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EP4261313A1 - Fil machine à haute résistance pour matriçage à froid, doté d'excellentes caractéristiques de traitement thermique et de rupture différée par l'hydrogène, élément de traitement thermique et procédés de fabrication associés - Google Patents

Fil machine à haute résistance pour matriçage à froid, doté d'excellentes caractéristiques de traitement thermique et de rupture différée par l'hydrogène, élément de traitement thermique et procédés de fabrication associés Download PDF

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Publication number
EP4261313A1
EP4261313A1 EP21906894.7A EP21906894A EP4261313A1 EP 4261313 A1 EP4261313 A1 EP 4261313A1 EP 21906894 A EP21906894 A EP 21906894A EP 4261313 A1 EP4261313 A1 EP 4261313A1
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EP
European Patent Office
Prior art keywords
heat treatment
wire rod
hydrogen
delayed fracture
resistance
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP21906894.7A
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German (de)
English (en)
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EP4261313A4 (fr
Inventor
Byung-in JUNG
Hanhwi KIM
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Posco Holdings Inc
Original Assignee
Posco Co Ltd
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Publication date
Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Publication of EP4261313A1 publication Critical patent/EP4261313A1/fr
Publication of EP4261313A4 publication Critical patent/EP4261313A4/fr
Pending legal-status Critical Current

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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
    • C22C38/18—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
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/22—Martempering
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • 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
    • 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
    • C21D1/58—Oils
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/02—Hardening by precipitation
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/10—Modifying the physical properties of iron or steel by deformation by cold working of the whole cross-section, e.g. of concrete reinforcing bars
    • 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
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
    • 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
    • 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
    • C22C38/001—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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C21D2211/001—Austenite
    • 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
    • C21D2211/002—Bainite
    • 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

Definitions

  • the present disclosure relates to a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, a heat-treated component, and a method for manufacturing the same. More particularly, it relates to a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, which is applicable to a high-strength bolt, etc., a heat-treated component, and a method for manufacturing the same.
  • wire rods for cold heading are classified into process-eliminated wire rods for cold heading with heat treatment and machining processes eliminated and high-strength wire rods for cold heading that allow weight reduction of components.
  • the high-strength wire rod for cold heading is manufactured by cold-heating a wire rod after spheroidization heat treatment, and then it is prepared into a heat-treated component such as a mechanical structure, an automobile part, etc. through quenching and tempering.
  • the metal structure of a general wire rod is mainly composed of pearlite, and there is an inconvenience in that heat treatment for a long time is required to dissolve cementite during austenitization heat treatment.
  • a tempered martensite microstructure is formed when austenitization heat treatment is performed. It is difficult to use the tempered martensite microstructure because it is very sensitive to resistance of hydrogen-delayed fracture at 1300 MPa or higher.
  • the present disclosure is directed to providing a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, a heat-treated component, and a method for manufacturing the same.
  • the present disclosure provides a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, which comprises, by wt%, 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al, 0.01-0.03% of N, and Fe and other impurities as the balance, and has a microstructure comprising, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite, and comprises 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm.
  • the high-strength wire rod may have a prior austenite average grain size of 10 ⁇ m or smaller.
  • the martensite may be comprised of 60% or higher in the prior austenite grain boundary.
  • the present disclosure also provides a method for manufacturing a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, which comprises: heating a billet comprising, by wt%, 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al, 0.01-0.03% of N and Fe and other impurities as the balance at 1000-1200 °C, conducting hot rolling at a finish hot rolling temperature of 750-950 °C, and conducting cooling at a cooling rate of 0.2-1.0 °C/s, wherein the cooled wire rod has a microstructure comprising, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite, and comprises 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm.
  • the present disclosure also provides a heat-treated component with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, which comprises, by wt%, 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al, 0.01-0.03% of N and Fe and other impurities as the balance, and has a microstructure comprising, by area fraction, 90% or more of tempered martensite, and comprises 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm.
  • the heat-treated component may have a prior austenite average grain size of 5 ⁇ m or smaller.
  • the heat-treated component with superior resistance of hydrogen-delayed fracture characteristics may have a tensile strength of 1400 MPa or higher and an impact toughness of 60 J or higher.
  • the present disclosure also provides a method for manufacturing a heat-treated component with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, which comprises: preparing a wire rod comprising, by wt%, 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al, 0.01-0.03% of N and Fe and other impurities as the balance and having a microstructure comprising, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite, wherein the martensite is comprised of 60% or higher in the prior austenite grain into a steel wire by conducting spheroidization heat treatment and drawing once or more times, preparing the prepared steel wire into a component by conducting cold heading, heating the prepared component at 800-900 °C for 1,000-2,000 seconds, quenching the heated component at 50-150 °C, and tempering the quenched component at 500-600 °C for
  • the microstructure comprises, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite, austenitization heat treatment can be conducted quickly and, thus, the energy consumed for heat treatment can be reduced.
  • the wire rod since the wire rod has a microstructure and fine carbide is distributed therein, resistance of hydrogen-delayed fracture resistance can be improved.
  • the present specification discloses a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, which comprises, by wt%, 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al, 0.01-0.03% of N and Fe and other impurities as the balance, and has a microstructure comprising, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite and comprises 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm.
  • a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics comprises, by wt%, 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al, 0.01-0.03% of N and Fe and other impurities as the balance.
  • the reason why the alloy composition is limited will be described in detail.
  • the composition means wt% unless specified otherwise.
  • C is an element added to ensure the strength of a product. If the content of C is less than 0.3%, it is difficult to ensure the target strength, and it is not easy to ensure sufficient hardenability after final Q/T (quenching/tempering) heat treatment. On the contrary, if the content of C exceeds 0.6%, fatigue life is reduced due to excessive generation of carbide. Accordingly, in the present disclosure, the upper limit of the C content is limited to 0.6%.
  • Si an element that is used not only for deoxidization of steel but also for ensuring strength through solid solution strengthening.
  • Si is added in an amount of 0.05% or more for ensuring deoxidization and strength. But, if the content is excessive, it is difficult to process complex parts such as a bolt because of unsatisfactory cold heading property. Accordingly, in the present disclosure, the upper limit of the Si content is limited to 0.3%.
  • Mn is an element which is advantageous in ensuring strength by improving the hardenability of parts, increases rollability and reduces brittleness. It is added in an amount of 0.2% or more in order to ensure sufficient strength. But, if the content is excessive, a hard tissue may be formed easily during cooling after hot rolling and fatigue property may be deteriorated due to the generation a large amount of MnS inclusions. Accordingly, in the present disclosure, the upper limit of the Mn content is limited to 1.0%.
  • Cr is an element which is effective for improving hardenability together with Mn and improves the corrosion resistance. If the Cr content is less than 0.5%, enough corrosion resistance cannot be ensured. On the other hand, if the content is excessive, there are problems that impact toughness is decreased and coarse carbide with poor resistance of hydrogen-delayed fracture resistance is formed. Accordingly, in the present disclosure, the upper limit of the Cr content is limited to 2.0%.
  • Mo is an element which improves hardenability through precipitation hardening by precipitation of fine carbide and solid solution hardening.
  • the improvement of hardenability by Mo is more effective as compared to Mn or Cr. If the Mo content is less than 0.5%, it is not easy to ensure strength because fine carbide is not precipitated sufficiently during Q/T heat treatment. On the other hand, if the content is excessive, the shape of the part is distorted after quenching due to excessively high hardenability, requiring an additional process for correction or resulting in microcrack defects in the parts. Accordingly, in the present disclosure, the upper limit of the Mo content is limited to 2.0%.
  • Al is an element widely used as a deoxidizing agent in steelmaking processes. Al reacts with N to form aluminum nitride (AlN) and refines austenite grains. If the Al content is less than 0.02%, grain refinement is not easy because the amount of the nitrogen compound is insufficient. On the other hand, if the content is excessive, the occurrence of defects may be intensified due to excessive formation of non-metallic inclusions such as alumina. Accordingly, in the present disclosure, the upper limit of the Al content is limited to 0.05%.
  • N is an element used for grain refinement instead of the expensive alloying element. N reacts with Al to form aluminum nitride (AlN) and refines austenite grains. If the content of N is less than 0.01%, grain refinement is not easy because the amount of the nitrogen compound is insufficient. On the other hand, if the content is excessive, dislocation and deposition occur during cold heading due to heading heat, resulting in decreased mold life due to fixation of free nitrogen and increased deformation strength. Accordingly, in the present disclosure, the upper limit of the N content is limited to 0.03%.
  • the remaining component is iron (Fe). But, the mixing of unwanted impurities from the raw materials or the surrounding environment cannot be excluded. The impurities will not be described in detail because they are known to those skilled in the art.
  • V vanadium
  • CHQ column heading quality
  • the wire rod for cold heading has a microstructure comprising, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite.
  • the heat treatment time for dissolving cementite during austenitization heat treatment can be reduced.
  • the microstructure may contain 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm and may have a prior austenite average grain size of 10 ⁇ m or smaller.
  • austenite grains can be refined and resistance of hydrogen-delayed fracture resistance can be improved.
  • the prior austenite grain boundary of the wire rod refers to the grain boundary of the austenite structure of the wire rod after winding and before cooling.
  • 60% or more of martensite may be comprised in the prior austenite grain boundary.
  • a tensile strength of 1400 MPa or higher and an impact toughness of 60 J or higher can be ensured.
  • the inventors of the present disclosure have found out that the strength and resistance of hydrogen-delayed fracture resistance of the wire rod for cold heading can be improved further when the contents of C, Cr and Mo satisfy a specific condition, and have derived the following relation.
  • the wire rod for cold heading may satisfy the following formula (1) while satisfying the above-described alloy composition. 7.2 C + Cr + 2.7 Mo ⁇ 6.65
  • C, Cr and Mo mean the wt% of each element. If there is an element other than C, Cr and Mo, 0 is allocated for the element.
  • fine carbide that can trap diffusible hydrogen is necessary.
  • the fine carbides that can trap hydrogen comprise CrC and MoC carbides having Cr and Mo as main components, respectively. Only when a certain number of the fine carbides is ensured, a strength of 1400 MPa or higher can be ensured at the tempering temperature of 500-600 °C and the effect of hydrogen trapping can be maximized. Considering this, by controlling the alloy composition to satisfy the formula (1), the strength and resistance of hydrogen-delayed fracture resistance of the heat-treated component at the high tempering temperature (500-600 °C) can be improved.
  • the method for manufacturing a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics may comprise a step of heating a billet satisfying the composition described above, a step of preparing the heated billet into a wire rod, and a step of cooling the wire rod.
  • the billet may satisfy the composition described above and may be heated at 1000-1200 °C.
  • the billet may satisfy the formula (1).
  • the heated billet may be prepared into a wire rod by finish hot-rolling at 750-950 °C and then winding.
  • the wire rod In the step of cooling the wire rod, the wire rod may be cooled at a cooling rate of 0.2-1.0 °C/s such that the average austenite grain size after winding is 10 ⁇ m or smaller.
  • the cooling may be performed by air cooling, although not being specially limited thereto.
  • the cooled wire rod may have a microstructure comprising, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite, and the aerial ratio of the martensite formed in the prior austenite grain boundary may be 60% or higher.
  • the prior austenite grain boundary refers to the grain boundary of the austenite structure of the wire rod after winding and before cooling.
  • the microstructure of the cooled wire rod may contain 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm.
  • the method for manufacturing a high-strength heat-treated component with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics may comprise a step of lowering strength by spheroidization heat-treating the cooled wire rod, a step of preparing the wire rod into a component through cold heading, a step of heating the component, a step of quenching the heated component, and a step of tempering the quenched component.
  • drawing may be performed at least once.
  • the cooled wire rod may be prepared into a steel wire by conducting spheroidization heat treatment and drawing at least once.
  • the spheroidization heat treatment is performed appropriately to process the steel before drawing, and the drawing may be performed appropriately in consideration of the drawing limit.
  • the wire rod may be prepared into a steel wire that can be prepared into a component of a complicated shape through spheroidization heat treatment and drawing.
  • the steel wire may be prepared into a component through cold heading.
  • the component may be, for example, a screw, a bolt, etc.
  • the bolt may have a body diameter of 12-30 mm.
  • the component may be heated at high temperature.
  • the carbide precipitated during the rolling of the wire rod is redissolved.
  • the component may be heated such that the alloy component has a uniform composition and has an average austenite grain size of 5 ⁇ m or smaller.
  • the component may be heated at 800-900 °C for 1000-2000 seconds.
  • the heated component may be quenched to 50-150 °C.
  • the quenching may be performed by immersing the heated component in an oil at 50-150 °C, although not being specially limited thereto.
  • the final microstructure of the heat-treated component is controlled to tempered martensite.
  • the tempering step may be performed by tempering at 500-600 °C. The tempering may be performed for 3000-10000 seconds.
  • the heat-treated component with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics prepared by the method described above may contain, by wt%, 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al, 0.01-0.03% of N and Fe and other impurities as the balance, and the microstructure may contain, by area fraction, 90% or more of tempered martensite and may contain 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm.
  • the prior austenite average grain size may be 5 ⁇ m or smaller.
  • the prior austenite grain boundary refers to the grain boundary of the austenite structure of the wire rod after winding and before cooling.
  • the tensile strength may be 1400 MPa or higher
  • the impact toughness may be 60 J or higher.
  • the final component with a body diameter of 12-30 mm may have a tensile strength of 1400 MPa or higher and an impact toughness of 60 J or higher.
  • the heat-treated component satisfying the alloy composition described above may satisfy the following formula (1).
  • the restriction in the formula (1) will not be described here because it was described earlier. 7.2 C + Cr + 2.7 Mo ⁇ 6.65
  • C, Cr and Mo mean the wt% of each element.
  • a billet having the composition described in Table 1 was heated to 1000-1200 °C, finish-rolled at 750-950 °C, and then wound at 730-900 °C. After the winding, the wire rod was cooled at a cooling rate of 0.2-1 °C/s. After the cooling was completed, the wire rod had a microstructure comprising, by area fraction, 80% or more of bainite, 1-15% of pearlite and 0.1-2% of martensite, and the ratio of martensite formed in the prior austenite grain boundary was 60% or higher. In addition, it comprised 2 ⁇ 10 19 /m 3 or more of aluminum nitride having a diameter of 5-50 nm.
  • 'formula (1)' was calculated by substituting the contents (wt%) of C, Cr and Mo in the '7.2 C + Cr + 2.7 Mo' of the formula (1).
  • the AlN number indicates the number of aluminum nitride with a size of 5-50 nm.
  • the values of the formula (1) were 6.65 or higher, the grain boundary martensite ratio was 60% or higher, and the number of aluminum nitride with a size of 5-50 nm was 2 ⁇ 10 19 /m 3 or more.
  • the values of the formula (1) were lower than 6.65, the grain boundary martensite ratio was lower than 60%, the number of aluminum nitride with a size of 5-50 nm was smaller than 2 ⁇ 10 19 /m 3 , or the alloy composition was outside the range of 0.3-0.6% of C, 0.05-0.3% of Si, 0.2-1.0% of Mn, 0.5-2.0% of Cr, 0.5-2.0% of Mo, 0.02-0.05% of Al and 0.01-0.03% of N.
  • the hot-rolled wire rod having the composition described in Table 1 was processed into a cylindrical sample with a diameter of 25 mm, heated at 860 °C for 1,500 seconds, quenched by immersing in an oil at 100 °C, and then tempering at 500-600 °C for 5,000 seconds. Then, after processing into a test sample according to ASTM E8 and ASTM E23, tensile test and impact test were performed. The result of tensile test and impact test is shown in FIG. 1 and FIG. 2 . All the examples exhibited a tensile strength of 1,400 MPa or higher and an impact toughness of 60 J or higher at the tempering temperature of 500-600 °C, whereas the comparative examples showed poor tensile strength and impact toughness.
  • the present disclosure may provide a high-strength wire rod for cold heading with superior heat treatment characteristics and resistance of hydrogen-delayed fracture characteristics, a heat-treated component, and a method for manufacturing the same.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
EP21906894.7A 2020-12-14 2021-11-18 Fil machine à haute résistance pour matriçage à froid, doté d'excellentes caractéristiques de traitement thermique et de rupture différée par l'hydrogène, élément de traitement thermique et procédés de fabrication associés Pending EP4261313A4 (fr)

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KR1020200174141A KR102448754B1 (ko) 2020-12-14 2020-12-14 열처리 특성 및 수소지연파괴 특성이 우수한 고강도 냉간압조용 선재, 열처리부품 및 이들의 제조방법
PCT/KR2021/016963 WO2022131589A1 (fr) 2020-12-14 2021-11-18 Fil machine à haute résistance pour matriçage à froid, doté d'excellentes caractéristiques de traitement thermique et de rupture différée par l'hydrogène, élément de traitement thermique et procédés de fabrication associés

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JPH07188840A (ja) * 1993-12-28 1995-07-25 Kobe Steel Ltd 耐水素脆化特性に優れた高強度鋼およびその製法
JP4629816B2 (ja) * 1999-08-20 2011-02-09 株式会社神戸製鋼所 耐遅れ破壊性に優れた高強度ボルトおよびその製造方法
JP4435953B2 (ja) * 1999-12-24 2010-03-24 新日本製鐵株式会社 冷間鍛造用棒線材とその製造方法
EP2546380B1 (fr) * 2010-03-11 2016-06-08 Nippon Steel & Sumitomo Metal Corporation Fil en acier à haute résistance et boulon à haute résistance dotés d'une excellente résistance à la rupture différée et leur procédé de fabrication
KR101867677B1 (ko) * 2016-07-22 2018-06-15 주식회사 포스코 내지연파괴 특성이 우수한 선재 및 그 제조방법
KR102090227B1 (ko) * 2017-12-20 2020-03-17 주식회사 포스코 고강도 선재 및 지연파괴 저항성이 우수한 고강도 강재와 그 제조방법
KR102090226B1 (ko) * 2017-12-20 2020-03-17 주식회사 포스코 고강도 선재 및 지연파괴 저항성이 우수한 고강도 강재와 그 제조방법
KR102042061B1 (ko) * 2017-12-21 2019-11-08 주식회사 포스코 수소지연파괴 저항성이 우수한 고강도 선재, 강재 및 이들의 제조방법
KR102117401B1 (ko) * 2018-08-21 2020-06-01 주식회사 포스코 수소취성 저항성이 우수한 고강도 선재, 이를 이용한 볼트용 강재, 이들의 제조방법
KR102117400B1 (ko) * 2018-08-31 2020-06-01 주식회사 포스코 냉간압조용 선재, 이를 이용한 가공품 및 이들의 제조방법

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KR20220084557A (ko) 2022-06-21
KR102448754B1 (ko) 2022-09-30
WO2022131589A1 (fr) 2022-06-23
EP4261313A4 (fr) 2024-06-12
CN116724131A (zh) 2023-09-08

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