WO2020130614A2 - High strength hot-rolled steel sheet having excellent hole expansion ratio and manufacturing method for same - Google Patents

High strength hot-rolled steel sheet having excellent hole expansion ratio and manufacturing method for same Download PDF

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Publication number
WO2020130614A2
WO2020130614A2 PCT/KR2019/017979 KR2019017979W WO2020130614A2 WO 2020130614 A2 WO2020130614 A2 WO 2020130614A2 KR 2019017979 W KR2019017979 W KR 2019017979W WO 2020130614 A2 WO2020130614 A2 WO 2020130614A2
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Prior art keywords
steel sheet
rolled steel
hot
less
hole expandability
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PCT/KR2019/017979
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French (fr)
Korean (ko)
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WO2020130614A3 (en
Inventor
박경수
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주식회사 포스코
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Priority to EP19899564.9A priority Critical patent/EP3901307A4/en
Priority to JP2021534941A priority patent/JP7216356B2/en
Priority to US17/414,743 priority patent/US20220074007A1/en
Priority to CN201980083649.5A priority patent/CN113195767A/en
Publication of WO2020130614A2 publication Critical patent/WO2020130614A2/en
Publication of WO2020130614A3 publication Critical patent/WO2020130614A3/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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • 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
    • 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
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • 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
    • C21D2211/005—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
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a hot-rolled steel sheet used as a material for a vehicle collision member parts and a structure support, and more particularly, to a hot-rolled steel sheet having high strength characteristics and excellent hole expandability, and a manufacturing method thereof.
  • Patent Document 1 proposes a technique for securing strength by precipitation strengthening with the addition of alloy elements. That is, Patent Document 1 is intended to secure high-strength properties by adding alloying elements such as Ti, Nb, V, and Mo, but these alloying elements are expensive elements, and their manufacturing cost is excessively increased, which is not preferable in terms of economic efficiency.
  • alloying elements such as Ti, Nb, V, and Mo
  • Patent Documents 2 to 4 propose a technique for securing strength and ductility by using a ferrite and martensite abnormal structure or by retaining austenite and utilizing a complex structure of ferrite, bainite and martensite.
  • ferrite or retained austenite has excellent ductility, but poor strength, so there is a technical difficulty that cannot sufficiently secure high strength properties.
  • Patent Document 1 Republic of Korea Patent Publication No. 10-2005-113247 (2005.12.01. public)
  • Patent Document 2 Japanese Patent Application Publication No. 2005-298967 (published on October 27, 2005)
  • Patent Document 3 U.S. Patent Publication No. 2005-0155673 (published on July 21, 2005)
  • Patent Document 4 European Patent Publication No. 1396549 (published on October 10, 2004)
  • a high strength hot rolled steel sheet having excellent hole expandability and a method for manufacturing the same can be provided.
  • High-strength hot-rolled steel sheet excellent in hole expandability by weight, carbon (C): 0.12% or more and less than 0.30%, manganese (Mn): 0.1-2.5%, silicon (Si): 0.5% Less than (excluding 0%), Boron (B): 0.0005 to 0.005%, Phosphorus (P) 0.02% or less, Sulfur (S): 0.01% or less, including the remaining iron (Fe) and unavoidable impurities, more than 95% by volume It contains martensite as a microstructure, and the product of tensile strength (TS) and hole expandability (HER) may be 30,000 MPa% or more.
  • the hot-rolled steel sheet may further include at least one of chromium (Cr): 0.5% or less and titanium (Ti): 0.005 to 0.2% by weight.
  • the microstructure may include one or more of ferrite, bainite, carbide, and residual austenite in a total volume of 5% or less.
  • the tensile strength (TS) of the hot rolled steel sheet may be 1,250 MPa or more.
  • the hole expandability (HER) of the hot rolled steel sheet may be 20% or more.
  • the thickness of the hot rolled steel sheet may be 1.8 mm or less.
  • Method for manufacturing a high-strength hot-rolled steel sheet excellent in hole expandability by weight, carbon (C): 0.12% or more but less than 0.30%, manganese (Mn): 0.1-2.5%, silicon (Si) : 0.5% or less (excluding 0%), boron (B): 0.0005 to 0.005%, phosphorus (P) 0.02% or less, sulfur (S): 0.01% or less, and the remaining slab containing iron (Fe) and unavoidable impurities Reheating; Hot rolling the reheated slab to provide a hot rolled steel sheet; Cooling the hot rolled steel sheet within 5 seconds from the end point of the hot rolling, and cooling the hot rolled steel sheet to a cooling end temperature of 350° C. or less at a cooling rate of 50 to 1,000° C./s; And winding the cooled hot rolled steel sheet.
  • C carbon
  • Mn manganese
  • Si silicon
  • B boron
  • P phosphorus
  • S sulfur
  • the slab may further include one or more of chromium (Cr): 0.5% or less and titanium (Ti): 0.005 to 0.2% by weight.
  • a hot-rolled steel sheet having a high-strength property and significantly improved hole expandability (HER) and a method for manufacturing the same.
  • the present invention relates to a high-strength hot-rolled steel sheet having excellent hole expandability and a method for manufacturing the same, and the following will describe preferred embodiments of the present invention.
  • the embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below.
  • the present embodiments are provided to those skilled in the art to further detail the present invention.
  • High-strength hot-rolled steel sheet excellent in hole expandability according to an aspect of the present invention by weight, carbon (C): 0.12% or more and less than 0.30%, manganese (Mn): 0.1-2.5%, silicon (Si): 0.5% The following (excluding 0%), boron (B): 0.0005 to 0.005%, phosphorus (P) 0.02% or less, sulfur (S): 0.01% or less, the remaining iron (Fe) and may contain unavoidable impurities.
  • the high-strength hot-rolled steel sheet having excellent hole expandability according to an aspect of the present invention may further include one or more of chromium (Cr): 0.5% or less and titanium (Ti): 0.005 to 0.2%. have.
  • the present invention may include carbon (C) of a certain level or more to secure the strength of the hot-rolled steel sheet.
  • carbon content (C) when the carbon content (C) is below a certain level, a problem may occur in which a low-temperature structure is formed in a large amount during cooling after hot rolling, thereby failing to secure the microstructure desired by the present invention.
  • the preferred carbon (C) content may be 0.125 or more, and the more preferred carbon (C) content may be 0.13% or more.
  • the present invention limits the carbon (C) content to less than 0.30%. can do.
  • the preferred carbon (C) content may be 0.29% or less, and the more preferred carbon (C) content may be 0.28% or less.
  • Manganese (Mn) is an element that effectively contributes to improving the strength and hardenability of steel.
  • manganese (Mn) is an element that can effectively prevent cracking due to sulfur (S) because it forms MnS by combining with sulfur (S), which is inevitably introduced during the steel manufacturing process. Therefore, the present invention may include more than 0.1% manganese (Mn) to achieve this effect.
  • the preferred manganese (Mn) content may be 0.3% or more, and the more preferred manganese (Mn) content may be 0.5% or more.
  • the present invention has an upper limit of manganese (Mn) content of 2.5%. Can be limited.
  • the preferred manganese (Mn) content may be 2.3% or less, and the more preferred manganese (Mn) content may be 2.1% or less.
  • the present invention can limit the upper limit of the silicon (Si) content to 0.5%.
  • the preferred silicon (Si) content may be 0.4% or less, and the more preferred silicon (Si) content may be 0.3% or less.
  • silicon (Si) not only acts as a deoxidizer but also contributes to improving the strength of steel, the present invention can exclude 0% from the lower limit of the silicon (Si) content.
  • Boron (B) is an element that effectively contributes to improving the hardenability of steel, and is an element capable of effectively suppressing transformation into low-temperature structures such as ferrite and pearlite during cooling after hot rolling even with a small amount added. Therefore, the present invention may include boron (B) of 0.0005% or more to achieve this effect.
  • the preferred boron (B) content may be 0.0007% or more, and the more preferred boron (B) content may be 0.0009% or more.
  • the present invention may limit the upper limit of the boron (B) content to 0.005%. .
  • the preferred boron (B) content may be 0.003% or less, and the more preferred moron (B) content may be 0.002% or less.
  • Phosphorus (P) is a major element that segregates at grain boundaries and causes the toughness of steel to deteriorate. Therefore, it is desirable to control the phosphorus (P) content as low as possible. Therefore, it is most advantageous in theory to limit the content of phosphorus (P) to 0%.
  • phosphorus (P) is an imperatively introduced impurity in the steel during the steelmaking process, and excessive process load may be caused to control its content to 0%. Therefore, the present invention can take this into consideration and limit the upper limit of the phosphorus (P) content to 0.02%.
  • Sulfur (S) is a major element that increases the amount of precipitates by forming MnS and embrittles the steel. Therefore, it is desirable to control the sulfur (S) content as low as possible. Therefore, it is most advantageous in theory to limit the content of sulfur (S) to 0%.
  • sulfur (S) is also an imperatively introduced impurity in the steel during the steelmaking process, and excessive process load may be caused to control its content to 0%. Therefore, the present invention can take this into consideration and limit the upper limit of the sulfur (S) content to 0.01%.
  • Chromium (Cr) is an element contributing to the formation of the hardenability of the steel, so the present invention may include chromium (Cr) to achieve this effect.
  • Cr chromium
  • the present invention has an upper limit of the chromium (Cr) content of 0.5. Can be limited to %.
  • the preferred chromium (Cr) content may be 0.4% or less, and the more preferred chromium (Cr) content may be 0.3% or less.
  • titanium (Ti) is an element known to form carbides and nitrides in combination with carbon (C) and nitrogen (N).
  • boron (B) is essentially added to steel to secure hardenability, but when nitrogen (N) and boron (B) contained in steel are combined, the effect of adding boron (B) desired by the present invention is It cannot be achieved.
  • titanium (Ti) is added, since nitrogen (N) before bonding with boron (B) is combined with titanium (Ti) to form a nitride, the effect of adding boron (B) can be improved more effectively. Therefore, the present invention can add titanium (Ti) of 0.005% or more to achieve this effect.
  • the preferred titanium (Ti) content may be 0.01% or more, and the more preferable titanium (Ti) content may be 0.015% or more.
  • the present invention may limit the upper limit of the titanium (Ti) content to 0.2%.
  • the preferred titanium (Ti) content may be 0.17% or less, and the more preferable titanium (Ti) content may be 0.15% or less.
  • the rest may include Fe and unavoidable impurities.
  • the unavoidable impurities can be unintentionally incorporated in the ordinary steel manufacturing process, and cannot be completely excluded, and the meaning can be easily understood by those skilled in the ordinary steel manufacturing field.
  • this invention does not exclude the addition of the composition other than the steel composition mentioned above entirely.
  • the inventors of the present invention have conducted research on conditions that can simultaneously secure steel strength and hole expandability (HER). Although the strength and workability of the steel have been widely recognized as incompatible properties, the inventors of the present invention have in-depth studies and the fraction of the unstructured steel of the steel as well as the fraction of a specific microstructure greatly influences the strength and hole expandability (HER) of the steel. It was found that it was a condition.
  • the hot-rolled steel sheet according to an aspect of the present invention includes martensite as a base structure, and the fraction of martensite may be 95 vol% or more compared to the volume of the pre-rolled hot-rolled steel sheet. Since the present invention contains at least 95% of martensite, which is a hard tissue, it is possible to effectively secure high-strength and hole expandability (HER) at the same time.
  • martensite as a base structure
  • the fraction of martensite may be 95 vol% or more compared to the volume of the pre-rolled hot-rolled steel sheet. Since the present invention contains at least 95% of martensite, which is a hard tissue, it is possible to effectively secure high-strength and hole expandability (HER) at the same time.
  • HER hole expandability
  • the hot-rolled steel sheet according to an aspect of the present invention does not entirely exclude the structure other than martensite.
  • the total fraction can be limited to 5% by volume or less, and more preferably, the total fraction is strictly limited to 3% by volume or less. Can.
  • hot-rolled steel sheet according to an aspect of the present invention may further include cementite and precipitates as a residual structure in addition to the above-described structure.
  • the hot-rolled steel sheet according to an aspect of the present invention may satisfy a tensile strength (TS) of 1,250 MPa or more and a hole expandability (HER) of 20% or more.
  • TS tensile strength
  • HER hole expandability
  • the hot-rolled steel sheet according to an aspect of the present invention can effectively achieve both strength and workability with a product of tensile strength (TS) and hole expandability (HER) of 30,000 MPa% or more.
  • the thickness of the hot-rolled steel sheet according to an aspect of the present invention is not particularly limited.
  • the hot-rolled steel sheet according to an aspect of the present invention has excellent strength and processability, and thus can effectively contribute to securing economical and lightweight properties of the final product through thinning.
  • the thickness of the hot-rolled steel sheet according to an aspect of the present invention may be 1.8 mm or less, and a more preferable thickness may be 1.5 mm or less.
  • Method for manufacturing a high-strength hot-rolled steel sheet having excellent hole expandability comprises the steps of reheating a slab provided with the above-mentioned steel composition; Hot rolling the reheated slab to provide a hot rolled steel sheet; Cooling the hot rolled steel sheet within 5 seconds from the end point of the hot rolling, and cooling the hot rolled steel sheet to a cooling end temperature of 350° C. or less at a cooling rate of 50 to 1000° C./s; And winding the cooled hot rolled steel sheet.
  • the slab steel composition of the present invention corresponds to the steel composition of the hot-rolled steel sheet described above, the description of the slab steel composition of the present invention is replaced by the description of the hot-rolled steel sheet composition.
  • Slabs manufactured by a conventional slab manufacturing process can be reheated in a certain temperature range.
  • the lower limit of the reheating temperature may be limited to 1,050°C for sufficient homogenization treatment, and the upper limit of the reheating temperature may be limited to 1,350°C in consideration of economic efficiency and surface quality.
  • the reheated slab may be finished rolled to a thickness of 1.8 mm or less, preferably 1.5 mm or less, by hot-rolling.
  • hot rolling may be performed under normal conditions, but the finish rolling temperature for controlling the rolling load and reducing the surface scale may range from 800 to 950°C.
  • the present invention intends to manufacture a hot-rolled steel sheet having a thin thickness by hot rolling, continuous rolling without continuously separating the preceding material and the trailing material is more preferable in terms of securing the thickness of the hot-rolled steel sheet.
  • Cooling in the quench condition may be performed on the hot-rolled steel sheet immediately after hot rolling.
  • the present invention is intended to strictly control the microstructure of the hot-rolled steel sheet, and the cooling of the present invention is preferably initiated within 5 seconds immediately after hot rolling. This is because ferrite, pearlite, and bainite, which the present invention does not intend, may be formed by air cooling in the air when the time from the hot rolling to the start of cooling exceeds 5 seconds. A more preferable time from the hot rolling to the start of cooling may be within 3 seconds.
  • the hot-rolled steel sheet immediately after hot rolling may be cooled to a cooling end temperature of 350°C or less at a cooling rate of 50 to 1,000°C/s. If the cooling rate is less than 50 °C / s, ferrite, pearlite, and transformation into bainite occurs during cooling, and thus there is a problem that the present invention cannot secure the desired microstructure.
  • the upper limit of the cooling rate is not particularly limited in order to secure the desired microstructure, but the upper limit of the cooling rate may be limited to 1,000°C/s in consideration of facility limitations and economics.
  • the cooling end temperature exceeds 350°C, transformation into ferrite, pearlite, and bainite is unavoidable, and thus there is a problem that the microstructure desired by the present invention cannot be secured.
  • the hot-rolled steel sheet manufactured by the above manufacturing method secures a tensile strength (TS) of 1,250 MPa or more and a hole expandability (HER) of 20% or more, and a product of tensile strength (TS) and hole expandability (HER) is 30,000 MPa%. To the above level, strength and processability can be effectively compatible.
  • a hot-rolled steel sheet specimen was prepared using the conditions of Table 2 below. Each slab was manufactured by a conventional manufacturing method, and was re-heated in a temperature range of 1,050 to 1,350°C to be homogenized.
  • the fraction of martensite is less than 95% by volume, or the product of tensile strength (TS) and hole expandability (HER) It can be confirmed that it is less than 30,000 MPa%.
  • the specimen 12 is a case in which the time from the end of rolling to the start of cooling exceeds 5 seconds, it is not possible to secure the desired martensite fraction and the tensile strength is poor.
  • the specimen 13 is a case where the cooling rate is low
  • the specimen 14 is a case where the cooling end temperature is high, transformation to martensite has not occurred sufficiently, and the desired tensile strength or hole expandability (HER) of the present invention is not secured. You can confirm that.
  • Specimen 15 is a case where the content of carbon (C) is low, and specimen 16 is a case where the content of boron (B) is low, indicating that the martensitic fraction is less than 50% by volume and the tensile strength is inferior. .
  • Specimen 17 is a case where the content of manganese (Mn) is high, it can be confirmed that the transformation to martensite does not occur sufficiently, and thus retained austenite is formed, and the tensile strength is excellent while the hole expandability (HER) is poor.
  • Mn manganese
  • Specimen 18 to 20 is a case where the content of silicon (Si), phosphorus (P), and sulfur (S) is high, respectively, and the tensile strength is high, but it can be confirmed that the hole expandability (HER) is poor.
  • the hot-rolled steel sheet according to one aspect of the present invention satisfies the tensile strength (TS) of 1,250 MPa or more and the hole expandability (HER) of 20% or more, in particular, the product of the tensile strength (TS) and the hole expandability (HER) It can be seen that the strength and workability are effectively compatible at a level of 30,000 MPa% or more.

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Abstract

A high strength hot-rolled steel sheet having an excellent hole expansion ratio according to an aspect of the present invention comprises, by weight %, 0.12% or more and less than 0.30% of carbon (C), 0.1-2.5% of manganese (Mn), 0.5% or less of silicon (Si) (not including 0%), 0.0005-0.005% of boron (B), 0.02% or less of phosphorus (P), 0.01% or less of sulfur (S), and the balance being iron (Fe) and unavoidable impurities, and comprises 95 volume% or more of martensite as a microstructure. And the product of the tensile strength (TS) and hole expansion ratio (HER) can be 30,000MPa% or greater.

Description

구멍확장성이 우수한 고강도 열연강판 및 그 제조방법High-strength hot-rolled steel sheet with excellent hole expandability and its manufacturing method
본 발명은 자동차용 충돌부재용 부품 및 구조물 지지대 등의 소재로 사용되는 열연강판에 관한 것이며, 상세하게는 고강도 특성을 구비하면서도 구멍확장성이 우수한 열연강판 및 그 제조방법에 관한 것이다. The present invention relates to a hot-rolled steel sheet used as a material for a vehicle collision member parts and a structure support, and more particularly, to a hot-rolled steel sheet having high strength characteristics and excellent hole expandability, and a manufacturing method thereof.
자동차 충돌 부재용 부품 및 구조물 지지대 등의 소재로 이용되는 강재는 안전성 확보를 위해 고강도 특성이 요구될 뿐만 아니라, 설계자의 요구에 부합하여 다양한 형태로 가공되기 위해 구멍확장성(Hole Expansion Ratio, HER)과 같은 가공성이 요구된다. 다만, 강재의 강도와 가공성은 양립되기 어려운 물성이므로, 강재의 강도와 가공성을 동시에 확보하기 위한 다양한 연구가 진행 중이다. Steel materials used as materials for automobile collision member parts and structure supports are required not only to have high-strength properties to secure safety, but also to expand the hole in order to be processed in various forms in accordance with the requirements of designers (Hole Expansion Ratio, HER) Processability such as is required. However, since the strength and workability of steel materials are difficult to be compatible, various studies are underway to ensure the strength and workability of steel materials at the same time.
열연강판의 고강도성 및 고성형성을 동시에 확보하기 위한 방법으로 다음의 특허문헌들이 알려져 있다.The following patent documents are known as a method for simultaneously securing high strength and high formability of a hot rolled steel sheet.
특허문헌 1은 합금원소 첨가에 따른 석출강화에 의해 강도를 확보하는 기술을 제안한다. 즉, 특허문헌 1은 Ti, Nb, V 및 Mo 등의 합금원소를 첨가하여 고강도 특성을 확보하고자 하나, 이들 합금원소는 고가의 원소로 제조비용이 과다하게 상승하여 경제성 측면에서 바람직하지 않다.Patent Document 1 proposes a technique for securing strength by precipitation strengthening with the addition of alloy elements. That is, Patent Document 1 is intended to secure high-strength properties by adding alloying elements such as Ti, Nb, V, and Mo, but these alloying elements are expensive elements, and their manufacturing cost is excessively increased, which is not preferable in terms of economic efficiency.
특허문헌 2 내지 4는 페라이트와 마르텐사이트 이상 조직을 이용하거나, 오스테나이트를 잔류시키고 페라이트, 베이나이트, 마르텐사이트의 복합 조직을 활용하여 강도와 연성을 확보하는 기술을 제안한다. 다만, 이와 같은 페라이트나 잔류 오스테나이트는 연성은 우수한 반면 강도가 열위하여, 고강도 특성을 충분히 확보하지 못하는 기술적 난점이 존재한다. Patent Documents 2 to 4 propose a technique for securing strength and ductility by using a ferrite and martensite abnormal structure or by retaining austenite and utilizing a complex structure of ferrite, bainite and martensite. However, such ferrite or retained austenite has excellent ductility, but poor strength, so there is a technical difficulty that cannot sufficiently secure high strength properties.
(선행기술문헌)(Advanced technical literature)
(특허문헌 1) 대한민국 공개특허공보 제10-2005-113247호 (2005.12.01. 공개)(Patent Document 1) Republic of Korea Patent Publication No. 10-2005-113247 (2005.12.01. public)
(특허문헌 2) 일본 공개특허공보 특개2005-298967호 (2005.10.27. 공개)(Patent Document 2) Japanese Patent Application Publication No. 2005-298967 (published on October 27, 2005)
(특허문헌 3) 미국 공개특허공보 제2005-0155673호 (2005.07.21. 공개)(Patent Document 3) U.S. Patent Publication No. 2005-0155673 (published on July 21, 2005)
(특허문헌 4) 유럽 공개특허공보 제1396549호 (2004.03.10. 공개)(Patent Document 4) European Patent Publication No. 1396549 (published on October 10, 2004)
본 발명의 한 가지 측면에 따르면 구멍확장성이 우수한 고강도 열연강판 및 그 제조방법이 제공될 수 있다According to one aspect of the present invention, a high strength hot rolled steel sheet having excellent hole expandability and a method for manufacturing the same can be provided.
본 발명의 과제는 상술한 내용에 한정되지 않는다. 통상의 기술자라면 본 명세서의 전반적인 내용으로부터 본 발명의 추가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.The subject of this invention is not limited to the above-mentioned content. Those skilled in the art will have no difficulty in understanding the additional subject matter of the present invention from the general contents of this specification.
본 발명의 일 측면에 따른 구멍확장성이 우수한 고강도 열연강판은, 중량%로, 탄소(C): 0.12% 이상 0.30% 미만, 망간(Mn): 0.1~2.5%, 실리콘(Si): 0.5% 이하(0% 제외), 보론(B): 0.0005~0.005%, 인(P) 0.02% 이하, 황(S): 0.01% 이하, 나머지 철(Fe) 및 불가피한 불순물을 포함하고, 95부피% 이상의 마르텐사이트를 미세조직으로 포함하고, 인장강도(TS)와 구멍확장성(HER)의 곱이 30,000MPa% 이상일 수 있다.High-strength hot-rolled steel sheet excellent in hole expandability according to an aspect of the present invention, by weight, carbon (C): 0.12% or more and less than 0.30%, manganese (Mn): 0.1-2.5%, silicon (Si): 0.5% Less than (excluding 0%), Boron (B): 0.0005 to 0.005%, Phosphorus (P) 0.02% or less, Sulfur (S): 0.01% or less, including the remaining iron (Fe) and unavoidable impurities, more than 95% by volume It contains martensite as a microstructure, and the product of tensile strength (TS) and hole expandability (HER) may be 30,000 MPa% or more.
상기 열연강판은, 중량%로, 크롬(Cr): 0.5% 이하 및 티타늄(Ti): 0.005~0.2% 중 1종 이상을 더 포함할 수 있다.The hot-rolled steel sheet may further include at least one of chromium (Cr): 0.5% or less and titanium (Ti): 0.005 to 0.2% by weight.
상기 미세조직은, 페라이트, 베이나이트, 탄화물 및 잔류오스테나이트 중 1종 이상을 합계 5부피% 이하로 포함할 수 있다.The microstructure may include one or more of ferrite, bainite, carbide, and residual austenite in a total volume of 5% or less.
상기 열연강판의 인장강도(TS)는 1,250MPa 이상일 수 있다.The tensile strength (TS) of the hot rolled steel sheet may be 1,250 MPa or more.
상기 열연강판의 구멍확장성(HER)은 20% 이상일 수 있다.The hole expandability (HER) of the hot rolled steel sheet may be 20% or more.
상기 열연강판의 두께는 1.8mm 이하일 수 있다.The thickness of the hot rolled steel sheet may be 1.8 mm or less.
본 발명의 일 측면에 따른 구멍확장성이 우수한 고강도 열연강판의 제조방법은, 중량%로, 탄소(C): 0.12% 이상 0.30% 미만, 망간(Mn): 0.1~2.5%, 실리콘(Si): 0.5% 이하(0% 제외), 보론(B): 0.0005~0.005%, 인(P) 0.02% 이하, 황(S): 0.01% 이하, 나머지 철(Fe) 및 불가피한 불순물을 포함하는 슬라브를 재가열하는 단계; 상기 재가열된 슬라브를 열간압연하여 열연강판을 제공하는 단계; 상기 열간압연의 종료시점으로부터 5초 이내에 상기 열연강판의 냉각을 개시하되, 50~1,000℃/s의 냉각속도로 350℃ 이하의 냉각 종료 온도까지 상기 열연강판을 냉각하는 단계; 및 상기 냉각된 열연강판을 권취하는 단계;를 포함할 수 있다.Method for manufacturing a high-strength hot-rolled steel sheet excellent in hole expandability according to an aspect of the present invention, by weight, carbon (C): 0.12% or more but less than 0.30%, manganese (Mn): 0.1-2.5%, silicon (Si) : 0.5% or less (excluding 0%), boron (B): 0.0005 to 0.005%, phosphorus (P) 0.02% or less, sulfur (S): 0.01% or less, and the remaining slab containing iron (Fe) and unavoidable impurities Reheating; Hot rolling the reheated slab to provide a hot rolled steel sheet; Cooling the hot rolled steel sheet within 5 seconds from the end point of the hot rolling, and cooling the hot rolled steel sheet to a cooling end temperature of 350° C. or less at a cooling rate of 50 to 1,000° C./s; And winding the cooled hot rolled steel sheet.
상기 슬라브는, 중량%로, 크롬(Cr): 0.5% 이하 및 티타늄(Ti): 0.005~0.2% 중 1종 이상을 더 포함할 수 있다.The slab may further include one or more of chromium (Cr): 0.5% or less and titanium (Ti): 0.005 to 0.2% by weight.
상기 과제의 해결 수단은 본 발명의 특징을 모두 열거한 것은 아니며, 본 발명의 다양한 특징과 그에 따른 장점과 효과는 아래의 구체적인 실시예를 참조하여 보다 상세하게 이해될 수 있을 것이다.The solving means of the above problem does not list all the features of the present invention, and various features of the present invention and the advantages and effects thereof may be understood in more detail with reference to specific embodiments below.
본 발명의 일 측면에 따르면, 고강도성을 구비하면서도 구멍확장성(HER)이 현저히 향상된 열연강판 및 그 제조방법을 제공할 수 있다.According to one aspect of the present invention, it is possible to provide a hot-rolled steel sheet having a high-strength property and significantly improved hole expandability (HER) and a method for manufacturing the same.
본 발명은 구멍확장성이 우수한 고강도 열연강판 및 그 제조방법에 관한 것으로, 이하에서는 본 발명의 바람직한 실시예들을 설명하고자 한다. 본 발명의 실시예들은 여러 가지 형태로 변형될 수 있으며, 본 발명의 범위가 아래에서 설명되는 실시예들에 한정되는 것으로 해석되어서는 안된다. 본 실시예들은 당해 발명이 속하는 기술분야에서 통상의 지식을 가지는 자에게 본 발명을 더욱 상세하기 위하여 제공되는 것이다.The present invention relates to a high-strength hot-rolled steel sheet having excellent hole expandability and a method for manufacturing the same, and the following will describe preferred embodiments of the present invention. The embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The present embodiments are provided to those skilled in the art to further detail the present invention.
이하, 본 발명의 강 조성에 대해 보다 상세히 설명한다. 이하, 특별히 달리 언급하지 않는 한 강 조성의 함량을 나타내는 %는 중량을 기준으로 한다.Hereinafter, the steel composition of the present invention will be described in more detail. Hereinafter, unless otherwise specified,% representing the content of the steel composition is based on weight.
본 발명의 일 측면에 따른 구멍확장성이 우수한 고강도 열연강판은, 중량%로, 탄소(C): 0.12% 이상 0.30% 미만, 망간(Mn): 0.1~2.5%, 실리콘(Si): 0.5% 이하(0% 제외), 보론(B): 0.0005~0.005%, 인(P) 0.02% 이하, 황(S): 0.01% 이하, 나머지 철(Fe) 및 불가피한 불순물을 포함할 수 있다. 또한, 본 발명의 일 측면에 따른 구멍확장성이 우수한 고강도 열연강판은, 중량%로, 크롬(Cr): 0.5% 이하 및 티타늄(Ti): 0.005~0.2% 중 1종 이상을 더 포함할 수 있다.High-strength hot-rolled steel sheet excellent in hole expandability according to an aspect of the present invention, by weight, carbon (C): 0.12% or more and less than 0.30%, manganese (Mn): 0.1-2.5%, silicon (Si): 0.5% The following (excluding 0%), boron (B): 0.0005 to 0.005%, phosphorus (P) 0.02% or less, sulfur (S): 0.01% or less, the remaining iron (Fe) and may contain unavoidable impurities. In addition, the high-strength hot-rolled steel sheet having excellent hole expandability according to an aspect of the present invention may further include one or more of chromium (Cr): 0.5% or less and titanium (Ti): 0.005 to 0.2%. have.
탄소(C): 0.12% 이상 0.30% 미만Carbon (C): 0.12% or more but less than 0.30%
탄소(C)는 강의 강도 향상에 효과적으로 기여하는 원소이므로, 본 발명은 열연강판의 강도 확보를 위해 일정 수준 이상의 탄소(C)를 포함할 수 있다. 또한, 탄소 함량(C)이 일정 수준이 이하인 경우, 열간압연 후 냉각 시 저온조직이 다량 형성되어 본 발명이 목적하는 미세조직을 확보하지 못하는 문제가 발생할 수 있으므로, 본 발명은 0.12% 이상의 탄소(C)를 포함할 수 있다. 바람직한 탄소(C) 함량은 0.125 이상일 수 있으며, 보다 바람직한 탄소(C) 함량은 0.13% 이상일 수 있다. 반면, 탄소(C)가 과다하게 첨가되는 경우, 강도는 향상되는 반면, 구멍확장성(HER) 및 용접성이 저하되는 문제가 발생할 수 있으므로, 본 발명은 탄소(C) 함량을 0.30% 미만으로 제한할 수 있다. 바람직한 탄소(C) 함량은 0.29% 이하일 수 있으며, 보다 바람직한 탄소(C) 함량은 0.28% 이하일 수 있다.Since carbon (C) is an element that effectively contributes to improving the strength of steel, the present invention may include carbon (C) of a certain level or more to secure the strength of the hot-rolled steel sheet. In addition, when the carbon content (C) is below a certain level, a problem may occur in which a low-temperature structure is formed in a large amount during cooling after hot rolling, thereby failing to secure the microstructure desired by the present invention. C). The preferred carbon (C) content may be 0.125 or more, and the more preferred carbon (C) content may be 0.13% or more. On the other hand, if the carbon (C) is added excessively, the strength is improved, while the hole expandability (HER) and weldability may be reduced, so the present invention limits the carbon (C) content to less than 0.30%. can do. The preferred carbon (C) content may be 0.29% or less, and the more preferred carbon (C) content may be 0.28% or less.
망간(Mn): 0.1~2.5%Manganese (Mn): 0.1-2.5%
망간(Mn)은 강의 강도 및 경화능 향상에 효과적으로 기여하는 원소이다. 또한, 망간(Mn)은 강의 제조공정 중 불가피하게 유입되는 황(S)과 결합하여 MnS를 형성하므로, 황(S)에 의한 크랙 발생을 효과적으로 방지 가능한 원소이기도 하다. 따라서, 본 발명은 이러한 효과 달성을 위해 0.1% 이상의 망간(Mn)을 포함할 수 있다. 바람직한 망간(Mn) 함량은 0.3% 이상일 수 있으며, 보다 바람직한 망간(Mn) 함량은 0.5% 이상일 수 있다. 다만, 망간(Mn)이 과다하게 첨가되는 경우, 잔류 오스테나이트에 의한 인장강도 저하가 우려될 뿐만 아니라, 용접성 및 경제성 측면에서 바람직하지 않으므로, 본 발명은 망간(Mn) 함량의 상한을 2.5%로 제한할 수 있다. 바람직한 망간(Mn) 함량은 2.3% 이하일 수 있으며, 보다 바람직한 망간(Mn) 함량은 2.1% 이하일 수 있다. Manganese (Mn) is an element that effectively contributes to improving the strength and hardenability of steel. In addition, manganese (Mn) is an element that can effectively prevent cracking due to sulfur (S) because it forms MnS by combining with sulfur (S), which is inevitably introduced during the steel manufacturing process. Therefore, the present invention may include more than 0.1% manganese (Mn) to achieve this effect. The preferred manganese (Mn) content may be 0.3% or more, and the more preferred manganese (Mn) content may be 0.5% or more. However, when manganese (Mn) is added excessively, not only is the tensile strength lowered by residual austenite concerned, but also undesirable in terms of weldability and economy, the present invention has an upper limit of manganese (Mn) content of 2.5%. Can be limited. The preferred manganese (Mn) content may be 2.3% or less, and the more preferred manganese (Mn) content may be 2.1% or less.
실리콘(Si): 0.5% 이하(0% 제외)Silicon (Si): 0.5% or less (excluding 0%)
실리콘(Si)은 산소와의 친화력이 강한 원소이므로, 다량 첨가되는 경우, 표면 스케일에 의한 표면품질의 저하를 유발할 수 있으며, 용접성 측면에서도 바람직하지 않다. 따라서, 본 발명은 실리콘(Si) 함량의 상한을 0.5%로 제한할 수 있다. 바람직한 실리콘(Si) 함량은 0.4% 이하일 수 있으며, 보다 바람직한 실리콘(Si) 함량은 0.3% 이하일 수 있다. 다만, 실리콘(Si)은 탈산제로 작용할 뿐만 아니라 강의 강도 향상에 기여하는 원소이기도 하므로, 본 발명은 실리콘(Si) 함량의 하한에서 0%를 제외할 수 있다. Since silicon (Si) is an element having a strong affinity for oxygen, when it is added in a large amount, it may cause a decrease in surface quality due to surface scale, and it is also undesirable in terms of weldability. Therefore, the present invention can limit the upper limit of the silicon (Si) content to 0.5%. The preferred silicon (Si) content may be 0.4% or less, and the more preferred silicon (Si) content may be 0.3% or less. However, since silicon (Si) not only acts as a deoxidizer but also contributes to improving the strength of steel, the present invention can exclude 0% from the lower limit of the silicon (Si) content.
보론(B): 0.0005~0.005%Boron (B): 0.0005~0.005%
보론(B)은 강의 경화능 향상에 효과적으로 기여하는 원소로써, 소량의 첨가에 의하더라도 열간압연 후 냉각 시 페라이트 및 펄라이트 등 저온조직으로의 변태를 효과적으로 억제 가능한 원소이다. 따라서, 본 발명은 이와 같은 효과 달성을 위해 0.0005% 이상의 보론(B)을 포함할 수 있다. 바람직한 보론(B) 함량은 0.0007% 이상일 수 있으며, 보다 바람직한 보론(B) 함량은 0.0009% 이상일 수 있다. 반면, 보론(B)이 과다하게 첨가되는 경우, 보론(B)이 철(Fe)과 반응하여 입계취성을 유발할 수 있으므로, 본 발명은 보론(B) 함량의 상한을 0.005%로 제한할 수 있다. 바람직한 보론(B) 함량은 0.003% 이하일 수 있으며, 보다 바람직한 모론(B) 함량은 0.002% 이하일 수 있다.Boron (B) is an element that effectively contributes to improving the hardenability of steel, and is an element capable of effectively suppressing transformation into low-temperature structures such as ferrite and pearlite during cooling after hot rolling even with a small amount added. Therefore, the present invention may include boron (B) of 0.0005% or more to achieve this effect. The preferred boron (B) content may be 0.0007% or more, and the more preferred boron (B) content may be 0.0009% or more. On the other hand, when boron (B) is excessively added, since the boron (B) may react with iron (Fe) to induce grain boundary embrittlement, the present invention may limit the upper limit of the boron (B) content to 0.005%. . The preferred boron (B) content may be 0.003% or less, and the more preferred moron (B) content may be 0.002% or less.
인(P) 0.02% 이하Phosphorus (P) 0.02% or less
인(P)은 결정립계에 편석되어 강의 인성을 저하를 유발하는 주요 원소이다. 따라서, 인(P) 함량을 가능한 한 낮게 제어하는 것이 바람직하다. 따라서, 인(P)의 함량을 0%로 제한하는 것이 이론상 가장 유리하다. 다만, 인(P)은 제강공정 중 강 중에 불가피하게 유입되는 불순물로, 그 함량을 0%로 제어하는 데에는 과도한 공정 부하가 유발될 수 있다. 따라서, 본 발명은 이와 같은 점을 고려하여, 인(P) 함량의 상한을 0.02%로 제한할 수 있다. Phosphorus (P) is a major element that segregates at grain boundaries and causes the toughness of steel to deteriorate. Therefore, it is desirable to control the phosphorus (P) content as low as possible. Therefore, it is most advantageous in theory to limit the content of phosphorus (P) to 0%. However, phosphorus (P) is an imperatively introduced impurity in the steel during the steelmaking process, and excessive process load may be caused to control its content to 0%. Therefore, the present invention can take this into consideration and limit the upper limit of the phosphorus (P) content to 0.02%.
황(S): 0.01% 이하Sulfur (S): 0.01% or less
황(S)은 MnS를 형성하여 석출물 양을 증가시키고, 강을 취화시키는 주요 원소이다. 따라서, 황(S) 함량을 가능한 한 낮게 제어하는 것이 바람직하다. 따라서, 황(S)의 함량을 0%로 제한하는 것이 이론상 가장 유리하다. 다만, 황(S) 역시 제강공정 중 강 중에 불가피하게 유입되는 불순물로, 그 함량을 0%로 제어하는 데에는 과도한 공정 부하가 유발될 수 있다. 따라서, 본 발명은 이와 같은 점을 고려하여, 황(S) 함량의 상한을 0.01%로 제한할 수 있다.Sulfur (S) is a major element that increases the amount of precipitates by forming MnS and embrittles the steel. Therefore, it is desirable to control the sulfur (S) content as low as possible. Therefore, it is most advantageous in theory to limit the content of sulfur (S) to 0%. However, sulfur (S) is also an imperatively introduced impurity in the steel during the steelmaking process, and excessive process load may be caused to control its content to 0%. Therefore, the present invention can take this into consideration and limit the upper limit of the sulfur (S) content to 0.01%.
크롬(Cr): 0.5% 이하Chromium (Cr): 0.5% or less
크롬(Cr)은 강의 경화능 형성에 기여하는 원소이므로, 본 발명은 이러한 효과를 달성하기 위하여 크롬(Cr)을 포함할 수 있다. 다만, 고가의 원소인 크롬(Cr)의 과다첨가는 경제적 측면에서 바람직하지 않으며, 크롬(Cr)이 과다하게 첨가되는 경우 용접성을 저하시킬 수 있으므로, 본 발명은 크롬(Cr) 함량의 상한을 0.5%로 제한할 수 있다. 바람직한 크롬(Cr) 함량은 0.4% 이하일 수 있으며, 보다 바람직한 크롬(Cr) 함량은 0.3% 이하일 수 있다.Chromium (Cr) is an element contributing to the formation of the hardenability of the steel, so the present invention may include chromium (Cr) to achieve this effect. However, excessive addition of chromium (Cr), which is an expensive element, is not desirable from an economical point of view, and when chromium (Cr) is added excessively, weldability may be deteriorated, so the present invention has an upper limit of the chromium (Cr) content of 0.5. Can be limited to %. The preferred chromium (Cr) content may be 0.4% or less, and the more preferred chromium (Cr) content may be 0.3% or less.
티타늄(Ti): 0.005~0.2%Titanium (Ti): 0.005~0.2%
일반적으로, 티타늄(Ti)은 탄소(C) 및 질소(N)와 결합하여 탄화물 및 질화물을 형성하는 것으로 알려진 원소이다. 본 발명은 경화능 확보를 위해 보론(B)을 강 중에 필수적으로 첨가하지만, 강 중 포함된 질소(N)와 보론(B)이 결합하는 경우, 본 발명이 목적하는 보론(B) 첨가 효과를 달성할 수 없게 된다. 반면, 티타늄(Ti)이 첨가되는 경우, 보론(B)과 결합하기 전의 질소(N)가 티타늄(Ti)과 결합하여 질화물을 형성하므로, 보론(B) 첨가 효과를 보다 효과적으로 향상시킬 수 있다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 0.005% 이상의 티타늄(Ti)을 첨가할 수 있다. 바람직한 티타늄(Ti) 함량은 0.01% 이상일 수 있으며, 보다 바람직한 티타늄(Ti) 함량은 0.015% 이상일 수 있다. 다만, 티타늄(Ti)이 과도하게 첨가되는 경우, 슬라브 제조 단계에서 연주성이 저하되는 문제가 발생하므로, 본 발명은 티타늄(Ti) 함량의 상한을 0.2%로 제한할 수 있다. 바람직한 티타늄(Ti) 함량은 0.17% 이하일 수 있으며, 보다 바람직한 티타늄(Ti) 함량은 0.15% 이하일 수 있다.In general, titanium (Ti) is an element known to form carbides and nitrides in combination with carbon (C) and nitrogen (N). In the present invention, boron (B) is essentially added to steel to secure hardenability, but when nitrogen (N) and boron (B) contained in steel are combined, the effect of adding boron (B) desired by the present invention is It cannot be achieved. On the other hand, when titanium (Ti) is added, since nitrogen (N) before bonding with boron (B) is combined with titanium (Ti) to form a nitride, the effect of adding boron (B) can be improved more effectively. Therefore, the present invention can add titanium (Ti) of 0.005% or more to achieve this effect. The preferred titanium (Ti) content may be 0.01% or more, and the more preferable titanium (Ti) content may be 0.015% or more. However, when titanium (Ti) is excessively added, a problem occurs in that the performance of the slab is deteriorated, so the present invention may limit the upper limit of the titanium (Ti) content to 0.2%. The preferred titanium (Ti) content may be 0.17% or less, and the more preferable titanium (Ti) content may be 0.15% or less.
본 발명은, 상술한 강 조성 이외에 나머지는 Fe 및 불가피한 불순물을 포함할 수 있다. 불가피한 불순물은 통상의 철강 제조공정에서 의도되지 않게 혼입될 수 있는 것으로, 이를 전면 배제할 수는 없으며, 통상의 철강제조 분야의 기술자라면 그 의미를 쉽게 이해할 수 있다. 또한, 본 발명은, 앞서 언급한 강 조성 이외의 다른 조성의 첨가를 전면적으로 배제하는 것은 아니다.The present invention, in addition to the above-mentioned steel composition, the rest may include Fe and unavoidable impurities. The unavoidable impurities can be unintentionally incorporated in the ordinary steel manufacturing process, and cannot be completely excluded, and the meaning can be easily understood by those skilled in the ordinary steel manufacturing field. In addition, this invention does not exclude the addition of the composition other than the steel composition mentioned above entirely.
이하, 본 발명의 미세조직에 대해 보다 상세히 설명한다.Hereinafter, the microstructure of the present invention will be described in more detail.
본 발명의 발명자들은 강의 강도와 구멍확장성(HER)을 동시에 확보 가능한 조건에 대해 연구를 수행하였다. 종래 강의 강도 및 가공성은 양립 불가능한 물성으로 널리 인식되었으나, 본 발명의 발명자들은 심도 있는 연구 끝에 강의 미제조직 종류뿐만 아니라 특정 미세조직의 분율이 강의 강도 및 구멍확장성(HER) 양립에 지대한 영향을 미치는 조건임을 도출할 수 있었다. The inventors of the present invention have conducted research on conditions that can simultaneously secure steel strength and hole expandability (HER). Although the strength and workability of the steel have been widely recognized as incompatible properties, the inventors of the present invention have in-depth studies and the fraction of the unstructured steel of the steel as well as the fraction of a specific microstructure greatly influences the strength and hole expandability (HER) of the steel. It was found that it was a condition.
본 발명의 일 측면에 따른 열연강판은 마르텐사이트를 기지조직으로 포함하며, 마르텐사이트의 분율은 전제 열연강판의 부피 대비 95부피% 이상일 수 있다. 본 발명은 경질조직인 마르텐사이트를 95% 이상 포함하므로, 고강도성을 효과적으로 확보함과 동시에 구멍확장성(HER)을 효과적으로 확보할 수 있다.The hot-rolled steel sheet according to an aspect of the present invention includes martensite as a base structure, and the fraction of martensite may be 95 vol% or more compared to the volume of the pre-rolled hot-rolled steel sheet. Since the present invention contains at least 95% of martensite, which is a hard tissue, it is possible to effectively secure high-strength and hole expandability (HER) at the same time.
본 발명의 일 측면에 따른 열연강판은 마르텐사이트 외의 조직이 포함되는 것을 전면적으로 배제하는 것은 아니다. 다만, 페라이트, 베이나이트, 탄화물 및 잔류 오스테나이트 등은 강도 확보에 바람직하지 않으므로 그 합계 분율을 5부피% 이하로 제한할 수 있으며, 보다 바람직하게는 그 합계 분율을 3부피% 이하로 엄격히 제한할 수 있다. The hot-rolled steel sheet according to an aspect of the present invention does not entirely exclude the structure other than martensite. However, since ferrite, bainite, carbide and residual austenite are not desirable for securing strength, the total fraction can be limited to 5% by volume or less, and more preferably, the total fraction is strictly limited to 3% by volume or less. Can.
또한, 본 발명의 일 측면에 따른 열연강판은 전술한 조직 외에 시멘타이트 및 석출물 등을 잔부조직으로 더 포함할 수 있다.In addition, the hot-rolled steel sheet according to an aspect of the present invention may further include cementite and precipitates as a residual structure in addition to the above-described structure.
따라서, 본 발명의 일 측면에 따른 열연강판은 1,250MPa 이상의 인장강도(TS) 및 20% 이상의 구멍확장성(HER)을 만족할 수 있다. 특히, 본 발명의 일 측면에 따른 열연강판은 인장강도(TS)와 구멍확장성(HER)의 곱이 30,000MPa% 이상의 수준으로 강도 및 가공성이 효과적으로 양립될 수 있다.Therefore, the hot-rolled steel sheet according to an aspect of the present invention may satisfy a tensile strength (TS) of 1,250 MPa or more and a hole expandability (HER) of 20% or more. In particular, the hot-rolled steel sheet according to an aspect of the present invention can effectively achieve both strength and workability with a product of tensile strength (TS) and hole expandability (HER) of 30,000 MPa% or more.
더불어, 본 발명의 일 측면에 따른 열연강판은 그 두께가 특별히 제한되는 것은 아니다. 다만, 본 발명의 일 측면에 따른 열연강판은 우수한 강도 및 가공성을 구비하므로, 박물화를 통해 최종 제품의 경제성 및 경량성 확보에 효과적으로 기여할 수 있다. 따라서, 본 발명의 일 측면에 따른 열연강판 두께는 1.8mm 이하일 수 있으며, 보다 바람직한 두께는 1.5mm 이하일 수 있다. In addition, the thickness of the hot-rolled steel sheet according to an aspect of the present invention is not particularly limited. However, the hot-rolled steel sheet according to an aspect of the present invention has excellent strength and processability, and thus can effectively contribute to securing economical and lightweight properties of the final product through thinning. Accordingly, the thickness of the hot-rolled steel sheet according to an aspect of the present invention may be 1.8 mm or less, and a more preferable thickness may be 1.5 mm or less.
이하, 본 발명의 제조방법에 대해 보다 상세히 설명한다.Hereinafter, the manufacturing method of the present invention will be described in more detail.
본 발명의 일 측면에 따른 구멍확장성이 우수한 고강도 열연강판의 제조방법은, 전술한 강 조성으로 구비되는 슬라브를 재가열하는 단계; 상기 재가열된 슬라브를 열간압연하여 열연강판을 제공하는 단계; 상기 열간압연의 종료시점으로부터 5초 이내에 상기 열연강판의 냉각을 개시하되, 50~1000℃/s의 냉각속도로 350℃ 이하의 냉각 종료 온도까지 상기 열연강판을 냉각하는 단계; 및 상기 냉각된 열연강판을 권취하는 단계;를 포함할 수 있다.Method for manufacturing a high-strength hot-rolled steel sheet having excellent hole expandability according to an aspect of the present invention comprises the steps of reheating a slab provided with the above-mentioned steel composition; Hot rolling the reheated slab to provide a hot rolled steel sheet; Cooling the hot rolled steel sheet within 5 seconds from the end point of the hot rolling, and cooling the hot rolled steel sheet to a cooling end temperature of 350° C. or less at a cooling rate of 50 to 1000° C./s; And winding the cooled hot rolled steel sheet.
슬라브 재가열 및 열간압연Slab reheating and hot rolling
본 발명의 슬라브 강 조성은 전술한 열연강판의 강 조성과 대응하므로, 본 발명의 슬라브 강 조성에 대한 설명은 전술한 열연강판 강 조성에 대한 설명으로 대신한다.Since the slab steel composition of the present invention corresponds to the steel composition of the hot-rolled steel sheet described above, the description of the slab steel composition of the present invention is replaced by the description of the hot-rolled steel sheet composition.
통상의 슬라브 제조 공정에 의해 제조된 슬라브는 일정 온도범위에서 재가열될 수 있다. 충분한 균질화 처리를 위해 재가열 온도 하한을 1,050℃로 제한할 수 있으며, 경제성 및 표면 품질을 고려하여 재가열 온도의 상한을 1,350℃로 제한할 수 있다.Slabs manufactured by a conventional slab manufacturing process can be reheated in a certain temperature range. The lower limit of the reheating temperature may be limited to 1,050°C for sufficient homogenization treatment, and the upper limit of the reheating temperature may be limited to 1,350°C in consideration of economic efficiency and surface quality.
재가열된 슬라브는 열갑안연에 의해 1.8mm 이하의 두께, 바람직하게는 1.5mm 이하의 두께로 마무리 압연될 수 있다. 본 발명은 열간압연은 통상의 조건에 의해 수행될 수 있으나, 압연하중 제어 및 표면 스케일 저감을 위한 마무리 압연 온도는 800~950℃의 범위일 수 있다. 또한, 본 발명은 열간압연에 의해 얇은 두께의 열연강판을 제조하고자 하므로, 선행재와 후행재를 분리하지 않고 연속적으로 압연하는 연속압연이 열연강판의 두께 확보 측면에서 보다 바람직하다. The reheated slab may be finished rolled to a thickness of 1.8 mm or less, preferably 1.5 mm or less, by hot-rolling. In the present invention, hot rolling may be performed under normal conditions, but the finish rolling temperature for controlling the rolling load and reducing the surface scale may range from 800 to 950°C. In addition, since the present invention intends to manufacture a hot-rolled steel sheet having a thin thickness by hot rolling, continuous rolling without continuously separating the preceding material and the trailing material is more preferable in terms of securing the thickness of the hot-rolled steel sheet.
냉각Cooling
열간압연 직후의 열연강판에 대해 급랭 조건의 냉각이 실시될 수 있다. Cooling in the quench condition may be performed on the hot-rolled steel sheet immediately after hot rolling.
본 발명은 열연강판의 미세조직을 엄격히 제어하고자 하는바, 본 발명의 냉각은 열간압연 직후 5초 이내에 개시되는 것이 바람직하다. 열간압연 후 냉각 개시 시점까지의 시간이 5초를 초과하는 경우, 대기 중에서의 공랭에 의해 본 발명이 의도하지 않는 페라이트, 펄라이트 및 베이나이트가 형성될 수 있기 때문이다. 열간압연 후 냉각 개시 시점까지의 보다 바람직한 시간은 3초 이내일 수 있다.The present invention is intended to strictly control the microstructure of the hot-rolled steel sheet, and the cooling of the present invention is preferably initiated within 5 seconds immediately after hot rolling. This is because ferrite, pearlite, and bainite, which the present invention does not intend, may be formed by air cooling in the air when the time from the hot rolling to the start of cooling exceeds 5 seconds. A more preferable time from the hot rolling to the start of cooling may be within 3 seconds.
또한, 열간압연 직후의 열연강판은 50~1,000℃/s의 냉각속도로 350℃ 이하의 냉각 종료 온도까지 냉각될 수 있다. 냉각속도가 50℃/s 미만인 경우, 냉각 중 페라이트, 펄라이트 및 베이나이트로의 변태가 일어나게 되므로, 본 발명이 목적하는 미세조직을 확보할 수 없는 문제점이 존재한다. 본 발명은 목적하는 미세조직 확보를 위해 냉각속도의 상한을 특별히 한정하지 않으나, 설비 한계 및 경제성을 고려하여 냉각속도의 상한을 1,000℃/s로 제한할 수 있다. 또한, 냉각 종료 온도가 350℃를 초과하는 경우 역시, 페라이트, 펄라이트 및 베이나이트로의 변태가 불가피하므로, 본 발명이 목적하는 미세조직을 확보할 수 없는 문제점이 존재한다.In addition, the hot-rolled steel sheet immediately after hot rolling may be cooled to a cooling end temperature of 350°C or less at a cooling rate of 50 to 1,000°C/s. If the cooling rate is less than 50 ℃ / s, ferrite, pearlite, and transformation into bainite occurs during cooling, and thus there is a problem that the present invention cannot secure the desired microstructure. In the present invention, the upper limit of the cooling rate is not particularly limited in order to secure the desired microstructure, but the upper limit of the cooling rate may be limited to 1,000°C/s in consideration of facility limitations and economics. In addition, when the cooling end temperature exceeds 350°C, transformation into ferrite, pearlite, and bainite is unavoidable, and thus there is a problem that the microstructure desired by the present invention cannot be secured.
이상의 제조방법에 의해 제조된 열연강판은, 1,250MPa 이상의 인장강도(TS) 및 20% 이상의 구멍확장성(HER)을 확보하며, 인장강도(TS)와 구멍확장성(HER)의 곱이 30,000MPa% 이상의 수준으로 강도 및 가공성이 효과적으로 양립될 수 있다.The hot-rolled steel sheet manufactured by the above manufacturing method secures a tensile strength (TS) of 1,250 MPa or more and a hole expandability (HER) of 20% or more, and a product of tensile strength (TS) and hole expandability (HER) is 30,000 MPa%. To the above level, strength and processability can be effectively compatible.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다. 하기의 실시예는 본 발명을 예시하여 보다 상세하게 설명하기 위한 것일 뿐, 본 발명의 권리범위를 한정하기 위한 것이 아니라는 점에 유의할 필요가 있다. 본 발명의 권리범위는 특허청구범위에 기재된 사항과 이로부터 합리적으로 유추되는 사항에 의해 결정되는 것이기 때문이다.Hereinafter, the present invention will be described in more detail through examples. It should be noted that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the items described in the claims and the items reasonably inferred therefrom.
(실시예)(Example)
하기 표 1의 조성을 가지는 슬라브를 제조한 후 하기 표 2의 조건을 이용하여 열연강판 시편을 제조하였다. 각각의 슬라브는 통상의 제조방법에 의해 제조되었으며, 1,050~1,350℃의 온도범위에서 재가열되어 균질화 처리되었다. After preparing a slab having the composition of Table 1, a hot-rolled steel sheet specimen was prepared using the conditions of Table 2 below. Each slab was manufactured by a conventional manufacturing method, and was re-heated in a temperature range of 1,050 to 1,350°C to be homogenized.
강종Steel CC MnMn SiSi PP SS CrCr TiTi BB
AA 0.2160.216 1.011.01 0.040.04 0.0070.007 0.0030.003 0.020.02 0.01800.0180 0.00200.0020
BB 0.1350.135 1.221.22 0.060.06 0.0120.012 0.0030.003 0.040.04 0.02000.0200 0.00220.0022
CC 0.1510.151 0.990.99 0.030.03 0.0160.016 0.0010.001 0.050.05 0.01800.0180 0.00210.0021
DD 0.2440.244 1.061.06 0.070.07 0.0130.013 0.0020.002 0.040.04 0.01900.0190 0.00200.0020
EE 0.2210.221 2.012.01 0.030.03 0.0150.015 0.0010.001 0.030.03 0.02000.0200 0.00190.0019
FF 0.2110.211 1.091.09 0.050.05 0.0070.007 0.0100.010 0.050.05 0.11000.1100 0.00210.0021
GG 0.2180.218 0.960.96 0.040.04 0.0060.006 0.0090.009 0.020.02 0.02000.0200 0.00200.0020
HH 0.0900.090 0.980.98 0.040.04 0.0070.007 0.0070.007 0.020.02 0.02100.0210 0.00180.0018
II 0.2210.221 1.011.01 0.070.07 0.0120.012 0.0010.001 0.030.03 0.02000.0200 0.00030.0003
JJ 0.1640.164 3.143.14 0.080.08 0.0110.011 0.0040.004 0.040.04 0.02100.0210 0.00190.0019
KK 0.2260.226 0.960.96 0.650.65 0.0090.009 0.0040.004 0.040.04 0.01900.0190 0.00180.0018
LL 0.2190.219 0.990.99 0.070.07 0.0220.022 0.0050.005 0.020.02 0.02200.0220 0.00180.0018
MM 0.2160.216 1.021.02 0.060.06 0.0130.013 0.0140.014 0.050.05 0.02200.0220 0.00220.0022
구분division 강종Steel 마무리압연 종료 온도(℃)Finish rolling end temperature (℃) 열연강판두께 (mm)Hot rolled steel sheet thickness (mm) 압연 종료 후 냉각 개시 시간 (sec)Cooling start time after rolling finish (sec) 냉각속도(℃/sec)Cooling rate (℃/sec) 냉각 종료 온도(℃)Cooling end temperature (℃)
1One AA 860860 1.41.4 1.21.2 100100 236236
22 AA 874874 1.41.4 1.51.5 200200 208208
33 AA 893893 1.41.4 0.90.9 300300 204204
44 AA 919919 1.41.4 0.80.8 100100 289289
55 AA 885885 1.21.2 2.62.6 100100 140140
66 BB 916916 1.41.4 1.21.2 100100 246246
77 CC 860860 1.41.4 1.11.1 100100 181181
88 DD 861861 1.41.4 0.50.5 100100 135135
99 EE 880880 1.41.4 0.80.8 100100 155155
1010 FF 897897 1.41.4 1.11.1 100100 245245
1111 GG 897897 1.41.4 1.71.7 100100 118118
1212 AA 884884 1.41.4 5.75.7 100100 129129
1313 AA 873873 1.41.4 1.01.0 3030 202202
1414 AA 882882 1.41.4 1.41.4 100100 413413
1515 HH 903903 1.41.4 0.50.5 100100 220220
1616 II 908908 1.41.4 1.61.6 100100 148148
1717 JJ 899899 1.41.4 1.61.6 100100 106106
1818 KK 903903 1.41.4 1.81.8 100100 225225
1919 LL 903903 1.41.4 1.91.9 100100 218218
2020 MM 903903 1.41.4 1.41.4 100100 165165
표 2의 조건으로 제조된 각 시편에 대해 미세조직 및 기계적 물성을 측정하여 표 3에 나타내었다. 미세조직은 광학현미경 및 주사전자현미경을 이용하여 측정한 후, 이미지 분석을 통해 평가하였다. 기계적 물성 중 인상강도는 DIN 규격을 이용하여 C 방향으로 인장시험을 실시하여 평가하였다. 기계적 물성 중 구멍확장성(HER)은 JFST 1001-1996 규격으로 평가하였으며, 각 시편에 홀(hole)을 가공한 후 펀치로 밀어올려 파단이 날 때까지의 구멍확장성을 측정하였다. It was shown in Table 3 by measuring the microstructure and mechanical properties for each specimen prepared under the conditions of Table 2. The microstructure was measured using an optical microscope and a scanning electron microscope, and then evaluated through image analysis. The impression strength among mechanical properties was evaluated by performing a tensile test in the C direction using DIN standards. Among the mechanical properties, hole expandability (HER) was evaluated according to the JFST 1001-1996 standard, and after each hole was processed in a specimen, it was pushed up with a punch to measure the hole expandability until fracture occurred.
구분division 강종Steel 마르텐사이트분율(부피%)Martensite fraction (% by volume) 인장강도 (TS, MPa)Tensile strength (TS, MPa) 구멍확장성 (HER, %)Hole expandability (HER, %) 인장강도*구멍확장성(MPa%)Tensile strength * hole expandability (MPa%)
1One AA 9898 16101610 3232 5152051520
22 AA 9797 16191619 2525 4047540475
33 AA 9898 15201520 4040 6080060800
44 AA 9696 16211621 3535 5673556735
55 AA 9797 16241624 2727 4384843848
66 BB 9696 12871287 3333 4247142471
77 CC 9696 13831383 3030 4149041490
88 DD 9696 16741674 2626 4352443524
99 EE 9797 16221622 2626 4217242172
1010 FF 9898 16481648 3535 5768057680
1111 GG 9696 15571557 3838 5916659166
1212 AA 6262 12111211 2020 2422024220
1313 AA 7171 11841184 3333 3907239072
1414 AA 6666 12961296 1919 2462424624
1515 HH 4242 949949 4040 3796037960
1616 II 4848 11311131 3838 4297842978
1717 JJ 8888 13151315 2222 2893028930
1818 KK 9797 16021602 1717 2723427234
1919 LL 9898 15431543 1919 2931729317
2020 MM 9696 15691569 1818 2824228242
본 발명의 합금조성 및 제조조건을 모두 만족하는 시편 1 내지 시편 11의 경우, 95부피% 이상의 마르텐사이트의 분율 및 30,000MPa% 이상의 인장강도(TS)와 구멍확장성(HER)의 곱을 모두 만족하는 것을 확인할 수 있다. 또한, 시편 1 내지 시편 11의 경우 1,250MPa 이상의 인장강도 및 20% 이상의 구멍확장성(HER)을 모두 만족함을 확인할 수 있다.In the case of Specimen 1 to Specimen 11 satisfying both the alloy composition and manufacturing conditions of the present invention, both the fraction of martensite of at least 95% by volume and the product of tensile strength (TS) and hole expandability (HER) of at least 30,000 MPa% are satisfied. You can confirm that. In addition, it can be seen that the specimens 1 to 11 satisfy both the tensile strength of 1,250 MPa or more and the hole expandability (HER) of 20% or more.
반면, 본 발명의 합금조성 및 제조조건 중 어느 하나 이상을 만족하지 않는 시편 12 내지 20의 경우, 마르텐사이트의 분율이 95부피% 미만이거나, 인장강도(TS)와 구멍확장성(HER)의 곱이 30,000MPa% 미만인 것을 확인할 수 있다.On the other hand, in the case of specimens 12 to 20 that do not satisfy any one or more of the alloy composition and manufacturing conditions of the present invention, the fraction of martensite is less than 95% by volume, or the product of tensile strength (TS) and hole expandability (HER) It can be confirmed that it is less than 30,000 MPa%.
구체적으로, 시편 12는 압연 종료 후 냉각 개시까지의 시간이 5초를 초과는 경우로, 본 발명이 목적하는 마르텐사이트 분율을 확보하지 못하며, 인장강도가 열위한 것을 확인할 수 있다.Specifically, the specimen 12 is a case in which the time from the end of rolling to the start of cooling exceeds 5 seconds, it is not possible to secure the desired martensite fraction and the tensile strength is poor.
시편 13은 냉각속도가 낮은 경우이고, 시편 14는 냉각 종료 온도가 높은 경우로, 마르텐사이트로의 변태가 충분히 일어나지 않았으며, 본 발명이 목적하는 인장강도 혹은 구멍확장성(HER)을 확보하지 못한 것을 확인할 수 있다.The specimen 13 is a case where the cooling rate is low, the specimen 14 is a case where the cooling end temperature is high, transformation to martensite has not occurred sufficiently, and the desired tensile strength or hole expandability (HER) of the present invention is not secured. You can confirm that.
시편 15는 탄소(C)의 함량이 낮은 경우이고, 시편 16은 보론(B)의 함량이 낮은 경우로, 마르텐사이트 분율이 50부피%에도 미치지 못한 수준으로 인장강도가 열위하게 나타나는 것을 확인할 수 있다.Specimen 15 is a case where the content of carbon (C) is low, and specimen 16 is a case where the content of boron (B) is low, indicating that the martensitic fraction is less than 50% by volume and the tensile strength is inferior. .
시편 17은 망간(Mn)의 함량이 높은 경우로, 마르텐사이트로의 변태가 충분히 일어나지 않아 잔류 오스테나이트가 형성되었으며, 인장강도는 우수한 반면 구멍확장성(HER)이 열위한 것을 확인할 수 있다.Specimen 17 is a case where the content of manganese (Mn) is high, it can be confirmed that the transformation to martensite does not occur sufficiently, and thus retained austenite is formed, and the tensile strength is excellent while the hole expandability (HER) is poor.
시편 18은 내지 시편 20은 각각 실리콘(Si), 인(P) 및 황(S)의 함량이 높은 경우로, 인장강도는 높은 반면 구멍확장성(HER)이 열위한 것을 확인할 수 있다.Specimen 18 to 20 is a case where the content of silicon (Si), phosphorus (P), and sulfur (S) is high, respectively, and the tensile strength is high, but it can be confirmed that the hole expandability (HER) is poor.
따라서, 본 발명의 일 측면에 따른 열연강판은 1,250MPa 이상의 인장강도(TS) 및 20% 이상의 구멍확장성(HER)을 만족하며, 특히, 인장강도(TS)와 구멍확장성(HER)의 곱이 30,000MPa% 이상의 수준으로 강도 및 가공성이 효과적으로 양립된 것을 확인할 수 있다. Therefore, the hot-rolled steel sheet according to one aspect of the present invention satisfies the tensile strength (TS) of 1,250 MPa or more and the hole expandability (HER) of 20% or more, in particular, the product of the tensile strength (TS) and the hole expandability (HER) It can be seen that the strength and workability are effectively compatible at a level of 30,000 MPa% or more.
이상에서 실시예를 통하여 본 발명을 상세하게 설명하였으나, 이와 다른 형태의 실시예들도 가능하다. 그러므로, 이하에 기재된 청구항들의 기술적 사상과 범위는 실시예들에 한정되지 않는다.Although the present invention has been described in detail through the above embodiments, other types of embodiments are possible. Therefore, the technical spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (8)

  1. 중량%로, 탄소(C): 0.12% 이상 0.30% 미만, 망간(Mn): 0.1~2.5%, 실리콘(Si): 0.5% 이하(0% 제외), 보론(B): 0.0005~0.005%, 인(P) 0.02% 이하, 황(S): 0.01% 이하, 나머지 철(Fe) 및 불가피한 불순물을 포함하고, In weight percent, carbon (C): 0.12% or more but less than 0.30%, manganese (Mn): 0.1 to 2.5%, silicon (Si): 0.5% or less (excluding 0%), boron (B): 0.0005 to 0.005%, Phosphorus (P) 0.02% or less, sulfur (S): 0.01% or less, including the remaining iron (Fe) and inevitable impurities,
    95부피% 이상의 마르텐사이트를 미세조직으로 포함하고,Contains at least 95% by volume of martensite as a microstructure,
    인장강도(TS)와 구멍확장성(HER)의 곱이 30,000MPa% 이상인, 구멍확장성이 우수한 고강도 열연강판.High-strength hot-rolled steel sheet with excellent hole expandability, where the product of tensile strength (TS) and hole expandability (HER) is 30,000 MPa% or more.
  2. 제1항에 있어서,According to claim 1,
    상기 열연강판은, 중량%로, 크롬(Cr): 0.5% 이하 및 티타늄(Ti): 0.005~0.2% 중 1종 이상을 더 포함하는, 구멍확장성이 우수한 고강도 열연강판.The hot-rolled steel sheet, by weight, chromium (Cr): 0.5% or less and titanium (Ti): 0.005 ~ 0.2% further comprising at least one of the high-strength hot-rolled steel sheet excellent in hole expandability.
  3. 제1항에 있어서,According to claim 1,
    상기 미세조직은, 페라이트, 베이나이트, 탄화물 및 잔류오스테나이트 중 1종 이상을 합계 5부피% 이하로 포함하는, 구멍확장성이 우수한 고강도 열연강판.The microstructure, high-strength hot-rolled steel sheet excellent in hole expandability, containing at least one of ferrite, bainite, carbide and residual austenite in a total of 5% by volume or less.
  4. 제1항에 있어서,According to claim 1,
    상기 열연강판의 인장강도(TS)는 1,250MPa 이상인, 구멍확장성이 우수한 고강도 열연강판. Tensile strength (TS) of the hot-rolled steel sheet is 1,250MPa or more, high-strength hot-rolled steel sheet excellent in hole expandability.
  5. 제1항에 있어서,According to claim 1,
    상기 열연강판의 구멍확장성(HER)은 20% 이상인, 구멍확장성이 우수한 고강도 열연강판.The hot-rolled steel sheet has a hole expandability (HER) of 20% or more, and a high-strength hot-rolled steel sheet having excellent hole expandability.
  6. 제1항에 있어서,According to claim 1,
    상기 열연강판의 두께는 1.5mm 이하인, 구멍확장성이 우수한 고강도 열연강판.The thickness of the hot-rolled steel sheet is 1.5mm or less, high-strength hot-rolled steel sheet excellent in hole expandability.
  7. 중량%로, 탄소(C): 0.12% 이상 0.30% 미만, 망간(Mn): 0.1~2.5%, 실리콘(Si): 0.5% 이하(0% 제외), 보론(B): 0.0005~0.005%, 인(P) 0.02% 이하, 황(S): 0.01% 이하, 나머지 철(Fe) 및 불가피한 불순물을 포함하는 슬라브를 재가열하는 단계;In weight percent, carbon (C): 0.12% or more but less than 0.30%, manganese (Mn): 0.1 to 2.5%, silicon (Si): 0.5% or less (excluding 0%), boron (B): 0.0005 to 0.005%, Reheating the slab containing phosphorus (P) 0.02% or less, sulfur (S): 0.01% or less, and the remaining iron (Fe) and inevitable impurities;
    상기 재가열된 슬라브를 열간압연하여 열연강판을 제공하는 단계; Hot rolling the reheated slab to provide a hot rolled steel sheet;
    상기 열간압연의 종료시점으로부터 5초 이내에 상기 열연강판의 냉각을 개시하되, 50~1,000℃/s의 냉각속도로 350℃ 이하의 냉각 종료 온도까지 상기 열연강판을 냉각하는 단계; 및Cooling the hot rolled steel sheet within 5 seconds from the end point of the hot rolling, and cooling the hot rolled steel sheet to a cooling end temperature of 350° C. or less at a cooling rate of 50 to 1,000° C./s; And
    상기 냉각된 열연강판을 권취하는 단계;를 포함하는, 구멍확장성이 우수한 고강도 열연강판의 제조방법. Winding the cooled hot-rolled steel sheet; including, method for manufacturing a high-strength hot-rolled steel sheet having excellent hole expandability.
  8. 제7항에 있어서,The method of claim 7,
    상기 슬라브는, 중량%로, 크롬(Cr): 0.5% 이하 및 티타늄(Ti): 0.005~0.2% 중 1종 이상을 더 포함하는, 구멍확장성이 우수한 고강도 열연강판의 제조방법.The slab, by weight, chromium (Cr): 0.5% or less and titanium (Ti): 0.005 ~ 0.2% further comprises at least one of the high-strength hot-rolled steel sheet manufacturing method excellent in hole expandability.
PCT/KR2019/017979 2018-12-19 2019-12-18 High strength hot-rolled steel sheet having excellent hole expansion ratio and manufacturing method for same WO2020130614A2 (en)

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US17/414,743 US20220074007A1 (en) 2018-12-19 2019-12-18 High strength hot-rolled steel sheet having excellent hole expansion ratio and manufacturing method for same
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1396549A1 (en) 2002-08-28 2004-03-10 ThyssenKrupp Stahl AG Process for manufacturing hot rolled pearlite-free steel strip and hot strip obtained thereby
US20050155673A1 (en) 2004-01-21 2005-07-21 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) High strength hot rolled steel sheet superior in workability, fatigue property, and surface quality
JP2005298967A (en) 2004-03-18 2005-10-27 Jfe Steel Kk Hot rolled steel sheet having excellent working hardenability and method for producing the same
KR20050113247A (en) 2003-03-24 2005-12-01 신닛뽄세이테쯔 카부시키카이샤 High strength hot rolled steel sheet excelling in bore expandability and ductility and process for producing the same

Family Cites Families (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07197186A (en) * 1993-12-30 1995-08-01 Kobe Steel Ltd Hot-rolled steel sheet having >=980n/mm2 strength represented by excellent delayed fracture resistant characteristic and its production
EP0910675B1 (en) * 1996-07-12 2004-10-06 ThyssenKrupp Stahl AG Hot-rolled steel strip and method of making it
JP3915460B2 (en) * 2001-09-26 2007-05-16 Ｊｆｅスチール株式会社 High strength hot rolled steel sheet and method for producing the same
CN100590217C (en) * 2005-03-31 2010-02-17 杰富意钢铁株式会社 Hot-rolled steel sheet, method for production thereof and molded article formed from hot-rolled steel sheet
JP5195413B2 (en) 2008-12-26 2013-05-08 新日鐵住金株式会社 High-strength hot-rolled steel sheet excellent in bending workability and toughness anisotropy and method for producing the same
WO2013065346A1 (en) * 2011-11-01 2013-05-10 Ｊｆｅスチール株式会社 High-strength hot-rolled steel sheet having excellent bending characteristics and low-temperature toughness and method for producing same
KR101412272B1 (en) * 2012-03-29 2014-06-25 현대제철 주식회사 Method of manufacturing high strength steel sheet
JP6136478B2 (en) 2013-04-02 2017-05-31 新日鐵住金株式会社 High-strength hot-rolled steel sheet excellent in toughness and rigidity in the rolling direction and method for producing the same
KR101546134B1 (en) * 2013-07-30 2015-08-21 현대제철 주식회사 High strength hot-rolled steel sheet and method of manufacturing the same
KR20150075307A (en) * 2013-12-25 2015-07-03 주식회사 포스코 Ultra-high strength hot-rolled steel sheet with solid diffusion bonding properties, and method for producing the same
CN105849295B (en) * 2013-12-26 2019-02-19 Posco公司 Weldability and the excellent hot rolled steel plate and preparation method thereof of deburring
WO2016182098A1 (en) * 2015-05-12 2016-11-17 주식회사 포스코 Ultra-high strength hot-rolled steel sheet having excellent bending workability and method for manufacturing same
JP6519016B2 (en) * 2015-09-17 2019-05-29 日本製鉄株式会社 Hot rolled steel sheet and method of manufacturing the same
KR101677396B1 (en) * 2015-11-02 2016-11-18 주식회사 포스코 Ultra high strength steel sheet having excellent formability and expandability, and method for manufacturing the same
JP6292353B2 (en) 2016-03-31 2018-03-14 Ｊｆｅスチール株式会社 Thin steel plate and plated steel plate, method for producing thin steel plate, and method for producing plated steel plate
KR101797387B1 (en) * 2016-08-31 2017-11-14 주식회사 포스코 Ultra high strength thin hot-rolled steel sheet having excellent formability and method for manufacturing same
CN110100030B (en) * 2016-12-23 2021-04-20 Posco公司 Ultrahigh-strength hot-rolled steel sheet having excellent bending workability and method for producing same

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1396549A1 (en) 2002-08-28 2004-03-10 ThyssenKrupp Stahl AG Process for manufacturing hot rolled pearlite-free steel strip and hot strip obtained thereby
KR20050113247A (en) 2003-03-24 2005-12-01 신닛뽄세이테쯔 카부시키카이샤 High strength hot rolled steel sheet excelling in bore expandability and ductility and process for producing the same
US20050155673A1 (en) 2004-01-21 2005-07-21 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) High strength hot rolled steel sheet superior in workability, fatigue property, and surface quality
JP2005298967A (en) 2004-03-18 2005-10-27 Jfe Steel Kk Hot rolled steel sheet having excellent working hardenability and method for producing the same

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP3901307A4

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