WO2017145651A1 - High strength ultra-thick steel plate having excellent brittle crack propagation stopping characteristics and manufaturing method of same - Google Patents

High strength ultra-thick steel plate having excellent brittle crack propagation stopping characteristics and manufaturing method of same Download PDF

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WO2017145651A1
WO2017145651A1 PCT/JP2017/003152 JP2017003152W WO2017145651A1 WO 2017145651 A1 WO2017145651 A1 WO 2017145651A1 JP 2017003152 W JP2017003152 W JP 2017003152W WO 2017145651 A1 WO2017145651 A1 WO 2017145651A1
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temperature
steel plate
crack propagation
thickness
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PCT/JP2017/003152
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French (fr)
Japanese (ja)
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孝一 中島
克行 一宮
長谷　和邦
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Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to JP2017533359A priority Critical patent/JP6338022B2/en
Priority to CN201780013041.6A priority patent/CN108779525A/en
Priority to KR1020187024221A priority patent/KR102192969B1/en
Priority to CN202211251915.0A priority patent/CN115652197A/en
Publication of WO2017145651A1 publication Critical patent/WO2017145651A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • 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
    • C22C38/02—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
    • C22C38/06—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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a high-strength extra-thick steel plate excellent in brittle crack propagation stopping characteristics having a thickness of 70 mm or more, and its manufacture, used for large structures such as ships, marine structures, low-temperature storage tanks, and construction / civil engineering structures Regarding the method.
  • the brittle crack propagation stopping property of a steel sheet tends to deteriorate as the strength increases or the wall becomes thicker. For this reason, the request
  • a method for increasing the Ni content in the steel has been conventionally known.
  • LNG liquefied natural gas
  • Patent Document 1 a steel sheet with an ultra-fine surface layer structure is proposed in Patent Document 1.
  • Patent Document 1 In the steel sheet excellent in brittle crack propagation stopping characteristics described in Patent Document 1, when a brittle crack propagates, shear lip (plastic deformation region) generated in the steel sheet surface layer portion is effective in improving the brittle crack propagation stopping characteristics. It was completed by paying attention to certain things, and is characterized by absorbing the propagation energy of the propagating brittle crack by refining the crystal grains of the shear lip. Patent Document 1 includes a step of cooling the surface layer portion below the Ar 3 transformation point by controlled cooling after hot rolling, and then stopping the controlled cooling to reheat the surface layer portion above the Ar 3 transformation point. It is described that by repeatedly reducing the steel sheet by repeatedly rolling the steel sheet repeatedly or repeatedly, a superfine ferrite structure or a bainite structure is generated in the surface layer part by causing repetitive transformation or processing recrystallization. .
  • both surface portions of the steel sheet have a circle-equivalent grain size of 5 ⁇ m or less and an aspect ratio: It is important to suppress the ferrite grain size variation while forming a ferrite structure having two or more ferrite grains in a layer having an area ratio of 50% or more, and one pass during finish rolling as a method of suppressing this variation. It is described that the local recrystallization phenomenon is suppressed by setting the maximum rolling reduction per hit to 12% or less.
  • Patent Document 3 discloses a technique on the extension of TMCP that improves brittle crack propagation stopping characteristics by focusing on subgrains formed in ferrite crystal grains as well as refinement of ferrite crystal grains. Is described. Specifically, in a steel sheet with a 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 to ensure fine ferrite crystal grains, (B) rolling conditions for producing a fine ferrite structure in a portion of 5% or more of the steel plate thickness; (C) Rolling conditions for developing a texture in fine ferrite and rearranging dislocations introduced by processing (rolling) by thermal energy to form subgrains; and (d) Fine ferrite grains formed and fine Cooling conditions to suppress coarsening of subgrain grains, Describes a technique for improving the brittle crack propagation stopping characteristics.
  • Patent Document 4 discloses that the (110) plane X-ray intensity ratio is 2 or more by controlled rolling, and the area ratio of coarse grains having a circle-equivalent diameter of 20 ⁇ m or more is 10% or less. It is described to improve.
  • Patent Document 5 as a steel for welded structure having excellent brittle crack propagation stopping characteristics of the joint portion, the X-ray plane strength ratio of the (100) plane in the rolled surface within the plate thickness is 1.5 or more.
  • a characteristic steel sheet is disclosed, and it is described that it has excellent brittle crack propagation stopping characteristics due to a shift in the angle between the stress load direction due to the texture development and the crack propagation direction.
  • Patent Document 6 discloses a brittle crack propagation stop property that develops a texture in each part (plate thickness 1/4 position, plate thickness center portion, etc.) in the plate thickness direction by defining the average rolling reduction in controlled rolling. A method for producing an excellent welded structural steel sheet is described.
  • Non-Patent Document 1 a brittle crack propagation stopping property of a steel sheet having a thickness of 65 mm is evaluated, and a result of a brittle crack not stopping in a large brittle crack propagation stopping test of a base material is reported.
  • Japanese Patent Publication No. 7-100814 JP 2002-256375 A Japanese Patent No. 3467767 Japanese Patent No. 3548349 Japanese Patent No. 2659661 Japanese Patent No. 5733425
  • Patent Documents 1 to 6 are all subject to a plate thickness of about 50 mm to 70 mm from manufacturing conditions and disclosed experimental data, and to a thick material of 70 mm or more. As for the application, it is unclear whether a predetermined characteristic can be obtained, and the crack propagation characteristic in the plate thickness direction required for a large structure has not been verified at all.
  • Non-Patent Document 1 the ESSO test of the specimen shows a result that the value of Kca at a use temperature of ⁇ 10 ° C. is less than 3000 N / mm 1.5 . In the case of a large structure to which a steel plate having a thickness exceeding 50 mm is applied, it is suggested that safety cannot be sufficiently ensured.
  • an object of the present invention is to provide a high-strength extra-thick steel plate having a plate thickness of 70 mm or more and excellent brittle crack propagation stopping characteristics and a method for producing the same.
  • the inventors have conducted intensive research on a high-strength ultra-thick steel plate having excellent brittle crack propagation stopping characteristics even at a plate thickness of 70 mm or more and a manufacturing method for stably obtaining the steel plate.
  • the (211) plane integration degree on the rolled surface at the center of the plate thickness is 1.2 or more
  • the (200) plane integration degree on the rolled surface on the steel sheet surface (sometimes simply referred to as “surface”) is Charpy fracture surface transition temperature vTrs is -40 ° C.
  • the present invention has been completed by further studying the above knowledge.
  • the gist of the present invention is as follows. [1] By mass%, C: 0.03-0.20%, Si: 0.03-0.5%, Mn: 0.5-2.2%, P: 0.01% or less, S: Ceq defined by the following formula (1) containing 0.005% or less, Ti: 0.005 to 0.03%, Al: 0.005 to 0.080% and N: 0.0050% or less
  • the composition is 0.36 or more and 0.40 or less, and the balance is Fe and inevitable impurities, and the (211) plane integration degree at the rolling surface in the center of the sheet thickness is 1.2 or more, and rolling on the steel sheet surface Has a texture with a (200) plane integration degree of 1.7 or more on the surface, and has a Charpy fracture surface transition temperature vTrs of ⁇ 40 ° C.
  • the component composition is further in terms of mass%, Nb: 0.005 to 0.05%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.5%, and Cr: 0.00.
  • the high-strength extra-thick steel sheet having excellent brittle crack propagation stopping properties as described in [1], containing one or more of 01 to 0.5%.
  • the component composition is further in mass%, Mo: 0.01 to 0.5%, V: 0.001 to 0.10%, B: 0.0030% or less, Ca: 0.0050% or less REM: A high-strength extra-thick steel plate having excellent brittle crack propagation stopping properties according to [1] or [2], which contains one or more of 0.0100% or less.
  • the temperature at the center of the plate thickness is the cumulative reduction in the austenite recrystallization temperature range.
  • the rate is 10% or more
  • the temperature at the center of the plate thickness is 50% or more at the austenite non-recrystallization temperature range
  • the surface temperature of the plate thickness is below the Ar 3 transformation point
  • the temperature at the center of the plate thickness is above the Ar 3 transformation point.
  • a high-strength ultra-thick steel plate with excellent brittle crack propagation stopping characteristics After cooling to a cooling stop temperature of 500 ° C. or lower, tempering to a temperature at which the center of the plate thickness is less than the Ac 1 transformation point [4] A method of manufacturing a steel sheet.
  • the texture in the plate thickness direction is appropriately controlled, so even a very thick steel plate having a plate thickness of 70 mm or more has excellent brittle crack propagation stopping properties, excellent toughness, and high strength. It is.
  • a high-strength extra heavy steel plate can be manufactured stably by an industrially very simple process by optimizing rolling conditions. For example, by applying the high-strength extra heavy steel plate of the present invention to a container ship in the shipbuilding field, a deck member joined to hatch side combing in a strong deck structure of a bulk carrier, it contributes to improving ship safety, It is extremely useful in industry.
  • C 0.03 to 0.20%
  • C is an element that improves the strength of steel.
  • the C content in order to secure a desired strength, is set to 0.03% or more.
  • the C content is in the range of 0.03 to 0.20%.
  • the lower limit is preferably 0.05% or more.
  • the upper limit is preferably 0.15% or less.
  • Si 0.03-0.5%
  • Si is effective as a deoxidizing element and as a strengthening element for steel. If the Si content is less than 0.03%, these effects cannot be obtained. On the other hand, when the Si content exceeds 0.5%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, the Si content is in the range of 0.03 to 0.5%.
  • Mn 0.5 to 2.2% Mn is included as a strengthening element. If the Mn content is less than 0.5%, the effect is not sufficient. On the other hand, if it exceeds 2.2%, the weldability deteriorates and the steel sheet cost also increases. Therefore, the Mn content is in the range of 0.5 to 2.2%.
  • P 0.01% or less
  • S 0.005% or less
  • P and S are inevitable impurities in steel.
  • the P content is suppressed to 0.01% or less and the S content is suppressed to 0.005% or less.
  • the P content is 0.006% or less
  • the S content is 0.003% or less, which are more desirable ranges.
  • Ti 0.005 to 0.03%
  • Ti has the effect of forming nitrides, carbides, or carbonitrides by adding a trace amount, and making the crystal grains finer to improve the base material toughness. The effect is acquired by making Ti content 0.005% or more.
  • the Ti content exceeds 0.03%, the toughness of the base material and the weld heat affected zone decreases. Therefore, the Ti content is in the range of 0.005 to 0.03%.
  • Al acts as a deoxidizer.
  • the Al content needs to be 0.005% or more.
  • the Al content is in the range of 0.005 to 0.080%.
  • the lower limit is preferably 0.020% or more.
  • the upper limit is preferably 0.060% or less.
  • N 0.0050% or less N combines with Al in the steel, adjusts the crystal grain size during rolling, and strengthens the steel.
  • the N content is preferably 0.0010% or more.
  • the toughness deteriorates.
  • the N content is in the range of 0.0050% or less.
  • the above is the basic component composition of the present invention, and the balance is Fe and inevitable impurities.
  • Nb, Cu, Ni, Cr in addition to the above component composition.
  • Nb 0.005 to 0.05%
  • Nb precipitates as NbC during ferrite transformation or reheating, and contributes to increasing the strength.
  • Nb has an effect of expanding the non-recrystallized region in rolling in the austenite region, and contributes to the refinement of ferrite. For this reason, containing Nb is also effective in improving toughness. The effect is exhibited when the Nb content is 0.005% or more. If the Nb content exceeds 0.05%, coarse NbC may precipitate, leading to a decrease in toughness. Therefore, when Nb is contained, the Nb content is preferably 0.005 to 0.05%.
  • Cu 0.05 to 1.0%
  • Cu is an element that enhances the hardenability of steel. This element contributes directly to improving the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited when the Cu content is 0.05% or more. On the other hand, excessive Cu content deteriorates toughness and weldability.
  • the Cu content is preferably set to 0.05 to 1.0% so that a steel plate having a thickness of 70 mm or more does not deteriorate toughness or weldability while maintaining sufficient strength.
  • Ni 0.05 to 1.5%
  • Ni is an element that enhances the hardenability of steel. Ni can be directly added to improve the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited by making the Ni content 0.05% or more. On the other hand, excessive Ni content deteriorates toughness and weldability.
  • the Ni content is preferably set to 0.05 to 1.5% so that a steel plate having a thickness of 70 mm or more does not deteriorate toughness or weldability while maintaining sufficient strength.
  • Cr 0.01 to 0.5% Cr is an element that enhances the hardenability of steel. This element contributes directly to improving the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited by making the Cr content 0.01% or more. On the other hand, excessive inclusion deteriorates toughness and weldability.
  • the Cr content is preferably 0.01 to 0.5% as a range in which sufficient strength is maintained even when the plate thickness is 70 mm or more and the toughness and weldability are not deteriorated.
  • Mo 0.01 to 0.5%
  • Mo is an element that increases the hardenability of steel. This element contributes directly to improving the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited by making the Mo content 0.01% or more. On the other hand, excessive inclusion deteriorates toughness and weldability.
  • the Mo content is preferably set to 0.01 to 0.5% so that sufficient strength is maintained even when the plate thickness is 70 mm or more, and the toughness and weldability are not deteriorated.
  • V 0.001 to 0.10%
  • V is an element that improves the strength of the steel by precipitation strengthening that precipitates as V (CN). This effect is exhibited when the V content is 0.001% or more. However, if the V content exceeds 0.10%, the toughness may decrease. For this reason, when V is contained, the V content is preferably in the range of 0.001 to 0.10%.
  • B 0.0030% or less
  • B is an element that enhances the hardenability of steel, and the above effect can be obtained even with a B content of 0.0030% or less. Moreover, when B content exceeds 0.0030%, the toughness of a welded part will fall. Therefore, when B is contained, the B content is preferably 0.0030% or less. From the viewpoint of obtaining the above effect, the lower limit of the B content is preferably 0.0006%.
  • the high-strength extra heavy steel sheet of the present invention has a Ceq represented by the following formula (1) of 0.36 or more and 0 in addition to each component composition being in the range of the above content. Adjust to 40 or less.
  • Ceq is less than 0.36, it is difficult to increase the degree of (211) plane integration on the rolled surface at the center of the plate thickness. In order to secure weldability, Ceq is set to 0.40 or less.
  • Ceq C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + Mo / 5 + V / 5
  • C, Mn, Cu, Ni, Cr, Mo and V in the formula (1) mean the content (% by mass) of each element, and 0 when not contained.
  • the high-strength ultra-thick steel sheet of the present invention has a (211) plane integration degree of 1.2 or more at the rolled surface at the center of the plate thickness, and the (200) plane at the rolled surface on the surface (range from the extreme surface to 1 mm below the surface). It has a texture with a degree of integration of 1.7 or more.
  • the high-strength extra-thick steel sheet according to the present invention is excellent in strength, toughness, and brittle crack propagation stopping characteristics even if the sheet thickness is 70 mm or more by controlling the composition and texture.
  • the heating temperature of the steel material is in the range of 1000 to 1200 ° C. From the viewpoint of improving the toughness of the steel sheet, the preferable range of the heating temperature is 1000 ° C. or more for the lower limit and 1150 ° C. or less for the upper limit.
  • the temperature of the steel material means the temperature at the center of the plate thickness of the steel plate.
  • the cumulative reduction ratio is 10% or more in the temperature range of the austenite recrystallization temperature range at the center of the plate thickness.
  • the Charpy fracture surface transition temperature (vTrs) at the 1 ⁇ 4 thickness position can be ⁇ 40 ° C. or less.
  • the upper limit of the cumulative rolling reduction is not particularly limited, but the cumulative rolling reduction is preferably 45% or less because the effect of improving the fine particles becomes small.
  • the above condition is preferably such that the cumulative rolling reduction in the temperature range of 1100 to 950 ° C. in the hot rolling is 10% or more.
  • the cumulative reduction ratio is 50% or more when the temperature at the center of the plate thickness is in the austenite non-recrystallization temperature range.
  • the cumulative rolling reduction in this temperature range is 50% or more, a texture in which the (211) plane integration degree on the rolled surface at the center of the sheet thickness is 1.2 or more is obtained.
  • the cumulative rolling reduction in this temperature range is less than 50%, a texture in which the (211) plane integration degree on the rolled surface at the sheet thickness center is 1.2 or more cannot be obtained.
  • the upper limit of the cumulative rolling reduction is not particularly limited, but is preferably 75% or less so as not to inhibit the rolling efficiency. In the case of the component composition of the present invention, the above conditions are preferably such that the cumulative rolling reduction in the temperature range of 950 to 700 ° C. in hot rolling is 50% or more.
  • the cumulative rolling reduction when the plate thickness surface temperature is below the Ar 3 transformation point and the temperature at the center of the plate thickness is in the temperature range above the Ar 3 transformation point is set to exceed 20%.
  • the (200) plane integration degree on the rolled surface on the steel sheet surface can be developed.
  • the (200) plane integration degree on the rolled surface on the steel sheet surface is 1.7 or more, and the Charpy fracture surface transition temperature (vTrs) on the steel sheet surface is ⁇ 80 ° C. or less. .
  • the plate thickness surface is in this temperature range and the cumulative rolling reduction is 20% or less, the desired texture and vTrs cannot be obtained.
  • Ar 3 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo
  • the element symbol in the above formula means the content (% by mass) of each element, and 0 is not included.
  • a suitable temperature range to the rolling in the temperature below Ar 3 transformation point of the surface is Ar 3 transformation point ⁇ (Ar 3 transformation point -80) ° C..
  • a suitable temperature range in the rolling is (Ar 3 transformation point +80) ° C. ⁇ Ar 3 transformation point.
  • rolling outside the specified temperature range is not limited, and at least the specified cumulative reduction rate may be reduced in the specified temperature range.
  • the rolled steel sheet is cooled to a cooling stop temperature of 500 ° C. or lower at a cooling rate of 0.5 ° C./s or higher.
  • the cooling rate is less than 0.5 ° C./s, the (211) plane integration degree on the rolled surface at the plate thickness center position cannot be ensured to be 1.2 or more. Further, when the cooling stop temperature does not satisfy 500 ° C. or less, the desired strength and texture cannot be obtained.
  • the Ac 1 transformation point is represented by the following equation.
  • Ac 1 751-26.6C + 17.6Si-11.6Mn-169Al-23Cu-23Ni + 24.1Cr + 22.5Mo + 233Nb-39.7V-5.7Ti-895B
  • the element symbol in the formula represents the content (mass%) of each element. Means and does not contain 0.
  • the temperature at the center of the plate thickness is obtained by heat transfer calculation from the surface temperature of the steel plate measured with a radiation thermometer. Further, the temperature condition in the cooling condition after rolling is the temperature at the center of the plate thickness, and the cooling rate is also an average cooling rate calculated based on the temperature at the center of the plate thickness.
  • Molten steel of each component composition shown in Table 1 was melted in a converter and made into a steel material by a continuous casting method. After hot rolling to a plate thickness of 70 to 100 mm, cooling was performed to obtain test steels shown in Table 2.
  • Table 2 shows heating conditions, hot rolling conditions, and cooling conditions. Moreover, the tempering temperature was also shown about what tempered after cooling.
  • a JIS No. 4 impact test specimen was taken from the 1/4 position of the plate thickness and the steel sheet surface so that the direction of the longitudinal axis of the specimen was parallel to the rolling direction, and a Charpy impact test was conducted. vTrs) was determined. Evaluation was made that the toughness was good when the vTrs at the 1/4 position of the plate thickness was ⁇ 40 ° C. or lower and the vTrs on the steel plate surface was ⁇ 80 ° C. or lower.
  • the (211) plane integration degree at the rolling surface at the center of the plate thickness and the rolling surface on the steel plate surface (the steel plate surface means a range from the extreme surface to 1 mm below the surface).
  • the (200) plane integration degree was measured.
  • the degree of surface integration was measured using an X-ray diffractometer (manufactured by Rigaku Corporation) and using a Mo ray source.
  • Kca ( ⁇ 10 ° C.) N / mm 1.5 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 1.5 ). .
  • Kca ( ⁇ 10 ° C.) N / mm 1.5 A sample having a Kca ( ⁇ 10 ° C.) of 6000 N / mm 1.5 or more was considered good.
  • the example of the present invention has a (211) plane integration degree of 1.2 or more at the rolling surface at the center of the plate thickness and a (200) plane integration degree at the rolling surface of the steel sheet surface. It has a texture of 1.7 or more, and has excellent toughness when the Charpy fracture surface transition temperature vTrs at 1 ⁇ 4 position of the sheet thickness is ⁇ 40 ° C. or less and the Charpy fracture surface transition temperature vTrs at the steel sheet surface is ⁇ 80 ° C. or less.
  • An excellent brittle crack propagation stop characteristic was obtained with a Kca ( ⁇ 10 ° C.) of 6000 N / mm 1.5 or more.
  • a comparative example that departs from the present invention does not satisfy any of YS, TS, texture, and vTrs. Further, all the values of Kca ( ⁇ 10 ° C.) were not satisfied.

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Abstract

The purpose of the present invention is to provide a high strength, ultra-thick steel plate having a plate thickness of 70 mm or more and excellent brittle crack propagation stopping characteristics and a manufacturing method of the same. The high strength, ultra-thick steel plate having a plate thickness of 70 mm or more and excellent brittle crack propagation stopping characteristics comprises: a component composition including, as a mass%, C: at 0.03-0.20%, Si: at 0.03-0.5%, Mn: at 0.5-2.2%, P: at 0.01 % or less, S: at 0.005% or less, Ti: at 0.005-0.03%, Al: at 0.005-0.080%, and N: at 0.0050% or less, and Ceq defined in formula (1) is 0.36 or more and 0.40 or less; and a remainder portion consisting of Fe and unavoidable impurities; and an aggregate structure in which the (211) plane integration degree in a rolled surface at a plate thickness center is 1.2 or more and the (200)plane integration degree in a rolled surface in a steel plate surface is 1.7 or more, wherein a Charpy fracture transition temperature vTrs in a plate thickness 1/4 position is -40 degrees Celsius or less; and wherein a Charpy fracture transition temperature vTrs in the steel plate surface is -80 degrees Celsius or less.

Description

脆性き裂伝播停止特性に優れた高強度極厚鋼板およびその製造方法High-strength extra-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７０ｍｍ以上の脆性き裂伝播停止特性に優れた高強度極厚鋼板およびその製造方法に関する。 The present invention relates to a high-strength extra-thick steel plate excellent in brittle crack propagation stopping characteristics having a thickness of 70 mm or more, and its manufacture, used for large structures such as ships, marine structures, low-temperature storage tanks, and construction / civil engineering structures Regarding the method.
　船舶や、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、脆性破壊に伴う事故が起きると、社会経済や環境などに及ぼす影響が大きい。このため、上記大型構造物は、安全性の向上が常に求められ、大型構造物の素材となる鋼板に対しては、使用温度における脆性き裂伝播停止特性が高いレベルで要求されている。 In large structures such as ships, marine structures, low-temperature storage tanks, and construction / civil engineering structures, if an accident involving brittle fracture occurs, the impact on the socio-economy and the environment will be significant. For this reason, the large structure is always required to be improved in safety, and the steel sheet used as the material of the large structure is required to have a high level of brittle crack propagation stopping characteristics at the use temperature.
　コンテナ船やバルクキャリアーなどの船舶においては、その構造上、船体外板に高強度の厚鋼板が使用される。最近では、船体の大型化に伴って一層の高強度化が求められ、素材となる厚鋼板の厚肉化が進んでいる。 In ships such as container ships and bulk carriers, high-strength thick steel plates are used for the hull outer plates because of their structures. Recently, with the increase in size of the hull, further increase in strength has been demanded, and the thick steel plates used as materials have been increasing in thickness.
　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になるほど劣化する傾向にある。このため、大型構造物に使用される厚鋼板に対する、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。 Generally, the brittle crack propagation stopping property of a steel sheet tends to deteriorate as the strength increases or the wall becomes thicker. For this reason, the request | requirement for the brittle crack propagation stop characteristic with respect to the thick steel plate used for a large-sized structure is further advanced.
　ここで、鋼板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、鋼中のＮｉ含有量を増加させる方法が知られている。例えば、液化天然ガス（ＬＮＧ）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。 Here, as a means for improving the brittle crack propagation stopping property of a steel sheet, a method for increasing the Ni content in the steel has been conventionally known. For example, in liquefied natural gas (LNG) storage tanks, 9% Ni steel is used on a commercial scale.
　但し、鋼中Ｎｉ含有量の増加は、製造コストの大幅な上昇を余儀なくさせる。このため、９％Ｎｉ鋼は、ＬＮＧ貯槽タンク以外の用途に適用し難い。 However, an increase in the Ni content in the steel necessitates a significant increase in production costs. For this reason, 9% Ni steel is difficult to apply to uses other than the LNG storage tank.
　他方、ＬＮＧのような極低温にまで至らない、例えば、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板に対しては、ＴＭＣＰ法により細粒化を図り、低温靭性を向上させることで、優れた脆性き裂伝播停止特性を実現することができる。 On the other hand, for a comparatively thin steel plate with a thickness of less than 50 mm used for ships and line pipes, which does not reach extremely low temperatures such as LNG, the fine graining is attempted by the TMCP method. By improving toughness, excellent brittle crack propagation stopping characteristics can be realized.
　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に、表層部の組織を超微細化した鋼板が、特許文献１において提案されている。 Further, in order to improve the brittle crack propagation stopping characteristics without increasing the alloy cost, a steel sheet with an ultra-fine surface layer structure is proposed in Patent Document 1.
　特許文献１に記載の脆性き裂伝播停止特性に優れた鋼板は、脆性き裂が伝播する際、鋼板表層部に発生するシアリップ（塑性変形領域）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て完成されたものであり、シアリップ部分の結晶粒を微細化させることで、伝播する脆性き裂が有する伝播エネルギーを吸収することを特徴としている。また、特許文献１には、熱間圧延後の制御冷却によって表層部をＡｒ３変態点以下に冷却した後、制御冷却を停止して表層部をＡｒ３変態点以上に復熱させる工程を１回以上繰り返して行う間に、鋼板に圧下を加えることにより、繰り返し変態を生じさせ、または加工再結晶させることで、表層部分に超微細なフェライト組織またはベイナイト組織を生成させることが記載されている。 In the steel sheet excellent in brittle crack propagation stopping characteristics described in Patent Document 1, when a brittle crack propagates, shear lip (plastic deformation region) generated in the steel sheet surface layer portion is effective in improving the brittle crack propagation stopping characteristics. It was completed by paying attention to certain things, and is characterized by absorbing the propagation energy of the propagating brittle crack by refining the crystal grains of the shear lip. Patent Document 1 includes a step of cooling the surface layer portion below the Ar 3 transformation point by controlled cooling after hot rolling, and then stopping the controlled cooling to reheat the surface layer portion above the Ar 3 transformation point. It is described that by repeatedly reducing the steel sheet by repeatedly rolling the steel sheet repeatedly or repeatedly, a superfine ferrite structure or a bainite structure is generated in the surface layer part by causing repetitive transformation or processing recrystallization. .
　特許文献２では、フェライト－パーライトが主体のミクロ組織とする鋼板において、脆性き裂伝播停止特性を向上させるために、鋼板の両表面部を、円相当粒径：５μｍ以下で、かつアスペクト比：２以上のフェライト粒を有するフェライト組織を、面積率で５０％以上有する層で構成しつつ、フェライト粒径のバラツキを抑えることが重要であること、この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を１２％以下とすることで局所的な再結晶現象を抑制することが記載されている。 In Patent Document 2, in order to improve brittle crack propagation stopping characteristics in a steel sheet mainly composed of ferrite-pearlite, both surface portions of the steel sheet have a circle-equivalent grain size of 5 μm or less and an aspect ratio: It is important to suppress the ferrite grain size variation while forming a ferrite structure having two or more ferrite grains in a layer having an area ratio of 50% or more, and one pass during finish rolling as a method of suppressing this variation. It is described that the local recrystallization phenomenon is suppressed by setting the maximum rolling reduction per hit to 12% or less.
　特許文献３には、フェライト結晶粒の微細化だけでなく、フェライト結晶粒内に形成されるサブグレインに着目することで、脆性き裂伝播停止特性を向上させるという、ＴＭＣＰの延長上にある技術が記載されている。具体的には、板厚：３０～４０ｍｍの鋼板において、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）鋼板板厚の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を発達させるとともに加工（圧延）により導入した転位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、および
（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技術が記載されている。 Patent Document 3 discloses a technique on the extension of TMCP that improves brittle crack propagation stopping characteristics by focusing on subgrains formed in ferrite crystal grains as well as refinement of ferrite crystal grains. Is described. Specifically, in a steel sheet with a 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 to ensure fine ferrite crystal grains,
(B) rolling conditions for producing a fine ferrite structure in a portion of 5% or more of the steel plate thickness;
(C) Rolling conditions for developing a texture in fine ferrite and rearranging dislocations introduced by processing (rolling) by thermal energy to form subgrains; and (d) Fine ferrite grains formed and fine Cooling conditions to suppress coarsening of subgrain grains,
Describes a technique for improving the brittle crack propagation stopping characteristics.
　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。これは、鋼板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方法である。 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. This is a method of increasing resistance to brittle fracture by causing separation on the fracture surface of the steel plate in a direction parallel to the plate surface and relaxing stress at the tip of the brittle crack.
　例えば、特許文献４には、制御圧延により（１１０）面Ｘ線強度比を２以上とし、かつ円相当径２０μｍ以上の粗大粒の面積率を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 the (110) plane X-ray intensity ratio is 2 or more by controlled rolling, and the area ratio of coarse grains having a circle-equivalent diameter of 20 μm or more is 10% or less. It is described to improve.
　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ており、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。 In Patent Document 5, as a steel for welded structure having excellent brittle crack propagation stopping characteristics of the joint portion, the X-ray plane strength ratio of the (100) plane in the rolled surface within the plate thickness is 1.5 or more. A characteristic steel sheet is disclosed, and it is described that it has excellent brittle crack propagation stopping characteristics due to a shift in the angle between the stress load direction due to the texture development and the crack propagation direction.
　さらに、特許文献６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１／４位置、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板の製造方法が記載されている。 Furthermore, Patent Document 6 discloses a brittle crack propagation stop property that develops a texture in each part (plate thickness 1/4 position, plate thickness center portion, etc.) in the plate thickness direction by defining the average rolling reduction in controlled rolling. A method for producing an excellent welded structural steel sheet is described.
　また、最近の６，０００ＴＥＵを超える大型コンテナ船では、板厚：７０ｍｍ以上の厚鋼板が使用される。非特許文献１では、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が報告されている。 In addition, in a large container ship exceeding 6,000 TEU, a steel plate having a thickness of 70 mm or more is used. In Non-Patent Document 1, a brittle crack propagation stopping property of a steel sheet having a thickness of 65 mm is evaluated, and a result of a brittle crack not stopping in a large brittle crack propagation stopping test of a base material is reported.
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 特許第５７３３４２５号公報Japanese Patent No. 5733425
　特許文献１、２に記載の技術では、鋼板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。このため、実生産規模での制御が容易でなく、特に板厚が７０ｍｍ以上の厚肉材の製造では、圧延設備、冷却設備への負荷が大きいプロセスである。 In the techniques described in Patent Documents 1 and 2, only the surface layer of the steel sheet is once cooled and then reheated, and a specific structure is obtained by applying processing during recuperation. For this reason, control on an actual production scale is not easy, and particularly in the manufacture of thick materials having a plate thickness of 70 mm or more, this is a process with a heavy load on rolling equipment and cooling equipment.
　また、特許文献１～６に記載された鋼板は、いずれも、製造条件や開示されている実験データから、板厚：５０ｍｍ～７０ｍｍ程度が主な対象であって、７０ｍｍ以上の厚肉材への適用については、所定の特性が得られるかが不明であり、大型構造物において必要な、板厚方向のき裂伝播特性に対しては全く検証されていない。 In addition, the steel sheets described in Patent Documents 1 to 6 are all subject to a plate thickness of about 50 mm to 70 mm from manufacturing conditions and disclosed experimental data, and to a thick material of 70 mm or more. As for the application, it is unclear whether a predetermined characteristic can be obtained, and the crack propagation characteristic in the plate thickness direction required for a large structure has not been verified at all.
　さらに、非特許文献１において、供試材のＥＳＳＯ試験は、使用温度－１０℃でのＫｃａの値が３０００Ｎ／ｍｍ１．５に満たない結果を示しており、非特許文献１の技術では、５０ｍｍを超える板厚の鋼板を適用した大型構造物の場合、安全性確保が十分とまではいえないことを示唆している。 Furthermore, in Non-Patent Document 1, the ESSO test of the specimen shows a result that the value of Kca at a use temperature of −10 ° C. is less than 3000 N / mm 1.5 . In the case of a large structure to which a steel plate having a thickness exceeding 50 mm is applied, it is suggested that safety cannot be sufficiently ensured.
　本発明は、かかる事情に鑑み、板厚が７０ｍｍ以上で脆性き裂伝播停止特性に優れた高強度極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。 In view of such circumstances, an object of the present invention is to provide a high-strength extra-thick steel plate having a plate thickness of 70 mm or more and excellent brittle crack propagation stopping characteristics and a method for producing the same.
　発明者らは、上記課題を解決するために、板厚７０ｍｍ以上でも優れた脆性き裂伝播停止特性を有する高強度極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た。その結果、板厚中央における圧延面での（２１１）面集積度を１．２以上とし、かつ、鋼板表面（単に「表面」という場合がある）における圧延面での（２００）面集積度を１．７以上とする集合組織を有し、靭性の指標である板厚１／４位置におけるシャルピー破面遷移温度ｖＴｒｓが－４０℃以下および鋼板表面におけるシャルピー破面遷移温度ｖＴｒｓが－８０℃以下である極厚鋼板が、極めて優れた脆性き裂伝播停止特性を有することを知見した。 In order to solve the above-mentioned problems, the inventors have conducted intensive research on a high-strength ultra-thick steel plate having excellent brittle crack propagation stopping characteristics even at a plate thickness of 70 mm or more and a manufacturing method for stably obtaining the steel plate. As a result, the (211) plane integration degree on the rolled surface at the center of the plate thickness is 1.2 or more, and the (200) plane integration degree on the rolled surface on the steel sheet surface (sometimes simply referred to as “surface”) is Charpy fracture surface transition temperature vTrs is -40 ° C. or lower at the 1/4 thickness position, which is an index of toughness, and the Charpy fracture surface transition temperature vTrs on the steel sheet surface is −80 ° C. or lower. It was found that the extra-thick steel plate has extremely excellent brittle crack propagation stopping characteristics.
　本発明は、上記した知見に、さらに検討を加えて完成されたものである。本発明の要旨構成は次のとおりである。
［１］質量％で、Ｃ：０．０３～０．２０％、Ｓｉ：０．０３～０．５％、Ｍｎ：０．５～２．２％、Ｐ：０．０１％以下、Ｓ：０．００５％以下、Ｔｉ：０．００５～０．０３％、Ａｌ：０．００５～０．０８０％およびＮ：０．００５０％以下を含有し、下記式（１）で定義されるＣｅｑが０．３６以上０．４０以下であり、残部がＦｅおよび不可避的不純物からなる成分組成と、板厚中央における圧延面での（２１１）面集積度が１．２以上であり、鋼板表面における圧延面での（２００）面集積度が１．７以上である集合組織を有し、板厚１／４位置におけるシャルピー破面遷移温度ｖＴｒｓが－４０℃以下であり、鋼板表面におけるシャルピー破面遷移温度ｖＴｒｓが－８０℃以下である板厚７０ｍｍ以上の脆性き裂伝播停止特性に優れた高強度極厚鋼板。
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｃｕ／１５＋Ｎｉ／１５＋Ｃｒ／５＋Ｍｏ／５＋Ｖ／５・・・（１）
ここで、式（１）におけるＣ、Ｍｎ、Ｃｕ、Ｎｉ、Ｃｒ、ＭｏおよびＶは各元素の含有量（質量％）を意味し、含有しない場合は０とする。
［２］前記成分組成は、さらに質量％で、Ｎｂ：０．００５～０．０５％、Ｃｕ：０．０５～１．０％、Ｎｉ：０．０５～１．５％およびＣｒ：０．０１～０．５％の１種または２種以上を含有する［１］に記載の脆性き裂伝播停止特性に優れた高強度極厚鋼板。
［３］前記成分組成は、さらに質量％で、Ｍｏ：０．０１～０．５％、Ｖ：０．００１～０．１０％、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［１］または［２］に記載の脆性き裂伝播停止特性に優れた高強度極厚鋼板。
［４］［１］～［３］のいずれかに記載の成分組成を有する鋼素材を、１０００～１２００℃の温度に加熱した後、板厚中央の温度がオーステナイト再結晶温度域での累積圧下率が１０％以上、板厚中央の温度がオーステナイト未再結晶温度域での累積圧下率が５０％以上、板厚表面温度がＡｒ３変態点以下かつ板厚中央の温度がＡｒ３変態点以上の温度域のときの累積圧下率が２０％超えの条件で熱間圧延を行った後、０．５℃／s以上の冷却速度にて５００℃以下の冷却停止温度まで冷却する板厚７０ｍｍ以上の脆性き裂伝播停止特性に優れた高強度極厚鋼板の製造方法。
［５］５００℃以下の冷却停止温度まで冷却した後、板厚中央の温度がＡｃ１変態点未満の温度に焼戻す［４］に記載の脆性き裂伝播停止特性に優れた高強度極厚鋼板の製造方法。 The present invention has been completed by further studying the above knowledge. The gist of the present invention is as follows.
[1] By mass%, C: 0.03-0.20%, Si: 0.03-0.5%, Mn: 0.5-2.2%, P: 0.01% or less, S: Ceq defined by the following formula (1) containing 0.005% or less, Ti: 0.005 to 0.03%, Al: 0.005 to 0.080% and N: 0.0050% or less The composition is 0.36 or more and 0.40 or less, and the balance is Fe and inevitable impurities, and the (211) plane integration degree at the rolling surface in the center of the sheet thickness is 1.2 or more, and rolling on the steel sheet surface Has a texture with a (200) plane integration degree of 1.7 or more on the surface, and has a Charpy fracture surface transition temperature vTrs of −40 ° C. or less at the 1/4 thickness position, and a Charpy fracture transition on the steel sheet surface. Brittle crack propagation stopping characteristics with a thickness of 70 mm or more with a temperature vTrs of -80 ° C or less Excellent high-strength extra-thick steel plate.
Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + Mo / 5 + V / 5 (1)
Here, C, Mn, Cu, Ni, Cr, Mo and V in the formula (1) mean the content (% by mass) of each element, and 0 when not contained.
[2] The component composition is further in terms of mass%, Nb: 0.005 to 0.05%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.5%, and Cr: 0.00. The high-strength extra-thick steel sheet having excellent brittle crack propagation stopping properties as described in [1], containing one or more of 01 to 0.5%.
[3] The component composition is further in mass%, Mo: 0.01 to 0.5%, V: 0.001 to 0.10%, B: 0.0030% or less, Ca: 0.0050% or less REM: A high-strength extra-thick steel plate having excellent brittle crack propagation stopping properties according to [1] or [2], which contains one or more of 0.0100% or less.
[4] After heating the steel material having the composition according to any one of [1] to [3] to a temperature of 1000 to 1200 ° C., the temperature at the center of the plate thickness is the cumulative reduction in the austenite recrystallization temperature range. The rate is 10% or more, the temperature at the center of the plate thickness is 50% or more at the austenite non-recrystallization temperature range, the surface temperature of the plate thickness is below the Ar 3 transformation point, and the temperature at the center of the plate thickness is above the Ar 3 transformation point. After carrying out hot rolling under the condition that the cumulative rolling reduction in the temperature range exceeds 20%, the sheet thickness is cooled to a cooling stop temperature of 500 ° C. or lower at a cooling rate of 0.5 ° C./s or higher. A high-strength ultra-thick steel plate with excellent brittle crack propagation stopping characteristics.
[5] After cooling to a cooling stop temperature of 500 ° C. or lower, tempering to a temperature at which the center of the plate thickness is less than the Ac 1 transformation point [4] A method of manufacturing a steel sheet.
　本発明によれば、板厚方向の集合組織が適切に制御されるため、板厚７０ｍｍ以上の極厚鋼板であっても、脆性き裂伝播停止特性に優れるとともに、靭性にも優れ、高強度である。また、本発明によれば、圧延条件を最適化することで工業的に極めて簡易なプロセスで、安定して高強度極厚鋼板を製造することができる。例えば、本発明の高強度極厚鋼板を、造船分野のコンテナ船、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し、産業上極めて有用である。 According to the present invention, the texture in the plate thickness direction is appropriately controlled, so even a very thick steel plate having a plate thickness of 70 mm or more has excellent brittle crack propagation stopping properties, excellent toughness, and high strength. It is. Moreover, according to this invention, a high-strength extra heavy steel plate can be manufactured stably by an industrially very simple process by optimizing rolling conditions. For example, by applying the high-strength extra heavy steel plate of the present invention to a container ship in the shipbuilding field, a deck member joined to hatch side combing in a strong deck structure of a bulk carrier, it contributes to improving ship safety, It is extremely useful in industry.
　以下、本発明の実施形態について説明する。なお、本発明は以下の実施形態に限定されない。 Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.
　＜成分組成＞
　以下、各成分について説明する。なお、成分の含有量を表す「％」は、「質量％」を意味する。 <Ingredient composition>
Hereinafter, each component will be described. In addition, “%” representing the content of a component means “% by mass”.
　Ｃ：０．０３～０．２０％
　Ｃは、鋼の強度を向上させる元素である。本発明では、所望の強度を確保するために、Ｃ含有量を０．０３％以上とする。また、Ｃ含有量が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含有量は０．０３～０．２０％の範囲とする。なお、下限は、好ましくは０．０５％以上である。上限は、好ましくは０．１５％以下である。 C: 0.03 to 0.20%
C is an element that improves the strength of steel. In the present invention, in order to secure a desired strength, the C content is set to 0.03% or more. On the other hand, if the C content exceeds 0.20%, the weldability is deteriorated and the toughness is also adversely affected. Therefore, the C content is in the range of 0.03 to 0.20%. The lower limit is preferably 0.05% or more. The upper limit is preferably 0.15% or less.
　Ｓｉ：０．０３～０．５％
　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。Ｓｉ含有量が０．０３％未満ではこれらの効果が得られない。一方、Ｓｉ含有量が０．５％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。したがって、Ｓｉ含有量は０．０３～０．５％の範囲とする。 Si: 0.03-0.5%
Si is effective as a deoxidizing element and as a strengthening element for steel. If the Si content is less than 0.03%, these effects cannot be obtained. On the other hand, when the Si content exceeds 0.5%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, the Si content is in the range of 0.03 to 0.5%.
　Ｍｎ：０．５～２．２％
　Ｍｎは、強化元素として含まれる。Ｍｎ含有量が０．５％より少ないとその効果が十分ではない。一方で、２．２％を超えると溶接性が劣化し、鋼板コストも上昇する。そのため、Ｍｎ含有量は０．５～２．２％の範囲とする。 Mn: 0.5 to 2.2%
Mn is included as a strengthening element. If the Mn content is less than 0.5%, the effect is not sufficient. On the other hand, if it exceeds 2.2%, the weldability deteriorates and the steel sheet cost also increases. Therefore, the Mn content is in the range of 0.5 to 2.2%.
　Ｐ：０．０１％以下、Ｓ：０．００５％以下
　Ｐ、Ｓは、鋼中の不可避的不純物である。これらの含有量が多くなると靭性が劣化する。板厚７０ｍｍ以上の鋼板において、良好な靭性を保つためには、Ｐ含有量を０．０１％以下、Ｓ含有量を０．００５％以下に抑制する。なお、Ｐ含有量は０．００６％以下、Ｓ含有量は０．００３％以下が、より望ましい範囲である。 P: 0.01% or less, S: 0.005% or less P and S are inevitable impurities in steel. When these contents increase, toughness deteriorates. In order to maintain good toughness in a steel plate having a thickness of 70 mm or more, the P content is suppressed to 0.01% or less and the S content is suppressed to 0.005% or less. In addition, the P content is 0.006% or less, and the S content is 0.003% or less, which are more desirable ranges.
　Ｔｉ：０．００５～０．０３％
　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、Ｔｉ含有量を０．００５％以上とすることによって得られる。一方、Ｔｉ含有量が０．０３％を超えると、母材および溶接熱影響部の靭性が低下する。したがって、Ｔｉ含有量は０．００５～０．０３％の範囲とする。 Ti: 0.005 to 0.03%
Ti has the effect of forming nitrides, carbides, or carbonitrides by adding a trace amount, and making the crystal grains finer to improve the base material toughness. The effect is acquired by making Ti content 0.005% or more. On the other hand, if the Ti content exceeds 0.03%, the toughness of the base material and the weld heat affected zone decreases. Therefore, the Ti content is in the range of 0.005 to 0.03%.
　Ａｌ：０．００５～０．０８０％
　Ａｌは、脱酸剤として作用する。Ａｌを脱酸剤として用いるためにはＡｌ含有量を０．００５％以上にする必要がある。また、Ａｌ含有量が０．０８０％を超えると、靭性が低下するとともに、溶接した場合に溶接金属部の靭性が低下する。このため、Ａｌ含有量は０．００５～０．０８０％の範囲とする。なお、下限は、好ましくは０．０２０％以上である。上限は、好ましくは０．０６０％以下である。 Al: 0.005 to 0.080%
Al acts as a deoxidizer. In order to use Al as a deoxidizer, the Al content needs to be 0.005% or more. Moreover, when Al content exceeds 0.080%, while toughness will fall, when welding, the toughness of a weld metal part will fall. Therefore, the Al content is in the range of 0.005 to 0.080%. The lower limit is preferably 0.020% or more. The upper limit is preferably 0.060% or less.
　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。この効果を得るためには、Ｎ含有量を０．００１０％以上にすることが好ましい。一方、Ｎ含有量が０．００５０％を超えると靭性が劣化する。本発明では、Ｎ含有量は０．００５０％以下の範囲とする。 N: 0.0050% or less N combines with Al in the steel, adjusts the crystal grain size during rolling, and strengthens the steel. In order to obtain this effect, the N content is preferably 0.0010% or more. On the other hand, if the N content exceeds 0.0050%, the toughness deteriorates. In the present invention, the N content is in the range of 0.0050% or less.
　以上が本発明の基本成分組成であり、残部はＦｅ及び不可避的不純物である。 The above is the basic component composition of the present invention, and the balance is Fe and inevitable impurities.
　本発明では、さらに特性を向上させるため、上記成分組成に加えて、Ｎｂ、Ｃｕ、Ｎｉ、Ｃｒの１種または２種以上を含有することが可能である。 In the present invention, in order to further improve the characteristics, it is possible to contain one or more of Nb, Cu, Ni, Cr in addition to the above component composition.
　Ｎｂ：０．００５～０．０５％
　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、Ｎｂは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。このため、Ｎｂ含有は靭性の改善にも有効である。その効果は、Ｎｂ含有量を０．００５％以上にすることで発揮される。Ｎｂ含有量が０．０５％を超えると、粗大なＮｂＣが析出して、靭性の低下を招く場合がある。そこで、Ｎｂを含有する場合、Ｎｂ含有量を０．００５～０．０５％とするのが好ましい。 Nb: 0.005 to 0.05%
Nb precipitates as NbC during ferrite transformation or reheating, and contributes to increasing the strength. Nb has an effect of expanding the non-recrystallized region in rolling in the austenite region, and contributes to the refinement of ferrite. For this reason, containing Nb is also effective in improving toughness. The effect is exhibited when the Nb content is 0.005% or more. If the Nb content exceeds 0.05%, coarse NbC may precipitate, leading to a decrease in toughness. Therefore, when Nb is contained, the Nb content is preferably 0.005 to 0.05%.
　Ｃｕ：０．０５～１．０％
　Ｃｕは、鋼の焼入れ性を高める元素である。この元素は、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る。これらの効果は、Ｃｕ含有量を０．０５％以上にすることによって発揮される。一方で、過度のＣｕ含有は靭性や溶接性を劣化させる。板厚７０ｍｍ以上の鋼板で十分な強度を保ちつつ靭性や溶接性を劣化させない範囲として、Ｃｕ含有量は０．０５～１．０％とすることが好ましい。 Cu: 0.05 to 1.0%
Cu is an element that enhances the hardenability of steel. This element contributes directly to improving the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited when the Cu content is 0.05% or more. On the other hand, excessive Cu content deteriorates toughness and weldability. The Cu content is preferably set to 0.05 to 1.0% so that a steel plate having a thickness of 70 mm or more does not deteriorate toughness or weldability while maintaining sufficient strength.
　Ｎｉ：０．０５～１．５％
　Ｎｉは、鋼の焼入れ性を高める元素である。Ｎｉは、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る。これらの効果は、Ｎｉ含有量を０．０５％以上にすることよって発揮される。一方で、過度のＮｉ含有は靭性や溶接性を劣化させる。板厚７０ｍｍ以上の鋼板で十分な強度を保ちつつ靭性や溶接性を劣化させない範囲として、Ｎｉ含有量は０．０５～１．５％とすることが好ましい。 Ni: 0.05 to 1.5%
Ni is an element that enhances the hardenability of steel. Ni can be directly added to improve the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited by making the Ni content 0.05% or more. On the other hand, excessive Ni content deteriorates toughness and weldability. The Ni content is preferably set to 0.05 to 1.5% so that a steel plate having a thickness of 70 mm or more does not deteriorate toughness or weldability while maintaining sufficient strength.
　Ｃｒ：０．０１～０．５％
　Ｃｒは、鋼の焼入れ性を高める元素である。この元素は、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る。これらの効果は、Ｃｒ含有量を０．０１％以上にすることによって発揮される。一方で、過度の含有は靭性や溶接性を劣化させる。板厚７０ｍｍ以上でも十分な強度を保ちつつ靭性や溶接性を劣化させない範囲として、Ｃｒ含有量は０．０１～０．５％とすることが好ましい。 Cr: 0.01 to 0.5%
Cr is an element that enhances the hardenability of steel. This element contributes directly to improving the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited by making the Cr content 0.01% or more. On the other hand, excessive inclusion deteriorates toughness and weldability. The Cr content is preferably 0.01 to 0.5% as a range in which sufficient strength is maintained even when the plate thickness is 70 mm or more and the toughness and weldability are not deteriorated.
　本発明では、さらに特性を向上させるため、上記成分組成に加えて、Ｍｏ、Ｖ、Ｂ、Ｃａ、ＲＥＭの１種または２種以上を含有することが可能である。 In the present invention, in order to further improve the characteristics, it is possible to contain one or more of Mo, V, B, Ca, and REM in addition to the above component composition.
　Ｍｏ：０．０１～０．５％
　Ｍｏは、いずれも鋼の焼入れ性を高める元素である。この元素は、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る。これらの効果は、Ｍｏ含有量を０．０１％以上にすることによって発揮される。一方で、過度の含有は靭性や溶接性を劣化させる。板厚７０ｍｍ以上でも十分な強度を保ちつつ靭性や溶接性を劣化させない範囲として、Ｍｏ含有量は０．０１～０．５％とすることが好ましい。 Mo: 0.01 to 0.5%
Mo is an element that increases the hardenability of steel. This element contributes directly to improving the strength after rolling, and can be contained for improving functions such as toughness, high-temperature strength, and weather resistance. These effects are exhibited by making the Mo content 0.01% or more. On the other hand, excessive inclusion deteriorates toughness and weldability. The Mo content is preferably set to 0.01 to 0.5% so that sufficient strength is maintained even when the plate thickness is 70 mm or more, and the toughness and weldability are not deteriorated.
　Ｖ：０．００１～０．１０％
　Ｖは、Ｖ（ＣＮ）として析出する析出強化によって、鋼の強度を向上させる元素である。この効果は、Ｖ含有量を０．００１％以上にすることにより発揮される。しかし、Ｖ含有量が０．１０％を超えると、靭性が低下する場合がある。このため、Ｖを含有させる場合には、Ｖ含有量を０．００１～０．１０％の範囲とすることが好ましい。 V: 0.001 to 0.10%
V is an element that improves the strength of the steel by precipitation strengthening that precipitates as V (CN). This effect is exhibited when the V content is 0.001% or more. However, if the V content exceeds 0.10%, the toughness may decrease. For this reason, when V is contained, the V content is preferably in the range of 0.001 to 0.10%.
　Ｂ：０．００３０％以下
　Ｂは、鋼の焼入れ性を高める元素であり、Ｂ含有量が０．００３０％以下のような微量でも上記効果が得られる。また、Ｂ含有量が０．００３０％を超えると溶接部の靭性が低下する。したがって、Ｂを含有させる場合には、Ｂ含有量は０．００３０％以下とすることが好ましい。なお、上記効果を得る観点からは、Ｂ含有量の下限は０．０００６％とすることが好ましい。 B: 0.0030% or less B is an element that enhances the hardenability of steel, and the above effect can be obtained even with a B content of 0.0030% or less. Moreover, when B content exceeds 0.0030%, the toughness of a welded part will fall. Therefore, when B is contained, the B content is preferably 0.0030% or less. From the viewpoint of obtaining the above effect, the lower limit of the B content is preferably 0.0006%.
　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る。これらの成分を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場合がある。そこで、これらの成分を含有させる場合には、含有量の上限をＣａ：０．００５０％、ＲＥＭ：０．０１００％とするのが好ましい。 Ca: 0.0050% or less, REM: 0.0100% or less Ca and REM refine the structure of the weld heat affected zone and improve toughness. Even if it contains these components, since the effect of this invention is not impaired, you may contain as needed. However, when it contains excessively, a coarse inclusion may be formed and the toughness of a base material may be deteriorated. Therefore, when these components are contained, the upper limit of the content is preferably Ca: 0.0050% and REM: 0.0100%.
　Ｃｅｑ：０．３６以上０．４０以下
　本発明の高強度極厚鋼板は、各成分組成が上記含有量の範囲にあることに加えて、下記式（１）で表すＣｅｑを０．３６以上０．４０以下に調整する。Ｃｅｑが０．３６未満では、板厚中央における圧延面での（２１１）面集積度を高くし難くなる。また、溶接性を確保するため、Ｃｅｑは０．４０以下とする。
Ｃｅｑ=Ｃ＋Ｍｎ／６＋Ｃｕ／１５＋Ｎｉ／１５＋Ｃｒ／５＋Ｍｏ／５＋Ｖ／５・・・（１）
式（１）におけるＣ、Ｍｎ、Ｃｕ、Ｎｉ、Ｃｒ、ＭｏおよびＶは各元素の含有量（質量％）を意味し、含有しない場合は０とする。 Ceq: 0.36 or more and 0.40 or less The high-strength extra heavy steel sheet of the present invention has a Ceq represented by the following formula (1) of 0.36 or more and 0 in addition to each component composition being in the range of the above content. Adjust to 40 or less. When Ceq is less than 0.36, it is difficult to increase the degree of (211) plane integration on the rolled surface at the center of the plate thickness. In order to secure weldability, Ceq is set to 0.40 or less.
Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + Mo / 5 + V / 5 (1)
C, Mn, Cu, Ni, Cr, Mo and V in the formula (1) mean the content (% by mass) of each element, and 0 when not contained.
　＜集合組織＞
　本発明の高強度極厚鋼板は、板厚中央における圧延面での（２１１）面集積度が１．２以上、表面（極表面から表面下１ｍｍの範囲）における圧延面での（２００）面集積度が１．７以上を満たす集合組織を有する。上記の成分組成を採用するとともに、後述する製造条件で集合組織が上記範囲を満たすように制御することで、脆性き裂伝播停止特性に優れた高強度極厚鋼板が得られる。 <Group organization>
The high-strength ultra-thick steel sheet of the present invention has a (211) plane integration degree of 1.2 or more at the rolled surface at the center of the plate thickness, and the (200) plane at the rolled surface on the surface (range from the extreme surface to 1 mm below the surface). It has a texture with a degree of integration of 1.7 or more. By adopting the above component composition and controlling the texture to satisfy the above range under the manufacturing conditions described later, a high-strength heavy steel plate excellent in brittle crack propagation stopping characteristics can be obtained.
　以上より、本発明では、成分組成および集合組織の制御により、板厚が７０ｍｍ以上であっても、本発明の高強度極厚鋼板は、強度、靭性および脆性き裂伝播停止特性に優れるといった効果を有する。 As described above, according to the present invention, the high-strength extra-thick steel sheet according to the present invention is excellent in strength, toughness, and brittle crack propagation stopping characteristics even if the sheet thickness is 70 mm or more by controlling the composition and texture. Have
　＜製造方法＞
　上記成分組成の溶鋼を、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。 <Manufacturing method>
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きない。一方、加熱温度が１２００℃超では、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って、歩留が低下する。したがって、鋼素材の加熱温度は、１０００～１２００℃の範囲とする。鋼板の靭性向上の観点から好ましい加熱温度の範囲は、下限は１０００℃以上、上限は１１５０℃以下である。なお、鋼素材の温度は鋼板の板厚中央の温度を意味する。 If the heating temperature is less than 1000 ° C., sufficient time for rolling in the austenite recrystallization temperature region cannot be secured. On the other hand, when the heating temperature is higher than 1200 ° C., the austenite grains become coarse, leading to a decrease in toughness, and an oxidation loss becomes remarkable, resulting in a decrease in yield. Therefore, the heating temperature of the steel material is in the range of 1000 to 1200 ° C. From the viewpoint of improving the toughness of the steel sheet, the preferable range of the heating temperature is 1000 ° C. or more for the lower limit and 1150 ° C. or less for the upper limit. The temperature of the steel material means the temperature at the center of the plate thickness of the steel plate.
　熱間圧延においては、まず、板厚中央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１０％以上とする圧延を行う。この温度域での累積圧下率を１０％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（ｖＴｒｓ）が－４０℃以下を達成できる。累積圧下率が１０％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が－４０℃以下を達成できない。上記累積圧下率の上限は特に限定されないが、上記累積圧下率は細粒化の向上効果が小さくなるため、４５％以下であることが好ましい。なお、本発明の成分組成の場合、上記条件は、好ましくは、上記熱間圧延において１１００～９５０℃に含まれる温度域での累積圧下率が１０％以上である。 In hot rolling, first, rolling is performed such that the cumulative reduction ratio is 10% or more in the temperature range of the austenite recrystallization temperature range at the center of the plate thickness. By setting the cumulative rolling reduction in this temperature range to 10% or more, the Charpy fracture surface transition temperature (vTrs) at the ¼ thickness position can be −40 ° C. or less. When the cumulative rolling reduction is less than 10%, the austenite is not sufficiently refined and the toughness is not improved, and the Charpy fracture surface transition temperature at the ¼ thickness position cannot be −40 ° C. or less. The upper limit of the cumulative rolling reduction is not particularly limited, but the cumulative rolling reduction is preferably 45% or less because the effect of improving the fine particles becomes small. In the case of the component composition of the present invention, the above condition is preferably such that the cumulative rolling reduction in the temperature range of 1100 to 950 ° C. in the hot rolling is 10% or more.
　さらに、板厚中央の温度がオーステナイト未再結晶温度域での累積圧下率が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、板厚中央における圧延面での（２１１）面集積度が１．２以上となる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、板厚中央における圧延面での（２１１）面集積度が１．２以上となる集合組織が得られない。上記累積圧下率の上限は特に限定されないが、圧延能率を阻害しないように７５％以下であることが好ましい。なお、本発明の成分組成の場合、上記条件は、好ましくは、熱間圧延において９５０～７００℃に含まれる温度域での累積圧下率が５０％以上である。 Further, rolling is performed such that the cumulative reduction ratio is 50% or more when the temperature at the center of the plate thickness is in the austenite non-recrystallization temperature range. By setting the cumulative rolling reduction in this temperature range to 50% or more, a texture in which the (211) plane integration degree on the rolled surface at the center of the sheet thickness is 1.2 or more is obtained. On the other hand, when the cumulative rolling reduction in this temperature range is less than 50%, a texture in which the (211) plane integration degree on the rolled surface at the sheet thickness center is 1.2 or more cannot be obtained. The upper limit of the cumulative rolling reduction is not particularly limited, but is preferably 75% or less so as not to inhibit the rolling efficiency. In the case of the component composition of the present invention, the above conditions are preferably such that the cumulative rolling reduction in the temperature range of 950 to 700 ° C. in hot rolling is 50% or more.
　さらに、本発明では、熱間圧延において、板厚表面温度がＡｒ３変態点以下かつ板厚中央の温度がＡｒ３変態点以上の温度域にあるときの累積圧下率が２０％超えとする。本発明では重要な要件であり、この条件で熱間圧延を行うことにより、鋼板表面における圧延面での（２００）面集積度を発達させることができる。そしてこの条件で熱間圧延を行うことにより、鋼板表面における圧延面での（２００）面集積度が１．７以上、鋼板表面におけるシャルピー破面遷移温度（ｖＴｒｓ）が－８０℃以下を得られる。板厚表面がこの温度域のときに累積圧下率が２０％以下であると、所望の集合組織およびｖＴｒｓが得られない。ここで、Ａｒ３変態点は以下の式で表す。
Ａｒ３＝９１０－３１０Ｃ－８０Ｍｎ－２０Ｃｕ－１５Ｃｒ－５５Ｎｉ－８０Ｍｏ
上記式中の元素記号は各元素の含有量（質量％）を意味し、含まないものは０とする。
なお、表面の温度がＡｒ３変態点以下の中で圧延に好適な温度域はＡｒ３変態点～（Ａｒ３変態点－８０）℃である。また、板厚中央の温度がＡｒ３変態点以上の中で、圧延に好適な温度域は（Ａｒ３変態点＋８０）℃～Ａｒ３変態点である。 Furthermore, in the present invention, in hot rolling, the cumulative rolling reduction when the plate thickness surface temperature is below the Ar 3 transformation point and the temperature at the center of the plate thickness is in the temperature range above the Ar 3 transformation point is set to exceed 20%. In the present invention, which is an important requirement, by performing hot rolling under these conditions, the (200) plane integration degree on the rolled surface on the steel sheet surface can be developed. By performing hot rolling under these conditions, the (200) plane integration degree on the rolled surface on the steel sheet surface is 1.7 or more, and the Charpy fracture surface transition temperature (vTrs) on the steel sheet surface is −80 ° C. or less. . When the plate thickness surface is in this temperature range and the cumulative rolling reduction is 20% or less, the desired texture and vTrs cannot be obtained. Here, the Ar 3 transformation point is represented by the following formula.
Ar 3 = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo
The element symbol in the above formula means the content (% by mass) of each element, and 0 is not included.
Incidentally, a suitable temperature range to the rolling in the temperature below Ar 3 transformation point of the surface is Ar 3 transformation point ~ (Ar 3 transformation point -80) ° C.. Further, in the temperature of the mid-thickness is more than Ar 3 transformation point, a suitable temperature range in the rolling is (Ar 3 transformation point +80) ° C. ~ Ar 3 transformation point.
　また、本発明における熱間圧延では、上記規定した温度域外での圧延を制限するものではなく、少なくとも、上記規定する温度域において規定の累積圧下率の圧下が行われていればよい。 Further, in the hot rolling in the present invention, rolling outside the specified temperature range is not limited, and at least the specified cumulative reduction rate may be reduced in the specified temperature range.
　圧延が終了した鋼板は、０．５℃／s以上の冷却速度にて５００℃以下の冷却停止温度まで冷却する。冷却速度が０．５℃／ｓ未満の場合は、板厚中央位置における圧延面での（２１１）面集積度が１．２以上を確保することができない。また、冷却停止温度が５００℃以下を満足しない場合、所望の強度および集合組織を得ることができない。 The rolled steel sheet is cooled to a cooling stop temperature of 500 ° C. or lower at a cooling rate of 0.5 ° C./s or higher. When the cooling rate is less than 0.5 ° C./s, the (211) plane integration degree on the rolled surface at the plate thickness center position cannot be ensured to be 1.2 or more. Further, when the cooling stop temperature does not satisfy 500 ° C. or less, the desired strength and texture cannot be obtained.
　さらに、５００℃以下の冷却停止温度まで冷却した後に焼戻処理を行う場合は、板厚中央の温度がＡｃ１変態点未満で行うことが必要である。焼戻処理がＡｃ１変態点以上の場合には、圧延時に発達させた集合組織を失うこととなるからである。ここで、Ａｃ１変態点は以下の式で表す。
Ａｃ１＝７５１－２６．６Ｃ＋１７．６Ｓｉ－１１．６Ｍｎ－１６９Ａｌ－２３Ｃｕ－２３Ｎｉ＋２４．１Ｃｒ＋２２．５Ｍｏ＋２３３Ｎｂ－３９．７Ｖ－５．７Ｔｉ－８９５Ｂ式中の元素記号は各元素の含有量（質量％）を意味し、含まないものは０とする。 Furthermore, when tempering is performed after cooling to a cooling stop temperature of 500 ° C. or lower, it is necessary that the temperature at the center of the plate thickness is less than the Ac 1 transformation point. This is because when the tempering treatment is at least the Ac 1 transformation point, the texture developed during rolling is lost. Here, the Ac 1 transformation point is represented by the following equation.
Ac 1 = 751-26.6C + 17.6Si-11.6Mn-169Al-23Cu-23Ni + 24.1Cr + 22.5Mo + 233Nb-39.7V-5.7Ti-895B The element symbol in the formula represents the content (mass%) of each element. Means and does not contain 0.
　なお、以上の説明において、板厚中央の温度は、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。また、圧延後の冷却条件における温度条件は、板厚中央の温度とし、冷却速度も板厚中央の温度に基づいて算出された平均冷却速度を意味する。 In the above description, the temperature at the center of the plate thickness is obtained by heat transfer calculation from the surface temperature of the steel plate measured with a radiation thermometer. Further, the temperature condition in the cooling condition after rolling is the temperature at the center of the plate thickness, and the cooling rate is also an average cooling rate calculated based on the temperature at the center of the plate thickness.
　次に、本発明の実施例について説明する。 Next, examples of the present invention will be described.
　表１に示す各成分組成の溶鋼を、転炉で溶製し、連続鋳造法で鋼素材とした。板厚を７０～１００ｍｍに熱間圧延後、冷却を行い表２に示す供試鋼を得た。表２に、加熱条件、熱間圧延条件、冷却条件を示す。また、冷却後に焼戻しを行ったものについては焼戻温度も示した。 Molten steel of each component composition shown in Table 1 was melted in a converter and made into a steel material by a continuous casting method. After hot rolling to a plate thickness of 70 to 100 mm, cooling was performed to obtain test steels shown in Table 2. Table 2 shows heating conditions, hot rolling conditions, and cooling conditions. Moreover, the tempering temperature was also shown about what tempered after cooling.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　得られた鋼板について、板厚１／４位置より、Φ１４ｍｍのＪＩＳ　１４Ａ号試験片を採取し、引張試験を行い、降伏強度（ＹＳ）、引張強さ（ＴＳ）を測定した。ＹＳが３９０ＭＰａ以上、ＴＳが５１０ＭＰａ以上のものを良好と評価した。 About the obtained steel plate, Φ14 mm JIS No. 14A test piece was sampled from the plate thickness ¼ position, a tensile test was performed, and the yield strength (YS) and the tensile strength (TS) were measured. A sample having a YS of 390 MPa or more and a TS of 510 MPa or more was evaluated as good.
　板厚の１／４位置及び鋼板表面よりＪＩＳ　４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、シャルピー破面遷移温度（ｖＴｒｓ）を求めた。板厚１／４位置のｖＴｒｓが－４０℃以下、鋼板表面のｖＴｒｓが－８０℃以下のものを靭性が良好であると評価とした。 A JIS No. 4 impact test specimen was taken from the 1/4 position of the plate thickness and the steel sheet surface so that the direction of the longitudinal axis of the specimen was parallel to the rolling direction, and a Charpy impact test was conducted. vTrs) was determined. Evaluation was made that the toughness was good when the vTrs at the 1/4 position of the plate thickness was −40 ° C. or lower and the vTrs on the steel plate surface was −80 ° C. or lower.
　また、鋼板の集合組織を評価するため、板厚中央における圧延面での（２１１）面集積度および鋼板表面（鋼板表面とは、極表面から表面下１ｍｍの範囲をいう。）における圧延面での（２００）面集積度をそれぞれ測定した。 Further, in order to evaluate the texture of the steel plate, the (211) plane integration degree at the rolling surface at the center of the plate thickness and the rolling surface on the steel plate surface (the steel plate surface means a range from the extreme surface to 1 mm below the surface). The (200) plane integration degree was measured.
　面集積度は、Ｘ線回折装置（理学電機株式会社製）を使用し、Ｍｏ線源を用いて測定を行った。 The degree of surface integration was measured using an X-ray diffractometer (manufactured by Rigaku Corporation) and using a Mo ray source.
　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／ｍｍ１．５とも記す。）を求めた。Ｋｃａ（－１０℃）が６０００Ｎ／ｍｍ１．５以上のものを良好とした。 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 1.5 ). . A sample having a Kca (−10 ° C.) of 6000 N / mm 1.5 or more was considered good.
　表３にこれらの試験結果を示す。 Table 3 shows the results of these tests.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表３に示された結果から、本発明例は、板厚中央における圧延面での（２１１）面集積度が１．２以上で、かつ鋼板表面における圧延面での（２００）面集積度が１．７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ｖＴｒｓが－４０℃以下および鋼板表面におけるシャルピー破面遷移温度ｖＴｒｓが－８０℃以下で靭性に優れるとともに、Ｋｃａ（－１０℃）が６０００Ｎ／ｍｍ１．５以上と優れた脆性き裂伝播停止特性が得られた。 From the results shown in Table 3, the example of the present invention has a (211) plane integration degree of 1.2 or more at the rolling surface at the center of the plate thickness and a (200) plane integration degree at the rolling surface of the steel sheet surface. It has a texture of 1.7 or more, and has excellent toughness when the Charpy fracture surface transition temperature vTrs at ¼ position of the sheet thickness is −40 ° C. or less and the Charpy fracture surface transition temperature vTrs at the steel sheet surface is −80 ° C. or less. An excellent brittle crack propagation stop characteristic was obtained with a Kca (−10 ° C.) of 6000 N / mm 1.5 or more.
　一方、本発明を外れる比較例は、ＹＳ、ＴＳ、集合組織、ｖＴｒｓのいずれかを満足しない。また、Ｋｃａ（－１０℃）の値はすべて満足しない結果となった。 On the other hand, a comparative example that departs from the present invention does not satisfy any of YS, TS, texture, and vTrs. Further, all the values of Kca (−10 ° C.) were not satisfied.

Claims (5)

  1. 　質量％で、
    Ｃ：０．０３～０．２０％、
    Ｓｉ：０．０３～０．５％、
    Ｍｎ：０．５～２．２％、
    Ｐ：０．０１％以下、
    Ｓ：０．００５％以下、
    Ｔｉ：０．００５～０．０３％、
    Ａｌ：０．００５～０．０８０％
    およびＮ：０．００５０％以下
    を含有し、下記式（１）で定義されるＣｅｑが０．３６以上０．４０以下であり、残部がＦｅおよび不可避的不純物からなる成分組成と、
    板厚中央における圧延面での（２１１）面集積度が１．２以上であり、鋼板表面における圧延面での（２００）面集積度が１．７以上である集合組織を有し、
    板厚１／４位置におけるシャルピー破面遷移温度ｖＴｒｓが－４０℃以下であり、
    鋼板表面におけるシャルピー破面遷移温度ｖＴｒｓが－８０℃以下である板厚７０ｍｍ以上の脆性き裂伝播停止特性に優れた高強度極厚鋼板。
    Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｃｕ／１５＋Ｎｉ／１５＋Ｃｒ／５＋Ｍｏ／５＋Ｖ／５・・・（１）
    ここで、式（１）におけるＣ、Ｍｎ、Ｃｕ、Ｎｉ、Ｃｒ、ＭｏおよびＶは各元素の含有量（質量％）を意味し、含有しない場合は０とする。     % By mass
    C: 0.03 to 0.20%,
    Si: 0.03-0.5%,
    Mn: 0.5 to 2.2%
    P: 0.01% or less,
    S: 0.005% or less,
    Ti: 0.005 to 0.03%,
    Al: 0.005 to 0.080%
    And N: 0.0050% or less, the Ceq defined by the following formula (1) is 0.36 or more and 0.40 or less, and the balance is composed of Fe and inevitable impurities,
    The (211) plane integration degree at the rolling surface at the sheet thickness center is 1.2 or more, and the (200) plane integration degree at the rolling surface on the steel sheet surface has a texture of 1.7 or more,
    Charpy fracture surface transition temperature vTrs at ¼ thickness position is −40 ° C. or lower,
    A high-strength ultra-thick steel plate with excellent brittle crack propagation stopping characteristics with a thickness of 70 mm or more, with a Charpy fracture surface transition temperature vTrs of −80 ° C. or less on the steel plate surface.
    Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + Mo / 5 + V / 5 (1)
    Here, C, Mn, Cu, Ni, Cr, Mo and V in the formula (1) mean the content (% by mass) of each element, and 0 when not contained.
  2. 　前記成分組成は、さらに質量％で、
    Ｎｂ：０．００５～０．０５％、
    Ｃｕ：０．０５～１．０％、
    Ｎｉ：０．０５～１．５％
    およびＣｒ：０．０１～０．５％
    の１種または２種以上を含有する請求項１に記載の脆性き裂伝播停止特性に優れた高強度極厚鋼板。     The component composition is further mass%,
    Nb: 0.005 to 0.05%,
    Cu: 0.05 to 1.0%,
    Ni: 0.05 to 1.5%
    And Cr: 0.01 to 0.5%
    The high-strength heavy steel plate excellent in the brittle crack propagation stop characteristic of Claim 1 containing 1 type (s) or 2 or more types of these.
  3. 　前記成分組成は、さらに質量％で、
    Ｍｏ：０．０１～０．５％、
    Ｖ：０．００１～０．１０％、
    Ｂ：０．００３０％以下、
    Ｃａ：０．００５０％以下、
    ＲＥＭ：０．０１００％以下
    の１種または２種以上を含有する請求項１または２に記載の脆性き裂伝播停止特性に優れた高強度極厚鋼板。     The component composition is further mass%,
    Mo: 0.01 to 0.5%,
    V: 0.001 to 0.10%,
    B: 0.0030% or less,
    Ca: 0.0050% or less,
    REM: The high-strength extra heavy steel plate excellent in the brittle crack propagation stop property of Claim 1 or 2 containing 0.0100% or less of 1 type or 2 types or more.
  4. 　請求項１～３のいずれかに記載の成分組成を有する鋼素材を、１０００～１２００℃の温度に加熱した後、
    板厚中央の温度がオーステナイト再結晶温度域での累積圧下率が１０％以上、板厚中央の温度がオーステナイト未再結晶温度域での累積圧下率が５０％以上、板厚表面温度がＡｒ３変態点以下かつ板厚中央の温度がＡｒ３変態点以上の温度域のときの累積圧下率が２０％超えの条件で熱間圧延を行った後、
    ０．５℃／s以上の冷却速度にて５００℃以下の冷却停止温度まで冷却する板厚７０ｍｍ以上の脆性き裂伝播停止特性に優れた高強度極厚鋼板の製造方法。     After heating the steel material having the component composition according to any one of claims 1 to 3 to a temperature of 1000 to 1200 ° C,
    The temperature at the center of the plate thickness is 10% or more at the austenite recrystallization temperature range, the temperature at the center of the plate thickness is 50% or more at the austenite non-recrystallization temperature region, and the surface thickness of the plate is Ar 3. after the temperature below and mid-thickness transformation was carried out hot rolling under the conditions of cumulative rolling reduction exceeds 20% at the temperature range of not lower than Ar 3 transformation point,
    A method for producing a high-strength extra-thick steel plate excellent in brittle crack propagation stopping characteristics having a thickness of 70 mm or more, which is cooled to a cooling stopping temperature of 500 ° C. or less at a cooling rate of 0.5 ° C./s or more.
  5. 　５００℃以下の冷却停止温度まで冷却した後、板厚中央の温度がＡｃ１変態点未満の温度に焼戻す請求項４に記載の脆性き裂伝播停止特性に優れた高強度極厚鋼板の製造方法。 The manufacturing of the high strength extra heavy steel plate excellent in brittle crack propagation stopping property according to claim 4, wherein the steel plate is cooled to a cooling stop temperature of 500 ° C or lower and then tempered to a temperature below the Ac 1 transformation point. Method.
PCT/JP2017/003152 2016-02-24 2017-01-30 High strength ultra-thick steel plate having excellent brittle crack propagation stopping characteristics and manufaturing method of same WO2017145651A1 (en)

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