WO2023234337A1 - Article formé par estampage à chaud - Google Patents

Article formé par estampage à chaud Download PDF

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Publication number
WO2023234337A1
WO2023234337A1 PCT/JP2023/020238 JP2023020238W WO2023234337A1 WO 2023234337 A1 WO2023234337 A1 WO 2023234337A1 JP 2023020238 W JP2023020238 W JP 2023020238W WO 2023234337 A1 WO2023234337 A1 WO 2023234337A1
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WIPO (PCT)
Prior art keywords
less
hot
content
stamped
molded product
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PCT/JP2023/020238
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English (en)
Japanese (ja)
Inventor
祐馬 浅田
翔平 藪
由梨 戸田
靖之 荻巣
環輝 鈴木
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日本製鉄株式会社
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Publication of WO2023234337A1 publication Critical patent/WO2023234337A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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

Definitions

  • the present invention relates to a hot stamp molded article.
  • This application claims priority based on Japanese Patent Application No. 2022-090847 filed in Japan on June 3, 2022, the contents of which are incorporated herein.
  • Hot stamping technology is progressing, in which press forming is performed after heating the steel plate to a high temperature in the austenite region where the steel plate becomes soft.
  • Hot stamping is attracting attention as a technology that achieves both moldability into automobile parts and strength of automobile parts by performing quenching treatment in a mold at the same time as press working.
  • Patent Document 1 discloses a quench-hardenable steel that has excellent cold formability properties and can be reheated and quench-hardened to obtain a steel with excellent impact strength and hardness. There is.
  • Patent Document 1 does not consider bendability.
  • the present invention has been made in view of the above problems, and an object of the present invention is to provide a hot stamp molded product having high strength and excellent bendability.
  • the hot stamp molded article according to one embodiment of the present invention has a chemical composition in mass %, C: 0.40-0.70%, Si: 0.010-3.000%, Mn: 0.10% or more, less than 0.60%, P: 0.100% or less, S: 0.0100% or less, N: 0.0100% or less, O: 0.0200% or less, Al: 0.0010-0.5000%, Nb: 0.0010-0.1000%, Ti: 0.010 to 0.100%, Cr: 0.010-1.000%, Mo: 0.050-1.000%, B: 0.0005-0.0100%, Co: 0-3.00%, Ni: 0-3.00%, Cu: 0-3.00%, V: 0 to 3.00%, W: 0-3.00%, Ca: 0-0.1000%, Mg: 0 to 1.0000%, REM: 0-1.0000%, Sb: 0 to 1.000%, Sn: 0-1.000%, Zr: 0 to 1.000%
  • the hot-stamped molded article according to (1) above has the chemical composition in mass %, Co: 0.01 to 3.00%, Ni: 0.01 to 3.00%, Cu: 0.01-3.00%, V: 0.01 to 3.00%, W: 0.01-3.00%, Ca: 0.0001-0.1000%, Mg: 0.0001 to 1.0000%, REM: 0.0001-1.0000%, Sb: 0.001 to 1.000%, Sn: 0.001 to 1.000%, Zr: 0.001 to 1.000%, and As: 0.001 to 0.100% It may contain one or more selected from the group consisting of:
  • the present inventors have attempted to control the texture of prior austenite and the average value of the block grain sizes of martensite, tempered martensite, and bainite at a position of 1/4 of the plate thickness from the surface of the hot-stamped compact. It was discovered that the bendability of hot-stamped products could be improved. In particular, the present inventors found that the hot-stamped body does not have a texture such as martensite, tempered martensite, or bainite, which is the metallographic structure of the hot-stamped body, but before the transformation into martensite, bainite, etc. It has been discovered that the bendability of hot-stamped products can be improved by controlling the texture of prior austenite (in the high-temperature austenite state) within a specific range.
  • the present inventors have found that it is particularly effective to strictly control the finish rolling conditions during hot rolling in order to obtain a hot-stamped molded product having the above characteristics.
  • the hot-stamped molded article according to the present embodiment has a chemical composition, in mass %, of C: 0.40 to 0.70%, Si: 0.010 to 3.000%, Mn: 0.10% or more, 0. Less than .60%, P: 0.100% or less, S: 0.0100% or less, N: 0.0100% or less, O: 0.0200% or less, Al: 0.0010 to 0.5000%, Nb: 0.0010-0.1000%, Ti: 0.010-0.100%, Cr: 0.010-1.000%, Mo: 0.050-1.000%, B: 0.0005-0. 0100%, and the balance: Contains Fe and impurities. Each element will be explained below.
  • C 0.40-0.70%
  • C is an element that improves the strength of the hot stamp molded product. If the C content is less than 0.40%, the desired strength cannot be obtained in the hot-stamped molded product. Therefore, the C content is set to 0.40% or more. The C content is preferably more than 0.40%, 0.42% or more, or 0.44% or more. On the other hand, if the C content exceeds 0.70%, the strength becomes too high and the bendability of the hot stamped product deteriorates. Therefore, the C content is set to 0.70% or less. Preferably, the C content is 0.65% or less or 0.60% or less.
  • Si 0.010-3.000% Si is an element that improves the strength of the hot stamp molded product through solid solution strengthening. If the Si content is less than 0.010%, the desired strength cannot be obtained in the hot-stamped molded product. Therefore, the Si content is set to 0.010% or more. The Si content is preferably 0.100% or more, 0.300% or more, or 0.500% or more. On the other hand, if the Si content exceeds 3.000%, the amount of ferrite increases, making it impossible to obtain the desired strength in the hot-stamped molded product. Therefore, the Si content is set to 3.000% or less. The Si content is preferably 2.000% or less, 1.000% or less, or 0.800% or less.
  • Mn 0.10% or more, less than 0.60%
  • Mn is an element that improves the hardenability of steel and increases the strength of hot stamped compacts. If the Mn content is less than 0.10%, the desired strength cannot be obtained in the hot-stamped molded product. Therefore, the Mn content is set to 0.10% or more. The Mn content is preferably 0.20% or more or 0.35% or more. On the other hand, if the Mn content is 0.60% or more, a desired texture cannot be obtained in prior austenite. Therefore, the Mn content is made less than 0.60%. Preferably, the Mn content is 0.55% or less or 0.50% or less.
  • P 0.100% or less P reduces grain boundary strength by segregating at grain boundaries. This deteriorates the bendability of the hot stamp molded product. If the P content exceeds 0.100%, the bendability of the hot-stamped product will be significantly deteriorated. Therefore, the P content is set to 0.100% or less.
  • the P content is preferably 0.050% or less or 0.010% or less.
  • the P content may be 0%. However, reducing the P content to less than 0.0001% significantly increases the cost of removing P, which is economically unfavorable. Therefore, the P content may be set to 0.0001% or more.
  • S 0.0100% or less S forms inclusions in steel. If the S content exceeds 0.0100%, the bendability of the hot-stamped molded product will be significantly deteriorated. Therefore, the S content is set to 0.0100% or less.
  • the S content is preferably 0.0080% or less, 0.0050% or less, or 0.0030% or less.
  • the S content may be 0%. However, if the S content is reduced to less than 0.0001%, the cost for removing S will increase significantly, which is economically unfavorable. Therefore, the S content may be set to 0.0001% or more.
  • N 0.0100% or less N forms nitrides in steel. If the N content exceeds 0.0100%, the bendability of the hot-stamped molded product will be significantly deteriorated. Therefore, the N content is set to 0.0100% or less.
  • the N content is preferably 0.0080% or less, 0.0060% or less, or 0.0040% or less.
  • the N content may be 0%. However, reducing the N content to less than 0.0001% significantly increases the cost of removing N, which is economically unfavorable. Therefore, the N content may be set to 0.0001% or more.
  • O 0.0200% or less
  • O content is set to 0.0200% or less.
  • the O content is preferably 0.0100% or less, 0.0070% or less, 0.0040% or less, or 0.0030% or less.
  • the O content may be 0%.
  • the O content may be set to 0.0005% or more.
  • Al 0.0010-0.5000%
  • Al is an element that has the effect of deoxidizing molten steel and making the steel sound (suppressing the occurrence of defects such as blowholes in the steel).
  • the Al content is set to 0.0010% or more.
  • the Al content is preferably 0.0050% or more, 0.0100% or more, or 0.0300% or more.
  • the Al content is set to 0.5000% or less.
  • the Al content is preferably 0.4000% or less, 0.3000% or less, 0.2000% or less, or 0.1000% or less.
  • Nb 0.0010-0.1000%
  • Nb is an element that forms carbonitrides in steel and improves the strength of hot stamped products through precipitation strengthening. If the Nb content is less than 0.0010%, the desired strength cannot be obtained in the hot stamp molded product. Therefore, the Nb content is set to 0.0010% or more.
  • the Nb content is preferably 0.0050% or more, 0.0100% or more, or 0.0200% or more.
  • the Nb content exceeds 0.1000%, a large amount of carbonitrides will be generated in the steel, resulting in deterioration of the bendability of the hot stamped product. Therefore, the Nb content is set to 0.1000% or less.
  • the Nb content is preferably 0.0800% or less or 0.0600% or less.
  • Ti 0.010-0.100%
  • Ti is an element that forms carbonitrides in steel and improves the strength of hot stamped products through precipitation strengthening. If the Ti content is less than 0.010%, the desired strength cannot be obtained in the hot stamp molded product. Therefore, the Ti content is set to 0.010% or more. The Ti content is preferably 0.020% or more or 0.025% or more. On the other hand, if the Ti content exceeds 0.100%, a large amount of coarse carbonitrides will be generated in the steel, and the bendability of the hot stamped product will deteriorate. Therefore, the Ti content is set to 0.100% or less. The Ti content is preferably 0.080% or less, 0.060% or less, or 0.050% or less.
  • Cr:0.010 ⁇ 1.000% Cr is an element that increases the strength of the hot-stamped molded product by forming a solid solution in the prior austenite grains during heating before hot-stamping. If the Cr content is less than 0.010%, the desired strength cannot be obtained in the hot stamp molded product. Therefore, the Cr content is set to 0.010% or more. The Cr content is preferably 0.100% or more, 0.150% or more, or 0.200% or more. On the other hand, if the Cr content exceeds 1.000%, the desired texture cannot be obtained in prior austenite. Therefore, the Cr content is set to 1.000% or less. The Cr content is preferably 0.700% or less, 0.500% or less, or 0.400% or less.
  • Mo 0.050-1.000%
  • Mo is an element that increases the strength of the hot-stamped molded product by forming a solid solution in the prior austenite grains during heating before hot-stamping. If the Mo content is less than 0.050%, desired strength cannot be obtained in the hot-stamped molded product. Therefore, the Mo content is set to 0.050% or more. Mo content is preferably 0.100% or more or 0.150% or more. On the other hand, if the Mo content exceeds 1.000%, a desired texture cannot be obtained in prior austenite. Therefore, the Mo content is set to 1.000% or less. Mo content is preferably 0.800% or less, 0.600% or less, or 0.400% or less.
  • B 0.0005-0.0100%
  • B is an element that improves the hardenability of steel. If the B content is less than 0.0005%, the desired strength cannot be obtained in the hot stamp molded product. Therefore, the B content is set to 0.0005% or more.
  • the B content is preferably 0.0020% or more or 0.0030% or more.
  • the B content exceeds 0.0100%, coarse intermetallic compounds will be formed in the hot stamped body. This deteriorates the bendability of the hot stamp molded product. Therefore, the B content is set to 0.0100% or less.
  • the B content is preferably 0.0080% or less, 0.0060% or less, or 0.0040% or less.
  • the chemical composition of the hot-stamped molded body 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%.
  • Co is an element that improves the strength of the hot stamp molded product through solid solution strengthening.
  • the Co content is preferably 0.01% or more, more preferably 0.05% or more.
  • the Co content is set to 3.00% or less. If necessary, the Co content may be limited to 2.00% or less, 1.50% or less, 1.00% or less, or 0.50% or less.
  • Ni 0.01-3.00%
  • Ni has the effect of increasing the strength of the hot-stamped molded product by solidly dissolving in the prior austenite grains during heating before hot-stamping.
  • the Ni content is preferably 0.01% or more.
  • the Ni content is set to 3.00% or less. If necessary, the Ni content may be limited to 2.00% or less, 1.50% or less, 1.00% or less, or 0.50% or less.
  • Cu 0.01 ⁇ 3.00%
  • Cu has the effect of increasing the strength of the hot-stamped molded product by solidly dissolving in the prior austenite grains during heating before hot-stamping.
  • the Cu content is preferably 0.01% or more, more preferably 0.05% or more.
  • the Cu content is set to 3.00% or less. If necessary, the Cu content may be limited to 2.00% or less, 1.50% or less, 1.00% or less, or 0.50% or less
  • V has the effect of forming carbonitrides in the steel and improving the strength of the hot stamped product through precipitation strengthening.
  • the V content is preferably 0.01% or more, more preferably 0.05% or more.
  • the V content is set to 3.00% or less. If necessary, the V content may be limited to 2.00% or less, 1.50% or less, 1.00% or less, or 0.50% or less
  • W 0.01 ⁇ 3.00% W has the effect of improving the strength of the hot stamp molded product.
  • the W content is preferably 0.01% or more, more preferably 0.05% or more.
  • the W content is set to 3.00% or less. If necessary, the W content may be limited to 2.00% or less, 1.50% or less, 1.00% or less, or 0.50% or less
  • Ca is an element that suppresses the formation of oxides that become the starting point of fracture, and contributes to improving the bendability of the hot-stamped molded product.
  • the Ca content is preferably 0.0001% or more, more preferably 0.0010% or more.
  • the Ca content is set to 0.1000% or less. If necessary, the Ca content may be limited to 0.0500% or less, 0.0200% or less, 0.0100% or less, or 0.0060% or less.
  • Mg 0.0001-1.0000% Mg forms oxides and sulfides in molten steel, suppresses the formation of coarse MnS, and disperses many fine oxides, thereby refining the metal structure. This contributes to improving the bendability of the hot stamp molded product.
  • the Mg content is preferably 0.0001% or more, more preferably 0.0010% or more.
  • the Mg content is set to 1.0000% or less. If necessary, the Mg content may be limited to 0.0500% or less, 0.0200% or less, 0.0100% or less, or 0.0060% or less.
  • REM 0.0001-1.0000% REM suppresses the formation of coarse oxides. This contributes to improving the bendability of the hot stamp molded product.
  • the REM content is preferably 0.0001% or more, more preferably 0.0010% or more.
  • the REM content is set to 1.0000% or less. If necessary, the REM content may be limited to 0.0500% or less, 0.0200% or less, 0.0100% or less, or 0.0060% or less.
  • REM refers to Sc, It refers to a total of 17 elements consisting of Y and lanthanoids, and the content of REM refers to the total content of these elements.
  • Sb 0.001-1.000% Sb suppresses the formation of coarse oxides. This contributes to improving the bendability of the hot stamp molded product. To ensure this effect, the Sb content is preferably 0.001% or more. On the other hand, since the above effect is saturated even if it is contained in a large amount, the Sb content is set to 1.000% or less. If necessary, the Sb content may be limited to 0.500% or less, 0.200% or less, 0.100% or less, or 0.050% or less.
  • Sn 0.001-1.000% Sn suppresses the formation of coarse oxides. This contributes to improving the bendability of the hot stamp molded product. To ensure this effect, the Sn content is preferably 0.001% or more. On the other hand, since the above effect is saturated even if it is contained in a large amount, the Sn content is set to 1.000% or less. If necessary, the Sn content may be limited to 0.500% or less, 0.200% or less, 0.100% or less, or 0.050% or less.
  • Zr 0.001-1.000% Zr suppresses the formation of coarse oxides. This contributes to improving the bendability of the hot stamp molded product. To ensure this effect, the Zr content is preferably 0.001% or more. On the other hand, since the above effect is saturated even if it is contained in a large amount, the Zr content is set to 1.000% or less. If necessary, the Zr content may be limited to 0.500% or less, 0.200% or less, 0.100% or less, or 0.050% or less.
  • the As content is preferably 0.001% or more.
  • the As content is set to 0.100% or less. If necessary, the As content may be limited to 0.500% or less, 0.200% or less, 0.100% or less, or 0.050% or less.
  • the remainder of the chemical composition of the hot-stamped molded body 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 chemical composition of the hot-stamped molded article described above may be measured by a general analytical method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Note that C and S may be measured using a combustion-infrared absorption method, N using an inert gas melting-thermal conductivity method, and O using an inert gas melting-non-dispersive infrared absorption method. When a plating layer, a paint film, etc. are provided on the surface of the hot stamp molded article, the chemical composition may be analyzed after removing the plating layer, paint film, etc. by mechanical grinding.
  • ICP-AES Inductively Coupled Plasma-Atomic Emission Spectrometry
  • the maximum value of the polar density of the orientation group expressed in degrees is 3.0 or more, and the average value of the block grain sizes of martensite, tempered martensite, and bainite is 1.20 ⁇ m or less.
  • the metal structure is defined at a position of 1/4 of the plate thickness from the surface of the hot-stamped compact (an area from 1/8 depth of the plate thickness from the surface to 3/8 depth of the plate thickness from the surface). .
  • the reason is that the metal structure at this position shows a typical metal structure of a hot-stamped molded body.
  • the "surface” here refers to the interface between the plating layer, paint film, etc. and the base steel plate.
  • the maximum value of (as may be described) is set to 3.0 or more.
  • it is 5.0 or more.
  • the maximum value of the polar density of the texture of the prior austenite in the orientation group may be 50.0 or less, 20.0 or less, 15.0 or less, or 10.0 or less.
  • the polar density of the texture of prior austenite is measured by the following method.
  • the extreme density of the texture of prior austenite is measured using an EBSD analysis device consisting of a thermal field emission scanning electron microscope and an EBSD detector, and the software “OIM Analysis (registered trademark)” included with the EBSD analysis device. .
  • EBSD Electro Back Scattering Diffraction
  • ODF crystal orientation distribution function
  • a cross section parallel to the rolling direction and perpendicular to the plate surface is mechanically polished, and distortions are removed by chemical polishing, electrolytic polishing, or the like.
  • the length was 150 ⁇ m
  • the thickness was 50 ⁇ m in the thickness direction.
  • the EBSD measurement is performed with the area as the measurement range and the measurement interval as 0.2 ⁇ m.
  • an EBSD analysis device consisting of a thermal field emission scanning electron microscope and an EBSD detector may be used.
  • an EBSD analysis device consisting of a JEOL JSM-7001F and a TSL DVC5 type detector may be used. Just use it.
  • the degree of vacuum in the EBSD analyzer may be 9.6 ⁇ 10 ⁇ 5 Pa or less
  • the acceleration voltage may be 15 kV
  • the irradiation current level may be 13.
  • the crystal orientation of prior austenite is calculated by the following method. The crystal orientation of prior austenite is calculated by the method described in Non-Patent Document 1, and the crystal orientation of prior austenite at each coordinate of the region measured by EBSD is specified.
  • the average value of the block grain size of martensite, tempered martensite, and bainite is set to 1.20 ⁇ m or less. Preferably it is 1.00 ⁇ m or less, more preferably 0.90 ⁇ m or less. Although the lower limit is not particularly specified, it may be 0.30 ⁇ m or more, 0.40 ⁇ m or more, or 0.50 ⁇ m or more.
  • the average value of block grain sizes of martensite, tempered martensite, and bainite is measured by the following method. Take the sample so that the thickness section parallel to the rolling direction can be observed from any position 50 mm or more away from the end face of the hot stamped product (if it is not possible to take a sample from this position, avoid the end as much as possible). break the ice. Although the size of the sample depends on the measuring device, it should be large enough to allow observation of at least 10 mm in the rolling direction.
  • an EBSD analysis device consisting of a thermal field emission scanning electron microscope and an EBSD detector may be used.
  • an EBSD analysis device consisting of a JEOL JSM-7001F and a TSL DVC5 type detector may be used. Just use it.
  • the degree of vacuum in the EBSD analyzer may be 9.6 ⁇ 10 ⁇ 5 Pa or less
  • the acceleration voltage may be 15 kV
  • the irradiation current level may be 13.
  • the grain boundaries with a crystal orientation difference of 15 degrees or more are regarded as grain boundaries, and the "Grain Size (diamiter)" function is used to calculate the size using the Number method.
  • the average value of the block grain sizes of martensite, tempered martensite, and bainite is obtained.
  • the rolling direction of the hot stamp molded body is determined by the following method. First, a test piece is taken so that the thickness cross section of the hot stamped body can be observed. After finishing the thickness section of the collected test piece with mirror polishing, it is observed using an optical microscope. The observation range is a width of 500 ⁇ m x total board thickness, and areas with low brightness are determined to be inclusions. Next, using the plate thickness cross section initially observed by the above method as a reference, the cross section is observed in a plane parallel to the plane rotated in 5° increments in the range of 0° to 180° with the plate thickness direction as an axis.
  • the average value of the length of the long axis of the inclusion in each cross section obtained is calculated for each cross section, and the long axis direction of the inclusion in the cross section where the average value of the length of the long axis of the inclusion is the maximum is calculated.
  • the parallel direction is determined as the rolling direction. Note that if the rolling direction of the hot stamp molded body is known in advance, the rolling direction of the hot stamp molded body may be determined without using the above-described determination method.
  • the metal structure of the hot-stamped molded product is not particularly limited as long as desired strength and bendability can be obtained.
  • it may consist of a total of 90% or more of martensite, bainite, and tempered martensite, and 10% or less of ferrite and retained austenite, in terms of area %.
  • the area ratio of each tissue is measured by the following method. Take the sample so that the thickness section parallel to the rolling direction can be observed from any position 50 mm or more away from the end face of the hot stamped product (if it is not possible to take a sample from this position, avoid the end as much as possible). break the ice. Although the size of the sample depends on the measuring device, it should be large enough to allow observation of at least 10 mm in the rolling direction.
  • an EBSD analysis device consisting of a thermal field emission scanning electron microscope and an EBSD detector may be used.
  • an EBSD analysis device consisting of a JEOL JSM-7001F and a TSL DVC5 type detector may be used. Just use it.
  • the degree of vacuum in the EBSD analyzer may be 9.6 ⁇ 10 ⁇ 5 Pa or less
  • the acceleration voltage may be 15 kV
  • the irradiation current level may be 13.
  • the remaining region (the region where "Grain Average Misorientation" exceeds 0.5°) is set to the total area ratio of martensite, tempered martensite, and bainite.
  • the hot stamp molded article according to this embodiment may have a plating layer, a paint film, etc. on the surface.
  • Plating layers include aluminum plating layer, aluminum-zinc plating layer, aluminum-silicon plating layer, hot-dip galvanizing layer, electrolytic galvanizing layer, alloyed hot-dip galvanizing layer, zinc-nickel plating layer, aluminum-magnesium-zinc system. Examples include a plating layer.
  • the thickness of the hot stamp molded product according to this embodiment is not particularly limited, but from the viewpoint of reducing the weight of the vehicle body, it is preferably 0.5 to 3.5 mm. There is no need to particularly limit the shape of the hot stamp molded body. Examples include flat shapes, curved shapes, and three-dimensional shapes such as hat shapes.
  • the hot-stamped molded article according to this embodiment preferably has a tensile strength of 2300 MPa or more. More preferably it is 2400 MPa or more, even more preferably 2500 MPa or more. Although it is not necessary to specify the upper limit of the tensile strength, the tensile strength may be set to 3000 MPa or less or 2800 MPa or less, if necessary.
  • the tensile strength is determined by preparing a No. 5 test piece as described in JIS Z 2241:2011 from a flat position of the hot-stamped molded product and according to the test method described in JIS Z 2241:2011.
  • the crosshead speed is 1 mm/min.
  • the load at 1/2 stroke of the maximum load is 8050 N or more. More preferably it is 8100N or more, even more preferably 8150N or more.
  • these standards are based on a case where the thickness of the hot stamp molded body is 1.6 mm.
  • the load at 1/2 stroke was determined by performing a bending test under the following conditions based on the VDA standard (VDA238-100:2017-04) stipulated by the German Automobile Manufacturers Association. Obtained by finding the load. If the thickness of the hot-stamped molded product exceeds 1.6 mm, the thickness is reduced to 1.6 mm, and then the bending test is performed.
  • the load at 1/2 stroke of the stroke at the maximum load is 8050 x t/1. It is preferable that it is 6 (N) or more.
  • the load at 1/2 stroke of the stroke at the maximum load (however, if the thickness of the hot stamp molded object is less than 1.6 mm, the load at 1/2 stroke was multiplied by 1.6/t).
  • the value (t is the plate thickness in mm) rarely exceeds 8500N, 8300N or 8200N.
  • Test piece size 60mm (rolling direction) x 30mm (direction parallel to the plate width direction) Bending ridgeline: parallel to the sheet width direction
  • Test method roll support, punch pushing Roll diameter: ⁇ 30mm
  • Punch shape: Tip R 0.4mm Distance between rolls: 2.0 x plate thickness (mm) + 0.5 mm
  • the hot stamping steel plate has the above-mentioned chemical composition.
  • the metal structure of the hot stamping steel sheet is not particularly limited as long as desired strength and bendability can be obtained after hot stamping.
  • it may consist of ferrite: 0 to 90%, bainite and martensite: 0 to 100%, pearlite: 0 to 80%, and retained austenite: 0 to 5% in area %.
  • the steel plate for hot stamping may have a plating layer, a paint film, etc. on the surface.
  • Plating layers include aluminum plating layer, aluminum-zinc plating layer, aluminum-silicon plating layer, hot-dip galvanizing layer, electrolytic galvanizing layer, alloyed hot-dip galvanizing layer, zinc-nickel plating layer, aluminum-magnesium-zinc system. Examples include a plating layer.
  • finish rolling it is preferable that the rolling of the stage before the final stage and the rolling of the final stage are each performed at a rolling reduction ratio of 50% or more.
  • Prior austenite can be controlled to have a predetermined texture by rolling at a reduction rate of 50% or more in each of the rolling stage before the final stage and the final stage rolling.
  • the rolling reduction ratio here can be expressed as (1-t1/t0) ⁇ 100(%), where t0 is the inlet side plate thickness of each stage and t1 is the outlet side plate thickness.
  • cooling After completion of finish rolling (after final stage rolling), it is preferable to start cooling after 5.0 seconds or more have elapsed. By allowing 5.0 seconds or more to elapse before cooling starts, granular austenite grains can be generated. As a result, flat austenite grains are reduced, and a sufficient number of granular austenite grains can be secured.
  • cooling here does not include air cooling (cooling with an average cooling rate of less than 10°C/s), and includes, for example, water cooling with an average cooling rate of 10°C/s or more.
  • the cooling stop temperature is preferably 550 to 650°C.
  • the coil after winding may be subjected to a softening heat treatment.
  • the method of softening heat treatment is not particularly limited, and general conditions may be used.
  • the total rolling reduction during cold rolling is preferably 50% or less.
  • the total rolling reduction ratio here can be expressed as (1-t3/t2) ⁇ 100(%), where the plate thickness after cold rolling is t3 and the plate thickness before cold rolling is t2.
  • Hot Stamping A hot-stamped molded body according to the present embodiment is obtained by hot-stamping the hot-stamping steel plate manufactured by the method described above.
  • conditions for hot stamping for example, it is preferable to heat the steel plate for hot stamping to a temperature range of 800° C. to 1000° C. and hold it in this temperature range for 60 to 1200 seconds.
  • Heating during hot stamping causes reverse transformation from pearlite to austenite. Since pearlite has a predetermined texture, the texture of austenite produced by reverse transformation develops. Cooling after hot stamping causes transformation of austenite to martensite. If the final structure becomes martensite, the austenite texture is preserved. Therefore, in the structure after hot stamping, the texture of prior austenite remains developed.
  • the heating temperature is less than 800° C. or the holding time is less than 60 seconds, austenitization will be insufficient, and the hot-stamped product may have poor bendability or may not have the desired strength.
  • the heating temperature exceeds 1000°C or the holding time exceeds 1200 seconds, prior austenite may grow excessively, leading to deterioration in bendability or the failure to obtain the desired strength in the hot stamped product. There is.
  • the heating atmosphere may be, for example, the atmosphere, a gas combustion atmosphere with a controlled ratio of air and fuel, or a nitrogen atmosphere, and the dew point of these gases may be controlled.
  • hot stamping is performed. After hot stamping, cooling may be performed to a temperature range of 250°C or lower at an average cooling rate of 20°C/s or higher.
  • heating methods before hot stamping include heating in an electric furnace, gas furnace, etc., flame heating, electrical heating, high frequency heating, induction heating, and the like.
  • a hot stamp molded article according to the present embodiment is obtained.
  • a tempering treatment at 130 to 600° C. may be performed after hot stamp molding, or a baking hardening treatment may be performed after painting.
  • a portion of the hot stamp molded body may be tempered by laser irradiation or the like to provide a partially softened region.
  • 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.
  • the obtained steel plate for hot stamping was hot stamped under the conditions listed in Tables 2A to 2E, and then cooled to a temperature range of 250° C. or lower at an average cooling rate of 20° C./s or higher.
  • hot-stamped molded bodies shown in Tables 3A to 3G were obtained.
  • some examples were subjected to heat treatment for plating or softening as described in the table.
  • the underline in the table indicates that it is outside the scope of the present invention, that it falls outside the preferred manufacturing conditions, or that the characteristic value is unfavorable.
  • the metal structure of the hot-stamped molded body according to the example of the present invention consisted of a total of 90% or more of martensite, bainite, and tempered martensite, and 10% or less of ferrite and retained austenite, in terms of area %. .
  • the plate thickness of the hot stamp molded article according to the example of the present invention was 0.5 to 3.5 mm.
  • the metallographic structure and mechanical properties of the hot-stamped molded body were measured by the above-mentioned measurement method.
  • the bending test according to the above-mentioned VDA standard (VDA238-100:2017-04) is widely performed on automobile parts, etc., but only flat plates are tested. Therefore, according to this VDA standard, it is not possible to evaluate the bendability of a hot stamp molded product having a shape other than a flat plate shape.
  • the hot stamp molded product has a bent part, it is affected by the degree of curvature of the bent part. For this reason, the inventors considered it appropriate to evaluate the bendability using the VDA standard using a flat hot-stamped molded product as a test material.
  • the bending test was performed on a flat hot-stamped body obtained by hot-stamping without bending (using a mold that can yield a hot-stamped body without bending). went.
  • the rolling direction of the hot-stamped compact was known in advance, the rolling direction of the hot-stamped compact was determined without determining the rolling direction using the above-described discrimination method.
  • a SHIMADZU AUTOGRAPH 20kN tester was used for the bending test.
  • the load at 1/2 stroke of the maximum load was 8050 N or more, it was judged as having excellent bendability and passed. On the other hand, when the load at 1/2 stroke was less than 8050N, it was determined that the product did not have excellent bendability and was rejected. However, if the thickness of the hot stamped product is less than 1.6 mm, the load at 1/2 stroke of the maximum load is 8050 x t/, where t is the thickness of the hot stamped product. When it was 1.6 (N) or more, it was judged as having excellent bendability and passed. On the other hand, when the load at 1/2 stroke was less than 8050 ⁇ t/1.6 (N), it was determined that the product did not have excellent bendability and was rejected.
  • the hot-stamped molded articles that are examples of the present invention have high strength and excellent bendability.
  • the hot-stamped molded article as a comparative example is inferior in one or more properties.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

Cet article formé par estampage à chaud a une composition chimique prescrite, et à un emplacement ayant 1/4 de l'épaisseur de feuille à partir de sa surface et dans une texture d'austénite antérieure, la densité de pôle maximale d'un groupe d'orientation, exprimée par l'angle d'Euler Φ = 60-90°, φ1 = 60-90° et φ2 = 45°, est d'au moins 3,0, et la taille moyenne de particule de bloc de martensite, de martensite revenue et de bainite n'est pas supérieure à 1,20 µm.
PCT/JP2023/020238 2022-06-03 2023-05-31 Article formé par estampage à chaud WO2023234337A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019003539A1 (fr) * 2017-06-30 2019-01-03 Ｊｆｅスチール株式会社 Élément pressé à chaud et son procédé de fabrication, et tôle d'acier laminé à froid pour pressage à chaud et son procédé de fabrication
WO2019186930A1 (fr) * 2018-03-29 2019-10-03 日本製鉄株式会社 Produit formé par estampage à chaud
WO2021230149A1 (fr) * 2020-05-13 2021-11-18 日本製鉄株式会社 Corps moulé estampé à chaud
WO2021230150A1 (fr) * 2020-05-13 2021-11-18 日本製鉄株式会社 Tôle d'acier pour estampage à chaud et corps moulé par estampage à chaud
WO2022239731A1 (fr) * 2021-05-13 2022-11-17 日本製鉄株式会社 Tôle d'acier pour estampage à chaud, et corps moulé par estampage à chaud

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019003539A1 (fr) * 2017-06-30 2019-01-03 Ｊｆｅスチール株式会社 Élément pressé à chaud et son procédé de fabrication, et tôle d'acier laminé à froid pour pressage à chaud et son procédé de fabrication
WO2019186930A1 (fr) * 2018-03-29 2019-10-03 日本製鉄株式会社 Produit formé par estampage à chaud
WO2021230149A1 (fr) * 2020-05-13 2021-11-18 日本製鉄株式会社 Corps moulé estampé à chaud
WO2021230150A1 (fr) * 2020-05-13 2021-11-18 日本製鉄株式会社 Tôle d'acier pour estampage à chaud et corps moulé par estampage à chaud
WO2022239731A1 (fr) * 2021-05-13 2022-11-17 日本製鉄株式会社 Tôle d'acier pour estampage à chaud, et corps moulé par estampage à chaud

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