WO2019004454A1

WO2019004454A1 - High-strength steel wire

Info

Publication number: WO2019004454A1
Application number: PCT/JP2018/024904
Authority: WO
Inventors: 真小此木; 直樹松井
Original assignee: 新日鐵住金株式会社
Priority date: 2017-06-30
Filing date: 2018-06-29
Publication date: 2019-01-03
Also published as: EP3647446A1; EP3647446A4; KR20200016289A; JP6485612B1; JPWO2019004454A1; CN110832096A

Abstract

A high-strength steel wire comprising a predetermined material composition, wherein: in a cross-section including a central axis of the steel wire and parallel to the central axis, the area ratio of pearlite structures in the steel wire is 90% or greater, the area ratio of pearlite structures in a surface layer part of the steel wire is 80% or greater, and from among the structures over the whole of the steel wire, the area ratio of lamellar pearlite structures with an average cementite length of 1.0 µm or larger is 30% to 65%, and the area ratio of fragmented pearlite structures with an average cementite length of 0.30 µm or smaller is 20% to 50%; and the steel wire has a tensile strength of 1,960 MPa or greater.

Description

High strength steel wire

The present disclosure relates to high strength steel wire.

For high strength steel wires such as rope steel wires, bridge cable steel wires, PC steel wires etc., high carbon steel wire is patented and made into pearlite structure, then wire drawn and aged steel wires It is manufactured using. In recent years, a high strength steel wire having a tensile strength of 1960 MPa or more is required for the purpose of reduction of construction cost or weight reduction of a structure. However, high strength steel wire has a small number of revolutions (breaking value) until fracture in a twisting test, and sometimes vertical cracks called delamination may occur, so it is an issue to have both twisting characteristics and high strength. It has become.

As a technique for improving the torsion characteristics of high strength steel wires, Patent Document 1 proposes a steel wire in which the hardness in the region of 0.1 d (d is the diameter of the wire) is adjusted from the surface layer in the cross section of the steel wire. It is done.
Patent Document 2 proposes a high-strength galvanized steel wire having a helical processed structure with two or more turns in the same direction with respect to a length per 100 d (d: wire diameter).
In Patent Document 3, the area ratio of non-pearlite structure is 10% or less in the portion of depth from the surface layer to 50 μm, the area ratio of non-pearlite structure is 5% or less in the entire cross section, and the plating adhesion amount is on the surface A galvanized steel wire plated with zinc of 300 to 500 g / m ² has been proposed.

Patent Document 4 proposes a method of manufacturing a steel wire which passes tension between steel wires and passes a plurality of rolls at a bending angle after drawing.
In Patent Document 5, after drawing, before zinc plating, T (20 + log t) 12 12700 (T: bruising temperature indicated by absolute temperature, t: bruce indicated by time) at a temperature of 430 ° C. or higher There has been proposed a method of producing a galvanized steel wire which is subjected to a bluing treatment so as to satisfy the following relationship.

Patent Document 1: Japanese Patent Application Laid-Open No. 2000-336459 Patent Document 2: Japanese Patent No. 3130445 Patent Document 3: Japanese Patent No. 5169839 Patent Document 4: Japanese Patent No. 3725576 Patent Document No. 5: Japanese Patent No. 2553612

However, when the tensile strength of the conventional high strength steel wire is increased, the twisting characteristics become unstable, so that the twisting value can not be improved and the occurrence of delamination can not be sufficiently suppressed. At present, coexistence of twisting characteristics and high strength is an issue.
Here, Patent Document 5 describes that a twisting characteristic can be improved by performing a predetermined bluing treatment on a steel wire after wire drawing. However, in Patent Document 5, a wire rod obtained by hot rolling and cooling by a usual method is reheated in a usual atmosphere (that is, an atmospheric atmosphere), immersed in a molten lead bath, cooled and drawn. A predetermined bluing treatment is performed on the obtained steel wire. Therefore, by decarburization of the surface layer portion in the manufacturing process, the area ratio of pearlite structure of the surface layer portion of the steel wire becomes low, and there is a large room for improvement of the twisting characteristics.

Therefore, one aspect of the present disclosure is to provide a high-strength steel wire having high strength and excellent twisting characteristics.

The above-mentioned subject is solved by the following means.

<1>
The component composition is in mass%,
C: 0.85 to 1.20%,
Si: 0.10 to 2.00%,
Mn: 0.20 to 1.00%,
P: 0.030% or less,
S: 0.030% or less,
N: 0.0010 to 0.0080%,
B: 0 to 0.0050%,
Al: 0 to 0.100%,
Ti: 0 to 0.050%,
Cr: 0 to 0.60%,
V: 0 to 0.10%,
Nb: 0 to 0.050%,
Zr: 0 to 0.050%, and
Ni: 0 to 1.00%
Containing the balance Fe and impurities,
In a cross section including the central axis of the steel wire and parallel to the central axis, the area ratio of pearlite structure in the steel wire is 90% or more, and the area ratio of pearlite structure in the surface layer of the steel wire is 80% or more,
Among the structures in the entire steel wire, the area ratio of lamellar pearlite structure having an average length of cementite of 1.0 μm or more is 30% to 65%, and the average length of cementite is 0.30 μm The area ratio of the divided perlite structure which is less than or equal to 20% and less than or equal to 50%,
And, a high strength steel wire having a tensile strength of 1960 MPa or more.
<2>
The composition of the steel wire is, in mass%, one or more of B: 0.0001 to 0.0050%, Al: 0.001 to 0.100%, and Ti: 0.001 to 0.050%. The high strength steel wire as described in <1> containing 2 or more types.
<3>
The composition of the steel wire is, in mass%, Cr: 0.01 to 0.60%, V: 0.01 to 0.10%, Nb: 0.001 to 0.050%, Zr: 0. The high strength steel wire according to <1> or <2>, containing one or more of 001 to 0.050% and Ni: 0.01 to 1.00%.
<4>
The high-strength steel wire according to any one of <1> to <3>, wherein the diameter of the steel wire is 1.5 to 8.0 mm.
<5>
The high strength steel wire according to any one of <1> to <4>, wherein a plated layer having any one of a Zn layer and a Zn alloy layer is coated on the surface of the steel wire.

According to one aspect of the present disclosure, a high strength steel wire having high strength and excellent twisting characteristics is provided.

FIG. 1 is a schematic view for explaining an observation area for measuring an area ratio of pearlite structure in an inner portion and a surface portion of a steel wire. FIG. 2 is a schematic view for explaining an observation area for measuring the area ratio of the lamellar pearlite structure and the area ratio of the divided pearlite structure.

An embodiment which is an example of the present disclosure will be described.
In the present specification, a numerical range represented using “to” means a range including numerical values described before and after “to” as the lower limit value and the upper limit value.
Further, a numerical range in which “super” or “less than” is added to the numerical values described before and after “to” means a range that does not include these numerical values as the lower limit value or the upper limit value.
Further, the content of the element of the component composition is expressed as an element amount (for example, an amount of C, an amount of Si, etc.).
Moreover, "%" means "mass%" about content of the element of a component composition.
Also, the term "step" is included in the term if the intended purpose of the step is achieved, even if it can not be distinguished clearly from the other steps, not only an independent step.

Also, "a cross section including the central axis of the steel wire and parallel to the central axis" includes the central axis of the steel wire and is cut along the longitudinal direction of the steel wire (that is, the drawing direction) parallel to the central axis It shows a cross section.
The "central axis" indicates an imaginary line extending in the axial direction, passing through the center point of the cross section orthogonal to the axial direction (longitudinal direction) of the steel wire.
Moreover, "the length of cementite" indicates the length of the long axis of cementite in pearlite structure when a cross section including the central axis of the steel wire and parallel to the central axis is observed.
Moreover, "the inside of a steel wire" shows the area | region of the depth which exceeded 100 micrometers toward the central axis (toward the radial direction) from the surface of a steel wire.
Moreover, "the surface layer part of a steel wire" shows the area | region of the depth to 100 micrometers toward the central axis (in the radial direction) from the surface of a steel wire.
In addition, the notation “XD” (X = numerical value) indicates that when the diameter of the steel wire is D, from the surface of the steel wire toward the central axis (in the radial direction), X times the diameter D Indicates the location of depth. For example, “0.25 D” indicates a position at a depth of 0.25 times the diameter D.

The high strength steel wire according to the present embodiment is a high strength steel wire having a predetermined component composition and having a metal structure satisfying the following (1) and (2) and having a tensile strength of 1960 MPa or more. .
(1) In a cross section including the central axis of the steel wire and parallel to the central axis, the area ratio of pearlite structure in the steel wire is 90% or more, and the area ratio of pearlite structure in the surface layer of the steel wire is 80% or more It is.
(2) The area ratio of the lamellar pearlite structure having an average length of cementite of 1.0 μm or more among the structures in the entire steel wire is 30% or more and 65% or less, and the average length of cementite is 0 The area ratio of the divided perlite structure which is 30 μm or less is 20% or more and 50% or less.

The high-strength steel wire according to the present embodiment is a steel wire having high strength and excellent twisting characteristics by the above configuration. The high strength steel wire according to the present embodiment was found by the following findings.

First, in order to improve the twisting characteristics of high strength steel wire with a tensile strength of 1960 MPa or more, the metallographic structure of the steel wire is pearlite, and the lamellar pearlite structure with a long cementite length and the cementite length It is effective to make a mixed structure of short and divided perlite tissue. The pearlite structure has a layered structure of cementite phase and ferrite phase.
When wire drawing of pearlite wire, the metallographic structure of the drawn steel wire is pearlite structure with fine layer spacing, pearlite structure with irregularly bent layers, pearlite structure with locally sheared layers, etc. Is a heterogeneous and complex organization. When ordinary hot-dip galvanizing treatment is performed by immersing the steel wire in this state in a hot-dip zinc bath at 440 to 460 ° C. for about 30 seconds, microscopic mechanical properties become uneven. Such non-uniform steel wires locally deform when subjected to torsional deformation, and the torsion value decreases.
On the other hand, when the microscopic mechanical properties of the steel wire are made uniform, the deformation at the time of torsional deformation becomes uniform, and the torsion value improves.

Therefore, the inventors investigated in detail the effects of the component composition and the metal structure of the steel wire on the torsion characteristics. As a result, the present inventors obtained the following findings. By adjusting the composition of the steel wire, the area ratio of the non-pearlite structure of the steel wire is reduced (that is, the area ratio of the pearlite structure of the steel wire is increased) and the cementite has a long lamellar pearlite structure and a long length. If the pearlite structure is a mixture of a divided pearlite structure having a short cementite length, the twisting characteristics are improved even with a high strength steel wire having a tensile strength of 1960 MPa or more.

That is, when the metallographic structure of the steel wire satisfies the above (1) and (2), it is possible to obtain high torsion characteristics even if the strength of the steel wire is 1960 MPa or more. Thus, it has become possible to improve the twisting characteristics of high strength steel wires by improving the structure of the steel wires.

From the above, it has been found that the high-strength steel wire according to the present embodiment is a steel wire having high strength and excellent twisting characteristics.
The high-strength steel wire according to the present embodiment is a steel wire having a tensile strength of 1960 MPa or more and excellent in torsion characteristics, and can be used, for example, as a steel wire for ropes, steel wire for bridge cables, PC steel wire, etc. . Therefore, the high-strength steel wire according to the present embodiment contributes, for example, to weight reduction of civil engineering and buildings and reduction of construction costs, and is extremely useful in industry.

(Component composition)
The composition of the high strength steel wire is, in mass%, C: 0.85 to 1.20%, Si: 0.10 to 2.00%, Mn: 0.20 to 1.00%, P: 0. 030% or less, S: 0.030% or less, N: 0.0010 to 0.0080%, B: 0 to 0.0050%, Al: 0 to 0.100%, Ti: 0 to 0.050%, Cr: 0 to 0.60%, V: 0 to 0.10%, Nb: 0 to 0.050%, Zr: 0 to 0.050%, and Ni: 0 to 1.00% It consists of the balance Fe and impurities.
However, B, Al, Ti, Cr, V, Nb, Zr, and Ni are optional elements. That is, these elements may not be contained in the high strength steel wire.

Hereinafter, the reason for limiting the range of the amount of each element contained in the high strength steel wire will be described.

C is added to secure the tensile strength of the steel wire. If the amount of C is less than 0.85%, pro-eutectoid ferrite is formed, and it is difficult to secure a predetermined tensile strength. On the other hand, when the amount of C exceeds 1.20%, the amount of proeutectoid cementite increases and the wire drawability deteriorates. Therefore, the amount of C is set to 0.85 to 1.20%. The lower limit of the preferable C amount to achieve both high strength and wire drawability is 0.90%. Moreover, the upper limit of the preferable C amount which makes high strength and wire-drawing workability compatible is 1.10%.

Si has the effect of enhancing tensile strength by solid solution strengthening, as well as enhancing the relaxation characteristics. If the amount of Si is less than 0.10%, these effects are insufficient. When the amount of Si exceeds 2.00%, these effects are saturated and the hot ductility is deteriorated to lower the manufacturability. Therefore, the amount of Si is set to 0.10 to 2.00%. The lower limit of the preferred amount of Si is 0.50%. More preferably, the lower limit of the amount of Si may be 1.00%. On the other hand, the upper limit of the preferable amount of Si is 1.80%. The upper limit of the amount of Si is more preferably 1.50%.

Mn has the effect of increasing the tensile strength of the steel after pearlite transformation. If the amount of Mn is less than 0.20%, the effect is insufficient. When the amount of Mn exceeds 1.00%, the effect is saturated. Therefore, the amount of Mn is set to 0.20 to 1.00%. The lower limit of the preferable amount of Mn is 0.30%. The upper limit of the preferable amount of Mn is 0.90%.

P and S are contained in the steel wire as impurities. P and S should be suppressed because they deteriorate ductility. Therefore, the upper limit of both P amount and S amount was made into 0.030%. The upper limit of preferable P amount and S amount is 0.020%. The upper limit of more preferable P amount and S amount is 0.015% or less. In addition, although the lower limit of P amount and S amount is preferably 0% (that is, although it is good not to include), it is more than 0% (or 0.0001% or more) from the viewpoint of reducing de-P cost and desulfurization cost. Good to have.

N forms nitrides with Al, Ti, Nb, V, etc., and has the effect of refining the grain size and improving the ductility. If the amount of N is less than 0.0010%, these effects are not obtained. If the amount of N exceeds 0.0080%, wire drawability and ductility are deteriorated. Therefore, the N content is set to 0.0010 to 0.0080%. The lower limit of the preferable N amount is 0.0020%. The upper limit of the preferable N amount is 0.0060%. The upper limit of the more preferable N amount is 0.0050%.

In the steel wire according to the present embodiment, in order to reduce the area ratio of the non-pearlite structure in the surface layer portion of the steel wire, B: 0.0001 to 0.0050%, Al: 0.001 to 100% by mass. It may contain one or more of 0.100% and Ti: 0.001 to 0.050%.

B is segregated at grain boundaries as solid solution B to suppress the formation of non-pearlite structure, and has an effect of improving twisting characteristics and wire drawability. If the B content exceeds 0.0050%, carbides may be formed at grain boundaries to deteriorate drawability. Therefore, the B content is preferably 0.0001 to 0.0050%. The lower limit of the preferable B amount is 0.0005%. On the other hand, the upper limit of the preferable B amount is 0.0030%. The upper limit of the amount of B is more preferably 0.0020%.

Al functions as a deoxidizing element. In addition, Al has the effect of forming AlN to refine crystal grains and improving ductility, the effect of reducing solid solution N and improving ductility, and promoting the formation of solid solution B to form a non-pearlite structure. There are effects such as suppressing and improving twisting characteristics and wire drawability. If the Al content exceeds 0.100%, the effect may be saturated and the productivity may be reduced. Therefore, the Al content is preferably 0.001 to 0.100%. The lower limit of the preferred amount of Al is 0.010%. The lower limit of the amount of Al is more preferably 0.020%. On the other hand, the upper limit of the preferable amount of Al is 0.080%. The upper limit of the amount of Al is more preferably 0.070%.

Ti functions as a deoxidizing element. In addition, Ti precipitates carbides and nitrides to increase tensile strength, reduces grain size to improve ductility, reduces solid solution N, and improves wire drawability, solid There is an effect of promoting the formation of melt B, suppressing the formation of non-pearlite structure, and improving the twist characteristics and wire drawability. When the amount of Ti exceeds 0.050%, these effects may be saturated and coarse oxides or nitrides may be formed to deteriorate wire drawability. Therefore, the amount of Ti is preferably 0.001 to 0.050%. The lower limit of the preferred amount of Ti is 0.010%. On the other hand, the upper limit of the preferable Ti amount is 0.030%. The upper limit of the amount of Ti is more preferably 0.025%.

The high strength steel wire according to the present embodiment has Cr: 0.01 to 0.60%, V: 0.01 to 0.10%, Nb: 0.001 to 200 for the purpose of improving the characteristics described below. It may contain one or more of 0.050%, Zr: 0.001 to 0.050%, and Ni: 0.01 to 1.00%.

Cr has the effect of increasing the tensile strength of the steel after pearlite transformation. When the amount of Cr exceeds 0.60%, a martensitic structure tends to be formed, which may deteriorate wire drawability and twisting characteristics. The amount of Cr is preferably 0.01 to 0.60%. The upper limit of the preferable amount of Cr is 0.50%. The upper limit of the amount of Cr is more preferably 0.40%.

V has the effect of precipitating carbide VC and enhancing the tensile strength. If the V content exceeds 0.10%, the alloy cost may increase and the twisting characteristics may be degraded. Therefore, the V content is preferably 0.01 to 0.10%. The upper limit of the preferable V amount is 0.08%. The upper limit of the more preferable V amount is 0.07%.

Nb has an effect of precipitating carbides and nitrides to enhance tensile strength, an effect of refining crystal grains to improve ductility, and an effect of reducing solid solution N to improve wire drawability. When the Nb content exceeds 0.050%, these effects may be saturated and the twisting characteristics may be degraded. Therefore, the Nb content is preferably 0.001 to 0.050%. The upper limit of the preferable Nb amount is 0.030%. The upper limit of the more preferable Nb amount is 0.020%.

Zr functions as a deoxidizing element. Further, Zr has the effect of reducing the solid solution S by forming a sulfide and improving the ductility. If the Zr content exceeds 0.050%, these effects saturate and coarse oxides may be formed, which may deteriorate wire drawability. Therefore, the amount of Zr is preferably 0.001 to 0.050%. The upper limit of the preferable amount of Zr is 0.030%. The upper limit of the more preferable amount of Zr is 0.020%.

Ni has the effect of suppressing the penetration of hydrogen and improving the resistance to hydrogen embrittlement. When the amount of Ni exceeds 1.00%, the alloy cost is increased, and a martensitic structure is easily formed, which may deteriorate wire drawability. Therefore, the amount of Ni is preferably 0.01 to 1.00%. The upper limit of the preferable amount of Ni is 0.50%. The upper limit of the amount of Ni is more preferably 0.30%.

In the component composition of the high strength steel wire according to the present embodiment, the balance is Fe and impurities.
Here, the term "impurity" refers to a component contained in the raw material or a component which is mixed in the process of production and is not intentionally contained. Furthermore, the impurities also include components that are intentionally contained, but in an amount that does not affect the performance of the steel wire.
As an impurity, O etc. are mentioned, for example. O is unavoidably contained in the steel wire and exists as an oxide such as Al or Ti. When the amount of O is high, coarse oxides are formed, which causes breakage during wire drawing. Therefore, it is preferable to suppress the amount of O to 0.010% or less.

(Metal structure)
Next, the reason for limitation of the metal structure of the high strength steel wire according to the present embodiment will be described.

In the metallographic structure, the area ratio of pearlite structure in the steel wire is 90% or more, and the area ratio of pearlite structure in the surface layer of the steel wire is 80% or more.
The area ratio of the pearlite structure is an area ratio in a cross section including the central axis of the line and parallel to the central axis.

In the metallographic structure inside the steel wire, if the area ratio of pearlite structure is less than 90%, the strength is reduced or the twisting property is deteriorated. For this reason, the lower limit of the area ratio of pearlite structure is set to 90%. The lower limit of the area ratio of the preferred perlite structure is 95%. The lower limit of the area ratio of the more preferable pearlite structure is 97%. The upper limit of the area ratio of the pearlite structure may be 100% or 99%.

Inside the steel wire, the remaining structure (i.e., non-pearlite structure) other than pearlite structure is ferrite, bainite, tempered bainite, martensite, tempered martensite, proeutectoid cementite or the like.

When the area ratio of the pearlite structure in the surface layer portion of the steel wire is less than 80%, the twisting characteristic or the wire drawability deteriorates. Therefore, the lower limit of the area ratio of pearlite structure in the surface layer portion is set to 80%. The lower limit of the area ratio of the preferred pearlite structure is 85%. The lower limit of the area ratio of the more preferable pearlite structure is 90%. The upper limit of the area ratio of the pearlite structure may be 95% or 99%. In addition, the area ratio of the perlite structure may be 100%.
As a method of setting the area ratio of the pearlite structure of the surface layer portion of the steel wire to 80% or more, for example, a method of containing B and further containing at least one of Al and Ti, or hot There is a method of controlling the cooling rate of the wire after rolling. By performing either or both of these methods, it is possible to increase the area ratio of pearlite structure in the surface layer of the steel wire.

In the surface layer portion of the steel wire, the remaining structure (i.e. non-pearlite structure) other than pearlite structure is ferrite, bainite, tempered bainite, martensite, tempered martensite, proeutectoid cementite or the like.

Here, in order to impart high twisting characteristics to a high strength steel wire having a tensile strength of 1960 MPa or more, a lamellar pearlite structure having a long cementite length and a divided pearlite structure having a short cementite length are used. It is effective to make the pearlite tissue mixed in an appropriate ratio. The steel wire in this embodiment has a non-uniform and complicated structure including the dislocation introduced by wire drawing after wire drawing and before the aging treatment. When ordinary hot dip galvanizing treatment (or equivalent aging treatment with heat treatment) is applied to steel wire with non-uniform pearlite structure, the microscopic mechanical properties after plating treatment (or after aging treatment) are not good. It becomes uniform. Such a steel wire has a small twist value because it locally deforms when subjected to torsional deformation. However, by applying appropriate aging treatment (or plating treatment under appropriate conditions) to the steel wire in this state, it is possible to reduce non-uniformity of microscopic mechanical properties and improve twisting characteristics.

The "lamellar pearlite structure" as used herein refers to a pearlite structure in which cementite has a long length and an average length of 1.0 μm or more. Of the perlite that had been present before the aging treatment, the part having a relatively small influence by the aging treatment is a lamellar pearlite structure. If the area ratio of the lamellar pearlite structure is less than 30%, the strength is reduced (that is, it is difficult to obtain a strength of 1960 MPa or more), and if it exceeds 65%, the twisting property is degraded.
Therefore, the area ratio of the lamellar pearlite structure is 30% or more and 65% or less. The lower limit of the area ratio of the preferred lamellar perlite structure is 40%, more preferably 50%. The upper limit of the area ratio of the preferred lamellar pearlite structure is 60%.

On the other hand, the "divided perlite structure" as used herein refers to a pearlite structure having a short cementite length and an average length of 0.30 μm or less. Among the pearlite that had been present until the aging treatment, the strain formed by wire drawing and the structure formed as a result of the cementite in the pearlite being divided by the influence of the aging treatment is a divided pearlite structure. And, if the area ratio of the divided pearlite structure is less than 20%, the twisting characteristics deteriorate, and if it exceeds 50%, the strength decreases.
Therefore, the area ratio of the divided perlite structure is set to 20% or more and 50% or less. The lower limit of the area ratio of the preferable split pearlite structure is 25%, and the more preferable lower limit is 30%. On the other hand, the upper limit of the area ratio of a preferable divided pearlite structure is 45%, more preferably 40%.
The method of setting the area ratio of split pearlite structure of steel wire to 20% or more and 50% or less is, for example, 80% or more of area ratio of pearlite structure of surface layer portion after wire drawing at a total reduction ratio of 65 to 95%. There is a method of holding the steel wire which is at 500 to 600 ° C. for 1 s or more and 20 s or less, or a method for holding the steel wire at 420 to 480 ° C. for 60 s or more and 600 s or less.
The measurement method of the organization was as follows.

Here, the area ratio of the pearlite structure inside the steel wire is determined by the following procedure.
First, a cross section including the central axis of the steel wire and parallel to the central axis (hereinafter also referred to as “L cross section”) is etched with picral to reveal a metal structure. Next, a metallographic structure in a region of 50 μm in the radial direction of the steel wire × 60 μm in the longitudinal direction of the steel wire is photographed at a magnification of 2000 times by a SEM (scanning electron microscope). Where the diameter of the steel wire is D, the location of the SEM photograph of the metallographic structure is a position of a depth of 0.25 D in the radial direction of the steel wire from the surface (that is, the outer peripheral surface) of the steel wire and At a depth of 0.5 D from the surface in the radial direction of the steel wire, three points are provided at intervals of 5 mm in the longitudinal direction of the steel wire, for a total of six places (see FIG. 1). In addition, OA1 shows the area | region of photography of the SEM photograph of the metallographic structure in the inside of a steel wire in FIG.
Non-perlite structures (structures of ferrite, bainite, tempered bainite, martensite, tempered martensite, and proeutectoid cementite) in the SEM photograph of the metallographic structure taken are visually marked, and the area ratio is determined by image analysis. The percent area of pearlite tissue is determined by subtracting the area of non-perlite tissue from the entire field of view. And this is measured about two samples, and let the average value of a total of 12 measured be the area ratio of the pearlite structure | tissue inside a steel wire.

Next, the pearlite structure of the surface layer portion of the steel wire is determined according to the following procedure.
First, in the same manner as described above, the L cross section of the steel wire is etched with picral to reveal a metallographic structure. The metallographic structure in the region of 50 μm from the surface in the depth direction (radial direction of the steel wire) and 60 μm in the longitudinal direction of the steel wire, including the surface of the steel wire, is photographed by SEM at 2000 × magnification. The places where the SEM photograph of the metal structure is taken are six places at intervals of 5 mm in the longitudinal direction of the steel wire (see FIG. 1). In addition, OA2 shows the area | region of photography of the SEM photograph of the metallographic structure in the surface layer part of a steel wire in FIG.
Non-perlite structures (structures of ferrite, bainite, tempered bainite, martensite, tempered martensite, and proeutectoid cementite) in the SEM photograph of the metallographic structure taken are visually marked, and the area ratio is determined by image analysis. The percent area of pearlite tissue is determined by subtracting the area of non-perlite tissue from the entire field of view. And this was measured about two samples, and the average value of a total of 12 measured was made into the area ratio of the pearlite structure of the surface layer part of a steel wire.

Next, the area ratio of the lamellar pearlite structure and the area ratio of the divided perlite structure are determined according to the following procedure.
First, in the same manner as described above, the L cross section of the steel wire is etched with picral to reveal a metallographic structure. Next, a metallographic structure in a region of 8 μm in the radial direction of the steel wire × 12 μm in the longitudinal direction of the steel wire is photographed at a magnification of 10000 by SEM. When the diameter of the steel wire is D, the location of the SEM photograph of the metallographic structure is 50 μm deep from the surface of the steel wire to the radial direction of the steel wire, and from the surface of the steel wire to the radial direction of the steel wire Three points at a distance of 5 mm in the direction parallel to the longitudinal direction of the steel wire, at a position of depth of 0.25 D and at a position of depth of 0.5 D in the radial direction of the steel wire from the surface of the steel wire There are nine places (see Figure 2). Note that, in FIG. 2, OA indicates an area for taking a SEM photograph.
On the SEM photograph image of the metallographic structure taken, a straight line group of 2 μm intervals parallel to the longitudinal direction of the steel wire is drawn. Furthermore, draw straight lines at intervals of 2 μm crossing these straight lines at right angles. Next, the tissue at each intersection of the two straight line groups is observed by the following method. The length of the cementite long axis is measured by image analysis in three cementite close to each intersection where the pearlite structure exists, and their average value is an average value of the cementite long axis (that is, the average length And). In addition, when cementite is small and it can not discriminate | determine by a 10000 times SEM photograph, you may expand the magnification of a SEM photograph. Determine the number of intersections where the average length of the major axes of three cementite in the vicinity of the intersection is 1.0 μm or more, and the number of all intersections including the intersection where there is no pearlite structure (that is, the two drawn The percentage of the value divided by the number of all intersections of the straight line group, that is, (the number of intersections in which the average length of the major axis of cementite is 1.0 μm or more) / (the number of all intersections) × 100 , And the area ratio of lamellar pearlite tissue.

The area ratio of the divided perlite structure is also the same procedure as described above, and the SEM photograph of the metal structure is taken, and the length of the long axis of cementite is measured by image analysis in three cementite close to each intersection where the perlite structure exists. Then, the average value of the long axis lengths of cementite (that is, the average length) is determined. Determine the number of intersections where the average value of the major axis lengths of three cementite in the vicinity of the intersection is 0.30 μm or less, and calculate the percentage of the value divided by the number of all intersections including the intersection where there is no pearlite structure , And the area ratio of the divided perlite structure.

(Characteristics of high strength steel wire)
Next, the tensile strength of the high strength steel wire according to the present embodiment will be described.
If the tensile strength of the steel wire is less than 1960 MPa, for example, when the steel wire is applied to a civil engineering / building structure application, the effects of reduction in construction cost and weight reduction become small. Therefore, the lower limit of the tensile strength of the steel wire is set to 1960 MPa.
The upper limit of the tensile strength of the steel wire is not particularly limited, but if the tensile strength is too high, the ductility may be reduced and cracking may occur when wire drawing is performed. In this respect, the upper limit of the tensile strength of the steel wire is preferably 3000 MPa (preferably 2800 MPa, more preferably 2500 MPa).

Next, the wire diameter of the high strength steel wire according to the present embodiment will be described.
The high-strength steel wire according to the present embodiment may be a high-strength steel wire used for a rope steel wire, a bridge cable steel wire, a PC steel wire, and the like. Therefore, if the wire diameter (diameter) of the steel wire is less than 1.5 mm, the cost at the time of manufacturing these products increases, and if it exceeds 8.0 mm, the strength and twisting characteristics are easily deteriorated. Therefore, the wire diameter (diameter) of the steel wire is preferably 1.5 mm to 8.0 mm. A more preferable range of the wire diameter (diameter) of the steel wire is 3.0 mm to 7.5 mm.

Here, in the high-strength steel wire according to the present embodiment, a plating layer having any one of a Zn layer and a Zn alloy layer may be coated on the surface of the steel wire. Examples of the Zn alloy layer include a ZnAl layer, a ZnAlMg alloy layer, and the like.
The high strength steel wire used for the steel wire for ropes, the steel wire for bridge cables, etc. may use the steel wire by which the surface was plated. And, even if the surface is plated, the high strength steel wire according to this embodiment is a steel wire which is high in strength and excellent in twisting characteristics.
In the high-strength steel wire according to the present embodiment, the surface of the steel wire or the surface of the plated steel wire may be coated with a resin coating layer (for example, an epoxy resin layer).

(Method of manufacturing high strength steel wire)
An example of the manufacturing method of the high strength steel wire concerning this embodiment is explained.
In the method of manufacturing a high strength steel wire according to the present embodiment, a steel piece having the component composition of the high strength steel wire according to the present embodiment is heated to 1000 to 1150 ° C., and thermal rolling is performed at a finish rolling temperature of 850 to 1000 ° C. It has a process of obtaining a wire rod by rolling.

In the method of manufacturing a high-strength steel wire according to the present embodiment, modes (1) to (6) having the following steps can be mentioned as steps after the step of obtaining a wire rod.

-Aspect (1)-
Cooling the wire, which is at 850 to 1000 ° C., to 500 to 600 ° C. at an average cooling rate of 30 to 80 ° C./s from 800 ° C. to 600 ° C. after hot rolling;
A pearlite transformation process by holding the wire after cooling to 500 to 600 ° C. for 50 s or more at 500 to 600 ° C .;
After the pearlite transformation treatment, the wire cooled to room temperature is drawn at a total reduction of area of 65 to 95%, held at 500 to 600 ° C. for 1 second to 20 seconds, and obtaining a steel wire;
A method of manufacturing a high strength steel wire having the

-Aspect (2)-
Cooling the wire, which is at 850 to 1000 ° C., to 500 to 600 ° C. at an average cooling rate of 800 to 600 ° C. at 30 to 80 ° C./s after hot rolling;
A pearlite transformation process by holding the wire after cooling to 500 to 600 ° C. for 50 seconds or more at 500 to 600 ° C .;
After the pearlite transformation treatment, the wire cooled to room temperature is drawn with a total reduction of area of 65 to 95%, held at 420 to 480 ° C. for 60 s or more and 600 s or less, to obtain a steel wire;
A method of manufacturing a high strength steel wire having the

-Aspect (3)-
Cooling the wire, which is at 850 to 1000 ° C., at an average cooling rate from 700 ° C. to 550 ° C. at 1.0 to 5.0 ° C./s after hot rolling;
Wire drawing after cooling to room temperature with a total reduction in area of 65 to 95% and holding at 500 to 600 ° C. for 1 s or more and 20 s or less to obtain a steel wire;
A method of manufacturing a high strength steel wire having the

-Aspect (4)-
Cooling the wire, which is at 850 to 1000 ° C., at an average cooling rate from 700 ° C. to 550 ° C. at 1.0 to 5.0 ° C./s after hot rolling;
Wire drawing after cooling to room temperature with a total reduction in area of 65 to 95% and holding at 420 to 480 ° C. for 60 seconds or more and 600 seconds or less to obtain a steel wire;
A method of manufacturing a high strength steel wire having the

-Aspect (5)-
Re-heating the cooled wire rod to 800 to 1050 ° C. after hot rolling and holding it at 480 to 600 ° C. for 20 seconds or more, and then cooling it;
Wire drawing after cooling to room temperature with a total reduction in area of 65 to 95% and holding at 500 to 600 ° C. for 1 s or more and 20 s or less to obtain a steel wire;
A method of manufacturing a high strength steel wire having the

-Aspect (6)-
Re-heating the cooled wire rod to 800 to 1050 ° C. after hot rolling and holding it at 480 to 600 ° C. for 20 seconds or more, and then cooling it;
Wire drawing after cooling to room temperature with a total reduction in area of 65 to 95% and holding at 420 to 480 ° C. for 60 seconds or more and 600 seconds or less to obtain a steel wire;
A method of manufacturing a high strength steel wire having the

Hereinafter, the detail of the manufacturing method of the high strength steel wire which concerns on this embodiment is demonstrated.

In the method for manufacturing a high strength steel wire according to the present embodiment, first, a steel piece having the component composition of the high strength steel wire according to the present embodiment is heated to 1000 to 1150 ° C.
When the heating temperature is less than 1000 ° C., deformation resistance in hot rolling increases and rolling cost increases. When the heating temperature exceeds 1150 ° C., the area ratio of the non-pearlite structure in the surface layer increases, and the wire drawability and twisting characteristics deteriorate. The lower limit of the preferred heating temperature range is 1050.degree. The upper limit of the preferred heating temperature range is 1100 ° C.

Next, the heated billet is hot-rolled at a finish rolling temperature of 850 to 1000 ° C. to obtain a wire rod.
When the finish rolling temperature is less than 850 ° C., deformation resistance in hot rolling increases and rolling cost increases. When the finish rolling temperature exceeds 1000 ° C., the metal structure becomes coarse and wire drawability deteriorates. The lower limit of the preferred finish rolling temperature range is 870 ° C. The upper limit of the preferred finish rolling temperature range is 980 ° C.
The finish rolling temperature refers to the surface temperature of the wire immediately after finish rolling.

Next, after hot rolling (specifically, after finish rolling), the wire rod at 850 to 1000 ° C. is cooled to 500 to 600 ° C. at an average cooling rate of 30 to 80 ° C./s from 800 ° C. to 600 ° C. Do.
When the average cooling rate is less than 30 ° C./s, the area ratio of the non-pearlite structure in the surface layer increases, and the wire drawability and the twisting property deteriorate. In order to make the average cooling rate 80 ° C./s or more, the manufacturing cost increases. The lower limit of the preferred average cooling rate range is 40 ° C./s. The upper limit of the preferable average cooling rate range is 75 ° C./s. In addition, an average cooling rate refers to the surface cooling rate of a wire.
When the cooling temperature is less than 500 ° C., the pearlite area ratio becomes small, and the twisting characteristics deteriorate. When the cooling temperature exceeds 600 ° C., the strength decreases. The lower limit of the preferred cooling temperature range is 530.degree. The upper limit of the preferred cooling temperature range is 580 ° C.

Next, the wire after cooling to 500 to 600 ° C. is subjected to pearlite transformation treatment by holding the wire at 500 to 600 ° C. for 50 seconds or more.
When the holding temperature is less than 500 ° C., the pearlite area ratio becomes small, and the twisting characteristics deteriorate. When the holding temperature exceeds 600 ° C., the strength decreases. The lower limit of the preferred holding temperature range is 530 ° C. The upper limit of the preferred holding temperature range is 580 ° C.
If the holding time is less than 50 s, pearlite transformation is incomplete, martensite is formed, and wire drawability and twisting characteristics deteriorate. However, from the viewpoint of manufacturing cost, the upper limit of the holding time is preferably 150 s. The lower limit of the preferred holding time range is 60 s. The upper limit of the preferred holding time range is 120 s. The holding at 500 to 600 ° C. is performed, for example, by a molten salt bath.

Here, in place of the above cooling and pearlite transformation treatment, after hot rolling, the wire rod at 850 to 1000 ° C. is cooled at an average cooling rate of 700 to 550 ° C. at 1.0 to 5.0 ° C./s You may The cooling is performed by, for example, a blast cooling facility such as Stelmore.
If the average cooling rate is less than 1.0 ° C./s, the strength decreases. When the average cooling rate exceeds 5.0 ° C./s, microscopic variations in strength and metallographic structure become large, and the torsion characteristics deteriorate. The lower limit of the preferred average cooling rate range is 1.2 ° C./s. The upper limit of the preferred average cooling rate range is 3.0 ° C./s.

Also, instead of the above cooling treatment and pearlite transformation treatment, after hot rolling, the wire rod cooled to room temperature (for example 25 ° C.) is reheated to 800 to 1050 ° C. and held for 20 s or more at 480 to 600 ° C. cooling You may
When the reheating temperature is less than 800 ° C., the austenitizing is insufficient and a uniform pearlite structure can not be obtained, and the strength is lowered and the wire drawability is deteriorated. When the reheating temperature exceeds 1050 ° C., the area ratio of the non-pearlite structure in the surface layer increases, and the wire drawability and the twisting property deteriorate. The lower limit of the preferred reheating temperature range is 940 ° C. The upper limit of the preferred reheating temperature range is 1020 ° C.
When the holding temperature is less than 480 ° C., the area ratio of pearlite structure decreases and the twisting characteristics deteriorate. When the holding temperature exceeds 600 ° C., the lamellar spacing of the perlite structure increases and the strength decreases. The lower limit of the preferred holding temperature range is 520 ° C. The upper limit of the preferred holding temperature range is 590.degree.
If the holding time is less than 20 s, pearlite transformation becomes incomplete, martensite is formed, and wire drawability and twisting characteristics deteriorate. However, from the viewpoint of manufacturing cost, the upper limit of the holding time is preferably 120 s. The lower limit of the preferred retention time range is 30 s. The upper limit of the preferred retention time range is 80 s.
When the reheating treatment is performed in an oxidizing atmosphere, the area ratio of pearlite structure in the surface layer portion of the steel wire may be reduced, and the wire drawability and the twisting property may be deteriorated. Therefore, the atmosphere for the reheat heat treatment is, for example, an inert gas (such as Ar gas), a neutral gas (such as nitrogen gas), or an endothermic modified gas. Further, the reheating treatment may be heating for a short time such as induction heating.
The holding at 480 to 600 ° C. is performed, for example, in a molten lead bath. Instead of the molten lead bath, a molten salt bath, a fluidized bed or the like may be used.

Then, the wire rod after the above pearlite transformation treatment or after cooling (specifically, the wire rod after cooling to room temperature (for example, 25 ° C.) is drawn at a total reduction of 65 to 95%, and 500 to 600 ° C. Hold for 1 s or more and 20 s or less to obtain a steel wire. By holding at 500 to 600 ° C. for 1 s or more and 20 s or less, the twisting characteristic is improved. The heat treatment after wire drawing is also referred to as "aging treatment".
If the total reduction rate is less than 65%, the strength decreases. If the total area reduction rate exceeds 95%, the ductility of the steel wire is reduced, and the wire drawability and twisting characteristics are degraded. The preferred total reduction rate is 70 to 90%. The total area reduction rate is the difference between the cross-sectional area of the wire before drawing (the area of the surface perpendicular to the longitudinal direction of the wire) and the cross-sectional area of the steel wire after drawing / wire drawing It is a value calculated by cross section area of wire before processing × 100.
When the holding temperature is less than 500 ° C., there is no effect of improving the twisting characteristics. When the holding temperature exceeds 600 ° C., the strength decreases. The preferred holding temperature range is 510-550.degree.
If the holding time is less than 1 s, there is no effect of improving the twisting characteristics. If the holding time exceeds 20 s, the strength decreases. The preferred holding temperature range is 2 to 15 s.

Here, after wire drawing, instead of holding at 500 to 600 ° C. for 1 s or more and 20 s or less, it may be held at 420 to 480 ° C. for 60 s or more and 600 s or less.
If the holding temperature is less than 420 ° C., the twisting characteristic is degraded. When the holding temperature exceeds 480 ° C., the strength decreases. The preferred holding temperature range is 430-470.degree.
If the holding time is less than 60 s, the twisting characteristics deteriorate. If the holding time exceeds 600 s, the manufacturing cost increases. The preferred holding temperature range is 100 to 500 s.

Through the above steps, the high strength steel wire according to the present embodiment is obtained.

The manufacturing method of the high strength steel wire according to the present embodiment is a step of performing plating treatment at 420 to 480 ° C. for covering the plating layer having any one of Zn layer and Zn alloy layer after the above-mentioned aging treatment May be included.

In addition, the manufacturing method of the high strength steel wire which concerns on this embodiment is replaced with said aging treatment,
Plating treatment for coating a plating layer having a Zn layer and any one layer of Zn alloy layer on the surface of a steel wire is performed under the conditions of 60s to 600s at 420 to 480 ° C, or 1s to 20s at 500 to 600 ° C. You may have the process performed on condition of the following. Also in this case, a similar structure is formed on the steel wire due to the temperature change of the steel wire accompanying the plating process.
That is, the surface of the steel wire is plated under the conditions of temperature and time corresponding to the above-mentioned aging treatment to provide the structural state of the steel wire according to the present embodiment, and any of the Zn layer and the Zn alloy layer A high strength steel wire coated with a plating layer having one layer is obtained.

In addition, the method for manufacturing a high strength steel wire according to the present embodiment further includes the step of covering the surface of the steel wire or the surface of the plated steel wire with a resin coating layer (for example, an epoxy resin layer). May be Even if the resin coating layer is present, excellent strength and twisting characteristics can be realized as long as the steel wire present inside the resin coating layer has the structure state of the steel wire according to the present embodiment.

Hereinafter, the present invention will be described in more detail by way of examples. However, these examples do not limit the present invention.

A steel wire was manufactured as follows using the steel pieces of steel types A to S having the component compositions shown in Table 1 under the conditions shown in Tables 2 to 6.

Specifically, steel wires of test numbers 1 to 30 shown in Table 2 were manufactured as follows.
First, after heating a steel piece, it was hot-rolled, and the obtained wire was wound into a ring and cooled to 500 to 600.degree. Next, the obtained wire was immersed in a molten salt bath at the rear of a hot rolling line to perform patenting (perlite transformation). Thereafter, the wire rod cooled to room temperature (25 ° C.) was drawn to the wire diameter shown in Table 2 (denoted as the wire diameter after wire drawing), and after heating, it was heated and aged. Through these steps, steel wires shown in Test Nos. 1 to 30 were produced.

The steel wires of test numbers 31 to 34 shown in Table 3 were manufactured as follows.
First, after heating a steel piece, it hot-rolled, wound the obtained wire rod like ring shape, and carried out blast cooling. Thereafter, the wire rod cooled to room temperature (25 ° C.) was drawn to the wire diameter shown in Table 3, and after the drawing, it was heated and aged. Through these steps, steel wires shown in Test Nos. 31 to 34 were manufactured.

In addition, steel wires of test numbers 35 to 40 shown in Table 4 were manufactured as follows.
After heating the billet, it was hot-rolled, and the obtained wire was wound into a ring, and cooled at an average cooling rate of 2.0 ° C./s. Next, the wire rod cooled to room temperature (25 ° C.) was reheated in a predetermined atmosphere and immersed in a molten lead bath. Thereafter, the wire rod cooled to room temperature (25 ° C.) was subjected to wire drawing to the wire diameter shown in Table 4, and after the wire drawing was heated for aging treatment. Through these steps, steel wires shown in Test Nos. 35 to 40 were manufactured.

Moreover, the steel wire of the test number 41 shown in Table 5 was manufactured as follows.
First, after heating a steel piece, it was hot-rolled, and the obtained wire was wound into a ring and cooled to 500 to 600.degree. Next, the obtained wire rod was dipped in a molten salt bath after the hot rolling line for patenting treatment. Thereafter, the wire rod cooled to room temperature (25 ° C.) was subjected to wire drawing to the wire diameter shown in Table 5, and after the wire drawing was heated for aging treatment. Thereafter, it was subjected to hot dip galvanization treatment. Through these steps, a steel wire shown in Test No. 41 was manufactured.

Moreover, the steel wire of the test number 42 shown in Table 6 was manufactured like the steel wire of the test number 22 except having changed the order of wiredrawing and aging treatment.

And metal structure was observed with respect to these steel wires, and a tension test and a torsion test were performed.

Area ratio of pearlite structure in steel wire, area ratio of pearlite structure in surface layer of steel wire, area ratio of lamellar pearlite structure (lamellar pearlite structure having an average length of cementite of 1.0 μm or more), division The area ratio of pearlite structure (divided pearlite structure having an average length of cementite of 0.30 μm or less) was measured according to the method described above. The results are shown in Tables 2 to 5.

In the tensile test, in accordance with JIS Z 2241 (2011), using a 9A test piece, three steel wires were evaluated at a time, and the average value was determined. The results are shown in Tables 2 to 5.

In the torsion test, 10 pieces of steel wire were evaluated in accordance with the torsion test method of JIS G 3521 (1991), and the presence or absence of delamination and the torsion value were evaluated. When delamination occurred even in 1 out of 10, it was determined that delamination was present. When the twist value was less than 12 times, it was determined to be defective. When no delamination occurred and the twist value was 12 or more, it was judged that the twist characteristics were good. The results are shown in Tables 2 to 6.

From the above results, the steel wires of test numbers 1 to 11, 21 to 25, 30 to 32, 35 to 38, and 41 that satisfy all the requirements specified in the present disclosure have a tensile strength of 1960 MPa or more and a twisting characteristic of It turns out that it is good.

On the other hand, in the steel wire of test No. 12, the area ratio of pearlite structure is less than the lower limit of the present disclosure.
In the steel wires of test numbers 13, 17, 27, 39, 42, the area ratio of the divided perlite structure is out of the range of the present disclosure.
In the steel wires of test numbers 18 and 40, the area ratio of pearlite structure in the surface layer portion is lower than the lower limit of the present disclosure. In addition, the steel wire of test number 40 is an example corresponded to the steel wire of patent document 5. FIG.

In the steel wires of test numbers 28 and 33, the area ratio of the lamellar pearlite structure exceeds the upper limit of the present disclosure.
In the steel wires of test numbers 14, 16, 26, and 29, the area ratio of the lamellar pearlite structure and the area ratio of the divided perlite structure are out of the scope of the present disclosure.

The steel wires of test numbers 15 and 34 are any of the area ratio of pearlite structure inside the steel wire, the area ratio of pearlite structure of the surface layer of the steel wire, the area ratio of lamellar pearlite structure, and the area ratio of divided pearlite structure The thigh is out of the scope of the present disclosure.
The test numbers 19, 20 have a C amount outside the scope of the present disclosure.

Any of the steel wires outside the scope of the present disclosure has poor twisting characteristics or insufficient tensile strength of the steel wire.

The disclosure of Japanese Patent Application No. 2017-128871 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards described herein are as specific and individually as individual documents, patent applications, and technical standards are incorporated by reference. Incorporated herein by reference.

Claims

The component composition is in mass%,
C: 0.85 to 1.20%,
Si: 0.10 to 2.00%,
Mn: 0.20 to 1.00%,
P: 0.030% or less,
S: 0.030% or less,
N: 0.0010 to 0.0080%,
B: 0 to 0.0050%,
Al: 0 to 0.100%,
Ti: 0 to 0.050%,
Cr: 0 to 0.60%,
V: 0 to 0.10%,
Nb: 0 to 0.050%,
Zr: 0 to 0.050%, and
Ni: 0 to 1.00%
Containing the balance Fe and impurities,
In a cross section including the central axis of the steel wire and parallel to the central axis, the area ratio of pearlite structure in the steel wire is 90% or more, and the area ratio of pearlite structure in the surface layer of the steel wire is 80% or more,
Among the structures in the entire steel wire, the area ratio of lamellar pearlite structure having an average length of cementite of 1.0 μm or more is 30% to 65%, and the average length of cementite is 0.30 μm The area ratio of the divided perlite structure which is less than or equal to 20% and less than or equal to 50%,
And, a high strength steel wire having a tensile strength of 1960 MPa or more.
The composition of the steel wire is, in mass%, one or more of B: 0.0001 to 0.0050%, Al: 0.001 to 0.100%, and Ti: 0.001 to 0.050%. The high strength steel wire according to claim 1 containing two or more kinds.
The composition of the steel wire is, in mass%, Cr: 0.01 to 0.60%, V: 0.01 to 0.10%, Nb: 0.001 to 0.050%, Zr: 0. The high strength steel wire according to claim 1 or 2, containing one or more of 001 to 0.050% and Ni: 0.01 to 1.00%.
The high strength steel wire according to any one of claims 1 to 3, wherein a diameter of the steel wire is 1.5 to 8.0 mm.
The high strength steel wire according to any one of claims 1 to 4, wherein a plating layer having any one of a Zn layer and a Zn alloy layer is coated on the surface of the steel wire.