JP2024011727A - Wire material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire material capable of suppressing the generation of blisters.

SOLUTION: There is provided a wire material having a chemical composition comprising by mass%, 0.70 to 1.20% of C, 0.10 to 1.00% of Si, 0.10 to 1.00% of Mn, 0.020% or less of P, 0.020% or less of S, 0.005% or less of Al, 0.0010 to 0.0100% of N, 0.010 to 0.500% of Cu, 0.010 to 0.500% of Ni, 0.003 to 0.100% of Sn and 0.0030% or less of O and the balance Fe with impurities, wherein when the index of a Cu content in the surface layer of the wire is defined as [Cu]_S, the index of a Sn content is defined as [Sn]_S, the index of a Cu content inside the wire is defined as [Cu]_B and the index of a Sn content is defined as [Sn]_B, the following expression (1) is satisfied. ([Cu]_S+[Sn]_S)/([Cu]_B+[Sn]_B)>1.10 (1).

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present disclosure relates to a wire.

Hard steel wire is used for bead wire, steel cord, wire rope, etc. A hard steel wire is manufactured by subjecting a wire rod or a heat-treated (patented) steel wire to a wire drawing process. After wire drawing, blueing or galvanizing may be applied. Thin hard steel wires may be further subjected to intermediate patenting or brass plating.

Oxidized scale is formed on the surface of the wire rod that is the raw material for hard steel wire. The oxidized scale formed on the surface of the wire suppresses rust from forming on the wire during storage or transportation.

However, many bulges called blisters may occur on a portion of the oxide scale formed on the surface of the wire. When blisters occur, the oxidized scale on the blister portions tends to crack and peel off during storage or transportation. When the oxide scale in the blister area cracks or flakes off, red rust forms in that area. Red rust is difficult to remove even with descaling treatment before wire drawing processing. Therefore, due to red rust, the wire drawability of the wire is reduced.

A technique for suppressing the occurrence of blisters in wire rods is proposed in Japanese Unexamined Patent Publication No. 2000-239796 (Patent Document 1).

The wire rod disclosed in Patent Document 1 has C: 0.7 to 1.1%, Si: 0.1 to 1.5%, Mn: 0.2 to 1%, and Cr: 0 to 1 in mass %. %, Al: 0.003% or less, S: 0.01% or less, and Y: 0.0005 to 0.02%, and further contains one or more of Ce, La, Nd, and Pr. Together with the Y content, the total content is 0.0005 to 0.02%, and the remainder consists of Fe and impurities. Patent Document 1 states that in this wire, the occurrence of blisters can be suppressed by having the above-mentioned chemical composition.

Japanese Patent Application Publication No. 2000-239796

The wire rod proposed in Patent Document 1 can suppress the occurrence of blisters. However, other techniques may be used to suppress the formation of blisters on the oxide scale of the wire.

An object of the present invention is to provide a wire rod that can suppress the occurrence of blisters.

The wire rod according to the present invention is
The chemical composition is in mass%,
C: 0.70-1.20%,
Si: 0.10-1.00%,
Mn: 0.10-1.00%,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.005% or less,
N: 0.0010-0.0100%,
Cu: 0.010-0.500%,
Ni: 0.010-0.500%,
Sn: 0.003 to 0.100%, and
Contains O: 0.0030% or less, the remainder consists of Fe and impurities,
Of the circular cross section perpendicular to the axial direction of the wire, in a line segment observation area from the surface position of the wire to a 100 μm depth position in the radial direction, from the surface position of the line segment observation area to the 100 μm depth position. Perform elemental analysis using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals to determine the Cu content and Sn content at each analysis position, and calculate the arithmetic mean value of the 101 Cu contents thus obtained. [Cu] _S is defined, and the arithmetic mean value of the 101 Sn contents determined is defined as [Sn] _S ,
Of the circular cross section perpendicular to the axial direction of the wire, in a square observation area that includes the center of the circular cross section and has a side of 10 μm, the square observation area is divided into minute squares of 1 μm on a side. Elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square, and the Cu content and Sn content at each analysis position were determined. When the arithmetic mean value of the amounts is defined as [Cu] _B , and the arithmetic mean value of the 121 Sn contents obtained is defined as [Sn] _B , formula (1) is satisfied.
([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1)

The wire rod according to the present invention is
The chemical composition is in mass%,
C: 0.70-1.20%,
Si: 0.10-1.00%,
Mn: 0.10-1.00%,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.005% or less,
N: 0.0010-0.0100%,
Cu: 0.010-0.500%,
Ni: 0.010-0.500%,
Sn: 0.003 to 0.100%, and
Contains O: 0.0030% or less,
Furthermore, it contains one or more selected from the group consisting of the first group and the second group, and the remainder consists of Fe and impurities,
Of the circular cross section perpendicular to the axial direction of the wire, in a line segment observation area from the surface position of the wire to a 100 μm depth position in the radial direction, from the surface position of the line segment observation area to the 100 μm depth position. Perform elemental analysis using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals to determine the Cu content and Sn content at each analysis position, and calculate the arithmetic mean value of the 101 Cu contents thus obtained. [Cu] _S is defined, and the arithmetic mean value of the 101 Sn contents determined is defined as [Sn] _S ,
Of the circular cross section perpendicular to the axial direction of the wire, in a square observation area that includes the center of the circular cross section and has a side of 10 μm, the square observation area is divided into minute squares of 1 μm on a side. Elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square, and the Cu content and Sn content at each analysis position were determined. When the arithmetic mean value of the amounts is defined as [Cu] _B , and the arithmetic mean value of the 121 Sn contents obtained is defined as [Sn] _B , formula (1) is satisfied.
[Group 1]
Cr: 0.50% or less,
Co: 0.50% or less,
Mo: 0.20% or less,
B: 0.005% or less,
W: 0.20% or less,
Ti: 0.10% or less,
Nb: 0.10% or less, and
V: 0.10% or less, one or more types selected from the group consisting of [Group 2]
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Zr: 0.010% or less, and
Rare earth element: 0.0050% or less, one or more selected from the group consisting of ([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1)

The wire rod of the present invention can suppress the occurrence of blisters.

FIG. 1 is a sectional view perpendicular to the axial direction of the wire. FIG. 2 is an enlarged view of a region of the circular cross section of FIG. 1 that includes a line segment observation area. FIG. 3 is an enlarged view of a region of the circular cross section of FIG. 1 that includes a square observation area.

The present inventors investigated a wire rod capable of suppressing the generation of blisters in the oxide scale formed on the surface from the viewpoint of chemical composition. As a result, the present inventors obtained the following findings.

Cu and Sn improve the adhesion of oxide scale generated on the wire surface after finish rolling. If the adhesion of the oxide scale to the wire surface increases, part of the oxide scale can be prevented from separating from the wire surface. As a result, the generation of blisters in the oxidized scale is suppressed.

However, Cu and Sn cause red heat embrittlement in a high temperature range. Therefore, when the wire contains Cu and Sn, cracks due to red heat embrittlement (intergranular cracks) are likely to occur during the hot working process. Ni has the effect of suppressing such red heat embrittlement. Therefore, it is effective to contain Cu and Sn in order to suppress the occurrence of blisters, and further to contain Ni in order to suppress red heat embrittlement due to the inclusion of Cu and Sn.

Based on the above findings, the present inventors investigated the chemical composition of the wire. As a result, the chemical composition, in mass%, was C: 0.70-1.20%, Si: 0.10-1.00%, Mn: 0.10-1.00%, P: 0.020%. Below, S: 0.020% or less, Al: 0.005% or less, N: 0.0010 to 0.0100%, Cu: 0.010 to 0.500%, Ni: 0.010 to 0.500%. , Sn: 0.003 to 0.100%, and O: 0.0030% or less, and when containing an arbitrary element, in place of a part of Fe, the above-mentioned first group and It is believed that if the wire contains one or more selected from the group consisting of two groups, with the remainder consisting of Fe and impurities, it is possible to suppress the occurrence of blisters and also to suppress the occurrence of cracks during hot working. Ta.

However, even if the wire material satisfies the above-mentioned chemical composition, there are still cases where the occurrence of blisters cannot be sufficiently suppressed. Therefore, the present inventors further investigated means for suppressing the occurrence of blisters in wire rods that satisfy the above chemical composition. As a result, the present inventors obtained the following knowledge.

As described above, if the Cu content and Sn content are increased, the adhesion of the oxide scale to the wire surface increases, but hot working cracks due to red heat embrittlement are more likely to occur. Therefore, further increasing the Cu content and Sn content is not effective. On the other hand, if the above-mentioned chemical composition is satisfied, the occurrence of hot working cracks due to red heat embrittlement can be suppressed. Furthermore, in order to improve the adhesion of oxide scale, it is sufficient to increase the Cu content and Sn content in the surface layer of the wire, and the Cu content and Sn content inside the wire are not related to the adhesion of oxide scale.

Therefore, in order to suppress the occurrence of blisters, the present inventors did not increase the Cu content and Sn content in the entire wire rod, but by concentrating Cu and Sn in the surface layer of the wire rod. We thought that we could suppress the occurrence of Therefore, the present inventors attempted to increase the Cu content and Sn content in the surface layer of the wire compared to the Cu content and Sn content inside the wire. As a result, [Cu] _S , which is an indicator of the Cu content in the surface layer of the wire, [Sn] _S , which is an indicator of the Sn content in the surface layer, and [, which is an indicator of the Cu content inside the wire, If [Cu] _B and [Sn] _B , which is an index of the internal Sn content, satisfy formula (1), it is possible to sufficiently suppress the occurrence of blisters while suppressing the occurrence of hot working cracks. I discovered something.
([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1)

The wire rod of this embodiment has been completed based on the above technical idea and has the following configuration.

[1]
A wire rod,
The chemical composition is in mass%,
C: 0.70-1.20%,
Si: 0.10-1.00%,
Mn: 0.10-1.00%,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.005% or less,
N: 0.0010-0.0100%,
Cu: 0.010-0.500%,
Ni: 0.010-0.500%,
Sn: 0.003 to 0.100%, and
Contains O: 0.0030% or less, the remainder consists of Fe and impurities,
Of the circular cross section perpendicular to the axial direction of the wire, in a line segment observation area from the surface position of the wire to a 100 μm depth position in the radial direction, from the surface position of the line segment observation area to the 100 μm depth position. Perform elemental analysis using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals to determine the Cu content and Sn content at each analysis position, and calculate the arithmetic mean value of the 101 Cu contents thus obtained. [Cu] _S is defined, and the arithmetic mean value of the 101 Sn contents determined is defined as [Sn] _S ,
Of the circular cross section perpendicular to the axial direction of the wire, in a square observation area that includes the center of the circular cross section and has a side of 10 μm, the square observation area is divided into minute squares of 1 μm on a side. Elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square, and the Cu content and Sn content at each analysis position were determined. When the arithmetic mean value of the amount is defined as [Cu] _B and the arithmetic mean value of the 121 Sn contents obtained is defined as [Sn] _B , formula (1) is satisfied.
wire.
([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1)

[2]
A wire rod,
The chemical composition is in mass%,
C: 0.70-1.20%,
Si: 0.10-1.00%,
Mn: 0.10-1.00%,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.005% or less,
N: 0.0010-0.0100%,
Cu: 0.010-0.500%,
Ni: 0.010-0.500%,
Sn: 0.003 to 0.100%, and
Contains O: 0.0030% or less,
Furthermore, it contains one or more selected from the group consisting of the first group and the second group, and the remainder consists of Fe and impurities,
Of the circular cross section perpendicular to the axial direction of the wire, in a line segment observation area from the surface position of the wire to a 100 μm depth position in the radial direction, from the surface position of the line segment observation area to the 100 μm depth position. Perform elemental analysis using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals to determine the Cu content and Sn content at each analysis position, and calculate the arithmetic mean value of the 101 Cu contents thus obtained. [Cu] _S is defined, and the arithmetic mean value of the 101 Sn contents determined is defined as [Sn] _S ,
Of the circular cross section perpendicular to the axial direction of the wire, in a square observation area that includes the center of the circular cross section and has a side of 10 μm, the square observation area is divided into minute squares of 1 μm on a side. Elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square, and the Cu content and Sn content at each analysis position were determined. When the arithmetic mean value of the amount is defined as [Cu] _B and the arithmetic mean value of the 121 Sn contents obtained is defined as [Sn] _B , formula (1) is satisfied.
wire.
[Group 1]
Cr: 0.50% or less,
Co: 0.50% or less,
Mo: 0.20% or less,
B: 0.005% or less,
W: 0.20% or less,
Ti: 0.10% or less,
Nb: 0.10% or less, and
V: 0.10% or less, one or more types selected from the group consisting of [Group 2]
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Zr: 0.010% or less, and
Rare earth element: 0.0050% or less, one or more selected from the group consisting of ([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1)

[3]
The wire rod according to [2],
containing the first group;
wire.

[4]
The wire rod according to [2] or [3],
containing the second group;
wire.

The wire according to this embodiment will be described in detail below.
Note that "%" regarding elements means mass % unless otherwise specified.

[Characteristics of the wire rod of this embodiment]
The wire rod of this embodiment includes the following features.
(Feature 1)
The chemical composition satisfies the range described in this embodiment.
(Feature 2)
Among the circular cross sections perpendicular to the axial direction of the wire, in the line segment observation area from the surface position of the wire to the 100 μm depth position in the radial direction, 101 points at 1 μm intervals from the surface position of the line segment observation area to the 100 μm depth position Perform elemental analysis using an electron beam microanalyzer at the analysis position to determine the Cu content and Sn content at each analysis position, and define the arithmetic mean value of the 101 Cu contents determined as [Cu] _S . , the arithmetic mean value of the 101 Sn contents determined is defined as [Sn] _S ,
Of the circular cross section perpendicular to the axial direction of the wire, in a square observation area that includes the center of the circular cross section and has a side of 10 μm, the square observation area is divided into minute squares of 1 μm on a side. Elemental analysis was performed using an electron beam microanalyzer at 121 analysis positions corresponding to the vertices to determine the Cu content and Sn content at each analysis position, and the arithmetic mean value of the 121 Cu contents obtained was calculated as [ When the arithmetic mean value of the 121 determined Sn contents is defined as [Sn] _{B ,} the formula (1) is satisfied.
([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1)
Each feature will be explained below.

[(Feature 1) Regarding chemical composition]
The chemical composition of the wire of this embodiment contains the following elements.

C: 0.70-1.20%
Carbon (C) increases the strength of the wire. When the C content is less than 0.70%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the C content exceeds 1.20%, pro-eutectoid cementite will be produced in excess even if the contents of other elements are within the range of this embodiment. In this case, the wire drawability of the wire is reduced. Furthermore, the toughness and ductility of the steel wire after wire drawing are reduced.
Therefore, the C content is between 0.70 and 1.20%.
The preferable lower limit of the C content is 0.74%, more preferably 0.78%, and still more preferably 0.82%.
A preferable upper limit of the C content is 1.16%, more preferably 1.12%, and still more preferably 1.08%.

Si: 0.10-1.00%
Silicon (Si) increases the strength of the wire. Si further deoxidizes steel in the steel manufacturing process during the wire manufacturing process. If the Si content is less than 0.10%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the Si content exceeds 1.00%, Si will segregate within the wire even if the content of other elements is within the range of this embodiment. In this case, bainite is generated in the region where Si is segregated, reducing the wire drawability of the wire.
Therefore, the Si content is 0.10 to 1.00%.
The preferable lower limit of the Si content is 0.15%, more preferably 0.20%, and still more preferably 0.25%.
A preferable upper limit of the Si content is 0.95%, more preferably 0.90%, and still more preferably 0.85%.

Mn: 0.10-1.00%
Manganese (Mn) improves the hardenability of steel materials and increases the strength of wire rods. Mn further fixes S in the steel material and improves hot workability. If the Mn content is less than 0.10%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the Mn content exceeds 1.00%, Mn will segregate within the wire even if the contents of other elements are within the range of this embodiment. In this case, bainite is generated in the region where Mn is segregated, reducing the wire drawability of the wire.
Therefore, the Mn content is 0.10-1.00%.
The lower limit of the Mn content is preferably 0.15%, more preferably 0.20%, and still more preferably 0.25%.
The upper limit of the Mn content is preferably 0.95%, more preferably 0.90%, and still more preferably 0.85%.

P: 0.020% or less Phosphorus (P) is an impurity. If the P content exceeds 0.020%, P will segregate at grain boundaries even if the contents of other elements are within the ranges of this embodiment. Therefore, the grain boundaries become brittle and the wire drawability of the wire decreases.
Therefore, the P content is 0.020% or less.
It is preferable that the P content is as low as possible. However, excessive reduction in P content increases manufacturing costs. Therefore, in consideration of normal industrial production, the lower limit of the P content is preferably more than 0%, more preferably 0.001%, even more preferably 0.003%, and even more preferably 0.005%. %.
A preferable upper limit of the P content is 0.018%, more preferably 0.016%, and still more preferably 0.014%.

S: 0.020% or less Sulfur (S) is an impurity. If the S content exceeds 0.020%, S will segregate at grain boundaries even if the contents of other elements are within the range of this embodiment. Furthermore, coarse MnS is produced excessively. Therefore, the wire drawability of the wire is reduced.
Therefore, the S content is 0.020% or less.
It is preferable that the S content is as low as possible. However, excessive reduction in S content increases manufacturing costs. Therefore, in consideration of normal industrial production, the preferable lower limit of the S content is more than 0%, more preferably 0.001%, even more preferably 0.002%, and still more preferably 0.003%. %.
A preferable upper limit of the S content is 0.018%, more preferably 0.016%, and still more preferably 0.014%.

Al: 0.005% or less If aluminum (Al) is 0.005% or less, sufficient wire drawability can be obtained in the wire rod. Therefore, the Al content is 0.005% or less.
A preferable lower limit of the Al content is more than 0%, more preferably 0.001%.
A preferable upper limit of the Al content is 0.004%, more preferably 0.003%.

N: 0.0010-0.0100%
Nitrogen (N) fixes dislocations during wire drawing and increases the strength of the steel wire after wire drawing. If the N content is less than 0.0010%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the N content exceeds 0.0100%, nitrides will be excessively produced in the wire even if the contents of other elements are within the range of this embodiment. In this case, the wire drawability of the wire is reduced.
Therefore, the N content is 0.0010 to 0.0100%.
The preferable lower limit of the N content is 0.0015%, more preferably 0.0020%, and still more preferably 0.0025%.
A preferable upper limit of the N content is 0.0090%, more preferably 0.0080%, and still more preferably 0.0070%.

Cu: 0.010-0.500%
Copper (Cu) increases the adhesion of oxide scale to the wire surface. If the Cu content is less than 0.010%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the Cu content exceeds 0.500%, even if the contents of other elements are within the ranges of this embodiment, Cu segregates at grain boundaries and red-hot embrittlement occurs. In this case, the hot workability of the wire is reduced.
Therefore, the Cu content is 0.010-0.500%.
The preferable lower limit of the Cu content is 0.012%, more preferably 0.030%, and still more preferably 0.040%.
A preferable upper limit of the Cu content is 0.490%, more preferably 0.480%, and still more preferably 0.450%.

Ni: 0.010-0.500%
Nickel (Ni) suppresses red heat embrittlement caused by Cu and Sn. Ni further suppresses ferrite decarburization that occurs during hot working, and suppresses a decrease in the strength of the wire rod. If the Ni content is less than 0.010%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the Ni content exceeds 0.500%, even if the contents of other elements are within the ranges of this embodiment, the scale of the wire becomes difficult to peel off, and sufficient descaling properties cannot be obtained.
Therefore, the Ni content is 0.010 to 0.500%.
The preferable lower limit of the Ni content is 0.012%, more preferably 0.030%, and still more preferably 0.040%.
A preferable upper limit of the Ni content is 0.490%, more preferably 0.480%, and still more preferably 0.450%.

Sn: 0.003-0.100%
Tin (Sn) increases the adhesion of oxide scale to the wire surface. Sn further suppresses ferrite decarburization that occurs during hot working, and suppresses a decrease in the strength of the wire rod. If the Sn content is less than 0.003%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the Sn content exceeds 0.100%, even if the contents of other elements are within the ranges of this embodiment, Sn will segregate at grain boundaries and red-hot embrittlement will occur. In this case, the hot workability of the wire is reduced.
Therefore, the Sn content is 0.003 to 0.100%.
The preferable lower limit of the Sn content is 0.005%, more preferably 0.010%, and still more preferably 0.015%.
A preferable upper limit of the Sn content is 0.095%, more preferably 0.090%, and still more preferably 0.085%.

O: 0.0030% or less Oxygen (O) is an impurity. If the O content exceeds 0.0030%, even if the contents of other elements are within the ranges of this embodiment, coarse oxides will be produced in the wire, and the wire drawability of the wire will deteriorate.
Therefore, the O content is 0.0030% or less.
It is preferable that the O content is as low as possible. However, excessive reduction in O content increases manufacturing costs. Therefore, in consideration of normal industrial production, the lower limit of the O content is preferably more than 0%, more preferably 0.0001%, even more preferably 0.0003%, and still more preferably 0.0005%. %.
A preferable upper limit of the O content is 0.0025%, more preferably 0.0020%.

The remainder of the chemical composition of the wire according to this embodiment consists of Fe and impurities. Here, impurities in the chemical composition are those that are mixed in from ores used as raw materials, scraps, or the manufacturing environment when wire rods are manufactured industrially, and are unintentionally contained. , means what is permissible within a range that does not adversely affect the wire according to this embodiment.

[About Optional Elements]
The chemical composition of the wire rod of this embodiment may further contain one or more selected from the group consisting of the first group and the second group in place of a part of Fe.
[Group 1]
Cr: 0.50% or less,
Co: 0.50% or less,
Mo: 0.20% or less,
B: 0.005% or less,
W: 0.20% or less,
Ti: 0.10% or less,
Nb: 0.10% or less, and
V: 0.10% or less, one or more types selected from the group consisting of [Group 2]
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Zr: 0.010% or less, and
Rare earth elements: 0.0050% or less, one or more selected from the group consisting of these arbitrary elements will be described below.

[Group 1: Cr, Co, Mo, B, W, Ti, Nb and V]
The chemical composition of the wire rod of this embodiment may further contain the above-mentioned first group instead of a part of Fe. These elements are optional elements, and all improve the hardenability of the steel material. Each element of the first group will be explained below.

Cr: 0.50% or less Chromium (Cr) is an optional element and does not need to be contained. That is, the Cr content may be 0%.
When contained, that is, when the Cr content is more than 0%, Cr improves the hardenability of the wire and increases the strength of the wire. If even a small amount of Cr is contained, the above effects can be obtained to some extent.
However, if the Cr content exceeds 0.50%, Cr will segregate within the wire even if the contents of other elements are within the range of this embodiment. In this case, bainite is generated in the region where Cr is segregated, and the wire drawability of the wire is reduced.
Therefore, the Cr content is 0 to 0.50%, and if contained, it is 0.50% or less.
The lower limit of the Cr content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.08%.
A preferable upper limit of the Cr content is 0.45%, more preferably 0.40%, and still more preferably 0.35%.

Co: 0.50% or less Cobalt (Co) is an optional element and does not need to be contained. That is, the Co content may be 0%.
When contained, that is, when the Co content is more than 0%, Co improves the hardenability of the wire and increases the strength of the wire. If even a small amount of Co is contained, the above effects can be obtained to some extent.
However, if the Co content exceeds 0.50%, even if the content of other elements is within the range of this embodiment, the hardness of the wire becomes excessively hard and the wire drawability of the wire decreases. .
Therefore, the Co content is 0 to 0.50%, and if contained, it is 0.50% or less.
The preferable lower limit of the Co content is 0.01%, more preferably 0.05%, and still more preferably 0.08%.
A preferable upper limit of the Co content is 0.45%, more preferably 0.40%, and still more preferably 0.35%.

Mo: 0.20% or less Molybdenum (Mo) is an optional element and may not be contained. That is, the Mo content may be 0%.
When Mo is contained, that is, when the Mo content is more than 0%, Mo improves the hardenability of the wire and increases the strength of the wire. If even a small amount of Mo is contained, the above effects can be obtained to some extent.
However, if the Mo content exceeds 0.20%, the hot workability of the steel material will decrease in the wire manufacturing process even if the other element contents are within the range of this embodiment.
Therefore, the Mo content is 0 to 0.20%, and if it is contained, it is 0.20% or less.
The lower limit of the Mo content is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.
A preferable upper limit of the Mo content is 0.18%, more preferably 0.16%, and still more preferably 0.14%.

B: 0.005% or less Boron (B) is an optional element and may not be contained. That is, the B content may be 0%.
When B is contained, that is, when the B content is more than 0%, B improves the hardenability of the wire and increases the strength of the wire. If even a small amount of B is contained, the above effects can be obtained to some extent.
However, if the B content exceeds 0.005%, the hot workability of the steel material will decrease in the wire manufacturing process even if the other element contents are within the range of this embodiment.
Therefore, the B content is 0 to 0.005%, and if contained, it is 0.005% or less.
The lower limit of the B content is preferably 0.001%, more preferably 0.002%.
A preferable upper limit of the B content is 0.004%, more preferably 0.003%.

W: 0.20% or less Tungsten (W) is an optional element and does not need to be contained. That is, the W content may be 0%.
When contained, that is, when the W content is more than 0%, W improves the hardenability of the wire and increases the strength of the wire. If even a small amount of W is contained, the above effects can be obtained to some extent.
However, if the W content exceeds 0.20%, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases in the wire manufacturing process.
Therefore, the W content is 0 to 0.20%, and if contained, it is 0.20% or less.
The preferable lower limit of the W content is 0.01%, more preferably 0.03%, and still more preferably 0.05%.
The upper limit of the W content is preferably 0.18%, more preferably 0.16%, and still more preferably 0.14%.

Ti: 0.10% or less Titanium (Ti) is an optional element and may not be contained. That is, the Ti content may be 0%.
When contained, that is, when the Ti content is more than 0%, Ti increases the hardenability of the wire and increases the strength of the wire. If even a small amount of Ti is contained, the above effects can be obtained to some extent.
However, if the Ti content exceeds 0.10%, the hot workability of the steel material decreases in the wire manufacturing process even if the other element contents are within the ranges of this embodiment.
Therefore, the Ti content is 0 to 0.10%, and if contained, it is 0.10% or less.
The lower limit of the Ti content is preferably 0.01%, more preferably 0.02%, and even more preferably 0.03%.
A preferable upper limit of the Ti content is 0.09%, more preferably 0.08%, and still more preferably 0.07%.

Nb: 0.10% or less Niobium (Nb) is an optional element and does not need to be contained. That is, the Nb content may be 0%.
When contained, that is, when the Nb content is more than 0%, Nb improves the hardenability of the wire and increases the strength of the wire. If even a small amount of Nb is contained, the above effects can be obtained to some extent.
However, if the Nb content exceeds 0.10%, the hot workability of the steel material decreases in the wire manufacturing process even if the other element contents are within the range of this embodiment.
Therefore, the Nb content is 0 to 0.10%, and if it is contained, it is 0.10% or less.
The lower limit of the Nb content is preferably 0.01%, more preferably 0.02%, and still more preferably 0.03%.
A preferable upper limit of the Nb content is 0.09%, more preferably 0.08%, and still more preferably 0.07%.

V: 0.10% or less Vanadium (V) is an optional element and may not be contained. That is, the V content may be 0%.
When contained, that is, when the V content is more than 0%, V increases the hardenability of the wire and increases the strength of the wire. If even a small amount of V is contained, the above effects can be obtained to some extent.
However, if the V content exceeds 0.10%, the wire drawability of the wire decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the V content is 0 to 0.10%, and if contained, it is 0.10% or less.
The lower limit of the V content is preferably 0.01%, more preferably 0.02%, and still more preferably 0.03%.
A preferable upper limit of the V content is 0.09%, more preferably 0.08%, and still more preferably 0.07%.

[Group 2: Ca, Mg, Zr and rare earth elements (REM)]
The chemical composition of the wire rod of this embodiment may further contain the above-mentioned second group instead of a part of Fe. These elements are optional elements, and all improve the ductility of the wire.

Ca: 0.0050% or less Calcium (Ca) is an optional element and may not be contained. That is, the Ca content may be 0%.
When contained, that is, when the Ca content is more than 0%, Ca reduces hard alumina-based inclusions and increases the ductility of the wire rod. If even a small amount of Ca is contained, the above effects can be obtained to some extent.
However, if the Ca content exceeds 0.0050%, even if the contents of other elements are within the ranges of the present embodiment, coarse oxides will be produced and the wire drawability of the wire will be reduced.
Therefore, the Ca content is 0 to 0.0050%, and if contained, it is 0.0050% or less.
The lower limit of the Ca content is preferably 0.0001%, more preferably 0.0005%, and still more preferably 0.0008%.
A preferable upper limit of the Ca content is 0.0045%, more preferably 0.0040%, and still more preferably 0.0035%.

Mg: 0.0050% or less Magnesium (Mg) is an optional element and may not be contained. That is, the Mg content may be 0%.
When contained, that is, when the Mg content is more than 0%, Mg forms fine oxides. The fine oxide refines the structure of the wire and increases the ductility of the wire. If even a small amount of Mg is contained, the above effects can be obtained to some extent.
However, if the Mg content exceeds 0.0050%, even if the contents of other elements are within the ranges of this embodiment, coarse oxides will be produced and the wire drawability of the wire will deteriorate.
Therefore, the Mg content is 0 to 0.0050%, and if contained, it is 0.0050% or less.
The preferable lower limit of the Mg content is 0.0001%, more preferably 0.0005%, and still more preferably 0.0008%.
A preferable upper limit of the Mg content is 0.0045%, more preferably 0.0040%, and still more preferably 0.0035%.

Zr: 0.010% or less Zirconium (Zr) is an optional element and does not need to be contained. That is, the Zr content may be 0%.
When contained, that is, when the Zr content is more than 0%, Zr forms fine oxides. The fine oxide refines the structure of the wire and increases the ductility of the wire. If even a small amount of Zr is contained, the above effects can be obtained to some extent.
However, if the Zr content exceeds 0.010%, even if the contents of other elements are within the ranges of this embodiment, coarse oxides will be produced and the wire drawability of the wire will deteriorate.
Therefore, the Zr content is 0 to 0.010%, and if contained, it is 0.010% or less.
The lower limit of the Zr content is preferably 0.001%, more preferably 0.002%, and still more preferably 0.003%.
A preferable upper limit of the Zr content is 0.009%, more preferably 0.008%, and still more preferably 0.007%.

Rare earth element: 0.0050% or less Rare earth element (REM) is an optional element and does not need to be contained. That is, the REM content may be 0%.
When contained, that is, when the REM content is more than 0%, REM forms fine sulfides and renders S harmless. Therefore, the ductility of the wire increases. If even a small amount of REM is contained, the above effects can be obtained to some extent.
However, if the REM content exceeds 0.0050%, even if the contents of other elements are within the ranges of this embodiment, coarse oxides will be produced and the wire drawability of the wire will deteriorate.
Therefore, the REM content is 0 to 0.0050%, and if contained, it is 0.0050% or less.
The lower limit of the REM content is preferably 0.0001%, more preferably 0.0005%, and still more preferably 0.0008%.
A preferable upper limit of the REM content is 0.0045%, more preferably 0.0040%, and still more preferably 0.0035%.

In this specification, REM refers to scandium (Sc) with an atomic number of 21, yttrium (Y) with an atomic number of 39, and lanthanoids such as lanthanum (La) with an atomic number of 57 to lutetium (with an atomic number of 71). means one or more elements selected from the group consisting of Lu). Moreover, the REM content in this specification means the total content of these elements.

[Method for measuring chemical composition of wire]
The chemical composition of the wire of this embodiment can be measured by a well-known component analysis method based on JIS G0321:2017. Specifically, chips are collected from the inside of the wire rod from which oxidized scale has been removed using a drill. The collected chips are dissolved in acid to obtain a solution. ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) is performed on the solution to perform elemental analysis of the chemical composition. The C content and S content are determined by the well-known high frequency combustion method (combustion-infrared absorption method). The N content is determined using the well-known inert gas melting-thermal conductivity method. The O content is determined using the well-known inert gas melting-infrared absorption method.

In addition, the content of each element is determined by rounding off the fraction of the measured value based on the significant figures specified in this embodiment, and calculates the value to the smallest digit of the content of each element specified in this embodiment. do. For example, the C content of the wire rod of this embodiment is defined as a numerical value to the second decimal place. Therefore, the C content is a value obtained by rounding off the measured value to the second decimal place.

Similarly, the content of other elements other than the C content of the wire of this embodiment is a value obtained by rounding off the measured value to the smallest digit specified in this embodiment. Let be the content of the element.

Note that rounding means rounding down if the fraction is less than 5, and rounding up if the fraction is 5 or more.

[(Feature 2) Regarding formula (1)]
Furthermore, in the wire of this embodiment, the Cu content and Sn content in the surface layer of the wire are higher than the Cu content and Sn content inside the wire. Specifically, the average content of Cu in the surface layer of the wire is defined as [Cu] _S , and the average content of Sn is defined as [Sn] _S . The average content of Cu at the center of the wire is defined as [Cu] _B , and the average content of Sn is defined as [Sn] _B. In this case, the wire of this embodiment satisfies formula (1).
([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1)

[Measurement method of [Cu] _S , [Sn] _S , [Cu] _B and [Sn] _B ]
[Cu] _S and [Sn] _S in the surface layer of the wire and [Cu] _B and [Sn] _B in the center of the wire are determined by the following method.

FIG. 1 is a sectional view perpendicular to the axial direction of the wire. As shown in FIG. 1, the cross section of the wire perpendicular to the axial direction is circular. Hereinafter, this cross section will be referred to as a circular cross section. In a circular cross section, [Cu] _S and [Sn] _S in the surface layer of the wire are determined by the following method.

In the circular cross section, a line segment from the surface of the wire to a depth of 100 μm in the radial direction is defined as a line segment observation area LA. When oxide scale is formed on the surface of the wire, "the surface of the wire" as used herein means the surface of the base material excluding the oxide scale. For example, mechanical descaling is performed to remove the oxide scale. Mechanical descaling applies, for example, a tensile strain of about 6% to remove oxide scale attached to the wire surface.

The Cu content and Sn content in the above-mentioned line segment observation area LA are determined by the following method. FIG. 2 is an enlarged view of a region 100 including the line segment observation area LA in the circular cross section of FIG. Referring to FIG. 2, on line segment observation area LA, positions at 1 μm intervals from surface position D0 to 1 μm depth position D100 are defined as analysis positions Dj (j=an integer from 0 to 100).

At each analysis position Dj, elemental analysis is performed using an electron probe micro analyzer (EPMA). In the elemental analysis by EPMA, the acceleration voltage is set to 15 kV. Furthermore, the elements to be measured are Fe, C, Cr, Cu, Sn, Si, Mn, and Ni.

The Cu content and Sn content in mass % at the analysis position Dj are determined by the above-mentioned EPMA. The arithmetic mean value of the Cu content at all analysis positions Dj (101 points in total) is defined as [Cu] _S . The arithmetic mean value of Sn content at all analysis positions Dj is defined as [Sn] _S . [Cu] _S and [Sn] _S in the wire surface layer are determined by the above method.

Furthermore, in the above-mentioned circular cross section, [Cu] _B and [Sn] _B inside the steel material are determined by the following method.

Of the circular cross section, a square area of 10 μm on a side that includes the center of the circular cross section is defined as a square observation area SA. The Cu content and Sn content in the square observation area SA are determined by the following method. FIG. 3 is an enlarged view of a region 200 including the square observation area SA in the circular cross section of FIG. Referring to FIG. 3, the square observation area SA is divided into minute squares SSA each side of which is 1 μm. At this time, the square observation area SA is divided into 100 minute squares SSA. Then, a position corresponding to the vertex of each minute square SSA in the square observation area SA is defined as an analysis position PT. In this case, the total number of analysis positions PT within the square observation area SA is 121.

At each analysis position PT, the above-described elemental analysis by EPMA is performed, and the Cu content and Sn content in mass % at each analysis position PT are determined. The arithmetic mean value of the Cu content at all analysis positions PT (121 points in total) is defined as [Cu] _B . The arithmetic mean value of Sn content at all analysis positions PT is defined as [Sn] _B . [Cu] _B and [Sn] _B inside the steel material are determined by the above method.

[About the effect of formula (1)]
Using [Cu] _S and [Sn] _S at the surface layer of the wire and [Cu] _B and [Sn] _B at the center of the wire, which were determined by the above measurement method, F1 defined by the following formula is calculated. demand.
F1 = ([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B )

F1 is an index for suppressing blistering on the surface of the wire. When F1 is 1.10 or less, in the wire, the total amount of Cu content and Sn content in the surface layer is not much different from the total amount of Cu content and Sn content in the inside. In this case, in the wire that satisfies feature 1, the concentration of Cu and Sn in the surface layer is not sufficient. Therefore, the adhesion of the oxide scale to the wire surface decreases. As a result, blisters are likely to occur in the wire. The oxide scale at the location where blistering occurred has peeled off from the surface of the wire. When blisters occur, even if descaling treatment such as pickling or shot blasting is performed before wire drawing, part of the oxide scale tends to remain on the surface of the wire. Therefore, wire drawability deteriorates.

In a wire that satisfies characteristic 1, if F1 is higher than 1.10, Cu and Sn are sufficiently concentrated in the surface layer. In this case, the occurrence of blisters can be sufficiently suppressed.

A preferable lower limit of F1 is 1.11, more preferably 1.12, still more preferably 1.13, still more preferably 1.14, and still more preferably 1.15.
The upper limit of F1 is not particularly limited. However, when the wire material satisfies characteristic 1, the upper limit of F1 is, for example, 1.70, and more preferably 1.65.

[Effects of the wire rod of this embodiment]
The wire rod of this embodiment satisfies Feature 1 and Feature 2. Therefore, in the wire rod of this embodiment, while suppressing hot working cracking of the wire rod due to excessive content of Cu and Sn, Cu and Sn are concentrated in the surface layer, and the oxide scale formed on the surface of the wire rod is suppressed. The occurrence of blisters can be suppressed.

[Applications to which the wire of this embodiment can be applied]
The wire rod of this embodiment is widely applicable, for example, as a material for hard steel wire manufactured by wire drawing. The hard steel wire can be applied to, for example, bead wire, steel cord, wire rope, and the like.

[An example of the method for manufacturing the wire rod of this embodiment]
An example of the method for manufacturing the wire rod of this embodiment will be described. The wire rod manufacturing method described below is an example for manufacturing the wire rod of this embodiment. Therefore, the wire rod having the above-described configuration may be manufactured by a manufacturing method other than the manufacturing method described below. However, the manufacturing method described below is a preferable example of the manufacturing method of the wire rod of this embodiment.

An example of the method for manufacturing the wire of this embodiment includes the following steps.
(Step 1) Material preparation step (Step 2) Rough rolling step (Step 3) Finish rolling step Each step will be explained below.

[(Process 1) Material preparation process]
In the material preparation step, a material for the wire of this embodiment is prepared. Specifically, molten steel whose chemical composition satisfies Feature 1 is manufactured. The refining method is not particularly limited, and any known method may be used. For example, molten metal produced by a well-known method is subjected to refining (primary refining) in a converter. Well-known secondary refining is performed on the molten steel tapped from the converter. Through the above steps, molten steel having a chemical composition that satisfies Feature 1 is manufactured.

Using the produced molten steel, a material is produced by a well-known casting method. For example, an ingot may be manufactured by an ingot-forming method using molten steel. Alternatively, the bloom may be manufactured by a continuous casting method using molten steel. A material (ingot or bloom) is manufactured by the above method.

[(Step 2) Rough rolling step]
In the rough rolling process, rough rolling is performed on the material (ingot or bloom) prepared in the material preparation process to produce a billet.

In the rough rolling process, first, the material is heated using a heating furnace using a well-known method. The heating temperature is not particularly limited. A well-known heating temperature is sufficient. The heating temperature is, for example, 1000 to 1200°C.

The heated material is rolled (roughly rolled) using a blooming mill, a decomposition rolling mill, and a continuous rolling mill to produce a billet. Specifically, the heated material is reverse rolled using a blooming mill to produce a billet. If a well-known continuous rolling mill is installed downstream of the blooming mill, the billet after blooming is further subjected to tandem rolling using the continuous mill to produce even smaller billets. You may. The manufactured billet is left to cool (air cool) to room temperature before the finish rolling process.

[(Process 3) Finish rolling process]
In the finish rolling process, finish rolling is performed on the billet produced in the rough rolling process to produce a wire rod. The finish rolling process includes the following steps.
(Step 31) Heating step (Step 32) Rolling step The heating step and rolling step in the finish rolling step will be described below.

[(Step 31) Heating step]
In the heating step, the billet produced in the blooming and rolling step is heated using a heating furnace. The heating temperature is 900 to 1150°C.

The heating step further satisfies the following conditions. Specifically, the heating time when the surface temperature of the billet is 700° C. or higher is defined as t _{700° C.} (minutes) among the time in the heating furnace in the heating step. The time t _700°C means the time (minutes) from when the surface temperature of the billet becomes 700°C or higher in the heating furnace until the billet is extracted from the heating furnace. Inside the heating furnace, radiation thermometers are arranged at predetermined intervals along the billet transport direction. The time when the surface temperature of the billet as measured by a radiation thermometer reaches 700°C is defined as the start time of _t700°C . Further, the time when the billet is extracted from the heating furnace is defined as the end time of t _700°C .

Time t _700℃ satisfies the following formula (A) t _S <t _700℃ <t _L (A)
Here, t _S (minutes) and t _L (minutes) are defined by the following formulas.
_tS =11+10(Cu+5Sn)
t _L =65-10(Cu+5Sn)
Note that the corresponding element content in the steel material (billet) is substituted for Cu and Sn in t _S and t _L in mass %.

The Cu and Sn concentrations in the surface layer of the wire are thought to be due to the following mechanism. When the surface temperature of the billet exceeds 700° C., oxide scale is formed on the billet surface. Due to the formation of oxide scale, Fe, which is easily oxidized in the chemical composition of the surface layer of the billet (steel material), moves to the outside of the billet and forms oxide scale. On the other hand, Cu and Sn are not easily oxidized. Therefore, it remains on the surface layer of the billet and becomes concentrated. If the time t _{700° C.} is less than t _S , Fe in the surface layer will not sufficiently move to the outside, and as a result, Cu and Sn will not be sufficiently concentrated in the surface layer. On the other hand, if the time _t700°C exceeds _tL , the heating time is excessively long. In this case, Cu and Sn concentrated in the surface layer will diffuse into the steel material. As a result, Cu and Sn are not sufficiently concentrated in the surface layer.

If t _700°C is longer than t _S and shorter than t _L , that is, if t _700°C satisfies formula (A), then t _700°C is an appropriate range. Therefore, Cu and Sn are sufficiently enriched in the surface layer of the wire, and F1 satisfies formula (1).

[(Step 32) Rolling step]
In the rolling process, the billet heated in the heating process is subjected to finish rolling (continuous rolling) using a continuous rolling mill to produce a wire rod. A continuous rolling mill includes a plurality of rolling stands arranged in a line from upstream to downstream. Each rolling stand includes a pair of work rolls. Each work roll is formed with a caliber, and the caliber of a pair of work rolls forms a hole pattern. The wire rod after finish rolling is cooled by a well-known method. Note that the winding temperature of the wire is 700° C. or higher.

The wire rod of this embodiment is manufactured by the above method.

[Method for manufacturing hard steel wire]
The method for manufacturing a hard steel wire using the wire rod of this embodiment is a well-known manufacturing method. The hard steel wire is, for example, a steel cord. A method for manufacturing a hard steel wire using the wire rod of this embodiment is, for example, as follows. Remove oxidized scale from the wire and perform lubrication treatment. The lubricated wire rod is subjected to primary wire drawing processing to produce a steel wire. The steel wire after the primary wire drawing process is further subjected to a secondary wire drawing process. A well-known patenting process is performed on the steel wire after the secondary wire drawing process. A well-known plating process is performed on the steel wire after the patenting process. Through the above manufacturing process, a hard steel wire is manufactured.

In the wire of this embodiment, the adhesion of the oxide scale to the wire surface is sufficiently high. Therefore, the occurrence of blisters is sufficiently suppressed. Therefore, in the descaling treatment before wire drawing, oxidized scale can be sufficiently removed from the wire. As a result, wire breakage during wire drawing due to residual oxide scale can be suppressed. In other words, sufficient wire drawability can be obtained in the wire rod.

The effects of the wire rod of this embodiment will be explained in more detail with reference to Examples. The conditions in the following examples are examples of conditions adopted to confirm the feasibility and effects of the wire rod of this embodiment. Therefore, the wire rod of this embodiment is not limited to this example of one condition.

[Material preparation process]
Wire rods having the chemical compositions shown in Tables 1-1 and 1-2 were manufactured by the following method.

[Rough rolling process]
A rough rolling process was performed on the produced bloom to produce a billet. Specifically, the bloom was heated to 1100° C. using a heating furnace. The heated bloom was rolled (roughly rolled) using a blooming mill and a continuous rolling mill to produce a billet. The billet produced in the rough rolling process was allowed to cool to room temperature.

[Finish rolling process]
The manufactured billet was subjected to a finish rolling process. Specifically, the billets of each test number were heated to 950 to 1150° C. using a heating furnace. The heating time t _700°C (min), t _S (min) and t _L (min) are shown in Table 2 as "t _700°C (min)", "t _S (min)" and "t _L (min)". ”.

Finish rolling (continuous rolling) was performed on the heated billet using a continuous rolling mill to produce a wire rod. The wire rod after finish rolling was wound up at a winding temperature of 800° C. or higher, and then cooled to room temperature in the atmosphere. Through the above manufacturing process, a wire rod having a wire diameter of 5.5 mm was manufactured.

[About the evaluation test]
The following wire evaluation tests (Test 1 to Test 4) were conducted on the manufactured wire rods of each test number.
(Test 1) Chemical composition measurement test of wire (Test 2) Measurement test of [Cu] _S , [Sn] _S , [Cu] _B and [Sn] _B (Test 3) Blister suppression evaluation test (Test 4) Hot Process crack evaluation test Each test will be explained below.

[(Test 1) Chemical composition measurement test of wire rod]
The chemical composition of the wire of each test number was analyzed based on the above-mentioned [method for measuring chemical composition of wire]. As a result, the chemical compositions of all test numbers were as shown in Tables 1-1 and 1-2.

[(Test 2) Measurement test of [Cu] _S , [Sn] _S , [Cu] _B and [Sn] _B ]
For the wire rod of each test number, [Cu] _S , [Sn] _S , [ _{Cu] S ,} [Sn] _{S ,} [ Cu] _B and [Sn] _B were determined in mass %. F1 was determined based on the obtained [Cu] _S , [Sn] _S , [Cu] _B , and [Sn] _B.
F1 = ([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B )
The obtained [Cu] _S , [Sn] _S , [Cu] _B , [Sn] _B and F1 are shown in Table 2.

[(Test 3) Blister suppression evaluation test]
The oxidized scale formed on the surface of the wire of each test number after being left to cool was visually observed to confirm the presence or absence of blistering. Specifically, an arbitrary observation range of 4 m in length was selected from among the wire rods. The entire surface (outer peripheral surface) of the wire in the selected observation range was visually observed for the presence or absence of blisters. If blisters were present, the number of blisters was counted. The counted number of blisters generated is shown in the "Number of blisters generated" column in Table 2.

[(Test 4) Hot work crack evaluation test]
After the above cooling, the surface of the wire of each test number was visually observed to confirm the presence or absence of cracks. Specifically, an arbitrary observation range of 4 m in length was selected from among the wire rods. The entire surface (outer peripheral surface) of the selected observation range was visually observed for the presence or absence of cracks. When no cracking was observed, it was determined that hot working cracking was sufficiently suppressed (indicated by "○" in the "hot working cracking" column in Table 2). On the other hand, if cracking was confirmed at even one location, it was determined that hot working cracking could not be sufficiently suppressed (indicated by an "x" in the "hot working cracking" column in Table 2).

[Test results]
Table 2 shows the test results. Referring to Table 1-1, Table 1-2, and Table 2, the wire rods of test numbers 1 to 31 satisfied Feature 1 and Feature 2. As a result, the number of blisters generated was 10 or less, and the generation of blisters was sufficiently suppressed. Furthermore, no hot working cracks were observed in the wire rods with these test numbers.

On the other hand, in test number 32, the Cu content was too low. Therefore, the occurrence of blisters could not be sufficiently suppressed.

In test number 33, the Cu content was too high. Therefore, hot working cracks were confirmed.

In test number 34, the Ni content was too low. Therefore, hot working cracks were confirmed.

In test number 35, the Sn content was too low. Therefore, the occurrence of blisters could not be sufficiently suppressed.

In test number 36, the Sn content was too high. Therefore, hot working cracks were confirmed.

In test numbers 37 to 39, although characteristic 1 was satisfied, t _700°C in the finish rolling process was t _S or less. Therefore, F1 was low. As a result, the occurrence of blisters could not be sufficiently suppressed.

In test numbers 40 to 42, although characteristic 1 was satisfied, t _700°C in the finish rolling process was greater than t _L. Therefore, F1 was low. As a result, the occurrence of blisters could not be sufficiently suppressed.

The embodiments of the present disclosure have been described above. However, the embodiments described above are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the embodiments described above, and the embodiments described above can be modified and implemented as appropriate without departing from the spirit thereof.

Claims (4)

A wire rod,
The chemical composition is in mass%,
C: 0.70-1.20%,
Si: 0.10-1.00%,
Mn: 0.10-1.00%,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.005% or less,
N: 0.0010-0.0100%,
Cu: 0.010-0.500%,
Ni: 0.010-0.500%,
Sn: 0.003 to 0.100%, and
Contains O: 0.0030% or less, the remainder consists of Fe and impurities,
Of the circular cross section perpendicular to the axial direction of the wire, in a line segment observation area from the surface position of the wire to a 100 μm depth position in the radial direction, from the surface position of the line segment observation area to the 100 μm depth position. Perform elemental analysis using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals to determine the Cu content and Sn content at each analysis position, and calculate the arithmetic mean value of the 101 Cu contents thus obtained. [Cu] _S is defined, and the arithmetic mean value of the 101 Sn contents determined is defined as [Sn] _S ,
Of the circular cross section perpendicular to the axial direction of the wire, in a square observation area that includes the center of the circular cross section and has a side of 10 μm, the square observation area is divided into minute squares of 1 μm on a side. Elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square, and the Cu content and Sn content at each analysis position were determined. When the arithmetic mean value of the amount is defined as [Cu] _B and the arithmetic mean value of the 121 Sn contents obtained is defined as [Sn] _B , formula (1) is satisfied.
wire.
([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1) A wire rod,
The chemical composition is in mass%,
C: 0.70-1.20%,
Si: 0.10-1.00%,
Mn: 0.10-1.00%,
P: 0.020% or less,
S: 0.020% or less,
Al: 0.005% or less,
N: 0.0010-0.0100%,
Cu: 0.010-0.500%,
Ni: 0.010-0.500%,
Sn: 0.003 to 0.100%, and
Contains O: 0.0030% or less,
Furthermore, it contains one or more selected from the group consisting of the first group and the second group, and the remainder consists of Fe and impurities,
Of the circular cross section perpendicular to the axial direction of the wire, in a line segment observation area from the surface position of the wire to a 100 μm depth position in the radial direction, from the surface position of the line segment observation area to the 100 μm depth position. Perform elemental analysis using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals to determine the Cu content and Sn content at each analysis position, and calculate the arithmetic mean value of the 101 Cu contents thus obtained. [Cu] _S is defined, and the arithmetic mean value of the 101 Sn contents determined is defined as [Sn] _S ,
Of the circular cross section perpendicular to the axial direction of the wire, in a square observation area that includes the center of the circular cross section and has a side of 10 μm, the square observation area is divided into minute squares of 1 μm on a side. Elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square, and the Cu content and Sn content at each analysis position were determined. When the arithmetic mean value of the amount is defined as [Cu] _B and the arithmetic mean value of the 121 Sn contents obtained is defined as [Sn] _B , formula (1) is satisfied.
wire.
[Group 1]
Cr: 0.50% or less,
Co: 0.50% or less,
Mo: 0.20% or less,
B: 0.005% or less,
W: 0.20% or less,
Ti: 0.10% or less,
Nb: 0.10% or less, and
V: 0.10% or less, one or more types selected from the group consisting of [Group 2]
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Zr: 0.010% or less, and
Rare earth element: 0.0050% or less, one or more selected from the group consisting of ([Cu] _S + [Sn] _S ) / ([Cu] _B + [Sn] _B ) > 1.10 (1) The wire according to claim 2,
containing the first group;
wire. The wire according to claim 2,
containing the second group;
wire.

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