JPS6218601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a heat treatment method which is suitable for use in removing internal defects and improving the properties of cast materials, powder sintered materials, and various mechanical parts having intergranular cavities due to creep. The present invention relates to an isostatic pressing method (hereinafter referred to as the HIP method) and a HIP device used to carry out the method.

Casting has traditionally been the most common metal forming technology and is currently used in many fields, but due to the gas that is inevitably generated during casting, large and small pores are likely to occur within the cast product. ,or,
It has been extremely difficult to completely prevent the formation of such pores. However, in conventional cast products, the presence of a few pores did not pose much of a problem because the performance required for the cast product was satisfied even if there were a large number of pores.

However, with the spread of energy saving ideas in recent years, it has become necessary to raise the inlet gas temperature to a considerably high temperature range in order to improve the efficiency of gas turbines. Along with the demand for parts manufacturing by
Since such parts are used under harsh conditions, pores generated during the casting process are a fatal defect that degrades mechanical properties, and methods to eliminate them have attracted attention.

On the other hand, with the advancement of powder metallurgy technology, sintered bodies are being used as various mechanical parts, but since pores are inevitably present in the normal sintering method, as long as such pores exist, the It was undeniable that the mechanical properties were inferior to other parts in terms of true density. However, the advantages of the fine and uniform metal structure of the sintered body, its improved and uniform mechanical strength, and the ease of forming irregularly shaped articles are very attractive, and therefore the performance improvement of such a sintered body is very attractive. Therefore, there are great expectations for pore sealing technology.

In response to the needs of the times, a technology has recently been proposed in which high-temperature, high-pressure Ar gas is applied to cast products or sintered bodies with internal defects to seal them using the HIP method, and this technique has attracted attention as a means of solving the above-mentioned problems. are collecting. According to the HIP method, the object to be processed, such as a cast or sintered body, is placed in a high-pressure container with a built-in heating device with its surface exposed, and is then heated to a pressure of about 1,000 atm and a temperature of 900 to 1,200°C. This method uses Ar gas at a high temperature to crush the pores, and then diffuses the metal in the pores to completely seal the pores without leaving any traces of the pores. In terms of modifying the molded body through decomposition, it can be said that this technology is fully suited to the purpose.

However, new problems have arisen with this HIP method as well. In other words, since the Ar gas used as a pressure medium and a heating medium in the HIP method is expensive, the Ar gas in the high-pressure container is always collected in a gas holder after the HIP process, but when the object to be processed is transferred to the high-pressure container. It is unavoidable that air gets mixed in when the container is opened and closed for loading and unloading, and that various impurity gases generated by the decomposition of oil and other substances adhering to the object to be processed are mixed in, and as a result, the purity of the recovered Ar gas gradually decreases. As the Ar gas decreases, impurity gases accumulate, and eventually a problem arises in that the object to be processed is contaminated by the impurity gases contained in this Ar gas.

The amount of impurities in Ar gas that causes this problem is at most
The absolute amount of impurities is about 200 ppm, but if you simply calculate it under a high pressure of 1000 atmospheres, the absolute amount of impurities is equivalent to that of normal pressure Ar gas containing 20% impurities (actually, it is about half that amount due to temperature effects). , and from 900
At a high temperature of 1200°C, the metal surface of the object to be processed is extremely activated, making it easy for even trace impurities to react with the metal on the surface of the object. In particular, oxygen as an impurity is the biggest problem, and even if oxygen exists at a few tens of ppm, a contamination layer (oxide layer) of several tens of micrometers will be formed on the surface of the object to be processed. properties will be significantly degraded. Therefore, unless the problem of contamination of the object to be processed by these impurities is solved, it will be difficult to put into practical use the technique for modifying the object to be processed by the HIP method described above.

As a solution to this problem, a method has been proposed in which the outer surface of the object to be processed is completely covered with a HIP capsule, but this method requires a lot of effort to separate the capsule and the object to be processed after HIP treatment, and When the body has a complex shape, there are problems such as it is extremely difficult to mold a capsule into such a shape and encapsulate the object to be treated inside it, making it difficult to put it into practical use. do not have.

Furthermore, for parts such as turbine parts that have been used under high stress for long periods of time, distortion occurs in crystal grains, and intergranular cavities occur due to creep, resulting in deterioration of mechanical strength. A method of reproducing the condition is also being considered, but since the formation of a contamination layer is not allowed on such parts, some kind of contamination countermeasure is required.

The present invention aims to solve these problems and to put into practical use the above-mentioned modification technology using the HIP method. The object to be processed is HIP-processed in a HIP furnace by surrounding it with a heat-resistant tube that has a gas flow opening at the bottom and is sealed at the top. By using only the gas inside the heat-resistant cylinder, even if the pressure medium gas contains impurities, the absolute amount of impurities that react with the object to be processed can be reduced and contamination of the object to be processed can be minimized. be.

The present invention will be further described in detail below using the accompanying drawings.

FIG. 1 is a cross-sectional view of a HIP device showing an example of the method of the present invention, in which a high-pressure container 1 for HIP includes a high-pressure cylinder 1a and upper and lower plugs 1b and 1 inserted into its upper and lower openings.
A furnace chamber 3 surrounded by a heat insulating outer layer 2 and having a heating device 9 disposed therein is formed in a high pressure chamber 8 in the container, and a lower plug 1c is formed of a heat insulating material. It is similar to the conventional method in that a pedestal 2' is arranged, and the object 4 to be processed is placed on the pedestal 2' for HIP processing, but in the present invention, the object 4 to be processed is further A heat-resistant cylinder 5 surrounds the
is provided on the pedestal 2'. The heat-resistant cylinder 5 has an upper part sealed, but an opening 6 for gas circulation is formed in the lower part, and the inside and outside of the cylinder are communicated only through the opening 6. Therefore, the pressure medium gas supplied from the gas supply port 10 into the high pressure chamber 8 during HIP processing is
The furnace chamber 3 passes between the high pressure cylinder 1a and the heat insulating outer layer 2.
It flows into the heat-resistant cylinder 5 from its lower part, and at the same time flows into the cylinder through the opening 6 of the heat-resistant cylinder 5. The gas supplied into the furnace chamber 3 is heated by the heating device 9, and at the same time the heat-resistant cylinder 5 is heated, and the pressure medium gas inside the cylinder is also heated by convection. 6, the convection of the pressure medium gas inside and outside the cylinder occurs independently, and after the gas supply is stopped, there is virtually no gas flow inside and outside the cylinder. For this purpose, the upper part of the heat-resistant cylinder is sealed. Therefore, while the object to be processed 4 is being subjected to HIP processing, the only pressure gas that comes into contact with it is the gas that initially flows into the heat-resistant cylinder 5, and impurities in the pressure gas that react with the object to be processed 4 are also removed from the inside of the cylinder. Since the amount of contamination by impurities on the object to be processed is reduced to a minimum, the amount of contamination due to impurities on the object to be processed can be minimized.

Since the heat-resistant cylinder 5 is usually used repeatedly, it is made of heat-resistant metal materials such as stainless steel and molybdenum steel, or ceramics. Since the heat-resistant cylinder 5 is stable, most of the impurities present in the heat-resistant cylinder 5 react with the object 4 to be processed. In order to further reduce the reaction between the object to be treated and the impure gas, the heat-resistant cylinder 5 itself is
Getter materials that easily react with nitrogen, i.e. Ti, Zr,
By forming the heat-resistant cylinder with an alloy such as Nb, Al, Mg, or Si, it is possible to react and absorb impurities in the heat-resistant cylinder itself and suppress the reaction between the object to be treated and the impurities as much as possible, but the most preferable getter material is Some Ti, Zr
is expensive, and there is no need to absorb impurities contained in the pressure gas outside the heat-resistant cylinder 5, so the inner surface of the heat-resistant cylinder 5 is lined with these getter materials by thermal spraying or the like. is preferable,
In particular, the lining layer formed by thermal spraying is
Since it is generally porous and has a large specific surface area, it has extremely good reactivity with impurities. Further, as shown in FIG. 2, if the powder of the getter material 7 is arranged and held inside the opening 6 of the heat-resistant cylinder 5 by a wire mesh 11, it will flow into the heat-resistant cylinder 5 under high temperature. A considerable amount of impurities in the pressurized gas to be processed is removed at the inlet, and the amount of reaction with the object to be processed 4 is also reduced accordingly.The degree of contamination of the object to be processed by impurities is also reduced, and the getter material is Since the tube 7 can be easily replaced, the life of the heat-resistant tube 5 can be extended and is more economical than when the heat-resistant tube 5 is made of getter material or its inner surface is lined with getter material. .

In the above example, the heat-resistant cylinder 5 is installed on the pedestal 2', so the heat-resistant cylinder must be attached to and removed from the pedestal for each HIP process. There are complications such as having to wait for the water to cool down. The example shown in FIG. 3 is a device of the present invention that eliminates this complexity, and is similar to the device shown in FIG. However, the remaining structure is the same. Further, the flow of the pressure medium gas into and out of the heat-resistant cylinder is performed only through the lower opening 6.

With such a configuration, the heat-resistant tube 5 is incorporated into the HIP furnace as one of the internal structures of the HIP furnace, so as mentioned above, the heat-resistant tube 5 must be attached or removed for each HIP process. This is practical as it eliminates the hassle of having to do so.

As described above, according to the present invention, by surrounding the object to be processed with a heat-resistant cylinder, the pressure medium gas that comes into contact with the object to be processed during HIP is limited to only the gas present in the heat-resistant cylinder. Even if the gas contains impurities, the contamination of the object to be processed can be minimized, and if the heat-resistant cylinder holds an impurity getter material, the contamination of the object to be processed can be further reduced. By making the heat-resistant cylinder as small as possible, the absolute amount of pressure gas that comes into contact with the object to be processed is reduced, and contamination of the object to be processed is further suppressed. Contamination caused by impurities has been almost eliminated, and it has become possible to use inexpensive low-purity Ar gas instead of expensive high-purity Ar gas as the pressure medium gas, which is expected to reduce the cost of HIP processing, among other notable effects. There is expected.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a hot isostatic press apparatus showing an example of the method of the present invention, Fig. 2 is a cross-sectional view of essential parts showing another example of the heat-resistant cylinder used in the present invention, and Fig. 3 is a cross-sectional view of a hot isostatic press device showing an example of the method of the present invention. FIG. 2 is a sectional view showing an example of such a hot isostatic press apparatus. DESCRIPTION OF SYMBOLS 1...High pressure container, 2...Insulating outer layer, 2'...Pedestal, 3...Furnace chamber, 4...Object to be treated, 5...Heat-resistant tube, 6...Opening, 7...Getter material, 8 ...High pressure chamber, 9...Heating device, 12...Holder.

Claims (1)

[Scope of Claims] 1. A workpiece 4 with an exposed surface is placed in a furnace chamber 3 surrounded by a heat insulating outer layer 2 in a high-pressure container 1, and the workpiece 4 is placed in a furnace chamber 3 with an exposed surface, and the workpiece 4 is sealed at an upper part and a lower part. A hot isostatic pressing method characterized in that the object to be processed is surrounded by a heat-resistant cylinder 5 having an opening 6 for gas flow, and hot isostatic pressing is performed on the object in that state. 2 Claim 1 in which the object to be treated is a cast material
The hot isostatic pressing method described in . 3. The hot isostatic pressing method according to claim 1, wherein the object to be processed is a powder sintered body. 4. A hot isostatic press according to claim 1, 2, or 3, wherein a getter material that selectively absorbs impurities in a pressure medium gas for hot isostatic pressing is held in a heat-resistant cylinder. Hydraulic press method. 5 A high pressure chamber 8 defined by a high pressure cylinder 1a and upper and lower plugs 1b and 1c attached to its upper and lower openings is surrounded by a heat insulating outer layer 2 and has a heating device 9 inside.
A heat-resistant cylinder 5 having a sealed upper part and a gas circulation opening 6 formed in the lower part is arranged inside the heating device in the furnace chamber 3 so as to surround the object to be processed. A hot isostatic press device characterized by: 6. The hot isostatic press apparatus according to claim 5, wherein the heat-resistant cylinder is formed of a getter material that selectively absorbs impurities in the pressure medium gas for hot isostatic press. 7. The hot isostatic press apparatus according to claim 5 or 6, wherein the inner surface of the heat-resistant cylinder is lined with getter material. 8. A hot isostatic press apparatus according to any one of claims 5 to 7, wherein the heat-resistant cylinder is integrally connected and held to the heat-insulating outer layer by a holder 12.