WO2021054344A1 - 厚鋼板および厚鋼板の製造方法 - Google Patents
厚鋼板および厚鋼板の製造方法 Download PDFInfo
- Publication number
- WO2021054344A1 WO2021054344A1 PCT/JP2020/034995 JP2020034995W WO2021054344A1 WO 2021054344 A1 WO2021054344 A1 WO 2021054344A1 JP 2020034995 W JP2020034995 W JP 2020034995W WO 2021054344 A1 WO2021054344 A1 WO 2021054344A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- less
- steel sheet
- temperature
- steel
- content
- Prior art date
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
-
- 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/72—Wind turbines with rotation axis in wind direction
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a thick steel sheet having high levels of strength, toughness and bendability.
- the present invention also relates to a method for manufacturing a thick steel sheet.
- the thick steel plate for wind power generators used in the monopile type which is the mainstream among the support structure types of wind power generators on the ocean, is formed into a pipe shape by bending. Furthermore, in offshore wind power generators, waves, drift ice, etc. collide with the surface layer of steel plates used for supporting structures. Therefore, the thick steel sheet needs to have high bending workability and excellent toughness at the surface layer of the steel sheet and the center of the sheet thickness.
- the toughness of a steel sheet can be improved by refining the crystal grain size of the steel structure.
- rolling is performed in a low temperature range in which recrystallization of austenite is suppressed and the unrecrystallized temperature range is reached, and the strain introduced there is transformed. It is known that controlled rolling used for nuclei is effective.
- Patent Document 2 contains appropriate amounts of C, Si, Mn, P, S, Al, Ti, N, Nb, V, and Cr in mass%, and further.
- Ti and N satisfy 4.0 ⁇ Ti / N ⁇ 2.0, and the carbon equivalent Ceq defined by a predetermined formula satisfies 0.35 to 0.50, consisting of the balance Fe and unavoidable impurities. It is a composition, and the structure in the range from the surface of the steel plate to the position of 5 mm in the plate thickness direction consists of a polygonal ferrite phase with an area ratio of 30 to 70%, and the balance is a bainite phase, a martensite phase, or a mixed phase thereof.
- the structure in the range from the position of 5 mm in the plate thickness direction from the surface of the steel plate to the position of the center of the plate thickness consists of a polygonal ferrite phase with an area ratio of 30% or less and a bainite phase, a pearlite phase, or a mixed phase thereof.
- a thick steel plate having a Vickers hardness HV of 260 HV or less at a position 1 mm in the plate thickness direction from the surface of the steel plate is described.
- Patent Document 2 aims to improve the strength and bendability, and the toughness of the surface layer of the steel sheet and the center of the thickness has not been studied.
- the temperature distribution in the plate thickness direction is large, especially for thick steel sheets, so the austenite structure changes to a low-temperature formation structure such as ferrite or pearlite near the surface layer of the steel sheet. Rolling is performed with the transformation occurring. As a result, processing strain due to rolling is introduced into the surface structure of the steel sheet, and bending workability and toughness are significantly deteriorated.
- the present invention has been made in view of the above problems, and has a high level of high strength, excellent toughness at the surface layer of the steel sheet and the center of the sheet thickness, and excellent bending workability, especially in a thick steel sheet.
- An object of the present invention is to provide a steel plate.
- Another object of the present invention is to provide a method for manufacturing the thick steel sheet.
- the high strength means that the yield strength at the center position of the plate thickness in the tensile test is 300 MPa or more and the tensile strength is 400 MPa or more.
- excellent toughness means that the impact absorption energy by the Charpy impact absorption test at ⁇ 40 ° C. at the position 1 mm below the surface of the steel sheet and the position at the center of the plate thickness is 60 J or more, respectively.
- the shock absorption energy is preferably 100 J or more.
- excellent bending workability means that a 180 ° bending test was performed on the surface layer of the steel sheet under the condition that the bending radius R (radius of the bending punch) / t (plate thickness) was 1.0, and no bending cracks occurred. Point to that.
- the above-mentioned tensile test, Charpy impact absorption test and bending test can be performed by the methods described in Examples described later.
- the present inventors have obtained the following findings as a result of diligent studies to solve the above problems.
- the carbon equivalent (Ceq) and the cooling rate between 700 and 550 ° C. which is the temperature range in which transformation occurs from austenite, were controlled.
- a structure in which a processing strain having poor bending workability and toughness is introduced is formed on the surface layer of the steel sheet. It is possible to reduce the unrecrystallized temperature range at the center position of the plate thickness while suppressing the above. For this reason, Nb having an effect of raising the unrecrystallized temperature range of austenite to the high temperature side by solid solution Nb and fine precipitation NbC was contained.
- the unrecrystallized temperature of the Nb-containing steel is (8250 [Nb] + 770 ° C.) or less.
- the hot rolling conditions of the surface layer of the steel sheet and the center of the sheet thickness should be appropriately controlled. Is valid. Therefore, in order to control the structure of the surface layer of the steel sheet, the control is performed as follows. With respect to the surface layer of the steel sheet, first, the surface layer of the steel sheet is once cooled to Ar3 temperature or less during hot rolling to transform austenite into a low-temperature formation structure such as ferrite, and then the surface layer of the steel sheet is heated to Ac3 temperature or more by reheating. The temperature is changed to austenite structure, and the surface layer of the steel sheet is made into fine austenite.
- processing strain is applied to the austenite of the steel sheet surface layer. Is introduced.
- rolling is performed so that the total rolling reduction in the temperature range where the surface layer temperature of the steel sheet is less than Ar3 temperature is 15% or less, thereby preventing the structure of the surface layer of the steel sheet from becoming ferrite or pearlite into which processing strain is introduced.
- the following control is performed while the above-mentioned hot rolling is performed on the surface layer of the steel sheet.
- the steel sheet By rolling the steel sheet with a total reduction ratio of 25% or more in a temperature range where the center temperature of the sheet thickness is the unrecrystallized temperature range (8250 [Nb] + 770 ° C.) or less with respect to the center of the sheet thickness.
- a high toughness structure having a fine crystal grain size can be obtained even at the center position.
- the steel sheet with a thick plate thickness Even so, it has been found that it is possible to combine high strength, excellent toughness of the surface layer of the steel sheet and the center of the sheet thickness, and excellent bending workability.
- the present invention has been made based on the above findings, and the gist thereof is as follows.
- [1] By mass% C: 0.04 to 0.14%, Si: 0.03 to 0.70%, Mn: 0.30 to 2.50%, P: 0.030% or less, S: 0.0200% or less, Nb: 0.001 to 0.100%, Al: 0.001 to 0.100%, O: 0.01% or less, and N: 0.01% or less, including
- the rest consists of Fe and unavoidable impurities
- the Ceq defined by the following equation (1) and the plate thickness t [mm] have a component composition satisfying 0.0004t + 0.25 ⁇ Ceq ⁇ 0.0004t + 0.45.
- the dislocation density ⁇ (m -2 ) at a position 1 mm below the surface of the steel sheet is ⁇ ⁇ 4 ⁇ 10 14 .
- the average crystal grain size at a position 1 mm below the surface of the steel sheet is 15 ⁇ m or less.
- Ceq [C] + [Mn] / 6+ ([Cr] + [Mo] + [V]) / 5+ ([Cu] + [Ni]) / 15 ... (1)
- each element symbol in the above formula (1) represents the content (mass%) of the element, and is set to 0 when the element is not contained.
- composition of the components is further increased by mass%.
- Cu 2.00% or less
- Mo 1.00% or less
- V 0.30% or less
- B 0.0100% or less
- W 0.50% or less
- Ca 0.0200% or less
- the thick steel sheet according to [1] which comprises one or more selected from the group consisting of Mg: 0.0200% or less and REM: 0.0500% or less.
- the total reduction rate is 25% or more.
- the average cooling rate in the temperature range of 700 to 550 ° C. at the center position of the plate thickness is 2500 ⁇ t- 1.7 ° C./sec or more when the plate thickness of the steel sheet is t [mm].
- a method for producing a thick steel plate and a thick steel plate which have high strength, excellent toughness of the surface layer of the steel plate and the center of the plate thickness, and excellent bending workability even if the steel plate is thick. be able to.
- the application of the thick steel plate of the present invention is not limited to offshore wind power generation, but can also be applied to, for example, shipbuilding, line pipes, marine structures, construction, and the like.
- C 0.04 to 0.14%
- C is an element that can improve the strength of the steel sheet at the lowest cost, and is an element that contributes to the strengthening of the austenite grain boundaries. If the C content is less than 0.04%, the grain boundary strength of austenite is lowered and hot cracking of the slab occurs, so that the manufacturability is significantly lowered. Moreover, the strength desired by the present invention cannot be obtained. On the other hand, if the C content exceeds 0.14%, the weldability is lowered. Toughness is also reduced. Therefore, the C content is set to 0.04 to 0.14%.
- the C content is preferably 0.05% or more, and the C content is preferably 0.12% or less. It is more preferably 0.06% or more, and more preferably 0.11% or less.
- Si 0.03 to 0.70%
- Si is an element effective for deoxidation, but if the Si content is less than 0.03%, a sufficient effect cannot be obtained. However, if the Si content exceeds 0.70%, the weldability deteriorates. Therefore, the Si content is set to 0.03 to 0.70%.
- the Si content is preferably 0.04% or more, and the Si content is preferably 0.60% or less. It is more preferably 0.05% or more, and more preferably 0.55% or less.
- Mn 0.30 to 2.50%
- Mn is an element capable of improving hardenability and strength of steel at low cost. In order to obtain the effect, it is necessary to contain Mn of 0.30% or more. On the other hand, if the Mn content exceeds 2.50%, the weldability deteriorates. Therefore, the Mn content is set to 0.30 to 2.50%.
- the Mn content is preferably 0.50% or more, and the Mn content is preferably 2.20% or less. It is more preferably 0.60% or more, and more preferably 2.10% or less.
- P 0.030% or less
- P is an element having a large effect of embrittlement of grain boundaries, and when it is contained in a large amount, the toughness of steel is lowered. Therefore, the P content is set to 0.030% or less.
- the P content is preferably 0.025% or less.
- the smaller the amount of P the more preferable it is. Therefore, the lower limit of the P content is not particularly limited and may be 0%.
- P is an element that is inevitably contained in steel as an impurity, and excessive reduction of P causes an increase in refining time and an increase in cost. Therefore, the P content may be 0.001% or more. preferable.
- S 0.0200% or less S reduces the toughness of steel, so the S content is 0.0200% or less.
- the S content is preferably 0.0100% or less.
- the lower limit of the S content is not particularly limited and may be 0%.
- S is an element that is unavoidably contained in steel as an impurity, and excessive reduction in S causes an increase in refining time and an increase in cost. Therefore, the S content may be 0.0001% or more. preferable.
- Nb 0.001 to 0.100%
- Nb is an element that has the effect of suppressing recrystallization when the austenite structure is strained by solid solution Nb and finely precipitated NbC, and raising the temperature of the unrecrystallized temperature range. In order to obtain the effect, it is necessary to contain 0.001% or more of Nb. On the other hand, the content of Nb exceeding 0.100% deteriorates weldability. Therefore, the Nb content is set to 0.001 to 0.100%.
- the Nb content is preferably 0.005% or more, and the Nb content is preferably 0.075% or less.
- the Nb content is more preferably 0.050% or less.
- Al 0.001 to 0.100%
- Al is an element that is effective as an antacid and has the effect of forming a nitride to reduce the austenite particle size.
- the Al content needs to be 0.001% or more.
- the Al content is set to 0.001 to 0.100%.
- the Al content is preferably 0.005% or more, and the Al content is preferably 0.080% or less.
- O 0.01% or less
- O is an element that lowers the ductility and toughness, so the O content is 0.01% or less.
- the lower limit of the O content is not particularly limited and may be 0%.
- O is an element that is unavoidably contained in steel as an impurity, and excessive reduction in O causes an increase in refining time and an increase in cost. Therefore, the O content may be 0.0005% or more. preferable.
- N 0.01% or less Since N is an element that lowers the ductility and toughness, the N content is 0.01% or less. On the other hand, the smaller the amount of N, the more preferable it is. Therefore, the lower limit of the N content is not particularly limited and may be 0%. However, since N is an element that is unavoidably contained in steel as an impurity, it may be industrially more than 0%. In addition, since excessively low N causes an increase in refining time and an increase in cost, the N content is preferably 0.0005% or more.
- the thick steel sheet of the present invention contains the above components, and the balance is Fe and unavoidable impurities.
- the thick steel sheet of the present invention has the above-mentioned components as the basic component composition.
- the above-mentioned essential elements can obtain the characteristics desired in the present invention, the following elements may be contained as necessary for the purpose of further improving the strength and weldability (toughness of welds, welding workability, etc.). Can be done.
- Cu 2.00% or less, Ni: 2.50% or less, Cr: 1.50% or less, Mo: 1.00% or less, Ti: 0.100% or less, V: 0.30% or less, B: One or two selected from the group consisting of 0.0100% or less, W: 0.50% or less, Ca: 0.0200% or less, Mg: 0.0200% or less, and REM: 0.0500% or less.
- Cu: 2.00% or less Cu is an element that can improve the strength of a steel sheet without significantly deteriorating the base material and toughness.
- the Cu content exceeds 2.00%, hot cracking due to the Cu concentrated layer formed directly under the scale becomes a problem. Therefore, when Cu is contained, the Cu content is preferably 2.00% or less. It should be noted that it is even more preferably 0.01% or more, and even more preferably 1.50% or less. It is more preferably 0.15% or more, still more preferably 1.00% or less.
- Ni 2.50% or less
- Ni is an element that has the effect of improving hardenability of steel and improving toughness.
- the Ni content is preferably 2.50% or less. It should be noted that it is even more preferably 0.01% or more, and even more preferably 2.00% or less. It is more preferably 0.15% or more, still more preferably 1.50% or less.
- Cr 1.50% or less Cr is an element that can improve the strength of a steel sheet by improving the hardenability of steel. On the other hand, if the Cr content exceeds 1.50%, the weldability deteriorates. Therefore, when Cr is contained, the Cr content is preferably 1.50% or less. It should be noted that it is even more preferably 0.01% or more, and even more preferably 1.20% or less. It is more preferably 0.15% or more, still more preferably 0.90% or less.
- Mo 1.00% or less Mo is an element that can improve the strength of a steel sheet by improving the hardenability of steel. On the other hand, if the Mo content exceeds 1.00%, the weldability is lowered. Therefore, when Mo is contained, the Mo content is preferably 1.00% or less. It should be noted that it is even more preferably 0.01% or more, and even more preferably 0.80% or less. It is more preferably 0.05% or more, still more preferably 0.60% or less.
- Ti 0.100% or less
- Ti is an element that has the effect of pinning the movement of grain boundaries by precipitating as TiN and suppressing grain growth.
- the Ti content exceeds 0.100%, the cleanliness of the steel structure is lowered, and as a result, the ductility and toughness are lowered. Therefore, when Ti is contained, the Ti content is preferably 0.100% or less. It should be noted that it is even more preferably 0.001% or more, and even more preferably 0.080% or less. It is more preferably 0.005% or more, still more preferably 0.050% or less.
- V 0.30% or less
- V is an element that can improve the hardenability of steel and the strength of steel sheet by forming carbonitride.
- the V content is preferably 0.30% or less. It should be noted that it is even more preferably 0.01% or more, and even more preferably 0.25% or less. More preferably, it is 0.15% or less.
- B 0.0100% or less
- B is an element having the effect of improving the strength of the steel sheet by improving the hardenability by adding a very small amount.
- the B content is preferably 0.0100% or less. It should be noted that it is even more preferably 0.0001% or more, and even more preferably 0.0070% or less. It is more preferably 0.0005% or more, still more preferably 0.0050% or less.
- W 0.50% or less W is an element that can improve the strength of the steel sheet by improving the hardenability of the steel. On the other hand, if the W content exceeds 0.50%, the weldability is lowered. Therefore, when W is contained, the W content is preferably 0.50% or less. It should be noted that it is even more preferably 0.01% or more, and even more preferably 0.40% or less. It is more preferably 0.05% or more, still more preferably 0.35% or less.
- Ca 0.0200% or less
- Ca is an element that improves weldability by forming an acid sulfide with high stability at high temperatures.
- the Ca content exceeds 0.0200%, the cleanliness is lowered and the toughness of the steel is impaired. Therefore, when Ca is contained, the Ca content is set to 0.0200% or less. It should be noted that it is even more preferably 0.0001% or more, and even more preferably 0.0180% or less. It is more preferably 0.0005% or more, still more preferably 0.0060% or less.
- Mg 0.0200% or less
- Mg is an element that improves weldability by forming an acid sulfide with high stability at high temperatures.
- the Mg content exceeds 0.0200%, the effect of adding Mg is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when Mg is contained, the Mg content is set to 0.0200% or less. It should be noted that it is even more preferably 0.0001% or more, and even more preferably 0.0180% or less. It is more preferably 0.0005% or more, still more preferably 0.0060% or less.
- REM 0.0500% or less REM (rare earth metal) is an element that improves weldability by forming an acid sulfide with high stability at high temperatures.
- the REM content exceeds 0.0500%, the effect of adding REM is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when REM is contained, the REM content is set to 0.0500% or less. It should be noted that it is even more preferably 0.0001% or more, and even more preferably 0.0450%. It is more preferably 0.0010% or more, still more preferably 0.0100% or less.
- composition of the thick steel sheet must further satisfy the following conditions.
- Ceq is an index of hardenability due to contained elements.
- Ceq is (0.0004t + 0.25). If it is less than, the required strength cannot be obtained.
- Ceq is larger than (0.0004t + 0.45), the strength becomes too high on the surface of the steel sheet where the cooling rate is faster than the center position of the plate thickness, so that the bending workability becomes low.
- the Ceq is preferably (0.0004t + 0.27) or more, and the Ceq is preferably (0.0004t + 0.43) or less. More preferably, it is (0.0004t + 0.28) or more, and (0.0004t + 0.42) or less.
- Ceq [C] + [Mn] / 6+ ([Cr] + [Mo] + [V]) / 5+ ([Cu] + [Ni]) / 15 ... (1)
- each element symbol in the formula (1) represents the content (mass%) of the element, and is set to 0 when the element is not contained.
- the thick steel sheet of the present invention has a dislocation density ⁇ (m -2 ) of ⁇ ⁇ 4 ⁇ 10 14 at a position 1 mm below the surface of the steel sheet of the thick steel sheet, and is located 1 mm below the surface of the steel sheet. It has a steel structure in which the average crystal grain size is 15 ⁇ m or less and the average crystal grain size at the center position of the thickness of the steel sheet is 20 ⁇ m or less. Therefore, the reason why the steel structure is limited as described above in the present invention will be described below.
- Dislocation density 1 mm below the surface of the steel sheet ⁇ ⁇ 4 ⁇ 10 14 (m- 2 )
- the bendability of a steel sheet is determined by the ductility of the surface structure of the steel sheet.
- the dislocation density at a position 1 mm below the surface of the steel sheet was set to 4 ⁇ 10 14 (m- 2 ) or less.
- the steel structure since the steel structure usually contains dislocations inevitably, it requires a very high manufacturing cost to reduce the size to 1 ⁇ 10 11 (m- 2) or less. Therefore, it is preferably 1 ⁇ 10 11 or more, and preferably 3 ⁇ 10 14 (m- 2 ) or less.
- Average crystal grain size 1 mm below the surface of the steel sheet 15 ⁇ m or less
- the average crystal grain size at a position 1 mm below the surface of the steel sheet is set to 15 ⁇ m or less. It is preferably 13 ⁇ m or less. It is preferably 4 ⁇ m or more.
- Average crystal grain size at the center of the plate thickness 20 ⁇ m or less
- the average crystal grain size at the center position of the plate thickness was set to 20 ⁇ m or less. It is preferably 15 ⁇ m or less. It is preferably 7 ⁇ m or more.
- “1 mm below the surface of the steel plate” refers to a depth position of 1 mm in the thickness direction from the surface of the thick steel plate.
- the “plate thickness center position” shall indicate the plate thickness 1/2 position of the thick steel plate.
- the “average crystal grain size” is the average of all crystal grains at the position 1 mm below the surface of the steel sheet and the center position of the plate thickness, when the region surrounded by the boundary with a crystal orientation difference of 15 ° or more is defined as the crystal grains. Shall refer to.
- the average crystal grain size can be measured by the method described in Examples described later.
- the "thick steel plate” in the present invention refers to a steel plate having a plate thickness of 6 mm or more.
- the thickness of the thick steel plate is preferably more than 40 mm, and even more preferably 70 mm or more.
- the upper limit of the plate thickness is not particularly limited and may be any thickness, but it is preferably 190 mm or less.
- the thick steel sheet of the present invention can be obtained by heating, hot rolling, and cooling a slab (steel material) having the above-mentioned composition under each of the above-mentioned conditions. After the cooling, an arbitrary tempering step can be further performed.
- the “° C.” indication regarding the temperature shall be the temperature of the slab, the surface temperature of the steel plate, and the temperature at the center position of the plate thickness (1/2 position of the plate thickness) unless otherwise specified.
- the surface temperature can be measured with, for example, a radiation thermometer. Further, the temperature at the center of the thickness of the slab or the steel plate is measured by attaching a thermocouple to the center of the thickness of the steel plate, or the temperature distribution in the cross section of the steel plate is calculated by heat transfer analysis, and the result is the steel plate. It can be obtained by correcting with the surface temperature of.
- the slab melting method is not particularly limited, and any known melting method such as a converter, an electric furnace, or a vacuum melting furnace is suitable.
- the slab is manufactured to a desired size, for example by a continuous casting method.
- the molten steel may be further subjected to secondary refining such as ladle refining.
- the produced slab is heated to a temperature of 1000-1200 ° C.
- the heating temperature of the slab was set to a temperature of 1000 to 1200 ° C. It is preferably 1030 ° C. or higher, and preferably 1170 ° C. or lower.
- the heated slab is then hot rolled.
- a temperature range exceeding (8250 [Nb] + 770 ° C.) at a temperature 1 mm below the surface of the steel sheet or at the center of the thickness is referred to as a recrystallization temperature range, and at a temperature 1 mm below the surface of the steel sheet or at the center of the thickness.
- the temperature range from (8250 [Nb] + 770 ° C.) to Ar3 temperature is referred to as an unrecrystallized temperature range.
- the above-mentioned [Nb] represents the content (mass%) of the element.
- Rolling conditions for the surface layer of the steel sheet First, the temperature of the steel sheet at a position 1 mm below the surface of the steel sheet is once cooled to Ar3 temperature or lower, and then reheated to exceed the Ac3 temperature. Next, the reduction is performed so that the reduction rate in the temperature range from (8250 [Nb] + 770 ° C.) to Ar3 temperature at the position 1 mm below the surface of the steel sheet is 25% or more with respect to the position 1 mm below the surface of the steel sheet. After that, the total reduction rate in the temperature range where the temperature of the steel sheet at a position 1 mm below the surface of the steel sheet is less than the Ar3 temperature is reduced to 15% or less.
- the surface layer of the steel sheet is once cooled to Ar3 temperature or less during hot rolling to transform austenite into a low-temperature formation structure such as ferrite, and the surface layer of the steel sheet is heated to Ac3 temperature or more by subsequent reheating.
- the austenite structure is retransformed into fine austenite on the surface layer of the steel plate.
- this cooling include water cooling and blast cooling, and the cooling method is not limited as long as it can be controlled to a predetermined temperature.
- cooling to Ar3 temperature or less is performed by water cooling, and the residence time at which the position 1 mm below the surface of the steel sheet is Ar3 temperature or less is preferably 5 seconds or more, and preferably 300 seconds or less.
- the reheat after cooling is to hold the steel sheet in the atmosphere, and the holding time is preferably 30 seconds or more, and preferably 600 seconds or less.
- the surface layer of the steel sheet is in the unrecrystallized temperature range (8250 [Nb] + 770 ° C.) to the temperature range of Ar3 temperature.
- the rolling reduction rate in this temperature range is preferably 80% or less, and even more preferably 70% or less.
- the upper limit of the number of passes in this temperature range is not particularly limited. Further, it is sufficient that the above-mentioned conditions for the reduction rate are satisfied, and for example, the process may be divided into a plurality of paths.
- Total reduction rate in the temperature range below Ar3 temperature 15% or less
- the total reduction rate in the temperature range below Ar3 temperature exceeds 15%, the ferrite structure or pearlite whose transformation is completed on the surface layer of the steel sheet
- the surface layer of the steel sheet can have a structure having a low dislocation density, a small grain size, and excellent bending workability and toughness.
- Rolling conditions at the center of plate thickness The reduction is applied so that the total reduction rate in the temperature range where the temperature of the steel plate at the center of the thickness is (8250 [Nb] + 770 ° C.) or less and Ar3 or more is 25% or more with respect to the center position of the thickness of the steel plate. ..
- rolling reduction of 25% or more in the temperature range from (8250 [Nb] + 770 ° C.) to Ar3 temperature where the center position of the plate thickness is the unrecrystallized temperature range processing strain is introduced into the austenite at the center position of the plate thickness. Will be done.
- a microstructure with good toughness can be obtained.
- the total reduction rate in the temperature range where the center temperature of the steel plate thickness is (8250 [Nb] + 770 ° C.) or less is set to 25% or more. It is preferably 35% or more. From the viewpoint of rolling efficiency, the total rolling reduction in this temperature range is preferably 70% or less, and even more preferably 67% or less.
- the temperature is Ar3 or higher.
- the temperature range may overlap within each of the above-mentioned rolling conditions.
- the reduction amount in the overlapping temperature range may be integrated as each reduction amount of the "steel plate surface layer” and the “plate thickness center position", and the integrated reduction amount may be within the range of each rolling condition. ..
- the total rolling reduction in the recrystallization temperature range at the surface layer of the steel sheet and the center position of the sheet thickness is in the temperature range exceeding (8250 [Nb] + 770 ° C.), the plate thickness at which the first rolling is started is r 0 , and the final rolling ratio is r 0.
- the total rolling reduction ratio (r 0 ⁇ r 1 ) / r 0 ⁇ 100 (%).
- the Ar3 temperature and the Ac3 temperature can be obtained by a four-master test or the like.
- the center position of the steel sheet can be made to have an excellent toughness structure with a small crystal grain size.
- the obtained thick steel sheet is cooled.
- the average cooling rate in the temperature range of 700 to 550 ° C. at the temperature at the center of the plate thickness of the steel plate should be 2500 x t- 1.7 ° C./sec or more when the plate thickness is t [mm].
- Examples of the cooling method include water cooling in which water is jetted from a nozzle at a large flow rate.
- Average cooling rate in the temperature range of 700 to 550 ° C at the center of the plate thickness 2500 ⁇ t -1.7 ° C / sec or more The average cooling rate between 700 and 550 ° C at the center of the plate thickness after hot rolling If the temperature is less than 2500 ⁇ t- 1.7 ° C / sec, the required strength desired in the present invention cannot be obtained due to insufficient cooling rate in the temperature range where austenite is transformed into a low-temperature transformed structure, and the strength is coarse. Since ferrite is formed, the toughness decreases. Therefore, the average cooling rate in the temperature range of 700 to 550 ° C. at the center position of the plate thickness was set to 2500 ⁇ t -1.7 ° C./sec or more. It is preferably 2800 ⁇ t- 1.7 ° C./sec or more, and preferably 15000 ⁇ t- 1.7 ° C./sec or less.
- tempering can be performed for the purpose of further improving the strength and toughness, if necessary.
- the steel sheet is cooled, it is tempered at a tempering temperature of 650 ° C. or lower.
- tempering temperature 650 ° C or less If the tempering temperature is higher than 650 ° C, significant softening may occur and the required strength may not be secured. Therefore, the tempering temperature is preferably 650 ° C. or lower. On the other hand, the lower limit of the tempering temperature is not particularly limited, but is preferably 200 ° C. or higher. The tempering time can be adjusted as appropriate. The tempering temperature here is the temperature of the surface of the steel sheet. It is even more preferably 250 ° C. or higher, and even more preferably 630 ° C. or lower.
- molten steel having the composition shown in Table 1 was melted, and a steel material (slab) was manufactured by continuous casting or the like.
- the blanks in Table 1 indicate that they are not intentionally added, and include not only the case where they are not contained (0%) but also the cases where they are unavoidably contained.
- each step of heating, hot rolling, and cooling was sequentially performed on the obtained slab to obtain a thick steel plate having a plate thickness of t (mm) shown in Table 2. Further, some of the obtained thick steel sheets were reheated for tempering after cooling.
- the manufacturing conditions for each step are as shown in Table 2.
- cooling is performed when the temperature 1 mm below the surface of the steel sheet is once set to Ar3 temperature or less, and the residence time when the position 1 mm below the surface of the steel sheet is set to Ar3 temperature or less is 5 seconds or more. It was cooled so as to be. Furthermore, the steel sheet after cooling was held in the atmosphere to wait for reheating. Further, cooling after hot rolling was performed by injecting water at a large flow rate from the front and back surfaces of the steel sheet. The surface temperature of the steel plate is measured by an emissivity thermometer, and the temperature at the center of the thickness is a value measured by attaching a thermocouple to the center of the thickness of the steel plate.
- the rolling start temperature of the example of the present invention shown in Table 2 was in the range of 990 to 1140 ° C. on the surface layer of the steel sheet, and the rolling finish temperature was in the range of 670 to 830 ° C. on the surface layer of the steel sheet.
- the dislocation density was carried out the average crystal grain size, and measurement of the temperature of the A r3 temperature and the A c3 temperature, tensile test, Charpy impact absorption test, a bending test. The measurement results and test results are shown in Table 3.
- Samples were taken from each of the obtained thick steel sheets so that the cross section in the longitudinal direction of the steel sheet at the position 1 mm below the surface of the steel sheet and the center position of the sheet thickness was the evaluation surface at the center positions in the longitudinal direction and the width direction of the steel sheet.
- the surface of the obtained sample was mirror-polished with a colloidal silica finish, and measured by EBSP (backscattered electron diffraction method) under the following conditions.
- the measurement area was 300 ⁇ m ⁇ 400 ⁇ m, and the measurement step size was 1 ⁇ m.
- the circle-equivalent diameter of the structure surrounded by the large-angle grain boundaries where the crystal orientation difference from the adjacent crystal grains is 15 ° or more is obtained, and the average value of the circle-equivalent diameters in the above measurement region is averaged.
- the crystal grain size was used.
- Both the surface layer of the steel sheet and the center of the thickness of the example of the present invention had a structure mainly composed of bainite and pseudopolygonal ferrite.
- test pieces were collected from the central positions in the longitudinal direction and the width direction of the steel sheet.
- the test piece had a shape from the outermost surface of the steel sheet to a position 12 mm below the surface layer: a test piece having a thickness of 12 mm, a width of 50 mm, and a length of 350 mm was collected so that the longitudinal direction of the bending test piece was parallel to the width direction of the steel sheet. ..
- each test piece was used to perform a three-point bending test in accordance with JIS Z2248 (2006). Using a punch with a bending radius of 12 mm, the original steel sheet was bent 180 ° in a direction in which the outermost surface side came to the outside of the bending, and the presence or absence of cracks was evaluated.
- the thick steel sheet satisfying the conditions of the present invention has high strength at the center position of the sheet thickness and excellent surface and center position of the sheet thickness in the extra-thick steel sheet up to 180 mm. It had both toughness and excellent bending workability.
- the steel sheet of the comparative example that does not satisfy the conditions of the present invention was inferior in any of strength, toughness, and bendability.
- the steel sheet 23 Since the P content of the steel sheet 23 is high, the steel sheet is brittle and has low toughness.
- the steel sheets 35 and 38 have insufficient toughness because the amount of reduction in the unrecrystallized region is insufficient and the structure is coarse.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
Description
また、優れた靱性とは、鋼板表面下1mm位置および板厚中心位置での-40℃でのシャルピー衝撃吸収試験による衝撃吸収エネルギーがそれぞれ60J以上であることを指す。衝撃吸収エネルギーは、好ましくは100J以上である。
また、優れた曲げ加工性とは、鋼板表層において、曲げ半径R(曲げパンチの半径)/t(板厚)が1.0の条件で180°曲げ試験を行い、曲げ割れが発生しなかったことを指す。
なお、上記の引張試験、シャルピー衝撃吸収試験および曲げ試験は、後述する実施例に記載の方法で行うことができる。
そこで、鋼板表層の組織制御のために、次のように制御する。鋼板表層に対して、まず、熱間圧延中に鋼板表層を一旦Ar3温度以下まで冷却することでオーステナイトからフェライト等の低温生成組織に変態させ、その後の復熱で鋼板表層をAc3温度以上の温度とすることでオーステナイト組織に再変態させ、鋼板表層を微細なオーステナイトとする。
続いて、鋼板表層温度が(8250[Nb]+770℃)~Ar3温度の未再結晶温度域における圧下率が25%以上の圧下を鋼板表層に加えることで、鋼板表層のオーステナイト中に加工ひずみを導入しておく。その後、鋼板表層温度がAr3温度未満の温度域における総圧下率が15%以下となるように圧延することで、鋼板表層の組織が加工ひずみの導入されたフェライトやパーライトになるのを防ぐ。これらの組織制御により、鋼板表層の組織を、転位密度が低く、かつ結晶粒径が小さい、優れた曲げ加工性と靱性を兼ね備えた組織とすることができる。
[1] 質量%で、
C :0.04~0.14%、
Si:0.03~0.70%、
Mn:0.30~2.50%、
P :0.030%以下、
S :0.0200%以下、
Nb:0.001~0.100%、
Al:0.001~0.100%、
O :0.01%以下、および
N :0.01%以下を含み、
残部がFe及び不可避不純物からなり、
下記(1)式で定義されるCeqと板厚t[mm]とが、0.0004t+0.25≦Ceq≦0.0004t+0.45を満足する成分組成を有し、
鋼組織は、鋼板表面下1mm位置における転位密度ρ(m-2)がρ≦4×1014であり、
鋼板表面下1mm位置における平均結晶粒径が15μm以下であり、
鋼板の板厚中心位置における平均結晶粒径が20μm以下である、厚鋼板。
Ceq=[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15・・・(1)
ただし、上記(1)式における各元素記号は当該元素の含有量(質量%)を表し、当該元素が含有されていない場合は0とする。
Cu:2.00%以下、
Ni:2.50%以下、
Cr:1.50%以下、
Mo:1.00%以下、
Ti:0.100%以下、
V :0.30%以下、
B :0.0100%以下、
W :0.50%以下、
Ca:0.0200%以下、
Mg:0.0200%以下、および
REM:0.0500%以下
からなる群より選択される1種または2種以上を含む、[1]に記載の厚鋼板。
前記成分組成を有するスラブを1000~1200℃の温度に加熱し、
加熱された前記スラブに熱間圧延を行う際に、
前記鋼板表面下1mm位置の鋼板温度を、一旦Ar3温度以下まで冷却し、その後復熱でAc3温度超とし、
前記鋼板表面下1mm位置の鋼板温度が(8250[Nb]+770℃)~Ar3温度の温度域における圧下率を25%以上とする圧下を加え、その後前記鋼板表層下1mm位置の鋼板温度がAr3温度未満の温度域における総圧下率を15%以下とする圧下を行うとともに、
前記板厚中心位置の鋼板温度が、(8250[Nb]+770℃)以下Ar3温度以上の温度域における総圧下率を25%以上とする圧下を行い、
前記熱間圧延後、板厚中心位置の温度で700~550℃の温度域における平均冷却速度が、鋼板の板厚をt[mm]としたとき、2500×t-1.7℃/秒以上で冷却する、厚鋼板の製造方法。
ただし、上記[Nb]は、当該元素の含有量(質量%)を表す。
本発明では、厚鋼板およびその製造に用いられる鋼素材が、上記した成分組成を有することが重要である。そこで、本発明において鋼素材の成分組成を上記のように限定した理由を説明する。なお、成分組成に関する「%」は、特に断らない限り「質量%」を意味する。
Cは、鋼板の強度を最も安価に向上させられる元素であり、またオーステナイト粒界の強化に寄与する元素である。C含有量が0.04%未満であると、オーステナイトの粒界強度が低下し、スラブの熱間割れが生じるため、製造性が著しく低下する。また本発明で目的とする強度を得られない。一方、C含有量が0.14%を超えると、溶接性が低下する。靭性も低下する。そのため、C含有量は0.04~0.14%とする。なお、C含有量は0.05%以上が好ましく、C含有量は0.12%以下が好ましい。より好ましくは0.06%以上であり、より好ましくは0.11%以下である。
Siは、脱酸に有効な元素であるが、Si含有量が0.03%未満であると十分な効果を得ることができない。しかし、Si含有量が0.70%を超えると溶接性が低下する。そのため、Si含有量を0.03~0.70%とする。なお、Si含有量は0.04%以上が好ましく、Si含有量は0.60%以下が好ましい。より好ましくは0.05%以上であり、より好ましくは0.55%以下である。
Mnは、低コストで鋼の焼入れ性を向上させ、強度を向上させることができる元素である。その効果を得るには0.30%以上のMnの含有が必要である。一方、Mn含有量が2.50%を超えると、溶接性が低下する。そのため、Mn含有量を0.30~2.50%とする。なお、Mn含有量は0.50%以上が好ましく、Mn含有量は2.20%以下が好ましい。より好ましくは0.60%以上であり、より好ましくは2.10%以下である。
Pは、粒界を脆化させる作用の大きい元素であり、多量に含有すると、鋼の靭性を低下させる。そのため、P含有量を0.030%以下とする。P含有量を0.025%以下とすることが好ましい。一方、Pは少ないほど好ましいため、P含有量の下限は特に限定されず、0%であってもよい。しかし、Pは不純物として鋼中に不可避的に含有される元素であり、過度の低P化は精錬時間の増加やコストの上昇を招くため、P含有量を0.001%以上とすることが好ましい。
Sは、鋼の靭性を低下させるため、S含有量を0.0200%以下とする。S含有量を0.0100%以下とすることが好ましい。一方、Sは少ないほど好ましいため、S含有量の下限は特に限定されず、0%であってもよい。しかし、Sは不純物として鋼中に不可避的に含有される元素であり、過度の低S化は精錬時間の増加やコストの上昇を招くため、S含有量を0.0001%以上とすることが好ましい。
Nbは、固溶Nbや微細析出したNbCによりオーステナイト組織にひずみが加わった際の再結晶を抑制し、また未再結晶温度域を高温化する効果のある元素である。その効果を得るためには0.001%以上のNbの含有が必要である。一方、0.100%を超えるNbの含有は溶接性を劣化させる。そのため、Nb含有量は0.001~0.100%とする。なお、Nb含有量は0.005%以上が好ましく、Nb含有量は0.075%以下が好ましい。Nb含有量は0.050%以下がより好ましい。
Alは、脱酸剤として有効であるとともに、窒化物を形成してオーステナイト粒径を小さくする効果を有する元素である。その効果を得るためにはAl含有量を0.001%以上とする必要がある。一方、Al含有量が0.100%を超えると、鋼素材や鋼板の清浄度が低下し、その結果、延性および靭性が低下する。そのため、Al含有量を0.001~0.100%とする。なお、Al含有量は0.005%以上が好ましく、Al含有量は0.080%以下が好ましい。
Oは、延性、靭性を低下させる元素であるため、O含有量を0.01%以下とする。一方、Oは少ないほど好ましいため、O含有量の下限は特に限定されず、0%であってもよい。しかし、Oは不純物として鋼中に不可避的に含有される元素であり、過度の低O化は精錬時間の増加やコストの上昇を招くため、O含有量は0.0005%以上とすることが好ましい。
Nは、延性、靭性を低下させる元素であるため、N含有量を0.01%以下とする。一方、Nは少ないほど好ましいため、N含有量の下限は特に限定されず、0%であってもよい。しかし、Nは不純物として鋼中に不可避的に含有される元素であるため、工業的には0%超であってもよい。なお、過度の低N化は精錬時間の増加やコストの上昇を招くため、N含有量は0.0005%以上とすることが好ましい。
Cu:2.00%以下
Cuは、母材および靭性を大きく劣化させることなく鋼板の強度を向上させることができる元素である。一方、Cu含有量が2.00%を超えると、スケール直下に生成するCu濃化層に起因する熱間割れが問題となる。そのため、Cuを含有する場合、Cu含有量を2.00%以下とすることが好ましい。なお、より一層好ましくは0.01%以上であり、より一層好ましくは1.50%以下である。さらに好ましくは0.15%以上であり、さらに好ましくは1.00%以下である。
Niは、鋼の焼入れ性を高めるとともに、靭性を向上させる効果を有する元素である。一方、Ni含有量が2.50%を超えると製造コストの増加が問題となる。そのため、Niを含有する場合、Ni含有量を2.50%以下とすることが好ましい。なお、より一層好ましくは0.01%以上であり、より一層好ましくは2.00%以下である。さらに好ましくは0.15%以上であり、さらに好ましくは1.50%以下である。
Crは、鋼の焼入れ性を向上させることにより鋼板の強度を向上させることができる元素である。一方、Cr含有量が1.50%を超えると、溶接性が低下する。そのため、Crを含有する場合、Cr含有量を1.50%以下とすることが好ましい。なお、より一層好ましくは0.01%以上であり、より一層好ましくは1.20%以下である。さらに好ましくは0.15%以上であり、さらに好ましくは0.90%以下である。
Moは、鋼の焼入れ性を向上させることにより鋼板の強度を向上させることができる元素である。一方、Mo含有量が1.00%を超えると、溶接性が低下する。そのため、Moを含有する場合、Mo含有量を1.00%以下とすることが好ましい。なお、より一層好ましくは0.01%以上であり、より一層好ましくは0.80%以下である。さらに好ましくは0.05%以上であり、さらに好ましくは0.60%以下である。
Tiは、TiNとして析出することで結晶粒界の移動をピン止めし、粒成長を抑制する効果を有する元素である。一方、Ti含有量が0.100%を超えると、鋼組織の清浄度が低下し、その結果、延性および靭性が低下する。そのため、Tiを含有する場合、Ti含有量を0.100%以下とすることが好ましい。なお、より一層好ましくは0.001%以上であり、より一層好ましくは0.080%以下である。さらに好ましくは0.005%以上であり、さらに好ましくは0.050%以下である。
Vは、鋼の焼入れ性の向上とともに、炭窒化物の生成により鋼板の強度を向上させることができる元素である。一方、V含有量が0.30%を超えると、溶接性が低下する。そのため、Vを含有する場合、V含有量を0.30%以下とすることが好ましい。なお、より一層好ましくは0.01%以上であり、より一層好ましくは0.25%以下である。さらに好ましくは0.15%以下である。
Bは、極微量の添加で焼入れ性を向上させることにより、鋼板の強度を向上させる効果を有する元素である。一方、B含有量が0.0100%を超えると、溶接性が低下する。そのため、Bを含有する場合、B含有量を0.0100%以下とすることが好ましい。なお、より一層好ましくは0.0001%以上であり、より一層好ましくは0.0070%以下である。さらに好ましくは0.0005%以上であり、さらに好ましくは0.0050%以下である。
Wは、鋼の焼入れ性を向上させることにより、鋼板の強度を向上させることができる元素である。一方、W含有量が0.50%を超えると、溶接性が低下する。そのため、Wを含有する場合、W含有量を0.50%以下とすることが好ましい。なお、より一層好ましくは0.01%以上であり、より一層好ましくは0.40%以下である。さらに好ましくは0.05%以上であり、さらに好ましくは0.35%以下である。
Caは、高温での安定性が高い酸硫化物を形成することで溶接性を向上させる元素である。一方、Ca含有量が0.0200%を超えると、清浄度が低下して鋼の靭性が損なわれる。そのため、Caを含有する場合、Ca含有量を0.0200%以下とする。なお、より一層好ましくは0.0001%以上であり、より一層好ましくは0.0180%以下である。さらに好ましくは0.0005%以上であり、さらに好ましくは0.0060%以下である。
Mgは、高温での安定性が高い酸硫化物を形成することで溶接性を向上させる元素である。一方、Mg含有量が0.0200%を超えると、Mgの添加効果が飽和して含有量に見合う効果が期待できず、経済的に不利となる。そのため、Mgを含有する場合、Mg含有量を0.0200%以下とする。なお、より一層好ましくは0.0001%以上であり、より一層好ましくは0.0180%以下である。さらに好ましくは0.0005%以上であり、さらに好ましくは0.0060%以下である。
REM(希土類金属)は、高温での安定性が高い酸硫化物を形成することで溶接性を向上させる元素である。一方、REM含有量が0.0500%を超えると、REMの添加効果が飽和して含有量に見合う効果が期待できず、経済的に不利となる。そのため、REMを含有する場合、REM含有量を0.0500%以下とする。なお、より一層好ましくは0.0001%以上であり、より一層好ましくは0.0450%である。さらに好ましくは0.0010%以上であり、さらに好ましくは0.0100%以下である。
下記(1)式で定義されるCeqは、含有元素による焼入れ性の指標である。本発明で目的とする高強度組織を得るためには、ある鋼板の板厚に応じた冷却速度および板厚に応じた合金添加量を制御する必要があり、Ceqが(0.0004t+0.25)未満であると必要な強度が得られない。一方、Ceqが(0.0004t+0.45)よりも大きくなると、板厚中心位置に比べて冷却速度の速い鋼板表面において、強度が高くなりすぎるため曲げ加工性が低位となる。そのため、0.0004t+0.25≦Ceq≦0.0004t+0.45とした。なお、Ceqは(0.0004t+0.27)以上とすることが好ましく、Ceqは(0.0004t+0.43)以下とすることが好ましい。より好ましくは(0.0004t+0.28)以上であり、(0.0004t+0.42)以下である。
Ceq=[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15・・・(1)
ただし、(1)式における各元素記号は当該元素の含有量(質量%)を表し、当該元素が含有されていない場合は0とする。
本発明の厚鋼板は、上記成分組成を有することに加えて、厚鋼板の鋼板表面下1mm位置における転位密度ρ(m-2)がρ≦4×1014であり、鋼板表面下1mm位置における平均結晶粒径が15μm以下であり、鋼板の板厚中心位置における平均結晶粒径が20μm以下である鋼組織を有する。そこで、本発明において鋼組織を上記のように限定した理由を以下に説明する。
鋼板の曲げ加工性は、鋼板の表層組織の延性によって決まる。熱間圧延時の加工ひずみにより表層組織の転位密度が増加すると、表層組織の変形限界が低下するため曲げ加工性が低下する。そのため、鋼板表面下1mm位置の転位密度を4×1014(m-2)以下とした。なお、通常、鋼組織は不可避的に転位を含有するため、1×1011(m-2)以下にするには非常に製造コストがかかる。そのため、好ましくは1×1011以上であり、好ましくは3×1014(m-2)以下である。
鋼板の表層組織の結晶粒径が細かくなるほど、鋼板表層の靱性は向上する。その効果を得るためには、鋼板表面下1mm位置の平均結晶粒径を15μm以下とする必要がある。そのため、鋼板表面下1mm位置の平均結晶粒径を15μm以下とする。なお好ましくは13μm以下である。好ましくは4μm以上である。
鋼板の板厚中心位置における鋼組織の結晶粒径が細かくなるほど、板厚中心位置での靱性は向上する。その効果を得るためには、板厚中心位置における平均結晶粒径を20μm以下とする必要がある。そのため、板厚中心位置の平均結晶粒径を20μm以下とした。なお好ましくは15μm以下である。好ましくは7μm以上である。
「平均結晶粒径」とは、結晶方位差が15°以上の境界によって囲まれた領域を結晶粒としたとき、鋼板表面下1mm位置および板厚中心位置のそれぞれにおいて、すべての結晶粒の平均を指すものとする。なお、平均結晶粒径は後述する実施例に記載の方法で測定することができる。
次に、本発明の一実施形態における厚鋼板の製造方法について説明する。
上記のとおり、製造されたスラブを、1000~1200℃の温度に加熱する。
スラブの加熱温度が1000℃未満になると、スラブ鋳造時にスラブ内部に析出していた粗大NbCが再固溶せずに残存する。これにより、固溶Nbや熱間圧延中に再析出する微細NbCによる未再結晶温度域の低温化効果が得られなくなる。それに伴い、制御圧延による結晶粒の微細化効果が小さくなり、靱性が低下する。一方、スラブの加熱温度が1200℃を超えると、オーステナイトの粒成長により熱間圧延開始時の結晶粒径が粗大になるため、それに伴い熱間圧延後の最終組織の結晶粒径も粗大になり、靱性が低下する。そのため、スラブの加熱温度は1000~1200℃の温度とした。好ましくは1030℃以上であり、好ましくは1170℃以下である。
なおここでは、鋼板表面下1mm位置あるいは板厚中心位置の温度で(8250[Nb]+770℃)を超える温度域を再結晶温度域と称し、鋼板表面下1mm位置あるいは板厚中心位置の温度で(8250[Nb]+770℃)~Ar3温度の温度域を未再結晶温度域と称する。なお、上記した[Nb]は当該元素の含有量(質量%)を表す。
まず、鋼板表面下1mm位置の鋼板温度を、一旦Ar3温度以下まで冷却し、その後復熱でAc3温度超えとする。次いで、鋼板表面下1mm位置に対して、鋼板表面下1mm位置の鋼板温度が(8250[Nb]+770℃)~Ar3温度の温度域における圧下率を25%以上とする圧下を行う。その後、鋼板表面下1mm位置の鋼板温度がAr3温度未満の温度域における総圧下率を15%以下とする圧下を行う。
なお、この冷却は、例えば水冷、送風冷却等の方法が挙げられ、所定の温度に制御できる限り方法は問わない。例えば、Ar3温度以下とする冷却は水冷で行い、鋼板表面下1mm位置がAr3温度以下となっている滞留時間は5秒以上とすることが好ましく、300秒以下とすることが好ましい。冷却後の復熱は、大気中で鋼板を保持することとし、保持時間は30秒以上とすることが好ましく、600秒以下とすることが好ましい。
続いて、鋼板表層が未再結晶温度域である(8250[Nb]+770℃)~Ar3温度の温度域で25%以上の圧下を加えることで、鋼板表層のオーステナイト中に加工ひずみが導入される。これが最終冷却時の変態核として作用することで、靱性が良好な微細組織が得られる。好ましくは30%以上とする。なお、圧延能率の観点から、この温度域での圧下率は80%以下とすることが好ましく、70%以下とすることがより一層好ましい。
なお、この温度域におけるパス数の上限は特に限定しない。また、上記した圧下率の条件を満たせば良く、例えば複数パスに分けて行ってもよい。
鋼板表層の温度がAr3温度未満の温度域での総圧下率が15%を超えると、鋼板表層で変態が完了したフェライト組織やパーライト組織に加工ひずみが導入されることで延性が低下し、曲げ加工性が劣化する。そのため、鋼板表層の温度がAr3温度未満の温度域での総圧下率を15%以下とした。好ましくは6%以下とする。
鋼板の板厚中心位置に対して、板厚中心位置の鋼板温度が、(8250[Nb]+770℃)以下Ar3温度以上の温度域における総圧下率が25%以上となるように圧下を加える。
(8250[Nb]+770℃)以下Ar3温度以上の温度域の総圧下率:25%以上
加熱されたスラブに対し、上記した鋼板表層の圧延条件で熱間圧延を行っている間、鋼板の板厚中心位置が未再結晶温度域である(8250[Nb]+770℃)~Ar3温度の温度域で25%以上の圧下を加えることで、板厚中心位置のオーステナイト中に加工ひずみが導入される。これが最終冷却時の変態核として作用することで靱性が良好な微細組織が得られる。そのため、鋼板板厚中心温度が(8250[Nb]+770℃)以下の温度域での総圧下率を25%以上とした。好ましくは35%以上とする。圧延能率の観点から、この温度域での総圧下率は70%以下とすることが好ましく、67%以下とすることがより一層好ましい。
また、Ar3温度、Ac3温度は、フォーマスタ試験などで求めることができる。
熱間圧延後の板厚中心位置での700~550℃間の平均冷却速度が2500×t-1.7℃/秒未満の場合、オーステナイトから低温変態組織への変態が生じる温度域での冷却速度不足により、本発明で目的とする必要な強度が得られず、また粗大なフェライトが生成するため靱性が低下する。したがって、板厚中心位置での700~550℃の温度域の平均冷却速度は、2500×t-1.7℃/秒以上とした。好ましくは2800×t-1.7℃/秒以上であり、好ましくは15000×t-1.7℃/秒以下である。
焼戻し温度が650℃より高いと、著しい軟化が生じて必要な強度を確保できなくなる場合がある。そのため、焼戻し温度を650℃以下とすることが好ましい。一方、焼戻し温度の下限は特に限定されないが、200℃以上とすることが好ましい。なお、焼戻しの時間は、適宜調整可能である。ここでの焼戻し温度とは、鋼板表面の温度である。より一層好ましくは250℃以上であり、より一層好ましくは630℃以下である。
得られた各鋼板の長手方向と幅方向の中央位置の、鋼板表面下1mm位置が評価面となるようにサンプルを採取した。該サンプルの表面を機械研磨と電解研磨仕上で鏡面研磨し、X線回折装置を用いてWilliamson-Hall法(参考文献1)で転位密度を評価した。
(参考文献1) G.K.Williams and W.H.Hall:Acta Metall.,1(1953),22
得られた各厚鋼板から、該鋼板の長手方向および幅方向の中央位置において、鋼板表面下1mm位置と板厚中心位置の鋼板長手方向断面が評価面となるように、サンプルを採取した。得られたサンプルの表面をコロイダルシリカ仕上で鏡面研磨し、次の条件でEBSP(後方散乱電子線回折法)により測定した。測定領域は300μm×400μm、測定ステップサイズは1μmとした。得られた結晶方位マップより、隣接する結晶粒との結晶方位差が15°以上となる大角粒界で囲まれた組織の円相当直径を求め、上記測定領域における円相当直径の平均値を平均結晶粒径とした。なお、本発明例の鋼板表層、板厚中心共にベイナイトや擬ポリゴナルフェライトを主体とする組織であった。
得られた各スラブの板厚1/4t位置からフォーマスタ試験片を採取した。フォーマスタ試験では、フォーマスタ試験片を用いて、室温から1000℃まで10℃/秒で加熱した際のAc3温度と、1000℃から室温まで0.1℃/秒で冷却した際のAr3温度を測定し、評価に用いた。
得られた各厚鋼板を用いて、該鋼板の長手方向および幅方向の中央位置における、板厚中心位置(板厚1/2位置)から、引張試験片の長手方向が鋼板の圧延方向と平行になるように引張試験片を採取した。次いで、引張試験片を用い、JIS Z2241(2011)に準拠した引張試験を行い、YS、TSを評価した。引張試験片はJIS4号形状のものを使用した。
得られた各厚鋼板を用いて、該鋼板の長手方向および幅方向の中央位置からシャルピー試験片を採取した。シャルピー試験片は、鋼板表面下1mmと板厚中心位置(板厚1/2位置)から、シャルピー試験片の長手方向が鋼板の板幅方向と平行になるように採取した。次いで、各シャルピー試験片を用い、JIS Z2242(2018)に準拠したシャルピー衝撃吸収試験を行い、衝撃吸収エネルギーを評価した。シャルピー試験片はVノッチの標準試験片を使用し、-40℃で3本試験した結果の平均値を評価に用いた。
得られた各厚鋼板を用いて、該鋼板の長手方向および幅方向の中央位置から試験片を採取した。試験片は、鋼板最表面~表層下12mm位置までの形状:厚さ12mm×幅50mm×長さ350mmの試験片を、曲げ試験片の長手方向が鋼板の幅方向と平行になるように採取した。次いで、各試験片を用い、JIS Z2248(2006)に準拠した3点曲げ試験を行った。曲げ半径12mmのパンチを用い、元鋼板の最表面側が曲げの外側に来る向きで180°曲げを行い、割れ発生の有無を評価した。
Claims (4)
- 質量%で、
C :0.04~0.14%、
Si:0.03~0.70%、
Mn:0.30~2.50%、
P :0.030%以下、
S :0.0200%以下、
Nb:0.001~0.100%、
Al:0.001~0.100%、
O :0.01%以下、および
N :0.01%以下を含み、
残部がFe及び不可避不純物からなり、
下記(1)式で定義されるCeqと板厚t[mm]とが、0.0004t+0.25≦Ceq≦0.0004t+0.45を満足する成分組成を有し、
鋼組織は、鋼板表面下1mm位置における転位密度ρ[m-2]がρ≦4×1014であり、
鋼板表面下1mm位置における平均結晶粒径が15μm以下であり、
鋼板の板厚中心位置における平均結晶粒径が20μm以下である、厚鋼板。
Ceq=[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15・・・(1)
ただし、上記(1)式における各元素記号は当該元素の含有量(質量%)を表し、当該元素が含有されていない場合は0とする。 - 前記成分組成が、さらに、質量%で、
Cu:2.00%以下、
Ni:2.50%以下、
Cr:1.50%以下、
Mo:1.00%以下、
Ti:0.100%以下、
V :0.30%以下、
B :0.0100%以下、
W :0.50%以下、
Ca:0.0200%以下、
Mg:0.0200%以下、および
REM:0.0500%以下
からなる群より選択される1種または2種以上を含む、請求項1に記載の厚鋼板。 - 請求項1または2に記載の厚鋼板の製造方法であって、
前記成分組成を有するスラブを1000~1200℃の温度に加熱し、
加熱された前記スラブに熱間圧延を行う際に、
前記鋼板表面下1mm位置の鋼板温度を、一旦Ar3温度以下まで冷却し、その後復熱でAc3温度超えとし、
前記鋼板表面下1mm位置の鋼板温度が(8250[Nb]+770℃)~Ar3温度の温度域における圧下率を25%以上とする圧下を加え、その後前記鋼板表層下1mm位置の鋼板温度がAr3温度未満の温度域における総圧下率を15%以下とする圧下を行うとともに、
前記板厚中心位置の鋼板温度が、(8250[Nb]+770℃)以下Ar3温度以上の温度域における総圧下率を25%以上とする圧下を行い、
前記熱間圧延後、板厚中心位置の温度で700~550℃の温度域における平均冷却速度が、鋼板の板厚をt[mm]としたとき、2500×t-1.7℃/秒以上で冷却する、厚鋼板の製造方法。
ただし、上記[Nb]は、当該元素の含有量(質量%)を表す。 - 前記冷却後、さらに、650℃以下の焼戻し温度で焼戻す、請求項3に記載の厚鋼板の製造方法。
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN202080065264.9A CN114402089B (zh) | 2019-09-20 | 2020-09-16 | 厚钢板和厚钢板的制造方法 |
EP20865982.1A EP4032992B1 (en) | 2019-09-20 | 2020-09-16 | Thick steel sheet, and method for producing thick steel sheet |
KR1020227008910A KR20220047363A (ko) | 2019-09-20 | 2020-09-16 | 후강판 및 후강판의 제조 방법 |
JP2021507702A JP6923103B1 (ja) | 2019-09-20 | 2020-09-16 | 厚鋼板および厚鋼板の製造方法 |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2019-171231 | 2019-09-20 | ||
JP2019171231 | 2019-09-20 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2021054344A1 true WO2021054344A1 (ja) | 2021-03-25 |
Family
ID=74884220
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/JP2020/034995 WO2021054344A1 (ja) | 2019-09-20 | 2020-09-16 | 厚鋼板および厚鋼板の製造方法 |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP4032992B1 (ja) |
JP (1) | JP6923103B1 (ja) |
KR (1) | KR20220047363A (ja) |
CN (1) | CN114402089B (ja) |
WO (1) | WO2021054344A1 (ja) |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS497291B1 (ja) | 1970-05-20 | 1974-02-19 | ||
JP2018031069A (ja) * | 2016-08-19 | 2018-03-01 | 株式会社神戸製鋼所 | 厚鋼板およびその製造方法 |
JP2018059187A (ja) * | 2016-09-28 | 2018-04-12 | Jfeスチール株式会社 | 耐摩耗鋼板および耐摩耗鋼板の製造方法 |
WO2018216665A1 (ja) * | 2017-05-22 | 2018-11-29 | Jfeスチール株式会社 | 厚鋼板およびその製造方法 |
JP2019052341A (ja) | 2017-09-14 | 2019-04-04 | Jfeスチール株式会社 | 曲げ加工性に優れた非調質低降伏比高張力厚鋼板およびその製造方法 |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS497291A (ja) | 1972-05-31 | 1974-01-22 | ||
JPS6320414A (ja) * | 1986-07-14 | 1988-01-28 | Sumitomo Metal Ind Ltd | 高靭性高張力鋼板の製造法 |
JPH10237551A (ja) * | 1997-02-25 | 1998-09-08 | Nkk Corp | 疲労特性及び伸びフランジ性に優れる熱延鋼板の製造方法 |
JP5643542B2 (ja) * | 2010-05-19 | 2014-12-17 | 株式会社神戸製鋼所 | 疲労特性に優れた厚鋼板 |
JP5618036B1 (ja) * | 2013-03-12 | 2014-11-05 | Jfeスチール株式会社 | 多層溶接継手ctod特性に優れた厚鋼板およびその製造方法 |
KR20170038071A (ko) * | 2014-09-05 | 2017-04-05 | 제이에프이 스틸 가부시키가이샤 | 다층 용접 조인트 ctod 특성이 우수한 후강판 및 그의 제조 방법 |
-
2020
- 2020-09-16 JP JP2021507702A patent/JP6923103B1/ja active Active
- 2020-09-16 EP EP20865982.1A patent/EP4032992B1/en active Active
- 2020-09-16 KR KR1020227008910A patent/KR20220047363A/ko not_active Application Discontinuation
- 2020-09-16 CN CN202080065264.9A patent/CN114402089B/zh active Active
- 2020-09-16 WO PCT/JP2020/034995 patent/WO2021054344A1/ja unknown
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS497291B1 (ja) | 1970-05-20 | 1974-02-19 | ||
JP2018031069A (ja) * | 2016-08-19 | 2018-03-01 | 株式会社神戸製鋼所 | 厚鋼板およびその製造方法 |
JP2018059187A (ja) * | 2016-09-28 | 2018-04-12 | Jfeスチール株式会社 | 耐摩耗鋼板および耐摩耗鋼板の製造方法 |
WO2018216665A1 (ja) * | 2017-05-22 | 2018-11-29 | Jfeスチール株式会社 | 厚鋼板およびその製造方法 |
JP2019052341A (ja) | 2017-09-14 | 2019-04-04 | Jfeスチール株式会社 | 曲げ加工性に優れた非調質低降伏比高張力厚鋼板およびその製造方法 |
Non-Patent Citations (1)
Title |
---|
See also references of EP4032992A4 |
Also Published As
Publication number | Publication date |
---|---|
KR20220047363A (ko) | 2022-04-15 |
JPWO2021054344A1 (ja) | 2021-09-30 |
JP6923103B1 (ja) | 2021-08-18 |
EP4032992A4 (en) | 2022-11-09 |
EP4032992A1 (en) | 2022-07-27 |
CN114402089A (zh) | 2022-04-26 |
EP4032992B1 (en) | 2024-03-27 |
CN114402089B (zh) | 2023-03-21 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
JP5522084B2 (ja) | 厚鋼板の製造方法 | |
JP5124988B2 (ja) | 耐遅れ破壊特性に優れた引張強度900MPa以上の高張力鋼板およびその製造方法 | |
JP4874434B1 (ja) | 厚鋼板の製造方法 | |
JP5266791B2 (ja) | 耐sr特性および変形性能に優れたx100グレード以上の高強度鋼板およびその製造方法 | |
JP5574059B2 (ja) | 低温靭性に優れた高強度h形鋼及びその製造方法 | |
JP5303856B2 (ja) | 低温靭性に優れ、かつ強度異方性が小さい高張力鋼材の製造方法 | |
JP5433964B2 (ja) | 曲げ加工性および低温靭性に優れる高張力鋼板の製造方法 | |
JP5659758B2 (ja) | 優れた生産性と溶接性を兼ね備えた、PWHT後の落重特性に優れたTMCP−Temper型高強度厚鋼板の製造方法 | |
JP5277672B2 (ja) | 耐遅れ破壊特性に優れた高張力鋼板ならびにその製造方法 | |
JP5181775B2 (ja) | 曲げ加工性および低温靭性に優れる高張力鋼材ならびにその製造方法 | |
JP6693607B1 (ja) | 熱延鋼板およびその製造方法 | |
CN109923237B (zh) | 具有优异的抗氢致开裂性的压力容器钢及其制造方法 | |
WO2014175122A1 (ja) | H形鋼及びその製造方法 | |
JP4379085B2 (ja) | 高強度高靭性厚鋼板の製造方法 | |
CN111542621B (zh) | 高强度高韧性的热轧钢板及其制造方法 | |
JP2008297570A (ja) | 低降伏比鋼板 | |
JP5157387B2 (ja) | 高変形能を備えた厚肉高強度高靭性鋼管素材の製造方法 | |
CN117568718A (zh) | 厚钢板及其制造方法 | |
JP2008013812A (ja) | 高靭性高張力厚鋼板およびその製造方法 | |
CN113737103A (zh) | 钢板及其制造方法 | |
JP2008280602A (ja) | 高生産性型高強度・高靭性鋼板とその製造方法 | |
JP6923103B1 (ja) | 厚鋼板および厚鋼板の製造方法 | |
JP2002363685A (ja) | 低降伏比高強度冷延鋼板 | |
JP4742617B2 (ja) | 溶接熱影響部靭性に優れた高強度鋼板の製造方法 | |
JP5935678B2 (ja) | 高靭性高張力鋼およびその製造方法 |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
ENP | Entry into the national phase |
Ref document number: 2021507702 Country of ref document: JP Kind code of ref document: A |
|
121 | Ep: the epo has been informed by wipo that ep was designated in this application |
Ref document number: 20865982 Country of ref document: EP Kind code of ref document: A1 |
|
ENP | Entry into the national phase |
Ref document number: 20227008910 Country of ref document: KR Kind code of ref document: A |
|
NENP | Non-entry into the national phase |
Ref country code: DE |
|
ENP | Entry into the national phase |
Ref document number: 2020865982 Country of ref document: EP Effective date: 20220420 |