US20240060162A1 - Wire rod and part with improved delayed fracture resistance, and methods for manufacturing same - Google Patents

Wire rod and part with improved delayed fracture resistance, and methods for manufacturing same Download PDF

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Publication number
US20240060162A1
US20240060162A1 US18/268,061 US202118268061A US2024060162A1 US 20240060162 A1 US20240060162 A1 US 20240060162A1 US 202118268061 A US202118268061 A US 202118268061A US 2024060162 A1 US2024060162 A1 US 2024060162A1
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Prior art keywords
wire rod
delayed fracture
formula
present disclosure
fracture resistance
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US18/268,061
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Inventor
Youngsoo CHUN
Sang-yoon Lee
Seok-Hwan Choi
Myungsoo CHOI
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Posco Holdings Inc
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Posco Co Ltd
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Assigned to POSCO CO., LTD reassignment POSCO CO., LTD ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: Choi, Myungsoo, CHOI, SEOK-HWAN, CHUN, Youngsoo, LEE, SANG-YOON
Publication of US20240060162A1 publication Critical patent/US20240060162A1/en
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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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • 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
    • 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
    • C21D9/0093—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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C21D2211/008—Martensite

Definitions

  • the present disclosure relates to a wire rod and a part with improved delayed fracture resistance, and methods for manufacturing the same, more specifically to a wire rod and a part that can be used in fastening bolts, etc. of automobiles and structures exposed to various stress and corrosion environments, and methods for manufacturing the same.
  • High strength is required for wire rods which are used for fastening bolts, etc. for automobiles and structures with the weight reduction and miniaturization of automobiles and structures.
  • cold working, grain refinement, martensite strengthening, precipitation strengthening, etc. are utilized to increase the strength of steel materials.
  • the dislocations, grain boundaries, martensite lath boundaries, fine precipitate boundaries, used for strengthening lead to inferior delayed fracture by acting as hydrogen traps in steel materials. For this reason, the delayed fracture becomes inferior in high-strength bolts with a tensile strength of 1 GPa or higher.
  • the Mn—B steel may cause cracking in the thread part of the bolt. Therefore, the steel with a high content of Mn, which is added to manufacture a high-strength bolt of 1 GPa or higher, is difficult to be used for a high-strength bolt because delayed fracture may occur in the bolt thread part due to cracking.
  • the present disclosure is directed to providing a wire rod with improved delayed fracture resistance for a high-strength bolt, by optimizing the solid solution strengthening effect of Mn—B steel and improving formability through control of alloy elements, the bolt and methods for manufacturing the same.
  • a wire rod with improved delayed fracture resistance contains, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance, and satisfies formula 1.
  • the wire rod may satisfy formula 2.
  • the size of TiN inclusions may be 15 ⁇ m or smaller.
  • a method for manufacturing a wire rod with improved delayed fracture resistance includes: a step of finish-rolling a steel material containing, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance and satisfying formula 1 at 880-980° C.; and a step of winding at 830-930° C.
  • the steel material may satisfy formula 2.
  • a method for manufacturing a part with improved delayed fracture resistance includes: a step of drawing a wire rod manufactured according to the present disclosure; a step of spheroidization heat-treating the drawn wire rod at 745-770° C.; a step of heating the spheroidization heat-treated drawn wire rod at 870-940° C.; a step of quenching the spheroidization heat-treated drawn wire rod at 50-80° C.; and a step of tempering the quenched part at 400-600° C.
  • a part with improved delayed fracture resistance according to an exemplary embodiment of the present disclosure contains, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance and satisfies formula 1.
  • the part satisfies formula 2.
  • the part includes, by volume fraction, 0.3-2% of a retained austenite structure and a residual tempered martensite structure.
  • a part with improved delayed fracture resistance for a high-strength a bolt improves formability during the processing of the thread part of a Mn—B steel bolt. Accordingly, delayed fracture in a 1 GPa-grade high-strength bolt may be suppressed by preventing cracks in the thread part of the bolt.
  • FIG. 1 is an image of a thread part of Comparative Example 3 before evaluation of delayed fracture resistance.
  • the inventors of the present disclosure have found out that, by controlling the contents of Si and Mn, formability can be improved by optimizing the solid solution strengthening effect while ensuring strength and, thus, delayed fracture resistance can be improved as cracking caused by poor formability of a thread part is suppressed.
  • a wire rod with improved delayed fracture resistance contains, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance.
  • the content of carbon (C) is 0.15-0.30%.
  • C is an element added to ensure the strength of a product. If the carbon content is less than 0.15%, it is difficult to ensure the target strength. And, if it exceeds 0.30%, the delayed fracture characteristics may become inferior as the formation of retained austenite with superior mechanical stability is hindered by the hydrostatic pressure formed at the lath martensite during quenching. Therefore, in the present disclosure, the C content is limited to 0.15-0.30%.
  • the content of silicon (Si) is 0.15-0.25%.
  • Si is an element that is used not only for deoxidization of steel but also for ensuring strength through solid solution strengthening. If the Si content is less than 0.15%, the deoxidization of steel and improvement of strength through solid solution strengthening may be insufficient. And, if it exceeds 0.25%, formability and impact characteristics may become inferior due to solid solution strengthening. Therefore, in the present disclosure, the Si content is limited to 0.15-0.25%.
  • the content of manganese (Mn) is 0.95-1.35%.
  • Mn is an element which improves hardenability. It is a very useful element that provides solid solution strengthening effect by forming a substitutional solid solution in the matrix structure. If the Mn content is less than 0.95%, it is difficult to ensure the strength desired in the present disclosure because the solid solution strengthening effect and hardenability are insufficient. And, if the Mn content exceeds 1.35%, formability may become inferior due to the solid solution strengthening effect. Therefore, in the present disclosure, the Mn content is limited to 0.95-1.35%.
  • the content of phosphorus (P) is 0.030% or less (excluding 0%).
  • P is an element which is segregated in the grain boundary and lowers toughness and delayed fracture resistance. Therefore, in the present disclosure, the upper limit of the P content is limited to 0.030%.
  • the content of sulfur (S) is 0.030% or less (excluding 0%).
  • the upper limit of the S content is limited to 0.030%.
  • the content of titanium (Ti) is 0.015-0.030%.
  • Ti is an element which binds to N introduced into steel to form titanium carbonitride (TiN).
  • TiN can prevent cracking caused by poor formability of a part and improve delayed fracture resistance by reducing grain size.
  • Ti since Ti forms TiN, it can prevent free N from binding to B, which forms BN that worsens formability. If the Ti content is less than 0.015%, TiN is not formed enough and free N forms BN. As a result, the hardening effect of B cannot be utilized. And, if it exceeds 0.03%, delayed fracture resistance may become inferior due to formation of coarse carbonitride. Therefore, in the present disclosure, the Ti content is limited to 0.015-0.03%.
  • the content of boron (B) is 0.0010-0.0040%.
  • B is an element which improves hardenability. If the B content is less than 0.0010%, it is difficult to expect the improvement of hardenability. And, if it exceeds 0.0040%, the delayed fracture resistance becomes inferior since the austenite grain boundary becomes brittle as Fe 23 (CB) 6 carbide is formed in the grain boundary and the formability becomes inferior due to the formation of BN. Therefore, in the present disclosure, the B content is limited to 0.0010-0.0040%.
  • the content of nitrogen (N) is 0.0010-0.0080%.
  • N is an element that forms a carbonitride. If the N content is less than 0.0010%, the TiN precipitate that reduces grain size may not be formed enough. And, if it exceeds 0.0080%, the toughness and ductility of steel may become inferior due to the increased content of dissolved nitrogen and free N may bind with B to form BN which worsens formability. Therefore, in the present disclosure, the N content is limited to 0.0010-0.0080%.
  • the remaining component of the alloy composition is iron (Fe).
  • the wire rod with improved delayed fracture resistance of the present disclosure may contain other impurities that can be included in common industrial steel production processes. These impurities are well known to those having ordinary knowledge in the art to which the present disclosure belongs, and their types and contents are not specially limited in the present disclosure.
  • the wire rod with improved delayed fracture resistance according to an exemplary embodiment of the present disclosure satisfies formula 1:
  • the contents of Si and Mn are controlled so that, while ensuring strength through the solid solution strengthening effect, the formability and delayed fracture resistance of a wire rod can be improved by suppressing excessive solid solution strengthening.
  • the formula 1 was is a formula for optimizing the solid solution strengthening effect.
  • the value of 5.5 ⁇ [Si]+[Mn] is smaller than 2.0, the strength desired by the present disclosure cannot be ensured.
  • the value of 5.5 ⁇ [Si]+[Mn] exceeds 2.4, delayed fracture may be induced due to cracking caused by poor formability during the forming of a high-strength part owing to excessive solid solution strengthening. Therefore, in the present disclosure, the value of 5.5 ⁇ [Si]+[Mn] is limited to 2.0-2.4 to improve the delayed fracture resistance.
  • wire rod with improved delayed fracture resistance according to an exemplary embodiment of the present disclosure satisfies formula 2.
  • the present disclosure aims at improving the delayed fracture resistance of a wire rod by reducing grain size and improving formability.
  • the inventors of the present disclosure have found out that grain size can be reduced by controlling the size of TiN inclusions and formability and delayed fracture resistance can be ensured by suppressing the formation of BN.
  • the formula 2 is a formula derived to control the size of TiN inclusions and suppress the formation of BN.
  • the value of [Ti]/3.42[N] is 1.0 or smaller, formability may become inferior due to BN, etc. formed by free N not bound to Ti.
  • the value of [Ti]/3.42[N] is 2.0 or larger, the size of TiN inclusions is increased due to excess Ti and the grain refinement effect cannot be achieved. Therefore, in the present disclosure, the value of [Ti]/3.42[N] is limited to satisfy 1.0 ⁇ [Ti]/3.42[N] ⁇ 2.0.
  • the size of TiN inclusions for reducing grain size may be 15 ⁇ m or smaller. If the size of the TiN inclusions exceeds 15 ⁇ m, it is difficult to ensure delayed fracture resistance through grain refinement.
  • a part with improved delayed fracture resistance manufactured from the wire rod according to the present disclosure includes, by volume fraction, 0.3-2% of a retained austenite structure and a residual tempered martensite structure. If the fraction of the retained austenite structure is less than 0.3%, it is difficult to expect the role as a barrier that delays the diffusion of hydrogen. And, if it exceeds 2%, the retained austenite is formed thickly not only in the lath boundary but also in the austenite grain boundary, etc., which makes it difficult to delay the diffusion of hydrogen and lowers the effect of improving delayed fracture resistance.
  • the wire rod and a part with improved delayed fracture resistance according to the present disclosure may be manufactured by various methods without particular limitation. As an exemplary embodiment, it may be manufactured by the following method.
  • the wire rod with improved delayed fracture resistance may be manufactured by a method including: a step of finish-rolling a steel material containing, by wt %, 0.15-0.30% of C, 0.15-0.25% of Si, 0.95-1.35% of Mn, 0.030% or less of P, 0.030% or less of S, 0.015-0.030% of Ti, 0.0010-0.0040% of B, 0.0010-0.0080% of N, and Fe and inevitable impurities as the balance at 880-980° C.; and step of winding at 830-930° C.
  • a steel material satisfying the above alloy composition is prepared and finish-rolled at 880-980° C. into a wire rod. Then, the rolled wire rod is wound at 830-930° C. into a coil shape.
  • a decarburized ferrite layer may be formed on the surface through phase transformation because the surface layer is a quasi-two-phase, and the delayed fracture resistance may become inferior since a decarburized ferrite layer is formed also on the surface of the bolt during heat treatment. In addition, delayed fracture resistance may become inferior since the prior austenite grain size of the bolt decreases and the fraction of retained austenite increases. If the wire rod finish rolling temperature exceeds 980° C. or if the winding temperature exceeds 930° C., a decarburized ferrite layer may be formed on the surface as decarburization is accelerated by hydrogen and the delayed fracture resistance may become inferior as the prior austenite grain size is increased.
  • the wound wire rod may be drawn, spheroidization heat-treated, coated, formed into a bolt, austenitized, quenched and then tempered to obtain a final part for a bolt.
  • it may be prepared by the following method.
  • a method for manufacturing a part for a bolt includes: a step of drawing the wire rod manufactured according to the present disclosure; a step of spheroidization heat-treating the drawn wire rod at 745-770° C.; a step of heating the spheroidization heat-treated drawn wire rod at 870-940° C.; a step of quenching the spheroidization heat-treated drawn wire rod at 50-80° C.; and a step of tempering at 400-600° C.
  • the spheroidization heat treatment may be performed at 745-770° C. If the heat treatment temperature is below 745° C. or exceeds 770° C., the degree of spheroidization may be decreased, which may cause increased hardness, poor formability of a thread part of the bolt after forming, and cracking of the thread part.
  • the austenitization heat treatment may be performed at 870-940° C. If the heat treatment temperature is below 870° C., toughness may become inferior as a martensite structure is formed nonuniformly after quenching due to insufficient reverse austenite transformation. If the heat treatment temperature exceeds 940° C., delayed fracture resistance may become inferior due to increased prior austenite grain size.
  • the quenching may be performed at 50-80° C. If the quenching temperature is below 50° C., fine quenching cracks may occur in the thread of the bolt due to thermal deformation, which can cause delayed fracture. And, if it exceeds 80° C., retained austenite may be formed in the prior austenite grain boundary in addition to the mechanically stable retained austenite formed in the lath due to insufficient quenching, and delayed fracture may be induced due to accumulation of hydrogen.
  • the tempering may be performed at 400-600° C. in order to provide strength and toughness according to the use and purpose of the final product. If the tempering temperature is below 400° C., brittleness may be caused by the tempering. And, if it exceeds 600° C., it is difficult to achieve the strength desired by the present disclosure.
  • the part with improved delayed fracture resistance manufactured according to the present disclosure includes, by volume fraction, 0.3-2% of a retained austenite structure and a residual tempered martensite structure.
  • Wire rods of Examples 1-9 and Comparative Examples 1-7 satisfying the alloy composition of Table 1 were prepared into final bolts for test under to the manufacturing condition of the present disclosure. Specifically, a steel piece satisfying the alloy composition of Table 1 was finish-rolled at 880-980° C. into a wire rod and wound into a coil shape at 830-930° C. The wound wire rod was spheroidization heat-treated at 745-770° C. Then, the spheroidization heat-treated wire rod was formed into a bolt, austenitized at 870-940° C., quenching at 50-80° C., and then tempered at 400-600° C. to ensure a tensile strength of 1050 ⁇ 16 MPa.
  • the delayed fracture resistance was tested according to the delayed fracture simulation method by fastening the bolt with a clamping force corresponding to the yield strength and immersing in a solution of 5% hydrochloric acid+95% distilled water for 10 minutes.
  • X indicates no cracking
  • O indicates the occurrence of cracks.
  • FIG. 1 shows the image of the thread part for Comparative Example 3 before the evaluation of delayed fracture resistance. As seen from FIG. 1 , delayed fracture cracks occurred for Comparative Example 3, which does not satisfy the requirements proposed by the present disclosure, indicating that delayed fracture resistance was not achieved.
  • Example 3 wherein the finish rolling temperature, winding temperature, spheroidization heat treatment temperature and austenitization temperature are satisfied, delayed fracture crack did not occur.
  • Comparative Example 6-1 wherein the rolling temperature exceeds the upper limit 980° C. proposed by the present disclosure as 990° C. and the winding temperature also exceeds the upper limit 930° C. proposed by the present disclosure as 940° C., delayed fracture cracks occurred as the prior austenite grain size was increased in the wire rod and in the bolt as well.

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  • Chemical & Material Sciences (AREA)
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  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
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US18/268,061 2020-12-18 2021-12-14 Wire rod and part with improved delayed fracture resistance, and methods for manufacturing same Pending US20240060162A1 (en)

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KR10-2020-0178274 2020-12-18
KR1020200178274A KR102492644B1 (ko) 2020-12-18 2020-12-18 지연파괴 저항성이 향상된 선재, 부품 및 그 제조방법
PCT/KR2021/018977 WO2022131752A1 (ko) 2020-12-18 2021-12-14 지연파괴 저항성이 향상된 선재, 부품 및 그 제조방법

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JP5776623B2 (ja) * 2012-05-08 2015-09-09 新日鐵住金株式会社 冷間加工性に優れた鋼線材・棒鋼とその製造方法
KR101665886B1 (ko) 2015-09-04 2016-10-13 주식회사 포스코 냉간가공성 및 충격인성이 우수한 비조질강 및 그 제조방법
CN107815594A (zh) * 2017-11-12 2018-03-20 湖南华菱湘潭钢铁有限公司 一种冷挤压齿轮盘条的生产方法

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