US20190160507A1 - Hot stamped steel - Google Patents

Hot stamped steel Download PDF

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Publication number
US20190160507A1
US20190160507A1 US16/097,771 US201616097771A US2019160507A1 US 20190160507 A1 US20190160507 A1 US 20190160507A1 US 201616097771 A US201616097771 A US 201616097771A US 2019160507 A1 US2019160507 A1 US 2019160507A1
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Prior art keywords
layer
base material
content
steel
plated
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US16/097,771
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Inventor
Akihiro SENGOKU
Hiroshi Takebayashi
Koji Akioka
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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Assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION reassignment NIPPON STEEL & SUMITOMO METAL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: AKIOKA, KOJI, SENGOKU, AKIHIRO, TAKEBAYASHI, HIROSHI
Assigned to NIPPON STEEL CORPORATION reassignment NIPPON STEEL CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: NIPPON STEEL & SUMITOMO METAL CORPORATION
Publication of US20190160507A1 publication Critical patent/US20190160507A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/261—After-treatment in a gas atmosphere, e.g. inert or reducing atmosphere
    • 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
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C23C2/29—Cooling or quenching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
    • C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
    • C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
    • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a hot stamped steel.
  • Patent Documents 1 to 3 disclose a technique in which a plated steel sheet is used as a steel sheet for hot stamping, thereby suppressing the formation of iron scales and, furthermore, improving the corrosion resistance of compacts.
  • Patent Document 1 discloses a plated steel sheet for hot pressing on which a Zn-plated layer is formed
  • Patent Document 2 discloses a plated steel sheet for a car member on which an Al-plated layer is formed
  • Patent Document 3 discloses a galvanized steel sheet for hot pressing in which a variety of elements such as Mn are added to a plated layer of the Zn-plated steel sheet.
  • these plated steel sheets have problems described below.
  • Patent Document 1 Japanese Unexamined Patent Application, First Publication No. 2003-73774
  • Patent Document 2 Japanese Unexamined Patent Application, First Publication No. 2003-49256
  • Patent Document 3 Japanese Unexamined Patent Application, First Publication No. 2005-113233
  • the present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a hot stamped steel being excellent in terms of fatigue properties, a phosphatability, coating adhesion, and weldability.
  • the gist of the present invention is as described below.
  • a hot stamped steel including a base material and a plated layer, in which the plated layer includes an interface layer, an intermediate layer, and an oxide layer in order from a base material side to a surface side; in the interface layer, a structure includes 99 area % or more in total of ⁇ Fe, Fe 3 Al, and FeAl, an average Al content is in a range of 8.0 mass % or more and 32.5 mass % or less, an average Zn content is limited to more than an Zn content of the base material and 5 mass % or less, a remainder of a chemical composition includes Fe and impurities, and an average layer thickness is 1.0 ⁇ m or more; in the intermediate layer, a structure includes 99 area % or more in total of Fe(Al, Zn) 2 and Fe 2 (Al, Zn) 5 , an average Al content is 30 mass % to 50 mass %, an average Zn content is 10 mass % to 40 mass %, a remainder of a chemical composition
  • the average layer thickness may be 1.0 ⁇ m to 10.0 ⁇ m in the interface layer.
  • a total weight per unit area of Al and Zn in the plated layer may be 20 g/m 2 or more and 100 g/m 2 or less.
  • the plated layer may further include more than 0 mass % and 10.0 mass % or less of Si on average, and, in the intermediate layer, 0 area % to 50 area % of the Fe(Al, Zn) 2 and the Fe 2 (Al, Zn) 5 may be substituted into Fe(Al, Si).
  • the hot stamped steel according to the present invention improvements were made respectively to the alloy form of the plated layer, the Al content and the Zn content in specific layers of the plated layer, and the layer thickness of an oxide formed as the outermost layer of the plated layer.
  • the hot stamped steel according to the present invention it is possible to achieve all of the improvement in the fatigue properties of the compact based on the suppression for generating of LME, the improvement in the phosphatability of the compact and the consequent improvement in the coating adhesion, and the improvement in the weldability of the compact.
  • FIG. 1 is an example of a cross-sectional SEM image showing a worked portion of a compact obtained by immediately performing hot-V-bent on an Al-Zn-based plated steel after heating under the conditions of Example 1.
  • FIG. 2 is an example of a cross-sectional SEM image showing a worked portion of a compact obtained by immediately performing hot-V-bent on a Zn-based plated steel after heating under the conditions of Example 1.
  • FIG. 3 is an example of a cross-sectional SEM image showing a worked portion of a compact obtained by immediately performing hot-V-bent on an Al-based plated steel after heating under the conditions of Example 1.
  • FIG. 4 is an example of a SEM image (secondary electron image) showing a surface of a compact in a case in which an Al-Zn-based plated steel is heated under the conditions of Example 1, immediately worked and rapidly cooled in a flat sheet die including a water-cooling jacket, and then subjected to a phosphating treatment.
  • SEM image secondary electron image
  • FIG. 5 is an example of a SEM image (secondary electron image) showing a surface of a compact in a case in which a Zn-based plated steel is heated under the conditions of Example 1, immediately worked and rapidly cooled in the flat sheet die including the water-cooling jacket, and then subjected to a phosphating treatment.
  • SEM image secondary electron image
  • FIG. 6 is an example of a SEM image (secondary electron image) showing a surface of a compact in a case in which an Al-based plated steel is heated under the conditions of Example 1, immediately worked and rapidly cooled in the flat sheet die including the water-cooling jacket, and then subjected to a phosphating treatment.
  • SEM image secondary electron image
  • FIG. 7 is a cross-sectional view of a vicinity of a surface of a hot stamped steel according to the present embodiment.
  • FIG. 8 is a schematic view of an Al concentration and a Zn concentration in the vicinity of the surface of the hot stamped steel according to the present embodiment.
  • the hot stamped steel refers to a compact obtained by carrying out hot stamping (hot pressing) on a plated steel for hot stamping.
  • hot stamping hot pressing
  • the hot stamped steel is simply referred to as the “compact”
  • the plated steel for hot stamping is simply referred to as the “steel” or the “plated steel”.
  • a structure of the interface layer includes 99 area % or more in total of ⁇ Fe, Fe 3 Al, and FeAl
  • an Al content is in a range of 8.0 mass % or more and 32.5 mass % or less and decreases toward the base material
  • an average Zn content is limited to 5 mass % or less
  • a remainder of a chemical composition of the interface layer includes Fe and impurities
  • an average layer thickness is 1.0 ⁇ m or more
  • a structure of the intermediate layer includes 99 area % or more in total of Fe(Al, Zn) 2 and Fe 2 (Al
  • a hot stamped steel 1 according to the present embodiment includes a base material 10 and a plated layer 20 as shown in FIG. 7 .
  • the base material in the hot stamped steel according to the present embodiment is not particularly limited. However, in a case in which the composition of the base material is in a range described below, a compact having preferred mechanical properties in addition to the LME resistance and the phosphatability can be obtained.
  • the unit “%” of the amounts of alloying elements included in the base material refers to “mass %”.
  • the strength of the hot stamped steel can be increased.
  • the C content in the base material may be set to 0.05% to 0.40%.
  • a more preferred lower limit value of the C content in the base material is 0.10%, and a still more preferred lower limit value is 0.13%.
  • a more preferred upper limit value of the C content in the base material is 0.35%.
  • Si has an effect of deoxidizing steel.
  • the Si content in the base material may be set to 0.5% or less.
  • a more preferred upper limit value of the Si content in the base material is 0.3%, and a still more preferred upper limit value of the Si content in the base material is 0.2%.
  • a more preferred lower limit value of the Si content in the base material can be determined depending on a required deoxidation level and is, for example, 0.05%.
  • the Mn content in the base material may be set to 0.5% to 2.5%.
  • a more preferred lower limit value of the Mn content in the base material is 0.6%, and a still more preferred lower limit value is 0.7%.
  • a more preferred upper limit value of the Mn content in the base material is 2.4%, and a still more preferred lower limit value is 2.3%.
  • Phosphorus (P) is an impurity that is included in steel.
  • P included in the base material in some cases, is segregated at crystal grain boundaries in the base material and thus degrades the toughness of the base material in the compact and degrades the delayed fracture resistance of the base material. Therefore, the P content in the base material may be set to 0.03% or less.
  • the P content in the base material is preferably as small as possible.
  • S Sulfur
  • S included in the base material in some cases, forms a sulfide and thus degrades the toughness of the base material in the compact and degrades the delayed fracture resistance of the base material. Therefore, the S content in the base material may be set to 0.01% or less.
  • the S content in the base material is preferably as small as possible.
  • Al content refers to the amount of sol.
  • Aluminum (Al) is generally used for the purpose of deoxidizing steel.
  • the Al content in the base material may be set to 0.10% or less.
  • a more preferred upper limit value of the Al content in the base material is 0.05%.
  • a more preferred lower limit value of the Al content in the base material is 0.01%.
  • N Nitrogen
  • B is included in the base material in order to improve the hardenability of steel before hot stamping
  • N included in the base material bonds to B and thus decreases the amount of a solid solution B and degrades a hardenability-improving effect of B. Therefore, the N content in the base material may be set to 0.01% or less.
  • the N content in the base material is preferably as small as possible.
  • the base material in the hot stamped steel of the present embodiment may further include one or more selected from the group consisting of B and Ti.
  • the B has an action of enhancing the hardenability of steel and is thus capable of increasing the strength of the base material in the compact after hot stamping.
  • the B content in the base material may be set to 0% to 0.0050%.
  • a more preferred lower limit value of the B content in the base material is 0.0001%.
  • Ti included in the base material bonds to N included in the base material and thus forms a nitride.
  • the bonding between B in the base material and N in the base material is suppressed, and thus the degradation of the hardenability of the base material by the formation of BN can be suppressed.
  • Ti included in the base material decreases the austenite grain sizes during heating in hot stamping due to austenite pinning effect and thus also has an effect of enhancing the toughness and the like of the compact.
  • the Ti content in the base material may be set to 0% to 0.10%.
  • a preferred lower limit value of the Ti content in the base material is 0.01%.
  • the base material configuring the hot stamped steel of the present embodiment may further include one or more selected from the group consisting of Cr and Mo.
  • the Cr included in the base material enhances the hardenability of the base material of steel before hot stamping.
  • the Cr content in the base material may be set to 0% to 0.5%.
  • a more preferred lower limit value of the Cr content in the base material is 0.1%.
  • Mo included in the base material enhances the hardenability of the base material of steel before hot stamping.
  • the Mo content in the base material may be set to 0% to 0.50%.
  • a more preferred lower limit value of the Mo content in the base material is 0.05%.
  • the base material configuring the hot stamped steel of the present embodiment may further include one or more selected from the group consisting of Nb and Ni.
  • Nb included in the base material forms a carbide and thus miniaturizes crystal grains in the base material during hot stamping and enhances the toughness of the compact.
  • the Nb content in the base material is excessive, the above-described effect is saturated.
  • the Nb content in the base material is excessive, there is a case in which the hardenability of the base material is degraded. Therefore, the Nb content may be set to 0% to 0.10%.
  • a more preferred lower limit value of the Nb content in the base material is 0.02%.
  • Ni Preferably 0% to 1.0%)
  • Ni included in the base material enhances the toughness of the base material in the compact. Ni in the base material also suppresses embrittlement attributed to the presence of molten Zn during heating in hot stamping. However, when the Ni content in the base material is excessive, these effects are saturated. Therefore, the Ni content in the base material may be set to 0% to 1.0%. A more preferred lower limit value of the Ni content in the base material is 0.1%.
  • a remainder of the chemical composition of the base material configuring the hot stamped steel of the present embodiment includes Fe and impurities.
  • an impurity refers to a substance that can be included in mineral or scraps as a raw material or a substance that can be mixed into the base material due to the manufacturing environment or the like during the industrial manufacturing of the compact.
  • the plated layer 20 in the hot stamped steel 1 includes an interface layer 21 , an intermediate layer 22 , and an oxide layer 23 in order from a base material 10 side of the compact 1 to a surface side of the compact 1 as shown in FIG. 7 .
  • the interface layer is formed adjacent to the base material.
  • a majority of the structure of the interface layer is configured of ⁇ Fe, Fe 3 Al, and FeAl. That is, the interface layer in the hot stamped steel according to the present embodiment is mainly configured of a Fe—Al alloy phase having a small Al content. Meanwhile, there is also a case in which a small amount of an inclusion or the like attributed to an impurity mixed into the interface layer during the formation of a plating is included in the interface layer.
  • the inventors confirmed that, in a case in which the interface layer is observed in a cross section of the plated layer in the hot stamped steel, when the structure includes 99 area % or more in total of ⁇ Fe, Fe 3 Al, and FeAl, the influence of the above-described inclusion can be ignored.
  • the interface layer Zn is present in a state of forming a solid solution in the above-described Fe—Al alloy phase.
  • Zn barely forms a solid solution, and the average Zn content in the interface layer is 5 mass % or less.
  • the presence of the interface layer enables the suppression of liquid metal embrittlement (LME).
  • LME liquid metal embrittlement
  • the Zn content in the interface layer is also not uniform, but LME is suppressed as long as the average Zn content in the interface layer is 5 mass % or less, and thus the interface layer may include a region including more than 5 mass % of Zn.
  • the Zn content in the interface layer is minimized in the interface between the interface layer and the base material. Therefore, the minimum value of the Zn content in the interface layer exceeds the Zn content in the base material.
  • the configuration of the interface layer is schematically shown in FIG. 8 .
  • the Al content in the interface layer 21 is not uniform.
  • the Al content in the interface between the base material 10 and the interface layer 21 is the same as the Al content in the base material 10 .
  • the Al content increases, and the structure changes to ⁇ Fe phase having the smallest Al content, Fe 3 Al phase having the second smallest Al content, and FeAl phase having the third smallest Al content in order.
  • the Zn content in the interface between the base material 10 and the interface layer 21 is the same as the Zn content in the base material 10 .
  • the Zn content also increases away from the interface between the base material 10 and the interface layer 21 , but the Zn content is suppressed at a low level, and the Zn content does not exceed 5 mass % on the average throughout the interface layer 21 .
  • the average layer thickness of the interface layer is less than 1.0 ⁇ m, the LME suppression effect cannot be sufficiently obtained. Therefore, it is necessary to set the average layer thickness of the interface layer is to 1.0 ⁇ m or more. In a case in which the average layer thickness of the interface layer is set to 2.0 ⁇ m or more, the above-described effect is exhibited at a higher level.
  • the lower limit value of the average layer thickness of the interface layer is more preferably 5.0 ⁇ m, 6.0 ⁇ m, or 7.0 ⁇ m.
  • the upper limit value of the average layer thickness of the interface layer is preferably 15.0 ⁇ m and more preferably 10.0 ⁇ m, 9.0 ⁇ m, or 8.0 ⁇ m.
  • the intermediate layer 22 is a layer including Fe, Al, and Zn and is formed on the interface layer 21 .
  • a majority of the structure of the intermediate layer is configured of Fe(Al, Zn) 2 and Fe 2 (Al, Zn) 5 .
  • Fe(Al, Zn) 2 is a phase in which some of Al in FeAl 2 that is a kind of a Fe—Al intermetallic compound is substituted into Zn
  • Fe 2 (Al, Zn) 5 is a phase in which some of Al in Fe 2 Al 5 that is a kind of a Fe—Al intermetallic compound is substituted into Zn.
  • the Al content and the Zn content are almost uniform.
  • the chemical composition of the intermediate layer includes, by unit mass %, 30% or more and 50% or less of Al on the average and 10% or more and 40% or less of Zn on the average.
  • the average Al content in the intermediate layer is above the average Al content in the interface layer.
  • the average Al content in the intermediate layer reaches 30 mass % or more.
  • the oxide layer is mainly configured of a Zn oxide
  • the average Al content in the intermediate layer reaches 50 mass % or less in a case in which an excellent phosphatability is imparted to the compact. That is, in a case in which the average Al content in the intermediate layer is outside a range of 30 mass % to 50 mass %, there is an extremely high likelihood of the configuration of the interface layer or the oxide layer becoming inappropriate.
  • the lower limit value of the average Al content in the interface layer is preferably 32 mass % or 35 mass %, and, in this case, it is possible to more reliably develop the LME suppression effect of the interface layer.
  • a preferred upper limit value of the average Al content in the interface layer is 50 mass % or 45 mass %, and, in this case, it is possible to more reliably improve the phosphatability of the oxide layer.
  • the average Zn content in the intermediate layer reaches 10 mass % or more.
  • the average Zn content in the intermediate layer reaches 30 mass % or less. That is, in a case in which the average Zn content in the intermediate layer is outside a range of 10 mass % to 40 mass %, there is an extremely high likelihood of the configuration of the interface layer or the oxide layer becoming inappropriate.
  • a preferred lower limit value of the average Zn content in the intermediate layer is 12 mass % or 13 mass %, and, in this case, it is possible to more reliably improve the phosphatability of the oxide layer.
  • a preferred upper limit value of the average Zn content in the intermediate layer is 28 mass % or 25 mass %, and, in this case, it is possible to more reliably develop the LME suppression effect of the interface layer.
  • the thickness of the intermediate layer does not have any direct influences on the phosphatability and the LME resistance of the compact.
  • the thickness of the intermediate layer is desirably set to 5.0 ⁇ m or more.
  • the thickness of the intermediate layer is desirably 30.0 ⁇ m or less.
  • the oxide layer 23 including a Zn oxide as a main component is formed as the outermost layer of the compact.
  • the oxide layer 23 is generated due to the oxidation of a plating of the plated steel for hot stamping in a heating process during the manufacturing of the hot stamped steel.
  • This oxide layer improves the phosphatability of the hot stamped steel.
  • the oxide layer is too thick, the corrosion resistance, weldability, and the like of the compact are adversely affected, and thus the average layer thickness of the oxide layer is set to 3.0 ⁇ m or less. Meanwhile, in a case in which the average layer thickness of the oxide layer is set to 2.0 ⁇ m or less, the performance of the corrosion resistance, weldability, or the like of the compact is exhibited at a high level, which is preferable.
  • the states of the interface layer, the intermediate layer, and the oxide layer can be specified by the following means.
  • the Al content in the interface layer can be obtained by cutting the compact perpendicularly to the surface, polishing the cross section, and analyzing the distribution of the Al content in a region including the interface layer in the cross section using an analyzer such as EPMA.
  • the average Zn content in the interface layer, the average Al content and the average Zn content in the intermediate layer, and the average Si content in the plated layer can be obtained on the basis of concentration distributions obtained using the above-described method.
  • the metallographic structures of the interface layer and the intermediate layer can be obtained by analyzing the crystal structure using TEM or the like.
  • the thicknesses of the interface layer, the intermediate layer, and the oxide layer can be obtained by capturing an enlarged photograph of the above-described cross section using an electronic microscope and image-analyzing this enlarged photograph.
  • the configuration of the plated layer in the compact according to the present embodiment is substantially not uniform along a direction parallel to the surface of the compact.
  • the thicknesses of the interface layer, the intermediate layer, and the oxide layer often differ in a worked region and a non-worked region. Therefore, the above-described analyses need to be carried out in a non-worked region of the compact.
  • a compact in which the state of the plated layer in a non-worked region is in the above-described range is considered as the compact according to the present embodiment.
  • the hot stamped steel according to the present embodiment having the configuration described above, improvements are made to the alloy forms of the interface layer and the intermediate layer configuring the plated layer, the Al content and the Zn content in the interface layer and the intermediate layer, and the thicknesses of the interface layer, the intermediate layer, and the oxide layer.
  • the hot stamped steel according to the present embodiment it is possible to satisfy both the improvement of the fatigue properties of the compact based on the suppression of the occurrence of LME and the improvement of the phosphatability.
  • the plated layer is preferably formed so that the total of the Al content and the Zn content in the plated layer reaches 20 g/m 2 or more and 100 g/m 2 or less.
  • the total of the Al content and the Zn content in the plated layer is set to 20 g/m 2 or more, the above-described effects (the fatigue properties and the phosphatability) of the interface layer, the intermediate layer, and the oxide layer can be further enhanced.
  • the total amount is set to 100 g/m 2 or less, it is possible to reduce the manufacturing costs by suppressing the cost for raw materials of the compact, and furthermore, the weldability of the hot stamped steel can be enhanced.
  • a preferred lower limit value of the total of the Al content and the Zn content in the plated layer is 30 g/m 2 .
  • a preferred upper limit value of the total of the Al content and the Zn content in the plated layer is 90 g/m 2 .
  • the total of the Al content and the Zn content included in the plated layer can be measured by melting the hot stamped steel in hydrochloric acid and carrying out inductively coupled plasma-atomic emission spectrometry (ICP-AES) on the molten liquid.
  • the Al content and the Zn content can be separately obtained using this method.
  • ICP-AES inductively coupled plasma-atomic emission spectrometry
  • the plated layer in the hot stamped steel includes Fe, and thus, in the above-described method, the plated layer in the hot stamped steel is not sufficiently melted or the melting rate is extremely slow.
  • the plated layer preferably further includes more than 0 mass % to 10.0 mass % of Si on the average.
  • the average Si content in the plated layer is set to more than 0 mass %, it is possible to enhance the adhesion between the base material and the plated layer.
  • the average Si content is set to 10.0 mass % or less, it is possible to prevent the degradation in the performance of the corrosion resistance, weldability, and the like of the hot stamped steel.
  • a more preferred lower limit value of the average Si content in the plated layer is 0.1 mass % or 0.3 mass %.
  • a more preferred upper limit value of the average Si content in the plated layer is 8.0 mass %.
  • the hot stamped steel according to the present embodiment has excellent properties, and thus the lower limit value of the average Si content in the plated layer is 0 mass %.
  • the configuration of phases in the intermediate layer is changed.
  • the intermediate layer includes 99 area % or more in total of Fe(Al, Zn) 2 and Fe2(Al, Zn) 5 , however, in a case in which the plated layer includes more than 0 mass % to 10.0 mass % of Si on the average, some of Fe(Al, Zn) 2 and Fe 2 (Al, Zn) 5 are substituted into Fe(Al, Si).
  • Fe(Al, Si) refers to a phase in which some of Al in FeAl is substituted to Si.
  • the hot stamped steel according to the present embodiment is manufactured so that the average Si content in the plated layer reaches 10.0 mass %, the amount of Fe(Al, Si) in the intermediate layer reaches approximately 50 area %. Therefore, in a case in which the plated layer includes more than 0 mass % to 10.0 mass % of Si on the average, the intermediate layer includes 99 area % or more in total of Fe(Al, Zn) 2 and Fe 2 (Al, Zn) 5 , and the amount of Fe(Al, Si) reaches 0 area % to 50 area %.
  • the Si content is small
  • Si forms a solid solution in of Fe(Al, Zn) 2 and Fe 2 (Al, Zn) 5 , and the configuration of the intermediate layer does not change.
  • the average Si content in the plated layer is 0 mass % to 0.1 mass %
  • Fe(Al, Si) is not generated in the intermediate layer.
  • the phase constitution of the interface layer does not change. Therefore, even in a case in which the plated layer includes more than 0 mass % to 10.0 mass % of Si on the average, the interface layer includes 99 area % or more in total of ⁇ Fe, Fe 3 Al, and FeAl.
  • the method for manufacturing the hot stamped steel according to the present embodiment includes a step of manufacturing the plated steel for hot stamping and a step of carrying out hot stamping on the plated steel for hot stamping.
  • the step of manufacturing the plated steel for hot stamping includes a step of manufacturing a base material of the plated steel for hot stamping and a step of forming an Al-Zn-plated layer on the base material of the plated steel for hot stamping.
  • the method for manufacturing the hot stamped steel according to the present embodiment includes a step of forming an antirust oil film and a blanking work step as necessary.
  • the respective step will be described in detail.
  • the plated steel which is a material of the hot stamped steel includes a base material and a plated layer.
  • the base material of the plated steel for hot stamping is manufactured.
  • molten steel having the same chemical composition as the chemical composition of the base material of the hot stamped steel according to the present embodiment exemplified above is manufactured, and a slab is manufactured by a casting method using this molten steel.
  • an ingot may be manufactured by an ingot-making method using molten steel manufactured as described above.
  • the slab or the ingot is hot-rolled, thereby obtaining the base material (hot-rolled sheet) of the plated steel for hot stamping.
  • a cold-rolled sheet obtained by carrying out a pickling treatment on the hot-rolled sheet and carrying out cold rolling on the hot-rolled sheet which has been subjected to the pickling treatment may be used as the base material of the plated steel for hot stamping.
  • an Al-Zn-plated layer is formed on the base material of the plated steel for hot stamping, thereby manufacturing the plated steel for hot stamping.
  • the Al content in a plating bath is set to 40 mass % to 70 mass %, and the Zn content is set to 30 mass % to 60 mass %.
  • the plating of the plated steel for hot stamping is formed using a plating bath having the above-described composition, and hot stamping is carried out on the plated steel for hot stamping under conditions described below, whereby the configuration of the plated layer of the hot stamped steel can be made as described above.
  • the Al content (Al concentration) and the Zn content (Zn concentration) in the plating bath are substantially the same as the Al content (Al concentration) and the Zn content (Zn concentration) in the plated layer of the plated steel for hot stamping, but the average Al content (Al concentration) and the average Zn content (Zn concentration) in the plated layer in the hot stamped steel are smaller than the average Al content (Al concentration) and the average Zn content (Zn concentration) in the plating bath. This is because Al and Zn in the plated layer and Fe in the base material form an alloy during hot stamping and thus the Fe concentration in the plated layer is increased.
  • the plated layer of the plated steel for hot stamping will be referred to as the non-alloyed plated layer in some cases.
  • the average Al content and the average Zn content in the non-alloyed plated layer can be measured by melting the non-alloyed plated layer in acid corrosion inhibitor-added hydrochloric acid, and then analyzing using inductively coupled plasma-atomic emission spectrometry.
  • the Si content in the non-alloyed plated layer is decreased since Fe in the plated layer diffuses during the alloying of the base material and the plating. Therefore, in a case in which the Si content in the non-alloyed plated layer is set to 0 mass % to 15 mass %, the Si content in the alloyed plated layer is reached 0 mass % to 10 mass %.
  • a method for forming the non-alloyed plated layer may be a hot-dip plating treatment or any other treatment such as a thermal-spraying plating treatment or a deposition plating treatment as long as the average Al content and the average Zn content in the non-alloyed plated layer are controlled as described below.
  • a plating treatment step includes a step of immersing a base material of the plated steel for hot stamping in a hot-dip plating bath including Al, Zn, and impurities and further randomly including Si and a step of lifting the base material of the plated steel for hot stamping to which plated metal is attached from the plating bath.
  • the plated layer is preferably formed on the base material with the total weight per unit area of Al and Zn in the plated layer being 20 g/m 2 or more and 100 g/m 2 or less.
  • the total weight per unit area of Al and Zn in the plated layer it is important to set the total weight per unit area of Al and Zn in the plated layer to 20 g/m 2 or more and 100 g/m 2 or less in the lifting of the base material of the plated steel for hot stamping from the plating bath.
  • the total weight per unit area of Al and Zn included in the plated layer slightly decreases during alloying due to oxidation and evaporation.
  • the total weight can be ensured by appropriately adjusting the lifting rate of the steel from the plating bath or the flow rate of gas during wiping.
  • the plated steel for hot stamping manufactured using the above-described method includes the base material and the non-alloyed plated layer, and the non-alloyed plated layer includes 40.0 mass % to 70.0 mass % of Al, 30.0 mass % to 60.0 mass % of Zn, and 0 mass % to 15.0 mass % of Si.
  • the hot stamped steel according to the present embodiment is obtained.
  • hot stamping conditions will be described in detail.
  • hot stamping is carried out on the above-described plated steel for hot stamping.
  • Ordinary hot stamping is carried out by heating steel up to a hot stamping temperature range (hot working temperature range), subsequently, hot-working the steel, and furthermore, cooling the steel.
  • a hot stamping temperature range hot working temperature range
  • heating steel up to the hot stamping temperature range sufficiently alloys the plated layer, and thus, in ordinary hot stamping techniques, the control of the heating conditions of steel is not considered to be important.
  • the plated steel for hot stamping is heated up to an alloying temperature range
  • the temperature of the plated steel for hot stamping is held in the alloying temperature range
  • the plated steel for hot stamping is heated up to the hot stamping temperature range
  • (4) the plated steel for hot stamping is hot-worked and cooled.
  • the present inventors found that, in order to obtain the plated layer having the above-described configuration, it is essential to hold the heating of the steel in the alloying temperature range for a short period of time and then resume the heating during the heating of the plated steel for hot stamping up to the hot stamping temperature range.
  • the plated steel for hot stamping is charged into a heating furnace (a gas furnace, an electric furnace, an infrared furnace, or the like).
  • a heating furnace a gas furnace, an electric furnace, an infrared furnace, or the like.
  • the plated steel for hot stamping is heated up to a temperature range of 500° C. to 750° C. (the alloying temperature range) and held in this temperature range for 10 seconds to 450 seconds. Due to the holding of the temperature, Fe in the base material diffuses into the plated layer, and alloying proceeds. Due to this alloying, the non-alloyed plated layer changes to a layer including an interface layer, an intermediate layer, and an oxide layer from the base material side toward the surface side of the compact.
  • the above-described holding time refers to a period of time during which the temperature of the plated steel for hot stamping is in the alloying temperature range.
  • the temperature of the plated steel for hot stamping may change in the alloying temperature range during the holding of the temperature as long as the above-described holding time condition is satisfied.
  • the alloying temperature range that is, lower than 500° C.
  • the alloying rate of the plated layer is extremely slow, and the heating time significantly extends, which is not preferable from the viewpoint of the productivity.
  • the temperature of the plated steel for hot stamping is held above the alloying temperature range, that is, higher than 750° C.
  • the growth of an oxide on the surface layer of the plated layer is excessively accelerated in this holding process, and the weldability of a compact to be obtained after HS degrades.
  • the time during which the temperature of the plated steel for hot stamping is held in the alloying temperature range is shorter than 10 seconds, the alloying of the plated layer is not completed, and thus a plated layer having the interface layer, the intermediate layer, and the oxide layer described above cannot be obtained.
  • the time during which the temperature of the plated steel for hot stamping is held in the alloying temperature range is longer than 450 seconds, the amount of the oxide grown becomes excessive, which leads to the degradation of the productivity.
  • the heating conditions during the heating the plated steel for hot stamping up to the above-described alloying temperature range are not particularly limited. However, from the viewpoint of the productivity, the heating time is desirably short.
  • the temperature of the plated steel for hot stamping is held in the alloying temperature range as described above, then, the plated steel for hot stamping is heated up to a temperature range of the AC 3 temperature to 950° C., and then hot working is carried out. At this time, it is necessary to limit the time during which the temperature of the plated steel for hot stamping is held in the temperature range of the AC 3 temperature to 950° C. (oxidation temperature range) to 60 seconds or shorter. When the temperature of the plated steel for hot stamping is held in the oxidation temperature range, the oxide layer on the surface layer of the plated layer grows.
  • the time during which the temperature of the plated steel for hot stamping is in the oxidation temperature range is longer than 60 seconds, there is a concern that an oxide film may excessively grow and thus the weldability of the compact may be degraded. Meanwhile, the generation rate of the oxide film is extremely fast, and thus the lower limit value of the time during which the temperature of the plated steel for hot stamping is in the oxidation temperature range is longer than 0 seconds.
  • the plated steel for hot stamping is heated in a non-oxidative atmosphere such as a 100% nitrogen atmosphere, the oxide layer is not formed, and thus the plated steel for hot stamping needs to be heated in an oxidative atmosphere such as the atmosphere.
  • the conditions such as the heating rate and the peak heating temperature are not particularly limited, and a variety of conditions under which hot stamping can be carried out can be selected.
  • the plated steel for hot stamping removed from the heating furnace is press-formed using a die.
  • the steel is quenched at the same time as the press-forming.
  • a cooling medium for example, water
  • the die accelerates the release of heat from the plated steel for hot stamping, thereby quenching the plated steel.
  • the plated steel for hot stamping was heated using the heating furnace.
  • the plated steel for hot stamping may be heated by energization heating. Even in this case, the steel is heated for a predetermined period of time by energization heating, and the steel is press-formed using the die.
  • the antirust oil film-forming step is a step of forming an antirust oil film by applying an antirust oil to the surface of the plated steel for hot stamping after the plating treatment step and before the hot stamping step and may be randomly included in the manufacturing method.
  • the time taken to carry out hot stamping from the manufacturing of the plated steel for hot stamping is long, there is a concern that the surface of the plated steel for hot stamping may be oxidized.
  • the surface of the plated steel for hot stamping on which an antirust oil film is formed by the antirust oil film-forming step is not easily oxidized, and thus the antirust oil film-forming step is capable of suppressing the formation of scales on the compact.
  • any well-known technique can be used as a method for forming the antirust oil film.
  • the present step is a step of forming the steel in a specific shape by carrying out a shearing work and/or a punching work on the plated steel for hot stamping after the antirust oil film-forming step and before the hot stamping step.
  • the sheared surface of the steel which has been subjected to the blanking work is easily oxidized.
  • the antirust oil film has been formed in advance on the steel surface, the antirust oil also spreads on the sheared surface to a certain extent. Therefore, the oxidation of the steel after the blanking work can be suppressed.
  • the present invention is not limited to the above-described embodiment and can be appropriately modified in design within the scope of the gist of the present invention.
  • the present inventors formed an Al-Zn-based plated layer, a Zn-based plated layer, and an Al-based plated layer on a base material 10 respectively.
  • the Al-Zn-based plated layer included 55.0 mass % of Al and 45.0 mass % of Zn, the Zn-based plated layer substantially included only Zn, and the Al-based plated layer substantially included only Al.
  • a steel on which each of the plated layers was formed (a plated steel configured of the base material and the plated layer) was charged into a first heating furnace, heated up to 700° C., and held in this temperature range for 120 seconds. After that, the plated steel was immediately charged into a second heating furnace and heated up to 900° C., and then the plated steel was removed from the second heating furnace so that the steel temperature was in a range of the Ac 3 temperature to 950° C. for 30 seconds. Immediately after the plated steel was removed from the second heating furnace, a hot V-bending test was carried out on the plated steel using a hand pressing machine.
  • the time taken from the removal of the steel from the furnace to the beginning of the work on the steel was approximately five seconds, and the bending work was carried out at a steel temperature of approximately 800° C.
  • V-bending was carried out so that the outer diameter of a bent portion increased by approximately 15% from that before the V-bending.
  • the steel was cooled, thereby quenching the steel.
  • the cooling was carried out so that the cooling rate from approximately 800° C. to a martensite transformation-starting point (approximately 410° C.) reached 50° C./second or faster.
  • a SEM image of the bent outside portion of the worked portion of the compact after the completion of the cooling was captured, and the fatigue properties (LME resistance) of the compact were evaluated on the basis of the presence or absence of the occurrence of LME.
  • FIGS. 1 to 3 are cross-sectional photographs of the worked portions of the compacts manufactured from the Al-Zn-based plated steel, the Zn-based plated steel, and the Al-based plated steel.
  • an alloyed Al-Zn-based plated layer 30 was formed on the base material 1
  • an alloyed Zn-based plated layer 40 was formed on the base material 1
  • an alloyed Al-based plated layer 50 was formed on the base material 1 in the compact of FIG. 3 .
  • the worked portion of the observed compact was a portion on which a tensile work was carried out and an outside portion of the V-bending worked portion with respect to the bending center in which the occurrence of LME was concerned.
  • the steel that had been heated and held in the specific temperature range as described above was removed from the furnace, the steel was formed using a flat sheet die including a water-cooling jacket and then quenched so that the cooling rate reached 50° C./second or faster until the martensite transformation-starting point (approximately 410° C.) even in a portion with a slow cooling rate.
  • the surface of the compact was conditioned, and a phosphating treatment was carried out on the compact.
  • a SEM image of the surface of the compact was captured, and the phosphatability was evaluated on the basis of the degree of a phosphate film formed.
  • FIGS. 4 to 6 are examples of SEM images (secondary electron images) showing the surfaces of the compacts in a case in which the Al-Zn-based plated steel, the Zn-based plated steel, and the Al-based plated steel removed from the second heating furnace were worked and rapidly cooled in the flat sheet die including the water-cooling jacket and then subjected to a phosphating treatment.
  • a slab was manufactured by a continuous casting method using molten steel having a chemical composition shown in Table 1.
  • the slab was hot-rolled so as to manufacture a hot-rolled material, and the hot-rolled material was further pickled and then cold-rolled, thereby manufacturing a cold-rolled steel.
  • this cold-rolled steel was used as a base material (sheet thickness: 1.4 mm) that was used to manufacture a hot stamped steel.
  • the Ac 3 temperature of the base material was approximately 810° C.
  • plating was formed on the base material manufactured as described above using a plating bath having a composition shown in Table 2, thereby obtaining the steel for hot stamping.
  • the adhesion amount of the plating was controlled so that the total weight of Al and Zn reached a value shown in Table 2.
  • This steel was heated up to an alloying temperature shown in Table 2, and the temperature was held for an alloying time shown in Table 2.
  • the steel was charged into a heating furnace and heated up to a range of the Ac 3 temperature to 950° C., and then the steel was removed from the heating furnace so that the temperature of the steel was held in this temperature range for a holding time shown in Table 2.
  • Hot V-bending work was immediately carried out on the steel removed from the heating furnace using a hand pressing machine.
  • the time taken from the removal of the steel from the heating furnace to the beginning of the work on the steel was set to five seconds.
  • shape of the die a shape which extended an outside portion having a bending radius by the V-bending work by approximately 15% at the end of the bending work was used.
  • Hot stamping was immediately carried out on the steel removed from the heating furnace using the flat sheet die including the water-cooling jacket, and then accelerated cooling was carried out.
  • the cooling rate was set to reach a cooling rate of 50° C./second or faster until approximately the martensite transformation-starting point (410° C.).
  • the surfaces were conditioned at room temperature for 20 seconds using a surface conditioning treatment agent (trade name: PREPALENE-X) manufactured by Nihon Parkerizing Co., Ltd.
  • a phosphating treatment was carried out on the respective hot stamped steels using a phosphating treatment liquid (trade name: PAUL BOND 3020) manufactured by Nihon Parkerizing Co., Ltd.
  • a phosphating treatment liquid (trade name: PAUL BOND 3020) manufactured by Nihon Parkerizing Co., Ltd.
  • the temperature of a treatment liquid was set to 43° C., and the hot stamped steels were immersed in the treatment liquid for 120 seconds.
  • the respective hot stamped steels were electrodeposition-coated with a cationic electrodeposition coating manufactured by NIPPONPAINT Co., Ltd. by slope energization at a voltage of 160 V and, furthermore, baking-coated at a baking temperature of 170° C. for 20 minutes.
  • the average of the thicknesses of the coatings after the electrodeposition coating was 10 ⁇ m in all of invention examples and comparative examples.
  • the states of interface layers, intermediate layers, and oxide layers in the invention example and the comparative examples were specified by the following means.
  • the average Al content and the average Zn content in the interface layer, the average Al content and the average Zn content in the intermediate layer, and the average Si content in the plated layer were obtained by cutting the compact perpendicularly to the surface of the compact, polishing a cross section, and analyzing this cross section using an analyzer such as EPMA.
  • the metallographic structures of the interface layer and the intermediate layer were obtained by analyzing the crystal structure using TEM or the like. Examples in which the metallographic structure satisfied the regulation of the present invention were indicated as “OK”, and examples in which the crystallographic structure did not satisfy the regulation were indicated as “NG”.
  • the thicknesses of the interface layer, the intermediate layer, and the oxide layer were obtained by capturing an enlarged photograph of the above-described cross section using an electronic microscope and image-analyzing this enlarged photograph. The above-described analyses were carried out on a non-worked region of the compact.
  • the total weight of Al and Zn in the plated layer in the invention examples and the comparative examples was measured by high-frequency inductively coupled plasma-atomic emission spectrometry (ICP-OES). That is, a sample was taken from the non-worked portion (a place which was not V-bent) in each of the invention examples and the comparative examples, and the plated layer was melted in an aqueous solution of 10% HCl and analyzed. The energy of plasma was imparted to each solution, component elements were excited, and the locations and intensities of emitted light rays (spectrum rays) being emitted were measured, thereby identifying the respective elements and measuring the amounts thereof.
  • ICP-OES high-frequency inductively coupled plasma-atomic emission spectrometry
  • the fatigue properties of the examples and the comparative examples were evaluated by the following means.
  • the presence and absence of the occurrence of liquid metal embrittlement (LME) was observed by observing a reflection electron image of a cross section of the V-bending worked portion in the steel thickness direction of each of the examples and the comparative examples using a scanning electron microscope (SEM) and a reflection electron detector.
  • SEM scanning electron microscope
  • GOOD favorable
  • BAD poor
  • the phosphating treatment properties of the examples and the comparative examples were evaluated by the following means.
  • a phosphate film formed on each of the phosphating-treated samples was melted and removed using a heavy ammonium chromate solution, and the weight difference of the steel before and after the removal of the film was measured and considered as the adhesion amount of the phosphate film.
  • samples having an adhesion amount of 2.0 g/m 2 or more were evaluated as being favorable (GOOD) in terms of the phosphatability.
  • samples having an adhesion amount of less than 2.0 g/m 2 were evaluated as being poor (BAD) in terms of the phosphatability.
  • the coating adhesion of the examples and the comparative examples were evaluated by the following means.
  • Each of the electrodeposition-coated samples was immersed in an aqueous solution of 5% NaCl having a temperature of 50° C. for 500 hours. After the immersion, polyester tape was attached to the entire surface of a 60 mm ⁇ 120 mm test region and then peeled off. The area of a region from which the coated film had been peeled off by pulling the tape was obtained, and the coated film peeling percentage (%) was obtained on the basis of the following expression.
  • Coated film peeling percentage ( A 2/ A 1) ⁇ 100
  • A2 represents the area (mm 2 ) of the region from which the coated film was peeled off.
  • Samples having a coated film peeling percentage of less than 5.0% were evaluated as being favorable (GOOD) in terms of the coating adhesion.
  • samples having a coated film peeling percentage of 5.0% or more were evaluated as being poor (BAD) in terms of the coating adhesion.
  • the weldability of the examples and the comparative examples were evaluated using a surface resistance value.
  • the surface resistance value of the sample was computed from a voltage value obtained when a current of 2A was made to flow through the sample using a pressurization-type direct-current inverter power supply at a welding pressure of 250 kgf. Samples having a surface resistance value of 20 m ⁇ or less were evaluated as being favorable (GOOD) in terms of the weldability.
  • Comparative Example 101 was manufactured using a plating bath including an insufficient Al content, and thus it was not possible to prevent LME. Therefore, the fatigue properties of Comparative Example 101 was poor.
  • Comparative Example 102 was manufactured using a plating bath including an insufficient Zn content, and thus the structure of the intermediate layer became inappropriate due to the lack of Zn. Therefore, in Comparative Example 102, the phosphatability was impaired, and the coating adhesion was poor.
  • Comparative Example 104 the alloying temperature during the hot stamping was too low, and thus the plated layer was not sufficiently alloyed, a Zn-rich phase was generated, and it was not possible to prevent LME. Therefore, the fatigue properties of Comparative Example 104 was poor.
  • Comparative Example 106 the alloying time during the hot stamping was too short, and thus the heating for alloying became insufficient. Therefore, in Comparative Example 106, LME occurred, and the fatigue properties degraded. Furthermore, in Comparative Example 106, heating was not sufficient, and thus the amount of the oxide was small, and the phosphatability and the coating adhesion lacked.
  • the present invention in the hot stamped steel in which the plated layer is formed on the surface of the base material, both the fatigue properties and the phosphatability are sufficiently exhibited. Therefore, the present invention is hopeful in the field of structural members and the like which are used in cars and the like.

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  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
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US11358369B2 (en) 2017-12-26 2022-06-14 Posco Plating steel sheet for hot press forming, forming member using same, and manufacturing method therefor
EP4239098A4 (en) * 2020-10-30 2023-12-06 Nippon Steel Corporation ZN-COATED HOT STAMPED BODY
US11884998B2 (en) 2017-03-31 2024-01-30 Nippon Steel Corporation Surface treated steel sheet

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JP7006256B2 (ja) * 2017-12-27 2022-02-10 日本製鉄株式会社 ホットスタンプ用溶融亜鉛めっき鋼板及びホットスタンプ用溶融亜鉛めっき鋼板の製造方法
JP7006257B2 (ja) * 2017-12-27 2022-01-24 日本製鉄株式会社 ホットスタンプ成形体及びホットスタンプ成形体の製造方法
WO2019180853A1 (ja) 2018-03-20 2019-09-26 日本製鉄株式会社 ホットスタンプ成形体
KR102153172B1 (ko) * 2018-08-30 2020-09-07 주식회사 포스코 열간 성형성 및 내식성이 우수한 알루미늄-아연 합금 도금강판 및 그 제조방법
US11965250B2 (en) * 2019-08-29 2024-04-23 Nippon Steel Corporation Hot stamped steel
EP4382630A1 (en) * 2021-10-29 2024-06-12 JFE Steel Corporation Hot-pressed member
WO2023074115A1 (ja) * 2021-10-29 2023-05-04 Ｊｆｅスチール株式会社 熱間プレス部材
KR20240089216A (ko) * 2021-10-29 2024-06-20 제이에프이 스틸 가부시키가이샤 열간 프레스 부재
WO2023074114A1 (ja) * 2021-10-29 2023-05-04 Ｊｆｅスチール株式会社 熱間プレス部材
WO2023149586A1 (ko) * 2022-02-03 2023-08-10 주식회사 포스코 표면 품질이 우수한 열간 프레스 성형용 도금 강판 및 이의 제조방법
JP7315129B1 (ja) 2022-03-29 2023-07-26 Ｊｆｅスチール株式会社 熱間プレス部材および熱間プレス用鋼板
WO2024122117A1 (ja) * 2022-12-09 2024-06-13 日本製鉄株式会社 ホットスタンプ成形体
WO2024122123A1 (ja) * 2022-12-09 2024-06-13 日本製鉄株式会社 めっき鋼板
CN116641009A (zh) * 2023-05-17 2023-08-25 宝山钢铁股份有限公司 具有优良耐蚀性的锌基镀层钢板、热冲压部件及其制造方法
CN116590640A (zh) * 2023-05-17 2023-08-15 宝山钢铁股份有限公司 一种锌基镀层钢板、锌基热冲压部件及其制造方法

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EP4239098A4 (en) * 2020-10-30 2023-12-06 Nippon Steel Corporation ZN-COATED HOT STAMPED BODY

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BR112018071451A2 (pt) 2019-02-05
CA3020663A1 (en) 2017-11-16
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EP3456854A1 (en) 2019-03-20
EP3456854A4 (en) 2019-10-02

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