JPS585962B2 - Hot isostatic pressing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the hot isostatic press molding method, and more specifically, it eliminates the degassing step that requires complicated equipment, and achieves shortening of working time and improvement of yield. The present invention relates to an improved hot isostatic pressing method for obtaining.

When densifying or pressure sintering a metal powder material by hot isostatic pressing (hereinafter referred to as HIP), the metal powder material is made of a gas-impermeable material such as metal, glass, etc. The capsule is filled into a container with an opening, heated and degassed by vacuum suction inside the capsule, sealed while continuing vacuum suction, and then passed through a preheating process and placed in a high-temperature, high-pressure HIP furnace. Conventionally, it has been common practice to perform isotropic compression inside.

In addition, in order to manufacture tool steel products with complex shapes by the HIP method, metal powder material is filled into a mold container with a shape corresponding to the product shape, and the mold container is placed on the outside containing pressure medium particles. It is already well known that the material is buried in a container and subjected to the same vacuum degassing and preheating steps as described above, followed by HIP treatment.

In this well-known and commonly used method, if the inside of the container is not sufficiently degassed, residual air or gas generated from the metal powder material may cause pores in the final product to the extent that it poses a practical problem. It is believed that this may lead to the formation of microstructures, so it is important to perform the degassing process carefully over a long period of time. Furthermore, since degassing creates a vacuum inside the container and reduces heat conduction, the preheating process takes a long time. It takes time, etc.
There were factors that significantly hindered process efficiency.

Japanese Patent Publication No. 51-18202 states that in order to provide effective heat conduction during the preheating process, the container is temporarily filled with an inert, low molecular weight gas such as helium or hydrogen after the degassing process, and the preheating time is A method is disclosed in which the gas is heated to a desired temperature, the gas is removed, and the HIP process is performed.

Even in this method, deaeration, gas replacement, and exhaust gas must be performed in sequence, and the process has not yet been simplified.

On the other hand, the present inventors have tried the HIP method on various materials to be treated and have made detailed studies. We came to the realization that a non-deaeration method, which had never been considered in the past, was used. In other words, after filling the powder material to be processed into a container with an opening, it was possible to directly open the container without vacuum or deaeration. Seal the part with a lid, and then
A method for performing IP treatment was developed and provided to the sac.

This method does not require a degassing process, so the degassing and sealing process is shortened, various complicated devices required for degassing and sealing are not required, and the shape and structure of the container can be simplified. Although there are many advantages, there is a problem that it is difficult to adopt the preheating method.
Gases such as nitrogen and oxygen present in the container are absorbed by the metal powder in the container, effectively creating a vacuum inside the container and producing a final product without pores. reactions, oxidation reactions) mainly occur in high temperature regions.

Therefore, if preheating is performed prior to charging into the HIP furnace, the gas absorption reaction will hardly occur during the temperature raising stage of the preheating process, and the gas inside the container will expand as the temperature rises, causing the container to lower its internal pressure. You will receive it.

For example, when a container that is sealed at room temperature is heated to 500 to 600 degrees Celsius, the internal pressure of the container will be approximately 3 atm.
In addition, the strength of the container material (for example, mild steel) is significantly reduced by the high temperature, which causes the container to expand and deform due to its internal pressure.

This phenomenon causes short-circuit accidents and damage to the heater due to contact between the container and the preheating furnace heater.If the container is significantly deformed, it may become impossible to charge the product into the HIP furnace, and the mold container may be deformed, resulting in defective products. In other words, this results in an increase in yield, which leads to a decrease in yield.

Therefore, in the non-deaeration method, it is not possible to adopt a preheating method, and since it is directly charged into the HIP furnace, the temperature rise time in the HIP furnace becomes longer, resulting in a decrease in productivity due to an increase in HIP cycle time, which still needs to be resolved. This remained a major problem.

The method of the present invention cleverly incorporates a preheating step into the non-degassing HIP method, which is extremely advantageous in terms of process rationalization, and leads to the solution of the above-mentioned problems at once.The method is characterized by: In a method in which an inner container filled with metal powder is buried in an outer container filled with pressure medium particles, the inner container is preheated, and then hot isostatic pressing is performed. Filling the inner container with metal powder and burying the inner container in the outer container, then preheating the inside of both containers to a predetermined temperature without degassing and sealing them, and degassing the inside of both containers after preheating is completed. The purpose is to immediately seal the outer container, and then subject the container to hot isostatic pressing in a high-temperature, high-pressure gas atmosphere to densify and condense the metal powder in the inner container.

Examples of the metal powder to be treated to which the method of the present invention is applied include Fe-based alloys, Ni-based alloys, titanium alloys,
Examples include metal powders such as cobalt, chromium, tungsten, vanadium, and molybdenum, and particularly Fe-based alloys and Ni-based alloys are most suitable for carrying out the present invention.

The inner container to be filled with the metal powder may be made of a material inert to the metal powder contained, such as, but not limited to, silica, alimina, zirconium or mixtures thereof, or metals containing these. It is not something that will be done.

The material is formed into a shape that corresponds to the shape of the final product and has an opening in a portion thereof.

Through this opening, the metal powder is filled into the inner container in the air or under a nitrogen gas atmosphere, preferably while stirring or shaking.

After filling, a lid with a nozzle is attached to the opening by welding, and this nozzle is further pressed or compressed to allow atmospheric pressure to flow, but to prevent the metal powder and pressure medium particles described below from flowing. It is preferable to close the gap while leaving a narrow gap.

By doing so, when the inner container is embedded in pressure medium particles, the pressure medium particles can be prevented from entering and mixing with the container and having an adverse effect on the product, and also preventing metal particles from leaking and overflowing. , ensuring free escape of the internal gas heated and expanded during the preheating process.

The outer container in which the inner container is housed is made of a gas-impermeable material, and does not necessarily need to be equipped with an exhaust pipe like conventional containers of this kind, and of course needs to be connected to a vacuum pump, etc. do not.

For example, it is sufficient if the structure has an opening and the opening can be easily sealed.

As the gas-impermeable material, metal, particularly mild steel, is preferable, and glass or a composite material of metal and glass can be used.

A suitable amount of pressure medium particles made of fine heat-resistant powder such as silica or alumina are stored in the outer container, and the pressure medium particles cover the entire circumferential surface of the inner container embedded therein and the inner wall of the outer container. It also fills the gap between the container and the container without any corners, and also positions the inner container.

The double container filled with metal particles and pressure medium particles as described above is preheated to a predetermined temperature in an open state without performing any degassing operation such as vacuum suction.

Since both the inner and outer containers are open during preheating, the gas expanded inside is discharged through the opening or nozzle, and the container is not deformed.

The preheating temperature varies depending on the type of metal powder to be processed and the conditions of the next HIP process, but it is usually 1000°C to 1500°C or even higher. Preferably, after preheating is completed, the container is sealed and the HIP equipment is heated. To allow for cooling during the charging operation, a temperature slightly above the HIP processing temperature is selected.

According to the method of the invention, the preheating operation is carried out in the presence of gas in the vessel, so that such gas provides effective heat transfer and is completed in a surprisingly short time.

This is in contrast to the fact that it takes a long time to heat and raise the temperature in a degassed vacuum state.

Once preheating to a predetermined temperature is completed, the outer container is immediately sealed without evacuating the inside and subjected to HIP treatment.

In this way, the outer container is sealed immediately after being preheated, so if the outer container is preheated to about 1000C, for example, 70 to 70% of the internal gas
Section 5 is released from the capsule due to thermal expansion, and when it is sealed in that state, the amount of internal residual gas is 25 to 25% when filled at room temperature.
30, which is virtually the same as when sealed under reduced pressure, and especially when filled in air, it is possible to minimize the adverse effects of oxygen.

In addition, when the preheating temperature reaches 1000℃ or higher, if the atmospheric gas is an active gas, the reaction with the metal powder becomes active, and the atmospheric gas actively flows into the inner container and is absorbed by the metal powder. The Rukoto.

Therefore, atmospheric gases include gases that are harmless even if absorbed.
Alternatively, a gas that is preferably absorbed, such as nitrogen gas, is preferable, and especially in the case of high-speed tool steel, nitrogen gas can be actively absorbed to generate nitrided high speed steel.

In addition, in this case, if the preheating furnace is a pressurized type and preheating is performed in a pressurized nitrogen atmosphere, the nitriding reaction rate can be increased and the necessary nitriding can be performed in a short preheating time. It is possible.

As mentioned above, gas from outside the container may flow back into the container due to gas absorption by the metal powder to be processed, or surrounding gas may flow back into the container during the sealing process after preheating, especially in the case of small containers. Sometimes.

Therefore, if a conduit equipped with a check valve that prevents gas from flowing into the container is attached to the outer container and preheated, during the gas expansion process during preheating, the internal gas will pass through the check valve and exit outside as it expands. However, even when gas absorption becomes active or when the temperature drops during the sealing process after preheating, the check valve prevents the external gas from flowing back, reducing the amount of residual gas inside the container. Since the state at the end of preheating is maintained, the influence of oxygen can be minimized, and if the nitriding reaction is to be avoided, it can be kept to a minimum.

According to the method of the present invention, the inner container filled with the metal powder to be treated is embedded in the media particles in the outer container, the container is preheated in an open state, and the outer container is immediately sealed without performing a degassing operation. When the metal powder is installed in a high-pressure, high-temperature furnace and subjected to the specified HIP treatment, the small amount of oxygen or nitrogen contained in the container is substantially completely absorbed into the metal powder during the HIP treatment process. However, this does not cause any problems in the quality of the final product, and may even give favorable results.

Furthermore, even if some of the argon in the atmosphere is absorbed into the metal powder during the treatment and some of it remains, this does not substantially impede the practicality of the product.

The accompanying drawings illustrate the steps of the method of the present invention in comparison with the conventional method, and FIGS. 1 and 2 show the steps of the method of the present invention,
3 and 4 respectively show the case of the method of the present invention.

As seen in FIG. 1, the conventional method includes (a) a step of filling the inner container 1 with metal powder 2 (a) a step of welding a lid 6 equipped with a nozzle 5 to the opening of the inner container; After filling the outer container 4 with the pressure medium particles 3 and embedding the inner container in the pressure medium particles, the lid 1 having the nozzle 9 is removed.
(d) A step of connecting the nozzle 9 to a vacuum pump to suction and deaerate the inside of the container; (e) A step of closing and sealing the nozzle 9 using an appropriate sealing device 11; (f) A step of preheating by the preheating device 12, (}) HIP
It has been essential to sequentially perform HIP processing steps using different devices.

Figure 2 shows a method proposed to simplify the conventional process shown in Figure 1. (A) to (C) are the same as above (D) Outer container sealing process (E) HIP treatment process Although the culm process has been shortened to just 5 steps, as mentioned above, it is not possible to preheat the sealed contents before subjecting them to the HIP process, so it is necessary to hold the container in the HIP device for a long time to heat it. H
This results in hindering the efficient operation of the IP device.

The steps of the method of the present invention shown in FIG. 3 include (a), (b), and (c), (d) a step of preheating with the nozzles 5 and 9 of the inner and outer containers open, and (1) vacuuming. It consists of a step of immediately sealing without suction, and (iii) a HIP treatment step.

FIG. 4 shows the nozzle 9 in the method of the present invention shown in FIG.
A case is shown in which a conduit 8 equipped with a check valve 7 is installed and the same process is carried out.

In Fig. 5, the nozzle 5 provided on the lid 6 of the inner container 1 filled with metal powder 2 is forged or squeezed as appropriate to allow gas to flow, but to prevent the metal powder and pressure medium particles from flowing. This shows a closed state with a narrow gap remaining.

Next, we will consider the case where high speed steel is subjected to HIP treatment using an inner container having an internal volume of 100 liters.

Now, if the initial powder filling rate is a typical 70 cm, then 701 parts of high speed steel powder and 301 parts of air are sealed in the inner container.

When converting the amount of high speed steel powder and air at this time into weight, it is 70 liters of high speed steel powder → degree of vacuum 8.12 g/cc → 568.4
kg Air 30l 02:20.93Vol%-8.97g N2:78.10VoA%→29.29gAr:0.9
325Vol%-0.498g.

When preheating this to 1100℃, the air volume becomes the formula It expands approximately 4.6 times.

(However, in this case, the room temperature was 27°C.) This means that the weight of air existing in the open capsule at 1100°C is reduced to 1/4.6 of that at room temperature, and therefore 1100°C. The theoretical amounts of each component present in a volume of 30 liters of air at °C are: 02: 1.95 g, N2: 6.37 g, Ar: 0.108 g.

Of these gas components, O2 and N2 are substantially completely absorbed into the HSS during the HIP process, and the respective ratios of O2 and N2 in the final product are as follows.

On the other hand, some of the Ar in the air is actually absorbed and some remains, but if we assume that all of it remains in the worst case and calculate the porosity of the final product, the initial Ar
is 30lXO. 9325 coefficient = 280 ffl If this is preheated to 1100° C., the volume will increase by 4.6 times, so the amount remaining in 301 will be 61 crl in terms of room temperature.

When this is subjected to HIP treatment at 1100C and 1000 atm, the volume relationship after HIP treatment is as follows.

From the above formula, the porosity of the final product due to Ar is as follows.

That is, the density of the final product is 99.999 times higher than the theoretical density.

Thus, from the above, it is proven that the amount of O2, the amount of N2, and the relative density can be obtained without any practical problems.

Although the initial powder filling rate was considered as 70% above, the filling rate naturally fluctuates depending on the type of metal powder to be processed.

However, the most practical range can be roughly estimated from the above case, and has almost no effect.

Next, specific examples of the method of the present invention will be listed.

Example I C: 1.57 ratio Cr: 4.21 ratio W: 12.50 ratio V: 4.71 ratio Co: 4.97 ratio Fe: remainder A high speed steel powder having the above composition was produced by a nitrogen gas atomization method. .

This powder was then filled into an alumina cylindrical container with an inner diameter of 100 mm and a height of 200 mm while being stirred in the atmosphere, and after filling, an alumina lid equipped with a ventilation nozzle was welded to the opening of the container.

This product was placed in a mild steel container with an inner diameter of 200 mm and a height of 300 mm.

Silica particles were placed in a mild steel container, and filled in all the gaps between the inner wall of the mild steel container and the alumina container so as to surround the alumina container.

A mild steel lid with a ventilation nozzle was then welded to the upper opening of the mild steel container.

The inside of this container was maintained in an open state without suction and degassing, and the container was charged into a preheating furnace in a nitrogen atmosphere and heated to 1100°C.

It took 60 minutes to complete such preheating.

After preheating, the ventilation nozzle of the mild steel container was immediately sealed by forging with a pair of hammers without vacuuming the inside of the container, and the sealed portion was further sealed by welding, and then loaded into a HIP furnace at 1100C. HIP under the conditions of 1000 atm, 30 minutes
processed.

When the obtained product was taken out, cut, and observed under a microscopic environment, the structure was found to be a healthy structure with a fine particle size and no oxide network, and no pores were found.

Also, according to the oxygen analysis results, the oxygen concentration in the product is 35pp.
It was m.

Example 2 C: 0.86 ratio Cr: 4.24% W: 6.14 ratio V: 1.89 ratio Mo: 5.01 ratio Fe: remainder A high speed steel powder having the above composition was produced by nitrogen gas atomization method. did.

As a result of oxygen analysis, this powder has an oxygen concentration of 65p. p.
It was m.

Next, this powder is filled into an alumina cylindrical container with an inner diameter of 40 mm and a height of 160 mm in the atmosphere to a filling rate of 70%. After filling, an alumina lid equipped with a ventilation nozzle is welded, and a ventilation nozzle is inserted in the middle of the container. was forged and closed, leaving a narrow gap as shown in Figure 5.

Next, this alumina container has an inner diameter of 80 mm and a height of 240 mm.
At the same time, the alumina container is charged into a mild steel cylindrical container, and the alumina container is positioned so that it is completely buried in the silica particles. Welded it to cover the area.

In addition, a conduit equipped with a check well is connected to the ventilation nozzle, and the structure is designed to allow gas to pass from the inside of the container to the outside, but to prevent the opposite flow. Heating was continued until the temperature was reached.

The time required for preheating was 80 minutes.

After completion of preheating, the ventilation nozzle was sealed and sealed in the same manner as in Example 1, loaded into a HIP device, and heated at 1100°C for 1 hour.
HIP treatment was performed under the conditions of 000 atm and 30 minutes.

When the obtained product was taken out and analyzed for oxygen, its oxygen concentration was 83 ppm.

Also, no pores were observed using a microscope, and their density was s.
The theoretical density was reached at 12g/c=3.

Since the method of the present invention does not require any degassing process as described above, it does not require any of the various complicated devices conventionally required for degassing, and can greatly reduce equipment costs. ,
Although the process is shortened and a non-degassing method is used,
Since preheating can be performed prior to HIP processing and preheating is performed in the presence of gas, the preheating time can be significantly shortened, and the HIP processing time can also be shortened, thereby increasing the efficiency of the HIP device.

Furthermore, the preheating operation is performed while the container is open, and the gas inside expands and escapes, and the container is immediately sealed in a diluted state.
Since it is transferred to HIP processing, the influence of residual gas is suppressed to a minimum, and not only can a high-quality product be obtained, but also when it is desired that the metal powder to be processed absorbs a specific gas, it can be preheated in the gas atmosphere. The present invention provides an industrially advantageous TIP treatment method by streamlining the steps described above, such as achieving the desired quality by performing the following steps.

[Brief explanation of drawings]

Figures 1A to 2E and 2A to 3E each show a conventional HIP process, and Figures 3A to 3E and 4E and 4E each illustrate the HIP process of the present invention. It is a process outline diagram showing an aspect. Further, FIG. 5 is a schematic diagram showing an example of a ventilation nozzle for the inner container suitably applied to the method of the present invention. DESCRIPTION OF SYMBOLS 1... Inner container, 2... Metal powder, 3... Pressure medium particles, 4... Outer container, 5, 9. ...Tuzzle, 11... Sealing device, 12... Preheating device.

Claims (1)

[Claims] 1. A method in which an inner container filled with metal powder is buried in an outer container filled with pressure medium particles, and after preheating this, a hot isostatic pressing treatment is performed. Filling the inner container with metal powder and burying the inner container in the outer container in a gas atmosphere, then preheating both containers to a predetermined temperature without deaerating and sealing them, and after preheating,
Immediately seal the outer container without evacuating the inside of both containers.
A hot isostatic press molding method, characterized in that the metal powder in the internal forming container is then densified and sintered by subjecting the container to hot isostatic pressing in a high-temperature, high-pressure gas atmosphere. 2. The inner container is a metal container having an opening, and after it is filled with metal powder, a lid having a nozzle is attached to the opening by welding, and the nozzle is used to control the flow of the metal powder and pressure medium particles. 2. The hot isostatic press molding method according to claim 1, wherein the hot isostatic press molding method is closed, leaving a gap large enough to prevent gas flow but permit gas flow. 3. In a method in which an inner container filled with metal powder is buried in an outer container filled with pressure medium particles, the inner container is preheated, and then subjected to hot isostatic pressing treatment, the inner container is buried in the air or under a nitrogen gas atmosphere. The inner container is filled with metal powder and the inner container is buried in the outer container, and a check valve is provided to prevent gas from flowing into the container from outside the outer container without degassing and sealing both containers. Attach a nozzle to the outer container and preheat it to a predetermined temperature. After preheating, immediately seal the outer container without evacuating the inside of both containers, and then heat the container in a high-temperature, high-pressure gas atmosphere. A hot isostatic press forming module 4 characterized in that the metal powder in the inner container is densified and sintered by performing an isostatic press treatment.A metal container in which the inner container has an opening, After filling it with metal powder, a lid having a nozzle is attached to the opening by welding, and the nozzle is connected to the opening so as to block the flow of the metal powder and the pressure medium particles, but leave a gap sufficient to allow the flow of gas. The hot isostatic press molding method according to claim 3, wherein the hot isostatic press molding method is closed. 5. A metal container in which the outer container has one opening,
After filling the pressure medium particles and burying the inner container, a lid having a nozzle is attached to the opening by welding, and the outer container is sealed after preheating by closing the nozzle. The hot isostatic press molding method according to item 3 or 4.