JPS5914290B2 - Casting defect treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method suitable for removing casting defects in cast materials, particularly superalloy cast materials used for gas turbine blades, vanes, etc.

Casting has traditionally been the most common metal forming technology and is used in many fields, but the gas that is inevitably generated during casting tends to cause small and large pores to form within the cast product. It has been extremely difficult to completely prevent the occurrence of such pores, so it has been unavoidable that some pores exist in conventional cast products. However, the presence of the pores did not pose much of a problem since the cast product could actually satisfy the performance required for the cast product.

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.
It has become necessary to manufacture parts by casting superalloys such as base alloys.

Due to the manner in which such parts are used, it is inevitable that they are used under harsh conditions, and the pores generated during the casting process are fatal defects that degrade mechanical properties, and how to eliminate them is an important issue.

Due to the demands of the times, hot isostatic pressing (HIP) has recently been introduced.
) method has been proposed in which a high-temperature, high-pressure pressurized gas such as Ar gas is applied to a cast or sintered body with internal defects to seal the pores, and this method has attracted much attention as a means of solving the above-mentioned problem. ing.

According to this HIP method, a molded product such as a cast product or a sintered product is charged into a high-pressure container equipped with a built-in heating device.
A at a pressure of about 1,000 atmospheres and a temperature of 900 to 1,200 degrees Celsius
It is possible to completely seal the pores without leaving any traces of the pores by applying r gas, crushing the pores by the action of temperature and pressure, and diffusion bonding the metal in the pores. The purpose can be fully achieved as far as the molded body is modified by the decomposition.

However, in this HIP method, the Ar gas used as a pressure medium and a heating medium is expensive, so after the HIP process, the Ar gas inside the high-pressure container is always collected in a gas holder, and therefore it is difficult to form the high-pressure container. It is unavoidable that air is mixed in when the container is opened and closed for loading and unloading the molded body, and various impurity gases generated by the decomposition of oil etc. adhering to the molded body are mixed in. Therefore, the purity of the recovered Ar gas cannot be avoided. As a result, the problem of contamination of the compact by impurity gases such as oxygen and nitrogen contained in the Ar gas remains.

This Ar gas-like impurity is about 200 ppm at most, but under a high pressure of 1000 atm, even by simple calculation, the absolute amount of the impurity is equivalent to that of normal pressure Ar gas containing 20% impurities. Since the metal surface of the molded body is extremely activated at high temperatures of 00 to 1200°C,
Even if it is a trace amount of impurity, it is likely to react with the metal on the surface of the molded product.

In particular, oxygen as an impurity is the most problematic, with concentrations of several tens of ppm
Even if a certain amount of oxygen is present, a contamination layer of several tens of micrometers, such as an oxide layer, will be formed on the surface of the molded product, and the properties of the molded product will be significantly deteriorated.

Therefore, unless the problem of contamination of molded bodies due to impurities is solved, it will be difficult to put into practical use the above-mentioned HIP method for modifying molded bodies.

On the other hand, one way to solve the problems of the HIP method is to bury a mold filled with metal powder in a pre-prepared mold inside a container filled with secondary pressure medium particles, and then insert the container into a HIP furnace and heat it to a high temperature. There is a method of performing HIP treatment under a high-pressure primary pressure medium gas atmosphere.

This method of consolidation using a secondary pressure medium differs from the normal HIP method that does not use a secondary pressure medium, because the mold itself filled with metal powder is buried in a container filled with secondary pressure medium particles. , there is no opportunity for impurities in the HIP furnace to come into contact with the surface of the molded product, and the problem of contamination of the molded product due to impurities is temporarily prevented. However, when the casting material is enclosed in a container and subjected to HIP treatment, HIP for removal
Depending on the conditions (temperature, pressure), the secondary pressure medium is also consolidated, which not only makes it extremely difficult to remove the internal object to be processed after processing, but also makes it difficult to reuse the pressure medium. There is no escape from the complication of having to crush it.

Therefore, it is desirable to use ceramic-based materials that are difficult to sinter as the secondary pressure medium, but these materials usually
Due to the manufacturing process, ultrafine powder of several micrometers in size is common, and if this is used for HIP processing, the filling rate is poor (and it often causes extreme shrinkage during HIP, eventually leading to container damage). It is.

In view of the above-mentioned facts, the present invention aims to improve the conventional method for treating defects in cast materials by HIP, and focuses particularly on the effectiveness of refractory material powder used as a secondary pressure medium. The purpose of this invention is to provide a casting defect treatment method that is not affected by

Therefore, the method of the present invention, which is suitable for such purpose, involves embedding the casting material in a refractory powder, and burying the casting material in a refractory powder at room temperature. Once pressure molded into blocks,
The feature is that the block is inserted into a HIP processing capsule and subjected to a predetermined HIP processing.

Hereinafter, specific aspects of the treatment method of the present invention will be explained in further order.

First, the basic structure of the method of the present invention is to first embed a cast material having casting defects in refractory material powder, and then press-form it by cold isostatic pressure treatment (CIP) or the like at room temperature. The second step is to put the block into a normal HIP molding capsule and perform HIP treatment.

The refractory material powder used in the first step of the present invention includes BN, Si3N4. Al2O3, zrO2, T
i02 is Vycor glass, which is appropriately selected from the refractory material powders made of these material groups depending on the type of casting material, especially in terms of its interfacial reactivity with the casting material.

Then, the cast material is buried in these refractory material powders and CIP is performed.
To carry out the treatment, in order to maintain the shape of the refractory material powder, a mold made of a flexible sheet material such as a rubber mold is usually used, the refractory material powder is filled into the mold, and the material to be treated is placed inside the mold. Bury the casting material.

Pressure molding of the cast material encapsulated in the refractory material powder by CIP treatment etc. only requires pressing with a pressure suitable for forming the refractory material powder and the cast material into a block, and severe conditions such as temperature and pressure are not necessarily required. However, due to the ease of the work process, it can be applied at about 4000 kg/ca at room temperature.
It is desirable to consolidate the refractory material powder for 3 minutes to form a block with a density of at least 60 to 80%, and the CIP treatment is the most effective pressure treatment.

The types and characteristics of the secondary pressure medium powder used in the method of the present invention are illustrated below.

As is clear from the table above, simply filling the pressure medium results in an extremely low apparent density. For example, in the case of NB, the apparent density is only 17.7% in terms of relative density, and this can be directly applied to HIP. It can be seen that the amount of deformation of the capsule after treatment is extremely large.

Next, the refractory powder material containing the cast material that has been made into blocks as described above is charged into a normal HIP molding capsule and transferred to the second HIP treatment.

The capsule in this case is preferably made of a metal such as mild steel, or a gas-impermeable material such as glass or a composite material of metal and glass, as is the case with conventional molded capsules, and its size is large enough to accommodate the above-mentioned blocks. required.

The capsule loaded with the block is then subjected to HIP treatment according to a conventional method, but prior to this treatment, the air remaining in the capsule is removed by degassing and the capsule is sealed.

The HIP treatment is carried out at 1200°C and 1000 kg/kg in an Ar gas atmosphere according to the commonly used HIP conditions.
cyrL, which takes approximately one hour, but it goes without saying that the time should be selected appropriately depending on the material, size, etc. of the object to be processed.

It should be noted that during deaeration during the HIP process, the refractory material powder that is the secondary pressure medium has already been densified to some extent by CIP, so there is no fear of side-stage pressure medium scattering.

Incidentally, after the treatment, the refractory material powder, which is the secondary pressure medium, is peeled off by appropriate means.

Even if the cast material that has been subjected to HIP treatment through the above-mentioned steps has internal defects, the defects will completely disappear and the cast material will be modified into a sound cast material.

Next, examples of the method of the present invention are listed.

Example I ALLOY 713 C (a precision cast material made of Ni-based superalloy was buried in a secondary pressure medium made of BN powder, and held at room temperature for 3 minutes at 4000 kg/c4 to give a CI
This was subjected to P treatment and formed into a block.

Next, put this block into a HIP device and heat it to ■200°C.
Under the conditions of x 1000 kg/crti x 1 hr,
When the HIP treatment was carried out in Ar gas and the state of disappearance of casting defects was investigated, results as shown in the enlarged photograph shown in FIG. 1 were obtained.

On the other hand, when the same material was subjected to HIP treatment under the same conditions without being subjected to pressure molding using a secondary pressure medium, an oxidized contamination layer was observed on the surface as shown in FIG.

As is clear from both figures, in the product according to the present invention, internal pores are completely eliminated and casting defects are eliminated, but only HI
It can be seen that the particles caused by the P treatment have not yet disappeared sufficiently.

Example 2 Next, in order to investigate the damage state of the capsule, a mild steel capsule was used, and BN powder was used as the secondary pressure medium, and 400
After holding at 0 kg/cwt for 2.5 minutes, ■ 200℃
HIP treatment was performed under the conditions of X 1000 kg/crA X 1 hr.

In this case, the appearance and cut surface of the capsule after HIP treatment were as shown in the reference photograph (IX2).

On the other hand, BN powder was used as the secondary pressure medium, and the object to be treated was buried in the secondary pressure medium and sealed in a mild steel capsule without being subjected to CIP treatment, and heated at 1200° C.
When subjected to HIP treatment at a rate of 0.00 kg/ciX 1 hr, the mild steel capsule exhibited an extremely large amount of deformation as shown in reference photograph (3).

As is clear from these photographs, even after HIP treatment, the CIP treatment according to the method of the present invention has a circular cross section that is almost the same as before treatment in the upper, middle, and lower parts, but the pressure molding In the case of the conventional method which does not carry out this process, the capsule cracks and Ar enters the capsule, causing surface contamination and extreme deformation.

As described above (according to the method of the present invention), various cast materials having internal casting defects such as pores can be modified without any contamination of their surfaces, and Ni-based alloys, carbon
It improves the modification effect of superalloy cast materials such as O-based alloys by HIP method, eliminates macroscopic casting defects, greatly improves product yield, and significantly improves the mechanical properties of molded products. This is expected to have the effect of dramatically improving the reliability of molded products.

Moreover, in the method of the present invention, blocks are formed in advance by pressure molding and then subjected to HIP treatment.
Easy to degas and seal during HIP treatment, and
Since the degree of filling can be increased compared to molding directly from powder, the processing effect is smooth and the capsule does not break.

Furthermore, since the cast material to be treated is directly buried in the refractory material powder, there is the advantage that the object to be treated can be easily taken out after treatment, making it extremely effective as a method for treating defects in cast materials.

[Brief explanation of the drawing]

Figures 1 and 2 are enlarged micrographs showing the disappearance of casting defects in the method of the present invention and the conventional method.
The figure shows the method according to the present invention, and FIG. 2 shows the case according to the conventional method.

Claims (1)

[Scope of Claims] 1. A method for removing defects in a cast material by subjecting the cast material having casting defects to hot isostatic pressing in a high-temperature, high-pressure gas atmosphere. This is pressure-molded at room temperature to form a block, and then the block is placed in a capsule for hot isostatic press molding, which is degassed and sealed. A casting defect treatment method characterized by performing isostatic press treatment. 2 Refractory material powder is NB, Si3N4, A1□03, Z
The casting defect treatment method according to claim 1, wherein the powder is selected from the group consisting of r02, TiO2, and Vycor glass. 3. The casting defect treatment method according to claim 1 or 2, wherein the powder relative density of the refractory material powder formed into blocks by embedding the casting material is 60 to 80%.