WO2020256140A1 - 線材 - Google Patents

線材 Download PDF

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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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wire
wire rod
less
steel
hydrogen embrittlement
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PCT/JP2020/024248
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English (en)
French (fr)
Japanese (ja)
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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 CN202080032029.1A priority patent/CN113748224B/zh
Priority to JP2021526947A priority patent/JP7226548B2/ja
Publication of WO2020256140A1 publication Critical patent/WO2020256140A1/ja

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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
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    • 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
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    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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    • 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
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    • 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
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    • 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
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    • 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
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    • 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.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
PCT/JP2020/024248 2019-06-19 2020-06-19 線材 WO2020256140A1 (ja)

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JP7469642B2 (ja) 2020-05-21 2024-04-17 日本製鉄株式会社 高強度鋼線
WO2024161785A1 (ja) * 2023-01-30 2024-08-08 Ｊｆｅスチール株式会社 熱延鋼材及びその製造方法
WO2024161659A1 (ja) * 2023-02-03 2024-08-08 日本製鉄株式会社 線材、鋼線、ロープ、及びロープの製造方法

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CN114807767B (zh) * 2022-05-06 2023-01-13 鞍钢股份有限公司 一种具有双重复相组织的高碳钢盘条及其制造方法

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WO2024161659A1 (ja) * 2023-02-03 2024-08-08 日本製鉄株式会社 線材、鋼線、ロープ、及びロープの製造方法

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EP3988678A1 (en) 2022-04-27
EP3988678A4 (en) 2022-07-06
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