WO2024162382A1 - 熱延鋼板 - Google Patents

熱延鋼板 Download PDF

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Publication number
WO2024162382A1
WO2024162382A1 PCT/JP2024/003023 JP2024003023W WO2024162382A1 WO 2024162382 A1 WO2024162382 A1 WO 2024162382A1 JP 2024003023 W JP2024003023 W JP 2024003023W WO 2024162382 A1 WO2024162382 A1 WO 2024162382A1
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hot
steel sheet
rolled steel
content
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PCT/JP2024/003023
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English (en)
French (fr)
Japanese (ja)
Inventor
隆 安富
雄斗 柘植
竜大 服部
昌史 東
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Nippon Steel Corp
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Nippon Steel Corp
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Priority to CN202480008617.XA priority Critical patent/CN120569507A/zh
Priority to EP24750331.1A priority patent/EP4660343A1/en
Priority to KR1020257024771A priority patent/KR20250130341A/ko
Priority to JP2024574967A priority patent/JPWO2024162382A1/ja
Publication of WO2024162382A1 publication Critical patent/WO2024162382A1/ja
Priority to MX2025008683A priority patent/MX2025008683A/es
Anticipated expiration legal-status Critical
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
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    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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    • C21D2211/00—Microstructure comprising significant phases
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Definitions

  • the present invention relates to a hot rolled steel sheet.
  • the present invention relates to a hot rolled steel sheet having high strength, excellent ductility and hole expansion properties, and excellent tensile bending properties in the rolling direction.
  • Automotive parts are manufactured by subjecting steel plate to various processes, so steel plate used in automotive parts is required to have excellent formability, especially ductility and hole expansion properties.
  • steel sheets When manufacturing automotive parts, steel sheets may be bent while tension is applied. Bending while tension is applied is often performed along the rolling direction of the steel sheet. Therefore, steel sheets used in automotive parts are required to have excellent tensile bending properties, especially in the rolling direction.
  • Patent Document 1 discloses a hot-rolled steel sheet having a structure consisting of 70% or more ferrite and pearlite in terms of area fraction, a sheet thickness T0 of 6 to 25 mm, an average grain size GC of the ferrite grains inside the sheet thickness of 5 to 15 ⁇ m, the hot-rolled steel sheet having a fine grain layer formed from the surface in the sheet thickness direction and having an average grain size of the ferrite grains less than 1.0 times the average grain size GC, the fine grain layer including a specific fine grain layer having an average grain size of the ferrite grains of 0.1 to 0.4 times the average grain size GC, and satisfying a predetermined formula when the thickness of the specific fine grain layer is TF0 and the thickness of an ultrafine grain layer of the fine grain layer in which the average grain size of the ferrite grains is less than 0.1 times the average grain size GC is TF1, and the average grain size of the ferrite grains of the specific fine grain layer and the ultrafine grain layer is 0.1 to 0.4 times the average grain size GC.
  • Patent Document 2 discloses a high-strength hot-rolled steel sheet with excellent hole expandability and weld fatigue properties, characterized in that the random strength ratio of the ⁇ 110 ⁇ 111> to ⁇ 110 ⁇ 001> orientation group in the thickness cross section in the region from the outermost layer to 1/6 of the sheet thickness is 3.5 or less.
  • Patent Documents 1 and 2 do not take into consideration the tensile bending characteristics in the rolling direction.
  • the present invention aims to provide a hot-rolled steel sheet that has high strength, excellent ductility and hole expansion properties, and excellent tensile bending properties in the rolling direction.
  • the inventors also discovered that controlling the rough rolling conditions and finish rolling conditions of hot rolling is effective in controlling the texture in the surface region of a hot-rolled steel sheet.
  • a hot-rolled steel sheet according to one embodiment of the present invention has a chemical composition, in mass%, C: 0.045-0.120%, Si: 0-3.00%, Mn: 1.20-2.60%, Ti: 0.020 to 0.180%, Al: 0.010-0.400%, P: 0.080% or less, S: 0.0100% or less, N: 0.0050% or less, O: 0.010% or less, Nb: 0 to 0.100%, V: 0 to 1.000%, Cu: 0 to 1.000%, Cr: 0-2.000%, Mo: 0-3.000%, Ni: 0 to 0.500%, B: 0 to 0.0100%, Ca: 0-0.0500%, Mg: 0 to 0.0500%, REM: 0-0.100%, Bi: 0-0.100%, Ta: 0-0.100%, Zr: 0 to 0.500%, Co: 0-3.000%, Zn: 0-0
  • a hot-rolled steel sheet having high strength, excellent ductility and hole expandability, and excellent tensile bending properties in the rolling direction. Furthermore, according to a preferred embodiment of the present invention, it is possible to provide a hot-rolled steel sheet having not only the above-mentioned properties but also excellent tensile bending properties in the width direction.
  • FIG. 13 is a diagram for explaining a tension bending test.
  • the chemical composition of the hot-rolled steel sheet according to this embodiment is, in mass%, C: 0.045 to 0.120%, Si: 0 to 3.00%, Mn: 1.20 to 2.60%, Ti: 0.020 to 0.180%, Al: 0.010 to 0.400%, P: 0.080% or less, S: 0.0100% or less, N: 0.0050% or less, and the balance: Fe and impurities.
  • C 0.045 to 0.120%
  • Si 0 to 3.00%
  • Mn 1.20 to 2.60%
  • Ti 0.020 to 0.180%
  • Al 0.010 to 0.400%
  • P 0.080% or less
  • S 0.0100% or less
  • N 0.0050% or less
  • Fe and impurities each element will be described in detail below.
  • C 0.045-0.120%
  • C is an element necessary for obtaining a desired tensile strength of the hot-rolled steel sheet. If the C content is less than 0.045%, the desired tensile strength cannot be obtained in the hot-rolled steel sheet. Therefore, the C content is set to 0.045% or more.
  • the C content is preferably 0.050% or more, more preferably 0.060% or more, and even more preferably 0.080% or more. be. On the other hand, if the C content exceeds 0.120%, the hole expandability of the hot-rolled steel sheet deteriorates. Therefore, the C content is set to 0.120% or less.
  • the C content is preferably 0.110% or less. and more preferably 0.100% or less.
  • Si 0-3.00% Si is an element that improves the tensile strength of a hot-rolled steel sheet by solid solution strengthening.
  • the hot-rolled steel sheet according to the present embodiment ensures sufficient tensile strength even without containing Si.
  • the Si content may be 0%.
  • the Si content is preferably 0.01% or more, and more preferably 0.03% or more.
  • the Si content is set to 3.00% or less.
  • the Si content is preferably 2.00% or less.
  • the Si content is set to 0 to 3.00%, thereby improving the strength and It is possible to achieve a good balance between elongation and hole expandability.
  • Mn 1.20-2.60%
  • Mn is an element necessary for improving the strength of a hot-rolled steel sheet. If the Mn content is less than 1.20%, the desired tensile strength cannot be obtained in the hot-rolled steel sheet.
  • the Mn content is 1.20% or more, preferably 1.40% or more, and more preferably 1.60% or more. On the other hand, if the Mn content exceeds 2.60%, the hole expandability of the hot-rolled steel sheet deteriorates. Therefore, the Mn content is set to 2.60% or less.
  • the Mn content is preferably 2.30% or less. % or less, and more preferably 2.20% or less.
  • Ti 0.020-0.180%
  • Ti is an element that forms fine nitrides in steel to increase the strength of the hot-rolled steel sheet. If the Ti content is less than 0.020%, the desired tensile strength cannot be obtained in the hot-rolled steel sheet. Therefore, the Ti content is set to 0.020% or more, preferably 0.050% or more, and more preferably 0.080% or more. On the other hand, if the Ti content exceeds 0.180%, the hole expandability of the hot-rolled steel sheet deteriorates. Therefore, the Ti content is set to 0.180% or less.
  • the Ti content is preferably 0. It is preferably 160% or less, and more preferably 0.150% or less.
  • Al 0.010-0.400%
  • Al is an element that acts as a deoxidizer and improves the cleanliness of steel. If the Al content is less than 0.010%, a sufficient deoxidizing effect cannot be obtained, and a large amount of Al inclusions in the steel are generated. Such inclusions deteriorate the workability, particularly the hole expandability, of the hot-rolled steel sheet. Therefore, the Al content is set to 0.010% or more.
  • the Al content is , preferably 0.020% or more, and more preferably 0.030% or more. On the other hand, if the Al content exceeds 0.400%, casting becomes difficult. Therefore, the Al content is set to 0.400% or less.
  • the Al content is preferably set to 0.300% or less, and more preferably 0.400% or less. It is preferably 0.200% or less, and even more preferably 0.100% or less.
  • P 0.080% or less
  • P is an element that segregates at grain boundaries in steel and promotes embrittlement of the grain boundaries. If the P content is too high, the elongation and hole expandability of the hot-rolled steel sheet are likely to decrease, and further, cracks in the slab due to embrittlement may occur, making hot rolling difficult. Therefore, the P content is set to 0.080% or less.
  • the P content is preferably 0.020% or less, and more preferably 0.010% or less. The lower the P content, the better, and 0% is preferable. However, if the P content is excessively reduced, the dephosphorization cost increases significantly, so the P content may be 0.001% or more.
  • S 0.0100% or less
  • S is an element that embrittles the slab when present as a sulfide.
  • S is also an element that deteriorates the workability of the hot-rolled steel sheet. If the S content exceeds 0.0100%, the hole expandability of the hot-rolled steel sheet deteriorates. Therefore, the S content is set to 0.0100% or less.
  • the S content is preferably 0.0080% or less, more preferably 0.0050% or less. The lower the S content, the better, and 0% is preferable. However, if the S content is excessively reduced, the desulfurization cost increases significantly, so the S content may be 0.0005% or more.
  • N 0.0050% or less
  • N is an element that forms coarse nitrides in steel and deteriorates the hole expandability of hot-rolled steel sheets. If the N content is too high, excessive nitrides are generated, which tends to reduce the elongation and hole expandability of the hot-rolled steel sheet, and furthermore, cracks in the slab due to embrittlement may occur, making hot rolling difficult. Therefore, the N content is set to 0.0050% or less.
  • the N content is preferably 0.0040% or less, and more preferably 0.0035% or less. The lower the N content, the better, and 0% is preferable. However, if the N content is excessively reduced, the cost of denitrification increases significantly, so the N content may be 0.0005% or more.
  • O 0.010% or less
  • O is an element that forms oxides and reduces the workability of hot-rolled steel sheets. If the O content exceeds 0.010%, the hole expandability of the hot-rolled steel sheet is likely to decrease due to excessive generation of oxides, etc. Therefore, the O content is set to 0.010% or less.
  • the O content is preferably 0.008% or less, and more preferably 0.006% or less. The lower the O content, the better, and 0% is preferable. However, if the O content is excessively reduced, the cost of deoxidization increases significantly, so the O content may be 0.001% or more.
  • the remainder of the chemical composition of the hot-rolled steel sheet according to this embodiment may be Fe and impurities.
  • impurities refer to substances that are mixed in from the raw materials such as ore, scrap, or the manufacturing environment, or substances that are acceptable to the extent that they do not adversely affect the hot-rolled steel sheet according to this embodiment.
  • the chemical composition of the hot-rolled steel sheet according to this embodiment may contain the following optional elements instead of a portion of Fe.
  • the lower limit of the content is 0%.
  • Nb 0.001-0.100%
  • Nb is an element that suppresses abnormal grain growth of austenite grains during hot rolling.
  • Nb is also an element that increases the strength of hot-rolled steel sheets by forming fine carbides.
  • the Nb content is preferably 0.001% or more, more preferably 0.010% or more, and even more preferably 0.030% or more.
  • the Nb content is set to 0.100% or less.
  • the Nb content is preferably 0.080% or less, and more preferably 0.060% or less.
  • V is an element that forms fine carbides in steel to increase the strength of the hot-rolled steel sheet.
  • the V content is preferably 0.001% or more.
  • the V content is more preferably 0.050% or more, and even more preferably 0.100% or more.
  • the V content is set to 1.000% or less.
  • the V content is preferably 0.500 % or less, and more preferably 0.300% or less.
  • Cu 0.001-1.000%
  • the Cu content is preferably 0.001% or more, more preferably 0.050% or more, and even more preferably 0.100% or more.
  • the Cu content is set to 1.000% or less.
  • the Cu content is preferably set to 0.500% or less. and more preferably 0.300% or less.
  • Cr:0.001 ⁇ 2.000% Cr is an element that exerts an effect similar to that of Mn.
  • the Cr content is preferably 0.001% or more.
  • the content is more preferably 0.050% or more, and even more preferably 0.100% or more.
  • the Cr content is set to 2.000% or less.
  • the Cr content is preferably is 1.000% or less, and more preferably 0.500% or less.
  • Mo 0.001 ⁇ 3.000%
  • Mo is an element that increases the strength of a hot-rolled steel sheet by forming fine carbides in the steel.
  • the Mo content is preferably 0.001% or more.
  • the Mo content is more preferably 0.050% or more, and even more preferably 0.100% or more.
  • the Mo content is set to 3.000% or less.
  • the Mo content is preferably 2.000% or less. % or less, and more preferably 1.000% or less.
  • Ni 0.001-0.500%
  • Ni is an element that enhances the hardenability of hot-rolled steel sheets.
  • Ni has the effect of effectively suppressing grain boundary cracking of slabs caused by Cu.
  • the Ni content is preferably 0.001% or more, more preferably 0.050% or more, and even more preferably 0.100% or more. be.
  • Ni is an expensive element, so it is economically undesirable to include a large amount of it. Therefore, the Ni content is set to 0.500% or less. From the viewpoint of reducing the alloy cost, the Ni content is , preferably 0.300% or less, and more preferably 0.200% or less.
  • B 0.0001-0.0100%
  • B is an element that increases the strength of a hot-rolled steel sheet.
  • the B content is preferably 0.0001% or more.
  • the B content is more preferably 0.0005% or more. % or more, and more preferably 0.0010% or more.
  • the B content is set to 0.0100% or less.
  • the B content is preferably set to 0.0070% or less. More preferably, it is 0.0050% or less.
  • Ca 0.0001-0.0500%
  • Ca is an element that enhances the ductility and hole expandability of the hot-rolled steel sheet by controlling the shape of inclusions to a preferred shape.
  • the Ca content is set to 0.0001% or more.
  • the Ca content is preferably 0.0010% or more, and more preferably 0.0050% or more.
  • the Ca content exceeds 0.0500%, excessive inclusions are generated in the steel, which may deteriorate the ductility and hole expandability of the hot-rolled steel sheet.
  • the Ca content is preferably 0.0300% or less, and more preferably 0.0100% or less.
  • Mg 0.0001-0.0500%
  • Mg is an element that enhances the ductility and hole expandability of the hot-rolled steel sheet by controlling the shape of inclusions to a preferred shape. In order to reliably obtain this effect, the Mg content should be 0.0001% or more.
  • the Mg content is preferably 0.0010% or more, and more preferably 0.0020% or more.
  • the Mg content exceeds 0.0500%, excessive inclusions are generated in the steel, which may deteriorate the ductility and hole expandability of the hot-rolled steel sheet.
  • the Mg content is preferably 0.0300% or less, and more preferably 0.0100% or less.
  • REM 0.001 ⁇ 0.100% REM is an element that improves the ductility and hole expandability of hot-rolled steel sheets by controlling the shape of inclusions to a preferred shape. To reliably obtain this effect, the REM content should be 0.001% or more.
  • the REM content is preferably 0.003% or more, and more preferably 0.005% or more.
  • the REM content exceeds 0.100%, excessive inclusions are generated in the steel, which may deteriorate the ductility and hole expandability of the hot-rolled steel sheet.
  • the REM content is preferably 0.050% or less, and more preferably 0.030% or less.
  • REM refers to a total of 17 elements consisting of Sc, Y and lanthanoids, and the content of the REM refers to the total content of these elements.
  • lanthanoids they are industrially added in the form of misch metal. will be done.
  • Bi 0.001 ⁇ 0.100%
  • Bi is an element that refines the solidification structure and thereby improves the ductility and hole expandability of the hot-rolled steel sheet.
  • the Bi content must be 0.001% or more.
  • the Bi content is preferably 0.002% or more, and more preferably 0.003% or more.
  • the Bi content is set to 0.100% or less. From the viewpoint of reducing alloy costs, The Bi content is preferably 0.050% or less, and more preferably 0.030% or less.
  • Ta 0.001 ⁇ 0.100%
  • Ta is an element that increases the strength of hot-rolled steel sheets by forming fine carbides in the steel.
  • the Ta content is set to 0.001% or more.
  • the Ta content is more preferably 0.005% or more, and even more preferably 0.010% or more.
  • the Ta content is set to 0.100% or less.
  • the Ta content is preferably 0.080 % or less, and more preferably 0.050% or less.
  • Zr 0.001-0.500%
  • Zr is an element that increases the strength of a hot-rolled steel sheet by solid solution strengthening.
  • the Zr content is preferably 0.001% or more.
  • the Zr content is more preferably is 0.005% or more, and more preferably 0.010% or more.
  • the Zr content is set to 0.500% or less.
  • the Zr content is preferably 0. It is preferably 0.300% or less, and more preferably 0.100% or less.
  • Co is an element that increases the strength of a hot-rolled steel sheet by solid solution strengthening.
  • the Co content is preferably 0.001% or more.
  • the Co content is more preferably is 0.005% or more, and more preferably 0.010% or more.
  • the Co content is set to 3.000% or less.
  • the Co content is preferably 1. It is preferably 0.000% or less, and more preferably 0.500% or less.
  • Zn 0.001-0.200%
  • Zn is an element that increases the strength of a hot-rolled steel sheet by solid solution strengthening.
  • the Zn content is preferably 0.001% or more.
  • the Zn content is more preferably is 0.005% or more, and more preferably 0.010% or more.
  • the Zn content is set to 0.200% or less.
  • the Zn content is preferably 0. .150% or less, more preferably 0.100% or less.
  • W 0.001-0.200%
  • W is an element that increases the strength of a hot-rolled steel sheet by solid solution strengthening.
  • the W content is preferably 0.001% or more.
  • the W content is more preferably is 0.005% or more, and more preferably 0.010% or more.
  • the W content is set to 0.200% or less.
  • the W content is preferably 0. .150% or less, more preferably 0.100% or less.
  • Sb 0.001-0.500%
  • Sb is an element that suppresses the generation of oxides that are the starting points of fracture, thereby improving the ductility and hole expandability of the hot-rolled steel sheet.
  • the Sb content is set to 0.001
  • the Sb content is preferably 0.005% or more, and more preferably 0.10% or more.
  • the Sb content is set to 0.500% or less.
  • the Sb content is preferably 0.300% or less, and more preferably 0.100% or less. % or less.
  • As is an element that reduces the austenite single-phase temperature, thereby refining prior austenite grains and improving the hole expandability of the hot-rolled steel sheet. To reliably obtain this effect, the As content should be kept at 0.
  • the As content is preferably 0.001% or more.
  • the As content is more preferably 0.005% or more, and even more preferably 0.010% or more.
  • the As content is set to 0.050% or less.
  • the As content is preferably set to 0.040% or less, and more preferably set to 0.030% or less. % or less.
  • Sn is an element that suppresses the generation of oxides that are the starting points of fracture, thereby improving the ductility and hole expandability of hot-rolled steel sheets.
  • the Sn content is 0.001% or more.
  • the Sn content is more preferably 0.005% or more, and even more preferably 0.010% or more.
  • the Sn content is set to 0.050% or less.
  • the Sn content is preferably 0.040% or less, and more preferably 0.030% or less. % or less.
  • the chemical composition of the above-mentioned hot-rolled steel sheet may be analyzed using a spark discharge optical emission spectrometer or the like. Note that, for C and S, values identified by burning in an oxygen stream using a gas composition analyzer or the like and measuring by an infrared absorption method are adopted. For N, values identified by melting a test piece taken from the steel sheet in a helium stream and measuring by a thermal conductivity method are adopted. When the hot-rolled steel sheet has a plating layer on the surface, the plating layer may be removed by mechanical grinding or the like, as necessary, before analyzing the chemical composition.
  • a peak position of ⁇ where the maximum value A is located is defined as ⁇ A
  • a peak position of ⁇ where the maximum value B is located is defined as ⁇ B
  • the texture is defined in a region from the end face to a 1/4 position in the width direction and from the surface to a depth of 500 ⁇ m in the sheet thickness direction.
  • the 1/4 position in the width direction from the end face here means a w/4 position from the end face in the width direction, where w is the length in the width direction. That is, "x/y position from the end face (here, x and y are natural numbers satisfying x ⁇ y)" means a position moved in the width direction from the end face in the width direction of the steel plate toward the center of the steel plate by a distance of x/y of the plate width.
  • plate thickness x/y position refers to a position moved in the plate thickness direction from the surface (plate surface) of the steel plate in the plate thickness direction toward the center of the steel plate by a distance (depth) of x/y of the plate thickness t.
  • depth the distance of x/y of the plate thickness t.
  • the "surface of the steel sheet” means the interface between the steel sheet and the coating
  • the "sheet thickness t” means the thickness of the steel sheet (base material) excluding the coating.
  • ⁇ 2 , ⁇ , and ⁇ 1 in the crystal orientation distribution function are rotation angles in each of Bunge's Euler notations shown in FIG. 4 of Light Metals 60 (2010), 12, pp. 666-675.
  • the maximum values A and B, and the peak positions of ⁇ at which these maximum values are located, are measured by the following method.
  • a sample is taken at a quarter position in the width direction from the end face of the hot-rolled steel sheet so that the metal structure of the cross section (thickness direction x rolling direction cross section) normal to the width direction can be observed.
  • the size of the sample depends on the measuring device, but it may be, for example, a rectangular parallelepiped with the full thickness in the thickness direction, 15 mm in the rolling direction, and 10 mm in the width direction.
  • the observation surface of the sample is mirror-polished, and then polished for 8 minutes at room temperature using colloidal silica that does not contain an alkaline solution to remove the strain introduced into the surface of the sample.
  • the region from the surface of the polished sample to a depth of 500 ⁇ m in the thickness direction and the region of 2000 ⁇ m or more at any position in the rolling direction are measured at measurement intervals of 5.0 ⁇ m.
  • a device combining a scanning electron microscope and an EBSD analyzer and an OIM Analysis (registered trademark) manufactured by TSL are used.
  • the above sample is analyzed using the EBSD (Electron Back Scattering Diffraction) method.
  • the crystal orientation distribution function (ODF: Orientation Distribution Function) is calculated from the obtained orientation data.
  • the rolling direction of the hot-rolled steel sheet is determined by the following method.
  • a test piece is taken so that a cross section parallel to the plate surface of the hot-rolled steel sheet can be observed.
  • a cross section at a position where the distance from the surface is 1/4 of the plate thickness is mirror-polished and then observed using an optical microscope.
  • the observation range is 500 ⁇ m ⁇ 500 ⁇ m or more, and the direction parallel to the extension direction of the crystal grains is determined to be the rolling direction.
  • the direction perpendicular to the determined rolling direction is determined to be the width direction of the hot-rolled steel sheet.
  • the absolute value of the difference between maximum value A and maximum value B at the position 1/4 from the end face in the width direction, the absolute value of the difference between maximum value A and maximum value B at the position 1/4-15 mm from the end face in the width direction, and the absolute value of the difference between maximum value A and maximum value B at the position 1/4+15 mm from the end face in the width direction are all set to 3.0 or less.
  • the position 1/4+15 mm in the width direction from the end face here refers to a position 15 mm away from the "w/4 position from the end face in the width direction" in the opposite direction to the end face, where w is the length in the width direction.
  • the position 1/4-15 mm in the width direction from the end face here refers to a position 15 mm away from the "w/4 position from the end face in the width direction" in the direction of the end face, where w is the length in the width direction.
  • the absolute value of the difference between maximum value A and maximum value B at each position is obtained by performing EBSD analysis using the method described above at a position 1/4 of the way from the end face in the width direction, a position 1/4-15 mm in the width direction from the end face, and a position 1/4+15 mm in the width direction from the end face, and calculating the crystal orientation distribution function.
  • the metal structure of the hot-rolled steel sheet according to this embodiment will be described.
  • the area ratio of the region where the GAM value exceeds 0.6° is 50% or more, and the sum of the area ratio of the region where the GAM value exceeds 3.0° and the area ratio of retained austenite is less than 15%.
  • the metal structure is defined at a position that is 1/4 the width from the end face and 1/4 the depth from the surface in the plate thickness direction.
  • the area ratio of the region where the GAM value is more than 0.6° is set to 50% or more.
  • the area ratio of the region where the GAM value is more than 0.6° is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more.
  • the area ratio of the region where the GAM value exceeds 0.6° may be set to 100%.
  • Sum of the area ratio of the region where the GAM value is more than 3.0° and the area ratio of the retained austenite less than 15% If the sum of the area ratio of the region where the GAM value is more than 3.0° and the area ratio of the retained austenite is 15% or more, the desired hole expandability may not be obtained in the hot-rolled steel sheet. Therefore, the sum of the area ratio of the region where the GAM value is more than 3.0° and the area ratio of the retained austenite is less than 15%.
  • the sum of the area ratio of the region where the GAM value is more than 3.0° and the area ratio of the retained austenite is preferably 10% or less, more preferably 5% or less.
  • the sum of the area ratio of the region where the GAM value exceeds 3.0° and the area ratio of the retained austenite may be 0% or may be 1% or more.
  • the hot-rolled steel sheet according to this embodiment has the above-mentioned chemical composition, texture, and metal structure, and may have either the first or second metal structure described below, depending on the desired strength, ductility, and tensile bending properties.
  • the first aspect is a metal structure suitable for cases where a higher level of strength and ductility is required.
  • the area ratio of the region where the GAM value is more than 0.6° and less than 2.0° is preferably 60% or more, more preferably 70% or more.
  • the area ratio of the region where the GAM value is more than 0.6° and less than 2.0° may be 100%.
  • the remaining structure other than the areas where the GAM value is greater than 0.6° and less than 2.0° may include areas where the GAM value is 2.0° or more and areas where the GAM value is 0.6° or less, with a total area ratio of 0 to 50%.
  • the second aspect is a metal structure suitable for cases where relatively higher strength is required.
  • the area ratio of the region where the GAM value is 2.0° or more is preferably 60% or more, more preferably 70% or more.
  • the area ratio of the region having a GAM value of 2.0° or more may be 100%.
  • the remaining structure other than the area where the GAM value is 2.0° or more may include an area ratio of 0 to 50% where the GAM value is less than 2.0°.
  • the area ratio of the region where the GAM value exceeds 0.6°, the area ratio of the region where the GAM value is greater than 0.6° and less than 2.0°, the area ratio of the region where the GAM value is 2.0° or more, and the area ratio of the region where the GAM value is greater than 3.0° are measured by the following method.
  • the "GAM value" of each structure of the hot-rolled steel sheet is measured by the EBSP (Electron Backscatter Pattern) method.
  • a sample is taken at a 1/4 position in the width direction from the end face of the hot-rolled steel sheet so that the metal structure of the cross section (thickness direction x rolling direction cross section) with the width direction as the normal direction can be observed.
  • the size of the sample depends on the measuring device, but it may be, for example, a rectangular parallelepiped with a total thickness in the thickness direction, 15 mm in the rolling direction, and 10 mm in the width direction.
  • the observation surface of the sample is mirror-polished, and then polished for 8 minutes at room temperature using colloidal silica that does not contain an alkaline solution to remove the strain introduced into the surface of the sample.
  • a region of 200 ⁇ m from the surface of the sample after the above polishing at a 1/4 depth position in the thickness direction and 400 ⁇ m or more at any position in the rolling direction is measured at a measurement interval of 0.2 ⁇ m to obtain crystal orientation information.
  • an EBSD analysis device consisting of a thermal field emission scanning electron microscope (JSM-7001F manufactured by JEOL) and an EBSD detector (HIKARI detector manufactured by TSL) is used. At this time, the degree of vacuum in the EBSD analysis device is 9.6 ⁇ 10 ⁇ 5 Pa or less, the acceleration voltage is 15 kV, the irradiation current level is 13, and the electron beam irradiation level is 62.
  • the "Phase Map” function installed in the software "OIM Analysis (registered trademark)" attached to the EBSD analyzer is used to identify regions with fcc crystal structure and regions with bcc crystal structure.
  • the region with bcc crystal structure a region surrounded by grain boundaries with an orientation difference of 15° or more is regarded as one crystal grain, and the GAM value of the crystal grain is calculated by calculating the average orientation difference between adjacent pixels within the crystal grain.
  • the area ratio of each region is obtained by calculating the area ratio of crystal grains with the obtained GAM value exceeding 0.6°, the area ratio of crystal grains with an orientation difference of more than 0.6° and less than 2.0°, the area ratio of crystal grains with an orientation difference of 2.0° or more, and the area ratio of crystal grains with an orientation difference of more than 3.0°.
  • the area ratio of retained austenite is measured by the following method.
  • a sample is taken so that the metal structure can be observed in a region of 1 mm or more at any position in the rolling direction and 1 mm or more from the end face in the cross section at 1/4 position in the sheet thickness direction from the surface of the hot-rolled steel sheet.
  • the sample is subjected to Co-K ⁇ radiation to obtain the integrated intensity of a total of six peaks, ⁇ (110), ⁇ (200), ⁇ (211), ⁇ (111), ⁇ (200), and ⁇ (220).
  • the volume ratio of retained austenite is calculated from the integrated intensity using the intensity averaging method.
  • the obtained volume ratio of retained austenite is regarded as the area ratio of retained austenite.
  • the tensile strength may be 940 MPa or more.
  • the upper limit of the tensile strength does not need to be particularly limited, but from the viewpoint of suppressing die wear, it may be 1400 MPa or less.
  • Uniform elongation 3.0% or more
  • the uniform elongation may be 3.0% or more.
  • it can be suitably applied to automobile parts.
  • the tensile strength and uniform elongation are measured by performing a tensile test in accordance with JIS Z 2241: 2022 using a No. 5 test piece of JIS Z 2241: 2022.
  • the tensile test piece is taken from the center position in the width direction, and the direction perpendicular to the rolling direction and the plate thickness direction (width direction) is defined as the longitudinal direction.
  • a minute test piece with the width direction as the longitudinal direction can be used instead as the test piece for measuring the tensile strength.
  • the hole expansion ratio may be 40% or more. By setting the hole expansion ratio to 40% or more, it can be suitably applied to automobile parts. There is no need to particularly limit the upper limit of the hole expansion ratio, but it may be 80% or less.
  • the hole expansion ratio is measured by performing a hole expansion test in accordance with JIS Z 2256:2020.
  • Tensile bending properties can be evaluated by performing a tension bending test by the method shown in Fig. 1.
  • LMAX / L0 when the tension bending test is performed in the rolling direction or width direction is used as an index of the tension bending properties.
  • the rolling direction is arranged in the direction of L 0 in FIG. 1, the punch is pressed down, and the amount of pressing h when the steel sheet breaks is measured.
  • the amount of pressing h is the stroke amount (mm) of the punch from when the punch contacts the steel sheet to when it breaks.
  • L MAX is calculated as twice the length L in FIG.
  • LMAX / L0 may be 1.028 or more when a tension bending test is performed in the rolling direction.
  • LMAX / L0 is 1.028 or more when a tension bending test is performed in the rolling direction, it can be determined that the steel sheet has excellent tension bending properties in the rolling direction.
  • L MAX /L 0 is 1.028 or more when a tension bending test is carried out in the width direction, it can be determined that the material has excellent tension bending properties also in the width direction.
  • LMAX / L0 may be 1.018 or more when a tension bending test is performed in the rolling direction.
  • the tensile strength is 1040 MPa or more
  • LMAX / L0 is 1.018 or more when a tension bending test is performed in the rolling direction
  • L MAX /L 0 is 1.018 or more when a tension bending test is carried out in the width direction
  • the material has excellent tension bending properties also in the width direction.
  • the tension bending test shown in Fig. 1 is performed under the following conditions.
  • the pressing force applied by the blank holder may be such that the hot-rolled steel sheet does not move.
  • the initial thickness t0 of the hot-rolled steel sheet before the test is 1.5 mm.
  • one surface of the hot-rolled steel sheet is mechanically ground to a thickness of 1.5 mm, and the mechanically ground surface is then placed on the punch side to perform the test.
  • the thickness of the hot-rolled steel plate is thinner than 1.5 mm, the test is performed without mechanical grinding.
  • the tensile bending properties are evaluated using the index L MAX /L 0 - (1.5 - t 0 ) x 0.0242 instead of L MAX /L 0 .
  • each embodiment may have the following strength, ductility, and tensile bending properties. Note that the desired hole expansion properties are the same in both embodiments, so explanations are omitted.
  • Tensile strength 940 MPa or more, uniform elongation: 4.0% or more
  • the tensile strength may be 940 MPa or more
  • the uniform elongation may be 4.0% or more
  • the tensile strength may be 980 MPa or less.
  • the uniform elongation may be 5.0% or less.
  • L MAX /L 0 may be set to 1.028 or more when a tension bending test is carried out in the rolling direction. In the first aspect, L MAX /L 0 may be 1.028 or more when a tension bending test is performed in the width direction.
  • Tensile strength 1040 MPa or more, uniform elongation: 3.0% or more
  • the tensile strength may be 1040 MPa or more, and the uniform elongation may be 3.0% or more.
  • the tensile strength may be 1080 MPa or less.
  • the uniform elongation may be 4.0% or less.
  • L MAX /L 0 may be set to 1.018 or more when a tension bending test is carried out in the rolling direction. In the second aspect, L MAX /L 0 may be 1.018 or more when a tension bending test is performed in the width direction.
  • the hot-rolled steel sheet according to this embodiment may be provided with a plating layer on the surface for the purpose of improving corrosion resistance, etc., to form a surface-treated steel sheet.
  • the plating layer may be an electroplating layer or a hot-dip plating layer.
  • electroplating layers include electrogalvanizing and electrogalvanizing Zn-Ni alloy plating.
  • hot-dip plating layers include hot-dip galvanizing, alloyed hot-dip galvanizing, hot-dip aluminum plating, hot-dip Zn-Al alloy plating, hot-dip Zn-Al-Mg alloy plating, and hot-dip Zn-Al-Mg-Si alloy plating.
  • an appropriate chemical conversion treatment for example, applying a silicate-based chromium-free chemical conversion treatment solution and drying
  • the hot-rolled steel sheet according to this embodiment can be stably manufactured.
  • the temperature of the slab and the temperature of the steel sheet in this embodiment refer to the surface temperature of the slab and the surface temperature of the steel sheet.
  • Steps (1) to (3) described below are common to the first and second aspects. As for the subsequent steps, steps (4) and (5) correspond to the first aspect, and step (6) corresponds to the second aspect.
  • a preferred method for producing a hot-rolled steel sheet according to this embodiment is as follows: (1) before rough rolling, a step of applying strain to a slab having the above-mentioned chemical composition one or more times so that the width direction strain is 3 to 15% in total; (2) performing rough rolling on the strained slab; (3) performing finish rolling so that the difference in the entry temperature between the immediately preceding final pass and the final pass is 30° C. or more and the finish rolling completion temperature is in a temperature range of 920° C. or more; Furthermore, the method includes one or more of the following steps (4) to (6).
  • Imparting strain before rough rolling common to the first and second embodiments Before rough rolling, a slab having the above-mentioned chemical composition is subjected to one or more strains so that the total width direction strain is 3 to 15%. This can reduce the unevenness of the surface layer of the slab while increasing the uniformity of the texture.
  • the imparting of strain may be performed after the slab is heated for rough rolling. If the strain imparted in the width direction of the slab is less than 3% or more than 15% in total, the peak positions of the maximum values A and B in the texture of the hot-rolled steel sheet may not be controlled within a preferred range.
  • the "width direction of the slab” refers to a direction perpendicular to the transport direction and thickness direction of the slab, and the transport direction of the slab corresponds to the rolling direction in the subsequent process.
  • the total strain imparted to the slab in the width direction can be expressed as (1-w1/w0) x 100 (%), where w0 is the width direction length of the slab before the first strain is imparted, and w1 is the width direction length of the slab after the final strain is imparted.
  • a method for imparting strain in the width direction of a slab includes, for example, passing the slab between rolls whose rotation axes are perpendicular to the plate surface and conveying direction of the slab to impart strain in the width direction to the slab (pressing down in the width direction).
  • the slab to which strain is applied is not particularly limited except for the chemical composition described above.
  • a slab produced by melting molten steel of the above chemical composition using a converter or electric furnace, etc. and then by continuous casting can be used.
  • an ingot casting method, thin slab casting method, etc. may be used.
  • the heating temperature may be in the range of 1100 to 1300°C.
  • Rough rolling common to the first and second aspects
  • the conditions of rough rolling are not particularly limited, and the rough rolling can be, for example, a process in which rolling is performed multiple times at a temperature of 1100 ° C. or higher to reduce the plate thickness to 30 to 60 mm.
  • finish rolling is performed so that the difference in the entry temperature between the pass immediately before the final pass and the final pass is 30°C or more, and the finish rolling completion temperature is in a temperature range of 920°C or more. If the difference in the entry temperature between the pass immediately before the final pass and the final pass is less than 30°C, the peak positions of maximum value A and maximum value B in the texture of the hot-rolled steel sheet may not be controlled to a preferred range. Also, if the finish rolling completion temperature is less than 920°C, maximum value A and maximum value B cannot be controlled to a preferred value.
  • Examples of a method for making the difference in the inlet temperature between the immediately preceding final pass and the final pass 30°C or more include controlling the amount of coolant such as water sprayed from a cooling device such as a cooling spray immediately after rolling, or controlling the conveying speed of the steel sheet during rolling.
  • the pass immediately before the final pass refers to the pass immediately before the final pass.
  • the pass immediately before the final pass refers to the pass F6.
  • the finish rolling completion temperature refers to the temperature at the outlet of the final pass of finish rolling.
  • Slow cooling (air cooling) in a temperature range of 580 to 680°C corresponds to the first embodiment. After the completion of finish rolling, accelerated cooling is performed to a temperature range of 580 to 680°C at an average cooling rate of 30°C/s or more, and slow cooling (air cooling) is performed in this temperature range for 2.0 seconds or more.
  • slow cooling air cooling
  • the area ratio of the region where the GAM value is more than 0.6° and less than 2.0° can be increased.
  • slow cooling (air cooling) refers to cooling at an average cooling rate of 20° C./s or less.
  • Accelerated cooling after completion of slow cooling corresponds to the first embodiment After completion of slow cooling (air cooling) in the temperature range of 580 to 680° C. (first embodiment), accelerated cooling is performed at an average cooling rate of 30° C./s or more until the temperature reaches 300° C. After completion of slow cooling (air cooling), accelerated cooling is performed at an average cooling rate of 30° C./s or more until the temperature reaches 300° C., whereby a desired metal structure can be obtained. After accelerated cooling to 300° C., the wire may be left to cool to room temperature or may be wound into a coil and then water-cooled.
  • Accelerated cooling down to 300° C. Corresponding to the second embodiment After the completion of finish rolling, accelerated cooling is performed at an average cooling rate of 30° C./s or more down to 300° C. By performing accelerated cooling down to 300° C. at an average cooling rate of 30° C./s or more without performing slow cooling (air cooling) during the accelerated cooling, the area ratio of the region having a GAM value of 2.0° or more can be increased. After accelerated cooling to 300° C., the wire may be left to cool to room temperature or may be wound into a coil and then water-cooled.
  • the average cooling rate is the temperature difference between the start and end points of the set range divided by the elapsed time from the start point to the end point.
  • the conditions in the embodiment are merely an example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this example of conditions.
  • Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.
  • accelerated cooling was performed at an average cooling rate of 30°C/s or more to the "start temperature of slow cooling" in the table.
  • Slow cooling was performed by air cooling, and the average cooling rate during slow cooling was 20°C/s or less.
  • accelerated cooling was performed at the "average cooling rate after completion of slow cooling until the temperature reaches 300°C" in the table. After accelerated cooling was stopped, coiling was performed immediately.
  • the obtained hot-rolled steel sheets were evaluated for texture, metal structure, tensile strength (TS), uniform elongation (uEl), hole expansion ratio ( ⁇ ) and tensile bending properties (L MAX /L 0 in the rolling direction (L direction) and L MAX /L 0 in the width direction (C direction)) by the above-mentioned methods.
  • the results obtained are shown in Tables 4A to 5C.
  • the value L MAX /L 0 - (1.5 - t 0 ) x 0.0242 was recorded instead of L MAX /L 0 .
  • TS tensile strength
  • the hole expansion ratio ( ⁇ ) was 40% or more, it was judged to have excellent hole expansion properties and to pass. On the other hand, if the hole expansion ratio ( ⁇ ) was less than 40%, it was judged to have no excellent hole expansion properties and to fail.
  • the tensile bending properties were evaluated according to the following criteria depending on the tensile strength.
  • the tensile strength is less than 1,040 MPa
  • the tensile bending property (L MAX /L 0 in the rolling direction (L direction)): 1.028 or more is pass, and less than 1.028 is fail.
  • L MAX /L 0 in the width direction (C direction) was 1.028 or more
  • the sheet had excellent tensile bending properties in the width direction as well.
  • the tensile strength is 1040 MPa or more
  • the tensile bending property (L MAX /L 0 in the rolling direction (L direction)): 1.018 or more is pass, and less than 1.018 is fail.
  • L MAX /L 0 in the width direction (C direction) was 1.018 or more, it was determined that the sheet had excellent tensile bending properties also in the width direction.
  • the hot-rolled steel sheets according to the examples of the present invention have high strength, as well as excellent ductility and hole expandability, and also have excellent tensile bending properties in the rolling direction.
  • the steel sheets according to the comparative examples are inferior in at least one of the characteristics.
  • a hot-rolled steel sheet having high strength, excellent ductility and hole expandability, and excellent tensile bending properties in the rolling direction. Furthermore, according to a preferred embodiment of the present invention, it is possible to provide a hot-rolled steel sheet having not only the above-mentioned properties but also excellent tensile bending properties in the width direction.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
PCT/JP2024/003023 2023-01-31 2024-01-31 熱延鋼板 Ceased WO2024162382A1 (ja)

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CN202480008617.XA CN120569507A (zh) 2023-01-31 2024-01-31 热轧钢板
EP24750331.1A EP4660343A1 (en) 2023-01-31 2024-01-31 Hot-rolled steel sheet
KR1020257024771A KR20250130341A (ko) 2023-01-31 2024-01-31 열연 강판
JP2024574967A JPWO2024162382A1 (https=) 2023-01-31 2024-01-31
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Publication number Priority date Publication date Assignee Title
WO2018138898A1 (ja) * 2017-01-30 2018-08-02 新日鐵住金株式会社 鋼板
JP6477020B2 (ja) 2015-02-27 2019-03-06 新日鐵住金株式会社 熱延鋼板及びその製造方法
JP6701954B2 (ja) 2016-05-20 2020-05-27 日本製鉄株式会社 穴拡げ性と溶接部疲労特性に優れた高強度熱延鋼板及びその製造方法
WO2021124864A1 (ja) * 2019-12-19 2021-06-24 日本製鉄株式会社 鋼板及びめっき鋼板
WO2022070608A1 (ja) * 2020-09-30 2022-04-07 日本製鉄株式会社 鋼板及び鋼板の製造方法
JP2023013128A (ja) 2021-07-15 2023-01-26 株式会社マキタ 運搬車
WO2023171492A1 (ja) * 2022-03-11 2023-09-14 日本製鉄株式会社 ホットスタンプ成形体

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JP6477020B2 (ja) 2015-02-27 2019-03-06 新日鐵住金株式会社 熱延鋼板及びその製造方法
JP6701954B2 (ja) 2016-05-20 2020-05-27 日本製鉄株式会社 穴拡げ性と溶接部疲労特性に優れた高強度熱延鋼板及びその製造方法
WO2018138898A1 (ja) * 2017-01-30 2018-08-02 新日鐵住金株式会社 鋼板
WO2021124864A1 (ja) * 2019-12-19 2021-06-24 日本製鉄株式会社 鋼板及びめっき鋼板
WO2022070608A1 (ja) * 2020-09-30 2022-04-07 日本製鉄株式会社 鋼板及び鋼板の製造方法
JP2023013128A (ja) 2021-07-15 2023-01-26 株式会社マキタ 運搬車
WO2023171492A1 (ja) * 2022-03-11 2023-09-14 日本製鉄株式会社 ホットスタンプ成形体

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Title
LIGHT METALS, vol. 12, 2010, pages 666 - 675
See also references of EP4660343A1

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