Conductive wire

Abstract

To achieve enhanced fatigue resistance in a conductive wire provided with a core wire and a coating layer.SOLUTION: A conductive wire comprises a first metal core wire and a first steel coating layer that covers a first outer circumferential surface, which is an outer circumferential surface of the core wire, wherein the first metal has an electrical conductivity greater than that of the first steel, wherein the core wire includes a deformation section, which is either a protruding section that extends from the first outer circumferential surface, the protruding section having a height (first height) of 3% to 50% of a thickness (first thickness) of the coating layer, and a width (first width) equal to or less than the first height, or a recessed section that is recessed from the first outer circumferential surface, the recessed section having a depth (first depth) of 3% to 50% of the first thickness, and a width (second width) equal to or less than the first depth.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a conductive wire. [Background technology]

[0002] A Be-Cu alloy (hereinafter, also referred to as Be-Cu), which is a Cu (copper) alloy containing 0.2 to 2 mass % Be (beryllium), is known as a material for forming a conductive wire. While Be-Cu has high strength, it has problems such as being expensive due to the inclusion of Be. In contrast, a conductive wire that does not contain Be is known that includes a Cu core wire and a stainless steel coating layer that covers the outer surface of the core wire (for example, see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 59-205105 [Patent Document 2] JP 2023-024277 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conductive wires may be required to have not only sufficient conductivity and strength but also durability against repeated bending fatigue, for example, when used in moving parts of equipment. In addition, when a conductive wire is deformed by a load and then the load is removed, the original shape is not reproduced and the deformation remains, which may cause a problem of "sag." The conductive wires disclosed in the above patent documents may not have sufficient sag resistance.

[0005] Therefore, one of the objects of the present disclosure is to achieve improved sag resistance in a conductive wire including a core wire and a coating layer. [Means for solving the problem]

[0006] The conductive wire according to the present disclosure includes a core wire made of a first metal and a first steel coating layer covering a first outer circumferential surface of the core wire. The electrical conductivity of the first metal is greater than that of the first steel. The core wire includes a protruding portion protruding from the first outer circumferential surface and having a first height that is 3% to 50% of the first thickness that is the thickness of the coating layer and a first width that is equal to or less than the first height, or a deformed portion that is a recessed portion recessed from the first outer circumferential surface and has a first depth that is 3% to 50% of the first thickness and a second width that is equal to or less than the first depth. Effect of the Invention

[0007] According to the above-mentioned conductive wire, in the conductive wire including the core wire and the covering layer, it is possible to achieve improved resistance to sag. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view showing a cross section perpendicular to the longitudinal direction of a conductive wire in embodiment 1. FIG. [Diagram 2] 3 is a schematic cross-sectional view showing an enlarged view of the vicinity of a deformed portion (protrusion) in a cross section perpendicular to the longitudinal direction of the conductive wire. FIG. [Diagram 3] 2 is a schematic cross-sectional view showing a structure in the vicinity of the interface between a core wire and a coating layer. FIG. [Figure 4] 11 is a schematic cross-sectional view showing a cross section perpendicular to the longitudinal direction of a conductive wire in accordance with a second embodiment. FIG. [Diagram 5] 11 is a schematic cross-sectional view showing a cross section perpendicular to the longitudinal direction of a conductive wire in embodiment 3. FIG. [Figure 6] 3 is a schematic cross-sectional view showing an enlarged view of the vicinity of a deformed portion (depressed portion) in a cross section perpendicular to the longitudinal direction of the conductive wire. FIG. [Figure 7] 11 is a schematic cross-sectional view showing a cross section perpendicular to the longitudinal direction of a conductive wire in accordance with a fourth embodiment. FIG. [Figure 8] 1 is a flowchart showing an outline of a method for producing a conductive wire. [Figure 9]FIG. 11 is a schematic cross-sectional view for explaining an interface bonding step. [Figure 10] FIG. 11 is a schematic cross-sectional view for explaining an interface bonding step. [Figure 11] FIG. 11 is a schematic cross-sectional view for explaining an interface bonding step. [Figure 12] 1 is an optical microscope photograph of the vicinity of the deformed portion (protruding portion). [Figure 13] FIG. 13 is a diagram showing the relationship between the formation of a deformed portion and settling resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be described. (1) A core wire made of a first metal and a coating layer made of a first steel covering a first outer circumferential surface of the core wire. The electrical conductivity of the first metal is greater than that of the first steel. The core wire includes a protruding portion protruding from the first outer circumferential surface and having a first height that is 3% to 50% of the first thickness that is the thickness of the coating layer, and a first width that is equal to or less than the first height, or a deformed portion that is a recessed portion recessed from the first outer circumferential surface and has a first depth that is 3% to 50% of the first thickness, and a second width that is equal to or less than the first depth.

[0010] The present inventors have studied ways to improve the sag resistance of a conductive wire including a core wire and a coating layer. As a result, they have found that the sag resistance can be improved by forming a deformed portion, which is a protrusion or a depression, on the outer peripheral surface of the core wire. This is thought to be due to the following reasons, for example. When a conductive wire is deformed, if peeling occurs between the core wire and the coating layer, a difference occurs between the deformation amounts of the two, and sag occurs. In contrast, the formation of the deformed portion provides an anchor effect, and the occurrence of peeling between the core wire and the coating layer is suppressed. As a result, the sag resistance of the conductive wire is improved. In the conductive wire of the present disclosure, the core wire includes a deformed portion. Therefore, according to the conductive wire of the present disclosure, the conductive wire including the core wire and the coating layer can achieve improved sag resistance.

[0011] In the present disclosure, the first height, which is the height of the protrusion, means the height of the protrusion in the thickness direction of the coating layer in a cross section perpendicular to the longitudinal direction of the conductive wire. The first width, which is the width of the protrusion, means the width of the protrusion in the tangential direction to the outer peripheral surface of the core wire at the position where the protrusion is formed in a cross section perpendicular to the longitudinal direction of the conductive wire. The first depth, which is the depth of the depression, means the depth of the depression in the thickness direction of the coating layer in a cross section perpendicular to the longitudinal direction of the conductive wire. The second width, which is the width of the depression, means the width of the depression in the tangential direction to the outer peripheral surface of the core wire at the position where the depression is formed in a cross section perpendicular to the longitudinal direction of the conductive wire.

[0012] (2) In the above (1), the core wire may include a plurality of deformed portions. With this configuration, improvement in settling resistance can be more reliably achieved.

[0013] (3) In the above (2), the plurality of deformed portions may include a pair of protruding portions and one recessed portion disposed between the pair of protruding portions in the circumferential direction of the core wire so as to be adjacent to the pair of protruding portions, or may include a pair of recessed portions and one protruding portion disposed between the pair of recessed portions in the circumferential direction of the core wire so as to be adjacent to the pair of recessed portions. With this configuration, improvement in sag resistance can be more reliably achieved.

[0014] (4) In any one of (1) to (3) above, the core wire may include a diffusion layer containing 0.5% by mass or more of Fe, arranged to form a first outer circumferential surface. The second thickness, which is the thickness of the diffusion layer, may be 0.4% to 5% of the diameter of the core wire. With this configuration, peeling between the core wire and the coating layer is further suppressed, and improvement in sag resistance can be more reliably achieved.

[0015] (5) In the above (4), the second thickness may be 0.85% or more of the diameter of the core wire. With this configuration, improvement in settling resistance can be more reliably achieved.

[0016] Here, the diameter of the core wire means the circle-equivalent diameter of the core wire in a cross section perpendicular to the longitudinal direction of the conductive wire. When the core wire in the cross section is circular, the circle-equivalent diameter is the diameter of the core wire. When the core wire in the cross section has a shape other than circular, the circle-equivalent diameter is the diameter of a circle corresponding to the area of ​​the core wire. The second thickness, which is the thickness of the diffusion layer, can be measured by line analysis using, for example, an EPMA (Electron Probe Micro Analyzer). Specifically, the conductive wire is first cut in a cross section perpendicular to the longitudinal direction. The concentration of Fe near the interface between the core wire and the coating layer in the cross section is subjected to line analysis in a direction perpendicular to the interface. Then, the thickness of the part where the Fe content is 0.5 mass % or more can be determined to be the thickness of the diffusion layer (second thickness).

[0017] (6) In any one of the above (1) to (5), the first metal may be made of at least one of Cu (copper), Ag (silver), Al (aluminum), a Cu alloy, an Ag alloy, and an Al alloy. These materials have high electrical conductivity and are therefore suitable as materials for forming the core wire.

[0018] (7) In the above (6), the first metal may be Cu. Cu is particularly suitable as a material for forming the core wire because it is low in cost among materials having high electrical conductivity.

[0019] (8) In any one of the above (1) to (7), the first steel may be stainless steel. This configuration makes it easy to impart corrosion resistance to the coating layer.

[0020] (9) In any one of the above (1) to (7), the first steel may be an austenitic stainless steel. Austenitic stainless steel having sufficient workability is suitable as the stainless steel constituting the coating layer.

[0021] [Details of the embodiment of the present disclosure] Next, an embodiment of the conductive wire of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated.

[0022] (Embodiment 1) 1, conductive wire 1 in the present embodiment includes a core wire 11 and a coating layer 12. Core wire 11 is made of metal. Coating layer 12 is made of steel. Coating layer 12 covers a surface (outer circumferential surface) 11A of core wire 11. The conductivity of the metal constituting core wire 11 is greater than the conductivity of the steel constituting coating layer 12.

[0023] Core wire 11 is preferably made of a metal having excellent electrical conductivity. Core wire 11 is made of at least one of Cu, Ag, Al, a Cu alloy, an Ag alloy, and an Al alloy (e.g., Cu (pure copper)). The shape of core wire 11 in a cross section perpendicular to the longitudinal direction is not particularly limited, but is circular in this embodiment as shown in Fig. 1. The shape of core wire 11 in a cross section perpendicular to the longitudinal direction may be a shape other than circular, for example, elliptical.

[0024] In a cross section perpendicular to the longitudinal direction, the coating layer 12 has a shape that follows the outer circumferential surface of the core wire 11. In this embodiment, the coating layer 12 has a hollow cylindrical shape. In a cross section perpendicular to the longitudinal direction, the thickness of the coating layer 12 is constant except for a region where a deformed portion, which will be described later, exists. The steel constituting the coating layer 12 may be stainless steel. As the stainless steel constituting the coating layer 12, for example, austenitic stainless steel (e.g., SUS304) having excellent workability and corrosion resistance, such as JIS standard SUS304 and SUS316, can be used.

[0025] Referring to FIG. 1, the outer diameter D (wire diameter) of the conductive wire 1 is not particularly limited, but is, for example, 10 μm or more and 60 mm or less. The outer diameter D of the conductive wire 1 may be 20 μm or more. The outer diameter D of the conductive wire 1 may be 30 mm or less. In a cross section perpendicular to the longitudinal direction, the ratio of the cross-sectional area of ​​the core wire 11 to the cross-sectional area of ​​the conductive wire 1 can be appropriately determined in consideration of the required strength and conductivity, and may be, for example, 10% or more and 90% or less. The ratio of the cross-sectional area of ​​the core wire 11 to the cross-sectional area of ​​the conductive wire 1 may be 15% or more, or even 20% or more. The ratio of the cross-sectional area of ​​the core wire 11 to the cross-sectional area of ​​the conductive wire 1 may be 85% or less, 80% or less, or even 75% or less.

[0026] The core wire 11 includes a deformation portion. With reference to Figs. 1 and 2, in this embodiment, the deformation portion is a protruding portion 11B protruding from the outer circumferential surface 11A. From another perspective, the protruding portion 11B is a region in which a part of the core wire 11 enters a recess formed in the coating layer 12. The height h1 of the protruding portion 11B is 3% or more and 50% or less of the thickness t1 of the coating layer 12. The width w1 of the protruding portion 11B is equal to or less than the height h1 of the protruding portion 11B (equal to or less than 100% of the height h1). The anchor effect of the protruding portion 11B, which is a deformation portion, suppresses the occurrence of peeling between the core wire 11 and the coating layer 12 when the conductive wire 1 is deformed. As a result, the conductive wire 1 of this embodiment is a conductive wire with improved resistance to sagging.

[0027] If the height h1 of the protrusion 11B is less than 3% of the thickness t1 of the coating layer 12, the anchor effect is not sufficiently obtained. If the height h1 of the protrusion 11B exceeds 50% of the thickness t1 of the coating layer 12, the fatigue strength may decrease when repeated stress is applied to the conductive wire 1. Therefore, the height h1 of the protrusion 11B needs to be 3% or more and 50% or less of the thickness t1 of the coating layer 12. From the viewpoint of obtaining the anchor effect more reliably, the height h1 of the protrusion 11B is preferably 3.5% or more, more preferably 4% or more, of the thickness t1 of the coating layer 12. From the viewpoint of suppressing the decrease in fatigue strength more reliably, the height h1 of the protrusion 11B is preferably 40% or less, more preferably 30% or less of the thickness t1 of the coating layer 12.

[0028] If the width w1 of the protrusion 11B exceeds the height h1 of the protrusion 11B, the anchor effect is not sufficiently obtained. Therefore, the width w1 of the protrusion 11B needs to be equal to or smaller than the height h1 of the protrusion 11B. From the viewpoint of obtaining the anchor effect more reliably, the width w1 of the protrusion 11B is preferably equal to or smaller than 50% of the height h1 of the protrusion 11B, and more preferably equal to or smaller than 20%. Moreover, if the width is too narrow, the effect of inhibiting deformation of the outer skin (coating layer 12) against torsional deformation is weakened. From this viewpoint, the width w1 of the protrusion 11B is preferably equal to or larger than 3% of the height h1 of the protrusion 11B, and more preferably equal to or larger than 8%.

[0029] FIG. 3 shows a structure near the interface between the core wire 11 and the coating layer 12. Referring to FIG. 3, the core wire 11 preferably includes a diffusion layer 11D containing 0.5 mass % or more of Fe arranged to form the outer peripheral surface 11A of the core wire 11. Referring to FIG. 3 and FIG. 1, the thickness t2 of the diffusion layer 11D is, for example, 0.4% or more and 5% or less of the diameter D1 of the core wire 11. The thickness t2 of the diffusion layer 11D is more preferably 0.7% or more, 0.85% or more, and further preferably 1% or more of the diameter D1 of the core wire 11. The thickness t2 of the diffusion layer 11D is more preferably 4% or less of the diameter D1 of the core wire 11. By forming such a diffusion layer 11D, it is possible to improve the settling resistance and durability against repeated bending fatigue of the conductive wire.

[0030] (Embodiment 2) Next, a second embodiment of the present disclosure will be described. With reference to Fig. 4 and Fig. 1, the conductive wire 1 of the second embodiment has basically the same structure as the conductive wire 1 of the first embodiment, and exerts the same effects. However, the conductive wire 1 of the second embodiment differs from the conductive wire 1 of the first embodiment in the number of deformation portions (protrusions 11B).

[0031] 4, in the conductive wire 1 of this embodiment, the core wire 11 includes a plurality of protruding portions 11B (deformed portions). More specifically, the core wire 11 includes three protruding portions 11B. The (three) protruding portions 11B are arranged at equal intervals in the circumferential direction of the core wire 11. By forming a plurality of protruding portions 11B, the anchor effect of the protruding portions 11B, which are deformed portions, is increased, and the occurrence of peeling between the core wire 11 and the coating layer 12 when the conductive wire 1 is deformed is more reliably suppressed. As a result, the conductive wire 1 of this embodiment is a conductive wire with further improved resistance to sagging.

[0032] (Embodiment 3) Next, a third embodiment of the present disclosure will be described. With reference to Fig. 5 and Fig. 1, the conductive wire 1 of the third embodiment has basically the same structure as the conductive wire 1 of the first embodiment, and exerts the same effects. However, the conductive wire 1 of the third embodiment is different from the first embodiment in that the core wire 11 of the conductive wire 1 of the third embodiment includes a recessed portion 11C as a deformation portion instead of the protruding portion 11B of the first embodiment.

[0033] 5 and 6, in this embodiment, the deformation portion is a depression 11C that is depressed from the outer circumferential surface 11A. From another perspective, the depression 11C is a region where a protrusion formed in the coating layer 12 penetrates into the core wire 11. The depth d1 of the depression 11C is 3% or more and 50% or less of the thickness t1 of the coating layer 12. The width w2 of the depression 11C is equal to or less than the depth d1 of the depression 11C (equal to or less than 100% of the depth d1). The anchor effect of the depression 11C, which is the deformation portion, suppresses the occurrence of peeling between the core wire 11 and the coating layer 12 when the conductive wire 1 is deformed. As a result, the conductive wire 1 of this embodiment is a conductive wire with improved resistance to sag.

[0034] If the depth d1 of the depression 11C is less than 3% of the thickness t1 of the coating layer 12, the anchor effect is not sufficiently obtained. If the depth d1 of the depression 11C exceeds 50% of the thickness t1 of the coating layer 12, the fatigue strength may decrease when repeated stress is applied to the conductive wire 1. Therefore, the depth d1 of the depression 11C needs to be 3% or more and 50% or less of the thickness t1 of the coating layer 12. From the viewpoint of obtaining the anchor effect more reliably, the depth d1 of the depression 11C is preferably 3.5% or more, more preferably 4% or more, of the thickness t1 of the coating layer 12. From the viewpoint of suppressing the decrease in fatigue strength more reliably, the depth d1 of the depression 11C is preferably 40% or less, more preferably 30% or less of the thickness t1 of the coating layer 12.

[0035] If the width w2 of the recess 11C exceeds the depth d1 of the recess 11C, the anchor effect is not sufficiently obtained. Therefore, the width w2 of the recess 11C needs to be equal to or smaller than the depth d1 of the recess 11C. From the viewpoint of obtaining the anchor effect more reliably, the width w2 of the recess 11C is preferably equal to or smaller than 50% of the depth d1 of the recess 11C, and more preferably equal to or smaller than 20%. Moreover, if the width is too narrow, the effect of inhibiting the deformation of the outer skin (coating layer 12) against torsional deformation is weakened. From this viewpoint, the width w2 of the recess 11C is preferably equal to or larger than 3% of the height h1 of the recess 11C, and more preferably equal to or larger than 8%.

[0036] (Embodiment 4) Next, a fourth embodiment of the present disclosure will be described. With reference to Fig. 7 and Fig. 1, the conductive wire 1 of the fourth embodiment has basically the same structure as the conductive wire 1 of the first embodiment, and exerts the same effects. However, the conductive wire 1 of the fourth embodiment differs from the conductive wire 1 of the first embodiment in the number of deformed portions and the formation mode.

[0037] 7, in the conductive wire 1 of the present embodiment, the core wire 11 includes a plurality of deformed portions. Specifically, in the present embodiment, the deformed portions include a pair of protruding portions 11B and one recessed portion 11C disposed between the pair of protruding portions 11B in the circumferential direction of the core wire 11 so as to be adjacent to the pair of protruding portions 11B. In this manner, by disposing the one recessed portion 11C so as to be sandwiched between the two protruding portions 11B, the anchor effect of the deformed portions is increased, and the occurrence of peeling between the core wire 11 and the coating layer 12 during deformation of the conductive wire 1 is more reliably suppressed. As a result, the conductive wire 1 of the present embodiment is a conductive wire having further improved resistance to sagging.

[0038] Instead of the above structure, the deformation portion may include a pair of depressions 11C and one protrusion 11B disposed between the pair of depressions 11C in the circumferential direction of the core wire 11 so as to be adjacent to the pair of depressions 11C. In this way, even with a structure in which one protrusion 11B is sandwiched between two depressions 11C, the anchor effect of the deformation portion is increased, and peeling between the core wire 11 and the coating layer 12 when the conductive wire 1 is deformed is more reliably suppressed. As a result, the settling resistance can be further improved.

[0039] (Method of manufacturing conductive wire) Next, an example of a method for manufacturing the conductive wire 1 will be described. With reference to FIG. 8, in the method for manufacturing the conductive wire 1 of the present embodiment, a cladding step is first performed as step (S10). In this step (S10), a strip-shaped steel material (steel strip) to become the coating layer 12 and a metal rod to become the core wire 11 are prepared. Specifically, for example, a steel strip made of JIS standard SUS304, which is an austenitic stainless steel, and a metal rod made of oxygen-free copper (pure Cu) are prepared. Then, the steel strip is deformed so that both ends in the width direction of the steel strip face each other (so that the cross section perpendicular to the longitudinal direction of the steel strip is annular), and both ends in the width direction of the steel strip are joined by welding, and the metal rod is inserted into the space surrounded by the steel strip, thereby obtaining a cladding material in which a copper metal rod is inserted into a stainless steel tube. The outer diameter of the cladding material can be, for example, about 5 mm.

[0040] Next, an interface bonding step is performed as step (S20). In this step (S20), the interface between the pipe (steel strip) and metal bar constituting the clad material produced in step (S10) is bonded. Specifically, the clad material obtained in step (S10) is subjected to wire drawing (drawing) at a relatively small processing rate (area reduction rate). Figures 9 to 11 are schematic cross-sectional views showing the deformation state of the steel strip and metal bar in step (S20). Figures 9 to 11 show a cross section perpendicular to the longitudinal direction of the clad material.

[0041] As shown in FIG. 9, the clad material produced in step (S10) includes a metal rod 11 and a steel strip 12 processed into a tubular shape so as to surround the metal rod 11. Both widthwise ends of the steel strip 12 are joined by beads 12A formed by welding. The region of the steel strip 12 where the beads are formed protrudes radially outward from the metal rod 11. The region of the steel strip 12 where the beads are formed is a region that is thicker in the radial direction of the metal rod 11. A gap 13 is formed between the metal rod 11 and the steel strip 12. The size of the gap 13 in the radial direction of the metal rod 11 can be, for example, 0.5 to 2.5 times the thickness of the steel strip 12.

[0042] When wire drawing is performed in step (S20), as shown in FIG. 10, first, only the steel strip 12 is processed and its outer diameter is reduced. At this time, the region where the bead 12A is formed is processed by the die more than other parts, and the protrusion to the radial outside disappears, while a pair of recesses 12B are formed on both sides in the circumferential direction. As the processing progresses further, the metal bar 11 is also processed as shown in FIG. 11, and a part of the metal bar 11 enters the recess 12B, forming a protrusion 11B. By the wire drawing, for example, the outer diameter of the clad material is made 3 mm. Then, by performing a heat treatment, the interface between the pipe and the metal bar constituting the clad material is joined. The heat treatment can be performed under conditions of heating to 950° C. or more and 1050° C. or less and holding for about 1 to 10 minutes.

[0043] Next, a first wire drawing step is performed as a step (S30). In this step (S30), a wire drawing process is performed on the clad material in which the interface between the steel strip and the metal bar is joined in the step (S20). Specifically, in this embodiment, the wire drawing process is performed so that the outer diameter of the clad material is, for example, 1.88 mm. The wire drawing process is performed by passing the clad material through a through hole formed in a die. The wire drawing process may be performed in one process using one die, or may be performed in multiple processes using multiple dies. As a result, a conductive wire 1 having an outer diameter D of 1.88 mm is obtained. The metal bar 11 becomes the core wire 11, and the steel strip 12 becomes the coating layer 12.

[0044] Next, a first solution treatment step is carried out as step (S40). In this step (S40), the wire having an outer diameter D of 1.88 mm obtained in step (S30) is subjected to a solution treatment. Specifically, the conductive wire 1 obtained in step (S30) is subjected to a heat treatment in which the wire is heated to a temperature range of 900°C to 1100°C, held for 5 seconds to 20 minutes, and then quenched. As a result, in the metal structure of the stainless steel constituting the coating layer 12, the crystal grains elongated by the wire drawing in step (S30) are recrystallized, and the martensite structure generated by the wire drawing disappears. As a result, the coating layer 12 work-hardened in step (S30) is softened, and the coating layer 12 becomes capable of being drawn again. The heating temperature in the solution treatment is set to the A temperature range of the stainless steel constituting the coating layer. C3 It is preferable to set the temperature at or above the A point of stainless steel. C3 The point can be calculated, for example, using the following formula: 937.2-436.5×(C%)+56×(Si%)-19.7×(Mn%)-16.3×(Cu%)-26.6×(Ni%)-4.9×(Cr%)+38.1×(Mo%)+124.8×(V%)+136.3×(Ti%)-19.1×(Nb%)+198.4×(Al%)+3315×(B%) (unit: °C). Here, (C%), (Si%), (Mn%), (Cu%), (Ni%), (Cr%), (Mo%), (V%), (Ti%), (Nb%), (Al%) and (B%) mean the content (percentage) of C (carbon), Si (silicon), Mn (manganese), Cu (copper), Ni (nickel), Cr (chromium), Mo (molybdenum), V (vanadium), Ti (titanium), Nb (niobium), Al (aluminum) and B (boron) contained in the stainless steel. When the stainless steel constituting the coating layer is an austenitic stainless steel such as JIS standard SUS304, the heating temperature in the solution treatment is preferably 900°C or higher, more preferably 950°C or higher.

[0045] The solution treatment causes Fe and Ni (nickel) contained in the stainless steel constituting the coating layer 12 to diffuse into the core wire 11. As a result, a diffusion layer 11D containing 0.5 mass % or more of Fe is formed (see FIG. 2). The Ni content in the diffusion layer 11D is, for example, 0.2 mass %. In the conductive wire 1 of this embodiment, the thickness t2 of the diffusion layer 11D is preferably 0.4% to 5% of the diameter D1 of the core wire 11, and more preferably 0.85% to 5%. The thickness t2 of the diffusion layer 11D is adjusted mainly in a diffusion layer thickness adjustment step (S70) described later. However, the diffusion of Fe from the coating layer 12 to the core wire 11 by the solution treatment also affects the thickness t2 of the diffusion layer 11D. Therefore, it is necessary to determine the conditions of the solution treatment in this step (S40) taking into consideration the conditions of the wire drawing and solution treatment in the subsequent steps. The diffusion rate (diffusion distance per unit time) of Fe (and Ni) increases as the heating temperature in the solution treatment increases. The heating temperature and heating time are determined taking into consideration production efficiency and ease of control of the thickness t2 of the diffusion layer 11D.

[0046] Next, a second wire drawing step is performed as step (S50). In this step (S50), the conductive wire 1 that has been solution-treated in step (S40) is drawn. Specifically, in this embodiment, the drawing is performed so that the outer diameter D of the conductive wire 1 becomes 0.7 mm. The drawing may be performed in one step using one die, as in step (S30), or may be performed in multiple steps using multiple dies. As a result, the conductive wire 1 having an outer diameter D of 0.7 mm is obtained.

[0047] Next, a second solution treatment is performed as step (S60). In this step (S60), the wire having an outer diameter D of 0.7 mm obtained in step (S50) is subjected to a solution treatment. Specifically, the conductive wire 1 obtained in step (S50) is subjected to a heat treatment in which the wire is heated to a temperature range of 900°C to 1100°C, held for 5 seconds to 20 minutes, and then quenched, as in step (S40). As a result, the crystal grains of the stainless steel constituting the coating layer 12 are recrystallized, and the martensite structure disappears, as in step (S40). As a result, the coating layer 12 work-hardened in step (S50) is softened, and the wire can be drawn again.

[0048] The solution treatment forms the diffusion layer 11D in the same manner as in step (S40). Unlike step (S40) in which two wiredrawing processes and one solution treatment are performed in the subsequent steps, step (S60) has a large effect on the ratio of the thickness t2 of the diffusion layer 11D to the diameter D1 of the core wire 11. This is because the thickness of the diffusion layer 11D formed in step (S40) is reduced by the two wiredrawing processes in steps (S50) and (S70). In order to set the thickness t2 of the diffusion layer 11D in a narrow range of 0.4% to 5% (or even 0.85% to 5%) of the diameter D1 of the core wire 11, it is necessary to determine the conditions of the solution treatment in this step (S60) in consideration of facilitating the adjustment of the thickness t2 of the diffusion layer 11D in the diffusion layer thickness adjustment step (S70) described later.

[0049] Next, a diffusion layer thickness adjustment step is performed as step (S70). In this step (S70), a heat treatment is performed on the conductive wire 1 that has been subjected to the solution treatment in step (S60) to adjust the thickness t2 of the diffusion layer 11D. Specifically, the conductive wire 1 is heated to a temperature range of 800°C to 1100°C, held for 5 seconds to 20 minutes, and then rapidly cooled. In order to set the thickness t2 of the diffusion layer 11D to a narrow range of 0.4% to 5% (or even 0.85% to 5%) of the diameter D1 of the core wire 11, it is necessary to strictly control the diffusion distance of Fe. By selecting a low heating temperature at which the diffusion rate of Fe is small and widening the allowable heating time range while allowing a certain degree of decrease in production efficiency, it becomes easy to form the diffusion layer 11D with an appropriate thickness. Note that this step (S70) is not an essential step, and can be omitted by appropriately setting the conditions of the solution treatment in steps (S40) and (S60). However, by making the thickness t2 of diffusion layer 11D formed in steps (S40) and (S60) sufficiently small and then performing step (S70), it becomes easy to set the thickness t2 of diffusion layer 11D within a narrow range of 0.4% or more and 5% or less (even 0.85% or more and 5% or less) of diameter D1 of core wire 11.

[0050] Next, a third wire drawing step is performed as step (S80). In this step (S80), the conductive wire 1 in which the thickness t2 of the diffusion layer 11D has been adjusted in step (S70) is subjected to wire drawing. Specifically, in this embodiment, the wire drawing is performed so that the outer diameter D of the conductive wire 1 becomes 0.3 mm. The wire drawing may be performed in one process using one die, as in the cases of steps (S30) and (S50), or may be performed in multiple processes using multiple dies. This completes the conductive wire 1 having a pair of protruding parts 11B, an outer diameter D of 0.3 mm, and a thickness t2 of the diffusion layer 11D of 0.4% to 5% (or even 0.85% to 5%) of the diameter D1 of the core wire 11.

[0051] According to the manufacturing method of the conductive wire of the present embodiment, the conductive wire 1 of the present embodiment can be easily manufactured. In the above embodiment, the case where a steel strip is used as the material of the coating layer 12 has been described, but the conductive wire of the present disclosure can also be manufactured by other methods. Specifically, for example, in step (S10), a steel (stainless steel) pipe is prepared instead of a steel strip. In addition, at least one of a convex portion and a concave portion having a shape that matches at least one of a protrusion and a depression, which are the desired deformation portion, is formed on the outer circumferential surface of the metal bar. Meanwhile, at least one of a concave portion and a convex portion corresponding to the shape of at least one of the convex portion and the concave portion is formed on the inner circumferential surface of the pipe. Then, the metal bar is inserted into the pipe so that at least one of the convex portion and the concave portion of the metal bar is fitted into at least one of the concave portion and the convex portion of the pipe, thereby obtaining a clad material in which the metal bar is inserted into the steel pipe. Then, steps (S20) to (S80) are performed in the same manner as in the above embodiment, and the conductive wire of the present disclosure can be manufactured. EXAMPLES

[0052] The conductive wire of the present disclosure was produced, and an experiment was conducted to confirm the improvement of the sag resistance. The procedure of the experiment is as follows.

[0053] First, a conductive wire according to the present disclosure was produced using a procedure including the same steps (S10) to (S80) as in the above embodiment (Example). Meanwhile, for comparison, a conductive wire without a deformed portion that satisfies the conditions of the present disclosure was also produced (Comparative Example). The wire diameter D of the conductive wire was 0.7 mm. The area ratio of the core wire 11 in the cross section perpendicular to the longitudinal direction of the conductive wire was 60%.

[0054] Fig. 12 is an optical microscope photograph showing an enlarged view of the vicinity of the deformed portion (protrusion) in a cross section perpendicular to the longitudinal direction of the conductive wire of the example. In Fig. 12, the optical microscope photograph is superimposed on the cross-sectional view in order to easily grasp the state of the formation of the protrusion 11B protruding from the core wire 11 toward the coating layer 12. Referring to Fig. 12, it is confirmed that the core wire 11 in the conductive wire of the example includes a deformed portion, which is the protrusion 11B protruding from the outer circumferential surface.

[0055] The conductive wires of the examples and the comparative examples prepared as described above were subjected to a sag resistance test. Specifically, the conductive wires were heated to 150°C and subjected to a torsional stress in the circumferential direction. The magnitude of the torsional stress was calculated as the torsional yield stress (τ 0.2 ) was set to 80% of the original deformation (rotation angle). The test piece was held in this state for 24 hours, and then the torsional stress was released. The state before the torsional stress was applied was set as the reference (0°), and the ratio (residual strain) of the remaining deformation (rotation angle) after the release of the torsional stress to the deformation (rotation angle) up to the state when the torsional stress was applied was calculated to evaluate the sag resistance (the smaller the residual strain, the better the sag resistance). The conductive wires of the examples and comparative examples prepared as described above were also subjected to a Hunter type rotating bending fatigue test, and 10 7 The maximum stress (fatigue limit) at which the wire could be subjected to repeated stresses without breaking was investigated, and fatigue strength was evaluated (the higher the fatigue limit, the better the fatigue strength). The structure of the conductive wire used in the experiment and the experimental results are shown in Table 1.

[0056] [Table 1]

[0057] Referring to Table 1, sample numbers 1 to 3 and 9 to 12 are conductive wires of the embodiment. Sample numbers 4 and 5 are conductive wires of comparative examples in which a steel pipe is used instead of a steel strip as the material of the coating layer 12, and w1 / h1, which is the value obtained by dividing the width w1 of the protrusion by the height h1 of the protrusion, exceeds 100%, which is outside the appropriate range. Sample numbers 6 to 8 are conductive wires of comparative examples in which the gap 13 between the steel strip 12 and the metal rod 11 is set to less than an appropriate value in step (S10), thereby making w1 / h1 exceed 100%, which is outside the appropriate range. Sample number 13 is a conductive wire of a comparative example in which the value obtained by dividing the height h1 of the protrusion by the thickness t1 of the coating layer 12, exceeds 50%, which is outside the appropriate range.

[0058] Referring to Table 1, the residual strain of the conductive wire of the comparative sample (sample numbers 4 to 8) which does not satisfy the conditions of the present disclosure due to w1 / h1 exceeding 100% is close to 0.06%, whereas the residual strain of the conductive wire of the example sample (sample numbers 1 to 3 and 9 to 12) is less than 0.05%. This is considered to be because the protruding portion (deformed portion) with a w1 / h1 value exceeding 100% does not exhibit a sufficient anchor effect, and peeling between the core wire and the coating layer could not be sufficiently suppressed. In addition, the fatigue limit of sample number 13 with a h1 / t1 value exceeding 50% is 25% or more smaller than the other samples. This is considered to be because the height of the protruding portion in sample number 13 is too large compared to the thickness of the coating layer, and the protruding portion acts as a defect, reducing the fatigue strength.

[0059] From the above experimental results, it is confirmed that the conductive wire of the embodiment can achieve improved sag resistance while maintaining fatigue strength.

[0060] In addition, an experiment was conducted to confirm that the improvement in sag resistance was not simply due to an increase in the thickness of the high-strength coating layer. Specifically, samples were made aiming for a core wire area ratio of 30% and 60% in the cross section perpendicular to the longitudinal direction of the conductive wire. For each of the samples aiming for 30% and 60%, samples with and without deformed sections were prepared. Then, a sag resistance test was conducted for each sample in the same manner as above. The test results are shown in Figure 13. In addition, the area ratio of the coating layer in the cross section perpendicular to the longitudinal direction was measured for each sample. The measurement results are shown in Table 2.

[0061] [Table 2]

[0062] Referring to FIG. 13, it can be seen that the amount of residual strain is reduced by forming the deformed portion in both cases where the area ratio of the core wire is 30% and 60%. From this, it can be said that the formation of the deformed portion improves the sag resistance regardless of the area ratio of the core wire. Also, referring to Table 2, in both cases where the area ratio of the core wire is 30% and 60%, the area ratio of the coating layer, which is mainly responsible for the strength of the conductive wire, is smaller in the sample in which the deformed portion is formed. In other words, even under conditions where the area ratio of the coating layer is small and is considered to be unfavorable from the viewpoint of strength, the formation of the deformed portion improves the sag resistance. From this, it is confirmed that the improvement in the sag resistance is not simply due to an increase in the thickness of the coating layer, which has high strength.

[0063] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Industrial Applicability]

[0064] The conductive wire of the present disclosure can be particularly advantageously applied to conductive wire that requires improved resistance to sag. [Explanation of symbols]

[0065] 1 Conductive wire 11 Core wire (metal rod) 11A Outer surface 11B Projection 11C Depression 11D Diffusion Layer 12 Covering layer (steel strip) 12A Bead 12B Recess 13 void D Outer diameter (wire diameter) D1 diameter d1 depth h1 height t1 coating thickness t2 Diffusion layer thickness

Claims

1. A first metal core wire; A first steel coating layer that covers a first outer circumferential surface of the core wire, the electrical conductivity of the first metal is greater than the electrical conductivity of the first steel; The core wire is a protruding portion protruding from the first outer peripheral surface and having a first height that is 3% to 50% of a first thickness that is the thickness of the coating layer, and a first width that is equal to or smaller than the first height; or a recessed portion recessed from the first outer peripheral surface, the recessed portion having a first depth that is 3% to 50% of the first thickness, and a second width that is equal to or smaller than the first depth; A conductive wire including a deformation portion.

2. The conductive wire according to claim 1 , wherein the core wire includes a plurality of the deformation portions.

3. The plurality of deformation portions include a pair of the protruding portions and one of the recessed portions disposed between the pair of the protruding portions in the circumferential direction of the core wire so as to be adjacent to the pair of the protruding portions, or 3. The conductive wire according to claim 2, comprising: a pair of the recesses; and one of the protrusions arranged between the pair of the recesses in the circumferential direction of the core wire so as to be adjacent to the pair of the recesses.

4. the core wire includes a diffusion layer that is arranged to configure the first outer circumferential surface and contains 0.5 mass % or more of Fe, The conductive wire according to claim 1 , wherein the second thickness, which is a thickness of the diffusion layer, is 0.4% to 5% of a diameter of the core wire.

5. The conductive wire according to claim 4 , wherein the second thickness is 0.85% or more of a diameter of the core wire.

6. 2. The conductive wire of claim 1, wherein the first metal is comprised of at least one of Cu, Ag, Al, a Cu alloy, an Ag alloy, and an Al alloy.

7. The conductive wire of claim 1 , wherein the first metal is Cu.

8. 2. The conductive wire of claim 1, wherein the first steel is stainless steel.

9. 2. The conductive wire of claim 1, wherein the first steel is an austenitic stainless steel.

Images