WO2017169837A1 - Tôle d'acier laminée à froid de haute résistance, tôle d'acier galvanisée par immersion à chaud de haute résistance, et procédé de production de tôle d'acier laminée à froid de haute résistance et de tôle d'acier galvanisée par immersion à chaud de haute résistance - Google Patents

Tôle d'acier laminée à froid de haute résistance, tôle d'acier galvanisée par immersion à chaud de haute résistance, et procédé de production de tôle d'acier laminée à froid de haute résistance et de tôle d'acier galvanisée par immersion à chaud de haute résistance Download PDF

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WO2017169837A1
WO2017169837A1 PCT/JP2017/010624 JP2017010624W WO2017169837A1 WO 2017169837 A1 WO2017169837 A1 WO 2017169837A1 JP 2017010624 W JP2017010624 W JP 2017010624W WO 2017169837 A1 WO2017169837 A1 WO 2017169837A1
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steel sheet
cooling
strength
value
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道高 経澤
道治 中屋
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株式会社神戸製鋼所
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • 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
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C21D2211/001—Austenite
    • 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
    • C21D2211/008—Martensite
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/20—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
    • G01N23/203—Measuring back scattering

Definitions

  • the present invention relates to a high-strength cold-rolled steel sheet, a high-strength hot-dip galvanized steel sheet, and a method for producing them, and more specifically, a high-strength cold-rolled steel sheet having a tensile strength of 980 MPa or more that is excellent in ductility and bendability and has a high yield ratio.
  • the present invention relates to high-strength hot-dip galvanized steel sheets and methods for producing them.
  • these high-strength cold-rolled steel sheets and high-strength hot-dip galvanized steel sheets may be collectively referred to as high-strength steel sheets.
  • YR Yield Ratio
  • the YR is a value obtained by dividing YS (Yield Strength), which is 0.2% proof stress, by TS (Tensile Strength), which is tensile strength, and multiplying by 100.
  • Patent Document 1 Japanese Patent Laid-Open No. 2014-237871
  • the balance between strength and bendability is improved by using martensite, bainite, or a microstructure in which they are combined, and the surface layer of the steel sheet is soft. It shows what you can do.
  • Patent Document 1 only high strength and the above formability are studied, and the yield ratio and ductility (elongation) are not considered.
  • Patent Document 2 Japanese Patent Laid-Open No. 2013-147736
  • one or more elements selected from Ti, Nb, and V are added, B is essential, a bainite and martensite-based structure is formed, and bainite A high-strength steel sheet having an average crystal grain size of 7 ⁇ m or less is shown.
  • the steel sheet disclosed in Patent Document 2 has a yield ratio in the 70% range and does not consider bendability.
  • An object of the present invention is to provide a high-strength steel sheet and a high-strength hot-dip galvanized steel sheet that have a high yield ratio, excellent ductility and bendability in a high-strength region having a tensile strength of 980 MPa or more, and methods for producing them. .
  • the high-strength cold-rolled steel sheet of the present invention that has achieved the above object is, in mass%, C: 0.12 to 0.19%, Si: more than 0%, 0.4% or less, Mn: 1.80 to 2. 45%, P: more than 0%, 0.020% or less, S: more than 0%, 0.0040% or less, Al: 0.015 to 0.06%, Ti: 0.010 to 0.035%, and B: 0.0025 to 0.0040% is contained, the balance is iron and inevitable impurities, X defined in the following (1) is 8.0 or less, Y defined in the following (2) The X difference value Y ⁇ X is 45 or more and 53 or less, the volume ratio of retained austenite to the whole structure is 2% or less, and the tensile strength is 980 MPa or more.
  • X is a value obtained by dividing the total number of measurement points equal to or less than [0.40 ⁇ (IQmax ⁇ IQmin) + IQmin] by 100 and multiplying by 100.
  • Y is a value obtained by dividing the total number of measurement points equal to or less than [0.75 ⁇ (IQmax ⁇ IQmin) + IQmin] by the total number of measurement points and multiplying by 100, in the above (1) and (2)
  • IQ means the sharpness of the electron beam backscatter diffraction pattern
  • IQmax is the maximum value of IQ at all measurement points
  • IQmin is the minimum value of IQ at all measurement points.
  • the present invention it is possible to provide a high-strength cold-rolled steel sheet in which the volume fraction of retained steel and retained austenite and IQ (Image Quality, image quality) are appropriately controlled. For this reason, it is possible to provide a cold-rolled steel sheet having a tensile strength of 980 MPa or more excellent in ductility and bendability, a high yield ratio, a manufacturing method thereof, and a hot-dip galvanized steel sheet.
  • FIG. 1 is a schematic diagram for explaining IQ requirements defined in the present invention.
  • FIG. 2 is a graph schematically showing the configuration of the annealing process recommended for obtaining the high-strength steel sheet of the present invention.
  • high-strength steel plate having a tensile strength of 980 MPa or more, a high yield ratio, and excellent ductility and bendability (hereinafter, sometimes referred to as workability).
  • the inventors have made extensive studies focusing on the retained austenite volume fraction and IQ. As a result, it was found that the steel components, retained austenite volume fraction, and IQ may be adjusted to the following ranges, respectively.
  • high strength means that the tensile strength is 980 MPa or more.
  • IQ is the sharpness of an EBSD (Electron Back Scatter Diffraction, electron beam backscatter diffraction) pattern.
  • IQ is known to be affected by the amount of strain in the crystal. Specifically, the smaller the IQ, the more strain tends to exist in the crystal. For example, martensite has a high dislocation density and includes disorder of the crystal structure, so that IQ tends to be small. Ferrite tends to have a high IQ due to its low dislocation density. Therefore, conventionally, a method for determining the metal structure using the absolute value of IQ as an index has been proposed.
  • the present inventors investigated the influence of the dispersion state of strain in the steel sheet, that is, the IQ distribution state, which is the sharpness of the EBSD pattern, on the yield ratio, ductility, and bendability. As a result, it has been found that it is important for IQ to satisfy the requirements described later in order to achieve any of good ductility, bendability, and high yield ratio. The details of the IQ measurement method will be described in the column of Examples described later.
  • the value X defined in (1) below is 8.0 or less, and the difference YX between the value Y defined in (2) below and the value X is 45 or more and 53 or less. is there.
  • the value X is a value obtained by dividing the total number of measurement points equal to or less than [0.40 ⁇ (IQmax ⁇ IQmin) + IQmin] by the total number of measurement points and multiplying by 100.
  • the value Y is a value obtained by dividing the total number of measurement points below [0.75 ⁇ (IQmax ⁇ IQmin) + IQmin] by the total number of measurement points and multiplying by 100.
  • IQ in the above (1) and (2) means the definition of the electron beam backscatter diffraction pattern
  • IQmax is the maximum value of IQ at all measurement points
  • IQmin is the minimum value of IQ at all measurement points.
  • X and Y are schematically shown in FIG.
  • the horizontal axis represents the IQ value
  • the vertical axis represents the number ratio (%) of the measurement points indicating each IQ value.
  • X is the ratio of the number of measurement points where the IQ value is [0.40 ⁇ (IQmax ⁇ IQmin) + IQmin] or less to all measurement points
  • Y is the IQ value of [0.75 ⁇ (IQmax ⁇ IQmin).
  • + IQmin] is the number ratio of measurement points to all measurement points. Therefore, if X is 8.0 or less, the ratio of the measurement points where the IQ value is [0.40 ⁇ (IQmax ⁇ IQmin) + IQmin] or less to the total measurement points is 8.0% or less.
  • the value of Y ⁇ X being 45 or more and 53 or less means that the IQ value exceeds [0.40 ⁇ (IQmax ⁇ IQmin) + IQmin] and [0.75 ⁇ (IQmax ⁇ IQmin). ) + IQmin] means that the ratio of measurement points to all measurement points is 45% or more and 53% or less.
  • X is preferably 6 or less, more preferably 5 or less. Although the minimum of X is not specifically limited, For example, it is 0.5.
  • X is 8.0 or less, and the value of Y ⁇ X is 45 or more and 53 or less.
  • the yield ratio decreases.
  • the value of YX exceeds 53, the yield ratio becomes too high and the ductility is lowered.
  • the reason why the yield ratio increases and the ductility decreases when the value of YX becomes too large is not necessarily clear, but as the value of YX increases, the strain distribution in the steel sheet becomes homogeneous and the yield ratio becomes lower. It is thought that the ductility increased and the ductility decreased.
  • YX is preferably 46 or more and 52 or less, and more preferably 47 or more and 51 or less.
  • the volume ratio of retained austenite with respect to the entire structure is set to 2% or less. As the volume fraction of retained austenite increases, the yield ratio decreases.
  • the volume fraction of retained austenite is preferably 1.5% or less, more preferably 1% or less, and most preferably 0%.
  • the volume fraction of retained austenite was measured using ISIJ Int. Vol. 33. (1933), no. 7, p. 776 is a value measured by the method described in 776.
  • the base structure is a bainite structure and includes a small amount of martensite structure.
  • the total ratio of these tissues to all tissues is, for example, 95 area% or more.
  • the chemical components in the steel sheet are controlled as follows. In the present specification, all chemical components mean mass%.
  • C 0.12 to 0.19% C is an element necessary for ensuring the strength of the steel sheet. If the amount of C is insufficient, the tensile strength decreases. Therefore, the lower limit of the C amount is 0.12% or more. The lower limit of the C amount is preferably 0.13% or more, more preferably 0.14% or more. However, if the amount of C becomes excessive, the X value calculated based on the IQ value increases, and the yield ratio and bendability decrease. Therefore, the upper limit of the C amount is set to 0.19% or less. The upper limit of the C amount is preferably 0.18% or less, and more preferably 0.17% or less.
  • Si more than 0%, 0.4% or less Si is known as a solid solution strengthening element, and is an element that effectively acts to improve the tensile strength while suppressing a decrease in ductility. It is also an element that improves bendability.
  • the Si content is preferably 0.01% or more, more preferably 0.1% or more.
  • the upper limit of Si content is set to 0.4% or less.
  • the upper limit of the Si amount is preferably 0.3% or less, and more preferably 0.25% or less.
  • Mn 1.80 to 2.45%
  • Mn is an element that contributes to increasing the strength of the steel sheet.
  • the lower limit of the amount of Mn is made 1.80% or more.
  • the amount of Mn is preferably 1.9% or more, more preferably 2.0% or more. If Mn is too small, the YX value calculated based on the IQ value will be low, and the yield ratio will be reduced. When the amount of Mn is excessive, the X value calculated based on the IQ value is high, the YX value is low, and the yield ratio and bendability are lowered. Therefore, the upper limit of the Mn amount is 2.45% or less.
  • the upper limit of the amount of Mn is preferably 2.35% or less, and more preferably 2.25% or less.
  • P more than 0% and 0.020% or less
  • P is an element inevitably contained.
  • P is an element that segregates at grain boundaries and promotes grain boundary embrittlement, and degrades bendability. For this reason, it is recommended to reduce the amount of P as much as possible. Therefore, the upper limit of the P amount is 0.020% or less.
  • the upper limit of the amount of P is preferably 0.015% or less, and more preferably 0.010% or less. Note that P is an impurity inevitably contained in the steel, and it is industrially impossible to reduce the amount to 0%.
  • S more than 0% and 0.0040% or less S is an element inevitably contained in the same manner as P. Since S generates inclusions and degrades bendability, it is recommended that the amount of S be reduced as much as possible. Therefore, the upper limit of the S amount is set to 0.0040% or less.
  • the upper limit of the amount of S is preferably 0.003% or less, more preferably 0.002% or less.
  • S is an impurity inevitably contained in steel, and it is industrially impossible to reduce the amount to 0%.
  • Al 0.015 to 0.06%
  • Al is an element that acts as a deoxidizer.
  • the lower limit of the Al content is set to 0.015% or more.
  • the lower limit of the Al content is preferably 0.025% or more, more preferably 0.030% or more.
  • the upper limit of the Al amount is set to 0.06% or less.
  • the upper limit of the Al content is preferably 0.055% or less, more preferably 0.050% or less.
  • Ti 0.010 to 0.035%
  • Ti is an element that improves the strength by forming carbides and nitrides.
  • Ti is also an element for effectively utilizing the hardenability of B. Specifically, Ti forms a nitride to reduce N in the steel. Thereby, formation of B nitride is suppressed, and B is in a solid solution state, so that the hardenability of B can be effectively exhibited.
  • the lower limit of the Ti amount is set to 0.010% or more.
  • the lower limit of the amount of Ti is preferably 0.013% or more, and more preferably 0.015% or more.
  • the upper limit of the Ti amount is set to 0.035% or less.
  • the upper limit of the Ti amount is preferably 0.030% or less. More preferably, it is 0.025% or less.
  • B 0.0025 to 0.0040% B is an element that contributes to increasing the strength of the steel sheet by improving the hardenability.
  • the lower limit of the B amount is set to 0.0025% or more.
  • the lower limit of the B amount is preferably 0.0027% or more, more preferably 0.0029% or more.
  • the upper limit of the B amount is set to 0.0040% or less.
  • the upper limit of the amount of B is preferably 0.0035% or less.
  • the basic components of the high-strength steel sheet of the present invention are as described above, and the balance is substantially iron. However, it is naturally allowed that inevitable impurities brought into the steel depending on the situation of raw materials, materials, manufacturing equipment, etc. are contained in the steel. Inevitable impurities include, for example, N and O in addition to the above-described P and S, and these are preferably in the following ranges, respectively.
  • N More than 0% and 0.01% or less N is inevitably present as an impurity element and deteriorates bendability.
  • the upper limit of N is preferably 0.01% or less, more preferably 0.006% or less, and still more preferably 0.005% or less. The smaller the amount of N, the better. However, it is industrially difficult to make it 0%.
  • O More than 0% and 0.002% or less O is unavoidably present as an impurity element and deteriorates bendability.
  • the upper limit of O is preferably 0.002% or less, more preferably 0.0015% or less, and still more preferably 0.0010% or less. The smaller the amount of O, the better. However, it is industrially difficult to make it 0%.
  • the high-strength cold-rolled steel sheet of the present invention is, in mass%, Cu: more than 0%, 0.3% or less, Ni: more than 0%, 0.3% or less, Cr: more than 0%, 0.25% or less, Mo: more than 0%, 0.1% or less, V: more than 0%, 0.05% or less, Nb: more than 0%, 0.08% or less, and Ca: more than 0%, 0.005% or less It is preferable to contain 1 or more types chosen from these.
  • Cu, Ni, Cr, Mo, V, and Nb are all effective elements for improving the strength. These elements may be contained alone or in appropriate combination within the following ranges.
  • Cu more than 0%, 0.3% or less Cu is an element that is further effective in improving the corrosion resistance of the steel sheet.
  • the lower limit of the Cu amount is preferably 0.03% or more, more preferably 0.05% or more.
  • the upper limit of the amount of Cu is preferably 0.3% or less, more preferably 0.2% or less, and still more preferably 0.15% or less.
  • Ni more than 0% and 0.3% or less
  • Ni is an element that is further effective in improving the corrosion resistance of the steel sheet.
  • the lower limit of the Ni amount is preferably 0.03% or more, more preferably 0.05% or more.
  • the upper limit of the Ni amount is preferably 0.3% or less, more preferably 0.2% or less, and still more preferably 0.15% or less.
  • Cr more than 0% and 0.25% or less Cr is an element showing the effect of increasing the strength.
  • the lower limit of the Cr amount is preferably 0.01% or more, more preferably 0.015% or more, still more preferably 0.03% or more, and particularly preferably 0.8%. 05% or more.
  • the upper limit of the amount of Cr is preferably 0.25% or less, more preferably 0.20% or less, and still more preferably 0.10% or less.
  • Mo more than 0%, 0.1% or less Mo is an element showing the effect of increasing the strength.
  • the lower limit of the amount of Mo is preferably 0.03% or more, more preferably 0.05% or more.
  • the upper limit of the Mo amount is preferably 0.1% or less.
  • V more than 0% and 0.05% or less
  • V is an element showing the effect of increasing the strength.
  • the lower limit of the amount of V is preferably 0.003% or more, and more preferably 0.005% or more.
  • the upper limit of the V amount is preferably 0.05% or less, more preferably 0.03% or less, and still more preferably 0.02% or less.
  • Nb more than 0% and 0.08% or less Nb is an element showing the effect of increasing the strength.
  • the lower limit of the Nb amount is preferably 0.003% or more, more preferably 0.005% or more.
  • the upper limit of the Nb amount is preferably 0.08% or less, more preferably 0.06% or less, and still more preferably 0.04% or less.
  • Ca more than 0% and 0.005% or less Ca is an element effective for spheroidizing sulfides in steel and enhancing bendability.
  • the lower limit of the Ca content is preferably 0.0005% or more, more preferably 0.001% or more.
  • the upper limit of the Ca content is preferably 0.005% or less, more preferably 0.003% or less, and still more preferably 0.0025% or less.
  • the high strength steel sheet of the present invention in which the chemical component composition, the area ratio of retained austenite, the values X and Y calculated from IQ values satisfy the above conditions, the tensile strength is 980 MPa or more, and the yield ratio, Excellent ductility and bendability.
  • the yield ratio of the high-strength steel sheet of the present invention can be, for example, 90% or more and 95% or less.
  • the high-strength steel sheet of the present invention that satisfies the above requirements includes processes of hot rolling, cold rolling, and annealing (soaking and cooling), and in particular, appropriately controls the annealing process after cold rolling. There is a feature.
  • the manufacturing process for obtaining the high-strength steel sheet of the present invention will be described in the order of hot rolling, cold rolling, and subsequent annealing.
  • Preferred conditions for hot rolling are as follows, for example.
  • the heating temperature before hot rolling is low, the solid solution of carbides such as TiC in austenite may be reduced. For this reason, the minimum of the heating temperature before hot rolling becomes like this. Preferably it is 1200 degreeC or more, More preferably, it is 1250 degreeC or more. If the heating temperature before hot rolling is high, the cost increases. For this reason, the upper limit of the heating temperature before hot rolling is preferably 1350 ° C. or less, more preferably 1300 ° C. or less.
  • finish rolling temperature of hot rolling is low, rolling cannot be performed in the austenite single-phase region, deformation resistance during rolling is large, and operation may be difficult. For this reason, finish rolling temperature becomes like this.
  • it is 850 degreeC or more, More preferably, it is 870 degreeC or more.
  • finish rolling temperature is high, the crystal may be coarsened. For this reason, finish rolling temperature becomes like this.
  • it is 980 degrees C or less, More preferably, it is 950 degrees C or less.
  • the average cooling rate from finish rolling to winding in hot rolling is preferably 10 ° C./second or more, more preferably 20 ° C./second or more in consideration of productivity.
  • the average cooling rate is high, the equipment cost becomes high. Therefore, it is preferably 100 ° C./second or less, and more preferably 50 ° C./second or less.
  • Winding temperature after hot rolling 550 ° C. or more
  • the coiling temperature after hot rolling is 550 ° C. or higher, preferably 570 ° C. or higher, more preferably 600 ° C. or higher.
  • the coiling temperature after hot rolling is preferably 800 ° C. or lower, more preferably 750 ° C. or lower.
  • Cold rolling rate 20% or more, 60% or less
  • the hot-rolled steel sheet is subjected to cold rolling after pickling to remove scale.
  • the plate thickness must be reduced in the hot rolling process in order to obtain a steel plate having a predetermined thickness. Become. This takes time for pickling and reduces productivity. Therefore, the lower limit of the cold rolling rate is preferably 20% or more, more preferably 25% or more.
  • the upper limit of the cold rolling rate is preferably 60% or less, more preferably 55% or less, and still more preferably 50% or less.
  • the annealing step after cold rolling is (a) a soaking step for heating and holding, (b) a first cooling step performed following the soaking step, (c) A holding step for holding in a predetermined temperature range after the first cooling step, (d) a second cooling step performed subsequent to the holding step, and (e) a third cooling performed subsequent to the second cooling step. It is important to appropriately adjust the conditions (a) to (e), including the steps.
  • FIG. 2 schematically shows the structures (a) to (e) of the annealing process of the present invention.
  • the soaking temperature is less than the Ac 3 point, the value of X becomes high, and it becomes difficult to ensure the yield ratio. Therefore, the lower limit of the soaking temperature is preferably Ac 3 point or higher, and more preferably Ac 3 point + 25 ° C. or higher.
  • the upper limit is preferably Ac 3 point + 200 ° C. or less, and more preferably Ac 3 point + 150 ° C. or less.
  • the heating rate up to the soaking temperature is not particularly limited, but the average heating rate is preferably 1 ° C./second or more and 20 ° C./second or less.
  • the lower limit of the average heating rate is preferably 1 ° C./second or more, more preferably 3 ° C./second or more, and further preferably 5 ° C./second or more.
  • the upper limit of the average heating rate is preferably 20 ° C./second or less, more preferably 18 ° C./second or less, and still more preferably 15 ° C./second or less.
  • the soaking temperature is soaked for 1 second to 100 seconds.
  • the soaking time is less than 1 second, the value of X becomes high and it becomes difficult to ensure the yield ratio. Therefore, the lower limit of the soaking time is preferably 1 second or longer, more preferably 10 seconds or longer.
  • the upper limit of the soaking time is preferably 100 seconds or less, more preferably 80 seconds or less.
  • the average cooling rate from the soaking temperature to the following cooling stop holding temperature is preferably 15 ° C / second or more and 50 ° C / second or less.
  • the lower limit of the average cooling rate is preferably 15 ° C./second or more, more preferably 20 ° C./second or more.
  • the upper limit of the average cooling rate is preferably 50 ° C./second or less, more preferably 40 ° C./second or less, still more preferably 30 ° C./second or less.
  • the cooling stop temperature in the first cooling step is preferably 380 ° C. or higher and 440 ° C. or lower. The reason why such a temperature range is preferable will be described later.
  • the first cooling is preferably held at a temperature of 380 ° C. or higher and 440 ° C. or lower for a predetermined time.
  • the cooling stop temperature and the holding temperature in the first cooling step are less than 380 ° C., the above-described YX value becomes high, the yield ratio becomes too high, and the ductility also decreases. Therefore, the lower limit of the cooling stop and holding temperature is preferably 380 ° C. or higher, more preferably 390 ° C. or higher.
  • the upper limit of the cooling stop and holding temperature is preferably 440 ° C. or less, more preferably 430 ° C. or less, and further preferably 420 ° C. or less.
  • the cooling stop temperature of the first cooling process is less than 380 ° C. and the end temperature of the holding process exceeds 440 ° C., the volume ratio of retained austenite increases and the yield ratio decreases.
  • the holding time in the holding step is preferably 20 seconds or longer and 30 seconds or shorter.
  • the holding time is less than 20 seconds, the value of X is high, the value of YX is low, the yield ratio is lowered, and the bendability is deteriorated. Therefore, the lower limit of the holding time is 20 seconds or longer, preferably 22 seconds or longer.
  • the holding time exceeds 30 seconds, the value of Y ⁇ X is increased, so that the yield ratio becomes too high and the bendability also decreases. Therefore, the upper limit of the holding time is 30 seconds or less, preferably 28 seconds or less.
  • (D) Second cooling step After the (c) holding step is finished, the cooling is stopped at an average cooling rate of 20 ° C / second or more and 50 ° C / second or less to a cooling stop temperature of 100 ° C or more and 310 ° C or less. It is preferable.
  • the average cooling rate in the second cooling step is less than 20 ° C./second, the value of YX increases, so that the yield ratio becomes too high and the ductility deteriorates. Therefore, the lower limit of the average cooling rate in the second cooling step is preferably 20 ° C./second or more, more preferably 25 ° C./second or more.
  • the upper limit of the average cooling rate is preferably 50 ° C./second or less, more preferably 40 ° C./second or less.
  • the lower limit of the cooling stop holding temperature is preferably 100 ° C. or higher, more preferably 200 ° C. or higher.
  • the upper limit of the cooling stop temperature is preferably 310 ° C. or lower, more preferably 300 ° C. or lower, and further preferably 290 ° C. or lower.
  • the upper limit of the average cooling rate is not particularly limited, and is, for example, 10 ° C./second.
  • the cooling stop temperature in the third cooling step is not particularly limited, and it may be normally cooled to room temperature.
  • the present invention includes a high-strength hot-dip galvanized steel sheet having a galvanized layer on the surface of a high-strength cold-rolled steel sheet.
  • the manufacturing method of the high-strength hot-dip galvanized steel sheet of the present invention includes a step of performing a galvanizing treatment between the above (c) holding step and (d) the second cooling step.
  • This galvanizing treatment is performed by immersing the cold-rolled steel sheet in a galvanizing bath at 440 ° C. or higher and 470 ° C. or lower for 1 second or longer and 5 seconds or shorter after the holding step.
  • the temperature of the galvanizing bath is preferably 455 ° C. or higher and 465 ° C. or lower.
  • An experimental slab having the composition shown in Table 1 below was manufactured.
  • the slab was heated to 1250 ° C. and hot-rolled to a thickness of 2.8 mm.
  • the finish rolling temperature was 900 ° C.
  • the average cooling rate from finish rolling to winding in hot rolling was 20 ° C./second
  • the winding temperature was 600 ° C.
  • the obtained hot-rolled steel sheet was pickled and then cold-rolled to a thickness of 1.4 mm.
  • heat treatment was performed under the conditions shown in FIG. In any of the heat treatments shown in Table 2, the average heating rate until the (a) soaking step was 8 ° C./second, and the average cooling rate in the first cooling step was 20 ° C./second.
  • temper rolling with an elongation of 0.1% was performed.
  • the blank means that it is not added, and P, S, N, and O are unavoidable impurities as described above, and the values shown in the P, S, N, and O columns are unavoidable. Means the amount contained.
  • IQ image quality
  • volume fraction of retained austenite volume fraction of retained austenite
  • IQ image quality
  • IQ image quality
  • a sample was prepared by mechanically polishing a cross section parallel to the rolling direction.
  • this sample was set in an OIM system manufactured by Texemra Laboratories Inc. and tilted by 70 °, and an area of 100 ⁇ m ⁇ 100 ⁇ m was taken as a measurement visual field, and acceleration voltage: 20 kV, 1 step: 185 ⁇ m at 0.25 ⁇ m EBSD measurement was performed.
  • IQ of a body-centered cubic lattice (BCC) crystal including a body-centered tetragonal lattice (BCT) was measured.
  • the body-centered tetragonal lattice is one in which the C atoms are dissolved in a specific interstitial position in the body-centered cubic lattice so that the lattice extends in one direction. Since the body-centered tetragonal lattice has the same structure as the body-centered cubic lattice, the measurement of the body-centered cubic lattice includes the body-centered square lattice in this embodiment. In addition, a measurement location is W / 4 part when the length in the direction perpendicular to the rolling direction in a plane parallel to rolling is W, and t / 4 part when the plate thickness is t. One field of view was carried out. From the measurement results, the values of X and Y described above were calculated.
  • the bendability (R / t) is obtained by taking a 1.4 mm ⁇ 30 mm ⁇ 20 mm test piece from the cold-rolled steel sheet so that the direction perpendicular to the rolling direction on the rolling surface is the length of the test piece, and JIS Z2248. The test was conducted according to the V-block method. And the minimum bending radius R which a crack and a crack do not generate
  • test No. in Table 3 Nos. 32 to 34 each use the steel type 2 in Table 1 that satisfies the composition of the present invention, and the heat treatment No. 2 in Table 2, which is a preferable heat treatment condition of the present invention.
  • Test No. in Table 3 Nos. 20 to 26 and 39 use the steel types 4 to 10 and 17 of Table 1 that do not satisfy the composition of the present invention. 3 is an example manufactured under the heat treatment conditions of No. 3.
  • Test No. No. 20 has a small amount of C, a small value of YX, and a low tensile strength (TS).
  • Test No. No. 21 has a large amount of C, a large value of X, a small value of YX, a high volume fraction of retained austenite, a low yield ratio (YR), and a bendability (R / t). Is not satisfied.
  • Test No. No. 22 has a small amount of Mn, a small YX value, and a low tensile strength (TS).
  • Test No. No. 23 has a large amount of Mn, a large X value, a small YX value, a low yield ratio (YR), and does not satisfy bendability.
  • Test No. No. 24 has a small Ti amount, a small Y-X value, a low tensile strength (TS), a low yield ratio (YR) and a ductility (El), and does not satisfy bendability (R / t).
  • Test No. No. 25 has a large Ti amount, a large X value, a small Y-X value, a low yield ratio (YR), and does not satisfy bendability.
  • Test No. No. 26 has a small amount of B, a small Y-X value, a low tensile strength (TS) and a low yield ratio (YR).
  • Test No. No. 39 has a large amount of Si, a large value of X, a small value of Y ⁇ X, and a low yield ratio (YR).
  • Test No. in Table 3 1, 2, 4 to 10, 15 to 19, 36, and 40 use steel types 1 to 3 and 16 in Table 1 that satisfy the composition of the present invention. This is an example of manufacturing under the heat treatment conditions of 1, 2, 4 to 9, 14 to 20.
  • Test No. No. 1 had a low soaking temperature, a large value of X, a low tensile strength (TS), and a low yield ratio (YR).
  • Test No. No. 2 has a low cooling stop temperature and a subsequent holding temperature, a large YX value, a high yield ratio (YR), and a low ductility (El).
  • Test No. 4, 5, 9, and 10 had a high cooling stop temperature and a subsequent holding temperature, a low YX value, and a low yield ratio (YR).
  • Test No. No. 36 is an example of processing under conditions where the cooling stop temperature is low and the holding end temperature is high.
  • the volume ratio of residual ⁇ is increased and the yield ratio (YR) is lowered.
  • Test No. No. 40 (a) The holding time in the soaking step was short (not held), the value of X was large, the tensile strength (TS) was low, and the yield ratio (YR) was low.

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Abstract

Cette tôle d'acier laminée à froid de haute résistance contient C, Si, Mn, P, S, Al, Ti et B ; elle est conçue de telle sorte que X, tel que défini ci-dessous, soit inférieur ou égal à 8,0 et de telle sorte que la différence Y - X, entre Y tel que défini ci-dessous et X, soit de 45 à 53 ; et elle a une fraction volumique d'austénite résiduelle inférieure ou égale à 2 %. X est le nombre total de points de mesure à ou au-dessous de [0,40 × (IQmax - IQmin) + IQmin] divisé par le nombre total de points de mesure et multiplié par 100, et Y représente le nombre total de points de mesure à ou au-dessous de [0,75 × (IQmax - IQmin) + IQmin] divisé par le nombre total de points de mesure et multiplié par 100. IQ est la netteté d'un diagramme de diffraction d'électrons rétrodiffusés, IQmax est la valeur IQ maximale parmi tous les points de mesure et IQmin est la valeur IQ minimale parmi tous les points de mesure.
PCT/JP2017/010624 2016-03-30 2017-03-16 Tôle d'acier laminée à froid de haute résistance, tôle d'acier galvanisée par immersion à chaud de haute résistance, et procédé de production de tôle d'acier laminée à froid de haute résistance et de tôle d'acier galvanisée par immersion à chaud de haute résistance WO2017169837A1 (fr)

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JP2021502563A (ja) * 2017-11-17 2021-01-28 ケプコ ニュークリア フューエル カンパニー リミテッド Ｅｂｓｄパターンクオリティを活用した核燃料用ジルコニウム合金被覆管再結晶度の測定方法
WO2021054290A1 (fr) * 2019-09-17 2021-03-25 株式会社神戸製鋼所 Tôle d'acier à haute résistance mécanique et son procédé de production

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WO2013047755A1 (fr) * 2011-09-30 2013-04-04 新日鐵住金株式会社 Feuille d'acier galvanisé par immersion à chaud et à haute résistance qui présente une excellente résistance aux chocs et procédé de production de cette dernière et feuille d'acier galvanisé par immersion à chaud alliée et à haute résistance et procédé de production correspondant
WO2016111275A1 (fr) * 2015-01-09 2016-07-14 株式会社神戸製鋼所 Tôle d'acier plaquée hautement résistante dotée d'excellentes propriétés de placage, d'usinage et de résistance à la fracture différée, et procédé de fabrication de celle-ci

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WO2013047755A1 (fr) * 2011-09-30 2013-04-04 新日鐵住金株式会社 Feuille d'acier galvanisé par immersion à chaud et à haute résistance qui présente une excellente résistance aux chocs et procédé de production de cette dernière et feuille d'acier galvanisé par immersion à chaud alliée et à haute résistance et procédé de production correspondant
WO2016111275A1 (fr) * 2015-01-09 2016-07-14 株式会社神戸製鋼所 Tôle d'acier plaquée hautement résistante dotée d'excellentes propriétés de placage, d'usinage et de résistance à la fracture différée, et procédé de fabrication de celle-ci

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JP2021502563A (ja) * 2017-11-17 2021-01-28 ケプコ ニュークリア フューエル カンパニー リミテッド Ｅｂｓｄパターンクオリティを活用した核燃料用ジルコニウム合金被覆管再結晶度の測定方法
EP3712601A4 (fr) * 2017-11-17 2021-08-11 Kepco Nuclear Fuel Co., Ltd Procédé de mesure du degré de recristallisation d'un tube de gainage en alliage de zirconium destiné à un combustible nucléaire à l'aide d'une qualité de motif ebsd
WO2021054290A1 (fr) * 2019-09-17 2021-03-25 株式会社神戸製鋼所 Tôle d'acier à haute résistance mécanique et son procédé de production
JP2021046571A (ja) * 2019-09-17 2021-03-25 株式会社神戸製鋼所 高強度鋼板およびその製造方法
JP7191796B2 (ja) 2019-09-17 2022-12-19 株式会社神戸製鋼所 高強度鋼板およびその製造方法
US11913088B2 (en) 2019-09-17 2024-02-27 Kobe Steel, Ltd. High-strength steel sheet and method for producing same

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