JP3458220B2 - Oxidation resistant molybdenum material and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molybdenum alloy having both oxidation resistance and high temperature deformation resistance, and a method for producing the same, and relates to high temperature structural materials such as molybdenum rods / wires, plates, And parts, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, structural members used at high temperatures include oxide ceramics such as alumina, magnesia and zirconia, non-oxide ceramics such as silicon nitride and silicon carbide, and refractory metals such as molybdenum and tungsten. Is used.

Among them, refractory metals have characteristics such as excellent workability and toughness as compared with ceramics.
In particular, molybdenum has advantages such as higher workability than tungsten and lower cost than tungsten.

However, molybdenum is extremely inferior in oxidation resistance, and when it is heated at a high temperature in an atmosphere containing oxygen and water vapor, it is consumed by oxidation and is deformed by its own weight or a load. For example, when molybdenum is heated to 650 ° C. or higher in air, MoO ₂ formed on the surface sublimes and explosively wears off. Therefore, molybdenum has a high melting point of 2610 ° C., and is relatively rich in workability, but it is unavoidable to use it in a vacuum, an inert gas, or a reducing atmosphere, and therefore, its use is extremely limited.

[0005]

As described above, molybdenum is limited in its use because it is easily oxidized in a high temperature atmosphere and an oxidizing atmosphere, and its oxide sublimes. Is. Therefore, it could not be used in an atmosphere containing high temperature oxygen and water vapor.

Molybdenum used in the plastically worked state is toughened by the fibrous structure produced by the plastic working. However, even when used in an inert atmosphere or a reducing atmosphere, when it is used at a temperature of 1000 ° C or higher, it recrystallizes and loses its fibrous structure, resulting in an aggregate structure of fine crystal grains close to a sphere. It has a certain fine equiaxed grain structure. The crystal grains generated by recrystallization are very fine, about several tens of μm, and macroscopically form linear grain boundaries in all directions. For this reason, there is a problem that the grain boundary slips easily occur during use at high temperature, and it is easily deformed. In addition, since the grain boundary of molybdenum is very fragile, under high temperature, not only the linear grain boundary in the plate thickness direction and the radial direction is deformed due to its own weight, applied load, and external force, but also at room temperature. Even with the impact, the inconvenience occurred that the cracks that had once propagated through the grain boundaries all at once, leading to fracture.

Therefore, a technical object of the present invention is to molybdenum rods / wires which have stable oxidation resistance even in a use environment in which they are heated to a high temperature in an atmosphere containing oxygen and water vapor, and are further loaded or rubbed. An object is to provide an oxidation resistant molybdenum material such as a plate material and a part, and a method for manufacturing the same.

[0008]

According to the present invention, a bar,
A molybdenum material having any of the forms of a wire rod, a plate and a component, wherein the ratio of the major axis to the minor axis is at least 1.
An oxidation resistant molybdenum material is obtained which is characterized by comprising 0 drawn crystal grains and having a molybdenum silicide layer on the surface.

Here, in the molybdenum material of the present invention, it is preferable that the outermost surface layer of the molybdenum silicide layer has a two-layer structure of Mo Si ₂ and Mo ₅ Si ₃ .

In other words, the inventors of the present invention, when the molybdenum crystal grains have a laminated structure of long crystal grains extended in the direction perpendicular to the plate thickness or in the longitudinal direction of the wire in the molybdenum material, cross the load direction. The number of crystal grains can be significantly reduced, and deformation due to grain boundary slip is less likely to occur,
It was also found that even at high temperatures, it is less likely to occur and this resistance to deformation is extremely effective for oxidation resistance. Also, in the molybdenum material having this structure, when cracks occur at grain boundaries, Since the crack does not have a straight grain boundary in the plate thickness direction and the radial direction in which the crack easily propagates, the crack stops in the middle, is hard to break, and is resistant to impact. Furthermore, in a molybdenum material having this structure, even if cracks occur within the grains, the fracture directions of adjacent crystal grains are different and energy is dispersed at the grain boundaries, so it is difficult for fracture to occur. It has been found.

In the present invention, the laminated structure of long crystal grains is realized by adding fine particles for preventing recrystallization of molybdenum, that is, fine particles of heat-resistant oxide such as lanthanum oxide.

To produce the molybdenum material of the present invention, a small amount of a metal salt forming a heat-resistant oxide such as lanthanum nitrate or yttrium nitrate is added to molybdenum oxide, and after mixing, A molybdenum powder in which fine particles of lanthanum oxide or yttrium oxide are dispersed is produced by hydrogen reduction, and this powder is pressed and sintered to form an ingot. The obtained ingot is added by rolling, drawing, or other plastic working. The oxide fine particles are dispersed with a substantially constant array length in the direction perpendicular to the plate thickness or wire diameter.
The material in such a state is preferably 1500 ° C. or higher, preferably 18
When heated to about 00 ° C., the arrayed oxide fine particles suppress the growth of molybdenum crystal grains in the plate thickness or the wire diameter direction, so that the crystal grains have a structure stretched in the direction perpendicular to the plate thickness or the wire diameter. It has become possible to obtain the above-mentioned laminated structure of long crystal grains.

That is, according to the present invention, the molybdenum rod / wire or plate material or part produced by plastic working such as rolling, wire drawing or casting is recrystallized so that the ratio of the major axis to the minor axis is 10 or more. At least 1 of Si powder, mixed powder of Si powder and Al powder, CrSi alloy powder, FeCrSi alloy powder, and AlSi alloy powder is used after forming drawn crystal grains and secondary processing to form a base material. In a non-oxidizing atmosphere and a reducing atmosphere, using a composite diffusing agent prepared by mixing a metal powder composed of seeds, a halogen compound powder, and an Al ₂ O ₃ powder so that the Si content in the total powder is 10 to 80%. , 100
At least two layers, a MoSi ₂ layer which is heat-treated at 0 ° C. to 1300 ° C. and has excellent oxidation resistance on the surface of the base material, and a Mo ₅ Si ₃ layer having a close thermal expansion coefficient on the base material side. A method for producing an oxidation resistant molybdenum material is obtained, which comprises forming

Further, as a result of examining the relationship between the ratio of the major axis to the minor axis of the crystal grain and the deformation at high temperature, the present inventors have found that if the ratio of the major axis to the minor axis exceeds 10, the molybdenum is less likely to be deformed at high temperature. I found that.

Here, the minor axis and the major axis are the crystal grain diameters in the directions perpendicular and parallel to the processing directions of the molybdenum wire rod and the plate material, respectively, and the average grain diameters measured by using a microstructure photograph.

Next, the oxidation resistance of the molybdenum material of the present invention will be described. It is known that the surface is coated with molybdenum silicide as a means for improving the oxidation resistance of a molybdenum material having extremely poor oxidation resistance. However, when such a hard and brittle material is coated, the coating layer cannot follow small deformation such as creep deformation of molybdenum under a load at high temperature, so that the coating layer is cracked and molybdenum is exposed. In such a state, as described above, molybdenum has a serious drawback that it is explosively consumed by oxidation.

In the present invention, before the surface is coated with molybdenum silicide, a treatment for obtaining the above-mentioned laminated structure of large crystal grains is performed to remarkably suppress creep deformation at high temperatures, thereby providing stable oxidation resistance. Can be given. That is, when the ratio of the major axis to the minor axis of the elongated major crystal grains is 10 or more, cracks are less likely to occur in the molybdenum silicide formed on the surface, and stable oxidation resistance can be obtained.

In the present invention, the ratio of the major axis to the minor axis of the stretched crystal grains is set to 10 or more. If the ratio is less than 10, the molybdenum silicide on the surface is cracked because the surface is easily deformed. This is because it tends to occur and is substantially equivalent to the case of equiaxed grain molybdenum, and the improvement in oxidation resistance is poor.

Further, in the present invention, Si is diffused and permeated into the surface of a molybdenum material having a laminated structure of long crystal grains to form a molybdenum silicide layer having excellent oxidation resistance,
By protecting the molybdenum base material, which is easily oxidized, from reaching oxygen, it can be used even in an atmosphere containing oxygen and water vapor at high temperature.

By the way, in the conventional method of coating the surface with molybdenum silicide, since the silicide layer is a single layer of molybdenum disilicide (MoSi ₂ ), the difference in the coefficient of thermal expansion from that of the base material, By using it repeatedly,
The molybdenum silicide layer was cracked and oxygen reached the molybdenum base material, so that the oxidation resistance could not be maintained.

However, in the present invention, the molybdenum silicide layer is composed of two layers having different compositions, MoSi ₂ having excellent oxidation resistance is formed on the surface, and Mo ₅ Si ₃ having a close thermal expansion coefficient is formed on the molybdenum side of the base material. As a result, it is possible to form a protective layer that is resistant to cracking even after repeated use and has a life that can withstand practical use.

[0022]

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

FIG. 1 is a diagram showing the relationship between the ratio of the major axis to the minor axis of crystal grains of molybdenum material and the deformation at high temperature. As shown in FIG. 1, when the ratio of the major axis to the minor axis exceeds 10, the molybdenum is less likely to be deformed at high temperature. Here, the short diameter and the long diameter are the crystal grain diameters in the directions perpendicular and parallel to the processing directions of the molybdenum wire rod and the plate material, respectively, and are the average grain diameters measured using a microstructure photograph.

Next, a specific production example of the molybdenum material of the present invention will be described.

Example 1 In Example 1 of the present invention, a molybdenum plate material will be described in detail as an example.

First, lanthanum nitrate was added to molybdenum oxide powder so as to obtain 0.1 to 1.0% by weight of lanthanum oxide powder, and then hydrogen reduction was performed at 1100 ° C. for 5 hours, followed by press molding, and hydrogen atmosphere. Ingot was sintered at 1800 ° C. for 10 hours to prepare an ingot having a thickness of 10 to 50 mm.

Next, 1100 to 900 are added to this ingot.
After hot-rolling at 2.0 ° C. to form a 2.0 mm plate, cold rolling was performed to form molybdenum crystal grains into a fibrous structure to obtain a molybdenum plate having a plate thickness of 1.5 mm.

The obtained molybdenum plate is heated in hydrogen at 1800 ° C. or higher, which is higher than the recrystallization temperature, for 10 hours to recrystallize the molybdenum crystal grains having a laminated structure of long crystal grains elongated in a certain direction. Got

Due to the difference in hot rolling rate, a structure having a ratio of major axis to minor axis of crystal grains of 8 to 80 was obtained.

This plate was cut into a piece having a width of 30 mm and a length of 120 mm and subjected to a treatment for forming a molybdenum silicide layer (hereinafter referred to as siliconizing treatment) as described below, and the molybdenum silicide layer was observed under a microscopic structure at 1000 ° C. ~ 1300 ° C
The oxidation resistance test was carried out in the atmospheric furnace and the deformation test was carried out in the inert atmosphere furnace at 1000 ° C to 1300 ° C.

Al ₂ O ₃ powder and NH, which is a halogen compound powder, are added to the CrSi alloy powder having a CrSi ratio of 1: 1 so that the Si content in the composite diffusing agent becomes 15%, 20% and 35%.
_Using three types of composite diffusing agents prepared by mixing ₄ Cl powder, heat treatment was performed at 1100 to 1200 ° C. for 10 hours in a hydrogen atmosphere. The processing conditions are shown in Table 1 below.

[0032]

[Table 1]

The molybdenum plate having the molybdenum silicide layer on the surface thus obtained was cut and the cross section was observed to investigate the thickness of the molybdenum silicide layer. Also,
With another sample, the oxidation resistance was examined in an atmospheric furnace at 1000 ° C to 1300 ° C, and the time until the film was destroyed (durability time) was examined.

In addition, the amount of deformation is 1000 ° C to 1300 ° C, and the amount of deformation in the thickness direction at that time is placed on a support base with a support interval of 100 mm, a load of about 1.5 kg is placed in the center and heated for 10 hours. (Amount of droop) and oxidation resistance were investigated.

The above results are shown in Table 2 below, which shows the siliconizing treatment conditions, the deformation amount at a test temperature of 1000 ° C. and the durability time of the oxidation resistance test. Similarly, the deformation amount at 1300 ° C. and the durability time of the oxidation resistance test are shown in Table 3 below.

[0036]

[Table 2]

[0037]

[Table 3]

Further, the results of the oxidation resistance test and the deformation resistance test of pure molybdenum are also shown in Tables 2 and 3 as comparative examples.

No. 2 in Table 2 is shown in FIG. 1, No. 4 and the results of the oxidation resistance test of the comparative material are shown. Referring to FIG. 2, molybdenum silicide composed of stretched crystal grains having a ratio of the major axis to the minor axis of 10 or more is not easily deformed even under a load at high temperature, and a crack is formed in the molybdenum silicide layer. It was hard to enter and showed good oxidation resistance.

FIG. 3 is a schematic view of a cross section of a sample showing good oxidation resistance. The portion indicated by reference numeral 1 is MoSi ₂
The portion with the reference numeral 2 is Mo ₅ Si ₃ , and the portion with the reference numeral 3 is the molybdenum substrate. 1000 under no load
It showed an oxidation resistance of 2000 hours or more at ° C.

Example 2 As in Example 1, lanthanum nitrate was added to the molybdenum oxide powder so as to obtain 0.1 to 1.0% by weight of lanthanum oxide powder, and then hydrogen reduction was carried out at 1100 ° C. for 5 hours. Was performed, press-molded, and sintered in a hydrogen atmosphere at 1800 ° C. for 10 hours to prepare an ingot having a diameter of 50 mm.

Next, 1100 to 900 are added to this ingot.
After performing hot inversion processing at ℃ to make a bar with a diameter of 20 mm,
This was cut and threaded to make bolts. The bolt was subjected to the same siliconizing treatment as in Example 1 to form a molybdenum silicide layer. Further, when this bolt was subjected to an oxidation resistance test in the same manner as in Example 1 in an atmospheric furnace at 1000 ° C., it showed an oxidation resistance of 3000 hours or more.

[0043]

As is clear from the above description, in the oxidation-resistant molybdenum material of the present invention, the surface of the molybdenum material having a laminated structure of long crystal grains and excellent in deformation resistance is subjected to the siliconization treatment so that the oxidation resistance is improved. Superior MoSi ₂ cannot be used in the atmosphere containing high temperature oxygen and water vapor by forming a molybdenum silicide layer consisting of two layers of Mo ₅ Si _{3 having} a close thermal expansion coefficient on the molybdenum side of the base material. Made molybdenum material available.
Therefore, its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing the results of examining the relationship between the ratio of the major axis to the minor axis of crystal grains of the oxidation-resistant molybdenum material of the present invention and the deformation at high temperature.

FIG. 2 is a diagram showing an oxidation resistance test result of an oxidation resistant molybdenum material according to Example 1 of the present invention.

FIG. 3 is a diagram schematically showing a cross section of a sample showing good oxidation resistance in the test result of FIG.

[Explanation of symbols]

1 MoSi ₂ 2 Mo ₅ Si ₃ 3 molybdenum substrate

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hironobu Murata 8 Oike-cho, Kosai-cho, Koga-gun, Shiga Japan Calorize Industry Co., Ltd. (72) Katsuhiko Ishikura 8 Oike-cho, Konishi-cho, Koga-gun, Shiga Incorporated (72) Inventor Rihei Yoshikawa 8 Oike-cho, Kosai-cho, Koga-gun, Shiga Japan Calorize Industry Co., Ltd. (56) Reference JP 61-186470 (JP, A) JP 60-228668 (JP) , A) JP-B-48-15778 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 10/44 C23C 10/30 C23C 10/08 C23C 10/20

Claims (3)

(57) [Claims] 1. A molybdenum material having any of the forms of a rod, a wire, a plate and a part, which is composed of elongated crystal grains having a ratio of major axis to minor axis of at least 10.
An oxidation-resistant molybdenum material having a molybdenum silicide layer on its surface. 2. The oxidation-resistant molybdenum material according to claim 1, wherein the outermost surface layer of the molybdenum silicide layer is Mo 2 S 3.
An oxidation resistant molybdenum material having a two-layer structure of i ₂ and Mo ₅ Si ₃ . 3. A recrystallized molybdenum rod / wire or plate material or part produced by plastic working such as rolling, wire drawing, casting, etc. to obtain drawn crystal grains having a ratio of major axis to minor axis of 10 or more. Then, after secondary processing to form a base material, a metal powder consisting of at least one of Si powder, mixed powder of Si powder and Al powder, CrSi alloy powder, FeCrSi alloy powder, and AlSi alloy powder. The halogen compound powder and the Al ₂ O ₃ powder are contained in a total amount of Si of 10 to 80.
%, Heat treatment was performed at 1000 ° C. to 1300 ° C. in a non-oxidizing atmosphere and a reducing atmosphere using a composite diffusing agent mixed so that the Mo on the surface of the base material had excellent oxidation resistance.
The Si ₂ layer and Mo ₅ S having a thermal expansion coefficient close to that of the base material side.
method for producing oxidation-resistant molybdenum material and forming at least two layers of the i ₃ layers.