Wire material and steel wire

Abstract

Provided is a wire material which can achieve excellent wire drawability even if the N content is more than 0.0060 mass% and which can achieve excellent shrinkage and excellent twisting properties in a steel wire produced using said wire material as a raw material. A wire material according to the present disclosure has a chemical composition which contains, in terms of mass%, 0.60-1.20% of C, 0.10-1.50% of Si, 0.10-1.00% of Mn, 0.002-0.050% of P, 0.002-0.050% of S, more than 0.0060% to 0.0120% of N, 0.0020-0.0120% of B and 0.0050% or less of O, with the remainder comprising Fe and impurities, and satisfies formula (1) and formula (2).　Formula (1): 9100N-12200B+9.7≤40.0; Formula (2): 1.265+279N-357B-C≥0.00.

Description

Wire rods and steel wires

[0001] The present disclosure relates to a wire rod and a steel wire. Note that the term "steel wire" in this specification is synonymous with the "hard steel wire" specified in No. 3609 of JIS G 0203 (2009) or the "piano wire" specified in No. 3610.

[0002] Steel wires, such as bead wires, steel cords, bridge wires, and wire ropes, are manufactured by drawing raw wire rods. Therefore, the raw wire rods must have excellent wiredrawability.

[0003] Furthermore, bead wires, steel cords, bridge wires, wire ropes, etc. are manufactured by twisting a plurality of drawn steel wires together. In the twisting process, tension, bending, and twisting are applied to the steel wires. Therefore, excellent drawing and twisting properties are required for steel wires manufactured from wire rods.

[0004] Techniques for improving wire drawing workability, drawing when made into steel wire, or twisting characteristics are proposed in International Publication No. 2018 / 117157 (Patent Document 1), International Publication No. 2016 / 021556 (Patent Document 2), and Japanese Patent Laid-Open No. 2021-161443 (Patent Document 3).

[0005] The wire rod disclosed in Patent Document 1 contains, by mass%, 0.90 to 1.20% C, 0.10 to 1.00% Si, 0.20 to 0.80% Mn, 0.10 to 0.40% Cr, 0 to 0.002% Al, 0 to 0.002% Ti, 0 to 0.0050% N, 0 to 0.020% P, 0 to 0.010% S, 0 to 0.0040% O, 0 to 0.20% Mo, and 0 to 0.0030% B, with the balance being Fe and impurities, and has a metal structure mainly composed of pearlite. Furthermore, the size of TiN and the segregation of Mn and Cr in this wire rod are adjusted to improve wiredrawability.

[0006] The wire rod disclosed in Patent Document 2 contains, by mass%, 0.70% to 1.20% C, 0.10% to 1.2% Si, 0.10% to 1.0% Mn, 0.001% to 0.012% P, 0.001% to 0.010% S, and 0.0010% to 0.0050% N, with the balance being Fe and impurities, and has a pearlite area ratio of 95% to 100%. Furthermore, the pearlite block size of this wire rod is adjusted to improve wiredrawability.

[0007] The wire rod disclosed in Patent Document 3 contains, by mass%, 0.80 to 1.10% C, 0.70 to 2.00% Si, 0.10 to 1.00% Mn, 0.030% or less P, 0.030% or less S, 0.0060% or less N, 0.0060% or less O, 0.0004 to 0.0040% B, 0.005% to 0.070% Al, and 0.004 to 0.025% Ti, with the balance being Fe and impurities. In this wire rod, the Si content and B content are further adjusted, and the Ti content and N content are also adjusted, thereby improving the twisting properties.

[0008] International Publication No. 2018 / 117157 International Publication No. 2016 / 021556 Japanese Patent Application Laid-Open No. 2021-161443

[0009] The wire rods disclosed in Patent Documents 1 to 3 are so-called blast furnace materials intended to be manufactured using a blast furnace, and the N content in the wire rod is 0.0060% or less. ２ Therefore, in order to achieve carbon neutrality, recently, instead of blast furnaces, ２ The production of steel using electric furnaces, which can reduce CO2 emissions, is attracting attention.

[0010] However, when wire rod is produced using an electric furnace, the N content of the wire rod is higher than that of blast furnace steel. Specifically, when wire rod is produced using an electric furnace, the N content is expected to exceed 0.0060% by mass. Therefore, even in such wire rod with a high N content, it is required that excellent wiredrawability be obtained, and that steel wire produced using such wire rod as a raw material be able to have excellent drawing properties and excellent twisting properties.

[0011] An object of the present disclosure is to provide a wire rod that can obtain excellent wiredrawability even when the N content exceeds 0.0060% by mass, and that can obtain excellent drawing and twisting properties in a steel wire manufactured using the wire rod as a raw material, and a steel wire that can obtain excellent wiredrawability in a manufacturing process and excellent drawing and twisting properties even when the N content exceeds 0.0060% by mass.

[0012] The wire rod of the present disclosure has a chemical composition, in mass%, of C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.150%, Cu: 0 to 0.400%, Contains Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance consisting of Fe and impurities, and satisfies the following formulas (1) and (2): 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the element symbols in formulas (1) and (2) are substituted with the content of the corresponding element in mass%.

[0013] The steel wire of the present disclosure has a chemical composition, in mass%, of C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.150%, Cu: 0 to 0.400%, Contains Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance consisting of Fe and impurities, and satisfies the following formulas (1) and (2): 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the element symbols in formulas (1) and (2) are substituted with the content of the corresponding element in mass%.

[0014] The wire rod according to the present disclosure exhibits excellent wiredrawability even when the N content exceeds 0.0060% by mass, and a steel wire manufactured using the wire rod according to the present disclosure as a raw material exhibits excellent drawing and twisting properties. The steel wire according to the present disclosure exhibits excellent wiredrawability in the manufacturing process and excellent drawing and twisting properties even when the N content exceeds 0.0060% by mass.

[0015] FIG. 1 is a graph showing the relationship between Fn2, which is the left side of formula (2), and the wire breakage limit strain, which is an index of the wire drawability of the wire rod.

[0016] The present inventors first investigated, from the standpoint of chemical composition, wire rods that have excellent wiredrawability and provide excellent drawing and twisting properties in steel wires even when the N content exceeds 0.0060% by mass. As a result, they found a wire rod containing, by mass, C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: more than 0.0060 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.010%. The inventors considered that if the steel wire had a chemical composition containing 150%, Cu: 0-0.400%, Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance being Fe and impurities, it would be possible to obtain excellent wiredrawability, and excellent drawing and twisting properties in the form of a steel wire.

[0017] The present inventors further investigated means for improving the wiredrawability of wire rods satisfying the above-mentioned chemical composition, and the drawing and twisting properties of steel wires manufactured using the wire rods as raw materials. When the N content in the wire rod exceeds 0.0060%, the amount of solute N in the wire rod increases. In this case, the excessive amount of solute N causes strain aging during wiredrawing or steel wire twisting. As a result, sufficient wiredrawability and sufficient drawing and twisting properties of the steel wire cannot be obtained.

[0018] Therefore, the present inventors have investigated means for reducing the amount of solute N in wire rods having an N content exceeding 0.0060%. In order to reduce the amount of solute N, it is effective to increase the content of elements that combine with solute N to form nitrides. However, if the nitrides that are formed are coarse, the wiredrawability of the wire rod will actually decrease.

[0019] Here, the inventors focused on B. B easily bonds with N to form B nitrides. Furthermore, B nitrides are fine. Therefore, B nitrides are less likely to become the starting point of cracks during wire drawing. Based on the above findings, the inventors decided to include 0.0020 to 0.0120% of B in the chemical composition of the above-mentioned wire rod in which the N content exceeds 0.0060%, and further studied the appropriate relationship between the N content and the B content. As a result, the following contents were found in mass %: C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: The inventors have discovered that, in a chemical composition consisting of 0 to 0.150%, Cu: 0 to 0.400%, Ni: 0 to 0.300%, Sn: 0 to 0.100%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Sb: 0 to 0.0500%, Bi: 0 to 0.0050%, rare earth elements (REM): 0 to 0.0050%, and the balance being Fe and impurities, if formula (1) is satisfied, excellent wiredrawability, excellent drawing efficiency, and excellent twisting properties of the steel wire can be obtained. 9100N-12200B+9.7≦40.0 (1) Here, the content of the corresponding element in mass % is substituted for each element symbol in formula (1).

[0020] However, even with a wire rod having the above chemical composition and satisfying formula (1), there are still cases where excellent wiredrawability, excellent drawing ability, and excellent twisting properties of the steel wire are not obtained. Therefore, the present inventors conducted further studies. As a result, the present inventors found the following.

[0021] The B in the wire rod having the above chemical composition is the pro-eutectoid cementite and Fe. ２３ (C, B) ６ Therefore, if the B content does not satisfy an appropriate relationship with not only the N content but also the C content, the formation of pro-eutectoid cementite and Fe ２３ (C, B) ６is produced in excess, which deteriorates the wire drawability, drawing and twisting properties of the steel wire.

[0022] Based on the above findings, the present inventors further investigated and examined the relationship between the B content, N content and C content and the wire drawability, and the drawing and twisting properties of the steel wire in the wire rod that satisfies the above-mentioned chemical composition and formula (1). As a result, the present inventors found that in the wire rod that satisfies the above-mentioned chemical composition and formula (1), by further satisfying the following formula (2), pro-eutectoid cementite and Fe ２３ (C, B) ６ The inventors have found that the formation of N is suppressed, resulting in excellent wiredrawability, excellent drawing ability and excellent twisting properties of the steel wire. 1.265+279N-357B-C≧0.00 (2) Here, the content of the corresponding element in mass % is substituted for each element symbol in formula (2).

[0023] Fn2 is defined as follows: Fn2 = 1.265 + 279N - 357B - C Fn2 is the left side of formula (2). Below, the relationship between wiredrawability and Fn2 will be described with reference to the drawings, as a representative example of the effects obtained when a wire rod satisfies formula (2).

[0024] Fig. 1 is a graph showing the relationship between Fn2 and the wire-breakage limit strain, which is an index of wire-drawability of the wire rod. Fig. 1 was created using the results of test numbers satisfying the above-mentioned chemical composition and formula (1) among the examples described later. Note that the results of test numbers in which the wire-breakage limit strain obtained by the test method described later was less than 0.2 were considered to be the wire-breakage limit strain of 0.2 and plotted on the graph in Fig. 1. Referring to Fig. 1, when Fn2 is 0.00 or more, the wire-breakage limit strain is significantly improved, reaching 2.0 or more. In other words, it can be confirmed that excellent wire-drawability can be obtained by further satisfying formula (2) when a wire rod satisfying the above-mentioned chemical composition and formula (1) is further satisfied.

[0025] The wire rod and steel wire of this embodiment have been completed based on the above technical concept, and have the following configuration.

[0026] The wire rod of the first configuration has a chemical composition, in mass %, of C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.150%, Cu: 0 to 0.400%, Contains Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance consisting of Fe and impurities, and satisfies the following formulas (1) and (2): 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the element symbols in formulas (1) and (2) are substituted with the content of the corresponding element in mass%.

[0027] The wire rod of a second configuration is the wire rod of the first configuration, wherein the chemical composition, in mass%, is Al: 0.001 to 0.010%, Cr: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Ti: 0.001 to 0.050%, Zr: 0.001 to 0.050%, Nb: 0.001 to 0.050%, V: 0.001 to 0.150%, Cu: 0.001 to 0.400%, Ni: 0.001 to 0.300%, Sn: 0.001 to 0.100%, Ca: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, Sb: 0.0001 to 0.0500%, It contains one or more elements selected from the group consisting of Bi: 0.0001 to 0.0050%, and rare earth elements (REM): 0.0001 to 0.0050%.

[0028] The steel wire of the first configuration has a chemical composition, in mass %, of C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.150%, Cu: 0 to 0.400%, Contains Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance consisting of Fe and impurities, and satisfies the following formulas (1) and (2): 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the element symbols in formulas (1) and (2) are substituted with the content of the corresponding element in mass%.

[0029] The steel wire of the second configuration is the steel wire of the first configuration, wherein the chemical composition, in mass%, is Al: 0.001 to 0.010%, Cr: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Ti: 0.001 to 0.050%, Zr: 0.001 to 0.050%, Nb: 0.001 to 0.050%, V: 0.001 to 0.150%, Cu: 0.001 to 0.400%, Ni: 0.001 to 0.300%, Sn: 0.001 to 0.100%, Ca: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, Sb: 0.0001 to 0.0500%, It contains one or more elements selected from the group consisting of Bi: 0.0001 to 0.0050%, and rare earth elements (REM): 0.0001 to 0.0050%.

[0030] The wire rod and steel wire of this embodiment will be described in detail below. Note that "%" regarding elements means mass % unless otherwise specified.

[0031] [Features of the wire rod of this embodiment] The wire rod of this embodiment satisfies the following features 1 and 2. (Feature 1) The chemical composition, in mass %, is: C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.0 50%, Zr: 0-0.050%, Nb: 0-0.050%, V: 0-0.150%, Cu: 0-0.400%, Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance consisting of Fe and impurities. (Feature 2) Satisfies formula (1) and formula (2). 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the content of the corresponding element in mass% is substituted for each element symbol in formula (1) and formula (2). Feature 1 and Feature 2 will be described below.

[0032] [(Feature 1) Chemical Composition] The wire rod of this embodiment contains the following elements.

[0033] C: 0.60 to 1.20% Carbon (C) increases the strength of the wire rod. If the C content is less than 0.60%, the above effect cannot be sufficiently achieved 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, excessive pro-eutectoid cementite is formed. In this case, the wire drawability of the wire rod deteriorates. Therefore, the C content is 0.60 to 1.20%. A preferred lower limit of the C content is 0.65%, more preferably 0.70%, and even more preferably 0.75%. A preferred upper limit of the C content is 1.15%, more preferably 1.10%, and even more preferably 1.00%. A preferred range of the C content is, for example, 0.65 to 1.15%, more preferably 0.70 to 1.10%, and even more preferably 0.75 to 1.00%.

[0034] Si: 0.10 to 1.50% Silicon (Si) increases the strength of wire rod. Si is also a useful element as a deoxidizer in the steelmaking process during the wire rod manufacturing process. If the Si content is less than 0.10%, the above-mentioned effect cannot be fully achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Si content exceeds 1.50%, decarburization of the wire rod surface is promoted during the wire rod manufacturing process, even if the contents of other elements are within the ranges of this embodiment. Therefore, the Si content is 0.10 to 1.50%. The preferred lower limit of the Si content is 0.11%, more preferably 0.12%, even more preferably 0.13%, and even more preferably 0.14%. The preferred upper limit of the Si content is 1.00%, more preferably 0.70%, and even more preferably 0.50%. The Si content is preferably in the range of, for example, 0.11 to 1.00%, more preferably 0.12 to 0.70%, even more preferably 0.13 to 0.50%, and still more preferably 0.14 to 0.50%.

[0035] Mn: 0.10 to 1.00% Manganese (Mn) increases the strength of wire rod. Furthermore, Mn fixes S in steel, suppressing hot brittleness of wire rod. If the Mn content is less than 0.10%, the above effects cannot be fully achieved, 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%, the amount of Mn segregation increases, even if the contents of other elements are within the ranges of this embodiment. In this case, the wire drawability of the wire rod deteriorates, impairing the mechanical properties of the drawn wire rod. Therefore, the Mn content is 0.10 to 1.00%. The preferred lower limit of the Mn content is 0.15%, more preferably 0.20%, and even more preferably 0.25%. The preferred upper limit of the Mn content is 0.90%, more preferably 0.85%, even more preferably 0.80%, and even more preferably 0.75%. The preferred range of the Mn content is, for example, 0.15 to 0.90%, more preferably 0.20 to 0.85%, even more preferably 0.25 to 0.80%, and still more preferably 0.25 to 0.75%.

[0036] P: 0.002 to 0.050% Phosphorus (P) is an impurity. If the P content exceeds 0.050%, the ductility of the steel decreases, even if the contents of other elements are within the ranges specified in this embodiment. As a result, the wiredrawability of the wire rod decreases. Furthermore, the drawing and twisting properties of steel wires manufactured using the wire rod as a raw material decrease. The P content is preferably as low as possible. However, excessive reduction in the P content increases manufacturing costs. Therefore, considering normal industrial production, the lower limit of the P content is 0.002%. Therefore, the P content is 0.002 to 0.050%. The preferred lower limit of the P content is 0.003%, more preferably 0.005%, and even more preferably 0.007%. The preferred upper limit of the P content is 0.040%, more preferably 0.025%, even more preferably 0.020%, and even more preferably 0.015%. The P content is preferably in the range of, for example, 0.003 to 0.040%, more preferably 0.005 to 0.025%, even more preferably 0.007 to 0.020%, and still more preferably 0.007 to 0.015%.

[0037] S: 0.002 to 0.050% Sulfur (S) is an impurity. If the S content exceeds 0.050%, even if the contents of other elements are within the ranges specified in this embodiment, excessive coarse MnS will be generated. This will reduce the wire drawability of the wire and impair the mechanical properties of the drawn wire. The S content is preferably as low as possible. However, excessive reduction in the S content increases production costs. Therefore, considering normal industrial production, the lower limit of the S content is 0.002%. Therefore, the S content is 0.002 to 0.050%. The preferred lower limit of the S content is 0.003%, more preferably 0.005%, and even more preferably 0.007%. The preferred upper limit of the S content is 0.040%, more preferably 0.025%, and even more preferably 0.020%. The preferred range of the S content is, for example, 0.003 to 0.040%, more preferably 0.005 to 0.025%, and even more preferably 0.007 to 0.020%.

[0038] N: More than 0.0060% to 0.0120% Nitrogen (N) is contained in large amounts in molten steel, for example, when molten steel is produced using an electric furnace. As a result, the N content in the wire rod may exceed 0.0060%. In the wire rod of this embodiment, even if the N content exceeds 0.0060%, excellent wiredrawing can be achieved as long as Features 1 and 2 are satisfied, and a steel wire produced from the wire rod exhibits excellent drawing and twisting properties. Furthermore, if the N content is 0.0120% or less, excellent wiredrawability and excellent drawing and twisting properties can be achieved in the steel wire, provided that the contents of other elements are within the ranges of this embodiment and Feature 2 is satisfied. Therefore, the N content is more than 0.0060% to 0.0120%. The lower limit of the N content is preferably 0.0061%, more preferably 0.0062%, even more preferably 0.0065%, even more preferably 0.0070%, and even more preferably 0.0075%. The upper limit of the N content is preferably 0.0115%, even more preferably 0.0110%, even more preferably 0.0100%, and even more preferably 0.0090%. The preferred range of the N content is, for example, 0.0061 to 0.0115%, even more preferably 0.0062 to 0.0110%, even more preferably 0.0065 to 0.0100%, even more preferably 0.0070 to 0.0090%, and even more preferably 0.0075 to 0.0090%.

[0039] B: 0.0020 to 0.0120% Boron (B) combines with solute N to form B nitrides, reducing the amount of solute N in the wire rod and steel wire. Therefore, even if the N content exceeds 0.0060%, excellent wiredrawability is obtained. Furthermore, excellent drawing and twisting properties are obtained in the steel wire. If the B content is less than 0.0020%, 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 B content exceeds 0.0120%, the pro-eutectoid cementite and Fe in the wire rod are formed. ２３ (C, B) ６is produced in excess. In this case, even if the contents of other elements are within the ranges of this embodiment, the wire drawability of the wire rod is reduced. Furthermore, the drawing and twisting properties of the steel wire are reduced. Therefore, the B content is 0.0020 to 0.0120%. A preferred lower limit of the B content is 0.0025%, more preferably 0.0030%, even more preferably 0.0035%, even more preferably more than 0.0050%, and even more preferably 0.0051%. A preferred upper limit of the B content is 0.0110%, even more preferably 0.0100%, and even more preferably 0.0095%. A preferred range of the B content is, for example, 0.0025 to 0.0110%, even more preferably 0.0030 to 0.0100%, and even more preferably 0.0035 to 0.0095%.

[0040] O: 0.0050% or less Oxygen (O) is an impurity. That is, the O content is greater than 0%. If the O content exceeds 0.0050%, coarse oxides are generated in the wire rod. Therefore, even if the contents of other elements are within the ranges of this embodiment, the wire drawability of the wire rod is reduced. Therefore, the O content is 0.0050% or less. The O content is preferably as low as possible. However, excessive reduction of the O content increases manufacturing costs. Therefore, considering normal industrial production, the preferred lower limit of the O content is 0.0001%, more preferably 0.0003%. The preferred upper limit of the O content is 0.0045%, more preferably 0.0040%. The preferred range of the O content is 0.0001 to 0.0045%, more preferably 0.0003 to 0.0040%.

[0041] The balance of the chemical composition of the wire rod according to this embodiment is composed of Fe and impurities. Here, the impurities in the chemical composition refer to substances that are mixed in from raw materials such as ore and scrap, or the manufacturing environment, during industrial production of the wire rod, and are acceptable within a range that does not adversely affect the wire rod according to this embodiment.

[0042] [Optional Elements] The chemical composition of the wire rod of this embodiment may further include, in place of a portion of Fe, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.150%, Cu: 0 to 0.400%, Ni: 0 to 0.300%, Sn: 0 to 0.100%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Sb: 0 to 0.0500%, Bi: 0 to 0.0050%, and rare earth elements (REM): 0 to 0.0050%. These elements are optional and may not be contained. These optional elements will be described below.

[0043] [First Group: Al] The chemical composition of the wire rod of this embodiment may further contain Al instead of a part of Fe. In the wire rod of this embodiment, Al is an impurity.

[0044] Al: 0 to 0.010% Aluminum (Al) is an optional element and does not necessarily need to be contained. That is, the Al content may be 0%. If Al is contained, that is, if the Al content exceeds 0%, Al forms hard alumina-based inclusions, reducing the wire drawability of the wire. If the Al content exceeds 0.010%, the wire drawability of the wire will be significantly reduced even if the contents of other elements are within the ranges of this embodiment. Therefore, the Al content is 0 to 0.010%. As mentioned above, since Al is an impurity, it is preferable to keep the Al content as low as possible. However, excessive reduction of the Al content increases manufacturing costs. Therefore, considering normal industrial production, the preferred lower limit of the Al content is 0.001%, more preferably 0.002%, even more preferably 0.003%, and even more preferably 0.005%. The preferred upper limit of the Al content is 0.009%, even more preferably 0.007%, and even more preferably 0.005%. The Al content is preferably in the range of 0.001 to 0.009%, more preferably 0.002 to 0.007%, and even more preferably 0.003 to 0.005%, for example.

[0045] [Second Group: Cr and Mo] The chemical composition of the wire rod of the present embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Cr and Mo. Any of these elements refines the lamellar spacing of the pearlite structure of the wire rod, thereby increasing the strength of the wire rod.

[0046] Cr: 0 to 0.50% Chromium (Cr) is an optional element and does not necessarily need to be contained. In other words, the Cr content may be 0%. When Cr is contained, that is, when the Cr content exceeds 0%, Cr refines the lamellar spacing of the pearlite structure, thereby increasing the strength of the wire rod. Even if even a small amount of Cr is contained, the above effect can be obtained to some extent. However, if the Cr content exceeds 0.50%, the amount of segregation within the wire rod increases even if the contents of other elements are within the ranges of this embodiment. In this case, the wire drawability of the wire rod decreases, and the mechanical properties of the drawn wire rod are impaired. Therefore, the Cr content is 0 to 0.50%. The preferred lower limit of the Cr content is 0.01%, more preferably 0.05%, and even more preferably 0.08%. The preferred upper limit of the Cr content is 0.45%, more preferably 0.40%, and even more preferably 0.35%. The Cr content is preferably in the range of 0.01 to 0.45%, more preferably 0.05 to 0.40%, and even more preferably 0.08 to 0.35%.

[0047] Mo: 0 to 0.20% Molybdenum (Mo) is an optional element and does not necessarily need to be contained. That is, the Mo content may be 0%. When contained, that is, when the Mo content exceeds 0%, Mo refines the lamellar spacing of the pearlite structure and increases the strength of the wire rod. Even if even a small amount of Mo is contained, the above effect can be obtained to some extent. However, if the Mo content exceeds 0.20%, the amount of segregation within the wire rod increases even if the contents of other elements are within the ranges of this embodiment. In this case, the wire drawability of the wire rod decreases, and the mechanical properties of the drawn wire rod are impaired. Therefore, the Mo content is 0 to 0.20%. The preferred lower limit of the Mo content is 0.01%, more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Mo content is 0.18%, more preferably 0.16%, and even more preferably 0.14%. The preferred range of the Mo content is, for example, 0.01 to 0.18%, more preferably 0.03 to 0.16%, and even more preferably 0.05 to 0.14%.

[0048] [Third Group: Ti, Zr, Nb, and V] The chemical composition of the wire rod of this embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Ti, Zr, Nb, and V. Any of these elements forms precipitates and refines crystal grains through a pinning effect, thereby increasing the reduction of area of ​​the wire rod.

[0049] Ti: 0 to 0.050% Titanium (Ti) is an optional element and does not necessarily need to be contained. That is, the Ti content may be 0%. When titanium is contained, that is, when the Ti content exceeds 0%, Ti forms precipitates and refines the crystal grains through a pinning effect. This increases the reduction of area of ​​the wire rod. Even if even a small amount of Ti is contained, the above effect can be achieved to some extent. However, if the Ti content exceeds 0.050%, coarse and hard TiN inclusions are formed. Therefore, even if the contents of other elements are within the ranges of this embodiment, the wire drawability of the wire rod decreases. Therefore, the Ti content is 0 to 0.050%. The preferred lower limit of the Ti content is 0.001%, more preferably 0.003%, and even more preferably 0.005%. The preferred upper limit of the Ti content is 0.045%, more preferably 0.040%, and even more preferably 0.035%. The preferred range of the Ti content is 0.001 to 0.045%, more preferably 0.003 to 0.040%, and even more preferably 0.005 to 0.035%.

[0050] Zr: 0 to 0.050% Zirconium (Zr) is an optional element and does not necessarily need to be contained. That is, the Zr content may be 0%. When Zr is contained, that is, when the Zr content exceeds 0%, Zr forms precipitates and refines the crystal grains through a pinning effect. This increases the reduction of area of ​​the wire rod. Even if even a small amount of Zr is contained, the above effect can be achieved to some extent. However, if the Zr content exceeds 0.050%, coarse and hard ZrN inclusions are formed. Therefore, even if the contents of other elements are within the ranges of this embodiment, the wire drawability of the wire rod decreases. Therefore, the Zr content is 0 to 0.050%. The preferred lower limit of the Zr content is 0.001%, more preferably 0.003%, and even more preferably 0.005%. The preferred upper limit of the Zr content is 0.045%, more preferably 0.040%, and even more preferably 0.035%. The Zr content is preferably in the range of 0.001 to 0.045%, more preferably 0.003 to 0.040%, and even more preferably 0.005 to 0.035%.

[0051] Nb: 0 to 0.050% Niobium (Nb) is an optional element and does not necessarily need to be contained. That is, the Nb content may be 0%. When Nb is contained, that is, when the Nb content exceeds 0%, Nb forms precipitates and refines the crystal grains through a pinning effect. This increases the reduction of area of ​​the wire rod. Even if even a small amount of Nb is contained, the above effect can be achieved to some extent. However, if the Nb content exceeds 0.050%, the plastic deformability of the steel wire is impaired and the twisting properties of the steel wire are reduced, even if the contents of other elements are within the ranges of this embodiment. Therefore, the Nb content is 0 to 0.050%. The preferred lower limit of the Nb content is 0.001%, more preferably 0.003%, and even more preferably 0.005%. The preferred upper limit of the Nb content is 0.040%, more preferably 0.030%, and even more preferably 0.020%. The Nb content is preferably in the range of 0.001 to 0.040%, more preferably 0.003 to 0.030%, and even more preferably 0.005 to 0.020%.

[0052] V: 0 to 0.150% Vanadium (V) is an optional element and does not necessarily need to be contained. In other words, the V content may be 0%. When vanadium (V) is contained, that is, when the V content exceeds 0%, V forms precipitates and refines the crystal grains through a pinning effect. This increases the reduction of area of ​​the wire rod. Even if even a small amount of V is contained, the above effect can be achieved to some extent. However, if the V content exceeds 0.150%, the plastic deformability of the steel wire is impaired and the twisting properties of the steel wire are reduced, even if the contents of other elements are within the ranges of this embodiment. Therefore, the V content is 0 to 0.150%. The preferred lower limit of the V content is 0.001%, more preferably 0.010%, and even more preferably 0.020%. The preferred upper limit of the V content is 0.100%, more preferably 0.080%, and even more preferably 0.060%. The V content is preferably in the range of 0.001 to 0.100%, more preferably 0.010 to 0.080%, and even more preferably 0.020 to 0.060%.

[0053] [Fourth Group: Cu, Ni, and Sn] The chemical composition of the wire rod of this embodiment may further contain one or more elements selected from the group consisting of Cu, Ni, and Sn, instead of a portion of Fe. All of these elements can be contained in scrap, which is the raw material when producing the wire rod in an electric furnace. In other words, these elements are so-called tramp elements.

[0054] Cu: 0 to 0.400% Copper (Cu) is an optional element and does not necessarily need to be contained. In other words, the Cu content may be 0%. If copper is contained, that is, if the Cu content exceeds 0%, the hot workability of the steel material from which the wire rod is made will be reduced if the Cu content exceeds 0.400%. In this case, even if the contents of other elements are within the ranges of this embodiment, it will be difficult to manufacture the wire rod. Therefore, the Cu content is 0 to 0.400%. A preferred lower limit of the Cu content is 0.010%, more preferably 0.050%, and even more preferably 0.100%. A preferred upper limit of the Cu content is 0.350%, more preferably 0.300%, and even more preferably 0.250%. A preferred range of the Cu content is, for example, 0.010 to 0.350%, more preferably 0.050 to 0.300%, and even more preferably 0.100 to 0.250%.

[0055] Ni: 0 to 0.300% Nickel (Ni) is an optional element and does not necessarily need to be contained. That is, the Ni content may be 0%. When contained, that is, when the Ni content exceeds 0%, Ni suppresses the deterioration of hot workability caused by Cu. When wire rod is produced using scrap as a raw material in an electric furnace, the inclusion of Ni suppresses the deterioration of hot workability caused by Cu contained in the scrap. Even if even a small amount of Ni is contained, the above effect can be obtained to some extent. However, if the Ni content exceeds 0.300%, the above effect saturates and further, the manufacturing cost (cost due to alloy addition) increases. Therefore, the Ni content is 0 to 0.300%. The preferred lower limit of the Ni content is 0.001%, more preferably 0.005%, and even more preferably 0.010%. The preferred upper limit of the Ni content is 0.250%, more preferably 0.200%, and even more preferably 0.150%. The Ni content is preferably in the range of 0.001 to 0.250%, more preferably 0.005 to 0.200%, and even more preferably 0.010 to 0.150%.

[0056] Sn: 0 to 0.100% Tin (Sn) is an optional element and does not necessarily need to be contained. In other words, the Sn content may be 0%. When tin is contained, that is, when the Sn content exceeds 0%, if the Sn content exceeds 0.100%, the ductility of the steel decreases. In this case, even if the contents of other elements are within the ranges of this embodiment, the wiredrawability of the wire rod decreases. Furthermore, the drawing and twisting properties of the steel wire decrease. Therefore, the Sn content is 0 to 0.100%. A preferred lower limit of the Sn content is 0.001%, more preferably 0.005%, and even more preferably 0.010%. A preferred upper limit of the Sn content is 0.090%, more preferably 0.080%, and even more preferably 0.070%. The preferred range of the Sn content is, for example, 0.001 to 0.090%, more preferably 0.005 to 0.080%, and even more preferably 0.010 to 0.070%.

[0057] [Fifth Group: Ca, Mg, Sb, Bi, and Rare Earth Elements (REM)] The chemical composition of the wire rod of this embodiment may further contain one or more elements selected from the group consisting of Ca, Mg, Sb, Bi, and rare earth elements (REM) in place of a portion of Fe. All of these elements improve the wire drawability of the wire rod.

[0058] Ca: 0 to 0.0050% 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 exceeds 0%, Ca reduces hard alumina-based inclusions and improves the wire drawability of the wire rod. Even if even a small amount of Ca is contained, the above effect can be obtained to some extent. However, if the Ca content exceeds 0.0050%, excessive coarse oxides are formed. In this case, even if the contents of other elements are within the ranges of this embodiment, the wire drawability of the wire rod will be reduced. Therefore, the Ca content is 0 to 0.0050%. The preferred lower limit of the Ca content is 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The preferred upper limit of the Ca content is 0.0040%, more preferably 0.0035%, and even more preferably 0.0030%. The Ca content is preferably in the range of, for example, 0.0001 to 0.0040%, more preferably 0.0005 to 0.0035%, and even more preferably 0.0010 to 0.0030%.

[0059] Mg: 0 to 0.0050% 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 exceeds 0%, Mg forms fine oxides. The fine oxides refine the structure of the wire rod and improve the wire drawability of the wire rod. Even if even a small amount of Mg is contained, the above effect can be obtained to some extent. However, if the Mg content exceeds 0.0050%, excessive coarse oxides are formed even if the contents of other elements are within the ranges of this embodiment. In this case, the wire drawability of the wire rod is reduced. Therefore, the Mg content is 0 to 0.0050%. The preferred lower limit of the Mg content is 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The preferred upper limit of the Mg content is 0.0040%, more preferably 0.0035%, and even more preferably 0.0030%. The Mg content is preferably in the range of 0.0001 to 0.0040%, more preferably 0.0005 to 0.0035%, and even more preferably 0.0010 to 0.0030%.

[0060] Sb: 0 to 0.0500% Antimony (Sb) is an optional element and does not necessarily need to be contained. That is, the Sb content may be 0%. When contained, that is, when the Sb content exceeds 0%, Sb enhances the lubricity of the wire during wire drawing and improves the wire drawability of the wire. Even if even a small amount of Sb is contained, the above effects can be obtained to some extent. However, if the Sb content exceeds 0.0500%, embrittlement of the steel will be promoted even if the contents of other elements are within the ranges of this embodiment. Therefore, the Sb content is 0 to 0.0500%. The preferred lower limit of the Sb content is 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The preferred upper limit of the Sb content is 0.0400%, more preferably 0.0300%, and even more preferably 0.0150%. The Sb content is preferably in the range of 0.0001 to 0.0400%, more preferably 0.0005 to 0.0300%, and even more preferably 0.0010 to 0.0150%.

[0061] Bi: 0 to 0.0050% Bismuth (Bi) is an optional element and does not necessarily need to be contained. That is, the Bi content may be 0%. When Bi is contained, that is, when the Bi content exceeds 0%, Bi refines the dendritic structure during solidification of the steel. As a result, the center segregation region is refined, improving the wire drawability of the wire rod. Even if even a small amount of Bi is contained, the above effect can be achieved to some extent. However, if the Bi content exceeds 0.0050%, the effect of refining the dendritic structure saturates even if the contents of other elements are within the ranges of this embodiment. As a result, the hot workability of the steel deteriorates. Therefore, the Bi content is 0 to 0.0050%. The preferred lower limit of the Bi content is 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The preferred upper limit of the Bi content is 0.0040%, more preferably 0.0035%, and even more preferably 0.0030%. The Bi content is preferably in the range of 0.0001 to 0.0040%, more preferably 0.0005 to 0.0035%, and even more preferably 0.0010 to 0.0030%.

[0062] Rare earth elements (REM): 0 to 0.0050% Rare earth elements (REM) are optional elements and do not necessarily need to be contained. That is, the REM content may be 0%. When contained, that is, when the REM content is greater than 0%, REM fixes S. Therefore, the wire drawability of the wire is improved. Even if even a small amount of REM is contained, the above effect can be achieved to some extent. On the other hand, if the REM content exceeds 0.0050%, excessive oxides are formed. In this case, even if the contents of other elements are within the ranges of this embodiment, the wire drawability of the wire is reduced. Therefore, the REM content is 0 to 0.0050%. The preferred lower limit of the REM content is 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The preferred upper limit of the REM content is 0.0040%, more preferably 0.0035%, and even more preferably 0.0030%. The REM content is preferably in the range of 0.0001 to 0.0040%, more preferably 0.0005 to 0.0035%, and even more preferably 0.0010 to 0.0030%.

[0063] [(Feature 2) Formula (1) and Formula (2)] The wire rod of this embodiment further satisfies formulas (1) and (2). 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the element symbols in formulas (1) and (2) are substituted with the content of the corresponding element in mass%. Formulas (1) and (2) will be explained below.

[0064] [Formula (1)] Fn1 is defined as follows: Fn1=9100N-12200B+9.7

[0065] Fn1 is an index showing the degree of reduction in the amount of dissolved N due to B in a wire rod having a chemical composition that satisfies Feature 1, that is, an N content of more than 0.0060%.

[0066] If Fn1 exceeds 40.0, the B content is too low relative to the amount of solute N. In this case, the amount of solute N consumed by B nitrides is small. Therefore, excessive solute N remains in the wire rod. As a result, the wire drawability of the wire rod deteriorates. Furthermore, the twisting properties of the steel wire deteriorate.

[0067] If Fn1 is 40.0 or less, a sufficient amount of B is present relative to the amount of solute N. Therefore, the amount of solute N in the wire rod is sufficiently reduced by the formation of B nitrides. As a result, provided that Feature 1 is satisfied and formula (2) is satisfied, excellent wiredrawability can be obtained in the wire rod, and excellent twisting properties can be obtained in the steel wire.

[0068] The upper limit of Fn1 is preferably 39.5, more preferably 39.0, even more preferably 38.5, even more preferably 37.0, and even more preferably 36.0. The lower limit of Fn1 is not particularly limited. When the chemical composition of the wire satisfies Feature 1, the lower limit of Fn1 is, for example, −82.1.

[0069] [Formula (2)] As described above, Fn2 is defined as follows: Fn2 = 1.265 + 279N - 357B - C

[0070] Fn2 is a wire rod having a chemical composition that satisfies Feature 1 (i.e., an N content of more than 0.0060 to 0.0120%), in which pro-eutectoid cementite and Fe ２３ (C, B) ６ It is an index showing the amount of production.

[0071] B is proeutectoid cementite and Fe ２３ (C, B) ６ Promotes the formation of proeutectoid cementite and Fe ２３ (C, B) ６ The proeutectoid cementite and Fe in the wire rod tend to become coarse precipitates. ２３ (C, B) ６ If excessive amounts of are produced, the wire drawing workability of the wire rod is reduced, and further, the drawing and twisting properties of the steel wire made from the wire rod are reduced.

[0072] If Fn2 is 0.00 or more, pro-eutectoid cementite and Fe due to the inclusion of B are ２３ (C, B) ６ Therefore, excellent wire drawing workability can be obtained in the wire rod, and excellent drawing and twisting properties can be obtained in the steel wire.

[0073] The lower limit of Fn2 is preferably 0.10, more preferably 0.20, even more preferably 0.30, even more preferably 0.40, and even more preferably 0.50. The upper limit of Fn2 is not particularly limited. When the chemical composition of the wire satisfies Feature 1, the upper limit of Fn2 is, for example, 2.50.

[0074] [Preferred embodiment] Preferably, the wire rod of this embodiment satisfies Features 1 and 2, and further satisfies Feature 3. (Feature 3) The chemical composition satisfies formula (3): 1.079+395N-513B-C≧0.00 (3) Here, each element symbol in formula (3) is substituted with the content of the corresponding element in mass%.

[0075] Fn3 is defined as follows: Fn3 = 1.079 + 395N - 513B - C

[0076] Fn3 is a formula that further restricts Fn2. If the characteristics 1 and 2 are satisfied and Fn3 is 0.00 or more, the pro-eutectoid cementite and Fe due to the inclusion of B can be obtained. ２３ (C, B) ６ As a result, the steel wire can have even better twisting properties.

[0077] The lower limit of Fn3 is preferably 0.10, more preferably 0.20, and even more preferably 0.30. The upper limit of Fn3 is not particularly limited. When the chemical composition of the wire satisfies Features 1 and 2, the upper limit of Fn3 is, for example, 1.82.

[0078] [Effects of the Wire Rod of the Present Embodiment] The wire rod of the present embodiment satisfies Features 1 and 2. Therefore, the wire rod of the present embodiment can obtain excellent wiredrawability even when the N content is more than 0.0060% to 0.0120%. Furthermore, a steel wire produced using the wire rod as a raw material can obtain excellent drawing properties and excellent twisting properties.

[0079] Preferably, the wire rod of the present embodiment further satisfies Features 1 to 3. In this case, excellent wiredrawability in the wire rod and excellent drawing property in the steel wire are obtained, and further excellent twisting properties are obtained.

[0080] [Uses of the Wire Rod of the Present Embodiment] The wire rod of the present embodiment is widely applicable, for example, as a material for steel wires produced by wire drawing, particularly as a material for steel wires that require excellent drawing or twisting properties. The wire rod of the present embodiment is particularly suitable as a material for bead wires, steel cords, bridge wires, wire ropes, etc.

[0081] [Microstructure of Wire Rod of Present Embodiment] The microstructure of the wire rod of this embodiment is substantially composed of a pearlite structure. Here, "substantially composed of a pearlite structure" means that the pearlite area ratio is 90% or more. The remainder of the microstructure of the wire rod excluding the pearlite structure is, for example, one or more types selected from the group consisting of ferrite, pro-eutectoid cementite, pearlite, bainite, and martensite.

[0082] [Method for Observing Microstructure of Wire Rod] Observation of the microstructure of the wire rod of this embodiment and measurement of the area ratio of pearlite are carried out by the following method.

[0083] A test piece is taken from the wire. A cross section of the surface of the test piece perpendicular to the axial direction of the wire is used as the observation surface. The observation surface is mirror-polished. The mirror-polished observation surface is etched with picral to reveal the structure. Four fields of view, D / 4 in length, of the etched observation surface are observed at 1000x magnification using an optical microscope or a scanning electron microscope. Here, D / 4 refers to the central part of the radius (i.e., the part located at a depth of D / 4 in the radial direction from the surface of the wire), where D is the diameter passing through the center of the circular observation surface. A photographic image of each field of view is generated. The size of each field of view is, for example, 70 μm x 110 μm.

[0084] Pearlite was identified based on the contrast of the photographic image in each field. The total area (μm) of pearlite identified in the four fields was calculated. ２ The pearlite area ratio (%) is calculated based on the total area of ​​the four fields of view and the total area of ​​pearlite.

[0085] It is known that the microstructure of wire rods for bead wire, steel cord, bridge wire, wire rope, etc. is substantially a pearlite structure.

[0086] [Shape of the Wire of the Present Embodiment] The cross section of the wire of the present embodiment perpendicular to the axial direction is circular. The diameter of the cross section of the wire is, for example, 3.5 to 7.0 mm. The wire may be wound in a coil shape or cut to a predetermined length.

[0087] [Tensile Strength of Wire Rod of This Embodiment] The tensile strength of the wire rod of this embodiment is not particularly limited, but is, for example, 850 to 1600 MPa. Considering the tensile strength obtained in a steel wire manufactured using the wire rod as a raw material, a preferable lower limit of the tensile strength of the wire rod is 900 MPa. On the other hand, considering the wiredrawability of the wire rod, a preferable upper limit of the tensile strength of the wire rod is 1550 MPa. The tensile strength of the wire rod is determined by a tensile test in air at room temperature (20±15°C) in accordance with JIS Z 2241:2022.

[0088] [Method for manufacturing wire rod according to this embodiment] A method for manufacturing wire rod according to this embodiment will be described below. The method for manufacturing wire rod described below is one example for manufacturing wire rod according to this embodiment. Therefore, 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 wire rod according to this embodiment.

[0089] An example of the method for manufacturing wire rod according to this embodiment includes the following steps: (Step 1) Material preparation step (Step 2) Blooming rolling step (Step 3) Finish rolling step Each step will be described below.

[0090] [(Step 1) Material Preparation Step] 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 Features 1 and 2 is produced. The wire rod of this embodiment has excellent wiredrawability even when the N content exceeds 0.0060%, and the steel wire has excellent drawing properties and excellent twisting properties. Therefore, the molten steel may be produced using an electric furnace instead of a blast furnace. The refining method for the molten steel is not particularly limited, and any well-known method may be used. Through the above steps, molten steel having a chemical composition that satisfies Features 1 is produced.

[0091] 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.

[0092] [(Step 2) Blooming Step] In the blooming step, the material (ingot or bloom) prepared in the material preparation step is bloomed to produce a billet. In the blooming step, the material is first heated in a heating furnace by a well-known method. The heating temperature is not particularly limited. Any well-known temperature will suffice. The heating temperature is, for example, 1200 to 1300°C.

[0093] The heated material is hot rolled (rough rolled) using a blooming mill, or a blooming mill and a continuous rolling mill, to produce billets. Specifically, the heated material is reverse rolled using the 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.

[0094] [(Step 3) Finish Rolling Step] In the finish rolling step, the billet produced in the blooming step is finish rolled to produce wire rod. In the finish rolling step, the billet produced in the blooming step is first heated using a heating furnace. The heating temperature is, for example, 1000 to 1150°C. The heated billet is then finish rolled (continuous rolling) using a continuous rolling mill to produce wire rod. The finish rolling temperature (temperature at the end of finish rolling) is, for example, 800 to 1000°C.

[0095] The wire rod after finish rolling is cooled. At this time, the cooling rate is appropriately adjusted so that the microstructure of the wire rod becomes substantially pearlite. Adjustment of the cooling rate is a well-known technical matter. Preferably, the cooling rate is set to 5 to 15°C / sec when the surface temperature of the wire rod is 800 to 600°C. In this case, a wire rod whose microstructure is substantially pearlite can be stably produced.

[0096] The wire rod of this embodiment is manufactured by the above manufacturing process.

[0097] [Features of the Steel Wire of the Present Embodiment] The steel wire of the present embodiment is manufactured by wiredrawing the wire rod of the present embodiment that satisfies Features 1 and 2. Therefore, the steel wire of the present embodiment satisfies the following Features 4 and 5. (Feature 4) The chemical composition, in mass%, is C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, and Ti: 0 to 0.0 50%, Zr: 0-0.050%, Nb: 0-0.050%, V: 0-0.150%, Cu: 0-0.400%, Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance consisting of Fe and impurities. (Feature 5) Satisfies formula (1) and formula (2). 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the content of the corresponding element in mass % is substituted for each element symbol in formulas (1) and (2).

[0098] The function of each element in Feature 4 is the same as the function of the corresponding element in Feature 1 of the wire rod of this embodiment. In addition, the technical significance of Feature 5 is the same as that of Feature 2 of the wire rod of this embodiment. Therefore, in the steel wire of this embodiment, even if the N content is more than 0.0060% to 0.0120%, excellent wiredrawability can be obtained in the manufacturing process, and excellent drawing and twisting properties can be obtained.

[0099] Preferably, the steel wire of the present embodiment satisfies Features 4 and 5, and further satisfies Feature 6. (Feature 6) The chemical composition satisfies formula (3): 1.079+395N-513B-C≧0.00 (3) Here, each element symbol in formula (3) is substituted with the content of the corresponding element in mass%.

[0100] The technical significance of Feature 6 is the same as that of Feature 3 of the wire rod of the present embodiment. Therefore, in a steel wire satisfying Feature 6, even if the N content is more than 0.0060% to 0.0120%, even better torsional properties can be obtained.

[0101] [Uses and Shapes of the Steel Wire of the Present Embodiment] The steel wire of the present embodiment is, for example, a bead wire, a steel cord, a bridge wire, a wire rope, etc. The cross section perpendicular to the axial direction of the steel wire of the present embodiment is circular. The diameter of the cross section of the steel wire is, for example, 0.05 to 3.00 mm. The steel wire of the present embodiment may be wound in a coil shape, or multiple wires may be twisted together. The steel wire may further have a plating layer formed on its surface. The plating layer is, for example, a brass plating layer or a bronze plating layer.

[0102] [Tensile Strength of Steel Wire of Present Embodiment] As described above, the steel wire of this embodiment is manufactured by wiredrawing the wire rod of this embodiment as a raw material. Due to the strengthening effect of wiredrawing, the tensile strength of the steel wire is improved compared to the wire rod used as the raw material. Therefore, the tensile strength of the steel wire of this embodiment is greater than the tensile strength of the wire rod of this embodiment. The tensile strength of the steel wire of this embodiment is, for example, greater than 1600 to 5000 MPa. When the steel wire is used as a bead wire, the tensile strength of the steel wire is preferably greater than 1600 to 3500 MPa. A more preferred lower limit of the tensile strength of the steel wire suitable for a bead wire is 2000 MPa. A more preferred upper limit of the tensile strength of the steel wire suitable for a bead wire is 3050 MPa. When the steel wire is used as a steel cord, the tensile strength of the steel wire is preferably 2000 to 5000 MPa. A more preferred lower limit of the tensile strength of the steel wire suitable for a steel cord is 2900 MPa. A more preferable upper limit of the tensile strength of a steel wire suitable for a steel cord is 4500 MPa. The tensile strength of the steel wire is determined by a tensile test in accordance with JIS Z 2241:2022 at room temperature (20±15°C) in the atmosphere.

[0103] [Method for manufacturing steel wire according to this embodiment] The steel wire according to this embodiment is manufactured by a well-known method using the wire rod according to this embodiment as a raw material. The method for manufacturing the steel wire according to this embodiment is, for example, as follows: Oxide scale is removed from the wire rod, and a lubrication treatment is carried out. The lubricated wire rod is subjected to dry wiredrawing to manufacture a steel wire. When it is necessary to draw the steel wire to an even finer wire diameter, as in the case of a steel cord, a well-known patenting treatment is further carried out on the steel wire after dry wiredrawing, and a well-known plating treatment is carried out. The heating temperature in the patenting treatment is, for example, 850 to 1000°C. Then, a wet wiredrawing is carried out. The steel wire according to this embodiment is manufactured by the above manufacturing steps.

[0104] The effects of the wire rod and steel wire of the present embodiment will be described more specifically with reference to examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the wire rod and steel wire of the present embodiment. Therefore, the wire rod and steel wire of the present embodiment are not limited to this one example of conditions.

[0105] Wires having the chemical compositions shown in Tables 1A and 1B were produced.

[0106]

[0107]

[0108] Specifically, a bloom was produced by continuous casting using the prepared molten steel. The produced bloom was subjected to a blooming process to produce a billet. In the blooming process, the bloom was heated to 1200 to 1300°C using a heating furnace. The heated bloom was hot rolled using a blooming mill and a continuous rolling mill to produce a billet. The billet produced in the blooming process was allowed to cool to room temperature.

[0109] The manufactured billets were subjected to a finish rolling process. Specifically, the billets of each test number were heated to 1000 to 1150°C. The heated billets were subjected to finish rolling (continuous rolling) using a continuous rolling mill. The finish rolling temperature in the finish rolling was 850 to 1000°C. In the cooling process after the finish rolling, the cooling rate in the temperature range of 800 to 600°C for the surface temperature of the wire rod was 5 to 15°C / sec. Through the above manufacturing process, a wire rod having a wire diameter of 5.5 mm was manufactured.

[0110] The microstructure of the wire rod of each test number was observed in accordance with the above-mentioned [Method for Observing Microstructure of Wire Rod]. As a result, in the wire rod of each test number, the microstructure was substantially composed of pearlite structure, and the pearlite area ratio was 90% or more.

[0111] [Evaluation Tests] The following evaluation tests were carried out on the wire rods with each test number: (Test 1) Wiredrawability evaluation test (Test 2) Tensile test of wire rods (Test 3) Tensile test of steel wires (Test 4) Measurement test of twisting properties Each test method will be explained below.

[0112] [(Test 1) Wiredrawability Evaluation Test] The wiredrawability of the wire of each test number was evaluated by the following method. The wire of each test number was pickled under the same conditions to remove oxide scale, and then lubricated under the same conditions. Furthermore, the wire after the lubrication treatment was subjected to dry wiredrawing. The wiredrawing speed was 400 m / min, and wiredrawing was repeated until the drawn wire broke. The true strain per pass of the wiredrawing was about 0.3, and the die angle was a half angle of 7°. Each time one pass of wiredrawing was completed, the wire diameter of the wire was measured. The wire diameter before the wiredrawing was defined as d0 (= 5.5 mm), and the wire diameter after the wiredrawing in the pass immediately before the pass that caused the breakage was defined as d1 (mm), and the strain amount ε was calculated using the following formula: Strain amount ε = 2 × ln (d0 / d1)

[0113] The above test was carried out twice for the wire of each test number. The arithmetic mean value of the two strain amounts ε obtained from the two tests was taken as the wire breakage limit strain. The wire breakage limit strain of the wire of each test number obtained is shown in the "wire breakage limit strain" column in Table 2. If the wire breakage limit strain of the wire was 2.0 or more, it was determined that the wire drawability of the wire was sufficiently high.

[0114]

[0115] [(Test 2) Tensile Test of Wire] Using the wire of each test number, a tensile test was conducted in air at room temperature (20±15°C) in accordance with JIS Z 2241:2022 to obtain the tensile strength TS (MPa) of the wire. The length of the tensile test specimen was 350 mm, and the wire was cut at a cross section perpendicular to the axial direction. The tensile test was conducted three times using three tensile test specimens. The chuck distance in the tensile test was 200 mm, and the tensile speed was 10 mm / min. The arithmetic mean value of the obtained tensile strengths was defined as the tensile strength TS (MPa) of the wire. The tensile strengths TS (MPa) of the obtained wire are shown in the "Tensile strength TS (MPa)" column in Table 2.

[0116] [Production of Steel Wire B and Steel Wire S] Steel wire B intended for bead wire and steel wire S intended for steel cord were produced using the wire rods of each test number. The wire diameter of steel wire B was 1.2 mm. The wire diameter of steel wire S was 0.225 mm. Steel wire B and steel wire S were each produced from the wire rods of each test number.

[0117] Steel wire B and steel wire S were manufactured by the following method. The oxide scale of the wire material was removed under the same conditions for each test number, and a lubrication treatment was performed under the same conditions for each test number. The lubrication-treated wire material was subjected to dry wire drawing to manufacture steel wire B with a wire diameter of 1.2 mm. Steel wire B was then heated at 950°C for 5 minutes. Thereafter, a patenting treatment was performed by immersing it in a lead bath at 560°C for 2.5 minutes. Furthermore, the patented steel wire was brass-plated under the same conditions. The brass-plated steel wire was subjected to wet wire drawing to manufacture steel wire S with a wire diameter of 0.225 mm.

[0118] [(Test 3) Tensile Test of Steel Wire] Using the steel wires (Steel Wire B and Steel Wire S) of each test number, a tensile test was conducted in air at room temperature (20±15°C) in accordance with JIS Z 2241:2022 to obtain the tensile strength TS (MPa) and reduction of area RA (%) of the steel wires. The length of the tensile test specimen was 350 mm, and the steel wire was cut at a cross section perpendicular to the axial direction. The tensile test was conducted three times using three tensile test specimens. The chuck distance in the tensile test was 200 mm, and the pulling speed was 10 mm / min. The arithmetic mean value of the obtained tensile strengths was defined as the tensile strength TS (MPa) of Steel Wire B and Steel Wire S, and the arithmetic mean value of the obtained reduction of area was defined as the reduction of area RA (%) of Steel Wire B and Steel Wire S. The obtained tensile strengths TS (MPa) of Steel Wire B and Steel Wire S and the reduction of area RA (%) of Steel Wire B and Steel Wire S are shown in Table 2. In Table 2, "-" in the "Tensile strength TS (MPa)" or "Area of ​​reduction RA (%)" column means that the wire drawability of the wire rod was low, and therefore Steel Wire B and Steel Wire S could not be manufactured.

[0119] [(Test 4) Measurement of torsional properties] The torsional properties of the steel wires of each test number were evaluated by the following method. A predetermined length of steel wire was cut from each steel wire (steel wire B, steel wire S) of each test number to prepare a test specimen for the torsional test. Of the test specimens, for both steel wire B and steel wire S, the gripping distance of the test specimen was set to 100 times the diameter. The torsional test was carried out by applying a load of 1 to 2% of the tensile strength TS of the steel wire of each test number. The torsional speed was 10 rpm. Five test specimens were prepared for each of steel wire B and steel wire S of each test number, and the torsional test was carried out for each test specimen.

[0120] The number of twists (times) until final breakage was determined. The arithmetic mean value of the number of twists of the five test specimens was taken as the twisting property (times). The obtained twisting properties are shown in the "Twisting property (times)" column of "Steel wire B" and the "Twisting property (times)" column of "Steel wire S" in Table 2. Note that "-" in the "Twisting property (times)" column means that Steel wire B and Steel wire S could not be produced due to poor wiredrawability of the wire rod.

[0121] [Test Results] With reference to Tables 1A, 1B, and 2, in test numbers 1 to 32, the wire rods satisfied Features 1 and 2, and Steel Wire B and Steel Wire S satisfied Features 4 and 5. Therefore, in these test numbers, the wire rods had a wire breakage limit strain of 2.0 or more, and excellent wiredrawability was obtained. Furthermore, Steel Wire B and Steel Wire S had a reduction of area RA of 30.0% or more, and excellent reduction of area was obtained. Furthermore, Steel Wire B had a twisting characteristic of 52.0 times or more, and Steel Wire S had a twisting characteristic of 14.0 times or more, and excellent twisting characteristics were obtained.

[0122] In particular, in test numbers 1 to 30, the wire rods satisfied not only feature 1 and feature 2 but also feature 3. Furthermore, the steel wires satisfied not only feature 4 and feature 5 but also feature 6. Therefore, compared with test numbers 31 and 32 which did not satisfy features 3 and 6, the torsional properties of Steel Wire B were 54.0 times or more, and the torsional properties of Steel Wire S were 26.5 times or more, and even more excellent torsional properties were obtained.

[0123] On the other hand, in Test Nos. 33, 34, 38, and 39, Fn2 was too low. Therefore, the wire breakage limit strain of the wire rod was less than 2.0, and excellent wire drawability of the wire rod was not obtained. Furthermore, wire breakage occurred, and Steel Wire B and Steel Wire S could not be produced.

[0124] In test number 35, the B content was too low. As a result, the wire breakage limit strain of the wire was less than 2.0, and sufficient wiredrawability was not obtained. Furthermore, steel wire B did not have sufficient twisting properties, and steel wire S did not have sufficient drawing ability or sufficient twisting properties.

[0125] In the test numbers 36 and 37, Fn1 was too high. As a result, the wire breakage limit strain of the wire was less than 2.0, and sufficient wiredrawability was not obtained. Furthermore, in the steel wires B and S, sufficient twisting properties were not obtained.

[0126] Note that Test No. 40 had a low N content of 0.0040%. Therefore, even without containing B, the steel wire had sufficient wiredrawability, and Steel Wire B and Steel Wire S had sufficient drawing ability and sufficient twisting properties.

[0127] 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. Chemical composition, in mass%, is: C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.150%, Cu: 0 to 0.400%, A wire rod containing Ni: 0 to 0.300%, Sn: 0 to 0.100%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Sb: 0 to 0.0500%, Bi: 0 to 0.0050%, and rare earth elements (REM): 0 to 0.0050%, with the balance consisting of Fe and impurities, and satisfying the following formulas (1) and (2): 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the element symbols in formulas (1) and (2) are substituted with the content of the corresponding element in mass%.

2. A wire rod according to claim 1, wherein the chemical composition is, in mass%, Al: 0.001 to 0.010%, Cr: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Ti: 0.001 to 0.050%, Zr: 0.001 to 0.050%, Nb: 0.001 to 0.050%, V: 0.001 to 0.150%, Cu: 0.001 to 0.400%, Ni: 0.001 to 0.300%, Sn: 0.001 to 0.100%, Ca: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, Sb: 0.0001 to 0.0500%, A wire rod containing one or more elements selected from the group consisting of Bi: 0.0001 to 0.0050%, and rare earth elements (REM): 0.0001 to 0.0050%.

3. Chemical composition, in mass%, is: C: 0.60 to 1.20%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00%, P: 0.002 to 0.050%, S: 0.002 to 0.050%, N: over 0.0060 to 0.0120%, B: 0.0020 to 0.0120%, O: 0.0050% or less, Al: 0 to 0.010%, Cr: 0 to 0.50%, Mo: 0 to 0.20%, Ti: 0 to 0.050%, Zr: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.150%, Cu: 0 to 0.400%, A steel wire containing Ni: 0-0.300%, Sn: 0-0.100%, Ca: 0-0.0050%, Mg: 0-0.0050%, Sb: 0-0.0500%, Bi: 0-0.0050%, and rare earth elements (REM): 0-0.0050%, with the balance consisting of Fe and impurities, and satisfying the following formulas (1) and (2): 9100N-12200B+9.7≦40.0 (1) 1.265+279N-357B-C≧0.00 (2) Here, the element symbols in formulas (1) and (2) are substituted with the content of the corresponding element in mass%.

4. A steel wire according to claim 3, wherein the chemical composition is, in mass%, Al: 0.001 to 0.010%, Cr: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Ti: 0.001 to 0.050%, Zr: 0.001 to 0.050%, Nb: 0.001 to 0.050%, V: 0.001 to 0.150%, Cu: 0.001 to 0.400%, Ni: 0.001 to 0.300%, Sn: 0.001 to 0.100%, Ca: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, Sb: 0.0001 to 0.0500%, A steel wire containing one or more elements selected from the group consisting of Bi: 0.0001 to 0.0050%, and rare earth elements (REM): 0.0001 to 0.0050%.

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