wire

Abstract

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, more than 0.005% to 0.080% 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

Description

[Technical Field]

[0001] The present disclosure relates to wire rods. [Background technology]

[0002] Hard steel wire is used for bead wire, steel cord, wire rope, etc. Hard steel wire is manufactured by drawing wire rod or heat-treated (patented) steel wire. After drawing, blueing or zinc plating may be applied. Thinner hard steel wire may be further subjected to intermediate patenting or brass plating.

[0003] An oxide scale is formed on the surface of the wire material used to make hard steel wire. The oxide scale formed on the surface of the wire material prevents rust from forming on the wire material during storage or transportation.

[0004] However, many swellings called blisters may occur in some parts of the oxide scale formed on the surface of the wire. When blisters occur, the oxide scale in the blistered areas is prone to cracking and peeling during storage or transportation. When the oxide scale in the blistered areas cracks or peels off, red rust forms in those areas. This red rust is difficult to remove even with descaling before wiredrawing. Therefore, the wiredrawability of the wire is reduced due to the red rust.

[0005] A technique for suppressing the occurrence of such blisters in wire is proposed in Japanese Patent Laid-Open Publication No. 2000-239796 (Patent Document 1).

[0006] The wire rod disclosed in Patent Document 1 contains, by mass%, 0.7-1.1% C, 0.1-1.5% Si, 0.2-1% Mn, 0-1% Cr, 0.003% or less Al, 0.01% or less S, and 0.0005-0.02% Y, and further contains at least one of Ce, La, Nd, and Pr together with the Y content for a total content of 0.0005-0.02%, with the balance consisting of Fe and impurities. Patent Document 1 states that by using the above chemical composition in this wire rod, the occurrence of blisters can be suppressed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-239796 Summary of the Invention [Problem to be solved by the invention]

[0008] The wire rod proposed in Patent Document 1 may be able to suppress the occurrence of blisters. However, other techniques may be used to suppress the occurrence of blisters on the oxide scale of the wire rod.

[0009] An object of the present invention is to provide a wire rod capable of suppressing the occurrence of blisters. [Means for solving the problem]

[0010] The wire according to the present invention is The chemical composition is, in mass%, C: 0.70~1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.020% or less, Al: over 0.005 to 0.080% N: 0.0010~0.0100%, Cu: 0.010~0.500%, Ni: 0.010~0.500%, Sn: 0.003 to 0.100%, and O: 0.0030% or less, the balance being Fe and impurities; In a line observation area of ​​a circular cross section perpendicular to the axial direction of the wire rod from the surface position of the wire rod to a depth position of 100 μm in the radial direction, elemental analysis was performed using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals from the surface position of the line observation area to the 100 μm depth position to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 101 determined Cu contents was defined as [Cu] S The arithmetic mean value of the Sn content of the 101 pieces was defined as [Sn] S and In the circular cross section perpendicular to the axial direction of the wire, in a square observation area including the center of the circular cross section and having a side length of 10 μm, the square observation area was divided into minute squares having a side length of 1 μm, and elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 121 determined Cu contents was defined as [Cu] B The arithmetic mean value of the Sn content of the 121 pieces was defined as [Sn] B When defined as above, equation (1) is satisfied. ([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )>1.10 (1)

[0011] The wire according to the present invention is The chemical composition is, in mass%, C: 0.70~1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.020% or less, Al: over 0.005 to 0.080% N: 0.0010~0.0100%, Cu: 0.010~0.500%, Ni: 0.010~0.500%, Sn: 0.003 to 0.100%, and O: 0.0030% or less, Further, the composition contains one or more elements selected from the group consisting of Group 1 and Group 2, with the remainder consisting of Fe and impurities; In a line observation area of ​​a circular cross section perpendicular to the axial direction of the wire rod from the surface position of the wire rod to a depth position of 100 μm in the radial direction, elemental analysis was performed using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals from the surface position of the line observation area to the 100 μm depth position to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 101 determined Cu contents was defined as [Cu] S The arithmetic mean value of the Sn content of the 101 pieces was defined as [Sn] S and In the circular cross section perpendicular to the axial direction of the wire, in a square observation area including the center of the circular cross section and having a side length of 10 μm, the square observation area was divided into minute squares having a side length of 1 μm, and elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 121 determined Cu contents was defined as [Cu] B The arithmetic mean value of the Sn content of the 121 pieces was defined as [Sn] B When defined as above, equation (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 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 ([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )>1.10 (1) [Effects of the Invention]

[0012] The wire rod of the present invention can suppress the occurrence of blisters. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view perpendicular to the axial direction of the wire. [Figure 2] FIG. 2 is an enlarged view of a region including a line segment observation area in the circular cross section of FIG. [Figure 3] FIG. 3 is an enlarged view of the area of ​​the circular cross section of FIG. 1 that includes the square observation area. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have investigated, from the viewpoint of chemical composition, wire rods capable of suppressing the formation of blisters in oxide scales formed on the surface, and have found the following.

[0015] Cu and Sn enhance the adhesion of the oxide scale that forms on the wire surface after finish rolling. The increased adhesion of the oxide scale to the wire surface prevents a portion of the oxide scale from detaching from the wire surface. As a result, the formation of blisters in the oxide scale is suppressed.

[0016] However, Cu and Sn cause red embrittlement at high temperatures. Therefore, when Cu and Sn are contained in a wire rod, cracks (intergranular cracks) due to red embrittlement are likely to occur during the hot working process. Ni has the effect of suppressing such red embrittlement. Therefore, it is effective to contain Cu and Sn to suppress the occurrence of blisters, and further to contain Ni to suppress red embrittlement due to the inclusion of Cu and Sn.

[0017] Based on the above findings, the present inventors investigated the chemical composition of the wire. As a result, it was considered that the occurrence of blisters can be suppressed and the occurrence of cracks during hot working can also be suppressed if the chemical composition contains, in mass%, C: 0.70 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.020% or less, Al: over 0.005 to 0.080%, 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 if any optional element is contained, further contains one or more elements selected from the group consisting of the above-mentioned first and second groups in place of a portion of Fe, with the balance being Fe and impurities.

[0018] However, even in wires satisfying 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 wires satisfying the above-mentioned chemical composition. As a result, the present inventors have obtained the following findings.

[0019] As described above, increasing the Cu and Sn contents improves the adhesion of the oxide scale to the wire surface, but also increases the likelihood of hot working cracks due to red embrittlement. Therefore, further increasing the Cu and Sn contents is not effective. On the other hand, satisfying the above-mentioned chemical composition can suppress the occurrence of hot working cracks due to red embrittlement. Furthermore, to improve the adhesion of the oxide scale, it is sufficient to increase the Cu and Sn contents in the surface layer of the wire; the Cu and Sn contents inside the wire are not related to the adhesion of the oxide scale.

[0020] Therefore, the inventors of the present invention considered that the occurrence of blisters could be suppressed by concentrating Cu and Sn in the surface layer of the wire, rather than increasing the Cu and Sn contents throughout the entire wire. Therefore, the inventors of the present invention attempted to increase the Cu and Sn contents in the surface layer of the wire relative to the Cu and Sn contents inside the wire. As a result, [Cu], which is an index of the Cu content in the surface layer of the wire, S and [Sn], which is an index of Sn content in the surface layer. S and [Cu], which is an index of the Cu content inside the wire. B and [Sn], which is an index of the internal Sn content. B However, it has been found that if formula (1) is satisfied, it is possible to sufficiently suppress the occurrence of blisters while suppressing the occurrence of hot working cracks. ([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )>1.10 (1)

[0021] The wire rod of this embodiment has been completed based on the above technical concept and has the following configuration.

[0022] [1] A wire rod, The chemical composition is, in mass%, C: 0.70~1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.020% or less, Al: over 0.005 to 0.080% N: 0.0010~0.0100%, Cu: 0.010~0.500%, Ni: 0.010~0.500%, Sn: 0.003 to 0.100%, and O: 0.0030% or less, the balance being Fe and impurities; In a line observation area of ​​a circular cross section perpendicular to the axial direction of the wire rod from the surface position of the wire rod to a depth position of 100 μm in the radial direction, elemental analysis was performed using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals from the surface position of the line observation area to the 100 μm depth position to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 101 determined Cu contents was defined as [Cu] S The arithmetic mean value of the Sn content of the 101 pieces was defined as [Sn] S and In the circular cross section perpendicular to the axial direction of the wire, in a square observation area including the center of the circular cross section and having a side length of 10 μm, the square observation area was divided into minute squares having a side length of 1 μm, and elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 121 determined Cu contents was defined as [Cu] B The arithmetic mean value of the Sn content of the 121 pieces was defined as [Sn] B When defined as above, equation (1) is satisfied. wire rod. ([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )>1.10 (1)

[0023] [2] A wire rod, The chemical composition is, in mass%, C: 0.70~1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.020% or less, Al: over 0.005 to 0.080% N: 0.0010~0.0100%, Cu: 0.010~0.500%, Ni: 0.010~0.500%, Sn: 0.003 to 0.100%, and O: 0.0030% or less, Further, the composition contains one or more elements selected from the group consisting of Group 1 and Group 2, with the remainder consisting of Fe and impurities; In a line observation area of ​​a circular cross section perpendicular to the axial direction of the wire rod from the surface position of the wire rod to a depth position of 100 μm in the radial direction, elemental analysis was performed using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals from the surface position of the line observation area to the 100 μm depth position to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 101 determined Cu contents was defined as [Cu] S The arithmetic mean value of the Sn content of the 101 pieces was defined as [Sn] S and In the circular cross section perpendicular to the axial direction of the wire, in a square observation area including the center of the circular cross section and having a side length of 10 μm, the square observation area was divided into minute squares having a side length of 1 μm, and elemental analysis was performed using the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 121 determined Cu contents was defined as [Cu] B The arithmetic mean value of the Sn content of the 121 pieces was defined as [Sn] B When defined as above, equation (1) is satisfied. wire rod. [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 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 ([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )>1.10 (1)

[0024] [3] [2] The wire according to [2], containing the first group, wire rod.

[0025] [4] The wire according to [2] or [3], containing the second group, wire rod.

[0026] The wire rod according to this embodiment will be described in detail below. Unless otherwise specified, "%" for elements means mass %.

[0027] [Characteristics of the wire rod of this embodiment] The wire rod of this embodiment has the following features. (Feature 1) The chemical composition satisfies the range described in this embodiment. (Feature 2) In a circular cross section perpendicular to the axial direction of the wire, elemental analysis was carried out at 101 analysis positions at 1 μm intervals from the surface position of the wire to a depth of 100 μm in the radial direction in a line observation area from the surface position of the wire to a depth of 100 μm using an electron beam microanalyzer to determine the Cu content and Sn content at each analysis position, and the arithmetic mean value of the 101 Cu contents determined was defined as [Cu] S The arithmetic mean value of the Sn content of 101 pieces was defined as [Sn] S and In the circular cross section perpendicular to the axial direction of the wire rod, an elemental analysis was carried out using an electron probe microanalyzer at 121 analysis positions corresponding to the vertices of each minute square when the square observation area was divided into minute squares each 1 μm long, in a square observation area including the center of the circular cross section and 10 μm on a side, to determine the Cu content and Sn content at each analysis position, and the arithmetic mean value of the 121 Cu contents determined was defined as [Cu] B The arithmetic mean value of the Sn content of the 121 samples was defined as [Sn] B When defined as above, equation (1) is satisfied. ([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )>1.10 (1) Each feature will be explained below.

[0028] [(Feature 1) Chemical composition] The chemical composition of the wire of this embodiment contains the following elements.

[0029] C: 0.70 to 1.20% Carbon (C) increases the strength of the wire rod. If 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 ranges of this embodiment. On the other hand, if the C content exceeds 1.20%, even if the contents of other elements are within the ranges of this embodiment, pro-eutectoid cementite is excessively formed. In this case, the wire drawability of the wire rod is deteriorated. Furthermore, the toughness and ductility of the steel wire after wire drawing are deteriorated. Therefore, the C content is 0.70 to 1.20%. The lower limit of the C content is preferably 0.74%, more preferably 0.78%, and even more preferably 0.82%. The upper limit of the C content is preferably 1.16%, more preferably 1.12%, and even more preferably 1.08%.

[0030] Si: 0.10 to 1.00% Silicon (Si) increases the strength of the wire rod. Furthermore, Si deoxidizes the steel during the steelmaking process in the wire rod 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 ranges of this embodiment. On the other hand, if the Si content exceeds 1.00%, Si segregates in the wire rod even if the contents of other elements are within the ranges of this embodiment. In this case, bainite is formed in the region where Si segregates, and the wire drawability of the wire rod deteriorates. Therefore, the Si content is 0.10 to 1.00%. The lower limit of the Si content is preferably 0.15%, more preferably 0.20%, and even more preferably 0.25%. The upper limit of the Si content is preferably 0.95%, more preferably 0.90%, and even more preferably 0.85%.

[0031] Mn: 0.10 to 1.00% Manganese (Mn) improves the hardenability of steel and increases the strength of wire rod. Mn also fixes S in the steel, improving 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 ranges of this embodiment. On the other hand, if the Mn content exceeds 1.00%, Mn segregates in the wire rod even if the contents of other elements are within the ranges of this embodiment. In this case, bainite is formed in the region where Mn segregates, and the wire drawability of the wire rod deteriorates. Therefore, the Mn content is 0.10 to 1.00%. The lower limit of the Mn content is preferably 0.15%, more preferably 0.20%, and even more preferably 0.25%. The upper limit of the Mn content is preferably 0.95%, more preferably 0.90%, and even more preferably 0.85%.

[0032] P:0.020% or less Phosphorus (P) is an impurity. If the P content exceeds 0.020%, P segregates at the grain boundaries even if the contents of other elements are within the ranges of this embodiment. This embrittles the grain boundaries, resulting in a decrease in the drawability of the wire rod. Therefore, the P content is 0.020% or less. The P content is preferably as low as possible. However, excessive reduction in the P content increases production costs. Therefore, taking into consideration 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%. The upper limit of the P content is preferably 0.018%, more preferably 0.016%, and even more preferably 0.014%.

[0033] S: 0.020% or less Sulfur (S) is an impurity. If the S content exceeds 0.020%, S segregates at grain boundaries even if the contents of other elements are within the ranges of this embodiment. Furthermore, excessive amounts of coarse MnS are produced. This reduces the drawability of the wire rod. Therefore, the S content is 0.020% or less. The S content is preferably as low as possible. However, excessive reduction in the S content increases production costs. Therefore, in consideration of normal industrial production, the lower limit of the S content is preferably more than 0%, more preferably 0.001%, even more preferably 0.002%, and even more preferably 0.003%. The upper limit of the S content is preferably 0.018%, more preferably 0.016%, and even more preferably 0.014%.

[0034] Al: Over 0.005 to 0.080% Aluminum (Al) functions as a deoxidizer. If the Al content is 0.005% or less, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Al content exceeds 0.080%, even if the contents of other elements are within the ranges of this embodiment, excessive coarse oxides are formed, which reduces the drawability of the wire rod. Therefore, the Al content is more than 0.005% to 0.080%. The lower limit of the Al content is preferably 0.008%, more preferably 0.010%, and even more preferably 0.015%. The upper limit of the Al content is preferably 0.075%, more preferably 0.070%, and even more preferably 0.065%.

[0035] N: 0.0010 to 0.0100% Nitrogen (N) fixes dislocations when drawing a wire rod, thereby increasing the strength of the steel wire after 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 ranges of this embodiment. On the other hand, if the N content exceeds 0.0100%, even if the contents of other elements are within the ranges of this embodiment, excessive nitrides are formed in the wire rod, which reduces the wire drawability of the wire rod. Therefore, the N content is 0.0010 to 0.0100%. The lower limit of the N content is preferably 0.0015%, more preferably 0.0020%, and even more preferably 0.0025%. The upper limit of the N content is preferably 0.0090%, more preferably 0.0080%, and even more preferably 0.0070%.

[0036] Cu: 0.010 to 0.500% Copper (Cu) improves the adhesion of oxide scale to the wire surface. If the Cu content is less than 0.010%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges 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 the grain boundaries, causing red embrittlement, which reduces the hot workability of the wire rod. Therefore, the Cu content is 0.010 to 0.500%. The lower limit of the Cu content is preferably 0.012%, more preferably 0.030%, and even more preferably 0.040%. The upper limit of the Cu content is preferably 0.490%, more preferably 0.480%, and even more preferably 0.450%.

[0037] Ni: 0.010 to 0.500% Nickel (Ni) suppresses red embrittlement caused by Cu and Sn. Ni also suppresses ferrite decarburization that occurs during hot working, thereby suppressing 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 ranges 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 on the wire rod becomes difficult to peel off, and sufficient descaling properties cannot be obtained. Therefore, the Ni content is 0.010 to 0.500%. The lower limit of the Ni content is preferably 0.012%, more preferably 0.030%, and even more preferably 0.040%. The upper limit of the Ni content is preferably 0.490%, more preferably 0.480%, and even more preferably 0.450%.

[0038] Sn: 0.003 to 0.100% Tin (Sn) enhances the adhesion of oxide scale to the wire surface. Sn also suppresses ferrite decarburization that occurs during hot working, thereby suppressing a decrease in the strength of the wire. 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 ranges 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 segregates at grain boundaries, causing red embrittlement, which reduces the hot workability of the wire rod. Therefore, the Sn content is 0.003 to 0.100%. The lower limit of the Sn content is preferably 0.005%, more preferably 0.010%, and even more preferably 0.015%. The upper limit of the Sn content is preferably 0.095%, more preferably 0.090%, and even more preferably 0.085%.

[0039] 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 are generated in the wire rod, and the wire drawability of the wire rod is reduced. Therefore, the O content is 0.0030% or less. The O content is preferably as low as possible. However, excessive reduction of the O content increases production costs. Therefore, taking into consideration 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 even more preferably 0.0005%. The upper limit of the O content is preferably 0.0025%, and more preferably 0.0020%.

[0040] The balance of the chemical composition of the wire rod according to this embodiment is Fe and impurities. Here, the impurities in the chemical composition refer to substances that are mixed in from raw materials such as ore or scrap or the manufacturing environment during industrial production of the wire rod, and are unintentionally contained, but are acceptable within a range that does not adversely affect the wire rod according to this embodiment.

[0041] [About optional elements] The chemical composition of the wire rod of this embodiment may further contain one or more elements selected from the group consisting of the first and second groups, in place of a portion 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 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 optional elements will be explained below.

[0042] [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 elements of the first group in place of a portion of Fe. These elements are optional elements, and all of them improve the hardenability of the steel material. Each element of the first group will be described below.

[0043] Cr:0.50% or less Chromium (Cr) is an optional element and may not 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 rod and increases the strength of the wire rod. Even 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 segregates in the wire rod even if the contents of other elements are within the ranges of this embodiment. In this case, bainite is formed in the region where Cr segregates, and the wire drawability of the wire rod deteriorates. 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%. The upper limit of the Cr content is preferably 0.45%, more preferably 0.40%, and even more preferably 0.35%.

[0044] Co:0.50% or less Cobalt (Co) is an optional element and may not be contained, that is, the Co content may be 0%. When Co is contained, that is, when the Co content exceeds 0%, Co improves the hardenability of the wire rod and increases the strength of the wire rod. Even 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 contents of other elements are within the ranges of this embodiment, the hardness of the wire becomes excessively high, and the drawability of the wire deteriorates. Therefore, the Co content is 0 to 0.50%, and if Co is contained, it is 0.50% or less. The lower limit of the Co content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.08%. The upper limit of the Co content is preferably 0.45%, more preferably 0.40%, and even more preferably 0.35%.

[0045] 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 exceeds 0%, Mo improves the hardenability of the wire rod and increases the strength of the wire rod. Even 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 be reduced in the wire rod manufacturing process even if the contents of other elements are within the ranges of this embodiment. Therefore, the Mo content is 0 to 0.20%, and if 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%. The upper limit of the Mo content is preferably 0.18%, more preferably 0.16%, and even more preferably 0.14%.

[0046] 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 exceeds 0%, B improves the hardenability of the wire rod and increases the strength of the wire rod. Even 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 be reduced in the wire rod manufacturing process even if the contents of other elements are within the ranges of this embodiment. Therefore, the B content is 0 to 0.005%, and if B is contained, it is 0.005% or less. The lower limit of the B content is preferably 0.001%, and more preferably 0.002%. The upper limit of the B content is preferably 0.004%, and more preferably 0.003%.

[0047] W: 0.20% or less Tungsten (W) is an optional element and may not be contained, that is, the W content may be 0%. When W is contained, that is, when the W content exceeds 0%, W improves the hardenability of the wire rod and increases the strength of the wire rod. Even 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%, the hot workability of the steel material will be reduced in the wire rod manufacturing process even if the contents of other elements are within the ranges of this embodiment. Therefore, the W content is 0 to 0.20%, and if W is contained, it is 0.20% or less. The lower limit of the W content is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%. The upper limit of the W content is preferably 0.18%, more preferably 0.16%, and even more preferably 0.14%.

[0048] 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 exceeds 0%, Ti improves the hardenability of the wire rod and increases the strength of the wire rod. Even 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 will be reduced in the wire rod manufacturing process even if the contents of other elements 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%. The upper limit of the Ti content is preferably 0.09%, more preferably 0.08%, and even more preferably 0.07%.

[0049] Nb: 0.10% or less Niobium (Nb) is an optional element and may not be contained, that is, the Nb content may be 0%. When Nb is contained, that is, when the Nb content is more than 0%, Nb improves the hardenability of the wire rod and increases the strength of the wire rod. Even 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 will be reduced in the wire rod manufacturing process even if the contents of other elements are within the ranges of this embodiment. Therefore, the Nb content is 0 to 0.10%, and if Nb is contained, it is 0.10% or less. The lower limit of the Nb content is preferably 0.01%, more preferably 0.02%, and even more preferably 0.03%. The upper limit of the Nb content is preferably 0.09%, more preferably 0.08%, and even more preferably 0.07%.

[0050] 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 V is contained, that is, when the V content exceeds 0%, V improves the hardenability of the wire rod and increases the strength of the wire rod. Even 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 rod will decrease 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 V is contained, it is 0.10% or less. The lower limit of the V content is preferably 0.01%, more preferably 0.02%, and even more preferably 0.03%. The upper limit of the V content is preferably 0.09%, more preferably 0.08%, and even more preferably 0.07%.

[0051] [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 elements of Group 2 in place of a portion of Fe. These elements are optional elements, and all of them increase the ductility of the wire rod.

[0052] 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. Even 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 this embodiment, coarse oxides are generated, and the drawability of the wire rod deteriorates. 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 even more preferably 0.0008%. The upper limit of the Ca content is preferably 0.0045%, more preferably 0.0040%, and even more preferably 0.0035%.

[0053] 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 Mg is contained, that is, when the Mg content is more than 0%, Mg forms fine oxides. The fine oxides refine the structure of the wire rod and increase the ductility of the wire rod. Even 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 are generated, and the drawability of the wire rod deteriorates. Therefore, the Mg content is 0 to 0.0050%, and if Mg is contained, it is 0.0050% or less. The lower limit of the Mg content is preferably 0.0001%, more preferably 0.0005%, and even more preferably 0.0008%. The upper limit of the Mg content is preferably 0.0045%, more preferably 0.0040%, and even more preferably 0.0035%.

[0054] Zr: 0.010% or less Zirconium (Zr) is an optional element and may not 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 oxides refine the structure of the wire rod and increase the ductility of the wire rod. Even 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 are generated, and the drawability of the wire rod deteriorates. 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 even more preferably 0.003%. The upper limit of the Zr content is preferably 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0055] Rare earth elements: 0.0050% or less Rare earth elements (REM) are optional elements and may not be contained, i.e., the REM content may be 0%. When REM is contained, that is, when the REM content is more than 0%, REM forms fine sulfides and neutralizes S, thereby increasing the ductility of the wire rod. Even if only 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 are generated, and the drawability of the wire rod deteriorates. 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 even more preferably 0.0008%. The upper limit of the REM content is preferably 0.0045%, more preferably 0.0040%, and even more preferably 0.0035%.

[0056] In this specification, REM refers to one or more elements selected from the group consisting of scandium (Sc), which has atomic number 21, yttrium (Y), which has atomic number 39, and the lanthanides lanthanum (La), which has atomic number 57, to lutetium (Lu), which has atomic number 71. In addition, in this specification, the REM content refers to the total content of these elements.

[0057] [Method for measuring the chemical composition of wire] The chemical composition of the wire rod of this embodiment can be measured by a known elemental analysis method in accordance with JIS G0321:2017. Specifically, using a drill, chips are collected from the inside of the wire rod after removing the oxide scale. The collected chips are dissolved in acid to obtain a solution. The solution is subjected to ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) to perform elemental analysis of the chemical composition. The C content and S content are determined by a known high-frequency combustion method (combustion-infrared absorption method). The N content is determined by a known inert gas fusion-thermal conductivity method. The O content is determined by a known inert gas fusion-infrared absorption method.

[0058] The content of each element is determined by rounding off the measured value to the nearest significant digit based on the significant digits specified in this embodiment. For example, the C content of the wire rod in this embodiment is determined to one decimal place. Therefore, the C content is determined to one decimal place by rounding off the measured value to two decimal places.

[0059] Similarly, the contents of elements other than the C content of the wire rod of this embodiment are determined by rounding off the measured value to the smallest digit specified in this embodiment, and this is the content of the element.

[0060] Rounding off means rounding down if the fraction is less than 5, and rounding up if the fraction is 5 or more.

[0061] [(Feature 2) Regarding Formula (1)] Furthermore, in the wire rod of this embodiment, the Cu content and Sn content in the surface layer of the wire rod are higher than the Cu content and Sn content in the interior of the wire rod. Specifically, the average Cu content in the surface layer of the wire rod is [Cu] S and the average Sn content is defined as [Sn] SThe average Cu content at the center of the wire is defined as [Cu] B and the average Sn content is defined as [Sn] B In this case, the wire rod of this embodiment satisfies the formula (1). ([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )>1.10 (1)

[0062] [[Cu] S , [Sn] S , [Cu] B and [Sn] B Measurement method] [Cu] on the surface of the wire S and [Sn] S and [Cu] at the center of the wire B and [Sn] B and are calculated in the following way:

[0063] Figure 1 is a cross-sectional view perpendicular to the axial direction of the wire. As shown in Figure 1, the cross-section perpendicular to the axial direction of the wire is circular. Hereinafter, this cross-section will be referred to as a circular cross-section. In the circular cross-section, [Cu] at the surface of the wire S and [Sn] S is calculated in the following way:

[0064] In the circular cross section, the line segment extending from the surface of the wire to a depth of 100 μm in the radial direction is defined as the line segment observation area LA. In the case where an oxide scale is formed on the surface of the wire, the "surface of the wire" refers to the surface of the base material excluding the oxide scale. The oxide scale is removed, for example, by mechanical descaling. Mechanical descaling involves applying a tensile strain of about 6% to remove the oxide scale adhering to the wire surface.

[0065] The Cu content and Sn content in the above-mentioned line segment observation area LA are determined by the following method. Figure 2 is an enlarged view of a region 100 including the line segment observation area LA in the circular cross section of Figure 1. Referring to Figure 2, on the line segment observation area LA, positions at 1 µm intervals from the surface position D0 to a 1 µm depth position D100 are defined as analysis positions Dj (j = an integer from 0 to 100).

[0066] At each analysis position Dj, elemental analysis is performed using an electron probe micro analyzer (EPMA). The acceleration voltage for elemental analysis using the EPMA is 15 kV. The elements to be measured are Fe, C, Cr, Cu, Sn, Si, Mn, and Ni.

[0067] The Cu content and Sn content in mass% at the analysis point Dj are determined by the above-mentioned EPMA. The arithmetic mean value of the Cu content at all the analysis points Dj (total of 101 points) is defined as [Cu] S The arithmetic mean value of the Sn content at all analysis locations Dj is defined as [Sn] S By the above method, [Cu] in the wire surface layer S and [Sn] S Ask for.

[0068] Furthermore, in the circular cross section mentioned above, [Cu] inside the steel B and [Sn] B is calculated in the following way:

[0069] Within the circular cross section, a square region including the center of the circular cross section and having a side length of 10 μm is defined as the square observation area SA. The Cu content and Sn content within the square observation area SA are determined using the following method. Figure 3 is an enlarged view of an area 200 within the circular cross section of Figure 1, including the square observation area SA. Referring to Figure 3, the square observation area SA is divided into minute squares SSA, each having a side length of 1 μm. In this case, the square observation area SA is divided into 100 minute squares SSA. The positions corresponding to the vertices of each minute square SSA within the square observation area SA are defined as analysis positions PT. In this case, the total number of analysis positions PT within the square observation area SA is 121.

[0070] At each analysis point PT, elemental analysis was performed using the EPMA described above, and the Cu content and Sn content in mass% at each analysis point PT were determined. The arithmetic mean value of the Cu content at all analysis points PT (a total of 121 points) was calculated as [Cu] B The arithmetic mean value of the Sn content at all analysis points PT is defined as [Sn] B By the above method, [Cu] inside the steel material B and [Sn] B Ask for.

[0071] [Regarding the action of formula (1)] [Cu] on the wire surface determined by the above measurement method S and [Sn] S and [Cu] at the center of the wire B and [Sn] B Using these, F1 defined by the following formula is found. F1=([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B )

[0072] F1 is an index for suppressing the occurrence of blisters on the surface of the wire. When F1 is 1.10 or less, the total amount of Cu and Sn in the surface layer of the wire is not significantly different from the total amount of Cu and Sn in the interior. In this case, in a wire satisfying Feature 1, the concentration of Cu and Sn in the surface layer is insufficient. This reduces the adhesion of the oxide scale to the wire surface. As a result, blisters are more likely to occur in the wire. The oxide scale at the location where blisters occur peels off from the surface of the wire. When blisters occur, even if descaling treatment such as pickling or shot blasting is performed before wiredrawing, some of the oxide scale is likely to remain on the surface of the wire. This reduces wiredrawability.

[0073] In a wire rod satisfying Feature 1, if F1 is higher than 1.10, Cu and Sn are sufficiently concentrated in the surface layer, and in this case, the occurrence of blisters can be sufficiently suppressed.

[0074] The lower limit of F1 is preferably 1.11, more preferably 1.12, even more preferably 1.13, even more preferably 1.14, and even more preferably 1.15. However, when the wire satisfies the characteristic 1, the upper limit of F1 is, for example, 1.70, and more preferably 1.65.

[0075] [Effects of the wire rod of this embodiment] The wire rod of this embodiment satisfies Features 1 and 2. Therefore, in the wire rod of this embodiment, hot working cracks of the wire rod due to an excessive content of Cu and Sn are suppressed, while Cu and Sn are concentrated in the surface layer, making it possible to suppress the occurrence of blisters in the oxide scale formed on the surface of the wire rod.

[0076] [Applications to which the wire rod of this embodiment can be applied] The wire rod of this embodiment can be widely used as a material for hard steel wires produced by wire drawing, for example, bead wires, steel cords, bridge wires, wire ropes, etc.

[0077] [One example of the method for manufacturing the wire rod according to this embodiment] An example of a method for manufacturing the wire rod of this embodiment will be described. The method for manufacturing the wire rod described below is one 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 preferred example of the method for manufacturing the wire rod of this embodiment.

[0078] An example of the method for manufacturing the wire of this embodiment includes the following steps. (Process 1) Material preparation process (Process 2) Rough rolling process (Process 3) Finishing rolling process Each step will be described below.

[0079] [(Process 1) Material preparation process] In the material preparation step, a material for the wire rod of this embodiment is prepared. Specifically, molten steel having a chemical composition that satisfies Feature 1 is produced. The refining method is not particularly limited, and a well-known method may be used. For example, molten pig iron produced by a well-known method is subjected to refining (primary refining) in a converter. The molten steel tapped from the converter is subjected to well-known secondary refining. Through the above steps, molten steel having a chemical composition that satisfies Feature 1 is produced.

[0080] The produced molten steel is used to produce a material by a well-known casting method. For example, an ingot may be produced by an ingot casting method using the molten steel. Alternatively, a bloom may be produced by a continuous casting method using the molten steel. By the above methods, a material (ingot or bloom) is produced.

[0081] [(Process 2) Rough rolling process] In the rough rolling step, the material (ingot or bloom) prepared in the material preparation step is subjected to rough rolling to produce a billet.

[0082] In the rough rolling process, first, the material is heated using a heating furnace by a well-known method. The heating temperature is not particularly limited. A well-known temperature is sufficient as the heating temperature. The heating temperature is, for example, 1000 to 1200°C.

[0083] The heated material is rolled (roughly rolled) using a blooming mill or a splitting mill and a continuous rolling mill to produce billets. Specifically, the heated material is reverse rolled using a blooming mill to produce billets. If a well-known continuous rolling mill is located downstream of the blooming mill, the billets after blooming may be further subjected to tandem rolling using the continuous rolling mill to produce smaller billets. The produced billets are allowed to cool (air-cooled) to room temperature before the finish rolling process.

[0084] [(Process 3) Finishing rolling process] In the finish rolling step, the billet produced in the rough rolling step is subjected to finish rolling to produce a wire rod. The finish rolling step includes the following steps. (Step 31) Heating step (Step 32) Rolling process The heating step and rolling step in the finish rolling step will be described below.

[0085] [(Step 31) Heating process] In the heating process, the billet produced in the blooming process is heated in a heating furnace at a heating temperature of 900 to 1150°C.

[0086] The heating process further satisfies the following condition: Specifically, the heating time during which the billet is kept in the heating furnace at a surface temperature of 700°C or higher is t 700℃ (minutes). Time t 700℃ means the time (minutes) from when the surface temperature of the billet reaches 700°C or higher in the heating furnace until the billet is removed from the heating furnace. Radiation thermometers are placed at regular intervals along the billet transport direction in the heating furnace. The time when the surface temperature of the billet measured by the radiation thermometer reaches 700°C is called t 700℃ The time when the billet is extracted from the heating furnace is defined as the start of t 700℃ The end time of the project.

[0087] Time t 700℃ satisfies the following formula (A): t S <t 700℃ <t L (A) where t S (minutes), t L (minutes) is defined by the following formula: t S =11+10(Cu+5Sn) t L =65-10(Cu+5Sn) In addition, t S and t L The Cu and Sn in the table are substituted with the corresponding element contents in the steel material (billet) in mass %.

[0088] The concentration of Cu and Sn in the surface layer of the wire rod is thought to be due to the following mechanism. When the surface temperature of the billet reaches 700°C or higher, an oxide scale forms on the surface of the billet. As the oxide scale forms, Fe, which is easily oxidized in the chemical composition of the surface layer of the billet (steel), moves to the outside of the billet and forms an oxide scale. On the other hand, Cu and Sn are not easily oxidized. Therefore, they remain on the surface layer of the billet and become concentrated. At time t 700℃ t S If the time is less than t, the Fe in the surface layer does not move out sufficiently, and as a result, Cu and Sn are not sufficiently concentrated in the surface layer. 700℃ t L If the heating time exceeds this limit, the heating time is excessively long. In this case, the Cu and Sn concentrated in the surface layer diffuse into the steel. As a result, the Cu and Sn do not concentrate sufficiently in the surface layer.

[0089] t 700℃ t S longer than t L If it is shorter than t 700℃ If satisfies equation (A), then t 700℃ Therefore, the concentration of Cu and Sn in the surface layer of the wire becomes sufficient, and F1 satisfies the formula (1).

[0090] [(Process 32) Rolling process] 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 wire rod. The continuous rolling mill includes multiple rolling stands arranged in a row from upstream to downstream. Each rolling stand includes a pair of work rolls. Each work roll is formed with a caliber, and the calibers of the pair of work rolls form a groove. The wire rod after finish rolling is cooled by a well-known method. The coiling temperature of the wire rod is 700°C or higher.

[0091] The wire rod of this embodiment is manufactured by the above method.

[0092] [Hard steel wire manufacturing method] The method for manufacturing a hard steel wire using the wire rod of this embodiment as a raw material is a well-known manufacturing method. The hard steel wire is, for example, a bead wire. The method for manufacturing a hard steel wire using the wire rod of this embodiment is, for example, as follows: Oxide scale is removed from the wire rod and a lubrication treatment is performed. The lubricated wire rod is subjected to a primary wiredrawing process to manufacture a steel wire. The steel wire after the primary wiredrawing process is further subjected to a secondary wiredrawing process. The steel wire after the secondary wiredrawing process is subjected to a well-known patenting process. The steel wire after the patenting process is subjected to a well-known plating process. The hard steel wire is manufactured by the above manufacturing steps.

[0093] In the wire rod of this embodiment, the adhesion of the oxide scale to the wire rod surface is sufficiently high. Therefore, the occurrence of blisters is sufficiently suppressed. Therefore, the oxide scale can be sufficiently removed from the wire rod in the descaling treatment before wiredrawing. As a result, wire breakage and the like during wiredrawing due to remaining oxide scale can be suppressed. In other words, the wire rod has sufficient wiredrawability. [Example]

[0094] The effects of the wire rod of this embodiment will be explained more specifically using examples. The conditions in the following examples are one example 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 one example of conditions.

[0095] [Material preparation process] Wires having the chemical compositions shown in Tables 1-1 and 1-2 were produced by the following method.

[0096] [Table 1-1]

[0097] [Table 1-2]

[0098] [Rough rolling process] The produced bloom was subjected to a rough rolling process to produce a billet. Specifically, the bloom was heated to 1100°C using a heating furnace. The heated bloom was rolled (rough rolling) 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.

[0099] [Finishing rolling process] The manufactured billets were 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 time t 700℃ (minutes), t S (min) and t L (min) in Table 2 700℃ (minutes)", "t S (min)" and "t L (min)"

[0100] [Table 2]

[0101] The heated billet was subjected to finish rolling (continuous rolling) using a continuous rolling mill to produce a wire rod. The wire rod after finish rolling was coiled at a coiling temperature of 800°C or higher, and then cooled to room temperature in the air. Through the above manufacturing process, a wire rod with a wire diameter of 5.5 mm was produced.

[0102] [About the evaluation test] The following wire evaluation tests (Tests 1 to 4) were carried out on the manufactured wires with each test number. (Test 1) Chemical composition measurement test of wire rod (Test 2) [Cu] S , [Sn] S , [Cu] B and [Sn] B Measurement test (Test 3) Blister Suppression Evaluation Test (Test 4) Hot working crack evaluation test Each test will be explained below.

[0103] [(Test 1) Chemical composition measurement test of wire rod] The chemical composition of the wires with each test number was analyzed based on the above-mentioned [Method for measuring the chemical composition of wires]. As a result, the chemical compositions of all test numbers were as shown in Tables 1-1 and 1-2.

[0104] [(Test 2) [Cu] S , [Sn] S , [Cu] B and [Sn] B Measurement test For each test number, the above [[Cu] S , [Sn] S , [Cu] B and [Sn] B Based on the measurement method, [Cu] S , [Sn] S , [Cu] B and [Sn] B was calculated in mass%. The obtained [Cu] S , [Sn] S , [Cu] B and [Sn] B Based on this, F1 was sought. F1=([Cu] S +[Sn] S ) / ([Cu] B +[Sn] B ) The obtained [Cu] S , [Sn] S , [Cu] B and [Sn] B and F1 are shown in Table 2.

[0105] [(Test 3) Blister Suppression Evaluation Test] After cooling, the oxide scale formed on the surface of each wire of each test number was visually observed to check for the presence or absence of blisters. Specifically, an arbitrary observation area of ​​4 m in length was selected from the wire. The entire surface (outer periphery) of the wire in the selected observation area was visually inspected for the presence or absence of blisters. If blisters were present, the number of blisters was counted. The number of blisters counted is shown in the "Number of blisters" column in Table 2.

[0106] [(Test 4) Hot working crack evaluation test] After cooling, the surface of the wire of each test number was visually inspected to check for the occurrence of cracks. Specifically, an arbitrary observation area of ​​4 m in length was selected within the wire. The entire surface (outer periphery) of the selected observation area was visually inspected for the occurrence of cracks. If no cracks were observed, it was determined that hot working cracks had been sufficiently suppressed (indicated by "○" in the "Hot working cracks" column in Table 2). On the other hand, if cracks were observed in even one location, it was determined that hot working cracks had not been sufficiently suppressed (indicated by "×" in the "Hot working cracks" column in Table 2).

[0107] [Test Results] The test results are shown in Table 2. Referring to Table 1-1, Table 1-2 and Table 2, the wire rods of test numbers 1 to 31 satisfied features 1 and 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 of these test numbers.

[0108] On the other hand, in test number 32, the Cu content was too low, and therefore the occurrence of blisters could not be sufficiently suppressed.

[0109] In test number 33, the Cu content was too high, which resulted in hot working cracks.

[0110] In test number 34, the Ni content was too low, which resulted in hot working cracks.

[0111] In test number 35, the Sn content was too low, so the occurrence of blisters could not be sufficiently suppressed.

[0112] In test number 36, the Sn content was too high, which resulted in hot working cracks.

[0113] Test numbers 37 to 39 satisfied Feature 1, but the t 700℃ t STherefore, F1 was low, and as a result, the occurrence of blisters could not be sufficiently suppressed.

[0114] Test numbers 40 to 42 satisfied Feature 1, but the t 700℃ t L As a result, the F1 was low, and the occurrence of blisters could not be sufficiently suppressed.

[0115] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure.

Claims

1. A wire rod, The chemical composition, in mass%, is 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: more than 0.005 to 0.080%, N: 0.0010-0.0100%, Cu: 0.010-0.500%, Ni: 0.010-0.500%, Sn: 0.003 to 0.100%, and O: 0.0030% or less, the balance being Fe and impurities; In a line observation area of ​​a circular cross section perpendicular to the axial direction of the wire rod from the surface position of the wire rod to a depth position of 100 μm in the radial direction, elemental analysis was performed using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals from the surface position of the line observation area to the 100 μm depth position to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 101 determined Cu contents was defined as [Cu] Ｓ The arithmetic mean value of the Sn content of the 101 pieces was defined as [Sn] Ｓ and In the circular cross section perpendicular to the axial direction of the wire, in a square observation area including the center of the circular cross section and having a side length of 10 μm, the square observation area is divided into minute squares having a side length of 1 μm. Elemental analysis is performed by the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the determined 121 Cu contents is defined as [Cu] Ｂ The arithmetic mean value of the Sn content of the 121 pieces was defined as [Sn] Ｂ When defined as above, equation (1) is satisfied. Wire rod. ([Cueateres� Ｓ +[S] Ｓ ) / ([Cu] Ｂ +[S] Ｂ )>1.10 (1)

2. A wire rod, The chemical composition, in mass%, is 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: more than 0.005 to 0.080%, N: 0.0010-0.0100%, Cu: 0.010-0.500%, Ni: 0.010-0.500%, Sn: 0.003 to 0.100%, and O: 0.0030% or less, Further, the alloy contains one or more elements selected from the group consisting of Group 1 and Group 2, with the remainder consisting of Fe and impurities; In a line observation area of ​​a circular cross section perpendicular to the axial direction of the wire rod from the surface position of the wire rod to a depth position of 100 μm in the radial direction, elemental analysis was performed using an electron beam microanalyzer at 101 analysis positions at 1 μm intervals from the surface position of the line observation area to the 100 μm depth position to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the 101 determined Cu contents was defined as [Cu] Ｓ The arithmetic mean value of the Sn content of the 101 pieces was defined as [Sn] Ｓ and In the circular cross section perpendicular to the axial direction of the wire, in a square observation area including the center of the circular cross section and having a side length of 10 μm, the square observation area is divided into minute squares having a side length of 1 μm. Elemental analysis is performed by the electron beam microanalyzer at 121 analysis positions corresponding to the vertices of each minute square to determine the Cu content and Sn content at each analysis position, and the arithmetic average value of the determined 121 Cu contents is defined as [Cu] Ｂ The arithmetic mean value of the Sn content of the 121 pieces was defined as [Sn] Ｂ When defined as above, equation (1) is satisfied. Wire rod. [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, and one or more 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 ([Cueateres� Ｓ +[S] Ｓ ) / ([Cu] Ｂ +[S] Ｂ )>1.10 (1)

3. The wire according to claim 2, containing the first group, Wire rod.

4. The wire according to claim 2, containing the second group, Wire rod.

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