JP2006002178A - Method for producing pure molybdenum or molybdenum alloy thin strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long-pure molybdenum or molybdenum alloy thin strip having high working efficiency at the time of using materials and inexpensive as possible. <P>SOLUTION: The method for producing a pure molybdenum or molybdenum alloy thin strip comprises a process where pure molybdenum or molybdenum alloy sheets with a thickness of 0.5 to 5.0 mm as stocks are welded each other, the weld is thereafter heated at 250 to 600°C, and is subjected to warm rolling at the total draft of 10 to 90%. Preferably, softening is performed at 700 to 1,100°C after the warm rolling. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing pure molybdenum or a molybdenum alloy ribbon used as a material for a discharge lamp electrode, for example.

Conventionally, for example, as a discharge lamp electrode used for a backlight of a liquid crystal display device, a component made of pure molybdenum or molybdenum alloy having a cup shape with excellent thermal conductivity and excellent electrode life is disclosed. (See Patent Document 1).
This cup-shaped component is usually manufactured by deep drawing a thin plate, but it is not easy to deep draw a pure molybdenum or molybdenum alloy thin plate having poor workability. Therefore, proposals have been made to improve the deep drawability of pure molybdenum and molybdenum alloys.

For example, by Keiichiro Yoshida: Development of a cross rolling mill, “Iron and Steel”, August 30, 1985, p. In 1637-1640 (see Non-Patent Document 1), a plate material supplied in the longitudinal direction is rolled in the width direction by a reciprocating rotary motion of a pair of oscillating rolls having an axis that is substantially parallel to the longitudinal direction but narrows in the traveling direction. However, a cross rolling technique of continuously rolling in the longitudinal direction is disclosed, and it is described that a thin plate of pure molybdenum manufactured using a cross rolling mill is excellent in deep drawability.
In addition, Japanese Patent Laid-Open No. 3-291101 proposes to further improve deep drawability by purifying pure molybdenum to be subjected to cross rolling (see Patent Document 2).
What is disclosed in these prior documents is to reduce the anisotropy of strength in a pure molybdenum thin plate and improve deep drawability by cross rolling.

JP2003-151696A Japanese Patent Laid-Open No. 3-291101 Yoshida Keiichiro: Development of cross rolling mill, “Iron and Steel”, August 30, 1985, p. 1637-1640

The pure molybdenum or molybdenum alloy thin plate manufactured by the cross rolling disclosed in Non-Patent Document 1 or Patent Document 2 described above reduces the anisotropy of strength in the thin plate, and provides excellent deep drawability. Although advantageous in terms, there is a problem in that the production efficiency is low and the manufacturing cost of the thin plate is high as compared with the unidirectionally rolled material.
Pure molybdenum or molybdenum alloy generally has a fine fibrous structure and exhibits a certain degree of ductility even at room temperature, so that it can be cold-rolled. Therefore, when the materials of the material to be rolled are welded together, the welded part and the surrounding heat-affected part are recrystallized, and the crystal grains become coarse. In particular, since the crystal grain coarsening of the welded portion is remarkable, the ductile-brittle transition temperature is increased as compared with the original fibrous structure, and the welded portion and the heat-affected zone are markedly brittle.
Therefore, pure molybdenum and molybdenum alloy thin plates are currently supplied as short thin plates that are not welded in the manufacturing process even if they are subjected to the above-mentioned cross rolling in order to improve the deep drawability. is there.
An object of the present invention is to provide a method for producing a pure molybdenum or molybdenum alloy ribbon which can be rolled by welding the materials of the material to be rolled to form a long pure molybdenum or molybdenum alloy ribbon. .

In order to obtain a long pure molybdenum or molybdenum alloy ribbon, the present inventor examined a process of rolling a pure molybdenum or molybdenum alloy plate, which has been conventionally difficult, by elongating by welding. As a result, the present inventors have found that by performing warm rolling at a temperature equal to or higher than the ductile-brittle transition temperature, it is possible to roll the welded portion where the crystal grains are coarsened and the surrounding heat-affected zone as well.
That is, according to the present invention, in a method for producing pure molybdenum or molybdenum alloy ribbon, pure molybdenum or molybdenum alloy plate having a thickness of 0.5 to 5.0 mm is used as a raw material, and the raw materials are welded to each other and heated to 250 to 600 ° C. And a method for producing pure molybdenum or a molybdenum alloy ribbon including a step of warm rolling at a total rolling reduction of 10 to 90%.
Preferably, the method is a pure molybdenum or molybdenum alloy ribbon manufacturing method in which soft annealing at 700 to 1100 ° C. is performed after warm rolling.
The present invention is not a conventional cross rolling, but a method for producing pure molybdenum or a molybdenum alloy ribbon that can be rolled in one direction during the warm rolling or the cold rolling.

  The pure molybdenum or molybdenum alloy ribbon manufactured by the method of the present invention is provided in a long length, so that, for example, the parts using the ribbon are continuously used as in deep drawing when manufacturing a discharge lamp electrode. This contributes to the improvement of production efficiency in mass production lines. As a result, it is effective in reducing the price of parts made of pure molybdenum or molybdenum alloy ribbon.

As described above, an important feature of the present invention is that, in order to obtain a long ribbon, a pure molybdenum or molybdenum alloy plate having a predetermined thickness is welded and then heated to an appropriate temperature range to obtain an appropriate reduction ratio. The production method of performing the warm rolling is employed.
Hereinafter, the reason for the definition in the present invention will be described.

Material thickness: 0.5-5.0mm
The thickness of the pure molybdenum or molybdenum alloy plate used as the material in the present invention is set to 0.5 to 5.0 mm. This is because a material having a thickness of less than 0.5 mm is difficult to weld and has a small effect of obtaining a long ribbon after rolling. On the contrary, in the range exceeding 5.0 mm, it becomes difficult to handle the material after welding. A more desirable range is 0.8 to 3.0 mm.

Heating temperature during warm rolling: 250-600 ° C
The reason for prescribing the heating temperature at the time of warm rolling performed after welding is that, in a temperature range of less than 250 ° C., the welded portion and the heat-affected zone in which the crystal grains are coarsened are brittle, and conversely at a temperature exceeding 600 ° C. This is because the surface oxidation of pure molybdenum or molybdenum alloy becomes remarkable. A more desirable range is 300 to 500 ° C, and a more preferred range is 400 to 450 ° C.

Total rolling reduction during warm rolling: 10 to 90%
By performing the warm rolling, the welded portion and the heat-affected zone in which the crystal grains are coarsened can be changed to a fibrous structure having good workability. However, if the total rolling reduction is less than 10%, the effect of making the structure fibrous is small. Conversely, if it exceeds 90%, a fibrous structure is obtained, but pure molybdenum or a molybdenum alloy is obtained during warm rolling. May reach the limit of plastic working and crack. Therefore, the range of the total rolling reduction is 10 to 90%. A more desirable range is 30 to 80%, and a more preferred range is 50 to 75%.
In actual work, if the reduction rate is 90% in the first pass, there is a high risk of fracture at the weld. Therefore, in the first pass, the reduction rate is 20% or less, preferably 10% or less, more preferably 5% or less at the maximum, and then the reduction rate is gradually increased, and finally the total reduction rate is 10 to 10%. 90% is good.
In addition, you may perform this warm rolling again, after giving the annealing mentioned later.

The pure molybdenum or molybdenum alloy in the present invention may be any known molybdenum material. For example, pure molybdenum of 3N level may be used, or a molybdenum alloy called TZM in which about 0.5% titanium and about 0.05% zircon are added to molybdenum may be used. Any element containing elements other than molybdenum may be used within a range of% or less.
Further, in the present invention, the manufacturing process of the material until it becomes a plate having a thickness of 0.5 to 5.0 mm is not particularly specified. For example, a plate hot-rolled after melting by electron beam melting or a plate hot-rolled from a powder sintered material may be used.
In the present invention, the welding method is not particularly specified, and any known welding method may be used. However, since electron beam welding and laser welding are expensive welding methods, economically, TIG welding in an atmosphere shielded with argon gas is desirable to prevent oxidation.

Next, the softening annealing specified as a preferable manufacturing method will be described.
Soft annealing temperature after warm rolling: 700-1100 ° C
When pure molybdenum or a molybdenum alloy produced by the method of the present invention is subjected to, for example, deep drawing, it is desirable to perform soft annealing after warm rolling.
The reason for this is that in the state of being warm-rolled, the hardness is increased by work hardening, so that it is not possible to obtain the necessary elongation and drawing during deep drawing. However, when the temperature is lower than 700 ° C., the effect of reducing the hardness is small. Conversely, when the temperature exceeds 1100 ° C., the fibrous structure formed during the warm rolling is coarsened and embrittled by recrystallization. Stipulated in the range. A more desirable softening annealing temperature range is 800 to 1000 ° C.
Further, in order to prevent embrittlement due to oxidation of pure molybdenum or molybdenum alloy, soft annealing is desirably performed in a non-oxidizing atmosphere, and specifically, in argon gas, hydrogen gas, or a mixed gas atmosphere thereof. .

As described above, according to the method of the present invention described above, a long pure molybdenum or molybdenum alloy ribbon is obtained by rolling in one direction of the rolling direction during the warm rolling or the cold rolling instead of the conventional cross rolling. Therefore, manufacturing efficiency can be improved and manufacturing cost can be reduced.
At this time, if reverse rolling is performed, the productivity is further improved. The one-way rolling referred to in the present invention includes reel-to-reel reverse rolling.

Next, in the present invention, if necessary, cold rolling may be performed after the above-described warm rolling or softening annealing.
Although cold rolling cannot be performed in a structure in which the crystal grains of the welded part and the heat-affected zone are coarsened, if the structure is a fibrous structure after the above-described warm rolling and softening annealing, Even in the heat-affected zone, cold rolling can be performed without breaking.
Also, since cold rolling is easier to control the plate thickness and surface skin than warm rolling, it is desirable that the final finish rolling be performed particularly cold.
The rolling reduction during the cold rolling is not particularly specified, but is preferably in the range of 5 to 50%. This is because it is difficult to control the plate thickness and the surface skin when rolling is less than 5%, and conversely, when it exceeds 50%, the plastic working limit is reached during the cold rolling and fracture occurs. More preferably, it is 10 to 30%, and work hardening occurs after cold rolling, so it is desirable to reduce the hardness by softening annealing. The softening annealing in this case is preferably performed in the range of 700 to 1100 ° C. as in the case of warm rolling.

The following examples further illustrate the present invention.
Two pure molybdenum plates having a composition (purity of 3N) shown in Table 1 having a thickness of 1.0 mm, a width of 100 mm, and a length of 200 mm were used as the material of the material to be rolled. This material is a plate obtained by hot rolling after sintering pure molybdenum powder.
The two materials (pure molybdenum plates) were butted together and welded by a TIG welder.
TIG welding conditions were a current value of 150 A, a welding speed of 500 mm / min, and the welding operation was performed in an atmosphere shielded with argon gas to prevent oxidation. A welding rod was not used.
Table 1 shows the chemical composition of the material of the material to be rolled.

The cross-sectional structure of the pure molybdenum plate, which is the raw material, and the cross-sectional structure of the welded part and the surrounding heat-affected part are shown in FIGS. While the material is a fibrous structure (FIG. 1), the weld 1 and the heat affected zone 2 are recrystallized.
In particular, the crystal grains in the weld are coarsened (FIG. 2). When the average crystal grain size was measured by image analysis, the welded portion 1 was 143 μm, and the heat affected zone 2 was 24 μm.

Two types of samples having a width of 10 mm, a length of 60 mm (hereinafter referred to as sample 1), and a width of 100 mm and a length of 120 mm (hereinafter referred to as sample 2) were cut out from the plate after TIG welding by an electric discharge machine. In any sample, the substantially central part in the length direction was made to be a TIG welded part.
These samples were heated to 430 ° C. and then warm-rolled to finish the plate thickness of each sample to 0.35 mm (sample 1) and 0.16 mm (sample 2), respectively. The total rolling reduction of sample 1 is 65%, and the total rolling reduction of sample 2 is 84%.
In addition, warm rolling was divided into a plurality of passes, and the sample was reheated to 430 ° C. every time one pass was completed. Moreover, in any sample, the direction of warm rolling was set to one direction, and it rolled only to the length direction of the sample. During the warm rolling, the welded part and the heat affected part did not break. As an example, FIG. 3 shows the appearance of sample 1 after warm rolling (total rolling reduction of 65%).
The cross-sectional structure after rolling is shown in FIGS. 4 is an observation structure at a low magnification, and FIG. 5 is an enlarged photograph of the structure of the welded portion in FIG. 4 in particular. 4-5, it turns out that the welded part (FIG. 2) from which the crystal grain became coarse after welding also changes to a fibrous structure | tissue by warm rolling of 65% of total reduction.

If the coarse grain (FIG. 2) of a welded part is changed into a fibrous structure (FIGS. 4 to 5) by warm rolling, the welded part can be handled in the same manner as other parts. In other words, after performing the warm rolling once after the welding, for example, a pure molybdenum or molybdenum alloy thin film is manufactured by a general method similar to that for producing a ribbon of another material such as a steel material by rolling. Bands can be manufactured.
That is, warm rolling and softening annealing can be repeated twice or more as necessary. Moreover, after performing warm rolling and softening annealing, cold rolling can also be performed.
However, as shown in Fig. 1, blowholes are likely to occur in the welded part, and the mechanical characteristics may differ from the parts other than the welded part. Is better to avoid.

Sample 2 (plate thickness 0.16 mm, total reduction rate 84%) rolled in one direction was subjected to soft annealing for 4 minutes in a hydrogen atmosphere furnace at 1080 ° C., and then subjected to the Erichsen test as a deep drawability evaluation. Provided.
As a result of testing by a method based on JIS Z2247, the obtained Erichsen value was 4.4 mm. As described in Patent Document 2, the Erichsen value, which is a possible guide for deep drawing, is about 4.0 mm, so that deep drawing properties that can withstand practical use can be obtained even with unidirectional rolling. ing.

(Comparative example)
A sample having a width of 10 mm and a length of 60 mm (hereinafter referred to as “sample 3”) was cut out from the pure molybdenum plate after TIG welding. Also in the sample 3, the substantially central portion in the length direction was made to be a TIG welded portion. When this sample 3 was subjected to cold rolling without heating, the sample was broken as shown in FIG. 6 and could not be rolled at all.
When the cross-sectional structure was confirmed, the weld 1 and the heat affected zone 2 were broken as shown in FIG. As shown in FIG. 6, the welded part and the heat-affected part remain as coarse crystal grains, and are not changed into a fibrous structure.

From the above examples, (1) warm rolling is required to perform rolling of the welded portion, and (2) coarse crystal grains of the welded portion have a ductile fibrous structure by warm rolling. And (3) it was found that deep drawability (Ericsen value) that can withstand practical use can be obtained even with relatively inexpensive unidirectional rolling. This example is the result of examination at the laboratory level, but it can also be applied to actual production of ribbons.
That is, by applying the manufacturing method of the present invention, it is possible to obtain a long pure molybdenum or molybdenum alloy ribbon that has not been obtained conventionally, for example, during deep drawing when manufacturing a discharge lamp electrode. Contributes to improved production efficiency. As a result, it is also effective in reducing the price of the discharge lamp electrode formed using the ribbon.

  According to the present invention, it is excellent in that the length of pure molybdenum or molybdenum alloy ribbon can be increased, so that it can contribute to the improvement of production efficiency in a mass production line that continuously manufactures parts using these ribbons. . In this specification, the electrode of the discharge lamp used for the backlight of the liquid crystal display device is given as an application example, but it can also be applied to a lead electrode of a semiconductor component, a cathode component in a cathode ray tube, or the like.

It is an optical microscope photograph which shows the cross-sectional structure | tissue of a raw material. It is an optical microscope photograph which shows the cross-sectional structure of a welding part and a heat affected zone. It is a photograph which shows the external appearance after rolling in the manufacturing method of this invention. It is an optical microscope photograph which shows the cross-sectional structure | tissue after rolling in the manufacturing method of this invention. It is an optical microscope photograph which shows the expanded structure of the welding part after rolling in the manufacturing method of this invention. It is a photograph which shows the external appearance after rolling in the manufacturing method of a comparative example. It is an optical microscope photograph which shows the cross-sectional structure | tissue after rolling in the manufacturing method of a comparative example.

Explanation of symbols

1. 1. Welded part Heat affected zone

Claims (3)

In a method for producing pure molybdenum or molybdenum alloy ribbon, a pure molybdenum or molybdenum alloy plate having a thickness of 0.5 to 5.0 mm is used as a raw material. A method for producing pure molybdenum or a molybdenum alloy ribbon, comprising a step of performing 10% to 90% warm rolling. The method for producing pure molybdenum or molybdenum alloy ribbon according to claim 1, wherein soft annealing at 700 to 1100 ° C is performed after warm rolling. The method for producing pure molybdenum or a molybdenum alloy ribbon according to claim 1 or 2, wherein the rolling direction during warm rolling or cold rolling is one direction.