Rhenium-tungsten wire rod and thermocouple using the same

Abstract

By homogenizing the Re content in any cross section of the ReW wire rod body, an ReW wire rod without material fluctuations, ensuring mechanical properties, greatly contributing to the stability of the thermoelectric power, can be achieved. ReW is usually produced by powder metallurgy, mixing, molding, sintering powders. Since the sintering of ReW proceeds by solid phase diffusion, using the particle size distribution of the powder, the mixing state, the molding and sintering conditions, a phase region with locally high Re composition ratio (segregated phase of σ phase) is generated. When such a sintered body with a large variation in Re composition is processed into a rod, wire (wire rod), a non-uniformity caused by fluctuations (variations) in the amount of Re occurs in the cross section in the processing direction, the axial vertical cross section. The ReW wire rod according to the embodiments is a wire rod made of a tungsten alloy containing rhenium, in which the rhenium content in any measurement area of 1 μm in diameter per unit area in the wire rod body is less than 30 wt%.

Description

Technical Field

[0001] The embodiments described later involve rhenium-tungsten wire rods and thermocouples using them. Background Technology

[0002] Previously, various tungsten (W) wires were used as cathode heaters for electron guns in televisions, filament materials for automotive lamps and lighting in household appliances, high-temperature structural components, contact materials, and materials for discharge electrodes. Among them, tungsten alloy (Re-W) wires containing a specified amount of rhenium (Re) improve the resistivity and wear resistance of W wires and are widely used in semiconductor inspection probes. In addition, improving the high-temperature strength and recrystallization ductility of W wires makes them widely used in heaters for electron tubes, filament materials for shock-resistant light bulbs, thermocouples, etc. Furthermore, through solid solution strengthening of Re, their strength and rigidity at room temperature are higher than those of stainless steel wires and W wires, and therefore they are also used in medical needles (Patent Document 2).

[0003] exist Figure 1 The diagram below illustrates an example of temperature measurement based on a thermocouple. A thermocouple is a temperature sensor that combines two dissimilar metals and utilizes their thermoelectric potential. Due to its simple structure and the ability to be used over a wide temperature range, from low to high temperatures, by selecting appropriate materials, it has been the most widely used material in industry for many years. Figure 2 The image shows a portion of the types of thermocouples according to JIS standards (refer to JIS C1602) as examples. Among the thermocouples used as high-temperature thermocouples are platinum-rhodium alloy B, S, and R thermocouples, and Re-W C thermocouples. C thermocouples are used extensively, especially in non-oxidizing atmospheres above approximately 1500°C.

[0004] For example, in the production of sintered metals and ceramics, after the mixture of raw material powder and wax as a binder is formed into a molded product, it is first heat-treated in a vacuum atmosphere below 1000°C to dewax it. Then, it is heat-treated and sintered at 1600–2000°C, and a C thermocouple is used for temperature measurement at 1600–2000°C. For example, in pressurized sintering (HP) furnaces and thermostatic pressure molding (HIP) devices, the pressure vessel reaches a high temperature of around 2000°C under a pressurized gas atmosphere. In optical temperature measurement such as radiation thermometers, openings are required for direct observation of the furnace chamber's radiation, which reduces the strength of the pressure vessel. Furthermore, heat loss due to the openings within the vessel is also introduced. Therefore, its application is very difficult, and the equipment is expensive. Therefore, in HP furnaces and HIP devices where high-pressure gas safety laws apply, C thermocouples are used for temperature measurement.

[0005] In recent years, the use of high-performance ceramics such as silicon nitride has been expanding in industrial equipment parts, including those for power semiconductor modules, insulating heat dissipation substrates for LED mounting, bearing balls for wind turbines and automotive engines, automotive components, and semiconductor manufacturing equipment. These ceramics are produced using the aforementioned heat treatment equipment, and temperature distribution management during heat treatment is crucial for maintaining high performance and good yield. Therefore, maintaining temperature measurement accuracy within and between thermocouple manufacturing batches is extremely important.

[0006] When using thermocouples, calibration becomes necessary to determine the relationship between the thermocouple's displayed value and the actual temperature. Calibration methods are broadly classified into the fixed-point method and the comparison method. The fixed-point method calibrates by assigning a correct temperature value at a fixed temperature point. The comparison method uses a standard thermocouple (reference line) to measure the temperature of an arbitrarily determined constant-temperature bath, calculates the error between this measurement and that of the thermocouple being calibrated, and then corrects for the difference. For C-type thermocouples, since measurements are taken above 1500℃, the comparison method is generally used.

[0007] It is believed that as long as the thermocouples used at high temperatures do not exhibit non-uniformity in the portions of their constituent filaments, the relationship between temperature and thermoelectric potential remains unchanged. Non-uniformity refers to "the change in thermoelectric potential per 1°C temperature difference" (see Non-Patent Document 1). That is, if a portion (non-uniform part) with this non-uniformity exists in the filament, creating a temperature gradient in that portion, the detected thermoelectric potential will show a different value compared to a thermocouple with a filament without this non-uniformity. For example, even with the aforementioned correction, the actual thermal gradient within the device is likely not reproducible, potentially resulting in a temperature deviation from the corrected value. Furthermore, if numerous portions of the filament exhibit non-uniformity, the difference from the baseline may increase excessively, potentially leading to an uncorrectable product.

[0008] On the other hand, in the case of medical needles, their shape is formed by cutting monofilaments to the desired length, then pressing and bending them. During pressing and bending, stress is applied to the cut monofilaments, requiring them to be resistant to cracking and free of cracks at the bends. Furthermore, medical needles are used as sutures during surgery. To suppress needle deflection and other behavioral variations caused by the forces applied during suturing, high tensile strength and low deviation are desirable. To prevent cracking during needle processing and the resulting decrease in yield due to cracks, and to obtain needles of stable quality, the cut monofilaments must be uniform; that is, the monofilaments used must be of uniform size.

[0009] One major cause of inhomogeneity is the fluctuation in the material composition of the monofilament. For example, in the case of Re-W, the manufacturing method typically employs powder metallurgy, which involves mixing W and Re powders, shaping, and sintering them. The sintering of Re-W is driven by solid-phase diffusion; therefore, it becomes impossible to achieve diffusion and homogenization (solid solution) of Re within the W matrix by considering the particle size distribution of each powder, the mixing state of the powders, and the shaping and sintering conditions. As a result, sometimes a phase region with a locally higher Re composition (a segregated σ phase) is formed. Furthermore, the formation of σ-phase segregated phases also creates regions with a lower-than-average Re composition ratio. When sintered bodies with such varying Re compositions are processed into bars or wires (wire-bars), inhomogeneity arises in the cross-section along the processing direction (axial) and in the cross-section perpendicular to the axial direction (radial). Regarding the segregated phase of the σ phase, for example, if the segregated phase of the σ phase is not uniformly present in a part, the wire is prone to breakage during wire drawing. Therefore, there are Re-W wires with the segregated phase of the σ phase having a maximum particle size of less than 10 μm and dispersed over a wide range (see Patent Document 1).

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent No. 4256126

[0013] Patent Document 2: Japanese Patent No. 5766833

[0014] Non-patent literature

[0015] Non-Patent Literature 1: Yoshio Monma and 5 others, “Deterioration Causes and Fluctuation Factors of PR Thermocouples Used in Long-Term Creep Tests”, Iron and Steel, 1989, No. 75, No. 4, pp. 665-672 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] The method described in Patent Document 1 aims to reduce the presence of the σ-phase segregated phase to a specified size rather than allowing it to exist unevenly in a specific region, thus dispersing it over a wide range and suppressing it to the point of no breakage in the wire, while allowing the presence of fine σ-phase segregated phase. However, even if the σ-phase segregated phase exists uniformly, variations in its proportion within a given volume can cause variations in Re (material change) in the axial and radial sections, potentially creating inhomogeneities.

[0018] exist Figure 3The example shown illustrates the Re content in the W matrix when a σ-phase segregated phase is present in a 26% Re-W line. This is based on semi-quantitative analysis using EPMA (accelerating voltage 15.0 kV, irradiation current 5.0 × E). -8 A. (Beam diameter less than 1 μm) indicates that the inclusion is a σ phase. Since the σ phase is harder than the matrix, it exists in this form as an inclusion. In the vicinity of this σ phase, the Re content in the matrix fluctuates. The presence of the σ phase thus causes fluctuations (inhomogeneity) in the Re content around it.

[0019] Methods for solving problems

[0020] To address the aforementioned issues, the rhenium-tungsten wire rod described in the embodiment is a wire rod made of a tungsten alloy containing rhenium, wherein the rhenium content is less than 30 wt% in any measurement region with a unit area of ​​1 μm in diameter within the wire rod body. Attached Figure Description

[0021] Figure 1 This is a simplified diagram of a temperature measurement system based on thermocouples.

[0022] Figure 2 A table showing the types of thermocouples.

[0023] Figure 3 A graph showing inclusions (σ phase) present in the ReW matrix and semi-quantitative analysis results (examples of previous materials).

[0024] Figure 4 This is a schematic diagram of the radial cross-section and surface layer of the sample.

[0025] Figure 5 This is a schematic diagram of the Re content measurement points.

[0026] Figure 6 This is a diagram illustrating the general particle size distribution.

[0027] Figure 7 This is a comparison graph of the tensile strength of Example 4 and Comparative Example 2. Detailed Implementation

[0028] Hereinafter, the rhenium-tungsten wire rod of the embodiment will be described with reference to the accompanying drawings. Hereinafter, the rhenium-tungsten wire rod will sometimes be referred to as a ReW wire rod. It should be noted that the drawings are schematic, and for example, the proportions of the dimensions of each part are not limited to those in the drawings.

[0029] exist Figure 4 An example radial cross-section of a sample taken from a ReW wire rod is shown. In the radial cross-section, the rhenium-tungsten wire rod body is represented by C. Additionally, in... Figure 4 The image shows an enlarged view of the portion denoted by A on the outer periphery of a rhenium-tungsten rod in a radial cross-section. (See image for details.) Figure 4As shown in the enlarged view, a surface mixture layer B is formed on the outer periphery of the rhenium-tungsten rod / wire body C. The surface mixture layer B contains W, O, and C as constituent elements. The diameter of the rod is preferably 0.1 mm or more and 5.0 mm or less, so that it can be used as a monofilament for various thermocouples and wire drawing processes. For example, in the case of thermocouples, if the wire diameter is less than 0.1 mm, it is prone to breakage due to evaporation during high-temperature use, resulting in a short lifespan. If the wire diameter exceeds 5.0 mm, the temperature of the object cannot be accurately measured due to the thermocouple's own heat capacity. A more preferred range is 0.2 mm or more and 3.5 mm or less. The ReW rod is processed to 0.1 mm or more and 5.0 mm or less through a forging (rotary forging: SW) process and a subsequent wire drawing (deep drawing: DW) process. The rod after SW and DW processes has a mixture layer on its surface. The mixture contains W, O, and C as constituent elements and is removed during product manufacturing, for example, through an electrolysis process. The main body portion after removing this mixture is used as a sample. Sampling locations are arbitrary, taking into account the yield rate of the finished product. However, for fluctuation evaluation, it is preferable to sample at two or more separate locations within a single ReW bar. Within a single ReW bar, there are sections where conditions become unstable, such as during the start-up and shutdown of the DW unit. These sections are not included in the sampling. The length of the unstable section varies depending on the layout and size of the unit.

[0030] The measurement can be of any cross-section of the collected sample, and the optimal method is selected based on the ease of sample processing. Figure 4 Such a radial cross-section. Observation becomes easy by embedding the sample in resin and then grinding and etching as needed. For the obtained measurement surface, for example, as... Figure 5 As shown, in the radial section of the rhenium-tungsten rod / wire body C, the Re content in a region with a diameter of 1 μm is quantified using an EPMA (electron beam microanalyzer) at 17 points: the intersections of four equally spaced concentric circles 2-5 with the X and Y axes (16 points in total) and the center point 1. Taking the measurement location as an example, any location can be measured; this location is preferred for unbiased measurement of the entire cross-section. Furthermore, regarding the radial section of the object being measured, it is not an arbitrary point on the rod, but rather a radial section at two or more separate locations.

[0031] In the ReW bar body of the embodiment, the rhenium content is less than 30 wt% in any measurement region with a unit area diameter of 1 μm. A Re content of 30 wt% or more exceeds the average addition amount. During the sintering process, insufficient diffusion of Re or W occurs, indicating fluctuations in the Re content along the axial and radial directions. These fluctuations in Re content are a cause of inhomogeneity, and in the ReW bar, fluctuations in thermoelectric potential due to location may occur.

[0032] Next, for the obtained Re values, the mean (Ave), standard deviation (Sd), and coefficient of variation (CV) calculated from Sd / Ave are determined. CV represents the ratio of the fluctuation relative to the mean data, allowing for comparison of fluctuations regardless of the Re ratio of the ReW bar.

[0033] The rhenium content CV of the ReW bar in the embodiment is preferably 0.10 or less. More preferably, it is 0.05 or less. When the CV is greater than 0.10, it indicates, for example, that even if the segregated σ phase is absent, the Re content fluctuates in both the axial and radial directions. This fluctuation in Re content is a cause of inhomogeneity; in the ReW bar, fluctuations in thermoelectric potential due to location may occur.

[0034] The Re content 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 less than 28 wt%. Regarding the Re content, the value obtained is obtained by inductively coupled plasma-mass spectrometry (ICP-MS), which is suitable for evaluating trace impurities, rather than by inductively coupled plasma-mass spectrometry (ICP-MS). Re improves the elongation of W at high temperatures and enhances processability. Furthermore, it increases strength through solid solution strengthening. However, when the content is less than 1 wt%, its effect is insufficient. For example, when used as a probe material, the deformation of the completed probe increases with the frequency of use, resulting in poor contact and reduced semiconductor inspection accuracy. When the Re content becomes greater than approximately 28 wt%, since it exceeds the solid solution limit with W, a σ-phase segregated phase is generated, easily leading to inhomogeneities in the wire rod. Because of the non-uniformity, fluctuations in thermoelectric potential and intensity occur. By making the Re content 1 wt% or more but less than 30 wt%, and 2 wt% or more but less than 28 wt%, for example, for thermocouples used in the +-side conductor and --side conductor (+-side conductor refers to the positive conductor, and --side conductor refers to the negative conductor) using the raw materials of this embodiment, and for probe ReW wire using the raw materials of this embodiment, it is possible to manufacture with high yield while ensuring thermoelectric potential characteristics (stability) and mechanical properties (strength, wear resistance).

[0035] The ReW wire rod of the embodiment may contain 30 wtppm or more and 90 wtppm or less of K as a dopant. By containing K, the tensile strength and creep strength at high temperatures can be improved by utilizing the doping effect. If the K content is less than 30 wtppm, the doping effect becomes insufficient. If it exceeds 90 wtppm, the processability decreases, which may significantly reduce the yield. By containing 30 wtppm or more and 90 wtppm or less of K as a dopant, for example, thermocouples used in the +-side conductor and --side conductor using this embodiment as the constituent material, and ReW wire for electron tube heaters using this embodiment as the material, it is possible to manufacture with high yield while ensuring high-temperature characteristics (preventing wire breakage and deformation during high-temperature use).

[0036] For the ReW bar implemented in this way, the standard deviation of the tensile strength can be made to be 35 N / mm. 2 The following describes how, by suppressing deviations in tensile strength, the processing stability of ReW wire bars can be improved, thus improving the yield of products using ReW wire bars (e.g., thermocouples, probes, medical needles). Furthermore, due to the stable tensile strength, the quality of medical needles is improved when used as a raw material. In the case of the ReW wire bar described in this embodiment, the standard deviation of tensile strength is 35 N / mm. 2 When the diameter of the wire rod is between 0.1 mm and 5.0 mm, better processing stability can be obtained.

[0037] Tensile strength was determined using a universal tensile and compression testing machine. Since the load is varied according to the wire diameter, the universal tensile and compression testing machine can have its load sensor adjusted based on the wire diameter, or the apparatus can be used separately. For example, a Shimadzu AG-I 5kN or a Minebea LTS 500N can be used. The test pieces are held in place by a flat plate with anti-slip sandpaper, and both ends are fixed to the apparatus. The distance between the marked points is set to 50 mm, and the tensile test is performed at a speed of 10 mm / min. If the fracture point is not within the marked points, the test is repeated.

[0038] According to this embodiment, a ReW wire bar that eliminates material fluctuations (non-uniformity) and significantly improves the stability of the thermoelectric potential can be used in high-temperature thermocouple applications. It can also be used in probe applications. The cross-section of the ReW wire bar is not limited to a circular cross-section; it can also have shapes other than a circle, such as ellipse or polygon.

[0039] Next, the manufacturing method of the ReW bar according to this embodiment will be described. There are no particular limitations on the manufacturing method; for example, the following methods can be listed.

[0040] W powder and Re powder are mixed in such a way 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 using water or an alcohol-based solution to form a slurry and then mixing is particularly preferred because it yields a powder with good dispersibility. Furthermore, to ensure the uniformity of powder batches, it is more preferable to dry the slurry and then combine the same batch of powder for dry mixing.

[0041] The mixed Re powder 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 The diagram illustrates the particle size distribution. The horizontal axis represents particle size (μm), the left vertical axis represents frequency (%), and the right vertical axis represents cumulative (%). Regarding the SD value, when d(84%) is set as the cumulative 84% particle size and d(16%) is set as the cumulative 16% particle size, the value calculated using SD = (d(84%) - d(16%)) / 2 becomes an indicator of the measured particle size distribution width. It should be noted that the particle size distribution is measured using laser diffraction. The amount of powder used in a single measurement is as recommended by the measuring apparatus. Generally, 0.02 g is recommended. Furthermore, for the sample being measured, it should be thoroughly stirred before measurement.

[0042] The W powder is either pure W powder free of unavoidable impurities or doped W powder containing a K amount considering the yield up to the wire rod. 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 as described above, the diffusion distance for the Re or W atoms to become more uniform increases, making it easier to form the σ phase.

[0043] The ratio of Re average particle size to W average particle size is preferably 0.4 or higher and 2.0 or lower. When the ratio of Re average particle size to W average particle size is less than 0.4 or greater than 2.0, the diffusion distance of Re atoms to the center of W particles or the diffusion distance of W atoms to the center of Re particles increases, which may make it easier to form the σ phase.

[0044] Next, the mixed powder is placed into a specified mold and pressed into shape. The pressing pressure is preferably 150 MPa or higher. For the molded body, to facilitate processing, pre-sintering can be performed in a hydrogen furnace at 1200–1400°C. The resulting molded body is then sintered in a hydrogen atmosphere, or in an inert gas atmosphere such as argon, or under vacuum. The sintering temperature is preferably 2500°C or higher. Below 2500°C, the diffusion of Re and W atoms during sintering is insufficient. The upper limit of the sintering temperature is 3400°C (below the melting point of W, which is 3422°C).

[0045] 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, which is expressed as [sintered body density / true density] × 100%. Furthermore, in a single sintered body, for example, the ratio of the density of the lowest portion, such as the lower end during electric sintering, to the average density of the entire sintered body is preferably 0.98 or higher. By ensuring that the relative density of the sintered body is 90% or higher and the ratio of the density of the lowest portion to the average density of the entire sintered body is 0.98 or higher, variations in the Re content can be suppressed.

[0046] The sintered body obtained in the main sintering process is subjected to a first SW process. The first SW process is preferably carried out at a heating temperature of 1300 to 1600°C. The reduction rate of cross-sectional area (area reduction rate) through one heat treatment (one heating) is preferably 5 to 15%.

[0047] It can also replace the first SW process and be used for calendering. Calendering is preferably performed at a heating temperature of 1200–1600°C. The surface area reduction rate in one heating cycle is preferably 40–75%. As the calender, a two-roll calender to a four-roll calender, a die-roll calender, etc., can be used. Calendering can significantly improve manufacturing efficiency. The first SW process can be combined with calendering.

[0048] For sintered bodies (ReW bars) that have undergone the first SW processing, or rolling processing, or a combination thereof, a second SW processing is performed. The second SW processing is preferably performed at a heating temperature of 1200–1500°C. The surface area reduction rate in one heating (single heating) is preferably about 5–20%.

[0049] For ReW bars that have completed the second SW process, a recrystallization treatment is then performed. The recrystallization treatment can be performed, for example, using a high-frequency heating device, in a hydrogen atmosphere, or in an inactive gas atmosphere such as argon, or in a vacuum, within a processing temperature range of 1800–2600°C.

[0050] The ReW bars 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 1200–1500°C. The surface area reduction rate in one heating is preferably about 10–30%. The third SW process is carried out until the ReW bars have a diameter suitable for wire drawing (preferably 2–4 mm).

[0051] For ReW bars that have completed the third SW processing, DW processing is performed, which involves repeatedly performing the following steps to enable smooth wire drawing (DW): applying lubricant to the surface, drying the lubricant and heating it to a processable temperature, and drawing the wire using a drawing die. A C-based lubricant with excellent heat resistance is preferred. The processing temperature is preferably below 1100°C. The processing temperature is set according to the wire diameter being DW. The reduction in surface area per die is preferably 10-35%. Annealing or surface grinding (e.g., electrolysis) processes may be added during the DW process as needed.

[0052] For an appropriate amount of ReW wire rods that have completed SW or DW processes, necessary steps such as heat treatment and surface grinding are performed to prepare raw materials for thermocouples. Then, thermocouples are manufactured using a prescribed combination.

[0053] (Example)

[0054] Examples 1-4 were manufactured using the aforementioned processing conditions to produce sintered bodies. Examples 5 and Comparative Example 1 were manufactured using Re and W powder sizes as existing conditions. Examples 6 and Comparative Example 2 were manufactured using W powder sizes as existing conditions. The analytical results for each example are shown in Table 1. The analysis of Re and K was performed using inductively coupled plasma-mass spectrometry (ICP-MS) instead of ICP-MS. It should be noted that the lower detection limit for K is 5 wtppm; values ​​below 5 wtppm without addition are marked as "-".

[0055] [Table 1]

[0056]

[0057] Each sintered body was processed to a diameter of 0.5 mm using the aforementioned processing steps. Examples 2 and 4, and Comparative Example 2, were processed to diameters of 5.0 mm and 0.1 mm, respectively. After processing, samples were taken from both ends of each wire rod using the aforementioned method. For one dimension, 17 points × 2 samples = a total of 34 points were used. EPMA (JXA-8100, manufactured by Nippon Electronics Co., Ltd., magnification 1000x, accelerating voltage 15.0 kV, irradiation current 5.0 × E) was used. -8A) Analyze the Re content in a region with a diameter of 1 μm. Then, calculate the CV from the analytical values. The evaluation results are shown in Table 2. "Less than 30 wt% of Re content at all measurement points" is indicated by "○", and "more than 30 wt% at one point" is indicated by "×". The diagonal lines in the table indicate the size of unprepared samples. Additionally, cases where K was not added and the analytical value was less than 5 wtppm are indicated by "-".

[0058] [Table 2]

[0059]

[0060] Next, using wire rods machined to a diameter of 0.5 mm, thermocouples were trial-produced using combinations shown in Table 3 (Trial Productions 1-8) through the prescribed procedures. Trial Production 2 also trial-produced thermocouples with diameters of 0.1 mm (Trial Production 2-2) and 5 mm (Trial Production 2-3). Regarding the raw materials, two samples were taken from each end. Four thermocouples were produced for each combination, ensuring no repetition in the positional combinations (front-front, front-back, back-front, back-back). One end of each wire rod was designated as the front, and the other end as the back. For example, front-front represents a combination of the front of one wire rod and the front of another wire rod. For each trial production, the thermocouples were placed in an electric furnace along with calibrated platinum-rhodium thermocouples, and heated at a temperature of 1600°C (as indicated by the platinum-rhodium thermocouple display). Figure 1 The system shown measures the thermoelectric potential and calculates the temperature (JISC1602). Figure 1 The temperature measurement system shown includes: a positive "+" side conductor and a negative "-" side conductor of a thermocouple, a temperature sensing contact, a reference contact, a measuring instrument, and compensating wires. The temperature sensing contact is formed by welding the front end of the positive side conductor of the thermocouple to the front end of the negative side conductor of the thermocouple. The positive side conductor and the negative side conductor of the thermocouple are respectively connected to the reference contact. The reference contact and the measuring instrument are connected using compensating wires. The maximum and minimum temperature difference (Max-Min) obtained using each prototype is shown in Table 3. As can be seen from the table, for the ReW bar involved in the embodiment, the Re fluctuation of the main body is suppressed, and the temperature fluctuation of the thermocouple using the same bar is suppressed. However, the ReW bar of the comparative example does not suppress the Re fluctuation, and the temperature fluctuation of the thermocouple using the same bar is large. Therefore, the yield of the embodiment as a thermocouple is significantly improved.

[0061] [Table 3]

[0062]

[0063] In addition, tensile strength was compared in Example 4 (0.5 mm diameter) and Comparative Example 2 (0.5 mm diameter). For the tensile specimens, 20 samples were collected evenly along their entire length. A universal tensile-compression testing machine (Shimadzu AG-I 5kN) was used. The specimens were held in place by a flat plate with anti-slip sandpaper, and both ends were fixed to the device. The distance between the markings was set to 50 mm, and the tensile test was performed at a speed of 10 mm / min. The results are shown below. Figure 7 Although the average tensile strength was not different, the standard deviation, representing fluctuation, was significantly smaller in Example 4 compared to Comparative Example 2. Therefore, the improved condition stability when using these examples as raw materials contributes to improved yield. Furthermore, the standard deviation of tensile strength was also 35 N / mm² in the other examples. 2 the following.

[0064] The improved condition stability during processing using the example as raw material contributes to improved yield. When the wire bar is cut into multiple pieces to manufacture medical needles, needles with stable tensile strength can be obtained.

[0065] The above examples illustrate several embodiments of the present invention. These embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These variations of the embodiments are included in the scope and spirit of the invention, and are included within the scope of the invention and its equivalents as described in the patent claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

[0066] Explanation of reference numerals in the attached figures

[0067] A…Rhenium-tungsten rod / wire outer periphery

[0068] B… Surface Mixture Layer

[0069] C…Rhenium-tungsten rod and wire body

[0070] 1…Center point of radial section

[0071] 2, 3, 4, 5… concentric circles of radial sections

[0072] X, Y... X-axis and Y-axis of radial section

Claims

1. A rhenium-tungsten wire rod, which is a wire rod made of a tungsten alloy containing more than 1 wt% and less than 30 wt% rhenium, with the remainder consisting of unavoidable impurities and tungsten. in, Rhenium powder with an average particle size of less than 8 μm and a particle size distribution SD value of less than 11 μm and tungsten powder with an average particle size of less than 16 μm and a particle size distribution SD value of less than 13 μm are mixed with a rhenium content of more than 1 wt% and less than 30 wt% to produce a sintered body. In any radial section separated from the main body of the wire rod, within any measurement region with a unit area of ​​1μm in diameter, at 16 points (16 intersections of 4 equally spaced concentric circles with the X-axis and Y-axis, plus the center point) of any two or more separate sections, the rhenium content is less than 30wt%. In the semi-quantitative analysis using EPMA, the amount of Re in a region with a diameter of 1 μm was quantified, and the coefficient of variation of the rhenium content was less than 0.

10.

2. The rhenium-tungsten wire rod according to claim 1, wherein, The rhenium content is above 2 wt% and below 28 wt%.

3. The rhenium-tungsten wire rod according to any one of claims 1 to 2, wherein, The tungsten alloy also contains potassium, with the potassium (K) content being above 30 wtppm and below 90 wtppm.

4. The rhenium-tungsten wire rod according to any one of claims 1 to 2, wherein, The diameter of the wire bar is 0.1 mm or more and 5.0 mm or less.

5. The rhenium-tungsten wire rod according to claim 4, wherein, The standard deviation of the tensile strength of the wire bar is 35 N / mm. 2 the following.

6. A thermocouple using a rhenium-tungsten wire rod according to any one of claims 1 to 5.

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