WO2013133166A1 - Feuille d'acier pour une utilisation de pressage à chaud, article moulé par pressage et procédé de fabrication d'un article moulé par pressage - Google Patents

Feuille d'acier pour une utilisation de pressage à chaud, article moulé par pressage et procédé de fabrication d'un article moulé par pressage Download PDF

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WO2013133166A1
WO2013133166A1 PCT/JP2013/055680 JP2013055680W WO2013133166A1 WO 2013133166 A1 WO2013133166 A1 WO 2013133166A1 JP 2013055680 W JP2013055680 W JP 2013055680W WO 2013133166 A1 WO2013133166 A1 WO 2013133166A1
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press
martensite
area
less
steel sheet
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PCT/JP2013/055680
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English (en)
Japanese (ja)
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村上　俊夫
純也 内藤
圭介 沖田
池田　周之
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株式会社神戸製鋼所
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Priority to KR1020147024781A priority Critical patent/KR101609967B1/ko
Priority to US14/382,158 priority patent/US20150027602A1/en
Priority to EP13757984.3A priority patent/EP2824209A4/fr
Priority to CN201380012504.9A priority patent/CN104160052B/zh
Publication of WO2013133166A1 publication Critical patent/WO2013133166A1/fr
Priority to US16/027,424 priority patent/US20180312947A1/en

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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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • 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
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • 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
    • C21D2221/00—Treating localised areas of an article
    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively

Definitions

  • the present invention is used when manufacturing a structural part of an automobile, and is a hot-press steel sheet suitable for hot press forming, a press-formed product obtained from such a hot-press steel plate, and a press-formed product.
  • a hot-press steel sheet suitable for hot press forming
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • a press-formed product obtained from such a hot-press steel plate
  • the steel sheet is heated to a predetermined temperature (for example, the temperature at which it becomes an austenite phase) to lower the strength, and then formed with a mold having a temperature lower than that of the steel sheet (for example, room temperature).
  • a hot press molding method is employed in the production of parts that performs quenching heat treatment (quenching) using the temperature difference between the two to ensure the strength after molding.
  • a hot press forming method is called by various names such as a hot forming method, a hot stamping method, a hot stamp method, and a die quench method in addition to the hot press method.
  • FIG. 1 is a schematic explanatory view showing a mold configuration for carrying out hot press molding as described above, in which 1 is a punch, 2 is a die, 3 is a blank holder, 4 is a steel plate (blank), BHF is a crease pressing force, rp is a punch shoulder radius, rd is a die shoulder radius, and CL is a punch / die clearance.
  • the punch 1 and the die 2 have passages 1a and 2a through which a cooling medium (for example, water) can pass, and the cooling medium is allowed to pass through the passages.
  • a cooling medium for example, water
  • the steel plate (blank) 4 is subjected to a two-phase region temperature (A c1 transformation point to A c3 transformation point) or an A c3 transformation. Molding is started in a state of being softened by heating to a single-phase temperature above the point. That is, the steel plate 4 in a high temperature state is sandwiched between the die 2 and the blank holder 3, and the steel plate 4 is pushed into the hole of the die 2 by the punch 1 to correspond to the outer shape of the punch 1 while reducing the outer diameter of the steel plate 4. Mold into shape.
  • a steel sheet for hot pressing that is widely used at present, a steel sheet made of 22MnB5 steel is known.
  • This steel sheet has a tensile strength of 1500 MPa and an elongation of about 6 to 8%, and is applied to an impact resistant member (a member that is not deformed as much as possible and does not break).
  • an impact resistant member a member that is not deformed as much as possible and does not break.
  • Patent Documents 1 to 4 As hot-press steel sheets exhibiting good elongation, techniques such as Patent Documents 1 to 4 have been proposed. In these technologies, the basic strength class of each steel sheet is adjusted by setting the carbon content in the steel sheet to various ranges, and ferrite with high deformability is introduced, and the average of ferrite and martensite Elongation is improved by reducing the particle size. These techniques are effective for improving the elongation, but are still insufficient from the viewpoint of improving the elongation according to the strength of the steel sheet. For example, the tensile strength TS is 1470 MPa or more and the elongation EL is about 10.2% at the maximum, and further improvement is required.
  • the part where deformation should be prevented is high strength (high strength side: impact resistant part side), and the part requiring energy absorption is low strength and high ductility (low strength side: energy absorbing part side).
  • High strength side impact resistant part side
  • low strength side energy absorbing part side
  • Technology has been proposed.
  • the impact resistance of the B-pillar and rear-side member components is considered in consideration of compatibility (function to protect the other party when a small car collides) in a side collision or a rear collision.
  • compatibility function to protect the other party when a small car collides
  • a tensile strength of 1500 MPa is achieved on the high strength side (impact resistant site side), but the maximum tensile strength is 700 MPa and the elongation EL is about 17% on the low strength side (energy absorption site side).
  • the energy absorption site side In order to further improve the energy absorption characteristics, it is required to realize higher strength and higher ductility.
  • the present invention has been made in view of the above circumstances, and its object is to perform hot press molding that can achieve a high level of balance between high strength and elongation when uniform characteristics are required in a molded product.
  • a region corresponding to an impact resistant part and an energy absorbing part is required in a single molded product, a high level of balance between high strength and elongation is achieved according to each region.
  • the steel sheet for hot pressing of the present invention that was able to achieve the above object, C: 0.15 to 0.5% (meaning mass%, hereinafter the same for chemical composition) Si: 0.2-3%, Mn: 0.5 to 3%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), Al: 0.01 to 1%, B: 0.0002 to 0.01%, Ti: 3.4 [N] + 0.01% or more, 3.4 [N] + 0.1% or less [where [N] indicates the content (% by mass) of N], and N: 0.0010 ⁇ 0.01%, Each of which contains iron and inevitable impurities, Among the Ti-containing precipitates contained in the steel sheet, the average equivalent circle diameter of those having an equivalent circle diameter of 30 nm or less is 3 nm or more, and the amount of precipitated Ti in the steel and the total Ti amount are expressed by the following formula (1).
  • the metal structure is characterized in that the total fraction of bainite and martensite is 80 area% or more.
  • the “equivalent circle diameter” means the diameter when converted to a circle of the same area when focusing on the size (area) of the Ti-containing precipitate (eg, TiC) (the “average equivalent circle diameter” is its average Value).
  • the hot-press forming steel sheet of the present invention if necessary, as another element, (a) one or more selected from the group consisting of V, Nb and Zr is 0.1% or less in total ( (B) 0% is not included), (b) one or more selected from the group consisting of Cu, Ni, Cr and Mo is 1% or less in total (not including 0%), (c) from Mg, Ca and REM It is also useful to contain one or more selected from the group consisting of 0.01% or less (not including 0%), etc., depending on the type of element contained, hot press-formed product The characteristics are further improved.
  • the method for producing a press-formed product of the present invention that has achieved the above object is to use the steel sheet for hot pressing according to the present invention as described above, with an A c1 transformation point + 20 ° C. or higher, an A c3 transformation point ⁇ 20 ° C. After heating to the following temperature, press molding is started, and during molding and after completion of molding, while maintaining an average cooling rate of 20 ° C./second or more in the mold, to a temperature lower than 100 ° C. below the bainite transformation start temperature Bs It is characterized by cooling.
  • the metal structure is retained austenite: 3 to 20 area%, annealed martensite and / or annealed bainite: 30 to 87 area%, as-quenched martensite: 10 to 67
  • the amount of carbon in the retained austenite is 0.60% or more, and the balance between high strength and elongation can be achieved as a uniform characteristic at a high level in the molded product.
  • the area ratio of annealed martensite and / or annealed bainite is the total area ratio of both structures when both structures are included, and the area ratio of the structure when either structure is formed. Means.
  • the steel sheet for hot pressing of the present invention as described above was used, and the heating region of the steel plate was divided into two regions, One region is heated to a temperature not lower than A c3 transformation point and not higher than 950 ° C., and the other region is heated to a temperature not lower than A c1 transformation point + 20 ° C. and not higher than A c3 transformation point ⁇ 20 ° C. And after the molding and after completion of molding, the mold is cooled to a temperature not higher than the martensite transformation start temperature Ms while ensuring an average cooling rate of 20 ° C./second or more.
  • the metal structure has a residual austenite: 3 to 20 area%, a martensite: 80 area% or more, and the metal structure has a residual austenite: 3 to 20 area. %, Annealed martensite and / or annealed bainite: 30 to 87 area%, as-quenched martensite: 10 to 67 area%, and the carbon content in the retained austenite is 0.60% or more. According to each region, the balance between high strength and elongation can be achieved at a high level, and there are regions corresponding to impact resistant sites and energy absorbing sites in a single molded product. .
  • the chemical composition is strictly defined, the size of Ti-containing precipitates is controlled, the deposition rate is controlled for Ti that does not form TiN, and the tempered hard phase is controlled for the metal structure. Since the steel plate is used in which the ratio of the hard phase (martensite phase, martensite phase, etc.), the hardened phase (martensite phase), and the retained austenite phase is adjusted, this is hot-pressed under specified conditions. Strength-elongation balance can be made high. Further, when hot pressing is performed in a plurality of regions under different conditions, an impact resistant part and an energy absorbing part can be formed in a single molded product, and a high strength and elongation balance can be achieved at a high level in each part.
  • the inventors of the present invention when heating a steel plate to a predetermined temperature and then producing a press-formed product by hot press forming, show good ductility (elongation) while ensuring high strength after press forming.
  • a hot-press steel sheet that can realize a simple press-formed product, we examined it from various angles.
  • the chemical composition of the steel sheet for hot pressing is strictly defined, the size of the Ti-containing precipitates and the amount of precipitated Ti are controlled, and the metal structure is made appropriate.
  • the present inventors completed the present invention by finding that a press-molded product having a higher retained ductility (residual ductility) can be obtained by securing a predetermined amount of retained austenite after press molding.
  • C is a region corresponding to an impact resistant site and an energy absorbing site in a single molded product in order to achieve a high balance between high strength and elongation when uniform characteristics are required in the molded product. Is an important element for securing retained austenite particularly in the low strength and high ductility regions. Moreover, at the time of heating by hot press molding, C concentrates to austenite, so that residual austenite can be formed after quenching. Furthermore, it contributes to an increase in the amount of martensite and raises the strength. In order to exert these effects, the C content needs to be 0.15% or more.
  • the target metal structure annealed martensite and / or in a low-strength and high-ductility site
  • the preferable lower limit of the C content is 0.17% or more (more preferably 0.20% or more), and the more preferable upper limit is 0.45% or less (more preferably 0.40% or less).
  • Si exhibits the effect of forming retained austenite by suppressing martensite from tempering to form cementite and decomposition of untransformed austenite during cooling of mold quenching.
  • the Si content needs to be 0.2% or more.
  • the Si content is excessive and exceeds 3%, ferrite tends to be formed, making it difficult to make a single phase during heating, and the required fraction of bainite and martensite cannot be ensured in the hot-press steel sheet.
  • the preferable lower limit of the Si content is 0.5% or more (more preferably 1.0% or more), and the preferable upper limit is 2.5% or less (more preferably 2.0% or less).
  • Mn is an element effective in enhancing hardenability and suppressing the formation of structures (ferrite, pearlite, bainite, etc.) other than martensite and retained austenite during cooling of mold hardening. Further, it is an element that stabilizes austenite and contributes to an increase in the amount of retained austenite. In order to exhibit such an effect, it is necessary to contain 0.5% or more of Mn. Considering only the characteristics, it is preferable that the Mn content is large, but the alloy addition cost increases, so the content was made 3% or less. The minimum with preferable Mn content is 0.7% or more (more preferably 1.0% or more), and a preferable upper limit is 2.5% or less (more preferably 2.0% or less).
  • P 0.05% or less (excluding 0%)
  • P is an element inevitably contained in the steel, but it deteriorates ductility, so it is preferable to reduce P as much as possible.
  • extreme reduction leads to an increase in steelmaking cost, and it is difficult to produce 0%, so 0.05% or less (excluding 0%) was set.
  • the upper limit with preferable P content is 0.045% or less (more preferably 0.040% or less).
  • S 0.05% or less (excluding 0%)
  • S is an element inevitably contained in steel, and deteriorates ductility. Therefore, S is preferably reduced as much as possible.
  • extreme reduction leads to an increase in steelmaking cost, and it is difficult to produce 0%, so 0.05% or less (excluding 0%) was set.
  • the upper limit with preferable S content is 0.045% or less (more preferably 0.040% or less).
  • Al 0.01 to 1%
  • Al is useful as a deoxidizing element, and also fixes solid solution N present in steel as AlN, which is useful for improving ductility.
  • the Al content needs to be 0.01% or more.
  • the minimum with preferable Al content is 0.02% or more (more preferably 0.03% or more), and a preferable upper limit is 0.8% or less (more preferably 0.6% or less).
  • B has an action of suppressing ferrite transformation, pearlite transformation, and bainite transformation on the high-strength portion side, so that during the cooling after heating to the two-phase region temperature (A c1 transformation point to A c3 transformation point), It is an element that prevents the formation of pearlite and bainite and contributes to securing retained austenite.
  • B needs to be contained in an amount of 0.0002% or more, but the effect is saturated even if it is contained in excess of 0.01%.
  • a preferable lower limit of the B content is 0.0003% or more (more preferably 0.0005% or more), and a preferable upper limit is 0.008% or less (more preferably 0.005% or less).
  • Ti 3.4 [N] + 0.01% or more, 3.4 [N] + 0.1% or less: [N] is N content (mass%)] Ti fixes N and allows B to be maintained in a solid solution state, thereby exhibiting an effect of improving hardenability. In order to exert such an effect, it is important to contain 0.01% or more than the stoichiometric ratio of Ti and N [3.4 times the N content]. However, when the Ti content becomes excessive and exceeds 3.4 [N] + 0.1%, the Ti-containing precipitate formed is finely dispersed, and the growth of martensite during cooling after heating in the two-phase region.
  • a lath having a small aspect ratio (lass-like martensite) is formed, the discharge of carbon (C) into the residual austenite between the laths is slowed, and the amount of carbon in the residual austenite is reduced.
  • the preferable lower limit of the Ti content is 3.4 [N] + 0.02% or more (more preferably 3.4 [N] + 0.05% or more), and the preferable upper limit is 3.4 [N] + 0.09%. Or less (more preferably 3.4 [N] + 0.08% or less).
  • N 0.001 to 0.01%
  • N is an element inevitably mixed in, and is preferably reduced.
  • 0.001% was set as the lower limit.
  • the upper limit was made 0.01%.
  • the upper limit with more preferable N content is 0.008% or less (more preferably 0.006% or less).
  • the basic chemical composition of the steel sheet for hot pressing according to the present invention is as described above, with the balance being iron and inevitable impurities other than P and S (for example, O, H, etc.). Further, in the steel sheet for hot pressing of the present invention, if necessary, (a) at least one selected from the group consisting of V, Nb and Zr is 0.1% or less in total (not including 0%), (B) 1% or more selected from the group consisting of Cu, Ni, Cr and Mo in total (not including 0%), (c) From the group consisting of Mg, Ca and REM (rare earth elements) It is also useful to contain a total of 0.01% or less (not including 0%) of one or more selected, depending on the type of element contained, the properties of the steel sheet for hot pressing Further improvement.
  • the preferable range when these elements are contained and the reason for limiting the range are as follows.
  • V, Nb, and Zr have the effect of forming fine carbides and making the structure fine by the pinning effect. In order to exhibit such an effect, it is preferable to contain 0.001% or more in total. However, when the content of these elements is excessive, coarse carbides are formed, and the ductility is deteriorated by becoming the starting point of fracture. For these reasons, the total content of these elements is preferably 0.1% or less. The more preferable lower limit of the content of these elements is 0.005% or more (more preferably 0.008% or more) in total, and the more preferable upper limit is 0.08% or less (more preferably 0.06%) in total. The following).
  • Cu, Ni, Cr and Mo in total 1% or less (excluding 0%)
  • Cu, Ni, Cr, and Mo suppress ferrite transformation, pearlite transformation, and bainite transformation, and thus prevent formation of ferrite, pearlite, and bainite during cooling after heating, and effectively act to secure retained austenite.
  • the more preferable lower limit of the content of these elements is 0.05% or more (more preferably 0.06% or more) in total, and the more preferable upper limit is 0.5% or less (more preferably 0.3% or less) in total. ).
  • a total of at least one selected from the group consisting of Mg, Ca and REM is 0.01% or less (excluding 0%)] Since these elements refine the inclusions, they effectively work to improve ductility. In order to exhibit these effects, it is preferable to contain 0.0001% or more in total. Considering only the characteristics, it is preferable that the content is large, but since the effect is saturated, the total content is preferably 0.01% or less. The more preferable lower limit of the content of these elements is 0.0002% or more (more preferably 0.0005% or more) in total, and the more preferable upper limit is 0.005% or less (more preferably 0.003% or less) in total. ).
  • the average equivalent circle diameter of those having an equivalent circle diameter of 30 nm or less is 3 nm or more
  • the amount of precipitated Ti (Mass%)-3.4 [N]> 0.5 ⁇ [total Ti amount (mass%)-3.4 [N]] [Relationship of formula (1)] is satisfied, (C It is also an important requirement that the metal structure contains at least one of bainite and martensite and the total fraction of bainite and martensite is 80 area% or more.
  • the average equivalent circle diameter of the equivalent circle diameter of 30 nm or less is 3 nm or more.
  • the equivalent circle diameter of the target Ti-containing precipitate is defined as 30 nm or less, except for TiN, which is coarsely formed in the melting stage and does not affect the structure change or properties thereafter. This is because it is necessary to control the Ti-containing precipitates.
  • the size of the Ti-containing precipitate (the average equivalent-circle diameter of the Ti-containing precipitate having an equivalent circle diameter of 30 nm or less) is preferably 5 nm or more, and more preferably 10 nm or more.
  • the Ti-containing precipitates that are the subject of the present invention include TiC and TiN as well as precipitates containing Ti such as TiVC, TiNbC, TiVCN, and TiNbCN.
  • the amount of Ti present as precipitates other than TiN is the remaining amount of 0.1% after subtracting the Ti forming TiN out of the total Ti. More than 5 times (that is, more than 0.5 ⁇ [total Ti amount (mass%) ⁇ 3.4 [N]]) [Requirement (B) above].
  • Precipitated Ti amount (mass%)-3.4 [N] is preferably 0.6 ⁇ [total Ti amount (mass%)-3.4 [N]] or more, more preferably 0.7 ⁇ [ The total Ti amount (% by mass) is ⁇ 3.4 [N]] or more.
  • the metal structure is essentially the control necessary to achieve the desired strength-elongation balance in the molded product, but the metal structure cannot be controlled only by the hot press conditions, and the raw steel (hot press) It is necessary to control the structure of the steel sheet) in advance.
  • the total fraction of bainite and martensite in the steel sheet needs to be 80 area% or more. .
  • the total fraction of bainite and martensite is preferably 90 area% or more, more preferably 95 area% or more.
  • the remainder of the metal structure is not particularly limited, and examples thereof include at least one of ferrite, pearlite, and retained austenite.
  • a slab obtained by melting a steel material having the chemical composition as described above is heated at a temperature of 1100 ° C. or higher (preferably 1150 ° C.). 1300 ° C. or lower (preferably 1250 ° C. or lower), the final rolling temperature is 750 ° C. or higher (preferably 780 ° C. or higher) and 850 ° C. or lower (preferably 830 ° C. or lower).
  • cooling slow cooling: intermediate cooling
  • 450 ° C. or lower preferably 350 ° C.
  • a steel sheet for hot pressing having the above-described chemical component composition, metal structure and Ti precipitation state may be used for the production of a hot press as it is, or a reduction ratio of 10 to 80% (preferably 20) after pickling. ( ⁇ 70%) may be cold rolled.
  • the steel sheet for hot pressing or its cold rolled material is heated to a temperature range (1000 ° C. or lower: for example, 870 to 900 ° C.) at which TiC is not completely dissolved, and then 450 ° C. or lower (preferably 400 ° C. or lower) to 20 ° C. After quenching at a cooling rate of at least 10 seconds / second (preferably at least 30 ° C./second), a heat treatment is performed such as holding at 450 ° C.
  • the steel plate for hot pressing according to the present invention may be plated on the surface (base steel plate surface) containing one or more of Al, Zn, Mg, and Si.
  • the austenite is formed between the martensite and bainite lath in the steel sheet, and the martensite and bainite are annealed to form annealed martensite and annealed bainite with excellent ductility. It is necessary to control the range.
  • the heating temperature of the steel sheet is less than the Ac1 transformation point + 20 ° C., a sufficient amount of austenite cannot be obtained during heating, and a predetermined amount of retained austenite cannot be secured in the final structure (structure of the molded product).
  • the amount of transformation to austenite increases too much during heating, and a predetermined amount of annealed martensite or annealed in the final structure (structure of the molded product). Cannot secure bainite.
  • the average cooling rate and the cooling end temperature during and after molding are appropriately controlled. There is a need. From such a viewpoint, the average cooling rate during molding must be 20 ° C./second or more, and the cooling end temperature must be 100 ° C. or lower than the bainite transformation start temperature Bs.
  • the average cooling rate during molding is preferably 30 ° C./second or more (more preferably 40 ° C./second or more).
  • the cooling end temperature By setting the cooling end temperature to the bainite transformation start temperature Bs or less, the formation of ferrite or pearlite is prevented, and austenite existing during heating is transformed into bainite or martensite, thereby securing bainite or martensite. However, a predetermined amount of retained austenite is secured by leaving fine austenite between bainite and martensite lath.
  • the cooling end temperature is higher than the temperature lower by 100 ° C. than the bainite transformation start temperature Bs or the average cooling rate is less than 20 ° C./second, a structure such as ferrite or pearlite is formed, and a predetermined amount of retained austenite is secured. This is not possible, and the elongation (ductility) of the molded product is deteriorated.
  • control of the average cooling rate is basically unnecessary when the temperature is lower than the bainite transformation start temperature Bs by 100 ° C. or less, for example, at an average cooling rate of 1 ° C./second or more and 100 ° C./second or less to room temperature. It may be cooled.
  • Control of the average cooling rate during molding and after molding is completed by controlling (a) the temperature of the molding die (cooling medium shown in FIG. 1) and (b) controlling the thermal conductivity of the die. It can be achieved by such means.
  • the metal structure is retained austenite: 3 to 20 area%, annealed martensite and / or annealed bainite: 30 to 87 area%, as-quenched martensite : 10 to 67 area%, and the carbon content in the retained austenite is 0.60% or more, and a balance between high strength and elongation can be achieved as a uniform characteristic at a high level in the molded product.
  • the reasons for setting the ranges of the requirements (basic structure and carbon content in retained austenite) in such a hot press-formed product are as follows.
  • Residual austenite has the effect of increasing the work hardening rate (transformation-induced plasticity) and improving the ductility of the press-formed product by transforming into martensite during plastic deformation.
  • the retained austenite fraction needs to be 3 area% or more.
  • the higher the retained austenite fraction the better.
  • the retained austenite that can be secured is limited, and the upper limit is about 20 area%.
  • the preferable lower limit of retained austenite is 5 area% or more (more preferably 7 area% or more).
  • the ductility (elongation) of the press-formed product can be enhanced while ensuring a predetermined strength.
  • the fraction of annealed martensite and / or annealed bainite is 30 area% or more. However, if this fraction exceeds 87 area%, the fraction of retained austenite becomes insufficient and ductility (residual ductility) decreases.
  • the preferable lower limit of the fraction of annealed martensite or annealed bainite is 40 area% or more (more preferably 50 area% or more), and the preferable upper limit is less than 80 area% (more preferably less than 70 area%).
  • As-quenched martensite is a structure with poor ductility, and when it is present in a large amount, it degrades the elongation, but in order to achieve high strength of over 100 kg in a structure where the matrix is annealed and martensite has low strength, It is necessary to secure a predetermined amount of martensite as it is quenched. From this viewpoint, the fraction of martensite as quenched is 10 area% or more. However, if the fraction of martensite as it is quenched is too high, the strength becomes too high and the elongation becomes insufficient. Therefore, the fraction needs to be 67 area% or less.
  • the preferable lower limit of the martensite fraction as-quenched is 20 area% or more (more preferably 30 area% or more), and the preferable upper limit is 60 area% or less (more preferably 50 area% or less).
  • ferrite, pearlite, bainite and the like may be included as the remaining structure, but these structures have a lower contribution to strength and ductility than other structures, and it is preferable that they are not basically contained ( It may be 0 area%). However, up to 20 area% is acceptable.
  • the remaining structure is more preferably 10 area% or less, and still more preferably 5 area% or less.
  • the amount of carbon in retained austenite affects the timing at which retained austenite undergoes work-induced transformation to martensite during deformation in tensile tests, etc., and transformation-induced plasticity (TRIP) is caused by processing-induced transformation in the higher strain region as the carbon content increases. Increase the effect.
  • TRIP transformation-induced plasticity
  • carbon is expelled from the formed martensite lath to the surrounding austenite during cooling. At that time, when Ti carbide or carbonitride dispersed in the steel is coarsely dispersed, the growth in the longitudinal direction of the martensite lath proceeds without being hindered, so the aspect ratio is narrow and long. Big martensite lath.
  • the carbon content in the retained austenite in the steel is defined as 0.60% or more.
  • the carbon content in the retained austenite can be concentrated to about 0.70%, but the limit is about 1.0%.
  • the properties such as strength and elongation of the press-formed product can be controlled by appropriately adjusting the press forming conditions (heating temperature and cooling rate) and high ductility. (Residual ductility) press-molded products can be obtained, so it can be applied to parts that have been difficult to apply with conventional press-molded products (for example, energy absorbing members). Useful.
  • the heating temperature and the conditions of each region at the time of molding are appropriately controlled.
  • a press-formed product that exhibits a strength-ductility balance corresponding to each region hereinafter sometimes referred to as a multi-region molded product
  • the heating region of the steel plate is divided into at least two regions, one of which is hereinafter referred to as the first region. Is heated to a temperature not lower than A c3 transformation point and not higher than 950 ° C., and another region (hereinafter referred to as second region) is not lower than A c1 transformation point + 20 ° C. and A c3 transformation point is not higher than ⁇ 20 ° C. Then, press molding is started for both the first and second regions, and during molding and after completion of molding, both the first and second regions have a temperature of 20 ° C./second or more in the mold. What is necessary is just to cool to the temperature below the martensitic transformation start temperature Ms, ensuring an average cooling rate.
  • the heating region of the steel sheet is divided into two regions (high-strength side region and low-strength side region), and the manufacturing conditions are controlled according to each region, so that the strength-ductility balance corresponding to each region is obtained.
  • a press-molded product that can be exhibited is obtained.
  • the second region corresponds to the low-strength side region
  • the manufacturing conditions, structure, and characteristics in this region are basically the same as those of the single-region molded product described above.
  • manufacturing conditions for forming the other first region corresponding to the high-strength side region
  • the heating temperature of the steel sheet is preferably Ac3 transformation point + 50 ° C. or higher and 900 ° C. or lower.
  • the average cooling rate and the cooling end temperature during and after molding are appropriately controlled. There is a need. From this point of view, the average cooling rate during molding needs to be 20 ° C./second or more, and the cooling end temperature needs to be lower than the martensite transformation start temperature (Ms point).
  • the average cooling rate during molding is preferably 30 ° C./second or more (more preferably 40 ° C./second or more).
  • the cooling end temperature is specifically 400 ° C. or lower, preferably 300 ° C. or lower.
  • the metal structure and precipitates are different between the first region and the second region.
  • the metal structures are retained austenite: 3 to 20 area% (the effect of retained austenite is the same as described above), and martensite: 80 area% or more.
  • the same metal structure as that of the single region molded product and the carbon content in the retained austenite satisfy 0.60% or more.
  • the area fraction of martensite needs to be 80 area% or more.
  • the fraction of martensite is preferably 85 area% or more (more preferably 90 area% or more).
  • the structure in the first region may partially include ferrite, pearlite, bainite, and the like.
  • Example 1 Steel materials (steel Nos. 1 to 32) having the chemical composition shown in Table 1 below are melted in vacuum to form experimental slabs, then hot rolled into steel plates, and then cooled and wound up. Simulated treatment was performed (plate thickness: 3.0 mm). In the winding simulation processing method, after cooling to the winding temperature, the sample was placed in a furnace heated to the winding temperature, held for 30 minutes, and then cooled in the furnace. The steel plate manufacturing conditions at this time are shown in Table 2 below. In Table 1, the A c1 transformation point, the A c3 transformation point, the Ms point, and the Bs point are obtained by using the following formulas (2) to (5) (for example, “Leslie Steel Materials Science Maruzen, (1985). Further, the treatments (1) to (3) shown in the remarks column of Table 2 are obtained by performing the following treatments (rolling, cooling, alloying).
  • a c1 transformation point (° C.) 723 + 29.1 ⁇ [Si] ⁇ 10.7 ⁇ [Mn] + 16.9 ⁇ [Cr] ⁇ 16.9 [Ni] (2)
  • a c3 transformation point (°C) 910-203 ⁇ [C ] 1/2 + 44.7 ⁇ [Si] -30 ⁇ [Mn] + 700 ⁇ [P] + 400 ⁇ [Al] + 400 ⁇ [Ti] + 104 ⁇ [V ] -11 ⁇ [Cr] + 31.5 ⁇ [Mo] ⁇ 20 ⁇ [Cu] ⁇ 15.2 ⁇ [Ni] (3)
  • Ms point (° C.) 550 ⁇ 361 ⁇ [C] ⁇ 39 ⁇ [Mn] ⁇ 10 ⁇ [Cu] ⁇ 17 ⁇ [Ni] ⁇ 20 ⁇ [Cr] ⁇ 5 ⁇ [Mo] + 30 ⁇ [Al] ( 4)
  • Bs point (° C.) 830 ⁇ 270 ⁇ [C]
  • Process (1) After finish rolling, after cooling to 650 ° C. at an average cooling rate of 50 ° C./second, cooling is performed at an average cooling rate of 650 ° C. to 5 ° C./second for 10 seconds, and then the average cooling rate to the winding temperature Cooled at 50 ° C./second. Then, in order to match
  • Process (2) After cold rolling the hot-rolled steel sheet, continuous annealing was simulated, heated to 860 ° C., cooled to 400 ° C. at an average cooling rate of 30 ° C./second, and held.
  • Process (3) After cold rolling the hot-rolled steel sheet, after heating to 860 ° C. to simulate a continuous hot-dip galvanizing line, cooling to 400 ° C. at an average cooling rate of 30 ° C./second, and further holding It was cooled after heating at 500 ° C. for 10 seconds.
  • the obtained steel sheet was subjected to analysis of Ti precipitation state and observation of metal structure (fraction of each structure) in the following manner.
  • the result is shown in the following table together with a calculated value [0.5 ⁇ (total Ti amount-3.4 [N])] of 0.5 ⁇ [total Ti amount (mass%) ⁇ 3.4 [N]]. 3 shows.
  • the amount of precipitated Ti (mass%)-3.4 [N] (the amount of Ti present as a precipitate) was subjected to extraction residue analysis using a mesh having a mesh diameter of 0.1 ⁇ m (in the extraction process, Precipitates aggregated and fine precipitates can be measured), and the amount of precipitated Ti (mass%)-3.4 [N] (in Table 3, expressed as precipitated Ti amount-3.4 [N]) was determined. .
  • the Ti-containing precipitate partially contained V or Nb, the content thereof was also measured.
  • Each steel plate (1.6 mm t ⁇ 150 mm ⁇ 200 mm) (with the exception of the above treatments (1) to (3), the thickness is adjusted to 1.6 mm by hot rolling), and a predetermined temperature in a heating furnace Then, press-molding and cooling treatment were performed using a hat-shaped mold (FIG. 1) to obtain a press-molded product.
  • Table 4 shows the press molding conditions (heating temperature, average cooling rate, rapid cooling end temperature during press molding).
  • the tensile strength (TS), elongation (total elongation EL), and observation of metal structure (fraction of each structure) were measured by the following methods.
  • Steel No. Those of 3, 6 to 10, 14, 18, and 22 are comparative examples that do not satisfy any of the requirements defined in the present invention, and any of the characteristics is deteriorated. That is, Steel No. No. 3 uses a steel sheet with a low Si content, and the retained austenite fraction in the molded product is not ensured, and the carbon content in the retained austenite is low, and the elongation is not. ing. Steel No. In No. 6, the heating temperature at the time of molding was high, and only a low elongation EL was obtained, and the strength-elongation balance (TS ⁇ EL) was also deteriorated.
  • TS ⁇ EL strength-elongation balance
  • Steel No. No. 14 uses a steel sheet having a metal structure of ferrite + pearlite 100 area% due to the coiling temperature, and can ensure annealing martensite and / or annealing bainite fraction in the molded product.
  • the strength-elongation balance (TS ⁇ EL) is deteriorated.
  • Steel No. No. 18 uses a steel sheet with an excessive C content, and the strength increases and only a low elongation EL is obtained.
  • Steel No. No. 22 uses a steel sheet with an excessive Ti content, and the strength-elongation balance (TS ⁇ EL) is deteriorated.
  • Example 2 Steel materials (steel Nos. 33 to 37) having the chemical composition shown in Table 7 below were vacuum-melted to form slabs for experiment, then hot-rolled, and then cooled and wound (sheet thickness) : 3.0 mm). The steel plate manufacturing conditions at this time are shown in Table 8 below.
  • the obtained steel sheet was analyzed in the same manner as in Example 1 for the analysis of the precipitation state of the Ti-containing precipitates and the observation of the metal structure (fraction of each structure). The results are shown in Table 9 below.
  • each steel sheet (3.0mm t ⁇ 150mm ⁇ 200mm) was heated to a predetermined temperature in a heating furnace, performing a press-forming and cooling process in a mold of hat-shaped (FIG. 1), and a molded article .
  • the steel plate is put in an infrared furnace, and the portion (steel plate portion corresponding to the first region) to be strengthened is directly irradiated with infrared rays so that it can be heated at a high temperature.
  • the steel plate portion corresponding to the second region was covered with a cover so as to block a part of infrared rays so that it could be heated at a low temperature, thereby giving a heating temperature difference. Therefore, the molded product has regions having different strengths within a single part.
  • Table 10 shows the press molding conditions (heating temperature, average cooling rate, rapid cooling end temperature in each region during press molding).
  • TS tensile strength
  • elongation total elongation EL
  • observation of metal structure fraction of each structure
  • carbon content in retained austenite in each region were the same as in Example 1. Asked.
  • the observation results (fraction of each structure) of the metal structure are shown in Table 11 below.
  • the mechanical properties (tensile strength TS, elongation EL and TS ⁇ EL) of the molded product are shown in Table 12 below.
  • the tensile strength (TS) on the high strength side is 1470 MPa or higher
  • the elongation (EL) satisfies 8% or higher
  • the strength-elongation balance (TS ⁇ EL) is 14000 (MPa ⁇ %) or higher.
  • evaluation criteria on the low strength side are the same as in Example 1).
  • Steel No. Nos. 34 and 36 are comparative examples that do not satisfy any of the requirements defined in the present invention, and any of the characteristics is deteriorated. That is, Steel No. In the case of No. 34, the heating temperature at the time of press molding is low, and the strength on the high strength side is lowered. Steel No. No. 36 uses a steel plate having a small Ti-containing precipitate, and only a low strength is obtained on the high strength side, and the strength-elongation balance (TS ⁇ EL) deteriorates on the low strength side. Yes.
  • TS ⁇ EL strength-elongation balance
  • the present invention is suitable for a steel sheet for hot pressing used when manufacturing a structural part of an automobile.

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Abstract

L'invention concerne une feuille d'acier pour une utilisation de pressage à chaud qui a une composition spécifiée en composants chimiques, dans laquelle une partie des précipités à teneur en Ti contenus dans la feuille d'acier, dont chacun a un diamètre de cercle équivalent de 30 nm ou moins, a un diamètre moyen de cercle équivalent de 3 nm ou plus; la quantité de Ti précipité et la quantité totale de Ti dans l'acier satisfont la relation représentée par la formule (1) présentée ci-après, et la somme totale de la fraction de bainite et de la fraction de martensite dans la structure métallographique est de 80 % en surface ou plus. Quantité de Ti précipité (% en masse) - 3,4[N] > 0,5 × [quantité totale de Ti (% en masse) - 3,4[N]]…..(1) (Dans la formule (1), [N] représente la teneur (% en masse) de N dans l'acier).
PCT/JP2013/055680 2012-03-09 2013-03-01 Feuille d'acier pour une utilisation de pressage à chaud, article moulé par pressage et procédé de fabrication d'un article moulé par pressage WO2013133166A1 (fr)

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KR1020147024781A KR101609967B1 (ko) 2012-03-09 2013-03-01 열간 프레스용 강판 및 프레스 성형품, 및 프레스 성형품의 제조 방법
US14/382,158 US20150027602A1 (en) 2012-03-09 2013-03-01 Steel sheet for hot pressing use, press-formed product, and method for manufacturing press-formed product
EP13757984.3A EP2824209A4 (fr) 2012-03-09 2013-03-01 Feuille d'acier pour une utilisation de pressage à chaud, article moulé par pressage et procédé de fabrication d'un article moulé par pressage
CN201380012504.9A CN104160052B (zh) 2012-03-09 2013-03-01 热压用钢板和冲压成形品以及冲压成形品的制造方法
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WO2015041159A1 (fr) * 2013-09-18 2015-03-26 新日鐵住金株式会社 Corps moulé par estampage à chaud et son procédé de production
CN105112629A (zh) * 2015-09-17 2015-12-02 重庆齿轮箱有限责任公司 一种大厚度高强度结构钢的热处理方法
EP3093360A4 (fr) * 2014-01-06 2018-03-07 Nippon Steel & Sumitomo Metal Corporation Élément façonné à chaud et son procédé de fabrication
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US20180312947A1 (en) 2018-11-01
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