Electrical wire

Abstract

An electrical wire comprising a core wire and a coating that covers the core wire, wherein the core wire contains iron as a main component, the coating includes a first layer, the first layer contains copper as a main component, and the first layer contains carbon at 10.5-20.5 ppm on a mass basis.

Description

electric wire

[0001] The present disclosure relates to an electric wire. This application claims priority to Japanese Patent Application No. 2023-018992, filed on February 10, 2023. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] BACKGROUND ART Electric wires including a core wire and a coating covering the core wire have been used in automobiles and the like (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2004-207080

[0004] An electric wire according to one embodiment of the present disclosure is an electric wire including a core wire and a coating covering the core wire, wherein the core wire contains iron as a main component, the coating includes a first layer, the first layer contains copper as a main component, and the first layer contains 10.5 ppm or more and 20.5 ppm or less of carbon by mass.

[0005] FIG. 1 is a schematic perspective view of an electric wire according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1 . FIG. 3 is a flowchart of a method for manufacturing an electric wire according to an embodiment of the present disclosure. FIG. 4 is an enlarged photograph of a cross section of an electric wire according to Sample 101. FIG. 5 is an enlarged photograph of a cross section of an electric wire according to Sample 1. FIG. 6 is an enlarged photograph of a cross section of an electric wire according to Sample 101 after being exposed to a 250°C environment for one hour and cooled in a 25°C environment for one hour. FIG. 7 is an enlarged photograph of region VII in FIG. 6 . FIG. 8 is an enlarged photograph of a cross section of an electric wire according to Sample 1 after being exposed to a 250°C environment for one hour and cooled in a 25°C environment for one hour. FIG. 9 is a schematic perspective view of an electric wire of a sample cut in Evaluation Test 2. FIG. 10 is a schematic cross-sectional view illustrating an evaluation method of Evaluation Test 2. FIG. 11 is a schematic cross-sectional view of an example of an electric wire of Evaluation Criterion A' of Evaluation Test 2. Fig. 12 is a schematic cross-sectional view of an example of a sample electric wire for evaluation criterion B' of evaluation test 2. Fig. 13 is a schematic cross-sectional view of another example of a sample electric wire for evaluation criterion B' of evaluation test 2. Fig. 14 is a schematic perspective view illustrating the evaluation method of evaluation test 3.

[0006] [Problem to be Solved by the Present Disclosure] An electric wire may be heated during processing, when a current flows through the electric wire, and when the electric wire is used in a high-temperature environment. Therefore, when the electric wire includes a core wire containing iron as a main component and a copper layer covering the core wire, stress is applied to the copper layer when the temperature of the electric wire increases with heating due to the difference in the thermal expansion coefficient between the core wire and the copper layer and the fact that the core wire is generally harder than the copper layer. Furthermore, when the temperature of the electric wire increases with heating, crystal grains grow in the copper layer. When a strong external stress is applied to the electric wire, the crystal grains can become the starting point for cracking of the copper layer. Therefore, in conventional electric wires, cracks occur at the interface of the copper layer on the core wire side due to the stress and the growth of the crystal grains when heated, and the copper layer is prone to peeling from the cracked points. Therefore, it is required to prevent the coating from peeling off when an external stress is applied to an electric wire exposed to high temperatures.

[0007] Therefore, an object of the present disclosure is to provide an electric wire that can suppress peeling of a coating when an external stress is applied to the electric wire exposed to a high temperature.

[0008] According to the present disclosure, it is possible to provide an electric wire that can suppress peeling of a coating when an external stress is applied to an electric wire exposed to high temperatures.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. [1] An electric wire according to one aspect of the present disclosure is an electric wire including a core wire and a coating covering the core wire, wherein the core wire contains iron as a main component, the coating includes a first layer, the first layer contains copper as a main component, and the first layer contains 10.5 ppm to 20.5 ppm of carbon by mass.

[0010] According to the present disclosure, it is possible to provide an electric wire that can suppress peeling of a coating when an external stress is applied to an electric wire exposed to high temperatures.

[0011] [2] In the above [1], the first layer may contain 11.5 ppm or more of carbon by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0012] [3] In the above [1] or [2], the first layer may contain 16.5 ppm or less of carbon by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0013] [4] In any one of the above [1] to [3], the first layer may contain hydrogen in an amount of 0.35 ppm to 1.30 ppm by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0014] [5] In the above [4], the first layer may contain 0.51 ppm or more of hydrogen by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0015] [6] In the above [4] or [5], the first layer may contain 1.12 ppm or less of hydrogen by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0016] [7] In any of the above [1] to [6], the first layer may contain 2.41 ppm or more and 5.62 ppm or less of oxygen by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0017] [8] In the above [7], the first layer may contain 3.01 ppm or more of oxygen by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0018] [9] In the above [7] or [8], the first layer may contain 5.01 ppm or less of oxygen by mass, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0019]

[10] In any one of the above [1] to [9], the first layer may contain 0.22 ppm to 0.65 ppm by mass of sulfur, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0020]

[11] In any one of the above [1] to

[10] , the first layer may have crystal grains, and the average grain size of the crystal grains may be 0.5 μm or more and 2 μm or less. This makes it possible to provide an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0021]

[12] In any one of the above [1] to

[11] , the coating may further include a second layer, the second layer being located between the core wire and the first layer, the second layer containing nickel as a main component, and a thickness of the second layer being 0.3 nm to 40.3 nm. This makes it possible to provide an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0022]

[13] In any one of the above [1] to

[12] , the diameter of the core wire may be 0.10 mm or more and 0.20 mm or less, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0023]

[14] In any one of the above [1] to

[13] , the thickness of the first layer may be 0.04 mm or more and 0.06 mm or less, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0024]

[15] In any of the above [1] to

[14] , the core wire may contain stainless steel or carbon steel, thereby providing an electric wire that can further suppress peeling of the coating when an external stress is applied to the electric wire exposed to a high temperature.

[0025] [Details of the embodiment of the present disclosure] Hereinafter, one embodiment of the present disclosure (hereinafter referred to as "the present embodiment") will be described. However, the present embodiment is not limited thereto. In this specification, an expression in the form of "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0026] In the present specification, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is understood to include any conventionally known atomic ratio, and is not necessarily limited to only those within the stoichiometric range.

[0027] [Embodiment 1: Electric Wire] An electric wire 1 according to an embodiment of the present disclosure will be described with reference to Figures 1 and 2. One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is an electric wire 1 including a core wire 2 and a coating 5 coating the core wire 2, wherein the core wire 2 contains iron as a main component, the coating 5 includes a first layer 4, the first layer 4 contains copper as a main component, and the first layer 4 contains 10.5 ppm or more and 20.5 ppm or less of carbon by mass.

[0028] According to the present disclosure, it is possible to provide an electric wire 1 that can suppress peeling of the coating 5 when an external stress is applied to the electric wire 1 that is exposed to a high temperature. The reason for this is presumed to be as follows.

[0029] During processing of an electric wire, the coating that constitutes the electric wire may be heated. Furthermore, when a current flows through the electric wire, the electric wire generates heat, which may heat the coating that constitutes the electric wire. Furthermore, when an electric wire is used in a high-temperature environment, the coating that constitutes the electric wire may be heated. When the coating is heated, the crystal grains that constitute the coating grow. As a result, if columnar crystals are formed in the coating in the thickness direction of the coating, the grain boundaries extend in the thickness direction, which makes it easy for cracks to occur in the thickness direction. These cracks become the starting point for peeling between the core wire and the coating that covers the core wire.

[0030] In the electric wire 1 according to this embodiment, the coating 5 includes a first layer 4. The first layer 4 contains copper as a primary component and 10.5 ppm to 20.5 ppm of carbon by mass. This facilitates suppression of grain growth of copper-containing crystal grains. As a result, the grain boundaries of the crystal grains in the first layer 4 are prevented from extending in the film thickness direction, making it difficult for cracks to occur in the film thickness direction. This prevents peeling between the core wire 2 and the coating 5 covering the core wire 2, which may occur at the cracks.

[0031] Therefore, according to the present disclosure, it is possible to provide an electric wire 1 that can suppress peeling of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures.

[0032] <Core Wire> <Composition of Core Wire> The electric wire 1 includes a core wire 2. The core wire 2 contains iron as a main component. Here, "iron" means "elemental iron." Furthermore, "the core wire 2 contains iron as a main component" means "the core wire 2 contains 50% by mass or more of iron." The lower limit of the iron content in the core wire 2 can be 51% by mass or more, 52% by mass or more, 53% by mass or more, or 73% by mass or more. The upper limit of the iron content can be 100% by mass or less, 99% by mass or less, or 98% by mass or less. The content can be 51% by mass or more and 100% by mass or less, 52% by mass or more and 99% by mass or less, or 53% by mass or more and 98% by mass or less.

[0033] The iron content of the core wire 2 can be determined by the following method. First, 1 part by mass of the core wire is dissolved in 99 parts by mass of a mixed acid of hydrochloric acid and nitric acid (mass ratio of hydrochloric acid:nitric acid = 3:1) to prepare a solution. Next, the solution is subjected to ICP (Inductively Coupled Plasma) atomic emission spectroscopy using an "iCAP6300" (manufactured by Thermo Fisher Scientific). The ICP atomic emission spectroscopy is performed by quantitatively analyzing elements detected at 5 mg / L or more (excluding C element, S element, and elements not targeted for ICP atomic emission spectroscopy) after a collective qualitative analysis. This method allows the iron content of the core wire 2 to be determined. It has been confirmed that there is no variability in the measurement results, even if the measurement location is arbitrarily selected, as long as the same electric wire 1 is measured.

[0034] The core wire 2 may contain stainless steel or carbon steel, which facilitates alloying with the first layer 4, thereby further improving the peeling resistance of the coating 5 when an external stress is applied to the electric wire 1 exposed to high temperatures.

[0035] Here, "stainless steel" refers to steel having an iron content of 74% by mass or less, a nickel content of 8% by mass or more, and a chromium content of 18% by mass or more. In addition to iron, nickel, and chromium, the stainless steel may contain unavoidable impurities. Examples of the unavoidable impurities include carbon (0.01% by mass or more and 0.08% by mass or less), silicon (0.1% by mass or more and 1.0% by mass or less), manganese (0.1% by mass or more and 2.0% by mass or less), phosphorus (0.01% by mass or more and 0.045% by mass or less), and sulfur (0.01% by mass or more and 0.03% by mass or less). An example of a material for the stainless steel is SUS304. Here, "iron" refers to "elemental iron." "Nickel" refers to "elemental nickel." "Chromium" refers to "elemental chromium." "Carbon" refers to "elemental carbon." "Silicon" refers to "elemental silicon." "Manganese" refers to "elemental manganese." "Phosphorus" means "elemental phosphorus." "Sulfur" means "elemental sulfur."

[0036] "Carbon steel" refers to steel having an iron content of 97.9% by mass or more and 99.8% by mass or less, and a carbon content of 0.02% by mass or more and 2.14% by mass or less. In addition to iron and carbon, the carbon steel may contain inevitable impurities. Examples of the inevitable impurities include sulfur (0.01% by mass or more and 0.03% by mass or less), phosphorus (0.001% by mass or more and 0.01% by mass or less), and silicon (0.01% by mass or more and 0.05% by mass or less). An example of a material for the carbon steel is piano wire. Here, "iron" means "elemental iron". "carbon" means "elemental carbon". "sulfur" means "elemental sulfur". "phosphorus" means "elemental phosphorus". "silicon" means "elemental silicon".

[0037] The carbon content in the core wire 2, the chromium content in the core wire 2, the nickel content in the core wire 2, the silicon content in the core wire 2, the manganese content in the core wire 2, the phosphorus content in the core wire 2, and the sulfur content in the core wire 2 can be determined by a method similar to the measurement method for the above-mentioned "iron content in the core wire 2."

[0038] It has been confirmed that as long as the same electric wire 1 is measured, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0039] <Structure of Core Wire> The diameter R of the core wire 2 may be 0.10 mm or more and 0.20 mm or less. This makes it less likely for breakage or cracking to occur when stress is applied from the outside to the electric wire 1, thereby further improving the peeling resistance of the coating 5 when stress is applied from the outside to the electric wire 1 exposed to high temperatures. The lower limit of the diameter R may be 0.10 mm or more, 0.12 mm or more, 0.14 mm or more, or 0.15 mm or more. The upper limit of the diameter R may be 0.20 mm or less, 0.19 mm or less, or 0.17 mm or less. The diameter R may be 0.12 mm or more and 0.19 mm or less, or 0.14 mm or more and 0.17 mm or less.

[0040] The diameter R of the core wire 2 can be determined by the following method. Specifically, first, a 20 mm electric wire 1 obtained by cutting the electric wire 1 along a plane perpendicular to the longitudinal direction is embedded in resin. Next, one of the cut surfaces of the resin-embedded electric wire 1 is pre-finished by mechanical polishing, and then a cross-section polisher (CP) is used with an Ar ion beam under the following conditions to obtain a polished cut surface. Next, CP-SEM (Scanning Electron Microscopy) is performed on the polished cut surface using a high-resolution scanning electron microscope "SU8020" manufactured by Hitachi High-Tech Corporation, and a 500x magnification image is obtained so that the entire polished cut surface is included in one field of view. Next, for any one point on the outer periphery of the core wire 2 in the image, the length of the longest line segment connecting the any one point and another point on the outer periphery is determined. Next, the lengths of the longest line segments are determined in the same manner for four further arbitrary points. The diameter R can be determined by calculating the average length of these longest line segments. (CP conditions) Acceleration voltage: 1.0 kV Inclination: 0°

[0041] <Coating> The electric wire 1 includes a coating 5 that covers the core wire 2. The thickness of the coating 5 may be 41 μm or more and 65 μm or less. If the thickness of the coating 5 is less than 41 μm, the conductivity of the coating 5 tends to decrease. If the thickness of the coating 5 is more than 65 μm, the drawability in a subsequent process tends to decrease. The thickness of the coating 5 may be 45 μm or more and 63 μm or less, or may be 50 μm or more and 60 μm or less.

[0042] The thickness of the coating 5 refers to the average value of the thickness of the coating 5 in the cross section of the electric wire 1. The measurement method will be described in more detail below. Specifically, first, microscopic images of five arbitrary cross sections of the electric wire 1 are obtained using a scanning electron microscope (SEM). Next, five arbitrary points are selected on the outer periphery (outermost surface) of the electric wire 1 in each of the images, and the shortest distance from the outer periphery to the core wire 2 at each point is determined, and this is taken as the thickness of the coating 5. The thickness of the coating 5 is measured at a total of 25 points, and an average value is calculated from the values ​​obtained, and this can be used as the thickness of the coating 5. Note that, if there are clearly abnormal values ​​in the above measurement, these abnormal values ​​are excluded from the calculation of the average value. If there are abnormal values ​​at three or more points, the same number of measurements are performed as alternatives, and the average value is calculated using the values ​​obtained thereby.

[0043] It has been confirmed that as long as the same electric wire 1 is measured, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0044] <First Layer> (Composition of First Layer) The coating 5 includes a first layer 4. Here, the first layer 4 may or may not be in contact with the outer circumferential surface of the core wire 2. When the first layer 4 is not in contact with the outer circumferential surface of the core wire 2, a second layer 3 (described later), another layer, or both may be present between the core wire 2 and the first layer 4. The coating 5 may consist of only the first layer 4, or may consist of only the first layer 4 and the second layer 3 (described later). The first layer 4 contains copper as a main component. This allows the first layer 4 to impart electrical conductivity to the electric wire 1. Here, "copper" means "elemental copper." Furthermore, "the first layer 4 contains copper as a main component" means "the first layer 4 contains 99% by mass or more of copper." The lower limit of the copper content in the first layer 4 may be 99.99 mass% or more, 99.991 mass% or more, or 99.992 mass% or more. The upper limit of the copper content may be 99.999 mass% or less, 99.998 mass% or less, or 99.997 mass% or less. The copper content may be 99.99 mass% or more and 99.999 mass% or less, 99.991 mass% or more and 99.998 mass% or less, or 99.992 mass% or more and 99.997 mass% or less.

[0045] The copper content in the first layer 4 can be determined by the following method. That is, it can be determined by performing D-SIMS (Dynamic Secondary Ion Mass Spectrometry) analysis under the following conditions. When performing the D-SIMS analysis, due to the principle of performing the D-SIMS analysis, it is necessary to determine the copper content in the first layer 4 by sputtering (i.e., scraping) the target sample from the outermost layer and calculating the average value of the content in the intermediate portion. For example, when analyzing copper in a first layer 4 having a thickness of 50 μm (i.e., 0.050 mm), it is necessary to determine the copper content in the first layer 4 by calculating the average value of the content in the portion sandwiched between a first imaginary plane 15 μm away from the interface on the surface side of the first layer and a second imaginary plane 35 μm away from the interface on the surface side of the first layer (i.e., the intermediate portion). The "carbon content in the first layer 4," "hydrogen content in the first layer 4," "oxygen content in the first layer 4," and "sulfur content in the first layer 4," which will be described later, can also be determined by the same method. (D-SIMS conditions) Apparatus: "IMS6f" manufactured by CAMECA Primary ion species: Cs ＋ Acceleration voltage: 15 kV Analysis area: 30 μm Φ

[0046] It has been confirmed that as long as measurements are made on the same electric wire 1, there is no variation in the measurement results even if the measurement location and the widths of the first and second imaginary planes are arbitrarily selected.

[0047] The first layer 4 contains 10.5 ppm to 20.5 ppm of carbon by mass. This provides a pinning effect, slowing grain boundary migration and making it easier to suppress the growth of crystal grains in the first layer. This improves the peeling resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. The lower limit of the carbon content in the first layer 4 may be 11.5 ppm or more, 12.0 ppm or more, or 12.3 ppm or more by mass. The upper limit of the carbon content in the first layer 4 may be 16.5 ppm or less, 15.5 ppm or less, or 14.4 ppm or less by mass. The carbon content in the first layer 4 may be, on a mass basis, 11.5 ppm to 16.5 ppm, 12.0 ppm to 15.5 ppm, or 12.3 ppm to 14.4 ppm. Here, "carbon" means "elemental carbon."

[0048] The first layer 4 may contain hydrogen in an amount of 0.35 ppm to 1.30 ppm by mass. This provides a pinning effect, slowing grain boundary migration and making it easier to suppress the growth of crystal grains in the first layer. This further improves the peeling resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. The lower limit of the hydrogen content in the first layer 4 may be 0.35 ppm or more, 0.51 ppm or more, or 0.67 ppm or more by mass. The upper limit of the hydrogen content in the first layer 4 may be 1.30 ppm or less, 1.12 ppm or less, or 0.94 ppm or less by mass. The hydrogen content in the first layer 4 may be 0.51 ppm or more to 1.12 ppm or less, or 0.67 ppm or more to 0.94 ppm by mass. Here, "hydrogen" means "elemental hydrogen."

[0049] The first layer 4 may contain 2.41 ppm to 5.62 ppm of oxygen by mass. This provides a pinning effect, slowing grain boundary migration and making it easier to suppress the growth of crystal grains in the first layer. This further improves the peeling resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. The lower limit of the oxygen content in the first layer 4 may be 2.41 ppm or more, 3.01 ppm or more, or 3.12 ppm or more by mass. The upper limit of the oxygen content in the first layer 4 may be 5.62 ppm or less, 5.01 ppm or less, or 4.32 ppm or less by mass. The oxygen content in the first layer 4 may be 3.01 ppm or more to 5.01 ppm or less, or 3.12 ppm or more to 4.32 ppm. Here, "oxygen" means "elemental oxygen."

[0050] The first layer 4 may contain 0.22 ppm to 0.65 ppm of sulfur by mass. This provides a pinning effect, slowing grain boundary migration and making it easier to suppress the growth of crystal grains in the first layer. This further improves the peeling resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. The lower limit of the sulfur content in the first layer 4 may be 0.22 ppm or more, 0.25 ppm or more, or 0.29 ppm or more by mass. The upper limit of the sulfur content in the first layer 4 may be 0.65 ppm or less, 0.55 ppm or less, or 0.45 ppm or less by mass. The sulfur content in the first layer 4 may be 0.25 ppm or more to 0.55 ppm or less, or 0.29 ppm or more to 0.45 ppm by mass. Here, "sulfur" means "elemental sulfur."

[0051] The first layer 4 may contain unavoidable impurities, such as nitrogen, phosphorus, and silicon, as long as the electric wire 1 has both electrical conductivity and peel resistance. The content of the unavoidable impurities can be determined by the same method as that for measuring the copper content in the first layer 4.

[0052] (Structure of First Layer) The thickness T1 of the first layer 4 may be 0.04 mm or more and 0.06 mm or less. This facilitates mutual diffusion of heat between the core wire 2 and the coating 5, thereby further improving the peel resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. The lower limit of the thickness T1 of the first layer 4 may be 0.04 mm or more, 0.045 mm or more, or 0.050 mm or more. The upper limit of the thickness T1 of the first layer 4 may be 0.06 mm or less, 0.058 mm or less, or 0.056 mm or less. The thickness T1 of the first layer 4 may be 0.045 mm or more and 0.058 mm or less, or 0.050 mm or more and 0.056 mm or less.

[0053] The thickness T1 of the first layer 4 can be determined in the same manner as the method for measuring the thickness of the coating 5, except for the following: "If the first layer 4 is present on the outermost surface of the coating 5, the shortest distance from the outer periphery to the interface of the first layer 4 on the core wire 2 side is determined, and this is taken as the thickness T1 of the first layer 4. If the first layer 4 is not present on the outermost surface of the coating 5, the shortest distance from the interface on the surface side of the first layer 4 to the interface of the first layer 4 on the core wire 2 side is determined, and this is taken as the thickness T1 of the first layer 4."

[0054] It has been confirmed that as long as the same electric wire 1 is measured, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0055] The first layer 4 may have crystal grains, and the average grain size of the crystal grains may be 0.5 μm or more and 2 μm or less. This makes it difficult for grain boundaries to reach from the surface of the coating 5 to the core wire 2 even if grain growth occurs, thereby further improving the peeling resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. The lower limit of the average grain size of the crystal grains may be 0.5 μm or more, 0.7 μm or more, or 0.9 μm or more. The upper limit of the average grain size of the crystal grains may be 2 μm or less, 1.4 μm or less, or 1.1 μm or less. The average grain size of the crystal grains may be 0.7 μm or more and 1.4 μm or less, or 0.9 μm or more and 1.1 μm or less.

[0056] The average particle size of the crystal particles can be determined by the following method. Specifically, first, a 20 mm electric wire 1 obtained by cutting the electric wire 1 along a plane perpendicular to the longitudinal direction is embedded in resin. Next, one of the cut surfaces of the resin-embedded electric wire 1 is pre-finished by mechanical polishing, and then a cross-section polisher (CP) is applied using an Ar ion beam under the following conditions to obtain a polished cut surface. Next, CP-SEM (Scanning Electron Microscopy) is performed on the polished cut surface using a high-resolution scanning electron microscope "SU8020" manufactured by Hitachi High-Tech Corporation, and a 5000x magnification image is obtained so that the entire polished cut surface is included in one field of view. Next, the particle size of each individual crystal particle in the image is calculated using the following formula (1), and the average value is taken as the average particle size of the crystal particles. (Crystal grain diameter) = {(Crystal grain width) + (Crystal grain height)} / 2 (1) Here, "crystal grain width" means the maximum distance between two points located on the outer edge of the crystal grain to be measured, where an imaginary line passing through the two points is perpendicular to the thickness direction of the coating. "Crystal grain height" means the maximum distance between two points located on the outer edge of the crystal grain to be measured, where an imaginary line passing through the two points is parallel to the thickness direction of the coating. The number of crystal grains to be measured is 10 randomly selected in one field of view of the same first layer, and the number of fields of view is 20. Note that one field of view is a rectangle with a length of 12 μm and a width of 9.6 μm. (CP conditions) Acceleration voltage: 1.0 kV Inclination: 0°

[0057] It has been confirmed that as long as the same electric wire 1 is measured, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0058] <Second Layer> (Composition of Second Layer) The coating 5 further includes a second layer 3, which is located between the core wire 2 and the first layer 4. The second layer 3 may contain nickel as a main component. This allows a metallic bond between the iron element of the core wire 2, the copper element of the coating 5, and the nickel element of the coating 5 when thermal diffusion occurs, thereby further improving the peeling resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. Here, as long as the second layer 3 is located between the core wire 2 and the first layer 4, the second layer 3 may or may not be in contact with the outer circumferential surface of the core wire 2. When the second layer 3 is not in contact with the outer circumferential surface of the core wire 2, another layer, described later, may be present between the core wire 2 and the second layer 3. Furthermore, as long as the second layer 3 is located between the core wire 2 and the first layer 4, the first layer 4 may or may not be in contact with the outer circumferential surface of the second layer 3. When the first layer 4 is not in contact with the outer circumferential surface of the second layer 3, another layer (described below) may be present between the second layer 3 and the first layer 4. Here, "nickel" means "elemental nickel." Furthermore, "the second layer 3 contains nickel as a main component" means "the second layer 3 contains 90% by mass or more of nickel." The lower limit of the nickel content in the second layer 3 can be 91% by mass or more, 92% by mass or more, 93% by mass or more, or 99% by mass or more. The upper limit of the nickel content can be 100% by mass or less, 99% by mass or less, or 98% by mass or less. The content can be 91% by mass or more and 100% by mass or less, 92% by mass or more and 99% by mass or less, or 93% by mass or more and 98% by mass or less.

[0059] The nickel content in the second layer 3 can be determined by the following method. That is, the nickel content can be determined by the following procedure.

[0060] (A1) The electric wire 1 is cut along a plane perpendicular to the longitudinal direction to obtain a cross section of the electric wire 1. Next, a micro-sampling process is performed on the cross section using a focused ion beam (FIB) of "Quanta3D" manufactured by FEI Company, USA. The micro-sampling process includes a rough process and a finish process. The rough process is performed under a condition of 30 kV, and the finish process is performed under a condition of 8 kV.

[0061] (B1) For the region of the second layer 3 of the micro-sampled cross section, an arbitrary rectangular observation field of 0.1 μm x 0.09 μm is set at a magnification of 2,000,000 times, and an image of the observation field is obtained.

[0062] (C1) The image is subjected to EDX analysis using a JEOL Ltd. "JEM-2100F" under the condition of 200 kV, thereby measuring the nickel content in the observation field.

[0063] (D1) For any other four observation fields, the nickel content in each observation field is measured by carrying out the above (B1) and (C1).

[0064] (E1) The nickel content in the second layer 3 can be determined by calculating the average value of the nickel content in a total of five observation fields.

[0065] It has been confirmed that as long as the same electric wire 1 is measured, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0066] The second layer 3 may contain unavoidable impurities, such as carbon, silicon, and sulfur, as long as the electric wire 1 has peel resistance. The content of the unavoidable impurities can be determined by the same method as that for measuring the nickel content in the second layer 3.

[0067] (Structure of Second Layer) The thickness T2 of the second layer 3 may be 0.3 nm or more and 40.3 nm or less. This allows iron elements in the core wire to be metallically bonded with copper or nickel elements in the coating when thermal diffusion occurs, thereby further improving the peeling resistance of the coating 5 when external stress is applied to the electric wire 1 exposed to high temperatures. The lower limit of the thickness T2 of the second layer 3 may be 0.3 nm or more, 5 nm or more, or 10 nm or more. The upper limit of the thickness T2 of the second layer 3 may be 40.3 nm or less, 30 nm or less, or 20 nm or less. The thickness T2 of the second layer 3 may be 5 nm or more and 30 nm or less, or 10 nm or more and 20 nm or less.

[0068] The thickness T2 of the second layer 3 can be determined in the same manner as the method for measuring the thickness of the coating 5, except that "the shortest distance from the interface on the surface side of the second layer 3 to the interface on the core wire 2 side of the second layer 3 is determined, and this is taken as the thickness T2 of the second layer 3."

[0069] It has been confirmed that as long as the same electric wire 1 is measured, there is no variation in the measurement results even if the measurement location is arbitrarily selected.

[0070] <Other Layers> The coating 5 may further include other layers. Examples of the other layers include a Ni—Cu layer, an Fe—Ni layer, and a ３ layers, etc.

[0071] The thickness of the other layer can be determined in the same manner as the method for measuring the thickness of the coating 5, except for the following: "If the other layer is located on the outermost surface of the coating 5, the shortest distance from the outer periphery to the interface of the other layer on the core wire 2 side is determined, and this is the thickness of the other layer. If the other layer is not located on the outermost surface of the coating 5, the shortest distance from the interface on the surface side of the other layer to the interface of the other layer on the core wire 2 side is determined, and this is the thickness of the other layer."

[0072] [Embodiment 2: Electric Wire Manufacturing Method] The electric wire manufacturing method of this embodiment will be described with reference to FIG. 3. FIG. 3 is a flowchart of the electric wire manufacturing method according to one embodiment of the present disclosure. As shown in FIG. 3, the electric wire manufacturing method of this embodiment is the electric wire manufacturing method described in Embodiment 1, and includes: a first step of preparing a core wire containing iron as a main component; and a second step of forming a coating on the outer peripheral surface of the core wire. The second step includes a first layer forming step of forming a first layer on the outer peripheral surface of the core wire. In the first layer forming step, an electrolytic plating bath containing an additive at 1 mg / L or more and 15 mg / L or less is used. In the electric wire manufacturing method of this embodiment, the second step can further include a second layer forming step of forming a second layer on the outer peripheral surface of the core wire before the first layer forming step.

[0073] <First Step> In the first step, a core wire containing iron as a main component is prepared. The first step of preparing the core wire can be performed, for example, by preparing a core wire made of stainless steel containing iron as a main component, or carbon steel containing iron as a main component, etc. Note that the first step may also include a step of degreasing the outer circumferential surface of the core wire and then rinsing it with water after degreasing.

[0074] <<Second Step>> In the second step, a coating is formed on the outer circumferential surface of the core wire. The second step includes a "first layer forming step" of forming a first layer on the outer circumferential surface of the core wire. The second step may further include a "second layer forming step" of forming a second layer on the outer circumferential surface of the core wire before the "first layer forming step." The second step may include a step of forming the other layer described above in addition to the "first layer covering step" or the "first layer covering step" and the "second layer covering step." The other layer may be formed by a conventional method.

[0075] <Second Layer Forming Step> In the second layer forming step, a second layer is formed on the outer peripheral surface of the core wire before the "first layer forming step." The second layer forming step can be performed, for example, by electrolytic plating using a Wood's bath to form the second layer on the outer peripheral surface of the core wire.

[0076] <First Layer Forming Step> In the first layer forming step, a first layer is formed on the outer peripheral surface of the core wire. This first layer forming step can be performed, for example, by electrolytic plating using copper sulfate plating to form the first layer on the outer peripheral surface of the core wire. After the first layer forming step, a step of washing the outer peripheral surface of the first layer with water may be performed.

[0077] In the first layer formation step, an electroplating bath containing additives is used. The additives refer to a polymer, a leveler, and a brightener. In the electroplating bath, the polymer content, the leveler content, and the brightener content are each 1 mg / L or more and 15 mg / L or less. This allows the carbon content, hydrogen content, and sulfur content in the first layer to be adjusted within desired ranges, thereby improving the peeling resistance of the coating when external stress is applied to an electric wire exposed to high temperatures. This was newly discovered by the present inventors as a result of extensive research. The electroplating bath may be a copper sulfate plating bath.

[0078] Examples of the polymer include polyethylene glycol (PEG), examples of the leveler include bis(3-sulfopropyl)disulfide (SPS), and examples of the brightener include Janus Green B (JGB).

[0079] The lower limit of the content of the additive in the electrolytic plating may be 1.5 mg / L or more, 2 mg / L or more, or 3 mg / L or more. The upper limit of the content of the additive in the electrolytic plating may be 13 mg / L or less, 10 mg / L or less, or 8 mg / L or less. The content of the additive in the electrolytic plating may be 1.5 mg / L or more and 13 mg / L or less, 2 mg / L or more and 10 mg / L or less, or 3 mg / L or more and 8 mg / L or less.

[0080] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0081] <<Preparation of Electric Wires>> Electric wires according to Samples 1 to 19 and Samples 101 to 106 were prepared as follows.

[0082] <First Step> First, the outer surface of the core wire having the configuration shown in Table 3 was subjected to a "degreasing step" using a degreasing liquid ("Ace Clean 220" (trademark) manufactured by Okuno Chemical Industries Co., Ltd.) under the following conditions, and then a "water-rinsing step" was performed under the following conditions. Note that when "stainless steel" or "carbon steel" is listed in the "stainless steel / carbon steel" column in Table 3, it means that the core wire contains "stainless steel" or "carbon steel." (Conditions for the degreasing step) Temperature: 50°C Time: 10 seconds (Conditions for the water-rinsing step) Immersion time: 10 seconds

[0083] <Second Layer Forming Step (Second Step)> Next, the second layer forming step was carried out by performing electrolytic plating on the outer peripheral surface of the core wire after the water washing step using a Wood's bath having the composition and pH shown in Table 1 under the temperature and current density conditions shown in Table 1. The electrolytic plating time was the time required for the second layer to have a thickness as shown in Table 3. In addition, if "-" is written in all of the columns in the "Second Layer Forming Step" column in Table 1, it means that the second layer forming step was not carried out.

[0084] <First Layer Forming Step (Second Step)> Next, a first layer was formed on the outer peripheral surface of the second layer formed in the second layer forming step by carrying out the first layer forming step using a copper sulfate plating (electrolytic plating) bath having the composition and pH shown in Table 2 under the temperature and current density conditions shown in Table 2. The electrolytic plating time was the time required for the first layer to reach a thickness as shown in Table 4.

[0085] Next, the outer peripheral surface of the first layer was subjected to a water washing process under the following conditions: (Conditions for the water washing process) Immersion time: 10 seconds

[0086]

[0087]

[0088] By the above steps, electric wires according to Samples 1 to 19 and Samples 101 to 106 having the configurations shown in Tables 3 and 4 were produced.

[0089] <Evaluation of Electric Wire Characteristics> <Composition of First Layer> For the electric wires of Samples 1 to 19 and Samples 101 to 106, the copper content in the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the "Cu [ppm]" column of Table 4. For the electric wires of Samples 1 to 19 and Samples 101 to 106, the carbon content in the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the "C [ppm]" column of Table 4. For the electric wires of Samples 1 to 19 and Samples 101 to 106, the hydrogen content in the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the "H [ppm]" column of Table 4. For the electric wires of Samples 1 to 19 and Samples 101 to 106, the oxygen content in the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the column "O [ppm]" in Table 4. For the electric wires according to Samples 1 to 19 and Samples 101 to 106, the sulfur content in the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the column "S [ppm]" in Table 4.

[0090] <Average grain size of crystal grains> For the electric wires according to Samples 1 to 19 and Samples 101 to 106, the average grain size of the crystal grains in the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the column "Average grain size of crystal grains [μm]" in Table 4. FIG. 4 is an enlarged photograph of the cross section of the electric wire according to Sample 101. FIG. 5 is an enlarged photograph of the cross section of the electric wire according to Sample 1.

[0091] <Composition of Second Layer> For the electric wires according to Samples 1 to 19 and Samples 101 to 106, the nickel content in the second layer was determined by the method described in Embodiment 1. The obtained results are shown in the "Ni [mass %]" column in Table 3. Note that, if "-" is entered in all the columns of the "Second Layer" in Table 3, it means that the second layer is not present.

[0092] <Coating Thickness> For the electric wires according to Samples 1 to 19 and Samples 101 to 106, the thickness of the coating was determined by the method described in Embodiment 1. The obtained results are shown in the column of "Coating Thickness [mm]" in Table 4.

[0093] <Evaluation Test 1> First, the electric wires of Samples 1 to 19 and Samples 101 to 106 were exposed to an environment at 250°C for 1 hour. Next, the electric wires of Samples 1 to 19 and Samples 101 to 106 were cooled in an environment at 25°C for 1 hour. Next, for the electric wires of Samples 1 to 19 and Samples 101 to 106, the average grain size of the crystal grains in the first layer was determined by the method described in Embodiment 1. The obtained results are shown in the "Evaluation Test 1" column in Table 4. The evaluation criteria were as follows. (Evaluation Criteria for Evaluation Test 1) A: The average grain size of the crystal grains was 3 μm or more and 10 μm or less. B: The average grain size of the crystal grains was more than 10 μm.

[0094] FIG. 6 is an enlarged photograph of the cross section of the electric wire of Sample 101 after being exposed to a 250°C environment for one hour and cooled in a 25°C environment for one hour, as described above. FIG. 7 is an enlarged photograph of region VII in FIG. 6. In FIG. 7, the area indicated by the arrow indicates the location where the grain boundaries of the crystal grains extend in the film thickness direction. FIG. 8 is an enlarged photograph of the cross section of the electric wire of Sample 1 after being exposed to a 250°C environment for one hour and cooled in a 25°C environment for one hour, as described above. The larger the average grain size of the crystal grains, the more likely cracks are to occur, and the more likely peeling of the coating occurs from the cracks. Therefore, a large average grain size of the crystal grains in Evaluation Test 1 means that the peeling resistance of the coating is reduced when external stress is applied to an electric wire exposed to high temperatures.

[0095] <Evaluation Test 2> The method of Evaluation Test 2 will be described below with reference to FIGS. 9 to 13. FIG. 9 is a schematic perspective view of a sample electric wire 1 cut in Evaluation Test 2. FIG. 10 is a schematic cross-sectional view illustrating the evaluation method of Evaluation Test 2. FIG. 11 is a schematic cross-sectional view of an example of a sample electric wire according to Evaluation Criterion A' in Evaluation Test 2. FIG. 12 is a schematic cross-sectional view of an example of a sample electric wire according to Evaluation Criterion B' in Evaluation Test 2. FIG. 13 is a schematic cross-sectional view of another example of a sample electric wire according to Evaluation Criterion B' in Evaluation Test 2. First, the electric wires 1 according to Samples 1 to 19 and Samples 101 to 106 were exposed to an environment at 250°C for 1 hour. Next, the electric wires 1 according to Samples 1 to 19 and Samples 101 to 106 were cooled in an environment at 25°C for 1 hour. Next, the electric wires 1 according to Samples 1 to 19 and Samples 101 to 106 were cut to a length of 50 mm as shown in FIG. 9. Next, as shown in FIG. 10 , the electric wire 1 was cut to a length of 50 mm and sandwiched between stainless steel plates 20a and 20b. Next, with the stainless steel plate 20b held in place, a pressure of 6000 N was applied to the electric wire 1 from the stainless steel plate 20a in the direction of arrow 21, so that the cross-sectional diameter of the electric wire 1 was reduced by 40%. Next, SEM images of the outer surfaces of the first layers 4 of the electric wires 1 of Samples 1 to 19 and Samples 101 to 106 after the pressure application were taken at 150x magnification, and the outer surfaces of the first layers 4 of the electric wires 1 of Samples 1 to 19 and Samples 101 to 106 were evaluated according to the evaluation criteria described below. The results are shown in the "Evaluation Test 2" column of Table 4. In Evaluation Test 2, Evaluation Criterion A', described below, specifically refers to the state shown in FIG. 11 , and Evaluation Criterion B', described below, specifically refers to the state shown in FIGS. 12 and 13 . Furthermore, if a crack occurs at the interface of the first layer on the core wire side, the coating is likely to peel off from the crack as a starting point. Therefore, if the crack occurs, even if the peeling has not yet occurred, it means that the peeling resistance of the coating has decreased when external stress is applied to the electric wire exposed to high temperatures.

[0096] <Evaluation Test 3> The method of Evaluation Test 3 will be described below with reference to FIG. 14. FIG. 14 is a schematic perspective view illustrating the evaluation method of Evaluation Test 3. First, the electric wires 1 according to Samples 1 to 19 and Samples 101 to 106 were exposed to an environment at 250°C for one hour. Next, the electric wires 1 according to Samples 1 to 19 and Samples 101 to 106 were cooled in an environment at 25°C for one hour. Next, as shown in FIG. 14, the electric wires 1 according to Samples 1 to 19 and Samples 101 to 106 were wound five times in the direction of the arrow around a wire 22 having a cross-sectional diameter of 0.25 mm (self-diameter bending). Next, 150x SEM (Scanning Electron Microscope) images were taken of the outer circumferential surface of the first layer of the electric wires 1 of Samples 1 to 19 and Samples 101 to 106 after the self-diameter bending. The outer circumferential surface of the first layer of the electric wires 1 of Samples 1 to 19 and Samples 101 to 106 was evaluated according to the following evaluation criteria. The results are shown in the "Evaluation Test 3" column of Table 4. Note that the larger the crystal grains, the more likely it is that cracks will occur that originate at the crystal grain boundaries and reach the core wire. The occurrence of cracks on the outer circumferential surface of the first layer indicates a decrease in the peel resistance of the coating when external stress is applied to an electric wire exposed to high temperatures. (Evaluation Criteria for Evaluation Tests 2 and 3) A': No cracks 31 occurred. B': Cracks 31 occurred.

[0097]

[0098]

[0099] The electric wires according to Samples 1 to 19 correspond to Examples, and the electric wires according to Samples 101 to 106 correspond to Comparative Examples. Based on the results of Evaluation Test 1 above, it was found that the electric wires according to Samples 1 to 15 and 17, compared to the electric wires according to Samples 101 to 106, exhibited significantly more suppressed crystal grain growth due to exposure to high temperatures, and thus suppressed a decrease in the peel resistance of the coating when external stress is applied to the electric wires exposed to high temperatures. Furthermore, based on the results of Evaluation Tests 2 and 3 above, it was found that the electric wires according to Samples 1 to 16, 18, and 19 exhibited significantly improved peel resistance of the coating when external stress is applied to the electric wires exposed to high temperatures, compared to the electric wires according to Samples 101 to 106. Thus, based on the results of Evaluation Tests 1 to 3 above, it was found that the electric wires according to Samples 1 to 19 exhibited significantly superior peel resistance of the coating when external stress is applied to the electric wires exposed to high temperatures, compared to the electric wires according to Samples 101 to 106.

[0100] From the above, it was found that the electric wires according to Samples 1 to 19 can prevent the coating from peeling off when an external stress is applied to an electric wire exposed to high temperatures.

[0101] Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined.

[0102] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0103] 1 Electric wire, 2 Core wire, 3 Second layer, 4 First layer, 5 Coating, 20a, 20b Stainless steel plate, 21 Arrow, 22 Wire, 31 Crack.

Claims

1. An electric wire comprising a core wire and a coating that covers the core wire, The core wire contains iron as a main component, the coating comprises a first layer; the first layer contains copper as a main component, The electric wire, wherein the first layer contains 10.5 ppm or more and 20.5 ppm or less of carbon by mass.

2. The electric wire of claim 1 , wherein the first layer contains 11.5 ppm or more of carbon by mass.

3. The electric wire according to claim 1 or 2, wherein the first layer contains 16.5 ppm or less of carbon by mass.

4. The electric wire according to claim 1 or 2, wherein the first layer contains hydrogen in an amount of 0.35 ppm or more and 1.30 ppm or less by mass.

5. The electric wire according to claim 4 , wherein the first layer contains hydrogen in an amount of 0.51 ppm or more by mass.

6. The electric wire of claim 4 , wherein the first layer contains 1.12 ppm or less of hydrogen by mass.

7. The electric wire according to claim 1 or 2, wherein the first layer contains 2.41 ppm or more and 5.62 ppm or less of oxygen on a mass basis.

8. The electric wire according to claim 7 , wherein the first layer contains 3.01 ppm or more of oxygen by mass.

9. 8. The wire of claim 7, wherein the first layer contains 5.01 ppm or less of oxygen by mass.

10. The electric wire according to claim 1 or 2, wherein the first layer contains sulfur in an amount of 0.22 ppm or more and 0.65 ppm or less by mass.

11. the first layer has crystalline particles; 3. The electric wire according to claim 1, wherein the average grain size of the crystal grains is 0.5 μm or more and 2 μm or less.

12. the coating further comprises a second layer; the second layer is located between the core wire and the first layer, the second layer contains nickel as a main component, The electric wire according to claim 1 or 2, wherein the second layer has a thickness of 0.3 nm or more and 40.3 nm or less.

13. 3. The electric wire according to claim 1, wherein the diameter of the core wire is 0.10 mm or more and 0.20 mm or less.

14. The electric wire according to claim 1 or 2, wherein the first layer has a thickness of 0.04 mm or more and 0.06 mm or less.

15. The electric wire according to claim 1 or 2, wherein the core wire comprises stainless steel or carbon steel.