Classifications

• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
• • 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
  • C22C38/04—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
  • C22C38/12—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
  • C22C38/18—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
  • 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
  • C21D2211/003—Cementite
• • 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
  • C21D2211/005—Ferrite
• • 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
  • C21D2211/008—Martensite
• • 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
  • 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
  • C22C38/08—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
  • C22C38/14—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
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
• • 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
  • C22C38/50—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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• the present disclosure relates to a wire rod, a steel wire, a rope, and a method for producing a rope.
• Steel wires such as bridge cable steel wires and rope steel wires are produced, for example, using a steel wire obtained by subjecting a high carbon wire rod to a patenting treatment to form a pearlite structure and then performing wire drawing and a plating treatment.
• a bridge cable is required to have a high strength in order to improve the degree of freedom in cable design, and a steel wire to be used is also required to have a high strength.
• Patent Literature 1 discloses a high-strength PC steel wire excellent in delayed fracture resistance properties, the PC steel wire containing, in % by mass, C: from 0.9 to 1.2%, Si: from 0.01 to 1.5%, Mn: from 0.2 to 1.5%, Al: from 0.001 to 0.05%, and N: from 0.0005 to 0.010% with a balance being Fe and unavoidable impurities, including 90% or more of wire drawn pearlite and 10% or less of ferrite and bainite structure, and having a tensile strength of 2000 MPa or more, in which in a case in which a diameter of the PC steel wire is taken as D, a ratio (Hv surface/Hv inner portion) of a surface layer Hv hardness (Hv surface) in a region (surface layer portion) of 0.1 D from the surface of the PC steel wire and an inner portion Hv hardness (Hv inner portion) in
• Patent Literature 2 discloses a plated steel wire for PWS having excellent torsion properties, in which a steel wire contains, in % by mass, C: from 0.8 to 1.1%, Si: from 0.8 to 1.3%, Mn: from 0.3 to 0.8%, N: from 0.001 to 0.006%, and B: from 0.0004 to 0.0060%, a quantity of solid solute B being 0.0002% or more, and further contains one or two of Al: from 0.005 to 0.1% or Ti: from 0.005 to 0.1%, with the balance being Fe and inevitable impurities, and the steel wire has an area ratio of a non-pearlite structure in a portion from a surface layer to a depth of 50 ⁇ m being 10% or less, and a total area ratio of the non-pearlite structure in the entire cross section being 5% or less, and in which a surface of the steel wire is galvanized with a plating quantity of from 300 to 500 g/m 2 .
• an object of the disclosure is to provide a wire rod suitable for producing a steel wire having a high strength and excellent torsion properties by wire drawing, a steel wire having a high strength and excellent torsion properties, a rope, and a method for producing a rope.
• a wire rod suitable for producing a steel wire having a high strength and excellent torsion properties by wire drawing, a steel wire having a high strength and excellent torsion properties, a rope, and a method for producing a rope are provided.
• a "surface layer” or “surface layer portion” of a wire rod means a range having a depth of from 0.5 to 1.0 mm from the surface (outer peripheral surface) of the wire rod (a region where the depth from the surface is 0.5 mm or more and 1.0 mm or less) in a cross section perpendicular to a longitudinal direction of the wire rod, and a “center portion” means a range within 1.0 mm from a center of the wire rod in the cross section perpendicular to the longitudinal direction of the wire rod.
• a “surface layer” of "surface layer portion” of a steel wire means a range having a depth of from 0.2 to 0.5 mm from the surface (outer peripheral surface) of the steel wire (a region where the depth from the surface is 0.2 mm or more and 0.5 mm or less) in a cross section parallel or perpendicular to a longitudinal direction of the steel wire, and a “center portion” means a range within 1.0 mm from a center of the steel wire in the cross section parallel or perpendicular to the longitudinal direction of the steel wire.
• a "central axis” means an imaginary line passing through a center point of a cross section perpendicular to an axial direction (longitudinal direction) of the wire rod or the steel wire and extending in the axial direction.
• a cross section perpendicular to the longitudinal direction of a wire rod or a steel wire may be referred to as a "transverse cross section", and a cross section parallel to the longitudinal direction and including a central axis may be referred to as a "longitudinal cross section”.
• a numerical range that has been indicated by use of “to” indicates the range that includes the numerical values which are described before and after “to”, as a lower limit value and an upper limit value, respectively.
• a numerical range in a case in which "more than” or “less than” is attached to the numerical values which are described before and after “to” means a range not including these numerical values as the lower limit value or the upper limit value.
• an upper limit value in one stepwise numerical range may be replaced with an upper limit value in another numerical range described in a stepwise manner, or may be replaced with a value shown in Examples.
• a lower limit value in one stepwise numerical range may be replaced with a lower limit value in another numerical range described in a stepwise manner, or may be replaced with a value shown in Examples.
• the content of the element of the chemical composition may be simply referred to as “amount” (for example, C amount, Si amount, or the like).
• % means “% by mass”.
• the element of the chemical composition in a case in which "0 to" is described as the lower limit value, it means that the element is an optional element and is not necessarily contained.
• step includes not only an independent step but also a step by which an intended action of the step is achieved, though the step cannot be clearly distinguished from other steps.
• a wire rod according to the disclosure has
• a total area ratio of a ferrite structure and a martensite structure in the disclosure, referred to as "area ratio of the ferrite structure and the martensite structure" in some cases) in a center portion within 1.0 mm from a center in a cross section perpendicular to a longitudinal direction is 5% or less, with the balance being a mixed structure composed of ferrite and cementite,
• the inventors of the disclosure have found the wire rod and the steel wire according to the disclosure through the following studies.
• a mixed structure composed of ferrite and cementite such as pearlite or bainite, which is excellent in work-hardenability, is used as a main structure.
• a structure containing almost no cementite a ferrite structure or a martensite structure
• pearlite and bainite are not distinguished from each other because in a case in which pearlite and bainite have the same hardness, pearlite and bainite have similar properties after wire drawing, and it is difficult to distinguish pearlite and bainite from a photograph as a structure.
• the diameter of the wire rod is often more than 7.0 mm.
• a pearlite transformation temperature and a bainite transformation temperature are different between the surface layer having a high cooling rate and the center portion having a low cooling rate. Therefore, the surface layer tends to be harder than the center portion.
• the hardness distribution formed in the wire rod is carried over until after wire drawing, and the steel wire also has a distribution in which the surface layer is hard. In a torsion test, since strain concentrates on the surface layer, the torsion properties are disadvantageous in a distribution in which the surface layer is hard.
• the inventors of the disclosure have studied sufficiently delaying the transformation so that the pearlite transformation or the bainite transformation can be performed at a temperature comparable to that of the surface layer even in the center portion where the cooling rate is slow.
• Mo has an effect of delaying the transformation, and that the uniformity of the hardness distribution in the transverse cross section of the wire rod (cross section perpendicular to the longitudinal direction of the wire rod) is improved by the addition of Mo, and have further confirmed that a steel wire containing a predetermined amount of Mo has favorable torsion properties even in a case in which the tensile strength is 2050 MPa or more.
• C is a component necessary for increasing the tensile strength of the wire rod and a steel wire obtained after wire drawing.
• the C content is preferably 0.85% or more, and particularly, in the case of 0.90% or more, more favorable properties are exhibited. From the viewpoint of torsion properties, the C content is preferably 1.05% or less, and particularly, in the case of 1.00% or less, more favorable properties are exhibited.
• Si from 0.10 to 1.50%
• Si is a component effective for increasing the tensile strength of the wire rod and a steel wire obtained after wire drawing.
• the Si content of the wire rod is less than 0.10%, the effect obtained by containing Si cannot be sufficiently obtained.
• the Si content of the wire rod is more than 1.50%, it becomes difficult to suppress the formation of the martensite structure as a hard phase, and even in a case in which other requirements are satisfied, the target torsion properties cannot be obtained.
• the Si content is preferably 0.50% or more, and particularly, in the case of 0.70% or more, more favorable properties are exhibited. From the viewpoint of torsion properties, the Si content is preferably 1.40% or less, and particularly, in the case of 1.30% or less, more favorable properties are exhibited.
• Mn from 0.10 to 1.00%
• Mn is a component effective for increasing the tensile strength of the wire rod and a steel wire obtained after wire drawing.
• Mn is a component having an action of fixing S in steel as MnS to suppress hot brittleness.
• the Mn content is preferably 0.25% or more. From the viewpoint of torsion properties, the Mn content is preferably 0.80% or less.
• P is an element that segregates at the grain boundary of the wire rod and deteriorates the torsion properties.
• the P content of the wire rod is 0.030% or less, deterioration of torsion properties is suppressed, and the target torsion properties can be obtained by satisfying other requirements.
• the upper limit of the P content is preferably 0.025% and more preferably 0.020% or less.
• the lower limit of the P content is not limited and may be 0% (that is, P is not contained), but may be more than 0% or 0.001% or more from the viewpoint of reducing the removal cost of P.
• S is an element that deteriorates the torsion properties.
• the target torsion properties can be obtained by satisfying other requirements.
• the preferred upper limit of the S content is 0.020%.
• the lower limit of the S content is not limited, but may be more than 0% or 0.001% or more from the viewpoint of reducing the removal cost of S.
• N is an element that deteriorates the torsion properties.
• the target torsion properties can be obtained by satisfying other requirements.
• the preferred upper limit of the N content is 0.0100% and the more preferred upper limit thereof is 0.0070%.
• the lower limit of the N content is not limited, but may be more than 0% or 0.0001 % or more from the viewpoint of reducing the refining cost.
• O is an element that easily forms an oxide-based inclusion in the wire rod.
• the O content of the wire rod is 0.0100% or less, coarsening of the oxide-based inclusion can be suppressed, and deterioration of torsion properties can be suppressed.
• the preferred upper limit of the O content is 0.0070% and the more preferred upper limit thereof is 0.0050%.
• the lower limit of the O content is not limited, but may be more than 0% or 0.0001 % or more from the viewpoint of reducing the refining cost.
• Al is an element having a deoxidizing action, and is necessary for reducing the amount of oxygen in the wire rod.
• the Al content of the wire rod is less than 0.005%, it is difficult to obtain the effect obtained by containing Al.
• Al is an element that easily forms a hard oxide-based inclusion.
• the Al content of the wire rod is more than 0.070%, a coarse oxide-based inclusion is remarkably easily formed, and the wire drawability is remarkably deteriorated.
• the Al content is preferably 0.010% or more and may be 0.020% or more. From the viewpoint of wire drawability, the Al content is preferably 0.050% or less and may be 0.040% or less.
• Mo is an element that can delay pearlite transformation and bainite transformation in a trace amount, and is an element effective particularly for improving the strength of the center portion of a wire rod having a diameter of 7.0 mm or more. Mo also has an effect of increasing the tensile strength of a steel wire to be obtained after the wire drawing.
• the Mo content is preferably 0.025% or more, and particularly, in the case of 0.03% or more, more favorable properties are exhibited. From the viewpoint of torsion properties, the Mo content is preferably 0.15% or less, and particularly, in the case of 0.12% or less, more favorable properties are exhibited.
• the wire rod according to the disclosure may contain, as an optional element, one or two or more of Cr, Cu, Ni, Sn, V, Ti, Nb, B, REM, Mg, Ca, Zr, W, Te, or Sb, instead of a part of Fe.
• These optional elements are not necessarily contained (that is, 0%), or may be contained within the following ranges.
• the lower limit value of the content in the case of containing these optional elements may be more than 0%.
• the Cr has an effect of increasing the tensile strength of the wire rod and a steel wire to be obtained after the wire drawing.
• the Cr content is preferably 0.03% or more.
• the Cr content is more than 1.00%, it is difficult to suppress the formation of the martensite structure as a hard phase, and the torsion properties are deteriorated.
• the Cr content is preferably within a range of from 0.03 to 1.00%.
• the content may be preferably 0.85% or less.
• the content is more preferably from 0.10 to 0.70%.
• the inclusion of Cu is optional.
• the Cu has an effect of enhancing the corrosion resistance of the wire rod and a steel wire to be obtained after the wire drawing.
• the Cu content is preferably 0.01% or more.
• the Cu content is preferably within a range of from 0.01 to 0.80%.
• the content is more preferably from 0.05 to 0.60%.
• Sn is optional.
• Sn has an effect of enhancing the corrosion resistance of the wire rod and a steel wire to be obtained after the wire drawing.
• the Sn content is preferably 0.005% or more.
• the Sn content is preferably within a range of from 0.001 to 0.50%.
• the content is more preferably from 0.005 to 0.40%.
• Ni from 0 to 0.50%
• Ni is optional.
• Ni has an effect of enhancing the corrosion resistance of the wire rod and a steel wire to be obtained after the wire drawing.
• the Ni content is preferably 0.01% or more.
• the Ni content is preferably within a range of from 0.01 to 0.50%.
• the content is more preferably from 0.05 to 0.40%.
• V from 0 to 0.15%
• V is optional.
• V has an effect of increasing the tensile strength of the wire rod and a steel wire to be obtained after the wire drawing.
• the V content of the wire rod is preferably 0.01% or more.
• the V content of the wire rod is preferably from 0.02 to 0.15%.
• the content is more preferably from 0.03% to 0.13% and still more preferably from 0.05% to 0.12%.
• Ti is optional.
• Ti has an effect of forming a carbide or a carbonitride in the wire rod and enhancing the torsion properties.
• the Ti content of the wire rod is preferably 0.002% or more.
• the Ti content of the wire rod is more than 0.050%, coarse carbides or carbonitrides are easily formed, and the torsion properties are deteriorated.
• the Ti content of the wire rod is preferably from 0.002 to 0.050%.
• the Ti content is more preferably from 0.005 to 0.030%.
• Nb from 0 to 0.050%
• Nb is optional.
• Nb has an effect of forming a carbide or a carbonitride in the wire rod and enhancing the torsion properties.
• the Nb content of the wire rod is preferably 0.002% or more.
• the Nb content of the wire rod is more than 0.050%, coarse carbides or carbonitrides are easily formed, and the torsion properties are deteriorated.
• the Nb content of the wire rod is preferably from 0.002 to 0.050%.
• the Nb content is more preferably from 0.005 to 0.030%.
• the B has an effect of suppressing a ferrite structure and enhancing the torsion properties.
• the B content of the wire rod is preferably 0.0003% or more.
• the content of B of the wire rod is preferably from 0.0003 to 0.0040%.
• the B content is more preferably from 0.0006 to 0.0030%.
• REM is optional.
• the REM content of the wire rod is preferably 0.002% or more.
• the REM content of the wire rod is preferably from 0.002 to 0.030%.
• REM refers to Sc, Y, and lanthanoids, 17 elements in total, and in the case of one type of REM, the REM content refers to the content thereof and in the case of two or more types of REM, the REM content refers to the total content thereof.
• Mg is optional.
• the Mg content of the wire rod is preferably 0.0002% or more.
• the Mg content of the wire rod is preferably from 0.0002 to 0.0040%.
• the inclusion of Ca is optional.
• the Ca content of the wire rod is preferably 0.0002% or more.
• the Ca content of the wire rod is preferably from 0.0002 to 0.0040%.
• Zr is optional.
• the Zr content of the wire rod is preferably 0.002% or more.
• the Zr content of the wire rod is more than 0.030%, coarse carbides or carbonitrides are easily formed, and the torsion properties are deteriorated.
• the Zr content of the wire rod is preferably from 0.002 to 0.030%.
• W is optional.
• the W content of the wire rod is preferably 0.02% or more.
• the W content of the wire rod is preferably from 0.02 to 0.10%.
• Te is optional.
• the Te content of the wire rod is preferably 0.001% or more.
• the Te content of the wire rod is preferably from 0.001 to 0.030%.
• Sb is optional.
• the Sb content of the wire rod is preferably 0.001% or more.
• the Sb content of the wire rod is preferably from 0.001 to 0.030%.
• the total area ratio of the ferrite structure and the martensite structure at the center portion of the transverse cross section (cross section perpendicular to the longitudinal direction) of the wire rod is 5% or less. These deteriorate the torsion properties of the steel wire after the wire drawing. In a case in which the total area ratio of the ferrite structure and the martensite structure at the center portion of the wire rod is 5% or less, the total area ratio of the ferrite structure and the martensite structure including up to the surface layer is low, and thus the center portion is measured as a representative.
• the total area ratio of the ferrite structure and the martensite structure at the center portion of the cross section of the wire rod may be 4% or less, 2% or less, or 1% or less.
• One of the ferrite structure or the martensite structure may be included, or both of them are not necessarily included. The same applies to the structure in the longitudinal cross section of the steel wire described later.
• the average Vickers hardness H in the transverse cross section satisfies Formula (1).
• the average Vickers hardness H in the transverse cross section depends on the amount of carbon [C] contained in the wire rod in % by mass. In a case in which the average value of the Vickers hardness is less than "480 ⁇ [C] - 40", it is difficult to stably impart the tensile strength (for example, 2050 MPa or more) required for the steel wire after the wire drawing.
• the average Vickers hardness H may be in a range satisfying the following Formula (1A) or in a range satisfying Formula (1B).
• the surface layer Vickers hardness Hs at a position of a depth of from 0.5 to 1.0 mm from the surface and the average Vickers hardness H satisfy the relationship of Formula (2). 0 ⁇ Hs ⁇ H ⁇ 30
• the relationship between the surface layer Vickers hardness Hs and the average Vickers hardness H may be in a range satisfying the following Formula (2A) or in a range satisfying Formula (2B). 0 ⁇ Hs ⁇ H ⁇ 25 0 ⁇ Hs ⁇ H ⁇ 20
• the center Vickers hardness Hc within 1.0 mm from the center in the transverse cross section and the average Vickers hardness H satisfy the relationship of Formula (3). 0 ⁇ H ⁇ Hc ⁇ 30
• the center Vickers hardness Hc is smaller than the average Vickers hardness H by 30 or more, it is difficult to stably impart the tensile strength (for example, 2050 MPa or more) required for the steel wire after the wire drawing.
• the relationship between the center Vickers hardness Hc and the average Vickers hardness H may be in a range satisfying the following Formula (3A) or in a range satisfying Formula (3B). 0 ⁇ H ⁇ Hc ⁇ 25 0 ⁇ H ⁇ Hc ⁇ 20
• the wire rod according to the disclosure has a diameter of 7.0 mm or more. In a case in which the diameter of the wire rod is less than 7.0 mm, the effect of the disclosure cannot be obtained.
• the upper limit of the diameter of the wire rod according to the disclosure is not particularly limited, but it is difficult to industrially produce a wire rod having a diameter of more than 20 mm by a normal production process.
• the diameter of the wire rod according to the disclosure may be from 7.5 to 18.0 mm or from 8.0 to 16.0 mm.
• a steel wire according to the disclosure has
• a total area ratio of a ferrite structure and a martensite structure in a center portion in a cross section parallel to a longitudinal direction and passing through a central axis is 5% or less with the balance being a mixed structure composed of ferrite and cementite,
• each of the difference (hs - h) between the surface layer Vickers hardness and the average Vickers hardness and the difference (h - hc) between the center Vickers hardness and the average Vickers hardness is less than 30.
• the hardness distribution is such that the surface layer is not too hard and the center is not too soft with respect to the average hardness, a steel wire having favorable torsion properties while achieving a high strength can be obtained.
• the steel wire according to the disclosure may be subjected to a plating treatment with zinc or a zinc alloy, or may be subjected to heat input by a degreasing treatment. That is, the steel wire according to the disclosure also includes a steel wire with a plated surface (plated wire). In a case in which the steel wire according to the disclosure has a plating layer, the chemical composition, the metallographic structure, and the hardness in the disclosure all mean values of a steel portion.
• the steel wire according to the disclosure may contain an optional element similar to the chemical composition of the wire rod described above.
• the diameter of the steel wire according to the disclosure is not particularly limited, and is, for example, from 3.0 to 8.0 mm and may be from 4.0 to 7.5 mm.
• the diameter of the wire rod or the steel wire to be measured is defined as D.
• Figs. 1(A) to 1(D) show examples of a pearlite structure, which is an example of a mixed structure in which ferrite and cementite are mixed, a martensite structure, a ferrite structure (denoted as "ferrite” in Fig. 1(C) ), and a mixed structure composed of ferrite and cementite.
• the ferrite structure and the martensite structure are structures not containing cementite, and the mixed structure composed of ferrite and cementite is pearlite, bainite, or the like, in which cementite is mixed in ferrite.
• (C) there is a pearlite structure (an example of a mixed structure of ferrite and cementite), which is a lamellar structure of ferrite (blackish portion) and cementite (whitish portion), but since cementite is not present in the arrow portion and is distinguished from the surrounding pearlite structure, it is determined as a ferrite structure.
• the two arrow portions have a structure in which more ferrite is present than cementite but in which divided cementite is present in ferrite, and it is determined that the structure is a mixed structure of ferrite and cementite.
• the area ratio (%) of the ferrite structure and the martensite structure is measured.
• the ferrite structure and the martensite structure which are structures not containing cementite, are not necessarily distinguished from each other. Specifically, after each SEM image is printed on the paper surface, a transparent sheet such as an over head projector (OHP) sheet is overlaid on the paper surface to color the structure (ferrite structure and martensite structure) not containing cementite. Thereafter, the transparent sheet in which the ferrite structure and the martensite structure are colored is analyzed by image analysis to measure the total area ratio of the ferrite structure and the martensite structure.
• OHP over head projector
• the area per visual field is set to 2.7 ⁇ 10 -3 mm 2 (length: 0.045 mm, width: 0.060 mm), and image analysis software (for example, LUZEX AP manufactured by NIRECO) is used for image analysis.
• image analysis software for example, LUZEX AP manufactured by NIRECO
• An average value is calculated from the total area ratio of the ferrite structure and the martensite structure of the five images, and the average value is taken as the total area ratio of the ferrite structure and the martensite structure of the wire rod.
• the center portion in the longitudinal cross section is photographed at intervals of 200 ⁇ m by five with a scanning electron microscope (SEM) at 3 ⁇ 10 -4 mm 2 (length: 0.015 mm, width: 0.02 mm).
• SEM scanning electron microscope
• Figs. 2(A) and 2(B) show examples of SEM photographs of the longitudinal cross sections of steel wires each including a ferrite structure or a martensite structure and a mixed structure composed of ferrite and cementite.
• (a) is an enlarged view of an arrow portion of (A)
• (b) is an enlarged view of an arrow portion of (B).
• the ferrite structure and the martensite structure are structures not containing cementite
• the mixed structure composed of ferrite and cementite is a structure obtained by subjecting pearlite, bainite, or the like to wire drawing, in which cementite is mixed in ferrite.
• the area ratio (%) of the ferrite structure and the martensite structure is measured.
• the ferrite structure and the martensite structure which are structures not containing cementite, are not necessarily distinguished from each other. Specifically, after each SEM image is printed on the paper surface, a transparent sheet such as an over head projector (OHP) sheet is overlaid on the paper surface to color the ferrite structure and the martensite structure. Thereafter, the transparent sheet in which the structures are colored is analyzed by image analysis to measure the total area ratio of the ferrite structure and the martensite structure.
• the area per visual field is set to 3 ⁇ 10 -4 mm 2 (length: 0.015 mm, width: 0.02 mm), and image analysis software (for example, LUZEX AP manufactured by NIRECO) is used for image analysis. An average value is calculated from the area ratio of the ferrite structure and the martensite structure of the five images, and the average value is taken as the total area ratio of the ferrite structure and the martensite structure of the steel wire.
• An indenter is pushed into the transverse cross section of the wire rod with a load of 1 kgf using a Vickers tester.
• Points are formed toward the center at a pitch of 0.5 mm starting from a position of 0.5 mm in depth from the surface (outer peripheral surface) of the wire rod. Points are formed from four directions at intervals of 90°.
• a portion within a depth of from 0.5 to 1.0 mm from the surface is taken as the surface layer portion, and an average value of the Vickers hardnesses at eight points in total formed at distances of 0.5 mm and 1.0 mm from the surface is taken as the surface layer Vickers hardness Hs.
• a portion within a range of 1.0 mm from the center (the central axis of the wire rod) in the transverse cross section is taken as the center portion, and an average value of the hardnesses at nine points in total formed at the center and at distances of 0.5 mm and 1.0 mm from the center is taken as the center Vickers hardness Hc.
• An average value of the Vickers hardnesses measured at the center and at intervals of 0.5 mm from the surface toward the center (excluding a region of less than 0.3 mm from the center) in the entire cross section, that is, the transverse cross section, is taken as the average Vickers hardness.
• the indenter is pushed into the transverse cross section of the steel wire with a load of 1 kgf using a Vickers tester.
• Points are formed toward the center at a pitch of 0.2 mm starting from a position of 0.2 mm in depth from the surface (outer peripheral surface) of the steel wire. Points are formed from four directions at intervals of 90°. In the plated steel wire, a position of 0.2 mm from the surface of the steel portion is set as a starting point.
• the average value of the Vickers hardnesses obtained by forming points within a range of from 0.2 to 0.5 mm in depth from the surface of the steel wire is taken as the surface layer Vickers hardness hs.
• the average value of the hardnesses obtained by forming points within 1 mm from the center is taken as the center Vickers hardness hc.
• An average value of the Vickers hardnesses measured at the center and at intervals of 0.2 mm from the surface toward the center (excluding a region of less than 0.2 mm from the center) in the entire cross section, that is, the transverse cross section is taken as the average Vickers hardness.
• Evaluation is performed based on the number of times until the steel wire is broken, and a minimum value is evaluated by performing this for each five wires.
• the distance between chucks is 100 ⁇ diameter D.
• the rotation speed is set to 20 rpm.
• the breakage of the steel wire described herein includes not only a case in which the entire steel wire is broken but also a case in which a partial crack occurs in the steel wire. That is, in a case in which a partial crack occurs in the steel wire during the test, the evaluation is performed based on the number of twists at that time.
• the wire rod to be subjected to a tensile test may be straightened to be a straight line.
• the length of the wire rod is set to 340 mm, the distance between chucks is set to 200 mm, and the tensile test is performed at a stroke speed of 10 mm/min.
• the diameter of the wire rod is measured in two directions orthogonal to each other at the center in the length direction of the wire rod using a caliper, and the average value thereof is taken as the diameter.
• the tensile strength is the maximum load (N) at the time of the tensile test/the cross-sectional area (mm 2 ) calculated from the diameter of the wire rod.
• the tensile test and the measurement of the diameter of the steel wire can be performed in the same manner as in the wire rod.
• the plating is peeled off to conduct a tensile test as only a steel wire.
• the plating peeling is performed by a chemical peeling method such as immersion in hydrochloric acid or a physical peeling method such as polishing.
• Methods for producing a wire rod and a steel wire according to the disclosure are not particularly limited, but an example of a suitable production method will be described below.
• a cast slab having the above-described chemical composition is produced.
• the cast slab obtained by casting is heated to from 1200 to 1250°C and then subjected to blooming to obtain a billet.
• the heating temperature of the billet is from 1020°C to 1080°C.
• the austenite structure becomes coarse, and untransformed austenite may remain when immersed in a molten salt described later, so that there is a possibility that martensite is mixed.
• the exit temperature (finish rolling temperature) of the finish rolling is from 900 to 1000°C.
• the finish rolling temperature is higher than 1000°C
• the austenite structure becomes coarse, and untransformed austenite may remain when immersed in a molten salt described later, so that there is a possibility that martensite is mixed.
• the cooling to from 800°C to 900°C is performed by water cooling or air cooling.
• the temperature is lower than 800°C
• the temperature is excessively lowered until immersion in a molten salt, and the pearlite transformation starts from the surface layer so that the surface layer is softened.
• the austenite structure becomes coarse, and untransformed austenite may remain when immersed in a molten salt described later, so that there is a possibility that martensite is mixed.
• Cooling is performed before immersion in a molten salt.
• cooling is performed at 10°C/sec or more to a temperature of from 740°C to 800°C (temperature before the molten salt).
• the pearlite transformation starts from the surface layer so that the surface layer is softened. Coarse pearlite degrades torsion properties.
• the temperature of the molten salt increases, and pearlite cannot be transformed at a target temperature.
• the cooling rate is less than 10°C/sec, the torsion properties are deteriorated due to precipitation of pro-eutectoid cementite.
• the upper limit of the cooling rate is not particularly limited, but may be 50°C/sec or less from a technical viewpoint.
• a molten salt tank is set to from 540°C to 570°C, and immersion is performed for from 60 seconds to 120 seconds.
• the ferrite structure increases.
• the cooling rate inside the wire rod is insufficient and the wire rod is softened.
• the immersion time in the molten salt is less than 60 seconds, there is a possibility that untransformed austenite remains and martensite is mixed.
• cementite may be spheroidized after transformation, and the strength may be reduced.
• the wire rod produced through the above steps can provide a steel wire having a high strength and excellent torsion properties by wire drawing.
• D 0 is the diameter before the wire drawing
• D is the diameter after the wire drawing.
• ⁇ is preferably from 1.0 to 2.5. In a case in which the wire drawing strain is lower than 1.0, the strength is less likely to be obtained, and in a case in which the wire drawing strain is higher than 2.5, the working ratio becomes excessive and the torsion properties are deteriorated. Before the wire drawing, it is preferable to perform a surface lubrication treatment such as a zinc phosphate coating or a borax coating.
• a steel wire having a high strength and excellent torsion properties can be produced through the above steps.
• post-treatment such as plating or a degreasing treatment may be performed.
• the degreasing treatment and the plating treatment with zinc or a zinc alloy are preferably performed with in a range of from 400 to 530°C.
• the temperature is lower than 400°C, the steel material is hardened by age hardening, and the torsion properties are deteriorated.
• the temperature is 530°C or higher, softening due to spheroidization of cementite or the like becomes remarkable, resulting in insufficient strength.
• the use application of the steel wire obtained by subjecting the wire rod according to the disclosure to wire drawing is not particularly limited, but it is suitable for various use applications such as a bridge cable steel wire and various ropes, which have a high strength and require torsion properties.
• the wire rod according to the disclosure is suitable as a material of a steel wire used for these use applications.
• a rope (strand) can be obtained by bundling a plurality of steel wires according to the disclosure.
• a plurality of plated wires obtained by plating the steel wire according to the disclosure with zinc may be bundled to form a rope.
• wire rod and the steel wire of the disclosure will be described more specifically with reference to Examples. However, these Examples do not limit the wire rod and the steel wire of the disclosure.
• a steel material having the chemical composition (unit: mass%) shown in Table 1 was produced, and a wire rod was produced by the method (condition) shown in Table 2.
• the notation of "-" in Table 1 indicates that the content of the element with the notation is at an impurity level, and it can be determined that the element is not substantially contained. The same applies to "-" in Table 4 described later.
• the balance of the chemical composition in Tables 1 and 4 is Fe and impurities.
• the total area ratio of the ferrite structure and the martensite structure in the center portion, the Vickers hardness, and the tensile strength were each measured by the methods described above.
• a steel wire with a diameter of 5.0 mm was produced by subjecting a wire rod to wire drawing, that is, in the case of a wire rod with a diameter of 14.0 mm, a steel wire with a drawing strain of 2.06 was produced, the Vickers hardness and the tensile strength of the steel wire after aging at 450°C for 30 seconds were measured by the methods described above, and the number of torsions was measured by a torsion test.
• a steel wire having a high strength (2050 MPa or more) and excellent torsion properties was obtained by wire drawing of the wire rods of Nos. 1 to 4.
• the ferrite structure or the martensite structure was mixed in the structure of the wire rod, the area ratio of the ferrite structure or the martensite structure was high, and wire breakage occurred in the wire drawing.
• the ferrite structure or the martensite structure was mixed in the structure of the wire rod, the area ratio of the ferrite structure or the martensite structure was high, and wire breakage occurred in the wire drawing.
• the ferrite structure or the martensite structure was mixed in the structure of the wire rod, the area ratio of the ferrite structure or the martensite structure was high, and wire breakage occurred in the wire drawing.
• a steel material having the chemical composition (unit: mass%) shown in Table 4 was produced, and a wire rod was produced under the condition of the production method A shown in Table 2.
• the total area ratio of the ferrite structure and the martensite structure, the Vickers hardness, and the tensile strength were each measured by the methods described above.
• a steel wire having a diameter of 5.0 mm was produced by subjecting the wire rod to wire drawing, the total area ratio of the ferrite structure and the martensite structure in the center portion, the Vickers hardness, and the tensile strength were each measured by the methods described above, and the number of torsions was measured by a torsion test.
• the wire rods Nos. 20 to 33 satisfied the requirements of the disclosure, and a steel wire having a high strength (2050 MPa or more) and excellent torsion properties was obtained by wire drawing.
• the wire rod according to the disclosure and the like have been described above, the wire rod according to the disclosure and the like are not limited to the above-described embodiments and examples.
• the method for producing a wire rod according to the disclosure is not limited to a method in which immersion in a molten salt is performed after winding.
• the wire rod according to the disclosure is produced by lead patenting in which a metallographic structure is formed by heating the wire rod and then immersing the wire rod in a lead bath
• the steel wire according to the disclosure is produced by subjecting the wire rod to wire drawing, and a rope (cable) is produced by bundling the steel wires is also included in the scope of the disclosure.

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