capsule structure formed in advance into a desired shape. A method of storing a molded metal structure in a pressure vessel and subjecting it to hot isostatic pressing using a pressure medium, in which a heat-resistant grease having fluidity is used as the pressure medium, and the structure heated to the required processing temperature,
A method for hot isostatic pressing using hydraulic pressure, characterized in that the metal powder or the metal molded structure is densified by applying a compressive force to the pressure medium under a pressure condition of 20,000 atmospheres or less. 2. The hot isostatic pressing method using hydraulic pressure according to claim 1, wherein the capsule container is a mild steel container. 3. Claim 1, in which getter powder is enclosed together with the metal powder in the capsule container in order to promote densification of the metal powder filled in the capsule container.
The hot isostatic press treatment method using hydraulic pressure according to item 1 or 2. 4. A hot isostatic press treatment method using hydraulic pressure according to claim 1, 2, or 3, which comprises disposing a heat insulating layer on the inner wall of a pressure vessel housing the structure. 5 Claims 1 and 2, which involve disposing a heat insulating layer on the outer periphery of a metal powder-filled capsule container.
The method for hot isostatic pressing using hydraulic pressure according to item 1 or 3. 6. The hot isostatic pressing method using hydraulic pressure according to any one of claims 1 to 5, wherein the heating temperature of the structure is below the solidus temperature of the capsule container material, preferably 700 to 1250°C. .