WO2016105062A1 - High-strength steel having excellent resistance to brittle crack propagation, and production method therefor - Google Patents

High-strength steel having excellent resistance to brittle crack propagation, and production method therefor Download PDF

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WO2016105062A1
WO2016105062A1 PCT/KR2015/014054 KR2015014054W WO2016105062A1 WO 2016105062 A1 WO2016105062 A1 WO 2016105062A1 KR 2015014054 W KR2015014054 W KR 2015014054W WO 2016105062 A1 WO2016105062 A1 WO 2016105062A1
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steel
crack propagation
brittle crack
rolling
propagation resistance
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PCT/KR2015/014054
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French (fr)
Korean (ko)
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WO2016105062A8 (en
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이학철
장성호
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주식회사 포스코
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Priority to JP2017532655A priority Critical patent/JP6788589B2/en
Priority to EP15873589.4A priority patent/EP3239331B1/en
Priority to CN201580070867.7A priority patent/CN107109597B/en
Priority to US15/535,582 priority patent/US20170327922A1/en
Publication of WO2016105062A1 publication Critical patent/WO2016105062A1/en
Publication of WO2016105062A8 publication Critical patent/WO2016105062A8/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
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
    • B21C37/02—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of sheets
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    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/001—Heat treatment of ferrous alloys containing Ni
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
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    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
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    • C21—METALLURGY OF IRON
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    • 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
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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    • 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
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation
    • 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
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling

Definitions

  • an object of the present invention is to provide a method for producing a high strength steel having excellent brittle crack propagation resistance.
  • C 0.05 to 0.1%
  • Mn 0.9 to 1.5%
  • Ni 0.8 to 1.5%
  • Nb 0.005 to 0.1%
  • Ti 0.005 to 0.1%
  • Cu 0.1 ⁇ 0.6%
  • Si 0.1-0.4%
  • P 100 ppm or less
  • S 40 ppm or less
  • Microstructure including a single structure selected from the group consisting of ferrite single phase structure, bainite single phase structure, ferrite and bainite complex, ferrite and perlite complex, and ferrite, bainite and perlite complex.
  • Have a high strength steel having excellent brittle crack propagation resistance having a thickness of 50 mm or more is provided.
  • the microstructure is secured to the center of steel by controlling the rolling reduction condition and securing a sufficient center-to-surface temperature difference during rough rolling.
  • C is the most important element for securing basic strength, it needs to be contained in steel within an appropriate range, and in order to obtain such an addition effect, it is preferable to add C 0.05% or more.
  • Ni is more preferably limited to 0.89 to 1.42%, even more preferably 1.01 to 1.35%.
  • Ti is a component that precipitates with TiN upon reheating and inhibits the growth of crystal grains of the base metal and the weld heat affected zone to greatly improve low-temperature toughness. To obtain such an additive effect, Ti is preferably added at least 0.005%.
  • Si improves the strength of the steel and has a strong deoxidation effect
  • coarse phase martensite (MA) phase may be generated to lower brittle crack propagation resistance, so the upper limit of the Si content is preferably limited to 0.4%.
  • the content of Si is more preferably limited to 0.22 to 0.32%, even more preferably 0.25 to 0.3%.
  • the ferrite is preferably polygonal ferrite or acicular ferrite, and bainite is preferably granular bainite.
  • the fraction of pearlite is preferably limited to 20% or less.
  • the steel may preferably have a particle size of 30 ⁇ m or less having a high-angle boundary of 15 degrees or more, as measured by the EBSD method of the center portion.
  • the area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction is minimized.
  • the temperature difference between the center and the surface of the slab or bar means a difference between the surface temperature of the slab or bar measured immediately before rough rolling and the center temperature calculated in consideration of the cooling conditions and the thickness of the slab or bar immediately before rough rolling. .
  • the austenite structure becomes a deformed austenite structure.
  • the final microstructure according to the miniaturization of the austenite grain may be refined, thereby increasing yield / tensile strength and improving low temperature toughness.
  • yield / tensile strength can be increased and low temperature toughness can be improved through the miniaturization of final microstructure, and also a decrease in the thickness of the center of thickness Can improve the toughness of the core through.
  • the steel sheet may have a thickness of 50 mm or more, preferably 50 to 100 mm, and more preferably 80 to 100 mm.
  • the steel sheet may be cooled at an average cooling rate of 3 to 300 ° C / s.
  • the Ni content is higher than the upper limit of the Ni content of the present invention. Due to the high hardenability, the microstructure of the base material is granular bainite and upper bainite, and is cooled during rough rolling. Although the particle size of the central austenite was refined, the final microstructure had a particle size of 31.2 ⁇ m, and the Kca value also had a value of 6000 or less at -10 ° C.
  • the microstructure has a light structure or acicular ferrite single phase tissue, or a complex structure of acicular ferrite and granular bainite, and a complex structure of acicular ferrite, pearlite and granular bainite.
  • the area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness having a range of 20% of the plate thickness centered on 1/2 part of the thickness is 40% or less, Kca It can be seen that the value also satisfies a value of 6000 or more at -10 ° C.
  • FIG. 1 shows a photograph of the thickness center of the inventive steel 1 observed with an optical microscope. As can be seen from FIG. 1, the thickness center structure is minute.
  • the grain size ( ⁇ m) before finishing rolling was changed to the same composition and manufacturing conditions as those of Inventive Steel 1 of Example 1, except that the grain size ( ⁇ m) was changed as shown in Table 4 below. Was investigated and the results are shown in Table 4 below.

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

The present invention provides high-strength steel having excellent resistance to brittle crack propagation and a production method therefor. Provided according to the present invention are: high-strength steel, which has excellent resistance to brittle crack propagation, comprises 0.05-0.1 wt% of C, 0.9-1.5 wt% of Mn, 0.8-1.5 wt% of Ni, 0.005-0.1 wt% of Nb, 0.005-0.1 wt% of Ti, 0.1-0.6 wt% of Cu, 0.1-0.4 wt% of Si, at most 100 ppm of P, and at most 40 ppm of S with the remainder being Fe and other inevitable impurities, and has microstructures including one structure selected from the group consisting of a single-phase structure of ferrite, a single-phase structure of bainite, a complex-phase structure of ferrite and bainite, a complex-phase structure of ferrite and pearlite, and a complex-phase structure of ferrite, bainite, and pearlite; and a production method therefor. According to the present invention, high-strength steel having high yield strength and excellent resistance to brittle crack propagation can be obtained.

Description

취성균열전파 저항성이 우수한 고강도 강재 및 그 제조방법High strength steel with excellent brittle crack propagation resistance and manufacturing method
본 발명은 취성균열전파 저항성이 우수한 고강도 강재 및 그 제조방법에 관한 것이다.The present invention relates to a high strength steel having excellent brittle crack propagation resistance and a method of manufacturing the same.
최근, 국내외 선박, 해양, 건축, 토목 분야에서 사용되는 구조물을 설계하는 데에 있어서, 고강도 특성을 갖는 극후물 강의 개발이 요구되고 있다.In recent years, in designing structures used in domestic and overseas ships, offshore, architecture, and civil engineering, development of ultra-thick steels having high strength properties is required.
구조물을 설계할시 고강도 강을 사용할 경우, 구조물의 형태를 경량화할 수 있어 경제적인 이득을 얻을 수 있을 뿐만 아니라, 강판의 두께를 얇게 할 수 있기 때문에 가공 및 용접 작업의 용이성을 동시에 확보 가능하다. When using high strength steel when designing the structure, the structure of the structure can be reduced in weight and economical benefits can be obtained, and the thickness of the steel sheet can be reduced, thereby ensuring ease of machining and welding operations.
일반적으로 고강도 강의 경우, 극후물재 제조시 총 압하율의 저하에 따라 중심부에 충분한 변형이 이루어지지 않기 때문에 중심부 조직이 조대해지게 되며, 이로 인해 경화능이 상승하여 베이나이트 등의 저온변태상이 생성된다.In general, in the case of high-strength steel, the core structure becomes coarse because sufficient deformation is not made in the center due to a decrease in the total reduction ratio during the manufacture of the ultra-thick material, and thus the hardenability is increased to generate a low temperature transformation phase such as bainite.
또한, 조대화된 조직으로 인해 중심부의 충격인성 확보에 어려움이 있을 수 있다.In addition, it may be difficult to secure the impact toughness of the center due to the coarse organization.
특히 구조물의 안정성을 나타내는 취성균열전파 저항성의 경우 선박 등의 주요 구조물에 적용시 보증을 요구하는 사례가 증가하고 있으나, 중심부에 저온변태상 생성시 취성균열전파 저항성이 매우 저하되는 현상이 발생하기 때문에 극후물 고강도 강재의 취성균열전파 저항상을 향상시키는 것은 매우 어려운 상황이다In particular, in the case of brittle crack propagation resistance indicating stability of the structure, there is an increasing number of cases requiring a guarantee when applied to major structures such as ships, but when the formation of low temperature transformation in the center, the brittle crack propagation resistance is very low. It is very difficult to improve the brittle crack propagation resistance phase of very thick high strength steel.
한편, 항복강도 390MPa이상의 고강도강의 경우 취성균열전파 저항성을 향상시키기 위해 표층부 입도 미세화를 위한 사상압연시 표면 냉각 적용 및 압연시 굽힘 응력 부여를 통한 입도 조절, 이상역 압연을 통한 표층 미세화 등의 다양한 기술이 도입되었다.On the other hand, in the case of high strength steel with a yield strength of 390 MPa or more, various technologies such as surface cooling at the time of finishing rolling for miniaturization of the brittle crack propagation, particle size control by applying bending stress during rolling, and surface layer refinement through abnormal reverse rolling are applied. This was introduced.
그러나, 이러한 기술의 경우 표층부 조직미세화에는 도움이 되지만 중심부 조직 조대화에 따른 충격인성 저하는 해결할 수 없기 때문에 취성균열전파 저항성에 대한 근본적인 대책이라 할 수 없다.However, this technique is helpful for the microstructure of the surface layer, but the impact toughness due to the coarse structure of the core cannot be solved, and thus it is not a fundamental countermeasure against brittle crack propagation resistance.
또한, 기술 자체가 일반적인 양산체제에 적용하기에는 생산성에 큰 저하가 예상되므로 상업적인 적용에는 무리가 있는 기술이라 할 수 있다.In addition, since the technology itself is expected to be significantly reduced in productivity to be applied to the general mass production system, it can be said that the technology is not suitable for commercial applications.
본 발명의 일 측면에 의하면, 취성균열전파 저항성이 우수한 고강도 강재를 제공하고자 하는데, 그 목적이 있다.According to an aspect of the present invention, to provide a high strength steel excellent in brittle crack propagation resistance, an object thereof.
본 발명의 다른 측면에 의하면, 취성균열전파 저항성이 우수한 고강도 강재의 제조방법을 제공하고자 하는데, 그 목적이 있다.According to another aspect of the present invention, an object of the present invention is to provide a method for producing a high strength steel having excellent brittle crack propagation resistance.
본 발명의 일 측면에 의하면, 중량%로, C: 0.05~0.1%, Mn: 0.9~1.5%, Ni: 0.8~1.5%, Nb: 0.005~0.1%, Ti: 0.005~0.1%, Cu: 0.1~0.6%, Si: 0.1~0.4%, P: 100ppm이하, S: 40ppm이하, 나머지 Fe 및 기타 불가피한 불순물을 포함하고; 페라이트 단상조직, 베이나이트 단상조직, 페라이트와 베이나이트의 복합조직, 페라이트와 퍼얼라이트의 복합조직, 및 페라이트, 베이나이트와 퍼얼라이트의 복합조직으로 이루어진 그룹으로부터 선택된 하나의 조직을 포함하는 미세조직을 갖고; 그리고 두께가 50mm이상인 취성균열전파 저항성이 우수한 고강도 강재가 제공된다. According to an aspect of the present invention, in weight%, C: 0.05 to 0.1%, Mn: 0.9 to 1.5%, Ni: 0.8 to 1.5%, Nb: 0.005 to 0.1%, Ti: 0.005 to 0.1%, Cu: 0.1 ˜0.6%, Si: 0.1-0.4%, P: 100 ppm or less, S: 40 ppm or less and the remaining Fe and other unavoidable impurities; Microstructure including a single structure selected from the group consisting of ferrite single phase structure, bainite single phase structure, ferrite and bainite complex, ferrite and perlite complex, and ferrite, bainite and perlite complex. Have; In addition, a high strength steel having excellent brittle crack propagation resistance having a thickness of 50 mm or more is provided.
상기 Cu 및 Ni의 함량은 Cu/Ni 중량비가 0.6이하, 바람직하게는 0.5 이하가 되도록 설정될 수 있다.The content of Cu and Ni may be set such that the Cu / Ni weight ratio is 0.6 or less, preferably 0.5 or less.
상기 강재는 바람직하게는 중심부의 EBSD 방법으로 측정한 15도 이상의 고경각 경계를 가지는 입도가 30㎛(마이크로미터)이하일 수 있다.The steel may preferably have a particle size of 30 μm (micrometer) or less having a high-angle boundary of 15 degrees or more, as measured by the EBSD method of the center portion.
상기 강재는 강재 두께의 1/2부를 중심으로 강재 두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률이 40% 이하일 수 있다.The steel may have an area ratio of (100) planes having an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness having a range of 20% of the steel thickness with respect to 1/2 part of the steel thickness. have.
상기 강재는 바람직하게는 항복강도가 390MPa 이상일 수 있다.The steel may preferably have a yield strength of at least 390 MPa.
본 발명의 다른 일 측면에 의하면, 중량 %로, C: 0.05~0.1%, Mn: 0.9~1.5%, Ni: 0.8~1.5%, Nb: 0.005~0.1%, Ti: 0.005~0.1%, Cu: 0.1~0.6%, Si : 0.1~0.4%, P : 100ppm이하, S: 40ppm이하, 나머지 Fe 및 기타 불가피한 불순물을 포함하는 슬라브를 950~1100℃로 재가열한 후 1100~900℃의 온도에서 조압연하는 단계; 상기 조압연된 바(bar)를 850~Ar3 이상의 온도에서 마무리 압연하여 두께 50mm이상의 강판을 얻는 단계; 상기 강판을 700℃ 이하의 온도까지 냉각하는 단계를 포함하고, 상기 조압연 시 압연 전의 슬라브 또는 바의 중심부- 표면간 온도차가 70℃ 이상이 되도록 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법이 제공된다.According to another aspect of the present invention, in weight%, C: 0.05 to 0.1%, Mn: 0.9 to 1.5%, Ni: 0.8 to 1.5%, Nb: 0.005 to 0.1%, Ti: 0.005 to 0.1%, Cu: 0.1 ~ 0.6%, Si: 0.1 ~ 0.4%, P: 100ppm or less, S: 40ppm or less and reheat the slab containing the remaining Fe and other unavoidable impurities to 950 ~ 1100 ℃, and then rough-roll at a temperature of 1100 ~ 900 ℃ Doing; Finishing rolling the rough rolled bar at a temperature of at least 850 to Ar 3 to obtain a steel sheet having a thickness of 50 mm or more; The method of manufacturing a high strength steel having excellent brittle crack propagation resistance, comprising the step of cooling the steel sheet to a temperature of 700 ° C. or lower, such that the temperature difference between the center and the surface of the slab or bar before rolling is roughly 70 ° C. or more during the rough rolling. Is provided.
상기 조압연 시 마지막 3 패스(pass)에 대해서는 패스(pass) 당 압하율은 5% 이상, 총 누적 압하율은 40% 이상인 것이 바람직하다For the last three passes during the rough rolling, the reduction rate per pass is preferably 5% or more and the total cumulative reduction rate is 40% or more.
상기 조압연 후 마무리압연 전의 바의 중심부 결정립 크기는 200㎛이하, 바람직하게는 150㎛이하, 보다 바람직하게는 100㎛이하일 수 있다.The center grain size of the bar after the rough rolling and before the finish rolling may be 200 μm or less, preferably 150 μm or less, and more preferably 100 μm or less.
상기 마무리압연 시 압하비는 슬라브 두께(mm)/마무리압연 후의 강판 두께(mm)의 비가 3.5이상, 바람직하게는 3.8이상이 되도록 설정될 수 있다.The rolling reduction ratio during the finish rolling may be set so that the ratio of slab thickness (mm) / thickness of the steel sheet after finishing rolling (mm) is 3.5 or more, preferably 3.8 or more.
상기 강판의 냉각은 2℃/s 이상의 중심부 냉각속도로 행할 수 있다.The steel sheet may be cooled at a central cooling rate of 2 ° C./s or more.
상기 강판의 냉각은 3~300℃/s의 평균 냉각속도로 행할 수 있다.Cooling of the steel sheet can be carried out at an average cooling rate of 3 ~ 300 ℃ / s.
덧붙여 상기한 과제의 해결수단은, 본 발명의 특징을 모두 열거한 것은 아니다.In addition, the solution of the said subject does not enumerate all the characteristics of this invention.
본 발명의 다양한 특징과 그에 따른 장점과 효과는 아래의 구체적인 실시형태를 참조하여 보다 상세하게 이해될 수 있을 것이다.Various features of the present invention and the advantages and effects thereof may be understood in more detail with reference to the following specific embodiments.
본 발명에 따르면, 높은 항복강도 및 우수한 취성균열전파 저항성이 우수한 고강도 강재를 얻을 수 있다.According to the present invention, it is possible to obtain a high strength steel excellent in high yield strength and excellent brittle crack propagation resistance.
도 1은 발명강 1의 두께 중심부를 광학현미경으로 관찰한 사진을 나타낸다.1 shows a photograph obtained by observing the thickness center of the inventive steel 1 with an optical microscope.
본 발명의 발명자들은 두께가 50mm이상의 두꺼운 강재의 항복강도 및 취성균열전파 저항성을 향상시키기 위하여 연구 및 실험을 행하고, 그 결과에 근거하여 본 발명을 제안하게 되었다.The inventors of the present invention conducted studies and experiments to improve the yield strength and brittle crack propagation resistance of thick steel having a thickness of 50 mm or more, and proposed the present invention based on the results.
본 발명은 강재의 강 조성, 조직, 집합조직 및 제조조건을 제어하여 두께가 두꺼운 강재의 항복강도 및 취성균열전파 저항성을 보다 향상시킨 것이다.The present invention is to improve the yield strength and brittle crack propagation resistance of thick steel by controlling the steel composition, structure, texture and manufacturing conditions of the steel.
본 발명의 주요 개념을 다음과 같다. The main concept of the present invention is as follows.
1) 고용강화를 통한 강도 향상을 얻기 위하여 강 조성을 적절히 제어한 것이다. 특히, 고용강화를 위하여 Mn, Ni, Cu 및 Si 함량을 최적화 한 것이다.1) Steel composition is properly controlled to obtain strength improvement through strengthening of solid solution. In particular, Mn, Ni, Cu and Si content is optimized for solid solution strengthening.
2) 경화능 향상을 통한 강도 향상을 얻기 위하여 강 조성을 적절히 제어한 것이다. 특히, 경화능 향상을 위하여 탄소 함량과 함께 Mn, Ni 및 Cu함량을 최적화 한 것이다.2) Steel composition is appropriately controlled to obtain strength improvement through improvement of hardenability. In particular, Mn, Ni and Cu content is optimized with the carbon content to improve the hardenability.
이렇게 경화능을 향상시킴으로써 느린 냉각속도에서도 50mm이상의 두꺼운 강재의 중심부까지 미세한 조직이 확보된다.By improving the hardenability, even at a slow cooling rate, the microstructure is secured to the center of the thick steel of 50 mm or more.
3) 바람직하게는, 강도 및 취성균열전파 저항성을 향상시키기 위하여 강재의 조직을 미세화 시킬 수 있다. 특히, 강재의 중심부 조직을 미세화시킨 것이다.3) Preferably, in order to improve the strength and resistance to brittle crack propagation, it is possible to refine the structure of the steel. In particular, the core structure of the steel is refined.
이렇게 강재의 중심부 조직을 미세화시킴으로써 결정립 강화를 통한 강도 향상과 함께 균열의 생성 및 전파가 최소화되어 취성균열전파 저항성이 향상된다.Thus, by miniaturizing the central structure of the steel material, the strength of the grains is enhanced and the generation and propagation of cracks is minimized, thereby improving brittle crack propagation resistance.
4) 바람직하게는, 취성균열전파 저항성을 향상시키기 위하여 강재의 집합조직을 제어할 수 있다. 4) Preferably, it is possible to control the texture of the steel in order to improve the brittle crack propagation resistance.
균열(crack)은 강재의 폭 방향, 즉, 압연방향에 수직한 방향으로 전파된다는 것과 체심입방구조(BCC)의 취성 파면이 (100)면이라는 점을 고려하여, 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100)면의 면적률이 최소화되도록 한 것이다.The crack is propagated in the width direction of the steel, that is, the direction perpendicular to the rolling direction, and the brittle wavefront of the body centered cubic structure (BCC) is the (100) plane, with respect to the surface perpendicular to the rolling direction. The area ratio of the (100) plane forming an angle within 15 degrees is to be minimized.
특히, 미세조직이 표면에 비하여 상대적으로 조대한 중심부 영역의 집합조직을 제어한 것이다.In particular, the microstructure controls the aggregate structure of the central region relatively coarse to the surface.
이렇게 강재의 집합조직, 특히 강재의 중심부 영역의 집합조직을 제어함으로써, 비록 균열이 생성되더라도 균열의 전파가 최소화되어 취성균열전파 저항성이 향상된다.By controlling the texture of the steel, in particular, the structure of the central region of the steel, even if a crack is generated, the propagation of the crack is minimized to improve the brittle crack propagation resistance.
5) 바람직하게는, 강재의 조직을 보다 미세화 시키기 위하여 조압연 조건을 제어할 수 있다.5) Preferably, the rough rolling conditions can be controlled in order to refine the structure of the steel.
특히, 조 압연 시 압하조건을 제어하고 충분한 중심부- 표면간 온도차를 확보함으로써 강재의 중심부까지 미세한 조직이 확보된다. In particular, the microstructure is secured to the center of steel by controlling the rolling reduction condition and securing a sufficient center-to-surface temperature difference during rough rolling.
이하, 본 발명의 일 측면인 취성균열전파 저항성이 우수한 고강도 강재에 대하여 상세히 설명한다. Hereinafter, a high strength steel having excellent brittle crack propagation resistance, which is an aspect of the present invention, will be described in detail.
본 발명의 일 측면인 취성균열전파 저항성이 우수한 고강도 강재는 중량% 로, C: 0.05~0.1%, Mn: 0.9~1.5%, Ni: 0.8~1.5%, Nb: 0.005~0.1%, Ti: 0.005~0.1%, Cu: 0.1~0.6%, Si: 0.1~0.4%, P: 100ppm이하, S: 40ppm이하, 나머지 Fe 및 기타 불가피한 불순물을 포함하고, 그리고 페라이트 단상조직, 베이나이트 단상조직, 페라이트와 베이나이트의 복합조직, 페라이트와 퍼얼라이트의 복합조직, 및 페라이트, 베이나이트와 퍼얼라이트의 복합조직으로 이루어진 그룹으로부터 선택된 하나의 조직을 포함하는 미세조직을 갖는다. High strength steel having excellent brittle crack propagation resistance, which is an aspect of the present invention, is weight%, C: 0.05 to 0.1%, Mn: 0.9 to 1.5%, Ni: 0.8 to 1.5%, Nb: 0.005 to 0.1%, and Ti: 0.005 ~ 0.1%, Cu: 0.1 ~ 0.6%, Si: 0.1 ~ 0.4%, P: 100ppm or less, S: 40ppm or less, containing the remaining Fe and other unavoidable impurities, and ferrite single phase structure, bainite single phase structure, ferrite and It has a microstructure comprising one tissue selected from the group consisting of a composite structure of bainite, a composite structure of ferrite and perlite, and a composite structure of ferrite, bainite and perlite.
이하, 본 발명의 강 성분 및 성분범위에 대하여 설명한다.Hereinafter, the steel component and the component range of this invention are demonstrated.
C(탄소): 0.05~0.10%(이하, 각 성분의 함량은 중량%를 의미함)C (carbon): 0.05 to 0.10% (hereinafter, the content of each component means weight%)
C은 기본적인 강도를 확보하는데 가장 중요한 원소이므로 적절한 범위 내에서 강 중에 함유될 필요가 있으며, 이러한 첨가효과를 얻기 위해서는 C은 0.05%이상 첨가하는 것이 바람직하다.Since C is the most important element for securing basic strength, it needs to be contained in steel within an appropriate range, and in order to obtain such an addition effect, it is preferable to add C 0.05% or more.
그러나, C의 함량이 0.10%를 초과하게 되면, 다량의 도상 마르텐사이트 생성 및 페라이트 자체의 높은 강도, 그리고 저온변태상의 다량 생성 등으로 인해 저온인성을 저하시키므로, 상기 C의 함량은 0.05~0.10%로 한정하는 것이 바람직하며, 보다 바람직하게는 0.061 ~ 0.091%로 한정하는 것이고, 보다 더 바람직하게는 0.065 ~ 0.085 %로 한정한다.However, when the content of C exceeds 0.10%, the low temperature toughness is lowered due to the formation of a large amount of phase martensite and the high strength of ferrite itself, and the formation of a large amount of low temperature transformation phase, and thus the content of C is 0.05 to 0.10%. It is preferable to limit to 0, more preferably to 0.061 to 0.091%, even more preferably to 0.065 to 0.085%.
Mn(망간): 0.9~1.5%Mn (manganese): 0.9-1.5%
Mn은 고용강화에 의해 강도를 향상시키고 저온변태상이 생성되도록 경화능을 향상시키는 유용한 원소로서, 이러한 효과를 얻기 위해서는 0.9% 이상 첨가되는 것이 바람직하다.Mn is a useful element that improves the strength by solid solution strengthening and improves the hardenability so that low-temperature transformation phase is produced. In order to obtain such an effect, Mn is preferably added at least 0.9%.
그러나, Mn의 함량이 1.5%를 초과하는 경우에는 과도한 경화능의 증가로 인해 상부 베이나이트(Upper bainite) 및 마르텐사이트 생성을 촉진하고, 중심부　편석을　야기시켜　조대한　저온변태상을　생성시켜 충격인성 및 취성균열전파 저항성을 저하시킨다.However, when the Mn content exceeds 1.5%, the excessive hardening capacity increases, thereby promoting the formation of upper bainite and martensite, and causing segregation of the core to create coarse low-temperature transformations, resulting in impact toughness. And lowers brittle crack propagation resistance.
따라서, 상기 Mn 함량은 0.9~1.5%로 한정하는 것이 바람직하며, 0.97~1.39%로 한정하는 것이고, 보다 더 바람직하게는 1.15 ~ 1.30 %로 한정한다.Therefore, the Mn content is preferably limited to 0.9 to 1.5%, limited to 0.97 to 1.39%, and more preferably limited to 1.15 to 1.30%.
Ni(니켈): 0.8~1.5%Ni (nickel): 0.8-1.5%
Ni은 저온에서 전위의 교차슬립(Cross slip)을 용이하게 만들어 충격인성을 향상시키고 경화능을 향상시켜 강도를 향상시키는데 중요한 원소로서, 이러한 효과를 얻기 위해서는 0.8% 이상 첨가되는 것이 바람직하다. 그러나, 상기 Ni이 1.5% 이상 첨가되면 경화능이 과도하게 상승되어 저온변태상이 생성되어 인성을 저하시키고 제조원가도 상승시킬 수 있으므로 상기 Ni 함량의 상한은 1.5%로 한정하는 것이 바람직하다.Ni is an important element for facilitating cross slip of dislocations at low temperatures, improving impact toughness, improving hardenability, and improving strength, and it is preferable to add 0.8% or more to obtain such effects. However, when the Ni is added at least 1.5%, the hardenability is excessively increased to form low-temperature transformation phase, which may lower toughness and increase manufacturing cost, so the upper limit of the Ni content is preferably limited to 1.5%.
보다 바람직한 Ni의 함량은 0.89 ~1.42%로 한정하는 것이고, 보다 더 바람직하게는 1.01 ~ 1.35 %로 한정한다.The content of Ni is more preferably limited to 0.89 to 1.42%, even more preferably 1.01 to 1.35%.
Nb(니오븀): 0.005~0.1%Nb (niobium): 0.005 to 0.1%
Nb는 NbC 또는 NbCN 의 형태로 석출하여 모재 강도를 향상시킨다.Nb precipitates in the form of NbC or NbCN to improve the base material strength.
또한, 고온으로 재가열시에 고용된 Nb는 압연시 NbC의 형태로 매우 미세하게 석출되어 오스테나이트의 재결정을 억제하여 조직을 미세화시키는 효과가 있다.In addition, Nb dissolved in reheating at a high temperature precipitates very finely in the form of NbC during rolling, thereby suppressing recrystallization of austenite, thereby miniaturizing the structure.
따라서, Nb는 0.005% 이상 첨가되는 것이 바람직하나, 과다하게 첨가될 경우에는 강재의 모서리에 취성크랙을 야기할 가능성이 있으므로, Nb 함량의 상한은 0.1% 로 제한하는 것이 바람직하다.Therefore, Nb is preferably added at least 0.005%, but if excessively added, there is a possibility of causing brittle cracks at the corners of the steel, so the upper limit of the Nb content is preferably limited to 0.1%.
보다 바람직한 Nb의 함량은 0.012 ~ 0.028%로 한정하는 것이고, 보다 더 바람직하게는 0.018 ~ 0.024%로 한정한다.The content of Nb is more preferably limited to 0.012 to 0.028%, and even more preferably 0.018 to 0.024%.
Ti(티타늄): 0.005~0.1%Ti (titanium): 0.005 to 0.1%
Ti은 재가열 시 TiN 으로 석출하여 모재 및 용접 열영향부의 결정립의 성장을 억제하여 저온인성을 크게 향상시키는 성분으로서, 이러한 첨가효과를 얻기 위해서는 0.005% 이상 첨가되는 것이 바람직하다.Ti is a component that precipitates with TiN upon reheating and inhibits the growth of crystal grains of the base metal and the weld heat affected zone to greatly improve low-temperature toughness. To obtain such an additive effect, Ti is preferably added at least 0.005%.
그러나, Ti가 0.1%를 초과하여 첨가되면, 연주 노즐의 막힘이나 중심부 정출에 의한 저온인성이 감소될 수 있으므로, Ti 함량은 0.005~0.1% 로 한정하는 것이 바람직하다.However, when Ti is added in excess of 0.1%, since the low temperature toughness due to clogging of the playing nozzle or the center portion determination may be reduced, the Ti content is preferably limited to 0.005 to 0.1%.
보다 바람직한 Ti의 함량은 0.009 ~ 0.024%로 한정하는 것이고, 보다 더 바람직하게는 0.011 ~ 0.018%로 한정한다.More preferably, the content of Ti is limited to 0.009 to 0.024%, even more preferably 0.011 to 0.018%.
P: 100ppm 이하, S: 40ppm 이하 P: 100 ppm or less, S: 40 ppm or less
P, S는 결정립계에 취성을 유발하거나 조대한 개재물을 형성시켜 취성을 유발하는 원소로써 취성균열 전파저항성을 향상시키기 위해서 P: 100ppm 이하 및 S: 40ppm 이하로 제한하는 것이 바람직하다.P, S is an element that causes brittleness or forms coarse inclusions at grain boundaries, and is preferably limited to P: 100 ppm or less and S: 40 ppm or less in order to improve brittle crack propagation resistance.
Si: 0.1~0.4%Si: 0.1 ~ 0.4%
Si은 강재의 강도를 향상시키고, 강력한 탈산효과를 가지고 있으므로 청정강 제조에 필수적인 원소로서 이러한 효과를 얻기 위해서는 0.1% 이상 첨가되는 것이 바람직하다. 그러나 다량 첨가 시 조대한 도상 마르텐사이트(MA)상을 생성시켜 취성균열 전파저항성을 저하시킬 수 있으므로, 상기 Si 함량의 상한은 0.4%로 제한하는 것이 바람직하다.Since Si improves the strength of the steel and has a strong deoxidation effect, it is preferable to add 0.1% or more in order to obtain such an effect as an essential element for producing clean steel. However, when a large amount is added, coarse phase martensite (MA) phase may be generated to lower brittle crack propagation resistance, so the upper limit of the Si content is preferably limited to 0.4%.
보다 바람직한 Si의 함량은 0.22 ~ 0.32%로 한정하는 것이고, 보다 더 바람직하게는 0.25 ~ 0.3 %로 한정한다.The content of Si is more preferably limited to 0.22 to 0.32%, even more preferably 0.25 to 0.3%.
Cu: 0.1~0.6%Cu: 0.1 ~ 0.6%
Cu은 경화능을 향상시키고 고용강화를　일으켜　강재의 강도를 향상시키는데 주요한 원소이고 템퍼링(tempering) 적용 시 입실론 Cu 석출물의 생성을 통해　항복강도를 올리는데 주요한 원소이므로, 0.1% 이상 첨가되는 것이 바람직하다. 그러나 다량 첨가 시 제강 공정에서 적열취성(hot shortness)에 의한 슬라브의 균열을 발생시킬 수 있으므로, 상기 Cu함량의 상한은 0.6%로 제한하는 것이 바람직하다.Cu is the main element to improve the hardenability and to increase the strength of the steel to increase the strength of the steel and to increase the yield strength through the generation of epsilon Cu precipitates when tempering (tempering), it is preferably added more than 0.1%. However, when a large amount is added, the slab may be cracked due to hot shortness in the steelmaking process, so the upper limit of the Cu content is preferably limited to 0.6%.
보다 바람직한 Cu의 함량은 0.21 ~ 0.51%로 한정하는 것이고, 보다 더 바람직하게는 0.18 ~ 0.3%로 한정한다.The content of Cu is more preferably limited to 0.21 to 0.51%, even more preferably 0.18 to 0.3%.
상기 Cu 및 Ni의 함량은 Cu/Ni 중량비가 0.6이하, 바람직하게는 0.5 이하가 되도록 설정될 수 있다.The content of Cu and Ni may be set such that the Cu / Ni weight ratio is 0.6 or less, preferably 0.5 or less.
상기와 같이 Cu/Ni 중량비를 설정하는 경우에는 표면품질이 보다 개선될 수 있다.When the Cu / Ni weight ratio is set as described above, the surface quality may be further improved.
본 발명의 나머지 성분은 철(Fe)이다.The remaining component of the present invention is iron (Fe).
다만, 통상의 제조과정에서는 원료 또는 주위 환경으로부터 의도되지 않는 불순물들이 불가피하게 혼입될 수 있으므로 이를 배제할 수는 없다.However, in the conventional manufacturing process, impurities which are not intended from the raw materials or the surrounding environment may be inevitably mixed, and thus cannot be excluded.
이들 불순물들은 통상의 기술자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 특별히 본 명세서에서 언급하지는 않는다.Since these impurities are known to those skilled in the art, not all of them are specifically mentioned herein.
본 발명의 강재는 페라이트 단상조직, 베이나이트 단상조직, 페라이트와 베이나이트의 복합조직, 페라이트와 퍼얼라이트의 복합조직, 및 페라이트, 베이나이트와 퍼얼라이트의 복합조직으로 이루어진 그룹으로부터 선택된 하나의 조직을 포함하는 미세조직을 갖는다.Steel of the present invention is a single structure selected from the group consisting of ferrite single phase structure, bainite single phase structure, ferrite and bainite complex structure, ferrite and perlite complex structure, and ferrite, bainite and perlite complex structure. It has a microstructure that contains.
상기 페라이트는 다각형 페라이트(Polygonal ferrite) 혹은 침상 페라이트(acicular ferrite)가 바람직하고, 베이나이트는 그래뉴얼 베이나이트(granular bainite)가 바람직하다.The ferrite is preferably polygonal ferrite or acicular ferrite, and bainite is preferably granular bainite.
예를 들면, 상기 Mn 및 Ni 함량이 증가할수록 침상 페라이트(acicular ferrite) 및 그래뉴얼 베이나이트(granular bainite)의 분율이 증가하며, 이에 따라 강도 또한 증가하게 된다.For example, as the Mn and Ni content increases, the fraction of acicular ferrite and granular bainite increases, thereby increasing the strength.
상기 강재의 미세조직이 펄라이트를 포함하는 복합조직인 경우 펄라이트의 분율은 20% 이하로 한정하는 것이 바람직하다.When the microstructure of the steel is a composite structure containing pearlite, the fraction of pearlite is preferably limited to 20% or less.
상기 강재는 바람직하게는 중심부의 EBSD 방법으로 측정한 15도 이상의 고경각 경계를 가지는 입도가 30㎛이하일 수 있다.The steel may preferably have a particle size of 30 μm or less having a high-angle boundary of 15 degrees or more, as measured by the EBSD method of the center portion.
이렇게 강재의 중심부 조직의 입도를 30㎛이하로 미세화시킴으로써 결정립 강화를 통한 강도 향상과 함께 균열의 생성 및 전파가 최소화되어 취성균열전파 저항성이 향상된다.Thus, by miniaturizing the grain size of the central structure of the steel material to 30㎛ or less, the strength of the grain through the strengthening of the grain is enhanced, and the generation and propagation of cracks is minimized to improve the brittle crack propagation resistance.
바람직하게는, 상기 강재 두께의 1/2부를 중심으로 강재 두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률이 40%이하일 수 있다.Preferably, the area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness having a range of 20% of the steel thickness with respect to 1/2 part of the steel thickness is 40%. It may be:
상기와 같이 집합조직을 제어한 주요한 이유는 다음과 같다.The main reasons for controlling the collective structure as described above are as follows.
균열(crack)은 강재의 폭 방향, 즉, 압연방향에 수직한 방향으로 전파되며, 체심입방구조(BCC)의 취성 파면은 (100)면이다.The crack propagates in the width direction of the steel, that is, the direction perpendicular to the rolling direction, and the brittle wavefront of the body centered cubic structure BCC is the (100) plane.
이에, 본 발명에서는 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100)면의 면적률이 최소화되도록 한 것이다.Thus, in the present invention, the area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction is minimized.
특히, 미세조직이 표면에 비하여 상대적으로 조대한 중심부 영역의 집합조직을 제어한 것이다.In particular, the microstructure controls the aggregate structure of the central region relatively coarse to the surface.
이렇게 강재의 집합조직, 특히, 강재 두께의 1/2부를 중심으로 강재 두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률을 40%이하로 제어함으로써, 비록 균열이 생성되더라도 균열의 전파가 최소화되어 취성균열전파 저항성이 향상된다.The area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness having a range of 20% of the steel thickness, particularly about 1/2 of the thickness of the steel, in particular. By controlling to less than 40%, even if a crack is generated, the propagation of the crack is minimized to improve the brittle crack propagation resistance.
상기 강재는 바람직하게는 항복강도가 390MPa이상이다.The steel material preferably has a yield strength of at least 390 MPa.
상기 강재는 50mm 이상의 두께를 갖고, 바람직하게는 50 ~ 100mm의 두께를 가질 수 있으며, 보다 바람직하게는 80 ~ 100mm의 두께를 가질 수 있다.The steel may have a thickness of 50 mm or more, preferably 50 to 100 mm, and more preferably 80 to 100 mm.
이하, 본 발명의 다른 측면인 취성균열전파 저항성이 우수한 고강도 강재의 제조방법에 대하여 상세히 설명한다. Hereinafter, a method of manufacturing a high strength steel having excellent brittle crack propagation resistance, which is another aspect of the present invention, will be described in detail.
본 발명의 다른 측면인 취성균열전파 저항성이 우수한 고강도 강재의 제조방법은 중량%로 C: 0.05~0.1%, Mn: 0.9~1.5%, Ni: 0.8~1.5%, Nb: 0.005~0.1%, Ti: 0.005~0.1%, Cu: 0.1~0.6%, Si : 0.1~0.4%, P: 100ppm이하, S: 40ppm이하, 나머지 Fe 및 기타 불가피한 불순물을 포함하는 슬라브를 950~1100℃로 재가열한 후 1100~900℃의 온도에서 조압연하는 단계; 상기 조압연된 바(bar)를 850℃~Ar3 이상의 온도에서 마무리 압연하여 강판을 얻는 단계; 상기 강판을 700℃ 이하의 온도까지 냉각하는 단계를 포함하며, 상기 조압연 시 압연 전의 슬라브 또는 바의 중심부-표면간 온도차가 70℃이상이 되도록 하는 것이다.Another aspect of the present invention is a method of manufacturing a high strength steel having excellent brittle crack propagation resistance by weight% C: 0.05 ~ 0.1%, Mn: 0.9 ~ 1.5%, Ni: 0.8 ~ 1.5%, Nb: 0.005 ~ 0.1%, Ti : 0.005 ~ 0.1%, Cu: 0.1 ~ 0.6%, Si: 0.1 ~ 0.4%, P: 100ppm or less, S: 40ppm or less, and reheat the slab containing the remaining Fe and other unavoidable impurities to 950 ~ 1100 ℃ to 1100 Rough rolling at a temperature of ˜900 ° C .; Obtaining a steel sheet by finishing rolling the roughly rolled bar at a temperature of 850 ° C. to Ar 3 or higher; And cooling the steel sheet to a temperature of 700 ° C. or less, so that the temperature difference between the center and the surface of the slab or bar before rolling during the rough rolling is 70 ° C. or more.
슬라브 재가열 Reheat slab
조압연에 앞서 슬라브를 재가열한다.Reheat the slab prior to rough rolling.
슬라브 재 가열온도는 950℃ 이상으로 설정하는 것이 바람직한데, 이는 주조 중에 형성된 Ti 및/또는 Nb의 탄질화물을 고용시키기 위함이다. 또한, Ti 및/또는 Nb의 탄질화물을 충분히 고용시키기 위해서는 1000℃ 이상으로 가열하는 것이 보다 바람직하다. 다만, 과다하게 높은 온도로 슬라브를 재가열할 경우에는 오스테나이트가 조대화될 우려가 있으므로, 상기 재가열 온도의 상한은 1100℃로 제한하는 것이 바람직하다.The slab reheating temperature is preferably set at 950 ° C. or higher, in order to solidify the carbonitrides of Ti and / or Nb formed during casting. Moreover, in order to fully solidify the carbonitride of Ti and / or Nb, it is more preferable to heat to 1000 degreeC or more. However, when the slab is reheated at an excessively high temperature, austenite may coarsen, so the upper limit of the reheating temperature is preferably limited to 1100 ° C.
조압연 Rough rolling
재가열된 슬라브를 조압연한다. Crimp the reheated slab.
조압연 온도는 오스테나이트의 재결정이 멈추는 온도(Tnr) 이상으로 하는 것이 바람직하다. 압연에 의해 주조중에 형성된 덴드라이트 등 주조조직이 파괴되고 그리고 오스테나이트의 크기를 작게 하는 효과도 얻을 수 있다. 이러한 효과를 얻기 위하여 조압연 온도는 1100~900℃로 제한하는 것이 바람직하다.It is preferable to make rough rolling temperature more than the temperature (Tnr) at which recrystallization of austenite stops. By casting, the casting structure such as the dendrite formed during casting is destroyed, and the effect of reducing the size of austenite can also be obtained. In order to obtain such an effect, the rough rolling temperature is preferably limited to 1100 ~ 900 ℃.
본 발명에서는 조압연 시 압연 직전의 슬라브 또는 바의 중심부-표면간 온도차가 70℃ 이상이 되도록 한다.In the present invention, the temperature difference between the center and the surface of the slab or bar immediately before rolling during rough rolling is 70 ° C. or more.
이와 같이 조 압연시 중심부-표면간 온도차를 부여함으로써 슬라브 또는 바의 표면부가 중심부보다 낮은 온도를 유지하게 되고, 이러한 온도차가 존재하는 상태에서 압연을 실시하게 되면 상대적으로 온도가 낮은 표면부보다 상대적으로 온도가 높은 중심부에 더 많은 변형이 일어나게 됨으로써, 중심부 결정립도가 보다 미세화된다. 이때, 바람직하게는, 중심부 평균 입도가 30㎛ 이하로 유지될 수 있다.As such, by providing the temperature difference between the center and the surface during the rough rolling, the surface of the slab or the bar is kept at a lower temperature than the central part. More strain occurs in the high temperature center portion, whereby the center grain size becomes finer. At this time, preferably, the central mean particle size may be maintained at 30 μm or less.
이는 상대적으로 온도가 낮은 표면부는 상대적으로 온도가 높은 중심부보다 높은 강도를 가지게 되므로 비교적 낮은 강도의 중심부에 더 많은 변형이 일어나는 현상을 활용한 기술이며, 효과적으로 중심부에 더 많은 변형을 부여하기 위해서는 중심부-표면간의 온도차가 100℃ 이상인 것이 바람직하며, 보다 바람직한 온도차는 100 ~ 300℃이다.This is a technology that utilizes the phenomenon that more deformation occurs in the center of relatively low strength because the surface of the relatively low temperature has higher strength than the center of relatively high temperature. It is preferable that the temperature difference between surfaces is 100 degreeC or more, and a more preferable temperature difference is 100-300 degreeC.
여기서, 슬라브 또는 바의 중심부-표면간 온도차는 조압연 직전에 실측된 슬라브 또는 바의 표면 온도와, 냉각조건 및 조압연 직전의 슬라브 또는 바의 두께를 고려하여 계산된 중심부 온도의 차이를 의미한다.Here, the temperature difference between the center and the surface of the slab or bar means a difference between the surface temperature of the slab or bar measured immediately before rough rolling and the center temperature calculated in consideration of the cooling conditions and the thickness of the slab or bar immediately before rough rolling. .
상기 슬라브의 표면온도 및 두께의 측정은 최초 조 압연하기 전에 행해지고, 상기 바의 표면온도 및 두께의 측정은 2회 조 압연부터 조압연 전에 행해진다.The measurement of the surface temperature and the thickness of the slab is carried out before the first rough rolling, and the measurement of the surface temperature and the thickness of the bar is carried out from the two rough rolling before the rough rolling.
그리고, 조압연을 2 패스 이상 행하는 경우, 슬라브 또는 바의 중심부-표면간 온도차는 조압연 각 패스(pass) 온도차를 측정하여 전체의 평균값을 계산한 온도차가 70℃이상인 것을 의미한다. When the rough rolling is performed for two or more passes, the temperature difference between the center and the surface of the slab or the bar means that the temperature difference obtained by measuring the average temperature of each pass of the rough rolling is calculated to be 70 ° C. or more.
본 발명에서는 조 압연시 중심부의 조직을 미세화하기 위해서 조압연 시 마지막 3 패스에 대해서는 패스 당 압하율은 5% 이상, 총 누적 압하율은 40% 이상인 것이 바람직하다In the present invention, in order to refine the structure of the center part at the time of rough rolling, it is preferable that the reduction rate per pass is 5% or more and the total cumulative reduction rate is 40% or more for the last three passes during rough rolling.
본 발명에서는 조 압연시 중심부의 조직을 미세화하기 위해서 조압연 시 마지막 3 패스에 대해서는 패스 당 압하율은 5% 이상, 총 누적 압하율은 40% 이상인 것이 바람직하다. In the present invention, in order to refine the structure of the center part during the rough rolling, the rolling reduction rate per pass is preferably 5% or more and the total cumulative reduction rate is 40% or more for the last three passes during rough rolling.
조압연 시 초기 압연으로 인해　재결정된 조직은 높은 온도로 인해　결정립 성장이 일어나게 되지만, 마지막 3패스를 실시할 때에는 압연 대기 중 바가 공냉됨에 따라　결정립 성장　속도가　느려지게 되며, 이로 인해 조압연 시 마지막 3 패스의 압하율이 최종 미세조직의 입도에 가장 크게 미치게 된다. In the early rolling during the rough rolling, the recrystallized structure causes grain growth due to the high temperature, but during the last three passes, the grain growth rate is slowed down as the bar is air-cooled in the rolling atmosphere. The rate of reduction of the pass is greatest for the particle size of the final microstructure.
또한 조압연의 패스당 압하율이 낮아지게 될 경우 중심부에 충분한 변형이 전달되지 않아 중심부 조대화로 인한 인성 저하가 발생할 수 있다. 따라서, 마지막 3 패스의 패스당 압하율을 5% 이상으로 제한하는 것이 바람직하다. In addition, when the rolling reduction per pass of the rough rolling is lowered, sufficient deformation is not transmitted to the center, and thus toughness may be reduced due to the coarsening of the center. Therefore, it is desirable to limit the rolling reduction per pass of the last three passes to 5% or more.
한편, 중심부의 조직의 미세화를 위하여 조압연 시 총 누적 압하율은 40% 이상으로 설정하는 것이 바람직하다.On the other hand, the total cumulative reduction rate during rough rolling is preferably set to 40% or more in order to refine the structure of the central portion.
마무리 압연 Finish rolling
조압연된 바를 850℃ ~ Ar3(페라이트 변태 개시 온도)이상에서 마무리 압연하여 강판을 얻는다. The rough rolled bar is finish rolled at 850 ° C. to Ar 3 (ferrite transformation start temperature) or higher to obtain a steel sheet.
보다 미세화된 미세조직을 얻기 위해서는 사상압연의 마무리 압연 온도를 850℃ 이하로 실시하는 것이 바람직하다.In order to obtain a finer microstructure, it is preferable to perform finishing rolling temperature of finishing rolling at 850 degreeC or less.
마무리 압연시 오스테나이트 조직이 변형된 오스테나이트 조직으로 된다.In finish rolling, the austenite structure becomes a deformed austenite structure.
상기 조압연 후 마무리압연 전의 바의 중심부 결정립 크기는 200㎛이하, 바람직하게는 150㎛이하, 보다 바람직하게는 100㎛이하가 되도록 할 수 있다.The grain size of the center portion of the bar after the rough rolling and before the finish rolling may be 200 μm or less, preferably 150 μm or less, and more preferably 100 μm or less.
상기 조압연 후 마무리압연 전의 바의 중심부 결정립 크기는 조압연 조건 등에 따라 제어될 수 있다. The grain size of the center portion of the bar after rough rolling and before finishing rolling may be controlled according to rough rolling conditions.
상기와 같이 상기 조압연 후 마무리압연 전의 바의 중심부 결정립 크기를 제어하는 경우 오스테나이트 결정립 미세화에 따른 최종 미세조직이 미세화 됨에 따라 항복/인장강도 상승 및 저온인성 향상을 가져올 수 있다.As described above, in the case of controlling the size of the central grain of the bar before the rough rolling after the rough rolling as described above, the final microstructure according to the miniaturization of the austenite grain may be refined, thereby increasing yield / tensile strength and improving low temperature toughness.
상기 마무리압연 시 압하비는 슬라브 두께(mm)/마무리압연 후의 강판 두께(mm)의 비가 3.5이상, 바람직하게는 3.8이상이 되도록 설정될 수 있다.The rolling reduction ratio during the finish rolling may be set so that the ratio of slab thickness (mm) / thickness of the steel sheet after finishing rolling (mm) is 3.5 or more, preferably 3.8 or more.
상기와 같이 마무리압연 시 압하비를 제어하는 경우 조압연 및 마무리 압연 시 압하량이 증가됨에 따라 최종 미세조직 미세화를 통한 항복/인장강도 상승 및 저온인성 향상을 가져올 수 있고, 또한 두께 중심부 입도의 감소를 통한 중심부 인성 향상을 가져올 수 있다.As described above, in the case of controlling the rolling reduction ratio during finishing rolling, as the rolling reduction during rough rolling and finishing rolling increases, yield / tensile strength can be increased and low temperature toughness can be improved through the miniaturization of final microstructure, and also a decrease in the thickness of the center of thickness Can improve the toughness of the core through.
마무리 압연 후 강판은 50mm 이상의 두께를 갖고, 바람직하게는 50 ~ 100mm의 두께를 가질 수 있으며, 보다 바람직하게는 80 ~ 100mm의 두께를 가질 수 있다.After finishing rolling, the steel sheet may have a thickness of 50 mm or more, preferably 50 to 100 mm, and more preferably 80 to 100 mm.
냉각Cooling
마무리 압연 후 강판을 700℃ 이하로 냉각시킨다.After finish rolling, the steel sheet is cooled to 700 ° C or lower.
냉각종료온도가 700℃를 초과하는 경우에는 미세조직이 적절하게 형성되지 않게 되어 항복강도가 390Mpa 이하로 될 가능성이 있다.If the cooling end temperature exceeds 700 ℃, the microstructure is not formed properly, there is a possibility that the yield strength is 390Mpa or less.
상기 강판의 냉각은 2℃/s 이상의 중심부 냉각속도로 행할 수 있고, 강판의 중심부 냉각속도가 2℃/s 미만인 경우에는 미세조직이 적절하게 형성되지 않게 되어 항복강도가 390Mpa 이하로 될 가능성이 있다.The cooling of the steel sheet can be performed at a central cooling rate of 2 ° C / s or more. If the central cooling rate of the steel sheet is less than 2 ° C / s, the microstructure is not formed properly, and the yield strength may be 390 Mpa or less. .
또한, 상기 강판의 냉각은 3~300℃/s의 평균 냉각속도로 행할 수 있다.The steel sheet may be cooled at an average cooling rate of 3 to 300 ° C / s.
이하, 실시 예를 통하여 본 발명을 보다 구체적으로 설명하고자 한다.Hereinafter, the present invention will be described in more detail with reference to the following examples.
다만, 하기의 실시 예는 예시를 통하여 본 발명을 설명하기 위한 것일 뿐 본 발명의 권리범위를 제한하기 위한 것이 아니라는 점에 유의할 필요가 있다.However, it is necessary to note that the following embodiments are only intended to describe the present invention by way of example, not to limit the scope of the present invention.
본 발명의 권리범위는 특허청구범위에 기재된 사항과 이로부터 합리적으로 유추되는 사항에 의해 결정되는 것이기 때문이다.This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.
(실시예 1)(Example 1)
하기 표 1의 조성을 갖는 400mm 두께의 강 슬라브를 1050℃의 온도로 재가열한 후, 1020℃의 온도에서 조압연을 실시하여 바를 제조하였다. 조압 시 슬라브의 조압연시 표면-중심부 평균 온도차는 하기 표 2와 같이 하였으며, 누적 압하율은 50%로 동일하게 적용하였다.The steel slab having a thickness of 400 mm having the composition shown in Table 1 was reheated to a temperature of 1050 ° C, and then rough-rolled at a temperature of 1020 ° C to prepare a bar. Surface roughness average temperature difference of the slab during rough rolling was as shown in Table 2, and the cumulative rolling rate was equally applied to 50%.
표 2의 조압연시 중심부-표면 평균 온도 차는 조압연 직전에 실측된 슬라브 또는 바 표면의 온도와, 바에 분사된 수량과 조압연 직전의 슬라브 두께를 고려하여 계산된 중심부 온도의 차이를 나타내며, 조압연 각 패스(pass) 온도 차를 측정하여 전체의 평균값을 계산한 결과이다.The center-surface average temperature difference in rough rolling in Table 2 represents the difference between the temperature of the slab or bar surface measured immediately before rough rolling, the center temperature calculated in consideration of the quantity sprayed on the bar and the slab thickness just before rough rolling. It is the result of calculating the average value of the whole by measuring the pass temperature difference of each rolling.
상기 조압연된 바의 두께는 180mm이였으며, 조압연 후 마무리압연 전의 결정립 크기는 80㎛이였다.The rough rolled bar had a thickness of 180 mm, and the rough grain size before rough rolling was 80 μm.
상기 조압연 후, 770 ℃의 마무리 압연온도에서 마무리 압연을 행하여 하기 표 2의 두께를 갖는 강판을 얻은 다음, 5℃/sec의 냉각속도로 700℃이하의 온도로 냉각하였다.After the rough rolling, a finish rolling was performed at a finish rolling temperature of 770 ° C. to obtain a steel sheet having the thickness shown in Table 2, and then cooled to a temperature of 700 ° C. or less at a cooling rate of 5 ° C./sec.
상기와 같이 제조된 강판에 대하여 미세조직, 항복강도, EBSD로 측정된 중심부 평균 입도, 두께의 1/2부를 중심으로 판두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률, Kca 값(취성 균열전파 저항성 계수)을 조사하고, 그 결과를 하기 표 2에 나타내었다.For the steel sheet manufactured as described above, the microstructure, the yield strength, the average particle size of the core measured by EBSD, and the thickness perpendicular to the rolling direction at a thickness having a range of 20% of the plate thickness with respect to 1/2 part of the thickness were measured. The area ratio of the (100) plane and the Kca value (brittle crack propagation resistance coefficient) which form angles within degrees are investigated, and the results are shown in Table 2 below.
표 2의 Kca 값은 강판에 대해 ESSO test를 실시하여 평가한 값이다.Kca value of Table 2 is the value evaluated by performing ESSO test on the steel sheet.
표 1
강종 강 조성(중량%)
C Si Mn Ni Cu Ti Nb P(ppm) S(ppm) Cu/Ni 중량비
발명강1 0.061 0.23 1.25 0.89 0.35 0.015 0.019 75 16 0.39
발명강2 0.082 0.31 1.36 0.95 0.44 0.016 0.017 77 25 0.46
발명강3 0.054 0.32 1.09 1.26 0.36 0.009 0.023 82 34 0.29
발명강4 0.072 0.22 1.39 1.13 0.21 0.024 0.012 65 19 0.19
발명강5 0.069 0.29 1.17 1.21 0.45 0.02 0.019 68 22 0.36
발명강6 0.091 0.31 0.97 1.42 0.51 0.019 0.028 71 31 0.36
비교강1 0.072 0.25 1.21 0.97 0.36 0.017 0.026 69 16 0.37
비교강2 0.12 0.29 1.32 1.12 0.39 0.017 0.023 59 13 0.35
비교강3 0.068 0.61 1.39 1.08 0.45 0.019 0.027 55 25 0.42
비교강4 0.077 0.32 1.95 1.32 0.21 0.026 0.019 67 26 0.16
비교강5 0.062 0.19 1.21 2.2 0.35 0.021 0.031 49 30 0.16
비교강6 0.072 0.22 1.06 1.11 0.48 0.016 0.022 130 65 0.43
Table 1
Steel grade Steel composition (% by weight)
C Si Mn Ni Cu Ti Nb P (ppm) S (ppm) Cu / Ni weight ratio
Inventive Steel 1 0.061 0.23 1.25 0.89 0.35 0.015 0.019 75 16 0.39
Inventive Steel 2 0.082 0.31 1.36 0.95 0.44 0.016 0.017 77 25 0.46
Invention Steel 3 0.054 0.32 1.09 1.26 0.36 0.009 0.023 82 34 0.29
Inventive Steel 4 0.072 0.22 1.39 1.13 0.21 0.024 0.012 65 19 0.19
Inventive Steel 5 0.069 0.29 1.17 1.21 0.45 0.02 0.019 68 22 0.36
Inventive Steel 6 0.091 0.31 0.97 1.42 0.51 0.019 0.028 71 31 0.36
Comparative Steel 1 0.072 0.25 1.21 0.97 0.36 0.017 0.026 69 16 0.37
Comparative Steel 2 0.12 0.29 1.32 1.12 0.39 0.017 0.023 59 13 0.35
Comparative Steel 3 0.068 0.61 1.39 1.08 0.45 0.019 0.027 55 25 0.42
Comparative Steel 4 0.077 0.32 1.95 1.32 0.21 0.026 0.019 67 26 0.16
Comparative Steel 5 0.062 0.19 1.21 2.2 0.35 0.021 0.031 49 30 0.16
Comparative Steel 6 0.072 0.22 1.06 1.11 0.48 0.016 0.022 130 65 0.43
표 2
강종 조압연시 중심부-표면 온도차(℃) 제품두께(mm) *미세조직,상분율(%) (001)texture 항복강도(Mpa) 중심부평균입도(㎛) Kca(N/mm1.5,@-10℃)
발명강1 165 85 PF+P(16%) 23 396 21.2 9012
발명강2 203 90 AF 18 442 12.7 8554
발명강3 112 85 AF+GB(24%) 26 509 15.6 7356
발명강4 215 85 AF+GB(20%) 19 492 13.9 7855
발명강5 188 90 AF+GB(38%) 21 521 17.7 6918
발명강6 196 100 PF+P(17%) 16 401 20.9 6522
비교강1 21 85 PF+P(18%) 43 398 35.4 4564
비교강2 116 90 UB 42 579 38.3 3866
비교강3 154 85 AF+UB(21%) 32 534 25.6 4211
비교강4 201 90 UB 42 607 34.2 3901
비교강5 165 90 GB,UB(22%) 31 551 31.2 3244
비교강6 123 95 AF+GB(17%) 29 498 23.1 4855
TABLE 2
Steel grade Center-surface temperature difference at rough rolling (℃) Product thickness (mm) * Microstructure, Percentage (%) (001) texture Yield strength (Mpa) Center Average Particle Size (㎛) Kca (N / mm 1.5 , @-10 ℃)
Inventive Steel 1 165 85 PF + P (16%) 23 396 21.2 9012
Inventive Steel 2 203 90 AF 18 442 12.7 8554
Invention Steel 3 112 85 AF + GB (24%) 26 509 15.6 7356
Inventive Steel 4 215 85 AF + GB (20%) 19 492 13.9 7855
Inventive Steel 5 188 90 AF + GB (38%) 21 521 17.7 6918
Inventive Steel 6 196 100 PF + P (17%) 16 401 20.9 6522
Comparative Steel 1 21 85 PF + P (18%) 43 398 35.4 4564
Comparative Steel 2 116 90 UB 42 579 38.3 3866
Comparative Steel 3 154 85 AF + UB (21%) 32 534 25.6 4211
Comparative Steel 4 201 90 UB 42 607 34.2 3901
Comparative Steel 5 165 90 GB, UB (22%) 31 551 31.2 3244
Comparative Steel 6 123 95 AF + GB (17%) 29 498 23.1 4855
* PF:폴리고날 페라이트(Polygonal ferrite), P:퍼얼라이트(Pearlite), AF:침상 페라이트(Acicular ferrite), GB:그래뉼러 베이나이트(Granular bainite), UB:상부 베이나이트( Upper bainite), 상분율(%): 부피 %* PF: Polygonal ferrite, P: Pearlite, AF: Acicular ferrite, GB: Granular bainite, UB: Upper bainite, upper Fraction (%): Volume%
상기 표 2에 나타난 바와 같이, 비교강 1 의 경우 본 발명에서 제시하는 조압연시 중심부-표면 평균온도 차가 70℃ 미만으로 제어된 것으로서, 조압연 시 중심부에 충분한 변형을 부여하지 못함에 따라, 중심부 입도가 35.4㎛이고, 두께의 1/2부를 중심으로 판두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률이 40% 이상이고, 또한, -10℃에서 측정된 Kca 값이 일반적인 조선용 강재에서 요구되는 6000을 초과하지 못함을 알 수 있다.As shown in Table 2, in the case of Comparative Steel 1, the difference between the center-surface average temperature during rough rolling of the present invention is controlled to be less than 70 ° C., and thus, the center portion is not provided with sufficient deformation in the center during rough rolling. The area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness having a particle size of 35.4 μm and having a range of 20% of the plate thickness centering on one half of the thickness is 40%. Above, and also, it can be seen that the Kca value measured at −10 ° C. does not exceed 6000 required for general shipbuilding steels.
비교강 2의 경우 C의 함량이 본 발명의 C함량의 상한보다 높은 값을 갖는 것으로서, 조압연시 냉각을 통해 중심부 오스테나이트의 입도를 미세화하였음에도 불구하고 상부 베이나이트(upper bainite)가 생성됨으로 인해 최종 미세조직의 입도가 38.3㎛이고, 두께의 1/2부를 중심으로 판두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률이 40% 이상이고, 또한 취성이 쉽게 발생하는 상부 베이나이트를 기지조직으로 가짐으로 인해서 Kca 값도 -10℃에서 6000 이하의 값을 가짐을 알 수 있다.In the case of Comparative Steel 2, the content of C is higher than the upper limit of the C content of the present invention, although the upper bainite is produced even though the grain size of the central austenite is refined through cooling during rough rolling. The area of the (100) plane with a particle size of 38.3 占 퐉, which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness ranging from 20% of the plate thickness to a half of the thickness. It can be seen that the Kca value has a value of 6000 or less at −10 ° C. due to the upper bainite having a rate of 40% or more and brittleness easily occurring as a matrix.
비교강 3의 경우 Si의 함량이 본 발명의 Si 함량의 상한보다 높은 값을 갖는 것으로서, 조압연 시 냉각을 통해 중심부 오스테나이트의 입도를 미세화하였음에도 불구하고 중심부에서 상부 베이나이트(upper bainite)가 일부 생성되고, 또한 Si이 다량 첨가됨에 따라 MA 조직이 조대하게 다량 생성되어, Kca 값도 -10℃에서 6000 이하의 값을 가짐을 알 수 있다.In the case of Comparative Steel 3, the content of Si is higher than the upper limit of the content of Si of the present invention, and although the upper bainite is partially formed in the center even though the grain size of the core austenite is refined through cooling during rough rolling, It can be seen that as a large amount of Si is added and a large amount of the MA structure is generated, the Kca value also has a value of 6000 or less at -10 ° C.
비교강 4의 경우 Mn 함량이 본 발명의 Mn 함량의 상한보다 높은 값을 갖는 것으로서, 높은 경화능으로 인해 모재의 미세조직이 상부 베이나이트이고, 조압연시 냉각을 통해 중심부 오스테나이트의 입도를 미세화하였음에도 불구하고 최종 미세조직의 입도가 34.2㎛를 나타내며, 두께의 1/2부를 중심으로 판두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률이 40% 이상이고, 또한, Kca 값도 -10℃에서 6000 이하의 값을 가짐을 알 수 있다.In the case of Comparative Steel 4, the Mn content has a higher value than the upper limit of the Mn content of the present invention. Due to the high hardenability, the microstructure of the base material is upper bainite, and the grain size of the central austenite is refined through cooling during rough rolling. Despite this, the final microstructure has a particle size of 34.2㎛ and forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness ranging from 20% of the plate thickness to a half of the thickness (100). The area ratio of the plane) is 40% or more, and the Kca value also has a value of 6000 or less at -10 ° C.
비교강 5의 경우 Ni 함량이 본 발명의 Ni 함량의 상한보다 높은 값을 갖는 것으로서, 높은 경화능으로 인해 모재의 미세조직이 그래뉼러 베이나이트(granular bainite)와 상부 베이나이트이고, 조압연시 냉각을 통해 중심부 오스테나이트의 입도를 미세화하였음에도 불구하고 최종 미세조직의 입도가 31.2㎛를 나타내며, 또한 Kca 값도 -10℃에서 6000 이하의 값을 가짐을 알 수 있다.In the case of Comparative Steel 5, the Ni content is higher than the upper limit of the Ni content of the present invention. Due to the high hardenability, the microstructure of the base material is granular bainite and upper bainite, and is cooled during rough rolling. Although the particle size of the central austenite was refined, the final microstructure had a particle size of 31.2 μm, and the Kca value also had a value of 6000 or less at -10 ° C.
비교강 6 경우 P, S의 함량이 본 발명의 P, S함량의 상한보다 높은 값을 갖는 것으로서, 타 조건이 모두 본 발명에서 제시하는 조건을 만족함에도 불구하고 높은 P, S로 인해 취성이 발생하여, Kca 값이 -10℃에서 6000 이하의 값을 가짐을 알 수 있다.In the case of Comparative Steel 6, the content of P and S has a higher value than the upper limit of the P and S content of the present invention. Although all other conditions satisfy the conditions of the present invention, brittleness occurs due to high P and S. Thus, it can be seen that the Kca value has a value of 6000 or less at -10 ° C.
이에 반하여, 본 발명의 성분 범위를 만족하고 조압연 시 냉각을 통해 중심부 오스텐나이트의 입도가 미세화 된 발명강 1~6의 경우에는 항복강도 390MPa 이상, 중심부 입도 30㎛이하를 만족시키며 페라이트와 퍼얼라이트 조직 또는 침상 페라이트 단상 조직, 또는 침상 페라이트와 그래뉴얼 베이나이트의 복합 조직, 침상 페라이트, 퍼얼라이트와 그래뉴얼 베이나이트의 복합 조직을 미세조직으로 가짐을 알 수 있다.On the contrary, in the case of the invention steels 1 to 6 in which the component range of the present invention is satisfied and the grain size of the central austenite is refined through cooling during rough rolling, the yield strength of 390 MPa or more and the central particle size of 30 μm or less are satisfied and ferrite and pearls are satisfied. It can be seen that the microstructure has a light structure or acicular ferrite single phase tissue, or a complex structure of acicular ferrite and granular bainite, and a complex structure of acicular ferrite, pearlite and granular bainite.
또한, 두께의 1/2부를 중심으로 판두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률이 40% 이하이며, Kca 값도 -10℃에서 6000 이상의 값을 만족시킴을 알 수 있다.Further, the area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness having a range of 20% of the plate thickness centered on 1/2 part of the thickness is 40% or less, Kca It can be seen that the value also satisfies a value of 6000 or more at -10 ° C.
도 1에는 발명강 1의 두께 중심부를 광학현미경으로 관찰한 사진이 나타나 있는데, 도 1에서도 알 수 바와 같이 두께 중심부 조직이 미세함을 알 수 있다.1 shows a photograph of the thickness center of the inventive steel 1 observed with an optical microscope. As can be seen from FIG. 1, the thickness center structure is minute.
(실시예 2)(Example 2)
강 슬라브의 Cu/Ni 중량비를 하기 표 3과 같이 변화시킨 것을 제외하고는 실시예 1의 발명강2와 동일한 조성 및 제조조건으로 강판을 제조하고, 제조된 강판의 표면특성을 조사하고 그 결과를 하기 표 3에 나타내었다.Except that the Cu / Ni weight ratio of the steel slab was changed as shown in Table 3 below, the steel sheet was manufactured under the same composition and manufacturing conditions as the inventive steel 2 of Example 1, and the surface characteristics of the manufactured steel sheet were investigated and the results were obtained. It is shown in Table 3 below.
하기 표 3에서 강판의 표면 특성은 특성은 Hot shortness에 의한 표면부 스타크랙의 발생여부를 측정한 것이다.In Table 3, the surface characteristics of the steel sheet are measured by the occurrence of surface cracks by hot shortness.
표 3
강종 강 조성(중량%) 표면특성
C Si Mn Ni Cu Ti Nb P(ppm) S(ppm) Cu/Ni 중량비
발명강7 0.082 0.31 1.36 0.84 0.41 0.016 0.017 77 25 0.48 미발생
발명강2 0.95 0.44 0.46 미발생
발명강8 0.37 0.12 0.32 미발생
발명강9 0.28 0.10 0.35 미발생
비교강7 0.23 0.18 0.78 발생
비교강8 0.48 0.33 0.71 발생
TABLE 3
Steel grade Steel composition (% by weight) Surface characteristics
C Si Mn Ni Cu Ti Nb P (ppm) S (ppm) Cu / Ni weight ratio
Inventive Steel 7 0.082 0.31 1.36 0.84 0.41 0.016 0.017 77 25 0.48 Not Occurred
Inventive Steel 2 0.95 0.44 0.46 Not Occurred
Inventive Steel 8 0.37 0.12 0.32 Not Occurred
Inventive Steel 9 0.28 0.10 0.35 Not Occurred
Comparative Steel 7 0.23 0.18 0.78 Occur
Comparative Steel 8 0.48 0.33 0.71 Occur
하기 표 3에 나타난 바와 같이, Cu/Ni 중량비를 적절히 제어하는 경우 강판의 표면특성이 개선됨을 알 수 있다.As shown in Table 3 below, it can be seen that the surface characteristics of the steel sheet are improved when the Cu / Ni weight ratio is properly controlled.
(실시예 3)(Example 3)
조압연 후 마무리압연 전의 결정립 크기(㎛)를 하기 표 4와 같이 변화시킨 것을 제외하고는 실시예 1의 발명강 1과 동일한 조성 및 제조조건으로 강판을 제조하고, 제조된 강판의 중심부 입도 평균 특성을 조사하고 그 결과를 하기 표 4에 나타내었다. After rough rolling, the grain size (μm) before finishing rolling was changed to the same composition and manufacturing conditions as those of Inventive Steel 1 of Example 1, except that the grain size (μm) was changed as shown in Table 4 below. Was investigated and the results are shown in Table 4 below.
표 4
강종 조압연 후 마무리압연 전의 결정립 크기(㎛) 중심부평균 입도(㎛)
발명강1 80 21.2
발명강10 125 29.7
발명강11 107 25.6
발명강12 75 19.8
발명강13 155 21.5
발명강14 110 24.5
Table 4
Steel grade Grain size after rough rolling and before finish rolling (㎛) Center Average Particle Size (㎛)
Inventive Steel 1 80 21.2
Inventive Steel 10 125 29.7
Inventive Steel 11 107 25.6
Inventive Steel 12 75 19.8
Inventive Steel 13 155 21.5
Inventive Steel 14 110 24.5
하기 표 4에 나타난 바와 같이, 조압연 후 바 상태의 중심부 결정립 크기가 감소할수록 중심부 평균 입도가 미세해 짐을 알 수 있으며, 이를 통해 취성균열 전파저항성이 향상될 것을 예상할 수 있다.As shown in Table 4, it can be seen that as the core grain size decreases in the bar state after rough rolling, the core mean particle size becomes finer, thereby improving the brittle crack propagation resistance.
이상 실시 예를 참조하여 설명하였지만, 해당 기술 분야의 숙련된 당업자는 하기의 특허 청구의 범위에 기재된 본 발명의 사상 및 영역으로부터 벗어나지 않는 범위내에서 본 발명을 다양하게 수정 및 변경시킬 수 있음을 이해할 수 있을 것이다.Although described with reference to the embodiments, it will be understood by those skilled in the art that the present invention may be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (18)

  1. 중량%로, C: 0.05~0.1%, Mn: 0.9~1.5%, Ni: 0.8~1.5%, Nb: 0.005~0.1%, Ti: 0.005~0.1%, Cu: 0.1~0.6%, Si: 0.1~0.4%, P: 100ppm 이하, S: 40ppm 이하, 나머지 Fe 및 기타 불가피한 불순물을 포함하고; 페라이트 단상조직, 베이나이트 단상조직, 페라이트와 베이나이트의 복합조직, 페라이트와 퍼얼라이트의 복합조직, 및 페라이트, 베이나이트와 퍼얼라이트의 복합조직으로 이루어진 그룹으로부터 선택된 하나의 조직을 포함하는 미세조직을 갖고; 그리고 두께가 50mm이상인 취성균열전파 저항성이 우수한 고강도 강재.By weight%, C: 0.05-0.1%, Mn: 0.9-1.5%, Ni: 0.8-1.5%, Nb: 0.005-0.1%, Ti: 0.005-0.1%, Cu: 0.1-0.6%, Si: 0.1- 0.4%, P: 100 ppm or less, S: 40 ppm or less, remaining Fe and other unavoidable impurities; Microstructure including a single structure selected from the group consisting of ferrite single phase structure, bainite single phase structure, ferrite and bainite complex, ferrite and perlite complex, and ferrite, bainite and perlite complex. Have; And high strength steel with excellent brittle crack propagation resistance more than 50mm thick.
  2. 청구항 1에 있어서, The method according to claim 1,
    상기 Cu 및 Ni의 함량은 Cu/Ni 중량비가 0.6이하가 되도록 설정되는 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재.The Cu and Ni content is a high strength steel with excellent brittle crack propagation resistance, characterized in that the Cu / Ni weight ratio is set to 0.6 or less.
  3. 청구항 1에 있어서, The method according to claim 1,
    상기 페라이트는 침상 페라이트(acicular ferrite) 또는 다각형 페라이트(polygonal ferrite)이고, 그리고 베이나이트는 그래뉴얼 베이나이트(granular bainite)인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재.The ferrite is acicular ferrite or polygonal ferrite, and bainite is brittle crack propagation resistance, characterized in that it is granular bainite.
  4. 청구항 1에 있어서, The method according to claim 1,
    상기 강재의 미세조직이 펄라이트를 포함하는 복합조직인 경우 펄라이트의 분율은 20% 이하인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재.When the microstructure of the steel is a composite structure containing pearlite, the fraction of pearlite is high strength steel having excellent brittle crack propagation resistance, characterized in that 20% or less.
  5. 청구항 1에 있어서,The method according to claim 1,
    상기 강재는 강재 두께의 중심부의 ESBD 방법으로 측정한 15도 이상의 고경각 경계를 가지는 입도가 30㎛ 이하인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재.The steel is a high-strength steel with excellent brittle crack propagation resistance, characterized in that the particle size having a high-angle boundary of more than 15 degrees measured by the ESBD method of the center of the steel thickness is 30㎛ or less.
  6. 청구항 1에 있어서,The method according to claim 1,
    상기 강재는 항복강도가 390MPa 이상인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재.The steel is a high strength steel with excellent brittle crack propagation resistance, characterized in that the yield strength of 390MPa or more.
  7. 청구항 1에 있어서,The method according to claim 1,
    강재 두께의 1/2부를 중심으로 강재 두께의 20%의 범위를 가지는 두께에서 압연방향에 수직한 면에 대해 15도 이내의 각도를 이루는 (100) 면의 면적률이 40% 이하인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재.An area ratio of the (100) plane which forms an angle within 15 degrees with respect to the plane perpendicular to the rolling direction at a thickness having a range of 20% of the steel thickness with respect to 1/2 part of the steel thickness is characterized by 40% or less. High strength steel with excellent brittle crack propagation resistance.
  8. 청구항 1에 있어서, The method according to claim 1,
    강재 두께가 80 ~ 100mm인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재.High strength steel with excellent brittle crack propagation resistance, characterized in that the steel thickness is 80 ~ 100mm.
  9. 중량 % 로, C: 0.05~0.1%, Mn: 0.9~1.5%, Ni: 0.8~1.5%, Nb: 0.005~0.1%, Ti: 0.005~0.1%, Cu: 0.1~0.6%, Si: 0.1~0.4%, P: 100ppm 이하, S: 40ppm 이하, 나머지 Fe 및 기타 불가피한 불순물을 포함하는 슬라브를 950~1100℃로 재가열한 후 1100~900℃의 온도에서 조압연하는 단계; 상기 조압연된 바(bar)를 850℃~Ar3 이상의 온도에서 마무리 압연하여 두께 50mm이상의 강판을 얻는 단계; 상기 강판을 700℃이하의 온도까지 냉각하는 단계를 포함하고, 상기 조압연 시 압연 전의 슬라브 또는 바의 중심부- 표면간 온도차가 70℃ 이상이 되도록 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.By weight%, C: 0.05-0.1%, Mn: 0.9-1.5%, Ni: 0.8-1.5%, Nb: 0.005-0.1%, Ti: 0.005-0.1%, Cu: 0.1-0.6%, Si: 0.1- Reheating the slab containing 0.4%, P: 100 ppm or less, S: 40 ppm or less, remaining Fe, and other unavoidable impurities to 950-1100 ° C., followed by rough rolling at a temperature of 1100-900 ° C .; Finishing roughly rolling the bar at a temperature of 850 ° C to Ar 3 or more to obtain a steel sheet having a thickness of 50 mm or more; And cooling the steel sheet to a temperature of 700 ° C. or less, wherein the temperature difference between the center and the surface of the slab or bar before rolling during the rough rolling is 70 ° C. or more.
  10. 청구항 9에 있어서, The method according to claim 9,
    상기 Cu 및 Ni의 함량은 Cu/Ni 중량비가 0.6이하가 되도록 설정되는 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.The content of Cu and Ni is a method of producing a high strength steel with excellent brittle crack propagation resistance, characterized in that the Cu / Ni weight ratio is set to 0.6 or less.
  11. 청구항 9에 있어서,The method according to claim 9,
    상기 슬라브 또는 바의 두께 상의 중심부와 상기 슬라브 또는 바의 외표면 간 온도차가 100~300℃인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.The temperature difference between the central portion on the thickness of the slab or bar and the outer surface of the slab or bar is 100 ~ 300 ℃ characterized in that the brittle crack propagation resistance is excellent manufacturing method of high strength steel.
  12. 청구항 9에 있어서,The method according to claim 9,
    상기 슬라브 또는 바의 두께 상의 중심부와 상기 슬라브 또는 바의 외표면 간 온도차는 조압연 직전에 실측된 슬라브 또는 바의 표면 온도와, 냉각조건 및 조압연 직전의 슬라브 또는 바의 두께를 고려하여 계산된 중심부 온도의 차이인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.The temperature difference between the center on the thickness of the slab or bar and the outer surface of the slab or bar is calculated by considering the surface temperature of the slab or bar measured immediately before rough rolling, the cooling conditions and the thickness of the slab or bar immediately before rough rolling. A method for producing a high strength steel having excellent brittle crack propagation resistance, characterized by a difference in core temperature.
  13. 청구항 9에 있어서,The method according to claim 9,
    상기 조압연이 2 패스 이상 행해지고, 그리고 슬라브 또는 바의 두께 상의 중심부와 상기 슬라브 또는 바의 외표면간 온도차는 조압연 각 패스(pass) 온도차를 측정하여 전체의 평균값을 계산한 온도차인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.The rough rolling is performed for two or more passes, and the temperature difference between the center of the thickness of the slab or the bar and the outer surface of the slab or the bar is a temperature difference obtained by measuring the average temperature of each pass of the rough rolling. A method for producing high strength steels with excellent brittle crack propagation resistance.
  14. 청구항 9에 있어서, The method according to claim 9,
    조압연 시 마지막 3 패스에 대해서는 패스 당 압하율은 5% 이상이고, 총 누적 압하율은 40%이상인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.The method of manufacturing high strength steel having excellent brittle crack propagation resistance, characterized in that the rolling reduction per pass is 5% or more and the total cumulative rolling reduction is 40% or more for the last three passes during rough rolling.
  15. 청구항 9에 있어서,The method according to claim 9,
    상기 조압연 후 마무리압연 전의 바의 중심부 결정립 크기는 200㎛이하인 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.The grain size of the central portion of the bar after the rough rolling before the finish rolling is less than 200㎛ characterized in that the brittle crack propagation resistance is excellent manufacturing method of high strength steel.
  16. 청구항 9에 있어서,The method according to claim 9,
    상기 마무리압연 시 압하비는 슬라브 두께(mm)/마무리압연 후의 강판 두께(mm)의 비가 3.5이상이 되도록 설정되는 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.The rolling reduction ratio during the finish rolling is set to a ratio of slab thickness (mm) / thickness of the steel sheet after finishing rolling (mm) of 3.5 or more, characterized in that the brittle crack propagation resistance is excellent manufacturing method of high strength steel.
  17. 청구항 9에 있어서,The method according to claim 9,
    상기 강판의 냉각은 2℃/s 이상의 중심부 냉각속도로 행하는 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.Cooling of the steel sheet is a method of producing a high strength steel with excellent brittle crack propagation resistance, characterized in that performed at a central cooling rate of 2 ℃ / s or more.
  18. 청구항 9에 있어서, The method according to claim 9,
    상기 강판의 냉각은 3~300℃/s의 평균 냉각속도로 행하는 것을 특징으로 하는 취성균열전파 저항성이 우수한 고강도 강재의 제조방법.Cooling of the steel sheet is a method of producing a high strength steel with excellent brittle crack propagation resistance, characterized in that performed at an average cooling rate of 3 ~ 300 ℃ / s.
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