JP6881665B2 - Wire rod, steel wire and aluminum coated steel wire - Google Patents

Description

The present disclosure relates to wire rods, steel wires and aluminum coated steel wires.

Conventionally, studies have been conducted on steel wires for reinforcing transmission lines.
For example, Patent Document 1 states that carbon (C) is 0.9 to 1.2% by weight, silicon (Si) is 1.0 to 1.5% by weight, and manganese (Mn) is 0.4 to 0.6% by weight. Chromium (Cr) 0.2-0.7% by weight, Sulfur (S) 0.015% by weight or less (not including 0%), Phosphorus (P) 0.015% by weight or less (not including 0%), The rest is the stage of drawing steel containing iron (Fe) and unavoidable impurities to manufacture steel wire, and the steel wire is primary plated in a zinc plating tank, and the iron is diffused to produce iron and zinc. The first plating step of forming the mixed iron-zinc alloy layer and the zinc-plated layer formed on the iron-zinc alloy layer, and the iron-zinc alloy layer are transformed into an iron-zinc-aluminum alloy layer. The iron-zinc layer comprises a second plating step of secondary plating in a zinc-aluminum plating tank after the first plating step so as to be transformed into a zinc-aluminum alloy layer. The thickness of the −aluminum alloy layer is characterized by being formed in a plated steel wire having a thickness of 40% to 60% of the total thickness of the iron-zinc-aluminum alloy layer and the zinc-aluminum alloy layer. A method for manufacturing a high-strength plated steel wire for reinforcing an overhead transmission line is disclosed.

On the other hand, with respect to steel materials, improvement in electrical conductivity may be required.
For example, in Patent Document 2, as a steel material for electric parts capable of cold forging with good dimensional accuracy and ensuring excellent electrical conductivity, C: 0.02% or less (0) in mass%. %), 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%) A steel material for electric parts, which satisfies the above requirements and has a ferrite single-phase structure and is excellent in cold forging property and electrical conductivity, 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, for applications such as transmission lines, aluminum conductor steel-reinforced cable (hereinafter sometimes referred to as "ACSR"), which is a cable using aluminum as a conductor, is used. There is.
The ACSR generally has a structure in which a single wire or a stranded wire of a galvanized steel wire is used as a core material and an aluminum wire is twisted on the outside. When ACSR with such a structure is used in a humid area such as a coastal area, zinc is corroded at the contact portion between zinc and aluminum having different electrode potentials using rainwater or the like as an electrolytic solution, and further exposed iron. And aluminum may come into contact with each other and the aluminum may corrode. Therefore, in these areas, as the core material of ACSR, an aluminum-coated steel wire (instead of the zinc-plated steel wire) is provided with a steel wire and an Al (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 an ACSR using an AC wire as a core material, an electric current flows not only in a portion of the aluminum wire twisted to 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 possible 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 to be effective. For that purpose, it is considered effective to reduce the electrical resistivity of the wire rod used for manufacturing the steel wire and to improve the tensile strength of the wire rod.
However, with the techniques disclosed in Patent Document 1 and Patent Document 2, it is difficult to obtain a wire rod having an reduced electrical resistivity and excellent tensile strength.

An object of the present disclosure is to provide a wire rod and a steel wire having a reduced electrical resistivity and an excellent tensile strength.
Another object of the present disclosure is to provide an aluminum-coated steel wire provided with the above steel wire.

Means for solving the above problems include the following aspects.

<1> The chemical composition is C: 0.80% or more and 1.10% or less in mass%.
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% or more and 0.030% or less,
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% or more and 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
Remaining: Consists of 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. The wire rod that is.
<2> The wire rod according to <1>, wherein the 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.
<3> The description in <1> or <2>, wherein when the mass% of Mo is [Mo], [Mo] and γ represented by the following formula (1) satisfy γ ≦ [Mo]. wire.
γ = 0.0018 / ([C] × ([Cr] +0.1) ² ) ・ ・ ・ (1)
Each element symbol in the formula (1) indicates the mass% of each element.
<4> The wire rod 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 the mass% of each element.
<5> The wire rod according to any one of <1> to <4>, wherein α represented by the following formula (2) and β _{2 represented by the following formula (4) satisfy α <β 2.} ..
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 the mass% of each element.
<6> Any one of <1> to <5> containing 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 in mass%. The wire rod described in one.
<7> The wire rod according to any one of <1> to <6>, which contains B: 0.0001% or more and 0.0030% or less in mass%.
<8> In the cross section perpendicular to the longitudinal direction, the average particle size of the pearlite block in the region within d / 10 from the center and the region within d / 10 from the outer peripheral surface is 23.0 μm or less, respectively. <1> The wire rod according to any one of ~ <7>.
<9> The wire rod according to any one of <1> to <8>, wherein the average lamellar spacing of the pearlite structure in the region within d / 10 from the center in the cross section perpendicular to the longitudinal direction is 90 nm or less. ..
<10> The wire rod according to any one of <1> to <9>, which satisfies the condition that the electrical resistivity in the longitudinal direction is less than 0.180 μΩm.
<11> The wire rod according to any one of <1> to <10>, which has a diameter of 3.0 mm or more and 10.0 mm or less.
<12> The wire rod according to any one of <1> to <11> used for manufacturing a steel wire in an aluminum-coated steel wire.
<13> A steel wire which is a wire drawn product of the wire rod 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% or more and 0.030% or less,
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% or more and 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
Remaining: Consists of 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%. As described above, the steel wire having an average particle diameter of 5.0 μm or less in the pearlite block in the region within D / 7 from the center.
<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, wire rods and steel wires having reduced electrical resistivity and excellent tensile strength are provided.
According to the present disclosure, an aluminum coated steel wire provided with the above steel wire is provided.

It is a schematic diagram which shows the central region and the surface layer region which measure the structure in the cross section (cross section) perpendicular to the longitudinal direction of a wire rod.

In the present specification, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the 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 described in the same manner.
In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range described stepwise may be replaced with the upper limit value or the lower limit value of the numerical range described stepwise. , Or you may replace it with the value shown in the examples.

〔wire〕
The wire rod of the present disclosure is
Chemical composition is C: 0.80% or more and 1.10% or less in mass%,
Si: 0.005% or more and 0.100% or less,
Mn: 0.05% or more and 0.30% or less,
P: 0% or more and 0.030% or less,
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% or more and 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
Remaining: Consists of 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 a reduced electrical resistivity and is excellent in tensile strength.
As used herein, the tensile strength of a wire rod means the tensile strength of the wire rod in the longitudinal direction at room temperature (for example, 20 ° C.).
In the present specification, the electrical resistivity of the wire rod means the electrical resistivity in the longitudinal direction of the wire rod at room temperature (for example, 20 ° C.).

The aforementioned effects of the wire rods of the present disclosure (ie, reduction of electrical resistivity and improvement of tensile strength) are achieved by a combination of the chemical composition and a metallographic structure in a cross section perpendicular to the longitudinal direction. ..
For example, in the chemical composition of the wire rod in the present disclosure, the content of Si, Mn, Cr, Mo and the like is reduced to be equal to or less than the upper limit of the content of each element. This reduces the electrical resistivity.
Generally, when alloying elements such as Si, Mn, Cr, and Mo are reduced, the tensile strength may decrease. In this regard, in the wire rods of the present disclosure, the average area ratio of the pearlite structure in the above-mentioned region is limited to 90% or more by the combined addition of Cr and Mo. This improves the tensile strength.
In the wire rod of the present disclosure, the reduction of the electrical resistivity and the improvement of the tensile strength of the wire rod are achieved by these configurations.

<Chemical composition of wire>
Hereinafter, the chemical composition of the wire rod of the present disclosure will be described.
The chemical composition of the wire rod of the present disclosure is as follows: 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% or more and 0.030% or less, 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% It consists of 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. Moreover, 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, molten steel, steel pieces (for example, billet), etc., which will be described later) is also the same as the chemical composition of the wire rod of the present disclosure. This is because the manufacturing process from the molten steel to the wire rod through the steel piece (for example, billet) does not affect the chemical composition.
Hereinafter, the chemical composition of the wire rod 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 rod of the present disclosure will be described.

(C: 0.80% or more and 1.10% or less)
C is an element effective for increasing the tensile strength of the wire rod. If the C content is less than 0.80%, the tensile strength of the wire rod may be insufficient. Therefore, the 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 rod may decrease. The reason for this is considered to be that when the C content exceeds 1.10%, it becomes 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 rod 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 Sis may not be sufficient. Therefore, the Si content is 0.005% or more. From the viewpoint of more stably enjoying the effect of adding Si, 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 rod. If the Si content exceeds 0.100%, the electrical resistivity of the wire rod may become excessively large. Therefore, the Si content is 0.100% or less. The Si content is preferably 0.090% or less, more preferably 0.070% or less, and even more preferably 0.050% or less.

(Mn: 0.05% or more and 0.30% or less)
Mn is an element having an action of increasing the tensile strength of the wire rod. Mn is also an element having an action of preventing hot brittleness of the wire rod by fixing S in the steel as MnS. However, if the Mn content is less than 0.05%, these effects may not be sufficient. Therefore, the Mn content is 0.05% or more. Further, in order to secure the tensile strength of the wire rod and prevent hot brittleness at a higher level, the Mn content is preferably 0.10% or more, more preferably 0.13% or more. Yes, more preferably 0.15% or more.
On the other hand, Mn has an effect of increasing the electrical resistivity of the wire rod. Therefore, if the Mn content exceeds 0.30%, the electrical resistivity of the wire rod may become excessively large. 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 rod. Therefore, if the N content exceeds 0.0060%, the electrical resistivity of the wire rod may become excessively large. Therefore, the 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 rod by fixing dislocations during cold wire drawing. From the viewpoint of such an effect, the N content may be more than 0%, 0.0010% or more, or 0.0020% or more.

(P: 0% or more and 0.030% or less)
P is an element that segregates at the grain boundaries of steel to increase the electrical resistivity. If the P content exceeds 0.030%, the electrical resistivity of the wire rod may become excessively large. Therefore, the P content is 0.030% or less. From the viewpoint of further reducing the electrical resistivity of the wire rod, the P content is preferably 0.025% or less, 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% or more and 0.030% or less)
S is an element that increases the electrical resistivity of the wire rod. If the S content exceeds 0.030%, the electrical resistivity of the wire rod may become excessively large. Therefore, the S content is 0.030% or less. From the viewpoint of further reducing the electrical resistivity of the wire rod, the S content is preferably 0.020% or less, more preferably 0.015% or less.
The S content may be 0%. However, from the viewpoint of reducing the production cost (desulfurization cost), 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. Therefore, it is an element that increases the area ratio of the pearlite structure and improves the tensile strength by the combined addition with Mo, which will be described later. Cr is also an element that reduces the lamellar spacing of the pearlite structure and increases the tensile strength of the wire rod. In order to obtain these effects, the Cr content needs to be 0.02% or more. The Cr content is preferably 0.05% or more, more preferably 0.07% or more, and further preferably 0.10% or more.
On the other hand, when the Cr content is 0.30% or more, the electrical resistivity of the wire rod may become excessively large. For example, when manufactured under manufacturing conditions in which Cr is not sufficiently distributed to ferrite during pearlite transformation, Cr may reduce the electrical resistivity. The Cr content is less than 0.30% from the viewpoint of suppressing an excessive increase in the electrical resistivity of the wire rod. The Cr content is more preferably 0.25% or less.

(Mo: 0.02% or more and 0.15% or less)
Mo is an element that improves hardenability. Therefore, it is an element that increases the area ratio of the pearlite structure and improves the tensile strength by the compound addition with Cr described above. In order to obtain 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 rod may become excessively large. In this case, the pearlite transformation during patenting may be insufficient, and the area ratio of the pearlite structure may decrease. Further, if the amount of Mo added is excessive, the electrical resistivity of the wire rod may become excessively large. From the viewpoint of wire rod production suitability, the Mo content is 0.15% or less, more preferably 0.13% or less.

When both Mo and Cr are added, they have the effect of increasing the area ratio of the pearlite structure and improving the tensile strength. The present inventors have found that this effect is further enhanced by the combined addition of both Mo and Cr. That is, when the above effect is obtained by adding Cr and Mo in combination, the required effect can be obtained with a smaller amount of alloy added as compared with the case where Cr is added alone or Mo is added alone. On the other hand, the electrical resistivity of the wire rod was not affected by the combined addition of Cr and Mo. That is, by adding Cr and Mo in combination, the amount of alloy added can be reduced and the electrical resistivity of the wire rod 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 the 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 rod, 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 each mass% of Mo, C, and Cr is set to [Mo], [C], and [Cr], it is represented by [Mo] and the following formula (1). It is desirable that the γ to be formed satisfies γ ≦ [Mo].
γ = 0.0018 / ([C] × ([Cr] +0.1) ² ) ・ ・ ・ (1)

(Al: 0% or more and 0.050% or less)
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 a nitride 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 rod may become excessively large. It is considered that the reason for this is that when the Al content exceeds 0.050%, coarse oxide-based inclusions are likely to be excessively formed in the wire rod. Therefore, the Al content is 0.050% or less. From the viewpoint of further reducing the electrical resistivity of the wire rod, the Al content is preferably 0.040% or less, more preferably 0.035% or less.

(Ti: 0% or more and 0.050% or less)
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. As a result, the ductility of the wire rod can be improved. From the viewpoint of such an action, the Ti content may be more than 0%, 0.002% or more, or 0.005% or more.
On the other hand, when the Ti content exceeds 0.050%, the amount of carbides or carbonitrides becomes large, and the austenite particle size becomes too fine, resulting in poor hardenability, resulting in a decrease in tensile strength. Therefore, the 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% or more and 0.0030% or less)
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 rod, and the electrical resistivity of the wire rod may increase. Therefore, the 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 rod by forming BN in the wire rod and reducing the solid solution N. From the viewpoint of such an action, the B content may be more than 0%, 0.0001% or more, or 0.0005% or more.

(Remaining: Fe and impurities)
In the chemical composition in the present disclosure, the balance excluding the above-mentioned 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.
Impurities include any element other than the elements described above. The element as an impurity may be only one kind or two or more kinds. For example, for Nb, V, Ni, and Cu, 0.03% or less of each may be regarded as an impurity.

The chemical composition in the present disclosure may contain 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 in mass%. In this case, the respective actions of Al and Ti and the preferable contents of each are as described above.

By controlling the chemical composition of the wire rod of the present disclosure within the above-mentioned range, both high tensile strength and low electrical resistivity can be achieved at the same time.
From the viewpoint of further reducing the electrical 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. In addition, [Si], [Mn], [Cr], [Mo], and [C] each represent the 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 rod>
Next, the metal structure of the wire rod of the present disclosure will be described. FIG. 1 is a schematic view showing a central region and a surface layer region for measuring a structure in a cross section perpendicular to the longitudinal direction of the wire rod of the present disclosure.

(Average area ratio of pearlite structure)
As shown in FIG. 1, the wire rod of the present disclosure is centered when the diameter of the wire rod 10 is d in a cross section perpendicular to the longitudinal direction of the wire rod 10 (also referred to as a “cross section” in the present specification). The average area ratio of the pearlite structure in the region within d / 7 from C (hereinafter, also referred to as “central region A”) and the region within d / 7 from the outer peripheral surface (hereinafter, also referred to as “surface layer region A”) is 90. % Or more. As a result, the tensile strength of the wire rod is improved.
If the average area ratio of the pearlite structure in the cross section is less than 90%, the tensile strength of the wire rod may decrease. Further, 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 rod may decrease.

From the viewpoint of further improving the tensile strength of the wire rod, the average area ratio of the pearlite structure in the cross section is more preferably 93% or more, 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. At least one species to be.

-Measuring method of average area ratio of pearlite structure-
In the present specification, the average area ratio of the pearlite structure in the cross section of the wire rod means a value measured by the following measuring method.
After mirror polishing the cross section of the wire, it is corroded with Piclar. In the corroded cross section, 5 points (5 fields of view) in the central region A and 5 places (5 fields of view) in the surface layer region A were magnified at 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 (length 0.045 mm, width 0.060 mm).
Next, a transparent sheet (for example, an OHP (Over Head Projector) sheet) is superposed on each photograph. In this state, the "non-pearlite structure" in each transparent sheet is colored. Next, the area ratio of the "colored area" (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. Find the area ratio of the pearlite structure in. The arithmetic mean value for 10 fields of view of the area ratio of the pearlite structure is calculated, and the obtained value is used as the average area ratio of the pearlite structure.

(Average length of cementite)
As shown in FIG. 1, the wire rod in the present disclosure is a region within d / 10 from the center C when the diameter of the wire rod 10 is d in a cross section (cross section) perpendicular to the longitudinal direction (hereinafter, “center region B”). The average length of cementite in (also referred to as) is 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. It is more preferably 2.1 μm or more, and further preferably 2.2 μm or more. As a result, the tensile strength of the wire rod is further improved.
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 be coarsened and the ductility may be reduced. It is preferably 0 μm or less.

-How to measure the 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 rod means a value measured by the following measuring method.
After mirror polishing the cross section perpendicular to the longitudinal direction of the wire (that is, the cross section of the wire), it is corroded with picral, and d / 10 from the center at a magnification of 5000 times using a field emission scanning electron microscope (FE-SEM). Observe 5 points at arbitrary positions within the area (central area B), and take a picture at each observation position.
Next, a straight line is drawn every 2 μm along two directions orthogonal to each of the obtained photographs, and the length of the cementite on the intersection of the straight lines (or the cementite closest to the intersection if there is no cementite on the intersection). The straight line distance between the two most distant points in the cementite is measured using a normal method, that is, image analysis software (image-J). However, since the total length of cementite cannot be measured in the range of less than 6 μm at the left, right, top, and bottom edges of the image, this range is excluded from the measurement. The length of cementite at 30 points is measured for each photograph, and the weighted average value of the length of cementite is calculated and used as the average length of cementite in the central region B of the cross section of the wire rod.

(Average lamellar spacing of pearlite tissue)
In the cross section of the wire rod of the present disclosure, 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. As a result, the tensile strength of the wire rod is further improved (for example, the tensile strength can be 1220 MPa or more). Moreover, the influence of the average lamella interval on the electrical resistivity is not so large. Therefore, it is advantageous that the average lamella spacing is 90 nm or less from the viewpoint of the balance between the improvement of the tensile strength and the reduction of the electrical resistivity.
The average lamella spacing is more preferably 85 nm or less, still more preferably 80 nm or less.
On the other hand, from the viewpoint of ease of manufacturing the wire rod, the average lamella spacing is preferably 50 nm or more, more preferably 55 nm or more, and further preferably 60 nm or more.

-Measuring method of average lamellar spacing of pearlite tissue-
In the present specification, the average lamellar spacing of the pearlite structure in the cross section of the wire means a value measured by the following measuring method.
After mirror polishing the cross section of the wire, it is corroded with Piclar. In the corroded cross section, five points (five fields of view) in the central region B are observed using a field emission scanning electron microscope (FE-SEM) at a magnification of 10000 times, and photographs are taken for each observation position. The area per field of view is 1.08 × 10 ^-4 mm ² (length 0.009 mm, width 0.012 mm).
In the pearlite tissue in each field of view (that is, each photograph), the lamella spacing is the smallest and the lamella spacing is the second smallest from the range in which the lamellas are oriented in the same direction and the length of 5 lamella intervals can be measured. Select the location as the measurement location. For each measurement point, the length for 5 lamella intervals is obtained, and the lamella interval is obtained by dividing the length for 5 lamella intervals by 5. The arithmetic mean value of the obtained lamella spacing for 10 measurement points (that is, 5 fields x 2 points) was obtained, and the obtained value was used as the average lamella spacing of the pearlite structure in the central region B of the cross section of the wire rod. And.

(Average particle size of pearlite block)
The wire rod of the present disclosure has a region within d / 10 from the center (that is, a central region B) and a region within d / 10 from the outer peripheral surface (hereinafter, “surface layer region B”) when the diameter is d in the cross section. The average particle size of the pearlite blocks in) is preferably 23.0 μm or less. Thereby, the ductility of the wire rod can be further improved. Further, the average particle size of the pearlite block does not have a great influence on the tensile strength and electrical resistivity of the wire rod. Therefore, the fact that the average particle size of the pearlite block in the central region B and the surface layer region B is 23.0 μm or less is also considered from the viewpoint of the balance between the improvement of ductility, the improvement of tensile strength, and the reduction of 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 manufacturing the wire rod, 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, still more preferably. It is 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 about the same in the surface layer region B and the central region B. In the wire rod of the present disclosure, the "average particle size of the pearlite block in the surface layer region B / the average particle size of the pearlite block in the central 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 size of the surface layer and the central pearlite block in the wire rod of the present disclosure is not necessarily limited to this.

In the present specification, the pearlite block is a block constituting the pearlite structure.
Further, in the present specification, the ductility of the wire rod is a physical property evaluated by the cross-sectional reduction rate described later.

-Measuring method of average particle size of pearlite block in wire rod-
In the present specification, the average particle size of each pearlite block in the central region B and the surface layer region B of the cross section of the wire rod 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 each of the central region B and the surface layer region B were observed at a magnification of 400 times using a field emission scanning electron microscope (FE-SEM), and EBSD measurement (electron backscatter diffraction method) was performed. (Measurement by) is performed. The area per visual field is 0.0324 ^{mm 2} (length 0.18 mm, width 0.18 mm), and the step at the time of measurement is 0.3 μm.
Next, for each field of view, the angle difference of the crystal orientation of 9 ° or more is defined as the grain boundary, and the weighted average of the particle size of the pearlite block is calculated. The obtained value is taken as the particle size of the pearlite block in the field of view. Next, the arithmetic mean value of the particle size of the pearlite block for four fields of view is obtained, and the obtained value is used as the average particle size of the pearlite block in the cross section of the wire rod. For example, the particle size of the pearlite block can be obtained by using OIM analysis (EBSD analysis software of TSL Solutions Co., Ltd., OIM: Origination Imaging Microscopy). When OIM analysis is used, pixels having a CI value of 0.1 or less and a mass of pixels having a CI value of 9 or less are regarded as noise because the reliability of the data is low, and are excluded.

<Tensile strength of wire>
As described above, the wire rod 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.
The tensile strength of the wire rod of 1220 MPa or more is particularly easy to achieve when the average value of the lamella spacing is 90 nm or less.
There is no particular limitation on the upper limit of the tensile strength of the wire. The tensile strength of the wire rod may be 1600 MPa or less from the viewpoint of ease of manufacturing the wire rod.

-Measuring method of tensile strength of wire rod-
In the present specification, the tensile strength of a wire rod means a value measured by the following measuring method.
The wire is cut to a length of 340 mm, and then the wire is fixed at 70 mm on one end side in the longitudinal direction and 70 mm on the other end side in the longitudinal direction with a wedge chuck, and a tensile test is performed.
Before this tensile test, the area of the cross section of the wire rod is measured in advance. Here, as the area of the cross section of the wire rod, the area of the cross section at the central portion in the longitudinal direction of the wire rod cut into 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 defined as the tensile strength of the wire.

<Cross-section reduction rate of wire rod>
The cross-sectional reduction rate of the wire rod of the present disclosure is preferably 30% or more, more preferably 32% or more. The cross-sectional reduction rate of the wire rod of 30% or more is particularly likely to be 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 particular limitation on the upper limit of the cross-sectional reduction rate of the wire rod. The cross-sectional reduction rate of the wire rod may be 50% or less from the viewpoint of ease of manufacturing the wire rod.

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

<Electrical resistivity of wire>
As described above, the wire rod of the present disclosure has a 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 particular limitation on the lower limit of the electrical resistivity of the wire. The electrical resistivity of the wire may be 0.150 μΩm or more from the viewpoint of manufacturing suitability of the wire.

-Measuring method of electrical resistivity of wire rod-
In the present specification, the electrical resistivity of a wire rod means a value measured by the following measuring method.
The wire is cut to a length of 100 mm, and then the oxidation scale on the surface of the wire is removed by sandblasting.
The electrical resistance value in the longitudinal direction of the wire rod from which the oxide scale has been removed (hereinafter referred to as “test piece”) is measured by the 4-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 are sandwiched between the pair of current terminals (that is, the current terminals, the voltage terminals, the voltage terminals, and the current terminals are arranged in this order). ). In the measurement in the present specification, the distance between the pair of voltage terminals is 20 mm. The pair of current terminals may be connected anywhere in the test piece as long as they are 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 resistivity 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 (that is, 20 mm), the electrical resistivity in the longitudinal direction of the test piece (that is, 20 mm) μΩm) is calculated. The obtained value is taken as the electrical resistivity (μΩm) of the wire rod.

<Diameter of wire>
The diameter of the wire is preferably 3.0 mm or more and 10.0 mm or less.
When the diameter of the wire rod is 3.0 mm or more, the wire drawing process when the wire rod is drawn to obtain a steel wire can be stabilized, and the steel wire can be stably manufactured.
When the diameter of the wire rod is 10.0 mm or less, the wire drawing strain when the wire rod is drawn to obtain a steel wire can be increased, and the strength of the steel wire can be increased.

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

<Use>
Since the wire rod of the present disclosure is a wire rod having a reduced electrical resistivity and an excellent tensile strength, it is preferably used for manufacturing a steel wire in which a reduction in the electrical resistivity and an improvement in the tensile strength are required. Examples of such a steel wire include a steel wire in an aluminum-coated steel wire (preferably a steel wire in an aluminum-coated steel wire for a power transmission line).

[Steel wire]
The steel wire of the present disclosure is a wire drawn product of the above-mentioned wire rod of the present disclosure. 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% or more and 0.030% or less,
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% or more and 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
Remaining: Consists of 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%. As described above, 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 the present specification, 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 rod described above, and thus the description thereof is omitted here.

(Average particle size of pearlite block)
The steel wire in the present disclosure contains a pearlite structure like the wire rod of the present disclosure described above, and is mainly composed of a plurality of pearlite blocks. Sufficient wire drawing can reduce the average particle size of the pearlite block and improve ductility (cross-section reduction rate). Since the pearlite block particle size has a small effect on the tensile strength and the electrical resistivity, the pearlite block is used to improve the balance between the improvement of the cross-sectional reduction rate, the improvement of the tensile strength, and the reduction of the electrical resistivity. The particle size should be reduced. Specifically, it is preferable that the average particle size of the pearlite block in the region within D / 7 from the center when the diameter of the steel wire is D in the cross section perpendicular to the longitudinal direction is 5.0 μm or less. More preferably, it is 4.0 μm or less. As a result, the cross-section reduction rate of the steel wire is further improved, and for example, it is easy to achieve a cross-section reduction rate of 40% or more.

-Measuring method of average particle size of pearlite block in steel wire-
In the present specification, the average particle size of the pearlite block in the central region within D / 7 from the center of the cross section of the steel wire means a value measured by the following measuring method. Except for the observation range, it is basically the same as the method for measuring the average particle size of the pearlite block in the wire rod 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, four visual fields are observed in the central region at a magnification of 2000 times using a field emission scanning electron microscope (FE-SEM), and EBSD measurement (measurement by electron backscatter diffraction method) is performed. The area per visual field is 0.0012 ^{mm 2} (length 0.03 mm, width 0.04 mm), and the step at the time of measurement is 0.10 μm.
Next, for each field of view, the angle difference of the crystal orientation of 9 ° or more is defined as the grain boundary, the weighted average of the particle size 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 mean) of the pearlite block particle diameters for the four visual fields in the central region is taken as the average particle diameter of the pearlite blocks in the cross section of the steel wire. For example, the particle size of the pearlite block can be obtained by using OIM analysis (EBSD analysis software of TSL Solutions Co., Ltd., OIM: Origination Imaging Microscopy). When OIM analysis is used, pixels having a CI value of 0.1 or less and a mass of pixels having a CI value of 9 or less are regarded as noise because the reliability of the data is low, 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 a wire rod of the present disclosure having a reduced electrical resistivity and excellent tensile strength. Therefore, the steel wire of the present disclosure also has a reduced electrical resistivity and is excellent in 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 process for obtaining the steel wire by the wire drawing process can be performed more stably.
When the diameter of the steel wire is 3.5 mm or less, the decomposition of cementite during wire drawing and the increase in electrical resistance due to this decomposition can be further suppressed.

When the wire rod of the present disclosure is drawn to obtain a steel wire, the wire drawing strain in the wire 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 the wire drawing process.
Further, the wire drawing strain in the wire drawing process is preferably 2.40 or less. When the wire drawing strain is 2.40 or less, the decomposition of cementite during wire drawing and the 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 formula (A), "ln" means the natural logarithm (ie, "log _e ").
Wire drawing strain = 2 x ln (diameter of wire rod (mm) / diameter of steel wire (mm)) ... Equation (A)

[Aluminum coated steel wire]
The aluminum-coated steel wire of the present disclosure includes the above-mentioned 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. Therefore, the aluminum-coated steel wire of the present disclosure also has excellent tensile strength and reduced 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 the aluminum-coated steel wire by the wire drawing process can be performed more stably.
When the diameter of the steel wire in the aluminum-coated steel wire is 3.5 mm or less, the decomposition of cementite during wire drawing and the 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 highest content (mass%).
The Al content 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 Al content 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. Specific examples of the preferred Al alloy include Al alloys in the 3000s to 7000s in the international aluminum alloy name.

The Al layer made of Al referred to here may contain impurities other than Al. Similarly, the Al alloy layer made of the Al alloy referred to here may contain impurities in addition to the above-mentioned 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 electric resistance of the entire aluminum-coated steel wire (specifically, the electric resistance in the longitudinal direction) 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%, further preferably 10% to 40%, 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 on the outside of the core material. , There are no particular restrictions.
As the aluminum-coated steel wire and the steel core aluminum stranded wire of the present disclosure, aluminum-coated steel wire for power transmission lines and steel core aluminum stranded wires for power transmission lines are preferable, respectively.

[Example of wire rod manufacturing method (manufacturing method X)]
Next, an example of a manufacturing method for manufacturing the wire rod 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 piece having a chemical component in the present disclosure; a step of heating the steel piece; a step of hot-rolling the heated steel piece to obtain hot-rolled steel; and a step of obtaining hot-rolled steel. It has a step of water-cooling and then winding; a step of cooling the hot-rolled steel after winding; and a step of patenting the cooled hot-rolled steel. Hereinafter, each step in the manufacturing method X will be described.

(Process for manufacturing steel pieces)
In this step, for example, the steel having the chemical composition in the present disclosure is melted, and the obtained steel is used to produce a steel piece having the chemical composition in the present disclosure.
Steel pieces are manufactured by known methods such as continuous casting and disassembly rolling.

(Process of heating steel pieces)
In this step, it is preferable to heat the steel pieces obtained in the step of manufacturing the steel pieces to a heating temperature of 1150 to 1250 ° C. Here, the heating temperature means the maximum temperature reached by the average temperature of the cross section of the steel piece. When the heating temperature is 1150 ° C. or higher, the increase in 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 pieces heated in the step of heating the steel pieces are hot-rolled to obtain hot-rolled steel.
The finishing temperature in hot rolling (specifically, the temperature of hot-rolled steel on the finished rolling side) is preferably more than 950 ° C. When the finishing temperature is more than 950 ° C., the increase in 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 lower, the coarsening of the austenite grains and the coarsening of the average particle size of the pearlite block after patenting can be further suppressed, and as a result, the decrease in ductility of the steel wire can be further suppressed.
Here, the finishing temperature means the temperature of the surface of the hot-rolled steel (the same applies to the preferable temperature in the steps after the “step of water-cooling the hot-rolled steel and then winding it” described later).

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

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

(Processing process of cooling 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 rod of the present disclosure is obtained.
Patting 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. When the immersion start temperature is 700 ° C. or higher, ferrite transformation can be suppressed, so that the wire rod of the present disclosure having an average area ratio of pearlite structure of 90% or higher can be easily obtained.
The immersion start temperature is preferably 750 ° C. or lower. When the immersion start temperature is 750 ° C. or lower, the temperature rise 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 the bainite structure can be suppressed, so that the wire rod of the present disclosure having an average area ratio of the pearlite structure of 90% or more can be easily obtained.
The temperature of the molten salt is preferably 540 ° C. or lower. When the temperature of the molten salt is 540 ° C. or lower, coarsening of the lamella spacing and a decrease in tensile strength of the wire rod due to this can be further suppressed.

The immersion time in the molten salt is preferably 20 seconds or more. When the immersion time in the molten salt is 20 seconds or more, the pearlite transformation is easily completed, so that the wire rod of the present disclosure having an average area ratio of the pearlite structure of 90% or more can be 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 it is also advantageous in terms of ductility.
On the other hand, the immersion time in the molten salt is preferably 200 seconds or less from the viewpoint of productivity.

When the wire rod of the present disclosure is manufactured through the above steps, it is preferable not to perform tempering treatment. If tempering is performed after the patenting process, cementite may be fragmented and shortened, resulting in a decrease in tensile strength. 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 with reference to Examples, but the present invention is not limited to the following Examples.

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

First, the steel a shown in Table 1 was melted by a converter and then lump-rolled by a usual method to obtain a billet (steel piece) of 122 mm square. Using the obtained billet, the steps after the step of heating the steel piece in the above-mentioned manufacturing method X were carried out under each of the manufacturing conditions A to Q shown in Table 3 below, and as a wire rod, the sample shown in Table 4 was used. AA to aQ were obtained, respectively. Here, the samples aA to aM are examples of the wire rods of the present disclosure, and the samples aN to aQ are comparative examples.
In Table 3 below, the heating temperature, finishing temperature, winding temperature, immersion start temperature, molten salt temperature, and immersion time are the heating temperature in the process of heating the steel pieces and the hot rolling of the heated steel pieces, respectively. Finishing temperature in the process of obtaining hot-rolled steel, winding temperature in the process of water-cooling the hot-rolled steel and then winding it, immersion start temperature in molten salt in the process of patenting the cooled hot-rolled steel, melting in the same step It means the temperature of the salt and the immersion time in the molten salt in the same step.
Further, in Table 3, the wire rod diameter indicates the diameter of the wire rod finally obtained.

Next, the steels 1 to 35 shown in Table 2 were melted by a converter and then slab-rolled by a usual method to obtain 122 mm square billets (steel pieces). Samples 1A to 35A shown in Table 5 were obtained as wire rods by carrying out the steps after the step of heating the steel pieces in the manufacturing method X using the billets obtained from the steels 1 to 35, respectively. Here, the conditions of the steps after the step of heating the steel pieces in the manufacturing method X are the above-mentioned manufacturing conditions A for all the samples. Samples 1A to 18A, 34A, and 35A are examples of the wire rods 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 size of the pearlite block (hereinafter, also referred to as "PBS"), the average lamellar spacing of the pearlite structure, and the cementite length. , Tensile strength, cross-sectional reduction rate, and electrical resistance were measured.
The methods for measuring the average area ratio of the pearlite structure, the average particle size of the pearlite block, the average lamellar 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 weighted average of the particle size of the pearlite block is calculated by OIM analysis ver. This was done using 7.0.
The results are shown in Tables 4 and 5 below.

-Explanation of Tables 4 and 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 rod.
-The numerical value in the "γ" column means γ represented by the above 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 equation (2).
-The numerical value in the "β 1" column means _{β 1 represented by the above formula (3).}
-The "α <β 1" column indicates whether _{α and β 1} satisfy 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.
-The "α <β 2" column indicates whether _{α and β 2} satisfy α <β _2. “A” means that α <β ₂ is satisfied, and “B” means that α <β ₂ is not satisfied.
"Central PBS" means the average particle size of the pearlite block in the central region within d / 10 of the center in the cross section.
"Surface PBS" means the average particle size of the pearlite block in the surface region within d / 10 of the outer peripheral surface in the cross section. Note that d is the diameter of the wire rod.
-"Cementite length" means the average length of cementite in the central region within d / 10 of the center in the cross section.
"Average lamellar spacing" means the average lamellar spacing of the pearlite structure in the central region within d / 10 of the center in the cross section.

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

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

Among the samples aA to aM of Examples, in the samples aA to aJ and aM in which the central PBS and the surface layer PBS were both 23.0 μm or less, the cross-sectional reduction rate, which is an index of the ductility of the wire rod, was further improved.
Further, among the samples aA to aM of Examples, the samples aA to aL having an average lamellar interval of 90 nm or less had higher tensile strength.

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

In contrast to these examples, Sample 19A containing no Mo had a low tensile strength.
The sample 20A having an excessively high Si content had a high electrical resistivity.
Sample 21A having an excessively high Mn content had a high electrical resistivity.
Sample 22A containing no Cr had a low tensile strength.
Sample 23A having an excessively high Cr content had a high electrical resistivity.
Sample 24A having an excessively low C content had a low tensile strength.
The sample 25A having an excessive Mo content had a high electrical resistivity.
Sample 26A having an excessively high Al content had a high electrical resistivity.
Sample 27A having an excessively high N content had a high electrical resistivity.
Sample 28A having an excessively high Ti content had a low tensile strength. It is presumed that the reason for this is that the austenite particle size immediately before patenting became finer, which reduced the hardenability.
Sample 29A having an excessively high B content had a high electrical resistivity.
Sample 30A having an excessively high C content had a high electrical resistivity. The reason for this is considered to be the formation of proeutectoid cementite.
Sample 31A had a low Mo content, poor hardenability, and low tensile strength.
Sample 32A had a low area ratio of the pearlite structure and a low tensile strength.
Sample 33A had a small total content of Mo and Cr, poor hardenability, and low tensile strength.

Among the samples 1A to 18A, 34A, and 35A of Examples, the electrical resistivity was further reduced in the samples 1A to 11A, 34A, and 35A satisfying _{α <β 1.}
Among these samples 1A to 11A, the electrical resistivity was particularly reduced in the samples 1A to 6A, 34A, and 35A satisfying _{α <β 2.}

[Manufacturing of steel wire]
The wire rods of Samples 1A to 18A, 34A, and 35A of Examples were subjected to wire drawing with a wire drawing strain of 1.50 to 2.40 with a surface reduction rate of 23 to 25% in each pass, and a diameter of 1 A steel wire of 0 to 3.5 mm was obtained. The wire drawing process was used as the pass, and the amount of change in the cross-sectional area of the pass was used as the surface reduction rate. The surface reduction rate R can be calculated as R = (S ₀ −S ₁ ) / S _{0 × 100, where S 0 is} the area of the cross section before _{machining and S 1} is the area of the cross section after machining.

[Evaluation]
With respect to the obtained steel wire by the method described above, 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 the average area ratio within D / 7 from the center. The average particle size of the pearlite block in the region was measured. The results are shown in Table 6.

As a result, the average area ratio of the pearlite structure of each steel wire was 90% or more, and the average particle size of the pearlite block was 5.0 μm or less.

Further, when the tensile strength and the electrical resistivity of the obtained steel wire were measured in the same manner as the measuring method for the wire rod, 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 wire in which the surface of the steel wire of Samples 1A to 18A, 34A, and 35A shown in Table 6 is coated with an Al-containing layer has a reduced electrical resistivity and a high electrical resistivity. Aluminum-coated steel wire with excellent tensile strength. Such an aluminum-coated steel wire can be obtained by either a method of forming an Al film on the wire rod of the present disclosure and then wire drawing, or a method of forming an Al-containing layer on the steel wire of the present disclosure after wire drawing. It can be manufactured.

The disclosure of Japanese Patent Application 2018-032547 filed on February 26, 2018 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.

Claims (15)

The chemical composition is by 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% or more and 0.030% or less,
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% or more and 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
Remaining: Consists of 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. The wire rod that is. The wire rod according to claim 1, wherein the 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 rod 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 = 0.0018 / ([C] × ([Cr] +0.1) ² ) ・ ・ ・ (1)
The element symbol in the formula (1) indicates the mass% of each element. The wire rod according to any one of claims 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)
The element symbols in the formulas (2) and (3) indicate the mass% of each element. The wire rod according to any one of claims 1 to 4, wherein α represented by the following formula (2) and β _{2 represented by the following formula (4) satisfy α <β 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 the mass% of each element. The invention according to any one of claims 1 to 5, which 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 in mass%. Wire rod. The wire rod according to any one of claims 1 to 6, which contains B: 0.0001% or more and 0.0030% or less in mass%. Claims 1 to claim that the average particle diameter of the pearlite block in the region within d / 10 from the center and the region within d / 10 from the outer peripheral surface in the cross section perpendicular to the longitudinal direction is 23.0 μm or less, respectively. The wire rod according to any one of 7. The wire rod according to any one of claims 1 to 8, wherein the average lamellar spacing of the pearlite structure in the region within d / 10 from the center in the cross section perpendicular to the longitudinal direction is 90 nm or less. The wire rod 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 rod according to any one of claims 1 to 10, wherein the wire has a diameter of 3.0 mm or more and 10.0 mm or less. The wire rod according to any one of claims 1 to 11, which is used for manufacturing a steel wire in an aluminum-coated steel wire. A steel wire which is a wire drawn product of the wire rod according to any one of claims 1 to 12. The chemical composition is by 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% or more and 0.030% or less,
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% or more and 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
Remaining: Consists of 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%. As described above, the steel wire having an average particle diameter of 5.0 μm or less in the pearlite block in the region within D / 7 from the center. An aluminum-coated steel wire comprising the steel wire according to claim 13 or 14, and an aluminum-containing layer that covers at least a part of the steel wire.

Images