WO2016047058A1 - Method of manufacturing hot press-formed product, and hot press-formed product - Google Patents

Method of manufacturing hot press-formed product, and hot press-formed product Download PDF

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Publication number
WO2016047058A1
WO2016047058A1 PCT/JP2015/004533 JP2015004533W WO2016047058A1 WO 2016047058 A1 WO2016047058 A1 WO 2016047058A1 JP 2015004533 W JP2015004533 W JP 2015004533W WO 2016047058 A1 WO2016047058 A1 WO 2016047058A1
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Prior art keywords
steel sheet
press
cooling
treated steel
hot press
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PCT/JP2015/004533
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French (fr)
Japanese (ja)
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WO2016047058A8 (en
Inventor
達也 中垣内
裕一 時田
簑手　徹
玉井　良清
Original Assignee
Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to EP15843885.3A priority Critical patent/EP3199257B1/en
Priority to KR1020177005467A priority patent/KR20170036086A/en
Priority to CN201580049874.9A priority patent/CN106714996B/en
Priority to US15/502,614 priority patent/US20170225215A1/en
Priority to MX2017003875A priority patent/MX2017003875A/en
Publication of WO2016047058A1 publication Critical patent/WO2016047058A1/en
Publication of WO2016047058A8 publication Critical patent/WO2016047058A8/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • B21D22/208—Deep-drawing by heating the blank or deep-drawing associated with heat treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • B21D22/201—Work-pieces; preparation of the work-pieces, e.g. lubricating, coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D24/00—Special deep-drawing arrangements in, or in connection with, presses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/16—Heating or cooling
    • 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
    • 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
    • C22C18/00—Alloys based on zinc
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—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
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
    • 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
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F17/00—Multi-step processes for surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by subclass C21D or C22F or class C25
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/56—Electroplating: Baths therefor from solutions of alloys
    • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces

Definitions

  • the present invention relates to a hot press-formed product and a method for producing the same, and in particular, when press-forming a pre-heated surface-treated steel sheet, it is possible to obtain a predetermined strength (tensile strength: 1180 MPa class or more) by quenching simultaneously with shape formation.
  • the present invention relates to a method for producing a hot press-formed product.
  • the present invention also relates to a hot press-formed product manufactured according to the above-described method for manufacturing a hot press-formed product.
  • Patent Document 1 discloses that when a blank plate (steel plate) heated to an austenite single phase region around 900 ° C. is subjected to hot press forming to produce a member having a predetermined shape, There has been proposed a technique for increasing the strength of a member by quenching.
  • Patent Document 1 Although excellent corrosion resistance is required for the undercarriage member and the vehicle body structural member of an automobile, the technology proposed in Patent Document 1 does not provide a rust preventive film such as a plating layer on the material steel plate. For this reason, the hot press-formed member obtained according to this technique has insufficient corrosion resistance.
  • a hot press molding technique that can suppress the formation of oxide scale during heating before hot press molding and can improve the corrosion resistance of members after hot press molding.
  • a surface-treated steel sheet provided with a coating such as a plating layer on the surface and a hot press forming method using the surface-treated steel sheet have been proposed.
  • a steel sheet coated with Zn or a Zn base alloy is heated to 700 to 1200 ° C. and then hot pressed to form a Zn—Fe base compound or a Zn—Fe—Al base on the surface.
  • a technique for forming a hot press-formed member provided with a compound has been proposed.
  • Patent Document 2 by using a steel sheet coated with Zn or a Zn base alloy, it becomes possible to suppress the oxidation of the steel sheet surface, which becomes a problem during heating before hot press forming, and has excellent corrosion resistance. Further, it is described that a hot press-formed member is obtained.
  • Patent Document 3 a surface-treated steel sheet in which a Zn-Fe-based plating layer is formed on the surface of the base steel sheet, the surface-treated steel sheet is brought to a temperature not lower than the Ac 1 transformation point of the base steel sheet and not higher than 950 ° C.
  • a method of starting press forming after heating and cooling the surface-treated steel sheet to a temperature below the freezing point of the plating layer has been proposed.
  • Patent Document 3 describes that liquid metal embrittlement cracking can be suppressed by starting press forming after cooling the surface-treated steel sheet to a temperature below the freezing point of the plating layer.
  • liquid metal embrittlement cracking occurs, that is, occurs on the surface of a hot press-formed member, and the depth from the plating layer-base steel plate (base metal) interface to the inside of the base steel plate is 100 ⁇ m. It is considered that cracks in which Zn is detected at the interface of the cracked portion (hereinafter referred to as “macro crack”) can be suppressed.
  • macro crack cracks in which Zn is detected at the interface of the cracked portion
  • the present inventors examined the use of Zn—Ni alloy plating containing about 9 to 25% Ni in Zn as a high melting point plating layer. In order to ensure the corrosion resistance of Zn-Ni alloy plating, it is necessary to use Zn-Ni alloy as the ⁇ phase.
  • the ⁇ phase present in the equilibrium diagram of the Zn-Ni alloy has a melting point of 860 ° C or higher and becomes a normal Zn-based plating layer. It is very high compared to the above, and the occurrence of macro cracks can be suppressed even under normal pressing conditions.
  • the depth from the plating layer-base steel plate interface to the base steel plate inside is not more than about 30 ⁇ m instead of the macro cracks described above, and Zn is present at the crack interface. It is known that microcracks that are not detected occur.
  • This microcrack is called a microcrack, penetrates the plating layer-base steel plate interface and reaches the inside of the base steel plate, and adversely affects various properties (such as fatigue resistance) of the hot press-formed member.
  • macro cracks also occur in a portion where only tensile strain occurs, such as the punch contact side of the die shoulder R portion.
  • microcracks do not occur in such portions, but occur in places where tensile strain is applied after (bending) compression (bending back) as in the die contact side of the vertical wall. For this reason, it is guessed that the generation mechanism differs between a macro crack and a micro crack.
  • the present invention has been made to solve such a problem.
  • a hot-pressed product is manufactured by hot-pressing a surface-treated steel sheet on which a Zn-Ni-based plating layer has been formed, It aims at providing the manufacturing method of the hot press-molded article which suppresses generation
  • an object of the present invention is to provide a hot press-formed product manufactured according to the above-described method for manufacturing a hot press-formed product.
  • microcracks which are problematic when hot-pressing a Zn-based plated steel sheet.
  • the generation mechanism of microcracks is not clear, but microcracks are generated on the surface of plated steel sheets by press-forming Zn-based plated steel sheets at a high temperature below the freezing point of plating.
  • similar microcracking occurs when a Zn-Ni plated steel sheet is press-formed.
  • the micro crack is a micro crack having a depth of about 30 ⁇ m from the plating layer-base steel plate interface and penetrates through the plating layer-base steel plate interface to the inside of the base steel plate.
  • micro-cracks do not occur only by simple tension, compression deformation and bending deformation, but micro-cracks occur in the portion subjected to bending-bending unbending deformation, where the once bent portion is stretched again.
  • the processing as described above may be limited to a specific portion, but depending on the shape of the molded product, the portion subjected to processing that generates microcracks may be widely spread on the steel sheet.
  • the surface-treated steel sheet is 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher.
  • the reason why the shape accuracy defect is suppressed by cooling with the cooling mold is considered as follows. That is, as a typical defective shape accuracy of the hat-shaped member, the angle change between the two surfaces sandwiching the bending ridge line is larger than the mold angle, and the surface of the vertical wall portion has a curvature. Wall warping that becomes. These are all caused by the difference in stress distribution in the thickness direction, and the higher the flow stress of the steel sheet during processing, the greater the difference in stress distribution and the lower the shape accuracy. That is, in hot press forming, the lower the press forming temperature, the higher the flow stress during press forming of the steel sheet and the lower the shape accuracy.
  • the temperature of the steel sheet at the time of press forming is lowered by cooling and the shape accuracy is lowered, it is cooled to a temperature of 550 ° C or lower and 410 ° C or higher at a cooling rate of 100 ° C / s or higher, within 5 seconds after cooling, and
  • a cooling rate 100 ° C / s or higher
  • press forming was started within the range where the steel plate temperature was 550 ° C. or lower and 400 ° C. or higher, almost no decrease in shape accuracy was observed.
  • the reason for this is that when the heated steel sheet is quenched with a cooling die and the steel sheet temperature is press-formed within a range of 550 ° C. or lower and 400 ° C. or higher, the steel sheet structure at the time of press forming is austenite.
  • a method for producing a hot press-formed product in which a hot-pressed product is produced by subjecting a surface-treated steel sheet having a Zn-Ni plating layer formed on the surface of a base steel plate to hot press, Heating the surface-treated steel sheet to a temperature range of 1000 ° C. or less above the Ac 3 transformation point;
  • the surface-treated steel sheet is 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher. Cooling to temperature, Within 5 seconds after the cooling, and the temperature of the surface-treated steel sheet is within a range of 550 ° C.
  • press molding of the surface-treated steel sheet is started using a press molding die to obtain a molded body Process
  • a method of manufacturing a hot press-molded product comprising: holding the molded body at a bottom dead center while being sandwiched between the press-molding dies, and quenching the molded body to obtain a hot press-molded product.
  • microcracks do not occur on the entire front and back surfaces, the hardness of the molded product is sufficient, there is no significant increase in molding load, and there is no problem with shape freezing properties. Since a hot press-formed product can be obtained, it becomes possible to manufacture automobile parts and the like having various product shapes using a high-strength surface-treated steel sheet.
  • the method for producing a hot press-formed product according to an embodiment of the present invention is performed by hot-pressing a surface-treated steel sheet 1 having a Zn-Ni plating layer formed on the surface of a base steel sheet as shown in FIG.
  • a method for producing a hot press-formed product for producing an intermediate press-formed product comprising a heating step (not shown) for heating the surface-treated steel sheet 1 to a temperature range not lower than the Ac 3 transformation point and not higher than 1000 ° C.
  • the cooling process (S1) for cooling to the surface, and the press of the surface-treated steel sheet 1 using the press mold 11 within 5 seconds after the cooling and the temperature of the surface-treated steel sheet 1 is in the range of 550 ° C. or lower and 400 ° C. or higher.
  • the material of the hot press-formed product, the heating step, the cooling step (S1), the press forming step (S2), and the quenching step (S3) will be described in detail.
  • a surface-treated steel sheet in which a Zn—Ni plating layer is provided on the surface of the base steel sheet is used.
  • the method for forming the Zn—Ni plating layer on the surface of the base steel plate is not particularly limited, and any method such as hot dipping or electroplating may be used.
  • the amount of plating is preferably 10 g / m 2 or more and 90 g / m 2 or less per side.
  • the Ni content in the plating layer is preferably 9% by mass or more and 25% by mass or less.
  • the surface-treated steel sheet 1 is heated to a temperature range from the Ac 3 transformation point to 1000 ° C.
  • the heating temperature of the surface-treated steel sheet 1 is lower than the Ac 3 transformation point, an adequate amount of austenite cannot be obtained during heating, and sufficient strength is obtained after hot press forming due to the presence of ferrite during press forming. It is difficult to ensure good shape freezing property.
  • the heating temperature of the surface-treated steel sheet 1 exceeds 1000 ° C., the oxidation resistance and the corrosion resistance of the hot press-formed product are deteriorated due to evaporation of the plating layer and excessive generation of oxide at the surface layer portion. Therefore, the heating temperature is set to the Ac 3 transformation point or higher and 1000 ° C. or lower.
  • the heating method of the surface-treated steel sheet 1 is not particularly limited, and any method such as heating with an electric furnace, an induction heating furnace, or a direct current heating furnace may be used.
  • the cooling step (S1) is a step in which the heated surface-treated steel sheet 1 is sandwiched between cooling dies 3 and cooled to a temperature of 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher.
  • the cooling mold 3 includes an upper mold 5 and a lower mold 7 whose contact surfaces with the surface-treated steel sheet 1 are flat, and the lower mold 7 is extended and contracted.
  • a lifter pin 9 of the type is installed. The heated surface-treated steel sheet 1 is placed on the lifter pin 9 and then cooled by being sandwiched between the upper mold 5 and the lower mold 7.
  • the heated surface-treated steel sheet 1 is sandwiched between the cooling molds 3, basically, the entire surface of the surface-treated steel sheet 1 is sandwiched between the cooling molds 3 as shown in FIG. However, the portion that is trimmed before the final product may be protruded from the cooling mold 3. Thereby, even if the part that undergoes processing that generates microcracks, that is, the part that undergoes bending-bending unreformation extends widely to the surface-treated steel sheet 1 that is the workpiece, the final press forming is obtained. It is possible to suppress the occurrence of microcracks over the entire front and back surfaces of the product.
  • the timing for sandwiching the heated surface-treated steel sheet 1 with the cooling mold 3 is preferably set to 800 ° C.
  • the temperature it is preferable to set the temperature to 670 ° C. or higher. Further, the cooling mold 3 may be pressed against one side surface of the surface-treated steel sheet 1 to be cooled.
  • FIG. 2 is a schematic diagram showing the relationship between a general metal structure, temperature, and cooling time when hot pressing a steel sheet using a press mold.
  • FIG. 2A shows a case where the press molding start temperature is high. In this case, after the press molding is started, the mold is rapidly cooled by heat removal from the mold to form a martensite single phase structure.
  • FIG. 2B when the press molding start temperature is low, ferrite and bainite are generated before the press molding starts, and the strength of the press molded product after press molding is lowered.
  • the reason why the cooling stop temperature in this cooling step is set to 550 ° C. or less is that if it exceeds 550 ° C., cooling becomes insufficient and micro cracks are generated after hot press forming. Preferably it is 500 degrees C or less.
  • the lower limit of the cooling stop temperature is set to 410 ° C., if the temperature is lower than 410 ° C., the surface-treated steel sheet 1 is excessively cooled before press forming, and the shape freezing property after press forming is lowered. Preferably it is 430 ° C or more.
  • the cooling rate and cooling stop temperature in this cooling step can be controlled by, for example, the time that the surface-treated steel sheet 1 is held by the cooling mold 3 (see FIG. 1).
  • the temperature change of the surface-treated steel sheet 1 by sandwiching the surface-treated steel sheet 1 with the cooling mold 3 is measured by inserting a 0.5 mm ⁇ sheath thermocouple 19 into the steel sheet shown in FIG. Can be obtained.
  • FIG. 5 is a graph showing an example of the result.
  • the vertical axis represents temperature (° C.) and the horizontal axis represents time (s).
  • FIG. 6 is a graph showing an enlarged horizontal axis of a portion surrounded by a broken line in FIG. As shown in FIG. 6, the temperature change during cooling by the cooling mold is about 160 ° C./s, and it can be seen that rapid cooling is possible.
  • a press-molded product was manufactured by changing the holding time in the cooling mold (particularly the cooling stop temperature by the cooling mold) and the press-molding start temperature described later in various ways.
  • evaluation items observe the cross section of the vertical wall of the press-molded product to confirm the presence or absence of microcracks, confirm the hardness of the molded product, confirm the press-molding load, and open the hat of the molded product.
  • the shape freezing property is confirmed by confirming the opening amount of the part (the difference between the width dimension of the opening part released after molding and the width of the molded product in the mold shape).
  • FIG. 7 shows the side of the vertical wall portion of the press-molded product in contact with the die 13 when the cooling time in the cooling die (cooling stop temperature by the cooling die) and the press molding start temperature are variously changed. It is a SEM image of a section of a surface layer. From FIG. 7, it can be seen that when the cooling time in the cooling mold is 0.9 s or more (press forming start temperature 550 ° C. or less), microcracks are not recognized in the base steel sheet. Moreover, it was confirmed that Hv> 450 under all conditions and there was no deterioration in hardenability.
  • FIG. 8 is a diagram showing the relationship between the press molding start temperature and the press molding load, where the vertical axis represents the press molding load (kN) and the horizontal axis represents the press molding start temperature (° C.).
  • the press molding load increases as the press molding start temperature decreases due to cooling in the cooling mold before press molding, but mild steel (at a temperature of about 550 ° C. at which generation of microcracks is eliminated. 270D, cold draw forming), which is equivalent to the press forming load.
  • FIG. 9 is a diagram showing the relationship between the press molding start temperature and the opening amount, where the vertical axis represents the opening amount (mm) of the molded product, and the horizontal axis represents the press molding start temperature (° C.).
  • the amount of opening increases as the press molding start temperature decreases due to cooling in the cooling mold before press molding, and the shape freezeability tends to decrease. There is almost no decrease in shape freezing property until the molding start temperature is 400 ° C.
  • the surface-treated steel sheet is cooled to a temperature of 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher.
  • the press forming step (S2) is a step of press forming the surface-treated steel sheet 1 into a product shape.
  • the press molding process is performed by the press molding die 11 after the cooling process.
  • the press molding die 11 includes a die 13 and a punch 17 as shown in FIG. Then, press-molding is performed by sandwiching the surface-treated steel sheet 1 between the die 13 and the punch 17 to obtain a molded body 1 ′.
  • the surface-treated steel sheet 1 is cooled to a temperature of 550 ° C. or lower and 410 ° C. or higher using the cooling die 3 at a cooling rate of 100 ° C./s or higher.
  • press forming with sufficient hardness and shape freezing property without increasing micro-cracking without increasing the press forming load.
  • the product can be manufactured.
  • the press molding process starts within 5 seconds after the cooling process. If the time until the press molding starts after cooling exceeds 5 seconds, ferrite, bainite, etc. are generated before the press molding starts.
  • the time until the start of press molding after cooling is preferably within 3 seconds.
  • the lower limit is not particularly limited, but it is usually preferably 1 second or longer.
  • the press molding method is not particularly limited. As shown in FIG. 10 (a), draw forming is performed with the die 13 and the blank holder 15 sandwiching the surface-treated steel sheet 1, or is the blank holder 15 lowered as shown in FIG. 10 (b)? Alternatively, it is possible to perform foam molding that performs molding without using the blank holder 15. From the viewpoint of suppressing microcracks, foam molding is preferable because the degree of processing of the vertical wall portion of the press-molded product is small.
  • the quenching step (S3) is a step of obtaining a hot press-molded product by holding the molded body 1 'while being sandwiched between the press-molding dies 11 and then quenching the molded body 1'.
  • the slide is stopped at the bottom dead center of the molding after the press molding.
  • the stop time varies depending on the amount of heat removed by the mold, but is preferably 3 seconds or more.
  • the upper limit of the stop time is not particularly limited, but is preferably 20 seconds or less from the viewpoint of productivity.
  • the hot-rolled steel sheet or the cold-rolled steel having a composition composed of Fe and inevitable impurities as the balance A steel plate can be used.
  • this component composition is demonstrated.
  • “%” indicating the content of a component means “% by mass” unless otherwise specified.
  • ⁇ C 0.15% to 0.50% ⁇ C is an element for improving the strength of the steel, and the amount is preferably 0.15% or more in order to increase the strength of the hot press-formed product.
  • the C content is preferably 0.15% or more and 0.50% or less, and more preferably 0.20% or more and 0.40% or less.
  • Si 0.05% or more and 2.00% or less
  • Si is an element that improves the strength of steel, and the amount is preferably 0.05% or more in order to increase the strength of a hot press-formed product.
  • the Si content is preferably 0.05% or more and 2.00% or less, and more preferably 0.10% or more and 1.50% or less.
  • Mn is an element that enhances the hardenability of steel, and is an effective element for improving the hardenability by suppressing the ferrite transformation of the base steel sheet during the cooling process after hot press forming. Further, Mn is an element effective for lowering the heating temperature of the surface-treated steel sheet 1 before hot press forming because it has an action of lowering the Ac 3 transformation point. In order to exhibit such an effect, the Mn content is preferably 0.50% or more. On the other hand, when the amount of Mn exceeds 3.00%, Mn is segregated and the uniformity of the properties of the base steel sheet and the hot press-formed member decreases. Therefore, the Mn content is preferably 0.50% or more and 3.00% or less, and more preferably 0.75% or more and 2.50% or less.
  • the P content is preferably 0.10% or less, and more preferably 0.01% or less.
  • P is preferably 0.003% or more.
  • S is an element that combines with Mn to form coarse sulfides and causes a reduction in the ductility of the steel. Therefore, it is preferable to reduce the S content as much as possible, but it is acceptable up to 0.050%. Therefore, the S content is preferably 0.050% or less, and more preferably 0.010% or less. However, excessive S reduction leads to an increase in desulfurization cost in the steel making process. Therefore, S is preferably 0.0005% or more.
  • the Al content is preferably 0.10% or less, and more preferably 0.07% or less.
  • Al has an action as a deoxidizing material, and from the viewpoint of improving the cleanliness of steel, the content is preferably 0.01% or more.
  • N 0.010% or less>
  • a nitride such as AlN is formed in the base steel sheet, resulting in a decrease in formability during hot press forming. Therefore, the N content is preferably 0.010% or less, and more preferably 0.005% or less.
  • N is preferably 0.001% or more.
  • this base steel plate may contain the following elements further as needed.
  • Cr 0.01% or more and 0.50% or less
  • V 0.01% or more and 0.50% or less
  • Mo 0.01% or more and 0.50% or less
  • Ni 0.01 or more and 0.50% or less
  • Cr, V, Mo and Ni are all It is an effective element for improving the hardenability of steel. This effect can be obtained by setting the content to 0.01% or more for any element. However, if the Cr, V, Mo, and Ni content exceeds 0.50%, the above effect is saturated, which increases the cost. Accordingly, when containing one or more of Cr, V, Mo, Ni, the content is preferably 0.01% or more and 0.50% or less, more preferably 0.10% or more and 0.40% or less. .
  • Ti 0.01% or more and 0.20% or less Ti is effective for strengthening steel.
  • the strength increasing effect by Ti can be obtained by setting its content to 0.01% or more, and if it is within the range specified here, it can be used for strengthening steel. However, when the Ti content exceeds 0.20%, the effect is saturated, resulting in a cost increase. Accordingly, when Ti is contained, it is preferably 0.01% or more and 0.20% or less, and more preferably 0.01% or more and 0.05% or less.
  • Nb 0.01% or more and 0.10% or less Nb is also effective for strengthening steel.
  • the effect of increasing the strength by Nb can be obtained by setting its content to 0.01% or more. If it is within the range specified here, it can be used for strengthening steel. However, if the Nb content exceeds 0.10%, the effect is saturated, resulting in a cost increase. Therefore, when Nb is contained, it is preferably 0.01% or more and 0.10% or less, and more preferably 0.01% or more and 0.05% or less.
  • B 0.0002% or more and 0.0050% or less
  • B is an element that enhances the hardenability of steel.
  • the base steel sheet is cooled after hot press forming, it suppresses the formation of ferrite from the austenite grain boundaries and obtains a hardened structure. Is an effective element.
  • the effect can be obtained when the B content is 0.0002% or more. However, if the B content exceeds 0.0050%, the effect is saturated, resulting in a cost increase. Therefore, when B is contained, the content is preferably 0.0002% or more and 0.0050% or less. More preferably, it is 0.0005% or more and 0.0030% or less.
  • Sb 0.003% or more and 0.030% or less Sb suppresses the decarburization layer generated in the surface layer of the base steel sheet from the time the steel sheet is heated before hot press forming until the steel sheet is cooled by a series of hot press forming processes.
  • the Sb content is preferably 0.003% or more.
  • the content is preferably 0.003% or more and 0.030% or less, and more preferably 0.005% or more and 0.010% or less.
  • components (remainder) other than the above components are Fe and inevitable impurities.
  • the surface-treated steel sheet 1 used as a raw material of the hot press-formed member is not particularly limited in its production conditions.
  • the production conditions of the base steel sheet are not particularly limited.
  • a hot-rolled steel sheet (pickled steel sheet) having a predetermined composition and a cold-rolled steel sheet obtained by cold rolling a hot-rolled steel sheet may be used as the base steel sheet.
  • the conditions at the time of forming the Zn-Ni plating layer on the surface of the base steel sheet to form the surface-treated steel sheet 1 are not particularly limited.
  • the surface-treated steel plate 1 can be obtained by subjecting the hot-rolled steel plate (pickled steel plate) to a Zn—Ni plating treatment.
  • the surface-treated steel sheet 1 can be obtained by performing a Zn-Ni plating process as it is after cold rolling or after annealing.
  • a Zn—Ni plating layer can be formed.
  • the Ni content in the plating layer can be adjusted to the desired Ni content (for example, 9% by mass to 25% by mass) by appropriately adjusting the concentration and current density of zinc sulfate heptahydrate within the above ranges. can do.
  • the coating weight of Zn-Ni plated layer, by adjusting the energization time can be desired adhesion amount (e.g., 10 g / m 2 or more per side 90 g / m 2 or less).
  • ⁇ Pure Zn plating layer> The cold-rolled steel sheet is passed through a continuous hot-dip galvanizing line, heated to a temperature range of 800 ° C. or higher and 900 ° C. or lower at a temperature increase rate of 10 ° C./s.
  • the Zn plating layer was formed by cooling to a temperature range of 460 ° C. or more and 500 ° C. or less at a cooling rate of ° C./s and dipping in a 450 ° C. zinc plating bath.
  • the adhesion amount of the Zn plating layer was adjusted to a predetermined adhesion amount by a gas wiping method.
  • ⁇ Zn-Fe plating layer> The cold-rolled steel sheet is passed through a continuous hot-dip galvanizing line, heated to a temperature range of 800 ° C. or higher and 900 ° C. or lower at a temperature increase rate of 10 ° C./s.
  • the Zn plating layer was formed by cooling to a temperature range of 460 ° C. or more and 500 ° C. or less at a cooling rate of ° C./s and dipping in a 450 ° C. zinc plating bath.
  • the adhesion amount of the Zn plating layer was adjusted to a predetermined adhesion amount by a gas wiping method.
  • a Zn—Fe plating layer was formed by immediately heating to 500 to 550 ° C. in an alloying furnace and holding for 5 to 60 seconds.
  • the Fe content in the plating layer was set to a predetermined content by changing the heating temperature in the alloying furnace and the residence time at the heating temperature within the above range.
  • ⁇ Zn-Ni plating layer> The cold-rolled steel sheet is passed through a continuous annealing line, heated to a temperature range of 800 ° C to 900 ° C at a rate of 10 ° C / s, and retained in the temperature range for 10s to 120s, then 15 ° C / s It cooled to the temperature range below 500 degreeC with the cooling rate of s.
  • a Zn—Ni plating layer was formed by performing an electroplating process in which a current of 10 to 100 s was applied at a current density of 100 A / dm 2 .
  • the Ni content in the plating layer was set to a predetermined content by appropriately adjusting the concentration and current density of zinc sulfate heptahydrate within the above ranges.
  • the adhesion amount of the Zn—Ni plating layer was set to a predetermined adhesion amount by appropriately adjusting the energization time within the above range.
  • a 200mm x 400mm blank plate is punched from the surface-treated steel plate obtained as described above, and the blank plate is heated by an electric furnace in an atmospheric atmosphere, and then the blank plate is placed in a cooling mold (material: SKD61). Then, under the conditions shown in Table 2, cooling with a mold, press molding, and quenching were performed. And after quenching in a metal mold
  • the molds were punch punch R: 6 mm and die shoulder R: 6 mm, and the punch-die clearance was 1.6 mm.
  • the surface-treated steel sheet before press forming was cooled by contact with a cooling mold.
  • the press molding was performed by a draw molding in which a 98 kN wrinkle pressing force was applied and a foam molding in which no wrinkle pressing was performed.
  • Table 2 shows the heating temperature of the blank plate, the type of the base steel plate, the type of the plating layer, the heating condition, the cooling condition, and the press molding condition.
  • a sample was taken from the vertical wall portion of the press-formed product with the obtained hat cross-sectional shape, and the cross section of the surface was observed with 10 fields of view for each sample at a magnification of 1000 using a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • microcrack depth refers to the length of the crack in the center direction of the thickness of the microcrack 21 measured from the interface between the plating layer 23 and the base steel plate 25 (see FIG. 12). 12, the length of h). When the number of observed microcracks was less than 20, the average depth of all the observed microcracks was taken. Further, regarding the shape accuracy of the obtained press-molded member, the difference (W ⁇ W 0) between the molded product width W after mold release of the press-molded product having the hat cross-sectional shape shown in FIG. 13 and the molded product width W 0 in the mold shape. ) was evaluated as the amount of opening. These results are also shown in Table 2.
  • a sample for hardness measurement was taken from the vertical wall portion of the press-formed product having the hat cross-sectional shape.
  • the hardness of the cross section of this sample was determined with a micro Vickers hardness tester. The test was conducted at a test load of 9.8 N, the central portion in the thickness direction was measured at five points, and the average value was taken as the hardness of the sample.
  • the target hardness is 400 Hv or more.
  • a JIS 13 B tensile test piece was collected from the vertical wall portion of the obtained press-formed product having a hat cross-sectional shape.
  • the type of plating layer Zn—Ni plating layer
  • cooling method mold cooling
  • cooling time 0.6 s to 1.7 s
  • cooling rate appropriate range: 100 ° C./s or more
  • the cooling stop temperature proper range: 410 ° C to 550 ° C
  • the time to start press forming after cooling proper range: within 5 seconds
  • the press molding start temperature proper range 400 ° C to 550 ° C
  • Comparative Example 1 was formed without cooling with a cooling mold.
  • the cooling stop temperature is outside the proper range (410 ° C. to 550 ° C.). Specifically, the cooling stop temperature of Comparative Example 2 is 600 ° C., and the cooling stop temperatures of Comparative Examples 3 and 4 are 340 ° C. and 290 ° C.
  • the opening amount is 0 mm, but microcracks are generated.
  • the forming start temperature of a steel plate is higher than 550 degreeC, it turns out that a micro crack generate
  • the opening amount is 8 mm to 9 mm.
  • the press forming start temperature is also less than 400 ° C, the strength of the steel sheet is increased, and the shape freezing property may be lowered. Recognize.
  • Comparative Examples 5 to 7 since the cooling method is gas cooling, the cooling rate is out of the appropriate range (100 ° C./s or more), and rapid cooling cannot be performed. Therefore, in Comparative Examples 5 and 6, the cooling stop temperature and press forming start temperature of the steel plate are also outside the appropriate ranges (cooling stop temperature: 410 ° C. to 550 ° C., press forming start temperature: 400 ° C. to 550 ° C.), and microcracks occur. appear. In Comparative Example 7, although the cooling stop temperature is 510 ° C. and falls within the proper range, the amount of opening of the mouth is 3 mm and the shape freezing property is reduced.
  • Comparative Examples 8 and 9 the time until the start of press forming is 10 seconds and 8 seconds, respectively, which is longer than the appropriate range within 5 seconds. Therefore, in Comparative Examples 8 and 9, the opening amount is 2 mm, and the hardness and tensile strength after press molding are also reduced.
  • Comparative Examples 10 and 11 have different types of plating layers, that is, Comparative Example 10 is a Zn-only plating layer, and Comparative Example 11 is a Zn-Fe plating layer.
  • the press molding start temperature at which microcracks are not generated in the Zn-only plating layer and the Zn-Fe plating layer is lower than the press molding start temperature at which microcracks are not generated in the Zn-Ni plating layer. Therefore, in Comparative Examples 10 and 11, microcracks are generated.

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Abstract

A method of manufacturing a hot press-formed product, in which the hot press-formed product is manufactured by hot pressing a surface-treated steel sheet (1) comprising a Zn-Ni plated layer formed on the surface of a base steel sheet, is provided with the following steps in order to suppress the generation of micro-cracks while suppressing deterioration in the shape-fixability during hot press-forming, namely: a step of heating the surface-treated steel sheet to a temperature in a range at least equal to the Ac3 transformation point and at most equal to 1000ºC; a step of cooling the surface-treated steel sheet at a cooling rate of at least 100ºC/s to a temperature at most equal to 550ºC and at least equal to 410ºC, by sandwiching the heated surface-treated steel sheet in a cooling die (3) of which the surface that is in contact with the surface-treated steel sheet is planar; a step of obtaining a formed body by starting to press-form the surface-treated steel sheet using a press-forming die (11) within 5 seconds after cooling, and while the temperature of the surface-treated steel sheet is in a range at most equal to 550ºC and at least equal to 400ºC; and a step of maintaining the formed body at bottom dead center of forming while the formed body is still sandwiched in the press-forming die, and quenching the formed body to yield the hot press-formed product.

Description

熱間プレス成形品の製造方法および熱間プレス成形品Manufacturing method of hot press-formed product and hot press-formed product
　本発明は、熱間プレス成形品およびその製造方法に関し、特に予め加熱した表面処理鋼板をプレス成形する際に、形状付与と同時に焼入れて所定強度（引張強さ：1180MPa級以上）を得ることができる熱間プレス成形品の製造方法に関するものである。
　また、本発明は、上記の熱間プレス成形品の製造方法に従い製造した熱間プレス成形品に関するものである。 The present invention relates to a hot press-formed product and a method for producing the same, and in particular, when press-forming a pre-heated surface-treated steel sheet, it is possible to obtain a predetermined strength (tensile strength: 1180 MPa class or more) by quenching simultaneously with shape formation. The present invention relates to a method for producing a hot press-formed product.
The present invention also relates to a hot press-formed product manufactured according to the above-described method for manufacturing a hot press-formed product.
　近年、自動車部品の高強度化・薄肉化が要求されている。このため、自動車部品に使用される鋼板の高強度化が進められているが、これに伴ってプレス加工性が低下し、鋼板を所望の部品形状に加工することが難しくなっている。
　このような問題を解決するものとして、高温に加熱した素材鋼板を、金型を用いて所望の形状に熱間プレス成形しつつ金型内で抜熱して焼入れし、熱間プレス成形後に得られる部材を高強度化する技術が知られている。
　例えば、特許文献１には900℃前後のオーステナイト単相域まで加熱したブランク板（鋼板）に熱間プレス成形を施して所定形状の部材を製造するに際し、熱間プレス成形と同時に金型内で焼入れを行うことで、部材の高強度化を図る技術が提案されている。 In recent years, it has been required to increase the strength and thickness of automobile parts. For this reason, although the strength of steel plates used for automobile parts is being increased, press workability is lowered along with this, making it difficult to process the steel plates into a desired part shape.
As a solution to such a problem, a raw steel plate heated to a high temperature is hot-pressed into a desired shape using a die, and is heat-extracted and quenched in the die, and obtained after hot press-forming. Techniques for increasing the strength of members are known.
For example, Patent Document 1 discloses that when a blank plate (steel plate) heated to an austenite single phase region around 900 ° C. is subjected to hot press forming to produce a member having a predetermined shape, There has been proposed a technique for increasing the strength of a member by quenching.
　しかし、特許文献１で提案された技術では、プレス成形前に鋼板を900℃前後の高温に加熱する際、鋼板表面に酸化スケール（鉄酸化物）が生成し、その酸化スケールが熱間プレス成形時に剥離して金型を損傷させたり、プレス成形後の部材表面を損傷させるという問題がある。また、部材表面に残った酸化スケールは、外観不良や塗装密着性の低下の原因にもなる。このため、通常は酸洗やショットブラストなどの処理を行って部材表面の酸化スケールを除去するが、これらの処理は生産性の低下を招く。更に、自動車の足回り部材や車体構造部材などには優れた耐食性も必要とされるが、特許文献１で提案された技術では素材鋼板にめっき層などの防錆皮膜が設けられていない。このため、この技術に従い得られた熱間プレス成形部材では、耐食性が不十分となる。 However, in the technique proposed in Patent Document 1, when a steel plate is heated to a high temperature of about 900 ° C. before press forming, oxide scale (iron oxide) is generated on the surface of the steel plate, and the oxide scale is hot press formed. There is a problem that it sometimes peels off and damages the mold or damages the surface of the member after press molding. In addition, the oxide scale remaining on the surface of the member also causes poor appearance and poor paint adhesion. For this reason, usually, treatment such as pickling or shot blasting is performed to remove the oxidized scale on the surface of the member, but these treatments cause a decrease in productivity. Furthermore, although excellent corrosion resistance is required for the undercarriage member and the vehicle body structural member of an automobile, the technology proposed in Patent Document 1 does not provide a rust preventive film such as a plating layer on the material steel plate. For this reason, the hot press-formed member obtained according to this technique has insufficient corrosion resistance.
　上記の理由により、熱間プレス成形前の加熱時に酸化スケールの生成を抑制するとともに、熱間プレス成形後の部材の耐食性を向上させることが可能な熱間プレス成形技術が要望されている。このような要望に対し、表面にめっき層などの皮膜を設けた表面処理鋼板や、表面処理鋼板を用いた熱間プレス成形方法が提案されている。
　例えば特許文献２には、ZnまたはZnベース合金で被覆された鋼板を、700～1200℃に加熱した後、熱間プレス成形することにより、表面にZn-Feベース化合物またはZn-Fe-Alベース化合物を備えた熱間プレス成形部材とする技術が提案されている。また、特許文献２には、ZnまたはZnベース合金で被覆された鋼板を用いることにより、熱間プレス成形前の加熱時に問題となる鋼板表面の酸化を抑制することが可能となり、しかも耐食性に優れた熱間プレス成形部材が得られると記載されている。 For the above reasons, there is a demand for a hot press molding technique that can suppress the formation of oxide scale during heating before hot press molding and can improve the corrosion resistance of members after hot press molding. In response to such a demand, a surface-treated steel sheet provided with a coating such as a plating layer on the surface and a hot press forming method using the surface-treated steel sheet have been proposed.
For example, in Patent Document 2, a steel sheet coated with Zn or a Zn base alloy is heated to 700 to 1200 ° C. and then hot pressed to form a Zn—Fe base compound or a Zn—Fe—Al base on the surface. A technique for forming a hot press-formed member provided with a compound has been proposed. Further, in Patent Document 2, by using a steel sheet coated with Zn or a Zn base alloy, it becomes possible to suppress the oxidation of the steel sheet surface, which becomes a problem during heating before hot press forming, and has excellent corrosion resistance. Further, it is described that a hot press-formed member is obtained.
　特許文献２で提案された技術によると、熱間プレス成形部材表面の酸化スケール生成はある程度抑制される。しかし、めっき層中のZnに起因する液体金属脆化割れが起こり、熱間プレス成形部材の表層部に深さ100μm程度のクラックが発生する場合がある。このようなクラックが発生すると、熱間プレス成形部材の耐疲労特性が低下するなど、様々な支障をきたす。 According to the technique proposed in Patent Document 2, generation of oxide scale on the surface of a hot press-formed member is suppressed to some extent. However, liquid metal embrittlement cracking due to Zn in the plating layer occurs, and a crack having a depth of about 100 μm may occur in the surface layer portion of the hot press-formed member. When such a crack occurs, various troubles such as deterioration of the fatigue resistance of the hot press-formed member are caused.
　このような問題に対し、特許文献３では、Zn-Fe系めっき層が素地鋼板表面に形成された表面処理鋼板を、前記表面処理鋼板を素地鋼板のAc1変態点以上950℃以下の温度に加熱し、めっき層の凝固点以下の温度まで表面処理鋼板を冷却した後、プレス成形を開始する方法が提案されている。そして、特許文献３には、めっき層の凝固点以下の温度まで表面処理鋼板を冷却してからプレス成形を開始することにより、液体金属脆化割れの抑制が可能であると記載されている。 In order to solve such a problem, in Patent Document 3, a surface-treated steel sheet in which a Zn-Fe-based plating layer is formed on the surface of the base steel sheet, the surface-treated steel sheet is brought to a temperature not lower than the Ac 1 transformation point of the base steel sheet and not higher than 950 ° C. A method of starting press forming after heating and cooling the surface-treated steel sheet to a temperature below the freezing point of the plating layer has been proposed. Patent Document 3 describes that liquid metal embrittlement cracking can be suppressed by starting press forming after cooling the surface-treated steel sheet to a temperature below the freezing point of the plating layer.
英国特許第1490535号公報GB 1490535 特許第3663145号Patent No. 3663145 特開2013-91099号公報JP 2013-91099 A
　特許文献３で提案された技術によると、液体金属脆化割れ、すなわち熱間プレス成形部材の表面に発生し、めっき層-素地鋼板（地鉄）界面から素地鋼板内部方向への深さが100μm程度であって、割れ部の界面にZnが検出されるクラック（以下、「マクロクラック」という）を抑制し得ると考えられる。
　このようなマクロクラックの抑制に対して、本発明者らは高融点のめっき層としてZnに9～25％程度のNiを含有したZn-Ni合金めっきを用いることを検討した。Zn-Ni合金めっきの耐食性確保にはZn-Ni合金をγ相とする必要があり、Zn-Ni合金の平衡状態図に存在するγ相は融点が860℃以上と通常のZn系めっき層に比べて非常に高く、通常のプレス条件でもマクロクラックの発生が抑制可能となる。
　しかしながら、熱間プレス成形部材の表面には、上記のマクロクラックではなく、めっき層-素地鋼板界面から素地鋼板内部方向への深さが約30μm以下であって、割れ部の界面にはZnが検出されない微小割れが発生することが知られている。この微小割れはミクロクラックと称され、めっき層-素地鋼板界面を貫通して素地鋼板の内部にまで至り、熱間プレス成形部材の諸特性（耐疲労特性等）に悪影響を及ぼす。
　マクロクラックは、例えば、ハット断面部材をプレス成形する際に、ダイ肩Ｒ部のパンチ接触側のような引張り歪のみが生ずる部分でも発生する。一方、ミクロクラックはそのような部分では発生せず、縦壁部のダイ接触側のような（曲げ）圧縮の後（曲げ戻し）引張り歪を受けるところで発生する。このため、マクロクラックとミクロクラックでは、その発生のメカニズムが異なるものと推察される。 According to the technique proposed in Patent Document 3, liquid metal embrittlement cracking occurs, that is, occurs on the surface of a hot press-formed member, and the depth from the plating layer-base steel plate (base metal) interface to the inside of the base steel plate is 100 μm. It is considered that cracks in which Zn is detected at the interface of the cracked portion (hereinafter referred to as “macro crack”) can be suppressed.
In order to suppress such macro cracks, the present inventors examined the use of Zn—Ni alloy plating containing about 9 to 25% Ni in Zn as a high melting point plating layer. In order to ensure the corrosion resistance of Zn-Ni alloy plating, it is necessary to use Zn-Ni alloy as the γ phase. The γ phase present in the equilibrium diagram of the Zn-Ni alloy has a melting point of 860 ° C or higher and becomes a normal Zn-based plating layer. It is very high compared to the above, and the occurrence of macro cracks can be suppressed even under normal pressing conditions.
However, on the surface of the hot press-formed member, the depth from the plating layer-base steel plate interface to the base steel plate inside is not more than about 30 μm instead of the macro cracks described above, and Zn is present at the crack interface. It is known that microcracks that are not detected occur. This microcrack is called a microcrack, penetrates the plating layer-base steel plate interface and reaches the inside of the base steel plate, and adversely affects various properties (such as fatigue resistance) of the hot press-formed member.
For example, when a hat cross-section member is press-molded, macro cracks also occur in a portion where only tensile strain occurs, such as the punch contact side of the die shoulder R portion. On the other hand, microcracks do not occur in such portions, but occur in places where tensile strain is applied after (bending) compression (bending back) as in the die contact side of the vertical wall. For this reason, it is guessed that the generation mechanism differs between a macro crack and a micro crack.
　この点、特許文献３の技術では、Zn-Fe系めっき層が形成された表面処理鋼板についてマクロクラックの発生抑制は可能であるが、Zn-Niめっき層が形成された表面処理鋼板におけるミクロクラックについては何らの考慮もされておらず、ミクロクラック発生抑制には必ずしも有効とは言えない。
　また、特許文献３で提案された技術では、表面処理鋼板全体をめっき層の凝固点以下の温度まで冷却した状態でプレス成形するとしており、プレス成形を開始する温度の下限値が示されていない。このため、プレス成形温度の低下によりプレス成形時の鋼板の強度上昇が起こるおそれがあり、形状凍結性（スプリングバック等がわずかであり、成形下死点での形状が維持される性質）が低下してスプリングバックが起きやすいという問題もある。 In this regard, in the technique of Patent Document 3, it is possible to suppress the occurrence of macro cracks in the surface-treated steel sheet on which the Zn—Fe plating layer is formed, but micro cracks in the surface-treated steel sheet on which the Zn—Ni plating layer is formed. No consideration is given to, and it is not necessarily effective in suppressing the occurrence of microcracks.
Further, in the technique proposed in Patent Document 3, the entire surface-treated steel sheet is press-formed while being cooled to a temperature not higher than the freezing point of the plating layer, and the lower limit value of the temperature at which press forming is started is not shown. For this reason, there is a risk that the strength of the steel sheet during press forming may increase due to the decrease in press forming temperature, and the shape freezing property (the property that the shape at the bottom dead center of forming is maintained) is reduced. There is also a problem that springback is likely to occur.
　本発明はかかる問題を解決するためになされたものであり、Zn-Ni系めっき層を形成した表面処理鋼板に熱間プレスを施して熱間プレス成形品を製造するに際し、熱間プレス成形時の形状凍結性の低下を抑制しつつ、ミクロクラックの発生を抑制する熱間プレス成形品の製造方法を提供することを目的とする。　また、本発明は、上記の熱間プレス成形品の製造方法に従い製造した熱間プレス成形品を提供することを目的とする。 The present invention has been made to solve such a problem. When a hot-pressed product is manufactured by hot-pressing a surface-treated steel sheet on which a Zn-Ni-based plating layer has been formed, It aims at providing the manufacturing method of the hot press-molded article which suppresses generation | occurrence | production of a microcrack, suppressing the fall of shape freezing property of this. Moreover, an object of the present invention is to provide a hot press-formed product manufactured according to the above-described method for manufacturing a hot press-formed product.
　本発明者らはまず、Zn系めっき鋼板を熱間プレス成形する際に問題となるミクロクラック（微小割れ）を抑制する手段について検討した。
　ミクロクラックの生成メカニズムについては明確になっていないが、Zn系のめっき鋼板をめっき凝固点以下の高温でプレス成形することによりめっき鋼板の表面に微小割れが発生する。また、Zn-Niめっき鋼板をプレス成形する場合においても同様の微小割れが発生する。そして、この微小割れは、めっき層-素地鋼板界面からの深さが30μm程度の微小な割れであり、めっき層-素地鋼板界面を貫通して素地鋼板内部に至る。
　このような問題に対し、本発明者らが種々の検討を行った結果、熱間プレス成形時の鋼板温度を低くすることによりミクロクラックが抑制されることを明らかにした。更に、上記のようなプレス成形時の鋼板温度の低下により、従来の熱間プレス用めっき鋼板で問題となっている金型へのめっき付着量も大幅に低減する効果が得られた。 The present inventors first examined means for suppressing microcracks (microcracks), which are problematic when hot-pressing a Zn-based plated steel sheet.
The generation mechanism of microcracks is not clear, but microcracks are generated on the surface of plated steel sheets by press-forming Zn-based plated steel sheets at a high temperature below the freezing point of plating. In addition, similar microcracking occurs when a Zn-Ni plated steel sheet is press-formed. The micro crack is a micro crack having a depth of about 30 μm from the plating layer-base steel plate interface and penetrates through the plating layer-base steel plate interface to the inside of the base steel plate.
As a result of various studies by the present inventors for such problems, it has been clarified that microcracks are suppressed by lowering the steel plate temperature during hot press forming. Furthermore, due to the decrease in the steel plate temperature during the press forming as described above, the effect of greatly reducing the amount of plating attached to the mold, which is a problem in the conventional hot-pressed plated steel plate, was obtained.
　しかし、プレス成形時の鋼板温度が低くなると、鋼板の強度が上昇するため形状凍結性の低下が起こり、熱間プレス成形時の利点を生かすことができなくなる。
　そこで、本発明者らは、プレス成形時にミクロクラックが発生するような加工を受ける部分のみを冷却した後、熱間プレス成形すればよいのではないかと考えた。そして、前記ミクロクラックが発生する加工とはいかなる加工であり、当該加工を受ける部分とはいかなる部分かについて検討した。
　まず、ミクロクラックが発生する加工を検討するに際し、加工歪みがミクロクラックの発生に及ぼす影響を種々検討した。その結果、単なる引張り、圧縮変形や曲げ変形のみではミクロクラックは発生せず、一旦曲げられた部分が再度伸ばされる、曲げ-曲げ戻し変形を受ける部分でミクロクラックが発生することを明らかにした。
　この点、上記のような加工は、特定の部位に限定される場合もあるが、成形品の形状によっては、ミクロクラックが発生する加工を受ける部位が鋼板に広く及ぶ場合もある。 However, when the steel plate temperature during press forming decreases, the strength of the steel plate increases and the shape freezing property decreases, making it impossible to take advantage of the advantages during hot press forming.
Therefore, the present inventors thought that it would be sufficient to perform hot press molding after cooling only the portion subjected to processing that generates microcracks during press molding. And what kind of process is the process in which the microcrack is generated, and what part is the part subjected to the process was examined.
First, when examining the processing in which microcracks occur, various effects of processing strain on the occurrence of microcracks were examined. As a result, it was clarified that micro-cracks do not occur only by simple tension, compression deformation and bending deformation, but micro-cracks occur in the portion subjected to bending-bending unbending deformation, where the once bent portion is stretched again.
In this respect, the processing as described above may be limited to a specific portion, but depending on the shape of the molded product, the portion subjected to processing that generates microcracks may be widely spread on the steel sheet.
　そこで、被加工部材である鋼板の特定部位に限定されることなくミクロクラックの発生を抑制できる方法について検討した。その結果、加熱した表面処理鋼板を、表面処理鋼板との接触面が平面である冷却用金型で挟むことにより、表面処理鋼板を100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却し、また冷却後5秒以内で、かつ表面処理鋼板の温度が550℃以下400℃以上の範囲内で、プレス成形金型を用いて表面処理鋼板のプレス成形を開始することで、最終的に得られるプレス成形品の表裏面全面に亘ってミクロクラックの発生を抑制しつつ、形状精度不良も抑制可能となることが明らかとなった。 Therefore, a method that can suppress the occurrence of microcracks without being limited to a specific portion of a steel plate as a workpiece was studied. As a result, by sandwiching the heated surface-treated steel sheet with a cooling mold having a flat contact surface with the surface-treated steel sheet, the surface-treated steel sheet is 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher. By cooling to a temperature, and within 5 seconds after cooling, and within a range where the temperature of the surface-treated steel sheet is 550 ° C. or lower and 400 ° C. or higher, by starting press forming of the surface-treated steel sheet using a press molding die, It has been clarified that it is possible to suppress poor shape accuracy while suppressing the occurrence of microcracks over the entire front and back surfaces of the press-formed product finally obtained.
　冷却用金型での冷却により形状精度不良が抑制された理由については以下のように考えられる。
　すなわち、ハット型部材の代表的な形状精度不良としては、曲げの稜線を挟む２つの面のなす角度が金型角度に対して大きくなる角度変化と、縦壁部の平面が曲率を持った面になる壁反りが挙げられる。これらはいずれも板厚方向の応力分布の差により生じ、加工時の鋼板の流動応力が高いほど、応力分布の差が拡大して形状精度が低下する。すなわち、熱間プレス成形においては、プレス成形温度が低いほど鋼板のプレス成形時の流動応力が高くなり形状精度が低下する。冷却によりプレス成形時の鋼板の温度が低くなり形状精度が低下すると考えられるが、100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却し、冷却後5秒以内で、かつ鋼板温度が550℃以下400℃以上の範囲内でプレス成形を開始することにより、ほとんど形状精度の低下は認められなかった。
　この理由は、加熱した鋼板を冷却用金型により急冷し、鋼板温度が550℃以下400℃以上の範囲内でプレス成形する場合、プレス成形時の鋼板組織がオーステナイトであり、プレス成形後にオーステナイトがマルテンサイトに変態してプレス成形時に入った応力が緩和されるためと考えられる。
　一方、加熱した鋼板を急冷せずにプレス成形開始温度を低下させると、プレス成形開始前にフェライトやベイナイトが生じるため、強度の低下とともに上記の角度変化が発生するものと考えられる。
　また、プレス成形開始時の鋼板温度が400℃未満となる場合には、プレス成形開始前に既にマルテンサイト変態が開始しているため、鋼板強度の増加も加わって、プレス成形時に入った応力により上記の壁反りが発生するものと考えられる。
　本発明は、上記のような知見に基づいてなされたものであり、具体的には以下の構成を備えてなるものである。 The reason why the shape accuracy defect is suppressed by cooling with the cooling mold is considered as follows.
That is, as a typical defective shape accuracy of the hat-shaped member, the angle change between the two surfaces sandwiching the bending ridge line is larger than the mold angle, and the surface of the vertical wall portion has a curvature. Wall warping that becomes. These are all caused by the difference in stress distribution in the thickness direction, and the higher the flow stress of the steel sheet during processing, the greater the difference in stress distribution and the lower the shape accuracy. That is, in hot press forming, the lower the press forming temperature, the higher the flow stress during press forming of the steel sheet and the lower the shape accuracy. Although it is thought that the temperature of the steel sheet at the time of press forming is lowered by cooling and the shape accuracy is lowered, it is cooled to a temperature of 550 ° C or lower and 410 ° C or higher at a cooling rate of 100 ° C / s or higher, within 5 seconds after cooling, and When press forming was started within the range where the steel plate temperature was 550 ° C. or lower and 400 ° C. or higher, almost no decrease in shape accuracy was observed.
The reason for this is that when the heated steel sheet is quenched with a cooling die and the steel sheet temperature is press-formed within a range of 550 ° C. or lower and 400 ° C. or higher, the steel sheet structure at the time of press forming is austenite. This is thought to be due to the relaxation of the stress that entered the press forming due to transformation to martensite.
On the other hand, if the press forming start temperature is lowered without rapidly cooling the heated steel plate, ferrite and bainite are generated before the start of press forming, so that it is considered that the above angle change occurs with a decrease in strength.
Also, when the steel plate temperature at the start of press forming is less than 400 ° C, the martensitic transformation has already started before the start of press forming. It is considered that the above wall warp occurs.
The present invention has been made on the basis of the above-described knowledge, and specifically comprises the following configuration.
（１）Zn-Niめっき層が素地鋼板の表面に形成された表面処理鋼板に熱間プレスを施して熱間プレス成形品を製造する熱間プレス成形品の製造方法であって、
　前記表面処理鋼板をAc3変態点以上で1000℃以下の温度域に加熱する工程と、
　前記加熱した表面処理鋼板を、前記表面処理鋼板との接触面が平面である冷却用金型で挟むことにより、前記表面処理鋼板を100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却する工程と、
　前記冷却後5秒以内で、かつ前記表面処理鋼板の温度が550℃以下400℃以上の範囲内で、プレス成形金型を用いて前記表面処理鋼板のプレス成形を開始して、成形体を得る工程と、
　前記成形体を前記プレス成形金型で挟んだまま成形下死点で保持して、前記成形体を焼入れ、熱間プレス成形品を得る工程とを備える、熱間プレス成形品の製造方法。 (1) A method for producing a hot press-formed product, in which a hot-pressed product is produced by subjecting a surface-treated steel sheet having a Zn-Ni plating layer formed on the surface of a base steel plate to hot press,
Heating the surface-treated steel sheet to a temperature range of 1000 ° C. or less above the Ac 3 transformation point;
By sandwiching the heated surface-treated steel sheet with a cooling mold having a flat contact surface with the surface-treated steel sheet, the surface-treated steel sheet is 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher. Cooling to temperature,
Within 5 seconds after the cooling, and the temperature of the surface-treated steel sheet is within a range of 550 ° C. or lower and 400 ° C. or higher, press molding of the surface-treated steel sheet is started using a press molding die to obtain a molded body Process,
A method of manufacturing a hot press-molded product, comprising: holding the molded body at a bottom dead center while being sandwiched between the press-molding dies, and quenching the molded body to obtain a hot press-molded product.
（２）前記表面処理鋼板におけるZn-Niめっき層中のNi含有量が9質量%以上25質量%以下である、前記１に記載の熱間プレス成形品の製造方法。 (2) The method for producing a hot press-formed product as described in 1 above, wherein the Ni content in the Zn-Ni plating layer in the surface-treated steel sheet is 9% by mass or more and 25% by mass or less.
（３）前記１または２に記載の方法により製造された熱間プレス成形品。 (3) A hot press-formed product manufactured by the method described in 1 or 2 above.
　本発明によれば、表面処理鋼板を素材として、表裏面全面にミクロクラックが発生することなく、成形品の硬度も十分であり、大幅な成形荷重の増加もなく、形状凍結性としても問題ない熱間プレス成形品が得ることができるので、高強度の表面処理鋼板を用いて種々の製品形状となる自動車部品等を製造することが可能となる。 According to the present invention, using a surface-treated steel sheet as a raw material, microcracks do not occur on the entire front and back surfaces, the hardness of the molded product is sufficient, there is no significant increase in molding load, and there is no problem with shape freezing properties. Since a hot press-formed product can be obtained, it becomes possible to manufacture automobile parts and the like having various product shapes using a high-strength surface-treated steel sheet.
本発明の一実施形態に係る熱間プレス成形品の製造方法の説明図である。It is explanatory drawing of the manufacturing method of the hot press-formed product which concerns on one Embodiment of this invention. 金属組織と温度、冷却時間との関係を示す模式図である（その１）。It is a schematic diagram which shows the relationship between a metal structure, temperature, and cooling time (the 1). 金属組織と温度、冷却時間との関係を示す模式図である（その２）。It is a schematic diagram which shows the relationship between a metal structure, temperature, and cooling time (the 2). 本発明の一実施形態における実験に用いた試験片の説明図である。It is explanatory drawing of the test piece used for the experiment in one Embodiment of this invention. 本発明の一実施形態における実験結果の説明図であって、試験片の温度変化を示すグラフである。It is explanatory drawing of the experimental result in one Embodiment of this invention, Comprising: It is a graph which shows the temperature change of a test piece. 図５の横軸の一部を拡大して示す図である。It is a figure which expands and shows a part of horizontal axis | shaft of FIG. 一実施形態における実験結果を示す図であって、プレス成形品の縦壁部のSEM像である。It is a figure which shows the experimental result in one Embodiment, Comprising: It is a SEM image of the vertical wall part of a press molded product. 一実施形態における実験結果を示す図であって、プレス成形開始温度とプレス成形荷重の関係を示す図である。It is a figure which shows the experimental result in one Embodiment, Comprising: It is a figure which shows the relationship between press molding start temperature and a press molding load. 一実施形態における実験結果を示す図であって、プレス成形開始温度と口開き量の関係を示す図である。It is a figure which shows the experimental result in one Embodiment, Comprising: It is a figure which shows the relationship between press molding start temperature and opening amount. 本発明の一実施形態における成形方法の説明図である。It is explanatory drawing of the shaping | molding method in one Embodiment of this invention. 実施例でプレス成形するプレス成形品の説明図である。It is explanatory drawing of the press-molded product press-molded in an Example. 実施例において検証するミクロクラックの説明図である。It is explanatory drawing of the microcrack verified in an Example. 実施例において検証する口開き量の説明図である。It is explanatory drawing of the opening amount verified in an Example.
　本発明の一実施形態に係る熱間プレス成形品の製造方法は、図１に示すようなZn-Niめっき層が素地鋼板の表面に形成された表面処理鋼板１に熱間プレスを施して熱間プレス成形品を製造する熱間プレス成形品の製造方法であって、表面処理鋼板１をAc3変態点以上で1000℃以下の温度域に加熱する加熱工程（図示せず）と、加熱した表面処理鋼板１を、表面処理鋼板１との接触面が平面である冷却用金型３で挟むことにより、表面処理鋼板１を100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却する冷却工程（Ｓ１）と、冷却後5秒以内で、かつ表面処理鋼板１の温度が550℃以下400℃以上の範囲内で、プレス成形金型１１を用いて表面処理鋼板１のプレス成形を開始して、成形体１´を得るプレス成形工程（Ｓ２）と、成形体１´をプレス成形金型１１で挟んだまま成形下死点で保持して、成形体１´を焼入れ、熱間プレス成形品を得る焼入れ工程（Ｓ３）とを備えるものである。
　以下、熱間プレス成形品の素材、加熱工程、冷却工程（Ｓ１）、プレス成形工程（Ｓ２）、焼入れ工程（Ｓ３）について詳細に説明する。 The method for producing a hot press-formed product according to an embodiment of the present invention is performed by hot-pressing a surface-treated steel sheet 1 having a Zn-Ni plating layer formed on the surface of a base steel sheet as shown in FIG. A method for producing a hot press-formed product for producing an intermediate press-formed product, comprising a heating step (not shown) for heating the surface-treated steel sheet 1 to a temperature range not lower than the Ac 3 transformation point and not higher than 1000 ° C. By sandwiching the surface-treated steel sheet 1 with a cooling mold 3 having a flat contact surface with the surface-treated steel sheet 1, the surface-treated steel sheet 1 is heated to a temperature of 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher. The cooling process (S1) for cooling to the surface, and the press of the surface-treated steel sheet 1 using the press mold 11 within 5 seconds after the cooling and the temperature of the surface-treated steel sheet 1 is in the range of 550 ° C. or lower and 400 ° C. or higher. Press forming step (S2) to start molding and obtain molded body 1 ′, and press molded body 1 ′ It remains sandwiched between the mold 11 and held in the molding bottom dead center, quenching the molded article 1 ', in which and a quenching step (S3) to obtain a hot press molded product.
Hereinafter, the material of the hot press-formed product, the heating step, the cooling step (S1), the press forming step (S2), and the quenching step (S3) will be described in detail.
＜熱間プレス成形品の素材＞
　熱間プレス成形品の素材としては、素地鋼板の表面にZn-Niめっき層が設けられた表面処理鋼板を用いる。素地鋼板表面にZn-Niめっき層を設けることにより、熱間プレス成形後の部材の耐食性を確保することができる。
　素地鋼板表面にZn-Niめっき層を形成する方法は特に限定されず、溶融めっき、電気めっきなどいずれの方法でもよい。めっきの付着量は、片面あたり10g/m2以上90g/m2以下とすることが好ましい。 <Material for hot press-molded products>
As a raw material of the hot press-formed product, a surface-treated steel sheet in which a Zn—Ni plating layer is provided on the surface of the base steel sheet is used. By providing a Zn—Ni plating layer on the surface of the base steel plate, the corrosion resistance of the member after hot press forming can be ensured.
The method for forming the Zn—Ni plating layer on the surface of the base steel plate is not particularly limited, and any method such as hot dipping or electroplating may be used. The amount of plating is preferably 10 g / m 2 or more and 90 g / m 2 or less per side.
　また、めっき層中のNi含有量を9質量%以上25質量%以下とすることが好ましい。電気めっき法によりZn-Niめっき層を素地鋼板表面に形成する際、めっき層中のNi含有量を9質量%以上25質量%以下とすることで、Ni2Zn11，NiZn3、Nｉ5Zn21のいずれかの結晶構造を有するγ相が形成される。このγ相は融点が高いことから、熱間プレス成形前の表面処理鋼板加熱時に懸念されるめっき層の蒸発を抑制する上で有利となる。また、高温の熱間プレス成形時に問題となる液体金属脆化割れの抑制にも有利となる。 Further, the Ni content in the plating layer is preferably 9% by mass or more and 25% by mass or less. When the Zn-Ni plating layer is formed on the surface of the base steel sheet by electroplating, Ni 2 Zn 11 , NiZn 3 , Ni 5 Zn A γ phase having any one of the 21 crystal structures is formed. Since this γ phase has a high melting point, it is advantageous for suppressing evaporation of the plating layer, which is a concern during heating of the surface-treated steel sheet before hot press forming. It is also advantageous for suppressing liquid metal embrittlement cracking, which is a problem during hot press forming at high temperatures.
＜加熱工程＞
　表面処理鋼板１は、Ac3変態点以上で1000℃以下の温度域に加熱する。表面処理鋼板１の加熱温度がAc3変態点未満であると、加熱時に適切な量のオーステナイトが得られず、プレス成形時にフェライトが存在することで、熱間プレス成形後に十分な強度を得ることや良好な形状凍結性を確保することが困難となる。一方、表面処理鋼板１の加熱温度が1000℃を超えると、めっき層の蒸発や表層部での酸化物の過度な生成により、耐酸化性や熱間プレス成形品の耐食性が低下する。したがって、加熱温度はAc3変態点以上1000℃以下とする。より好ましくはAc3変態点+30℃以上950℃以下である。表面処理鋼板１の加熱方法は特に限定されず、電気炉や誘導加熱炉、直接通電加熱炉による加熱等、いずれの方法であってもよい。 <Heating process>
The surface-treated steel sheet 1 is heated to a temperature range from the Ac 3 transformation point to 1000 ° C. When the heating temperature of the surface-treated steel sheet 1 is lower than the Ac 3 transformation point, an adequate amount of austenite cannot be obtained during heating, and sufficient strength is obtained after hot press forming due to the presence of ferrite during press forming. It is difficult to ensure good shape freezing property. On the other hand, when the heating temperature of the surface-treated steel sheet 1 exceeds 1000 ° C., the oxidation resistance and the corrosion resistance of the hot press-formed product are deteriorated due to evaporation of the plating layer and excessive generation of oxide at the surface layer portion. Therefore, the heating temperature is set to the Ac 3 transformation point or higher and 1000 ° C. or lower. More preferably, it is Ac 3 transformation point + 30 ° C. or higher and 950 ° C. or lower. The heating method of the surface-treated steel sheet 1 is not particularly limited, and any method such as heating with an electric furnace, an induction heating furnace, or a direct current heating furnace may be used.
＜冷却工程＞
　冷却工程（Ｓ１）は、加熱した表面処理鋼板１を冷却用金型３で挟んで100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却する工程である。
　冷却用金型３は、図１に示すように、表面処理鋼板１との接触面が平面状になっている上金型５と下金型７とを有し、下金型７には伸縮式のリフターピン９が設置されている。加熱した表面処理鋼板１は、リフターピン９上に載置され、その後、上金型５と下金型７とで挟むことで冷却される。
　また、加熱した表面処理鋼板１を冷却用金型３で挟む場合には、図１に示すように、基本的には表面処理鋼板１の表裏面全面を冷却用金型３で挟むようにすればよいが、最終製品とする前にトリミングされるような部分については、この部分が冷却用金型３からはみ出るようにしてもよい。これにより、ミクロクラックが発生するような加工をうける部分、すなわち曲げ-曲げ戻し変形を受ける部分が被加工材である表面処理鋼板１に広く及ぶ場合であっても、最終的に得られるプレス成形品の表裏面全面に亘ってミクロクラックの発生を抑制することが可能となる。
　なお、加熱した表面処理鋼板１を冷却用金型３で挟むタイミングとしては、Zn-Niめっき層が金型に付着する危険性のない800℃以下とすることが好ましく、熱間プレス成形後の強度確保の点から670℃以上とすることが好ましい。また、冷却用金型３は表面処理鋼板１の片側面に押し当てて冷却してもよい。 <Cooling process>
The cooling step (S1) is a step in which the heated surface-treated steel sheet 1 is sandwiched between cooling dies 3 and cooled to a temperature of 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher.
As shown in FIG. 1, the cooling mold 3 includes an upper mold 5 and a lower mold 7 whose contact surfaces with the surface-treated steel sheet 1 are flat, and the lower mold 7 is extended and contracted. A lifter pin 9 of the type is installed. The heated surface-treated steel sheet 1 is placed on the lifter pin 9 and then cooled by being sandwiched between the upper mold 5 and the lower mold 7.
Further, when the heated surface-treated steel sheet 1 is sandwiched between the cooling molds 3, basically, the entire surface of the surface-treated steel sheet 1 is sandwiched between the cooling molds 3 as shown in FIG. However, the portion that is trimmed before the final product may be protruded from the cooling mold 3. Thereby, even if the part that undergoes processing that generates microcracks, that is, the part that undergoes bending-bending unreformation extends widely to the surface-treated steel sheet 1 that is the workpiece, the final press forming is obtained. It is possible to suppress the occurrence of microcracks over the entire front and back surfaces of the product.
The timing for sandwiching the heated surface-treated steel sheet 1 with the cooling mold 3 is preferably set to 800 ° C. or less without risk of the Zn—Ni plating layer adhering to the mold. From the viewpoint of securing strength, it is preferable to set the temperature to 670 ° C. or higher. Further, the cooling mold 3 may be pressed against one side surface of the surface-treated steel sheet 1 to be cooled.
　ここに、冷却速度を100℃/s以上としたのは、コストアップすることなく、マルテンサイト単相組織として高強度化を可能とするためである。
　この点をさらに詳細に説明する。
　図２は、プレス成形金型を用いて鋼板を熱間プレス成形する場合の一般的な金属組織と温度、冷却時間との関係を示す模式図である。図２（ａ）はプレス成形開始温度が高い場合を示しており、この場合、プレス成形開始後、金型への抜熱によって急冷され、マルテンサイト単相組織となる。
　他方、図２（ｂ）に示すように、プレス成形開始温度が低い場合には、プレス成形開始前にフェライトやベイナイトが生成し、プレス成形後のプレス成形品の強度が低下する。
　このように、単にプレス成形開始温度を下げるだけでは、図２（ｂ）の形態となる。
　一方、本発明では、プレス成形開始前に急冷が可能な冷却工程を採用することにより、図３の破線の曲線で示すように、成形開始温度を低くしながらも、マルテンサイト単相組織とすることを可能としている。
　なお、冷却速度の上限は、通常500℃/s程度である。 The reason why the cooling rate is set to 100 ° C./s or more is to enable high strength as a martensite single-phase structure without increasing the cost.
This point will be described in more detail.
FIG. 2 is a schematic diagram showing the relationship between a general metal structure, temperature, and cooling time when hot pressing a steel sheet using a press mold. FIG. 2A shows a case where the press molding start temperature is high. In this case, after the press molding is started, the mold is rapidly cooled by heat removal from the mold to form a martensite single phase structure.
On the other hand, as shown in FIG. 2B, when the press molding start temperature is low, ferrite and bainite are generated before the press molding starts, and the strength of the press molded product after press molding is lowered.
Thus, simply lowering the press molding start temperature results in the form of FIG.
On the other hand, in the present invention, by adopting a cooling process capable of rapid cooling before the start of press molding, a martensitic single phase structure is obtained while lowering the molding start temperature as shown by the dashed curve in FIG. Making it possible.
The upper limit of the cooling rate is usually about 500 ° C./s.
　また、この冷却工程における冷却停止温度を550℃以下としているのは、550℃超では冷却が不十分となり、熱間プレス成形後にミクロクラックが生成するからである。好ましくは500℃以下である。一方、冷却停止温度の下限値を410℃としたのは、410℃未満ではプレス成形前に表面処理鋼板１が過度に冷却されてプレス成形後の形状凍結性が低下するからである。好ましくは430℃以上である。 Also, the reason why the cooling stop temperature in this cooling step is set to 550 ° C. or less is that if it exceeds 550 ° C., cooling becomes insufficient and micro cracks are generated after hot press forming. Preferably it is 500 degrees C or less. On the other hand, the lower limit of the cooling stop temperature is set to 410 ° C., if the temperature is lower than 410 ° C., the surface-treated steel sheet 1 is excessively cooled before press forming, and the shape freezing property after press forming is lowered. Preferably it is 430 ° C or more.
　この冷却工程における冷却速度および冷却停止温度は、例えば、冷却用金型３で表面処理鋼板１を保持している時間によって制御することができる（図１参照）。また、冷却用金型３で表面処理鋼板１を挟むことによる表面処理鋼板１の温度変化は、図４に示す鋼板に0.5mmφのシース熱電対１９を挿入して表面処理鋼板１の温度を測定することにより求めることができる。図５はその結果の一例を示すグラフであり、縦軸が温度（℃）、横軸が時間（ｓ）を示している。また、図６は図５における破線で囲んだ部分の横軸を拡大して示すグラフである。冷却用金型による冷却時の温度変化は、図６に示すように、約160℃/sであり急冷が可能であることが分かる。 The cooling rate and cooling stop temperature in this cooling step can be controlled by, for example, the time that the surface-treated steel sheet 1 is held by the cooling mold 3 (see FIG. 1). The temperature change of the surface-treated steel sheet 1 by sandwiching the surface-treated steel sheet 1 with the cooling mold 3 is measured by inserting a 0.5 mmφ sheath thermocouple 19 into the steel sheet shown in FIG. Can be obtained. FIG. 5 is a graph showing an example of the result. The vertical axis represents temperature (° C.) and the horizontal axis represents time (s). FIG. 6 is a graph showing an enlarged horizontal axis of a portion surrounded by a broken line in FIG. As shown in FIG. 6, the temperature change during cooling by the cooling mold is about 160 ° C./s, and it can be seen that rapid cooling is possible.
　また、一実施形態における実験として、冷却用金型での保持時間（特に冷却用金型による冷却停止温度）と、後述するプレス成形開始温度を種々変化させて、プレス成形品を作製し、次の評価を行った。評価項目としては、プレス成形品の縦壁部の断面を観察して、ミクロクラックの有無を確認すること、成形品の硬度を確認すること、プレス成形荷重を確認すること、成形品のハット開口部の口開き量（成形後に離型した開口部の幅寸法と金型形状での成形品幅との差）を確認することで形状凍結性を確認することである。 Further, as an experiment in one embodiment, a press-molded product was manufactured by changing the holding time in the cooling mold (particularly the cooling stop temperature by the cooling mold) and the press-molding start temperature described later in various ways. Was evaluated. As evaluation items, observe the cross section of the vertical wall of the press-molded product to confirm the presence or absence of microcracks, confirm the hardness of the molded product, confirm the press-molding load, and open the hat of the molded product. The shape freezing property is confirmed by confirming the opening amount of the part (the difference between the width dimension of the opening part released after molding and the width of the molded product in the mold shape).
　図７は、冷却用金型での冷却時間（冷却用金型による冷却停止温度）およびプレス成形開始温度を種々変化させた場合における、プレス成形品の縦壁部のダイ１３と接した側の表層の断面のSEM像である。図７より、冷却用金型での冷却時間が0.9s以上（プレス成形開始温度550℃以下）で素地鋼板にミクロクラックが認められなくなることが分かる。また、全ての条件でHv＞450であり焼入れ性の低下がないことが確認された。 FIG. 7 shows the side of the vertical wall portion of the press-molded product in contact with the die 13 when the cooling time in the cooling die (cooling stop temperature by the cooling die) and the press molding start temperature are variously changed. It is a SEM image of a section of a surface layer. From FIG. 7, it can be seen that when the cooling time in the cooling mold is 0.9 s or more (press forming start temperature 550 ° C. or less), microcracks are not recognized in the base steel sheet. Moreover, it was confirmed that Hv> 450 under all conditions and there was no deterioration in hardenability.
　図８はプレス成形開始温度とプレス成形荷重の関係を示す図であり、縦軸がプレス成形荷重（kN）、横軸がプレス成形開始温度（℃）である。図８に示すように、プレス成形前の冷却用金型での冷却によるプレス成形開始温度の低下に伴い、プレス成形荷重が増加するが、ミクロクラックの発生が無くなる550℃程度の温度では軟鋼（270D、冷間ドロー成形）と同等レベルのプレス成形荷重であり、問題ないことがわかる。 FIG. 8 is a diagram showing the relationship between the press molding start temperature and the press molding load, where the vertical axis represents the press molding load (kN) and the horizontal axis represents the press molding start temperature (° C.). As shown in FIG. 8, the press molding load increases as the press molding start temperature decreases due to cooling in the cooling mold before press molding, but mild steel (at a temperature of about 550 ° C. at which generation of microcracks is eliminated. 270D, cold draw forming), which is equivalent to the press forming load.
　図９はプレス成形開始温度と口開き量の関係を示す図であり、縦軸が成形品の口開き量（mm）、横軸がプレス成形開始温度（℃）である。図９に示すように、プレス成形前の冷却用金型での冷却によるプレス成形開始温度の低下に伴い、口開き量が増しており、形状凍結性が低下する傾向を示しているが、プレス成形開始温度が400℃まではほとんど形状凍結性の低下は認められない。 FIG. 9 is a diagram showing the relationship between the press molding start temperature and the opening amount, where the vertical axis represents the opening amount (mm) of the molded product, and the horizontal axis represents the press molding start temperature (° C.). As shown in FIG. 9, the amount of opening increases as the press molding start temperature decreases due to cooling in the cooling mold before press molding, and the shape freezeability tends to decrease. There is almost no decrease in shape freezing property until the molding start temperature is 400 ° C.
　以上のことから、所定の冷却用金型を用いて、表面処理鋼板を100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却し、さらに、後述するように、冷却後5秒以内で、かつ550℃以下400℃以上の温度でプレス成形を開始することにより、プレス成形荷重を増すことなく、ミクロクラックの発生のない、十分な硬度と形状凍結性を有するプレス成形品を製造できることがわかる。 From the above, using a predetermined cooling mold, the surface-treated steel sheet is cooled to a temperature of 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher. By starting press molding within a second and at a temperature of 550 ° C or lower and 400 ° C or higher, a press-molded product with sufficient hardness and shape freezing property that does not generate microcracks without increasing the press molding load. It can be seen that it can be manufactured.
＜プレス成形工程＞
　プレス成形工程（Ｓ２）は、表面処理鋼板１を製品形状にプレス成形する工程である。プレス成形工程は、冷却工程の後、プレス成形金型１１により行う。プレス成形金型１１は、図１に示すように、ダイ１３とパンチ１７を備える。そして、ダイ１３とパンチ１７で表面処理鋼板１を挟むことでプレス成形を行い、成形体１´とする。 <Press molding process>
The press forming step (S2) is a step of press forming the surface-treated steel sheet 1 into a product shape. The press molding process is performed by the press molding die 11 after the cooling process. The press molding die 11 includes a die 13 and a punch 17 as shown in FIG. Then, press-molding is performed by sandwiching the surface-treated steel sheet 1 between the die 13 and the punch 17 to obtain a molded body 1 ′.
　上述したように、冷却工程において、冷却用金型３を用いて表面処理鋼板１を100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却し、ついで冷却用金型３から表面処理鋼板１を抜き出し、550℃以下400℃以上の温度でプレス成形を開始することで、プレス成形荷重を増すことなく、ミクロクラックの発生のない、十分な硬度と形状凍結性を有するプレス成形品を製造することが可能となる。
　また、冷却工程の後、5秒以内にプレス成形工程を開始するのは、冷却後、プレス成形を開始するまでの時間が5秒を超えると、プレス成形開始前にフェライトやベイナイトなどの生成が起こり、マルテンサイト単相組織が得られず、プレス成形品の硬度が不十分となるためである。冷却後、プレス成形開始までの時間は、好ましくは3秒以内である。なお、下限については特に限定されるものではないが、通常、1秒以上とすることが好適である。 As described above, in the cooling process, the surface-treated steel sheet 1 is cooled to a temperature of 550 ° C. or lower and 410 ° C. or higher using the cooling die 3 at a cooling rate of 100 ° C./s or higher. By extracting the surface-treated steel sheet 1 and starting press forming at a temperature of 550 ° C or lower and 400 ° C or higher, press forming with sufficient hardness and shape freezing property without increasing micro-cracking without increasing the press forming load. The product can be manufactured.
In addition, the press molding process starts within 5 seconds after the cooling process. If the time until the press molding starts after cooling exceeds 5 seconds, ferrite, bainite, etc. are generated before the press molding starts. This is because a martensite single-phase structure cannot be obtained and the hardness of the press-formed product becomes insufficient. The time until the start of press molding after cooling is preferably within 3 seconds. The lower limit is not particularly limited, but it is usually preferably 1 second or longer.
　プレス成形方法については特に限定されない。図１０(a)に示したように、ダイ１３とブランクホルダ１５で表面処理鋼板１を挟んだまま成形を行うドロー成形、あるいは図１０(b)に示したように、ブランクホルダ１５を下げるか、または、ブランクホルダ１５を使用せずに成形を行うフォーム成形などが可能である。ミクロクラック抑制の観点からはプレス成形品の縦壁部の加工度合いが小さくなるフォーム成形の方が好ましい。 The press molding method is not particularly limited. As shown in FIG. 10 (a), draw forming is performed with the die 13 and the blank holder 15 sandwiching the surface-treated steel sheet 1, or is the blank holder 15 lowered as shown in FIG. 10 (b)? Alternatively, it is possible to perform foam molding that performs molding without using the blank holder 15. From the viewpoint of suppressing microcracks, foam molding is preferable because the degree of processing of the vertical wall portion of the press-molded product is small.
＜焼入れ工程＞
　焼入れ工程（Ｓ３）は、プレス成形後、成形体１´をプレス成形金型１１で挟んだまま保持して成形体１´を焼入れ、熱間プレス成形品を得る工程である。プレス成形後にプレス成形金型１１により成形体１´を焼入れるためには、プレス成形後に成形下死点においてスライドを停止する。停止時間は金型による抜熱量により異なるが3秒以上とすることが好ましい。停止時間の上限については特に限定されるものではないが、生産性の観点から20秒以下とすることが好ましい。 <Hardening process>
The quenching step (S3) is a step of obtaining a hot press-molded product by holding the molded body 1 'while being sandwiched between the press-molding dies 11 and then quenching the molded body 1'. In order to quench the molded body 1 ′ by the press molding die 11 after the press molding, the slide is stopped at the bottom dead center of the molding after the press molding. The stop time varies depending on the amount of heat removed by the mold, but is preferably 3 seconds or more. The upper limit of the stop time is not particularly limited, but is preferably 20 seconds or less from the viewpoint of productivity.
　なお、金型内に所定時間保持して素地鋼板を焼入れ組織とするには、例えば、質量%で、C：0.15%以上0.50%以下、Si：0.05%以上2.00%以下、Mn：0.50%以上3.00%以下、P：0.10%以下、S：0.050%以下、Al：0.10%以下、N：0.010%以下を含有し、残部がFeおよび不可避的不純物からなる成分組成を有する熱延鋼板や冷延鋼板を用いることができる。以下、この成分組成について説明する。ここで、成分の含有量を示す「%」は特に断らない限り「質量%」を意味する。 In order to make the base steel sheet into a quenched structure by holding it in the mold for a predetermined time, for example, in mass%, C: 0.15% to 0.50%, Si: 0.05% to 2.00%, Mn: 0.50% or more 3.00% or less, P: 0.10% or less, S: 0.050% or less, Al: 0.10% or less, N: 0.010% or less, the hot-rolled steel sheet or the cold-rolled steel having a composition composed of Fe and inevitable impurities as the balance A steel plate can be used. Hereinafter, this component composition is demonstrated. Here, “%” indicating the content of a component means “% by mass” unless otherwise specified.
《C：0.15%以上0.50%以下》
　Cは鋼の強度を向上させる元素であり、熱間プレス成形品の高強度化のためにはその量を0.15%以上とすることが好ましい。一方、C量が0.50%を超えると、熱間プレス成形品の溶接性や素材（素地鋼板）のブランキング性が著しく低下する。したがって、C含有量は0.15%以上0.50%以下とすることが好ましく、0.20%以上0.40%以下とすることがより好ましい。 《C: 0.15% to 0.50%》
C is an element for improving the strength of the steel, and the amount is preferably 0.15% or more in order to increase the strength of the hot press-formed product. On the other hand, when the amount of C exceeds 0.50%, the weldability of hot press-formed products and the blanking property of the material (base steel plate) are significantly reduced. Therefore, the C content is preferably 0.15% or more and 0.50% or less, and more preferably 0.20% or more and 0.40% or less.
《Si：0.05%以上2.00%以下》
　SiはCと同様に鋼の強度を向上させる元素であり、熱間プレス成形品の高強度化のためにはその量を0.05%以上とすることが好ましい。一方、Si量が2.00%を超えると、素地鋼板を製造する際、熱間圧延時に赤スケールと呼ばれる表面欠陥の発生が著しく増大する。したがって、Si含有量は0.05%以上2.00%以下とすることが好ましく、0.10%以上1.50%以下とすることがより好ましい。 << Si: 0.05% or more and 2.00% or less >>
Si, like C, is an element that improves the strength of steel, and the amount is preferably 0.05% or more in order to increase the strength of a hot press-formed product. On the other hand, when the Si content exceeds 2.00%, the occurrence of surface defects called red scale during hot rolling significantly increases during the production of the base steel sheet. Therefore, the Si content is preferably 0.05% or more and 2.00% or less, and more preferably 0.10% or more and 1.50% or less.
《Mn：0.50%以上3.00%》
　Mnは鋼の焼入れ性を高める元素であり、熱間プレス成形後の冷却過程で素地鋼板のフェライト変態を抑制して焼入れ性を向上させるのに効果的な元素である。また、MnはAc3変態点を低下させる作用を有するため、熱間プレス成形前の表面処理鋼板１の加熱温度を低温化するのに有効な元素である。このような効果の発現のためには、Mn含有量を0.50%以上とすることが好ましい。一方、Mn量が3.00%を超えると、Mnが偏析して素地鋼板および熱間プレス成形部材の特性の均一性が低下する。したがってMn含有量は0.50%以上3.00%以下とすることが好ましく、0.75%以上2.50%以下とすることがより好ましい。 《Mn: 0.50% to 3.00%》
Mn is an element that enhances the hardenability of steel, and is an effective element for improving the hardenability by suppressing the ferrite transformation of the base steel sheet during the cooling process after hot press forming. Further, Mn is an element effective for lowering the heating temperature of the surface-treated steel sheet 1 before hot press forming because it has an action of lowering the Ac 3 transformation point. In order to exhibit such an effect, the Mn content is preferably 0.50% or more. On the other hand, when the amount of Mn exceeds 3.00%, Mn is segregated and the uniformity of the properties of the base steel sheet and the hot press-formed member decreases. Therefore, the Mn content is preferably 0.50% or more and 3.00% or less, and more preferably 0.75% or more and 2.50% or less.
《P：0.10%以下》
　P含有量が0.10%を超えると、Pが粒界に偏析して素地鋼板および熱間プレス成形部材の低温靭性が低下する。したがって、P含有量は0.10%以下とすることが好ましく、0.01%以下とすることがより好ましい。ただし、過度のP低減は、製鋼工程におけるコストの増加を招く。そのため、Pは0.003%以上とすることが好ましい。 << P: 0.10% or less >>
When the P content exceeds 0.10%, P is segregated at the grain boundaries, and the low temperature toughness of the base steel sheet and the hot press-formed member decreases. Therefore, the P content is preferably 0.10% or less, and more preferably 0.01% or less. However, excessive P reduction causes an increase in cost in the steelmaking process. Therefore, P is preferably 0.003% or more.
《S：0.050%以下》
　SはMnと結合して粗大な硫化物を形成し、鋼の延性低下を招く元素である。そのため、S含有量は極力低減することが好ましいが、0.050%までは許容できる。したがって、S含有量は0.050%以下とすることが好ましく、0.010%以下とすることがより好ましい。ただし、過度のS低減は、製鋼工程における脱硫コストの増加を招く。そのため、Sは0.0005%以上とすることが好ましい。 << S: 0.050% or less >>
S is an element that combines with Mn to form coarse sulfides and causes a reduction in the ductility of the steel. Therefore, it is preferable to reduce the S content as much as possible, but it is acceptable up to 0.050%. Therefore, the S content is preferably 0.050% or less, and more preferably 0.010% or less. However, excessive S reduction leads to an increase in desulfurization cost in the steel making process. Therefore, S is preferably 0.0005% or more.
《Al：0.10%以下》
　Al含有量が0.10%を超えると酸化物系介在物の増加を招き、鋼の延性が低下する。したがって、Al含有量は0.10%以下とすることが好ましく、0.07%以下とすることがより好ましい。ただし、Alは脱酸材としての作用を有し、鋼の清浄度向上の観点からは、その含有量を0.01%以上とすることが好ましい。 <Al: 0.10% or less>
If the Al content exceeds 0.10%, the oxide inclusions increase and the ductility of the steel decreases. Therefore, the Al content is preferably 0.10% or less, and more preferably 0.07% or less. However, Al has an action as a deoxidizing material, and from the viewpoint of improving the cleanliness of steel, the content is preferably 0.01% or more.
《N：0.010%以下》
　N含有量が0.010%を超えると、素地鋼板中にAlN等の窒化物が形成され、熱間プレス成形時の成形性の低下を招く。したがって、N含有量は0.010%以下とすることが好ましく、0.005%以下とすることがより好ましい。ただし、過度のN低減は製鋼工程におけるコストの増加を招く。そのため、Nは0.001%以上とすることが好ましい。 <N: 0.010% or less>
When the N content exceeds 0.010%, a nitride such as AlN is formed in the base steel sheet, resulting in a decrease in formability during hot press forming. Therefore, the N content is preferably 0.010% or less, and more preferably 0.005% or less. However, excessive N reduction causes an increase in cost in the steelmaking process. Therefore, N is preferably 0.001% or more.
　以上が本発明の製造方法おいて素材として使用する素地鋼板の好ましい基本成分であるが、該素地鋼板は必要に応じて更に以下の元素を含有してもよい。
Cr：0.01%以上0.50%以下、V：0.01%以上0.50%以下、Mo：0.01%以上0.50%以下、Ni：0.01以上0.50%以下のうちの１種以上
　Cr、V、Mo、Niはいずれも鋼の焼き入れ性を向上させるのに有効な元素である。この効果は、いずれの元素の場合も含有量を0.01%以上とすることにより得られる。しかし、Cr、V、Mo、Niはいずれも含有量が0.50％を超えると上記効果は飽和し、コストアップの要因となる。したがって、Cr、V、Mo、Niのうちの1種以上を含有する場合には、それぞれ含有量を0.01%以上0.50%以下とすることが好ましく、0.10%以上0.40%以下とすることがより好ましい。 Although the above is a preferable basic component of the base steel plate used as a raw material in the manufacturing method of this invention, this base steel plate may contain the following elements further as needed.
Cr: 0.01% or more and 0.50% or less, V: 0.01% or more and 0.50% or less, Mo: 0.01% or more and 0.50% or less, Ni: 0.01 or more and 0.50% or less, Cr, V, Mo and Ni are all It is an effective element for improving the hardenability of steel. This effect can be obtained by setting the content to 0.01% or more for any element. However, if the Cr, V, Mo, and Ni content exceeds 0.50%, the above effect is saturated, which increases the cost. Accordingly, when containing one or more of Cr, V, Mo, Ni, the content is preferably 0.01% or more and 0.50% or less, more preferably 0.10% or more and 0.40% or less. .
　Ti：0.01%以上0.20%以下
　Tiは鋼の強化に有効である。Tiによる強度上昇効果は、その含有量を0.01%以上とすることで得られ、ここで規定する範囲内であれば、鋼の強化に使用して差し支えない。しかし、Ti含有量が0.20%を超えるとその効果は飽和し、コストアップの要因となる。従って、Tiを含有する場合には、0.01%以上0.20%以下とすることが好ましく、0.01%以上0.05%以下とすることがより好ましい。 Ti: 0.01% or more and 0.20% or less Ti is effective for strengthening steel. The strength increasing effect by Ti can be obtained by setting its content to 0.01% or more, and if it is within the range specified here, it can be used for strengthening steel. However, when the Ti content exceeds 0.20%, the effect is saturated, resulting in a cost increase. Accordingly, when Ti is contained, it is preferably 0.01% or more and 0.20% or less, and more preferably 0.01% or more and 0.05% or less.
　Nb：0.01%以上0.10%以下
Nbも鋼の強化に有効である。Nbによる強度上昇効果は、その含有量を0.01%以上とすることで得られ、ここで規定する範囲内であれば、鋼の強化に使用して差し支えない。しかし、Nb含有量が0.10%を超えるとその効果は飽和し、コストアップの要因となる。従って、Nbを含有する場合には、0.01%以上0.10%以下とすることが好ましく、0.01%以上0.05%以下とすることがより好ましい。 Nb: 0.01% or more and 0.10% or less
Nb is also effective for strengthening steel. The effect of increasing the strength by Nb can be obtained by setting its content to 0.01% or more. If it is within the range specified here, it can be used for strengthening steel. However, if the Nb content exceeds 0.10%, the effect is saturated, resulting in a cost increase. Therefore, when Nb is contained, it is preferably 0.01% or more and 0.10% or less, and more preferably 0.01% or more and 0.05% or less.
　B：0.0002%以上0.0050%以下
　Bは鋼の焼入れ性を高める元素であり、熱間プレス成形後に素地鋼板が冷却される際、オーステナイト粒界からのフェライトの生成を抑制して焼入れ組織を得るのに有効な元素である。その効果はB含有量を0.0002%以上で得られるが、0.0050%を超えるとその効果は飽和し、コストアップの要因となる。したがって、Bを含有する場合には、その含有量を0.0002%以上0.0050%以下とすることが好ましい。より好ましくは0.0005%以上0.0030%以下である。 B: 0.0002% or more and 0.0050% or less B is an element that enhances the hardenability of steel. When the base steel sheet is cooled after hot press forming, it suppresses the formation of ferrite from the austenite grain boundaries and obtains a hardened structure. Is an effective element. The effect can be obtained when the B content is 0.0002% or more. However, if the B content exceeds 0.0050%, the effect is saturated, resulting in a cost increase. Therefore, when B is contained, the content is preferably 0.0002% or more and 0.0050% or less. More preferably, it is 0.0005% or more and 0.0030% or less.
　Sb：0.003%以上0.030%以下
　Sbは熱間プレス成形前に鋼板を加熱してから熱間プレス成形の一連の処理によって鋼板を冷却するまでの間に、素地鋼板表層部に生じる脱炭層を抑制する効果を有する。このような効果の発現のためには、Sb含有量を0.003%以上とすることが好ましい。しかし、Sb含有量が0.030%を超えると素地鋼板製造時に圧延荷重の増大を招き、生産性の低下が懸念される。したがって、Sbを含有する場合には、その含有量を0.003%以上0.030%以下とすることが好ましく、0.005%以上0.010%以下とすることがより好ましい。 Sb: 0.003% or more and 0.030% or less Sb suppresses the decarburization layer generated in the surface layer of the base steel sheet from the time the steel sheet is heated before hot press forming until the steel sheet is cooled by a series of hot press forming processes. Has the effect of In order to exhibit such an effect, the Sb content is preferably 0.003% or more. However, if the Sb content exceeds 0.030%, the rolling load increases during the production of the base steel sheet, and there is a concern that the productivity may be reduced. Therefore, when Sb is contained, the content is preferably 0.003% or more and 0.030% or less, and more preferably 0.005% or more and 0.010% or less.
　なお、上記成分以外の成分(残部)は、Feおよび不可避的不純物である。 In addition, components (remainder) other than the above components are Fe and inevitable impurities.
　本発明において熱間プレス成形部材の素材として用いる表面処理鋼板１は、その製造条件に特段の制限はない。素地鋼板の製造条件は特に限定されず、例えば所定の成分組成を有する熱延鋼板（酸洗鋼板）や熱延鋼板に冷間圧延を施すことにより得られる冷延鋼板を素地鋼板としても良い。
　また、素地鋼板の表面に、Zn-Niめっき層を形成して表面処理鋼板１とする際の条件も、特に限定されない。素地鋼板として熱延鋼板（酸洗鋼板）を用いる場合には、熱延鋼板（酸洗鋼板）にZn-Niめっき処理を施すことにより、表面処理鋼板１とすることができる。 In the present invention, the surface-treated steel sheet 1 used as a raw material of the hot press-formed member is not particularly limited in its production conditions. The production conditions of the base steel sheet are not particularly limited. For example, a hot-rolled steel sheet (pickled steel sheet) having a predetermined composition and a cold-rolled steel sheet obtained by cold rolling a hot-rolled steel sheet may be used as the base steel sheet.
Moreover, the conditions at the time of forming the Zn-Ni plating layer on the surface of the base steel sheet to form the surface-treated steel sheet 1 are not particularly limited. When a hot-rolled steel plate (pickled steel plate) is used as the base steel plate, the surface-treated steel plate 1 can be obtained by subjecting the hot-rolled steel plate (pickled steel plate) to a Zn—Ni plating treatment.
　一方、素地鋼板として冷延鋼板を用いる場合には、冷間圧延後そのまま、あるいは焼鈍処理を行った後、Zn-Niめっき処理を施すことにより、表面処理鋼板１とすることができる。 On the other hand, when a cold-rolled steel sheet is used as the base steel sheet, the surface-treated steel sheet 1 can be obtained by performing a Zn-Ni plating process as it is after cold rolling or after annealing.
　また、素地鋼板表面にZn-Niめっき層を形成する場合、例えば、素地鋼板を、脱脂、酸洗した後、100g/L以上400g/L以下の硫酸ニッケル六水和物、10g/L以上400g/L以下の硫酸亜鉛七水和物を含有するpH1.0以上3.0以下、浴温30℃以上70℃以下のめっき浴中で、10A/dm2以上150A/dm2以下の電流密度で電気めっき処理を行うことにより、Zn-Niめっき層を形成することができる。
　なお、素地鋼板として冷延鋼板を用いる場合には、上記脱脂、酸洗に先立ち、冷延鋼板に焼鈍処理を施してもよい。めっき層中のNi含有量は、硫酸亜鉛七水和物の濃度や電流密度を上記の範囲内で適宜調整することにより、所望のNi含有量（例えば、9質量%以上25質量%以下）とすることができる。また、Zn-Niめっき層の付着量は、通電時間を調整することにより、所望の付着量（例えば、片面あたり10g/m2以上90g/m2以下）とすることができる。 Also, when forming a Zn-Ni plating layer on the surface of the base steel plate, for example, after degreasing and pickling the base steel plate, nickel sulfate hexahydrate of 100 g / L to 400 g / L, 10 g / L to 400 g Electroplating at a current density of 10 A / dm 2 or more and 150 A / dm 2 or less in a plating bath containing zinc sulfate heptahydrate at a pH of 1.0 to 3.0 and a bath temperature of 30 ° C. to 70 ° C. By performing the treatment, a Zn—Ni plating layer can be formed.
In addition, when using a cold-rolled steel plate as a base steel plate, you may anneal a cold-rolled steel plate prior to the said degreasing | defatting and pickling. The Ni content in the plating layer can be adjusted to the desired Ni content (for example, 9% by mass to 25% by mass) by appropriately adjusting the concentration and current density of zinc sulfate heptahydrate within the above ranges. can do. The coating weight of Zn-Ni plated layer, by adjusting the energization time can be desired adhesion amount (e.g., 10 g / m 2 or more per side 90 g / m 2 or less).
　本発明に係る熱間プレス成形品の製造方法の効果を確認する実験を行ったので、以下これについて説明する。
　表1に示す成分を有する鋼を溶製して鋳片として、該鋳片を1200℃に加熱し、870℃の仕上げ圧延終了温度で熱間圧延を施した後、600℃で巻き取り、熱延鋼板とした。 Since an experiment for confirming the effect of the method for producing a hot press-formed product according to the present invention was conducted, this will be described below.
As a slab by melting steel having the components shown in Table 1, the slab is heated to 1200 ° C, subjected to hot rolling at a finish rolling finish temperature of 870 ° C, and then wound up at 600 ° C and heated. A rolled steel sheet was used.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　次いで、該熱延鋼板を酸洗後50%の圧下率で冷間圧延し、板厚1.6mmの冷延鋼板とした。表1に記載のAc3変態点は、以下の（１）式より算出した（William C.Leslie著、幸田成康監訳、熊井浩、野田龍彦訳、「レスリー鉄鋼材料学」、丸善株式会社、1985年、p.273参照）。
　Ac3（℃）=910-203[C]0.5+44.7×[Si]-30×[Mn]+700×[P]+400×[Al]　・・・（１）
なお、（１）式において、[C]、[Si]、[Mn]、[P]、[Al]は、各元素（C、Si、Mn、P、Al）の鋼中含有量（質量%）である。
　以上のようにして得られた冷延鋼板を素地鋼板とし、素地鋼板の表面に、純Znめっき層、Zn-Feめっき層、Zn-Niめっき層の各めっき層を形成して表面処理鋼板１とした。各めっき層は、以下の条件で形成した。 Next, the hot-rolled steel sheet was pickled and cold-rolled at a reduction rate of 50% to obtain a cold-rolled steel sheet having a thickness of 1.6 mm. The Ac 3 transformation point shown in Table 1 was calculated from the following equation (1) (William C. Leslie, translated by Kouda Shigeyasu, Kumai Hiroshi, Noda Tatsuhiko, "Leslie Steel Materials Science", Maruzen Co., Ltd., 1985 Year, p.273).
Ac 3 (℃) = 910-203 [C] 0.5 + 44.7 × [Si] -30 × [Mn] + 700 × [P] + 400 × [Al] (1)
In the formula (1), [C], [Si], [Mn], [P], and [Al] are the contents (% by mass) of each element (C, Si, Mn, P, Al) in steel. ).
The cold-rolled steel sheet obtained as described above is used as a base steel sheet, and a surface-treated steel sheet 1 is formed by forming each of the pure Zn plating layer, Zn-Fe plating layer, and Zn-Ni plating layer on the surface of the base steel plate. It was. Each plating layer was formed under the following conditions.
＜純Znめっき層＞
　冷延鋼板を連続溶融亜鉛めっきラインに通板し、10℃/sの昇温速度で800℃以上900℃以下の温度域まで加熱し、該温度域に10s以上120s以下滞留させた後、15℃/sの冷却速度で460℃以上500℃以下の温度域まで冷却し、450℃の亜鉛めっき浴に浸漬することにより、Znめっき層を形成した。Znめっき層の付着量は、ガスワイピング法により所定の付着量に調整した。 <Pure Zn plating layer>
The cold-rolled steel sheet is passed through a continuous hot-dip galvanizing line, heated to a temperature range of 800 ° C. or higher and 900 ° C. or lower at a temperature increase rate of 10 ° C./s. The Zn plating layer was formed by cooling to a temperature range of 460 ° C. or more and 500 ° C. or less at a cooling rate of ° C./s and dipping in a 450 ° C. zinc plating bath. The adhesion amount of the Zn plating layer was adjusted to a predetermined adhesion amount by a gas wiping method.
＜Zn-Feめっき層＞
　冷延鋼板を連続溶融亜鉛めっきラインに通板し、10℃/sの昇温速度で800℃以上900℃以下の温度域まで加熱し、該温度域に10s以上120s以下滞留させた後、15℃/sの冷却速度で460℃以上500℃以下の温度域まで冷却し、450℃の亜鉛めっき浴に浸漬することにより、Znめっき層を形成した。Znめっき層の付着量は、ガスワイピング法により所定の付着量に調整した。ガスワイピング法により所定の付着量に調整した後、直ちに合金化炉で500～550℃に加熱して5～60s保持することにより、Zn-Feめっき層を形成した。めっき層中のFe含有量は、合金化炉での加熱温度や該加熱温度での滞留時間を上記の範囲内で変更することにより、所定の含有量とした。 <Zn-Fe plating layer>
The cold-rolled steel sheet is passed through a continuous hot-dip galvanizing line, heated to a temperature range of 800 ° C. or higher and 900 ° C. or lower at a temperature increase rate of 10 ° C./s. The Zn plating layer was formed by cooling to a temperature range of 460 ° C. or more and 500 ° C. or less at a cooling rate of ° C./s and dipping in a 450 ° C. zinc plating bath. The adhesion amount of the Zn plating layer was adjusted to a predetermined adhesion amount by a gas wiping method. After adjusting to a predetermined adhesion amount by a gas wiping method, a Zn—Fe plating layer was formed by immediately heating to 500 to 550 ° C. in an alloying furnace and holding for 5 to 60 seconds. The Fe content in the plating layer was set to a predetermined content by changing the heating temperature in the alloying furnace and the residence time at the heating temperature within the above range.
＜Zn-Niめっき層＞
　冷延鋼板を連続焼鈍ラインに通板し、10℃/sの昇温速度で800℃以上900℃以下の温度域まで加熱し、該温度域に10ｓ以上120ｓ以下滞留させた後、15℃/sの冷却速度で500℃以下の温度域まで冷却した。次いで、脱脂、酸洗した後、200g/Lの硫酸ニッケル六水和物、10～300g/Lの硫酸亜鉛七水和物を含有するpH1.3、浴温50℃のめっき浴中、30～100A/dm2の電流密度で10～100s通電する電気めっき処理を行うことにより、Zn-Niめっき層を形成した。めっき層中のNi含有量は、硫酸亜鉛七水和物の濃度や電流密度を上記の範囲内で適宜調整することにより、所定の含有量とした。また、Zn-Niめっき層の付着量は、通電時間を上記の範囲内で適宜調整することにより、所定の付着量とした。 <Zn-Ni plating layer>
The cold-rolled steel sheet is passed through a continuous annealing line, heated to a temperature range of 800 ° C to 900 ° C at a rate of 10 ° C / s, and retained in the temperature range for 10s to 120s, then 15 ° C / s It cooled to the temperature range below 500 degreeC with the cooling rate of s. Next, after degreasing and pickling, in a plating bath containing 200 g / L nickel sulfate hexahydrate and 10 to 300 g / L zinc sulfate heptahydrate at a pH of 1.3 and a bath temperature of 50 ° C., 30 to A Zn—Ni plating layer was formed by performing an electroplating process in which a current of 10 to 100 s was applied at a current density of 100 A / dm 2 . The Ni content in the plating layer was set to a predetermined content by appropriately adjusting the concentration and current density of zinc sulfate heptahydrate within the above ranges. Moreover, the adhesion amount of the Zn—Ni plating layer was set to a predetermined adhesion amount by appropriately adjusting the energization time within the above range.
　以上のようにして得られた表面処理鋼板から、200mm×400mmのブランク板を打抜き、該ブランク板を大気雰囲気の電気炉により加熱したのち、ブランク板を冷却用金型（材料：SKD61）に設置し、表２に示す条件で、金型による冷却、プレス成形および焼入れを行った。そして、金型内で焼入れた後、離型することにより、図１１に示すハット断面形状のプレス成形品を製造した。金型の形状は、パンチ肩R：6mm、ダイ肩R：6mmの金型を用い、パンチ-ダイのクリアランス：1.6mmとした。プレス成形前の表面処理鋼板の冷却は、冷却用金型との接触で行った。プレス成形は、98ｋNのしわ押さえ力をかけたまま成形するドロー成形と、しわ押さえ無しで成形するフォーム成形にて行った。 A 200mm x 400mm blank plate is punched from the surface-treated steel plate obtained as described above, and the blank plate is heated by an electric furnace in an atmospheric atmosphere, and then the blank plate is placed in a cooling mold (material: SKD61). Then, under the conditions shown in Table 2, cooling with a mold, press molding, and quenching were performed. And after quenching in a metal mold | die, the press molded article of the hat cross-sectional shape shown in FIG. 11 was manufactured by releasing. The molds were punch punch R: 6 mm and die shoulder R: 6 mm, and the punch-die clearance was 1.6 mm. The surface-treated steel sheet before press forming was cooled by contact with a cooling mold. The press molding was performed by a draw molding in which a 98 kN wrinkle pressing force was applied and a foam molding in which no wrinkle pressing was performed.
　ブランク板の加熱温度、素地鋼板の種類、めっき層の種類、加熱条件、冷却条件およびプレス成形条件を表２に示す。 Table 2 shows the heating temperature of the blank plate, the type of the base steel plate, the type of the plating layer, the heating condition, the cooling condition, and the press molding condition.
　また、得られたハット断面形状のプレス成形品の縦壁部からサンプルを採取し、その表面の断面を、走査型電子顕微鏡（SEM）を用いて倍率1000倍で各サンプルにつき10視野観察し、ミクロクラック（サンプル表面に生じる微小割れであって、めっき層-素地鋼板の界面を貫通して素地鋼板内部に至る微小割れ）の有無、およびミクロクラックの平均深さを調べた。ミクロクラックの平均深さは、任意のミクロクラック20個分のミクロクラック深さの平均値として求めた。なお、ここでいう「ミクロクラック深さ」とは、図１２に示すようにミクロクラック２１の、めっき層２３と素地鋼板２５の界面から測定される板厚中央方向への割れの長さ（図１２中、hの長さ）を意味する。観察されるミクロクラックの個数が20個未満である場合には、観察される全てのミクロクラック深さの平均深さとした。
　また、得られたプレス成形部材の形状精度について図１３に示すハット断面形状のプレス成形品の離型後の成形品幅Ｗと金型形状での成形品幅Ｗ0の差（Ｗ－Ｗ0）を口開き量として評価した。
　これらの結果も表２に併記する。 In addition, a sample was taken from the vertical wall portion of the press-formed product with the obtained hat cross-sectional shape, and the cross section of the surface was observed with 10 fields of view for each sample at a magnification of 1000 using a scanning electron microscope (SEM). The presence or absence of microcracks (microcracks that occurred on the surface of the sample and penetrated through the plating layer-base steel plate interface to the inside of the base steel plate) and the average depth of the microcracks were examined. The average depth of microcracks was determined as the average value of the depth of microcracks for 20 arbitrary microcracks. As used herein, “microcrack depth” refers to the length of the crack in the center direction of the thickness of the microcrack 21 measured from the interface between the plating layer 23 and the base steel plate 25 (see FIG. 12). 12, the length of h). When the number of observed microcracks was less than 20, the average depth of all the observed microcracks was taken.
Further, regarding the shape accuracy of the obtained press-molded member, the difference (W−W 0) between the molded product width W after mold release of the press-molded product having the hat cross-sectional shape shown in FIG. 13 and the molded product width W 0 in the mold shape. ) Was evaluated as the amount of opening.
These results are also shown in Table 2.
　さらに、得られたハット断面形状のプレス成形品の縦壁部から、硬度測定用のサンプルを採取した。このサンプルの断面の硬度をマイクロビッカース硬度計にて求めた。試験荷重を9.8Ｎとして試験を行い、板厚方向中央部を５点測定し、その平均値をサンプルの硬度とした。なお、ここで目標とする硬度は400Hv以上である。
　加えて、得られたハット断面形状のプレス成形品の縦壁部から、JIS 13 B号引張試験片を採取した。この採取した試験片を用いて、JIS G 0567(1998)に準拠して引張試験を行い、室温（22±5℃）における引張強さを測定した。なお、引張試験はいずれも、クロスヘッドスピード：10mm/minで行った。なお、ここで目標とする引張強さは1180MPa以上である。
　これらの結果も表２に併記する。 Further, a sample for hardness measurement was taken from the vertical wall portion of the press-formed product having the hat cross-sectional shape. The hardness of the cross section of this sample was determined with a micro Vickers hardness tester. The test was conducted at a test load of 9.8 N, the central portion in the thickness direction was measured at five points, and the average value was taken as the hardness of the sample. Here, the target hardness is 400 Hv or more.
In addition, a JIS 13 B tensile test piece was collected from the vertical wall portion of the obtained press-formed product having a hat cross-sectional shape. Using this collected specimen, a tensile test was performed according to JIS G 0567 (1998), and the tensile strength at room temperature (22 ± 5 ° C.) was measured. All tensile tests were performed at a crosshead speed of 10 mm / min. The target tensile strength here is 1180 MPa or more.
These results are also shown in Table 2.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　発明例１～１０において、めっき層の種類（Zn-Niめっき層）、冷却方法（金型冷却）、冷却時間（0.6s～1.7s）、冷却速度（適正範囲：100℃/s以上）、および冷却停止温度（適正範囲：410℃～550℃）、冷却後プレス成形開始までの時間（適正範囲：５秒以内）、プレス成形開始温度（適正範囲400℃～550℃）は、すべて適正範囲内にある。プレス後サンプルには、ミクロクラックは発生せず、口開き量も0mmであった。これにより、本発明のプレス成形方法では、良好な形状凍結性を確保しつつ、ミクロクラックの生成を抑制することが可能であることがわかる。 In Invention Examples 1 to 10, the type of plating layer (Zn—Ni plating layer), cooling method (mold cooling), cooling time (0.6 s to 1.7 s), cooling rate (appropriate range: 100 ° C./s or more), Also, the cooling stop temperature (proper range: 410 ° C to 550 ° C), the time to start press forming after cooling (proper range: within 5 seconds), and the press molding start temperature (proper range 400 ° C to 550 ° C) are all in the proper range. Is in. The sample after pressing had no microcracks and the opening amount was 0 mm. Thereby, in the press molding method of this invention, it turns out that the production | generation of a microcrack can be suppressed, ensuring favorable shape freezing property.
　一方、比較例１は、冷却用金型で冷却することなく成形を行ったものである。また、比較例２～４は、冷却停止温度が適正範囲（410℃～550℃）外のものである。具体的には、比較例２の冷却停止温度が600℃、比較例３、４の冷却停止温度が340℃、290℃である。 On the other hand, Comparative Example 1 was formed without cooling with a cooling mold. In Comparative Examples 2 to 4, the cooling stop temperature is outside the proper range (410 ° C. to 550 ° C.). Specifically, the cooling stop temperature of Comparative Example 2 is 600 ° C., and the cooling stop temperatures of Comparative Examples 3 and 4 are 340 ° C. and 290 ° C.
　比較例１、２では、口開き量は0mmであるが、ミクロクラックが発生している。これにより、鋼板の成形開始温度が550℃より高い場合には、ミクロクラックが発生することがわかる。
　比較例３、４では、ミクロクラックは発生していないが、口開き量が8mm～9mmである。これにより、冷却時間が長く、鋼板の冷却停止温度が410℃未満となる場合には、プレス成形開始温度も400℃未満となり、鋼板の強度が上昇して、形状凍結性の低下が起こることがわかる。 In Comparative Examples 1 and 2, the opening amount is 0 mm, but microcracks are generated. Thereby, when the forming start temperature of a steel plate is higher than 550 degreeC, it turns out that a micro crack generate | occur | produces.
In Comparative Examples 3 and 4, no microcracks are generated, but the opening amount is 8 mm to 9 mm. As a result, when the cooling time is long and the cooling stop temperature of the steel sheet is less than 410 ° C, the press forming start temperature is also less than 400 ° C, the strength of the steel sheet is increased, and the shape freezing property may be lowered. Recognize.
　比較例５～７では、冷却方法がガス冷却であるため、冷却速度が適正範囲（100℃/s以上）から外れて、急速冷却することができない。そのため、比較例５、６では鋼板の冷却停止温度及びプレス成形開始温度も適正範囲（冷却停止温度：410℃～550℃、プレス成形開始温度：400℃～550℃）から外れて、ミクロクラックが発生する。また、比較例７では、冷却停止温度が510℃であり適正範囲内となるものの、口開き量が3mmと形状凍結性の低下が生じている。これは、ガス冷却のために冷却速度が遅いために、プレス成形品の曲げの稜線を挟む２つの面のなす角度が金型角度よりも大きくなったことが原因であるものと考えられる。
　さらに、比較例６、７ではガス冷却である程度まで緩冷却し、プレス成形した後での焼入れとなったため、プレス成形後の硬度および引張強さも低下している。 In Comparative Examples 5 to 7, since the cooling method is gas cooling, the cooling rate is out of the appropriate range (100 ° C./s or more), and rapid cooling cannot be performed. Therefore, in Comparative Examples 5 and 6, the cooling stop temperature and press forming start temperature of the steel plate are also outside the appropriate ranges (cooling stop temperature: 410 ° C. to 550 ° C., press forming start temperature: 400 ° C. to 550 ° C.), and microcracks occur. appear. In Comparative Example 7, although the cooling stop temperature is 510 ° C. and falls within the proper range, the amount of opening of the mouth is 3 mm and the shape freezing property is reduced. This is considered to be caused by the fact that the angle formed by the two surfaces sandwiching the bending ridge line of the press-molded product is larger than the mold angle because the cooling rate is slow due to gas cooling.
Furthermore, in Comparative Examples 6 and 7, since it was quenched after gas cooling to some extent and quenched after press molding, the hardness and tensile strength after press molding also decreased.
　比較例８、９では、プレス成形開始までの時間がそれぞれ10秒、8秒と、適正範囲である5秒以内よりも長時間になっている。そのため、比較例８、９では、口開き量が2mmとなり、またプレス成形後の硬度および引張強さも低下している。 In Comparative Examples 8 and 9, the time until the start of press forming is 10 seconds and 8 seconds, respectively, which is longer than the appropriate range within 5 seconds. Therefore, in Comparative Examples 8 and 9, the opening amount is 2 mm, and the hardness and tensile strength after press molding are also reduced.
　比較例１０、１１では、めっき層の種類が異なる、すなわち比較例１０はZnのみのめっき層、比較例１１はZn-Feのめっき層である。Znのみのめっき層およびZn-Feのめっき層におけるミクロクラックが発生しなくなるプレス成形開始温度は、Zn-Niのめっき層においてミクロクラックが発生しなくなるプレス成形開始温度よりさらに低い。そのため、比較例１０、１１では、ミクロクラックが発生している。 Comparative Examples 10 and 11 have different types of plating layers, that is, Comparative Example 10 is a Zn-only plating layer, and Comparative Example 11 is a Zn-Fe plating layer. The press molding start temperature at which microcracks are not generated in the Zn-only plating layer and the Zn-Fe plating layer is lower than the press molding start temperature at which microcracks are not generated in the Zn-Ni plating layer. Therefore, in Comparative Examples 10 and 11, microcracks are generated.
　１　　表面処理鋼板
　１´　成形体
　３　　冷却用金型
　５　　上金型
　７　　下金型
　９　　リフターピン
　１１　プレス成形金型
　１３　ダイ
　１５　ブランクホルダ
　１７　パンチ
　１９　熱電対
　２１　ミクロクラック
　２３　めっき層
　２５　素地鋼板 DESCRIPTION OF SYMBOLS 1 Surface treatment steel plate 1 'Molding body 3 Cooling die 5 Upper die 7 Lower die 9 Lifter pin 11 Press die 13 Die 15 Blank holder 17 Punch 19 Thermocouple 21 Micro crack 23 Plating layer 25 Base steel plate

Claims (3)

  1. 　Zn-Niめっき層が素地鋼板の表面に形成された表面処理鋼板に熱間プレスを施して熱間プレス成形品を製造する熱間プレス成形品の製造方法であって、
    　前記表面処理鋼板をAc3変態点以上で1000℃以下の温度域に加熱する工程と、
    　前記加熱した表面処理鋼板を、前記表面処理鋼板との接触面が平面である冷却用金型で挟むことにより、前記表面処理鋼板を100℃/s以上の冷却速度で550℃以下410℃以上の温度まで冷却する工程と、
    　前記冷却後5秒以内で、かつ前記表面処理鋼板の温度が550℃以下400℃以上の範囲内で、プレス成形金型を用いて前記表面処理鋼板のプレス成形を開始して、成形体を得る工程と、
    　前記成形体を前記プレス成形金型で挟んだまま成形下死点で保持して、前記成形体を焼入れ、熱間プレス成形品を得る工程とを備える、熱間プレス成形品の製造方法。     A hot press-formed product manufacturing method for manufacturing a hot press-formed product by hot-pressing a surface-treated steel sheet having a Zn-Ni plating layer formed on the surface of a base steel plate,
    Heating the surface-treated steel sheet to a temperature range of 1000 ° C. or less above the Ac 3 transformation point;
    By sandwiching the heated surface-treated steel sheet with a cooling mold having a flat contact surface with the surface-treated steel sheet, the surface-treated steel sheet is 550 ° C. or lower and 410 ° C. or higher at a cooling rate of 100 ° C./s or higher. Cooling to temperature,
    Within 5 seconds after the cooling, and the temperature of the surface-treated steel sheet is within a range of 550 ° C. or lower and 400 ° C. or higher, press molding of the surface-treated steel sheet is started using a press molding die to obtain a molded body Process,
    A method of manufacturing a hot press-molded product, comprising: holding the molded body at a bottom dead center while being sandwiched between the press-molding dies, and quenching the molded body to obtain a hot press-molded product.
  2. 　前記表面処理鋼板におけるZn-Niめっき層中のNi含有量が9質量%以上25質量%以下である、請求項１に記載の熱間プレス成形品の製造方法。 The method for producing a hot press-formed product according to claim 1, wherein the Ni content in the Zn-Ni plating layer in the surface-treated steel sheet is 9 mass% or more and 25 mass% or less.
  3. 　請求項１または２に記載の方法により製造された熱間プレス成形品。 A hot press-formed product manufactured by the method according to claim 1 or 2.
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CN201580049874.9A CN106714996B (en) 2014-09-25 2015-09-07 The manufacturing method of hot-forming product and hot-forming product
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