WO2023018101A1 - Acier pare-balles à dureté élevée ayant une excellente résistance à basse température, et son procédé de production - Google Patents

Acier pare-balles à dureté élevée ayant une excellente résistance à basse température, et son procédé de production Download PDF

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WO2023018101A1
WO2023018101A1 PCT/KR2022/011499 KR2022011499W WO2023018101A1 WO 2023018101 A1 WO2023018101 A1 WO 2023018101A1 KR 2022011499 W KR2022011499 W KR 2022011499W WO 2023018101 A1 WO2023018101 A1 WO 2023018101A1
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hardness
steel
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김용우
조현관
변영섭
조남영
김인호
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Posco Holdings Inc
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    • 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
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/22—Martempering
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • 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
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/02—Hardening by precipitation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys 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
    • C21D9/42—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for armour plate
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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 high-hardness bulletproof steel with excellent low-temperature toughness and a manufacturing method thereof. More specifically, it relates to high-hardness bulletproof steel with excellent low-temperature toughness that can be preferably used for armored vehicles, explosion-proof structures, and the like, and a manufacturing method thereof.
  • Patent Document 1 relates to steel materials used for crushing of industrial waste and wear parts of grinders, and seeks to secure surface hardness by actively utilizing Nb together with a large amount of Cr and Mo, but it is difficult to secure low-temperature toughness due to excessive content. There are limits.
  • Patent Document 2 is a technique for securing high hardness by causing the retained austenite structure to cause plastic-induced machining hardening after forming the steel or when the steel is applied to a product and in use, or in the case of bulletproof steel, deformation / impact by bullets The speed is very high, and it is difficult to obtain the effect by the above phenomenon.
  • Patent Document 1 Japanese Unexamined Patent Publication No. 10-102185
  • Patent Document 2 Japanese Unexamined Patent Publication No. 07-173571
  • One aspect of the present invention is to provide a high-hardness bulletproof steel with excellent low-temperature toughness and a manufacturing method thereof.
  • carbon (C) 0.28 ⁇ 0.32%, silicon (Si): 0.5% or less (excluding 0%), manganese (Mn): 0.2 ⁇ 1.1%, nickel (Ni) : 0.7 ⁇ 1.2%, Chromium (Cr): 0.2 ⁇ 1.1%, Phosphorus (P): 0.03% or less (excluding 0%), Sulfur (S): 0.015% or less (excluding 0%), Nitrogen (N) : 0.006% or less (excluding 0%), Aluminum (Al): 0.05% or less (excluding 0%), Molybdenum (Mo): 0.2 to 1.0%, Vanadium (V): 0.02 to 0.5%, Calcium (Ca) : 0.0005 to 0.004%, the balance includes Fe and other unavoidable impurities, and the unavoidable impurities include Nb: 0.0015% or less and B: 0.0008% or less, satisfy the following relational expression 1, in area%, tempered martensite contains a micro
  • carbon (C) 0.28 to 0.32%, silicon (Si): 0.5% or less (excluding 0%), manganese (Mn): 0.2 to 1.1%, nickel (Ni) : 0.7 ⁇ 1.2%, Chromium (Cr): 0.2 ⁇ 1.1%, Phosphorus (P): 0.03% or less (excluding 0%), Sulfur (S): 0.015% or less (excluding 0%), Nitrogen (N) : 0.006% or less (excluding 0%), Aluminum (Al): 0.05% or less (excluding 0%), Molybdenum (Mo): 0.2 to 1.0%, Vanadium (V): 0.02 to 0.5%, Calcium (Ca) : 0.0005 to 0.004%, the balance includes Fe and other unavoidable impurities, and the unavoidable impurities include Nb: 0.0015% or less and B: 0.0008% or less, heating a slab satisfying the following relational expression 1 at 1050 to 1250 ° C.
  • step; Obtaining a bar by rough rolling the heated slab at 950 to 1150 ° C; After finishing hot rolling the bar at 850 ⁇ 950 °C to obtain a hot-rolled steel sheet, cooling to room temperature;
  • T max is 112.5[C]-5.7[Mn]+18.8[Cr]-1.3[Ni]+114.3[V]+169.4[Mo]+200, and in the above relational expression 1 and T max The content of each element means % by weight.
  • Carbon (C) is effective in improving strength and hardness in steel having a low-temperature transformation phase such as martensite or bainite, and is an element effective in improving hardenability.
  • the content of C is preferably in the range of 0.28 to 0.32%.
  • the lower limit of the C content is more preferably 0.29%.
  • the upper limit of the C content is more preferably 0.31%.
  • Silicon (Si) is an effective element for improving hardness due to solid solution strengthening along with a deoxidation effect, and is particularly advantageous for securing low-temperature toughness by suppressing the formation of coarse cementite in tempered martensite.
  • the content of Si is limited to 0.5% or less.
  • the Si content is more preferably 0.48% or less, even more preferably 0.45% or less, and most preferably 0.4% or less.
  • Manganese (Mn) is an element advantageous for securing hardness by improving hardenability of steel, suppressing the formation of ferrite and promoting the formation of martensite. If the content is less than 0.2%, it is difficult to obtain the above-mentioned effects, and if it exceeds 1.1%, the weldability of the steel is deteriorated and center segregation is promoted, so there is a risk of lowering the toughness of the center of the steel. Therefore, the Mn content is preferably in the range of 0.2 to 1.1%. The lower limit of the Mn content is more preferably 0.22%, even more preferably 0.25%, and most preferably 0.3%. The upper limit of the Mn content is more preferably 1.08%, even more preferably 1.05%, and most preferably 1.0%.
  • Nickel (Ni) is an advantageous element for simultaneously improving the strength and toughness of steel. If the content is less than 0.7%, it is difficult to obtain the above-mentioned effect, and if it exceeds 1.2%, since Ni is an expensive element, economic efficiency may be reduced and weldability may be deteriorated. Therefore, the Ni content is preferably in the range of 0.7 to 1.2%. The lower limit of the Ni content is more preferably 0.72%, even more preferably 0.75%, and most preferably 0.8%. The upper limit of the Ni content is more preferably 1.18%, even more preferably 1.15%, and most preferably 1.1%.
  • Chromium (Cr) is an element that improves strength by increasing hardenability of steel and effectively contributes to securing the hardness of the surface and center of steel. In addition, since it is a relatively inexpensive element, it is also an element that can secure hardness and toughness economically. If the content is less than 0.2%, it is difficult to obtain the above-mentioned effect, and if it exceeds 1.1%, weldability may be deteriorated. Therefore, the Cr content is preferably in the range of 0.2 to 1.1%. The lower limit of the Cr content is more preferably 0.22%, even more preferably 0.25%, and most preferably 0.3%. The upper limit of the Cr content is more preferably 1.08%, more preferably 1.05%, and most preferably 1.0%.
  • Phosphorus (P) is an impurity that is unavoidably contained, and since it inhibits the weldability of steel and is a major cause of increasing brittleness by segregating at grain boundaries, it is desirable to control its content as low as possible. Theoretically, it is advantageous to limit the content of P to 0%, but it is inevitably contained in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the P content is limited to 0.03% or less. The P content is more preferably 0.025% or less, even more preferably 0.02% or less, and most preferably 0.015% or less.
  • S is an impurity that is unavoidably contained like the phosphorus (P), and it is preferable to suppress the content as much as possible because it combines with Mn and the like to form non-metallic inclusions, thereby greatly reducing the toughness of steel.
  • P phosphorus
  • S is an impurity that is unavoidably contained like the phosphorus (P)
  • S Sulfur
  • the S content is more preferably 0.01% or less, even more preferably 0.008% or less, and most preferably 0.006% or less.
  • N Nitrogen
  • P phosphorus
  • N contributes somewhat to securing the hardness of the steel, but it is difficult to control, and like phosphorus (P), it is segregated at the grain boundary and serves to increase the brittleness of the steel.
  • N content is limited to 0.006% or less.
  • the N content is more preferably 0.0058% or less, even more preferably 0.0055% or less, and most preferably 0.005% or less.
  • Aluminum (Al) is an element added for deoxidation of molten steel. However, if the content exceeds 0.05%, it may be advantageous to increase strength by grain refinement, but there is a problem of causing nozzle clogging during steelmaking or continuous casting. Therefore, in the present invention, the Al content is limited to 0.05% or less.
  • the Al content is more preferably 0.048% or less, even more preferably 0.045% or less, and most preferably 0.04% or less.
  • Molybdenum (Mo) increases the hardenability of steel, and is particularly advantageous for improving low-temperature toughness. If the content is less than 0.2%, it is difficult to obtain the above-mentioned effects, and if it exceeds 1.0%, manufacturing costs may increase as well as poor weldability. Therefore, the Mo content is preferably in the range of 0.2 to 1.0%.
  • the lower limit of the Mo content is more preferably 0.22%, even more preferably 0.25%, and most preferably 0.3%.
  • the upper limit of the Mo content is more preferably 0.98%, more preferably 0.95%, and most preferably 0.9%.
  • Vanadium (V) is an element advantageous for securing hardness and toughness by suppressing the growth of austenite crystal grains by forming VC carbide during reheating after hot rolling and improving hardenability of steel. If the content is less than 0.02%, it is difficult to obtain the above-mentioned effect, and if it exceeds 0.5%, since V is an expensive element, economic efficiency may be reduced and toughness may also be deteriorated. Therefore, the content of V is preferably in the range of 0.02 to 0.5%.
  • the lower limit of the V content is more preferably 0.022%, even more preferably 0.025%, and most preferably 0.03%.
  • the upper limit of the V content is more preferably 0.48%, even more preferably 0.45%, and most preferably 0.4%.
  • Ca has a good binding force with sulfur (S), so it generates CaS around (circumference) MnS to suppress elongation of MnS and is an advantageous element for improving toughness in a direction perpendicular to the rolling direction.
  • CaS produced by the addition of calcium (Ca) can increase resistance to corrosion in a humid external environment. If the content is less than 0.0005%, it is difficult to obtain the above-mentioned effects, and if it exceeds 0.004%, defects such as nozzle clogging may be caused during steelmaking operations. Therefore, the content of Ca is preferably in the range of 0.0005 to 0.004%.
  • the lower limit of the Ca content is more preferably 0.0006%, more preferably 0.0007%, and most preferably 0.0008%.
  • the upper limit of the Ca content is more preferably 0.0038%, more preferably 0.0035%, and most preferably 0.003%.
  • the remaining components of the present invention are iron (Fe).
  • Fe iron
  • the above impurities can be known to anyone skilled in the art, all of them are not specifically mentioned in the present invention.
  • the unavoidable impurities may include Nb: 0.0015% or less and B: 0.0008% or less.
  • the Nb may form coarse precipitates after the QT heat treatment to reduce low-temperature toughness, and if the B is non-uniformly segregated, it causes a difference in the phase transformation time in the quenching heat treatment process. may cause poor low-temperature toughness, and may cause shape defects. Therefore, in the present invention, low-temperature toughness can be improved by controlling the upper limit of the amount that can be included as an impurity without intentionally adding Nb and B.
  • the Nb content is more preferably 0.0012% or less, and even more preferably 0.001% or less.
  • the B content is more preferably 0.0006% or less, and even more preferably 0.0005% or less.
  • the bulletproof steel of the present invention preferably satisfies the above-described alloy composition and at the same time satisfies the following relational expression 1.
  • the following Relational Equation 1 is an equation derived in order to sufficiently obtain an effect of improving hardness, and when Relational Equation 1 is not satisfied, it is difficult to secure high hardness.
  • the value of the following relational expression 1 is more preferably 225 or more, more preferably 230 or more, and most preferably 235 or more.
  • the upper limit of the value of the relational expression 1 is not particularly limited. However, in terms of manufacturing cost, the upper limit of the value of Equation 1 below may be 600.
  • the upper limit of the value of the following relational expression 1 is more preferably 580, even more preferably 550, and most preferably 500.
  • the bulletproof steel of the present invention preferably includes a microstructure in which tempered martensite is 90% or more (including 100%) by area%.
  • the tempered martensite is a structure that is advantageous for securing excellent levels of hardness and low-temperature toughness at the same time.
  • the fraction of the tempered martensite is less than 90%, there may be some advantages in improving low-temperature toughness by the secondary phase, but it may be disadvantageous in securing hardness.
  • the secondary phase may be one or more of retained austenite, bainite, pearlite, and ferrite, and the fraction thereof is preferably 10 area% or less in total.
  • the fraction of the tempered martensite is more preferably 92% or more, even more preferably 94% or more, and most preferably 95% or more.
  • the average effective grain size of the tempered martensite is preferably 20 ⁇ m or less.
  • the low-temperature toughness can be improved to a more excellent level by minimizing the average effective grain size of the tempered martensite, and when the size exceeds 20 ⁇ m, it may be difficult to sufficiently obtain the above-described effect.
  • the average effective grain size of the tempered martensite is more preferably 18 ⁇ m or less, even more preferably 15 ⁇ m or less, and most preferably 12 ⁇ m or less.
  • the average effective grain size means the average size of grains having a grain boundary with a high angle of 15° or more.
  • the KAM of the tempered martensite is preferably 0.3 to 3.0.
  • the KAM is an index for estimating the dislocation density. It is interpreted that the higher the KAM, the higher the dislocation density. In the present invention, when the KAM is less than 0.3, it may be difficult to secure sufficient hardness due to low dislocation density, and when it exceeds 3.0, it may be difficult to secure low-temperature toughness.
  • the lower limit of the KAM is more preferably 0.4, even more preferably 0.45, and most preferably 0.5.
  • the upper limit of the KAM is more preferably 2.8, even more preferably 2.5, and most preferably 2.0.
  • V(C,N)-based precipitates are included in the grains of the tempered martensite, and the average size of the V(C,N)-based precipitates is preferably 30 nm or less. In this way, by miniaturizing the size of V(C,N)-based precipitates, high hardness can be secured through precipitation strengthening. On the other hand, when the average size of the V(C,N)-based precipitates exceeds 30 nm, it may be difficult to sufficiently obtain the above-described effects.
  • the average size of the V(C,N)-based precipitates is more preferably 28 nm or less, even more preferably 25 nm or less, and most preferably 20 nm or less.
  • the V(C,N)-based precipitates may include V-based carbides, V-based nitrides, and V-based carbonitrides.
  • the ratio of the number of precipitates having a size greater than 100 nm to the total number of precipitates is 10% or less.
  • the number of V(C,N)-based precipitates exceeding 100 nm in size exceeds 10% relative to the total number of precipitates, not only the precipitation hardening effect may be reduced, but also the low-temperature toughness may be deteriorated.
  • the number of precipitates having a size exceeding 100 nm is more preferably 8% or less, more preferably 6% or less, and most preferably 5% or less relative to the total number of precipitates.
  • the bulletproof steel according to one embodiment of the present invention provided as described above may have a surface hardness of 480 to 530 HB, an impact absorption energy of 16 J or more at -40 ° C, and a thickness of 5 to 40 mm.
  • a slab satisfying the above alloy composition and relational expression 1 is heated at 1050 to 1250 ° C. If the slab heating temperature is less than 1050 ° C., the deformation resistance of the steel increases and the subsequent rolling process cannot be effectively performed. On the other hand, if it exceeds 1250 ° C., austenite crystal grains become coarse and low-temperature toughness may deteriorate.
  • the lower limit of the slab heating temperature is more preferably 1060 ° C, more preferably 1070 ° C, and most preferably 1080 ° C.
  • the upper limit of the slab heating temperature is more preferably 1240 ° C, more preferably 1230 ° C, and most preferably 1220 ° C.
  • the heated slab is crudely rolled at 950 to 1150° C. to obtain a bar.
  • the rough rolling temperature is less than 950 ° C., the rolling load increases and the deformation is not sufficiently transmitted to the center in the thickness direction of the slab as the rolling load increases and the reduction is relatively weak, and as a result, there is a risk that defects such as voids may not be removed.
  • the temperature exceeds 1150 ° C., the recrystallized grain size becomes excessively coarse, and there is a possibility that the toughness may deteriorate.
  • the lower limit of the rough rolling temperature is more preferably 960°C, even more preferably 970°C, and most preferably 980°C.
  • the upper limit of the rough rolling temperature is more preferably 1140°C, even more preferably 1130°C, and most preferably 1120°C.
  • the bar is finished hot-rolled at 850 to 950° C. to obtain a hot-rolled steel sheet, and then cooled to room temperature.
  • the finish hot rolling temperature is less than 850 ° C, two-phase rolling is performed and ferrite may be generated in the microstructure. On the other hand, if it exceeds 950 ° C, the grain size of the final microstructure becomes coarse, resulting in poor low-temperature toughness.
  • the lower limit of the finish hot rolling temperature is more preferably 860°C, even more preferably 870°C, and most preferably 880°C.
  • the upper limit of the finish hot rolling temperature is more preferably 945°C, even more preferably 940°C, and most preferably 935°C.
  • Heating during the primary heat treatment is for reverse transformation of the hot-rolled steel sheet in which the microstructure is composed of ferrite and pearlite into an austenite single phase.
  • the heating temperature during the first heat treatment is less than 880° C., austenitization is not sufficiently achieved and coarse soft ferrite is mixed, and thus the hardness of the final product may be lowered.
  • the lower limit of the heating temperature during the first heat treatment is more preferably 882°C, more preferably 885°C, and most preferably 890°C.
  • the upper limit of the heating temperature during the first heat treatment is more preferably 928°C, more preferably 925°C, and most preferably 920°C.
  • the heating time in the first heat treatment is more preferably 1.3t + 35 minutes or more, more preferably 1.3t + 40 minutes or more, and most preferably 1.3t + 45 minutes or more.
  • the longer the heating time during the primary heat treatment is, the more favorable it is for austenitization and the re-dissolution of coarse V(C,N)-based precipitates, so the upper limit of the heating time is not particularly limited in the present invention.
  • the upper limit of the heating time during the first heat treatment may be 1.3t + 60 minutes.
  • the cooling is intended to transform the austenitized microstructure into martensite.
  • the cooling is preferably rapid cooling through water cooling.
  • the cooling rate is more preferably 12 °C/s or more, more preferably 15 °C/s or more, and most preferably 20 °C/s or more.
  • the upper limit of the cooling rate is not particularly limited.
  • the cooling end temperature is more preferably 100°C or less, even more preferably 80°C or less, and most preferably 50°C or less.
  • the lower limit of the cooling end temperature is not particularly limited, and may be, for example, room temperature.
  • a second heat treatment is performed on the hot-rolled steel sheet subjected to the first heat treatment by tempering heat treatment for 1.5t + 32 minutes (t: sheet thickness (mm)) to 1.5t + 60 minutes to satisfy the condition of the following relational expression 2.
  • the tempering heat treatment releases the internal stress of the hot-rolled steel sheet in which the microstructure is transformed into martensite by the first heat treatment to secure excellent low-temperature toughness, and to secure high hardness by precipitating fine V (C, N)-based precipitates. will be. If the tempering heat treatment temperature is less than 200 ° C., it is possible to prevent the decrease in hardness, but there is a disadvantage in securing low-temperature toughness because the internal stress is not sufficiently released after quenching.
  • the hardness of the final product may be reduced due to excessive reduction.
  • the lower limit of the tempering heat treatment temperature is more preferably 202°C, even more preferably 205°C, and most preferably 210°C.
  • the upper limit of the tempering heat treatment temperature is more preferably T max -5°C, more preferably T max -10°C, and most preferably T max -15°C.
  • the tempering heat treatment time exceeds 1.5 t + 60 minutes, it may not be easy to secure a desired high hardness because the dislocation inside martensite is reduced.
  • the lower limit of the tempering heat treatment time is more preferably 1.5t + 35 minutes, more preferably 1.5t + 38 minutes, and most preferably 1.5t + 40 minutes.
  • the upper limit of the tempering heat treatment time is more preferably 1.5t + 57 minutes, more preferably 1.5t + 55 minutes, and most preferably 1.5t + 50 minutes.
  • T max is 112.5 [C] -5.7 [Mn] + 18.8 [Cr] -1.3 [Ni] + 114.3 [V] + 169.4 [Mo] + 200, and in the T max Content means % by weight.)
  • the slab heating - rough rolling - finish hot rolling - primary heat treatment - secondary heat treatment are performed to produce bulletproof steel did At this time, air cooling was applied to room temperature after water cooling to the cooling end temperature during the first heat treatment, and air cooling was applied to room temperature after the second heat treatment.
  • the microstructure and mechanical properties of the bulletproof steel thus prepared were measured, and the results are shown in Table 5 below.
  • the microstructure was prepared by cutting the manufactured steel sheet into an arbitrary size to make a specimen, mirror-processing it, corroding it using a nital etchant, and using a scanning electron microscope to examine the 1/4t (t: thickness) portion of the steel sheet. Observed.
  • the average effective grain size of tempered martensite was measured based on a misorientation angle of 15° or more using EBSD.
  • KAM of tempered martensite was examined using a scanning electron microscope (SEM) JSM-7001F manufactured by JEOL Co., Ltd., on the polished surface of the cross section in the rolling direction of the steel sheet, in a field of view of 100 ⁇ m ⁇ 100 ⁇ m EBSD (Electron Backscatter Diffraction analysis (measurement step: 0.05 ⁇ m) was performed at a position of 1/4 of the plate thickness, and the average value of the orientation difference (°) between each pixel in the crystal grain and the adjacent pixel was calculated.
  • SEM scanning electron microscope
  • JSM-7001F manufactured by JEOL Co., Ltd.
  • the V(C,N)-based precipitates formed in the tempered martensite grains are prepared by cutting the manufactured steel sheet into a random size and then preparing a specimen, and then at a magnification of 50,000 times (2 ⁇ m ⁇ 2 ⁇ m) at 5 random areas, and then the average value was calculated.
  • Hardness was measured 3 times using a Brinell hardness tester (load 3000 kgf, 10 mm tungsten indentation) after milling the surface of the steel plate by 2 mm, and then expressed as an average value.
  • the low-temperature toughness was measured three times at -40 ° C after processing a 1/4t (t: thickness) part of the steel plate into a specimen using a Charpy impact tester, and then expressed as an average value of impact absorption energy.
  • the alloy composition of the present invention is satisfactory, but the average effective crystal grain size of tempered martensite increases as the heating time is not sufficient during the first heat treatment, and the average size of precipitates and total precipitates proposed by the present invention It can be seen that the low-temperature toughness is low because the ratio of the number of precipitates having a size of more than 100 nm to the number is not satisfied.
  • the alloy composition of the present invention is satisfactory, but the tempering heat treatment time during the secondary heat treatment is not sufficient, so the average size of precipitates proposed by the present invention, the ratio of the number of precipitates whose size exceeds 100 nm to the total number of precipitates , it can be seen that the low-temperature toughness is low because it does not satisfy the KAM.

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Abstract

La présente invention concerne un acier pare-balles à dureté élevée ayant une excellente résistance à basse température, et son procédé de production. Plus spécifiquement, la présente invention concerne un acier pare-balles à dureté élevée ayant une excellente résistance à basse température, et son procédé de production, l'acier pare-balles à dureté élevée étant de préférence utilisable dans un véhicule blindé, une structure antidéflagrante et similaire.
PCT/KR2022/011499 2021-08-11 2022-08-03 Acier pare-balles à dureté élevée ayant une excellente résistance à basse température, et son procédé de production Ceased WO2023018101A1 (fr)

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CN116790987B (zh) * 2023-06-28 2026-03-20 鞍钢股份有限公司 一种耐寒工具钢及其生产方法

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