Copper conductors, stranded conductors, and electric wires

Abstract

The present invention provides a copper-based conductor which requires little force to bend and which has little springback after being bent. The present invention also provides a stranded wire conductor and an electric wire in each of which the copper-based conductor is used.　Provided is a copper-based conductor wherein: when, in a view of a cross section thereof perpendicular to the direction in which the conductor extends, the contour shape of the cross section is assumed to be a first imaginary circle that has the same area as the area of the cross section and the contour shape of a crystal grain in the cross section is assumed to be a second imaginary circle that has the same area as the area of the crystal grain, the average diameter of the second imaginary circle is not less than 0.10 where the diameter of the first imaginary circle regarded as 1, and the average diameter of the second imaginary circle is more than 150 μm; and, in a crystal orientation analysis performed in a measurement region in the cross section by an electron backscatter diffraction (EBSD) method, the percent of the area of the measurement region accounted for by a region having a GOS value of less than 1° is not less than 80%.

Description

Technical Field

[0005]

[0001] The present invention relates to a copper-based conductor, a stranded conductor, and an electric wire.

Background Art

[0002] As an electric wire used in electrical products, in-vehicle parts of automobiles, etc., a copper-based conductor with high conductivity is used. In particular, since it is necessary to arrange the electric wire in a limited space, a soft copper-based conductor that can reduce the bending diameter is used.

[0003] As such a copper-based conductor, for example, in Patent Document 1, as a rectangular wire for a coil in which a rectangular conductor having a rectangular cross section is coated with an insulating coating layer, the rectangular conductor is formed of copper, its purity is 4N or more, and its crystal grain size is 0.060 mm or more, and a rectangular wire for a coil having a 0.2% proof stress of 100 MPa or less is described. Thereby, the rectangular conductor can be made relatively soft, and thus, even for a coil with a small bending diameter, it is said that high coil shape retention performance can be obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When arranging an electric wire in a limited space inside an electrical product or an automobile, if the copper-based conductor lacks softness, the force required to bend the electric wire increases, and the springback after bending the electric wire also increases, making it easier for the bent electric wire to have a wire kink. As a result, the workability of the arrangement deteriorates, especially the handling becomes poor. Therefore, there has been a demand for a copper-based conductor that requires less force to bend and has a small springback after bending.

[0006] In this regard, the flat rectangular wire for coils described in Patent Document 1 has not been sufficiently considered from the standpoint of controlling crystal orientation and processing strain, and there was room for improvement in particular in that the copper-based conductor should be made even softer, taking these aspects into consideration.

[0007] Therefore, the present invention has been made in view of the above problems, and aims to provide a copper-based conductor that requires little force to bend and has little springback after bending, as well as stranded conductors and electric wires using the same. [Means for solving the problem]

[0008] As a result of diligent research, the inventors focused on controlling the crystal structure of copper-based conductors, more specifically, on simultaneously controlling the crystal orientation and grain size of copper-based conductors. They discovered that the ratio of the average diameter of a second virtual circle (with an area equal to the area of ​​the crystal grains) to the diameter of a first virtual circle (with an area equal to the area of ​​the cross-section of the copper-based conductor), the size of the average diameter of the second virtual circle, and the area ratio of regions with a GOS value of less than 1° when crystal orientation analysis is performed on the cross-section affect the 0.2% yield strength of the copper-based conductor, and further affect the magnitude of springback. As a result, they found that they were able to achieve a copper-based conductor that requires less force to bend and exhibits less springback after bending, as well as stranded conductors and wires that are less prone to kinking and have high workability in wiring, thus completing the present invention.

[0009] To achieve the above objective, the gist of the present invention is as follows. (1) A copper-based conductor wherein, when viewed in a cross-section perpendicular to the extension direction of the conductor, the contour shape of the cross-section is assumed to be a first virtual circle having the same area as the area of ​​the cross-section, and the contour shape of the crystal grains within the cross-section is assumed to be a second virtual circle having the same area as the area of ​​the crystal grains, the average diameter of the second virtual circle is 0.10 or more when the diameter of the first virtual circle is 1, the average diameter of the second virtual circle is greater than 150 μm, and in a crystal orientation analysis by electron backscatter diffraction (EBSD) performed in the measurement region of the cross-section, the area ratio of the region having a GOS value of less than 1° in the measurement region is 80% or more. (2) The copper-based conductor described in (1) above, wherein, in the crystal orientation analysis performed in the measurement area of ​​the cross-section, all of the crystal grains forming the outer contour of the conductor have a GOS value of less than 1°. (3) In the crystal orientation analysis performed in the measurement area of ​​the cross-section, the direction of the x-axis is determined within the cross-section, and <111> Crystal orientations within ±15° <111> When considering the orientation group, with respect to the total area of ​​crystal grains included in the measurement region, in the direction of the x-axis <111> A copper-based conductor as described in (1) or (2) above, wherein the area ratio of crystal grains having orientation groups is 70% or less. (4) A copper-based conductor as described in any one of items (1) to (3) above, which is made of copper-based wire material having the shape of a round wire, ribbon wire, flat wire, or rectangular wire. (5) A stranded conductor formed by twisting together a plurality of copper wires, each made of a copper conductor as described in any one of items (1) to (3) above. (6) A wire having at least an insulating coating layer formed on the surface of the copper-based conductor described in (4) above, or the stranded conductor described in (5) above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a copper-based conductor that requires little force to bend and exhibits little springback after bending, as well as stranded conductors and electric wires using the same. [Modes for carrying out the invention]

[0011] Preferred embodiments of the copper-based conductor of the present invention will be described in detail below. Note that in the component composition of the copper-based conductor of the present invention, "mass%" may sometimes be simply represented as "%".

[0012] For copper-based conductors, when viewed in a cross-section perpendicular to the extension direction of the conductor, assuming the contour shape of the cross-section is a first virtual circle with the same area as the area of ​​the cross-section, and assuming the contour shape of the crystal grains within the cross-section is a second virtual circle with the same area as the area of ​​the crystal grains, the average diameter of the second virtual circle is 0.10 or greater when the diameter of the first virtual circle (D1) is set to 1, the average diameter of the second virtual circle is greater than 150 μm, and in the crystal orientation analysis by electron backscatter diffraction (EBSD) performed in the measurement area of ​​the cross-section, the area ratio of the region with a GOS value of less than 1° in the measurement area is 80% or greater.

[0013] In the copper-based conductor of the present invention, in particular, by setting the average diameter of the second virtual circle to 0.10 or more when the diameter (D1) of the first virtual circle is 1, setting the average diameter of the second virtual circle to more than 150 μm, and setting the area ratio of the region having a GOS value of less than 1° to 80% or more, the 0.2% yield strength of the copper-based conductor can be lowered, thereby reducing the force required to bend the copper-based conductor, and further reducing the springback after bending the copper-based conductor.

[0014] The present invention provides copper-based conductors that require little force to bend and exhibit minimal springback after bending, as well as stranded conductors and electric wires using these conductors. This allows for wiring in electrical products and automobiles with minimal force, and also suppresses wire kinking due to springback, enabling the use of complex wiring in limited spaces and improving the efficiency of wire wiring. Furthermore, because the copper-based conductors according to the present invention require little force to bend and exhibit minimal springback after bending, they can be suitably used in edgewise-wound coils requiring tight bending, and bonding wires that are joined by deforming the wires.

[0015] [1] Physical properties of copper conductors In the copper-based conductor according to the present invention, when viewed in a cross-section perpendicular to the stretching direction of the conductor, assuming that the contour shape of the cross-section is a first virtual circle having the same area as the area of ​​the cross-section, and assuming that the contour shape of the crystal grains within the cross-section is a second virtual circle having the same area as the area of ​​the crystal grains, the average diameter (D2) of the second virtual circle is 0.10 or greater, when the diameter (D1) of the first virtual circle is set to 1, and the average diameter (D2) of the second virtual circle is greater than 150 μm.

[0016] Here, there is a certain correlation between the average grain size and yield strength. When the average grain size, i.e., the average diameter of the second virtual circle (D2), is less than 150 μm, the 0.2% yield strength tends to be higher, and the force required to bend the copper-based conductor increases. Similarly, when the diameter of the first virtual circle (D1), which has the same area as the cross-sectional area of ​​the copper-based conductor, is set to 1, if the average diameter of the second virtual circle (D2), which has the same area as the grains, is less than 0.10, the number of grains in the copper-based conductor increases, leading to more grain boundaries, which also tends to increase the 0.2% yield strength, thus requiring a greater force to bend the copper-based conductor. Therefore, the average diameter of the second virtual circle (D2) is preferably 200 μm or more, and more preferably 300 μm or more. Furthermore, when the diameter of the first virtual circle (D1) is set to 1, the average diameter of the second virtual circle (D2) is preferably 0.20 or more, more preferably 0.33 or more (or 1 / 3 or more), and even more preferably 0.43 or more. On the other hand, there is no particular upper limit to the grain size of the crystal grains, but for example, it is less than or equal to the diameter (D1) of the first virtual circle.

[0017] Here, the average diameter (D2) of the second virtual circle can be used as the average grain size of the crystal grains contained in the copper-based conductor. This average grain size is calculated by selecting the chart-grain size (diameter) of the analysis software as the analysis target for the entire measurement area in the analysis of crystal orientation data by the electron backscatter diffraction (EBSD) method described later, and then using the area method. More specifically, when a boundary where the orientation difference with an adjacent measurement point is 15° or more is defined as a crystal grain interface (grain boundary), the average diameter of the crystal grain equivalent to a circle can be used as the average grain size when the cross-sectional area of ​​the crystal grain is calculated using the number of consecutive measurement points in the area enclosed by the grain boundary and the step size during measurement. This average grain size is taken as the average diameter (D2) of the second virtual circle having the same area as the crystal grains of the copper-based conductor.

[0018] Furthermore, the diameter (D1) of the first virtual circle having the same area as the cross-sectional area of ​​the copper-based conductor can be directly measured using a micrometer or similar instrument if the cross-section is circular. On the other hand, for ribbon wires, rectangular wires, and flat wires, the area of ​​the cross-section observed using an optical microscope can be determined, and the diameter of the circle having the same area can be taken as the diameter (D1) of the first virtual circle.

[0019] Furthermore, in the copper-based conductor according to the present invention, in crystal orientation analysis by electron backscatter diffraction (EBSD) performed in a measurement area of ​​a cross-section perpendicular to the stretching direction of the conductor, the area ratio of regions having a GOS (Grain Orientation Spread) value of less than 1° in the measurement area is 80% or more. Here, if the area ratio of regions having a GOS value of less than 1° is less than 80%, the 0.2% yield strength tends to be higher, and therefore the force required to bend the copper-based conductor becomes larger. For this reason, the area ratio of regions having a GOS value of less than 1° in the measurement area is preferably 85% or more, and more preferably 90% or more. On the other hand, a larger area ratio of regions having a GOS value of less than 1° is preferable from the viewpoint of making the copper-based conductor easier to bend, and its upper limit is 100%.

[0020] In addition, in the crystal orientation analysis by the electron backscatter diffraction (EBSD) method performed in the measurement region of the cross section perpendicular to the stretching direction of the copper-based conductor according to the present invention, it is preferable that all of the crystal grains forming the outer peripheral contour of the copper-based conductor have a GOS value of less than 1°. As a result, crystal grains having a GOS value of less than 1° are present so as to include the surface layer portion of the copper-based conductor, and thus the copper-based conductor can be made even easier to bend.

[0021] The GOS value can be obtained, for example, by continuously measuring crystal orientation data using an EBSD detector (manufactured by TSL, OIM5.0 HIKARI) attached to a high-resolution scanning transmission electron microscope (manufactured by JEOL Ltd., JSM-7001FA), and calculating (processing) the measured crystal orientation data with analysis software (manufactured by TSL Solutions, OIM Analysis). "EBSD" is an abbreviation for Electron BackScatter Diffraction, and it is a crystal orientation analysis technique that utilizes reflection electron Kikuchi line diffraction that occurs when an electron beam is irradiated onto a copper-based conductor, which is a measurement sample, in a scanning electron microscope (SEM). The measurement target is the surface of a cross section perpendicular to the stretching direction of a single copper-based conductor that has been polished to a mirror finish, and the measurement region can be, for example, the entire range of the cross section. For the polishing of the cross section, in addition to polishing using a cross section polisher (registered trademark) device, wet polishing, means capable of mirror finishing such as FIB or microtome can be used, and the specific means is not limited. The measurement is performed, for example, with a step size of 1 μm. Using the analysis software, from Map-Grain Orientation Spread, the area ratio of the region having a GOS value of less than 1° in the entire measurement region and the area ratio of the region having a GOS value of less than 1° in the area of the crystal grains forming the outer peripheral contour of the copper-based conductor were calculated. Usually, this measurement is performed three times (n = 3), and their average values can be calculated and used for evaluation. Here, by using analysis software for the analysis of crystal orientation data, when a specific angular range is allowed as the crystal orientation difference from an adjacent measurement point, it is possible to easily determine whether or not the crystal orientation difference from an adjacent measurement point is within the allowable range for each measurement point.

[0022] Further, in the copper-based conductor according to the present invention, in the crystal orientation analysis by the electron backscatter diffraction (EBSD) method performed in the measurement region of the cross section perpendicular to the stretching direction of the conductor, when the direction of the x-axis is defined in the cross section and the crystal orientations within ±15° of the <111> orientation are defined as the <111> orientation group, the area ratio of the crystal grains having the <111> orientation group with respect to the direction of the x-axis to the total area of the crystal grains included in the measurement region is preferably 70% or less. Here, by setting the area ratio of the crystal grains having the <111> orientation group with respect to the direction of the x-axis to 70% or less, the 0.2% proof stress of the copper-based conductor can be made smaller, and thereby the copper-based conductor can be made even easier to bend. Therefore, the area ratio of the crystal grains having the <111> orientation group with respect to the direction of the x-axis is preferably 40% or less, more preferably 20% or less. On the other hand, from the viewpoint of making the copper-based conductor even easier to bend, the lower the area ratio of the crystal grains having the <111> orientation group with respect to the direction of the x-axis, the more preferable, and it may be 0% as the lower limit.

[0023] Here, as will be described later, when the copper-based conductor is composed of a copper-based wire having a ribbon wire or a flat wire shape, the direction of the x-axis can be defined as a direction parallel to the longitudinal direction of the cross section (the width direction of the wire). Further, when the cross section of the copper-based conductor is composed of a copper-based wire having a rectangular wire shape, the direction of the x-axis can be defined as a direction parallel to any one side of the rectangle forming the cross section. Further, when the cross section of the copper-based conductor is composed of a copper-based wire having a round wire shape, the direction of the x-axis can be defined as an arbitrary direction parallel to the cross section.

[0024] The copper-based conductor according to the present invention has a low 0.2% proof stress from the viewpoint of making the copper-based conductor easy to bend. More specifically, the 0.2% proof stress of the copper-based conductor is 150 MPa or less, preferably 100 MPa or less, more preferably 50 MPa or less. On the other hand, the lower limit of the 0.2% of the copper-based conductor is not particularly limited, but for example, from the viewpoint of facilitating handling during manufacturing, it may be 8 MPa.

[0025] In particular, to reduce the force required to bend copper conductors and enable work with weaker forces, a low 0.2% yield strength of the copper conductor is required. Here, there are two types of material deformation: elastic deformation and plastic deformation. In elastic deformation, there is a relationship σ=Eε (σ: stress, E: Young's modulus, ε: strain), where the stress acts in proportion to the applied strain. That is, a lower Young's modulus results in slower deformation, thus reducing the load. Beyond a certain strain range, plastic deformation occurs, where the material no longer returns to its original state. The stress at which this plastic deformation begins is called the yield strength. Therefore, a lower yield strength makes plastic deformation easier, allowing for a reduction in the force (load) required when bending. Furthermore, the amount of return when the load is removed is called springback, and the higher the yield strength and the lower the Young's modulus, the greater the springback.

[0026] The copper-based conductor according to the present invention exhibits minimal springback after bending. For example, when a copper-based conductor cut to a length of 1000 mm is wrapped around a cylinder having an outer diameter of 200 mm, the circumference of the copper-based conductor when released is preferably 210 mm or less.

[0027] [2] Materials for copper-based conductors Copper-based conductors are composed of copper or copper alloys. Here, the copper-based conductor may be a copper alloy containing small amounts of elements such as silver (Ag), chromium (Cr), and tin (Sn), but from the viewpoint of making the copper-based conductor more flexible, it is preferable that it be copper (Cu), and more specifically, pure copper of 99.00 mass% or more. Among these, since conductivity is higher the higher the copper content, it is preferable that it be tough pitch copper consisting of 99.90 mass% or more copper (Cu) and unavoidable impurities, and more preferably oxygen-free copper consisting of 99.96 mass% or more Cu, 10 ppm or less of oxygen, and unavoidable impurities.

[0028] The copper alloy constituting the copper-based conductor preferably has an alloy composition containing at least one of the following elements: Ag in an amount of 0.1% to 1.0% by mass, Cr in an amount of 0.1% to 1.0% by mass, and Sn in an amount of 0.1% to 1.0% by mass, with the remainder being Cu and unavoidable impurities.

[0029] If the content of at least one of Ag, Cr, and Sn is 0.1% by mass or more, the tensile durability of copper-based conductors can be improved. On the other hand, if the content of at least one of Ag, Cr, and Sn exceeds 1.0% by mass, it can be a factor that reduces the conductivity of copper-based conductors. From this viewpoint, when a copper alloy contains Ag, the upper limit for the Ag content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less. When a copper alloy contains Cr, the upper limit for the Cr content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less. When a copper alloy contains Sn, the upper limit for the Sn content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less.

[0030] Any elements other than those mentioned above are unavoidable impurities. Unavoidable impurities refer to impurities that are inevitably introduced during the manufacturing process. Depending on the amount of unavoidable impurities, they can reduce the conductivity of copper-based conductors, so it is preferable to have a low amount of unavoidable impurities.

[0031] Unavoidable impurities in copper-based conductors include elements such as aluminum (Al), beryllium (Be), cadmium (Cd), iron (Fe), magnesium (Mg), nickel (Ni), phosphorus (P), lead (Pd), silicon (Si), and titanium (Ti). Unavoidable impurities also include small amounts of elements such as silver (Ag), chromium (Cr), and tin (Sn) that do not meet the content requirements for the alloy composition of the copper alloy. Preferably, the upper limit of the content of unavoidable impurities is 30 ppm or less in total for the above elements.

[0032] [3] Shapes and applications of copper conductors The shape of the copper conductor can be appropriately selected according to the amount of current required by the electrical product or automobile to which it will be wired, the wiring space, etc., but among these, it is preferable to use copper wires having the shape of round wires, ribbon wires, flat rectangular wires, or rectangular wires, and it is more preferable to use copper wires having the shape of round wires, flat rectangular wires, or rectangular wires. In particular, by using copper wires having the shape of round wires, flat rectangular wires, or rectangular wires, it is possible to make it less likely for parts with high GOS values ​​to remain in the crystal grains that form the outer contour of the resulting conductor. Here, a round wire is a copper wire in which the shape of the cross section perpendicular to the extension direction of the conductor is circular. A ribbon wire is a copper wire in which the cross section perpendicular to the extension direction of the conductor is enclosed by two straight lines and two curves connecting the ends of the two straight lines, a so-called track shape. A flat rectangular wire is a copper wire in which the cross section is enclosed by four straight lines. A rectangular wire is a copper wire in which the cross section is rectangular.

[0033] When a copper conductor is made of a copper wire having a round shape, a wire diameter of 100 μm is preferable from the viewpoint of being able to pass a relatively high current through the copper wire. Furthermore, a wire diameter of 900 μm or less is preferable from the viewpoint of being able to adequately accommodate wiring space and being easily bendable.

[0034] Furthermore, when the copper wire is composed of copper wires in the shape of ribbon wires or flat wires, it is preferable that the thickness of the copper wire (ribbon wire, flat wire) is 100 μm or more from the viewpoint of being able to pass a relatively high current through the copper wire. Also, it is preferable that the thickness of the copper wire (ribbon wire, flat wire) is 900 μm or less from the viewpoint of being able to adequately accommodate the wiring space and being easy to bend. On the other hand, the width of the copper wire (ribbon wire, flat wire) is not particularly limited, but from the viewpoint of enabling higher current to flow and being easy to bend, for example, it is preferable that the width is in the same range as the thickness of the copper wire (ribbon wire, flat wire), that is, in the range of 100 μm to 900 μm.

[0035] Furthermore, multiple strands of copper wire, consisting of the aforementioned copper-based conductors, can be twisted together to form a stranded conductor. In this case, a stranded conductor can be obtained that requires less force to bend and exhibits even less springback after bending. Here, the number of strands and the total cross-sectional area of ​​the stranded conductor are not limited, but it is also possible to form a thin-diameter stranded conductor by twisting together copper-based conductors of the aforementioned diameters in a number ranging from 7 to 19 strands.

[0036] Furthermore, the copper-based conductor of the present invention is preferably used in electric wires. More specifically, an electric wire can be constructed in which at least an insulating coating layer is formed on the surface of the above-mentioned copper-based conductor or stranded conductor. Such an electric wire requires little force to bend and exhibits little springback after bending, thus suppressing wire kinking due to springback and accommodating complex wiring in limited spaces.

[0037] Here, the material of the insulating coating layer is not particularly limited, but it is preferably a coating layer made of polyvinyl chloride, for example. The insulating coating layer can be formed, for example, by extruding molten resin onto the surface of a copper-based conductor or stranded conductor.

[0038] [4] An example of a method for manufacturing copper conductors Next, a method for manufacturing the copper-based conductor of this embodiment will be described.

[0039] In the manufacturing method of the copper-based conductor of this embodiment, a casting process is first carried out. In the casting process, electrolytic copper is melted under a reducing atmosphere to obtain a cylindrical ingot called a billet.

[0040] Following the casting process, either an extrusion or rolling process is carried out. In the extrusion process, the billet is processed into a round bar by hot extrusion. In the rolling process, the billet is processed into a round bar by repeatedly rolling it in an up-and-down or left-and-right direction.

[0041] Following the extrusion or rolling process, a wire drawing process is performed. In the wire drawing process, the round bar obtained in the above process is drawn to a predetermined wire diameter. Preferably, a deskinning process to remove surface defects that occurred up to the above process is included in the wire drawing process. If necessary, one or more heat treatment processes may be performed before the wire drawing process to remove processing distortion and to facilitate wire drawing.

[0042] If stranded conductors are to be formed after the wire drawing process, a stranding process may be performed in which multiple drawn copper-based conductors are twisted together to form a stranded conductor. In this case, the conductors may be compressed using a compression die, or the copper-based conductors may be twisted together without compression using a compression die.

[0043] Subsequently, a heat treatment process is carried out. Here, a first heat treatment process and a second heat treatment process are performed for copper-based conductors or stranded conductors.

[0044] In the first heat treatment step, inter-running annealing is performed, which involves heat treatment by passing the wire through a heating furnace, and current annealing is performed, which involves passing an electric current through a wire that passes between multiple pulleys acting as electrodes. By performing inter-running annealing or current annealing in the first heat treatment step, the copper-based conductor and stranded conductor can be heated up in a short time. This allows for the formation of a mixed grain structure of large and small crystal grains in the initial stages of the first heat treatment step, and then the growth of crystal grains contained in the copper-based conductor and stranded conductor in the subsequent second heat treatment step, making it possible to increase the average diameter (D2) of the second virtual circle to more than 150 μm and increase the area ratio of regions with a GOS value of less than 1° in the cross-section to more than 80%. Among these, inter-running annealing is preferable in the first heat treatment step from the viewpoint of preventing the heating rate from becoming too high, thereby preventing high-GOS-value areas from remaining in the crystal grains that form the outer contour of the resulting conductor.

[0045] In the first heat treatment step, the temperature and time for heating the copper-based conductor or stranded conductor can be appropriately adjusted according to the desired average diameter (D2) of the second virtual circle. For example, increasing the temperature for heating the copper-based conductor or stranded conductor can increase the average diameter (D2) of the second virtual circle. Similarly, increasing the heating time for the copper-based conductor or stranded conductor can also increase the average diameter (D2) of the second virtual circle. Furthermore, increasing the current used during current annealing can also increase the average diameter (D2) of the second virtual circle.

[0046] In the first heat treatment step, when heating copper-based conductors or stranded conductors, it is preferable that the time from room temperature to 400°C (time to reach 400°C) be short, 3 seconds or less; in other words, a high heating rate. Such a short heating time can be achieved by current annealing or intermittent annealing. In particular, when using intermittent annealing, this can be achieved by passing the copper-based conductor or stranded conductor through a heating furnace filled with a hydrogen atmosphere, or by forcibly blowing hydrogen gas onto the copper-based conductor or stranded conductor passing through the heating furnace. In particular, from the viewpoint of preventing high GOS values ​​from remaining in the crystal grains that form the outer contour of the resulting conductor by not making the heating rate too high, it is preferable that the time from room temperature to 400°C in intermittent annealing be 1 second or more. On the other hand, in the case of current annealing, the time from room temperature to 400°C can be shorter than that.

[0047] Furthermore, when heating copper-based conductors or stranded conductors in the first heat treatment step, the holding time in the temperature range of 400°C to 520°C is preferably 5 seconds or less. In particular, if the holding time in the temperature range of 400°C to 520°C in the first heat treatment step exceeds 5 seconds, the grain size becomes almost uniform by the time the first heat treatment step is completed, making it difficult to obtain a mixed grain structure. As a result, it becomes difficult to increase the average diameter (D2) of the second virtual circle to more than 150 μm in the subsequent second heat treatment step. On the other hand, the lower limit of the holding time in the temperature range of 400°C to 520°C is not particularly limited and may be, for example, less than 1 second.

[0048] Furthermore, the maximum temperature (heat treatment temperature) when heating copper-based conductors or stranded conductors in the first heat treatment step is preferably in the range of over 400°C and 520°C or less. In particular, if the heat treatment temperature in the first heat treatment step is 400°C or less, crystal growth cannot be sufficiently advanced, and the average diameter of the second virtual circle (D2) cannot be increased to over 150 μm even in the subsequent second heat treatment step. On the other hand, if the heat treatment temperature in the first heat treatment step exceeds 520°C, the crystal grain size becomes almost uniform at the end of the first heat treatment step, making it difficult to obtain a mixed grain structure, and thus it becomes difficult to increase the average diameter of the second virtual circle (D2) to over 150 μm in the subsequent second heat treatment step. Moreover, if the heat treatment temperature in the first heat treatment step exceeds 520°C, crystal growth is suppressed in the subsequent second heat treatment step, making it difficult to achieve a GOS value of less than 1° in the cross-section of 80% or more.

[0049] Furthermore, when current annealing is performed in the first heat treatment step, the temperature of copper-based conductors and stranded conductors rises instantaneously, which can make it difficult to accurately determine the temperature because the thermocouple's response speed cannot keep up. Therefore, when setting the heat treatment conditions for current annealing, the voltage, current value, linear velocity, and inter-electrode distance may be set so that they are equivalent to the average grain size obtained when performing inter-running annealing. In this case, the annealing can be performed under the same temperature conditions as the inter-running annealing used as a comparison for the average grain size.

[0050] After the first heat treatment process, a second heat treatment process is performed. In the second heat treatment process, a batch-type heat treatment (batch annealing) can be used, in which copper-based conductors or stranded conductors wound on spools are placed in a heating furnace and heat-treated.

[0051] The heat treatment temperature in the second heat treatment step is preferably 500°C or higher. If the heat treatment temperature in the second heat treatment step is less than 500°C, the crystal grains will not grow during the heat treatment, and therefore the average diameter (D2) of the second virtual circle cannot be increased to more than 150 μm. On the other hand, there is no particular upper limit to the heat treatment temperature in the second heat treatment step, but from the viewpoint of making adhesion of copper-based conductors and stranded conductors placed in the heating furnace less likely, it is preferably 750°C or lower.

[0052] The heat treatment time in the second heat treatment step is preferably long, more specifically, 1 hour or longer, from the viewpoint of growing crystal grains contained in copper-based conductors and stranded conductors, and from the viewpoint of achieving a GOS value of less than 1° in the cross-section of 80% or more. Also, from the same viewpoint, the heat treatment time in the second heat treatment step is preferably longer than the heat treatment time in the first heat treatment step.

[0053] It is preferable to produce electric wires by forming an insulating coating layer on the surface of the copper-based conductor and stranded conductor obtained in this manner by extruding molten resin.

[0054] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and includes all aspects included in the concept and claims of the present invention, and can be modified in various ways within the scope of the present invention. [Examples]

[0055] Next, in order to further clarify the effects of the present invention, examples and comparative examples of the present invention will be described, but the present invention is not limited to these examples.

[0056] (Examples 1-9 of the present invention and Comparative Examples 1-2) Copper-based materials composed of the components shown in Table 1 were subjected to casting, extrusion, and wire drawing processes. In the wire drawing process, after forming a wire with a diameter of 8 mm from a round bar obtained in the extrusion process, the wire was finished into round wire, ribbon wire, or rectangular wire in the shapes shown in Table 2 using a round-hole die, a rectangular die, or a cassette roller die (CRD) that draws the wire through a gap between two rolls. Subsequently, a first heat treatment process was performed under the conditions shown in Table 1. For Invention Examples 1 to 9, where the presence or absence of a second heat treatment process is indicated as "Yes" in Table 1, a second heat treatment process was performed under the conditions shown in Table 1 to obtain copper-based conductors. For Invention Examples 1 to 3, 5 to 9, and Comparative Example 1, where inter-running annealing was performed in the first heat treatment process, the copper-based conductors and stranded conductors were passed through a heating furnace filled with a hydrogen atmosphere, and the temperature was raised so that the time to reach 400°C from room temperature was the value shown in Table 1. On the other hand, for Comparative Examples 1 and 2, where Table 1 indicates "none" for the presence or absence of the second heat treatment step, copper-based conductors were obtained by performing only the first heat treatment step without the second heat treatment step.

[0057] (Examples 10-14 and Comparative Example 3 of the present invention) Copper-based materials composed of the components shown in Table 3 were subjected to casting, extrusion, and wire drawing processes. In the wire drawing process, after forming a wire with a diameter of 8 mm from the round bar obtained in the extrusion process, it was finished into a round wire with the shape shown in Table 4 using a round die. Next, a stranding process was performed to form stranded conductors by twisting together the number of round wires (copper-based conductors) shown in Table 4. Subsequently, a first heat treatment process was performed under the conditions shown in Table 3. For Invention Examples 10 to 14, where the presence or absence of a second heat treatment process is indicated as "Yes" in Table 3, a second heat treatment process was performed under the conditions shown in Table 3 to obtain stranded conductors. For Invention Examples 10 to 12, 14, and Comparative Example 3, where inter-running annealing was performed in the first heat treatment process, the copper-based conductors and stranded conductors were passed through a heating furnace filled with a hydrogen atmosphere, and the temperature was raised so that the time to reach 400°C from room temperature was the value shown in Table 3. On the other hand, in Comparative Example 3, where the presence or absence of the second heat treatment step is "none" in Table 3, a stranded conductor was obtained by performing only the first heat treatment step without the second heat treatment step. Subsequently, an insulating coating layer was formed on the surface of the obtained stranded conductor by extruding molten resin made of polyvinyl chloride to obtain an electric wire.

[0058] [Various measurement and evaluation methods] The following characteristic evaluations were performed using the copper-based conductors and stranded conductors according to the above-described examples and comparative examples of the present invention. The evaluation conditions for each characteristic are as follows.

[0059] [1] Component analysis Samples obtained by pressing the wire rods from the wire drawing process in the manufacturing stage described above into flat plates were measured and analyzed using an emission spectrometer (manufactured by Shimadzu Corporation). Measurements were performed with n=3, and the average values ​​were calculated and shown in Tables 1 and 3. Elements that were intentionally added are listed in separate columns, and if they were not intentionally added, these elements were included in the total amount of unavoidable impurities. If the detected amount of a component is less than 0.001% by mass, it is considered that the component is not present, and "-" is indicated in the table.

[0060] [2] Measurement of area ratio of regions with a GOS value of less than 1° The area ratio of regions with GOS values ​​less than 1° was obtained by continuously measuring using an EBSD detector (TSL, OIM5.0 HIKARI) attached to a high-resolution scanning electron microscope (JEOL Ltd., JSM-7001FA) to collect EBSD patterns. Crystal orientation data obtained from the EBSD patterns was then analyzed using analysis software (TSL, OIM Analysis) to obtain crystal orientation analysis data. The measurement target was a polished, mirror-finished surface of a copper-based conductor (or, in the case of a stranded conductor, a single copper-based conductor constituting the stranded conductor) with a cross-section perpendicular to the extension direction. The measurement area encompassed the entire cross-section. Measurements were performed with a step size of 1 μm. From the Map-Grain Orientation Spread obtained using the analysis software, the area ratio of regions with GOS values ​​less than 1° within the entire measurement area and the area ratio of regions with GOS values ​​less than 1° within the area of ​​crystal grains forming the outer contour of the copper-based conductor were calculated. The average values ​​from three measurements (n=3) were calculated and are shown in Tables 2 and 4.

[0061] [3] With respect to the total area of ​​the crystal grains included in the measurement region, <111> Measurement of the area ratio of crystal grains with orientation groups With respect to the x-axis <111> The area ratio of crystal grains with orientation groups was determined as follows: In the analysis of crystal orientation data obtained in the cross-section by an EBSD detector, as described above, the crystal grain was defined as a set of consecutive measurement points within the area enclosed by grain boundaries, using the chart-crystal direction obtained with analysis software, where the boundary where the orientation difference between adjacent measurement points is 15° or more was defined as the crystal grain interface (grain boundary). Furthermore, in the cross-section perpendicular to the extension direction of the wire, the direction parallel to the longitudinal direction of the cross-section (width direction of the wire) was defined as the x-axis direction.

[0062] Here, when the cross-section of the copper conductor is made up of copper wire having a round shape, the direction of the x-axis is set to any direction parallel to the cross-section. Also, when the copper conductor is made up of copper wire having a ribbon or rectangular shape, the direction of the x-axis is set to a direction parallel to the longitudinal direction of the cross-section.

[0063] At this time, the total area of ​​the crystal grains within the measurement region is considered in relation to the x-axis. <111> The crystal orientation is within ±15°. <111> The area ratio of crystal grains with orientation groups was determined, and the average value of this area ratio measured three times (n=3) was calculated and is shown in Tables 2 and 4.

[0064] [4] Measurement of the diameter (D1) of the first virtual circle For round wires, the diameter (D1) of the first virtual circle having the same area as the cross-sectional area was measured directly using a micrometer or similar instrument. On the other hand, for ribbon wires and rectangular wires, the area of ​​the cross-sectional area observed using an optical microscope was determined, and the diameter of the circle having the same area was measured to determine the diameter (D1) of the first virtual circle. The average value of this measurement was calculated after performing it three times (n=3), and is shown in Tables 2 and 4.

[0065] [5] Measurement of the average diameter (D2) of the second virtual circle The average diameter (D2) of the second virtual circle was determined by analyzing the crystal orientation data from the electron backscatter diffraction (EBSD) method described above. The entire measurement area was selected as the analysis target, the chart-grain size (diameter) of the analysis software was selected, and the average grain size calculated using the area method was measured to determine the average diameter (D2) of the second virtual circle. This measurement was performed three times (n=3), and the average value was calculated and shown in Tables 2 and 4. Furthermore, based on the obtained measured average diameter (D2) of the second virtual circle and the measured diameter (D1) of the first virtual circle described above, the relative value (D2 / D1) of the measured average diameter (D2) of the second virtual circle, with the diameter (D1) of the first virtual circle set to 1, was calculated and shown in Tables 2 and 4.

[0066] [6] Evaluation of 0.2% yield strength For the copper-based conductors according to the present invention example and comparative example, tensile tests were performed using a precision universal testing machine (manufactured by Shimadzu Corporation) in accordance with JIS Z2241, and the 0.2% yield strength (MPa) was determined using the offset method. Each measurement was performed three times (n=3), and the average value of the three measurements was calculated as the measured value. In addition, the 0.2% yield strength (MPa) was measured for the stranded conductors according to the present invention example and comparative example using the same method as for the copper-based conductors.

[0067] Regarding the obtained 0.2% yield strength measurements, those with a value of 67 MPa or less were evaluated as "A" because they were particularly excellent in that they required a small amount of force to bend. Furthermore, those with a 0.2% yield strength measurement between 67 MPa and 100 MPa were evaluated as "B" because they were excellent in that they required a small amount of force to bend. Similarly, those with a 0.2% yield strength measurement between 100 MPa and 150 MPa were evaluated as "C" because they were good in that they required a small amount of force to bend. On the other hand, those with a 0.2% yield strength measurement exceeding 150 MPa were evaluated as "D" because they required a large amount of force to bend and were therefore poor. In this example, "A," "B," and "C" were evaluated as acceptable levels. The results are shown in Tables 2 and 4.

[0068] [7] Measurement of curvature after springback For copper-based conductors and stranded conductors according to the present invention example and comparative example, a bending test was performed by winding a 1000 mm length of copper-based conductor around a cylinder having an outer diameter of 200 mm. The circumference of the copper-based conductor when released was determined and used as the measured value of the curvature after springback, which is the curvature after the bending test.

[0069] Regarding the measured curvature after the bending test, a value of 205 mm or less was evaluated as "◎" (excellent) due to its low springback. A value between 205 mm and 210 mm was evaluated as "○" (good) due to its low springback. Conversely, a value exceeding 210 mm was evaluated as "×" (poor) due to its high springback. In this example, "◎" and "○" were considered acceptable levels. The results are shown in Tables 2 and 4.

[0070] [8] Overall rating If one or both of the two evaluation results for 0.2% yield strength and curvature after bending test were rated "A" or "◎", and both evaluations were at an acceptable level, the overall evaluation was rated "◎", indicating that at least one of the 0.2% yield strength and curvature after bending test was excellent. Furthermore, if the evaluation result for 0.2% yield strength was rated "B" or "C", and both evaluation results for curvature after bending test were rated "○", the overall evaluation was rated "○", indicating that both characteristics were good. On the other hand, if the evaluation result for 0.2% yield strength was "D", and the evaluation result for curvature after bending test was "×", the overall evaluation was rated "×", indicating that at least one of these two characteristics was insufficient. The results are shown in Tables 2 and 4.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] [Table 4]

[0075] As shown in Tables 1-4, in Examples 1-14 of the present invention, the relative value of the diameter of the second virtual circle (D2) when the diameter of the first virtual circle (D1) is set to 1, the average diameter of the second virtual circle (D2), and the area ratio of the region having a GOS value of less than 1° in the entire measurement area were controlled to be within a predetermined range. As a result, the force required to bend copper-based conductors and stranded conductors was reduced, and the springback after bending was also reduced.

[0076] On the other hand, in Comparative Examples 1 to 3, the average diameter (D2) of the second virtual circle was not controlled within the predetermined range. As a result, in Comparative Examples 1 and 3, the force required to bend the copper-based conductor increased, and the springback after bending the copper-based conductor also increased. Similarly, in Comparative Example 2, the springback after bending the copper-based conductor also increased.

Claims

1. A copper-based conductor, Viewed in a cross-section perpendicular to the direction of extension of the conductor, Assuming that the contour shape of the cross-section is a first virtual circle having the same area as the area of ​​the cross-section, and assuming that the contour shape of the crystal grains within the cross-section is a second virtual circle having the same area as the area of ​​the crystal grains, The average diameter of the second virtual circle is 0.10 or greater, when the diameter of the first virtual circle is set to 1. The average diameter of the second virtual circle is greater than 150 μm, and A copper-based conductor in which, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in the measurement region of the aforementioned cross-section, the area ratio of the region having a GOS value of less than 1° in the measurement region is 80% or more.

2. The copper-based conductor according to claim 1, wherein, in the crystal orientation analysis performed in the measurement area of ​​the cross-section, all of the crystal grains forming the outer contour of the conductor have a GOS value of less than 1°.

3. The copper-based conductor according to claim 1, wherein, in the crystal orientation analysis performed in the measurement region of the cross-section, the x-axis direction is defined within the cross-section, and crystal orientations within ±15° of the <111> orientation are defined as the <111> orientation group, and the area ratio of crystal grains having the <111> orientation group with respect to the x-axis direction to the total area of ​​crystal grains included in the measurement region is 70% or less.

4. The copper-based conductor according to claim 1, comprising copper-based wire material having the shape of a round wire, ribbon wire, flat rectangular wire, or rectangular wire.

5. A stranded conductor formed by twisting together a plurality of copper-based wires, each made of the copper-based conductor described in claim 1.

6. An electric wire having at least an insulating coating layer formed on the surface of the copper-based conductor according to claim 4, or the stranded conductor according to claim 5.

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