Plated steel wire

Abstract

To provide a plated steel wire having excellent workability and high corrosion resistance.SOLUTION: A coated steel wire according to the present disclosure includes a base steel wire and a coating layer formed on a surface of the base steel wire, wherein the chemical composition of the coating layer contains, by mass%, Al: 8.0 to 15.0% and Mg: 0.3 to 5.0%, with the balance being Zn and impurities, in a transverse cross section which is a cross section perpendicular to an axial direction of the plated steel wire, a microstructure of the plating layer includes an Al primary crystal phase containing Al and Zn and having a total area fraction of 10% to 60%, a Zn phase, and a Zn-Mg phase containing Zn and Mg, and contains a eutectic structure having a total area fraction of 10% to 70% and a Zn phase containing Zn and having a total area fraction of 0% to 50%, and in the Al primary crystal phase, a total area fraction of a high Al concentration region having an Al concentration of 13.0% or more in terms of mass% is 50% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to plated 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. In this specification, a steel wire having a plating layer formed on its surface is also referred to as a "plated steel wire."

[0003] The plating layer of a plated steel wire is required to have corrosion resistance. For example, zinc plating, zinc alloy plating, etc. 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. A plated steel wire having a zinc alloy plating layer has higher corrosion resistance than a plated steel wire 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, typically bending. In a plated steel wire having a crack in the zinc alloy plating layer, the corrosion resistance of the cracked portion is reduced. Therefore, a plated steel wire having a zinc alloy plating layer is required to have high formability that can suppress the occurrence of cracks in the plating layer during processing.

[0005] A technique for improving the workability and corrosion resistance of a plating layer is disclosed, for example, in International Publication No. 2019 / 124485 (Patent Document 1).

[0006] The plated steel wire disclosed in Patent Document 1 has a plating layer containing, in mass%, Mg: 0.10 to less than 1.00%, Al: 5.0 to 15.0%, Si: 0 to 2.0%, Fe: 0 to 1.0%, Sb: 0 to 1.0%, Pb: 0 to 1.0%, Sn: 0 to 1.0%, Ca: 0 to 1.0%, Co: 0 to 1.0%, Mo: 0 to 1.0%, Mn: 0 to 1.0%, P: 0 to 1.0%, B: 0 to 1.0%, Bi: 0 to 1.0%, Cr: 0 to 1.0%, REM: 0 to 1.0%, Ni: 0 to 1.0%, Ti: 0 to 1.0%, Zr: 0 to 1.0%, and Sr: 0 to 1.0%, with the remainder being Zn and impurities. In the microstructure of this coating layer, the Zn phase containing 90% or more Zn by mass accounts for 25 to 70% in area. Furthermore, the Zn phase, which has a circularly converted crystal grain size of 2 to 5 μm, accounts for 20 to 100% in area. In the coating layer of this coated steel wire, if the Zn phase containing 90% or more Zn accounts for 25 to 70% in area and the Zn phase has a crystal grain size of 2 to 5 μm, the workability of the coated steel wire is improved. Furthermore, even if a crack occurs along the grain boundary of the Zn phase, the crack does not penetrate the coating layer but remains fine. Patent Document 1 states that this results in improved corrosion resistance of the coated steel wire. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2019 / 124485 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the workability and corrosion resistance of the plated steel wire may be improved by other means different from the means proposed in Patent Document 1.

[0009] An object of the present disclosure is to provide a plated steel wire having excellent workability and high corrosion resistance. [Means for solving the problem]

[0010] The plated steel wire according to the present disclosure comprises: A base steel wire; a plating layer formed on the surface of the base steel wire, The chemical composition of the plating layer is, in mass%, Al: 8.0 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 microstructure of the plating layer is as follows: an Al primary phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure containing a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the eutectic structure having a total area ratio of 10 to 70%; and a Zn phase consisting of Zn and having a total area ratio of 0 to 50%, In the Al primary phase, the total area ratio of high Al concentration regions where the Al concentration is 13.0% or more by mass is 50% or less.

[0011] The plated steel wire according to the present disclosure comprises: A base steel wire; a plating layer formed on the surface of the base steel wire, The chemical composition of the plating layer is, in mass%, Al: 8.0-15.0%, Mg: 0.3 to 5.0%, and Contains one or more selected from the group consisting of Groups 1 to 3, the balance being Zn and impurities, In a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is as follows: an Al primary phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure containing a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the eutectic structure having a total area ratio of 10 to 70%; and a Zn phase consisting of Zn and having a total area ratio of 0 to 50%, In the Al primary phase, the total area ratio of high Al concentration regions where the Al concentration is 13.0% or more by mass is 50% or less. [Group 1] Si:0.50% or less [Group 2] Fe:2.00% or less [Group 3] Bi: 0.50% or less, Pb: 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, 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, Ni: 0.50% or less, B: 0.10% or less, and Co: 0.50% or less, one or more selected from the group consisting of [Effects of the Invention]

[0012] The plated steel wire of the present disclosure has excellent workability and high corrosion resistance. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a part of a portion near the surface layer including the plating layer in a cross section, which is a cross section perpendicular to the axial direction of a plated steel wire. [Figure 2] FIG. 2 is a schematic cross-sectional view of a plated steel wire different from that shown in FIG. [Figure 3]FIG. 3 is a schematic diagram of a cross section of a rectangular observation area divided into a plurality of minute square areas. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have investigated, from the perspective of chemical composition, the coating layer of a coated steel wire that has high formability capable of suppressing the occurrence of cracks in the coating layer during processing and high corrosion resistance. As a result, the chemical composition of the coating layer of a coated steel wire is, in mass%, Al: 8.0-15.0%, Mg: 0.3-5.0%, Si: 0-0.50%, Fe: 0-2.00%, Bi: 0-0.50%, Pb: 0-0.50%, Sr: 0-0.50%, V: 0-0.50%, Cr: 0-0.50%, Mn: 0-0.50%, Sn: 0-0.50%, Ti: 0-0.50%, Be: 0-0.50%, Na: 0-0.50%, and K: 0-0.50%. The present inventors considered that high workability and corrosion resistance can be obtained with a chemical composition containing 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%, Ni: 0-0.50%, B: 0-0.10%, and Co: 0-0.50%, with the balance being Zn and impurities.

[0015] However, even when the plating layer of a plated steel wire has the above-mentioned chemical composition, there are cases in which high workability and corrosion resistance cannot be obtained. Therefore, the present inventors conducted further studies.

[0016] The coating layer having the above-mentioned chemical composition contains an Al primary phase consisting of Al and Zn, a eutectic structure including a Zn phase and a Zn-Mg phase, and may further contain a Zn phase consisting of Zn. The present inventors considered that when the above-mentioned microstructure constituting the coating layer satisfies the following configuration, the coating layer can achieve both high workability and corrosion resistance.

[0017] (microstructure) In a cross section, which is a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the coating layer contains an Al primary phase consisting of Al and Zn and occupying a total area ratio of 10 to 60%, a Zn phase, a Zn-Mg phase consisting of Zn and Mg and occupying a total area ratio of 10 to 70%, and a Zn phase consisting of Zn and 0 to 50%.

[0018] When a plated steel wire has a plating layer having the above-described chemical composition and microstructure, the workability is improved and the occurrence of cracks in the plating layer is suppressed. However, even if the workability of the plating layer is improved, the corrosion resistance may be reduced. Therefore, the progress of corrosion when corrosion occurs in a plated steel wire having the above-described chemical composition and microstructure was investigated and studied.

[0019] First, the inventors observed the corrosion site of the coating layer using an optical microscope, and found that among the three microstructures (Al primary phase, eutectic structure, and Zn phase) that make up the coating layer, corrosion occurred preferentially in the Al primary phase.

[0020] Therefore, the present inventors conducted further investigation into the factors that cause corrosion of the Al primary crystal phase. As a result, it was found that the Al concentration is higher in regions of the Al primary crystal phase where corrosion has occurred compared to regions where corrosion has not occurred. Although the reason for this is not clear, based on the above investigation results, the present inventors hypothesized the reason why corrosion is promoted in regions of the Al primary crystal phase where the Al concentration is high as follows.

[0021] As mentioned above, the Al primary phase consists of Al and Zn. In areas where the Al concentration is high in the Al primary phase, the Al concentration is relatively high compared to the Zn concentration. In this case, contact between Al and Zn in the Al primary phase increases. Here, the natural potential of Al is lower than that of Zn. Therefore, if Al and Zn come into contact, galvanic corrosion may occur due to the difference in natural potential. If contact between Al and Zn increases, galvanic corrosion is more likely to occur. On the other hand, if the Al concentration in the Al primary phase is low, the Al concentration will be low relative to the Zn concentration. In this case, contact between Al and Zn decreases, thereby suppressing galvanic corrosion.

[0022] Based on the above findings, the present inventors believed that corrosion resistance could be improved by minimizing the number of regions with high Al concentration in the Al primary phase. Therefore, further investigations were conducted. As a result, it was discovered that corrosion resistance could be improved by reducing the total area ratio of regions with an Al concentration of 13.0% or more by mass (hereinafter referred to as high Al concentration regions) in the Al primary phase of a coating layer that satisfies the above-mentioned chemical composition and microstructure to 50% or less. The plated steel wire of this embodiment has been completed based on the above technical concept and has the following configuration.

[0023] The plated steel wire of the first configuration is A base steel wire; a plating layer formed on a surface of the base steel wire, The chemical composition of the plating layer is, in mass%, Al: 8.0 to 15.0%, and Mg: 0.3 to 5.0%; the balance being Zn and impurities, In a cross section that is a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is an Al primary phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure containing a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the eutectic structure having a total area ratio of 10 to 70%; and a Zn phase consisting of Zn and having a total area ratio of 0 to 50%, In the Al primary phase, the total area ratio of high Al concentration regions having an Al concentration of 13.0% or more by mass is 50% or less.

[0024] The second configuration of the plated steel wire is A base steel wire; a plating layer formed on a surface of the base steel wire, The chemical composition of the plating layer is, in mass%, Al: 8.0-15.0%, Mg: 0.3 to 5.0%, and Contains one or more selected from the group consisting of Groups 1 to 3, the balance being Zn and impurities, In a cross section that is a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is an Al primary phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure containing a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the eutectic structure having a total area ratio of 10 to 70%; and a Zn phase consisting of Zn and having a total area ratio of 0 to 50%, In the Al primary phase, the total area ratio of high Al concentration regions having an Al concentration of 13.0% or more by mass is 50% or less. [Group 1] Si:0.50% or less [Group 2] Fe:2.00% or less [Group 3] Bi: 0.50% or less, Pb: 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, 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, Ni: 0.50% or less, B: 0.10% or less, and Co: 0.50% or less, one or more selected from the group consisting of

[0025] The third configuration of plated steel wire is A plated steel wire of a second configuration, The chemical composition includes the first group.

[0026] The fourth configuration of plated steel wire is A plated steel wire having the second or third configuration, The chemical composition includes the second group.

[0027] The fifth configuration of plated steel wire is A plated steel wire having any of the second to fourth configurations, The chemical composition includes the third group.

[0028] The plated steel wire of this embodiment will be described in detail below. Note that "%" regarding elements means mass % unless otherwise specified.

[0029] [About plated steel wire 1] FIG. 1 is a cross-section of a plated steel wire perpendicular to its axial direction, and is a schematic diagram showing a portion of the cross-section near the surface layer including the plating layer. Referring to FIG. 1, a plated steel wire 1 of this embodiment includes a base steel wire 10 and a plating layer 20. The plating layer 20 is formed on the surface of the base steel wire 10. The plated steel wire 1 may include an alloy layer 30 between the base steel wire 10 and the plating layer 20. The plated steel wire 1 does not have to include the alloy layer 30. In other words, the alloy layer 30 has any configuration. The plating layer 20 includes an Al primary phase PC and a eutectic structure TE, and may further include a Zn phase SP.

[0030] [About base steel wire 10] The base steel wire 10 is a steel wire obtained by drawing a wire material at least once. The base steel wire 10 may or may not be annealed. The steel type of the base steel wire 10 is not particularly limited. The steel type of the base steel wire 10 may be selected appropriately depending on the mechanical properties (e.g., tensile strength, workability, etc.) required of the plated steel wire 1. The chemical composition of the base steel wire 10 is not particularly limited. The chemical composition of the base steel wire 10 is, for example, the chemical composition of a soft steel wire material specified in JIS G 3505:2017 or the chemical composition of a hard steel wire material specified in JIS G 3506:2017.

[0031] [Regarding plating layer 20] The plating layer 20 is formed on the surface of the base steel wire 10. Specifically, when an alloy layer 30 described later is not formed, the plating layer 20 is formed on the surface of the base steel wire 10. When an alloy layer 30 is formed, the plating layer 20 is formed on the alloy layer 30 formed on the surface of the base steel wire 10.

[0032] [Alloy layer 30] The alloy layer 30 does not have to be formed on the plated steel wire 1. In other words, the alloy layer 30 has any configuration. When the plated steel wire 1 includes the alloy layer 30, the alloy layer 30 is formed between the base steel wire 10 and the plating layer 20. The alloy layer 30 contains Zn, Al, and Fe. The alloy layer 30 is composed of an intermetallic compound mainly composed of Zn, Al, and Fe. The alloy layer 30 is a layer well known to those skilled in the art.

[0033] The plating layer 20 satisfies the following characteristics 1 to 3. (Feature 1) The chemical composition of the plating layer 20 of the plated steel wire 1 is, in mass %, Al: 8.0 to 15.0%, Mg: 0.3 to 5.0%, Si: 0 to 0.50%, Fe: 0 to 2.00%, Bi: 0 to 0.50%, Pb: 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%, Ti: 0 to 0.50%, Be: 0 to 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%, Ni: 0-0.50%, B: 0-0.10%, and Co: 0-0.50%, with the remainder being Zn and impurities. (Feature 2) In a cross section, which is a cross section perpendicular to the axial direction of the plated steel wire 1, the microstructure of the plating layer 20 contains an Al primary phase consisting of Al and Zn and occupying a total area ratio of 10 to 60%, a Zn phase, and a Zn-Mg phase consisting of Zn and Mg and occupying a total area ratio of 10 to 70%, and a Zn phase consisting of Zn and occupying a total area ratio of 0 to 50%. (Feature 3) In the Al primary phase, the total area ratio of high Al concentration regions where the Al concentration is 13.0% or more by mass is 50% or less.

[0034] Features 1 to 3 of the plating layer 20 will be described below.

[0035] [(Feature 1) Chemical composition of plating layer 20] The chemical composition of the plating layer 20 contains the following elements.

[0036] [Essential elements] Al: 8.0 to 15.0% Aluminum (Al) enhances the corrosion resistance of the plated steel wire 1 through sacrificial corrosion protection. Furthermore, Al suppresses the formation of Mg oxides in a plating bath containing Mg. If the Al content is less than 8.0%, 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 above-mentioned Al primary phase PC is excessively formed in the microstructure of the coating layer 20. In this case, even if the contents of other elements are within the ranges of this embodiment, the coating layer 20 becomes excessively hard. This reduces the workability of the coated steel wire 1. As a result, cracks are more likely to occur in the coating layer 20 during processing. Furthermore, if the Al content exceeds 15.0%, even if the contents of other elements are within the ranges of this embodiment, the melting point of the coating bath becomes high. In this case, the formation of oxides in the coating bath is promoted. This makes it necessary to remove the oxides during the manufacturing process, resulting in a decrease in production efficiency. Therefore, the Al content is 8.0 to 15.0%. The lower limit of the Al content is preferably 8.5%, more preferably 9.0%, and even more preferably 9.5%. The upper limit of the Al content is preferably less than 15.0%, more preferably 14.0%, even more preferably 13.5%, even more preferably 13.0%, and even more preferably 12.0%.

[0037] Mg: 0.3 to 5.0% Magnesium (Mg) sacrificially protects the plated steel wire 1, thereby increasing its corrosion resistance. If the Mg content is less than 0.3%, 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 Mg content exceeds 5.0%, the Zn-Mg phase, which is an intermetallic compound consisting of Zn and Mg, is excessively formed in the microstructure of the coating layer 20. In this case, even if the contents of other elements are within the ranges of this embodiment, the coating layer 20 becomes excessively hard. This reduces the workability of the coated steel wire 1. As a result, cracks are more likely to occur in the coating layer 20 during processing. Therefore, the Mg content is 0.3 to 5.0%. The lower limit of the Mg content is preferably 0.4%, more preferably 0.5%, and even more preferably 0.7%. The upper limit of the Mg content is preferably 4.0%, more preferably 3.5%, and even more preferably 3.0%.

[0038] The remainder of the chemical composition of the plating layer 20 is composed of Zn and impurities. Here, the term "impurities" refers to substances that are mixed in from raw materials or the manufacturing environment during industrial production of the plating layer 20, but are not intentionally contained and are allowed within a range that does not adversely affect the plating layer 20.

[0039] [Optional elements] The chemical composition of the plating layer 20 may further contain, in place of a portion of Zn, one or more elements selected from the group consisting of the following first to third groups. [Group 1] Si:0.50% or less [Group 2] Fe:2.00% or less [Group 3] Bi: 0.50% or less, Pb: 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, 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, Ni: 0.50% or less, B: 0.10% or less, and Co: 0.50% or less, one or more selected from the group consisting of Each group will be explained below.

[0040] [Group 1: Si] Si:0.50% or less Silicon (Si) is an optional element and may not be contained, that is, the Si content may be 0%. When Si is contained, Si bonds with Mg to form an Mg-Si phase. The Mg-Si phase enhances the corrosion resistance of the plated steel wire 1. The formation of the Mg-Si phase further suppresses the formation of an Fe-Al phase and suppresses the formation of a Zn-Mg phase. This improves the workability of the plated steel wire 1. As a result, the occurrence of cracks in the plating layer 20 during processing is suppressed. Even if even a small amount of Si is contained, the above effects can be obtained to some extent. However, if the Si content exceeds 0.50%, the Mg—Si phase becomes excessively coarse, which reduces the workability of the plated steel wire 1. As a result, cracks are more likely to occur in the plated layer 20 during processing. Therefore, the Si content is 0 to 0.50%, and when Si is contained, it is 0.50% or less (more than 0 to 0.50%). The lower limit of the Si content is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, and still more preferably 0.15%. The upper limit of the Si content is preferably 0.48%, more preferably 0.45%, and even more preferably 0.40%.

[0041] [Group 2: Fe] Fe:2.00% or less Iron (Fe) is an optional element and may not be contained, that is, the Fe content may be 0%. During the manufacturing process of the plated steel wire 1, Fe in the steel wire may combine with Zn to form an alloy layer 30. The alloy layer 30 improves the corrosion resistance of the plated steel wire 1. Even if only a small amount of Fe is contained, the above effect can be obtained to some extent. However, if the Fe content exceeds 2.00%, the alloy layer 30 is formed in excess, which reduces the workability of the plated steel wire 1. As a result, cracks are more likely to occur in the plated layer 20 during processing. Therefore, the Fe content is 0 to 2.00%, and when contained, it is 2.00% or less (more than 0 to 2.00%). The lower limit of the Fe content is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, and still 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%.

[0042] [Group 3: Regarding Bi, Pb, Sr, V, Cr, Mn, Sn, Ti, Be, Na, K, Ca, Cu, La, Ce, Hf, Mo, W, Nb, Ta, Ni, B and Co] Bismuth (Bi), lead (Pb), strontium (Sr), vanadium (V), chromium (Cr), manganese (Mn), tin (Sn), titanium (Ti), beryllium (Be), sodium (Na), potassium (K), calcium (Ca), copper (Cu), lanthanum (La), cerium (Ce), hafnium (Hf), molybdenum (Mo), tungsten (W), niobium (Nb), tantalum (Ta), nickel (Ni), boron (B), and cobalt (Co) are all optional elements and may not be contained. If contained, these elements further enhance the corrosion resistance of the plated steel wire 1. The above effect can be obtained to some extent if even a small amount of one or more of these elements is contained. However, if the content of each of the elements Bi, Pb, Sr, V, Cr, Mn, Sn, Ti, Be, Na, K, Ca, Cu, La, Ce, Hf, Mo, W, Nb, Ta, Ni, and Co exceeds 0.50%, or if the content of B exceeds 0.10%, the corrosion resistance of the plated steel wire 1 decreases. Furthermore, the formation of the Zn-Mg phase is suppressed, and the corrosion resistance of the plated steel wire 1 decreases. Therefore, the content of each of Bi, Pb, Sr, V, Cr, Mn, Sn, Ti, Be, Na, K, Ca, Cu, La, Ce, Hf, Mo, W, Nb, Ta, Ni, and Co is 0 to 0.50%, and the content of B is 0 to 0.10%. When contained, the content of each of Bi, Pb, Sr, V, Cr, Mn, Sn, Ti, Be, Na, K, Ca, Cu, La, Ce, Hf, Mo, W, Nb, Ta, Ni, and Co is 0.50% or less (more than 0 to 0.50%), and the content of B is 0.10% or less (more than 0 to 0.10%).

[0043] The lower limit of the content of each of the elements Bi, Pb, Sr, V, Cr, Mn, Sn, Ti, Be, Na, K, Ca, Cu, La, Ce, Hf, Mo, W, Nb, Ta, Ni, and Co is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%. The upper limit of each of the element contents of Bi, Pb, Sr, V, Cr, Mn, Sn, Ti, Be, Na, K, Ca, Cu, La, Ce, Hf, Mo, W, Nb, Ta, Ni, and Co is preferably 0.48%, more preferably 0.46%, even more preferably 0.45%, even more preferably 0.40%, even more preferably 0.30%, even more preferably 0.26%, even more preferably 0.24%, even more preferably 0.22%, even more preferably 0.20%, and even more preferably 0.16%. The lower limit of the B content is preferably 0.01%, more preferably 0.02%, and even more preferably 0.03%. The upper limit of the B content is preferably 0.09%, more preferably 0.08%, and even more preferably 0.07%.

[0044] [Method for analyzing the chemical composition of the plating layer 20] The chemical composition of the plating layer 20 is determined by the following method. In accordance with JIS H 0401:2021 "Test Method for Hot-Dip Galvanizing," the plated steel wire 1 is immersed in a hydrochloric acid solution to dissolve the plating layer 20, and a solution is obtained. The obtained solution is subjected to ICP (Inductively Coupled Plasma) emission spectroscopy, and elemental analysis of the chemical composition of the plating layer 20 is performed.

[0045] The content of each element is determined by rounding off the measured value to the nearest significant digit based on the significant digits specified in this embodiment. For example, the Al content of the plating layer 20 is determined to one decimal place. Therefore, the Al content is determined to one decimal place by rounding off the measured value to one decimal place.

[0046] Similarly, the content of other elements other than the Al content of the plating layer 20 is determined by rounding the measured value to the smallest digit specified in this embodiment.

[0047] Rounding off means rounding down if the fraction is less than 5, and rounding up if the fraction is 5 or more.

[0048] [(Feature 2) Microstructure of plating layer 20] Referring to FIG. 1, in a cross section that is a cross section perpendicular to the axial direction of the plated steel wire 1, the microstructure of the plating layer 20 includes a structure with the following total area ratio. (1) Primary Al phase PC: Total area ratio 10-60% (2) Eutectic structure TE: Total area ratio 10 to 70% (3) Zn phase SP: Total area ratio 0 to 50% As described above, the Zn phase SP is an optional structure, that is, the plating layer 20 may or may not contain a Zn phase.

[0049] [Al primary phase PC] The Al primary phase PC is composed of Al and Zn. The Al primary phase PC can be identified as an area that is less bright than the eutectic structure TE in a backscattered electron composition (COMPO) image. The gray area that is less bright than the eutectic structure TE corresponds to the Al primary phase PC. More specifically, the area that is less bright than the eutectic structure TE in a backscattered electron composition image and in which Al and Zn are detected in energy dispersive X-ray analysis (EDS) is defined as the Al primary phase PC.

[0050] [About eutectic structure TE] The eutectic structure TE includes a Zn phase that is brighter than the Al primary crystalline phase PC, and a Zn-Mg phase that is brighter than the Al primary crystalline phase PC but is brighter than the Zn phase. The eutectic structure TE includes a Zn phase and a Zn-Mg phase, and may further include an Al phase. The Al phase is a phase with a lower brightness than the Zn-Mg phase. When the eutectic structure TE includes an Al phase, the Zn phase and the Zn-Mg phase are present in greater amounts than the Al phase in the eutectic structure TE. The Al phase is a phase with finer grains than the Zn phase and the Zn-Mg phase.

[0051] The Zn phase in the eutectic structure TE is brighter than the Al primary phase PC and the Zn-Mg phase in a backscattered electron composition image, and can be easily distinguished by contrast. Furthermore, the Zn phase in the eutectic structure TE is a phase in which Zn is detected and almost no Mg is detected by EDS. The Zn-Mg phase in the eutectic structure TE is brighter than the Zn phase in a backscattered electron composition image, and is a phase in which Zn and Mg are detected by EDS.

[0052] [About Zn-phase SP] As described above, the Zn phase is an optional phase. In other words, the plating layer 20 may or may not contain a Zn phase SP. The Zn phase SP is made of Zn. The Zn phase SP can be identified as a region that is brighter than the Al primary crystalline phase PC and the eutectic structure TE in a backscattered electron composition image. Furthermore, because the Zn phase is a single phase, it does not have multiple phases mixed together in a layered or granular form, as in the eutectic structure TE. The Zn phase is brighter than the Al primary crystalline phase PC and the eutectic structure TE in a backscattered electron composition image, and is a phase in which Zn is detected and almost no other elements are detected in EDS.

[0053] [Total area ratio of Al primary phase PC] The total area ratio of the Al primary phase PC in the coating layer 20 affects the workability and corrosion resistance of the plated steel wire 1. If the total area ratio of the Al primary phase PC is less than 10%, the plated steel wire 1 does not have sufficient corrosion resistance. On the other hand, if the total area ratio of the Al primary phase PC exceeds 60%, the workability of the plated steel wire 1 decreases. As a result, cracks are more likely to occur in the coating layer 20 when the plated steel wire 1 is processed. Therefore, the total area ratio of the Al primary phase PC is 10 to 60%. The lower limit of the total area ratio of the Al primary crystal phase PC is preferably 15%, more preferably 19%, even more preferably 20%, even more preferably 22%, and even more preferably 25%. The upper limit of the total area ratio of the Al primary crystal phase PC is preferably 58%, more preferably 56%, and even more preferably 50%.

[0054] [Total area ratio of eutectic structure TE] The total area ratio of the eutectic structure TE in the plating layer 20 affects the workability and corrosion resistance of the plated steel wire 1. If the total area ratio of the eutectic structure TE is less than 10%, the crystallization amounts of the Zn phase and the Zn-Mg phase consisting of Zn and Mg in the eutectic structure TE are too small. As a result, the plated steel wire 1 does not have sufficient corrosion resistance. On the other hand, the eutectic structure TE is harder than the Al primary crystal phase PC. Therefore, if the total area ratio of the eutectic structure TE exceeds 70%, the workability of the plated steel wire 1 decreases. As a result, cracks are likely to occur in the plating layer 20 during processing of the plated steel wire 1. Therefore, the total area ratio of the eutectic structure TE is 10 to 70%. The lower limit of the total area ratio of the eutectic structure TE is preferably 12%, more preferably 15%, even more preferably 20%, and still more preferably 25%. The upper limit of the total area ratio of the eutectic structure TE is preferably 65%, more preferably 60%, even more preferably 55%, and still more preferably 50%.

[0055] [Total area ratio of Zn phase SP] As described above, the Zn phase SP is an optional structure and does not necessarily have to be formed. Depending on the chemical composition of the plating layer 20, the Zn phase may be generated. Specifically, when the Al content in the plating layer 20 is low, the Zn phase is generated. In the case of the chemical composition of the plating layer 20 of this embodiment, the total area ratio of the Zn phase SP is 0 to 50%. The lower limit of the total area ratio of the Zn phase SP is preferably 1%, more preferably 2%, and even more preferably 5%. The upper limit of the total area ratio of the Zn phase SP is preferably 45%, and more preferably 40%.

[0056] [Method for measuring the total area ratio of the Al primary phase PC, the total area ratio of the eutectic structure TE, and the total area ratio of the Zn phase SP] The total area ratio of the Al primary crystal phase PC, the eutectic structure TE, and the Zn phase SP in the plating layer 20 can be determined by the following method. A test piece is taken by cutting the plated steel wire 1 perpendicular to the axial direction of the plated steel wire 1. The cross section of the surface of the test piece that includes the plating layer 20 and is perpendicular to the axial direction of the plated steel wire 1 is defined as the observation surface. The observation surface is mirror-polished. On the mirror-polished observation surface, four observation fields that include the plating layer 20 are selected at 90° intervals around the central axis of the plated steel wire 1. Each observation field is observed at 1000x magnification using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS), and a backscattered electron composition image of each observation region that includes the plating layer 20 is generated. The area of ​​the observation field is 8000 μm 2 Let's say.

[0057] 1, the thickness direction of the plating layer 20 is defined as the T direction, and the direction perpendicular to the T direction is defined as the C direction.

[0058] In the cross section, a rectangular observation area AR is defined as follows: The rectangular observation area AR is composed of a pair of C-direction sides SC each having a length of 40 μm in the C direction and a pair of T-direction sides ST each having a length of 5N μm (N is a natural number) in the T direction.

[0059] The T-direction side ST is determined according to the thickness of the plating layer 20. FIG. 2 is a schematic diagram of a cross section of a plated steel wire 1 different from that in FIG. 1. In FIG. 2, the plating layer 20 is thinner than in FIG. 1. In this case, the T-direction side ST of the rectangular observation area AR is shorter than the T-direction side ST of the rectangular observation area AR in FIG. 1. The length of ST is adjusted, and the size of the rectangular observation area AR is determined, so that the pair of C-direction sides SC and the pair of T-direction sides ST of the rectangular observation area AR form a rectangular area of ​​the maximum size that is included in the plating layer 20.

[0060] After the size of the rectangular observation area AR is determined, the rectangular observation area AR is divided into a plurality of minute square areas, each measuring 5 μm x 5 μm. FIG. 3 is a schematic diagram of a cross section of the rectangular observation area AR divided into a plurality of minute square areas. Referring to FIG. 3, in the rectangular observation area AR, a plurality of line segments are arranged parallel to the C-direction side SC at a 5 μm pitch in the T direction. Furthermore, a plurality of line segments are arranged parallel to the T-direction side ST at a 5 μm pitch in the C direction. These line segments divide the rectangular observation area into a plurality of minute square areas SS, each having a 5 μm side in the T direction and a 5 μm side in the C direction.

[0061] The rectangular observation area AR (40 μm in the C direction, 5N μm in the T direction, where N is a natural number) is set in the plating layer 20 in the backscattered electron composition image obtained by the SEM observation described above. The rectangular observation areas AR are set in four observation fields on the observation surface.

[0062] In the backscattered electron composition images of each observation field, the base steel wire 10, the plating layer 20, and the alloy layer 30 have different contrasts. Therefore, a person skilled in the art would be able to distinguish between the base steel wire 10, the plating layer 20, and the alloy layer 30 based on the contrast of the backscattered electron composition images.

[0063] Furthermore, the Al primary crystalline phase PC, eutectic structure TE, and Zn phase SP of the plating layer 20 in each observation region contain different elements. Therefore, in the backscattered electron composition image, the Al primary crystalline phase PC, eutectic structure TE, and Zn phase SP can be clearly identified based on the contrast. The Al primary crystalline phase PC, eutectic structure TE, and Zn phase SP can also be identified by EDS point analysis. When EDS point analysis is performed, the electron beam current value is set to 70 to 80 nA, and the analysis time is set to 30 seconds. Using the above method, the Al primary crystalline phase PC, eutectic structure TE, and Zn phase SP are identified in the observation region. When EDS point analysis is performed, the point analysis is performed at the vertices of each small square region SS in the rectangular observation region AR.

[0064] The total area ratio of the Al primary phase PC, the eutectic structure TE, and the Zn phase SP identified by the above method is determined using the following intersection method.

[0065] The structure overlapping each vertex of the small square region SS in the rectangular observation region AR shown in Figure 3 is identified using a backscattered electron composition image as being either the Al primary phase PC, the eutectic structure TE, or the Zn phase SP. If different structures exist within a radius of 0.5 μm from the vertex, the vertex is determined to be the boundary between the different structures. For example, if the eutectic structure TE and the Zn phase SP exist within a radius of 0.5 μm from the vertex, the vertex is determined to be the boundary between the eutectic structure TE and the Zn phase SP.

[0066] If the vertex is within one structure, that structure is counted as 1. If the vertex is the boundary between n structures, each structure is counted as 1 / n (n is a natural number). For example, if the vertex is the boundary between the Al primary phase PC and the eutectic structure TE, the Al primary phase PC is counted as 0.5, and the eutectic structure TE is counted as 0.5. Similarly, if the vertex is the boundary between the Al primary phase PC and the Zn phase SP, the Al primary phase PC is counted as 0.5, and the Zn phase SP is counted as 0.5. If the vertex is located at the boundary between the eutectic structure TE and the Zn phase SP, the eutectic structure TE is counted as 0.5, and the Zn phase SP is counted as 0.5. If the vertex is the boundary between the Al primary phase PC, the eutectic structure TE, and the Zn phase SP, the Al primary phase PC is counted as 0.3, the eutectic structure TE is counted as 0.3, and the Zn phase SP is counted as 0.3. The ratio (%) of the total number of vertices overlapping with the Al primary phase PC to the total number of vertices of the minute square region SS in the rectangular observation region AR is defined as the area ratio (%) of the Al primary phase PC. Similarly, the ratio (%) of the total number of vertices overlapping with the eutectic structure TE to the total number of vertices of the minute square region SS is defined as the area ratio (%) of the eutectic structure TE. The ratio (%) of the total number of vertices overlapping with the Zn phase SP to the total number of vertices of the minute square region SS is defined as the area ratio (%) of the Zn phase SP.

[0067] The arithmetic mean value of the area ratios (%) of the Al primary phase PC obtained in the four observation regions is defined as the total area ratio (%) of the Al primary phase PC in the coating layer 20 of the coated steel wire 1. Similarly, the arithmetic mean value of the area ratios (%) of the eutectic structure TE obtained in the four observation regions is defined as the total area ratio (%) of the eutectic structure TE in the coating layer 20 of the coated steel wire 1. Similarly, the arithmetic mean value of the area ratios (%) of the Zn phase SP obtained in the four observation regions is defined as the total area ratio (%) of the Zn phase SP in the coating layer 20 of the coated steel wire 1. The total area ratio is an integer obtained by rounding the arithmetic mean value to one decimal place.

[0068] The microstructure in the plating layer 20 may contain structures other than the Al primary crystal phase PC, the eutectic structure TE, and the Zn phase SP. Examples of the other structures include a Zn-Mg phase, a reaction phase of Mg and an optional element (e.g., an Mg-Sn phase), and an Fe-Al alloy phase.

[0069] [(Feature 3) Total area ratio of high Al concentration regions in the primary Al phase PC] In the plated layer 20 of the plated steel wire 1 of this embodiment, the total area ratio of high Al concentration regions in the Al primary phase PC, where the Al concentration is 13.0% or more by mass, is 50% or less.

[0070] In a high Al concentration region in the Al primary phase PC, where the Al concentration is 13.0% or more, corrosion is likely to progress in a corrosive environment. Therefore, if the total area ratio of the high Al concentration region in the Al primary phase PC is set to 50% or less, the occurrence of corrosion can be suppressed and the corrosion resistance of the plated steel wire 1 can be improved.

[0071] If the total area ratio of the high Al concentration regions exceeds 50%, corrosion of the plating layer 20 is accelerated, and therefore the plated steel wire 1 does not have sufficient corrosion resistance.

[0072] The upper limit of the total area ratio of the high Al concentration regions is preferably 47%, more preferably 45%, and even more preferably 40%. The lower limit of the total area ratio of the high Al concentration regions is not particularly limited. However, excessive reduction in the total area ratio of the high Al concentration regions increases the manufacturing cost. Therefore, the lower limit of the total area ratio of the high Al concentration regions is preferably 10%, more preferably 15%, and even more preferably 20%.

[0073] [Method for measuring the total area ratio of high Al concentration regions in the primary Al phase PC] The total area ratio of the high Al concentration regions in the Al primary crystal phase PC can be determined by the following method. Referring to FIG. 1, a sample including a plating layer 20 is taken from a plated steel wire 1. Of the surface of the sample, a cross section including the plating layer 20 and perpendicular to the longitudinal direction of the plated steel wire 1 is defined as the observation surface. The observation surface is mirror-polished. In the plating layer 20 on the observation surface after mirror polishing, a region of 20 μm in the T direction and 80 μm in the C direction of the plating layer 20 is defined as the observation region. Four observation regions are arbitrarily selected.

[0074] Each observation area is subjected to area analysis using an electron probe micro analyzer (EPMA) with an acceleration voltage of 15 kV, a probe current of 500 nA, an electron beam diameter of 1 μm, and a measurement pitch of 0.4 μm.

[0075] In the backscattered electron composition images obtained for each observation region, the region that is less bright than the eutectic structure TE and in which Al and Zn are detected by EPMA is defined as the Al primary phase PC. Furthermore, the region in the Al primary phase PC region where the Al concentration is 13.0% or more is defined as the high Al concentration region. The ratio (%) of the area of ​​the high Al concentration region to the area of ​​the Al primary phase PC in the observation region where area analysis was performed is defined as the area ratio (%) of the high Al concentration region. The arithmetic average of the high Al concentration regions determined in the four observation regions is defined as the total area ratio (%) of the high Al concentration region in the Al primary phase PC of the coated steel wire 1.

[0076] [Effects of plated steel wire 1] As described above, the plated steel wire 1 of this embodiment includes the base steel wire 10 and the plating layer 20, and the plating layer 20 satisfies Features 1 to 3. Therefore, the plated steel wire 1 of this embodiment has high workability that can suppress the occurrence of cracks in the plating layer during processing, and high corrosion resistance. In particular, the plated steel wire 1 of this embodiment can suppress preferential corrosion of the Al primary crystal phase PC of the plating layer 20, thereby improving corrosion resistance.

[0077] [Shapes and uses of plated steel wire 1] The plated steel wire 1 of this embodiment has a circular cross section perpendicular to the axial direction of the plated steel wire 1. There are no particular limitations on the wire diameter D (mm) of the plated steel wire 1. The wire diameter D of the plated steel wire 1 is, for example, 1.0 mm to 8.0 mm. The plated steel wire 1 can be widely used in applications requiring excellent corrosion resistance, and is used, for example, as a material for wire mesh, fences, power transmission wires, and the like.

[0078] [Method of manufacturing plated steel wire 1] An example of a method for manufacturing the plated steel wire 1 of this embodiment will be described. The method for manufacturing the plated steel wire 1 described below is one example for manufacturing the plated steel wire 1. Therefore, the plated steel wire 1 including the plating layer 20 that satisfies the above-mentioned Features 1 to 3 may be manufactured by a manufacturing method other than the manufacturing method described below.

[0079] The manufacturing process of the plated steel wire 1 includes the following steps. (Process 1) Steel wire preparation process (Process 2) First plating process (Step 3) Second plating step Steps 1 to 3 will be explained below.

[0080] [(Process 1) Steel wire preparation process] In the steel wire preparation step, a base steel wire 10 manufactured by a known method is prepared. The base steel wire 10 may be supplied by a third party. The base steel wire 10 may be manufactured by the manufacturer of the plated steel wire 1. The base steel wire 10 is manufactured by drawing a wire material. The base steel wire 10 may be manufactured by subjecting the wire material after drawing to a well-known annealing treatment. The annealing treatment may or may not be performed.

[0081] [(Process 2) First plating process] In the first plating step, a well-known galvanizing process is performed on the base steel wire 10 prepared in the steel wire preparation step. In the first plating step, a galvanized layer is formed on the surface of the base steel wire 10. This improves the adhesion of the plating layer 20 formed in the next second plating step to the base steel wire 10. The method of galvanizing is not particularly limited. The galvanizing process may be a well-known hot-dip galvanizing process or a well-known electrogalvanizing process. The coating weight is not particularly limited, but the coating weight may be, for example, 50 to 350 g / m 2 is.

[0082] The steel wire before the galvanizing treatment may be subjected to a well-known pickling treatment and / or a well-known flux treatment. The pickling treatment and / or the flux treatment are optional treatments and may not be performed. The pickling treatment and the flux treatment can improve the adhesion of the galvanized layer to the base steel wire 10.

[0083] [(Step 3) Second plating step] In the second plating step, the base steel wire 10 on which the zinc plating layer has been formed is subjected to a hot dip plating process to form a plating layer 20. The coating weight is not particularly limited, but the coating weight is, for example, 50 to 350 g / m 2 The second plating step includes the following steps: (Step 31) Pretreatment step (Step 32) Hot-dip plating process (Step 33) Cooling step (Step 34) Heating and holding step Each step will be described below.

[0084] [(Step 31) Pretreatment step] The pretreatment step is an optional step and may not be performed. When the pretreatment step is carried out, in the pretreatment step, the base steel wire 10 on which the zinc plating layer is formed after the first plating step is subjected to a known pickling treatment and / or a known flux treatment.

[0085] [(Step 32) Hot-dip plating process] In the immersion step, a hot-dip galvanizing treatment is performed on the base steel wire 10 on which the zinc-plated layer has been formed. Specifically, the base steel wire 10 is immersed in a galvanizing bath.

[0086] The chemical composition of the plating bath is adjusted so that the chemical composition of the plating layer 20 formed after the second plating step satisfies Feature 1. The temperature (bath temperature) of the plating bath and the immersion time during the hot dip plating step are not particularly limited. The bath temperature may be, for example, 420 to 470°C. The immersion time in the plating bath may be, for example, 3 to 60 seconds.

[0087] [(Step 33) Cooling step] In the cooling step, the base steel wire 10 is pulled out of the plating bath and cooled. The cooling step is performed under the following cooling conditions. (Cooling conditions) The average cooling rate CR from the bath temperature to 280°C is set to 5.0 to 30.0°C / sec. The cooling conditions will be explained below.

[0088] [Cooling conditions] In the temperature range from the bath temperature to 280°C, solidification of the coating begins from the liquid phase and is then completed. In this temperature range, the Al primary phase PC, the eutectic structure TE, and the Zn phase SP crystallize. Therefore, the average cooling rate CR in the temperature range from the bath temperature to 280°C is set to 5.0 to 30.0°C / s. If the average cooling rate CR is less than 5.0°C / sec, the Al primary crystal phase PC may become coarse and the amount of crystallization may increase. In this case, the total area ratio of the Al primary crystal phase PC in the coating layer 20 may exceed 60%. On the other hand, if the average cooling rate CR exceeds 30.0°C / sec, the amount of crystallization of the eutectic structure TE may decrease. In this case, the total area ratio of the eutectic structure TE in the coating layer 20 will be less than 10%. If the average cooling rate CR is 5.0 to 30.0°C / sec, the total area ratio of the Al primary phase PC in the coating layer 20 is 10 to 60%, the total area ratio of the eutectic structure TE is 10 to 70%, and the Zn phase SP is 0 to 50%.

[0089] The average cooling rate CR can be determined by the following method. The temperature of the base steel wire 10 pulled up from the coating bath is measured with a thermometer. The thermometer is, for example, a contact thermometer using a thermocouple. The time it takes for the temperature of the base steel wire 10 to reach 280°C after solidification from the bath temperature (when the base steel wire 10 is pulled up) is measured. The average cooling rate CR (°C / sec) is determined based on the temperature range and the measured time.

[0090] The cooling rate from below 280° C. to room temperature is not particularly limited. Cooling may be achieved by standing, mist cooling, or water cooling.

[0091] [(Step 34) Heating and holding step] In the heating and holding step, the base steel wire 10 after being cooled to room temperature is heated up to a holding temperature T. Furthermore, the base steel wire 10 is held at the holding temperature T for a holding time t. By the heating and holding step, the total area ratio of the high Al concentration region in the Al primary phase PC can be set to 50% or less. Specifically, the heating and holding step satisfies the following conditions.

[0092] (Heating and holding conditions) Holding temperature T: 100~250℃ Holding time: 12~48 hours The conditions for the heating and holding step will be explained below.

[0093] If the holding temperature T is less than 100° C., the Al concentration in the Al primary crystal phase PC is less likely to decrease, and as a result, the total area ratio of high Al concentration regions in the Al primary crystal phase PC exceeds 50%.

[0094] On the other hand, if the holding temperature T exceeds 250°C, the Al concentration in the Al primary phase PC is less likely to decrease. The reason for this is thought to be as follows: In the process of decreasing the Al concentration from the Al primary phase PC during the heating and holding step, Al and Zn in the Al primary phase PC separate. This separation proceeds somewhat slowly, resulting in a decrease in the Al concentration in the Al primary phase PC. However, if the holding temperature T exceeds 250°C, the separation of Al and Zn proceeds excessively. In this case, a lumpy Zn phase is formed in the Al primary phase PC. When a lumpy Zn phase is formed, the Al concentration in the Al primary phase PC is less likely to decrease. As a result, the total area ratio of high Al concentration regions in the Al primary phase PC exceeds 50%.

[0095] If the holding time t is less than 12 hours, the Al concentration in the Al primary phase PC is less likely to decrease. In this case, the total area ratio of high Al concentration regions in the Al primary phase PC exceeds 50%. On the other hand, if the holding time t exceeds 48 hours, the manufacturing cost becomes excessively high. Therefore, considering actual industrial production, the upper limit of the holding time t is 48 hours.

[0096] Through the above manufacturing process, a plated steel wire satisfying Features 1 to 3 is manufactured. [Example]

[0097] 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.

[0098] [Manufacturing of plated steel wire] Plated steel wires were produced by the following method. First, a steel wire having the chemical composition of mild steel wire specified in JIS G 3505:2017 was prepared. Specifically, a wire rod was prepared. The wire rod was subjected to wire drawing and then annealed to produce a base steel wire having a wire diameter of 2.6 mm. The base steel wire was prepared through the above process.

[0099] The first plating step was carried out on the prepared base steel wire. First, the base steel wire was pickled and fluxed by a known method. After fluxing, the base steel wire was hot-dip galvanized by a known method to form a zinc plating layer on the surface of the base steel wire. The coating weight in the first plating step was 185 to 230 g / m 2 It was.

[0100] The base steel wire on which the zinc-plated layer was formed was subjected to a second plating process. A plating bath for each test number was prepared so that the plating layer of the manufactured plated steel wire would have the chemical composition shown in Table 1 (Table 1A and Table 1B). A well-known flux treatment was performed under the same conditions on the steel wire on which the zinc-plated layer of each test number was formed. The steel wire was then immersed in the prepared plating bath to perform a hot-dip plating process. The plated steel wire was removed from the plating bath and cooled. The average cooling rate CR in the cooling step of the second plating process was as shown in Table 2. After cooling, a heating and holding process was performed. The holding temperature T and holding time t in the heating and holding process of the second plating process were as shown in Table 2. Note that a "-" in the column for the heating and holding process in Table 2 indicates that the heating and holding process was not performed. Note that the coating weight in the second plating process was 1550 to 240 g / m 2 It was.

[0101] [Table 1A]

[0102] [Table 1B]

[0103] [Table 2]

[0104] According to the above manufacturing process, plated steel wires with each test number were manufactured.

[0105] [Evaluation test] The plated steel wires with each test number were subjected to the following evaluation tests. (Test 1) Measurement test of the total area ratio of the Al primary phase, eutectic structure, and Zn phase in the coating layer (Test 2) Measurement test of the total area ratio of high Al concentration regions in the Al primary phase PC of the coating layer (Test 3) Workability evaluation test (Test 4) Corrosion resistance evaluation test Tests 1 to 4 will be explained below.

[0106] [(Test 1) Measurement test of the total area ratio of the Al primary phase, eutectic structure, and Zn phase in the coating layer] The total area fractions of the Al primary phase, eutectic structure, and Zn phase in the coating layer of the plated steel wire of each test number were determined by the method described above in [Method for measuring the total area fraction of the Al primary phase PC, the total area fraction of the eutectic structure TE, and the total area fraction of the Zn phase SP]. The resulting total area fractions (%) of the Al primary phase, the total area fractions (%) of the eutectic structure, and the total area fractions (%) of the Zn phase are shown in Table 3 under the columns "Al primary phase (%)," "eutectic structure (%)," and "Zn phase (%)."

[0107] [Table 3]

[0108] [(Test 2) Measurement test of the total area ratio of high Al concentration regions in the Al primary phase PC of the coating layer] The total area ratio of high Al concentration regions in the Al primary crystal phase in the coating layer of the plated steel wire of each test number was determined by the method described above in "Method for measuring the total area ratio of high Al concentration regions in the Al primary crystal phase PC." The resulting total area ratio (%) of high Al concentration regions in the Al primary crystal phase is shown in the "Total area ratio of high Al concentration regions (%)" column in Table 3.

[0109] [(Test 3) Workability evaluation test] The plated steel wire of each test number was cut perpendicular to the longitudinal direction to obtain a 400 mm long test piece, the diameter of which was the same as that of the plated steel wire. The test piece was wound five times around a core material, the diameter of which was classified according to the Mg content of the plating layer as shown below. Core diameter (Mg content: less than 0.8%): same as the diameter of plated steel wire Core diameter (Mg content: 0.8 to less than 1.5%): twice the diameter of the plated steel wire Core diameter (Mg content: 1.5 to less than 2.5%): 3 times the diameter of the plated steel wire Core diameter (Mg content: 2.5% or more): 5 times the diameter of the plated steel wire

[0110] The winding direction was adjusted to be as perpendicular as possible to the longitudinal direction of the core material. During winding, the test pieces were wound spirally around the core material so that the test pieces did not overlap and so that the gaps between adjacent test piece portions were as small as possible. After winding, the surface of the test specimen (i.e., the surface of the coating layer) was visually inspected for cracks. If cracks of 100 μm or more in width in the longitudinal direction of the steel wire were found on the surface of the coating layer, it was determined that cracks had occurred in the coating layer during processing (denoted by "Bad" (B) in the "Processability" column in Table 3). On the other hand, if cracks occurred on the surface of the coating layer but the width in the longitudinal direction of the steel wire was less than 100 μm, it was determined that cracks in the coating layer had been suppressed during processing (denoted by "E" (Excellent) in the "Processability" column in Table 3).

[0111] [(Test 4) Corrosion resistance evaluation test] The corrosion resistance evaluation test of the plated steel wires of each test number was carried out in the following manner. Each plated steel wire with each test number was cut perpendicular to its longitudinal direction to obtain 200 mm long test pieces. The test pieces were subjected to a neutral salt spray cycle test in accordance with JIS H 8502:1999. The neutral salt spray cycle test was conducted under the conditions specified in JASO M609. Specifically, the following steps were carried out under the conditions specified in JASO M609. (Step 1: Salt spray process) The test specimen is placed in the test chamber. The temperature inside the test chamber is set to 35±1℃, and the spray solution is a 5% NaCl aqueous solution, and the spray solution is sprayed continuously inside the test chamber for 2 hours. (Step 2: Drying process) The spraying of the spray solution is stopped, and the test specimen is left in the test chamber, with the temperature set to 60±1°C and the relative humidity RH set to 20-30% or higher, and maintained for 4 hours. (Step 3: Wetting process) With the test specimens stored inside, the temperature in the test chamber is maintained at 50±1°C and the relative humidity at 95% or higher for 2 hours. Steps 1, 2, and 3 were performed in this order, and steps 1 to 3 constitute one cycle, which was repeated 30 times. The ends of the test specimens (plated steel wires) were covered with resin or the like to prevent corrosion from initiating or progressing from the ends of the test specimens. After 30 cycles, the corrosion weight loss of the test specimens with each test number was measured.

[0112] Here, the corrosion weight loss of the test specimens of each test number is likely to vary depending on the Al content and Mg content of the test specimens. Therefore, the test specimens of each test number were classified based on the Al concentration and Mg content of the test specimens, and the corrosion resistance was evaluated by the following method.

[0113] First, the chemical composition of the plating layer of the test piece with each test number was classified into ranges including the Al content and Mg content shown in the following plating types (a) to (h). The plating type of the test piece with each test number is shown in the "Plating type" column in Table 1. (Plating type) (a) Al content: 8.0 to less than 10.0%, and Mg content: 0.3 to less than 0.8% (b) Al content: 8.0 to less than 10.0%, and Mg content: 0.8 to less than 2.5% (c) Al content: 8.0~less than 10.0% and Mg content: 2.5~5.0% (d) Al content: 10.0 to less than 12.0%, and Mg content: 0.3 to less than 0.8% (e) Al content: 10.0 to less than 12.0%, and Mg content: 0.8 to less than 1.8% (f) Al content: 10.0 to less than 12.0%, and Mg content: 1.8 to less than 2.2% (g) Al content: 10.0 to less than 12.0%, and Mg content: 2.2 to 5.0% (h) Al content: 12.0~15.0% and Mg content: 1.8~2.2%

[0114] Among the test specimens classified into plating types (a) to (h), test numbers 52 to 59, which were not subjected to a heating and holding process and in which the total area ratio of the high Al concentration region exceeded 50%, were used as reference test specimens. For each test specimen, if the corrosion weight loss of the test specimen was 0.70 or less relative to the corrosion weight loss of the reference test specimen, the test specimen was judged to have excellent corrosion resistance (as indicated by "E" (Excellent) in the "Corrosion Resistance" column in Table 3). On the other hand, if the corrosion weight loss of the test specimen exceeded 0.70, the test specimen was judged to have insufficient corrosion resistance (as indicated by "B" (Bad) in the "Corrosion Resistance" column in Table 3). The corrosion resistance of the reference test specimens (test numbers 52 to 59) was evaluated as "B."

[0115] Here, the correspondence between the plating types (a) to (h) and the test pieces with each test number will be explained. Furthermore, the reference test piece used as the reference in measuring the corrosion weight loss of the test piece with each test number will be explained.

[0116] For example, test number 1 belonged to plating type (a). The corrosion weight loss of test number 1 was compared with the corrosion weight loss of test number 52, which is a reference test piece belonging to plating type (a), to evaluate corrosion resistance. For the other plating types, the corresponding test specimens and reference test specimens were selected in the same way. For plating type (b), test numbers 6 and 16 belonged, and the reference test specimen was test number 57. For plating type (c), test number 4 belonged, and the reference test specimen was test number 55. For plating type (d), test numbers 8, 11, 17, and 43 belonged, and the reference test specimen was test number 59. For plating type (e), test numbers 3, 9, and 14 belonged, and the reference test specimen was test number 54. For plating type (f), test numbers 2, 13, 15, 18, 19, 21 to 38, 46 to 51, 60, and 61 belonged, and the reference test specimen was test number 53. For plating type (g), test numbers 5 and 12 belonged, and the reference test specimen was test number 56. The plating type (h) included test numbers 7, 10, 20, 44, and 45, and the reference test piece was test number 58.

[0117] On the other hand, for the test specimens (test numbers 39 to 42) that could not be classified into any of the plating types (a) to (h), the reference test specimens were selected using the following method. First, the Al content of each test specimen was compared with the Al content of the reference test specimens (test numbers 52 to 59), and the reference test specimen with the closest Al content was selected. Next, the Mg content of the test specimen was compared with the Mg content of the selected reference test specimen, and the reference test specimen with the closest Mg content was selected. Through the above process, one reference test specimen was selected. For example, for test number 39, test number 52 was the reference test specimen, for test number 40, test number 58 was the reference test specimen, for test number 41, test number 59 was the reference test specimen, and for test number 42, test number 55 was the reference test specimen. Note that "-" was entered in the "Plating type" column of Table 1 for test numbers 39 to 42.

[0118] [Test Results] Referring to Tables 1 to 3, the plated steel wires of test numbers 1 to 38 had appropriate chemical compositions of the plating layers and appropriate manufacturing methods. Therefore, the plating layers of the plated steel wires of these test numbers satisfied Features 1 to 3. As a result, the plated steel wires of these test numbers exhibited high formability that could suppress the occurrence of cracks in the plating layer during processing, as well as high corrosion resistance.

[0119] On the other hand, in Test No. 39, the Al content in the coating layer was too low. Therefore, the area ratio of the primary Al phase in the coating layer was too low. As a result, the corrosion resistance of the plated steel wire was low.

[0120] In Test No. 40, the Al content in the coating layer was too high. As a result, the area ratio of the primary Al phase in the coating layer was too high. As a result, the occurrence of cracks in the coating layer could not be sufficiently suppressed during processing of the plated steel wire. As a result, the processability of the plated steel wire was poor.

[0121] In Test No. 41, the Mg content in the coating layer was too low. Therefore, the area ratio of the eutectic structure in the coating layer was too low. As a result, the corrosion resistance of the plated steel wire was low.

[0122] In Test No. 42, the Mg content in the coating layer was too high. As a result, the area ratio of the eutectic structure in the coating layer was too high. As a result, the occurrence of cracks in the coating layer could not be sufficiently suppressed during processing of the plated steel wire. As a result, the processability of the plated steel wire was poor.

[0123] In Test No. 43, the cooling rate CR in the cooling process was too fast. As a result, the area ratio of the eutectic structure in the coating layer was too low. As a result, the corrosion resistance of the coated steel wire was low.

[0124] In Test Nos. 44 and 45, the cooling rate CR in the cooling step was too slow. As a result, the area ratio of the Al primary phase in the coating layer was too high. As a result, the occurrence of cracks in the coating layer could not be sufficiently suppressed during processing of the coated steel wire. As a result, the processability of the coated steel wire was poor.

[0125] In Test Nos. 46 and 47, the holding temperature T in the heating and holding step was too low. As a result, the total area ratio of the high Al concentration region in the Al primary phase exceeded 50%. As a result, the corrosion resistance of the plated steel wire was low.

[0126] In Test Nos. 48 and 49, the holding temperature T in the heating and holding step was too high. As a result, the total area ratio of the high Al concentration region in the Al primary phase exceeded 50%. As a result, the corrosion resistance of the plated steel wire was low.

[0127] In test numbers 50 and 51, the holding time t in the heating and holding step was too short. As a result, the total area ratio of the high Al concentration region in the Al primary phase exceeded 50%. As a result, the corrosion resistance of the plated steel wire was low.

[0128] In test numbers 52 to 61, the heating and holding step was not performed. As a result, the total area ratio of the high Al concentration region in the Al primary phase exceeded 50%. As a result, the corrosion resistance of the plated steel wire was low.

[0129] 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]

[0130] 1. Plated steel wire 10 Base steel wire 20 plating layer PC Al primary phase TE eutectic structure SP Zn phase

Claims

1. A plated steel wire, A base steel wire; a plating layer formed on a surface of the base steel wire, The chemical composition of the plating layer is, in mass %, Al: 8.0 to 15.0%, and Mg: 0.3 to 5.0%; the balance being Zn and impurities; In a cross section that is a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is an Al primary phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure containing a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the eutectic structure having a total area ratio of 10 to 70%; and a Zn phase consisting of Zn and having a total area ratio of 0 to 50%, In the Al primary crystal phase, the total area ratio of high Al concentration regions having an Al concentration of 13.0% by mass or more is 50% or less. Plated steel wire.

2. A plated steel wire, A base steel wire; a plating layer formed on a surface of the base steel wire, The chemical composition of the plating layer is, in mass %, Al: 8.0-15.0%, Mg: 0.3 to 5.0%, and Contains one or more selected from the group consisting of Groups 1 to 3, the balance being Zn and impurities; In a cross section that is a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is an Al primary phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure containing a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the eutectic structure having a total area ratio of 10 to 70%; and a Zn phase consisting of Zn and having a total area ratio of 0 to 50%, In the Al primary crystal phase, the total area ratio of high Al concentration regions having an Al concentration of 13.0% by mass or more is 50% or less. Plated steel wire. [Group 1] Si: 0.50% or less [Group 2] Fe: 2.00% or less [Group 3] Bi: 0.50% or less, Pb: 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, 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, Ni: 0.50% or less, B: 0.10% or less, and Co: 0.50% or less, one or more selected from the group consisting of

3. The plated steel wire according to claim 2, the chemical composition contains the first group; Plated steel wire.

4. The plated steel wire according to claim 2, The chemical composition contains the second group. Plated steel wire.

5. The plated steel wire according to claim 2, The chemical composition contains the third group. Plated steel wire.

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