Plated Steel Wire

Abstract

To provide a plated steel wire with a plating layer in which crack is inhibited from being generated at the time of processing.SOLUTION: A plated steel wire includes: a steel wire; and a plating layer formed on a surface of the steel wire. The plating layer includes, by mass, 0.5-15.0% Al, 0.3-5.0% Mg, and the balance Zn with impurities. An arithmetic mean value of Vickers hardness is 100-150 HV in hardness measurement areas A1-A4 in four points shifted by 90 degrees in a circumferential direction in the thickness central position of the plating layer at a cross section perpendicular to an axial direction of the plated steel wire, and a standard deviation of Vickers hardness is 20.0 HV or less in the hardness measurement areas A1-A4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a plated steel wire having a plating layer formed on the surface of the steel wire. [Background technology]

[0002] Steel wires used for applications such as wire mesh, fences, and power transmission wires may be subjected to a plating process to form a plating layer on the surface of the steel wire. Such steel wires are called "plated steel wires." In order to obtain a required shape, plated steel wires may be subjected to processing, typically bending.

[0003] Generally, the plating layer formed on the surface of a plated steel wire is required to have excellent corrosion resistance. For example, zinc plating and zinc alloy plating are used as the plating layer of a plated steel wire. Zinc plating is a plating made of Zn. Zinc alloy plating is a plating made of an alloy of Zn and other alloying elements. Examples of zinc alloy plating include Zn-Al alloy plating containing Zn and Al, or Zn-Al-Mg alloy plating containing Zn, Al, and Mg. Plated steel wires having a zinc alloy plating layer have higher corrosion resistance than plated steel wires having a zinc plating layer.

[0004] However, the above-mentioned zinc alloy plating layer tends to be harder than the zinc plating layer. Therefore, in a plated steel wire having a zinc alloy plating layer, cracks are likely to occur in the zinc alloy plating layer during processing. In a plated steel wire having a crack in the zinc alloy plating layer, the corrosion resistance of the cracked portion is reduced. Therefore, in a plated steel wire having a zinc alloy plating layer, it is necessary to suppress the occurrence of cracks in the plating layer during processing.

[0005] A technology for suppressing cracks in a plating layer during processing is disclosed, for example, in JP-T-2020-503439 (Patent Document 1).

[0006] The alloy-plated steel material disclosed in Patent Document 1 includes a zinc alloy plating layer. The zinc alloy plating layer contains 0.5 to 2.5% Mg, 0.5 to 3.0% Al, and the remainder Zn and inevitable impurities. The zinc alloy plating layer includes a single Zn phase and a mixed phase of Zn and Mg, and the mixed phase of Zn and Mg has a lamellar structure composed of a Zn phase and an Mg-Zn alloy phase. The average width of the lamellar structure is 1.5 μm or less. In this document, the average width of the lamellar structure in the zinc alloy plating layer is set to 1.5 μm or less. Patent Document 1 states that this suppresses the occurrence of cracks in the plating layer during processing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2020-503439 Summary of the Invention [Problem to be solved by the invention]

[0008] However, it may be possible to suppress the occurrence of cracks in the plating layer during processing by means other than the means disclosed in the above-mentioned Patent Document 1.

[0009] An object of the present invention is to provide a plated steel wire capable of suppressing the occurrence of cracks in the plating layer during processing. [Means for solving the problem]

[0010] The plated steel wire according to the present invention has the following configuration.

[0011] A plated steel wire, Steel wire, a plating layer formed on the surface of the steel wire, The plating layer is In mass%, Al: 0.5 to 15.0%, and Mg: 0.3 to 5.0%; the balance being Zn and impurities, In a cross section perpendicular to the axial direction of the plated steel wire, the arithmetic mean value of Vickers hardness in four hardness measurement areas A1 to A4 at the thickness center of the plating layer, which are shifted by 90 degrees in the circumferential direction, is 100 to 150 HV; The standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 is 20.0 HV or less. Plated steel wire. [Effects of the Invention]

[0012] The plated steel wire of the present invention can suppress the occurrence of cracks in the plating layer during processing. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view perpendicular to the axial direction of the plated steel wire of this embodiment. [Figure 2] FIG. 2 is a cross-sectional view perpendicular to the axial direction of the plated steel wire of this embodiment. [Figure 3] FIG. 3 is a flow chart showing an example of a manufacturing process for a plated steel wire according to this embodiment. [Figure 4] FIG. 4 is a schematic diagram of a hot-dip zinc alloy plating treatment apparatus. [Figure 5] FIG. 5 is a schematic diagram of the cooling device shown in FIG. [Figure 6] FIG. 6 is a schematic diagram of the cooling device shown in FIG. 4 in the case where the passing position of the plated steel wire deviates from the pass line when the plated steel wire passes through the cooling device. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors first investigated the composition of the alloys, in mass %, as follows: Al: 0.5 to 15.0%, Mg: 0.3 to 5.0%, Pb: 0 to 0.50%, Bi: 0 to 0.50%, Sr: 0 to 0.50%, V: 0 to 0.50%, Cr: 0 to 0.50%, Mn: 0 to 0.50%, Sn: 0 to 0.50%, Si: 0 to 0.50%, Ti: 0 to 0.50%, Be: 0 to 0.50%, Na: 0 to 0.50%, K: 0 to 0.50%, Ca: 0 to 0.50%, Cu: 0 to 0.50% The present inventors investigated and studied means for suppressing cracking of the plating layer during processing in a plated steel wire comprising a plating layer containing 0% by weight, La: 0-0.50%, Ce: 0-0.50%, Hf: 0-0.50%, Mo: 0-0.50%, W: 0-0.50%, Nb: 0-0.50%, Ta: 0-0.50%, and Fe: 0-2.00%, with the balance being Zn and impurities, and a steel wire having the plating layer formed on its surface. The present inventors focused on the hardness of the plated steel wire.

[0015] If the plating layer is excessively hard, it is likely to crack during processing. Therefore, the present inventors first considered that it may be possible to suppress the occurrence of cracks in the plating layer during processing by appropriately controlling the hardness of the plating layer having the above-mentioned chemical composition. Specifically, they attempted to suppress the occurrence of cracks in the plating layer during processing by setting the Vickers hardness of the plating layer to 100 to 150 HV.

[0016] However, it was found that even when the hardness of the plating layer is set to 100 to 150 HV in Vickers hardness, the occurrence of cracks in the plating layer during processing may not be sufficiently suppressed in some cases. Therefore, the present inventors conducted further studies.

[0017] The present inventors investigated the Vickers hardness in the vicinity of a crack in a plating layer where a crack occurred during processing. As a result, it was found that the Vickers hardness varies in the circumferential direction of the plating layer. When the circumferential hardness variation of the plating layer is large in a cross section perpendicular to the axial direction, a high-hardness region and a low-hardness region are present in the circumferential direction of the plating layer. The high-hardness region and the low-hardness region have different degrees of deformation when the same load is applied during processing. Therefore, local strain is likely to occur in the circumferential direction of the plating layer during processing. The local strain promotes the occurrence of cracks in the plating layer. Therefore, when the circumferential hardness variation of the plating layer is large, cracks are likely to occur during processing.

[0018] Therefore, the present inventors investigated the relationship between the circumferential hardness variation of the plating layer and the occurrence of cracks during processing. As a result, they found that, in a plating layer having the above-mentioned chemical composition, if the plating layer has a Vickers hardness of 100 to 150 HV and the standard deviation of the Vickers hardness of the plating layer in the circumferential direction is 20.0 HV or less, the occurrence of cracks in the plating layer during processing can be sufficiently suppressed.

[0019] The plated steel wire according to this embodiment, which has been completed based on the above findings, has the following configuration.

[0020] [1] A plated steel wire, Steel wire, a plating layer formed on the surface of the steel wire, The plating layer is In mass%, Al: 0.5 to 15.0%, and Mg: 0.3 to 5.0%; the balance being Zn and impurities, In a cross section perpendicular to the axial direction of the plated steel wire, the arithmetic mean value of Vickers hardness in four hardness measurement areas A1 to A4 at the thickness center of the plating layer, which are shifted by 90 degrees in the circumferential direction, is 100 to 150 HV; The standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 is 20.0 HV or less. Plated steel wire.

[0021] [2] The plated steel wire according to [1], further comprising: The plating layer is In place of a part of the Zn, in mass%, Pb: 0.50% or less, Bi: 0.50% or less, Sr: 0.50% or less, V: 0.50% or less, Cr: 0.50% or less, Mn: 0.50% or less, Sn: 0.50% or less, Si: 0.50% or less, Ti: 0.50% or less, Be: 0.50% or less, Na: 0.50% or less, K: 0.50% or less, Ca: 0.50% or less, Cu: 0.50% or less, La: 0.50% or less, Ce: 0.50% or less, Hf: 0.50% or less, Mo: 0.50% or less W: 0.50% or less, Nb: 0.50% or less, Ta: 0.50% or less, and Fe: 2.00% or less, Contains one or more selected from the group consisting of Plated steel wire.

[0022] The plated steel wire of this embodiment will be described in detail below. Unless otherwise specified, "%" for elements means mass %. For numerical ranges expressed using "to", the number before "to" indicates the lower limit. If the number before "to" is preceded by "over", the numerical range does not include the number before "over". If the number after "to" is preceded by "less than", the numerical range does not include the number before "less than". In the present specification, the upper limit of a numerical range described in stages may be replaced with the upper limit of another numerical range described in stages. The lower limit of a numerical range may be replaced with the lower limit of another numerical range described in stages. Furthermore, the upper or lower limit may be replaced with a value shown in the examples.

[0023] [Composition of plated steel wire] Fig. 1 is a cross-sectional view perpendicular to the axial direction of a plated steel wire according to this embodiment. Referring to Fig. 1, the plated steel wire 1 according to this embodiment includes a steel wire 100 and a plating layer 10. The plating layer 10 is formed on the surface of the steel wire 100.

[0024] The plated steel wire 1 of this embodiment may include a steel wire 100, a plating layer 10, and an alloy layer 11. With reference to FIG. 2 , when the plated steel wire 1 of this embodiment includes the alloy layer 11, the alloy layer 11 is formed between the steel wire 100 and the plating layer 10.

[0025] Here, the alloy layer 11 refers to a layer containing an Fe-Zn intermetallic compound that is formed between the steel wire 100 and the plating layer 10. When the plated steel wire 1 of this embodiment has an alloy layer, the chemical composition of the alloy layer is not particularly limited. The alloy layer 11 may have a chemical composition containing Fe, Al, Zn, and Mg, for example. The alloy layer 11 may have a chemical composition containing elements contained in the plating layer 10 in addition to Fe, Al, Zn, and Mg, for example. The steel wire 100, the alloy layer 11, and the plating layer 10 can be easily distinguished by observing backscattered electron images with a scanning electron microscope (SEM).

[0026] The steel wire 100 and the plating layer 10 will be described below.

[0027] [About Steel Wire 100] The steel wire is a steel material in a linear form obtained by drawing a wire material. The steel wire 100 may be a known steel wire applied to plated steel wires depending on the mechanical properties (e.g., tensile strength, workability, fatigue properties, etc.) required for the plated steel wire to be manufactured. For example, the steel wire 100 may be a steel wire for wire mesh, a steel wire for fences, or a steel wire for power transmission wires.

[0028] As described above, it is sufficient for the steel wire 100 to have a known chemical composition. The steel wire is not particularly limited, but may be, for example, a steel wire having the chemical composition of a soft steel wire material specified in JIS G3505 (2017) or a steel wire having the chemical composition of a hard steel wire material specified in JIS G3506 (2017).

[0029] [Regarding plating layer 10] The plating layer 10 is formed on the surface of the steel wire 100. The chemical composition of the plating layer 10 contains the following elements.

[0030] Al: 0.5 to 15.0% Aluminum (Al) improves the corrosion resistance of plated steel wire. When Mg is contained in the plating layer, the formation of oxides is promoted on the surface of the hot-dip zinc alloy plating bath, etc. Al suppresses the formation of oxides in the hot-dip zinc alloy plating bath. Therefore, the inclusion of Al enables stable production of plated steel wire. If the Al content is less than 0.5%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Al content exceeds 15.0%, the melting point of the hot-dip zinc alloy plating bath becomes high even if the contents of other elements are within the ranges of this embodiment. This promotes the formation of oxides on the surface of the hot-dip zinc alloy plating bath, etc. In this case, work to remove the oxides on the surface of the hot-dip zinc alloy plating bath, etc. is required. The higher the melting point of the hot-dip zinc alloy plating bath, the more wear on the hot-dip zinc alloy plating bath will be. This reduces production efficiency. Therefore, the Al content is 0.5 to 15.0%. The lower limit of the Al content is preferably 3.0%, more preferably 4.0%, and even more preferably 5.0%. The upper limit of the Al content is preferably 14.0%, more preferably 13.5%, and even more preferably 13.0%.

[0031] Mg: 0.3 to 5.0% Magnesium (Mg) enhances the corrosion resistance of plated steel wire. If the Mg content is less than 0.3%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mg content exceeds 5.0%, a large amount of Zn-Mg intermetallic compounds is formed in the microstructure of the coating layer, even if the contents of other elements are within the ranges of this embodiment. Zn-Mg intermetallic compounds are hard. Therefore, if a large amount of Zn-Mg intermetallic compounds is formed, the hardness of the coating layer increases excessively. As a result, it is not possible to sufficiently suppress the occurrence of cracks in the coating layer during processing. Therefore, the Mg content is 0.3 to 5.0%. The lower limit of the Mg content is preferably 0.5%, more preferably 0.7%, and even more preferably 0.9%. The upper limit of the Mg content is preferably 4.0%, more preferably 3.0%, and even more preferably 2.5%.

[0032] In the plated steel wire according to the present embodiment, the balance of the chemical composition of the plating layer is composed of Zn and impurities. Here, the impurities refer to substances that are mixed in from the molten metal as a raw material or the manufacturing environment during industrial production of the plating layer, and are acceptable within a range that does not adversely affect the plated steel wire according to the present embodiment.

[0033] [Optional elements] In the plated steel wire of the present embodiment, the chemical composition of the plating layer further contains, in place of a portion of Zn, Pb: 0.50% or less, Bi: 0.50% or less, Sr: 0.50% or less, V: 0.50% or less, Cr: 0.50% or less, Mn: 0.50% or less, Sn: 0.50% or less, Si: 0.50% or less, Ti: 0.50% or less, Be: 0.50% or less, Na: 0.50% or less, K: 0.50% or less, Ca: 0.50% or less, Cu: 0.50% or less, La: 0.50% or less, Ce: 0.50% or less, Hf: 0.50% or less, Mo: 0.50% or less W: 0.50% or less, Nb: 0.50% or less, Ta: 0.50% or less, and Fe: 2.00% or less, The optional elements may be contained in the composition of the present invention. The optional elements will be described below.

[0034] [Group 1: Pb, Bi, Sr, V, Cr, Mn and Sn] In the plated steel wire of this embodiment, the chemical composition of the plating layer may further contain, in place of a portion of Zn, one or more elements selected from the group consisting of Pb: 0.50% or less, Bi: 0.50% or less, Sr: 0.50% or less, V: 0.50% or less, Cr: 0.50% or less, Mn: 0.50% or less, and Sn: 0.50% or less.

[0035] Each of the elements Pb, Bi, Sr, V, Cr, Mn, and Sn is an optional element and may not be contained, that is, the content of each of Pb, Bi, Sr, V, Cr, Mn, and Sn may be 0%. When contained, that is, when the content of one or more elements selected from the group consisting of Pb, Bi, Sr, V, Cr, Mn, and Sn is greater than 0%, these elements can suppress the occurrence of cracks in the plating layer during processing. The above effect can be obtained to some extent even if even a small amount of one or more elements selected from the group consisting of Pb, Bi, Sr, V, Cr, Mn, and Sn is contained. However, if the content of each of Pb, Bi, Sr, V, Cr, Mn, or Sn exceeds 0.50%, the above effects saturate, resulting in increased manufacturing costs, even if the contents of other elements are within the ranges of this embodiment. Each of Pb, Bi, Sr, V, Cr, Mn, or Sn may segregate. Therefore, if the content of each of Pb, Bi, Sr, V, Cr, Mn, or Sn exceeds 0.50%, cracks may occur in the coating layer during processing. If the content of each of Pb, Bi, Sr, V, Cr, Mn, or Sn exceeds 0.50%, the corrosion resistance of the coated steel wire may decrease. Therefore, the content of each of Pb, Bi, Sr, V, Cr, Mn, and Sn is 0 to 0.50%. When contained, the content of each of Pb, Bi, Sr, V, Cr, Mn, and Sn is 0.50% or less, that is, more than 0 to 0.50%.

[0036] The lower limit of the content of each of the elements Pb, Bi, Sr, V, Cr, Mn, and Sn is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, and still more preferably 0.15%. The upper limit of the content of each of the elements Pb, Bi, Sr, V, Cr, Mn, and Sn is preferably 0.48%, more preferably 0.45%, and even more preferably 0.40%.

[0037] [Group 2: Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf] In the plated steel wire of this embodiment, the chemical composition of the plating layer may further contain, in place of a portion of Zn, one or more elements selected from the group consisting of Si: 0.50% or less, Ti: 0.50% or less, Be: 0.50% or less, Na: 0.50% or less, K: 0.50% or less, Ca: 0.50% or less, Cu: 0.50% or less, La: 0.50% or less, Ce: 0.50% or less, and Hf: 0.50% or less.

[0038] The elements Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf are optional elements and may not be contained, that is, the content of each of Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf may be 0%. When contained, that is, when the content of one or more elements selected from the group consisting of Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf exceeds 0%, these elements all enhance the corrosion resistance of the plated steel wire. The above effect can be obtained to some extent even if even a small amount of one or more elements selected from the group consisting of Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf is contained. However, if the content of each of Si, Ti, Be, Na, K, Ca, Cu, La, Ce, or Hf exceeds 0.50%, the above effects saturate and manufacturing costs increase even if the contents of other elements are within the ranges of this embodiment.Furthermore, if the content of each of Si, Ti, Be, Na, K, Ca, Cu, La, Ce, or Hf exceeds 0.50%, it is not possible to sufficiently suppress the occurrence of cracks in the plating layer during processing. Therefore, the content of each of Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf is 0 to 0.50%. When contained, the content of each of Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf is 0.50% or less, that is, more than 0 to 0.50%.

[0039] The lower limit of the content of each of the elements Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, and still more preferably 0.15%. The upper limit of the content of each of the elements Si, Ti, Be, Na, K, Ca, Cu, La, Ce, and Hf is preferably 0.48%, more preferably 0.45%, and even more preferably 0.40%.

[0040] [Group 3: Mo, W, Nb, Ta and Fe] In the plated steel wire of this embodiment, the chemical composition of the plating layer may further contain, in place of a portion of Zn, one or more elements selected from the group consisting of Mo: 0.50% or less, W: 0.50% or less, Nb: 0.50% or less, Ta: 0.50% or less, and Fe: 2.00% or less.

[0041] Each of the elements Mo, W, Nb, Ta, and Fe is an optional element and may not be contained, that is, the content of each of Mo, W, Nb, Ta, and Fe may be 0%. When the contents of Mo, W, Nb, Ta, and Fe are within the above-mentioned ranges, the effects of the plated steel wire according to this embodiment can be obtained. Therefore, the content of each of Mo, W, Nb, and Ta is 0 to 0.50%, and the content of Fe is 0 to 2.00%. When contained, the content of each of Mo, W, Nb, and Ta is 0.50% or less, that is, more than 0 to 0.50%. When contained, the content of Fe is 2.00% or less, that is, more than 0 to 2.00%.

[0042] The lower limit of each of the Mo, W, Nb, and Ta elements is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, and even more preferably 0.15%. The upper limit of each of the Mo, W, Nb, and Ta elements is preferably 0.48%, more preferably 0.45%, and even more preferably 0.40%.

[0043] The lower limit of the Fe content is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, and even more preferably 0.15%. The upper limit of the Fe content is preferably 1.90%, more preferably 1.75%, and even more preferably 1.50%.

[0044] [About the hardness of the plating layer] In the plated steel wire of this embodiment, the Vickers hardness is appropriately controlled in a cross section, which is a cross section perpendicular to the axial direction of the plated steel wire. This point will be described below.

[0045] Referring to Figure 1, the cross section of the plated steel wire is circular. The thickness of the plating layer 10 is defined as t (µm). In this cross section, four hardness measurement regions A1 to A4 are located at the center of the plating layer thickness t (µm), and are circumferentially shifted by 90 degrees. In the four hardness measurement regions A1 to A4, the arithmetic mean value of the Vickers hardness is 100 to 150 HV.

[0046] If the arithmetic mean value of the Vickers hardness exceeds 150 HV, the hardness of the plating layer becomes excessively high even when the contents of each element in the plating layer are within the above ranges and the standard deviation of the Vickers hardness (described later) is 20.0 HV or less, which makes the plating layer prone to cracking during processing of the plated steel wire. On the other hand, if the arithmetic mean value of the Vickers hardness is less than 100 HV, the hardness of the plating layer is low even if the content of each element in the plating layer is within the above range and the standard deviation of the Vickers hardness (described later) is 20.0 HV or less. Therefore, the plating layer is easily scratched. If the hardness of the plating layer is low, the plating layer is easily worn. Wear of the plating layer reduces the coating weight of the plated steel wire. Scratches on the plating layer and reduced coating weight reduce the corrosion resistance of the plated steel wire. Therefore, the arithmetic mean value of the Vickers hardness is 100 to 150 HV.

[0047] The upper limit of the arithmetic mean value of the Vickers hardness is preferably 145 HV, more preferably 140 HV, and even more preferably 135 HV. The lower limit of the arithmetic mean value of the Vickers hardness is preferably 105 HV, more preferably 110 HV, and even more preferably 115 HV.

[0048] [About variation in plating layer hardness] In the plated steel wire of this embodiment, not only is the arithmetic mean value of the Vickers hardness of the plating layer set to 100 to 150 HV, but the circumferential hardness variation of the plating layer is also sufficiently suppressed. Specifically, in the plated steel wire of this embodiment, in a cross section perpendicular to the axial direction of the plated steel wire, the standard deviation of the Vickers hardness at four hardness measurement areas A1 to A4 at the thickness center of the plating layer and shifted by 90 degrees in the circumferential direction is 20.0 HV or less.

[0049] If the standard deviation of the Vickers hardness exceeds 20.0 HV, the variation in hardness in the circumferential direction of the plating layer is not sufficiently suppressed, even if the content of each element in the plating layer is within the above range and the arithmetic mean value of the Vickers hardness is 100 to 150 HV. In this case, the degree of deformation when the same load is applied differs between the high-hardness region and the low-hardness region. Therefore, localized strain is likely to occur during processing. The localized strain promotes the occurrence of cracks in the plating layer during processing. Therefore, if the variation in hardness in the circumferential direction of the plating layer is large, cracks are likely to occur during processing. Therefore, the standard deviation of the Vickers hardness is 20.0 HV or less.

[0050] The upper limit of the standard deviation of the Vickers hardness is preferably 18.0 HV, more preferably 15.0 HV, and even more preferably 13.0 HV. The standard deviation of the Vickers hardness is preferably as small as possible. However, excessive reduction in the standard deviation of the Vickers hardness increases production costs. Therefore, in consideration of normal industrial production, the lower limit of the standard deviation of the Vickers hardness is preferably greater than 0 HV, more preferably 1.0 HV, and even more preferably 5.0 HV.

[0051] [Vickers hardness measurement method] The arithmetic mean value of the Vickers hardness and the standard deviation of the Vickers hardness can be measured by the following method. The Vickers hardness is measured in a total of four hardness measurement areas, including one each of the hardness measurement areas A1 to A4. A Vickers hardness test in accordance with JIS Z 2244 (2009) is performed in the hardness measurement areas A1 to A4. JIS Z 2244 (2009) specifies that the distance from the center of the indentation where hardness is measured to the edge of the sample (test piece) must be 2.5d or more relative to the average diagonal length d of the indentation. However, in the plated steel wire of this embodiment, the thickness of the plating layer is relatively thin, and the distance from the center of the indentation where hardness is measured to the edge of the sample (test piece) may be less than 2.5d. Even if the distance from the center of the indentation where hardness is measured to the edge of the sample (test piece) is less than 2.5d, the Vickers hardness test shall be carried out in the same way as when the distance from the center of the indentation where hardness is measured to the edge of the sample (test piece) is 2.5d or more. The test force shall be 0.1N (10gf).

[0052] The Vickers hardness test is performed three times for each hardness measurement area. In other words, a total of 12 Vickers hardness tests are performed. The arithmetic mean value of the obtained 12 Vickers hardness measurements is defined as the arithmetic mean value of the Vickers hardness in the hardness measurement areas A1 to A4. The unbiased standard deviation of the obtained 12 Vickers hardness measurements is defined as the standard deviation of the Vickers hardness in the hardness measurement areas A1 to A4.

[0053] [Method of manufacturing plated steel wire] An example of a method for manufacturing the plated steel wire of this embodiment will be described below. The method for manufacturing the plated steel wire described below is one example for manufacturing the plated steel wire of this embodiment. Therefore, the plated steel wire having the above-described configuration may be manufactured by a manufacturing method other than the manufacturing method described below.

[0054] Fig. 3 is a flow chart showing an example of a manufacturing process of a plated steel wire according to this embodiment. Referring to Fig. 3, this example of a manufacturing method of a plated steel wire according to this embodiment includes a step of preparing a steel wire (steel wire preparation step: S1), a step of performing a zinc plating process on the steel wire as a pretreatment for hot-dip zinc alloy plating (primary plating process step: S2), and a step of performing a hot-dip zinc alloy plating process on the steel wire after the primary plating process (hot-dip zinc alloy plating process step: S3).

[0055] [Steel wire preparation process (S1)] In the steel wire preparation step, a steel wire is prepared by a well-known method. The manufacturer of the plated steel wire of this embodiment may prepare the steel wire by receiving steel wire from a third party. Alternatively, the manufacturer may manufacture and prepare the steel wire. When manufacturing the steel wire, the manufacturing method of the steel wire is not particularly limited, but includes a step of drawing a wire rod to a desired wire diameter (wiredrawing step: S11) and a step of performing heat treatment on the steel wire after the wiredrawing step, as necessary (heat treatment step: S12).

[0056] The wire rod used in the wire drawing process is prepared by a known method. The manufacturer of the plated steel wire of this embodiment may prepare the wire rod by receiving the wire rod from a third party. Alternatively, the manufacturer may manufacture the wire rod. When manufacturing the wire rod, the manufacturing method of the wire rod is not particularly limited, but molten steel having a known chemical composition is manufactured by a known refining method. The manufactured molten steel is used to manufacture a material (bloom, ingot, or billet). The manufactured material is hot-rolled to manufacture the wire rod.

[0057] [Wire drawing process (S11)] In the wire drawing process, the wire is drawn by a known method. The method of wire drawing is not particularly limited, but the hot-rolled wire is subjected to pickling or a mechanical method to remove scale adhering to the surface of the wire. Thereafter, the wire is drawn to a desired wire diameter, thereby producing a steel wire.

[0058] [Heat treatment process (S12)] The heat treatment step is an optional step. The heat treatment step is performed depending on the mechanical properties required for the plated steel wire. The heat treatment step may or may not be performed. When the heat treatment step is performed, the steel wire after the wire drawing step is subjected to annealing treatment by a well-known method. A steel wire can be obtained by the above method.

[0059] [Primary plating process (S2)] In the primary plating process step (S2), the steel wire prepared in the steel wire preparation process (S1) is plated with zinc to produce a steel wire to be subjected to the hot-dip zinc alloy plating process described below. By performing the zinc plating process in the primary plating process step, the plating layer 10 can be efficiently formed in the hot-dip zinc alloy plating process step (S3) described below. The primary plating process step is performed by a known method.

[0060] In the primary plating process, the steel wire may be subjected to pickling and / or flux treatment before the galvanizing treatment. When the steel wire is subjected to pickling and / or flux treatment before the galvanizing treatment, the method of pickling and flux treatment is not particularly limited. If pickling and flux treatment are performed before the galvanizing treatment, the adhesion of the galvanized coating to the steel wire can be improved.

[0061] The method of galvanizing in the primary plating step is not particularly limited. The galvanizing may be, for example, hot-dip galvanizing or electrogalvanizing. Hot-dip galvanizing or electrogalvanizing may be carried out by a well-known method.

[0062] When hot-dip galvanizing is performed as the galvanizing treatment, the steel wire after the galvanizing treatment is cooled. The cooling method is not particularly limited. For example, the cooling method may be water cooling, air blast cooling, or air-water cooling.

[0063] The steel wire to be subjected to the hot-dip zinc alloy plating treatment can be manufactured by the above-described method. In addition, the manufacturer of the plated steel wire of this embodiment may receive a supply of the steel wire to be subjected to the hot-dip zinc alloy plating treatment from a third party and prepare the steel wire to be subjected to the hot-dip zinc alloy plating treatment.

[0064] [Hot-dip zinc alloy plating process (S3)] In the hot-dip zinc alloy plating process (S3), the steel wire to be subjected to the hot-dip zinc alloy plating process after the primary plating process (S2) is subjected to the hot-dip zinc alloy plating process, whereby the plating layer of the present embodiment is formed on the surface of the steel wire to be subjected to the hot-dip zinc alloy plating process after the primary plating process (S2).

[0065] FIG. 4 is a schematic diagram of an apparatus used for hot-dip zinc alloy plating (hot-dip zinc alloy plating processing apparatus) and an apparatus used for cooling (cooling apparatus 50). Referring to FIG. 4, a hot-dip zinc alloy plating bath 20 is filled with a hot-dip zinc alloy plating bath 21. The hot-dip zinc alloy plating bath 20 is equipped with a sinker roll 30. A steel wire 2 to be subjected to the hot-dip zinc alloy plating process is immersed in the hot-dip zinc alloy plating bath 21 and drawn upward along the sinker roll 30. The plated steel wire 1 drawn upward after hot-dip zinc alloy plating passes through an air breaker 40 and is cooled in a cooling apparatus 50. The air breaker 40 is preferably filled with an inert gas. After cooling, the plated steel wire 1 advances along a pull-up roll 60 and is wound into a ring shape.

[0066] The hot-dip zinc alloy plating process includes, for example, a step of performing pretreatment on the steel wire as necessary (pretreatment step: S31), a step of immersing the steel wire in a hot-dip zinc alloy plating bath (immersion step: S32), and a step of withdrawing the steel wire from the hot-dip zinc alloy plating bath and cooling it (cooling step: S33).

[0067] [Pretreatment process (S31)] The pretreatment step is an optional step. The pretreatment step may or may not be performed. When the pretreatment step is performed, for example, pickling and / or flux treatment may be performed on the steel wire to be subjected to the hot-dip zinc alloy plating treatment. When the pretreatment step is performed, the method of pickling and flux treatment performed in the pretreatment step is not particularly limited. If the pretreatment step is performed, the plating layer 10 can be formed more efficiently in the immersion step (S32) and cooling step (S33) described below.

[0068] [Soaking process (S32)] In the immersion step, if a pretreatment step is performed, the steel wire after the first plating treatment step (S2) is pretreated and then immersed in a hot-dip zinc alloy plating bath 21. If a pretreatment step is not performed, the steel wire after the first plating treatment step (S2) is immersed in a hot-dip zinc alloy plating bath 21.

[0069] The chemical composition of the hot-dip zinc alloy coating bath 21 is the same as that of the coating layer of the coated steel wire of this embodiment. Specifically, the chemical composition of the hot-dip zinc alloy coating bath 21 is, in mass %, Al: 0.5 to 15.0%, Mg: 0.3 to 5.0%, Pb: 0 to 0.50%, Bi: 0 to 0.50%, Sr: 0 to 0.50%, V: 0 to 0.50%, Cr: 0 to 0.50%, Mn: 0 to 0.50%, Sn: 0 to 0.50%, Si: 0 to 0.50%, Ti: 0 to 0.50%, and Be: 0 to 0.50%. The zinc alloy coating material contains 0.50%, Na: 0-0.50%, K: 0-0.50%, Ca: 0-0.50%, Cu: 0-0.50%, La: 0-0.50%, Ce: 0-0.50%, Hf: 0-0.50%, Mo: 0-0.50%, W: 0-0.50%, Nb: 0-0.50%, Ta: 0-0.50%, and Fe: 0-2.00%, with the balance being Zn and impurities. The temperature of the zinc alloy coating bath 21 in the zinc alloy coating bath 20 and the immersion time in the zinc alloy coating bath 21 are not particularly limited. The temperature of the zinc alloy coating bath 21 in the zinc alloy coating bath 20 may be, for example, 400-500°C. The immersion time in the zinc alloy coating bath 21 may be, for example, 3-60 seconds.

[0070] [Cooling process (S33)] In the cooling step, the plated steel wire 1 is drawn out from the hot-dip zinc alloy plating bath 21 and cooled. In the cooling step, it is preferable to minimize the variation in the cooling rate in the circumferential direction of the plated steel wire and to cool the plated steel wire to a sufficiently low temperature. Preferred conditions for minimizing the variation in the cooling rate and cooling the plated steel wire to a sufficiently low temperature are, for example, as follows. Number of cooling nozzles N (pieces) provided in the cooling device: multiple Tension applied to plated steel wire TN (N): Tensile strength of plated steel wire TS (MPa) × Cross-sectional area of ​​plated steel wire S (mm 2 ) 20-50% Fn defined by the following formula (1): 4.00 or more Fn=TN / (TS×PS)×100 (1) Here, TN in equation (1) is the tension (N) applied to the plated steel wire when it is pulled up from the plating bath, TS is the tensile strength (MPa) of the plated steel wire, and PS is the pulling speed (m / min) of the plated steel wire when it is cooled. Cooling stop temperature T (℃): 200℃ or less Average cooling rate when the surface temperature of the plated steel wire is 350-200°C: 12°C / s or more

[0071] [Number of cooling nozzles N provided in the cooling device] FIG. 5 is a schematic diagram of the cooling device 50 shown in FIG. 4. The cooling device 50 is equipped with multiple cooling nozzles 51. When the cooling device 50 is equipped with multiple cooling nozzles 51, it is possible to cool the plated steel wire to a sufficiently low temperature. Therefore, after cooling is stopped, the temperature rise due to heat recovery from the steel wire is reduced. Therefore, changes in plating hardness due to heat recovery are suppressed. When the cooling device 50 is equipped with multiple cooling nozzles 51, it is further possible to sufficiently suppress variations in the cooling rate of the surface in the circumferential direction of the plated steel wire. As a result, variations in hardness in the circumferential direction of the plated steel wire are sufficiently suppressed. In other words, the standard deviation of Vickers hardness in the hardness measurement regions A1 to A4 is 20.0 HV or less.

[0072] The number of cooling nozzles 51 provided in the circumferential direction of the plated steel wire 1, i.e., in the circumferential direction of the cooling device 50, may be two or more. When the number of cooling nozzles 51 provided in the circumferential direction of the cooling device 50 is two or more, the cooling nozzles 51 may be arranged at intervals of 60 to less than 180 degrees around the center of a cross section (transverse section) perpendicular to the longitudinal direction of the cooling device 50. When the cooling nozzles 51 are arranged at intervals of 60 to less than 180 degrees around the center of the transverse section, interference between the cooling media 52 sprayed from the cooling nozzles 51 is suppressed, allowing for more efficient cooling. As a result, variations in hardness in the circumferential direction of the plated steel wire are sufficiently suppressed.

[0073] The direction parallel to the longitudinal direction of the cooling device 50 is defined as the height direction of the cooling device 50. The cooling device 50 may be provided with, for example, two or more stages of cooling nozzles 51 in the height direction of the cooling device 50. When two or more stages of cooling nozzles 51 are provided in the height direction of the cooling device 50, cooling can be performed more efficiently. As a result, variation in hardness in the circumferential direction of the plated steel wire is sufficiently suppressed. The cooling medium sprayed from the cooling nozzle is not particularly limited, and may be, for example, water, air jet, or air-water mixture.

[0074] [Tension TN applied to plated steel wire] In the cooling process, the tension TN (N) applied to the plated steel wire is calculated by multiplying the tensile strength TS (MPa) of the plated steel wire by the cross-sectional area S (mm 2) is 20 to 50% of the tension applied to the plated steel wire 1 when the plated steel wire 1 passes through the cooling device 50. Referring to FIG. 5, the cooling device 50 is usually installed on the assumption that the line along which the plated steel wire 1 passes (the pass line) passes through the center of the cooling device 50. Referring to FIG. 5, the plated steel wire 1 passes near the center of the cooling device 50. Therefore, the plated steel wire 1 and the pass line are almost aligned. Therefore, there is little variation in the distance between each cooling nozzle 51 and the plated steel wire 1. In this case, it is possible to sufficiently suppress variation in the amount of contact between the cooling medium 52 sprayed from each cooling nozzle 51 and the plated steel wire 1. Therefore, it is possible to sufficiently suppress variation in the cooling rate in the circumferential direction of the plated steel wire. Therefore, it is possible to sufficiently suppress variation in the hardness in the circumferential direction of the plated steel wire.

[0075] FIG. 6 is a schematic diagram of the cooling device 50 shown in FIG. 4 when the passing position of the plated steel wire 1 deviates from the pass line 3 when the plated steel wire 1 passes through the cooling device 50. Referring to FIG. 6, the passing position of the plated steel wire 1 is away from the center of the cooling device 50. In other words, the passing position of the plated steel wire 1 is deviated from the pass line 3. Therefore, the distance between each cooling nozzle 51 and the plated steel wire 1 is likely to vary. In this case, the variation in the amount of contact between the cooling medium 52 sprayed from each cooling nozzle 51 and the plated steel wire 1 cannot be sufficiently suppressed. Therefore, the variation in the cooling rate of the plated steel wire in the circumferential direction cannot be sufficiently suppressed. Therefore, the variation in the hardness of the plated steel wire in the circumferential direction cannot be sufficiently suppressed. Therefore, if the passing position of the plated steel wire 1 can be controlled to be as close to the center of the cooling device 50 as possible, the variation in the hardness of the plated steel wire in the circumferential direction can be sufficiently suppressed.

[0076] The tension applied to the plated steel wire (TN (N)) is calculated by multiplying the tensile strength (TS) of the plated steel wire (MPa) by the cross-sectional area (S) of the plated steel wire (mm 2), assuming that other manufacturing conditions are satisfied, the passing position of the plated steel wire 1 approaches the center of the cooling device 50. In other words, as shown in FIG. 5, the passing position of the plated steel wire 1 is near the center of the cooling device 50 and almost coincides with the pass line. Therefore, the variation in hardness in the circumferential direction of the plated steel wire can be sufficiently suppressed. In other words, the standard deviation of the Vickers hardness in the hardness measurement areas A1 to A4 becomes 20.0 HV or less. The tension TN (N) applied to the plated steel wire is calculated by multiplying the tensile strength TS (MPa) of the plated steel wire by the cross-sectional area S (mm 2 ), deformation of the plated steel wire due to tension can be suppressed. Therefore, change in the wire diameter of the plated steel wire can be suppressed. In this case, the yield will decrease. Therefore, the tension TN (N) applied to the plated steel wire is calculated by multiplying the tensile strength TS (MPa) of the plated steel wire by the cross-sectional area S (mm 2 ) is 20-50%.

[0077] The preferable lower limit of the tension TN (N) applied to the plated steel wire is the tensile strength TS (MPa) of the plated steel wire × the cross-sectional area S (mm 2 ), and more preferably, the tensile strength of the plated steel wire TS (MPa) × the cross-sectional area of ​​the plated steel wire S (mm 2 The preferred upper limit of the tension TN (N) applied to the plated steel wire is the product of the tensile strength TS (MPa) of the plated steel wire and the cross-sectional area S (mm 2 ), and more preferably, the tensile strength of the plated steel wire TS (MPa) × the cross-sectional area of ​​the plated steel wire S (mm 2 ) is 40%.

[0078] The tension TN (N) applied to the plated steel wire can be measured using a commercially available tension meter. The tension of the plated steel wire 1 at the outlet side of the cooling device 50 measured using a commercially available tension meter is defined as the tension applied to the plated steel wire. The tensile strength TS (MPa) of the plated steel wire can be measured by conducting a tensile test on the plated steel wire in accordance with JIS Z 2241 (2011).

[0079] [Regarding formula (1)] Furthermore, in the cooling step, Fn defined by the following formula (1) is set to 4.00 or more. Fn=TN / (TS×PS)×100 (1) Here, TN in equation (1) is the tension (N) applied to the plated steel wire when it is pulled up from the plating bath, TS is the tensile strength (MPa) of the plated steel wire, and PS is the pulling speed (m / min) of the plated steel wire when it is cooled.

[0080] The tension TN (N) applied to the plated steel wire is calculated by multiplying the tensile strength TS (MPa) of the plated steel wire by the cross-sectional area S (mm 2 ), the passing position of the plated steel wire 1 coincides with the pass line to some extent. However, if the tension TN (N) applied to the plated steel wire is greater than the tensile strength TS (MPa) of the plated steel wire x the cross-sectional area S (mm 2 ), the passing position of the plated steel wire 1 may deviate from the pass line depending on the pulling speed PS (m / min) of the plated steel wire during cooling and the tensile strength TS (MPa) of the plated steel wire. As a result, the cooling state of the plated steel wire 1 may vary greatly in the circumferential direction.

[0081] Specifically, if the pulling-up speed of the plated steel wire during cooling is high, the plated steel wire is more likely to vibrate during cooling. As a result, the passing position of the plated steel wire during cooling is more likely to deviate from the pass line. If the pulling-up speed of the plated steel wire during cooling is high, the cooling time of the plated steel wire is further shortened. As a result, if the passing position of the plated steel wire during cooling deviates from the pass line, the circumferential cooling state of the plated steel wire is likely to vary greatly. Furthermore, if the tensile strength of the plated steel wire is high, the plated steel wire is more likely to bend during cooling. As a result, the passing position of the plated steel wire during cooling is more likely to deviate from the pass line.

[0082] Therefore, it is preferable to appropriately control the balance between the tension TN (N) applied to the plated steel wire, the pulling speed PS (m / min) of the plated steel wire during cooling, and the tensile strength TS (MPa) of the plated steel wire. Specifically, when Fn defined by the above formula (1) is 4.00 or more, the variation in hardness in the circumferential direction of the plated steel wire is sufficiently suppressed.

[0083] The lower limit of Fn is preferably 4.50, more preferably 5.00, and even more preferably 5.50. The upper limit of Fn is not particularly limited, but is preferably 15.00, more preferably 12.00, and even more preferably 10.00. The numerical value of Fn is a value obtained by rounding off to two decimal places.

[0084] [About the cooling stop temperature T] In the cooling process, after the plated steel wire 1 is drawn out of the hot-dip zinc alloy coating bath 21, cooling is performed until the surface temperature of the plated steel wire reaches 200°C or below. That is, in the cooling process, the cooling stop temperature T is 200°C or below. Here, the cooling stop temperature T refers to the surface temperature of the plated steel wire at the outlet side of the cooling device 50. If the cooling stop temperature T is 200°C or below, the temperature of the plated steel wire is sufficiently low. Therefore, after cooling is stopped, heat recovery from the steel wire to the coating layer is sufficiently suppressed, and therefore, changes in the hardness of the coating layer due to heat recovery are sufficiently suppressed. As a result, the circumferential hardness variation of the plated steel wire is sufficiently suppressed. That is, the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 is 20.0 HV or below. Therefore, the cooling stop temperature T is 200°C or below.

[0085] The upper limit of the cooling stop temperature T is preferably 170°C, more preferably 150°C. The lower limit of the cooling stop temperature T is not particularly limited, but it is preferable that it is as low as possible. However, excessive reduction of the cooling stop temperature T increases production costs. Therefore, considering normal industrial production, the lower limit of the cooling stop temperature T is preferably room temperature. When the cooling medium is an air blast, the lower limit of the cooling stop temperature T is preferably 50°C, more preferably 100°C. The cooling start temperature is not particularly limited, but may be, for example, at least 350°C below the melting point of the molten zinc alloy in the hot-dip zinc alloy plating bath.

[0086] [Average cooling rate between 350 and 200°C] In the cooling process, the average cooling rate is controlled to 12°C / s or more when the surface temperature of the plated steel wire is between 350°C and 200°C. The temperature range of 350°C to 200°C is where the transformation of the zinc alloy plating is completed near the completion of solidification of the zinc alloy plating, and where changes in the plating structure become small. As the zinc alloy plating solidifies and cooling progresses, the microstructure of the plating layer is determined. Therefore, if the average cooling rate is 12°C / s or more when the surface temperature of the plated steel wire is between 350°C and 200°C, the circumferential hardness variation of the plated steel wire can be sufficiently suppressed. In other words, the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 is 20.0 HV or less. Therefore, the average cooling rate is 12°C / s or more when the surface temperature of the plated steel wire is between 350°C and 200°C.

[0087] When the surface temperature of the plated steel wire is 350°C to 200°C, the lower limit of the average cooling rate is preferably 15°C / s, and more preferably 20°C / s. When the surface temperature of the plated steel wire is 350°C to 200°C, the upper limit of the average cooling rate is not particularly limited. The upper limit of the average cooling rate is, for example, 1500°C / s. After the cooling step, the plated steel wire is wound into a ring shape.

[0088] The plated steel wire according to this embodiment is manufactured by the above manufacturing process. The plated steel wire manufactured by the above manufacturing process has an arithmetic mean value of Vickers hardness in the hardness measurement regions A1 to A4 of 100 to 150 HV, and a standard deviation of Vickers hardness in the hardness measurement regions A1 to A4 of 20.0 HV or less. Therefore, the plated steel wire according to this embodiment can suppress cracks in the plating layer during processing. [Example]

[0089] The effects of the plated steel wire of this embodiment will be described more specifically with reference to examples. The conditions in the following examples are examples adopted to confirm the feasibility and effects of the plated steel wire of this embodiment. Therefore, the plated steel wire of this embodiment is not limited to these examples.

[0090] A steel wire having the chemical composition of mild steel wire specified in JIS G3505 (2017) was used. Molten steel having the chemical composition specified in JIS G3505 (2017) was produced by a well-known refining method. A billet was produced using the produced molten steel. The produced billet was hot-rolled to produce a wire rod with a wire diameter of 5.5 mm. The produced wire rod was subjected to scale removal by pickling. The pickled wire rod was subjected to lime coating treatment and then wiredrawing. After wiredrawing, annealing was performed to obtain a steel wire with a wire diameter of 2.0 mm.

[0091] The steel wire after the annealing treatment was subjected to pickling and flux treatment by a known method. The steel wire after the flux treatment was subjected to hot-dip galvanizing treatment by a known method. After the hot-dip galvanizing treatment, water cooling was performed. The steel wire after the water cooling was subjected to flux treatment again by a known method.

[0092] After the flux treatment, the steel sheet was immersed in a hot-dip zinc alloy plating bath having the chemical composition shown in Table 1. The temperature of the hot-dip zinc alloy plating bath in the hot-dip zinc alloy plating bath was 440 to 470° C. The immersion time in the hot-dip zinc alloy plating bath was 10 to 30 seconds.

[0093] [Table 1]

[0094] In Table 1, a "-" sign means that the content of the corresponding element is 0% in the number of digits specified in the embodiment. In other words, when the content of the corresponding element is rounded to the specified number of digits in the above-mentioned embodiment, it means that it is 0%. For example, the Bi content in this embodiment is specified as a numerical value to two decimal places. Therefore, in test number 1 in Table 1, when the measured Bi content is rounded to two decimal places, it means that it was 0%. Note that rounding means that if the digit (fraction) to the right of the specified digit is less than 5, it is rounded down, and if it is 5 or more, it is rounded up. The remainder other than the elements listed in Table 1 was Zn and impurities.

[0095] The plated steel wire was withdrawn from the hot-dip zinc alloy plating bath and cooled. The number of cooling nozzles N (pieces) provided in the cooling device, the pulling speed PS (m / min) of the plated steel wire during cooling, the tensile strength TS (MPa) of the plated steel wire, the tension TN (N) applied to the plated steel wire, the Fn value, the cooling stop temperature T (°C), and the average cooling rate (°C / s) when the surface temperature of the plated steel wire was 350 to 200°C were as shown in Table 2. The tension TN (N) applied to the plated steel wire was measured using a commercially available tension meter. The tensile strength TS (MPa) of the plated steel wire was measured by a tensile test in accordance with JIS Z 2241 (2011). The length of the test specimen used in the tensile test was 400 mm. The pulling speed in the tensile test was 20 mm / min.

[0096] When the cooling device had multiple cooling nozzles, the nozzles were installed at intervals of 60 to less than 180 degrees around the center of the cross section (transverse section) perpendicular to the longitudinal direction of the cooling device. When the cooling device had multiple cooling nozzles, the number of cooling nozzles in the height direction of the cooling device was 2 to 7. The cooling medium sprayed from the cooling nozzles was water, air blast, or air-water mixture. After the cooling process, the plated steel wire was wound into a ring shape.

[0097] [Table 2]

[0098] [Evaluation test] The arithmetic mean value and standard deviation of the Vickers hardness were determined for the plated steel wires of test numbers 1 to 34. Furthermore, the plated steel wires of test numbers 1 to 34 were subjected to a workability evaluation test and a corrosion resistance evaluation test.

[0099] [Arithmetic mean value and standard deviation of Vickers hardness] The arithmetic mean value and standard deviation of the Vickers hardness of the plated steel wire of each test number were measured using the following method. The Vickers hardness measurements were carried out in a total of four hardness measurement areas, including one each of the hardness measurement areas A1 to A4. The Vickers hardness test conforming to JIS Z 2244 (2009) was carried out in the hardness measurement areas A1 to A4. The test force was 0.1 N (10 gf).

[0100] The Vickers hardness test was performed three times for each hardness measurement region. In other words, a total of 12 Vickers hardness tests were performed. The arithmetic mean of the obtained 12 Vickers hardness measurements was defined as the arithmetic mean of the Vickers hardness in the hardness measurement regions A1 to A4. The unbiased standard deviation of the obtained 12 Vickers hardness measurements was defined as the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4. The results of the arithmetic mean and standard deviation of the Vickers hardness are shown in the "Arithmetic mean (HV)" and "Standard deviation (HV)" columns of Table 2.

[0101] [Processability evaluation test] The plated steel wire of each test number was wrapped around a core material five times, and the presence or absence of cracks on the plated surface was examined. The diameter of the plated steel wire was 2.0 mm, and the diameter of the core material was three times that of the plated steel wire. The results of the workability evaluation test are shown in the "Workability Evaluation" column in Table 2. If no cracks were visually observed on the plated surface, it was determined that the occurrence of cracks in the plated layer had been sufficiently suppressed, and this was marked as "Good." If cracks were visually observed on the plated surface, it was determined that the occurrence of cracks in the plated layer had not been sufficiently suppressed, and this was marked as "Poor."

[0102] [Corrosion resistance evaluation test] The corrosion resistance evaluation test for each test number of plated steel wire was conducted in the following manner. A neutral salt spray cycle test was conducted on each test number of plated steel wire in accordance with JIS H 8052 (1999). The neutral salt spray cycle test was conducted under the conditions specified in JASO M609. Specifically, the conditions specified in JASO M609 are as follows: (1) Salt spray process: 35±1°C, 5% NaCl aqueous solution, 2 hours (2) Drying process: 60±1℃, 20~30%RH, 4 hours (3) Wetting process: 50±1℃, 95% RH or more, 2 hours (4) Repeat steps (1) to (3) 30 times.

[0103] After repeating the above steps (1) to (3) 30 times (after 30 cycles), the corrosion weight loss of the plated steel wire of each test number was measured. The results of the corrosion resistance evaluation test are shown in the "Corrosion Resistance Evaluation" column in Table 2. When the corrosion weight loss was 50 g / m 2 If the corrosion weight loss is less than 50g / m, the plated steel wire is judged to have high corrosion resistance and is rated as "Good." 2 In the above cases, the corrosion resistance of the plated steel wire was determined to be low, and the result was marked "X."

[0104] [Test Results] The test results are shown in Table 2. Referring to Table 2, test numbers 1 to 23 had appropriate chemical compositions for the plating layers, and the manufacturing processes were also appropriate. As a result, the arithmetic mean values ​​of the Vickers hardness in the hardness measurement regions A1 to A4 were 100 to 150 HV, and the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 was 20.0 HV or less. As a result, it was possible to sufficiently suppress the occurrence of cracks in the plating layer during processing.

[0105] Test No. 24 had an excessively low Al content, which resulted in poor corrosion resistance of the plated steel wire. Furthermore, cracks in the plated layer during processing could not be sufficiently prevented.

[0106] Test No. 25 had an excessively low Mg content, and therefore the arithmetic mean value of the Vickers hardness in the hardness measurement regions A1 to A4 was less than 100 HV, and the corrosion resistance of the plated steel wire was low.

[0107] Test No. 26 had an excessively high Mg content. As a result, the arithmetic mean value of the Vickers hardness in the hardness measurement areas A1 to A4 exceeded 150 HV. As a result, it was not possible to sufficiently prevent cracks from occurring in the plating layer during processing.

[0108] In test number 27, the number of cooling nozzles provided in the cooling device was too small. As a result, the standard deviation of the Vickers hardness in the hardness measurement areas A1 to A4 exceeded 20.0 HV. As a result, it was not possible to sufficiently suppress the occurrence of cracks in the plating layer during processing.

[0109] For test number 28, the number of cooling nozzles provided in the cooling device was too small. Furthermore, for test number 28, Fn was less than 4.00. Furthermore, for test number 28, the cooling stop temperature T was too high. As a result, the standard deviation of Vickers hardness in the hardness measurement regions A1 to A4 exceeded 20.0 HV. As a result, it was not possible to sufficiently suppress the occurrence of cracks in the plating layer during processing.

[0110] Test Nos. 29 and 34 are tests in which the tension applied to the plated steel wire is the tensile strength TS (MPa) of the plated steel wire x the cross-sectional area S (mm 2) was less than 20% of the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4. As a result, it was not possible to sufficiently suppress the occurrence of cracks in the plating layer during processing.

[0111] In test number 30, the cooling stop temperature T was too high. As a result, the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 exceeded 20.0 HV. As a result, it was not possible to sufficiently suppress the occurrence of cracks in the plating layer during processing.

[0112] For test number 31, the cooling stop temperature T was too high. Furthermore, for test number 31, the average cooling rate from 350 to 200°C was less than 12°C / s. As a result, the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 exceeded 20.0 HV. As a result, the occurrence of cracks in the plating layer during processing could not be sufficiently suppressed.

[0113] For test number 32, the average cooling rate from 350 to 200°C was less than 12°C / s. Therefore, the standard deviation of the Vickers hardness in the hardness measurement regions A1 to A4 exceeded 20.0 HV. As a result, the occurrence of cracks in the plating layer during processing could not be sufficiently suppressed.

[0114] For test number 33, Fn was less than 4.00. Therefore, the standard deviation of Vickers hardness in the hardness measurement regions A1 to A4 exceeded 20.0 HV. As a result, it was not possible to sufficiently suppress the occurrence of cracks in the plating layer during processing.

[0115] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure. [Explanation of symbols]

[0116] 1. Plated steel wire 2. Steel wire to be subjected to hot-dip zinc alloy plating treatment 3 Pass Line 10 plating layer 11 alloy layer 20 Hot dip zinc alloy plating bath 21 Hot-dip zinc alloy plating bath 30 Sinker Roll 40 Cut-off Cylinder 50 Cooling device 51 Cooling nozzle 52 Cooling medium 60 Pulling Roll 100 Steel Wire

Claims

1. A plated steel wire, Steel wire, a plating layer formed on the surface of the steel wire, The plating layer is In mass%, Al: 0.5 to 15.0%, and Mg: 0.3 to 5.0%; the balance being Zn and impurities; In a cross section perpendicular to the axial direction of the plated steel wire, the arithmetic mean value of Vickers hardness in four hardness measurement areas A1 to A4 at the thickness center of the plating layer, which are shifted by 90 degrees in the circumferential direction, is 100 to 150 HV; The standard deviation of the Vickers hardness in the hardness measurement areas A1 to A4 is 20.0 HV or less. Plated steel wire.

2. The plated steel wire according to claim 1, further comprising: The plating layer is In place of a part of the Zn, Pb: 0.50% or less, Bi: 0.50% or less, Sr: 0.50% or less, V: 0.50% or less, Cr: 0.50% or less, Mn: 0.50% or less, Sn: 0.50% or less, Si: 0.50% or less, Ti: 0.50% or less, Be: 0.50% or less, Na: 0.50% or less, K: 0.50% or less, Ca: 0.50% or less, Cu: 0.50% or less, La: 0.50% or less, Ce: 0.50% or less, Hf: 0.50% or less, Mo: 0.50% or less, W: 0.50% or less, Nb: 0.50% or less, Ta: 0.50% or less, and Fe: 2.00% or less, Contains one or more selected from the group consisting of Plated steel wire.

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