WO2014207982A1 - 熱間プレス用鋼板 - Google Patents
熱間プレス用鋼板 Download PDFInfo
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- WO2014207982A1 WO2014207982A1 PCT/JP2014/002505 JP2014002505W WO2014207982A1 WO 2014207982 A1 WO2014207982 A1 WO 2014207982A1 JP 2014002505 W JP2014002505 W JP 2014002505W WO 2014207982 A1 WO2014207982 A1 WO 2014207982A1
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- plating layer
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
- B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
- B32B15/015—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium the said other metal being copper or nickel or an alloy thereof
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- 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
- C25D5/60—Electroplating characterised by the structure or texture of the layers
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/62—Quenching devices
- C21D1/673—Quenching devices for die quenching
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
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- 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
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- 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- 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
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- 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
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- 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- 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
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- 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
- C25D5/10—Electroplating with more than one layer of the same or of different metals
- C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
- C25D5/14—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium two or more layers being of nickel or chromium, e.g. duplex or triplex layers
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- 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
- C25D5/50—After-treatment of electroplated surfaces by heat-treatment
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- 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
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/615—Microstructure of the layers, e.g. mixed structure
- C25D5/617—Crystalline layers
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
- C25D7/06—Wires; Strips; Foils
- C25D7/0614—Strips or foils
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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- 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
- C25D3/12—Electroplating: Baths therefor from solutions of nickel or cobalt
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- 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
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- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12785—Group IIB metal-base component
- Y10T428/12792—Zn-base component
- Y10T428/12799—Next to Fe-base component [e.g., galvanized]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12861—Group VIII or IB metal-base component
- Y10T428/12937—Co- or Ni-base component next to Fe-base component
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12861—Group VIII or IB metal-base component
- Y10T428/12944—Ni-base component
Definitions
- the present invention relates to a steel plate for hot pressing suitable for manufacturing an automobile undercarriage member, a vehicle body structural member, and the like by hot pressing.
- Patent Document 1 discloses a processing technique called a hot press that enables both easy processing and high strength by simultaneously processing a heated steel sheet using a die and a punch and simultaneously cooling it. Proposed.
- a hot press the steel plate is heated to a high temperature of around 950 ° C. before hot pressing, so scale (iron oxide) is generated on the surface of the steel plate and the scale peels off during hot pressing.
- the mold is damaged or the surface of the member after hot pressing is damaged.
- the scale remaining on the surface of the member also causes poor appearance and poor paint adhesion.
- the scale on the surface of the member is usually removed by processing such as pickling or shot blasting. However, this complicates the manufacturing process and reduces productivity.
- excellent corrosion resistance is also required for automobile suspension members and body structure members.
- the hot press member manufactured by the process as described above is not provided with a rust preventive film such as a plating layer, the corrosion resistance is very insufficient.
- Patent Document 2 discloses a hot pressed member excellent in corrosion resistance in which a steel sheet coated with Zn or a Zn base alloy is hot pressed and a Zn—Fe base compound or a Zn—Fe—Al base compound is provided on the surface. A manufacturing method is disclosed.
- Patent Document 3 a Zn—Ni plating layer having an adhesion amount of 10 to 90 g / m 2 is applied on an upper layer of a lower plating layer having an adhesion amount of 0.01 to 5 g / m 2 mainly composed of Ni.
- a steel sheet for hot pressing is disclosed.
- the hot-pressed member manufactured by the method described in Patent Document 2 uses a galvanized steel sheet or a zinc-aluminum-plated steel sheet having a low melting point, zinc in the plating layer penetrates into the steel sheet during hot press forming. So-called liquid metal brittle cracks that cause cracks may occur.
- the present invention has been made in view of the above circumstances, and does not cause liquid metal brittle cracking even under hot press conditions with a short conveying time for the purpose of improving productivity, and is excellent in resistance to liquid metal brittleness. Another object is to provide a hot-press steel sheet.
- the plating layer contains 60% by mass or more of Ni, the balance being a high melting point plating layer made of Zn and inevitable impurities, and a plating layer having an adhesion amount of more than 5 g / m 2 and 50 g / m 2 or less.
- a Zn—Ni plating layer containing 10 to 25% by mass of Ni in the upper layer, the balance being Zn and inevitable impurities, and having an adhesion amount of 10 to 90 g / m 2 or less. It has been found that it is possible to provide a hot-press steel sheet with excellent liquid metal brittleness resistance that does not cause liquid metal brittle cracking even under hot press conditions with a short conveying time for the purpose of improving productivity. The present invention has been reached.
- the present invention has been made on the basis of such knowledge.
- the steel sheet surface contains 60% by mass or more of Ni, the balance is made of Zn and unavoidable impurities, and the adhesion amount per side exceeds 5 g / m 2.
- the first plating layer of 50 g / m 2 or less and the upper layer of the first plating layer contain 10 to 25% by mass of Ni, the balance is made of Zn and inevitable impurities, and the adhesion amount per side is 10 to 10%.
- It is a steel sheet for hot press characterized by having a second plating layer of 90 g / m 2 or less.
- liquid metal brittle cracking does not occur even under hot press conditions with a short conveying time for the purpose of improving productivity, and excellent in liquid metal brittleness resistance. It is possible to manufacture a hot press member.
- the hot press member manufactured using the hot-press steel plate of the present invention is excellent in liquid metal brittleness resistance, and is suitable for an automobile suspension member and a vehicle body structure member.
- FIG. 1 is a view showing a steel plate after hat-shaped forming according to the first embodiment.
- Plating layer in order to ensure excellent liquid metal brittleness resistance even under hot pressing conditions with a short conveying time for the purpose of improving productivity, 60 mass% or more of Ni is provided on the steel plate surface. 10 to 25% by mass in the first plating layer with the balance consisting of Zn and inevitable impurities, the adhesion amount per one side exceeding 5 g / m 2 and 50 g / m 2 or less, and the upper layer of the first plating layer And a second plating layer having a balance of 10 to 90 g / m 2 or less, the balance being made of Zn and inevitable impurities, and the remaining amount being 10 to 90 g / m 2 .
- the hot press forming start temperature becomes high, and thus press forming may be started in a state where the solidification of the plating layer is not completed. As a result, liquid metal brittle cracks may occur.
- the reason why the Ni content of the first plating layer is set to 60% by mass or more is that the melting point of the first plating layer is set to an extremely high temperature of 1000 ° C. or higher that does not melt even during heating before hot pressing. is there.
- the adhesion amount per one side of the first plating layer is more than 5 g / m 2 and 50 g / m 2 or less.
- the adhesion amount is 5 g / m 2 or less, the shielding effect by the first plating layer is not recognized.
- the adhesion amount exceeds 50 g / m 2 , the effect is not only saturated but also the cost is increased. Accordingly, the adhesion amount of the first plating layer is set to 5 g / m 2 greater than 50 g / m 2 or less.
- the second plating layer contains 10 to 25% by mass of Ni in the upper layer of the first plating layer, the balance is made of Zn and inevitable impurities, and the adhesion amount per side is 10 to 90 g / m 2 .
- the reason why the Ni content of the second plating layer is 10 to 25% by mass is that the phase structure of the second plating layer is a ⁇ phase having excellent corrosion resistance and a melting point of 881 ° C.
- the Ni content of the plating layer is 10 to 25% by mass.
- a high ⁇ phase having a melting point of 881 ° C. having a crystal structure of Ni 2 Zn 11 , NiZn 3 , or Ni 5 Zn 21 is formed.
- the formation reaction of ZnO during heating can be minimized.
- the corrosion resistance of Zn exhibits excellent corrosion resistance.
- the ⁇ phase has a crystal structure of any of Ni 2 Zn 11 , NiZn 3 , and Ni 5 Zn 21 and can be confirmed by an X-ray diffraction method or an electron beam diffraction method using TEM (Transmission Electron Microscopy). It is.
- the adhesion amount per one side of the second plating layer is 10 to 90 g / m 2 .
- the adhesion amount is less than 10 g / m 2 , the corrosion resistance of the hot pressed member is insufficient. If the adhesion amount exceeds 90 g / m 2 , the cost increases. For this reason, the adhesion amount of the plating layer is in the range of 10 to 90 g / m 2 .
- the adhesion amount of the plating layer can be obtained by a wet analysis method. Specifically, for example, the entire plating layer with a known adhesion area is dissolved in an aqueous solution obtained by adding 1 g / l of hexamethylenetetramine as an inhibitor to a 6% by mass hydrochloric acid aqueous solution. Find it.
- the method for forming such a plating layer is not particularly limited, and a known electroplating method is suitable. Moreover, the adhesion amount of the plating layer can be controlled by adjusting the energization time, as is usually done.
- C 0.15-0.50% C is an element that improves the strength of steel.
- TS tensile strength
- the amount needs to be 0.15% or more.
- the amount of C exceeds 0.50%, the blanking workability of the raw steel plate is significantly lowered. Therefore, the C content is 0.15 to 0.50%.
- Si 0.05-2.00% Si, like C, is an element that improves the strength of steel.
- the amount needs to be 0.05% or more.
- the Si content exceeds 2.00%, the plating processability may be adversely affected when a plating process for forming a plating film mainly composed of Zn or Al on the steel sheet surface is performed. Therefore, the Si content is 0.05 to 2.00%.
- Mn 0.5 to 3.0%
- Mn is an element effective for suppressing the ferrite transformation and improving the hardenability, and also reduces the Ac 3 transformation point, so that it is an effective element for lowering the heating temperature before hot pressing. is there. In order to exhibit such an effect, the amount needs to be 0.5% or more.
- the amount of Mn exceeds 3.0%, it segregates and the uniformity of the characteristics of the raw steel plate and hot pressed member is lowered. Therefore, the Mn content is 0.5 to 3.0%.
- P 0.10% or less
- the amount of P exceeds 0.10%, segregation occurs and the uniformity of the characteristics of the steel plate and the hot pressed member is reduced, and the toughness is also significantly reduced. Therefore, the P content is 0.10% or less.
- Al 0.10% or less
- the Al content is 0.10% or less.
- N 0.010% or less
- the N content is 0.010% or less.
- the balance is Fe and inevitable impurities.
- Cr 0.01 to 1.0% Cr is an element effective for strengthening steel and improving hardenability. In order to exhibit such an effect, the Cr content is preferably 0.01% or more. On the other hand, if the Cr content exceeds 1.0%, the cost is significantly increased, so the upper limit is preferably set to 1.0%.
- Ti 0.20% or less
- Ti is an element effective for strengthening steel and improving toughness by refining. Further, it is also an element effective for forming a nitride in preference to B described below and exhibiting the effect of improving hardenability by solid solution B.
- the upper limit may be 0.20%. preferable.
- B 0.0005 to 0.0800%
- B is an element effective for improving the hardenability during hot pressing and toughness after hot pressing.
- the B content is preferably 0.0005% or more.
- the upper limit is preferably 0.0800%.
- Sb 0.003 to 0.030%
- Sb has an effect of suppressing a decarburized layer generated in the steel sheet surface layer portion between the time when the steel plate is heated before hot pressing and the time when the steel plate is cooled by a series of processes of hot pressing. In order to exhibit such an effect, the amount needs to be 0.003% or more. On the other hand, if the amount of Sb exceeds 0.030%, the rolling load increases and the productivity is lowered. Therefore, the Sb content is preferably 0.003 to 0.030%.
- Hot press member can be manufactured by giving the hot-pressing steel plate of this invention mentioned above to the hot press by a conventional method.
- hot pressing may be performed after heating the steel sheet for hot pressing to a temperature in the range of 850 to 950 ° C., which is a temperature equal to or higher than the Ac 3 transformation point.
- the heating method before hot pressing include heating by an electric furnace or a gas furnace, flame heating, energization heating, high frequency heating, induction heating, far infrared heating, and the like.
- a hot press member is manufactured by setting the hot press steel plate heated as described above in a die having a die and a punch, performing press forming, and cooling under a desired cooling condition.
- the first plating layer was plated at a current density of 5 A / dm 2 in a plating bath containing 240 g / L nickel sulfate hexahydrate, 30 g / L boric acid, pH 3.6 and bath temperature 50 ° C. went.
- the plating adhesion amount was adjusted by changing the energization time.
- the second plating layer had a current density of 5 in a plating bath containing 200 g / L nickel sulfate hexahydrate, 10 to 100 g / L zinc sulfate heptahydrate, pH 1.5, bath temperature 50 ° C.
- Plating was performed at ⁇ 100 A / dm 2 .
- the Ni content was adjusted by changing the addition amount of zinc sulfate heptahydrate and the current density, and the plating adhesion amount was adjusted by changing the energization time.
- the cooling rate of the steel sheet in the conveying process after heating is approximately 20 ° C./second, for example, the steel sheet heated to 900 ° C. is conveyed to the press machine in a conveying time of approximately 10 seconds.
- the molding start temperature is about 700 ° C.
- the conveying time was 4 to 6 seconds, which was faster than usual, the molding start temperature was 820 ° C. or higher.
- the produced hat-type parts were evaluated for liquid metal brittleness resistance by the following method.
- Liquid metal brittleness A sample for cross-sectional observation is taken from the shoulder R part (outer surface side) of the hat-shaped part, observed with a scanning electron microscope (SEM), and the maximum depth of cracks entering the base material is determined. evaluated.
- SEM scanning electron microscope
- ⁇ Maximum crack depth ⁇ 0.01 mm (occurring)
- Steel plate No. Table 1 shows the details of the plated layers 1 to 16, the hot press conditions, and the liquid metal brittleness evaluation results.
- Nos. 1 to 10 are excellent in resistance to liquid metal brittleness even under hot press conditions where the forming start temperature is high, that is, under hot press conditions where the conveying time is short.
- the steel plate for hot pressing of the present invention No. 1 to 10 and steel plate No. All hat-type parts manufactured using 11 to 16 had a strength of 980 MPa or more.
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Abstract
Description
また、部材表面に残ったスケールは、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スケールは除去される。しかし、これは製造工程を複雑にし、生産性の低下を招く。
さらに、自動車の足廻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。しかし、上述のような工程により製造された熱間プレス部材ではめっき層などの防錆皮膜が設けられていないため、耐食性が甚だ不十分である。
本発明では、生産性の向上を目的とする搬送時間の短い熱間プレス条件下においても、優れた耐液体金属脆性を確保するために、鋼板表面に、60質量%以上のNiを含有し、残部がZnおよび不可避的不純物からなり、片面あたりの付着量が5g/m2超え50g/m2以下の第一めっき層と、第一めっき層の上層に、10~25質量%のNiを含有し、残部がZnおよび不可避的不純物からなり、片面あたりの付着量が10~90g/m2以下の第二めっき層とを有することを、特徴とする。
980MPa以上の強度を有する熱間プレス部材を得るには、めっき層の下地鋼板として、例えば、質量%で、C:0.15~0.50%、Si:0.05~2.00%、Mn:0.5~3.0%、P:0.10%以下、S:0.05%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。各成分元素の限定理由を、以下に説明する。ここで、成分の含有量を表す「%」は、特に断らない限り「質量%」を意味する。
Cは、鋼の強度を向上させる元素であり、熱間プレス部材の引張強度(TS)を980MPa以上にするには、その量を0.15%以上とする必要がある。一方、C量が0.50%を超えると、素材の鋼板のブランキング加工性が著しく低下する。したがって、C量は0.15~0.50%とする。
Siは、Cと同様に、鋼の強度を向上させる元素であり、熱間プレス部材のTSを980MPa以上にするには、その量を0.05%以上とする必要がある。一方、Si量が2.00%を超えると、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とともに、圧延荷重が増大したり、熱延鋼板の延性の劣化を招く。さらに、Si量が2.00%を超えると、ZnやAlを主体としためっき皮膜を鋼板表面に形成するめっき処理を施す際に、めっき処理性に悪影響を及ぼす場合がある。したがって、Si量は0.05~2.00%とする。
Mnは、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り、また、Ac3変態点を低下させるので、熱間プレス前の加熱温度を低下するにも有効な元素である。このような効果の発現のためには、その量を0.5%以上とする必要がある。一方、Mn量が3.0%を超えると、偏析して素材の鋼板および熱間プレス部材の特性の均一性が低下する。したがって、Mn量は0.5~3.0%とする。
P量が0.10%を超えると、偏析して素材の鋼板および熱間プレス部材の特性の均一性が低下するとともに、靭性も著しく低下する。したがって、P量は0.10%以下とする。
S量が0.05%を超えると、熱間プレス部材の靭性が低下する。したがって、S量は0.05%以下とする。
Al量が0.10%を超えると、素材の鋼板のブランキング加工性や焼入れ性を低下させる。したがって、Al量は0.10%以下とする。
N量が0.010%を超えると、熱間圧延時や熱間プレス前の加熱時にAlNの窒化物が形成され、素材の鋼板のブランキング加工性や焼入れ性が低下する。したがって、N量は0.010%以下とする。
Crは、鋼を強化するとともに、焼入れ性を向上させるのに有効な元素である。こうした効果の発現のためには、Cr量を0.01%以上とすることが好ましい。一方、Cr量が1.0%を超えると、著しいコスト高を招くため、その上限は1.0%とすることが好ましい。
Tiは、鋼を強化するとともに、細粒化により靭性を向上させるのに有効な元素である。また、次に述べるBよりも優先して窒化物を形成して、固溶Bによる焼入れ性の向上効果を発揮させるのに有効な元素でもある。しかし、Ti量が0.20%を超えると、熱間圧延時の圧延荷重が極端に増大し、また、熱間プレス部材の靭性が低下するので、その上限は0.20%とすることが好ましい。
Bは、熱間プレス時の焼入れ性や熱間プレス後の靭性向上に有効な元素である。こうした効果の発現のためには、B量を0.0005%以上とすることが好ましい。一方、B量が0.0800%を超えると、熱間圧延時の圧延荷重が極端に増大し、また、熱間圧延後にマルテンサイト相やベイナイト相が生じて鋼板の割れなどが生じるので、その上限は0.0800%とすることが好ましい。
Sbは、熱間プレス前に鋼板を加熱してから熱間プレスの一連の処理によって鋼板を冷却するまでの間に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その量を0.003%以上とする必要がある。一方、Sb量が0.030%を超えると、圧延荷重の増大を招き、生産性を低下させる。したがって、Sb量は0.003~0.030%とすることが好ましい。
上記した本発明の熱間プレス用鋼板を、常法による熱間プレスを施して熱間プレス部材を製造することができる。例えば、熱間プレス用鋼板の板温がAc3変態点以上の温度である850~950℃の範囲となるように加熱した後、熱間プレスを行えばよい。熱間プレス前の加熱方法としては、電気炉やガス炉などによる加熱、火炎加熱、通電加熱、高周波加熱、誘導加熱、遠赤外線加熱などを例示できる。
耐液体金属脆性:ハット型部品の肩R部(外面側)より断面観察用のサンプルを採取し、走査型電子顕微鏡(SEM)で観察し、母材に侵入しているクラックの最大深さを評価した。
○:最大クラック深さ=0mm(発生なし)
×:最大クラック深さ≧0.01mm(発生あり)
鋼板No.1~16のめっき層の詳細、熱間プレス条件および耐液体金属脆性の評価結果を表1に示す。
Claims (1)
- 鋼板表面に、60質量%以上のNiを含有し、残部がZnおよび不可避的不純物からなり、片面あたりの付着量が5g/m2超え50g/m2以下の第一めっき層と、
前記第一めっき層の上層に、10~25質量%のNiを含有し、残部がZnおよび不可避的不純物からなり、片面あたりの付着量が10~90g/m2以下の第二めっき層と
を有することを特徴とする熱間プレス用鋼板。
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EP14818596.0A EP3015572B1 (en) | 2013-06-25 | 2014-05-13 | Hot press formed part manufacturing process |
US14/901,147 US10093077B2 (en) | 2013-06-25 | 2014-05-13 | Steel sheet for hot press-forming |
MX2015017493A MX2015017493A (es) | 2013-06-25 | 2014-05-13 | Lamina de acero para estampacion en caliente. |
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