WO2024043608A1 - 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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WO2024043608A1
WO2024043608A1 PCT/KR2023/012157 KR2023012157W WO2024043608A1 WO 2024043608 A1 WO2024043608 A1 WO 2024043608A1 KR 2023012157 W KR2023012157 W KR 2023012157W WO 2024043608 A1 WO2024043608 A1 WO 2024043608A1
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steel sheet
less
content
present
carbon
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PCT/KR2023/012157
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Korean (ko)
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김상헌
오진근
김성우
이세웅
이상철
소슬기
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주식회사 포스코
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C47/00—Winding-up, coiling or winding-off metal wire, metal band or other flexible metal material characterised by features relevant to metal processing only
    • B21C47/02—Winding-up or coiling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C23C2/04—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
    • C23C2/34—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

Definitions

  • the present invention relates to galvanized steel sheets for hot forming, hot forming members, and methods for manufacturing the same. More specifically, it relates to galvanized steel sheets for hot forming with excellent collision resistance, hot forming members, and methods for manufacturing them.
  • Hot forming members have recently been widely applied to structural members of automobiles for the purpose of improving fuel efficiency and protecting passengers by reducing the weight of automobiles.
  • they can be used in bumpers, doors, or pillar reinforcements that require ultra-high strength or energy absorption.
  • Patent Document 1 was proposed as a representative technology regarding this hot forming technology.
  • ultra-high strength with high tensile strength can be secured by heating Al-Si plated steel sheet to over 850°C and then forming the structure of the member into martensite by hot forming with a press and rapid cooling.
  • complex shapes can be easily formed because they are formed at high temperatures, and a weight reduction effect due to high strength can be expected through an increase in strength due to rapid cooling in the mold.
  • Patent Document 1 U.S. Patent Publication No. 6296805 (published on October 2, 2001)
  • it is intended to provide a galvanized steel sheet for hot forming with excellent collision resistance, a hot forming member, and a method for manufacturing the same.
  • One aspect of the present invention includes a base steel sheet containing, in weight percent, carbon (C): 0.06 to 0.5% and antimony (Sb): 0.01 to 0.1%, and a plating layer formed on the surface of the base steel sheet,
  • the base steel plate includes an antimony (Sb) concentrated layer therein,
  • the depth at which the antimony (Sb) content in the antimony (Sb) enriched layer shows the maximum value (Sb max ) It is possible to provide a plated steel sheet in which the carbon (C) content is 10 to 70% of the nominal carbon content (C 0 ) of the base steel sheet.
  • the 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%.
  • the plated steel sheet may have a point where the carbon (C) content is 50% of the nominal carbon content (C 0 ) at a depth of more than 1.5 ⁇ m and less than 6 ⁇ m in the thickness direction from the interface of the base steel sheet and the plating layer.
  • the plated steel sheet may have a point where the carbon (C) content is 80% of the nominal carbon content (C 0 ) at a depth of more than 6 ⁇ m and less than 15 ⁇ m in the thickness direction from the interface between the base steel sheet and the plating layer.
  • the plated steel sheet has an R value defined in equation 1 below of 1.2 or more
  • the B value defined in Equation 2 below may be 0.008 or more.
  • Sb max represents the maximum value of Sb content in the Sb enriched layer
  • Sb coat represents the average Sb content in the plating layer
  • ⁇ t measures Sb max from the interface between the plating layer and the base steel sheet. It represents the straight line distance between one points, and the unit is ⁇ m.
  • the area from the interface between the base steel plate and the plating layer to a depth of 10 ⁇ m in the thickness direction may have a microstructure containing ferrite as the main phase and more than 1 area% of pearlite.
  • the base steel sheet contains carbon (C): 0.06-0.5%, antimony (Sb): 0.01-0.1%, silicon (Si): 0.001-2%, manganese (Mn): 0.1-4%, molybdenum (Mo): 1 % or less, phosphorus (P): 0.05% or less, sulfur (S): 0.02% or less, aluminum (Al): 0.001 to 1%, chromium (Cr): 1% or less, nitrogen (N): 0.02% or less, titanium (Ti): 0.1% or less, boron (B): 0.01% or less, and may include remaining iron (Fe) and impurities.
  • the plating layer may be made of aluminum or aluminum alloy.
  • Another aspect of the present invention includes base iron containing 0.06 to 0.5% of carbon (C) and 0.01 to 0.1% of antimony (Sb), in weight percent, and a plating layer formed on the surface of the base iron,
  • the base iron includes an antimony (Sb) enriched layer within it,
  • the depth at which the antimony (Sb) content in the antimony (Sb) enriched layer shows the maximum value (Sb max ) It is possible to provide a member in which the carbon (C) content is 80% or less of the nominal carbon content (C 0 ) of the base iron.
  • the member may have a carbon (C) content of 15 to 80% of the nominal carbon content (C 0 ) of the base iron at a depth where the antimony (Sb) content reaches its maximum value (Sb max ).
  • the member has an R value defined in equation 1 below of 1.5 or more,
  • the B value defined in Equation 2 below may be 0.01 or more.
  • Sb max represents the maximum value of Sb content in the Sb enriched layer
  • Sb coat represents the average Sb content in the plating layer
  • ⁇ t measures Sb max from the interface where the plating layer and the base iron contact. It represents the straight line distance between one points, and the unit is ⁇ m.
  • a region with a depth of 45 to 100 ⁇ m in the thickness direction from the interface between the base iron and the plating layer may have a softening rate ( ⁇ ) of 2 to 7%.
  • the area from the interface between the base iron and the plating layer to a depth of 50 ⁇ m in the thickness direction may include less than 5 area% of ferrite as a microstructure.
  • the area from the interface of the base iron and the plating layer to a depth of 50 ⁇ m in the thickness direction may have martensite as the main phase as a microstructure, and may include less than 5 area% of ferrite and the remaining upper and lower bainite.
  • the base iron contains carbon (C): 0.06 to 0.5%, antimony (Sb): 0.01 to 0.1%, silicon (Si): 0.001 to 2%, manganese (Mn): 0.1 to 4%, and molybdenum (Mo): 1. % or less, phosphorus (P): 0.05% or less, sulfur (S): 0.02% or less, aluminum (Al): 0.001 to 1%, chromium (Cr): 1% or less, nitrogen (N): 0.02% or less, titanium (Ti): 0.1% or less, boron (B): 0.01% or less, and may include remaining iron (Fe) and impurities.
  • the plating layer may be made of aluminum or aluminum alloy.
  • the product of the tensile strength and bending angle of the member may be 80,000 MPa ⁇ ° or more.
  • the member may have a diffusible hydrogen content of 0.2ppm or less.
  • One aspect of the present invention includes preparing a cold-rolled steel sheet containing, in weight percent, carbon (C): 0.06 to 0.5% and antimony (Sb): 0.01 to 0.1%;
  • the product of the annealing time and the absolute humidity is 10,000 to 80,000 s ⁇ g/m 3 .
  • the average temperature increase rate from room temperature to 500°C is 2.7 to 10.0°C/s
  • the average temperature increase rate in the 500 to 700°C section is 0.5 to 2.5°C/s
  • the annealing time is 100 to 200 seconds, and the absolute humidity may be 100 to 400 g/m 3 .
  • the steel slab contains carbon (C): 0.06-0.5%, antimony (Sb): 0.01-0.1%, silicon (Si): 0.001-2%, manganese (Mn): 0.1-4%, molybdenum (Mo): 1 % or less, phosphorus (P): 0.05% or less, sulfur (S): 0.02% or less, aluminum (Al): 0.001 to 1%, chromium (Cr): 1% or less, nitrogen (N): 0.02% or less, titanium (Ti): 0.1% or less, boron (B): 0.01% or less, and may include remaining iron (Fe) and impurities.
  • plating may be done with aluminum or aluminum alloy.
  • Another aspect of the present invention includes manufacturing one plated steel sheet as a blank
  • a method of manufacturing a member may be provided including the steps of forming and cooling the heated blank.
  • cooling can be performed at a cooling rate of 20°C/s or more.
  • a galvanized steel sheet for hot forming with excellent collision resistance, a hot forming member, and a method for manufacturing the same can be provided.
  • a plated steel sheet for hot forming with excellent fatigue resistance and collision resistance, a hot forming member, and a method for manufacturing the same.
  • Figure 1 schematically shows an exemplary change in Sb content of the present invention to represent a Sb enriched layer.
  • Figure 2 schematically shows the Sb and C content profile from the interface to the thickness direction in a plated steel sheet according to an embodiment of the present invention.
  • Figure 3 schematically shows the decarburization rate ( ⁇ ) profile from the interface to the thickness direction in a plated steel sheet according to an embodiment of the present invention.
  • Figure 4 schematically shows the Sb enriched layer profile of a plated steel sheet according to an embodiment of the present invention.
  • Figure 5 schematically shows the Sb and C content profile from the interface to the thickness direction in a member according to an embodiment of the present invention.
  • Figure 6 schematically shows the hardness softening rate ( ⁇ ) profile from the interface to the thickness direction in a member according to an embodiment of the present invention.
  • Figure 7 shows the C content profile in a plated steel sheet according to an embodiment of the present invention.
  • Figure 8 is a photograph of the microstructure of a plated steel sheet according to an embodiment of the present invention observed with a scanning electron microscope (SEM).
  • Figure 9 is a photograph observing the microstructure of a member according to an embodiment of the present invention.
  • One aspect of the present invention is directed to a plated steel sheet including a base steel sheet and a plating layer formed on the surface of the base steel sheet. Collision resistance and fatigue resistance can be greatly affected by the degree of decarburization of the steel sheet, and the effects of the present invention can be advantageously obtained when the decarburization rate is appropriately controlled using the thickened layer formed in the base steel sheet. That is, the plated steel sheet according to one aspect of the present invention includes a base steel plate and a plating layer formed on the surface of the base steel sheet (which may mean the interface between the base steel sheet and the plating layer), and the base steel sheet contains antimony (Sb) formed within the base steel sheet. ) may include a thickening layer.
  • the decarburization rate according to the depth in the thickness direction of the steel sheet can be appropriately controlled according to the formation of the Sb enriched layer.
  • Figure 1 schematically shows an exemplary change in Sb content of the present invention to express the Sb enriched layer.
  • the It represents the distance
  • the y-axis represents the Sb content measured using a glow discharge spectrometer (GDS).
  • GDS glow discharge spectrometer
  • the Sb enriched layer 2 may have an Sb content of 1.05 times or more than the nominal Sb content (Sb 0 ) of the base steel plate, and within the Sb enriched layer 2, there is a point (200) where the Sb content is at its maximum value. Sb max ) may exist.
  • the Sb enriched layer 2 has a Sb content increasing section 21 in which the Sb content increases to the point (200; Sb max ) where the Sb content is the maximum as it progresses in the x-axis direction, and a point where the Sb content is the maximum. It may include a Sb content lowering section 22 in which the Sb content decreases while proceeding from (200; Sb max ) in the x-axis direction.
  • the last contact point (11) can be used as the starting point of the Sb content increase section (21).
  • the Sb average content line 10 of the plating layer 1 is a point 15 ⁇ m away from the point (200, Sb max ) where the Sb content is the maximum in the Sb enriched layer 2 toward the plating layer 1. It may mean an extension line that extends horizontally the average Sb content of the section from point A to point B, which is 20 ⁇ m away.
  • the Sb average content line 30 of the base steel plate and the Sb content line The first contact point (31) in the x-axis (+) direction of (100) is regarded as the end point of the Sb enriched layer (2).
  • the average Sb content line 30 of the base steel sheet 3 excluding the Sb enriched layer is from the point 200 (Sb max ) where the Sb content is the maximum in the Sb enriched layer 2.
  • Sb max the Sb content is the maximum in the Sb enriched layer 2.
  • It can mean an extension line that extends the average Sb content of the section horizontally from point C, which is 15 ⁇ m away, to point D, which is 20 ⁇ m away.
  • the Sb enriched layer may be formed directly below the interface between the base steel sheet and the plating layer.
  • the Al content profile is analyzed from the surface of the plated steel sheet in the depth (thickness) direction using a glow discharge spectrometer (GDS), it can be defined as the point where the Al content is 15%.
  • the thickness of the concentrated layer may be 1 to 30 ⁇ m.
  • antimony (Sb) when analyzing the content of antimony (Sb) in the thickness direction of the base steel sheet using a glow discharge spectrometer (GDS), antimony (Sb) is present in the antimony (Sb) enriched layer.
  • the carbon (C) content at the depth where the content represents the maximum value (Sb max ) may be 10 to 70% of the nominal carbon content (C 0 ) of the base steel plate.
  • the nominal carbon content (C 0 ) may mean the average carbon content in the thickness 1/4 to 3/4 region based on the cross-section of the base steel plate, and specifically, glow discharge spectroscopy
  • the average carbon content can be obtained by analyzing the carbon profile at a distance of 50 ⁇ m or more from any point in the area of 1/4 to 3/4 of the thickness of the base steel plate using an analyzer (GDS).
  • Figure 2 schematically shows the profile of Sb and C contents from the interface to the thickness direction in a plated steel sheet according to an embodiment of the present invention.
  • the x-axis of FIG. 2 represents the depth ( ⁇ m) from the interface between the base steel plate and the plating layer, and the y-axis may represent the element content (wt%).
  • 70% of the nominal carbon content (C 0 ) is 0.154%.
  • the nominal carbon content (C 0 ) is 0.22%, and as described above, a certain thickness (depth) is analyzed using a glow discharge spectrometer (GDS) in the 1/4 to 3/4 thickness area of the base steel plate. can be obtained. At this time, it can be confirmed that at the depth where the Sb content shows the maximum value (Sb max ), the carbon content is 70% or less of the nominal carbon content (C 0 ).
  • GDS glow discharge spectrometer
  • the ratio of the carbon content to the nominal carbon content (C 0 ) is 10 to 70. It is controlled by %, and the carbon content at this time affects the surface hardness softening rate and bendability of the member.
  • the carbon content in the Sb enriched layer exceeds 70% of the nominal carbon content (C 0 ) at the depth where the Sb content reaches its maximum value (Sb max )
  • the hardness of the surface layer may increase and the bendability may deteriorate.
  • the carbon content is less than 10% of the nominal carbon content (C 0 )
  • the hardness may be excessively lowered and the fatigue resistance may be inferior.
  • the ratio of the carbon content to the nominal carbon content (C 0 ) may be 10.0 to 70.0%.
  • the decarburization rate ( ⁇ ) of carbon (C) in the area 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%.
  • Figure 3 schematically shows the decarburization rate ( ⁇ ) profile from the interface to the thickness direction in a plated steel sheet according to an embodiment of the present invention.
  • the decarburization rate ( ⁇ ) can be obtained from the results of measuring the carbon of the plated steel sheet using a glow discharge spectrometer (GDS).
  • GDS glow discharge spectrometer
  • the y-axis represents the ratio (%) of the carbon content at the corresponding position to the nominal carbon content (C 0 )
  • the x-axis represents the distance ( ⁇ m) in the thickness (depth) direction from the interface of the base steel plate and the plating layer.
  • a rectangle can be drawn with a horizontal side corresponding to a length of 0 to 30 ⁇ m in depth from the interface to the base steel sheet thickness direction in the x-axis direction, and a vertical side corresponding to a length of 0 to 100% in the y-axis direction.
  • the carbon profile curve represents the ratio of the carbon content at that depth to the nominal carbon content (C 0 ) in the square, resulting in the ratio (%) of the area above the carbon profile curve within the square to the total area of the square.
  • the decarburization rate ( ⁇ ) of the present invention has the distance ( ⁇ m) in the thickness (depth) direction from the interface between the base steel sheet and the plating layer as the abscissa, and is calculated as the ratio of the carbon content at that position to the nominal carbon content (C 0 ).
  • ratio (%) as the vertical axis, it means the ratio (%) of the area above the carbon profile curve to the total area of the rectangle.
  • the carbon (C) decarburization rate ( ⁇ ) in the area from the interface to a depth of 30 ⁇ m in the thickness direction is less than 14%, the carbon concentration of the base steel plate excessively increases the hardness in the member after hot forming, so the bendability improvement effect is significantly reduced. It can be.
  • the decarburization rate exceeds 35%, the amount of carbon in the surface layer of the base steel sheet decreases, and the martensite hardness in the member significantly decreases, which may cause the member to have inferior fatigue resistance properties.
  • the decarburization rate ( ⁇ ) of carbon (C) in the area 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%.
  • the carbon (C) content is 50% of the nominal carbon content (C 0 ) at a depth of more than 1.5 ⁇ m and less than 6 ⁇ m in the thickness direction from the interface between the base steel sheet and the plating layer. This can exist.
  • Controlling the ratio of carbon (C) content according to the nominal carbon content (C 0 ) at a depth of more than 1.5 ⁇ m to less than 6 ⁇ m in the thickness direction from the interface is to simultaneously secure fatigue resistance and crash resistance.
  • the carbon (C) content is 50% of the nominal carbon content (C 0 )
  • the 50% point is 6 ⁇ m or more. If present at depth, fatigue resistance may be deteriorated due to excessive decarburization.
  • the 50% point exists at a depth of 1.5 ⁇ m or less, there may be difficulty in securing the desired bendability due to insufficient decarburization.
  • the carbon (C) content at a depth of more than 1.50 ⁇ m and less than 6.0 ⁇ m in the thickness direction from the interface between the base steel sheet and the plating layer is 50.0% of the nominal carbon content (C 0 ). Branches may exist.
  • the carbon (C) content is 80% of the nominal carbon content (C 0 ) at a depth of more than 6 ⁇ m and less than 15 ⁇ m in the thickness direction from the interface between the base steel plate and the plating layer.
  • the ratio of carbon (C) content according to the nominal carbon content (C 0 ) is 80% at a depth of more than 6 ⁇ m to less than 15 ⁇ m in the thickness direction from the interface, appropriate bendability is secured and excessive fatigue resistance deterioration is suppressed. can be advantageous.
  • the 80% point is at a depth of 15 ⁇ m or more, the fatigue resistance may be reduced due to excessive decarburization, and if the 80% point is at a depth of 6 ⁇ m or less, the desired bendability may be lost due to insufficient decarburization. may be difficult to secure.
  • the carbon (C) content is 80.0% of the nominal carbon content (C 0 ) at a depth of more than 6.0 ⁇ m and less than 15.0 ⁇ m in the thickness direction from the interface between the base steel plate and the plating layer.
  • the R value defined in equation 1 below may be 1.2 or more, and the B value defined in equation 2 below may be 0.008 or more.
  • the R value defined in equation 1 below may be 1.20 or more, and the B value defined in equation 2 below may be 0.0080 or more.
  • the decarburization rate can be appropriately controlled by controlling the Sb content according to the thickness direction depth, and the present invention proposes the following relational equations 1 and 2.
  • Sb max represents the maximum value of Sb content in the Sb enriched layer
  • Sb coat represents the average Sb content in the plating layer
  • ⁇ t measures Sb max from the interface between the plating layer and the base steel sheet. It represents the straight line distance between one points, and the unit is ⁇ m.
  • Figure 4 schematically shows the Sb enriched layer profile of a coated steel sheet according to an embodiment of the present invention.
  • the area corresponding to the B value of relational equation 2 is shown as a colored part, and the above-mentioned area represents the degree of Sb enrichment according to ⁇ t, which represents the distance between the point where Sb coat was measured and the point where Sb max was measured. You can.
  • the R value defined in Equation 1 may be limited to 1.5 or more.
  • the B value defined in Equation 2 above may be limited to 0.02 or more.
  • the upper limit of the R value can be limited to 6.5.
  • the upper limit of the B value may be limited to 0.15.
  • the R value defined in Equation 1 may be limited to 1.50 or more.
  • the B value defined in Equation 2 above may be limited to 0.020 or more.
  • the upper limit of the R value can be limited to 6.50.
  • the upper limit of the B value may be limited to 0.150.
  • the R value and B value of the plated steel sheet can be controlled to an appropriate range, thereby effectively suppressing the intrusion of hydrogen.
  • the plated steel sheet may have a microstructure containing ferrite as the main phase and more than 1 area% of pearlite in an area from the interface between the base steel sheet and the plating layer to a depth of 10 ⁇ m in the thickness direction.
  • a phase accounting for more than 50 area% of the total microstructure fraction can be regarded as the main phase.
  • the fatigue resistance characteristics of the member may be inferior.
  • pearlite In the area up to 10 ⁇ m in the thickness (depth) direction from the interface between the base steel sheet and the plating layer, pearlite provides carbon to the structure directly under the plating layer during heat treatment for hot forming, thereby preventing the hardness of the surface layer from deteriorating. It can play a role. Therefore, in the present invention, pearlite may be included in an amount of 1 area% or more.
  • the hardness of the surface layer may decrease excessively after hot forming, which may increase the hardness softening rate and cause the problem of inferior fatigue resistance of the member.
  • the area from the interface between the base steel sheet and the plating layer to a depth of 10.0 ⁇ m in the thickness direction may have ferrite as the main phase and contain pearlite in an amount of 1.0 area% or more.
  • the base steel plate according to one embodiment of the present invention may include carbon (C): 0.06 to 0.5% and antimony (Sb): 0.01 to 0.1% by weight.
  • the base steel plate according to one embodiment of the present invention may include carbon (C): 0.060 to 0.50% and antimony (Sb): 0.010 to 0.10% by weight.
  • the % indicating the content of each element is based on weight.
  • Carbon (C) is an element that improves the strength of hot-formed members and improves hardenability. It is an essential element to control strength and must be added appropriately. If the carbon (C) content is less than 0.06%, hardenability is low, so when the cooling rate is reduced, sufficient martensite cannot be secured, and it may be difficult to secure the desired strength due to the formation of ferrite. In one embodiment of the present invention, the carbon (C) content may be 0.1% or more. On the other hand, if the content exceeds 0.5%, the strength may increase excessively, cause brittleness, and weldability may be poor. In one embodiment of the present invention, the upper limit of the carbon (C) content may be 0.45%.
  • carbon (C) may contain 0.060 to 0.50%.
  • carbon (C) may be 0.10% or more.
  • the upper limit may be 0.450%.
  • Antimony (Sb) can play a role in controlling the amount of carbon escaping when internal oxidation annealing is applied by concentrating within the base steel sheet and preventing excessive decline in hardness in the member. If the antimony (Sb) content is less than 0.01%, a sufficient thickening layer is not formed at the interface between the plating layer and the base steel plate, resulting in excessive decarburization, which may result in an excessive decrease in surface hardness and poor fatigue resistance properties. According to one embodiment of the present invention, the lower limit of antimony (sb) may be 0.02%. On the other hand, if the content exceeds 0.1%, excessive antimony (Sb) is precipitated at the grain boundaries, which may cause grain boundary destruction when stress occurs, thereby deteriorating the material. According to one embodiment, the upper limit of the antimony (Sb) content may be 0.08%.
  • antimony (Sb) may contain 0.010 to 0.10%.
  • antimony (Sb) may be 0.020% or more.
  • the upper limit may be 0.080%.
  • the type and content are not particularly limited as long as it is an element that can be added normally.
  • elements that can be added to the base steel sheet according to one embodiment of the present invention include silicon (Si), manganese (Mn), molybdenum (Mo), phosphorus (P), and 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 rare earth elements (REM), one or more of these More may be included.
  • the base steel plate contains, in weight percent, silicon (Si): 0.001 to 2%, manganese (Mn): 0.1 to 4%, molybdenum (Mo): 1.0% or less, phosphorus (P): 0.05% or less, Sulfur (S): 0.02% or less, Aluminum (Al): 0.001 to 1%, Chromium (Cr): 1.00% or less, Nitrogen (N): 0.02% or less, Titanium (Ti): 0.1% or less, Boron (B): 0.01% or less, may include remaining iron (Fe) and impurities.
  • Silicon (Si) can be added as a deoxidizer in steelmaking.
  • Si can be added as a solid solution strengthening element and an element that suppresses carbide formation, it is not only effective in uniforming the internal structure, but also contributes to increasing the strength of hot-formed members and is added as an effective element in material uniformity.
  • the content is less than 0.001%, the above effect cannot be expected, and if the silicon (Si) content exceeds 2%, the plating property may be greatly reduced due to excessive Si oxide generated on the surface of the steel sheet during annealing.
  • the lower limit of the silicon (Si) content may be 0.005%, and in some cases, 0.01%.
  • the upper limit of the silicon (Si) content may be 0.7%, and in some cases, 0.65%.
  • silicon (Si) may contain 0.001 to 2.0%.
  • silicon (Si) may be 0.0050% or more.
  • the upper limit may be ⁇ 0.70%.
  • silicon (Si) may be 0.010% or more.
  • the upper limit may be 0.650%.
  • Manganese (Mn) needs to be added to not only secure the desired strength due to the solid solution strengthening effect, but also to suppress ferrite formation during hot forming by improving hardenability. If the manganese (Mn) content is less than 0.1%, it is difficult to obtain sufficient hardenability effect, and other expensive alloy elements are excessively required for insufficient hardenability, which may lead to a significant increase in manufacturing cost. According to one embodiment of the present invention, it may contain 0.5% or more of manganese (Mn), and in another embodiment, it may contain 0.8% or more. However, if the content exceeds 4%, the band-like structure arranged in the microstructure rolling direction becomes deeper, causing non-uniformity of the internal structure, which may deteriorate the collision resistance. In one embodiment of the present invention, the upper limit of the manganese (Mn) content may be 3.5%.
  • manganese (Mn) may contain 0.010 to 4.0%.
  • manganese (Mn) may contain 0.050 to 4.0%.
  • manganese (Mn) may contain 0.080 to 4.0%.
  • manganese (Mn) may contain 0.050 to 3.50%.
  • manganese (Mn) may contain 0.080 to 3.50%.
  • Molybdenum (Mo) may be included as an element that can improve bendability by strengthening crystal grains. However, if the content exceeds 1.0%, the manufacturing cost may increase significantly. According to one embodiment of the present invention, the upper limit of molybdenum (Mo) content may be 0.5%, and in some cases, may be 0.45%.
  • molybdenum (Mo) may contain 1.0% or less.
  • the upper limit of molybdenum (Mo) content may be 0.50%, and in some cases, may be 0.450%.
  • Phosphorus (P) exists as an impurity in steel, and if its content exceeds 0.05%, the weldability of hot-formed members and material properties may be deteriorated due to high-temperature grain boundary segregation.
  • the upper limit may be limited to 0.015%.
  • the lower limit can be limited to 0.001%.
  • phosphorus (P) may contain 0.050% or less.
  • the upper limit may be limited to 0.0150%.
  • the lower limit can be limited to 0.0010%.
  • S is an impurity in steel and is an element that impairs the ductility, impact properties, and weldability of the member, so the upper limit can be limited to 0.02%. In one embodiment of the present invention, controlling the content to a very small amount may significantly increase manufacturing costs, so the lower limit may be limited to 0.0001%.
  • sulfur (S) may contain 0.020% or less. According to one embodiment, the lower limit may be limited to 0.00010%.
  • Aluminum (Al), along with Si, is an element that increases the cleanliness of steel by acting as a deoxidizer in steelmaking. If the aluminum (Al) content is less than 0.001%, it may be difficult to achieve the above effect. According to one embodiment of the present invention, the lower limit of aluminum (Al) may be 0.01%, and in some cases, 0.02%. On the other hand, if the content exceeds 1%, high-temperature ductility is reduced due to excessive AlN precipitates formed during the casting process, and slab cracks may occur, which may cause manufacturing problems. In one embodiment, the upper limit may be limited to 0.1%, and in some cases, it may be limited to 0.09%.
  • aluminum (Al) may contain 0.0010 to 1.0%.
  • aluminum (Al) may contain 0.010 to 1.0%.
  • aluminum (Al) may contain 0.020 to 1.0%.
  • aluminum (Al) may contain 0.010 to 0.10%.
  • aluminum (Al) may contain 0.010 to 0.090%.
  • aluminum (Al) may contain 0.020 to 0.10%.
  • aluminum (Al) may contain 0.020 to 0.090%.
  • the upper limit may be 0.8%.
  • the lower limit may be limited to 0.01%, and in some cases, may be limited to 0.05%.
  • chromium (Cr) may contain 1.0% or less.
  • chromium (Cr) may contain 0.80% or less.
  • chromium (Cr) may contain 0.01 to 1.0%.
  • chromium (Cr) may contain 0.01 to 0.8%.
  • chromium (Cr) may contain 0.05 to 1.0%.
  • chromium (Cr) may contain 0.05 to 0.8%.
  • Nitrogen (N) may be included as an impurity in steel. If the nitrogen (N) content exceeds 0.02%, there is a risk that AlN will be formed together with the added Al, resulting in slab cracks. On the other hand, since excessive manufacturing costs may be incurred to control the content to a very small amount, the lower limit of nitrogen (N) may be limited to 0.001% according to one embodiment of the present invention.
  • nitrogen (N) may contain 0.020% or less.
  • nitrogen (N) may contain 0.0010 to 0.02%.
  • nitrogen (N) may contain 0.0010 to 0.020%.
  • Titanium (Ti) combines with N remaining as an impurity in steel to create TiN, thereby protecting B from becoming a compound to ensure hardenability.
  • precipitation strengthening and grain refinement effects can be expected through the formation of TiC precipitates.
  • the content exceeds 0.1%, a large amount of coarse TiN is formed, which may deteriorate the steel material.
  • the upper limit of the content may be limited to 0.09%.
  • titanium (Ti) may contain 0.10% or less.
  • titanium (Ti) may contain 0.090% or less.
  • Boron (B) is an element that can effectively improve hardenability, and is an element that is segregated at the grain boundaries of old austenite and can suppress the embrittlement of hot-formed members due to grain boundary segregation of impurities P or S.
  • the content exceeds 0.01%, brittleness may occur during hot rolling due to the formation of Fe 23 CB 6 complex compounds.
  • the upper limit of the boron (B) content may be limited to 0.008%.
  • boron (B) may contain 0.010% or less.
  • boron (B) may contain 0.0080% or less.
  • Zr zirconium
  • Bi bismuth
  • REM rare earth elements
  • Zr zirconium
  • Bi bismuth
  • REM rare earth element
  • the base steel sheet of the present invention may contain remaining iron (Fe) and inevitable impurities in addition to the composition described above. Since unavoidable impurities may be unintentionally introduced during the normal manufacturing process, they cannot be excluded. Since these impurities are known to anyone skilled in the field of steel manufacturing, all of them are not specifically mentioned in this 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 include Si, Mg, and Fe in addition to Al, and in some cases, Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, and Sr. , Zn, etc. may be included.
  • the thickness of the plating layer is not particularly limited, and may have a plating layer thickness within a general range.
  • the plating layer contains one or two or more types selected from Si: 5-11%, Fe: 5% or less, and Mg: 5% or less, in weight percent, and the balance is Al and other impurities. may include. If necessary, the above-mentioned composition may further include elements such as Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, Sr, and Zn in a total amount of 30% or less.
  • the plating layer contains one or two or more types selected from Si: 5.0 to 11.0%, Fe: 5.0% or less, and Mg: 5.0% or less, in weight percent, and the balance is Al and other impurities. may include. If necessary, the above-mentioned composition may further include elements such as Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, Sr, and Zn in a total amount of 30.0% or less.
  • a member according to one embodiment of the present invention may include base iron and a plating layer formed on the surface of the base iron.
  • the base iron according to one aspect of the present invention may have the same alloy composition as the base steel sheet of the plated steel sheet proposed in the present invention.
  • the plating layer may be formed on at least one surface of the base iron.
  • the plating layer of the member may have an alloy composition in which the plating layer of the above-described plated steel sheet and components including Fe of the base steel sheet are diffused.
  • a member according to one embodiment of the present invention may include an antimony (Sb) enriched layer formed in the base iron.
  • Sb antimony
  • the Sb enriched layer of the present invention can be distinguished by analyzing the change in Sb content in the thickness direction of the base iron from any point of the plating layer using a glow discharge spectrometer (GDS).
  • GDS glow discharge spectrometer
  • the method for classifying the Sb enriched layer in the plated steel sheet proposed in the present invention can be applied in the same way.
  • an antimony (Sb) enriched layer may be formed directly below the interface where the base iron and the plating layer are in contact.
  • the interface between the base iron and the plating layer may mean a point where the Al content is 15%.
  • the antimony (Sb) content in the antimony (Sb) enriched layer is maximum.
  • the carbon (C) content at the depth representing the value (Sb max ) may be 80% or less of the nominal carbon content (C 0 ) of the base iron.
  • the antimony (Sb) content in the antimony (Sb) enriched layer is maximum.
  • the carbon (C) content at the depth representing the value (Sb max ) may be 80.0% or less of the nominal carbon content (C 0 ) of the base iron.
  • the carbon content at the depth where the Sb content in the Sb enriched layer reaches its maximum value (Sb max ) affects the hardness of the surface layer structure and bendability.
  • the carbon content at the depth where the Sb content reaches the maximum value (Sb max ) in the Sb enriched layer exceeds 80% of the nominal carbon content (C 0 )
  • the hardness of the surface layer may increase and the bendability may deteriorate.
  • the carbon content in the Sb enriched layer at the depth where the Sb content reaches its maximum value (Sb max ) is excessively low, there may be difficulty in securing fatigue resistance characteristics due to insufficient hardness of the surface layer. Therefore, in one embodiment of the present invention, the lower limit can be limited to 15%. In one embodiment of the present invention, the lower limit may be limited to 15.0%.
  • Figure 5 schematically shows the profile of Sb and C contents from the interface to the thickness direction in a member according to an embodiment of the present invention.
  • the x-axis of FIG. 5 may represent the depth ( ⁇ m) from the interface between the base iron and the plating layer, and the y-axis may represent the element content (wt%).
  • 80% of the nominal carbon content (C 0 ) is 0.176%.
  • the nominal carbon content (C 0 ) is 0.22%, and as previously explained, a certain thickness (depth) is analyzed using a glow discharge spectrometer (GDS) in the 1/4 to 3/4 thickness region of the base iron. can be obtained. At this time, it can be confirmed that at the depth where the Sb content reaches its maximum value, the carbon content is 80% or less of the nominal carbon content (C 0 ).
  • GDS glow discharge spectrometer
  • the member according to one embodiment of the present invention may have an R value defined in equation 1 below of 1.5 or more, and a B value defined in equation 2 below may be 0.01 or more.
  • the member according to one embodiment of the present invention may have an R value defined in equation 1 below of 1.50 or more, and a B value defined in equation 2 below may be 0.010 or more.
  • Sb max represents the maximum value of Sb content in the Sb enriched layer
  • Sb coat represents the average Sb content in the plating layer
  • ⁇ t measures Sb max from the interface between the plating layer and the base iron. It represents the straight line distance between one points, and the unit is ⁇ m.
  • the degree of Sb enrichment in the Sb enrichment layer may become more severe.
  • the Sb enriched layer effectively protects against infiltrating diffusible hydrogen, and since diffusible hydrogen promotes the occurrence of grain boundary cracks when stress occurs, bendability can be increased by reducing this. You can. That is, if the above relational equation is not satisfied, specifically, if the R value defined in relational equation 1 is less than 1.5 or the B value defined in relational equation 2 is less than 0.01, the diffusive hydrogen penetrating during hot forming is not sufficiently protected. There is a risk that crash resistance will be deteriorated.
  • the R value defined in Equation 1 may be 1.7 or more.
  • the B value defined in Equation 2 may be 0.014 or more.
  • the upper limit of the R value may be limited to 6.4.
  • the upper limit of the B value may be limited to 0.5.
  • the R value defined in Equation 1 may be 1.70 or more. Additionally, in one embodiment of the present invention, the B value defined in Equation 2 may be 0.0140 or more. In one embodiment of the present invention, the upper limit of the R value may be limited to 6.40. Additionally, in one embodiment of the present invention, the upper limit of the B value may be limited to 0.50.
  • the member according to one aspect of the present invention may have a softening rate ( ⁇ ) of 2 to 7% in a region with a depth of 45 to 100 ⁇ m in the thickness direction from the interface between the base iron and the plating layer.
  • An area with a depth of 45 to 100 ⁇ m in the thickness direction from the interface between the base iron and the plating layer affects the hardness of the surface layer of the member and may affect bendability.
  • the softening rate in the area from 45 to 100 ⁇ m in the thickness direction is less than 2%, the hardness of the surface layer may become too high, which may reduce the effect of improving bendability. On the other hand, if the softening rate exceeds 7%, the hardness of the surface layer becomes too low, which may cause the problem of deterioration in fatigue resistance properties.
  • the hardness softening rate can be measured as shown in Figure 6.
  • Figure 6 schematically shows the hardness softening rate ( ⁇ ) profile at a depth of 45 to 100 ⁇ m in the thickness direction from the interface in a member according to an embodiment of the present invention.
  • Vickers Hardness is measured and hardness is measured by applying a weight of 1 kg.
  • the hardness inside the base iron is taken as the standard hardness (H O ), and at this time, the standard hardness (H O ) can be measured at 1/5 of the thickness of the base iron.
  • the y-axis represents the ratio (%) of the hardness value (H) at the corresponding position to the reference hardness value (H 0 ), and the x-axis represents the distance ( ⁇ m) from the interface in the thickness direction.
  • a rectangle was 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 representing the ratio of hardness values according to the depth from the interface is shown, and the ratio of the area of the upper area within the rectangle of the hardness profile to the total area of the rectangle is defined as the hardness softening rate ( ⁇ , %). can do.
  • the hardness profile is determined at a depth of 45 to 100 ⁇ m. It was created and used for the hardness softening rate ( ⁇ ).
  • the hardness softening rate ( ⁇ ) of the present invention is the distance ( ⁇ m) in the thickness (depth) direction from the interface between the base steel sheet and the plating layer as the abscissa, and the hardness value at the corresponding position with respect to the reference hardness value (H 0 ).
  • the ratio (%) of (H) as the vertical axis it means the ratio (%) of the area above the hardness profile curve to the total area of the rectangle.
  • the member according to one aspect of the present invention may have a softening rate ( ⁇ ) of 2.0 to 7.0% in a region with a depth of 45.0 to 100.0 ⁇ m in the thickness direction from the interface between the base iron and the plating layer.
  • the member may include less than 5 area% of ferrite as a microstructure in a region from the interface between the base iron and the plating layer to a depth of 50 ⁇ m in the thickness direction.
  • Ferrite in an area up to a depth of 50 ⁇ m in the thickness direction from the interface between the base iron and the plating layer may cause the propagation of cracks.
  • ferrite is more than 5% in the corresponding area, when stress occurs in the surface layer, local stress is concentrated on the relatively soft ferrite, which promotes crack propagation, which may deteriorate bendability and fatigue resistance.
  • the member according to one embodiment of the present invention has martensite as the main phase in the area from the interface between the base iron and the plating layer to a depth of 50 ⁇ m in the thickness direction, and contains less than 5 area% of ferrite and the remaining upper and lower bainite. You can have an organization.
  • a phase having an area fraction of 50% or more of the total microstructure fraction can be regarded as the main phase.
  • the physical properties desired in the present invention may be insufficient.
  • the member may include less than 5.0 area% of ferrite as a microstructure in a region from the interface between the base iron and the plating layer to a depth of 50.0 ⁇ m in the thickness direction.
  • the member according to one embodiment of the present invention includes martensite as the main phase in the area from the interface between the base iron and the plating layer to a depth of 50.0 ⁇ m in the thickness direction, less than 5.0 area% of ferrite, and the remaining upper and lower bainite. It may have a fine structure.
  • a phase having an area fraction of 50.0% or more in the total microstructure fraction can be regarded as the main phase.
  • the plated steel sheet according to one aspect of the present invention can be manufactured by annealing and plating a cold rolled steel sheet satisfying the above-described alloy composition.
  • the cold rolled steel sheet can be manufactured by reheating, hot rolling, coiling, cooling, and cold rolling a steel slab that satisfies the above-described alloy composition.
  • Steel slabs satisfying the alloy composition according to one embodiment of the present invention can be reheated to a temperature range of 1050 to 1300°C.
  • the reheating temperature is less than 1050°C, the slab structure is not sufficiently homogenized, so it may be difficult to re-employ when using precipitated elements.
  • the temperature exceeds 1300°C, an excessive oxidation layer is formed, which increases manufacturing costs for removing the oxide layer and is likely to cause surface defects after hot rolling.
  • the reheated steel slab can be finish rolled at a temperature range of 800 to 950°C.
  • finish rolling temperature is less than 800°C, biphasic rolling occurs, ferrite is introduced into the surface layer of the steel sheet, and plate shape control may be difficult. On the other hand, if the temperature exceeds 950°C, grain coarsening may occur.
  • the rolled steel can be coiled and cooled in a temperature range of 500 to 700°C.
  • the coiling temperature is less than 500°C, tension may become excessively high during coiling, which may cause defects in the width shape of the hot rolled coil and equipment problems.
  • the temperature exceeds 700°C, coarse carbides are excessively formed and crack generation is promoted when stress is generated in the hot-formed member, which may lead to a problem of reduced collision resistance.
  • a cold rolled steel sheet can be manufactured by cold rolling the cooled steel at a reduction ratio of 30 to 80%.
  • the cold rolling reduction rate is not specifically limited, but may be implemented within the range of 30 to 80% to obtain a predetermined target thickness.
  • the cold rolled steel sheet can be annealed in a temperature range of Ac 1 to Ac 3 .
  • the annealing temperature is less than Ac 1 , recrystallization of the cold rolled structure is not sufficiently completed, so the plate shape may be poor, and antimony may not be sufficiently concentrated, making it difficult to fully demonstrate the effect of the invention in the final member.
  • the temperature exceeds Ac 3 , it may cause equipment problems in the annealing furnace and cause defects on the surface due to acceleration of surface oxide formation.
  • the lower limit of the annealing temperature may be 750°C.
  • the upper limit of the annealing temperature may be limited to 860°C.
  • the product of the annealing time and absolute humidity may be 10,000 to 80,000 s ⁇ g/m 3 .
  • the atmosphere and humidity can be adjusted using hydrogen gas, hydrogen-nitrogen mixed gas, etc. to create an oxidizing atmosphere, and the annealing time in the temperature range of Ac 1 to Ac 3 is used to obtain an appropriate decarburization rate of the steel sheet. and it is important to control absolute humidity.
  • 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 .
  • the average temperature increase rate from room temperature to 500°C is 2.7 ⁇ 10.0°C/s
  • the average temperature increase rate between 500°C and 700°C is 0.5 ⁇ 2.5°C/s
  • the annealing temperature at 700°C The average temperature increase rate can be controlled to 0.01 ⁇ 0.4°C/s.
  • the average temperature increase rate from room temperature to 500°C is limited to 2.7 ⁇ 10.0°C/s to secure the Sb enriched layer. If the average temperature increase rate from room temperature to 500°C exceeds 2.7 to 10.0°C/s, specifically, if it is less than 2.7°C/s, there is a problem in which the concentrated layer is not sufficiently formed, and if it exceeds 10°C/s, Due to rapid heating, the temperature unevenness in the width direction of the steel sheet increases, which can lead to tissue differences and line trouble problems. In the section where the surface temperature of the steel plate is 500 ⁇ 700°C, Sb enrichment of base iron may be affected.
  • the temperature at which a Sb-enriched layer is sufficiently formed in the base iron is from 700°C to the desired annealing temperature of the steel sheet.
  • the average temperature increase rate is 0.01 ⁇ . It is preferably 0.4°C/s.
  • the annealed cold rolled steel sheet can be plated.
  • the plating bath according to one aspect of the present invention may be aluminum or an aluminum-based alloy.
  • the plating bath composition may include Si, Mg, and Fe in addition to Al, and in some cases, Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, Sr, It may also contain Zn and the like.
  • the adhesion amount is not particularly limited and may be within a general range.
  • the composition of the plating bath in weight percent, includes one or two or more selected from among Si: 5-11%, Fe: 5% or less, and Mg: 5% or less, with the balance being Al. and other impurities.
  • an alloying process may be included after plating, and the alloying process is not particularly limited and can be performed under normal conditions.
  • the member according to one aspect of the present invention can be manufactured by manufacturing, heating, maintaining, forming, and cooling the plated steel sheet manufactured by the above-described method into a blank.
  • the plated steel sheet proposed in the present invention can be manufactured as a blank for hot forming.
  • the prepared blank can be heated to a temperature range of Ac 3 to 975°C and maintained for 10 to 1000 seconds.
  • the blank heating temperature is less than Ac 3 , it may be difficult to secure strength and collision resistance due to the presence of untransformed ferrite in the ideal region.
  • the heating temperature exceeds 975°C, excessive oxides are generated on the surface of the member, making it difficult to secure spot weldability and manufacturing costs for maintaining the high temperature may increase.
  • the subsequently heated blank has a heat treatment residence time of 10 to 1000 seconds in the above temperature range. If the holding time is less than 10 seconds, it is difficult to achieve uniform temperature distribution throughout the blank, which may cause material deviation by location.
  • the holding time exceeds 1000 seconds, as when the heating temperature is exceeded, excessive oxide is generated on the surface of the member and an interdiffusion layer grows excessively, which not only makes it difficult to secure spot weldability but also causes an increase in the manufacturing cost of the member.
  • the heated blank can be molded and cooled.
  • the final member can be manufactured by transferring the heated blank to a press and performing hot forming and die quenching at a cooling rate of 20°C/s or more. At a cooling rate of less than 20°C/s, a ferrite phase may be introduced during cooling and formed at grain boundaries, which may deteriorate strength and collision resistance. According to one embodiment of the present invention, after forming the blank, it can be cooled to 25°C/s or more.
  • the coated steel sheet of the present invention manufactured in this way can maintain the surface hardness below a certain level and can maintain the blade life above a certain level when shearing for producing a blank for hot forming, thereby reducing the cost. It works.
  • the member of the present invention manufactured in this way has a product of tensile strength and bending angle of 80,000 MPa ⁇ ° or more, a diffusible hydrogen content of 0.2 ppm or less, and can have excellent fatigue resistance and bending properties.
  • tensile strength (TS) * bending angle (BA) was used as an indicator for measuring collision resistance.
  • the bending angle which is an indicator of crash resistance, is influenced by tensile strength, which tends to be inversely proportional. Therefore, as the product of tensile strength and bending angle (TS*BA) increases, crash resistance increases.
  • the BA value can be measured through bendability evaluation according to the VDA238-100 standard, and is expressed as the bending outer angle converted from the maximum bending strength.
  • a 40 mm thick slab containing Sb in the content shown in Table 1 below and having the composition of 0.22C-0.25Si-1.25Mn-0.2Cr-0.03Al-0.03Ti-0.0025B was manufactured by vacuum melting.
  • the slab was heated to 1200°C and held for 1 hour, then hot rolled at a hot rolling end temperature of 900°C and coiled at a temperature of 600°C. Afterwards, a pickling process was performed, and cold rolling was performed at a reduction ratio of 30 to 80% to manufacture cold rolled steel sheets.
  • the cold-rolled steel sheet was annealed at a temperature of Ac 1 to Ac 3 , but the annealing time (s) and absolute humidity (g/m 3 ) were adjusted, and the resulting value of the product of annealing time and absolute humidity is shown in Table 1.
  • plating was performed by immersing the steel sheet in a plating bath consisting of Al-9%Si-2%Fe and trace amounts of impurities.
  • Table 2 below shows the Sb enriched layer, microstructure, and decarburization rate of the manufactured plated steel sheet.
  • SEM scanning electron microscopy
  • the remaining fractions were observed to be ferrite.
  • GDS850A model name, manufactured by LECO
  • DC and RF equipment were used to measure the carbon decarburization rate in an area from the interface to a depth of 30 ⁇ m in the thickness direction of the base steel plate, and the decarburization rate ( ⁇ ) was determined through the carbon profile obtained through the equipment. ) and the depth according to the ratio of carbon content are shown in Table 2 below.
  • Sb max represents the maximum value of Sb content in the Sb enriched layer
  • Sb coat represents the average Sb content in the plating layer
  • ⁇ t measures Sb max from the interface between the plating layer and the base steel sheet. It represents the straight line distance between one points, and the unit is ⁇ m.
  • a member was manufactured by hot forming using a plated steel sheet in which no unplated area was observed.
  • the heat treatment temperature and time for hot forming were 900°C and 360 seconds, and the transfer time from the heat treatment furnace to the forming press was 10 seconds.
  • Table 3 shows the structure and properties of the member manufactured through hot forming, measured in the same manner as described above.
  • Vickers hardness was measured by applying a load of 1.0 kg at a depth of 45 to 100 ⁇ m from the interface between the plating layer of the member and the base iron, and the hardness softening rate ( ⁇ ) was recorded using FIG. 6 and the method described above.
  • the amount of diffusible hydrogen was measured using TDA equipment (Thermal Desorption Analysis) (Bruker G8; model name). Specifically, the temperature was raised to 400°C at a rate of 20°C/min, and the diffusion hydrogen curve was measured by maintaining it for a certain period of time so that the diffusible hydrogen peak sufficiently appeared. This curve was integrated to determine diffusion in the steel. The amount of sexual hydrogen was obtained.
  • the ferrite area fraction within a depth of 30 ⁇ m from the interface between the base iron and the plating layer was measured using optical microscopy and is shown in Table 3. At this time, all specimens were observed to be martensite except for the ferrite area fraction.
  • more than 10,000,000 repetitive fatigue tests were performed to measure the measured fatigue limit strength. If the fatigue limit strength divided by the tensile strength is 0.25 or more, it is O, and if it is less than 0.25, it is X. Fatigue resistance characteristics were confirmed by marking.
  • crash resistance characteristics were expressed as the product of tensile strength and bending angle, and the tensile strength value was measured through a room temperature tensile test in accordance with the ISO6892 standard using a JIS-5 specimen.
  • the bending angle was recorded as the bending outer angle converted from the maximum bending strength specified in the standard according to the bendability evaluation method according to the VDA238-100 standard.
  • Sb max represents the maximum value of Sb content in the Sb enriched layer
  • Sb coat represents the average Sb content in the plating layer
  • ⁇ t measures Sb max from the interface between the plating layer and the base iron. It represents the straight line distance between one points, and the unit is ⁇ m.
  • Comparative Examples 1 and 2 were cases in which the product of annealing time and absolute humidity during annealing was below the range suggested by the present invention, and the decarburization rate of the coated steel sheet was outside the suggested range. As a result, the hardness softening rate of the member decreased, and the collision resistance deteriorated due to excessive carbon concentration in the surface layer.
  • Figure 7 shows a carbon profile in a plated steel sheet according to an embodiment of the present invention.
  • Invention Examples 1 and 3 of Figure 7 confirm that the decarburization control proposed in the present invention was sufficiently achieved, and as a result, the product of tensile strength and bending angle and fatigue resistance characteristics above a certain level were secured. On the other hand, it can be confirmed that in Comparative Example 1, decarburization according to depth was not sufficiently achieved, and in Comparative Example 3, excessive decarburization occurred due to insufficient production of the Sb enriched layer, resulting in inferior physical properties.
  • Figure 8 is a photograph of the structure directly below the interface of the plated steel sheets of Inventive Example 3 and Comparative Example 3 according to an embodiment of the present invention observed with an SEM. In the case of Inventive Example 3, 2.9% of pearlite was observed, but in the case of Comparative Example 3, it can be confirmed that less than 1% of pearlite was observed.
  • Figure 9 is an optical photograph of the interface between the plating layer and the base iron in the members of Inventive Example 3 and Comparative Example 3 of the present invention.
  • ferrite was observed to be less than 1%, but in Comparative Example 3, the ferrite content was 7.3%, which did not ensure the fatigue resistance desired in the present invention.
  • Comparative Example 4 the product of the Sb content in the steel, annealing time, and absolute humidity is outside the range proposed by the present invention, and the amount of diffusible hydrogen in the member is excessive, deteriorating bendability, and tensile strength, which is an index of collision resistance, The product value of the bending angle did not reach the desired level.

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

Abstract

La présente invention concerne une tôle d'acier plaquée pour formage à la presse à chaud, une pièce formée par pressage à chaud, et des procédés de fabrication de celle-ci et, plus spécifiquement, une tôle d'acier plaquée pour formage à la presse à chaud ayant une excellente résistance aux chocs, une pièce formée par pressage à chaud et des procédés de fabrication de celle-ci.
PCT/KR2023/012157 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 WO2024043608A1 (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
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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

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KR20210098514A (ko) * 2018-12-11 2021-08-10 닛폰세이테츠 가부시키가이샤 성형성 및 내충격성이 우수한 고강도 강판, 및 성형성 및 내충격성이 우수한 고강도 강판의 제조 방법
KR20220062962A (ko) * 2020-11-09 2022-05-17 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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JP6296805B2 (ja) 2014-01-23 2018-03-20 Ａｉ Ｔｅｃｈｎｏｌｏｇｙ株式会社 検知装置

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Publication number Priority date Publication date Assignee Title
JP2004250767A (ja) * 2003-02-21 2004-09-09 Nippon Steel Corp 冷間加工性に優れた機械構造用鋼及びその製造方法
KR20150074951A (ko) * 2013-12-24 2015-07-02 주식회사 포스코 열간성형용 냉연강판, 이를 이용한 열간성형 부재 및 이들의 제조방법
KR101858868B1 (ko) * 2016-12-23 2018-05-16 주식회사 포스코 충격특성이 우수한 열간성형용 도금강판, 열간성형 부재 및 그들의 제조방법
KR20210098514A (ko) * 2018-12-11 2021-08-10 닛폰세이테츠 가부시키가이샤 성형성 및 내충격성이 우수한 고강도 강판, 및 성형성 및 내충격성이 우수한 고강도 강판의 제조 방법
KR20220062962A (ko) * 2020-11-09 2022-05-17 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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