WO2016114146A1 - Thick high-toughness high-strength steel sheet and method for manufacturing same - Google Patents

Thick high-toughness high-strength steel sheet and method for manufacturing same Download PDF

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Publication number
WO2016114146A1
WO2016114146A1 PCT/JP2016/000197 JP2016000197W WO2016114146A1 WO 2016114146 A1 WO2016114146 A1 WO 2016114146A1 JP 2016000197 W JP2016000197 W JP 2016000197W WO 2016114146 A1 WO2016114146 A1 WO 2016114146A1
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Prior art keywords
toughness
less
steel sheet
thick
point
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PCT/JP2016/000197
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French (fr)
Japanese (ja)
Inventor
茂樹 木津谷
克行 一宮
長谷　和邦
Original Assignee
Ｊｆｅスチール株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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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 SG11201704242TA priority Critical patent/SG11201704242TA/en
Priority to CN201680005979.9A priority patent/CN107208212B/en
Priority to JP2016532648A priority patent/JP6048626B1/en
Priority to US15/543,364 priority patent/US20170369958A1/en
Priority to KR1020177019203A priority patent/KR101994784B1/en
Priority to CA2969200A priority patent/CA2969200C/en
Priority to EP16737217.6A priority patent/EP3246426B1/en
Publication of WO2016114146A1 publication Critical patent/WO2016114146A1/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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
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    • B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
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    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
    • B21B1/024—Forging or pressing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
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    • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
    • B21B1/026—Rolling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
    • B21B2001/028—Slabs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
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    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals

Definitions

  • the present invention relates to a thick, high-toughness, high-strength steel sheet used for steel structures such as buildings, bridges, shipbuilding, marine structures, construction machinery, tanks, and penstock, and a method for producing the same.
  • This invention is excellent in the toughness of a steel plate surface, the intensity
  • the steel sheet has a thickness of 100 mm or more and a yield strength of 620 MPa or more.
  • bainite or a mixed structure of bainite and martensite is formed in the thickness center during quenching. It is important to let For this purpose, it is necessary to add a large amount of alloy elements such as Mn, Ni, Cr, and Mo.
  • a martensitic structure is formed on the surface of the steel sheet, which has a higher cooling rate and lower toughness than the thickness center part. Therefore, in a high-strength steel plate having a thickness of 100 mm or more, it is difficult to achieve both surface toughness and strength and toughness inside the steel plate.
  • Non-Patent Document 1 describes a material with a plate thickness of 210 mm
  • Non-Patent Document 2 describes a material with a plate thickness of 180 mm.
  • the above non-patent document describes that the strength and toughness of the central portion of the plate thickness are good. However, there is no description about the toughness (Charpy impact property) of the steel sheet surface. Such thick materials are usually manufactured by a quenching and tempering process, but a martensite structure is formed on the surface of the steel plate, which has a faster cooling rate than the center of the plate thickness, and the toughness of the steel plate surface (Charpy impact properties). In view of the decrease in the thickness, the above-mentioned non-patent document does not describe the point of manufacturing a steel sheet that stably satisfies the toughness of the steel sheet surface.
  • the present invention has been made to solve the above-mentioned problems, and its object is to provide a thick-walled, high-toughness, high-strength steel sheet having both surface toughness and strength and toughness inside the steel sheet, and a method for producing the same. There is.
  • the inventors have made a microstructure for achieving both the toughness of the steel sheet surface and the strength and toughness at the center of the sheet thickness for a thick steel sheet having a yield strength of 620 MPa or more and a sheet thickness of 100 mm or more.
  • % which is the unit of the said ratio means volume%.
  • the steel composition (component composition) is appropriately selected and the cooling rate is low. It is also important that the microstructure can be martensite and / or bainite. For this purpose, it is necessary to appropriately select alloy components, and in particular, the carbon equivalent (Ceq) needs to be 0.65% or more. In addition to appropriate component design, it is also important to create a structure by hot working and heat treatment.
  • the present invention has been made by further studying the above knowledge, and provides the following.
  • Ceq IIW C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) /5 ⁇ 0.65 (1) (C L -C) / C L ⁇ 100 ⁇ 30 (2)
  • CL is defined by the following equation.
  • C L 0.2 ⁇ ( ⁇ 0.1 ⁇ (0.2 ⁇ Si) ⁇ 0.03 ⁇ (1.1 ⁇ Mn) ⁇ 0.12 ⁇ (0.2 ⁇ Cu) ⁇ 0.11 ⁇ ( 3-Ni) + 0.025 ⁇ (1.2-Cr) + 0.1 ⁇ (0.5-Mo) + 0.2 ⁇ (0.04-V) ⁇ 0.05 ⁇ (0.06-Al)) (3)
  • the element symbol is the content (% by mass) of each alloy component, and 0 is not included.
  • Mg 0.0001 to 0.0050%
  • Ta 0.01 to 0.20%
  • Zr 0.005 to 0.1%
  • Y 0.001 to 0.00.
  • [6] A method for producing a thick, high toughness and high strength steel sheet according to any one of [1] to [5], wherein the steel material is heated to 1200 to 1350 ° C., and the cumulative reduction amount is 25% or more.
  • the hot forging is performed and heated to Ac3 point or higher and 1200 ° C or lower, hot rolled to a cumulative reduction of 40% or higher, allowed to cool, reheated to Ac3 point or higher and 1050 ° C or lower, and Ac3 point.
  • a method for producing a thick, high-toughness, high-strength steel sheet characterized by quenching from the above temperature to a lower temperature of 350 ° C. or lower or an Ar 3 point or lower and tempering at a temperature of 450 ° C. to 700 ° C.
  • a thick, high-toughness, high-strength steel sheet characterized by being rapidly cooled from a temperature of Ar 3 point or higher to 350 ° C or lower or a lower temperature of Ar 3 or lower and tempered at a temperature of 450 ° C. to 700 ° C. Method.
  • [8] A method for producing the thick, high toughness and high strength steel sheet according to any one of [1] to [5],
  • the steel material is heated to 1200 to 1350 ° C. and subjected to partial rolling to make the cumulative reduction amount 40% or more, and heated to the Ac3 point or more and 1200 ° C. or less, and the hot rolling to make the cumulative reduction amount 40% or more.
  • a method for producing a thick-walled, high-toughness, high-strength steel sheet is a method for producing a thick-walled, high-toughness, high-strength steel sheet.
  • the present invention it is possible to obtain a thick high toughness high strength steel sheet having a thickness of 100 mm or more and having a yield strength of 620 MPa or more and excellent toughness. If this thick-walled high-toughness high-strength steel plate is used, a steel structure with high safety can be produced.
  • the composition of the thick-walled, high-toughness, high-strength steel sheet of the present invention is, by mass, C: 0.08 to 0.20%, Si: 0.40% or less (including 0%), Mn: 0.0. 5 to 5.0%, P: 0.010% or less (including 0%), S: 0.0050% or less (including 0%), Cr: 3.0% or less (provided that 0) %), Ni: 0.1 to 5.0%, Al: 0.010 to 0.080%, N: 0.0070% or less (including 0%), O: 0.0025% or less (However, 0% is included).
  • C 0.08 to 0.20%
  • Si 0.40% or less
  • Mn 0.0. 5 to 5.0%
  • P 0.010% or less
  • S 0.0050% or less
  • Cr 3.0% or less
  • Ni 0.1 to 5.0%
  • N: 0.0070% or less including 0%
  • O 0.0025% or less
  • C 0.08 to 0.20%
  • C is an element useful for obtaining the strength required for structural steel at a low cost. In order to obtain the effect, the C content needs to be 0.08% or more. On the other hand, when the C content exceeds 0.20%, the toughness of the base metal and the welded portion is significantly deteriorated when a steel structure is produced by welding using a thick, high toughness and high strength steel plate. Therefore, the upper limit of the C content is set to 0.20%. The preferred C content is 0.08% to 0.14%.
  • Si 0.40% or less Si is added for deoxidation.
  • the steel sheet of the present invention may not contain Si. If the Si content exceeds 0.40%, the toughness of the base metal and the weld heat affected zone is significantly reduced when a steel structure is produced by welding using a thick, high toughness, high strength steel sheet. For this reason, Si content shall be 0.40% or less.
  • a preferred Si content is in the range of 0.05 to 0.3%. More preferably, it is in the range of 0.1 to 0.3%.
  • Mn 0.5 to 5.0% Mn is added from the viewpoint of securing the strength of the base material. If the Mn content is less than 0.5%, the effect is not sufficient. Further, when the Mn content exceeds 5.0%, the center segregation is promoted, the casting defect of the slab becomes large, and when the steel structure is manufactured by welding using a thick-walled high-toughness high-strength steel plate, The characteristics of the will deteriorate. Therefore, the upper limit of the Mn content is 5.0%.
  • the Mn content is preferably in the range of 0.6 to 2%, more preferably 0.6 to 1.6%.
  • the P content exceeds 0.010%, the toughness of the base material and the weld heat-affected zone is reduced when a steel structure is produced by welding using a thick, high-toughness, high-strength steel sheet. It drops significantly.
  • the P content is preferably as small as possible (it may not be included), and is limited to 0.010% or less.
  • the S content exceeds 0.0050%, when a steel structure is manufactured by welding using a thick-walled high-toughness high-strength steel sheet, the toughness of the base material and the weld heat-affected zone is low. Remarkably reduced. For this reason, the S content is preferably as small as possible (it may not be included), and is made 0.0050% or less.
  • Cr 3.0% or less Cr is an element effective for increasing the strength of the base material. However, when the Cr content is excessive, the weldability is lowered. Therefore, the Cr content is 3.0% or less.
  • a preferable Cr content is 0.1% to 2%. More preferably, it is in the range of 0.7% to 1.7%. Further, the Cr content may be 0%.
  • Ni 0.1-5.0%
  • Ni is a beneficial element that improves the strength of the steel and the toughness of the heat affected zone. In order to obtain this effect, the Ni content is set to 0.1% or more. On the other hand, if the Ni content exceeds 5.0%, the economic efficiency is significantly reduced. Therefore, the upper limit of the Ni content is 5.0%.
  • the Ni content is preferably 0.4 to 4%, more preferably 0.8% to 3.8%.
  • Al 0.010 to 0.080% Al is added to sufficiently deoxidize the molten steel. If the Al content is less than 0.010%, the effect is insufficient. On the other hand, when the Al content exceeds 0.080%, when a steel structure is produced by welding using a thick, high toughness, high strength steel sheet, the Al content that is dissolved in the base material increases, The toughness of the material decreases. Therefore, the Al content is set to 0.080% or less.
  • the Al content is preferably in the range of 0.030 to 0.080%, more preferably in the range of 0.030 to 0.070%.
  • N 0.0070% or less
  • N is a base material and weld when a microstructure is formed by forming a nitride with Ti or the like, and a steel structure is manufactured by welding using a thick, high toughness, high strength steel plate. It has the effect of improving the toughness of the heat affected zone. Since the effect of improving toughness can be obtained by a configuration other than N, the steel plate of the present invention may not contain N. However, from the viewpoint of obtaining this effect with N, the N content is preferably 0.0015% or more. On the other hand, when the N content exceeds 0.0070%, when a steel structure is produced by welding using a thick, high toughness, high strength steel plate, the amount of N dissolved in the base material increases.
  • the toughness is remarkably lowered, and coarse carbonitride is formed also in the weld heat affected zone, and the toughness is lowered. Therefore, the N content is set to 0.0070% or less. Preferably, it is 0.006% or less, more preferably 0.005% or less.
  • O 0.0025% or less
  • the thick, high toughness and high strength steel sheet of the present invention can contain at least one of Cu, Mo, V, Nb and Ti for the purpose of further increasing the strength and / or toughness in addition to the above elements. .
  • Cu 0.50% or less If Cu is contained, the strength of steel can be improved without impairing toughness. If the Cu content exceeds 0.50%, the steel sheet surface may be cracked during hot working. Therefore, when Cu is contained, its content is set to 0.50% or less.
  • Mo 1.50% or less Mo contributes to increasing the strength of a base material when a steel structure is produced by welding using a thick, high-toughness, high-strength steel sheet. However, if the Mo content exceeds 1.50%, the hardness increases due to precipitation of alloy carbides, and the toughness decreases. Therefore, when Mo is contained, the upper limit of the Mo content is set to 1.50%. A preferable Mo content is in the range of 0.2% to 0.8%.
  • V 0.400% or less V contributes to the improvement of the strength and toughness of the base metal when a steel structure is produced by welding using a thick, high toughness, high strength steel plate. Further, V is effective for lowering solid solution N by precipitating as VN. However, if the V content exceeds 0.400%, the toughness decreases due to precipitation of hard VC. Therefore, when V is added, the V content is preferably 0.400% or less. More preferably, it is in the range of 0.01 to 0.1%.
  • Nb 0.100% or less Nb is effective because it is effective in improving the strength of the base material.
  • the upper limit of the Nb content is set to 0.100%. Preferably, it is 0.025% or less.
  • Ti 0.005 to 0.020% Ti produces TiN during heating, effectively suppresses coarsening of austenite, and when steel structures are produced by welding using thick, high toughness, high strength steel sheets, the toughness of the base metal and the weld heat affected zone To improve.
  • the Ti content exceeds 0.020%, the Ti nitride becomes coarse and the toughness of the base material is lowered. Therefore, when Ti is contained, the Ti content is in the range of 0.005% to 0.020%. Preferably, it is in the range of 0.008% to 0.015%.
  • the thick-walled high-toughness high-strength steel sheet of the present invention can contain at least one of Mg, Ta, Zr, Y, B, Ca, and REM for the purpose of further improving the material. .
  • Mg 0.0001 to 0.0050%
  • Mg is an effective element for forming a stable oxide at a high temperature, effectively suppressing the coarsening of old ⁇ grains in the weld heat affected zone, and improving the toughness of the weld zone.
  • the Mg content is set to 0.0001% or more. However, if the Mg content exceeds 0.0050%, the amount of inclusions increases and the toughness decreases. Therefore, when Mg is contained, its content is preferably 0.0050% or less. More preferably, it is in the range of 0.0001% to 0.015%.
  • Ta 0.01-0.20% Adding an appropriate amount of Ta is effective for improving the strength. Specifically, it is effective to make the Ta content 0.01% or more. However, when the content exceeds 0.20%, the toughness decreases due to the formation of precipitates. Therefore, when Ta is contained, its content is set to 0.01% to 0.20%.
  • Zr 0.005 to 0.1%
  • Zr is an element effective for increasing the strength. In order to obtain this effect, it is effective to make the Zr content 0.005% or more. On the other hand, when the Zr content exceeds 0.1%, coarse precipitates are generated and the toughness is lowered. Therefore, when Zr is contained, the content is made 0.005 to 0.1%.
  • Y 0.001 to 0.01%
  • Y is an element effective for forming a stable oxide at a high temperature, effectively suppressing the coarsening of the old ⁇ grains in the weld heat affected zone, and improving the toughness of the weld zone. In order to obtain this effect, it is effective to make the Y content 0.001% or more. However, if the Y content exceeds 0.01%, the amount of inclusions increases and the toughness decreases. Therefore, when Y is contained, the content is made 0.001 to 0.01%.
  • B 0.0030% or less B has the effect of suppressing the ferrite transformation from the grain boundary by segregating at the austenite grain boundary and increasing the hardenability. However, if the B content exceeds 0.0030%, B precipitates as a carbonitride, lowering the hardenability and lowering the toughness. Therefore, the B content is set to 0.0030% or less. When B is contained, its content is preferably in the range of 0.0003 to 0.0030%. More preferably, it is in the range of 0.0005 to 0.002%.
  • Ca 0.0005 to 0.0050%
  • Ca is an element useful for controlling the morphology of sulfide inclusions. In order to exhibit the effect, it is necessary to make Ca content 0.0005% or more. However, if the Ca content exceeds 0.0050%, the cleanliness is lowered and the toughness is deteriorated. Therefore, when Ca is contained, its content is preferably 0.0050% or less. More preferably, it is in the range of 0.0005% to 0.0025%.
  • REM 0.0005 to 0.0100% REM also has the effect of improving material quality by forming oxides and sulfides in steel like Ca.
  • the REM content needs to be 0.0005% or more.
  • the REM content is saturated.
  • the content shall be 0.0100% or less.
  • the preferred REM content is in the range of 0.0005 to 0.005%.
  • Ceq IIW ⁇ 0.65%
  • Ceq IIW C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) /5 ⁇ 0.65 (1)
  • each element symbol in a formula shows content (mass%) of each element. In addition, 0 is not included.
  • a steel plate having good characteristics can be obtained even when it is manufactured from a steel material cast at a cooling rate of 1 ° C./s or less when the slab surface is solidified. .
  • the cooling rate during solidification of the slab surface is 1 ° C./s.
  • the primary crystal at the time of solidification must be the ⁇ phase, and the ratio of the ⁇ phase at the start of the ⁇ phase generation ((C L -C) / C L ⁇ 100) must be 30% or more.
  • C L 0.2 ⁇ ( ⁇ 0.1 ⁇ (0.2 ⁇ Si) ⁇ 0.03 ⁇ (1.1 ⁇ Mn) ⁇ 0.12 ⁇ (0.2 ⁇ Cu) ⁇ 0.11 ⁇ ( 3-Ni) + 0.025 ⁇ (1.2-Cr) + 0.1 ⁇ (0.5-Mo) + 0.2 ⁇ (0.04-V) ⁇ 0.05 ⁇ (0.06-Al)) (3)
  • the element symbol is the content (% by mass) of each alloy component, and 0 is not included.
  • the coefficient was determined based on the result of calculating the influence of the alloy element on the C solid solubility limit (C L ) of the ⁇ phase using the thermodynamic calculation software “Thermo-Calc”. For example, the coefficient “-0.1” of “Si” indicates that when 1% Si is contained, the solid solubility limit of C in the ⁇ phase decreases by 0.1%, and the necessary ⁇ phase ratio is ensured. This indicates that the C content of the base material needs to be reduced.
  • the present invention 0.12% of C as a component on which to base the calculation of C L in 0.2% of Si, and Mn 1.1%, 0.2% and Cu, 1.2% of Cr,
  • the coefficient is calculated by calculating the change from the amount of solute C when the content of each alloy element is changed with Ni 3%, Mo 0.5%, V 0.04% and Al 0.06%. It was.
  • the percentage of C added to the solid solubility limit of C in the ⁇ phase calculated in this way: (C L -C) / C L ⁇ 100 is set to 30% or more, so that at the start of ⁇ phase generation.
  • the ratio of the ⁇ phase can be 30% or more.
  • the diaphragm in the thickness direction at the center of the thickness measured by the method described in the examples is 40% or more.
  • the temperature “° C.” means the temperature at the center of the plate thickness excluding the quenching temperature when quenching without cooling after rolling.
  • the quenching temperature when quenching without cooling after rolling is the steel sheet surface temperature. This is because the steel plate temperature distribution in the plate thickness direction increases during rolling, and it is necessary to consider the temperature drop on the steel plate surface.
  • the temperature at the center of the plate thickness is obtained by simulation calculation or the like from the plate thickness, surface temperature, cooling conditions, and the like. For example, the plate thickness center temperature is obtained by calculating the temperature distribution in the plate thickness direction using the difference method.
  • the partial thickness rolling may be performed to reduce the thickness of the material.
  • Conditions for hot forging of steel material A slab or steel slab having the above composition is heated to 1200 to 1350 ° C. If the reheating temperature is less than 1200 ° C, it will cause an increase in the load to secure the cumulative reduction amount of the predetermined hot working, and it will not be possible to secure a sufficient reduction amount, but it must be heated again during the processing if necessary. In some cases, the production efficiency must be reduced. For this reason, reheating temperature shall be 1200 degreeC or more. Further, when the alloy element addition amount is high as in the case of a steel having a carbon equivalent of 0.65% or more, the casting defects such as center porosity and zaku in the steel material are remarkably coarsened.
  • a slab or steel slab having the above composition is heated to 1200 to 1350 ° C. If the reheating temperature is less than 1200 ° C, it will cause an increase in the load to secure the cumulative reduction amount of the predetermined hot working, and it will not be possible to secure a sufficient reduction amount, but it must be heated again during the processing if necessary. In some cases, the production efficiency must be reduced. For this reason, reheating temperature shall be 1200 degreeC or more. In order to make the casting defect harmless by crimping and to obtain the effect of the present invention, the cumulative rolling amount may be 30% or more, but the cumulative rolling amount is from the viewpoint of excellent drawing (RA). Is preferably 40% or more. On the other hand, if the reheating temperature exceeds 1350 ° C., excessive energy is consumed, surface flaws are likely to occur due to the scale during heating, and the maintenance load after hot forging increases, so the upper limit is made 1350 ° C.
  • the steel material after forging is heated to an Ac3 transformation point or higher and 1200 ° C or lower in order to homogenize the steel into a single austenite structure.
  • the temperature is preferably 1000 ° C. or more and 1200 ° C. or less.
  • Ac3 transformation point a value calculated by the following formula (4) is used.
  • Ac3 937.2-476.5C + 56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr + 38.1Mo + 124.8V + 136.3Ti + 198.4Al + 3315B (4)
  • Each element symbol in the formula (4) indicates the content (% by mass) of each alloy element.
  • Hot rolling conditions The steel material is processed to a desired thickness by hot rolling.
  • the steel material is processed to a desired thickness by hot rolling.
  • the effect of grain size reduction and refinement of the old ⁇ grain size by heat treatment is fully demonstrated.
  • Construction is necessary. Specifically, by setting the cumulative reduction amount in rolling to 40% or more, it is possible to achieve grain sizing at the rolling stage even in the central portion of the plate thickness where recrystallization due to processing hardly occurs.
  • Heat treatment conditions In order to obtain the strength and toughness at the center of the plate thickness, in the present invention, it is allowed to cool after hot rolling (for example, air cooling) or 350 ° C. from a temperature of Ar 3 point or higher without being allowed to cool after hot rolling. Cool to the following temperature. When it is allowed to cool, it is reheated from Ac 3 point to 1050 ° C. and rapidly cooled from the temperature of Ac 3 point or higher to 350 ° C. or lower. The reheating temperature is set to 1050 ° C.
  • the quenching temperature is set to Ar3 point or higher because quenching is performed from the austenite single phase region.
  • the quenching stop temperature is set to a lower temperature of 350 ° C. or lower or Ar 3 point or lower in order to reliably obtain a transformed structure in the entire steel sheet. That is, the stop temperature needs to be Ar3 point or less and 350 ° C or less.
  • Ar3 transformation point a value calculated by the following formula (5) is used.
  • Ar3 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo (5)
  • Each element symbol in the formula (5) indicates the content (mass%) of each alloy element.
  • the quenching method is generally water cooling industrially, but the cooling rate is preferably as fast as possible. For this reason, the cooling method may be other than water cooling, for example, there is a method such as gas cooling.
  • Tempering conditions The reason for tempering at 450 to 700 ° C. after rapid cooling is as follows. Below 450 ° C., the residual stress removal effect is small. On the other hand, when the temperature exceeds 700 ° C., various carbides precipitate, and when a steel structure is manufactured by welding using a thick, high toughness, high strength steel sheet, the structure of the base material becomes coarse, and the strength and toughness are reduced. Decrease significantly.
  • quenching may be repeated, but at the time of final quenching, it is necessary to heat from Ac 3 point to 1050 ° C., then rapidly cool to 350 ° C. or less, and then temper at 450 to 700 ° C. .
  • [delta] phase fraction for each of the base metal components using the value of the C content value and the base material of C L obtained by formula (3) is a value calculated by equation (2).
  • the cooling rate at the time of solidification when manufacturing the steel material is a value calculated by heat transfer calculation based on data obtained by measuring the temperature of the mold surface with a radiation thermometer.
  • Tensile test A round bar tensile test piece ( ⁇ 12.5 mm, GL50 mm) was sampled in the direction perpendicular to the rolling direction from the center of the thickness of each steel plate, and the yield strength (YS) and tensile strength (TS) were measured.
  • Plate Thickness Direction Tensile Test A plate thickness direction round bar tensile test piece ( ⁇ 10 mm) was collected from a region including the center portion of the thickness of each steel plate, and the drawing (RA) was measured. The drawing is the percentage of the difference between the minimum cross-sectional area and the original cross-sectional area after fracture of the test piece with respect to the original cross-sectional area.
  • test results are shown in Table 2. From these results, the steel sheets (sample Nos. 1 to 21 and 41) of the inventive examples in which the component composition of the steel complies with the present invention are all YS is 620 MPa or more, TS is 720 MPa or more, and the surface of the base material at ⁇ 40 ° C. It can also be seen that the toughness (vE-40) at the center of the plate thickness is 70 J or more, and the strength and toughness of the base material is excellent. No. 5 and 6; Comparison with 41 confirmed that the aperture (RA) was also good when the lump condition met a specific condition.
  • the comparative steel plates (sample Nos. 22 to 32) that deviate from the component composition of the present invention have a YS of the base material of less than 620 MPa, a TS of less than 720 MPa, and a toughness (vE-40) of less than 70 J. It corresponds to any one or more of, and the characteristic is inferior.

Abstract

Provided is a technique whereby internal strength and toughness in a steel sheet and toughness of the surface thereof are both obtained at the same time. A thick high-toughness high-strength steel sheet having a specific composition and excellent toughness of the steel sheet surface and internal strength and toughness in the steel sheet, the steel sheet being manufactured from a steel raw material cast under conditions of a cooling rate of 1°C/s during solidification of the surface thereof, and the toughness (vE – 40) of the steel sheet surface being 70 J or greater and the sheet thickness being 100 mm or greater.

Description

厚肉高靭性高強度鋼板およびその製造方法Thick, high toughness, high strength steel plate and method for producing the same
　本発明は、建築、橋梁、造船、海洋構造物、建産機、タンク、ペンストックなど鋼製構造物に用いられる厚肉高靭性高強度鋼板およびその製造方法に関する。本発明は、特に、鋼板表面の靭性と鋼板内部の強度、靭性に優れたものである。なお、本鋼板は、板厚１００ｍｍ以上、かつ降伏強度が６２０ＭＰａ以上のものである。 The present invention relates to a thick, high-toughness, high-strength steel sheet used for steel structures such as buildings, bridges, shipbuilding, marine structures, construction machinery, tanks, and penstock, and a method for producing the same. Especially this invention is excellent in the toughness of a steel plate surface, the intensity | strength inside a steel plate, and toughness. The steel sheet has a thickness of 100 mm or more and a yield strength of 620 MPa or more.
　建築、橋梁、造船、海洋構造物、建産機、タンク、ペンストック等の各分野で鋼材が使用される場合、通常、所望の形状になるように鋼材は溶接される。近年、鋼構造物の大型化が著しく進展しており、使用される鋼材の高強度化や厚肉化が顕著に進んでいる。 When steel materials are used in various fields such as architecture, bridges, shipbuilding, offshore structures, construction machinery, tanks, penstock, etc., the steel materials are usually welded so as to have a desired shape. In recent years, the size of steel structures has been remarkably increased, and the strength and thickness of steel materials used have been remarkably advanced.
　板厚１００ｍｍ以上の厚肉かつ高強度の鋼板で、板厚中心部の強度、靭性に優れた鋼板を製造しようとしても、板厚中心部は、冷却速度が低下することで、フェライトなど比較的低強度の組織が形成されやすくなる。そこで、そのような組織の生成を抑制するために、多量の合金元素を添加することが必要となる。 Even when trying to manufacture a steel plate with a thickness of 100 mm or more and a high strength steel plate with excellent strength and toughness at the center of the thickness, the central thickness of the plate is relatively low due to the reduced cooling rate. A low-strength structure is easily formed. Therefore, in order to suppress the formation of such a structure, it is necessary to add a large amount of alloy elements.
　特に、厚肉材（板厚１００ｍｍ以上の厚肉鋼板）の板厚中心部の強度と靭性を満足させるためには、焼入時にベイナイトまたはベイナイトとマルテンサイトの混合組織を板厚中心部に形成させることが重要である。これには、Ｍｎ、Ｎｉ、Ｃｒ、Ｍｏ等の合金元素を多量に添加する必要がある。 In particular, in order to satisfy the strength and toughness of the thickness center of thick materials (thick steel plates with a thickness of 100 mm or more), bainite or a mixed structure of bainite and martensite is formed in the thickness center during quenching. It is important to let For this purpose, it is necessary to add a large amount of alloy elements such as Mn, Ni, Cr, and Mo.
　また、鋼板表面においては板厚中心部に比べて冷却速度が速く靭性が低いマルテンサイト組織が形成される。そのため、板厚１００ｍｍ以上の高強度鋼板において、表面の靭性と鋼板内部の強度、靭性を両立させることは困難である。 Also, a martensitic structure is formed on the surface of the steel sheet, which has a higher cooling rate and lower toughness than the thickness center part. Therefore, in a high-strength steel plate having a thickness of 100 mm or more, it is difficult to achieve both surface toughness and strength and toughness inside the steel plate.
　本特許に関連する鋼板を記載した文献として、例えば次の２件の非特許文献が存在する。非特許文献１では、板厚２１０ｍｍの材料に関する記載があり、非特許文献２では、板厚１８０ｍｍの材料に関する記載がある。 There are, for example, the following two non-patent documents as documents describing steel sheets related to this patent. Non-Patent Document 1 describes a material with a plate thickness of 210 mm, and Non-Patent Document 2 describes a material with a plate thickness of 180 mm.
　上記の非特許文献には、板厚中心部の強度、靭性が良好であることが記載されている。しかし、鋼板表面の靭性（シャルピー衝撃特性）についての記述がない。このような厚肉材は、通常焼入れ焼もどしプロセスで製造されるが、板厚中心部に比べて冷却速度が速い鋼板表面では、マルテンサイト組織が形成され、鋼板表面の靭性（シャルピー衝撃特性）が低下することを考慮すれば、上記の非特許文献には、鋼板表面の靭性をも安定的に満足する鋼板を製造する点が記載されていない。 The above non-patent document describes that the strength and toughness of the central portion of the plate thickness are good. However, there is no description about the toughness (Charpy impact property) of the steel sheet surface. Such thick materials are usually manufactured by a quenching and tempering process, but a martensite structure is formed on the surface of the steel plate, which has a faster cooling rate than the center of the plate thickness, and the toughness of the steel plate surface (Charpy impact properties). In view of the decrease in the thickness, the above-mentioned non-patent document does not describe the point of manufacturing a steel sheet that stably satisfies the toughness of the steel sheet surface.
　本発明は、上記課題を解決するためになされたものであり、その目的は、表面の靭性と鋼板内部の強度、靭性を両立させた、厚肉高靭性高強度鋼板およびその製造方法を提供することにある。 The present invention has been made to solve the above-mentioned problems, and its object is to provide a thick-walled, high-toughness, high-strength steel sheet having both surface toughness and strength and toughness inside the steel sheet, and a method for producing the same. There is.
　本発明者らは、上記課題を解決するため、降伏強度６２０ＭＰａ以上かつ板厚１００ｍｍ以上の厚鋼板を対象に、鋼板表面の靭性と板厚中心部における強度及び靭性とを両立させるためのミクロ組織制御因子について鋭意研究を行い、以下の知見を得た。 In order to solve the above-mentioned problems, the inventors have made a microstructure for achieving both the toughness of the steel sheet surface and the strength and toughness at the center of the sheet thickness for a thick steel sheet having a yield strength of 620 MPa or more and a sheet thickness of 100 mm or more. We have earnestly studied the control factors and obtained the following findings.
　１．原料となる鋼素材の凝固時の冷却速度が１℃／sを超える場合は、ミクロ偏析の形成と凝固反応が競合する。その結果、ミクロ偏析が軽減される。大型の鋼素材を製造する場合、上記鋼素材の凝固時の冷却速度が１℃／s以下まで低下する結果、ミクロ編成が顕著になる。そのような場合でも、焼入時にマルテンサイト組織となる鋼板表面において良好な靭性を得るためには、Ｐ含有量の低減に加えて、凝固時のミクロ偏析を低減することが重要である。さらに凝固時の初晶をδ相とし、γ相生成開始時におけるδ相の比率を３０％以上とすることでミクロ偏析が低減し靭性が向上する。なお、上記比率の単位である％は、体積％を意味する。 1. When the cooling rate at the time of solidification of the raw steel material exceeds 1 ° C./s, the formation of microsegregation competes with the solidification reaction. As a result, microsegregation is reduced. When producing a large steel material, the cooling rate during solidification of the steel material is reduced to 1 ° C./s or less, and as a result, micro-knitting becomes prominent. Even in such a case, in order to obtain good toughness on the surface of the steel sheet that becomes a martensite structure during quenching, it is important to reduce microsegregation during solidification in addition to reducing the P content. Further, by setting the primary crystal upon solidification to the δ phase and the ratio of the δ phase at the start of γ phase generation to 30% or more, microsegregation is reduced and toughness is improved. In addition,% which is the unit of the said ratio means volume%.
　２．熱間加工後の冷却時に、鋼板表面に比べて著しく冷却速度が低い板厚中心部において良好な強度、靭性を得るためには、鋼組成（成分組成）を適切に選定し、低い冷却速度においてもミクロ組織をマルテンサイトおよび／またはベイナイト組織にできることが重要である。そのためには、合金成分を適切に選定する必要があり、特に炭素当量（Ｃｅｑ）を０．６５%以上とする必要がある。また、適切な成分設計に加えて、熱間加工および熱処理による組織の造りこみも重要である。 2. In order to obtain good strength and toughness at the center of the plate thickness where the cooling rate is significantly lower than that of the steel plate surface during cooling after hot working, the steel composition (component composition) is appropriately selected and the cooling rate is low. It is also important that the microstructure can be martensite and / or bainite. For this purpose, it is necessary to appropriately select alloy components, and in particular, the carbon equivalent (Ceq) needs to be 0.65% or more. In addition to appropriate component design, it is also important to create a structure by hot working and heat treatment.
　３．靭性を改善するためには、旧γ粒径の微細化が有効である。熱処理後の旧γ粒径の微細化には、熱処理前の旧γ粒径の微細化、すなわち熱間加工ままでの旧γ粒径の微細化が重要である。このためには、適切な熱間加工条件および圧延条件の選定が重要である。 3. In order to improve the toughness, it is effective to refine the old γ grain size. To refine the old γ grain size after the heat treatment, it is important to refine the old γ grain size before the heat treatment, that is, refine the old γ grain size as it is during hot working. For this purpose, selection of appropriate hot working conditions and rolling conditions is important.
　本発明は、上記の知見にさらに検討を加えてなされたものであり、以下のものを提供する。 The present invention has been made by further studying the above knowledge, and provides the following.
　［１］質量％で、Ｃ：０．０８～０．２０％、Ｓｉ：０．４０％以下、Ｍｎ:０．５～５．０％、Ｐ:０．０１０％以下、Ｓ:０．００５０％以下、Ｃｒ:３．０％以下、Ｎｉ:０．１～５．０％、Ａｌ：０．０１０～０．０８０％、Ｎ：０．００７０％以下、Ｏ：０．００２５％以下を含有し、（１）式および（２）式の関係を満たし、残部はＦｅおよび不可避的不純物からなり、鋼板表面における靭性（ｖＥ－４０）が７０Ｊ以上であり、板厚が１００ｍｍ以上である、鋼板表面の靭性と鋼板内部の強度、靭性に優れた厚肉高靭性高強度鋼板。
ＣｅｑＩＩＷ＝Ｃ＋Ｍｎ／６＋（Ｃｕ＋Ｎｉ）／１５＋（Ｃｒ＋Ｍｏ＋Ｖ）／５≧０．６５　（１）
（ＣＬ－Ｃ）／ＣＬ×１００≧３０　（２）
ここでＣＬは次式で定義する。
ＣＬ＝０．２－（－０．１×（０．２－Ｓｉ）－０．０３×（１．１－Ｍｎ）－０．１２×（０．２－Ｃｕ）－０．１１×（３－Ｎｉ）＋０．０２５×（１．２－Ｃｒ）＋０．１×（０．５－Ｍｏ）＋０．２×（０．０４－Ｖ）－０．０５×（０．０６－Ａｌ））　（３）
ただし、上記式において元素記号は各合金成分の含有量（質量％）とし、含有しないものは０とする。 [1] By mass%, C: 0.08 to 0.20%, Si: 0.40% or less, Mn: 0.5 to 5.0%, P: 0.010% or less, S: 0.0050 %: Cr: 3.0% or less, Ni: 0.1-5.0%, Al: 0.010-0.080%, N: 0.0070% or less, O: 0.0025% or less And the balance of the formulas (1) and (2), the balance being Fe and inevitable impurities, the toughness (vE-40) on the steel plate surface is 70 J or more, and the plate thickness is 100 mm or more. A thick-walled, high-toughness, high-strength steel sheet with excellent surface toughness, internal strength and toughness.
Ceq IIW = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) /5≧0.65 (1)
(C L -C) / C L × 100 ≧ 30 (2)
Here, CL is defined by the following equation.
C L = 0.2 − (− 0.1 × (0.2−Si) −0.03 × (1.1−Mn) −0.12 × (0.2−Cu) −0.11 × ( 3-Ni) + 0.025 × (1.2-Cr) + 0.1 × (0.5-Mo) + 0.2 × (0.04-V) −0.05 × (0.06-Al)) (3)
However, in the above formula, the element symbol is the content (% by mass) of each alloy component, and 0 is not included.
　［２］更に、質量％で、Ｃｕ：０．５０％以下、Ｍｏ：１．５０％以下、Ｖ：０．４００％以下、Ｎｂ:０．１００％以下、Ｔｉ：０．００５％～０．０２０％の１種または２種以上を含有することを特徴とする［１］に記載の厚肉高靭性高強度鋼板。 [2] Further, in terms of mass%, Cu: 0.50% or less, Mo: 1.50% or less, V: 0.400% or less, Nb: 0.100% or less, Ti: 0.005% to 0.005. The thick-walled, high-toughness, high-strength steel sheet according to [1], containing 020% of one kind or two or more kinds.
　［３］更に、質量％で、Ｍｇ：０．０００１～０．００５０％、Ｔａ：０．０１～０．２０％、Ｚｒ：０．００５～０．１％、Ｙ：０．００１～０．０１％、Ｂ：０．００３０％以下、Ｃａ：０．０００５～０．００５０％、ＲＥＭ：０．０００５～０．０１００％の１種または２種を含有することを特徴とする［１］又は［２］に記載の厚肉高靭性高強度鋼板。 [3] Further, by mass, Mg: 0.0001 to 0.0050%, Ta: 0.01 to 0.20%, Zr: 0.005 to 0.1%, Y: 0.001 to 0.00. [01] characterized by containing one or two of 01%, B: 0.0030% or less, Ca: 0.0005 to 0.0050%, REM: 0.0005 to 0.0100% The thick-walled, high-toughness, high-strength steel sheet according to [2].
　［４］降伏強度が６２０ＭＰａ以上である［１］～［３］のいずれかに記載の厚肉高靭性高強度鋼板。 [4] The thick-walled, high-toughness, high-strength steel sheet according to any one of [1] to [3], wherein the yield strength is 620 MPa or more.
　［５］板厚中心の板厚方向の絞りが４０％以上であることを特徴とする［１］～［４］のいずれかに記載の厚肉高靭性高強度鋼板。 [5] The thick, high toughness and high strength steel plate according to any one of [1] to [4], wherein the drawing in the thickness direction at the thickness center is 40% or more.
　［６］［１］～［５］のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を２５％以上とする熱間鍛造を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、放冷し、Ａｃ３点以上１０５０℃以下に再加熱し、Ａｃ３点以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０℃～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。 [6] A method for producing a thick, high toughness and high strength steel sheet according to any one of [1] to [5], wherein the steel material is heated to 1200 to 1350 ° C., and the cumulative reduction amount is 25% or more. The hot forging is performed and heated to Ac3 point or higher and 1200 ° C or lower, hot rolled to a cumulative reduction of 40% or higher, allowed to cool, reheated to Ac3 point or higher and 1050 ° C or lower, and Ac3 point. A method for producing a thick, high-toughness, high-strength steel sheet, characterized by quenching from the above temperature to a lower temperature of 350 ° C. or lower or an Ar 3 point or lower and tempering at a temperature of 450 ° C. to 700 ° C.
　［７］［１］～［５］のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、
　鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を２５％以上とする熱間鍛造を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、Ａｒ３点℃以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０℃～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。 [7] A method for producing a thick, high toughness, high strength steel sheet according to any one of [1] to [5],
The steel material is heated to 1200 to 1350 ° C., and hot forging is performed to make the cumulative reduction amount 25% or more, and the steel material is heated to Ac 3 point or more and 1200 ° C. or less, and hot rolling to make the cumulative reduction amount 40% or more. A thick, high-toughness, high-strength steel sheet characterized by being rapidly cooled from a temperature of Ar 3 point or higher to 350 ° C or lower or a lower temperature of Ar 3 or lower and tempered at a temperature of 450 ° C. to 700 ° C. Method.
　［８］［１］～［５］のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、
　鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を４０％以上とする分塊圧延を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、放冷し、Ａｃ３点以上１０５０℃以下に再加熱し、Ａｃ３点以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。 [8] A method for producing the thick, high toughness and high strength steel sheet according to any one of [1] to [5],
The steel material is heated to 1200 to 1350 ° C. and subjected to partial rolling to make the cumulative reduction amount 40% or more, and heated to the Ac3 point or more and 1200 ° C. or less, and the hot rolling to make the cumulative reduction amount 40% or more. Perform, cool, reheat to Ac3 point or higher and 1050 ° C or lower, quench rapidly from Ac3 point or higher to 350 ° C or lower or Ar3 point or lower, and perform tempering at a temperature of 450 to 700 ° C A method for producing a thick-walled, high-toughness, high-strength steel sheet.
　［９］［１］～［５］のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、
　鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を４０％以上とする分塊圧延を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、Ａｒ３点℃以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０℃～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。 [9] A method for producing the thick, high toughness and high strength steel sheet according to any one of [1] to [5],
The steel material is heated to 1200 to 1350 ° C. and subjected to partial rolling to make the cumulative reduction amount 40% or more, and heated to the Ac3 point or more and 1200 ° C. or less, and the hot rolling to make the cumulative reduction amount 40% or more. A thick, high-toughness, high-strength steel sheet characterized by being rapidly cooled from a temperature of Ar 3 point or higher to 350 ° C or lower or a lower temperature of Ar 3 or lower and tempered at a temperature of 450 ° C. to 700 ° C. Method.
　本発明によれば、降伏強度が６２０ＭＰａ以上の強度を有するとともに、靭性にも優れた板厚１００ｍｍ以上の厚肉高靭性高強度鋼板が得られる。この厚肉高靭性高強度鋼板を用いれば、安全性の高い鋼構造物を製造することができる。 According to the present invention, it is possible to obtain a thick high toughness high strength steel sheet having a thickness of 100 mm or more and having a yield strength of 620 MPa or more and excellent toughness. If this thick-walled high-toughness high-strength steel plate is used, a steel structure with high safety can be produced.
　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.
　＜厚肉高靭性高強度鋼板＞
　本発明の厚肉高靭性高強度鋼板の成分組成は、質量％で、Ｃ：０．０８～０．２０％、Ｓｉ：０．４０％以下（但し、０％を含む）、Ｍｎ:０．５～５．０％、Ｐ:０．０１０％以下（但し、０％を含む）、Ｓ:０．００５０％以下（但し、０％を含む）、Ｃｒ:３．０％以下（但し、０％を含む）、Ｎｉ:０．１～５．０％、Ａｌ：０．０１０～０．０８０％、Ｎ：０．００７０％以下（但し、０％を含む）、Ｏ：０．００２５％以下（但し、０％を含む）を含有する。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。 <Thick wall high toughness high strength steel plate>
The composition of the thick-walled, high-toughness, high-strength steel sheet of the present invention is, by mass, C: 0.08 to 0.20%, Si: 0.40% or less (including 0%), Mn: 0.0. 5 to 5.0%, P: 0.010% or less (including 0%), S: 0.0050% or less (including 0%), Cr: 3.0% or less (provided that 0) %), Ni: 0.1 to 5.0%, Al: 0.010 to 0.080%, N: 0.0070% or less (including 0%), O: 0.0025% or less (However, 0% is included). Hereinafter, each component will be described. “%” Representing the content of the component means “mass%”.
　Ｃ：０．０８～０．２０％
　Ｃは、構造用鋼に求められる強度を安価に得るために有用な元素である。その効果を得るためにＣ含有量を０．０８％以上とする必要がある。一方、Ｃ含有量が０．２０％を超えると、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材および溶接部の靭性が顕著に劣化する。そこで、Ｃ含有量の上限を０．２０％とした。好ましいＣ含有量は０．０８％～０．１４％である。 C: 0.08 to 0.20%
C is an element useful for obtaining the strength required for structural steel at a low cost. In order to obtain the effect, the C content needs to be 0.08% or more. On the other hand, when the C content exceeds 0.20%, the toughness of the base metal and the welded portion is significantly deteriorated when a steel structure is produced by welding using a thick, high toughness and high strength steel plate. Therefore, the upper limit of the C content is set to 0.20%. The preferred C content is 0.08% to 0.14%.
　Ｓｉ：０．４０％以下
　Ｓｉは脱酸のために添加する。しかし、他の元素を脱酸のために添加する場合には、本発明の鋼板はＳｉを含まなくてもよい。Ｓｉ含有量が０．４０％を超えると、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材および溶接熱影響部の靭性が顕著に低下する。このため、Ｓｉ含有量は０．４０％以下とする。好ましいＳｉ含有量は０．０５～０．３％の範囲である。より好ましくは０．１～０．３％の範囲である。 Si: 0.40% or less Si is added for deoxidation. However, when other elements are added for deoxidation, the steel sheet of the present invention may not contain Si. If the Si content exceeds 0.40%, the toughness of the base metal and the weld heat affected zone is significantly reduced when a steel structure is produced by welding using a thick, high toughness, high strength steel sheet. For this reason, Si content shall be 0.40% or less. A preferred Si content is in the range of 0.05 to 0.3%. More preferably, it is in the range of 0.1 to 0.3%.
　Ｍｎ：０．５～５．０％
　Ｍｎは母材強度を確保する観点から添加する。Ｍｎ含有量が０．５％未満ではその効果が十分でない。また、Ｍｎ含有量が５．０％を超えると、中心偏析を助長しスラブの鋳造欠陥が大型化し、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材の特性が劣化する。そこで、Ｍｎ含有量の上限を５．０％とする。Ｍｎ含有量は、０．６～２％の範囲であることが好ましく、より好ましくは０．６～１．６％である。 Mn: 0.5 to 5.0%
Mn is added from the viewpoint of securing the strength of the base material. If the Mn content is less than 0.5%, the effect is not sufficient. Further, when the Mn content exceeds 5.0%, the center segregation is promoted, the casting defect of the slab becomes large, and when the steel structure is manufactured by welding using a thick-walled high-toughness high-strength steel plate, The characteristics of the will deteriorate. Therefore, the upper limit of the Mn content is 5.0%. The Mn content is preferably in the range of 0.6 to 2%, more preferably 0.6 to 1.6%.
　Ｐ：０．０１０％以下
　Ｐ含有量が０．０１０％を超えると、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材および溶接熱影響部の靭性が著しく低下する。このため、Ｐ含有量は少ないほど好ましく（含まなくてもよい）、０．０１０％以下に制限する。 P: 0.010% or less When the P content exceeds 0.010%, the toughness of the base material and the weld heat-affected zone is reduced when a steel structure is produced by welding using a thick, high-toughness, high-strength steel sheet. It drops significantly. For this reason, the P content is preferably as small as possible (it may not be included), and is limited to 0.010% or less.
　Ｓ：０．００５０％以下
　Ｓ含有量が０．００５０％を超えると、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材および溶接熱影響部の靭性が顕著に低下する。このため、Ｓ含有量は少ないほど好ましく（含まなくてもよい）、０．００５０％以下とする。 S: 0.0050% or less When the S content exceeds 0.0050%, when a steel structure is manufactured by welding using a thick-walled high-toughness high-strength steel sheet, the toughness of the base material and the weld heat-affected zone is low. Remarkably reduced. For this reason, the S content is preferably as small as possible (it may not be included), and is made 0.0050% or less.
　Ｃｒ：３．０％以下
　Ｃｒは、母材の高強度化に有効な元素である。しかし、Ｃｒ含有量が過剰になると溶接性が低下する。そこで、Ｃｒ含有量は３．０％以下とする。好ましいＣｒ含有量は、０．１％～２％である。より好ましくは、０．７％～１．７％の範囲である。また、Ｃｒ含有量は０％でもよい。 Cr: 3.0% or less Cr is an element effective for increasing the strength of the base material. However, when the Cr content is excessive, the weldability is lowered. Therefore, the Cr content is 3.0% or less. A preferable Cr content is 0.1% to 2%. More preferably, it is in the range of 0.7% to 1.7%. Further, the Cr content may be 0%.
　Ｎｉ：０．１～５．０％
　Ｎｉは、鋼の強度および溶接熱影響部の靭性を向上させる有益な元素である。この効果を得るためにＮｉ含有量を０．１％以上とする。一方、Ｎｉ含有量が５．０％を超えると、経済性が著しく低下する。そこで、Ｎｉ含有量の上限は５．０％とする。また、Ｎｉ含有量は、０．４～４％であることが好ましく、より好ましくは、０．８％～３．８％である。 Ni: 0.1-5.0%
Ni is a beneficial element that improves the strength of the steel and the toughness of the heat affected zone. In order to obtain this effect, the Ni content is set to 0.1% or more. On the other hand, if the Ni content exceeds 5.0%, the economic efficiency is significantly reduced. Therefore, the upper limit of the Ni content is 5.0%. The Ni content is preferably 0.4 to 4%, more preferably 0.8% to 3.8%.
　Ａｌ：０．０１０～０．０８０％
　Ａｌは溶鋼を十分に脱酸するために添加される。Ａｌ含有量が０．０１０％未満の場合はその効果が不十分である。一方、Ａｌ含有量が０．０８０％を超えると、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材中に固溶するＡｌ含有量が多くなり、母材靭性が低下する。そこで、Ａｌ含有量は０．０８０％以下とする。Ａｌ含有量は、０．０３０～０．０８０％の範囲であることが好ましく、より好ましくは、０．０３０～０．０７０％の範囲である。 Al: 0.010 to 0.080%
Al is added to sufficiently deoxidize the molten steel. If the Al content is less than 0.010%, the effect is insufficient. On the other hand, when the Al content exceeds 0.080%, when a steel structure is produced by welding using a thick, high toughness, high strength steel sheet, the Al content that is dissolved in the base material increases, The toughness of the material decreases. Therefore, the Al content is set to 0.080% or less. The Al content is preferably in the range of 0.030 to 0.080%, more preferably in the range of 0.030 to 0.070%.
　Ｎ：０．００７０％以下
　Ｎは、Ｔｉなどと窒化物を形成することによって組織を微細化し、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材および溶接熱影響部の靭性を向上させる効果を有する。この靭性向上の効果はＮ以外の構成により得ることができるため、本発明の鋼板はＮを含まなくてもよい。しかし、Ｎによりこの効果を得る観点からはＮ含有量を０．００１５％以上とすることが好ましい。一方、Ｎ含有量が０．００７０％を超えると、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材中に固溶するＮ量が増大し、母材靭性が著しく低下し、さらに溶接熱影響部においても粗大な炭窒化物を形成し靭性が低下する。そこで、Ｎ含有量は０．００７０％以下とする。好ましくは、０．００６％以下、より好ましくは０．００５％以下である。 N: 0.0070% or less N is a base material and weld when a microstructure is formed by forming a nitride with Ti or the like, and a steel structure is manufactured by welding using a thick, high toughness, high strength steel plate. It has the effect of improving the toughness of the heat affected zone. Since the effect of improving toughness can be obtained by a configuration other than N, the steel plate of the present invention may not contain N. However, from the viewpoint of obtaining this effect with N, the N content is preferably 0.0015% or more. On the other hand, when the N content exceeds 0.0070%, when a steel structure is produced by welding using a thick, high toughness, high strength steel plate, the amount of N dissolved in the base material increases. The toughness is remarkably lowered, and coarse carbonitride is formed also in the weld heat affected zone, and the toughness is lowered. Therefore, the N content is set to 0.0070% or less. Preferably, it is 0.006% or less, more preferably 0.005% or less.
　Ｏ:０．００２５％以下
　Ｏは、０．００２５％を超えると、鋼中で硬質な酸化物が生成し、靭性が顕著に低下する。そこで、Ｏ含有量は少ないほど好ましく（含まなくてもよい）、０．００２５％以下とする。 O: 0.0025% or less When O exceeds 0.0025%, a hard oxide is generated in the steel, and the toughness is significantly reduced. Therefore, the smaller the O content, the better (may not be included), and 0.0025% or less.
　本発明の厚肉高靭性高強度鋼板は、上記元素に加えて、強度及び／又は靭性をさらに高める目的で、Ｃｕ、Ｍｏ、Ｖ、Ｎｂ及びＴｉの中から少なくとも１種類を含有することができる。 The thick, high toughness and high strength steel sheet of the present invention can contain at least one of Cu, Mo, V, Nb and Ti for the purpose of further increasing the strength and / or toughness in addition to the above elements. .
　Ｃｕ：０．５０％以下
　Ｃｕを含有すれば、靭性を損なうことなく鋼の強度を向上させることができる。Ｃｕ含有量が０．５０％を超えると熱間加工時に鋼板表面に割れを生じる場合がある。そこで、Ｃｕを含有する場合、その含有量は０．５０％以下とする。 Cu: 0.50% or less If Cu is contained, the strength of steel can be improved without impairing toughness. If the Cu content exceeds 0.50%, the steel sheet surface may be cracked during hot working. Therefore, when Cu is contained, its content is set to 0.50% or less.
　Ｍｏ：１．５０％以下
　Ｍｏは、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材の高強度化に寄与する。しかし、Ｍｏ含有量が１．５０％を超えると、合金炭化物の析出による硬度の上昇を引き起こし、靭性が低下する。そこで、Ｍｏを含有する場合、Ｍｏ含有量の上限を１．５０％とする。好ましいＭｏ含有量は、０．２％～０．８％の範囲である。 Mo: 1.50% or less Mo contributes to increasing the strength of a base material when a steel structure is produced by welding using a thick, high-toughness, high-strength steel sheet. However, if the Mo content exceeds 1.50%, the hardness increases due to precipitation of alloy carbides, and the toughness decreases. Therefore, when Mo is contained, the upper limit of the Mo content is set to 1.50%. A preferable Mo content is in the range of 0.2% to 0.8%.
　Ｖ：０．４００％以下
　Ｖは、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材の強度・靭性の向上に寄与する。また、Ｖは、ＶＮとして析出することで固溶Ｎの低下に有効である。しかし、Ｖ含有量が０．４００％を超えると硬質なＶＣの析出により靭性が低下する。そこで、Ｖを添加する場合は、Ｖ含有量を０．４００％以下とするのが好ましい。より好ましくは、０．０１～０．１％の範囲である。 V: 0.400% or less V contributes to the improvement of the strength and toughness of the base metal when a steel structure is produced by welding using a thick, high toughness, high strength steel plate. Further, V is effective for lowering solid solution N by precipitating as VN. However, if the V content exceeds 0.400%, the toughness decreases due to precipitation of hard VC. Therefore, when V is added, the V content is preferably 0.400% or less. More preferably, it is in the range of 0.01 to 0.1%.
　Ｎｂ:０．１００％以下
　Ｎｂは、母材の強度の向上に効果があるため有効である。Ｎｂ含有量が０．１００％を超えると、母材の靭性が顕著に低下する。そこで、Ｎｂ含有量の上限を０．１００％とする。好ましくは、０．０２５%以下である。 Nb: 0.100% or less Nb is effective because it is effective in improving the strength of the base material. When the Nb content exceeds 0.100%, the toughness of the base material is significantly reduced. Therefore, the upper limit of the Nb content is set to 0.100%. Preferably, it is 0.025% or less.
　Ｔｉ：０．００５～０．０２０％
　Ｔｉは加熱時にＴｉＮを生成し、オーステナイトの粗大化を効果的に抑制し、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材および溶接熱影響部の靭性を向上させる。しかし、Ｔｉ含有量が０．０２０％を超えると、Ｔｉ窒化物が粗大化し母材の靭性を低下させる。そこで、Ｔｉを含有する場合は、Ｔｉ含有量は０．００５％～０．０２０％の範囲とする。好ましくは、０．００８％～０．０１５％の範囲である。 Ti: 0.005 to 0.020%
Ti produces TiN during heating, effectively suppresses coarsening of austenite, and when steel structures are produced by welding using thick, high toughness, high strength steel sheets, the toughness of the base metal and the weld heat affected zone To improve. However, when the Ti content exceeds 0.020%, the Ti nitride becomes coarse and the toughness of the base material is lowered. Therefore, when Ti is contained, the Ti content is in the range of 0.005% to 0.020%. Preferably, it is in the range of 0.008% to 0.015%.
　本発明の厚肉高靭性高強度鋼板は、上記組成に加えて、さらに材質を改善する目的でＭｇ、Ｔａ、Ｚｒ、Ｙ、Ｂ、Ｃａ、ＲＥＭの中から少なくとも１種類を含有することができる。 In addition to the above composition, the thick-walled high-toughness high-strength steel sheet of the present invention can contain at least one of Mg, Ta, Zr, Y, B, Ca, and REM for the purpose of further improving the material. .
　Ｍｇ：０．０００１～０．００５０％
　Ｍｇは高温で安定な酸化物を形成し、溶接熱影響部の旧γ粒の粗大化を効果的に抑制し、溶接部の靭性を向上させるのに有効な元素である。この効果を得るためには、Ｍｇ含有量を０．０００１％以上とする。しかし、Ｍｇ含有量が０．００５０％を超えると、介在物量が増加し靭性が低下する。そこで、Ｍｇを含有する場合、その含有量は０．００５０％以下とするのが好ましい。より好ましくは、０．０００１％～０．０１５％の範囲である。 Mg: 0.0001 to 0.0050%
Mg is an effective element for forming a stable oxide at a high temperature, effectively suppressing the coarsening of old γ grains in the weld heat affected zone, and improving the toughness of the weld zone. In order to obtain this effect, the Mg content is set to 0.0001% or more. However, if the Mg content exceeds 0.0050%, the amount of inclusions increases and the toughness decreases. Therefore, when Mg is contained, its content is preferably 0.0050% or less. More preferably, it is in the range of 0.0001% to 0.015%.
　Ｔａ：０．０１～０．２０％
　Ｔａを適正量添加すると、強度向上に有効である。具体的にはＴａ含有量を０．０１％以上にすることが有効である。しかし、その含有量が０．２０％を超える場合は析出物生成により靭性が低下する。そこで、Ｔａを含有する場合、その含有量は０．０１％～０．２０％とする。 Ta: 0.01-0.20%
Adding an appropriate amount of Ta is effective for improving the strength. Specifically, it is effective to make the Ta content 0.01% or more. However, when the content exceeds 0.20%, the toughness decreases due to the formation of precipitates. Therefore, when Ta is contained, its content is set to 0.01% to 0.20%.
　Ｚｒ:０．００５～０．１％
　Ｚｒは強度上昇に有効な元素である。この効果を得るためにはＺｒ含有量を０．００５％以上にすることが有効である。一方、Ｚｒ含有量が０．１％を超える場合には粗大な析出物が生成し靭性が低下する。そこで、Ｚｒを含有する場合、その含有量は０．００５～０．１％とする。 Zr: 0.005 to 0.1%
Zr is an element effective for increasing the strength. In order to obtain this effect, it is effective to make the Zr content 0.005% or more. On the other hand, when the Zr content exceeds 0.1%, coarse precipitates are generated and the toughness is lowered. Therefore, when Zr is contained, the content is made 0.005 to 0.1%.
　Ｙ：０．００１～０．０１％
　Ｙは高温で安定な酸化物を形成し、溶接熱影響部の旧γ粒の粗大化を効果的に抑制し、溶接部の靭性を向上させるのに有効な元素である。この効果を得るためには、Ｙ含有量を０．００１％以上にすることが有効である。しかし、Ｙ含有量が０．０１％を超えると、介在物量が増加し靭性が低下する。そこで、Ｙを含有する場合、その含有量は、０．００１～０．０１％とする。 Y: 0.001 to 0.01%
Y is an element effective for forming a stable oxide at a high temperature, effectively suppressing the coarsening of the old γ grains in the weld heat affected zone, and improving the toughness of the weld zone. In order to obtain this effect, it is effective to make the Y content 0.001% or more. However, if the Y content exceeds 0.01%, the amount of inclusions increases and the toughness decreases. Therefore, when Y is contained, the content is made 0.001 to 0.01%.
　Ｂ：０．００３０％以下
　Ｂは、オーステナイト粒界に偏析することで粒界からのフェライト変態を抑制し、焼入性を高める効果を有する。しかし、Ｂ含有量が０．００３０％を超えると、Ｂは炭窒化物として析出し焼入性を低下させ靭性が低下する。そこで、Ｂ含有量は０．００３０％以下とする。Ｂを含有する場合、その含有量は０．０００３～０．００３０％の範囲とするのが好ましい。より好ましくは０．０００５～０．００２％の範囲である。 B: 0.0030% or less B has the effect of suppressing the ferrite transformation from the grain boundary by segregating at the austenite grain boundary and increasing the hardenability. However, if the B content exceeds 0.0030%, B precipitates as a carbonitride, lowering the hardenability and lowering the toughness. Therefore, the B content is set to 0.0030% or less. When B is contained, its content is preferably in the range of 0.0003 to 0.0030%. More preferably, it is in the range of 0.0005 to 0.002%.
　Ｃａ：０．０００５～０．００５０％
　Ｃａは硫化物系介在物の形態制御に有用な元素である。その効果を発揮させるためには、Ｃａ含有量を０．０００５％以上にすることが必要である。しかしＣａ含有量が０．００５０％を超えると、清浄度の低下を招き靭性が劣化する。そこで、Ｃａを含有する場合、その含有量は０．００５０％以下とするのが好ましい。より好ましくは０．０００５％～０．００２５％の範囲である。 Ca: 0.0005 to 0.0050%
Ca is an element useful for controlling the morphology of sulfide inclusions. In order to exhibit the effect, it is necessary to make Ca content 0.0005% or more. However, if the Ca content exceeds 0.0050%, the cleanliness is lowered and the toughness is deteriorated. Therefore, when Ca is contained, its content is preferably 0.0050% or less. More preferably, it is in the range of 0.0005% to 0.0025%.
　ＲＥＭ：０．０００５～０．０１００％
　ＲＥＭもＣａと同様に鋼中で酸化物および硫化物を形成して材質を改善する効果がある。その効果を得るためにはＲＥＭ含有量を０．０００５％以上にすることが必要である。しかし、ＲＥＭ含有量が０．０１００％を超えても、その効果が飽和する。そこで、ＲＥＭを含有する場合、その含有量は０．０１００％以下とする。好ましいＲＥＭ含有量は０．０００５～０．００５％の範囲である。 REM: 0.0005 to 0.0100%
REM also has the effect of improving material quality by forming oxides and sulfides in steel like Ca. In order to obtain the effect, the REM content needs to be 0.0005% or more. However, even if the REM content exceeds 0.0100%, the effect is saturated. Then, when it contains REM, the content shall be 0.0100% or less. The preferred REM content is in the range of 0.0005 to 0.005%.
　なお、上記任意元素の含有量が下限値未満の場合、これらの元素は本発明の効果を害さない。このため、上記任意元素の含有量が下限値未満の場合、これらの元素は不可避的不純物として含まれるとする。 In addition, when content of the said arbitrary element is less than a lower limit, these elements do not impair the effect of this invention. For this reason, when content of the said arbitrary elements is less than a lower limit, these elements shall be contained as an unavoidable impurity.
　ＣｅｑＩＩＷ≧０．６５％
　本発明では、板厚１００ｍｍ以上の厚肉高靭性高強度鋼板の板厚中心部において、降伏強度で６２０ＭＰａ以上の強度と良好な靭性を確保するために、適切な合金成分の添加が必要である。具体的には、下記の式（１）のとおり、炭素当量（ＣｅｑＩＩＷ）が０．６５％以上となるように合金元素の含有量を調整する必要がある。
ＣｅｑＩＩＷ＝Ｃ＋Ｍｎ／６＋（Ｃｕ＋Ｎｉ）／１５＋（Ｃｒ＋Ｍｏ＋Ｖ）／５≧０．６５　（１）
なお、式中の各元素記号はそれぞれの元素の含有量（質量％）を示す。また、含有しないものは０とする。 Ceq IIW ≧ 0.65%
In the present invention, it is necessary to add an appropriate alloy component in order to ensure a yield strength of 620 MPa or more and good toughness at the center of the thickness of a thick high toughness high strength steel sheet having a thickness of 100 mm or more. . Specifically, as shown in the following formula (1), it is necessary to adjust the content of the alloy element so that the carbon equivalent (Ceq IIW ) is 0.65% or more.
Ceq IIW = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) /5≧0.65 (1)
In addition, each element symbol in a formula shows content (mass%) of each element. In addition, 0 is not included.
　（ＣＬ－Ｃ）／ＣＬ×１００≧３０　（２）
　後述する通り、本発明によれば、スラブ表面の凝固時における冷却速度が１℃／s以下の範囲で鋳造される鋼素材から製造される場合であっても、良好な特性の鋼板が得られる。本発明では、板厚１００ｍｍ以上の厚肉高靭性高強度鋼板の鋼板表面において良好な靭性（ｖＥ－４０≧７０Ｊ）を満足するために、特にスラブ表面の凝固時における冷却速度が１℃／s以下の範囲で鋳造される鋼素材から製造される場合において、ミクロ偏析を低減する必要がある。そのためには、凝固時の初晶をδ相とし、γ相生成開始時におけるδ相の比率（（ＣＬ－Ｃ）／ＣＬ×１００）を３０％以上とする必要がある。
ＣＬ＝０．２－（－０．１×（０．２－Ｓｉ）－０．０３×（１．１－Ｍｎ）－０．１２×（０．２－Ｃｕ）－０．１１×（３－Ｎｉ）＋０．０２５×（１．２－Ｃｒ）＋０．１×（０．５－Ｍｏ）＋０．２×（０．０４－Ｖ）－０．０５×（０．０６－Ａｌ））　（３）
上記式（３）において元素記号は各合金成分の含有量（質量％）とし、含有しないものは０とする。 (C L -C) / C L × 100 ≧ 30 (2)
As will be described later, according to the present invention, a steel plate having good characteristics can be obtained even when it is manufactured from a steel material cast at a cooling rate of 1 ° C./s or less when the slab surface is solidified. . In the present invention, in order to satisfy good toughness (vE-40 ≧ 70 J) on the surface of a thick, high toughness, high strength steel sheet having a thickness of 100 mm or more, the cooling rate during solidification of the slab surface is 1 ° C./s. When manufactured from a steel material cast in the following range, it is necessary to reduce microsegregation. For this purpose, the primary crystal at the time of solidification must be the δ phase, and the ratio of the δ phase at the start of the γ phase generation ((C L -C) / C L × 100) must be 30% or more.
C L = 0.2 − (− 0.1 × (0.2−Si) −0.03 × (1.1−Mn) −0.12 × (0.2−Cu) −0.11 × ( 3-Ni) + 0.025 × (1.2-Cr) + 0.1 × (0.5-Mo) + 0.2 × (0.04-V) −0.05 × (0.06-Al)) (3)
In the above formula (3), the element symbol is the content (% by mass) of each alloy component, and 0 is not included.
　δ相形成には、ＳｉやＭｎ等のＣ以外の成分に応じてＣ量の範囲を規定する必要がある。δ相のＣ固溶限（ＣＬ）におよぼす合金元素の影響を熱力学計算ソフトウェア「Ｔｈｅｒｍｏ－Ｃａｌｃ」を用いて計算した結果を元に係数を決定した。例えば「Ｓｉ」の係数の「－０．１」は、Ｓｉを１％含有するとδ相のＣの固溶限が０．１％低下することを表しており、必要なδ相比率を確保するためには母材のＣ量を低下させる必要があることを示している。なお、本発明ではＣＬの計算のベースとなる成分としてＣを０．１２％、Ｓｉを０．２％、Ｍｎを１．１％、Ｃｕを０．２％、Ｃｒを１．２％、Ｎｉを３％、Ｍｏを０．５％、Ｖを０．０４％、Ａｌを０．０６％とし、各合金元素の含有量を変化させた場合の固溶Ｃ量からの変化を計算し係数とした。このようにして計算したδ相中のＣの固溶限に対して添加するＣの百分率：（ＣＬ－Ｃ）／ＣＬ×１００を３０％以上とすることで、γ相生成開始時におけるδ相の比率を３０％以上とすることができる。 For the δ phase formation, it is necessary to define the range of the C amount according to components other than C such as Si and Mn. The coefficient was determined based on the result of calculating the influence of the alloy element on the C solid solubility limit (C L ) of the δ phase using the thermodynamic calculation software “Thermo-Calc”. For example, the coefficient “-0.1” of “Si” indicates that when 1% Si is contained, the solid solubility limit of C in the δ phase decreases by 0.1%, and the necessary δ phase ratio is ensured. This indicates that the C content of the base material needs to be reduced. The present invention 0.12% of C as a component on which to base the calculation of C L in 0.2% of Si, and Mn 1.1%, 0.2% and Cu, 1.2% of Cr, The coefficient is calculated by calculating the change from the amount of solute C when the content of each alloy element is changed with Ni 3%, Mo 0.5%, V 0.04% and Al 0.06%. It was. The percentage of C added to the solid solubility limit of C in the δ phase calculated in this way: (C L -C) / C L × 100 is set to 30% or more, so that at the start of γ phase generation. The ratio of the δ phase can be 30% or more.
　また、本発明においては、実施例に記載の方法で測定した、板厚中心の板厚方向の絞りが４０％以上であることが鋼材の使用中の安全性を確保する観点から好ましい。 In the present invention, it is preferable from the viewpoint of ensuring safety during use of the steel that the diaphragm in the thickness direction at the center of the thickness measured by the method described in the examples is 40% or more.
　＜厚肉高靭性高強度鋼板の製造方法＞
　次に、本発明の製造条件について説明する。説明において、温度「℃」は、圧延後放冷せずに焼入れする場合の焼入れ温度を除き、板厚中心部における温度を意味するものとする。圧延後放冷せずに焼入れする場合の焼入れ温度は、鋼板表面温度とする。これは圧延時に板厚方向の鋼板温度分布が大きくなり、鋼板表面の温度低下を考慮する必要があるためである。板厚中心部の温度は、板厚、表面温度および冷却条件等から、シミュレーション計算等により求められる。例えば、差分法を用い、板厚方向の温度分布を計算することにより、板厚中心温度が求められる。 <Method for producing thick, high toughness, high strength steel sheet>
Next, the manufacturing conditions of the present invention will be described. In the description, the temperature “° C.” means the temperature at the center of the plate thickness excluding the quenching temperature when quenching without cooling after rolling. The quenching temperature when quenching without cooling after rolling is the steel sheet surface temperature. This is because the steel plate temperature distribution in the plate thickness direction increases during rolling, and it is necessary to consider the temperature drop on the steel plate surface. The temperature at the center of the plate thickness is obtained by simulation calculation or the like from the plate thickness, surface temperature, cooling conditions, and the like. For example, the plate thickness center temperature is obtained by calculating the temperature distribution in the plate thickness direction using the difference method.
　鋼素材
　上記組成の溶鋼を、転炉、電気炉、真空溶解炉等の通常の方法で溶製し、連続鋳造法および造塊法等の通常の鋳造方法でスラブ、ビレットなどの鋼素材とする。この時の凝固時の冷却速度は、熱電対等を用いた直接測定および伝熱計算などによるシミュレーション計算によって決定する方法がある。上記の通り、本発明では、鋼素材として、表面の凝固時における冷却速度が１℃／s以下の条件で製造されたものを好ましく用いることができる。 Steel material Molten steel of the above composition is melted by a normal method such as a converter, electric furnace, vacuum melting furnace, etc., and is made into a steel material such as a slab or billet by a normal casting method such as a continuous casting method or an ingot forming method. . There is a method of determining the cooling rate at the time of solidification at this time by direct measurement using a thermocouple or the like and simulation calculation such as heat transfer calculation. As above-mentioned, in this invention, what was manufactured on the conditions whose cooling rate at the time of solidification of the surface is 1 degrees C / s or less can be preferably used as a steel raw material.
　また、鍛造機および圧延機の荷重等の制約がある場合には、分塊圧延を行い、素材の板厚を小さくしてもよい。 Also, when there are restrictions such as the load on the forging machine and rolling machine, the partial thickness rolling may be performed to reduce the thickness of the material.
　鋼素材の熱間鍛造条件
　上述の組成を有する鋳片または鋼片を、１２００～１３５０℃に加熱する。再加熱温度が１２００℃未満では、所定の熱間加工の累積圧下量を確保するための荷重の増大を招き、十分な圧下量を確保できないばかりか、必要に応じて加工中に再度加熱しなければならない場合も発生し、製造能率の低下を招く。このため、再加熱温度は１２００℃以上とする。また、炭素当量が０．６５％以上の本鋼のように合金元素添加量が高い場合、鋼素材中のセンターポロシティやザクなどの鋳造欠陥が著しく粗大化する。それらを圧着して無害化するために、累積圧下量を２５％以上とする必要がある。一方、再加熱温度が１３５０℃を超えると、過大なエネルギーを消費し、加熱時のスケールにより表面疵が生じやすくなり、熱間鍛造後の手入れ負荷が増大するため、上限は１３５０℃とする。 Conditions for hot forging of steel material A slab or steel slab having the above composition is heated to 1200 to 1350 ° C. If the reheating temperature is less than 1200 ° C, it will cause an increase in the load to secure the cumulative reduction amount of the predetermined hot working, and it will not be possible to secure a sufficient reduction amount, but it must be heated again during the processing if necessary. In some cases, the production efficiency must be reduced. For this reason, reheating temperature shall be 1200 degreeC or more. Further, when the alloy element addition amount is high as in the case of a steel having a carbon equivalent of 0.65% or more, the casting defects such as center porosity and zaku in the steel material are remarkably coarsened. In order to make them harmless by pressure bonding, it is necessary to make the cumulative reduction amount 25% or more. On the other hand, if the reheating temperature exceeds 1350 ° C., excessive energy is consumed, surface flaws are likely to occur due to the scale during heating, and the maintenance load after hot forging increases, so the upper limit is made 1350 ° C.
　鋼素材の分塊圧延条件
　上述の組成を有する鋳片または鋼片を、１２００～１３５０℃に加熱する。再加熱温度が１２００℃未満では、所定の熱間加工の累積圧下量を確保するための荷重の増大を招き、十分な圧下量を確保できないばかりか、必要に応じて加工中に再度加熱しなければならない場合も発生し、製造能率の低下を招く。このため、再加熱温度は１２００℃以上とする。また、鋳造欠陥を圧着して無害化し、本発明の効果を得るためには、累積圧下量を３０％以上とすればよいが、絞り（ＲＡ）にも優れたものとする観点から累積圧下量を４０％以上とすることが好ましい。一方、再加熱温度が１３５０℃を超えると、過大なエネルギーを消費し、加熱時のスケールにより表面疵が生じやすくなり、熱間鍛造後の手入れ負荷が増大するため、上限は１３５０℃とする。 Condition of rolling the steel material A slab or steel slab having the above composition is heated to 1200 to 1350 ° C. If the reheating temperature is less than 1200 ° C, it will cause an increase in the load to secure the cumulative reduction amount of the predetermined hot working, and it will not be possible to secure a sufficient reduction amount, but it must be heated again during the processing if necessary. In some cases, the production efficiency must be reduced. For this reason, reheating temperature shall be 1200 degreeC or more. In order to make the casting defect harmless by crimping and to obtain the effect of the present invention, the cumulative rolling amount may be 30% or more, but the cumulative rolling amount is from the viewpoint of excellent drawing (RA). Is preferably 40% or more. On the other hand, if the reheating temperature exceeds 1350 ° C., excessive energy is consumed, surface flaws are likely to occur due to the scale during heating, and the maintenance load after hot forging increases, so the upper limit is made 1350 ° C.
　鍛造後または分塊圧延後の鋼素材の再加熱
　鍛造後の鋼素材をＡｃ３変態点以上１２００℃以下に加熱するのは、鋼をオーステナイト組織一相に均一化するためであり、加熱温度としては、１０００℃以上１２００℃以下とするのが好ましい。
なお、Ａｃ３変態点は、下記式（４）により計算される値を用いる。
Ａｃ３＝９３７．２－４７６．５Ｃ＋５６Ｓｉ－１９．７Ｍｎ－１６．３Ｃｕ－２６．６Ｎｉ－４．９Ｃｒ＋３８．１Ｍｏ＋１２４．８Ｖ＋１３６．３Ｔｉ＋１９８．４Ａｌ＋３３１５Ｂ　（４）
（４）式での各元素記号はそれぞれの合金元素の含有量（質量％）を示す。 Reheating of steel material after forging or after bulk rolling The steel material after forging is heated to an Ac3 transformation point or higher and 1200 ° C or lower in order to homogenize the steel into a single austenite structure. The temperature is preferably 1000 ° C. or more and 1200 ° C. or less.
As the Ac3 transformation point, a value calculated by the following formula (4) is used.
Ac3 = 937.2-476.5C + 56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr + 38.1Mo + 124.8V + 136.3Ti + 198.4Al + 3315B (4)
Each element symbol in the formula (4) indicates the content (% by mass) of each alloy element.
　熱間圧延条件
　鋼素材は、熱間圧延により所望の板厚に加工される。板厚１００ｍｍ以上の厚肉鋼板の板厚中心部の特性を確保するために、熱処理による旧γ粒径の整粒化、細粒化の効果を十分に発揮するため、圧延段階での材料のつくり込みが必要である。具体的には、圧延における累積圧下量を４０％以上とすることで、加工による再結晶が起こりにくい板厚中心部においても圧延段階で整粒化を図ることができる。 Hot rolling conditions The steel material is processed to a desired thickness by hot rolling. In order to ensure the properties of the center of the thickness of thick steel plates with a thickness of 100 mm or more, the effect of grain size reduction and refinement of the old γ grain size by heat treatment is fully demonstrated. Construction is necessary. Specifically, by setting the cumulative reduction amount in rolling to 40% or more, it is possible to achieve grain sizing at the rolling stage even in the central portion of the plate thickness where recrystallization due to processing hardly occurs.
　熱処理条件
　板厚中心部での強度と靭性を得るために、本発明では熱間圧延後放冷（例えば空冷）する、または、熱間圧延後放冷せずにＡｒ３点以上の温度から３５０℃以下の温度まで急冷する。放冷した場合は、Ａｃ３点～１０５０℃に再加熱し、Ａｃ３点以上の温度から３５０℃以下になるまで急冷する。再加熱温度を１０５０℃以下とするのは、１０５０℃を超える高温の再加熱ではオーステナイト粒の粗大化により、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材靭性の低下が著しく低下するためである。また、再加熱温度をＡｃ３点以上とするのは鋼板全体をオーステナイト組織にするためである。また、Ａｃ３点未満の温度ではフェライトとオーステナイトからなる不均一組織を形成し必要な特性が得られないため、焼入れ温度はＡｃ３点以上とする。また、放冷せずに急冷する場合は、オーステナイト単相域から焼入するため焼入温度はＡｒ３点以上とする。また、急冷の停止温度は鋼板全体で変態後の組織を確実に得るために３５０℃以下またはＡｒ３点以下の低い方の温度とする。つまり、停止温度はＡｒ３点以下且つ３５０℃以下である必要がある。
なお、Ａｒ３変態点は、下記式（５）により計算される値を用いる。
Ａｒ３＝９１０－３１０Ｃ－８０Ｍｎ－２０Ｃｕ－１５Ｃｒ－５５Ｎｉ－８０Ｍｏ　（５）
（５）式での各元素記号はそれぞれの合金元素の含有量（質量％）を示す。 Heat treatment conditions In order to obtain the strength and toughness at the center of the plate thickness, in the present invention, it is allowed to cool after hot rolling (for example, air cooling) or 350 ° C. from a temperature of Ar 3 point or higher without being allowed to cool after hot rolling. Cool to the following temperature. When it is allowed to cool, it is reheated from Ac 3 point to 1050 ° C. and rapidly cooled from the temperature of Ac 3 point or higher to 350 ° C. or lower. The reheating temperature is set to 1050 ° C. or lower because, when reheating at a high temperature exceeding 1050 ° C., austenite grains become coarse, and when a steel structure is produced by welding using a thick, high toughness, high strength steel plate, This is because the reduction in material toughness is significantly reduced. The reason for setting the reheating temperature to Ac3 or higher is to make the entire steel sheet an austenitic structure. Moreover, since the heterogeneous structure | tissue which consists of a ferrite and austenite is formed at the temperature below Ac3 point and a required characteristic is not acquired, hardening temperature shall be more than Ac3 point. Moreover, when quenching without allowing to cool, the quenching temperature is set to Ar3 point or higher because quenching is performed from the austenite single phase region. The quenching stop temperature is set to a lower temperature of 350 ° C. or lower or Ar 3 point or lower in order to reliably obtain a transformed structure in the entire steel sheet. That is, the stop temperature needs to be Ar3 point or less and 350 ° C or less.
As the Ar3 transformation point, a value calculated by the following formula (5) is used.
Ar3 = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo (5)
Each element symbol in the formula (5) indicates the content (mass%) of each alloy element.
　急冷の方法は、工業的には水冷とすることが一般的であるが、冷却速度は可能な限り速いほうが望ましい。このため、冷却方法は水冷以外でもよく、例えばガス冷却などの方法もある。 The quenching method is generally water cooling industrially, but the cooling rate is preferably as fast as possible. For this reason, the cooling method may be other than water cooling, for example, there is a method such as gas cooling.
　焼戻し条件
　急冷後、４５０～７００℃で焼戻す理由は以下の通りである。４５０℃未満では残留応力の除去効果が少ない。一方、７００℃を超える温度では、種々の炭化物が析出するとともに、厚肉高靭性高強度鋼板を用いて溶接により鋼構造物を製造したときに、母材の組織が粗大化し、強度、靭性が大幅に低下する。 Tempering conditions The reason for tempering at 450 to 700 ° C. after rapid cooling is as follows. Below 450 ° C., the residual stress removal effect is small. On the other hand, when the temperature exceeds 700 ° C., various carbides precipitate, and when a steel structure is manufactured by welding using a thick, high toughness, high strength steel sheet, the structure of the base material becomes coarse, and the strength and toughness are reduced. Decrease significantly.
　工業的には、鋼の強靭化を目的に繰返し焼入れする場合がある。本発明においても繰り返し焼入れしてもよいが、最終の焼入れの際に、Ａｃ３点～１０５０℃に加熱後、３５０℃以下になるまで急冷し、その後４５０～７００℃で焼もどすことが必要である。 Industrially, it may be repeatedly quenched for the purpose of strengthening steel. In the present invention, quenching may be repeated, but at the time of final quenching, it is necessary to heat from Ac 3 point to 1050 ° C., then rapidly cool to 350 ° C. or less, and then temper at 450 to 700 ° C. .
　表１に示したＮｏ．１～３０の鋼を、表２に示す条件で、溶製、鋳造し鋼素材とした後、熱間鍛造（試料番号５、６、４１以外）又は分塊圧延（試料番号５、６、４１）を行い、その後、熱間圧延により、表２に示す板厚の鋼板とし、その後、水焼入れ、焼戻し処理を行い、試料Ｎｏ．１～３８の鋼板を製造し、下記の試験に供した。なお、本例では再加熱焼入の場合は再加熱温度が焼入温度となる。 No. shown in Table 1. Steels 1 to 30 were melted and cast under the conditions shown in Table 2 to obtain steel materials, and then hot forging (other than sample numbers 5, 6, 41) or split rolling (sample numbers 5, 6, 41) After that, the steel plate having the thickness shown in Table 2 was obtained by hot rolling, and then water quenching and tempering treatment were performed. 1 to 38 steel plates were produced and subjected to the following tests. In this example, in the case of reheating and quenching, the reheating temperature is the quenching temperature.
　なお、δ相比率は、それぞれの母材成分について式（３）で得られるＣＬの値と母材のＣ量の値を用いて、（２）式により算出した値である。 Incidentally, [delta] phase fraction for each of the base metal components using the value of the C content value and the base material of C L obtained by formula (3) is a value calculated by equation (2).
　また、鋼素材製造時の凝固時の冷却速度は、放射温度計により鋳型表面の温度を測定したデータを元に伝熱計算により算出した値である。 In addition, the cooling rate at the time of solidification when manufacturing the steel material is a value calculated by heat transfer calculation based on data obtained by measuring the temperature of the mold surface with a radiation thermometer.
　引張試験
　各鋼板の板厚中心部から、圧延方向と直角方向に丸棒引張試験片（Φ１２．５ｍｍ、ＧＬ５０ｍｍ）を採取し、降伏強度（ＹＳ）、引張強度（ＴＳ）を測定した。 Tensile test A round bar tensile test piece (Φ12.5 mm, GL50 mm) was sampled in the direction perpendicular to the rolling direction from the center of the thickness of each steel plate, and the yield strength (YS) and tensile strength (TS) were measured.
　シャルピー衝撃試験
　各鋼板の鋼板表面および板厚中心部から圧延方向を長手方向とする２ｍｍＶノッチシャルピー試験片を各３本ずつ採取し、各試験片について、試験温度：－４０℃でシャルピー衝撃試験により吸収エネルギーを測定し、それらの平均値を求めた（板厚中心部の試験片の平均値および表面の試験片の平均値をそれぞれ求めた。）。 Charpy impact test Three 2mmV notch Charpy test pieces each having a rolling direction as the longitudinal direction were taken from the steel plate surface and the thickness center of each steel plate, and each test piece was subjected to a Charpy impact test at a test temperature of -40 ° C. The absorbed energy was measured, and the average value thereof was determined (the average value of the test piece at the center of the plate thickness and the average value of the test piece on the surface were respectively determined).
　板厚方向引張試験
　各鋼板の板厚中心部を含む領域について板厚方向丸棒引張試験片（Φ１０ｍｍ）を採取し、絞り（ＲＡ）を測定した。なお、絞りは試験片破断後における最小断面積とその原断面積との差の原断面積に対する百分率である。 Plate Thickness Direction Tensile Test A plate thickness direction round bar tensile test piece (Φ10 mm) was collected from a region including the center portion of the thickness of each steel plate, and the drawing (RA) was measured. The drawing is the percentage of the difference between the minimum cross-sectional area and the original cross-sectional area after fracture of the test piece with respect to the original cross-sectional area.
　上記の試験結果を表２に示す。この結果から、鋼の成分組成が本発明に適合する発明例の鋼板（試料Ｎｏ．１～２１、４１）は、いずれもＹSが６２０ＭＰａ以上、ＴＳが７２０ＭＰａ以上、－４０℃における母材の表面および板厚中心部の靭性（ｖＥ－４０）が７０Ｊ以上であり母材の強度・靭性に優れていることがわかる。また、Ｎｏ．５及び６と、Ｎｏ．４１との比較から、分塊条件が特定の条件を満たす場合には絞り（ＲＡ）も良好になることが確認された。 The test results are shown in Table 2. From these results, the steel sheets (sample Nos. 1 to 21 and 41) of the inventive examples in which the component composition of the steel complies with the present invention are all YS is 620 MPa or more, TS is 720 MPa or more, and the surface of the base material at −40 ° C. It can also be seen that the toughness (vE-40) at the center of the plate thickness is 70 J or more, and the strength and toughness of the base material is excellent. No. 5 and 6; Comparison with 41 confirmed that the aperture (RA) was also good when the lump condition met a specific condition.
　これに対して、本発明の成分組成を外れる比較例の鋼板（試料Ｎｏ．２２～３２）は、母材のＹＳが６２０ＭＰａ未満、ＴＳが７２０ＭＰａ未満、靭性（ｖＥ－４０）が７０Ｊ未満の中のいずれか１つ以上に該当しており特性が劣っている。 On the other hand, the comparative steel plates (sample Nos. 22 to 32) that deviate from the component composition of the present invention have a YS of the base material of less than 620 MPa, a TS of less than 720 MPa, and a toughness (vE-40) of less than 70 J. It corresponds to any one or more of, and the characteristic is inferior.
　また、試料Ｎｏ．３３～４０に示すように、鋼の成分組成が本発明に適合する鋼板でも製造条件が本発明条件（Ｎｏ．４１は累積圧下量が３０％であり、本発明の効果を得る上での最低条件は満たしているため、本発明条件範囲外ではないとする。）に適合していない場合、ＹＳ、ＴＳ、靭性（ｖＥ－４０）、のいずれか１つ以上の特性が劣っている。 Sample No. As shown in 33 to 40, even when the steel composition is in conformity with the present invention, the manufacturing conditions are the same as those of the present invention (No. 41 has a cumulative reduction amount of 30%, which is the minimum for obtaining the effects of the present invention. If the condition is satisfied and is not outside the range of the present invention), one or more of YS, TS, and toughness (vE-40) is inferior.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002

Claims (9)

  1. 　質量％で、Ｃ：０．０８～０．２０％、Ｓｉ：０．４０％以下、Ｍｎ:０．５～５．０％、Ｐ:０．０１０％以下、Ｓ:０．００５０％以下、Ｃｒ:３．０％以下、Ｎｉ:０．１～５．０％、Ａｌ：０．０１０～０．０８０％、Ｎ：０．００７０％以下、Ｏ：０．００２５％以下を含有し、（１）式および（２）式の関係を満たし、残部はＦｅおよび不可避的不純物からなり、
    　鋼板表面における靭性（ｖＥ－４０）が７０Ｊ以上であり、
    　板厚が１００ｍｍ以上である厚肉高靭性高強度鋼板。
    ＣｅｑＩＩＷ＝Ｃ＋Ｍｎ／６＋（Ｃｕ＋Ｎｉ）／１５＋（Ｃｒ＋Ｍｏ＋Ｖ）／５≧０．６５　（１）
    （ＣＬ－Ｃ）／ＣＬ×１００≧３０　（２）
    ここでＣＬは次式で定義する。
    ＣＬ＝０．２－（－０．１×（０．２－Ｓｉ）－０．０３×（１．１－Ｍｎ）－０．１２×（０．２－Ｃｕ）－０．１１×（３－Ｎｉ）＋０．０２５×（１．２－Ｃｒ）＋０．１×（０．５－Ｍｏ）＋０．２×（０．０４－Ｖ）－０．０５×（０．０６－Ａｌ））　（３）
    ただし、上記式において元素記号は各合金成分の含有量（質量％）とし、含有しないものは０とする。     In mass%, C: 0.08 to 0.20%, Si: 0.40% or less, Mn: 0.5 to 5.0%, P: 0.010% or less, S: 0.0050% or less, Cr: 3.0% or less, Ni: 0.1-5.0%, Al: 0.010-0.080%, N: 0.0070% or less, O: 0.0025% or less, 1) satisfying the relationship of the formula and the formula (2), the balance is composed of Fe and inevitable impurities,
    The toughness (vE-40) on the steel sheet surface is 70 J or more,
    A thick-walled, high-toughness, high-strength steel sheet having a thickness of 100 mm or more.
    Ceq IIW = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) /5≧0.65 (1)
    (C L -C) / C L × 100 ≧ 30 (2)
    Here, CL is defined by the following equation.
    C L = 0.2 − (− 0.1 × (0.2−Si) −0.03 × (1.1−Mn) −0.12 × (0.2−Cu) −0.11 × ( 3-Ni) + 0.025 × (1.2-Cr) + 0.1 × (0.5-Mo) + 0.2 × (0.04-V) −0.05 × (0.06-Al)) (3)
    However, in the above formula, the element symbol is the content (% by mass) of each alloy component, and 0 is not included.
  2. 　更に、質量％で、Ｃｕ：０．５０％以下、Ｍｏ：１．５０％以下、Ｖ：０．４００％以下、Ｎｂ:０．１００％以下、Ｔｉ：０．００５％～０．０２０％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１に記載の厚肉高靭性高強度鋼板。 Further, in terms of mass%, Cu: 0.50% or less, Mo: 1.50% or less, V: 0.400% or less, Nb: 0.100% or less, Ti: 0.005% to 0.020% The thick-walled, high-toughness, high-strength steel sheet according to claim 1, comprising one or more kinds.
  3. 　更に、質量％で、Ｍｇ：０．０００１～０．００５０％、Ｔａ：０．０１～０．２０％、Ｚｒ：０．００５～０．１％、Ｙ：０．００１～０．０１％、Ｂ：０．００３０％以下、Ｃａ：０．０００５～０．００５０％、ＲＥＭ：０．０００５～０．０１００％の１種または２種を含有することを特徴とする請求項１又は２に記載の厚肉高靭性高強度鋼板。 Further, by mass, Mg: 0.0001 to 0.0050%, Ta: 0.01 to 0.20%, Zr: 0.005 to 0.1%, Y: 0.001 to 0.01%, 3. One or two of B: 0.0030% or less, Ca: 0.0005 to 0.0050%, and REM: 0.0005 to 0.0100% are contained. Thick steel plate with high toughness and high strength.
  4. 　降伏強度が６２０ＭＰａ以上である請求項１～３のいずれかに記載の厚肉高靭性高強度鋼板。 The thick-walled, high-toughness, high-strength steel sheet according to any one of claims 1 to 3, wherein the yield strength is 620 MPa or more.
  5. 　板厚中心の板厚方向の絞りが４０％以上であることを特徴とする請求項１～４のいずれかに記載の厚肉高靭性高強度鋼板。 5. The thick-walled, high-toughness, high-strength steel sheet according to any one of claims 1 to 4, wherein the drawing in the thickness direction at the thickness center is 40% or more.
  6. 　請求項１～５のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、
    　鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を２５％以上とする熱間鍛造を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、放冷し、Ａｃ３点以上１０５０℃以下に再加熱し、Ａｃ３点以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。     A method for producing a thick, high toughness, high strength steel sheet according to any one of claims 1 to 5,
    The steel material is heated to 1200 to 1350 ° C., and hot forging is performed to make the cumulative reduction amount 25% or more, and the steel material is heated to Ac 3 point or more and 1200 ° C. or less, and hot rolling to make the cumulative reduction amount 40% or more. Perform, cool, reheat to Ac3 point or higher and 1050 ° C or lower, quench rapidly from Ac3 point or higher to 350 ° C or lower or Ar3 point or lower, and perform tempering at a temperature of 450 to 700 ° C A method for producing a thick-walled, high-toughness, high-strength steel sheet.
  7. 　請求項１～５のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、
    　鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を２５％以上とする熱間鍛造を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、Ａｒ３点℃以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０℃～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。     A method for producing a thick, high toughness, high strength steel sheet according to any one of claims 1 to 5,
    The steel material is heated to 1200 to 1350 ° C., and hot forging is performed to make the cumulative reduction amount 25% or more, and the steel material is heated to Ac 3 point or more and 1200 ° C. or less, and hot rolling to make the cumulative reduction amount 40% or more. A thick, high-toughness, high-strength steel sheet characterized by being rapidly cooled from a temperature of Ar 3 point or higher to 350 ° C or lower or a lower temperature of Ar 3 or lower and tempered at a temperature of 450 ° C. to 700 ° C. Method.
  8. 　請求項１～５のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、
    　鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を４０％以上とする分塊圧延を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、放冷し、Ａｃ３点以上１０５０℃以下に再加熱し、Ａｃ３点以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。     A method for producing a thick, high toughness, high strength steel sheet according to any one of claims 1 to 5,
    The steel material is heated to 1200 to 1350 ° C. and subjected to partial rolling to make the cumulative reduction amount 40% or more, and heated to the Ac3 point or more and 1200 ° C. or less, and the hot rolling to make the cumulative reduction amount 40% or more. Perform, cool, reheat to Ac3 point or higher and 1050 ° C or lower, quench rapidly from Ac3 point or higher to 350 ° C or lower or Ar3 point or lower, and perform tempering at a temperature of 450 to 700 ° C A method for producing a thick-walled, high-toughness, high-strength steel sheet.
  9. 　請求項１～５のいずれかに記載の厚肉高靭性高強度鋼板を製造する方法であって、
    　鋼素材を、１２００～１３５０℃に加熱し、累積圧下量を４０％以上とする分塊圧延を行い、Ａｃ３点以上１２００℃以下に加熱し、累積圧下量を４０％以上とする熱間圧延を行い、Ａｒ３点℃以上の温度から３５０℃以下またはＡｒ３点以下の低い方の温度まで急冷し、４５０℃～７００℃の温度で焼戻しを行うことを特徴とする厚肉高靭性高強度鋼板の製造方法。     A method for producing a thick, high toughness, high strength steel sheet according to any one of claims 1 to 5,
    The steel material is heated to 1200 to 1350 ° C. and subjected to partial rolling to make the cumulative reduction amount 40% or more, and heated to the Ac3 point or more and 1200 ° C. or less, and the hot rolling to make the cumulative reduction amount 40% or more. A thick, high-toughness, high-strength steel sheet characterized by being rapidly cooled from a temperature of Ar 3 point or higher to 350 ° C or lower or a lower temperature of Ar 3 or lower and tempered at a temperature of 450 ° C. to 700 ° C. Method.
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