JPH06212376A - Production of rod, wire or tube of molybdenum or molybdenum alloy - Google Patents

Abstract

PURPOSE:To establish means by which the rod, wire or tube of Mo or an Mo alloy excellent in workability and thermal stress resistance and free from the generation of impurity gas even if being used at a high temp. in a high vacuum can be mass-produced at a low cost. CONSTITUTION:An Mo or Mo alloy cast ingot (preferably having <=30mm grain size) is subjected to canning by a sheath material and is subjected to forging or extruding, or, after the forging or extruding, it is furthermore heated to 500 to 1200 deg.C and is subjected to reducing and thinning working. Moreover, after the completion of any working stages, the obtd. worked material is subjected to vacuum heat treatment at 800 to 1200 deg.C for 0.5 to 4hr to regulate the average grain size into <=500mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has good workability (plastic workability, weldability, etc.) and is resistant to thermal stress, and most of the impurities gas is generated even when used under high temperature and high vacuum. Bar made of molybdenum or molybdenum alloy,
The present invention relates to a method of manufacturing a wire or a tube.

[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 the high value exceeding 0, the vapor pressure of the oxide is extremely low, so the production of the required materials (bars, wire rods, pipes, etc.) is possible by means applied to ordinary metals. It is difficult and requires special measures to manufacture the metal member made of molybdenum or molybdenum alloy.

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 a desired shape.

However, the molybdenum or molybdenum alloy member produced in this way has recently been
A problem has come to be pointed out that "when used under high temperature and high vacuum, impurity gas is released from the member during use, which adversely affects facility performance." This is powder
In the case of a "sintered ingot" made by sintering raw materials, impurities (particularly gas components such as O, N, C, S, and H) are inevitably mixed in, and even in the product members after plastic working. It is thought that it was caused by being brought.
In addition, the molybdenum or molybdenum alloy member manufactured by the above method is vulnerable to thermal stress, and has a problem that weldability is poor because gas is apt to be generated in the molten portion.

On the other hand, apart from these problems, the following disadvantages have been obliged when manufacturing molybdenum or molybdenum alloy members. 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. . And, molybdenum or molybdenum alloy material contaminated with gas components in this way has poor workability,
When processing such as forging was performed, defects such as cracks were often generated even at a low working ratio. 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 was also very poor because it had to be carried out, and it was not an industrially satisfactory means.

In view of the above, the object of the present invention is that the workability such as weldability and the heat stress performance are excellent, and no impurity gas is generated even when used under high temperature and high vacuum. The aim was to establish a means for producing rods, wires or tubing made of molybdenum or molybdenum alloy with good yield and stable production 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) Molybdenum or a molybdenum alloy as a processing material for producing a bar, wire or tube made of molybdenum or a molybdenum alloy, an electron beam melting method, a vacuum arc melting method or an electron beam cold hold method. -When using a "casting ingot" that has been melted and cast by the srimelt method, etc., and when processing this in a state (environment) with little impurity gas contamination, the amount of gas generated under high temperature and high vacuum is very small, Moreover, it becomes possible to obtain a rod, wire or pipe which is excellent not only in plastic workability but also in weldability and heat stress resistance.

B) Further, when a cast ingot made of molybdenum or a molybdenum alloy is subjected to plastic working such as forging or extrusion, the "canning" which has been conventionally used for forming a powder material or the like is applied to the cast ingot. In particular, if the entire surface of the cast ingot is sealed with another material and then processed, molding can be performed even in the atmosphere without concern of contamination by gas components, and at the same time defects (cracks, etc.) occur. As a result, it is possible to carry out sound molding processing in a stable manner by suppressing it as much as possible.

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 average crystal grain size (casting) can be determined by adding a substance that becomes crystal nuclei, (3) secondarily cooling the solidified material extracted from the mold, or combining these means to suppress grain growth. When using a molybdenum or molybdenum alloy cast ingot in which the average crystal grain size in the cross section perpendicular to the direction is particularly suppressed to "30 mm or less (more preferably 10 mm or less)", the processing such as forging and extruding is further performed. In addition to making it easier, it is possible to obtain rods, wires or pipes that are superior in terms of the amount of gas generated when used under high temperature and high vacuum, workability (plastic workability, weldability), and heat stress resistance. become.

D) When the cast ingot of molybdenum or molybdenum alloy is forged or extruded, the obtained processed material (forged or extruded material) has a sound structure and deformability. Known diameter reduction and thickness reduction processing (swaging, extrusion, forging, groove roll rolling, drawing, etc.) can be applied to the processed material. Further, it is possible to stably manufacture a product having a small diameter and a thin wall.

E) Moreover, the bar, wire or tube obtained by the above steps is further subjected to heat treatment under specific conditions so that the average crystal grain size is 500 μm or less (particularly preferably 1).
If it is adjusted to 0 to 200 μm), more stable mechanical strength and structure are secured.

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 an average crystal grain size of 30 mm or less), which is used as a sheath material. Gas generated under high temperature and high vacuum by forging or extruding after canning at 1, or by further forging or extruding and then heating at 500 to 1200 ° C to reduce the diameter and reduce the wall thickness. It has a major feature in that it enables stable mass production of rods, wires or pipes with a small amount and excellent workability (plastic workability, weldability), heat stress resistance, etc. “After the above processing steps are completed,
By performing vacuum heat treatment at 0 ° C for 0.5 to 4 hours to adjust the average crystal grain size to 500 µm or less, the properties of the obtained rod, wire or tube can be further improved and stabilized. "
It also has features.

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 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 to use a high-purity ingot having an average crystal grain size (average crystal grain size in a cross section perpendicular to the casting direction) of 30 mm or less, particularly preferably 10 mm or less. . When the grain size of the molybdenum or molybdenum alloy cast ingot is 30 mm or less (more preferably 10 mm or less), the total area of the grain boundaries is significantly increased due to the refinement of the crystal grains, so that the segregation of gas components and the like at the grain boundaries is small. Therefore, the amount of impurity segregation per grain boundary area at the crystal grain boundary becomes a very small value. This leads to a remarkable improvement in plastic workability and further facilitates processing such as forging and extrusion, and further leads to further improvement in heat stress resistance. Further, since the amount of impurity gas existing in the product after processing is reduced, almost no gas is generated even when used in a high temperature / vacuum environment.

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.

Canning of a molybdenum or molybdenum alloy cast ingot prevents defects such as cracks due to surface contamination during heating and processing, and enables triaxial compression processing by the hydrostatic effect to form a structure with improved deformability. It is done to realize. Then, with molybdenum or a molybdenum alloy having a structure advantageous for this processing, conventional diameter reduction processing and thickness reduction processing can be easily performed.

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

(A) Molding can be performed even in the atmosphere without fear of contamination by gas components. (B) When a thick canning material having a relatively high strength is used, a hydrostatic pressure effect that can apply not only a uniaxial compressive load but a triaxial compressive load to a work material (casting ingot) is also added. The occurrence of defects (cracks, etc.) during processing (forging, etc.) can be effectively suppressed (the hydrostatic effect described above is particularly effective for difficult-to-process materials such as molybdenum or molybdenum alloys).

(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 bar material, a wire material, a pipe material or the like by a very industrially 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 clearance volume 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 / processing has been completed. 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 extrusion and the material of the ingot, but in the case of expecting the hydrostatic pressure effect, the thicker the wall, the better the material. It is desirable that the material to be processed has characteristics close to the deformation resistance of molybdenum or molybdenum alloy ingot. Generally, heat-resistant steel such as the commercially available 316 stainless steel and 310 stainless steel exemplified above is preferable 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 that has undergone the above-mentioned canning can be easily forged and extruded 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. In other words, the processed material (forged material, extruded material) obtained by such a method can also be subjected to general hot rolling and cold rolling, and has excellent characteristics (plastic workability, weldability, low gas emission). It is possible to easily and stably form even smaller size molybdenum or molybdenum alloy rods, wires or tubes with a certain size.

Rods that have been implemented in common metallic materials,
Extrusion, drawing, forging, groove rolling for reducing the diameter of wires and pipes
Examples include rolling, swaging, etc.
Any of these diameter reduction processes can be applied to the "forged or extruded material of the canned molybdenum or molybdenum alloy cast ingot".

However, from the viewpoint of ease of processing, it is desirable to carry out this diameter reduction processing while heating at 500 to 1200 ° C. This is because if the heating temperature during processing is less than 500 ° C, cracks often occur on the surface, while 1
This is because heating to a temperature exceeding 200 ° C. causes coarsening of the structure and severe surface contamination.

The canning material used during the forging or extruding may be removed after the forging or extruding and then subjected to the diameter reduction processing. However, the diameter reduction processing may be performed without removing the canning material while the canning material is covered. It is also possible to do so. Especially 1
It is effective to prevent surface contamination if the canning material is coated while being heated to 000 ° C. or higher. Furthermore, it can be said that the processing with the canning material covered is preferable because the number of reheating due to the temperature decrease is reduced, which leads to a reduction in the number of processing passes.

Of course, with respect to "forged or extruded material of canned molybdenum or molybdenum alloy cast ingot", extrusion, drawing, forging, swaging, etc., which are generally applied as thinning processing for pipe materials, can also be performed. It can be applied, and preferable processing conditions in this case are the same as those in the case of the diameter reduction processing.

The molybdenum or molybdenum alloy rod, wire or tube manufactured by subjecting to the above-mentioned diameter reduction or thickness reduction is 800
Stable mechanical strength and metallic structure can be added by performing vacuum heat treatment at ˜1200 ° C. for 0.5 to 4 hours. 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. In other words, the degree of vacuum is 10 ^-4 torr
If it is lower than the above range, the surface tends to be colored due to gas contamination (reaction with O and N).

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

【Example】

[Embodiment 1] First, by means of melting and casting using an electron beam cold hearth remelt method, the crystal grain size was 10 in each case.
mm or less "Pure molybdenum ingot", "Mo-0.1wt% B alloy ingot", "Mo-0.05wt% C alloy ingot" and
"TZM (Mo-Zr-Ti alloy) ingot" was manufactured.
The diameter of each ingot was 120 mm.

"Pure molybdenum ingot" and
The chemical analysis values of "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% or less,
Zr: 0.08wt%, W: 0.01wt% or less, O: 5ppm, N: 1p
pm or less, C: 30ppm, S: 1ppm or less, H: 1ppm or less, M
o: bal ...

Next, these pure molybdenum and molybdenum alloy ingots were canned as shown in FIG. 1 by using a tube made of SUS316 steel (thickness 20 mm) and a disk having a thickness of 30 mm, and then the billet was obtained. (Outer diameter D: 150 mm, length L: 450 mm) was heated to 1150 ° C. and extruded at a surface reduction rate of 90% to produce a bar (diameter 50 mm).

By this test, it was confirmed that a sound bar can be obtained in a stable extruded state without any defects such as cracks. In addition, FIG. 2 shows a photograph of a sectional structure of a pure molybdenum ingot extruded material (bar material) as a typical example. In addition, when each extruded material (bar material) was heated at high temperature in vacuum and the gas generation situation 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.

[Example 2] The same melting / casting ingot as in Example 1 was used, subjected to perforation processing, and then subjected to canning using the same material as in Example 1, and then at 1150 ° C. A tube material (outer diameter 50 mm, inner diameter 30 mm) was manufactured by heating and extruding at a surface reduction rate of 90%.

By this test, it was confirmed that a sound pipe material can be obtained in a stable extruded state without any occurrence of defects such as cracks. In addition, FIG. 3 shows a photograph of a cross-sectional structure of a pure molybdenum ingot extruded material (tubular material) as a typical example. Moreover, when each extruded material (tubular material) was heated at high temperature in a vacuum and the gas generation situation 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. It was

[Example 3] "Bar material obtained in Example 1" and "tube material obtained in Example 2" were used as raw materials, and these materials were heated to 1000 ° C in vacuum before swaging. The diameter is 0.2mm and the outer diameter is 35mm.
A thin tube with an inner diameter of 32 mm was manufactured by. In this case, it was also confirmed that a sound product can be obtained in a stable processed state without causing defects such as cracks.

In FIG. 4, as a typical example, the obtained pure molybdenum thin wire (diameter 0.2 mm) is 1200 ° C. × 1 hr.
The photograph of the cross-section structure when vacuum heat treatment was performed is shown in FIG. As is clear from FIG. 4, the fine wire after heat treatment has a grain size of 10
It can be seen that the fine recrystallized structure is around μm.

Example 4 Using the rod material obtained in Example 1 as a raw material, the rod material was heated to 1000 ° C. in a vacuum and swaged to produce a wire rod having a diameter of 3 mm. Then, these were heated in vacuum to various temperatures and kept at that temperature for 1 hour to investigate the change in hardness when the average crystal grain size was adjusted to around 50 μm. The results are summarized in FIG.

As is clear from the results shown in FIG. 5, even if the pure molybdenum wire is subjected to the above-mentioned treatment, it has a high hardness of about Hv250 after being heated at 1000 ° C. It can be seen that the target strength is shown. I understand. Further, in the case of the wire material of the molybdenum alloy "TZM", the hardness around Hv330 is maintained even after heating to 1400 ° C, and it can be confirmed that stable mechanical strength is exhibited even at higher temperatures.

[0046]

[Summary of Effects] As described above, according to the present invention, workability (plastic workability, weldability, etc.) and heat resistance are excellent.
Moreover, molybdenum or molybdenum alloy rods, wire rods or pipes that produce almost no impurity gas even when used under high temperature and high vacuum can be mass-produced at low cost.
It can be applied to aerospace equipment members, electron tube members, electric resistor members, nuclear reactor members, corrosion-resistant equipment members, etc., to further improve its performance, thus providing an extremely useful effect 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 rod extruded according to the method of the present invention.

FIG. 3 is a photograph showing a cross-sectional structure of a molybdenum tube extruded according to the method of the present invention.

FIG. 4 is a photograph showing a cross-sectional structure of a molybdenum thin wire that has been formed according to the method of the present invention and that has been heat-treated under vacuum.

FIG. 5 is a diagram showing a change in hardness of molybdenum or a molybdenum alloy wire produced according to the method of the present invention depending on a heating temperature.

[Explanation of symbols]

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

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[Procedure amendment]

[Submission date] November 17, 1993

[Procedure Amendment 2]

[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 rod extruded according to the method of the present invention.

[Procedure 3]

[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 of a cross section of a molybdenum tube extruded according to the method of the present invention.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

FIG. 4 is a photograph of a metallographic structure of a cross section of a molybdenum thin wire formed and vacuum-heat treated according to the method of the present invention.

Claims (4)

[Claims] 1. A bar, wire or tube made of molybdenum or a molybdenum alloy, which is characterized in that a cast ingot of molybdenum or a molybdenum alloy is used, which is canned with a sheath material and then forged or extruded. Method. 2. A molybdenum or molybdenum alloy, characterized in that a cast ingot of molybdenum or a molybdenum alloy having an average crystal grain size of 30 mm or less is used, which is forged or extruded after being canned by a sheath material. Manufacturing method of rod, wire or pipe. 3. The canned ingot is forged or extruded, and then heated to 500 to 1200 ° C. to reduce the diameter and reduce the thickness.
A method for manufacturing a bar, wire or tube made of molybdenum or a molybdenum alloy according to 1. 4. After finishing the processing step according to any one of claims 1 to 3, the processed material is heated at 800 to 1200 ° C.
Vacuum heat treatment for 0.5 to 4 hours to obtain an average crystal grain size of 50
A method for producing a rod, wire or tube made of molybdenum or a molybdenum alloy, which is characterized by adjusting the thickness to 0 μm or less.