Tungsten wire

Abstract

To provide a tungsten wire with an improved circularity.SOLUTION: A tungsten wire 1 comprises tungsten as a main component. When the tensile strength of the tungsten wire 1 is T (unit: MPa) and the wire diameter is D (unit: mm), 4758×D2-7258.3×D+5275.5≤T≤4758×D2-7258.3×D+6100 is satisfied. The circularity of the tungsten wire 1 is at most 2.0%.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a tungsten wire.

Background Art

[0002] Patent Document 1 discloses a tungsten wire having a tensile strength of 4800 MPa or more.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] In the above-mentioned conventional tungsten wire, as the tensile strength increases and the amount of additives increases, the workability of wire drawing using a die deteriorates. For this reason, the die is easily worn, which degrades the roundness of the tungsten wire.

[0005] Accordingly, an object of the present invention is to provide a tungsten wire with improved roundness.

Means for Solving the Problem

[0006] The tungsten wire according to one aspect of the present invention contains tungsten as a main component. When tensile strength is T (unit: MPa) and wire diameter is D (unit: mm), 4758×D 2 -7258.3×D+5275.5≦T≦4758×D 2 -7258.3×D+6100 is satisfied. The roundness of the tungsten wire is 2.0% or less.

Effect of the Invention

[0007] According to the present invention, a tungsten wire with improved roundness can be realized. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the appearance and cross-section of a tungsten wire according to an embodiment. [Figure 2] Figure 2 is a diagram illustrating the roundness ratio. [Figure 3] Figure 3 is a flowchart showing an example of a method for manufacturing tungsten wire according to an embodiment. [Figure 4] Figure 4 is a flowchart showing another example of a method for manufacturing tungsten wire according to an embodiment. [Figure 5] Figure 5 shows the relationship between the wire diameter and tensile strength of tungsten wire containing rhenium or cerium. [Figure 6] Figure 6 shows the relationship between rhenium content, tensile strength, and roundness for a 50 μm diameter tungsten wire containing rhenium. [Figure 7] Figure 7 shows the relationship between rhenium content, tensile strength, and roundness for a 30 μm diameter tungsten wire containing rhenium. [Figure 8] Figure 8 shows the relationship between cerium content, tensile strength, and roundness for a 30 μm diameter tungsten wire containing cerium. [Modes for carrying out the invention]

[0009] In the following, a tungsten wire according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below are all specific examples of the present invention. Therefore, the numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit the present invention. Accordingly, components in the following embodiments that are not described in an independent claim will be described as optional components.

[0010] Also, each drawing is a schematic diagram and is not necessarily strictly illustrated. Therefore, for example, the scale and the like do not necessarily match in each drawing. Also, in each drawing, substantially identical configurations are denoted by the same reference signs, and overlapping descriptions are omitted or simplified.

[0011] Also, in the present specification, terms indicating relationships between elements, terms indicating shapes of elements, and numerical ranges are not expressions that represent only strict meanings, but are expressions meaning that they include substantially equivalent ranges, for example, differences of about several percent.

[0012] (Embodiment) [Tungsten Wire] First, a tungsten wire according to an embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram showing the appearance and cross section of a tungsten wire 1 according to the present embodiment.

[0013] As shown in FIG. 1, the tungsten wire 1 is wound around a winding reel 2 and stored. The winding reel 2 may be referred to as a bobbin, a reel, a spool, a drum, or the like. The tungsten wire 1 has a total length on the order of kilometers, for example, 50 km or more and 300 km or less.

[0014] The tungsten wire 1 shown in FIG. 1 is used for manufacturing tungsten products. For example, the tungsten wire 1 is used as a core wire of a saw wire. Specifically, the saw wire is a fixed-abrasive type wire, which includes the tungsten wire 1 as a core wire, and further includes abrasive grains such as diamond particles or cubic boron nitride (CBN) particles. The abrasive grains are fixed to the surface of the tungsten wire 1. The fixation may be performed by electrodeposition or by resin bonding. The saw wire may also be a free-abrasive type wire. For example, the saw wire may be the tungsten wire 1 itself without including abrasive grains.

[0015] A saw wire is used, for example, for cutting semiconductor ingots such as silicon (Si) or silicon carbide (SiC). A semiconductor wafer can be manufactured by slicing a semiconductor ingot with a saw wire. In this case, the smaller the wire diameter of the saw wire, the smaller the kerf, which reduces loss and increases the number of wafers that can be obtained. Note that the object to be cut is not limited to semiconductor ingots, and may be glass, concrete, crystal, ceramics, or the like.

[0016] The tungsten wire 1 contains tungsten (W) as a main component. The "main component" means that the content (content ratio) of the element is more than 50 wt%. For example, the content of tungsten contained in the tungsten wire 1 is 97 wt% or more. The content of tungsten contained in the tungsten wire 1 may be 99 wt% or more, 99.9 wt% or more, or 99.99 wt% or more. The tungsten wire 1 may contain inevitable impurities that cannot be avoided during the manufacturing process, in addition to additives described later.

[0017] The tungsten wire 1 contains, for example, rhenium (Re). The content of rhenium in the tungsten wire 1 is, for example, 0.1 wt% or more and 3 wt% or less. Rhenium forms an alloy (solid solution) with tungsten.

[0018] When the rhenium content is high, the tensile strength of the tungsten wire 1 can be increased. On the other hand, when the rhenium content is excessively high, it is difficult to reduce the wire diameter while maintaining high tensile strength of the tungsten wire 1. Specifically, wire breakage is likely to occur, making it difficult to perform wire drawing on long wires. By reducing the rhenium content and setting the tungsten content to 97 wt% or more, the processability of the tungsten wire 1 can be improved. In addition, reducing the content of rare and expensive rhenium enables low-cost mass production of long tungsten wires 1.

[0019] Furthermore, the metal used in the alloy with tungsten may be osmium (Os), ruthenium (Ru), or iridium (Ir). The content of osmium, ruthenium, or iridium is, for example, the same as the content of rhenium. In these cases as well, the same effects as in the rhenium-tungsten alloy can be obtained. Also, the tungsten wire 1 may be made of an alloy of tungsten and two or more other metals.

[0020] The tungsten wire 1 may contain potassium (K). The potassium content in the tungsten wire 1 is, for example, 0.001 wt% or more and 0.01 wt% or less. The potassium is present at the grain boundaries of the tungsten crystal. Even with the potassium-containing tungsten wire 1, a higher tensile strength than that of typical piano wire can be achieved.

[0021] Furthermore, tungsten wire 1 may contain rare earth elements. The content of rare earth elements in tungsten wire 1 may be, for example, 0.03 wt% or more and 0.3 wt% or less. The content of rare earth elements in tungsten wire 1 may also be, for example, 0.03 wt% or more and 0.09 wt% or less. Examples of rare earth elements include cerium (Ce), lanthanum (La), yttrium (Y), or samarium (Sm). Rare earth elements are present at the grain boundaries of tungsten. Even tungsten wire 1 containing rare earth elements can achieve a tensile strength higher than that of typical piano wire.

[0022] As an example, the diameter of tungsten wire 1 is 100 μm or less. The smaller the diameter of tungsten wire 1, the less material loss can be reduced when used as the core wire of a saw wire. The diameter of tungsten wire 1 may be 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less. Furthermore, according to the manufacturing method described later, tungsten wire 1 with an extremely thin diameter of 13 μm or less can also be realized. The diameter of tungsten wire 1 may be 10 μm or less, 8 μm or less, or 7 μm or less. The diameter of tungsten wire 1 is, for example, 5 μm or more, but is not limited to this.

[0023] As an example, the tensile strength of tungsten wire 1 is 4800 MPa or higher. The tensile strength may also be 4900 MPa or higher, 5000 MPa or higher, 5200 MPa or higher, or 5500 MPa or higher. Furthermore, tungsten wire 1 with an extremely high tensile strength of 5800 MPa or higher can also be realized. The tensile strength of tungsten wire 1 may also be 5900 MPa or higher, or 6000 MPa or higher. The tensile strength can be measured, for example, based on the tensile test of the Japanese Industrial Standard (JIS H 4460 8).

[0024] The tungsten wire 1 according to this embodiment satisfies a predetermined relationship when the tensile strength is T (unit: MPa) and the wire diameter is D (unit: mm). Specifically, a tungsten wire 1 with a higher tensile strength relative to the wire diameter than conventional wires has been realized. The specific relationship between tensile strength T and wire diameter D will be explained later with reference to Figure 5, along with a specific example.

[0025] In this embodiment, the roundness of the tungsten wire 1 is 2.0% or less. That is, the shape of the cross-section of the tungsten wire 1 (the cross-section perpendicular to the direction of the wire axis) is sufficiently close to a perfect circle. Note that in Figure 1, the difference between the cross-section of the tungsten wire 1 and a perfect circle is exaggerated in the illustration.

[0026] Here, we will explain roundness using Figure 2. Figure 2 is a diagram for explaining roundness. Roundness is an index that represents the degree of deviation of the cross-sectional shape of the tungsten wire 1 from a perfect circle. The smaller the roundness, the smaller the deviation, that is, the closer the cross-sectional shape of the tungsten wire 1 is to a perfect circle. The larger the roundness, the larger the deviation, that is, the further the cross-sectional shape of the tungsten wire 1 is from a perfect circle.

[0027] Specifically, the roundness ratio f (in %) is expressed by the following formula (1).

[0028] (1) f = (AB) / ((A + B) / 2) × 100

[0029] A and B are as shown in Figure 2. Specifically, first, the maximum inscribed circle and minimum circumscribed circle are defined for the cross-section of the tungsten wire 1. The maximum inscribed circle and minimum circumscribed circle are defined to be concentric circles and to minimize the distance between them. That is, if the radius of the minimum circumscribed circle is r(A) and the radius of the maximum inscribed circle is r(B), then r(A)-r(B) is minimized.

[0030] In this case, A is the diameter of the smallest circumscribed circle and is expressed as 2 × r(A). B is the diameter of the largest inscribed circle and is expressed as 2 × r(B). The roundness ratio f is, as shown in equation (1) above, the ratio of the difference between the diameter of the smallest circumscribed circle and the diameter of the largest inscribed circle to the average value of the diameters of the smallest circumscribed circle and the diameter of the largest inscribed circle, expressed as a percentage. If f = 0, the smallest circumscribed circle and the largest inscribed circle coincide, so the cross-section of tungsten wire 1 is a perfect circle.

[0031] According to this embodiment, it is possible to realize a tungsten wire 1 that has higher tensile strength relative to the wire diameter than conventional wires, and also has improved roundness (i.e., a cross-section that is close to a perfect circle). For example, when the tungsten wire 1 is used as the core wire of a saw wire, the improved roundness can suppress variations in the thickness of the sliced ​​material (wafer). In particular, when the roundness exceeds 2% or 3%, the Total Thickness Variation (TTV), which is the variation in wafer thickness, deteriorates rapidly.

[0032] [Manufacturing method] Next, the method for manufacturing the tungsten wire 1 according to this embodiment will be explained using Figures 3 and 4. Figures 3 and 4 are flowcharts showing examples of the method for manufacturing the tungsten wire 1 according to this embodiment.

[0033] As shown in Figure 3, first, additives are added to tungsten (S10). For example, to a predetermined amount of tungsten powder, only additives (doping elements) or a compound containing additives (e.g., an oxide or aqueous solution) is added. The doping elements are rhenium, potassium, or rare earth elements such as cerium or lanthanum. Unwanted components in the compound are removed by subsequent sintering or other processes. The amount of doping elements added is adjusted by adding tungsten powder to the obtained doped tungsten powder in a predetermined ratio. That is, the amount of doping elements may be increased to a level greater than the desired doping element content.

[0034] In this way, after adding doping elements to a small amount of tungsten powder, the doping elements can be diluted (the content reduced) by adding more tungsten powder. That is, since only a small amount of material needs to be processed in the doping element addition process, a small addition device can be used. In addition, since a large amount of doped tungsten powder can be obtained in a single addition process, the number of man-hours required for the addition process can be reduced. This increases the productivity of tungsten wire 1.

[0035] Next, a tungsten ingot is produced by pressing and sintering the resulting aggregate of doped tungsten powder (S12).

[0036] Next, the fabricated tungsten ingot is subjected to swaging (S14). Specifically, the tungsten ingot is forged and compressed from all sides to form a wire-shaped tungsten wire. Rolling may be performed instead of swaging.

[0037] For example, by repeatedly performing swaging, a tungsten ingot with a diameter of approximately 15 mm to 25 mm is formed into a tungsten wire with a diameter of approximately 3 mm to 4 mm. Annealing is performed during an intermediate step in the swaging process to ensure processability in subsequent processes. For example, annealing is performed at a temperature of 2000°C to 2400°C for diameters between 8 mm and 10 mm. However, in order to ensure tensile strength through grain refinement, annealing is not performed in the swaging process for diameters less than 8 mm.

[0038] Next, the tungsten wire is heated to 900°C before the heated drawing process (S16). Specifically, the tungsten wire is heated directly with a burner or similar device. Heating the tungsten wire forms an oxide layer on its surface to prevent breakage during subsequent heated drawing processes.

[0039] Next, heated wire drawing is performed (S18). Specifically, tungsten wire is drawn using one or more wire drawing dies, that is, the tungsten wire is drawn (thinned) while heating. The heating temperature is, for example, 1000°C. Note that the higher the heating temperature, the easier the tungsten wire is to process, so it can be drawn more easily. Heated wire drawing is repeated while changing the wire drawing dies. The reduction in cross-sectional area of ​​the tungsten wire by one drawing pass using one wire drawing die is, for example, 10% to 40%. In the heated wire drawing process, a lubricant in which graphite is dispersed in water may be used.

[0040] The heated drawing process (S18) is repeated until a tungsten wire of the desired diameter is obtained (No. in S20). The desired diameter here is the diameter when there are two drawing cycles remaining, for example, about 150 μm.

[0041] Furthermore, in repeated heated wire drawing, a wire drawing die with a smaller bore diameter than the one used in the previous drawing is employed. Also, in repeated heated wire drawing, the tungsten wire is heated at a lower temperature than the heating temperature used in the previous drawing. In other words, the heating temperature decreases in stages. The final heating temperature is, for example, 400°C, which contributes to the refinement of the crystal grains.

[0042] If a tungsten wire of the desired diameter is obtained and there are two remaining drawing cycles (Yes in S20), then room temperature drawing is performed (S22). Note that, as shown in Figure 4, electrolytic polishing may be performed before room temperature drawing (S22) (S21). Room temperature drawing achieves further grain refinement by drawing the tungsten wire without heating. Room temperature drawing also has the effect of aligning the crystal orientation in the direction of the processing axis (specifically, in the direction parallel to the wire axis of tungsten wire 1).

[0043] Room temperature refers to a temperature range of, for example, 0°C to 50°C, with 30°C being one example. Specifically, tungsten wire is drawn using multiple wire drawing dies with different bore diameters. In room temperature wire drawing, a liquid lubricant such as water-soluble liquid is used. Since no heating is performed in room temperature wire drawing, evaporation of the liquid is suppressed. Therefore, it can function sufficiently as a liquid lubricant. Compared to conventional tungsten wire processing methods using heated wire drawing at 600°C or higher, by processing the tungsten wire without heating and while cooling it with a liquid lubricant, dynamic recovery and dynamic recrystallization are suppressed, contributing to grain refinement without wire breakage, and high tensile strength can be obtained.

[0044] The processing rate in room temperature wire drawing is, for example, 70% or more. The processing rate is expressed by the following equation (2), using the wire diameter Db immediately before room temperature wire drawing and the wire diameter Da immediately after room temperature wire drawing.

[0045] (2) Processing rate={1-(Da / Db) 2}×100

[0046] As can be seen from equation (2), the greater the reduction in wire diameter due to room-temperature drawing, the larger the processing rate. For example, even if the wire diameter Db immediately before room-temperature drawing is the same, the larger the processing rate, the smaller the wire diameter Da immediately after room-temperature drawing will be. Increasing the processing rate increases the degree of thinning of the tungsten wire by room-temperature drawing, that is, a thinner tungsten wire can be obtained. The processing rate for room-temperature drawing is 70% or more, but it may be 80% or more, 90% or more, or 95% or more. The wire diameter immediately after room-temperature drawing is, for example, in the range of approximately 50 μm to 120 μm.

[0047] Next, after drawing at room temperature, low-temperature hot drawing is performed (S24). That is, the final drawing of the tungsten wire is performed while heating at a low temperature. The temperature at this time is higher than the temperature of room temperature drawing (S22) but lower than the temperature of heated drawing (S18). Specifically, the temperature for low-temperature hot drawing is in the range of 100°C to 300°C, for example, 200°C or 300°C. The wire diameter after low-temperature hot drawing is, for example, in the range of approximately 20 μm to 100 μm.

[0048] Finally, electropolishing is performed on the tungsten wire formed by low-temperature hot drawing to fine-tune its diameter (S26). Electropolishing is performed by immersing the tungsten wire and the counter electrode in an electrolyte solution, such as an aqueous sodium hydroxide solution, and generating a potential difference between the tungsten wire and the counter electrode.

[0049] Through the above process, the tungsten wire 1 according to this embodiment is manufactured. As a result of this process, the length of the tungsten wire 1 immediately after manufacture is, for example, 50 km or more, making it industrially usable. The tungsten wire 1 can be cut to an appropriate length depending on the intended use and used in the shape of a needle or rod.

[0050] The steps shown in the manufacturing method for tungsten wire 1 are performed, for example, in line. Specifically, the multiple wire drawing dies used in step S18 are arranged on the production line in order of decreasing bore diameter. Heating devices such as burners are placed between each wire drawing die. Electropolishing devices may also be placed between each wire drawing die. Downstream (towards the next process) of the wire drawing die used in step S18, one or more wire drawing dies used in step S22 and one or more wire drawing dies used in step S24 are arranged in order of decreasing bore diameter, with the electropolishing device placed downstream of the wire drawing die with the smallest bore diameter. Note that each step may be performed individually.

[0051] Furthermore, the manufacturing method of the tungsten wire 1 described above is merely one example, and the temperature and wire diameter in each step can be adjusted as appropriate.

[0052] As described above, in the method for manufacturing the tungsten wire 1 according to this embodiment, heating and drawing is performed at a first temperature which is high temperature, then room temperature drawing is performed at a second temperature which is room temperature, and then low temperature hot drawing is performed at a third temperature which is low temperature. The third temperature is higher than the second temperature (room temperature) and lower than the first temperature (high temperature).

[0053] Thus, tungsten wire 1 is manufactured by implementing a new process called low-temperature hot drawing (also called low-temperature hot working). Low-temperature hot drawing results in tungsten wire 1 with a smaller diameter, higher tensile strength, and improved roundness.

[0054] [Relationship between tensile strength and wire diameter] Next, the relationship between the tensile strength and wire diameter of the tungsten wire 1 according to this embodiment will be explained using Figure 5.

[0055] Figure 5 shows the relationship between the wire diameter and tensile strength of tungsten wire 1 containing rhenium or cerium. In Figure 5, the horizontal axis represents the wire diameter of tungsten wire 1 (unit: μm), and the vertical axis represents the tensile strength (unit: MPa).

[0056] The inventors of this invention manufactured several samples of tungsten wire 1 based on the manufacturing method described above. The rhenium content (Re content) was adjusted by adjusting the amount of rhenium powder added to the tungsten powder. The wire diameter was adjusted using drawing dies with different bore diameters. The tensile strength was an actual measured value obtained by measuring the tensile strength of the manufactured tungsten wire 1. The tensile strength was measured, for example, based on the tensile test of the Japanese Industrial Standards (JIS H 4460 8). Furthermore, by adjusting the heating temperature and / or processing rate in the wire drawing process, it was possible to obtain tungsten wire 1 with different tensile strengths even with the same Re content and the same wire diameter.

[0057] Tables 1 and 2 show the specific values ​​for the Re content, wire diameter, and tensile strength of several samples of tungsten wire 1 shown in Figure 5.

[0058] Table 1 shows the wire diameter and tensile strength of tungsten wire 1 containing a predetermined amount of rhenium (Re).

[0059] [Table 1]

[0060] Table 2 shows the tensile strength of tungsten wire 1 with diameters of 50 μm and 30 μm, categorized by Re content.

[0061] [Table 2]

[0062] As shown in Figure 5, there is a negative correlation between wire diameter and tensile strength. In other words, the smaller the wire diameter, the higher the tensile strength, and the larger the wire diameter, the lower the tensile strength.

[0063] In the tungsten wire 1 according to this embodiment, when the wire diameter is D [mm], the range of the following equation (3) is satisfied.

[0064] (3) 4758×D 2 -7258.3 × D + 5275.5 ≤ T ≤ 4758 × D 2 -7258.3 × D + 6100

[0065] The quadratic function on the left side of inequality (3) is represented by the lower dashed line in Figure 5. The lower dashed line in Figure 5 was obtained by polynomial approximation using multiple samples from Table 1 that yield the smallest tensile strength for each wire diameter. The quadratic function on the right side of inequality (3) is represented by the upper dashed line in Figure 5. The upper dashed line in Figure 5 was obtained by shifting the above polynomial so that all the samples obtained in Tables 1 and 2 fall between the two dashed lines.

[0066] Figure 5 also shows the relationship between the wire diameter and tensile strength of tungsten wire 1 containing cerium. The specific values ​​are shown in Table 3. Table 3 is a table showing the wire diameter and tensile strength of tungsten wire 1 containing a predetermined amount of cerium (Ce).

[0067] [Table 3]

[0068] As shown in Figure 5 and Table 3, tungsten wire 1 containing cerium also satisfies the relationship expressed by equation (3) above. Here, cerium was used as an example, but similar results can be obtained when other rare earth elements such as lanthanum (La), which have similar characteristics to cerium, are included.

[0069] [Tensile strength and roundness] Next, we will explain the relationship between the tensile strength and roundness of tungsten wire 1.

[0070] <If it contains rhenium (Re)> Figure 6 shows the relationship between rhenium content, tensile strength, and roundness for a 50 μm diameter tungsten wire containing rhenium. Table 4 shows the tensile strength and roundness of a tungsten wire with a predetermined amount of rhenium and a diameter of 50 μm.

[0071] [Table 4]

[0072] As shown in Figure 6 and Table 4, the tensile strength increased sharply from 5240 MPa to 5570 MPa as the Re content increased from 0.1 wt% to 0.5 wt%, and then gradually increased to around 5690 MPa as the Re content increased from 1.0 wt% to 5.0 wt%. Furthermore, it can be seen that the roundness increased at a nearly constant rate from 0.4% to 2.7% as the Re content increased from 0.1 wt% to 5 wt%. In the range of Re content below 3.0 wt%, the roundness was 2.0% or less, whereas at an Re content of 5.0 wt%, the roundness became greater than 2.0%.

[0073] In the tungsten wire 1 with a diameter of 50 μm according to this embodiment, it is possible to achieve both a tensile strength of 5200 MPa or more and a roundness of 2.0% or less. Furthermore, in the range of Re content from 0.5 wt% to 1.0 wt%, a tensile strength of 5500 MPa or more and a roundness of 1.0% or less can be achieved. In other words, it is possible to achieve both high tensile strength and improved roundness.

[0074] Figure 7 shows the relationship between rhenium content, tensile strength, and roundness for a 30 μm diameter tungsten wire containing rhenium. Table 5 shows the tensile strength and roundness of a 30 μm diameter tungsten wire containing a predetermined amount of rhenium.

[0075] [Table 5]

[0076] As shown in Figure 7 and Table 5, the tensile strength increased sharply from 5420 MPa to 5770 MPa as the Re content increased from 0.1 wt% to 0.5 wt%, and then gradually increased to 5890 MPa as the Re content increased from 1.0 wt% to 5.0 wt%. This trend is similar to that of the 50 μm wire diameter, but the tensile strength is higher than that of the 50 μm wire diameter due to the smaller wire diameter.

[0077] Furthermore, it can be seen that as the Re content increases from 0.1 wt% to 5 wt%, the roundness increases at a nearly constant rate from 0.3% to 3.2%. In the range where the Re content is 3.0 wt% or less, the roundness is 2.0% or less, whereas when the Re content reaches 5.0 wt%, the roundness becomes greater than 2.0%. This trend is similar to that of the 50 μm wire diameter, but because the tensile strength increases with the smaller wire diameter, the rate of increase in roundness is larger compared to the 50 μm wire diameter case.

[0078] In this embodiment, the 30 μm diameter tungsten wire 1 achieves both a tensile strength of 5400 MPa or more and a roundness of 2.0% or less. Furthermore, in the range of Re content from 0.5 wt% to 1.0 wt%, a tensile strength of 5750 MPa or more and a roundness of 1.0% or less can be achieved. In other words, it is possible to achieve both high tensile strength and improved roundness.

[0079] Thus, in the range of Re content from 0.1 wt% to 3.0 wt%, the roundness is improved compared to conventional materials. Furthermore, in the range of Re content from 0.1 wt% to 3.0 wt%, higher tensile strength can be achieved. In the range of Re content from 0.5 wt% to 1.0 wt%, both higher tensile strength and improved roundness can be achieved. Incidentally, the tensile strength can be further increased by reducing the wire diameter.

[0080] <If it contains cerium (Ce)> Figure 8 shows the relationship between Ce content, tensile strength, and roundness for a 30 μm diameter tungsten wire 1 containing cerium. Table 6 shows the tensile strength and roundness of a tungsten wire with a predetermined amount of cerium (Ce) and a diameter of 30 μm.

[0081] [Table 6]

[0082] As shown in Figure 8 and Table 6, the tensile strength increased sharply from 5400 MPa to 5730 MPa as the cerium content (Ce content) increased from 0.02 wt% to 0.09 wt%, and then gradually increased to 5920 MPa as the Ce content increased from 0.09 wt% to 0.50 wt%. The tensile strength was 5500 MPa or higher when the Ce content was 0.03 wt% or higher. In particular, a high tensile strength of 5900 MPa or higher was achieved when the Ce content was 0.30 wt% or higher.

[0083] Furthermore, it can be seen that as the Ce content increases from 0.02 wt% to 0.5 wt%, the roundness increases at a nearly constant rate from 0.4% to 3.1%. In the range of Ce content below 0.30 wt%, the roundness is 2.0% or less, whereas when the Ce content reaches 0.50 wt%, the roundness becomes greater than 2.0%. Also, in the range of Ce content between 0.03 wt% and 0.09 wt%, the roundness is 1.0% or less, indicating an improvement in roundness.

[0084] [Effects, etc.] As described above, the tungsten wire 1 according to this embodiment contains tungsten as its main component. When the tensile strength is T (unit: MPa) and the wire diameter is D (unit: mm), the tensile strength is 4758 × D 2 -7258.3 × D + 5275.5 ≤ T ≤ 4758 × D 2 The equation -7258.3 × D + 6100 is satisfied. The roundness of tungsten wire 1 is 2.0% or less.

[0085] This makes it possible to create a tungsten wire 1 that has higher tensile strength relative to its diameter than conventional wires, and also has improved roundness (i.e., a cross-section that is closer to a perfect circle).

[0086] Furthermore, for example, tungsten wire 1 may contain rhenium. In this case, the rhenium content in tungsten wire 1 is 0.1 wt% or more and 3 wt% or less.

[0087] This makes it possible to create a tungsten wire 1 with improved roundness and higher tensile strength.

[0088] Furthermore, for example, tungsten wire 1 may contain rare earth elements. In this case, the content of rare earth elements in tungsten wire 1 is 0.03 wt% or more and 0.3 wt% or less.

[0089] This makes it possible to create a tungsten wire 1 with improved roundness and higher tensile strength.

[0090] Furthermore, for example, the content of rare earth elements in tungsten wire 1 may be between 0.03 wt% and 0.09 wt%. In this case, the roundness of tungsten wire 1 is 1.0% or less.

[0091] This makes it possible to create a tungsten wire 1 with improved roundness and higher tensile strength.

[0092] Furthermore, for example, the tensile strength of tungsten wire 1 is 5800 MPa or more.

[0093] This allows the saw wire to be tensioned more strongly when tungsten wire 1 is used as the core wire of the saw wire, thereby suppressing the vibration of the saw wire when cutting the ingot. By suppressing the vibration of the saw wire, the amount of ingot cut can be reduced, thus reducing losses.

[0094] Furthermore, for example, the tungsten content in tungsten wire 1 may be 97 wt% or more.

[0095] Furthermore, for example, the diameter of the tungsten wire 1 may be 100 μm or less.

[0096] As a result, because the wire diameter is small, if tungsten wire 1 is used, for example, as a saw wire for slicing ingots, the cutting allowance can be reduced, and the number of wafers that can be cut can be increased.

[0097] Furthermore, for example, tungsten wire 1 is used as the core wire of a saw wire.

[0098] As a result, when using tungsten wire 1 with improved roundness to slice an ingot, for example, variations in wafer thickness can be suppressed. In other words, high-quality wafers can be manufactured.

[0099] (others) Although the tungsten wire according to the present invention has been described above based on the above embodiments, the present invention is not limited to the above embodiments.

[0100] For example, the tungsten wire 1 may contain two or more elements from among rhenium, potassium, and rare earth elements.

[0101] Furthermore, the tungsten wire 1 may be used for purposes other than the core wire of a saw wire. For example, the tungsten wire 1 may be used as the warp and weft threads of a mesh. Specifically, tungsten mesh is manufactured by weaving using the tungsten wire 1. The tungsten mesh is used for screen printing mesh or cut-resistant clothing, etc.

[0102] Alternatively, the tungsten wire 1 may be used as a single strand of stranded wire. Specifically, stranded wire is manufactured by twisting the tungsten wire 1. Stranded wire can be used for ropes, catheters, etc.

[0103] Furthermore, the tungsten wire 1 may be used in twisting with nonwoven fabrics, nylon or other organic fibers, or in knitting. For example, the tungsten wire 1 may be cut to a predetermined length or less, and then processed into a nonwoven fabric to produce a nonwoven fabric.

[0104] By improving the roundness of the tungsten wire 1, the stress applied to the tungsten wire 1 during processing or use becomes more uniform. In other words, the application of large localized stresses to the tungsten wire 1 is suppressed, thereby preventing the occurrence of breakage and other problems.

[0105] Furthermore, the present invention also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art could conceive, as well as forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of the present invention. [Explanation of Symbols]

[0106] 1 Tungsten wire

Claims

1. A tungsten wire consisting of tungsten and unavoidable impurities, When the tensile strength is T (unit: MPa) and the wire diameter is D (unit: mm), 4758×D ２ -7258.3×D+5275.5≦T≦4758×D ２ -7258.3×D+6100 Satisfying the conditions, The roundness is 2.0% or less. When A is the diameter of the smallest circumscribed circle for a cross-section perpendicular to the direction of the tungsten wire's axis, and B is the diameter of the largest inscribed circle for the same cross-section, the roundness f (in %) is: f=(A-B) / ((A+B) / 2)×100 It is represented as, The minimum circumscribed circle and the maximum inscribed circle are concentric circles and are defined such that the distance between them is minimized. Tungsten wire.

2. A tungsten wire comprising rhenium, osmium, ruthenium, iridium, potassium, and at least one of rare earth elements, with the remainder being tungsten and unavoidable impurities, (i) When the tungsten wire contains rhenium, osmium, ruthenium, or iridium, the content of rhenium, osmium, ruthenium, or iridium in the tungsten wire is 0.1 wt% or more and 3 wt% or less. (ii) When the tungsten wire contains potassium, the potassium content in the tungsten wire is 0.001 wt% or more and 0.01 wt% or less. (iii) When the tungsten wire contains rare earth elements, the content of rare earth elements in the tungsten wire is 0.03 wt% or more and 0.3 wt% or less. When the tensile strength is T (unit: MPa) and the wire diameter is D (unit: mm), 4758 × D² - 7258.3 × D + 5275.5 ≤ T ≤ 4758 × D² - 7258.3 × D + 6100 Satisfying the conditions, The roundness is 2.0% or less. When A is the diameter of the smallest circumscribed circle for a cross-section perpendicular to the direction of the tungsten wire's axis, and B is the diameter of the largest inscribed circle for the same cross-section, the roundness f (in %) is: f=(A-B) / ((A+B) / 2)×100 It is represented as, The minimum circumscribed circle and the maximum inscribed circle are concentric circles and are defined such that the distance between them is minimized. Tungsten wire.

3. The content of rare earth elements in the tungsten wire is 0.03 wt% or more and 0.09 wt% or less. The roundness of the tungsten wire is 1.0% or less. The tungsten wire according to claim 2.

4. The tensile strength of the tungsten wire is 5800 MPa or more. A tungsten wire according to any one of claims 1 to 3.

5. The tungsten content in the tungsten wire is 97 wt% or more. A tungsten wire according to any one of claims 1 to 3.

6. The diameter of the tungsten wire is 100 μm or less. A tungsten wire according to any one of claims 1 to 3.

7. The aforementioned tungsten wire is used as the core wire of a saw wire. A tungsten wire according to any one of claims 1 to 3.

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