WO2023121027A1 - Steel plate having high strength and excellent low-temperature impact toughness, and method for manufacturing same - Google Patents

Steel plate having high strength and excellent low-temperature impact toughness, and method for manufacturing same Download PDF

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WO2023121027A1
WO2023121027A1 PCT/KR2022/019039 KR2022019039W WO2023121027A1 WO 2023121027 A1 WO2023121027 A1 WO 2023121027A1 KR 2022019039 W KR2022019039 W KR 2022019039W WO 2023121027 A1 WO2023121027 A1 WO 2023121027A1
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Prior art keywords
steel sheet
thickness
less
steel
rolling
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PCT/KR2022/019039
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French (fr)
Korean (ko)
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김우겸
김상호
변영섭
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주식회사 포스코
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Publication of WO2023121027A1 publication Critical patent/WO2023121027A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/63—Quenching devices for bath quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—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
    • C22C38/18—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
    • C22C38/48—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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to a thick steel plate and a manufacturing method thereof, and more particularly, to a thick steel plate having high strength and excellent low-temperature impact toughness and a manufacturing method thereof.
  • renewable energy is a term that combines new energy (hydrogen, fuel cell, etc.) and renewable energy (solar heat, wind power, bio, etc.). It is gaining attention as an energy source.
  • onshore wind power installed on land has recently been rapidly growing, centering on Europe, on offshore wind power built on the sea due to its duties, optimal wind formation, and space limitations.
  • the substructure of offshore wind power is largely divided into monopile and jacket, and the jacket type substructure is divided into pinpile or suction bucket type according to the fixing method of the seabed.
  • the monopile substructure In the case of the monopile substructure, it is divided into a monopile part that is driven into the sea floor and a transition piece that connects the monopile and the tower part. In this structure, the load rises the most, and high-strength steel can be mainly applied to the connection portion between the monopile and the transition piece, which is a joint.
  • An important supporting part of such an offshore wind power substructure is a thick steel plate capable of guaranteeing not only high strength but also ultra-thickness and low-temperature toughness.
  • it is intended to provide a thick steel plate having high strength and excellent low-temperature impact toughness and a manufacturing method thereof.
  • C 0.04 ⁇ 0.08%, Si: 0.1 ⁇ 0.35%, Mn: 1.4 ⁇ 1.8%, Sol.Al: 0.01 ⁇ 0.035%, Ni: 0.2 ⁇ 0.5%, Cr: 0.1 ⁇ 0.3%, Mo: 0.05 ⁇ 0.15%, Nb: 0.015 ⁇ 0.035%, Ti: 0.005 ⁇ 0.02%, N: 0.002 ⁇ 0.006%, P: 0.01% or less, S: 0.003% or less, balance iron (Fe) and other unavoidable impurities;
  • the microstructure at the 1/4th of the thickness is mainly composed of a mixture of escular ferrite and bainite, and contains less than 2 area% of residual cementite and MA in total,
  • the steel sheet may include 40 to 60 area% of escular ferrite and 40 to 60 area% of bainite with a microstructure of 1/4 of the thickness.
  • the steel sheet may include 1 area% or less in total of cementite and MA.
  • the steel sheet may have an average grain size of 15 to 25 ⁇ m of escular ferrite at a thickness of 1/4.
  • the steel sheet may have a thickness of 50 to 100 mm.
  • the steel sheet may have a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness of 100 J or more at -50 ° C.
  • C 0.04 ⁇ 0.08%
  • Si 0.1 ⁇ 0.35%
  • Mn 1.4 ⁇ 1.8%
  • Sol.Al 0.01 ⁇ 0.035%
  • Ni 0.2 ⁇ 0.5%
  • Cr 0.1 ⁇ 0.3%
  • Mo 0.05 ⁇ 0.15%
  • Nb 0.015 ⁇ 0.035%
  • Ti 0.005 ⁇ 0.02%
  • N 0.002 ⁇ 0.006%
  • P 0.01% or less
  • S 0.003% or less
  • balance iron (Fe ) and other unavoidable impurities and reheating a steel slab having an R value of 0.85 to 1.35 defined in relational expression 1 below;
  • It is possible to provide a steel sheet manufacturing method comprising the step of water-cooling the non-recrystallization station rolled steel sheet to a temperature range of 400° C. or less based on a point of 1/4 of the steel sheet thickness.
  • the reheating it is carried out in a temperature range of 1020 to 1100 ° C,
  • the cumulative reduction ratio may be 30 to 50%.
  • the cooling it may be cooled at a cooling rate of 5 to 10° C./s based on a point of 1/4 of the thickness of the steel sheet.
  • the steel sheet may have a thickness of 50 to 100 mm.
  • a thick steel plate that can be applied as a steel for ultra-thick offshore wind power because of its excellent strength and low-temperature impact toughness, and can also be used as a structural steel for infrastructure industries such as construction and bridges, and a manufacturing method thereof. there is.
  • FIG. 1 is a photograph of a microstructure of an inventive example according to an embodiment of the present invention observed at 500 magnification using an optical microscope.
  • % indicating the content of each element is based on weight.
  • Carbon (C) is an element for securing tensile strength by causing solid solution strengthening and existing as a carbonitride by Nb or the like, and its content can be limited to 0.04% or more. On the other hand, if the carbon (C) content exceeds 0.08%, it not only promotes the formation of MA, but also generates pearlite, which can deteriorate impact properties at low temperatures, and when welding structures, there is a concern that the welding properties may be deteriorated. there is A more preferable upper limit of carbon (C) may be 0.07%.
  • Silicon (Si) serves to deoxidize molten steel by assisting Al and is an element necessary for securing yield strength and tensile strength, and may contain 0.1% or more of its content. However, if the content exceeds 0.35%, there may be a problem of promoting MA formation by hindering the diffusion of C. More preferably, silicon (Si) may be included in an amount of 0.15% or more, and more preferably, 0.25% or less.
  • Manganese (Mn) is preferably added in an amount of 1.4% or more because the effect of increasing strength by solid solution strengthening is large. On the other hand, if the content is excessive, it may cause a decrease in toughness due to the formation of MnS inclusions and central segregation, so the upper limit may be limited to 1.8%.
  • Aluminum (Sol.Al) is a major deoxidizing agent for steel, and it is preferable to add 0.01% or more to obtain the effect.
  • the content exceeds 0.035%, the Al 2 O 3 inclusion fraction and size may increase, which may cause low-temperature toughness to deteriorate.
  • low-temperature toughness may be deteriorated by accelerating the generation of MA in the base metal and the weld heat-affected zone. More preferably, it may contain 0.015% or more, and more preferably, it may contain 0.03% or less.
  • Nickel (Ni) is an element that improves strength without reducing impact toughness, and since it can increase strength by promoting the formation of an appropriate amount of escular ferrite, it is preferable to add 0.2% or more. On the other hand, if the content exceeds 0.5%, bainite may be formed by lowering the Ar3 temperature, and there is a risk of lowering impact toughness in ultra-thick materials. A more preferred lower limit may be 0.3%.
  • Chromium (Cr) is a carbide-forming element that is advantageous for securing strength, but in ultra-thick steels, it can form coarse carbide depending on the cooling rate of the steel to impair impact toughness, so its content should be limited to 0.1 ⁇ 0.3% can A more preferable lower limit of the content may be 0.15%.
  • Molybdenum (Mo) is an element that effectively increases strength with a small amount of addition, and it is preferable to add 0.05% or more because Mo-C-based precipitates are formed to improve strength.
  • the upper limit may be limited to 0.15%.
  • the lower limit of the more preferred content may be 0.08%, and the upper limit of the more preferred content may be 0.12%.
  • Niobium (Nb) is an element that suppresses recrystallization during rolling or cooling by precipitating solid solution or carbonitride to make the structure fine and increases strength, and may be added in an amount of 0.015% or more.
  • the upper limit can be limited to 0.035% because C concentration occurs due to C affinity and promotes MA production, which can lower toughness and fracture characteristics at low temperatures.
  • a more preferred lower limit may be 0.02%, and a more preferred upper limit may be 0.03%.
  • Titanium (Ti) may form a precipitate by combining with oxygen or nitrogen. Since these precipitates play a role of suppressing the coarsening of the structure, contributing to miniaturization, and improving toughness, it is preferable to add 0.005% or more. However, if the content exceeds 0.02%, there is a risk of causing destruction due to coarsening of precipitates. A more preferred lower limit may be 0.01%, and a more preferred upper limit may be 0.018%.
  • Nitrogen (N) forms precipitates together with Ti, Nb, Al, etc., and refines the austenite structure during reheating, thereby helping to improve strength and toughness.
  • N Nitrogen
  • it if it is excessively contained, it can cause surface cracking and form precipitates at high temperatures, and the remaining nitrogen (N) exists in an atomic state and there is a risk of reducing toughness. can be limited
  • Phosphorus (P) 0.01% or less
  • Phosphorus (P) is an element that causes grain boundary segregation and can cause steel to become embrittled, so its upper limit can be limited to 0.01%. However, 0% can be excluded in consideration of the level inevitably added to steel.
  • S Sulfur
  • MnS inclusions Sulfur (S) may be mainly combined with Mn to form MnS inclusions, and as a result, it may be a factor that inhibits low-temperature toughness. Therefore, the upper limit may be limited to 0.003% in order to secure low-temperature toughness and low-temperature fatigue characteristics. However, 0% can be excluded in consideration of the level inevitably added to steel.
  • the steel of the present invention may include remaining iron (Fe) and unavoidable impurities in addition to the above-described composition. Since unavoidable impurities may be unintentionally incorporated in the normal manufacturing process, they cannot be excluded. Since these impurities are known to anyone skilled in the steel manufacturing field, not all of them are specifically mentioned in this specification.
  • copper (Cu) may be added as an impurity, but in the present invention, the content of copper (Cu) may be limited to less than 0.05%.
  • the steel according to one aspect of the present invention may have an R value of 0.85 to 1.35 defined in the following relational expression 1.
  • relational expression 1 is proposed to secure strength and low-temperature toughness at -50 ° C at the same time.
  • Relational Equation 1 relates to a component formula for securing strength and toughness, and by controlling the R value of Relational Equation 1, it is possible to secure desired levels of strength and low-temperature toughness in the present invention. If the R value in relational expression 1 is less than 0.85, there is a problem in that the desired yield strength cannot be secured due to lack of solid solution hardening, precipitation hardening, and hardenability, etc., and when the value exceeds 1.35, hard structures such as MA and bainite Formation may result in poor impact toughness.
  • % representing the fraction of the microstructure is based on the area unless otherwise specified.
  • the steel according to one aspect of the present invention has a microstructure of 1/4 of the thickness, and may contain 40 to 60 area% of escular ferrite, 40 to 60 area% of bainite, and 2% or less in total of residual cementite and MA. there is.
  • the size, dislocation density, etc. of escular ferrite are important, and it is preferable to minimize cementite and MA. More preferably, cementite and MA may be included in an amount of 1% or less in total.
  • the thickness 1/4 point in the present invention means t/4, where t means the thickness of the steel sheet.
  • an average grain size of escular ferrite at a thickness of 1/4 may be 25 ⁇ m or less.
  • the average grain size of escular ferrite may be limited to 25 ⁇ m or less in order to secure low-temperature impact toughness. If the size exceeds 25 ⁇ m, there may be a problem in that the value of impact absorption energy at -50 ° C is lowered. On the other hand, due to the nature of the thick steel plate having a thickness of 50 mm or more, which is intended in the present invention, there is a limit to the refinement of crystal grains, so the lower limit of the size can be limited to 15 ⁇ m.
  • Steel according to one aspect of the present invention can be produced by reheating, rolling and cooling a steel slab satisfying the above-described alloy composition.
  • a steel slab satisfying the alloy composition of the present invention can be reheated to a temperature range of 1020 to 1100 ° C.
  • the reheating temperature exceeds 1100° C.
  • the austenite crystal grains are coarsened, and the toughness may be reduced due to the development of a bainite structure due to the increase in hardenability.
  • the temperature is less than 1020 ° C., Ti, Nb, etc. may not be sufficiently dissolved, resulting in a decrease in strength.
  • the reheated steel slab may be subjected to recrystallization rolling with a rolling reduction of 15 to 25 mm in the last pass in a temperature range of 900 ° C. or higher.
  • the recrystallization rolling step is for complete recrystallization of austenite, refinement of austenite, and suppression of growth.
  • Recrystallization station rolling is preferably performed in a temperature range of 900° C. or higher for complete recrystallization of austenite, and the final pass reduction may be performed at 15 to 25 mm for initial austenite refinement. If the final pass reduction is less than 15 mm, it may be difficult to secure the desired level of refinement. Meanwhile, during rolling, the upper limit may be limited to 25 mm in consideration of productivity according to facility specifications.
  • the recrystallization station rolled steel sheet may be subjected to non-recrystallization station rolling at a rolling end temperature of Ar3 + 20 to Ar3 + 60 and a cumulative reduction ratio of 30 to 50%.
  • the rolling end temperature is closer to the Ar3 temperature for miniaturization of the size of the escular ferrite. If the non-recrystallization zone rolling end temperature is less than Ar3+20, the surface before cooling may enter the ideal zone of austenite and ferrite, and there may be a problem of forming a light phase on the surface when cooled. On the other hand, if the temperature exceeds Ar 3 + 60, there may be a problem in that crystal grains cannot be refined in non-recrystallization station rolling.
  • the cumulative reduction ratio is 30 to 50%. If the cumulative rolling reduction is less than 30%, the amount of non-recrystallization rolling is reduced, resulting in pan-caking of the structure and difficulty in miniaturization.
  • Ar3 910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]
  • the non-recrystallization station rolled steel sheet may be cooled to a temperature range of 400° C. or less at a cooling rate of 5 to 10° C./s based on a thickness of 1/4 point.
  • the thick steel plate for the purpose of the present invention secures the impact toughness around the 1/4 of the thickness. Therefore, the cooling rate limited in the present invention may be based on the 1/4 of the thickness. When the cooling end temperature exceeds 400° C. or the cooling rate exceeds 10° C./s, MA formation is promoted, resulting in poor impact toughness. On the other hand, if the cooling rate is less than 5 °C / s, it may be difficult to secure a desired level of strength. In the present invention, water cooling may be used as a cooling method.
  • the steel of the present invention thus prepared has a thickness of 50 to 100 mm, a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness of 100 J or more at -50 ° C., having high strength and excellent low-temperature impact toughness. characteristics can be provided.
  • Ar3 910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]
  • microstructure of the manufactured steel sheet was measured and described.
  • the microstructure was measured at a point of 1/4 of the thickness of the steel, and the fractions of escular ferrite (AF), cementite, and MA were shown, respectively, and the remaining fractions were observed as bainite.
  • AF escular ferrite
  • MA escular ferrite
  • the size of the crystal grains of escular ferrite at the point of 1/4 of the thickness of the steel was measured and shown.
  • the microstructure was measured by magnifying and analyzing at 500 times using an optical microscope.
  • Table 3 shows the measured physical property values for each of the prepared specimens. Yield strength (YS), tensile strength (TS), and elongation (El) were evaluated by performing a tensile test. According to EN-ISO 6892-1 standard, an annular specimen was taken in the direction perpendicular to the rolling direction at 1/4 of the thickness and twice. The tested average was determined. In addition, the impact toughness value at -50 °C was measured. Impact toughness was measured by taking specimens in the parallel direction of rolling at 1/4 of the thickness according to EN ISO 148-1 standard and measuring the average of three tests.
  • FIG. 1 is a photograph of a microstructure of an inventive example according to an embodiment of the present invention observed at 500 magnification using an optical microscope.
  • Comparative Examples 1 and 2 are examples that do not satisfy the alloy composition of the present invention, and did not secure the level of strength or impact toughness desired in the present invention. Specifically, in Comparative Example 1, the value of relational expression 1 was less than the range of the present invention, and the bainite fraction decreased, resulting in a decrease in strength. In Comparative Example 2, when the value of relational expression 1 exceeded the scope of the present invention, bainite was excessively formed, resulting in inferior impact toughness.
  • Comparative Example 3 is an example in which the cooling end temperature is outside the range of the present invention, and a large amount of cementite and MA fraction is formed, resulting in poor impact toughness.
  • Comparative Example 4 it can be seen that the non-recrystallization zone rolling end temperature is high, and the yield strength is lowered and the impact toughness at -50 ° C is inferior at the same time due to the lack of crystal grain refinement.
  • Comparative Example 6 satisfies the range of components proposed in the present invention, but does not satisfy the value of relational expression 1, and the impact toughness is rapidly decreased due to the decrease of escular ferrite and the excessive increase of bainite.

Abstract

The present invention pertains to a steel plate and a method for manufacturing same. More specifically, the present invention pertains to a steel plate having high strength and excellent low-temperature impact toughness, and a method for manufacturing same.

Description

저온 충격인성이 우수한 고강도 후강판 및 그 제조방법High-strength thick steel sheet with excellent low-temperature impact toughness and manufacturing method thereof
본 발명은 후강판 및 그 제조방법에 관한 것으로, 보다 상세하게는 고강도를 구비하면서도 저온 충격인성이 우수한 후강판 및 그 제조방법에 관한 것이다.The present invention relates to a thick steel plate and a manufacturing method thereof, and more particularly, to a thick steel plate having high strength and excellent low-temperature impact toughness and a manufacturing method thereof.
2000년대 이후 환경문제 및 온실가스 감축을 위한 신재생 에너지에 대하여 관심이 집중되고 있다. 신재생 에너지는 신에너지(수소, 연료전지 등)와 재생에너지(태양열, 풍력, 바이오 등)를 합쳐 지칭하는 용어로, 이 중에서 풍력 발전은 폐기물의 발생이 없고, 공해가 없는 친환경 발전 방식으로 차세대 에너지원으로 각광받고 있다. 풍력 발전 중에서 육상에 설치되는 육상 풍력은 소임 및 최적의 바람 형성과 공간의 제한 등으로 최근에는 바다에 건설하는 해상풍력(offshore wind)이 유럽을 중심으로 급격한 성장이 진행되고 있다.Since the 2000s, attention has been focused on renewable energy for environmental problems and greenhouse gas reduction. Renewable energy is a term that combines new energy (hydrogen, fuel cell, etc.) and renewable energy (solar heat, wind power, bio, etc.). It is gaining attention as an energy source. Among wind power generation, onshore wind power installed on land has recently been rapidly growing, centering on Europe, on offshore wind power built on the sea due to its duties, optimal wind formation, and space limitations.
이러한 해상풍력은 육상풍력보다 뒤늦게 활성화되었지만, 강판 풍속, 소음 발생에 대한 낮은 염려와 넓은 면적을 확보할 수 있다는 여러 장점으로 기술 수준이 발전하면서 육상풍력 대비 해상풍력의 상대적 우위가 점점 부각되고 있다. 특히, 풍력 1기당 발전용량을 육상풍력 대비 증가시킬 수 있다는 큰 장점이 있다. 다시 말해, 평균 발전용량이 육상풍력의 2배 정도이고, 유럽기준 1기당 터빈 신규 설치 평균 용량은 '15년 4MW에서 '19년 7.2MW로 급속하게 증대되고 있으며 2~3년 내에 10MW 이상으로 예상되고 있다.Although offshore wind power was activated later than onshore wind power, the relative superiority of offshore wind power over onshore wind power is gradually emerging as the technology level develops due to low concerns about steel plate wind speed and noise generation and various advantages of securing a large area. In particular, there is a great advantage that the generation capacity per wind power can be increased compared to onshore wind power. In other words, the average power generation capacity is about twice that of onshore wind power, and the average capacity of new turbine installation per unit in Europe is rapidly increasing from 4MW in 2015 to 7.2MW in 2019, and is expected to exceed 10MW within 2-3 years. It is becoming.
이에 따라, 적용되는 후강판의 강도가 점차 증가되어 두께 80mm 기준 항복강도 325MPa급이 대부분이었으나, 20년대 들어서면서 항복강도 380, 410MPa급 등이 적용되고 있다. 이러한 해상풍력의 하부구조는 크게 모노파일(Monopile)과 자켓(Jacket)으로 구분되며 자켓타입 하부구조는 해저면의 고정방식에 따라 핀파일(PinPile) 또는 석션버켓(Suction Bucket) 타입으로 나누어진다.Accordingly, the strength of the thick steel plate applied gradually increased, and the yield strength of 325 MPa based on the thickness of 80 mm was mostly applied, but in the 20s, yield strengths of 380 and 410 MPa were applied. The substructure of offshore wind power is largely divided into monopile and jacket, and the jacket type substructure is divided into pinpile or suction bucket type according to the fixing method of the seabed.
모노파일 하부구조의 경우 해저면 속으로 박히는 모노파일부, 모노파일과 타워부를 연결하는 트랜지션피스부(Transition Piece)로 구분된다. 이러한 구조에서 하중이 가장 상승하고, 이음부분인 모노파일과 트랜지션피스 연결부분에 고강도강이 주로 적용될 수 있다. 이러한 해상풍력 하부구조의 중요 지지 부위는 고강도뿐 아니라, 극후물, 저온인성 보증이 가능한 후강판이 사용된다.In the case of the monopile substructure, it is divided into a monopile part that is driven into the sea floor and a transition piece that connects the monopile and the tower part. In this structure, the load rises the most, and high-strength steel can be mainly applied to the connection portion between the monopile and the transition piece, which is a joint. An important supporting part of such an offshore wind power substructure is a thick steel plate capable of guaranteeing not only high strength but also ultra-thickness and low-temperature toughness.
본 발명의 일 측면에 따르면 고강도를 구비하면서도 저온 충격인성이 우수한 후강판 및 그 제조방법을 제공하고자 하는 것이다.According to one aspect of the present invention, it is intended to provide a thick steel plate having high strength and excellent low-temperature impact toughness and a manufacturing method thereof.
본 발명의 과제는 상술한 내용에 한정되지 않는다. 통상의 기술자라면 본 명세서의 전반적인 내용으로부터 본 발명의 추가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.The object of the present invention is not limited to the above. A person skilled in the art will have no difficulty understanding the further subject matter of the present invention from the general content of this specification.
본 발명의 일 측면은, 중량%로, C: 0.04~0.08%, Si: 0.1~0.35%, Mn: 1.4~1.8%, Sol.Al: 0.01~0.035%, Ni: 0.2~0.5%, Cr: 0.1~0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% 이하, S: 0.003% 이하, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함하고,One aspect of the present invention, in weight percent, C: 0.04 ~ 0.08%, Si: 0.1 ~ 0.35%, Mn: 1.4 ~ 1.8%, Sol.Al: 0.01 ~ 0.035%, Ni: 0.2 ~ 0.5%, Cr: 0.1~0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% or less, S: 0.003% or less, balance iron (Fe) and other unavoidable impurities;
하기 관계식 1에서 정의되는 R 값이 0.85~1.35이고,The R value defined in the following relational expression 1 is 0.85 to 1.35,
두께 1/4 지점의 미세조직은 에시큘라 페라이트 및 베이나이트 혼합조직을 주조직으로 하고, 잔여 시멘타이트와 MA를 합으로 2면적% 이하 포함하며,The microstructure at the 1/4th of the thickness is mainly composed of a mixture of escular ferrite and bainite, and contains less than 2 area% of residual cementite and MA in total,
두께 1/4 지점의 에시큘라 페라이트의 결정립 평균 크기가 25μm 이하인 강판을 제공할 수 있다.It is possible to provide a steel sheet having an average grain size of 1/4 of the thickness of escular ferrite of 25 μm or less.
[관계식 1][Relationship 1]
R = [Ni]+3[Mo]+2[Cr]R = [Ni]+3[Mo]+2[Cr]
(여기서, [Ni], [Mo] 및 [Cr]은 각 원소의 중량%이다.)(Where [Ni], [Mo] and [Cr] are the weight percent of each element.)
상기 강판은 두께 1/4 지점의 미세조직으로 에시큘라 페라이트를 40~60면적%, 베이나이트를 40~60면적% 포함할 수 있다.The steel sheet may include 40 to 60 area% of escular ferrite and 40 to 60 area% of bainite with a microstructure of 1/4 of the thickness.
상기 강판은 시멘타이트와 MA를 합으로 1면적% 이하 포함할 수 있다.The steel sheet may include 1 area% or less in total of cementite and MA.
상기 강판은 두께 1/4 지점의 에시큘라 페라이트의 결정립 평균 크기가 15~25μm일 수 있다.The steel sheet may have an average grain size of 15 to 25 μm of escular ferrite at a thickness of 1/4.
상기 강판은 두께가 50~100mm일 수 있다.The steel sheet may have a thickness of 50 to 100 mm.
상기 강판은 항복강도가 460MPa 이상이고, 인장강도가 580MPa 이상이고, -50℃에서의 충격인성이 100J 이상일 수 있다.The steel sheet may have a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness of 100 J or more at -50 ° C.
본 발명의 다른 일 측면은, 중량%로, C: 0.04~0.08%, Si: 0.1~0.35%, Mn: 1.4~1.8%, Sol.Al: 0.01~0.035%, Ni: 0.2~0.5%, Cr: 0.1~0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% 이하, S: 0.003% 이하, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함하고, 하기 관계식 1에서 정의되는 R 값이 0.85~1.35인 강 슬라브를 재가열하는 단계;Another aspect of the present invention, in weight%, C: 0.04 ~ 0.08%, Si: 0.1 ~ 0.35%, Mn: 1.4 ~ 1.8%, Sol.Al: 0.01 ~ 0.035%, Ni: 0.2 ~ 0.5%, Cr : 0.1~0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% or less, S: 0.003% or less, balance iron (Fe ) and other unavoidable impurities, and reheating a steel slab having an R value of 0.85 to 1.35 defined in relational expression 1 below;
상기 재가열된 강 슬라브를 900℃ 이상의 온도범위에서 마지막 패스의 압하량 15~25mm로 재결정역 압연하는 단계;Recrystallization reverse rolling of the reheated steel slab at a temperature range of 900° C. or higher with a rolling reduction of 15 to 25 mm in the last pass;
상기 재결정역 압연된 강판을 Ar3+20~Ar3+60의 압연종료온도로 미재결정역 압연하는 단계; 및 non-recrystallization station rolling of the steel sheet subjected to recrystallization station rolling at a rolling end temperature of Ar3+20 to Ar3+60; and
상기 미재결정역 압연된 강판을 강판 두께 1/4 지점을 기준으로 400℃ 이하의 온도범위까지 수냉하는 단계를 포함하는 강판 제조방법을 제공할 수 있다.It is possible to provide a steel sheet manufacturing method comprising the step of water-cooling the non-recrystallization station rolled steel sheet to a temperature range of 400° C. or less based on a point of 1/4 of the steel sheet thickness.
[관계식 1][Relationship 1]
R = [Ni]+3[Mo]+2[Cr]R = [Ni]+3[Mo]+2[Cr]
(여기서, [Ni], [Mo] 및 [Cr]은 각 원소의 중량%이다.)(Where [Ni], [Mo] and [Cr] are the weight percent of each element.)
상기 재가열 시, 1020~1100℃의 온도범위로 행하고,During the reheating, it is carried out in a temperature range of 1020 to 1100 ° C,
상기 미재결정역 압연 시, 누적 압하율은 30~50%일 수 있다.During the rolling of the non-recrystallization region, the cumulative reduction ratio may be 30 to 50%.
상기 냉각 시, 강판 두께 1/4 지점을 기준으로 5~10℃/s의 냉각속도로 냉각할 수 있다.During the cooling, it may be cooled at a cooling rate of 5 to 10° C./s based on a point of 1/4 of the thickness of the steel sheet.
상기 강판은 두께가 50~100mm일 수 있다.The steel sheet may have a thickness of 50 to 100 mm.
본 발명의 일 측면에 따르면 고강도를 구비하면서도 저온 충격인성이 우수한 후강판 및 그 제조방법을 제공할 수 있다.According to one aspect of the present invention, it is possible to provide a thick steel plate having high strength and excellent low-temperature impact toughness and a manufacturing method thereof.
본 발명의 일 측면에 따르면 강도 및 저온 충격인성이 우수하여 극후물 해상풍력용 강재로 적용할 수 있으며, 건설, 교량 등의 인프라 산업용 구조용 강재로도 사용 가능한 후강판 및 그 제조방법을 제공할 수 있다.According to one aspect of the present invention, it is possible to provide a thick steel plate that can be applied as a steel for ultra-thick offshore wind power because of its excellent strength and low-temperature impact toughness, and can also be used as a structural steel for infrastructure industries such as construction and bridges, and a manufacturing method thereof. there is.
도 1은 본 발명의 일 실시예에 따른 발명예의 미세조직을 광학현미경을 이용하여 500배율로 관찰한 사진이다.1 is a photograph of a microstructure of an inventive example according to an embodiment of the present invention observed at 500 magnification using an optical microscope.
이하에서는 본 발명의 바람직한 구현예들을 설명하고자 한다. 본 발명의 구현예들은 여러 가지 형태로 변형될 수 있으며, 본 발명의 범위가 아래에서 설명되는 구현예들에 한정되는 것으로 해석되어서는 안된다. 본 구현예들은 당해 발명이 속하는 기술분야에서 통상의 기술자에게 본 발명을 더욱 상세하게 설명하기 위하여 제공되는 것이다.Hereinafter, preferred embodiments of the present invention will be described. Embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. These embodiments are provided to explain the present invention in more detail to those skilled in the art.
이하, 본 발명에 대하여 상세히 설명한다.Hereinafter, the present invention will be described in detail.
이하에서는, 본 발명의 강 조성에 대해 자세히 설명한다.Hereinafter, the steel composition of the present invention will be described in detail.
본 발명에서 특별히 달리 언급하지 않는 한 각 원소의 함량을 표시하는 %는 중량을 기준으로 한다.In the present invention, unless otherwise specified, % indicating the content of each element is based on weight.
본 발명의 일 측면에 따르는 강은 중량%로, C: 0.04~0.08%, Si: 0.1~0.35%, Mn: 1.4~1.8%, Sol.Al: 0.01~0.035%, Ni: 0.2~0.5%, Cr: 0.1~0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% 이하, S: 0.003% 이하, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함할 수 있다.Steel according to one aspect of the present invention, by weight%, C: 0.04 ~ 0.08%, Si: 0.1 ~ 0.35%, Mn: 1.4 ~ 1.8%, Sol.Al: 0.01 ~ 0.035%, Ni: 0.2 ~ 0.5%, Cr: 0.1 to 0.3%, Mo: 0.05 to 0.15%, Nb: 0.015 to 0.035%, Ti: 0.005 to 0.02%, N: 0.002 to 0.006%, P: 0.01% or less, S: 0.003% or less, balance iron ( Fe) and other unavoidable impurities.
탄소(C): 0.04~0.08%Carbon (C): 0.04 to 0.08%
탄소(C)는 고용강화를 일으키고 Nb 등에 의해 탄질화물로 존재하여 인장강도 확보를 위한 원소로, 그 함량을 0.04% 이상으로 제한할 수 있다. 반면, 탄소(C)의 함량이 0.08%를 초과할 경우 MA의 형성을 조장할 뿐 아니라, 펄라이트가 생성되어 저온에서의 충격 특성을 열화시킬 수 있으며, 구조물의 용접 시, 용접 특성을 악화시킬 우려가 있다. 보다 바람직한 탄소(C)의 상한은 0.07%일 수 있다.Carbon (C) is an element for securing tensile strength by causing solid solution strengthening and existing as a carbonitride by Nb or the like, and its content can be limited to 0.04% or more. On the other hand, if the carbon (C) content exceeds 0.08%, it not only promotes the formation of MA, but also generates pearlite, which can deteriorate impact properties at low temperatures, and when welding structures, there is a concern that the welding properties may be deteriorated. there is A more preferable upper limit of carbon (C) may be 0.07%.
실리콘(Si): 0.1~0.35%Silicon (Si): 0.1 to 0.35%
실리콘(Si)은 Al을 보조하여 용강을 탈산하는 역할을 수행하고, 항복강도 및 인장강도 확보를 위해 필요한 원소로, 그 함량을 0.1% 이상 포함할 수 있다. 그러나, 그 함량이 0.35%를 초과하면 C의 확산을 방해하여 MA 형성을 조장하는 문제점이 있을 수 있다. 보다 바람직하게는 실리콘(Si)을 0.15% 이상 포함할 수 있으며, 보다 바람직하게는 0.25% 이하로 포함할 수 있다.Silicon (Si) serves to deoxidize molten steel by assisting Al and is an element necessary for securing yield strength and tensile strength, and may contain 0.1% or more of its content. However, if the content exceeds 0.35%, there may be a problem of promoting MA formation by hindering the diffusion of C. More preferably, silicon (Si) may be included in an amount of 0.15% or more, and more preferably, 0.25% or less.
망간(Mn): 1.4~1.8%Manganese (Mn): 1.4 to 1.8%
망간(Mn)은 고용강화에 의한 강도 증가 효과가 크기 때문에 1.4% 이상 첨가하는 것이 바람직하다. 반면, 그 함량이 과도할 경우 MnS 개재물의 형성 및 중심부 편석으로 인해 인성의 저하를 야기할 수 있으므로, 그 상한은 1.8%로 제한할 수 있다.Manganese (Mn) is preferably added in an amount of 1.4% or more because the effect of increasing strength by solid solution strengthening is large. On the other hand, if the content is excessive, it may cause a decrease in toughness due to the formation of MnS inclusions and central segregation, so the upper limit may be limited to 1.8%.
알루미늄(Sol.Al): 0.01~0.035%Aluminum (Sol.Al): 0.01~0.035%
알루미늄(Sol.Al)은 강의 주요한 탈산제로, 그 효과를 얻기 위해서는 0.01% 이상 첨가하는 것이 바람직하다. 다만, 그 함량이 0.035%를 초과할 경우, Al2O3 개재물의 분율 및 크기의 증가로 저온인성을 저하시키는 원인이 될 수 있다. 또한, Si과 유사하게 모재 및 용접 열영향부의 MA의 생성을 촉진하여 저온인성 특성을 저하시킬 우려가 있다. 보다 바람직하게는 0.015% 이상 포함할 수 있으며, 보다 바람직하게는 0.03% 이하 포함할 수 있다.Aluminum (Sol.Al) is a major deoxidizing agent for steel, and it is preferable to add 0.01% or more to obtain the effect. However, when the content exceeds 0.035%, the Al 2 O 3 inclusion fraction and size may increase, which may cause low-temperature toughness to deteriorate. In addition, similar to Si, there is a concern that low-temperature toughness may be deteriorated by accelerating the generation of MA in the base metal and the weld heat-affected zone. More preferably, it may contain 0.015% or more, and more preferably, it may contain 0.03% or less.
니켈(Ni): 0.2~0.5%Nickel (Ni): 0.2 to 0.5%
니켈(Ni)은 충격인성을 저하하지 않으면서 동시에 강도를 향상시키는 원소로서, 적정량의 에시큘라 페라이트의 형성을 촉진하여 강도를 증가시킬 수 있으므로 0.2% 이상 첨가하는 것이 바람직하다. 반면, 그 함량이 0.5%를 초과하는 경우, Ar3 온도를 하락시켜 베이나이트를 형성시킬 수 있으며, 그로 인해 극후물에서의 충격인성이 저하될 위험이 있다. 보다 바람직한 하한은 0.3%일 수 있다.Nickel (Ni) is an element that improves strength without reducing impact toughness, and since it can increase strength by promoting the formation of an appropriate amount of escular ferrite, it is preferable to add 0.2% or more. On the other hand, if the content exceeds 0.5%, bainite may be formed by lowering the Ar3 temperature, and there is a risk of lowering impact toughness in ultra-thick materials. A more preferred lower limit may be 0.3%.
크롬(Cr): 0.1~0.3%Chromium (Cr): 0.1~0.3%
크롬(Cr)은 카바이드 형성 원소로 강도를 확보하기에 유리한 원소이지만, 극후물 강재에서 강의 냉각속도에 따라 조대한 카바이드를 형성하여 충격인성을 저해할 수 있으므로 그 함량을 0.1~0.3%로 제한할 수 있다. 보다 바람직한 함량의 하한은 0.15%일 수 있다.Chromium (Cr) is a carbide-forming element that is advantageous for securing strength, but in ultra-thick steels, it can form coarse carbide depending on the cooling rate of the steel to impair impact toughness, so its content should be limited to 0.1~0.3% can A more preferable lower limit of the content may be 0.15%.
몰리브덴(Mo): 0.05~0.15%Molybdenum (Mo): 0.05 to 0.15%
몰리브덴(Mo)은 소량의 첨가로 강도를 효과적으로 상승시키는 원소로, Mo-C 계열의 석출물을 형성하여 강도를 향상시키기 때문에 0.05% 이상 첨가하는 것이 바람직하다. 다만, 과도한 몰리브덴(Mo) 첨가로 인해 석출물의 조대화가 발생할 수 있으므로, 그 상한은 0.15%로 제한할 수 있다. 보다 바람직한 함량의 하한은 0.08%일 수 있으며, 보다 바람직한 함량의 상한은 0.12%일 수 있다.Molybdenum (Mo) is an element that effectively increases strength with a small amount of addition, and it is preferable to add 0.05% or more because Mo-C-based precipitates are formed to improve strength. However, since excessive addition of molybdenum (Mo) may cause coarsening of precipitates, the upper limit may be limited to 0.15%. The lower limit of the more preferred content may be 0.08%, and the upper limit of the more preferred content may be 0.12%.
니오븀(Nb): 0.015~0.035%Niobium (Nb): 0.015 to 0.035%
니오븀(Nb)은 고용 또는 탄질화물을 석출함으로써 압연 또는 냉각 중 재결정을 억제하여 조직을 미세하게 만들고, 강도를 증가시키는 원소로, 0.015% 이상 첨가할 수 있다. 그러나, C 친화력에 의해 C 집중이 발생하여 MA 생성을 촉진하여 저온에서의 인성과 파괴특성을 저하시킬 수 있으므로 그 상한을 0.035%로 제한할 수 있다. 보다 바람직한 하한은 0.02%일 수 있으며, 보다 바람직한 상한은 0.03%일 수 있다.Niobium (Nb) is an element that suppresses recrystallization during rolling or cooling by precipitating solid solution or carbonitride to make the structure fine and increases strength, and may be added in an amount of 0.015% or more. However, the upper limit can be limited to 0.035% because C concentration occurs due to C affinity and promotes MA production, which can lower toughness and fracture characteristics at low temperatures. A more preferred lower limit may be 0.02%, and a more preferred upper limit may be 0.03%.
티타늄(Ti): 0.005~0.02%Titanium (Ti): 0.005 to 0.02%
티타늄(Ti)은 산소 또는 질소와 결합하여 석출물을 형성할 수 있다. 이러한 석출물은 조직의 조대화를 억제하여 미세화에 기여하고, 인성을 향상시키는 역할을 수행하므로 0.005% 이상 첨가하는 것이 바람직하다. 다만, 그 함량이 0.02%를 초과할 경우, 석출물의 조대화에 의해 파괴의 원인이 될 우려가 있다. 보다 바람직한 하한은 0.01%일 수 있으며, 보다 바람직한 상한은 0.018%일 수 있다.Titanium (Ti) may form a precipitate by combining with oxygen or nitrogen. Since these precipitates play a role of suppressing the coarsening of the structure, contributing to miniaturization, and improving toughness, it is preferable to add 0.005% or more. However, if the content exceeds 0.02%, there is a risk of causing destruction due to coarsening of precipitates. A more preferred lower limit may be 0.01%, and a more preferred upper limit may be 0.018%.
질소(N): 0.002~0.006%Nitrogen (N): 0.002 to 0.006%
질소(N)는 Ti, Nb, Al 등과 함께 석출물을 형성하여 재가열 시, 오스테나이트 조직을 미세화하여 강도와 인성 향상에 도움이 될 수 있다. 그러나, 과도하게 함유할 경우, 고온에서 표면 크랙을 유발하고 석출물을 형성할 수 있으며, 잔류하는 질소(N)는 원자상태로 존재하여 인성을 감소시킬 우려가 있으므로, 그 함량을 0.002~0.006%로 제한할 수 있다.Nitrogen (N) forms precipitates together with Ti, Nb, Al, etc., and refines the austenite structure during reheating, thereby helping to improve strength and toughness. However, if it is excessively contained, it can cause surface cracking and form precipitates at high temperatures, and the remaining nitrogen (N) exists in an atomic state and there is a risk of reducing toughness. can be limited
인(P): 0.01% 이하Phosphorus (P): 0.01% or less
인(P)는 입계편석을 일으키는 원소로, 강을 취화시키는 원인이 될 수 있으므로 그 상한을 0.01%로 제한할 수 있다. 다만, 강 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외할 수 있다.Phosphorus (P) is an element that causes grain boundary segregation and can cause steel to become embrittled, so its upper limit can be limited to 0.01%. However, 0% can be excluded in consideration of the level inevitably added to steel.
황(S): 0.003% 이하Sulfur (S): 0.003% or less
황(S)은 주로 Mn과 결합하여 MnS 개재물을 형성할 수 있으며, 그 결과 저온인성을 저해하는 요인이 될 수 있다. 따라서, 저온인성과 저온 피로특성을 확보하기 위하여 그 상한을 0.003%로 제한할 수 있다. 다만, 강 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외할 수 있다.Sulfur (S) may be mainly combined with Mn to form MnS inclusions, and as a result, it may be a factor that inhibits low-temperature toughness. Therefore, the upper limit may be limited to 0.003% in order to secure low-temperature toughness and low-temperature fatigue characteristics. However, 0% can be excluded in consideration of the level inevitably added to steel.
본 발명의 강은, 상술한 조성 이외에 나머지 철(Fe) 및 불가피한 불순물을 포함할 수 있다. 불가피한 불순물은 통상의 제조공정에서 의도되지 않게 혼입될 수 있으므로, 이를 배제할 수는 없다. 이러한 불순물들은 통상의 철강제조분야의 기술자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 특별히 본 명세서에서 언급하지는 않는다.The steel of the present invention may include remaining iron (Fe) and unavoidable impurities in addition to the above-described composition. Since unavoidable impurities may be unintentionally incorporated in the normal manufacturing process, they cannot be excluded. Since these impurities are known to anyone skilled in the steel manufacturing field, not all of them are specifically mentioned in this specification.
특히, 불순물로 구리(Cu)가 첨가될 수 있으나, 본 발명에서는 구리(Cu)의 함량을 0.05% 미만으로 제한할 수 있다.In particular, copper (Cu) may be added as an impurity, but in the present invention, the content of copper (Cu) may be limited to less than 0.05%.
본 발명의 일 측면에 따르는 강은 하기 관계식 1에서 정의되는 R 값이 0.85~1.35일 수 있다.The steel according to one aspect of the present invention may have an R value of 0.85 to 1.35 defined in the following relational expression 1.
본 발명에서는 강도 확보와 동시에 -50℃의 저온인성을 확보하기 위해 관계식 1을 제안한다. 관계식 1은 강도와 인성 확보를 위한 성분식에 관한 것으로, 관계식 1의 R 값을 제어함으로써 본원발명에서 목적하는 수준의 강도와 저온인성을 확보할 수 있다. 관계식 1의 R 값이 0.85 미만일 경우 고용강화, 석출강화 및 경화능 등이 부족하여 목적하는 항복강도를 확보할 수 없는 문제점이 있으며, 그 값이 1.35를 초과할 경우 MA, 베이나이트 등 경한 조직이 형성되어 충격인성의 열위가 발생할 수 있다.In the present invention, relational expression 1 is proposed to secure strength and low-temperature toughness at -50 ° C at the same time. Relational Equation 1 relates to a component formula for securing strength and toughness, and by controlling the R value of Relational Equation 1, it is possible to secure desired levels of strength and low-temperature toughness in the present invention. If the R value in relational expression 1 is less than 0.85, there is a problem in that the desired yield strength cannot be secured due to lack of solid solution hardening, precipitation hardening, and hardenability, etc., and when the value exceeds 1.35, hard structures such as MA and bainite Formation may result in poor impact toughness.
[관계식 1][Relationship 1]
R = [Ni]+3[Mo]+2[Cr]R = [Ni]+3[Mo]+2[Cr]
(여기서, [Ni], [Mo] 및 [Cr]은 각 원소의 중량%이다.)(Where [Ni], [Mo] and [Cr] are the weight percent of each element.)
이하에서는, 본 발명의 강 미세조직에 대해 자세히 설명한다.Hereinafter, the steel microstructure of the present invention will be described in detail.
본 발명에서 특별히 달리 언급하지 않는 한 미세조직의 분율을 표시하는 %는 면적을 기준으로 한다.In the present invention, % representing the fraction of the microstructure is based on the area unless otherwise specified.
본 발명의 일 측면에 따르는 강은 두께 1/4 지점의 미세조직으로 에시큘라 페라이트를 40~60면적%, 베이나이트를 40~60면적%, 잔여 시멘타이트와 MA를 합으로 2% 이하 포함할 수 있다.The steel according to one aspect of the present invention has a microstructure of 1/4 of the thickness, and may contain 40 to 60 area% of escular ferrite, 40 to 60 area% of bainite, and 2% or less in total of residual cementite and MA. there is.
본 발명에서는 두께 1/4 지점의 -50℃ 충격인성을 구현하기 위해서는 에시큘라 페라이트의 사이즈, 전위밀도 등이 중요하며, 시멘타이트와 MA를 최소화하는 것이 바람직하다. 보다 바람직하게는 시멘타이트와 MA를 합으로 1% 이하 포함할 수 있다. 본 발명에서의 두께 1/4 지점은 t/4를 의미하며, 여기서 t는 강판의 두께를 의미한다.In the present invention, in order to implement -50 ° C impact toughness at the thickness 1/4 point, the size, dislocation density, etc. of escular ferrite are important, and it is preferable to minimize cementite and MA. More preferably, cementite and MA may be included in an amount of 1% or less in total. The thickness 1/4 point in the present invention means t/4, where t means the thickness of the steel sheet.
본 발명의 일 측면에 따르는 강은 두께 1/4 지점의 에시큘라 페라이트의 결정립 평균 크기가 25μm 이하일 수 있다. In the steel according to one aspect of the present invention, an average grain size of escular ferrite at a thickness of 1/4 may be 25 μm or less.
본 발명에서는 저온 충격인성을 확보하기 위하여 에시큘라 페라이트의 결정립 평균 크기를 25μm 이하로 제한할 수 있다. 그 크기가 25μm를 초과하면 -50℃에서 충격 흡수에너지 값이 저하되는 문제점이 있을 수 있다. 한편, 본 발명에서 목적하는 두께 50mm 이상의 후강판의 특성상 결정립의 미세화에 한계가 있어 그 크기의 하한을 15μm로 제한할 수 있다.In the present invention, the average grain size of escular ferrite may be limited to 25 μm or less in order to secure low-temperature impact toughness. If the size exceeds 25 μm, there may be a problem in that the value of impact absorption energy at -50 ° C is lowered. On the other hand, due to the nature of the thick steel plate having a thickness of 50 mm or more, which is intended in the present invention, there is a limit to the refinement of crystal grains, so the lower limit of the size can be limited to 15 μm.
이하에서는, 본 발명의 강 제조방법에 대해 자세히 설명한다.Hereinafter, the steel manufacturing method of the present invention will be described in detail.
본 발명의 일 측면에 따르는 강은 상술한 합금조성을 만족하는 강 슬라브를 재가열, 압연 및 냉각하여 제조될 수 있다.Steel according to one aspect of the present invention can be produced by reheating, rolling and cooling a steel slab satisfying the above-described alloy composition.
재가열reheat
본 발명의 합금조성을 만족하는 강 슬라브를 1020~1100℃의 온도범위로 재가열할 수 있다.A steel slab satisfying the alloy composition of the present invention can be reheated to a temperature range of 1020 to 1100 ° C.
재가열 온도가 1100℃를 초과하면 오스테나이트의 결정립이 조대화되어 경화능 증대에 의해 베이나이트 조직의 발현으로 인성을 저하시킬 수 있다. 반면, 그 온도가 1020℃ 미만이면 Ti, Nb 등이 충분히 고용되지 않는 경우가 발생하여 강도의 하락을 초래할 수 있다.When the reheating temperature exceeds 1100° C., the austenite crystal grains are coarsened, and the toughness may be reduced due to the development of a bainite structure due to the increase in hardenability. On the other hand, if the temperature is less than 1020 ° C., Ti, Nb, etc. may not be sufficiently dissolved, resulting in a decrease in strength.
재결정역 압연recrystallization station rolling
상기 재가열된 강 슬라브를 900℃ 이상의 온도범위에서 마지막 패스의 압하량이 15~25mm로 재결정역 압연을 행할 수 있다.The reheated steel slab may be subjected to recrystallization rolling with a rolling reduction of 15 to 25 mm in the last pass in a temperature range of 900 ° C. or higher.
본 발명에서 재결정역 압연 단계는 오스테나이트를 완전 재결정하고, 오스테나이트의 미세화 및 성장 억제를 위한 것이다. 재결정역 압연은 오스테나이트 완전 재결정을 위해 900℃ 이상의 온도범위에서 행하는 것이 바람직하며, 마지막 패스 압하량은 초기 오스테나이트 미세화를 위하여 15~25mm로 행할 수 있다. 마지막 패스 압하량이 15mm 미만이면 목적하는 수준의 미세화를 확보하기에 어려움이 있을 수 있다. 한편, 압연 시, 설비 사양에 따른 생산성을 고려하여 그 상한을 25mm로 제한할 수 있다.In the present invention, the recrystallization rolling step is for complete recrystallization of austenite, refinement of austenite, and suppression of growth. Recrystallization station rolling is preferably performed in a temperature range of 900° C. or higher for complete recrystallization of austenite, and the final pass reduction may be performed at 15 to 25 mm for initial austenite refinement. If the final pass reduction is less than 15 mm, it may be difficult to secure the desired level of refinement. Meanwhile, during rolling, the upper limit may be limited to 25 mm in consideration of productivity according to facility specifications.
미재결정역 non-redetermination area
상기 재결정역 압연된 강판을 Ar3+20~Ar3+60의 압연종료온도와 30~50%의 누적 압하율로 미재결정역 압연을 행할 수 있다.The recrystallization station rolled steel sheet may be subjected to non-recrystallization station rolling at a rolling end temperature of Ar3 + 20 to Ar3 + 60 and a cumulative reduction ratio of 30 to 50%.
본 발명에서는 에시큘라 페라이트 사이즈 미세화를 위해 압연종료온도가 Ar3 온도 직상에 가까울수록 바람직하다. 미재결정역 압연종료온도가 Ar3+20 미만일 경우, 냉각 전 표면이 오스테나이트, 페라이트의 이상역에 들어갈 수 있고, 냉각을 하게 되면 표면부에 경한 상이 형성되는 문제가 있을 수 있다. 반면, 그 온도가 Ar3+60을 초과할 경우 미재결정역 압연에서 결정립을 미세화하지 못하는 문제가 있을 수 있다.In the present invention, it is preferable that the rolling end temperature is closer to the Ar3 temperature for miniaturization of the size of the escular ferrite. If the non-recrystallization zone rolling end temperature is less than Ar3+20, the surface before cooling may enter the ideal zone of austenite and ferrite, and there may be a problem of forming a light phase on the surface when cooled. On the other hand, if the temperature exceeds Ar 3 + 60, there may be a problem in that crystal grains cannot be refined in non-recrystallization station rolling.
또한, 두께 50mm 이상의 후물재의 경우 누적 압하율이 30~50%인 것이 바람직하다. 누적 압하율이 30% 미만일 경우 미재결정역 압연량이 저하되어 조직의 팬케이킹, 미세화되기 어려운 문제점이 있으며, 50%를 초과하면 재결정역 압연량이 부족하여 저온 충격인성이 열위될 우려가 있다.In addition, in the case of a thick material having a thickness of 50 mm or more, it is preferable that the cumulative reduction ratio is 30 to 50%. If the cumulative rolling reduction is less than 30%, the amount of non-recrystallization rolling is reduced, resulting in pan-caking of the structure and difficulty in miniaturization.
[식][ceremony]
Ar3 = 910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]Ar3 = 910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]
(여기서, [C], [Mn], [Cu], [Cr], [Ni] 및 [Mo]는 각 원소의 중량%이다.)(Where [C], [Mn], [Cu], [Cr], [Ni] and [Mo] are the weight percent of each element.)
냉각Cooling
상기 미재결정역 압연된 강판을 두께 1/4 지점 기준으로 5~10℃/s의 냉각속도로 400℃ 이하의 온도범위까지 냉각할 수 있다.The non-recrystallization station rolled steel sheet may be cooled to a temperature range of 400° C. or less at a cooling rate of 5 to 10° C./s based on a thickness of 1/4 point.
본 발명에서 목적으로 하는 후강판은 두께 1/4 지점 부근에서 충격인성을 확보하는 것이 바람직하다. 따라서, 본원발명에서 제한하는 냉각속도는 두께 1/4 지점을 기준으로 할 수 있다. 냉각종료온도가 400℃를 초과하거나, 냉각속도가 10℃/s를 초과할 경우, MA 형성이 촉진되어 충격인성이 열위할 수 있다. 반면, 그 냉각속도가 5℃/s 미만일 경우, 목적하는 수준의 강도를 확보하기에 어려움이 있을 수 있다. 본 발명에서는 냉각 방법으로 수냉을 이용할 수 있다.It is preferable that the thick steel plate for the purpose of the present invention secures the impact toughness around the 1/4 of the thickness. Therefore, the cooling rate limited in the present invention may be based on the 1/4 of the thickness. When the cooling end temperature exceeds 400° C. or the cooling rate exceeds 10° C./s, MA formation is promoted, resulting in poor impact toughness. On the other hand, if the cooling rate is less than 5 °C / s, it may be difficult to secure a desired level of strength. In the present invention, water cooling may be used as a cooling method.
이와 같이 제조된 본 발명의 강은 두께가 50~100mm이고, 항복강도가 460MPa 이상이고, 인장강도가 580MPa 이상이고, -50℃에서의 충격인성이 100J 이상으로, 고강도를 가지면서 우수한 저온 충격인성 특성을 구비할 수 있다.The steel of the present invention thus prepared has a thickness of 50 to 100 mm, a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness of 100 J or more at -50 ° C., having high strength and excellent low-temperature impact toughness. characteristics can be provided.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다. 다만, 아래의 실시예는 본 발명을 예시하여 보다 상세하게 설명하기 위한 것일 뿐, 본 발명의 권리범위를 제한하기 위한 것이 아니라는 점에 유의할 필요가 있다.Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are only for illustrating the present invention in more detail and are not intended to limit the scope of the present invention.
(실시예)(Example)
하기 표 1의 합금조성을 가지는 용강을 준비한 후, 연속주조를 이용하여 슬라브를 제조하였다. 상기 슬라브를 하기 표 2의 조건으로 재가열, 압연, 냉각하여 강판을 제조하였다. 표 2에 개시되지 않은 재결정역 압연온도는 900℃ 이상의 온도로 모두 동일하게 적용하였으며, 미재결정역 압연 시, 누적 압하율은 30~50%의 범위 내로 동일하게 적용하였다. 또한, 표 1에는 각 강종의 합금조성에 따른 Ar3 온도와 관계식 1의 R 값을 계산하여 나타내었다.After preparing the molten steel having the alloy composition shown in Table 1 below, a slab was manufactured using continuous casting. Steel sheets were manufactured by reheating, rolling, and cooling the slabs under the conditions shown in Table 2 below. Recrystallization rolling temperatures not disclosed in Table 2 were all applied the same at a temperature of 900 ° C or higher, and during non-recrystallization rolling, the cumulative rolling reduction was applied equally within the range of 30 to 50%. In addition, in Table 1, the Ar3 temperature according to the alloy composition of each steel type and the R value of relational expression 1 are calculated and shown.
강종steel grade 합금조성(wt%)Alloy composition (wt%) Ar3
(℃)Ar3
(℃) 		관계식 1Relation 1
CC SiSi MnMn PP SS AlAl NiNi CrCr MoMo TiTi NbNb NN
AA 0.0560.056 0.140.14 1.621.62 0.00750.0075 0.00180.0018 0.0250.025 0.350.35 0.210.21 0.120.12 0.0130.013 0.0240.024 0.00370.0037 731731 1.131.13
BB 0.0630.063 0.180.18 1.581.58 0.00820.0082 0.00190.0019 0.0240.024 0.360.36 0.180.18 0.090.09 0.0120.012 0.0260.026 0.00410.0041 734734 0.990.99
CC 0.0650.065 0.190.19 1.551.55 0.00680.0068 0.00200.0020 0.0260.026 0.420.42 0.230.23 0.10.1 0.0120.012 0.0210.021 0.00420.0042 731731 1.181.18
DD 0.0620.062 0.150.15 1.611.61 0.00830.0083 0.00150.0015 0.0190.019 0.120.12 0.070.07 0.030.03 0.0110.011 0.0280.028 0.00360.0036 752752 0.350.35
EE 0.0570.057 0.200.20 1.591.59 0.0820.082 0.0190.019 0.0240.024 0.620.62 0.380.38 0.180.18 0.0120.012 0.0250.025 0.00390.0039 711711 1.921.92
FF 0.060.06 0.180.18 1.631.63 0.00910.0091 0.00220.0022 0.0250.025 0.410.41 0.230.23 0.10.1 0.0120.012 0.0260.026 0.0400.040 727727 1.171.17
GG 0.0570.057 0.180.18 1.611.61 0.0090.009 0.00180.0018 0.0230.023 0.40.4 0.250.25 0.110.11 0.0120.012 0.0250.025 0.00380.0038 729729 1.231.23
HH 0.0610.061 0.150.15 1.631.63 0.00820.0082 0.00180.0018 0.0220.022 0.480.48 0.260.26 0.130.13 0.0110.011 0.0250.025 0.00420.0042 720720 1.391.39
[관계식 1][Relationship 1]
R = [Ni]+3[Mo]+2[Cr]R = [Ni]+3[Mo]+2[Cr]
(여기서, [Ni], [Mo] 및 [Cr]은 각 원소의 중량%이다.)(Where [Ni], [Mo] and [Cr] are the weight percent of each element.)
[식][ceremony]
Ar3 = 910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]Ar3 = 910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]
(여기서, [C], [Mn], [Cu], [Cr], [Ni] 및 [Mo]는 각 원소의 중량%이다.)(Where [C], [Mn], [Cu], [Cr], [Ni] and [Mo] are the weight percent of each element.)
시편
번호Psalter
number 		강종steel grade 재가열reheat 재결정역 압연recrystallization station rolling 미재결정역 압연Unrecrystallized area rolling 냉각Cooling
온도(℃)Temperature (℃) 마지막 패스
압하량(mm)last pass
reduction (mm) 		종료온도(℃)End temperature (℃) 종료온도(℃)End temperature (℃) 속도(℃/s)Rate (℃/s)
1One AA 10861086 21.421.4 789789 365365 7.17.1
22 BB 10801080 22.522.5 791791 345345 8.28.2
33 CC 10931093 18.618.6 786786 384384 7.87.8
44 DD 10881088 19.319.3 794794 356356 6.86.8
55 EE 10851085 18.718.7 765765 374374 7.17.1
66 FF 10871087 20.420.4 787787 507507 7.57.5
77 GG 10901090 17.417.4 829829 394394 6.96.9
88 GG 10881088 10.310.3 775775 342342 7.07.0
99 HH 10921092 20.420.4 778778 354354 6.86.8
하기 표 3에는 제조된 강판의 미세조직을 측정하여 기재하였다. 미세조직은 강의 두께 1/4 지점에서 측정하였으며, 에시큘라 페라이트(AF), 시멘타이트 및 MA 분율을 각각 나타내었으며, 나머지 분율은 베이나이트로 관찰되었다. 또한, 강의 두께 1/4 지점에서의 에시큘라 페라이트 결정립 크기를 측정하여 나타내었다. 미세조직은 광학현미경을 이용하여 500배로 확대 분석하여 측정하였다. In Table 3 below, the microstructure of the manufactured steel sheet was measured and described. The microstructure was measured at a point of 1/4 of the thickness of the steel, and the fractions of escular ferrite (AF), cementite, and MA were shown, respectively, and the remaining fractions were observed as bainite. In addition, the size of the crystal grains of escular ferrite at the point of 1/4 of the thickness of the steel was measured and shown. The microstructure was measured by magnifying and analyzing at 500 times using an optical microscope.
더하여, 표 3에는 제조된 각 시편에 대한 물성 값을 측정하여 나타내었다. 항복강도(YS), 인장강도(TS) 및 연신율(El)은 인장시험을 하여 평가되었으며, EN-ISO 6892-1 규격으로 두께 1/4 지점에서 압연의 직각 방향으로 환형시편을 채취하여 2회 테스트한 평균을 측정하였다. 또한, -50℃에서의 충격인성 값을 측정하였다. 충격인성은 EN ISO 148-1 규격에 의해 두께 1/4 위치에서 압연의 평행 방향으로 시편을 채취하여 3회 테스트한 평균을 측정하였다.In addition, Table 3 shows the measured physical property values for each of the prepared specimens. Yield strength (YS), tensile strength (TS), and elongation (El) were evaluated by performing a tensile test. According to EN-ISO 6892-1 standard, an annular specimen was taken in the direction perpendicular to the rolling direction at 1/4 of the thickness and twice. The tested average was determined. In addition, the impact toughness value at -50 ℃ was measured. Impact toughness was measured by taking specimens in the parallel direction of rolling at 1/4 of the thickness according to EN ISO 148-1 standard and measuring the average of three tests.
시편
번호Psalter
number 		강종steel grade 미세조직microstructure 기계적 물성mechanical properties 구분division
AF(%)AF (%) 시멘타이트
및 MA(%)cementite
and MA (%) 		AF 결정립
크기(μm)AF grain
Size (μm) 		항복강도
(MPa)yield strength
(MPa) 		인장강도
(MPa)tensile strength
(MPa) 		연신율
(%)elongation rate
(%) 		충격인성
(-50℃, J)impact toughness
(-50℃, J)
1One AA 5555 0.70.7 2121 520520 618618 2424 338338 발명예1Invention example 1
22 BB 5858 0.60.6 2222 491491 612612 2626 376376 발명예2Invention example 2
33 CC 4949 0.80.8 2121 498498 618618 2525 316316 발명예3Invention example 3
44 DD 6969 0.80.8 2323 445445 568568 2727 274274 비교예1Comparative Example 1
55 EE 2727 0.70.7 2020 534534 654654 2121 2626 비교예2Comparative Example 2
66 FF 4242 2.62.6 2121 459459 598598 2727 2828 비교예3Comparative Example 3
77 GG 5555 0.70.7 3434 441441 581581 3131 2828 비교예4Comparative Example 4
88 GG 5656 2.62.6 3333 438438 596596 2626 3131 비교예5Comparative Example 5
99 HH 3434 3.23.2 2020 482482 635635 2121 3232 비교예6Comparative Example 6
표 3에 나타난 바와 같이, 본 발명의 합금조성 및 제조조건을 만족하는 발명예의 경우, 본 발명에서 제안하는 미세조직 특징을 만족하였으며, 본 발명에서 목적하는 물성을 확보하였다. 도 1은 본 발명의 일 실시예에 따른 발명예의 미세조직을 광학현미경을 이용하여 500배율로 관찰한 사진이다.As shown in Table 3, in the case of the inventive example satisfying the alloy composition and manufacturing conditions of the present invention, the microstructure characteristics proposed in the present invention were satisfied, and the desired physical properties were secured in the present invention. 1 is a photograph of a microstructure of an inventive example according to an embodiment of the present invention observed at 500 magnification using an optical microscope.
반면, 비교예 1 및 2는 본 발명의 합금조성을 만족하지 않는 예시로, 본 발명에서 목적하는 수준의 강도 또는 충격인성을 확보하지 못하였다. 구체적으로, 비교예 1은 관계식 1의 값이 본 발명의 범위에 미달되는 경우로, 베이나이트 분율이 감소하여 강도의 하락을 초래하였다. 비교예 2는 관계식 1의 값이 본 발명의 범위를 초과하는 경우로, 베이나이트가 과도하게 형성되어 충격인성이 열위하였다.On the other hand, Comparative Examples 1 and 2 are examples that do not satisfy the alloy composition of the present invention, and did not secure the level of strength or impact toughness desired in the present invention. Specifically, in Comparative Example 1, the value of relational expression 1 was less than the range of the present invention, and the bainite fraction decreased, resulting in a decrease in strength. In Comparative Example 2, when the value of relational expression 1 exceeded the scope of the present invention, bainite was excessively formed, resulting in inferior impact toughness.
비교예 3은 냉각종료온도가 본 발명의 범위를 벗어난 예로, 시멘타이트 및 MA 분율이 다량 생성되어 충격인성 특성이 열위하였다.Comparative Example 3 is an example in which the cooling end temperature is outside the range of the present invention, and a large amount of cementite and MA fraction is formed, resulting in poor impact toughness.
비교예 4는 미재결정역 압연종료온도가 높아 결정립 미세화의 부족으로 인하여 항복강도 하락과 동시에 -50℃ 충격인성이 열위함을 알 수 있다.In Comparative Example 4, it can be seen that the non-recrystallization zone rolling end temperature is high, and the yield strength is lowered and the impact toughness at -50 ° C is inferior at the same time due to the lack of crystal grain refinement.
비교예 5는 재결정역 압연의 마지막 패스의 압하량이 부족하여 초기 오스테나이트 미세화가 잘 이루어지지 못하기 때문에 최종 페라이트 결정립 크기의 증가, 경화능 증가로 인한 시멘타이트 및 MA의 형성 등으로 인해 항복강도와 충격인성의 하락을 확인 할 수 있었다.In Comparative Example 5, since the initial austenite refinement was not performed well due to insufficient rolling reduction in the last pass of recrystallization rolling, the yield strength and impact were increased due to the increase in the final ferrite grain size and the formation of cementite and MA due to the increase in hardenability. A decrease in toughness could be confirmed.
비교예 6은 본 발명에서 제안하는 성분 범위를 만족하지만, 관계식 1의 값을 만족하지 않는 경우로, 에시큘라 페라이트의 감소, 베이나이트의 과도한 증가로 인해 충격인성이 급격히 하락되었다.Comparative Example 6 satisfies the range of components proposed in the present invention, but does not satisfy the value of relational expression 1, and the impact toughness is rapidly decreased due to the decrease of escular ferrite and the excessive increase of bainite.
이상에서 실시예를 통하여 본 발명을 상세하게 설명하였으나, 이와 다른 형태의 실시예들도 가능하다. 그러므로, 이하에 기재된 청구항들의 기술적 사상과 범위는 실시예들에 한정되지 않는다.Although the present invention has been described in detail through examples above, other types of embodiments are also possible. Therefore, the spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (10)

  1. 중량%로, C: 0.04~0.08%, Si: 0.1~0.35%, Mn: 1.4~1.8%, Sol.Al: 0.01~0.035%, Ni: 0.2~0.5%, Cr: 0.1~0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% 이하, S: 0.003% 이하, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함하고,In weight percent, C: 0.04-0.08%, Si: 0.1-0.35%, Mn: 1.4-1.8%, Sol.Al: 0.01-0.035%, Ni: 0.2-0.5%, Cr: 0.1-0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% or less, S: 0.003% or less, the balance contains iron (Fe) and other unavoidable impurities, ,
    하기 관계식 1에서 정의되는 R 값이 0.85~1.35이고,The R value defined in the following relational expression 1 is 0.85 to 1.35,
    두께 1/4 지점의 미세조직은 에시큘라 페라이트 및 베이나이트 혼합조직을 주조직으로 하고, 잔여 시멘타이트와 MA를 합으로 2면적% 이하 포함하며,The microstructure at the 1/4th of the thickness is mainly composed of a mixture of escular ferrite and bainite, and contains less than 2 area% of residual cementite and MA in total,
    두께 1/4 지점의 에시큘라 페라이트의 결정립 평균 크기가 25μm 이하인 강판.A steel sheet with an average grain size of 1/4 of the thickness of escular ferrite of 25 μm or less.
    [관계식 1][Relationship 1]
    R = [Ni]+3[Mo]+2[Cr]R = [Ni]+3[Mo]+2[Cr]
    (여기서, [Ni], [Mo] 및 [Cr]은 각 원소의 중량%이다.)(Where [Ni], [Mo] and [Cr] are the weight percent of each element.)
  2. 제1항에 있어서,According to claim 1,
    상기 강판은 두께 1/4 지점의 미세조직으로 에시큘라 페라이트를 40~60면적%, 베이나이트를 40~60면적% 포함하는 강판.The steel sheet is a steel sheet containing 40 to 60 area% of escular ferrite and 40 to 60 area% of bainite with a microstructure of 1/4 of the thickness.
  3. 제1항에 있어서,According to claim 1,
    상기 강판은 시멘타이트와 MA를 합으로 1면적% 이하 포함하는 강판.The steel sheet is a steel sheet containing less than 1 area% of cementite and MA in total.
  4. 제1항에 있어서,According to claim 1,
    상기 강판은 두께 1/4 지점의 에시큘라 페라이트의 결정립 평균 크기가 15~25μm인 강판.The steel sheet is a steel sheet having an average grain size of 15 to 25 μm of escular ferrite at a thickness of 1/4.
  5. 제1항에 있어서,According to claim 1,
    상기 강판은 두께가 50~100mm인 강판.The steel plate is a steel plate having a thickness of 50 to 100 mm.
  6. 제1항에 있어서,According to claim 1,
    상기 강판은 항복강도가 460MPa 이상이고, 인장강도가 580MPa 이상이고, -50℃에서의 충격인성이 100J 이상인 강판.The steel sheet has a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness at -50 ° C of 100 J or more.
  7. 중량%로, C: 0.04~0.08%, Si: 0.1~0.35%, Mn: 1.4~1.8%, Sol.Al: 0.01~0.035%, Ni: 0.2~0.5%, Cr: 0.1~0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% 이하, S: 0.003% 이하, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함하고, 하기 관계식 1에서 정의되는 R 값이 0.85~1.35인 강 슬라브를 재가열하는 단계;In weight percent, C: 0.04-0.08%, Si: 0.1-0.35%, Mn: 1.4-1.8%, Sol.Al: 0.01-0.035%, Ni: 0.2-0.5%, Cr: 0.1-0.3%, Mo: 0.05~0.15%, Nb: 0.015~0.035%, Ti: 0.005~0.02%, N: 0.002~0.006%, P: 0.01% or less, S: 0.003% or less, the balance contains iron (Fe) and other unavoidable impurities, , Reheating a steel slab having an R value of 0.85 to 1.35 defined in the following relational expression 1;
    상기 재가열된 강 슬라브를 900℃ 이상의 온도범위에서 마지막 패스의 압하량 15~25mm로 재결정역 압연하는 단계;Recrystallization reverse rolling of the reheated steel slab at a temperature range of 900° C. or higher with a rolling reduction of 15 to 25 mm in the last pass;
    상기 재결정역 압연된 강판을 Ar3+20~Ar3+60의 압연종료온도로 미재결정역 압연하는 단계; 및 non-recrystallization station rolling of the steel sheet subjected to recrystallization station rolling at a rolling end temperature of Ar3+20 to Ar3+60; and
    상기 미재결정역 압연된 강판을 강판 두께 1/4 지점을 기준으로 400℃ 이하의 온도범위까지 수냉하는 단계를 포함하는 강판 제조방법.Steel sheet manufacturing method comprising the step of water-cooling the non-recrystallization station rolled steel sheet to a temperature range of 400 ° C. or less based on the steel sheet thickness 1/4 point.
    [관계식 1][Relationship 1]
    R = [Ni]+3[Mo]+2[Cr]R = [Ni]+3[Mo]+2[Cr]
    (여기서, [Ni], [Mo] 및 [Cr]은 각 원소의 중량%이다.)(Where [Ni], [Mo] and [Cr] are the weight percent of each element.)
  8. 제7항에 있어서,According to claim 7,
    상기 재가열 시, 1020~1100℃의 온도범위로 행하고,During the reheating, it is carried out in a temperature range of 1020 to 1100 ° C,
    상기 미재결정역 압연 시, 누적 압하율은 30~50%인 강판 제조방법.When the non-recrystallization station rolling, the cumulative reduction ratio is 30 to 50% steel sheet manufacturing method.
  9. 제7항에 있어서,According to claim 7,
    상기 냉각 시, 강판 두께 1/4 지점을 기준으로 5~10℃/s의 냉각속도로 냉각하는 강판 제조방법.During the cooling, a steel plate manufacturing method for cooling at a cooling rate of 5 to 10 ° C / s based on a point of 1/4 of the steel plate thickness.
  10. 제7항에 있어서,According to claim 7,
    상기 강판은 두께가 50~100mm인 강판 제조방법.The steel plate is a steel plate manufacturing method having a thickness of 50 ~ 100mm.
PCT/KR2022/019039 2021-12-21 2022-11-29 Steel plate having high strength and excellent low-temperature impact toughness, and method for manufacturing same WO2023121027A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20090070484A (en) * 2007-12-27 2009-07-01 주식회사 포스코 High-strength and high-toughness thick steel plate and method for producing the same
EP1577412B2 (en) * 2002-12-24 2014-11-12 Nippon Steel & Sumitomo Metal Corporation High strength steel sheet exhibiting good burring workability and excellent resistance to softening in heat-affected zone and method for production thereof
WO2015030210A1 (en) * 2013-08-30 2015-03-05 新日鐵住金株式会社 Steel sheet for thick-walled high-strength line pipe having exceptional souring resistance, crush resistance properties, and low-temperature ductility, and line pipe
KR20190076163A (en) * 2017-12-22 2019-07-02 현대제철 주식회사 High strength steel and method of manufacturing the same
KR20210126995A (en) * 2020-04-13 2021-10-21 주식회사 포스코 Steel sheet having excellent low temperature toughness and low yield ratio and method of manufacturing the same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1577412B2 (en) * 2002-12-24 2014-11-12 Nippon Steel & Sumitomo Metal Corporation High strength steel sheet exhibiting good burring workability and excellent resistance to softening in heat-affected zone and method for production thereof
KR20090070484A (en) * 2007-12-27 2009-07-01 주식회사 포스코 High-strength and high-toughness thick steel plate and method for producing the same
WO2015030210A1 (en) * 2013-08-30 2015-03-05 新日鐵住金株式会社 Steel sheet for thick-walled high-strength line pipe having exceptional souring resistance, crush resistance properties, and low-temperature ductility, and line pipe
KR20190076163A (en) * 2017-12-22 2019-07-02 현대제철 주식회사 High strength steel and method of manufacturing the same
KR20210126995A (en) * 2020-04-13 2021-10-21 주식회사 포스코 Steel sheet having excellent low temperature toughness and low yield ratio and method of manufacturing the same

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