SAWWIRE

Abstract

Saw wire comprising a tungsten wire (10) containing a tungsten alloy, wherein the tungsten alloy consists of: Tungsten and at least 0.1 wt% and at most 10 wt% of a transition metal selected from rhenium (Re), iridium (Ir), ruthenium (Ru) or osmium (Os), and not more than 0.01% by weight potassium, wherein the tungsten wire has an average crystal grain size in a cross-section (30) perpendicular to an axis (P) of the tungsten wire (10) of at most 0.16 µm, wherein the average crystal grain size in the cross-section (30) in an edge portion (32) closer to the surface (20) is at least 5% smaller than in a center portion (31), the edge portion (32) being located outside the center portion (31) in the cross-section (30), wherein the tensile strength of the tungsten wire (10) is at least 4800 MPa and at most 5500 MPa, wherein the diameter of the tungsten wire (10) is at most 100 µm and wherein the surface of the tungsten wire (10) is coated by an oxide film or a nitride film.

Description

[Technical field]

[0001] The present invention relates to a saw wire. [State of the art]

[0002] Medical needles comprising a tungsten alloy wire with a high tensile strength and an increased alloy content with respect to tungsten are conventionally known (see, for example, Patent Document (PTL) 1). PTL 1 discloses that a tungsten alloy wire with a diameter of 0.10 mm has a maximum tensile strength of 4459.0 N / mm 2 (= MPa).

[0003] PTL 2 describes a sawing wire and a cutting device. PTL 3, PTL 4, and PTL 5 also describe sawing wires and cutting devices. PTL 6 describes a rhenium-tungsten wire, a method for its manufacture, and a medical needle using the wire. PTL 7 describes the use of tungsten as a filament for incandescent lamps and for other purposes. NPTL 1 describes tensile properties of tungsten-rhenium wires with a nanofiber structure. NPTL 2 describes the reduction of tensile residual stresses during the drawing of tungsten wires. NPTL 3 describes the effects of low-temperature rolling on the tensile behavior of commercially pure tungsten. [Document List][Patent Documents] [PTL 1] JP 2014- 169 499 A [PTL 2] DE 10 2018 104 005 A1 [PTL 3] US 2018 / 0 326 519 A1 [PTL 4] US 2018 / 0 326 517 A1 PTL5] JP 2018- 167 390 A [PTL 6] US 2011 / 0 319 931 A1 [PTL 7] US 1 082 933 A [NPTL 1] N. Qiu et al., International Journal of Minerals, Metallurgy and Materials, Vol. 25, 2018, No. 9, 1055-1059. [NPTL 2] M. Ripoll et al., Materials Science and Engineering A, Vol. 527, 2010, 3064-3072. [NPTL 3] Q. Wei, Materials Science and Engineering A, Vol. 491, 2008, 62-69. [Summary of the invention][Technical problem]

[0004] Tungsten, which has a smaller diameter and higher tensile strength than conventional tungsten, has been required for effective use in various fields, such as saw wires, screen printing mesh, etc., in addition to medical needles. Tungsten is chemically more stable and has a higher elastic modulus and melting point than piano wire, which has the greatest strength as a metal wire. Such tungsten has great industrial and commercial potential.

[0005] In view of the foregoing, it is an object of the present invention to provide a saw wire having a higher tensile strength than a general tensile strength of a piano wire and a smaller diameter. [Solution to the problem]

[0006] To achieve the above-described object, a saw wire according to claim 1 is provided. [Advantageous effects of the invention]

[0007] The present invention makes it possible to provide a saw wire having a higher tensile strength than a general tensile strength of a piano wire and a smaller diameter. [Brief description of the drawings] [ Fig. 1] Fig. 1 is a perspective view schematically showing a tungsten wire according to an embodiment. [ Fig. 2A] Fig.2A is a diagram showing an enlarged view of a surface of a tungsten wire having a tensile strength of 4320 MPa according to Comparative Example 1. [ Fig. 2B] Fig. 2B is a diagram showing an enlarged view of a surface of a tungsten wire having a tensile strength of 4800 MPa according to Working Example 1. [ Fig. 2C] Fig. 2C is a diagram showing an enlarged view of a surface of a tungsten wire having a tensile strength of 5040 MPa according to Working Example 2. [ Fig. 2D] Fig. 2D is a diagram showing an enlarged view of a surface of a tungsten wire having a tensile strength of 5430 MPa according to Working Example 3. [ Fig. 2E] Fig.2E is a diagram showing an enlarged view of a surface of a tungsten wire (with a purity of 4800 MPa) with a tensile strength of 4800 MPa according to Working Example 4. [ Fig. 3] Fig. 3 is a graph showing a relationship between a tensile strength and an average width of surface crystal grains of a tungsten wire. [ Fig. 4A] Fig. 4A is a diagram showing an enlarged view of a cross section of the tungsten wire having a tensile strength of 4800 MPa according to Working Example 1. [ Fig. 4B] Fig. 4B is a diagram showing an enlarged view of a cross section of the tungsten wire having a tensile strength of 5040 MPa according to Working Example 2. [ Fig. 4C] Fig.4C is a diagram showing an enlarged view of a cross section of the tungsten wire having a tensile strength of 5430 MPa according to Working Example 3. [ Fig. 5] Fig. 5 is a graph showing a relationship between a tensile strength and an average crystal grain size in the cross section of a tungsten wire. [ Fig. 6] Fig. 6 is a graph showing a relationship between a tensile strength and a secondary recrystallization temperature of a tungsten wire. [ Fig. 7] Fig. 7 is a flowchart showing a manufacturing method of the tungsten wire according to the embodiment. [ Fig. 8] Fig. 8 is a perspective view showing a cutting device according to the embodiment. [Description of embodiments]

[0008] Hereinafter, a tungsten wire included in a saw wire according to an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiment described below shows a specific example of the present invention. The numerical values, shapes, materials, structural components, the arrangement and connection of the structural components, etc. described in the following embodiment are merely examples and are not intended to limit the present invention. Furthermore, of the structural components in the following embodiment, components not recited in the independent claims, each of which expresses the broadest concept of the present invention, are described merely as arbitrary structural components.

[0009] Furthermore, each diagram is a schematic diagram and not necessarily strictly illustrated. Consequently, the scales of the drawings, for example, are not necessarily precise. In the drawings, substantially the same structural components are denoted by the same reference numerals, and redundant descriptions are omitted or simplified.

[0010] In addition, a term such as "perpendicular" or "identical," which represents a relationship between the components, as well as a term such as "circular," which represents a shape, and numerical ranges are used in this specification. Such terms and ranges do not represent only a strict meaning of the term or range, but imply that a substantially identical range, such as a range encompassing a small difference, such as a few percent, is included within the term or range. [Embodiment]Tungsten wire

[0011] First, a structure of a tungsten wire included in a saw wire according to the present embodiment will be described.

[0012] The Fig. 1 is a perspective view schematically showing a tungsten wire 10 according to the present embodiment. Fig. 1 shows an example in which the tungsten wire 10 is wound or wound around a winding core material. In addition, the Fig. 1 schematically shows a partially enlarged view of the tungsten wire 10.

[0013] The tungsten wire 10 according to the present embodiment contains a tungsten alloy. The tungsten content of the tungsten wire 10 is, for example, at least 90 wt%. The tungsten content may be at least 95 wt%, at least 99 wt%, or 99.9 wt%. It should be noted that the tungsten content is the ratio of the weight of tungsten to the total weight of the tungsten wire 10. The same applies to the content of other metal elements, etc., such as rhenium (Re) and potassium (K), which will be described later.

[0014] For example, tungsten alloy is an alloy containing rhenium and tungsten, namely, ReW alloy. As the rhenium content increases, the strength of tungsten wire 10 can be increased. However, an excessively high rhenium content deteriorates the machinability of tungsten wire 10, making it difficult to thin tungsten wire 10.

[0015] According to the present embodiment, the rhenium content of the tungsten wire 10 is at least 0.1 wt% and at most 10 wt%. For example, the rhenium content may be at least 0.5 wt% and at most 5 wt%. An example of the rhenium content is 1 wt%, but the rhenium content may be 3 wt%.

[0016] The tungsten wire 10 has a diameter of less than or equal to 100 µm. For example, the diameter of the tungsten wire 10 may be 60 µm or less, or may be 40 µm or less. The diameter of the tungsten wire 10 may be 30 µm or less, or may be 20 µm or less. The diameter of the tungsten wire 10 may be, for example, 10 µm.

[0017] According to the present embodiment, the diameter of the tungsten wire 10 is constant. However, the diameter of the tungsten wire 10 does not necessarily have to be completely constant and may differ at different sections along the axis by a certain percentage, such as 1%. As shown in the Fig. 1, the tungsten wire 10 has, for example, a circular cross-sectional shape in the cross section orthogonal to the axis P. The cross-sectional shape of the tungsten wire 10 may be a square, a rectangle, an oval, or the like.

[0018] The tungsten wire 10 containing a tungsten alloy has a tensile strength of at least 4800 MPa and at most 5500 MPa. The tensile strength of the tungsten wire 10 may be at least 5000 MPa or may be at least 5300 MPa. The tensile strength of the tungsten wire 10 can be adjusted to a desired value by appropriately adjusting (i) a diameter, (ii) at least one of an average width of surface crystal grains or an average crystal grain size, and (iii) a tungsten content. For example, a tungsten wire 10 having a tensile strength of about 5500 MPa can be provided.

[0019] Furthermore, the elastic modulus of the tungsten wire 10 is at least 350 GPa and at most 450 GPa. The elastic modulus is a longitudinal elastic modulus. The elastic modulus of piano wire generally ranges from 150 GPa to 250 GPa. In other words, the tungsten wire 10 has an elastic modulus about twice that of piano wire.

[0020] Since the tungsten wire 10 has a Young's modulus greater than or equal to 350 GPa, it is resistant to deformation. In other words, the tungsten wire 10 is less likely to stretch. Furthermore, since the tungsten wire 10 has a Young's modulus less than or equal to 450 GPa, it can be deformed when a force of a certain magnitude is applied. In particular, since the tungsten wire 10 can be bent when the tungsten wire 10 is used as a saw wire, it is possible, for example, to simply guide the saw wire in a loop over a guide pulley or the like.

[0021] The tungsten wire 10 according to the present embodiment has at least two of three crystallinity-related characteristics, namely the average crystal grain size characteristics as defined below. The third characteristic, the surface crystal grain width, is an optional feature. The crystallinity characteristics will be described in detail below. Width of a surface crystal grain (optional feature)

[0022] First, the width of a surface crystal grain of the tungsten wire 10 is described.

[0023] A surface crystal grain is a crystal grain of tungsten or a tungsten alloy on the surface 20 of the tungsten wire 10. In the tungsten wire 10, the width of a surface crystal grain in a direction perpendicular to the axis P is preferably less than or equal to 76 nm. The width of a surface crystal grain in the direction perpendicular to the axis P refers to a length along the direction perpendicular to the axis P.

[0024] A relationship between a tensile strength and a width of a surface crystal grain of samples of a plurality of tungsten wires prepared by the inventors is described below.

[0025] The Fig. 2A to Fig.2E are diagrams showing enlarged views of the surface of the tungsten wire according to Comparative Example 1 and Working Examples 1 to 4, respectively. The tungsten wires according to Comparative Example 1 and Working Examples 1 to 3 each contain a rhenium-tungsten alloy containing 1 wt% of rhenium. The tungsten wire according to Working Example 4 contains 99.9 wt% of tungsten.

[0026] The tensile strength of the tungsten wire according to Comparative Example 1 is 4320 MPa. The tensile strengths of the tungsten wires according to Working Examples 1, 2, and 3 are 4800 MPa, 5040 MPa, and 5430 MPa, respectively. The tensile strength of the tungsten wire according to Working Example 4 is 4800 MPa. It should be noted that in each of Comparative Example 1 and Working Examples 1 to 4, the diameter of the tungsten wire is 50 µm.

[0027] The tungsten wires according to Working Examples 1 to 4 are samples of the tungsten wires produced using a manufacturing method described later. Furthermore, the tungsten wire according to Comparative Example 1 is a sample thinned to a diameter of 50 µm by hot drawing (step S16 in the Fig. 7) without performing room temperature drawing in the manufacturing process described later (step S20 in the Fig. 7). The same applies to Comparative Examples 2 and 3, which are described later.

[0028] The Fig. 2A to Fig. 2E each show a partially enlarged view of the surface 20 of the tungsten wire 10, which is in the Fig.1. Each of the diagrams shows a scanning electron microscope (SEM) image of the surface 20 of the sample of the tungsten wire 10. In each of the diagrams, an area with a uniform density (color) represents a single crystal grain. The lateral direction in the figure of each of the drawings is a direction parallel to the axis P, and the surface crystal grain extends elongated in a direction along the axis P.

[0029] In each of the diagrams, the solid line L in the center is a straight line extending in a direction perpendicular to the axis P. The average width of the surface crystal grains is calculated by counting a total number of boundaries between crystal grains (i.e., grain boundaries) along the solid line L within the range indicated in each of the diagrams. Specifically, the average width of the surface crystal grains is calculated by dividing the length of a counting range, i.e., the vertical length of each of the diagrams, by the number obtained by adding 1 to the total number of grain boundaries. It should be noted that in each of the diagrams, a plurality of short lines perpendicular to the solid line L each indicate a grain boundary.

[0030] Table 1 shows the relationship between a tensile strength and an average width of surface crystal grains calculated based on the result of counting the total number of grain boundaries. [Table 1] Tensile strength [MPa] Number of grain boundaries Average width of surface crystal grains [nm] Comparison example 1 4320 16 100 Working example 1 4800 21 76 Working example 2 5040 25 65 Working example 3 5430 28 56 Working example 4 4800 24 67

[0031] The Fig. 3 is a graph showing a relationship between a tensile strength and an average width of the surface crystal grains of the tungsten wire 10 according to the present embodiment. Fig. 3, the horizontal axis represents an average width [nm] of surface crystal grains and the vertical axis represents a tensile strength [MPa].

[0032] As shown in Table 1 and the Fig.As shown in Figure 3, there is a negative correlation between the average width of surface crystal grains and tensile strength. In other words, as the average width of the surface crystal grain decreases, the tensile strength increases. In the tungsten wire 10 according to the present embodiment, the average width of surface crystal grains is less than or equal to 76 nm. This provides a tungsten wire with a high tensile strength of at least 4800 MPa. Furthermore, for example, by setting an average width of the surface crystal grains to at most 56 nm, a tungsten wire with a high tensile strength of at least 5430 MPa can be provided.

[0033] When comparing Working Example 4, in which the tungsten wire has a high tungsten content, and Working Example 1, in which the tungsten wire contains a rhenium-tungsten alloy, the average width of the surface crystal grains of Working Example 1 is larger than the average width of the surface crystal grains of Working Example 4 to provide the same tensile strength. This is because a crystal grain of a rhenium-tungsten alloy has higher strength than a crystal grain of pure tungsten. In other words, by increasing the rhenium content, the tensile strength can be increased to more than 4800 MPa even when the width of a surface crystal grain is larger than 76 nm. Accordingly, the average width of the surface crystal grains does not necessarily have to be less than or equal to 76 nm.For example, with increasing rhenium content, the width of a surface crystal grain of the tungsten wire 10 with a tensile strength of 4800 MPa increases.

[0034] As described above, the tungsten wire 10 according to the present embodiment is a tungsten wire containing a tungsten alloy, and the average width of the surface crystal grains in the direction perpendicular to the axis P of the tungsten wire 10 is at most 76 nm.

[0035] According to this structure, a tungsten wire 10 having a high tensile strength can be provided.

[0036] In addition, for example, the tungsten content of the tungsten wire 10 is at least 90 wt%.

[0037] According to this structure, even in the case where the tungsten wire 10 contains a tungsten alloy, the rhenium content can be set to, for example, less than 10 wt%. As a result, the workability of the tungsten wire 10 can be improved. Average crystal grain size (essential characteristics)

[0038] Next, the average crystal grain size of the tungsten wire 10 is described.

[0039] The average crystal grain size is a numerical value calculated based on the number of crystals per unit area in the cross-section 30 of the tungsten wire 10. As the value of the average crystal grain size decreases, the size of each crystal decreases; that is, the number of crystals increases.

[0040] The average crystal grain size is calculated by averaging the crystal grain sizes in a plurality of target regions. For example, the crystal grain size can be measured by the planimetric method, where the target is a region with an area of ​​600 nm × 600 nm in cross section 30. Specifically, the crystal grain size is calculated using the following expression (1). Crystal grain size = (target area / number of crystals) (1 / 2)

[0041] It should be noted that in the expression (1), “X ^ (1 / 2)” represents the square root of X.

[0042] According to the present embodiment, the average crystal grain size of the tungsten wire 10 in the cross section 30 is 0.16 µm or less. Moreover, according to the present embodiment, in the cross section 30 perpendicular to the axis P of the tungsten wire 10, as shown in FIG. Fig.1, the average crystal grain size in the center portion 31 and the average crystal grain size in the edge portion 32 are different from each other. Specifically, the average crystal grain size in the edge portion 32 is at least 5% smaller than the average crystal grain size in the center portion 31.

[0043] For example, the center section 31 is a predetermined area through which the axis P runs. In the Fig. 1, the axis P passes through the center of the center portion 31. The edge portion 32 is a portion located outward from the center portion 31. The edge portion 32 in the cross-section 30 of the tungsten wire 10 is closer to the surface 20 than the center of the radius connection axis P (i.e., the center) and a point on the surface 20.

[0044] A relationship between the tensile strength and the average crystal grain size of samples of a plurality of the tungsten wires prepared by the inventors will be described below.

[0045] The tensile strengths of the tungsten wires according to Comparative Example 1 and Working Examples 1, 2 and 3 described below are 4320 MPa, 4800 MPa, 5040 MPa and 5430 MPa, respectively, which are equivalent to the case described in Fig. 2A to Fig. 2D. In addition, as Comparative Examples 2 and 3, the average crystal grain sizes are also calculated for tungsten wires having tensile strengths of 3800 MPa and 4000 MPa, respectively.

[0046] The Fig. 4A to Fig.4C are diagrams each showing enlarged views of the cross section 30 of the tungsten wire 10 according to Working Examples 1 to 3. In each of the diagrams, (a) shows an SEM image of the edge portion 32 of the cross section 30 of a sample of the tungsten wire 10, and (b) shows an SEM image of the center portion 31. Each of the diagrams also shows, in each of (a) and (b), five target regions, each of which is a 600 nm × 600 nm square and indicated by a solid line, and the result of counting the number of crystals included in each of the target regions is indicated adjacent to a corresponding one of the target regions. It should be noted that when counting the number of crystals, a crystal that lies entirely within the target region is counted as one crystal, and a crystal that lies at least partially outside the target region is counted as half of a crystal.

[0047] The average crystal grain size of each of the center portion 31 and the edge portion 32 is obtained by averaging the crystal grain size calculated in each of the five target regions. For example, the average crystal grain size of the cross section 30 as a whole is obtained by averaging the crystal grain sizes of a total of 10 target regions, including the target regions of the center portion 31 and the edge portion 32.

[0048] Table 2 shows a relationship between the tensile strength and the average crystal grain size of the cross section 30 as a whole. [Table 2] Tensile strength [MPa] Average crystal grain size [µm] Comparison example 1 3800 0,247 Comparison example 2 4000 0,203 Comparison example 3 4320 0,178 Working example 1 4800 0,155 Working example 2 5040 0,150 Working example 3 5430 0,146

[0049] The Fig. 5 is a graph showing a relationship between the tensile strength and the average crystal grain size of the cross section 30 of the tungsten wire 10 according to the present embodiment. Fig.5, the horizontal axis represents the average crystal grain size [µm] in cross section 30 and the vertical axis represents a tensile strength [MPa].

[0050] As shown in Table 2 and the Fig.As shown in Figure 5, the tensile strength increases with decreasing average crystal grain size. Specifically, the tensile strength increases significantly when the average crystal grain size drops below 0.20 μm, and the tensile strength increases even more significantly when the average crystal grain size reaches or below 0.16 μm. In the tungsten wire 10 according to the present embodiment, the average crystal grain size in the cross section 30 is at most 0.160 μm. This provides a tungsten wire with a high tensile strength of at least 4800 MPa. Furthermore, for example, by setting the average width of surface crystal grains to at most 0.146 μm, a tungsten wire with a high tensile strength of at least 5430 MPa can be provided.

[0051] A relationship between the tensile strength and the average crystal grain size of each of the center portion 31 and the edge portion 32 is shown in Table 3. [Table 3] Tensile strength [MPa] Average crystal grain size of the edge section [µm] Average crystal grain size of the center section [µm] Edge section / Center section [%] Working example 1 4800 0,155 0,173 90 Working example 2 5040 0,150 0,172 87 Working example 3 5430 0,146 0,162 90

[0052] As shown in Table 3, in the tungsten wire 10 according to Working Examples 1 to 3, the average crystal grain size of the edge portion 32 is at least 5% smaller than the average crystal grain size of the center portion 31. For example, in the tungsten wire 10 according to Working Examples 1 to 3, the average crystal grain size of the edge portion 32 is at least 10% smaller than the average crystal grain size of the center portion 31. In Comparative Examples 1 to 3, such a difference of at least 5% was not observed. For example, in Comparative Example 3, the average crystal grain size of the edge portion 32 was 0.178 μm, and the average crystal grain size of the center portion 31 was 0.173 μm.This means that in Comparative Example 3, the average crystal grain size of the edge portion 32 is only about 3% smaller than the average crystal grain size of the center portion 31.

[0053] As described above, the tungsten wire 10 according to the present embodiment is a tungsten wire containing tungsten or a tungsten alloy and having an average crystal grain size of 0.16 μm or less in the cross section perpendicular to the axis P of the tungsten wire 10. The average crystal grain size of the edge portion 32 outside the center portion 31 in the cross section 30 is at least 5% smaller than the average crystal grain size of the center portion 31 in the cross section 30.

[0054] As described above, in the tungsten wire 10 according to the present embodiment, the crystal grain of tungsten in the peripheral portion 32 is smaller than in the center portion 31 of the cross section 30. The smaller crystal grains of the tungsten wire 10 can increase the tensile strength of the tungsten wire 10. In other words, a tungsten wire 10 with high tensile strength can be provided. Secondary recrystallization temperature

[0055] Next, a secondary recrystallization temperature of the tungsten wire 10 will be described.

[0056] The tungsten wire 10 according to the present embodiment includes small primary recrystallization grains as a result of being manufactured by the manufacturing method described later. When the tungsten wire 10 is heated at a high temperature, the primary recrystallization grains are recrystallized again. As a result, large secondary recrystallization grains are formed. The temperature at which the secondary recrystallization grains form is the secondary recrystallization temperature. The secondary recrystallization temperature of the tungsten wire 10 according to the present embodiment is at least 2200 degrees Celsius.

[0057] A relationship between the tensile strength and the secondary recrystallization temperature of samples of a plurality of tungsten wires prepared by the inventors will be described below.

[0058] The Fig.Figure 6 is a graph showing a relationship between the tensile strength and the secondary recrystallization temperature of a tungsten wire. Fig. Figure 6 shows an SEM image of the surface 20 of the tungsten wire of each of Comparative Example 1 and Working Example 1 after the tungsten wire was subjected to heat treatment. The heat treatment temperatures were 2200 degrees Celsius and 2300 degrees Celsius, respectively. The heat treatment was performed while passing electricity through the tungsten wire.

[0059] As it is in the Fig.As shown in Fig. 6, in Comparative Example 1, it is confirmed that a secondary recrystallization grain larger than a primary recrystallization grain was generated in a portion of the tungsten wire 10 as a result of the heat treatment at 2200 degrees Celsius. When the heat treatment is performed at 2300 degrees Celsius, the secondary recrystallization grains are generated in almost the entire portion of the tungsten wire 10.

[0060] Furthermore, in Working Example 1, it is confirmed that secondary recrystallization of the tungsten wire 10 did not occur due to the heat treatment at 2200 degrees Celsius, and that primary recrystallization grains were generated in almost the entire portion of the tungsten wire 10. When the heat treatment is performed at 2300 degrees Celsius, it is confirmed that secondary recrystallization grains were generated in a portion of the tungsten wire 10.

[0061] As described above, the tungsten wire 10 according to the present embodiment is a tungsten wire containing a tungsten alloy, and the secondary recrystallization temperature of the tungsten wire is at least 2200 degrees Celsius. Furthermore, for example, the secondary recrystallization temperature of the tungsten wire 10 may be less than 2300 degrees Celsius.

[0062] According to this structure, a tungsten wire 10 with high tensile strength can be provided. Furthermore, the tensile strength decreases as secondary recrystallization grains are generated. Since the secondary recrystallization temperature of the tungsten wire 10 is at least 2200 degrees Celsius, the tungsten wire 10 can maintain high tensile strength even in a high-temperature environment of at least 2200 degrees Celsius and at most the secondary recrystallization temperature. Accordingly, the tungsten wire 10 is expected to be used in various high-temperature environments. Process for producing the tungsten wire

[0063] Next, a method of manufacturing the tungsten wire 10 according to the present embodiment will be described with reference to FIG. Fig. 7. The Fig. 7 is a flowchart showing a method for manufacturing the tungsten wire 10 according to the present embodiment.

[0064] As it is in the Fig. As shown in Figure 7, a tungsten ingot is first prepared (S10). Specifically, a tungsten ingot is prepared by preparing an aggregation of tungsten powder and pressing and sintering the aggregation of the tungsten powder.

[0065] It should be noted that when manufacturing a tungsten wire 10 containing a tungsten alloy, a mixture obtained by mixing a tungsten powder and a metal powder (for example, a rhenium powder) in a predetermined ratio is prepared instead of aggregating a tungsten powder. The average grain diameter of a tungsten powder and a rhenium powder is, for example, in the range of at least 3 μm to at most 4 μm, but is not limited to this example.

[0066] Next, closed-die forging processing is applied to the produced tungsten ingot (S12). Specifically, the tungsten ingot is press-forged and stretched from its periphery to obtain a tungsten wire having a wire shape. Instead of closed-die forging processing, the tungsten ingot may be subjected to rolling processing. For example, a tungsten ingot with a diameter of about 15 mm is formed into a tungsten wire with a diameter of about 3 mm by repeatedly applying closed-die forging processing to the tungsten ingot. During closed-die forging processing, annealing is performed to ensure machinability in subsequent processes. For example, annealing is performed at 2400 degrees Celsius in a diameter range of at least 8 mm to at most 10 mm.However, to ensure tensile strength through crystal grain refinement, annealing is not performed in drop forging with a diameter of less than 8 mm.

[0067] Next, the tungsten wire is heated to 900 degrees Celsius before hot drawing (S14).

[0068] Specifically, the tungsten wire is directly heated by a torch or the like. An oxide layer is formed on the surface of the tungsten wire by heating the tungsten wire, preventing wire breakage during processing in the subsequent hot drawing.

[0069] Next, hot drawing is performed (S16). Specifically, drawing of the tungsten wire, namely, a wire drawing process (thinning) of the tungsten wire, is performed using a single wire drawing die while heating. The heating temperature is, for example, 1000 degrees Celsius. The workability of a tungsten wire increases as the heating temperature increases, and thus drawing can be easily performed. The reduction in the area of ​​the tungsten wire by drawing using a single wire drawing die is, for example, at least 10% and at most 40%. In the drawing processing, a lubricant comprising graphite dispersed in water can be used.

[0070] After drawing, electrolytic polishing can be performed to smooth the surface of the tungsten wire. Electrolytic polishing is performed, for example, by generating a potential difference between a tungsten wire and a counter electrode in a state where the tungsten wire and the counter electrode are immersed in an electrolyte such as aqueous sodium hydroxide.

[0071] Hot drawing (S16) is performed repeatedly until a tungsten wire with a desired diameter is obtained (No in S18). The desired diameter is a diameter at the stage immediately before the final drawing processing (S20) is performed and is, for example, at most 250 µm.

[0072] When repeating hot drawing, a wire drawing die with a smaller hole diameter than a hole diameter of a wire drawing die used in the immediately preceding drawing is used. Moreover, when repeating hot drawing, the tungsten wire is heated at a heating temperature lower than a heating temperature of the immediately preceding drawing. For example, the heating temperature in the drawing processing immediately before the final drawing processing is lower than any of the previous heating temperatures, such as 400 degrees Celsius, which contributes to the refinement of crystal grains. It should be noted that the heating temperature in the hot drawing is adjusted so that the amount of oxide adhering to the surface of the tungsten wire is in a range of, for example, at least 0.8 wt% to at most 1.6 wt% of the tungsten wire.When repeating the hot drawing process, electrolytic polishing can be omitted.

[0073] When a tungsten wire with a desired diameter is obtained and the next drawing processing is the final drawing processing (Yes in S18), room temperature drawing is performed (S20). Specifically, a tungsten wire is drawn without heating, thereby achieving further refinement of crystal grains. Moreover, room temperature drawing achieves a beneficial effect of aligning crystal orientations in a processing axis direction (specifically, a direction parallel to the P axis). Room temperature is, for example, a temperature in a range of at least 0 degrees Celsius to at most 50 degrees Celsius, and is, for example, 30 degrees Celsius. Specifically, the tungsten wire is drawn using a plurality of wire dies having different hole diameters. In room temperature drawing, a liquid lubricant such as a water-soluble lubricant is used.Since heating is not performed during drawing at room temperature, liquid evaporation is prevented. Accordingly, it can perform a sufficient function as a lubricant. Unlike hot drawing at 600 degrees Celsius or higher, which is the conventional tungsten wire processing method, the tungsten wire is not heated and is processed while being cooled with the liquid lubricant. As a result, dynamic recovery and dynamic recrystallization can be inhibited, contributing to the refinement of crystal grains without wire breakage, and high tensile strength can be achieved.

[0074] Finally, electrolytic polishing is performed on the tungsten wire having a desired diameter obtained by drawing at room temperature (S22). Electrolytic polishing is performed, for example, as a result of generating a potential difference between a tungsten wire and a counter electrode in a state where the tungsten wire and the counter electrode are immersed in an electrolyte such as aqueous sodium hydroxide.

[0075] Through the above-described processes, the tungsten wire 10 according to the present embodiment is manufactured. Through the above-described processes, the tungsten wire 10 has a length of, for example, at least 50 km immediately after manufacture and is thus industrially available. The tungsten wire 10 is cut to an appropriate length according to the aspect in which the tungsten wire 10 is to be used, and can also be used in the form of a needle or a rod. As described above, according to the present embodiment, the tungsten wire 10 to be used in various fields such as medical needles, saw wires, screen printing nets, etc., can be subjected to industrial mass production.

[0076] Tungsten wires 10 according to Working Examples 1 to 4 are tungsten wires manufactured by the processes described above. The differences in tensile strength between Working Examples 1 to 3 can be provided, for example, by lowering an annealing temperature of the annealing performed during die forging processing with a tungsten rod having a diameter in a range of at least 8 mm to at most 10 mm. For example, the tensile strength can be improved by 3% as a result of lowering the annealing temperature by 200 degrees Celsius with respect to a normal annealing temperature. In the same manner as above, the tensile strength can be improved by 5% as a result of lowering the annealing temperature by 400 degrees Celsius. Furthermore, the tensile strength can be further improved by starting drawing at room temperature (S20) with a larger diameter.The methods described above and the combination of these methods enable the production of a tungsten wire with a higher tensile strength (for example, Working Example 3).

[0077] Each of the processes specified in the method for producing the tungsten wire 10 is performed, for example, as an in-line process. Specifically, the plurality of wire dies used in step S16 are arranged in a manufacturing facility in descending order of hole diameters. A heating device such as a burner is arranged between the respective wire dies. Furthermore, an electrolytic polishing device may be arranged between the respective wire dies. The plurality of wire dies used in step S20 are arranged in descending order of hole diameters on the downstream side (i.e., the subsequent process side) of the wire dies used in step S16, and the electrolytic polishing device is arranged on the downstream side of the wire die with the smallest hole diameter.It should be noted that each of the operations can be performed individually. saw wire

[0078] The tungsten wire 10 according to the present embodiment can be used, for example, as a saw wire 2 of the cutting device 1 which cuts an object such as a silicon block or concrete, as shown in FIG. Fig. 8 is shown. The Fig. 8 is a perspective view showing a cutting device 1 according to the present embodiment.

[0079] As it is in the Fig.As shown in Figure 8, the cutting device 1 is a multi-wire saw including the saw wire 2. The cutting device 1 produces, for example, wafers by cutting the ingot 50 into thin slices. The ingot 50 is, for example, a silicon ingot comprising single-crystal silicon. Specifically, the cutting device 1 simultaneously produces a plurality of silicon wafers by cutting the ingot 50 using a plurality of saw wires 2.

[0080] It should be noted that the block 50 is, but is not limited to, a silicon block. For example, a block comprising another substance, such as silicon carbide or sapphire, may be employed. Alternatively, an object to be cut by the cutting device 1 may be concrete, glass, etc.

[0081] According to the present embodiment, the saw wire 2 comprises the tungsten wire 10. Specifically, the saw wire 2 is simply the tungsten wire 10 according to the present embodiment. Alternatively, the saw wire 2 may comprise the tungsten wire 10 and a plurality of abrasive particles incorporated into a surface of the tungsten wire 10.

[0082] As it is in the Fig. 8, the cutting device 1 further comprises two guide rollers 3, a block holder 4 and a tension release device 5.

[0083] A single saw wire 2 is looped multiple times over and between two guide rollers 3. Here, for ease of explanation, one loop of the saw wire 2 is considered as one saw wire 2, and it is assumed that a plurality of saw wires 2 are looped over and between two guide rollers 3. In other words, the plurality of saw wires 2 form a single continuous saw wire 2. It should be noted that the plurality of saw wires 2 may be a plurality of saw wires that are separated from each other.

[0084] Each of the two guide rollers 3 rotates in a state where the plurality of saw wires 2 are straightened with a predetermined tension, thereby causing the plurality of saw wires 2 to rotate at a predetermined speed. The plurality of saw wires 2 are arranged parallel to each other and equally spaced. Specifically, each of the two guide rollers 3 is provided with grooves arranged at predetermined intervals so that the saw wires 2 fit therein. The intervals between the grooves are determined according to the thickness of the wafers to be cut. The width of the groove is substantially identical to the diameter φ of the saw wire 2.

[0085] It should be noted that the cutting device 1 may comprise three or more guide rollers 3. The saw wires 2 may be looped over and between the three or more guide rollers 3.

[0086] The block holder 4 holds the block 50, which is an object to be cut. The block holder 4 pushes the block 50 through the saw wires 2, and thereby the block 50 is cut by the saw wires 2.

[0087] The tension release device 5 is a device that releases a tension exerted on the saw wire 2. The tension release device 5 is, for example, an elastic body such as a coil or disc spring. As shown in the Fig. As shown in Figure 8, one end of the tension release device 5, which is, for example, a coil spring, is connected to the guide roller 3, and the other end is attached to a predetermined wall surface. The tension release device 5 can release the tension applied to the saw wire 2 by adjusting the position of the guide roller 3.

[0088] It should be noted that, although not shown in the diagram, the cutting device 1 may be a free abrasive particle type cutting device and may include a feeding device that supplies a slurry to the saw wires 2. The slurry is a cutting fluid, such as a coolant, comprising abrasive particles dispersed therein. The abrasive particles included in the slurry adhere to the saw wire 2, and thereby the block 50 can be easily cut.

[0089] The saw wire 2, which includes the tungsten wire 10 with high tensile strength, can be looped over and between guide rollers 3 with strong tension. Accordingly, vibrations of the saw wire 2 caused during the process of cutting the block 50 are prevented, and consequently, the cutting loss of the block 50 can be reduced.

[0090] It should be noted that the tungsten wire 10 can also be used as a metal mesh, such as a screen mesh for screen printing. For example, a screen mesh comprises a plurality of tungsten wires 10 woven as warp and weft yarns.

[0091] In addition, the tungsten wire 10 can also be used as a medical needle or test needle. Furthermore, the tungsten wire 10 can also be used, for example, as a reinforcing wire for an elastic component such as a tire, a conveyor belt, or a catheter. For example, a tire comprises a plurality of tungsten wires 10 bundled in layers as a belt or tire base layer. Miscellaneous

[0092] Although the tungsten wire and the saw wire according to the present invention have been described so far based on the above-described embodiment, the present invention is not limited to the above-described embodiment.

[0093] For example, the metal contained in a tungsten alloy does not have to be rhenium. A tungsten alloy is an alloy of tungsten and at least one metal other than tungsten. The metal other than tungsten is a transition metal, namely rhenium (Re), iridium (Ir), ruthenium (Ru), or osmium (Os). The content of the metal other than tungsten is at least 0.1 wt% and at most 10 wt%.

[0094] Furthermore, the tungsten wire 10 may, for example, contain tungsten doped with potassium (K). Potassium is present in the tungsten grain boundaries of the tungsten wire 10. The tungsten content of the tungsten wire 10 is, for example, at least 99 wt.%.

[0095] The potassium content of the tungsten wire 10 is preferably 0.01 wt% or less, but is not limited to this example. For example, the potassium content of the tungsten wire 10 may be at least 0.005 wt% and at most 0.010 wt%.

[0096] The diameter, elastic modulus, and tensile strength of the tungsten wire containing potassium-doped tungsten (i.e., a potassium-doped tungsten wire) are equivalent to those of the above-described embodiment. Furthermore, at least one of the average width of the surface crystal grains, the average crystal grain size, or the secondary recrystallization temperature is also equivalent to those of the above-described embodiment. The crystal grain size is at least 5% larger in the edge portion 32 than in the center portion 31 in the cross section perpendicular to the axis P of the potassium-doped tungsten wire.

[0097] Since the tungsten wire contains a small amount of potassium, crystal grain growth in the radial direction of the tungsten wire is prevented, as described above. In other words, since the width of the surface crystal grains can be reduced, the tensile strength can be increased.

[0098] The potassium-doped tungsten wire can be manufactured by a manufacturing method equivalent to the manufacturing method of the embodiment using a doped tungsten powder doped with potassium instead of a tungsten powder.

[0099] In addition, the surface of the tungsten wire 10 is coated by an oxide film or a nitride film.

[0100] It should be noted that the present invention also includes other forms in which various modifications apparent to a person skilled in the art are applied to the embodiment, or forms in which structural components and functions in the embodiment are arbitrarily combined within the scope of the present invention. [List of reference symbols] 2 saw wire 10 tungsten wire 30 cross section 31 central section

Claims

[1] Saw wire comprising a tungsten wire (10) containing a tungsten alloy, the tungsten alloy consisting of: Tungsten and at least 0.1 wt.% and at most 10 wt.% of a transition metal selected from rhenium (Re), iridium (Ir), ruthenium (Ru) or osmium (Os), and not more than 0.01% by weight potassium, wherein the tungsten wire has an average crystal grain size in a cross-section (30) perpendicular to an axis (P) of the tungsten wire (10) of at most 0.16 µm, wherein the average crystal grain size in the cross-section (30) in an edge portion (32) closer to the surface (20) is at least 5% smaller than in a center portion (31), the edge portion (32) being located outside the center portion (31) in the cross-section (30), wherein the tensile strength of the tungsten wire (10) is at least 4800 MPa and at most 5500 MPa, wherein the diameter of the tungsten wire (10) is at most 100 µm and wherein the surface of the tungsten wire (10) is coated by an oxide film or a nitride film. [2] The saw wire according to claim 1, wherein the average width of surface crystal grains on a surface (20) of the tungsten wire (10) in directions perpendicular to an axis (P) of the tungsten wire (10) is at most 76 nm [3] Saw wire (10) according to claim 1 or 2, wherein the secondary recrystallization temperature of the tungsten wire (10) is at least 2200 degrees Celsius. [4] Saw wire (10) according to one of claims 1 to 3, wherein the tungsten content of the tungsten wire (10) is at least 90 wt.%.

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