WO2024048584A1 - 熱延鋼板 - Google Patents

熱延鋼板 Download PDF

Info

Publication number
WO2024048584A1
WO2024048584A1 PCT/JP2023/031225 JP2023031225W WO2024048584A1 WO 2024048584 A1 WO2024048584 A1 WO 2024048584A1 JP 2023031225 W JP2023031225 W JP 2023031225W WO 2024048584 A1 WO2024048584 A1 WO 2024048584A1
Authority
WO
WIPO (PCT)
Prior art keywords
less
rolled steel
steel sheet
hot
ferrite
Prior art date
Application number
PCT/JP2023/031225
Other languages
English (en)
French (fr)
Japanese (ja)
Inventor
秀斗 廣嶋
洋志 首藤
由起子 小林
和政 筒井
Original Assignee
日本製鉄株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日本製鉄株式会社 filed Critical 日本製鉄株式会社
Priority to KR1020257006190A priority Critical patent/KR20250044350A/ko
Priority to CN202380061905.7A priority patent/CN119768550A/zh
Priority to JP2024544287A priority patent/JPWO2024048584A1/ja
Publication of WO2024048584A1 publication Critical patent/WO2024048584A1/ja
Priority to MX2025002286A priority patent/MX2025002286A/es

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

Definitions

  • the present invention relates to a hot rolled steel plate. Specifically, the present invention relates to hot-rolled steel sheets that are used after being formed into various shapes by press working or the like, and particularly to hot-rolled steel sheets that have high strength and are excellent in ductility, fatigue properties, and shear workability.
  • This application claims priority based on Japanese Patent Application No. 2022-135960 filed in Japan on August 29, 2022, the contents of which are incorporated herein.
  • Blank plates manufactured by shearing must have excellent end face accuracy after shearing. For example, if a secondary shear surface occurs in which the end surface after shearing (sheared end surface) is sheared surface-fractured surface-sheared surface, the accuracy of the sheared end surface is significantly deteriorated.
  • Patent Document 1 discloses a high-strength steel plate with excellent ductility and stretch-flangeability and a tensile strength of 980 MPa or more, in which a second phase consisting of retained austenite and/or martensite is finely dispersed in the crystal grains. Disclosed.
  • Patent Document 2 discloses a technique for controlling the burr height after punching by controlling the ratio d s /d b of the ferrite grain size d s in the surface layer and the ferrite crystal grain d b in the interior to 0.95 or less. is disclosed.
  • Patent Documents 1 and 2 are techniques for improving either ductility or end surface properties after shearing. However, Patent Documents 1 and 2 do not mention any technology that achieves both of these characteristics.
  • high-strength steel plates may be required to have better fatigue properties.
  • the present invention has been made in view of the above-mentioned problems of the prior art, and aims to provide a hot-rolled steel sheet that has high strength as well as excellent ductility, fatigue properties, and shear workability.
  • the gist of the invention is as follows. (1)
  • the hot rolled steel sheet according to one aspect of the present invention has a chemical composition in mass %, C: 0.050-0.250%, Si: 0.05-3.00%, Mn: 1.00-4.00%, One or more of Ti, Nb and V: 0.060 to 0.500% in total, sol.
  • the hot rolled steel sheet according to (1) above has the chemical composition in mass%, Cu: 0.01-2.00%, Cr: 0.01-2.00%, Mo: 0.01-1.00%, Ni: 0.02-2.00%, B: 0.0001 to 0.0100%, Ca: 0.0005-0.0200%, Mg: 0.0005-0.0200%, REM: 0.0005-0.1000%, Bi: 0.0005 to 0.0200%, and As: 0.001 to 0.100% It may contain one or more selected from the group consisting of:
  • the hot-rolled steel sheet according to the above aspect of the present invention is suitable as an industrial material used for automobile parts, mechanical structural parts, and even building parts.
  • FIG. 1 is an example of a sheared end surface of a hot rolled steel plate according to an example of the present invention. It is an example of a sheared end surface of a hot rolled steel plate according to a comparative example.
  • the hot rolled steel sheet according to the present embodiment has, in mass %, C: 0.050 to 0.250%, Si: 0.05 to 3.00%, Mn: 1.00 to 4.00%, Ti , Nb and V: 0.060 to 0.500% in total, sol. Al: 0.001 to 2.000%, P: 0.100% or less, S: 0.0300% or less, N: 0.1000% or less, O: 0.0100% or less, and balance: Fe and impurities including.
  • C 0.050 to 0.250%
  • Si 0.05 to 3.00%
  • Mn 1.00 to 4.00%
  • Ti , Nb and V 0.060 to 0.500% in total
  • Al 0.001 to 2.000%
  • P 0.100% or less
  • S 0.0300% or less
  • N 0.1000% or less
  • O 0.0100% or less
  • balance: Fe and impurities including Each element will be explained in detail below.
  • C 0.050-0.250%
  • C increases the area ratio of the hard phase and also increases the strength of ferrite by combining with precipitation-strengthening elements such as Ti, Nb, and V. If the C content is less than 0.050%, desired strength cannot be obtained. Therefore, the C content is set to 0.050% or more.
  • the C content is preferably 0.060% or more, more preferably 0.070% or more, even more preferably more than 0.070%, 0.075% or more, or 0.080% or more.
  • the C content exceeds 0.250%, the area ratio of ferrite decreases, and the ductility of the hot rolled steel sheet decreases. Therefore, the C content is set to 0.250% or less.
  • the C content is preferably 0.200% or less, 0.180% or less, or 0.150% or less.
  • Si 0.05-3.00%
  • Si has the function of promoting the formation of ferrite to improve the ductility of the hot-rolled steel sheet, and the function of solid solution strengthening of ferrite to increase the strength of the hot-rolled steel sheet. Further, Si has the effect of making the steel sound by deoxidizing (suppressing the occurrence of defects such as blowholes in the steel). If the Si content is less than 0.05%, the above effects cannot be obtained. Therefore, the Si content is set to 0.05% or more.
  • the Si content is preferably 0.50% or more, more preferably 0.80% or more.
  • the Si content is set to 3.00% or less.
  • the Si content is preferably 2.50% or less, more preferably 2.00% or less or 1.50% or less.
  • Mn 1.00-4.00% Mn has the effect of suppressing ferrite transformation and increasing the strength of the hot rolled steel sheet. If the Mn content is less than 1.00%, the desired tensile strength cannot be obtained. Therefore, the Mn content is set to 1.00% or more. The Mn content is preferably 1.30% or more, more preferably 1.50% or more. On the other hand, if the Mn content exceeds 4.00%, the hard phase becomes periodic band-like due to segregation of Mn, making it difficult to obtain desired shearing workability. Therefore, the Mn content is set to 4.00% or less. The Mn content is preferably 3.50% or less, more preferably 3.00% or less or 2.50% or less.
  • Ti, Nb and V 0.060 to 0.500% in total Ti, Nb, and V are finely precipitated in steel as carbides and nitrides, and improve the strength of steel through precipitation strengthening. Furthermore, it is an essential element in order to obtain desired fatigue properties. If the total content of Ti, Nb and V is less than 0.060%, these effects cannot be obtained. Therefore, the total content of Ti, Nb, and V is set to 0.060% or more. Note that it is not necessary that all of Ti, Nb, and V be contained; it is sufficient that at least one of them is contained, and the content thereof may be 0.060% or more.
  • the total content of Ti, Nb and V is preferably 0.080% or more, more preferably 0.100% or more, even more preferably 0.120% or more.
  • the total content of Ti, Nb and V is set to 0.500% or less. Preferably it is 0.300% or less, more preferably 0.250% or less, even more preferably 0.200% or less.
  • sol. Al 0.001-2.000% Like Si, Al has the effect of making the steel sound by deoxidizing it, and also has the effect of promoting the formation of ferrite and increasing the ductility of the hot-rolled steel sheet. sol. If the Al content is less than 0.001%, the above effects cannot be obtained. Therefore, sol. Al content shall be 0.001% or more. sol. The Al content is preferably 0.010% or more, more preferably 0.020% or more or 0.030% or more. On the other hand, sol. If the Al content exceeds 2.000%, the above effects are saturated and it is economically unfavorable, so sol. Al content shall be 2.000% or less. sol. The Al content is preferably 0.400% or less, more preferably 0.300% or less, even more preferably 0.250% or less. In addition, sol. Al means acid-soluble Al, and indicates solid solution Al that exists in steel in a solid solution state.
  • P 0.100% or less
  • P is also an element that has the effect of increasing the strength of the hot rolled steel sheet through solid solution strengthening. Therefore, P may be actively included.
  • P is an element that tends to segregate, and when the P content exceeds 0.100%, the ductility decreases significantly due to grain boundary segregation. Therefore, the P content is set to 0.100% or less.
  • the P content is preferably 0.030% or less.
  • the lower limit of the P content does not need to be specifically defined, but from the viewpoint of refining costs, it is preferably 0.001%.
  • S 0.0300% or less S forms sulfide inclusions in the steel and reduces the ductility of the hot rolled steel sheet.
  • the S content is set to 0.0300% or less.
  • the S content is preferably 0.0050% or less. Although there is no need to particularly specify the lower limit of the S content, from the viewpoint of refining costs, it is preferably 0.0001%.
  • N 0.1000% or less N has the effect of reducing the ductility of the hot rolled steel sheet.
  • the N content is set to 0.1000% or less.
  • the N content is preferably 0.0800% or less, more preferably 0.0700% or less, even more preferably 0.0050% or less.
  • the N content is preferably 0.0010% or more, more preferably 0.0020% or more.
  • O 0.0100% or less
  • O content is set to 0.0100% or less.
  • the O content is preferably 0.0080% or less, more preferably 0.0055% or less, even more preferably 0.0050% or less.
  • the O content may be 0.0005% or more, or 0.0010% 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 things that are mixed in from ore as a raw material, scrap, or the manufacturing environment, and/or things that are allowed within a range that does not adversely affect the hot rolled steel sheet according to this embodiment. do.
  • the hot rolled steel sheet according to this embodiment may contain the following elements as optional elements in place of a part of Fe.
  • the lower limit of the content when no arbitrary element is contained is 0%. The arbitrary elements will be explained in detail below.
  • Cu, Cr, Mo, Ni, and B all have the effect of improving the hardenability of the hot rolled steel sheet. Further, Cu and Mo precipitate as carbides in the steel and have the effect of increasing the strength of the hot rolled steel sheet. Furthermore, when containing Cu, Ni has the effect of effectively suppressing intergranular cracking of the slab caused by Cu. Therefore, one or more of these elements may be contained.
  • the Cu content is preferably 0.01% or more, more preferably 0.05% or more. However, if the Cu content exceeds 2.00%, intergranular cracking of the slab may occur. Therefore, the Cu content is set to 2.00% or less. The Cu content is preferably 1.50% or less, more preferably 1.00% or less.
  • the Cr content is preferably 0.01% or more, more preferably 0.05% or more.
  • the Cr content is set to 2.00% or less.
  • Mo has the effect of increasing the hardenability of the hot-rolled steel sheet and the effect of precipitating as carbides in the steel to increase the strength of the hot-rolled steel sheet.
  • the Mo content is preferably 0.01% or more, more preferably 0.02% or more.
  • the Mo content is set to 1.00% or less.
  • Mo content is preferably 0.50% or less, more preferably 0.20% or less.
  • Ni has the effect of increasing the hardenability of the hot rolled steel sheet. Further, when containing Cu, Ni has the effect of effectively suppressing intergranular cracking of the slab caused by Cu. In order to more reliably obtain the effects of the above action, the Ni content is preferably 0.02% or more. Since Ni is an expensive element, it is economically undesirable to contain a large amount of Ni. Therefore, the Ni content is set to 2.00% or less.
  • B has the effect of increasing the hardenability of the hot rolled steel sheet.
  • the B content is preferably 0.0001% or more, more preferably 0.0002% or more.
  • the B content is set to 0.0100% or less.
  • the B content is preferably 0.0050% or less.
  • Ca, Mg, and REM all have the effect of increasing the ductility of the hot rolled steel sheet by adjusting the shape of inclusions in the steel to a preferable shape. Furthermore, Bi has the effect of increasing the ductility of the hot rolled steel sheet by making the solidification structure finer. Therefore, one or more of these elements may be contained. In order to more reliably obtain the effects of the above action, it is preferable that at least one of Ca, Mg, REM, and Bi be 0.0005% or more.
  • the Ca content or Mg content exceeds 0.0200%, or if the REM content exceeds 0.1000%, inclusions will be excessively generated in the steel, which will actually reduce the ductility of the hot rolled steel sheet. There may be cases where Moreover, even if the Bi content exceeds 0.0200%, the effect of the above action will be saturated, which is not economically preferable. Therefore, the Ca content and Mg content should be 0.0200% or less, the REM content should be 0.1000% or less, and the Bi content should be 0.0200% or less. Bi content is preferably 0.0100% or less.
  • REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids
  • the content of REM refers to the total content of these elements.
  • lanthanoids they are added industrially in the form of mischmetal.
  • the As content be 0.001% or more.
  • the As content is set to 0.100% or less.
  • Zr, Co, Zn and W 0 to 1.00% in total Sn: 0-0.05%
  • the present inventors have confirmed that the effect of the hot rolled steel sheet according to the present embodiment is not impaired even if these elements are contained in a total of 1.00% or less. There is. Therefore, one or more of Zr, Co, Zn, and W may be contained in a total amount of 1.00% or less.
  • the present inventors have confirmed that even if a small amount of Sn is contained, the effect of the hot rolled steel sheet according to the present embodiment is not impaired. However, if a large amount of Sn is contained, defects may occur during hot rolling, so the Sn content is set to 0.05% or less.
  • the chemical composition of the hot-rolled steel sheet described above may be measured by a general analytical method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).
  • sol. Al may be measured by ICP-AES using a filtrate obtained by thermally decomposing a sample with an acid.
  • C and S may be measured using a combustion-infrared absorption method, N using an inert gas melting-thermal conductivity method, and O using an inert gas melting-non-dispersive infrared absorption method. If the hot-rolled steel sheet has a plating layer, paint film, etc. on its surface, the chemical composition is analyzed after removing the plating layer, paint film, etc. by mechanical grinding or the like, if necessary.
  • the hot-rolled steel sheet according to the present embodiment has a metal structure in which, in area%, retained austenite is less than 3.0%, ferrite is 15.0% or more and less than 60.0%, and pearlite is 5.0%.
  • the average spherical equivalent radius of the alloy carbides in the ferrite is 0.5 nm or more and less than 10.0 nm, and the average number density is 0.10 x 10 16 pieces/cm 3 or more and 1.45 x 10 16 pieces/ cm3
  • the E value indicating the periodicity of the metal structure is 10.7 or more
  • the I value indicating the uniformity of the metal structure is 1.020 or more
  • the standard deviation of the Mn concentration is 0.60% by mass or less.
  • the hot-rolled steel sheet according to the present embodiment has the above metallographic structure, it can obtain high strength, as well as excellent ductility, fatigue properties, and shear workability.
  • a region (rolling direction is The microstructure fraction of the metal structure, the average equivalent sphere radius and average number density of alloy carbides, the E value, the I value, and the standard deviation of the Mn concentration at an arbitrary position) are defined. The reason is that the metal structure at this position shows a typical metal structure of a steel plate.
  • the "surface” here refers to the interface between the plating layer and the steel sheet when the hot rolled steel sheet includes a plating layer, a coating film, or the like.
  • Retained austenite is a metal structure that exists as a face-centered cubic lattice even at room temperature. Retained austenite has the effect of increasing the ductility of hot rolled steel sheets through transformation induced plasticity (TRIP). On the other hand, retained austenite transforms into high-carbon martensite during shearing, thereby inhibiting stable crack initiation and causing the formation of secondary shear surfaces. When the area ratio of retained austenite is 3.0% or more, the above-mentioned effect becomes obvious and the shearing workability of the hot rolled steel sheet deteriorates. Therefore, the area ratio of retained austenite is set to be less than 3.0%. The area percentage of retained austenite is preferably less than 1.5%, more preferably less than 1.0%. Since it is preferable to have as little retained austenite as possible, the area ratio of retained austenite may be 0%.
  • Methods for measuring the area ratio of retained austenite include methods using X-ray diffraction, EBSP (electron back scattering diffraction method, Electron Back Scattering Diffraction Pattern) analysis, and magnetic measurement.
  • the area ratio of retained austenite is measured by X-ray diffraction.
  • X-ray diffraction first, in a cross section at a quarter position from the surface in the thickness direction of a hot rolled steel sheet, 1 mm or more at any position in the rolling direction, A sample is taken so that the metal structure can be observed in an area of 1 mm or more centered on the 1/4 position from the end face.
  • Area ratio of ferrite 15.0% or more and less than 60.0%
  • Ferrite is a structure that is generated when fcc is transformed into bcc at a relatively high temperature. Since ferrite has a high work hardening rate, it has the effect of increasing the strength-ductility balance of hot rolled steel sheets. In order to obtain the above effect, the area ratio of ferrite is set to 15.0% or more.
  • the area ratio of ferrite is preferably 20.0% or more, more preferably 25.0% or more, and even more preferably 30.0% or more.
  • the ferrite area ratio is set to less than 60.0%. Preferably it is 50.0% or less, more preferably 45.0% or less.
  • Pearlite is a lamellar metal structure in which cementite is precipitated in layers between ferrite particles, and is a soft metal structure compared to bainite and martensite. If the area ratio of pearlite is 5.0% or more, carbon is consumed by cementite contained in pearlite, and the strength of martensite and bainite, which are the remaining structures, decreases, making it impossible to obtain the desired strength. Furthermore, microvoids that deteriorate ductility are generated early at the interface between ferrite and cementite contained in pearlite, so if the area ratio of pearlite is 5.0% or more, it is difficult to obtain the desired ductility and fatigue properties. Can not.
  • the area ratio of pearlite is made less than 5.0%.
  • the area ratio of pearlite is preferably 3.0% or less.
  • the steel sheet according to the present embodiment includes bainite, martensite, and tempered martensite with a total area ratio of 32.0% or more and less than 85.0% as residual structures other than retained austenite, ferrite, and pearlite.
  • Hard tissues composed of one or more types are included.
  • the area ratio of metal structures other than retained austenite is measured by the following method. First, a sample is taken at a 1/4 position from the end face in the sheet width direction of the hot rolled steel sheet in a cross section parallel to the rolling direction so that the metallographic structure in a region at 1/4 position from the surface in the sheet thickness direction can be observed. .
  • the size of the sample is such that it can be observed about 10 mm in the rolling direction, although it depends on the measuring device.
  • the observed cross section of the sample is polished to a mirror finish, 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 layer of the sample.
  • an EBSD analysis device consisting of a thermal field emission scanning electron microscope (JSM-7001F manufactured by JEOL) and an EBSD detector (DVC5 type detector manufactured by TSL) is used.
  • the degree of vacuum in the EBSD analyzer is 9.6 ⁇ 10 ⁇ 5 Pa or less
  • the acceleration voltage is 15 kV
  • the irradiation current level is 13
  • the electron beam irradiation level is 62.
  • a backscattered electron image is taken in the same field of view.
  • crystal grains in which ferrite and cementite are precipitated in a layered manner are identified from a backscattered electron image, and the area ratio of the crystal grains is calculated to obtain the area ratio of pearlite.
  • the obtained crystal orientation information is used for the crystal grains excluding the crystal grains determined to be pearlite using the "Grain Average Misorientation" function installed in the software "OIM Analysis (registered trademark)" included with the EBSD analyzer.
  • a region where the Grain Average Misorientation value is 1.0° or less is determined to be ferrite.
  • the Grain Tolerance Angle is set to 15°, and the area ratio of ferrite is obtained by determining the area of the region determined to be ferrite.
  • the area ratio of the residual structure is obtained by subtracting the area ratio of retained austenite, pearlite, and ferrite from 100%. From the chemical composition and manufacturing conditions of the hot rolled steel sheet, it can be estimated that the remaining structure is a hard structure consisting of one or more of bainite, martensite, and tempered martensite. Note that the rolling direction of the hot rolled steel sheet is determined by the following method. First, a test piece is taken so that the cross section of the hot rolled steel sheet can be observed. The cross-section of the collected test piece is polished to a mirror surface, corroded with a saturated picric acid solution, and then observed using an optical microscope. The observation range is the entire thickness of the plate, and the stretching direction of the crystal grains is determined.
  • the angular difference between the stretching direction and the plate thickness direction is assumed to be ⁇ . Furthermore, a surface at a position of 1/4 of the plate thickness, which is perpendicular to the plate thickness direction and parallel to the above-mentioned stretching direction, is polished in the same manner as the plate thickness cross section, and the stretching direction of the crystal grains is determined.
  • the angle difference between the plate thickness cross section and the stretching direction is defined as ⁇ .
  • the direction in which the deviation angles are ⁇ and ⁇ obtained from the stretching direction of the crystal grains in the two cross sections described above is determined as the rolling direction.
  • the “Analyze Particles” function of the image analysis software “ImageJ” can be used to obtain the stretching direction of the crystal grains by setting Circularity to 0.7 or less.
  • Average sphere equivalent radius of alloy carbides in ferrite 0.5 nm or more and less than 10.0 nm
  • the average sphere equivalent radius and average number density of alloy carbides in ferrite are preferably controlled. . If the average equivalent sphere radius of the alloy carbide in the ferrite is less than 0.5 nm, the strength against repeated deformation of the ferrite cannot be sufficiently increased, and the desired fatigue strength cannot be obtained. Therefore, the average spherical equivalent radius of the alloy carbide in the ferrite is set to 0.5 nm or more.
  • the average sphere equivalent radius of the alloy carbide in the ferrite is preferably 1.0 nm or more.
  • the average spherical equivalent radius of the alloy carbides in ferrite is 10.0 nm or more, the strength of the ferrite cannot be sufficiently increased, and due to the hardness difference between grains, A crack is generated from the cutting edge of the shearing tool, forming a fractured surface, and then a sheared surface is formed again. As a result, secondary shear surfaces are likely to be formed, making it impossible to obtain desired shear workability in the hot rolled steel sheet. Therefore, the average equivalent sphere radius of the alloy carbide in the ferrite is less than 10.0 nm.
  • the average equivalent sphere radius of the alloy carbide in the ferrite is preferably 8.0 nm or less, 6.0 nm or less, 4.0 nm or less, and more preferably less than 2.0 nm.
  • Average number density of alloy carbides in ferrite 0.10 ⁇ 10 16 pieces/cm 3 or more, less than 1.45 ⁇ 10 16 pieces/cm 3
  • Average number density of alloy carbides in ferrite is 0.10 ⁇ 10 16 pieces If the number is less than 1.45 ⁇ 10 16 pieces/cm 3 or more than 1.45 ⁇ 10 16 pieces/cm 3 , the strength against repeated deformation of ferrite cannot be sufficiently increased, and the desired fatigue strength cannot be obtained. Therefore, the average number density of alloy carbides in the ferrite is set to 0.10 ⁇ 10 16 pieces/cm 3 or more and less than 1.45 ⁇ 10 16 pieces/cm 3 .
  • the average number density of alloy carbides in the ferrite is preferably 0.50 ⁇ 10 16 pieces/cm 3 or more, more preferably 1.00 ⁇ 10 16 pieces/cm 3 or more. Further, the average number density of alloy carbides in the ferrite is preferably 1.40 x 10 16 pieces/cm 3 or less, more preferably 1.20 x 10 16 pieces/cm 3 or less, even more preferably It is 1.10 ⁇ 10 16 pieces/cm 3 or less.
  • the alloy carbide refers to a carbide containing one or more of Ti, Nb, Mo, and V.
  • the equivalent sphere radius and number density of alloy carbides in ferrite are measured using a three-dimensional atom probe.
  • the laser wavelength ( ⁇ ) is 355 nm
  • the laser power is 30 pJ
  • the temperature of the needle-like test piece is 50K.
  • the device used for three-dimensional atom probe measurement is not particularly limited.
  • the three-dimensional atom probe measuring device is, for example, LEAP4000XHR manufactured by Ametek Corporation.
  • a sample is collected using an FIB (focused ion beam) device for the ferrite grains within the observation field by the above-mentioned EBSD, in which the area ratio of each structure was measured.
  • FIB focused ion beam
  • the equivalent sphere radius and number density of fine precipitates ranging from less than 1 nm to several tens of nanometers in equivalent sphere radius can be accurately measured.
  • the number density of precipitates can be obtained by dividing the number of precipitates included in the area measured with a three-dimensional atom probe by the volume of the measurement area for precipitates identified as alloy carbides by the method described below. Can be done.
  • the total volume of precipitates in the measurement region is obtained by dividing the total number of atoms of alloying elements (Ti, Nb, Mo, V, C) contained in all the precipitates in the measurement region by the atomic density of the alloy carbide. .
  • the volume of precipitates is obtained by dividing the total volume of precipitates by the number of precipitates. From the volume of the obtained precipitate, the spherical equivalent radius is calculated assuming that the precipitate is spherical.
  • the average number density and the average sphere equivalent radius are obtained by performing the above-described method on five or more pieces of measurement data having a measurement area volume of 30,000 nm 3 or more.
  • the region where Ga introduced during FIB processing is less than 0.025 at% is defined as the observation region, and the region where Ga is mixed in at 0.025 at% or more is excluded from the measurement region.
  • the amount of Ga in the longitudinal direction of the needle sample can be confirmed using the 1D Concentration Profile function of the data analysis software IVAS 3.6.14 (manufactured by CAMECA Instruments Inc.).
  • E value: 10.7 or more I value: 1.020 or more In order to suppress the occurrence of secondary shear surfaces, it is important to form a fracture surface after a sufficient shear surface has been formed, and the tool It is necessary to suppress early crack formation from the cutting edge. For this purpose, it is important that the periodicity of the metal structure is low and the uniformity of the metal structure is high.
  • the generation of secondary shear planes is suppressed by controlling the E (Entropy) value, which indicates the periodicity of the metal structure, and the I (Inverse difference normalized) value, which indicates the uniformity of the metal structure.
  • the E value represents the periodicity of the metal structure.
  • the E value represents the periodicity of the metal structure.
  • the E value decreases.
  • the E value is less than 10.7, secondary shear surfaces are likely to occur. Starting from the periodically arranged structure, cracks occur from the cutting edge of the shearing tool very early in the shearing process, forming a fractured surface, and then a sheared surface is formed again. It is estimated that this makes secondary shear planes more likely to occur. Therefore, the E value is set to 10.7 or more.
  • it is 10.8 or more, more preferably 11.0 or more.
  • the I value represents the uniformity of the metal structure, and increases as the area of a region with a certain brightness increases.
  • a high I value means that the uniformity of the metal structure is high.
  • the I value is set to 1.020 or more. Preferably it is 1.025 or more, more preferably 1.030 or more. The higher the I value, the better, and although the upper limit is not particularly specified, it may be 1.200 or less, 1.150 or less, or 1.100 or less.
  • the E value and I value can be obtained by the following method.
  • the imaging area of the SEM image taken to calculate the E value and I value is a cross section parallel to the rolling direction at a 1/4 position from the end face in the sheet width direction, and from the surface in the sheet thickness direction.
  • the area is 200 ⁇ m ⁇ 200 ⁇ m centered at the 1/4 position, and the number of observation fields is 5.
  • an SU-6600 Schottky electron gun manufactured by Hitachi High-Technologies Corporation is used, with a tungsten emitter and an accelerating voltage of 1.5 kV. Based on the above settings, a SEM image is output at a magnification of 1000 times and a gray scale of 256 gradations.
  • the obtained SEM image was cut out into an area of 880 x 880 pixels, and a smooth image with a tile grid size of 8 x 8 was applied using a contrast enhancement limit magnification of 2.0 as described in Non-Patent Document 3.
  • Apply chemical treatment By rotating the smoothed SEM image counterclockwise in 1 degree increments from 0 degrees to 179 degrees, excluding 90 degrees, and creating images in 1 degree increments, a total of 179 images are obtained. .
  • frequency values of brightness between adjacent pixels are collected in the form of a matrix using the gray level co-occurrence matrix method (GLCM method) described in Non-Patent Document 1. .
  • GLCM method gray level co-occurrence matrix method
  • the E value and the I value are calculated using the following formula (1) and formula (2) described in Non-Patent Document 2, respectively. Note that the average value obtained by measuring the entire visual field is calculated.
  • P(i,j) in the following formulas (1) and (2) is a gray level co-occurrence matrix, and the value at the i-th row and j-th column of the matrix P is expressed as P(i,j).
  • P(i,j) it is calculated using the 256 x 256 matrix P, so if you want to emphasize this point, you can modify the following formula (1) to the following formula (1'), and the following formula (2) can be modified to the following equation (2').
  • equations (1') and (2') below the value at the i-th row and j-th column of the matrix P is expressed as P ij .
  • Standard deviation of Mn concentration 0.60% by mass or less
  • the standard deviation of Mn concentration of the hot rolled steel sheet according to the present embodiment is 0.60% by mass or less.
  • the standard deviation of the Mn concentration is preferably 0.50% by mass or less, more preferably 0.47% by mass or less.
  • the lower limit of the standard deviation of the Mn concentration is preferably as small as possible from the viewpoint of suppressing excessive burrs, but due to manufacturing process constraints, the actual lower limit is 0.10% by mass.
  • the standard deviation of Mn concentration can be obtained by the following method. First, a sample is taken at a 1/4 position from the end face in the width direction of the plate so that a 1/4 area from the surface in the thickness direction can be observed in a cross section parallel to the rolling direction. The size of the sample is such that it can be observed about 10 mm in the rolling direction, although it depends on the measuring device. Next, after mirror polishing the sample, the standard deviation of the Mn concentration is measured using an electron probe microanalyzer (EPMA).
  • EPMA electron probe microanalyzer
  • the measurement conditions are an accelerating voltage of 15 kV, a magnification of 5,000 times, and distribution images of more than 40,000 locations are measured in an area of 20 ⁇ m in the rolling direction and 20 ⁇ m in the plate thickness direction at a measurement interval of 0.1 ⁇ m.
  • the standard deviation of the Mn concentration is obtained by calculating the standard deviation based on the Mn concentration obtained from all measurement points.
  • Tensile Properties Among the mechanical properties of hot rolled steel sheets, tensile strength properties (tensile strength, total elongation) are evaluated in accordance with JIS Z 2241:2011.
  • the test piece is a JIS Z 2241:2011 No. 5 test piece.
  • the test piece may be collected at a 1/4 position from the end face of the hot rolled steel sheet in the sheet width direction, with the sheet width direction being the longitudinal direction of the test piece.
  • the hot rolled steel sheet according to this embodiment preferably has a tensile (maximum) strength of 980 MPa or more.
  • the tensile strength is more preferably 1000 MPa or more.
  • the applicable parts are not limited and it can greatly contribute to reducing the weight of the vehicle body. Although there is no need to specifically limit the upper limit, it may be set to 1780 MPa from the viewpoint of suppressing mold wear.
  • the total elongation is preferably 10.0% or more, and the product of tensile strength and total elongation (TS ⁇ El) is preferably 13000 MPa ⁇ % or more.
  • the total elongation is more preferably 11.0% or more, even more preferably 13.0% or more.
  • the product of tensile strength and total elongation is more preferably 14,000 MPa ⁇ % or more, and even more preferably 15,000 MPa ⁇ % or more.
  • the torque during the fatigue test or the value of the strain gauge attached to the test piece is measured to evaluate the change in repeated stress.
  • the repeated stress at 100 repetitions is taken as the reference stress, and if the repeated stress is 5% or more higher than the above reference stress in the range of 100,000 to 1 million repetitions, cyclic hardening occurs and excellent fatigue properties are obtained. It can be determined that it is a hot rolled steel sheet.
  • the thickness of the hot rolled steel plate according to this embodiment is not particularly limited, but may be 0.5 to 8.0 mm. If the thickness of the hot rolled steel plate is less than 0.5 mm, it may be difficult to ensure the rolling completion temperature and the rolling load may become excessive, making hot rolling difficult. Therefore, the thickness of the hot rolled steel plate according to this embodiment may be 0.5 mm or more. Preferably it is 1.2 mm or more or 1.4 mm or more. On the other hand, if the plate thickness exceeds 8.0 mm, it may be difficult to refine the metal structure and obtain the above-mentioned metal structure. Therefore, the plate thickness may be 8.0 mm or less. Preferably it is 6.0 mm or less.
  • the hot rolled steel sheet according to the present embodiment having the above-mentioned chemical composition and metallographic structure 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. Examples of the electroplating layer include electrogalvanizing, electrolytic Zn--Ni alloy plating, and the like.
  • hot-dip plating layer examples 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. Ru.
  • the amount of plating deposited is not particularly limited, and may be the same as the conventional one. Further, it is also possible to further improve the corrosion resistance by performing an appropriate chemical conversion treatment (for example, applying and drying a silicate-based chromium-free chemical conversion treatment liquid) after plating.
  • a preferred method for manufacturing the hot rolled steel sheet according to this embodiment having the above-mentioned chemical composition and metallographic structure is as follows.
  • hot rolling is performed after heating the slab under predetermined conditions, accelerated cooling to a predetermined temperature range, then slow cooling, and cooling until coiling. It is effective to control the history.
  • the following steps (1) to (10) are sequentially performed.
  • the temperature of the slab and the temperature of the steel plate in this embodiment refer to the surface temperature of the slab and the surface temperature of the steel plate.
  • stress refers to the tension applied to the steel plate in the rolling direction. The stress can be controlled by adjusting the rotational speed of the rolling stand and the winding device, and can be determined by dividing the measured load in the rolling direction by the cross-sectional area of the plate being passed.
  • Hot rolling is performed in a temperature range of 850° C. or higher and 1100° C. or lower such that the plate thickness is reduced by 90% or more in total.
  • Rolling of the first stage before the final stage is carried out at 900°C or higher and lower than 1010°C, and a stress of 170 kPa or more is applied to the steel plate after rolling one stage before the final stage of hot rolling and before rolling of the final stage. load on.
  • the rolling reduction in the final stage of hot rolling is 8% or more, and the hot rolling is completed so that the rolling completion temperature Tf is 900°C or more and less than 1010°C.
  • Light reduction is performed in a temperature range of 840° C. or higher and lower than 900° C.
  • Slab, slab temperature and holding time when subjected to hot rolling can be slabs obtained by continuous casting, slabs obtained by casting/blowing, etc. Depending on the type of material, those subjected to hot working or cold working may be used.
  • the slab to be subjected to hot rolling is preferably held at a temperature range of 700° C. or higher and 850° C. or lower for 900 seconds or more during slab heating, and then further heated and held at a temperature range of 1100° C. or higher for 6000 seconds or more.
  • the steel plate temperature when holding the steel plate in a temperature range of 700°C or higher and 850°C or lower, the steel plate temperature may be varied within this temperature range or may be kept constant. Moreover, when holding the temperature at 1100° C. or higher, the steel plate temperature may be varied in the temperature range of 1100° C. or higher, or may be kept constant.
  • Mn is distributed between ferrite and austenite, and by lengthening the transformation time, Mn can diffuse within the ferrite region. This eliminates the Mn micro-segregation that is unevenly distributed in the slab and significantly reduces the standard deviation of the Mn concentration. Therefore, it is preferable to hold the temperature in a temperature range of 700°C or more and 850°C or less for 900 seconds or more. Further, by holding the temperature in a temperature range of 1100° C. or higher for 6000 seconds or more, the standard deviation of the Mn concentration can be significantly reduced.
  • a reverse mill or a tandem mill As multi-pass rolling, it is preferable to use a reverse mill or a tandem mill as multi-pass rolling. Particularly from the viewpoint of industrial productivity and the stress load on the steel plate during rolling, it is more preferable that at least the last two stages are hot rolled using a tandem mill.
  • Reduction rate of hot rolling A total thickness reduction of 90% or more in the temperature range of 850°C or higher and 1100°C or lower A total thickness reduction of 90% or more in the temperature range of 850°C or higher and 1100°C or lower
  • the recrystallized austenite grains are mainly refined, and the accumulation of strain energy in the unrecrystallized austenite grains is promoted. Then, the recrystallization of austenite is promoted and the atomic diffusion of Mn is promoted, so that the standard deviation of the Mn concentration can be reduced. Therefore, it is preferable to perform hot rolling in a temperature range of 850° C. or higher and 1100° C. or lower such that the plate thickness is reduced by 90% or more in total.
  • the total plate thickness reduction in the temperature range of 850°C or higher and 1100°C or lower is defined as the inlet thickness before the first rolling in rolling in this temperature range, and the reduction in the final stage of rolling in this temperature range.
  • the subsequent exit plate thickness is t 1 , it can be expressed as ⁇ (t 0 ⁇ t 1 )/t 0 ⁇ 100(%).
  • the pre-stage rolling is performed at 900° C. or higher and lower than 1010° C.
  • the stress applied to the steel plate after rolling one step before the final stage of hot rolling and before rolling at the final stage is 170 kPa or higher. This makes it possible to reduce the number of crystal grains having the ⁇ 110 ⁇ 001> crystal orientation in the recrystallized austenite after rolling one stage before the final stage.
  • the stress applied to the steel plate is less than 170 kPa, it may not be possible to obtain the desired E value.
  • the stress applied to the steel plate is more preferably 190 kPa or more. Note that the stress applied to the steel plate refers to the tension applied in the longitudinal direction of the steel plate, and can be controlled by adjusting the roll rotation speed during tandem rolling.
  • the upper limit of the stress applied to the steel plate is not particularly limited, but may be 350 kPa or less.
  • Reduction ratio in the final stage of hot rolling 8% or more, hot rolling completion temperature Tf: 900°C or more, less than 1010°C
  • the rolling reduction ratio in the final stage of hot rolling is 8% or more, and hot rolling is completed.
  • the temperature Tf is 900°C or higher.
  • the formation of ferrite in the final structure (metal structure of the hot-rolled steel sheet after manufacture) can be suppressed, and desired strength can be obtained. Further, by setting Tf to less than 1010° C., coarsening of the austenite grain size can be suppressed, periodicity of the metal structure can be reduced, and a desired E value can be obtained.
  • the upper limit of the rolling reduction in the final stage of hot rolling is not particularly limited, but may be 30% or less, preferably 20% or less, and more preferably 15% or less.
  • Light reduction is performed in a temperature range of 840° C. or higher and lower than 900° C. such that the plate thickness is reduced by 5% or more and less than 8% in total.
  • After rolling in the final stage of hot rolling it is preferable to perform light reduction in a temperature range of 840° C. or higher and lower than 900° C. so as to reduce the plate thickness by 5% or more and less than 8% in total.
  • Light rolling may be performed, for example, at the final stage of the finishing mill, or by introducing new rolling equipment between the finishing mill and the cooling bed.
  • the total plate thickness reduction in light reduction is defined as ⁇ ( It can be expressed as t 0 ⁇ t 1 )/t 0 ⁇ 100(%).
  • the stress applied to the steel plate after the final stage of hot rolling and before the first rolling of light reduction, and the stress applied to the steel plate after rolling of the final stage of light reduction and before the steel plate is cooled to 800°C.
  • Stress applied less than 200 kPa
  • the stress applied to each steel plate is preferably less than 200 kPa. By setting the stress applied to the steel plate at the above locations to be less than 200 kPa, recrystallization of austenite proceeds preferentially in the rolling direction, and an increase in the periodicity of the metal structure can be suppressed. As a result, a desired E value can be obtained. More preferably, the stress applied to the steel plate at each of the above locations is 180 kPa or less.
  • the average cooling rate here refers to the temperature drop range of the steel plate from the start of accelerated cooling (when the steel plate is introduced into the cooling equipment) to the end of accelerated cooling (when the steel plate is taken out from the cooling equipment). This is the value divided by the time required from the start to the completion of accelerated cooling.
  • the average cooling rate is preferably 300° C./second or less.
  • the area ratio of ferrite is 15.0% or more
  • the average number density of alloy carbides in ferrite is 0.10 ⁇ 10 16 pieces/cm 3 or more
  • the average equivalent sphere radius of alloy carbides in ferrite is 0.10 ⁇ 10 16 pieces/cm 3 or more.
  • the cooling stop temperature of accelerated cooling is preferably 600° C. or more.
  • cooling with a high average cooling rate may be performed after completion of light reduction, for example, by injecting cooling water onto the surface of the steel plate.
  • the time for performing slow cooling is preferably 3.0 seconds or more.
  • the upper limit of the time for slow cooling is determined by the equipment layout, but may be approximately less than 10.0 seconds. Further, although there is no particular lower limit to the average cooling rate of slow cooling, since increasing the temperature without cooling involves a large investment in equipment, it may be set to 0° C./s or more.
  • Average cooling rate to coiling temperature 50°C/second or more
  • the average cooling rate from the cooling stop temperature of slow cooling to the coiling temperature is 50°C/second. /second or more is preferable.
  • the matrix structure can be made hard, and the average sphere equivalent radius and average number density of the alloy carbides in the desired ferrite can be controlled to desired amounts.
  • the average cooling rate here refers to the range of temperature drop of the steel plate from the cooling stop temperature in slow cooling, where the average cooling rate is less than 5°C/s, to the coiling temperature, and the average cooling rate is less than 5°C/s. It is the value divided by the time required from the stop of slow cooling to the time of winding.
  • Winding temperature 350°C or lower
  • the winding temperature is preferably 350°C or lower.
  • the conditions in the Examples are examples of conditions adopted to confirm the feasibility and effects of the present invention.
  • the present invention is not limited to this example of one condition.
  • the present invention can adopt various conditions as long as the purpose of the present invention is achieved without departing from the gist of the present invention.
  • the obtained hot-rolled steel sheet was subjected to the above-mentioned method to determine the area ratio of the metal structure, E value, I value, standard deviation of Mn concentration, average sphere equivalent radius and average number density of alloy carbide in ferrite, and tensile strength. TS and total elongation El were determined. In addition, fatigue properties were evaluated by performing plane bending fatigue properties using the method described above. The measurement results obtained are shown in Tables 5A to 6B.
  • Fatigue properties A plane bending fatigue test was conducted using the method described above, and if the repeated stress was 5% or more higher than the standard stress in the range of 100,000 to 1 million repetitions, cyclic hardening occurred, indicating excellent fatigue properties. It was determined that the hot-rolled steel sheet had passed the test. On the other hand, if the repeated stress does not exceed the standard stress by 5% or more in the range of 100,000 to 1,000,000 repetitions, cyclic hardening does not occur and the sheet is rejected as not having excellent fatigue properties. It was determined that Examples that were determined to be passed were written as "Good” in the column of fatigue properties in the table, and examples that were judged to be rejected were written as "NG" in the table.
  • Shearing workability (secondary shear surface evaluation) The shear workability of the hot rolled steel sheet was evaluated by a punching test. Three punched holes were made for each example using a hole diameter of 10 mm, a clearance of 10%, and a punching speed of 3 m/s. Next, the plate thickness cross section perpendicular to the rolling direction and the plate thickness cross section parallel to the rolling direction of the punched holes were embedded in resin, and the cross-sectional shapes were photographed using a scanning electron microscope. In the obtained observation photograph, a sheared end surface as shown in FIG. 1 or 2 can be observed. Note that FIG. 1 is an example of a sheared end surface of a hot rolled steel sheet according to an example of the present invention, and FIG.
  • FIG. 2 is an example of a sheared end surface of a hot rolled steel sheet according to a comparative example.
  • the diagram shows a sag, a sheared surface, a fractured surface, and a sheared end surface of a burr.
  • the sheared end surface of the burr is shown as sag, shear surface, fracture surface, shear surface, fracture surface, and burr.
  • the sag is the area of the smooth R-shaped surface
  • the sheared surface is the area of the punched end face separated by shear deformation
  • the fractured surface is the area of the punched end face separated by a crack generated near the cutting edge.
  • a burr is a surface having protrusions protruding from the lower surface of a hot-rolled steel sheet.
  • sheared end faces if a sheared surface-fractured surface-sheared surface is observed on two surfaces perpendicular to the rolling direction and two surfaces parallel to the rolling direction, as shown in FIG. determined that a secondary shear plane was formed. A total of 12 surfaces, 4 surfaces for each punched hole, were observed, and when there was no surface where a secondary shear surface appeared, the hot rolled steel sheet was judged to have passed the test as having excellent shearability. On the other hand, if even one secondary shear plane was formed, the hot rolled steel sheet was determined to be rejected as not having excellent shearing workability. Examples that were determined to be acceptable were written as "Good" in the shear workability column in the table, and examples that were judged to be unacceptable were written as "NG" in the table.
  • the hot rolled steel sheets according to the examples of the present invention have high strength, as well as excellent ductility, fatigue properties, and shear workability.
  • the hot rolled steel sheet according to the comparative example does not have any one or more of the above characteristics.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
PCT/JP2023/031225 2022-08-29 2023-08-29 熱延鋼板 WO2024048584A1 (ja)

Priority Applications (4)

Application Number Priority Date Filing Date Title
KR1020257006190A KR20250044350A (ko) 2022-08-29 2023-08-29 열연 강판
CN202380061905.7A CN119768550A (zh) 2022-08-29 2023-08-29 热轧钢板
JP2024544287A JPWO2024048584A1 (enrdf_load_stackoverflow) 2022-08-29 2023-08-29
MX2025002286A MX2025002286A (es) 2022-08-29 2025-02-25 Chapa de acero laminada en caliente

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2022-135960 2022-08-29
JP2022135960 2022-08-29

Publications (1)

Publication Number Publication Date
WO2024048584A1 true WO2024048584A1 (ja) 2024-03-07

Family

ID=90099548

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2023/031225 WO2024048584A1 (ja) 2022-08-29 2023-08-29 熱延鋼板

Country Status (5)

Country Link
JP (1) JPWO2024048584A1 (enrdf_load_stackoverflow)
KR (1) KR20250044350A (enrdf_load_stackoverflow)
CN (1) CN119768550A (enrdf_load_stackoverflow)
MX (1) MX2025002286A (enrdf_load_stackoverflow)
WO (1) WO2024048584A1 (enrdf_load_stackoverflow)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0479722B2 (enrdf_load_stackoverflow) * 1983-08-23 1992-12-16 Hitachi Ltd
WO2022044493A1 (ja) * 2020-08-27 2022-03-03 日本製鉄株式会社 熱延鋼板
WO2023149374A1 (ja) * 2022-02-02 2023-08-10 日本製鉄株式会社 熱延鋼板

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3355970B2 (ja) 1996-12-10 2002-12-09 日本鋼管株式会社 打ち抜き性に優れる冷延鋼板の製造方法
JP4109619B2 (ja) 2003-12-16 2008-07-02 株式会社神戸製鋼所 伸び、及び伸びフランジ性に優れた高強度鋼板

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0479722B2 (enrdf_load_stackoverflow) * 1983-08-23 1992-12-16 Hitachi Ltd
WO2022044493A1 (ja) * 2020-08-27 2022-03-03 日本製鉄株式会社 熱延鋼板
WO2023149374A1 (ja) * 2022-02-02 2023-08-10 日本製鉄株式会社 熱延鋼板

Also Published As

Publication number Publication date
JPWO2024048584A1 (enrdf_load_stackoverflow) 2024-03-07
CN119768550A (zh) 2025-04-04
KR20250044350A (ko) 2025-03-31
MX2025002286A (es) 2025-04-02

Similar Documents

Publication Publication Date Title
JP7239009B2 (ja) 熱延鋼板
JP7495640B2 (ja) 熱延鋼板
JP7260824B2 (ja) 熱延鋼板
JP7648952B2 (ja) 熱間圧延鋼板
JP7564463B2 (ja) 熱延鋼板
US20250101553A1 (en) Hot-rolled steel sheet
JP7495641B2 (ja) 熱延鋼板
JP7564464B2 (ja) 熱延鋼板
JP7260825B2 (ja) 熱延鋼板
JP7648953B2 (ja) 熱間圧延鋼板
JP7440804B2 (ja) 熱間圧延鋼板
WO2024048584A1 (ja) 熱延鋼板
KR102858559B1 (ko) 열연 강판
WO2024053701A1 (ja) 熱延鋼板
WO2024095809A1 (ja) 熱延鋼板
WO2024080327A1 (ja) 熱延鋼板
WO2024142492A1 (ja) 熱延鋼板

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 23860346

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: 2024544287

Country of ref document: JP

WWE Wipo information: entry into national phase

Ref document number: 202517014608

Country of ref document: IN

ENP Entry into the national phase

Ref document number: 20257006190

Country of ref document: KR

Kind code of ref document: A

WWE Wipo information: entry into national phase

Ref document number: 1020257006190

Country of ref document: KR

Ref document number: MX/A/2025/002286

Country of ref document: MX

Ref document number: 202380061905.7

Country of ref document: CN

WWE Wipo information: entry into national phase

Ref document number: 2501001231

Country of ref document: TH

WWP Wipo information: published in national office

Ref document number: 202517014608

Country of ref document: IN

WWP Wipo information: published in national office

Ref document number: 1020257006190

Country of ref document: KR

NENP Non-entry into the national phase

Ref country code: DE

WWP Wipo information: published in national office

Ref document number: MX/A/2025/002286

Country of ref document: MX

WWP Wipo information: published in national office

Ref document number: 202380061905.7

Country of ref document: CN

122 Ep: pct application non-entry in european phase

Ref document number: 23860346

Country of ref document: EP

Kind code of ref document: A1