JPH0533009A - Method for regenerating gaseous ar for hot isotropic pressing - Google Patents

Abstract

PURPOSE:To reduce the concn. of impurities in gaseous Ar by forming Cr, Al and Ti as impurity fixing materials into a stable shape and size by which breakage is almost prevented and bringing the gaseous Ar into contact with the materials in a hot isotropic pressing furnace. CONSTITUTION:At the time of hot isotropic pressing operation, Cr, Al and Ti as impurity fixing materials are formed into a stable shape and size by which breakage is almost prevented and gaseous Ar as a pressure medium is brought into contact with the materials in a hot isotropic pressing furnace. Even when impurities are rapidly generated during hot isotropic pressing, the concn. does not increase and a sintered product is not affected at all by impurities, accordingly a high quality product can stably be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention removes impurities mixed in high-purity Ar gas for compression during the operation of hot isotropic compression,
The present invention relates to a technique for regenerating high-purity Ar gas.

[0002]

2. Description of the Related Art In recent years, as one of the techniques for molding powders of ceramics, metals and the like, hot isotropic compression treatment has been widely used, in which these powders are hot pressed and sintered.

In this process, the temperature is in the range of a few thousand degrees and the pressure is in the range of a few hundreds of atmospheres, and an inert gas is used as a pressure medium for isotropic compression. This is to prevent the diffusion and reaction of harmful components in order to maintain the quality of the product, and the inert gas used is a high-purity gas higher than or equal to foranein. N ₂ and Ar are often used as the inert gas, but some metals react with N _2, and high-purity Ar is an inert gas that is particularly noteworthy.

However, if this high-purity gas is also used in the HIP process, the amount of impurities increases and the purity can no longer be maintained. At this point, the inert gas was discarded and replaced with a new high-purity gas, but recently, from the viewpoint of resource saving, it has been attempted to recycle and use it.

That is, this is a regeneration technique in which an impurity absorption device is provided in the flow path to remove impurities in the used inert gas. For example, in JP-A-63-41786, Ti
It has been proposed to provide an impurity absorption device containing fibers or zeolite in the inert gas flow path.

[0006]

However, fine Ti fibers are easily crushed, and when the fine particles enter the hot isostatic pressing furnace, they may contaminate the surface of the product and impair its quality. For this reason, this fiber cannot be placed in a hot isotropic compression treatment furnace and used in an open state, that is, in a state where the inert gas in the furnace is easily contacted. Also, zeolite adsorbs gas molecules,
In particular, these components are removed by adsorbing polar molecules such as carbon dioxide and water, and it is difficult to use them at a high temperature exceeding 1000 ° C. Therefore, these absorbents are contained in the impurity absorbing device and act in the inert gas flow path, and cannot act in the hot isotropic compression furnace.

On the other hand, impurities in the inert gas mainly increase during this high temperature treatment. The concentration of impurities increased during processing often exceeds the allowable range.In such a case, if the impurities are not removed in the processing furnace, the product will be exposed to an excessive concentration of impurities in the latter half of the processing. Will be done.

The above-mentioned problems remain in the conventional technique. The present invention has been made to solve this problem, and by using a stable impurity absorbent that can be used even in a high temperature hot isotropic compression processing furnace, impurities in an inert gas are always allowed to fall within a permissible range. The purpose is to maintain the Ar gas at a high purity so that it can be operated in the state of being maintained.

[0009]

Means for achieving the object is to react Ar gas used for operation with impurities such as a metal such as Cr, Al or Ti or an alloy containing one or more of these, or It is sucked and fixed, and the shape and dimensions of these impurity-fixing materials have a mesh size of 2.
It is a lump that remains on a 0 mm sieve, or has a long and slender shape with a diameter of 0.5 mm or more, and this impurity fixing material is placed in a hot isotropic compression treatment. Is a method of regenerating an argon gas for hot isotropic compression, in which the impurities contained therein are removed by bringing the Ar gas into contact during the hot isotropic compression treatment.

[0010]

As described above, the hot isostatic pressing (hereinafter referred to as HIP) is carried out at a high temperature and a high pressure using an inert gas as a pressure medium. By this process, it is possible to perform compression molding of powder, diffusion bonding, densification of sintered products, removal of internal holes in cast products, etc.
The presence of impurities in the inert gas causes various alterations to the product.

For example, O₂Or CO₂, CO, H₂O etc.
Oxygen in the carbon oxidizes or discolors the surface of the product
Produces carbides and changes hardness. Besides, H₂
And N ₂If the concentration is high, hydrogen embrittlement, hardening, surface discoloration, etc.
May cause problems. Therefore, HIP processing
High-purity Ar gas is used for the impurities, and the impurities are shown in Table 1.
So most of them are less than a few ppm.

[0012]

[Table 1]

However, such a high-purity gas is also H
When it is used for IP processing, it is contaminated by gas or the like generated or brought in from the processed product and the impurity concentration becomes high. If it is used as it is, the quality of the treated product is deteriorated as described above, but it can be reused if these impurities are removed and the amount is reduced to the allowable amount or less.

To remove these impurities, it is sufficient to bring them into contact with a metal that reacts with or absorbs the impurities. Cr, Al, Ti, and the like are such metals that are inexpensive, easy to handle, and practical.

Cr is a metal having a high oxygen affinity and takes in and fixes oxygen as its oxide. At 1200 ° C, Cr
₂ O ₃ is a solid, and the O ₂ partial pressure at which it is in equilibrium is 10
^-17 atm. That is, most of O ₂ is fixed. C
O ₂ and CO are dissociated into oxygen and C at high temperature. CO
₂ = CO + _1/2 in the reaction of O _2, the equilibrium constant ^{_{Kp = P CO P O2 1/2 /}} P CO2 at 1200 ° C. is 10 ^-8 atm, C
When O ₂ is contained in an amount of about 1 ppm, the oxygen partial pressure at equilibrium is about 10 ⁻¹⁴ atmosphere. The partial pressure of dissociated oxygen is 10
^The amount exceeding ^-17 atm is fixed by Cr. Therefore, the dissociation of CO ₂ progresses rapidly and the release of C progresses. The liberated C reacts with Cr to form a carbide or becomes a solid and adheres onto Cr grains or the like. In this way
CO ₂ and CO are removed by Cr.

Al, like Cr, is a metal having a high oxygen affinity, and has a high melting point of the oxide, and takes in and fixes oxygen as the oxide. O _{2 in} equilibrium with Al ₂ O ₃ at 600 ° C
The partial pressure is 10 ^-28 atm. The action of removing CO ₂ and CO is the same as that of Cr except for the formation of carbide. Furthermore, A
l has a large nitrogen affinity, and the O ₂ partial pressure at which it equilibrates with AlN is 10 ⁻¹¹ atmospheres. Therefore, most of N ₂ reacts and is fixed as a nitride, and also ammonia which is a nitrogen compound is removed while being dissociated like CO ₂ .

Since Cr and Al have strong oxygen affinity in this way, they also fix oxygen from dissociated H ₂ O and promote decomposition of H ₂ O. When used in combination with a H ₂ sucker material such as Fe—Ni alloy, H ₂ O can be removed.

Ti has an oxygen affinity and a nitrogen affinity both of which are Cr.
It is a metal larger than Al and Al, and in addition to this, it reacts with C to form TiC, and also inhales H ₂ well. Therefore, CO ₂ , CO, O ₂ , N ₂ , NH ₃ , H ₂ , H ₂
Not only O can be removed, but also hydrocarbons such as methane and ethane that are slightly contained in Ar can be removed.

These Al, Cr or Ti metals may be used as pure metals, but since they do not lose the above-mentioned effects even in the state of an alloy, they can be used as an alloy. In Al, the melting point of metal is as low as 660 ° C., and its use temperature may be limited. There is no problem when the temperature inside the furnace is 300 ° C. or lower as in the case of HIP treatment of Mg, but when the temperature inside the furnace is high, it melts and the surface area decreases and handling becomes complicated. In such a case, the alloy can be used by increasing its melting point. When a Ti-36Al alloy is used, the melting point rises to 1460 ° C.

Other alloys that are easily available and easy to use are Cr-based alloys such as Fe-18Cr, Cr-25Al and Cr.
-15Ti, Cr-25Si, Ti-based Ti-6Al-
Fe-based superalloy containing 4V, Ti-5Al-25Sn, Cr, Ti, and Al (for example, Fe-15Cr-
3.5Mo-15Co-4Ti-5Al) and so on.

As can be inferred from the above description, a metal having a large oxygen affinity or a metal having a large nitrogen affinity can be used as an impurity fixing material if the dimensions are limited as described later. These impurity fixing materials can be appropriately selected depending on the type of processed product. For example, in the processing of ceramics, since H ₂ contained in the ppm order does not matter, an Al-based or Cr-based fixing material is used.

It is considered that the smaller the size of the impurity fixing material and the more complicated the shape thereof, the larger the surface area per unit volume, which is considered to be effective. However, on the other hand, the impurity fixing material is liable to be broken and fine pieces are easily generated. If fine particles are generated, when they enter the furnace, they will contaminate Ar gas and the product surface.

In order to prevent the generation of these fine pieces, the fine particles are left on the sieve having an opening of 2.0 mm. In the case of a linear shape, one having a diameter of 0.5 mm or more is used to prevent generation of fine pieces.

Further, the place where these impurity fixing materials are brought into contact with Ar gas may be in the HIP processing furnace or in the Ar gas flow path outside the furnace. However, when they are contacted outside the furnace, they must be heated in order to accelerate the reaction, or in order to prevent the generated fine particles from being brought into the Ar gas, the cross-sectional area of the flow path must be increased to install a filter, etc. Measures are needed. What is more important than that is that the HIP process is carried out in a state in which impurities generated during the process are included.

That is, immediately after the HIP process is started, the Ar gas maintains a high purity, but the gas generated from the processed product reduces the purity of the Ar gas in the processing furnace. In the latter half of the process, the Ar gas is processed. The item will be exposed to impurities. In order to avoid this situation, impurities have to be removed in the HIP treatment furnace.

When contact is made in the HIP processing furnace, a large amount of impurities are generated, and if the impurities are not removed, it is possible to prevent an increase in the impurity concentration even if it exceeds the permissible range during processing.

If the impurity fixing material having the above-mentioned size and shape is used, there is no concern that fine particles will be generated even if it is left in the processing furnace, and it can be exposed to Ar gas in the furnace in a state of being sufficiently in contact therewith. .. Therefore, it is possible to complete the HIP process while maintaining the low impurity concentration state without increasing the impurity concentration.

[0028]

[Examples] While regenerating Ar gas using an impurity fixing material, alumina particles, stainless castings, and carbon steel were subjected to HIP treatment, and the state of regeneration was investigated and the alteration of the product was also investigated.

The case where the impurity fixing material was brought into contact with Ar gas in the furnace and the case where it was brought into contact with the Ar gas flow path outside the furnace were examined and compared.

FIG. 1 shows the positional relationship in the former case. The impurity fixing material 1 is placed inside the HIP processing furnace 2, and Ar gas is pumped from the gas storage tank 3 into the HIP processing furnace 2 and fed. The Ar gas used for the HIP process is returned to the gas storage tank 3 and reused again. In the investigation of impurities, samples were sent to the analyzer 4 from the inlet side and the outlet side of the HIP processing furnace 2 for analysis, and the amount of impurities before and after the HIP operation was examined.

In the same manner, the impurity fixing material has an average diameter of 0.1.
A conventional example using mm mm Ti fiber was also investigated and compared.

FIG. 2 shows the positional relationship in the latter case. It is the same as in the case of FIG. 1 that Ar gas from the gas storage tank 3 is pressurized and sent to the HIP processing furnace 2 by a pump, and Ar gas used for HIP processing is returned to the gas storage tank 3 and circulated again. .. The regeneration device 5 was provided in the Ar gas flow path outside the HIP processing furnace 2, and the impurity fixing material 1 was housed therein. The inside of the regenerator 5 can be heated and pressurized as needed. In the investigation of impurities, samples are sent from the inlet side and outlet side of the HIP processing furnace 2 and the outlet side of the regeneration processing device to the analyzer 4 for analysis, and each position before and after HIP operation and after regeneration and after regeneration. Then, the amount of impurities in the Ar gas was examined. Incidentally, the Ar gas before the operation is also regenerated. The difference in the amount of impurities before and after the HIP operation is the amount of impurities in the case where the regeneration treatment is not performed, and using this, the Examples and Comparative Examples of the present invention were considered.

Regarding the alteration of the product, the alumina sintered product was examined for surface discoloration, the stainless sintered product was examined for surface oxide layer thickness, and the carbon steel was examined for surface appearance.

Table 1 shows HIP operation conditions, Ar gas regeneration treatment conditions, and investigation results. Regarding the purification status of Ar gas, the amount of impurities increased by the HIP operation and the regeneration treatment was shown by numbers, and a total of 0 and X was also displayed. That is, ◯: Satisfactory purification ×: Dissatisfaction with the degree of purification

Regarding the deterioration of the products, the quality characteristics are stable and not deteriorated, respectively, ◯, variations are recognized, Δ: deterioration is clearly observed, and characteristics are clearly distorted. Was evaluated and filled in the table.

[0036]

[Table 2]

In the examples of the invention in which the impurity fixing material is working in the HIP processing furnace, the increase amount of impurities is 1 ppm or less in all the examples of No. 1 to No. 4, and the impurities are slightly different. Is even decreasing. This situation means that Ar gas is sufficiently purified, and no alteration of the product is observed.

In Comparative Example A regenerated outside the furnace after HIP operation, the amount of increase of any impurities was small. But HI
At the end of the P treatment, the product was exposed to the atmosphere containing the amount of impurities shown in Comparative Example B, so that the product was found to be altered.

In Comparative Example B in which the regenerating process is not performed, the amount of impurities is increased, although the type differs depending on the processed product. An increase in H ₂ was conspicuous in No. 7 treated with alumina and No. 8 treated with stainless steel, while CO increased in No. 9 treated with carbon steel.
The increase of ₂ is remarkable. The characteristic values of the product were found to vary and change.

In No. 10 of the conventional example, unevenness was observed on the product surface due to contamination of fine particles on the Ti fiber, and H and C were detected together with Ti in the analysis sample.

In addition to impurities generated from the processed product, there may be gas mixed in from other sources. For example, even if there is a very slight leak in the Ar gas flow channel, the concentration of N ₂ , O ₂ or hydrocarbon may increase. Even in such a case, the impurity fixing material in the furnace sufficiently prevents the treated product from being exposed to these impurities.

[0042]

As described above, according to the present invention, the impurity fixing material of Cr, Al and Ti is made into a stable shape and size which is not easily broken and is sufficiently contacted with Ar gas in the HIP processing furnace. .. Therefore, even if impurities are rapidly generated during the HIP process, the concentration thereof does not increase, and the sintered product is not affected by the impurities at all, and a product of good quality can be stably manufactured. In addition, no special device is required for using the impurity fixing material. In this way, the effect of the present invention for improving the quality of products by a simple method is great.

[Brief description of drawings]

FIG. 1 is a perspective view of an impurity fixing material according to an embodiment of the present invention, which is Ar.
The figure which shows the position which contacts gas.

FIG. 2 is a diagram showing an example of bringing an impurity fixing material, which is an embodiment, into contact with Ar gas.

[Explanation of symbols]

 1 Impurity Fixing Material 2 HIP Treatment Furnace 3 Gas Storage Tank 4 Analyzer 5 Regeneration Device 6 Treated Product

Claims (1)

Claim: What is claimed is: 1. Ar gas used for the operation is a metal such as Cr, Al or Ti or an alloy containing one or more of them, and the lumps or diameters which remain on the sieve having an opening of 2.0 mm. 0.5
The impurities in the Ar gas are removed by bringing them into contact with a linear impurity fixing material having a thickness of mm or more in a hot isotropic compression treatment furnace. How to play.