Plated steel wire

Abstract

To provide a plated steel wire excellent in corrosion resistance, and capable of suppressing generation of breakage of a plated layer when processing.SOLUTION: A plated steel wire 1 includes a base material steel wire 10 and a plated layer 20. The plated wire 20 includes 4.5 to 15.0% of AL, 0.3 to 4.0% of Mg, and a balance of Zn and impurities. A micro structure of the plated layer 20 includes 10 to 60% of an α phase in a gross area ratio, 10 to 70% of a eutectic structure in a gross area ratio, and 0 to 50% of a Zn phase in a gross area ratio. When defining a thickness direction of the plated layer 20 as a T direction, defining a direction vertical to the T direction as a C direction in a cross section vertical to an axis direction of the plated steel wire, and dividing a rectangle observation region into minute square regions having sides of 5 μm×5 μm in a rectangle observation region composed of a pair of C direction sides and a pair of T direction sides, and included in the plated layer 20, the intersection density of sides of the minute square regions with interfaces of the α phase, the eutectic structure and the Zn phase is 3.0×10-2 to 9.0×10-2 pieces / μm2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a plated steel wire. [Background technology]

[0002] Plated steel wire is used as a material for wire mesh, fences, power transmission wires, etc. The plated steel wire includes a base steel wire and a plating layer formed on the surface of the base 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 is likely 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 in which cracks have occurred 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 required to suppress the occurrence of cracks in the plating layer during processing.

[0005] A technology for suppressing the occurrence of 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 0.5-2.5% Mg, 0.5-3.0% Al, and the balance 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 with the Zn phase and the 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 describes 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, the occurrence of cracks in the plating layer during processing may be suppressed 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 which is excellent in corrosion resistance and which can suppress 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 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: 4.5 to 15.0%, and Mg: 0.3 to 4.0%; The balance is Zn and impurities. In a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is An α phase consisting of Al and Zn and having a total area ratio of 10 to 60%; A eutectic structure including a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the total area ratio of which is 10 to 70%, The Zn phase is made of Zn and has a total area ratio of 0 to 50%, In the cross section, when the thickness direction of the plating layer is defined as a T direction and the direction perpendicular to the T direction is defined as a C direction, A rectangular region is defined as a rectangular region having a maximum size in which a pair of C-direction sides having a length of 40 μm in the C direction and a pair of T-direction sides having a length of 5 N μm (N is a natural number) in the T direction in the cross section, and the pair of C-direction sides and the pair of T-direction sides are entirely included in the plating layer, and the rectangular region is defined as a rectangular observation region; When the rectangular observation area is divided into a plurality of minute square areas each having a side of 5 μm in the T direction and a side of 5 μm in the C direction, The density of the intersections between the sides of the minute square regions and the interfaces of the α phase, the eutectic structure, and the Zn phase is 3.0×10 -2 ~9.0×10 -2 pieces / μm 2 It is.

[0011] The plated steel wire according to the present invention has 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: 4.5-15.0%, Mg: 0.3 to 4.0%, and Contains one or more selected from the group consisting of Groups 1 to 3, The balance is Zn and impurities. In a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is An α phase consisting of Al and Zn and having a total area ratio of 10 to 60%; A eutectic structure including a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the total area ratio of which is 10 to 70%, The Zn phase is made of Zn and has a total area ratio of 0 to 50%, In the cross section, when the thickness direction of the plating layer is defined as a T direction and the direction perpendicular to the T direction is defined as a C direction, A rectangular region is defined as a rectangular region having a maximum size in which a pair of C-direction sides having a length of 40 μm in the C direction and a pair of T-direction sides having a length of 5 N μm (N is a natural number) in the T direction in the cross section, and the pair of C-direction sides and the pair of T-direction sides are entirely included in the plating layer, and the rectangular region is defined as a rectangular observation region; When the rectangular observation area is divided into a plurality of minute square areas each having a side of 5 μm in the T direction and a side of 5 μm in the C direction, The density of the intersections between the sides of the minute square regions and the interfaces of the α phase, the eutectic structure, and the Zn phase is 3.0×10 -2 ~9.0×10 -2 pieces / μm 2 It is. [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 Effect of the Invention

[0012] The plated steel wire of the present invention has excellent corrosion resistance and can suppress the occurrence of cracks in the plated layer during processing. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a part of a surface vicinity portion including a plating layer in a cross section, which is a cross section perpendicular to the axial direction, of a plated steel wire. [Diagram 2] FIG. 2 is a schematic diagram of a cross section of a plated steel wire different from that in FIG. [Diagram 3] FIG. 3 is a schematic diagram of a cross section of a rectangular observation region divided into a number of small square regions. [Figure 4] FIG. 4 is an example of a microstructure image showing the intersection between the sides of a minute square region in a rectangular observation region in a cross-section of a plating layer and the interface of the plating layer structure (α phase, eutectic structure, and Zn phase). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present inventors have investigated the chemical composition of the plating layer of a plated steel wire that has excellent corrosion resistance and can suppress the occurrence of cracks in the plating layer during processing. As a result, the chemical composition of the plating layer of the plated steel wire is, in mass%, Al: 4.5-15.0%, Mg: 0.3-4.0%, 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%, K: 0-0.50%, and Mg: 0-0.50%. The present inventors considered that excellent corrosion resistance would be obtained if the chemical composition contained 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 balance being Zn and impurities.

[0015] The present inventors have further investigated the workability of plated steel wires having the above-mentioned chemical composition. In plated steel wires, the plating layer has lower workability than the base steel wire. Therefore, the workability of plated steel wires depends on the workability of the plating layer. Specifically, when the plated steel wire is processed, cracks are generated in the plating layer and the cracks propagate. As a result, cracks are generated on the surface of the plated steel wire (surface of the plating layer).

[0016] Therefore, the present inventors have studied means for suppressing the propagation of cracks in the coating layer. A cross section perpendicular to the axial direction of a coated steel wire is defined as a transverse section. The coating layer having the above-mentioned chemical composition contains an α phase consisting of Al and Zn, a eutectic structure containing a Zn phase, a Zn-Mg phase and an Al phase, and a primary Zn phase consisting of Zn.

[0017] The present inventors focused on the interface between the above-mentioned three structures (α phase, eutectic structure, and primary Zn phase) that constitute the plating layer. Cracks are likely to initiate and propagate in the Zn-Mg phase in the eutectic structure. However, the interfaces (interfaces between different phases) between the α phase, eutectic structure, and Zn phase provide resistance to the crack propagation. On the other hand, when there are too many interfaces in the cross section, the structure is too fine. In this case, when a crack occurs in the plating layer, the crack is likely to bypass the fine structure. Therefore, the resistance to the crack propagation is reduced. As a result, it is considered that cracks are likely to occur in the plating layer 20 during processing of the plated steel wire.

[0018] On the other hand, if the number of interfaces is too small in the cross section, when a crack occurs in the plating layer, there are too few interfaces that provide resistance to the propagation of the crack. Therefore, the crack is likely to propagate. As a result, it is considered that cracks are likely to occur in the plating layer 20 during processing of the plated steel wire.

[0019] Based on the above findings, the inventors considered that in order to suppress the propagation of cracks in the plating layer during processing, it would be effective to set the interface density of the three structures (α phase, eutectic structure, and Zn phase) in the plating layer within an appropriate range.

[0020] Therefore, the present inventors have investigated the appropriate range of interface density in the plating layer in the cross section, and have obtained the following findings.

[0021] Fig. 1 is a schematic diagram showing a part of a surface layer vicinity portion including a plating layer in a cross section, which is a cross section perpendicular to the axial direction of a plated steel wire. Referring to Fig. 1, the cross section of the plated steel wire includes a base steel wire 10 and a plating layer 20 formed on the surface of the base steel wire 10. The plating layer 20 includes an α-phase AL, a eutectic structure TE (Ternary Eutectic structure), and a Zn phase ZN. The thickness direction of the plating layer 20 is defined as a T direction. Furthermore, a direction perpendicular to the T direction is defined as a C direction.

[0022] In the cross section, a rectangular observation area AR is defined in the following manner: The rectangular observation area AR is composed of a pair of C-direction sides SC having a length of 40 μm in the C direction and a pair of T-direction sides ST having a length of 5N μm (N is a natural number) in the T direction.

[0023] 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 a pair of C-direction sides SC and a pair of T-direction sides ST of the rectangular observation area AR form a rectangular area of ​​the maximum size included in the plating layer 20.

[0024] 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 of which is 5 μm×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 in parallel with the C-direction side SC at a pitch of 5 μm in the T direction. Furthermore, a plurality of line segments are arranged in parallel with the T-direction side ST at a pitch of 5 μm in the C direction. These line segments divide the rectangular observation area into a plurality of minute square areas SS, each of which has a side of 5 μm in the T direction and a side of 5 μm in the C direction.

[0025] As described above, after dividing the rectangular observation area AR into a plurality of minute square areas SS, intersection points P between the sides of the minute square areas SS and the interfaces between the α phase AL, the eutectic structure TE, and the Zn phase ZN are identified. Fig. 4 is an example of a microstructure image showing intersection points P in the rectangular observation area AR in the cross section of the plating layer 20. As shown in Fig. 4, all intersection points P between the sides of the minute square areas SS and the interfaces between the α phase AL, the eutectic structure TE, and the Zn phase ZN are identified.

[0026] The number of intersections P correlates with the density of the interfaces between the α phase AL, the eutectic structure TE, and the Zn phase ZN in the coating layer 20. Therefore, the inventors have determined the density of the intersections P (number / μm 2) and the workability of plated steel wire. As a result, the inventors found that the density of the intersections P was 3.0×10 -2 ~9.0×10 -2 pieces / μm 2 It has been found that, if the above condition is satisfied, the occurrence of cracks in the plating layer 20 of the plated steel wire 1 during processing can be suppressed.

[0027] The plated steel wire according to the present embodiment has been completed based on the above technical concept. The plated steel wire according to the present embodiment has the following configuration.

[0028] [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: 4.5 to 15.0%, and Mg: 0.3 to 4.0%; The balance is Zn and impurities. In a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is An α phase consisting of Al and Zn and having a total area ratio of 10 to 60%; A eutectic structure including a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the total area ratio of which is 10 to 70%, The Zn phase is made of Zn and has a total area ratio of 0 to 50%, In the cross section, when the thickness direction of the plating layer is defined as a T direction and the direction perpendicular to the T direction is defined as a C direction, A rectangular region is defined as a rectangular region having a maximum size in which a pair of C-direction sides having a length of 40 μm in the C direction and a pair of T-direction sides having a length of 5 N μm (N is a natural number) in the T direction in the cross section, and the pair of C-direction sides and the pair of T-direction sides are entirely included in the plating layer, and the rectangular region is defined as a rectangular observation region; When the rectangular observation area is divided into a plurality of minute square areas each having a side of 5 μm in the T direction and a side of 5 μm in the C direction, The density of the intersections between the sides of the minute square regions and the interfaces of the α phase, the eutectic structure, and the Zn phase is 3.0×10 -2 ~9.0×10 -2 pieces / μm 2 That is, Plated steel wire.

[0029] [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: 4.5-15.0%, Mg: 0.3 to 4.0%, and Contains one or more selected from the group consisting of Groups 1 to 3, The balance is Zn and impurities. In a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is An α phase consisting of Al and Zn and having a total area ratio of 10 to 60%; A eutectic structure including a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the total area ratio of which is 10 to 70%, The Zn phase is made of Zn and has a total area ratio of 0 to 50%, In the cross section, when the thickness direction of the plating layer is defined as a T direction and the direction perpendicular to the T direction is defined as a C direction, A rectangular region is defined as a rectangular region having a maximum size in which a pair of C-direction sides having a length of 40 μm in the C direction and a pair of T-direction sides having a length of 5 N μm (N is a natural number) in the T direction in the cross section, and the pair of C-direction sides and the pair of T-direction sides are entirely included in the plating layer, and the rectangular region is defined as a rectangular observation region; When the rectangular observation area is divided into a plurality of minute square areas each having a side of 5 μm in the T direction and a side of 5 μm in the C direction, The density of the intersections between the sides of the minute square regions and the interfaces of the α phase, the eutectic structure, and the Zn phase is 3.0×10 -2 ~9.0×10 -2 pieces / μm 2That is, 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

[0030] [3] The plated steel wire according to [2], Containing the first group, Plated steel wire.

[0031] [4] The plated steel wire according to [2] or [3], Containing the second group, Plated steel wire.

[0032] [5] The plated steel wire according to any one of [2] to [4], Containing the third group, Plated steel wire.

[0033] The plated steel wire of this embodiment will be described in detail below. Unless otherwise specified, "%" for an element means mass%.

[0034] [About plated steel wire 1] With reference 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 may not include the alloy layer 30. In other words, the alloy layer 30 may have any configuration.

[0035] [About base steel wire 10] The base steel wire 10 means a wire material that has been subjected to at least one wire drawing process. The steel type of the base steel wire 10 is not particularly limited. The steel type of the base steel wire 10 may be appropriately selected according to the mechanical properties (e.g., tensile strength, workability, etc.) required for 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 defined in JIS G3505 (2017) or the chemical composition of a hard steel wire material defined in JIS G3506 (2017).

[0036] [About 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 may have 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 plated 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.

[0037] [Regarding plating layer 20] The plating layer 20 is formed on the surface of the base steel wire 10. Specifically, when the alloy layer 30 is not formed, the plating layer 20 is formed on the surface of the base steel wire 10. When the 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.

[0038] 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: 4.5 to 15.0%, Mg: 0.3 to 4.0%, 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%, Mn: 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 perpendicular to the axial direction of the plated steel wire 1, the microstructure of the plating layer 20 is α-phase Al consisting of Al and Zn, with a total area ratio of 10 to 60%, A eutectic structure TE including a Zn phase and a Zn-Mg phase consisting of Zn and Mg, the total area ratio of which is 10 to 70%; It contains Zn and a Zn phase ZN having a total area ratio of 0 to 50%. (Feature 3) In a cross section perpendicular to the axial direction of the plated steel wire 1, when 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, A rectangular region having a maximum size, in which the pair of C-direction sides SC having a length of 40 μm in the C direction and the pair of T-direction sides ST having a length of 5 N μm (N is a natural number) in the T direction are included in the plating layer 20, is defined as a rectangular observation region AR; When a rectangular observation area AR is divided into a number of minute square areas SS each having a side of 5 μm in the T direction and a side of 5 μm in the C direction, The density of the intersections between the sides of the small square region SS and the interfaces of the α phase AL, the eutectic structure TE, and the Zn phase ZN is 3.0×10 -2 ~9.0×10 -2 pieces / μm 2 It is.

[0039] Features 1 to 3 of the plating layer 20 will be described below.

[0040] [(Feature 1) Chemical composition of plating layer 20] The chemical composition of the plating layer 20 contains the following elements.

[0041] [Essential elements] Al: 4.5-15.0% Aluminum (Al) enhances the corrosion resistance of the plated steel wire 1 by sacrificial corrosion protection. Furthermore, Al suppresses the generation of Mg oxides in a plating bath containing Mg. If the Al content is less than 4.5%, 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 plating bath becomes high even if the contents of other elements are within the range of this embodiment. In this case, the generation of oxides in the plating bath is promoted. Therefore, it becomes necessary to remove the oxides during the manufacturing process, and the production efficiency decreases. Therefore, the Al content is 4.5 to 15.0%. The lower limit of the Al content is preferably 5.0%, more preferably 5.5%, and further preferably 6.0%. The upper limit of the Al content is preferably less than 15.0%, more preferably 14.0%, further preferably 13.5%, and further preferably 13.0%.

[0042] Mg: 0.3-4.0% Magnesium (Mg) enhances the corrosion resistance of the plated steel wire 1 through sacrificial corrosion protection. 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 4.0%, an excessive amount of the Zn-Mg phase, which is an intermetallic compound consisting of Zn and Mg, is generated in the microstructure of the plating layer 20. In this case, even if the contents of other elements are within the ranges of this embodiment, the plating layer 20 becomes excessively hard. Therefore, cracks in the plating layer are likely to occur during processing. Therefore, the Mg content is 0.3 to 4.0%. 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 3.5%, more preferably 3.0%, and even more preferably 2.5%.

[0043] The balance 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 when the plating layer 20 is industrially manufactured, but are not intentionally contained and are permissible within a range that does not adversely affect the plating layer 20.

[0044] [About 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.

[0045] [Group 1: About Si] Si:0.50% or less Silicon is an optional element and may not be contained, that is, the silicon content may be 0%. When 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 inhibits the formation of an Fe-Al phase and inhibits the formation of a Zn-Mg phase. This enhances the workability of the plated steel wire 1. Even if even a small amount of Si is contained, the above effects can be obtained to a certain extent. However, if the Si content exceeds 0.50%, the Mg-Si phase becomes excessively coarse, which may result in a decrease in workability of the plated steel wire 1. Therefore, the Si content is 0 to 0.50%, and if 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%, further preferably 0.10%, and further preferably 0.15%. The upper limit of the Si content is preferably 0.48%, more preferably 0.45%, and further preferably 0.40%.

[0046] [Group 2: Fe] Fe:2.00% or less 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 enhances the corrosion resistance of the plated steel wire. Even if only a small amount of Fe is contained, the above effect can be obtained to a certain extent. However, if the Fe content exceeds 2.00%, the alloy layer 30 is formed in excess, which leads to a decrease in workability of the plated steel wire 1. Therefore, the Fe content is 0 to 2.00%, and if 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%, further preferably 0.10%, and further preferably 0.15%. The upper limit of the Fe content is preferably 1.90%, more preferably 1.75%, and further preferably 1.50%.

[0047] [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, any of these elements further enhances the corrosion resistance or workability of the plated steel wire 1. If any one or more of these elements is contained even a little, the above effect can be obtained to some extent. However, if the contents 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 exceed 0.50%, or if the B content exceeds 0.10%, the corrosion resistance or workability of the plated steel wire 1 decreases. Furthermore, the generation of the Zn-Mg phase is suppressed, and the corrosion resistance of the plated steel wire 1 decreases. Therefore, 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 are 0 to 0.50%, and the B content is 0 to 0.10%. When contained, 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 are 0.50% or less (more than 0 to 0.50%), and the B content is 0.10% or less (more than 0 to 0.10%).

[0048] The lower limit 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 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 0.48%, more preferably 0.45%, and even more preferably 0.40%. The lower limit of the B content is preferably 0.01%, more preferably 0.02%, and further preferably 0.03%. The upper limit of the B content is preferably 0.09%, more preferably 0.08%, and further preferably 0.07%.

[0049] [Method of 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 (1999) "Testing method for hot-dip galvanizing," the plated steel wire is immersed in a hydrochloric acid solution to dissolve the plating layer and obtain a solution. The obtained solution is subjected to ICP (Inductively Coupled Plasma) emission spectroscopy to perform elemental analysis of the chemical composition of the plating layer 20.

[0050] The content of each element is determined by rounding off the measured value based on the significant figures defined in this embodiment to the lowest digit of the content of each element defined in this embodiment. For example, the Al content of the plating layer 20 is defined as a value up to one decimal place. Therefore, the Al content is determined as a value up to one decimal place obtained by rounding off the measured value to one decimal place.

[0051] Similarly, the contents of other elements other than the Al content of the plating layer 20 are determined by rounding off the measured value to the minimum digit specified in this embodiment, and the value obtained is the content of that element.

[0052] In addition, rounding off means rounding down if the fraction is less than 5, and rounding up if the fraction is 5 or more.

[0053] [(Feature 2) Regarding the microstructure of the plating layer 20] Referring to FIG. 1, in a cross section perpendicular to the axial direction of the plated steel wire 1, the microstructure of the plating layer 20 includes a structure having the following total area ratio. (1) α-phase AL: Total area ratio 10-60% (2) Eutectic structure TE: Total area ratio 10 to 70% (3) Zn phase ZN: total area ratio 0 to 50% As described above, the Zn phase ZN is an optional structure, that is, the plating layer 20 may or may not contain a Zn phase.

[0054] [About α-phase AL] The α-phase AL is composed of Al and Zn. As shown in Figure 4, the α-phase AL can be identified as an area that is less bright than the eutectic structure TE in the backscattered electron composition (COMPO) image. In Figure 4, the gray area that is less bright than the eutectic structure TE corresponds to the α-phase AL. More specifically, the area that is less bright than the eutectic structure TE in the backscattered electron composition image and where Al and Zn are detected in the energy dispersive X-ray analysis (EDS) is defined as the α-phase AL.

[0055] [About eutectic structure TE] As shown in FIG. 4, the eutectic structure TE includes a Zn phase having a higher brightness than the α phase AL, and a Zn-Mg phase having a lower brightness than the Zn phase but a higher brightness than the α phase AL. In the eutectic structure TE, the Zn phase and the Zn-Mg phase are mixed in a layered or granular form. The eutectic structure TE includes the Zn phase and the Zn-Mg phase, and may further include an Al phase. The Al phase is a phase having a lower brightness than the Zn phase and 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 granular phase that is finer than the Zn phase and the Zn-Mg phase.

[0056] The Zn phase in the eutectic structure TE is brighter than the α-phase AL and the Zn-Mg phase in the backscattered electron composition image, and can be easily distinguished from the α-phase AL and the Zn-Mg phase by contrast. In addition, this phase is where Zn is detected and where Mg is hardly detected in the EDS. The Zn-Mg phase in the eutectic structure TE is brighter than the Zn phase in the backscattered electron composition image, and where Zn and Mg are detected in the EDS.

[0057] [About the Zn phase ZN] The Zn phase is composed of Zn. As shown in FIG. 4, the Zn phase can be identified as an area brighter than the α-phase AL and the eutectic structure TE in the backscattered electron composition image. Furthermore, since the Zn phase is a single phase, multiple phases are not mixed in layers or particles as in the eutectic structure TE. The Zn phase is a phase that is brighter than the α-phase AL and the eutectic structure TE in the backscattered electron composition image, and in which Zn is detected and almost no other elements are detected in the EDS.

[0058] [Area ratio of α-phase AL] The area ratio of α-phase AL in the plating layer 20 affects the corrosion resistance and workability of the plated steel wire 1. If the area ratio of α-phase AL is less than 10%, the plated steel wire 1 does not have sufficient corrosion resistance or workability. On the other hand, if the area ratio of α-phase AL exceeds 60%, the area ratios of the eutectic structure TE and the Zn phase ZN decrease. In this case, the plated steel wire 1 does not have sufficient workability. Therefore, the area ratio of α-phase AL is 10 to 60%. The lower limit of the area ratio of the α-phase AL is preferably 15%, more preferably 20%, and even more preferably 25%. The upper limit of the area ratio of the α-phase AL is preferably 57%, more preferably 55%, and further preferably 50%.

[0059] [Regarding the area ratio of eutectic structure TE] The area ratio of the eutectic structure TE in the plating layer 20 affects the corrosion resistance and workability of the plated steel wire 1. If the area ratio of the eutectic structure TE is less than 10%, sufficient corrosion resistance cannot be obtained in the plated steel wire 1. On the other hand, the eutectic structure TE is harder than the α-phase AL. Therefore, if the area ratio of the eutectic structure TE exceeds 70%, the workability of the plated steel wire 1 decreases. In other words, cracks are likely to occur in the plating layer 20 during processing of the plated steel wire 1. Therefore, the area ratio of the eutectic structure TE is 10 to 70%. The lower limit of the area ratio of the eutectic structure TE is preferably 15%, more preferably 20%, and further preferably 25%. The upper limit of the area ratio of the eutectic structure TE is preferably 68%, more preferably 65%, further preferably 63%, and further preferably 60%.

[0060] [Area ratio of Zn phase ZN] As described above, the Zn phase ZN is an optional structure and may not 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 area ratio of the Zn phase ZN is 0 to 50%. The lower limit of the area ratio of the Zn phase ZN is preferably 5%, more preferably 10%, and further preferably 15%. The upper limit of the area ratio of the Zn phase ZN is preferably 45%, and more preferably 40%.

[0061] [Method of measuring the area ratio of α phase AL, the area ratio of eutectic structure TE, and the area ratio of Zn phase ZN] The area ratios of the α phase AL, the eutectic structure TE, and the Zn phase ZN 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. A cross section of the surface of the test piece, which 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 observation surface after mirror polishing, four observation fields including 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 including the plating layer 20 is generated. The area of ​​the observation field is 8000 μm 2 Let us assume that.

[0062] The above-mentioned rectangular observation area AR (40 μm in the C direction, 5N μm in the T direction, N is a natural number) is set in the plating layer 20 in the obtained backscattered electron composition image. The rectangular observation areas AR are set at any four points on the observation surface.

[0063] 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 can distinguish the base steel wire 10, the plating layer 20, and the alloy layer 30 from the contrasts of the backscattered electron composition images.

[0064] Furthermore, the α-phase AL, eutectic structure TE, and Zn phase ZN of the plating layer 20 in each observation area contain different elements. Therefore, in the backscattered electron composition image, the α-phase AL, eutectic structure TE, and Zn phase ZN can be clearly identified based on the contrast. The α-phase AL, eutectic structure TE, and Zn phase ZN can also be identified by performing point analysis of EDS. When performing point analysis of EDS, the current value of the electron beam is set to 70 to 80 nA, and the analysis time is set to 30 seconds. By the above method, the α-phase AL, eutectic structure TE, and Zn phase ZN are identified in the observation area. When performing point analysis of EDS, the point analysis is performed at the vertices of each minute square area SS of the rectangular observation area AR.

[0065] The area ratios of the α phase AL, the eutectic structure TE, and the Zn phase ZN identified by the above method are determined using the following intersection method.

[0066] Using the backscattered electron composition image, it is determined whether the structure overlapping each vertex of the minute square region SS in the rectangular observation region AR shown in Figures 3 and 4 is the α phase AL, the eutectic structure TE, or the Zn phase ZN. If different structures exist within a radius of 0.5 μm from the vertex, the vertex is determined to be the boundary between different structures. For example, if the eutectic structure TE and the Zn phase ZN 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 ZN.

[0067] When the apex is within one structure, the structure is counted as 1. When the apex is the boundary of n structures, each structure is counted as 1 / n (n is a natural number). For example, when the apex is the boundary between α phase AL and eutectic structure TE, α phase AL is counted as 0.5 and eutectic structure TE is counted as 0.5. Similarly, when the apex is the boundary between α phase AL and Zn phase ZN, α phase AL is counted as 0.5 and Zn phase ZN is counted as 0.5. When the apex is located at the boundary between eutectic structure TE and Zn phase ZN, eutectic structure TE is counted as 0.5 and Zn phase ZN is counted as 0.5. When the apex is located at the boundary between α phase AL, eutectic structure TE, and Zn phase ZN, α phase AL is counted as 0.3, eutectic structure TE is counted as 0.3, and Zn phase ZN is counted as 0.3. The ratio (%) of the total number of vertices that overlap with the α phase AL 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 α phase AL. Similarly, the ratio (%) of the total number of vertices that overlap 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 that overlap with the Zn phase ZN to the total number of vertices of the minute square region SS is defined as the area ratio (%) of the Zn phase ZN.

[0068] The arithmetic mean value of the area ratio (%) of the α-phase AL obtained in the four observation regions is defined as the area ratio (%) of the α-phase AL in the plating layer 20 of the plated steel wire 1. Similarly, the arithmetic mean value of the area ratio (%) of the eutectic structure TE obtained in the four observation regions is defined as the area ratio (%) of the eutectic structure TE in the plating layer 20 of the plated steel wire 1. Similarly, the arithmetic mean value of the area ratio (%) of the Zn phase ZN obtained in the four observation regions is defined as the area ratio (%) of the Zn phase ZN in the plating layer 20 of the plated steel wire 1. The area ratio is an integer obtained by rounding off the first decimal place of the arithmetic mean value.

[0069] The microstructure in the plating layer 20 may contain structures other than the α-phase AL, the eutectic structure TE, and the Zn-phase ZN. The other structures are, for example, a Zn-Mg phase, a reaction phase of Mg and an optional element (e.g., an Mg-Sn phase), an Fe-Al alloy phase, and the like.

[0070] [(Feature 3) Regarding the density of intersections DE between the micro square domains SS and the interface] In a cross section, which is a section perpendicular to the axial direction of the plated steel wire 1 of this embodiment, 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. In the cross section, a rectangular region consisting of a pair of C-direction sides SC having a length of 40 μm in the C direction and a pair of T-direction sides ST having a length of 5N μm (N is a natural number) in the T direction, in which the pair of C-direction sides SC and the pair of T-direction sides ST are entirely included in the plating layer 20, is defined as a rectangular observation region AR. When the rectangular observation region AR is divided into a plurality of minute square regions SS having sides of 5 μm in the T direction and sides of 5 μm in the C direction, the density DE (Density) of the intersections between the sides of the minute square regions SS and the interfaces between the α phase AL, the eutectic structure TE, and the Zn phase ZN is 3.0×10 -2 ~9.0×10 -2 pieces / μm 2 It is.

[0071] As described above, the intersection density DE correlates with the density of the interfaces between the α phase AL, the eutectic structure TE, and the Zn phase ZN in the coating layer 20. -2 pieces / μm 2If it is less than 100%, the number of interfaces between the structures (α-phase AL, eutectic structure TE, and Zn-phase ZN) in the plating layer 20 is too small. As described above, the interfaces act as resistance to the propagation of cracks. Therefore, if a crack occurs in the plating layer 20 with too few interfaces, the crack is likely to propagate. As a result, cracks are likely to occur in the plating layer 20 during processing of the plated steel wire 1.

[0072] On the other hand, the intersection density DE is 9.0×10 -2 pieces / μm 2 If the thickness exceeds 100 μm, the plating layer 20 has too many texture interfaces. In this case, the plating layer 20 has too many fine textures (α-phase AL, eutectic texture TE, and Zn-phase ZN), and the texture is too fine. Therefore, when a crack occurs in the plating layer, the crack tends to bypass the fine textures. Therefore, resistance to the crack propagation is reduced. As a result, cracks are more likely to occur in the plating layer 20 during processing of the plated steel wire.

[0073] The intersection density DE is 3.0×10 -2 ~9.0×10 -2 pieces / μm 2 If so, the interface density is appropriate, and the sizes of the structures (α-phase AL, eutectic structure TE, and Zn-phase ZN) are appropriate in the plating layer 20. In this case, the occurrence of cracks in the plating layer 20 during processing of the plated steel wire 1 can be sufficiently suppressed.

[0074] The preferred lower limit for the intersection density DE is 3.2×10 -2 pieces / μm 2 and more preferably 3.4×10 -2 pieces / μm 2 and more preferably 3.6×10 -2 pieces / μm 2 and more preferably 3.8×10 -2 pieces / μm 2 and more preferably 4.0×10 -2 pieces / μm 2 It is. The preferred upper limit for the intersection density DE is 8.6×10 -2 pieces / μm 2 and more preferably 8.2×10 -2 pieces / μm2 and more preferably 7.8×10 -2 pieces / μm 2 and more preferably 7.4 × 10 -2 pieces / μm 2 and more preferably 7.0×10 -2 pieces / μm 2 It is.

[0075] [Measuring method for intersection density DE] The intersection density DE can be calculated in the following manner. A test piece is taken by cutting the plated steel wire 1 perpendicular to the axial direction of the plated steel wire 1. A cross section of the surface of the test piece, which 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 observation surface after mirror polishing, four observation fields including 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 a magnification of 1000 times 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 including the plating layer 20 is generated.

[0076] The above-mentioned rectangular observation area AR (40 μm in the C direction, 5N μm in the T direction, N is a natural number) is set in the plating layer 20 in the obtained backscattered electron composition image. The rectangular observation areas AR are set at any four points on the observation surface. Furthermore, as shown in FIG. 3, the rectangular observation area AR is divided into a number of minute square areas SS having sides of 5 μm in the T direction and sides of 5 μm in the C direction.

[0077] After dividing the rectangular observation area AR into a number of minute square areas SS, the intersection points P between the sides of the minute square areas SS and the interfaces of the α phase AL, the eutectic structure TE, and the Zn phase ZN are identified. In each rectangular observation area AR, the intersection density (number / μm 2 The arithmetic mean value of the intersection densities obtained in the four rectangular observation areas AR is taken as the intersection density DE (number / μm 2 ) is defined as

[0078] [Summary of plated steel wire 1] As described above, the plated steel wire 1 of the present 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 the present embodiment has excellent corrosion resistance, and can suppress the occurrence of cracks in the plating layer 20 during processing.

[0079] [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 is no particular limitation 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 is widely applicable to applications requiring excellent corrosion resistance and excellent workability. For example, the plated steel wire 1 is used as a material for wire mesh, fences, power transmission wires, etc.

[0080] [Method of manufacturing plated steel wire 1] An example of a manufacturing method of the plated steel wire 1 of the present embodiment will be described. The manufacturing method of 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.

[0081] The manufacturing process of the plated steel wire 1 includes the following steps. (Step 1) Steel wire preparation step (Step 2) First plating step (Step 3) Second plating step Steps 1 to 3 will be explained below.

[0082] [(Step 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 performing wire drawing on a wire material. The base steel wire 10 may be manufactured by performing a well-known annealing treatment on the wire material after the wire drawing. The annealing treatment may or may not be performed.

[0083] [(Step 2) First plating step] In the first plating step, a 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 enhances the adhesion of the plating layer 20 formed in the next second plating step to the base steel wire 10. The method of the galvanizing process is not particularly limited. The galvanizing process may be a known hot-dip galvanizing process or a known electrogalvanizing process.

[0084] The steel wire before the galvanizing process may be subjected to a well-known pickling process and / or a well-known fluxing process. The pickling process and / or fluxing process are optional processes and may not be performed. The pickling process and fluxing process can increase the adhesion of the galvanized layer to the base steel wire 10.

[0085] [(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 the plating layer 20. The second plating step includes the following steps. (Step 31) Pretreatment step (Step 32) Hot-dip plating process (Step 33) Cooling step Each step will be described below.

[0086] [(Step 31) Pretreatment step] The pretreatment step is an optional step. The pretreatment step does not have to 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 well-known pickling and / or a well-known flux treatment.

[0087] [(Step 32) Hot-dip plating process] In the immersion step, a hot-dip galvanizing process is performed on the base steel wire 10 on which the zinc-plated layer is formed. Specifically, the base steel wire 10 is immersed in a galvanizing bath.

[0088] The chemical composition of the plating bath is adjusted so that the chemical composition of the plating layer 20 formed after the second plating process satisfies Feature 1. Furthermore, in the hot-dip plating process, the bath temperature T1 (°C) and the immersion time t (seconds) of the plating bath during the hot-dip plating process are adjusted so as to satisfy the following Condition 1. (Condition 1) X0≦T1×(t 0.5 )≦X1(A) Here, X0 and X1 are defined by the following formula. X0=(10×Al+880)×0.9×exp(0.025×D) X1=(45×Al+2100) / (0.95×exp(0.015×D)) Here, the Al content (mass %) in the plating layer 20 is substituted for "Al" in X0 and X1, and the wire diameter (mm) of the plated steel wire 1 is substituted for "D."

[0089] FA = T1 × (t 0.5 ) FA affects the area ratio of α-phase AL and / or the intersection density DE in the plating layer 20 of the plated steel wire 1. If FA exceeds X1, that is, if formula (A) is satisfied, the area ratio of α-phase AL in the plating layer 20 is too small and the intersection density DE is too small. If FA is less than X0, bare spots occur and a plating layer may not be formed. If FA satisfies condition 1, the plating layer 20 of the manufactured plated steel wire 1 satisfies features 1 to 3, provided that the conditions in the cooling step of step 33 described below are satisfied.

[0090] [(Step 33) Cooling step] In the cooling step, the base steel wire 10 is pulled out of the coating bath and cooled. As described above, in the cooling step, the following conditions 2 to 4 are satisfied. (Condition 2) The average cooling rate CR1 from the bath temperature T1 (°C) to the cooling rate switching temperature T2 (°C) is set to less than 5 to 50°C / sec. (Condition 3) The cooling speed changeover temperature T2 is set to 350 to 380°C. (Condition 4) The average cooling rate CR2 from the cooling rate switching temperature T2 to 200°C is 50°C / sec or more.

[0091] The α-phase AL is crystallized by cooling from the bath temperature T1 to the cooling rate switching temperature T2. Then, by adjusting the average cooling rate CR1, the cooling rate switching temperature T2, and the average cooling rate CR2 from the cooling rate switching temperature T2 to 200°C, the characteristics 2 and 3 of the plating layer 20 are adjusted.

[0092] [Regarding condition 2] In the temperature range from the bath temperature T1 (℃) to the cooling rate switching temperature T2 (℃), the plating starts to solidify from the liquid phase in the initial process, and α-phase AL crystallizes. Therefore, the average cooling rate CR1 in this temperature range is set to 5 to less than 50℃ / sec.

[0093] If the average cooling rate CR1 is less than 5°C / sec, the α-phase AL becomes coarse. Therefore, the intersection density DE becomes too low. On the other hand, if the average cooling rate CR1 exceeds 50°C / sec, the α-phase AL becomes too fine. In this case, the intersection density becomes too high. Therefore, the average cooling rate CR1 is set to 5 to less than 50°C / sec.

[0094] The average cooling rate CR1 can be determined by the following method. The temperature of the steel wire pulled out of the coating bath is measured with a thermometer. The thermometer is, for example, a thermograph. The time it takes for the temperature of the steel wire to reach the cooling speed switching temperature T2 from the bath temperature T1 is measured. The average cooling rate CR1 (°C / sec) is determined based on the temperature range and the measured time.

[0095] [Regarding condition 3] The cooling rate switching temperature T2 (°C) means the temperature at which the cooling rate is switched from the average cooling rate CR1 to the average cooling rate CR2. If the cooling rate switching temperature T2 is too low, the period during which the plating layer 20 is cooled at the average cooling rate CR1 becomes too long. In this case, the structure of the plating layer 20 becomes too coarse, and as a result, the intersection density becomes too low. On the other hand, if the cooling rate switching temperature T2 is too high, the period during which the plating layer 20 is cooled at the average cooling rate CR2 becomes too long. In this case, the structure of the plating layer 20 becomes too fine, and as a result, the intersection density becomes too high. Therefore, the cooling rate switching temperature T2 is 350 to 380°C.

[0096] [Regarding condition 4] The average cooling rate CR2 in the temperature range from the cooling rate switching temperature T2 to 200° C. affects the sizes of the α phase AL, the eutectic structure TE, and the Zn phase ZN. The average cooling rate CR2 in this temperature range is set to 50° C. / sec or more.

[0097] If the average cooling rate CR2 is too slow, the structure of the plating layer 20 becomes too coarse, and as a result, the intersection density becomes too low. Therefore, the average cooling rate CR2 is set to 50°C / sec or more. The upper limit of the average cooling rate CR2 is not particularly limited. The upper limit of the average cooling rate CR2 is, for example, 1500°C / sec.

[0098] The average cooling rate CR2 can be determined by the following method. Using a thermometer, the time required for the temperature of the steel wire to reach the cooling rate switching temperature T2 to 200°C is measured. The average cooling rate CR2 (°C / sec) is determined based on the temperature range and the measured time.

[0099] Through the above-described manufacturing steps, the plated steel wire according to the present embodiment is manufactured. EXAMPLES

[0100] 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 one example of conditions 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 this one example of conditions.

[0101] [Manufacturing of plated steel wire] A plated steel wire was produced by the following method. First, a steel wire having the chemical composition of mild steel wire specified in JIS G3505 (2017) was prepared. Specifically, a wire rod was prepared. The wire rod was subjected to wire drawing and then annealed to produce base steel wires of various wire diameters D (mm). The base steel wires were prepared by the above process.

[0102] The first plating step was carried out on the prepared base steel wire. First, the base steel wire was pickled and flux-treated by a known method. After flux treatment, the base steel wire was subjected to hot-dip galvanizing treatment by a known method to form a zinc-plated layer on the surface of the base steel wire.

[0103] A second plating step was carried out on the base steel wire on which the zinc plating layer was formed. 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. A well-known flux treatment was carried out on the steel wire on which the zinc plating layer was formed for each test number under the same conditions. Thereafter, the steel wire was immersed in the prepared plating bath to carry out a hot-dip plating treatment. The plated steel wire was pulled out of the plating bath and cooled. Conditions 1 to 4 in the second plating step were as shown in Table 2.

[0104] [Table 1]

[0105] [Table 2]

[0106] According to the above manufacturing process, plated steel wires having each test number were manufactured.

[0107] [Evaluation test] The following evaluation tests were carried out on the plated steel wires having each test number. (Test 1) Measurement test of the area ratio of the α phase, eutectic structure and Zn phase of the coating layer (Test 2) Measurement test of intersection density DE (Test 3) Bare plating evaluation test (Test 4) Corrosion resistance evaluation test (Test 5) Workability evaluation test Tests 1 to 5 will be described below.

[0108] [(Test 1) Measurement test of the area ratio of the α phase, eutectic structure, and Zn phase of the coating layer] The area fractions of the α 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 in the above-mentioned [Method for measuring the area fraction of the α phase AL, the area fraction of the eutectic structure TE, and the area fraction of the Zn phase ZN]. The obtained area fractions of the α phase (%), the eutectic structure (%), and the Zn phase (%) are shown in Table 3.

[0109] [Table 3]

[0110] [(Test 2) Measurement test of intersection density DE] The intersection density DE (pieces / μm 2 The intersection density DE was determined by the method described in the above [Method of measuring intersection density DE]. The intersection density DE obtained is shown in Table 3.

[0111] [(Test 3) Non-plating evaluation test] The plated steel wire of each test number was visually evaluated for the presence or absence of unplated areas. The presence or absence of unplated areas was confirmed at an observation point 200 mm from one end of the steel wire in the longitudinal direction of the steel wire (i.e., the total length of the observation point was 200 mm). Since the steel wire has both ends, there were two observation points, and one of these observation points was selected to confirm the presence or absence of unplated areas. At the selected observation point, 2 When no unplated area having an area of ​​2 mm or more was confirmed, it was determined that a plating layer was formed on the surface of the base steel wire (indicated as "E" (Excellent) in the "Presence or Absence of Unplated Area" column in Table 3). 2If even one unplated area having an area of ​​100 mm or more was confirmed, it was determined that a sufficient plating layer was not formed on the surface of the base steel wire (shown as "B" (Bad) in the "Unplated" column in Table 3). Note that for plated steel wires with test numbers in which unplated areas occurred, Tests 1, 2, 4, and 5 were not performed.

[0112] [(Test 4) Corrosion resistance evaluation test] The corrosion resistance evaluation test of the plated steel wire of each test number was carried out in the following manner. The plated steel wire of each test number was cut perpendicular to the longitudinal direction to obtain a test piece having a length of 200 mm. The test pieces were used to carry out a neutral salt spray cycle test in accordance with JIS H 8052:1999. The neutral salt spray cycle test was carried out under the conditions specified in JASO M609. Specifically, the following process was 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 in 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 in the test chamber for 2 hours. (Step 2: Drying process) Stop spraying the spray solution. Then, with the test pieces still in the tank, maintain the temperature at 60±1°C and the relative humidity at 20-30% or higher for 4 hours. (Step 3: Wetting process) With the test specimens still inside the test chamber, maintain the temperature at 50±1℃ and the relative humidity at 95% or higher for two hours. Steps 1, 2, and 3 were carried out in that order, and steps 1 to 3 were counted as one cycle, and 30 cycles were repeated. The ends of the test pieces (plated steel wires) were covered with resin or the like to prevent corrosion from starting or progressing from the ends of the test pieces.

[0113] After 30 cycles, the corrosion weight loss of each test piece was measured. The corrosion weight loss was 50g / m 2 If the corrosion loss is less than 50g / m2, the corrosion resistance of the plated steel wire is judged to be high (shown as "E" (Excellent) in the "Corrosion Resistance" column in Table 3). 2In the above cases, the corrosion resistance of the plated steel wire was judged to be low (shown as "B" (Bad) in the "Corrosion Resistance" column in Table 3).

[0114] [(Test 5) Workability evaluation test] The plated steel wire of each test number was cut perpendicular to the longitudinal direction to obtain a test piece having a length of 400 mm. The diameter of the test piece was the same as that of the plated steel wire. The test piece was wound five times around a core material having a diameter three times that of the test piece. At this time, the winding direction was adjusted to be as perpendicular to the longitudinal direction of the core material as possible. When winding, the test piece was wound around the core material in a spiral shape so that the test pieces did not overlap and the gap between adjacent test piece portions was as small as possible. After winding, the surface of the test piece (i.e., the surface of the plating layer) was visually inspected for the presence or absence of cracks. If cracks of 100 μm or more in width in the longitudinal direction of the steel wire were confirmed on the surface of the plating layer, it was determined that cracks had occurred in the plating layer during processing (indicated as "B" (Bad) in the "Workability" column in Table 3). On the other hand, if no such cracks were confirmed on the surface of the plating layer, it was determined that cracks in the plating layer had been suppressed during processing (indicated as "E" (Excellent) in the "Workability" column in Table 3).

[0115] [Test Results] With reference to Tables 1 to 3, the plated steel wires of test numbers 1 to 43 had appropriate chemical compositions of the plated layers, and the manufacturing methods were also appropriate. Therefore, the plated steel wires of these test numbers satisfied Features 1 to 3. As a result, the plated steel wires of these test numbers had excellent corrosion resistance, and the occurrence of cracks in the plated layers during processing could be sufficiently suppressed.

[0116] On the other hand, in test number 44, the Al content in the plating layer was too low, and therefore the corrosion resistance of the plated steel wire was low.

[0117] In the test number 45, the Al content in the coating layer was too high. Therefore, the area ratio of the α phase in the coating layer was too high. As a result, the occurrence of cracks in the coating layer during processing of the plated steel wire could not be sufficiently suppressed.

[0118] In test number 46, the Mg content in the plating layer was too low, so the corrosion resistance of the plated steel wire was low.

[0119] In test number 47, the Mg content in the coating layer was too high, and therefore the occurrence of cracks in the coating layer could not be sufficiently suppressed during processing of the coated steel wire.

[0120] In the test numbers 48 and 50, the average cooling rate CR1 in the second plating step was too slow, and therefore the intersection density DE was too low, so that the occurrence of cracks in the plating layer during processing of the plated steel wire could not be sufficiently suppressed.

[0121] In the test numbers 49 and 51, the average cooling rate CR1 in the second plating step was too fast. Therefore, the intersection density DE was too high. As a result, the occurrence of cracks in the plating layer during processing of the plated steel wire could not be sufficiently suppressed.

[0122] In the test numbers 52 and 54, the cooling speed switching temperature T2 in the second plating step was too high. Therefore, the intersection density DE was too high. As a result, the occurrence of cracks in the plating layer during processing of the plated steel wire could not be sufficiently suppressed.

[0123] In the test numbers 53 and 55, the cooling speed switching temperature T2 in the second plating step was too low. Therefore, the intersection density DE was too low. As a result, the occurrence of cracks in the plating layer during processing of the plated steel wire could not be sufficiently suppressed.

[0124] In the test numbers 56 and 57, the average cooling rate CR2 in the second plating step was too slow, and therefore the intersection density DE was too low, so that the occurrence of cracks in the plating layer during processing of the plated steel wire could not be sufficiently suppressed.

[0125] In the test numbers 58 to 60, in the second plating process, FA exceeded X1, and formula (A) was not satisfied. Therefore, the area ratio of the α phase was too low, and the intersection density DE was too low. As a result, the occurrence of cracks in the plating layer during processing of the plated steel wire could not be sufficiently suppressed.

[0126] In test numbers 61 to 63, FA was less than X0 in the second plating step, and formula (A) was not satisfied. Therefore, non-plating occurred.

[0127] 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 without departing from the spirit of the present disclosure. [Explanation of symbols]

[0128] 1. Plated steel wire 10 Base steel wire 20 Plating layer AL α phase TE eutectic structure ZN 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: 4.5 to 15.0%, and Mg: 0.3 to 4.0%; The balance is Zn and impurities, In a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is An α phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure including 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 having a total area ratio of 0 to 50%. In the cross section, when the thickness direction of the plating layer is defined as a T direction and the direction perpendicular to the T direction is defined as a C direction, a rectangular region having a maximum size including a pair of C-direction sides having a length of 40 μm in the C-direction and a pair of T-direction sides having a length of 5 N μm (N is a natural number) in the T-direction in the cross section, the pair of C-direction sides and the pair of T-direction sides being entirely included in the plating layer, is defined as a rectangular observation region; When the rectangular observation area is divided into a plurality of minute square areas each having a side of 5 μm in the T direction and a side of 5 μm in the C direction, The density of the intersections between the sides of the minute square regions and the interfaces of the α phase, the eutectic structure, and the Zn phase is 3.0 × 10 －２ ~9.0 x 10 －２ pieces / μm ２ That is, 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: 4.5-15.0%, Mg: 0.3 to 4.0%, and Contains one or more selected from the group consisting of Groups 1 to 3, The balance is Zn and impurities, In a cross section perpendicular to the axial direction of the plated steel wire, the microstructure of the plating layer is An α phase consisting of Al and Zn and having a total area ratio of 10 to 60%; a eutectic structure including 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 having a total area ratio of 0 to 50%. In the cross section, when the thickness direction of the plating layer is defined as a T direction and the direction perpendicular to the T direction is defined as a C direction, a rectangular region having a maximum size including a pair of C-direction sides having a length of 40 μm in the C-direction and a pair of T-direction sides having a length of 5 N μm (N is a natural number) in the T-direction in the cross section, the pair of C-direction sides and the pair of T-direction sides being entirely included in the plating layer, is defined as a rectangular observation region; When the rectangular observation area is divided into a plurality of minute square areas each having a side of 5 μm in the T direction and a side of 5 μm in the C direction, The density of the intersections between the sides of the minute square regions and the interfaces of the α phase, the eutectic structure, and the Zn phase is 3.0 × 10 －２ ~9.0 x 10 －２ pieces / μm ２ That is, 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, Containing the first group, Plated steel wire.

4. The plated steel wire according to claim 2, Containing the second group, Plated steel wire.

5. The plated steel wire according to claim 2, Containing the third group, Plated steel wire.

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