Plated steel wire, rope, and method for producing rope

Abstract

Provided is a plated steel wire in which: a steel portion has a prescribed steel composition; in a central part within 1.0 mm from a center axis in a cross-section that is parallel to a longitudinal direction and passes through the center axis, the area ratio of a mixed structure of ferrite and cementite phases is 95.0% or greater; the diameter of the steel portion is 5.0 mm or greater; the surface of the steel portion is covered, at an amount of at least 100 g / m2, by a Zn-based plating layer containing Zn as the main component; the tensile strength TS is 1900-2250 MPa; and the ratio YS / TS of the yield strength (0.2% proof stress) YS to the tensile strength TS is 0.87 or greater. Also provided is a rope obtained by bundling a plurality of the plated steel wires.

Description

Plated steel wire, rope, and rope manufacturing method

[0001] The present disclosure relates to a plated steel wire, a rope, and a method for manufacturing the rope.

[0002] Steel wires for bridge cables, ropes, and the like are typically made by patenting high-carbon steel wire rods to form pearlite structures and then drawing them. In recent years, high-strength steel wires have been in demand for reducing construction costs and reducing the weight of structures. However, when high-strength steel wires are used in environments where hydrogen penetrates or in corrosive environments, they are more likely to break due to the progression of hydrogen embrittlement and corrosion. Therefore, high-strength steel wires are desired to have excellent resistance to hydrogen embrittlement and corrosion resistance. High-strength plated steel bars and plated steel wires that are high in strength and excellent in resistance to hydrogen embrittlement have been proposed (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1: JP 2003-328077 A Patent Document 2: JP 2021-183709 A

[0004] Steel wire for bridges and other structures is plated to ensure corrosion resistance, but if the plating peels off during years of use, corrosion will progress. Recently, steel wire for bridges has become stronger, and the possibility of delayed fracture increases if the plating peels off. Steel wire that has been drawn from wire rod is thought to have a large amount of hydrogen penetration because the drawing process introduces a large amount of dislocations. If the amount of hydrogen penetration is large, there is a possibility of delayed fracture occurring, so it is necessary to suppress hydrogen penetration.

[0005] Furthermore, increasing the strength reduces the delayed fracture resistance. In particular, the possibility of delayed fracture increases when the tensile strength exceeds 1900 MPa. One way to prevent delayed fracture is to prevent hydrogen penetration. In addition, plated steel wires for bridges and other applications require torsional properties as ductility.

[0006] In view of the above circumstances, an object of the present disclosure is to provide a plated steel wire, a rope, and a method for manufacturing the rope that are high in strength and have both excellent torsional properties and hydrogen penetration resistance.

[0007] The means for solving the above problems include the following aspects. <1> The steel portion contains, in mass%, C: 0.80 to 1.10%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.050% or less, S: 0.050% or less, N: 0.0120% or less, O: 0.0100% or less, Al: 0.005 to 0.070%, Cu: 0.04 to 0.80%, Mo: 0 to 0.20%, Cr: 0 to 1.00%, V: 0 to 0.15%, Sn: 0 to 0.50%, Ni: 0 to 0.80%, Ti: 0 to 0.050%, Nb: 0 to 0.050%, B: 0 to 0.0040%, REM: 0 to 0.030%, a steel portion having a steel composition of Bi: 0 to 0.020%, Mg: 0 to 0.0040%, Ca: 0 to 0.0040%, Zr: 0.030%, W: 0 to 0.10%, Te: 0 to 0.030%, Sb: 0 to 0.030%, and the balance being Fe and impurities, wherein an area ratio of a mixed structure consisting of a ferrite phase and a cementite phase is 95.0% or more at a center portion within 1.0 mm from a central axis of a cross section parallel to the longitudinal direction and passing through the central axis, the steel portion having a diameter of 5.0 mm or more, and a surface of the steel portion having a Zn-based plating layer containing Zn as a main component and coated with a Zn-based plating layer having a thickness of 100 g / m ２<2> The plated steel wire according to <1>, wherein the steel portion is coated with at least one of a tensile strength (TS) of 1900 MPa to 2250 MPa, a tensile strength (TS) of 1900 MPa to 2250 MPa, and a ratio (YS / TS) of a yield strength (0.2% proof stress) YS to the tensile strength (TS) of 0.87 or more. (Group A) One or more selected from the group consisting of Mo: 0.20% or less, Cr: 1.00% or less, and V: 0.15% or less. (Group B) One or more selected from the group consisting of Sn: 0.50% or less, and Ni: 0.80% or less. (Group C) One or more selected from the group consisting of Ti: 0.050% or less, Nb: 0.050% or less, B: 0.0040% or less, REM: 0.030% or less, Bi: 0.020% or less, Mg: 0.0040% or less, Ca: 0.0040% or less, Zr: 0.030% or less, W: 0.10% or less, Te: 0.030% or less, and Sb: 0.030% or less. <3> <2> The plated steel wire according to <2>, wherein the steel composition includes Group A. <4> The plated steel wire according to <2> or <3>, wherein the steel composition includes Group B. <5> The plated steel wire according to any one of <2> to <4>, wherein the steel composition includes Group C. <6> A rope comprising a plurality of plated steel wires according to any one of <1> to <5> bundled together. <7> A method for manufacturing a rope, comprising a step of bundling a plurality of plated steel wires according to any one of <1> to <5> into a rope.

[0008] According to the present disclosure, there are provided a plated steel wire, a rope, and a method for manufacturing the rope, which are high in strength and have both excellent torsional properties and hydrogen penetration resistance.

[0009] 1A is an example of an SEM image of a longitudinal cross section of a steel wire including a mixed structure of a ferrite phase and a cementite phase and an immixed structure; FIG. 1B is an enlarged image of a portion including an immixed structure in FIG. 1A; FIG. 2A is another example of an SEM image of a longitudinal cross section of a steel wire including a mixed structure of a ferrite phase and a cementite phase and an immixed structure; and FIG. 2B is an enlarged image of a portion including an immixed structure in FIG.

[0010] An embodiment serving as an example of the present disclosure will be described. In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. However, when the numerical values ​​before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit. The content of an element in a chemical composition may be expressed by adding "amount" to the element symbol (e.g., C content, Si content, etc.). Regarding the content of an element in a chemical composition, "%" means "mass %." When the content of an element in a chemical composition is described as "0 to," this means that the element may not be included. The term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. The "surface" of a steel wire means the "outer peripheral surface." The "center axis" of a steel wire means an imaginary line that passes through the center point of a cross section perpendicular to the longitudinal direction of the steel wire and extends in the longitudinal direction (axial direction).

[0011] Through repeated experiments and investigations, the inventors have discovered the following: (a) Plated steel wires have many dislocations, resulting in a large amount of hydrogen penetration. If the coating peels off, a large amount of hydrogen penetrates into the steel wire (base steel), potentially leading to delayed fracture. (b) Adding Cu is effective in suppressing the amount of hydrogen penetration. (c) When the wire is heated to approximately 450°C for several tens of seconds during plating after drawing, carbon adheres to the dislocation core, preventing hydrogen from adhering to the dislocations and reducing the amount of diffusible hydrogen that contributes to delayed fracture. However, if the coating peels off, a large amount of diffusible hydrogen still penetrates. (d) Heating to above 450°C is effective in further reducing the amount of diffusible hydrogen, but this is not applicable because the coating remelts at temperatures above 450°C. (e) Therefore, by simultaneously performing aging and constant load application (heat stretching) after plating, carbon can be efficiently adhered to the dislocation core, further reducing the amount of diffusible hydrogen (and increasing the 0.2% yield strength as a material characteristic). (f) By combining the addition of Cu and heat stretching after plating, hydrogen penetration can be effectively suppressed even if the plating peels off, thereby producing a plated steel wire that reduces the possibility of delayed fracture. (g) Note that without plating, the numerous dislocations introduced into lamellar ferrite during wiredrawing cannot be recovered or recrystallized, resulting in a decrease in torsional properties and a lack of delayed fracture resistance. (h) When bundling multiple plated steel wires to manufacture ropes for bridges and other applications, a small diameter of the plated steel wire results in insufficient structural rigidity. Therefore, the diameter (wire diameter) of the steel wire before plating used for bridge ropes and other applications is usually required to be 5.0 mm or more. On the other hand, if the area reduction rate during wiredrawing is reduced to increase the diameter of the steel wire, the tensile strength will be insufficient. Therefore, the diameter of a high-strength steel wire for manufacturing plated steel wires for bridges and other applications is preferably 7.5 mm or less.

[0012] The plated steel wire, rope, and method for manufacturing the rope according to the present disclosure have been discovered based on these findings.

[0013] [Plated Steel Wire] The plated steel wire according to the present disclosure has a steel composition containing, in mass%, C: 0.80 to 1.10%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.050% or less, S: 0.050% or less, N: 0.0120% or less, O: 0.0100% or less, Al: 0.005 to 0.070%, and Cu: 0.04 to 0.80%, with the balance being Fe and impurities, or Fe, optional elements, and impurities. The steel portion of the plated steel wire according to the present disclosure is parallel to the longitudinal direction and has an area ratio of a mixed structure consisting of a ferrite phase and a cementite phase (sometimes referred to as a "mixed structure of a ferrite phase and a cementite phase" or simply as a "mixed structure" in the present disclosure) of 95.0% or more in the center within 1.0 mm from the central axis in a cross section passing through the central axis. The plated steel wire according to the present disclosure has a steel portion (i.e., steel wire portion) with a diameter of 5.0 mm or more, and a surface with a Zn-based plating layer containing Zn as the main component with a Zn content of 100 g / m ２ The plated steel wire according to the present disclosure has a tensile strength of 1900 MPa or more and 2250 MPa or less, and a ratio YS / TS of the yield strength (0.2% proof stress) YS to the tensile strength TS of 0.87 or more.

[0014] (Steel Composition) The steel composition refers to the chemical composition of the steel wire portion coated with the Zn-based plating layer in the plated steel wire according to the present disclosure. Hereinafter, the contents of each element in the steel composition will be described.

[0015] C: 0.80 to 1.10% C is a component necessary for increasing the tensile strength of a steel wire. If the C content is less than 0.80%, the tensile strength will be insufficient. On the other hand, if the C content of a steel wire is too high, the steel wire will harden and the delayed fracture properties will deteriorate. If the C content of a steel wire exceeds 1.10%, it will become difficult to suppress the formation of pro-eutectoid cementite, and the torsional properties will deteriorate. Therefore, the C content is set to 0.80 to 1.10%. From the viewpoint of tensile strength, the C content is preferably 0.85% or more, and in particular, if it is 0.90% or more, better properties will be exhibited. On the other hand, from the viewpoint of compatibility with torsional properties, the C content is preferably 1.05% or less, and in particular, if it is 1.00% or less, better properties will be exhibited.

[0016] Si: 0.10 to 1.50% Si is an effective component for increasing the tensile strength of steel wire. If the Si content of the steel wire is less than 0.10%, the effect of containing Si cannot be fully obtained. On the other hand, if the Si content of the steel wire exceeds 1.50%, it becomes difficult to suppress the formation of a martensite structure, which is a hard layer, and wiredrawability deteriorates. Therefore, the Si content is set to 0.10 to 1.50%, preferably 0.50 to 1.40%, and more preferably 0.70 to 1.30%.

[0017] Mn: 0.10 to 1.00% Mn is an effective component for increasing the tensile strength of steel wire. Furthermore, Mn fixes S in steel as MnS, suppressing hot brittleness. If the Mn content of the steel wire is less than 0.10%, the effects of Mn inclusion are not fully achieved. On the other hand, if the Mn content of the steel wire exceeds 1.00%, it becomes difficult to suppress the formation of a martensite structure, which is a hard layer, and wiredrawability deteriorates. Therefore, the Mn content is set to 0.10 to 1.00%, and preferably 0.25 to 0.80%.

[0018] P: 0.050% or less P is an element that segregates at the grain boundaries of a steel wire and reduces the delayed fracture resistance. If the P content of the steel wire is 0.050% or less, the reduction in delayed fracture resistance is suppressed, and by satisfying other requirements, the target delayed fracture resistance can be obtained. The upper limit of the P content is preferably 0.030%, and more preferably 0.020% or less. Note that the lower limit of the P content is not limited, and is preferably 0% (i.e., no P is contained), but from the viewpoint of reducing the dephosphorization cost, it may be more than 0% or may be 0.001% or more.

[0019] S: 0.050% or less S is an element that reduces delayed fracture resistance. If the S content of the steel wire is 0.050% or less, the target delayed fracture resistance can be obtained while satisfying other requirements. A preferable upper limit of the S content is 0.030%. Note that the lower limit of the S content is not limited, but may be more than 0% or may be 0.001% or more from the viewpoint of reducing desulfurization costs.

[0020] N: 0.0120% or less N is an element that deteriorates torsional properties. If the N content of the steel wire is 0.0120% or less, the target delayed fracture properties can be obtained while satisfying other requirements. A preferred upper limit of the N content is 0.0100%, and a more preferred upper limit is 0.0070%. Note that the lower limit of the N content is not limited, but may be more than 0% or may be 0.0001% or more from the viewpoint of reducing refining costs.

[0021] O: 0.0100% or less O is an element that easily forms oxide-based inclusions in a steel wire. If the O content of the steel wire is 0.0100% or less, coarsening of the oxide-based inclusions is suppressed, and deterioration of torsional properties and delayed fracture properties can be suppressed. A preferred upper limit of the O content is 0.0070%, and a more preferred upper limit is 0.0050%. Note that the lower limit of the O content is not limited, but may be more than 0% or may be 0.0001% or more from the viewpoint of reducing refining costs.

[0022] Al: 0.005 to 0.070% Al is an element that has a deoxidizing effect and is necessary for reducing the amount of oxygen in the steel wire. If the Al content of the steel wire is less than 0.005%, it is difficult to obtain the effects of containing Al. On the other hand, Al is an element that easily forms hard oxide-based inclusions. If the Al content of the steel wire exceeds 0.070%, coarse oxide-based inclusions are significantly more likely to form, resulting in a significant decrease in wire drawability. Therefore, the Al content is set to 0.005 to 0.070%, preferably 0.010 to 0.050%, and more preferably 0.020 to 0.040%.

[0023] Cu: 0.04 to 0.80% Cu has the effect of suppressing hydrogen penetration and is necessary for improving delayed fracture resistance. If the Cu content of the steel wire is less than 0.04%, the effect of containing Cu is not fully obtained. On the other hand, if the Cu content of the steel wire exceeds 0.80%, it becomes difficult to suppress the formation of a martensite structure, which is a hard layer, and wiredrawability deteriorates. Therefore, the Cu content is set to 0.04 to 0.80%, and preferably 0.10 to 0.60%.

[0024] The plated steel wire according to the present disclosure may contain elements (optional elements) other than those described above, provided that the elements do not impair the delayed fracture properties. The optional elements that may be contained in the steel portion (steel wire) of the plated steel wire according to the present disclosure are described below. The optional elements that may be contained in the steel portion of the plated steel wire according to the present disclosure are divided into the following groups A to C in terms of their effects. (Group A) One or more elements selected from the group consisting of Mo: 0.20% or less, Cr: 1.00% or less, and V: 0.15% or less. (Group B) One or more elements selected from the group consisting of Sn: 0.50% or less, and Ni: 0.80% or less. (Group C) One or more elements selected from the group consisting of Ti: 0.050% or less, Nb: 0.050% or less, B: 0.0040% or less, REM: 0.030% or less, Bi: 0.020% or less, Mg: 0.0040% or less, Ca: 0.0040% or less, Zr: 0.030% or less, W: 0.10% or less, Te: 0.030% or less, and Sb: 0.030% or less. Each optional element will be described below.

[0025] Mo: 0 to 0.20% The inclusion of Mo is optional. Mo has the effect of increasing the tensile strength of the steel wire. In order to stably obtain this effect, it is preferable that the Mo content be 0.01% or more. On the other hand, even if the Mo content of the steel wire exceeds 0.20%, the effect saturates. Therefore, when Mo is intentionally contained in the steel wire, the Mo content is preferably within the range of 0.01 to 0.20%, and more preferably 0.02 to 0.10%.

[0026] Cr: 0 to 1.00% The inclusion of Cr is optional. Cr has the effect of increasing the tensile strength of the steel wire. To stably obtain this effect, the Cr content is preferably 0.03% or more. If the Cr content exceeds 1.00%, it becomes difficult to suppress the formation of the martensite structure, which is a hard layer, and wiredrawability deteriorates. Therefore, when Cr is intentionally contained in the steel wire, the Cr content is preferably within the range of 0.03 to 1.00%. Furthermore, the Cr content may preferably be 0.85% or less. More preferably, it is 0.10 to 0.70%.

[0027] V: 0 to 0.15% The inclusion of V is optional. V has the effect of increasing the tensile strength of steel wire. In order to stably obtain this effect, it is preferable that the V content of the steel wire be 0.01% or more. On the other hand, if the V content of the steel wire exceeds 0.15%, the wiredrawability decreases. Therefore, when V is intentionally contained in the steel wire, the V content of the steel wire is preferably 0.02 to 0.15%. A more preferable V content is 0.03 to 0.13%, and even more preferably 0.05 to 0.12%.

[0028] Sn: 0 to 0.50% The inclusion of Sn is optional. Sn has the effect of increasing the corrosion resistance of steel wire. In order to stably obtain this effect, it is preferable that the Sn content be 0.005% or more. On the other hand, even if the Sn content of the steel wire exceeds 0.50%, the effect saturates. Therefore, when Sn is intentionally contained in the steel wire, the Sn content is preferably within the range of 0.001 to 0.50%. More preferably, it is 0.005 to 0.40%.

[0029] Ni: 0 to 0.80% The inclusion of Ni is optional. Ni has the effect of increasing the corrosion resistance of steel wire. In order to stably obtain this effect, it is preferable that the Ni content be 0.01% or more. On the other hand, even if the Ni content of the steel wire exceeds 0.80%, the effect saturates. Therefore, when Ni is intentionally contained in the steel wire, the Ni content is preferably within the range of 0.01 to 0.80%. More preferably, it is 0.05 to 0.60%.

[0030] Ti: 0 to 0.050% The inclusion of Ti is optional. Ti forms carbides or carbonitrides in the steel wire, improving delayed fracture resistance. To achieve this effect, the Ti content of the steel wire is preferably 0.002% or more. On the other hand, if the Ti content of the steel wire exceeds 0.050%, coarse carbides or carbonitrides are likely to be formed, resulting in a decrease in wiredrawability. Therefore, when Ti is intentionally contained in the steel wire, the Ti content of the steel wire is preferably 0.002 to 0.050%. More preferably, it is 0.005 to 0.030%. The Ti content may be 0.025% or less.

[0031] Nb: 0 to 0.050% The inclusion of Nb is optional. Nb forms carbides or carbonitrides in the steel wire, improving delayed fracture resistance. To achieve this effect, the Nb content of the steel wire is preferably 0.002% or more. On the other hand, if the Nb content of the steel wire exceeds 0.050%, coarse carbides or carbonitrides are likely to be formed, resulting in a decrease in wiredrawability. Therefore, when Nb is intentionally contained in the steel wire, the Nb content of the steel wire is preferably 0.002 to 0.050%, more preferably 0.005 to 0.030%. The Nb content may be 0.025% or less.

[0032] B: 0 to 0.0040% The inclusion of B is optional. B has the effect of suppressing the formation of ferrite structures and improving delayed fracture resistance. To obtain this effect, the B content of the steel wire is preferably 0.0003% or more. On the other hand, if the B content of the steel wire exceeds 0.0040%, coarse carbides are likely to be formed, and wiredrawability deteriorates. Therefore, when B is intentionally contained in the steel wire, the B content of the steel wire is preferably 0.0003 to 0.0040%. More preferably, it is 0.0006 to 0.0030%.

[0033] REM: 0 to 0.030% The inclusion of REM is optional. The inclusion of REM allows the steel wire to more stably exhibit high delayed fracture resistance. To obtain this effect, it is preferable that the REM content of the steel wire be 0.002% or more. On the other hand, if the REM content of the steel wire exceeds 0.030%, the effect saturates. Therefore, when REM is intentionally included, the REM content of the steel wire is preferably 0.002 to 0.030%. The REM content may be 0.020% or less. Note that REM refers to a total of 17 elements, namely Sc, Y, and lanthanoids, and the REM content refers to the content of one type of REM when there is one type of REM, and the total content of two or more types of REM when there are two or more types of REM.

[0034] Bi: 0 to 0.020% The inclusion of Bi is optional. If Bi is included, high delayed fracture resistance can be more stably exhibited. To obtain this effect, the Bi content of the steel wire is preferably 0.001% or more. On the other hand, if the Bi content of the steel wire exceeds 0.020%, the effect saturates. Therefore, when Bi is intentionally included in the steel wire, the Bi content of the steel wire is preferably 0.001 to 0.020%. The Bi content may be 0.015% or less.

[0035] Mg: 0 to 0.0040% The inclusion of Mg is optional. If Mg is included, high delayed fracture resistance can be more stably exhibited. To obtain this effect, the Mg content of the steel wire is preferably 0.0002% or more. On the other hand, if the Mg content of the steel wire exceeds 0.0040%, the effect saturates. Therefore, when Mg is intentionally included in the steel wire, the Mg content of the steel wire is preferably 0.0002 to 0.0040%. The Mg content may be 0.0030% or less.

[0036] Ca: 0 to 0.0040% The inclusion of Ca is optional. If Ca is included, high delayed fracture resistance can be more stably exhibited. To obtain this effect, it is preferable that the Ca content of the steel wire be 0.0002% or more. On the other hand, if the Ca content of the steel wire exceeds 0.0040%, the effect saturates. Therefore, when Ca is intentionally included in the steel wire, the Ca content of the steel wire is preferably 0.0002 to 0.0040%. The Ca content may be 0.0030% or less.

[0037] Zr: 0 to 0.030% The inclusion of Zr is optional. If Zr is included, high delayed fracture resistance can be more stably exhibited. To obtain this effect, the Zr content of the steel wire is preferably 0.002% or more. On the other hand, if the Zr content of the steel wire exceeds 0.030%, coarse carbides or carbonitrides are likely to be formed, resulting in a decrease in wiredrawability. Therefore, when Zr is intentionally included in the steel wire, the Zr content of the steel wire is preferably 0.002 to 0.030%. The Zr content may be 0.025% or less.

[0038] W: 0 to 0.10% The inclusion of W is optional. If W is included, high delayed fracture resistance can be more stably exhibited. To obtain this effect, it is preferable that the W content of the steel wire be 0.02% or more. On the other hand, if the W content of the steel wire exceeds 0.10%, the effect saturates. Therefore, when W is intentionally included in the steel wire, the W content of the steel wire is preferably 0.02 to 0.10%. The W content may be 0.08% or less.

[0039] Te: 0 to 0.030%. The content of Te is optional. If Te is contained, high delayed fracture resistance can be more stably exhibited. To obtain this effect, the Te content of the steel wire is preferably 0.001% or more. On the other hand, if the Te content of the steel wire exceeds 0.030%, the effect saturates. Therefore, when Te is intentionally contained in the steel wire, the Te content of the steel wire is preferably 0.001 to 0.030%. The Te content may be 0.020% or less.

[0040] Sb: 0 to 0.030% The inclusion of Sb is optional. If Sb is included, high delayed fracture resistance can be more stably exhibited. To obtain this effect, the Sb content of the steel wire is preferably 0.001% or more. On the other hand, if the Sb content of the steel wire exceeds 0.030%, the effect saturates. Therefore, when Sb is intentionally included in the steel wire, the Sb content of the steel wire is preferably 0.001 to 0.030%. The Sb content may be 0.020% or less.

[0041] (Metallic Structure) The steel portion (steel wire) of the plated steel wire according to the present disclosure has an area ratio of a mixed structure of ferrite and cementite phases of 95.0% or more in the center of a cross section (longitudinal cross section) parallel to the longitudinal direction of the steel wire and passing through the central axis, within 1.0 mm from the central axis. If the area ratio of the mixed structure of ferrite and cementite phases in the center of the longitudinal cross section (cross section parallel to the longitudinal direction of the steel wire) of the steel wire is 95.0% or more, the delayed fracture properties of the steel wire after wiredrawing will be good. If the area ratio of the mixed structure of ferrite and cementite phases in the center of the steel wire is 95.0% or more, and if the area ratio of the mixed structure of ferrite and cementite phases is 95.0% or more including the surface layer, the total area ratio of the remainder is low, so the center is measured as a representative. The area ratio of the mixed structure of ferrite and cementite phases in the center of the cross section of the steel wire may be 96.0% or more, 97.0% or more, 98.0% or more, 99.0% or more, or 100.0%.

[0042] -Measurement of area ratio of metal structure- The center of the longitudinal cross section of the steel wire was measured using a scanning electron microscope (SEM) at a resolution of 3 x 10 －４ mm ２Five images are taken every 200 μm (0.015 mm long, 0.02 mm wide). Picral is used for etching. FIG. 1A shows an example of an SEM image of a longitudinal cross section of a steel wire including a mixed structure of ferrite and cementite phases and a portion that is not a mixed structure of ferrite and cementite phases (sometimes referred to as a "non-mixed structure" in this disclosure). The portion M indicated by the arrow is the non-mixed structure. FIG. 1B is an enlarged image of the portion including the non-mixed structure M in FIG. 1A. FIG. 2B is another example of an SEM image of a longitudinal cross section of a steel wire including a mixed structure of ferrite and cementite phases and a non-mixed structure, and FIG. 2B is an enlarged image of the portion including the non-mixed structure M in FIG. 2A. In each of FIGS. 1B and 2B, the region M surrounded by a black dotted line is the non-mixed structure. A mixed structure of ferrite and cementite phases is formed by wiredrawing pearlite, bainite, etc., and the cementite phase is mixed in the ferrite phase. The area ratio (%) of each SEM image is measured. Specifically, each SEM image is printed on paper, and then a transparent sheet such as an OHP (Overhead Projector) sheet is placed on the paper to color the unmixed structure. The colored transparent sheet is then analyzed by image analysis to measure the total area ratio of the unmixed structure. The area per field of view is 3 × 10 －４ mm ２ The dimensions are 0.015 mm long and 0.02 mm wide, and image analysis software (for example, Luzex AP manufactured by Nireco Corporation) is used for image analysis. The average value (%) is calculated from the area ratio of the non-mixed structure of the five images, and the value obtained by subtracting the average value from 100.0 is taken as the area ratio of the mixed structure of the ferrite phase and cementite phase of the steel wire.

[0043] (Diameter of Steel Portion) The diameter of the steel portion (steel wire) of the plated steel wire according to the present disclosure is 5.0 mm or more. The diameter of the steel portion may be 5.1 mm or more, 5.3 mm or more, 5.5 mm or more, or 6.0 mm or more. There is no particular upper limit to the diameter of the steel portion, but for bridge use, it may be 10.0 mm or less, 8.0 mm or less, or 7.0 mm or less.

[0044] (Tensile strength) The plated steel wire according to the present disclosure has a tensile strength TS of 1900 MPa or more and 2250 MPa or less. If the tensile strength of the plated steel wire is 1900 MPa or more, the delayed fracture resistance deteriorates. This is because the amount of hydrogen penetration increases and the cracking susceptibility due to hydrogen increases. Even if the plated steel wire according to the present disclosure has a tensile strength of 1900 MPa, the delayed fracture resistance can be improved by satisfying other requirements. If the tensile strength of the steel wire exceeds 2250 MPa, the torsional properties deteriorate. Therefore, the upper limit of the tensile strength is set to 2250 MPa.

[0045] (Yield Ratio) The plated steel wire according to the present disclosure has a ratio of the yield strength (0.2% proof stress) YS to the tensile strength TS (yield ratio: YS / TS) of 0.87 or more. When the ratio of the yield strength YS to the tensile strength TS of the steel wire (YS / TS) is 0.87 or more, it is presumed that carbon is fixed at the dislocation core, which suppresses hydrogen fixation around the dislocation, thereby suppressing hydrogen penetration. More preferably, the yield ratio (YS / TS) of the steel wire is 0.90 or more, and even more preferably 0.93 or more.

[0046] - Measurement of tensile strength and yield strength - Plated steel wires used in tensile tests may be straightened. Severe straightening will change the YS, so if the wire is bent and cannot be chucked, multi-point bending may be performed. The tensile test is performed with a plated steel wire length of 340 mm, a chuck distance of 200 mm, and a stroke speed of 10 mm / min. The diameter D of the plated steel wire is measured in two perpendicular directions at the center of the steel wire length using a vernier caliper, and the average value is used. The tensile strength is calculated from the cross-sectional area (mm ２ The yield strength is calculated as the strength at 0.2% plastic deformation (0.2% proof stress) using the linear relationship between stress and strain for tensile strength of 0.2 to 0.4.

[0047] (Zn-based plating layer) In the plated steel wire according to the present disclosure, the surface of the steel wire (base steel, i.e., steel portion) is coated with a Zn-based plating layer containing Zn as the main component to a thickness of 100 g / m ２The Zn-based plating layer, which is mainly composed of Zn, is a plating layer having the highest Zn content (mass %), and may be a plating layer consisting of Zn alone, or a plating layer consisting of an alloy of Zn and other elements. Examples of elements that may be contained in the Zn-based plating layer other than Zn include one or more selected from the group consisting of Al, Cu, Sn, Mg, and Si. The Zn-based plating layer is formed on the surface of the steel wire (base steel) at a rate of 100 g / m ２ By covering with the above, it is possible to effectively suppress the penetration of hydrogen.

[0048] Here, the methods for measuring the torsion characteristics, plating coverage, and diffusible hydrogen content in the examples described later will be described.

[0049] (Twisting characteristics) Evaluation was based on the number of twists until breakage of the plated steel wire, with five wires being tested and the minimum value being evaluated. The chuck distance was 100 × wire diameter D. The rotation speed was 20 rpm. Breakage of the plated steel wire included not only the breakage of the entire plated steel wire, but also the occurrence of a partial crack in the plated steel wire. In other words, if a partial crack occurred in the plated steel wire during the test, the number of twists at that point was used for evaluation. The occurrence of a crack during rotation can be determined by a sudden drop in torque.

[0050] (Plating Weight) The plating weight is calculated from the weight difference when the plating is peeled and the peeled area. After cutting the plated steel wire into 100 mm pieces, the wire is immersed in a chemical solution containing hydrochloric acid and an inhibitor to chemically peel off the plating layer. The plating weight is calculated by dividing the weight difference before and after peeling of the plating layer by the surface area calculated from the wire diameter and length after peeling.

[0051] (Amount of Diffusible Hydrogen) In accordance with JASO M610-92 (Method for Testing Appearance Corrosion of Automotive Parts), one cycle is performed on a steel wire from which plating has been removed: spraying with a 5% aqueous solution of sodium chloride at 35°C for 2 hours, drying at 60°C and 30% RH for 4 hours, and wetting at 50°C and 95% RH for 2 hours. After 168 cycles, the wire is recovered, rust is removed by sandblasting, and then a temperature-programmed hydrogen analysis is performed using a gas chromatograph. The amount of released hydrogen below 200°C is measured for two samples, and the average value is taken as the amount of diffusible hydrogen (HE) absorbed in the usage environment.

[0052] [Method for Manufacturing Plated Steel Wire] The method for manufacturing the plated steel wire according to the present disclosure is not particularly limited, but an example of a suitable manufacturing method will be described below.

[0053] (Production of Wire Rod) A wire rod having the above-described chemical composition (steel composition) is used. In order to adjust the structure of the wire rod to be suitable for wire drawing, it is preferable to heat the wire rod to 950 to 1100°C and then immerse it in a molten salt or lead bath at 550 to 650°C to form a pearlite structure.

[0054] (Wire drawing) The wire rod is drawn to form a steel wire. The wire drawing strain ε due to the wire drawing is expressed by the following formula: ε = Ln(D ０ / D) ２ D ０ is the diameter before wiredrawing, and D is the diameter after wiredrawing. The wiredrawing strain ε is preferably 1.00 or more and 2.50 or less. If the wiredrawing strain ε is lower than 1.00, it is difficult to obtain strength, and if it is higher than 2.50, the strength becomes excessive and the torsional characteristics deteriorate. It is preferable to perform a surface lubrication treatment such as a zinc phosphate coating or a borax coating before wiredrawing. As mentioned above, the diameter D of the steel wire is 5.0 mm or more. There is no particular upper limit for the diameter D of the steel wire, but if it exceeds 7.5 mm, it becomes difficult to obtain the target strength, so the diameter range of the steel wire is set to 5.0 mm to 7.5 mm.

[0055] (Hot-dip galvanizing) After wire drawing, a degreasing treatment is performed, followed by a galvanizing treatment or a zinc-based alloy plating treatment. The molten zinc temperature is preferably within the range of 400 to 530°C. If the molten zinc temperature is less than 400°C, the steel material will harden due to age hardening and the torsional properties will deteriorate. On the other hand, if the molten zinc temperature is above 530°C, softening due to spheroidization of cementite will become significant, resulting in insufficient strength. Therefore, it is preferable to perform the plating treatment at a molten zinc temperature within the range of 400 to 530°C.

[0056] (Heat Stretching) In order to increase the ratio of yield strength YS to tensile strength TS (YS / TS), it is preferable to apply a load of approximately 0.35 to 0.55 times the tensile strength TS of the plated steel wire at 300 to 400°C after the above-mentioned hot-dip galvanizing for approximately 10 to 45 seconds. If the temperature during such heat stretching is less than 300°C, the strength of the plated steel wire increases and the torsional properties deteriorate. On the other hand, if the temperature exceeds 400°C, an improvement in the durability ratio cannot be expected, and delayed fracture properties do not improve. Furthermore, if the temperature is 420°C or higher, there is a possibility that the plating will remelt. Therefore, heat stretching is preferably performed at 300 to 400°C.

[0057] The plated steel wire according to the present disclosure can be manufactured through the above steps. Note that the above method is one example of a preferred method for manufacturing the plated steel wire according to the present disclosure, and the method for manufacturing the plated steel wire according to the present disclosure is not limited to the above method.

[0058] (Applications) The applications of the plated steel wire according to the present disclosure are not particularly limited, but it is suitable for a variety of applications requiring high strength, delayed fracture properties, and torsional properties, such as steel wires for bridge cables and various ropes, etc. For example, a rope (strand) obtained by bundling a plurality of plated steel wires according to the present disclosure can be used for a bridge cable.

[0059] The plated steel wire according to the present disclosure will be described in more detail below with reference to examples. However, these examples do not limit the plated steel wire, rope, and rope manufacturing method according to the present disclosure.

[0060] Example 1 A steel material (steel 1) having the chemical composition (unit: mass %) shown in Table 1 was prepared, and a wire material was produced by the method (conditions) shown in Table 2. Plated steel wires were then produced through wire drawing, hot-dip galvanizing, and heat stretching. The notation "-" in Table 1 indicates that the content of the element in question is at the impurity level and that it can be determined that the element is not substantially contained. The same applies to the notation "-" in Table 4 described below. The remainder of the chemical compositions in Tables 1 and 4 is Fe and impurities. The notation "-" in Table 2 indicates that plating was not performed. In each table, underlines indicate that the element is outside the scope of the present disclosure.

[0061]

[0062]

[0063] For the plated steel wires manufactured by the above-mentioned manufacturing method, the area ratio of the mixed structure of ferrite and cementite phases in the center of the longitudinal cross section of the steel wire portion (base steel), tensile strength, yield strength (0.2% proof stress) YS, coating weight, torsion value, and diffusible hydrogen content HE were measured using the methods described above. Note that the structure other than the mixed structure of ferrite and cementite phases (non-mixed structure) was mainly ferrite and martensite. The following cases were evaluated as good: - torsion value: 10 or more - diffusible hydrogen content HE: 0.100 ppm or less The measurement results are shown in Table 3. The torsion value and diffusible hydrogen content HE that did not meet the above criteria for "good" are underlined. Note that Comparative Example 9 was not plated, and the measurements were taken on a steel wire after wiredrawing.

[0064]

[0065] The plated steel wires of Examples 1 to 4 had high strength of 1900 MPa or more and 2250 MPa or less, and both torsional properties and hydrogen penetration resistance properties were good. In Comparative Example 1, the heating temperature during wire production was high, resulting in coarse grains, and pearlite transformation was not completed during immersion in molten salt, resulting in the formation of martensitic structures, which reduced workability and caused cracks during wiredrawing. In Comparative Example 2, the wiredrawing strain was high, resulting in excessive strength, and therefore insufficient torsional properties. In Comparative Example 3, the heating temperature during heat stretching was low, resulting in excessive strength, and therefore insufficient torsional properties. In Comparative Examples 4 to 8, the proof stress ratio was insufficient and the diffusible hydrogen content HE was high. In Comparative Example 9, the torsional properties were insufficient. This is thought to be because there was no heat input during plating, and ductility was reduced by heat stretching.

[0066] Example 2 Steel materials (steels 2 to 25) having the chemical compositions (unit: mass %) shown in Table 4 were prepared, and plated steel wires were produced under the conditions of manufacturing method A shown in Table 2.

[0067]

[0068] The total area ratio of the ferrite and martensite structures, tensile strength, yield strength (0.2% proof stress) YS, coating weight, torsion value, and diffusible hydrogen content HE of the produced plated steel wires were measured by the methods described above. The structures other than the mixed structure consisting of ferrite and cementite were mainly ferrite and martensite. The measurement results are shown in Table 5.

[0069]

[0070] The plated steel wires of Examples 11 to 24 had high strength of 1900 MPa or more and 2250 MPa or less, and were excellent in both torsional properties and hydrogen penetration resistance. Comparative Example 11 had an insufficient C content, resulting in insufficient strength of less than 1900 MPa. Comparative Example 12 had an excessive C content, resulting in too high strength and insufficient torsional properties. Comparative Example 13 had an excessive Si content, resulting in martensite formation and reduced workability. Comparative Example 14 had an excessive Mn content, resulting in martensite formation and reduced workability. Comparative Example 15 had an excessive N content, resulting in insufficient torsional properties. Comparative Example 16 had an excessive Al content, resulting in reduced workability. Comparative Example 17 had an excessive Cu content, resulting in martensite formation and reduced workability. Comparative Example 18 had a Cu content below the lower limit, resulting in a high diffusible hydrogen content HE. In Comparative Example 19, the amount of Mo was excessive, martensite was formed, and workability was reduced.In Comparative Example 20, the amount of Cr was excessive, and workability was reduced.

[0071] The above describes the plated steel wire, etc. according to the present disclosure, but the plated steel wire, etc. according to the present disclosure are not limited to the above embodiments and examples. For example, the method for producing a plated steel wire according to the present disclosure may involve winding a wire rod, immersing it in a molten salt to produce a wire rod having a desired metal structure, drawing the wire rod to produce a steel wire, and then galvanizing and heat stretching the wire to produce a plated steel wire. Furthermore, the present disclosure also encompasses the case where the plated steel wires are bundled to produce a rope (cable).

[0072] (Additional Notes) The present disclosure includes the following aspects. <1> The steel portion has steel components containing, by mass%, C: 0.80 to 1.10%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.050% or less, S: 0.050% or less, N: 0.0120% or less, O: 0.0100% or less, Al: 0.005 to 0.070%, and Cu: 0.04 to 0.80%, with the balance being Fe and impurities; the steel portion is parallel to the longitudinal direction and has a central portion within 1.0 mm from the center in a cross section passing through the central axis, the total area ratio of ferrite and martensite structures in a central portion within 1.0 mm from the center being 5.0% or less, and the balance being a mixed structure made of ferrite and cementite; the surface of the steel portion is coated with a Zn-based plating layer containing Zn as a main component in an amount of 100 g / m2 or more; A plated steel wire having a tensile strength TS of 1900 MPa or more and 2250 MPa or less, and a ratio YS / TS of a yield strength (0.2% proof stress) YS to the tensile strength TS of 0.87 or more.<2> The steel portion contains, in mass%, C: 0.80 to 1.10%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.050% or less, S: 0.050% or less, N: 0.0120% or less, O: 0.0100% or less, Al: 0.005 to 0.070%, Cu: 0.04 to 0.80%, and further contains one or more elements selected from the group consisting of Group A to Group C below, with the balance being Fe and impurities. (Group A) One or more elements selected from the group consisting of Mo: 0.20% or less, Cr: 1.00% or less, and V: 0.15% or less (Group B) Sn: 0.50% or less, Ni: 0.80% or less, one or two types selected from the group consisting of (Group C) Ti: 0.050% or less, Nb: 0.050% or less, B: 0.0040% or less, REM: 0.030% or less, Bi: 0.020% or less, Mg: 0.0040% or less, Ca: 0.0040% or less, Zr: 0.030% or less, W: 0.10% or less, Te: 0.030% or less, and Sb: 0.030% or less, wherein the total area ratio of the ferrite structure and the martensite structure in the central portion within 1.0 mm from the center in a cross section parallel to the longitudinal direction and passing through the central axis is 5.0% or less, and the remainder is a mixed structure consisting of ferrite and cementite, A plated steel wire, the surface of which is coated with a Zn-based plating layer containing Zn as a main component at a thickness of 100 g / m2 or more, and which has a tensile strength TS of 1900 MPa or more and 2250 MPa or less, and a ratio YS / TS of the yield strength (0.2% proof stress) YS to the tensile strength TS of 0.87 or more. <3> The plated steel wire according to <2>, wherein the steel components include Group A. <4> The plated steel wire according to <2> or <3>, wherein the steel components include Group B. <5> The plated steel wire according to any one of <2> to <4>, wherein the steel components include Group C. <6> A rope comprising a plurality of plated steel wires according to any one of <1> to <5> bundled together. <7> A method for manufacturing a rope, comprising a step of bundling a plurality of plated steel wires according to any one of <1> to <6>.

[0073] The disclosure of Japanese Patent Application No. 2024-067775, filed on April 18, 2024, is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated herein by reference.

Claims

1. The steel portion contains, in mass%, C: 0.80 to 1.10%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.050% or less, S: 0.050% or less, N: 0.0120% or less, O: 0.0100% or less, Al: 0.005 to 0.070%, Cu: 0.04 to 0.80%, Mo: 0 to 0.20%, Cr: 0 to 1.00%, V: 0 to 0.15%, Sn: 0 to 0.50%, Ni: 0 to 0.80%, Ti: 0 to 0.050%, Nb: 0 to 0.050%, B: 0 to 0.0040%, REM: 0 to 0.030%, a steel portion having a steel composition of Bi: 0 to 0.020%, Mg: 0 to 0.0040%, Ca: 0 to 0.0040%, Zr: 0.030%, W: 0 to 0.10%, Te: 0 to 0.030%, Sb: 0 to 0.030%, and the balance being Fe and impurities, wherein an area ratio of a mixed structure consisting of a ferrite phase and a cementite phase is 95.0% or more at a center portion within 1.0 mm from a central axis of a cross section parallel to the longitudinal direction and passing through the central axis, the steel portion having a diameter of 5.0 mm or more, and a surface of the steel portion having a Zn-based plating layer containing Zn as a main component and coated with a Zn-based plating layer having a thickness of 100 g / m ２ a tensile strength TS of 1900 MPa or more and 2250 MPa or less, and a ratio YS / TS of a yield strength (0.2% proof stress) YS to the tensile strength TS of 0.87 or more.

2. The plated steel wire according to claim 1, wherein the steel portion contains, by mass %, one or more elements selected from the group consisting of Groups A to C below: (Group A) One or more elements selected from the group consisting of Mo: 0.20% or less, Cr: 1.00% or less, and V: 0.15% or less. (Group B) One or more elements selected from the group consisting of Sn: 0.50% or less, and Ni: 0.80% or less. (Group C) One or more elements selected from the group consisting of Ti: 0.050% or less, Nb: 0.050% or less, B: 0.0040% or less, REM: 0.030% or less, Bi: 0.020% or less, Mg: 0.0040% or less, Ca: 0.0040% or less, Zr: 0.030% or less, W: 0.10% or less, Te: 0.030% or less, and Sb: 0.030% or less.

3. The plated steel wire according to claim 2, wherein the steel composition includes the Group A steel.

4. A plated steel wire according to claim 2 or 3, wherein the steel composition includes the B group.

5. A plated steel wire according to any one of claims 2 to 4, wherein the steel composition includes the C group.

6. A rope comprising a plurality of plated steel wires according to any one of claims 1 to 5 bound together.

7. A method for manufacturing a rope, comprising the step of bundling a plurality of plated steel wires according to any one of claims 1 to 5 into a rope.

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