EP2708614B1 - Wire rod having good superior surface properties, high strength, and high toughness - Google Patents

Wire rod having good superior surface properties, high strength, and high toughness Download PDF

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Publication number
EP2708614B1
EP2708614B1 EP12786772.9A EP12786772A EP2708614B1 EP 2708614 B1 EP2708614 B1 EP 2708614B1 EP 12786772 A EP12786772 A EP 12786772A EP 2708614 B1 EP2708614 B1 EP 2708614B1
Authority
EP
European Patent Office
Prior art keywords
wire rod
antimony
oxides
steel
strength
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.)
Not-in-force
Application number
EP12786772.9A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP2708614A4 (en
EP2708614A2 (en
Inventor
Dong-Hyun Kim
You-Hwan Lee
Hyung-Keun Cho
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Posco Holdings Inc
Original Assignee
Posco Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Publication of EP2708614A2 publication Critical patent/EP2708614A2/en
Publication of EP2708614A4 publication Critical patent/EP2708614A4/en
Application granted granted Critical
Publication of EP2708614B1 publication Critical patent/EP2708614B1/en
Not-in-force legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21D9/525—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
    • 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
    • C22C38/04—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
    • C22C38/60—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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

Definitions

  • the present invention relates to a wire rod used in a structural steel, in particular, used in automobile components such as bolts, tie-rods and the like, requiring cold forging.
  • JP S63 307251 A discloses a steel wire rod.
  • JP 2011 074467 A discloses a steel for carburization.
  • JP 2004250767 A discloses a steel for machine structural.
  • Most structural steels may be heat treated steels formed by reheating, quenching and tempering steel after hot processing to increase the strength and toughness thereof.
  • non-heat treated steel refers to steel having degrees of strength and toughness almost similar to those of a heat treated steel material, even without a heat treatment being performed thereon after hot processing.
  • the term 'non-heat treated steel' is used in Korea and Japan and is also known as 'microalloyed steel' because a material thereof is formed by adding a small amount of an alloying element.
  • an iron oxide unavoidably generated at the time of rolling wire rods may cause surface defects in the wire rod during wire drawing after the manufacturing of the wire rod to deteriorate quality thereof.
  • an iron oxide (scale) layer on the surface of the wire rod needs to be removed through post-processing such as pickling or the like, after the manufacturing of the wire rod.
  • post-processing such as pickling or the like
  • controlled rolling and cooling processes through acceleration may be necessarily required in rolling and cooling operations, together with the addition of an alloying element such as titanium (Ti), vanadium (V), niobium (Nb) or the like.
  • Such controlled rolling and cooling processes may be advantageous in that they may enable wire rods having minute particle sizes to be obtained, such that wire rods having excellent strength and ductility may be manufactured thereby.
  • the controlled rolling and cooling processes may inevitably increase processing costs in accordance with an increase in the price of alloying elements and multiple process variations, and thus, the application thereof may be restricted.
  • Japanese Patent Laid-Open Publication No. 2010-242170 discloses a technology of manufacturing bainite wire rods through a heat treatment after performing the addition of Cr, V, Ti, and B and rapid cooling.
  • the technology has limitations in that processing costs are increased and a cooling device is further required.
  • a non-heat treated wire rod having high strength may be manufactured through controlled rolling and cooling processes by adding Al, Cu, Ni, Mo, V or the like thereto, in order to control an initial austenite microstructure, but processing costs may inevitably be increased due to the necessity of further equipment installations.
  • 1998-008209 discloses that an alloying element such as Cr, V or the like is essentially added at the time of manufacturing a high strength and high toughness wire rod configured of ferrite and pearlite, but the effectiveness thereof is degraded due to the addition of an expensive alloying element in order to improve cold workability.
  • an alloying element such as Cr, V or the like
  • the present invention provides a wire rod capable of having high strength and high toughness and suppressing the generation of a surface oxide, as well as having superior surface properties through uniform oxide formation.
  • a wire rod according to claim 1 having superior surface properties, high strength, and high toughness
  • a wire rod having high strength and high toughness is provided, surface defects of which are suppressed, a tensile strength and ductility of the wire rod may be increased while the refinement of grains thereof may be realized by forming oxides through the addition of a small amount of antimony (Sb), and a thickness of a final scale may be reduced by suppressing the growth of an iron oxide at high temperatures during hot rolling in a heating furnace and uniformly forming the iron oxide.
  • a wire rod according to embodiments of the present invention is manufactured using a generic technology for manufacturing a high strength and high ductility wire rod, and demand therefor is unlimited.
  • the method for manufacturing a wire rod according to the embodiment of the present invention may have predominance in terms of price competitiveness through the omission of relatively expensive alloying elements, tensile strength, and surface qualities, as compared to those of the existing competing products, and may be a generic technology in that it provides a novel manufacturing method having no process condition limitations.
  • a small amount of antimony (Sb) is included at the time of manufacturing of a wire rod, such that grain size growth of austenite grains may be suppressed and the formation of an oxide on a surface of the wire rod may be adjusted through a structure control using antimony (Sb) oxides to improve strength and toughness of the wire rod. Further, the formation of an iron oxide (scale) on the surface of the wire rod may be suppressed to enable a thin, uniform oxide to be formed, thereby reducing surface defects.
  • the wire rod according to the embodiment of the present invention includes 0.005 to 0.02% of antimony (Sb), in terms of weight percentage.
  • the antimony (Sb) an element playing a key role in the embodiment of the present invention, enables antimony (Sb) oxides (commonly Sb 2 O 5 ) to be formed in an austenitic base structure to suppress the growth of grain boundaries and suppress the formation of the iron oxide, thereby allowing for a fine final surface of the wire rod.
  • the antimony (Sb) When the antimony (Sb) is included in an amount less than 0.005%, an amount thereof reacting with oxygen may be insufficient, such that thermodynamically sufficient antimony (Sb) oxides may not be formed, to lead to a failure to form a solid solution in the form of antimony (Sb) metal, thereby leading to difficulties in oxide formation.
  • the antimony (Sb) When the antimony (Sb) is included in an amount greater than 0.02%, an excessive amount of antimony (Sb) beyond an amount thereof capable of forming oxygen affinity is added and may be eluted into the austenitic base structure, in the form of solute atoms, thereby causing breakage to the wire rod during wire drawing and simultaneously, rapidly degrading cold forging properties. Thus, it may be necessary to limit the amount of antimony (Sb).
  • the wire rod according to the embodiment of the present invention may not include precipitate elements added thereto, in addition to antimony (Sb).
  • the precipitate elements may representatively include titanium (Ti), niobium (Nb), vanadium (V) and the like.
  • Ti titanium
  • Nb niobium
  • V vanadium
  • Nb or V it may be advantageous in terms of the refinement of austenite grains, but a cost increase may be inevitably generated.
  • Nb or V may easily react with oxygen and hinder the antimony (Sb) oxides from being formed, effective grain refining effects may not be obtained.
  • the wire rod according to the invention includes C: 0.25 to 0.45%, Si: 0.1 to 0.2%, and Mn: 0.1 to 0.7%, in terms of weight percentage, in addition to the antimony (Sb).
  • the components are limited due to the following reasons.
  • Carbon (C) may be an element ensuring a strength of steel. When carbon (C) is included in an amount less than 0.25%, the strength may not be easily ensured, while carbon (C) is included in an amount greater than 0.45%, it may cause cracks in or breakage to the wire rod during a rolling or wire drawing process.
  • Silicon (Si) may be dissolved in ferrite to reinforce strength of a basic material.
  • silicon (Si) is included in an amount less than 0.1%, the strength may be insufficiently increased through the dissolution, while when silicon (Si) is included in an amount greater than 0.2%, work hardening effects may be increased during cold forging to cause a deterioration in toughness.
  • Manganese (Mn) may increase strength of steel and reinforce rolling properties, while decreasing brittleness. When manganese (Mn) is included in an amount less than 0.1%, strength reinforcement may be incomplete while when manganese (Mn) is included in an amount greater than 0.7%, a hardening phenomenon according to the increased strength may be intensified.
  • the remainder includes Fe and inevitable impurities.
  • the wire rod according to the embodiment of the present invention includes the antimony (Sb) oxides and the form of the antimony (Sb) oxides may commonly be Sb 2 O 5 .
  • the antimony (Sb) oxides may suppress the growth of grain boundaries using the drag effect in which the growth of grains is controlled through the extraction of the grain boundaries, to refine ferrite and pearlite grains, thereby increasing the tensile strength and ductility of the wire rod.
  • the antimony (Sb) oxides may suppress the growth of the iron oxide at high temperatures during hot rolling in a heating furnace and allow for the uniform formation of iron oxide, to reduce a thickness of a final scale, thereby suppressing surface defects.
  • An average grain diameter of the antimony (Sb) oxides is 20 to 50 nm.
  • the antimony (Sb) oxides may be provided to control grain diameters of ferrite and pearlite through the growth of grains thereof. In order to optimize grain boundary pinning effects, the antimony (Sb) oxides have an average grain diameter of 20 to 50 nm.
  • An amount of the antimony (Sb) oxides distributed per unit area ( ⁇ m 2 ) in the wire rod is 50 to 100.
  • an amount of the antimony (Sb) oxides distributed in the unit area is greater than 100, since the extraction may be performed from within the grains, as well as from the ground boundaries, the strength is rapidly increased, leading to a reduction in ductility.
  • the number of the antimony (Sb) oxides distributed in the unit area is less than 50, the pinning effects may be insufficient to deteriorate the strength.
  • 50 to 100 antimony (Sb) oxides per unit area ( ⁇ m 2 ) are advantageous.
  • the microstructure of the wire rod according to the embodiment of the present invention may include ferrite and pearlite.
  • a relative area of ferrite may be 70% or more and pearlite may occupy the remainder of the area thereof.
  • An average grain size of ferrite may be 10 to 20 ⁇ m and an average grain size of pearlite may be 20 to 25 ⁇ m.
  • a fraction of the microstructure may correlate with strength and ductility. That is, since the ductility is high in accordance with an increase in ferrite fraction, in a case in which the relative area of ferrite having a small average grain size is large, strength and ductility may be simultaneously increased. Thus, the grain size and the fraction may be restricted.
  • the average grain size of ferrite may be 15 to 20 ⁇ m.
  • the ferrite fraction when the ferrite fraction is less than 70%, since the ductility may not be reinforced in accordance with the increase in strength, the ferrite fraction may be 70% or more.
  • the wire rod according to the present invention has the scale (iron oxide) formed on the surface thereof at a thickness of 20 to 150 ⁇ m.
  • the thickness of the scale is less than 20 ⁇ m, since coupling force between the surface of the wire rod and the scale may be significantly strong, a separate device such as a water sprayer or the like may be required in order to remove the scale.
  • a separate device such as a water sprayer or the like may be required in order to remove the scale.
  • the thickness of the scale is significantly small, defects may be generated in the surface of the wire rod.
  • time and process conditions for removing the scale are additionally required, thereby leading to an increase in processing costs. Despite such processing, the wire rod having a fine surface may not be obtained due to the thick scale.
  • the thickness of the scale is 20 to 150 ⁇ m
  • wire drawing may be performed using the scale itself due to the scale having an adequate thickness, and further, the wire rod having a fine surface due to the removal of the scale may be advantageously manufactured.
  • the wire rod according to the embodiment of the present invention may have a tensile strength of 600 to 900 MPa and an elongation of 25% or more.
  • steel including 0.005 to 0.02% of antimony (Sb) in terms of weight percentage may be reheated.
  • the reheating may be provided to realize a homogenizing treatment, and a temperature therefor may be 1100 °C or more.
  • the reheated steel may be hot rolled.
  • the hot rolling may be a wire rod-hot rolling and may be undertaken at a temperature of 900 to 1100°C, preferably, 800 to 1050°C.
  • rolling may be performed in a two-phase area to cause a drop in pressure, thereby leading to a rapid rolling of the structure, such that a spreading rate of oxygen may be insufficient, causing difficulties in the extraction of the antimony (Sb) oxides.
  • the antimony (Sb) oxides When the temperature is greater than 1100°C, the antimony (Sb) oxides may be completely dissolved during the rolling, but they may not be effectively spread to grain boundaries to result in an increase in precipitate sizes.
  • the wire rod manufactured through the rolling may be cooled at a cooling rate of 0.5 to 2°C/s.
  • the cooling rate is less than 0.5°C/s
  • the wire rod may be configured of ferrite and pearlite, structures of which are elongated, and grain orientations which are varied, thereby causing impacts due to structural anisotropy and deteriorated ductility.
  • the strength of an as-rolled wire rod may be naturally increased to deteriorate ductility.
  • the cooling rate is equal to or greater than 2°C/s, even in a case in which the wire rod is a medium carbon steel wire rod, martensite may be formed on the surface of the wire rod in accordance with a lowering of the martensite transformation point to thereby exhibit brittleness. Thus, the cooling rate may be restricted.
  • the aging phenomenon according to a degradation in the cooling rate may cause structural anisotropy, and since martensite, a low-temperature structure, may be formed in the wire rod in the case of a cooling rate greater than 2°C/s, the cooling rate may be 0.5 to 2°C/s.
  • wire drawing may be performed on the wire rod, such that a wire rod may be manufactured.
  • FIG. 1A and FIG. 1B respectively show microstructures of the related art steel and inventive steel 1, observed using an optical microscope.
  • the related art steel had a ferrite-pearlite structure, but a ferrite fraction thereof was less than 40% and a structure size thereof was about 35 to 50 ⁇ m.
  • the ferrite fraction was 40% or more and the structure size was minute, in a range of 20 to 25 ⁇ m.
  • FIG. 2A shows antimony (Sb) oxides of inventive steel 1.
  • the antimony (Sb) oxides were formed as nano-sized oxides. Further, 50 to 100 antimony (Sb) oxides per unit area were distributed. According to the embodiment of the present invention, an adequate amount of minute antimony (Sb) oxides as described above were distributed to suppress the initial grain growth of austenite grains due to grain boundary pinning effects, thereby reducing an average grain size of ferrite.
  • inventive steel 1 ensured a high degree of strength and toughness in accordance with an increase in the content of minute ferrite grains.
  • Wire drawing was performed on the wire rods manufactured according to Table 1 to manufacture wire rods. With respect to the manufacture respective wire rods, tensile strength and elongation were measured according to an amount of wire drawing, and the measured results are shown in Table 2 and FIG. 3 .
  • inventive steels according to the embodiment of the present invention strength thereof was increased in accordance with an increase in the amount of wire drawing, while excellent elongation was secured. That is, in the inventive steels according to the embodiment of the present invention, 25% or more of elongation was secured in the case of 80% of wire drawing. However, in the case of the related art steel or comparative steels, it could be confirmed that the strength was marginally exhibited and elongation was rapidly degraded.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
EP12786772.9A 2011-05-13 2012-05-11 Wire rod having good superior surface properties, high strength, and high toughness Not-in-force EP2708614B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR1020110045353A KR20120127095A (ko) 2011-05-13 2011-05-13 표면특성이 우수한 고강도 고인성 선재 및 그 제조방법
PCT/KR2012/003720 WO2012157902A2 (ko) 2011-05-13 2012-05-11 표면특성이 우수한 고강도 고인성 선재 및 그 제조방법

Publications (3)

Publication Number Publication Date
EP2708614A2 EP2708614A2 (en) 2014-03-19
EP2708614A4 EP2708614A4 (en) 2015-02-25
EP2708614B1 true EP2708614B1 (en) 2018-03-21

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EP12786772.9A Not-in-force EP2708614B1 (en) 2011-05-13 2012-05-11 Wire rod having good superior surface properties, high strength, and high toughness

Country Status (6)

Country Link
US (1) US20140027025A1 (ko)
EP (1) EP2708614B1 (ko)
JP (1) JP5908066B2 (ko)
KR (1) KR20120127095A (ko)
CN (1) CN103517999B (ko)
WO (1) WO2012157902A2 (ko)

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US10416759B2 (en) * 2014-05-13 2019-09-17 Lenovo (Singapore) Pte. Ltd. Eye tracking laser pointer
CN104561736A (zh) * 2014-12-29 2015-04-29 芜湖国鼎机械制造有限公司 高强度灰铸铁、铸件及其制备方法

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Also Published As

Publication number Publication date
JP2014518942A (ja) 2014-08-07
US20140027025A1 (en) 2014-01-30
KR20120127095A (ko) 2012-11-21
EP2708614A4 (en) 2015-02-25
JP5908066B2 (ja) 2016-04-26
CN103517999B (zh) 2016-09-28
EP2708614A2 (en) 2014-03-19
WO2012157902A3 (ko) 2013-01-17
CN103517999A (zh) 2014-01-15
WO2012157902A2 (ko) 2012-11-22

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