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EP4578987A1 - Tôle d'acier plaquée pour formage à la presse à chaud ayant une excellente résistance aux chocs, pièce formée par pressage à chaud et ses procédés de fabrication - Google Patents

Tôle d'acier plaquée pour formage à la presse à chaud ayant une excellente résistance aux chocs, pièce formée par pressage à chaud et ses procédés de fabrication Download PDF

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Publication number
EP4578987A1
EP4578987A1 EP23857642.5A EP23857642A EP4578987A1 EP 4578987 A1 EP4578987 A1 EP 4578987A1 EP 23857642 A EP23857642 A EP 23857642A EP 4578987 A1 EP4578987 A1 EP 4578987A1
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European Patent Office
Prior art keywords
steel sheet
less
content
present disclosure
carbon
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23857642.5A
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German (de)
English (en)
Other versions
EP4578987A4 (fr
Inventor
Sang-Heon Kim
Jin-Keun Oh
Seong-Woo Kim
Sea-Woong LEE
Sang-Cheol Lee
Seul-Gi SO
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Posco Holdings Inc
Original Assignee
Posco Co Ltd
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Filing date
Publication date
Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Publication of EP4578987A1 publication Critical patent/EP4578987A1/fr
Publication of EP4578987A4 publication Critical patent/EP4578987A4/fr
Pending legal-status Critical Current

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    • 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
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
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    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
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    • 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
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
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    • C21—METALLURGY OF IRON
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
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    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • 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
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    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • 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
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • 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
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • 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
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    • 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
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    • 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
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    • C23C2/36—Elongated material
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    • 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
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
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    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present disclosure relates to a plated steel sheet for hot press forming, a hot press formed part, and manufacturing methods thereof, and in particular, to a plated steel sheet for hot press forming having excellent impact resistance, a hot press formed part, and manufacturing methods thereof.
  • Patent Document 1 was suggested as a representative technology regarding the hot press forming technology.
  • an Al-Si plated steel sheet is heated to 850°C or higher, and then hot press forming and quenching by a press are performed to form a structure of a part with martensite, such that ultra-high strength with high tensile strength may be secured.
  • a complex shape may be easily formed because the formation is performed at high temperature, and a weight reduction effect may be expected through an increase in strength by quenching in a mold.
  • Patent Document 1 U.S. Patent No. 6,296,805 (published on October 2, 2001 )
  • a point at which a content of carbon (C) is 50% of the nominal carbon content (C 0 ) may exist at a depth of more than 1.5 ⁇ m and less than 6 ⁇ m from an interface between the base steel sheet and the plating layer in the thickness direction.
  • a point at which a content of carbon (C) is 80% of the nominal carbon content (C 0 ) may exist at a depth of more than 6 ⁇ m and less than 15 ⁇ m from an interface between the base steel sheet and the plating layer in the thickness direction.
  • the plated steel sheet may have an R value defined in the following Relational Expression 1 of 1.2 or more, and
  • a region from an interface between the base steel sheet and the plating layer to a depth of 10 ⁇ m in the thickness direction may have a microstructure containing ferrite as a main phase and 1 area% or more of pearlite.
  • the base steel sheet may contain 0.06 to 0.5% of carbon (C), 0.01 to 0.1% of antimony (Sb), 0.001 to 2% of silicon (Si), 0.1 to 4% of manganese (Mn), 1% or less of molybdenum (Mo), 0.05% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.001 to 1% of aluminum (Al), 1% or less of chromium (Cr), 0.02% or less of nitrogen (N), 0.1% or less of titanium (Ti), 0.01% or less of boron (B), and a balance of iron (Fe) and impurities.
  • the plating layer may be formed of aluminum or an aluminum alloy.
  • a part includes a base steel containing, by wt%, 0.06 to 0.5% of carbon (C) and 0.01 to 0.1% of antimony and a plating layer formed on a surface of the base steel,
  • the content of carbon (C) at the depth at which the content of antimony (Sb) shows the maximum value (Sb max ) may be 15 to 80% of the nominal carbon content (C 0 ) of the base steel.
  • the part may have an R value defined in the following Relational Expression 1 of 1.5 or more, and
  • a softening rate ( ⁇ ) in a region from an interface between the base steel and the plating layer to a depth of 45 to 100 ⁇ m in the thickness direction may be 2 to 7%.
  • a region from an interface between the base steel and the plating layer to a depth of 50 ⁇ m in the thickness direction may have a microstructure containing less than 5 area% of ferrite.
  • a region from an interface between the base steel and the plating layer to a depth of 50 ⁇ m in the thickness direction may have a microstructure containing martensite as a main phase, less than 5 area% of ferrite, and a balance of upper and lower bainite.
  • the base steel may contain 0.06 to 0.5% of carbon (C), 0.01 to 0.1% of antimony (Sb), 0.001 to 2% of silicon (Si), 0.1 to 4% of manganese (Mn), 1% or less of molybdenum (Mo), 0.05% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.001 to 1% of aluminum (Al), 1% or less of chromium (Cr), 0.02% or less of nitrogen (N), 0.1% or less of titanium (Ti), 0.01% or less of boron (B), and a balance of iron (Fe) and impurities.
  • the Sb average content line 30 of the base steel sheet 3 excluding the Sb-enriched layer may mean an extended line obtained by horizontally extending the Sb average content in a section from a point C spaced apart from the point (200: Sb max ) at which the content of Sb in the Sb-enriched layer 2 is the maximum value to the base steel sheet 3 by 15 ⁇ m to a point D spaced apart from Sb max by 20 ⁇ m.
  • the Sb-enriched layer may be formed directly under the interface between the base steel sheet and the plating layer.
  • the interface between the base steel sheet and the plating layer may be defined as a point at which a content of Al is 15%.
  • a thickness of the enriched layer may be 1 to 30 ⁇ m.
  • a content of antimony (Sb) when analyzed in the thickness direction of the base steel sheet using a glow discharge spectrometer (GDS), a content of carbon (C) at a depth at which a content of antimony (Sb) in the antimony (Sb)-enriched layer exhibits a maximum value (Sb max ) may be 10 to 70% of a nominal carbon content (C 0 ) of the base steel sheet.
  • GDS glow discharge spectrometer
  • the nominal carbon content (C 0 ) may mean a carbon average content in a region corresponding to 1/4 to 3/4 of the thickness based on a cross section of the base steel sheet, and specifically, may be an average carbon content obtained by analyzing a carbon profile at a distance of 50 ⁇ m or more from an arbitrary point in the region corresponding to 1/4 to 3/4 of the thickness of the base steel sheet using a glow discharge spectrometer (GDS).
  • GDS glow discharge spectrometer
  • FIG. 2 schematically illustrates content profiles of Sb and C in the thickness direction from the interface in the plated steel sheet according to an exemplary embodiment in the present disclosure.
  • the X-axis may represent a depth ( ⁇ m) from the interface between the base steel sheet and the plating layer
  • the Y-axis may represent a content (wt%) of element.
  • 70% of the nominal carbon content (C 0 ) is 0.154%.
  • the nominal carbon content (C 0 ) is 0.22%, which may be obtained by analyzing a certain thickness (depth) using a glow discharge spectrometer (GDS) in the region corresponding to 1/4 to 3/4 of the thickness of the base steel sheet as described above. In this case, it can be confirmed that the content of carbon at the depth at which the content of Sb shows the maximum value (Sb max ) exhibits a content of carbon of 70% or less of the nominal carbon content (C 0 ).
  • GDS glow discharge spectrometer
  • a ratio of the content of carbon to the nominal carbon content (C 0 ) is controlled to 10 to 70%, and in this case, the content of carbon affects a hardness softening rate of the surface layer and bendability of the part.
  • the hardness of the surface layer part may increase, which may cause deterioration of the bendability.
  • the content of carbon is less than 10% of the nominal carbon content (C 0 )
  • the hardness decreases excessively, and thus, the fatigue resistance may be deteriorated.
  • the ratio of the content of carbon to the nominal carbon content (C 0 ) may be 10.0 to 70.0%.
  • a decarburization rate ( ⁇ ) of carbon (C) in a region from the interface between the base steel sheet and the plating layer to a depth of 30 ⁇ m in the thickness direction may be 14 to 35%.
  • FIG. 3 schematically illustrates a decarburization rate ( ⁇ ) profile in the thickness direction from the interface in the plated steel sheet according to an exemplary embodiment in the present disclosure.
  • the decarburization rate ( ⁇ ) may be obtained from the results of measuring carbon in the plated steel sheet using a glow discharge spectrometer (GDS).
  • GDS glow discharge spectrometer
  • the Y-axis represents a ratio of the content of carbon at the corresponding position to the nominal carbon content (C 0 )
  • the X-axis represents a distance ( ⁇ m) in the thickness (depth) direction from the interface between the base steel sheet and the plating layer.
  • a carbon profile curve indicating a ratio of a content of carbon at the corresponding depth to the nominal carbon content (C 0 ) is drawn, and a ratio (%) of an area above the carbon profile curve in the square to the entire area of the square may be defined as the decarburization rate ( ⁇ ).
  • the decarburization rate ( ⁇ ) of the present disclosure means a ratio (%) of the area above the carbon profile curve to the entire area of the square in the square in which a horizontal axis represents the distance ( ⁇ m) in the thickness (depth) direction from the interface between the base steel sheet and the plating layer, and a vertical axis represents the ratio (%) of the content of carbon at the corresponding position to the nominal carbon content (C 0 ).
  • the decarburization rate ( ⁇ ) of carbon (C) in the region from the interface to the depth of 30 ⁇ m in the thickness direction is less than 14%, a carbon enrichment degree in the base steel sheet may excessively increase the hardness in the part after hot press forming, and thus, the effect of improving bendability may be significantly reduced.
  • the decarburization rate exceeds 35% the martensite hardness in the part may decrease significantly due to a decrease in the amount of carbon in the surface layer of the base steel sheet, which may cause deterioration of the fatigue resistance of the part.
  • a decarburization rate ( ⁇ ) of carbon (C) in a region from the interface between the base steel sheet and the plating layer to a depth of 30.0 ⁇ m in the thickness direction may be 14.0 to 35.0%.
  • a point at which a content of carbon (C) is 50% of the nominal carbon content (C 0 ) may exist at a depth of more than 1.5 ⁇ m and less than 6 ⁇ m from the interface between the base steel sheet and the plating layer in the thickness direction.
  • Controlling the ratio of the content of carbon (C) to the nominal carbon content (C 0 ) at the depth of more than 1.5 ⁇ m and less than 6 ⁇ m from the interface in the thickness direction is to secure both the fatigue resistance and the impact resistance.
  • a point at which the content of carbon (C) is 50% of the nominal carbon content (C 0 ) exists at the depth in the corresponding range it is advantageous for securing both the impact resistance and the fatigue resistance, but when the point of 50% exists at a depth of 6 ⁇ m or more, the fatigue resistance may be deteriorated due to excessive decarburization. Meanwhile, when the point of 50% exists at a depth of 1.5 ⁇ m or less, it may be difficult to secure the desired bendability due to insufficient decarburization.
  • a point at which a content of carbon (C) is 50.0% of the nominal carbon content (C 0 ) may exist at a depth of more than 1.50 ⁇ m and less than 6.0 ⁇ m from the interface between the base steel sheet and the plating layer in the thickness direction.
  • a point at which a content of carbon (C) is 80% of the nominal carbon content (C 0 ) may exist at a depth of more than 6 ⁇ m and less than 15 ⁇ m from the interface between the base steel sheet and the plating layer in the thickness direction.
  • FIG. 4 schematically illustrates a profile of the Sb-enriched layer of the plated steel sheet according to an exemplary embodiment in the present disclosure.
  • an area corresponding to the B value of Relational Expression 2 is indicated by the colored portion, and the area may indicate an Sb enriched degree according to ⁇ t, which represents the distance between the point where Sb coat is measured and the point where Sb max is measured.
  • a region from the interface between the base steel sheet and the plating layer to a depth of 10.0 ⁇ m in the thickness direction may contain ferrite as a main phase and 1.0 area% or more of pearlite.
  • the base steel sheet according to an exemplary embodiment in the present disclosure may contain, by wt%, 0.06 to 0.5% of carbon (C) and 0.01 to 0.1% of antimony.
  • the base steel sheet according to an exemplary embodiment in the present disclosure may contain, by wt%, 0.060 to 0.50% of carbon (C) and 0.010 to 0.10% of antimony.
  • % indicating a content of each element is based on weight.
  • Carbon (C) is an element that increases strength of a hot press formed part and improves hardenability, and should be appropriately added as an essential element for controlling the strength.
  • a content of carbon (C) is less than 0.06%, since the hardenability is low, when a cooling rate is reduced, sufficient martensite is not secured, and ferrite is formed, which may make it difficult to secure the desired strength.
  • the content of carbon (C) may be 0.1% or more.
  • an upper limit of the content of carbon (C) may be 0.45%.
  • carbon (C) may be contained in an amount of 0.060 to 0.50%.
  • carbon (C) may be 0.10% or more.
  • the upper limit of carbon (C) may be 0.450%.
  • Antimony (Sb) is enriched inside the base steel sheet, and may thus play a role in preventing an excessive decrease in hardness in the part by controlling the amount of carbon that escapes when internal oxidation annealing is applied.
  • a content of antimony (Sb) is less than 0.01%, since a sufficient enriched layer is not formed at the interface between the plating layer and the base steel sheet, excessive decarburization occurs, which may cause an excessive decrease in hardness of the surface layer, resulting in deterioration of the fatigue resistance.
  • a lower limit of antimony (Sb) may be 0.02%.
  • an upper limit of the content of antimony (Sb) may be 0.08%.
  • antimony (Sb) may be contained in an amount of 0.010 to 0.10%.
  • antimony (Sb) may be 0.020% or more.
  • the upper limit of antimony (Sb) may be 0.080%.
  • the types and contents thereof are not limited as long as they are elements that may be generally added.
  • the elements that may be added to the base steel sheet include silicon (Si), manganese (Mn), molybdenum (Mo), phosphorus (P), sulfur (S), aluminum (Al), chromium (Cr), nitrogen (N), titanium (Ti), boron (B), copper (Cu), nickel (Ni), vanadium (V), calcium (Ca), niobium (Nb), tin (Sn), tungsten (W), magnesium (Mg), cobalt (Co), arsenic (As), zirconium (Zr), bismuth (Bi), and a rare earth element (REM), and the base steel sheet may further contain one or more of these elements.
  • the base steel sheet may contain, by wt%, 0.001 to 2% of silicon (Si), 0.1 to 4% of manganese (Mn), 1% or less of molybdenum (Mo), 0.05% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.001 to 1% of aluminum (Al), 1.00% or less of chromium (Cr), 0.02% or less of nitrogen (N), 0.1% or less of titanium (Ti), 0.01% or less of boron (B), and a balance of iron (Fe) and impurities.
  • Silicon (Si) may be added as a deoxidizer in steelmaking.
  • silicon (Si) is a solid solution strengthening element and a carbide formation suppressing element, and is added as an element that is effective in internal structure uniformity, contributes to increasing the strength of the hot press formed part, and is effective in material uniformity.
  • a content of silicon (Si) is less than 0.001%, the above effects are not expected, and when the content of silicon (Si) exceeds 2%, plating properties may be significantly deteriorated due to excessive Si oxides formed on the surface of the steel sheet during annealing.
  • a lower limit of the content of silicon (Si) may be 0.005%, and may be 0.01% in some cases.
  • an upper limit of the content of silicon (Si) may be 0.7%, and may be 0.65% in some cases.
  • silicon (Si) may be contained in an amount of 0.001 to 2.0%.
  • silicon (Si) may be 0.0050% or more.
  • the upper limit of silicon (Si) may be 0.70%.
  • silicon (Si) may be 0.010% or more.
  • the upper limit of carbon (C) may be 0.650%.
  • Manganese (Mn) needs to be added not only to secure the desired strength due to a solid solution strengthening effect thereof, but also to suppress the formation of ferrite during hot press forming through improvement of hardenability.
  • a content of manganese (Mn) is less than 0.1%, it is difficult to obtain a sufficient hardenability effect and other expensive alloying elements are excessively required to compensate for the insufficient hardenability, and thus, manufacturing costs may increase significantly.
  • manganese (Mn) may be contained in an amount of 0.5% or more, and as another exemplary embodiment, manganese (Mn) may be contained in an amount of 0.8% or more.
  • an upper limit of the content of manganese (Mn) may be 3.5%.
  • chromium (Cr) may be contained in an amount of 0.01 to 1.0%.
  • chromium (Cr) may be contained in an amount of 0.05 to 1.0%.
  • chromium (Cr) may be contained in an amount of 0.05 to 0.8%.
  • Nitrogen (N) may be contained in the steel as an impurity.
  • N When a content of nitrogen (N) exceeds 0.02%, N forms AlN with added Al, which may cause slab cracks. Meanwhile, a large amount of manufacturing costs may be required to control the content of nitrogen (N) to an extremely small amount, and thus, according to an exemplary embodiment in the present disclosure, a lower limit of nitrogen (N) may be limited to 0.001%.
  • nitrogen (N) may be contained in an amount of 0.020% or less.
  • nitrogen (N) may be contained in an amount of 0.0010 to 0.020%.
  • titanium (Ti) may be contained in an amount of 0.10% or less.
  • titanium (Ti) may be contained in an amount of 0.090% or less.
  • Boron (B) is an element that may effectively improve hardenability, and is an element that is segregated at a prior austenite grain boundary and may thus suppress brittleness of the hot press formed part due to grain boundary segregation of P or S, which is an impurity. Meanwhile, when a content of boron (B) exceeds 0.01%, brittleness may be caused in hot rolling due to the formation of a Fe 23 CB 6 composite compound. In an exemplary embodiment in the present disclosure, an upper limit of the content of boron (B) may be limited to 0.008%.
  • boron (B) may be contained in an amount of 0.010% or less.
  • the base steel sheet may further contain one or more of 1% or less of copper (Cu), 1% or less of nickel (Ni), 1.0% or less of vanadium (V), 0.01% or less of calcium (Ca), 0.1% or less of niobium (Nb), 1% or less of tin (Sn), 1% or less of tungsten (W), 0.1% or less of magnesium (Mg), 1% or less of cobalt (Co), 1% or less of arsenic (As), 1% or less of zirconium (Zr), 1% or less of bismuth (Bi), and 0.3% or less of a rare earth element (REM).
  • Cu copper
  • Ni nickel
  • V vanadium
  • V vanadium
  • Ca calcium
  • Nb niobium
  • Sn tin
  • W tungsten
  • Mg magnesium
  • Co cobalt
  • REM rare earth element
  • the base steel sheet may further contain one or more of 1.0% or less of copper (Cu), 1.0% or less of nickel (Ni), 1.0% or less of vanadium (V), 0.010% or less of calcium (Ca), 0.10% or less of niobium (Nb), 1.0% or less of tin (Sn), 1.0% or less of tungsten (W), 0.10% or less of magnesium (Mg), 1.0% or less of cobalt (Co), 1.0% or less of arsenic (As), 1.0% or less of zirconium (Zr), 1.0% or less of bismuth (Bi), and 0.30% or less of a rare earth element (REM).
  • Cu copper
  • Ni nickel
  • V vanadium
  • Ca calcium
  • Nb niobium
  • Sn tin
  • W tungsten
  • Mg magnesium
  • Co cobalt
  • Ac arsenic
  • Zr zirconium
  • Bi bismuth
  • REM rare earth element
  • the base steel sheet of the present disclosure may contain a balance of iron (Fe) and unavoidable impurities in addition to the composition described above. Since the unavoidable impurities may be unintentionally incorporated in a general manufacturing process, the unavoidable impurities may not be excluded. Since these impurities are known to those skilled in a general steel manufacturing field, all the contents thereof are not particularly described in the present specification.
  • the plating layer of the plated steel sheet may be an aluminum or aluminum-based alloy plating layer.
  • the plating layer may be an alloyed aluminum-based plating layer.
  • the plating layer may contain, in addition to Al, Si, Mg, and Fe, and may contain Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, Sr, Zn, and the like in some cases.
  • a thickness of the plating layer is not particularly limited, and the plating layer may have a thickness within a general range.
  • the plating layer may contain, by wt%, one or two or more selected from 5 to 11% of Si, 5% or less of Fe, and 5% or less of Mg, and may contain a balance of Al and other impurities.
  • the plating layer may further contain 30% or less of elements such as Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, Sr, and Zn in total.
  • the plating layer may contain, by wt%, one or two or more selected from 5.0 to 11.0% of Si, 5.0% or less of Fe, and 5.0% or less of Mg, and may contain a balance of Al and other impurities.
  • the plating layer may further contain 30.0% or less of elements such as Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, Sr, and Zn in total.
  • a part according to an exemplary embodiment in the present disclosure may include a base steel and a plating layer formed on a surface of the base steel.
  • the same alloy composition as that of the base steel sheet of the plated steel sheet suggested in the present disclosure may be applied to the base steel according to an aspect of the present disclosure.
  • the plating layer may be formed on at least one surface of the base steel.
  • the plating layer of the part may have an alloy composition in which components including Fe in the plating layer and the base steel sheet of the plated steel sheet described above are diffused.
  • the part according to an exemplary embodiment in the present disclosure may include an antimony (Sb)-enriched layer in the base steel.
  • the Sb-enriched layer of the present disclosure may be determined by analyzing a change in content of Sb from an arbitrary point of the plating layer in a thickness direction on a side of the base steel using a glow discharge spectrometer (GDS).
  • GDS glow discharge spectrometer
  • the method for determining the Sb-enriched layer in the plated steel sheet suggested in the present disclosure may be applied in the same manner.
  • the antimony (Sb)-enriched layer may be formed directly under an interface where the base steel and the plating layer are in contact with each other.
  • the interface between the base steel and the plating layer may mean a point at which a content of Al is 15%.
  • a content of carbon (C) at a depth at which a content of antimony (Sb) in the antimony (Sb)-enriched layer exhibits a maximum value (Sb max ) may be 80% or less of a nominal carbon content (C 0 ) of the base steel.
  • the content of carbon (C) at the depth at which the content of antimony (Sb) in the antimony (Sb)-enriched layer shows the maximum value (Sb max ) may be 80.0% or less of the nominal carbon content (C 0 ) of the base steel.
  • the content of carbon at the depth at which the content of Sb in the Sb-enriched layer shows the maximum value (Sb max ) affects the hardness of the surface layer structure and affects the bendability. Meanwhile, when the content of carbon at the depth at which the content of Sb in the Sb-enriched layer shows the maximum value (Sb max ) exceeds 80% of the nominal carbon content (C 0 ), the hardness of the surface layer part may increase, which may cause deterioration of the bendability. However, when the content of carbon at the depth at which the content of Sb in the Sb-enriched layer shows the maximum value (Sb max ) is excessively low, the hardness of the surface layer part may be insufficient, which makes it difficult to secure fatigue resistance. Therefore, as an exemplary embodiment in the present disclosure, a lower limit thereof may be limited to 15%. As an exemplary embodiment in the present disclosure, the lower limit thereof may be limited to 15.0%.
  • FIG. 5 schematically illustrates content profiles of Sb and C in the thickness direction from the interface in the part according to an exemplary embodiment in the present disclosure.
  • the X-axis may represent a depth ( ⁇ m) from the interface between the base steel and the plating layer
  • the Y-axis may represent a content (wt%) of element.
  • 80% of the nominal carbon content (C 0 ) is 0.176%.
  • the nominal carbon content (C 0 ) is 0.22%, which may be obtained by analyzing a certain thickness (depth) using a glow discharge spectrometer (GDS) in a region corresponding to 1/4 to 3/4 of the thickness of the base steel as described above. In this case, it can be confirmed that the content of carbon at the depth at which the content of Sb shows the maximum value exhibits a content of carbon of 80% or less of the nominal carbon content (C 0 ).
  • GDS glow discharge spectrometer
  • the part according to an exemplary embodiment in the present disclosure may have an R value defined in the following Relational Expression 1 of 1.5 or more and a B value defined in the following Relational Expression 2 of 0.01 or more.
  • the part according to an exemplary embodiment in the present disclosure may have an R value defined in the following Relational Expression 1 of 1.50 or more and a B value defined in the following Relational Expression 2 of 0.010 or more.
  • an Sb enrichment degree in the Sb-enriched layer may be more increased.
  • the Sb-enriched layer serves to effectively block penetration of diffusible hydrogen, and the bendability may be increased by reducing diffusible hydrogen since diffusible hydrogen accelerates the occurrence of grain boundary cracks when stress occurs. That is, when the relational expressions are not satisfied, and specifically, when the R value defined in Relational Expression 1 is less than 1.5 or the B value defined in Relational Expression 2 is less than 0.01, during hot press forming, the penetration of diffusible hydrogen is not sufficiently blocked, and thus, the impact resistance may be deteriorated.
  • the R value defined in Relational Expression 1 may be 1.7 or more.
  • the B value defined in Relational Expression 2 may be 0.014 or more.
  • an upper limit of the R value may be limited to 6.4.
  • an upper limit of the B value may be limited to 0.5.
  • the R value defined in Relational Expression 1 may be 1.70 or more.
  • the B value defined in Relational Expression 2 may be 0.0140 or more.
  • the upper limit of the R value may be limited to 6.40.
  • an upper limit of the B value may be limited to 0.50.
  • a softening rate ( ⁇ ) in a region from the interface between the base steel and the plating layer to a depth of 45 to 100 ⁇ m in the thickness direction may be 2 to 7%.
  • the region from the interface between the base steel and the plating layer to the depth of 45 to 100 ⁇ m in the thickness direction may affect the hardness of the surface layer part of the part, and may affect the bendability.
  • the softening rate in a region to a depth of 45 to 100 ⁇ m in the thickness direction is less than 2%, the hardness of the surface layer part increases excessively, and thus, the effect of improving bendability may be reduced.
  • the softening rate exceeds 7% the hardness of the surface layer part decreases excessively, and thus, the fatigue resistance may be deteriorated.
  • the hardness softening rate may be measured as illustrated in FIG. 6.
  • FIG. 6 schematically illustrates a hardness softening rate ( ⁇ ) profile at a depth of 45 to 100 ⁇ m in the thickness direction from the interface in the part according to an exemplary embodiment in the present disclosure. Specifically, a Vickers hardness is measured and the hardness is measured by applying a weight of 1 kg. The hardness inside the base steel is set as a reference hardness (H O ), and the reference hardness (H O ) may be measured at a point of 1/5 of the thickness of the base steel.
  • H O reference hardness
  • the Y-axis represents a ratio (%) of a hardness value (H) at the corresponding position to the reference hardness value (H O ), and the X-axis represents a distance ( ⁇ m) from the interface in the thickness direction.
  • a square is drawn with 0 to 100% as the Y-axis range and a depth of 45 to 100 ⁇ m from the interface as the X-axis range.
  • a hardness profile curve indicating a ratio of hardness values according to the depth from the interface in the square may be indicated, and a ratio of an area of an upper region in the square of the hardness profile to the entire area of the square may be defined as the hardness softening rate ( ⁇ , %).
  • a hardness profile is created at a depth of 45 to 100 ⁇ m and used for the hardness softening rate ( ⁇ ).
  • the hardness softening rate ( ⁇ ) of the present disclosure means a ratio (%) of the area above the hardness profile curve to the entire area of the square in the square in which a horizontal axis represents the distance ( ⁇ m) from the interface between the base steel sheet and the plating layer in the thickness (depth) direction, and a vertical axis represents the ratio (%) of the hardness value (H) at the corresponding position to the reference hardness (H O ).
  • a softening rate ( ⁇ ) in a region from an interface between the base steel and the plating layer to a depth of 45.0 to 100.0 ⁇ m in the thickness direction may be 2.0 to 7.0%.
  • the ferrite in the region from the interface between the base steel and the plating layer to the depth of 50 ⁇ m in the thickness direction may cause propagation of cracks. That is, in a case where the ferrite is 5% or more in the corresponding region, when stress occurs in the surface layer part, the stress is locally concentrated on the relatively soft ferrite, and the propagation of cracks is accelerated, which may cause deterioration of the bendability and the fatigue resistance.
  • the physical properties desired in the present disclosure may be insufficient.
  • a region from the interface between the base steel and the plating layer to a depth of 50.0 ⁇ m in the thickness direction may have a microstructure containing less than 5.0 area% of ferrite.
  • the part according to an exemplary embodiment in the present disclosure may have a microstructure containing martensite as a main phase in a region from the interface between the base steel and the plating layer to a depth of 50.0 ⁇ m in the thickness direction, less than 5.0 area% of ferrite, and a balance of upper and lower bainite.
  • a phase having an area fraction of 50.0% or more of the total microstructure fraction may be regarded as the main phase.
  • the plated steel sheet according to an aspect of the present disclosure may be manufactured by annealing and plating a cold-rolled steel sheet satisfying the alloy composition described above.
  • the cold-rolled steel sheet may be manufactured by reheating, hot rolling, coiling, cooling, and cold rolling a steel slab satisfying the alloy composition described above.
  • the reheating temperature is lower than 1,050°C, a slab structure is not sufficiently homogenized, and thus, when precipitated elements are used, it is difficult to solid-dissolve these elements again.
  • the temperature exceeds 1,300°C, an oxide layer is excessively formed, which may cause an increase in manufacturing costs for removing the oxide layer and the occurrence of surface defects occurring after hot rolling.
  • the reheated steel slab may be finish rolled in a temperature range of 800 to 950°C.
  • finish rolling temperature is lower than 800°C, two-phase region rolling is performed, and ferrite is introduced into the surface layer part of the steel sheet, which may make it difficult to control a sheet shape.
  • the temperature exceeds 950°C, coarsening of grains may occur.
  • the rolled steel may be coiled and cooled in a temperature range of 500 to 700°C.
  • a cold-rolled steel sheet may be manufactured by cold rolling the cooled steel at a reduction ratio of 30 to 80%.
  • the reduction ratio is not particularly limited, and cold rolling may be performed at a reduction ratio of 30 to 80% to obtain a predetermined target thickness.
  • the cold-rolled steel sheet may be annealed in a temperature range of Ac 1 to Ac 3 .
  • a lower limit of the annealing temperature may be 750°C.
  • an upper limit of the annealing temperature may be limited to 860°C.
  • a product of an annealing time and an absolute humidity may be 10,000 to 80,000 s ⁇ g/m 3 .
  • the atmosphere and humidity may be controlled by using hydrogen gas, hydrogen-nitrogen mixed gas, and the like to form an oxidizing atmosphere, and it is important to control the annealing time and the absolute humidity in the temperature range of Ac 1 to Ac 3 to obtain an appropriate decarburization rate of the steel sheet.
  • the product of the annealing time and the absolute humidity may be 10,000 to 80,000 s ⁇ g/m 3 .
  • the annealing time may be 100 to 200 seconds.
  • the absolute humidity may be 100 to 400 g/m 3 .
  • an average temperature increase rate from room temperature to 500°C may be controlled to 2.7 to 10.0°C/s
  • an average temperature increase rate in a section of 500 to 700°C may be controlled to 0.5 to 2.5°C/s
  • an average temperature increase rate from 700°C to the annealing temperature may be controlled to 0.01 to 0.4°C/s.
  • the average temperature increase rate from room temperature to 500°C is limited to 2.7 to 10.0°C/s to secure an Sb-enriched layer.
  • the average temperature increase rate from room temperature to 500°C is outside of the range of 2.7 to 10.0°C/s, specifically, when the average temperature increase rate is less than 2.7°C/s, an enriched layer is not sufficiently formed, and when the average temperature increase rate exceeds 10°C/s, temperature unevenness in a width direction of the steel sheet increases due to rapid heating, which may cause differences in structure and line trouble.
  • the Sb enrichment of the base steel may be affected.
  • the Sb-enriched layer may not be sufficiently formed.
  • the temperature of the surface of the steel sheet from 700°C to the desired annealing temperature is a temperature at which an Sb-enriched layer is sufficiently formed in the base steel, and it is preferable that the average temperature increase rate is 0.01 to 0.4°C/s in order to prevent defects of the Sb-enriched layer satisfying Relational Expressions 1 and 2 and the surface part of the steel sheet.
  • the annealed cold-rolled steel sheet may be plated.
  • a plating bath according to an aspect of the present disclosure may be formed of aluminum or an aluminum-based alloy.
  • the composition of the plating bath may contain, in addition to Al, Si, Mg, and Fe, and may contain Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, Sr, Zn, and the like in some cases.
  • a coating amount is not particularly limited, and may be a coating amount in a general range.
  • the composition of the plating bath may contain, by wt%, one or two or more selected from 5 to 11% of Si, 5% or less of Fe, and 5% or less of Mg, and may contain a balance of Al and other impurities.
  • an alloying process may be included after plating, and the alloying process is not particularly limited and may be performed under general conditions.
  • the part according to an aspect of the present disclosure may be manufactured by manufacturing a blank using a plated steel sheet to be manufactured by the method described, and heating, maintaining, forming, and cooling the blank.
  • the heated blank has a heat treatment residence time of 10 to 1,000 seconds in the above temperature range.
  • the maintenance time is shorter than 10 seconds, it is difficult to uniformly distribute the temperature throughout the blank, which may cause a material variation for each position.
  • the plated steel sheet of the present disclosure manufactured as described above may maintain the hardness of the surface layer at a certain level or lower, and may maintain a blade lifespan at a certain level or lower when shearing is performed to manufacture a blank for hot press forming, thereby having the effect of reducing the costs consumed.
  • the part of the present disclosure manufactured as described above may have excellent fatigue resistance and bendability with a product of a tensile strength and a bending angle of 80,000 MPa ⁇ ° or more and the amount of diffusible hydrogen of 0.2 ppm or less.
  • tensile strength (TS)*bending angle (BA) is used as an index to measure the impact resistance.
  • the bending angle which is an index of the impact resistance, is affected by the tensile strength and has an inversely proportional tendency. Therefore, as the value of the product of the tensile strength and the bending angle (TS*BA) increases, the impact resistance increases.
  • the BA value may be measured through a bendability evaluation according to the VDA238-100 standard and is expressed as a bending outer angle converted from a maximum bending strength.
  • Slabs containing Sb in the contents disclosed in Table 1 and having a composition of 0.22C-0.25Si-1.25Mn-0.2Cr-0.03Al-0.03Ti-0.0025B and a thickness of 40 mm were manufactured by vacuum dissolving.
  • the slabs were heated to 1,200°C and maintained for 1 hour, the heated slabs were hot-rolled at a hot rolling end temperature of 900°C, and then the hot-rolled slabs were coiled at a temperature of 600°C. Thereafter, a pickling process was performed, and cold rolling was performed at a reduction ratio of 30 to 80%, thereby manufacturing cold-rolled steel sheets.
  • the cold-rolled steel sheets were annealed at a temperature of Ac 1 to Ac 3 , an annealing time (s) and an absolute humidity (g/m 3 ) were controlled, and values of a product of the annealing time and the absolute humidity were shown in Table 1.
  • plating was performed by immersing the steel sheets in a plating bath formed of Al-9%Si-2%Fe and trace impurities. [Table 1] Specimen Nos.
  • Annealing Sb (wt%) Annealing time ⁇ absolute humidity (s ⁇ g/m 3 ) Steel sheet surface average temperature increase rate (°C/s) Room temperature to 500°C 500 to 700°C 700°C to annealing temperature 1 0.072 10,654 2.9 2.0 0.03 2 0.045 22,347 6.7 1.6 0.10 3 0.036 40,451 4.5 1.0 0.16 4 0.015 58,363 9.
  • Table 2 shows the results of measuring an Sb-enriched layer, a microstructure, and a decarburization rate of each of the manufactured plated steel sheets.
  • an area fraction of pearlite was measured by observing the structure directly under an interface using scanning electron microscopy (SEM). At this time, in all the specimens, the residual fraction excluding the area fraction of pearlite was observed as ferrite.
  • a part was manufactured by hot press forming using a plated steel sheet in which a non-plated area was not observed.
  • a heat treatment temperature and time for hot press forming were 900°C and 360 seconds, and a transfer time from a heat treatment furnace to a forming press was set to 10 seconds.
  • Table 3 shows the structure and properties of the parts manufactured through the hot press forming were measured by the same method as described above.
  • a Vickers hardness was measured by applying a load of 1.0 kg in a region from the interface between the plating layer and the base steel of the part to a depth of 45 to 100 ⁇ m, and a hardness softening rate ( ⁇ ) was shown using FIG. 6 and the method described above.
  • the amount of diffusible hydrogen was measured using a thermal desorption analysis (TDA) equipment (Bruker G8, model name). Specifically, the temperature was increased to 400°C at 20°C/min and maintained for a certain time so that a diffusible hydrogen peak sufficiently appeared to measure a diffusible hydrogen curve, and the curve was integrated to obtain the amount of diffusible hydrogen in the steel.
  • TDA thermal desorption analysis
  • a ferrite area fraction in a range from the interface between the base steel and the plating layer to a depth of 30 ⁇ m was measured using optical microscopy and was shown in Table 3. At this time, in all the specimens, the residual fraction excluding the ferrite area fraction was observed as martensite.
  • the fatigue limit strength was measured by repeatedly performing a fatigue test 10,000,000 times or more by applying the JIS Z2275 standard, a case in which the value of the fatigue limit strength obtained by dividing the fatigue limit strength by the tensile strength was 0.25 or more was marked as O, and a case in which the value of the fatigue limit strength was less than 0.025 was marked as X.
  • the impact resistance was expressed as the product of the tensile strength and the bending angle, and the tensile strength value was measured through a tensile test at room temperature using a JIS-5 specimen according to the ISO6892 standard.
  • the bending angle was expressed as the bending outer angle converted from the maximum bending strength specified in the standard according to the bendability evaluation method of the VDA238-100 standard. [Table 3] Specime n Nos.
  • FIG. 7 illustrates a carbon profile in the plated steel sheet according to an exemplary embodiment in the present disclosure.
  • the decarburization control suggested in the present disclosure was sufficiently achieved, and as a result, the product of the tensile strength and the bending angle and the fatigue resistance at certain levels or higher were secured.
  • Comparative Example 1 the decarburization was not sufficiently achieved according to the depth, and in Comparative Example 3, excessive decarburization occurred due to insufficient formation of the Sb-enriched layer, and thus, the physical properties were deteriorated.
  • FIG. 8 illustrates photographs of the structures directly under the interfaces in the plated steel sheets of Inventive Example 3 and Comparative Example 3 according to an exemplary embodiment in the present disclosure observed with SEM. It was confirmed that, in Inventive Example 3, 2.9% of pearlite was observed, and in Comparative Example 3, less than 1% of pearlite was observed.
  • FIG. 9 illustrates optical photographs of the interfaces between the plating layers and the base steels in the parts of Inventive Example 3 and Comparative Example 3 of the present disclosure.
  • Inventive Example 3 less than 1% of ferrite was observed, but in Comparative Example 3, ferrite was 7.3%, and thus, the fatigue resistance desired in the present disclosure was not secured.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Coating With Molten Metal (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
  • Heat Treatment Of Articles (AREA)
EP23857642.5A 2022-08-26 2023-08-17 Tôle d'acier plaquée pour formage à la presse à chaud ayant une excellente résistance aux chocs, pièce formée par pressage à chaud et ses procédés de fabrication Pending EP4578987A4 (fr)

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KR1020220107402A KR20230038389A (ko) 2022-08-26 2022-08-26 내충돌성이 우수한 열간 성형용 도금강판, 열간 성형 부재 및 이들의 제조방법
PCT/KR2023/012157 WO2024043608A1 (fr) 2022-08-26 2023-08-17 Tôle d'acier plaquée pour formage à la presse à chaud ayant une excellente résistance aux chocs, pièce formée par pressage à chaud et ses procédés de fabrication

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KR20230038389A (ko) * 2022-08-26 2023-03-20 주식회사 포스코 내충돌성이 우수한 열간 성형용 도금강판, 열간 성형 부재 및 이들의 제조방법
KR20250093756A (ko) * 2023-12-15 2025-06-25 주식회사 포스코 열간성형용 강판, 열간 성형 부재 및 이들의 제조방법
KR20250094784A (ko) * 2023-12-18 2025-06-26 주식회사 포스코 알루미늄계 도금강재, 열간성형부재 및 그 제조방법

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FR2780984B1 (fr) 1998-07-09 2001-06-22 Lorraine Laminage Tole d'acier laminee a chaud et a froid revetue et comportant une tres haute resistance apres traitement thermique
JP4057930B2 (ja) * 2003-02-21 2008-03-05 新日本製鐵株式会社 冷間加工性に優れた機械構造用鋼及びその製造方法
KR101568522B1 (ko) * 2013-12-24 2015-11-11 주식회사 포스코 열간성형용 냉연강판, 이를 이용한 열간성형 부재 및 이들의 제조방법
JP6296805B2 (ja) 2014-01-23 2018-03-20 Ａｉ Ｔｅｃｈｎｏｌｏｇｙ株式会社 検知装置
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KR101858868B1 (ko) * 2016-12-23 2018-05-16 주식회사 포스코 충격특성이 우수한 열간성형용 도금강판, 열간성형 부재 및 그들의 제조방법
MX2021006649A (es) * 2018-12-11 2021-07-15 Nippon Steel Corp Lamina de acero de alta resistencia que tiene excelente moldeabilidad y resistencia al impacto, y metodo para fabricar lamina de acero de alta resistencia que tiene excelente moldeabilidad y resistencia al impacto.
KR102869614B1 (ko) * 2020-11-09 2025-10-13 주식회사 포스코 내수소취성 및 내충돌성이 우수한 열간성형용 도금강판, 열간성형 부재 및 이들의 제조방법
KR20230038389A (ko) * 2022-08-26 2023-03-20 주식회사 포스코 내충돌성이 우수한 열간 성형용 도금강판, 열간 성형 부재 및 이들의 제조방법

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JP2025528267A (ja) 2025-08-26
WO2024043608A1 (fr) 2024-02-29

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