JPH06256918A - Production of molybdenum or molybdenum alloy sheet - Google Patents

Abstract

PURPOSE:To stably produce a cold rolled sheet of molybdenum or molybdenum alloy, excellent in workability, such as weldability and formability, and free from impurity gas generation even if used at and under high temp. and high vacuum, in high yield on an industrial scale. CONSTITUTION:A cast ingot of molybdenum or molybdenum alloy (preferably, of <=30mm crystalline grain size) is used. This ingot is canned with a sheathing material, forged, warm-rolled or hot-rolled at 500-1200 deg.C heating temp. at >=50% draft, and further cold-rolled (cross rolling is preferred) under the condition of >=30% draft, or, after this cold rolling, the resulting cold rolled sheet is subjected to vacuum heat treatment at 800-1200 deg.C for 0.5-4hr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to molybdenum or molybdenum which has good workability (plastic workability, weldability, etc.) and produces almost no impurity gas even when used under high temperature and high vacuum. The present invention relates to a method for manufacturing an alloy plate.

[0002]

2. Description of the Related Art Molybdenum is one of the refractory metals that has been industrially produced for a relatively long time and has been used as a heat-resistant material, vacuum tube material, electric resistor, etc. . In particular, the strength of molybdenum and molybdenum alloys at high temperatures is outstanding among practical metal materials, and a huge number of studies aiming at application to aerospace equipment-related members etc. as the only heat-resistant material reliable at around 1000 ° C. Is up.

However, molybdenum has a melting point of 2600 ° C.
In addition to having a high value exceeding 0, the vapor pressure of the oxide is extremely low, so it is difficult to produce the required plate materials by means applied to ordinary metals, and molybdenum or The production of metal parts made of molybdenum alloy required special measures.

That is, what has been adopted so far as an industrial production means of a metal member made of molybdenum or a molybdenum alloy is that "a powder of molybdenum or a molybdenum alloy is pressure-molded and then sintered. It is an ingot, and the ingot is subjected to plastic working such as forging and rolling to finish it into the required shape.

However, recently, regarding the molybdenum or molybdenum alloy material produced in this way, "when used under high temperature and high vacuum, impurity gas is released from the member during use, which adversely affects facility performance. The problem of "affect" has come to be pointed out. This is due to the phenomenon that impurities (particularly gas components such as O, N, C, S and H) are often mixed in the case of "sintered ingot" prepared by sintering powder raw materials. It is considered that the above-mentioned inconvenience is brought about because the impurities are brought to the processed product member. In addition, since the molybdenum or molybdenum alloy material produced by the above method tends to generate gas when melted, a blower blower is used at the time of welding accompanied by partial melting.
It also had the problem that the weldability was poor and the weldability was poor.

On the other hand, apart from these problems, production of molybdenum or a molybdenum alloy material has the following disadvantages. In other words, molybdenum or a molybdenum alloy material (such as an ingot) is very active in the atmosphere, and when heated to a high temperature, it reacts violently with gas components such as oxygen and nitrogen in the atmosphere to contaminate the surface and the vicinity of the surface. . The molybdenum or molybdenum alloy material thus contaminated with gas components has poor workability, and when processed such as forging and rolling, defects such as cracks often occur even at low workability. Further, even if the processing is completed safely, a considerable amount of the contaminated surface layer has to be removed, so that the processing yield in this respect is also greatly reduced.

Although it is possible to perform processing in an atmosphere (for example, in vacuum or in argon gas) free from contamination of the gas components, in this case, expensive equipment and facilities are required, and the batch method is also used. However, the production efficiency is very poor because of the above-mentioned work, and therefore it cannot be said that it is satisfactory as a mass production means for plate materials and the like for which demand for low cost and large quantity supply has been particularly strong.

In view of the above, the object of the present invention is to provide molybdenum which is excellent in workability such as weldability and formability and does not generate an impurity gas even when used under high temperature and high vacuum. Alternatively, it was to establish a means capable of stably producing a molybdenum alloy plate with a good yield and on an industrial scale.

[0009]

Therefore, the inventors of the present invention have made extensive studies from various viewpoints in order to achieve the above object, and have been able to obtain the following new findings.

A) As a raw material for producing a molybdenum or molybdenum alloy plate, molybdenum or a molybdenum alloy is melted by an electron beam melting method, a vacuum arc melting method, an electron beam cold hearth remelt method, or the like. When a cast "casting ingot" is used and hot-worked in a state (environment) where there is little impurity gas contamination, the amount of gas generated at high temperature and high vacuum is very small, and it has excellent weldability. It is possible to obtain a member having

B) When hot forging a cast ingot made of molybdenum or a molybdenum alloy, "casting", which has been conventionally used for forming powder materials, is applied to the cast ingot. By sealing the entire surface of the cast ingot with a separate material and then forging, it becomes possible to carry out the forging even in the atmosphere without fear of contamination by gas components, and at the same time, the occurrence of defects (cracks, etc.) is suppressed as much as possible. And sound forging can be performed stably.

C) Furthermore, as a "casting ingot" which is a processing material, "(1) Vibration is applied during casting of the molten metal melted by the electronic beam cold hearth remelt method, (2)
The crystal grain size (casting direction) can be controlled by adding a substance that becomes crystal nuclei, (3) secondarily cooling the solidified material that is extracted from the mold, or combining these means to suppress grain growth. When using a molybdenum or molybdenum alloy cast ingot whose average grain size in a vertical section is 10 mm or less (particularly preferably 10 mm or less), forging, warm or hot rolling is performed. In addition to making it even easier, it becomes possible to obtain a more excellent member in terms of the amount of gas generated when used under high temperature and high vacuum, workability (forming workability, weldability), and the like.

D) Incidentally, when a cast ingot of molybdenum or molybdenum alloy is forged,
The obtained forged material has a sound structure and high deformability, and since it is possible to perform hot or hot rolling and cold rolling on this forged material, if this is used as a material, it is possible to obtain desired dimensions. It becomes possible to mass-produce molybdenum or a molybdenum alloy cold-rolled sheet on an industrial scale with high productivity.

E) Moreover, when the cold-rolled sheet obtained in the above-mentioned step is subjected to heat treatment under specific conditions, a stable annealed structure is formed, strains and the like are removed, and the stability of the material is further improved.

The present invention has been completed based on the above findings and the like, and uses a "molybdenum or molybdenum alloy cast ingot (preferably having a crystal grain size of 30 mm or less), which is used as a sheath material. After canning and forging, it is subjected to warm or hot rolling at a heating temperature of 500 to 1200 ° C. with a reduction of 50% or more, and further cold rolling (preferably cross rolling) under conditions of a reduction of 30% or more. Alternatively, after this cold rolling, the obtained cold rolled sheet has 800-1
Stable molybdenum or molybdenum alloy plate with high workability (formability, weldability), etc. by generating vacuum heat treatment at 200 ° C for 0.5 to 4 hours at high temperature and high vacuum. Moreover, it has a major feature in that it enables mass production at low cost. "

The molybdenum or molybdenum alloy cast ingot used in the present invention can be obtained, for example, by any of the following means. i) A virgin material or scrap material of molybdenum or a molybdenum alloy is compression molded, or these raw materials are packed in a box or a tube made of the same material to form a melting electrode, and the electrode is an electron beam. "Electron beam melting method" or "vacuum arc" in which melting or vacuum arc melting is performed to form an ingot
Ii) Electron beam melted raw material melt is once held in a water-cooled cold heart to diffuse impurities into a vacuum environment, which is then overheated into the mold. The "electron beam cold hearth remelting method" in which the ingot is pulled out from below while continuously solidifying by flow.

As described above, when molybdenum or a molybdenum alloy that is melted and cast rather than by the powder metallurgy method is used as the material, the content of easily volatilized impurities, mainly gas components, is small, so that workability is improved. In addition to being good, there is almost no generation of gas even when partially melted for welding or when the final product is used under high temperature and vacuum, and the risk of welding defects and environmental pollution is extremely reduced.

However, it is desirable to use an ingot obtained by the "electron beam cold hearth remelt method" having a smaller impurity content, whereby the effect of the present invention becomes more remarkable. This is because the grain boundaries of molybdenum or molybdenum alloy ingots obtained by the "electron beam melting method" or "vacuum arc melting method" are somewhat fragile, and the reduction of impurities is reduced by one melting operation. Electronic bee
This is because it is not sufficient as in the case of the "Mukold hearth remelt method".

It is further recommended that the crystal grain size (average grain size in a cross section perpendicular to the casting direction) be 3
The use of a high-purity ingot suppressed to 0 mm or less, particularly preferably 10 mm or less. When the crystal grain size of the molybdenum or molybdenum alloy cast ingot becomes 30 mm or less (particularly preferably 10 mm or less), the total area of the grain boundaries remarkably increases due to the refinement of the crystal grains, so that the segregation of gas components etc. at the crystal grain boundaries is small. Therefore, the amount of impurity segregation per grain boundary area at the crystal grain boundary becomes a very small value. Then, this leads to a remarkable improvement in workability, and the work such as forging and rolling is further facilitated. In addition, since the amount of impurity gas existing in the final product is small, almost no gas is generated even when it is used at high temperature and in vacuum.

However, such a fine crystal ingot is
Even if the known "electron beam cold hearth remelt method" is applied as it is, it cannot be obtained stably. The ingot is produced by melting molybdenum or a molybdenum alloy material by an electronic beam cold hearth remelt method,
At that time, (1) vibration is applied to the molten pool in the mold,
(2) Adding molybdenum or molybdenum alloy particles to the molten pool, (3) secondary cooling of the solidified material extracted from the mold to promote cooling, (4) appropriate combination of the above means, It can be obtained by taking measures such as "to promote miniaturization" and "prevent growth and coarsening" of crystal grains. Of course, the smaller the crystal grain size of the ingot, the more preferable.

The canning of molybdenum or molybdenum alloy cast ingots prevents defects such as cracks due to surface contamination during heating and forging, and enables triaxial compression processing by the hydrostatic effect through forging to improve deformability. It is done to realize the organization. Then, with molybdenum or a molybdenum alloy having a structure advantageous for this processing, warm or hot rolling or cold rolling can be relatively easily performed.

The following is a summary of the main operational effects when the canning, which has been conventionally used for forming a powder material or the like, is applied to a molybdenum or molybdenum alloy cast ingot and forged.

(A) Forging can be performed even in the atmosphere without fear of contamination by gas components. (B) Hydrostatic effect that can effectively apply not only the compressive load in the uniaxial direction but also the compressive load in the triaxial direction to the work material (casting ingot) by using the canning material with relatively high strength and thick wall In addition, defects (cracks, etc.) during forging
The generation is effectively suppressed (the hydrostatic effect as described above is particularly effective for a difficult-to-process material such as molybdenum or a molybdenum alloy).

(C) Furthermore, in the case of processing a workpiece heated to a high temperature with a forging device such as a hammer or a press,
Since the work is supported by a tool such as a cold anvil and a compressive load is applied to the work, the heat of the work is taken by the tool, causing the surface temperature of the work to drop and causing defects, but canning By applying the above, it is possible to effectively prevent such a temperature decrease and perform sound processing. In addition, the "isothermal forging method" is known as a method for preventing temperature drop during high temperature processing and performing processing at a constant temperature and at a low strain rate (processing speed), but this isothermal forging method is also expensive. However, it is not a practical method in terms of production efficiency because it requires a large amount of equipment and is a preferable processing method from the viewpoint of quality, but the strain rate must be kept low.

(D) In other words, by adopting the "canning method" which brings about the above-mentioned three effects of "contamination of gas components", "triaxial compression due to hydrostatic pressure effect" and "prevention of decrease in surface temperature", molybdenum is adopted. Alternatively, it becomes possible to easily form a molybdenum alloy cast ingot into a plate material by industrially extremely advantageous means.

For canning, for example, as shown in FIG.
In order to coat molybdenum or molybdenum alloy ingot 1 which is a cylindrical work material, commercially available heat-resistant steel (SUS31
6, a SUS310 tube, etc., cut into a suitable length, and a disc 2 and two discs 3 (which are preferably made of the same material as the sheath) covering both end surfaces thereof. I'm fine. The cylindrical sheath 2 and the disc 3 are joined and sealed by an appropriate welding method such as TIG. Reference numeral 4 in FIG. 1 indicates this welded portion.

The smaller the clearance (clearance) between the inner diameter of the sheath 2 and the molybdenum or molybdenum alloy ingot 1, the better, but even if this clearance is large, it is not necessary to perform degassing treatment for removing the residual gas component. .
However, if the volume of clearance exceeds 5%, the amount of gas components that come into contact with the surface of molybdenum or molybdenum alloy ingot 1 will increase, and as a result, extra peeling will be required after heating and forging are finished. The yield will be reduced.

It is appropriate that the cross-sectional area occupied by the sheath material in the workpiece after canning is 10 to 40% of the whole, and the thickness of the sheath should be adjusted within this range depending on the material. That is, when the cross-sectional area of the sheath is less than 10%, among the three effects of the above-mentioned canning, "3 due to the hydrostatic pressure effect" is obtained.
"Axial compression" and "prevention of decrease in surface temperature" are not sufficient. On the other hand, when the cross-sectional area of the sheath exceeds 40%, joining by welding or the like becomes difficult, and material cost increases depending on the canning material. .

The size and material of the sheath are determined by the heating temperature before forging and the material of the ingot. However, if the hydrostatic pressure effect is expected more, the wall thickness should be thicker and the material should be processed. A material having a characteristic close to that of the deformation resistance of the material molybdenum or molybdenum alloy ingot is desirable. Generally, the commercially available 316 stainless steel or 31 as exemplified above is used.
Heat resistant steel such as 0 stainless steel is desirable as the canning material, but cheaper carbon steel can be used as the canning material by making it thicker.

The molybdenum or molybdenum alloy cast ingot subjected to the above-mentioned canning can be easily hot forged even in the atmosphere as described above, which makes it easy to form a processed material having a sound structure and deformability. Can be obtained. When forging, the heating temperature of the ingot is 5
It is suitable that the temperature is from 00 to 1200 ° C. and the heating and holding time is from 0.5 to 4 hours. That is, the heating temperature is 500
If the temperature is lower than ℃, the deformability of molybdenum or a molybdenum alloy is insufficient and the number of times of forging to obtain a predetermined dimension increases, which is not preferable. On the other hand, if the heating temperature exceeds 1200 ℃, the canning material (for example, heat-resistant steel) softens. There is a risk that it may pass through or cause surface oxidation, making it impossible to maintain its role as a canning material. Also, the heating and holding time is determined by the size and weight of the material to be heated, but if it is less than 0.5 hours, it will not be soaked to the center, and if it exceeds 4 hours, the surface oxidation of the canning material will be remarkable. Not preferable. In practice, it is desirable that the initial heating be performed for about 1 hour or more, and in the case of reheating during forging, it may be about 0.5 hour.

As described above, the forged material obtained by such treatment has a good deformability and can be hot-rolled or hot-rolled and cold-rolled. It can be processed into molybdenum or molybdenum alloy cold-rolled sheet with characteristics (formability, weldability, low gas emission).

However, the warm or hot rolling performed after removing the canning material after forging is performed at a heating temperature of 500 to 1
It is necessary to perform it at 200 ° C. under the condition of a reduction rate (working rate) of 50% or more. This is because if the heating temperature during warm or hot rolling is less than 500 ° C, cracks often occur at the edge part of the material to be rolled, while if heated to a temperature over 1200 ° C, the structure becomes coarse. Or surface contamination becomes severe. Further, if the reduction ratio of warm or hot rolling is less than 50%, a non-uniform cross-section structure is often obtained, and in order to obtain a uniform cross-section structure, a reduction ratio of 50% or more, particularly preferably 60% or more. You need a rate. In addition,
The material after forging that is subjected to warm or hot rolling may be subjected to strain relief heat treatment (vacuum heat treatment), if necessary.

The warm or hot rolling, followed by cold rolling, is carried out after removing the scale layer on the surface by a suitable treatment. The reduction ratio in cold rolling is preferably 30% or more. This is because if the rolling reduction is less than 30%, it is difficult to obtain a uniform cross-sectional structure, and a beautiful cold-worked skin cannot be obtained. In cold rolling,
By changing the rolling direction on the way and crossing and rolling, a molybdenum or molybdenum alloy plate having a structure with small in-plane anisotropy and mechanical properties can be obtained. Such a plate having a small in-plane anisotropy is advantageous for plastic working such as overhanging and deep drawing.

The molybdenum or molybdenum alloy plate obtained by cold rolling is further subjected to 0.5 to 0.5 at 800 to 1200 ° C.
By performing the vacuum heat treatment for 4 hours, an annealed material having a more stable structure can be obtained. In this case, if the heating temperature is less than 800 ° C., the removal of the working strain is insufficient, and it may be deformed by heating such as welding. Further, at a heating temperature higher than 1200 ° C., the crystal grains may grow and become coarse, causing embrittlement. Regarding the heating time, if the heating time is shorter than 0.5 hours, the strain may be insufficiently removed. On the other hand, if the heating time is longer than 4 hours, coarsening of crystal grains may occur. To be elected. The vacuum heat treatment is preferably performed at a vacuum degree of 10 ⁻⁴ torr or more. That is, if the vacuum degree is lower than 10 ^-4 torr, gas contamination (O, N
The reaction tends to cause the surface to be colored.

Next, the present invention will be described more specifically by way of examples.

EXAMPLE First, by melting and casting using the electron beam cold hearth remelt method, the average crystal grain size in the cross section perpendicular to the casting direction was 10 mm or less and the diameter was 12 mm in both cases.
0mm "pure molybdenum ingot" and "TZM (Mo-
Zr-Ti alloy) ingot "was manufactured.

The chemical analysis values of "pure molybdenum ingot" and "TZM ingot" were as follows. Pure molybdenum ingot Al: 0.0003wt%, Fe: 0.001wt%, Ti: 0.01wt% or less,
W: 0.02wt%, O: 4ppm, N: 1ppm or less, C: 25ppm
, S: 1ppm or less, H: 1ppm or less, Mo: 99.95wt% or more. TZM ingot Al: 0.0004wt%, Fe: 0.002wt%, Ti: 0.48wt%, Zr:
0.08wt%, W: 0.01wt% or less, O: 5ppm, N: 1ppm or less, C: 30ppm, S: 1ppm or less, H: 1ppm or less, Mo: ba
l ...

Next, these pure molybdenum and molybdenum alloy ingots were canned as shown in FIG. 1 using a tube made of SUS316 steel (thickness 20 mm) and a disc 30 mm thick (canning). Material is outer diameter D: 150
mm, length L: 450 mm), these were heated to 1200 ° C. and hot forged at a working rate of 90%. Even if hot forging with a high working ratio was performed, neither ingot was cracked. For example, FIG. 2 is a photograph of the cross-sectional structure of a pure molybdenum ingot after forging, and it can be seen that no defect has occurred.

Subsequently, the obtained forged material was peeled (cutting) to remove the canning material, heated to 1000 ° C. and hot-rolled at a reduction rate of 90%. It could be easily made into a plate without cracking.

Next, the scale was removed from the hot rolled sheet by shot blasting and cold rolling was performed at a reduction rate of 85%. As a result, a cold rolled sheet having a thickness of 0.3 mm could be obtained without cracks such as edges. It was In addition, FIG. 3 shows, as a representative example, a photograph of the cross-sectional structure of the obtained pure molybdenum cold-rolled sheet. As is clear from FIG. 3, a uniform cold-worked structure is obtained over the entire plate thickness. You can see that

Then, when each of these cold-rolled sheets was heated to a high temperature in a vacuum and the gas generation state was investigated, it was confirmed that the amount of gas generation was small enough to be sufficiently satisfied as a heat-resistant interior material for high vacuum equipment. Was done. Further, it was found by a molding test that the moldability was relatively good.

Further, FIG. 4 shows the cold rolled sheet having a thickness of 0.3 mm as shown in FIG.
A photograph of a cross-sectional structure after performing a vacuum heat treatment at 200 ° C. for 1 hour is shown, but it can be confirmed that a uniform recrystallization structure is obtained by the vacuum heat treatment.

By the way, FIGS. 5 and 6 compare the weldability of a conventional rolled sheet of pure molybdenum sintered material and the cold rolled sheet of pure molybdenum produced according to the method of the present invention. While gas holes (pinholes) and cracks as shown in FIG. 5 were generated in the electron beam welded portion of the rolled material plate, as shown in FIG. 6, it was obtained according to the present invention. It can be confirmed that an extremely sound weld can be obtained with the rolled plate.

[0043]

[Summary of Effects] As described above, according to the present invention, workability (forming workability, weldability, etc.) is excellent, and almost no impurity gas is generated even when used under high temperature and high vacuum. It is possible to mass-produce molybdenum or molybdenum alloy sheet materials without cost, and improve its performance by applying it to aerospace equipment members, electron tube members, electric resistance member members, nuclear reactor members, corrosion resistant equipment members, etc. It has very useful effects in industry.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating an example of an ingot canning method.

FIG. 2 is a photograph showing a cross-sectional structure of a molybdenum ingot after forging.

FIG. 3 is a cross-sectional structure photograph of a molybdenum cold-rolled sheet obtained according to the method of the present invention.

FIG. 4 is a cross-sectional structural photograph of a molybdenum cold-rolled sheet that has been cold rolled and vacuum heat treated according to the method of the present invention.

FIG. 5 is a photograph showing a cross-sectional structure of an electron beam welded portion of a rolled plate obtained from a conventional molybdenum sintered material.

FIG. 6 is a photograph of a cross-sectional structure of an electron beam welded portion of a molybdenum cold-rolled sheet manufactured according to the method of the present invention.

[Explanation of symbols]

 1 Molybdenum or molybdenum alloy ingot 2 Series (cylindrical) 3 Disc 4 Welded part

[Procedure amendment]

[Submission date] November 17, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

FIG. 2 is a metallographic photograph of a cross section of a molybdenum ingot after forging.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

FIG. 3 is a metallographic photograph showing a cross section of a molybdenum cold-rolled sheet obtained according to the method of the present invention.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

FIG. 4 is a metallographic photograph of a cross section of a cold-rolled molybdenum cold rolled sheet that has been cold rolled and vacuum heat treated according to the method of the present invention.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

FIG. 5 is a metallographic photograph of a cross section of an electron beam welded portion of a rolled plate obtained from a conventional molybdenum sintered material.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

FIG. 6 is a metallographic photograph of a cross section of an electron beam welded portion of a cold rolled molybdenum sheet manufactured according to the method of the present invention.

Claims (4)

[Claims] 1. A cast ingot of molybdenum or a molybdenum alloy is used, which is forged by canning with a sheath material and then hot or hot rolled at a heating temperature of 500 to 1200 ° C. with a reduction of 50% or more. A method for producing a molybdenum or molybdenum alloy sheet, which is characterized in that it is subjected to cold rolling under conditions of a rolling reduction of 30% or more. 2. A casting ingot of molybdenum or a molybdenum alloy having a crystal grain size of 30 mm or less is used.
A method for producing a molybdenum or molybdenum alloy sheet, which comprises hot rolling at a rolling reduction of 50% or more at 00 ° C., and further cold rolling the rolling at a rolling reduction of 30% or more. 3. The method for producing a molybdenum or molybdenum alloy plate according to claim 1, wherein cross rolling is performed as cold rolling. 4. The cold-rolled sheet obtained after completion of cold rolling is subjected to vacuum heat treatment at 800 to 1200 ° C. for 0.5 to 4 hours, according to any one of claims 1 to 3. Method for producing molybdenum or molybdenum alloy plate.