JPS602637A - Manufacture of ni superalloy billet for superplastic forging - Google Patents

Abstract

PURPOSE:To obtain easily a billet having a desired grain size and suitable for superplastic forging when the titled billet is manufactured by molding and caking alloy powder prepd. by atomization with gaseous Ar, by specifying the particle size of the powder, the heating temp. and the gamma' content. CONSTITUTION:Ni superalloy powder having <=50mum diameter and contg. 50- 90vol% gamma' (precipitate) is prepd. by atomization with gaseous Ar, and the powder is molded and caked at <=1,100 deg.C to obtain an Ni superalloy billet for superplastic forging. The diameter of crystals produced in the molded body is controlled to <=6mum. The molding and caking are carried out by HIP, forging, extrusion or other means.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a superalloy product having fine grains, particularly a billet for superplastic forging of an N1-base superalloy suitable for superplastic forging.

When heat-resistant superalloy materials are superplastically forged and processed into various shapes, if the crystal grains are made finer, superplastic behavior will occur.
It is a known fact that complex shapes can be easily obtained, and therefore various methods have been attempted to make crystal grains finer. The effective means of this type of method currently being researched and developed and put into practical use can be roughly classified into the following means.

That is, the first method is to drop a molten stream of a heat-resistant superalloy through a tundish into a gas atomization chamber using argon gas, etc., to pulverize the droplets, and to place this powder into a capsule. In the second method, powdering and capsule filling are the same as in the first method. In the third method, powdering by gas atomization is the same as the first and second methods, but strain is added in advance to the obtained powdered particles in the cold. Cold prestrain processing (rolling by passing through rollers, impact by ball mill, etc.) is performed, and the processed powder is filled into capsules, which are consolidated by H-process and then subjected to superplastic forging. It is something. However, each of these means has its own problems as follows. In other words, in the first method, the amount of strain differs between the outer periphery and the inside during extrusion using a conventional press for grain refinement, and the amount of heat generated during processing is partially different due to this. Moreover, since the extrusion is performed at a low temperature below the recrystallization temperature, the deformation resistance is high and a large-capacity press is required. When attempting to refine the crystals of the forged material by the first stage forging in a two-stage forging means, if it is necessary to use an extremely slow strain rate in this forging stage, cold prestraining treatment is performed in the powder state. Therefore, there are no problems that arise with the first and second methods, but instead, the cold prestraining process is increased, and during this process, for example, when processing by passing through rolling rolls, Fine particle powder adheres to the circumferential surface of the roll, and it is necessary to scrape it off with a brush or other means. At this time, troubles such as contamination of the powder due to debris from the brush etc. are likely to occur, and forgings made of this type of superalloy powder Because it is used in high-heat, high-load equipment and parts such as aircraft engines and generator turbines, contamination with substances other than powder can cause serious accidents, so it is a problem in terms of processing. occurs.

In view of the problems of the conventional method as described above, the present invention aims to solve the problems by determining the relationship between the particle size of powder and the heating temperature.
The purpose of this method is to provide a material with a desired crystal grain size by focusing on the amount of precipitates (amount of precipitates) and strictly controlling these conditions.

That is, the present invention solves the above-mentioned various problems by providing a method for producing a billet for superplastic forging of an N1-base superalloy, which is compacted and solidified at a temperature below 100 µm, and which controls the crystal grain size produced in the compact to 6 μm or less. be.

In more detail below, the first feature of the present invention is to use a powder of 50 μm or less and containing 50 to 90% by volume of γ'; In particular, it is molded and solidified at a temperature of 1100° C. or lower.

Figure 1 shows the results of considering the relationship between the particle size of N1-based superalloy powder and the crystal grain size after H-P (hot still water pressing) treatment. It is immediately understood that as the diameter becomes smaller, the crystal grain size also tends to become smaller.

In particular, it goes without saying that crystal grains that are generally advantageous in exhibiting superplastic behavior are preferably as fine as possible, but it is thought that the crystal grains required for superplastic forging are about 6 Im. In other words, 6 μm is the upper limit of grain size required for superplastic forging.

Incidentally, one of the advantages of superplastic forging is that this 6 μm crystal grain is the upper limit, and by forging in an area with low deformation resistance, it can be forged with a small press with low power.
In order to take advantage of this feature, the deformation resistance must be 1” ”rrrm.
It is required that it be 2 or less.

For this purpose, it will be understood from the figure that the crystal grain size of the material must be 6 μm or less.

Therefore, it can be said that the crystal grain size of 6 μm is the upper limit of the crystal grain size required for superplastic forging.

Therefore, if we turn to Figure 1 again, with a powder particle size of 50 μm,
It can be seen that when the heating temperature is 1100°C, the size of crystal grains present in the powder is 6Pn.

If the powder becomes coarser than this or the temperature is too high, the crystal grains will become coarser.

This indicates that the necessary conditions are that the powder particle size is 50 degrees or less and that it is formed and solidified at a temperature of 1100 degrees Celsius or less, and the lack of either of these conditions indicates that the crystals required for superplastic forging are required. Grain size cannot be obtained. Therefore, the means of forming and solidifying include H-P, forging, extrusion, etc. If shock waves are used, the strength of superalloys will be the same at room temperature, but the strength of superalloys will be The strength is determined by γ' (amount of precipitates), and the strongest point exists when the amount of γ' is around 65% by volume. Figure 3 considers the strength by showing the relationship between the amount of γ′ and the fracture life.
○ mark), 10oo℃, 12t2 (△ mark) and 0: l O
Both exhibit the same tendency under the creep conditions of 0°C and 10KL2 (x mark), and the maximum point is seen between 65 and 75% by volume.

The amount of γ′ is usually proportional to the amount of g and Ti, and the amount of other Nb
, Ta, etc. are also involved. When the amount of γ' reaches 30% by volume or more, it becomes difficult to process with normal forging, especially when the amount of 50%
If it exceeds the volume percentage, it cannot be forged unless it is superplastic forged.

Figure 4 shows the relationship between the I content and AA + Ti + /2 + /2, and when the γ' content is 50% by volume, which cannot be processed without superplastic forging, the total amount of γ'-generating elements is approximately 9%.
becomes.

Therefore, for superplastic forging, it is important that the amount of γ' is 50% by volume or more. However, from the composition of the N1-base superalloy, 100
Volume % is almost unthinkable.

Thus, through the above-mentioned considerations and examinations, the conditions of the present invention have been found, whereby a billet suitable for use in superplastic forging can be obtained using powder with a crystal grain size of 6 μm or less.

Hereinafter, further examples will be given and concretely explained.

Example Ar gas atomization with the following components: 0.060-12.50r-18,3Co-3,18M
o -5-IA7-4.41Ti -, O,'74V-
A N1-based superalloy powder having a particle size of 30 μm or less and containing 60% by volume of γ' consisting of residual particles was prepared and solidified by HIP treatment under the following conditions to produce a billet.

The density of the obtained billet was held at 1100°C x 9003 x 1 hour, showing a true density ratio of 100%,
When the structure was examined, the average crystal grain size was 5 μm.

Next, the material having the above crystal grain size was heated at 1050°C.
A high-temperature tensile test was carried out at a strain rate of 8.times.x]-0 sec. The resistance was 30.zeta.2, the elongation was 12%, and no superplastic properties were observed.

As described above, the present invention uses N1-based superalloy powder with a particle size of 5.
11 powder containing 50 to 90% by volume of I with a diameter of 0 μm or less
This is a method of producing a billet for superplastic forging by compacting and solidifying at a temperature of 00°C or less and controlling the crystal grain size in the compact to 6 doors or less.The powder diameter and γ' are set as above, Billets exhibiting superplastic behavior can be easily produced by forming at the required temperature, and superplastic forging of high-strength N1-based superalloys is possible by specifically determining the amount of I. Expanding the applications of various types of forging using powder,
Furthermore, this method has a remarkable effect on the production of high-strength products, and holds great promise for future industrialization.

[Brief explanation of drawings]

FIG. 1 is a chart showing the relationship between the powder particle size and crystal grain size of N1-based superalloys (containing 50% by weight of i) at various temperatures;
Figure 2 shows the strain rate and deformation resistance of each grain size and the deformation resistance patent applicant Agency of Industrial Science and Technology

Claims (1)

[Claims] 1. Diameter made by Ar gas atomization is 50/liter
N1 having T1 or less and containing 50 to 90% by volume of γ'
A superalloy billet suitable for superplastic forging is created by molding and solidifying the base superalloy powder at a temperature of 1100°C or less, and setting the crystal grain size in the compact to 6 μm or less.