JPH0565609A - High strength tungsten wire - Google Patents

Abstract

(57) [Abstract] [Purpose] The object of the present invention is to generate small islands, to prevent breakage due to vibration and shock, and to withstand thermal stress even if heat treatment is performed above the secondary recrystallization temperature. It is to provide a high strength tungsten wire. [Structure] A high-strength tungsten wire according to the present invention is a high-strength tungsten wire obtained by machining a pressure-molded body of a tungsten powder or a tungsten alloy powder to which a doping agent has been added, followed by secondary recrystallization grains. It is characterized in that the length of the aligned bubbles inside is 40 μm or more.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a high strength tungsten wire mainly used as a filament material, and
The present invention relates to a high-strength tungsten wire which is less likely to be broken by vibration or shock.

[0002]

2. Description of the Related Art Tungsten wires are widely used in incandescent light bulbs as well as filament materials for vibration-proof light bulbs for automobiles and copying machines, vacuum vapor deposition elements, and filament materials for electron tube heaters.

The tungsten wire used as the filament material does not hang (sag) during high temperature lighting, has a small deformation during filament molding, and does not deform due to vibration and shock during lighting and non-lighting. There are demands for characteristics such as low breakage and high strength.

Conventionally, this kind of tungsten wire is composed of alumina (Al ₂ O ₃ ), silica (SiO ₂ ), potassium (K ₂ O).
A tungsten powder or a tungsten alloy powder to which a small amount of a dopant such as is added is pressure-molded, sintered at a temperature of about 3000 ° C., and further subjected to a wire drawing process. The obtained doped tungsten wire is further coiled, then heat-treated in the primary recrystallization region to be shaped and strain-relieved, and then incorporated into the bulb as a filament and then heated to the secondary recrystallization region. Subject to the process.

When the tungsten wire is heated to a temperature higher than the secondary crystal temperature to form a secondary recrystallized structure, a small amount of potassium (K) present in the tungsten wire evaporates, so that the axis of the tungsten wire is increased. A row of minute holes (alignment bubbles) arranged in the direction is formed. The aligned bubbles suppress the growth of crystal grains in the direction perpendicular to the axis, and form a secondary recrystallized structure composed of long wedge-shaped secondary recrystallized grains grown in the axial direction as shown in FIG. Form.

Due to the formation of these long secondary recrystallized grains 1,
Compared with the conventional tungsten wire composed of isotropic secondary recrystallized grains, the grain boundary sliding area is significantly reduced. for that reason,
Fusing of the tungsten wire due to overheating of the reduced cross section caused by grain boundary slip was reduced, and the life of the filament was significantly improved.

[0007]

Recently, however, due to the demand for downsizing, high output, and long life, halogen lamps are used at operating temperatures of 3000K or higher, which are higher than those of conventional incandescent lamps. Is also increasing. In particular, a filament for an anti-vibration bulb for automobiles is required to have no breakage and a long life for safety reasons, and the demand for improvement in strength and reliability of the tungsten wire is further increasing.

However, when the filament material formed by using the conventional tungsten wire is incorporated into the light bulb and the filament is heated to the secondary recrystallization region, as shown in FIG. In some cases, a secondary recrystallized structure composed of crystal grains 1 is formed, and further, fine crystal grains of tungsten (referred to as small islands) are formed at the grain boundaries of the secondary recrystallized grains.

When a light bulb or the like having a filament formed of a tungsten wire having such a small island 2 is lit at a high temperature, the concave portion formed between the small island 2 and the grain boundary 3 serves as a stress concentration source, and the concave portion is formed. The filament easily breaks due to thermal stress starting from the portion. Further, even at low temperature lighting, when impact or vibration acts, the impact force causes a crack to be generated from the recessed portion, and there is a drawback that the fracture occurs within a short period of time.

The cause of the occurrence of the small islands is that in the conventional tungsten wire, the length of the alignment bubble formed by the added dopant is 10 to 20 μm.
Since the length is short, the effect of suppressing the growth of crystal grains in the direction perpendicular to the axis of the tungsten wire in the secondary recrystallization treatment is reduced, and recrystallization in the direction perpendicular to the axis partially progresses at the ends of the alignment bubbles. It is thought that small small islands are formed. By the way, microscopic observation of the fracture surface of the fractured filament confirmed that the crack propagated from the concave portion of the small island generated between the large secondary recrystallized grain and the grain boundary.

The present invention has been made in order to solve the above problems. Even if a heat treatment is carried out at a temperature higher than the secondary recrystallization temperature, small islands are not formed much, and breakage is caused by vibration or impact. An object of the present invention is to provide a high-strength tungsten wire which is resistant to thermal stress.

[0012]

SUMMARY OF THE INVENTION From the above viewpoints, the inventors of the present invention aim to suppress the occurrence of small islands that cause the breakage of a tungsten wire as much as possible.
As a result of studying and experimenting the correlation between the length of the aligned bubbles in the secondary recrystallized structure and the strength of tungsten, when the aligned bubble length in the secondary recrystallized grains was 40 μm or more, it was compared with the conventional one. As a result, it was possible to obtain a high-strength tungsten wire with a long life with almost no generation of small islands.

The present invention is based on the above findings.

As the powder used for the high-strength tungsten wire to which the present invention is applied, not only pure tungsten powder but also tungsten alloy powder containing a small amount of Co is used.

The characteristics desired by the present invention are obtained when the pressure-molded body of the above-mentioned powder is heat-treated and then machined so that the length of aligned bubbles in the secondary recrystallized grains is 40 μm or more. .. The tungsten wire of the present invention having the above-mentioned alignment valve can be manufactured, for example, as follows.

First, a tungsten ore is purified by a conventional method to obtain an ammonium salt. Next, the ammonium salt is reduced to obtain tungsten oxide. By setting the reduction temperature at this time to be 50 to 150 ° C. higher than in the conventional method, impurities contained in the tungsten oxide can be reduced.
Then, a dopant such as K, Si, or Al is added to the tungsten oxide as an aqueous solution of a compound, for example, K, Si,
In terms of Al, the weight ratio to tungsten oxide is 0.1.
04-0.4%, 0.2-0.6%, 0.02-0.2
% And mixed and subjected to main reduction in hydrogen at a temperature of 600 to 900 ° C. to obtain a tungsten metal powder, and then acid washing is performed to remove an excessive doping agent.

The obtained tungsten metal powder is compacted and molded by a conventional method, pre-sintered in a hydrogen furnace, and then subjected to electric current sintering to obtain a tungsten sintered body.

The sintered body thus obtained is hot rolled and drawn. In order to improve the workability in the middle of these processings, the strain is removed by recrystallization processing performed plural times. Of the series of recrystallization treatments, the wire diameter to be subjected to the final recrystallization treatment is increased by 30 to 50% in terms of cross-sectional area ratio by a conventional method, whereby the subsequent processing rate is increased.

As described above, the length of the aligned bubbles is set by adjusting the amount of the doping agent added during the production of the metal powder, the heat treatment conditions, and the workability in rolling wire drawing.

In this case, the length of the aligned bubbles has a large influence on the amount of small islands that cause breakage. If it is less than 40 μm, recrystallization in the direction perpendicular to the axis in the secondary recrystallization treatment is suppressed. Effect is small, small islands are easily formed at the ends of the alignment bubbles,
This causes a decrease in the strength of the tungsten wire. Here, the length of the alignment bubble is applied when the diameter of the wire is 0.39 mm or more.

On the other hand, when the length of the aligned bubbles is 40 μm or more, recrystallization in the direction perpendicular to the axis is almost completely suppressed, the secondary recrystallization temperature is raised, and the secondary recrystallization grown in the axial direction is large. It is possible to form only tissue. Therefore, even when a lamp using this tungsten wire as a filament is lit at a high temperature, it is possible to provide a lamp that has a long life with little breakage.

[0022]

EXAMPLES The present invention will be described below with reference to examples.

Tungsten ore is purified by a conventional method to obtain an ammonium salt.
Reduction is performed at 50 ° C. (100 ° C. higher than the conventional method) to obtain tungsten oxide. This tungsten oxide can be
1, doping agents such as Si, K, etc. were added in the amounts shown in Table 1,
After carrying out the main reduction, a tungsten metal powder was obtained, and then acid washing was carried out to remove an excess doping agent.

The obtained tungsten metal powder was compacted and molded by a conventional method, pre-sintered at 1200 ° C. in a hydrogen furnace, and then 2
Example 1 was carried out by sintering at 700 to 3000 ° C. for 30 minutes.
Thus, tungsten sintered compacts 2 and 2 were obtained. Further, the obtained sintered body was subjected to a rolling step, a recrystallization treatment, and a wire drawing step under the conditions shown in Table 1 to finally obtain a tungsten wire having a wire diameter of 0.4 mm. Next, each tungsten wire was energized in a hydrogen stream at 90% value (90% FC) of fusing current (FC) for 5 minutes to carry out a secondary recrystallization treatment, and a secondary recrystallized grain of the obtained tungsten wire was obtained. The length of the alignment bubble inside was measured.

Further, each tungsten wire has a wire diameter of 80 μm.
After the wire drawing process, a coil was prepared and enclosed as a filament in a lamp, a recrystallization process was performed, and then a blinking test was performed. As for the lamp, 20 bulbs were prepared, 10 bulbs each using the same tungsten wire, and 17 bulbs were used for each bulb.
Blinking 100,000 times at an output of 0 V and 200 W was repeated at 5-second intervals, and the number of light bulbs that broke during the measurement was measured.

On the other hand, as Comparative Examples 1 and 2, the same ammonium salt as in Examples 1 and 2 was used, and under the conditions shown in Table 1, the amount of doping agent added, the transfer step, the recrystallization treatment,
After the wire drawing process, the wire diameter is 0.4 mm, and the average length of the alignment valve in the secondary recrystallized grains is 26 μm and 14 μm, respectively.
A tungsten wire of m was prepared and a blinking test was conducted in the same manner as in Examples 1 and 2, and the results shown in Table 1 below were obtained.

[0027]

[Table 1]

As is clear from the results shown in Table 1, in Examples 1 and 2 in which the length of the aligned bubbles was set to 40 μm or more, the number of fractures was larger than that of the conventional tungsten wires shown in Comparative Examples 1 and 2. Significantly reduced, alignment bubble length is 45
It is found that when the thickness is more than μm, breakage is extremely reduced under the test conditions, and a tungsten wire having high strength and long life can be obtained.

When the fractured portions of the fractured filaments were observed under a microscope, small islands were observed in all the fractured portions, and it was confirmed that cracks propagated from these small islands and led to fracture.

Further, when the metallographic structure of the tungsten wire used in Examples 1 and 2 was observed with a microscope, both were as shown in FIG.
As shown in (1), it was formed only from a large number of large secondary recrystallized grains 1a intricately wedge-shaped, and generation of small islands was not observed at the boundary with the grain boundary 3a.
Therefore, it was possible to obtain a tungsten wire having excellent high temperature characteristics, impact resistance, and earthquake resistance, high strength, and a long life.

[0031]

As described above, according to the high-strength tungsten wire according to the present invention, small islands hardly occur in the secondary recrystallization structure. Therefore, it is possible to provide a high-strength tungsten wire having high strength against high thermal stress, vibration and impact, and having a long life, and it is possible to significantly improve the reliability of a tungsten product such as a filament for a lamp.

[Brief description of drawings]

FIG. 1 is a diagram showing a secondary recrystallization structure of a high-strength tungsten wire according to the present invention.

FIG. 2 is a diagram showing a secondary recrystallization structure of a conventional tungsten wire.

[Explanation of symbols]

 1,1a Secondary recrystallized grain 2 Small island (fine grain) 3,3a Grain boundary

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isamu Ozeki 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company Toshiba Yokohama office

Claims (1)

[Claims] 1. A high-strength tungsten wire obtained by machining a pressure-molded body of a tungsten powder or a tungsten alloy powder to which a doping agent has been added, followed by machining.
A high-strength tungsten wire having a length of aligned bubbles in the secondary recrystallized grains of 40 μm or more.