WO2020256140A1 - Wire rod - Google Patents

Wire rod Download PDF

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Publication number
WO2020256140A1
WO2020256140A1 PCT/JP2020/024248 JP2020024248W WO2020256140A1 WO 2020256140 A1 WO2020256140 A1 WO 2020256140A1 JP 2020024248 W JP2020024248 W JP 2020024248W WO 2020256140 A1 WO2020256140 A1 WO 2020256140A1
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Prior art keywords
wire
wire rod
less
steel
hydrogen embrittlement
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PCT/JP2020/024248
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French (fr)
Japanese (ja)
Inventor
直樹 松井
大羽　浩
真 小此木
俊彦 手島
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日本製鉄株式会社
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Priority to EP20827854.9A priority Critical patent/EP3988678B1/en
Priority to JP2021526947A priority patent/JP7226548B2/en
Priority to CN202080032029.1A priority patent/CN113748224B/en
Publication of WO2020256140A1 publication Critical patent/WO2020256140A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C21D1/32—Soft annealing, e.g. spheroidising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • C21D1/44—Methods of heating in heat-treatment baths
    • C21D1/46—Salt baths
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • C21D1/44—Methods of heating in heat-treatment baths
    • C21D1/48—Metal baths
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/607—Molten salts
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys

Definitions

  • This disclosure relates to wire rods.
  • high-strength steel wires used in fields such as high-strength rope steel wires, bridge cable steel wires, and PC steel wires are required to have a high tensile strength of 1700 MPa or more.
  • These high-strength steel wires are manufactured, for example, by subjecting a rolled wire having a diameter of 5.0 to 16.0 mm to a pearlite structure and then performing wire drawing.
  • the tensile strength of the steel wire after the wire drawing process is high, there is a high possibility that the steel wire will be affected by the strain aging due to the processing heat generated in the wire drawing process and become embrittlement.
  • high-strength steel wire Due to strain aging, high-strength steel wire has a smaller number of rotations (twisting value) until fracture in the twisting test, and vertical cracks called delamination may occur.
  • the occurrence of delamination in the twist test causes breakage in the stranded wire process for producing a steel wire, which deteriorates manufacturability. Therefore, it is particularly desirable for high-strength steel wires to have both tensile strength and torsional characteristics. Further, the higher the strength of the steel wire, the higher the risk of breakage due to the progress of corrosion or hydrogen embrittlement when the steel wire or the product after the stranded wire is used in a corrosive environment. Therefore, it is desired that the high-strength steel wire used in the above field and the wire rod as a material thereof have excellent corrosion resistance and hydrogen embrittlement resistance.
  • Patent Document 1 describes, in terms of mass%, C: 0.75 to 1.10%, Si: 0.10 to 1.40%, Mn: 0. .10 to 1.0%, Al: 0 to 0.10%, Ti: 0 to 0.10%, Cr: 0 to 0.60%, V: 0 to 0.10%, Nb: 0 to 0.
  • the balance is substantially Fe
  • the area ratio of the metallographic structure is in the region on the axis side of the depth of 100 ⁇ m from the surface of the L cross section along the axial direction including the axis of the steel wire.
  • the metal structure contains a wire drawn pearlite having an area ratio of 70% or more, and the diameter of the steel wire (D [mm]).
  • C 0.70 to 1.20%, Si: 0.10 to 2.00%, Mn: 0. 20 to 1.00%, P: 0.030% or less, S: 0.030% or less, N: 0.0010 to 0.0100%, Al: 0 to 0.100%, Cr: 0 to 2.00 %, V: 0 to 0.30%, B: 0 to 0.0050%, Ti: 0 to 0.050%, Nb: 0 to 0.050%, Zr: 0 to 0.050%, Ni: 0 It is a chemical component consisting of ⁇ 2.00%, Cu: 0 to 1.00%, Sn: 0 to 0.50%, Mg: 0 to 0.010%, Ca: 0 to 0.010%, and is a metal.
  • the structure has a pearlite structure of 95 area% or more, the average aspect ratio R of the pearlite block measured on the surface layer in the axial cross section including the axis of the steel wire is 2.0 or more, and the diameter of the steel wire is D.
  • R average aspect ratio measured on the surface layer
  • D average aspect ratio measured at the position of 0.25D
  • a high-strength steel wire having excellent hydrogen embrittlement resistance of 1800 MPa or more has been proposed.
  • Patent Document 3 in addition to containing C: 0.5 to 1.0%, one or more selected from the group consisting of Cu, Ni and Ti (provided that Cu and / or Ni is contained). It is characterized by being made of steel containing the following formula (1) so as to satisfy the following formula, having a pearlite structure area ratio of 80% or more, and having a strength of 1200 N / mm 2 or more. High-strength steel wire having excellent delayed fracture resistance and corrosion resistance has been proposed. 3.1 ⁇ 3 [Cu] + [Ni] + 6 [Ti] ⁇ 0.24 (%)... (1) However, [Cu], [Ni] and [Ti] indicate the contents (mass%) of Cu, Ni and Ti, respectively.
  • Patent Document 4 C: 0.39 to 0.65%, Si: 1.5 to 2.5%, Mn: 0.15 to 1.2%, P: more than 0%, 0.015. % Or less, S: more than 0%, 0.015% or less, Al: 0.001 to 0.1%, Cu: 0.1 to 0.80%, Ni: 0.1 to 0.80%
  • the balance is iron and unavoidable impurities, the amount of non-diffusible hydrogen is 0.40 mass ppm or less, the area ratio of ferrite expressed as a percentage satisfies the following equation (1), and the total of bainite and martensite.
  • the pearlite fraction is 90% or more
  • the average spacing of pearlite lamellas is 150 to 300 nm
  • the standard deviation of the pearlite lamella spacing is 25 nm or less.
  • Fn1 3Si + Mn + 1.5Cr ... [1]
  • the element symbol in the formula [1] means the content (mass%) of each element.
  • Patent Document 1 International Publication No. 2018/012625
  • Patent Document 2 International Publication No. 2018/021574
  • Patent Document 3 Patent No. 4124590
  • Patent Document 4 Japanese Patent Application Laid-Open No. 2015-143391
  • Patent Document 5 Japanese Patent Application Laid-Open No. 2014-37592 Gazette
  • the present disclosure is a wire rod suitable as a material for high-strength steel wire that requires a high tensile strength (ultimate tensile strength) of 1700 MPa or more, has excellent corrosion resistance and hydrogen embrittlement resistance, and is a steel after wire drawing.
  • An object of the present invention is to provide a wire rod having excellent twisting characteristics, which is less likely to cause delamination in the wire.
  • the means for solving the above problems include the following aspects. ⁇ 1>
  • the chemical composition is mass%, C: 0.60 to 1.15%, Si: 0.01 to 1.80%, Mn: 0.20 to 0.90%, P: 0.015% or less, S: 0.015% or less, Al: 0.005 to 0.080%, N: 0.0015 to 0.0060%, Cu: 0.10 to 0.65%, Ni: 0.05 to less than 0.65%, Cr: 0 to 0.30%, Mo: 0 to 0.30%, Ti: 0 to 0.100%, Nb: 0 to 0.100%, V: 0 to 0.20%, Sn: 0 to 0.30%, B: 0 to 0.0050%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Zr: 0 to 0.100%, REM: 0-0.0200%, and balance: Fe and impurities,
  • it is a wire rod suitable as a material for high-strength steel wire that requires a high tensile strength of 1700 MPa or more, has excellent corrosion resistance and hydrogen embrittlement resistance, and is used in steel wire after wire drawing.
  • a wire rod having excellent twisting characteristics, which is less likely to cause lamination, is provided.
  • the numerical range represented by using “-” means a range including the numerical values before and after “-” as the lower limit value and the upper limit value.
  • the numerical range when "greater than” or “less than” is added to the numerical values before and after “to” means a range in which these numerical values are not included as the lower limit value or the upper limit value.
  • the upper limit value of a certain stepwise numerical range may be replaced with the upper limit value of another numerical range described stepwise, and a certain stepwise numerical value may be replaced.
  • the lower limit of the range may be replaced with the lower limit of the numerical range described in other steps.
  • the upper limit value or the lower limit value may be replaced with the value shown in the embodiment.
  • “%” indicating the content of a component (element) means “mass%”.
  • the content of C (carbon) may be referred to as "C amount”.
  • the content of other elements may be described in the same manner.
  • the "surface" of a wire rod or steel wire means an outer peripheral surface.
  • the "surface” of a sample collected by cutting a wire rod or a steel wire also means an outer peripheral surface.
  • the present inventors describe a wire rod suitable as a material for a high-strength steel wire that requires a high tensile strength of 1700 MPa or more (in the present disclosure, it is referred to as a “wire rod for high-strength steel wire”).
  • a wire rod for high-strength steel wire In some cases), various studies were conducted on the corrosion resistance, hydrogen brittleness resistance, and the effect of elements and metal structures on the twisting characteristics after wire drawing, and the findings (a) to (c) below were obtained.
  • a high-strength steel wire having a tensile strength of 1700 MPa or more is liable to cause delamination and is liable to break due to corrosion or hydrogen embrittlement.
  • corrosion resistance and hydrogen embrittlement resistance are considered by considering the range of chemical components of the raw material so that the twisting characteristics do not deteriorate.
  • the characteristics may be improved, and Cu: 0.10 to 0.65% and Ni: 0.05 to less than 0.65% are contained in a range satisfying [Cu]> [Ni], and the following formula ⁇ 1 Mn, Cr, Cu, and Ni may be contained within a range in which Y1 represented by> satisfies 1.70 ⁇ Y1 ⁇ 4.50.
  • Y1 3 x [Cr] + 5 x [Mn] + [Cu] + [Ni] ... ⁇ 1>
  • [Mn], [Cr], [Cu], and [Ni] in the above formula represent the content of each element in mass%.
  • High-strength steel wire is manufactured by drawing a wire rod.
  • a high-strength steel wire having a tensile strength of 1700 MPa or more tends to increase in temperature and heat generation due to frictional heat with a die in wire drawing, and is easily brittle due to the influence of strain aging. Due to strain aging, high-strength steel wire undergoes vertical cracks called delamination in the twist test, and the number of revolutions until fracture, that is, the twist value becomes small. Furthermore, while preventing breakage due to corrosion or hydrogen embrittlement of high-strength steel wire with a tensile strength of 1700 MPa or more, the effect of strain aging is minimized by wire drawing, and the twist value after wire drawing is improved.
  • C, Si, Ti, and N may be contained within a range in which Y2 represented by the following formula ⁇ 2> satisfies Y2 ⁇ 1.81.
  • Y2 [C] + [Si] / 10 + A ... ⁇ 2>
  • a 350 ⁇ ([N] ⁇ 0.29 ⁇ [Ti]) ⁇ ⁇ ⁇ ⁇ 4>
  • [C], [Si], [N], and [Ti] in the above formula represent the content of each element in mass%
  • A is related to a represented by the formula ⁇ 4>. It is a parameter.
  • the wire rod according to the present disclosure has been completed based on the above findings, and the chemical composition is mass%.
  • the chemical composition of the wire rod for high-strength steel wire according to the present disclosure is C: 0.60 to 1.15%, Si: 0.01 to 1.80%, Mn: 0.20 to 0.90 in mass%. %, P: 0.015% or less, S: 0.015% or less, Al: 0.005 to 0.080%, N: 0.0015 to 0.0060%, and further, [Cu]> Cu: 0.10 to 0.65% and Ni: 0.05 to less than 0.65% are contained within a range satisfying [Ni], and Cr: 0 to 0.30 is optionally contained.
  • C 0.60 to 1.15% C is contained to increase the tensile strength of the wire rod. If the amount of C is less than 0.60%, proeutectoid ferrite is generated, and the tensile strength required for high-strength steel wire cannot be secured. Therefore, the amount of C is set to 0.60% or more. From the viewpoint of ensuring excellent hydrogen embrittlement resistance and twisting characteristics, the amount of C is 0.67% or more in order to obtain high-strength steel wire without increasing the machining reduction rate of wire drawing too much. It is preferably 0.70% or more, more preferably 0.85% or more, and even more preferably 0.85% or more.
  • the amount of C exceeds 1.15%, the amount of pro-eutectoid cementite increases and the wire drawing workability deteriorates, which makes it difficult to obtain a high-strength steel wire and also deteriorates the twisting characteristics of the steel wire. to degrade. Therefore, the amount of C is often 1.10% or less, and more preferably 1.05% or less.
  • Si 0.01 to 1.80% Si has the effect of increasing the tensile strength by strengthening the solid solution, and has the effect of enhancing the hydrogen embrittlement resistance. If the amount of Si is less than 0.01%, these effects cannot be obtained. Therefore, the amount of Si should be 0.01% or more. In order to surely obtain these effects, the amount of Si is preferably 0.21% or more, and more preferably 0.70% or more. However, if the amount of Si exceeds 1.80%, these effects are saturated and the hot ductility is deteriorated, so that surface defects are likely to occur at the stage of rolling the wire rod, and the manufacturability is lowered. In addition, the twisting characteristics of the high-strength steel wire after wire drawing are deteriorated. Therefore, the amount of Si is preferably 1.49% or less, and more preferably 1.35% or less.
  • Mn 0.20 to 0.90% Mn has the effect of increasing the hardenability of steel and increasing the tensile strength of steel after pearlite transformation. If the amount of Mn is less than 0.20%, the above effect cannot be sufficiently obtained. Therefore, the amount of Mn is set to 0.20% or more. In order to surely obtain these effects, the amount of Mn is preferably 0.30% or more, and more preferably 0.35% or more. On the other hand, when the amount of Mn exceeds 0.90%, the hardenability of the steel becomes too high, the above effect is saturated, the ductility of the wire rod decreases, and the twisting characteristics of the high-strength steel wire obtained after the wire drawing process. Deteriorates. Therefore, the amount of Mn is preferably 0.80% or less, and more preferably 0.75% or less.
  • P 0.015% or less P is contained as an impurity. Since P segregates at the grain boundaries and deteriorates the hydrogen embrittlement resistance and the wire drawing workability, it is desirable that the amount of P is low. Therefore, the upper limit of the amount of P is 0.015%.
  • the preferred range of the amount of P is 0.012% or less, more preferably 0.010% or less.
  • the lower limit of the amount of P is not particularly limited, but may exceed 0%, and may be 0.0001% or more from the viewpoint of reducing steelmaking costs, for example.
  • S 0.015% or less S is contained as an impurity. Since S segregates at the grain boundaries to deteriorate the hydrogen embrittlement resistance and the wire drawing workability, it is necessary to suppress the amount of S. Therefore, the upper limit of the amount of S is 0.015%.
  • the preferable range of the amount of S is 0.012% or less, and the more preferable range is 0.010% or less.
  • the lower limit of the amount of S is not particularly limited, but may exceed 0%, and may be 0.0001% or more from the viewpoint of reducing desulfurization cost, for example.
  • Al 0.005 to 0.080%
  • Al is a deoxidizing element, and when the amount of Al is less than 0.005%, the oxide becomes coarse and becomes a starting point of cracking due to hydrogen embrittlement, so that the hydrogen embrittlement resistance property of the wire rod is deteriorated. Therefore, the amount of Al is set to 0.005% or more. In order to surely obtain the above effect, the Al amount is preferably 0.008% or more, and more preferably 0.010% or more. However, when the amount of Al exceeds 0.080%, the above effect is saturated, the oxides and nitrides containing Al become coarse, surface defects occur during rolling, and the manufacturability of the wire rod is lowered. On the contrary, it lowers the hydrogen embrittlement resistance. Therefore, the amount of Al is often 0.060% or less, and more preferably 0.050% or less.
  • N 0.0015 to 0.0060% N reacts with an alloying element such as Ti in steel to form nitrides and carbonitrides to refine the crystal grains of the wire rod, which has an effect of improving ductility. Therefore, the amount of N should be 0.0015% or more. In order to surely obtain the above effect, the amount of N is preferably 0.0021% or more, and more preferably 0.0025% or more. On the other hand, when manufacturing high-strength steel wire by wire drawing, N dissolved in the steel greatly affects the strain aging and the twisting characteristics deteriorate, so care must be taken in the content, and the N amount is Must be 0.0060% or less. The amount of N is preferably 0.0049% or less, and more preferably 0.0040% or less.
  • Cu 0.10 to 0.65%
  • Cu is an important element having an effect of improving the corrosion resistance and hydrogen embrittlement resistance of the wire rod for high-strength steel wire according to the present disclosure, and contains 0.10% or more. Since Cu exists as a solid solution in the pearlite structure, it has the effect of improving the corrosion resistance and hydrogen embrittlement resistance of the wire rod. If Cu is less than 0.10%, the above effect cannot be obtained, so the amount of Cu is set to 0.10% or more. In order to surely obtain the above effect, the amount of Cu is preferably 0.15% or more, and more preferably 0.20% or more.
  • the amount of Cu is preferably 0.65% or less, preferably 0.60% or less, and more preferably 0.50% or less.
  • Ni 0.05 to less than 0.65%
  • Ni is an essential element for suppressing surface defects during rolling when manufacturing a wire rod containing Cu, and has the effect of improving the hardenability of the wire rod. ..
  • excessive content induces cracking during wire drawing and deteriorates hydrogen embrittlement resistance.
  • Ni is contained in an amount of 0.05% or more. If Ni is less than 0.05%, surface defects occur on the surface of the wire during rolling, which causes disconnection during wire drawing and deteriorates the hydrogen embrittlement resistance of the wire.
  • the amount of Ni is preferably 0.10% or more, and more preferably 0.15% or more.
  • the amount of Ni is 0.65% or more, the hardenability becomes too high, and the hydrogen embrittlement resistance is deteriorated. Therefore, the amount of Ni is preferably less than 0.65%, preferably 0.60% or less, and even more preferably 0.50% or less.
  • the high-strength steel wire after wire drawing in the present disclosure by containing Cu and Ni in a range satisfying [Cu]> [Ni], that is, [Cu] / [Ni]> 1.00, the high-strength steel wire after wire drawing in the present disclosure. Good twisting characteristics can be ensured.
  • [Cu] / [Ni] is 1.00 or less, that is, the content of Ni is equal to or more than the content of Cu, the wire rod for high-strength steel wire according to the present disclosure has too high hardenability, so that the wire is drawn. Sufficient twisting characteristics cannot be ensured with processed high-strength steel wire. Therefore, Cu and Ni must contain [Cu]> [Ni] in a satisfactory range.
  • [Cu] / [Ni] is preferably 1.20 or more, and more preferably 1.50 or more.
  • Cu and Ni may satisfy [Cu]> [Ni], and the upper limit is not limited to [Cu] / [Ni], but if it is too high, surface defects may occur in the hot rolling process of the wire rod.
  • the manufacturability of the wire rod is reduced due to the occurrence. Therefore, in consideration of the manufacturability of the wire rod, [Cu] / [Ni] is preferably 5 or less, and more preferably 4 or less.
  • the wire rod for high-strength steel wire contains one or more of each element of Cr, Mo, Ti, Nb, V, Sn, B, Ca, Mg, Zr, and REM as an optional element. You may. When these arbitrary elements are contained, Cr: 0 to 0.30%, Mo: 0 to 0.30%, Ti: 0 to 0.100%, Nb: 0 to 0.100%, V in mass%. : 0 to 0.20%, Sn: 0 to 0.30%, B: 0 to 0.0050%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Zr: 0 to 0. It may contain one or more of 100% and REM: 0 to 0.0200%.
  • Cr 0 to 0.30% Cr has the effect of enhancing the hardenability of the wire rod and increasing the tensile strength of the wire rod after the pearlite transformation, and may be contained when this effect is desired.
  • the amount of Cr is preferably 0.01% or more.
  • the amount of Cr is preferably 0.05% or more, and more preferably 0.10% or more.
  • the amount of Cr is preferably 0.30% or less, preferably 0.25% or less, and even more preferably 0.20% or less.
  • Mo 0 to 0.30%
  • Mo has the effect of enhancing the hardenability of the wire rod and increasing the tensile strength of the wire rod after the pearlite transformation, and may be contained when this effect is desired.
  • the amount of Mo is preferably 0.01% or more.
  • the amount of Mo is preferably 0.03% or more, and more preferably 0.05% or more.
  • the amount of Mo is preferably 0.30% or less, preferably 0.20% or less, and even more preferably 0.10% or less.
  • Ti 0 to 0.100% Ti has the effect of combining with C or N to precipitate carbides or carbonitrides and finely graining the crystal grains to improve the ductility of the wire rod, and improves the hydrogen embrittlement resistance and twisting characteristics after wire drawing. It has the effect of improving. Further, since the solid solution N can be reduced by containing Ti, there is also an effect of suppressing strain aging and improving the twisting characteristics of the steel wire after wire drawing. Since the above effect due to the inclusion of Ti is effective in obtaining the wire rod for high-strength steel wire according to the present disclosure, Ti may be positively contained. In order to obtain these effects, Ti may be contained in an amount of 0.002% or more.
  • the amount of Ti is preferably 0.005% or more, and more preferably 0.008% or more.
  • the amount of Ti is preferably 0.10% or less, preferably 0.050% or less, and more preferably 0.025% or less.
  • Nb 0 to 0.100%
  • Nb has the effect of precipitating carbides or carbonitrides and finely graining the crystal grains to improve the ductility of the wire rod, and has the effect of improving the hydrogen embrittlement resistance and twisting characteristics after wire drawing.
  • the amount of Nb is preferably 0.005% or more, and more preferably 0.008% or more.
  • the amount of Nb is preferably 0.100% or less, preferably 0.050% or less, and even more preferably 0.025% or less.
  • V 0 to 0.20%
  • V has the effect of precipitating carbide VC to increase the tensile strength and the hydrogen embrittlement resistance, and may be contained when it is desired to obtain this effect. In order to obtain this effect, it is preferable that V is contained in an amount of 0.01% or more. In order to surely obtain the above effect, the amount of V is preferably 0.03% or more, and more preferably 0.05% or more. However, even if V is contained in excess of 0.20%, not only the above effect is saturated, but also the hydrogen embrittlement resistance and twisting characteristics of the steel wire after wire drawing are deteriorated. Therefore, when V is contained, the amount of V is preferably 0.20% or less, preferably 0.15% or less, and even more preferably 0.10% or less.
  • Sn 0 to 0.30%
  • Sn has an effect of enhancing corrosion resistance and hydrogen embrittlement resistance by being dissolved in a pearlite structure, and may be contained when it is desired to obtain this effect.
  • Sn is preferably contained in an amount of 0.01% or more.
  • the Sn amount is preferably 0.03% or more, and more preferably 0.05% or more.
  • the Sn amount is preferably 0.01 to 0.30%. Therefore, when Sn is contained, the Sn amount is preferably 0.30% or less, preferably 0.20% or less, and even more preferably 0.15% or less.
  • B 0 to 0.0050%
  • B has the effect of increasing the pearlite structure fraction after isothermal transformation and improving the twisting characteristics of the high-strength steel wire after wire drawing, and may be contained when this effect is desired.
  • B is preferably contained in an amount of 0.0002% or more.
  • the amount of B is preferably 0.0005% or more, and more preferably 0.0007% or more.
  • B is contained in an amount of more than 0.0050%, not only the above effect is saturated, but also the wire rod is embrittled, surface defects occur during rolling, the manufacturability is deteriorated, and the wire drawing is performed.
  • the amount of B is preferably 0.0050% or less, preferably 0.0030% or less, and even more preferably 0.0020% or less.
  • Ca 0 to 0.0050%
  • Ca has an effect of being solid-solved in MnS and finely dispersing MnS, and has an effect of improving hydrogen embrittlement resistance. Therefore, Ca may be contained when an effect is desired. Ca may not be contained (Ca: 0%), but in order to obtain the effect of improving the hydrogen embrittlement resistance by Ca, it is sufficient that Ca is contained in an amount of 0.0002% or more, which is more effective. If it is desired to obtain it, it may contain 0.0005% or more. However, even if the Ca content exceeds 0.0050%, the effect is saturated, the oxide produced by reacting with oxygen in the steel becomes coarse, and the twisting characteristics after wire drawing are deteriorated. Invite. Therefore, the appropriate amount of Ca to be contained is 0.0050% or less. From the viewpoint of improving the hydrogen embrittlement resistance and the twisting property, the Ca amount is preferably 0.0030% or less, and more preferably 0.0025% or less.
  • Mg 0 to 0.0050%
  • Mg has an effect of being dissolved in MnS and finely dispersing MnS, and has an effect of improving hydrogen embrittlement resistance. Therefore, Mg may be contained when an effect is desired. Although it is not necessary to contain Mg (Mg: 0%), in order to obtain the effect of improving the hydrogen embrittlement resistance by Mg, it is sufficient to contain Mg in an amount of 0.0002% or more, which is more effective. If it is desired to obtain it, it may contain 0.0005% or more. However, even if the amount of Mg exceeds 0.0050%, the effect is saturated, the oxide produced by reacting with oxygen in the steel becomes coarse, and the twisting characteristics after wire drawing are deteriorated. Invite. Therefore, the appropriate amount of Mg when contained is 0.0050% or less. From the viewpoint of improving hydrogen embrittlement resistance and twisting characteristics, the amount of Mg is preferably 0.0030% or less, and more preferably 0.0025% or less.
  • Zr 0 to 0.100% Zr reacts with O to form an oxide, and if it is contained in a small amount, it finely disperses the oxide and has the effect of suppressing hydrogen embrittlement resistance and twisting characteristics after wire drawing, and the effect thereof. It may be contained when it is desired to obtain. In order to obtain this effect, Zr may be contained in an amount of 0.0002% or more, and when a higher effect is desired, it may be contained in an amount of 0.001% or more. However, when the Zr content exceeds 0.10%, the effect is saturated and coarse nitrides or sulfides are produced. Therefore, the hydrogen embrittlement resistance after wire drawing is obtained and the hydrogen embrittlement resistance is increased. It causes deterioration of twisting characteristics.
  • the content of Zr when contained is 0.100% or less.
  • the Zr content is preferably 0.080% or less, preferably 0.050% or less, from the viewpoint of reducing inclusions that adversely affect the hydrogen embrittlement resistance and twisting characteristics after wire drawing. More preferred.
  • REM 0-0.0200% REM is a general term for rare earth elements, and the content of REM is the total content of rare earth elements. Like Ca and Mg, REM dissolves in MnS and has the effect of finely dispersing MnS. Since MnS can be finely dispersed to improve hydrogen embrittlement resistance, it may be contained. REM may not be contained (REM: 0%), but in order to obtain the effect of improving hydrogen embrittlement resistance by REM, 0.0002% or more of REM may be contained, and a higher effect can be obtained. If it is desired to obtain it, it may contain 0.0005% or more.
  • the appropriate amount of REM when contained is 0.0200% or less.
  • the REM amount is preferably 0.0100% or less, and more preferably 0.0050% or less.
  • Residue Fe and impurities
  • the balance is Fe and impurities.
  • the “impurity” is a component unintentionally contained in a steel material, and refers to a component mixed from ore, scrap, or a manufacturing environment as a raw material when a steel material is industrially manufactured.
  • impurities include P, S, N, elements unintentionally contained in the steel material among the above optional elements, and O (oxygen) and the like.
  • O (oxygen) is preferably 0.0030% or less because if it is contained in a large amount, the oxide formed in the steel becomes coarse and the twisting characteristics after wire drawing are deteriorated. Is preferably 0.0025% or less.
  • the wire rod for high-strength steel wire contains each component in the above range, and Y1 represented by the following formula ⁇ 1> is represented by 1.70 ⁇ Y1 ⁇ 4.50 and formula ⁇ 2>.
  • Y2 satisfies Y2 ⁇ 1.81.
  • Y1 3 x [Cr] + 5 x [Mn] + [Cu] + [Ni] ... ⁇ 1>
  • Y2 [C] + [Si] / 10 + A ...
  • ⁇ 2> a 350 ⁇ ([N] ⁇ 0.29 ⁇ [Ti]) ⁇ ⁇ ⁇ ⁇ 4>
  • [C], [Si], [Mn], [Cr], [Cu], [Ni], [N], and [Ti] in the above formula are the contents of each element in mass%.
  • Cr and Ti are optional elements, and when these optional elements are not substantially contained in the wire rod according to the present disclosure (no addition, that is, at the impurity level), the case is considered.
  • the element content is set to "0", and Y1, Y2, and a are calculated respectively.
  • Y1 is mainly related to the hardenability of the wire rod for high-strength steel wire, and is a parameter necessary for increasing the tensile strength of the wire rod and improving the hydrogen embrittlement resistance. Further, by setting Y1 in the range of 1.70 ⁇ Y1 ⁇ 4.50, the hydrogen embrittlement resistance of the wire rod for high-strength steel wire can be improved, and the hydrogen embrittlement resistance of the high-strength steel wire after wire drawing is improved. The embrittlement characteristics can be improved.
  • High-strength steel wire can be obtained by wire drawing a wire rod whose chemical composition and metal structure are appropriately controlled. Before the wire drawing process, the wire rod is reheated for a patenting process, or after rolling, it is directly immersed in a salt bath furnace for an isothermal transformation process to obtain a fine pearlite structure with high uniformity up to the center. It is preferable to do so.
  • Y1 is a parameter necessary for controlling the hardenability of the wire rod, giving the strength required for a fine pearlite structure having high uniformity from the surface to the center, and improving the hydrogen embrittlement resistance of the wire rod. It must be 1.70 or more and 4.50 or less.
  • Y1 is preferably 2.00 or more, and more preferably 2.50 or more.
  • Y1 exceeds 4.50, a non-pearlite structure other than the pearlite structure such as bainite and martensite is formed after the patenting treatment or the isothermal transformation treatment after rolling, and the hydrogen embrittlement resistance of the wire rod is rather deteriorated.
  • Y1 is 4.50 or less, preferably 4.22 or less.
  • Y1 may be set to 4.00 or less, and more preferably 3.75 or less.
  • Y2 is a parameter that mainly affects the twisting characteristics of the steel wire after wire drawing.
  • the wire rod for high-strength steel wire according to the present disclosure contains Cu and Ni in order to improve corrosion resistance and hydrogen embrittlement resistance, and since the tensile strength of the wire rod is relatively high, it is a die for wire drawing. Due to the temperature rise due to frictional heat with the steel wire, it tends to become brittle due to the influence of strain aging, and the twisting characteristics of the steel wire after wire drawing are likely to deteriorate. In particular, since C, Si, and N dissolved in steel have a great influence on the strain aging due to wire drawing, Y2 can be expressed as the following formula ⁇ 2>.
  • [C], [Si], [N], and [Ti] in the above formula represent the content of each element in mass%
  • A is related to a represented by the formula ⁇ 4>. It is a parameter.
  • the value of Y2 is set to less than 1.81 in order to minimize the influence of strain aging in wire drawing.
  • the value of Y2 is preferably less than 1.70, and even more preferably less than 1.50.
  • the value of Y2 may be less than 1.81 and the lower limit is not particularly limited, but from the viewpoint of ensuring the tensile strength after wire drawing, it is preferably 0.50 or more, and 0.80 or more. If there is, it is more preferable.
  • the metal structure of the wire rod for high-strength steel wire according to the present disclosure occupies 90% or more of the pearlite structure which is a layered structure of ferrite and cementite. This is the stage of patenting or isothermal transformation of the wire, and ferrite, bainite, or martensite may be formed due to changes in chemical composition, ⁇ particle size before transformation, or cooling rate, and these structures Increases the variation in surface hardness of the wire rod in the longitudinal direction, and lowers the hydrogen embrittlement resistance property of the wire rod. When the variation in surface hardness in the longitudinal direction of the wire is large, the hydrogen embrittlement resistance and twisting characteristics of the steel wire after wire drawing are deteriorated.
  • the metal structure of the wire rod for high-strength steel wire according to the present disclosure preferably has a pearlite structure of 92% or more, and more preferably 95% or more.
  • the residual structure (non-pearlite structure) other than the pearlite structure include martensite, bainite, proeutectoid ferrite, and proeutectoid cementite.
  • the non-pearlite structure proeutectoid ferrite and pseudo-pearlite are preferable, and pseudo-pearlite is more preferable, from the viewpoint of not extremely deteriorating the twisting property and hydrogen embrittlement resistance of the steel wire after wire drawing.
  • the pearlite structure refers to pearlite that maintains a lamellar structure, and pseudo-pearlite with a collapsed lamellar structure is treated as a non-pearlite structure in the present disclosure.
  • the variation in hardness of the surface layer of the wire due to the variation in the chemical composition or metal structure that occurs in the longitudinal direction of the wire also affects the hydrogen embrittlement resistance and the characteristics of the steel wire after wire drawing.
  • the hydrogen embrittlement resistance is affected by the variation in hardness of the wire surface layer, and if there is a portion having high hardness on the wire surface layer, it becomes the starting point of hydrogen embrittlement, so that the hydrogen embrittlement resistance deteriorates.
  • the depth is 50 ⁇ m from the surface of the wire rod in the axial cross section (cross section parallel to the longitudinal direction including the central axis) of each sample (hereinafter, , "50 ⁇ m depth"), so that the relationship between the maximum value Hv simax of the Vickers hardness Hv si and the average value Hv siave satisfies the following (4).
  • the "surface layer" of the wire rod is a region from the surface (outer peripheral surface) of the wire rod to a depth of 100 ⁇ m, and the hardness is measured at a depth of 50 ⁇ m at an intermediate point of the surface layer.
  • Samples for measuring Vickers hardness are taken at arbitrary equal intervals according to the length of the wire to be measured. Since the wire rod is usually manufactured in a state of being wound in a ring shape, if the wire rod has a length corresponding to one ring or more, eight samples are collected at equal intervals from the length corresponding to one ring. It is preferable to measure the Vickers hardness of each sample and obtain the average value and the maximum value of the Vickers hardness of each sample.
  • the axial cross section (i is an integer of 1 to 8) is measured in each sample.
  • the average value of Vickers hardness in each sample at a depth of 50 ⁇ m from the surface of the wire rod in the longitudinal direction including the central axis is Hv si , and 8 Hv si (i is an integer of 1 to 8).
  • the Hv si of each sample uses a sample in which the axial cross section is resin-filled from the wire and mirror-polished, and the position at a depth of 50 ⁇ m from the surface of the wire in the axial cross section with an automatic Vickers hardness tester is 1 with a load of 0.98 N. It may be obtained by measuring 50 points (that is, 10 mm length) at a pitch of 200 ⁇ m per sample.
  • Hv Simax the maximum value, among the eight samples of 25mm length taken apart 600 mm, depth 50 ⁇ m from the surface of the wire rod in the axial section
  • Hydrogen embrittlement of the wire is affected by variations in the hardness of the surface layer of the wire, and the portion where the hardness of the surface layer of the wire is locally high becomes the starting point of fracture, and fracture due to hydrogen embrittlement occurs.
  • the Hv simax measured in 8 samples is higher than the overall average Vickers hardness at the 50 ⁇ m depth position including other samples by more than 50, the possibility of breakage due to hydrogen embrittlement increases at that site, and the wire rod Hydrogen embrittlement resistance is reduced. Further, in the steel wire obtained by wire drawing the wire rod, the variation in surface hardness in the longitudinal direction becomes larger, and the decrease in hydrogen embrittlement resistance of the steel wire becomes more remarkable.
  • the value of Y3 is 50 or less, the deterioration of the hydrogen embrittlement resistance property of the wire rod is suppressed, and further, the deterioration of the hydrogen embrittlement resistance property of the steel wire obtained by the wire drawing process is also suppressed.
  • the value of Y3 is preferably as small as possible from the viewpoint of improving the hydrogen embrittlement resistance property, preferably 30 or less, and even more preferably 25 or less.
  • the number of 25 mm long samples collected at intervals of 600 mm from the longitudinal direction of the wire is eight. That is, if the average value Hv si of the Vickers hardness in each sample at a position of 50 ⁇ m from the surface of the wire rod in the axial cross section of the eight samples is obtained, the hardness variation of the wire rod surface layer can be known.
  • the variation in hardness of the wire rod surface layer it is preferable to investigate the variation in surface layer hardness within a range corresponding to at least one ring of the wire rod coil rolled up. This is because the wire rod ring wound up in the austenite region after hot rolling is conveyed on the conveyor with a part of it overlapping the front and rear rings, so the parts or distances in contact within one ring.
  • the variation in surface hardness was verified within a range of approximately 4200 mm in the longitudinal direction of the wire, and the length was equivalent to one ring or more of the wire coil. Variations in surface hardness can be verified. Since the variation between the rings is small as described above, the variation in the wire coil can be verified by the above sampling method.
  • the length of the wire rod according to the present disclosure and the length of one ring at the time of manufacture are not particularly limited, and the interval for collecting a sample from the wire rod is not limited to 600 mm.
  • the wire rod according to the present disclosure may satisfy the characteristics by satisfying Hv simax- Hv siave ⁇ 50 regardless of the length and the interval at which samples for measuring Vickers hardness are taken. it can. In the actual production of the wire rod, there is a variation in the length direction of the wire rod. Therefore, if the manufacturing method is appropriately adjusted, a wire rod with reduced variation in the length direction of the wire rod can be obtained.
  • the characteristics can be confirmed in the length direction of the wire coil by performing the Vickers hardness test at intervals of 600 mm. If the length of one ring is not 4200 mm, eight samples are taken at equal intervals from the length corresponding to one ring, the Vickers hardness Hv si of each sample is measured, and the maximum value Hv simax maximum value is measured. The Vickers hardness in the length direction of the wire rod coil can be confirmed by calculating the difference between the average value Hv hybrid and the average value Hv hybrid .
  • the length of the wire is less than one ring, eight samples are taken at equal intervals from the whole, and the Vickers hardness Hv si of each sample is measured, and the maximum value Hv simax and the average value Hv siave are measured . It is preferable to calculate the difference.
  • the tensile strength of the wire rod before wire drawing is 1000 MPa or more and to manufacture a high-strength steel wire without excessively increasing the processing surface reduction rate of wire drawing. If the fine pearlite structure has a tensile strength of 1000 MPa or more at the wire rod stage, deterioration of the tensile strength and hydrogen embrittlement resistance of the steel wire after wire drawing is suppressed. In order to improve the twisting property and the hydrogen embrittlement resistance of the steel wire, it is more preferable that the tensile strength of the wire is 1200 MPa or more, and further preferably 1300 MPa or more.
  • the tensile strength of the wire rod exceeds 1650 MPa, the ductility of the wire rod is lowered, and the twisting characteristics and hydrogen embrittlement resistance of the steel wire after the wire drawing process may be lowered.
  • the tensile strength of the wire is preferably 1600 MPa or less, and more preferably 1550 MPa or less.
  • the high-strength steel wire rod according to the present disclosure By wire drawing using the high-strength steel wire rod according to the present disclosure, it is possible to obtain a high-strength steel wire having excellent corrosion resistance and hydrogen embrittlement resistance even at a high strength exceeding 1700 MPa. This is because the segregation of chemical components, the metal structure, and the hardness distribution of the surface layer of the wire are controlled at the stage of manufacturing the wire to improve the corrosion resistance and the hydrogen embrittlement resistance.
  • the wire rod according to the present disclosure has excellent corrosion resistance and hydrogen embrittlement resistance, and also has excellent twisting characteristics in steel wire after wire drawing. Therefore, the strength is increased by wire drawing and steel for high-strength rope. It can be used as high-strength steel wire such as wire, steel wire for bridge cables, and PC steel wire.
  • ⁇ Measurement method> The metallographic structure of the wire, the tensile strength of the wire and the steel wire, the variation in the surface hardness of the wire, the corrosion resistance of the wire, the hydrogen embrittlement resistance of the wire and the steel wire, and the twisting property of the steel wire are investigated by the following methods. did.
  • Metal structure of wire rod The area ratio of the metal structure of the wire was parallel to the longitudinal direction of the wire, and after mirror polishing a microsample in which the cross section passing through the central axis was embedded with resin, the metal structure was revealed using a picral solution. Next, when the diameter of the wire is D, the metal structure of the part corresponding to the position at a depth of 0.25D from the surface of the wire is measured at 10 points at a magnification of 1000 times using a scanning electron microscope (SEM). A tissue photograph was taken.
  • SEM scanning electron microscope
  • the structure other than the pearlite structure is a non-pearlite structure that cannot be distinguished as a pearlite structure, which is a layered structure of cementite and ferrite, such as partially formed martensite, bainite, and proeutectoid ferrite.
  • Corrosion resistance of wire rod Two ⁇ 7 ⁇ 100 mmL test pieces machined to a diameter of 7 mm were cut out by evenly cutting the outer peripheral portion of the test piece cut with a length of 100 mm from the central axial direction of the wire rod.
  • a dry and wet repeated corrosion tester capable of spraying salt water was used, (1) salt water spray (5% NaCl spray, 35 ° C, 2 hr), (2) drying (humidity 20%, 60 ° C, 4 hr), ( 3)
  • a test was conducted in which wetness (humidity 95%, 50 ° C., 2 hr) was used as one cycle.
  • the test period was 12 weeks, and the volume reduction rate due to corrosion of each of the two test pieces was determined, and the average value was used as an evaluation index of the corrosion resistance of each wire rod.
  • the test piece volume before corrosion test is the position before the test. The average value of the diameter of the test piece and the length of the test piece measured at three points was obtained, and the volume of the test piece before the corrosion test was calculated.
  • the volume of the test piece after the corrosion test is the average value of the diameter of the test piece and the length of the test piece measured at three points after completely removing the corrosion products on the surface of the test piece using sandblasting after the corrosion test. The volume of the test piece after the corrosion test was calculated.
  • Hydrogen embrittlement resistance of wire rods and steel wires The hydrogen embrittlement resistance properties of the wire and the steel wire after wire drawing were evaluated by the FIP test standardized by the International Federation of Prestressed Concrete (Federation International de la Precontrainte). After pickling the wire or the steel wire after wire drawing to remove the scale or lubricating film on the surface, straightening is performed to ensure straightness, and a sample cut to a length of 700 mm L is used as a test piece. There was.
  • the test piece was immersed in an aqueous solution of ammonium thiocyanate (NH 4 SCN) at 50 ° C., and the breaking load of 70 obtained from the tensile test was obtained. A constant load of% was applied to the test piece, and the time until fracture was measured. The upper limit of the breaking time was 200 hours.
  • the test was carried out on each wire rod or 6 test pieces collected from each steel wire, the average value of the breaking time was calculated, and the hydrogen embrittlement resistance property of the wire rod and the steel wire was evaluated.
  • Twisting characteristics of steel wire are such that the steel wire is cut so that the twisting test can be performed with a length 100 times the diameter of the steel wire, and after straightening, 15 rotations per minute.
  • a twisting test was conducted in which the steel wire was twisted until the wire was broken at the speed of. For the occurrence of delamination, the torque curve at the time of twisting was measured, and it was determined that delamination occurred when the torque decreased by 20% or more before the disconnection occurred.
  • the twisting test was performed for each steel wire by five, and when no delamination occurred, it was judged that the twisting characteristics were good.
  • the wire rod for high-strength steel wire according to the present disclosure can obtain the effect of the steel wire of the present disclosure regardless of the manufacturing method of the wire rod if the requirements of the present disclosure are satisfied, but for example, the manufacturing method shown below can be used.
  • Wire rods may be manufactured, and high-strength steel wires may be manufactured using them as raw materials.
  • the following manufacturing process is an example, and even if a wire rod whose chemical composition and other requirements are within the scope of the present disclosure is obtained by a process other than the following, the wire rod is included in the wire rod according to the present disclosure. Is done.
  • the wire rod for high-strength steel wire is generated in the longitudinal direction of the wire rod by adjusting the chemical composition at the stage of melting the steel and controlling the manufacturing conditions such as the heating condition of the slab and the heating temperature at the time of rolling. It is preferable to reduce the segregation of chemical components or control the pearlite structure with high uniformity. Specifically, steel ingots or slabs in which chemical components such as C, Si, Mn, Cu, Ni, and Al are adjusted and melted and cast by a converter or an electric furnace are subjected to a slab-rolling process. After that, it is used as a steel piece as a material for rolling products.
  • the heat treatment is performed at 1260 ° C. or higher for 12 hr or more. After that, the steel piece is reheated and the product is rolled hot, and finally finished as a wire rod having a predetermined diameter.
  • the steel pieces obtained by block rolling are reheated and heated to 1000 ° C. or higher.
  • the heating at this time may be 1150 ° C. or lower, preferably 1130 ° C. or lower, in order to suppress coarsening and mixing of austenite grains.
  • the holding time after reaching the heating temperature is preferably less than 90 minutes in order to suppress the mixing of austenite particles.
  • the steel pieces heated under the above conditions are roughly rolled and then finish-rolled to obtain a wire rod having a diameter of 5.0 to 16.0 mm.
  • the temperature of finish rolling is adjusted in the range of 850 ° C. to 950 ° C. If the temperature is lower than 850 ° C, the austenite grains become too fine and the pearlite transformation becomes non-uniform. If the temperature exceeds 950 ° C, it becomes difficult to control the austenite grains in the subsequent cooling process, and the hardness variation of the wire surface layer becomes large. Then, the steel material after hot rolling is held at a temperature not lower than 800 ° C. for 15 seconds or more to adjust the austenite grains.
  • the molten salt held at a temperature of 500 to 580 ° C. may be directly immersed to transform the pearlite structure into an isothermal structure, and then cooled.
  • the hot rolled steel was cooled to about room temperature air blast cooling, subjected to heating at a temperature in the austenite region of the three or more points A, immersed in the pearlite structure into molten lead held at a temperature of 500 ⁇ 600 ° C. It may be cooled after being isothermally transformed.
  • the wire rod obtained by the above process may be used for wire drawing to obtain a steel wire having a required diameter.
  • the processing surface reduction rate of wire drawing may be determined according to the required diameter and strength of the steel wire, but if the processing surface reduction rate of wire drawing is excessively increased, the surface reduction rate after wire drawing may be determined.
  • the twisting characteristics and hydrogen embrittlement resistance of steel wire are deteriorated.
  • the processing reduction rate of wire drawing is preferably 70 to 92%. If the processing reduction rate is less than 70%, it is difficult to obtain the required tensile strength. On the other hand, when the processing reduction rate exceeds 92%, the twisting characteristics and hydrogen embrittlement resistance of the steel wire tend to deteriorate.
  • the method of wire drawing is not particularly limited, but in order to reduce the variation in hardness of the surface layer of the steel wire, the strain aging of the steel wire due to the heat generated during the wire drawing is suppressed, such as by cooling the steel wire with water after the wire drawing. It is preferable to use the method of Further, if necessary, after the wire drawing process, a step of heating the steel wire such as hot dip galvanizing, bluing, or heat stretching treatment may be performed.
  • the steels having the chemical components shown in Tables 1 and 2 were melted to prepare wire rods and steel wires by the following methods.
  • the notation of "-" in Tables 1 and 2 indicates that the content of the element is at the impurity level and it can be determined that the element is not substantially contained.
  • the values underlined in Tables 2 to 5 mean that they are outside the scope of the present disclosure or do not satisfy the above-mentioned manufacturing method (manufacturing conditions).
  • test No. 1 shown in Table 3 was used. a0, a1, a0-1 to a0-4, Test No. The wire rod was rolled according to the production conditions of b0, b1, b0-1 to b0-4.
  • Test No. A0-1 to a0-4 are steel Nos.
  • the slab of A0 was subjected to Test No. b0-1 to b0-4 are steel Nos.
  • the slabs were heated to 1280 ° C., heat-treated to hold them for 24 hours, and the steel slabs lump-rolled to 122 mm square were used as the rolling material.
  • the rolling conditions were changed as shown in Table 3 in order to separately produce wire rods having different tensile strength or surface hardness variation in the longitudinal direction even if the steel had the same composition.
  • the test No. In a0-1 and b0-1 the heating temperature at the time of rolling the wire rod was set to 1150 ° C. or higher, and Test No.
  • the holding time for heating during wire rolling was 90 minutes or more.
  • the finish rolling temperature of the wire rod was set to 850 ° C. or lower
  • the finish rolling temperature of wire rod rolling was 950 ° C. or higher.
  • each wire was drawn to produce a steel wire. Specifically, after pickling each wire rod to remove scale, a zinc phosphate film is formed on the surface by chemical conversion treatment in order to improve lubricity, and wire drawing is performed using a carbide die. went. For wire drawing, wire drawing is performed until the wire diameter reaches 5.2 mm with a path schedule adjusted so that the processing reduction rate of each die is around 20% (the wire drawing process under this condition is called "wire drawing process A". It may be referred to as). Next, the wire-drawn steel wire was immersed in a lead bath heated to 400 ° C. for 30 seconds and cooled with water.
  • Test No. For the wires a0, a0-1, and a0-4, the surface hardness was measured for each of the eight samples collected at arbitrary positions with a length of 25 mm at intervals of 50 mm in the longitudinal direction of the wires. The results are shown in Table 4B. Items other than the surface hardness of the wire rod in Table 4B are the same as those in Table 4A.
  • each of the steel pieces was heated at a heating temperature aimed at 1080 ° C. for 60 minutes, and then rolled into a wire rod having a wire diameter of 8.0 to 12.5 mm.
  • the finish rolling temperature was aimed at 900 ° C., and the material was wound around a wire coil.
  • the wound wire coil was directly immersed in a molten salt bath kept at 550 ° C. for isothermal transformation treatment, and water-cooled to 300 ° C. or lower to obtain a wire rod.
  • Each wire was drawn to produce a steel wire.
  • the wire drawing process was performed by the same method as the wire drawing process A described above so as to obtain a steel wire having a wire diameter of 3.8 to 5.2 mm.
  • the wire-drawn steel wire was immersed in a lead bath heated to 400 ° C. for 30 seconds and cooled with water.
  • FIG. 1 shows the relationship between the tensile strength of the wire rod and the FIP breaking time, which is an index of hydrogen embrittlement resistance, obtained in the examples of the present disclosure.
  • FIG. 2 shows the relationship between the tensile strength of the steel wire after wire drawing and the FIP fracture time, which is an index of hydrogen embrittlement resistance, obtained in the examples of the present disclosure.
  • Test No. which is an example of the present disclosure. Since a0 and b0 satisfy the chemical composition and other requirements in the present disclosure and the manufacturing conditions of the wire rod are appropriate, the corrosion volume reduction rate, which is an evaluation index of the corrosion resistance of the wire rod, is less than 25%, and the resistance to corrosion is less than 25%. A wire rod having a breaking time of 100 hr or more and excellent corrosion resistance and hydrogen embrittlement resistance of FIP, which is an index of hydrogen embrittlement characteristics, has been obtained. Furthermore, the test No.
  • the steel wire after wire drawing obtained in a0 and b0 also has a tensile strength of 1700 MPa or more, a FIP breaking time of 30 hr or more, no delamination in the twisting test, and hydrogen embrittlement resistance.
  • a steel wire with excellent chemical properties has been obtained.
  • the Vickers hardness in the surface layer portion is not limited to the case where samples are collected and measured at intervals of 600 mm assuming the length of one ring, and even when samples are collected and measured at intervals of 50 mm, "Hv" is obtained. It can be seen that it is effective if the relationship of " simax- Hv siave ⁇ 50" is satisfied.
  • test No. a1 and test No. A0-1 to a0-4 are test numbers, respectively. Steel A1 having almost the same chemical composition as a0 or steel No. having the same chemical composition. A0 was used, and Test No. b1 and test No. Each of b0-1 to b0-4 has a test No. Steel No. which has almost the same chemical composition as b0. B1 or steel No. which has the same chemical composition.
  • the wire rod was rolled using B0, the variation in surface hardness or the area ratio of the pearlite structure did not satisfy the requirements of the present disclosure because the production conditions of the wire rod were not appropriate. Therefore, the hydrogen embrittlement resistance of the wire is inferior, and the hydrogen embrittlement resistance of the steel wire after wire drawing is inferior.
  • the test No. a0-1 to a0-4 Test No. In b0-1 to b0-4, delamination occurs in the twisting test of the steel wire after the wire drawing process, and the twisting characteristics are also inferior.
  • Test No. which is an example of the present disclosure. Since all of c1 to c24 satisfy the chemical composition and the requirements of the present disclosure and the manufacturing conditions of the steel material are appropriate, the tensile strength is in the range of 1000 MPa to 1650 MPa, and the corrosion resistance and the same tensile strength are obtained. Excellent hydrogen embrittlement resistance when compared in terms of strength.
  • Test No. d1 and d2 are [Cu] / [Ni] ⁇ 1.00, and d2 is Y2 of 1.81 or more, delamination occurs in the steel wire after wire drawing, and the twisting characteristic is bad.
  • the hydrogen embrittlement resistance of the steel wire is also inferior to that of the steel wire having the same level of tensile strength in the examples.
  • Test No. The value of Y1 of d3 is less than 1.70, and the hydrogen embrittlement resistance property of the wire rod and the hydrogen embrittlement resistance property of the steel wire after wire drawing are inferior. Test No.
  • the value of Y1 of d4 exceeds 4.50, and the hydrogen embrittlement resistance property of the wire rod, the hydrogen embrittlement resistance property of the steel wire after wire drawing, and the twisting property are inferior.
  • Test No. The value of Y2 of d5 is 1.81 or more, and the hydrogen embrittlement resistance property of the wire rod, the hydrogen embrittlement resistance property of the steel wire after the wire drawing process, and the twisting property are inferior.
  • any of the chemical components in the present disclosure is outside the scope of the present disclosure, or the value of Y2 is 1.81 or more, and the hydrogen embrittlement resistance of the wire rod and the hydrogen embrittlement resistance / Or the hydrogen embrittlement resistance and twisting characteristics of the steel wire after wire drawing are inferior.
  • Test No. Since the chemical components of d9 and d22 were outside the scope of the present disclosure and the wire was broken at the stage of wire drawing, the tensile strength, hydrogen embrittlement resistance, and twisting characteristics of the steel wire were not investigated.
  • the use of the wire rod according to the present disclosure is not limited to the above-described embodiments and examples.
  • the wire rod according to the present disclosure is not limited to a steel wire material having a tensile strength of 1700 MPa or more, and may be used as a steel wire material having a required tensile strength of less than 1700 MPa.

Abstract

This wire rod has predetermined chemical components, satisfies the following (1)-(3), contains a pearlite structure having at least 90% of a metal structure, and satisfies the following (4) when Hvsi denotes each sample value of the Vickers hardness of a surface part with respect to each of eight samples si taken at arbitrary equal intervals in the longitudinal direction of the wire rod, Hvsiave denotes an average value of Hvsi, and Hvsimax denotes a maximum value: (1) [Cu]/[Ni]＞1.00; (2) 1.70≤Y1≤4.50 Y1=3×[Cr]＋5×[Mn]＋[Cu]＋[Ni]; (3) Y2＜1.81 Y2=[C]＋[Si]/10＋AA, where the value of a=350×([N]-0.29×[Ti]) is A=a when a≥0, and A=0 when a＜0; and (4) Hvsimax-Hvsiave≤50.

Description

線材wire
　本開示は、線材に関する。 This disclosure relates to wire rods.
　近年、高強度ロープ用鋼線、橋梁ケーブル用鋼線、ＰＣ鋼線等の分野に使用される高強度鋼線には、１７００ＭＰａ以上の高い引張強さが要求される。これら高強度鋼線は、例えば、直径５．０～１６．０ｍｍの圧延された線材をパテンティング処理して金属組織をパーライト組織とした後、伸線加工を行うことで製造される。
　伸線加工後の鋼線の引張強さが高い場合、伸線加工において生じる加工発熱によってひずみ時効の影響を受け、脆化するおそれが高い。ひずみ時効によって高強度鋼線は、捻回試験での破断までの回転数（捻回値）が小さくなり、さらにデラミネーションと呼ばれる縦割れが発生する場合がある。捻回試験におけるデラミネーションの発生は、鋼線を製品とするための撚り線工程において破断要因となるため、製造性が劣化する。そのため、高強度鋼線では特に引張強さと捻回特性を両立することが望ましい。
　また、鋼線の強度が高くなるほど、鋼線又は撚り線後の製品が腐食環境で使用された際、腐食の進行又は水素脆化によって破断が生じる危険性が高くなる。そのため、上記分野に用いられる高強度鋼線及びその素材となる線材には、優れた耐食性と耐水素脆化特性を有することが望まれる。 In recent years, high-strength steel wires used in fields such as high-strength rope steel wires, bridge cable steel wires, and PC steel wires are required to have a high tensile strength of 1700 MPa or more. These high-strength steel wires are manufactured, for example, by subjecting a rolled wire having a diameter of 5.0 to 16.0 mm to a pearlite structure and then performing wire drawing.
When the tensile strength of the steel wire after the wire drawing process is high, there is a high possibility that the steel wire will be affected by the strain aging due to the processing heat generated in the wire drawing process and become embrittlement. Due to strain aging, high-strength steel wire has a smaller number of rotations (twisting value) until fracture in the twisting test, and vertical cracks called delamination may occur. The occurrence of delamination in the twist test causes breakage in the stranded wire process for producing a steel wire, which deteriorates manufacturability. Therefore, it is particularly desirable for high-strength steel wires to have both tensile strength and torsional characteristics.
Further, the higher the strength of the steel wire, the higher the risk of breakage due to the progress of corrosion or hydrogen embrittlement when the steel wire or the product after the stranded wire is used in a corrosive environment. Therefore, it is desired that the high-strength steel wire used in the above field and the wire rod as a material thereof have excellent corrosion resistance and hydrogen embrittlement resistance.
　高強度鋼線の捻回特性を向上させる技術として、例えば特許文献１には、質量％で、Ｃ：０．７５～１．１０％、Ｓｉ：０．１０～１．４０％、Ｍｎ：０．１０～１．０％、Ａｌ：０～０．１０％、Ｔｉ：０～０．１０％、Ｃｒ：０～０．６０％、Ｖ：０～０．１０％、Ｎｂ：０～０．１０％、Ｍｏ：０～０．２０％、Ｗ：０～０．５０％、Ｂ：０～０．００３０％含有し、Ｎ：０．００６％以下、Ｐ：０．０３％以下、Ｓ：０．０３％以下に制限され、残部が実質的にＦｅからなり、鋼線の軸線を含む軸方向に沿ったＬ断面の表面から１００μｍの深さよりも軸線側の領域において、金属組織が面積率で９０％以上の伸線パーライトを含み、前記Ｌ断面の表面から１００μｍの深さまでの領域において、金属組織が面積率で７０％以上の伸線パーライトを含み、鋼線の直径（Ｄ［ｍｍ］）、鋼線の表面のビッカース硬さの標準偏差（σＨＶ）、鋼線の降伏強度（Ｒｐ０．２）が、下記（１）式を満たし、引張強さが１７７０ＭＰａ以上の高強度を有する鋼線が提案されている。
σＨＶ＜（－９５００×ｌｎ（ｄ）＋３００００）×ｅｘｐ（－０．００３×Ｒｐ０．２）・・・（１） As a technique for improving the twisting characteristics of high-strength steel wire, for example, Patent Document 1 describes, in terms of mass%, C: 0.75 to 1.10%, Si: 0.10 to 1.40%, Mn: 0. .10 to 1.0%, Al: 0 to 0.10%, Ti: 0 to 0.10%, Cr: 0 to 0.60%, V: 0 to 0.10%, Nb: 0 to 0. Contains 10%, Mo: 0 to 0.20%, W: 0 to 0.50%, B: 0 to 0.0030%, N: 0.006% or less, P: 0.03% or less, S: Limited to 0.03% or less, the balance is substantially Fe, and the area ratio of the metallographic structure is in the region on the axis side of the depth of 100 μm from the surface of the L cross section along the axial direction including the axis of the steel wire. In the region from the surface of the L cross section to a depth of 100 μm, the metal structure contains a wire drawn pearlite having an area ratio of 70% or more, and the diameter of the steel wire (D [mm]). ), The standard deviation (σHV) of the Vickers hardness of the surface of the steel wire, and the yield strength (Rp0.2) of the steel wire satisfy the following equation (1), and the steel wire has a high tensile strength of 1770 MPa or more. Has been proposed.
σHV <(-9500 x ln (d) +30000) x exp (-0.003 x Rp0.2) ... (1)
　また、高強度鋼線の耐水素脆化特性を向上させる技術として、例えば特許文献２では、Ｃ：０．７０～１．２０％、Ｓｉ：０．１０～２．００％、Ｍｎ：０．２０～１．００％、Ｐ：０．０３０％以下、Ｓ：０．０３０％以下、Ｎ：０．００１０～０．０１００％、Ａｌ：０～０．１００％、Ｃｒ：０～２．００％、Ｖ：０～０．３０％、Ｂ：０～０．００５０％、Ｔｉ：０～０．０５０％、Ｎｂ：０～０．０５０％、Ｚｒ：０～０．０５０％、Ｎｉ：０～２．００％、Ｃｕ：０～１．００％、Ｓｎ：０～０．５０％、Ｍｇ：０～０．０１０％、Ｃａ：０～０．０１０％、からなる化学成分であり、金属組織が９５面積％以上のパーライト組織を有し、鋼線の軸を含む軸方向の断面における表層で測定したパーライトブロックの平均アスペクト比Ｒが２．０以上であり、鋼線の直径をＤとしたとき、鋼線の軸を含む軸方向の断面において、（表層で測定した平均アスペクト比）／（０．２５Ｄの位置で測定した平均アスペクト比）が１．１以上であり、引張強さが１８００ＭＰａ以上である耐水素脆化特性に優れた高強度鋼線が提案されている。 Further, as a technique for improving the hydrogen embrittlement resistance of high-strength steel wire, for example, in Patent Document 2, C: 0.70 to 1.20%, Si: 0.10 to 2.00%, Mn: 0. 20 to 1.00%, P: 0.030% or less, S: 0.030% or less, N: 0.0010 to 0.0100%, Al: 0 to 0.100%, Cr: 0 to 2.00 %, V: 0 to 0.30%, B: 0 to 0.0050%, Ti: 0 to 0.050%, Nb: 0 to 0.050%, Zr: 0 to 0.050%, Ni: 0 It is a chemical component consisting of ~ 2.00%, Cu: 0 to 1.00%, Sn: 0 to 0.50%, Mg: 0 to 0.010%, Ca: 0 to 0.010%, and is a metal. The structure has a pearlite structure of 95 area% or more, the average aspect ratio R of the pearlite block measured on the surface layer in the axial cross section including the axis of the steel wire is 2.0 or more, and the diameter of the steel wire is D. When the steel wire is crossed in the axial direction including the shaft, (average aspect ratio measured on the surface layer) / (average aspect ratio measured at the position of 0.25D) is 1.1 or more, and the tensile strength is high. A high-strength steel wire having excellent hydrogen embrittlement resistance of 1800 MPa or more has been proposed.
　さらに、特許文献３では、Ｃ：０．５～１．０％を含有する他、Ｃｕ，Ｎｉ及びＴｉよりなる群から選ばれる１種以上（但し、Ｃｕ及び／又はＮｉを含有する）であって、下記（１）式を満足するように含有する鋼からなり、パーライト組織の面積率を８０％以上としたものであり、且つ１２００Ｎ／ｍｍ２以上の強度を有するものであることを特徴とする耐遅れ破壊性及び耐食性に優れた高強度鋼線が提案されている。
　３．１≧３［Ｃｕ］＋［Ｎｉ］＋６［Ｔｉ］≧０．２４（％）　…（１）
但し、［Ｃｕ］，［Ｎｉ］及び［Ｔｉ］は夫々Ｃｕ，Ｎｉ及びＴｉの含有量（質量％）を示す。
　また、特許文献４には、Ｃ：０．３９～０．６５％、Ｓｉ：１．５～２．５％、Ｍｎ：０．１５～１．２％、Ｐ：０％超、０．０１５％以下、Ｓ：０％超、０．０１５％以下、Ａｌ：０．００１～０．１％、Ｃｕ：０．１～０．８０％、Ｎｉ：０．１～０．８０％を含有し、残部が鉄及び不可避不純物であり、非拡散性水素量が０．４０質量ｐｐｍ以下であり、百分率で表されるフェライトの面積率が下記（１）式を満たすとともに、ベイナイトとマルテンサイトの合計面積率が２％以下であることを特徴とする高強度ばね用圧延材が提案されている。
フェライト面積率＜｛（０．７７－［Ｃ］）／０．７７－［Ｃ］／３＋０．０８｝×１００・・・（１）
　但し、上記（１）式中、［元素名］は各元素の質量％で表される含有量を意味する。
　また、特許文献５では、Ｃ：０．５５～０．７５％、Ｓｉ：０．１～１．０％、Ｍｎ：０．３～１．５％、Ｃｒ：０．１～２．０％、Ｓ：０．００２～０．０５％、Ａｌ：０．０１～０．２％およびＮ：０．００２～０．０１％を含有し、残部はＦｅおよび不純物からなり、不純物中のＰおよびＯがそれぞれ、Ｐ：０．０２５％以下およびＯ：０．００２％以下で、さらに下記の［１］式で表されるＦｎ１が２．５～４．５である化学組成を有し、組織が、パーライト分率が９０％以上、パーライトラメラの平均間隔が１５０～３００ｎｍで、かつパーライトラメラ間隔の標準偏差が２５ｎｍ以下である、ことを特徴とする熱間圧延棒鋼または線材が提案されている。
Ｆｎ１＝３Ｓｉ＋Ｍｎ＋１．５Ｃｒ・・・［１］
ただし、［１］式中の元素記号は、各元素の含有量（質量％）を意味する。 Further, in Patent Document 3, in addition to containing C: 0.5 to 1.0%, one or more selected from the group consisting of Cu, Ni and Ti (provided that Cu and / or Ni is contained). It is characterized by being made of steel containing the following formula (1) so as to satisfy the following formula, having a pearlite structure area ratio of 80% or more, and having a strength of 1200 N / mm 2 or more. High-strength steel wire having excellent delayed fracture resistance and corrosion resistance has been proposed.
3.1 ≧ 3 [Cu] ＋ [Ni] ＋ 6 [Ti] ≧ 0.24 (%)… (1)
However, [Cu], [Ni] and [Ti] indicate the contents (mass%) of Cu, Ni and Ti, respectively.
Further, in Patent Document 4, C: 0.39 to 0.65%, Si: 1.5 to 2.5%, Mn: 0.15 to 1.2%, P: more than 0%, 0.015. % Or less, S: more than 0%, 0.015% or less, Al: 0.001 to 0.1%, Cu: 0.1 to 0.80%, Ni: 0.1 to 0.80% The balance is iron and unavoidable impurities, the amount of non-diffusible hydrogen is 0.40 mass ppm or less, the area ratio of ferrite expressed as a percentage satisfies the following equation (1), and the total of bainite and martensite. A rolled material for a high-strength spring, characterized in that the area ratio is 2% or less, has been proposed.
Ferrite area ratio << (0.77- [C]) /0.77-[C]/3+0.08} × 100 ... (1)
However, in the above formula (1), [element name] means the content represented by the mass% of each element.
Further, in Patent Document 5, C: 0.55 to 0.75%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr: 0.1 to 2.0%. , S: 0.002-0.05%, Al: 0.01-0.2% and N: 0.002-0.01%, the balance consisting of Fe and impurities, P and in the impurities O has a chemical composition of P: 0.025% or less and O: 0.002% or less, respectively, and Fn1 represented by the following formula [1] is 2.5 to 4.5, and has a structure. However, hot-rolled steel bars or wire rods are proposed, characterized in that the pearlite fraction is 90% or more, the average spacing of pearlite lamellas is 150 to 300 nm, and the standard deviation of the pearlite lamella spacing is 25 nm or less. ..
Fn1 = 3Si + Mn + 1.5Cr ... [1]
However, the element symbol in the formula [1] means the content (mass%) of each element.
　特許文献１：国際公開第２０１８／０１２６２５号
　特許文献２：国際公開第２０１８／０２１５７４号
　特許文献３：特許第４１２４５９０号
　特許文献４：特開２０１５－１４３３９１号公報
　特許文献５：特開２０１４－３７５９２号公報 Patent Document 1: International Publication No. 2018/012625 Patent Document 2: International Publication No. 2018/021574 Patent Document 3: Patent No. 4124590 Patent Document 4: Japanese Patent Application Laid-Open No. 2015-143391 Patent Document 5: Japanese Patent Application Laid-Open No. 2014-37592 Gazette
　本開示は、１７００ＭＰａ以上の高い引張強さ（ultimate tensile strength）が要求される高強度鋼線の素材として好適な線材であって、耐食性及び耐水素脆化特性に優れ、伸線加工後の鋼線においてデラミネーションが発生しにくい、捻回特性に優れた線材を提供することを課題とする。 The present disclosure is a wire rod suitable as a material for high-strength steel wire that requires a high tensile strength (ultimate tensile strength) of 1700 MPa or more, has excellent corrosion resistance and hydrogen embrittlement resistance, and is a steel after wire drawing. An object of the present invention is to provide a wire rod having excellent twisting characteristics, which is less likely to cause delamination in the wire.
　上記課題を解決するための手段には、以下の態様が含まれる。
＜１＞　化学成分が、質量％で、
Ｃ：０．６０～１．１５％、
Ｓｉ：０．０１～１．８０％、
Ｍｎ：０．２０～０．９０％、
Ｐ：０．０１５％以下、
Ｓ：０．０１５％以下、
Ａｌ：０．００５～０．０８０％、
Ｎ：０．００１５～０．００６０％、
Ｃｕ：０．１０～０．６５％、
Ｎｉ：０．０５～０．６５％未満、
Ｃｒ：０～０．３０％、
Ｍｏ：０～０．３０％、
Ｔｉ：０～０．１００％、
Ｎｂ：０～０．１００％、
Ｖ：０～０．２０％、
Ｓｎ：０～０．３０％、
Ｂ：０～０．００５０％、
Ｃａ：０～０．００５０％、
Ｍｇ：０～０．００５０％、
Ｚｒ：０～０．１００％、
ＲＥＭ：０～０．０２００％、並びに
残部：Ｆｅ及び不純物、からなり、
線材に含まれるＣ、Ｓｉ、Ｍｎ、Ｃｒ、Ｃｕ、Ｎｉ、Ｎ、及びＴｉのそれぞれの元素の質量％での含有量を、［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｃｒ］、［Ｃｕ］、［Ｎｉ］、［Ｎ］、及び［Ｔｉ］で表した場合に、下記（１）～（３）を満たし、
（１）［Ｃｕ］／［Ｎｉ］＞１．００
（２）１．７０≦Ｙ１≦４．５０
　Ｙ１＝３×［Ｃｒ］＋５×［Ｍｎ］＋［Ｃｕ］＋［Ｎｉ］
（３）Ｙ２＜１．８１
　Ｙ２＝［Ｃ］＋［Ｓｉ］／１０＋Ａ
　Ａは、ａ＝３５０×（［Ｎ］－０．２９×［Ｔｉ］）の値が、
　ａ≧０の場合は、Ａ＝ａ
　ａ＜０の場合は、Ａ＝０
　金属組織が、線材の中心軸を含む長手方向に平行な断面における面積率で９０％以上のパーライト組織を含み、
　前記線材の長手方向に任意の等間隔で採取した８個の各々のサンプルｓｉ（ｉは１～８の整数）について、各サンプルの前記断面において前記線材の表面から深さ５０μｍの位置で測定されるビッカース硬さをそれぞれＨｖｓｉとし、前記Ｈｖｓｉの平均値をＨｖｓｉａｖｅ、最大値をＨｖｓｉｍａｘとしたとき、下記（４）を満たす、線材。
（４）Ｈｖｓｉｍａｘ－Ｈｖｓｉａｖｅ≦５０
＜２＞　前記任意の等間隔が、６００ｍｍの間隔である、＜１＞に記載の線材。
＜３＞　前記化学成分が、前記Ｆｅの一部に代えて、質量％で、
Ｃｒ：０．０１～０．３０％、
Ｍｏ：０．０１～０．３０％
Ｔｉ：０．００２～０．１００％、
Ｎｂ：０．００２～０．１００％、
Ｖ：０．０１～０．２０％、
Ｓｎ：０．０１～０．３０％、
Ｂ：０．０００２～０．００５０％
Ｃａ：０．０００２～０．００５０％、
Ｍｇ：０．０００２～０．００５０％、
Ｚｒ：０．０００２～０．１００％、及び
ＲＥＭ：０．０００２～０．０２００％、
からなる群より選択される１種又は２種以上を含む、＜１＞又は＜２＞に記載の線材。 The means for solving the above problems include the following aspects.
<1> The chemical composition is mass%,
C: 0.60 to 1.15%,
Si: 0.01 to 1.80%,
Mn: 0.20 to 0.90%,
P: 0.015% or less,
S: 0.015% or less,
Al: 0.005 to 0.080%,
N: 0.0015 to 0.0060%,
Cu: 0.10 to 0.65%,
Ni: 0.05 to less than 0.65%,
Cr: 0 to 0.30%,
Mo: 0 to 0.30%,
Ti: 0 to 0.100%,
Nb: 0 to 0.100%,
V: 0 to 0.20%,
Sn: 0 to 0.30%,
B: 0 to 0.0050%,
Ca: 0 to 0.0050%,
Mg: 0 to 0.0050%,
Zr: 0 to 0.100%,
REM: 0-0.0200%, and balance: Fe and impurities,
The content of each element of C, Si, Mn, Cr, Cu, Ni, N, and Ti contained in the wire rod in mass% is determined by [C], [Si], [Mn], [Cr], [ When represented by [Cu], [Ni], [N], and [Ti], the following (1) to (3) are satisfied.
(1) [Cu] / [Ni]> 1.00
(2) 1.70 ≤ Y1 ≤ 4.50
Y1 = 3 x [Cr] + 5 x [Mn] + [Cu] + [Ni]
(3) Y2 <1.81
Y2 = [C] + [Si] / 10 + A
In A, the value of a = 350 × ([N] −0.29 × [Ti]) is
When a ≧ 0, A = a
If a <0, then A = 0
The metallographic structure contains a pearlite structure having an area ratio of 90% or more in a cross section parallel to the longitudinal direction including the central axis of the wire rod.
For each of the eight samples si (i is an integer of 1 to 8) collected at arbitrary equal intervals in the longitudinal direction of the wire, the cross section of each sample was measured at a depth of 50 μm from the surface of the wire. that Vickers hardness and each Hv si, the Hv si average value Hv Siave, when the maximum value was Hv Simax, satisfies the following (4), the wire.
(4) Hv simax -Hv siave ≦ 50
<2> The wire rod according to <1>, wherein the arbitrary equal spacing is 600 mm.
<3> The chemical composition is, in mass%, instead of a part of the Fe.
Cr: 0.01-0.30%,
Mo: 0.01-0.30%
Ti: 0.002 to 0.100%,
Nb: 0.002 to 0.100%,
V: 0.01 to 0.20%,
Sn: 0.01 to 0.30%,
B: 0.0002 to 0.0050%
Ca: 0.0002 to 0.0050%,
Mg: 0.0002 to 0.0050%,
Zr: 0.0002 to 0.100%, and REM: 0.0002 to 0.0200%,
The wire rod according to <1> or <2>, which comprises one kind or two or more kinds selected from the group consisting of.
　本開示によれば、１７００ＭＰａ以上の高い引張強さが要求される高強度鋼線の素材として好適な線材であって、耐食性及び耐水素脆化特性に優れ、伸線加工後の鋼線においてデラミネーションが発生しにくい、捻回特性に優れた線材が提供される。 According to the present disclosure, it is a wire rod suitable as a material for high-strength steel wire that requires a high tensile strength of 1700 MPa or more, has excellent corrosion resistance and hydrogen embrittlement resistance, and is used in steel wire after wire drawing. A wire rod having excellent twisting characteristics, which is less likely to cause lamination, is provided.
本開示の実施例で得られた、線材の引張強さと耐水素脆化特性の指標であるＦＩＰ破断時間の関係を示す図である。It is a figure which shows the relationship between the tensile strength of a wire rod and the FIP breaking time which is an index of hydrogen embrittlement resistance property obtained in the Example of this disclosure. 本開示の実施例で得られた、伸線加工後の鋼線の引張強さと耐水素脆化特性の指標であるＦＩＰ破断時間の関係を示す図である。It is a figure which shows the relationship between the tensile strength of a steel wire after wire drawing process and the FIP breaking time which is an index of hydrogen embrittlement resistance property obtained in the Example of this disclosure.
　本開示の一例である実施形態について説明する。
　本開示において、「～」を用いて表される数値範囲は、「～」の前後に記載される数値を下限値及び上限値として含む範囲を意味する。ただし、「～」の前後に記載される数値に「超」又は「未満」が付されている場合の数値範囲は、これら数値を下限値又は上限値として含まない範囲を意味する。
　また、本開示に段階的に記載されている数値範囲において、ある段階的な数値範囲の上限値は、他の段階的な記載の数値範囲の上限値に置き換えてもよく、ある段階的な数値範囲の下限値は、他の段階的な記載の数値範囲の下限値に置き換えてもよい。また、上限値又は下限値を実施例に示されている値に置き換えてもよい。
　本開示において、成分（元素）の含有量を示す「％」は、「質量％」を意味する。
　本開示において、Ｃ（炭素）の含有量を、「Ｃ量」と表記することがある。他の元素の含有量についても同様に表記することがある。
　本開示において、線材又は鋼線の「表面」とは、外周面を意味する。また、線材又は鋼線を切断して採取されたサンプルの「表面」も外周面を意味する。 An embodiment which is an example of the present disclosure will be described.
In the present disclosure, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value. However, the numerical range when "greater than" or "less than" is added to the numerical values before and after "to" means a range in which these numerical values are not included as the lower limit value or the upper limit value.
Further, in the numerical range described stepwise in the present disclosure, the upper limit value of a certain stepwise numerical range may be replaced with the upper limit value of another numerical range described stepwise, and a certain stepwise numerical value may be replaced. The lower limit of the range may be replaced with the lower limit of the numerical range described in other steps. Further, the upper limit value or the lower limit value may be replaced with the value shown in the embodiment.
In the present disclosure, "%" indicating the content of a component (element) means "mass%".
In the present disclosure, the content of C (carbon) may be referred to as "C amount". The content of other elements may be described in the same manner.
In the present disclosure, the "surface" of a wire rod or steel wire means an outer peripheral surface. In addition, the "surface" of a sample collected by cutting a wire rod or a steel wire also means an outer peripheral surface.
　本発明者らは、前記した課題を解決するために、１７００ＭＰａ以上の高い引張強さが要求される高強度鋼線の素材として好適な線材（本開示において「高強度鋼線用線材」と記す場合がある。）の耐食性、耐水素脆化特性、及び伸線加工後の捻回特性に及ぼす元素及び金属組織の影響などについて種々の検討を実施し、下記（ａ）～（ｃ）の知見を得た。 In order to solve the above-mentioned problems, the present inventors describe a wire rod suitable as a material for a high-strength steel wire that requires a high tensile strength of 1700 MPa or more (in the present disclosure, it is referred to as a “wire rod for high-strength steel wire”). In some cases), various studies were conducted on the corrosion resistance, hydrogen brittleness resistance, and the effect of elements and metal structures on the twisting characteristics after wire drawing, and the findings (a) to (c) below were obtained. Got
（ａ）引張強さが１７００ＭＰａ以上の高強度鋼線は、デラミネーションが発生しやすく、腐食又は水素脆化による破断を起こしやすい。高強度鋼線のデラミネーションの発生を抑え、腐食又は水素脆化による破断を防ぐためには、捻回特性が低下しないよう、素材となる線材の化学成分の範囲を考えて耐食性と耐水素脆化特性を向上させればよく、Ｃｕ：０．１０～０．６５％、Ｎｉ：０．０５～０．６５％未満を［Ｃｕ］＞［Ｎｉ］を満足する範囲で含有し、下記式＜１＞で表されるＹ１が１．７０≦Ｙ１≦４．５０を満足する範囲でＭｎ、Ｃｒ、Ｃｕ、Ｎｉを含有させればよい。
Ｙ１＝３×［Ｃｒ］＋５×［Ｍｎ］＋［Ｃｕ］＋［Ｎｉ］　　・・・＜１＞
ここで、上記式における［Ｍｎ］、［Ｃｒ］、［Ｃｕ］、［Ｎｉ］は、それぞれの元素の質量％での含有量を表す。 (A) A high-strength steel wire having a tensile strength of 1700 MPa or more is liable to cause delamination and is liable to break due to corrosion or hydrogen embrittlement. In order to suppress the occurrence of delamination of high-strength steel wire and prevent breakage due to corrosion or hydrogen embrittlement, corrosion resistance and hydrogen embrittlement resistance are considered by considering the range of chemical components of the raw material so that the twisting characteristics do not deteriorate. The characteristics may be improved, and Cu: 0.10 to 0.65% and Ni: 0.05 to less than 0.65% are contained in a range satisfying [Cu]> [Ni], and the following formula <1 Mn, Cr, Cu, and Ni may be contained within a range in which Y1 represented by> satisfies 1.70 ≦ Y1 ≦ 4.50.
Y1 = 3 x [Cr] + 5 x [Mn] + [Cu] + [Ni] ... <1>
Here, [Mn], [Cr], [Cu], and [Ni] in the above formula represent the content of each element in mass%.
（ｂ）高強度鋼線は、線材を伸線加工することで製造される。引張強さが１７００ＭＰａ以上の高強度鋼線は、伸線加工におけるダイスとの摩擦熱等による温度上昇及び加工発熱が大きくなる傾向があり、ひずみ時効の影響を受けて脆化しやすい。ひずみ時効によって高強度鋼線は、捻回試験において、デラミネーションと呼ばれる縦割れが発生し、破断までの回転数、すなわち捻回値が小さくなる。さらに引張強さが１７００ＭＰａ以上の高強度鋼線の腐食又は水素脆化による破断を防ぎつつ、かつ伸線加工によってひずみ時効の影響を最小限に抑え、伸線加工後の捻回値を向上させるためには、下記式＜２＞で表されるＹ２がＹ２＜１．８１を満足する範囲でＣ、Ｓｉ、Ｔｉ、Ｎを含有させればよい。
Ｙ２＝［Ｃ］＋［Ｓｉ］／１０＋Ａ　　　　　　　　　　　　　・・・＜２＞
ここで、式＜２＞におけるＡは、下記式＜４＞によって算出される値がａ≧０の場合はＡ＝ａであり、ａ＜０の場合はＡ＝０とする。
ａ＝３５０×（［Ｎ］－０．２９×［Ｔｉ］）　・・・＜４＞
ここで、上記式における［Ｃ］、［Ｓｉ］、［Ｎ］、［Ｔｉ］は、それぞれの元素の質量％での含有量を表し、Ａは式＜４＞で表されるａに関連するパラメータである。 (B) High-strength steel wire is manufactured by drawing a wire rod. A high-strength steel wire having a tensile strength of 1700 MPa or more tends to increase in temperature and heat generation due to frictional heat with a die in wire drawing, and is easily brittle due to the influence of strain aging. Due to strain aging, high-strength steel wire undergoes vertical cracks called delamination in the twist test, and the number of revolutions until fracture, that is, the twist value becomes small. Furthermore, while preventing breakage due to corrosion or hydrogen embrittlement of high-strength steel wire with a tensile strength of 1700 MPa or more, the effect of strain aging is minimized by wire drawing, and the twist value after wire drawing is improved. For this purpose, C, Si, Ti, and N may be contained within a range in which Y2 represented by the following formula <2> satisfies Y2 <1.81.
Y2 = [C] + [Si] / 10 + A ... <2>
Here, A in the formula <2> is A = a when the value calculated by the following formula <4> is a ≧ 0, and A = 0 when a <0.
a = 350 × ([N] −0.29 × [Ti]) ・ ・ ・ <4>
Here, [C], [Si], [N], and [Ti] in the above formula represent the content of each element in mass%, and A is related to a represented by the formula <4>. It is a parameter.
（ｃ）線材の耐食性及び耐水素脆化特性を向上させるために、Ｍｎ、Ｃｒ、Ｃｕ、Ｎｉを含有した場合、線材の焼き入れ性が高まり、線材の製造条件によって線材表層の硬度ばらつきが大きくなる傾向がある。この線材表層の硬度ばらつきが原因となり、線材の長手方向に表層硬度が局部的に高い部分が存在すると、耐水素脆化特性が急激に低下する。線材の耐水素脆化特性の低下は、線材を伸線加工することによって得られる高強度鋼線の耐水素脆化特性の低下を招く。そのため、線材の耐食性と耐水素脆化特性を同時に向上させるためには、特定の化学成分の範囲を満足するとともに、線材表層の硬度ばらつきを小さくし、表層硬度が局部的に高くなる部分を無くすことが必要である。 (C) When Mn, Cr, Cu, and Ni are contained in order to improve the corrosion resistance and hydrogen embrittlement resistance of the wire rod, the hardenability of the wire rod is enhanced, and the hardness of the wire rod surface layer varies widely depending on the manufacturing conditions of the wire rod. Tends to be. Due to the variation in hardness of the surface layer of the wire rod, if there is a portion where the surface layer hardness is locally high in the longitudinal direction of the wire rod, the hydrogen embrittlement resistance property is sharply lowered. The deterioration of the hydrogen embrittlement resistance of the wire rod causes the deterioration of the hydrogen embrittlement resistance property of the high-strength steel wire obtained by wire drawing the wire rod. Therefore, in order to simultaneously improve the corrosion resistance and hydrogen embrittlement resistance of the wire rod, the range of specific chemical components is satisfied, the hardness variation of the wire rod surface layer is reduced, and the portion where the surface layer hardness is locally increased is eliminated. It is necessary.
　本開示に係る線材は上記の知見に基づいて完成されたものであり、化学成分が、質量％で、
Ｃ：０．６０～１．１５％、
Ｓｉ：０．０１～１．８０％、
Ｍｎ：０．２０～０．９０％、
Ｐ：０．０１５％以下、
Ｓ：０．０１５％以下、
Ａｌ：０．００５～０．０８０％、
Ｎ：０．００１５～０．００６０％、
Ｃｕ：０．１０～０．６５％、
Ｎｉ：０．０５～０．６５％未満、
Ｃｒ：０～０．３０％、
Ｍｏ：０～０．３０％、
Ｔｉ：０～０．１００％、
Ｎｂ：０～０．１００％、
Ｖ：０～０．２０％、
Ｓｎ：０～０．３０％、
Ｂ：０～０．００５０％、
Ｃａ：０～０．００５０％、
Ｍｇ：０～０．００５０％、
Ｚｒ：０～０．１００％、
ＲＥＭ：０～０．０２００％、並びに
残部：Ｆｅ及び不純物、からなり、
線材に含まれるＣ、Ｓｉ、Ｍｎ、Ｃｒ、Ｃｕ、Ｎｉ、Ｎ、及びＴｉのそれぞれの元素の質量％での含有量を、［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｃｒ］、［Ｃｕ］、［Ｎｉ］、［Ｎ］、及び［Ｔｉ］で表した場合に、下記（１）～（３）を満たし、
（１）［Ｃｕ］／［Ｎｉ］＞１．００
（２）１．７０≦Ｙ１≦４．５０
　Ｙ１＝３×［Ｃｒ］＋５×［Ｍｎ］＋［Ｃｕ］＋［Ｎｉ］
（３）Ｙ２＜１．８１
　Ｙ２＝［Ｃ］＋［Ｓｉ］／１０＋Ａ
　Ａは、ａ＝３５０×（［Ｎ］－０．２９×［Ｔｉ］）の値が、
　ａ≧０の場合は、Ａ＝ａ
　ａ＜０の場合は、Ａ＝０
　金属組織が、線材の中心軸を含む長手方向に平行な断面（本開示において「軸方向断面」と称する場合がある。）における面積率で９０％以上のパーライト組織を含み、
　線材の長手方向に任意の等間隔で採取した８個の各々のサンプルｓｉ（ｉは１～８の整数）について、各サンプルの軸方向断面において、線材の表面（外周面）から深さ５０μｍの位置で測定されるビッカース硬さをそれぞれＨｖｓｉとし、Ｈｖｓｉの平均値をＨｖｓｉａｖｅ、最大値をＨｖｓｉｍａｘとしたとき、下記（４）を満たす。
（４）Ｈｖｓｉｍａｘ－Ｈｖｓｉａｖｅ≦５０ The wire rod according to the present disclosure has been completed based on the above findings, and the chemical composition is mass%.
C: 0.60 to 1.15%,
Si: 0.01 to 1.80%,
Mn: 0.20 to 0.90%,
P: 0.015% or less,
S: 0.015% or less,
Al: 0.005 to 0.080%,
N: 0.0015 to 0.0060%,
Cu: 0.10 to 0.65%,
Ni: 0.05 to less than 0.65%,
Cr: 0 to 0.30%,
Mo: 0 to 0.30%,
Ti: 0 to 0.100%,
Nb: 0 to 0.100%,
V: 0 to 0.20%,
Sn: 0 to 0.30%,
B: 0 to 0.0050%,
Ca: 0 to 0.0050%,
Mg: 0 to 0.0050%,
Zr: 0 to 0.100%,
REM: 0-0.0200%, and balance: Fe and impurities,
The content of each element of C, Si, Mn, Cr, Cu, Ni, N, and Ti contained in the wire rod in mass% is determined by [C], [Si], [Mn], [Cr], [ When represented by [Cu], [Ni], [N], and [Ti], the following (1) to (3) are satisfied.
(1) [Cu] / [Ni]> 1.00
(2) 1.70 ≤ Y1 ≤ 4.50
Y1 = 3 x [Cr] + 5 x [Mn] + [Cu] + [Ni]
(3) Y2 <1.81
Y2 = [C] + [Si] / 10 + A
In A, the value of a = 350 × ([N] −0.29 × [Ti]) is
When a ≧ 0, A = a
If a <0, then A = 0
The metallographic structure contains a pearlite structure having an area ratio of 90% or more in a cross section parallel to the longitudinal direction including the central axis of the wire rod (sometimes referred to as a “axial cross section” in the present disclosure).
For each of the eight samples si (i is an integer of 1 to 8) collected at arbitrary equal intervals in the longitudinal direction of the wire, in the axial cross section of each sample, the depth is 50 μm from the surface (outer peripheral surface) of the wire. Vickers hardness measured at the location of the Hv si respectively, when the average value of Hv Siave of Hv si, the maximum value was Hv Simax, satisfies the following (4).
(4) Hv simax -Hv siave ≦ 50
＜化学成分＞
　まず、本開示に係る高強度鋼線用線材に含有される元素の範囲を限定した理由を説明する。
　本開示に係る高強度鋼線用線材の化学成分は、質量％で、Ｃ：０．６０～１．１５％、Ｓｉ：０．０１～１．８０％、Ｍｎ：０．２０～０．９０％、Ｐ：０．０１５％以下、Ｓ：０．０１５％以下、Ａｌ：０．００５～０．０８０％、Ｎ：０．００１５～０．００６０％、を含有し、さらに、［Ｃｕ］＞［Ｎｉ］を満足する範囲でＣｕ：０．１０～０．６５％、Ｎｉ：０．０５～０．６５％未満を含有し、さらに任意に含有される成分が、Ｃｒ：０～０．３０％、Ｍｏ：０～０．３０％、Ｔｉ：０～０．１００％、Ｎｂ：０～０．１００％、Ｖ：０～０．２０％、Ｓｎ：０～０．３０％、Ｂ：０～０．００５０％、Ｃａ：０～０．００５０％、Ｍｇ：０～０．００５０％、Ｚｒ：０～０．１００％、及びＲＥＭ：０～０．０２００％であり、残部はＦｅ及び不純物からなる。 <Chemical composition>
First, the reason for limiting the range of elements contained in the wire rod for high-strength steel wire according to the present disclosure will be described.
The chemical composition of the wire rod for high-strength steel wire according to the present disclosure is C: 0.60 to 1.15%, Si: 0.01 to 1.80%, Mn: 0.20 to 0.90 in mass%. %, P: 0.015% or less, S: 0.015% or less, Al: 0.005 to 0.080%, N: 0.0015 to 0.0060%, and further, [Cu]> Cu: 0.10 to 0.65% and Ni: 0.05 to less than 0.65% are contained within a range satisfying [Ni], and Cr: 0 to 0.30 is optionally contained. %, Mo: 0 to 0.30%, Ti: 0 to 0.100%, Nb: 0 to 0.100%, V: 0 to 0.20%, Sn: 0 to 0.30%, B: 0 ~ 0.0050%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Zr: 0 to 0.100%, and REM: 0 to 0.0200%, and the balance is Fe and impurities. Consists of.
Ｃ：０．６０～１．１５％
　Ｃは線材の引張強さを高めるため含有する。Ｃ量が０．６０％未満では初析フェライトが生成し、高強度鋼線に必要な引張強さを確保できない。そのため、Ｃ量は０．６０％以上とする。優れた耐水素脆化特性及び捻回特性を確保する観点から伸線加工の加工減面率を上げ過ぎずに、高強度鋼線を得るためには、Ｃ量は０．６７％以上であることが好ましく、０．７０％以上であることがより好ましく、０．８５％以上であることが一層好ましい。一方、Ｃ量が１．１５％を越えると、初析セメンタイト量が増加して伸線加工性が劣化するため、高強度鋼線を得ることが困難となるし、鋼線の捻回特性も劣化する。そのため、Ｃ量は１．１０％以下とすることがよく、１．０５％以下とすることがなお好ましい。 C: 0.60 to 1.15%
C is contained to increase the tensile strength of the wire rod. If the amount of C is less than 0.60%, proeutectoid ferrite is generated, and the tensile strength required for high-strength steel wire cannot be secured. Therefore, the amount of C is set to 0.60% or more. From the viewpoint of ensuring excellent hydrogen embrittlement resistance and twisting characteristics, the amount of C is 0.67% or more in order to obtain high-strength steel wire without increasing the machining reduction rate of wire drawing too much. It is preferably 0.70% or more, more preferably 0.85% or more, and even more preferably 0.85% or more. On the other hand, if the amount of C exceeds 1.15%, the amount of pro-eutectoid cementite increases and the wire drawing workability deteriorates, which makes it difficult to obtain a high-strength steel wire and also deteriorates the twisting characteristics of the steel wire. to degrade. Therefore, the amount of C is often 1.10% or less, and more preferably 1.05% or less.
Ｓｉ：０．０１～１．８０％
　Ｓｉは固溶強化により引張強さを高める効果があり、耐水素脆化特性を高める効果がある。Ｓｉ量が０．０１％未満では、これらの効果が得られない。そのためＳｉ量は０．０１％以上にする。これら効果を確実に得るためには、Ｓｉ量を０．２１％以上含有させることが好ましく、０．７０％以上とすることがなお好ましい。ただし、Ｓｉ量が１．８０％を越えると、これらの効果が飽和するとともに熱間延性が劣化して、線材を圧延する段階で表面疵が発生しやすくなるなど、製造性が低下する。また伸線加工後の高強度鋼線の捻回特性が劣化する。そのため、Ｓｉ量は１．４９％以下とすることが好ましく、１．３５％以下とすることがなお好ましい。 Si: 0.01 to 1.80%
Si has the effect of increasing the tensile strength by strengthening the solid solution, and has the effect of enhancing the hydrogen embrittlement resistance. If the amount of Si is less than 0.01%, these effects cannot be obtained. Therefore, the amount of Si should be 0.01% or more. In order to surely obtain these effects, the amount of Si is preferably 0.21% or more, and more preferably 0.70% or more. However, if the amount of Si exceeds 1.80%, these effects are saturated and the hot ductility is deteriorated, so that surface defects are likely to occur at the stage of rolling the wire rod, and the manufacturability is lowered. In addition, the twisting characteristics of the high-strength steel wire after wire drawing are deteriorated. Therefore, the amount of Si is preferably 1.49% or less, and more preferably 1.35% or less.
Ｍｎ：０．２０～０．９０％
　Ｍｎは鋼の焼き入れ性を高め、パーライト変態後の鋼の引張強さを高める効果がある。Ｍｎ量が０．２０％未満では上記効果が十分に得られない。そのためＭｎ量は０．２０％以上にする。これら効果を確実に得るためには、Ｍｎ量を０．３０％以上含有させることが好ましく、０．３５％以上とすることがなお好ましい。一方、Ｍｎ量が０．９０％を越えると鋼の焼き入れ性が高くなり過ぎ、上記効果が飽和するとともに、線材の延性が低下し、伸線加工後に得られる高強度鋼線の捻回特性が劣化する。そのため、Ｍｎ量は０．８０％以下とすることが好ましく、０．７５％以下とすることがなお好ましい。 Mn: 0.20 to 0.90%
Mn has the effect of increasing the hardenability of steel and increasing the tensile strength of steel after pearlite transformation. If the amount of Mn is less than 0.20%, the above effect cannot be sufficiently obtained. Therefore, the amount of Mn is set to 0.20% or more. In order to surely obtain these effects, the amount of Mn is preferably 0.30% or more, and more preferably 0.35% or more. On the other hand, when the amount of Mn exceeds 0.90%, the hardenability of the steel becomes too high, the above effect is saturated, the ductility of the wire rod decreases, and the twisting characteristics of the high-strength steel wire obtained after the wire drawing process. Deteriorates. Therefore, the amount of Mn is preferably 0.80% or less, and more preferably 0.75% or less.
Ｐ：０．０１５％以下
　Ｐは、不純物として含有される。Ｐは結晶粒界に偏析して耐水素脆化特性を劣化させるとともに、伸線加工性も劣化させるため、Ｐ量は低ければ低い方が望ましい。そのため、Ｐ量の上限は０．０１５％である。Ｐ量の好ましい範囲は、０．０１２％以下であり、より好ましくは０．０１０％以下である。なお、Ｐ量の下限値は特に限定されないが、０％超でもよく、例えば、製鋼コスト低減の点から、０．０００１％以上であってもよい。 P: 0.015% or less P is contained as an impurity. Since P segregates at the grain boundaries and deteriorates the hydrogen embrittlement resistance and the wire drawing workability, it is desirable that the amount of P is low. Therefore, the upper limit of the amount of P is 0.015%. The preferred range of the amount of P is 0.012% or less, more preferably 0.010% or less. The lower limit of the amount of P is not particularly limited, but may exceed 0%, and may be 0.0001% or more from the viewpoint of reducing steelmaking costs, for example.
Ｓ：０．０１５％以下
　Ｓは、不純物として含有される。Ｓは結晶粒界に偏析して耐水素脆化特性を劣化させるとともに、伸線加工性も劣化させるため、Ｓ量は抑制する必要がある。そのため、Ｓ量の上限は０．０１５％である。Ｓ量の好ましい範囲は、０．０１２％以下であり、より好ましい範囲は０．０１０％以下である。なお、Ｓ量の下限値は特に限定されないが、０％超でもよく、例えば、脱硫コスト低減の点から、０．０００１％以上であってもよい。 S: 0.015% or less S is contained as an impurity. Since S segregates at the grain boundaries to deteriorate the hydrogen embrittlement resistance and the wire drawing workability, it is necessary to suppress the amount of S. Therefore, the upper limit of the amount of S is 0.015%. The preferable range of the amount of S is 0.012% or less, and the more preferable range is 0.010% or less. The lower limit of the amount of S is not particularly limited, but may exceed 0%, and may be 0.0001% or more from the viewpoint of reducing desulfurization cost, for example.
Ａｌ：０．００５～０．０８０％
　Ａｌは脱酸元素であり、Ａｌ量が０．００５％未満の場合、酸化物が粗大となり、水素脆化による割れの起点となることから、線材の耐水素脆化特性を低下させる。そのため、Ａｌ量は０．００５％以上にする。上記効果を確実に得るために、Ａｌ量は０．００８％以上であることが好ましく、０．０１０％以上であることが一層好ましい。しかし、Ａｌ量が０．０８０％を超えると、上記効果が飽和するとともに、Ａｌを含む酸化物及び窒化物が粗大になり、圧延時に表面疵が発生するなど線材の製造性を低下させるし、かえって耐水素脆化特性を低下させる。そのため、Ａｌ量は０．０６０％以下とすることがよく、０．０５０％以下とすることがなお好ましい。 Al: 0.005 to 0.080%
Al is a deoxidizing element, and when the amount of Al is less than 0.005%, the oxide becomes coarse and becomes a starting point of cracking due to hydrogen embrittlement, so that the hydrogen embrittlement resistance property of the wire rod is deteriorated. Therefore, the amount of Al is set to 0.005% or more. In order to surely obtain the above effect, the Al amount is preferably 0.008% or more, and more preferably 0.010% or more. However, when the amount of Al exceeds 0.080%, the above effect is saturated, the oxides and nitrides containing Al become coarse, surface defects occur during rolling, and the manufacturability of the wire rod is lowered. On the contrary, it lowers the hydrogen embrittlement resistance. Therefore, the amount of Al is often 0.060% or less, and more preferably 0.050% or less.
Ｎ：０．００１５～０．００６０％
　Ｎは鋼中でＴｉなどの合金元素と反応し、窒化物及び炭窒化物を形成して線材の結晶粒を微細化するため、延性を向上させる効果がある。そのため、Ｎ量は０．００１５％以上にする。上記効果を確実に得るために、Ｎ量は０．００２１％以上であることが好ましく、０．００２５％以上であることが一層好ましい。一方、伸線加工によって高強度鋼線を製造する際、鋼中に固溶したＮがひずみ時効に大きく影響し、捻回特性が低下するため、含有量には注意を要し、Ｎ量は０．００６０％以下でなければならない。Ｎ量は０．００４９％以下とすることが好ましく、０．００４０％以下とすることがなお好ましい。 N: 0.0015 to 0.0060%
N reacts with an alloying element such as Ti in steel to form nitrides and carbonitrides to refine the crystal grains of the wire rod, which has an effect of improving ductility. Therefore, the amount of N should be 0.0015% or more. In order to surely obtain the above effect, the amount of N is preferably 0.0021% or more, and more preferably 0.0025% or more. On the other hand, when manufacturing high-strength steel wire by wire drawing, N dissolved in the steel greatly affects the strain aging and the twisting characteristics deteriorate, so care must be taken in the content, and the N amount is Must be 0.0060% or less. The amount of N is preferably 0.0049% or less, and more preferably 0.0040% or less.
Ｃｕ：０．１０～０．６５％
　Ｃｕは本開示に係る高強度鋼線用線材の耐食性及び耐水素脆化を向上する効果がある重要な元素であり、０．１０％以上含有させる。Ｃｕはパーライト組織内に固溶して存在するため、線材の耐食性及び耐水素脆化特性を向上する効果がある。Ｃｕが０．１０％未満の場合、上記効果は得られないため、Ｃｕ量は０．１０％以上にする。上記効果を確実に得るために、Ｃｕ量は０．１５％以上であることが好ましく、０．２０％以上であることが一層好ましい。一方、０．６５％を超えて含有した場合、線材を脆化させるため、伸線加工時に断線が発生しやすく、かえって線材の耐水素脆化特性を劣化させる。そのため、Ｃｕ量は０．６５％以下とし、０．６０％以下とすることが好ましく、０．５０％以下とすることがなお好ましい。 Cu: 0.10 to 0.65%
Cu is an important element having an effect of improving the corrosion resistance and hydrogen embrittlement resistance of the wire rod for high-strength steel wire according to the present disclosure, and contains 0.10% or more. Since Cu exists as a solid solution in the pearlite structure, it has the effect of improving the corrosion resistance and hydrogen embrittlement resistance of the wire rod. If Cu is less than 0.10%, the above effect cannot be obtained, so the amount of Cu is set to 0.10% or more. In order to surely obtain the above effect, the amount of Cu is preferably 0.15% or more, and more preferably 0.20% or more. On the other hand, if it is contained in excess of 0.65%, the wire is embrittled, so that wire breakage is likely to occur during wire drawing, and the hydrogen embrittlement resistance of the wire is deteriorated. Therefore, the amount of Cu is preferably 0.65% or less, preferably 0.60% or less, and more preferably 0.50% or less.
Ｎｉ：０．０５～０．６５％未満
　ＮｉはＣｕを含有する線材を製造する際に、圧延時に表面疵を抑制するために必須の元素であり、線材の焼き入れ性も向上させる効果がある。ただし、過剰な含有は伸線加工時の割れを誘発し、耐水素脆化特性を劣化させる。上記効果を得るために、Ｎｉは０．０５％以上含有させる。Ｎｉが０．０５％未満の場合、圧延時に線材の表面に表面疵が発生し、伸線加工時の断線発生要因となるし、線材の耐水素脆化特性も劣化させる。上記効果を得るために、Ｎｉ量は０．１０％以上であることが好ましく、０．１５％以上であることが一層好ましい。一方、Ｎｉ量を０．６５％以上含有した場合は焼き入れ性が高くなり過ぎ、かえって耐水素脆化特性を低下させる。そのため、Ｎｉ量は０．６５％未満とし、０．６０％以下とすることが好ましく、０．５０％以下とすることがなお好ましい。 Ni: 0.05 to less than 0.65% Ni is an essential element for suppressing surface defects during rolling when manufacturing a wire rod containing Cu, and has the effect of improving the hardenability of the wire rod. .. However, excessive content induces cracking during wire drawing and deteriorates hydrogen embrittlement resistance. In order to obtain the above effect, Ni is contained in an amount of 0.05% or more. If Ni is less than 0.05%, surface defects occur on the surface of the wire during rolling, which causes disconnection during wire drawing and deteriorates the hydrogen embrittlement resistance of the wire. In order to obtain the above effect, the amount of Ni is preferably 0.10% or more, and more preferably 0.15% or more. On the other hand, when the amount of Ni is 0.65% or more, the hardenability becomes too high, and the hydrogen embrittlement resistance is deteriorated. Therefore, the amount of Ni is preferably less than 0.65%, preferably 0.60% or less, and even more preferably 0.50% or less.
　また、Ｃｕ及びＮｉは［Ｃｕ］＞［Ｎｉ］、すなわち、［Ｃｕ］／［Ｎｉ］＞１．００を満足する範囲で含有することで、本開示における伸線加工後の高強度鋼線で良好な捻回特性を確保することができる。
　［Ｃｕ］／［Ｎｉ］が１．００以下、すなわちＮｉの含有量がＣｕの含有量以上である場合、本開示に係る高強度鋼線用線材では焼き入れ性が高くなり過ぎるため、伸線加工した高強度鋼線で十分な捻回特性が確保できなくなる。そのため、Ｃｕ及びＮｉは［Ｃｕ］＞［Ｎｉ］を満足する範囲で含有しなければならない。伸線加工後の鋼線の捻回特性を安定して確保するためには、［Ｃｕ］／［Ｎｉ］は１．２０以上であることが好ましく、１．５０以上であれば、さらに好ましい。Ｃｕ及びＮｉは［Ｃｕ］＞［Ｎｉ］を満足すればよく、［Ｃｕ］／［Ｎｉ］に上限は限定されないが、過剰に高すぎる場合には、線材の熱間圧延の工程で表面疵が発生するなど線材の製造性が低下する。そのため、線材の製造性を考慮し、［Ｃｕ］／［Ｎｉ］は５以下であることが好ましく、４以下であることが、なお好ましい。 Further, by containing Cu and Ni in a range satisfying [Cu]> [Ni], that is, [Cu] / [Ni]> 1.00, the high-strength steel wire after wire drawing in the present disclosure. Good twisting characteristics can be ensured.
When [Cu] / [Ni] is 1.00 or less, that is, the content of Ni is equal to or more than the content of Cu, the wire rod for high-strength steel wire according to the present disclosure has too high hardenability, so that the wire is drawn. Sufficient twisting characteristics cannot be ensured with processed high-strength steel wire. Therefore, Cu and Ni must contain [Cu]> [Ni] in a satisfactory range. In order to stably secure the twisting characteristics of the steel wire after wire drawing, [Cu] / [Ni] is preferably 1.20 or more, and more preferably 1.50 or more. Cu and Ni may satisfy [Cu]> [Ni], and the upper limit is not limited to [Cu] / [Ni], but if it is too high, surface defects may occur in the hot rolling process of the wire rod. The manufacturability of the wire rod is reduced due to the occurrence. Therefore, in consideration of the manufacturability of the wire rod, [Cu] / [Ni] is preferably 5 or less, and more preferably 4 or less.
　本開示に係る高強度鋼線用線材は、任意元素として、Ｃｒ、Ｍｏ、Ｔｉ、Ｎｂ、Ｖ、Ｓｎ、Ｂ、Ｃａ、Ｍｇ、Ｚｒ、ＲＥＭの各元素の１種又は２種以上を含有してもよい。これらの任意元素を含有する場合、質量％で、Ｃｒ：０～０．３０％、Ｍｏ：０～０．３０％、Ｔｉ：０～０．１００％、Ｎｂ：０～０．１００％、Ｖ：０～０．２０％、Ｓｎ：０～０．３０％、Ｂ：０～０．００５０％、Ｃａ：０～０．００５０％、Ｍｇ：０～０．００５０％、Ｚｒ：０～０．１００％、及びＲＥＭ：０～０．０２００％の１種又は２種以上を含有してもよい。 The wire rod for high-strength steel wire according to the present disclosure contains one or more of each element of Cr, Mo, Ti, Nb, V, Sn, B, Ca, Mg, Zr, and REM as an optional element. You may. When these arbitrary elements are contained, Cr: 0 to 0.30%, Mo: 0 to 0.30%, Ti: 0 to 0.100%, Nb: 0 to 0.100%, V in mass%. : 0 to 0.20%, Sn: 0 to 0.30%, B: 0 to 0.0050%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Zr: 0 to 0. It may contain one or more of 100% and REM: 0 to 0.0200%.
Ｃｒ：０～０．３０％
　Ｃｒは線材の焼き入れ性を高め、パーライト変態後の線材の引張強さを高める効果があり、この効果を得たい場合に含有してもよい。この効果を得るためには、Ｃｒ量は０．０１％以上含有させることが好ましい。上記効果を確実に得るために、Ｃｒ量は０．０５％以上であることが好ましく、０．１０％以上であることが一層好ましい。しかし、Ｃｒ量が０．３０％を超えると、マルテンサイト又はベイナイト組織が生じ易くなって、伸線加工性及び伸線加工後の高強度鋼線の耐水素脆化特性を劣化させる。そのため、Ｃｒを含有させる場合、Ｃｒ量は０．３０％以下とし、０．２５％以下とすることが好ましく、０．２０％以下とすることがなお好ましい。 Cr: 0 to 0.30%
Cr has the effect of enhancing the hardenability of the wire rod and increasing the tensile strength of the wire rod after the pearlite transformation, and may be contained when this effect is desired. In order to obtain this effect, the amount of Cr is preferably 0.01% or more. In order to surely obtain the above effect, the amount of Cr is preferably 0.05% or more, and more preferably 0.10% or more. However, if the amount of Cr exceeds 0.30%, martensite or bainite structure is likely to occur, which deteriorates the wire drawing workability and the hydrogen embrittlement resistance property of the high-strength steel wire after the wire drawing process. Therefore, when Cr is contained, the amount of Cr is preferably 0.30% or less, preferably 0.25% or less, and even more preferably 0.20% or less.
Ｍｏ：０～０．３０％
　Ｍｏは線材の焼き入れ性を高め、パーライト変態後の線材の引張強さを高める効果があり、この効果を得たい場合に含有してもよい。この効果を得るためには、Ｍｏ量は０．０１％以上であることが好ましい。上記効果を確実に得るために、Ｍｏ量は０．０３％以上であることが好ましく、０．０５％以上であることが一層好ましい。しかし、Ｍｏ量を０．３０％を超えて含有させると、マルテンサイト又はベイナイト組織が生じ易くなって、伸線加工性及び伸線加工後の高強度鋼線の耐水素脆化特性を劣化させる。そのため、Ｍｏを含有させる場合、Ｍｏ量は０．３０％以下とし、０．２０％以下とすることが好ましく、０．１０％以下とすることがなお好ましい。 Mo: 0 to 0.30%
Mo has the effect of enhancing the hardenability of the wire rod and increasing the tensile strength of the wire rod after the pearlite transformation, and may be contained when this effect is desired. In order to obtain this effect, the amount of Mo is preferably 0.01% or more. In order to surely obtain the above effect, the amount of Mo is preferably 0.03% or more, and more preferably 0.05% or more. However, if the amount of Mo exceeds 0.30%, martensite or bainite structure is likely to occur, which deteriorates the wire drawing workability and the hydrogen embrittlement resistance of the high-strength steel wire after the wire drawing process. .. Therefore, when Mo is contained, the amount of Mo is preferably 0.30% or less, preferably 0.20% or less, and even more preferably 0.10% or less.
Ｔｉ：０～０．１００％
　ＴｉはＣ又はＮと結合して炭化物又は炭窒化物を析出し、結晶粒を細粒化して線材の延性を向上させる効果があり、伸線加工後の耐水素脆化特性及び捻回特性を向上させる効果がある。また、Ｔｉの含有によって固溶Ｎを低減させることができるため、ひずみ時効を抑制し、伸線加工後の鋼線の捻回特性を向上する効果もある。Ｔｉ含有による上記効果は、本開示に係る高強度鋼線用線材を得るのに有効であることからＴｉは積極的に含有してよい。これら効果を得るためには、Ｔｉは０．００２％以上含有させればよい。上記効果を確実に得るために、Ｔｉ量は０．００５％以上であることが好ましく、０．００８％以上であることが一層好ましい。しかし、Ｔｉを０．１０％を超えて含有させても、上記効果が飽和するだけではなく、線材の強度が高くなり過ぎ、かえって伸線加工後の鋼線の耐水素脆化特性及び捻回特性が劣化する。そのため、Ｔｉを含有させる場合、Ｔｉ量は０．１０％以下とし、０．０５０％以下とすることが好ましく、０．０２５％以下とすることがなお好ましい。 Ti: 0 to 0.100%
Ti has the effect of combining with C or N to precipitate carbides or carbonitrides and finely graining the crystal grains to improve the ductility of the wire rod, and improves the hydrogen embrittlement resistance and twisting characteristics after wire drawing. It has the effect of improving. Further, since the solid solution N can be reduced by containing Ti, there is also an effect of suppressing strain aging and improving the twisting characteristics of the steel wire after wire drawing. Since the above effect due to the inclusion of Ti is effective in obtaining the wire rod for high-strength steel wire according to the present disclosure, Ti may be positively contained. In order to obtain these effects, Ti may be contained in an amount of 0.002% or more. In order to surely obtain the above effect, the amount of Ti is preferably 0.005% or more, and more preferably 0.008% or more. However, even if Ti is contained in excess of 0.10%, not only the above effect is saturated, but also the strength of the wire becomes too high, and on the contrary, the hydrogen embrittlement resistance and twisting of the steel wire after wire drawing are performed. The characteristics deteriorate. Therefore, when Ti is contained, the amount of Ti is preferably 0.10% or less, preferably 0.050% or less, and more preferably 0.025% or less.
Ｎｂ：０～０．１００％
　Ｎｂは炭化物又は炭窒化物を析出し、結晶粒を細粒化して線材の延性を向上させる効果があり、伸線加工後の耐水素脆化特性及び捻回特性を向上させる効果がある。この効果を得るためには、Ｎｂは０．００２％以上含有させることが好ましい。上記効果を確実に得るために、Ｎｂ量は０．００５％以上であることが好ましく、０．００８％以上であることが一層好ましい。しかし、Ｎｂを０．１００％を超えて含有させても、上記効果が飽和するだけではなく、分塊圧延によって鋼片を得る段階又は線材を圧延する段階で表面疵が発生しやすくなり、製造性が悪化する。そのため、Ｎｂを含有させる場合、Ｎｂ量は０．１００％以下とし、０．０５０％以下とすることが好ましく、０．０２５％以下とすることがなお好ましい。 Nb: 0 to 0.100%
Nb has the effect of precipitating carbides or carbonitrides and finely graining the crystal grains to improve the ductility of the wire rod, and has the effect of improving the hydrogen embrittlement resistance and twisting characteristics after wire drawing. In order to obtain this effect, it is preferable that Nb is contained in an amount of 0.002% or more. In order to surely obtain the above effect, the amount of Nb is preferably 0.005% or more, and more preferably 0.008% or more. However, even if Nb is contained in an amount of more than 0.100%, not only the above effect is saturated, but also surface defects are likely to occur at the stage of obtaining steel pieces by lump-rolling or at the stage of rolling the wire rod, and the production Sex gets worse. Therefore, when Nb is contained, the amount of Nb is preferably 0.100% or less, preferably 0.050% or less, and even more preferably 0.025% or less.
Ｖ：０～０．２０％
　Ｖは炭化物ＶＣを析出して、引張強さを高めるとともに、耐水素脆化特性を向上させる効果があり、この効果を得たい場合に含有してもよい。この効果を得るためには、Ｖは０．０１％以上含有させることが好ましい。上記効果を確実に得るために、Ｖ量は０．０３％以上であることが好ましく、０．０５％以上であることが一層好ましい。しかし、Ｖを０．２０％を超えて含有させても、上記効果が飽和するだけではなく、伸線加工後の鋼線の耐水素脆化特性及び捻回特性が劣化する。そのため、Ｖを含有させる場合、Ｖ量は０．２０％以下とし、０．１５％以下とすることが好ましく、０．１０％以下とすることがなお好ましい。 V: 0 to 0.20%
V has the effect of precipitating carbide VC to increase the tensile strength and the hydrogen embrittlement resistance, and may be contained when it is desired to obtain this effect. In order to obtain this effect, it is preferable that V is contained in an amount of 0.01% or more. In order to surely obtain the above effect, the amount of V is preferably 0.03% or more, and more preferably 0.05% or more. However, even if V is contained in excess of 0.20%, not only the above effect is saturated, but also the hydrogen embrittlement resistance and twisting characteristics of the steel wire after wire drawing are deteriorated. Therefore, when V is contained, the amount of V is preferably 0.20% or less, preferably 0.15% or less, and even more preferably 0.10% or less.
Ｓｎ：０～０．３０％
　Ｓｎはパーライト組織に固溶して、耐食性及び耐水素脆化特性を高める効果があり、この効果を得たい場合に含有してもよい。この効果を得るためには、Ｓｎは０．０１％以上含有させることが好ましい。上記効果を確実に得るために、Ｓｎ量は０．０３％以上であることが好ましく、０．０５％以上であることが一層好ましい。しかし、Ｓｎを０．３０％を超えて含有させても、上記効果が飽和するだけではなく、線材を脆化させるため、圧延時に表面疵が発生し、圧延材の製造性が悪くなる。そのため、Ｓｎを含有させる場合には、Ｓｎ量は０．０１～０．３０％とすることが好ましい。そのため、Ｓｎを含有させる場合、Ｓｎ量は０．３０％以下とし、０．２０％以下とすることが好ましく、０．１５％以下とすることがなお好ましい。 Sn: 0 to 0.30%
Sn has an effect of enhancing corrosion resistance and hydrogen embrittlement resistance by being dissolved in a pearlite structure, and may be contained when it is desired to obtain this effect. In order to obtain this effect, Sn is preferably contained in an amount of 0.01% or more. In order to surely obtain the above effect, the Sn amount is preferably 0.03% or more, and more preferably 0.05% or more. However, even if Sn is contained in an amount of more than 0.30%, not only the above effect is saturated but also the wire material is embrittled, so that surface defects occur during rolling and the manufacturability of the rolled material deteriorates. Therefore, when Sn is contained, the Sn amount is preferably 0.01 to 0.30%. Therefore, when Sn is contained, the Sn amount is preferably 0.30% or less, preferably 0.20% or less, and even more preferably 0.15% or less.
Ｂ：０～０．００５０％
　Ｂは等温変態後のパーライト組織分率を高め、伸線加工後の高強度鋼線の捻回特性を改善する効果があり、この効果を得たい場合に含有してもよい。この効果を得るためには、Ｂは０．０００２％以上含有させることが好ましい。上記効果を確実に得るために、Ｂ量は０．０００５％以上であることが好ましく、０．０００７％以上であることが一層好ましい。しかし、Ｂを０．００５０％を超えて含有させても、上記効果が飽和するだけではなく、線材を脆化させてしまい、圧延時に表面疵が発生し、製造性が悪くなるとともに、伸線加工後の高強度鋼線の捻回特性をかえって劣化させる。そのため、Ｂを含有させる場合、Ｂ量は０．００５０％以下とし、０．００３０％以下とすることが好ましく、０．００２０％以下とすることがなお好ましい。 B: 0 to 0.0050%
B has the effect of increasing the pearlite structure fraction after isothermal transformation and improving the twisting characteristics of the high-strength steel wire after wire drawing, and may be contained when this effect is desired. In order to obtain this effect, B is preferably contained in an amount of 0.0002% or more. In order to surely obtain the above effect, the amount of B is preferably 0.0005% or more, and more preferably 0.0007% or more. However, even if B is contained in an amount of more than 0.0050%, not only the above effect is saturated, but also the wire rod is embrittled, surface defects occur during rolling, the manufacturability is deteriorated, and the wire drawing is performed. The twisting characteristics of the high-strength steel wire after processing are rather deteriorated. Therefore, when B is contained, the amount of B is preferably 0.0050% or less, preferably 0.0030% or less, and even more preferably 0.0020% or less.
Ｃａ：０～０．００５０％
　Ｃａは、ＭｎＳ中に固溶し、ＭｎＳを微細に分散する効果があり、耐水素脆化特性を改善する効果があるため、効果を得たい場合に含有してもよい。Ｃａは含有しなくてもよいが（Ｃａ：０％）、Ｃａによって耐水素脆化特性を改善する効果を得るためには、Ｃａは０．０００２％以上含有させればよく、より高い効果を得たい場合には、０．０００５％以上を含有させればよい。しかし、Ｃａ量が０．００５０％を超えて含有しても、その効果は飽和するし、鋼中の酸素と反応して生成する酸化物が粗大となり、伸線加工後の捻回特性の低下を招く。したがって、含有させる場合の適正なＣａ量は、０．００５０％以下である。耐水素脆化特性及び捻回特性を向上させる観点から、Ｃａ量は０．００３０％以下であることが好ましく、０．００２５％以下であれば一層好ましい。 Ca: 0 to 0.0050%
Ca has an effect of being solid-solved in MnS and finely dispersing MnS, and has an effect of improving hydrogen embrittlement resistance. Therefore, Ca may be contained when an effect is desired. Ca may not be contained (Ca: 0%), but in order to obtain the effect of improving the hydrogen embrittlement resistance by Ca, it is sufficient that Ca is contained in an amount of 0.0002% or more, which is more effective. If it is desired to obtain it, it may contain 0.0005% or more. However, even if the Ca content exceeds 0.0050%, the effect is saturated, the oxide produced by reacting with oxygen in the steel becomes coarse, and the twisting characteristics after wire drawing are deteriorated. Invite. Therefore, the appropriate amount of Ca to be contained is 0.0050% or less. From the viewpoint of improving the hydrogen embrittlement resistance and the twisting property, the Ca amount is preferably 0.0030% or less, and more preferably 0.0025% or less.
Ｍｇ：０～０．００５０％
　Ｍｇは、ＭｎＳ中に固溶し、ＭｎＳを微細に分散する効果があり、耐水素脆化特性を改善する効果があるため、効果を得たい場合に含有してもよい。Ｍｇは含有しなくてもよいが（Ｍｇ：０％）、Ｍｇによって耐水素脆化特性を改善する効果を得るためには、Ｍｇは０．０００２％以上含有させればよく、より高い効果を得たい場合には、０．０００５％以上を含有させればよい。しかし、Ｍｇ量が０．００５０％を超えて含有しても、その効果は飽和するし、鋼中の酸素と反応して生成する酸化物が粗大となり、伸線加工後の捻回特性の低下を招く。したがって、含有させる場合の適正なＭｇ量は、０．００５０％以下である。耐水素脆化特性及び捻回特性を向上させる観点から、Ｍｇ量は０．００３０％以下であることが好ましく、０．００２５％以下であれば一層好ましい。 Mg: 0 to 0.0050%
Mg has an effect of being dissolved in MnS and finely dispersing MnS, and has an effect of improving hydrogen embrittlement resistance. Therefore, Mg may be contained when an effect is desired. Although it is not necessary to contain Mg (Mg: 0%), in order to obtain the effect of improving the hydrogen embrittlement resistance by Mg, it is sufficient to contain Mg in an amount of 0.0002% or more, which is more effective. If it is desired to obtain it, it may contain 0.0005% or more. However, even if the amount of Mg exceeds 0.0050%, the effect is saturated, the oxide produced by reacting with oxygen in the steel becomes coarse, and the twisting characteristics after wire drawing are deteriorated. Invite. Therefore, the appropriate amount of Mg when contained is 0.0050% or less. From the viewpoint of improving hydrogen embrittlement resistance and twisting characteristics, the amount of Mg is preferably 0.0030% or less, and more preferably 0.0025% or less.
Ｚｒ：０～０．１００％
　Ｚｒは、Ｏと反応して酸化物を生成し、微量に含有すれば酸化物を微細に分散し、伸線加工後の耐水素脆化特性及び捻回特性を抑制する効果があり、その効果を得たい場合に含有してもよい。この効果を得るためには、Ｚｒは０．０００２％以上含有させればよく、より高い効果を得たい場合には、０．００１％以上を含有させればよい。しかし、Ｚｒの含有量が０．１０％を超えて含有させた場合、その効果は飽和するし、粗大な窒化物又は硫化物を生成するため、かえって伸線加工後の耐水素脆化特性及び捻回特性の低下を招く。したがって、含有させる場合のＺｒの含有量は、０．１００％以下である。伸線加工後の耐水素脆化特性及び捻回特性に悪影響を与える介在物を低減させる観点から、Ｚｒの含有量は０．０８０％以下であることが好ましく、０．０５０％以下であれば一層好ましい。 Zr: 0 to 0.100%
Zr reacts with O to form an oxide, and if it is contained in a small amount, it finely disperses the oxide and has the effect of suppressing hydrogen embrittlement resistance and twisting characteristics after wire drawing, and the effect thereof. It may be contained when it is desired to obtain. In order to obtain this effect, Zr may be contained in an amount of 0.0002% or more, and when a higher effect is desired, it may be contained in an amount of 0.001% or more. However, when the Zr content exceeds 0.10%, the effect is saturated and coarse nitrides or sulfides are produced. Therefore, the hydrogen embrittlement resistance after wire drawing is obtained and the hydrogen embrittlement resistance is increased. It causes deterioration of twisting characteristics. Therefore, the content of Zr when contained is 0.100% or less. The Zr content is preferably 0.080% or less, preferably 0.050% or less, from the viewpoint of reducing inclusions that adversely affect the hydrogen embrittlement resistance and twisting characteristics after wire drawing. More preferred.
ＲＥＭ：０～０．０２００％
　ＲＥＭは希土類元素の総称であり、ＲＥＭの含有量は希土類元素の合計含有量である。ＲＥＭはＣａ及びＭｇと同じようにＭｎＳ中に固溶し、ＭｎＳを微細に分散する効果がある。ＭｎＳを微細に分散することで、耐水素脆化特性を改善することができるため、含有してもよい。ＲＥＭは含有しなくてもよいが（ＲＥＭ：０％）、ＲＥＭによって耐水素脆化特性を改善する効果を得るためには、ＲＥＭは０．０００２％以上含有させればよく、より高い効果を得たい場合には、０．０００５％以上を含有させればよい。しかし、ＲＥＭ量が０．０２０％を超えて含有しても、その効果は飽和するし、鋼中の酸素と反応して生成する酸化物が粗大となり、かえって伸線加工後の捻回特性の低下を招く。したがって、含有させる場合の適正なＲＥＭ量は、０．０２００％以下である。耐水素脆化特性及び捻回特性を向上させる観点から、ＲＥＭ量は０．０１００％以下であることが好ましく、０．００５０％以下であれば一層好ましい。 REM: 0-0.0200%
REM is a general term for rare earth elements, and the content of REM is the total content of rare earth elements. Like Ca and Mg, REM dissolves in MnS and has the effect of finely dispersing MnS. Since MnS can be finely dispersed to improve hydrogen embrittlement resistance, it may be contained. REM may not be contained (REM: 0%), but in order to obtain the effect of improving hydrogen embrittlement resistance by REM, 0.0002% or more of REM may be contained, and a higher effect can be obtained. If it is desired to obtain it, it may contain 0.0005% or more. However, even if the amount of REM is more than 0.020%, the effect is saturated and the oxide produced by reacting with oxygen in the steel becomes coarse, and rather the twisting characteristics after wire drawing are exhibited. It causes a decline. Therefore, the appropriate amount of REM when contained is 0.0200% or less. From the viewpoint of improving hydrogen embrittlement resistance and twisting characteristics, the REM amount is preferably 0.0100% or less, and more preferably 0.0050% or less.
残部：Ｆｅ及び不純物
　残部はＦｅ及び不純物である。「不純物」とは、意図せずに鋼材中に含有される成分であり、鉄鋼材料を工業的に製造する際に、原料としての鉱石、スクラップ、又は製造環境などから混入するものを指す。不純物としては、Ｐ、Ｓ、Ｎのほか、上記任意元素のうち意図せずに鋼材中に含有される元素、さらに、Ｏ（酸素）などが挙げられる。例えば、Ｏ（酸素）は、多量に含まれると鋼中で生成する酸化物が粗大となり、伸線加工後の捻回特性の低下を招くことから０．００３０％以下であることが好ましく、さらには０．００２５％以下であることが望ましい。 Residue: Fe and impurities The balance is Fe and impurities. The “impurity” is a component unintentionally contained in a steel material, and refers to a component mixed from ore, scrap, or a manufacturing environment as a raw material when a steel material is industrially manufactured. Examples of impurities include P, S, N, elements unintentionally contained in the steel material among the above optional elements, and O (oxygen) and the like. For example, O (oxygen) is preferably 0.0030% or less because if it is contained in a large amount, the oxide formed in the steel becomes coarse and the twisting characteristics after wire drawing are deteriorated. Is preferably 0.0025% or less.
　本開示に係る高強度鋼線用線材は、上記範囲で各成分を含有するとともに、下記式＜１＞で表されるＹ１が１．７０≦Ｙ１≦４．５０、式＜２＞で表されるＹ２がＹ２＜１．８１を満足する。
Ｙ１＝３×［Ｃｒ］＋５×［Ｍｎ］＋［Ｃｕ］＋［Ｎｉ］　　　・・・＜１＞
Ｙ２＝［Ｃ］＋［Ｓｉ］／１０＋Ａ　　　　　　　　　　　　　・・・＜２＞
ａ＝３５０×（［Ｎ］－０．２９×［Ｔｉ］）　・・・＜４＞
　ここで、上記式における［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｃｒ］、［Ｃｕ］、［Ｎｉ］、［Ｎ］、［Ｔｉ］は、それぞれの元素の質量％での含有量を表し、式＜２＞におけるＡは上記式＜４＞で表されるａに関連するパラメータであり、式＜４＞によって算出される値がａ≧０の場合はＡ＝ａであり、ａ＜０の場合はＡ＝０とする。
　なお、本開示に係る線材においてＣｒ及びＴｉは任意元素であり、これらの任意元素が本開示に係る線材に実質的に含まれない場合（無添加、すなわち、不純物レベルである場合）は、その元素の含有量は「０」としてＹ１、Ｙ２、ａをそれぞれ算出する。 The wire rod for high-strength steel wire according to the present disclosure contains each component in the above range, and Y1 represented by the following formula <1> is represented by 1.70 ≦ Y1 ≦ 4.50 and formula <2>. Y2 satisfies Y2 <1.81.
Y1 = 3 x [Cr] + 5 x [Mn] + [Cu] + [Ni] ... <1>
Y2 = [C] + [Si] / 10 + A ... <2>
a = 350 × ([N] −0.29 × [Ti]) ・ ・ ・ <4>
Here, [C], [Si], [Mn], [Cr], [Cu], [Ni], [N], and [Ti] in the above formula are the contents of each element in mass%. Represented, A in the formula <2> is a parameter related to a represented by the above formula <4>, and when the value calculated by the formula <4> is a ≧ 0, A = a, and a < If it is 0, A = 0.
In the wire rod according to the present disclosure, Cr and Ti are optional elements, and when these optional elements are not substantially contained in the wire rod according to the present disclosure (no addition, that is, at the impurity level), the case is considered. The element content is set to "0", and Y1, Y2, and a are calculated respectively.
　Ｙ１は、主に高強度鋼線用線材の焼き入れ性に関わり、線材の引張強さを高め、耐水素脆化特性を向上させるために必要なパラメータである。また、Ｙ１を１．７０≦Ｙ１≦４．５０の範囲とすることで高強度鋼線用線材の耐水素脆化特性を向上させることができ、伸線加工後の高強度鋼線の耐水素脆化特性を向上させることができる。 Y1 is mainly related to the hardenability of the wire rod for high-strength steel wire, and is a parameter necessary for increasing the tensile strength of the wire rod and improving the hydrogen embrittlement resistance. Further, by setting Y1 in the range of 1.70 ≦ Y1 ≦ 4.50, the hydrogen embrittlement resistance of the wire rod for high-strength steel wire can be improved, and the hydrogen embrittlement resistance of the high-strength steel wire after wire drawing is improved. The embrittlement characteristics can be improved.
　高強度鋼線は、化学成分及び金属組織を適切に制御した線材を伸線加工することによって得ることができる。伸線加工前に、線材を再加熱してパテンティング処理を行ったり、圧延後に直接、塩浴炉に浸漬して等温変態処理を行うこと等により、中心部まで均一性が高い微細パーライト組織とすることが好ましい。Ｙ１は、線材の焼き入れ性を制御し、表面から中心部まで均一性が高い微細なパーライト組織として必要な強度を与えると共に、線材の耐水素脆化特性を向上させるのに必要なパラメータであり、１．７０以上４．５０以下でなければならない。Ｙ１が１．７０未満の場合、耐水素脆化特性が低下し、伸線加工後の鋼線においても、十分な耐水素脆化特性を得ることができない。上記効果を確実に得るために、Ｙ１は２．００以上であることが好ましく、２．５０以上であることがなお好ましい。一方、Ｙ１が４．５０を超える場合、パテンティング処理又は圧延後の等温変態処理後に、ベイナイト及びマルテンサイトなどのパーライト組織以外の非パーライト組織が生成し、かえって線材の耐水素脆化特性を低下させる。Ｙ１は４．５０以下とし、４．２２以下であることが好ましい。線材の強度を確保し、より安定的に耐水素脆化特性を確保したい場合は、Ｙ１は４．００以下とすればよく、３．７５以下であれば、なお好ましい。 High-strength steel wire can be obtained by wire drawing a wire rod whose chemical composition and metal structure are appropriately controlled. Before the wire drawing process, the wire rod is reheated for a patenting process, or after rolling, it is directly immersed in a salt bath furnace for an isothermal transformation process to obtain a fine pearlite structure with high uniformity up to the center. It is preferable to do so. Y1 is a parameter necessary for controlling the hardenability of the wire rod, giving the strength required for a fine pearlite structure having high uniformity from the surface to the center, and improving the hydrogen embrittlement resistance of the wire rod. It must be 1.70 or more and 4.50 or less. If Y1 is less than 1.70, the hydrogen embrittlement resistance is lowered, and sufficient hydrogen embrittlement resistance cannot be obtained even in the steel wire after wire drawing. In order to surely obtain the above effect, Y1 is preferably 2.00 or more, and more preferably 2.50 or more. On the other hand, when Y1 exceeds 4.50, a non-pearlite structure other than the pearlite structure such as bainite and martensite is formed after the patenting treatment or the isothermal transformation treatment after rolling, and the hydrogen embrittlement resistance of the wire rod is rather deteriorated. Let me. Y1 is 4.50 or less, preferably 4.22 or less. When it is desired to secure the strength of the wire rod and more stably the hydrogen embrittlement resistance, Y1 may be set to 4.00 or less, and more preferably 3.75 or less.
　Ｙ２は、主に伸線加工後の鋼線の捻回特性に影響を及ぼすパラメータである。本開示に係る高強度鋼線用線材は、耐食性及び耐水素脆化特性を向上させるため、Ｃｕ及びＮｉを含有しており、線材の引張強さが比較的高いため、伸線加工でのダイスとの摩擦熱等による温度上昇によって、ひずみ時効の影響を受けて脆化しやすく、伸線加工後の鋼線の捻回特性が低下しやすい。特に、伸線加工によるひずみ時効には、Ｃ、Ｓｉ、鋼中に固溶したＮが大きく影響するため、Ｙ２は下記式＜２＞の通りに表すことができる。
Ｙ２＝［Ｃ］＋［Ｓｉ］／１０＋Ａ　　　　　　・・・＜２＞
ａ＝３５０×（［Ｎ］－０．２９×［Ｔｉ］）　・・・＜４＞
　ここで、上記式における［Ｃ］、［Ｓｉ］、［Ｎ］、［Ｔｉ］は、それぞれの元素の質量％での含有量を表し、Ａは式＜４＞で表されるａに関連するパラメータである。式＜４＞の右辺は固溶Ｎの影響を表しており、右辺の値が負になる場合は、固溶Ｎによるひずみ時効に及ぼす影響がなくなるので、Ａ＝０となる。伸線加工におけるひずみ時効の影響を最小限に抑えるため、Ｙ２の値は１．８１未満とする。Ｙ２が１．８１以上の場合、伸線加工によるひずみ時効の影響により、伸線加工後の捻回特性が低下する。伸線加工後の捻回特性を向上させるために、Ｙ２の値は１．７０未満であることが好ましく、１．５０未満であればなお好ましい。Ｙ２の値は１．８１未満であればよく、特に下限値は限定されないが、伸線加工後の引張強さを確保する観点から、０．５０以上であることが好ましく、０．８０以上であれば、さらに好ましい。 Y2 is a parameter that mainly affects the twisting characteristics of the steel wire after wire drawing. The wire rod for high-strength steel wire according to the present disclosure contains Cu and Ni in order to improve corrosion resistance and hydrogen embrittlement resistance, and since the tensile strength of the wire rod is relatively high, it is a die for wire drawing. Due to the temperature rise due to frictional heat with the steel wire, it tends to become brittle due to the influence of strain aging, and the twisting characteristics of the steel wire after wire drawing are likely to deteriorate. In particular, since C, Si, and N dissolved in steel have a great influence on the strain aging due to wire drawing, Y2 can be expressed as the following formula <2>.
Y2 = [C] + [Si] / 10 + A ... <2>
a = 350 × ([N] −0.29 × [Ti]) ・ ・ ・ <4>
Here, [C], [Si], [N], and [Ti] in the above formula represent the content of each element in mass%, and A is related to a represented by the formula <4>. It is a parameter. The right side of the equation <4> represents the influence of the solid solution N, and when the value on the right side is negative, the influence of the solid solution N on the strain aging disappears, so that A = 0. The value of Y2 is set to less than 1.81 in order to minimize the influence of strain aging in wire drawing. When Y2 is 1.81 or more, the twisting characteristics after the wire drawing process are deteriorated due to the influence of the strain aging caused by the wire drawing process. In order to improve the twisting characteristics after wire drawing, the value of Y2 is preferably less than 1.70, and even more preferably less than 1.50. The value of Y2 may be less than 1.81 and the lower limit is not particularly limited, but from the viewpoint of ensuring the tensile strength after wire drawing, it is preferably 0.50 or more, and 0.80 or more. If there is, it is more preferable.
＜金属組織＞
　本開示に係る高強度鋼線用線材の金属組織は、フェライトとセメンタイトの層状組織であるパーライト組織が９０％以上を占める。これは線材をパテンティング処理する段階又は等温変態処理する段階で、化学成分、変態前のγ粒径、又は冷却速度の変化によってフェライト、ベイナイト、又はマルテンサイトが生成する場合があり、これらの組織は、線材の長手方向における表層硬度のばらつきを増大させ、線材の耐水素脆化特性を低下させる。線材の長手方向における表層硬度のばらつきが大きい場合、伸線加工後の鋼線の耐水素脆化特性及び捻回特性が低下する。本開示に係る高強度鋼線用線材の金属組織は、パーライト組織が９２％以上であることが好ましく、９５％以上であることがより好ましい。
　なお、パーライト組織以外の残部組織（非パーライト組織）としては、マルテンサイト、ベイナイト、初析フェライト、初析セメンタイトなどが挙げられる。非パーライト組織としては、伸線加工後の鋼線の捻回特性及び耐水素脆化特性を極端に低下させない点から初析フェライト及び疑似パーライトが好ましく、疑似パーライトがより好ましい。なお、パーライト組織はラメラ構造を保つパーライトを指し、ラメラ構造が崩れた疑似パーライトは非パーライト組織として本開示では取り扱う。 <Metal structure>
The metal structure of the wire rod for high-strength steel wire according to the present disclosure occupies 90% or more of the pearlite structure which is a layered structure of ferrite and cementite. This is the stage of patenting or isothermal transformation of the wire, and ferrite, bainite, or martensite may be formed due to changes in chemical composition, γ particle size before transformation, or cooling rate, and these structures Increases the variation in surface hardness of the wire rod in the longitudinal direction, and lowers the hydrogen embrittlement resistance property of the wire rod. When the variation in surface hardness in the longitudinal direction of the wire is large, the hydrogen embrittlement resistance and twisting characteristics of the steel wire after wire drawing are deteriorated. The metal structure of the wire rod for high-strength steel wire according to the present disclosure preferably has a pearlite structure of 92% or more, and more preferably 95% or more.
Examples of the residual structure (non-pearlite structure) other than the pearlite structure include martensite, bainite, proeutectoid ferrite, and proeutectoid cementite. As the non-pearlite structure, proeutectoid ferrite and pseudo-pearlite are preferable, and pseudo-pearlite is more preferable, from the viewpoint of not extremely deteriorating the twisting property and hydrogen embrittlement resistance of the steel wire after wire drawing. The pearlite structure refers to pearlite that maintains a lamellar structure, and pseudo-pearlite with a collapsed lamellar structure is treated as a non-pearlite structure in the present disclosure.
＜特性＞
（表層硬度のばらつき）
　線材の長手方向に生じる化学成分又は金属組織のばらつきに起因する線材表層の硬度ばらつきは、耐水素脆化特性にも影響を及ぼし、伸線加工後の鋼線の特性にも大きな影響を及ぼす。特に、耐水素脆化特性は線材表層の硬度ばらつきが影響し、線材表層に硬度が高い部分が存在すると、水素脆化の起点となるため、耐水素脆化特性が低下する。
　本開示に係る線材は、任意の等間隔で８個のサンプルを採取し、各サンプルの軸方向断面（中心軸を含む長手方向に平行な断面）において線材の表面から深さ５０μｍの位置（以下、「５０μｍ深さ」と記す場合がある。）で測定されるビッカース硬さＨｖｓｉの最大値Ｈｖｓｉｍａｘと平均値Ｈｖｓｉａｖｅとの関係が下記（４）を満たすようにする。
（４）Ｈｖｓｉｍａｘ－Ｈｖｓｉａｖｅ≦５０ <Characteristics>
(Variation of surface hardness)
The variation in hardness of the surface layer of the wire due to the variation in the chemical composition or metal structure that occurs in the longitudinal direction of the wire also affects the hydrogen embrittlement resistance and the characteristics of the steel wire after wire drawing. In particular, the hydrogen embrittlement resistance is affected by the variation in hardness of the wire surface layer, and if there is a portion having high hardness on the wire surface layer, it becomes the starting point of hydrogen embrittlement, so that the hydrogen embrittlement resistance deteriorates.
In the wire rod according to the present disclosure, eight samples are taken at arbitrary equal intervals, and the depth is 50 μm from the surface of the wire rod in the axial cross section (cross section parallel to the longitudinal direction including the central axis) of each sample (hereinafter, , "50 μm depth"), so that the relationship between the maximum value Hv simax of the Vickers hardness Hv si and the average value Hv siave satisfies the following (4).
(4) Hv simax -Hv siave ≦ 50
　なお、本開示において線材の「表層」とは、線材の表面（外周面）から深さ１００μｍまでの領域であり、表層の中間地点の５０μｍ深さで硬度測定を行う。
　ビッカース硬さを測定するためのサンプルは、測定対象となる線材の長さに応じて任意の等間隔で採取する。線材は、通常、リング状に巻かれた状態で製造されるため、１リングに相当する長さ以上の線材であれば、１リングに相当する長さから等間隔で８個のサンプルを採取して各サンプルのビッカース硬さを測定し、各サンプルのビッカース硬さの平均値と最大値を求めることが好ましい。具体的には、線材の長手方向から６００ｍｍの間隔をあけ、２５ｍｍ長さで採取した８個の各サンプルｓｉ（ｉは１～８の整数）について、各サンプルで測定される、軸方向断面（中心軸を含む長手方向に平行な断面）の線材の表面から深さ５０μｍの位置におけるビッカース硬さの各サンプル内の平均値をそれぞれＨｖｓｉ、８個のＨｖｓｉ（ｉは１～８の整数）の最大値をＨｖｓｉｍａｘとしたとき、式＜３＞で表されるＹ３の値を５０以下にする。 In the present disclosure, the "surface layer" of the wire rod is a region from the surface (outer peripheral surface) of the wire rod to a depth of 100 μm, and the hardness is measured at a depth of 50 μm at an intermediate point of the surface layer.
Samples for measuring Vickers hardness are taken at arbitrary equal intervals according to the length of the wire to be measured. Since the wire rod is usually manufactured in a state of being wound in a ring shape, if the wire rod has a length corresponding to one ring or more, eight samples are collected at equal intervals from the length corresponding to one ring. It is preferable to measure the Vickers hardness of each sample and obtain the average value and the maximum value of the Vickers hardness of each sample. Specifically, for each of the eight samples si (i is an integer of 1 to 8) collected at a distance of 600 mm from the longitudinal direction of the wire and having a length of 25 mm, the axial cross section (i is an integer of 1 to 8) is measured in each sample. The average value of Vickers hardness in each sample at a depth of 50 μm from the surface of the wire rod in the longitudinal direction including the central axis is Hv si , and 8 Hv si (i is an integer of 1 to 8). ) Is set to Hv simax, and the value of Y3 represented by the equation <3> is set to 50 or less.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　式＜３＞の右辺は、８個のサンプルで得られたＨｖｓｉの最大値Ｈｖｓｉｍａｘと８個のサンプルで得られたＨｖｓｉの下記式（ｎ＝８）で算出される平均値Ｈｖｓｉａｖｅ（本開示において「全体平均ビッカース硬さ」と称する場合がある。）との差を示している。 Wherein the right side of the <3> has an average value Hv Siave calculated by the following equation Hv si obtained by the maximum value Hv Simax and eight samples of Hv si obtained in 8 samples (n = 8) (In this disclosure, it may be referred to as "overall average Vickers hardness".).
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　各サンプルのＨｖｓｉは、線材から軸方向断面を樹脂埋めして鏡面研磨したサンプルを用い、自動ビッカース硬度計によって軸方向断面における線材の表面から深さ５０μｍの位置を０．９８Ｎの荷重で１つのサンプルにつき２００μｍのピッチで５０点（すなわち、１０ｍｍ長さ）測定して求めればよい。
　こうして求めた８個のＨｖｓｉのうち、最大値であるＨｖｓｉｍａｘは、６００ｍｍの間隔をあけて採取した２５ｍｍ長さの８個のサンプルの中で、軸方向断面における線材の表面から深さ５０μｍの位置の硬度が最も高いサンプルのビッカース硬度であり、言い換えれば線材の長手方向における表層硬度のばらつきのなかで、最も高い平均硬度が測定された部位のビッカース硬度を意味している。線材の水素脆化は、線材表層の硬度ばらつきが影響し、線材表層の硬度が局部的に高い部分が破壊の起点となって、水素脆化による破断が発生する。８個のサンプルで測定されたＨｖｓｉｍａｘが他のサンプルも含めた５０μｍ深さ位置の全体平均ビッカース硬さよりも、５０を超えて高い場合、その部位において水素脆化による破断可能性が高まり、線材の耐水素脆化特性が低下する。さらに線材を伸線加工することで得られる鋼線では、長手方向における表層硬度のばらつきはさらに大きくなり、鋼線における耐水素脆化特性の低下はより顕著になる。Ｙ３の値が５０以下であれば、線材の耐水素脆化特性を低下させることが抑制され、さらに伸線加工によって得られる鋼線の耐水素脆化特性の低下も抑制される。Ｙ３の値は、耐水素脆化特性を向上させる観点から小さいほど好ましく、３０以下であることが好ましく、さらに２５以下であればなお好ましい。 The Hv si of each sample uses a sample in which the axial cross section is resin-filled from the wire and mirror-polished, and the position at a depth of 50 μm from the surface of the wire in the axial cross section with an automatic Vickers hardness tester is 1 with a load of 0.98 N. It may be obtained by measuring 50 points (that is, 10 mm length) at a pitch of 200 μm per sample.
Of the eight Hv si thus determined, Hv Simax the maximum value, among the eight samples of 25mm length taken apart 600 mm, depth 50μm from the surface of the wire rod in the axial section The Vickers hardness of the sample with the highest hardness at the position of, in other words, the Vickers hardness of the portion where the highest average hardness was measured among the variations in the surface hardness in the longitudinal direction of the wire rod. Hydrogen embrittlement of the wire is affected by variations in the hardness of the surface layer of the wire, and the portion where the hardness of the surface layer of the wire is locally high becomes the starting point of fracture, and fracture due to hydrogen embrittlement occurs. If the Hv simax measured in 8 samples is higher than the overall average Vickers hardness at the 50 μm depth position including other samples by more than 50, the possibility of breakage due to hydrogen embrittlement increases at that site, and the wire rod Hydrogen embrittlement resistance is reduced. Further, in the steel wire obtained by wire drawing the wire rod, the variation in surface hardness in the longitudinal direction becomes larger, and the decrease in hydrogen embrittlement resistance of the steel wire becomes more remarkable. When the value of Y3 is 50 or less, the deterioration of the hydrogen embrittlement resistance property of the wire rod is suppressed, and further, the deterioration of the hydrogen embrittlement resistance property of the steel wire obtained by the wire drawing process is also suppressed. The value of Y3 is preferably as small as possible from the viewpoint of improving the hydrogen embrittlement resistance property, preferably 30 or less, and even more preferably 25 or less.
　線材の長手方向から６００ｍｍの間隔をあけて採取される２５ｍｍ長さのサンプル数は８である。すなわち、８個のサンプルについて、軸方向断面における線材の表面から深さ５０μｍの位置におけるビッカース硬さの各サンプル内の平均値Ｈｖｓｉを求めれば、線材表層の硬度ばらつきを知ることができる。線材表層の硬度ばらつきは、圧延して捲き取られた線材コイルの少なくとも１リングに相当する範囲で表層硬度のばらつきを調査することが好ましい。これは、熱間圧延後にオーステナイト域で捲き取られた線材リングは前後のリングと一部が重なった状態でコンベア上を搬送されるため、一つのリングの中で接触している部位、あるいは距離が近い部位（重なり部）と、前後のリングと離れている部位（非重なり部）が存在している。このような理由により、捲き取り後にコイルの１リング内で冷却速度の違いが生じるため、重なり部と非重なり部のパーライト変態温度に差が生じる。これによって重なり部と非重なり部のパーライトラメラ間隔に差が生じ、結果として大きな表層硬度のばらつきが生じる。一方、線材コイル内の各リングは基本的に同条件（一定の条件）で捲き取られているので、各リング間のばらつきは小さい。そのため、６００ｍｍの間隔をあけて、８個のサンプルを採取すれば、線材の長手方向の略４２００ｍｍの範囲で表層硬度のばらつきを検証したこととなり、線材コイルの１リング以上に相当する長さで表層硬度のばらつきを検証できる。上述の通り各リング間のバラツキは小さいので、上記のサンプル採取法によって線材コイル内のバラツキを検証できる。 The number of 25 mm long samples collected at intervals of 600 mm from the longitudinal direction of the wire is eight. That is, if the average value Hv si of the Vickers hardness in each sample at a position of 50 μm from the surface of the wire rod in the axial cross section of the eight samples is obtained, the hardness variation of the wire rod surface layer can be known. As for the variation in hardness of the wire rod surface layer, it is preferable to investigate the variation in surface layer hardness within a range corresponding to at least one ring of the wire rod coil rolled up. This is because the wire rod ring wound up in the austenite region after hot rolling is conveyed on the conveyor with a part of it overlapping the front and rear rings, so the parts or distances in contact within one ring. There are parts that are close to each other (overlapping parts) and parts that are separated from the front and rear rings (non-overlapping parts). For this reason, a difference in cooling rate occurs within one ring of the coil after winding, so that a difference occurs in the pearlite transformation temperature between the overlapping portion and the non-overlapping portion. This causes a difference in the pearlite lamella spacing between the overlapping portion and the non-overlapping portion, resulting in a large variation in surface hardness. On the other hand, since each ring in the wire coil is basically wound under the same conditions (constant conditions), the variation between the rings is small. Therefore, if eight samples were taken at intervals of 600 mm, the variation in surface hardness was verified within a range of approximately 4200 mm in the longitudinal direction of the wire, and the length was equivalent to one ring or more of the wire coil. Variations in surface hardness can be verified. Since the variation between the rings is small as described above, the variation in the wire coil can be verified by the above sampling method.
　なお、本開示に係る線材の長さ及び製造時の１リングの長さは特に限定されず、線材からサンプルを採取する間隔は６００ｍｍに限定されない。本開示に係る線材は、長さに関わらず、また、ビッカース硬さを測定するためのサンプルを採取する間隔に関わらず、Ｈｖｓｉｍａｘ－Ｈｖｓｉａｖｅ≦５０を満たすことで、特性を満足することができる。なお、実際の線材の製造においては、線材の長さ方向にバラツキが生じる。このため製造方法を適宜調整すれば、線材の長さ方向にバラツキを低減した線材が得られる。１リングの長さが約４２００ｍｍの線材であれば、ビッカース硬さ試験を６００ｍｍ間隔で行うことで、線材コイルの長さ方向に特性を確認することができる。また、１リングの長さが４２００ｍｍでない場合は、１リングに相当する長さから等間隔で８個のサンプルを採取して各サンプルのビッカース硬さＨｖｓｉを測定し、最大値Ｈｖｓｉｍａｘ最大値と平均値Ｈｖｓｉａｖｅの差を算出することで線材コイルの長さ方向のビッカース硬さを確認することができる。また、線材の長さが１リングに満たない場合は、全体から等間隔で８個のサンプルを採取して各サンプルのビッカース硬さＨｖｓｉを測定し、最大値Ｈｖｓｉｍａｘと平均値Ｈｖｓｉａｖｅの差を算出することが好ましい。 The length of the wire rod according to the present disclosure and the length of one ring at the time of manufacture are not particularly limited, and the interval for collecting a sample from the wire rod is not limited to 600 mm. The wire rod according to the present disclosure may satisfy the characteristics by satisfying Hv simax- Hv siave ≤ 50 regardless of the length and the interval at which samples for measuring Vickers hardness are taken. it can. In the actual production of the wire rod, there is a variation in the length direction of the wire rod. Therefore, if the manufacturing method is appropriately adjusted, a wire rod with reduced variation in the length direction of the wire rod can be obtained. If the length of one ring is about 4200 mm, the characteristics can be confirmed in the length direction of the wire coil by performing the Vickers hardness test at intervals of 600 mm. If the length of one ring is not 4200 mm, eight samples are taken at equal intervals from the length corresponding to one ring, the Vickers hardness Hv si of each sample is measured, and the maximum value Hv simax maximum value is measured. The Vickers hardness in the length direction of the wire rod coil can be confirmed by calculating the difference between the average value Hv hybrid and the average value Hv hybrid . If the length of the wire is less than one ring, eight samples are taken at equal intervals from the whole, and the Vickers hardness Hv si of each sample is measured, and the maximum value Hv simax and the average value Hv siave are measured . It is preferable to calculate the difference.
（引張強さ）
　線材及び鋼線の強度が高ければ高いほど、腐食の進行又は水素脆化による破断を発生しやすいが、本開示に係る高強度鋼線用線材を用いて鋼線を製造した場合、引張強さが１７００ＭＰａを超える場合であっても、耐食性及び耐水素脆化特性に優れるため、鋼線又は撚り線後の製品を腐食環境で使用した場合にも破断が発生しにくくなる。また、線材の引張強さが高くない場合でも伸線加工での加工減面率を大きくすることで、引張強さが１７００ＭＰａを超える高強度鋼線を得ることができるが、伸線加工の加工減面率を大きくし過ぎた場合、捻回特性が低下するし、耐水素脆化特性も低下する。そのため、伸線加工前の線材で引張強さを１０００ＭＰａ以上とし、伸線加工の加工減面率を過剰に大きくすることなく、高強度鋼線を製造することが好ましい。線材の段階で微細パーライト組織として１０００ＭＰａ以上の引張強さがあれば、伸線加工後の鋼線における引張強さ及び耐水素脆化特性の低下が抑制される。
　鋼線における捻回特性及び耐水素脆化特性を向上させるため、線材の引張強さが１２００ＭＰａ以上であればより好ましく、１３００ＭＰａ以上であれば、さらに好ましい。
　一方、線材の引張強さが１６５０ＭＰａを超える場合は、線材の延性が低下し、伸線加工後の鋼線の捻回特性及び耐水素脆化特性がかえって低下する可能性がある。この観点から、線材の引張強さは１６００ＭＰａ以下であることが好ましく、１５５０ＭＰａ以下であれば、さらに好ましい。 (Tensile strength)
The higher the strength of the wire and steel wire, the more likely it is that corrosion will progress or breakage will occur due to hydrogen embrittlement. However, when a steel wire is manufactured using the high-strength steel wire wire according to the present disclosure, the tensile strength Even when it exceeds 1700 MPa, it is excellent in corrosion resistance and hydrogen embrittlement resistance, so that breakage is less likely to occur even when the product after steel wire or stranded wire is used in a corrosive environment. Further, even when the tensile strength of the wire rod is not high, a high-strength steel wire having a tensile strength exceeding 1700 MPa can be obtained by increasing the processing surface reduction rate in the wire drawing process. If the surface reduction rate is made too large, the twisting characteristics are lowered and the hydrogen embrittlement resistance is also lowered. Therefore, it is preferable to set the tensile strength of the wire rod before wire drawing to 1000 MPa or more and to manufacture a high-strength steel wire without excessively increasing the processing surface reduction rate of wire drawing. If the fine pearlite structure has a tensile strength of 1000 MPa or more at the wire rod stage, deterioration of the tensile strength and hydrogen embrittlement resistance of the steel wire after wire drawing is suppressed.
In order to improve the twisting property and the hydrogen embrittlement resistance of the steel wire, it is more preferable that the tensile strength of the wire is 1200 MPa or more, and further preferably 1300 MPa or more.
On the other hand, when the tensile strength of the wire rod exceeds 1650 MPa, the ductility of the wire rod is lowered, and the twisting characteristics and hydrogen embrittlement resistance of the steel wire after the wire drawing process may be lowered. From this point of view, the tensile strength of the wire is preferably 1600 MPa or less, and more preferably 1550 MPa or less.
　本開示に係る高強度鋼線用線材を用いて伸線加工することで、１７００ＭＰａを超える高い強度でも、耐食性と耐水素脆化特性に優れた高強度鋼線を得ることができる。これは、線材を製造する段階で化学成分の偏析、金属組織、及び線材表層の硬度分布を制御し、耐食性と耐水素脆化特性を向上させているためである。
　本開示に係る線材は、優れた耐食性と耐水素脆化特性を有し、伸線加工後の鋼線における捻回特性にも優れることから、伸線加工によって強度を高め、高強度ロープ用鋼線、橋梁ケーブル用鋼線、ＰＣ鋼線等の高強度鋼線として利用可能である。 By wire drawing using the high-strength steel wire rod according to the present disclosure, it is possible to obtain a high-strength steel wire having excellent corrosion resistance and hydrogen embrittlement resistance even at a high strength exceeding 1700 MPa. This is because the segregation of chemical components, the metal structure, and the hardness distribution of the surface layer of the wire are controlled at the stage of manufacturing the wire to improve the corrosion resistance and the hydrogen embrittlement resistance.
The wire rod according to the present disclosure has excellent corrosion resistance and hydrogen embrittlement resistance, and also has excellent twisting characteristics in steel wire after wire drawing. Therefore, the strength is increased by wire drawing and steel for high-strength rope. It can be used as high-strength steel wire such as wire, steel wire for bridge cables, and PC steel wire.
＜測定方法＞
　線材の金属組織、線材及び鋼線の引張強さ、線材の表層硬度のばらつき、線材の耐食性、線材及び鋼線の耐水素脆化特性、並びに鋼線の捻回特性はそれぞれ以下の方法で調査した。 <Measurement method>
The metallographic structure of the wire, the tensile strength of the wire and the steel wire, the variation in the surface hardness of the wire, the corrosion resistance of the wire, the hydrogen embrittlement resistance of the wire and the steel wire, and the twisting property of the steel wire are investigated by the following methods. did.
〈１〉線材の金属組織：
　線材の金属組織の面積率は、線材の長手方向に平行であり、中心軸を通る断面を樹脂埋めしたミクロサンプルを鏡面研磨した後、ピクラール溶液を用いて金属組織を現出させた。次に、線材の直径をＤとしたとき、線材表面から０．２５Ｄの深さの位置に相当する部位の金属組織を走査型電子顕微鏡（ＳＥＭ）を用いて、１０００倍の倍率で１０箇所の組織写真を撮影した。撮影された各写真についてセメンタイトとフェライトの層状組織と判断される、パーライト組織に相当する部分を塗りつぶし、画像解析によって面積値を測定してパーライト面積率を算出し、１０箇所の測定値を平均してパーライト面積率を求めた。なお、パーライト組織以外の組織は、部分的に生成したマルテンサイト、ベイナイト、及び初析フェライトなど、セメンタイトとフェライトの層状組織であるパーライト組織として判別できない非パーライト組織である。 <1> Metal structure of wire rod:
The area ratio of the metal structure of the wire was parallel to the longitudinal direction of the wire, and after mirror polishing a microsample in which the cross section passing through the central axis was embedded with resin, the metal structure was revealed using a picral solution. Next, when the diameter of the wire is D, the metal structure of the part corresponding to the position at a depth of 0.25D from the surface of the wire is measured at 10 points at a magnification of 1000 times using a scanning electron microscope (SEM). A tissue photograph was taken. For each photograph taken, the part corresponding to the pearlite structure, which is judged to be the layered structure of cementite and ferrite, is filled in, the area value is measured by image analysis to calculate the pearlite area ratio, and the measured values at 10 points are averaged. The pearlite area ratio was calculated. The structure other than the pearlite structure is a non-pearlite structure that cannot be distinguished as a pearlite structure, which is a layered structure of cementite and ferrite, such as partially formed martensite, bainite, and proeutectoid ferrite.
〈２〉線材及び鋼線の引張強さ：
　引張試験は、線材及び伸線加工後の鋼線の長手方向に２５０～３００ｍｍの間隔をあけて採取した、４００ｍｍ長さの試験片を用い、ＪＩＳ　Ｚ　２２４１：２０１１に準拠して行った。試験片が破断に至るまでの最大試験力を引張試験前に測定した直径から求められる断面積で除し、引張強さを求めた。試験は８本の試験片を用いて測定し、その平均値を線材及び鋼線の引張強さとした。 <2> Tensile strength of wire rod and steel wire:
The tensile test was carried out in accordance with JIS Z 2241: 2011 using a test piece having a length of 400 mm, which was collected at intervals of 250 to 300 mm in the longitudinal direction of the wire rod and the steel wire after wire drawing. The maximum test force until the test piece broke was divided by the cross-sectional area obtained from the diameter measured before the tensile test to obtain the tensile strength. The test was measured using eight test pieces, and the average value was taken as the tensile strength of the wire and steel wire.
〈３〉線材の表層硬度のばらつき：
　表層硬度の測定は、線材の長手方向に６００ｍｍの間隔（等間隔の一例）をあけて採取した、２５ｍｍ長さの試験片を用いた。試験片は、８個（ｎ＝８）のサンプルを採取し、線材の長さ方向に平行な断面を樹脂埋めした後、鏡面研磨したミクロサンプルを用いた。各ミクロサンプルに対し、自動ビッカース硬度計を用いてＪＩＳ　Ｚ　２２４４：２００９に準拠して、硬度測定を行った。硬度測定の試験荷重は０．９８Ｎであり、各ミクロサンプルにおける線材表面から５０μｍ深さの位置におけるビッカース硬度を５０箇所測定して平均値を算出し、各試験片のＨｖｓｉ（ｉ＝１、２、・・・８）を求めた。さらに、各ミクロサンプルで測定されたＨｖｓｉの最大値Ｈｖｓｉｍａｘを求め、併せてＨｖｓｉの全体平均ビッカース硬さＨｖｓｉａｖｅを算出し、下記式＜３＞で表されるＹ３を算出した。 <3> Variation in surface hardness of wire rod:
The surface hardness was measured using a test piece having a length of 25 mm, which was collected at intervals of 600 mm (an example of equal intervals) in the longitudinal direction of the wire. As the test piece, eight (n = 8) samples were taken, a cross section parallel to the length direction of the wire was embedded with resin, and then a mirror-polished micro sample was used. Hardness measurements were performed on each microsample using an automatic Vickers hardness tester in accordance with JIS Z 2244: 2009. The test load for hardness measurement is 0.98 N, and the Vickers hardness at a depth of 50 μm from the wire surface in each microsample is measured at 50 points to calculate the average value, and the Hv si (i = 1, 1,) of each test piece is calculated. 2, ... 8) was requested. Further, the maximum value Hv simax of Hv si measured in each micro sample was obtained, and the overall average Vickers hardness Hv siave of Hv si was also calculated, and Y3 represented by the following formula <3> was calculated.
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
〈４〉線材の耐食性：
　線材の中心部軸方向から長さ１００ｍｍで切断した試験片の外周部を均等に削って直径７ｍｍに機械加工したφ７×１００ｍｍＬの試験片を各２本ずつ切り出した。腐食試験は、塩水噴霧が可能な乾湿繰り返し腐食試験機を用い、（１）塩水噴霧（５％ＮａＣｌ噴霧、３５℃、２ｈｒ）、（２）乾燥（湿度２０％、６０℃、４ｈｒ）、（３）湿潤（湿度９５％、５０℃、２ｈｒ）を１サイクルとする試験を行った。試験期間は１２週間とし、各２本の試験片の腐食による体積減少率を求め、その平均値を各線材の耐食性の評価指標とした。腐食による体積減少率（％）は下記式によって求めた。
　腐食体積減少率（％）＝１００×（腐食試験前の試験片体積－腐食試験後の試験片体積）／腐食試験前の試験片体積
　腐食試験前の試験片体積は、試験前に、位置を変えて３点測定した試験片の直径及び試験片長さの平均値を求め、腐食試験前の試験片体積を算出した。腐食試験後の試験片体積は、腐食試験後にサンドブラストを使って試験片表面の腐食生成物を完全に除去した後、位置を変えて３点測定した試験片の直径及び試験片長さの平均値を求め、腐食試験後の試験片体積を算出した。 <4> Corrosion resistance of wire rod:
Two φ7 × 100 mmL test pieces machined to a diameter of 7 mm were cut out by evenly cutting the outer peripheral portion of the test piece cut with a length of 100 mm from the central axial direction of the wire rod. For the corrosion test, a dry and wet repeated corrosion tester capable of spraying salt water was used, (1) salt water spray (5% NaCl spray, 35 ° C, 2 hr), (2) drying (humidity 20%, 60 ° C, 4 hr), ( 3) A test was conducted in which wetness (humidity 95%, 50 ° C., 2 hr) was used as one cycle. The test period was 12 weeks, and the volume reduction rate due to corrosion of each of the two test pieces was determined, and the average value was used as an evaluation index of the corrosion resistance of each wire rod. The volume reduction rate (%) due to corrosion was calculated by the following formula.
Corrosion volume reduction rate (%) = 100 × (Test piece volume before corrosion test-Test piece volume after corrosion test) / Test piece volume before corrosion test The test piece volume before corrosion test is the position before the test. The average value of the diameter of the test piece and the length of the test piece measured at three points was obtained, and the volume of the test piece before the corrosion test was calculated. The volume of the test piece after the corrosion test is the average value of the diameter of the test piece and the length of the test piece measured at three points after completely removing the corrosion products on the surface of the test piece using sandblasting after the corrosion test. The volume of the test piece after the corrosion test was calculated.
〈５〉線材及び鋼線の耐水素脆化特性：
　線材及び伸線加工後の鋼線の耐水素脆化特性は、国際プレストレストコンクリート連盟（Ｆｅｄｅｒａｔｉｏｎ　Ｉｎｔｅｒｎａｔｉｏｎａｌｅ　ｄｅ　ｌａ　Ｐｒｅｃｏｎｔｒａｉｎｔｅ）で規格化されたＦＩＰ試験によって評価した。線材あるいは伸線加工後の鋼線を酸洗処理して表面のスケール又は潤滑皮膜を除去した後、矯直加工を行って真直性を確保し、７００ｍｍＬ長さに切断したサンプルを試験片として用いた。次いで試験片の中心部を含む２００ｍｍ長さが浸漬できる溶液セルを用い、５０℃のチオシアン酸アンモニウム（ＮＨ４ＳＣＮ）水溶液に試験片を浸漬させた状態とし、引張試験から得た破断荷重の７０％の一定荷重を試験片に負荷し、破断までの時間を測定した。破断時間の上限は２００時間とした。試験は各線材、あるいは各鋼線から採取した６本の試験片に対して行い、破断時間の平均値を算出し、線材及び鋼線の耐水素脆化特性を評価した。 <5> Hydrogen embrittlement resistance of wire rods and steel wires:
The hydrogen embrittlement resistance properties of the wire and the steel wire after wire drawing were evaluated by the FIP test standardized by the International Federation of Prestressed Concrete (Federation International de la Precontrainte). After pickling the wire or the steel wire after wire drawing to remove the scale or lubricating film on the surface, straightening is performed to ensure straightness, and a sample cut to a length of 700 mm L is used as a test piece. There was. Next, using a solution cell that can be immersed in a 200 mm length including the center of the test piece, the test piece was immersed in an aqueous solution of ammonium thiocyanate (NH 4 SCN) at 50 ° C., and the breaking load of 70 obtained from the tensile test was obtained. A constant load of% was applied to the test piece, and the time until fracture was measured. The upper limit of the breaking time was 200 hours. The test was carried out on each wire rod or 6 test pieces collected from each steel wire, the average value of the breaking time was calculated, and the hydrogen embrittlement resistance property of the wire rod and the steel wire was evaluated.
〈６〉鋼線の捻回特性：
　伸線加工後の鋼線の捻回特性は、鋼線の直径の１００倍の長さで捻回試験ができるように鋼線を切断し、矯直加工を行った後、１分間に１５回転の速さで断線が発生するまで、鋼線を捻回する捻回試験を行った。デラミネーションの発生は、捻回時のトルク曲線を測定し、断線が発生する前にトルクが２０％以上減少した場合にデラミネーションが発生したと判断した。捻回試験は各鋼線について５本ずつ行い、１本もデラミネーションが発生しなかった場合を捻回特性が良好であると判断した。 <6> Twisting characteristics of steel wire:
The twisting characteristics of the steel wire after wire drawing are such that the steel wire is cut so that the twisting test can be performed with a length 100 times the diameter of the steel wire, and after straightening, 15 rotations per minute. A twisting test was conducted in which the steel wire was twisted until the wire was broken at the speed of. For the occurrence of delamination, the torque curve at the time of twisting was measured, and it was determined that delamination occurred when the torque decreased by 20% or more before the disconnection occurred. The twisting test was performed for each steel wire by five, and when no delamination occurred, it was judged that the twisting characteristics were good.
＜線材の製造方法＞
　本開示に係る高強度鋼線用線材は、本開示の要件を満たせば、線材の製造方法によらず、本開示の鋼線の効果は得ることができるが、例えば、下記に示す製造方法によって、線材を製造し、それを素材として高強度鋼線を製造すればよい。なお、下記の製造プロセスは一例であり、下記以外のプロセスによって化学成分及びその他の要件が本開示の範囲である線材が得られた場合であっても、その線材は本開示に係る線材に含まれる。 <Manufacturing method of wire rod>
The wire rod for high-strength steel wire according to the present disclosure can obtain the effect of the steel wire of the present disclosure regardless of the manufacturing method of the wire rod if the requirements of the present disclosure are satisfied, but for example, the manufacturing method shown below can be used. , Wire rods may be manufactured, and high-strength steel wires may be manufactured using them as raw materials. The following manufacturing process is an example, and even if a wire rod whose chemical composition and other requirements are within the scope of the present disclosure is obtained by a process other than the following, the wire rod is included in the wire rod according to the present disclosure. Is done.
　本開示に係る高強度鋼線用線材は、鋼を溶製する段階での化学成分の調整並びに、鋳片の加熱条件及び圧延時の加熱温度など製造条件をコントロールし、線材の長手方向に生じる化学成分の偏析を低減したり、均一性が高いパーライト組織に制御することが好ましい。
　具体的には、Ｃ、Ｓｉ、Ｍｎ、Ｃｕ、Ｎｉ、Ａｌ等の化学成分を調整し、転炉又は電気炉等によって溶製、鋳造された鋼塊又は鋳片は、分塊圧延の工程を経て、製品圧延用素材となる鋼片とする。製品圧延前、すなわち分塊圧延の加熱時か、あるいはその前の鋼塊又は鋳片の段階で、１２６０℃以上で１２ｈｒ以上の加熱処理をする。その後、鋼片を再加熱して熱間で製品圧延し、所定の径の線材として最終的に仕上げる。
　このように線材へ製品圧延する前の段階で高温かつ長時間の加熱処理を加えることで、化学成分の偏析を抑えることができるため、製品圧延後の線材の長手方向における表層硬度のばらつきを抑えることができる。また、このように、通常の製造条件では行わない高温・長時間での加熱処理及び、溶鋼から鋳片又は鋼塊へ凝固させるときの冷却速度を制御するなど、化学成分の偏析を低減するための工程を加えることで、圧延後の線材の長手方向における硬度ばらつきを低減させることが可能となる。 The wire rod for high-strength steel wire according to the present disclosure is generated in the longitudinal direction of the wire rod by adjusting the chemical composition at the stage of melting the steel and controlling the manufacturing conditions such as the heating condition of the slab and the heating temperature at the time of rolling. It is preferable to reduce the segregation of chemical components or control the pearlite structure with high uniformity.
Specifically, steel ingots or slabs in which chemical components such as C, Si, Mn, Cu, Ni, and Al are adjusted and melted and cast by a converter or an electric furnace are subjected to a slab-rolling process. After that, it is used as a steel piece as a material for rolling products. Before rolling the product, that is, at the time of heating the block rolling, or at the stage of the ingot or slab before that, the heat treatment is performed at 1260 ° C. or higher for 12 hr or more. After that, the steel piece is reheated and the product is rolled hot, and finally finished as a wire rod having a predetermined diameter.
By applying a high-temperature and long-term heat treatment to the wire rod before rolling the product in this way, segregation of chemical components can be suppressed, so that variation in surface hardness in the longitudinal direction of the wire rod after product rolling is suppressed. be able to. Further, in order to reduce segregation of chemical components, such as heat treatment at high temperature and long time, which is not performed under normal manufacturing conditions, and control of the cooling rate when solidifying from molten steel to slabs or ingots. By adding the above steps, it is possible to reduce the variation in hardness of the rolled wire in the longitudinal direction.
　次いで、分塊圧延によって得られた鋼片を再加熱し、１０００℃以上の加熱を行う。この際の加熱は、オーステナイト粒の粗大化と混粒化を抑制するために１１５０℃以下、好ましくは１１３０℃以下とすればよい。また、加熱温度到達後の保持時間は、オーステナイト粒の混粒化を抑制するために、９０分未満とするのが好ましい。 Next, the steel pieces obtained by block rolling are reheated and heated to 1000 ° C. or higher. The heating at this time may be 1150 ° C. or lower, preferably 1130 ° C. or lower, in order to suppress coarsening and mixing of austenite grains. Further, the holding time after reaching the heating temperature is preferably less than 90 minutes in order to suppress the mixing of austenite particles.
　前記条件で加熱した鋼片を粗圧延に次いで、仕上げ圧延を行い、直径が５．０～１６．０ｍｍの線材を得る。この際、仕上げ圧延の温度は８５０℃～９５０℃の範囲内で調整する。８５０℃を下回ればオーステナイト粒が微細化し過ぎてパーライト変態が不均一となり、９５０℃を超えればその後の冷却過程でオーステナイト粒の制御が難しくなり、線材表層の硬度ばらつきが大きくなる。その後、熱間圧延後の鋼材を、８００℃を下回らない温度で１５秒間以上保持し、オーステナイト粒を調整する。次いで、５００～５８０℃の温度で保持した溶融ソルトに直接浸漬を行ってパーライト組織に等温変態させた後、冷却すればよい。あるいは、熱延鋼材を衝風冷却により室温程度まで冷却した後、Ａ３点以上のオーステナイト領域の温度での加熱を行い、５００～６００℃の温度で保持した溶融鉛に浸漬してパーライト組織に等温変態させた後、冷却してもよい。 The steel pieces heated under the above conditions are roughly rolled and then finish-rolled to obtain a wire rod having a diameter of 5.0 to 16.0 mm. At this time, the temperature of finish rolling is adjusted in the range of 850 ° C. to 950 ° C. If the temperature is lower than 850 ° C, the austenite grains become too fine and the pearlite transformation becomes non-uniform. If the temperature exceeds 950 ° C, it becomes difficult to control the austenite grains in the subsequent cooling process, and the hardness variation of the wire surface layer becomes large. Then, the steel material after hot rolling is held at a temperature not lower than 800 ° C. for 15 seconds or more to adjust the austenite grains. Then, the molten salt held at a temperature of 500 to 580 ° C. may be directly immersed to transform the pearlite structure into an isothermal structure, and then cooled. Alternatively, the hot rolled steel was cooled to about room temperature air blast cooling, subjected to heating at a temperature in the austenite region of the three or more points A, immersed in the pearlite structure into molten lead held at a temperature of 500 ~ 600 ° C. It may be cooled after being isothermally transformed.
＜鋼線の製造方法＞
　一例として上述のプロセスによって得た線材を用いて、伸線加工を行い、必要な径の鋼線とすればよい。伸線加工の加工減面率は、必要とされる鋼線の直径と強度に応じて決定すればよいが、過剰に伸線加工の加工減面率を大きくし過ぎると、伸線加工後の鋼線の捻回特性及び耐水素脆化特性が低下してしまう。伸線加工の加工減面率は、７０～９２％とするのがよい。加工減面率が７０％未満では、所要の引張強さが得られ難い。一方、加工減面率が９２％を超えると、鋼線の捻回特性及び耐水素脆化特性が低下し易い。伸線加工の方法については特に限定されないが、鋼線表層の硬度ばらつきを低下するために、伸線加工後に鋼線を水冷するなど、伸線加工中の加工発熱による鋼線のひずみ時効を抑制する方法とするのが好ましい。
　また、必要に応じて伸線加工後に、溶融亜鉛めっき、ブルーイング、又はヒートストレッチング処理など鋼線を加熱する工程を実施してもよい。 <Steel wire manufacturing method>
As an example, the wire rod obtained by the above process may be used for wire drawing to obtain a steel wire having a required diameter. The processing surface reduction rate of wire drawing may be determined according to the required diameter and strength of the steel wire, but if the processing surface reduction rate of wire drawing is excessively increased, the surface reduction rate after wire drawing may be determined. The twisting characteristics and hydrogen embrittlement resistance of steel wire are deteriorated. The processing reduction rate of wire drawing is preferably 70 to 92%. If the processing reduction rate is less than 70%, it is difficult to obtain the required tensile strength. On the other hand, when the processing reduction rate exceeds 92%, the twisting characteristics and hydrogen embrittlement resistance of the steel wire tend to deteriorate. The method of wire drawing is not particularly limited, but in order to reduce the variation in hardness of the surface layer of the steel wire, the strain aging of the steel wire due to the heat generated during the wire drawing is suppressed, such as by cooling the steel wire with water after the wire drawing. It is preferable to use the method of
Further, if necessary, after the wire drawing process, a step of heating the steel wire such as hot dip galvanizing, bluing, or heat stretching treatment may be performed.
　以下、本開示に係る線材及び鋼線について実施例を挙げてさらに具体的に説明する。ただし、これら各実施例は、本開示に係る線材及び鋼線を制限するものではない。 Hereinafter, the wire rod and the steel wire according to the present disclosure will be described in more detail with reference to examples. However, each of these examples does not limit the wire rod and steel wire according to the present disclosure.
　具体的には、表１、表２に示す化学成分の鋼を溶製し、以下の方法で線材及び鋼線を作製した。なお、表１、表２中の「－」の表記は、当該元素の含有量が不純物レベルであり、実質的に含有されていないと判断できることを示す。また、表２～表５において下線を付した値は、本開示の範囲外である、又は前述した製造方法（製造条件）を満たさないことを意味する。 Specifically, the steels having the chemical components shown in Tables 1 and 2 were melted to prepare wire rods and steel wires by the following methods. The notation of "-" in Tables 1 and 2 indicates that the content of the element is at the impurity level and it can be determined that the element is not substantially contained. Further, the values underlined in Tables 2 to 5 mean that they are outside the scope of the present disclosure or do not satisfy the above-mentioned manufacturing method (manufacturing conditions).
Figure JPOXMLDOC01-appb-T000004
 
Figure JPOXMLDOC01-appb-T000004
 
Figure JPOXMLDOC01-appb-T000005
 
Figure JPOXMLDOC01-appb-T000005
 
　化学成分が同等である鋼を用いて、引張強さ又は長手方向における表層硬度のばらつきが異なる線材を造り分けるため、表３に示す試験Ｎｏ．ａ０、ａ１、ａ０－１～ａ０－４、試験Ｎｏ．ｂ０、ｂ１、ｂ０－１～ｂ０－４の製造条件によって線材を圧延した。 In order to make different wire rods with different variations in tensile strength or surface hardness in the longitudinal direction using steels with the same chemical composition, the test No. 1 shown in Table 3 was used. a0, a1, a0-1 to a0-4, Test No. The wire rod was rolled according to the production conditions of b0, b1, b0-1 to b0-4.
Figure JPOXMLDOC01-appb-T000006
 
Figure JPOXMLDOC01-appb-T000006
 
［線材及び鋼線の製造（１）］
　表１に示す化学成分の鋼Ｎｏ．Ａ０、Ａ１、Ｂ０、Ｂ１を溶製した。鋼Ｎｏ．Ａ０とＡ１、鋼Ｎｏ．Ｂ０とＢ１はほぼ同等成分であるが、引張強さ又は長手方向における表層硬度のばらつきが異なる線材を造り分けるために、試験Ｎｏ．ａ０とｂ０については、それぞれ鋼Ｎｏ．Ａ０とＢ０の化学成分の鋳片を用いて、鋼片へ分塊圧延を行う前に、鋳片を１２８０℃に加熱し、２４ｈｒ保持する加熱処理を行い、１２２ｍｍ角に分塊圧延した鋼片を圧延用素材とした。
　試験Ｎｏ．ａ１とｂ１については、それぞれ鋼Ｎｏ．Ａ１とＢ１の鋳片を用い、鋼片へ分塊圧延を行う前に、１２６０℃以上の温度で加熱を行わず、通常条件である１２００℃で４ｈｒ保持する加熱を行い、１２２ｍｍ角に分塊圧延した鋼片を圧延用素材とした。次いで、それぞれの鋼片を１１００℃で６０分間加熱した後、線材に圧延した。この際、仕上げ圧延温度は表３に示す通りであり、仕上げ圧延後、線材コイルに捲き取った。捲き取った線材コイルは、そのまま５５０℃に保持した溶融ソルト浴に直接浸漬して等温変態処理を行った後、３００℃以下まで水冷して線材を得た。 [Manufacturing of wire rods and steel wires (1)]
Steel No. of the chemical composition shown in Table 1. A0, A1, B0 and B1 were melted. Steel No. A0 and A1, Steel No. B0 and B1 are almost the same components, but in order to make different wire rods with different variations in tensile strength or surface hardness in the longitudinal direction, Test No. For a0 and b0, the steel Nos. Using slabs of chemical components A0 and B0, the slabs were heated to 1280 ° C., heat-treated to hold them for 24 hours, and slab-rolled to 122 mm square before slab-rolling. Was used as the material for rolling.
Test No. For a1 and b1, each steel No. Using the slabs of A1 and B1, before rolling into steel pieces by slabbing, heating is performed at 1200 ° C., which is a normal condition, for 4 hours without heating at a temperature of 1260 ° C. or higher, and slabbing into 122 mm square. The rolled steel pieces were used as a rolling material. Next, each piece of steel was heated at 1100 ° C. for 60 minutes and then rolled into a wire rod. At this time, the finish rolling temperature is as shown in Table 3, and after the finish rolling, it was wound around a wire coil. The wound wire wire coil was directly immersed in a molten salt bath kept at 550 ° C. for isothermal transformation treatment, and then water-cooled to 300 ° C. or lower to obtain a wire rod.
　試験Ｎｏ．ａ０－１～ａ０－４は鋼Ｎｏ．Ａ０の鋳片を、試験Ｎｏ．ｂ０－１～ｂ０－４は鋼Ｎｏ．Ｂ０の鋳片をそれぞれ用い、鋼片へ分塊圧延を行う前に、鋳片を１２８０℃に加熱し、２４ｈｒ保持する加熱処理を行い、１２２ｍｍ角に分塊圧延した鋼片を圧延用素材として用いた。同じ成分の鋼であっても、引張強さ又は長手方向の表層硬度ばらつきが異なる線材を造り分けるため、圧延条件を表３に示すように変化させた。具体的には、試験Ｎｏ．ａ０－１、ｂ０－１は、線材圧延の際の加熱温度を１１５０℃以上とし、試験Ｎｏ．ａ０－２、ｂ０－２は線材圧延の際の加熱の保持時間を９０分以上とした。また、試験Ｎｏ．ａ０－３、ｂ０－３は線材圧延の仕上げ圧延温度を８５０℃以下として圧延し、試験Ｎｏ．ａ０－４、ｂ０－４は、線材圧延の仕上げ圧延温度を９５０℃以上で圧延した。その他は表３に示す圧延条件とし、仕上げ圧延後、線材コイルに捲き取った。捲き取った線材コイルは、そのまま５５０℃に保持した溶融ソルト浴に直接浸漬して等温変態処理を行った後、３００℃以下まで水冷して線材を得た。 Test No. A0-1 to a0-4 are steel Nos. The slab of A0 was subjected to Test No. b0-1 to b0-4 are steel Nos. Using each of the B0 slabs, the slabs were heated to 1280 ° C., heat-treated to hold them for 24 hours, and the steel slabs lump-rolled to 122 mm square were used as the rolling material. Using. The rolling conditions were changed as shown in Table 3 in order to separately produce wire rods having different tensile strength or surface hardness variation in the longitudinal direction even if the steel had the same composition. Specifically, the test No. In a0-1 and b0-1, the heating temperature at the time of rolling the wire rod was set to 1150 ° C. or higher, and Test No. For a0-2 and b0-2, the holding time for heating during wire rolling was 90 minutes or more. In addition, the test No. In a0-3 and b0-3, the finish rolling temperature of the wire rod was set to 850 ° C. or lower, and the test No. For a0-4 and b0-4, the finish rolling temperature of wire rod rolling was 950 ° C. or higher. Others were rolled under the rolling conditions shown in Table 3, and after finish rolling, they were wound into a wire coil. The wound wire wire coil was directly immersed in a molten salt bath kept at 550 ° C. for isothermal transformation treatment, and then water-cooled to 300 ° C. or lower to obtain a wire rod.
　次いで、それぞれの線材を伸線加工し、鋼線を製造した。具体的には、それぞれの線材を酸洗処理してスケールを除去した後、潤滑性を向上させるため、表面に化成処理によってりん酸亜鉛皮膜を形成させ、超硬ダイスを用いて伸線加工を行った。伸線加工は各ダイスでの加工減面率が２０％前後となるように調整したパススケジュールで線径５．２ｍｍとなるまで伸線加工（この条件による伸線加工を「伸線加工Ａ」と称する場合がある。）を行った。次いで、伸線加工した鋼線を４００℃に加熱した鉛浴に３０ｓｅｃ浸漬させ、水冷した。 Next, each wire was drawn to produce a steel wire. Specifically, after pickling each wire rod to remove scale, a zinc phosphate film is formed on the surface by chemical conversion treatment in order to improve lubricity, and wire drawing is performed using a carbide die. went. For wire drawing, wire drawing is performed until the wire diameter reaches 5.2 mm with a path schedule adjusted so that the processing reduction rate of each die is around 20% (the wire drawing process under this condition is called "wire drawing process A". It may be referred to as). Next, the wire-drawn steel wire was immersed in a lead bath heated to 400 ° C. for 30 seconds and cooled with water.
［評価（１）］
　上述の方法によって得られた試験Ｎｏ．ａ０、ａ１、ａ０－１～ａ０－４、試験Ｎｏ．ｂ０、ｂ１、ｂ０－１～ｂ０－４の線材及び鋼線について、線材の金属組織、線材及び鋼線の引張強さ、線材の表層硬度のばらつき、線材の耐食性、線材及び鋼線の耐水素脆化特性、並びに鋼線の捻回特性を評価した。その結果を表４Ａに示す。パーライト以外の金属組織としては、初析フェライト及び疑似パーライトの一方又は両方が観察された。 [Evaluation (1)]
Test No. obtained by the above method. a0, a1, a0-1 to a0-4, Test No. Regarding the wire rods and steel wires of b0, b1, b0-1 to b0-4, the metal structure of the wire rod, the tensile strength of the wire rod and steel wire, the variation in the surface hardness of the wire rod, the corrosion resistance of the wire rod, and the hydrogen resistance of the wire rod and steel wire. The embrittlement characteristics and the twisting characteristics of the steel wire were evaluated. The results are shown in Table 4A. As the metallographic structure other than pearlite, one or both of proeutectoid ferrite and pseudo-pearlite were observed.
Figure JPOXMLDOC01-appb-T000007
Figure JPOXMLDOC01-appb-T000007
　試験Ｎｏ．ａ０、ａ０－１、ａ０－４の線材について、任意の位置において線材の長手方向に５０ｍｍの間隔をあけてそれぞれ２５ｍｍ長さで採取した８個の各サンプルについて表層硬度を測定した。結果を表４Ｂに示す。表４Ｂにおいて線材の表層硬度以外の項目は表４Ａと同様である。 Test No. For the wires a0, a0-1, and a0-4, the surface hardness was measured for each of the eight samples collected at arbitrary positions with a length of 25 mm at intervals of 50 mm in the longitudinal direction of the wires. The results are shown in Table 4B. Items other than the surface hardness of the wire rod in Table 4B are the same as those in Table 4A.
Figure JPOXMLDOC01-appb-T000008
Figure JPOXMLDOC01-appb-T000008
［線材及び鋼線の製造（２）］
　本開示における化学成分の効果を確認するため、表２に示した化学成分の鋼Ｎｏ．Ｃ１～Ｃ２４、及び鋼Ｎｏ．Ｄ１～Ｄ２２を電気炉にて溶製した。鋼Ｎｏ．Ｃ１～Ｃ２４は本開示の要件を満足する実施例、鋼Ｎｏ．Ｄ１～Ｄ２２は本開示の要件のうち、いずれか一つ以上を満足していない比較例の鋼である。
　鋼片へ分塊圧延を行う前に、鋼Ｎｏ．Ｃ１～Ｃ２４、及び鋼Ｎｏ．Ｄ１～Ｄ２２の鋳片をそれぞれ１２８０℃狙いで加熱し、２４ｈｒ保持する加熱処理を行い、続いて１２２ｍｍ角に分塊圧延した鋼片を圧延用素材とした。
　次いで、鋼片をそれぞれ１０８０℃狙いの加熱温度で６０分間加熱した後、線径８．０～１２．５ｍｍの線材に圧延した。この際、仕上げ圧延温度は９００℃狙いとし、線材コイルに捲き取った。捲き取った線材コイルは、そのまま５５０℃に保持した溶融ソルト浴に直接浸漬して等温変態処理を行い、３００℃以下まで水冷して線材を得た。 [Manufacturing of wire rods and steel wires (2)]
In order to confirm the effect of the chemical composition in the present disclosure, the steel No. of the chemical composition shown in Table 2 is shown. C1 to C24 and steel No. D1 to D22 were melted in an electric furnace. Steel No. Examples C1 to C24 satisfy the requirements of the present disclosure, Steel No. D1 to D22 are comparative steels that do not satisfy any one or more of the requirements of the present disclosure.
Before performing block rolling on the steel pieces, the steel No. C1 to C24 and steel No. The slabs of D1 to D22 were each heated at 1280 ° C., heat-treated to hold them for 24 hours, and then the steel slabs that were block-rolled to 122 mm square were used as the rolling material.
Next, each of the steel pieces was heated at a heating temperature aimed at 1080 ° C. for 60 minutes, and then rolled into a wire rod having a wire diameter of 8.0 to 12.5 mm. At this time, the finish rolling temperature was aimed at 900 ° C., and the material was wound around a wire coil. The wound wire coil was directly immersed in a molten salt bath kept at 550 ° C. for isothermal transformation treatment, and water-cooled to 300 ° C. or lower to obtain a wire rod.
　それぞれの線材を伸線加工し、鋼線を製造した。具体的には、前述の伸線加工Ａと同じ方法で線径３．８～５．２ｍｍの鋼線となるように、伸線加工を行った。次いで、伸線加工した鋼線を４００℃に加熱した鉛浴に３０ｓｅｃ浸漬させ、水冷した。 Each wire was drawn to produce a steel wire. Specifically, the wire drawing process was performed by the same method as the wire drawing process A described above so as to obtain a steel wire having a wire diameter of 3.8 to 5.2 mm. Next, the wire-drawn steel wire was immersed in a lead bath heated to 400 ° C. for 30 seconds and cooled with water.
［評価（２）］
　上述の方法によって得られた試験Ｎｏ．ｃ１～ｃ２４、及び試験Ｎｏ．ｄ１～ｄ２２の線材、及び鋼線について、既述の方法により、線材の金属組織、線材及び鋼線の引張強さ、線材の表層硬度のばらつき、線材の耐食性、線材及び鋼線の耐水素脆化特性、並びに鋼線の捻回特性をそれぞれ評価した。その結果を表５に示す。パーライト以外の金属組織としては、マルテンサイト、ベイナイト、初析フェライトおよび疑似パーライトが観察された。 [Evaluation (2)]
Test No. obtained by the above method. c1 to c24, and test No. For the wires and steel wires d1 to d22, the metal structure of the wires, the tensile strength of the wires and steel wires, the variation in the surface hardness of the wires, the corrosion resistance of the wires, and the hydrogen embrittlement of the wires and steel wires The embrittlement characteristics and the twisting characteristics of the steel wire were evaluated. The results are shown in Table 5. As metal structures other than pearlite, martensite, bainite, proeutectoid ferrite and pseudo-pearlite were observed.
Figure JPOXMLDOC01-appb-T000009
 
Figure JPOXMLDOC01-appb-T000009
 
　図１に本開示の実施例で得られた、線材の引張強さと耐水素脆化特性の指標であるＦＩＰ破断時間の関係を示す。
　図２に本開示の実施例で得られた、伸線加工後の鋼線の引張強さと耐水素脆化特性の指標であるＦＩＰ破断時間の関係を示す。 FIG. 1 shows the relationship between the tensile strength of the wire rod and the FIP breaking time, which is an index of hydrogen embrittlement resistance, obtained in the examples of the present disclosure.
FIG. 2 shows the relationship between the tensile strength of the steel wire after wire drawing and the FIP fracture time, which is an index of hydrogen embrittlement resistance, obtained in the examples of the present disclosure.
　表４Ａ及び表４Ｂから、本開示の実施例である試験Ｎｏ．ａ０、ｂ０は、本開示における化学成分とその他の要件を満足し、かつ線材の製造条件が適切であることから、いずれも線材の耐食性の評価指標である腐食体積減少率が２５％未満、耐水素脆化特性の指標であるＦＩＰの破断時間が１００ｈｒ以上であり、耐食性と耐水素脆化特性に優れた線材が得られている。さらに、試験Ｎｏ．ａ０、ｂ０で得られた伸線加工後の鋼線においても、引張強さが１７００ＭＰａ以上であり、ＦＩＰ破断時間が３０ｈｒ以上、捻回試験においてもデラミネーションが発生しておらず、耐水素脆化特性に優れた鋼線が得られている。
　また、表層部のおけるビッカース硬さは、１リングの長さを想定した６００ｍｍ間隔でサンプルを採取して測定した場合に限らず、５０ｍｍの間隔でサンプルを採取して測定した場合でも、「Ｈｖｓｉｍａｘ－Ｈｖｓｉａｖｅ≦５０」の関係を満たせば有効であることがわかる。 From Table 4A and Table 4B, Test No. which is an example of the present disclosure. Since a0 and b0 satisfy the chemical composition and other requirements in the present disclosure and the manufacturing conditions of the wire rod are appropriate, the corrosion volume reduction rate, which is an evaluation index of the corrosion resistance of the wire rod, is less than 25%, and the resistance to corrosion is less than 25%. A wire rod having a breaking time of 100 hr or more and excellent corrosion resistance and hydrogen embrittlement resistance of FIP, which is an index of hydrogen embrittlement characteristics, has been obtained. Furthermore, the test No. The steel wire after wire drawing obtained in a0 and b0 also has a tensile strength of 1700 MPa or more, a FIP breaking time of 30 hr or more, no delamination in the twisting test, and hydrogen embrittlement resistance. A steel wire with excellent chemical properties has been obtained.
Further, the Vickers hardness in the surface layer portion is not limited to the case where samples are collected and measured at intervals of 600 mm assuming the length of one ring, and even when samples are collected and measured at intervals of 50 mm, "Hv" is obtained. It can be seen that it is effective if the relationship of " simax- Hv siave ≤ 50" is satisfied.
　これに対し、試験Ｎｏ．ａ１と試験Ｎｏ．ａ０－１～ａ０－４は、それぞれ試験Ｎｏ．ａ０とほぼ同じ化学成分である鋼Ａ１又は同じ化学成分である鋼Ｎｏ．Ａ０を用い、また、試験Ｎｏ．ｂ１と試験Ｎｏ．ｂ０－１～ｂ０－４は、それぞれ試験Ｎｏ．ｂ０とほぼ同じ化学成分である鋼Ｎｏ．Ｂ１又は同じ化学成分である鋼Ｎｏ．Ｂ０を用いて線材を圧延したが、線材の製造条件が適切でなかったために、表層硬度のばらつき又はパーライト組織の面積率が本開示の要件を満足していない。そのため、線材の耐水素脆化特性が劣っており、伸線加工後の鋼線の耐水素脆化特性が劣っている。また、試験Ｎｏ．ａ０－１～ａ０－４、試験Ｎｏ．ｂ０－１～ｂ０－４では、伸線加工後の鋼線の捻回試験でデラミネーションが発生しており、捻回特性にも劣っている。 On the other hand, test No. a1 and test No. A0-1 to a0-4 are test numbers, respectively. Steel A1 having almost the same chemical composition as a0 or steel No. having the same chemical composition. A0 was used, and Test No. b1 and test No. Each of b0-1 to b0-4 has a test No. Steel No. which has almost the same chemical composition as b0. B1 or steel No. which has the same chemical composition. Although the wire rod was rolled using B0, the variation in surface hardness or the area ratio of the pearlite structure did not satisfy the requirements of the present disclosure because the production conditions of the wire rod were not appropriate. Therefore, the hydrogen embrittlement resistance of the wire is inferior, and the hydrogen embrittlement resistance of the steel wire after wire drawing is inferior. In addition, the test No. a0-1 to a0-4, Test No. In b0-1 to b0-4, delamination occurs in the twisting test of the steel wire after the wire drawing process, and the twisting characteristics are also inferior.
　表５から、本開示の実施例である試験Ｎｏ．ｃ１～ｃ２４は、いずれも化学成分と本開示の要件を満足し、かつ鋼材の製造条件が適切であることから、引張強さがいずれも１０００ＭＰａ～１６５０ＭＰａの範囲であり、耐食性及び、同等の引張強さで比較した場合に耐水素脆化特性が優れている。 From Table 5, Test No., which is an example of the present disclosure. Since all of c1 to c24 satisfy the chemical composition and the requirements of the present disclosure and the manufacturing conditions of the steel material are appropriate, the tensile strength is in the range of 1000 MPa to 1650 MPa, and the corrosion resistance and the same tensile strength are obtained. Excellent hydrogen embrittlement resistance when compared in terms of strength.
　試験Ｎｏ．ｄ１、ｄ２は[Ｃｕ]／[Ｎｉ]＜１．００であり、さらにｄ２はＹ２も１．８１以上であり、伸線加工後の鋼線においてデラミネーションが発生しており、捻回特性が悪い。また、鋼線での耐水素脆化特性も実施例における同等レベルの引張強さの鋼線と比べて、劣っている。
　試験Ｎｏ．ｄ３はＹ１の値が１．７０未満であり、線材の耐水素脆化特性及び伸線加工後の鋼線の耐水素脆化特性が劣っている。
　試験Ｎｏ．ｄ４はＹ１の値が４．５０を超えており、線材の耐水素脆化特性及び伸線加工後の鋼線の耐水素脆化特性、捻回特性が劣っている。
　試験Ｎｏ．ｄ５はＹ２の値が１．８１以上であり、線材の耐水素脆化特性及び伸線加工後の鋼線の耐水素脆化特性、捻回特性が劣っている。
　試験Ｎｏ．ｄ６、ｄ７、ｄ８、ｄ１０、ｄ１２～ｄ２１については、本開示における化学成分のいずれかが本開示の範囲外、又は、Ｙ２の値が１．８１以上であり、線材の耐水素脆化特性及び／又は伸線加工後の鋼線の耐水素脆化特性、捻回特性が劣っている。
　試験Ｎｏ．ｄ９、ｄ２２は化学成分が本開示の範囲外であり、伸線加工する段階で断線が生じたことから、鋼線の引張強さ、耐水素脆化特性、捻回特性を調査しなかった。
　試験Ｎｏ．ｄ１１は化学成分が本開示の範囲外（Ｙ２も１．８１以上）であり、線材を圧延した段階で、大きな表面疵が現れていたことから、線材の耐食性、耐水素脆化特性を調査せず、さらに伸線加工を行わなかった。 Test No. d1 and d2 are [Cu] / [Ni] <1.00, and d2 is Y2 of 1.81 or more, delamination occurs in the steel wire after wire drawing, and the twisting characteristic is bad. In addition, the hydrogen embrittlement resistance of the steel wire is also inferior to that of the steel wire having the same level of tensile strength in the examples.
Test No. The value of Y1 of d3 is less than 1.70, and the hydrogen embrittlement resistance property of the wire rod and the hydrogen embrittlement resistance property of the steel wire after wire drawing are inferior.
Test No. The value of Y1 of d4 exceeds 4.50, and the hydrogen embrittlement resistance property of the wire rod, the hydrogen embrittlement resistance property of the steel wire after wire drawing, and the twisting property are inferior.
Test No. The value of Y2 of d5 is 1.81 or more, and the hydrogen embrittlement resistance property of the wire rod, the hydrogen embrittlement resistance property of the steel wire after the wire drawing process, and the twisting property are inferior.
Test No. Regarding d6, d7, d8, d10, d12 to d21, any of the chemical components in the present disclosure is outside the scope of the present disclosure, or the value of Y2 is 1.81 or more, and the hydrogen embrittlement resistance of the wire rod and the hydrogen embrittlement resistance / Or the hydrogen embrittlement resistance and twisting characteristics of the steel wire after wire drawing are inferior.
Test No. Since the chemical components of d9 and d22 were outside the scope of the present disclosure and the wire was broken at the stage of wire drawing, the tensile strength, hydrogen embrittlement resistance, and twisting characteristics of the steel wire were not investigated.
Test No. Since the chemical composition of d11 is outside the scope of the present disclosure (Y2 is also 1.81 or more) and large surface flaws appear at the stage of rolling the wire, investigate the corrosion resistance and hydrogen embrittlement resistance of the wire. No further wire drawing was performed.
　本開示に係る線材の用途等は、上述した実施形態及び実施例に限定されない。例えば、本開示に係る線材は、引張強さが１７００ＭＰａ以上の鋼線の素材に限定されず、要求される引張強さが１７００ＭＰａ未満である鋼線の素材として用いてもよい。 The use of the wire rod according to the present disclosure is not limited to the above-described embodiments and examples. For example, the wire rod according to the present disclosure is not limited to a steel wire material having a tensile strength of 1700 MPa or more, and may be used as a steel wire material having a required tensile strength of less than 1700 MPa.
　２０１９年６月１９日に出願された日本特許出願２０１９－１１３７２０の開示はその全体が参照により本明細書に取り込まれる。本明細書に記載された全ての文献、特許出願、および技術規格は、個々の文献、特許出願、および技術規格が参照により取り込まれることが具体的かつ個々に記された場合と同程度に、本明細書中に参照により取り込まれる。
  The disclosure of Japanese Patent Application 2019-11320, filed June 19, 2019, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.

Claims (3)

  1. 　化学成分が、質量％で、
    Ｃ：０．６０～１．１５％、
    Ｓｉ：０．０１～１．８０％、
    Ｍｎ：０．２０～０．９０％、
    Ｐ：０．０１５％以下、
    Ｓ：０．０１５％以下、
    Ａｌ：０．００５～０．０８０％、
    Ｎ：０．００１５～０．００６０％、
    Ｃｕ：０．１０～０．６５％、
    Ｎｉ：０．０５～０．６５％未満、
    Ｃｒ：０～０．３０％、
    Ｍｏ：０～０．３０％、
    Ｔｉ：０～０．１００％、
    Ｎｂ：０～０．１００％、
    Ｖ：０～０．２０％、
    Ｓｎ：０～０．３０％、
    Ｂ：０～０．００５０％、
    Ｃａ：０～０．００５０％、
    Ｍｇ：０～０．００５０％、
    Ｚｒ：０～０．１００％、
    ＲＥＭ：０～０．０２００％、並びに
    残部：Ｆｅ及び不純物、からなり、
    線材に含まれるＣ、Ｓｉ、Ｍｎ、Ｃｒ、Ｃｕ、Ｎｉ、Ｎ、及びＴｉのそれぞれの元素の質量％での含有量を、［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｃｒ］、［Ｃｕ］、［Ｎｉ］、［Ｎ］、及び［Ｔｉ］で表した場合に、下記（１）～（３）を満たし、
    （１）［Ｃｕ］／［Ｎｉ］＞１．００
    （２）１．７０≦Ｙ１≦４．５０
    　Ｙ１＝３×［Ｃｒ］＋５×［Ｍｎ］＋［Ｃｕ］＋［Ｎｉ］
    （３）Ｙ２＜１．８１
    　Ｙ２＝［Ｃ］＋［Ｓｉ］／１０＋Ａ
    　Ａは、ａ＝３５０×（［Ｎ］－０．２９×［Ｔｉ］）の値が、
    　ａ≧０の場合は、Ａ＝ａ
    　ａ＜０の場合は、Ａ＝０
    　金属組織が、線材の中心軸を含む長手方向に平行な断面における面積率で９０％以上のパーライト組織を含み、
    　前記線材の長手方向に任意の等間隔で採取した８個の各々のサンプルｓｉ（ｉは１～８の整数）について、各サンプルの前記断面において前記線材の表面から深さ５０μｍの位置で測定されるビッカース硬さをそれぞれＨｖｓｉとし、前記Ｈｖｓｉの平均値をＨｖｓｉａｖｅ、最大値をＨｖｓｉｍａｘとしたとき、下記（４）を満たす、線材。
    （４）Ｈｖｓｉｍａｘ－Ｈｖｓｉａｖｅ≦５０     The chemical composition is mass%,
    C: 0.60 to 1.15%,
    Si: 0.01 to 1.80%,
    Mn: 0.20 to 0.90%,
    P: 0.015% or less,
    S: 0.015% or less,
    Al: 0.005 to 0.080%,
    N: 0.0015 to 0.0060%,
    Cu: 0.10 to 0.65%,
    Ni: 0.05 to less than 0.65%,
    Cr: 0 to 0.30%,
    Mo: 0 to 0.30%,
    Ti: 0 to 0.100%,
    Nb: 0 to 0.100%,
    V: 0 to 0.20%,
    Sn: 0 to 0.30%,
    B: 0 to 0.0050%,
    Ca: 0 to 0.0050%,
    Mg: 0 to 0.0050%,
    Zr: 0 to 0.100%,
    REM: 0-0.0200%, and balance: Fe and impurities,
    The content of each element of C, Si, Mn, Cr, Cu, Ni, N, and Ti contained in the wire rod in mass% is determined by [C], [Si], [Mn], [Cr], [ When represented by [Cu], [Ni], [N], and [Ti], the following (1) to (3) are satisfied.
    (1) [Cu] / [Ni]> 1.00
    (2) 1.70 ≤ Y1 ≤ 4.50
    Y1 = 3 x [Cr] + 5 x [Mn] + [Cu] + [Ni]
    (3) Y2 <1.81
    Y2 = [C] + [Si] / 10 + A
    In A, the value of a = 350 × ([N] −0.29 × [Ti]) is
    When a ≧ 0, A = a
    If a <0, then A = 0
    The metallographic structure contains a pearlite structure having an area ratio of 90% or more in a cross section parallel to the longitudinal direction including the central axis of the wire rod.
    For each of the eight samples si (i is an integer of 1 to 8) collected at arbitrary equal intervals in the longitudinal direction of the wire, the cross section of each sample was measured at a depth of 50 μm from the surface of the wire. that Vickers hardness and each Hv si, the Hv si average value Hv Siave, when the maximum value was Hv Simax, satisfies the following (4), the wire.
    (4) Hv simax -Hv siave ≦ 50
  2. 　前記任意の等間隔が、６００ｍｍの間隔である、請求項１に記載の線材。 The wire rod according to claim 1, wherein the arbitrary equal spacing is 600 mm.
  3. 　前記化学成分が、前記Ｆｅの一部に代えて、質量％で、
    Ｃｒ：０．０１～０．３０％、
    Ｍｏ：０．０１～０．３０％
    Ｔｉ：０．００２～０．１００％、
    Ｎｂ：０．００２～０．１００％、
    Ｖ：０．０１～０．２０％、
    Ｓｎ：０．０１～０．３０％、
    Ｂ：０．０００２～０．００５０％
    Ｃａ：０．０００２～０．００５０％、
    Ｍｇ：０．０００２～０．００５０％、
    Ｚｒ：０．０００２～０．１００％、及び
    ＲＥＭ：０．０００２～０．０２００％、
    からなる群より選択される１種又は２種以上を含む、請求項１又は請求項２に記載の線材。     The chemical component replaces a part of the Fe in mass%.
    Cr: 0.01-0.30%,
    Mo: 0.01-0.30%
    Ti: 0.002 to 0.100%,
    Nb: 0.002 to 0.100%,
    V: 0.01 to 0.20%,
    Sn: 0.01 to 0.30%,
    B: 0.0002 to 0.0050%
    Ca: 0.0002 to 0.0050%,
    Mg: 0.0002 to 0.0050%,
    Zr: 0.0002 to 0.100%, and REM: 0.0002 to 0.0200%,
    The wire rod according to claim 1 or 2, which comprises one kind or two or more kinds selected from the group consisting of.
PCT/JP2020/024248 2019-06-19 2020-06-19 Wire rod WO2020256140A1 (en)

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JP7469642B2 (en) 2020-05-21 2024-04-17 日本製鉄株式会社 High-strength steel wire

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