WO2023199777A1 - Hot-stamp formed article - Google Patents

Hot-stamp formed article Download PDF

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Publication number
WO2023199777A1
WO2023199777A1 PCT/JP2023/013803 JP2023013803W WO2023199777A1 WO 2023199777 A1 WO2023199777 A1 WO 2023199777A1 JP 2023013803 W JP2023013803 W JP 2023013803W WO 2023199777 A1 WO2023199777 A1 WO 2023199777A1
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WIPO (PCT)
Prior art keywords
hot
less
concentration
content
stamped
Prior art date
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PCT/JP2023/013803
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French (fr)
Japanese (ja)
Inventor
純 芳賀
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日本製鉄株式会社
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Publication of WO2023199777A1 publication Critical patent/WO2023199777A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • 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
    • C22C38/18—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

Definitions

  • the present invention relates to a hot stamp molded article.
  • This application claims priority based on Japanese Patent Application No. 2022-067026 filed in Japan on April 14, 2022, the contents of which are incorporated herein.
  • Patent Document 1 discloses that a member having a tensile strength of 1400 MPa or more can be obtained by hot stamping a steel plate having a tensile strength of 500 to 600 MPa.
  • the strength of the hot-stamped member can be further increased by increasing the C content of the steel plate.
  • the C content of the steel plate is increased, the deformability of the member decreases as the member strength increases, and when the member deforms during a collision, cracks are likely to occur in the initial stage of deformation.
  • Patent Document 2 discloses a high-strength brace component having a tensile strength of 1300 MPa or more and high shock absorption, and a method for manufacturing the same.
  • Patent Document 3 discloses a hot stamping member for an automobile, which has a tensile strength of 1100 MPa or more and has improved bendability from the viewpoint of absorbing impact energy, and a method for manufacturing the same.
  • a hot stamping steel plate having a decarburized layer on the surface layer is hot stamped under predetermined conditions to form a soft layer on the surface layer of the hot stamping member. This improves the collision resistance of the component.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hot-stamped molded article having a high tensile strength of 1900 MPa or more and excellent collision resistance.
  • the gist of the present invention is as follows.
  • a hot-stamped molded body is a hot-stamped molded body that includes a steel plate, and all or part of the steel plate has a chemical composition in mass %, C: more than 0.32%, less than 0.70%, Si: less than 2.00%, Mn: 0.01 to 3.00%, P: 0.200% or less, S: 0.0200% or less, sol.
  • the hot-stamped molded article according to (1) above has the chemical composition in mass %, Cr: 0.01-2.00%, Mo: 0.01-2.00%, W: 0.01-2.00%, Cu: 0.01-2.00%, Ni: 0.01-2.00%, Ti: 0.001 to 0.200%, Nb: 0.001-0.200%, V: 0.001-0.200%, Zr: 0.001 to 0.200%, Ca: 0.0001-0.1000%, Mg: 0.0001-0.1000%, REM: 0.0001-0.1000%, Sn: 0.001-0.200%, As: 0.001 to 0.100%, and Bi: 0.0001 to 0.0500% It may contain one or more types from the group consisting of.
  • the hot-stamped molded article having a high tensile strength of 1900 MPa or more and excellent collision resistance.
  • the hot-stamped molded article according to the above aspect has excellent collision resistance properties and does not crack at the initial stage of deformation during a collision, so it can be suitably applied to automobile parts such as pillars and bumpers.
  • FIG. 3 is a diagram showing a test specimen for a three-point bending test manufactured in an example.
  • FIG. 3 is a diagram for explaining a three-point bending test conducted in an example.
  • the present inventors studied a method for suppressing the occurrence of cracks at the initial stage of deformation during a collision for a hot-stamped molded body having a tensile strength of 1900 MPa or more, and as a result, obtained the following knowledge.
  • the present inventors Based on the findings of (A) to (D) above, the present inventors adjusted the B concentration and O concentration to a specific range in the surface layer region (including the surface layer region and the outermost layer region described below) of the hot stamp molded product. It has been found that by doing so, a hot-stamped molded article having a tensile strength of 1900 MPa or more and excellent collision resistance can be obtained.
  • the hot stamp molded article according to this embodiment will be described in detail. First, the reason for limiting the chemical composition of the steel plate constituting the hot-stamped molded body according to the present embodiment will be explained.
  • All or part of the steel plate included in the hot-stamped molded body according to the present embodiment has the following chemical composition.
  • the hot-stamped molded body is made of only a steel plate, it can be said that all or part of the hot-stamped molded body has the chemical composition shown below. Note that the numerically limited range described below with “ ⁇ ” in between includes the lower limit value and the upper limit value. Numerical values indicated as “less than” or “greater than” do not include the value within the numerical range. All percentages regarding chemical composition indicate mass %.
  • the hot stamped molded article includes a part having a tensile strength of 1900 MPa or more and a part having a tensile strength of less than 1900 MPa, at least the part having a tensile strength of 1900 MPa or more has the following chemical composition. All you have to do is do it.
  • All or part of the steel plate included in the hot-stamped molded body according to the present embodiment has a chemical composition, in mass %, of C: more than 0.32% and 0.70% or less, Si: less than 2.00%, and Mn. : 0.01 to 3.00%, P: 0.200% or less, S: 0.0200% or less, sol. Al: 0.001 to 1.000%, N: 0.0200% or less, O: 0.0005 to 0.0200%, B: 0.0005 to 0.0200%, and balance: Contains Fe and impurities. . Each element will be explained below.
  • C More than 0.32%, 0.70% or less C is an element that improves the tensile strength of the steel plate after hot stamping (the steel plate that constitutes the hot stamped body). If the C content is 0.32% or less, the tensile strength of the steel plate after hot stamping will be less than 1900 MPa, resulting in insufficient strength of the hot stamped product. Moreover, the collision resistance properties of the hot stamped molded body deteriorate. Therefore, the C content is set to more than 0.32%. The C content is preferably greater than 0.34%, greater than 0.38%, greater than 0.42%, or greater than 0.45%.
  • the C content is set to 0.70% or less.
  • the C content is 0.65% or less, 0.60% or less, 0.55% or less or 0.50% or less.
  • Si less than 2.00% Si is an element that may be contained as an impurity in steel and makes the steel brittle. When the Si content exceeds 2.00%, its adverse effects become particularly large. Therefore, the Si content is made less than 2.00%.
  • the Si content is preferably less than 1.00%, less than 0.75%, less than 0.50% or less than 0.20%.
  • the lower limit of the Si content is not particularly limited, but may be 0%. Since excessively lowering the Si content causes an increase in steel manufacturing costs, the Si content is preferably 0.001% or more. Further, since Si has the effect of improving the hardenability of steel, it may be actively included. From the viewpoint of improving hardenability, the Si content is preferably 0.05% or more, 0.10% or more, or 0.15% or more.
  • Mn 0.01-3.00%
  • Mn is an element that combines with S, which is an impurity, to form MnS and has the effect of suppressing the harmful effects of S. If the Mn content is less than 0.01%, the above effects cannot be obtained. Therefore, the Mn content is set to 0.01% or more.
  • Mn is an element that improves the hardenability of steel, and forms a metal structure mainly composed of martensite inside the steel sheet after hot stamping, which is effective for ensuring the strength of the hot stamped product. It is an element. From the viewpoint of ensuring strength, the Mn content is preferably 0.50% or more, 0.75% or more, 1.00% or more, or 1.25% or more.
  • the Mn content is set to 3.00% or less.
  • the Mn content is preferably 2.50% or less, 2.00% or less, or 1.50% or less.
  • P 0.200% or less
  • P is an element that may be contained as an impurity in steel and makes the steel brittle. If the P content exceeds 0.200%, the adverse effects will be particularly large, and weldability will also deteriorate significantly. Therefore, the P content is set to 0.200% or less.
  • the P content is preferably less than 0.100%, less than 0.050% or less than 0.020%.
  • the P content may be 0%, but if the P content is reduced to less than 0.001%, the cost of removing P will increase significantly, which is economically unfavorable. % or more.
  • S 0.0200% or less
  • S is an element that may be contained as an impurity in steel and makes the steel brittle.
  • the S content is set to 0.0200% or less.
  • the S content is preferably less than 0.0050%, less than 0.0020% or less than 0.0010%.
  • the S content may be 0%, but if the S content is reduced to less than 0.0001%, the S removal cost will increase significantly and it is economically unfavorable. % or more.
  • sol. Al 0.001-1.000%
  • Al is an element that has the effect of deoxidizing molten steel. sol. If the Al content (acid-soluble Al content) is less than 0.001%, deoxidation will be insufficient. Therefore, sol. Al content shall be 0.001% or more. sol. The Al content is preferably 0.005% or more, 0.010% or more, or 0.020% or more. On the other hand, sol. If the Al content is too high, the transformation point will rise, making it difficult to heat the steel plate to a temperature exceeding Ac 3 in the hot stamping heating process. In addition, the strength and collision resistance of the hot stamped body deteriorate. Therefore, sol. Al content shall be 1.000% or less. sol. The Al content is preferably less than 0.500%, less than 0.100%, less than 0.060% or less than 0.040%.
  • N 0.0200% or less
  • N is an element that may be contained as an impurity in steel and forms nitrides during continuous casting of steel. Since this nitride deteriorates the ductility of the steel sheet after hot stamping, it is preferable that the N content is low. If the N content exceeds 0.0200%, its adverse effects will be particularly large. Therefore, the N content is set to 0.0200% or less.
  • the N content is preferably less than 0.0100%, less than 0.0080%, or less than 0.0050%.
  • the N content may be 0%, but if the N content is reduced excessively, the cost of removing N will increase significantly and it is economically unfavorable. It may be .0020% or more.
  • O 0.0005-0.0200%
  • O is an element that forms B oxide by combining with B and reduces the hardenability of steel, and is an effective element for softening the surface layer of a steel sheet after hot stamping. If the O content is less than 0.0005%, the surface layer of the hot-stamped steel sheet will not become soft, and the collision resistance of the hot-stamped product will deteriorate. Therefore, the O content is set to 0.0005% or more. The O content is preferably 0.0010% or more, 0.0015% or more, or 0.0020% or more. On the other hand, if the O content exceeds 0.0200%, a large amount of coarse oxide inclusions are formed in the steel. This deteriorates the collision resistance properties of the hot stamp molded body. Therefore, the O content is set to 0.0200% or less. The O content is preferably 0.0150% or less, 0.0100% or less, 0.0060% or less, or 0.0040% or less.
  • B 0.0005-0.0200%
  • B is an element that improves the hardenability of steel, and is an effective element for forming a metal structure mainly composed of martensite inside the steel plate after hot stamping, and ensuring the strength of the hot stamped product. be. If the B content is less than 0.0005%, the desired strength cannot be obtained in the hot stamp molded product. Moreover, the collision resistance properties of the hot stamped molded body deteriorate. Therefore, the B content is set to 0.0005% or more.
  • the B content is preferably 0.0010% or more, 0.0015% or more, or 0.0020% or more.
  • the B content exceeds 0.0200%, carborides are formed in the hot-stamped compact, and the hardenability improvement effect of B is impaired. Therefore, the B content is set to 0.0200% or less.
  • the B content is preferably less than 0.0050%, less than 0.0040% or less than 0.0030%.
  • the remainder of the chemical composition of the steel plate constituting the hot-stamped molded body according to this embodiment may be Fe and impurities.
  • impurities include elements that are unavoidably mixed in from steel raw materials or scraps and/or during the steel manufacturing process and are allowed within a range that does not impede the properties of the hot-stamped molded product according to the present embodiment.
  • the steel plate constituting the hot-stamped molded product according to the present embodiment may contain the following elements as optional elements in place of a part of Fe. When the following arbitrary elements are not included, the content is 0%.
  • Cr is an element that increases the strength of the hot stamped body by increasing the hardenability of steel.
  • the Cr content is preferably 0.01% or more.
  • the Cr content is more preferably 0.05% or more or 0.10% or more.
  • the Cr content is set to 2.00% or less.
  • the Cr content is preferably less than 0.50%, less than 0.40% or less than 0.30%.
  • Mo 0.01 ⁇ 2.00%
  • Mo is an element that increases the strength of the hot stamped body by increasing the hardenability of steel.
  • the Mo content is preferably 0.01% or more.
  • Mo content is more preferably 0.05% or more, 0.10% or more, or 0.15% or more.
  • the Mo content is set to 2.00% or less.
  • the Mo content is preferably less than 0.50%, less than 0.40% or less than 0.30%.
  • W 0.01 ⁇ 2.00%
  • W is an element that increases the strength of the hot stamped body by increasing the hardenability of the steel.
  • the W content is preferably 0.01% or more.
  • the W content is more preferably 0.05% or more or 0.10% or more.
  • the W content is set to 2.00% or less.
  • the W content is preferably less than 0.50%, less than 0.40% or less than 0.30%.
  • Cu 0.01-2.00% Cu is an element that increases the strength of the hot stamped body by increasing the hardenability of steel.
  • the Cu content is preferably 0.01% or more.
  • the Cu content is more preferably 0.10% or more.
  • the Cu content is set to 2.00% or less.
  • the Cu content is preferably less than 1.00% or less than 0.50%.
  • Ni 0.01-2.00%
  • Ni is an element that increases the strength of the hot stamped body by increasing the hardenability of steel.
  • the Ni content is preferably 0.01% or more.
  • the Ni content is more preferably 0.10% or more.
  • the Ni content is preferably 2.00% or less.
  • the Ni content is preferably less than 1.00% or less than 0.50%.
  • Ti 0.001-0.200%
  • Ti is an element that forms carbonitrides in steel and increases the strength of hot stamped products through precipitation strengthening. Further, Ti is an element that improves the collision resistance of the hot stamped body through refinement of the metal structure. To ensure these effects, the Ti content is preferably 0.001% or more. The Ti content is more preferably 0.005% or more or 0.010% or more. On the other hand, if the Ti content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot-stamped body. Therefore, the Ti content is set to 0.200% or less. The Ti content is preferably less than 0.050% or less than 0.030%.
  • Nb 0.001-0.200%
  • Nb is an element that forms carbonitrides in steel and increases the strength of hot stamped products through precipitation strengthening. Furthermore, Nb is an element that improves the collision resistance of the hot stamped body through refinement of the metal structure. To ensure these effects, the Nb content is preferably 0.001% or more. The Nb content is more preferably 0.005% or more or 0.010% or more. On the other hand, if the Nb content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot stamped body. Therefore, the Nb content is set to 0.200% or less. The Nb content is preferably less than 0.050%, less than 0.030% or less than 0.020%.
  • V is an element that forms carbonitrides in steel and increases the strength of the hot stamped product through precipitation strengthening. Further, V is an element that improves the collision resistance properties of the hot-stamped molded product through refinement of the metal structure. To ensure these effects, the V content is preferably 0.001% or more. The V content is more preferably 0.005% or more or 0.010% or more. On the other hand, if the V content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot stamped body. Therefore, the V content is set to 0.200% or less. The V content is preferably less than 0.100% or less than 0.050%.
  • Zr 0.001-0.200%
  • Zr is an element that forms carbonitrides in steel and increases the strength of hot-stamped products through precipitation strengthening. Furthermore, Zr is an element that improves the collision resistance of the hot stamped product through refinement of the metal structure. To ensure these effects, the Zr content is preferably 0.001% or more. The Zr content is more preferably 0.005% or more or 0.010% or more. On the other hand, if the Zr content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot stamped body. Therefore, the Zr content is set to 0.200% or less. The Zr content is preferably less than 0.100% or less than 0.050%.
  • Ca is an element that improves the ductility of the steel sheet after hot stamping by adjusting the shape of inclusions.
  • the Ca content is preferably 0.0001% or more.
  • the Ca content is set to 0.1000% or less.
  • Ca content is preferably less than 0.0100%.
  • Mg 0.0001-0.1000%
  • Mg is an element that improves the ductility of the steel sheet after hot stamping by adjusting the shape of inclusions. To ensure these effects, the Mg content is preferably 0.0001% or more. On the other hand, even if a large amount of Mg is contained, the above-mentioned effects are saturated, and furthermore, excessive costs occur, so the Mg content is set to 0.1000% or less. The Mg content is preferably less than 0.0100%.
  • REM 0.0001 ⁇ 0.1000% REM is an element that improves the ductility of a steel plate after hot stamping by adjusting the shape of inclusions. To ensure this effect, the REM content is preferably 0.0001% or more. On the other hand, even if a large amount of REM is contained, the above-mentioned effects are saturated, and furthermore, excessive costs occur, so the REM content is set to 0.1000% or less. The REM content is preferably less than 0.0100%. In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the content of REM refers to the total content of these elements.
  • Sn 0.001-0.200%
  • Sn is an element that has the effect of improving the corrosion resistance of the hot stamp molded product.
  • the Sn content is preferably 0.001% or more.
  • the Sn content is more preferably 0.005% or more, 0.015% or more, or 0.030% or more.
  • Sn content is set to 0.200% or less.
  • Sn content is preferably 0.150% or less or 0.100% or less.
  • As is an element that has the effect of increasing the strength of the hot stamp molded product.
  • the As content is preferably 0.001% or more.
  • the As content is set to 0.100% or less.
  • Bi 0.0001 ⁇ 0.0500%
  • Bi is an element that improves the collision resistance of the hot-stamped body by making the solidified structure finer.
  • the Bi content is preferably 0.0001% or more.
  • the Bi content is set to 0.0500% or less.
  • Bi content is preferably 0.0100% or less or 0.0050% or less.
  • the chemical composition of the steel plate constituting the hot-stamped body described above can be determined by taking a test piece from the steel plate constituting the hot-stamping body, removing the paint film if the steel plate has been painted, and then using a general method.
  • the average element content throughout the plate thickness may be measured using an analytical method. For example, measurement may be performed using inductively coupled plasma optical emission spectrometry or inductively coupled plasma mass spectrometry.
  • C and S may be measured using a combustion-infrared absorption method
  • O and N may be measured using an inert gas melting-infrared absorption method or an inert gas melting-thermal conductivity method.
  • the chemical composition may be measured after removing the plating layer.
  • the hot stamp molded article when the hot stamp molded article includes a portion having a tensile strength of 1900 MPa or more and a portion having a tensile strength of less than 1900 MPa, at least the portion having a tensile strength of 1900 MPa or more is as described above.
  • the chemical composition is as follows. In order to analyze the chemical composition of a part with a tensile strength of 1900 MPa or more, a tensile test described below was performed and a tensile test piece was collected from a tensile test piece that had a tensile strength of 1900 MPa or more. A test piece for chemical composition analysis may be taken from a part adjacent to the part.
  • the B concentration distribution and O concentration distribution in the thickness direction of the steel plate constituting the hot-stamped molded body according to the present embodiment will be described.
  • B present in the surface layer region is diffused to the outermost layer region, and B is mixed in the outermost layer region. It is possible to combine with O and improve the collision resistance of the hot stamp molded product.
  • the hot-stamped molded article according to the present embodiment has an average B concentration in a region from a depth of 5.0 ⁇ m to a depth of 25.0 ⁇ m from the surface of the steel plate constituting the hot-stamped molded article, and an average concentration of B in a region from a depth of 100 ⁇ m from the surface to a depth of 100 ⁇ m from the surface. is 0.700 times or less than the B concentration at the position, and the average B concentration in a region from 0.5 ⁇ m deep to 4.0 ⁇ m deep from the surface is 0.700 times or less than the B concentration at the position 100 ⁇ m deep from the surface.
  • the B concentration is 1.600 times or more, and the average O concentration in the region from a depth of 0.5 ⁇ m to a depth of 4.0 ⁇ m from the surface is more than 0.0150% by mass.
  • the region from 5.0 ⁇ m deep to the surface of the steel plate to 25.0 ⁇ m deep from the surface starts from a position 5.0 ⁇ m deep from the surface of the steel plate and starts at a position 25.0 ⁇ m deep from the surface. In other words, it is the region that is the end point.
  • the region from 0.5 ⁇ m deep to 4.0 ⁇ m deep from the surface of the steel plate starts from a position 0.5 ⁇ m deep from the surface of the steel plate and starts at a position 4.0 ⁇ m deep from the surface. In other words, it is the region that is the end point.
  • the hot-stamped molded product includes a portion having a tensile strength of 1900 MPa or more and a portion having a tensile strength of less than 1900 MPa, at least the portion having a tensile strength of 1900 MPa or more has the following B concentration distribution and It is sufficient as long as it has an O concentration distribution.
  • Each regulation will be explained below.
  • Average B concentration in the region from 5.0 ⁇ m depth to the surface to 25.0 ⁇ m depth from the surface 0.700 times or less of the B concentration at a position 100 ⁇ m deep from the surface 5.0 ⁇ m depth from the surface to 25.0 ⁇ m depth from the surface. If the average B concentration in the 0 ⁇ m depth region (hereinafter sometimes referred to as surface layer region) is more than 0.700 times the B concentration at a position 100 ⁇ m deep from the surface, the surface layer region will not soften. Desired collision resistance properties cannot be obtained in the hot-stamped molded product. Therefore, the average B concentration in the surface layer region is set to be 0.700 times or less of the B concentration at a position 100 ⁇ m deep from the surface.
  • the average B concentration in the surface layer region is preferably 0.700 times or less of the B concentration at a depth of 100 ⁇ m from the surface and 0.0015% by mass or less. More preferably, the average B concentration in the surface layer region is 0.500 times or less or 0.300 times or less of the B concentration at a depth of 100 ⁇ m from the surface. Further, the average B concentration in the surface layer region is more preferably 0.0010% by mass or less or 0.0006% by mass or less. Although the lower limit is not particularly defined, the average B concentration in the surface layer region may be set to 0.0002% by mass or more, since if it is lowered too much, the above effect will not only be saturated, but also the strength of the hot-stamped molded article will be reduced.
  • the surface refers to the surface of the steel plate that constitutes the hot stamp molded body.
  • the surface refers to the interface between the plating layer and the steel plate.
  • Average B concentration in a region from 0.5 ⁇ m depth to 4.0 ⁇ m depth from the surface 1.600 times or more of the B concentration at a position 100 ⁇ m deep from the surface. 0.5 ⁇ m depth from the surface to 4.0 ⁇ m depth from the surface. If the average B concentration in the 0 ⁇ m depth region (hereinafter sometimes referred to as the outermost layer region) is less than 1.600 times the B concentration at a position 100 ⁇ m deep from the surface, the maximum B and O do not combine sufficiently in the surface layer region, and the outermost layer region does not become soft. As a result, it is not possible to obtain desired collision resistance properties in the hot-stamped molded article.
  • the average B concentration in the outermost layer region is 1.600 times or more the B concentration at a position 100 ⁇ m deep from the surface.
  • the average B concentration in the outermost layer region is preferably at least 1.600 times the B concentration at a depth of 100 ⁇ m from the surface and at least 0.0040% by mass. More preferably, the average B concentration in the outermost layer region is 2.000 times or more, 3.000 times or more, or 4.000 times or more the B concentration at a depth of 100 ⁇ m from the surface. Further, the average B concentration in the outermost layer region is more preferably 0.0050% by mass or more, 0.0060% by mass or more, or 0.0070% by mass or more.
  • the upper limit is not particularly defined, but if the average B concentration in the outermost layer region is increased too much, the above effect will not only be saturated, but also the productivity of the hot stamped molded product will be significantly impaired, so it may be set to 0.2000% by mass or less. .
  • Average O concentration in the region from 0.5 ⁇ m depth to the surface to 4.0 ⁇ m depth from the surface More than 0.0150% by mass Region from 0.5 ⁇ m depth to the surface to 4.0 ⁇ m depth from the surface (uppermost layer region) If the average O concentration in is 0.0150% by mass or less, the amount of O that combines with B is insufficient, the amount of B in solid solution increases, and the outermost layer region does not become soft. As a result, it is not possible to obtain desired collision resistance properties in the hot-stamped molded article. Therefore, the average O concentration in the outermost layer region is set to exceed 0.0150% by mass.
  • the average O concentration in the outermost layer region is preferably greater than 0.0200% by mass, greater than 0.0300% by mass, or greater than 0.0400% by mass.
  • the upper limit is not particularly specified, but if the average O concentration in the outermost layer region is increased too much, the above effect will not only be saturated, but also the productivity of the hot stamped molded product will be greatly impaired, so it may be set to 1.0000% by mass or less. .
  • the average B concentration in the surface layer region, the average B concentration and average O concentration in the outermost layer region, and the B concentration at a depth of 100 ⁇ m from the surface are measured by the following method.
  • a test piece is taken from the hot-stamped molded product, and after removing the paint film if the steel plate is coated, it is measured at a depth from the measurement starting surface using Glow Discharge Optical Emission Spectrometry (GDS analysis).
  • GDS analysis Glow Discharge Optical Emission Spectrometry
  • the concentration (mass %) of each element is measured at a depth of 100 ⁇ m or more in the width direction (plate thickness direction). Note that the "measurement start surface” here is different from the "surface of the steel plate.”
  • the measurement pitch is adjusted so that there are 1200 to 1800 measurement points from the surface of the steel plate to a depth of 100 ⁇ m.
  • the surface of the steel plate Defined as the surface of the steel plate.
  • the depth at which the Fe concentration initially becomes 95% or more of "the Fe concentration at a depth of 100 ⁇ m from the measurement starting surface” is set as the plating layer. It is defined as the interface with the steel plate, that is, the surface of the steel plate.
  • the average B concentration in the surface layer region is obtained by calculating the average value of the B concentration in the region from 5.0 ⁇ m depth to the steel sheet surface to 25.0 ⁇ m depth from the steel sheet surface.
  • the average B concentration and average O concentration in the outermost layer region can be calculated. get. Further, by determining the B concentration at a position 100 ⁇ m deep from the surface of the steel plate, the B concentration at a position 100 ⁇ m deep from the surface is obtained.
  • the first measured value beyond the position 100 ⁇ m deep from the surface may be taken as the B concentration at a position 100 ⁇ m deep from the surface.
  • the GDS analysis is performed on test pieces taken from three or more locations of the hot-stamped molded body, and the average value of the obtained results is taken as the B concentration and the O concentration.
  • the test piece may be taken from a part adjacent to a part where a tensile test piece having a tensile strength of 1900 MPa or more was taken after conducting a tensile test to be described later.
  • the metal structure of the steel plate constituting the hot-stamped molded product is not particularly limited as long as the desired strength and collision resistance characteristics can be obtained, but it is preferable to have the metal structure shown below.
  • all or part of the steel plate constituting the hot-stamped molded body according to the present embodiment has a metal structure containing martensite in the amount shown below.
  • “%" means “volume %”.
  • the hot-stamped molded body has a part having a tensile strength of 1900 MPa or more and a part having a tensile strength of less than 1900 MPa, at least the part having a tensile strength of 1900 MPa or more has the following metal structure. All you have to do is do it.
  • Metal structure of the inner layer region (area from 100 ⁇ m depth to the center of the plate thickness (1/2 position of the plate thickness) from the surface of the steel plate constituting the hot-stamped compact) is more than 90.0% martensite. It is preferable to include.
  • Martensite is an effective structure for increasing the tensile strength of the steel plate after hot stamping, so martensite is a structure that is effective for increasing the tensile strength of the steel plate after hot stamping. It is preferable that the volume fraction of martensite is more than 90.0%. If the volume fraction of martensite in the inner layer region is 90.0% or less, the tensile strength of the hot-stamped molded product is less than 1900 MPa, which may result in insufficient strength. Therefore, it is preferable that the volume fraction of martensite in the inner layer region be more than 90.0%. The volume fraction of martensite in the inner layer region is more preferably over 91.0%, over 93.0%, or over 95.0%.
  • the volume fraction of martensite in the inner layer region is preferably 99.0% or less or 98.0% or less.
  • martensite includes fresh martensite that has not been tempered, as well as tempered martensite that has been tempered and has iron carbides inside.
  • the remainder of the metal structure in the inner layer region may contain ferrite, pearlite, bainite, or retained austenite, and may also contain precipitates such as cementite or oxides existing alone. Since it is not necessary to contain ferrite, pearlite, bainite, retained austenite, and precipitates, the lower limit of the volume fraction of ferrite, pearlite, bainite, retained austenite, and precipitates is all 0%.
  • Retained austenite has the effect of improving the ductility of the steel plate after hot stamping.
  • the volume fraction of retained austenite in the inner layer region is 0.5% or more, 1.0% or more, or 2.0% or more.
  • the volume fraction of retained austenite in the inner layer region is preferably less than 9.0%, less than 7.0%, less than 5.0%, or less than 4.0%.
  • Metal structure of the outermost layer region preferably contains more than 5.0% ferrite.
  • the volume fraction of ferrite in the outermost layer region be more than 5.0%.
  • the volume fraction of ferrite in the outermost layer region is more preferably more than 10.0%, more than 20.0%, more than 40.0%, or more than 60.0%.
  • the ferrite includes acicular ferrite and bainitic ferrite, which have a high dislocation density, in addition to polygonal ferrite.
  • the outermost layer region contains polygonal ferrite, which is the softest, at the above-mentioned volume percentage.
  • the remainder of the metal structure in the outermost layer region may contain pearlite, bainite, retained austenite, or martensite, and may also contain precipitates such as cementite or oxides existing alone. Since it is not necessary to contain pearlite, bainite, retained austenite, martensite, and precipitates, the lower limit of the volume percentage of pearlite, bainite, retained austenite, martensite, and precipitates is all 0%. When martensite is contained excessively, the outermost layer region becomes hard, and the collision resistance of the hot-stamped product may deteriorate. Therefore, the volume fraction of martensite in the outermost layer region is preferably less than 90.0%, less than 40.0%, less than 10.0%, or less than 5.0%.
  • Bainite is softer than martensite and has the effect of improving the collision resistance of the hot stamped body.
  • the volume fraction of bainite in the outermost layer region be more than 10.0%.
  • the volume fraction of bainite in the outermost layer region is more preferably more than 20.0% or more than 40.0%.
  • the volume fraction of bainite in the outermost layer region be less than 80.0% or less than 60.0%.
  • the volume fraction of each tissue is measured by the following method.
  • a test piece is taken from a hot-stamped compact, and after buffing the longitudinal section (thickness section) of the steel plate, the structure is observed in the inner layer region and the outermost layer region.
  • the structure is observed in a region from a depth of 100 ⁇ m to the center of the plate thickness (1/2 position of the plate thickness) from the surface of the steel plate constituting the hot-stamped compact.
  • the structure is observed in a region from 0.5 ⁇ m deep to 4.0 ⁇ m deep from the surface of the steel plate.
  • a microstructure photograph is taken using an optical microscope and a scanning electron microscope (SEM), and the resulting microstructure photographs are analyzed based on brightness differences or presence within the phase.
  • SEM scanning electron microscope
  • the area percentages of ferrite, pearlite, bainite, tempered martensite, and precipitates are obtained.
  • the structure was photographed using an optical microscope and a scanning electron microscope (SEM), and image analysis was performed on the obtained structure photograph. Calculate the total area ratio of "austenite and fresh martensite".
  • the area ratio of retained austenite is measured using a SEM equipped with an electron beam backscatter pattern analyzer (EBSP device).
  • EBSP device electron beam backscatter pattern analyzer
  • the area ratio of retained austenite is obtained by calculating the area ratio of a region having an fcc crystal structure from the crystal orientation information obtained by the EBSP analysis.
  • the area ratio of fresh martensite is obtained by subtracting the area ratio of retained austenite from the sum of the area ratios of the above-mentioned "retained austenite and fresh martensite.”
  • tempered martensite can be distinguished from fresh martensite by the presence of iron carbides inside. Furthermore, tempered martensite can be distinguished from bainite in that the iron carbide present inside extends not in a single direction but in multiple directions. Note that elongation in a single direction means that the difference in elongation direction is within 5°.
  • the plate thickness of the hot-stamped body according to the present embodiment is not particularly limited, but from the viewpoint of reducing the weight of the vehicle body, it is 2.5 mm or less, 2.5 mm or less, It is preferable to set it as 0 mm or less, 1.8 mm or less, or 1.6 mm or less. On the other hand, from the viewpoint of ensuring the amount of shock absorption, the plate thickness is preferably 0.4 mm or more, 0.6 mm or more, 0.8 mm or more, or 1.0 mm or more.
  • All or part of the hot stamp molded article according to this embodiment has a tensile strength of 1900 MPa or more.
  • the tensile strength of all or part of the steel plate constituting the hot-stamped molded product according to this embodiment is 1900 MPa or more. If the tensile strength of at least a portion of the hot-stamped molded product is not 1900 MPa or more, the deformation load of the hot-stamped molded product cannot be ensured. As a result, the collision resistance properties of the hot-stamped molded product deteriorate. Therefore, the tensile strength of all or part of the hot stamp molded product is set to 1900 MPa or more.
  • the tensile strength of all or part of the hot-stamped molded product is 2000 MPa or more, 2100 MPa or more, 2300 MPa or more, or 2500 MPa or more.
  • the tensile strength of the hot-stamped molded product is preferably less than 3000 MPa or less than 2800 MPa.
  • the hot stamp molded product according to the present embodiment may have a tensile strength of 1900 MPa or more as a whole (the entire hot stamp molded product), but a portion of the hot stamp molded product having a tensile strength of 1900 MPa or more may have a tensile strength of 1900 MPa or more. There may be a mixture of portions that are less than the above. By providing portions with different strengths, it becomes possible to control the deformation state of the hot stamp molded body at the time of collision.
  • a hot-stamped molded body having parts with different strengths can be produced by hot-stamping after joining two or more types of steel plates with different chemical compositions, or by adjusting the heating temperature of the steel plate or the cooling rate after hot-stamping in the hot-stamping process. It can be produced by a method of partially changing the shape, a method of partially reheating a hot stamp molded product, and the like.
  • the tensile strength of a hot-stamped compact is obtained by taking a small strip-shaped piece from the hot-stamping compact, processing it into a tensile test piece without surface grinding the steel plate, and performing a tensile test. Specifically, it is preferable to take a No. 13B plate-shaped test piece from the hot-stamped molded product in accordance with JIS Z 2241:2011 and conduct a tensile test at a tensile speed of 10 mm/min. If it is not possible to collect a No.
  • the hot stamp molded article according to this embodiment may have a plating layer on the surface.
  • corrosion resistance can be improved after hot stamping.
  • the plating layer include a zinc-based plating layer and an aluminum-based plating layer.
  • a hot-stamped molded body having these plating layers is obtained by hot-stamping using a zinc-based plated steel sheet or an aluminum-based plated steel sheet.
  • the plating layer may be formed on both sides of the hot-stamped molded body, or may be formed on one side.
  • the plating layer of the hot stamp molded body can be formed by hot stamping using a plated steel plate provided with the plating layer.
  • the plating layer provided on the plated steel sheet prevents the formation of a preferable B concentration distribution and O concentration distribution in the surface layer region and the outermost layer region of the hot stamped product during the process of manufacturing the hot stamped product, so it must be manufactured more strictly. It is necessary to control the method, and the productivity of hot-stamped molded products may be significantly reduced. Therefore, from the viewpoint of productivity, it is preferable that the hot stamp molded product does not have a plating layer on the surface.
  • the chemical composition of the hot stamping steel sheet may be the same as that of the hot stamping molded product described above.
  • the chemical composition of the hot stamping steel plate may be determined by taking a test piece from the hot stamping steel plate and measuring it in the same manner as in the case of the hot stamping molded product.
  • the average B concentration in a region (surface layer region) from 5.0 ⁇ m deep to 25.0 ⁇ m deep from the surface of the steel plate is 0.0% of the B concentration at a position 100 ⁇ m deep from the surface of the steel plate. It is preferable that it is 850 times or less. If the average B concentration in the surface layer region is more than 0.850 times the B concentration at a depth of 100 ⁇ m from the surface of the steel sheet, even if the hot stamping conditions described below are applied, B concentration distribution and O concentration distribution cannot be favorably controlled in the surface layer region. As a result, desired collision resistance properties cannot be obtained in the hot-stamped molded article.
  • the surface refers to the interface between the plating layer and the steel plate.
  • the B concentration distribution in the thickness direction of a hot stamping steel sheet can be determined by taking a test piece from the hot stamping steel sheet and performing a GDS analysis in the same manner as in the case of a hot stamping compact.
  • Steel plates for hot stamping are produced through a hot rolling process in which a slab having the above-mentioned chemical composition is hot-rolled to produce a hot-rolled steel plate, and a cold-rolled steel plate is obtained by cold-rolling the hot-rolled steel plate. It is manufactured by a manufacturing method including a cold rolling step and an annealing step of annealing the cold rolled steel sheet to obtain an annealed steel sheet.
  • the method for manufacturing the slab used in the method for manufacturing a hot stamping steel plate is not particularly limited.
  • Steel having the above-mentioned chemical composition is melted by known means and then made into a steel ingot by a continuous casting method, or made into a steel ingot by any casting method and then made into a steel ingot by a method such as blooming. It is considered a piece.
  • the continuous casting process in order to suppress the occurrence of surface defects due to inclusions, it is preferable to cause the molten steel to undergo external additional flow such as electromagnetic stirring within the mold.
  • Steel ingots or billets may be once cooled and then reheated and subjected to hot rolling, or steel ingots in a high temperature state after continuous casting or steel billets in a high temperature state after blooming rolling may be used as they are.
  • the material may be subjected to hot rolling by keeping it warm or by performing auxiliary heating.
  • Such steel ingots and slabs are collectively referred to as "slabs" as materials for hot rolling.
  • the heating temperature of the slab subjected to hot rolling is preferably less than 1250°C, more preferably less than 1200°C, in order to prevent coarsening of austenite. Since rolling becomes difficult if the slab heating temperature is low, the slab heating temperature may be set to 1050° C. or higher.
  • Hot rolling is preferably completed in a temperature range of Ar 3 or higher in order to refine the metal structure of the hot rolled steel sheet by transforming austenite after rolling is completed.
  • the winding temperature is preferably less than 550°C. If the winding temperature is 550° C. or higher, thermally stable iron carbides are generated, which may deteriorate the collision resistance properties of the hot-stamped molded product. On the other hand, if the coiling temperature becomes too low, the hot rolled steel sheet will become excessively hard and it will be difficult to perform cold rolling, so the coiling temperature is preferably over 500°C.
  • the hot-rolled steel sheet that has been hot-rolled and wound up is pickled according to a conventional method, and then cold-rolled according to a conventional method to obtain a cold-rolled steel sheet.
  • the cumulative reduction rate in cold rolling is 40% or more. If the cumulative rolling reduction is less than 40%, the metal structure of the hot stamping steel sheet may become coarse. If the metal structure of the steel plate for hot stamping is coarse, the metal structure of the hot stamp molded body will become coarse after hot stamping, which will cause the collision resistance of the molded body to deteriorate.
  • the cumulative rolling reduction is preferably less than 70%. After cold rolling, treatments such as degreasing may be performed in a conventional manner.
  • a cold-rolled steel plate is annealed to become an annealed steel plate.
  • the soaking temperature be higher than 700°C. If the soaking temperature is 700° C. or lower, it may not be possible to preferably control the B concentration distribution in the surface layer region of the hot stamping steel sheet. As a result, it may not be possible to obtain desired collision resistance properties in the hot-stamped molded article.
  • the heating rate is too slow, the soaking temperature is too high, or the soaking time is too long, the metal structure of the annealed steel sheet will become coarse due to grain growth, and the collision resistance of the hot stamped product may deteriorate. There is. Therefore, it is preferable that the average heating rate up to the soaking temperature is 1°C/sec or more, the soaking temperature is preferably 800°C or less, and the soaking time (holding time at the soaking temperature) is less than 600 seconds.
  • the dew point of the atmosphere in the annealing furnace should be set to -20°C or higher and lower than 0°C, and the residence time in the temperature range of 700°C or higher and lower than (Ac 3 points -30°C) should be set to more than 360 seconds and less than 600 seconds. It is preferable to do so.
  • the atmosphere in the annealing furnace is preferably a nitrogen-hydrogen atmosphere containing 1% by volume or more and less than 4% by volume of hydrogen.
  • the dew point is less than -20°C or 0°C or more, or the residence time in the temperature range of 700°C or more and less than (Ac 3 points -30°C) is 360 seconds or less, B in the surface area of the hot stamping steel plate In some cases, it may not be possible to control the concentration distribution favorably. As a result, it may not be possible to obtain desired collision resistance properties in the hot-stamped molded article.
  • the residence time in the above temperature range is 600 seconds or more, excessive decarburization may occur in the hot stamping steel plate, and the strength of the hot stamped molded product may be insufficient after hot stamping.
  • the annealed steel sheet produced by the method described above may be plated according to a conventional method to obtain a plated steel sheet.
  • the annealed steel sheet or plated steel sheet thus obtained may be subjected to temper rolling according to a conventional method.
  • the Ac 3 point is the temperature at which ferrite disappears in the metal structure when the raw steel sheet is heated, and can be determined from the thermal expansion change when a cold rolled steel sheet is heated at a heating rate of 8°C/sec. can.
  • the hot stamping molded article according to the present embodiment includes a heating process of heating a hot stamping steel plate (annealed steel plate or plated steel plate) produced by the method described above, and a hot stamping process of hot stamping the heated steel plate for hot stamping. It can be obtained by a manufacturing method including a stamping step.
  • hot-stamping is preferably performed by the following method.
  • a hot stamping steel sheet having the above-described chemical composition and B concentration distribution in the thickness direction is heated.
  • a gas combustion furnace using a flammable gas containing propane gas to heat the hot stamping steel plate at an air ratio of 0.84 or less.
  • the heating temperature is higher than 950° C. and higher than 3 Ac points, and the holding time at the heating temperature is higher than 360 seconds.
  • the air ratio is the ratio (A/A 0 ) of the amount of air (A) actually introduced to the theoretical amount of air (A 0 ).
  • the Ac 3 points in the heating process means the Ac 3 points of the inner layer region of the hot stamping steel sheet, and may be the same value as the Ac 3 points of the cold rolled steel sheet determined by the above method.
  • the heating temperature is 950°C or less, or the holding time is 360 seconds or less, the B concentration distribution and O concentration distribution in the surface layer region and the outermost layer region of the hot stamp molded article In some cases, it may not be possible to control the Moreover, if the heating temperature is 3 points or less of Ac, the volume fraction of martensite may be insufficient in the metal structure of the inner layer region of the hot-stamped molded product, and the strength of the hot-stamped molded product may decrease. On the other hand, if the heating temperature is too high or the holding time at the heating temperature is too long, the metal structure of the hot stamped product will become coarser, which will reduce the collision resistance of the hot stamped product and reduce its strength. There is. Therefore, the heating temperature is preferably less than 1050°C, and the holding time is preferably less than 600 seconds.
  • the hot stamping step it is preferable to take out the heated steel plate for hot stamping from the heating furnace and allow it to cool in the atmosphere, and then start hot stamping in a temperature range of over 750°C. If the starting temperature of hot stamping is 750° C. or lower, ferrite may be excessively produced in the metal structure of the inner layer region of the hot stamped body, and the strength of the hot stamped body may decrease.
  • the hot stamp molded product is cooled while being held in a mold, and/or the hot stamp molded product is taken out from the mold and cooled by an arbitrary method.
  • the average cooling rate from the hot stamping start temperature to 400°C is preferably 30°C/second or more, 60°C/second or more, or 90°C/second or more.
  • the cooling stop temperature by the above-mentioned cooling is less than 90°C.
  • a hot stamp molded article according to the present embodiment is obtained.
  • reheating treatment may be performed as long as the strength of the hot stamp molded product is ensured.
  • the heating temperature is preferably lower than (Ac 3 point - 100°C). If the heating temperature of the reheating treatment is (Ac 3 points - 100°C) or higher, the surface layer region and the outermost layer region of the hot stamped molded product will not be sufficiently softened, and the collision resistance properties of the hot stamped molded product will deteriorate. There are cases.
  • a portion of the hot stamp molded body may be reheated by laser irradiation or the like to provide a partially softened region. Further, the hot stamp molded body may be subjected to blasting treatment, or may be subjected to painting and baking treatment.
  • the conditions in the example are examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is based on this example of conditions. It is not limited.
  • 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.
  • a steel material having the chemical composition shown in Table 1 was obtained by casting molten steel using a vacuum melting furnace.
  • the obtained steel material was heated to 1200° C. and held for 60 minutes, and then hot rolled for 10 passes in a temperature range of 900° C. or higher to obtain a hot rolled steel plate with a thickness of 3.5 mm.
  • the hot rolled steel sheet was cooled to 540° C. with water spray.
  • the cooling end temperature was defined as the coiling temperature, and the hot rolled steel sheet was charged into an electric heating furnace maintained at this coiling temperature and maintained for 60 minutes. Thereafter, the hot rolled steel sheet was furnace cooled to room temperature at an average cooling rate of 20° C./hour to simulate slow cooling after winding.
  • the cumulative reduction rate during cold rolling was 60%.
  • the obtained cold rolled steel sheets were annealed using a continuous annealing simulator under the annealing conditions shown in Table 2A and Table 2B. Note that heating was performed at an average heating rate of 8° C./sec to the soaking temperature shown in Table 2A and Table 2B.
  • the atmosphere in the annealing furnace was a nitrogen-hydrogen atmosphere containing 3% by volume of hydrogen, and the dew points were as shown in Tables 2A and 2B.
  • an annealed steel plate (a steel plate for hot stamping) was obtained by cooling to room temperature.
  • Test pieces for GDS analysis were taken from three locations on the obtained steel plate for hot stamping, the surface of the test piece was used as the measurement starting surface, and GDS was performed from the measurement starting surface to a depth of 120 ⁇ m in the sheet thickness direction using the method described above. Analysis was carried out. As a result, the average B concentration in a region (surface layer region) from 5.0 ⁇ m deep to 25.0 ⁇ m deep from the surface of the hot stamping steel plate and the B concentration at a position 100 ⁇ m deep from the surface were obtained. The number of measurement points from the surface of the steel plate to a depth of 100 ⁇ m was 1500 points. The results obtained are shown in Table 2.
  • a blank plate for hot stamping with a width of 240 mm and a length of 800 mm is taken from the obtained steel plate for hot stamping, and hot stamping is performed to obtain a hat member (hot stamp molded body) having the shape shown in Fig. 1. Ta.
  • the hot stamping blanks were heated under the conditions shown in Table 3 using a gas combustion furnace. Specifically, propane gas was used as the combustion gas, and the heating temperature, holding time, and air ratio were as shown in Table 3. Thereafter, the blank for hot stamping was taken out from the heating furnace and allowed to cool, and then placed between molds equipped with a cooling device, and hat molding was performed at a molding start temperature of 770° C. or higher.
  • the average cooling rate from the molding start temperature to 400°C was set to 50°C/sec or more, and the mold was cooled to a cooling stop temperature of 80°C or less.
  • oxide scale iron oxide generated on the surface of the hat member was removed by shot blasting.
  • test piece was taken from the vertical wall of the obtained hat member, and its chemical composition was measured by the method described above.
  • a No. 13B plate-shaped test piece shall be taken from the vertical wall portion of the hat member along the longitudinal direction of the hat member in accordance with JIS Z 2241:2011, and a tensile test shall be conducted at a tensile speed of 10 mm/min.
  • the tensile strength was determined. When the obtained tensile strength was 1900 MPa or more, it was determined that the product had high strength and passed. On the other hand, when the obtained tensile strength was less than 1900 MPa, it was determined that the product did not have high strength and was rejected.
  • test pieces for GDS analysis were taken from three locations on the vertical wall of the hat member, and using the surface of the test piece as the measurement starting surface, the method described above was carried out to a depth of 120 ⁇ m in the thickness direction from the measurement starting surface. GDS analysis was performed. As a result, the average B concentration in the region from 5.0 ⁇ m depth to 25.0 ⁇ m depth from the surface (surface layer region), and the average B concentration in the region from 0.5 ⁇ m depth to 4.0 ⁇ m depth from the surface (surface layer region). ), and the B concentration at a depth of 100 ⁇ m from the surface were determined. The number of measurement points from the surface of the steel plate to a depth of 100 ⁇ m was 1500 points.
  • test piece for tissue observation was taken from the vertical wall of the hat member, and after polishing the longitudinal section of this test piece, the area from 0.5 ⁇ m deep to 4.0 ⁇ m deep from the surface was prepared using the method described above. (the outermost layer region) and the metal structure at a depth of 100 ⁇ m from the surface to 1/2 the plate thickness (inner layer region) were observed.
  • a test specimen for a three-point bending test was obtained by welding a closing plate with a thickness of 1.4 mm, a width of 130 mm, and a length of 800 mm to the hat member.
  • a steel plate having a tensile strength of 1553 MPa was used for the closing plate.
  • the test specimen with a length of 800 mm was placed on two supporting rolls arranged with a roll interval of 700 mm, with the closing plate facing downward, and the specimen was rolled at a speed of 2 m/min.
  • a three-point bending test was conducted at a test speed of seconds.
  • the maximum load and the displacement from when the test piece and the impactor came into contact until the test piece started to crack were determined. If the tensile strength of the steel plate constituting the hot-stamped compact is less than 2300 MPa, the maximum load is 18.0 kN or more, and the displacement at which cracking occurs is 50 mm or more. It was judged as passing the test.
  • the tensile strength is 2300 MPa or more
  • the maximum load is 23.0 kN or more
  • the cracking displacement is 35 mm or more
  • Tables 4A and 4B show the results of measuring the chemical composition of the hot-stamped molded product, the results of measuring the mechanical properties of the hot-stamped molded product, the results of measuring the B and O concentration distribution in the hot-stamped molded product, and the results of measuring the hot-stamped molded product.
  • the results of evaluating the collision resistance properties of the molded body are shown. Note that the contents of the elements other than C in the hot-stamped molded body were omitted because they were the same as the contents of the elements shown in Table 1.
  • the hot-stamped molded article according to the example of the present invention had a tensile strength of 1900 MPa or more, and had high strength. Further, the average B concentration in the surface layer region was low, the average B concentration and the average O concentration in the outermost layer region were high, and the collision resistance was excellent.
  • the volume fraction of martensite in the inner layer region was 91.0% or more, and the total volume fraction of structures other than martensite was 9.0% or less. . Further, in the outermost layer region, the volume fraction of ferrite was 6.0% or more, and the total volume fraction of structures other than ferrite was 94.0% or less.
  • test number 15 the C content was too high, so the cracking displacement of the hot-stamped molded product was low and the crash resistance was poor.
  • early breakage occurred and the tensile strength could not be determined, and the breaking strength was less than 1900 MPa.
  • test number 16 the B content was too low, so the tensile strength of the hot-stamped molded product was less than 1900 MPa, resulting in poor strength. Furthermore, the average B concentration and average O concentration in the outermost layer region were low, and the maximum load and crack initiation displacement were low, resulting in poor collision resistance.
  • the chemical composition of the hot-stamped molded product was within the preferred range, but the comparative example test numbers 3, 4, 7, 8, 10, 11, 13, 14, 24, 25, and 27 had manufacturing conditions outside the preferred range. , the average B concentration in the surface layer region, the average B concentration in the outermost layer region, and the average O concentration in the outermost layer region were out of the invention range. Therefore, the cracking displacement of the hot-stamped molded body was low, or the maximum load and cracking displacement were low, resulting in poor collision resistance.

Abstract

This hot-stamp formed article comprises a steel sheet. The steel sheet has a prescribed chemical composition. In the steel sheet, the average B-concentration in a region between a depth of 5.0 μm from the surface and a depth of 25.0 μm from the surface is at most 0.700 times the B-concentration in a position at a depth of 100 μm from the surface. The average B-concentration in a region between a depth of 0.5 μm from the surface and a depth of 4.0 μm from the surface is at least 1.600 times the B-concentration in a position at a depth of 100 μm from the surface. The average O-concentration in said region between a depth of 0.5 μm from the surface and a depth of 4.0 μm from the surface is more than 0.0150 mass%.

Description

ホットスタンプ成形体hot stamp molded body
　本発明は、ホットスタンプ成形体に関する。
　本願は、２０２２年４月１４日に、日本に出願された特願２０２２－０６７０２６号に基づき優先権を主張し、その内容をここに援用する。 The present invention relates to a hot stamp molded article.
This application claims priority based on Japanese Patent Application No. 2022-067026 filed in Japan on April 14, 2022, the contents of which are incorporated herein.
　近年、環境保護及び省資源化の観点から自動車車体の軽量化が求められており、自動車部材へ高強度鋼板が適用されている。高強度鋼板を適用した場合、鋼板の板厚を薄くして車体を軽量化しながら、所望の強度を車体に付与することができる。自動車部材は鋼板をプレス成形することによって製造されるが、鋼板の高強度化に伴い成形荷重が増加するだけでなく、成形性が低下して割れやしわが発生しやすくなる。また、高強度鋼板をプレス成形すると、部材を金型から取り出した際にスプリングバックにより部材の形状が大きく変化するので、部材の寸法精度を確保することが困難となる。このように、プレス成形により高強度の車体部材を製造することは容易ではない。 In recent years, there has been a demand for lighter automobile bodies from the viewpoint of environmental protection and resource conservation, and high-strength steel plates are being applied to automobile parts. When high-strength steel plates are used, desired strength can be imparted to the vehicle body while reducing the thickness of the steel plate and reducing the weight of the vehicle body. Automotive parts are manufactured by press forming steel plates, but as the strength of the steel plates increases, not only does the forming load increase, but also the formability decreases, making cracks and wrinkles more likely to occur. Furthermore, when a high-strength steel plate is press-formed, the shape of the member changes significantly due to springback when the member is taken out of the mold, making it difficult to ensure the dimensional accuracy of the member. As described above, it is not easy to manufacture high-strength vehicle body members by press molding.
　上記のような課題を解決するため、これまでに、例えば特許文献１に開示されているように、加熱した鋼板を低温のプレス金型を用いてプレス成形する技術が提案されている。この技術はホットスタンプまたは熱間プレス等と呼ばれており、高温に加熱されて軟質な状態の鋼板をプレス成形するので、複雑な形状の部材を高い寸法精度で製造することができる。また、金型との接触により鋼板が急冷されるので、焼入れにより、プレス成形と同時に強度を大幅に高めることが可能となる。特許文献１には、引張強さが５００～６００ＭＰａである鋼板をホットスタンプすることで、引張強さが１４００ＭＰａ以上である部材が得られることが開示されている。 In order to solve the above problems, a technique has been proposed so far, as disclosed in Patent Document 1, for example, in which a heated steel plate is press-formed using a low-temperature press mold. This technique is called hot stamping or hot pressing, and because it press-forms a soft steel plate by heating it to a high temperature, it is possible to manufacture members with complex shapes with high dimensional accuracy. In addition, since the steel plate is rapidly cooled by contact with the mold, it is possible to significantly increase the strength by quenching at the same time as press forming. Patent Document 1 discloses that a member having a tensile strength of 1400 MPa or more can be obtained by hot stamping a steel plate having a tensile strength of 500 to 600 MPa.
　ホットスタンプ部材の強度は、鋼板のＣ含有量を高めることにより、さらに上昇させることができる。しかし、鋼板のＣ含有量を高めると、部材強度の上昇に伴い部材の変形能が低下し、衝突時に部材が変形する際、変形初期に割れが発生し易くなる。このように、優れた耐衝突特性を備えた高強度ホットスタンプ部材を製造することは容易ではなく、特に、部材の引張強さが１９００ＭＰａを超える場合、強度と耐衝突特性とを両立させることが困難となる。 The strength of the hot-stamped member can be further increased by increasing the C content of the steel plate. However, when the C content of the steel plate is increased, the deformability of the member decreases as the member strength increases, and when the member deforms during a collision, cracks are likely to occur in the initial stage of deformation. As described above, it is not easy to produce a high-strength hot-stamped member with excellent crash-resistance properties, and especially when the tensile strength of the member exceeds 1900 MPa, it is difficult to achieve both strength and crash-resistance properties. It becomes difficult.
　耐衝突特性に優れたホットスタンプ部材を製造する技術として、特許文献２には、引張強さが１３００ＭＰａ以上の強度を有し高い衝撃吸収性を備えた高強度ブレス部品およびその製造方法が開示されている。また、特許文献３には、引張強さが１１００ＭＰａ以上であり、衝撃エネルギー吸収の観点から部材の曲げ性を高めた自動車用ホットスタンプ部材およびその製造方法が開示されている。特許文献２および特許文献３に開示された方法では、表層部に脱炭層を備えたホットスタンプ用鋼板を所定の条件でホットスタンプし、ホットスタンプ部材の表層部に軟質層を形成することにより、部材の耐衝突特性を向上させている。 As a technology for manufacturing a hot stamped member with excellent collision resistance, Patent Document 2 discloses a high-strength brace component having a tensile strength of 1300 MPa or more and high shock absorption, and a method for manufacturing the same. ing. Further, Patent Document 3 discloses a hot stamping member for an automobile, which has a tensile strength of 1100 MPa or more and has improved bendability from the viewpoint of absorbing impact energy, and a method for manufacturing the same. In the methods disclosed in Patent Document 2 and Patent Document 3, a hot stamping steel plate having a decarburized layer on the surface layer is hot stamped under predetermined conditions to form a soft layer on the surface layer of the hot stamping member. This improves the collision resistance of the component.
日本国特開２００２－１０２９８０号公報Japanese Patent Application Publication No. 2002-102980 日本国特開２０１５－３０８９０号公報Japanese Patent Application Publication No. 2015-30890 国際公開第２０１８／１７９８３９号International Publication No. 2018/179839
　しかしながら、本発明者らの検討によると、表層部を脱炭した鋼板を用いてホットスタンプすると、ホットスタンプの加熱工程において、鋼板の内部から表層部へＣが流入して脱炭層のＣ濃度が上昇し、部材の表層部が軟質化せず、耐衝突特性が十分に向上しない場合があることが分かった。 However, according to studies conducted by the present inventors, when hot stamping is performed using a steel plate whose surface layer has been decarburized, C flows from the inside of the steel plate into the surface layer during the hot stamping heating process, and the C concentration in the decarburized layer decreases. It was found that there are cases where the surface layer of the member does not become soft and the collision resistance properties are not sufficiently improved.
　本発明は上記実情に鑑みてなされたものであり、引張強さが１９００ＭＰａ以上である高い強度および優れた耐衝突特性を有するホットスタンプ成形体を提供することを目的とする。 The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hot-stamped molded article having a high tensile strength of 1900 MPa or more and excellent collision resistance.
　本発明の要旨は以下の通りである。 The gist of the present invention is as follows.
（１）本発明の一態様に係るホットスタンプ成形体は、鋼板を備えるホットスタンプ成形体であって、前記鋼板の全部または一部は、化学組成が、質量％で、
Ｃ　：０．３２％超、０．７０％以下、
Ｓｉ：２．００％未満、
Ｍｎ：０．０１～３．００％、
Ｐ　：０．２００％以下、
Ｓ　：０．０２００％以下、
ｓｏｌ．Ａｌ：０．００１～１．０００％、
Ｎ　：０．０２００％以下、
Ｏ　：０．０００５～０．０２００％、
Ｂ　：０．０００５～０．０２００％、
Ｃｒ：０～２．００％、
Ｍｏ：０～２．００％、
Ｗ　：０～２．００％、
Ｃｕ：０～２．００％、
Ｎｉ：０～２．００％、
Ｔｉ：０～０．２００％、
Ｎｂ：０～０．２００％、
Ｖ　：０～０．２００％、
Ｚｒ：０～０．２００％、
Ｃａ：０～０．１０００％、
Ｍｇ：０～０．１０００％、
ＲＥＭ：０～０．１０００％、
Ｓｎ：０～０．２００％、
Ａｓ：０～０．１００％、および
Ｂｉ：０～０．０５００％を含有し、
　残部がＦｅおよび不純物からなり、
　引張強さが１９００ＭＰａ以上であり、
　前記鋼板の表面から５．０μｍ深さ～前記表面から２５．０μｍ深さの領域における平均Ｂ濃度が、前記表面から１００μｍ深さの位置におけるＢ濃度の０．７００倍以下であり、
　前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの領域における平均Ｂ濃度が、前記表面から１００μｍ深さの前記位置における前記Ｂ濃度の１．６００倍以上であり、
　前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの前記領域における平均Ｏ濃度が、０．０１５０質量％超である。
（２）上記（１）に記載のホットスタンプ成形体は、前記化学組成が、質量％で、
Ｃｒ：０．０１～２．００％、
Ｍｏ：０．０１～２．００％、
Ｗ　：０．０１～２．００％、
Ｃｕ：０．０１～２．００％、
Ｎｉ：０．０１～２．００％、
Ｔｉ：０．００１～０．２００％、
Ｎｂ：０．００１～０．２００％、
Ｖ　：０．００１～０．２００％、
Ｚｒ：０．００１～０．２００％、
Ｃａ：０．０００１～０．１０００％、
Ｍｇ：０．０００１～０．１０００％、
ＲＥＭ：０．０００１～０．１０００％、
Ｓｎ：０．００１～０．２００％、
Ａｓ：０．００１～０．１００％、および
Ｂｉ：０．０００１～０．０５００％
からなる群のうち１種または２種以上を含有してもよい。 (1) A hot-stamped molded body according to one aspect of the present invention is a hot-stamped molded body that includes a steel plate, and all or part of the steel plate has a chemical composition in mass %,
C: more than 0.32%, less than 0.70%,
Si: less than 2.00%,
Mn: 0.01 to 3.00%,
P: 0.200% or less,
S: 0.0200% or less,
sol. Al: 0.001-1.000%,
N: 0.0200% or less,
O: 0.0005 to 0.0200%,
B: 0.0005-0.0200%,
Cr: 0-2.00%,
Mo: 0-2.00%,
W: 0-2.00%,
Cu: 0-2.00%,
Ni: 0-2.00%,
Ti: 0-0.200%,
Nb: 0 to 0.200%,
V: 0 to 0.200%,
Zr: 0-0.200%,
Ca: 0-0.1000%,
Mg: 0 to 0.1000%,
REM: 0-0.1000%,
Sn: 0-0.200%,
Contains As: 0 to 0.100% and Bi: 0 to 0.0500%,
The remainder consists of Fe and impurities,
The tensile strength is 1900 MPa or more,
The average B concentration in a region from a depth of 5.0 μm to a depth of 25.0 μm from the surface of the steel plate is 0.700 times or less of the B concentration at a position 100 μm deep from the surface,
The average B concentration in a region from a depth of 0.5 μm to a depth of 4.0 μm from the surface is 1.600 times or more of the B concentration at the position 100 μm deep from the surface,
The average O concentration in the region from a depth of 0.5 μm to a depth of 4.0 μm from the surface is more than 0.0150% by mass.
(2) The hot-stamped molded article according to (1) above has the chemical composition in mass %,
Cr: 0.01-2.00%,
Mo: 0.01-2.00%,
W: 0.01-2.00%,
Cu: 0.01-2.00%,
Ni: 0.01-2.00%,
Ti: 0.001 to 0.200%,
Nb: 0.001-0.200%,
V: 0.001-0.200%,
Zr: 0.001 to 0.200%,
Ca: 0.0001-0.1000%,
Mg: 0.0001-0.1000%,
REM: 0.0001-0.1000%,
Sn: 0.001-0.200%,
As: 0.001 to 0.100%, and Bi: 0.0001 to 0.0500%
It may contain one or more types from the group consisting of.
　本発明に係る上記態様によれば、引張強さが１９００ＭＰａ以上の高い強度および優れた耐衝突特性を有するホットスタンプ成形体を提供することができる。上記態様に係るホットスタンプ成形体は、耐衝突特性に優れ、衝突時の変形初期に割れが生じることが無いため、ピラーやバンパーなどの自動車部材に好適に適用することができる。 According to the above aspect of the present invention, it is possible to provide a hot-stamped molded article having a high tensile strength of 1900 MPa or more and excellent collision resistance. The hot-stamped molded article according to the above aspect has excellent collision resistance properties and does not crack at the initial stage of deformation during a collision, so it can be suitably applied to automobile parts such as pillars and bumpers.
実施例で製造したハット部材を示す図。The figure which shows the hat member manufactured in the Example. 実施例で製造した３点曲げ試験用の試験体を示す図。FIG. 3 is a diagram showing a test specimen for a three-point bending test manufactured in an example. 実施例で行った３点曲げ試験を説明するための図。FIG. 3 is a diagram for explaining a three-point bending test conducted in an example.
　本発明者らは、引張強さが１９００ＭＰａ以上であるホットスタンプ成形体について、衝突時の変形初期の割れの発生を抑制する方法について検討した結果、以下の知見を得た。 The present inventors studied a method for suppressing the occurrence of cracks at the initial stage of deformation during a collision for a hot-stamped molded body having a tensile strength of 1900 MPa or more, and as a result, obtained the following knowledge.
（Ａ）ホットスタンプ成形体の表層部を軟質化することにより、ホットスタンプ成形体の耐衝突特性が向上する。 (A) By softening the surface layer portion of the hot-stamped molded product, the collision resistance properties of the hot-stamped molded product are improved.
（Ｂ）ホットスタンプ成形体の表層部を軟質化するためには、表層部に脱炭層を備えたホットスタンプ用鋼板を用いてホットスタンプすることが有効である。しかし、ホットスタンプ用鋼板を加熱する過程で鋼板の内部から表層部へＣが拡散してしまい、表層部のＣ濃度が上昇する現象（復炭現象という）が起こる。そのため、ホットスタンプ成形体の表層部が十分に軟質化せず、ホットスタンプ成形体の耐衝突特性を十分に高めることができない場合がある。 (B) In order to soften the surface layer of the hot-stamped molded product, it is effective to hot-stampe using a hot-stamping steel plate having a decarburized layer on the surface layer. However, in the process of heating a steel plate for hot stamping, C diffuses from the inside of the steel plate to the surface layer, and a phenomenon (referred to as recarburization phenomenon) occurs in which the C concentration in the surface layer increases. Therefore, the surface layer portion of the hot-stamped molded product may not be sufficiently softened, and the collision resistance properties of the hot-stamped molded product may not be sufficiently improved.
（Ｃ）ホットスタンプ成形体において、（ａ）ホットスタンプ成形体を構成する鋼板の表面から５．０μｍ深さ～前記表面から２５．０μｍ深さの領域の平均Ｂ濃度を低くすること、（ｂ）前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの領域の平均Ｂ濃度を高めること、（ｃ）前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの前記領域の平均Ｏ濃度を高めることにより、ホットスタンプの加熱過程で復炭現象が生じても、ホットスタンプ成形体の耐衝突特性を向上させることができる。 (C) In the hot-stamped compact, (a) lowering the average B concentration in a region from a depth of 5.0 μm to a depth of 25.0 μm from the surface of the steel plate constituting the hot-stamped compact; (b) ) increasing the average B concentration in a region from 0.5 μm deep to 4.0 μm deep from the surface; (c) increasing the average B concentration in a region from 0.5 μm deep to 4.0 μm deep from the surface; By increasing the average O concentration in the region, it is possible to improve the collision resistance of the hot-stamped molded body even if a recarburization phenomenon occurs during the hot-stamping heating process.
（Ｄ）この理由は明らかではないが、（ａ）ホットスタンプ成形体を構成する鋼板の表面から５．０μｍ深さ～前記表面から２５．０μｍ深さの領域では、平均Ｂ濃度の低下により鋼板の焼入れ性が低下すること、および（ｂ）前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの領域では、ＢとＯとが結合して鋼板の焼入れ性が低下することで、復炭現象によりホットスタンプ成形体の表層部のＣ濃度が上昇していても、表層部が軟質化するためであると推定される。 (D) Although the reason for this is not clear, (a) In the region from 5.0 μm deep to 25.0 μm deep from the surface of the steel plate constituting the hot stamped body, the average B concentration decreases, causing the steel plate to (b) In the region from 0.5 μm depth to 4.0 μm depth from the surface, B and O combine and the hardenability of the steel sheet decreases. This is presumed to be because even though the C concentration in the surface layer of the hot-stamped compact increases due to the recarburization phenomenon, the surface layer becomes soft.
　上記（Ａ）～（Ｄ）の知見から、本発明者らは、ホットスタンプ成形体の表層部（後述する表層領域および最表層領域を含む）において、Ｂ濃度およびＯ濃度を特定の範囲に調整することにより、引張強さが１９００ＭＰａ以上であり、耐衝突特性に優れたホットスタンプ成形体が得られることを見出した。
　以下、本実施形態に係るホットスタンプ成形体について詳細に説明する。まず、本実施形態に係るホットスタンプ成形体を構成する鋼板の化学組成の限定理由について説明する。 Based on the findings of (A) to (D) above, the present inventors adjusted the B concentration and O concentration to a specific range in the surface layer region (including the surface layer region and the outermost layer region described below) of the hot stamp molded product. It has been found that by doing so, a hot-stamped molded article having a tensile strength of 1900 MPa or more and excellent collision resistance can be obtained.
Hereinafter, the hot stamp molded article according to this embodiment will be described in detail. First, the reason for limiting the chemical composition of the steel plate constituting the hot-stamped molded body according to the present embodiment will be explained.
　本実施形態に係るホットスタンプ成形体が備える鋼板の全部または一部は、以下の化学組成を有する。ホットスタンプ成形体が鋼板のみからなる場合には、ホットスタンプ成形体の全部または一部が以下に示す化学組成を有すると言える。
　なお、以下に記載する「～」を挟んで記載される数値限定範囲には、下限値および上限値がその範囲に含まれる。「未満」、「超」と示す数値には、その値が数値範囲に含まれない。化学組成についての％は全て質量％を示す。 All or part of the steel plate included in the hot-stamped molded body according to the present embodiment has the following chemical composition. When the hot-stamped molded body is made of only a steel plate, it can be said that all or part of the hot-stamped molded body has the chemical composition shown below.
Note that the numerically limited range described below with "~" in between includes the lower limit value and the upper limit value. Numerical values indicated as "less than" or "greater than" do not include the value within the numerical range. All percentages regarding chemical composition indicate mass %.
　ホットスタンプ成形体が、１９００ＭＰａ以上の引張強さを有する部分と、１９００ＭＰａ未満の引張強さを有する部分とを備えている場合、少なくとも引張強さが１９００ＭＰａ以上となる部分が以下の化学組成を有していればよい。 When the hot stamped molded article includes a part having a tensile strength of 1900 MPa or more and a part having a tensile strength of less than 1900 MPa, at least the part having a tensile strength of 1900 MPa or more has the following chemical composition. All you have to do is do it.
　本実施形態に係るホットスタンプ成形体が備える鋼板の全部または一部は、化学組成が、質量％で、Ｃ：０．３２％超、０．７０％以下、Ｓｉ：２．００％未満、Ｍｎ：０．０１～３．００％、Ｐ：０．２００％以下、Ｓ：０．０２００％以下、ｓｏｌ．Ａｌ：０．００１～１．０００％、Ｎ：０．０２００％以下、Ｏ：０．０００５～０．０２００％、Ｂ：０．０００５～０．０２００％、並びに、残部：Ｆｅおよび不純物を含む。
　以下、各元素について説明する。 All or part of the steel plate included in the hot-stamped molded body according to the present embodiment has a chemical composition, in mass %, of C: more than 0.32% and 0.70% or less, Si: less than 2.00%, and Mn. : 0.01 to 3.00%, P: 0.200% or less, S: 0.0200% or less, sol. Al: 0.001 to 1.000%, N: 0.0200% or less, O: 0.0005 to 0.0200%, B: 0.0005 to 0.0200%, and balance: Contains Fe and impurities. .
Each element will be explained below.
　Ｃ：０．３２％超、０．７０％以下
　Ｃは、ホットスタンプ後の鋼板（ホットスタンプ成形体を構成する鋼板）の引張強さを向上させる元素である。Ｃ含有量が０．３２％以下では、ホットスタンプ後の鋼板の引張強さが１９００ＭＰａ未満となりホットスタンプ成形体の強度が不足する。また、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｃ含有量は０．３２％超とする。Ｃ含有量は、好ましくは０．３４％超、０．３８％超、０．４２％超、または０．４５％超である。
　一方、Ｃ含有量が０．７０％超では、ホットスタンプ成形体の強度が高くなりすぎ、優れた耐衝突特性を得ることができない。そのため、Ｃ含有量は０．７０％以下とする。好ましくは、Ｃ含有量は、０．６５％以下、０．６０％以下、０．５５％以下または０．５０％以下である。 C: More than 0.32%, 0.70% or less C is an element that improves the tensile strength of the steel plate after hot stamping (the steel plate that constitutes the hot stamped body). If the C content is 0.32% or less, the tensile strength of the steel plate after hot stamping will be less than 1900 MPa, resulting in insufficient strength of the hot stamped product. Moreover, the collision resistance properties of the hot stamped molded body deteriorate. Therefore, the C content is set to more than 0.32%. The C content is preferably greater than 0.34%, greater than 0.38%, greater than 0.42%, or greater than 0.45%.
On the other hand, if the C content exceeds 0.70%, the strength of the hot-stamped molded product becomes too high, making it impossible to obtain excellent collision resistance. Therefore, the C content is set to 0.70% or less. Preferably, the C content is 0.65% or less, 0.60% or less, 0.55% or less or 0.50% or less.
　Ｓｉ：２．００％未満
　Ｓｉは、鋼中に不純物として含有される場合があり、鋼を脆化させる元素である。Ｓｉ含有量が２．００％を超えるとその悪影響が特に大きくなる。そのため、Ｓｉ含有量は２．００％未満とする。Ｓｉ含有量は、好ましくは１．００％未満、０．７５％未満、０．５０％未満または０．２０％未満である。
　Ｓｉ含有量の下限は特に限定しないが、０％であってもよい。Ｓｉ含有量を過度に低下させることは製鋼コストの上昇を引き起こすため、Ｓｉ含有量は０．００１％以上とすることが好ましい。また、Ｓｉは、鋼の焼入れ性を高める作用を有するので、積極的に含有させてもよい。焼入れ性向上の観点からは、Ｓｉ含有量は０．０５％以上、０．１０％以上または０．１５％以上であることが好ましい。 Si: less than 2.00% Si is an element that may be contained as an impurity in steel and makes the steel brittle. When the Si content exceeds 2.00%, its adverse effects become particularly large. Therefore, the Si content is made less than 2.00%. The Si content is preferably less than 1.00%, less than 0.75%, less than 0.50% or less than 0.20%.
The lower limit of the Si content is not particularly limited, but may be 0%. Since excessively lowering the Si content causes an increase in steel manufacturing costs, the Si content is preferably 0.001% or more. Further, since Si has the effect of improving the hardenability of steel, it may be actively included. From the viewpoint of improving hardenability, the Si content is preferably 0.05% or more, 0.10% or more, or 0.15% or more.
　Ｍｎ：０．０１～３．００％
　Ｍｎは、不純物であるＳと結合してＭｎＳを形成し、Ｓによる弊害を抑制する作用を有する元素である。Ｍｎ含有量が０．０１％未満であると上記効果を得ることができない。そのため、Ｍｎ含有量は０．０１％以上とする。また、Ｍｎは、鋼の焼入れ性を向上させる元素であり、ホットスタンプ後の鋼板の内部において、マルテンサイトを主体とする金属組織を形成し、ホットスタンプ成形体の強度を確保するために有効な元素である。強度確保の観点からは、Ｍｎ含有量は、好ましくは０．５０％以上、０．７５％以上、１．００％以上または１．２５％以上である。
　一方、Ｍｎ含有量が３．００％超では、ホットスタンプ成形体において優れた耐衝突特性を得ることができない。そのため、Ｍｎ含有量は３．００％以下とする。Ｍｎ含有量は、好ましくは２．５０％以下、２．００％以下または１．５０％以下である。 Mn: 0.01-3.00%
Mn is an element that combines with S, which is an impurity, to form MnS and has the effect of suppressing the harmful effects of S. If the Mn content is less than 0.01%, the above effects cannot be obtained. Therefore, the Mn content is set to 0.01% or more. In addition, Mn is an element that improves the hardenability of steel, and forms a metal structure mainly composed of martensite inside the steel sheet after hot stamping, which is effective for ensuring the strength of the hot stamped product. It is an element. From the viewpoint of ensuring strength, the Mn content is preferably 0.50% or more, 0.75% or more, 1.00% or more, or 1.25% or more.
On the other hand, if the Mn content exceeds 3.00%, excellent collision resistance properties cannot be obtained in the hot-stamped molded article. Therefore, the Mn content is set to 3.00% or less. The Mn content is preferably 2.50% or less, 2.00% or less, or 1.50% or less.
　Ｐ：０．２００％以下
　Ｐは、鋼中に不純物として含有される場合があり、鋼を脆化させる元素である。Ｐ含有量が０．２００％を超えるとその悪影響が特に大きくなり、さらに溶接性も著しく劣化する。そのため、Ｐ含有量は０．２００％以下とする。Ｐ含有量は、好ましくは０．１００％未満、０．０５０％未満または０．０２０％未満である。
　Ｐ含有量は０％であってもよいが、Ｐ含有量を０．００１％未満に低減すると脱Ｐコストが大幅に上昇し、経済的に好ましくないため、０．００１％以上または０．００５％以上としてもよい。 P: 0.200% or less P is an element that may be contained as an impurity in steel and makes the steel brittle. If the P content exceeds 0.200%, the adverse effects will be particularly large, and weldability will also deteriorate significantly. Therefore, the P content is set to 0.200% or less. The P content is preferably less than 0.100%, less than 0.050% or less than 0.020%.
The P content may be 0%, but if the P content is reduced to less than 0.001%, the cost of removing P will increase significantly, which is economically unfavorable. % or more.
　Ｓ：０．０２００％以下
　Ｓは、鋼中に不純物として含有される場合があり、鋼を脆化させる元素である。Ｓ含有量が０．０２００％を超えるとその悪影響が特に大きくなる。そのため、Ｓ含有量は０．０２００％以下とする。Ｓ含有量は、好ましくは０．００５０％未満、０．００２０％未満または０．００１０％未満である。
　Ｓ含有量は０％であってもよいが、Ｓ含有量を０．０００１％未満に低減すると脱Ｓコストが大幅に上昇し、経済的に好ましくないため、０．０００１％以上または０．０００２％以上としてもよい。 S: 0.0200% or less S is an element that may be contained as an impurity in steel and makes the steel brittle. When the S content exceeds 0.0200%, the adverse effects become particularly large. Therefore, the S content is set to 0.0200% or less. The S content is preferably less than 0.0050%, less than 0.0020% or less than 0.0010%.
The S content may be 0%, but if the S content is reduced to less than 0.0001%, the S removal cost will increase significantly and it is economically unfavorable. % or more.
　ｓｏｌ．Ａｌ：０．００１～１．０００％
　Ａｌは、溶鋼を脱酸する作用を有する元素である。ｓｏｌ．Ａｌ含有量（酸可溶Ａｌ含有量）が０．００１％未満であると脱酸が不十分となる。そのため、ｓｏｌ．Ａｌ含有量は０．００１％以上とする。ｓｏｌ．Ａｌ含有量は、好ましくは０．００５％以上、０．０１０％以上または０．０２０％以上である。
　一方、ｓｏｌ．Ａｌ含有量が高すぎると、変態点が上昇することで、ホットスタンプの加熱工程でＡｃ３点を超える温度に鋼板を加熱することが困難となる。また、ホットスタンプ成形体の強度および耐衝突特性が劣化する。そのため、ｓｏｌ．Ａｌ含有量は１．０００％以下とする。ｓｏｌ．Ａｌ含有量は好ましくは０．５００％未満、０．１００％未満、０．０６０％未満または０．０４０％未満である。 sol. Al: 0.001-1.000%
Al is an element that has the effect of deoxidizing molten steel. sol. If the Al content (acid-soluble Al content) is less than 0.001%, deoxidation will be insufficient. Therefore, sol. Al content shall be 0.001% or more. sol. The Al content is preferably 0.005% or more, 0.010% or more, or 0.020% or more.
On the other hand, sol. If the Al content is too high, the transformation point will rise, making it difficult to heat the steel plate to a temperature exceeding Ac 3 in the hot stamping heating process. In addition, the strength and collision resistance of the hot stamped body deteriorate. Therefore, sol. Al content shall be 1.000% or less. sol. The Al content is preferably less than 0.500%, less than 0.100%, less than 0.060% or less than 0.040%.
　Ｎ：０．０２００％以下
　Ｎは、鋼中に不純物として含有される場合があり、鋼の連続鋳造中に窒化物を形成する元素である。この窒化物はホットスタンプ後の鋼板の延性を劣化させるので、Ｎ含有量は低い方が好ましい。Ｎ含有量が０．０２００％超であると、その悪影響が特に大きくなる。そのため、Ｎ含有量は０．０２００％以下とする。Ｎ含有量は、好ましくは０．０１００％未満、０．００８０％未満、または０．００５０％未満である。
　Ｎ含有量は０％であってもよいが、Ｎ含有量を過度に低減すると脱Ｎコストが大幅に上昇し、経済的に好ましくないため、０．０００５％以上、０．００１０％以上または０．００２０％以上としてもよい。 N: 0.0200% or less N is an element that may be contained as an impurity in steel and forms nitrides during continuous casting of steel. Since this nitride deteriorates the ductility of the steel sheet after hot stamping, it is preferable that the N content is low. If the N content exceeds 0.0200%, its adverse effects will be particularly large. Therefore, the N content is set to 0.0200% or less. The N content is preferably less than 0.0100%, less than 0.0080%, or less than 0.0050%.
The N content may be 0%, but if the N content is reduced excessively, the cost of removing N will increase significantly and it is economically unfavorable. It may be .0020% or more.
　Ｏ：０．０００５～０．０２００％
　Ｏは、Ｂと結合することでＢ酸化物を形成し、鋼の焼入れ性を低下させる元素であり、ホットスタンプ後の鋼板の表層部を軟質化するために有効な元素である。Ｏ含有量が０．０００５％未満であると、ホットスタンプ後の鋼板の表層部が軟質化せず、ホットスタンプ成形体において耐衝突特性が劣化する。そのため、Ｏ含有量は０．０００５％以上とする。Ｏ含有量は、好ましくは０．００１０％以上、０．００１５％以上または０．００２０％以上である。
　一方、Ｏ含有量が０．０２００％超であると、鋼中に粗大な酸化物系介在物が多量に形成される。これにより、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｏ含有量は０．０２００％以下とする。Ｏ含有量は、好ましくは０．０１５０％以下、０．０１００％以下、０．００６０％以下または０．００４０％以下である。 O: 0.0005-0.0200%
O is an element that forms B oxide by combining with B and reduces the hardenability of steel, and is an effective element for softening the surface layer of a steel sheet after hot stamping. If the O content is less than 0.0005%, the surface layer of the hot-stamped steel sheet will not become soft, and the collision resistance of the hot-stamped product will deteriorate. Therefore, the O content is set to 0.0005% or more. The O content is preferably 0.0010% or more, 0.0015% or more, or 0.0020% or more.
On the other hand, if the O content exceeds 0.0200%, a large amount of coarse oxide inclusions are formed in the steel. This deteriorates the collision resistance properties of the hot stamp molded body. Therefore, the O content is set to 0.0200% or less. The O content is preferably 0.0150% or less, 0.0100% or less, 0.0060% or less, or 0.0040% or less.
　Ｂ：０．０００５～０．０２００％
　Ｂは、鋼の焼入れ性を向上させる元素であり、ホットスタンプ後の鋼板の内部において、マルテンサイトを主体とする金属組織を形成し、ホットスタンプ成形体の強度を確保するために有効な元素である。Ｂ含有量が０．０００５％未満であると、ホットスタンプ成形体において所望の強度を得ることができない。また、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｂ含有量は０．０００５％以上とする。Ｂ含有量は、好ましくは０．００１０％以上、０．００１５％以上または０．００２０％以上である。
　一方、Ｂ含有量が０．０２００％超であると、ホットスタンプ成形体において炭硼化物が形成され、Ｂの焼入れ性向上効果が損なわれる。そのため、Ｂ含有量は０．０２００％以下とする。Ｂ含有量は、好ましくは０．００５０％未満、０．００４０％未満または０．００３０％未満である。 B: 0.0005-0.0200%
B is an element that improves the hardenability of steel, and is an effective element for forming a metal structure mainly composed of martensite inside the steel plate after hot stamping, and ensuring the strength of the hot stamped product. be. If the B content is less than 0.0005%, the desired strength cannot be obtained in the hot stamp molded product. Moreover, the collision resistance properties of the hot stamped molded body deteriorate. Therefore, the B content is set to 0.0005% or more. The B content is preferably 0.0010% or more, 0.0015% or more, or 0.0020% or more.
On the other hand, if the B content exceeds 0.0200%, carborides are formed in the hot-stamped compact, and the hardenability improvement effect of B is impaired. Therefore, the B content is set to 0.0200% or less. The B content is preferably less than 0.0050%, less than 0.0040% or less than 0.0030%.
　本実施形態に係るホットスタンプ成形体を構成する鋼板の化学組成の残部は、Ｆｅ及び不純物であってもよい。不純物としては、鋼原料もしくはスクラップから及び／又は製鋼過程で不可避的に混入し、本実施形態に係るホットスタンプ成形体の特性を阻害しない範囲で許容される元素が例示される。 The remainder of the chemical composition of the steel plate constituting the hot-stamped molded body according to this embodiment may be Fe and impurities. Examples of impurities include elements that are unavoidably mixed in from steel raw materials or scraps and/or during the steel manufacturing process and are allowed within a range that does not impede the properties of the hot-stamped molded product according to the present embodiment.
　本実施形態に係るホットスタンプ成形体を構成する鋼板は、Ｆｅの一部に代えて、任意元素として、以下の元素を含有してもよい。以下の任意元素を含有しない場合の含有量は０％である。 The steel plate constituting the hot-stamped molded product according to the present embodiment may contain the following elements as optional elements in place of a part of Fe. When the following arbitrary elements are not included, the content is 0%.
　Ｃｒ：０．０１～２．００％
　Ｃｒは、鋼の焼入れ性を高めることで、ホットスタンプ成形体の強度を高める元素である。この効果を確実に得る場合、Ｃｒ含有量は０．０１％以上とすることが好ましい。Ｃｒ含有量は、より好ましくは０．０５％以上または０．１０％以上である。
　一方、Ｃｒ含有量が２．００％超であると、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｃｒ含有量は２．００％以下とする。Ｃｒ含有量は、好ましくは０．５０％未満、０．４０％未満または０．３０％未満である。 Cr:0.01~2.00%
Cr is an element that increases the strength of the hot stamped body by increasing the hardenability of steel. To ensure this effect, the Cr content is preferably 0.01% or more. The Cr content is more preferably 0.05% or more or 0.10% or more.
On the other hand, if the Cr content is more than 2.00%, the collision resistance of the hot stamped body will deteriorate. Therefore, the Cr content is set to 2.00% or less. The Cr content is preferably less than 0.50%, less than 0.40% or less than 0.30%.
　Ｍｏ：０．０１～２．００％
　Ｍｏは、鋼の焼入れ性を高めることで、ホットスタンプ成形体の強度を高める元素である。この効果を確実に得る場合、Ｍｏ含有量は０．０１％以上とすることが好ましい。Ｍｏ含有量は、より好ましくは０．０５％以上、０．１０％以上または０．１５％以上である。
　一方、Ｍｏ含有量が２．００％超であると、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｍｏ含有量は２．００％以下とする。Ｍｏ含有量は、好ましくは０．５０％未満、０．４０％未満または０．３０％未満である。 Mo: 0.01~2.00%
Mo is an element that increases the strength of the hot stamped body by increasing the hardenability of steel. To ensure this effect, the Mo content is preferably 0.01% or more. Mo content is more preferably 0.05% or more, 0.10% or more, or 0.15% or more.
On the other hand, if the Mo content exceeds 2.00%, the collision resistance properties of the hot-stamped molded product deteriorate. Therefore, the Mo content is set to 2.00% or less. The Mo content is preferably less than 0.50%, less than 0.40% or less than 0.30%.
　Ｗ：０．０１～２．００％
　Ｗは、鋼の焼入れ性を高めることで、ホットスタンプ成形体の強度を高める元素である。この効果を確実に得る場合、Ｗ含有量は０．０１％以上とすることが好ましい。Ｗ含有量は、より好ましくは０．０５％以上または０．１０％以上である。
　一方、Ｗ含有量が２．００％超であると、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｗ含有量は２．００％以下とする。Ｗ含有量は、好ましくは０．５０％未満、０．４０％未満または０．３０％未満である。 W: 0.01~2.00%
W is an element that increases the strength of the hot stamped body by increasing the hardenability of the steel. To ensure this effect, the W content is preferably 0.01% or more. The W content is more preferably 0.05% or more or 0.10% or more.
On the other hand, if the W content exceeds 2.00%, the collision resistance of the hot-stamped body deteriorates. Therefore, the W content is set to 2.00% or less. The W content is preferably less than 0.50%, less than 0.40% or less than 0.30%.
　Ｃｕ：０．０１～２．００％
　Ｃｕは、鋼の焼入れ性を高めることで、ホットスタンプ成形体の強度を高める元素である。これらの効果を確実に得る場合、Ｃｕ含有量は０．０１％以上とすることが好ましい。Ｃｕ含有量は、より好ましくは０．１０％以上である。
　一方、Ｃｕ含有量が２．００％超であると、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｃｕ含有量は２．００％以下とする。Ｃｕ含有量は、好ましくは１．００％未満または０．５０％未満である。 Cu: 0.01-2.00%
Cu is an element that increases the strength of the hot stamped body by increasing the hardenability of steel. In order to reliably obtain these effects, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.10% or more.
On the other hand, if the Cu content exceeds 2.00%, the collision resistance of the hot-stamped body deteriorates. Therefore, the Cu content is set to 2.00% or less. The Cu content is preferably less than 1.00% or less than 0.50%.
　Ｎｉ：０．０１～２．００％
　Ｎｉは、鋼の焼入れ性を高めることで、ホットスタンプ成形体の強度を高める元素である。この効果を確実に得る場合、Ｎｉ含有量は０．０１％以上とすることが好ましい。Ｎｉ含有量は、より好ましくは０．１０％以上である。
　一方、Ｎｉ含有量が２．００％超であると、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｎｉ含有量は２．００％以下とすることが好ましい。Ｎｉ含有量は、好ましくは１．００％未満または０．５０％未満である。 Ni: 0.01-2.00%
Ni is an element that increases the strength of the hot stamped body by increasing the hardenability of steel. To ensure this effect, the Ni content is preferably 0.01% or more. The Ni content is more preferably 0.10% or more.
On the other hand, if the Ni content exceeds 2.00%, the collision resistance of the hot-stamped body deteriorates. Therefore, the Ni content is preferably 2.00% or less. The Ni content is preferably less than 1.00% or less than 0.50%.
　Ｔｉ：０．００１～０．２００％
　Ｔｉは、鋼中に炭窒化物を形成して、析出強化によりホットスタンプ成形体の強度を高める元素である。また、Ｔｉは、金属組織の微細化を通じ、ホットスタンプ成形体の耐衝突特性を向上させる元素である。これらの効果を確実に得る場合、Ｔｉ含有量は０．００１％以上とすることが好ましい。Ｔｉ含有量は、より好ましくは０．００５％以上または０．０１０％以上である。
　一方、Ｔｉ含有量が０．２００％超であると、鋼中に粗大な炭窒化物が多量に生成して、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｔｉ含有量は０．２００％以下とする。Ｔｉ含有量は、好ましくは０．０５０％未満または０．０３０％未満である。 Ti: 0.001-0.200%
Ti is an element that forms carbonitrides in steel and increases the strength of hot stamped products through precipitation strengthening. Further, Ti is an element that improves the collision resistance of the hot stamped body through refinement of the metal structure. To ensure these effects, the Ti content is preferably 0.001% or more. The Ti content is more preferably 0.005% or more or 0.010% or more.
On the other hand, if the Ti content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot-stamped body. Therefore, the Ti content is set to 0.200% or less. The Ti content is preferably less than 0.050% or less than 0.030%.
　Ｎｂ：０．００１～０．２００％
　Ｎｂは、鋼中に炭窒化物を形成して、析出強化によりホットスタンプ成形体の強度を高める元素である。また、Ｎｂは、金属組織の微細化を通じ、ホットスタンプ成形体の耐衝突特性を向上させる元素である。これらの効果を確実に得る場合、Ｎｂ含有量は０．００１％以上とすることが好ましい。Ｎｂ含有量は、より好ましくは０．００５％以上または０．０１０％以上である。
　一方、Ｎｂ含有量が０．２００％超であると、鋼中に粗大な炭窒化物が多量に生成して、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｎｂ含有量は０．２００％以下とする。Ｎｂ含有量は、好ましくは０．０５０％未満、０．０３０％未満または０．０２０％未満である。 Nb: 0.001-0.200%
Nb is an element that forms carbonitrides in steel and increases the strength of hot stamped products through precipitation strengthening. Furthermore, Nb is an element that improves the collision resistance of the hot stamped body through refinement of the metal structure. To ensure these effects, the Nb content is preferably 0.001% or more. The Nb content is more preferably 0.005% or more or 0.010% or more.
On the other hand, if the Nb content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot stamped body. Therefore, the Nb content is set to 0.200% or less. The Nb content is preferably less than 0.050%, less than 0.030% or less than 0.020%.
　Ｖ：０．００１～０．２００％
　Ｖは、鋼中に炭窒化物を形成して、析出強化によりホットスタンプ成形体の強度を高める元素である。また、Ｖは、金属組織の微細化を通じ、ホットスタンプ成形体の耐衝突特性を向上させる元素である。これらの効果を確実に得る場合、Ｖ含有量は０．００１％以上とすることが好ましい。Ｖ含有量は、より好ましくは０．００５％以上または０．０１０％以上である。
　一方、Ｖ含有量が０．２００％超であると、鋼中に粗大な炭窒化物が多量に生成して、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｖ含有量は０．２００％以下とする。Ｖ含有量は、好ましくは０．１００％未満または０．０５０％未満である。 V:0.001~0.200%
V is an element that forms carbonitrides in steel and increases the strength of the hot stamped product through precipitation strengthening. Further, V is an element that improves the collision resistance properties of the hot-stamped molded product through refinement of the metal structure. To ensure these effects, the V content is preferably 0.001% or more. The V content is more preferably 0.005% or more or 0.010% or more.
On the other hand, if the V content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot stamped body. Therefore, the V content is set to 0.200% or less. The V content is preferably less than 0.100% or less than 0.050%.
　Ｚｒ：０．００１～０．２００％
　Ｚｒは、鋼中に炭窒化物を形成して、析出強化によりホットスタンプ成形体の強度を高める元素である。また、Ｚｒは、金属組織の微細化を通じ、ホットスタンプ成形体の耐衝突特性を向上させる元素である。これらの効果を確実に得る場合、Ｚｒ含有量を０．００１％以上とすることが好ましい。Ｚｒ含有量は、より好ましくは０．００５％以上または０．０１０％以上である。
　一方、Ｚｒ含有量が０．２００％超であると、鋼中に粗大な炭窒化物が多量に生成して、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、Ｚｒ含有量は０．２００％以下とする。Ｚｒ含有量は、好ましくは０．１００％未満または０．０５０％未満である。 Zr: 0.001-0.200%
Zr is an element that forms carbonitrides in steel and increases the strength of hot-stamped products through precipitation strengthening. Furthermore, Zr is an element that improves the collision resistance of the hot stamped product through refinement of the metal structure. To ensure these effects, the Zr content is preferably 0.001% or more. The Zr content is more preferably 0.005% or more or 0.010% or more.
On the other hand, if the Zr content exceeds 0.200%, a large amount of coarse carbonitrides will be generated in the steel, resulting in deterioration of the collision resistance of the hot stamped body. Therefore, the Zr content is set to 0.200% or less. The Zr content is preferably less than 0.100% or less than 0.050%.
　Ｃａ：０．０００１～０．１０００％
　Ｃａは、介在物の形状を調整することにより、ホットスタンプ後の鋼板の延性を向上させる元素である。この効果を確実に得る場合、Ｃａ含有量は０．０００１％以上とすることが好ましい。
　一方、Ｃａを多量に含有させても上記効果は飽和し、さらには、過剰なコストが発生するため、Ｃａ含有量は０．１０００％以下とする。Ｃａ含有量は、好ましくは０．０１００％未満である。 Ca:0.0001~0.1000%
Ca is an element that improves the ductility of the steel sheet after hot stamping by adjusting the shape of inclusions. To ensure this effect, the Ca content is preferably 0.0001% or more.
On the other hand, even if a large amount of Ca is contained, the above-mentioned effects are saturated, and furthermore, excessive costs occur, so the Ca content is set to 0.1000% or less. Ca content is preferably less than 0.0100%.
　Ｍｇ：０．０００１～０．１０００％
　Ｍｇは、介在物の形状を調整することにより、ホットスタンプ後の鋼板の延性を向上させる元素である。これらの効果を確実に得る場合、Ｍｇ含有量は０．０００１％以上とすることが好ましい。
　一方、Ｍｇを多量に含有させても上記効果は飽和し、さらには、過剰なコストが発生するため、Ｍｇ含有量は、０．１０００％以下とする。Ｍｇ含有量は、好ましくは０．０１００％未満である。 Mg: 0.0001-0.1000%
Mg is an element that improves the ductility of the steel sheet after hot stamping by adjusting the shape of inclusions. To ensure these effects, the Mg content is preferably 0.0001% or more.
On the other hand, even if a large amount of Mg is contained, the above-mentioned effects are saturated, and furthermore, excessive costs occur, so the Mg content is set to 0.1000% or less. The Mg content is preferably less than 0.0100%.
　ＲＥＭ：０．０００１～０．１０００％
　ＲＥＭは、介在物の形状を調整することにより、ホットスタンプ後の鋼板の延性を向上させる元素である。この効果を確実に得る場合、ＲＥＭ含有量は０．０００１％以上とすることが好ましい。
　一方、ＲＥＭを多量に含有させても上記効果は飽和し、さらには、過剰なコストが発生するため、ＲＥＭ含有量は０．１０００％以下とする。ＲＥＭ含有量は、好ましくは０．０１００％未満である。
　なお、本実施形態においてＲＥＭとは、Ｓｃ、Ｙ及びランタノイドからなる合計１７元素を指し、ＲＥＭの含有量とはこれらの元素の合計含有量を指す。 REM: 0.0001~0.1000%
REM is an element that improves the ductility of a steel plate after hot stamping by adjusting the shape of inclusions. To ensure this effect, the REM content is preferably 0.0001% or more.
On the other hand, even if a large amount of REM is contained, the above-mentioned effects are saturated, and furthermore, excessive costs occur, so the REM content is set to 0.1000% or less. The REM content is preferably less than 0.0100%.
In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the content of REM refers to the total content of these elements.
　Ｓｎ：０．００１～０．２００％
　Ｓｎは、ホットスタンプ成形体の耐食性を向上させる作用を有する元素である。この効果を確実に得る場合、Ｓｎ含有量は０．００１％以上とすることが好ましい。Ｓｎ含有量は、より好ましくは０．００５％以上、０．０１５％以上または０．０３０％以上である。
　一方、Ｓｎを多量に含有させても上記効果は飽和し、さらには、過剰なコストが発生するため、Ｓｎ含有量は０．２００％以下とする。Ｓｎ含有量は、好ましくは０．１５０％以下または０．１００％以下である。 Sn: 0.001-0.200%
Sn is an element that has the effect of improving the corrosion resistance of the hot stamp molded product. To ensure this effect, the Sn content is preferably 0.001% or more. The Sn content is more preferably 0.005% or more, 0.015% or more, or 0.030% or more.
On the other hand, even if a large amount of Sn is contained, the above-mentioned effects are saturated and, furthermore, excessive costs occur, so the Sn content is set to 0.200% or less. Sn content is preferably 0.150% or less or 0.100% or less.
　Ａｓ：０．００１～０．１００％
　Ａｓは、ホットスタンプ成形体の強度を高める作用を有する元素である。この効果を確実に得る場合、Ａｓ含有量は０．００１％以上とすることが好ましい。
　一方、Ａｓを多量に含有させても上記効果は飽和し、さらには、過剰なコストが発生するため、Ａｓ含有量は０．１００％以下とする。 As: 0.001-0.100%
As is an element that has the effect of increasing the strength of the hot stamp molded product. To ensure this effect, the As content is preferably 0.001% or more.
On the other hand, even if a large amount of As is contained, the above-mentioned effects will be saturated and furthermore, excessive costs will occur, so the As content is set to 0.100% or less.
　Ｂｉ：０．０００１～０．０５００％
　Ｂｉは、凝固組織を微細化することにより、ホットスタンプ成形体の耐衝突特性を高める元素である。この効果を確実に得る場合、Ｂｉ含有量は０．０００１％以上とすることが好ましい。
　一方、Ｂｉを多量に含有させても上記効果は飽和し、さらには、過剰なコストが発生するため、Ｂｉ含有量は０．０５００％以下とする。Ｂｉ含有量は、好ましくは０．０１００％以下または０．００５０％以下である。 Bi:0.0001~0.0500%
Bi is an element that improves the collision resistance of the hot-stamped body by making the solidified structure finer. To ensure this effect, the Bi content is preferably 0.0001% or more.
On the other hand, even if a large amount of Bi is contained, the above-mentioned effects will be saturated and furthermore, excessive costs will occur, so the Bi content is set to 0.0500% or less. Bi content is preferably 0.0100% or less or 0.0050% or less.
　上述したホットスタンプ成形体を構成する鋼板の化学組成は、ホットスタンプ成形体を構成する鋼板から試験片を採取し、鋼板に塗装が施されている場合は塗膜を除去した後、一般的な分析方法によって、板厚全体の平均的な元素含有量を測定すればよい。例えば、誘導結合プラズマ発光分析法や誘導結合プラズマ質量分析法を用いて測定すればよい。なお、ＣおよびＳは燃焼－赤外線吸収法を用い、ＯおよびＮは不活性ガス溶融－赤外線吸収法や不活性ガス融解－熱伝導度法を用いて測定すればよい。ホットスタンプ成形体を構成する鋼板の表面にめっき層を備える場合は、めっき層を除去してから化学組成の測定を行えばよい。 The chemical composition of the steel plate constituting the hot-stamped body described above can be determined by taking a test piece from the steel plate constituting the hot-stamping body, removing the paint film if the steel plate has been painted, and then using a general method. The average element content throughout the plate thickness may be measured using an analytical method. For example, measurement may be performed using inductively coupled plasma optical emission spectrometry or inductively coupled plasma mass spectrometry. Note that C and S may be measured using a combustion-infrared absorption method, and O and N may be measured using an inert gas melting-infrared absorption method or an inert gas melting-thermal conductivity method. When a plating layer is provided on the surface of the steel plate constituting the hot-stamped compact, the chemical composition may be measured after removing the plating layer.
　上述したように、ホットスタンプ成形体が、１９００ＭＰａ以上の引張強さを有する部分と、１９００ＭＰａ未満の引張強さを有する部分とを備えている場合、少なくとも引張強さが１９００ＭＰａ以上となる部分が上述の化学組成を有していればよい。引張強さが１９００ＭＰａ以上となる部分について化学組成の分析を行うためには、後述する引張試験を行い、１９００ＭＰａ以上の引張強さが得られた引張試験片から、あるいは、引張試験片を採取した部分と隣接する部分から、化学組成分析用の試験片を採取すればよい。 As described above, when the hot stamp molded article includes a portion having a tensile strength of 1900 MPa or more and a portion having a tensile strength of less than 1900 MPa, at least the portion having a tensile strength of 1900 MPa or more is as described above. It is sufficient that the chemical composition is as follows. In order to analyze the chemical composition of a part with a tensile strength of 1900 MPa or more, a tensile test described below was performed and a tensile test piece was collected from a tensile test piece that had a tensile strength of 1900 MPa or more. A test piece for chemical composition analysis may be taken from a part adjacent to the part.
　次に、本実施形態に係るホットスタンプ成形体を構成する鋼板の板厚方向のＢ濃度分布およびＯ濃度分布について説明する。
　本実施形態では、ホットスタンプ用鋼板を加熱する工程で、ホットスタンプ用鋼板を特定の条件で加熱することにより、表層領域に存在するＢを最表層領域へ拡散させるとともに、最表層領域でＢとＯとを結合させることができ、ホットスタンプ成形体の耐衝突特性を向上させることができる。 Next, the B concentration distribution and O concentration distribution in the thickness direction of the steel plate constituting the hot-stamped molded body according to the present embodiment will be described.
In this embodiment, in the step of heating the hot stamping steel plate, by heating the hot stamping steel plate under specific conditions, B present in the surface layer region is diffused to the outermost layer region, and B is mixed in the outermost layer region. It is possible to combine with O and improve the collision resistance of the hot stamp molded product.
　本実施形態に係るホットスタンプ成形体は、ホットスタンプ成形体を構成する鋼板の表面から５．０μｍ深さ～前記表面から２５．０μｍ深さの領域における平均Ｂ濃度が、前記表面から１００μｍ深さの位置におけるＢ濃度の０．７００倍以下であり、前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの領域における平均Ｂ濃度が、前記表面から１００μｍ深さの前記位置における前記Ｂ濃度の１．６００倍以上であり、前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの前記領域における平均Ｏ濃度が、０．０１５０質量％超である。
　なお、鋼板の表面から５．０μｍ深さ～前記表面から２５．０μｍ深さの領域は、鋼板の表面から５．０μｍ深さの位置を始点として、前記表面から２５．０μｍ深さの位置を終点とする領域、と換言することができる。また、鋼板の表面から０．５μｍ深さ～前記表面から４．０μｍ深さの領域は、鋼板の表面から０．５μｍ深さの位置を始点として、前記表面から４．０μｍ深さの位置を終点とする領域、と換言することができる。 The hot-stamped molded article according to the present embodiment has an average B concentration in a region from a depth of 5.0 μm to a depth of 25.0 μm from the surface of the steel plate constituting the hot-stamped molded article, and an average concentration of B in a region from a depth of 100 μm from the surface to a depth of 100 μm from the surface. is 0.700 times or less than the B concentration at the position, and the average B concentration in a region from 0.5 μm deep to 4.0 μm deep from the surface is 0.700 times or less than the B concentration at the position 100 μm deep from the surface. The B concentration is 1.600 times or more, and the average O concentration in the region from a depth of 0.5 μm to a depth of 4.0 μm from the surface is more than 0.0150% by mass.
Note that the region from 5.0 μm deep to the surface of the steel plate to 25.0 μm deep from the surface starts from a position 5.0 μm deep from the surface of the steel plate and starts at a position 25.0 μm deep from the surface. In other words, it is the region that is the end point. In addition, the region from 0.5 μm deep to 4.0 μm deep from the surface of the steel plate starts from a position 0.5 μm deep from the surface of the steel plate and starts at a position 4.0 μm deep from the surface. In other words, it is the region that is the end point.
　ホットスタンプ成形体が、１９００ＭＰａ以上の引張強さを有する部分と、１９００ＭＰａ未満の引張強さを有する部分とを備えている場合、少なくとも引張強さが１９００ＭＰａ以上となる部分が以下のＢ濃度分布およびＯ濃度分布を有していればよい。
　以下、各規定について説明する。 When the hot-stamped molded product includes a portion having a tensile strength of 1900 MPa or more and a portion having a tensile strength of less than 1900 MPa, at least the portion having a tensile strength of 1900 MPa or more has the following B concentration distribution and It is sufficient as long as it has an O concentration distribution.
Each regulation will be explained below.
　表面から５．０μｍ深さ～表面から２５．０μｍ深さの領域における平均Ｂ濃度：表面から１００μｍ深さの位置におけるＢ濃度の０．７００倍以下
　表面から５．０μｍ深さ～表面から２５．０μｍ深さの領域（以下、表層領域と記載する場合がある）における平均Ｂ濃度が、表面から１００μｍ深さの位置におけるＢ濃度の０．７００倍超であると、表層領域が軟質化せずホットスタンプ成形体において所望の耐衝突特性を得ることができない。そのため、表層領域の平均Ｂ濃度は、表面から１００μｍ深さの位置におけるＢ濃度の０．７００倍以下とする。表層領域の平均Ｂ濃度は、好ましくは、表面から１００μｍ深さの位置におけるＢ濃度の０．７００倍以下かつ０．００１５質量％以下である。さらに好ましくは、表層領域の平均Ｂ濃度は、表面から１００μｍ深さの位置におけるＢ濃度の０．５００倍以下または０．３００倍以下である。また、表層領域の平均Ｂ濃度は、さらに好ましくは、０．００１０質量％以下または０．０００６質量％以下である。
　下限は特に規定しないが、過度に低下させても前記効果が飽和するばかりか、ホットスタンプ成形体の強度が低下するので、表層領域の平均Ｂ濃度は０．０００２質量％以上としてもよい。 Average B concentration in the region from 5.0 μm depth to the surface to 25.0 μm depth from the surface: 0.700 times or less of the B concentration at a position 100 μm deep from the surface 5.0 μm depth from the surface to 25.0 μm depth from the surface. If the average B concentration in the 0 μm depth region (hereinafter sometimes referred to as surface layer region) is more than 0.700 times the B concentration at a position 100 μm deep from the surface, the surface layer region will not soften. Desired collision resistance properties cannot be obtained in the hot-stamped molded product. Therefore, the average B concentration in the surface layer region is set to be 0.700 times or less of the B concentration at a position 100 μm deep from the surface. The average B concentration in the surface layer region is preferably 0.700 times or less of the B concentration at a depth of 100 μm from the surface and 0.0015% by mass or less. More preferably, the average B concentration in the surface layer region is 0.500 times or less or 0.300 times or less of the B concentration at a depth of 100 μm from the surface. Further, the average B concentration in the surface layer region is more preferably 0.0010% by mass or less or 0.0006% by mass or less.
Although the lower limit is not particularly defined, the average B concentration in the surface layer region may be set to 0.0002% by mass or more, since if it is lowered too much, the above effect will not only be saturated, but also the strength of the hot-stamped molded article will be reduced.
　なお、表面とはホットスタンプ成形体を構成する鋼板の表面のことである。ホットスタンプ成形体が表面にめっき層を有する場合は、表面とはめっき層と鋼板との界面のことである。 Note that the surface refers to the surface of the steel plate that constitutes the hot stamp molded body. When the hot-stamped molded body has a plating layer on the surface, the surface refers to the interface between the plating layer and the steel plate.
　表面から０．５μｍ深さ～表面から４．０μｍ深さの領域における平均Ｂ濃度：表面から１００μｍ深さの位置におけるＢ濃度の１．６００倍以上
　表面から０．５μｍ深さ～表面から４．０μｍ深さの領域（以下、最表層領域と記載する場合がある）における平均Ｂ濃度が、表面から１００μｍ深さの位置におけるＢ濃度の１．６００倍未満であると、後述するように、最表層領域でＢとＯとが十分に結合せず、最表層領域が軟質化しない。これにより、ホットスタンプ成形体において所望の耐衝突特性を得ることができない。そのため、最表層領域における平均Ｂ濃度は、表面から１００μｍ深さの位置におけるＢ濃度の１．６００倍以上とする。最表層領域における平均Ｂ濃度は、好ましくは、表面から１００μｍ深さの位置におけるＢ濃度の１．６００倍以上かつ０．００４０質量％以上である。さらに好ましくは、最表層領域における平均Ｂ濃度は、表面から１００μｍ深さの位置におけるＢ濃度の２．０００倍以上、３．０００倍以上または４．０００倍以上である。また、最表層領域における平均Ｂ濃度は、さらに好ましくは、０．００５０質量％以上、０．００６０質量％以上または０．００７０質量％以上である。
　上限は特に規定しないが、最表層領域における平均Ｂ濃度を過度に高めても前記効果が飽和するばかりか、ホットスタンプ成形体の生産性が大きく損なわれるので、０．２０００質量％以下としてもよい。 Average B concentration in a region from 0.5 μm depth to 4.0 μm depth from the surface: 1.600 times or more of the B concentration at a position 100 μm deep from the surface. 0.5 μm depth from the surface to 4.0 μm depth from the surface. If the average B concentration in the 0 μm depth region (hereinafter sometimes referred to as the outermost layer region) is less than 1.600 times the B concentration at a position 100 μm deep from the surface, the maximum B and O do not combine sufficiently in the surface layer region, and the outermost layer region does not become soft. As a result, it is not possible to obtain desired collision resistance properties in the hot-stamped molded article. Therefore, the average B concentration in the outermost layer region is 1.600 times or more the B concentration at a position 100 μm deep from the surface. The average B concentration in the outermost layer region is preferably at least 1.600 times the B concentration at a depth of 100 μm from the surface and at least 0.0040% by mass. More preferably, the average B concentration in the outermost layer region is 2.000 times or more, 3.000 times or more, or 4.000 times or more the B concentration at a depth of 100 μm from the surface. Further, the average B concentration in the outermost layer region is more preferably 0.0050% by mass or more, 0.0060% by mass or more, or 0.0070% by mass or more.
The upper limit is not particularly defined, but if the average B concentration in the outermost layer region is increased too much, the above effect will not only be saturated, but also the productivity of the hot stamped molded product will be significantly impaired, so it may be set to 0.2000% by mass or less. .
　表面から０．５μｍ深さ～表面から４．０μｍ深さの領域における平均Ｏ濃度：０．０１５０質量％超
　表面から０．５μｍ深さ～表面から４．０μｍ深さの領域（最表層領域）における平均Ｏ濃度が０．０１５０質量％以下であると、Ｂと結合するＯ量が不足し、固溶状態のＢ量が増加し、最表層領域が軟質化しない。これにより、ホットスタンプ成形体において所望の耐衝突特性を得ることができない。そのため、最表層領域における平均Ｏ濃度は０．０１５０質量％超とする。最表層領域における平均Ｏ濃度は、好ましくは０．０２００質量％超、０．０３００質量％超または０．０４００質量％超である。
　上限は特に規定しないが、最表層領域における平均Ｏ濃度を過度に高めても前記効果が飽和するばかりか、ホットスタンプ成形体の生産性が大きく損なわれるので、１．００００質量％以下としてもよい。 Average O concentration in the region from 0.5 μm depth to the surface to 4.0 μm depth from the surface: More than 0.0150% by mass Region from 0.5 μm depth to the surface to 4.0 μm depth from the surface (uppermost layer region) If the average O concentration in is 0.0150% by mass or less, the amount of O that combines with B is insufficient, the amount of B in solid solution increases, and the outermost layer region does not become soft. As a result, it is not possible to obtain desired collision resistance properties in the hot-stamped molded article. Therefore, the average O concentration in the outermost layer region is set to exceed 0.0150% by mass. The average O concentration in the outermost layer region is preferably greater than 0.0200% by mass, greater than 0.0300% by mass, or greater than 0.0400% by mass.
The upper limit is not particularly specified, but if the average O concentration in the outermost layer region is increased too much, the above effect will not only be saturated, but also the productivity of the hot stamped molded product will be greatly impaired, so it may be set to 1.0000% by mass or less. .
　表層領域の平均Ｂ濃度、最表層領域の平均Ｂ濃度および平均Ｏ濃度、並びに、表面から１００μｍ深さの位置におけるＢ濃度は以下の方法により測定する。
　ホットスタンプ成形体から試験片を採取し、鋼板に塗装が施されている場合は塗膜を除去した後、グロー放電発光分光法（Ｇｌｏｗ　Ｄｉｓｃｈａｒｇｅ　Ｏｐｔｉｃａｌ　Ｅｍｉｓｓｉｏｎ　Ｓｐｅｃｔｒｏｍｅｔｒｙ、ＧＤＳ分析）により、測定開始面から深さ方向（板厚方向）に１００μｍ以上の深さ位置にかけて各元素の濃度（質量％）を測定する。なお、ここでいう「測定開始面」は、「鋼板の表面」とは異なる。 The average B concentration in the surface layer region, the average B concentration and average O concentration in the outermost layer region, and the B concentration at a depth of 100 μm from the surface are measured by the following method.
A test piece is taken from the hot-stamped molded product, and after removing the paint film if the steel plate is coated, it is measured at a depth from the measurement starting surface using Glow Discharge Optical Emission Spectrometry (GDS analysis). The concentration (mass %) of each element is measured at a depth of 100 μm or more in the width direction (plate thickness direction). Note that the "measurement start surface" here is different from the "surface of the steel plate."
　ＧＤＳ分析では、鋼板の表面から１００μｍ深さ位置までの測定点が１２００～１８００点となるように測定のピッチを調整する。測定開始面に付着する油分等の異物の影響を排除するために、測定開始から、Ｆｅ濃度が最初に「測定開始面から１００μｍ深さの位置のＦｅ濃度」の９５％以上となる深さを鋼板の表面と定める。また、ホットスタンプ成形体が表面にめっき層を有する場合も同様に、Ｆｅ濃度が最初に「測定開始面から１００μｍ深さの位置のＦｅ濃度」の９５％以上となる深さを、めっき層と鋼板との界面、すなわち鋼板の表面と定める。 In the GDS analysis, the measurement pitch is adjusted so that there are 1200 to 1800 measurement points from the surface of the steel plate to a depth of 100 μm. In order to eliminate the influence of foreign substances such as oil adhering to the measurement starting surface, from the start of the measurement, set the depth at which the Fe concentration is at least 95% of the "Fe concentration at a depth of 100 μm from the measurement starting surface". Defined as the surface of the steel plate. Similarly, when the hot stamp molded body has a plating layer on the surface, the depth at which the Fe concentration initially becomes 95% or more of "the Fe concentration at a depth of 100 μm from the measurement starting surface" is set as the plating layer. It is defined as the interface with the steel plate, that is, the surface of the steel plate.
　得られた測定結果から、鋼板の表面から５．０μｍ深さ～鋼板の表面から２５．０μｍ深さの領域におけるＢ濃度の平均値を算出することで、表層領域の平均Ｂ濃度を得る。また、鋼板の表面から０．５μｍ深さ～鋼板の表面から４．０μｍ深さの領域におけるＢ濃度およびＯ濃度の平均値をそれぞれ算出することで、最表層領域の平均Ｂ濃度および平均Ｏ濃度を得る。また、鋼板の表面から１００μｍ深さの位置におけるＢ濃度を求めることで、表面から１００μｍ深さの位置におけるＢ濃度を得る。なお、鋼板の表面から１００μｍ深さの位置にＧＤＳ分析の測定値がない場合は、表面から１００μｍ深さの位置を超える最初の測定値を、表面から１００μｍ深さ位置におけるＢ濃度とすればよい。 From the obtained measurement results, the average B concentration in the surface layer region is obtained by calculating the average value of the B concentration in the region from 5.0 μm depth to the steel sheet surface to 25.0 μm depth from the steel sheet surface. In addition, by calculating the average values of B concentration and O concentration in the region from 0.5 μm depth to 4.0 μm depth from the surface of the steel plate, the average B concentration and average O concentration in the outermost layer region can be calculated. get. Further, by determining the B concentration at a position 100 μm deep from the surface of the steel plate, the B concentration at a position 100 μm deep from the surface is obtained. In addition, if there is no measured value of GDS analysis at a position 100 μm deep from the surface of the steel plate, the first measured value beyond the position 100 μm deep from the surface may be taken as the B concentration at a position 100 μm deep from the surface. .
　ＧＤＳ分析は、ホットスタンプ成形体の３カ所以上から採取した試験片について行い、得られた結果の平均値を前記Ｂ濃度および前記Ｏ濃度とすることが好ましい。なお、試験片は、後述する引張試験を行い、１９００ＭＰａ以上の引張強さが得られた引張試験片を採取した部分と隣接する部分から、採取すればよい。 It is preferable that the GDS analysis is performed on test pieces taken from three or more locations of the hot-stamped molded body, and the average value of the obtained results is taken as the B concentration and the O concentration. In addition, the test piece may be taken from a part adjacent to a part where a tensile test piece having a tensile strength of 1900 MPa or more was taken after conducting a tensile test to be described later.
　ホットスタンプ成形体を構成する鋼板の金属組織は、所望の強度および耐衝突特性を得ることができれば特に限定されないが、以下に示す金属組織を有することが好ましい。 The metal structure of the steel plate constituting the hot-stamped molded product is not particularly limited as long as the desired strength and collision resistance characteristics can be obtained, but it is preferable to have the metal structure shown below.
　本実施形態に係るホットスタンプ成形体を構成する鋼板の全部または一部は、以下に示す量のマルテンサイトを含む金属組織を有することが好ましい。金属組織に関する以下の説明において、「％」は、「体積％」を意味する。ホットスタンプ成形体が、１９００ＭＰａ以上の引張強さを有する部分と、１９００ＭＰａ未満の引張強さを有する部分とを備えている場合、少なくとも引張強さが１９００ＭＰａ以上となる部分が以下の金属組織を有していればよい。 It is preferable that all or part of the steel plate constituting the hot-stamped molded body according to the present embodiment has a metal structure containing martensite in the amount shown below. In the following description regarding metallographic structure, "%" means "volume %". When the hot-stamped molded body has a part having a tensile strength of 1900 MPa or more and a part having a tensile strength of less than 1900 MPa, at least the part having a tensile strength of 1900 MPa or more has the following metal structure. All you have to do is do it.
　内層領域の金属組織
　内層領域（ホットスタンプ成形体を構成する鋼板の表面から１００μｍ深さ～板厚中心（板厚１／２位置）の領域）の金属組織は、９０．０％超のマルテンサイトを含むことが好ましい。 Metal structure of the inner layer region The metal structure of the inner layer region (area from 100 μm depth to the center of the plate thickness (1/2 position of the plate thickness) from the surface of the steel plate constituting the hot-stamped compact) is more than 90.0% martensite. It is preferable to include.
　マルテンサイトは、ホットスタンプ後の鋼板の引張強さを高めるために有効な組織であるので、ホットスタンプ成形体を構成する鋼板の表面から１００μｍ深さ～板厚中心の領域（以下、内層領域と記載する場合がある）においてマルテンサイトの体積率が９０．０％超であることが好ましい。内層領域のマルテンサイトの体積率が９０．０％以下であると、ホットスタンプ成形体の引張強さが１９００ＭＰａ未満となり強度が不足する場合がある。そのため、内層領域のマルテンサイトの体積率を９０．０％超とすることが好ましい。内層領域のマルテンサイトの体積率は、より好ましくは９１．０％超、９３．０％超、または９５．０％超である。 Martensite is an effective structure for increasing the tensile strength of the steel plate after hot stamping, so martensite is a structure that is effective for increasing the tensile strength of the steel plate after hot stamping. It is preferable that the volume fraction of martensite is more than 90.0%. If the volume fraction of martensite in the inner layer region is 90.0% or less, the tensile strength of the hot-stamped molded product is less than 1900 MPa, which may result in insufficient strength. Therefore, it is preferable that the volume fraction of martensite in the inner layer region be more than 90.0%. The volume fraction of martensite in the inner layer region is more preferably over 91.0%, over 93.0%, or over 95.0%.
　内層領域のマルテンサイトの体積率の上限は特に定める必要がないが、マルテンサイトの体積率を大きく上昇させるためには、ホットスタンプを行う工程において、ホットスタンプ用鋼板の加熱温度を過度に高めたり、冷却速度を過度に高めたりする必要があり、ホットスタンプ成形体の生産性が大きく損なわれる。したがって、内層領域のマルテンサイトの体積率は９９．０％以下または９８．０％以下とすることが好ましい。 There is no need to set a particular upper limit for the volume fraction of martensite in the inner layer region, but in order to greatly increase the volume fraction of martensite, it is necessary to excessively raise the heating temperature of the steel plate for hot stamping during the hot stamping process. , it is necessary to increase the cooling rate excessively, and the productivity of the hot-stamped molded product is greatly impaired. Therefore, the volume fraction of martensite in the inner layer region is preferably 99.0% or less or 98.0% or less.
　本実施形態において、マルテンサイトには、焼戻しされていないフレッシュマルテンサイトの他に、焼戻され、内部に鉄炭化物が存在する焼戻しマルテンサイトが含まれる。 In the present embodiment, martensite includes fresh martensite that has not been tempered, as well as tempered martensite that has been tempered and has iron carbides inside.
　内層領域の金属組織の残部は、フェライト、パーライト、ベイナイトまたは残留オーステナイトを含んでいてもよく、さらに、単独で存在するセメンタイトや酸化物などの析出物を含んでいてもよい。フェライト、パーライト、ベイナイト、残留オーステナイトおよび析出物を含有する必要はないので、フェライト、パーライト、ベイナイト、残留オーステナイトおよび析出物の体積率の下限はいずれも０％である。 The remainder of the metal structure in the inner layer region may contain ferrite, pearlite, bainite, or retained austenite, and may also contain precipitates such as cementite or oxides existing alone. Since it is not necessary to contain ferrite, pearlite, bainite, retained austenite, and precipitates, the lower limit of the volume fraction of ferrite, pearlite, bainite, retained austenite, and precipitates is all 0%.
　残留オーステナイトは、ホットスタンプ後の鋼板の延性を向上させる作用を有する。この効果を得る場合、内層領域の残留オーステナイトの体積率を０．５％以上、１．０％以上または２．０％以上とすることが好ましい。
　一方、残留オーステナイトの体積率を過度に上昇させるためには、ホットスタンプ後に高温でオーステンパー処理を施す必要があり、ホットスタンプ成形体の生産性が大幅に低下する。また、残留オーステナイトを過剰に含有すると、ホットスタンプ成形体の耐衝突特性が劣化する場合がある。そのため、内層領域の残留オーステナイトの体積率を９．０％未満、７．０％未満、５．０％未満または４．０％未満とすることが好ましい。 Retained austenite has the effect of improving the ductility of the steel plate after hot stamping. In order to obtain this effect, it is preferable that the volume fraction of retained austenite in the inner layer region is 0.5% or more, 1.0% or more, or 2.0% or more.
On the other hand, in order to excessively increase the volume fraction of retained austenite, it is necessary to perform an austempering treatment at a high temperature after hot stamping, which significantly reduces the productivity of the hot stamped molded product. Furthermore, if the residual austenite is contained excessively, the collision resistance properties of the hot-stamped molded article may be deteriorated. Therefore, the volume fraction of retained austenite in the inner layer region is preferably less than 9.0%, less than 7.0%, less than 5.0%, or less than 4.0%.
　最表層領域の金属組織
　最表層領域の金属組織は、５．０％超のフェライトを含むことが好ましい。 Metal structure of the outermost layer region The metal structure of the outermost layer region preferably contains more than 5.0% ferrite.
　フェライトは、軟質でありホットスタンプ成形体の耐衝突特性を向上させる作用を有する。この効果を得る場合、最表層領域のフェライトの体積率を５．０％超とすることが好ましい。最表層領域のフェライトの体積率は、１０．０％超、２０．０％超、４０．０％超、または６０．０％超とすることがより好ましい。
　本実施形態において、フェライトには、ポリゴナルフェライトの他に、転位密度が高いアシキュラーフェライトやベイニティックフェライトが含まれる。ホットスタンプ成形体の耐衝突特性を効率的に向上させるために、最表層領域において、最も軟質であるポリゴナルフェライトを上述の体積率で含むことがより好ましい。 Ferrite is soft and has the effect of improving the collision resistance of the hot stamp molded product. In order to obtain this effect, it is preferable that the volume fraction of ferrite in the outermost layer region be more than 5.0%. The volume fraction of ferrite in the outermost layer region is more preferably more than 10.0%, more than 20.0%, more than 40.0%, or more than 60.0%.
In this embodiment, the ferrite includes acicular ferrite and bainitic ferrite, which have a high dislocation density, in addition to polygonal ferrite. In order to efficiently improve the collision resistance properties of the hot-stamped molded product, it is more preferable that the outermost layer region contains polygonal ferrite, which is the softest, at the above-mentioned volume percentage.
　最表層領域の金属組織の残部は、パーライト、ベイナイト、残留オーステナイトまたはマルテンサイトを含んでいてもよく、さらに、単独で存在するセメンタイトや酸化物などの析出物を含んでいてもよい。パーライト、ベイナイト、残留オーステナイト、マルテンサイトおよび析出物を含有する必要はないので、パーライト、ベイナイト、残留オーステナイト、マルテンサイトおよび析出物の体積率の下限はいずれも０％である。マルテンサイトを過剰に含有すると、最表層領域が硬質化し、ホットスタンプ成形体の耐衝突特性が劣化する場合がある。そのため、最表層領域のマルテンサイトの体積率を９０．０％未満、４０．０％未満、１０．０％未満または５．０％未満とすることが好ましい。
　ベイナイトは、マルテンサイトよりも軟質でありホットスタンプ成形体の耐衝突特性を向上させる作用を有する。この効果を得る場合、最表層領域のベイナイトの体積率を１０．０％超とすることが好ましい。最表層領域のベイナイトの体積率は、２０．０％超または４０．０％超とすることがより好ましい。一方、ベイナイトを過剰に含有すると、最表層領域が硬質化し、ホットスタンプ成形体の耐衝突特性が劣化する場合がある。そのため、最表層領域のベイナイトの体積率を８０．０％未満または６０．０％未満とすることが好ましい。 The remainder of the metal structure in the outermost layer region may contain pearlite, bainite, retained austenite, or martensite, and may also contain precipitates such as cementite or oxides existing alone. Since it is not necessary to contain pearlite, bainite, retained austenite, martensite, and precipitates, the lower limit of the volume percentage of pearlite, bainite, retained austenite, martensite, and precipitates is all 0%. When martensite is contained excessively, the outermost layer region becomes hard, and the collision resistance of the hot-stamped product may deteriorate. Therefore, the volume fraction of martensite in the outermost layer region is preferably less than 90.0%, less than 40.0%, less than 10.0%, or less than 5.0%.
Bainite is softer than martensite and has the effect of improving the collision resistance of the hot stamped body. In order to obtain this effect, it is preferable that the volume fraction of bainite in the outermost layer region be more than 10.0%. The volume fraction of bainite in the outermost layer region is more preferably more than 20.0% or more than 40.0%. On the other hand, when bainite is contained excessively, the outermost layer region becomes hard, and the collision resistance of the hot-stamped molded article may deteriorate. Therefore, it is preferable that the volume fraction of bainite in the outermost layer region be less than 80.0% or less than 60.0%.
　本実施形態において、各組織の体積率は以下の方法により測定する。
　まず、ホットスタンプ成形体から試験片を採取し、鋼板の縦断面（板厚断面）をバフ研磨した後、内層領域および最表層領域において組織観察する。内層領域は、ホットスタンプ成形体を構成する鋼板の表面から１００μｍ深さ～板厚中心（板厚１／２位置）の領域について組織観察を行う。最表層領域は、鋼板の表面から０．５μｍ深さ～表面から４．０μｍ深さの領域について組織観察を行う。 In this embodiment, the volume fraction of each tissue is measured by the following method.
First, a test piece is taken from a hot-stamped compact, and after buffing the longitudinal section (thickness section) of the steel plate, the structure is observed in the inner layer region and the outermost layer region. For the inner layer region, the structure is observed in a region from a depth of 100 μm to the center of the plate thickness (1/2 position of the plate thickness) from the surface of the steel plate constituting the hot-stamped compact. For the outermost layer region, the structure is observed in a region from 0.5 μm deep to 4.0 μm deep from the surface of the steel plate.
　具体的には、研磨面をナイタール腐食または電解研磨した後、光学顕微鏡および走査電子顕微鏡（ＳＥＭ）を用いて組織写真を撮影し、得られた組織写真に対して、輝度差または相内に存在する鉄炭化物の形態の違いに基づく画像解析を行うことによって、フェライト、パーライト、ベイナイト、焼戻しマルテンサイトおよび析出物のそれぞれの面積率を得る。その後、同様の観察位置に対し、レペラー腐食をした後、光学顕微鏡および走査電子顕微鏡（ＳＥＭ）を用いて組織写真を撮影し、得られた組織写真に対して画像解析を行うことによって、「残留オーステナイトおよびフレッシュマルテンサイト」の面積率の合計を算出する。 Specifically, after subjecting the polished surface to nital corrosion or electrolytic polishing, a microstructure photograph is taken using an optical microscope and a scanning electron microscope (SEM), and the resulting microstructure photographs are analyzed based on brightness differences or presence within the phase. By performing image analysis based on the differences in the morphology of iron carbides, the area percentages of ferrite, pearlite, bainite, tempered martensite, and precipitates are obtained. After that, after repeller corrosion was performed on the same observation position, the structure was photographed using an optical microscope and a scanning electron microscope (SEM), and image analysis was performed on the obtained structure photograph. Calculate the total area ratio of "austenite and fresh martensite".
　また、同様の観察位置について、縦断面を電解研磨した後、電子線後方散乱パターン解析装置（ＥＢＳＰ装置）を備えたＳＥＭを用いて、残留オーステナイトの面積率を測定する。なお、ＥＢＳＰ解析によって得られた結晶方位情報から、結晶構造がｆｃｃである領域の面積率を算出することで、残留オーステナイトの面積率を得る。
　上述の「残留オーステナイトおよびフレッシュマルテンサイト」の面積率の合計から、残留オーステナイトの面積率を引くことで、フレッシュマルテンサイトの面積率を得る。 Further, after electrolytically polishing the longitudinal section at the same observation position, the area ratio of retained austenite is measured using a SEM equipped with an electron beam backscatter pattern analyzer (EBSP device). Note that the area ratio of retained austenite is obtained by calculating the area ratio of a region having an fcc crystal structure from the crystal orientation information obtained by the EBSP analysis.
The area ratio of fresh martensite is obtained by subtracting the area ratio of retained austenite from the sum of the area ratios of the above-mentioned "retained austenite and fresh martensite."
　これらの結果に基づいて、フェライト、パーライト、ベイナイト、マルテンサイト（焼戻しマルテンサイトおよびフレッシュマルテンサイト）、残留オーステナイト、析出物のそれぞれの面積率を得る。そして、面積率は体積率と等しいとして、得られた面積率を各組織の体積率とみなす。 Based on these results, obtain the area percentages of ferrite, pearlite, bainite, martensite (tempered martensite and fresh martensite), retained austenite, and precipitates. Then, assuming that the area ratio is equal to the volume ratio, the obtained area ratio is regarded as the volume ratio of each tissue.
　組織観察において、焼戻しマルテンサイトは、内部に鉄炭化物が存在する点でフレッシュマルテンサイトと区別することができる。また、焼き戻しマルテンサイトは、内部に存在する鉄炭化物が単一の方向でなく複数の方向に伸長している点で、ベイナイトと区別することができる。なお、単一の方向に伸長するとは、伸長方向の差異が５°以内であることを意味する。 In microstructural observation, tempered martensite can be distinguished from fresh martensite by the presence of iron carbides inside. Furthermore, tempered martensite can be distinguished from bainite in that the iron carbide present inside extends not in a single direction but in multiple directions. Note that elongation in a single direction means that the difference in elongation direction is within 5°.
　板厚
　本実施形態に係るホットスタンプ成形体の板厚（ホットスタンプ成形体が鋼板のみからなる場合は鋼板の板厚）は特に限定しないが、車体軽量化の観点から、２．５ｍｍ以下、２．０ｍｍ以下、１．８ｍｍ以下または１．６ｍｍ以下とすることが好ましい。
　一方、衝撃吸収量を確保する観点から、板厚は０．４ｍｍ以上、０．６ｍｍ以上、０．８ｍｍ以上または１．０ｍｍ以上とすることが好ましい。 Plate Thickness The plate thickness of the hot-stamped body according to the present embodiment (the thickness of the steel plate when the hot-stamped body is made only of steel plates) is not particularly limited, but from the viewpoint of reducing the weight of the vehicle body, it is 2.5 mm or less, 2.5 mm or less, It is preferable to set it as 0 mm or less, 1.8 mm or less, or 1.6 mm or less.
On the other hand, from the viewpoint of ensuring the amount of shock absorption, the plate thickness is preferably 0.4 mm or more, 0.6 mm or more, 0.8 mm or more, or 1.0 mm or more.
　引張強さ
　本実施形態に係るホットスタンプ成形体の全部または一部は、引張強さが１９００ＭＰａ以上である。このためには、本実施形態に係るホットスタンプ成形体を構成する鋼板の全部または一部の引張強さが１９００ＭＰａ以上であることが必要である。ホットスタンプ成形体の少なくとも一部の引張強さが１９００ＭＰａ以上でない場合、ホットスタンプ成形体の変形荷重を確保することができなくなる。その結果、ホットスタンプ成形体の耐衝突特性が劣化する。そのため、ホットスタンプ成形体の全部または一部の引張強さは１９００ＭＰａ以上とする。好ましくは、ホットスタンプ成形体の全部または一部において、引張強さが２０００ＭＰａ以上、２１００ＭＰａ以上、２３００ＭＰａ以上または２５００ＭＰａ以上である。
　一方、ホットスタンプ成形体の強度を過度に高めることは耐衝突特性の低下を引き起こすため、ホットスタンプ成形体の引張強さは３０００ＭＰａ未満または２８００ＭＰａ未満とすることが好ましい。 Tensile Strength All or part of the hot stamp molded article according to this embodiment has a tensile strength of 1900 MPa or more. For this purpose, it is necessary that the tensile strength of all or part of the steel plate constituting the hot-stamped molded product according to this embodiment is 1900 MPa or more. If the tensile strength of at least a portion of the hot-stamped molded product is not 1900 MPa or more, the deformation load of the hot-stamped molded product cannot be ensured. As a result, the collision resistance properties of the hot-stamped molded product deteriorate. Therefore, the tensile strength of all or part of the hot stamp molded product is set to 1900 MPa or more. Preferably, the tensile strength of all or part of the hot-stamped molded product is 2000 MPa or more, 2100 MPa or more, 2300 MPa or more, or 2500 MPa or more.
On the other hand, since excessively increasing the strength of the hot-stamped molded product causes a decrease in collision resistance, the tensile strength of the hot-stamped molded product is preferably less than 3000 MPa or less than 2800 MPa.
　本実施形態に係るホットスタンプ成形体は、全部（ホットスタンプ成形体の全体）の引張強さが１９００ＭＰａ以上であってもよいが、ホットスタンプ成形体内に引張強さが１９００ＭＰａ以上である部分と１９００ＭＰａ未満である部分とが混在していてもよい。強度の異なる部位を設けることで、衝突時のホットスタンプ成形体の変形状態を制御することが可能となる。強度の異なる部位を有するホットスタンプ成形体は、化学組成が異なる二種類以上の鋼板を接合してからホットスタンプする方法、ホットスタンプを行う工程において、鋼板の加熱温度またはホットスタンプ後の冷却速度を部分的に変化させる方法、並びに、ホットスタンプ成形体に部分的に再加熱処理を施す方法などにより製造することができる。 The hot stamp molded product according to the present embodiment may have a tensile strength of 1900 MPa or more as a whole (the entire hot stamp molded product), but a portion of the hot stamp molded product having a tensile strength of 1900 MPa or more may have a tensile strength of 1900 MPa or more. There may be a mixture of portions that are less than the above. By providing portions with different strengths, it becomes possible to control the deformation state of the hot stamp molded body at the time of collision. A hot-stamped molded body having parts with different strengths can be produced by hot-stamping after joining two or more types of steel plates with different chemical compositions, or by adjusting the heating temperature of the steel plate or the cooling rate after hot-stamping in the hot-stamping process. It can be produced by a method of partially changing the shape, a method of partially reheating a hot stamp molded product, and the like.
　ホットスタンプ成形体の引張強さは、ホットスタンプ成形体から短冊状の小片を採取し、鋼板の表面研削を行うことなく引張試験片に加工し、引張試験を行うことで得る。具体的には、ホットスタンプ成形体から、ＪＩＳ　Ｚ　２２４１：２０１１に準拠して１３Ｂ号の板状試験片を採取し、１０ｍｍ／分の引張速度で引張試験を行うことが好ましい。ホットスタンプ成形体のサイズが小さかったり、形状が複雑であったりするために、１３Ｂ号の板状試験片を採取できない場合には、任意の幅の平行部を有する短冊状の小片を採取し、１０ｍｍ／分の引張速度で引張試験を行い、最大試験力と平行部の原断面積から引張強さを求めてもよい。
　なお、ホットスタンプ成形体内に高強度の部分と低強度の部分とが混在している場合には、高強度の部分から引張試験片を採取する。 The tensile strength of a hot-stamped compact is obtained by taking a small strip-shaped piece from the hot-stamping compact, processing it into a tensile test piece without surface grinding the steel plate, and performing a tensile test. Specifically, it is preferable to take a No. 13B plate-shaped test piece from the hot-stamped molded product in accordance with JIS Z 2241:2011 and conduct a tensile test at a tensile speed of 10 mm/min. If it is not possible to collect a No. 13B plate-shaped test piece because the size of the hot-stamped molded product is small or the shape is complicated, a small strip-shaped piece having a parallel part of an arbitrary width is collected, A tensile test may be performed at a tensile speed of 10 mm/min, and the tensile strength may be determined from the maximum test force and the original cross-sectional area of the parallel portion.
In addition, when a hot-stamped molded article contains a high-strength part and a low-strength part coexisting, a tensile test piece is taken from the high-strength part.
　本実施形態に係るホットスタンプ成形体は、表面にめっき層を有していてもよい。表面にめっき層を有することで、ホットスタンプ後において、耐食性を向上することができる。めっき層の種類として、亜鉛系めっき層またはアルミニウム系めっき層が挙げられる。これらのめっき層を有するホットスタンプ成形体は、亜鉛系めっき鋼板またはアルミニウム系めっき鋼板を用いてホットスタンプすることで得られる。めっき層はホットスタンプ成形体の両面に形成されていてもよく、片面に形成されていてもよい。ホットスタンプ成形体のめっき層は、めっき層を備えるめっき鋼板を用いてホットスタンプすることにより形成させることができる。しかし、めっき鋼板が備えるめっき層は、ホットスタンプ成形体を製造する工程で、ホットスタンプ成形体の表層領域および最表層領域における好ましいＢ濃度分布およびＯ濃度分布の形成を妨げるので、より厳格に製造方法を制御する必要があり、ホットスタンプ成形体の生産性が大きく低下する場合がある。したがって、生産性の観点からは、ホットスタンプ成形体は、表面にめっき層を有さないことが好ましい。 The hot stamp molded article according to this embodiment may have a plating layer on the surface. By having a plating layer on the surface, corrosion resistance can be improved after hot stamping. Examples of the plating layer include a zinc-based plating layer and an aluminum-based plating layer. A hot-stamped molded body having these plating layers is obtained by hot-stamping using a zinc-based plated steel sheet or an aluminum-based plated steel sheet. The plating layer may be formed on both sides of the hot-stamped molded body, or may be formed on one side. The plating layer of the hot stamp molded body can be formed by hot stamping using a plated steel plate provided with the plating layer. However, the plating layer provided on the plated steel sheet prevents the formation of a preferable B concentration distribution and O concentration distribution in the surface layer region and the outermost layer region of the hot stamped product during the process of manufacturing the hot stamped product, so it must be manufactured more strictly. It is necessary to control the method, and the productivity of hot-stamped molded products may be significantly reduced. Therefore, from the viewpoint of productivity, it is preferable that the hot stamp molded product does not have a plating layer on the surface.
　次に、本実施形態に係るホットスタンプ成形体を得るために好適な、ホットスタンプ用鋼板について説明する。
　ホットスタンプを行うことによる化学組成の変化は無視できるほど小さいので、ホットスタンプ用鋼板の化学組成は、上述したホットスタンプ成形体と同じ化学組成であればよい。ホットスタンプ用鋼板の化学組成は、ホットスタンプ用鋼板から試験片を採取し、ホットスタンプ成形体の場合と同じ方法で測定すればよい。 Next, a hot stamping steel plate suitable for obtaining a hot stamping molded article according to the present embodiment will be described.
Since the change in chemical composition caused by hot stamping is negligibly small, the chemical composition of the hot stamping steel sheet may be the same as that of the hot stamping molded product described above. The chemical composition of the hot stamping steel plate may be determined by taking a test piece from the hot stamping steel plate and measuring it in the same manner as in the case of the hot stamping molded product.
　ホットスタンプ用鋼板は、鋼板の表面から５．０μｍ深さ～表面から２５．０μｍ深さの領域（表層領域）における平均Ｂ濃度が、鋼板の表面から１００μｍ深さの位置におけるＢ濃度の０．８５０倍以下であることが好ましい。表層領域の平均Ｂ濃度が、鋼板の表面から１００μｍ深さの位置におけるＢ濃度の０．８５０倍超であると、後述のホットスタンプ条件を適用しても、ホットスタンプ成形体の表層領域および最表層領域においてＢ濃度分布およびＯ濃度分布を好ましく制御することができない。その結果、ホットスタンプ成形体において所望の耐衝突特性を得ることができない。なお、ホットスタンプ用鋼板がめっき層を有する場合は、表面とはめっき層と鋼板との界面のことである。 In a steel plate for hot stamping, the average B concentration in a region (surface layer region) from 5.0 μm deep to 25.0 μm deep from the surface of the steel plate is 0.0% of the B concentration at a position 100 μm deep from the surface of the steel plate. It is preferable that it is 850 times or less. If the average B concentration in the surface layer region is more than 0.850 times the B concentration at a depth of 100 μm from the surface of the steel sheet, even if the hot stamping conditions described below are applied, B concentration distribution and O concentration distribution cannot be favorably controlled in the surface layer region. As a result, desired collision resistance properties cannot be obtained in the hot-stamped molded article. In addition, when the steel plate for hot stamping has a plating layer, the surface refers to the interface between the plating layer and the steel plate.
　ホットスタンプ用鋼板における板厚方向のＢ濃度分布は、ホットスタンプ用鋼板から試験片を採取し、ホットスタンプ成形体の場合と同じ方法でＧＤＳ分析を行うことにより求めることができる。 The B concentration distribution in the thickness direction of a hot stamping steel sheet can be determined by taking a test piece from the hot stamping steel sheet and performing a GDS analysis in the same manner as in the case of a hot stamping compact.
　以下、本実施形態に係るホットスタンプ成形体を得るための、ホットスタンプ用鋼板の製造方法について説明する。 Hereinafter, a method for manufacturing a hot stamping steel plate for obtaining a hot stamping molded body according to the present embodiment will be described.
　ホットスタンプ用鋼板は、上述の化学組成を有するスラブに対して、熱間圧延を施して熱延鋼板とする熱間圧延工程と、前記熱延鋼板に冷間圧延を施して冷延鋼板とする冷間圧延工程と、前記冷延鋼板に焼鈍を施して焼鈍鋼板とする焼鈍工程とを含む製造方法によって製造される。 Steel plates for hot stamping are produced through a hot rolling process in which a slab having the above-mentioned chemical composition is hot-rolled to produce a hot-rolled steel plate, and a cold-rolled steel plate is obtained by cold-rolling the hot-rolled steel plate. It is manufactured by a manufacturing method including a cold rolling step and an annealing step of annealing the cold rolled steel sheet to obtain an annealed steel sheet.
　ホットスタンプ用鋼板の製造方法に供されるスラブの製造方法は、特に限定されない。上述した化学組成を有する鋼は、公知の手段により溶製された後に、連続鋳造法により鋼塊とされるか、または、任意の鋳造法により鋼塊とした後に分塊圧延する方法等により鋼片とされる。連続鋳造工程では、介在物に起因する表面欠陥の発生を抑制するために、鋳型内にて電磁攪拌等の外部付加的な流動を溶鋼に生じさせることが好ましい。鋼塊または鋼片は、一旦冷却されたものを再加熱して熱間圧延に供してもよく、連続鋳造後の高温状態にある鋼塊または分塊圧延後の高温状態にある鋼片をそのまま、あるいは保温して、あるいは補助的な加熱を行って熱間圧延に供してもよい。このような鋼塊および鋼片を、熱間圧延の素材として「スラブ」と総称する。 The method for manufacturing the slab used in the method for manufacturing a hot stamping steel plate is not particularly limited. Steel having the above-mentioned chemical composition is melted by known means and then made into a steel ingot by a continuous casting method, or made into a steel ingot by any casting method and then made into a steel ingot by a method such as blooming. It is considered a piece. In the continuous casting process, in order to suppress the occurrence of surface defects due to inclusions, it is preferable to cause the molten steel to undergo external additional flow such as electromagnetic stirring within the mold. Steel ingots or billets may be once cooled and then reheated and subjected to hot rolling, or steel ingots in a high temperature state after continuous casting or steel billets in a high temperature state after blooming rolling may be used as they are. Alternatively, the material may be subjected to hot rolling by keeping it warm or by performing auxiliary heating. Such steel ingots and slabs are collectively referred to as "slabs" as materials for hot rolling.
　熱間圧延に供するスラブの加熱温度は、オーステナイトの粗大化を防止するために、１２５０℃未満とすることが好ましく、１２００℃未満とすることがより好ましい。スラブ加熱温度が低いと圧延が困難になるので、スラブ加熱温度は１０５０℃以上としてもよい。 The heating temperature of the slab subjected to hot rolling is preferably less than 1250°C, more preferably less than 1200°C, in order to prevent coarsening of austenite. Since rolling becomes difficult if the slab heating temperature is low, the slab heating temperature may be set to 1050° C. or higher.
　加熱されたスラブに対して、熱間圧延を行って熱延鋼板を得る。熱間圧延は、圧延完了後にオーステナイトを変態させることにより熱延鋼板の金属組織を微細化するために、Ａｒ３点以上の温度域で完了させることが好ましい。 The heated slab is hot rolled to obtain a hot rolled steel plate. Hot rolling is preferably completed in a temperature range of Ar 3 or higher in order to refine the metal structure of the hot rolled steel sheet by transforming austenite after rolling is completed.
　熱間圧延後の熱延鋼板を巻取る場合、巻取温度を５５０℃未満とすることが好ましい。巻取温度が５５０℃以上であると、熱的に安定な鉄炭化物が生成し、ホットスタンプ成形体の耐衝突特性が劣化する場合がある。
　一方、巻取温度が低くなりすぎると、熱延鋼板が過度に硬質化して冷間圧延を行うことが困難となるので、巻取温度は５００℃超とすることが好ましい。 When winding up the hot-rolled steel sheet after hot rolling, the winding temperature is preferably less than 550°C. If the winding temperature is 550° C. or higher, thermally stable iron carbides are generated, which may deteriorate the collision resistance properties of the hot-stamped molded product.
On the other hand, if the coiling temperature becomes too low, the hot rolled steel sheet will become excessively hard and it will be difficult to perform cold rolling, so the coiling temperature is preferably over 500°C.
　熱間圧延され、巻取られた熱延鋼板は、常法にしたがって酸洗された後、常法にしたがって冷間圧延され冷延鋼板となる。冷間圧延工程では、冷間圧延における累積圧下率を４０％以上とすることが好ましい。累積圧下率が４０％未満であると、ホットスタンプ用鋼板の金属組織が粗大化する場合がある。ホットスタンプ用鋼板の金属組織が粗大であると、ホットスタンプ後にホットスタンプ成形体の金属組織が粗大化し、成形体の耐衝突特性が低下する原因となる。
　一方、累積圧下率を過度に上昇させることは、圧延設備への負荷を高め生産性の低下を引き起こすので、累積圧下率は７０％未満とすることが好ましい。冷間圧延の後に、常法にしたがって脱脂等の処置を施してもよい。 The hot-rolled steel sheet that has been hot-rolled and wound up is pickled according to a conventional method, and then cold-rolled according to a conventional method to obtain a cold-rolled steel sheet. In the cold rolling process, it is preferable that the cumulative reduction rate in cold rolling is 40% or more. If the cumulative rolling reduction is less than 40%, the metal structure of the hot stamping steel sheet may become coarse. If the metal structure of the steel plate for hot stamping is coarse, the metal structure of the hot stamp molded body will become coarse after hot stamping, which will cause the collision resistance of the molded body to deteriorate.
On the other hand, excessively increasing the cumulative rolling reduction increases the load on the rolling equipment and causes a decrease in productivity, so the cumulative rolling reduction is preferably less than 70%. After cold rolling, treatments such as degreasing may be performed in a conventional manner.
　冷延鋼板は、焼鈍が施され焼鈍鋼板となる。焼鈍工程では、再結晶により焼鈍鋼板（ホットスタンプ用鋼板）の金属組織を微細化するために、均熱温度を７００℃超とすることが好ましい。均熱温度が７００℃以下であると、ホットスタンプ用鋼板の表層領域においてＢ濃度分布を好ましく制御することができない場合がある。その結果、ホットスタンプ成形体において所望の耐衝突特性を得ることができない場合がある。
　一方、加熱速度が遅すぎたり、均熱温度が高すぎたり、均熱時間が長すぎたりすると、粒成長により焼鈍鋼板の金属組織が粗大化し、ホットスタンプ成形体の耐衝突特性が低下する場合がある。そのため、均熱温度までの平均加熱速度を１℃／秒以上とすることが好ましく、均熱温度を８００℃以下とすることが好ましく、均熱時間（均熱温度における保持時間）を６００秒未満とすることが好ましい。また、焼鈍炉内の雰囲気の露点を－２０℃以上、０℃未満とし、且つ、７００℃以上、（Ａｃ３点－３０℃）未満の温度域の滞在時間を３６０秒超、６００秒未満とすることが好ましい。また、焼鈍炉内の雰囲気は水素を１体積％以上、４体積％未満含有する窒素－水素雰囲気とすることが好ましい。 A cold-rolled steel plate is annealed to become an annealed steel plate. In the annealing step, in order to refine the metal structure of the annealed steel plate (steel plate for hot stamping) by recrystallization, it is preferable that the soaking temperature be higher than 700°C. If the soaking temperature is 700° C. or lower, it may not be possible to preferably control the B concentration distribution in the surface layer region of the hot stamping steel sheet. As a result, it may not be possible to obtain desired collision resistance properties in the hot-stamped molded article.
On the other hand, if the heating rate is too slow, the soaking temperature is too high, or the soaking time is too long, the metal structure of the annealed steel sheet will become coarse due to grain growth, and the collision resistance of the hot stamped product may deteriorate. There is. Therefore, it is preferable that the average heating rate up to the soaking temperature is 1°C/sec or more, the soaking temperature is preferably 800°C or less, and the soaking time (holding time at the soaking temperature) is less than 600 seconds. It is preferable that In addition, the dew point of the atmosphere in the annealing furnace should be set to -20°C or higher and lower than 0°C, and the residence time in the temperature range of 700°C or higher and lower than (Ac 3 points -30°C) should be set to more than 360 seconds and less than 600 seconds. It is preferable to do so. Further, the atmosphere in the annealing furnace is preferably a nitrogen-hydrogen atmosphere containing 1% by volume or more and less than 4% by volume of hydrogen.
　露点が－２０℃未満または０℃以上であるか、７００℃以上、（Ａｃ３点－３０℃）未満の温度域における滞在時間が３６０秒以下であると、ホットスタンプ用鋼板の表層領域においてＢ濃度分布を好ましく制御することができない場合がある。その結果、ホットスタンプ成形体において所望の耐衝突特性を得ることができない場合がある。
　一方、上記温度域における滞在時間が６００秒以上であると、ホットスタンプ用鋼板において過度の脱炭が生じ、ホットスタンプ後にホットスタンプ成形体の強度が不足する場合がある。上述した方法で製造された焼鈍鋼板に、常法にしたがってめっきを行いめっき鋼板としてもよい。このようにして得られた焼鈍鋼板またはめっき鋼板には、常法にしたがって調質圧延を行ってもよい。 If the dew point is less than -20°C or 0°C or more, or the residence time in the temperature range of 700°C or more and less than (Ac 3 points -30°C) is 360 seconds or less, B in the surface area of the hot stamping steel plate In some cases, it may not be possible to control the concentration distribution favorably. As a result, it may not be possible to obtain desired collision resistance properties in the hot-stamped molded article.
On the other hand, if the residence time in the above temperature range is 600 seconds or more, excessive decarburization may occur in the hot stamping steel plate, and the strength of the hot stamped molded product may be insufficient after hot stamping. The annealed steel sheet produced by the method described above may be plated according to a conventional method to obtain a plated steel sheet. The annealed steel sheet or plated steel sheet thus obtained may be subjected to temper rolling according to a conventional method.
　なお、Ａｃ３点とは、素材鋼板を加熱した際に金属組織中でフェライトが消失する温度であり、冷延鋼板を８℃／秒の加熱速度で加熱した際の熱膨張変化から求めることができる。 The Ac 3 point is the temperature at which ferrite disappears in the metal structure when the raw steel sheet is heated, and can be determined from the thermal expansion change when a cold rolled steel sheet is heated at a heating rate of 8°C/sec. can.
　本実施形態に係るホットスタンプ成形体は、上述の方法により製造したホットスタンプ用鋼板（焼鈍鋼板またはめっき鋼板）を加熱する加熱工程と、加熱されたホットスタンプ用鋼板に対してホットスタンプを行うホットスタンプ工程とを含む製造方法によって得ることができる。本実施形態に係るホットスタンプ成形体を安定的に得るために、ホットスタンプは以下の方法により行うことが好ましい。 The hot stamping molded article according to the present embodiment includes a heating process of heating a hot stamping steel plate (annealed steel plate or plated steel plate) produced by the method described above, and a hot stamping process of hot stamping the heated steel plate for hot stamping. It can be obtained by a manufacturing method including a stamping step. In order to stably obtain the hot-stamped molded article according to this embodiment, hot-stamping is preferably performed by the following method.
　加熱工程では、ホットスタンプ工程に先立ち、上述の化学組成および板厚方向のＢ濃度分布を有するホットスタンプ用鋼板を加熱する。加熱工程では、プロパンガスを含む可燃性ガスを用いたガス燃焼炉を使用し、空気比を０．８４以下としてホットスタンプ用鋼板を加熱することが好ましい。加熱温度は９５０℃超かつＡｃ３点超とし、加熱温度での保持時間は３６０秒超とすることが好ましい。なお、空気比とは、理論空気量（Ａ０）に対して実際に投入する空気量（Ａ）の比率（Ａ／Ａ０）である。また、加熱工程におけるＡｃ３点は、ホットスタンプ用鋼板の内層領域のＡｃ３点を意味し、上述の方法で求めた冷延鋼板のＡｃ３点と同じ値とすればよい。 In the heating step, prior to the hot stamping step, a hot stamping steel sheet having the above-described chemical composition and B concentration distribution in the thickness direction is heated. In the heating step, it is preferable to use a gas combustion furnace using a flammable gas containing propane gas to heat the hot stamping steel plate at an air ratio of 0.84 or less. It is preferable that the heating temperature is higher than 950° C. and higher than 3 Ac points, and the holding time at the heating temperature is higher than 360 seconds. Note that the air ratio is the ratio (A/A 0 ) of the amount of air (A) actually introduced to the theoretical amount of air (A 0 ). Moreover, the Ac 3 points in the heating process means the Ac 3 points of the inner layer region of the hot stamping steel sheet, and may be the same value as the Ac 3 points of the cold rolled steel sheet determined by the above method.
　空気比が０．８４超であるか、加熱温度が９５０℃以下であるか、保持時間が３６０秒以下であると、ホットスタンプ成形体の表層領域および最表層領域におけるＢ濃度分布およびＯ濃度分布を好ましく制御することができない場合がある。また、加熱温度がＡｃ３点以下であると、ホットスタンプ成形体の内層領域の金属組織においてマルテンサイトの体積率が不足し、ホットスタンプ成形体の強度が低下する場合がある。
　一方、加熱温度が高すぎたり、加熱温度での保持時間が長すぎたりすると、ホットスタンプ成形体の金属組織が粗大化し、ホットスタンプ成形体の耐衝突特性が低下するとともに、強度が低下する場合がある。そのため、加熱温度は１０５０℃未満とすることが好ましく、保持時間は６００秒未満とすることが好ましい。 If the air ratio is more than 0.84, the heating temperature is 950°C or less, or the holding time is 360 seconds or less, the B concentration distribution and O concentration distribution in the surface layer region and the outermost layer region of the hot stamp molded article In some cases, it may not be possible to control the Moreover, if the heating temperature is 3 points or less of Ac, the volume fraction of martensite may be insufficient in the metal structure of the inner layer region of the hot-stamped molded product, and the strength of the hot-stamped molded product may decrease.
On the other hand, if the heating temperature is too high or the holding time at the heating temperature is too long, the metal structure of the hot stamped product will become coarser, which will reduce the collision resistance of the hot stamped product and reduce its strength. There is. Therefore, the heating temperature is preferably less than 1050°C, and the holding time is preferably less than 600 seconds.
　ホットスタンプ工程では、加熱されたホットスタンプ用鋼板を加熱炉から取り出し大気中で放冷した後、７５０℃超の温度域でホットスタンプを開始することが好ましい。ホットスタンプの開始温度が７５０℃以下であると、ホットスタンプ成形体の内層領域の金属組織においてフェライトが過剰に生成し、ホットスタンプ成形体の強度が低下する場合がある。ホットスタンプにより成形を行った後、金型内でホットスタンプ成形体を保持しながら冷却、および／または、金型からホットスタンプ成形体を取り出して任意の方法で冷却する。 In the hot stamping step, it is preferable to take out the heated steel plate for hot stamping from the heating furnace and allow it to cool in the atmosphere, and then start hot stamping in a temperature range of over 750°C. If the starting temperature of hot stamping is 750° C. or lower, ferrite may be excessively produced in the metal structure of the inner layer region of the hot stamped body, and the strength of the hot stamped body may decrease. After molding by hot stamping, the hot stamp molded product is cooled while being held in a mold, and/or the hot stamp molded product is taken out from the mold and cooled by an arbitrary method.
　冷却速度が低いと、ホットスタンプ成形体の内層領域の金属組織においてマルテンサイトの体積率が不足し、ホットスタンプ成形体の強度が低下する場合がある。そのため、ホットスタンプ開始温度から４００℃までの平均冷却速度は３０℃／秒以上、６０℃／秒以上または９０℃／秒以上とすることが好ましい。また、冷却停止温度が高いと、ホットスタンプ成形体の内層領域の金属組織においてマルテンサイトの体積率が不足し、ホットスタンプ成形体の強度が低下する場合がある。そのため、上記冷却による冷却停止温度は９０℃未満とすることが好ましい。 If the cooling rate is low, the volume fraction of martensite may be insufficient in the metal structure of the inner layer region of the hot-stamped body, and the strength of the hot-stamped body may decrease. Therefore, the average cooling rate from the hot stamping start temperature to 400°C is preferably 30°C/second or more, 60°C/second or more, or 90°C/second or more. Furthermore, if the cooling stop temperature is high, the volume fraction of martensite may be insufficient in the metal structure of the inner layer region of the hot-stamped body, and the strength of the hot-stamped body may decrease. Therefore, it is preferable that the cooling stop temperature by the above-mentioned cooling is less than 90°C.
　以上の方法により、本実施形態に係るホットスタンプ成形体を得る。なお、ホットスタンプ成形後に、ホットスタンプ成形体の強度が確保される範囲で、再加熱処理を行ってもよい。再加熱処理を行う場合には、加熱温度は（Ａｃ３点－１００℃）未満とすることが好ましい。再加熱処理の加熱温度が（Ａｃ３点－１００℃）以上であると、ホットスタンプ成形体の表層領域および最表層領域が十分に軟質化せず、ホットスタンプ成形体の耐衝突特性が低下する場合がある。ホットスタンプ成形体の一部をレーザー照射等により再加熱して部分的に軟化領域を設けても良い。また、ホットスタンプ成形体にブラスト処理を行ってもよいし、塗装および焼付け処理を行ってもよい。 By the above method, a hot stamp molded article according to the present embodiment is obtained. Note that after the hot stamp molding, reheating treatment may be performed as long as the strength of the hot stamp molded product is ensured. When performing reheating treatment, the heating temperature is preferably lower than (Ac 3 point - 100°C). If the heating temperature of the reheating treatment is (Ac 3 points - 100°C) or higher, the surface layer region and the outermost layer region of the hot stamped molded product will not be sufficiently softened, and the collision resistance properties of the hot stamped molded product will deteriorate. There are cases. A portion of the hot stamp molded body may be reheated by laser irradiation or the like to provide a partially softened region. Further, the hot stamp molded body may be subjected to blasting treatment, or may be subjected to painting and baking treatment.
　次に、本発明の実施例について説明するが、実施例での条件は、本発明の実施可能性及び効果を確認するために採用した一条件例であり、本発明は、この一条件例に限定されるものではない。本発明は、本発明の要旨を逸脱せず、本発明の目的を達成する限りにおいて、種々の条件を採用し得るものである。 Next, an example of the present invention will be described. The conditions in the example are examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is based on this example of conditions. It is not limited. 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.
　真空溶解炉を用いて溶鋼を鋳造することで表１に示す化学組成を有する鋼材を得た。得られた鋼材を１２００℃に加熱して６０分間保持した後、９００℃以上の温度域で１０パスの熱間圧延を施すことで、厚さ３．５ｍｍの熱延鋼板を得た。熱間圧延後、水スプレーで、熱延鋼板を５４０℃まで冷却した。冷却終了温度を巻取温度とし、この巻取温度に保持した電気加熱炉中に熱延鋼板を装入して６０分間保持した。その後、熱延鋼板を２０℃／時間の平均冷却速度で室温まで炉冷却して、巻取り後の徐冷をシミュレートした。炉冷却後の熱延鋼板を酸洗した後、冷間圧延を施すことで厚さ１．４ｍｍの冷延鋼板を得た。冷間圧延時の累積圧下率は６０％とした。 A steel material having the chemical composition shown in Table 1 was obtained by casting molten steel using a vacuum melting furnace. The obtained steel material was heated to 1200° C. and held for 60 minutes, and then hot rolled for 10 passes in a temperature range of 900° C. or higher to obtain a hot rolled steel plate with a thickness of 3.5 mm. After hot rolling, the hot rolled steel sheet was cooled to 540° C. with water spray. The cooling end temperature was defined as the coiling temperature, and the hot rolled steel sheet was charged into an electric heating furnace maintained at this coiling temperature and maintained for 60 minutes. Thereafter, the hot rolled steel sheet was furnace cooled to room temperature at an average cooling rate of 20° C./hour to simulate slow cooling after winding. After the hot-rolled steel sheet was cooled in the furnace, it was pickled and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 1.4 mm. The cumulative reduction rate during cold rolling was 60%.
　なお、表１中の「－」は当該元素の含有量が検出限界値未満であったことを示す。
　表１中のＡｃ３点は、鋼Ａ～Ｎの冷延鋼板を８℃／秒で加熱した際の熱膨張変化から求めた。 Note that "-" in Table 1 indicates that the content of the element was below the detection limit.
The three Ac points in Table 1 were determined from the change in thermal expansion when cold-rolled steel plates of steels A to N were heated at 8° C./sec.
　得られた冷延鋼板を、連続焼鈍シミュレーターを用いて表２Ａおよび表２Ｂに示す焼鈍条件で焼鈍した。なお、表２Ａおよび表２Ｂに記載の均熱温度まで、８℃／秒の平均加熱速度で加熱した。焼鈍炉内の雰囲気は、水素を３体積％含有する窒素－水素雰囲気とし、露点は表２Ａおよび表２Ｂに記載の通りとした。均熱後、室温まで冷却することで焼鈍鋼板（ホットスタンプ用鋼板）を得た。 The obtained cold rolled steel sheets were annealed using a continuous annealing simulator under the annealing conditions shown in Table 2A and Table 2B. Note that heating was performed at an average heating rate of 8° C./sec to the soaking temperature shown in Table 2A and Table 2B. The atmosphere in the annealing furnace was a nitrogen-hydrogen atmosphere containing 3% by volume of hydrogen, and the dew points were as shown in Tables 2A and 2B. After soaking, an annealed steel plate (a steel plate for hot stamping) was obtained by cooling to room temperature.
　得られたホットスタンプ用鋼板の３カ所からＧＤＳ分析用試験片を採取し、試験片の表面を測定開始面とし、上述の方法により、測定開始面から板厚方向に１２０μｍの深さ位置までＧＤＳ分析を行った。これにより、ホットスタンプ用鋼板の表面から５．０μｍ深さ～表面から２５．０μｍ深さの領域（表層領域）における平均Ｂ濃度、および表面から１００μｍ深さ位置におけるＢ濃度を得た。鋼板の表面から１００μｍ深さ位置までの測定点は１５００点とした。得られた結果を表２に示す。 Test pieces for GDS analysis were taken from three locations on the obtained steel plate for hot stamping, the surface of the test piece was used as the measurement starting surface, and GDS was performed from the measurement starting surface to a depth of 120 μm in the sheet thickness direction using the method described above. Analysis was carried out. As a result, the average B concentration in a region (surface layer region) from 5.0 μm deep to 25.0 μm deep from the surface of the hot stamping steel plate and the B concentration at a position 100 μm deep from the surface were obtained. The number of measurement points from the surface of the steel plate to a depth of 100 μm was 1500 points. The results obtained are shown in Table 2.
　次に、得られたホットスタンプ用鋼板から、幅２４０ｍｍ、長さ８００ｍｍのホットスタンプ用素板を採取し、ホットスタンプを行うことにより図１に示す形状のハット部材（ホットスタンプ成形体）を得た。ホットスタンプ工程では、ガス燃焼炉を用いて、表３に示す条件でホットスタンプ用素板を加熱した。具体的には、燃焼ガスにプロパンガスを用い、加熱温度、保持時間、空気比を表３に示す条件とした。その後、ホットスタンプ用素板を加熱炉から取り出して放冷した後、冷却装置を備えた金型に挟んで、成形開始温度を７７０℃以上としてハット成形を行った。続いて、成形開始温度から４００℃までの平均冷却速度は５０℃／秒以上とし、８０℃以下の冷却停止温度まで金型内で冷却した。また、ハット部材の表面に生成した酸化スケール（鉄の酸化物）をショットブラストにより除去した。 Next, a blank plate for hot stamping with a width of 240 mm and a length of 800 mm is taken from the obtained steel plate for hot stamping, and hot stamping is performed to obtain a hat member (hot stamp molded body) having the shape shown in Fig. 1. Ta. In the hot stamping step, the hot stamping blanks were heated under the conditions shown in Table 3 using a gas combustion furnace. Specifically, propane gas was used as the combustion gas, and the heating temperature, holding time, and air ratio were as shown in Table 3. Thereafter, the blank for hot stamping was taken out from the heating furnace and allowed to cool, and then placed between molds equipped with a cooling device, and hat molding was performed at a molding start temperature of 770° C. or higher. Subsequently, the average cooling rate from the molding start temperature to 400°C was set to 50°C/sec or more, and the mold was cooled to a cooling stop temperature of 80°C or less. In addition, oxide scale (iron oxide) generated on the surface of the hat member was removed by shot blasting.
　得られたハット部材の縦壁部から試験片を採取し、上述した方法により化学組成を測定した。 A test piece was taken from the vertical wall of the obtained hat member, and its chemical composition was measured by the method described above.
　また、ハット部材の縦壁部から、ハット部材の長手方向に沿ってＪＩＳ　Ｚ　２２４１：２０１１に準拠して１３Ｂ号の板状試験片を採取し、１０ｍｍ／分の引張速度で引張試験を行うことで引張強さを求めた。
　得られた引張強さが１９００ＭＰａ以上であった場合、高い強度を有するとして合格と判定した。一方、得られた引張強さが１９００ＭＰａ未満であった場合、高い強度を有さないとして不合格と判定した。 In addition, a No. 13B plate-shaped test piece shall be taken from the vertical wall portion of the hat member along the longitudinal direction of the hat member in accordance with JIS Z 2241:2011, and a tensile test shall be conducted at a tensile speed of 10 mm/min. The tensile strength was determined.
When the obtained tensile strength was 1900 MPa or more, it was determined that the product had high strength and passed. On the other hand, when the obtained tensile strength was less than 1900 MPa, it was determined that the product did not have high strength and was rejected.
　また、ハット部材の縦壁部の３カ所からＧＤＳ分析用試験片を採取し、試験片の表面を測定開始面とし、上述の方法により、測定開始面から板厚方向に１２０μｍの深さ位置までＧＤＳ分析を行った。これにより、表面から５．０μｍ深さ～表面から２５．０μｍ深さの領域（表層領域）における平均Ｂ濃度、表面から０．５μｍ深さ～表面から４．０μｍ深さの領域（最表層領域）における平均Ｂ濃度および平均Ｏ濃度、並びに、表面から１００μｍ深さ位置におけるＢ濃度を求めた。鋼板の表面から１００μｍ深さ位置までの測定点は１５００点とした。 In addition, test pieces for GDS analysis were taken from three locations on the vertical wall of the hat member, and using the surface of the test piece as the measurement starting surface, the method described above was carried out to a depth of 120 μm in the thickness direction from the measurement starting surface. GDS analysis was performed. As a result, the average B concentration in the region from 5.0 μm depth to 25.0 μm depth from the surface (surface layer region), and the average B concentration in the region from 0.5 μm depth to 4.0 μm depth from the surface (surface layer region). ), and the B concentration at a depth of 100 μm from the surface were determined. The number of measurement points from the surface of the steel plate to a depth of 100 μm was 1500 points.
　また、ハット部材の縦壁部から組織観察用試験片を採取し、この試験片の縦断面を研磨した後、上述した方法により表面から０．５μｍ深さ～表面から４．０μｍ深さの領域（最表層領域）および表面から１００μｍ深さ～板厚１／２位置（内層領域）における金属組織を観察した。 In addition, a test piece for tissue observation was taken from the vertical wall of the hat member, and after polishing the longitudinal section of this test piece, the area from 0.5 μm deep to 4.0 μm deep from the surface was prepared using the method described above. (the outermost layer region) and the metal structure at a depth of 100 μm from the surface to 1/2 the plate thickness (inner layer region) were observed.
　また、図２に示すように、ハット部材に厚さ１．４ｍｍ、幅１３０ｍｍ、長さ８００ｍｍのクロージングプレートを溶接することで、３点曲げ試験用の試験体を得た。クロージングプレートには引張強さが１５５３ＭＰａである鋼板を用いた。 Further, as shown in FIG. 2, a test specimen for a three-point bending test was obtained by welding a closing plate with a thickness of 1.4 mm, a width of 130 mm, and a length of 800 mm to the hat member. A steel plate having a tensile strength of 1553 MPa was used for the closing plate.
　得られた試験体を、図３に示すように、ロール間隔７００ｍｍで配置された２本の支持ロールの上に、長さ８００ｍｍの試験体をクロージングプレートが下側になるように乗せ、２ｍ／秒の試験速度で３点曲げ試験を行った。これにより、最高荷重、および、試験体とインパクターとが接触してから試験体に割れが生じ始めるまでの変位（割れ発生変位）を求めた。
　ホットスタンプ成形体を構成する鋼板の引張強さが２３００ＭＰａ未満である場合は、最高荷重が１８．０ｋＮ以上であり、且つ、割れ発生変位が５０ｍｍ以上であった場合を、優れた耐衝突特性を有するとして合格と判定した。また、引張強さが２３００ＭＰａ以上である場合は、最高荷重が２３．０ｋＮ以上であり、且つ、割れ発生変位が３５ｍｍ以上であった場合、優れた耐衝突特性を有するとして合格と判定した。これらの条件を満たさなかった場合は、優れた耐衝突特性を有さないとして不合格と判定した。 As shown in Fig. 3, the test specimen with a length of 800 mm was placed on two supporting rolls arranged with a roll interval of 700 mm, with the closing plate facing downward, and the specimen was rolled at a speed of 2 m/min. A three-point bending test was conducted at a test speed of seconds. As a result, the maximum load and the displacement from when the test piece and the impactor came into contact until the test piece started to crack (cracking occurrence displacement) were determined.
If the tensile strength of the steel plate constituting the hot-stamped compact is less than 2300 MPa, the maximum load is 18.0 kN or more, and the displacement at which cracking occurs is 50 mm or more. It was judged as passing the test. In addition, when the tensile strength is 2300 MPa or more, the maximum load is 23.0 kN or more, and the cracking displacement is 35 mm or more, it is judged as having excellent collision resistance properties and passed. If these conditions were not met, it was determined that the product did not have excellent collision resistance and was rejected.
　表４Ａおよび表４Ｂに、ホットスタンプ成形体の化学組成を測定した結果、ホットスタンプ成形体の機械特性を測定した結果、ホットスタンプ成形体におけるＢおよびＯ濃度分布を測定した結果、並びに、ホットスタンプ成形体の耐衝突特性を評価した結果を示す。
　なお、ホットスタンプ成形体のＣを除く元素の含有量は、表１に示す元素の含有量と同一であったため省略している。 Tables 4A and 4B show the results of measuring the chemical composition of the hot-stamped molded product, the results of measuring the mechanical properties of the hot-stamped molded product, the results of measuring the B and O concentration distribution in the hot-stamped molded product, and the results of measuring the hot-stamped molded product. The results of evaluating the collision resistance properties of the molded body are shown.
Note that the contents of the elements other than C in the hot-stamped molded body were omitted because they were the same as the contents of the elements shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000006
Figure JPOXMLDOC01-appb-T000006
　本発明例に係るホットスタンプ成形体は、引張強さが１９００ＭＰａ以上であり、高い強度を有していた。また、表層領域における平均Ｂ濃度が低く、最表層領域における平均Ｂ濃度および平均Ｏ濃度が高く、耐衝突特性に優れていた。
　本発明例に係るホットスタンプ成形体の金属組織は、内層領域ではマルテンサイトの体積率は９１．０％以上であり、マルテンサイト以外の組織の合計の体積率は９．０％以下であった。
　また、最表層領域では、フェライトの体積率は６．０％以上であり、フェライト以外の組織の合計の体積率は９４．０％以下であった。 The hot-stamped molded article according to the example of the present invention had a tensile strength of 1900 MPa or more, and had high strength. Further, the average B concentration in the surface layer region was low, the average B concentration and the average O concentration in the outermost layer region were high, and the collision resistance was excellent.
In the metal structure of the hot-stamped molded article according to the example of the present invention, the volume fraction of martensite in the inner layer region was 91.0% or more, and the total volume fraction of structures other than martensite was 9.0% or less. .
Further, in the outermost layer region, the volume fraction of ferrite was 6.0% or more, and the total volume fraction of structures other than ferrite was 94.0% or less.
　これに対して、ホットスタンプ成形体の化学組成が発明範囲から外れる比較例（試験番号１、５および１７）は、Ｃ含有量が低すぎたか、または、ｓｏｌ．Ａｌ含有量が高すぎたため、ホットスタンプ成形体の引張強さが１９００ＭＰａ未満となり強度が劣り、且つ、最高荷重が低く耐衝突特性が劣った。 On the other hand, in the comparative examples (test numbers 1, 5 and 17) in which the chemical composition of the hot-stamped molded body was outside the scope of the invention, the C content was too low or the sol. Because the Al content was too high, the tensile strength of the hot-stamped molded product was less than 1900 MPa, resulting in poor strength, and the maximum load was low, resulting in poor collision resistance.
　試験番号１５は、Ｃ含有量が高すぎたため、ホットスタンプ成形体の割れ発生変位が低く耐衝突特性が劣った。なお、引張試験では早期破断が生じ引張強さを求めることができず、破断強度は１９００ＭＰａ未満であった。 In test number 15, the C content was too high, so the cracking displacement of the hot-stamped molded product was low and the crash resistance was poor. In addition, in the tensile test, early breakage occurred and the tensile strength could not be determined, and the breaking strength was less than 1900 MPa.
　試験番号１６は、Ｂ含有量が低すぎたため、ホットスタンプ成形体の引張強さが１９００ＭＰａ未満となり強度が劣った。また、最表層領域における平均Ｂ濃度および平均Ｏ濃度が低く、最高荷重および割れ発生変位が低く耐衝突特性が劣った。 In test number 16, the B content was too low, so the tensile strength of the hot-stamped molded product was less than 1900 MPa, resulting in poor strength. Furthermore, the average B concentration and average O concentration in the outermost layer region were low, and the maximum load and crack initiation displacement were low, resulting in poor collision resistance.
　ホットスタンプ成形体の化学組成は好ましい範囲内であるが、製造条件が好ましい条件から外れた比較例の試験番号３、４、７、８、１０、１１、１３、１４、２４、２５および２７は、表層領域における平均Ｂ濃度、最表層領域における平均Ｂ濃度および最表層領域における平均Ｏ濃度のうち、一つ以上が発明範囲を外れた。そのため、ホットスタンプ成形体の割れ発生変位が低く、または、最高荷重および割れ発生変位が低く、耐衝突特性が劣った。 The chemical composition of the hot-stamped molded product was within the preferred range, but the comparative example test numbers 3, 4, 7, 8, 10, 11, 13, 14, 24, 25, and 27 had manufacturing conditions outside the preferred range. , the average B concentration in the surface layer region, the average B concentration in the outermost layer region, and the average O concentration in the outermost layer region were out of the invention range. Therefore, the cracking displacement of the hot-stamped molded body was low, or the maximum load and cracking displacement were low, resulting in poor collision resistance.
　本発明に係る上記態様によれば、高い強度および優れた耐衝突特性を有するホットスタンプ成形体を提供することができる。 According to the above aspect of the present invention, it is possible to provide a hot-stamped molded article having high strength and excellent collision resistance.

Claims (2)

  1. 　鋼板を備えるホットスタンプ成形体であって、
    　前記鋼板の全部または一部は、化学組成が、質量％で、
    Ｃ　：０．３２％超、０．７０％以下、
    Ｓｉ：２．００％未満、
    Ｍｎ：０．０１～３．００％、
    Ｐ　：０．２００％以下、
    Ｓ　：０．０２００％以下、
    ｓｏｌ．Ａｌ：０．００１～１．０００％、
    Ｎ　：０．０２００％以下、
    Ｏ　：０．０００５～０．０２００％、
    Ｂ　：０．０００５～０．０２００％、
    Ｃｒ：０～２．００％、
    Ｍｏ：０～２．００％、
    Ｗ　：０～２．００％、
    Ｃｕ：０～２．００％、
    Ｎｉ：０～２．００％、
    Ｔｉ：０～０．２００％、
    Ｎｂ：０～０．２００％、
    Ｖ　：０～０．２００％、
    Ｚｒ：０～０．２００％、
    Ｃａ：０～０．１０００％、
    Ｍｇ：０～０．１０００％、
    ＲＥＭ：０～０．１０００％、
    Ｓｎ：０～０．２００％、
    Ａｓ：０～０．１００％、および
    Ｂｉ：０～０．０５００％を含有し、
    　残部がＦｅおよび不純物からなり、
    　引張強さが１９００ＭＰａ以上であり、
    　前記鋼板の表面から５．０μｍ深さ～前記表面から２５．０μｍ深さの領域における平均Ｂ濃度が、前記表面から１００μｍ深さの位置におけるＢ濃度の０．７００倍以下であり、
    　前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの領域における平均Ｂ濃度が、前記表面から１００μｍ深さの前記位置における前記Ｂ濃度の１．６００倍以上であり、
    　前記表面から０．５μｍ深さ～前記表面から４．０μｍ深さの前記領域における平均Ｏ濃度が、０．０１５０質量％超であることを特徴とするホットスタンプ成形体。     A hot stamped molded body comprising a steel plate,
    All or part of the steel plate has a chemical composition in mass%,
    C: more than 0.32%, less than 0.70%,
    Si: less than 2.00%,
    Mn: 0.01 to 3.00%,
    P: 0.200% or less,
    S: 0.0200% or less,
    sol. Al: 0.001-1.000%,
    N: 0.0200% or less,
    O: 0.0005 to 0.0200%,
    B: 0.0005-0.0200%,
    Cr: 0-2.00%,
    Mo: 0-2.00%,
    W: 0-2.00%,
    Cu: 0-2.00%,
    Ni: 0-2.00%,
    Ti: 0-0.200%,
    Nb: 0 to 0.200%,
    V: 0 to 0.200%,
    Zr: 0-0.200%,
    Ca: 0-0.1000%,
    Mg: 0 to 0.1000%,
    REM: 0-0.1000%,
    Sn: 0-0.200%,
    Contains As: 0 to 0.100% and Bi: 0 to 0.0500%,
    The remainder consists of Fe and impurities,
    The tensile strength is 1900 MPa or more,
    The average B concentration in a region from a depth of 5.0 μm to a depth of 25.0 μm from the surface of the steel plate is 0.700 times or less of the B concentration at a position 100 μm deep from the surface,
    The average B concentration in a region from a depth of 0.5 μm to a depth of 4.0 μm from the surface is 1.600 times or more of the B concentration at the position 100 μm deep from the surface,
    A hot-stamped molded article characterized in that the average O concentration in the region from a depth of 0.5 μm to a depth of 4.0 μm from the surface is more than 0.0150% by mass.
  2. 　前記化学組成が、質量％で、
    Ｃｒ：０．０１～２．００％、
    Ｍｏ：０．０１～２．００％、
    Ｗ　：０．０１～２．００％、
    Ｃｕ：０．０１～２．００％、
    Ｎｉ：０．０１～２．００％、
    Ｔｉ：０．００１～０．２００％、
    Ｎｂ：０．００１～０．２００％、
    Ｖ　：０．００１～０．２００％、
    Ｚｒ：０．００１～０．２００％、
    Ｃａ：０．０００１～０．１０００％、
    Ｍｇ：０．０００１～０．１０００％、
    ＲＥＭ：０．０００１～０．１０００％、
    Ｓｎ：０．００１～０．２００％、
    Ａｓ：０．００１～０．１００％、および
    Ｂｉ：０．０００１～０．０５００％
    からなる群のうち１種または２種以上を含有することを特徴とする請求項１に記載のホットスタンプ成形体。     The chemical composition is in mass%,
    Cr: 0.01-2.00%,
    Mo: 0.01-2.00%,
    W: 0.01-2.00%,
    Cu: 0.01-2.00%,
    Ni: 0.01-2.00%,
    Ti: 0.001 to 0.200%,
    Nb: 0.001-0.200%,
    V: 0.001-0.200%,
    Zr: 0.001 to 0.200%,
    Ca: 0.0001-0.1000%,
    Mg: 0.0001-0.1000%,
    REM: 0.0001-0.1000%,
    Sn: 0.001-0.200%,
    As: 0.001 to 0.100%, and Bi: 0.0001 to 0.0500%
    The hot-stamped molded article according to claim 1, characterized in that it contains one or more of the group consisting of:
PCT/JP2023/013803 2022-04-14 2023-04-03 Hot-stamp formed article WO2023199777A1 (en)

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JP2022-067026 2022-04-14

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006152427A (en) * 2004-10-29 2006-06-15 Sumitomo Metal Ind Ltd Hot-pressed steel sheet member, manufacturing method therefor and steel sheet to be hot-pressed
WO2016163469A1 (en) * 2015-04-08 2016-10-13 新日鐵住金株式会社 Heat-treated steel sheet member, and production method therefor
WO2019003449A1 (en) * 2017-06-30 2019-01-03 Ｊｆｅスチール株式会社 Hot-pressed member and method for manufacturing same, and cold-rolled steel sheet for hot pressing
JP2021155793A (en) * 2020-03-26 2021-10-07 日本製鉄株式会社 Steel plate for hot-stamping component and method for manufacturing the same

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006152427A (en) * 2004-10-29 2006-06-15 Sumitomo Metal Ind Ltd Hot-pressed steel sheet member, manufacturing method therefor and steel sheet to be hot-pressed
WO2016163469A1 (en) * 2015-04-08 2016-10-13 新日鐵住金株式会社 Heat-treated steel sheet member, and production method therefor
WO2019003449A1 (en) * 2017-06-30 2019-01-03 Ｊｆｅスチール株式会社 Hot-pressed member and method for manufacturing same, and cold-rolled steel sheet for hot pressing
JP2021155793A (en) * 2020-03-26 2021-10-07 日本製鉄株式会社 Steel plate for hot-stamping component and method for manufacturing the same

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