WO2013099177A1 - High-strength thick steel plate for construction having excellent characteristics for preventing diffusion of brittle cracks, and production method therefor - Google Patents

High-strength thick steel plate for construction having excellent characteristics for preventing diffusion of brittle cracks, and production method therefor Download PDF

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Publication number
WO2013099177A1
WO2013099177A1 PCT/JP2012/008174 JP2012008174W WO2013099177A1 WO 2013099177 A1 WO2013099177 A1 WO 2013099177A1 JP 2012008174 W JP2012008174 W JP 2012008174W WO 2013099177 A1 WO2013099177 A1 WO 2013099177A1
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Prior art keywords
strength
less
rolling
thick steel
steel plate
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PCT/JP2012/008174
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French (fr)
Japanese (ja)
Inventor
佳子 竹内
西村　公宏
長谷　和邦
三田尾　眞司
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Ｊｆｅスチール株式会社
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Priority to CN201280065122.8A priority Critical patent/CN104024456B/en
Priority to KR1020147020336A priority patent/KR101676710B1/en
Priority to JP2013551221A priority patent/JP5733424B2/en
Priority to BR112014015780A priority patent/BR112014015780A8/en
Publication of WO2013099177A1 publication Critical patent/WO2013099177A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • 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
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention has a brittle crack propagation arresting property (brittle crack arrestability) suitable as a steel plate having a plate thickness exceeding 50 mm for use in large structures such as ships, marine structures, low-temperature storage tanks, and construction / civil engineering structures.
  • the present invention relates to an excellent structural high-strength steel plate and a method for producing the same.
  • Ni steel is on a commercial scale. Used in.
  • the increase in the amount of Ni necessitates a significant increase in cost, it is difficult to apply to applications other than the LNG storage tank.
  • TMCP Thermo-Mechanical Control Process
  • TMCP Thermo-Mechanical Control Process
  • Fine graining can be achieved by the method, low temperature toughness can be improved, and excellent brittle crack propagation stopping characteristics can be imparted.
  • Patent Document 1 proposes a steel material in which the structure of the surface layer portion is ultrafine-grained in order to improve the brittle crack propagation stopping characteristics without increasing the alloy cost.
  • the surface layer portion is cooled to an Ar 3 transformation point (Ar 3 temperature) or lower by controlled cooling after hot rolling, and then the controlled cooling is stopped to recover the surface layer portion to the transformation point or higher (
  • the process of reheating is repeated one or more times, and during this time, the steel material is subjected to reduction, and is repeatedly transformed or processed and recrystallized, so that a superfine ferrite structure or bainite structure is formed on the surface layer portion. ) Is generated.
  • both surface portions of the steel material have an equivalent grain size (average grain diameter).
  • a suppression method it is described that a maximum reduction ratio (rolling reduction ratio) per pass during finish rolling is set to 12% or less to suppress a local recrystallization phenomenon.
  • Patent Documents 1 and 2 the steel materials excellent in brittle crack propagation stopping characteristics described in Patent Documents 1 and 2 are obtained by recooling only the steel material surface layer portion and then reworking and processing during recuperation to obtain a specific structure.
  • control is not easy on the actual production scale, and in particular, a thick material with a plate thickness exceeding 50 mm is a process with a heavy load on the rolling and cooling equipment.
  • Patent Document 3 is on the extension of TMCP, focusing not only on the refinement of ferrite crystal grains but also on the subgrains formed in ferrite crystal grains and improving the brittle crack propagation stopping characteristics. The technology is described.
  • Patent Document 4 discloses that (110) plane X-ray intensity ratio (X-ray diffraction intensity according to (110) plane) is 2 or more by controlled rolling, and equivalent circle diameter (average grain diameter equivalent to a circle). It is described that the brittle fracture resistance is improved by making coarse grains of 20 ⁇ m or more 10% or less.
  • Patent Document 5 is characterized in that, as a welded structural steel excellent in brittle crack propagation stopping characteristics of a joint, the X-ray plane strength ratio of the (100) plane in the rolled surface inside the plate thickness is 1.5 or more.
  • a steel sheet is disclosed, and it is described that it has excellent brittle crack propagation stopping characteristics due to a shift in angle in the stress load direction and crack propagation direction due to the texture development.
  • Patent Documents 6 and 7 a brittle crack propagation that develops a texture in each part in the sheet thickness direction (1/4 part of the sheet thickness, center part of the sheet thickness, etc.) by defining an average reduction ratio in the controlled rolling.
  • a method for producing welded structural steel with excellent stopping properties is described.
  • Non-Patent Document 1 evaluates the brittle crack propagation stopping characteristics of a steel plate having a thickness of 65 mm, and reports a result that the brittle crack does not stop in a large-scale brittle crack propagation stopping test of the base material.
  • the Kca value at a use temperature of ⁇ 10 ° C. is less than 3000 N / mm 3/2.
  • a hull structure to which a steel plate having a thickness exceeding 50 mm is applied it has been suggested that ensuring safety is an issue.
  • Patent Documents 1 to 5 are mainly applied to a thick material exceeding 50 mm in thickness of about 50 mm from the manufacturing conditions and disclosed experimental data. In this case, it is unclear whether the predetermined characteristics can be obtained, and the characteristics with respect to crack propagation in the plate thickness direction necessary for the hull structure have not been verified at all.
  • the present invention is capable of stopping brittle crack propagation that can be stably produced in an industrially simple process that optimizes rolling conditions and controls the texture in the thickness direction even for thick steel plates exceeding 50 mm.
  • An object is to provide a high-strength thick steel plate having excellent characteristics and a method for producing the same.
  • the inventors of the present invention have conducted extensive research on a high-strength thick steel plate having excellent brittle crack propagation stopping characteristics even in a thick steel plate having a thickness of more than 50 mm, and a production method for stably obtaining the steel plate, and has excellent base material toughness.
  • ⁇ 311 ⁇ ⁇ 011> azimuth strength X-ray diffraction intensity according to ⁇ 311 ⁇ ⁇ 011> direction measured for a plane parallel to the surface of the ⁇ rolled plate
  • the ⁇ 110 ⁇ ⁇ 001> orientation strength at the rolling surface at the 1/4 thickness part has a texture of 0.7 or more, excellent brittle crack propagation stopping characteristics are obtained.
  • the present invention has been made by further examining the obtained knowledge, the present invention, 1. It is a high strength thick steel sheet for structure, and ⁇ 311 ⁇ ⁇ 011> orientation strength at a rolled surface at the center position of the sheet thickness is 2.5 or more in the texture, and ⁇ 110 ⁇ ⁇ 001> has a texture with an orientation strength of 0.7 or more, and a Charpy fracture surface transition temperature at 1 ⁇ 4 position of the plate thickness is ⁇ 40 ° C. or less. Excellent structural high strength thick steel plate.
  • the chemical composition of steel is mass%, C: 0.03-0.20%, Si: 0.03-0.50%, Mn: 0.5-2.2%, P: 0.030% or less S: 0.010% or less, Ti: 0.005 to 0.030%, Al: 0.005 to 0.080%, N: 0.0050% or less, the balance being made of Fe and inevitable impurities 1.
  • the chemical composition of the steel is, by mass, Nb: 0.005 to 0.050%, Cu: 0.01 to 0.50%, Ni: 0.01 to 1.00%, Cr: 0.01 ⁇ 0.50%, Mo: 0.01 ⁇ 0.50%, V: 0.001 ⁇ 0.100%, B: 0.0030% or less, Ca: 0.0050% or less, REM: 0.0100%
  • Nb 0.005 to 0.050%
  • Cu 0.01 to 0.50%
  • Ni 0.01 to 1.00%
  • Cr 0.01 ⁇ 0.50%
  • Mo 0.01 ⁇ 0.50%
  • V 0.001 ⁇ 0.100%
  • B 0.0030% or less
  • Ca 0.0050% or less
  • REM 0.0100%
  • the structural high-strength thick steel plate having excellent brittle crack propagation stopping characteristics according to 2 characterized by containing one or more of the following.
  • the steel material having the chemical composition described in either 5.2 or 3 is heated to a temperature of 1000 to 1200 ° C., and in hot rolling, the cumulative reduction ratio is in the temperature range where the center of the plate thickness is the austenite recrystallization temperature range. 30% or more, after rolling at a cumulative reduction ratio of 50% or more in the temperature range where the central part of the plate thickness is austenite non-recrystallization temperature, 3.0 ° C / s or more from the temperature range within 40 ° C from the rolling end temperature
  • the texture is appropriately controlled according to each position in the plate thickness direction, so that it has excellent brittle crack propagation stopping characteristics.
  • Applying the present invention to a steel plate having a plate thickness of 50 mm or more, preferably more than 50 mm, more preferably 55 mm or more, and even more preferably 60 mm or more is more prominent than steels according to the prior art. Effective because it demonstrates its superiority. For example, in the shipbuilding field, it contributes to improving the safety of ships by applying to deck members joined to hatch side combing in the strong deck structure of container ships and bulk carriers, which is extremely useful industrially.
  • Texture inside the steel plate Define the base metal toughness. 1.
  • the ⁇ 311 ⁇ ⁇ 011> orientation and the ⁇ 110 ⁇ ⁇ 001> orientation act independently on the crack stop.
  • the azimuth intensity is calculated from (200), (110) and (211) positive pole figures using an X-ray diffractometer, and from the obtained positive pole figure (pole figure). It can be obtained by calculating a three-dimensional crystallographic distribution function.
  • the steel sheet according to the present invention also has the desired brittleness at the Charpy fracture surface transition temperature at the 1/4 thickness position. It is specified appropriately according to the crack propagation stop characteristics.
  • the Charpy fracture surface transition temperature at the 4 position is defined as -40 ° C or lower.
  • C 0.03 to 0.20%
  • C is an element that improves the strength of steel. In the present invention, it is necessary to contain 0.03% or more in order to ensure a desired strength, but if it exceeds 0.20%, the weldability deteriorates. As well as adversely affecting toughness. Therefore, C is specified in the range of 0.03 to 0.20%. Preferably, the content is 0.05 to 0.15%.
  • Si 0.03-0.50% Si is effective as a deoxidizing element and as a strengthening element for steel, but if its content is less than 0.03%, it has no effect. On the other hand, if it exceeds 0.50%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, the content is made 0.03 to 0.50%. Preferably it is 0.05 to 0.45%.
  • Mn 0.5 to 2.2% Mn is contained as a strengthening element. If it is less than 0.5%, the effect is not sufficient, and if it exceeds 2.2%, the weldability deteriorates and the cost of the steel material increases, so 0.5 to 2.2%. Preferably it is 0.60 to 2.10%.
  • P, S P and S are inevitable impurities in the steel, but P exceeds 0.030%, and if S exceeds 0.010%, the toughness deteriorates. % Or less. 0.020% or less and 0.005% or less are desirable respectively.
  • Al acts as a deoxidizer, and for this purpose, it needs to contain 0.005% or more. However, if it contains more than 0.080%, the toughness is lowered and, when welded, weld metal Reduce the toughness of the part. Therefore, Al is specified in the range of 0.005 to 0.080%. Preferably, the content is 0.020 to 0.040%.
  • N 0.0050% or less N combines with Al in the steel, adjusts the crystal grain size at the time of rolling, and strengthens the steel. However, if it exceeds 0.0050%, the toughness deteriorates. 0050% or less. Preferably it is 0.0045% or less.
  • Ti 0.005 to 0.030%
  • Ti has the effect of forming nitrides, carbides, or carbonitrides due to the inclusion of a small amount, and making the crystal grains finer to improve the base material toughness. The effect is obtained when the content is 0.005% or more. However, if the content exceeds 0.030%, the toughness of the base metal and the weld heat-affected zone is deteriorated, so the content is made 0.005 to 0.030%. Preferably, the content is 0.008 to 0.028%.
  • the above is the basic component composition of the present invention and the balance Fe and inevitable impurities, but in order to further improve the characteristics, one or more of Nb, Cu, Ni, Cr, Mo, V, B, Ca, REM are added. It is possible to contain.
  • Nb 0.005 to 0.050%
  • Nb precipitates as NbC at the time of ferrite transformation or reheating, and contributes to the increase in strength.
  • it has the effect of expanding the non-recrystallized region in the rolling of the austenite region and contributes to the refinement of ferrite, so it is also effective in improving toughness.
  • the effect is exhibited by the content of 0.005% or more, but if it exceeds 0.050%, coarse NbC precipitates and conversely causes a decrease in toughness.
  • the upper limit is preferably 0.050%. More preferably, it is 0.008 to 0.045%.
  • the upper limit is preferably set to 0.50% for Cu, 1.00% for Ni, 0.50% for Cr, and 0.50% for Mo. . More preferably, Cu is 0.05 to 0.45%, Ni is 0.05 to 0.95%, Cr is 0.05 to 0.45%, and Mo is 0.03 to 0.45%. .
  • V 0.001 to 0.100%
  • V is an element that improves the strength of the steel by precipitation strengthening as V (CN), and this effect is exhibited by containing 0.001% or more. However, when it exceeds 0.100%, toughness is reduced. Therefore, when V is contained, the content is preferably in the range of 0.001 to 0.100%. More preferably, it is 0.008 to 0.095%.
  • B 0.0030% or less B may be contained in a small amount as an element that enhances the hardenability of steel. However, if contained over 0.0030%, the toughness of the welded portion is reduced. Therefore, when B is contained, the content is preferably 0.0030% or less, and more preferably 0.0006% or more. Is preferred. More preferably, Cu is 0.0008 to 0.0028%.
  • REM 0.0100% or less Ca
  • REM is necessary because it refines the structure of the weld heat affected zone to improve toughness, and even if contained, the effect of the present invention is not impaired. It may be contained accordingly. However, when it is excessively contained, coarse inclusions are formed and the toughness of the base material is deteriorated. Therefore, when it is included, the upper limit of the content is preferably 0.0050% and 0.0100%, respectively.
  • the molten steel having the above composition is melted in a converter or the like, made into a steel material (slab) by continuous casting or the like, heated to 1000 to 1200 ° C., and then hot-rolled.
  • the heating temperature is set to 1000 to 1200 ° C. From the viewpoint of toughness, the preferred heating temperature range is 1000 to 1150 ° C, more preferably 1000 to 1050 ° C.
  • hot rolling is performed such that the temperature at the center of the plate thickness is 30% or more in the austenite recrystallization temperature range.
  • the cumulative reduction ratio in this temperature range is 30% or more, a Charpy fracture surface transition temperature at a 1 ⁇ 4 position of the plate thickness is achieved at ⁇ 40 ° C. or less.
  • austenite is not sufficiently refined and the toughness is not improved, and a Charpy fracture surface transition temperature of -40 ° C. or less cannot be obtained at the 1/4 thickness position.
  • the cumulative rolling reduction in this temperature range is preferably 35% or more, but if it is 60% or more, the effect is saturated. From the viewpoint of rolling efficiency, the upper limit of the cumulative rolling reduction is preferably 60%.
  • the cumulative rolling reduction in this temperature range is preferably 52% or more, but from the viewpoint of rolling efficiency, the upper limit of the cumulative rolling reduction is preferably 65%.
  • rolling outside the specified temperature range is not limited. It is sufficient that the specified cumulative reduction is performed in the temperature range specified above.
  • the rolling end temperature is preferably Ar 3 points or more.
  • the steel sheet that has been rolled is cooled within a range of 40 ° C. from the rolling end temperature of the final pass, and is cooled to 600 ° C. or lower at a cooling rate of 3.0 ° C./s or higher.
  • the steel plate is cooled after rolling, and cooling is started within a range of 40 ° C. from the rolling end temperature of the final pass, 3.0 ° C. It is necessary to cool to 600 ° C. or lower at a cooling rate of at least / s.
  • the cooling start temperature When the cooling start temperature is lower than the final pass rolling end temperature by more than 40 ° C., it is introduced into the steel by rolling in the austenite non-recrystallization temperature range, but strain is recovered. The effect of rolling is not fully exhibited.
  • the cooling rate is less than 3.0 ° C./s, or when the cooling end temperature exceeds 600 ° C., the strength of the steel sheet may be lowered, and a target texture cannot be obtained.
  • the temperature at the center of the plate thickness is obtained by heat transfer calculation from the steel plate surface temperature measured with a radiation thermometer.
  • the temperature condition in the cooling condition after rolling is also the sheet thickness center temperature.
  • Molten steel (steel symbols A to T) of each composition shown in Table 1 is melted in a converter, made into a steel material (slab 280 mm thick) by a continuous casting method, hot rolled to a plate thickness of 50 to 80 mm, and then cooled. No. 1-26 test steels were obtained.
  • Table 2 shows hot rolling conditions and cooling conditions.
  • a JIS No. 4 impact test piece was sampled from the 1/4 position of the plate thickness so that the direction of the longitudinal axis of the test piece was parallel to the rolling direction, and a Charpy impact test was conducted to determine the fracture surface transition temperature (vTrs). .
  • the azimuth strength is 3 from the obtained positive electrode point diagram using an X-ray diffractometer (manufactured by Rigaku Corporation), obtaining (200), (110) and (211) positive electrode point diagrams using a Mo ray source. It was determined by calculating the dimensional crystal orientation density function.
  • Table 3 shows the results of these tests.
  • the ⁇ 311 ⁇ ⁇ 011> orientation strength at the rolled surface at the plate thickness center position is 2.5 or more and ⁇ 110 ⁇ at the rolled surface at the plate thickness 1/4 position. It has a texture with an ⁇ 001> orientation strength of 0.7 or more, a Charpy fracture surface transition temperature at 1 ⁇ 4 position of the plate thickness is ⁇ 40 ° C. or lower, and Kca ( ⁇ 10 ° C.) is 6000 N / mm 3/2 As described above, excellent brittle crack propagation stopping characteristics were obtained.
  • the ⁇ 311 ⁇ ⁇ 011> orientation strength at the rolled surface at the plate thickness central position is 2.5 or more
  • the rolled surface at the 1/4 position of the plate thickness ⁇ 110 ⁇ ⁇ 001> orientation strength is 0.7 or more
  • Charpy fracture surface transition temperature at 1 ⁇ 4 position is -40 ° C or less
  • Kca value is 4500 N / mm It was 3/2 or less.
  • Japanese Patent Publication No. 7-100814 JP 2002-256375 A Japanese Patent No. 3467767 Japanese Patent No. 3548349 Japanese Patent No. 2659661

Abstract

Provided are: a high-strength thick steel plate having excellent characteristics for preventing the diffusion of brittle cracks; and a method for producing the thick steel plate. The high-strength thick steel plate for construction has an aggregate structure wherein the {311}<011> orientation strength in a rolled surface at the mid-thickness position, and the {110}<001> orientation strength in a rolled surface at a 1/4 thickness position, and, further, a Charpy fracture appearance transition temperature at the 1/4 thickness position are specified according to the desired characteristics for preventing the diffusion of brittle cracks. After hot rolling, rolling under strong pressure is carried out in recrystallization regions and non-recrystallization regions, and the temperature at the plate thickness center subsequently cools.

Description

脆性き裂伝播停止特性に優れた構造用高強度厚鋼板およびその製造方法Structural high-strength thick steel plate with excellent brittle crack propagation stopping characteristics and method for producing the same
　本発明は、船舶、海洋構造物、低温貯蔵タンク、建築・土木構造物等の大型構造物に使用する、板厚５０ｍｍ超えの厚鋼板として好適な脆性き裂伝播停止特性(brittle crack arrestability)に優れた構造用高強度厚鋼板(high strength steel plate)およびその製造方法に関する。 The present invention has a brittle crack propagation arresting property (brittle crack arrestability) suitable as a steel plate having a plate thickness exceeding 50 mm for use in large structures such as ships, marine structures, low-temperature storage tanks, and construction / civil engineering structures. The present invention relates to an excellent structural high-strength steel plate and a method for producing the same.
　船舶、海洋構造物、低温貯蔵タンク、建築・土木構造物等の大型構造物においては、脆性破壊(brittle fracture)に伴う事故が経済や環境に及ぼす影響が大きい。そのため、安全性の向上が常に求められ、使用される鋼材に対しては、使用温度における靭性(toughness）や、脆性き裂伝播停止特性が要求されている。 In large structures such as ships, offshore structures, low-temperature storage tanks, and construction / civil engineering structures, accidents associated with brittle fractures have a great impact on the economy and the environment. Therefore, improvement of safety is always required, and steel materials to be used are required toughness at use temperature and brittle crack propagation stopping characteristics.
　コンテナ船やバルクキャリアーなどの船舶はその構造上、船体外板(outer plate of ship's hull)に高強度の厚肉材を使用する。最近は船体の大型化に伴い一層の高強度厚肉化が進展している。一般に、鋼板の脆性き裂伝播停止特性は高強度あるいは厚肉材ほど劣化する傾向があるため、脆性き裂伝播停止特性への要求も一段と高度化している。 Ships such as container ships and bulk carriers use high-strength, thick materials for the outer shell plate (outer plate plate of ship's hull). Recently, with increasing size of the hull, higher strength and thicker wall have been developed. In general, since the brittle crack propagation stopping characteristics of steel sheets tend to deteriorate as the strength and thickness of the steel increases, the demand for brittle crack propagation stopping characteristics is further advanced.
　鋼材の脆性き裂伝播停止特性を向上させる手段として、従来からＮｉ含有量を増加させる方法が知られており、液化天然ガス（Liquefied Natural Gas）の貯槽タンクにおいては、９％Ｎｉ鋼が商業規模で使用されている。
しかし、Ｎｉ量の増加はコストの大幅な上昇を余儀なくさせるため、ＬＮＧ貯槽タンク以外の用途には適用が難しい。 As a means of improving the brittle crack propagation stopping characteristics of steel materials, a method of increasing the Ni content has been conventionally known. In a liquefied natural gas storage tank, 9% Ni steel is on a commercial scale. Used in.
However, since the increase in the amount of Ni necessitates a significant increase in cost, it is difficult to apply to applications other than the LNG storage tank.
　一方、ＬＮＧのような極低温(cryogenic temperature)にまで至らない、船舶やラインパイプに使用される、板厚が５０ｍｍ未満の比較的薄手の鋼材に対しては、ＴＭＣＰ(Thermo-Mechanical Control Process)法により細粒化を図り、低温靭性を向上させて、優れた脆性き裂伝播停止特性を付与することができる。 On the other hand, TMCP (Thermo-Mechanical Control Process) for relatively thin steel materials with a thickness of less than 50mm used for ships and line pipes that do not reach cryogenic temperatures such as LNG. Fine graining can be achieved by the method, low temperature toughness can be improved, and excellent brittle crack propagation stopping characteristics can be imparted.
　また、合金コストを上昇させることなく、脆性き裂伝播停止特性を向上させるため表層部の組織を超微細化(ultrafine-grained)した鋼材が特許文献１で提案されている。 Further, Patent Document 1 proposes a steel material in which the structure of the surface layer portion is ultrafine-grained in order to improve the brittle crack propagation stopping characteristics without increasing the alloy cost.
　特許文献１記載の脆性き裂伝播停止特性に優れた鋼材は、脆性き裂が伝播する際、鋼材表層部に発生するシアリップ（塑性変形領域shear-lips）が脆性き裂伝播停止特性の向上に効果があることに着目し、シアリップ部分の結晶粒を微細化させて、伝播する脆性き裂が有する伝播エネルギーを吸収させることを特徴とする。
製造方法として、熱間圧延後の制御冷却により表層部分をＡｒ３変態点(Ar3 temperature)以下に冷却し、その後制御冷却(controlled cooling)を停止して表層部分を変態点以上に復熱(reheat)させる工程を１回以上繰り返して行い、この間に鋼材に圧下を加えることにより、繰り返し変態させ又は加工再結晶させて、表層部分に超微細なフェライト組織(ferrite structure)又はベイナイト組織(bainite structure)を生成させることが記載されている。 In steel materials with excellent brittle crack propagation stopping characteristics described in Patent Document 1, when a brittle crack propagates, a shear lip (plastic deformation region shear-lips) generated in the steel surface layer improves the brittle crack propagation stopping characteristics. Focusing on the effect, it is characterized in that the propagation energy possessed by the brittle crack propagating is absorbed by refining the crystal grains of the shear lip portion.
As a manufacturing method, the surface layer portion is cooled to an Ar 3 transformation point (Ar 3 temperature) or lower by controlled cooling after hot rolling, and then the controlled cooling is stopped to recover the surface layer portion to the transformation point or higher ( The process of reheating is repeated one or more times, and during this time, the steel material is subjected to reduction, and is repeatedly transformed or processed and recrystallized, so that a superfine ferrite structure or bainite structure is formed on the surface layer portion. ) Is generated.
　さらに、特許文献２では、フェライト－パーライト(pearlite)を主体のミクロ組織とする鋼材において脆性き裂伝播停止特性を向上させるために、鋼材の両表面部は円相当粒径(average grain diameter equivalent to a circle)：５μｍ以下、アスペクト比(aspect ratio of the grains)：２以上のフェライト粒を有するフェライト組織を５０％以上有する層で構成し、フェライト粒径のバラツキを抑えることが重要で、バラツキを抑える方法として仕上げ圧延中の１パス当りの最大圧下率(rolling reduction ratio)を１２％以下とし局所的な再結晶現象を抑制することが記載されている。 Further, in Patent Document 2, in order to improve the brittle crack propagation stopping characteristics in a steel material mainly composed of ferrite-pearlite, both surface portions of the steel material have an equivalent grain size (average grain diameter). a circle): 5 μm or less, aspect ratio (of the grain): It is composed of a layer having 50% or more of ferrite structure having two or more ferrite grains, and it is important to suppress the variation of ferrite grain size. As a suppression method, it is described that a maximum reduction ratio (rolling reduction ratio) per pass during finish rolling is set to 12% or less to suppress a local recrystallization phenomenon.
　しかし、特許文献１、２に記載の脆性き裂伝播停止特性に優れた鋼材は、鋼材表層部のみを一旦冷却した後に復熱させ、かつ復熱中に加工を加えることによって、特定の組織を得るもので、実生産規模では制御が容易でなく、特に板厚が５０ｍｍを超える厚肉材では圧延、冷却設備への負荷が大きいプロセスである。 However, the steel materials excellent in brittle crack propagation stopping characteristics described in Patent Documents 1 and 2 are obtained by recooling only the steel material surface layer portion and then reworking and processing during recuperation to obtain a specific structure. However, control is not easy on the actual production scale, and in particular, a thick material with a plate thickness exceeding 50 mm is a process with a heavy load on the rolling and cooling equipment.
　一方、特許文献３には、フェライト結晶粒の微細化のみならずフェライト結晶粒内に形成されるサブグレイン(subgrain)に着目し、脆性き裂伝播停止特性を向上させる、ＴＭＣＰの延長上にある技術が記載されている。 On the other hand, Patent Document 3 is on the extension of TMCP, focusing not only on the refinement of ferrite crystal grains but also on the subgrains formed in ferrite crystal grains and improving the brittle crack propagation stopping characteristics. The technology is described.
　具体的には、板厚３０～４０ｍｍにおいて、鋼板表層の冷却および復熱などの複雑な温度制御を必要とせずに、（ａ）微細なフェライト結晶粒を確保する圧延条件、（ｂ）鋼材板厚の５％以上の部分に微細フェライト組織を生成する圧延条件、（ｃ）微細フェライトに集合組織(texture)を発達させるとともに加工（圧延）により導入した転位(dislocation)を熱的エネルギーにより再配置しサブグレインを形成させる圧延条件、（ｄ）形成した微細なフェライト結晶粒と微細なサブグレイン粒の粗大化を抑制する冷却条件、によって脆性き裂伝播停止特性を向上させる。 Specifically, in a plate thickness of 30 to 40 mm, without requiring complicated temperature control such as cooling and recuperation of the steel sheet surface layer, (a) rolling conditions for securing fine ferrite crystal grains, (b) steel plate Rolling conditions for generating a fine ferrite structure in a portion of 5% or more of the thickness, (c) Dislocations introduced by processing (rolling) while rearranging dislocation introduced by processing (rolling) and relocating by thermal energy The brittle crack propagation stopping characteristics are improved by rolling conditions for forming subgrains and (d) cooling conditions for suppressing coarsening of the formed fine ferrite crystal grains and fine subgrain grains.
　また、制御圧延において、変態したフェライトに圧下を加えて集合組織を発達させることにより、脆性き裂伝播停止特性を向上させる方法も知られている。鋼材の破壊面上にセパレーションを板面と平行な方向に生ぜしめ、脆性き裂先端の応力を緩和させることにより、脆性破壊に対する抵抗を高める。 Also known is a method of improving the brittle crack propagation stop property by controlling the rolling of the transformed ferrite to develop a texture in controlled rolling. Separation occurs on the fracture surface of the steel material in a direction parallel to the plate surface, and the stress at the brittle crack tip is relaxed, thereby increasing the resistance to brittle fracture.
　例えば、特許文献４には、制御圧延により（１１０）面Ｘ線強度比(X-ray diffraction intensity according to (110) plane)を２以上とし、かつ円相当径(average grain diameter equivalent to a circle)２０μｍ以上の粗大粒を１０％以下とすることにより、耐脆性破壊特性を向上させることが記載されている。 For example, Patent Document 4 discloses that (110) plane X-ray intensity ratio (X-ray diffraction intensity according to (110) plane) is 2 or more by controlled rolling, and equivalent circle diameter (average grain diameter equivalent to a circle). It is described that the brittle fracture resistance is improved by making coarse grains of 20 μm or more 10% or less.
　特許文献５には継手部の脆性き裂伝播停止特性の優れた溶接構造用鋼として、板厚内部の圧延面における（１００）面のＸ線面強度比が１．５以上を有することを特徴とする鋼板が開示され、当該集合組織発達による応力負荷方向とき裂伝播方向の角度のずれにより脆性き裂伝播停止特性に優れることが記載されている。更に、特許文献６、７には制御圧延における平均圧下率を規定することで板厚方向の各部（板厚の１／４部、板厚中央部など）において集合組織を発達させる脆性き裂伝播停止特性の優れた溶接構造用鋼の製造方法が記載されている。 Patent Document 5 is characterized in that, as a welded structural steel excellent in brittle crack propagation stopping characteristics of a joint, the X-ray plane strength ratio of the (100) plane in the rolled surface inside the plate thickness is 1.5 or more. A steel sheet is disclosed, and it is described that it has excellent brittle crack propagation stopping characteristics due to a shift in angle in the stress load direction and crack propagation direction due to the texture development. Further, in Patent Documents 6 and 7, a brittle crack propagation that develops a texture in each part in the sheet thickness direction (1/4 part of the sheet thickness, center part of the sheet thickness, etc.) by defining an average reduction ratio in the controlled rolling. A method for producing welded structural steel with excellent stopping properties is described.
　ところで、最近の６、０００ＴＥＵ(Twenty-foot Equivalent Unit)を超える大型コンテナ船では板厚５０ｍｍを超える厚鋼板が使用される。非特許文献１は、板厚６５ｍｍの鋼板の脆性き裂伝播停止特性を評価し、母材の大型脆性き裂伝播停止試験で脆性き裂が停止しない結果を報告している。 By the way, in the recent large container ships exceeding 6,000 TEU (Twenty-foot Equivalent Unit), thick steel plates exceeding 50 mm are used. Non-Patent Document 1 evaluates the brittle crack propagation stopping characteristics of a steel plate having a thickness of 65 mm, and reports a result that the brittle crack does not stop in a large-scale brittle crack propagation stopping test of the base material.
　また、供試材のＥＳＳＯ試験(ESSO test compliant with the guideline for brittle crack arrest design(2009, CLASS NK))では使用温度－１０℃におけるＫｃａの値が３０００Ｎ／ｍｍ３／２に満たない結果が示され、５０ｍｍを超える板厚の鋼板を適用した船体構造の場合、安全性確保が課題となることが示唆されている。 In addition, in the ESSO test of the specimen (ESSO test compliant with the guideline for brittle crack arrest design (2009, CLASS NK)), the Kca value at a use temperature of −10 ° C. is less than 3000 N / mm 3/2. In the case of a hull structure to which a steel plate having a thickness exceeding 50 mm is applied, it has been suggested that ensuring safety is an issue.
　上述した特許文献１～５に記載の脆性き裂伝播停止特性に優れる鋼板は、製造条件や開示されている実験データから板厚５０ｍｍ程度が主な対象で、５０ｍｍを超える厚肉材へ適用した場合、所定の特性が得られるか不明で、船体構造で必要な板厚方向のき裂伝播に対しての特性については全く検証されていない。 The above-described steel sheets having excellent brittle crack propagation stopping characteristics described in Patent Documents 1 to 5 are mainly applied to a thick material exceeding 50 mm in thickness of about 50 mm from the manufacturing conditions and disclosed experimental data. In this case, it is unclear whether the predetermined characteristics can be obtained, and the characteristics with respect to crack propagation in the plate thickness direction necessary for the hull structure have not been verified at all.
　そこで本発明は、板厚５０ｍｍを超える厚鋼板においても、圧延条件を最適化し、板厚方向での集合組織を制御する工業的に極めて簡易なプロセスで安定して製造し得る脆性き裂伝播停止特性に優れる高強度厚鋼板およびその製造方法を提供することを目的とする。 Therefore, the present invention is capable of stopping brittle crack propagation that can be stably produced in an industrially simple process that optimizes rolling conditions and controls the texture in the thickness direction even for thick steel plates exceeding 50 mm. An object is to provide a high-strength thick steel plate having excellent characteristics and a method for producing the same.
　本発明者らは、板厚５０ｍｍを超える厚肉鋼板でも優れた脆性き裂伝播停止特性を有する高強度厚鋼板および当該鋼板を安定して得る製造方法について鋭意研究を重ね、優れた母材靭性を有することを前提に、板厚中央部における圧延面での｛３１１｝＜０１１＞方位強度(X-ray diffraction intensity according to {311}<011> direction measured for a plane parallel to the surface of the rolled plate)が２．５以上、かつ板厚１／４部における圧延面での｛１１０｝＜００１＞方位強度が０．７以上の集合組織を有する場合に優れた脆性き裂伝播停止特性が得られることを知見した。 The inventors of the present invention have conducted extensive research on a high-strength thick steel plate having excellent brittle crack propagation stopping characteristics even in a thick steel plate having a thickness of more than 50 mm, and a production method for stably obtaining the steel plate, and has excellent base material toughness. {311} <011> azimuth strength (X-ray diffraction intensity according to {311} <011> direction measured for a plane parallel to the surface of the に rolled plate) is 2.5 or more, and when the {110} <001> orientation strength at the rolling surface at the 1/4 thickness part has a texture of 0.7 or more, excellent brittle crack propagation stopping characteristics are obtained. I found out that
　本発明は得られた知見に更に検討を加えてなされたもので、本発明は、
１．構造用高強度厚鋼板であって、前記集合組織で板厚中央位置における圧延面での｛３１１｝＜０１１＞方位強度が２．５以上、かつ板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度が０．７以上の集合組織を有し、板厚１／４位置におけるシャルピー破面遷移温度が－４０℃以下であることを特徴とする脆性き裂伝播停止特性に優れた構造用高強度厚鋼板。 The present invention has been made by further examining the obtained knowledge, the present invention,
1. It is a high strength thick steel sheet for structure, and {311} <011> orientation strength at a rolled surface at the center position of the sheet thickness is 2.5 or more in the texture, and { 110} <001> has a texture with an orientation strength of 0.7 or more, and a Charpy fracture surface transition temperature at ¼ position of the plate thickness is −40 ° C. or less. Excellent structural high strength thick steel plate.
　２．鋼の化学成分が、質量％で、Ｃ：０．０３～０．２０％、Ｓｉ：０．０３～０．５０％、Ｍｎ：０．５～２．２％、Ｐ：０．０３０％以下、Ｓ：０．０１０％以下、Ｔｉ：０．００５～０．０３０％、Ａｌ：０．００５～０．０８０％、Ｎ：０．００５０％以下、残部がＦｅおよび不可避的不純物からなることを特徴とする１記載の脆性き裂伝播停止特性に優れた構造用高強度厚鋼板。 2. The chemical composition of steel is mass%, C: 0.03-0.20%, Si: 0.03-0.50%, Mn: 0.5-2.2%, P: 0.030% or less S: 0.010% or less, Ti: 0.005 to 0.030%, Al: 0.005 to 0.080%, N: 0.0050% or less, the balance being made of Fe and inevitable impurities 1. A structural high-strength thick steel plate having excellent brittle crack propagation stopping characteristics according to 1.
　３．鋼の化学成分が、更に、質量％で、Ｎｂ：０．００５～０．０５０％、Ｃｕ：０．０１～０．５０％、Ｎｉ：０．０１～１．００％、Ｃｒ：０．０１～０．５０％、Ｍｏ：０．０１～０．５０％、Ｖ：０．００１～０．１００％、Ｂ：０．００３０％以下、Ｃａ：０．００５０％以下、ＲＥＭ：０．０１００％以下の１種または２種以上を含有することを特徴とする２記載の脆性き裂伝播停止特性に優れた構造用高強度厚鋼板。 3. Further, the chemical composition of the steel is, by mass, Nb: 0.005 to 0.050%, Cu: 0.01 to 0.50%, Ni: 0.01 to 1.00%, Cr: 0.01 ~ 0.50%, Mo: 0.01 ~ 0.50%, V: 0.001 ~ 0.100%, B: 0.0030% or less, Ca: 0.0050% or less, REM: 0.0100% The structural high-strength thick steel plate having excellent brittle crack propagation stopping characteristics according to 2, characterized by containing one or more of the following.
　４．板厚が５０ｍｍ超えであることを特徴とする１乃至３のいずれか一つに記載の脆性き裂伝播停止特性に優れた構造用高強度厚鋼板。 4. The structural high-strength thick steel plate having excellent brittle crack propagation stopping characteristics according to any one of 1 to 3, wherein the plate thickness exceeds 50 mm.
　５．２または３のいずれかに記載の化学成分を有する鋼素材を、１０００～１２００℃の温度に加熱し、熱間圧延において板厚中央部がオーステナイト再結晶温度域の温度域では累積圧下率３０％以上、板厚中央部がオーステナイト未再結晶温度域の温度域では累積圧下率５０％以上の圧延を行った後、圧延終了温度から４０℃以内の温度域より３．０℃／ｓ以上の冷却速度にて６００℃以下まで冷却することを特徴とする脆性き裂伝播停止特性に優れた構造用高強度厚鋼板の製造方法。 The steel material having the chemical composition described in either 5.2 or 3 is heated to a temperature of 1000 to 1200 ° C., and in hot rolling, the cumulative reduction ratio is in the temperature range where the center of the plate thickness is the austenite recrystallization temperature range. 30% or more, after rolling at a cumulative reduction ratio of 50% or more in the temperature range where the central part of the plate thickness is austenite non-recrystallization temperature, 3.0 ° C / s or more from the temperature range within 40 ° C from the rolling end temperature A method for producing a structural high strength thick steel plate having excellent brittle crack propagation stopping characteristics, characterized by cooling to 600 ° C. or less at a cooling rate of 5 ° C.
　本発明により得られる厚鋼板は板厚５０ｍｍ超えであっても、板厚方向の各位置に応じて集合組織が適切に制御されるので、脆性き裂伝播停止特性に優れる。本発明を、板厚５０ｍｍ以上、好ましくは板厚５０ｍｍ超え、より好ましくは板厚５５ｍｍ以上、さらに好ましくは板厚６０ｍｍ以上の鋼板に適用することが、従来技術に係る鋼に対してより顕著な優位性を発揮するため、有効である。例えば、造船分野ではコンテナ船、バルクキャリアーの強力甲板部構造においてハッチサイドコーミングに接合される甲板部材へ適用することにより船舶の安全性向上に寄与するところ大で産業上極めて有用である。 Even if the thick steel plate obtained by the present invention has a plate thickness exceeding 50 mm, the texture is appropriately controlled according to each position in the plate thickness direction, so that it has excellent brittle crack propagation stopping characteristics. Applying the present invention to a steel plate having a plate thickness of 50 mm or more, preferably more than 50 mm, more preferably 55 mm or more, and even more preferably 60 mm or more is more prominent than steels according to the prior art. Effective because it demonstrates its superiority. For example, in the shipbuilding field, it contributes to improving the safety of ships by applying to deck members joined to hatch side combing in the strong deck structure of container ships and bulk carriers, which is extremely useful industrially.
　本発明では、１．鋼板内部の集合組織、２．母材靭性を規定する。
１．鋼板内部の集合組織
本発明では、圧延方向または圧延直角方向など板面に平行な方向に伝播するき裂に対してき裂伝播停止特性を向上させるため、板厚中央位置において圧延面での｛３１１｝＜０１１＞方位強度と、板厚１／４位置において圧延面での｛１１０｝＜００１＞方位強度を規定する。 In the present invention, 1. Texture inside the steel plate Define the base metal toughness.
1. In the present invention, in order to improve the crack propagation stop property with respect to a crack propagating in a direction parallel to the plate surface, such as a rolling direction or a direction perpendicular to the rolling direction, in the present invention, {311 } <011> azimuth strength and {110} <001> azimuth strength on the rolling surface at the 1/4 thickness position.
　板厚１／４位置において圧延面での｛１００｝＜０１１＞方位を発達させると、き裂の屈曲すなわち応力付加方向からき裂が逸れることによるき裂先端の応力拡大係数が低下する効果や、微細なセパレーションの発生によりき裂先端の応力緩和の効果により脆性き裂伝播停止特性が向上する。 When the {100} <011> orientation on the rolling surface is developed at the 1/4 thickness position, the effect of reducing the stress intensity factor at the crack tip due to crack bending, that is, the crack deviating from the stress application direction, The generation of fine separation improves the brittle crack propagation stop property by the effect of stress relaxation at the crack tip.
　板厚中央位置で圧延面に平行に｛３１１｝＜０１１＞方位を発達させると、き裂進展に先立ち微視的なクラックが発生し、き裂進展の抵抗となる。 When the {311} <011> orientation is developed in parallel with the rolling surface at the center of the plate thickness, a microscopic crack is generated prior to the crack propagation, which becomes a resistance to crack propagation.
　板厚の１／４の位置で圧延面に平行に｛１１０｝＜００１＞方位を発達させると、き裂伝播停止特性が向上する理由は、き裂突入直後のき裂伝播エネルギーの吸収能力が高くなり、き裂進展が抑制されるためと考えられるが、詳細は不明である。 When the {110} <001> orientation is developed parallel to the rolling surface at a position of 1/4 of the plate thickness, the reason for the improvement of crack propagation stopping characteristics is that the ability to absorb crack propagation energy immediately after crack entry This is thought to be due to the increase in crack growth, but details are unknown.
　上述のように、｛３１１｝＜０１１＞方位と｛１１０｝＜００１＞方位とは、き裂の停止に対してそれぞれ独立に作用するものである。このように、き裂の停止に対して互いに独立した有効な作用を有する組織を素材全体の断面内で複数種類有することが、本発明の大きな特徴である。 As described above, the {311} <011> orientation and the {110} <001> orientation act independently on the crack stop. As described above, it is a major feature of the present invention to have a plurality of types of structures having effective effects independent of each other with respect to the crack stop in the cross section of the entire material.
　最近のコンテナ船やバルクキャリアーなど船体外板に用いられるようになった板厚５０ｍｍを超える厚肉材で、構造安全性を確保する上で目標とされるＫｃａ（－１０℃）≧６０００Ｎ／ｍｍ３／２の脆性き裂伝播停止特性を得る場合、板厚中央位置における圧延面での｛３１１｝＜０１１＞方位強度を２．５以上、かつ板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度を０．７以上とする。 Kca (-10 ° C) ≧ 6000 N / mm, which is a target for securing structural safety, with a thick material exceeding 50 mm thick that has been used for hull outer plates such as recent container ships and bulk carriers. When the brittle crack propagation stop characteristic of 3/2 is obtained, the {311} <011> orientation strength at the rolled surface at the plate thickness center position is 2.5 or more and { 110} <001> The orientation strength is 0.7 or more.
　ここで、方位強度は、X線回折装置を使用し、Ｍｏ線源を用いて（２００）、（１１０）および（２１１）正極点図を求め、得られた正極点図(pole figure)から３次元結晶方位分布密度関数(three-dimensional crystallographic orientation distribution function)を計算することにより求めることができる。 Here, the azimuth intensity is calculated from (200), (110) and (211) positive pole figures using an X-ray diffractometer, and from the obtained positive pole figure (pole figure). It can be obtained by calculating a three-dimensional crystallographic distribution function.
  ２．母材靭性
　母材靭性が、良好な特性を有することがき裂の進展を抑制するための前提となるので、本発明に係る鋼板では板厚１／４位置におけるシャルピー破面遷移温度も所望する脆性き裂伝播停止特性に応じて適宜規定する。 2. Base material toughness Since the base material toughness is a precondition for suppressing the growth of cracks, having good properties, the steel sheet according to the present invention also has the desired brittleness at the Charpy fracture surface transition temperature at the 1/4 thickness position. It is specified appropriately according to the crack propagation stop characteristics.
　板厚５０ｍｍを超える厚肉材で、構造安全性を確保する上で目標とされるＫｃａ（－１０℃）≧６０００Ｎ／ｍｍ３／２の脆性き裂伝播停止特性を得る場合、板厚１／４位置におけるシャルピー破面遷移温度は－４０℃以下と規定する。 When a brittle crack propagation stopping characteristic of Kca (−10 ° C.) ≧ 6000 N / mm 3/2 , which is a target for ensuring structural safety, is obtained with a thick material exceeding a plate thickness of 50 mm, the plate thickness 1 / The Charpy fracture surface transition temperature at the 4 position is defined as -40 ° C or lower.
　以下、板厚５０ｍｍを超える厚肉材で、Ｋｃａ（－１０℃）≧６０００Ｎ／ｍｍ３／２の脆性き裂伝播停止特性を得る場合に好ましい鋼の化学成分と製造条件について説明する。
［化学成分］説明において％は質量％である。 Hereinafter, steel chemical components and production conditions preferable for obtaining a brittle crack propagation stopping characteristic of Kca (−10 ° C.) ≧ 6000 N / mm 3/2 with a thick material exceeding 50 mm in thickness will be described.
[Chemical component] In the description,% means mass%.
　Ｃ：０．０３～０．２０％
Ｃは鋼の強度を向上する元素であり、本発明では、所望の強度を確保するためには０．０３％以上の含有を必要とするが、０．２０％を超えると、溶接性が劣化するばかりか靭性にも悪影響がある。このため、Ｃは、０．０３～０．２０％の範囲に規定した。なお、好ましくは０．０５～０．１５％である。 C: 0.03 to 0.20%
C is an element that improves the strength of steel. In the present invention, it is necessary to contain 0.03% or more in order to ensure a desired strength, but if it exceeds 0.20%, the weldability deteriorates. As well as adversely affecting toughness. Therefore, C is specified in the range of 0.03 to 0.20%. Preferably, the content is 0.05 to 0.15%.
　Ｓｉ：０．０３～０．５０％
Ｓｉは脱酸元素として、また、鋼の強化元素として有効であるが、０．０３％未満の含有量ではその効果がない。一方、０．５０％を超えると鋼の表面性状を損なうばかりか靭性が極端に劣化する。従ってその含有量を０．０３～０．５０％とする。好ましくは０．０５～０．４５％である。 Si: 0.03-0.50%
Si is effective as a deoxidizing element and as a strengthening element for steel, but if its content is less than 0.03%, it has no effect. On the other hand, if it exceeds 0.50%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, the content is made 0.03 to 0.50%. Preferably it is 0.05 to 0.45%.
　Ｍｎ：０．５～２．２％
Ｍｎは、強化元素として含有する。０．５％より少ないとその効果が十分でなく、２．２％を超えると溶接性が劣化し、鋼材コストも上昇するため、０．５～２．２％とする。好ましくは０．６０～２．１０％である。 Mn: 0.5 to 2.2%
Mn is contained as a strengthening element. If it is less than 0.5%, the effect is not sufficient, and if it exceeds 2.2%, the weldability deteriorates and the cost of the steel material increases, so 0.5 to 2.2%. Preferably it is 0.60 to 2.10%.
　Ｐ、Ｓ
Ｐ、Ｓは、鋼中の不可避的不純物であるが、Ｐは０．０３０％を超え、Ｓは０．０１０％を超えると靭性が劣化するため、それぞれ、０．０３０％以下、０．０１０％以下とする。それぞれ、０．０２０％以下、０．００５％以下が望ましい。 P, S
P and S are inevitable impurities in the steel, but P exceeds 0.030%, and if S exceeds 0.010%, the toughness deteriorates. % Or less. 0.020% or less and 0.005% or less are desirable respectively.
　Ａｌ：０．００５～０．０８０％
Ａｌは、脱酸剤として作用し、このためには０．００５％以上の含有を必要とするが、０．０８０％を超えて含有すると、靭性を低下させるとともに、溶接した場合に、溶接金属部の靭性を低下させる。このため、Ａｌは、０．００５～０．０８０％の範囲に規定した。なお、好ましくは、０．０２０～０．０４０％である。 Al: 0.005 to 0.080%
Al acts as a deoxidizer, and for this purpose, it needs to contain 0.005% or more. However, if it contains more than 0.080%, the toughness is lowered and, when welded, weld metal Reduce the toughness of the part. Therefore, Al is specified in the range of 0.005 to 0.080%. Preferably, the content is 0.020 to 0.040%.
　Ｎ：０．００５０％以下
Ｎは、鋼中のＡｌと結合し、圧延加工時の結晶粒径を調整し、鋼を強化するが、０．００５０％を超えると靭性が劣化するため、０．００５０％以下とする。好ましくは０．００４５％以下である。 N: 0.0050% or less N combines with Al in the steel, adjusts the crystal grain size at the time of rolling, and strengthens the steel. However, if it exceeds 0.0050%, the toughness deteriorates. 0050% or less. Preferably it is 0.0045% or less.
　Ｔｉ：０．００５～０．０３０％
Ｔｉは微量の含有により、窒化物、炭化物、あるいは炭窒化物を形成し、結晶粒を微細化して母材靭性を向上させる効果を有する。その効果は０．００５％以上の含有によって得られるが、０．０３０％を超える含有は、母材および溶接熱影響部の靭性を低下させるので、０．００５～０．０３０％とする。好ましくは０．００８～０．０２８％である。 Ti: 0.005 to 0.030%
Ti has the effect of forming nitrides, carbides, or carbonitrides due to the inclusion of a small amount, and making the crystal grains finer to improve the base material toughness. The effect is obtained when the content is 0.005% or more. However, if the content exceeds 0.030%, the toughness of the base metal and the weld heat-affected zone is deteriorated, so the content is made 0.005 to 0.030%. Preferably, the content is 0.008 to 0.028%.
　以上が本発明の基本成分組成で残部Ｆｅ及び不可避的不純物であるが、更に特性を向上させるため、Ｎｂ、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ、Ｂ、Ｃａ、ＲＥＭの一種または二種以上を含有することが可能である。 The above is the basic component composition of the present invention and the balance Fe and inevitable impurities, but in order to further improve the characteristics, one or more of Nb, Cu, Ni, Cr, Mo, V, B, Ca, REM are added. It is possible to contain.
　Ｎｂ：０．００５～０．０５０％
Ｎｂは、ＮｂＣとしてフェライト変態時あるいは再加熱時に析出し、高強度化に寄与する。また、オーステナイト域の圧延において未再結晶域を拡大させる効果を有し、フェライトの細粒化に寄与するので、靭性の改善にも有効である。その効果は０．００５％以上の含有により発揮されるが、０．０５０％を超えて含有すると、粗大なＮｂＣが析出して逆に、靭性の低下を招くので、Ｎｂを含有する場合、その上限は０．０５０％とするのが好ましい。より好ましくは０．００８～０．０４５％である。 Nb: 0.005 to 0.050%
Nb precipitates as NbC at the time of ferrite transformation or reheating, and contributes to the increase in strength. In addition, it has the effect of expanding the non-recrystallized region in the rolling of the austenite region and contributes to the refinement of ferrite, so it is also effective in improving toughness. The effect is exhibited by the content of 0.005% or more, but if it exceeds 0.050%, coarse NbC precipitates and conversely causes a decrease in toughness. The upper limit is preferably 0.050%. More preferably, it is 0.008 to 0.045%.
　Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ
Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏはいずれも鋼の焼入れ性を高める元素である。圧延後の強度向上に直接寄与するとともに、靭性、高温強度、あるいは耐候性などの機能向上のために含有させることができ、これらの効果は、いずれも、０．０１％以上の含有によって発揮される。しかし、過度の含有は靭性や溶接性を劣化させるため、それぞれ上限をＣｕは０．５０％、Ｎｉは１．００％、Ｃｒは０．５０％、Ｍｏは０．５０％とすることが好ましい。より好ましくは、Ｃｕは０．０５～０．４５％、Ｎｉは０．０５～０．９５％、Ｃｒは０．０５～０．４５％、Ｍｏは０．０３～０．４５％、である。 Cu, Ni, Cr, Mo
Cu, Ni, Cr, and Mo are all elements that enhance the hardenability of steel. It contributes directly to strength improvement after rolling, and can be contained for improving functions such as toughness, high-temperature strength, or weather resistance. All of these effects are exhibited by inclusion of 0.01% or more. The However, since excessive inclusion deteriorates toughness and weldability, the upper limit is preferably set to 0.50% for Cu, 1.00% for Ni, 0.50% for Cr, and 0.50% for Mo. . More preferably, Cu is 0.05 to 0.45%, Ni is 0.05 to 0.95%, Cr is 0.05 to 0.45%, and Mo is 0.03 to 0.45%. .
　Ｖ：０．００１～０．１００％
Ｖは、Ｖ（ＣＮ）としての析出強化により、鋼の強度を向上させる元素であり、この効果は０．００１％以上含有させることにより発揮される。しかし、０．１００％を超えて含有すると、靭性を低下させる。このため、Ｖを含有させる場合には、０．００１～０．１００％の範囲の含有とすることが好ましい。より好ましくは、０．００８～０．０９５％である。 V: 0.001 to 0.100%
V is an element that improves the strength of the steel by precipitation strengthening as V (CN), and this effect is exhibited by containing 0.001% or more. However, when it exceeds 0.100%, toughness is reduced. Therefore, when V is contained, the content is preferably in the range of 0.001 to 0.100%. More preferably, it is 0.008 to 0.095%.
　Ｂ：０．００３０％以下
Ｂは微量で鋼の焼入れ性を高める元素で含有しても良い。しかし、０．００３０％を超えて含有すると溶接部の靭性を低下させるので、Ｂを含有させる場合には０．００３０％以下の含有とすることが好ましく、また、０．０００６％以上とすることが好ましい。より好ましくは、Ｃｕは０．０００８～０．００２８％である。 B: 0.0030% or less B may be contained in a small amount as an element that enhances the hardenability of steel. However, if contained over 0.0030%, the toughness of the welded portion is reduced. Therefore, when B is contained, the content is preferably 0.0030% or less, and more preferably 0.0006% or more. Is preferred. More preferably, Cu is 0.0008 to 0.0028%.
　Ｃａ：０．００５０％以下、ＲＥＭ：０．０１００％以下
Ｃａ、ＲＥＭは溶接熱影響部の組織を微細化し靭性を向上させ、含有しても本発明の効果が損なわれることはないので必要に応じて含有してもよい。しかし、過度に含有すると、粗大な介在物を形成し母材の靭性を劣化させるので、含有させる場合には、含有量の上限をそれぞれ０．００５０％、０．０１００％とするのが好ましい。 Ca: 0.0050% or less, REM: 0.0100% or less Ca, REM is necessary because it refines the structure of the weld heat affected zone to improve toughness, and even if contained, the effect of the present invention is not impaired. It may be contained accordingly. However, when it is excessively contained, coarse inclusions are formed and the toughness of the base material is deteriorated. Therefore, when it is included, the upper limit of the content is preferably 0.0050% and 0.0100%, respectively.
　［製造条件］
上記組成の溶鋼を、転炉等で溶製し、連続鋳造等で鋼素材（スラブ）とし、１０００～１２００℃に加熱後、熱間圧延を行う。 [Production conditions]
The molten steel having the above composition is melted in a converter or the like, made into a steel material (slab) by continuous casting or the like, heated to 1000 to 1200 ° C., and then hot-rolled.
　加熱温度が１０００℃未満では、オーステナイト再結晶温度域における圧延を行う時間が十分に確保でない。また、１２００℃超えではオーステナイト粒が粗大化し、靭性の低下を招くばかりか、酸化ロスが顕著となり、歩留が低下するので、加熱温度は１０００～１２００℃とする。靭性の観点から好ましい加熱温度の範囲は１０００～１１５０℃であり、より好ましくは１０００～１０５０℃である。 If the heating temperature is less than 1000 ° C., the time for rolling in the austenite recrystallization temperature range is not sufficiently secured. If the temperature exceeds 1200 ° C., the austenite grains become coarse, leading to a decrease in toughness, as well as significant oxidation loss and a decrease in yield. Therefore, the heating temperature is set to 1000 to 1200 ° C. From the viewpoint of toughness, the preferred heating temperature range is 1000 to 1150 ° C, more preferably 1000 to 1050 ° C.
　熱間圧延はまず、板厚中央部の温度がオーステナイト再結晶温度域での累積圧下率を３０％以上とする圧延を行う。この温度域での累積圧下率を３０％以上とすることにより、板厚１／４位置におけるシャルピー破面遷移温度として－４０℃以下が達成される。累積圧下率が３０％未満であると、オーステナイトの細粒化が不十分で靭性が向上せず、板厚１／４位置におけるシャルピー破面遷移温度として－４０℃以下が得られない。この温度域での累積圧下率は、３５％以上であることが好ましいが、６０％以上とすると効果が飽和するため圧延効率の観点から、累積圧下率の上限は６０％とすることが好ましい。 First, hot rolling is performed such that the temperature at the center of the plate thickness is 30% or more in the austenite recrystallization temperature range. By setting the cumulative reduction ratio in this temperature range to 30% or more, a Charpy fracture surface transition temperature at a ¼ position of the plate thickness is achieved at −40 ° C. or less. When the cumulative rolling reduction is less than 30%, austenite is not sufficiently refined and the toughness is not improved, and a Charpy fracture surface transition temperature of -40 ° C. or less cannot be obtained at the 1/4 thickness position. The cumulative rolling reduction in this temperature range is preferably 35% or more, but if it is 60% or more, the effect is saturated. From the viewpoint of rolling efficiency, the upper limit of the cumulative rolling reduction is preferably 60%.
　次に、板厚中央部の温度がオーステナイト未再結晶温度域において累積圧下率５０％以上の圧延を行う。この温度域での累積圧下率を５０％以上とすることにより、板厚１／２位置の｛３１１｝＜０１１＞方位強度が２．５以上かつ板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度が０．７以上の集合組織が得られる。逆に、この温度域での累積圧下率が５０％未満であると板厚１／２位置の｛３１１｝＜０１１＞方位強度が２．５以上かつ板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度が０．７以上の集合組織が得られない。この温度域での累積圧下率は、５２％以上であることが好ましいが、圧延効率の観点から、累積圧下率の上限は６５％とすることが好ましい。 Next, rolling is performed at a cumulative reduction of 50% or more in the austenite non-recrystallization temperature range at the center of the plate thickness. By setting the cumulative rolling reduction in this temperature range to 50% or more, the {311} <011> orientation strength at the plate thickness 1/2 position is 2.5 or more and the rolling surface {at the plate thickness 1/4 position { 110} <001> Texture with orientation strength of 0.7 or more is obtained. Conversely, if the cumulative rolling reduction in this temperature range is less than 50%, the {311} <011> orientation strength at the plate thickness 1/2 position is 2.5 or more and the rolling surface at the plate thickness 1/4 position is A texture with {110} <001> orientation strength of 0.7 or more cannot be obtained. The cumulative rolling reduction in this temperature range is preferably 52% or more, but from the viewpoint of rolling efficiency, the upper limit of the cumulative rolling reduction is preferably 65%.
　なお、熱間圧延では規定した温度域外での圧延を制限するものではない。上記に規定する温度域で規定の累積圧下がおこなわれていればよい。圧延終了温度はＡｒ３点以上であることが好ましい。 In hot rolling, rolling outside the specified temperature range is not limited. It is sufficient that the specified cumulative reduction is performed in the temperature range specified above. The rolling end temperature is preferably Ar 3 points or more.
　圧延が終了した鋼板は、最終パスの圧延終了温度から４０℃以内の範囲内で冷却を開始し、３．０℃／ｓ以上の冷却速度にて６００℃以下まで冷却する。オーステナイト温度域圧延およびオーステナイト→フェライト変態時に得られる集合組織が損なわれないように、圧延後には鋼板を、最終パスの圧延終了温度から４０℃以内の範囲内で冷却を開始し、３．０℃／ｓ以上の冷却速度にて６００℃以下まで冷却する必要がある。冷却開始温度が最終パスの圧延終了温度よりも４０℃を超えて低い場合には、オーステナイト未再結晶温度域での圧延により鋼中に導入されたが歪みが回復するため、未再結晶温度域圧延の効果が十分に発揮されない。冷却速度が３．０℃／ｓを下回る場合、あるいは、冷却終了温度が６００℃を超える場合には、鋼板の強度が低くなるおそれがあるほか、目標とする集合組織が得られなくなる。 The steel sheet that has been rolled is cooled within a range of 40 ° C. from the rolling end temperature of the final pass, and is cooled to 600 ° C. or lower at a cooling rate of 3.0 ° C./s or higher. In order not to damage the texture obtained during the austenite temperature range rolling and austenite → ferrite transformation, the steel plate is cooled after rolling, and cooling is started within a range of 40 ° C. from the rolling end temperature of the final pass, 3.0 ° C. It is necessary to cool to 600 ° C. or lower at a cooling rate of at least / s. When the cooling start temperature is lower than the final pass rolling end temperature by more than 40 ° C., it is introduced into the steel by rolling in the austenite non-recrystallization temperature range, but strain is recovered. The effect of rolling is not fully exhibited. When the cooling rate is less than 3.0 ° C./s, or when the cooling end temperature exceeds 600 ° C., the strength of the steel sheet may be lowered, and a target texture cannot be obtained.
　以上の説明において、板厚中央部の温度は、放射温度計で測定した鋼板表面温度から、伝熱計算により求める。圧延後の冷却条件における温度条件も板厚中央部温度とする。 In the above description, the temperature at the center of the plate thickness is obtained by heat transfer calculation from the steel plate surface temperature measured with a radiation thermometer. The temperature condition in the cooling condition after rolling is also the sheet thickness center temperature.
　表１に示す各組成の溶鋼（鋼記号Ａ～Ｔ）を、転炉で溶製し、連続鋳造法で鋼素材（スラブ２８０ｍｍ厚）とし、板厚５０～８０ｍｍに熱間圧延後、冷却を行いＮｏ．１～２６の供試鋼を得た。表２に熱間圧延条件と冷却条件を示す。 Molten steel (steel symbols A to T) of each composition shown in Table 1 is melted in a converter, made into a steel material (slab 280 mm thick) by a continuous casting method, hot rolled to a plate thickness of 50 to 80 mm, and then cooled. No. 1-26 test steels were obtained. Table 2 shows hot rolling conditions and cooling conditions.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　得られた厚鋼板について、板厚１／４部よりΦ１４のＪＩＳ１４Ａ号試験片を採取し、引張試験を行い、降伏強度（Yield Strength）、引張強さ（Tensile Strength）を測定した。 About the obtained thick steel plate, Φ14 JIS14A test piece was collected from 1/4 part of the plate thickness, subjected to a tensile test, and the yield strength (Yield Strength) and the tensile strength (Tensile Strength) were measured.
　板厚の１／４位置よりＪＩＳ４号衝撃試験片を試験片の長手軸の方向が圧延方向と平行となるように採取し、シャルピー衝撃試験を行って、破面遷移温度（ｖＴｒｓ）を求めた。 A JIS No. 4 impact test piece was sampled from the 1/4 position of the plate thickness so that the direction of the longitudinal axis of the test piece was parallel to the rolling direction, and a Charpy impact test was conducted to determine the fracture surface transition temperature (vTrs). .
　また、鋼板の集合組織を評価するため、板厚中央位置における圧延面での｛３１１｝＜０１１＞方位強度と、板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度を測定した。 Further, in order to evaluate the texture of the steel sheet, the {311} <011> orientation strength at the rolling surface at the center position of the sheet thickness and the {110} <001> orientation strength at the rolling surface at the position of the sheet thickness 1/4. It was measured.
　方位強度は、Ｘ線回折装置（理学電機株式会社製）を使用し、Ｍｏ線源を用いて（２００）、（１１０）および（２１１）正極点図を求め、得られた正極点図から３次元結晶方位密度関数を計算することにより求めた。 The azimuth strength is 3 from the obtained positive electrode point diagram using an X-ray diffractometer (manufactured by Rigaku Corporation), obtaining (200), (110) and (211) positive electrode point diagrams using a Mo ray source. It was determined by calculating the dimensional crystal orientation density function.
　次に、脆性き裂伝播停止特性を評価するため、温度勾配型ＥＳＳＯ試験を行い、－１０℃におけるＫｃａ値（以下、Ｋｃａ（－１０℃）Ｎ／ｍｍ３／２とも記す）を求めた。 Next, in order to evaluate the brittle crack propagation stopping characteristics, a temperature gradient type ESSO test was performed to obtain a Kca value at -10 ° C. (hereinafter also referred to as Kca (−10 ° C.) N / mm 3/2 ).
　表３にこれらの試験結果を示す。製造番号（Ｎｏ．）１～１３の場合、板厚中央位置における圧延面での｛３１１｝＜０１１＞方位強度が２．５以上、かつ板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度が０．７以上の集合組織を有し、板厚１／４位置におけるシャルピー破面遷移温度が－４０℃以下であり、Ｋｃａ（－１０℃）が６０００Ｎ／ｍｍ３／２以上と優れた脆性き裂伝播停止特性が得られた。 Table 3 shows the results of these tests. In the case of production numbers (No.) 1 to 13, the {311} <011> orientation strength at the rolled surface at the plate thickness center position is 2.5 or more and {110} at the rolled surface at the plate thickness 1/4 position. It has a texture with an <001> orientation strength of 0.7 or more, a Charpy fracture surface transition temperature at ¼ position of the plate thickness is −40 ° C. or lower, and Kca (−10 ° C.) is 6000 N / mm 3/2 As described above, excellent brittle crack propagation stopping characteristics were obtained.
　一方、製造番号（Ｎｏ．）１４～２６の場合、板厚中央位置における圧延面での｛３１１｝＜０１１＞方位強度が２．５以上、かつ板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度が０．７以上、板厚１／４位置におけるシャルピー破面遷移温度が－４０℃以下、のいずれかの規定を満足しておらず、Ｋｃａの値が４５００Ｎ／ｍｍ３／２以下であった。 On the other hand, in the case of the production numbers (No.) 14 to 26, the {311} <011> orientation strength at the rolled surface at the plate thickness central position is 2.5 or more, and the rolled surface at the 1/4 position of the plate thickness { 110} <001> orientation strength is 0.7 or more, Charpy fracture surface transition temperature at ¼ position is -40 ° C or less, and Kca value is 4500 N / mm It was 3/2 or less.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
特公平７－１００８１４号公報Japanese Patent Publication No. 7-100814 特開２００２－２５６３７５号公報JP 2002-256375 A 特許第３４６７７６７号公報Japanese Patent No. 3467767 特許第３５４８３４９号公報Japanese Patent No. 3548349 特許第２６５９６６１号公報Japanese Patent No. 2659661

Claims (5)

  1. 　構造用高強度厚鋼板であって、前記集合組織で板厚中央位置における圧延面での｛３１１｝＜０１１＞方位強度が２．５以上、かつ板厚１／４位置における圧延面での｛１１０｝＜００１＞方位強度が０．７以上の集合組織を有し、板厚１／４位置におけるシャルピー破面遷移温度が－４０℃以下であることを特徴とする構造用高強度厚鋼板。 It is a high strength thick steel sheet for structure, and {311} <011> orientation strength at a rolled surface at the center position of the sheet thickness is 2.5 or more in the texture, and { 110} <001> A high strength thick steel sheet for structural use, having a texture with an orientation strength of 0.7 or more and a Charpy fracture surface transition temperature at ¼ position of the plate thickness of −40 ° C. or less.
  2. 　鋼の化学成分が、質量％で、Ｃ：０．０３～０．２０％、Ｓｉ：０．０３～０．５０％、Ｍｎ：０．５～２．２％、Ｐ：０．０３０％以下、Ｓ：０．０１０％以下、Ｔｉ：０．００５～０．０３０％、Ａｌ：０．００５～０．０８０％、Ｎ：０．００５０％以下、残部がＦｅおよび不可避的不純物からなることを特徴とする請求項１記載の構造用高強度厚鋼板。 The chemical composition of steel is mass%, C: 0.03-0.20%, Si: 0.03-0.50%, Mn: 0.5-2.2%, P: 0.030% or less S: 0.010% or less, Ti: 0.005 to 0.030%, Al: 0.005 to 0.080%, N: 0.0050% or less, the balance being made of Fe and inevitable impurities The structural high-strength thick steel plate according to claim 1.
  3. 　鋼の化学成分が、更に、質量％で、Ｎｂ：０．００５～０．０５０％、Ｃｕ：０．０１～０．５０％、Ｎｉ：０．０１～１．００％、Ｃｒ：０．０１～０．５０％、Ｍｏ：０．０１～０．５０％、Ｖ：０．００１～０．１００％、Ｂ：０．００３０％以下、Ｃａ：０．００５０％以下、ＲＥＭ：０．０１００％以下の１種または２種以上を含有することを特徴とする請求項２記載の構造用高強度厚鋼板。 Further, the chemical composition of the steel is, by mass, Nb: 0.005 to 0.050%, Cu: 0.01 to 0.50%, Ni: 0.01 to 1.00%, Cr: 0.01 ~ 0.50%, Mo: 0.01 ~ 0.50%, V: 0.001 ~ 0.100%, B: 0.0030% or less, Ca: 0.0050% or less, REM: 0.0100% The structural high-strength thick steel plate according to claim 2, comprising one or more of the following.
  4. 　板厚が５０ｍｍ超えであることを特徴とする請求項１乃至３のいずれか一つに記載の構造用高強度厚鋼板。 The structural high-strength thick steel plate according to any one of claims 1 to 3, wherein the plate thickness exceeds 50 mm.
  5. 　請求項２または３のいずれかに記載の化学成分を有する鋼素材を、１０００～１２００℃の温度に加熱し、熱間圧延において板厚中央部がオーステナイト再結晶温度域の温度域では累積圧下率３０％以上、板厚中央部がオーステナイト未再結晶温度域の温度域では累積圧下率５０％以上の圧延を行った後、圧延終了温度から４０℃以内の温度域より３．０℃／ｓ以上の冷却速度にて６００℃以下まで冷却することを特徴とする構造用高強度厚鋼板の製造方法。 The steel material having the chemical component according to any one of claims 2 and 3 is heated to a temperature of 1000 to 1200 ° C, and in hot rolling, the cumulative reduction ratio is in the temperature range where the central portion of the plate thickness is the austenite recrystallization temperature range. 30% or more, after rolling at a cumulative reduction ratio of 50% or more in the temperature range where the central part of the plate thickness is austenite non-recrystallization temperature, 3.0 ° C / s or more from the temperature range within 40 ° C from the rolling end temperature The manufacturing method of the structural high-strength thick steel plate characterized by cooling to 600 degrees C or less with the cooling rate of.
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