Copper-plated steel wire and insulated electrical wire

Abstract

A copper-clad steel wire contains a core wire made of austenitic stainless steel, a plating layer composed of copper or a copper alloy covering an outer circumferential surface of the core wire, and an intermediate layer composed of nickel located between the core wire and the plating layer. In a cross-section of the copper-clad steel wire perpendicular to its longitudinal direction, the difference between a maximum value t max and a minimum value t min the thickness of the coating layer 9% or less relative to the maximum value t max .

Description

Technical field

[0001] The present disclosure relates to a copper-coated steel wire and an insulated electrical wire.

[0002] The present application enjoys priority over Japanese patent application No. 2023-152403, filed on September 20, 2023, the entire contents of which are hereby incorporated by this notice. Technical background

[0003] There are cases where electrical wires require both strength and conductivity. In such cases, a copper-clad steel wire, which contains a steel core wire and a copper plating layer covering the outer surface of the core wire, can be used as an electrical wire. Furthermore, if a copper-clad steel wire is used in an environment requiring corrosion resistance, austenitic stainless steel can be used for the core wire.

[0004] An electrical wire may be crimped to a connector at its end. When a connector is crimped to the end of an electrical wire containing a copper-clad steel wire, the core wire may break during the crimping process, reducing the connection strength (crimp strength) between the copper-clad steel wire and the connector. This can cause the copper-clad steel wire to slip out of the connector when a tensile load is applied to the connected section. In response, a measure has been proposed that addresses the aforementioned problem by appropriately adjusting the hardness of the core wire and the plating layer, as well as the tensile strength of the core wire (see, for example, Japanese patent application disclosure no. 2022-157046 (Patent Reference 1)). List of citations from patent literature

[0005] Patent Literature 1: Japanese Patent Application Disclosure No. 2022-157046 Brief description of the invention

[0006] A copper-clad steel wire according to the present disclosure is a copper-clad steel wire comprising: a core wire made of austenitic stainless steel; a coating layer composed of copper or a copper alloy covering the outer circumferential surface of the core wire; and an intermediate layer composed of nickel located between the core wire and the coating layer. In a cross-section of the copper-clad steel wire perpendicular to its longitudinal direction, the difference between a maximum value t max and a minimum value t min the thickness of the coating layer 9% or less relative to the maximum value t max . Brief description of the drawings [ Fig. 1] Fig.Figure 1 is a schematic view showing the structure of a copper-coated steel wire. [ Fig. 2] Fig. Figure 2 is an enlarged schematic cross-sectional view of the area around the boundary between the core wire and the coating layer in Fig. 1 around. [ Fig. 3] Fig. Figure 3 is a schematic view showing the structure of an insulated electrical wire. [ Fig. 4] Fig. Figure 4 is a schematic cross-sectional view showing the structure of the copper-coated steel wire. [ Fig. 5] Fig. Figure 5 is a flowchart that schematically illustrates the process for manufacturing the copper-clad steel wire and the insulated electrical wire. [ Fig. 6] Fig. Figure 6 is a schematic perspective view showing the connected state of an insulated electrical wire and a crimp terminal. [ Fig. 7] Fig. Figure 7 is a schematic diagram illustrating a tensile testing procedure. Description of embodiments [Problems to be solved by the present disclosure]

[0007] However, even if the hardness of the core wire and coating layer, as well as the tensile strength of the core wire, are adjusted, further improvement may be required to correct the reduction in crimp strength caused by breakage of the core wire during crimping.

[0008] In view of the foregoing, one of the objectives of the present disclosure is to provide a copper-coated steel wire and an insulated electrical wire containing the copper-coated steel wire, which can suppress the reduction in crimp strength. [Beneficial effects of the present disclosure]

[0009] According to the copper-coated steel wire described above, it is possible to provide a copper-coated steel wire that can suppress the reduction in crimp strength. [Description of embodiments of the present disclosure]

[0010] First, embodiments of the present disclosure are listed and described. A copper-coated steel wire of the present disclosure is: (1) A copper-clad steel wire comprising: a core wire of austenitic stainless steel; a coating layer composed of copper or a copper alloy covering an outer circumferential surface of the core wire; and an intermediate layer composed of nickel situated between the core wire and the coating layer. In a cross-section of the copper-clad steel wire perpendicular to its longitudinal direction, the difference between a maximum value t maxand a minimum value t min the thickness of the coating layer 9% or less relative to the maximum value t max .

[0011] The inventors investigated why the reduction in crimp strength caused by core wire breakage during crimping could not be sufficiently suppressed even when adjusting the hardness of the core wire and coating layer, as well as the tensile strength of the core wire. Based on the findings of this investigation, they explored ways to suppress this reduction in crimp strength. As a result, they obtained the following insights and found a way to suppress the reduction in crimp strength.

[0012] According to the investigations of the inventors of the present invention, variations in the thickness of the coating layer of the copper-clad steel wire have a significant influence on the breakage of the core wire during crimping. The inventors then discovered that the reduction in crimp strength can be effectively suppressed by increasing the difference between the maximum value t max and the minimum value t min the thickness of the coating layer in a cross-section of the copper-coated steel wire perpendicular to its longitudinal direction is limited to a region that has a certain value, namely 9% or less, relative to the maximum value t max does not exceed.

[0013] In the copper-coated steel wire of the present disclosure, the difference between the maximum value t is max and the minimum value t minthe thickness of the coating layer in a cross-section of the copper-coated steel wire perpendicular to its longitudinal direction 9% or less relative to the maximum value t max This allows the copper-coated steel wire of the present disclosure to suppress the reduction in crimp strength. In the present application, the maximum value t max and the minimum value t min the thickness of the coating layer is defined as the mean of ten maximum values ​​or the mean of ten minimum values ​​obtained by randomly selecting and examining ten cross-sections of the copper-coated steel wire perpendicular to its longitudinal direction and measuring the maximum and minimum values ​​of the thickness of the coating layer at each cross-section.

[0014] (2) In (1) above, the following equation (1) may be satisfied: 450≤HVST≤1660×CST+2850×tmax / D where HV ST the Vickers hardness of the core wire is CST the carbon content of the core wire in mass percent is, t max where is the maximum value of the coating layer thickness and D is the wire diameter of the copper-coated steel wire.

[0015] By setting the hardness of the core wire to 450 HV or higher, it becomes easier to impart sufficient strength to the copper-clad steel wire. On the other hand, by setting the hardness of the core wire to a value not greater than that calculated according to a specific formula (expression (1)) using the carbon content of the core wire and the ratio of the coating thickness to the wire diameter of the copper-clad steel wire as parameters, core wire breakage during crimping can be suppressed. More precisely, the austenitic stainless steel from which the core wire is constructed achieves the desired strength when hardened by wire drawing. The lower the carbon content of the austenitic stainless steel, the greater the effort required to achieve the desired strength.As the carbon content decreases, the steel is therefore used in a state closer to its working limit, resulting in a lower tolerance for deformation during crimping and making the core wire more prone to breakage. Furthermore, the greater the ratio of the coating thickness to the wire diameter of the copper-coated steel wire, the more the highly deformable coating absorbs the deformation caused by crimping, thus preventing core wire breakage. According to the investigations of the inventors of the present invention, core wire breakage during crimping can be suppressed by adjusting the core wire's hardness to a value no greater than the sum of the values ​​of these parameters multiplied by certain coefficients.In the present application, the wire diameter D of the copper-coated steel wire is defined as the mean value of the wire diameters (diameters) of the copper-coated steel wire measured at ten points along the longitudinal direction. The hardness HV. ST The hardness of the core wire can be measured at a cross-section perpendicular to the longitudinal direction of the core wire using a micro-Vickers hardness tester under a load of, for example, 0.196 N. The measurement can be performed on a line segment corresponding to the diameter of the cross-section at a point that corresponds to the midpoint between the center of the line segment (the center of the cross-section) and one end of the line segment.

[0016] (3) In (2) above, the t described above can be used. max / D 0.25 or less. This configuration makes it easier to give the copper-clad steel wire sufficient strength. The above-described t max / D can be 0.23 or less.

[0017] (4) In each of the preceding (1) to (3), the copper-clad steel wire may have a wire diameter D of not less than 200 µm and not more than 400 µm. The copper-clad steel wire of the present disclosure, which is able to suppress the reduction in crimp strength, is particularly suitable for a copper-clad steel wire with a wire diameter of not less than 200 µm and not more than 400 µm.

[0018] (5) In each of the preceding (1) to (4), the austenitic stainless steel of which the core wire is made may conform to JIS standard SUS301, SUS304, SUS310S or SUS316. JIS standards SUS301, SUS304, SUS310S and SUS316 are particularly suitable for the material of which the core wire is made.

[0019] (6) In each of the preceding (1) to (5), the coating layer may have a hardness of not less than 50 HV and not more than 140 HV. This configuration facilitates the suppression of the reduction in the crimp strength of the copper-coated steel wire. In the present application, the hardness of the coating layer may be defined as the mean of measurements taken at four points, each located at the midpoint of the thickness of the coating layer in a cross-section of the copper-coated steel wire perpendicular to its longitudinal direction.

[0020] (7) An insulated electrical wire of the present disclosure comprises: the copper-clad steel wire according to any of paragraphs (1) to (6) above; and an insulating layer coating an outer circumferential surface of the copper-clad steel wire. The insulated electrical wire of the present disclosure comprises the copper-clad steel wire described above and can therefore suppress the reduction in crimp strength. [Details of embodiments of the present disclosure]

[0021] Embodiments of the copper-clad steel wire and the insulated electrical wire according to the present disclosure are described below with reference to the drawings. In the drawings referenced below, identical or corresponding sections are marked with the same reference numerals, and their description is not repeated. (Version 1)

[0022] Fig. Figure 1 is a schematic view showing the structure of a copper-coated steel wire. Fig. Figure 2 is an enlarged schematic cross-sectional view of the area around the boundary between the core wire and the coating layer in Fig. 1. With reference to the Fig. 1 and Fig.In the present embodiment, the copper-coated steel wire 1 comprises a core wire 10, a coating layer 20, and an intermediate layer 40. The core wire 10 is made of austenitic stainless steel. The coating layer 20 is arranged to cover an outer circumferential surface 11 of the core wire 10. The intermediate layer 40 is arranged between the core wire 10 and the coating layer 20. The coating layer 20 is in contact with the intermediate layer 40 at its inner outer circumferential surface 21. The core wire 10 is in contact with the intermediate layer 40 at its outer circumferential surface 11. The intermediate layer 40 is arranged between the core wire 10 and the coating layer 20. The coating layer 20 has an outer circumferential surface 22, which forms the outer circumferential surface of the copper-coated steel wire 1.

[0023] Fig.Figure 3 is a schematic representation showing the structure of an insulated electrical wire. With reference to Fig.In the present embodiment, the insulated electrical wire 100 comprises the copper-clad steel wire 1 described above and an insulating layer 30. The insulating layer 30 is arranged such that it covers an outer circumferential surface 1A of the copper-clad steel wire 1 (the outer circumferential surface 22 of the coating layer 20). The insulating layer 30 covers the entire circumference of the outer circumferential surface 1A of the copper-clad steel wire 1. The insulating layer 30 is in contact with the outer circumferential surface 1A of the copper-clad steel wire 1 at its inner outer surface 31. The insulating layer 30 has an outer circumferential surface 32 that forms the outer circumferential surface of the insulated electrical wire 100. The insulating layer 30 consists of an insulating material such as a resin.Examples of resins that can be used to form the insulating layer 30 are polyethylene and vinyl chloride.

[0024] Fig. Figure 4 is a schematic cross-sectional view showing the structure of the copper-coated steel wire. Fig. Figure 4 shows a cross-section perpendicular to the longitudinal direction of the copper-coated steel wire 1. With reference to Fig.4. The copper-clad steel wire 1 has a wire diameter D (diameter of the cross-section perpendicular to the longitudinal direction) of, for example, not less than 200 µm and not more than 400 µm, although the diameter is not specifically limited. For the austenitic stainless steel of which the core wire 10 is made, JIS standards SUS301, SUS304, SUS310S, or SUS316, for example, can be used. The core wire 10 can, for example, have a tensile strength of not less than 1500 MPa and not more than 3000 MPa. The core wire 10 can, for example, have a Vickers hardness HV. ST of not less than 450 HV and not more than 840 HV.

[0025] The coating layer 20 is made of copper (Cu) or a copper alloy. The coating layer 20 covers the outer circumferential surface 11 (surface) of the core wire 10. The coating layer 20 can be a plated layer. The coating layer 20 can be a layer formed by plating. The coating layer 20 has, for example, a hardness of not less than 50 HV and not more than 140 HV. The difference between a maximum value t max and a minimum value t min The thickness of the coating layer 20 in a cross-section of the copper-coated steel wire 1 perpendicular to its longitudinal direction is 9% or less relative to the maximum value t. max .

[0026] With reference to Fig.2. The intermediate layer 40 consists of nickel (Ni). Although the thickness of the intermediate layer 40 is not particularly limited, it can be set smaller than the thickness of the coating layer 20. For example, the thickness of the intermediate layer 40 can be no less than 0.0001 µm, preferably 0.005 µm or more. The thickness of the intermediate layer 40 can be no more than 1 µm, preferably 0.8 µm or less. The intermediate layer 40 serves to improve the adhesion between the core wire 10 and the coating layer 20. The intermediate layer 40 can be a plated layer. The intermediate layer 40 can be a layer formed by plating.

[0027] In the copper-coated steel wire 1 of the present embodiment, the fluctuation in the thickness of the coating layer 20 is suppressed in such a way that the difference between the maximum value t max and the minimum value t minthe thickness of the coating layer 20 9% or less relative to the maximum value t max as described above. Consequently, the copper-clad steel wire 1 of the present embodiment is a copper-clad steel wire in which the reduction in crimp strength is suppressed. Furthermore, the insulated electrical wire 100 containing this copper-clad steel wire 1 is an insulated electrical wire in which the reduction in crimp strength is suppressed. The reduction in crimp strength can be further suppressed by reducing the difference between the maximum value t max and the minimum value t min the thickness of the coating layer 20 to no more than 8%, no more than 7%, no more than 6% or further to no more than 5% relative to the maximum value t max is determined.

[0028] For the copper-coated steel wire 1 of the present embodiment, the following equation (1) can be satisfied: 450≤HVST≤1660×CST+2850×tmax / D where HV ST the Vickers hardness of the core wire is 10, C ST The carbon content of the core wire is 10 in mass percent, t max The maximum value of the coating layer thickness 20 is in µm, and D is the wire diameter of the copper-coated steel wire 1 in µm. By adjusting the hardness of the core wire 10 to 450 HV or more, it becomes easier to give the copper-coated steel wire 1 sufficient strength. On the other hand, by adjusting the hardness of the core wire 10 to a value not greater than that given by formula (1) using the carbon content of the core wire 10 and the ratio of the maximum value t maxThe thickness of the coating layer 20 was calculated as a parameter relative to the wire diameter D of the copper-coated steel wire 1, which suppresses the breaking of the core wire 10 during crimping.

[0029] In the copper-coated steel wire 1 of the present embodiment, sufficient strength can be more easily imparted to the copper-coated steel wire 1 if the ratio t described above is max / D is 0.25 or less.

[0030] A method for producing the copper-coated steel wire 1 and the insulated electrical wire 100 in the present embodiment is described below. Fig. Figure 5 is a flowchart that schematically illustrates the process for manufacturing copper-clad steel wire and insulated electrical wire. With reference to Fig.In the present embodiment of the process for manufacturing the copper-clad steel wire 1 and the insulated electrical wire 100, a first step, S10, is carried out as the manufacturing step of the material steel wire. In this step S10, a material steel wire is produced. In particular, a material steel wire is produced from an austenitic stainless steel, such as JIS standard SUS301, SUS304, SUS310S, or SUS316 with a desired carbon content. The material steel wire can, for example, have an outer diameter of not less than 0.3 mm and not more than 1 mm.

[0031] Next, an intermediate layer formation step, step S20, is performed. In this step S20, an intermediate layer 40 is formed on the surface of the material steel wire produced in step S10. Specifically, for example, a nickel intermediate layer 40 is formed by plating the core wire 10. In this way, a material steel wire is obtained with the intermediate layer 40 formed on its surface. The thickness of the intermediate layer 40 to be formed in step S20 is determined taking into account the reduction in thickness that occurs during processing in a wire drawing step described below, such that the desired thickness is achieved in the finished state of the copper-clad steel wire 1.

[0032] Next, the wire drawing step is performed as step S30. In this step S30, the material steel wire with the intermediate layer 40 formed in step S20 is subjected to a wire drawing (drawing process). The actual elongation during wire drawing in step S30, for example, cannot be less than 1.3 and cannot be more than 2.6. This adjusts the outer diameter of the material steel wire to the desired value, while imparting the desired hardness and tensile strength to the material steel wire, thus transforming it into the core wire 10 (see Fig. 1) Wire drawing can be carried out through a variety of stages.

[0033] Next, a coating layer formation step, step S40, is performed. In this step S40, a coating layer 20 is formed on the surface of the core wire 10 with the intermediate layer 40 obtained in steps up to S30. Specifically, a coating layer 20 of copper (pure copper), for example, is formed on the core wire 10 with the intermediate layer 40, for example, by plating. Alternatively, in addition to copper, metal layers of tin (Sn), zinc (Zn), and the like can be formed by plating, and these layers can be alloyed together to form a copper alloy coating layer 20. In this way, a copper-clad steel wire 1 is obtained, containing the core wire 10 and the coating layer 20. The formation of the coating layer 20 can be carried out in a variety of stages.

[0034] Next, a step to standardize the coating layer thickness is performed as step S50. In this step S50, the copper-coated steel wire 1 obtained by forming the coating layer 20 in step S40 is subjected to a low-work wire drawing process to reduce variations in the thickness of the coating layer 20. For example, the actual elongation during wire drawing in step S50 must be no less than 0.1 and no more than 0.5.

[0035] Next, a heat treatment step, step S60, is performed. In this step S60, the copper-coated steel wire 1 obtained by steps up to S50 is subjected to a heat treatment. Specifically, the copper-coated steel wire 1 undergoes a heat treatment in which it is held, for example, at a temperature of not less than 275°C and not more than 450°C, preferably not less than 350°C and not more than 450°C, for a period of not less than 30 minutes and not more than 120 minutes, before being air-cooled to room temperature. This causes the copper or copper alloy from which the coating layer 20 is built up to recrystallize and soften to a suitable hardness, and also eliminates the internal stress in the core wire 10, thereby adjusting the hardness of the core wire 10 to a suitable range.The copper-coated steel wire 1 of the present embodiment is obtained by the above method (see . Fig. 1).

[0036] Furthermore, step S70 is performed to form an insulating layer. In this step S70, an insulating layer 30 is formed to coat the outer circumferential surface of the copper-clad steel wire 1 of the present embodiment, which was obtained by steps up to S60. The insulating layer 30 can, for example, consist of a resin. The insulated electrical wire 100 of the present embodiment is obtained by the method described above (see Fig. 3). EXAMPLES

[0037] To confirm the effect of suppressing the reduction in crimp strength when connecting to a crimp terminal, an experiment was carried out using the copper-clad steel wire and the insulated electrical wire of the present disclosure. The experimental procedure was as follows.

[0038] Insulated electrical wires 100 were manufactured according to the manufacturing process described in the preceding embodiment. The material of the steel wire produced in step S10 complied with JIS standards SUS301 and SUS304. In step S20, an intermediate layer 40 with a thickness of 0.6 µm was formed in the finished state (after completion of step S70). In step S40, a coating layer 20 of pure copper was formed by plating. For comparison, insulated electrical wires were also produced by omitting step S50 without standardizing the thickness of the coating layer 20. Samples A to Q were thus obtained. The strength of the crimped section of the obtained samples when connected to the crimp terminal was measured as follows.

[0039] Fig.Figure 6 is a schematic perspective view showing the connection state of an insulated electrical wire and a crimp terminal. Fig. Figure 7 is a schematic diagram illustrating a tensile testing procedure. Referring to Fig.The crimp connector 80 comprises a body section 83, a conductor cylinder 81 connected to the body section 83, and an insulating cylinder 82 connected to a side of the conductor cylinder 81 opposite the side connected to the body section 83. When the insulated electrical wire 100 is connected to the crimp connector 80, the insulating layer 30 at one end of the insulated electrical wire 100 is first removed to expose the copper-clad steel wire 1. The conductor cylinder 81 is then crimped to hold the exposed copper-clad steel wire 1 to the conductor cylinder 81 and also the insulating layer 30 to the insulating cylinder 82. If cracks occur in the core wire 10 of the copper-clad steel wire 1 held by the conductor cylinder 81 at this time, the strength (crimp strength) of the connected section between the conductor cylinder 81 and the copper-clad steel wire 1 is reduced.

[0040] In the present experiment, for each sample, the insulated electrical wire 100 and the crimp connector 80 were connected in the state in which the copper-clad steel wire 1 was held with the conductor cylinder 81 as described above, while the insulating layer 30 was not held with the insulating cylinder 82. At this point, the compression ratio, expressed as 1 - (cross-sectional area of ​​the coating layer 20 before crimping) / (cross-sectional area of ​​the coating layer 20 after crimping), was set to 15%. This is the condition that ensures sufficient crimp strength if the core wire 10 does not break. Subsequently, as described in Fig.Figure 12 shows that a tensile test was performed in which the body section 83 of the crimp connector 80 was held by a first clamping device 91 of a tensile testing machine and the insulated electrical wire 100 was held by a second clamping device 92 of the tensile testing machine to investigate the load at the time of fracture. The probability (success rate) that the load obtained at the time of fracture was 60% or more of the load at the time of fracture without crimping was calculated. The test results are shown in Table 1. [Table 1] core wire Step S40 Wire diameter D (µm) Coating layer thickness (µm) variation Carbon content of the core wire (mass percent) Hardness of the core wire (HV) 1660 ×CST; +2850 ×t max / D Success rate (%) t max t min t max t min (t max -t min ) / D A SUS304 Ready 300 61,1 59,4 1,7 2,78 0,02 597 613,7 100 B SUS304 Ready 300 59,6 57,3 2,3 3,86 0,07 658 682,4 100 C SUS304 Ready 300 60 55,8 4,2 7,00 0,08 690 702,8 100 D SUS304 Ready 300 62,1 57 5,1 8,21 0,07 658 706,2 100 E SUS304 Ready 200 38,6 37,5 1,1 2,85 0,07 662 666,3 100 F SUS304 Ready 400 80,4 76,1 4,3 5,35 0,07 671 689,1 100 G SUS304 Omitted 303 62,9 55 7,9 12,56 0,08 715 724,4 30 H SUS304 Omitted 301 61,3 55,5 5,8 9,46 0,02 597 613,6 40 I SUS304 Ready 300 59,1 56,7 2,4 4,06 0,02 610 594,7 90 J SUS304 Ready 300 60,1 57,6 2,5 4,16 0,08 728 703,8 90 K SUS304 Omitted 302 62,3 54,5 7,8 12,52 0,02 640 621,1 10 L SUS304 Omitted 302 62,1 54,9 7,2 11,59 0,08 710 718,8 30 M SUS304 Ready 300 55,8 53,1 2,7 4,84 0,07 658 646,3 90 N SUS304 Omitted 200 40,1 36,3 3,8 9,48 0,07 643 687,6 40 O SUS304 Omitted 399 80,5 71,4 9,1 11,30 0,07 661 691,2 30 P SUS301 Ready 300 60,9 58,8 2,1 3,45 0,14 795 811,0 100 Q SUS301 Omitted 300 63,4 57,2 6,2 9,78 0,14 795 834,7 40

[0041] Referring to Table 1, in samples AF, I, J, M and P produced using the method including the coating thickness standardization step (S50), the difference between the maximum value t is max and the minimum value t minthe thickness of the coating layer 20 9% or less relative to the maximum value t max . On the other hand, in samples G, H, K, L, N, O and Q, which were produced using the method without the step to unify the thickness of the coating layer (S50), the difference between the maximum value t max and the minimum value t min the thickness of the coating layer 20 more than 9% relative to the maximum value t max The success rate is between 90% and 100% for samples AF, I, J, M and P, where the difference between the maximum value t max and the minimum value t min 9% or less of the maximum value t maxThe success rate for samples G, H, K, L, N, O, and Q, where the difference exceeds 9%, is no more than 40%. The foregoing confirms that the copper-clad steel wires and the insulated electrical wires of the present disclosure with a difference between t max and t min of 9% or less relative to t max can suppress the reduction in crimp strength.

[0042] Furthermore, among the samples with a difference between the maximum value t max and the minimum value t min of 9% or less relative to t max Samples A to F, which satisfy the condition of equation (1) above, have a success rate of 100%. This confirms that the reduction in crimp strength can be further suppressed by increasing the hardness HV. ST of the core wire, the carbon content C STof the austenitic stainless steel from which the core wire is made, and the ratio of the maximum value t max The thickness of the coating layer is adjusted to the wire diameter D of the copper-coated steel wire so that equation (1) is satisfied.

[0043] It is understood that the embodiments and examples disclosed herein are in every respect illustrative and not limiting. The scope of the present invention is defined by the terms of the claims and not by the preceding description and is intended to include all modifications that are within the scope and meaning of the terms of the claims. Reference symbol list 1 copper-coated steel wire; 1A Outer circumferential surface; 10 core wire; 11 Outer circumferential surface; 20 coating layers; 21 inner outer surface; 22 Outer circumferential surface; 30 Insulation layer; 31 inner outer surface; 32 Outer circumferential surface; 40 Intermediate shift; 80 crimp terminals; 81 ladder cylinders; 82 insulating cylinders; 83 Body section; 91 first clamping device; 92 second clamping device; 100 insulated electrical wire; C ST Carbon content of the core wire; D Wire diameter of the copper-coated steel wire; HV ST Hardness of the core wire; S10 to S70 step; t max Maximum value of the coating layer thickness; and t min Minimum value of the coating layer thickness. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2023-152403

[0002] JP 2022-157046 [0004, 0005]

Claims

[1] Copper-coated steel wire comprising: a core wire made of austenitic stainless steel; a coating layer composed of copper or a copper alloy, covering the outer circumferential surface of the core wire; and an intermediate layer made of nickel and positioned between the core wire and the coating layer; where the difference between the maximum value t max and the minimum value t min the thickness of the coating layer in a cross-section of the copper-coated steel wire perpendicular to its longitudinal direction 9% or less of the maximum value t max amounts. [2] Copper-coated steel wire according to claim 1, wherein the following equation is satisfied: 450≤HVST≤1660×CST+2850×tmax / D where HV ST the Vickers hardness of the core wire is C ST the carbon content of the core wire in mass percent is, tmax where is the maximum value of the coating layer thickness and D is the wire diameter of the copper-coated steel wire. [3] Copper-coated steel wire according to claim 2, wherein t max / D is 0.25 or less. [4] Copper-coated steel wire according to any one of claims 1 to 3, having a wire diameter D of not less than 200 µm and not more than 400 µm. [5] Copper-coated steel wire according to any one of claims 1 to 4, wherein the austenitic stainless steel constituting the core wire conforms to JIS standard SUS301, SUS304, SUS310S or SUS316. [6] Copper-coated steel wire according to any one of claims 1 to 5, wherein the coating layer has a hardness of not less than 50 HV and not more than 140 HV. [7] Insulated electrical wire, comprising: the copper-coated steel wire according to any one of claims 1 to 6; and an insulating layer that coats an outer circumferential surface of the copper-plated steel wire.

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