Tungsten wire and tungsten wire processing method and electrolytic wire using the same

Abstract

The tungsten wire of the embodiment is a tungsten wire made of a W alloy containing Re, and at least a portion of its surface has a mixture containing W, C, and O as constituent elements. When the radial cross-sectional thickness of the mixture is set to A mm and the diameter of the tungsten wire is set to B mm, the average value of the ratio A / B of A to B is 0.3% or more and 0.8% or less.

Description

Technical Field

[0001] The embodiments described later relate to tungsten wires, tungsten wire processing methods using the same, and electrolytic wires. Background Technology

[0002] Traditionally, various tungsten (W) wires have been used as cathode heaters for TV electron guns, filament materials for automotive lights or household appliances, high-temperature structural components, contact materials, and discharge electrodes. Among these, tungsten alloy (ReW) wires containing a specified amount of rhenium (Re) exhibit excellent high-temperature strength and ductility after recrystallization, and are widely used in electron tube heaters and filament materials for vibration-damping light bulbs. Furthermore, their excellent resistance and wear resistance make them suitable for use as the material for the pins (probe pins) of probe cards used for electrical characteristic testing of high-temperature thermocouples, particularly semiconductor integrated circuit (LSI) wafers. This testing is performed by directly pressing the probe pins, whose tips have been chemically or mechanically shaped for optimal contact, against the terminals of the object being tested.

[0003] With the increasing integration of semiconductors and the development of miniaturization technology, probe cards are constantly requiring narrower pin pitches and smaller diameters. Currently, ReW pins with wire diameters of 0.02mm to 0.04mm are also used. If the wire diameter of the probe pins is reduced, the number of pins per unit area can be increased, which is advantageous for the inspection of highly integrated LSIs.

[0004] In the case of such small-diameter W-shaped wires (fine wires), the sintered body is first subjected to forging, wire drawing (drawing) and other processes (one-time processing) to produce single wires within a certain diameter range (0.3mm to 1.5mm). Then, an appropriate number of single wires undergo additional drawing and heat treatment processes to produce tungsten wires (wire diameter). During this wire thinning process, wire breakage during drawing and fine linear irregularities (die marks: described in JIS H0201 718) on the material surface in the drawing direction are prone to occur. In multi-stage wire drawing machines that utilize multiple dies, wire breakage during the drawing process, in particular, significantly reduces the yield. Furthermore, repairing and re-running broken wires increases the number of processing steps. Die marks, which cannot be removed even by subsequent surface grinding and probe pin processing, become defects, resulting in unsatisfactory yield and processing costs.

[0005] In previous strategies for dealing with wire breakage, some methods involved controlling the recrystallization number during heat treatment in intermediate processes to improve processability. For example, with ReW wire: when the cross-sectional area reduction rate (reduction ratio) from the sintered body of the formed product exceeds 75% but reaches below 90%, a final recrystallization treatment is implemented to adjust the recrystallization number in the center and surface of the formed product to 500 particles / mm. 2 ~800 pieces / mm 2(Refer to Patent Document 1).

[0006] In addition, some methods improve processability by controlling the Re segregation phase (σ phase) in the W matrix. For example, if the σ phase is not uniform, it is easy to break the wire starting from the σ phase during the wire drawing process. Therefore, there are ReW wires with the maximum particle size of the σ phase set to less than 10 μm (see Patent Document 2).

[0007] Furthermore, in secondary processing such as coil manufacturing, if lubricant containing graphite (C) remains in the recesses of the blank surface, this C component can sometimes contaminate the W at the high temperatures during processing, causing it to become brittle. Therefore, some methods prevent embrittlement by controlling surface roughness. For example, there is a ReW wire where, after being drawn to a wire diameter of 0.175 mm, the average spacing and maximum height of the unevenness on the blank surface are adjusted to a specified range by electrolysis (see Patent Document 3).

[0008] Regarding die marks, they are generally removed by a chemical polishing (electrolysis) process after the wire has been drawn to a specified size. For example, there is a method for manufacturing W electrodes that specifies the average roughness of the center wire and the average roughness of ten points, and electrolyzes them to these values ​​(see Patent Document 4).

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent No. 2637255

[0012] Patent Document 2: Japanese Patent No. 4256126

[0013] Patent Document 3: Japanese Patent No. 3803675

[0014] Patent Document 4: Japanese Patent Application Publication No. 2000-100377 Summary of the Invention

[0015] The problem that the invention aims to solve

[0016] The method described in Patent Document 1, which controls the number of crystals through heat treatment in an intermediate process, requires a specified reduction rate of surface area from the sintered body to the recrystallization treatment. Furthermore, there are effects related to processing up to the aforementioned blank size with a diameter of 1.0 mm. Considering applications with fine filaments, the cross-sectional area of ​​the sintered body needs to be very small, resulting in very poor manufacturability. Additionally, because the size decreases during recrystallization, the strength at the finished size is likely to decrease significantly. For example, probe pins require strength that prevents deformation due to contact with the terminals of the object being inspected, making their use difficult.

[0017] The method described in Patent Document 2 is very effective against fractures originating from the σ phase. However, the segregation of the σ phase is controlled during the processes up to the sintered body manufacturing stage, and subsequent processes are the same as before. Therefore, wire breakage caused by factors such as die marks is not suppressed.

[0018] Patent Document 3 describes a method that prevents embrittlement caused by the reaction between W and C by setting the filament to have favorable surface properties, allowing residual C on the surface to easily evaporate during high-temperature heating in secondary processing such as winding. In the filament processing of Patent Document 3, C-based lubricants with excellent heat resistance are typically used. The strategy of evaporating C would worsen lubricity, creating risks such as sintering of the wire and the drawing die.

[0019] Patent document 4 describes a method for removing and managing mold marks, but does not describe the suppression of mold marks.

[0020] The problem to be solved by the present invention is to provide a W-type wire for wire drawing that improves the resistance to breakage and surface unevenness during wire drawing.

[0021] Methods for solving problems

[0022] To address the aforementioned issues, the tungsten (W) wire of the embodiment is a W wire composed of a W alloy containing rhenium (Re), and at least a portion of its surface has a mixture containing W, C, and O as constituent elements. When the radial cross-sectional thickness of the mixture is set to A mm and the diameter of the W wire is set to B mm, the average value of the ratio A / B of A to B is 0.3% or more and 0.8% or less. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating an example of a tungsten monofilament used in wire drawing according to an embodiment.

[0024] Figure 2 This is a radial cross-sectional view of a tungsten monofilament. Figure 1 (The XX section).

[0025] Figure 3 This is a schematic diagram of the mixture at any point A on the radial cross section.

[0026] Figure 4-1 This is a graph showing the change in oxygen content of the mixture on a radial cross section in Comparative Example 3 (EPMA line analysis).

[0027] Figure 4-2 This is a graph showing the change in oxygen content of the mixture on a radial cross section in Example 2 (EPMA line analysis).

[0028] Figure 5 It is a cross-sectional schematic diagram showing the deformation model of the wire in the wire drawing process and the stress at the center and surface.

[0029] Figure 6-1 This is a schematic diagram of Comparative Example 3 used to show the different shapes of the mixture layers in Comparative Example 3 and Example 2 in radial cross-section.

[0030] Figure 6-2 This is a schematic diagram of Example 2 used to illustrate the different shapes of the mixture layers in Comparative Example 3 and Example 2 on a radial cross-section.

[0031] Figure 7-1 It is a sectional view showing the radial cross-sectional shape (overall view) of the wire body before electrolytic grinding.

[0032] Figure 7-2 It is a sectional view showing the radial cross-sectional shape (overall view) of the wire body after electrolytic grinding. Detailed Implementation

[0033] Hereinafter, the tungsten wire for wire drawing according to the embodiments will be described with reference to the accompanying drawings. Hereafter, the tungsten wire for wire drawing will sometimes be referred to as W-wire for wire drawing. Furthermore, the drawings are schematic, and for example, the ratios of the dimensions of each part are not limited to those in the drawings.

[0034] Figure 1 This section presents an example of a W-wire sample selected from the W-wire used in the wire drawing process. The sample length is preferably 100mm to 150mm, allowing for observation of multiple cross-sections through resin embedding. The sampling location is arbitrary, but for high yield utilization in subsequent processes, sampling from locations other than the front and rear ends is preferable. The front and rear ends are excluded from sampling because conditions become unstable due to the start-up and shutdown of the wire drawing device. The length of the unstable portion varies depending on the layout and size of the device. The diameter of the selected sample in the XY direction is measured using a micrometer. Measurements are performed at three locations, and the average of the six obtained data points is taken as the diameter B (mm) of each sample.

[0035] Figure 2 express Figure 1 XX section diagram (section perpendicular to the drawing direction: radial section). As shown in the figure, draw a straight line that passes through the center and divides it into eight equal parts, and set the intersection points with the outer perimeter as A1 to A8. Observe the above mixture at eight equally spaced points on this arbitrary outer perimeter. Figure 3 A schematic diagram showing any location of the mixture described above. For example, by embedding the sample in resin and grinding, the image becomes clearer, but sometimes the mixture peels off during this process. Such portions are removed from the measurement site. Using SEM images viewed at 10000x magnification, the thickest part of the mixture (A) is determined within a 30μm × 30μm area. max ) and the thinnest part (A minThe thickness of the sample is calculated, and its average value is taken as the thickness of the mixture. Similarly, the thicknesses at 8 points (A1 to A8) on the same cross section are calculated. The thickness at any one point is taken as A (mm). Using the observed sample diameter B, the ratio A / B (%) is calculated. There are 8 data points for A / B on the same cross section. Based on the number of observed samples (n), the number of data points for A / B is "8×n".

[0036] The average A / B ratio of the tungsten wire in the embodiment is 0.3% or more and 0.8% or less (0.003 or more and 0.008 or less). More preferably, it is 0.3% or more and 0.6% or less (0.003 or more and 0.006 or less). If the average A / B ratio is less than 0.3%, wire breakage occurs during drawing; if the A / B ratio is greater than 0.8%, the rate of die marks increases. If the average A / B ratio is within the range of 0.3% or more and 0.8% or less, wire breakage and die marks during drawing can be suppressed.

[0037] Figure 4 Figure 4-1 and Figure 4-2 The result of the analysis of the O (oxygen) content in the mixture at a radial cross section with a diameter of 0.80 mm is shown as an example. Figure 4-1 This is a diagram of a part measured in Comparative Example 3. Figure 4-2 This is a diagram of a region measured in Example 2. Analysis was performed using an EPMA (Electron X-ray Microscope: JXA-8100, Nippon Electron Ltd.), with an accelerating voltage of 15 kV and a sample current of 5.0 × 10⁻⁶ kV. -8 A. The analysis was performed under the following conditions: electron beam diameter: Spot (~Φ1μm), analysis time: 500ms / point, scanning mode: stage scanning, analysis distance: 29.7μm (151 points). The vertical axis represents the count value, and the horizontal axis represents the distance in the observation direction. Comparative Example 3 will sometimes be referred to as the conventional W-wire.

[0038] Regarding the A / B ratio of this observation site, the content of W filament was 1.4% (0.014) in the conventional case and 0.7% (0.007) in Example 2. In the conventional W filament mixture, O varied along the cross-sectional direction (length L of the mixture), while in Example 2 it was stable. O in the mixture exists as a compound (oxide) with W. The oxide composition of W includes WO3 and W... 20 O 58 W 18 O 49 WO2 and W3O have different physical properties (strength, adhesion). In the past, the variation of O in the cross-section of W wire mixtures indicated that there were oxides with different compositions within the cross-section. As a result, deformation during wire drawing caused inhomogeneity, which became the cause of cracking or peeling of the oxide film. The peeled-off parts are highly likely to become die marks.

[0039] Figure 5 This represents the deformation model of the wire during the wire drawing process and the stress at the center and on the surface. Shear force is generated on the surface layer of the wire through contact with the drawing die during drawing. The outer periphery 1 also undergoes plastic deformation due to shear force. Therefore, the material does not elongate uniformly in the radial section, but rather moves further forward towards the center 2. When the surface mixture is thicker, the shear deformation of the mixture layer is greater compared to when the surface mixture is thinner. Therefore, when the layer is thicker, the shear force acting between W and the mixture is greater. This is the cause of localized detachment of the mixture. The presence of oxides with different compositions within the aforementioned mixture makes detachment more likely.

[0040] When the average A / B ratio is less than 0.3% (0.003), W and C react directly, increasing the risk of embrittlement. Additionally, lubrication may not be adequately ensured.

[0041] Next, for the same cross-section (data point 8), the mean (Ave), standard deviation (Sd), and coefficient of variation (CV) calculated from Sd / Ave are obtained for A / B. CV represents the ratio of the deviation of the data from the mean, and can compare deviations regardless of the layer thickness.

[0042] The CV (conversion value) of the tungsten wire on the same cross-section in the embodiment is preferably 0.30 or less. More preferably, it is 0.20 or less. If the CV is greater than 0.30, the possibility of breakage or die marks during wire drawing increases. If the thickness deviation of the mixture is large, the A / B ratio may become partially large or small. Such a partial deviation carries the risk of defects such as the aforementioned mixture shedding or cracking, and embrittlement of the W wire.

[0043] In Figure 6 ( Figure 6-1 and Figure 6-2 In the example, a schematic diagram is used to illustrate the different shapes of mixtures with a radial cross-section of 0.8 mm in diameter. For actual samples, the outer perimeter length of the cross-section of 60 μm was observed using SEM at 5000x magnification, along with the thickness difference of the filaments (A). max -A min The thickness of Example 1 is 6 μm, while that of Example 2 is 1 μm, a significant difference. Furthermore, the CV (coefficient of thickness) of this cross-section is 0.5 for the conventional wire and 0.1 for Example 2. With a large CV, not only the thickness difference (deviation) at the outer periphery can be large, but the thickness difference (deviation) at the same location can also be significant. Such a mixed layer results in uneven processing force during wire drawing, making it prone to cracking or detachment.

[0044] The cross-sections for which the above A / B data were obtained were subjected to energy-dispersive X-ray analysis using a Phenom ProX desktop scanning electron microscope (EDS: accelerating voltage 15 kV, magnification 10,000x, measurement range 30 μm × 30 μm). The A of the mixture within the measurement range... max and A min The thickness of the mixture was measured at its central point along the thickness direction, and the average value was calculated. Measurements were taken at any 5 out of 8 locations (A1–A8) on the cross-section, and the ratio (Owt% / Wwt%) of each location was calculated from the obtained W (wt%) and O (wt%) data. Furthermore, W (wt%) represents the mass percentage of tungsten, and O (wt%) represents the mass percentage of oxygen.

[0045] Regarding the W-shaped wire in the embodiment, the average value of the ratio of O (wt%) to W (wt%) (Owt%) in the central part of the thickness direction of the mixture is preferably 0.10 or less. If it exceeds 0.10, the formation of WO3 in the W oxide may be accelerated. Because WO3 is very brittle, the mixture is prone to detachment. The lower limit value is not particularly limited, but it is preferably 0.05 or more. If it is less than 0.05, the formation of W oxide is insufficient, and the reaction between C and W in the C layer is likely to occur.

[0046] The Re content in the W wire of the embodiment is preferably 1 wt% or more and 30 wt% or less, more preferably 2 wt% or more and 28 wt% or less. When the Re content is less than 1 wt%, the strength decreases. For example, when used as a probe pin, the amount of deformation increases with the frequency of use, resulting in poor contact and reduced inspection accuracy of the semiconductor. If the Re content is greater than about 28 wt%, it exceeds the solid solution limit with W, and therefore, inhomogeneity of the σ phase is easily generated. This phase may become the starting point of fracture during wire drawing, resulting in a significant decrease in the yield. By setting the Re content to 1 wt% or more and 30 wt% or less, or 2 wt% or more and 28 wt% or less, for example, for electrolytic wire used as a blank for probe pins according to this embodiment, it is possible to manufacture with a high yield while ensuring mechanical properties (strength, wear resistance).

[0047] The W-wire in this embodiment may also contain 30 wtppm or more but less than 90 wtppm of K as a dopant. By containing K, the tensile strength and creep strength at high temperatures are improved by utilizing the doping effect. If the K content is less than 30 wtppm, the doping effect is insufficient. If it exceeds 90 wtppm, the processability may decrease, resulting in a significant decrease in yield. By using K as a dopant, for example, for filaments used in thermocouples or electron tube heaters using this embodiment as the blank, it is possible to manufacture them with a high yield while ensuring high-temperature characteristics (preventing wire breakage and deformation during high-temperature use).

[0048] According to this embodiment, a tungsten wire for wire drawing can be produced that significantly contributes to improving yield by suppressing breakage and surface unevenness during filament processing. It can be applied to electrolytic wire for probe pins. Additionally, it can be applied to thermocouples for high-temperature applications.

[0049] Next, the manufacturing method of the W-wire for wire drawing according to this embodiment will be described. The manufacturing method is not particularly limited, and the following methods can be cited as examples.

[0050] W powder and Re powder are mixed with a Re content of 1 wt% or more, for example, 3 wt% or more and 30 wt% or less. The mixing method is not particularly limited, but from the viewpoint of obtaining powder with good dispersibility, a method of preparing the powder into a slurry using water or an alcohol-based solution and then mixing it is particularly preferred. The maximum particle size of the mixed Re powder is preferably less than 100 μm. Furthermore, the average particle size is preferably less than 20 μm. The W powder is pure W powder with unavoidable impurities removed, or doped W powder containing a K amount considering the yield up to the filament. The average particle size of the W powder is preferably less than 30 μm. If the maximum or average particle size of the Re powder is as described above or higher, coarse σ phase is easily formed. Furthermore, if the average particle size of the W powder is as described above or higher, the formability decreases during subsequent stamping processes, and the molded body is prone to breakage, notches, cracks, etc.

[0051] For example, in the case of manufacturing W-Re mixed powder with a Re content exceeding 18 wt%, firstly, after producing a ReW alloy with a Re content of less than 18 wt% by means of powder metallurgy or melting, it is then finely pulverized using conventional methods. Furthermore, there are methods for mixing insufficient amounts of Re to achieve the desired composition. Later, tungsten wire containing Re is sometimes referred to as ReW wire.

[0052] Next, the mixed powder is placed into a specified mold and stamped. The stamping pressure is preferably 100 MPa or higher. For ease of handling, the formed body can also be pre-sintered in a hydrogen furnace at 1200°C to 1400°C. The resulting formed body is then sintered in a hydrogen atmosphere, an inert gas atmosphere such as argon, or under vacuum. The sintering temperature is preferably 2125°C or higher. If the temperature is below 2125°C, the densification achieved by sintering will not be sufficient. The upper limit of the sintering temperature is 3400°C (the melting point of W is below 3422°C). The relative density after sintering (relative density (%) relative to true density = [sintered body density / true density] × 100%) is preferably 90% or higher. By setting the relative density of the sintered body to 90% or higher, cracking, notches, and breakage can be reduced in subsequent forging (SW) processes.

[0053] Forming and sintering can also be carried out simultaneously by hot pressing under a hydrogen atmosphere, an inert gas atmosphere such as argon, or a vacuum. The pressing pressure is preferably 100 MPa or higher, and the heating temperature is preferably 1700℃~2825℃. This hot pressing method can obtain a dense sintered body even at relatively low temperatures.

[0054] The sintered body obtained in this sintering process is subjected to a first forging process. The first forging process is preferably carried out at a heating temperature of 1300°C to 1600°C. The reduction rate of cross-sectional area (area reduction rate) achieved through a single heat treatment (one-time heating) is preferably 5% to 15%.

[0055] Rolling can also replace the first type of forging. Rolling is preferably performed at a heating temperature of 1200℃ to 1600℃. The surface area reduction during a single heating is preferably 40% to 75%. Two-roll mills, four-roll mills, or knurling mills can be used as the rolling mill. Rolling significantly improves manufacturing efficiency. The first type of forging and rolling can also be combined.

[0056] A second forging process is performed on the sintered body (ReW bar) that has undergone the first forging, rolling, or a combination thereof. The second forging is preferably performed at a heating temperature of 1200°C to 1500°C. The surface area reduction during a single heating is preferably around 5% to 20%.

[0057] Next, the ReW bar stock, after completing the second forging process, undergoes recrystallization treatment. This recrystallization treatment can be performed, for example, using a high-frequency heating device in a hydrogen atmosphere, an inert gas atmosphere such as argon, or under vacuum, within a treatment temperature range of 1800°C to 2600°C.

[0058] The ReW bars that have undergone recrystallization treatment are then subjected to a third forging process. This third forging is preferably performed at a heating temperature of 1200℃ to 1500℃. The surface area reduction during a single heating cycle is preferably around 10% to 30%. The third forging is continued until the ReW bars reach a diameter suitable for wire drawing (preferably 2mm to 4mm).

[0059] ReW bars that have undergone the third forging process are capable of smooth wire drawing, so a first wire drawing process is performed until the diameter becomes 0.7 mm to 1.2 mm. In this first wire drawing process, the following steps are repeated: applying lubricant to the surface, drying the lubricant and heating it to a workable temperature, and drawing the wire using a drawing die. A C-based lubricant with excellent heat resistance is preferred. The processing temperature is preferably 800°C to 1100°C. The workable temperature varies depending on the diameter; the larger the diameter, the higher the workable temperature. If the temperature is lower than the workable temperature, cracking or wire breakage is more likely. If the temperature is higher than the workable temperature, sintering between the wire and the drawing die, or a decrease in the wire's deformation resistance, can occur, resulting in a change in the diameter of the drawn wire (the diameter of the drawn wire is smaller than the die's aperture). The reduction rate is preferably 15% to 35%. If it is less than 15%, internal and external structural differences or residual stress will occur during processing, leading to cracking. If the draw ratio is greater than 35%, the drawing force will be too high, resulting in a significant change in the diameter of the drawn wire and causing breakage. The drawing speed is determined by the capacity of the heating device, the distance from the device to the drawing die, and the balance of the reduction ratio.

[0060] Depending on the processing conditions (heating temperature, atmosphere, etc.), the composition of the mixture formed on the surface, especially the W oxide, varies. Due to repeated heating, the processing conditions are prone to variation. Furthermore, the optimal processing temperature changes due to variations in diameter. Especially with larger diameters, higher heating temperatures are required, and conditions are easily subject to change. Therefore, it is highly likely that different W oxide compositions will form as the thickness increases. Therefore, for wires already drawn to a diameter of 0.7 mm to 1.2 mm, grinding is performed to remove the mixture formed on the surface during previous processing, or the unevenness of the wire surface, in a single operation.

[0061] Grinding processes include, for example, electrochemical grinding (electrolytic grinding) in a 7wt% to 15wt% sodium hydroxide aqueous solution. The surface reduction rate during grinding is preferably 10% to 25%. If it is less than 10%, it may not be able to remove the surface irregularities and adhering mixtures generated during the forging and first wire drawing processes. If it exceeds 25%, the material yield deteriorates. In the case of electrolytic grinding, the processing speed is preferably 0.5 m / min to 2.0 m / min. If it is slower than 0.5 m / min, the number of processing steps increases significantly. If it exceeds 2.0 m / min, the electrolysis rate per unit time becomes large, resulting in rapid electrolysis, and the correction of the wire cross-sectional shape may be insufficient. Alternatively, a very large apparatus may be required. (See Figure 7...) Figure 7-1 and Figure 7-2 The diagram illustrates the results of observing the radial cross-sectional shape of the ReW filament body before and after electropolishing. Electropolishing eliminates the unevenness on the filament surface.

[0062] After grinding, the line undergoes a heat treatment in an atmospheric furnace to form a dense and homogeneous oxide layer on the surface. The heating temperature is preferably 700°C to 1100°C. If the temperature is lower than 700°C, oxide formation is difficult. If the temperature is higher than 1100°C, the oxide composition deviates. The processing speed is preferably 5 m / min to 20 m / min. If the speed is below 5 m / min, the number of processing steps increases significantly. If the speed is above 20 m / min, greater heat is required to raise the temperature, and the oxide layer easily becomes heterogeneous. Alternatively, the apparatus needs to be very large.

[0063] To form and bond the C layer over the oxide layer, a process is performed involving applying a lubricant to the surface, drying the lubricant and heating it to a processable temperature, and then drawing the material using a drawing die. This bonding of the C layer prevents changes or peeling of the oxide layer in subsequent processes. The reduction ratio is preferably 10% to 30%, more preferably 15% to 25%. If it is less than 10%, the oxide layer and the C layer may not bond sufficiently. If it is greater than 30%, the drawing force is too high, which may cause peeling of the layer on the die entry side.

[0064] Next, a second wire drawing process is performed. The heating temperature is preferably below 1000°C. If it exceeds 1000°C, the carbon in the sealed C layer may react with oxygen in the air to become CO2 and detach, causing the C layer to become thinner and the composition of the underlying oxide layer to change. The reduction rate of the second wire drawing process is the same as that of the first wire drawing process, preferably 15% to 35%. Through the second wire drawing process, a wire with a diameter of 0.3 mm to 1.0 mm is produced for wire drawing.

[0065] Subsequently, necessary processes such as drawing and heat treatment are added to an appropriate amount of W-wire for wire drawing to produce W-wire with the required properties (strength, hardness, etc.) at a specified wire diameter. This is then electrolytically ground to produce electrolytic wire.

[0066] <Example>

[0067] Using the powder mixing, molding, and sintering methods described above, sintered bodies with the compositions shown in Table 1 were manufactured. Examples 1-6 underwent a first forging process, a rolling process, a second forging process, a recrystallization treatment, a third forging process, a first wire drawing process, an electrolytic grinding process, a heat treatment for forming an oxide layer, a wire drawing process to seal the C layer, and a second wire drawing process, resulting in the diameters shown in Table 1.

[0068] Example 7 reduced the surface area reduction to 8% through an electrolytic polishing process following the first wire drawing. Comparative Example 1 reduced the mixture layer by lowering the processing temperature to 680°C–700°C through a heat treatment for forming the oxide layer after electrolytic polishing. Comparative Example 2 thickened the mixture layer by increasing the heating temperature to 1150°C through a second wire drawing process. Comparative Examples 3–5 performed a second wire drawing process as before after the first wire drawing, following conventional processing steps. The wires were processed to the diameters shown in Table 1. The analysis of Re and K was performed not using inductively coupled plasma-mass spectrometry (ICP-MS), which is suitable for evaluating trace impurities, but rather using inductively coupled plasma-optical emission spectrometry (ICP-OES), which is suitable for evaluating constituent elements. Furthermore, the lower detection limit for K was 5 wtppm; cases where no K was added but the analytical value was below 5 wtppm were recorded as "-".

[0069] [Table 1]

[0070] Table 1

[0071] Re(wt%) K (wt ppm) diameter Example 1 3％ - 0.3mm Example 2 3％ - 0.8mm Example 3 3％ - 1.0mm Example 4 3％ 61ppm 0.8mm Example 5 5％ - 0.8mm Example 6 26％ - 0.8mm Example 7 3％ - 0.8mm Electrolytic grinding has a low surface area reduction rate Comparative Example 1 3％ - 0.8mm Low oxide layer formation processing temperature Comparative Example 2 3％ - 0.3mm The second wire drawing heating temperature is high. Comparative Example 3 3％ - 0.8mm Previous processing Comparative Example 4 3％ 54ppm 0.8mm Previous processing Comparative Example 5 26％ - 0.8mm Previous processing

[0072] Samples were taken from the obtained wire, and the A / B ratio, CV, and Owt% / Wwt% were evaluated using the methods described above. Furthermore, the mixture contained W, C, and O as constituent sources. Using 1 kg of each of these wires, the wire was drawn to a diameter of 0.08 mm. The breakage rate during the drawing process and the finished appearance defect rate were investigated.

[0073] The breakage rate is calculated by dividing the total amount of broken wires by the weight of the wires used in the process (1 kg). The breakage rate is determined by counting the weight of broken wires as defective weights when the weight of the broken wires is ≤0.05 kg.

[0074] Regarding the appearance defect rate, 100m of each end of the drawn wire was cut into 50mm lengths, and the mixture was removed by boiling with caustic soda. Then, the wire was observed under a 30x microscope. In cases where identifiable defects or unevenness were found on the surface, the 50mm length was counted as mold mark defects. The length of the defect was calculated as defect length / evaluation length (200m). The results are shown in Table 2.

[0075] [Table 2]

[0076] Table 2

[0077]

[0078] As shown in the table, the W-wire used in the wire drawing process of the embodiment reduces the wire breakage rate and appearance defect rate. In contrast, the comparative example shows a worse wire breakage rate and appearance defect rate.

[0079] The above embodiments of the present invention have been illustrated, but 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 modifications can be made without departing from the spirit of the invention. These embodiments, and their variations, are included within the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents. Furthermore, the above-described embodiments can be combined with each other.

[0080] Explanation of reference numerals in the attached figures

[0081] XX is the cross-section perpendicular to the drawing axis in the radial direction.

[0082] Y mixture

[0083] Z ReW silk body

[0084] Points A1 to A8 that divide the outer perimeter into eight equal parts on the radial section surface.

[0085] A max Maximum thickness of the mixture within the field of view

[0086] A min Minimum thickness of the mixture within the field of view

[0087] 1 Peripheral part

[0088] 2. Central Section

Claims

1. A tungsten wire, composed of a tungsten alloy containing rhenium, characterized in that, The surface has at least a portion of a mixture containing W, C, and O as constituent elements, and when the radial cross-sectional thickness of the mixture is set to A mm and the diameter of the tungsten filament is set to B mm, the average value of the ratio A / B of A to B is more than 0.3% and less than 0.8%.

2. The tungsten wire according to claim 1, characterized in that, The variation coefficient of A / B on the same cross section is less than 0.

30.

3. The tungsten wire according to claim 1 or 2, characterized in that, In the mixture, the average value of the ratio of O (wt%) to W (wt%) (Owt%) to W (wt%) in the central part of the thickness direction of the radial section is 0.05 or more and 0.10 or less.

4. The tungsten wire according to claim 1 or 2, characterized in that, The rhenium content is 1 wt% or more and 30 wt% or less.

5. The tungsten wire according to claim 1 or 2, characterized in that, The rhenium content is above 2 wt% and below 28 wt%.

6. The tungsten wire according to claim 1 or 2, characterized in that, The potassium (K) content of the tungsten alloy is above 30 wtppm and below 90 wtppm.

7. The tungsten wire according to claim 1 or 2, characterized in that, The diameter of the tungsten wire is greater than 0.3 mm and less than 1.0 mm.

8. A method for processing tungsten wire, characterized in that, The tungsten wire described in claim 1 or 2 is used for wire drawing.

9. An electrolytic wire, characterized in that, The tungsten wire used is the tungsten wire drawn using the tungsten wire processing method described in claim 8.

10. The tungsten wire according to claim 1 or 2, characterized in that, The tungsten wire is used for wire drawing.

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