ReW wire for electron tube heaters

Abstract

To provide a medical needle composed of a rhenium-tungsten alloy capable of greatly contributing to improving a stability of thermoelectromotive force while securing mechanical characteristics without any variation of material quality, and also to provide a probe pin and an electron tube heater.SOLUTION: A medical needle includes a tungsten alloy containing rhenium of 1 wt% to less than 30 wt% and a balance tungsten with inevitable impurities. A rhenium content is less than 30 wt%, at a measurement region with a unit area of a diameter 1 μm at 17 points in total, comprising a center point and 16 intersection points of 4 concentric circles with regular intervals and 2 straight diameters in a radial section of a body of the medical needle in two locations. The rhenium content has a variation coefficient of 0.10 or less in semi-quantitative analysis using an EPMA.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The embodiments described below relate to rhenium tungsten wire rods and thermocouples using the same.

Background Art

[0002] Conventionally, various tungsten (W) wires have been used as cathode heaters for electron guns for TVs, filament materials for lighting in automotive lamps and household electrical appliances, high-temperature structural members, contact materials, and constituent materials for discharge electrodes. Among these, tungsten alloy (Re-W) wires containing a predetermined amount of rhenium (Re) improve the electrical resistance characteristics and wear resistance of W wires and are widely used for probe pins for semiconductor inspection. Also, they improve the high-temperature strength and ductility after recrystallization of W wires and are widely used for heaters for electron tubes, filament materials for vibration-resistant electric bulbs, thermocouples, etc. Further, due to the solid solution strengthening of Re, the strength and rigidity at room temperature are higher than those of stainless steel wires and W wires, so they are also used for medical needles. (Patent Document 2) Fig. 1 schematically shows an example of temperature measurement using a thermocouple. A thermocouple is a temperature sensor that combines two dissimilar metals and utilizes their thermoelectromotive force. Due to features such as a simple structure and the ability to be used in a wide temperature range from a low temperature range to a high temperature range by selecting materials, it has been the most widely used in the industry for many years. Fig. 2 shows, as an example, a part of the types of thermocouples according to JIS standards (see JIS C1602). Those used for high temperatures include platinum-rhodium alloy-based B, S, R thermocouples and Re-W-based C thermocouples. In particular, in a non-oxidizing atmosphere of about 1500°C or higher, C thermocouples are widely used.

[0003] For example, in the production of sintered metals and sintered ceramics, a mixture of raw material powder and wax as a binder is formed into a molded product, which is then heat-treated in a vacuum atmosphere below 1000°C to remove the wax. Subsequently, it is heat-treated at 1600-2000°C to sinter, and C thermocouples are used to measure the temperature at 1600-2000°C. For example, in HP furnaces and HIP (High-Pressure Isolation) equipment, the pressure vessel reaches high temperatures of around 2000°C in a gas-pressurized atmosphere. Optical temperature measurement using radiation thermometers requires openings to directly observe the radiation from the furnace chamber, which reduces the strength of the pressure vessel. It also leads to heat loss due to the openings in the vessel. For this reason, application is very difficult and the equipment is expensive. Therefore, C thermocouples are used for temperature measurement in HP furnaces and HIP equipment subject to the High-Pressure Gas Safety Act.

[0004] In recent years, the use of high-performance ceramics such as silicon nitride has expanded to include insulating heat dissipation substrates for power semiconductor modules and LED mounting, bearing balls for wind turbines and automotive engines, and industrial equipment components such as automotive parts and semiconductor manufacturing equipment. These ceramics are produced using the aforementioned heat treatment equipment, and temperature profile control during heat treatment is crucial for maintaining high performance and achieving good yields. Therefore, maintaining temperature measurement accuracy within and between manufacturing lots of thermocouples is extremely important.

[0005] When using thermocouples, calibration is necessary to determine the relationship between the value indicated by the thermocouple and the actual temperature. There are two main calibration methods: the fixed-point method and the comparison method. The fixed-point method involves providing an accurate temperature value at a fixed temperature point for calibration, while the comparison method involves measuring the temperature of an arbitrarily determined constant-temperature bath using a standard thermocouple (reference line) and calculating the error between that measurement and the thermocouple being calibrated. For C thermocouples, the comparison method is generally used because they measure temperatures above 1500°C.

[0006] It is believed that for thermocouples used at high temperatures, the relationship between temperature and thermoelectric power remains unchanged as long as there is no heterogeneity in any part of the wires that make up the thermocouple. Here, heterogeneity refers to "the change in thermoelectric power per 1°C temperature difference" (see Non-Patent Literature 1). In other words, if there is a part with this heterogeneity (heterogeneous part) in the wire, and a temperature gradient occurs in that part, the detected thermoelectric power will show a different value than that of a thermocouple with wires that do not have heterogeneous parts. For example, even if the above calibration is performed, there is a high possibility that the heat gradient in the actual device cannot be reproduced, and a temperature deviation from the calibration may occur. Also, if many parts of the wire have heterogeneity, the difference from the reference line may become too large, and the product may not be able to be calibrated.

[0007] On the other hand, medical needles are formed by cutting strands of wire to the desired length and then pressing or bending them. During pressing and bending, stress is applied to the cut strands, so it is necessary that cracks do not occur easily and that no splits occur in the bent parts. Medical needles are also used for suturing during surgery. To suppress variations in needle behavior, such as needle deflection caused by the force applied during suturing, it is desirable that the needles have high tensile strength and low variability. In order to prevent a decrease in yield due to cracks and splits during needle processing and to obtain needles of stable quality, it is necessary that the multiple cut strands are homogeneous, that is, that the strands used are homogeneous.

[0008] The main cause of heterogeneity is variation in the material of the wire strands. For example, Re-W is typically manufactured using powder metallurgy, which involves mixing W powder and Re powder, molding the mixture, and sintering it. Since the sintering of Re-W proceeds by solid-phase diffusion, depending on the particle size distribution of each powder, the mixing state of the powders, and the molding and sintering conditions, it may be impossible to diffuse and homogenize (solid-solve) Re into the W matrix. As a result, a phase region with a locally high Re composition ratio (a segregated phase of the σ phase) may be formed. The formation of a segregated phase of the σ phase means that there are also parts where the Re composition ratio is lower than average. When a sintered body with such fluctuations in Re composition is processed into rods or wires, heterogeneity occurs in the axial (processing direction) cross-section and the radial (perpendicular to the axial direction) cross-section due to variations in the amount of Re. Regarding this σ phase segregation, for example, if the σ phase segregation is concentrated in one area, wire breakage is more likely to occur during wire drawing. Therefore, there are Re-W wires in which the σ phase segregation has a maximum particle size of 10 μm or less and is dispersed over a wide area (see Patent Document 1). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent No. 4256126 [Patent Document 2] Japanese Patent No. 5766833 [Non-patent literature]

[0010] [Non-Patent Document 1] Yoshio Monma, et al., "Causes of Degradation and Variation Factors in PR Thermocouples Used in Long-Term Creep Tests," Iron and Steel, 1989, Vol. 75, No. 4, pp. 665-672. [Overview of the project] [Problems that the invention aims to solve]

[0011] The method described in Patent Document 1 aims to suppress the segregation of the σ phase to a level where there is no breakage during wire drawing by refining the region of existence to a predetermined size or smaller and dispersing it over a wide area, rather than having the segregated σ phase concentrated in a specific region, thus allowing the presence of fine σ phase segregation. However, even if the σ phase segregation is present homogeneously, if the proportion of existence in a given volume changes, fluctuations in the amount of Re (changes in material) may occur in the axial cross-section and radial cross-section, potentially creating heterogeneous areas.

[0012] Figure 3 shows, as an example, the amount of Re in the W matrix when a segregated σ phase is present at the 26% Re-W line. Semi-quantitative analysis results by EPMA (acceleration voltage 15.0 kV, irradiation current 5.0 × E -8 From A (beam diameter 1 μm or less), it can be seen that the inclusions are σ phase. Because the σ phase is harder than the matrix, it exists in this form as an inclusion. In the vicinity of this σ phase, there is variation in the amount of Re in the matrix. Thus, the presence of the σ phase causes variation (inhomogeneity) in the amount of Re in its surrounding area. [Means for solving the problem]

[0013] To solve the above problems, the rhenium-tungsten wire rod according to the embodiment is a wire rod made of a tungsten alloy containing 1 wt% to less than 30 wt% rhenium, with the remainder being tungsten and unavoidable impurities. In two radial cross-sections of the wire rod body, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, consisting of 17 points in total: 16 intersection points between four equally spaced concentric circles and two perpendicular diameter lines, and the center. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA. Furthermore, according to the embodiment, a wire rod is provided which is made of a tungsten alloy containing 1 wt% to less than 30 wt% rhenium and 90 wt ppm or less potassium (K), with the remainder being tungsten and unavoidable impurities. In two radial cross-sections of the wire body, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, consisting of 17 points in total: 16 intersection points of four equally spaced concentric circles and two perpendicular diameter lines, and the center. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA. Furthermore, according to the embodiment, a thermocouple is provided that uses a rhenium-tungsten wire rod according to the embodiment. According to the embodiment, a medical needle is provided which is made of a tungsten alloy containing 1 wt% to less than 30 wt% rhenium, with the remainder being tungsten and unavoidable impurities. In two radial cross-sections of the medical needle body, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, consisting of 17 points in total: 16 intersection points between four equally spaced concentric circles and two perpendicular diameter lines, and the center. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA. According to the embodiment, a medical needle is provided which is made of a tungsten alloy containing 1 wt% to less than 30 wt% rhenium and 90 wt ppm or less potassium (K), with the remainder being tungsten and unavoidable impurities. In two radial cross-sections of the medical needle body, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, consisting of 17 points in total: 16 intersection points between four equally spaced concentric circles and two perpendicular diameter lines, and the center. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA. According to the embodiment, a probe pin is provided which is made of a tungsten alloy containing 1 wt% to less than 30 wt% rhenium, with the remainder being tungsten and unavoidable impurities. In two radial cross-sections of the probe pin body, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, consisting of 17 points in total: 16 intersection points between four equally spaced concentric circles and two perpendicular diameter lines, and the center. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA. According to the embodiment, a probe pin is provided which is made of a tungsten alloy containing 1 wt% to less than 30 wt% rhenium and 90 wt ppm or less potassium (K), with the remainder being tungsten and unavoidable impurities. In two radial cross-sections of the probe pin body, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, consisting of 17 points in total: 16 intersection points between four equally spaced concentric circles and two perpendicular diameter lines, and the center. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA. According to the embodiment, a ReW wire for electron tube heaters is provided, which is made of a tungsten alloy containing 1 wt% to less than 30 wt% rhenium, with the remainder being tungsten and unavoidable impurities. In two radial cross-sections of the ReW wire body for electron tube heaters, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, consisting of 17 points in total: 16 intersection points between four equally spaced concentric circles and two perpendicular diameters, and the center. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA. Also, according to an embodiment, there is provided a ReW wire for an electron tube heater made of a tungsten alloy containing 1 wt% or more and less than 30 wt% of rhenium, 90 wtppm or less of potassium (K), and the balance being tungsten and inevitable impurities. In two radial cross-sections of the ReW wire body for the electron tube heater, at a total of 17 points including 16 intersection points of four concentric circles at equal intervals and two perpendicular diameters, and the center, in a measurement area with a unit area of a diameter of 1 μm, the rhenium content is less than 30 wt%. The coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA.

Brief Description of the Drawings

[0014] [Figure 1] Schematic diagram of a temperature measurement system using a thermocouple. [Figure 2] Table showing the types of thermocouples. [Figure 3] Diagram showing inclusions (σ phase) present in the ReW matrix and semi-quantitative analysis results (example of a conventional material). [Figure 4] Schematic diagram of the sample radial cross-section and the surface layer part. [Figure 5] Schematic diagram of the rhenium content measurement points. [Figure 6] General explanatory diagram of the particle size distribution.

Embodiments for Carrying Out the Invention

[0015] <m Hereinafter, the rhenium tungsten wire rod of the embodiment will be described with reference to the drawings. Hereinafter, the rhenium tungsten wire rod may also be referred to as a ReW wire rod. Note that the drawings are schematic, and for example, the ratio of dimensions of each part is not limited to those in the drawings.

[0016] Figure 4 shows an example of a radial cross-section of a sample taken from a ReW wire rod. In the radial cross-section, the rhenium tungsten wire body is indicated by C. Figure 4 also shows an enlarged view of the portion indicated by A on the outer circumference of the rhenium tungsten wire rod in the radial cross-section. As shown in the enlarged view of Figure 4, a surface mixture layer B is formed on the outer circumference of the rhenium tungsten wire body C. The surface mixture layer B contains W, O, and C as constituent elements. The diameter of the wire rod is preferably 0.1 mm to 5.0 mm so that it can be used as various thermocouples or wires for wire drawing. For example, when used for thermocouples, if the wire diameter is less than 0.1 mm, breakage is likely to occur due to evaporation and consumption at high temperatures, resulting in a short lifespan. If the wire diameter exceeds 5.0 mm, the heat capacity of the thermocouple itself makes it impossible to accurately measure the temperature of the object. A more preferable range is 0.2 mm to 3.5 mm. ReW wire rods are processed to a thickness of 0.1 mm to 5.0 mm through a forging (swaging: SW) process and a subsequent wire drawing (DW) process. Wire rods that have undergone SW or DW have a mixture layer on their surface. This mixture contains W, O, and C as constituent elements and is removed during the manufacturing process, for example, through an electrolytic process. The main body portion, excluding this mixture, is used as the sample. The sampling location is arbitrary, but considering the yield in the product and in order to evaluate variability, it is desirable to take samples from two or more separate locations within a single wire rod. Within a single ReW wire, the ends may have unstable conditions, for example, due to the start and stop of the DW equipment. These parts should not be included in the sample. The length of the unstable part varies depending on the layout and size of the equipment.

[0017] Measurement can be performed on any cross-section of the collected sample, but a radial cross-section as shown in Figure 4 is preferred due to the ease of sample processing. The sample is embedded in resin and, if necessary, polished and etched to facilitate observation. On the obtained measurement surface, for example as shown in Figure 5, an EPMA (electron beam microanalyzer) is used to quantify the amount of Re in a 1 μm diameter region at a total of 17 points: the intersections of four equally spaced concentric circles 2-5 with the X and Y axes (16 points), and the center point 1, in the radial cross-section of the rhenium tungsten rod body C. The measurement locations are examples, and measurements can be taken anywhere, but these locations are preferable for unbiased measurement of the entire cross-section. Furthermore, the radial cross-section of the object to be measured should be taken from two or more separate locations on the rod, rather than just one arbitrary point.

[0018] In the ReW wire rod body of the embodiment, the rhenium content is less than 30 wt% in any measurement area with a unit area and a diameter of 1 μm. Re content of 30 wt% or more exceeds the average addition amount. This indicates that sufficient diffusion of Re or W did not occur during the sintering process, and that there is variation in Re content in the axial and radial cross-sectional directions. Variation in Re content is a cause of heterogeneity and may lead to variation in thermoelectric power depending on the position in the ReW wire rod.

[0019] Next, for the obtained Re data, we calculate the mean (Ave), the standard deviation (Sd), and the coefficient of variation (CV) calculated as Sd / Ave. CV represents the ratio of the data's variability to the mean, allowing us to compare variability regardless of whether the Re ratio of the ReW bar is high or low.

[0020] The CV of the rhenium content in the ReW wire rod of the embodiment is preferably 0.10 or less. More preferably, it is 0.05 or less. If the CV is greater than 0.10, for example, it indicates that there is variation in the Re content in the axial or radial cross-sectional direction, even if there is no segregated σ phase. Variation in Re content is a cause of heterogeneity and can lead to variation in thermoelectric power depending on the position in the ReW wire rod.

[0021] The amount of Re contained in the ReW wire rod of the embodiment is preferably 1 wt% or more and less than 30 wt%, and more preferably 2 wt% or more and 28 wt% or less. The amount of Re is the value analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES), which is suitable for evaluating constituent elements, rather than inductively coupled plasma-mass spectroscopy (ICP-MS), which is suitable for evaluating trace impurities. Re improves the elongation of W at high temperatures and enhances processability. It also increases strength through solid solution strengthening. However, if the content is less than 1 wt%, the effect is insufficient. For example, when used as a material for probe pins, the amount of deformation of the finished probe pin increases with frequency of use, leading to contact failure and a decrease in the inspection accuracy of semiconductors. If the Re content exceeds about 28 wt%, it exceeds the solid solution limit with W, so a segregated phase of the σ phase is generated, and heterogeneous parts are easily generated in the wire rod. The occurrence of heterogeneity leads to variations in thermoelectric power and strength. By setting the Re content to 1 wt% to less than 30 wt% and 2 wt% to 28 wt%, for example, thermocouples (where the + side conductor is the positive side conductor and the - side conductor is the negative side conductor) and ReW wires for probe pins made from this embodiment can be manufactured with good yield while ensuring thermoelectric power characteristics (stability) and mechanical properties (strength and wear resistance).

[0022] The ReW wire rod of this embodiment may contain 30 wtppm to 90 wtppm of potassium (K) as a doping agent. The inclusion of K improves tensile strength and creep strength at high temperatures through the doping effect. If the K content is less than 30 wtppm, the doping effect will be insufficient. If it exceeds 90 wtppm, processability will decrease, potentially significantly reducing yield. By including 30 wtppm to 90 wtppm of K as a doping agent, for example, thermocouples using this embodiment as the constituent material for the positive and negative conductors, or ReW wires for electron tube heaters using this embodiment as the material, can be manufactured with good yield while ensuring high-temperature characteristics (prevention of breakage and deformation during high-temperature use).

[0023] The ReW wire rod of this embodiment has a tensile strength with a standard deviation of 35 N / mm². 2 The following can be achieved: By suppressing variations in tensile strength, the processing stability of the ReW wire rod can be improved, and thus, an improvement in the yield of products using the ReW wire rod (e.g., thermocouples, probe pins, medical needles) can be expected. In addition, by stabilizing the tensile strength, the quality of medical needles can be improved when used as a material for medical needles. The ReW wire rod of the embodiment has a standard deviation of tensile strength of 35 N / mm 2 The following conditions, along with a wire rod diameter of 0.1 mm to 5.0 mm, can be met to obtain superior processing stability. Tensile strength is measured using a universal tensile and compression testing machine. Since the load changes depending on the wire diameter, the universal tensile and compression testing machine may be modified by changing the load cell or using different equipment depending on the wire diameter. For example, a Shimadzu AG-I 5kN or a Minebea LTS 500N may be used. The test specimen is chucked with a flat plate via sandpaper to prevent slippage, and both ends of these are fixed to the machine. The gauge length is 50 mm, and the tensile test is performed at a speed of 10 mm / min. If the fracture is not between the gauge points, the measurement is repeated.

[0024] This embodiment makes it possible to realize a ReW wire rod that is free from material variations (inhomogeneities) and greatly contributes to improving the stability of thermoelectric power, and can be applied to high-temperature thermocouple applications. It can also be applied to ReW wire applications for probe pins. The ReW wire rod is not limited to having a circular cross-section, but may have a cross-section of a shape other than a circle, such as an ellipse or polygon.

[0025] Next, a method for manufacturing ReW wire rods according to this embodiment will be described. The manufacturing method is not particularly limited, but examples include the following.

[0026] The W powder and Re powder are mixed so that the Re content is 1 wt% or more and less than 30 wt%. There are no particular limitations on the mixing method, but a method of mixing the powders in a slurry using water or an alcohol-based solution is particularly preferred because it yields a powder with good dispersibility. Furthermore, in order to ensure homogeneity of the powder lot, it is even more preferable to dry the slurry and then dry-mix all the powders from the same lot together.

[0027] The Re powder to be mixed preferably has an average particle size of less than 8 μm. The particle size distribution preferably has an SD value of less than 11 μm. Figure 6 shows an explanatory diagram of the particle size distribution. The horizontal axis represents particle diameter (μm), the left vertical axis represents frequency (%), and the right vertical axis represents cumulative (%). The SD value is calculated using the formula SD = (d(84%)-d(16%)) / 2, where d(84%) represents the particle size of 84% of the cumulative particles and d(16%) represents the particle size of 16% of the cumulative particles. This value serves as an indicator of the distribution width of the measured particle size. The particle size distribution shall be measured using laser diffraction. The amount of powder used for a single measurement shall be the amount recommended by the measuring device. Generally, 0.02 g is recommended. Furthermore, the measurement sample shall be thoroughly stirred before weighing.

[0028] The W powder is either pure W powder with unavoidable impurities removed, or doped W powder containing a K content that takes into account the yield to the wire. The W powder preferably has an average particle size of less than 16 μm. The particle size distribution preferably has an SD value of less than 13 μm. If the average particle size and particle size distribution of the Re powder and W powder are above the above, the diffusion distance of Re atoms or W atoms required for homogeneity increases, making it easier to form the σ phase.

[0029] The ratio of average Re particle size to average W particle size is preferably between 0.4 and 2.0. If the ratio of average Re particle size to average W particle size is less than 0.4 or greater than 2.0, the diffusion distance of Re atoms to the center of W grains, or the diffusion distance of W atoms to the center of Re grains, becomes larger, which may increase the likelihood of σ phase formation.

[0030] Next, the mixed powder is placed in a predetermined mold and press-molded. The pressing pressure at this time is preferably 150 MPa or higher. To facilitate handling, the molded body may be pre-sintered in a hydrogen furnace at 1200 to 1400°C. The obtained molded body is sintered in a hydrogen atmosphere, an inert gas atmosphere such as argon, or under vacuum. The sintering temperature is preferably 2500°C or higher. If the temperature is below 2500°C, the diffusion of Re atoms and W atoms will not proceed sufficiently during sintering. The upper limit of the sintering temperature is 3400°C (below the melting point of W, 3422°C).

[0031] The relative density of the sintered body is preferably 90% or higher. The relative density after sintering is the relative density (%) relative to the true density, and the relative density (%) relative to the true density is expressed as [sintered body density / true density] × 100%. Furthermore, within a single sintered body, the ratio of the density of the lowest part, such as the lower end in electrically sintered sintering, to the overall average density of the same sintered body is preferably 0.98 or higher. By setting the relative density of the sintered body to 90% or higher and the ratio of the density of the lowest part to the overall average density of the same sintered body to 0.98 or higher, fluctuations in the Re content can be suppressed.

[0032] The sintered body obtained in this sintering process is subjected to a first SW (sintering) process. The first SW process is preferably carried out at a heating temperature of 1300 to 1600°C. The reduction rate of the cross-sectional area (area reduction ratio) processed in one heat treatment (1 heat) is preferably 5 to 15%.

[0033] Instead of the first SW processing, rolling may be performed. Rolling is preferably performed at a heating temperature of 1200 to 1600°C. The surface area reduction rate per heat is preferably 40 to 75%. A two-way roller rolling mill, a four-way roller rolling mill, or a die roll rolling mill can be used as the rolling mill. Rolling can significantly increase manufacturing efficiency. The first SW processing and rolling may also be combined.

[0034] A second SW process is performed on a sintered body (ReW bar stock) that has undergone either the first SW process, rolling, or a combination of these processes. The second SW process is preferably performed at a heating temperature of 1200 to 1500°C. The reduction in surface area per heating cycle (1 heat) is preferably about 5 to 20%.

[0035] After the second SW process is completed, the ReW rod material is subjected to a recrystallization treatment. The recrystallization treatment can be carried out, for example, using a high-frequency heating device, under a hydrogen atmosphere, an inert gas atmosphere such as argon, or under vacuum, at a treatment temperature in the range of 1800 to 2600°C.

[0036] The ReW rods that have undergone recrystallization treatment are subjected to a third SW process. The third SW process is preferably carried out at a heating temperature of 1200 to 1500°C. The reduction in surface area per heat is preferably about 10 to 30%. The third SW process is carried out until the ReW rods reach a diameter that can be drawn (preferably 2 to 4 mm in diameter).

[0037] The ReW rod, having completed the third SW processing, undergoes drawing (DW) processing to enable smooth wire drawing (DW) processing. This process involves repeatedly applying a lubricant to the surface, drying the lubricant, heating to a machinable temperature, and drawing using a drawing die. It is desirable to use a C-type lubricant with excellent heat resistance. The processing temperature is preferably 1100°C or lower. The processing temperature is set according to the wire diameter to be DW'd. The reduction ratio per die is preferably 10-35%. Annealing and surface polishing processes (e.g., electrolytic processes) may be added during the DW process as needed.

[0038] Appropriate amounts of ReW wire rods, either SW-processed or DW-processed, are subjected to additional processes such as heat treatment and surface polishing to create thermocouple material. Afterward, thermocouples are manufactured using the specified combinations. (Examples) Examples 1-4 were manufactured using the processing conditions described above. Reference Example 5 and Comparative Example 1 were manufactured using conventional conditions for Re powder and W powder size. Reference Example 6 and Comparative Example 2 were manufactured using conventional conditions for W powder size. Table 1 shows the analysis results for each example. The analysis of Re and K was performed using inductively coupled plasma-atomography (ICP-OES) rather than inductively coupled plasma-mass spectrometry (ICP-MS). The lower detection limit for K is 5 wtppm, and if the analytical value is below 5 wtppm without addition, it is indicated with "-".

[0039] [Table 1]

[0040] Each sintered body was processed to a diameter of 0.5 mm using the processing steps described above. Examples 2 and 4 and Comparative Example 2 were separately processed to a diameter of 5.0 mm and a diameter of 0.1 mm, respectively. After processing was completed, samples were taken from both ends of each wire rod using the method described above, and 17 points × 2 samples = a total of 34 points were collected for each size and subjected to irradiation using an EPMA (JXA-8100 manufactured by JEOL Ltd., magnification 1000x, acceleration voltage 15.0kV, irradiation current 5.0 × E)-8 Using method A), the Re content in a 1 μm diameter region was analyzed. Next, the coefficient of variation (CV) was calculated from the analytical values. Table 2 shows the evaluation results. Re content is indicated by "○" if "less than 30 wt% at all measurement points" and "×" if "30 wt% or more at one or more points". Shaded lines in the table indicate sizes for which samples were not prepared. Also, for K, "-" is used if the analytical value was below 5 wt ppm without addition.

[0041] [Table 2]

[0042] Next, using wire rods processed to a diameter of 0.5 mm, thermocouples were fabricated in the combinations of prototypes 1 to 8 shown in Table 3, following the prescribed process. For prototype 2, prototypes with a diameter of 0.1 mm (prototype 2-2) and 5 mm (prototype 2-3) were also fabricated. Two samples were taken from each end of the material. To ensure that the position combinations did not overlap (front-front, front-back, back-front, back-back), four thermocouples were fabricated for each combination. Here, one end of a single wire rod is the front, and the other end of the same wire rod is the back. For example, front-front refers to the combination of the front of one wire rod and the front of the other wire rod. For each prototype, the thermocouples were placed in an electric furnace along with a calibrated platinum-rhodium thermocouple, and the thermoelectric voltage was measured using the system shown in Figure 1 at a temperature of 1600°C for the platinum-rhodium thermocouple, and the temperature was calculated (JISC1602). The temperature measurement system shown in Figure 1 comprises a thermocouple's positive (+) and negative (-) conductors, a temperature sensing junction, a reference junction, a measuring instrument, and a compensating wire. The temperature sensing junction is formed by welding the tip of the thermocouple's positive conductor to the tip of its negative conductor. The positive and negative conductors are connected to the reference junction, respectively. The reference junction and the measuring instrument are connected by a compensating wire. Table 3 shows the maximum-minimum temperature difference (Max-Min) obtained using each prototype. As can be seen from the table, the ReW wire rod according to the embodiment suppressed Re variation in the main body and suppressed temperature variation in thermocouples using the same wire rod. In contrast, the comparative example did not suppress Re variation, and the temperature variation of thermocouples using the same wire rod was large. Therefore, the yield is greatly improved when the embodiment is used as a thermocouple.

[0043] [Table 3]

[0044] Furthermore, the tensile strength of Example 4, with a diameter of 0.5 mm, and Comparative Example 2, also with a diameter of 0.5 mm, were compared. Twenty samples were taken evenly from the entire length of the tensile specimen. The test was performed using a universal tensile and compression testing machine (Shimadzu AG-I 5kN). The test specimen was chucked with a flat plate via sandpaper to prevent slipping, and both ends were fixed to the machine. The gauge length was set to 50 mm, and the tensile test was performed at a speed of 10 mm / min. The results are shown in Table 4. Although there was no difference in the average tensile strength, the standard deviation, which indicates the variation, was significantly smaller for Example 4 compared to Comparative Example 2. Therefore, the stability of conditions when processing using the example as a material is greatly improved, contributing to improved yield. In addition, the standard deviation of tensile strength for the other examples was 35 N / mm. 2 The results were as follows: The stability of processing conditions when using the example as a material is greatly improved, contributing to improved yield. When multiple of these wire rods are cut to manufacture medical needles, needles with stable tensile strength can be obtained.

[0045] [Table 4]

[0046] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Modifications of these embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other. The invention described in the original claims of this application is listed below. [1] A rhenium-tungsten wire rod made of a rhenium-containing tungsten alloy, wherein the rhenium content is less than 30 wt% in any measurement area of ​​the wire body with a unit area of ​​diameter 1 μm. [2] The rhenium tungsten wire rod according to [1], wherein the rhenium content has a coefficient of variation of 0.10 or less in semi-quantitative analysis using EPMA. [3] The rhenium tungsten wire rod according to any one of items [1] or [2], wherein the rhenium content is 1 wt% or more and less than 30 wt%. [4] The rhenium-tungsten wire rod according to any one of items [1] or [2], wherein the rhenium content is 2 wt% or more and 28 wt% or less. [5] The rhenium-tungsten wire rod according to any one of items [1] to [4], wherein the tungsten alloy has a potassium (K) content of 30 wt ppm or more and 90 wt ppm or less. [6] The rhenium-tungsten wire rod according to any one of items [1] to [5], wherein the diameter of the wire rod is 0.1 mm or more and 5.0 mm or less. [7] The standard deviation of the tensile strength of the wire rod is 35 N / mm 2 The following is a rhenium-tungsten wire rod as described in [6]. A thermocouple using a rhenium-tungsten wire rod as described in any one of items [8][1] to [7]. [Explanation of symbols]

[0047] A...Rhenium tungsten rod outer circumference B…Surface mixture layer C...Rhenium tungsten wire body 1...Center point of radial cross section 2, 3, 4, 5…Concentric circles in the radial cross-section X, Y...X axis and Y axis of the radial cross-section

Claims

1. A ReW wire for an electron tube heater, comprising a tungsten alloy containing rhenium in an amount of 1 wt% or more and less than 30 wt%, potassium (K) in an amount of 30 wt ppm or more and 90 wt ppm or less, with the remainder being tungsten and unavoidable impurities, In two radial cross-sections of the ReW wire body for electron tube heaters, the rhenium content is less than 30 wt% in a measurement area with a unit area of ​​1 μm in diameter, where there are 17 points in total, consisting of 16 intersection points between four equally spaced concentric circles and two perpendicular diameter lines, and the center, and the coefficient of variation of the rhenium content is 0.10 or less in semi-quantitative analysis using EPMA.

2. The ReW wire for an electron tube heater according to claim 1, wherein the rhenium content is 2 wt% or more and 28 wt% or less.

3. The ReW wire for an electron tube heater according to any one of claims 1 to 2, wherein the diameter of the ReW wire for the electron tube heater is 0.1 mm or more and 5.0 mm or less.

4. The standard deviation of the tensile strength of the ReW wire for the electron tube heater is 35 N / mm 2 The following is a ReW wire for an electron tube heater according to any one of claims 1 to 3.

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