WO2011108459A1 - 冷間鍛造性に優れた鋼線及びその製造方法 - Google Patents

冷間鍛造性に優れた鋼線及びその製造方法 Download PDF

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WO2011108459A1
WO2011108459A1 PCT/JP2011/054314 JP2011054314W WO2011108459A1 WO 2011108459 A1 WO2011108459 A1 WO 2011108459A1 JP 2011054314 W JP2011054314 W JP 2011054314W WO 2011108459 A1 WO2011108459 A1 WO 2011108459A1
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steel wire
wire
steel
spherical
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PCT/JP2011/054314
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English (en)
French (fr)
Japanese (ja)
Inventor
真 小此木
真吾 山崎
大羽　浩
細川　浩一
秀世 冨澤
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新日本製鐵株式会社
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Priority to KR1020127020053A priority Critical patent/KR101297539B1/ko
Priority to JP2012503112A priority patent/JP5026626B2/ja
Priority to CN201180007849.6A priority patent/CN102741441B/zh
Publication of WO2011108459A1 publication Critical patent/WO2011108459A1/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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • 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
    • C21D1/56—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
    • 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
    • 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
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • C21D9/5732—Continuous furnaces for strip or wire with cooling of wires; of 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
    • C22C38/001—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
    • C22C38/02—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • 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

Definitions

  • the present invention relates to a steel wire that is used as a material for machine parts such as bolts, screws, and nuts, and is formed by cold forging, rolling, or the like, and a manufacturing method thereof.
  • the present invention particularly relates to a steel wire excellent in cold forgeability capable of suppressing forming cracks and a method for producing the same.
  • the steel wire which is the object of the present invention includes a “burn-in coil” in which a hot-rolled steel bar is wound in a coil shape.
  • Patent Document 1 a region where the average grain size of ferrite grains is 2 to 5.5 ⁇ m, the major axis is 3 ⁇ m or less, and the ratio of cementite having an aspect ratio of 3 or less is 70% or more with respect to the total cementite from the surface. It is disclosed that cold workability is improved by setting the diameter to 10% or more. This method is effective in processing where the crack generation position is in the vicinity of the surface of the rolled wire, but the effect of improving workability is small for processing where the crack generation position is inside the rolled wire. In actual cold forging, since the cold wire forging is performed after the rolled wire is cut, the vicinity of the surface of the rolled wire often does not become a crack generation position, and the effect is limited.
  • Patent Document 2 the value obtained by dividing the standard deviation of the distance between cementites by the average value of the distance between cementites is set to 0.50 or less, that is, the distance between the cementites is substantially uniform. It is disclosed that the deformation resistance is reduced and cracking is reduced.
  • the structure after hot rolling becomes a structure mainly composed of pseudo pearlite or bainite structure.
  • the microstructure before annealing is such a microstructure, there is a problem that the ferrite grains do not become coarse after annealing, the deformation resistance is high, and the mold load becomes high during cold forging.
  • An object of the present invention is to provide a steel wire capable of imparting strength necessary for machine structure and having excellent cold forgeability and a method for producing the same.
  • the present invention has been made to solve the above problems, and the gist thereof is as follows.
  • the component composition is mass%, C: 0.25% to 0.60%, Si: 0.01% to 0.40%, Mn: 0.20% to 1.50%, Cr: 0.20% or less, P: 0.030% or less, S: 0.040% or less, N: 0.010% or less, O: 0.0040% or less
  • the balance is a steel wire composed of iron and inevitable impurities, and the metal structure is substantially composed of ferrite grains and spherical carbides.
  • the ferrite particles have an average particle size of 15 ⁇ m or more, and the spherical carbide has an average particle size of 0.8 ⁇ m or less, a maximum particle size of 4.0 ⁇ m or less, and the number per 1 mm 2 is 0. 0.5 ⁇ 10 6 ⁇ C% to 5.0 ⁇ 10 6 ⁇ C%, and among the spherical carbides, the maximum distance between spherical carbides having a particle size of 0.1 ⁇ m or more is 10 ⁇ m or less.
  • the steel wire according to the above (1) is such that the component composition is mass%, Al: 0.001 to 0.060%, Ti: 0.002 to 0.050%, Ca: 0.00.
  • Mg 0.0001 to 0.010%
  • Zr 0.0001 to 0.010%
  • B 0.0001 to 0.0060%
  • Mo 0.01 to 0.10%
  • Cu 0.01-0.25%
  • Nb 0.001-0.04%
  • V 0.01-0.20%
  • Co 0.001 It may contain at least one of up to 0.2%
  • REM 0.0005 to 0.01%.
  • the heating step for heating the steel slab having the component composition described in (1) or (2) above, and the rolling end temperature is set to Ar1 temperature or higher for the steel slab
  • a hot rolling step of obtaining a rolled wire by performing the hot rolling performed cooling the rolled wire from the rolling end temperature to 600 ° C. at an average cooling rate of 20 ° C./s to 100 ° C./s
  • the present invention by improving the deformability of the steel wire, it becomes possible to form a complex shaped part by cold forging, and the product yield and productivity are improved. In addition, it is possible to integrally form complex shaped parts, which has been difficult in the past.
  • the present inventors examined the influence of the metal structure on deformation resistance and ductility in order to improve the cold forgeability of the steel wire. As a result, focusing on the influence of the number density of carbides and the ferrite grain size on deformation resistance, in order to obtain good workability by lowering deformation resistance, the number density of carbides is reduced, It was found that increasing the ferrite grain size is effective. On the other hand, paying attention to the influence of the carbide particle size and ferrite particle size on ductility, in order to increase the ductility, it is effective to reduce the carbide particle size and refine the ferrite grains. The knowledge that there is.
  • the present inventors examined improvement of the metal structure of the steel wire. did. as a result, (A) making ferrite grains coarse; (B) limiting the number density of the spherical carbide within a specific range; (C) reducing the average particle size and the maximum particle size of the spherical carbide; (D) uniform dispersion between the spherical carbides, It was found that it is effective to satisfy the above conditions simultaneously.
  • E a steel component with reduced Cr
  • F the structure of the hot-rolled wire is a pearlite structure having a small pro-eutectoid ferrite fraction and a fine lamellar spacing
  • G introducing dislocations in wire drawing, etc.
  • H Carbide spheroidization is performed in a temperature range of Ac1 or lower, Found that is important.
  • the reason why the steel wire having a structure of coarse ferrite and fine spherical carbide is excellent in cold forgeability is to suppress the generation of cracks by making the particle size of spherical carbides that are likely to be the starting point of forming cracks. This is considered to be because ductility deterioration is suppressed even if the ferrite grains are coarse to reduce deformation resistance.
  • the metal structure of the steel wire according to the present embodiment is substantially composed of ferrite grains and spherical carbides.
  • a bainite structure or a martensite structure is included in the metal structure, deformation resistance increases and ductility decreases and cold forgeability deteriorates. Therefore, it is preferable that these structures are not included.
  • the fact that the metal structure is substantially composed of ferrite grains and spherical carbide means that the area ratio of 97% or more of the metal structure is ferrite grains and spherical carbide, in other words, if the area ratio is less than 3%. It means that the presence of a bainite structure, a martensite structure, etc. is allowed.
  • the coarsening of ferrite grains lowers deformation resistance and reduces the mold load during cold forging.
  • the average grain size of the ferrite grains is less than 15 ⁇ m, the effect of reducing deformation resistance is small. Accordingly, the lower limit of the average grain size of the ferrite grains is preferably 15 ⁇ m.
  • the average particle diameter of the ferrite grains is measured using, for example, an EBSP (Electron Back Scattering Pattern) apparatus. Specifically, in the steel wire cross section perpendicular to the longitudinal direction of the steel wire, the vicinity of the surface layer (surface) and the 1 / 4D portion (1 / D of the diameter D of the steel wire from the surface of the steel wire to the center of the steel wire). A region of 275 ⁇ m ⁇ 165 ⁇ m is measured at a part 4) and a 1 / 2D part (center part of the steel wire). From the measured crystal orientation map of the ferrite structure, a boundary having an orientation difference of 15 degrees or more is recognized as a ferrite grain boundary. In addition, the circle equivalent particle diameter of one ferrite grain is defined as the grain diameter of the ferrite grain, and the volume average is defined as the average grain diameter. The volume average is calculated after excluding crystal grains having a particle diameter of less than 1 ⁇ m.
  • the maximum particle size of the spherical carbide influences the occurrence of molding cracks. When the maximum particle size becomes coarse, cracks are generated from the periphery of the strained carbide, and cracks are likely to occur. If the maximum particle size of the spherical carbide exceeds 4.0 ⁇ m, the ductility is lowered and cold forging cracks are likely to occur. For this reason, the upper limit of the maximum particle size of the spherical carbide is set to 4.0 ⁇ m, preferably 3.0 ⁇ m or less.
  • the upper limit of the average particle diameter of the spherical carbide is set to 0.8 ⁇ m, preferably 0.6 ⁇ m.
  • the spherical carbide means cementite having an aspect ratio represented by a major axis / minor axis of the carbide of 5 or less. If the volume ratio of cementite other than spherical carbide to the total cementite is less than 5%, the influence on cold forgeability is small, so less than 5% cementite other than spherical carbide may be contained.
  • the average particle diameter of the spherical carbide means the number average of the equivalent circle diameter of the spherical carbide. The number average is calculated after excluding the spherical carbide having an equivalent circle diameter of less than 0.1 ⁇ m.
  • the lower limit of the number of spherical carbides per 1 mm 2 is 0.5 ⁇ 10 6 ⁇ C%, preferably 1.0 ⁇ 10 6 ⁇ C%, and the upper limit is 5.0 ⁇ 10 6 ⁇ C%.
  • the number is preferably 2.0 ⁇ 10 6 ⁇ C%.
  • the notation of Mn%, Mo%, Si%, Cr%, etc. means the content of each component.
  • Maximum distance between spherical carbides When the maximum distance between spherical carbides of 0.1 ⁇ m or more exceeds 10 ⁇ m, the distribution of the spherical carbides becomes non-uniform and non-uniform strength portions are generated. If there is a non-uniform portion of strength, cold forging cracks may occur due to local concentration of deformation during forging. For this reason, the upper limit of the maximum distance between spherical carbides is 10 ⁇ m, more preferably 8 ⁇ m.
  • the average particle size of spherical carbide, the maximum particle size of spherical carbide, the number of spherical carbides / C, and the distance between spherical carbides can be obtained by image analysis of scanning electron micrographs, for example. Specifically, in the steel wire cross section perpendicular to the longitudinal direction of the steel wire, the vicinity of the surface layer (surface) and the 1 / 4D portion (1 / D of the diameter D of the steel wire from the surface of the steel wire to the center of the steel wire).
  • a field of view of 25 ⁇ m ⁇ 20 ⁇ m is observed with 5 fields of view at a magnification of 5000, a total of 15 fields, and the photographed photograph is analyzed by image analysis. be able to.
  • the number average of the equivalent circle diameters of the spherical carbides is defined as the average particle diameter, and the maximum particle diameter in the measurement field is defined as the maximum particle diameter.
  • carbonized_material of 0.1 micrometer or more be the maximum distance between carbide
  • the steel wire according to the present embodiment contains C, Si, and Mn as essential chemical components.
  • the range of the preferable content of each chemical component and the reason will be described below.
  • % which shows content in this application means the mass%.
  • C (C: 0.25 to 0.60%) C ensures the strength as a machine part. If it is less than 0.25%, the strength required as a machine part cannot be secured, and if it exceeds 0.60%, ductility and toughness deteriorate. Therefore, for the C content, the lower limit is 0.25%, preferably 0.30%, more preferably 0.35%, and the upper limit is 0.60%, preferably 0.55%, more preferably Is 0.50%.
  • Si 0.01-0.40%
  • Si is an element that functions as a deoxidizing element, imparts necessary strength and hardenability to steel, and improves temper softening resistance. If the content is less than 0.01%, these effects are insufficient. If the content exceeds 0.40%, the toughness and ductility deteriorate, and the hardness increases and the cold forgeability deteriorates. Therefore, for the Si content, the lower limit is set to 0.01%, preferably 0.03%, more preferably 0.05%, and the upper limit is set to 0.40%, preferably 0.35%, more preferably. Is 0.30%.
  • Mn is an element necessary for imparting necessary strength and hardenability to steel. If it is less than 0.20%, the effect is insufficient, and if it exceeds 1.50%, the toughness is deteriorated and the hardness is increased to deteriorate the cold forgeability. Therefore, for the Mn content, the lower limit is 0.20%, preferably 0.25%, more preferably 0.30%, and the upper limit is 1.50%, preferably 1.25%, more preferably Is 1.00%.
  • the contents of P, S, Cr, N, and O are limited.
  • the range of acceptable contents of each chemical component and the reason thereof will be described below.
  • P 0.030% or less
  • P increases deformation resistance during cold forging and deteriorates toughness. Further, it is desirable to reduce the grain boundary because it segregates and embrittles the crystal grain boundary after quenching and tempering to deteriorate toughness. For this reason, the P content is limited to 0.030% or less, preferably 0.025% or less, and more preferably 0.020% or less.
  • S 0.040% or less
  • S reacts with an alloy element such as Mn and exists as a sulfide. These sulfides improve machinability.
  • the S content exceeds 0.040%, the cold forgeability is deteriorated, and the crystal grain boundary after quenching and tempering is embrittled to deteriorate toughness. Therefore, the S content is limited to 0.040% or less, preferably 0.035% or less, and more preferably 0.030% or less.
  • Cr 0.20% or less
  • Cr has the effect of improving the hardenability of the steel by increasing the content by 0.01% or more and increasing the strength.
  • increasing the content inhibits the spheroidization of lamellar pearlite during annealing, and cold forgeability. Deteriorate.
  • the content exceeds 0.20%, it becomes difficult to spheroidize in an annealing time that can be mass-produced industrially at low cost.
  • the Cr content is limited to 0.20% or less, preferably 0.15% or less, and more preferably 0.10% or less.
  • N 0.010% or less
  • N improves the toughness by refining the prior austenite crystal grains.
  • N combines with Al, Ti and the like to form nitrides, functions as pinning particles, and makes crystal grains fine. If the N content is less than 0.001%, the amount of deposited nitride is insufficient, the crystal grains become coarse, and the ductility deteriorates. Therefore, even if the lower limit is specified to be 0.001%, preferably 0.002% Good.
  • the N content exceeds 0.010%, the deformation resistance increases due to dynamic strain aging due to the solid solution N, and the workability deteriorates. For this reason, the N content is limited to 0.010% or less, preferably 0.008% or less, and more preferably 0.006% or less.
  • O oxygen
  • oxide such as Al or Ti.
  • O content it is 0.0040% or less, Preferably it is 0.0030% or less, More preferably, it suppresses to 0.0020% or less.
  • the component composition (remainder) other than the above chemical components is composed of iron and inevitable impurities when it does not contain the selectively added chemical components shown below.
  • the content of inevitable impurities is permissible as long as it does not significantly deteriorate the effects of the present invention, but it is preferable to reduce it as much as possible.
  • the steel wire according to the present embodiment has at least one of Al, Ti, Ca, Mg, Zr, B, Mo, Ni, Cu, Nb, V, Co, W, and REM as chemical components to be selectively added. May further be contained.
  • the preferred contents and reasons for adding each chemical component to the steel wire are as follows. In addition, since these components are components added selectively, it can be said that the lower limit of each component is 0%.
  • Al 0.001 to 0.060%
  • Al is added for the purpose of deoxidation and refinement of austenite crystal grains.
  • toughness is improved when strength is given to mechanical parts by quenching and tempering.
  • Al functions as a deoxidizing element, forms AlN and functions as pinning particles, and reduces the austenite crystal grain size.
  • solid solution N is fixed, dynamic strain aging is suppressed, and deformation resistance is reduced. If the added amount of Al is less than 0.001%, these effects do not function, and if it exceeds 0.060%, the effect is saturated and the productivity of the steel material is deteriorated, so the upper limit is made 0.060%. .
  • Ti 0.002 to 0.050%
  • Ti is added for the purpose of deoxidation and refinement of austenite crystal grains.
  • toughness is improved when strength is given to mechanical parts by quenching and tempering.
  • Ti functions as a deoxidizing element, forms TiN and functions as a pinning particle, and reduces the austenite crystal grain size.
  • solid solution N is fixed, dynamic strain aging is suppressed, and deformation resistance is reduced. If the addition amount of Ti is less than 0.002%, these effects do not function, and if it exceeds 0.050%, coarse TiN is generated and the fatigue characteristics are deteriorated, so the upper limit is made 0.050%.
  • Ca 0.0001 to 0.010%
  • Mg 0.0001-0.010%
  • Zr 0.0001 to 0.010%
  • Ca, Mg and Zr are added for the purpose of deoxidation. These elements are effective for deoxidation and have the effect of improving fatigue strength by refining oxides. If the addition amount is less than 0.0001%, there is no effect, and if it exceeds 0.010%, a coarse oxide is formed and the fatigue characteristics are deteriorated. Therefore, the lower limit is 0.0001% and the upper limit is 0.010%. To do.
  • the steel wire may contain 0.0001 to 0.0060% B in order to improve hardenability. If it is less than 0.0001%, the effect is insufficient, and even if added over 0.0060%, the effect is saturated, so 0.0001 to 0.0060% is set.
  • Mo 0.01-0.10%
  • Mo has the effect of improving the hardenability of steel and increasing the strength by generating carbides such as Mo 2 C. If less than 0.01%, there is no effect, and if added over 0.10%, carbide spheroidization is inhibited and cold forgeability deteriorates, so the lower limit is 0.01% and the upper limit is 0.10%. To do.
  • Ni 0.01-0.20% Ni has the effect of improving the hardenability of the steel and increasing the strength. If it is less than 0.01%, there is no effect, and if adding over 0.20%, the alloy cost is increased, so the lower limit is made 0.01% and the upper limit is made 0.20%.
  • Cu 0.01-0.25%)
  • Cu has the effect of improving the hardenability of steel and increasing the strength by precipitation. If less than 0.01%, there is no effect, and if added over 0.25%, hot ductility is degraded and surface defects are likely to be generated. Therefore, the lower limit is made 0.01% and the upper limit is made 0.25%.
  • Nb 0.001 to 0.04%
  • Nb has the effect of generating carbides such as NbC and increasing the strength. If it is less than 0.001%, there is no effect, and if it exceeds 0.04%, cold forgeability is deteriorated, so the lower limit is made 0.001% and the upper limit is made 0.04%.
  • V 0.01-0.20%
  • V has an effect of increasing the strength by generating carbides such as VC. If it is less than 0.01%, there is no effect, and if it exceeds 0.20%, cold forgeability deteriorates, so the lower limit is made 0.01% and the upper limit is made 0.20%.
  • Co 0.001 to 0.2%)
  • W 0.001 to 0.2%)
  • W is effective for improving the strength by precipitating WC by adding 0.001% or more. If added over 0.2%, the effect is saturated and the alloy cost is increased, so the upper limit is made 0.2%.
  • REM 0.0005-0.01%) REM (Rare Earth Metal) has the effect of reducing the solid solution S and improving the ductility by generating sulfide by addition of 0.0005% or more. If added over 0.01%, a coarse oxide is formed and the toughness is lowered, so the upper limit is made 0.01%.
  • the steel wire manufacturing method includes at least a heating process, a hot rolling process, a first cooling process, a second cooling process, a holding process, a wire drawing process, and an annealing process. .
  • a heating process a hot rolling process
  • a first cooling process a second cooling process
  • a holding process a wire drawing process
  • an annealing process a process for annealing
  • Heating process In the heating step, a steel slab containing the component composition described in the first embodiment is prepared and heated to 950 ° C. or higher and 1300 ° C. or lower.
  • the heated steel slab is hot-rolled at a rolling end temperature equal to or higher than the Ar1 temperature (° C.) to produce a rolled wire rod.
  • the rolling end temperature is lower than the Ar1 temperature (° C.)
  • the ferrite grains become finer and a structure with an average grain size of 15 ⁇ m or more cannot be obtained.
  • First cooling step In the first cooling step, the temperature from the rolling end temperature to 600 ° C. is cooled at a first average cooling rate of 20 ° C./s to 100 ° C./s.
  • the cooling rate and composition affect the structure of the steel wire. That is, when the contents of C, Mn, and Cr are low, if the cooling rate is low, the fraction of the pro-eutectoid ferrite structure increases, and the maximum distance between the carbides after annealing increases. For this reason, what is necessary is just to select a component and a cooling rate so that a predetermined structure
  • the fraction of the pro-eutectoid ferrite structure increases, and the maximum distance between the spherical carbides after annealing exceeds 10 ⁇ m.
  • the 1st average cooling rate increases in order for the 1st average cooling rate to exceed 100 degrees C / s.
  • (Second cooling step) cooling is performed from 600 ° C. to 550 ° C. at a second average cooling rate of 15 ° C./s or less.
  • the second average cooling rate exceeds 15 ° C./s, a bainite structure is formed in a component having a high content of alloy elements such as Si, Cr, and Mo, and the cold forgeability after annealing deteriorates.
  • holding is performed for 30 seconds to 150 seconds in a temperature range of 500 ° C. to 600 ° C. and 450 + 8.5 ⁇ F 1 ° C. or higher.
  • holding temperature is less than 500 degreeC, a martensitic structure and a bainite structure will produce
  • the holding temperature exceeds 600 ° C.
  • the increase in the fraction of pro-eutectoid ferrite structure, the coarsening of the pearlite lamellar spacing, the non-uniform dispersion of carbide after annealing, and the coarsening of the average particle size Occurs and degrades the cold forgeability.
  • the influence of holding temperature and components greatly affects the structure of steel wire, suppresses the formation of bainite structure and martensite structure, and makes the structure mainly composed of pearlite structure, after wire drawing and annealing It becomes possible to make the average particle diameter of ferrite 15 ⁇ m or more.
  • a bainite structure is likely to be generated.
  • required by 20xSi% + 35xCr% + 55xMo% is high and 450 + 8.5xF1 (degreeC) exceeds 500 degreeC, a holding temperature shall be 450 + 8.5xF1 degreeC or more. This is because the formation of a bainite structure is suppressed and the cold forgeability after annealing is not deteriorated.
  • a preferable holding temperature range is 550 degreeC or more and 600 degrees C or less.
  • the holding time is less than 30 seconds, the pearlite transformation is not completed, and the volume ratio of the retained austenite structure after cooling is increased, so that the cold forgeability after annealing is deteriorated. If it is longer than 150 seconds, productivity is impaired.
  • Wire drawing process The rolled wire after the holding step is cooled and then subjected to wire drawing.
  • the spheroidization of the carbide is promoted during the subsequent annealing, and the growth of the ferrite crystal grains is promoted to make the ferrite grains coarse.
  • the area reduction ratio of the wire drawing is less than 25%, these effects are insufficient and the cold forgeability deteriorates.
  • the present invention will be further described based on examples, but the conditions in the examples are condition examples adopted for confirming the feasibility and effects of the present invention, and the present invention is not limited to these condition examples.
  • the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
  • Tables 1 and 2 show the composition of the steel slabs A to L used to manufacture the steel wires 1 to 35.
  • the steel wires 1 to 25 are (1) hot-rolled to a heated steel slab, (2) cooled at a predetermined temperature and time in a molten salt bath on the rolling line, and (3) rolled wire rod
  • the wire drawing material was subjected to wire drawing to produce a wire drawing material, and (4) the wire drawing material was annealed.
  • Steel wires 26 to 35 which are comparison targets, are (1) hot-rolled on a heated steel slab, (2) cooled after winding, and (3) drawn on a rolled wire.
  • the wire drawing material was manufactured by applying (4), and the wire drawing material was annealed, that is, manufactured by a conventional manufacturing method.
  • the average grain size of ferrite grains, the average grain size of spherical carbides, the maximum grain size of spherical carbides, the number of carbides / C, and the maximum distance between carbides are as follows. It was measured. The average particle diameter of the ferrite grains was measured using an EBSP apparatus. Specifically, in the steel wire cross section perpendicular to the longitudinal direction of the steel wire, the vicinity of the surface layer (surface) and the 1 / 4D portion (1 / D of the diameter D of the steel wire from the surface of the steel wire to the center of the steel wire).
  • the area of 275 ⁇ m ⁇ 165 ⁇ m was measured at a part 4) and a 1 / 2D part (center part of the steel wire). From the measured crystal orientation map of the ferrite structure, a boundary having an orientation difference of 15 degrees or more was recognized as a ferrite grain boundary.
  • the average particle size of spherical carbide, the maximum particle size of spherical carbide, the number of spherical carbides / C, and the distance between spherical carbides were determined by image analysis of scanning electron micrographs.
  • the number average of the equivalent circle diameters of the spherical carbides was defined as the average particle diameter
  • the maximum particle diameter in the measurement field of view was defined as the maximum particle diameter.
  • the maximum diameter of a circle drawn in a region not containing 0.1 ⁇ m or more of carbide was defined as the maximum distance between carbides.
  • deformation resistance and critical compressibility were measured for steel wires 1 to 35 as evaluation of cold forgeability.
  • a test piece having a diameter of 5.0 ⁇ 7.5 mm was taken from the annealed steel wire, and the compression test was performed by constraining the end surface with a concentric die.
  • Deformation resistance was equivalent strain 1.6, and equivalent stress at the time of processing 73.6% in terms of compressibility.
  • the critical compression ratio is a test piece having a notch with a curvature of 0.15 mm, a depth of 0.8 mm, and an angle of 30 ° in the circumferential axial direction of a compression test piece having a diameter of 5.0 ⁇ 7.5 mm.
  • the maximum compression rate that does not occur was defined as the critical compression rate.
  • Table 4 further shows the comparison results of the steel wires 1 to 13, 16 to 25 and the normal annealed material (steel wires 26 to 35). “Good” indicates that cold forgeability is superior to conventional spheroidized annealed materials, and “Fair” is equivalent cold forgeability (with deformation resistance within ⁇ 20 MPa, limit compressibility ⁇ 2%) "Poor” indicates that the cold forgeability is inferior.
  • the steel wire to which the chemical component content and the manufacturing method defined in the present invention are applied has a deformation resistance equal to or higher than that of the steel wires 26 to 35 to be compared, and the critical compressibility is all excellent. You can see that
  • FIG. 1 to 7 show the evaluation results for the steel wires 1 to 35.
  • FIG. FIG. 1 shows the relationship between ferrite grain size and deformation resistance for steel wires 1 to 35. From this figure, it can be seen that the steel wire having a ferrite grain size of 15 ⁇ m or more has low deformation resistance.
  • FIG. 2 shows the relationship between the maximum particle size of the spherical carbide and the critical compressibility for the steel wires 1 to 35. From this figure, it can be seen that the steel wire having a spherical carbide maximum particle size of 4 ⁇ m or less has a high critical compressibility.
  • FIG. 3 shows the relationship between the carbide average particle size and the critical compressibility for steel wires 1 to 35.
  • FIG. 4 shows the relationship between the value obtained by dividing the number of spherical carbides by C% and the critical compression rate for steel wires 1 to 35. From this figure, it can be seen that the limit compressibility of the steel wire having the number per 1 mm 2 of 0.5 ⁇ 10 6 ⁇ C% to 5.0 ⁇ 10 6 ⁇ C% is high.
  • FIG. 5 shows the relationship between the maximum distance between carbides and the critical compressibility for steel wires 1 to 35.
  • FIG. 6 shows the relationship between the Cr amount and deformation resistance.
  • steel wires 3, 13, 14, 15 using steel slab types C, I and J having similar contents of C, Si and Mn are used. The relationship between Cr content and deformation resistance was shown. From this figure, it can be seen that when the Cr content exceeds 0.2%, the deformation resistance increases rapidly.
  • FIG. 7 shows the relationship between the F1 value and the holding temperature.
  • 25 the relationship between the F1 value and the holding temperature is shown.
  • Steel wires 20 and 25 having a high holding temperature were inferior in deformation resistance and critical compressibility because the ferrite grain size and the maximum distance between carbides were not desirable.
  • Steel wires 4, 17, 18, 19, and 24 having a low holding temperature were inferior in deformation resistance because the ferrite grain size was undesirable.
  • the average particle size, the maximum particle size, the ferrite particle size, and the maximum distance between the spherical carbides of the spherical carbide are appropriate. Therefore, it can be seen that the deformation resistance is equal to or higher than that of the conventional spheroidized annealing material, and the critical compression ratio is increased.

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JP2016172888A (ja) * 2015-03-16 2016-09-29 新日鐵住金株式会社 冷間加工性に優れた鋼線材およびその製造方法
WO2017038436A1 (ja) * 2015-09-03 2017-03-09 株式会社神戸製鋼所 機械構造部品用鋼線
US9845519B2 (en) 2012-03-26 2017-12-19 Kobe Steel, Ltd. Boron-added high strength steel for bolt and high strength bolt having excellent delayed fracture resistance
JP2018003106A (ja) * 2016-07-04 2018-01-11 株式会社神戸製鋼所 冷間加工用機械構造用鋼およびその製造方法
JP2018083231A (ja) * 2012-09-07 2018-05-31 コンパニー ゼネラール デ エタブリッスマン ミシュラン ワイヤ引き抜き方法
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KR20210130212A (ko) 2019-05-16 2021-10-29 닛폰세이테츠 가부시키가이샤 강선 및 열간 압연 선재
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US9845519B2 (en) 2012-03-26 2017-12-19 Kobe Steel, Ltd. Boron-added high strength steel for bolt and high strength bolt having excellent delayed fracture resistance
JP2018083231A (ja) * 2012-09-07 2018-05-31 コンパニー ゼネラール デ エタブリッスマン ミシュラン ワイヤ引き抜き方法
KR20160088372A (ko) 2013-12-02 2016-07-25 가부시키가이샤 고베 세이코쇼 볼트용 강선 및 볼트, 및 그들의 제조 방법
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JP2016172888A (ja) * 2015-03-16 2016-09-29 新日鐵住金株式会社 冷間加工性に優れた鋼線材およびその製造方法
WO2017038436A1 (ja) * 2015-09-03 2017-03-09 株式会社神戸製鋼所 機械構造部品用鋼線
JP2019500489A (ja) * 2015-11-12 2019-01-10 ポスコＰｏｓｃｏ 冷間鍛造性に優れた線材及びその製造方法
WO2018008355A1 (ja) * 2016-07-04 2018-01-11 株式会社神戸製鋼所 冷間加工用機械構造用鋼およびその製造方法
JP2018003106A (ja) * 2016-07-04 2018-01-11 株式会社神戸製鋼所 冷間加工用機械構造用鋼およびその製造方法
KR20210130212A (ko) 2019-05-16 2021-10-29 닛폰세이테츠 가부시키가이샤 강선 및 열간 압연 선재
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CN113710821B (zh) * 2019-05-16 2023-06-23 日本制铁株式会社 钢线以及热轧线材
CN115612927A (zh) * 2022-09-27 2023-01-17 联峰钢铁（张家港）有限公司 一种含矾合金工具钢及其生产工艺
CN115612927B (zh) * 2022-09-27 2023-07-14 联峰钢铁（张家港）有限公司 一种含钒合金工具钢及其生产工艺

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