WO2017169837A1 - High-strength cold-rolled steel sheet, high-strength hot-dip-galvanized steel sheet, and production method for high-strength cold-rolled steel sheet and high-strength hot-dip-galvanized steel sheet - Google Patents
High-strength cold-rolled steel sheet, high-strength hot-dip-galvanized steel sheet, and production method for high-strength cold-rolled steel sheet and high-strength hot-dip-galvanized steel sheet Download PDFInfo
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- 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
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—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
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- 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
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/021—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
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—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
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- C—CHEMISTRY; METALLURGY
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- 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
This high-strength cold-rolled steel sheet: contains C, Si, Mn, P, S, Al, Ti, and B; is configured such that X, as defined below, is 8.0 or less and such that the difference Y-X between Y, as defined below, and X is 45-53; and has a volume fraction of retained austenite of 2% or less. X is the total number of measurement points at or below [0.40×(IQmax-IQmin)+IQmin] divided by the total number of measurement points and multiplied by 100, and Y is the total number of measurement points at or below [0.75×(IQmax-IQmin)+IQmin] divided by the total number of measurement points and multiplied by 100. IQ is the sharpness of an electron backscatter diffraction pattern, IQmax is the maximum IQ value from among all measurement points, and IQmin is the minimum IQ value from among all measurement points.
Description
本発明は、高強度冷延鋼板および高強度溶融亜鉛めっき鋼板並びにそれらの製造方法に関し、より詳細には、延性、曲げ性に優れ高降伏比である引張強度980MPa以上の高強度冷延鋼板および高強度溶融亜鉛めっき鋼板並びにそれらの製造方法に関する。以下では、これら高強度冷延鋼板と高強度溶融亜鉛めっき鋼板をまとめて、単に高強度鋼板と呼ぶ場合がある。
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. Hereinafter, 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.
近年、自動車用鋼板や輸送機械用鋼板等の部材の高強度化に伴い、延性、曲げ性といった加工性が低下している。このため、自動車用鋼板および輸送機械用鋼板をプレス成形することによって複雑な形状の部材に加工することは困難であった。よって、上記加工性に優れた高強度鋼板が求められている。
In recent years, workability such as ductility and bendability has been reduced with increasing strength of members such as automobile steel plates and transport machinery steel plates. For this reason, it was difficult to process a steel plate for automobiles and a steel plate for transport machinery into a member having a complicated shape by press forming. Therefore, a high-strength steel sheet having excellent workability is demanded.
また、自動車用鋼板を車体構造用部材に適用した場合、同じ引張強度では降伏比が高い程、衝撃吸収エネルギーが優れる。一方、降伏比が高すぎる場合、スプリングバックが大きくなる等、成形した際の形状凍結性が悪化する。従って、YR(Yield Ratio)で表される降伏比が、例えば90%以上95%以下の鋼板が求められている。なお前記YRとは、0.2%耐力であるYS(Yield Strength)を、引張強度であるTS(Tensile Strength)で除して100を乗じた値である。
In addition, when an automotive steel plate is applied to a vehicle body structural member, the higher the yield ratio, the better the impact absorption energy at the same tensile strength. On the other hand, when the yield ratio is too high, the shape freezing property at the time of molding deteriorates, for example, the spring back becomes large. Therefore, a steel sheet having a yield ratio represented by YR (Yield Ratio) of, for example, 90% to 95% is demanded. 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.
上記要求特性のうち、高強度鋼板の加工性を向上するための技術として、下記特許文献が提案されている。特許文献1(特開2014-237887号公報)では、マルテンサイト、ベイナイト、もしくはそれらを複合させたミクロ組織とし、且つ、鋼板の表層を軟質とすることによって、強度と曲げ性とのバランスを向上できることを示している。しかし、特許文献1は、高強度化および上記成形性について検討されているに留まり、降伏比および延性(伸び)は考慮されていない。
Among the above required characteristics, the following patent documents have been proposed as techniques for improving the workability of high-strength steel sheets. In 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. However, in Patent Document 1, only high strength and the above formability are studied, and the yield ratio and ductility (elongation) are not considered.
特許文献2(特開2013-147736号公報)では、Ti、Nb、Vから選択される一種以上の元素を添加し、且つBの添加を必須とし、ベイナイトおよびマルテンサイト主体の組織とし、且つベイナイトの平均結晶粒径を7μm以下に制御した高強度鋼板が示されている。特許文献2に開示の高強度鋼板によれば、高い降伏比と優れた延性(伸び)を確保することができる。しかし、上記特許文献2に開示されている鋼板は、降伏比が70%台であり、且つ、曲げ性を考慮していない。
In 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 μm or less is shown. According to the high-strength steel sheet disclosed in Patent Document 2, a high yield ratio and excellent ductility (elongation) can be ensured. However, the steel sheet disclosed in Patent Document 2 has a yield ratio in the 70% range and does not consider bendability.
上記特許文献では、引張強度、降伏比、伸び、および曲げ性の全てを満足する高強度鋼板を作製する方法は検討されていない。
In the above-mentioned patent document, a method for producing a high-strength steel sheet that satisfies all of the tensile strength, yield ratio, elongation, and bendability has not been studied.
本発明の目的は、引張強度980MPa以上の高強度領域において、高降伏比であり、延性および曲げ性に優れた高強度鋼板および高強度溶融亜鉛めっき鋼板並びにそれらの製造方法を提供することにある。
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. .
上記目的を達成した本発明の高強度冷延鋼板は、質量%で、C:0.12~0.19%、Si:0%超、0.4%以下、Mn:1.80~2.45%、P:0%超、0.020%以下、S:0%超、0.0040%以下、Al:0.015~0.06%、Ti:0.010~0.035%、およびB:0.0025~0.0040%を含有し、残部が鉄および不可避不純物であり、下記(1)で定義されるXが8.0以下であり、下記(2)で定義されるYと前記Xの差の値Y-Xが45以上53以下であり、全組織に対する残留オーステナイトの体積率が2%以下であり、引張強度が980MPa以上である。
(1)Xは、[0.40×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
(2)Yは、[0.75×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、上記(1)、(2)におけるIQは、電子線後方散乱回折パターンの鮮明度を意味し、IQmaxは全測定点中のIQの最大値であり、IQminは全測定点中のIQの最小値である。 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.
(1) 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.
(2) 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, and IQmin is the minimum value of IQ at all measurement points.
(1)Xは、[0.40×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
(2)Yは、[0.75×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、上記(1)、(2)におけるIQは、電子線後方散乱回折パターンの鮮明度を意味し、IQmaxは全測定点中のIQの最大値であり、IQminは全測定点中のIQの最小値である。 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.
(1) 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.
(2) 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, and IQmin is the minimum value of IQ at all measurement points.
本発明によれば、鋼中成分および残留オーステナイトの体積率およびIQ(Image Quality、イメージクオリティ)が適切に制御された高強度冷延鋼板を提供することができる。このため、延性、曲げ性に優れた引張強度980MPa以上、且つ、高降伏比の冷延鋼板およびその製造方法並びに溶融亜鉛めっき鋼板を提供することができる。
According to 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.
本発明者らは、引張強度が980MPa以上で、且つ、高降伏比であって、延性および曲げ性(以下、加工性と呼ぶことが有る)に優れる高強度鋼板を提供するため、鋼中成分、残留オーステナイト体積率およびIQに着目して鋭意検討を重ねてきた。その結果、鋼中成分、残留オーステナイト体積率およびIQを、それぞれ以下の範囲に調整すれば良いことを突き止めた。なお、本明細書において高強度とは、引張強度が980MPa以上であることを意味する。
In order to provide a 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. In the present specification, high strength means that the tensile strength is 980 MPa or more.
まず、本発明を最も特徴付けるIQについて詳細を説明する。IQとは、EBSD(Electron Back Scatter Diffraction、電子線後方散乱回折)パターンの鮮明度である。IQは結晶中の歪量に影響を受けることが知られている。具体的にはIQが小さいほど、結晶中に歪が多く存在する傾向にある。例えば、マルテンサイトは高転位密度で結晶構造の乱れを含むためIQが小さくなる傾向がある。フェライトは低転位密度のためIQが高くなる傾向にある。そのため、従来では、IQの絶対値を指標として金属組織を判定する方法が提案されている。従来では、例えばIQが4000以上の組織をフェライトと判定する方法などが提案されている。しかし、本発明者らの検討結果によれば、IQの絶対値に基づく方法は、組織観察のための研磨条件や検出器などの影響を受け易く、IQの絶対値が変動し易いことが分かった。
First, the IQ that characterizes the present invention will be described in detail. 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. Conventionally, for example, a method of determining a structure having an IQ of 4000 or more as ferrite has been proposed. However, according to the examination results of the present inventors, it is found that the method based on the absolute value of IQ is easily affected by polishing conditions for structure observation, a detector, and the like, and the absolute value of IQ is likely to fluctuate. It was.
そこで本発明者らは、鋼板中の歪の分散状態、すなわちEBSDパターンの鮮明度であるIQの分布状態が降伏比、延性、曲げ性に与える影響を調査した。その結果、IQが後述する要件を満足することが、良好な延性、曲げ性、および高降伏比のいずれをも達成するために重要であることを見出した。IQの測定方法の詳細は後述する実施例の欄で説明する。
Therefore, 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.
本発明では、下記(1)で定義される値Xが8.0以下であり、下記(2)で定義される値Yと前記値Xの差の値Y-Xが45以上、53以下である。
(1)値Xは、[0.40×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
(2)値Yは、[0.75×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
上記(1)、(2)におけるIQは、電子線後方散乱回折パターンの鮮明度を意味し、
IQmaxは全測定点中のIQの最大値であり、IQminは全測定点中のIQの最小値である。 In the present invention, 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.
(1) 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.
(2) 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, and IQmin is the minimum value of IQ at all measurement points.
(1)値Xは、[0.40×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
(2)値Yは、[0.75×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
上記(1)、(2)におけるIQは、電子線後方散乱回折パターンの鮮明度を意味し、
IQmaxは全測定点中のIQの最大値であり、IQminは全測定点中のIQの最小値である。 In the present invention, 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.
(1) 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.
(2) 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, and IQmin is the minimum value of IQ at all measurement points.
XとYによって特定される事項を図1に模式的に表す。図1の横軸はIQ値であり、縦軸は各IQ値を示す測定点の個数割合(%)を示す。Xとは、IQ値が[0.40×(IQmax-IQmin)+IQmin]以下となる測定点の、全測定点に対する個数割合であり、YとはIQ値が[0.75×(IQmax-IQmin)+IQmin]以下である測定点の、全測定点に対する個数割合である。従って、Xが8.0以下であるということは、IQ値が[0.40×(IQmax-IQmin)+IQmin]以下となる測定点の、全測定点に対する割合が8.0%以下であるということであり、またY-Xの値が45以上、53以下であるということは、IQ値が[0.40×(IQmax-IQmin)+IQmin]を超え、且つ[0.75×(IQmax-IQmin)+IQmin]以下である測定点の、全測定点に対する割合が45%以上、53%以下であることを意味する。
The items specified by X and Y are schematically shown in FIG. In FIG. 1, the horizontal axis represents the IQ value, and 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, and 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. In addition, 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の値が8を超えると降伏比が低くなり、曲げ性も劣化する。この理由は、Xの値が大きくなることにより歪みの多い結晶が増える。歪の多い結晶が増えることにより、可動転移が増加し、降伏比が低下すると考えられる。曲げ性劣化については、歪の多い結晶の周辺で破壊の起点となるミクロクラックが増加したことに起因すると考えている。Xは、好ましくは6以下であり、より好ましくは5以下である。Xの下限は特に限定されないが、例えば0.5である。
When the value of X exceeds 8, the yield ratio is lowered and the bendability is also deteriorated. The reason for this is that as the value of X increases, the number of crystals with much distortion increases. It is considered that the increase in the number of strained crystals increases the movable transition and lowers the yield ratio. It is considered that the bendability deterioration is caused by an increase in microcracks that are the starting points of fracture in the vicinity of a strained crystal. 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.
本発明では、Xが8.0以下であると共に、Y-Xの値が45以上、53以下である。Y-Xの値が45未満となると、降伏比が低下する。一方、Y-Xの値が53を超えると、降伏比が高くなりすぎ、且つ、延性が低下する。Y-Xの値が大きくなりすぎると降伏比が高くなり延性が低下する理由は、必ずしも明確ではないが、Y-Xの値が大きくなるに従い、鋼板中の歪分布が均質となり、降伏比が増加し延性が低下したと考えられる。Y-Xは、好ましくは46以上52以下であり、より好ましくは47以上51以下である。
In the present invention, X is 8.0 or less, and the value of Y−X is 45 or more and 53 or less. When the value of Y−X is less than 45, the yield ratio decreases. On the other hand, if 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.
また、本発明では、全組織に対する残留オーステナイトの体積率を2%以下とする。残留オーステナイトの体積率が大きくなると、降伏比が低下する。残留オーステナイトの体積率は、好ましくは1.5%以下、より好ましくは1%以下であり、最も好ましくは0%である。残留オーステナイトの体積率は、後記する実施例の通り、ISIJ Int.Vol.33.(1933),No.7,P.776に記載の方法によって測定される値である。
In the present invention, 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.
本発明の高強度鋼板のミクロ組織は、基地組織がベイナイト組織であり、少量のマルテンサイト組織を含む。全組織に対するこれら組織の合計割合は、例えば95面積%以上である。
In the microstructure of the high-strength steel sheet of the present invention, 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.
本発明では上記のようにIQと残留オーステナイトの体積率を制御することに加えて、鋼板中の化学成分を下記の通り制御する。なお、本明細書において、化学成分はいずれも質量%を意味する。
In the present invention, in addition to controlling the volume ratio of IQ and retained austenite as described above, the chemical components in the steel sheet are controlled as follows. In the present specification, all chemical components mean mass%.
C:0.12~0.19%
Cは、鋼板の強度を確保するために必要な元素である。C量が不足すると、引張強度が低下する。そのためにC量の下限を0.12%以上とする。C量の下限は、好ましくは0.13%以上であり、より好ましくは0.14%以上である。しかし、C量が過剰になるとIQの値に基づいて算出される上記X値が高くなり、降伏比および曲げ性が低下する。そこで、C量の上限を0.19%以下とする。C量の上限は、好ましくは0.18%以下であり、より好ましくは0.17%以下である。 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.
Cは、鋼板の強度を確保するために必要な元素である。C量が不足すると、引張強度が低下する。そのためにC量の下限を0.12%以上とする。C量の下限は、好ましくは0.13%以上であり、より好ましくは0.14%以上である。しかし、C量が過剰になるとIQの値に基づいて算出される上記X値が高くなり、降伏比および曲げ性が低下する。そこで、C量の上限を0.19%以下とする。C量の上限は、好ましくは0.18%以下であり、より好ましくは0.17%以下である。 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:0%超、0.4%以下
Siは固溶強化元素として知られており、延性の低下を抑えつつ、引張強度を向上させることに有効に作用する元素である。更に、曲げ性を向上させる元素でもある。このような効果を有効に発揮させるため、Si量は0.01%以上が好ましく、より好ましくは0.1%以上である。しかし、Siを過剰に添加すると、IQの値に基づいて算出される上記X値が高くなり、降伏比が低下する。そのためにSi量の上限を0.4%以下とする。Si量の上限は、好ましくは0.3%以下であり、より好ましくは0.25%以下である。 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. In order to effectively exhibit such an effect, the Si content is preferably 0.01% or more, more preferably 0.1% or more. However, when Si is added excessively, the X value calculated based on the IQ value increases and the yield ratio decreases. Therefore, 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.
Siは固溶強化元素として知られており、延性の低下を抑えつつ、引張強度を向上させることに有効に作用する元素である。更に、曲げ性を向上させる元素でもある。このような効果を有効に発揮させるため、Si量は0.01%以上が好ましく、より好ましくは0.1%以上である。しかし、Siを過剰に添加すると、IQの値に基づいて算出される上記X値が高くなり、降伏比が低下する。そのためにSi量の上限を0.4%以下とする。Si量の上限は、好ましくは0.3%以下であり、より好ましくは0.25%以下である。 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. In order to effectively exhibit such an effect, the Si content is preferably 0.01% or more, more preferably 0.1% or more. However, when Si is added excessively, the X value calculated based on the IQ value increases and the yield ratio decreases. Therefore, 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:1.80~2.45%
Mnは、鋼板の高強度化に寄与する元素である。このような効果を有効に発揮させるために、Mn量の下限を1.80%以上とする。Mn量は好ましくは1.9%以上であり、より好ましくは2.0%以上である。Mnが少なすぎると、IQの値に基づいて算出される上記Y-X値が低くなり、降伏比が低下する。またMn量が過剰になると、IQの値に基づいて算出される上記X値が高く、上記Y-X値が低くなり、降伏比および曲げ性が低下する。そのため、Mn量の上限を2.45%以下とする。Mn量の上限は、好ましくは2.35%以下であり、より好ましくは2.25%以下である。 Mn: 1.80 to 2.45%
Mn is an element that contributes to increasing the strength of the steel sheet. In order to exhibit such an effect effectively, 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.
Mnは、鋼板の高強度化に寄与する元素である。このような効果を有効に発揮させるために、Mn量の下限を1.80%以上とする。Mn量は好ましくは1.9%以上であり、より好ましくは2.0%以上である。Mnが少なすぎると、IQの値に基づいて算出される上記Y-X値が低くなり、降伏比が低下する。またMn量が過剰になると、IQの値に基づいて算出される上記X値が高く、上記Y-X値が低くなり、降伏比および曲げ性が低下する。そのため、Mn量の上限を2.45%以下とする。Mn量の上限は、好ましくは2.35%以下であり、より好ましくは2.25%以下である。 Mn: 1.80 to 2.45%
Mn is an element that contributes to increasing the strength of the steel sheet. In order to exhibit such an effect effectively, 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:0%超、0.020%以下
Pは、不可避的に含有される元素である。Pは、粒界に偏析して粒界脆化を助長する元素であり、曲げ性を劣化させる。このため、P量はできるだけ低減することが推奨される。そのため、P量の上限は、0.020%以下とする。P量の上限は、好ましくは0.015%以下であり、より好ましくは0.010%以下である。なお、Pは鋼中に不可避的に含まれる不純物であり、その量を0%にすることは工業上不可能である。 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%.
Pは、不可避的に含有される元素である。Pは、粒界に偏析して粒界脆化を助長する元素であり、曲げ性を劣化させる。このため、P量はできるだけ低減することが推奨される。そのため、P量の上限は、0.020%以下とする。P量の上限は、好ましくは0.015%以下であり、より好ましくは0.010%以下である。なお、Pは鋼中に不可避的に含まれる不純物であり、その量を0%にすることは工業上不可能である。 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:0%超、0.0040%以下
SもPと同様に不可避的に含有される元素である。Sは、介在物を生成し、曲げ性を劣化させるため、S量はできるだけ低減することが推奨される。そのため、S量の上限は、0.0040%以下とする。S量の上限は、好ましくは0.003%以下、より好ましくは0.002%以下である。なお、Sは鋼中に不可避的に含まれる不純物であり、その量を0%にすることは工業上不可能である。 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. In addition, S is an impurity inevitably contained in steel, and it is industrially impossible to reduce the amount to 0%.
SもPと同様に不可避的に含有される元素である。Sは、介在物を生成し、曲げ性を劣化させるため、S量はできるだけ低減することが推奨される。そのため、S量の上限は、0.0040%以下とする。S量の上限は、好ましくは0.003%以下、より好ましくは0.002%以下である。なお、Sは鋼中に不可避的に含まれる不純物であり、その量を0%にすることは工業上不可能である。 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. In addition, S is an impurity inevitably contained in steel, and it is industrially impossible to reduce the amount to 0%.
Al:0.015~0.06%
Alは、脱酸剤として作用する元素である。この作用を有効に発揮させるには、Al量の下限を0.015%以上とする。Al量の下限は、好ましくは0.025%以上であり、より好ましくは0.030%以上である。しかし、Al量が過剰になると鋼板中にアルミナなどの介在物が多く生成し、曲げ性を劣化させることがある。このため、Al量の上限を0.06%以下とする。Al量の上限は、好ましくは0.055%以下であり、より好ましくは0.050%以下である。 Al: 0.015 to 0.06%
Al is an element that acts as a deoxidizer. In order to exhibit this effect effectively, 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. However, when the amount of Al becomes excessive, many inclusions such as alumina are generated in the steel sheet, and the bendability may be deteriorated. For this reason, 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.
Alは、脱酸剤として作用する元素である。この作用を有効に発揮させるには、Al量の下限を0.015%以上とする。Al量の下限は、好ましくは0.025%以上であり、より好ましくは0.030%以上である。しかし、Al量が過剰になると鋼板中にアルミナなどの介在物が多く生成し、曲げ性を劣化させることがある。このため、Al量の上限を0.06%以下とする。Al量の上限は、好ましくは0.055%以下であり、より好ましくは0.050%以下である。 Al: 0.015 to 0.06%
Al is an element that acts as a deoxidizer. In order to exhibit this effect effectively, 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. However, when the amount of Al becomes excessive, many inclusions such as alumina are generated in the steel sheet, and the bendability may be deteriorated. For this reason, 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:0.010~0.035%
Tiは、炭化物や窒化物を形成して強度を向上させる元素である。また、Tiは、Bの焼入れ性を有効に活用するための元素でもある。詳細には、Tiが窒化物を形成することにより鋼中のNを低減する。これによりB窒化物の形成を抑制し、Bが固溶状態となるので、有効にBの焼入れ性を発揮できる。このように、Tiは焼入れ性を向上させるので、鋼板の高強度化に寄与する。このような効果を有効に発揮させるために、Ti量の下限を0.010%以上とする。Ti量の下限は、好ましくは0.013%以上であり、より好ましくは0.015%以上である。しかし、Ti量が過剰になると、Ti炭化物やTi窒化物が過剰となる。これによりIQの値に基づいて算出される上記X値が高く、上記Y-X値が低くなるので、曲げ性を劣化させ、且つ、降伏比も低下する。このため、Ti量の上限を0.035%以下とする。Ti量の上限は、好ましくは0.030%以下である。より好ましくは0.025%以下である。 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. Thus, since Ti improves hardenability, it contributes to the strengthening of a steel plate. In order to effectively exhibit such an effect, 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. However, when the amount of Ti is excessive, Ti carbide and Ti nitride are excessive. Accordingly, the X value calculated based on the IQ value is high and the YX value is low, so that the bendability is deteriorated and the yield ratio is also reduced. For this reason, 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.
Tiは、炭化物や窒化物を形成して強度を向上させる元素である。また、Tiは、Bの焼入れ性を有効に活用するための元素でもある。詳細には、Tiが窒化物を形成することにより鋼中のNを低減する。これによりB窒化物の形成を抑制し、Bが固溶状態となるので、有効にBの焼入れ性を発揮できる。このように、Tiは焼入れ性を向上させるので、鋼板の高強度化に寄与する。このような効果を有効に発揮させるために、Ti量の下限を0.010%以上とする。Ti量の下限は、好ましくは0.013%以上であり、より好ましくは0.015%以上である。しかし、Ti量が過剰になると、Ti炭化物やTi窒化物が過剰となる。これによりIQの値に基づいて算出される上記X値が高く、上記Y-X値が低くなるので、曲げ性を劣化させ、且つ、降伏比も低下する。このため、Ti量の上限を0.035%以下とする。Ti量の上限は、好ましくは0.030%以下である。より好ましくは0.025%以下である。 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. Thus, since Ti improves hardenability, it contributes to the strengthening of a steel plate. In order to effectively exhibit such an effect, 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. However, when the amount of Ti is excessive, Ti carbide and Ti nitride are excessive. Accordingly, the X value calculated based on the IQ value is high and the YX value is low, so that the bendability is deteriorated and the yield ratio is also reduced. For this reason, 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:0.0025~0.0040%
Bは、焼入れ性を向上させて鋼板の高強度化に寄与する元素である。このような効果を有効に発揮させるために、B量の下限を0.0025%以上とする。Bが少なすぎると、IQの値に基づいて算出される上記Y-X値が低くなり、降伏比が低下する。B量の下限は、好ましくは0.0027%以上、より好ましくは0.0029%以上である。しかし、B量が過剰になると、その効果が飽和し、コストが増加する。このため、B量の上限を0.0040%以下とする。B量の上限は、好ましくは0.0035%以下である。 B: 0.0025 to 0.0040%
B is an element that contributes to increasing the strength of the steel sheet by improving the hardenability. In order to effectively exhibit such an effect, the lower limit of the B amount is set to 0.0025% or more. When B is too small, the YX value calculated based on the IQ value is lowered, and the yield ratio is lowered. The lower limit of the B amount is preferably 0.0027% or more, more preferably 0.0029% or more. However, when the amount of B becomes excessive, the effect is saturated and the cost increases. For this reason, 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.
Bは、焼入れ性を向上させて鋼板の高強度化に寄与する元素である。このような効果を有効に発揮させるために、B量の下限を0.0025%以上とする。Bが少なすぎると、IQの値に基づいて算出される上記Y-X値が低くなり、降伏比が低下する。B量の下限は、好ましくは0.0027%以上、より好ましくは0.0029%以上である。しかし、B量が過剰になると、その効果が飽和し、コストが増加する。このため、B量の上限を0.0040%以下とする。B量の上限は、好ましくは0.0035%以下である。 B: 0.0025 to 0.0040%
B is an element that contributes to increasing the strength of the steel sheet by improving the hardenability. In order to effectively exhibit such an effect, the lower limit of the B amount is set to 0.0025% or more. When B is too small, the YX value calculated based on the IQ value is lowered, and the yield ratio is lowered. The lower limit of the B amount is preferably 0.0027% or more, more preferably 0.0029% or more. However, when the amount of B becomes excessive, the effect is saturated and the cost increases. For this reason, 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.
本発明の高強度鋼板の基本成分は上記の通りであり、残部は実質的に鉄である。但し、原材料、資材、製造設備等の状況によって持ち込まれる不可避不純物が鋼中に含まれることは当然に許容される。不可避不純物としては、上述したP、Sの他、例えば、N、Oなどが含まれ、これらはそれぞれ以下の範囲であることが好ましい。
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:0%超、0.01%以下
Nは、不純物元素として不可避的に存在し、曲げ性を劣化させる。Nの上限は0.01%以下が好ましく、より好ましくは0.006%以下、更に好ましくは0.005%以下である。N量は少なければ少ない程好ましいが、0%にすることは工業上困難である。 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%.
Nは、不純物元素として不可避的に存在し、曲げ性を劣化させる。Nの上限は0.01%以下が好ましく、より好ましくは0.006%以下、更に好ましくは0.005%以下である。N量は少なければ少ない程好ましいが、0%にすることは工業上困難である。 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:0%超、0.002%以下
Oは、不純物元素として不可避的に存在し、曲げ性を劣化させる。Oの上限は0.002%以下が好ましく、より好ましくは0.0015%以下、更に好ましくは0.0010%以下である。O量は少なければ少ない程好ましいが、0%にすることは工業上困難である。 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%.
Oは、不純物元素として不可避的に存在し、曲げ性を劣化させる。Oの上限は0.002%以下が好ましく、より好ましくは0.0015%以下、更に好ましくは0.0010%以下である。O量は少なければ少ない程好ましいが、0%にすることは工業上困難である。 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%.
さらに本発明では、必要に応じて以下に示す範囲で、(a)Cu、Ni、Cr、Mo、VおよびNbの1種以上または(b)Caを含むことが好ましい。
Furthermore, in the present invention, it is preferable that (a) one or more of Cu, Ni, Cr, Mo, V and Nb or (b) Ca is contained within the following range as required.
本発明の高強度冷延鋼板は、質量%で、Cu:0%超、0.3%以下、Ni:0%超、0.3%以下、Cr:0%超、0.25%以下、Mo:0%超、0.1%以下、V:0%超、0.05%以下、Nb:0%超、0.08%以下およびCa:0%超、0.005%以下よりなる群から選ばれる1種以上を含有することが好ましい。
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、およびNbはいずれも強度向上に有効な元素である。これらの元素は、夫々以下に示す範囲で、単独でまたは適宜組み合わせて含有させても良い。
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:0%超、0.3%以下
Cuは、更に鋼板の耐食性向上に有効な元素である。このような効果を有効に発揮させるために、Cu量の下限を、好ましくは0.03%以上、より好ましくは0.05%以上とする。しかし、Cu量が過剰になると、その効果が飽和し、コストが増加する。そのため、Cu量の上限は、好ましくは0.3%以下、より好ましくは0.2%以下、更に好ましくは0.15%以下である。 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. In order to effectively exhibit such an effect, the lower limit of the Cu amount is preferably 0.03% or more, more preferably 0.05% or more. However, when the amount of Cu becomes excessive, the effect is saturated and the cost increases. Therefore, 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.
Cuは、更に鋼板の耐食性向上に有効な元素である。このような効果を有効に発揮させるために、Cu量の下限を、好ましくは0.03%以上、より好ましくは0.05%以上とする。しかし、Cu量が過剰になると、その効果が飽和し、コストが増加する。そのため、Cu量の上限は、好ましくは0.3%以下、より好ましくは0.2%以下、更に好ましくは0.15%以下である。 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. In order to effectively exhibit such an effect, the lower limit of the Cu amount is preferably 0.03% or more, more preferably 0.05% or more. However, when the amount of Cu becomes excessive, the effect is saturated and the cost increases. Therefore, 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:0%超、0.3%以下
Niは、更に鋼板の耐食性向上に有効な元素である。このような効果を有効に発揮させるために、Ni量の下限を、好ましくは0.03%以上、より好ましくは0.05%以上とする。しかし、Ni量が過剰になると、その効果が飽和し、コストが増加する。そのため、Ni量の上限は、好ましくは0.3%以下、より好ましくは0.2%以下、更に好ましくは0.15%以下である。 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. In order to effectively exhibit such an effect, the lower limit of the Ni amount is preferably 0.03% or more, more preferably 0.05% or more. However, when the amount of Ni becomes excessive, the effect is saturated and the cost increases. Therefore, 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.
Niは、更に鋼板の耐食性向上に有効な元素である。このような効果を有効に発揮させるために、Ni量の下限を、好ましくは0.03%以上、より好ましくは0.05%以上とする。しかし、Ni量が過剰になると、その効果が飽和し、コストが増加する。そのため、Ni量の上限は、好ましくは0.3%以下、より好ましくは0.2%以下、更に好ましくは0.15%以下である。 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. In order to effectively exhibit such an effect, the lower limit of the Ni amount is preferably 0.03% or more, more preferably 0.05% or more. However, when the amount of Ni becomes excessive, the effect is saturated and the cost increases. Therefore, 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:0%超、0.25%以下
Crは、高強度化の効果を示す元素である。Crの高強度化を有効に発揮させるために、Cr量の下限を、好ましくは0.01%以上、より好ましくは0.015%以上、更に好ましくは0.03%以上、特に好ましくは0.05%以上とする。しかし、Cr量が過剰になると、不めっきを発生させるため、Cr量の上限は0.25%以下が好ましく、より好ましくは0.20%以下、更に好ましくは0.10%以下である。 Cr: more than 0% and 0.25% or less Cr is an element showing the effect of increasing the strength. In order to effectively increase the strength of Cr, 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. However, when the amount of Cr becomes excessive, unplating occurs, so 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.
Crは、高強度化の効果を示す元素である。Crの高強度化を有効に発揮させるために、Cr量の下限を、好ましくは0.01%以上、より好ましくは0.015%以上、更に好ましくは0.03%以上、特に好ましくは0.05%以上とする。しかし、Cr量が過剰になると、不めっきを発生させるため、Cr量の上限は0.25%以下が好ましく、より好ましくは0.20%以下、更に好ましくは0.10%以下である。 Cr: more than 0% and 0.25% or less Cr is an element showing the effect of increasing the strength. In order to effectively increase the strength of Cr, 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. However, when the amount of Cr becomes excessive, unplating occurs, so 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:0%超、0.1%以下
Moは、高強度化の効果を示す元素である。Moの高強度化を有効に発揮させるために、Mo量の下限は好ましくは0.03%以上、より好ましくは0.05%以上とする。しかし、Mo量が過剰になると、その効果が飽和し、コストが増加する。そのため、Mo量の上限は0.1%以下が好ましい。 Mo: more than 0%, 0.1% or less Mo is an element showing the effect of increasing the strength. In order to effectively increase the strength of Mo, the lower limit of the amount of Mo is preferably 0.03% or more, more preferably 0.05% or more. However, when the amount of Mo becomes excessive, the effect is saturated and the cost increases. Therefore, the upper limit of the Mo amount is preferably 0.1% or less.
Moは、高強度化の効果を示す元素である。Moの高強度化を有効に発揮させるために、Mo量の下限は好ましくは0.03%以上、より好ましくは0.05%以上とする。しかし、Mo量が過剰になると、その効果が飽和し、コストが増加する。そのため、Mo量の上限は0.1%以下が好ましい。 Mo: more than 0%, 0.1% or less Mo is an element showing the effect of increasing the strength. In order to effectively increase the strength of Mo, the lower limit of the amount of Mo is preferably 0.03% or more, more preferably 0.05% or more. However, when the amount of Mo becomes excessive, the effect is saturated and the cost increases. Therefore, the upper limit of the Mo amount is preferably 0.1% or less.
V:0%超、0.05%以下
Vは、高強度化の効果を示す元素である。Vの高強度化を有効に発揮させるために、V量の下限は0.003%以上が好ましく、より好ましくは0.005%以上である。しかし、V量が過剰になると、その効果が飽和し、コストが増加する。そのため、V量の上限は、0.05%以下が好ましく、より好ましくは0.03%以下、更に好ましくは0.02%以下である。 V: more than 0% and 0.05% or less V is an element showing the effect of increasing the strength. In order to effectively increase the strength of V, the lower limit of the amount of V is preferably 0.003% or more, and more preferably 0.005% or more. However, when the amount of V becomes excessive, the effect is saturated and the cost increases. Therefore, 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.
Vは、高強度化の効果を示す元素である。Vの高強度化を有効に発揮させるために、V量の下限は0.003%以上が好ましく、より好ましくは0.005%以上である。しかし、V量が過剰になると、その効果が飽和し、コストが増加する。そのため、V量の上限は、0.05%以下が好ましく、より好ましくは0.03%以下、更に好ましくは0.02%以下である。 V: more than 0% and 0.05% or less V is an element showing the effect of increasing the strength. In order to effectively increase the strength of V, the lower limit of the amount of V is preferably 0.003% or more, and more preferably 0.005% or more. However, when the amount of V becomes excessive, the effect is saturated and the cost increases. Therefore, 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:0%超、0.08%以下
Nbは、高強度化の効果を示す元素である。Nbの高強度化を有効に発揮させるために、Nb量の下限を、0.003%以上とすることが好ましく、より好ましくは0.005%以上とする。しかし、Nb量が過剰になると、曲げ性を劣化させる。そのため、Nb量の上限は、好ましくは0.08%以下、より好ましくは0.06%以下、更に好ましくは0.04%以下である。 Nb: more than 0% and 0.08% or less Nb is an element showing the effect of increasing the strength. In order to effectively increase the strength of Nb, the lower limit of the Nb amount is preferably 0.003% or more, more preferably 0.005% or more. However, if the amount of Nb is excessive, bendability is deteriorated. Therefore, 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.
Nbは、高強度化の効果を示す元素である。Nbの高強度化を有効に発揮させるために、Nb量の下限を、0.003%以上とすることが好ましく、より好ましくは0.005%以上とする。しかし、Nb量が過剰になると、曲げ性を劣化させる。そのため、Nb量の上限は、好ましくは0.08%以下、より好ましくは0.06%以下、更に好ましくは0.04%以下である。 Nb: more than 0% and 0.08% or less Nb is an element showing the effect of increasing the strength. In order to effectively increase the strength of Nb, the lower limit of the Nb amount is preferably 0.003% or more, more preferably 0.005% or more. However, if the amount of Nb is excessive, bendability is deteriorated. Therefore, 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:0%超、0.005%以下
Caは、鋼中の硫化物を球状化し、曲げ性を高めることに有効な元素である。このような効果を有効に発揮させるために、Ca量の下限を、好ましくは0.0005%以上、より好ましくは0.001%以上とする。しかし、Ca量が過剰になると、その効果が飽和し、コストが増加する。そのため、Ca量の上限は0.005%以下が好ましく、より好ましくは0.003%以下であり、更に好ましくは0.0025%以下である。 Ca: more than 0% and 0.005% or less Ca is an element effective for spheroidizing sulfides in steel and enhancing bendability. In order to effectively exhibit such an effect, the lower limit of the Ca content is preferably 0.0005% or more, more preferably 0.001% or more. However, when the amount of Ca becomes excessive, the effect is saturated and the cost increases. Therefore, 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.
Caは、鋼中の硫化物を球状化し、曲げ性を高めることに有効な元素である。このような効果を有効に発揮させるために、Ca量の下限を、好ましくは0.0005%以上、より好ましくは0.001%以上とする。しかし、Ca量が過剰になると、その効果が飽和し、コストが増加する。そのため、Ca量の上限は0.005%以下が好ましく、より好ましくは0.003%以下であり、更に好ましくは0.0025%以下である。 Ca: more than 0% and 0.005% or less Ca is an element effective for spheroidizing sulfides in steel and enhancing bendability. In order to effectively exhibit such an effect, the lower limit of the Ca content is preferably 0.0005% or more, more preferably 0.001% or more. However, when the amount of Ca becomes excessive, the effect is saturated and the cost increases. Therefore, 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.
化学成分組成、残留オーステナイトの面積率、IQ値から算出される値X、Yが上記の条件を満足している本発明の高強度鋼板は、引張強度が980MPa以上であり、且つ、降伏比、延性、曲げ性のすべてに優れている。本発明の高強度鋼板の降伏比は、例えば90%以上、95%以下とできる。
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.
次に、本発明の高強度鋼板を製造する方法について説明する。
Next, a method for producing the high strength steel plate of the present invention will be described.
上記要件を満足する本発明の高強度鋼板は、熱間圧延、冷間圧延、および焼鈍(均熱および冷却)の工程を含み、特に冷間圧延後の焼鈍工程を適切に制御して製造するところに特徴がある。以下、本発明の高強度鋼板を得るための製造工程を、熱間圧延、冷間圧延、その後の焼鈍の順に説明する。
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. Hereinafter, 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.
熱間圧延の好ましい条件は、例えば以下のとおりである。
Preferred conditions for hot rolling are as follows, for example.
熱間圧延前の加熱温度が低いと、オーステナイト中への、TiCなどの炭化物の固溶が低下するおそれがある。このため、熱間圧延前の加熱温度の下限は、好ましくは1200℃以上、より好ましくは1250℃以上である。熱間圧延前の加熱温度が高いとコストアップとなる。このため、熱間圧延前の加熱温度の上限は、好ましくは1350℃以下、より好ましくは1300℃以下である。
If 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.
熱間圧延の仕上げ圧延温度が低いと、オーステナイト単相域で圧延できず、圧延時の変形抵抗が大きく、操業が困難になるおそれがある。このため、仕上げ圧延温度は、好ましくは850℃以上、より好ましくは870℃以上である。仕上げ圧延温度が高いと結晶が粗大化するおそれがある。このため、仕上げ圧延温度は、好ましくは980℃以下、より好ましくは950℃以下である。
If the 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. Preferably it is 850 degreeC or more, More preferably, it is 870 degreeC or more. If the finish rolling temperature is high, the crystal may be coarsened. For this reason, finish rolling temperature becomes like this. Preferably it is 980 degrees C or less, More preferably, it is 950 degrees C or less.
熱間圧延の仕上げ圧延から巻取りまでの平均冷却速度は、生産性を考慮し、好ましくは10℃/秒以上、より好ましくは20℃/秒以上である。一方、平均冷却速度が速いと設備コストが高くなるため、好ましくは100℃/秒以下、より好ましくは50℃/秒以下である。
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. On the other hand, when 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.
次に、熱間圧延後の工程の好ましい条件について説明する。
Next, preferable conditions for the process after hot rolling will be described.
熱間圧延後の巻取り温度:550℃以上
熱間圧延後の巻取り温度が、550℃未満になると、熱延板の強度が高くなり、冷間圧延で圧下し難くなる。そのため、熱間圧延後の巻取り温度は550℃以上、好ましくは570℃以上、更に好ましくは600℃以上である。一方、熱間圧延後の巻取り温度が、高くなりすぎるとスケール除去のための酸洗性が劣化する。そのため、熱間圧延後の巻取り温度は、好ましくは800℃以下、より好ましくは750℃以下である。 Winding temperature after hot rolling: 550 ° C. or more When the winding temperature after hot rolling is less than 550 ° C., the strength of the hot rolled sheet increases and it is difficult to reduce the temperature by cold rolling. Therefore, the coiling temperature after hot rolling is 550 ° C. or higher, preferably 570 ° C. or higher, more preferably 600 ° C. or higher. On the other hand, if the coiling temperature after hot rolling becomes too high, the pickling property for removing the scale deteriorates. Therefore, the coiling temperature after hot rolling is preferably 800 ° C. or lower, more preferably 750 ° C. or lower.
熱間圧延後の巻取り温度が、550℃未満になると、熱延板の強度が高くなり、冷間圧延で圧下し難くなる。そのため、熱間圧延後の巻取り温度は550℃以上、好ましくは570℃以上、更に好ましくは600℃以上である。一方、熱間圧延後の巻取り温度が、高くなりすぎるとスケール除去のための酸洗性が劣化する。そのため、熱間圧延後の巻取り温度は、好ましくは800℃以下、より好ましくは750℃以下である。 Winding temperature after hot rolling: 550 ° C. or more When the winding temperature after hot rolling is less than 550 ° C., the strength of the hot rolled sheet increases and it is difficult to reduce the temperature by cold rolling. Therefore, the coiling temperature after hot rolling is 550 ° C. or higher, preferably 570 ° C. or higher, more preferably 600 ° C. or higher. On the other hand, if the coiling temperature after hot rolling becomes too high, the pickling property for removing the scale deteriorates. Therefore, the coiling temperature after hot rolling is preferably 800 ° C. or lower, more preferably 750 ° C. or lower.
冷延率:20%以上、60%以下
熱間圧延鋼板は、スケール除去のために酸洗を施した後に冷間圧延に供する。冷間圧延の冷延率が20%未満になると、所定厚さの鋼板を得るために熱間圧延工程で板厚を薄くしなければならず、熱間圧延工程で薄くすると鋼板長さが長くなる。これにより酸洗に時間がかかり、生産性が低下する。そのため、冷延率の下限を、好ましくは20%以上、より好ましくは25%以上とする。一方、冷延率が60%を超えると、冷間圧延機の高い能力が必要となる。そのため、冷延率の上限は、好ましくは60%以下、より好ましくは55%以下、更に好ましくは50%以下である。 Cold rolling rate: 20% or more, 60% or less The hot-rolled steel sheet is subjected to cold rolling after pickling to remove scale. When the cold rolling ratio of cold rolling is less than 20%, 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. On the other hand, if the cold rolling rate exceeds 60%, a high capability of the cold rolling mill is required. Therefore, 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.
熱間圧延鋼板は、スケール除去のために酸洗を施した後に冷間圧延に供する。冷間圧延の冷延率が20%未満になると、所定厚さの鋼板を得るために熱間圧延工程で板厚を薄くしなければならず、熱間圧延工程で薄くすると鋼板長さが長くなる。これにより酸洗に時間がかかり、生産性が低下する。そのため、冷延率の下限を、好ましくは20%以上、より好ましくは25%以上とする。一方、冷延率が60%を超えると、冷間圧延機の高い能力が必要となる。そのため、冷延率の上限は、好ましくは60%以下、より好ましくは55%以下、更に好ましくは50%以下である。 Cold rolling rate: 20% or more, 60% or less The hot-rolled steel sheet is subjected to cold rolling after pickling to remove scale. When the cold rolling ratio of cold rolling is less than 20%, 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. On the other hand, if the cold rolling rate exceeds 60%, a high capability of the cold rolling mill is required. Therefore, 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.
本発明の高強度鋼板を得るためには、冷延後の焼鈍工程が(a)加熱して保持する均熱工程、(b)均熱工程に引き続き行われる第1の冷却工程、(c)前記第1の冷却工程後に所定温度範囲で保持する保持工程、(d)前記保持工程に引き続いて行われる第2の冷却工程、(e)第2の冷却工程に引き続いて行われる第3の冷却工程を含み、この(a)~(e)の条件をそれぞれ適切に調整することが重要である。本発明の焼鈍工程の上記(a)~(e)の構成を、図2に模式的に示す。
In order to obtain the high-strength steel sheet of the present invention, 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.
(a)均熱工程
上記冷間圧延後、Ac3点~Ac3点+200℃の温度(均熱温度)に加熱して所定時間保持して均熱する(均熱工程)。均熱温度がAc3点未満になると、上記Xの値が高くなり、降伏比の確保が難くなる。そのため、均熱温度の下限は、Ac3点以上が好ましく、より好ましくはAc3点+25℃以上とする。一方、上記均熱温度がAc3点+200℃を超えると、工業的に生産するためのエネルギーが過剰に必要となる。そのため、上限は、Ac3点+200℃以下が好ましく、より好ましくはAc3点+150℃以下である。 (A) Soaking step After the cold rolling, the steel is heated to a temperature of Ac 3 point to Ac 3 point + 200 ° C. (soaking temperature) and held for a predetermined time soaking (soaking step). When 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. On the other hand, if the soaking temperature exceeds the Ac 3 point + 200 ° C., excessive energy is required for industrial production. Therefore, the upper limit is preferably Ac 3 point + 200 ° C. or less, and more preferably Ac 3 point + 150 ° C. or less.
上記冷間圧延後、Ac3点~Ac3点+200℃の温度(均熱温度)に加熱して所定時間保持して均熱する(均熱工程)。均熱温度がAc3点未満になると、上記Xの値が高くなり、降伏比の確保が難くなる。そのため、均熱温度の下限は、Ac3点以上が好ましく、より好ましくはAc3点+25℃以上とする。一方、上記均熱温度がAc3点+200℃を超えると、工業的に生産するためのエネルギーが過剰に必要となる。そのため、上限は、Ac3点+200℃以下が好ましく、より好ましくはAc3点+150℃以下である。 (A) Soaking step After the cold rolling, the steel is heated to a temperature of Ac 3 point to Ac 3 point + 200 ° C. (soaking temperature) and held for a predetermined time soaking (soaking step). When 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. On the other hand, if the soaking temperature exceeds the Ac 3 point + 200 ° C., excessive energy is required for industrial production. Therefore, the upper limit is preferably Ac 3 point + 200 ° C. or less, and more preferably Ac 3 point + 150 ° C. or less.
上記Ac3点温度は、下式に基づいて算出される。式中の[%(元素名)]は各元素の含有量(質量%)である。この式は、「レスリー鉄鋼材料学」(丸善株式会社発行、William C.Leslie著、p.273)に記載されている。なお、含有しない元素は、含有量を0%として計算する。
Ac3=910-203√(%C)-15.2(%Ni)+44.7(%Si)+104(%V)+31.5(%Mo)+13.1(%W)-30(%Mn)-11(%Cr)-20(%Cu)+700(%P)+400(%Al)+120(%As)+400(%Ti) The Ac 3 point temperature is calculated based on the following equation. [% (Element name)] in the formula is the content (% by mass) of each element. This formula is described in “Leslie Steel Material Science” (published by Maruzen Co., Ltd., William C. Leslie, p. 273). In addition, the element which does not contain is calculated on the assumption that the content is 0%.
Ac 3 = 910−203√ (% C) −15.2 (% Ni) +44.7 (% Si) +104 (% V) +31.5 (% Mo) +13.1 (% W) −30 (% Mn ) -11 (% Cr) -20 (% Cu) +700 (% P) +400 (% Al) +120 (% As) +400 (% Ti)
Ac3=910-203√(%C)-15.2(%Ni)+44.7(%Si)+104(%V)+31.5(%Mo)+13.1(%W)-30(%Mn)-11(%Cr)-20(%Cu)+700(%P)+400(%Al)+120(%As)+400(%Ti) The Ac 3 point temperature is calculated based on the following equation. [% (Element name)] in the formula is the content (% by mass) of each element. This formula is described in “Leslie Steel Material Science” (published by Maruzen Co., Ltd., William C. Leslie, p. 273). In addition, the element which does not contain is calculated on the assumption that the content is 0%.
Ac 3 = 910−203√ (% C) −15.2 (% Ni) +44.7 (% Si) +104 (% V) +31.5 (% Mo) +13.1 (% W) −30 (% Mn ) -11 (% Cr) -20 (% Cu) +700 (% P) +400 (% Al) +120 (% As) +400 (% Ti)
上記均熱温度までの加熱速度は特に限定されないが、平均加熱速度は1℃/秒以上、20℃/秒以下であることが好ましい。上記冷間圧延後の平均加熱速度が1℃/秒未満となると、生産性が悪化する。そのため、上記平均加熱速度の下限を1℃/秒以上とすることが好ましく、より好ましくは3℃/秒以上、更に好ましくは5℃/秒以上とする。一方、上記平均加熱速度が20℃/秒を超えると、鋼板温度が制御し難くなり、設備コストも増加する。そのため、上記平均加熱速度の上限は20℃/秒以下が好ましく、より好ましくは18℃/秒以下、更に好ましくは15℃/秒以下である。
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. When the average heating rate after the cold rolling is less than 1 ° C./second, productivity is deteriorated. Therefore, 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. On the other hand, when the average heating rate exceeds 20 ° C./second, the steel plate temperature becomes difficult to control, and the equipment cost increases. Therefore, 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.
上記均熱温度では、1秒以上100秒以下均熱することが好ましい。上記均熱時間が1秒未満となると、上記Xの値が高くなり、降伏比の確保が難しくなる。そのため、上記均熱時間の下限は1秒以上が好ましく、より好ましくは10秒以上とする。一方、上記均熱時間が100秒を超えると、生産性が悪化する。そのため、上記均熱時間の上限は100秒以下が好ましく、より好ましくは80秒以下である。
It is preferable that the soaking temperature is soaked for 1 second to 100 seconds. When 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. On the other hand, when the soaking time exceeds 100 seconds, productivity deteriorates. Therefore, the upper limit of the soaking time is preferably 100 seconds or less, more preferably 80 seconds or less.
(b)第1の冷却工程
上記均熱工程後、上記均熱温度から下記冷却停止保持温度までの平均冷却速度は15℃/秒以上、50℃/秒以下とすることが好ましい。第1の冷却工程での平均冷却速度が、15℃/秒未満になると、生産性が悪化する。そのため、上記平均冷却速度の下限は15℃/秒以上が好ましく、より好ましく20℃/秒以上とする。一方、上記平均冷却速度が50℃/秒を超えると、鋼板温度を制御し難くなり、設備コストが増加する。そのため、上記平均冷却速度の上限は50℃/秒以下が好ましく、より好ましくは40℃/秒以下、更に好ましくは30℃/秒以下である。 (B) First cooling step After the soaking step, 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. When the average cooling rate in the first cooling step is less than 15 ° C./second, the productivity is deteriorated. Therefore, the lower limit of the average cooling rate is preferably 15 ° C./second or more, more preferably 20 ° C./second or more. On the other hand, when the average cooling rate exceeds 50 ° C./second, it becomes difficult to control the steel plate temperature, and the equipment cost increases. Therefore, 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.
上記均熱工程後、上記均熱温度から下記冷却停止保持温度までの平均冷却速度は15℃/秒以上、50℃/秒以下とすることが好ましい。第1の冷却工程での平均冷却速度が、15℃/秒未満になると、生産性が悪化する。そのため、上記平均冷却速度の下限は15℃/秒以上が好ましく、より好ましく20℃/秒以上とする。一方、上記平均冷却速度が50℃/秒を超えると、鋼板温度を制御し難くなり、設備コストが増加する。そのため、上記平均冷却速度の上限は50℃/秒以下が好ましく、より好ましくは40℃/秒以下、更に好ましくは30℃/秒以下である。 (B) First cooling step After the soaking step, 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. When the average cooling rate in the first cooling step is less than 15 ° C./second, the productivity is deteriorated. Therefore, the lower limit of the average cooling rate is preferably 15 ° C./second or more, more preferably 20 ° C./second or more. On the other hand, when the average cooling rate exceeds 50 ° C./second, it becomes difficult to control the steel plate temperature, and the equipment cost increases. Therefore, 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.
第1の冷却工程の冷却停止温度は、380℃以上、440℃以下とするのが好ましい。このような温度範囲が好ましい理由は、後述する。
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.
(c)保持工程
前記第1の冷却を380℃以上、440℃以下の温度範囲で停止した後、380℃以上、440℃以下の温度で所定時間保持するのが好ましい。第1の冷却工程の冷却停止温度及び保持温度が380℃未満になると、前記したY-Xの値が高くなって、降伏比が高くなりすぎ、且つ、延性も低下する。そのため、上記冷却停止及び保持温度の下限は380℃以上が好ましく、より好ましくは390℃以上とする。一方、上記冷却停止及び保持温度が440℃を超えると、逆に前記Y-Xの値が低くなり、降伏比が低下する。そのため、上記冷却停止及び保持温度の上限は440℃以下が好ましく、より好ましくは430℃以下、更に好ましくは420℃以下である。特に、第1の冷却工程の冷却停止温度が380℃未満であり、保持工程の終了温度が440℃を超える場合には、残留オーステナイトの体積率が高くなり、降伏比が低下する。 (C) Holding Step After the first cooling is stopped in a temperature range of 380 ° C. or higher and 440 ° C. or lower, the first cooling is preferably held at a temperature of 380 ° C. or higher and 440 ° C. or lower for a predetermined time. When 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. On the other hand, when the cooling stop and holding temperature exceeds 440 ° C., the value of Y−X decreases, and the yield ratio decreases. Therefore, 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. In particular, when 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.
前記第1の冷却を380℃以上、440℃以下の温度範囲で停止した後、380℃以上、440℃以下の温度で所定時間保持するのが好ましい。第1の冷却工程の冷却停止温度及び保持温度が380℃未満になると、前記したY-Xの値が高くなって、降伏比が高くなりすぎ、且つ、延性も低下する。そのため、上記冷却停止及び保持温度の下限は380℃以上が好ましく、より好ましくは390℃以上とする。一方、上記冷却停止及び保持温度が440℃を超えると、逆に前記Y-Xの値が低くなり、降伏比が低下する。そのため、上記冷却停止及び保持温度の上限は440℃以下が好ましく、より好ましくは430℃以下、更に好ましくは420℃以下である。特に、第1の冷却工程の冷却停止温度が380℃未満であり、保持工程の終了温度が440℃を超える場合には、残留オーステナイトの体積率が高くなり、降伏比が低下する。 (C) Holding Step After the first cooling is stopped in a temperature range of 380 ° C. or higher and 440 ° C. or lower, the first cooling is preferably held at a temperature of 380 ° C. or higher and 440 ° C. or lower for a predetermined time. When 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. On the other hand, when the cooling stop and holding temperature exceeds 440 ° C., the value of Y−X decreases, and the yield ratio decreases. Therefore, 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. In particular, when 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.
上記保持工程での保持時間は20秒以上30秒以下とすることが好ましい。該保持時間が20秒未満になると、上記Xの値が高く、上記Y-Xの値が低くなり、降伏比が低下し、且つ、曲げ性が劣化する。そのため、該保持時間の下限は、20秒以上、好ましくは22秒以上とする。一方、該保持時間が30秒を超えると、逆に上記Y-Xの値が高くなることで、降伏比が高くなりすぎ、且つ、曲げ性も低下する。そのため、該保持時間の上限は30秒以下、好ましくは28秒以下である。
The holding time in the holding step is preferably 20 seconds or longer and 30 seconds or shorter. When 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. On the other hand, if 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)第2の冷却工程
上記(c)保持工程を終了した後、100℃以上、310℃以下の冷却停止温度までを20℃/秒以上、50℃/秒以下の平均冷却速度で冷却することが好ましい。第2の冷却工程における平均冷却速度が20℃/秒未満になると、上記Y-Xの値が高くなることで、降伏比が高くなりすぎ、延性が劣化する。そのため、第2の冷却工程における平均冷却速度の下限は、20℃/秒以上が好ましく、より好ましくは25℃/秒以上とする。一方、上記平均冷却速度が50℃/秒を超えると、設備コストが増加する。そのため、上記平均冷却速度の上限は50℃/秒以下が好ましく、より好ましくは40℃/秒以下である。 (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. When 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. On the other hand, when the average cooling rate exceeds 50 ° C./second, the equipment cost increases. Therefore, the upper limit of the average cooling rate is preferably 50 ° C./second or less, more preferably 40 ° C./second or less.
上記(c)保持工程を終了した後、100℃以上、310℃以下の冷却停止温度までを20℃/秒以上、50℃/秒以下の平均冷却速度で冷却することが好ましい。第2の冷却工程における平均冷却速度が20℃/秒未満になると、上記Y-Xの値が高くなることで、降伏比が高くなりすぎ、延性が劣化する。そのため、第2の冷却工程における平均冷却速度の下限は、20℃/秒以上が好ましく、より好ましくは25℃/秒以上とする。一方、上記平均冷却速度が50℃/秒を超えると、設備コストが増加する。そのため、上記平均冷却速度の上限は50℃/秒以下が好ましく、より好ましくは40℃/秒以下である。 (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. When 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. On the other hand, when the average cooling rate exceeds 50 ° C./second, the equipment cost increases. Therefore, the upper limit of the average cooling rate is preferably 50 ° C./second or less, more preferably 40 ° C./second or less.
第2の冷却工程における冷却停止温度が100℃未満になると、設備コストが増加する。そのため、上記冷却停止保持温度の下限は100℃以上が好ましく、より好ましくは200℃以上とする。一方、上記冷却停止保持温度が310℃を超えると、上記Y-Xの値が高くなり、降伏比が高くなりすぎる。そのため、上記冷却停止温度の上限は、310℃以下が好ましく、より好ましくは300℃以下、更に好ましくは290℃以下である。
When the cooling stop temperature in the second cooling step is less than 100 ° C., the equipment cost increases. Therefore, the lower limit of the cooling stop holding temperature is preferably 100 ° C. or higher, more preferably 200 ° C. or higher. On the other hand, when the cooling stop holding temperature exceeds 310 ° C., the value of YX becomes high and the yield ratio becomes too high. Therefore, 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.
(e)第3の冷却工程
第2の冷却工程の後、1℃/秒以上の平均冷却速度で冷却することが好ましい。前記平均冷却速度の上限は特に限定されず、例えば10℃/秒である。また第3の冷却工程の冷却停止温度も特に限定されず、通常、室温まで冷却すれば良い。 (E) Third Cooling Step After the second cooling step, it is preferable to cool at an average cooling rate of 1 ° C./second or more. The upper limit of the average cooling rate is not particularly limited, and is, for example, 10 ° C./second. Further, the cooling stop temperature in the third cooling step is not particularly limited, and it may be normally cooled to room temperature.
第2の冷却工程の後、1℃/秒以上の平均冷却速度で冷却することが好ましい。前記平均冷却速度の上限は特に限定されず、例えば10℃/秒である。また第3の冷却工程の冷却停止温度も特に限定されず、通常、室温まで冷却すれば良い。 (E) Third Cooling Step After the second cooling step, it is preferable to cool at an average cooling rate of 1 ° C./second or more. The upper limit of the average cooling rate is not particularly limited, and is, for example, 10 ° C./second. Further, the cooling stop temperature in the third cooling step is not particularly limited, and it may be normally cooled to room temperature.
本発明には、高強度冷延鋼板の表面に亜鉛めっき層を有する高強度溶融亜鉛めっき鋼板も包含される。本発明の高強度溶融亜鉛めっき鋼板の製造方法は、上記(c)保持工程と(d)第2の冷却工程の間に、亜鉛めっき処理を行う工程を含む。この亜鉛めっき処理は、保持工程の後、冷間圧延された鋼板を440℃以上470℃以下の亜鉛めっき浴に1秒以上5秒以下浸漬させることによって行われる。この亜鉛めっき処理を行うことにより、鋼板の表面に亜鉛めっき層を形成することができる。上記亜鉛めっき浴の温度は455℃以上465℃以下であることが好ましい。
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. By performing this galvanizing treatment, a galvanized layer can be formed on the surface of the steel sheet. The temperature of the galvanizing bath is preferably 455 ° C. or higher and 465 ° C. or lower.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明は下記実施例によって制限されず、前・後記の趣旨に適合し得る範囲で変更を加えて実施することも可能であり、それらはいずれも本発明の技術的範囲に含有される。
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and can be implemented with modifications within a range that can meet the purpose described above and below. They are all included in the technical scope of the present invention.
下記表1に示す成分組成の実験用スラブを製造した。そのスラブを1250℃まで加熱し、板厚2.8mmまで熱間圧延を施した。仕上げ圧延温度は900℃、熱間圧延の仕上げ圧延から巻取りまでの平均冷却速度は20℃/秒、巻取り温度は、600℃で行った。次いで得られた熱間圧延鋼板を酸洗した後、板厚1.4mmまで冷間圧延した。その後、図2、表2に示す条件で熱処理を行った。表2に示すいずれの熱処理も、(a)均熱工程までの平均加熱速度は8℃/秒であり、第1の冷却工程での平均冷却速度は20℃/秒であった。更に伸び率0.1%の調質圧延を施した。なお、表1中、空欄は添加していないことを意味し、またP、S、N、Oは上述の通り不可避的不純物であり、P、S、N、Oの欄に示した値は不可避的に含まれた量を意味する。
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, and the winding temperature was 600 ° C. Subsequently, the obtained hot-rolled steel sheet was pickled and then cold-rolled to a thickness of 1.4 mm. Thereafter, 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. Furthermore, temper rolling with an elongation of 0.1% was performed. In Table 1, 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.
また、表2の熱処理21~23では、溶融亜鉛めっき鋼板と同様の熱履歴を与えた。溶融亜鉛めっき鋼板の熱履歴として、(c)保持工程終了の後に2秒で460℃(溶融亜鉛めっき浴温度を模擬)まで加熱し、その温度に2秒間保持した後、(d)第2の冷却工程以降の処理を行った。
Further, in heat treatments 21 to 23 in Table 2, the same heat history as that of the hot-dip galvanized steel sheet was given. As the heat history of the hot dip galvanized steel sheet, (c) after the holding step is completed, the heat is heated to 460 ° C. (simulating the hot dip galvanizing bath temperature) in 2 seconds, and held at that temperature for 2 seconds. Processing after the cooling step was performed.
このようにして得られた各冷延鋼板について、IQ(イメージクオリティ)、残留オーステナイトの体積率、および各種特性を以下のようにして測定した。
For each cold-rolled steel sheet thus obtained, IQ (image quality), volume fraction of retained austenite, and various properties were measured as follows.
[残留オーステナイトの体積率]
残留オーステナイトは、上記焼鈍後の冷延鋼板から1.4mm×20mm×20mmの試験片を切り出した。この試験片の板厚の1/4部まで研削した後、化学研磨してからX線回折法により残留オーステナイト量を測定した(ISIJ Int.Vol.33.(1933),No.7,P.776)。 [Volume ratio of retained austenite]
Residual austenite was cut out from a 1.4 mm × 20 mm × 20 mm test piece from the annealed cold rolled steel sheet. After grinding to 1/4 part of the thickness of the test piece, the amount of retained austenite was measured by X-ray diffractometry after chemical polishing (ISIJ Int. Vol. 33. (1933), No. 7, P.A. 776).
残留オーステナイトは、上記焼鈍後の冷延鋼板から1.4mm×20mm×20mmの試験片を切り出した。この試験片の板厚の1/4部まで研削した後、化学研磨してからX線回折法により残留オーステナイト量を測定した(ISIJ Int.Vol.33.(1933),No.7,P.776)。 [Volume ratio of retained austenite]
Residual austenite was cut out from a 1.4 mm × 20 mm × 20 mm test piece from the annealed cold rolled steel sheet. After grinding to 1/4 part of the thickness of the test piece, the amount of retained austenite was measured by X-ray diffractometry after chemical polishing (ISIJ Int. Vol. 33. (1933), No. 7, P.A. 776).
[IQ(イメージクオリティ)]
また、EBSDパターンの鮮明度であるIQ(イメージクオリティ)は以下のように測定した。まず、圧延方向に平行な断面を機械研磨した試料を用意した。次いで、この試料を、テクセムラボラトリーズ社製OIMシステムにセットして70°傾斜させた状態で、100μm×100μmの領域を測定視野とし、加速電圧:20kV、1ステップ:0.25μmで18万点のEBSD測定を行った。この測定により、体心正方格子(BCT:Body centered Tetragonal)を含む体心立方格子(BCC:Body Centered Cubic)結晶のIQを測定した。ここで体心正方格子は、C原子が体心立方格子内の特定の侵入型位置に固溶することで格子が一方向に伸長したものである。体心正方格子は、構造自体は体心立方格子と同等であるため、本実施例では、体心立方格子の測定には体心正方格子を含むものとした。なお、測定箇所は、圧延に平行な面における圧延方向に垂直な方向の長さをWとしたときのW/4部、且つ板厚をtとした時のt/4部であり、測定は1視野について実施した。この測定結果より、上記したX及びYの値をそれぞれ算出した。 [IQ (Image Quality)]
Moreover, IQ (image quality) which is the definition of an EBSD pattern was measured as follows. First, a sample was prepared by mechanically polishing a cross section parallel to the rolling direction. Next, this sample was set in an OIM system manufactured by Texemra Laboratories Inc. and tilted by 70 °, and an area of 100 μm × 100 μm was taken as a measurement visual field, and acceleration voltage: 20 kV, 1 step: 185 μm at 0.25 μm EBSD measurement was performed. By this measurement, IQ of a body-centered cubic lattice (BCC) crystal including a body-centered tetragonal lattice (BCT) was measured. Here, 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.
また、EBSDパターンの鮮明度であるIQ(イメージクオリティ)は以下のように測定した。まず、圧延方向に平行な断面を機械研磨した試料を用意した。次いで、この試料を、テクセムラボラトリーズ社製OIMシステムにセットして70°傾斜させた状態で、100μm×100μmの領域を測定視野とし、加速電圧:20kV、1ステップ:0.25μmで18万点のEBSD測定を行った。この測定により、体心正方格子(BCT:Body centered Tetragonal)を含む体心立方格子(BCC:Body Centered Cubic)結晶のIQを測定した。ここで体心正方格子は、C原子が体心立方格子内の特定の侵入型位置に固溶することで格子が一方向に伸長したものである。体心正方格子は、構造自体は体心立方格子と同等であるため、本実施例では、体心立方格子の測定には体心正方格子を含むものとした。なお、測定箇所は、圧延に平行な面における圧延方向に垂直な方向の長さをWとしたときのW/4部、且つ板厚をtとした時のt/4部であり、測定は1視野について実施した。この測定結果より、上記したX及びYの値をそれぞれ算出した。 [IQ (Image Quality)]
Moreover, IQ (image quality) which is the definition of an EBSD pattern was measured as follows. First, a sample was prepared by mechanically polishing a cross section parallel to the rolling direction. Next, this sample was set in an OIM system manufactured by Texemra Laboratories Inc. and tilted by 70 °, and an area of 100 μm × 100 μm was taken as a measurement visual field, and acceleration voltage: 20 kV, 1 step: 185 μm at 0.25 μm EBSD measurement was performed. By this measurement, IQ of a body-centered cubic lattice (BCC) crystal including a body-centered tetragonal lattice (BCT) was measured. Here, 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.
[引張特性]
引張強度(TS)、0.2%耐力(YS)、および延性(El)については、上記冷間圧延の圧延面と平行な面における圧延方向と直角な方向が試験片の長手となるように、JIS 13B号試験片(標点距離50mm、平行部幅12.5mm)を採取し、JIS Z2241に従って試験した。測定結果を下記表3に示す。また、引張強度(TS)と0.2%耐力(YS)に基づいて、降伏比(YR)を算出した。この結果を下記表3に示す。 [Tensile properties]
Regarding the tensile strength (TS), 0.2% yield strength (YS), and ductility (El), the direction perpendicular to the rolling direction in the plane parallel to the rolling surface of the cold rolling is the length of the test piece. , JIS No. 13B test piece (mark distance: 50 mm, parallel part width: 12.5 mm) was collected and tested according to JIS Z2241. The measurement results are shown in Table 3 below. The yield ratio (YR) was calculated based on the tensile strength (TS) and the 0.2% yield strength (YS). The results are shown in Table 3 below.
引張強度(TS)、0.2%耐力(YS)、および延性(El)については、上記冷間圧延の圧延面と平行な面における圧延方向と直角な方向が試験片の長手となるように、JIS 13B号試験片(標点距離50mm、平行部幅12.5mm)を採取し、JIS Z2241に従って試験した。測定結果を下記表3に示す。また、引張強度(TS)と0.2%耐力(YS)に基づいて、降伏比(YR)を算出した。この結果を下記表3に示す。 [Tensile properties]
Regarding the tensile strength (TS), 0.2% yield strength (YS), and ductility (El), the direction perpendicular to the rolling direction in the plane parallel to the rolling surface of the cold rolling is the length of the test piece. , JIS No. 13B test piece (mark distance: 50 mm, parallel part width: 12.5 mm) was collected and tested according to JIS Z2241. The measurement results are shown in Table 3 below. The yield ratio (YR) was calculated based on the tensile strength (TS) and the 0.2% yield strength (YS). The results are shown in Table 3 below.
[曲げ性]
曲げ性(R/t)は、圧延面において圧延方向と垂直となる方向が試験片の長手となるように、上記冷延鋼板から1.4mm×30mm×20mmの試験片を採取し、JIS Z2248のVブロック法に従って試験を行った。そして、試験片に割れや亀裂が発生しない最小曲げ半径Rを測定した。なお、曲げ方向は試験片長手方向である。また、Vブロックの曲げ角度は90°で行った。曲げ試験により判明したRを公称板厚1.4mmで割った値をR/tとした。測定結果を下記表3に示す。 [Bendability]
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 | occur | produce in a test piece was measured. The bending direction is the longitudinal direction of the test piece. The bending angle of the V block was 90 °. A value obtained by dividing R found by a bending test by a nominal plate thickness of 1.4 mm was defined as R / t. The measurement results are shown in Table 3 below.
曲げ性(R/t)は、圧延面において圧延方向と垂直となる方向が試験片の長手となるように、上記冷延鋼板から1.4mm×30mm×20mmの試験片を採取し、JIS Z2248のVブロック法に従って試験を行った。そして、試験片に割れや亀裂が発生しない最小曲げ半径Rを測定した。なお、曲げ方向は試験片長手方向である。また、Vブロックの曲げ角度は90°で行った。曲げ試験により判明したRを公称板厚1.4mmで割った値をR/tとした。測定結果を下記表3に示す。 [Bendability]
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 | occur | produce in a test piece was measured. The bending direction is the longitudinal direction of the test piece. The bending angle of the V block was 90 °. A value obtained by dividing R found by a bending test by a nominal plate thickness of 1.4 mm was defined as R / t. The measurement results are shown in Table 3 below.
得られた鋼板の引張強度に応じて下記基準で特性を評価した。これらの結果を表3に示す。
(i)引張強度が980MPa以上1180MPa未満の鋼板
伸び(El)が8%以上、曲げ性(R/t)が3以下を合格とした。Elは高いほどよく(上限は特に限定されないが、通常15%程度)、R/tは小さいほど良い(下限は特に限定されないが、通常0.5)。
(ii)引張強度が1180MPa以上の鋼板
伸び(El)が7%以上、曲げ性(R/t)が4以下を合格とした。Elは高いほどよく(上限は特に限定されないが、通常13%程度)、R/tは小さいほど良い(下限は特に限定されないが、通常1.0)。 The characteristics were evaluated according to the following criteria according to the tensile strength of the obtained steel sheet. These results are shown in Table 3.
(I) Steel sheet having a tensile strength of 980 MPa or more and less than 1180 MPa. Elongation (El) was 8% or more and bendability (R / t) was 3 or less. The higher the El, the better (the upper limit is not particularly limited, but usually about 15%), and the smaller the R / t, the better (the lower limit is not particularly limited, but usually 0.5).
(Ii) Steel sheet having a tensile strength of 1180 MPa or more Elongation (El) was 7% or more and bendability (R / t) was 4 or less. The higher the El, the better (the upper limit is not particularly limited, but usually about 13%), and the smaller the R / t, the better (the lower limit is not particularly limited, but usually 1.0).
(i)引張強度が980MPa以上1180MPa未満の鋼板
伸び(El)が8%以上、曲げ性(R/t)が3以下を合格とした。Elは高いほどよく(上限は特に限定されないが、通常15%程度)、R/tは小さいほど良い(下限は特に限定されないが、通常0.5)。
(ii)引張強度が1180MPa以上の鋼板
伸び(El)が7%以上、曲げ性(R/t)が4以下を合格とした。Elは高いほどよく(上限は特に限定されないが、通常13%程度)、R/tは小さいほど良い(下限は特に限定されないが、通常1.0)。 The characteristics were evaluated according to the following criteria according to the tensile strength of the obtained steel sheet. These results are shown in Table 3.
(I) Steel sheet having a tensile strength of 980 MPa or more and less than 1180 MPa. Elongation (El) was 8% or more and bendability (R / t) was 3 or less. The higher the El, the better (the upper limit is not particularly limited, but usually about 15%), and the smaller the R / t, the better (the lower limit is not particularly limited, but usually 0.5).
(Ii) Steel sheet having a tensile strength of 1180 MPa or more Elongation (El) was 7% or more and bendability (R / t) was 4 or less. The higher the El, the better (the upper limit is not particularly limited, but usually about 13%), and the smaller the R / t, the better (the lower limit is not particularly limited, but usually 1.0).
表3より、以下のように考察することができる。表3の試験No.3、11~14、27~31、35、37、38、41、42は、それぞれ、本発明の組成を満足する表1の鋼種1~3、11~16、18、19を用い、本発明の好ましい熱処理条件である表2の熱処理No.3、10~13で製造した本発明例である。これらは、本発明の要件を満足しているため、引張強度が980MPa以上、且つ、降伏比が90%以上95%以下であって、延性(El)、曲げ性(R/t)に優れているものが得られている。
From Table 3, it can be considered as follows. Test No. in Table 3 3, 11-14, 27-31, 35, 37, 38, 41, and 42, steel types 1-3, 11-16, 18, 19 of Table 1 satisfying the composition of the present invention were used, respectively. The heat treatment No. in Table 2 which is a preferred heat treatment condition of 3 is an example of the present invention manufactured in 10-13. Since these satisfy the requirements of the present invention, the tensile strength is 980 MPa or more, the yield ratio is 90% or more and 95% or less, and the ductility (El) and bendability (R / t) are excellent. What you are getting is obtained.
また、表3の試験No.32~34は、それぞれ、本発明の組成を満足する表1の鋼種2を用い、本発明の好ましい熱処理条件である表2の熱処理No.21~23で製造した本発明例であり、溶融亜鉛めっきを模擬した熱履歴を経たものである。これらも、本発明の要件を満足しているため、引張強度が980MPa以上、且つ、降伏比が90%以上95%以下であって、延性(El)、曲げ性(R/t)に優れているものが得られている。
Also, 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. It is an example of the present invention manufactured in 21 to 23, and has undergone a thermal history simulating hot dip galvanizing. Since these also satisfy the requirements of the present invention, the tensile strength is 980 MPa or more, the yield ratio is 90% or more and 95% or less, and the ductility (El) and bendability (R / t) are excellent. What you are getting is obtained.
なお、試験No.3、11~14、27~35、37、38、41、42では、ベイナイト及びマルテンサイトの合計面積率が95%以上であることを確認している。
Test No. 3, 11 to 14, 27 to 35, 37, 38, 41 and 42, it was confirmed that the total area ratio of bainite and martensite was 95% or more.
これに対し、本発明のいずれかの要件を満足しない下記の例は、所望とする特性が得られないことが確認された。
On the other hand, it was confirmed that the following characteristics that do not satisfy any of the requirements of the present invention do not provide the desired characteristics.
表3の試験No.20~26、39は、本発明の組成を満足しない表1の鋼種4~10、17を用い、表2の熱処理No.3の熱処理条件で製造した例である。
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.
試験No.20は、C量が少なく、Y-Xの値が小さく、引張強度(TS)が低い。
Test No. No. 20 has a small amount of C, a small value of YX, and a low tensile strength (TS).
試験No.21は、C量が多く、Xの値が大きいと共に、Y-Xの値が小さく、更に残留オーステナイト体積率が高く、降伏比(YR)が低いことに加えて、曲げ性(R/t)も満たしていない。
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.
試験No.22は、Mn量が少なく、Y-Xの値が小さく、引張強度(TS)が低い。
Test No. No. 22 has a small amount of Mn, a small YX value, and a low tensile strength (TS).
試験No.23は、Mn量が多く、Xの値が大きいと共に、Y-Xの値が小さく、降伏比(YR)が低く、曲げ性も満たしていない。
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.
試験No.24は、Ti量が少なく、Y-Xの値が小さく、引張強度(TS)が低いと共に、降伏比(YR)及び延性(El)が低く、曲げ性(R/t)も満たしていない。
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).
試験No.25は、Ti量が多く、Xの値が大きいと共に、Y-Xの値が小さく、降伏比(YR)が低く、曲げ性も満たしていない。
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.
試験No.26は、B量が少なく、Y-Xの値が小さく、引張強度(TS)が低いと共に、降伏比(YR)が低い。
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).
試験No.39は、Si量が多く、Xの値が大きいと共に、Y-Xの値が小さく、降伏比(YR)が低い。
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).
表3の試験No.1、2、4~10、15~19、36、40は、本発明の組成を満足する表1の鋼種1~3、16を用い、表2の熱処理No.1、2、4~9、14~20の熱処理条件で製造した例である。
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.
試験No.1は、均熱温度が低く、Xの値が大きく、引張強度(TS)が低いとともに、且つ降伏比(YR)が低くなった。
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).
試験No.2は、冷却停止温度及びその後の保持温度が低く、Y-Xの値が大きく、降伏比(YR)が高くなり、延性(El)が低い。
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).
試験No.4、5、9及び10は、冷却停止温度及びその後の保持温度が高く、Y-Xの値が小さく、降伏比(YR)が低くなった。
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).
試験No.6は、冷却停止温度及びその後の保持温度が高く、且つ、保持時間が長いため、Y-Xの値が小さく、引張強度(TS)が低く、且つ降伏比(YR)が低くなった。
Test No. In No. 6, since the cooling stop temperature and the subsequent holding temperature were high and the holding time was long, the value of YX was small, the tensile strength (TS) was low, and the yield ratio (YR) was low.
試験No.7は、冷却停止温度及びその後の保持温度が非常に高く、Xの値が高く、Y-Xの値が小さく、降伏比(YR)が低く、曲げ性(R/t)が悪化した。
Test No. In No. 7, the cooling stop temperature and the subsequent holding temperature were very high, the value of X was high, the value of YX was small, the yield ratio (YR) was low, and the bendability (R / t) deteriorated.
試験No.8は、冷却停止温度及びその後の保持温度が低く、Y-Xの値が大きく、降伏比(YR)が高くなりすぎ、延性(El)が悪化した。
Test No. In No. 8, the cooling stop temperature and the subsequent holding temperature were low, the value of YX was large, the yield ratio (YR) was too high, and the ductility (El) was deteriorated.
試験No.15、16は、(c)保持工程の保持時間が短く、Xの値が大きく、Y-Xの値が小さく、降伏比(YR)が低くなり、曲げ性(R/t)が悪化した。
Test No. 15 and 16, (c) The holding time of the holding step was short, the value of X was large, the value of YX was small, the yield ratio (YR) was low, and the bendability (R / t) was deteriorated.
試験No.17、18は、(c)保持工程の保持時間が長く、Y-Xの値が大きく、引張強度(TS)が小さいと共に、降伏比(YR)が高くなりすぎ、且つ延性(El)が悪化した。
Test No. 17 and 18, (c) The holding time of the holding process is long, the value of YX is large, the tensile strength (TS) is small, the yield ratio (YR) is too high, and the ductility (El) is deteriorated. did.
試験No.19は、(d)第2の冷却工程の冷却停止温度が高く、Y-Xの値が大きく、引張強度(TS)が小さいと共に、降伏比(YR)が高くなりすぎ、且つ延性(El)が悪化した。
Test No. No. 19 (d) The cooling stop temperature of the second cooling step is high, the value of YX is large, the tensile strength (TS) is small, the yield ratio (YR) is too high, and the ductility (El) Worsened.
試験No.36は、冷却停止温度が低く、且つ保持終了温度が高い条件で処理した例であり、残留γの体積率が多くなり、降伏比(YR)が低くなった。
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 γ is increased and the yield ratio (YR) is lowered.
試験No.40は、(a)均熱工程で保持する時間が短く(保持していない)、Xの値が大きく、引張強度(TS)が低く、且つ降伏比(YR)が低くなった。
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.
この出願は、2016年3月30日に出願された日本国特許出願特願2016-068769号および2016年11月17日に出願された日本国特許出願特願2016-223986号を基礎とするものであり、その内容は、本願に含まれるものである。
This application is based on Japanese Patent Application No. 2016-068769 filed on Mar. 30, 2016 and Japanese Patent Application No. 2016-223986 filed on Nov. 17, 2016. The content of which is included in the present application.
Claims (5)
- 質量%で、
C :0.12~0.19%、
Si:0%超、0.4%以下、
Mn:1.80~2.45%、
P :0%超、0.020%以下、
S :0%超、0.0040%以下、
Al:0.015~0.06%、
Ti:0.010~0.035%、および
B :0.0025~0.0040%
を含有し、残部が鉄および不可避不純物であり、
下記(1)で定義されるXが8.0以下であり、下記(2)で定義されるYと前記Xの差の値Y-Xが45以上53以下であり、
全組織に対する残留オーステナイトの体積率が2%以下であり、
引張強度が980MPa以上であることを特徴とする高強度冷延鋼板。
(1)Xは、[0.40×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
(2)Yは、[0.75×(IQmax-IQmin)+IQmin]以下である測定点数の合計を全測定点数で除して100を掛けた値であり、
上記(1)、(2)におけるIQは、電子線後方散乱回折パターンの鮮明度を意味し、IQmaxは全測定点中のIQの最大値であり、IQminは全測定点中のIQの最小値である。 % By 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%
The balance is iron and inevitable impurities,
X defined in the following (1) is 8.0 or less, and the value Y-X between Y defined in the following (2) and the X is 45 or more and 53 or less,
The volume ratio of retained austenite with respect to the whole structure is 2% or less,
A high-strength cold-rolled steel sheet having a tensile strength of 980 MPa or more.
(1) 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.
(2) 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.
IQ in the above (1) and (2) means the sharpness of the electron beam backscatter diffraction pattern, IQmax is the maximum IQ value in all measurement points, and IQmin is the minimum IQ value in all measurement points. It is. - 更に、質量%で、
Cu:0%超、0.3%以下、
Ni:0%超、0.3%以下、
Cr:0%超、0.25%以下、
Mo:0%超、0.1%以下、
V :0%超、0.05%以下、
Nb:0%超、0.08%以下および
Ca:0%超、0.005%以下
よりなる群から選ばれる1種以上を含有する請求項1に記載の高強度冷延鋼板。 Furthermore, 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,
The high-strength cold-rolled steel sheet according to claim 1, comprising at least one selected from the group consisting of Nb: more than 0%, 0.08% or less and Ca: more than 0%, 0.005% or less. - 請求項1または2に記載の高強度冷延鋼板の表面に亜鉛めっき層を有する高強度溶融亜鉛めっき鋼板。 A high-strength hot-dip galvanized steel sheet having a galvanized layer on the surface of the high-strength cold-rolled steel sheet according to claim 1 or 2.
- 請求項1または2に記載の高強度冷延鋼板の製造方法であって、
請求項1または2に記載の各成分の含有量を満たす、冷間圧延された鋼板を、1~20℃/秒の平均加熱速度で加熱し、Ac3点~Ac3点+200℃の範囲で1~100秒保持する均熱工程と、
前記均熱工程の後、前記鋼板を15~50℃/秒の平均冷却速度で、380~440℃の温度範囲まで冷却する第1の冷却工程と、
前記第1の冷却工程の後、前記鋼板を380℃以上440℃以下の温度に20秒以上30秒以下保持する保持工程と、
前記保持工程の後、前記鋼板を20~50℃/秒の平均冷却速度で、100~310℃の温度範囲まで冷却する第2の冷却工程と、
前記第2の冷却工程の後、前記鋼板を1℃/秒以上の平均冷却速度で室温まで冷却する第3の冷却工程と、を含み、
前記Ac3の温度は、下記式(a)に基づいて算出される高強度冷延鋼板の製造方法。
Ac3=910-203√(%C)-15.2(%Ni)+44.7(%Si)+104(%V)+31.5(%Mo)+13.1(%W)-30(%Mn)-11(%Cr)-20(%Cu)+700(%P)+400(%Al)+120(%As)+400(%Ti)・・・(a)
(前記式(a)中の[%(元素名)]は各元素の含有量(質量%)である。) A method for producing a high-strength cold-rolled steel sheet according to claim 1 or 2,
A cold-rolled steel sheet satisfying the content of each component according to claim 1 or 2 is heated at an average heating rate of 1 to 20 ° C./second, and in a range of Ac 3 points to Ac 3 points + 200 ° C. A soaking step for 1 to 100 seconds;
After the soaking step, a first cooling step of cooling the steel sheet to a temperature range of 380 to 440 ° C. at an average cooling rate of 15 to 50 ° C./second;
After the first cooling step, holding the steel plate at a temperature of 380 ° C. or higher and 440 ° C. or lower for 20 seconds or longer and 30 seconds or shorter;
After the holding step, a second cooling step of cooling the steel sheet to a temperature range of 100 to 310 ° C. at an average cooling rate of 20 to 50 ° C./second;
After the second cooling step, a third cooling step of cooling the steel sheet to room temperature at an average cooling rate of 1 ° C./second or more,
Temperature of the Ac 3 The method for manufacturing a high-strength cold-rolled steel sheet is calculated based on the following formula (a).
Ac 3 = 910−203√ (% C) −15.2 (% Ni) +44.7 (% Si) +104 (% V) +31.5 (% Mo) +13.1 (% W) −30 (% Mn ) -11 (% Cr) -20 (% Cu) +700 (% P) +400 (% Al) +120 (% As) +400 (% Ti) (a)
([% (Element name)] in the formula (a) is the content (% by mass) of each element.) - 請求項3に記載の高強度溶融亜鉛めっき鋼板の製造方法であって、
請求項1または2に記載の各成分の含有量を満たす、冷間圧延された鋼板を、1~20℃/秒の平均加熱速度で加熱し、Ac3点~Ac3点+200℃の範囲で1~100秒保持する均熱工程と、
前記均熱工程の後、前記鋼板を15~50℃/秒の平均冷却速度で、380~440℃の温度範囲まで冷却する第1の冷却工程と、
前記第1の冷却工程の後、前記鋼板を380℃以上440℃以下の温度に20秒以上30秒以下保持する保持工程と、
前記保持工程の後、前記鋼板を440℃以上470℃以下の亜鉛めっき浴に1秒以上5秒以下浸漬させることによって前記鋼板の表面に亜鉛めっき層を形成する工程と、
前記亜鉛めっき層を形成する工程の後、前記鋼板を20~50℃/秒の平均冷却速度で、100~310℃の温度範囲まで冷却する第2の冷却工程と、
前記第2の冷却工程の後、前記鋼板を1℃/秒以上の平均冷却速度で室温まで冷却する第3の冷却工程と、を含み、
前記Ac3の温度は、下記式(a)に基づいて算出される高強度溶融亜鉛めっき鋼板の製造方法。
Ac3=910-203√(%C)-15.2(%Ni)+44.7(%Si)+104(%V)+31.5(%Mo)+13.1(%W)-30(%Mn)-11(%Cr)-20(%Cu)+700(%P)+400(%Al)+120(%As)+400(%Ti)・・・(a)
(前記式(a)中の[%(元素名)]は各元素の含有量(質量%)である。) A method for producing a high-strength hot-dip galvanized steel sheet according to claim 3,
A cold-rolled steel sheet satisfying the content of each component according to claim 1 or 2 is heated at an average heating rate of 1 to 20 ° C./second, and in a range of Ac 3 points to Ac 3 points + 200 ° C. A soaking step for 1 to 100 seconds;
After the soaking step, a first cooling step of cooling the steel sheet to a temperature range of 380 to 440 ° C. at an average cooling rate of 15 to 50 ° C./second;
After the first cooling step, holding the steel plate at a temperature of 380 ° C. or higher and 440 ° C. or lower for 20 seconds or longer and 30 seconds or shorter;
After the holding step, the step of forming a galvanized layer on the surface of the steel sheet by immersing the steel sheet in a galvanizing bath at 440 ° C. or higher and 470 ° C. or lower for 1 second or more and 5 seconds or less;
After the step of forming the galvanized layer, a second cooling step of cooling the steel sheet to a temperature range of 100 to 310 ° C. at an average cooling rate of 20 to 50 ° C./second;
After the second cooling step, a third cooling step of cooling the steel sheet to room temperature at an average cooling rate of 1 ° C./second or more,
Temperature of the Ac 3 The method for manufacturing a high strength galvanized steel sheet is calculated based on the following formula (a).
Ac 3 = 910−203√ (% C) −15.2 (% Ni) +44.7 (% Si) +104 (% V) +31.5 (% Mo) +13.1 (% W) −30 (% Mn ) -11 (% Cr) -20 (% Cu) +700 (% P) +400 (% Al) +120 (% As) +400 (% Ti) (a)
([% (Element name)] in the formula (a) is the content (% by mass) of each element.)
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