Classifications

• • 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
• • 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
  • 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
• • 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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • 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
  • C22C38/04—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
  • C22C38/16—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
  • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/22—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
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/009—Pearlite

Definitions

• the present invention relates to a steel wire rod.
• an aluminum stranded cable used for a power line or the like strands of steel wire are used as a core to reinforce the strength.
• This stranded cable is generally called “aluminum conductor steel-reinforced cable”.
• the aluminum conductor steel-reinforced cable will be abbreviated as "ACSR”.
• steel wire used as a core of ACSR is produced by cold drawing a piano wire rod such as SWRS72B or SWRS82B specified in the JIS standard.
• a heat treatment called patenting or aluminum plating treatment is performed before or during cold drawing.
• ACSR In ACSR, not only aluminum wire but also steel wire as a core are electrically charged. Therefore, in a case where the electrical resistivity of steel wire increases, the total electrical resistivity of ACSR increases, and thus the amount of heat generated during power transmission is increased. As a result, the transmission efficiency decreases.
• steel wire having a low electrical resistivity and a high strength and a steel wire rod having a low electrical resistivity and a high strength as a material of the steel wire, are required.
• the electrical resistivity of steel increases as the amounts of elements in the steel increase. Therefore, in steel disclosed in Patent Document 1, by reducing the amounts of major elements such as C, Mn, or Cr, the electrical resistivity is reduced.
• the C content and the Si content in the steel are adjusted to be low in order to reduce the electrical resistivity and to improve cold forgeability. Therefore, the tensile strength is insufficient.
• hypereutectoid steel wire having high strength and high toughness disclosed in Patent Document 3 by specifying the contents of elements such as C, Si, or Mn in the steel and a metallographic structure thereof, the tensile strength and drawability are secured.
• the Si content is 0.5% or more, and a metallographic structure is not optimized to reduce the electrical resistivity. Therefore, the electrical resistivity is high.
• Patent Document 4 discloses a high carbon steel wire rod in which the spheroidizing heat treatment time is reduced by increasing the Cr content in a carbide.
• the Cr content in the carbide is 6.0 mass% or more. Therefore, a reduction in electrical resistivity and an increase in tensile strength cannot be achieved at the same time.
• the present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide a steel wire rod having a high strength and a low electrical resistivity.
• the Si content which increases the electrical resistivity is limited, and the Cr content in cementite in pearlite is increased within a range where the electrical resistivity and the tensile strength are well-balanced, and conversely, the Cr content in ferrite in pearlite is reduced. As a result, an increase in electrical resistivity is prevented.
• the tensile strength is increased, and the reduction in the electrical resistivity and the improvement of the tensile strength are achieved at the same time.
• the steel wire rod according to the present invention is a material before performing cold drawing, and includes a hot rolled wire rod and a steel obtained by performing a heat treatment on the hot rolled wire rod.
• a steel wire rod having a high strength and a low electrical resistivity can be provided.
• the steel wire rod according to the aspect is suitable as a material of steel wire which is used for reinforcing the strength of a power line and reduces power loss.
• steel wire which is obtained by cold drawing the steel wire rod according to the aspect and optionally performing the aluminum plating treatment after cold drawing, has a high strength and a low electrical resistivity. Therefore, when ACSR is produced using this steel wire, a predetermined strength can be secured and the electrical resistivity can be further reduced in the ACSR. Therefore, the contribution to the industry is remarkable.
• a steel wire rod according to an embodiment will be described.
• C is an element which is effective for allowing a metallographic structure of the steel wire rod to include pearlite and to thereby improve the tensile strength.
• the C content is less than 0.8%, it is difficult to stably impart a high tensile strength of, for example, 1350 MPa to the steel wire rod. Therefore, the lower limit of the C content is set to 0.8%.
• the C content is preferably 0.9% or more and more preferably 1.0% or more.
• the steel wire rod is hardened, and it causes deterioration in drawability.
• the C content is higher than 1.1%, since it is difficult to industrially stably suppress the formation of cementite precipitating along a prior austenite grain boundary, that is, proeutectoid cementite, drawability deteriorates significantly. Therefore, the upper limit of the C content is set to 1.1%.
• Si is an element which is effective for improving the strength of the steel wire rod by solid solution strengthening and is also necessary as a deoxidizer.
• the Si content is less than 0.02%, these effects are not sufficient. Therefore, the lower limit of the Si content is set to 0.02%.
• the Si content is preferably 0.05% or more.
• the Si content increases, the electrical resistivity increases.
• the Si content is higher than 0.30%, the improvement of the tensile strength and the reduction in the electrical resistivity cannot be achieved at the same time. Therefore, the upper limit of the Si content is set to 0.30%.
• the Si content is preferably 0.20% or less and more preferably 0.10% or less.
• Mn is an element which has effects of improving the strength of the steel wire rod and preventing hot brittleness by fixing S as MnS in the steel wire rod.
• the lower limit of the Mn content is set to 0.1%. Further, in order to secure the strength and further prevent hot brittleness, the Mn content is preferably 0.2% or more and is more preferably 0.3% or more.
• the Mn content increases, the electrical resistivity increases.
• the Mn content is higher than 0.6%, the improvement of the tensile strength and the reduction in the electrical resistivity cannot be achieved at the same time. Therefore, the upper limit of the Mn content is set to 0.6%.
• the Mn content is preferably 0.5% or less and is more preferably 0.4% or less.
• Cr has an effect of reducing the average lamellar spacing of pearlite to improve the tensile strength of the steel wire rod.
• Cr when Cr is solid soluted in ferrite in pearlite, Cr increases the electrical resistivity. Therefore, an effect of suppressing an increase in electrical resistivity can be obtained by increasing the Cr content in cementite such that the Cr content in ferrite is relatively reduced.
• the Cr content is lower than 0.3%, a sufficient tensile strength of the steel wire rod cannot be secured, and the Cr content in cementite cannot be increased. Therefore, in order to achieve the improvement of the tensile strength and the reduction in the electrical resistivity at the same time, it is necessary that the Cr content is 0.3% or more. In order to obtain a higher tensile strength, the Cr content is preferably 0.4% or more and more preferably 0.5% or more.
• the upper limit of the Cr content is set to 1.5%.
• the Cr content is preferably 1.0% or less and more preferably 0.8% or less.
• Al is an element which has a deoxidation effect and is necessary to reduce the oxygen content in the steel wire rod.
• the lower limit of the Al content is set to 0.01%.
• the Al content is preferably 0.02% or more.
• Al is an element which forms a hard oxide-based inclusion and deteriorates the ductility of the steel wire rod.
• the Al content is higher than 0.05%, a coarse oxide-based inclusion is likely to be formed. Therefore, the drawability of the steel wire rod deteriorates significantly. Therefore, the upper limit of the Al content is set to 0.05%.
• the Al content is preferably 0.04% or less and more preferably 0.03% or less.
• N is an element which is pinned to dislocations in the steel to deteriorate drawability during cold drawing.
• the N content is limited to 0.008% or less.
• the N content is preferably 0.005% or less and more preferably 0.004% or less.
• the lower limit of the N content may be 0%.
• the lower limit of the N content is preferably 0.0001%.
• P is an element which segregates in a grain boundary and deteriorates drawability.
• the P content is limited to 0.03% or less.
• the P content is preferably 0.02% or less and more preferably 0.01% or less.
• the lower limit of the P content may be 0%. However, in consideration of the current refining technique and the production costs, the lower limit of the P content is preferably 0.001%.
• S is an element which deteriorates drawability.
• the S content is higher than 0.02%, the drawability deteriorates significantly. Accordingly, the S content is limited to 0.02% or less.
• the S content is preferably 0.01% or less.
• the lower limit of the S content may be 0%. However, in consideration of the current refining technique and the production costs, the lower limit of the S content is preferably 0.001%.
• the basic chemical composition of the steel wire rod according to the embodiment has been described, and the remainder thereof includes iron and impurities.
• impurities described in the expression “the remainder of Fe and impurities” refer to elements which are unavoidably incorporated from raw materials such as ore or scrap or unavoidably incorporated in various production environments, when the steel is industrially produced.
• the steel wire rod according to the embodiment optionally includes one or more elements selected from the group consisting of Mo, V, Ti, Nb, and B instead of a portion of Fe in the remainder.
• the addition of Mo is optional, and the lower limit of the Mo content is 0%.
• Mo due to the addition of Mo, an effect of improving a balance between the tensile strength and the electrical resistivity of the steel wire rod can be stably obtained.
• the upper limit of the Mo content is preferably 0.20%. More preferably, the upper limit of the Mo content is 0.10%.
• V 0.15% or less
• V is optional, and the lower limit of the V content is 0%.
• V has an effect of forming a carbide or a carbonitride in the steel wire rod to reduce the pearlite block size. Therefore, due to the addition of V, the drawability can be improved. In order to obtain this effect, it is preferable that 0.02% or more of V is added. More preferably, the V content is 0.05% or more.
• the upper limit of the V content is preferably 0.15%. More preferably, the upper limit of the V content is 0.08%.
• the addition of Ti is optional, and the lower limit of the Ti content is 0%.
• Ti has an effect of forming a carbide or a carbonitride in the steel wire rod to reduce the pearlite block size. Therefore, due to the addition of Ti, the drawability can be improved. In order to obtain this effect, it is preferable that 0.002% or more of Ti is added. More preferably, the Ti content is 0.005% or more.
• the upper limit of the Ti content is preferably 0.050%. More preferably, the upper limit of the Ti content is 0.030%.
• Nb 0.050% or less
• Nb is optional, and the lower limit of the Nb content is 0%.
• Nb has an effect of forming a carbide or a carbonitride in the steel wire rod to reduce the pearlite block size. Therefore, due to the addition of Nb, the drawability can be improved. In order to obtain this effect, it is preferable that 0.002% or more of Nb is added. More preferably, the Nb content is 0.005% or more.
• the upper limit of the Nb content is preferably 0.050%. More preferably, the upper limit of the Nb content is 0.020%.
• the addition of B is optional, and the lower limit of the B content is 0%.
• B has an effect of binding to N, which is solid soluted in the steel wire rod, to form BN and to thereby reduce solid solution N. Therefore, due to the addition of B, the drawability can be improved. In order to obtain this effect, it is preferable that 0.0003% or more of B is added. More preferably, the B content is 0.0007% or more.
• the upper limit of the B content is preferably 0.0030%. More preferably, the upper limit of the B content is 0.0020%.
• the metallographic structure of the steel wire rod according to the embodiment includes pearlite in which ferrite and cementite form a layered lamellar structure.
• the main metallographic structure of the steel wire rod according to the embodiment is pearlite.
• "main metallographic structure” refers to a metallographic structure having an area ratio of 85% or more in a C cross section which is perpendicular to a longitudinal direction of the steel wire rod or in a L cross section which is parallel to the longitudinal direction of the steel wire rod.
• the area ratio of pearlite can be obtained by subtracting an area ratio of a non-pearlite structure from 100%.
• the area ratio of pearlite is 85% or more and is preferably 90% or more and more preferably 95% or more.
• the area ratio of pearlite may be 100%.
• the remainder in the metallographic structure of the steel wire rod according to the embodiment, that is, a microstructure other than pearlite is a non-pearlite structure including proeutectoid ferrite, bainite, degenerate-pearlite, proeutectoid cementite, or the like.
• a non-pearlite structure including proeutectoid ferrite, bainite, degenerate-pearlite, proeutectoid cementite, or the like.
• the area ratio of the non-pearlite structure is higher than 15%, the drawability deteriorates. Therefore, the area ratio of the non-pearlite structure is 15% or less.
• the area ratio of the non-pearlite structure is preferably 10% or less and more preferably 5% or less.
• the area ratio of the non-pearlite structure may be 0%.
• the area ratio of pearlite can be obtained as follows.
• a C cross section of a sample of the steel wire rod which is perpendicular to a longitudinal direction of the steel wire rod, is mirror polished and then is etched with nital.
• an arbitrary area of the sample etched with nital was imaged using a SEM at a magnification to 5000-fold in ten visual fields.
• the area per visual field is 3.6 ⁇ 10 -4 mm 2 .
• the area ratio of pearlite per visual field can be obtained using a typical image analysis method.
• the area ratio of pearlite in the steel wire rod can be obtained.
• the tensile strength of the steel wire rod can be improved by reducing the average lamellar spacing of the pearlite, as above described.
• the average lamellar spacing has little effect on the electrical resistivity. Therefore, in order to achieve the improvement of the tensile strength of the steel wire rod and the reduction in the electrical resistivity at the same time, it is necessary to reduce the average lamellar spacing.
• the average lamellar spacing of pearlite is higher 100 nm, the effect of improving the tensile strength is not sufficient. Therefore, in the steel wire rod according to the embodiment, in order to obtain this effect, the average lamellar spacing of pearlite is set to 100 nm or less.
• the average lamellar spacing of pearlite is preferably 75 nm or less.
• the average lamellar spacing of pearlite is set to 50 nm or more.
• the average lamellar spacing of pearlite is preferably 55 nm or more.
• the average lamellar spacing of pearlite can be measured as follows. For example, as shown in Examples described below, a C cross section of a sample of the steel wire rod is polished and is etched such that pearlite appears. Next, the C cross section on which pearlite appears is imaged with a scanning electron microscope (SEM) in multiple visual fields to obtain metallographic structure images of the sample. Using the obtained metallographic structure images, the average lamellar spacing of pearlite can be measured.
• SEM scanning electron microscope
• the measurement can be performed using the following method.
• plural positions where five lamellar spacings can be measured are selected in a range of the visual field where lamellar orientations are aligned.
• a straight line perpendicular to lamellar is drawn to measure the length of five lamellar spacings.
• two positions in order from the smallest length of five spacings are selected from the selected multiple positions.
• the measured length of five lamellar spacings is divided by 5 to obtain the lamellar spacing at the position.
• the lamellar spacings at two positions can be obtained from each visual field.
• the average value of lamellar spacings obtained as described above at 20 positions in total in the ten visual fields can be obtained as "the average lamellar spacing of pearlite" of the sample.
• pearlitic transformation is completed at a low temperature of about 600°C after setting a cooling rate in a cooling process after hot rolling to be 50 °C/sec or faster.
• Si is an element contributing to solid solution strengthening. Therefore, when the Si content in the steel wire rod increases, the strength of the steel wire rod can be improved. On the other hand, however, when the Si content in the steel wire rod increases, the electrical resistivity increases. Therefore, according as the Si content increases, a high tensile strength and a low electrical resistivity can be achieved at the same time by increasing the Cr content in cementite in pearlite.
• the Si content, the Cr content in cementite in pearlite, and the Cr content in ferrite in pearlite satisfy the following expression (1), by mass%.
• the Si content is represented by [%Si] by mass%
• the Cr content in cementite in pearlite is represented by [%Cr ⁇ ] by mass%
• the Cr content in ferrite in pearlite is represented by [%Cr ⁇ ].
• the improvement of the tensile strength and the reduction in the electrical resistivity can be achieved at the same time.
• the Cr content in cementite in pearlite that is, [%Cr ⁇ ] in the expression (1) can be obtained, for example, by chemically analyzing a residue extracted by electrolysis.
• the Cr content in cementite in pearlite can be obtained using the following method. First, the steel wire rod according to the embodiment is cut into a size which is suitable for electrolysis, and electrolysis is performed at a current density of 250 to 350 A/m 2 using a 10% AA electrolytic solution as general conditions of electrolytic polishing so as to extract a solution. Next, the extracted solution was filtered through a filter having a mesh size of 0.2 ⁇ m to obtain a residue. The filtrate, that is, the residue can be obtained by performing a general chemical analysis thereon.
• metal elements included in cementite in pearlite are Fe, Mn, and Cr.
• Fe and Cr are less likely to be extracted from a microstructure other than cementite, and Mn is more likely to form MnS rather than cementite. Therefore, the Cr content in cementite in pearlite, that is, [%Cr ⁇ ] can be calculated using the following expression (2).
• the Cr content in the residue, the Fe content in the residue, and the Mn content in the residue are represented by [%Residue Cr], [%Residue Fe], and [%Residue Mn] by mass%, respectively, and the S content in the steel wire rod is represented by [%S] by mass%.
• % Cr ⁇ 100 ⁇ % Residue Cr / % Residue Fe + % Residue Mn + % Residue Cr ⁇ % S ⁇ 55 / 32
• the Cr content in cementite in pearlite is 0.80% to 5.80% by mass%.
• the Cr content in ferrite in pearlite can be calculated based on, for example, the Cr content in the steel wire rod, that is, [%Cr], the Cr content in cementite in pearlite, that is, [%Cr ⁇ ], and the volume fraction of cementite obtained from the C content, that is, [ ⁇ ].
• the volume fraction of cementite in pearlite can be obtained from the following expression (3).
• the C content is represented by [%C] by mass%
• the volume fraction of cementite in pearlite is represented by [ ⁇ 0].
• % Cr ⁇ % Cr ⁇ % Cr ⁇ ⁇ ⁇ / ⁇
• the tensile strength TS of the steel wire rod according to the embodiment is 1350 MPa or more.
• an absolute value of the tensile strength TS of the steel wire rod is 64 times or more an absolute value of an electrical resistivity p expressed in units of ⁇ cm.
• the tensile strength TS of the steel wire rod according to the embodiment is preferably 1350 MPa or more, more preferably 1400 MPa or more, and still more preferably 1500 MPa or more.
• the tensile strength TS of the steel wire rod By setting the tensile strength TS of the steel wire rod to 1350 MPa or more, for example, in a case where the diameter of the steel wire rod is 11 mm to 5 mm, when the cold drawing is performed at a true strain of 1.6 as a general drawing amount, the tensile strength of the steel wire rod after cold drawing can be set to 1900 MPa or more.
• the steel wire rod according to the embodiment from the viewpoint of realizing a high strength and a low electrical resistivity of the steel wire rod at the same time, it is preferable that a relationship between the absolute value of the tensile strength TS and the absolute value of the electrical resistivity p expressed in units of ⁇ cm satisfies the following numerical value range.
• the absolute value of the tensile strength TS thereof is about 55 times the absolute value of the electrical resistivity p.
• the unit of tensile strength of the wire rod is MPa, and the unit of electrical resistivity is ⁇ cm.
• the absolute value of the tensile strength TS of the wire rod is 55 times the absolute value of the electrical resistivity p expressed in units of ⁇ cm, that is, when the value of the tensile strength TS which is 55 times the absolute value of the electrical resistivity p is set as a reference value
• the absolute value of the tensile strength TS of the steel wire rod according to the embodiment is 64 times or more the absolute value of the electrical resistivity ⁇ thereof expressed in units of ⁇ cm so as to be 15% or more of the reference value.
• the absolute value of the tensile strength TS of the steel wire rod according to the embodiment is 67 times the absolute value of the electrical resistivity ⁇ thereof expressed in units of ⁇ cm so as to be 20% or more of the reference value.
• the strength of the steel wire rod can be increased, and the electrical resistivity can be reduced.
• the reinforcement number can be reduced.
• an increase in the total electrical resistivity of ACSR can be suppressed, the heat generation during power transmission can be suppressed, and a stable transmission efficiency can be secured.
• the absolute value of the electrical resistivity p expressed in units of ⁇ cm is not particularly limited. That is, in the steel wire rod according to the embodiment, it is preferable that the absolute value of the tensile strength TS and the absolute value of the electrical resistivity ⁇ thereof expressed in units of ⁇ cm satisfy the following expression (6). Absolute Value of Tensile Strength TS ⁇ Absolute Value of Electrical resistivity ⁇ ⁇ 64
• the tensile strength of the steel wire rod can be secured to be significantly higher than that in the prior art.
• the reinforcement number can be reduced, and an increase in the total electrical resistivity of ACSR can be suppressed.
• the steel wire rod in which the improvement of the strength and the reduction in the electrical resistivity can be achieved at the same time can be obtained.
• the steel wire rod may be produced using a production method described below. Next, a preferable method of producing the steel wire rod according to the embodiment will be described.
• the steel wire rod according to the embodiment can be produced as follows.
• the method of producing the steel wire rod described below is an example of a method of obtaining the steel wire rod according to the embodiment.
• the present invention is not limited to the following procedure and method, and any method which can realize the configuration of the present invention can be adopted.
• steel having the above-described chemical composition is melted and continuously cast to produce a billet, and the billet is hot rolled. After continuous casting, blooming may be performed.
• the central part of the billet is heated to 1000°C to 1100°C using a general method, and the finishing temperature is set to be 900°C to 1000°C.
• the hot rolled wire rod is primarily cooled to 700°C or less by using a combination of water cooling and wind cooling with air. During this primary cooling, the average cooling rate is preferably 50 °C/sec or faster.
• the wire rod After the primary cooling, in order to complete pearlitic transformation, the wire rod is secondarily cooled to 590°C to 620°C by being immersed into a nitrate molten salt at 500°C to 530°C. After the secondary cooling, the wire rod is held in the molten salt at 550°C to 570°C for 30 seconds to 50 seconds. As a result, Cr can be concentrated into cementite. Next, water is sprayed to the wire rod so as to remove the molten salt, the wire rod is tertiarily cooled to room temperature, and is wound. In addition, the winding may be performed immediately after primary cooling or secondary cooling.
• the average cooling rate is preferably 30 °C/sec or faster.
• the wire rod is held in a range of 600°C to 550°C for 30 seconds to 50 seconds.
• a lead bath or a fluidized bed furnace may be used.
• the wire rod is not necessarily cooled to 700°C during primary cooling and secondary cooling and holding may be performed in the same lead bath. In this case, it is preferable that the wire rod is held in a lead bath at 550°C to 600°C for 35 seconds to 60 seconds.
• cooling and holding the wire rod after finish rolling can be performed using only a lead bath.
• the temperature of the wire rod after finish rolling is in a range of 900°C to 700°C
• the average cooling rate of the wire rod is 100 °C/sec to 200 °C/sec.
• the average cooling rate of the wire rod is 40 °C/sec to 50 °C/sec
• the average cooling rate of the wire rod is 60 °C/sec to 70 °C/sec
• the average cooling rate of the wire rod is 90 °C/sec to 100 °C/sec.
• finishing temperature during the hot rolling refers to the surface temperature of the steel wire rod immediately after finish rolling.
• average cooling rate during cooling after finish rolling refers to the cooling rate of the surface of the steel wire rod.
• Each of the ingots was heated at 1250°C for 1 hour and was hot-forged under a condition of a finishing temperature 950°C or more until the diameter reached 15 mm.
• the ingot was naturally cooled to room temperature to obtain a hot-forged material.
• This hot-forged material was cut to obtain a cut material having a diameter of 10 mm and a length of 1000 mm.
• each of the obtained cut materials was heated in a nitrogen atmosphere at 1050°C for 15 minutes such that the temperature of the center of the cut material was 1000°C or more.
• the cut material was hot rolled under a condition of a finishing temperature of 950°C to 1000°C until the diameter thereof reached 7 mm.
• a wire rod was obtained.
• the wire rod was immersed into a lead bath under conditions shown in Table 2 and was held.
• the wire rod was taken out from the lead bath and was naturally cooled to room temperature. As a result, a steel wire rod was obtained.
• the average cooling rate of the wire rod was 100 °C/sec to 200 °C/sec.
• the average cooling rate of the wire rod was 40 °C/sec to 50 °C/sec
• the average cooling rate of the wire rod was 60 °C/sec to 70 °C/sec
• the average cooling rate of the wire rod was 90 °C/sec to 100 °C/sec.
• the average cooling rate was 12 °C/sec to 14 °C/sec, and in a case where the temperature of the wire rod after finish rolling was 700°C to 620°C, the average cooling rate was 6 °C/sec to 7 °C/sec.
• a C cross section perpendicular to a longitudinal direction of the steel wire rod was mirror polished and was etched with nital.
• an arbitrary area of the sample etched with nital was imaged using a SEM at a magnification to 5000-fold in ten visual fields.
• the area per visual field was 3.6 ⁇ 10 -4 mm 2 .
• the area ratio of pearlite was obtained from each of the images of the visual fields using a typical image analysis method.
• the obtained average value of the area ratios of pearlite in the ten visual fields was set as the area ratio of pearlite in the steel wire rod.
• an arbitrary area of the sample etched with nital was imaged using a SEM at a magnification to 10000-fold in ten visual fields.
• the area per visual field was 9.0 ⁇ 10 -5 mm 2 .
• Each of the steel wire rods was cut into a diameter of 6 mm, and electrolysis is performed at a current density of 250 to 350 A/m 2 using a 10% AA electrolytic solution as general conditions of electrolytic polishing so as to extract a solution.
• the 10% AA electrolytic solution was a methanol solution including 10 vol% of acetyl acetone and 1 mass% of tetramethylammonium chloride.
• the extracted solution was filtered through a filter having a mesh size of 0.2 ⁇ m to obtain a residue, and this residue was dissolved in an acidic solution.
• the Cr content in the residue [%Residue Cr], the Fe content in the residue [%Residue Fe], and the Mn content in the residue [%Residue Mn] were obtained.
• the Cr content in cementite in pearlite, that is, [%Cr ⁇ ] was calculated using the following expression (A). In this case, the following conditions were defined: “metal elements in cementite were substantially Fe, Mn, and Cr”; “Fe and Cr were not extracted from a microstructure other than cementite”; and "in a case where S is included in the steel, Mn formed MnS prior to cementite".
• the Cr content, the Fe content, and the Mn content in the residue are represented by [%Residue Cr], [%Residue Fe], and [%Residue Mn] by mass%, respectively, and the S content in the steel wire rod is represented by [%S] by mass%.
• % Cr ⁇ 100 ⁇ % Residue Cr / % Residue Fe + % Residue Mn + % Residue Cr ⁇ % S ⁇ 55 / 32
• the Cr content in ferrite was calculated as follows. First, the volume fraction [ ⁇ ] of cementite in pearlite was obtained from the following expression (B), and the volume fraction [ ⁇ ] of ferrite in pearlite was obtained from the following expression (C). Next, the Cr content in ferrite [%Cr ⁇ ] was calculated from the following expression (D).
• the total C content in the steel wire rod is represented by [%C] by mass%.
• the total Cr content in the steel wire rod is represented by [%Cr] by mass%.
• test piece for measuring the electrical resistivity p As a test piece for measuring the electrical resistivity p, a rectangular test piece having a size of 3.0 mm ⁇ 4.0 mm ⁇ 60 mm was obtained from the central part of each of the steel wire rods, and the electrical resistivity of the test piece was measured using a typical four-terminal method at a temperature of 20°C.
• the unit of the obtained electrical resistivity ⁇ is ⁇ cm.
• Test Nos. 1, 3, 6, 7, 9 to 11, 14, 17, 18, 20 to 22, 24, 26, 27, 30, 33, 34, 36, and 44 to 47 did not satisfy at least one of the technical features specified in the present invention including the chemical composition, the metallographic structure, the average lamellar spacing of pearlite, the relationship between the Si content, the Cr content in cementite in pearlite, and the Cr content in ferrite in pearlite.
• Test Nos. 45 and 47 the drawability was low.
• Test Nos. 2, 4, 5, 8, 12, 13, 15, 16, 19, 23, 25, 28, 29, 31, 32, 35, 37 to 43, and 48 satisfied all of the technical features specified in the present invention including the chemical composition, the metallographic structure, the average lamellar spacing of pearlite, the relationship between the Si content, the Cr content in cementite in pearlite, and the Cr content in ferrite in pearlite.
• a steel wire rod having a high strength and a low electrical resistivity can be obtained, which remarkably contributes to the industry.

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• 2015
  • 2015-06-02 JP JP2016525185A patent/JP6288264B2/ja active Active
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  • 2015-06-02 WO PCT/JP2015/065897 patent/WO2015186701A1/ja active Application Filing
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