WO2019164015A1

WO2019164015A1 - Wire rod, steel wire, and aluminum-coated steel wire

Info

Publication number: WO2019164015A1
Application number: PCT/JP2019/007342
Authority: WO
Inventors: 俊彦手島; 直樹松井
Original assignee: 日本製鉄株式会社
Priority date: 2018-02-26
Filing date: 2019-02-26
Publication date: 2019-08-29
Also published as: JP6881665B2; JPWO2019164015A1

Abstract

This wire rod has a chemical composition containing, in mass%, 0.80-1.10% of C, 0.005-0.100% of Si, 0.05-0.30% of Mn, 0-0.030% of P, 0-0.030% of S, 0-0.0060% of N, not less than 0.02% but less than 0.30% of Cr, 0.02-0.15% of Mo, 0-0.050% of Al, 0-0.050% of Ti, and 0-0.0030% of B, the balance being Fe and impurities, and the total amount of Mo and Cr being 0.13% or more, wherein the average area ratio of a pearlite structure in a region within d/7 from the center of the wire rod and a region within d/7 from the peripheral surface of the wire rod is 90% or more in a cross-section perpendicular to the longitudinal direction of the wire rod, where d represents the diameter of the wire rod. This steel wire is obtained by subjecting the wire rod to a drawing process. This aluminum-coated steel wire is obtained by coating the steel wire with an aluminum-containing layer.

Description

Wire, steel wire and aluminum coated steel wire

This disclosure relates to wire rods, steel wires, and aluminum-coated steel wires.

Conventionally, studies on steel wires for reinforcing transmission lines have been made.
For example, Patent Document 1 includes carbon (C) 0.9 to 1.2% by weight, silicon (Si) 1.0 to 1.5% by weight, manganese (Mn) 0.4 to 0.6% by weight, Chromium (Cr) 0.2 to 0.7 wt%, sulfur (S) 0.015 wt% or less (excluding 0%), phosphorus (P) 0.015 wt% or less (excluding 0%), And the rest is a step of producing a steel wire by drawing steel containing iron (Fe) and inevitable impurities, and primary plating the steel wire in a galvanizing tank, the iron is diffused, and the iron and zinc are A mixed iron-zinc alloy layer; a first plating step for forming a zinc plating layer formed on the iron-zinc alloy layer; and the iron-zinc alloy layer is transformed into an iron-zinc-aluminum alloy layer. The first plating step so that the galvanized layer is transformed into a zinc-aluminum alloy layer. A second plating step of performing secondary plating in a zinc-aluminum plating bath, and the thickness of the iron-zinc-aluminum alloy layer includes the iron-zinc-aluminum alloy layer, the zinc-aluminum alloy layer, A method for producing a high-strength plated steel wire for reinforcing an overhead power transmission line is disclosed which is formed into a plated steel wire having a thickness of 40% to 60% of the total thickness.

On the other hand, there is a case where improvement in electrical conductivity is required for steel materials.
For example, in Patent Document 2, as a steel material for electrical parts capable of performing cold forging with good dimensional accuracy and ensuring excellent electrical conductivity, C: 0.02% or less (0 %), Si: 0.1% or less (not including 0%), Mn: 0.1 to 0.5%, P: 0.02% or less (including 0%), S: 0.02 % Or less (including 0%), Al: 0.01% or less (including 0%), N: 0.005% or less (including 0%), O: 0.02% or less (including 0%) The steel material for electrical parts excellent in cold forgeability and electrical conductivity which satisfy | fills (3) and a metal structure is a ferrite single phase structure is disclosed.

Patent Document 1: Japanese Patent Application Laid-Open No. 2016-076482 Patent Document 2: Japanese Patent Application Laid-Open No. 2003-226938

By the way, a steel core aluminum stranded cable (hereinafter sometimes referred to as “ACSR”), which is a cable using aluminum as a conductor, is used for applications such as power transmission lines. There is.
The ACSR generally has a structure in which a galvanized steel wire or a stranded wire is used as a core material and an aluminum wire is twisted outside. When an ACSR having such a structure is used in a high humidity area such as a coastal area, zinc is corroded at a contact portion between zinc and aluminum having different electrode potentials by using rainwater or the like as an electrolytic solution. May come into contact with aluminum and corrode aluminum. Therefore, in these areas, instead of the galvanized steel wire, as the core material of the ACSR, an aluminum-coated steel wire having an aluminum (aluminum) -containing layer that covers at least a part of the steel wire ( Aluminum-clad steel wire (hereinafter sometimes referred to as “AC wire”) may be used.

In the ACSR using an AC wire as a core material, current flows not only in the aluminum wire portion twisted on the outside of the core material but also in the AC wire as the core material. Therefore, from the viewpoint of improving the power transmission efficiency, it may be required to reduce the electrical resistivity of the AC line.
On the other hand, it may be required to improve the tensile strength of the AC wire.

In order to reduce the electrical resistivity of the AC wire and improve the tensile strength, it is necessary to reduce the electrical resistivity of the steel wire in the AC wire and improve the tensile strength of the steel wire. It is considered effective. For this purpose, it is considered effective to reduce the electrical resistivity of the wire used for the production of the steel wire and to improve the tensile strength of the wire.
However, with the techniques disclosed in Patent Document 1 and Patent Document 2, it is difficult to obtain a wire material with reduced electrical resistivity and excellent tensile strength.

An object of the present disclosure is to provide a wire and a steel wire that have reduced electrical resistivity and excellent tensile strength.
Moreover, the subject of this indication is providing the aluminum covering steel wire provided with the said steel wire.

The means for solving the above problems include the following aspects.

<1> C: 0.80% or more and 1.10% or less in terms of mass%
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% to 0.030%,
S: 0% or more and 0.030% or less,
N: 0% or more and 0.0060% or less,
Cr: 0.02% or more and less than 0.30%,
Mo: 0.02% to 0.15%,
Al: 0% or more and 0.050% or less,
Ti: 0% or more and 0.050% or less,
B: 0% or more and 0.0030% or less, and
The balance: Fe and impurities, and the total amount of Mo and Cr is 0.13% or more,
In a cross section perpendicular to the longitudinal direction, when the diameter of the wire is d, the average area ratio of the pearlite structure in the region within d / 7 from the center and the region within d / 7 from the outer peripheral surface is 90% or more Is a wire rod.
<2> The wire according to <1>, wherein an average length of cementite in a region within d / 10 from the center is 2.0 μm or more in a cross section perpendicular to the longitudinal direction.
<3> When the mass% of Mo is [Mo], [Mo] and γ represented by the following formula (1) satisfy γ ≦ [Mo]. wire.
γ = 0.018 / ([C] × ([Cr] +0.1) ² ) (1)
Each element symbol in the formula (1) indicates mass% of each element.
<4> The wire according to any one of <1> to <3>, wherein α represented by the following formula (2) and β ₁ represented by the following formula (3) satisfy α <β ₁ .
α = 4.4 × [Si] + 2.2 × [Mn] + [Cr] + [Mo] (2)
β ₁ = 0.54 / [C] ² + [C] / 10 (3)
Each element symbol in the formulas (2) and (3) indicates mass% of each element.
<5> represented by alpha and the following formula by the following formula (2) (4) and beta ₂ which is expressed by, alpha <satisfy beta ₂ <1> ~ wire according to any one of <4> .
α = 4.4 × [Si] + 2.2 × [Mn] + [Cr] + [Mo] (2)
β ₂ = 0.54 / [C] ² (4)
Each element symbol in the formulas (2) and (4) indicates mass% of each element.
<6> Any one of <1> to <5>, containing at least one of Al: 0.005% to 0.050% and Ti: 0.005% to 0.050% by mass% Wire described in one.
<7> The wire according to any one of <1> to <6>, which contains B: 0.0001% to 0.0030% by mass.
<8> In a cross section perpendicular to the longitudinal direction, the average particle diameters of the pearlite blocks in a region within d / 10 from the center and a region within d / 10 from the outer peripheral surface are 23.0 μm or less, respectively The wire according to any one of to <7>.
<9> The wire according to any one of <1> to <8>, wherein an average lamella spacing of the pearlite structure in a region within d / 10 from the center is 90 nm or less in a cross section perpendicular to the longitudinal direction. .
<10> The wire according to any one of <1> to <9>, which satisfies that the electrical resistivity in the longitudinal direction is less than 0.180 μΩm.
<11> The wire according to any one of <1> to <10>, wherein the diameter is 3.0 mm or greater and 10.0 mm or less.
<12> The wire according to any one of <1> to <11>, which is used for producing a steel wire in an aluminum-coated steel wire.
<13> A steel wire that is a drawn product of the wire according to any one of <1> to <12>.
<14> The chemical composition is mass%,
C: 0.80% or more and 1.10% or less,
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% to 0.030%,
S: 0% or more and 0.030% or less,
N: 0% or more and 0.0060% or less,
Cr: 0.02% or more and less than 0.30%,
Mo: 0.02% to 0.15%,
Al: 0% or more and 0.050% or less,
Ti: 0% or more and 0.050% or less,
B: 0% or more and 0.0030% or less, and
The balance: Fe and impurities, and the total amount of Mo and Cr is 0.13% or more,
In the cross section perpendicular to the longitudinal direction, when the diameter of the steel wire is D, the average area ratio of the pearlite structure in the region within D / 7 from the center and the region within D / 7 from the outer peripheral surface is 90%. The steel wire in which the average particle diameter of the pearlite block in the region within D / 7 from the center is 5.0 μm or less.
<15> An aluminum-coated steel wire comprising the steel wire according to <13> or <14> and an aluminum-containing layer that covers at least a part of the steel wire.

According to the present disclosure, it is possible to provide a wire and a steel wire that have reduced electrical resistivity and excellent tensile strength.
According to this indication, an aluminum covering steel wire provided with the above-mentioned steel wire is provided.

It is the schematic which shows the center area | region and surface layer area | region which measure a structure | tissue in a cross section (cross section) perpendicular | vertical with respect to the longitudinal direction of a wire.

In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In the present specification, “%” indicating the content of a component (element) means “mass%”.
In the present specification, the content of C (carbon) may be referred to as “C content”. The content of other elements may be expressed in the same manner.
In the numerical ranges described stepwise in this specification, the upper limit value or lower limit value of a stepwise numerical range may be replaced with the upper limit value or lower limit value of another stepwise numerical range. Also, the values shown in the examples may be substituted.

〔wire〕
The wire of the present disclosure is
Chemical composition is C: 0.80% or more and 1.10% or less by mass%
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% to 0.030%,
S: 0% or more and 0.030% or less,
N: 0% or more and 0.0060% or less,
Cr: 0.02% or more and less than 0.30%,
Mo: 0.02% to 0.15%,
Al: 0% or more and 0.050% or less,
Ti: 0% or more and 0.050% or less,
B: 0% or more and 0.0030% or less, and
The balance: Fe and impurities, and the total amount of Mo and Cr is 0.13% or more,
In the cross section perpendicular to the longitudinal direction, when the diameter is d, the average area ratio of the pearlite structure in the region within d / 7 from the center and the region within d / 7 from the outer peripheral surface is 90% or more.

The wire rod of the present disclosure has reduced electrical resistivity and excellent tensile strength.
In this specification, the tensile strength of a wire means the tensile strength in the longitudinal direction of the wire at room temperature (for example, 20 ° C.).
In this specification, the electrical resistivity of a wire means the electrical resistivity in the longitudinal direction of the wire at room temperature (for example, 20 ° C.).

The aforementioned effects of the wire of the present disclosure (that is, reduction in electrical resistivity and improvement in tensile strength) are achieved by a combination of the chemical composition and a metal structure in a cross section perpendicular to the longitudinal direction. .
For example, in the chemical composition of the wire according to the present disclosure, the content of Si, Mn, Cr, Mo, or the like is reduced below the upper limit value of the content of each element. As a result, the electrical resistivity is reduced.
Generally, when alloy elements such as Si, Mn, Cr, and Mo are reduced, the tensile strength may be reduced. In this regard, in the wire according to the present disclosure, the average area ratio of the pearlite structure in the above-described region is limited to 90% or more by the combined addition of Cr and Mo. Thereby, the tensile strength is improved.
In the wire according to the present disclosure, the electrical resistivity of the wire is improved and the tensile strength is improved by these configurations.

<Chemical composition of wire>
Hereinafter, the chemical composition of the wire of the present disclosure will be described.
The chemical composition of the wire of the present disclosure is C: 0.80% to 1.10%, Si: 0.005% to 0.100%, Mn: 0.05% to 0.30%, P: 0% to 0.030%, S: 0% to 0.030%, N: 0% to 0.0060%, Cr: 0.02% to less than 0.30%, Mo: 0.02% 0.15% or less, Al: 0% or more and 0.050% or less, Ti: 0% or more and 0.050% or less, B: 0% or more and 0.0030% or less, and the balance: Fe and impurities, And the total amount of Mo and Cr is 0.13% or more.
The chemical composition of the raw material of the wire rod of the present disclosure (for example, melted steel, steel slab (for example, billet) described later) is the same as the chemical composition of the wire rod of the present disclosure. This is because the production process from molten steel to steel wire (for example, billet) to the wire does not affect the chemical composition.
Hereinafter, the chemical composition of the wire or steel wire of the present disclosure may be referred to as “chemical composition in the present disclosure”.
Hereinafter, the content of each element in the chemical composition of the wire of the present disclosure will be described.

(C: 0.80% to 1.10%)
C is an element effective for increasing the tensile strength of the wire. If the C content is less than 0.80%, the tensile strength of the wire may be insufficient. For this reason, C content is 0.80% or more. The C content is preferably 0.85% or more.
On the other hand, if the C content exceeds 1.10%, the ductility of the wire may decrease. The reason for this is considered that when the C content exceeds 1.10%, it is industrially difficult to suppress the formation of proeutectoid cementite (cementite precipitated along the former austenite grain boundaries). . Therefore, the C content is 1.10% or less. The C content is preferably 1.05% or less, and more preferably 1.00% or less.

(Si: 0.005% or more and 0.100% or less)
Si is an element effective for increasing the tensile strength of the wire by solid solution strengthening, and is also an element necessary as a deoxidizer. However, if the Si content is less than 0.005%, the effect of adding these Si may not be sufficient. For this reason, Si content is 0.005% or more. From the viewpoint of more stably enjoying these Si addition effects, the Si content is preferably 0.010%, more preferably 0.015% or more.
On the other hand, Si is an element that increases the electrical resistivity of the wire. If the Si content exceeds 0.100%, the electrical resistivity of the wire may be excessively increased. Therefore, the Si content is 0.100% or less. Si content becomes like this. Preferably it is 0.090% or less, More preferably, it is 0.070% or less, More preferably, it is 0.050% or less.

(Mn: 0.05% or more and 0.30% or less)
Mn is an element having an effect of increasing the tensile strength of the wire. Mn is also an element having an action of preventing hot brittleness of the wire by fixing S in steel as MnS. However, if the Mn content is less than 0.05%, these effects may not be sufficient. For this reason, the Mn content is 0.05% or more. Furthermore, in order to achieve the higher level of securing the tensile strength of the wire and preventing hot brittleness, the Mn content is preferably 0.10% or more, more preferably 0.13% or more. More preferably 0.15% or more.
On the other hand, Mn has the effect of increasing the electrical resistivity of the wire. For this reason, when Mn content exceeds 0.30%, the electrical resistivity of a wire may become large too much. Therefore, the Mn content is 0.30% or less. The Mn content is preferably 0.25% or less.

(N: 0% or more and 0.0060% or less)
N is an element that increases the electrical resistivity of the wire. For this reason, when N content exceeds 0.0060%, the electrical resistivity of a wire may become large too much. For this reason, N content is 0.0060% or less. From the viewpoint of further reducing the electrical resistivity of the wire, the N content is preferably 0.0050% or less.
The N content may be 0%. However, N is also an element that increases the tensile strength of the wire by fixing dislocations during cold drawing. From the viewpoint of such effects, the N content may be greater than 0%, may be 0.0010% or more, and may be 0.0020% or more.

(P: 0% to 0.030%)
P is an element that segregates at the grain boundaries of steel and increases the electrical resistivity. If the P content exceeds 0.030%, the electrical resistivity of the wire may be excessively increased. For this reason, P content is 0.030% or less. From the viewpoint of further reducing the electrical resistivity of the wire, the P content is preferably 0.025% or less, and more preferably 0.020% or less.
The P content may be 0%. However, from the viewpoint of reducing the manufacturing cost (dephosphorization cost), the P content may be more than 0%, 0.0005% or more, or 0.0010% or more. .

(S: 0% to 0.030%)
S is an element that increases the electrical resistivity of the wire. If the S content exceeds 0.030%, the electrical resistivity of the wire may be excessively increased. For this reason, S content is 0.030% or less. From the viewpoint of further reducing the electrical resistivity of the wire, the S content is preferably 0.020% or less, and more preferably 0.015% or less.
The S content may be 0%. However, from the viewpoint of reducing manufacturing costs (desulfurization costs), the S content may be more than 0%, 0.002% or more, or 0.005% or more.

(Cr: 0.02% or more and less than 0.30%)
Cr is an element that improves hardenability. For this reason, it is an element which raises the area ratio of a pearlite structure | tissue and improves tensile strength by compound addition with Mo mentioned later. Cr is also an element that increases the tensile strength of the wire by reducing the lamella spacing of the pearlite structure. In order to acquire these effects, it is necessary to make Cr content 0.02% or more. Cr content becomes like this. Preferably it is 0.05% or more, More preferably, it is 0.07% or more, More preferably, it is 0.10% or more.
On the other hand, if the Cr content is 0.30% or more, the electrical resistivity of the wire may be excessively increased. For example, when manufactured under manufacturing conditions in which the distribution of Cr to ferrite is not sufficient during the pearlite transformation, Cr may reduce the electrical resistivity. From the viewpoint of suppressing an excessive increase in the electrical resistivity of the wire, the Cr content is less than 0.30%. The Cr content is more preferably 0.25% or less.

(Mo: 0.02% to 0.15%)
Mo is an element that improves hardenability. For this reason, it is an element which raises the area ratio of a pearlite structure | tissue and improves tensile strength by compound addition with Cr mentioned above. In order to acquire this effect, it is necessary to make it 0.02% or more.
On the other hand, if the Mo content exceeds 0.15%, the hardenability of the wire may be excessively increased. In this case, the pearlite transformation during patenting becomes insufficient, and the area ratio of the pearlite structure may decrease. Moreover, when the addition amount of Mo becomes excessive, the electrical resistivity of a wire may become excessively large. From the viewpoint of suitability for manufacturing the wire, the Mo content is 0.15% or less, and more preferably 0.13% or less.

Addition of both Mo and Cr has the effect of increasing the area ratio of the pearlite structure and improving the tensile strength. The present inventors have found that this effect can be further enhanced by adding both Mo and Cr in combination. That is, in the case where the above effect is obtained by adding Cr and Mo in combination, the necessary effect can be obtained with a small amount of alloy addition, compared with the case where Cr is added alone or Mo is added alone. On the other hand, the electrical resistivity of the wire was not affected by the combined addition of Cr and Mo. That is, by adding Cr and Mo in combination, the amount of alloy addition can be reduced and the electrical resistivity of the wire can be reduced while ensuring the required area ratio and tensile strength of the pearlite structure.
From the viewpoint of further exerting the effect of combined addition of Mo and Cr, the total amount of Mo and Cr is 0.13% or more, preferably 0.15% or more in mass%.
On the other hand, from the viewpoint of further reducing the electrical resistivity of the wire, the total amount of Mo and Cr is mass%, preferably 0.40% or less, and more preferably 0.36% or less.

From the viewpoint of further improving the tensile strength of the wire, when the respective mass percentages of Mo, C, and Cr are [Mo], [C], and [Cr], respectively, [Mo] and the following formula (1) are used. It is preferable that γ satisfies γ ≦ [Mo].
γ = 0.018 / ([C] × ([Cr] +0.1) ² ) (1)

(Al: 0% to 0.050%)
Al is an arbitrary element. That is, the Al content may be 0%.
Al is an element having a deoxidizing action, and is an element that reduces the pearlite block particle size by forming nitrides in the wire and refining the austenite particle size. It may be added to reduce the amount of oxygen in the wire. From the viewpoint of such action, the Al content may be more than 0%, 0.005% or more, or 0.030% or more.
On the other hand, if the Al content exceeds 0.050%, the electrical resistivity of the wire may be excessively increased. The reason for this is considered that when the Al content exceeds 0.050%, coarse oxide inclusions are easily formed in the wire. For this reason, Al content is 0.050% or less. From the viewpoint of further reducing the electrical resistivity of the wire, the Al content is preferably 0.040% or less, and more preferably 0.035% or less.

(Ti: 0% to 0.050%)
Ti is an arbitrary element. That is, the Ti content may be 0%.
Ti is an element that reduces the pearlite block particle size by forming carbides or carbonitrides in the wire and refining the austenite particle size. Thereby, the ductility of a wire is improved. From the viewpoint of such action, the Ti content may be more than 0%, 0.002% or more, or 0.005% or more.
On the other hand, if the Ti content exceeds 0.050%, the amount of carbide or carbonitride increases, and the austenite grain size is excessively refined, resulting in poor hardenability, resulting in a decrease in tensile strength. For this reason, Ti content is 0.050% or less. From the viewpoint of further reducing the electrical resistivity of the wire, the Ti content is preferably 0.030% or less.

(B: 0% to 0.0030%)
B is an arbitrary element. That is, the B content may be 0%.
If the B content exceeds 0.0030%, coarse carbides or carbonitrides are likely to be formed in the wire, which may increase the electrical resistivity of the wire. For this reason, B content is 0.0030% or less. From the viewpoint of further reducing the electrical resistivity of the wire, the B content is preferably 0.0025% or less.
On the other hand, B is an element that reduces the electrical resistivity of the wire by forming BN in the wire and reducing the solid solution N. From the viewpoint of such action, the B content may be more than 0%, 0.0001% or more, or 0.0005% or more.

(Balance: Fe and impurities)
In the chemical composition in the present disclosure, the balance excluding the above-described elements is Fe and impurities.
Here, the impurity refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally contained in the steel.
Examples of impurities include all elements other than the elements described above. The element as the impurity may be only one type or two or more types. For example, for Nb, V, Ni, and Cu, 0.03% or less may be regarded as impurities.

The chemical composition in the present disclosure may contain at least one of Al: 0.005% to 0.050% and Ti: 0.005% to 0.050% in mass%. In this case, the actions and preferred contents of Al and Ti are as described above.

By controlling the chemical composition of the wire rod of the present disclosure within the above-described range, both high tensile strength and low electrical resistivity can be achieved.
From the viewpoint of further reducing the electric resistivity of the wire, it is desirable that α represented by the following formula (2) and β ₁ represented by the following (3) satisfy α <β ₁ . Note that [Si], [Mn], [Cr], [Mo], and [C] represent mass% of each element.
α = 4.4 × [Si] + 2.2 × [Mn] + [Cr] + [Mo] (2)
β ₁ = 0.54 / [C] ² + [C] / 10 (3)

From the viewpoint of further reducing the electrical resistivity of the wire, it is desirable that α represented by the above formula (2) and β ₂ represented by the following (4) satisfy α <β ₂ .
β ₂ = 0.54 / [C] ² (4)

<Metal structure of wire>
Next, the metal structure of the wire of the present disclosure will be described. FIG. 1 is a schematic diagram illustrating a center region and a surface layer region in which a structure is measured in a cross section perpendicular to the longitudinal direction of a wire rod of the present disclosure.

(Average area ratio of pearlite structure)
As shown in FIG. 1, the wire of the present disclosure is centered when the diameter of the wire 10 is d in a cross section perpendicular to the longitudinal direction of the wire 10 (also referred to as “cross section” in this specification). The average area ratio of the pearlite structure in a region within 7 d from C (hereinafter also referred to as “center region A”) and a region within 7 d from the outer peripheral surface (hereinafter also referred to as “surface layer region A”) is 90 % Or more. Thereby, the tensile strength of a wire improves.
When the average area ratio of the pearlite structure in the cross section is less than 90%, the tensile strength of the wire may be lowered. Moreover, in the cross section, when the average area ratio of the pearlite structure is less than 90% and the area ratio of the martensite structure is high, the electrical resistivity of the wire may decrease.

From the viewpoint of further improving the tensile strength of the wire, the average area ratio of the pearlite structure in the cross section is more preferably 93% or more, and still more preferably 95% or more.
The upper limit of the average area ratio of the pearlite structure in the cross section is not particularly limited, and the average area ratio of the pearlite structure may be 100%.

When the average area ratio of the pearlite structure in the cross section is less than 100%, the structure other than the pearlite structure (hereinafter also referred to as “non-pearlite structure”) is preferably selected from the group consisting of ferrite, bainite, and martensite. Is at least one kind.

-Measurement method of average area ratio of pearlite structure-
In this specification, the average area ratio of the pearlite structure in the cross section of a wire means the value measured with the following measuring methods.
After the cross section of the wire is mirror-polished, it corrodes with picral. In the corroded cross section, 5 points (5 fields of view) in the central region A and 5 points (5 fields of view) in the surface layer region A were used at a magnification of 2000 times using a field emission scanning electron microscope (FE-SEM). Observe and take a picture of each observation position. The area per field of view is 2.7 × 10 ⁻³ mm ² (vertical 0.045 mm, horizontal 0.060 mm).
Next, a transparent sheet (for example, an OHP (Over Head Projector) sheet) is overlaid on each photograph. In this state, a color is applied to the “non-perlite structure” in each transparent sheet. Next, the area ratio of the “colored region” (that is, the non-pearlite structure) in each transparent sheet is obtained by image analysis software, and the area ratio of the obtained non-pearlite structure is subtracted from 100% to obtain an individual visual field. The area ratio of the pearlite structure in is obtained. The arithmetic average value for 10 visual fields of the area ratio of the pearlite structure is calculated, and the obtained value is set as the average area ratio of the pearlite structure.

(Average length of cementite)
As shown in FIG. 1, the wire in the present disclosure is a region within d / 10 from the center C (hereinafter referred to as “central region B”) where the diameter of the wire 10 is d in a cross section (cross section) perpendicular to the longitudinal direction. The average length of cementite is also preferably 2.0 μm or more. When the average area ratio of the pearlite structure is 90% or more and the average length of cementite is 2.0 μm or more, the tensile strength can be further improved. More preferably, it is 2.1 micrometers or more, More preferably, it is 2.2 micrometers or more. This further improves the tensile strength of the wire.
The upper limit of the average length of cementite in the central region B of the wire is not particularly limited, but if the average length exceeds 4.0 μm, the structure may become coarse and the ductility may be reduced. 0 μm or less is preferable.

-Measurement method of average length of cementite-
In the present specification, the average length of cementite in the central region B of the cross section of the wire means a value measured by the following measuring method.
A cross section perpendicular to the longitudinal direction of the wire (that is, a cross section of the wire) is mirror-polished, then corroded with picral, and d / 10 from the center at a magnification of 5000 using a field emission scanning electron microscope (FE-SEM). Five locations at arbitrary positions in the inner region (central region B) are observed, and a photograph is taken at each observation position.
Next, draw a straight line every 2 μm along two directions orthogonal to each photograph obtained, and the length of cementite on the intersection of the straight lines (if there is no cementite on the intersection, the length of the cementite closest to the intersection) The straight line distance between the two most distant points in the cementite is measured using an ordinary method, that is, image analysis software (image-J). However, the range of less than 6 μm at the left, right, top and bottom edges of the image is often excluded from the measurement because the total length of cementite cannot be measured in many cases. The length of 30 cementites is measured for each photograph, the weighted average value of the cementite lengths is calculated, and the average length of the cementite in the central region B of the cross section of the wire is taken.

(Average lamella spacing of pearlite structure)
In the wire rod of the present disclosure, in the cross section of the wire rod, when the diameter of the wire rod is d, the average lamella spacing of the pearlite structure in the region within d / 10 from the center (center region B) (that is, the average value of the lamella spacing) ) Is preferably 90 nm or less. Thereby, the tensile strength of a wire improves more (for example, tensile strength can be 1220 Mpa or more). Further, the influence of the average lamella spacing on the electrical resistivity is not so great. For this reason, the average lamellar spacing of 90 nm or less is advantageous from the viewpoint of the balance between improvement in tensile strength and reduction in electrical resistivity.
The average lamella interval is more preferably 85 nm or less, and still more preferably 80 nm or less.
On the other hand, from the viewpoint of easy manufacture of the wire, the average lamella spacing is preferably 50 nm or more, more preferably 55 nm or more, and further preferably 60 nm or more.

-Measurement of mean lamella spacing in pearlite structure-
In this specification, the average lamella interval of the pearlite structure in the cross section of a wire means the value measured by the following measuring methods.
After the cross section of the wire is mirror-polished, it corrodes with picral. In the corroded cross section, five places (five fields of view) in the central region B are observed at a magnification of 10,000 times using a field emission scanning electron microscope (FE-SEM), and a photograph of each observation position is taken. The area per field of view is 1.08 × 10 ⁻⁴ mm ² (vertical 0.009 mm, horizontal 0.012 mm).
In the pearlite structure in each field of view (that is, each photograph), the lamella orientation is the same and the lamella spacing is the smallest and the second lamella spacing is the smallest from the range in which the length corresponding to 5 lamellas can be measured. Select the location as the measurement location. About each measurement location, the length for 5 lamella intervals is calculated | required, The length for this 5 lamella intervals is divided by 5, and a lamella interval is calculated | required. An arithmetic average value of 10 measurement locations (that is, 5 fields × 2 locations) of the obtained lamella spacing is obtained, and the obtained value is used as the average lamella spacing of the pearlite structure in the central region B of the cross section of the wire. And

(Average particle size of pearlite block)
The wire rod of the present disclosure has an area within d / 10 from the center (that is, the center area B) and an area within d / 10 from the outer peripheral surface (hereinafter referred to as “surface layer area B”) when the diameter is d in the cross section. The average particle size of the pearlite block in each case is preferably 23.0 μm or less. Thereby, the ductility of a wire can be improved more. Moreover, the influence which the average particle diameter of a pearlite block has on the tensile strength and electrical resistivity of a wire is not so great. Therefore, the average particle diameters of the pearlite blocks in the central region B and the surface layer region B are 23.0 μm or less, respectively, also from the viewpoint of the balance of improvement in ductility, improvement in tensile strength, and reduction in electrical resistivity. It is advantageous. The average particle size of the pearlite block is more preferably 21.0 μm or less.
On the other hand, from the viewpoint of ease of production of the wire, the average particle size of each pearlite block in the central region B and the surface layer region B is preferably 10.0 μm or more, more preferably 11.0 μm or more, and still more preferably. 13.0 μm or more.
When the hardenability is sufficiently high due to the combined effect of Cr and Mo, the average particle size of the pearlite block is approximately the same in the surface layer region B and the central region B. In the wire rod of the present disclosure, “average particle size of pearlite block in surface region B / average particle size of pearlite block in center region B” is 0.88 or more, and a structure having high uniformity in the cross section can be obtained. However, the ratio of the average particle diameter of the surface layer and the pearlite block at the center in the wire rod of the present disclosure is not necessarily limited to this.

In this specification, the pearlite block is a block constituting a pearlite structure.
Moreover, in this specification, the ductility of a wire is a physical property evaluated by the below-mentioned cross-sectional reduction rate.

-Measuring method of average particle size of pearlite block in wire-
In this specification, the average particle diameter of each pearlite block in the center region B and the surface layer region B of the cross section of the wire means a value measured by the following measuring method.
The cross section of the wire is mirror-polished and then polished with colloidal silica. In the polished cross section, four visual fields in the central region B and the surface layer region B are observed at a magnification of 400 times using a field emission scanning electron microscope (FE-SEM), and EBSD measurement (electron beam backscatter diffraction method) is performed. Measurement). The area per field of view is 0.0324 mm ² (vertical 0.18 mm, horizontal 0.18 mm), and the measurement step is 0.3 μm.
Next, for each visual field, an angle difference between crystal orientations of 9 ° or more is defined as a grain boundary, and a weighted average of grain sizes of pearlite blocks is calculated. The obtained value is defined as the particle size of the pearlite block in the visual field. Next, the arithmetic average value for the four visual fields of the particle size of the pearlite block is obtained, and the obtained value is set as the average particle size of the pearlite block in the cross section of the wire. For example, the particle size of a pearlite block can be obtained by using OIM analysis (EBSD analysis software of TSL Solutions, OIM: Orientation Imaging Microscopy). When using OIM analysis, a pixel having a CI value of 0.1 or less and a cluster of 9 or less pixels are regarded as noise because they have low data reliability, and are excluded.

<Tensile strength of wire>
As described above, the wire of the present disclosure is excellent in tensile strength.
The tensile strength of the wire is preferably 1220 MPa or more, more preferably 1260 MPa or more, and particularly preferably 1300 MPa or more.
That the tensile strength of the wire is 1220 MPa or more is particularly easily achieved when the average value of the lamella spacing is 90 nm or less.
There is no restriction | limiting in particular in the upper limit of the tensile strength of a wire. The tensile strength of the wire may be 1600 MPa or less from the viewpoint of ease of manufacturing the wire.

-Measuring method of tensile strength of wire-
In this specification, the tensile strength of a wire means a value measured by the following measuring method.
The wire is cut to a length of 340 mm, and then the longitudinal end 70 mm and the other end 70 mm of the wire are fixed with a wedge chuck, and a tensile test is performed.
Prior to this tensile test, the area of the cross section of the wire is measured in advance. Here, as the area of the cross section of the wire, the area of the cross section at the center in the longitudinal direction of the wire cut to a length of 340 mm is measured.
The value obtained by dividing the maximum load obtained by the tensile test by the area of the cross section of the wire before the tensile test is taken as the tensile strength of the wire.

<Cross section reduction rate of wire>
The cross-sectional reduction rate of the wire rod of the present disclosure is preferably 30% or more, and more preferably 32% or more. That the cross-section reduction rate of the wire is 30% or more is particularly easily achieved when the average particle size of the pearlite block is 23.0 μm or less in both the central region B and the surface layer region B.
There is no restriction | limiting in particular in the upper limit of the cross-section reduction rate of a wire. The cross-sectional reduction rate of the wire may be 50% or less from the viewpoint of ease of manufacturing the wire.

-Measuring method of cross-section reduction rate of wire-
In this specification, the cross-sectional reduction rate of the wire means a value measured by the following measuring method.
The wire is cut to a length of 340 mm, and then the longitudinal end 70 mm and the other end 70 mm of the wire are fixed with a wedge chuck, and a tensile test is performed.
Prior to this tensile test, the area of the cross section of the wire is measured in advance.
After the tensile test (that is, when the wire is broken), the cross-sectional area of the wire at the portion where the wire diameter becomes the smallest is measured.
The amount of reduction in the area of the cross section before and after the tensile test is divided by the area of the cross section before the tensile test, and then multiplied by 100, and the obtained value is taken as the cross-sectional reduction rate (%) of the wire.

<Electric resistivity of wire>
As described above, the wire rod of the present disclosure has reduced electrical resistivity.
The electrical resistivity of the wire is preferably less than 0.180 μΩm, more preferably 0.170 μΩm or less.
There is no restriction | limiting in particular in the minimum of the electrical resistivity of a wire. The electric resistivity of the wire may be 0.150 μΩm or more from the viewpoint of suitability for manufacturing the wire.

-Measuring method of electrical resistivity of wire-
In this specification, the electrical resistivity of a wire means a value measured by the following measurement method.
The wire is cut to a length of 100 mm, and then the oxidized scale on the surface layer of the wire is removed using sandblasting.
The electrical resistance value in the longitudinal direction of the wire from which the oxide scale has been removed (hereinafter referred to as “test piece”) is measured by a four-terminal method at a temperature of 20 ° C. In the four-terminal method, a pair of voltage terminals and a pair of current terminals are connected to the test piece. The arrangement of the pair of voltage terminals and the pair of current terminals is such that the pair of voltage terminals is sandwiched between the pair of current terminals (that is, the current terminal, the voltage terminal, the voltage terminal, and the current terminal are arranged in this order). ). In the measurement in this specification, the distance between a pair of voltage terminals is 20 mm. The pair of current terminals may be connected to any part of the test piece as long as it is arranged as described above. In this state, a current is passed between the pair of current terminals, the voltage between the pair of voltage terminals is measured, and the electric resistance value is calculated based on the relationship between the current and the voltage. By multiplying the obtained electrical resistance value by the area of the cross section of the test piece and dividing the obtained value by the distance between the pair of voltage terminals (ie, 20 mm), the electrical resistivity in the longitudinal direction of the test piece ( μΩm) is calculated. The obtained value is defined as the electrical resistivity (μΩm) of the wire.

<Diameter of wire>
The diameter of the wire is preferably 3.0 mm or greater and 10.0 mm or less.
When the diameter of the wire is 3.0 mm or more, the wire drawing when the wire is drawn to obtain a steel wire can be stabilized, and the production of the steel wire can be performed stably.
When the diameter of a wire is 10.0 mm or less, the wire drawing distortion | strain at the time of drawing a wire and obtaining a steel wire can be raised, and a steel wire can be strengthened.

For example, the wire rod having a diameter of 3.0 mm or more and 10.0 mm or less is manufactured by drawing a steel wire in an aluminum-coated steel wire (preferably, a steel wire in an aluminum-coated steel wire for power transmission lines). It is particularly suitable as a material for the purpose.

<Application>
Since the wire rod of the present disclosure is a wire rod having reduced electrical resistivity and excellent tensile strength, it is preferably used for manufacturing a steel wire that requires reduction in electrical resistivity and improvement in tensile strength. Examples of such steel wires include steel wires in aluminum-coated steel wires (preferably, steel wires in aluminum-coated steel wires for power transmission lines).

[Steel wire]
The steel wire of the present disclosure is a drawn product of the wire rod of the present disclosure described above. That is, the steel wire of the present disclosure has a chemical composition of mass%,
C: 0.80% or more and 1.10% or less,
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% to 0.030%,
S: 0% or more and 0.030% or less,
N: 0% or more and 0.0060% or less,
Cr: 0.02% or more and less than 0.30%,
Mo: 0.02% to 0.15%,
Al: 0% or more and 0.050% or less,
Ti: 0% or more and 0.050% or less,
B: 0% or more and 0.0030% or less, and
The balance: Fe and impurities, and the total amount of Mo and Cr is 0.13% or more,
In the cross section perpendicular to the longitudinal direction, when the diameter of the steel wire is D, the average area ratio of the pearlite structure in the region within D / 7 from the center and the region within D / 7 from the outer peripheral surface is 90% The average particle size of the pearlite block in the region within D / 7 from the center is 5.0 μm or less.

-Measuring method of average area ratio of pearlite structure in steel wire-
In this specification, since the average area ratio of the pearlite structure in the cross section of the steel wire is the same as the method for measuring the average area ratio of the pearlite structure in the wire described above, description thereof is omitted here.

(Average particle size of pearlite block)
The steel wire in the present disclosure includes a pearlite structure like the wire rod of the present disclosure described above, and is mainly composed of a plurality of pearlite blocks. When the wire drawing is sufficiently performed, the average particle diameter of the pearlite block can be reduced, and ductility (cross-sectional reduction rate) can be improved. In addition, since the influence of the pearlite block particle size on the tensile strength and electrical resistivity is not so large, in order to improve the balance between the improvement of the cross-section reduction rate, the improvement of the tensile strength, and the reduction of the electrical resistivity, the pearlite block The particle size should be small. Specifically, it is preferable that the average particle diameter of the pearlite block in a region within D / 7 from the center when the diameter of the steel wire is D in a cross section perpendicular to the longitudinal direction is 5.0 μm or less. More preferably, it is 4.0 μm or less. Thereby, the cross-section reduction rate of a steel wire improves more, for example, it is easy to achieve the cross-section reduction rate of 40% or more.

-Measurement method of average particle size of pearlite block in steel wire-
In this specification, the average particle diameter of the pearlite block in the center region within D / 7 from the center of the cross section of the steel wire means a value measured by the following measuring method. The method other than the observation range is basically the same as the method for measuring the average particle size of the pearlite block in the wire described above.
A cross section perpendicular to the longitudinal direction of the steel wire (that is, a cross section of the steel wire) is mirror-polished and then polished with colloidal silica. In the polished cross section, a field emission scanning electron microscope (FE-SEM) is used to observe four visual fields in the central region at a magnification of 2000 times, and EBSD measurement (measurement by electron beam backscatter diffraction method) is performed. The area per field of view is 0.0012 mm ² (vertical 0.03 mm, horizontal 0.04 mm), and the measurement step is 0.10 μm.
Next, for each field of view, an angle difference between crystal orientations of 9 ° or more is defined as a grain boundary, a weighted average of the particle sizes of the pearlite block is calculated, and the obtained value is defined as the pearlite block particle size in the field of view. The average value (arithmetic average) of the pearlite block particle diameters for four visual fields in the central region is defined as the average particle diameter of the pearlite blocks in the cross section of the steel wire. For example, the particle size of a pearlite block can be obtained by using OIM analysis (EBSD analysis software of TSL Solutions, OIM: Orientation Imaging Microscopy). When using OIM analysis, a pixel having a CI value of 0.1 or less and a cluster of 9 or less pixels are regarded as noise because they have low data reliability, and are excluded.

The steel wire of the present disclosure having the above chemical composition and the average particle size of the pearlite block is obtained by drawing the wire of the present disclosure having reduced electrical resistivity and excellent tensile strength. For this reason, the steel wire of the present disclosure also has a reduced electrical resistivity and excellent tensile strength.
The diameter of the steel wire is preferably 1.0 mm or more and 3.5 mm or less.
When the diameter of the steel wire is 1.0 mm or more, the wire drawing when obtaining the steel wire by wire drawing can be performed more stably.
When the diameter of the steel wire is 3.5 mm or less, decomposition of cementite during wire drawing and an increase in electrical resistance due to this decomposition can be further suppressed.

In the case of obtaining a steel wire by drawing the wire according to the present disclosure, the drawing strain in the drawing is preferably 1.50 or more. When the wire drawing strain is 1.50 or more, the electrical resistivity can be further reduced by wire drawing.
The wire drawing strain in the wire drawing is preferably 2.40 or less. When the wire drawing strain is 2.40 or less, decomposition of cementite during wire drawing and an increase in electrical resistance due to this decomposition can be further suppressed.
Here, the wire drawing strain refers to a value obtained by the following formula (A). In the formula (A), “ln” means a natural logarithm (ie, “log _e ”).
Drawing strain = 2 × ln (wire diameter (mm) / steel wire diameter (mm)) Formula (A)

[Aluminum-coated steel wire]
The aluminum-coated steel wire of the present disclosure includes the above-described steel wire of the present disclosure and an aluminum-containing layer (hereinafter, Al-containing layer) that covers at least a part of the steel wire.
The aluminum-coated steel wire of the present disclosure includes the steel wire of the present disclosure having excellent tensile strength and reduced electrical resistivity. For this reason, the aluminum-coated steel wire of the present disclosure is also excellent in tensile strength and reduced in electrical resistivity.

The diameter of the steel wire in the aluminum-coated steel wire is preferably 1.0 mm or more and 3.5 mm or less.
When the diameter of the steel wire in the aluminum-coated steel wire is 1.0 mm or more, the wire-drawing process for obtaining an aluminum-coated steel wire by wire drawing can be performed more stably.
When the diameter of the steel wire in the aluminum-coated steel wire is 3.5 mm or less, decomposition of cementite during wire drawing and an increase in electrical resistance due to this decomposition can be further suppressed.

The Al-containing layer is preferably a layer containing Al as a main component.
Here, the layer containing Al as a main component means a layer containing Al as a component having the largest content (mass%).
The content of Al in the Al-containing layer is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more.
As the Al-containing layer, an Al layer made of Al (that is, pure Al) or an Al alloy layer made of an Al alloy is preferable.
As the Al alloy, an Al alloy containing Al and at least one selected from the group consisting of Mg, Si, Zn, and Mn is preferable. The content of Al in the Al alloy is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more. As a preferable Al alloy, specifically, Al alloys in the 3000 to 7000 range in the international aluminum alloy name can be cited.

Here, the Al layer made of Al may contain impurities in addition to Al. Similarly, the Al alloy layer made of an Al alloy here may contain impurities in addition to the above-described elements (Al, Mg, Si, Zn, Mn).

In the aluminum-coated steel wire of the present disclosure, the area ratio of the Al-containing layer with respect to the entire cross section is preferably 10% to 64%.
When the area ratio of the Al-containing layer is 10% or more, the electrical resistance (specifically, the electrical resistance in the longitudinal direction) of the entire aluminum-coated steel wire is further reduced.
When the area ratio of the Al-containing layer is 64% or less, the tensile strength of the entire aluminum-coated steel wire is further improved.
The area ratio of the Al-containing layer is more preferably 10% to 50%, still more preferably 10% to 40%, and still more preferably 15% to 35%.

The aluminum-coated steel wire of the present disclosure described above is preferably used as a core material of a steel core aluminum stranded wire (ACSR).
Examples of the steel core aluminum stranded wire include a general steel core aluminum stranded wire having a structure in which the aluminum-coated steel wire of the present disclosure is used as a core material, and an aluminum wire or an aluminum alloy wire is twisted outside the core material. There is no particular limitation.
The aluminum-coated steel wire and the steel core aluminum stranded wire of the present disclosure are preferably an aluminum-coated steel wire for power transmission lines and a steel core aluminum stranded wire for power transmission lines, respectively.

[Example of production method of wire (production method X)]
Next, an example of a manufacturing method for manufacturing the wire of the present disclosure (hereinafter referred to as “manufacturing method X”) will be described.
The manufacturing method X includes a step of producing a steel slab having a chemical component in the present disclosure; a step of heating the steel slab; a step of hot rolling the heated steel slab to obtain hot-rolled steel; Water cooling and then winding up; cooling the hot rolled steel after winding; and patenting the cooled hot rolled steel. Hereinafter, each process in the manufacturing method X is demonstrated.

(Process to manufacture steel slab)
In this step, for example, steel having a chemical component in the present disclosure is melted, and a steel piece having the chemical component in the present disclosure is manufactured using the obtained steel.
The steel slab is manufactured by a known method such as continuous casting or crack rolling.

(Step of heating the steel piece)
In this step, the steel slab obtained in the steel slab manufacturing step is preferably heated to a heating temperature of 1150 to 1250 ° C. Here, the heating temperature means the highest temperature reached at the average temperature of the cross section of the steel slab. When the heating temperature is 1150 ° C. or higher, an increase in the reaction force during hot rolling can be further suppressed. When the heating temperature is 1250 ° C. or lower, excessive decarburization can be further suppressed.

(Process to obtain hot rolled steel)
In this step, the steel slab heated in the step of heating the steel slab is hot-rolled to obtain hot rolled steel.
The finishing temperature in hot rolling (specifically, the temperature of hot-rolled steel on the finish rolling exit side) is preferably higher than 950 ° C. When the finishing temperature is higher than 950 ° C., an increase in the reaction force during hot rolling can be further suppressed.
The finishing temperature in hot rolling is preferably 1100 ° C. or lower. When the finishing temperature is 1100 ° C. or less, the austenite grains can be further coarsened and the average grain diameter of the pearlite block after patenting can be further suppressed, and as a result, the ductility of the steel wire can be further reduced.
Here, the finishing temperature means the temperature of the surface of the hot-rolled steel (the same applies to preferable temperatures in the steps after the “step of cooling the hot-rolled steel with water and then winding”, which will be described later).

(Hot-rolled steel is water-cooled and then wound up)
In this step, the hot-rolled steel obtained in the step of obtaining hot-rolled steel is water-cooled and then wound up.
The coiling temperature (that is, the water cooling stop temperature) is preferably 820 ° C. to 875 ° C. When the coiling temperature is 820 ° C. or higher, excessive reduction in the austenite grain size and the resulting decrease in hardenability can be further suppressed.
When the coiling temperature is 875 ° C. or less, excessive coarsening of austenite grains and coarsening of the average particle diameter of the pearlite block after patenting can be suppressed, and as a result, a decrease in ductility can be further suppressed.
The water cooling is preferably started immediately after the end of hot rolling.

(Process to cool hot rolled steel after winding)
In this step, the hot-rolled steel after winding is cooled.
The cooling attainment temperature in the cooling corresponds to the immersion start temperature in the molten salt in the patenting described later.
A preferable range of the cooling attainment temperature (that is, the immersion start temperature in molten salt) will be described later.

(Process for patenting cooled hot-rolled steel)
In this step, the hot-rolled steel cooled in the step of cooling the hot-rolled steel after winding is patented. By this patenting, the wire of the present disclosure is obtained.
Patenting is performed by immersing the cooled hot-rolled steel in a molten salt.

The immersion start temperature in the molten salt (hereinafter also simply referred to as “immersion start temperature”) is preferably 700 ° C. or higher. Since the ferrite transformation can be suppressed when the immersion start temperature is 700 ° C. or higher, it is easy to obtain the wire according to the present disclosure in which the average area ratio of the pearlite structure is 90% or higher.
The immersion starting temperature is preferably 750 ° C. or lower. When the immersion start temperature is 750 ° C. or lower, an increase in the temperature of the molten salt can be further suppressed.

The temperature of the molten salt is preferably 480 ° C. or higher. When the temperature of the molten salt is 480 ° C. or higher, excessive formation of a bainite structure can be suppressed, and thus the wire rod of the present disclosure in which the average area ratio of the pearlite structure is 90% or more is easily obtained.
Moreover, it is preferable that the temperature of molten salt is 540 degrees C or less. When the temperature of the molten salt is 540 ° C. or less, it is possible to further suppress the coarsening of the lamella interval and the decrease in the tensile strength of the wire due thereto.

The immersion time in the molten salt is preferably 20 seconds or longer. When the immersion time in the molten salt is 20 seconds or more, the pearlite transformation is easily completed, and thus the wire of the present disclosure having an average area ratio of the pearlite structure of 90% or more is easily obtained. Further, when the immersion time in the molten salt is 20 seconds or more, the formation of martensite can be further suppressed, so that the increase in electrical resistivity can be further suppressed, and the ductility is also advantageous.
On the other hand, the immersion time in the molten salt is preferably 200 seconds or less from the viewpoint of productivity.

In addition, when manufacturing the wire of this indication through the said process, it is preferable not to perform a tempering process. If tempering is performed after the patenting step, the cementite is divided and shortened, and the tensile strength may be reduced. By not performing such tempering treatment, the average length of cementite in the region within d / 10 from the center can be maintained at 2.0 μm or more in the cross section perpendicular to the longitudinal direction.

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the following examples.

[Manufacture of wire]
Steels a and steels 1 to 35 having the chemical compositions shown in Tables 1 and 2 were melted, and wires were produced by the method described later.
The numerical value of each element in Table 1 and Table 2 represents mass%, and the notation “−” indicates that the corresponding element is not contained (not intentionally added).
Further, the balance excluding the elements shown in Tables 1 and 2 is Fe and impurities.
In Tables 1 to 5, underlined numerical values or steel numbers indicate that they are outside the range of the chemical composition in the present disclosure.

First, steel a shown in Table 1 was melted by a converter, and then a 122 mm square billet (steel piece) was obtained by ingot rolling by a normal method. By using the obtained billet and carrying out the steps after the step of heating the steel slab in the production method X described above under each of the production conditions A to Q shown in Table 3 below, a sample shown in Table 4 is used as a wire. aA to aQ were obtained respectively. Here, samples aA to aM are examples of the wire of the present disclosure, and samples aN to aQ are comparative examples.
In Table 3 below, the heating temperature, finishing temperature, winding temperature, soaking start temperature, molten salt temperature, and soaking time are respectively the heating temperature in the step of heating the steel slab, and the heated steel slab is hot rolled. Finishing temperature in the process of obtaining hot-rolled steel, winding temperature in the process of water-cooling and rolling the hot-rolled steel, temperature of starting immersion in molten salt in the process of patenting the cooled hot-rolled steel, melting in the same process It means the temperature of the salt and the immersion time in the molten salt in the same step.
Moreover, in Table 3, a wire diameter shows the diameter of the wire finally obtained.

Next, steels 1 to 35 shown in Table 2 were melted by a converter, and then a billet (steel piece) of 122 mm square was obtained by block rolling by a normal method. Samples 1A to 35A shown in Table 5 were obtained as wire rods by using the billets obtained from Steels 1 to 35, respectively, and carrying out the steps after the step of heating the steel slab in Production Method X. Here, the conditions of the process after the process of heating the steel slab in the production method X were the above-described production condition A in any sample. Samples 1A to 18A, 34A, and 35A are examples of the wire of the present disclosure, and samples 19A to 33A are comparative examples.

[Evaluation]
For each of the samples aA to aQ and 1A to 35A obtained above, the average area ratio of the pearlite structure, the average particle diameter of the pearlite block (hereinafter also referred to as “PBS”), the average lamella spacing of the pearlite structure, and the cementite length. , Tensile strength, cross-sectional reduction rate, and electrical resistivity were measured.
The methods for measuring the average area ratio of the pearlite structure, the average particle diameter of the pearlite block, the average lamella spacing of the pearlite structure, the cementite length, the tensile strength, the cross-sectional reduction rate, and the electrical resistivity are as described above. In the measurement of the average particle size of the pearlite block, the calculation of the weighted average of the particle size of the pearlite block was performed using OIM analysis ver. Performed with 7.0.
The results are shown in Table 4 and Table 5 below.

-Explanation of Table 4 and Table 5-
The numerical value in the “[Mo] + [Cr] (%)” column means the total amount (mass%) of Mo and Cr in the chemical composition of the wire.
The numerical value in the “γ” column means γ represented by the above-described formula (1).
The “γ ≦ Mo” column indicates whether [Mo] and γ satisfy γ ≦ [Mo] when the mass% of Mo is [Mo]. “A” means that γ ≦ [Mo] is satisfied, and “B” means that γ ≦ [Mo] is not satisfied.
The numerical value in the “α” column means α represented by the above-described formula (2).
The numerical value in the “β1” column means β ₁ represented by the above-described formula (3).
· "Α <β1" column, α and β ₁ and is indicative of whether or not to satisfy the α <β _1. “A” means that α <β ₁ is satisfied, and “B” means that α <β ₁ is not satisfied.
- figures "β2" column refers to beta ₂ of the formula (4) above.
· "Α <β2" column, and the α and β ₂ is indicative of whether or not to satisfy the α <β _2. “A” means that α <β ₂ is satisfied, and “B” means that α <β ₂ is not satisfied.
“Center PBS” means the average particle diameter of the pearlite block in the center region within d / 10 from the center in the cross section.
“Surface PBS” means the average particle diameter of pearlite blocks in the surface area within d / 10 from the outer peripheral surface in the cross section. Here, d is the diameter of the wire.
“Cementite length” means the average length of cementite in the central region within d / 10 from the center in the cross section.
The “average lamella spacing” means the average lamella spacing of the pearlite structure in the central region within d / 10 from the center in the cross section.

As shown in Table 4, the samples aA to aM, which are examples of the wire rod according to the present disclosure, had a reduced electrical resistivity and an excellent tensile strength.

In contrast to these examples, the samples aN to aP (all of the comparative examples) in which the area ratio of the pearlite structure was less than 90% had low tensile strength.
In the sample aN, the reason why the area ratio of the pearlite structure was less than 90% is considered that the heating temperature was high and the decarburization on the surface of the wire progressed.
The reason why the area ratio of the pearlite structure was less than 90% in the sample aO is considered to be that the immersion start temperature was low and the ferrite structure was formed before the immersion.
In the sample aP, the reason why the area ratio of the pearlite structure was less than 90% and the cementite length was short is considered to be that the molten salt temperature was low and a large amount of bainite structure was formed.
Further, the wire of the sample aQ (comparative example) in which the area ratio of the pearlite structure was less than 90% had a high electric resistivity. In sample aQ, the area ratio of the pearlite structure was less than 90%, and the reason why the electrical resistivity was high was that the immersion time in the molten salt was short, the pearlite transformation was not completed, and the martensite structure was formed. It is done.

Among the samples aA to aM which are examples, in the samples aA to aJ and aM in which the central PBS and the surface layer PBS are both 23.0 μm or less, the cross-section reduction rate, which is an index of ductility of the wire, was further improved.
Among the samples aA to aM which are examples, the samples aA to aL having an average lamella spacing of 90 nm or less had higher tensile strength.

Further, as shown in Table 5, Samples 1A to 18A, 34A, and 35A, which are examples of the wire of the present disclosure, had reduced electrical resistivity and excellent tensile strength.

In contrast to these examples, Sample 19A not containing Mo had a low tensile strength.
Sample 20A having too much Si content had a high electrical resistivity.
Sample 21A with too much Mn content had high electrical resistivity.
Sample 22A not containing Cr had a low tensile strength.
Sample 23A with too much Cr content had high electrical resistivity.
Sample 24A having too little C content had a low tensile strength.
Sample 25A with too much Mo content had high electrical resistivity.
Sample 26A with too much Al content had a high electrical resistivity.
Sample 27A with too much N content had a high electrical resistivity.
Sample 28A having too much Ti content had low tensile strength. The reason for this is presumed that the austenite grain size immediately before patenting was refined, thereby reducing the hardenability.
The sample 29A having an excessive content of B had a high electrical resistivity.
Sample 30A with too much C content had high electrical resistivity. The reason for this is considered that pro-eutectoid cementite was formed.
Sample 31A had a low Mo content, poor hardenability, and low tensile strength.
In Sample 32A, the area ratio of the pearlite structure was low, and the tensile strength was low.
Sample 33A had a low total content of Mo and Cr, poor hardenability, and low tensile strength.

Samples 1A ~ 18A is an example, 34A, among 35A, the alpha <Sample 1A ~ 11A satisfying β _1, 34A, 35A, the electrical resistivity has been further reduced.
Among these samples 1A ~ 11A, the alpha <Sample 1A ~ 6A satisfying β _2, 34A, 35A, the electrical resistivity has been particularly reduced.

[Manufacture of steel wire]
Samples 1A to 18A, 34A, and 35A, which are examples, were subjected to wire drawing with a wire drawing strain of 1.50 to 2.40 with a reduction in area of 23 to 25% in each pass, and a diameter of 1 A steel wire of 0.0 to 3.5 mm was obtained. In addition, the wire drawing process was defined as a pass, and the amount of change in the cross-sectional area of the pass was defined as the area reduction rate. The area of the area reduction rate R before processing cross section _{S 0,} the area of the cross section after processing when the _{_{_{S 1, R = (S 0}}} -S 1) / S 0 can be calculated as × 100.

[Evaluation]
About the obtained steel wire, the average area ratio of the pearlite structure in the region within D / 7 from the center of the cross section and the region within D / 7 from the outer peripheral surface, and within D / 7 from the center, by the method described above. The average particle size of the pearlite block in the region was measured. The results are shown in Table 6.

As a result, in all the steel wires, the average area ratio of the pearlite structure was 90% or more, and the average particle diameter of the pearlite block was 5.0 μm or less.

Further, when the tensile strength and electrical resistivity of the obtained steel wire were measured in the same manner as the measurement method for the wire, the tensile strength was 2000 MPa or more and the electrical resistivity was less than 0.200 μΩm. It was.

Further, from the above results, the aluminum-coated steel wires in which the surfaces of the steel wires of Samples 1A to 18A, 34A, and 35A, which are the examples shown in Table 6, are coated with an Al-containing layer have reduced electrical resistivity, and Aluminum coated steel wire with excellent tensile strength. Such an aluminum-coated steel wire is obtained by either a method of drawing after forming an Al coating on the wire of the present disclosure or a method of forming an Al-containing layer on the steel wire of the present disclosure after the wire drawing. It can be manufactured.

The entire disclosure of Japanese Patent Application No. 2018-032547 filed on February 26, 2018 is incorporated herein by reference. All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims

Chemical composition is mass%,
C: 0.80% or more and 1.10% or less,
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% to 0.030%,
S: 0% or more and 0.030% or less,
N: 0% or more and 0.0060% or less,
Cr: 0.02% or more and less than 0.30%,
Mo: 0.02% to 0.15%,
Al: 0% or more and 0.050% or less,
Ti: 0% or more and 0.050% or less,
B: 0% or more and 0.0030% or less, and
The balance: Fe and impurities, and the total amount of Mo and Cr is 0.13% or more,
In a cross section perpendicular to the longitudinal direction, when the diameter of the wire is d, the average area ratio of the pearlite structure in the region within d / 7 from the center and the region within d / 7 from the outer peripheral surface is 90% or more Is a wire rod.
2. The wire according to claim 1, wherein an average length of cementite in a region within d / 10 from the center in a cross section perpendicular to the longitudinal direction is 2.0 μm or more.
The wire according to claim 1 or 2, wherein [Mo] and γ represented by the following formula (1) satisfy γ ≤ [Mo] when the mass% of Mo is [Mo].
γ = 0.018 / ([C] × ([Cr] +0.1) 2 ) (1)
The element symbol in Formula (1) shows the mass% of each element.
Following formula (2) represented by alpha and the following formula (3) beta 1 and which is expressed by, alpha <satisfy beta 1 claims 1 to wire according to any one of claims 3.
α = 4.4 × [Si] + 2.2 × [Mn] + [Cr] + [Mo] (2)
β 1 = 0.54 / [C] 2 + [C] / 10 (3)
The element symbols in the formulas (2) and (3) indicate mass% of each element.
Following formula (2) represented by alpha and the following formula (4) and beta 2 which is expressed by, alpha <wire according to any one of claims 1 to 4 satisfying the beta 2.
α = 4.4 × [Si] + 2.2 × [Mn] + [Cr] + [Mo] (2)
β 2 = 0.54 / [C] 2 (4)
The element symbols in the formulas (2) and (4) indicate mass% of each element.
The mass% contains at least one of Al: 0.005% or more and 0.050% or less and Ti: 0.005% or more and 0.050% or less. Wire rod.
The wire according to any one of claims 1 to 6, which contains B: 0.0001% or more and 0.0030% or less in terms of mass%.
In the cross section perpendicular to the longitudinal direction, the average particle diameters of the pearlite blocks in the region within d / 10 from the center and the region within d / 10 from the outer peripheral surface are 23.0 μm or less, respectively. The wire according to any one of 7.
The wire rod according to any one of claims 1 to 8, wherein an average lamella spacing of the pearlite structure in a region within d / 10 from the center is 90 nm or less in a cross section perpendicular to the longitudinal direction.
The wire according to any one of claims 1 to 9, wherein the electrical resistivity in the longitudinal direction is less than 0.180 µΩm.
The wire according to any one of claims 1 to 10, wherein the diameter is 3.0 mm or more and 10.0 mm or less.
The wire according to any one of claims 1 to 11, which is used for producing a steel wire in an aluminum-coated steel wire.
A steel wire, which is a wire drawing product of the wire according to any one of claims 1 to 12.
Chemical composition is mass%,
C: 0.80% or more and 1.10% or less,
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% to 0.030%,
S: 0% or more and 0.030% or less,
N: 0% or more and 0.0060% or less,
Cr: 0.02% or more and less than 0.30%,
Mo: 0.02% to 0.15%,
Al: 0% or more and 0.050% or less,
Ti: 0% or more and 0.050% or less,
B: 0% or more and 0.0030% or less, and
The balance: Fe and impurities, and the total amount of Mo and Cr is 0.13% or more,
In the cross section perpendicular to the longitudinal direction, when the diameter of the steel wire is D, the average area ratio of the pearlite structure in the region within D / 7 from the center and the region within D / 7 from the outer peripheral surface is 90%. The steel wire in which the average particle diameter of the pearlite block in the region within D / 7 from the center is 5.0 μm or less.
An aluminum-coated steel wire comprising: the steel wire according to claim 13 or claim 14; and an aluminum-containing layer that covers at least a part of the steel wire.