JPH11264045A - Mulybdenum material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the molybdenum material in which crystal particles hardly change to coarse even if the material is heated at high temp. in a sintered body before being subjected to a plastic processing and excellent in toughness at low temp. and to provide the production method of the Mo material provided with a desired crystal particle size. SOLUTION: In the molybdenum sintered body in which 0.2-3.0 mass % tantalum carbide(TaC) is dispersed, at least either one of facts in which crystal particle size is 1-10 μm or ductility-brittleness transition temp. is <=-50 deg.C is satisfied. The sintered body having the crystal particle size within a range of 1.0-25 μm is produced by adding 0.2-3.0 mass % TaC powder to a molybdenum powder and subjecting the mixture to a mechanical alloying treatment, and after subjecting the produced powder to a hot isotropic press, subjecting the pressed matter to heat treatment and controlling a temp. and time of the heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for heat-resistant materials such as high-temperature structural materials, sintered parts and block products. The present invention relates to a material and a method for producing a molybdenum material capable of adjusting crystal grains to an arbitrary size.

[0002]

2. Description of the Related Art Molybdenum (hereinafter referred to as Mo) is widely used as a heat-resistant material, particularly at a high temperature of 1500 ° C. or higher, because of its high melting point and good plastic workability.

[0003] However, pure Mo processed material is 1000 ° C.
If heated above this level, it will recrystallize and become brittle, and its high-temperature strength will be significantly reduced. At higher temperatures, the crystal grains become coarser and become brittle. Further, since the ductile-brittle transition temperature (hereinafter referred to as DBTT) of this recrystallized material is near room temperature, it becomes extremely brittle below this temperature. These embrittlements are due to Mo
Is essentially brittle, that is, due to grain boundary embrittlement.

[0004] In order to improve the grain boundary embrittlement, single crystallization without any crystal grain boundaries is performed, but it is not industrially easy to obtain a material having a practical size.

[0005] In addition, a method of reducing the influence of crystal grain boundaries by adding an oxide such as lanthanum, silicon, or potassium and controlling the structure of the laminated structure of long crystal grains has been performed. However, in order to control the structure, plastic working with a high working ratio by hot forging, hot rolling or the like is indispensable. For example, Japanese Patent Publication No. 61-27459, Japanese Patent Application Laid-Open No.
According to Japanese Patent No. 150071 and US Pat. No. 4,514,234, a molybdenum material to which one or more of aluminum, silicon and potassium elements are added is:
It is said that plastic working with a working ratio of 85% or more is required.

[0006] In the manufacturing technique based on the structure control method, there is a limit in manufacturing a thick molybdenum sintered body.

For example, in order to obtain a plate having a thickness of 50 mm by rolling, it is necessary to calculate a molybdenum sintered body having a thickness of at least 330 mm or more. And other problems. That is, it is difficult to obtain a material having a large thickness with improved grain boundary brittleness by a structure control method that requires plastic working at a high working rate, and it is difficult to apply the material to a thick plate, a block, or a sintered part.

[0008]

SUMMARY OF THE INVENTION In order to develop a Mo material which can be manufactured without the need for plastic working at a high working ratio and has improved grain boundary embrittlement, it is necessary to develop a Mo sintered body itself before plastic working. It is necessary to improve strength and toughness.

If a high-strength and tough Mo sintered body can be obtained,
This is because not only can the sintered body itself be used, but also a high-strength and high-toughness molybdenum material can be obtained by performing only a small amount of plastic working.

[0010] Therefore, a technical object of the present invention is to provide a Mo material which is hardly coarsened even when heated to a high temperature in a sintered body before plastic working, and which is rich in toughness at a low temperature.

Another technical object of the present invention is to provide a manufacturing method for obtaining the Mo material having a desired crystal grain size.

[0012]

According to the present invention, 0.2.
To 3.0 mass% (or weight%) of tantalum carbide (Ta
C) is a molybdenum sintered body in which the crystal grain size (average crystal grain size) is 1 to 10 μm or less;
A molybdenum material having a ductile-brittle transition temperature of −50 ° C. or lower is obtained.

Here, in the present invention, the range of the amount of TaC added to molybdenum is limited to 0.2 to 3.0% by mass, when the content is less than 0.2% by mass. This is because the reinforcement is poor, it is difficult to suppress the coarsening of crystal grains at high temperatures, and it is difficult to improve the strength and toughness. On the other hand, if it exceeds 3.0% by mass, it is difficult to densify,
It is also because it becomes brittle and easily cracks when subjected to plastic working, which lowers the yield. Further, in the present invention, tantalum carbide (TaC) is more preferably in the above range, and the crystal grain size is 1.6 smaller than 3.3 μm.
% By mass.

Further, according to the present invention, the molybdenum powder is mixed with 0.2 to 3.0% by mass of TaC powder and subjected to mechanical alloying treatment. And controlling the temperature and time of the heat treatment to obtain a molybdenum sintered body having a crystal grain size (average crystal grain size) in the range of 1.0 to 25 μm. A manufacturing method is obtained.

Further, according to the present invention, in the method for producing a molybdenum material, the mechanical alloying treatment and the hot isostatic pressing are performed without being exposed to the atmosphere. A manufacturing method is obtained.

The reason why TaC is used in the present invention is that TaC has a high melting point and is thermally stable, and it has been found that DBTT is lowered by increasing the grain boundary strength of Mo. In addition, it has been found that TaC has an effect of suppressing the coarsening of crystal grains.

Further, in the present invention, the mechanical alloying treatment is performed by mixing TaC at high energy to atomize TaC and dispersing it in Mo.
It has been found that the bonding force between Mo and Mo is further enhanced, and as a result, strength and toughness can be improved. Here, in the present invention, the mechanical alloying treatment does not mean a powder treatment method in a narrow sense for the purpose of alloying, but the powder is finely dispersed or dispersed particles ( Here, this means a broadly-defined powder embedding method of embedding TaC) in a metal powder (here, Mo).

Further, in the present invention, the hot isostatic pressing is performed because the sintering temperature can be lowered and the densification can be achieved as compared with the commonly used hydrogen sintering. . Therefore, the powder which has been subjected to the mechanical alloying process and made finer can be densified without being coarsened. In addition, it has been found that, in a material that has been densified by low-temperature sintering, crystal grains are unlikely to become coarse even when heated to a high temperature. Incidentally, as is well known, the mass% used in the present invention has the same meaning as the weight%.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) Average particle size 4.1 μm
Of MoC powder with TaC powder having an average particle diameter of 1.1 μm
3.2% by mass was added, and a mechanical alloying (MA) treatment was performed for 30 hours in a planetary ball mill using a cemented carbide container and balls. The handling of the powder before and after the MA treatment was performed in a glove box replaced with high-purity argon gas. The obtained powder is sealed in a glass container after CIP molding, and then at 1300 ° C. and 1500 kgf / c.
Hot isostatic pressing (HIP) sintering was performed for m ² , 3 hours. Thus, until after HIP sintering, the material was fabricated and densified without exposure to air. The obtained sintered body (HIP
Material) and a HIP material heated from 1800 ° C. for 1 hour (1800 heated material) to a thickness of 1 mm, a width of 2 mm, and a length of 2
A test piece of 5 mm was cut out and subjected to a static three-point bending test (a distance between support pins of 16 mm and a load speed of 1 mm / min) in a temperature range of -196 to 90 ° C to examine DBTT.

Here, the yield strength temperature curve 2 shown in FIG.
And the temperature 6 at the intersection 5 of the temperature curve 1 with the maximum strength was defined as DBTT. This temperature is a critical temperature showing ductility, and the bending angle is almost 0 degree. As a comparative material, DBTT was also examined on a pure Mo plate having a crystal grain size of 20 μm.

Further, the crystal grain size was determined by heating at various temperatures and times and observing the structure, and the crystal grain growth by high temperature heating was examined. Here, the crystal grain size was measured by the area measurement method.

Table 1 below shows that the TaC-dispersed Mo sintered body (HIP material) according to the first embodiment of the present invention and the HIP material
The crystal grain size and DBTT after heating at 800 ° C. for 1 hour (heated material at 1800 ° C.) are shown. At the same time, the crystal grain size and DBTT of the pure Mo plate of the comparative example are also shown.

[0024]

[Table 1] As shown in Table 1 above, in the case of the HIP material, in the case of the HIP material, by adding 0.1% by mass of TaC (Sample 2), a pure MO sintered body manufactured without adding TaC (Sample 1). The grain size is smaller than that of. In the case of the heating material at 1800 ° C., the pure Mo sintered body (sample 1) is extremely coarse, but by adding 0.1% by mass of TaC (sample 2),
Coarsening is suppressed.

When the amount of TaC added increases, the crystal grain size further decreases, and the growth of crystal grains is suppressed. However, when the addition amount is 3.2% by mass (sample No. 8), the density increases. It did not rise and had many pores.

In the DBTT, any HIP
In the material and the 1800 ° C heating material, TaC is 0.1
By adding the mass% (sample 2), the DBTT is significantly reduced as compared with a pure Mo sintered body (sample 1) manufactured without adding TaC. However, the DBTT of the sintered body of Sample 2 is
There is almost no change compared to the pure Mo plate of the comparative material.

When the amount of TaC added increased, the DBTT decreased, but when the amount of addition was 3.2% by mass (sample 8), the density did not increase and embrittlement occurred.

Table 2 below shows Ta according to the embodiment of the present invention.
C-dispersed Mo sintered body (HIP material) and HIP material of 2000
The crystal grain size after heating at 100C for 1 hour and 100 hours is shown.

By adding TaC in an amount of 0.2% by mass or more, coarsening is suppressed even when heating is performed at 2000 ° C. for 100 hours.

[0030]

[Table 2] FIG. 2 shows 1.6% by mass TaC according to an embodiment of the present invention.
It is an optical microscope structure photograph which shows the metal structure of a dispersed Mo sintered compact (a) and a pure Mo sintered compact (b). Also, FIG.
1.6 mass% TaC-Mo after heating at 1800 ° C. for 1 hour
It is an optical microscope photograph which shows the metal structure of a sintered compact (a) and a Mo sintered compact (b). After sintering, the crystal grains are refined by dispersing TaC. When heated at 1800 ° C. for 1 hour, the crystal grain size of the pure Mo sintered body becomes 1-2 mm,
While the crystal grains are coarse, in the case of the TaC-dispersed Mo sintered body, the crystal grain size is as small as about 10 μm, and the grain growth is significantly suppressed.

FIG. 4 is a graph showing a bending angle of a heating material at 1800 ° C. of a 1.6 mass% TaC-dispersed Mo sintered body (sample 5) and a pure Mo sintered body (sample 1) and a bending angle of a pure Mo plate according to an embodiment of the present invention. FIG. 3 is a diagram showing the temperature dependence of the present invention. In FIG. 4, a TaC-dispersed Mo sintered body, curve 12 is a pure Mo plate for comparison, curve 1
3 shows the relationship between the bending angle of the pure Mo sintered body and the test temperature, respectively. As is clear from FIG. 4, the TaC-dispersed Mo sintered body (curve 11) was a pure Mo plate for comparison (curve 1).
The DBTT of 2) and the pure Mo sintered body (curve 13) have extremely low curves, indicating that the low-temperature ductility is excellent. FIG.
As shown in curve 11, the DBTT of the TaC-dispersed Mo sintered body was extremely lower than that of the pure Mo plate and the pure Mo sintered body shown in the curves 12 and 13, indicating that the low-temperature ductility was excellent. ing.

[0032]

As described above, according to the present invention,
In the sintered body before the plastic working, the crystal grains are hardly coarsened even when heated at a high temperature, and a Mo material having a high toughness at a low temperature can be provided.

According to the present invention, the above-mentioned advantages are provided.
A manufacturing method for obtaining a Mo material having a desired crystal grain size can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature dependence of the yield strength, maximum strength, and bending angle of a molybdenum material.

FIG. 2 shows 1.6% by mass TaC according to an embodiment of the present invention.
It is an optical microscope structure photograph which shows the metal structure of a dispersed Mo sintered compact (a) and a pure Mo sintered compact (b).

FIG. 3 shows 1.6% by mass TaC according to an embodiment of the present invention.
18 of the dispersed Mo sintered body (a) and the pure Mo sintered body (b)
It is an optical microscope photograph which shows the metal structure after heating at 00 degreeC for 1 hour.

FIG. 4 shows 1.6 mass% TaC according to an embodiment of the present invention.
It is the figure which showed the 1800 degreeC heating material of a dispersion | distribution Mo sintered compact and a pure Mo sintered compact, and the temperature dependence of the bending angle of a pure Mo board.

[Description of Signs] 1 Temperature curve of maximum strength 2 Temperature curve of yield strength 3 Temperature curve of bending angle 5 Intersection 6 DBTT at intersection

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 687 C22F 1/00 687 691 691Z

Claims (3)

[Claims] 1. A molybdenum sintered body in which 0.2 to 3.0% by mass of tantalum carbide (TaC) is dispersed, having a crystal grain size of 1 to 10 μm and a ductile-brittle transition temperature of -5.
A molybdenum material having a temperature of 0 ° C. or lower. 2. 0.2 to 3.0 mass% of molybdenum powder
TaC powder is mixed and mechanically alloyed,
After the generated powder is hot isostatically pressed, heat treatment is performed, and by controlling the temperature and time of the heat treatment, 1.
A method for producing a molybdenum material, comprising obtaining a molybdenum sintered body having a crystal grain size in a range of 0 to 25 µm. 3. The method for producing a molybdenum material according to claim 2, wherein the mechanical alloying treatment and the hot isostatic pressing are performed without being exposed to the atmosphere. .