WO2023199638A1 - Article formé par estampage à chaud - Google Patents

Article formé par estampage à chaud Download PDF

Info

Publication number
WO2023199638A1
WO2023199638A1 PCT/JP2023/007855 JP2023007855W WO2023199638A1 WO 2023199638 A1 WO2023199638 A1 WO 2023199638A1 JP 2023007855 W JP2023007855 W JP 2023007855W WO 2023199638 A1 WO2023199638 A1 WO 2023199638A1
Authority
WO
WIPO (PCT)
Prior art keywords
less
hot
content
region
stamped
Prior art date
Application number
PCT/JP2023/007855
Other languages
English (en)
Japanese (ja)
Inventor
由梨 戸田
真吾 藤中
純 芳賀
祐馬 浅田
Original Assignee
日本製鉄株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日本製鉄株式会社 filed Critical 日本製鉄株式会社
Publication of WO2023199638A1 publication Critical patent/WO2023199638A1/fr

Links

Images

Classifications

    • 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

Definitions

  • the present invention relates to a hot stamp molded article.
  • This application claims priority based on Japanese Patent Application No. 2022-067020 filed in Japan on April 14, 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 high-yield ratio, high-strength electrogalvanized steel sheet in which the amount of diffusible hydrogen in the steel is 0.20 mass ppm or less and excellent bendability.
  • Hydrogen embrittlement cracking is a phenomenon in which a steel member under high stress during use breaks down due to hydrogen penetrating into the steel from the external environment. This phenomenon is also called delayed fracture because of the manner in which the fracture occurs. It is generally known that hydrogen embrittlement cracking of a steel plate occurs more easily as the tensile strength of the steel plate increases. This is thought to be because the higher the tensile strength of the steel plate, the greater the stress remaining in the steel plate after forming the part. This susceptibility to hydrogen embrittlement cracking (delayed fracture) is called hydrogen embrittlement resistance.
  • Early fracture is a phenomenon in which fracture occurs at a stress lower than the tensile strength estimated from the hardness of the steel member. This susceptibility to early rupture is referred to as early rupture resistance.
  • Patent Document 1 bendability is considered, but hydrogen embrittlement resistance and early rupture resistance are not considered.
  • An object of the present invention is to provide a hot-stamped molded article having high strength and excellent hydrogen embrittlement resistance and early breakage resistance.
  • the hot stamp molded article according to one embodiment of the present invention has a chemical composition in mass %, C: more than 0.40%, less than 0.70%, Si: 0.010-3.00%, Mn: 0.60-3.00%, P: 0.100% or less, S: 0.0100% or less, N: 0.0200% or less, O: 0.0200% or less, Al: 0.0010-0.5000%, Nb: 0.0010 to 0.100%, Ti: 0.010-0.200%, Cr: 0.01-0.80%, Mo: 0.0010-1.000%, B: 0.0005-0.0200%, Co: 0-4.00%, Ni: 0-3.00%, Cu: 0-3.00%, V: 0 to 3.00%, W: 0-3.00%, Ca: 0-1.000%, Mg: 0-1.000%, REM: 0-1.000%, Sb: 0 to 1.000%, Sn: 0-1.000%, Zr: 0 to 1.000%, As: 0
  • the hot-stamped molded article according to (1) above has the chemical composition in mass %, Co: 0.01-4.00%, Ni: 0.01 to 3.00%, Cu: 0.01-3.00%, V: 0.01 to 3.00%, W: 0.01-3.00%, Ca: 0.001-1.000%, Mg: 0.001-1.000%, REM: 0.001-1.000%, 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:
  • FIG. 3 is a diagram for explaining how to obtain a B-free index.
  • the present inventors have discovered that by reducing the standard deviation of the crystal grain size of prior austenite grains in the internal region, it is possible to improve the hydrogen embrittlement resistance and early rupture resistance of a hot stamped compact.
  • the present inventors improved hydrogen embrittlement resistance by generating a desired amount of bainite in the surface layer region, creating a texture with a desired crystal orientation, and setting a desired B removal index. We discovered that further improvements can be made.
  • the present inventors have found that in order to obtain a hot-stamped molded body having the above-mentioned characteristics, it is particularly effective to perform finish rolling and annealing under desired conditions when manufacturing a steel plate to be subjected to hot-stamping. did.
  • the hot stamp molded article according to this embodiment will be explained in detail.
  • the reason for limiting the chemical composition of the hot-stamped molded article according to this embodiment will be explained.
  • 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 according to this embodiment has a chemical composition in mass %: C: more than 0.40% and 0.70% or less, Si: 0.010 to 3.00%, Mn: 0.60 to 3.00%, P: 0.100% or less, S: 0.0100% or less, N: 0.0200% or less, O: 0.0200% or less, Al: 0.0010 to 0.5000%, Nb: 0.0010-0.100%, Ti: 0.010-0.200%, Cr: 0.01-0.80%, Mo: 0.0010-1.000%, B: 0.0005-0. 0200%, and the remainder: contains Fe and impurities. Each element will be explained below.
  • C More than 0.40% and 0.70% or less 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 exceed 0.40%. The C content is preferably 0.42% or more or 0.44% or more. On the other hand, if the C content exceeds 0.70%, the toughness of martensite is too low and excellent early rupture resistance cannot be obtained. 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 ⁇ 3.00% 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%, desired strength cannot be obtained. Therefore, the Si content is set to 0.010% or more.
  • the Si content is preferably 0.05% or more, 0.10% or more, or 0.15% or more.
  • the Si content is set to 3.00% or less.
  • the Si content is preferably 2.00% or less, 1.00% or less, or 0.70% or less.
  • Mn 0.60-3.00%
  • Mn is an element that promotes the transformation from prior austenite to pearlite in the hot rolled steel sheet having the chemical composition according to the present embodiment, and contributes to controlling the prior austenite grain size distribution of the hot stamped compact.
  • the Mn content is set to 0.60% or more.
  • the Mn content is preferably 0.70% or more or 1.00% or more.
  • the Mn content is set to 3.00% or less.
  • the Mn content is 2.50% or less or 2.30% or less.
  • P 0.100% or less
  • P is an impurity element, and when it segregates at grain boundaries, it becomes a starting point for fracture and deteriorates early rupture resistance, so 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 lower limit of the P content is not particularly limited, but 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 0.0001% or more, 0.001% or more, or 0.005% or more.
  • S 0.0100% or less
  • S is an impurity element and forms inclusions in steel. Since this inclusion becomes a starting point for fracture and deteriorates early fracture resistance, 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 lower limit of the S content is not particularly limited, but 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 0.0001% or more, 0.0002% or more, 0.0003% or more, or 0.0010% or more.
  • N is an impurity element and forms nitrides in steel. Since this nitride becomes a starting point for fracture and deteriorates early fracture resistance, the N content is set to 0.0200% or less.
  • the N content is preferably 0.0150% or less, 0.0100% or less, 0.0060% or less, or 0.0040% or less.
  • the lower limit of the N content is not particularly limited, but 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 0.0001% or more or 0.0010% or more.
  • the O content is set to 0.0200% or less.
  • the O content is preferably 0.00100% or less, 0.0070% or less, or 0.0040% or less.
  • the O content may be 0%, but in order to disperse a large number of fine oxides during deoxidation of molten steel, the O content may be 0.0005% or more or 0.0010% or more.
  • Al 0.0010-0.5000%
  • Al is an element that has the effect of deoxidizing molten steel and making the steel sound.
  • 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 0.0010-0.100%
  • 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%, desired strength cannot be obtained. Therefore, the Nb content is set to 0.0010% or more. The Nb content is preferably 0.005% or more, 0.009% or more, or 0.015% or more. On the other hand, if the Nb content exceeds 0.100%, a large amount of carbonitrides will be generated in the steel, and the early breakage resistance of the hot-stamped body will deteriorate. Therefore, the Nb content is set to 0.100% or less. The Nb content is preferably 0.080% or less or 0.060% or less.
  • Ti 0.010-0.200%
  • 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%, desired strength cannot be obtained. 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.
  • the Ti content is set to 0.200% or less.
  • the Ti content is preferably 0.150% or less, 0.100% or less, 0.080% or less, 0.060% or less, or 0.050% or less.
  • 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 0.01%, desired strength cannot be obtained. Therefore, the Cr content is set to 0.01% or more.
  • the Cr content is preferably 0.10% or more, 0.15% or more, or 0.20% or more.
  • the Cr content is set to 0.80% or less.
  • the Cr content is preferably 0.70% or less, 0.50% or less, or 0.40% or less.
  • Mo 0.0010-1.000%
  • 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 0.0010%, desired strength cannot be obtained. Therefore, the Mo content is set to 0.0010% or more.
  • the Mo content is preferably 0.010% or more, 0.050% or more, or 0.100% or more.
  • 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 0.0005-0.0200%
  • B is an element that improves the hardenability of steel. If the B content is less than 0.0005%, desired strength cannot be obtained. Therefore, the B content is set to 0.0005% or more.
  • the B content is preferably 0.0010% or more or 0.0015% or more.
  • the B content exceeds 0.0200%, coarse intermetallic compounds are formed in the hot-stamped molded product, and the early rupture resistance deteriorates. Therefore, the B content is set to 0.0200% or less.
  • the B content is preferably 0.0150% or less, 0.0100% or less, 0.0080% or less, 0.0040% or less, or 0.0030% 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 hot stamp molded product may contain the following elements as optional elements. 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, the Co content is 0.05% or more.
  • the Co content is set to 4.00% or less. If necessary, the upper limit of the Co content may be set to 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • Ni 0-3.00%
  • 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 3.00% or less. If necessary, the upper limit of the Ni content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • Cu 0-3.00%
  • 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.
  • the Cu content is more preferably 0.05% or more.
  • the Cu content is preferably 3.00% or less. If necessary, the upper limit of the Cu content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • V 0-3.00%
  • 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.
  • the V content is more preferably 0.05% or more.
  • the V content is set to 3.00% or less. If necessary, the upper limit of the V content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • W 0-3.00% W has the effect of improving the strength of the hot stamp molded product.
  • the W content is preferably 0.01% or more.
  • the W content is preferably 0.05% or more.
  • the W content is set to 3.00% or less. If necessary, the upper limit of the W content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • Ca 0-1.000% Ca is an element that suppresses the formation of oxides that become fracture starting points, and contributes to improving early fracture resistance. To ensure this effect, the Ca 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 Ca content is set to 1.000% or less. If necessary, the upper limit of the Ca content may be set to 0.100%, 0.010%, 0.005%, 0.001%, 0.0005% or 0.0002%.
  • Mg 0-1.000% Mg forms oxides and sulfides in molten steel, suppresses the formation of coarse MnS, disperses many fine oxides, refines the metal structure, and contributes to improving early fracture resistance. In order to reliably obtain these effects, it is preferable that the Mg content is 0.001% or more. On the other hand, since the above effect is saturated even if it is contained in a large amount, the Mg content is set to 1.000% or less. If necessary, the upper limit of the Mg content may be set to 0.100%, 0.010%, 0.005%, 0.001%, 0.0005% or 0.0002%.
  • REM 0 ⁇ 1.000% REM suppresses the formation of oxides that become the starting point of fracture, and contributes to improving early fracture resistance.
  • the REM content is preferably 0.001% or more.
  • the REM content is set to 1.000% or less. If necessary, the upper limit of the REM content may be set to 0.100%, 0.010%, 0.005%, 0.001%, 0.0005% or 0.0002%.
  • 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.
  • Sb 0-1.000% Sb suppresses the formation of oxides that become fracture starting points, and contributes to improving early fracture resistance. 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 upper limit of the Sb content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • Sn 0-1.000% Sn suppresses the formation of oxides that become a starting point for fracture, and contributes to improving early fracture resistance. 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 upper limit of the Sn content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • Zr 0-1.000% Zr suppresses the formation of oxides that become fracture starting points, and contributes to improving early fracture resistance. 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 upper limit of the Zr content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • the As content is preferably 0.001% or more.
  • the As content is set to 0.100% or less. If necessary, the upper limit of the As content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • 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. If the surface of the hot-stamped body is provided with a plating layer, paint film, etc., the chemical composition is analyzed after removing the plating layer, paint film, etc. by mechanical grinding.
  • ICP-AES Inductively Coupled Plasma-Atomic Emission Spectrometry
  • the hot-stamped molded product according to the present embodiment has a depth from the surface of the hot-stamped molded product to a depth of 4/16 of the plate thickness (thickness of the hot-stamped molded product) to a depth of 5/16 of the plate thickness from the surface.
  • the standard deviation of the crystal grain size of prior austenite grains is 5.0 ⁇ m or less
  • the surface region which is a region from the surface to a depth of 1/25 of the plate thickness, bainite
  • the area ratio of is more than 10%
  • the maximum value of the polar density of the texture is 4.0 or less
  • the B removal index is 0.05 or more.
  • the internal region refers to a region from a depth of 4/16 of the plate thickness from the surface of the hot stamp molded product to a depth of 5/16 of the plate thickness from the surface.
  • the surface layer region refers to a region from the surface of the hot stamp molded product to a depth of 1/25 of the plate thickness from the surface.
  • the "surface” here refers to the interface between the plating layer and the base steel plate, and for convenience, the plating from the hot-stamped molded product is Exclude layers, paint films, etc.
  • the surface of the hot-stamped molded product has a plating layer, a paint film, etc., as described below, for convenience, the area where the iron concentration is less than 90% by mass in GD-OES measurement, that is, the plating layers, paint films, etc. are excluded from the hot-stamped molded body, and the measurement point where the iron concentration is 90% by mass (that is, the interface between the base steel material and the plating layer, etc.) is regarded as the surface of the hot-stamped molded body.
  • the plating layer, paint film, etc. were excluded from the hot-stamped product, but the thickness of the plating layer, paint film, etc.
  • the plate thickness (thickness) of the molded body may be the plate thickness (thickness) including the plating layer, paint film, etc.
  • Standard deviation of the crystal grain size of prior austenite grains 5.0 ⁇ m or less.
  • the lower limit of the standard deviation of the crystal grain size of prior austenite grains does not need to be particularly limited, but may be 0.1 ⁇ m, 0.5 ⁇ m, 1.0 ⁇ m or 1.5 ⁇ m.
  • the standard deviation of the grain size of prior austenite grains is obtained by the following method.
  • a sample is cut out from an arbitrary position 50 mm or more away from the end surface of the hot-stamped compact (if the sample cannot be taken from this position, avoid the end) so that the thickness cross section parallel to the rolling direction can be observed.
  • the size of the sample depends on the measuring device, it should be large enough to allow observation of about 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 crystal orientation of prior austenite grains is calculated from the crystal orientation relationship between general prior austenite grains and crystal grains with a body-centered structure after transformation, and this is used to calculate prior austenite grains. After calculating the average crystal grain size of the grains, its standard deviation is calculated.
  • the method for calculating the crystal orientation of prior austenite grains is as follows. First, a crystal orientation map of prior austenite grains is created using the method described in Non-Patent Document 1. For one of the prior austenite grains included in the observation field, the average value of the shortest diameter and the longest diameter is calculated, and the average value is taken as the grain size of the prior austenite grain. Perform the above operation for all prior austenite grains, excluding prior austenite grains whose entire crystal grains are not included in the photographic field of view, such as at the edges of the photographic field of view, to determine the grain size of all prior austenite grains in the relevant photographic field of view. .
  • the rolling direction of the hot stamp molded body is determined by the following method. First, a test piece is taken from an arbitrary position 50 mm or more away from the end of the hot-stamped molded body so that the cross-section of the plate thickness can be observed. After finishing the thickness section of the sampled test piece by mirror polishing, it is observed using an optical microscope at 100x, 200x, 500x, and 1000x magnification. Depending on the size of the inclusion, select an observation result with an appropriate magnification that allows the size of the inclusion to be measured.
  • the observation range is a width of 500 ⁇ m or more and the full thickness of the plate, and areas with low brightness are determined to be inclusions.
  • the same method as above is applied to the plane parallel to the plane rotated in 5° increments in the range of 0° to 180° with the thickness direction as the axis, using the thickness cross section initially observed by the above method as a reference.
  • the average value of the lengths of the long axes of the plurality of inclusions in each cross section is calculated for each cross section.
  • the cross section in which the average length of the long axes of the obtained inclusions is maximum is identified.
  • a direction parallel to the longitudinal direction of the inclusion in the cross section is determined as the rolling direction.
  • the metal structure of the internal region is not particularly limited as long as the desired strength, hydrogen embrittlement resistance, and early fracture resistance can be obtained, but for example, the metal structure in the internal region is 90 to 100% in total (90% or more, 100% (below) martensite and bainite, and 0 to 10% (0% or more, 10% or less) of ferrite and retained austenite.
  • martensite in this embodiment includes untempered martensite (fresh martensite) and tempered martensite.
  • the metallographic structure of the hot-stamped compact is measured by the following method.
  • 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 area ratio of the remaining region (the area where "Grain Average Misorientation" exceeds 0.5°) is calculated, and this area ratio is taken as the total area ratio of martensite and bainite.
  • the dislocation density in the surface region can be reduced.
  • the intrusion of hydrogen from the external environment can be suppressed, and the hydrogen embrittlement resistance of the hot-stamped molded article can be improved.
  • the area ratio of bainite in the surface layer region is set to exceed 10%.
  • it is 20% or more, 40% or more, or 60% or more.
  • the upper limit of the area ratio of bainite is not particularly limited, but may be 100%, 90%, or 80%.
  • the metal structure of the surface layer region includes 0 to 90% (0% or more, 90% or less) of martensite, and a total of 0 to 65% (0% or more, 65% or less) of ferrite and residual Austenite may be included.
  • the area ratio of the metal structure is calculated for the surface layer region (the region from the surface to a depth of 1/25 of the plate thickness) by the following method.
  • 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. You can use At this time, the degree of vacuum in the EBSD analyzer may be 9.6 ⁇ 10 ⁇ 5 Pa or less, the acceleration voltage may be 15 kV, and the irradiation current level may be 13.
  • the area ratio of bainite is obtained by calculating the area ratio of the extracted bainite. Subsequently, a region where "Grain Average Misorientation" is 0.5° or less is extracted as ferrite. The area ratio of ferrite is obtained by calculating the area ratio of the extracted ferrite. The remaining area (area where "Grain Average Misorientation" exceeds 0.75°) is extracted as martensite, and the area rate of martensite is calculated by calculating the area rate of martensite.
  • the maximum value of the polar density of the texture is 4.0 or less
  • the maximum value of the polar density of the texture in the surface layer region is set to 4.0 or less.
  • it is 3.5 or less, 3.0 or less, or 2.5 or less.
  • the lower limit of the polar density of the texture in the surface layer region is not particularly limited, but may be set to 1.0 or 1.2.
  • the texture in the surface layer region is obtained for the surface layer region (the region from the surface to a depth of 1/25 of the plate thickness) by the following method.
  • a sample is cut out from an arbitrary position 50 mm or more away from the end surface of the hot-stamped compact (if the sample cannot be taken from this position, avoid the end) so that the thickness cross section parallel to the rolling direction can be observed.
  • the size of the sample depends on the measuring device, it should be large enough to allow observation of about 10 mm in the rolling direction.
  • 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 obtained crystal orientation information is used to calculate a harmonic function (Harmonic Series) for crystal grains whose crystal structure is bcc. Intensity calculations are performed using (Expansion). At this time, the expansion order is 16, and the half width when applied to Gaussian distribution is 5°.
  • B removal index 0.05 or more
  • the B removal index is an index that quantitatively represents the amount of decrease in B concentration in the surface layer region.
  • the strength of the prior austenite before transformation is reduced, the deformability of the prior austenite grains is improved, and randomly oriented crystal grains are more likely to be generated in the surface layer region.
  • the de-B index is set to 0.05 or more. Preferably, it is 0.20 or more, 0.30 or more, or 0.35 or more.
  • the upper limit of the B removal index is not particularly limited, but may be 1.00, 0.80, or 0.60.
  • the B removal index in the surface layer region is obtained by the following method.
  • Glow Discharge Optical Emission Spectrometry (GD-OES: Marcus type high frequency glow discharge optical emission spectrometer, GD-PROFILER-HR manufactured by Horiba, Ltd.) was used to determine the element concentration distribution in the thickness direction of the hot stamped compact. Measure.
  • the measurement conditions are an analysis diameter of 4 mm ⁇ , a sputtering rate of 4 ⁇ m/min, an argon pressure of 600 Pa, an RF output of 35 W, and a measurement interval of 0.02 ⁇ m or less. Measurements are performed for all elements contained in the hot stamped compact.
  • the hot-stamped molded body has a plating layer or the like on the surface
  • the "surface” here refers to the interface between the plating layer or the like and the base steel plate. If the surface has a plating layer, paint film, etc., mechanical polishing or Part or all of the plating layer, paint, etc. is removed by chemical polishing, and then subjected to GD-OES measurement. In the GD-OES measurement, the measurement point where the iron concentration is 90% by mass is regarded as the surface of the hot stamped body.
  • the hot-stamped molded body may be referred to as a base material steel plate.
  • the B concentration is measured from the surface of the hot-stamped molded article to a depth of at least 100 ⁇ m from the surface.
  • the absolute value of the difference between the average B concentration in the 80 to 100 ⁇ m region and the maximum measured B concentration in the 80 to 100 ⁇ m region is 0.0006. % by mass or less
  • the absolute value of the difference between the average value of the B concentration in the 80 to 100 ⁇ m region and the minimum value of the measured B concentration in the 80 to 100 ⁇ m region is 0.0006 mass % or less
  • the measurement of the B concentration in the depth direction is completed at a depth of 100 ⁇ m from the surface.
  • the measurement of the B concentration in the depth direction is continued. Then, each time a new B concentration measurement value is obtained in the depth direction, calculate the average value of the B concentration in an area of 20 ⁇ m from the deepest part to the surface side, and from the deepest part to the surface side.
  • the absolute value of the difference between the average value of B concentration in a region of 20 ⁇ m from the deepest part to the maximum value of the measured value of B concentration in a region of 20 ⁇ m from the deepest part to the surface side is 0.0006% by mass or less, and , the absolute value of the difference between the average value of the B concentration in the region of 20 ⁇ m from the deepest part to the surface side and the minimum value of the measured value of B concentration in the region of 20 ⁇ m from the deepest part to the surface side is 0. If it is .0006% by mass or less, the measurement of the B concentration in the depth direction ends at that position.
  • the measured value of the B concentration is obtained at a depth of 150 ⁇ m from the surface, the average value of the B concentration in the region 130 to 150 ⁇ m deep from the surface and the measured value of the B concentration in the region 130 to 150 ⁇ m deep from the surface.
  • the area from the deepest part (the deepest position where the B concentration used for calculating the B removal index was obtained) to the region 20 ⁇ m from the deepest part to the surface side is The average value of the B concentration (hereinafter, the average value of the B concentration in this region will be referred to as the average B concentration at the deepest part of 20 ⁇ m) is used in the calculation of the B removal index below.
  • the above-mentioned termination condition for B concentration measurement in the depth direction is satisfied in a region 100 to 200 ⁇ m deep from the surface.
  • the shallowest depth position may be found, and if that position is found, the B removal index may be calculated without using the B concentration measurement results at positions deeper than that depth position.
  • the B concentration may be measured from the surface to a depth of 200 ⁇ m, and in this case, in a region 100 ⁇ m or more from the surface, the shallowest depth position that satisfies the termination condition for the B concentration measurement in the depth direction. If there is, it is assumed that the measurement has ended at that depth position, and the B removal index is calculated.
  • the amount of decrease in B concentration per unit depth in the region from the deepest part to 20 ⁇ m from the deepest part to the surface side of the hot stamped compact (the B concentration at each measurement point was subtracted from the average B concentration at the deepest part of 20 ⁇ m) value) is calculated, and the integral value of the product of the unit depth and the amount of decrease in B concentration is determined to determine the area of the B-deficient region (area of region A in FIG. 1).
  • the product of the average B concentration at the deepest part of 20 ⁇ m and the length of 200 ⁇ m is calculated as a reference area (area of rectangular region B in FIG. 1).
  • the value obtained by dividing the B deficient area (area of region A) by the reference area (area of region B) is defined as the B depletion index (area of region A/area of region B).
  • the reference area (area of region B) is calculated by assuming that the length by which the average B concentration at the deepest part of 20 ⁇ m is multiplied is 200 ⁇ m.
  • the hot stamp molded article according to this embodiment may have a plating layer 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 hot stamping steel plate has the above-mentioned chemical composition.
  • the metal structure of the steel sheet for hot stamping is not particularly limited as long as the desired strength, hydrogen embrittlement resistance, and early fracture resistance can be obtained after hot stamping, but for example, in terms of area percentage, ferrite: 5 to 90%, bainite. and martensite: 0 to 100%, pearlite: 10 to 95%, and retained austenite: 0 to 5%.
  • iron carbides, alloy carbides, intermetallic compounds, and inclusions may be included.
  • the steel plate for hot stamping may have a plating layer 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 rolling reduction ratio (final rolling ratio) of the final pass is preferably 20% or more.
  • the final rolling reduction ratio here is ⁇ (t 0 - t 1 )/t 0 ⁇ 100, where the plate thickness before rolling in the final pass is t 0 and the plate thickness after rolling in the final pass is t 1 . It can be expressed as (%).
  • the early breakage resistance of the hot-stamped molded product can be improved. More preferably, it is 30% or more, 40% or more, or 45% or more.
  • the Mn content is 0.60% or more, as in the chemical composition of the hot-stamped molded product according to the present embodiment, in order to preferably control the texture of the surface layer region of the hot-stamped molded product, it is necessary to perform finish rolling. It is important to increase the final rolling reduction as described above.
  • the conditions for heating before hot rolling, rough rolling, winding, and cold rolling are not particularly limited, and may be general conditions.
  • the winding temperature may be 750° C. or lower.
  • the coiling temperature By setting the coiling temperature to 750° C. or lower, it is possible to suppress ferrite from being arranged in a connected manner in the hot-rolled steel sheet after rolling, and pearlite is uniformly dispersed.
  • This pearlite becomes a reverse transformation site of prior austenite during heating during hot stamping. Therefore, when pearlite is uniformly dispersed, the standard deviation of the crystal grain size of prior austenite grains in the hot-stamped molded body becomes small. As a result, the early breakage resistance of the hot-stamped molded product can be improved.
  • 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.
  • Annealing After cold rolling, it is preferable to perform annealing by heating in an oxidizing atmosphere for 15 seconds or more. Normally, it is preferable to perform annealing in a reducing atmosphere in order to suppress scale formation, but in this embodiment, scale formation on the steel plate surface is promoted by performing annealing in an oxidizing atmosphere.
  • the scale formed on the surface of the steel sheet becomes an oxidation source, and C and B in the surface layer region are oxidized. Since the oxidized C and B separate from the surface layer of the steel sheet, the amounts of C and B are reduced in the surface layer region. As a result, the strength of the prior austenite grains decreases and becomes easily deformed, making it easier to generate randomly oriented crystal grains.
  • the heating temperature during annealing may be in the range of 730 to 900°C, and by staying in this heating temperature range for 15 seconds or more, scale formation can be promoted while suppressing scale peeling. can.
  • the time for annealing is preferably 100 seconds or more, more preferably 200 seconds or more, and even more preferably 300 seconds or more.
  • annealing for more than 3,600 seconds is undesirable because the prior austenite grain size becomes coarser, the grain boundary diffusion rate of B decreases, B removal does not proceed, and the B removal index does not exceed 0.05. . Therefore, the annealing time is preferably 3600 seconds or less. Note that, after annealing in an oxidizing atmosphere, the annealing process may be performed again in an oxidizing atmosphere or a non-oxidizing atmosphere unless a treatment for removing oxide scale (for example, pickling) is performed.
  • the oxidizing atmosphere may be any heating atmosphere that generates oxide scale on the surface layer of the steel sheet, and may be a general condition.
  • a gas combustion atmosphere it is preferable to create an atmosphere in which the mixture ratio of air and fuel (air-fuel ratio) is controlled to 0.80 or more, and more preferably to be controlled to exceed 1.00.
  • air-fuel ratio air-fuel ratio
  • the oxidized scale on the surface of the steel sheet remain in subsequent steps. That is, it is preferable to perform hot stamping, which will be described later, with the oxide scale remaining. Oxide scale is removed by shot blasting after hot stamping.
  • oxide scale remains at the interface between the base steel sheet and the plating layer.
  • the oxide scale disappears after hot stamping due to an alloying reaction during heating before 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.
  • the hot stamping conditions are not particularly limited, but it is preferable, for example, 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 600 seconds. If the heating temperature is less than 800°C, austenitization will be insufficient, the desired prior austenite grain size distribution cannot be obtained, and the early rupture resistance may deteriorate. On the other hand, if the heating temperature exceeds 1000° C., the grains of prior austenite will grow excessively, making it impossible to obtain the desired prior austenite grain size distribution, and the early rupture resistance may deteriorate.
  • the holding time is less than 60 seconds, austenitization becomes insufficient, a desired prior austenite particle size distribution cannot be obtained, and the early rupture resistance may deteriorate. If the holding time exceeds 600 seconds, grains of prior austenite will grow excessively, making it impossible to obtain a desired prior austenite grain size distribution, and the early rupture resistance may deteriorate.
  • the heating atmosphere is not particularly limited and may be under normal conditions, such as 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 is controlled. Also good.
  • 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 is heated to a temperature range higher than 800°C in a furnace continuously supplied with nitrogen gas (hot stamp heating), held in the temperature range, hot stamped, and then heated to 250°C.
  • Hot stamping was performed under conditions of cooling at an average cooling rate of 20° C./s or more to the following temperature range.
  • a gas combustion atmosphere was used in which the mixture ratio of air and fuel (air-fuel ratio) was controlled to 0.85.
  • heating in a furnace adjusted to a different atmosphere, reannealing, plating, tempering, hot stamp heating, etc. were performed.
  • 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 metallographic structure including the standard deviation of the crystal grain size of austenite grains), deboronization index, and ultra-density of the texture of the hot-stamped compact were measured by the methods described above.
  • the mechanical properties of the hot-stamped molded product were evaluated by the following method.
  • the hydrogen embrittlement resistance of the hot-stamped molded product was evaluated by the following method.
  • a test piece with a length of 68 mm and a width of 6 mm is taken from any position of the hot stamp molded body, and the edges of the test piece are polished using #200 to #1500 silicon carbide paper, and the grain size is 1 to 1.
  • a mirror finish was obtained using a liquid in which 6 ⁇ m diamond powder was dispersed in diluted liquid such as alcohol and pure water. Furthermore, the corners of the test pieces were chamfered using #200 to #1500 silicon carbide paper.
  • a stress of 800 MPa or more was applied to the test piece, and the test piece was immersed in 1 liter of hydrochloric acid adjusted to pH 4 at room temperature for 48 hours, and the presence or absence of cracks was determined.
  • a case in which no cracking occurred even under a load stress of 800 MPa or more was judged to be acceptable.
  • the case where there was cracking at a load stress of 800 MPa was determined to be a failure and was written as "Bad" in the table.
  • the early rupture resistance properties are calculated by dividing the tensile strength of the hot-stamped molded product obtained by the above method by the value obtained by multiplying the Vickers hardness obtained by the following method by 3.3 (tensile strength/ (Vickers hardness x 3.3)). When this value was 0.60 or more, it was determined to be excellent in early breakage resistance and was determined to pass, and when this value was less than 0.60, it was determined to be rejected.
  • the value obtained by multiplying the Vickers hardness by 3.3 is the tensile strength estimated from the hardness, and if the measured value of the tensile strength is 0.60 times or more of the estimated tensile strength, then the early rupture resistance is can be judged to be excellent.
  • the Vickers hardness used to evaluate early breakage resistance was obtained by the following method. First, a sample was cut out so that a cross section perpendicular to the surface (thickness cross section) could be observed from an arbitrary position 50 mm or more away from the end surface of the hot stamp molded body. The sample was sized to allow observation of 10 mm in the rolling direction, although it depends on the measuring device. After polishing the cross section of the sample using #600 to #1500 silicon carbide paper, it was finished to a mirror surface using a liquid in which diamond powder with a particle size of 1 to 6 ⁇ m was dispersed in a diluted solution such as alcohol and pure water. .
  • the hot-stamped molded articles according to the present invention have high strength and excellent hydrogen embrittlement resistance and early fracture resistance.
  • the hot-stamped molded article as a comparative example is inferior in one or more properties.

Landscapes

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

Abstract

Article formé par estampage à chaud présentant une composition chimique spécifiée, dans laquelle l'écart-type des diamètres de grain cristallin des grains avant austénite dans une région interne est inférieur ou égal à 5,0 µm, le rapport de surface de bainite dans une région de couche superficielle est supérieur à 10 %, la valeur maximale d'une densité polaire dans une texture est inférieure ou égale à 4,0, et l'indice de baisse de B est supérieur ou égal à 0,05.
PCT/JP2023/007855 2022-04-14 2023-03-02 Article formé par estampage à chaud WO2023199638A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2022067020 2022-04-14
JP2022-067020 2022-04-14

Publications (1)

Publication Number Publication Date
WO2023199638A1 true WO2023199638A1 (fr) 2023-10-19

Family

ID=88329346

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2023/007855 WO2023199638A1 (fr) 2022-04-14 2023-03-02 Article formé par estampage à chaud

Country Status (1)

Country Link
WO (1) WO2023199638A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020213179A1 (fr) * 2019-04-17 2020-10-22 日本製鉄株式会社 Tôle d'acier et procédé de fabrication associé, et article moulé
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

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020213179A1 (fr) * 2019-04-17 2020-10-22 日本製鉄株式会社 Tôle d'acier et procédé de fabrication associé, et article moulé
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

Similar Documents

Publication Publication Date Title
KR101614230B1 (ko) 베이킹 경화성이 우수한 고강도 용융 아연 도금 강판, 고강도 합금화 용융 아연 도금 강판 및 그것들의 제조 방법
EP2246456B9 (fr) Tôle d'acier haute résistance et son procédé de production
EP3216886A1 (fr) Tôle d'acier galvanisée par immersion à chaud
JP7173303B2 (ja) 鋼板及びその製造方法
JP2017048412A (ja) 溶融亜鉛めっき鋼板、合金化溶融亜鉛めっき鋼板、およびそれらの製造方法
CN110475892B (zh) 高强度冷轧钢板及其制造方法
JPWO2015097891A1 (ja) 熱間プレス鋼板部材、その製造方法及び熱間プレス用鋼板
KR102544884B1 (ko) 고강도 용융 아연 도금 강판 및 그의 제조 방법
WO2022149502A1 (fr) Tôle d'acier et son procédé de production
KR20180119638A (ko) 박강판 및 도금 강판, 그리고 열연 강판의 제조 방법, 냉연 풀하드 강판의 제조 방법, 열 처리판의 제조 방법, 박강판의 제조 방법 및 도금 강판의 제조 방법
WO2021140663A1 (fr) Tôle d'acier galvanisée à haute résistance et procédé de production associé
KR20210151935A (ko) 핫 스탬프 성형체
WO2019131099A1 (fr) Tôle en acier laminée à chaud, et procédé de fabrication de celle-ci
CN112714800B (zh) 钢板
KR20180019213A (ko) 냉연 강판, 도금 강판 및 이것들의 제조 방법
JP7216933B2 (ja) 鋼板およびその製造方法
WO2023199638A1 (fr) Article formé par estampage à chaud
WO2020203979A1 (fr) Élément en acier revêtu, tôle d'acier revêtue et procédés de production d'un tel élément et d'une telle tôle d'acier
WO2023199635A1 (fr) Article formé par estampage à chaud
EP4079884A1 (fr) Tôle d'acier, élément et procédés respectivement pour la production de ladite tôle d'acier et dudit élément
CN115244204A (zh) 热轧钢板
JPWO2020017607A1 (ja) 鋼板
CN114945690B (zh) 钢板及其制造方法
JP7063414B2 (ja) 鋼板
WO2022196733A1 (fr) Tôle d'acier, élément en acier et élément en acier revêtu

Legal Events

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

Ref document number: 23788060

Country of ref document: EP

Kind code of ref document: A1