Copper-coated steel wire and insulated wire

Abstract

The copper-clad steel wire is a copper-clad steel wire comprising an austenitic stainless steel core wire, a copper or copper alloy coating layer covering the outer periphery of the core wire, and a nickel intermediate layer disposed between the core wire and the coating layer. The copper-clad steel wire has a maximum thickness t max and the minimum value t min The difference between the maximum value and t max This is less than 9%.

Description

[Technical field]

[0001] The present disclosure relates to copper clad steel wire and insulated wire.

[0002] This application claims priority to Japanese Application No. 2023-152403, filed on September 20, 2023, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0003] In some cases, electric wires are required to have both strength and electrical conductivity. In such cases, a copper-coated steel wire having a steel core and a copper coating layer covering the outer periphery of the core can be used as the electric wire. In addition, when the copper-coated steel wire is used in an environment requiring corrosion resistance, austenitic stainless steel may be used as the steel constituting the core.

[0004] A terminal may be attached to the end of an electric wire by crimping. When a terminal is attached to the end of an electric wire including a copper-coated steel wire by crimping, the core wire may break during crimping, reducing the connection strength (crimping strength) between the copper-coated steel wire and the terminal, and a problem may occur in which the copper-coated steel wire comes off the terminal when a tensile load is applied to the connection part. In response to this, a measure has been proposed to address the above problem by appropriately setting the hardness of the core wire and the coating layer, as well as the tensile strength of the core wire (see, for example, JP 2022-157046 A (Patent Document 1)). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-157046 A Summary of the Invention

[0006] The 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 made of copper or a copper alloy covering the outer circumferential surface of the core wire, and an intermediate layer made of nickel disposed between the core wire and the coating layer. max and the minimum value t min The difference between the maximum value and t max This is less than 9%. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a copper-coated steel wire. [Diagram 2] FIG. 2 is an enlarged schematic cross-sectional view showing the boundary between the core wire and the coating layer of FIG. [Diagram 3] FIG. 3 is a schematic diagram showing the structure of an insulated wire. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the structure of a copper-coated steel wire. [Diagram 5] FIG. 5 is a flow chart showing an outline of a method for producing a copper-coated steel wire and an insulated electric wire. [Figure 6] FIG. 6 is a schematic perspective view showing a connected state between an insulated wire and a crimp terminal. [Figure 7] FIG. 7 is a schematic diagram for explaining the method of the tensile test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Problem that this disclosure aims to solve] However, even when the hardness of the core wire and the covering layer, and the tensile strength of the core wire are adjusted, there are cases where further improvement in the crimping strength is required to prevent breakage of the core wire during crimping.

[0009] Therefore, an object of the present disclosure is to provide a copper-coated steel wire and an insulated electric wire including a copper-coated steel wire that can suppress a decrease in crimp strength.

[0010] [Effects of this disclosure] According to the above-mentioned copper-coated steel wire, it is possible to provide a copper-coated steel wire capable of suppressing a decrease in crimping strength.

[0011] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be described. The copper-clad steel wire of the present disclosure has the following features: (1) A copper-coated steel wire comprising an austenitic stainless steel core wire, a copper or copper alloy coating layer covering the outer periphery of the core wire, and a nickel intermediate layer disposed between the core wire and the coating layer. This copper-coated steel wire has a maximum coating layer thickness t max and the minimum value t min The difference between the maximum value and t max This is less than 9%.

[0012] The present inventors investigated the reason why the decrease in crimp strength caused by breakage of the core wire during crimping cannot be sufficiently suppressed even when the hardness of the core wire and the covering layer and the tensile strength of the core wire are adjusted, and considered measures for suppressing the decrease in crimp strength based on the findings obtained from the investigation. As a result, the inventors obtained the following findings and found a measure for suppressing the decrease in crimp strength.

[0013] According to the study by the inventors, the breakage of the core wire during crimping is greatly affected by the variation in the thickness of the coating layer of the copper-coated steel wire. max and the minimum value t min The difference between the maximum value t max It has been found that a decrease in compression strength can be effectively suppressed by setting the ratio of the tensile strength to a specific value or less, specifically, 9% or less.

[0014] In the copper-coated steel wire of the present disclosure, the maximum thickness t of the coating layer in a cross section perpendicular to the longitudinal direction of the copper-coated steel wire max and the minimum value t min The difference between the maximum value and t maxAs a result, the copper-clad steel wire of the present disclosure can suppress the decrease in crimp strength. max and the minimum value t min is defined as the average of the 10 maximum values ​​and the 10 minimum values ​​obtained by randomly examining 10 cross sections perpendicular to the longitudinal direction of a copper-coated steel wire and measuring the maximum and minimum values ​​of the coating layer thickness in each cross section.

[0015] (2) In (1) above, the Vickers hardness of the core wire is HV ST The carbon content of the core wire is expressed in mass% as C ST , the maximum thickness of the coating layer is t max , where D is the diameter of the copper-coated steel wire, and the following formula (1) is used. 450≦HV ST ≦1660×C ST +2850×t max / D···(1) may be satisfied.

[0016] By setting the hardness of the core wire to 450HV or more, it becomes easy to impart sufficient strength to the copper-coated steel wire. On the other hand, by setting the hardness of the core wire to a value calculated according to a specific calculation formula (formula (1)) or less using the carbon content of the core wire and the ratio of the thickness of the coating layer to the wire diameter of the copper-coated steel wire as parameters, the breakage of the core wire during crimping can be suppressed. More specifically, the austenitic stainless steel constituting the core wire is hardened by wire drawing to obtain a desired strength. At this time, the lower the carbon content of the austenitic stainless steel, the greater the amount of processing required to obtain the desired strength. Therefore, the lower the carbon content, the smaller the tolerance for deformation during crimping, since it is used in a state close to the processing limit, and the more likely the core wire is to break. In addition, the greater the ratio of the thickness of the coating layer to the wire diameter of the copper-coated steel wire, the greater the deformation capacity of the coating layer, which bears the deformation due to crimping, and the more suppressed the breakage of the core wire. According to the study by the present inventors, by setting the hardness of the core wire to a value equal to or less than the sum of the values ​​obtained by multiplying these parameters by specific coefficients, the breakage of the core wire during crimping can be suppressed. In this application, the wire diameter D of the copper-coated steel wire is defined as the average value of the wire diameter (diameter) of the copper-coated steel wire measured at 10 points in the longitudinal direction. ST can be measured on a cross section perpendicular to the longitudinal direction of the core wire using a micro Vickers hardness tester under conditions of, for example, a load of 0.196 N. The measurement points can be on a line segment corresponding to the diameter of the cross section, at points corresponding to the midpoint of the line segment (center of the cross section) and the midpoints between both ends of the line segment.

[0017] (3) In (2) above, max / D may be 0.25 or less. This configuration makes it easy to impart sufficient strength to the copper-coated steel wire. max / D may be less than or equal to 0.23.

[0018] (4) In any of the above (1) to (3), the copper-coated steel wire may have a wire diameter D of 200 μm or more and 400 μm or less. The copper-coated steel wire of the present disclosure capable of suppressing a decrease in crimp strength is particularly suitable for a copper-coated steel wire having a wire diameter of 200 μm or more and 400 μm or less.

[0019] (5) In any of the above (1) to (4), the austenitic stainless steel constituting the core wire may be JIS standard SUS301, SUS304, SUS310S, or SUS316. JIS standard SUS301, SUS304, SUS310S, and SUS316 are particularly suitable as materials constituting the core wire.

[0020] (6) In any of the above (1) to (5), the hardness of the coating layer may be 50 HV or more and 140 HV or less. This configuration makes it easy to suppress a decrease in the crimp strength of the copper-coated steel wire. In the present application, the hardness of the coating layer can be defined as an average value of four measurements taken at the center of the thickness of the coating layer in a cross section perpendicular to the longitudinal direction of the copper-coated steel wire.

[0021] (7) An insulated wire according to the present disclosure includes the copper-coated steel wire according to any one of (1) to (6) above and an insulating layer that coats the outer circumferential surface of the copper-coated steel wire. By including the copper-coated steel wire according to the present disclosure, the insulated wire according to the present disclosure can suppress a decrease in crimp strength.

[0022] [Details of the embodiment of the present disclosure] Next, embodiments of the copper-clad steel wire and the insulated electric wire according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated.

[0023] (Embodiment 1) FIG. 1 is a schematic diagram showing the structure of a copper-coated steel wire. FIG. 2 is a schematic cross-sectional view showing an enlarged view of the boundary between the core wire and the coating layer in FIG. 1. Referring to FIG. 1 and FIG. 2, the copper-coated steel wire 1 in this embodiment includes 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 disposed so as to cover the outer peripheral surface 11 of the core wire 10. The intermediate layer 40 is disposed between the core wire 10 and the coating layer 20. The coating layer 20 is in contact with the intermediate layer 40 at the inner peripheral surface 21. The core wire 10 is in contact with the intermediate layer 40 at the outer peripheral surface 11. The intermediate layer 40 is interposed between the core wire 10 and the coating layer 20. The outer peripheral surface 22 of the coating layer 20 constitutes the outer peripheral surface of the copper-coated steel wire 1.

[0024] FIG. 3 is a schematic diagram showing the structure of an insulated wire. Referring to FIG. 3, an insulated wire 100 in the present embodiment includes the copper-coated steel wire 1 of the present embodiment and an insulating layer 30. The insulating layer 30 is disposed so as to cover the outer peripheral surface 1A (the outer peripheral surface 22 of the coating layer 20) of the copper-coated steel wire 1. The insulating layer 30 covers the entire outer peripheral surface 1A of the copper-coated steel wire 1. The insulating layer 30 contacts the outer peripheral surface 1A of the copper-coated steel wire 1 at an inner peripheral surface 31. The outer peripheral surface 32 of the insulating layer 30 constitutes the outer peripheral surface of the insulated wire 100. The insulating layer 30 is made of an insulator such as a resin. For example, polyethylene, polyvinyl chloride, or the like can be adopted as the resin constituting the insulating layer 30.

[0025] FIG. 4 is a schematic cross-sectional view showing the structure of a copper-coated steel wire. FIG. 4 shows a cross section perpendicular to the longitudinal direction of the copper-coated steel wire 1. Referring to FIG. 4, the wire diameter D (diameter of the cross section perpendicular to the longitudinal direction) of the copper-coated steel wire 1 is not particularly limited, but is, for example, 200 μm or more and 400 μm or less. As the austenitic stainless steel constituting the core wire 10, for example, JIS standard SUS301, SUS304, SUS310S or SUS316 can be adopted. The tensile strength of the core wire 10 can be, for example, 1500 MPa or more and 3000 MPa or less. The Vickers hardness HV of the core wire 10 is, for example, 1000 MPa or more and 1000 MPa or less. ST can be, for example, 450HV or more and 840HV or less.

[0026] 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 may be a plated layer. The coating layer 20 may be a layer formed by plating. The hardness of the coating layer 20 is, for example, 50 HV or more and 140 HV or less. The maximum thickness t of the coating layer 20 in a cross section perpendicular to the longitudinal direction of the copper-coated steel wire 1 is max and the minimum value t min The difference between the maximum value t max This is less than 9%.

[0027] Referring to FIG. 2, the intermediate layer 40 is made of nickel (Ni). The thickness of the intermediate layer 40 is not particularly limited, but can be set to be smaller than the thickness of the coating layer 20. The thickness of the intermediate layer 40 can be, for example, 0.0001 μm or more, preferably 0.005 μm or more. The thickness of the intermediate layer 40 can be, for example, 1 μm or less, 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 may be a plated layer. The intermediate layer 40 may be a layer formed by plating.

[0028] In the copper-coated steel wire 1 of the present embodiment, as described above, the maximum thickness t max and the minimum value t min The difference between the maximum value t max The variation in thickness of the coating layer 20 is suppressed to be 9% or less of the maximum thickness t of the coating layer 20. As a result, the copper-coated steel wire 1 of the present embodiment is a copper-coated steel wire in which the decrease in crimping strength is suppressed. Furthermore, the insulated electric wire 100 including this copper-coated steel wire 1 is an insulated electric wire in which the decrease in crimping strength is suppressed. max and the minimum value t min The difference between the maximum value t max By setting the ratio to 8% or less, 7% or less, 6% or less, or even 5% or less, the decrease in compression strength can be further suppressed.

[0029] In the copper-coated steel wire 1 of this embodiment, the Vickers hardness of the core wire 10 is HVST The carbon content of the core wire 10 is expressed in mass% as C ST The maximum thickness of the coating layer 20 is expressed in μm as t max The wire diameter of the copper-coated steel wire 1 is expressed in μm as D, and the following formula (1) is used. 450≦HV ST ≦1660×C ST +2850×t max / D···(1) By setting the hardness of the core wire 10 to 450 HV or more, it becomes easy to impart sufficient strength to the copper-coated steel wire 1. On the other hand, the hardness of the core wire 10 can be determined by the carbon content of the core wire 10 and the maximum value t max By setting the value calculated according to formula (1) using the ratio of the above as parameters to be equal to or less than the value calculated according to formula (1), breakage of the core wire 10 during crimping can be suppressed.

[0030] In the copper-coated steel wire 1 of this embodiment, the above t max When / D is 0.25 or less, it becomes easy to impart sufficient strength to the copper-coated steel wire 1.

[0031] Next, a method for manufacturing the copper-coated steel wire 1 and the insulated electric wire 100 in the present embodiment will be described. FIG. 5 is a flow chart showing an outline of the method for manufacturing the copper-coated steel wire and the insulated electric wire. With reference to FIG. 5, in the method for manufacturing the copper-coated steel wire 1 and the insulated electric wire 100 in the present embodiment, a raw steel wire preparation step is first carried out as step S10. In this step S10, a raw steel wire is prepared. Specifically, a raw steel wire made of austenitic stainless steel, for example, JIS standard SUS301, SUS304, SUS310S or SUS316 having a desired carbon content is prepared. The outer diameter of the raw steel wire can be, for example, 0.3 mm or more and 1 mm or less.

[0032] Next, an intermediate layer forming step is carried out as step S20. In this step S20, an intermediate layer 40 is formed on the surface of the raw steel wire prepared in step S10. Specifically, for example, the intermediate layer 40 made of nickel is formed on the core wire 10 by plating. This results in a raw steel wire having the intermediate layer 40 formed on its surface. The thickness of the intermediate layer 40 formed in step S20 is determined so that the copper-coated steel wire 1 has a desired thickness in a completed state, taking into consideration that the thickness will be reduced by processing in the wire drawing step described below.

[0033] Next, a wiredrawing step is performed as step S30. In this step S30, the raw steel wire on which the intermediate layer 40 has been formed in step S20 is subjected to wiredrawing (drawing). The true strain in the wiredrawing in step S30 can be, for example, 1.3 to 2.6. This adjusts the outer diameter of the raw steel wire to a desired value, and imparts desired hardness and tensile strength to the raw steel wire, turning the raw steel wire into a core wire 10 (see FIG. 1). The wiredrawing may be performed in multiple steps.

[0034] Next, a coating layer forming step is performed as step S40. In this step S40, a coating layer 20 is formed on the surface of the core wire 10 having the intermediate layer 40 obtained by performing steps up to S30. Specifically, for example, the coating layer 20 made of copper (pure copper) is formed by plating on the core wire 10 having the intermediate layer 40. In addition to copper, a metal layer of tin (Sn), zinc (Zn), or the like may be formed by plating, and the copper alloy coating layer 20 may be formed by alloying these. In this way, a copper-coated steel wire 1 including the core wire 10 and the coating layer 20 is obtained. The coating layer 20 may be formed in multiple steps.

[0035] Next, a coating layer thickness uniformization step 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 wiredrawing with a small processing amount in order to reduce the variation in thickness of the coating layer 20. The true strain of the wiredrawing in step S50 can be, for example, 0.1 or more and 0.5 or less.

[0036] Next, a heat treatment step is performed as step S60. In this step S60, the copper-coated steel wire 1 obtained by performing steps up to S50 is subjected to a heat treatment. Specifically, the copper-coated steel wire 1 is subjected to a heat treatment in which the wire is held in a temperature range of 275°C to 450°C, preferably in a temperature range of 350°C to 450°C, for example, for 30 minutes to 120 minutes, and then air-cooled to room temperature. As a result, the copper or copper alloy constituting the coating layer 20 is recrystallized and softened to an appropriate hardness, and the internal stress of the core wire 10 is removed, thereby adjusting the hardness of the core wire 10 to an appropriate range. The above procedure results in the copper-coated steel wire 1 of the present embodiment (see FIG. 1).

[0037] Furthermore, an insulating layer forming step is carried out as step S70. In this step S70, an insulating layer 30 is formed so as to cover the outer peripheral surface of the copper-coated steel wire 1 of the present embodiment obtained by carrying out steps up to S60. The insulating layer 30 may be made of, for example, resin. Through the above procedure, the insulated electric wire 100 of the present embodiment is obtained (see FIG. 3). EXAMPLES

[0038] An experiment was conducted to confirm the effect of suppressing a decrease in crimp strength when the copper-coated steel wire and the insulated electric wire of the present disclosure are connected to a crimp terminal. The procedure of the experiment is as follows.

[0039] An insulated electric wire 100 was prepared according to the manufacturing method described in the above embodiment. JIS standard SUS301 and SUS304 were adopted as materials for the raw steel wire prepared in step S10. In step S20, an intermediate layer 40 was formed so that the thickness in the completed state (at the stage where step S70 was completed) would be 0.6 μm. In step S40, a coating layer 20 made of pure copper was formed by plating. For comparison, an insulated electric wire in which the thickness of the coating layer 20 was not made uniform by omitting step S50 was also prepared. In this manner, samples A to Q were obtained. Then, the strength of the crimped portion of the obtained samples when connected to a crimp terminal was measured as follows.

[0040] FIG. 6 is a schematic perspective view showing a connection state between an insulated electric wire and a crimp terminal. FIG. 7 is a schematic view for explaining a method of a tensile test. Referring to FIG. 6, the crimp terminal 80 includes a main body 83, a conductor barrel 81 connected to the main body 83, and an insulation barrel 82 connected to the side of the conductor barrel 81 opposite to the side connected to the main body 83. When connecting the insulated electric wire 100 to the crimp terminal 80, first, the insulation layer 30 at the end of the insulated electric wire 100 is removed to expose the copper-coated steel wire 1. Then, the conductor barrel 81 is crimped to hold the exposed copper-coated steel wire 1 by the conductor barrel 81, and the insulation layer 30 is held by the insulation barrel 82. At this time, if a crack occurs in the core wire 10 of the copper-coated steel wire 1 held by the conductor barrel 81, the strength (crimping strength) of the connection part between the conductor barrel 81 and the copper-coated steel wire 1 decreases.

[0041] In this experiment, the insulated electric wire 100 and the crimp terminal 80 were connected in a state where the copper-coated steel wire 1 was held by the conductor barrel 81 as described above, while the insulating layer 30 was not held by the insulation barrel 82. At this time, the compression ratio expressed by 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 a condition where sufficient crimp strength can be obtained if the core wire 10 does not break. Then, as shown in FIG. 12, a tensile test was performed with the main body 83 of the crimp terminal 80 held by the first chuck 91 of the tensile tester and the insulated electric wire 100 held by the second chuck 92 of the tensile tester, and the load at break was investigated. The probability (pass rate) that the obtained load at break was 60% or more of the load at break in a state where crimping was not performed was calculated. The experimental results are shown in Table 1.

[0042] [Table 1] Referring to Table 1, in samples A to F, I, J, M, and P produced by a process including the coating layer thickness uniformization step (S50), the maximum thickness t max and the minimum value t min The difference between the maximum value and t maxOn the other hand, in the samples G, H, K, L, N, O, and Q produced by a process that does not include the coating layer thickness uniformization step (S50), the maximum thickness t max and the minimum value t min The difference between the maximum value and t max The maximum value t max and the minimum value t min The difference between the maximum value and t max The pass rates of samples A to F, I, J, M and P, which are 9% or less, are 90 to 100%, while the pass rates of samples G, H, K, L, N, O and Q, which are over 9%, are 40% or less. max and min The difference between max It has been confirmed that the copper-coated steel wire and insulated electric wire of the present disclosure, which have a copper content of 9% or less, can suppress a decrease in crimp strength.

[0043] Furthermore, t max and the minimum value t min The difference between max Among the samples with a core hardness of 9% or less, samples A to F that satisfy the condition of formula (1) above have a pass rate of 100%. ST , the carbon content C of the austenitic stainless steel that constitutes the core wire ST and the maximum thickness of the coating layer for the wire diameter D of the copper-coated steel wire, t max It has been confirmed that the decrease in compression strength can be further suppressed by adjusting the ratio of

[0044] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0045] 1 copper-coated steel wire, 1A outer circumferential surface, 10 core wire, 11 outer circumferential surface, 20 coating layer, 21 inner circumferential surface, 22 outer circumferential surface, 30 insulating layer, 31 inner circumferential surface, 32 outer circumferential surface, 40 intermediate layer, 80 crimp terminal, 81 conductor barrel, 82 insulation barrel, 83 main body, 91 first chuck, 92 second chuck, 100 insulated wire, C ST Carbon content of the core wire, D Diameter of copper-clad steel wire, HV ST Hardness of core wire, S10~S70 Process, t max Maximum thickness of the coating layer, t min The minimum thickness of the coating layer.

Claims

1. A core wire made of austenitic stainless steel; a coating layer made of copper or a copper alloy and covering an outer circumferential surface of the core wire; A copper-coated steel wire having an intermediate layer made of nickel, the intermediate layer being disposed between the core wire and the coating layer, The maximum thickness t of the coating layer in a cross section perpendicular to the longitudinal direction of the copper-coated steel wire ｍａｘ and the minimum value t ｍｉｎ The difference between the maximum value and ｍａｘ 9% or less of copper-coated steel wire.

2. The Vickers hardness of the core wire is HV ＳＴ The carbon content of the core wire is expressed in mass% as C ＳＴ The maximum thickness of the coating layer is t ｍａｘ The wire diameter of the copper-coated steel wire is D, and the following formula is used. 450≦HV ＳＴ ≦1660×C ＳＴ +2850×t ｍａｘ / D The copper-clad steel wire according to claim 1 ,

3. t ｍａｘ 3. The copper-coated steel wire according to claim 2, wherein / D is 0.25 or less.

4. The copper-coated steel wire according to claim 1, wherein the wire diameter D of the copper-coated steel wire is 200 μm or more and 400 μm or less.

5. 2. The copper-clad steel wire according to claim 1, wherein the austenitic stainless steel constituting the core wire is JIS standard SUS301, SUS304, SUS310S or SUS316.

6. 2. The copper-coated steel wire according to claim 1, wherein the hardness of the coating layer is 50 HV or more and 140 HV or less.

7. The copper-coated steel wire according to any one of claims 1 to 6, and an insulating layer covering an outer peripheral surface of the copper-coated steel wire.

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