EP3604602A1 - Pièce moulée estampée à chaud - Google Patents

Pièce moulée estampée à chaud Download PDF

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Publication number
EP3604602A1
EP3604602A1 EP17903939.1A EP17903939A EP3604602A1 EP 3604602 A1 EP3604602 A1 EP 3604602A1 EP 17903939 A EP17903939 A EP 17903939A EP 3604602 A1 EP3604602 A1 EP 3604602A1
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EP
European Patent Office
Prior art keywords
layer
content
plated
hot
base metal
Prior art date
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EP17903939.1A
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German (de)
English (en)
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EP3604602A4 (fr
Inventor
Akihiro Sengoku
Hiroshi Takebayashi
Koji Akioka
Kenichiro Matsumura
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Nippon Steel Corp
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Nippon Steel Corp
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Publication of EP3604602A1 publication Critical patent/EP3604602A1/fr
Publication of EP3604602A4 publication Critical patent/EP3604602A4/fr
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • 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
    • C22C21/00—Alloys based on aluminium
    • C22C21/10—Alloys based on aluminium with zinc 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
    • C22C38/02—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
    • C22C38/06—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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • 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
    • 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
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • 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
    • C23C28/32—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
    • C23C28/3225—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 with at least one zinc-based 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
    • C23C28/34—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

Definitions

  • the present invention relates to a hot stamped body.
  • Structural members used for automobiles or the like may be produced by performing hot stamping (hot pressing) so as to increase both strength and dimensional accuracy.
  • hot stamping hot pressing
  • a steel sheet is heated to the Ac 3 point or above, and is rapidly cooled while being subjected to pressing by press tooling. That is, in this production process, pressing and quenching are performed simultaneously.
  • hot stamping it is possible to produce a formed body having high dimensional accuracy and high strength.
  • Patent Document 1 discloses a steel sheet for hot pressing having a Zn plated layer.
  • Patent Document 2 discloses an aluminum plated steel sheet for high strength automobile component having an Al plated layer.
  • Patent Document 3 discloses a Zn-based plated steel material for hot pressing where various elements, such as Mn, are added into the plated layer of a Zn plated steel sheet.
  • Patent Document 2 Al having a higher fusing point than Zn is used for a plated layer and hence, different from Patent Document 1, molten metal is less likely to enter a steel sheet. Accordingly, it is predicted that excellent fatigue property can be obtained and, eventually, the formed body subjected to hot stamping is excellent in fatigue property.
  • a steel material on which an Al plated layer is formed has a problem that it is difficult to form a phosphate film at the time of performing phosphate treatment, which is performed before coating is applied to automobile components. In other words, some steel materials may not obtain sufficient phosphatability, thus degrading corrosion resistance after coating.
  • An objective of the present invention which has been made to overcome the above-mentioned problems, is to provide a hot stamped body excellent in fatigue property, spot weldability, and corrosion resistance after coating.
  • the present invention has been made to overcome the above-mentioned problems, and the gist of the present invention is the following hot stamped body.
  • Inventors of the present invention have conducted studies on a method for achieving both of LME resistance at the time of performing hot stamping forming and spot weldability and corrosion resistance after coating of a hot stamped body.
  • the inventors of the present invention have conducted studies on a method for enhancing corrosion resistance after coating of a formed body. As a result, the inventors of the present invention have found that corrosion resistance can be enhanced by causing a plated layer of the formed body to contain Mg. However, it is found that, in the case of producing a formed body whose plated layer contains Mg, LME easily occurs at the time of performing hot stamping forming, thus deteriorating fatigue property. Further, when Mg content in the plated layer is excessively high, spot weldability is also decreased.
  • the inventors of the present invention have conducted extensive studies on a method for enhancing corrosion resistance without deteriorating fatigue property and spot weldability. As a result, the following results are obtained. All of the above-mentioned properties can be ensured with a good balance by causing a plated layer to adopt a structure including a layer on the base metal side which contains an Fe-Al alloy as a main component, an oxide layer on the outer layer side, and a layer positioned between these layers, and by causing an appropriate amount of Mg to be concentrated in the oxide layer formed on the outer layer.
  • Figure 1 is a view for describing the structure of the hot stamped body according to one embodiment of the present invention.
  • Figure 2 shows one example of an image of the cross section of the hot stamped body according to one embodiment of the present invention obtained by performing SEM observation.
  • the hot stamped body 1 according to one embodiment of the present invention includes a base metal 10 and a plated layer 20 formed on the surface of the base metal 10.
  • the base metal of the hot stamped body according to this embodiment is not particularly limited. However, when the components of the base metal fall within ranges described hereinafter, it is possible to obtain the formed body having favorable mechanical properties in addition to fatigue property, spot weldability, and corrosion resistance after coating.
  • C is an element which increases strength of a hot stamped body.
  • the C content is set to 0.05 to 0.4%.
  • the C content is preferably 0.10% or more, and is more preferably 0.13% or more. Further, the C content is preferably 0.35% or less.
  • Si silicon is an element which is inevitably contained, and has an action of deoxidizing steel.
  • Si in steel is diffused during heating of a hot stamp and hence, oxide is formed on the surface of a steel sheet, thus degrading phosphatability.
  • Si is also an element which raises the Ac 3 point of a steel sheet. When the Ac 3 point is raised, there is a possibility that a heating temperature at the time of performing hot stamping exceeds the evaporation temperature of Zn plating. Accordingly, the Si content is set to 0.5% or less.
  • the Si content is preferably 0.3% or less, and is more preferably 0.2% or less.
  • the lower limit value of the Si content there is no limitation on the lower limit value of the Si content in terms of the above-mentioned properties of a product.
  • Si is used for deoxidation and hence, there is a substantial lower limit value.
  • the lower limit value of the Si content varies according to the required level of deoxidation, the lower limit value of the Si content is usually 0.05%.
  • Mn Manganese
  • Mn is an element which increases hardenability, thus increasing strength of a steel material on which hot stamping is performed.
  • the Mn content is set to a value within a range from 0.5 to 2.5%.
  • the Mn content is preferably 0.6% or more, and is more preferably 0.7% or more.
  • the Mn content is preferably 2.4% or less, and is more preferably 2.3% or less.
  • P phosphorus
  • P is an impurity contained in steel. P segregates at crystal grain boundaries, thus decreasing toughness of the steel hence leading to degrading delayed fracture resistance. Accordingly, a content of P is set to 0.03% or less. It is preferable to reduce the P content as much as possible.
  • S sulfur
  • S is an impurity contained in steel. S forms sulfides, thus decreasing toughness of the steel hence leading to degrading delayed fracture resistance. Accordingly, a content of S is set to 0.01% or less. It is preferable to reduce the S content as much as possible.
  • Al is an element which is generally used for deoxidizing steel, and is inevitably contained.
  • the Al content is set to 0.1% or less.
  • the Al content is preferably 0.05% or less.
  • the Al content is preferably 0.01% or more.
  • the Al content means content of sol. Al (acid-soluble Al).
  • N nitrogen
  • B is contained in steel
  • N is bonded to B, thus reducing the amount of dissolved B and, eventually, decreasing hardenability. Accordingly, a content of N is set to 0.01% or less. It is preferable to reduce the N content as much as possible.
  • B (boron) has an effect of increasing hardenability of the steel, thus increasing strength of a steel material on which hot stamping is performed. Accordingly, B may be contained when necessary. However, when a content of B is excessively high, this effect is saturated. Accordingly, the B content is set to 0.005% or less. To obtain the above-mentioned advantageous effects, the B content is preferably 0.0001% or more.
  • Ti titanium
  • Ti titanium
  • the Ti content is set to 0.1% or less.
  • Ti makes a fine austenite grain size at the time of heating by a hot stamp by pinning effect of Ti, thus increasing toughness and the like of the steel material.
  • the Ti content is preferably 0.01% or more.
  • Cr chromium
  • Cr has an effect of increasing hardenability of the steel. Accordingly, Cr may be contained when necessary. However, when a content of Cr is excessively high, Cr carbide is formed. This Cr carbide is not easily dissolved at the time of heating the hot stamp and hence, austenitization is prevented from easily progressing, thus degrading hardenability. Accordingly, the Cr content is set to 0.5% or less. To obtain the above-mentioned advantageous effects, the Cr content is preferably 0.1% or more.
  • Mo mobdenum
  • Mo has an effect of increasing hardenability of the steel. Accordingly, Mo may be contained when necessary. However, when a content of Mo is excessively high, the above-mentioned effect is saturated. Accordingly, the Mo content is set to 0.5% or less. To obtain the above-mentioned advantageous effects, the Mo content is preferably 0.05% or more.
  • Nb niobium
  • Nb forms carbides, thus having an effect of refining grains at the time of performing hot stamping hence leading to an increase in toughness of the steel. Accordingly, Nb may be contained when necessary.
  • the Nb content is set to 0.1% or less. To obtain the above-mentioned advantageous effects, the Nb content is preferably 0.02% or more.
  • Ni nickel
  • Ni has an effect of increasing toughness of the steel. Further, Ni suppresses embrittlement attributable to the presence of molten Zn at the time of heating by the hot stamp. Accordingly, Ni may be contained when necessary. However, when a content of Ni is excessively high, these effects are saturated. Accordingly, the Ni content is set to 1.0% or less. To obtain the above-mentioned advantageous effects, the Ni content is preferably 0.1% or more.
  • the balance consists of Fe and impurities.
  • impurity means a component which, in industrially producing steel materials, may be mixed in ores or scrap forming raw materials, or a component which may be mixed due to a production environment or the like, the component not being intentionally added.
  • the plated layer 20 in this embodiment includes, in order from the base metal 10 side, an interface layer 21, an intermediate layer 22, and an oxide layer 23.
  • an average film thickness means an average value between the maximum film thickness and the minimum film thickness of a target layer (film).
  • the interface layer 21 is formed adjacently to the base metal 10, and has a microstructure which contains an Fe-Al alloy as a main component.
  • Fe-Al alloy is a collective term for ⁇ Fe, Fe 3 Al and FeAl. That is, the interface layer 21 has a microstructure which contains one or more kinds selected from ⁇ Fe, Fe 3 Al and FeAl.
  • the description "contains an Fe-Al alloy as a main component” means that the total area fraction of an Fe-Al alloy is 90% or more.
  • the total area fraction of an Fe-Al alloy is preferably 95% or more, and more preferably 99% or more.
  • a content of Al in the interface layer 21 is 30% or less in mass%, and the Al content gradually decreases as a distance from the base metal 10 reduces.
  • Forming the interface layer 21 adjacently to the base metal 10 can suppress LME. Further, there may be a case where Zn, Si or the like is dissolved in an Fe-Al alloy and hence, the interface layer 21 may contain Zn: 10% or less, or Si: 10% or less.
  • the average film thickness of the interface layer 21 is preferably 1.0 ⁇ m or more, and is more preferably 2.0 ⁇ m or more.
  • the lower limit of the average film thickness of the interface layer 21 is further preferably 5.0 ⁇ m, 6.0 ⁇ m, or 7.0 ⁇ m.
  • the interface layer 21 having the average film thickness of 15.0 ⁇ m may deteriorate properties, such as corrosion resistance, and such an interface layer 21 is not preferable. Accordingly, the average film thickness of the interface layer 21 is preferably 15.0 ⁇ m or less.
  • the upper limit of the average film thickness of the interface layer 21 is preferably 12.0 ⁇ m, 11.0 ⁇ m, or 10.0 ⁇ m.
  • the intermediate layer 22 has a microstructure which contains an Fe-Al-Zn phase as a main component.
  • the term "Fe-Al-Zn phase” is a collective term for Fe(Al, Zn) 2 , Fe 2 (Al, Zn) 5 , and Fe(Al, Zn) 3 . That is, the intermediate layer 22 has a microstructure which contains one or more kinds selected from Fe(Al, Zn) 2 , Fe 2 (Al, Zn) 5 and Fe(Al, Zn) 3 .
  • the description "contains an Fe-Al-Zn phase as a main component” means that the total area fraction of an Fe-Al-Zn phase is 50% or more.
  • the total area fraction of an Fe-Al-Zn phase is preferably 90% or more, is more preferably 95% or more, and is further preferably 99% or more.
  • the intermediate layer 22 further contains an Fe-Al-Si phase.
  • Fe-Al-Si phase is a collective term for Fe 3 (Al, Si) and Fe(Al, Si). That is, the intermediate layer 22 further contains one kind or two kinds selected from Fe 3 (Al, Si) and Fe(Al, Si).
  • the total area fraction of an Fe-Al-Zn phase and an Fe-Al-Si phase is preferably 90% or more, is more preferably 95% or more, and is further preferably 99% or more.
  • the intermediate layer 22 has an average composition containing, in mass%, Al: 30 to 50% and Zn: 15 to 30%.
  • the intermediate layer 22 By setting a content of Al in the intermediate layer 22 to 30% or more, LME can be suppressed, thus enhancing fatigue property. Further, setting the Al content to 50% or less allows excellent phosphatability to be ensured, thus enhancing corrosion resistance after coating.
  • the Al content is preferably 32% or more, and is more preferably 35% or more. Further, the Al content is preferably 48% or less, and is more preferably 45% or less.
  • the Zn content is preferably 17% or more, and is more preferably 20% or more. Further, the Zn content is preferably 28% or less, and is more preferably 25% or less.
  • the Mg content is preferably 1.0% or less.
  • the intermediate layer 22 may contain Si: 25% or less.
  • the limitation is not particularly imposed on the film thickness of the intermediate layer.
  • the intermediate layer has a small film thickness, corrosion resistance property of a formed body is degraded. Accordingly, it is desirable to set the film thickness of the intermediate layer to 5.0 ⁇ m or more.
  • the film thickness of the intermediate layer be 30.0 ⁇ m or less.
  • the oxide layer 23 is an oxide layer which contains Zn as a main component, and the oxide layer 23 contains Mg.
  • an oxide layer which contains Zn as a main component specifically means that 50 mass% or more of a metal component contained in oxide is Zn. Due to the presence of the oxide layer 23, phosphatability is enhanced. However, excessively large thickness of the oxide layer 23 adversely affects corrosion resistance, weldability and the like of a formed body and hence, the average film thickness of the oxide layer 23 is set to 3.0 ⁇ m or less. To enhance properties of the hot stamped body, such as spot weldability and corrosion resistance after coating, the average film thickness of the oxide layer 23 is preferably set to 2.0 ⁇ m or less.
  • Causing the oxide layer 23 to contain Mg allows corrosion resistance after coating to be enhanced.
  • a content of Mg in the oxide layer 23 is set to 0.05 g/m 2 or more.
  • Mg oxide has high electrical resistance and hence, when the Mg content increases, spot weldability is decreased. Accordingly, to ensure spot weldability, it is necessary to set the Mg content to 1.00 g/m 2 or less.
  • Mg may be contained in a plated layer before hot stamping is performed, or a film which contains Mg may be formed on a plated steel sheet in the form of coating or the like.
  • the oxide layer 23 may contain these elements. However, these oxides also have high electrical resistance in the same manner as Mg and hence, when these elements are excessively concentrated, weldability of a hot stamped body may be deteriorated. Accordingly, the total content of Mg, Cr, Ca, Sr and Ti in the oxide layer 23 is preferably 2.0 g/m 2 or less.
  • the total content of Al and Zn in the plated layer 20 is preferably 20 to 100 g/m 2 .
  • the total content of Al and Zn is preferably 20 to 100 g/m 2 .
  • the total content is preferably 30 g/m 2 or more, and the total content is preferably 90 g/m 2 or less.
  • the plated layer 20 further contain, in mass%, 0.1 to 15% of Si. Setting a content of Si in the plated layer to 0.1% or more allows adhesiveness between the base metal and the plated layer to be enhanced. On the other hand, setting the Si content to 15% or less allows properties of a hot stamped body, such as corrosion resistance and weldability, to be ensured.
  • the Si content is preferably 0.3% or more, and the Si content is preferably 10% or less.
  • the limitation is not particularly imposed on the film thickness of the entire plated layer 20. However, from a viewpoint of ensuring corrosion resistance, it is preferable to set the film thickness of the entire plated layer 20 to more than 6.0 ⁇ m. On the other hand, from a viewpoint of economic efficiency, it is preferable to set the film thickness of the entire plated layer 20 to 48.0 ⁇ m or less.
  • the microstructures, the average compositions and the thicknesses of the interface layer, the intermediate layer, and the oxide layer, and the chemical composition of the plated layer are obtained by the following method.
  • a formed body is cut perpendicular to the surface of the formed body, and the cross section is polished. Then, concentrations of respective elements in the region of the interface layer and in the region of the intermediate layer on the cross section are analyzed with an Electron Probe Micro Analyzer (EPMA).
  • EPMA Electron Probe Micro Analyzer
  • mapping analysis is performed in a region which extends upward and downward in the film thickness direction of each layer by 25% or more from the film thickness center of the layer, and which extends in the width direction by 20 ⁇ m or more, and the average composition of the region is used. With such analysis, the Al content and the Zn content in the interface layer, and the contents of Al, Zn and Mg in the intermediate layer are measured.
  • an average Si content in the entire plated layer is obtained by the following method. First, line analysis is performed by an EPMA at 0.2 ⁇ m pitch from the base metal side toward the surface side of the plated layer. Then, the average value of the measurement result in the plated layer is obtained, and the obtained value is set as the average composition of the entire plated layer.
  • a portion at which concentration of Fe is lower than average composition of base metal is assumed as one end portion of the plated layer
  • a portion at which concentration of Zn of metal components contained in the oxide layer becomes less than 50 mass% is assumed as the other end portion of the plated layer
  • the region between one end portion and the other end portion of the plated layer is assumed as the plated layer.
  • line analysis is performed at five or more portions, and the average value of these line analyses is adopted.
  • the total content of Al and Zn contained in the plated layer can be measured such that a hot stamped body is dissolved with hydrochloric acid, and the dissolved solution is subjected to inductively coupled plasma emission spectrometry (ICP spectrometry). With the use of this method, the amount of Al and the amount of Zn can be obtained individually.
  • ICP spectrometry inductively coupled plasma emission spectrometry
  • inhibitor which suppresses dissolution of Fe in the base metal is generally added to a hydrochloric acid.
  • the plated layer of the hot stamped body contains Fe and hence, the plated layer of the hot stamped body is not sufficiently dissolved with the above-mentioned method.
  • contents of Mg, Cr, Ca, Sr and Ti contained in the oxide layer are measured such that the hot stamped body is dissolved with an ammonium dichromate solution, and the dissolved solution is subjected to ICP spectrometry. With the use of the above-mentioned solution, only the oxide layer can be dissolved. With the use of this method, the content of each of Mg, Cr, Ca, Sr or Ti can be obtained individually.
  • the microstructure of the interface layer and the microstructure of the intermediate layer can be obtained by performing crystal structure analysis using a TEM. Further, the thicknesses of the interface layer, the intermediate layer, and the oxide layer can be obtained such that the above-mentioned cross section is photographed by an SEM, and this microscope photograph is subjected to image analysis.
  • the configuration of the plated layer of the formed body according to this embodiment is not substantially uniform along the direction parallel to the surface of the formed body.
  • the thicknesses of the interface layer, the intermediate layer and the oxide layer vary in many cases between a worked region and an unworked region. Accordingly, the above-mentioned analysis is required to be performed on an unworked region of the formed body.
  • a formed body where the state of an unworked region of the plated layer falls within the above-mentioned range is assumed as the formed body according to this embodiment.
  • the method for producing a hot stamped body of this embodiment includes a step of producing a hot stamping plated steel material and a step of performing hot stamping on the hot stamping plated steel material. Further, the step of producing a hot stamping plated steel material includes a step of producing a base metal of the hot stamping plated steel material, and a step of forming an Al-Zn plated layer on the base metal of the hot stamping plated steel material. Further, a rust preventive oil film forming step and a blanking step may be performed before the step of performing hot stamping when necessary.
  • each step is described in detail.
  • a base metal of a hot stamping plated steel material is produced.
  • molten steel is produced which has a chemical composition equal to the chemical composition of the base metal of the hot stamped body according to this embodiment exemplified above. Then, using this molten steel, a slab is produced by a casting process, or an ingot is produced by an ingot-making process.
  • the slab or the ingot is subjected to hot rolling, thus obtaining a base metal (hot-rolled sheet) of the hot stamping plated steel material.
  • a base metal hot-rolled sheet
  • pickling treatment is performed on the above-mentioned hot-rolled sheet, and cold rolling is performed on the hot-rolled sheet on which the pickling treatment is performed, thus obtaining a cold rolled sheet, and this cold rolled sheet is used as the base metal of the hot stamping plated steel material.
  • an Al-Zn-Mg plated layer is formed on the base metal of the above-mentioned hot stamping plated steel material, thus producing a hot stamping plated steel material.
  • hot dip plating treatment may be adopted.
  • any other treatment may be adopted such as spraying plating treatment or vapor deposition plating treatment.
  • An example of forming the Al-Zn-Mg plated layer by hot dip plating treatment is as follows. That is, the base metal is immersed into a hot dipping bath consisting of Al, Zn, Mg and impurities to cause a plated layer to adhere to the surface of the base metal. Next, the base metal to which the plated layer is caused to adhere is pulled up from the plating bath.
  • the total content of Al and Zn in the plated layer of the hot stamped body be 20 to 100 g/m 2 .
  • the total content of Al and Zn in the plated layer can be adjusted.
  • the intermediate layer of the plated layer of the hot stamped body contains, in mass%, 30 to 50% of Al and 15 to 30% of Zn. These contents of Al and Zn can be also controlled mainly in this step (plating treatment step). To be more specific, in this step, when Al content in the plating bath is set to 40 to 60%, and Zn content is set to 40 to 60%, it is possible to allow contents of Al and Zn in the hot stamped body to fall within the above-mentioned ranges.
  • the Mg content in the plating bath is preferably set to 0.5 to 2.0%, and is more preferably set to 1.0 to 1.5%.
  • the situation may vary depending on the adhesion amount on the plated steel sheet, when a concentration of Mg in the plating bath is high, the amount of Mg contained in plating increases and hence, the amount of Mg contained in oxide in the outer layer of the formed product increases, whereby there is a possibility that weldability is decreased. Further, when the amount of Mg which remains in the intermediate layer exceeds 1.0%, there is also a possibility that LME resistance is decreased. On the other hand, when a concentration of Mg in the plating bath is low, the amount of Mg contained in oxide in the outer layer of the formed product decreases so that there is a possibility that sufficient corrosion resistance after coating cannot be obtained.
  • Mg may be applied by coating such that treatment solution which contains Mg oxide is applied by coating on the plated layer by a bar coater, and the treatment solution is baked and dried by an oven.
  • Mg it is preferable to set the content of Mg to be applied by coating to 0.050 to 1.00 g/m 2 .
  • hot stamping is performed on the above-mentioned hot stamping plated steel material.
  • Normal hot stamping is performed such that a steel material is heated to a temperature within a hot stamping temperature range (hot working temperature range) and, then, the steel material is subjected to hot working and, further, the steel material is cooled.
  • a hot stamping temperature range hot working temperature range
  • the plated layer is sufficiently alloyed. Accordingly, in the normal hot stamping technique, an importance is not placed on control of heating conditions of the steel material.
  • the hot stamping plated steel material is heated to a hot stamping temperature (quenching heating temperature), and is subjected to hot working and cooling.
  • a hot stamping temperature quenching heating temperature
  • alloying heat treatment where the hot stamping plated steel material is held for a fixed time within a predetermined temperature range, is performed and hence, a plated layer having the above-mentioned configuration can be formed.
  • the hot stamping plated steel material is charged into a heating furnace (gas furnace, electric furnace, infrared furnace or the like).
  • the hot stamping plated steel material is heated to a temperature range from 500 to 750°C in the heating furnace, and alloying heat treatment is performed, where the plated steel material is held for 10 to 450s within this temperature range.
  • alloying heat treatment causes Fe in the base metal to diffuse in the plated layer so that alloying process progresses. Due to such alloying process, the plated layer is changed to a layer which includes an interface layer, an intermediate layer, and an oxide layer in order from the base metal side.
  • An alloying heating temperature is not necessarily set to a fixed temperature, and may vary within a range from 500 to 750°C.
  • an alloying heating time is less than 10s, alloying process of the plated layer is not completed and hence, a plated layer including the above-mentioned interface layer, intermediate layer, and oxidized layer cannot be obtained.
  • an alloying heating time exceeds 450s, the amount of growth of oxide increases excessively, and such a long time leads to declining of productivity.
  • the hot stamping plated steel material is heated to a temperature range from the Ac 3 point to 950°C and, then, is subjected to hot working.
  • a time during which the temperature of the hot stamping plated steel material falls within a temperature range (oxidation temperature range) from the Ac 3 point to 950°C is limited to 60s or less.
  • the temperature of the hot stamping plated steel material falls within the oxidation temperature range, the oxidized layer forming the outer layer of the plated layer grows.
  • the time during which the temperature of the hot stamping plated steel material falls within the oxidation temperature range exceeds 60s, there is a possibility that the oxide film excessively grows, thus degrading weldability of the formed body.
  • a speed at which oxide coating is formed is extremely high and hence, the lower limit value of the time during which the temperature of the hot stamping plated steel material falls within the oxidation temperature range is more than 0s.
  • a non-oxidizing atmosphere such as 100% nitrogen atmosphere
  • an oxidized layer is not formed. Accordingly, the hot stamping plated steel material is heated in an oxidizing atmosphere, such as an air atmosphere.
  • the time during which the temperature of the hot stamping plated steel material falls within the oxidation temperature range is 60s or less, conditions, such as a heating speed and a maximum heating temperature, are not particularly defined, and various conditions under which hot stamping can be performed may be selected.
  • the hot stamping plated steel material which is taken out from the heating furnace is subjected to press forming using press tooling.
  • the steel material is quenched by the press tooling simultaneously with this press forming.
  • a cooling medium water, for example
  • the hot stamping plated steel material may be heated by resistance heating. Also in this case, the steel material is heated for a predetermined time by resistance heating, and the steel material is subjected to press forming using press tooling.
  • the rust preventive oil film forming step is a step which is performed after the plating treatment step and before the hot stamping step, and where rust preventive oil is applied by coating to the surface of a hot stamping plated steel material to form a rust preventive oil film.
  • the rust preventive oil film forming step may be arbitrarily included in the production method. In the case where a long time is required before hot stamping is performed after a hot stamping plated steel material is produced, there is a possibility that the surface of the hot stamping plated steel material is oxidized. However, when a rust preventive oil film is formed on a hot stamping plated steel material by the rust preventive oil film forming step, the surface of the hot stamping plated steel material is not easily oxidized. Accordingly, performing the rust preventive oil film forming step can suppress the formation of scale on the formed body. Any known technique may be used as a method for forming a rust preventive oil film.
  • This step is a step which is performed after the rust preventive oil film forming step and before the hot stamping step, and where shearing and/or blanking is performed on the hot stamping plated steel material to form the steel material into a particular shape.
  • the sheared surface of the steel material on which blanking is performed is easily oxidized.
  • rust preventive oil expands also to the above-mentioned sheared surface to some extent. With such expansion of the rust preventive oil, it is possible to suppress oxidization of the steel material on which blanking is performed.
  • a base metal was prepared. That is, a slab was produced by continuous casting process using molten steel having the chemical composition shown in Table 1. Next, the slab was subjected to hot rolling so as to produce a hot rolled steel sheet, and the hot rolled steel sheet was further subjected to pickling. Thereafter, the hot rolled steel sheet was subjected to cold rolling, thus producing a cold rolled steel sheet. This cold rolled steel sheet was used as a base metal (sheet thickness: 1.4 mm) for producing a hot stamped body.
  • hot stamping plated steel materials (materials No. 1 to 28) were prepared in accordance with production conditions shown in Table 2 using the base metals produced as described above. Further, the time during which each base metal is immersed in the plating bath at the time of performing plating treatment was set to 5s, and a cooling speed at which the plated steel material is cooled to 450°C after being pulled up from the plating bath was set to 10°C/s.
  • Table 2 Material No. Plating treatment conditions Coating conditions Composition of plating bath (mass%) Total content of Al, Zn in the plated layer (g/m 2 ) Mg coating Mg content (g/m 2 ) Al Zn Si Mg Cr+Ca+Sr+Ti 1 55.0 44.5 0 0.5 0 60 absent 0 2 55.0 44.5 0 0.5 0 80 absent 0 3 55.0 44.0 0 1.0 0 60 absent 0 4 55.0 44.0 0 1.0 0 75 absent 0 5 55.0 42.4 1.6 1.0 0 60 absent 0 6 45.0 39.0 15.0 1.0 0 60 absent 0 7 55.0 44.0 0 2.0 0 40 absent 0 8 55.0 44.0 0 2.0 0 50 absent 0 9 60.0 39.0 0 1.0 0 60 absent 0 10 50.0 49.0 0 1.0 0 60 absent 0 11 55.0 45.0 0 0 0 60 present 0.05 12 55.0 45.0 0 0 0 60 present 0.25 13 5
  • the above-mentioned hot stamping plated steel materials were heated under conditions (heating No. 1 to 9) shown in Table 3 and, immediately after the heating, were subjected to V-bending simulating a hot stamp using a hand press machine so as to produce hot stamped bodies of respective test examples.
  • the shape of press tooling is set such that an outer side portion in the bending radius direction to which V-bending is applied is extended by approximately 15% at the time when bending is finished. Further, quenching was performed such that even a portion where a cooling speed at the time of performing working is slow has a cooling speed of 50°C/s or more until the portion is cooled to an approximate point (410°C) at which martensitic transformation starts.
  • test piece for observing the structure of the plated layer a test piece for ICP spectrometry, a test piece for spot weldability evaluation test, and a test piece for corrosion resistance after coating evaluation test were cut out. Further, a test piece for LME resistance evaluation test was cut out from a portion to which bending is applied.
  • the cross section perpendicular to the surface of the formed body was polished and, thereafter, the contents of Al and Zn in the interface layer and the contents of Al, Zn and Mg in the intermediate layer were measured using an EPMA.
  • EPMA analysis mapping analysis was performed in a region which extends upward and downward in the film thickness direction of each layer by 25% or more from the film thickness center of the layer, and which extends in the width direction by 20 ⁇ m or more, and the average composition in the region was calculated.
  • line analysis was performed by an EPMA at 0.2 ⁇ m pitch from the base metal side toward the surface side of the plated layer, and the average value of the measurement result of the plated layer was calculated. Line analysis was performed at five portions, and the average value of the line analyses was used as the average composition of the entire plated layer.
  • each layer was photographed by an SEM, and the microscope photograph was subjected to image analysis so as to measure the thickness of each layer.
  • the microstructure of each layer was determined by performing crystal structure analysis with a TEM on a thin piece obtained from the same place of each test piece.
  • a plated layer was dissolved with hydrochloric acid at a temperature of 50°C and, thereafter, the dissolved solution was subjected to ICP spectrometry so as to obtain the total content of Al and Zn contained in the plated layer. Further, in the same manner, only the oxide layer of the test piece for ICP spectrometry was dissolved with an ammonium dichromate solution, and the dissolved solution was subjected to ICP spectrometry so as to obtain the contents of Mg, Cr, Ca, Sr and Ti.
  • LME resistance evaluation test spot weldability evaluation test, and corrosion resistance after coating evaluation test were performed as described below.
  • EDS energy dispersive X-ray spectroscopy
  • Spot welding was performed on the test piece for weldability evaluation test of each test example using a DC power source at an applied pressure of 350 kgf. Tests were performed at various welding currents. A value of welding current at which the nugget diameter of a welding portion exceeds 4.7 mm was set to the lower limit value. A value of welding current was suitably increased, and a value of welding current at which dust is generated during welding was set to the upper limit value. Values between the upper limit value and the lower limit value are set as the proper current range, and the difference between the upper limit value and the lower limit value was used as an index of spot weldability. In the evaluation of spot weldability, a test piece with this value of 1.5 A or more is evaluated as excellent (1).
  • test piece with this value of 1.0 A or more and less than 1.5 A is evaluated as good (2).
  • a test piece with this value of 0.5 A or more and less than 1.0 A is evaluated as fair (3).
  • a test piece with this value of less than 0.5 A is evaluated as fail (4).
  • cationic electrodeposition paint made by NIPPONPAINT Co., Ltd. was applied to each formed body by electrodeposition coating by slope energization at a voltage of 160 V and, further, was subjected to baking coating for 20 minutes at a baking temperature of 170°C. Control of the film thickness of the paint after the electrodeposition coating was performed under conditions that electrodeposition coating on a steel material before hot stamping forming is performed has a thickness of 15 ⁇ m.
  • a cross-cut was made on the formed body on which electrodeposition coating was performed such that the cross-cut reaches the steel material which is a base metal, and a composite corrosion test (JASO M610 cycle) was performed. Corrosion resistance was evaluated based on the width of coating blister.
  • a composite corrosion test of 180 cycles is performed on a formed body, the formed body with a width of coating blister of 2.0 mm or less is evaluated as excellent (1), the formed body with a width of coating blister of more than 2.0 mm and 3.0 mm or less is evaluated as good (2), the formed body with a width of coating blister of more than 3.0 mm and 4.0 mm or less is evaluated as fair (3), and the formed body with a width of coating blister of more than 4.0 mm is evaluated as fail (4).
  • the hot stamped bodies according to the present invention are excellent in all of fatigue property (LME resistance), spot weldability, and corrosion resistance after coating with a good balance.
  • the hot stamped body according to the present invention can be favorably used for a structural member or the like used in an automobile or the like.

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US11965250B2 (en) 2019-08-29 2024-04-23 Nippon Steel Corporation Hot stamped steel
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CN116463572A (zh) * 2022-01-11 2023-07-21 宝山钢铁股份有限公司 一种具有Al-Zn-Mg-Si镀层的热冲压钢板及其热冲压方法
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WO2018179395A1 (fr) 2018-10-04
BR112019019587A2 (pt) 2020-04-14
EP3604602A4 (fr) 2020-08-05
MX2019011731A (es) 2019-11-21
KR20190133754A (ko) 2019-12-03
RU2019134830A3 (fr) 2021-04-30
JPWO2018179395A1 (ja) 2019-12-12
US20200032360A1 (en) 2020-01-30
RU2019134830A (ru) 2021-04-30

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