WO2019124793A1 - High strength steel sheet and manufacturing method therefor - Google Patents

High strength steel sheet and manufacturing method therefor Download PDF

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Publication number
WO2019124793A1
WO2019124793A1 PCT/KR2018/014855 KR2018014855W WO2019124793A1 WO 2019124793 A1 WO2019124793 A1 WO 2019124793A1 KR 2018014855 W KR2018014855 W KR 2018014855W WO 2019124793 A1 WO2019124793 A1 WO 2019124793A1
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steel sheet
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content
present
steel
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PCT/KR2018/014855
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French (fr)
Korean (ko)
Inventor
홍순택
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주식회사 포스코
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Priority to EP18891912.0A priority Critical patent/EP3730655B1/en
Priority to US16/957,021 priority patent/US20200347478A1/en
Priority to JP2020535011A priority patent/JP7096337B2/en
Priority to CN201880082338.2A priority patent/CN111566249B/en
Publication of WO2019124793A1 publication Critical patent/WO2019124793A1/en

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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
    • 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
    • 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
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0221—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
    • 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
    • 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
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a high strength steel sheet and a manufacturing method thereof, and more particularly, to a high strength steel sheet which is excellent in tensile strength and impact toughness and is particularly suitable for a reactor containment vessel of a nuclear power plant and a method for manufacturing the same.
  • a variety of materials are used depending on the type, use, and safety of the materials that make up the structures and facilities used in nuclear power plants.
  • steel is used as a material for containment vessels, and A516-70 steel produced by thickening steel material by normalizing heat treatment method is mainly used.
  • the A516-70 steel exhibits a somewhat lower tensile strength (500 MPa level) to ensure the safety of nuclear power plants, its range of use is extremely limited. That is, since the tensile strength of A516-70 steel is somewhat low, when a containment vessel of a nuclear power plant is manufactured, there is a risk that it can not withstand the high pressure inside it, . Accordingly, it is urgent to develop a material particularly suitable for a nuclear reactor containment vessel while having a tensile strength higher than a certain level.
  • Patent Document 1 proposes a high-strength steel sheet which can be used for a reactor containment vessel of a nuclear power plant, and which has improved tensile strength.
  • the steel sheet of Patent Document 1 has a tensile strength at a level that can be used for a steel plate for a reactor containment vessel, but is not suitable as a material for a reactor containment vessel to open a low temperature toughness and a nil-ductility temperature characteristic .
  • Patent Document 1 Korean Patent Laid-Open No. 10-2010-0076745 (Published on Jun. 6, 2010)
  • a high strength steel sheet comprises 0.05 to 0.2% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% Ni + Cr + Mo: not more than 1.5%, and the balance Fe and unavoidable impurities, wherein the content of Ca is 0.0005 to 0.005%, the content of Ca is 0.005 to 0.025%, the content of Ti is 0.005 to 0.025%, the content of N is 0.002 to 0.006% Below; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: 1.0 or more, and the microstructure may include a mixed structure of tempered martensite and tempered bainite.
  • the tempered martensite is contained in an area fraction of 30 to 60%
  • the tempered bainite is contained in an area fraction of 40 to 70%
  • the sum of the areas of the tempered martensite and the tempered bainite Can be 100%.
  • the tempered martensite may be contained in an area fraction of 40 to 60%, and the tempered bainite may be contained in an area fraction of 40 to 60%.
  • the nil-ductility transition temperature of the steel sheet may be lower than -50 ° C.
  • the tensile strength of the steel sheet may be 600 MPa or more.
  • the Charpy impact toughness of the steel sheet may be 250 J or higher at -60 ⁇ .
  • the aspect ratio (major axis / minor axis) of the microstructure may be 1.1 to 2.5.
  • a high strength steel sheet comprises 0.05 to 0.2% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% Ni + Cr + Mo: not more than 1.5%, and the balance Fe and unavoidable impurities, wherein the content of Ca is 0.0005 to 0.005%, the content of Ca is 0.005 to 0.025%, the content of Ti is 0.005 to 0.025%, the content of N is 0.002 to 0.006% Below; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: not less than 1.0; reheating the steel slab to a temperature range of 1050 to 1250 ⁇ ⁇ ; Rolling the slab in a temperature range from Tn
  • the cumulative rolling reduction of the rolling may be 50 to 90%.
  • the crystal aspect ratio (major axis / minor axis) of the steel sheet microstructure can be controlled in the range of 1.1 to 2.5.
  • the austenizing heat treatment may be performed for a time of 1.6 * t (where t represents the thickness (mm) of the steel sheet) + (10 to 30 minutes).
  • the tempering heat treatment may be performed for a time of 2.4 * t (where t represents the thickness (mm) of the steel sheet) + (10-30 minutes).
  • a tensile strength of 600 MPa or more, a Charpy impact toughness of 250 J or more at -60 ⁇ , and a nil-ductility temperature of -50 ⁇ or less are secured, a high strength steel sheet particularly suitable for a containment vessel and a method for manufacturing the same.
  • the present invention relates to a high-strength steel sheet and a method of manufacturing the same, and a preferred embodiment of the present invention will be described below.
  • the embodiments of the present invention can 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 embodiments are provided to further explain the present invention to a person having ordinary skill in the art to which the present invention belongs.
  • the high strength steel sheet according to an embodiment of the present invention may contain 0.05 to 0.2% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% 0.004 to 0.04% of Ca, 0.005 to 0.005% of Ca, 0.005 to 0.025% of Ti, 0.002 to 0.006% of N, less than 0.0005% of B, and the balance Fe and unavoidable impurities.
  • the present invention can limit the lower limit of the carbon (C) content to 0.05% in order to prevent the strength reduction of the base phase.
  • the carbon content of the present invention may be 0.05 to 0.2%, and the carbon content may more preferably be 0.08 to 0.15%.
  • Silicon (Si) is an element added for the deoxidation effect, the solid solution strengthening effect and the impact transition temperature increasing effect. Therefore, the present invention can limit the lower limit of the silicon (Si) content to 0.15% to achieve this effect.
  • the lower limit of the preferred silicon (Si) content may be 0.2%, and the lower limit of the more preferred silicon (Si) content may be 0.3%.
  • silicon (Si) is added excessively, the weldability of the steel sheet may be deteriorated and the oxide film may be severely formed on the surface of the steel sheet, so that the present invention can limit the upper limit of the silicon (Si) content to 0.55%.
  • the upper limit of the preferred silicon (Si) content may be 0.5%, and the upper limit of the more preferred silicon (Si) content may be 0.4%.
  • the present invention can limit the lower limit of the manganese (Mn) content to 0.9% in order to achieve this effect.
  • the lower limit of the preferred manganese (Mn) content may be 1.0%, and more preferably the lower limit of the manganese (Mn) content may be 1.2%.
  • manganese (Mn) binds with sulfur (S) to form nonmetallic inclusions such as MnS.
  • S sulfur
  • the present invention can limit the upper limit of manganese (Mn) content to 1.75%.
  • the upper limit of the preferred manganese (Mn) content may be 1.7%, and the upper limit of the more preferred manganese (Mn) content may be 1.6%.
  • the present invention can limit the lower limit of the aluminum (Al) content to 0.001% for the effect of deoxidation in the steelmaking process.
  • the present invention can limit the upper limit of aluminum (Al) content to 0.05%.
  • a more preferable aluminum (Al) content may be 0.01 to 0.04%.
  • Phosphorus (P) not more than 0.03%
  • phosphorus (P) is an element that damages low-temperature toughness, it is desirable to control the content of phosphorus (P) as low as possible.
  • the phosphorus (P) is an element which is inevitably contained in the steelmaking process, and it may take an excessive cost to completely remove the phosphorus (P), so that the upper limit of phosphorus (P) content can be limited to 0.03%.
  • the upper limit of the preferred phosphorus (P) content may be 0.02%, and the upper limit of the phosphorus (P) content more preferably may be 0.01%.
  • Sulfur (S) is also an element which adversely affects the low temperature toughness in addition to phosphorus (P), so it is desirable to control the content to a maximum as low as possible.
  • sulfur (S) is inevitably contained in the steelmaking process as in phosphorus (P), it may take an excessive amount of time to completely remove the sulfur.
  • the upper limit of the sulfur content is 0.03% Can be limited.
  • the upper limit of the preferred sulfur (S) content may be 0.02%, and the upper limit of the more preferred sulfur (S) content may be 0.01%.
  • the present invention can limit the lower limit of the chromium (Cr) content to 0.05% in order to achieve this effect.
  • chromium (Cr) is an expensive element and is not preferable from the viewpoint of economy when it is added in excess. Therefore, the present invention can limit the upper limit of the chromium (Cr) content to 0.3%.
  • the chromium (Cr) content of the present invention may be 0.05 to 0.3%, and more preferably, the chromium (Cr) content may be 0.05 to 0.2%.
  • Nickel (Ni) is an effective element for improving the low temperature toughness. Therefore, the present invention can limit the lower limit of the nickel (Ni) content to 0.05% in order to achieve this effect. However, nickel (Ni) is an expensive element, and if it is added in excess, the production cost is increased.
  • the present invention can limit the upper limit of nickel (Ni) content to 0.6%. Accordingly, the nickel content of the present invention may be 0.05 to 0.6%, and more preferably, the nickel content may be 0.2 to 0.6%.
  • Copper (Cu) is an effective element for increasing the strength. Therefore, the present invention can limit the lower limit of the copper (Cu) content to 0.005% to achieve this effect. However, copper (Cu) is an expensive element, and if it is added in an excessive amount, the production cost is increased. Therefore, the present invention can limit the upper limit of copper (Cu) content to 0.35%. Accordingly, the copper (Cu) content of the present invention may be 0.005 to 0.35%, and more preferably, the copper (Cu) content may be 0.01 to 0.3%.
  • Molybdenum (Mo) is an element which is effective for improving the strength and is an element which forms a sulfide to prevent the occurrence of cracks. Therefore, the present invention can limit the lower limit of the molybdenum (Mo) content to 0.05% in order to achieve this effect. However, molybdenum (Mo) is also an expensive element, and if it is added in excess, the production cost is increased. The present invention can limit the upper limit of molybdenum (Mo) content to 0.2%. Accordingly, the molybdenum (Mo) content of the present invention may be 0.05 to 0.2%, and more preferably, the molybdenum (Mo) content may be 0.1 to 0.2%.
  • Vanadium (V) is an effective element for improving low-temperature toughness. Therefore, the present invention can limit the lower limit of the vanadium (V) content to 0.005% in order to achieve this effect. However, when vanadium (V) is also an expensive element, if it is added in excess, the production cost is increased.
  • the present invention can limit the upper limit of vanadium (V) content to 0.07%. Accordingly, the vanadium (V) content of the present invention may be 0.005 to 0.07%, and more preferably, the vanadium (V) content may be 0.01 to 0.07%.
  • Niobium (Nb) is an element that is solidified in austenite and increases the hardenability of austenite.
  • Niobium (Nb) is an element which is precipitated in carbonitride (Nb (C, N)) which is in conformity with the matrix in addition to titanium (Ti).
  • the present invention can limit the lower limit of the niobium (Nb) content to 0.005% in order to achieve this effect.
  • coarse precipitates are formed in the course of performance and can act as a starting point of hydrogen organic cracking (HIC).
  • the present invention is characterized in that the upper limit of the content of niobium (Nb) . Accordingly, the niobium (Nb) content of the present invention can be 0.005 to 0.04%, and more preferably, the niobium (Nb) content can be 0.01 to 0.03%.
  • the present invention can limit the lower limit of the calcium (Ca) content to 0.0005% in order to achieve this effect.
  • the present invention can limit the upper limit of calcium (Ca) content to 0.005%. Accordingly, the calcium content of the present invention may be 0.0005 to 0.005%, and more preferably, the calcium content may be 0.001 to 0.003%.
  • the titratable amount of titanium (Ti) can be flexibly limited depending on the content of nitrogen (N). If the content of titanium (Ti) is relatively small compared to the content of nitrogen (N), the amount of TiN produced becomes small, which is disadvantageous in refining the crystal grains. On the other hand, when titanium (Ti) is added in an excessive amount, TiN becomes coarse during the heating process and the effect of inhibiting grain growth is decreased. Therefore, in the present invention, the content of titanium (Ti) can be limited within the range of 0.005 to 0.025% in consideration of the content (0.002 to 0.006%) of nitrogen (N) normally contained. A more preferable titanium (Ti) content may be 0.01 to 0.02%.
  • Nitrogen (N) is widely known as an element that plays a role in increasing the toughness of the base material and impact toughness of the heat affected zone (HAZ) by forming TiN precipitates together with titanium (Ti) to refine the crystal grains.
  • (N) is an element that must be added in order to achieve the purpose of grain refinement. Therefore, the present invention can limit the lower limit of the nitrogen (N) content to 0.002% to achieve this effect. However, if the nitrogen (N) content is excessively added, the amount of TiN may be excessively increased and the low temperature toughness may be lowered. Therefore, the present invention can limit the upper limit of the nitrogen (N) content to 0.006%. Accordingly, the nitrogen (N) content of the present invention may be 0.002 to 0.006%, and more preferably, the nitrogen (N) content may be 0.002 to 0.004%.
  • the present invention positively suppresses the content of boron (B), but excessive cost may be consumed to completely remove boron (B) that is inevitably introduced in the steelmaking process. Therefore, the present invention can limit the boron (B) content to less than 0.005%.
  • the preferred boron (B) content may be 0.0002% or less, and more preferably, the boron (B) content may be 0.0001% or less.
  • a high strength steel sheet comprising: a steel sheet having a composition of Cu + Ni + Cr + Mo: 1.5% or less; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: 1.0 or more can be satisfied.
  • V + Nb not more than 0.1%
  • the relationship between Cu + Ni + Cr + Mo, Cr + Mo, and V + Nb is a numerical value limited by the basic standard (ASTM A20) of steel for pressure vessels, and the content of Cu + Ni + Cr + Mo is 1.5% , The content of Cr + Mo is 0.4% or less, and the content of V + Nb is 0.1% or less.
  • the Ca / s ratio is an essential constituent ratio for improving the hydrogen organic cracking resistance by spheroidizing the MnS inclusions. When the ratio is less than 1.0, the effect is not expected to be expected, and the ratio can be limited to satisfy 1.0 or more.
  • the high strength steel sheet according to one aspect of the present invention may include a mixed structure of tempered martensite and tempered bainite in a microstructure.
  • Microstructure Mixed texture of tempered martensite and tempered bainite
  • the microstructure of the steel material has a microstructure of tempered martensite and tempered bainite.
  • the tempered martensite and the tempered bainite are contained in an area fraction of 30 to 60% and 40 to 70%, respectively.
  • the tensile strength is 600 MPa
  • the nil-ductility temperature characteristic and a Charpy tensile strength of 250 J or more at -60 ⁇ .
  • the preferred area of the tempered martensite may be 40 to 60%
  • the preferred area of the tempered bainite may be 40 to 60%.
  • the sum of the area fraction of the tempered martensite and the tempered bait knit may be 100%.
  • Grain aspect ratio 1.1? Long axis / Short axis? 2.5
  • the present invention can control the ratio of crystal grains (long axis / short axis ratio) to a certain range in order to secure high impact toughness and strength, and such a grain aspect ratio can be controlled through a rolling (recrystallization controlled rolling) process.
  • a rolling recrystallization controlled rolling
  • the aspect ratio of the crystal grains is less than 1.1, the shape of the crystal grains is rounded, the surface energy is small, and it is difficult to expect finer crystal grains, which makes it difficult to secure sufficient impact toughness and strength.
  • the aspect ratio of the crystal grains exceeds 2.5, the rolling load for forming the crystal grains becomes excessively large and the impact toughness is lowered, which is not preferable. Therefore, in the present invention, the crystal aspect ratio (long axis / short axis ratio) can be limited to a range of 1.1 to 2.5.
  • the high strength steel sheet according to one aspect of the present invention comprises 0.05 to 0.20% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% Ni + Cr + Mo: not more than 1.5%, and the balance Fe and unavoidable impurities, wherein the content of Ca is 0.0005 to 0.005%, the content of Ca is 0.005 to 0.025%, the content of Ti is 0.005 to 0.025%, the content of N is 0.002 to 0.006% Below; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: not less than 1.0; reheating the steel slab to a temperature range of 1050 to 1250 ⁇ ⁇ ; Rolling the slab in a temperature range from
  • the alloy composition and the content of the slab of the present invention correspond to the alloy composition and the content of the high-strength steel sheet described above.
  • the description of the alloy composition and the content thereof of the slab of the present invention is based on the description of the alloy composition and the content thereof .
  • the slab having the above-described alloy composition can be reheated at a temperature of 1050 to 1250 ° C.
  • the reheating temperature is lower than 1050 ⁇ ⁇ , it is difficult to sufficiently solidify the solute atoms, and when the reheating temperature exceeds 1250 ⁇ ⁇ , the size of the austenite grains becomes excessively coarse and the physical properties of the steel sheet deteriorate.
  • Recrystallization Control Rolling Cumulative rolling reduction of 50 to 90% at a temperature range of Tnr to (Tnr + 100 ° C), a reduction rate of 10% or more per each rolling pass,
  • the recrystallization control rolling means rolling at a temperature not lower than the non-recrystallization temperature, and the non-recrystallization temperature Tnr can be derived from the previously known formula (1).
  • the unit of each alloy element in the following formula 1 means weight%.
  • Tnr (° C.) 887-464 ⁇ C + 890 ⁇ Ti + 363 ⁇ Al-357 ⁇ Si + (6445 ⁇ Nb-644 ⁇ Nb 1/2 ) + (732 ⁇ V-230 ⁇ V 1/2 )
  • the average grain size of the old austenite In order to improve the strength, it is necessary to make the average grain size of the old austenite to 30 ⁇ m or less in the recrystallization controlled rolling process. If the average particle diameter of the old austenite exceeds 30 ⁇ , the strength and toughness of the product can not be sufficiently exhibited, so that the safety of the product can not be guaranteed to the level that can be used in the reactor containment vessel.
  • rolling is performed in a temperature range of Tnr to Tnr + 100 ⁇ ⁇ .
  • a reduction rate of 10% or more is applied to each rolling pass, and the rolling is finally performed within a range of 50 to 90% of cumulative rolling reduction.
  • This reduction amount is intended to control the average size (less than 30 ⁇ ⁇ ) and the aspect ratio (major axis / minor axis) of the microstructure required in the present invention to 1.1 to 2.5. Therefore, when the cumulative rolling reduction is less than 50%, it is difficult to expect a finer microstructure and a control effect of the grain shape ratio, and when the cumulative rolling reduction exceeds 90%, the rolling load is excessively applied.
  • the quenching process is an important process for obtaining a mixed structure of tempered martensite and tempered bainite.
  • the quenching process has a tensile strength of 600 MPa or more, a Charpy impact toughness of -60 ° C. of 250 J or more, and a nil-ductility temperature It is necessary to strictly control the process conditions in order to form the microstructure capable of securing the characteristics of the microstructure.
  • an austenizing heat treatment can be performed in a temperature range of 870 to 950 ⁇ for 1.6 x t (t means the thickness (mm) of the steel plate) + (10 to 30 minutes).
  • Such austenizing heat treatment is a heat treatment for austenitizing the structure before quenching.
  • the temperature of the heat treatment is less than 870 ⁇ ⁇ , it is difficult to secure the strength by reusing the solid solute elements. If the heat treatment temperature exceeds 950 ⁇ ⁇ , The growth of crystal grains occurs, and a coarse grain is generated, which may damage low-temperature toughness. Therefore, the osteonizing heat treatment temperature range of the present invention can be limited to a temperature range of 870 to 950 ⁇ ⁇ .
  • the osteonizing heat treatment may be performed for a time of 1.6 * t (where t represents the thickness (mm) of the steel plate) + (10 to 30 minutes). If the austenizing heat treatment time is excessively short, sufficient heating time is not sufficient and sufficient osteonizing effect can not be expected, and homogenization of the structure may be difficult. On the other hand, if the austenizing heat treatment time is excessively long, product production may be prolonged and productivity may be deteriorated. Therefore, the osteonizing heat treatment time of the present invention can be limited to 1.6 * t (where t denotes the thickness (mm) of the steel plate) + (10 to 30 minutes). For reference, an austenizing heat treatment can be performed by setting the heating time to 1.6 * t in the steel sheet manufacturing process and setting the holding time to 10 to 30 minutes when the target temperature is reached.
  • the steel sheet subjected to the austenizing heat treatment may be quenched, preferably water-cooled, and transformed into a mixed structure of martensite and bainite.
  • the quenching treatment in the present invention is not particularly limited and the quenching treatment method including ordinary water cooling is applicable to the quenching of the present invention.
  • it is preferable that the steel sheet subjected to osteonizing heat treatment is cooled to a temperature of 300 ° C or less.
  • Tempering heat treatment 2.4 ⁇ t in the temperature range of 595 ⁇ 700 °C (t means thickness (mm) of steel plate) + (10 ⁇ 30 minutes)
  • the steel material quenched at 300 ° C or less is subjected to tempering treatment to remove the residual stress of the structure, It can have a knit structure.
  • the tempering heat treatment temperature range of the present invention can be limited to 595 to 700 ⁇ .
  • the tempering heat treatment temperature is less than 595 DEG C, precipitation of carbides and the like is not smooth, and when the tempering heat treatment temperature exceeds 700 DEG C, the strength of the steel material may be lowered.
  • the tempering heat treatment of the present invention can be performed for 2.4 * t (where t means the thickness (mm) of the steel sheet) + (10-30 minutes) for obtaining a sufficient tempering effect.
  • t means the thickness (mm) of the steel sheet
  • the tempering heat treatment can be performed by setting the holding time to 10 to 30 minutes.
  • a slab having an alloy composition shown in Table 1 was prepared.
  • test specimens were produced by reheating, recrystallization controlled rolling, austenizing annealing and quenching and tempering heat treatment using the slabs prepared in the composition of the inventive steel and the comparative steel as shown in Table 2 below.
  • Strength, low-temperature toughness, and nil-ductility transition temperature The results are shown in Table 3 below.
  • the low-temperature impact toughness was evaluated by the Charpy impact energy value obtained by performing the Charpy impact test on the specimen having the V notch at -60 ° C.
  • the nil-ductility transition temperature is a value according to the drop test transition temperature set by the ASTM E208-06 method.
  • Grain aspect ratio Grain length axis / Grain length shortening
  • Inventive Examples 1 to 7 show the microstructure of 30 to 60% tempered martensite as an area fraction and 40 to 70% tempered bainite mixed texture as an area fraction And it is confirmed that the tensile strength of 600 MPa or more, the impact toughness of 300 J or more at -60 ° C, and the nil-ductility temperature characteristic of -50 ° C or less are secured.
  • the steel sheet according to one embodiment of the present invention can be manufactured by controlling the steel composition, the microstructure and the manufacturing process under the optimum conditions, so that the tensile strength of 600 MPa or more, the Charpy impact toughness of 250 J or more at -60 ⁇ , It is possible to provide a high-strength steel plate having physical properties suitable for a reactor containment vessel of a nuclear power plant, by ensuring nil-ductility temperature characteristics.

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Abstract

A high strength steel sheet according to an aspect of the present invention comprises, by weight %, 0.05-0.20% of C, 0.15-0.55% of Si, 0.9-1.75% of Mn, 0.001-0.05% of Al, 0.03% or less of P, 0.03% or less of S, 0.05-0.3% of Cr, 0.05-0.6% of Ni, 0.005-0.35% of Cu, 0.05-0.2% of Mo, 0.005-0.07% of V, 0.005-0.04% of Nb, 0.0005-0.005% of Ca, 0.005-0.025% of Ti, 0.002-0.006% of N, less than 0.0005% of B, the balance of Fe and inevitable impurities, with the proviso of satisfying the relation that Cu + Ni + Cr + Mo: 1.5% or less; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; and Ca/S: 1.0 or higher and may include a combined structure of tempered martensite and tempered bainite as a microstructure.

Description

고강도 강판 및 그 제조방법High strength steel sheet and manufacturing method thereof
본 발명은 고강도 강판 및 제조방법에 관한 것으로, 상세하게는 인장강도 및 충격인성이 우수하여 원자력발전소의 원자로 격납 용기용으로 특히 적합한 고강도 강판 및 그 제조방법에 관한 것이다.The present invention relates to a high strength steel sheet and a manufacturing method thereof, and more particularly, to a high strength steel sheet which is excellent in tensile strength and impact toughness and is particularly suitable for a reactor containment vessel of a nuclear power plant and a method for manufacturing the same.
원자력 발전소에 사용되는 구조, 설비 등을 구성하는 재료는 그 종류, 용도, 안전성 등에 따라 다양한 소재가 이용되고 있다. 특히, 원자로 격납 용기(containment vessel)용 소재로 철강재가 이용되고 있으며, 두꺼운 강판 재료로 노멀라이징 열처리법으로 제조된 A516-70강이 주로 사용되고 있다.A variety of materials are used depending on the type, use, and safety of the materials that make up the structures and facilities used in nuclear power plants. In particular, steel is used as a material for containment vessels, and A516-70 steel produced by thickening steel material by normalizing heat treatment method is mainly used.
하지만, A516-70강은 원자력 발전소의 안전성을 보증하기에는 다소 낮은 인장강도(500MPa 수준)를 나타내기 때문에, 그 사용 범위가 극히 제한적이다. 즉, A516-70강은 인장강도가 다소 낮은 수준이므로, 이를 이용하여 원자력 발전소의 원자로 격납 용기(containment vessel)를 제작하는 경우, 내부의 높은 압력을 견디지 못하여 파손 또는 폭발될 위험성이 존재하기 때문이다. 따라서, 일정 수준 이상의 인장강도를 가지면서도, 원자로 격납 용기에 특히 적합한 소재의 개발이 시급한 실정이다.However, since the A516-70 steel exhibits a somewhat lower tensile strength (500 MPa level) to ensure the safety of nuclear power plants, its range of use is extremely limited. That is, since the tensile strength of A516-70 steel is somewhat low, when a containment vessel of a nuclear power plant is manufactured, there is a risk that it can not withstand the high pressure inside it, . Accordingly, it is urgent to develop a material particularly suitable for a nuclear reactor containment vessel while having a tensile strength higher than a certain level.
인장강도의 향상을 위하여 강재에 고가의 합금원소를 다량 첨가하거나 별도의 열처리를 수행하는 경우, 인장강도가 향상되는 것은 별론, 합금원소의 첨가에 따른 비용의 증가가 불가피하며, 기타 다른 부수적인 문제가 수반될 가능성이 존재한다. In the case of adding a large amount of expensive alloying elements to the steel material or performing a separate heat treatment in order to improve the tensile strength, the increase in the cost due to the addition of the alloying element is inevitable, unlike the increase in tensile strength. There is a possibility that it is accompanied.
특허문헌 1은 원자력 발전소의 원자로 격납 용기용으로 사용 가능한 고강도 강판으로, 인장강도가 향상된 고강도 강판을 제안한다. 하지만, 특허문헌 1의 강판은 원자로 격납 용기용 강판으로 사용 가능한 수준의 인장강도를 구비하나, 저온인성 및 무연성 천이온도(nil-ductility temperature) 특성이 열위하여 원자로 격납 용기용 소재로 적합하지 않다. Patent Document 1 proposes a high-strength steel sheet which can be used for a reactor containment vessel of a nuclear power plant, and which has improved tensile strength. However, the steel sheet of Patent Document 1 has a tensile strength at a level that can be used for a steel plate for a reactor containment vessel, but is not suitable as a material for a reactor containment vessel to open a low temperature toughness and a nil-ductility temperature characteristic .
(특허문헌 1) 대한민국 공개특허공보 제10-2010-0076745호(2010.07.06. 공개)(Patent Document 1) Korean Patent Laid-Open No. 10-2010-0076745 (Published on Jun. 6, 2010)
본 발명의 일 측면에 따르면, 인장강도, 저온인성 및 무연성 천이온도(nil-ductility temperature) 특성이 우수하여 원자력발전소의 원자로 격납 용기(containment vessel)용 소재로 특히 적합한 고강도 강판 및 그 제조방법이 제공될 수 있다.According to an aspect of the present invention, there is provided a high-strength steel sheet excellent in tensile strength, low-temperature toughness and nil-ductility temperature characteristics, and particularly suitable as a material for a containment vessel of a nuclear power plant, Can be provided.
본 발명의 과제는 상술한 내용에 한정되지 않는다. 통상의 기술자라면 본 발명의 명세서의 전반적인 내용으로부터 본 발명의 추가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.The object of the present invention is not limited to the above description. It will be apparent to those of ordinary skill in the art that there is no difficulty in understanding the further task of the present invention from the overall contents of the specification of the present invention.
본 발명의 일 측면에 따른 고강도 강판은, 중량 %로, C: 0.05~0.2%, Si: 0.15~0.55%, Mn: 0.9~1.75%, Al: 0.001~0.05%, P: 0.03% 이하, S: 0.03% 이하, Cr: 0.05~0.3%, Ni: 0.05~0.6%, Cu: 0.005~0.35%, Mo: 0.05~0.2%, V: 0.005~0.07%, Nb: 0.005~0.04%, Ca: 0.0005~0.005%, Ti: 0.005~0.025%, N: 0.002~0.006%, B: 0.0005% 미만, 잔부 Fe 및 불가피한 불순물을 포함하며, Cu + Ni + Cr + Mo: 1.5% 이하; Cr + Mo: 0.4% 이하; V + Nb: 0.1% 이하; 및 Ca/S: 1.0 이상의 관계를 만족하며, 템퍼드 마르텐사이트 및 템퍼드 베이나이트의 혼합조직을 미세조직으로 포함할 수 있다.A high strength steel sheet according to one aspect of the present invention comprises 0.05 to 0.2% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% Ni + Cr + Mo: not more than 1.5%, and the balance Fe and unavoidable impurities, wherein the content of Ca is 0.0005 to 0.005%, the content of Ca is 0.005 to 0.025%, the content of Ti is 0.005 to 0.025%, the content of N is 0.002 to 0.006% Below; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: 1.0 or more, and the microstructure may include a mixed structure of tempered martensite and tempered bainite.
상기 템퍼드 마르텐사이트는 30~60%의 면적분율로 포함되고, 상기 템퍼드 베이나이트는 40~70%의 면적분율로 포함되며, 상기 템퍼드 마르텐사이트 및 상기 템퍼드 베이나이트의 면적분율의 합은 100%일 수 있다.The tempered martensite is contained in an area fraction of 30 to 60%, the tempered bainite is contained in an area fraction of 40 to 70%, the sum of the areas of the tempered martensite and the tempered bainite Can be 100%.
상기 템퍼드 마르텐사이트는 40~60%의 면적분율로 포함되고, 상기 템퍼드 베이나이트는 40~60%의 면적분율로 포함될 수 있다.The tempered martensite may be contained in an area fraction of 40 to 60%, and the tempered bainite may be contained in an area fraction of 40 to 60%.
상기 강판의 무연성 천이온도(nil-ductility transition temperature)는 -50℃ 이하일 수 있다.The nil-ductility transition temperature of the steel sheet may be lower than -50 ° C.
상기 강판의 인장강도는 600MPa 이상일 수 있다.The tensile strength of the steel sheet may be 600 MPa or more.
상기 강판의 샤르피 충격인성은 -60℃에서 250J 이상일 수 있다.The Charpy impact toughness of the steel sheet may be 250 J or higher at -60 캜.
상기 미세조직의 결정립 형상비(장축/단축)는 1.1~2.5일 수 있다.The aspect ratio (major axis / minor axis) of the microstructure may be 1.1 to 2.5.
본 발명의 일 측면에 따른 고강도 강판은, 중량 %로, C: 0.05~0.2%, Si: 0.15~0.55%, Mn: 0.9~1.75%, Al: 0.001~0.05%, P: 0.03% 이하, S: 0.03% 이하, Cr: 0.05~0.3%, Ni: 0.05~0.6%, Cu: 0.005~0.35%, Mo: 0.05~0.2%, V: 0.005~0.07%, Nb: 0.005~0.04%, Ca: 0.0005~0.005%, Ti: 0.005~0.025%, N: 0.002~0.006%, B: 0.0005% 미만, 잔부 Fe 및 불가피한 불순물을 포함하며, Cu + Ni + Cr + Mo: 1.5% 이하; Cr + Mo: 0.4% 이하; V + Nb: 0.1% 이하; 및 Ca/S: 1.0 이상;의 관계를 만족하는 강 슬라브를 1050~1250℃의 온도범위로 재가열하고; Tnr~(Tnr+100℃)의 온도범위에서 상기 슬라브를 압연하여 강판을 제공하고; 870~950℃의 온도범위에서 상기 강판을 오스테나이징 열처리하고; 상기 오스테나이징 열처리된 강판을 300℃ 이하의 온도범위로 급냉하고; 595~700℃의 온도범위에서 상기 급냉된 강판을 템퍼링 열처리하여 제조될 수 있다.A high strength steel sheet according to one aspect of the present invention comprises 0.05 to 0.2% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% Ni + Cr + Mo: not more than 1.5%, and the balance Fe and unavoidable impurities, wherein the content of Ca is 0.0005 to 0.005%, the content of Ca is 0.005 to 0.025%, the content of Ti is 0.005 to 0.025%, the content of N is 0.002 to 0.006% Below; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: not less than 1.0; reheating the steel slab to a temperature range of 1050 to 1250 占 폚; Rolling the slab in a temperature range from Tnr to (Tnr + 100 占 폚) to provide a steel sheet; Subjecting the steel sheet to an osteonizing heat treatment in a temperature range of 870 to 950 캜; Quenching the austenized heat treated steel sheet to a temperature range of 300 DEG C or less; And tempering the quenched steel sheet in a temperature range of 595 to 700 ° C.
상기 압연의 누적압하량은 50~90%일 수 있다.The cumulative rolling reduction of the rolling may be 50 to 90%.
상기 압연에 의해 상기 강판 미세조직의 결정립 형상비(장축/단축)가 1.1~2.5의 범위로 제어될 수 있다.By this rolling, the crystal aspect ratio (major axis / minor axis) of the steel sheet microstructure can be controlled in the range of 1.1 to 2.5.
상기 오스테나이징 열처리는 1.6*t(단, 여기서 t는 강판의 두께(mm)를 의미함) + (10~30분)의 시간동안 수행될 수 있다.The austenizing heat treatment may be performed for a time of 1.6 * t (where t represents the thickness (mm) of the steel sheet) + (10 to 30 minutes).
상기 템퍼링 열처리는 2.4*t(단, 여기서 t는 강판의 두께(mm)를 의미함) + (10~30분)의 시간동안 수행될 수 있다.The tempering heat treatment may be performed for a time of 2.4 * t (where t represents the thickness (mm) of the steel sheet) + (10-30 minutes).
본 발명의 바람직한 일 측면에 따르면, 600MPa 이상의 인장강도, -60℃에서 250J 이상의 샤르피 충격인성 및 -50℃ 이하의 무연성 천이온도(nil-ductility temperature) 특성을 확보하여 원자력발전소의 원자로 격납 용기(containment vessel)에 특히 적합한 고강도 강판 및 그 제조방법을 제공할 수 있다.According to a preferred aspect of the present invention, a tensile strength of 600 MPa or more, a Charpy impact toughness of 250 J or more at -60 캜, and a nil-ductility temperature of -50 캜 or less are secured, a high strength steel sheet particularly suitable for a containment vessel and a method for manufacturing the same.
본 발명은 고강도 강판 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 steel sheet and a method of manufacturing the same, and a preferred embodiment of the present invention will be described below. The embodiments of the present invention can 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 embodiments are provided to further explain the present invention to a person having ordinary skill in the art to which the present invention belongs.
이하, 본 발명의 강 조성에 대하여 보다 상세히 설명한다. 이하, 특별히 달리 표시하지 않는 한 각 원소의 함량을 나타내는 %는 중량을 기준으로 한다.Hereinafter, the steel composition of the present invention will be described in more detail. Hereinafter, unless otherwise indicated, the percentages representing the content of each element are by weight.
본 발명의 일 구현예에 따른 고강도 강판은, 중량%로, C: 0.05~0.2%, Si: 0.15~0.55%, Mn: 0.9~1.75%, Al: 0.001~0.05%, P: 0.03% 이하, S: 0.03% 이하, Cr: 0.05~0.3%, Ni: 0.05~0.6%, Cu: 0.005~0.35%, Mo: 0.05~0.2%, V: 0.005~0.07%, Nb: 0.005~0.04%, Ca: 0.0005~0.005%, Ti: 0.005~0.025%, N: 0.002~0.006%, B: 0.0005% 미만, 잔부 Fe 및 불가피한 불순물을 포함할 수 있다.The high strength steel sheet according to an embodiment of the present invention may contain 0.05 to 0.2% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% 0.004 to 0.04% of Ca, 0.005 to 0.005% of Ca, 0.005 to 0.025% of Ti, 0.002 to 0.006% of N, less than 0.0005% of B, and the balance Fe and unavoidable impurities.
탄소(C): 0.05~0.2%Carbon (C): 0.05 to 0.2%
탄소(C)는 강도 확보에 효과적인 원소이므로, 본 발명은 기지 상의 강도 저하를 방지하기 위하여 탄소(C) 함량의 하한을 0.05%로 제한할 수 있다. 반면, 탄소(C)가 과다하게 첨가되는 경우, 인성 및 용접성이 저하되어 원자로 격납 용기(containment vessel)용으로 사용하기에 적합하지 않은바, 본 발명은 탄소(C) 함량의 상한을 0.2%로 제한할 수 있다. 따라서, 본 발명의 탄소(C) 함량은 0.05~0.2% 일 수 있으며, 보다 바람직한 탄소(C) 함량은 0.08~0.15%일 수 있다. Since carbon (C) is an effective element for securing the strength, the present invention can limit the lower limit of the carbon (C) content to 0.05% in order to prevent the strength reduction of the base phase. On the other hand, when the carbon (C) is added excessively, the toughness and the weldability are lowered and it is not suitable for use in a containment vessel. Can be limited. Therefore, the carbon content of the present invention may be 0.05 to 0.2%, and the carbon content may more preferably be 0.08 to 0.15%.
실리콘(Si): 0.15~0.55%Silicon (Si): 0.15-0.55%
실리콘(Si)은 탈산 효과, 고용 강화 효과 및 충격 천이 온도 상승 효과를 위하여 첨가되는 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 실리콘(Si) 함량의 하한을 0.15%로 제한할 수 있다. 바람직한 실리콘(Si) 함량의 하한은 0.2%일 수 있으며, 더욱 바람직한 실리콘(Si) 함량의 하한은 0.3%일 수 있다. 다만, 실리콘(Si)이 과다하게 첨가되는 경우, 강판의 용접성이 저하되고 강판 표면에 산화 피막이 심하게 형성될 수 있으므로, 본 발명은 실리콘(Si) 함량의 상한을 0.55%로 제한할 수 있다. 바람직한 실리콘(Si) 함량의 상한은 0.5% 일 수 있으며, 더욱 바람직한 실리콘(Si) 함량의 상한은 0.4% 일 수 있다.Silicon (Si) is an element added for the deoxidation effect, the solid solution strengthening effect and the impact transition temperature increasing effect. Therefore, the present invention can limit the lower limit of the silicon (Si) content to 0.15% to achieve this effect. The lower limit of the preferred silicon (Si) content may be 0.2%, and the lower limit of the more preferred silicon (Si) content may be 0.3%. However, when silicon (Si) is added excessively, the weldability of the steel sheet may be deteriorated and the oxide film may be severely formed on the surface of the steel sheet, so that the present invention can limit the upper limit of the silicon (Si) content to 0.55%. The upper limit of the preferred silicon (Si) content may be 0.5%, and the upper limit of the more preferred silicon (Si) content may be 0.4%.
망간(Mn): 0.9~1.75%Manganese (Mn): 0.9 to 1.75%
망간(Mn)은 강도 확보에 효과적인 원소인바, 본 발명은 이러한 효과를 달성하기 위하여 망간(Mn) 함량의 하한을 0.9%로 제한할 수 있다. 바람직한 망간(Mn) 함량의 하한은 1.0% 일 수 있으며, 더욱 바람직한 망간(Mn) 함량의 하한은 1.2% 일 수 있다. 다만, 망간(Mn)은 황(S)과 결합하여 MnS와 같은 비금속개재물을 형성하는바, 망간(Mn)이 과다하게 첨가되는 경우, 상온 연신율 및 저온인성이 저하될 수 있다. 따라서, 본 발명은 망간(Mn) 함량의 상한을 1.75%로 제한할 수 있다. 바람직한 망간(Mn) 함량의 상한은 1.7%일 수 있으며, 더욱 바람직한 망간(Mn) 함량의 상한은 1.6%일 수 있다.Since manganese (Mn) is an element effective in securing strength, the present invention can limit the lower limit of the manganese (Mn) content to 0.9% in order to achieve this effect. The lower limit of the preferred manganese (Mn) content may be 1.0%, and more preferably the lower limit of the manganese (Mn) content may be 1.2%. However, manganese (Mn) binds with sulfur (S) to form nonmetallic inclusions such as MnS. When manganese (Mn) is added excessively, the room temperature elongation and low temperature toughness may be lowered. Therefore, the present invention can limit the upper limit of manganese (Mn) content to 1.75%. The upper limit of the preferred manganese (Mn) content may be 1.7%, and the upper limit of the more preferred manganese (Mn) content may be 1.6%.
알루미늄(Al): 0.001~0.05% Aluminum (Al): 0.001 to 0.05%
알루미늄(Al)은 강력한 탈산제 원소이므로, 본 발명은 제강공정에서의 탈산효과를 위해 알루미늄(Al) 함량의 하한을 0.001%로 제한할 수 있다. 다만, 알루미늄(Al)이 과다하게 첨가되는 경우, 탈산 효과는 포화되는 반면, 제조원가는 상승하게 되는바, 본 발명은 알루미늄(Al) 함량의 상한을 0.05%로 제한할 수 있다. 보다 바람직한 알루미늄(Al) 함량은 0.01~0.04%일 수 있다.Since aluminum (Al) is a strong deoxidizing element, the present invention can limit the lower limit of the aluminum (Al) content to 0.001% for the effect of deoxidation in the steelmaking process. However, when aluminum (Al) is added in excess, the effect of deoxidation is saturated while the cost of production is increased, so that the present invention can limit the upper limit of aluminum (Al) content to 0.05%. A more preferable aluminum (Al) content may be 0.01 to 0.04%.
인(P): 0.03% 이하 Phosphorus (P): not more than 0.03%
인(P)은 저온 인성을 해치는 원소이므로 최대한 그 함량을 낮게 관리하는 것이 바람직하다. 다만, 인(P)은 제강 공정에서 불가피하게 함유되는 원소로서, 이를 완전히 제거하는데 과다한 비용이 소요될 수 있는바, 본 발명은 인(P) 함량의 상한을 0.03%로 제한할 수 있다. 바람직한 인(P) 함량의 상한은 0.02%일 수 있으며, 보다 바람직한 인(P) 함량의 상한은 0.01%일 수 있다.Since phosphorus (P) is an element that damages low-temperature toughness, it is desirable to control the content of phosphorus (P) as low as possible. However, the phosphorus (P) is an element which is inevitably contained in the steelmaking process, and it may take an excessive cost to completely remove the phosphorus (P), so that the upper limit of phosphorus (P) content can be limited to 0.03%. The upper limit of the preferred phosphorus (P) content may be 0.02%, and the upper limit of the phosphorus (P) content more preferably may be 0.01%.
황(S): 0.03% 이하Sulfur (S): not more than 0.03%
황(S) 역시 인(P)와 더불어 저온인성에 악영향을 미치는 원소이므로 최대한 그 함량을 낮게 관리하는 것이 바람직하다. 다만, 황(S)은 인(P)와 마찬가지로 제강 공정에서 불가피하게 함유되는 원소로서, 이를 완전히 제거하는 데에는 과다한 비용이 소요될 수 있는바, 본 발명은 황(S) 함량의 상한을 0.03%로 제한할 수 있다. 바람직한 황(S) 함량의 상한은 0.02%일 수 있으며, 보다 바람직한 황(S) 함량의 상한은 0.01%일 수 있다.Sulfur (S) is also an element which adversely affects the low temperature toughness in addition to phosphorus (P), so it is desirable to control the content to a maximum as low as possible. However, since sulfur (S) is inevitably contained in the steelmaking process as in phosphorus (P), it may take an excessive amount of time to completely remove the sulfur. In the present invention, the upper limit of the sulfur content is 0.03% Can be limited. The upper limit of the preferred sulfur (S) content may be 0.02%, and the upper limit of the more preferred sulfur (S) content may be 0.01%.
크롬(Cr): 0.05~0.3%Cr (Cr): 0.05 to 0.3%
크롬(Cr)은 강도 증대에 기여하는 원소이므로, 본 발명은 이러한 효과를 달성하기 위하여 크롬(Cr) 함량의 하한을 0.05%로 제한할 수 있다. 다만, 크롬(Cr)은 고가의 원소로서, 과다하게 첨가되는 경우 경제성 측면에서 바람직하지 않다. 따라서, 본 발명은 크롬(Cr) 함량의 상한을 0.3%로 제한할 수 있다. 따라서, 본 발명의 크롬(Cr) 함량은 0.05~0.3%일 수 있으며, 보다 바람직한 크롬(Cr) 함량은 0.05~0.2%일 수 있다. Since chromium (Cr) is an element contributing to the increase in strength, the present invention can limit the lower limit of the chromium (Cr) content to 0.05% in order to achieve this effect. However, chromium (Cr) is an expensive element and is not preferable from the viewpoint of economy when it is added in excess. Therefore, the present invention can limit the upper limit of the chromium (Cr) content to 0.3%. Accordingly, the chromium (Cr) content of the present invention may be 0.05 to 0.3%, and more preferably, the chromium (Cr) content may be 0.05 to 0.2%.
니켈(Ni): 0.05~0.6%Nickel (Ni): 0.05 to 0.6%
니켈(Ni)은 저온 인성의 향상에 효과적인 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 니켈(Ni) 함량의 하한을 0.05%로 제한할 수 있다. 다만, 니켈(Ni)은 고가의 원소이므로, 과다하게 첨가되는 경우 생산비용의 상승을 초래하는바, 본 발명은 니켈(Ni) 함량의 상한을 0.6%로 제한할 수 있다. 따라서, 본 발명의 니켈(Ni) 함량은 0.05~0.6%일 수 있으며, 보다 바람직한 니켈(Ni) 함량은 0.2~0.6%일 수 있다.Nickel (Ni) is an effective element for improving the low temperature toughness. Therefore, the present invention can limit the lower limit of the nickel (Ni) content to 0.05% in order to achieve this effect. However, nickel (Ni) is an expensive element, and if it is added in excess, the production cost is increased. The present invention can limit the upper limit of nickel (Ni) content to 0.6%. Accordingly, the nickel content of the present invention may be 0.05 to 0.6%, and more preferably, the nickel content may be 0.2 to 0.6%.
구리(Cu): 0.005~0.35% Copper (Cu): 0.005 to 0.35%
구리(Cu)는 강도 증가에 효과적인 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 구리(Cu) 함량의 하한을 0.005%로 제한할 수 있다. 다만, 구리(Cu)는 고가의 원소이므로, 과다하게 첨가되는 경우 생산비용의 상승을 초래하는바, 본 발명은 구리(Cu) 함량의 상한을 0.35%로 제한할 수 있다. 따라서, 본 발명의 구리(Cu) 함량은 0.005~0.35%일 수 있으며, 보다 바람직한 구리(Cu) 함량은 0.01~0.3%일 수 있다.Copper (Cu) is an effective element for increasing the strength. Therefore, the present invention can limit the lower limit of the copper (Cu) content to 0.005% to achieve this effect. However, copper (Cu) is an expensive element, and if it is added in an excessive amount, the production cost is increased. Therefore, the present invention can limit the upper limit of copper (Cu) content to 0.35%. Accordingly, the copper (Cu) content of the present invention may be 0.005 to 0.35%, and more preferably, the copper (Cu) content may be 0.01 to 0.3%.
몰리브덴(Mo): 0.05~0.2%Molybdenum (Mo): 0.05 to 0.2%
몰리브덴(Mo)은 강도 향상에 유효한 합금 원소이며, 황화물을 형성하여 균열 발생을 방지하는 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 몰리브덴(Mo) 함량의 하한을 0.05%로 제한할 수 있다. 다만, 몰리브덴(Mo) 역시 고가의 원소로서, 과다하게 첨가되는 경우 생산비용의 상승을 초래하는바, 본 발명은 몰리브덴(Mo) 함량의 상한을 0.2%로 제한할 수 있다. 따라서, 본 발명의 몰리브덴(Mo) 함량은 0.05~0.2%일 수 있으며, 보다 바람직한 몰리브덴(Mo) 함량은 0.1~0.2%일 수 있다.Molybdenum (Mo) is an element which is effective for improving the strength and is an element which forms a sulfide to prevent the occurrence of cracks. Therefore, the present invention can limit the lower limit of the molybdenum (Mo) content to 0.05% in order to achieve this effect. However, molybdenum (Mo) is also an expensive element, and if it is added in excess, the production cost is increased. The present invention can limit the upper limit of molybdenum (Mo) content to 0.2%. Accordingly, the molybdenum (Mo) content of the present invention may be 0.05 to 0.2%, and more preferably, the molybdenum (Mo) content may be 0.1 to 0.2%.
바나듐(V): 0.005~0.07%Vanadium (V): 0.005 to 0.07%
바나듐(V)은 저온 인성의 향상에 효과적인 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 바나듐(V) 함량의 하한을 0.005%로 제한할 수 있다. 다만, 바나듐(V) 역시 고가의 원소로서, 과다하게 첨가되는 경우 생산비용의 상승을 초래하는바, 본 발명은 바나듐(V) 함량의 상한을 0.07%로 제한할 수 있다. 따라서, 본 발명의 바나듐(V) 함량은 0.005~0.07%일 수 있으며, 보다 바람직한 바나듐(V) 함량은 0.01~0.07%일 수 있다.Vanadium (V) is an effective element for improving low-temperature toughness. Therefore, the present invention can limit the lower limit of the vanadium (V) content to 0.005% in order to achieve this effect. However, when vanadium (V) is also an expensive element, if it is added in excess, the production cost is increased. The present invention can limit the upper limit of vanadium (V) content to 0.07%. Accordingly, the vanadium (V) content of the present invention may be 0.005 to 0.07%, and more preferably, the vanadium (V) content may be 0.01 to 0.07%.
니오븀(Nb): 0.005~0.04%Niobium (Nb): 0.005 to 0.04%
니오븀(Nb)은 오스테나이트에 고용되어 오스테나이트의 경화능을 증대시키는 원소이다. 또한, 니오븀(Nb)은 티타늄(Ti)과 더불어 기지(Matric)와 정합을 이루는 탄질화물(Nb(C, N))로 석출되는 원소로서, 본 발명이 추구하는 600MPa 이상의 인장강도를 얻는데 주요한 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 니오븀(Nb) 함량의 하한을 0.005%로 제한할 수 있다. 다만, 니오븀(Nb)이 과다하게 첨가되는 경우, 연주 과정에서 조대한 석출물을 형성하여 수소유기균열(HIC)의 개시점으로 작용할 수 있는바, 본 발명은 니오븀(Nb) 함량의 상한을 0.04%로 제한할 수 있다. 따라서, 본 발명의 니오븀(Nb) 함량은 0.005~0.04%일 수 있으며, 보다 바람직한 니오븀(Nb) 함량은 0.01~0.03%일 수 있다.Niobium (Nb) is an element that is solidified in austenite and increases the hardenability of austenite. Niobium (Nb) is an element which is precipitated in carbonitride (Nb (C, N)) which is in conformity with the matrix in addition to titanium (Ti). In order to obtain the tensile strength of 600 MPa or more pursued by the present invention, to be. Therefore, the present invention can limit the lower limit of the niobium (Nb) content to 0.005% in order to achieve this effect. However, when excess niobium (Nb) is added, coarse precipitates are formed in the course of performance and can act as a starting point of hydrogen organic cracking (HIC). The present invention is characterized in that the upper limit of the content of niobium (Nb) . Accordingly, the niobium (Nb) content of the present invention can be 0.005 to 0.04%, and more preferably, the niobium (Nb) content can be 0.01 to 0.03%.
칼슘(Ca): 0.0005~0.005%Calcium (Ca): 0.0005 to 0.005%
칼슘(Ca)은 황(S)과 결합되어 CaS 석출물을 형성하는바, MnS의 형성 억제에 효과적인 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 칼슘(Ca) 함량의 하한을 0.0005%로 제한할 수 있다. 다만, 칼슘(Ca)이 과다하게 첨가되는 경우, 강중의 산소와 반응하여 비금속 개재물인 CaO를 생성하므로, 본 발명은 칼슘(Ca) 함량의 상한을 0.005%로 제한할 수 있다. 따라서, 본 발명의 칼슘(Ca) 함량은 0.0005~0.005%일 수 있으며, 보다 바람직한 칼슘(Ca) 함량은 0.001~0.003%일 수 있다.Calcium (Ca) binds with sulfur (S) to form CaS precipitate, which is an element effective for inhibiting the formation of MnS. Therefore, the present invention can limit the lower limit of the calcium (Ca) content to 0.0005% in order to achieve this effect. However, when calcium (Ca) is added in excess, it reacts with oxygen in the steel to produce CaO, which is a nonmetallic inclusion. Therefore, the present invention can limit the upper limit of calcium (Ca) content to 0.005%. Accordingly, the calcium content of the present invention may be 0.0005 to 0.005%, and more preferably, the calcium content may be 0.001 to 0.003%.
티타늄(Ti): 0.005~0.025%Titanium (Ti): 0.005 to 0.025%
티타늄(Ti)의 적정 함량은 질소(N)의 함량에 따라 유동적으로 제한될 수 있다. 만일 질소(N)의 함량에 비해 티타늄(Ti)의 함량이 상대적으로 작은 경우, TiN의 생성량이 작아져서 결정립을 미세화시키는데 불리하다. 반면, 티타늄(Ti)이 과량으로 첨가되면 가열 공정 중 TiN이 조대해져서 결정립 성장 억제 효과가 감소하게 된다. 따라서, 본 발명은 통상적으로 함유되는 질소(N)의 함량(0.002~0.006%)을 고려하여 티타늄(Ti)의 함량을 0.005~0.025%의 범위로 제한할 수 있다. 보다 바람직한 티타늄(Ti) 함량은 0.01~0.02%일 수 있다.The titratable amount of titanium (Ti) can be flexibly limited depending on the content of nitrogen (N). If the content of titanium (Ti) is relatively small compared to the content of nitrogen (N), the amount of TiN produced becomes small, which is disadvantageous in refining the crystal grains. On the other hand, when titanium (Ti) is added in an excessive amount, TiN becomes coarse during the heating process and the effect of inhibiting grain growth is decreased. Therefore, in the present invention, the content of titanium (Ti) can be limited within the range of 0.005 to 0.025% in consideration of the content (0.002 to 0.006%) of nitrogen (N) normally contained. A more preferable titanium (Ti) content may be 0.01 to 0.02%.
질소(N): 0.002~0.006%Nitrogen (N): 0.002 to 0.006%
질소(N)는 티타늄(Ti)과 함께 TiN 석출물을 형성하여 결정립을 미세화시킴으로써, 모재의 인성 및 열영향부(HAZ)의 충격 인성을 증대시키는 역할을 하는 원소로 널리 알려져 있으며, 본 발명에서도 질소(N)는 결정립 미세화의 목적을 달성하기 위하여 반드시 첨가되어야 하는 원소이다. 따라서, 본 발명은 이러한 효과를 달성하기 위하여 질소(N) 함량의 하한을 0.002%로 제한할 수 있다. 다만, 질소(N) 함량이 과다하게 첨가된 경우, TiN의 생성량이 지나치게 증가하고, 저온인성이 저하될 수 있는바, 본 발명은 질소(N) 함량의 상한을 0.006%로 제한할 수 있다. 따라서, 본 발명의 질소(N) 함량은 0.002~0.006%일 수 있으며, 보다 바람직한 질소(N) 함량은 0.002~0.004%일 수 있다. Nitrogen (N) is widely known as an element that plays a role in increasing the toughness of the base material and impact toughness of the heat affected zone (HAZ) by forming TiN precipitates together with titanium (Ti) to refine the crystal grains. (N) is an element that must be added in order to achieve the purpose of grain refinement. Therefore, the present invention can limit the lower limit of the nitrogen (N) content to 0.002% to achieve this effect. However, if the nitrogen (N) content is excessively added, the amount of TiN may be excessively increased and the low temperature toughness may be lowered. Therefore, the present invention can limit the upper limit of the nitrogen (N) content to 0.006%. Accordingly, the nitrogen (N) content of the present invention may be 0.002 to 0.006%, and more preferably, the nitrogen (N) content may be 0.002 to 0.004%.
보론(B): 0.0005% 미만Boron (B): less than 0.0005%
본 발명은 보론(B)의 함량을 적극적으로 억제하나, 제강공정상 불가피하게 유입되는 보론(B)을 완전 제거하는 데에는 과다한 비용이 소모될 수 있다. 따라서, 본 발명은 보론(B) 함량을 0.005% 미만으로 제한할 수 있다. 바람직한 보론(B) 함량은 0.0002% 이하일 수 있으며, 더욱 바람직한 보론(B) 함량은 0.0001% 이하일 수 있다.The present invention positively suppresses the content of boron (B), but excessive cost may be consumed to completely remove boron (B) that is inevitably introduced in the steelmaking process. Therefore, the present invention can limit the boron (B) content to less than 0.005%. The preferred boron (B) content may be 0.0002% or less, and more preferably, the boron (B) content may be 0.0001% or less.
본 발명의 일 측면에 따른 고강도 강판은, Cu + Ni + Cr + Mo: 1.5% 이하; Cr + Mo: 0.4% 이하; V + Nb: 0.1% 이하; 및 Ca/S: 1.0 이상의 관계를 만족할 수 있다.According to an aspect of the present invention, there is provided a high strength steel sheet comprising: a steel sheet having a composition of Cu + Ni + Cr + Mo: 1.5% or less; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: 1.0 or more can be satisfied.
이하 본 발명의 관계식에 대해 보다 상세히 설명한다.Hereinafter, the relational expression of the present invention will be described in more detail.
Cu + Ni + Cr + Mo: 1.5% 이하Cu + Ni + Cr + Mo: 1.5% or less
Cr + Mo: 0.4% 이하Cr + Mo: not more than 0.4%
V + Nb: 0.1% 이하V + Nb: not more than 0.1%
Ca/S: 1.0 이상Ca / S: 1.0 or higher
Cu + Ni + Cr +Mo, Cr + Mo 및 V + Nb의 관계는 압력용기용 강재의 기본 규격(ASTM A20)에서 각각 제한하고 있는 수치로서, Cu + Ni + Cr + Mo의 함량은 1.5% 이하, Cr + Mo의 함량은 0.4% 이하, 그리고 V + Nb의 함량은 0.1% 이하로 제한할 수 있다. 또한, Ca/s의 비는 MnS 개재물을 구상화시켜 수소유기균열 저항성을 향상시키는 필수 구성비로서, 1.0 미만에서는 그 효과를 기대하기 어려운바, 그 비율이 1.0 이상을 만족하도록 제한할 수 있다.The relationship between Cu + Ni + Cr + Mo, Cr + Mo, and V + Nb is a numerical value limited by the basic standard (ASTM A20) of steel for pressure vessels, and the content of Cu + Ni + Cr + Mo is 1.5% , The content of Cr + Mo is 0.4% or less, and the content of V + Nb is 0.1% or less. Further, the Ca / s ratio is an essential constituent ratio for improving the hydrogen organic cracking resistance by spheroidizing the MnS inclusions. When the ratio is less than 1.0, the effect is not expected to be expected, and the ratio can be limited to satisfy 1.0 or more.
이하, 본 발명의 미세조직에 대해 보다 상세히 설명한다.Hereinafter, the microstructure of the present invention will be described in more detail.
본 발명의 일 측면에 따른 고강도 강판은, 템퍼드 마르텐사이트 및 템퍼드 베이나이트의 혼합조직을 미세조직으로 포함할 수 있다.The high strength steel sheet according to one aspect of the present invention may include a mixed structure of tempered martensite and tempered bainite in a microstructure.
미세조직: 템퍼드 마르텐사이트 및 템퍼드 베이나이트의 혼합조직Microstructure: Mixed texture of tempered martensite and tempered bainite
전술한 합금 조성으로 구비되는 강재를 급냉 및 템퍼링 처리를 하는 경우, 강재의 미세조직은 템퍼드 마르텐사이트 및 템퍼드 베이나이트의 미세조직을 가지게 된다. 본 발명에서 템퍼드 마르텐사이트 및 템퍼드 베이나이트는 면적분율로 30~60% 및 40~70%로 각각 포함되는바, 600MPa급의 인장강도, -50℃ 이하의 무연성 천이온도(nil-ductility temperature) 특성 및 -60℃에서 250J 이상의 샤르피 인장강도를 효과적으로 확보할 수 있다. 바람직한 템퍼드 마르텐사이트의 면적분율은 40~60%일 수 있으며, 바람직한 템퍼드 베이나이트의 면적분율은 40~60%일 수 있다. 또한, 템퍼드 마르텐사이트 및 템퍼드 베이트나이트의 면적분율의 합은 100%일 수 있다.When the steel material having the above-described alloy composition is quenched and tempered, the microstructure of the steel material has a microstructure of tempered martensite and tempered bainite. In the present invention, the tempered martensite and the tempered bainite are contained in an area fraction of 30 to 60% and 40 to 70%, respectively. The tensile strength is 600 MPa, the nil-ductility temperature characteristic and a Charpy tensile strength of 250 J or more at -60 캜. The preferred area of the tempered martensite may be 40 to 60%, and the preferred area of the tempered bainite may be 40 to 60%. In addition, the sum of the area fraction of the tempered martensite and the tempered bait knit may be 100%.
결정립 형상비: 1.1≤장축/단축≤2.5Grain aspect ratio: 1.1? Long axis / Short axis? 2.5
본 발명은 높은 충격인성 및 강도를 확보하기 위해 결정립 형상비(장축/단축의 비율)을 일정범위로 제어할 수 있으며, 이와 같은 결정립 형상비는 압연(재결정 제어 압연) 공정을 통해 제어될 수 있다. 결정립 형상비가 1.1 미만인 경우, 결정립의 형상이 둥글게 되어 표면 에너지가 작아지고, 결정립의 미세화를 기대하기 어려운바, 충분한 충격인성 및 강도의 확보가 어렵게 된다. 또한, 결정립의 형상비가 2.5를 초과하는 경우, 결정립을 형성하기 위한 압연 부하가 지나치게 커지며, 충격인성 저하가 우려되는바, 바람직하지 않다. 따라서, 본 발명은 결정립 형상비(장축/단축의 비율)를 1.1~2.5의 범위로 제한할 수 있다.The present invention can control the ratio of crystal grains (long axis / short axis ratio) to a certain range in order to secure high impact toughness and strength, and such a grain aspect ratio can be controlled through a rolling (recrystallization controlled rolling) process. When the aspect ratio of the crystal grains is less than 1.1, the shape of the crystal grains is rounded, the surface energy is small, and it is difficult to expect finer crystal grains, which makes it difficult to secure sufficient impact toughness and strength. In addition, when the aspect ratio of the crystal grains exceeds 2.5, the rolling load for forming the crystal grains becomes excessively large and the impact toughness is lowered, which is not preferable. Therefore, in the present invention, the crystal aspect ratio (long axis / short axis ratio) can be limited to a range of 1.1 to 2.5.
이하, 본 발명의 제조방법에 대해 보다 상세히 설명한다.Hereinafter, the production method of the present invention will be described in more detail.
본 발명의 일 측면에 따른 고강도 강판은, 중량%로, C: 0.05~0.20%, Si: 0.15~0.55%, Mn: 0.9~1.75%, Al: 0.001~0.05%, P: 0.03% 이하, S: 0.03% 이하, Cr: 0.05~0.3%, Ni: 0.05~0.6%, Cu: 0.005~0.35%, Mo: 0.05~0.2%, V: 0.005~0.07%, Nb: 0.005~0.04%, Ca: 0.0005~0.005%, Ti: 0.005~0.025%, N: 0.002~0.006%, B: 0.0005% 미만, 잔부 Fe 및 불가피한 불순물을 포함하며, Cu + Ni + Cr + Mo: 1.5% 이하; Cr + Mo: 0.4% 이하; V + Nb: 0.1% 이하; 및 Ca/S: 1.0 이상;의 관계를 만족하는 강 슬라브를 1050~1250℃의 온도범위로 재가열하고; Tnr~(Tnr+100℃)의 온도범위에서 상기 슬라브를 압연하여 강판을 제공하고; 870~950℃의 온도범위에서 상기 강판을 오스테나이징 열처리하고; 상기 오스테나이징 열처리된 강판을 급냉하고; 595~700℃의 온도범위에서 상기 급냉된 강판을 템퍼링 열처리하여 제조될 수 있다.The high strength steel sheet according to one aspect of the present invention comprises 0.05 to 0.20% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% Ni + Cr + Mo: not more than 1.5%, and the balance Fe and unavoidable impurities, wherein the content of Ca is 0.0005 to 0.005%, the content of Ca is 0.005 to 0.025%, the content of Ti is 0.005 to 0.025%, the content of N is 0.002 to 0.006% Below; Cr + Mo: 0.4% or less; V + Nb: 0.1% or less; And Ca / S: not less than 1.0; reheating the steel slab to a temperature range of 1050 to 1250 占 폚; Rolling the slab in a temperature range from Tnr to (Tnr + 100 占 폚) to provide a steel sheet; Subjecting the steel sheet to an osteonizing heat treatment in a temperature range of 870 to 950 캜; Quenching the austenized heat treated steel sheet; And tempering the quenched steel sheet in a temperature range of 595 to 700 ° C.
본 발명 슬라브의 합금조성 및 그 함량은 전술한 고강도 강판의 합금조성 및 그 함량과 대응하는바, 본 발명 슬라브의 합금조성 및 그 함량에 대한 설명은 전술한 강판의 합금조성 및 그 함량에 대한 설명으로 대신한다. The alloy composition and the content of the slab of the present invention correspond to the alloy composition and the content of the high-strength steel sheet described above. The description of the alloy composition and the content thereof of the slab of the present invention is based on the description of the alloy composition and the content thereof .
슬라브 재가열: 1050~1250℃Reheating slab: 1050 ~ 1250 ℃
본 발명에서는 전술한 합금조성으로 구비되는 슬라브를 1050~1250℃의 온도에서 재가열할 수 있다. 재가열 온도가 1050℃ 미만인 경우, 용질원자의 충분한 고용이 어렵고, 재가열 온도가 1250℃를 초과하는 경우, 오스테나이트 결정립의 크기가 지나치게 조대화되어 강판의 물성이 저하되기 때문이다.In the present invention, the slab having the above-described alloy composition can be reheated at a temperature of 1050 to 1250 ° C. When the reheating temperature is lower than 1050 占 폚, it is difficult to sufficiently solidify the solute atoms, and when the reheating temperature exceeds 1250 占 폚, the size of the austenite grains becomes excessively coarse and the physical properties of the steel sheet deteriorate.
재결정 제어 압연: Tnr~(Tnr+100℃)의 온도범위, 각 압연 패스당 10% 이상의 압하율로 누적압하량 50~90%Recrystallization Control Rolling: Cumulative rolling reduction of 50 to 90% at a temperature range of Tnr to (Tnr + 100 ° C), a reduction rate of 10% or more per each rolling pass,
재결정 제어 압연은 미재결정 이상의 온도에서 압연을 행하는 것을 의미하며, 미재결정온도인 Tnr은 기공지된 하기의 식 1을 통해 도출 가능하다. 단, 하기의 식 1에서 각 합금원소의 단위는 중량%를 의미한다.The recrystallization control rolling means rolling at a temperature not lower than the non-recrystallization temperature, and the non-recrystallization temperature Tnr can be derived from the previously known formula (1). However, the unit of each alloy element in the following formula 1 means weight%.
[식 1][Formula 1]
Tnr(℃)=887-464×C+890×Ti+363×Al-357×Si+(6445×Nb-644×Nb1/2)+(732×V-230×V1/2)Tnr (° C.) = 887-464 × C + 890 × Ti + 363 × Al-357 × Si + (6445 × Nb-644 × Nb 1/2 ) + (732 × V-230 × V 1/2 )
강도의 향상을 위해서는 재결정 제어 압연 과정에서 구 오스테나이트의 평균 입경을 30㎛ 이하로 미세화시킬 필요가 있다. 구 오스테나이트의 평균 입경이 30㎛를 초과하는 경우에는 제품의 강도 및 인성이 충분히 나타날 수 없으므로, 원자로 격납 용기로 사용할 수 있는 수준의 안전성을 보증할 수 없다. 이를 위하여, 본 발명에서는 Tnr~Tnr+100℃의 온도 범위에서 압연을 실시한다.In order to improve the strength, it is necessary to make the average grain size of the old austenite to 30 μm or less in the recrystallization controlled rolling process. If the average particle diameter of the old austenite exceeds 30 탆, the strength and toughness of the product can not be sufficiently exhibited, so that the safety of the product can not be guaranteed to the level that can be used in the reactor containment vessel. For this purpose, in the present invention, rolling is performed in a temperature range of Tnr to Tnr + 100 占 폚.
이 경우, 압연 구간에서는 각 압연 패스당 10% 이상의 압하율을 가하여 최종적으로 누적압하량 50~90% 의 범위로 압연이 이루어진다. 이러한 압하량은 본 발명에서 요구하는 미세조직의 평균 크기(30㎛ 이하)와 결정립 형상비(장축/단축)를 1.1~2.5로 제어하기 위한 것이다. 따라서, 누적압하량이 50% 미만인 경우, 미세조직의 미세화 및 결정립 형상비의 제어 효과를 기대하기 어렵고, 누적 압하량이 90%를 초과하는 경우, 압연부하가 과도하게 가해지므로 공정상 문제가 발생할 수 있다.In this case, in the rolling section, a reduction rate of 10% or more is applied to each rolling pass, and the rolling is finally performed within a range of 50 to 90% of cumulative rolling reduction. This reduction amount is intended to control the average size (less than 30 占 퐉) and the aspect ratio (major axis / minor axis) of the microstructure required in the present invention to 1.1 to 2.5. Therefore, when the cumulative rolling reduction is less than 50%, it is difficult to expect a finer microstructure and a control effect of the grain shape ratio, and when the cumulative rolling reduction exceeds 90%, the rolling load is excessively applied.
열처리 및 급냉: 870~950℃의 온도범위에서 1.6×t(단, t는 강판의 두께(mm)를 의미함) + (10~30분)간 오스테나이징 열처리한 후 급냉Heat treatment and quenching: 1.6 × t in the temperature range of 870 ~ 950 ℃ (t means thickness (mm) of the steel plate) + (10-30 minutes)
급냉 공정은 템퍼드 마르텐사이트 및 템퍼드 베이나이트의 혼합조직을 얻기 위한 중요한 공정으로, 600MPa 이상의 인장 강도, 250J 이상의 -60℃ 샤르피 충격인성 및 -50℃ 이하의 무연성 천이온도(nil-ductility temperature) 특성을 확보 가능한 미세조직 형성을 위하여 공정 조건을 엄격하게 제어할 필요가 있다.The quenching process is an important process for obtaining a mixed structure of tempered martensite and tempered bainite. The quenching process has a tensile strength of 600 MPa or more, a Charpy impact toughness of -60 ° C. of 250 J or more, and a nil-ductility temperature It is necessary to strictly control the process conditions in order to form the microstructure capable of securing the characteristics of the microstructure.
본 발명에서는 870~950℃의 온도범위에서 1.6×t(단, t는 강판의 두께(mm)를 의미함)+(10~30분)간 오스테나이징 열처리를 실시할 수 있다. 이러한 오스테나이징 열처리는 급냉 전에 조직을 오스테나이트화 시키기 위한 가열 처리로서, 열처리의 온도가 870℃ 미만인 경우, 고용 용질 원소들의 재고용이 어려워 강도 확보가 어려워지며, 열처리 온도가 950℃를 초과하는 경우, 결정립의 성장이 일어나 조대립이 발생하여 저온인성을 해칠 수 있다. 따라서, 본 발명의 오스테나이징 열처리 온도범위는 870~950℃의 온도범위로 제한할 수 있다.In the present invention, an austenizing heat treatment can be performed in a temperature range of 870 to 950 캜 for 1.6 x t (t means the thickness (mm) of the steel plate) + (10 to 30 minutes). Such austenizing heat treatment is a heat treatment for austenitizing the structure before quenching. When the temperature of the heat treatment is less than 870 占 폚, it is difficult to secure the strength by reusing the solid solute elements. If the heat treatment temperature exceeds 950 占 폚 , The growth of crystal grains occurs, and a coarse grain is generated, which may damage low-temperature toughness. Therefore, the osteonizing heat treatment temperature range of the present invention can be limited to a temperature range of 870 to 950 占 폚.
또한, 본 발명에서 오스테나이징 열처리리는 1.6*t(단, 여기서 t는 강판의 두께(mm)를 의미함) + (10~30분)의 시간동안 실시될 수 있다. 오스테나이징 열처리 시간이 과도하게 짧은 경우, 가열 시간이 충분하지 않아 충분한 오스테나이징의 효과를 기대할 수 없으며, 조직을 균질화가 어려울 수 있다. 반면, 오스테나이징 열처리 시간이 과도하게 긴 경우, 제품 생산 시간이 장기화되어 생산성이 저하될 수 있다. 따라서, 본 발명의 오스테나이징 열처리 시간은 1.6*t(단, 여기서 t는 강판의 두께(mm)를 의미함) + (10~30분)으로 한정할 수 있다. 참고로, 강판 제조 공정에 있어서, 1.6 * t를 가열 시간으로 책정하고, 목표 온도에 도달할 경우 10~30분을 유지 시간으로 책정하여 오스테나이징 열처리를 수행할 수 있다.In the present invention, the osteonizing heat treatment may be performed for a time of 1.6 * t (where t represents the thickness (mm) of the steel plate) + (10 to 30 minutes). If the austenizing heat treatment time is excessively short, sufficient heating time is not sufficient and sufficient osteonizing effect can not be expected, and homogenization of the structure may be difficult. On the other hand, if the austenizing heat treatment time is excessively long, product production may be prolonged and productivity may be deteriorated. Therefore, the osteonizing heat treatment time of the present invention can be limited to 1.6 * t (where t denotes the thickness (mm) of the steel plate) + (10 to 30 minutes). For reference, an austenizing heat treatment can be performed by setting the heating time to 1.6 * t in the steel sheet manufacturing process and setting the holding time to 10 to 30 minutes when the target temperature is reached.
오스테나이징 열처리가 종료된 강판은 급랭, 바람직하게는 수냉 처리되어 마르텐사이트 및 베이나이트의 혼합조직으로 변태될 수 있다. 본 발명에서의 급랭 처리는 특별히 그 조건을 제한하지 않으며, 통상적인 수냉을 비롯한 급랭 처리 방법이라면 본 발명의 급랭에 적용 가능하다. 다만, 본 발명이 목적하는 미세조직을 얻기 위하여 오스테나이징 열처리가 종료된 강판은 300℃ 이하의 온도로 냉각되는 것이 바람직하다.The steel sheet subjected to the austenizing heat treatment may be quenched, preferably water-cooled, and transformed into a mixed structure of martensite and bainite. The quenching treatment in the present invention is not particularly limited and the quenching treatment method including ordinary water cooling is applicable to the quenching of the present invention. However, in order to obtain the desired microstructure of the present invention, it is preferable that the steel sheet subjected to osteonizing heat treatment is cooled to a temperature of 300 ° C or less.
템퍼링 열처리: 595~700℃의 온도범위에서 2.4×t(단, t는 강판의 두께(mm)를 의미함)+(10~30분)간 실시Tempering heat treatment: 2.4 × t in the temperature range of 595 ~ 700 ℃ (t means thickness (mm) of steel plate) + (10 ~ 30 minutes)
본 발명에서는 우수한 인장강도, 무연성 천이온도 특성 및 저온인성을 확보하기 위하여, 300℃ 이하로 급랭 처리된 강재를 템퍼링 열처리하여 조직의 잔류 응력을 제거하며, 그에 따라 템퍼드 마르텐사이트 및 템퍼드 베이나이트 조직을 가질 수 있다.In the present invention, in order to secure an excellent tensile strength, a non-transition temperature characteristic and a low temperature toughness, the steel material quenched at 300 ° C or less is subjected to tempering treatment to remove the residual stress of the structure, It can have a knit structure.
본 발명의 템퍼링 열처리 온도범위는 595~700℃로 제한할 수 있다. 템퍼링 열처리 온도가 595℃ 미만이 경우, 탄화물 등의 석출이 원활하지 않고, 템퍼링 열처리 온도가 700℃를 초과하는 경우, 강재의 강도가 저하될 수 있기 때문이다.The tempering heat treatment temperature range of the present invention can be limited to 595 to 700 캜. When the tempering heat treatment temperature is less than 595 DEG C, precipitation of carbides and the like is not smooth, and when the tempering heat treatment temperature exceeds 700 DEG C, the strength of the steel material may be lowered.
또한, 본 발명의 템퍼링 열처리는 충분한 템퍼링 효과를 얻기 위하여 2.4*t(단, 여기서 t는 강판의 두께(mm)를 의미함) + (10~30분) 동안 실시될 수 있다. 참고로, 강판 제조 공정에 있어서, 2.4*t를 가열 시간으로 책정하고, 목표 온도에 도달할 경우 10~30분을 유지 시간으로 책정하여 템퍼링 열처리를 수행할 수 있다.Further, the tempering heat treatment of the present invention can be performed for 2.4 * t (where t means the thickness (mm) of the steel sheet) + (10-30 minutes) for obtaining a sufficient tempering effect. For reference, in the steel sheet manufacturing process, 2.4 * t is set as the heating time, and when reaching the target temperature, the tempering heat treatment can be performed by setting the holding time to 10 to 30 minutes.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다. 다만, 후술하는 실시예는 본 발명을 예시하여 보다 구체화하기 위한 것일 뿐, 본 발명의 권리범위를 제한하기 위한 것이 아니라는 점에 유의할 필요가 있다. Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the embodiments described below are for the purpose of further illustrating the present invention and are not for limiting the scope of the present invention.
하기 표 1의 합금조성으로 구비되는 슬라브를 제조하였다.A slab having an alloy composition shown in Table 1 was prepared.
조성(중량%)Composition (% by weight) 발명강 aInventive steel 발명강 bInvention river b 발명강 cInventive Steel c 비교강 dComparative River d 비교강 eComparative River e 비교강 fComparative steel f
CC 0.100.10 0.090.09 0.120.12 0.060.06 0.070.07 0.090.09
MnMn 1.511.51 1.581.58 0.920.92 1.301.30 1.351.35 0.780.78
AlAl 0.020.02 0.030.03 0.0320.032 0.0350.035 0.0300.030 0.0320.032
SiSi 0.350.35 0.360.36 0.360.36 0.350.35 0.340.34 0.360.36
PP 0.0090.009 0.0100.010 0.0080.008 0.0080.008 0.0100.010 0.0100.010
SS 0.00100.0010 0.00080.0008 0.00110.0011 0.00130.0013 0.00140.0014 0.00120.0012
CuCu 0.030.03 0.040.04 0.030.03 0.050.05 -- --
NiNi 0.500.50 0.550.55 0.530.53 0.050.05 0.150.15 0.100.10
CrCr 0.050.05 0.050.05 0.060.06 0.030.03 0.050.05 0.040.04
MoMo 0.150.15 0.180.18 0.170.17 0.150.15 0.100.10 0.160.16
VV 0.0300.030 0.0250.025 0.0300.030 0.0030.003 0.0050.005 0.0300.030
NbNb 0.0120.012 0.0140.014 0.0130.013 0.0130.013 0.0120.012 0.0150.015
BB -- -- -- 0.00150.0015 0.00120.0012 0.00070.0007
TiTi 0.0120.012 0.0100.010 0.0130.013 0.0130.013 0.0120.012 0.0130.013
NN 0.00280.0028 0.00350.0035 0.00340.0034 0.00280.0028 0.00350.0035 0.00320.0032
CaCa 0.00200.0020 0.00190.0019 0.00210.0021 0.00180.0018 0.00210.0021 0.00200.0020
상기 발명강 및 비교강의 조성으로 제조된 각각의 슬라브를 이용하여 하기의 표 2의 조건과 같이 재가열, 재결정 제어 압연, 오스테나이징 열처리 및 급냉, 템퍼링 열처리를 하여 시험편을 제조하였으며, 각각의 시험편 대한 강도, 저온인성, 무연성 천이온도(nil-ductility transition temperature) 등의 물성을 평가하여 그 결과를 하기의 표 3에 나타내었다. 하기의 표 3에서 저온 충격인성은 -60℃에서 V 노치를 갖는 시편을 샤르피 충격 시험을 행하여 얻은 샤르피 충격 에너지 값으로 평가한 것이다. 또한, 무연성 천이온도(nil-ductility transition temperature)는 ASTM E208-06 방법에 의해 실시되는 낙중시험 천이온도 설정에 따른 결과값이다.The test specimens were produced by reheating, recrystallization controlled rolling, austenizing annealing and quenching and tempering heat treatment using the slabs prepared in the composition of the inventive steel and the comparative steel as shown in Table 2 below. Strength, low-temperature toughness, and nil-ductility transition temperature. The results are shown in Table 3 below. In the following Table 3, the low-temperature impact toughness was evaluated by the Charpy impact energy value obtained by performing the Charpy impact test on the specimen having the V notch at -60 ° C. In addition, the nil-ductility transition temperature is a value according to the drop test transition temperature set by the ASTM E208-06 method.
구분division 조건Condition 강판두께(mm)Steel plate thickness (mm) 슬라브재가열온도(℃)Reheating temperature of slab (℃) 압연온도(℃)Rolling temperature (캜) 재결정제어 압연누적 압하량(%)Recrystallization Control Rolling cumulative rolling reduction (%) 결정립형상비*Grain aspect ratio * 오스테나이징온도(℃)Austenizing temperature (캜) 템퍼링온도(℃)Tempering temperature (℃)
발명강 aInventive steel a-1a-1 4545 12001200 780780 6060 1.751.75 900900 680680
a-2a-2 8080 11801180 780780 5555 1.951.95 920920 660660
a-3a-3 100100 11001100 790790 5050 1.251.25 910910 650650
a-4a-4 5050 11001100 790790 4545 1.011.01 910910 660660
발명강 bInvention river b b-1b-1 4545 11501150 780780 7070 2.152.15 910910 680680
b-2b-2 8080 11001100 780780 6060 2.002.00 920920 660660
b-3b-3 100100 11001100 790790 5555 1.651.65 900900 650650
발명강 cInventive Steel c CC 5050 11501150 780780 7575 1.981.98 900900 660660
비교강 dComparative River d d-1d-1 4545 12001200 780780 2020 1.021.02 920**920 ** 680680
d-2d-2 100100 11501150 790790 3030 1.051.05 900**900 ** 650650
비교강 eComparative River e EE 100100 11001100 780780 4040 1.061.06 900**900 ** 650650
비교강 fComparative steel f ff 8080 11501150 790790 5555 1.031.03 900900 650650
* 결정립 형상비: 결정립 장축/결정립 단축* Grain aspect ratio: Grain length axis / Grain length shortening
** 비교재의 금냉 온도는 노멀라이징 온도임** The cooling temperature of the comparative material is the normalizing temperature
구분division 조건Condition 템퍼드마르텐사이트조직분율(%)Tempated Martensite Tissue Fraction (%) 템퍼드베이나이트조직분율(%)Tempered bainite Tissue fraction (%) YS(MPa)YS (MPa) TS(MPa)TS (MPa) -60℃충격인성(J)***-60 ℃ Impact Toughness (J) *** NDT천이온도(℃)****NDT transition temperature (캜) **** 비고Remarks
발명강 aInventive steel a-1a-1 5656 4444 634634 649649 334334 -80-80 발명예 1Inventory 1
a-2a-2 5151 4949 641641 641641 324324 -70-70 발명예 2Inventory 2
a-3a-3 4848 5252 628628 634634 313313 -65-65 발명예 3Inventory 3
a-4a-4 6262 3838 580580 701701 5858 -40-40 비교예 1Comparative Example 1
발명강 bInvention river b b-1b-1 5858 4242 642642 660660 324324 -85-85 발명예 4Honorable 4
b-2b-2 5050 5050 648648 652652 318318 -70-70 발명예 5Inventory 5
b-3b-3 4545 5555 634634 635635 334334 -70-70 발명예 6Inventory 6
발명강 cInventive Steel c CC 5555 4545 542542 650650 320320 -80-80 발명예 7Honorable 7
비교강 dComparative River d d-1d-1 8585 1515 370370 639639 180180 -40-40 비교예 2Comparative Example 2
d-2d-2 8080 2020 365365 630630 172172 -45-45 비교예 3Comparative Example 3
비교강 eComparative River e EE 8282 1818 358358 630630 193193 -40-40 비교예 4Comparative Example 4
비교강 fComparative steel f FF 8585 1515 443443 650650 140140 -30-30 비교예 5Comparative Example 5
*** 충격인성: T방향(압연방향에 직각으로 V-노치를 줌) 충격인성임*** Impact Toughness: T direction (V-notch perpendicular to the rolling direction) Impact Toughness
**** NDT 천이온도: ASTM208-06 방법에 의해 실시되는 낙중시험 천이온도임**** NDT transition temperature: Falling test transition temperature as per ASTM 208-06 method
상기 표 2 및 표 3의 결과를 살펴보면, 발명예 1 내지 발명예 7은 면적분율로 30~60%의 템퍼드 마르텐사이트 및 면적분율로 40~70%의 템퍼드 베이나이트 혼합조직의 미세조직을 가지며, 600MPa 이상의 인장강도, -60℃에서 300J 이상의 충격인성 및 -50℃ 이하의 무연성 천이온도(nil-ductility temperature) 특성을 확보하는 것을 확인할 수 있다. From the results of Tables 2 and 3, Inventive Examples 1 to 7 show the microstructure of 30 to 60% tempered martensite as an area fraction and 40 to 70% tempered bainite mixed texture as an area fraction And it is confirmed that the tensile strength of 600 MPa or more, the impact toughness of 300 J or more at -60 ° C, and the nil-ductility temperature characteristic of -50 ° C or less are secured.
반면, 비교예 1의 경우, 강 조성은 본 발명의 강 조성을 만족하나, 재결정 제어 압연 누적 압하량이 본 본 발명이 범위에 미치지 못하는바, 본 발명의 미세조직 면적분율을 만족하지 못하며, 그에 따라 및 -50℃ 이하의 무연성 천이온도(nil-ductility temperature) 특성을 확보하지 못하는 것을 확인할 수 있다.On the other hand, in the case of Comparative Example 1, the steel composition satisfies the steel composition of the present invention, but the rolling regression control rolling reduction amount does not fall within the scope of the present invention, so that the microstructure area fraction of the present invention is not satisfied, It can be confirmed that the nil-ductility temperature characteristic of -50 ° C or less can not be secured.
또한, 비교예 2 내지 비교예 5의 경우, 강 조성이 본 발명의 강 조성을 만족하지 못하는바, 면적분율로 80% 이상의 템퍼드 마르텐사이트 및 면적분율로 20% 이하의 템퍼드 베이나이트 혼합조직의 미세조직을 가지며, 인장강도, 충격인성 및 무연성 천이온도((nil-ductility temperature) 특성이 열위한 것을 확인할 수 있다. In the case of Comparative Examples 2 to 5, since the steel composition does not satisfy the steel composition of the present invention, tempered martensite having an area fraction of 80% or more and tempered bainite mixed structure having an area fraction of 20% It can be confirmed that the microstructure has tensile strength, impact toughness and nil-ductility temperature characteristics.
따라서, 본 발명의 일 실시예에 의한 강판은 강 조성, 미세조직 및 제조공정을 최적의 조건으로 제어하여, 600MPa 이상의 인장강도, -60℃에서 250J 이상의 샤르피 충격인성 및 -50℃ 이하의 무연성 천이온도(nil-ductility temperature) 특성을 확보하는바, 원자력발전소의 원자로 격납 용기에 적합한 물성을 구비하는 고강도 강판을 제공할 수 있다.Therefore, the steel sheet according to one embodiment of the present invention can be manufactured by controlling the steel composition, the microstructure and the manufacturing process under the optimum conditions, so that the tensile strength of 600 MPa or more, the Charpy impact toughness of 250 J or more at -60 캜, It is possible to provide a high-strength steel plate having physical properties suitable for a reactor containment vessel of a nuclear power plant, by ensuring nil-ductility temperature characteristics.
이상에서 실시예를 통하여 본 발명을 상세하게 설명하였으나, 이와 다른 형태의 실시예들도 가능하다. 그러므로, 이하에 기재된 청구항들의 기술적 사상과 범위는 실시예들에 한정되지 않는다.While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, Therefore, the technical idea and scope of the claims set forth below are not limited to the embodiments.

Claims (12)

  1. 중량%로, C: 0.05~0.20%, Si: 0.15~0.55%, Mn: 0.9~1.75%, Al: 0.001~0.05%, P: 0.03% 이하, S: 0.03% 이하, Cr: 0.05~0.3%, Ni: 0.05~0.6%, Cu: 0.005~0.35%, Mo: 0.05~0.2%, V: 0.005~0.07%, Nb: 0.005~0.04%, Ca: 0.0005~0.005%, Ti: 0.005~0.025%, N: 0.002~0.006%, B: 0.0005% 미만, 잔부 Fe 및 불가피한 불순물을 포함하며,The steel sheet contains 0.05 to 0.20% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% 0.001 to 0.04% of Ca, 0.005 to 0.005% of Ca, 0.005 to 0.025% of Ti, 0.002 to 0.006% of N, less than 0.0005% of B, the balance Fe and unavoidable impurities,
    Cu + Ni + Cr + Mo: 1.5% 이하;Cu + Ni + Cr + Mo: 1.5% or less;
    Cr + Mo: 0.4% 이하;Cr + Mo: 0.4% or less;
    V + Nb: 0.1% 이하; 및V + Nb: 0.1% or less; And
    Ca/S: 1.0 이상의 관계를 만족하며,Ca / S: 1.0 or more,
    템퍼드 마르텐사이트 및 템퍼드 베이나이트의 혼합조직을 미세조직으로 포함하는 고강도 강판. A high strength steel sheet comprising microstructure of mixed structure of tempered martensite and tempered bainite.
  2. 제1항에 있어서,The method according to claim 1,
    상기 템퍼드 마르텐사이트는 30~60%의 면적분율로 포함되고,The tempered martensite is contained in an area fraction of 30 to 60%
    상기 템퍼드 베이나이트는 40~70%의 면적분율로 포함되며,The tempered bainite is included in an area fraction of 40 to 70%
    상기 템퍼드 마르텐사이트 및 상기 템퍼드 베이나이트의 면적분율의 합은 100%인, 고강도 강판.Wherein the sum of the areas of the tempered martensite and the tempered bainite is 100%.
  3. 제2항에 있어서,3. The method of claim 2,
    상기 템퍼드 마르텐사이트는 40~60%의 면적분율로 포함되고,The tempered martensite is contained in an area fraction of 40 to 60%
    상기 템퍼드 베이나이트는 40~60%의 면적분율로 포함되는, 고강도 강판.Wherein the tempered bainite is included in an area fraction of 40 to 60%.
  4. 제1항 내지 제3항 중 어느 한 항에 있어서,4. The method according to any one of claims 1 to 3,
    상기 강판의 무연성 천이온도(nil-ductility transition temperature)는 -50℃ 이하인, 고강도 강판. Wherein the nil-ductility transition temperature of the steel sheet is not higher than -50 ° C.
  5. 제1항 내지 제3항 중 어느 한 항에 있어서,4. The method according to any one of claims 1 to 3,
    상기 강판의 인장강도는 600MPa 이상인, 고강도 강판. The tensile strength of the steel sheet is 600 MPa or more.
  6. 제1항 내지 제3항 중 어느 한 항에 있어서,4. The method according to any one of claims 1 to 3,
    상기 강판의 샤르피 충격인성은 -60℃에서 300J 이상인, 고강도 강판.The Charpy impact toughness of the steel sheet is not less than 300 J at -60 캜.
  7. 제1항 내지 제3항 중 어느 한 항에 있어서,4. The method according to any one of claims 1 to 3,
    상기 미세조직의 결정립 형상비(장축/단축)는 1.1~2.5인, 고강도 강판.Wherein the crystal grain ratio (major axis / minor axis) of the microstructure is 1.1 to 2.5.
  8. 중량%로, C: 0.05~0.20%, Si: 0.15~0.55%, Mn: 0.9~1.75%, Al: 0.001~0.05%, P: 0.03% 이하, S: 0.03% 이하, Cr: 0.05~0.3%, Ni: 0.05~0.6%, Cu: 0.005~0.35%, Mo: 0.05~0.2%, V: 0.005~0.07%, Nb: 0.005~0.04%, Ca: 0.0005~0.005%, Ti: 0.005~0.025%, N: 0.002~0.006%, B: 0.0005% 미만, 잔부 Fe 및 불가피한 불순물을 포함하며,The steel sheet contains 0.05 to 0.20% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, P: not more than 0.03%, S: not more than 0.03%, Cr: 0.05-0.3%, Ni: 0.05-0.6%, Cu: 0.005-0.35%, Mo: 0.05-0.2%, V: 0.005-0.07% 0.001 to 0.04% of Ca, 0.005 to 0.005% of Ca, 0.005 to 0.025% of Ti, 0.002 to 0.006% of N, less than 0.0005% of B, the balance Fe and unavoidable impurities,
    Cu + Ni + Cr + Mo: 1.5% 이하;Cu + Ni + Cr + Mo: 1.5% or less;
    Cr + Mo: 0.4% 이하;Cr + Mo: 0.4% or less;
    V + Nb: 0.1% 이하; 및V + Nb: 0.1% or less; And
    Ca/S: 1.0 이상;의 관계를 만족하는 강 슬라브를 1050~1250℃의 온도범위로 재가열하고;The steel slab satisfying the relation of Ca / S: 1.0 or more is reheated in a temperature range of 1050 to 1250 占 폚;
    Tnr~Tnr + 100℃의 온도범위에서 상기 슬라브를 압연하여 강판을 제공하고;Rolling the slab in a temperature range from Tnr to Tnr + 100 占 폚 to provide a steel sheet;
    870~950℃의 온도범위에서 상기 강판을 오스테나이징 열처리하고;Subjecting the steel sheet to an osteonizing heat treatment in a temperature range of 870 to 950 캜;
    상기 오스테나이징 열처리된 강판을 300℃ 이하의 온도범위로 급냉하고;Quenching the austenized heat treated steel sheet to a temperature range of 300 DEG C or less;
    595~700℃의 온도범위에서 상기 급냉된 강판을 템퍼링 열처리;하는 고강도 강판의 제조방법. Tempering the quenched steel sheet in a temperature range of 595 to 700 占 폚.
  9. 제8항에 있어서,9. The method of claim 8,
    상기 압연의 누적압하량은 50~90%인, 고강도 강판의 제조방법.Wherein the cumulative rolling reduction of the rolling is 50 to 90%.
  10. 제8항 또는 제9항에 있어서,10. The method according to claim 8 or 9,
    상기 압연에 의해 상기 강판 미세조직의 결정립 형상비(장축/단축)가 1.1~2.5의 범위로 제어되는, 고강도 강판의 제조방법.(Long axis / short axis) of the steel microstructure is controlled to fall within the range of 1.1 to 2.5 by the rolling.
  11. 제8항에 있어서,9. The method of claim 8,
    상기 오스테나이징 열처리는 1.6*t(단, 여기서 t는 강판의 두께(mm)를 의미함) + (10~30분)의 시간동안 수행되는, 고강도 강판의 제조방법.Wherein the austenizing heat treatment is performed for a period of 1.6 * t (where t represents the thickness (mm) of the steel sheet) + (10 to 30 minutes).
  12. 제8항에 있어서,9. The method of claim 8,
    상기 템퍼링 열처리는 2.4*t(단, 여기서 t는 강판의 두께(mm)를 의미함) + (10~30분)의 시간동안 수행되는, 고강도 강판의 제조방법.Wherein the tempering heat treatment is performed for a time of 2.4 * t (where t is the thickness of the steel sheet in mm) + (10 to 30 minutes).
PCT/KR2018/014855 2017-12-24 2018-11-28 High strength steel sheet and manufacturing method therefor WO2019124793A1 (en)

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