Metal wire and saw wire

Abstract

To provide a durable metal wire.SOLUTION: The metal wire is made of tungsten or tungsten alloy, and the number of times until wire breakage is 20,000 or more when a fatigue test is performed at maximum stress of 4400 MPa according to the JIS C6821 standard.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a metal wire and a saw wire. [Background technology]

[0002] Patent Document 1 discloses a saw wire including a core wire made of a piano wire and a plurality of abrasive grains fixed to the core wire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-65205 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional saw wires have insufficient durability.

[0005] Therefore, an object of the present invention is to provide a metal wire and a saw wire that are highly durable. [Means for solving the problem]

[0006] A metal wire according to one embodiment of the present invention is made of tungsten or a tungsten alloy, and can withstand 20,000 or more cycles before breaking when fatigue tested at a maximum stress of 4400 MPa according to JIS C6821.

[0007] A saw wire according to one aspect of the present invention includes the metal wire according to the above aspect and abrasive grains electrodeposited on a surface of the metal wire. [Effects of the Invention]

[0008] According to the present invention, a metal wire and a saw wire having high durability can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a cutting device to which a saw wire according to an embodiment is attached. [Figure 2] FIG. 2 is a schematic diagram of a test device used in a fatigue test of the metal wire according to the embodiment. [Figure 3A] 3A is a perspective side view of the jig of the testing apparatus shown in FIG. 2. FIG. [Figure 3B] 3B is a perspective view of the jig of the testing device shown in FIG. 2, seen from below. [Figure 4] FIG. 4 shows the results of the fatigue test. [Figure 5A] FIG. 5A is a cross-sectional view of a metal wire according to Example 1. FIG. [Figure 5B] FIG. 5B is a cross-sectional view of a metal wire according to Example 2. As shown in FIG. [Figure 5C] FIG. 5C is a cross-sectional view of a metal wire according to the third embodiment. [Figure 5D] FIG. 5D is a cross-sectional view of a metal wire according to Example 4. [Figure 6] FIG. 6 is a flowchart showing a method for manufacturing a metal wire according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, metal wires and saw wires according to embodiments of the present invention will be described in detail with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present invention. Therefore, the numerical values, shapes, materials, components, component arrangements and connection forms, steps, and step orders shown in the following embodiments are merely examples and are not intended to limit the present invention. Therefore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0011] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0012] Furthermore, in this specification, terms indicating the relationship between elements, such as straight line or orthogonal line, terms indicating the shape of elements, such as circle or cylinder, and numerical ranges are not expressions that only express the strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0013] (Embodiment) [Metal wire and saw wire composition] First, the configurations of the metal wire and saw wire according to this embodiment will be described.

[0014] Fig. 1 is a schematic diagram of a cutting device 100 to which a saw wire 3 according to the present embodiment is attached. The saw wire 3 is attached to the cutting device 100 and used to cut an ingot 5. As shown enlarged within the dashed circular frame in Fig. 1, the saw wire 3 includes a metal wire 1 and a plurality of abrasive grains 2.

[0015] The metal wire 1 is the core wire of the saw wire 3. The metal wire 1 is made of tungsten or a tungsten alloy. The tungsten content of the metal wire 1 is, for example, 90 wt% or more, but is not limited to this. The tungsten content of the metal wire 1 may be 95 wt% or more, 99 wt% or more, 99.9 wt% or more, or 99.99 wt% or more. The metal wire 1 may contain unavoidable impurities that are mixed in during the manufacturing process.

[0016] The tungsten alloy is, for example, an alloy of tungsten (W) and one or more metals other than tungsten. The metal other than tungsten is, for example, rhenium (Re). The rhenium content of the metal wire 1 made of the rhenium-tungsten alloy (ReW) is, for example, 0.1 wt% or more and 10 wt% or less, but is not limited thereto. For example, the rhenium content may be 1 wt% or more, 3 wt% or more, or 5 wt% or more.

[0017] If the rhenium content is high, the tensile strength of the metal wire 1 can be increased. On the other hand, if the rhenium content is too high, it is difficult to thin the metal wire 1 while maintaining its high tensile strength. Specifically, wire breakage occurs more easily, making it difficult to draw long lengths. By lowering the rhenium content and increasing the tungsten content to 90 wt% or more, the workability of the metal wire 1 can be improved. Furthermore, by lowering the content of rare and expensive rhenium, it becomes possible to mass-produce long, inexpensive metal wires 1.

[0018] 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 the same as that of rhenium, for example. In these cases, the same effects as in the case of a rhenium-tungsten alloy can be obtained. The metal wire 1 may be made of an alloy of tungsten and two or more metals other than tungsten.

[0019] The metal wire 1 has a substantially circular cross section perpendicular to the wire axis direction. The wire axis direction is the direction in which the metal wire 1 extends. The metal wire 1 has a substantially constant wire diameter along the wire axis direction. The wire diameter of the metal wire 1 is, for example, 100 μm or less, but is not limited to this. The wire diameter of the metal wire 1 may be 80 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less.

[0020] The smaller the diameter of the metal wire 1, the smaller the diameter of the saw wire 3. The smaller the diameter of the saw wire 3, the smaller the cutting allowance of the workpiece. This reduces loss of the workpiece and increases the number of wafers that can be obtained.

[0021] The wire diameter of the metal wire 1 is, for example, 5 μm or more, so that the cross-sectional area of ​​the metal wire 1 does not become too small, and the absolute strength of the metal wire 1 can be ensured within a range that allows it to be used as a saw wire.

[0022] The tensile strength of the metal wire 1 is 4800 MPa (=4.8 GPa) or more. The tensile strength may be 5000 MPa or more, 5200 MPa or more, 5500 MPa or more, or 5700 MPa or more. The tensile strength is, for example, 6000 MPa or less, but may also exceed 6000 MPa. The tensile strength can be measured, for example, based on the tensile test of the Japanese Industrial Standards (JIS H 4460 8).

[0023] The higher the tensile strength of the metal wire 1, the stronger the tension of the metal wire 1 (saw wire 3) can be applied to the guide roller, thereby reducing the swinging amplitude of the metal wire 1. The smaller the swinging amplitude, the smaller the cut margin of the workpiece. This reduces the loss of the workpiece.

[0024] The metal wire 1 according to this embodiment can withstand 20,000 or more cycles before breaking when subjected to a fatigue test at a maximum stress of 4400 MPa in accordance with JIS C6821. In other words, the metal wire 1 has excellent durability. Specific details of the fatigue test will be described later.

[0025] The abrasive grains 2 are hard particles, such as diamond or CBN (cubic boron nitride) particles. A plurality of the abrasive grains 2 are dispersed and arranged on the surface of the metal wire 1. The average particle size of the plurality of abrasive grains 2 is, for example, 10 μm or less. The plurality of abrasive grains 2 are dispersed and arranged over the entire surface around the entire circumference of the axis of the metal wire 1.

[0026] The plurality of abrasive grains 2 are electrodeposited on the surface of the metal wire 1. Specifically, the plurality of abrasive grains 2 are at least partially coated with a plating layer (not shown), thereby adhering to the surface of the metal wire 1. The plating layer is, for example, a metal layer made of nickel alone or an alloy layer containing nickel. The plating layer may have a multi-layer structure.

[0027] [Configuration and operation of cutting device] Next, the configuration and operation of the cutting device 100 will be described.

[0028] As shown in FIG. 1, the cutting apparatus 100 is a multi-wire saw apparatus to which a saw wire 3 is attached. The cutting apparatus 100 cuts (slices) an ingot 5 into thin plates to manufacture wafers (substrates). The ingot 5 is an example of an object to be cut by the cutting apparatus 100, and is, for example, a semiconductor ingot such as silicon or silicon carbide. The object to be cut is not limited to a semiconductor ingot, and may be a solid object (lump) made of various solid materials such as metal, resin, glass, or concrete.

[0029] As shown in FIG. 1, the cutting device 100 includes a saw wire 3, two guide rollers 110, a support section 120, an unwinding section 130, and a winding section 140.

[0030] A single saw wire 3 is wound multiple times around the two guide rollers 110. The saw wire 3 is wound alternately and repeatedly around the two guide rollers 110 from the unwinding section 130 to the winding section 140. Each of the two guide rollers 110 has multiple grooves at a predetermined pitch into which the saw wire 3 is inserted. The groove pitch is determined according to the thickness of the wafer to be cut out. The width of the groove is approximately the same as the wire diameter of the saw wire 3. The saw wire 3 is arranged parallel to each other and at equal intervals for each revolution. When the two guide rollers 110 rotate, the saw wire 3 rotates in conjunction with the rotation.

[0031] The support part 120 supports an ingot 5, which is an object to be cut. The support part 120, while supporting the ingot 5, is movable toward the saw wire 3 (downward in the drawing).

[0032] The unwinding section 130 has a reel around which the saw wire 3 is wound, and the saw wire 3 is unwound from the reel in accordance with the rotation of the guide roller 110 .

[0033] The winding section 140 has a winding frame for winding the saw wire 3, and winds the saw wire 3 onto the winding frame in accordance with the rotation of the guide roller 110.

[0034] Next, the operation of cutting the ingot 5 by the cutting device 100 will be described.

[0035] When cutting the ingot 5, the cutting device 100 rotates each of the two guide rollers 110 to which the saw wire 3 is attached. The saw wire 3 rotates in conjunction with the rotation of the guide rollers 110 while being stretched straight with a predetermined tension. The predetermined tension is, for example, 3600 MPa.

[0036] The support part 120 pushes the ingot 5 toward the saw wire 3, and the ingot 5 is cut (sliced) by the saw wire 3. When cutting, a maximum stress of approximately 4400 MPa is momentarily applied to the saw wire 3.

[0037] The guide roller 110 can rotate not only in the direction from the unwinding section 130 to the winding section 140 (forward rotation), but also in the opposite direction (reverse rotation). The guide roller 110 rotates repeatedly between forward and reverse rotations when cutting the ingot 5, and the saw wire 3 gradually moves from the unwinding section 130 to the winding section 140.

[0038] This rotation and movement causes the saw wire 3 to be repeatedly bent and straightened thousands of times in one cut. For this reason, if a piano wire with low durability is used as the saw wire, the piano wire will break due to fatigue after one cut. Even if it does not break due to fatigue, it will not be able to withstand a second cut, so a new piano wire must be prepared.

[0039] In contrast, the saw wire 3 according to the present embodiment can be cycled 20,000 times or more before breaking when subjected to a fatigue test at a maximum stress of 4400 MPa in accordance with JIS C6821. In other words, the saw wire 3 is unlikely to break due to fatigue even when used to cut the ingot 5, and can be reused for the second or subsequent cutting.

[0040] When reusing the saw wire 3, the worn abrasive grains 2 and plating layer may be peeled off. That is, after returning the saw wire 3 to the state of the metal wire 1 (element wire), a plurality of abrasive grains 2 are again attached to the surface of the metal wire 1 by electrodeposition. In this way, the saw wire 3 having the abrasive grains 2 attached thereto is manufactured again, and can be reused for cutting the ingot 5.

[0041] [Fatigue test] Next, a fatigue test conducted by the inventors of the present invention to confirm the durability of the metal wire 1 according to this embodiment will be described.

[0042] The fatigue test was conducted in accordance with JIS C6821 standard (testing method for mechanical properties of optical fibers). Fig. 2 is a schematic diagram of a test apparatus 10 used in the fatigue test of the metal wire 1 according to the present embodiment. Figs. 3A and 3B are perspective views, seen from the side and below, respectively, of a jig 20 of the test apparatus 10 shown in Fig. 2.

[0043] As shown in FIG. 2, the test device 10 includes jigs 20 and 30, a cover 40, and a hanger 50.

[0044] Jigs 20 and 30 are each a disk-shaped member with a predetermined thickness. Jig 20 has a groove 21 formed along its circumferential side surface. Jig 30 has a groove 31 formed along its circumferential side surface. Jig 30 is fixed to, for example, the floor (ground). A hoisting tool 50 is fixed to jig 20. The hoisting tool 50 can apply a load to jig 20 in a vertically upward direction.

[0045] In a fatigue test, a metal wire 1 of a predetermined length is arranged so as to span one revolution between jigs 20 and 30. Specifically, as shown in FIG. 2, the metal wire 1 is arranged in each of grooves 21 of jig 20 and grooves 31 of jig 30. As shown in FIG. 3B, groove 21 is provided with through-holes 22 into which the metal wire 1 can be inserted. As shown in FIG. 2, both ends of the metal wire 1 are inserted into through-holes 22. In this state, as shown in FIG. 3A, a cover 40 is fixed to jig 20 so as to cover groove 21, thereby fixing the metal wire 1.

[0046] The diameter of each of grooves 21 of jig 20 and grooves 31 of jig 30 is 30 mm. As a result, the distance between the floating portions of metal wire 1 is also 30 mm. The length of the floating portions of metal wire 1, i.e., the portion between jig 20 and jig 30, was set to 80 mm.

[0047] In the fatigue test, as shown in FIG. 2, a vertically upward load was repeatedly applied to a jig 20 with the metal wire 1 fixed, and the number of tests was counted until the metal wire 1 broke, i.e., was broken. By applying a load to the jig 20, stress was applied to the metal wire 1. The application of a load from a predetermined initial value to a maximum load was counted as one test. The initial value was set to 10% of the maximum load. The test frequency, i.e., the number of tests per second, was set to 10 Hz (= 10 times / second).

[0048] The maximum load is a value at which the stress (i.e., maximum stress) applied to the metal wire 1 when the maximum load is applied is 4400 MPa. This value corresponds to the maximum value of stress that can be applied to the saw wire 3 (metal wire 1) when the saw wire 3 (metal wire 1) attached to the cutting device 100 cuts the ingot 5. Note that it is not necessary to apply a maximum stress of 4400 MPa exactly, and a deviation of several percent is acceptable.

[0049] The metal wires used in the fatigue test were a tungsten alloy wire containing 1 wt% Re (ReW wire), a pure tungsten wire (pure W wire), and a piano wire as a comparative example. The pure tungsten wire has a sufficiently high tungsten content of 99.95 wt% or more.

[0050] Table 1 below shows the physical properties, test conditions, and test results of the tungsten alloy wire and piano wire used.

[0051] [Table 1]

[0052] The diameter of each of the ReW wire, pure W wire, and piano wire is approximately 37 μm. The cross-sectional area of ​​each of the ReW wire, pure W wire, and piano wire is approximately 0.0022 mm. 2 is.

[0053] In Table 1, "Sample" indicates the type of metal wire subjected to the fatigue test. "1%ReW" indicates a tungsten alloy wire (ReW wire) containing 1 wt% Re. "Pure W" indicates a pure tungsten wire (pure W wire). "Porosity" is the percentage of voids contained in the metal wire. Details of porosity will be explained later. "Elemental wire strength" indicates the strength of the metal wire. "Tensile strength" indicates the tensile strength of the metal wire.

[0054] "Load" represents the maximum load that the hoisting tool 50 shown in FIG. 2 applies vertically upward to the jig 20. "Load (one wire)" represents the load applied to one metal wire. As shown in FIG. 2, the metal wire is hung between the two jigs 20 and 30 so as to make one round trip, and for convenience, it is shown as "two" metal wires. The load applied to the jig 20 is distributed to the "two" metal wires, so the load per wire is half of the load applied to the jig 20.

[0055] "Maximum stress" represents the stress applied to the metal wire when the maximum load is applied. "Stress amplitude" represents the range of stress change in a fatigue test. As mentioned above, in a fatigue test, the load changes from 10% of the maximum load to the maximum load, so the stress applied to the metal wire also changes from 10% of the maximum stress (initial stress) to the maximum stress. "Stress amplitude" is equivalent to half the difference between the maximum stress and the initial stress.

[0056] The "number of times" indicates the number of repetitions until the metal wire breaks as a result of a fatigue test.

[0057] FIG. 4 shows the results of the fatigue test. In FIG. 4, the vertical axis represents the maximum stress applied to the metal wire in the fatigue test. The horizontal axis represents the number of test repetitions until the metal wire breaks. In other words, the further to the right of the graph, the less likely the metal wire is to break, and the more durable the metal wire is. Note that the graph in FIG. 4 shows the maximum number of fatigue tests up to 1 million, but the maximum number of times the fatigue test was actually conducted was 100,000.

[0058] As shown in Figure 4, for both piano wire and tungsten alloy wire, the smaller the maximum stress, the more the number of repeated tests.When the maximum stress is 4400MPa, the number of repeated tests for piano wire is 228 times.In contrast, for tungsten alloy wire or pure tungsten wire, the number of repeated tests is more than 20,000 times, specifically, more than 21,288 times.In other words, it can be seen that tungsten alloy wire or pure tungsten wire has durability more than 100 times that of piano wire.

[0059] Furthermore, even if the maximum stress is reduced to 900 MPa, piano wire breaks at 5512 times, 15846 times, or 21746 times. It can be assumed that if the maximum stress is further reduced, there is room for the number of repetitions to increase, but it is less suitable for use as saw wire than tungsten alloy wire. In other words, even if the maximum stress of saw wire is small, such as when cutting soft ingots, the number of repetitions of the test on piano wire is not sufficient. For this reason, piano wire is not only difficult to reuse, but also may break when cutting ingots, so it is less suitable for saw wire than tungsten alloy wire.

[0060] On the other hand, in the case of tungsten alloy wire, the extension of the number of cycles is large with respect to the reduction of the maximum stress.That is, even if the maximum stress is only slightly reduced, the number of cycles increases greatly.Therefore, by reducing the stress when cutting ingot 5, it can further increase the possibility of reuse.

[0061] Although the fatigue test results show only the results of one sample of pure tungsten wire, the same effect as that of tungsten alloy wire is obtained. In addition, in the case of tungsten alloy wire, metals other than rhenium (such as osmium) also have the same effect.

[0062] [Relationship between void ratio and test results] As described above, the metal wire 1 according to the present embodiment has higher durability than a piano wire and can be reused after being used as the saw wire 3. The inventors of the present application have found that there is a significant relationship between the porosity of the metal wire 1 and durability (number of repetitions). The relationship between the porosity of the metal wire 1 and the test results of the fatigue test will be described below.

[0063] The porosity indicates the proportion of voids contained in the metal wire 1. Specifically, it represents the proportion of the area occupied by voids per predetermined unit area in the cross section of the metal wire 1. The porosity can be calculated by observing a cross-sectional SEM (Scanning Electron Microscope) image of the metal wire 1.

[0064] 5A to 5D are cross-sectional views of the metal wires according to Examples 1 to 4 in Table 1, respectively. As shown in each figure, the black parts are voids. The voids are mainly present at the grain boundaries. The porosity of the metal wires according to Examples 1 to 4 decreases in this order.

[0065] Examples 1 to 4 are samples that underwent fatigue testing at a maximum stress of 4400 MPa. As shown in Table 1 and Fig. 4, the smaller the porosity, the greater the number of test repetitions. In other words, the smaller the porosity, the higher the durability of the metal wire 1.

[0066] Specifically, as shown in Example 1, if the porosity of the metal wire 1 is 0.25% or less, it is found to have durability approximately 100 times or more than that of piano wire. If the porosity of the metal wire 1 is 0.18% or less, it is found to have durability approximately three times or more than that of 0.25%. Furthermore, if the porosity of the metal wire 1 is 0.11% or less, it is found to have durability approximately four times or more than that of 0.25%. If the porosity of the metal wire 1 is 0.07%, it is found that the metal wire 1 does not break even after 100,000 fatigue tests, and is extremely durable. The porosity of the metal wire 1 may be less than 0.07%.

[0067] [Manufacturing method] Next, a method for manufacturing a metal wire according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the method for manufacturing a metal wire according to this embodiment.

[0068] 6, first, a tungsten ingot is prepared (S10). Specifically, an aggregate of tungsten powder is prepared, and the prepared aggregate is pressed and sintered to produce the tungsten ingot.

[0069] When manufacturing the metal wire 1 made of a tungsten alloy, a mixture of tungsten powder and metal powder (e.g., rhenium powder) in a predetermined ratio is prepared instead of the aggregate of tungsten powder. The average particle size of the tungsten powder and the rhenium powder is, for example, in the range of 3 μm to 4 μm, but is not limited thereto.

[0070] Next, the produced tungsten ingot is subjected to swaging (S12). Specifically, the tungsten ingot is forged and compressed from the periphery to be stretched and formed into a wire-shaped tungsten wire. Rolling may be used instead of swaging. For example, by repeatedly performing swaging, a tungsten ingot with a diameter of approximately 15 mm is formed into a tungsten wire with a wire diameter of approximately 3 mm. An annealing treatment is performed during the swaging process to ensure subsequent workability. By adjusting the annealing conditions at this time, it is possible to produce metal wires 1 with different porosities as described above. Specific annealing conditions will be described later.

[0071] Next, the tungsten wire is heated to 900°C before hot drawing (S14). Specifically, the tungsten wire is directly heated using a burner or the like. By heating the tungsten wire, an oxide layer is formed on the surface of the tungsten wire to prevent breakage during the subsequent hot drawing process.

[0072] Next, hot drawing is performed (S16). Specifically, the tungsten wire is drawn using one wire drawing die, that is, the tungsten wire is drawn (thinned) while being heated. The heating temperature is, for example, 1000°C. Note that the higher the heating temperature, the more easily the tungsten wire can be worked, and therefore the easier the wire drawing can be. The cross-sectional area reduction rate of the tungsten wire in one drawing using one wire drawing die is, for example, 10% to 40%. In the wire drawing process, a lubricant in which graphite is dispersed in water may be used.

[0073] After the drawing step, the surface of the tungsten wire may be smoothed by electrolytic polishing, which is performed by immersing the tungsten wire and a counter electrode in an electrolyte such as an aqueous sodium hydroxide solution and generating a potential difference between the tungsten wire and the counter electrode.

[0074] The hot drawing process (S16) is repeated until a tungsten wire of the desired diameter is obtained (No in S18). The desired diameter here is the diameter of the wire just before the final drawing process (S20), which is, for example, 250 μm or less.

[0075] In the repeated hot wiredrawing, a wiredrawing die with a smaller hole diameter than the wiredrawing die used in the immediately preceding wiredrawing is used. Furthermore, in the repeated hot wiredrawing, the tungsten wire is heated at a lower heating temperature than the heating temperature in the immediately preceding wiredrawing. For example, the heating temperature in the wiredrawing step immediately before the final wiredrawing step is lower than the previous heating temperatures, e.g., 400°C, which contributes to the refinement of crystal grains. The heating temperature in the hot wiredrawing is adjusted so that the amount of oxide adhering to the surface of the tungsten wire is in the range of, for example, 0.8 wt% to 1.6 wt% of the tungsten wire. In the repeated hot wiredrawing, electropolishing may be omitted.

[0076] If a tungsten wire of the desired diameter is obtained and the next wiredrawing process is the last (Yes in S18), room-temperature wiredrawing is performed (S20). In other words, by drawing the tungsten wire without heating, further refinement of the crystal grains is achieved. Room-temperature wiredrawing also has the effect of aligning the crystal orientation in the processing axis direction (specifically, the direction parallel to the wire axis). Room temperature is, for example, a temperature in the range of 0°C to 50°C, and one example is 30°C. Specifically, the tungsten wire is drawn using multiple wiredrawing dies with different hole diameters.

[0077] In cold wire drawing, a liquid lubricant such as a water-soluble one is used. Since no heating is performed during cold wire drawing, evaporation of the liquid is suppressed, allowing the lubricant to function satisfactorily. Unlike the traditional method of drawing tungsten wire at temperatures above 600°C, this method does not heat the tungsten wire and instead uses a liquid lubricant to cool it while drawing. This suppresses dynamic recovery and dynamic recrystallization, prevents wire breakage, contributes to the refinement of crystal grains, and achieves high tensile strength.

[0078] Finally, the tungsten wire having the desired diameter formed by the room temperature wire drawing is subjected to electrolytic polishing (S22), which is performed by immersing the tungsten wire and a counter electrode in an electrolyte such as a sodium hydroxide solution and generating a potential difference between the tungsten wire and the counter electrode.

[0079] The metal wire 1 according to the present embodiment is manufactured through the above steps. By undergoing the above manufacturing steps, the length of the metal wire 1 immediately after manufacturing is, for example, 50 km or more, making it suitable for industrial use. The metal wire 1 can also be cut to an appropriate length depending on the mode of use, and used in the shape of a needle or rod.

[0080] Each step shown in the method for manufacturing the metal wire 1 is performed, for example, inline. Specifically, the multiple wiredrawing dies used in step S16 are arranged on the production line in order of decreasing hole diameter. A heating device such as a burner is disposed between each wiredrawing dies. An electrolytic polishing device may be disposed between each wiredrawing dies. Downstream (toward the subsequent process) of the wiredrawing die used in step S16, the multiple wiredrawing dies used in step S20 are arranged in order of decreasing hole diameter, and the electrolytic polishing device is disposed downstream of the wiredrawing die with the smallest hole diameter. Each step may be performed individually.

[0081] The annealing conditions in the swaging step (S12) for adjusting the porosity will be explained below with reference to Table 2.

[0082] [Table 2]

[0083] The swaging process is carried out in stages, multiple times depending on the diameter of the tungsten wire. Annealing is then performed to improve the tensile strength and the workability in the subsequent wire drawing process.

[0084] As shown in Table 2, in Example 1, annealing was performed at a temperature ranging from 1800°C to 1900°C with a wire diameter ranging from 11mm to 12mm. Tungsten recrystallizes when annealed at a temperature exceeding 2000°C. By performing annealing under conditions that prevent recrystallization, the tensile strength of the final product, metal wire 1, can be increased. As shown in Table 1, the tensile strength of the ReW wire according to Example 1 was higher than that of the pure tungsten wire according to Example 2 and the ReW wires according to Examples 3 and 4.

[0085] Next, in Example 1, annealing was performed at a temperature of 1800°C to 1900°C for wire diameters in the range of 5mm to 8mm. By performing annealing within a temperature range where recrystallization does not occur, it is possible to improve workability in subsequent steps without significantly reducing strength.

[0086] In Examples 2 to 4, annealing was performed at a temperature of 2000°C to 2100°C for wire diameters in the range of 11 mm to 12 mm. Because the temperature was 2000°C or higher, tungsten recrystallization occurred, causing existing voids to migrate to the grain boundaries. By keeping the temperature at 2100°C or lower, the grain size due to recrystallization was suppressed to approximately 100 μm in the pure tungsten wire of Example 2. This allowed for the formation of many grain boundaries, allowing the voids to be dispersed within the tungsten wire. Furthermore, in the ReW wires of Examples 3 and 4, the grain size due to recrystallization was suppressed to approximately 50 μm. This allowed for more void dispersion. In the subsequent swaging process, the voids could be expelled to the outside of the tungsten wire through the grain boundaries, reducing the void ratio. In Examples 3 and 4, the voids were well dispersed, allowing for a lower void ratio than in Example 2. The difference in porosity between Examples 3 and 4 is due to manufacturing variations or measurement variations in porosity.

[0087] In Examples 2 to 4, annealing was further performed at a temperature of 1600°C to 1700°C inclusive when the wire diameter was in the range of 5 mm to 8 mm. By performing annealing in a temperature range where recrystallization does not occur, it is possible to improve workability in subsequent steps without reducing strength. In Examples 2 to 4, the temperature in the first annealing was higher than in Example 1. Therefore, the temperature in the second annealing was lower than in Example 1. As a result, the tensile strength of the metal wire 1 in Examples 2 to 4 was ensured to be 4800 MPa or more.

[0088] [Effects, etc.] As described above, the metal wire 1 according to this embodiment is made of tungsten or a tungsten alloy, and when subjected to a fatigue test in accordance with the JIS C6821 standard at a maximum stress of 4400 MPa, it can be cycled 20,000 times or more before breaking.

[0089] This makes it possible to realize a highly durable metal wire 1. For example, when the metal wire 1 is used as the saw wire 3, it can be reused.

[0090] Furthermore, for example, the number of times until the disconnection occurs is 60,000 or more.

[0091] This makes the metal wire 1 more durable, which is more effective for reuse.

[0092] Moreover, for example, the porosity of tungsten in the metal wire 1 is 0.25% or less.

[0093] This can increase the durability of the metal wire 1.

[0094] Moreover, for example, the tensile strength of the metal wire 1 is 4.8 GPa or more.

[0095] This allows the metal wire 1 (saw wire 3) to be tightly stretched around the guide roller, thereby reducing the swinging amplitude of the metal wire 1. The reduced swinging amplitude reduces the cutting margin of the workpiece, thereby reducing loss of the workpiece.

[0096] Moreover, for example, the saw wire 3 according to the present embodiment includes a metal wire 1 and abrasive grains 2 electrodeposited on the surface of the metal wire 1.

[0097] This makes it possible to realize a highly durable saw wire 3. For example, the saw wire 3 used to cut an ingot 5 can be reused by removing the abrasive grains 2 and the plating layer from the saw wire 3 and then electrodepositing the abrasive grains 2.

[0098] (others) Although the metal wire and saw wire according to the present invention have been described based on the above-mentioned embodiment, the present invention is not limited to the above-mentioned embodiment.

[0099] For example, the saw wire 3 may not have electrodeposited abrasive grains 2. For example, the saw wire 3 may have only a metal wire 1 and be used in a loose abrasive cutting device.

[0100] Furthermore, for example, the tungsten content of the metal wire 1 may be less than 90 wt%. For example, the tungsten content of the metal wire 1 may be greater than 50 wt%. The tungsten content of the metal wire 1 may be 70 wt% or more, 75 wt% or more, 80 wt% or more, or 85 wt% or more.

[0101] Furthermore, for example, in the above-described embodiment, the metal wire 1 may be doped with a small amount of potassium or the like. The doped potassium is present in the grain boundaries of tungsten. The potassium (K) content is, for example, 0.010 wt% or less. As with tungsten alloy wires, potassium-doped tungsten wires can also realize metal wires with tensile strengths higher than the general tensile strength of piano wires. Similar effects can be obtained with oxides of other substances, such as cerium or lanthanum, rather than with oxides of potassium.

[0102] Furthermore, for example, the metal wire 1 may be used for purposes other than the saw wire 3. For example, the metal wire 1 may be used for other purposes such as a metallic mesh, stranded wire, or rope.

[0103] In addition, the present invention also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions of each embodiment within the scope of the present invention. [Explanation of symbols]

[0104] 1 metal wire 2 abrasive grains 3 Saw wire

Claims

1. A metal wire made of tungsten or a tungsten alloy, When fatigue testing is conducted in accordance with JIS C6821 standard at a maximum stress of 4400 MPa, the number of cycles until wire breakage occurs is 20,000 or more, the porosity of the tungsten in the metal wire is 0.25% or less; The tensile strength of the metal wire is 4.8 GPa or more. Metal wire.

2. When fatigue testing is conducted in accordance with JIS C6821 standard at a maximum stress of 4400 MPa, the number of cycles until breakage occurs is 60,000 or more. The metal wire of claim 1 .

3. The metal wire according to claim 1 or 2; abrasive grains electrodeposited on the surface of the metal wire; Saw wire.

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