Copper-based conductor, stranded wire conductor, and electric wire

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

Copper-based conductors, stranded conductors and wires

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

[0002] Copper-based conductors with high electrical conductivity are used for electric wires used in electrical appliances and automotive components. In particular, since electric wires must be routed in limited spaces, soft copper-based conductors that can be bent with a small diameter are used.

[0003] As an example of such a copper-based conductor, Patent Document 1 describes a flat coil wire in which a flat conductor with a flat cross section is coated with an insulating coating layer, the flat conductor being made of copper, with a purity of 4N or more, a crystal grain size of 0.060 mm or more, and a 0.2% yield strength of 100 MPa or less. This makes it possible to make the flat conductor relatively soft, and therefore, it is possible to obtain high coil shape retention performance even for coils with a small bending diameter.

[0004] JP 2014-107227 A

[0005] When routing electric wires in limited spaces inside electrical appliances or automobiles, if copper-based conductors lack flexibility, the force required to bend the electric wire increases and the springback after bending also increases, making the electric wire prone to becoming bent after bending, which reduces the workability of routing and makes it particularly difficult to handle. Therefore, there has been a demand for copper-based conductors that require less force to bend and have less springback after bending.

[0006] In this regard, the rectangular coil wire described in Patent Document 1 has not been sufficiently considered in terms of controlling crystal orientation and processing strain, and there is room for improvement, particularly in terms of making the copper-based conductor even softer, taking these points into consideration.

[0007] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a copper-based conductor that requires a small force to bend and has small springback after bending, and a stranded conductor and an electric wire using the same.

[0008] The present inventors, after extensive research, have focused on controlling the crystalline structure of a copper-based conductor, more specifically, on simultaneously controlling the crystal orientation and crystal grain size of the copper-based conductor, and have found that the ratio of the average diameter of a second virtual circle having the same area as the crystal grains to the diameter of a first virtual circle having the same area as 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 having 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 also affect the magnitude of springback. As a result, the present inventors have discovered that it is possible to achieve a copper-based conductor that requires little bending force and has little springback after bending, and to obtain a stranded conductor and electric wire that are less likely to become bent and have high installation workability, thereby completing the present invention.

[0009] To achieve the above object, the present invention provides the following key configurations: (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 imaginary circle having the same area as the cross section, and the contour shape of a crystal grain in the cross section is assumed to be a second imaginary circle having the same area as the crystal grain, the average diameter of the second imaginary circle is 0.10 or more when the diameter of the first imaginary circle is 1, the average diameter of the second imaginary circle is greater than 150 μm, and in a crystal orientation analysis performed on a measurement region of the cross section by electron backscatter diffraction (EBSD) method, the area ratio of regions having a GOS value of less than 1° in the measurement region is 80% or more. (2) The copper-based conductor according to (1), wherein, in the crystal orientation analysis performed on the measurement region 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 (1) or (2) above, wherein, in the crystal orientation analysis performed on the measurement region of the cross section, when the direction of the x-axis is defined within the cross section and the crystal orientations within ±15° of the <111> orientation are defined as a <111> orientation group, the area ratio of crystal grains having a <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 any one of (1) to (3) above, which is constituted by a copper-based wire material having a round wire, ribbon wire, rectangular wire or rectangular wire shape. (5) A stranded conductor formed by twisting together a plurality of copper-based element wires made of the copper-based conductor according to any one of (1) to (3) above. (6) An electric wire in which at least an insulating coating layer is formed on the surface of the copper-based conductor according to (4) above or the stranded conductor according to (5) above.

[0010] According to the present invention, it is possible to provide a copper-based conductor that requires a small force to bend and has a small springback after bending, as well as a stranded conductor and an electric wire using the same.

[0011] Hereinafter, preferred embodiments of the copper-based conductor of the present invention will be described in detail. In the component composition of the copper-based conductor of the present invention, "mass %" may be simply represented as "%".

[0012] When viewed in a cross section perpendicular to the extension direction of the conductor, the copper-based conductor has a first imaginary circle whose contour shape is a circle having the same area as the cross section, and a second imaginary circle whose contour shape of a crystal grain in the cross section is a circle having the same area as the crystal grain, where the average diameter of the second imaginary circle is 0.10 or more when the diameter (D1) of the first imaginary circle is 1, and the average diameter of the second imaginary circle is more than 150 μm. In addition, in a crystal orientation analysis performed on a measurement region of the cross section by electron backscatter diffraction (EBSD) method, the area ratio of the region having a GOS value of less than 1° to the measurement region is 80% or more.

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

[0014] The copper-based conductor according to the present invention can provide a copper-based conductor that requires a small bending force and has small springback after bending, as well as a stranded conductor and an electric wire using the same. This allows for wire routing inside electrical appliances and automobiles to be performed with a small force and suppresses wire curl due to springback, making it possible to accommodate complex wiring in limited spaces, thereby improving workability when routing the electric wire. Furthermore, because the copper-based conductor according to the present invention requires a small bending force and has small springback after bending, it can be suitably used for edgewise wound coils, which require severe bending, and bonding wires, which are bonded by deforming wires.

[0015] [1] Physical properties of copper-based conductor When viewed in a cross section perpendicular to the extension direction of the conductor, the copper-based conductor according to the present invention has a cross section whose contour shape is assumed to be a first imaginary circle having the same area as the cross section, and a crystal grain in the cross section whose contour shape is assumed to be a second imaginary circle having the same area as the crystal grain, where the diameter (D1) of the first imaginary circle is taken as 1, the average diameter (D2) of the second imaginary circle is 0.10 or more, and the average diameter (D2) of the second imaginary 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 (D2) of the second virtual circles, is less than 150 μm, the 0.2% yield strength tends to be high, and the force required to bend the copper-based conductor increases. Similarly, when the diameter (D1) of the first virtual circle having the same area as the cross-sectional area of ​​the copper-based conductor is set to 1, the average diameter (D2) of the second virtual circle having the same area as the crystal grains is less than 0.10. This also increases the number of crystal grains contained in the copper-based conductor, resulting in a greater number of crystal grain boundaries, which tends to increase the 0.2% yield strength, and therefore increases the force required to bend the copper-based conductor. Therefore, the average diameter (D2) of the second virtual circles is preferably 200 μm or more, more preferably 300 μm or more. When the diameter (D1) of the first virtual circle is set to 1, the average diameter (D2) of the second virtual circles 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, the upper limit of the grain size of the crystal grains is not particularly limited, but is, for example, equal to or less than the diameter (D1) of the first imaginary circle.

[0017] Here, the average diameter (D2) of the second virtual circle can be determined by analyzing crystal orientation data using the electron backscatter diffraction (EBSD) method described below, selecting the chart-grain size (diameter) of the analysis software with the entire measurement area as the analysis target, and calculating the average crystal grain size using the area method. More specifically, when the boundary where the orientation difference between adjacent measurement points is 15° or more is defined as the interface (grain boundary) of the crystal grain, the number of consecutive measurement points in the area surrounded by the grain boundary and the step size during measurement are used to calculate the cross-sectional area of ​​the crystal grain, and the average diameter (D2) of the second virtual circle can be determined by calculating the average diameter of the crystal grain equivalent to the circle. This average crystal grain size is defined as the average diameter (D2) of the second virtual circle having the same area as the area of ​​the crystal grain of the copper-based conductor.

[0018] Furthermore, the diameter (D1) of the first imaginary circle having the same area as the cross-sectional area of ​​the copper-based conductor can be directly measured using a micrometer, etc., if the cross-sectional area is a round wire with a circular shape. On the other hand, for ribbon wires, rectangular wires, and rectangular wires, the area of ​​the cross-section observed using an optical microscope can be determined, and the diameter (D1) of the first imaginary circle can be determined as the diameter of a circle having the same area as that area.

[0019] Furthermore, in the copper-based conductor according to the present invention, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) on a measurement region of a cross section perpendicular to the extension direction of the conductor, the area ratio of a region having a GOS (grain orientation spread) value of less than 1° in the measurement region is 80% or more. Here, if the area ratio of the region having a GOS value of less than 1° is less than 80%, the 0.2% proof stress tends to be high, and therefore the force required to bend the copper-based conductor increases. Therefore, the area ratio of the region having a GOS value of less than 1° in the measurement region is preferably 85% or more, more preferably 90% or more. On the other hand, the larger the area ratio of the region having a GOS value of less than 1°, the easier it is to bend the copper-based conductor, and the upper limit is 100%.

[0020] Furthermore, in the copper-based conductor according to the present invention, it is preferable that all of the crystal grains forming the outer contour of the copper-based conductor have a GOS value of less than 1° in a crystal orientation analysis by electron backscatter diffraction (EBSD) performed on a measurement region of a cross section perpendicular to the extension direction of the conductor. This makes it possible to make the copper-based conductor even easier to bend, since the 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.

[0021] The GOS value can be obtained, for example, from crystal orientation analysis data obtained by continuously measuring crystal orientation data using an EBSD detector (TSL, OIM5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (JEOL, JSM-7001FA), and calculating (processing) the measured crystal orientation data using analysis software (TSL Solutions, OIM Analysis). "EBSD" stands for Electron Backscatter Diffraction, and is a crystal orientation analysis technique that utilizes reflected electron Kikuchi diffraction that occurs when a copper-based conductor, which is a measurement sample, is irradiated with an electron beam within a scanning electron microscope (SEM). The measurement target is a mirror-finished surface of a cross section of a single copper-based conductor perpendicular to the extension direction, and the measurement area can be, for example, the entire range of the cross section. The cross section can be polished using a Cross-Section Polisher (registered trademark) device, as well as wet polishing, FIB, microtome, or other means capable of achieving a mirror finish. The specific method is not critical. Measurements are performed, for example, with a step size of 1 μm. Using analysis software, the area ratio of the region having a GOS value at an angle of less than 1° relative to the entire measurement area and the area ratio of the region having a GOS value at an angle of less than 1° relative to the area of ​​the crystal grains forming the outer contour of the copper-based conductor were calculated from the Map-Grain Orientation Spread. Typically, this measurement is performed three times (n = 3), and the average value is calculated and used for evaluation. Here, by using analysis software to analyze the crystal orientation data, it is possible to easily determine whether the crystal orientation difference between adjacent measurement points is within an acceptable range when a specific angle range is allowed for the crystal orientation difference between adjacent measurement points.

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

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

[0024] The copper-based conductor according to the present invention has a low 0.2% yield strength in order to make the copper-based conductor easy to bend. More specifically, the 0.2% yield strength of the copper-based conductor is 150 MPa or less, preferably 100 MPa or less, and more preferably 50 MPa or less. On the other hand, the lower limit of 0.2% of the copper-based conductor is not particularly limited, but may be 8 MPa, for example, in order to make it easy to handle during manufacturing.

[0025] In particular, to reduce the force required to bend a copper-based conductor and enable work with less force, a low 0.2% yield strength is required for the copper-based conductor. Material deformation can be classified into elastic and plastic deformation. Elastic deformation is related to σ = Eε (σ: stress, E: Young's modulus, ε: strain), and stress acts in proportion to the applied strain. That is, a lower Young's modulus results in a more gradual deformation and therefore a smaller load. Beyond a certain strain range, plastic deformation occurs, where the material cannot return to its original shape. The stress at which this plastic deformation begins is called yield strength. For this reason, a material with a lower yield strength is more susceptible to plastic deformation, reducing the force (load) required for bending. The amount of return when a 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 has small springback after bending. For example, when a copper-based conductor cut to a length of 1000 mm is wound around a cylinder having an outer diameter of 200 mm and released, the circumference of the copper-based conductor is preferably 210 mm or less.

[0027] [2] Material of the Copper-Based Conductor The copper-based conductor is made of copper or a copper alloy. Here, the copper-based conductor may be a copper alloy containing small amounts of elements such as silver (Ag), chromium (Cr), or tin (Sn). However, from the viewpoint of making the copper-based conductor easier to bend, it is preferably copper (Cu), more specifically, 99.00% by mass or more of pure copper. Among them, since the higher the copper content, the higher the electrical conductivity, tough pitch copper containing 99.90% by mass or more of copper (Cu) and inevitable impurities is preferred, and oxygen-free copper containing 99.96% by mass or more of Cu and 10 ppm or less of oxygen and inevitable impurities is more preferred.

[0028] The copper alloy constituting the copper-based conductor preferably has an alloy composition containing at least one element selected from the group consisting of 0.1% by mass to 1.0% by mass of Ag, 0.1% by mass to 1.0% by mass of Cr, and 0.1% by mass to 1.0% by mass of Sn, with the remainder being Cu and unavoidable impurities.

[0029] When at least one of the Ag, Cr, and Sn contents is 0.1% by mass or more, the tensile durability of the copper-based conductor can be improved. On the other hand, when at least one of the Ag, Cr, and Sn contents exceeds 1.0% by mass, it may cause a decrease in the conductivity of the copper-based conductor. From this perspective, when the copper alloy contains Ag, the upper limit of the Ag content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less. When the copper alloy contains Cr, the upper limit of the Cr content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less. When the copper alloy contains Sn, the upper limit of the Sn content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less.

[0030] The remainder other than the above elements are unavoidable impurities. The unavoidable impurities refer to impurities at a level that is inevitably mixed in during the manufacturing process. Depending on the content of the unavoidable impurities, they may be a factor in reducing the conductivity of the copper-based conductor, so it is preferable that the content of the unavoidable impurities is small.

[0031] Examples of inevitable impurities contained 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). In addition, inevitable impurities also include small amounts of elements such as silver (Ag), chromium (Cr), and tin (Sn), which do not satisfy the silver (Ag), chromium (Cr), and tin (Sn) content requirements in the alloy composition of the copper alloy. The upper limit of the content of inevitable impurities is preferably 30 ppm or less in total of the above elements.

[0032] [3] Shape and Use of Copper-Based Conductors The shape of a copper-based conductor can be selected appropriately depending on the current flow and installation space required for the electrical appliance or automobile to be installed. Among these, copper-based conductors are preferably constructed using copper-based wires having round, ribbon, rectangular, or rectangular shapes, and more preferably copper-based wires having round, rectangular, or rectangular shapes. In particular, copper-based conductors constructed using copper-based wires having round, rectangular, or rectangular shapes can prevent high GOS values ​​from remaining in the crystal grains that form the outer contour of the resulting conductor. Here, a round wire is a copper-based wire having a circular cross section perpendicular to the extension direction of the conductor. A ribbon wire is a copper-based wire having a cross section perpendicular to the extension direction of the conductor that is surrounded by two straight lines and two curved lines connecting the ends of the two straight lines, i.e., a track shape. A rectangular wire is a copper-based wire having a cross section surrounded by four straight lines. A rectangular wire is a copper-based wire having a rectangular cross section.

[0033] When the copper-based conductor is made of a copper-based wire having a round wire shape, it is preferable that the diameter of the copper-based wire (round wire) is 100 μm, from the viewpoint of allowing a relatively high current to flow through the copper-based wire, and it is preferable that the diameter of the copper-based wire (round wire) is 900 μm or less, from the viewpoint of being able to sufficiently secure wiring space and being easily bendable.

[0034] Furthermore, when the copper-based wire is formed of a copper-based wire having a ribbon or rectangular wire shape, it is preferable that the thickness of the copper-based wire (ribbon wire, rectangular wire) is 100 μm or more, from the viewpoint of being able to pass a relatively high current through the copper-based wire. Furthermore, it is preferable that the thickness of the copper-based wire (ribbon wire, rectangular wire) is 900 μm or less, from the viewpoint of being able to sufficiently secure wiring space and being easy to bend. On the other hand, the width of the copper-based wire (ribbon wire, rectangular wire) is not particularly limited, but is preferably in the same range as the thickness of the copper-based wire (ribbon wire, rectangular wire), i.e., in the range of 100 μm to 900 μm, from the viewpoint of being able to pass a higher current and being easy to bend.

[0035] Furthermore, a stranded conductor can be constructed by twisting together a plurality of copper-based wires made of the above-mentioned copper-based conductor, which requires less bending force and has even less springback after bending. Here, the number of twists in the stranded conductor and the total cross-sectional area of ​​the stranded wire are not limited, but a small-diameter stranded conductor can be constructed by twisting together 7 to 19 copper-based conductors having the above-mentioned wire diameters.

[0036] Furthermore, the copper-based conductor of the present invention is preferably used for an electric wire. More specifically, an electric wire can be constructed by forming at least an insulating coating layer on the surface of the above-mentioned copper-based conductor or stranded conductor. Such an electric wire requires less bending force and has little springback after bending, so that wire curl due to springback can be suppressed and it can be used for complex wiring in a limited space.

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

[0038] [4] An Example of a Method for Producing a Copper-Based Conductor Next, a method for producing a copper-based conductor according to an embodiment will be described.

[0039] In the method for producing a copper-based conductor according to the embodiment, a casting step is first performed in which electrolytic copper is melted in a reducing atmosphere to obtain a cylindrical ingot called a billet.

[0040] After the casting process, the billet is subjected to the extrusion or rolling process. 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 from the top or bottom or the left or right.

[0041] After the extrusion or rolling process, a wiredrawing process is carried out. In the wiredrawing process, the round bar obtained in the above process is drawn to a predetermined wire diameter. Here, it is preferable that the wiredrawing process includes a peeling process to remove surface defects that have occurred up to the above process. Furthermore, if necessary, one or more heat treatment processes may be carried out before the wiredrawing process in order to remove processing strain and to make the wiredrawing easier.

[0042] When a stranded conductor is formed after the wire drawing process, a stranding process may be performed in which a plurality of drawn copper-based conductors are twisted together to form a stranded conductor. At this time, the conductor may be compressed using a compression die, or the copper-based conductors may be twisted together without being compressed using a compression die.

[0043] Thereafter, a heat treatment step is performed. Here, the heat treatment steps performed on the copper-based conductor or the stranded conductor include a first heat treatment step and a second heat treatment step.

[0044] The first heat treatment step involves running annealing, which involves heat treatment by passing a wire through a heating furnace, or current annealing, which involves heat treatment by passing an electric current through a wire passing through multiple pulleys that function as electrodes. By performing running annealing or current annealing in the first heat treatment step, the copper-based conductor or the stranded conductor can be heated in a short time. This allows a mixed grain structure of large and small crystal grains to be formed in the initial stage of the first heat treatment step, and the crystal grains contained in the copper-based conductor or the stranded conductor to grow in the subsequent second heat treatment step, thereby increasing the average diameter (D2) of the second imaginary circle to more than 150 μm and increasing the area ratio of the region in the cross section having a GOS value of less than 1° to 80% or more. Among these, running annealing is preferred in the first heat treatment step from the viewpoint of preventing an excessively high heating rate and thus preventing high GOS values ​​from remaining in the crystal grains that form the outer peripheral contour of the resulting conductor.

[0045] The temperature and time for heating the copper-based conductor or the stranded conductor in the first heat treatment step can be appropriately adjusted depending on the desired average diameter (D2) of the second virtual circle. For example, the average diameter (D2) of the second virtual circle can be increased by increasing the temperature for heating the copper-based conductor or the stranded conductor. Furthermore, the average diameter (D2) of the second virtual circle can be increased by extending the time for heating the copper-based conductor or the stranded conductor. Furthermore, the average diameter (D2) of the second virtual circle can be increased by increasing the current used in current annealing.

[0046] When heating the copper-based conductor or the stranded conductor in the first heat treatment step, it is preferable that the time required to reach 400°C from room temperature (time required to reach 400°C) is a short time of 3 seconds or less, in other words, that the temperature rise rate is high. Such a short temperature rise can be achieved by current annealing or annealing while running. In particular, when annealing while running is performed, this can be achieved by passing the copper-based conductor or the stranded conductor in a heating furnace filled with a hydrogen atmosphere, or by forcibly blowing hydrogen gas through the copper-based conductor or the stranded conductor passing through the heating furnace. In particular, from the viewpoint of preventing the temperature rise rate from becoming too high and preventing high GOS values ​​from remaining in the crystal grains that form the outer peripheral contour of the resulting conductor, it is preferable that the time required to reach 400°C from room temperature in annealing while running is 1 second or more. On the other hand, in the case of current annealing, the time required to reach 400°C from room temperature can be shorter.

[0047] Furthermore, when heating the copper-based conductor or stranded conductor in the first heat treatment step, the holding time in the temperature range of more than 400°C and not more than 520°C is preferably 5 seconds or less. In particular, if the holding time in the temperature range of more than 400°C and not more than 520°C in the first heat treatment step exceeds 5 seconds, the crystal grain size becomes almost uniform at the time of completion of the first heat treatment step, making it difficult to obtain a mixed grain structure, and it becomes difficult to increase the average diameter (D2) of the second imaginary 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 more than 400°C and not more than 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 the copper-based conductor or stranded conductor in the first heat treatment step is preferably in the range of more than 400°C and not more than 520°C. In particular, if the heat treatment temperature in the first heat treatment step is 400°C or less, crystal growth cannot be sufficiently promoted, and the average diameter (D2) of the second virtual circles cannot be increased to more than 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. This also makes it difficult to increase the average diameter (D2) of the second virtual circles to more than 150 μm in the subsequent second heat treatment step. Furthermore, 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 80% or more at angles less than 1° in the cross section.

[0049] When current annealing is performed in the first heat treatment step, the temperature of the copper-based conductor or the stranded conductor rises instantaneously, and the thermocouple response speed may not be able to keep up, making it difficult to accurately grasp the temperature. Therefore, when setting the heat treatment conditions for current annealing, conditions such as voltage, current value, wire speed, and electrode distance may be set so that the average grain size is equivalent to that of grains obtained when annealing while running is performed, and in this case, annealing can be performed under the same temperature conditions as those for annealing while running, which are used to compare the average grain size.

[0050] After the first heat treatment step, the second heat treatment step is performed, which may be, for example, a batch heat treatment (batch annealing) in which a copper-based conductor or a stranded conductor wound on a spool is 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., crystal grains do not grow during the heat treatment, and the average diameter (D2) of the second imaginary circle cannot be increased to more than 150 μm. On the other hand, the upper limit of the heat treatment temperature in the second heat treatment step is not particularly limited, but is preferably 750° C. or lower from the viewpoint of preventing adhesion of the copper-based conductor and the stranded conductor placed in the heating furnace.

[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 the copper-based conductor or the stranded conductor and from the viewpoint of making the GOS value of less than 1° in the cross section 80% or more. 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 form an insulating coating layer by extruding a molten resin onto the surface of the copper-based conductor and stranded conductor thus obtained, thereby producing an electric wire.

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

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

[0056] (Invention Examples 1 to 9 and Comparative Examples 1 and 2) A copper-based material having the components shown in Table 1 was subjected to a casting process, an extrusion process, and a wiredrawing process. In the wiredrawing process, a wire having a wire diameter of 8 mm was formed from the round bar obtained by the extrusion process. The wire was then drawn using a round die, a rectangular die, or a cassette roller die (CRD) that draws the wire through a gap between two rolls to produce a round wire, ribbon wire, or rectangular wire having the shape shown in Table 2. Subsequently, a first heat treatment process was performed under the conditions shown in Table 1. For Invention Examples 1 to 9, for which the presence or absence of a second heat treatment process is marked "Yes" in Table 1, a second heat treatment process was performed under the conditions shown in Table 1 to obtain a copper-based conductor. For Invention Examples 1 to 3, 5 to 9, and Comparative Example 1, which underwent annealing while running in the first heat treatment process, the copper-based conductor or stranded conductor was passed through a heating furnace filled with a hydrogen atmosphere, and the temperature was raised from room temperature to 400°C in the time shown in Table 1. On the other hand, for Comparative Examples 1 and 2, in which the presence or absence of the second heat treatment step is marked "No" in Table 1, the copper-based conductor was obtained by performing only the first heat treatment step without performing the second heat treatment step.

[0057] (Inventive Examples 10 to 14 and Comparative Example 3) A copper-based material having the components shown in Table 3 was subjected to a casting process, an extrusion process, and a wiredrawing process. Here, in the wiredrawing process, a wire having a wire diameter of 8 mm was formed from the round bar obtained by the extrusion process, and then the wire was finished into a round wire having the shape shown in Table 4 using a round-hole die. Next, a stranding process was performed in which element wires consisting of the number of round wires (copper-based conductors) shown in Table 4 were twisted together to form a stranded conductor. Subsequently, a first heat treatment process was performed under the conditions shown in Table 3, and then, for Inventive Examples 10 to 14, for which the presence or absence of a second heat treatment process is marked "Yes" in Table 3, a second heat treatment process was performed under the conditions shown in Table 3 to obtain a stranded conductor. Here, for Inventive Examples 10 to 12 and 14 and Comparative Example 3, which were subjected to annealing while running in the first heat treatment process, the copper-based conductor or the stranded conductor was passed through a heating furnace filled with a hydrogen atmosphere, and the temperature was raised from room temperature to 400°C in the time shown in Table 3. On the other hand, for Comparative Example 3, for which the presence or absence of the second heat treatment step is marked "No" in Table 3, the stranded conductor was obtained by performing only the first heat treatment step without performing the second heat treatment step. Then, an insulating coating layer made of polyvinyl chloride was formed on the surface of the obtained stranded conductor, thereby obtaining an electric wire.

[0058] [Various Measurement and Evaluation Methods] The copper-based conductors and stranded conductors according to the present invention and comparative examples were used to carry out the following characteristic evaluations. The evaluation conditions for each characteristic were as follows.

[0059] [1] Component Analysis A sample obtained by pressing the wire obtained in the wire drawing process in the above-mentioned manufacturing stage into a flat plate was measured and analyzed using an optical emission spectrometer (manufactured by Shimadzu Corporation). Measurements were performed three times, and the average values ​​were calculated and shown in Tables 1 and 3. Elements that were intentionally added are listed in their respective columns, and elements that were not intentionally added were included in the total of unavoidable impurities. When the detected amount of a component was less than 0.001% by mass, the component was considered not to be contained, and this was indicated by "-" in the tables.

[0060] [2] Measurement of the Area Ratio of Regions Having a GOS Value of Less than 1° The area ratio of regions having a GOS value of less than 1° was measured using an EBSD detector (TSL, OIM5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (JEOL, JSM-7001FA) to collect continuous EBSD patterns. The 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 mirror-finished surface of a cross section perpendicular to the extension direction of a copper-based conductor (in the case of a stranded conductor, a single copper-based conductor constituting the stranded conductor). The measurement area was the entire range of the cross section. The measurement was performed with a step size of 1 μm. From the map-grain orientation spread obtained using analysis software, the area ratio of the region having a GOS value with an angle of less than 1° to the entire measurement region and the area ratio of the region having a GOS value with an angle of less than 1° to the area of ​​the crystal grains forming the outer contour of the copper-based conductor were calculated. The measurement was performed three times (n = 3), and the average values ​​were calculated and shown in Tables 2 and 4.

[0061] [3] Measurement of the area ratio of crystal grains having a <111> orientation group relative to the total area of ​​crystal grains included in the measurement region. The area ratio of crystal grains having a <111> orientation group relative to the x-axis direction was determined by analyzing the crystal orientation data obtained in the cross section using the EBSD detector as described above. The boundary where the orientation difference between adjacent measurement points is 15° or more from the chart-crystal direction obtained using analysis software was defined as the interface (grain boundary) of the crystal grain. Furthermore, in the cross section perpendicular to the elongation direction of the wire, the direction parallel to the longitudinal direction of the cross section (the width direction of the wire) was defined as the x-axis direction.

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

[0063] At this time, the area ratio of crystal grains having a group of <111> orientations, which are crystal orientations within ±15° of the <111> orientation relative to the x-axis direction, to the total area of ​​crystal grains in the measurement region was calculated, and the average value of the area ratio measurements performed three times (n = 3) was calculated and shown in Tables 2 and 4.

[0064] [4] Measurement of the diameter (D1) of the first imaginary circle The diameter (D1) of the first imaginary circle having the same area as the area of ​​the cross section was measured directly using a micrometer, etc., for the examples of round wire. On the other hand, for the examples of ribbon wire and rectangular wire, the area of ​​the cross section observed using an optical microscope was determined, and the diameter of a circle having the same area was measured and used as the diameter (D1) of the first imaginary circle. This measurement was performed three times (n = 3), and the average value was calculated and 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 of the electron backscatter diffraction (EBSD) method described above, selecting the chart-grain size (diameter) of the analysis software as the entire measurement area as the analysis target, measuring the average grain size calculated by the area method, and setting it as the average diameter (D2) of the second virtual circle. This measurement was performed three times (n = 3) to calculate the average value, which is shown in Tables 2 and 4. In addition, based on the obtained average diameter (D2) of the second virtual circle and the measured value (D1) of the diameter of the first virtual circle described above, the relative value (D2 / D1) of the measured value of the average diameter (D2) of the second virtual circle when the diameter (D1) of the first virtual circle was set to 1 was calculated, and shown in Tables 2 and 4.

[0066] [6] Evaluation of 0.2% Proof Stress For the copper-based conductors according to the present invention and comparative examples, tensile tests were performed using a precision universal testing machine (manufactured by Shimadzu Corporation) in accordance with JIS Z2241, and the 0.2% proof stress (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. Furthermore, for the stranded conductors according to the present invention and comparative examples, the 0.2% proof stress (MPa) was determined using the same method as for the copper-based conductors.

[0067] Regarding the measured value of the 0.2% yield strength, when it was 67 MPa or less, it was evaluated as "A" because it was particularly excellent in that the force required for bending was small. When the measured value of the 0.2% yield strength was more than 67 MPa and less than 100 MPa, it was evaluated as "B" because it was excellent in that the force required for bending was small. When the measured value of the 0.2% yield strength was more than 100 MPa and less than 150 MPa, it was evaluated as "C" because it was good in that the force required for bending was small. On the other hand, when the measured value of the 0.2% yield strength exceeded 150 MPa, it was evaluated as "D" because the force required for bending was too large and it was poor. In this example, "A", "B", and "C" were evaluated as pass levels. The results are shown in Tables 2 and 4.

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

[0069] Regarding the measured value of the curvature after the bending test, if it was 205 mm or less, it was evaluated as "◎" because it was particularly excellent in terms of small springback. If the measured value of the curvature after the bending test was more than 205 mm and 210 mm or less, it was evaluated as "◯" because it was good in terms of small springback. On the other hand, if the measured value of the curvature after the bending test exceeded 210 mm, it was evaluated as "×" because it was poor in terms of large springback. In this example, "◎" and "◯" were evaluated as pass levels. The results are shown in Tables 2 and 4.

[0070] [8] Overall Evaluation When one or both of the two evaluation results for the 0.2% proof stress and the curvature after the bending test were evaluated as "A" or "◎", and both evaluations were at the pass level, at least one of the 0.2% proof stress and the curvature after the bending test was deemed to be excellent, and the overall evaluation was evaluated as "◎". When the evaluation result for the 0.2% proof stress was evaluated as "B" or "C", and both the evaluation results for the curvature after the bending test were evaluated as "○", these two properties were deemed to be good, and the overall evaluation was evaluated as "○". On the other hand, when the evaluation result for the 0.2% proof stress was "D" or when the evaluation result for the curvature after the bending test was "×", at least one of these two properties was deemed to be insufficient, and the overall evaluation was evaluated as "×". The results are shown in Tables 2 and 4.

[0071]

[0072]

[0073]

[0074]

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

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

Claims

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 imaginary circle having the same area as the cross section, and the contour shape of a crystal grain in the cross section is assumed to be a second imaginary circle having the same area as the crystal grain, the average diameter of the second imaginary circle is 0.10 or more when the diameter of the first imaginary circle is 1, the average diameter of the second imaginary circle is more than 150 μm, and in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) on a measurement area of ​​the cross section, the area ratio of areas having a GOS value of less than 1° in the measurement area is 80% or more.

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

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

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

5. A stranded conductor formed by twisting together a plurality of copper-based wires made of the copper-based conductor according to claim 1.

6. An electric wire in which at least an insulating coating layer is 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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