Wire material, steel wire and twisted wire

Abstract

Provided are: a wire material which has a chemical composition containing, in terms of mass%, 0.50-1.10% of C, 0.10-1.00% of Si, 10.0-18.0% of Mn, 0.050% or less of P, 0.050% or less of S and 0.005-0.035% of N, with the remainder comprising Fe and impurities, includes an austenite structure, has a relative magnetic permeability of 1.100 or less, and is such that in a cross section perpendicular to the length direction of the wire material, the areal ratio of carbides having a maximum length of 0.5 μm or more in a central part is 0.05-2.00% and the degree of segregation of carbon in a center segregation part is 1.20 or less, and in a cross section parallel to the length direction including the center axis of the wire material, the average aspect ratio of austenite grains in the austenite structure is less than 1.40; a steel wire in which the average aspect ratio of austenite grains in the austenite structure is 1.40 or more; and a twisted wire that includes the steel wire.

Description

Wire rods, steel wires and stranded wires

[0001] The present disclosure relates to wire rods, steel wires, and stranded wires.

[0002] The reinforcing steel material for general power transmission lines is carbon steel, which is a ferromagnetic material. During power transmission, the temperature of the power transmission line rises not only due to the electrical resistance of the line but also due to electromagnetic induction from the reinforcing wire. It is known that the temperature rise of the power transmission line ultimately leads to power loss. Therefore, there is a demand for non-magnetic wire that does not cause electromagnetic induction during power transmission.

[0003] Patent Document 1 discloses a non-magnetic, high-strength wire rod suitable for use as a core wire for power lines, which has high strength and non-magnetic properties and a low thermal expansion coefficient, and which contains, by weight, 27 to 42% manganese (Mn), 0.35% or less (excluding 0%) carbon (C), 0.5% or less silicon (Si), 0.03% or less phosphorus (P), and 0.03% or less sulfur (S), with the balance being Fe and other unavoidable impurities, and which has a Neel temperature exceeding 150°C.

[0004] Patent Document 2 discloses a non-magnetic steel that achieves high strength, high yield strength, and low magnetic permeability, and that is excellent in bending workability at room temperature and also in bending workability at low temperatures, containing C: 0.8 to 1.2% (meaning % by mass; the same applies hereinafter to chemical components), Si: 0.1 to 0.6%, Mn: more than 13% but not more than 20%, Al: 0.001% or more but less than 0.02%, P: 0.040% or less (not including 0%), S: 0.045% or less (not including 0%), and N: 0.025 to 0.05%, with the balance being iron and unavoidable impurities, with 99.0% or more by area of ​​the microstructure being an austenite structure and with an austenite grain size number of 8.0 to 10.5.

[0005] Patent Document 3 discloses a non-magnetic steel that exhibits high strength and low magnetic permeability, and further has excellent bending workability, particularly bending workability at low temperatures, even when a decarburized layer is present. The non-magnetic steel has a chemical composition, in mass %, of C: 0.8 to 1.2%, Si: 0.1 to 0.6%, Mn: more than 13% and less than 20%, Al: 0.001% or more and less than 0.02%, P: more than 0% and 0.040% or less, S: more than 0% and 0.045% or less, and N: 0.025 to 0.05%, with the balance being iron and inevitable impurities, and the hydrogen concentration in the steel being suppressed to 4.5 mass ppm or less.

[0006] Patent Document 4 discloses a non-magnetic steel wire rod or steel bar containing C: 0.40 to 0.8%, Si: 0.50% or less (excluding 0%), Mn: 8 to 25%, P: 0.03% or less (excluding 0%), S: 0.030% or less (excluding 0%), Al: 0.010 to 0.10%, N: 0.0010 to 0.020%, the balance being iron and unavoidable impurities, the amount of N in a solid solution state being 0.001% or less (including 0%), the structure being an austenite single-phase structure, and the number of austenite crystal grains with a crystal grain size of 30 to 80 μm being 80% or more of all austenite crystal grains.

[0007] Patent Document 5 discloses a steel material having a component composition containing, by mass%, C: 0.10% to 2.50%, Mn: 8.0% to 45.0%, P: 0.300% or less, S: 0.1000% or less, Ti: 0.10% to 5.00%, Al: 0.001% to 5.000%, N: 0.5000% or less, and O (oxygen): 0.1000% or less, and containing C, Ti, and Mn in ranges that satisfy the following formula (1), with the balance being Fe and unavoidable impurities, and having a structure containing, by area ratio, 90% or more of an austenite phase and 0.2% or more of Ti carbide. 25([C]-12.01[Ti] / 47.87)+[Mn]≧25 (1) where [C], [Ti], and [Mn] are the contents (mass%) of each element.

[0008] Patent Document 1: JP-T-2022-551861A Patent Document 2: JP-A-2014-177662 Patent Document 3: JP-A-2017-179395 Patent Document 4: JP-A-2013-023743 Patent Document 5: WO 2020-054553

[0009] An object of the present disclosure is to provide a wire rod capable of producing a non-magnetic steel wire while suppressing wire breakage during wire drawing, a non-magnetic steel wire, and a stranded wire using the non-magnetic steel wire.

[0010] The means for solving the above problems include the following aspects. <1> In mass%, C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, N: 0.005 to 0.035%, Cu: 0 to 0.40%, Ni: 0 to 0.40%, Cr: 0-2.50%, Mo: 0-1.00%, V: 0-0.25%, Ti: 0-0.100%, Al: 0-0.100%, Nb: 0-0.050%, Sn: 0-0.050%, B: 0-0.0050%, Bi: 0-0.20%, Pb: 0 to 0.09%, A wire rod having a chemical composition of Ca: 0 to 0.0100% and Mg: 0 to 0.0100%, with the balance being Fe and impurities, containing an austenite structure, and having a relative permeability of 1.100 or less, in a cross section perpendicular to the longitudinal direction of the wire rod, an area ratio of carbides having a maximum length of 0.5 μm or more at the center of the cross section is 0.05 to 2.00%, and the degree of carbon segregation in a central segregation portion is 1.20 or less, and in a cross section parallel to the longitudinal direction and including the central axis of the wire rod, the number average aspect ratio of austenite grains in the austenite structure is less than 1.40. <2> The wire rod according to <1>, wherein the chemical composition includes, in mass %, one or more selected from the group consisting of the following first, second, and third groups: (Group 1) One or two selected from the group consisting of Cu: 0.05 to 0.40%, and Ni: 0.05 to 0.40% or less. (Group 2) One or two or more selected from the group consisting of Cr: 0.02 to 2.50%, Mo: 0.02 to 1.00%, V: 0.002 to 0.25%, Ti: 0.005 to 0.100%, Al: 0.005 to 0.100%, and Nb: 0.002 to 0.050%. (Group 3) Sn: 0.002 to 0.050%, B: 0.0001 to 0.0050%, Bi: 0.002 to 0.20%, Pb: 0.002 to 0.09%, <3> The wire rod according to <1> or <2>, wherein the maximum thickness of the carbide is 0.50 μm or less.<4> The wire rod according to any one of <1> to <3>, wherein the grain size of the austenite grains in the austenite structure is 8.0 μm or more and 14.0 μm or less. <5> In mass%, C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, Cu: 0 to 0.40%, Ni: 0 to 0.40%, Cr: 0 to 2.50%, Mo: 0 to 1.00%, V: 0 to 0.25%, Ti: 0 to 0.100%, Al: 0 to 0.100%, Nb: 0 to 0.050%, Sn: 0 to 0.050%, B: 0 to 0.0050%, Bi: 0 to 0.20%, Pb: 0 to 0.09%, <6> A steel wire according to <5>, having a chemical composition of Ca: 0 to 0.0100% and Mg: 0 to 0.0100%, with the balance being Fe and impurities, containing an austenitic structure, and having a relative permeability of 1.100 or less, in a cross section perpendicular to the longitudinal direction of the steel wire, carbides having a maximum length of 0.5 μm or more at the center of the cross section are 0.05 to 2.00% in terms of area ratio, and the degree of carbon segregation in a central segregation portion is 1.20 or less, and in a cross section parallel to the longitudinal direction and including the central axis of the steel wire, the number average aspect ratio of austenite grains in the austenitic structure is 1.40 or more.(Group 1) One or two selected from the group consisting of Cu: 0.05 to 0.40%, and Ni: 0.05 to 0.40% or less. (Group 2) One or two or more selected from the group consisting of Cr: 0.02 to 2.50%, Mo: 0.02 to 1.00%, V: 0.002 to 0.25%, Ti: 0.005 to 0.100%, Al: 0.005 to 0.100%, and Nb: 0.002 to 0.050%. (Group 3) Sn: 0.002 to 0.050%, B: 0.0001 to 0.0050%, Bi: 0.002 to 0.20%, Pb: 0.002 to 0.09%, <7> The steel wire according to <5> or <6>, which has a plating layer on its surface. <8> A stranded wire comprising the steel wire according to any one of <5> to <7>.

[0011] According to the present disclosure, there are provided a wire rod, a non-magnetic steel wire, and a stranded wire using the non-magnetic steel wire, which can produce a non-magnetic steel wire while suppressing wire breakage during wire drawing.

[0012] FIG. 1 is a diagram showing an example of carbides that become the starting points of cracks during wire drawing of a wire rod.

[0013] An embodiment of the present disclosure will be described. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, when "greater than" or "less than" is added to the numerical values ​​before and after "to," the numerical range does not include these numerical values ​​as the lower or upper limit. In numerical ranges described in stages in this specification, the upper limit of a certain numerical range may be replaced with the upper limit of another numerical range described in stages, or may be replaced with a value shown in an example. In numerical ranges described in stages in this specification, the lower limit of a certain numerical range may be replaced with the lower limit of another numerical range described in stages, or may be replaced with a value shown in an example. The content of an element in a chemical composition may be simply expressed as "amount" (e.g., C content, Si content, etc.). Regarding the content of an element in a chemical composition, "%" means "mass %." The term "process" does not only refer to an independent process, but also includes processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0014] The inventors of the present disclosure conducted extensive research to find a wire rod and steel wire that can suppress wire breakage during wiredrawing and are nonmagnetic, and as a result, they discovered the following: (a) A metastable austenite structure can be utilized as a high Mn component. However, it is known that metastable austenite undergoes deformation-induced martensitic transformation during cold working, making it difficult to maintain low magnetic properties in drawn steel wires such as power transmission cables. (b) As a component that can prevent deformation-induced martensitic transformation and maintain low magnetic properties even after high strength following wiredrawing, they investigated a high-carbon, high-Mn component system, and arrived at a component system that maintains low magnetic properties even after wiredrawing. (c) On the other hand, high-carbon components generate carbides in the center, which can become crack initiation sites during wiredrawing, leading to wire breakage during wiredrawing and reduced wire ductility. It was effective to keep the carbide area ratio at 2% or less. (d) Furthermore, if there is variation, such as a high solute carbon concentration in the center, wiredrawability deteriorates. The precipitation of carbides is effective in reducing variations in the concentration of solute carbon. (e) The wire rod, steel wire, and stranded wire according to the present disclosure were developed as a result of satisfying the conditions for maintaining wiredrawability and non-magnetic properties after wiredrawing.

[0015] [Wire Rod] The wire rod according to the present disclosure will be described. The wire rod according to the present disclosure has a chemical composition, in mass %, of C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, with the balance being Fe and impurities. The wire rod includes an austenitic structure and has a relative permeability of 1.100 or less. In a cross section perpendicular to the longitudinal direction of the wire rod, carbides having a maximum length of 0.5 μm or more at the center of the cross section account for 0.05 to 2.00% in terms of area ratio, the degree of carbon segregation in central segregation regions is 1.20 or less, and in a cross section parallel to the longitudinal direction and including the central axis of the wire rod, the number average aspect ratio of austenite grains in the austenitic structure is less than 1.40. Furthermore, the wire rod according to the present disclosure may contain optional elements described below in place of a portion of Fe.

[0016] <Chemical Composition> The chemical composition (content of each element) of the wire rod according to the present disclosure will be described.

[0017] C: 0.50 to 1.10% Carbon (C) stabilizes austenite and suppresses the deformation-induced martensitic transformation after wire drawing. This results in sufficient non-magnetic properties. If the C content is less than 0.50%, the above effect is not fully achieved. On the other hand, if the C content exceeds 1.10%, excessive carbides precipitate. The precipitated carbides become the starting point for cracks during processing. As a result, sufficient workability is not achieved. Therefore, the C content is 0.50 to 1.10%. The preferred lower limit of the C content is 0.60%, more preferably 0.70%, and even more preferably 0.80%. The preferred upper limit of the C content is 1.05%, more preferably 1.03%, and even more preferably 1.00%.

[0018] Si: 0.10 to 1.00% Silicon (Si) has the effect of deoxidizing steel. Si also increases the strength of steel through solid solution strengthening. If the Si content is less than 0.10%, the above effect cannot be sufficiently obtained. On the other hand, if the Si content exceeds 1.00%, wire drawability decreases. Therefore, the Si content is 0.10 to 1.00%. The preferred lower limit of the Si content is 0.15%, more preferably 0.18%, and even more preferably 0.20%. The preferred upper limit of the Si content is 0.90%, more preferably 0.80%, and even more preferably 0.70%.

[0019] Mn: 10.0 to 18.0% Manganese (Mn) stabilizes austenite and suppresses strain-induced martensitic transformation. Therefore, sufficient non-magnetic properties are obtained. If the Mn content is less than 10.0%, the above effects are not fully achieved. On the other hand, if the Mn content exceeds 18.0%, even if the soaking treatment described below diffuses and reduces the carbides present in large amounts in the center of the cast slab, the area ratio and segregation degree of carbides in the center cannot be sufficiently reduced. Therefore, the Mn content is 10.0 to 18.0%. The preferred lower limit of the Mn content is 11.0%, more preferably 11.5%, and even more preferably 12.0%. The preferred upper limit of the Mn content is 17.0%, more preferably 16.5%, and even more preferably 16.0%.

[0020] P: 0.050% or less Phosphorus (P) is an impurity. P segregates at the grain boundaries of austenite crystal grains, reducing wiredrawability. If the P content of the wire rod is 0.050% or less, the reduction in workability is suppressed, and the target properties can be obtained while satisfying other requirements. The upper limit of the P content is preferably 0.045%, and more preferably 0.040% or less. The lower limit of the P content is not limited, and is preferably 0% (i.e., no P is contained), but from the viewpoint of reducing the dephosphorization cost, it may be more than 0% or may be 0.001% or more.

[0021] S: 0.050% or less Sulfur (S) reduces workability. If the S content of the wire rod is 0.050% or less, the target properties can be obtained by satisfying other requirements. A preferable upper limit of the S content is 0.040%. Note that the lower limit of the S content is not limited, but from the viewpoint of reducing desulfurization costs, it may be more than 0% or may be 0.001% or more.

[0022] N: 0.005 to 0.035% Nitrogen (N) stabilizes austenite and suppresses deformation-induced martensitic transformation. This results in sufficient non-magnetic properties. N also increases the strength of steel through solid solution strengthening. If the N content is less than 0.005%, the above effect is not fully achieved. On the other hand, if the N content exceeds 0.035%, defects such as blowholes are more likely to occur in the steel. This reduces the drawability of the wire rod. Therefore, the N content is 0.005 to 0.35%. The preferred lower limit of the N content is 0.007%, more preferably 0.010%, and even more preferably 0.012%. The preferred upper limit of the N content is 0.030%, more preferably 0.024%, and even more preferably 0.020%.

[0023] The wire rod according to the present disclosure may contain one or more of Cu, Ni, Cr, Mo, V, Ti, Al, Nb, Sn, B, Bi, Pb, Ca, and Mg as optional elements in place of a portion of Fe. These optional elements may be absent or may be contained within the following ranges. When these optional elements are contained, the lower limit of the content may be greater than 0%. Furthermore, these optional elements are divided into the following first to third groups from the viewpoint of their effects.

[0024] [First Group] Cu and Ni The chemical composition of the wire according to the present disclosure may further contain one or two elements selected from the first group described above in place of a portion of Fe. These elements are optional elements, and all of them improve the non-magnetic properties of the steel material and increase the toughness of the steel material. Each element will be described below.

[0025] Cu: 0.40% or less Copper (Cu) is an optional element. That is, the Cu content may be 0%. Cu is an element that stabilizes austenite and improves the non-magnetic properties of steel. In view of this effect, the Cu content may be more than 0%, 0.05% or more, 0.10% or more, or 0.20% or more. On the other hand, if the Cu content exceeds 0.40%, the wire drawability of the wire rod decreases. In view of further improving the wire drawability of the wire rod, the Cu content is 0.40% or less. The Cu content is preferably 0.35% or less.

[0026] Ni: 0.40% or less Nickel (Ni) is an optional element. That is, the Ni content may be 0%. Ni is an element that stabilizes austenite and improves the non-magnetic properties of steel. In view of this effect, the Ni content may be more than 0%, 0.05% or more, 0.10% or more, or 0.20% or more. On the other hand, if the Ni content exceeds 0.40%, the wire drawability of the wire rod decreases. In view of further improving the wire drawability of the wire rod, the Ni content is 0.40% or less. The Ni content is more preferably 0.35% or less.

[0027] [Second Group] Cr, Mo, V, Ti, Al, and Nb The chemical composition of the wire rod according to the present disclosure may further contain one or more elements selected from the second group described above in place of a portion of Fe. These elements are optional elements, and all of them increase the strength of the steel material and the steel wire. Each element will be described below.

[0028] Cr: 2.50% or less Chromium (Cr) is an optional element. That is, the Cr content may be 0%. Cr is an element that forms carbides and increases the strength of steel material through precipitation strengthening. Cr further stabilizes austenite and improves the non-magnetic properties of steel material. This results in increased strength and improved non-magnetic properties of wire rod and steel wire. In view of this effect, the Cr content may be more than 0%, 0.02% or more, or 0.05% or more. On the other hand, if the Cr content exceeds 2.50%, coarse Cr carbides are generated, reducing the wire drawability of the wire rod. Therefore, the Cr content is 2.50% or less. In view of further improving the wire drawability of the wire rod, the Cr content is preferably 2.00% or less.

[0029] Mo: 1.00% or less Molybdenum (Mo) is an optional element. That is, the Mo content may be 0%. Mo is an element that generates carbides and increases the strength of steel material through precipitation strengthening. It also has the effect of increasing the tensile strength of the steel wire obtained after wire drawing. From this perspective, the Mo content of the wire rod may be greater than 0% or may be 0.02% or greater. On the other hand, if the Mo content of the wire rod exceeds 1.00%, the above effect saturates and the manufacturing cost of the wire rod further increases. Therefore, the Mo content is preferably in the range of 0.02 to 1.00%, more preferably 0.04 to 0.90%.

[0030] V: 0.25% or less Vanadium (V) is an optional element. That is, the V content may be 0%. V is an element that forms carbides or nitrides to increase the strength of steel materials through precipitation strengthening. This increases the strength of wire rods and steel wires. In view of this effect, the V content may be more than 0%, 0.002% or more, or 0.005% or more. On the other hand, if the V content exceeds 0.25%, the amount of carbides or carbonitrides increases, resulting in a decrease in wire drawability. Therefore, the V content is 0.25% or less. In view of further improving the wire drawability of wire rods, the V content is preferably 0.15% or less.

[0031] Ti: 0.100% or less Titanium (Ti) is an optional element. That is, the Ti content may be 0%. Ti is an element that forms carbides and nitrides to increase the strength of steel materials through precipitation strengthening. This increases the strength of wire rods and steel wires. In view of this effect, the Ti content may be more than 0%, 0.005% or more, or 0.007% or more. On the other hand, if the Ti content exceeds 0.100%, the amount of carbides or carbonitrides increases, resulting in a decrease in wire drawability. Therefore, the Ti content is 0.100% or less. In view of further improving the wire drawability of wire rods, the Ti content is preferably 0.050% or less.

[0032] Al: 0.100% or less Aluminum (Al) is an optional element. That is, the Al content may be 0%. Al is an element that forms nitrides and refines austenite grains through a pinning effect. Refining austenite grains increases the strength of steel materials and steel wires. Al may be added to reduce the amount of oxygen in steel wires. In view of this effect, the Al content may be greater than 0%, 0.005% or more, or 0.030% or more. On the other hand, if the Al content exceeds 0.100%, excessive Al nitrides are formed. In this case, the amount of solute N in the steel material decreases, the stability of austenite decreases, and the nonmagnetic properties deteriorate. Therefore, the Al content is 0.100% or less. In view of further improving the nonmagnetic properties of wire materials and steel wires, the Al content is preferably 0.050% or less, more preferably 0.035% or less.

[0033] Nb: 0.050% or less Niobium (Nb) is an optional element. That is, the Nb content may be 0%. Nb is an element that forms nitrides and refines austenite grains through a pinning effect. Refining austenite grains increases the strength of the steel material. This increases the strength of wire rods and steel wires. In view of this effect, the Nb content may be more than 0%, 0.002% or more, or 0.005% or more. On the other hand, if the Nb content exceeds 0.050%, the amount of carbides or carbonitrides increases, deteriorating wiredrawability. Therefore, the Nb content is 0.050% or less. In view of further improving the wiredrawability of the wire rod, the Nb content is preferably 0.030% or less.

[0034] [Third Group] Sn, B, Bi, Pb, Ca, and Mg The chemical composition of the wire rod according to the present disclosure may further contain one or more elements selected from the third group described above in place of a portion of Fe. These elements are optional elements, and all of them improve the wiredrawability of the wire rod. Each element will be described below.

[0035] Sn: 0.050% or less Tin (Sn) is an optional element. That is, the Sn content may be 0%. Sn is an element that improves wiredrawability. From the viewpoint of this effect, the Sn content may be more than 0%, 0.002% or more, or 0.005% or more. On the other hand, if the Sn content exceeds 0.050%, the hot workability decreases. Therefore, the Sn content is 0.050% or less. From the viewpoint of further improving the hot workability, the Sn content is preferably 0.030% or less.

[0036] B: 0.0050% or less Boron (B) is an optional element. That is, the B content may be 0%. B is an element that segregates at grain boundaries to increase grain boundary strength. This improves the wiredrawability of the steel material. In view of this effect, the B content may be more than 0%, 0.0001% or more, or 0.0005% or more. If the B content exceeds 0.0050%, coarse carbonitrides are likely to be formed in the wire rod, which may deteriorate the non-magnetic properties of the wire rod and steel wire. Therefore, the B content is 0.0050% or less. In view of further reducing the electrical resistivity of the steel wire, the B content is preferably 0.0040% or less.

[0037] Bi: 0.20% or less Bismuth (Bi) is an optional element. That is, the Bi content may be 0%. Bi is an element that refines the dendritic structure during solidification. This refines inclusions and improves the wire drawability of the wire rod. In view of this effect, the Bi content may be more than 0%, 0.002% or more, or 0.005% or more. On the other hand, if the Bi content exceeds 0.20%, the hot workability of the steel material decreases. Therefore, the Bi content is 0.20% or less. In view of further improving the hot workability, the Bi content is preferably 0.10% or less.

[0038] Pb: 0.09% or less Lead (Pb) is an optional element. That is, the Pb content may be 0%. Pb is an element that improves the wiredrawability of steel. From the viewpoint of this effect, the Pb content may be more than 0%, 0.002% or more, or 0.005% or more. On the other hand, if the Pb content exceeds 0.09%, the hot workability decreases. Therefore, the Pb content is 0.09% or less. From the viewpoint of further improving the hot workability, the Pb content is preferably 0.05% or less.

[0039] Ca: 0.0100% or less Calcium (Ca) is an optional element. That is, the Ca content may be 0%. Ca forms Ca sulfides and has the effect of suppressing the coarsening of MnS. By suppressing the coarsening of MnS, cracking during wire drawing is suppressed, and high-strength steel wire can be produced. In view of this effect, the Ca content may be more than 0%, 0.0002% or more, or 0.0005% or more. On the other hand, even if the Ca content exceeds 0.0100%, the effect saturates. Furthermore, since a large amount of coarse Ca-based oxides is formed, the wire drawability is actually reduced. Therefore, the Ca content is 0.0100% or less. In view of further improving the wire drawability of the wire rod, the Ca content is preferably 0.0050% or less.

[0040] Mg: 0.0100% or less Magnesium (Mg) is an optional element. That is, the Mg content may be 0%. Mg dissolves in MnS and has the effect of finely dispersing MnS. Finely dispersing MnS suppresses cracking during wire drawing and enables processing into high-strength steel wire. In view of this effect, the Mg content may be more than 0%, 0.0002% or more, or 0.0005% or more. On the other hand, even if the Mg content exceeds 0.0100%, the effect saturates. Furthermore, the formation of oxides actually reduces wire drawability. Therefore, the Mg content is 0.0100% or less. In view of further improving the wire drawability of the wire rod, the Mg content is preferably 0.0050% or less.

[0041] <Magnetic Properties> Relative Permeability: 1.100 or Less The wire according to the present disclosure has a relative permeability of 1.100 or less. Relative permeability represents the ratio of the magnetic permeability of a material to the magnetic permeability of a vacuum μ0 (= 4π × 10-7 [H / m]) as a reference, and is calculated by the following formula: μr = μ / μ0 (μr: relative permeability, μ: magnetic permeability, μ0: vacuum permeability) The closer the relative permeability is to 1, the less likely it is to be magnetized, and in the present disclosure, a relative permeability of 1.100 or less is considered "non-magnetic." The relative permeability of the wire according to the present disclosure is measured and calculated by the method described in the examples below.

[0042] <Metallic Structure> Next, the metallic structure of the wire rod according to the present disclosure will be described. Note that, with regard to the parameters described below regarding the metallic structure of the wire rod, the number average aspect ratio of austenite grains is a value in a cross section (sometimes referred to as a "longitudinal cross section") parallel to the longitudinal direction of the wire rod including the central axis of the wire rod, and the other parameters mean values ​​in a cross section (sometimes referred to as a "transverse cross section") perpendicular to the longitudinal direction of the wire rod unless otherwise specified. The same applies to the parameters regarding the metallic structure of the steel wire described later.

[0043] Austenite structure The wire rod according to the present disclosure includes an austenite structure. The austenite phase is non-magnetic. From the viewpoint of having sufficient non-magnetic properties, the wire rod according to the present disclosure preferably has a high area ratio of the austenite structure, particularly preferably 98.00% or more. However, if the area ratio of the austenite structure is 100.00%, workability decreases, so the area ratio of the austenite structure is preferably less than 100.00%. Structures other than the austenite structure (preferably a total of 2.00% or less) include, for example, ferrite and cementite, which are ferromagnetic at room temperature.

[0044] Carbon segregation degree in the central segregation region: 1.20 or less If the carbon segregation degree is high in the central region where the cooling rate is slow during the wire manufacturing process, carbides will precipitate excessively at the grain boundaries. Carbides will become the starting point for cracks during wire drawing. Therefore, if the carbon segregation degree in the central segregation region is high, sufficient wiredrawability will not be obtained. Therefore, the carbon segregation degree in the central segregation region in the cross section of the wire is 1.20 or less.

[0045] Area ratio of carbides (sometimes simply referred to as "carbides" in this disclosure) with a maximum length of 0.5 μm or more in the center: 0.05 to 2.00%. The center is representative of carbides because the carbides precipitated in the wire manufacturing process are most abundant in the center, where the cooling rate is slow. When a large amount of carbides precipitate in the center, they often cover grain boundaries. This increases the thickness of the carbides, making them prone to becoming crack initiation points during processing, resulting in insufficient workability. Figure 1 shows an example of carbides (white areas) that can become crack initiation points during wiredrawing. The presence of such plate-like carbides in the center of the wire makes them prone to becoming crack initiation points during wiredrawing. On the other hand, when the carbide area ratio is less than 0.05%, workability deteriorates. This is thought to be due to the partial precipitation of solute carbon in the center, reducing the variation in solute carbon and improving workability. To obtain sufficient workability, the area ratio of carbides in the central portion of the cross section of the wire is 0.05 to 2.00%, preferably 0.07 to 1.90%, more preferably 0.10 to 1.80%.

[0046] Number average aspect ratio of austenite grains: less than 1.40 If the number average aspect ratio of austenite grains in the longitudinal section of the wire is less than 1.40, it can be said that the wire is in a state where it has not been processed during production, and wiredrawability can be further improved.

[0047] Maximum thickness of carbide: preferably 0.50 μm or less Among carbides, thick cementite precipitated at grain boundaries is particularly the starting point for cracks during processing. By making the maximum thickness of carbide in the cross section of the wire rod preferably 0.50 μm or less, workability can be further improved.

[0048] Grain size of austenite grains in the austenite structure: preferably 8.0 μm or more and 14.0 μm or less The grain size of austenite affects strength. In the cross section of the wire rod, if the grain size of the austenite grains in the austenite structure is 8.0 μm or more, an increase in the frequency of nucleation of grain boundary carbides is suppressed, making it difficult for grain boundary carbides to form, and improving workability. If the grain size of the austenite grains in the austenite structure is 14.0 μm or less, coarse grains are not formed, and workability is improved. Therefore, the grain size of the austenite grains in the austenite structure is preferably 8.0 to 14.0 μm.

[0049] [Steel Wire] Next, a steel wire according to the present disclosure will be described. The steel wire according to the present disclosure has a chemical composition, in mass %, of C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, with the balance being Fe and impurities, and includes an austenitic structure, and has a relative permeability of 1.100 or less, in a cross section perpendicular to the longitudinal direction of the steel wire, carbides having a maximum length of 0.5 μm or more at the center of the cross section account for 0.05 to 2.00% in terms of area ratio, and the degree of carbon segregation in a central segregation portion is 1.20 or less, and in a cross section parallel to the longitudinal direction and including the central axis of the steel wire, the number average aspect ratio of austenite grains in the austenitic structure is 1.40 or more.

[0050] The chemical composition of the steel wire according to the present disclosure, including any optional elements that may be contained other than the elements mentioned above and the content of each element, is the same as that of the wire rod, and therefore a description thereof will be omitted here. Furthermore, the magnetic properties of the steel wire according to the present disclosure are also the same as those of the wire rod, with a relative permeability of 1.100 or less.

[0051] The metal structure of the steel wire according to the present disclosure is the same as that of the wire rod, except that the number average aspect ratio of the austenite grains in the austenite structure in the longitudinal cross section is 1.40 or more.

[0052] Number-average aspect ratio of austenite grains in the austenite structure of the steel wire: 1.40 or more The steel wire according to the present disclosure has high strength due to the number-average aspect ratio of the austenite grains being 1.40 or more as a result of wiredrawing. A high-strength, non-magnetic steel wire can be obtained by satisfying the same requirements as those of the wire rod described above, namely, that the area fraction of carbides in the center of a cross section (transverse cross section) perpendicular to the longitudinal direction of the steel wire is 0.05 to 2.00%, and the degree of carbon segregation in the central segregation region is 1.20 or less, in a cross section perpendicular to the longitudinal direction of the steel wire. Note that, like the wire rod, the austenite structure of the steel wire preferably has an area fraction of 98.00% or more and less than 100.00%.

[0053] Plated wire (alloy-coated) and stranded wire The steel wire of the present disclosure can be coated with a metal such as zinc, a zinc alloy, aluminum, or an aluminum alloy. Furthermore, the steel wire of the present disclosure and alloy-coated steel wires can be bundled or twisted. Because the steel wire of the present disclosure has nonmagnetic properties, for example, if a stranded wire including the steel wire of the present disclosure is applied to a power transmission line, the temperature rise of the power transmission line due to electromagnetic induction can be suppressed, and power loss can be reduced.

[0054] <Measuring Method> Next, a method for measuring the metallographic structure described above will be described.

[0055] (Carbon Segregation Degree in the Central Segregation Region) To determine the carbon segregation degree, measurements are performed using an electron probe microanalyzer (EPMA). EPMA measures a D / 2 mm × D / 2 mm region, with a beam diameter of 10 μm and a measurement interval of 10 μm, with D being the wire diameter of the wire, centered at a point within 0.5 mm from the center position of the wire cross section. From the obtained data, the carbon concentration of a 50 μm × 50 μm region with a high carbon concentration is calculated. The ratio of the carbon concentration of the 50 μm × 50 μm region to the carbon concentration (average carbon concentration) of the entire D / 2 mm × D / 2 mm range is defined as the segregation degree. Five locations with high carbon concentrations are selected, and the average value of these segregation degrees is defined as the carbon segregation degree of the central segregation region. The five 50 μm square regions are selected in descending order of carbon concentration, starting with the region with the highest carbon concentration within the measurement range. However, if there are any contaminations or pinholes on the measurement surface, the carbon concentration will be very high. To exclude such areas, any area where the carbon concentration is three times or more the carbon concentration in the entire range of D / 2 mm × D / 2 mm is excluded.

[0056] (Carbide at the Center) The cross section of steel (wire rod or steel wire) is polished. After polishing, it is washed with alcohol and immediately etched with picral. If the polished surface is washed with water or over time, etching becomes impossible. Etching with picral allows for clearer identification of carbides. Picral etching is performed while adjusting the conditions for revealing the structure, as the conditions vary depending on the number of times the solution is used and the polishing conditions. For example, the etching is performed at room temperature for approximately 60 seconds, and after confirming whether the structure is revealed, the polishing process is resumed or the etching time is extended, depending on the appropriate condition. An SEM image is taken at 100x magnification (1.1 mm x 0.8 mm) of an area within a radius of 0.5 mm from the center position. Carbides are binarized using image analysis software (e.g., Image-J), and the carbide area ratio is calculated from the ratio to the total number of pixels. Five cross sections are observed, and the average is taken as the carbide area ratio. The area ratio of carbides is measured for carbides having a maximum length of 0.5 μm or more.

[0057] (Area Fraction of Austenite Structure) The cross section of steel (wire rod or steel wire) is polished. After polishing, it is washed with alcohol and immediately etched with picral. If the polished section is washed with water or if time passes, etching will become impossible. The austenite structure fraction (area fraction) is measured by observing five cross sections at 100x magnification using an SEM, one field of view each, centered on the surface region (within 1.5 mm from the surface), the middle region (within 1 mm from the center at ¼ D from the surface, assuming the wire diameter is D), and the center region (within 1 mm from the center at ½ D from the surface). The area fraction of carbide, as well as the area fractions of ferrite, pearlite, bainite, and martensite, are determined in the same manner as above, and the area fraction of the austenite structure is calculated by subtracting these from 100%. In this observation, the ferrite phase is judged as a recessed portion relative to the majority of the austenite phase. Furthermore, the cementite phase is judged as a portion that appears charged up and white because it is convex and dispersed relative to the austenite and ferrite phases. Bainite and martensite structures are considered to be structures in which cementite phases are dispersed within ferrite phases.

[0058] (Maximum Thickness of Carbide) The area within a radius of 0.5 mm from the center of the cross section is observed with an SEM at 100x magnification to identify the location where the carbide is thickest, and the carbide is then photographed at 10,000x magnification. The thickness of the carbide is measured using image analysis software (e.g., Image-J).

[0059] (Austenite grain size) The cross section of steel (wire rod or steel wire) is polished. After polishing, it is washed with alcohol or the like and immediately etched with picral. If the polishing is followed by washing with water or if time passes, etching will no longer be possible. An area within a radius of 0.5 mm from the center position of the cross section is observed at 500x magnification using an SEM, and the grain size is calculated using quadrature.

[0060] (Number-average aspect ratio of austenite grains) The longitudinal cross section of steel (wire rod or steel wire) is polished. After polishing, it is washed with alcohol or the like and immediately etched with picral. Etching will become impossible if the austenite grains are washed with water after polishing or if time passes. When the austenite grains revealed in the longitudinal cross section are measured in all directions, the largest diameter obtained is defined as the "major diameter," and the direction in which the "major diameter" is obtained is defined as the "major diameter direction." The length of a line segment perpendicular to the major diameter direction that is separated (cut off) by the austenite grain boundary is defined as the "minor diameter." The aspect ratio is defined as "major diameter / minor diameter." An area within a radius of 0.5 mm from the center position of the longitudinal cross section is observed at 500x magnification using an SEM, and the total aspect ratio of each austenite grain is divided by the number of austenite grains measured to calculate the number-average aspect ratio of the austenite grains.

[0061] <Method for manufacturing wire rod and steel wire> The method for manufacturing the wire rod and steel wire according to the present disclosure is not particularly limited, but an example of a suitable manufacturing method will be described below.

[0062] (Soaking Treatment) Molten steel having the above-described chemical composition is produced in a steelmaking process and poured into a mold of a billet caster (continuous casting device) to produce a slab (bloom). After casting, in order to suppress the remaining coarse carbides that could cause breakage during wiredrawing, a soaking treatment is performed, for example, by holding the slab in an atmosphere at 1250°C for 10 hours or more. The soaking treatment is a heat treatment in which the center of the slab is held at a high temperature for a long period of time, for example, about 10 hours, in order to diffuse the carbon that is segregated in large amounts at the center and reduce the degree of segregation. This is a heating method with a fundamentally different purpose from the heating performed to shape the slab in a typical hot rolling process or to reduce the rolling reaction force (for example, an atmosphere temperature of about 1300°C for thick plates).

[0063] (Blooming) The slab is heated to 1000 to 1250°C, and after blooming into a billet, it is allowed to cool. By heating the slab to a relatively high temperature of 1000 to 1250°C, it is possible to reduce carbides in the center.

[0064] (Wire Rod Rolling) A steel billet is rolled to obtain a rolled wire rod. The heating temperature of the steel billet before rolling is 1000°C to 1250°C, and the holding time is more than 10 minutes to 150 minutes. If the heating temperature of the steel billet before rolling is less than 1000°C, the carbides generated in the center during casting of the billet (bloom) are not sufficiently dissolved, and many coarse carbides that may cause breakage during wire drawing remain in the center. In addition, by increasing the reheating temperature before wire rod rolling, the austenite grain size becomes coarse, which has the effect of suppressing the remaining coarse carbides that may cause breakage during wire drawing.

[0065] The finish rolling temperature is set to 800° C. or higher. If the finish rolling temperature is lower than 800° C., the number average aspect ratio of austenite grains tends to exceed 1.40. Furthermore, if finish rolling is performed at an even lower temperature, the amount of carbides precipitated in the center tends to increase.

[0066] By cooling the central portion after finish rolling at 5.0°C / sec or more, the carbide content in the central portion can be reduced to 0.05 to 2.00%. To achieve a central portion of 5.0°C / sec or more, the cooling rate in the surface layer is set to 7.0°C / sec or more. If the cooling rate in the surface layer is less than 7.0°C / sec, the amount of carbide precipitated in the central portion tends to be high. If the cooling rate in the surface layer exceeds 25.0°C / sec, the amount of carbide precipitated in the central portion tends to be excessively low. Each temperature is measured using a radiation thermometer.

[0067] Through the above steps, it is possible to produce a wire rod according to the present disclosure in which carbide segregation in the center portion is suppressed. Note that when producing a steel billet by continuous casting, center segregation may be suppressed by soft reduction.

[0068] Although the wire diameter (diameter) of the wire rod according to the present disclosure is not particularly limited, a smaller diameter can ensure a sufficient hot-rolling area reduction rate from the billet to the wire rod, and can promote the dispersal of coarse carbides formed in the center during bloom casting, thereby reducing the coarse carbides that could cause breakage during subsequent wiredrawing. For example, when hot-rolling from a 122 mm square billet, a target upper limit for the wire diameter that is effective for ensuring a sufficient area reduction rate and dispersing the coarse carbides in the center is approximately 10 mm. Since hot-rolling to a diameter of 3.5 mm or less to achieve this effect increases the rolling cost, a target lower limit for the wire diameter is 3.5 mm.

[0069] Furthermore, the steel wire according to the present disclosure can be manufactured by drawing the obtained wire rod. The wire diameter (diameter) of the steel wire is not particularly limited and is, for example, 2.0 mm or more and 5.0 mm or less. When the diameter of the steel wire is 3.0 mm or more, the drawing process can be more stably performed when obtaining a steel wire by drawing.

[0070] Furthermore, by forming a stranded wire using the steel wire according to the present disclosure, the stranded wire according to the present disclosure can be manufactured.

[0071] <Applications> The applications of the wire rod and steel wire according to the present disclosure are not particularly limited. Because the steel wire according to the present disclosure is high-strength and non-magnetic, by applying a stranded wire including the steel wire according to the present disclosure as a reinforcing wire for a power transmission line, for example, the temperature rise of the power transmission line due to electromagnetic induction can be suppressed, which can contribute to suppressing power loss (power transmission loss).

[0072] The wire rod, steel wire, and stranded wire of the present disclosure will be described in more detail below with reference to examples, although these examples do not limit the wire rod, steel wire, and stranded wire of the present disclosure.

[0073] Example 1 Steel materials having the chemical compositions (units: mass%) shown in Table 1 were prepared, and wire rods and steel wires were manufactured by the methods (conditions) shown in Table 2. The notation "-" in Table 1 indicates that the content of the element in question is at the impurity level, and it can be determined that the element is not substantially contained. The same applies to the notation "-" in Table 4 described below. The remainder of the chemical compositions in Tables 1 and 4 is Fe and impurities.

[0074]

[0075]

[0076] After casting, the slab was subjected to a soaking heat treatment at 1250°C for 12 hours.

[0077] The metal structures of the produced wire rods and steel wires were measured by the above-mentioned method.

[0078] When the wire rod could be drawn to the steel wire diameter shown in Table 2 and the tensile strength was obtained in the subsequent tensile test, it was evaluated as "Y." When the wire rod could not be drawn to the steel wire diameter shown in Table 2 or broke during the subsequent tensile test, it was evaluated as "N."

[0079] The magnetic properties of the wire rod and steel wire were evaluated based on the relative magnetic permeability. The relative magnetic permeability was measured using a vibrating sample type automatic magnetization measuring device (BHV-50, manufactured by Riken Denshi Co., Ltd.). At room temperature in the atmosphere, the wire was magnetized from a demagnetized state to a maximum magnetic field of 15 kOe, then to a maximum magnetic field of -15 kOe on the negative side, and further to a maximum magnetic field of 15 kOe. The relative magnetic permeability was calculated using the magnetic field strength and magnetic polarization in the range of 5 kOe or more. In the present disclosure, a relative magnetic permeability of 1.100 or less was determined to be "non-magnetic."

[0080] The results are shown in Tables 3A and 3B. The γ fraction refers to the area ratio of the austenite structure, and the γ grain size refers to the grain size of the austenite grains. The underlined values ​​indicate values ​​outside the scope of the present disclosure.

[0081]

[0082]

[0083] Wire rods No. 1-1A to 1-5A satisfy the requirements of the present disclosure, and are non-magnetic and prevent breakage during wiredrawing. Wire rods No. 1-1B to 1-4B have excessive or insufficient amounts of carbides, and breakage occurred during wiredrawing. Wire rod No. 1-5B has a number-average aspect ratio of austenite grains exceeding 1.40, and breakage occurred during wiredrawing.

[0084] Steels 2 to 18 having the chemical compositions shown in Table 4 were used to produce wire rods and steel wires in the same manner as under production condition A, and the evaluations were carried out in the same manner as described above. The results are shown in Table 5. The underlines in Tables 4 and 5 indicate values ​​outside the scope of the present disclosure.

[0085]

[0086]

[0087]

[0088] Wire rods Nos. 2A to 11A and 19A to 21A satisfy the requirements of the present disclosure, achieving both wire breakage prevention during wiredrawing and non-magnetic properties. No. 12B had an excessive C content, resulting in increased carbide precipitation and poor workability, resulting in wire breakage during wiredrawing. No. 13B had an insufficient C content, resulting in low austenite stability, and the steel wire after wiredrawing did not become non-magnetic. Furthermore, since the wire broke before the transition from uniform elongation to local elongation during the tensile test, its tensile strength could not be measured. No. 14B had an excessive Si content, resulting in poor workability and wire breakage during wiredrawing. No. 16B had an insufficient Mn content, resulting in low austenite stability in the wire rod, resulting in the steel wire after wiredrawing not becoming non-magnetic. Furthermore, since the wire broke during the tensile test, its tensile strength could not be measured. No. 17B had an excessively high N content, which resulted in poor workability and wire breakage during wiredrawing. No. 18B had an insufficient N content, which resulted in low austenite stability, and the steel wire did not become nonmagnetic after wiredrawing. In addition, since the wire broke before the transition from uniform elongation to local elongation occurred during the tensile test, the tensile strength could not be measured.

[0089] [Notes] <1> A wire rod having a chemical composition, in mass%, of C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, with the balance being Fe and impurities; in a cross section perpendicular to the longitudinal direction of the wire rod, the austenite structure has an area ratio of 98.00% or more and less than 100.00%, the carbides in the central portion have an area ratio of 0.05 to 2.00%, and the degree of carbon segregation in the central segregation portion is 1.20 or less; and in a cross section parallel to the longitudinal direction and including the central axis of the wire rod, the average aspect ratio of austenite grains in the austenite structure is less than 1.40. <2> A steel sheet having a chemical composition, in mass%, of C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, and further containing one or more elements selected from the group consisting of the following first, second, and third groups, with the balance being Fe and impurities; (First group) One or two elements selected from the group consisting of Cu: 0.40% or less, and Ni: 0.40% or less; (Second group) Cr: 2.50% or less, Mo: 1.00% or less, V: 0.25% or less, Ti: 0.100% or less, Al: 0.100% or less, (Group 3) One or more elements selected from the group consisting of Sn: 0.050% or less, B: 0.0050% or less, Bi: 0.20% or less, Pb: 0.09% or less, and Ca: 0.0100% or less. In a cross section perpendicular to the longitudinal direction of the wire, the austenite structure has an area fraction of 98.00% or more and less than 100.00%, the carbides in the center portion have an area fraction of 0.05 to 2.00%, and the degree of carbon segregation in the central segregation portion is 1.20 or less. In a cross section parallel to the longitudinal direction and including the central axis of the wire, the average aspect ratio of austenite grains in the austenite structure is less than 1.40. <3> The wire according to <1> or <2>, wherein the maximum thickness of the carbides is 0.50 μm or less.<4> The wire rod according to any one of <1> to <3>, wherein the grain size of the austenite grains in the austenite structure is 8.0 μm or more and 14.0 μm or less. <5> A steel wire having a chemical composition, in mass%, of C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, with the balance being Fe and impurities, wherein in a cross section perpendicular to the longitudinal direction of the steel wire, the austenite structure has an area ratio of 98.00% or more and less than 100.00%, the carbides in the central portion have an area ratio of 0.05 to 2.00%, and the degree of carbon segregation in a central segregation portion is 1.20 or less, and wherein in a cross section parallel to the longitudinal direction and including a central axis of the steel wire, the average aspect ratio of austenite grains in the austenite structure is 1.40 or more.<6> A steel sheet having a chemical composition, in mass%, of C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, and further containing one or more elements selected from the group consisting of the following first, second, and third groups, with the balance being Fe and impurities; (First group) One or two elements selected from the group consisting of Cu: 0.40% or less, and Ni: 0.40% or less; (Second group) Cr: 2.50% or less, Mo: 1.00% or less, V: 0.25% or less, Ti: 0.100% or less, Al: 0.100% or less, (Group 3) One or more elements selected from the group consisting of Sn: 0.050% or less, B: 0.0050% or less, Bi: 0.20% or less, Pb: 0.09% or less, and Ca: 0.0100% or less, with the balance being Fe and impurities, wherein in a cross section perpendicular to the longitudinal direction of the steel wire, the austenite structure has an area fraction of 98.00% or more and less than 100.00%, the area fraction of carbides in the central portion is 0.05 to 2.00%, and the degree of carbon segregation in the central segregation portion is 1.20 or less, and in a cross section parallel to the longitudinal direction and including the central axis of the steel wire, the average aspect ratio of austenite grains in the austenite structure is 1.40 or more. <7> The steel wire according to <5> or <6>, having a plating layer on its surface. <8> A stranded wire comprising the steel wire according to any one of <5> to <7>.

[0090] The disclosure of Japanese Patent Application No. 2024-059232, filed on April 1, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated herein by reference.

Claims

1. In mass%, C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, N: 0.005 to 0.035%, Cu: 0 to 0.40%, Ni: 0 to 0.40%, Cr: 0-2.50%, Mo: 0-1.00%, V: 0-0.25%, Ti: 0-0.100%, Al: 0-0.100%, Nb: 0-0.050%, Sn: 0-0.050%, B: 0-0.0050%, Bi: 0-0.20%, Pb: 0 to 0.09%, A wire having a chemical composition of Ca: 0 to 0.0100%, and Mg: 0 to 0.0100%, with the balance being Fe and impurities, containing an austenite structure, and having a relative permeability of 1.100 or less, in a cross section perpendicular to the longitudinal direction of the wire, carbides having a maximum length of 0.5 μm or more at the center of the cross section account for 0.05 to 2.00% in terms of area ratio, and the degree of carbon segregation in a central segregation portion is 1.20 or less, and in a cross section parallel to the longitudinal direction and including the central axis of the wire, the number average aspect ratio of austenite grains in the austenite structure is less than 1.

40.

2. The wire according to claim 1, wherein the chemical composition includes, in mass %, one or more elements selected from the group consisting of the first, second, and third groups below. (Group 1) One or two selected from the group consisting of Cu: 0.05 to 0.40%, and Ni: 0.05 to 0.40% or less. (Group 2) One or two or more selected from the group consisting of Cr: 0.02 to 2.50%, Mo: 0.02 to 1.00%, V: 0.002 to 0.25%, Ti: 0.005 to 0.100%, Al: 0.005 to 0.100%, and Nb: 0.002 to 0.050%. (Group 3) Sn: 0.002 to 0.050%, B: 0.0001 to 0.0050%, Bi: 0.002 to 0.20%, Pb: 0.002 to 0.09%, One or more selected from the group consisting of Ca: 0.0002 to 0.0100%, and Mg: 0.0002 to 0.0100% 3. A wire according to claim 1 or 2, wherein the maximum thickness of the carbide is 0.50 μm or less.

4. A wire rod according to any one of claims 1 to 3, wherein the grain size of the austenite grains in the austenite structure is 8.0 µm or more and 14.0 µm or less.

5. In mass%, C: 0.50 to 1.10%, Si: 0.10 to 1.00%, Mn: 10.0 to 18.0%, P: 0.050% or less, S: 0.050% or less, and N: 0.005 to 0.035%, Cu: 0 to 0.40%, Ni: 0 to 0.40%, Cr: 0 to 2.50%, Mo: 0 to 1.00%, V: 0 to 0.25%, Ti: 0 to 0.100%, Al: 0 to 0.100%, Nb: 0 to 0.050%, Sn: 0 to 0.050%, B: 0 to 0.0050%, Bi: 0 to 0.20%, Pb: 0 to 0.09%, A steel wire having a chemical composition of Ca: 0 to 0.0100%, and Mg: 0 to 0.0100%, with the balance being Fe and impurities, containing an austenite structure, and having a relative permeability of 1.100 or less, in a cross section perpendicular to the longitudinal direction of the steel wire, carbides having a maximum length of 0.5 μm or more at a center of the cross section are 0.05 to 2.00% in terms of area ratio, and the degree of carbon segregation in a central segregation portion is 1.20 or less, and in a cross section parallel to the longitudinal direction and including a central axis of the steel wire, the number average aspect ratio of austenite grains in the austenite structure is 1.40 or more.

6. The steel wire according to claim 5, wherein the chemical composition includes, in mass %, one or more elements selected from the group consisting of the following first, second, and third groups: (Group 1) One or two selected from the group consisting of Cu: 0.05 to 0.40%, and Ni: 0.05 to 0.40% or less. (Group 2) One or two or more selected from the group consisting of Cr: 0.02 to 2.50%, Mo: 0.02 to 1.00%, V: 0.002 to 0.25%, Ti: 0.005 to 0.100%, Al: 0.005 to 0.100%, and Nb: 0.002 to 0.050%. (Group 3) Sn: 0.002 to 0.050%, B: 0.0001 to 0.0050%, Bi: 0.002 to 0.20%, Pb: 0.002 to 0.09%, One or more selected from the group consisting of Ca: 0.0002 to 0.0100%, and Mg: 0.0002 to 0.0100% 7. A steel wire according to claim 5 or 6, which has a plating layer on its surface.

8. A stranded wire comprising the steel wire according to any one of claims 5 to 7.

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