WO2023113219A1 - Steel material having high strength and excellent impact toughness, and manufacturing method therefor - Google Patents

Steel material having high strength and excellent impact toughness, and manufacturing method therefor Download PDF

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WO2023113219A1
WO2023113219A1 PCT/KR2022/016882 KR2022016882W WO2023113219A1 WO 2023113219 A1 WO2023113219 A1 WO 2023113219A1 KR 2022016882 W KR2022016882 W KR 2022016882W WO 2023113219 A1 WO2023113219 A1 WO 2023113219A1
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steel
less
impact toughness
high strength
slab
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PCT/KR2022/016882
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French (fr)
Korean (ko)
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소태일
강상덕
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주식회사 포스코
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Priority to CN202280057234.2A priority Critical patent/CN117836460A/en
Publication of WO2023113219A1 publication Critical patent/WO2023113219A1/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
    • 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
    • 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
    • C22C38/02—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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • 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

  • Patent Document 1 proposes a method for producing a steel having excellent impact toughness without normalizing heat treatment.
  • Patent Document 1 has a low carbon content, but may be advantageous in securing sufficient low-temperature impact toughness, but there is a side that is difficult to secure sufficient strength, and furthermore, there is a limit that the strength may decrease significantly as the thickness becomes thicker.
  • C 0.12 ⁇ 0.18%
  • Si 0.2 ⁇ 0.5%
  • Mn 1.0 to 1.7%
  • P 0.012% or less
  • S 0.003% or less
  • Al 0.015 to 0.045%
  • Nb 0.02 to 0.05%
  • V 0.01 to 0.08%
  • Ti 0.005 to 0.017%
  • N 0.002 ⁇ 0.01%
  • the remainder including Fe and unavoidable impurities
  • the S is an element that greatly inhibits the hydrogen-induced cracking resistance and impact toughness of the steel by combining with Mn in the steel to form MnS or the like. Therefore, it is advantageous to manage the S content as low as possible. In the present invention, even if the S is contained in a maximum of 0.003%, there is no difficulty in securing the target physical properties, so the content can be limited to 0.003% or less. However, considering the level that is unavoidably added, 0% can be excluded.
  • the Nb precipitates in the form of NbC or Nb(C,N) to greatly improve the strength of the base material, and when reheated to a high temperature, the dissolved Nb inhibits recrystallization of austenite and transformation of ferrite or bainite, thereby improving the structure refinement effect. You can get it.
  • it is preferable to include 0.02% or more.
  • the upper limit of Nb is preferably 0.05%. More advantageously, it may contain 0.035 to 0.045%.
  • Ti When the Ti is included together with N, it forms TiN, so it serves to reduce the occurrence of surface cracks due to the formation of AlN precipitates, so it is preferable to include 0.005% or more. However, if the content exceeds 0.017%, coarse TiN is formed during reheating of the steel slab, which acts as a factor impairing low-temperature impact toughness. Therefore, Ti is preferably 0.005 to 0.017%, more preferably 0.01 to 0.015%.
  • the Cu is an element capable of greatly improving strength by solid solution strengthening.
  • the content of Cu is excessive, there is a problem of not only impairing weldability by increasing the carbon equivalent, but also significantly degrading the surface quality of the product. Therefore, when the Cu is added, it may be included in a maximum of 0.5%.
  • the Cu is not essential.
  • the remainder includes iron (Fe) and unavoidable impurities.
  • Fe iron
  • Inevitable impurities can be unintentionally mixed in the normal steel manufacturing process, and cannot be completely excluded, and those skilled in the ordinary steel manufacturing field can easily understand the meaning.
  • the present invention does not entirely exclude the addition of other compositions than the aforementioned steel composition.
  • the microstructure of the steel of the present invention includes, in area fraction, 60 to 85% of ferrite and the remainder of pearlite. If the fraction of the ferrite is less than 60% or the fraction of the remaining pearlite exceeds 40%, it may be advantageous to secure strength, but impact toughness may be greatly reduced. In addition, when the ferrite fraction exceeds 85%, it may be advantageous to secure impact toughness, but it is difficult to secure sufficient strength, so the steel of the present invention preferably has 60 to 85 area% ferrite and the remainder is pearlite.
  • the average grain size of the ferrite is preferably 30 ⁇ m or less.
  • the average grain size of the ferrite exceeds 30 ⁇ m, it is difficult to secure yield strength and impact toughness may be greatly reduced. Therefore, the average grain size is preferably 30 ⁇ m or less.
  • NbC and/or VC precipitates may be included in the microstructure of the steel.
  • the size of the precipitate is preferably 50 nm or less. If the size of the precipitate exceeds 50 nm, it is not preferable because impact toughness may be greatly reduced. It is preferable that the precipitate exists in ferrite crystal grains.
  • the manufacturing method is prepared by heating and hot rolling a steel slab having the above-mentioned alloy composition and carbon equivalent (Ceq) of 0.48 or less of [Relationship 1].
  • Ceq carbon equivalent
  • the heating temperature of the steel slab does not satisfy the condition of the following relational expression 2, the precipitates (carbon, nitride) formed in the slab are not sufficiently re-dissolved, so the formation of precipitates is reduced in the process after hot rolling, and finally presented in the present invention. It is difficult to satisfy the required yield strength and tensile strength.
  • the slab extraction temperature exceeds 1200 ° C, there is a concern that the austenite crystal grains are coarsened and the physical properties of the steel are deteriorated, so it is preferable not to exceed 1200 ° C.
  • the heated steel slab is hot rolled. After rough rolling the heated steel slab at a temperature range of 900 to 1100 ° C., it is preferable to perform finish hot rolling on Ar3 or higher. If the temperature during the rough rolling is less than 950 ° C., there is a problem that the temperature becomes too low during the subsequent finish hot rolling. On the other hand, if the finish hot rolling temperature is less than Ar3, the rolling load becomes large and there is a possibility that quality defects such as surface cracks may occur.
  • the steel material of the present invention manufactured by the above method can secure high strength and excellent impact toughness without performing subsequent heat treatment, for example, normalizing heat treatment.
  • a slab was manufactured by continuously casting molten steel having an alloy composition (% by weight, the remainder being Fe and unavoidable impurities) shown in Table 1 below. At this time, the slab was manufactured to a thickness of 300 mm.
  • Invention Examples 1 to 4 of Table 1 are cases in which both the alloy composition and relational expression 1 presented in the present invention are satisfied, and in comparative example 1, the content of C and relational expression 1 are out of the values suggested in the present invention, Comparative Example 3 is that the Nb content is out of the value suggested in the present invention.
  • the slab was heated and rough-rolled under the conditions of Table 2, and finished hot-rolled at a temperature range of 880 to 900° C. to prepare a hot-rolled steel sheet having a thickness of 5 mm and air-cooled to room temperature.
  • Inventive Examples 1 to 4 and Comparative Examples 1 and 3 satisfy the process conditions presented in the present invention, but in the case of Comparative Example 2, the condition of the following relational expression 2 was not satisfied.
  • microstructure and mechanical properties of the steel material prepared as described above were evaluated.
  • the microstructure was observed with an optical microscope, and the ferrite fraction and diameter were measured using an analysis program, and the average diameter of the precipitate was measured using a transmission electron microscope.
  • the microstructure was measured at the point of t/4 (t is the thickness of the steel, mm) in the thickness direction of each steel, and the results are shown in Table 3 below.
  • Table 4 shows tensile properties and low-temperature impact toughness before and after normalizing. At this time, the normalizing treatment was held at 870 ° C. for 128 minutes and then air-cooled.
  • Comparative Example 1 the C content and relational expression 1 are outside the range proposed in the present invention, and the yield/tensile strength may satisfy the value suggested in the present invention due to the excessive addition of C content, but the impact toughness It can be confirmed that does not satisfy the proposed value.
  • Comparative Example 2 satisfies all the component ranges presented in the present invention, but does not satisfy the relational expression 2, and the slab extraction temperature is very low. After as-rolled and normalizing heat treatment, the yield strength and tensile strength presented in the present invention It can be seen that it is not satisfied. In addition, it can be seen that the drop in yield strength is very large compared to Inventive Examples 1 to 4.
  • Comparative Example 3 is a case where the content of Nb is outside the value suggested in the present invention, and even though Nb is heated at a temperature at which it is sufficiently dissolved in the slab, the content itself is very low, and NbC precipitates are not sufficiently precipitated. It can be seen that the yield strength and tensile strength are not satisfied, and Comparative Example 3 also confirms that the yield strength significantly decreases after normalizing heat treatment.
  • a steel material having a thickness of 75 mmt was manufactured by rolling a slab having the components of Example 1 of Example 1 above.
  • the results of the relational expression 2 of the extraction temperature are different, the results of the relationship between the extraction temperature and the yield strength are shown in FIG. It can be seen that when the extraction temperature does not satisfy relational expression 2, the yield strength presented in the present invention is not satisfied, whereas when relational expression 2 is satisfied, all exhibit excellent yield strength.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
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Abstract

The present invention relates to: a steel material having high strength and excellent impact toughness, the steel material being usable for a land wind power generator and the like; and a method for manufacturing same.

Description

고강도 및 충격인성이 우수한 강재 및 그 제조방법Steel with excellent high strength and impact toughness and its manufacturing method
본 발명은 육상용 풍력발전기 등에 사용될 수 있는 강재로서, 고강도 및 충격인성이 우수한 강재와 이를 제조하는 방법에 관한 것이다. The present invention relates to a steel material that can be used for onshore wind power generators, etc., and relates to a steel material with excellent high strength and impact toughness and a method for manufacturing the same.
최근 육상용 풍력발전기의 타워 높이가 점차 고도화됨에 따라, 하중저항 능력이 우수한 후물 고강도 강재에 대한 요구가 증대되고, 동시에 충격인성 보증도 요구되고 있다. Recently, as the tower height of onshore wind power generators has gradually increased, the demand for high-strength steel materials having excellent load resistance capability has increased, and at the same time, impact toughness is also required.
강재의 고강도 및 우수한 충격인성을 구현하기 위해서는 결정립 미세화가 필수적인데, 압연 공정이 결정립 미세화의 대표적인 방법 중 하나이다. 재결정이 가능한 온도에서 압연을 실시하면 압하력에 의해 생성된 내부 응력을 구동력으로 새로운 오스테나이트 미세 결정립이 생성된다. 한편, 미재결정역 온도 영역에서의 압연은 결정립이 응력을 받아서 압연방향으로 밴드 구조가 형성되게 되고, 내부에 많은 전위(dislocation)가 발생하여 오스테나이트가 상변태될 때, 보다 많은 핵생성 사이트를 제공하여 결정립 미세화 효과를 유발할 수 있다. In order to realize high strength and excellent impact toughness of steel, crystal grain refinement is essential, and the rolling process is one of the representative methods of crystal grain refinement. When rolling is performed at a temperature at which recrystallization is possible, new austenite fine grains are created using the internal stress generated by the reduction force as a driving force. On the other hand, rolling in the non-recrystallization zone temperature region provides more nucleation sites when crystal grains receive stress and a band structure is formed in the rolling direction, and many dislocations occur inside to phase transform austenite. This can cause grain refinement effect.
그러나, 강재의 두께가 증가할수록 압연으로 가할 수 있는 압하력이 제한을 받게 되며, 내부조직 특히, 강재의 중심부에 가까워질수록 압연을 통한 미세한 결정립 형성이 용이하지 않다. 오스테나이트 결정립은 Ae3 이상의 온도에서 고온일수록, 가열시간이 길수록 성장하는 경향을 보이기 때문이다. However, as the thickness of the steel material increases, the reduction force that can be applied by rolling is limited, and it is not easy to form fine crystal grains through rolling as the internal structure, in particular, approaches the center of the steel material. This is because austenite crystal grains show a tendency to grow at a temperature higher than Ae3 as the temperature increases and as the heating time increases.
한편, 오스테나이트 결정립 미세화가 주로 일어나는 과정인 슬라브 재가열 및 압연만을 통해서는 충분히 작은 크기의 결정립을 확보하기 어려운 경우가 많다. 특히, 압연되는 강재가 고온일수록 압연시 변형저항이 감소하므로, 용이한 압연을 위해 슬라브 재가열은 주로 Ae3 온도 대비 훨씬 높은 온도에서 실시되는데, 그때 오스테나이트 결정립은 크게 성장하게 된다. 압연을 통한 결정립 미세화 효과가 충분치 못할 경우에, 압연공정 후에 재열처리를 통해서 추가적인 오스테나이트 결정립 미세화 효과를 기대할 수 있는데, 일반적으로 노멀라이징(Normalizing) 열처리가 이에 해당된다. On the other hand, in many cases it is difficult to secure grains of a sufficiently small size only through slab reheating and rolling, which are processes in which austenite grain refinement mainly occurs. In particular, since the deformation resistance during rolling decreases as the temperature of the steel to be rolled increases, the slab reheating is mainly performed at a temperature much higher than the Ae3 temperature for easy rolling, at which time the austenite crystal grains greatly grow. When the effect of grain refinement through rolling is not sufficient, an additional austenite grain refinement effect can be expected through re-heat treatment after the rolling process, and normalizing heat treatment generally corresponds to this.
풍력타워용 소재는 전통적으로 노멀라이징(Normalizing) 열처리된 강재를 적용해 오고 있으나, 제조공정상 위와 같은 열처리가 적용되는 경우 제조단가가 크게 증가하여 As-rolled 강재 또는 TMCP(Thermo Mechanical Controlled Process) 강재에 비해 상업적으로 용이하지 않은 측면이 있다. 이에 노멀라이징 열처리를 하지 않고도 노멀라이징 열처리한 강재와 유사한 물성을 갖는 강재 제조가 요구되고 있는 실정이다.Traditionally, normalizing heat treated steel has been applied to the material for wind towers, but when the above heat treatment is applied in the manufacturing process, the manufacturing cost increases significantly, compared to as-rolled steel or TMCP (Thermo Mechanical Controlled Process) steel. There are aspects that are not commercially easy. Accordingly, there is a demand for manufacturing steel materials having properties similar to those of steel materials subjected to the normalizing heat treatment without performing the normalizing heat treatment.
특허문헌 1에는 노멀라이징 열처리 없이도 충격인성이 우수한 강재를 제조하는 방법을 제시하고 있다. 그러나, 상기 특허문헌 1은 탄소함량이 낮아 충분한 저온 충격인성을 확보에는 유리할 수 있으나, 충분한 강도를 확보하기 어려운 측면이 있으며, 더욱이 두께가 후물화 될수록 강도가 크게 하락할 수 있다는 한계가 있다.Patent Document 1 proposes a method for producing a steel having excellent impact toughness without normalizing heat treatment. However, Patent Document 1 has a low carbon content, but may be advantageous in securing sufficient low-temperature impact toughness, but there is a side that is difficult to secure sufficient strength, and furthermore, there is a limit that the strength may decrease significantly as the thickness becomes thicker.
(특허문헌 1)한국 등록특허공보 제10-1917453호(Patent Document 1) Korean Patent Registration No. 10-1917453
본 발명의 일측면은, 열처리 공정을 생략하더라도 우수한 강도와 충격인성을 갖는 강재와 이를 제조하는 방법을 제공하고자 하는 것이다.One aspect of the present invention is to provide a steel material having excellent strength and impact toughness even if the heat treatment process is omitted, and a method for manufacturing the same.
본 발명의 과제는 상술한 사항에 한정되지 아니한다. 본 발명의 추가적인 과제는 명세서 전반적인 내용에 기술되어 있으며, 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자라면 본 발명의 명세서에 기재된 내용으로부터 본 발명의 추가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.The object of the present invention is not limited to the above. Additional tasks of the present invention are described throughout the specification, and those skilled in the art will have no difficulty in understanding the additional tasks of the present invention from the contents described in the specification of the present invention.
본 발명의 일태양은 중량%로, C: 0.12~0.18%, Si: 0.2~0.5%. Mn: 1.0~1.7%, P: 0.012% 이하, S: 0.003% 이하, Al: 0.015~0.045%, Nb: 0.02~0.05%, V: 0.01~0.08%, Ti: 0.005~0.017%, N: 0.002~0.01%, 나머지는 Fe 및 불가피한 불순물을 포함하고,One aspect of the present invention, by weight%, C: 0.12 ~ 0.18%, Si: 0.2 ~ 0.5%. Mn: 1.0 to 1.7%, P: 0.012% or less, S: 0.003% or less, Al: 0.015 to 0.045%, Nb: 0.02 to 0.05%, V: 0.01 to 0.08%, Ti: 0.005 to 0.017%, N: 0.002 ~0.01%, the remainder including Fe and unavoidable impurities,
하기 [관계식 1]의 탄소당량(Ceq)가 0.48 이하이고,The carbon equivalent (Ceq) of the following [Relational Expression 1] is 0.48 or less,
미세조직은 면적분율로 페라이트 60~85%, 나머지는 펄라이트를 포함하며, 상기 미세조직 내에 NbC 및 VC 중 하나 이상의 석출물을 포함하고, 상기 석출물의 크기는 50㎚ 이하인 고강도 및 충격인성이 우수한 강재에 관한 것이다.The microstructure includes 60 to 85% of ferrite and pearlite in the area fraction, and includes one or more precipitates of NbC and VC in the microstructure, and the size of the precipitates is 50 nm or less. it's about
[관계식 1][Relationship 1]
Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
(상기 C, Mn, Cr, Mo, V, Cu, Ni은 각 성분의 함량(중량%) 값임)(The C, Mn, Cr, Mo, V, Cu, and Ni are the contents (% by weight) of each component)
본 발명의 다른 일태양은 중량%로, C: 0.12~0.18%, Si: 0.2~0.5%. Mn: 1.0~1.7%, P: 0.012% 이하, S: 0.003% 이하, Al: 0.015~0.045%, Nb: 0.02~0.05%, V: 0.01~0.08%, Ti: 0.005~0.017%, N: 0.002~0.01%, 나머지는 Fe 및 불가피한 불순물을 포함하고, 하기 [관계식 1]의 탄소당량(Ceq)가 0.48 이하인 강 슬라브를 하기 [관계식 2]의 조건으로 가열하는 단계; 및 Another aspect of the present invention, by weight%, C: 0.12 ~ 0.18%, Si: 0.2 ~ 0.5%. Mn: 1.0 to 1.7%, P: 0.012% or less, S: 0.003% or less, Al: 0.015 to 0.045%, Nb: 0.02 to 0.05%, V: 0.01 to 0.08%, Ti: 0.005 to 0.017%, N: 0.002 ~0.01%, the remainder including Fe and unavoidable impurities, and heating a steel slab having a carbon equivalent (Ceq) of 0.48 or less in the following [Relational Expression 1] under the conditions of [Relational Expression 2]; and
상기 가열된 강 슬라브를 900~1100℃의 온도범위에서 조압연한 후, Ar3 이상에 마무리 열간압연하는 단계를 포함하는 고강도 및 충격인성이 우수한 강재의 제조방법에 관한 것이다.After rough rolling the heated steel slab at a temperature range of 900 to 1100 ° C., it relates to a method for manufacturing a steel material having excellent high strength and impact toughness, including the step of hot rolling the finish over Ar3.
[관계식 1][Relationship 1]
Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
(상기 C, Mn, Cr, Mo, V, Cu, Ni은 각 성분의 함량(중량%) 값임)(The C, Mn, Cr, Mo, V, Cu, and Ni are the contents (% by weight) of each component)
[관계식 2][Relationship 2]
슬라브 추출온도(℃) > 10300 / {4.09 - log([Nb][C]0.24[N]0.65)} - 273 Slab extraction temperature (℃) > 10300 / {4.09 - log([Nb][C] 0.24 [N] 0.65 )} - 273
(상기 관계식 2에서, [Nb], [C] 및 [N]은 각각 합금조성의 함량(중량%)를 의미함)(In the above relationship 2, [Nb], [C] and [N] mean the content (% by weight) of the alloy composition, respectively)
본 발명에 의하면, 압연 후에 노멀라이징(Normalizing) 열처리를 행하지 않아도, 우수한 강도 및 충격인성을 확보하는 강재를 제공하여, 풍력구조용 등을 널리 사용될 수 있다. 또한, 열처리 생략에 따른 제조비용을 절감하여 상업적으로 유용한 강재를 제공하는 것이 가능한다. According to the present invention, a steel material that secures excellent strength and impact toughness without performing normalizing heat treatment after rolling is provided, and can be widely used for wind power structures and the like. In addition, it is possible to provide a commercially useful steel by reducing manufacturing costs due to omission of heat treatment.
본 발명의 다양하면서도 유익한 장점과 효과는 상술한 내용에 한정되지 않고, 본 발명의 구체적인 실시 태양을 설명하는 과정에서 보다 쉽게 이해될 수 있을 것이다.Various advantageous advantages and effects of the present invention are not limited to the above description, and will be more easily understood in the process of describing specific embodiments of the present invention.
도 1은 본 발명의 실시예에서 보여주는 슬라브 추출온도와 항복강도의 관계를 도시한 그래프이다.1 is a graph showing the relationship between slab extraction temperature and yield strength shown in an embodiment of the present invention.
본 명세서에서 사용되는 용어는 본 발명을 설명하기 위한 것이고, 본 발명을 한정하는 것을 의도하지 않는다. 또한, 본 명세서에서 사용되는 단수 형태들은 관련 정의가 이와 명백히 반대되는 의미를 나타내지 않는 한 복수 형태들도 포함한다. The terms used herein are intended to describe the present invention and are not intended to limit the present invention. Also, the singular forms used herein include the plural forms unless the related definition clearly dictates the contrary.
명세서에서 사용되는 "포함하는"의 의미는 구성을 구체화하고, 다른 구성의 존재나 부가를 제외하는 것은 아니다.The meaning of "comprising" as used in the specification specifies a component, and does not exclude the presence or addition of other components.
달리 정의하지 않는 한, 본 명세서에서 사용되는 기술 용어 및 과학 용어를 포함하는 모든 용어들은 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자가 일반적으로 이해하는 의미와 동일한 의미를 가진다. 사전에 정의된 용어들은 관련 기술문헌과 현재 개시된 내용에 부합하는 의미를 가지도록 해석된다.Unless otherwise defined, all terms including technical terms and scientific terms used in this specification have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. The terms defined in the dictionary are interpreted to have a meaning consistent with the related technical literature and the currently disclosed content.
본 발명자들은 압연 후 노멀라이징(Normaliing) 열처리를 하지 않고도, 노멀라이징 열처리한 강재와 동등 그 이상의 물성을 갖는 온도 범위에서 열간 압연 후 공냉하는 제조법으로 NR(Normalized Rolling)법이 있다. 이를 최적의 성분설계와 제조조건 정립을 통해, 노멀라이징 열처리재와 동등하거나 그 이상의 물성을 확보할 수 있음을 인지하게 되었다.The present inventors have a NR (Normalized Rolling) method as a manufacturing method in which air cooling is performed after hot rolling in a temperature range having physical properties equal to or greater than those of steel materials subjected to normalizing heat treatment without performing normalizing heat treatment after rolling. It was recognized that through the establishment of optimal component design and manufacturing conditions, it was possible to secure physical properties equal to or higher than those of normalizing heat treated materials.
특히, 육상용 풍력타워 등으로 사용되는 구조용강의 경우, 대형화되고 경제성이 요구됨에 따라 그 소재에 요구되는 물성을 확보하면서, 경제적으로 제조할 수 수 있는 방안이 필요하다. 이에, 합금설계에 있어서, 합금조성 및 일부 성분간의 관계를 규명하여 최적화하고, 제조조건을 최적화함으로써 목표 물성을 가지는 강재를 제공할 수 있음을 확인하고 본 발명을 완성하기에 이르렀다.In particular, in the case of structural steel used for onshore wind towers, etc., as large-scale and economic efficiency are required, there is a need for a method that can be economically manufactured while securing physical properties required for the material. Accordingly, in the alloy design, it was confirmed that a steel material having target properties can be provided by identifying and optimizing the relationship between the alloy composition and some components and optimizing the manufacturing conditions, thereby completing the present invention.
이하, 본 발명 강재의 일구현예에 대해 상세히 설명한다. Hereinafter, an embodiment of the steel of the present invention will be described in detail.
먼저, 상기 강재의 합금조성에 대해 상세히 설명한다. 본 발명의 강재는 중량%로, C: 0.12~0.18%, Si: 0.2~0.5%. Mn: 1.0~1.7%, P: 0.012% 이하, S: 0.003% 이하, Al: 0.015~0.045%, Nb: 0.02~0.05%, V: 0.01~0.08%, Ti: 0.005~0.017%, N: 0.002~0.01%를 포함하고, First, the alloy composition of the steel will be described in detail. The steel material of the present invention is by weight%, C: 0.12 ~ 0.18%, Si: 0.2 ~ 0.5%. Mn: 1.0 to 1.7%, P: 0.012% or less, S: 0.003% or less, Al: 0.015 to 0.045%, Nb: 0.02 to 0.05%, V: 0.01 to 0.08%, Ti: 0.005 to 0.017%, N: 0.002 contains ~0.01%;
Cu: 0.5% 이하 및 Ni: 0.5% 이하 중 하나 이상을 더 포함할 수 있다.Cu: 0.5% or less and Ni: 0.5% or less may further include one or more.
탄소(C): 0.12~0.18 중량%(이하, %라 함, 본 발명에서 특별히 언급하지 않는 하 각 원소의 함량은 중량%를 기준으로 한다.)Carbon (C): 0.12 to 0.18% by weight (hereinafter, referred to as %, unless otherwise specified in the present invention, the content of each element is based on weight%.)
상기 C는 강의 강도를 향상시키는데 효과적인 원소이다. 이를 위해 상기 C를 0.12% 이상 포함하는 것이 바람직하다. 다만, 그 함량이 0.18%를 초과하게 되면 강재 중심부의 편석도가 증가되고, 도상 마르텐사이트(MA) 조직이 형성되어 저온 충격인성을 크게 저해하는 문제가 있다. 보다 유리하게는 0.17% 이하로 포함할 수 있다.The C is an element effective in improving the strength of steel. For this purpose, it is preferable to include 0.12% or more of the C. However, when the content exceeds 0.18%, the degree of segregation in the center of the steel material increases, and an island martensitic (MA) structure is formed, which greatly impairs low-temperature impact toughness. More advantageously, it may contain 0.17% or less.
실리콘(Si): 0.2~0.5%Silicon (Si): 0.2 to 0.5%
상기 Si는 탈산제로 사용될 뿐만 아니라, 강의 강도 향상 및 인성 향상에 유리한 원소이다. 이러한 효과를 충분히 얻기 위해서는 상기 Si가 0.2% 이상 포함되는 것이 바람직하다. 그러나, 그 함량이 0.5%를 초과하는 경우에는 MA를 과다하게 형성시켜 저온 충격인성이 열위해질 우려가 있다. 따라서, 상기 Si은 0.2~0.5%인 것이 바람직하다.The Si is not only used as a deoxidizing agent, but also is an element that is advantageous for improving strength and toughness of steel. In order to sufficiently obtain these effects, it is preferable that the Si content is 0.2% or more. However, if the content exceeds 0.5%, MA may be excessively formed, resulting in poor low-temperature impact toughness. Therefore, the Si content is preferably 0.2 to 0.5%.
망간(Mn): 1.0~1.7%Manganese (Mn): 1.0 to 1.7%
상기 Mn은 고용강화 효과로 강의 강도를 향상시키는데 유리한 원소이다. 그 효과를 충분히 얻기 위해서 상기 Mn을 1.0% 이상 포함하는 것이 바람직하다. 다만, 그 함량이 1.7%를 초과하게 되면, 강 중 황(S)과 결합하여 MnS를 형성함으로써, 저온 충격인성을 크게 저해할 수 있다. 따라서, 상기 Mn은 1.0~1.7% 포함하는 것이 바람직하며, 보다 유리하게는 1.35~1.65%로 포함할 수 있다.The Mn is an element that is advantageous for improving the strength of steel through a solid solution strengthening effect. In order to sufficiently obtain the effect, it is preferable to contain 1.0% or more of Mn. However, when the content exceeds 1.7%, by combining with sulfur (S) in steel to form MnS, low-temperature impact toughness can be significantly impaired. Therefore, it is preferable to include 1.0 to 1.7% of Mn, and more advantageously, 1.35 to 1.65% of Mn may be included.
인(P): 0.012% 이하Phosphorus (P): 0.012% or less
상기 P은 강의 강도 향상 및 내식성 확보에 유리한 원소이지만, 강의 충격인성을 크게 저해할 수 있으므로, 가능한 낮은 함량으로 제한하는 것이 바람직하다. 본 발명에서 상기 P을 최대 0.012%로 함유하더라도 목표로 하는 물성 확보에 무리는 없으므로, 그 함량을 0.012% 이하로 하는 것이 바람직하다. 다만, 불가피하게 첨가되는 수준을 고려하면 0%는 제외할 수 있다. P is an element that is advantageous for improving strength and securing corrosion resistance of steel, but since it can greatly impair the impact toughness of steel, it is preferable to limit the content to as low as possible. In the present invention, even if the P is contained at a maximum of 0.012%, it is not unreasonable to secure the target physical properties, so it is preferable to set the content to 0.012% or less. However, considering the level that is unavoidably added, 0% can be excluded.
황(S): 0.003% 이하Sulfur (S): 0.003% or less
상기 S는 강 중 Mn과 결합하여 MnS 등을 형성함으로써, 강의 수소유기균열 저항성과 충격인성을 크게 저해하는 원소이다. 따라서, 상기 S은 가능한 낮은 함량으로 관리함이 유리하다. 본 발명에서 상기 S을 최대 0.003% 함유하더라도 목표로 하는 물성 확보에 무리가 없으므로, 그 함량을 0.003% 이하로 제한할 수 있다. 다만, 불가피하게 첨가되는 수준을 고려하면 0%는 제외할 수 있다.The S is an element that greatly inhibits the hydrogen-induced cracking resistance and impact toughness of the steel by combining with Mn in the steel to form MnS or the like. Therefore, it is advantageous to manage the S content as low as possible. In the present invention, even if the S is contained in a maximum of 0.003%, there is no difficulty in securing the target physical properties, so the content can be limited to 0.003% or less. However, considering the level that is unavoidably added, 0% can be excluded.
알루미늄(Al): 0.015~0.045%Aluminum (Al): 0.015 to 0.045%
상기 Al은 용강을 저렴하게 탈산할 수 있는 원소로서, 상술한 효과를 충분히 얻기 위해서는 상기 Al을 0.015% 이상 포함하는 것이 바람직하나, 그 함량이 과다하여 0.045%를 초과하게 되면 연속주조시 노즐 막힘을 유발할 뿐만 아니라 Al계 산화성 개재물 형성으로 충격인성이 큰 폭으로 저하될 수 있으므로 바람직하지 못하다. 따라서 상기 Al은 0.015~0.045%로 포함하는 것이 바람직하다.Al is an element that can deoxidize molten steel at low cost. In order to sufficiently obtain the above-described effect, it is preferable to include 0.015% or more of Al, but if the content exceeds 0.045%, nozzle clogging during continuous casting may occur. This is not preferable because impact toughness may be greatly reduced due to the formation of Al-based oxidizing inclusions. Therefore, the Al is preferably included in 0.015 to 0.045%.
니오븀(Nb): 0.02~0.05%Niobium (Nb): 0.02 to 0.05%
상기 Nb은 NbC 또는 Nb(C,N)의 형태로 석출하여 모재의 강도를 크게 향상시키며, 고온으로 재가열시 고용된 Nb이 오스테나이트의 재결정 및 페라이트 또는 베이나이트의 변태를 억제함으로써 조직 미세화 효과를 얻을 수 있다. 이를 위해 0.02% 이상 포함하는 것이 바람직하다. 그러나, 그 함량이 과도하게 디면 미용해된 Nb이 TiNb(C,N) 형태로 형성되어, UT 불량 및 저온 충격인성을 저해하는 요인이 되므로, 상기 Nb의 상한은 0.05%인 것이 바람직하다. 보다 유리하게는 0.035~0.045% 포함할 수 있다.The Nb precipitates in the form of NbC or Nb(C,N) to greatly improve the strength of the base material, and when reheated to a high temperature, the dissolved Nb inhibits recrystallization of austenite and transformation of ferrite or bainite, thereby improving the structure refinement effect. You can get it. For this purpose, it is preferable to include 0.02% or more. However, if the content is excessive, undissolved Nb is formed in the form of TiNb(C,N), which becomes a factor that inhibits UT defects and low-temperature impact toughness. Therefore, the upper limit of Nb is preferably 0.05%. More advantageously, it may contain 0.035 to 0.045%.
바나듐(V): 0.01~0.08%Vanadium (V): 0.01 to 0.08%
상기 V는 다른 합금원소들에 비해 고용되는 온도가 낮으며, 열간압연 후 공냉 과정에서 VC를 형성하여 강도 증가에 크게 기여하는 효과가 있다. 본 발명과 같은 강재는 용접 후 열처리(PWHT) 후 강도가 충분히 확보되지 못할 수 있다. 이에 상기 V을 0.01% 이사 포함함으로써 강도 향상 효과를 얻을 수 있다. 다만, 그 함량이 0.08%를 초과하게 되면 MA와 같은 경질상의 분율이 높아져 저온 충격인성이 큰 폭으로 저하되는 문제가 있다. 따라서, 상기 V 함량은 0.01~0.08%인 것이 바람직하다.The V has a low melting temperature compared to other alloying elements, and has an effect of greatly contributing to an increase in strength by forming VC in an air cooling process after hot rolling. Steel materials such as those of the present invention may not sufficiently secure strength after post-weld heat treatment (PWHT). Accordingly, by including 0.01% or more of the above V, it is possible to obtain an effect of improving strength. However, when the content exceeds 0.08%, there is a problem in that the fraction of the hard phase such as MA increases and the low-temperature impact toughness is significantly lowered. Therefore, the V content is preferably 0.01 to 0.08%.
티타늄(Ti): 0.005~0.017%Titanium (Ti): 0.005 to 0.017%
상기 Ti는 N과 함께 포함되면 TiN을 형성함으로써, AlN 석출물의 형성에 의한 표면 크랙 발생을 저감하는 역할을 하므로, 0.005% 이상 포함하는 것이 바람직하다. 다만, 그 함량이 0.017%를 초과하게 되면 강 슬라브의 재가열 중에 조대한 TiN이 형성되어 저온 충격인성을 저해하는 요인으로 작용한다. 따라서, 상기 Ti는 0.005~0.017%인 것이 바람직하며, 보다 바람직하게는 0.01~0.015% 이다.When the Ti is included together with N, it forms TiN, so it serves to reduce the occurrence of surface cracks due to the formation of AlN precipitates, so it is preferable to include 0.005% or more. However, if the content exceeds 0.017%, coarse TiN is formed during reheating of the steel slab, which acts as a factor impairing low-temperature impact toughness. Therefore, Ti is preferably 0.005 to 0.017%, more preferably 0.01 to 0.015%.
질소(N): 0.002~0.01%Nitrogen (N): 0.002 to 0.01%
상기 N는 Ti와 함께 포함되면, TiN을 형성하여 용접시 열영향에 의한 결정립 성장을 억제하는데 유리한 원소이다. 상기 Ti의 첨가시 상술한 효과를 충분히 얻기 위해서는 상기 N를 0.002% 이상으로 포함할 수 있다. 다만, 그 함량이 0.01%를 초과하게 되면 조대한 TiN이 형성되어 저온 충격인성이 저해되므로 바람직하지 못하다. 따라서, 상기 N의 함량은 0.002~0.01%인 것이 바람직하다.When N is included together with Ti, it is an advantageous element for forming TiN and suppressing crystal grain growth due to thermal effects during welding. When the Ti is added, N may be included in an amount of 0.002% or more in order to sufficiently obtain the above effects. However, if the content exceeds 0.01%, coarse TiN is formed and low-temperature impact toughness is impaired, which is not preferable. Therefore, the content of N is preferably 0.002 to 0.01%.
추가적으로, 상기 조성이외에 구리(Cu): 0.5% 이하 및 니켈(Ni): 0.5% 이하 중 하나 이상을 더 포함할 수 있다.Additionally, in addition to the above composition, one or more of copper (Cu): 0.5% or less and nickel (Ni): 0.5% or less may be further included.
구리 (Cu): 0.5% 이하Copper (Cu): 0.5% or less
상기 Cu는 고용강화에 의해 강도를 크게 향상시킬 수 있는 원소이다. 그러나, 상기 Cu의 함량이 과도하면 탄소당량을 높여 용접성을 저해할 뿐만 아니라, 제품의 표면 품질을 크게 열화시키는 문제가 있다. 따라서, 상기 Cu 첨가시 최대 0.5%로 포함할 수 있다. 다만, 본 발명에서는 상기 Cu를 첨가하지 않더라도 목표로 하는 물성을 확보하는데 무리가 없으므로, 상기 Cu는 필수가 아님을 밝혀둔다.The Cu is an element capable of greatly improving strength by solid solution strengthening. However, if the content of Cu is excessive, there is a problem of not only impairing weldability by increasing the carbon equivalent, but also significantly degrading the surface quality of the product. Therefore, when the Cu is added, it may be included in a maximum of 0.5%. However, in the present invention, since there is no problem in securing the target physical properties even if the Cu is not added, it should be noted that the Cu is not essential.
니켈(Ni): 0.5% 이하Nickel (Ni): 0.5% or less
상기 NI은 모재의 강도와 저온 충격인성을 동시에 향상시킬 수 있는 원소이나, 고가의 원소로서 그 함량이 0.5%를 초과하게 되면 경제성이 크게 저하되는 문제가 있다. 따라서, 상기 Ni은 0.5% 이하로 포함하는 것이 바람직하다. 다만, 본 발명에서는 상기 Ni을 첨가하지 않더라도 목표로 하는 물성을 확보하는데 무리가 없으므로, 상기 Ni은 필수가 아님을 밝혀둔다.The NI is an element that can simultaneously improve the strength and low-temperature impact toughness of a base material, but is an expensive element, and when its content exceeds 0.5%, there is a problem in that economical efficiency is greatly reduced. Therefore, it is preferable to include the Ni at 0.5% or less. However, in the present invention, since there is no problem in securing the target physical properties even if the Ni is not added, it should be noted that the Ni is not essential.
나머지는 철(Fe) 및 불가피한 불순물을 포함한다. 불가피한 불순물은 통상의 철강 제조공정에서 의도되지 않게 혼입될 수 있는 것으로, 이를 전면 배제할 수는 없으며, 통상의 철강제조 분야의 기술자라면 그 의미를 쉽게 이해할 수 있다. 또한, 본 발명은, 앞서 언급한 강 조성 이외의 다른 조성의 첨가를 전면적으로 배제하는 것은 아니다.The remainder includes iron (Fe) and unavoidable impurities. Inevitable impurities can be unintentionally mixed in the normal steel manufacturing process, and cannot be completely excluded, and those skilled in the ordinary steel manufacturing field can easily understand the meaning. Further, the present invention does not entirely exclude the addition of other compositions than the aforementioned steel composition.
본 발명 강재는 목표 수준의 강도와 더불어 충격인성을 확보하기 위하여, 이러한 물성 향상에 유리한 원소들을 일정량 첨가함에 있어서, 그들의 함량을 적절히 조절하는 것이 바람직하다. 이에, 하기 [관계식 1]로 나타내는 탄소당량(Ceq)이 0.48 이하인 것이 바람직하다. 상기 탄소당량(Ceq)가 0.48를 초과하게 되면, 강도 확보에는 유리할 수 있으나, 용접 후 물성을 크게 저해할 우려가 있다. 또한, 다량의 합금원소가 포함되면 원가 상승으로 인해 경제성을 해치게 되므로 탄소당량(Ceq)은 0.48 이하인 것이 바람직하다.In order to secure the impact toughness as well as the strength of the target level of the steel of the present invention, in adding a certain amount of elements advantageous to the improvement of physical properties, it is preferable to properly adjust their content. Accordingly, it is preferable that the carbon equivalent (Ceq) represented by the following [Relational Expression 1] is 0.48 or less. If the carbon equivalent (Ceq) exceeds 0.48, it may be advantageous to secure strength, but there is a concern that the physical properties after welding may be significantly impaired. In addition, if a large amount of alloying elements are included, economic feasibility is impaired due to cost increase, so the carbon equivalent (Ceq) is preferably 0.48 or less.
[관계식 1][Relationship 1]
Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
(상기 C, Mn, Cr, Mo, V, Cu, Ni은 각 성분의 함량(중량%) 값임)(The C, Mn, Cr, Mo, V, Cu, and Ni are the contents (% by weight) of each component)
본 발명 강재의 미세조직은 면적분율로, 페라이트 60~85%를 포함하고, 잔부 펄라이트를 포함한다. 상기 페라이트의 분율이 60% 미만이거나, 잔부인 펄라이트 분율이 40%를 초과하게 되면, 강도 확보에는 유리할 수 있으나 충격인성이 큰 폭으로 감소할 수 있다. 또한, 페라이트 분율이 85%를 초과하게 되면, 충격인성 확보에는 유리할 수 있으나, 충분한 강도를 확보하기 어려우므로, 본 발명 강재는 페라이트가 60~85 면적%, 잔부는 펄라이트인 것이 바람직하다. The microstructure of the steel of the present invention includes, in area fraction, 60 to 85% of ferrite and the remainder of pearlite. If the fraction of the ferrite is less than 60% or the fraction of the remaining pearlite exceeds 40%, it may be advantageous to secure strength, but impact toughness may be greatly reduced. In addition, when the ferrite fraction exceeds 85%, it may be advantageous to secure impact toughness, but it is difficult to secure sufficient strength, so the steel of the present invention preferably has 60 to 85 area% ferrite and the remainder is pearlite.
상기 페라이트의 평균 결정립 크기는 30㎛ 이하인 것이 바람직하다. 상기 페라이트의 평균 결정립 크기는 30㎛를 초과하게 되면 항복강도 확보에 어려움이 있고 충격인성이 크게 저하될 수 있으므로, 평균 결정립 크기는 30㎛ 이하인 것이 바람직하다. The average grain size of the ferrite is preferably 30 μm or less. When the average grain size of the ferrite exceeds 30 μm, it is difficult to secure yield strength and impact toughness may be greatly reduced. Therefore, the average grain size is preferably 30 μm or less.
상기 강재의 미세조직 내에 NbC 및/또는 VC 석출물을 포함할 수 있다. 상기 석출물의 크기는 50㎚ 이하인 것이 바람직하다. 상기 석출물의 크기가 50㎚를 초과하게 되면 충격인성이 크게 저하될 수 있으므로 바람직하지 못하다. 상기 석출물은 페라이트 결정립 내에 존재하는 것이 바람직하다.NbC and/or VC precipitates may be included in the microstructure of the steel. The size of the precipitate is preferably 50 nm or less. If the size of the precipitate exceeds 50 nm, it is not preferable because impact toughness may be greatly reduced. It is preferable that the precipitate exists in ferrite crystal grains.
한편, 본 발명의 강재는 두께 방향 t/4 지점(여기서, t는 강재의 두께(mm)를 의미함)에서 압연방향의 수직으로 평가한 항복강도가 370MPa 이상, 인장강도가 520MPa 이상, -20℃에서의 샤르피 충격흡수에너지(CVN, -20℃) 값이 평균 40J 이상으로 우수한 강도와 저온 충격인성을 갖는다.On the other hand, the steel of the present invention has a yield strength of 370 MPa or more, a tensile strength of 520 MPa or more, -20 It has excellent strength and low-temperature impact toughness with an average Charpy impact absorption energy (CVN, -20 ℃) value at ℃ of more than 40J.
다음으로, 본 발명 강재의 제조방법에 대한 일구현예에 대해 상세히 설명한다. 상기 제조방법은 전술한 합금조성 및 [관계식 1]의 탄소당량(Ceq)이 0.48 이하인 강 슬라브를 가열하여, 열간압연하여 제조한다. 이하, 각 공정에 대해 상세히 설명한다.Next, an embodiment of the manufacturing method of the steel of the present invention will be described in detail. The manufacturing method is prepared by heating and hot rolling a steel slab having the above-mentioned alloy composition and carbon equivalent (Ceq) of 0.48 or less of [Relationship 1]. Hereinafter, each process is explained in detail.
강 슬라브 가열steel slab heating
전술한 합금조성을 충족하는 강 슬라브를 가열하여 균질화 처리를 행하는 것이 바람직하다. 이때, 하기 [관계식 2]로 규정하는 온도조건을 충족하도록 가열을 행하는 것이 바람직하다. 한편, 하기 [관계식 2]의 슬라브 추출온도는 1200℃를 넘지 않는 것이 바람직하다. It is preferable to perform homogenization treatment by heating a steel slab satisfying the above-mentioned alloy composition. At this time, it is preferable to perform heating so as to satisfy the temperature conditions defined by the following [Relational Expression 2]. On the other hand, it is preferable that the slab extraction temperature of [Relationship 2] below does not exceed 1200 ° C.
상기 강 슬라브의 가열온도가 하기 관계식 2의 조건을 만족하지 못하면 슬라브 내에 형성된 석출물(탄,질화물)이 충분히 재고용되지 못하여 열간압연 이후의 공정에서 석출물의 형성이 감소하게 되고, 최종적으로 본 발명에서 제시한 항복강도 및 인장강도를 만족하기 어렵다. 한편, 상기 슬라브 추출온도가 1200℃를 초과하면 오스테나이트 결정립이 조대화되어 강의 물성을 저해할 우려가 있으므로, 1200℃는 넘지 않는 것이 바람직하다. If the heating temperature of the steel slab does not satisfy the condition of the following relational expression 2, the precipitates (carbon, nitride) formed in the slab are not sufficiently re-dissolved, so the formation of precipitates is reduced in the process after hot rolling, and finally presented in the present invention. It is difficult to satisfy the required yield strength and tensile strength. On the other hand, if the slab extraction temperature exceeds 1200 ° C, there is a concern that the austenite crystal grains are coarsened and the physical properties of the steel are deteriorated, so it is preferable not to exceed 1200 ° C.
[관계식 2][Relationship 2]
슬라브 추출온도(℃) > 10300 / {4.09 - log([Nb][C]0.24[N]0.65)} - 273 Slab extraction temperature (℃) > 10300 / {4.09 - log([Nb][C] 0.24 [N] 0.65 )} - 273
(상기 관계식 2에서, [Nb], [C] 및 [N]은 각각 합금조성의 함량(중량%)를 의미함)(In the above relationship 2, [Nb], [C] and [N] mean the content (% by weight) of the alloy composition, respectively)
열간압연hot rolled
상기 가열된 강 슬라브를 열간압연한다. 상기 가열된 강 슬라브를 900~1100℃의 온도범위에서 조압연한 후, Ar3 이상에 마무리 열간압연하는 것이 바람직하다. 상기 조압연시 온도가 950℃ 미만일 경우, 후속하는 마무리 열간압연시 온도가 너무 낮어지는 문제가 있다. 한편, 마무리 열간압연 온도가 Ar3 미만이면 압연 부하겨 커져 표면 크랙 등의 품질 불량이 발생할 우려가 있다.The heated steel slab is hot rolled. After rough rolling the heated steel slab at a temperature range of 900 to 1100 ° C., it is preferable to perform finish hot rolling on Ar3 or higher. If the temperature during the rough rolling is less than 950 ° C., there is a problem that the temperature becomes too low during the subsequent finish hot rolling. On the other hand, if the finish hot rolling temperature is less than Ar3, the rolling load becomes large and there is a possibility that quality defects such as surface cracks may occur.
Ar3 = 910-310C-80Mn-20Cu-55Ni-80Mo+119V+124Ti-18Nb+179AlAr3 = 910-310C-80Mn-20Cu-55Ni-80Mo+119V+124Ti-18Nb+179Al
(여기서, 각 원소는 함량(중량%)을 의미함)(Here, each element means the content (% by weight))
상기 열간압연 후 공냉을 행한다. After the hot rolling, air cooling is performed.
상기 방법으로 제조된 본 발명의 강재는 후속하는 열처리, 예를 들면 노멀라이징(Normalizing) 열처리 등을 행하지 않아도, 높은 강도 및 우수한 충격인성을 확보할 수 있다.The steel material of the present invention manufactured by the above method can secure high strength and excellent impact toughness without performing subsequent heat treatment, for example, normalizing heat treatment.
다음으로, 본 발명의 실시예에 대해 설명한다. Next, examples of the present invention will be described.
하기 실시예는 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자라면 본 발명의 범주에서 벗어나지 않는 한도 내에서 여러 가지 변형이 가능함은 물론이다. 하기 실시예는 본 발명의 이해를 위한 것으로서, 본 발명의 권리범위는 하기 실시예에 국한되어 정해져서는 안되며, 후술하는 청구범위뿐만 아니라, 이와 균등한 것들에 의해 정해져야 한다.Of course, the following examples can be modified in various ways without departing from the scope of the present invention to those skilled in the art. The following examples are for understanding of the present invention, and the scope of the present invention should not be limited to the following examples and should not be defined, but should be defined by the claims described later as well as those equivalent thereto.
(실시예 1)(Example 1)
하기 표 1에 나타낸 합금조성(중량%, 나머지는 Fe 및 불가피한 불순물)을 갖는 용강을 연속 주조하여 슬라브를 제조하였다. 이때 상기 슬라브는 300mm의 두께로 제조하였다. 표 1의 발명예 1 내지 4는 본 발명에서 제시하는 합금조성 및 관계식 1을 모두 만족하는 경우이며, 비교예 1은 C의 함량과 관계식 1이 본 발명에서 제시한 값을 벗어난 경우이며, 비교예 3은 Nb 함량이 본 발명에서 제시한 값을 벗어난 것이다.A slab was manufactured by continuously casting molten steel having an alloy composition (% by weight, the remainder being Fe and unavoidable impurities) shown in Table 1 below. At this time, the slab was manufactured to a thickness of 300 mm. Invention Examples 1 to 4 of Table 1 are cases in which both the alloy composition and relational expression 1 presented in the present invention are satisfied, and in comparative example 1, the content of C and relational expression 1 are out of the values suggested in the present invention, Comparative Example 3 is that the Nb content is out of the value suggested in the present invention.
구분　division CC SiSi MnMn PP SS AlAl NbNb CuCu NiNi VV TiTi NN 관계식 1Relation 1
발명예1Invention example 1 0.1500.150 0.4500.450 1.5301.530 0.0080.008 0.0020.002 0.0300.030 0.0450.045 0.0000.000 0.0000.000 0.0400.040 0.0120.012 0.00350.0035 0.4130.413
발명예2Invention Example 2 0.1600.160 0.4500.450 1.6501.650 0.0080.008 0.0020.002 0.0300.030 0.0450.045 0.0000.000 0.0000.000 0.0400.040 0.0120.012 0.00360.0036 0.4430.443
발명예3Invention Example 3 0.1550.155 0.4500.450 1.6001.600 0.0090.009 0.0020.002 0.0300.030 0.0350.035 0.0000.000 0.0000.000 0.0550.055 0.0120.012 0.00350.0035 0.4330.433
발명예4Invention Example 4 0.1600.160 0.4000.400 1.6501.650 0.0080.008 0.0020.002 0.0300.030 0.0450.045 0.1000.100 0.2000.200 0.0450.045 0.0120.012 0.00350.0035 0.4640.464
비교예1Comparative Example 1 0.1850.185 0.4000.400 1.6501.650 0.0090.009 0.0020.002 0.0300.030 0.0400.040 0.1000.100 0.1500.150 0.0450.045 0.0120.012 0.00360.0036 0.4860.486
비교예2Comparative Example 2 0.1500.150 0.4500.450 1.6001.600 0.0080.008 0.0020.002 0.0300.030 0.0450.045 0.0000.000 0.0000.000 0.0300.030 0.0120.012 0.00350.0035 0.4230.423
비교예3Comparative Example 3 0.1600.160 0.4500.450 1.5501.550 0.0080.008 0.0020.002 0.0300.030 0.0150.015 0.0000.000 0.0000.000 0.0350.035 0.0120.012 0.00360.0036 0.4250.425
상기 표 1에서 관계식 1은 아래와 같이 계산된다. In Table 1, relational expression 1 is calculated as follows.
Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15 Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
(상기 C, Mn, Cr, Mo, V, Cu, Ni은 각 성분의 함량(중량%) 값임)(The above C, Mn, Cr, Mo, V, Cu, and Ni are the contents (% by weight) of each component)
상기 슬라브를 표 2의 조건으로 가열, 조압연하고, 880~900℃의 온도범위로 마무리 열간압연하여 두께 5mm의 열연강판을 제조하고, 상온까지 공냉하였다. 발명예 1 내지 4, 비교예 1 및 3은 본 발명에서 제시한 공정조건을 만족하나, 비교예 2의 경우는 하기 관계식 2의 조건을 만족하지 못하였다.The slab was heated and rough-rolled under the conditions of Table 2, and finished hot-rolled at a temperature range of 880 to 900° C. to prepare a hot-rolled steel sheet having a thickness of 5 mm and air-cooled to room temperature. Inventive Examples 1 to 4 and Comparative Examples 1 and 3 satisfy the process conditions presented in the present invention, but in the case of Comparative Example 2, the condition of the following relational expression 2 was not satisfied.
비고note 추출온도
(℃)extraction temperature
(℃) 		재로시간
(min.)zero time
(min.) 		잔압하율
(%)Residual pressure drop rate
(%) 		압연시작온도 (℃)Rolling start temperature (℃) 압연종료온도 (℃)End rolling temperature (℃) 관계식 2Relation 2 관계식 2 만족여부Satisfaction of relational expression 2
발명예1Invention example 1 11611161 362362 5050 930930 900900 11511151 ○○
발명예2Invention example 2 11651165 360360 5050 928928 898898 11541154 ○○
발명예3Invention Example 3 11601160 360360 5050 915915 880880 11311131 ○○
발명예4Invention Example 4 11621162 362362 5050 920920 890890 11531153 ○○
비교예1Comparative Example 1 11601160 362362 5050 920920 890890 11471147 ○○
비교예2Comparative Example 2 11251125 360360 5050 925925 895895 11511151 XX
비교예3Comparative Example 3 11641164 361361 5050 930930 900900 10661066 ○○
상기 표 2에서 관계식 2는 다음과 같다.In Table 2, relational expression 2 is as follows.
[관계식 2][Relationship 2]
슬라브 추출온도(℃) > 10300 / {4.09 - log([Nb][C]0.24[N]0.65)} - 273 Slab extraction temperature (℃) > 10300 / {4.09 - log([Nb][C] 0.24 [N] 0.65 )} - 273
(상기 관계식 2에서, [Nb], [C] 및 [N]은 각각 합금조성의 함량(중량%)를 의미함)(In the above relationship 2, [Nb], [C] and [N] mean the content (% by weight) of the alloy composition, respectively)
상기와 같이 제조된 강재에 대해 미세조직 및 기계적 물성을 평가하였다. 미세조직은 광학현미경으로 관찰한 다음, 분석 프로그램으로 이용하여 페라이트의 분율과 직경을 측정하였으며, 석출물의 크기는 투과전자현미경을 활용하여 평균 직경을 측정하였다. 이때, 상기 미세조직은 각 강재의 두께 방향 t/4 (t는 강재 두께, mm) 지점에서 측정하고, 그 결과를 하기 표 3에 나타내었다. The microstructure and mechanical properties of the steel material prepared as described above were evaluated. The microstructure was observed with an optical microscope, and the ferrite fraction and diameter were measured using an analysis program, and the average diameter of the precipitate was measured using a transmission electron microscope. At this time, the microstructure was measured at the point of t/4 (t is the thickness of the steel, mm) in the thickness direction of each steel, and the results are shown in Table 3 below.
그리고, 각 강재의 두께 방향 1/4t 지점에서 기계적 물성을 평가하였으며, 이때 인장시편은 압연방향에 수직한 방향으로 각 두께 방향 지점에서 채취하여 인장강도(TS), 항복강도(YS) 및 연신율(El)을 측정하였으며, 충격시편은 JIS 4호 규격 시험편을 압연 방향으로 두께 방향 1/4t 지점에서 채취하여 -20℃에서의 평균 충격인성(CVN)을 측정하고, 그 결과를 하기 표 4에 나타내었다.In addition, the mechanical properties were evaluated at the 1/4t point in the thickness direction of each steel, and at this time, the tensile specimen was taken at each thickness direction point in the direction perpendicular to the rolling direction, and the tensile strength (TS), yield strength (YS) and elongation ( El) was measured, and the impact specimen was taken from a JIS No. 4 standard test piece at the 1/4t point in the thickness direction in the rolling direction, and the average impact toughness (CVN) at -20 ° C was measured. The results are shown in Table 4 below. was
비고note 미세조직microstructure
폴리고날 페라이트
(면적 %)polygonal ferrite
(area %) 		펄라이트
(면적 %)perlite
(area %) 		페라이트 결정립 크기
(㎛)ferrite grain size
(μm) 		석출물 크기
(nm)precipitate size
(nm)
발명예1Invention example 1 8080 2020 2626 3535
발명예2Invention example 2 7676 2424 2222 3434
발명예3Invention example 3 7777 2323 2727 4242
발명예4Invention example 4 7676 2424 2020 4141
비교예1Comparative Example 1 6868 3232 3636 6767
비교예2Comparative Example 2 8181 1919 2828 3636
비교예3Comparative Example 3 7676 2424 3434 3030
상기 표 3 에 나타낸 바와 같이, 본 발명에서는 제안하는 합금조성, 성분관계 및 제조조건에 의해 제조된 발명강 1 내지 4는 본 발명에서 제시한 폴리고날 페라이트의 분율, 결정립 크기 및 석출물 크기를 만족하고 있다. 반면, 비교예 1 및 3은 폴리고날 페라이트의 분율은 만족하고 있으나 페라이트 결정립 크기가 본 발명에서 제시한 값을 벗어났다. 또한, 비교예 1은 본 발명에서 제시한 석출물의 크기를 벗어났다.As shown in Table 3, inventive steels 1 to 4 manufactured by the alloy composition, component relationship and manufacturing conditions proposed in the present invention satisfy the polygonal ferrite fraction, crystal grain size and precipitate size presented in the present invention, there is. On the other hand, Comparative Examples 1 and 3 satisfied the polygonal ferrite fraction, but the ferrite grain size was out of the value suggested in the present invention. In addition, Comparative Example 1 was out of the size of the precipitate suggested in the present invention.
구분division As-rolledAs-rolled NormalizedNormalized
인장물성tensile properties 충격인성
(J)impact toughness
(J) 		인장물성tensile properties 충격인성
(J)impact toughness
(J)
YP (MPa)YP (MPa) TS (MPa)TS (MPa) El.(%)El.(%) YP (MPa)YP (MPa) TS (MPa)TS (MPa) El.(%)El.(%)
발명예1Invention example 1 383383 536536 2727 210210 377377 524524 2828 223223
발명예2Invention Example 2 402402 552552 2626 196196 396396 530530 2727 200200
발명예3Invention Example 3 410410 556556 2525 174174 400400 542542 2626 186186
발명예4Invention example 4 401401 548548 2626 195195 393393 529529 2727 203203
비교예1Comparative Example 1 410410 544544 2424 3535 374374 524524 2424 4242
비교예2Comparative Example 2 336336 497497 2929 168168 316316 488488 3030 173173
비교예3Comparative Example 3 351351 520520 2626 7575 330330 509509 2828 9494
상기 표 4에서는 노멀라이징 전·후 인장물성 및 저온 충격인성을 나타내었다. 이때 노멀라니징(Normalizing) 처리는 870℃에서 128분 유지 후 공냉하였다.Table 4 shows tensile properties and low-temperature impact toughness before and after normalizing. At this time, the normalizing treatment was held at 870 ° C. for 128 minutes and then air-cooled.
발명예 1 내지 4의 경우 본 발명에서 제시한 성분 범위, 관계식 1과 2 및 미세조직 특성을 만족하여 인장물성 및 저온 충격인성을 모두 만족하고 있다. 구체적으로 발명예 1 내지 4의 경우 As-rolled 및 노멀라이징 열처리 후의 결과를 비교해보면, 열처리 이후 항복강도 및 인장강도가 소폭 하락하지만 여전히 본 발명에서 제시한 강도를 만족하고 있다. 충격인성의 경우에도 열처리 이후 NR법으로 제조한 경우 대비 소폭 증가하였으며, 본 발명에서 제시한 충격인성을 만족하는 것을 확인할 수 있다. In the case of Inventive Examples 1 to 4, both tensile properties and low-temperature impact toughness were satisfied by satisfying the component range, relational expressions 1 and 2, and microstructure characteristics presented in the present invention. Specifically, in the case of Inventive Examples 1 to 4, when comparing the results after As-rolled and normalized heat treatment, the yield strength and tensile strength slightly decrease after heat treatment, but still satisfy the strength proposed in the present invention. Even in the case of impact toughness, after heat treatment, it was slightly increased compared to the case of manufacturing by the NR method, and it can be confirmed that the impact toughness presented in the present invention is satisfied.
반면, 비교예 1의 경우, C의 함량과 관계식 1이 본 발명에서 제안한 범위를 벗어난 성분계로서, C 함량 과다 첨가로 인해 항복/인장강도는 본 발명에서 제시한 값을 만족하고 있을지 모르나, 충격인성은 제시한 값을 만족시키지 못하는 것을 확인할 수 있다. 비교예 2는 본 발명에서 제시한 성분 범위를 모두 만족하고 있으나 관계식 2를 만족하지 못해 슬라브 추출온도가 매우 낮은 경우로써, as-rolled 및 노멀라이징 열처리 후 모두 본 발명에서 제시한 항복강도와 인장강도를 만족시키지 못한 것을 알 수 있다. 또한, 발명예 1 내지 4에 비해 항복강도의 하락폭이 매우 큰 것을 알 수 있다. 이는 Nb가 슬라브 내에서 충분히 고용되지 못해 압연 중 NbC가 충분히 석출되지 못함에 따라 강도가 크게 하락된 것으로 판단된다. 비교예 3은 이와 반대로 Nb의 함량이 본 발명에서 제시한 값을 벗어난 경우로써, Nb가 슬라브 내에 충분히 고용되는 온도에서 가열되었음에도 함량 그 자체가 매우 낮아 NbC 석출물이 충분히 석출되지 못하여 본 발명에서 제시한 항복강도 및 인장강도를 만족하지 못하는 것을 확인할 수 있으며, 비교예 3 역시 노멀라이징 열처리 후 항복강도가 큰 폭으로 하락하는 것을 확인할 수 있다.On the other hand, in the case of Comparative Example 1, the C content and relational expression 1 are outside the range proposed in the present invention, and the yield/tensile strength may satisfy the value suggested in the present invention due to the excessive addition of C content, but the impact toughness It can be confirmed that does not satisfy the proposed value. Comparative Example 2 satisfies all the component ranges presented in the present invention, but does not satisfy the relational expression 2, and the slab extraction temperature is very low. After as-rolled and normalizing heat treatment, the yield strength and tensile strength presented in the present invention It can be seen that it is not satisfied. In addition, it can be seen that the drop in yield strength is very large compared to Inventive Examples 1 to 4. This is considered to be due to the fact that Nb is not sufficiently employed in the slab and thus NbC is not sufficiently precipitated during rolling, resulting in a significant decrease in strength. Comparative Example 3, on the contrary, is a case where the content of Nb is outside the value suggested in the present invention, and even though Nb is heated at a temperature at which it is sufficiently dissolved in the slab, the content itself is very low, and NbC precipitates are not sufficiently precipitated. It can be seen that the yield strength and tensile strength are not satisfied, and Comparative Example 3 also confirms that the yield strength significantly decreases after normalizing heat treatment.
(실시예 2)(Example 2)
한편, 별도의 실시예로써 상기 실시예 1의 발명예 1의 성분을 가지는 슬라브를 압연하여 두께 75mmt를 가지는 강재를 제조하였다. 이때 슬라브 추출온도에 따른 항복강도를 나타내는 확인하기 위해서, 추출온도의 상기 관계식 2의 결과를 달리하여 행한 경우, 상기 추출온도와 항복강도의 관계의 결과를 도 1에 나타내었다. 추출온도가 관계식 2를 만족하지 못하는 경우에는 본 발명에서 제시한 항복강도를 만족하지 못하는 반면, 관계식 2를 만족하는 경우에는 모두 우수한 항복강도를 나타냄을 알 수 있다.On the other hand, as a separate example, a steel material having a thickness of 75 mmt was manufactured by rolling a slab having the components of Example 1 of Example 1 above. At this time, in order to confirm the yield strength according to the slab extraction temperature, when the results of the relational expression 2 of the extraction temperature are different, the results of the relationship between the extraction temperature and the yield strength are shown in FIG. It can be seen that when the extraction temperature does not satisfy relational expression 2, the yield strength presented in the present invention is not satisfied, whereas when relational expression 2 is satisfied, all exhibit excellent yield strength.

Claims (8)

  1. 중량%로, C: 0.12~0.18%, Si: 0.2~0.5%. Mn: 1.0~1.7%, P: 0.012% 이하, S: 0.003% 이하, Al: 0.015~0.045%, Nb: 0.02~0.05%, V: 0.01~0.08%, Ti: 0.005~0.017%, N: 0.002~0.01%, 나머지는 Fe 및 불가피한 불순물을 포함하고,In weight percent, C: 0.12-0.18%, Si: 0.2-0.5%. Mn: 1.0 to 1.7%, P: 0.012% or less, S: 0.003% or less, Al: 0.015 to 0.045%, Nb: 0.02 to 0.05%, V: 0.01 to 0.08%, Ti: 0.005 to 0.017%, N: 0.002 ~0.01%, the remainder including Fe and unavoidable impurities,
    하기 [관계식 1]의 탄소당량(Ceq)가 0.48 이하이고,The carbon equivalent (Ceq) of the following [Relational Expression 1] is 0.48 or less,
    미세조직은 면적분율로 페라이트 60~85%, 나머지는 펄라이트를 포함하며, 상기 미세조직 내에 NbC 및 VC 중 하나 이상의 석출물을 포함하고, 상기 석출물의 크기는 50㎚ 이하인 고강도 및 충격인성이 우수한 강재.The microstructure includes 60 to 85% of ferrite in area fraction and pearlite with the rest, and includes one or more precipitates of NbC and VC in the microstructure, and the size of the precipitates is 50 nm or less. Steel with excellent high strength and impact toughness.
    [관계식 1][Relationship 1]
    Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
    (상기 C, Mn, Cr, Mo, V, Cu, Ni은 각 성분의 함량(중량%) 값임)(The C, Mn, Cr, Mo, V, Cu, and Ni are the contents (% by weight) of each component)
  2. 청구항 1에 있어서,The method of claim 1,
    상기 강재는 Cu: 0.5% 이하 및 Ni: 0.5% 이하 중 하나 이상을 더 포함하는 고강도 및 충격인성이 우수한 강재.The steel material is Cu: 0.5% or less and Ni: 0.5% or less of high strength and impact toughness excellent steel further comprising one or more of.
  3. 청구항 1에 있어서,The method of claim 1,
    상기 페라이트 결정립 크기는 30㎛ 이하인 고강도 및 충격인성이 우수한 강재.The ferrite grain size is a steel having excellent high strength and impact toughness of 30 μm or less.
  4. 청구항 1에 있어서,The method of claim 1,
    상기 NbC 및 VC 중 하나 이상의 석출물은 페라이트 결정립 내에 존재하는 고강도 및 충격인성이 우수한 강재.One or more precipitates of NbC and VC are present in ferrite crystal grains and have excellent high strength and impact toughness.
  5. 청구항 1에 있어서,The method of claim 1,
    상기 강재는 두께 방향 t/4 지점(여기서, t는 강재의 두께(mm)를 의미함)에서 압연방향의 수직으로 평가한 항복강도가 370MPa 이상이며, 인장강도가 520MPa 이상이고, -20℃에서의 샤르피 충격흡수에너지(CVN, -20℃) 값이 평균 40J 이상인 고강도 및 충격인성이 우수한 강재.The steel material has a yield strength of 370 MPa or more and a tensile strength of 520 MPa or more, evaluated vertically in the rolling direction at the thickness direction t / 4 point (where t means the thickness (mm) of the steel material), and at -20 ° C Charpy shock absorption energy (CVN, -20 ℃) value of 40J or more on average, high strength and excellent impact toughness steel.
  6. 중량%로, C: 0.12~0.18%, Si: 0.2~0.5%. Mn: 1.0~1.7%, P: 0.012% 이하, S: 0.003% 이하, Al: 0.015~0.045%, Nb: 0.02~0.05%, V: 0.01~0.08%, Ti: 0.005~0.017%, N: 0.002~0.01%, 나머지는 Fe 및 불가피한 불순물을 포함하고, 하기 [관계식 1]의 탄소당량(Ceq)가 0.48 이하인 강 슬라브를 하기 [관계식 2]의 조건으로 가열하는 단계; 및 In weight percent, C: 0.12-0.18%, Si: 0.2-0.5%. Mn: 1.0 to 1.7%, P: 0.012% or less, S: 0.003% or less, Al: 0.015 to 0.045%, Nb: 0.02 to 0.05%, V: 0.01 to 0.08%, Ti: 0.005 to 0.017%, N: 0.002 ~0.01%, the remainder including Fe and unavoidable impurities, and heating a steel slab having a carbon equivalent (Ceq) of 0.48 or less in the following [Relational Expression 1] under the conditions of [Relational Expression 2]; and
    상기 가열된 강 슬라브를 900~1100℃의 온도범위에서 조압연한 후, Ar3 이상에 마무리 열간압연하는 단계;After rough rolling the heated steel slab at a temperature range of 900 to 1100 ° C, finishing hot rolling to Ar3 or higher;
    를 포함하는 고강도 및 충격인성이 우수한 강재의 제조방법.Method for producing a steel having excellent high strength and impact toughness comprising a.
    [관계식 1][Relationship 1]
    Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
    (상기 C, Mn, Cr, Mo, V, Cu, Ni은 각 성분의 함량(중량%) 값임)(The C, Mn, Cr, Mo, V, Cu, and Ni are the contents (% by weight) of each component)
    [관계식 2][Relationship 2]
    슬라브 추출온도(℃) > 10300 / {4.09 - log([Nb][C]0.24[N]0.65)} - 273 Slab extraction temperature (℃) > 10300 / {4.09 - log([Nb][C] 0.24 [N] 0.65 )} - 273
    (상기 관계식 2에서, [Nb], [C] 및 [N]은 각각 합금조성의 함량(중량%)를 의미함)(In the above relationship 2, [Nb], [C] and [N] mean the content (% by weight) of the alloy composition, respectively)
  7. 청구항 6에 있어서,The method of claim 6,
    상기 강 슬라브는 Cu: 0.5% 이하 및 Ni: 0.5% 이하 중 하나 이상을 더 포함하는 고강도 및 충격인성이 우수한 강재의 제조방법.The steel slab is Cu: 0.5% or less and Ni: a method for producing a steel having excellent high strength and impact toughness further comprising at least one of 0.5% or less.
  8. 청구항 6에 있어서,The method of claim 6,
    상기 슬라브 추출온도는 1200℃ 이하인 고강도 및 충격인성이 우수한 강재의 제조방법.The slab extraction temperature is a method for producing a steel having excellent high strength and impact toughness of 1200 ℃ or less.
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KR101205144B1 (en) * 2010-06-28 2012-11-26 현대제철 주식회사 H-steel for building structure and method for producing the same
KR20150026581A (en) * 2013-09-03 2015-03-11 동국제강주식회사 Thick steel plate having excellent bend property for tower of wind power generator and method of manufacturing the same
JP2016125077A (en) * 2014-12-26 2016-07-11 新日鐵住金株式会社 High-strength and high-ductility thick steel plate and production method thereof
KR101917453B1 (en) 2016-12-22 2018-11-09 주식회사 포스코 Steel plate having excellent ultra low-temperature toughness and method for manufacturing same

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Publication number Priority date Publication date Assignee Title
JPH11315341A (en) * 1998-03-05 1999-11-16 Kawasaki Steel Corp Extra thick wide flange shape excellent in toughness and having more than 325 mpa of yield strength
JP2003003229A (en) * 2001-06-19 2003-01-08 Nippon Steel Corp Thick steel plate having excellent fatigue strength and production method therefor
KR101205144B1 (en) * 2010-06-28 2012-11-26 현대제철 주식회사 H-steel for building structure and method for producing the same
KR20150026581A (en) * 2013-09-03 2015-03-11 동국제강주식회사 Thick steel plate having excellent bend property for tower of wind power generator and method of manufacturing the same
JP2016125077A (en) * 2014-12-26 2016-07-11 新日鐵住金株式会社 High-strength and high-ductility thick steel plate and production method thereof
KR101917453B1 (en) 2016-12-22 2018-11-09 주식회사 포스코 Steel plate having excellent ultra low-temperature toughness and method for manufacturing same

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