WO2019188622A1 - ホットスタンプ用鋼板 - Google Patents

ホットスタンプ用鋼板 Download PDF

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WO2019188622A1
WO2019188622A1 PCT/JP2019/011606 JP2019011606W WO2019188622A1 WO 2019188622 A1 WO2019188622 A1 WO 2019188622A1 JP 2019011606 W JP2019011606 W JP 2019011606W WO 2019188622 A1 WO2019188622 A1 WO 2019188622A1
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mass
steel sheet
hot stamping
content
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PCT/JP2019/011606
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English (en)
French (fr)
Japanese (ja)
Inventor
晴香 荒木
紗江 濱本
浅井　達也
Original Assignee
株式会社神戸製鋼所
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Priority claimed from JP2019029207A external-priority patent/JP7353768B2/ja
Application filed by 株式会社神戸製鋼所 filed Critical 株式会社神戸製鋼所
Priority to US17/041,223 priority Critical patent/US20210054488A1/en
Priority to MX2020009944A priority patent/MX2020009944A/es
Priority to BR112020019522-7A priority patent/BR112020019522A2/pt
Priority to CN202211151222.4A priority patent/CN115404409A/zh
Priority to KR1020207030386A priority patent/KR102409015B1/ko
Priority to CA3094926A priority patent/CA3094926C/en
Priority to EP19775683.6A priority patent/EP3760755A4/en
Priority to RU2020134949A priority patent/RU2766947C1/ru
Priority to CN201980021455.2A priority patent/CN111902558A/zh
Publication of WO2019188622A1 publication Critical patent/WO2019188622A1/ja

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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
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    • C21D6/00—Heat treatment of ferrous alloys
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
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    • 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
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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    • 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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
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    • 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
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    • 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
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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

Definitions

  • the present invention relates to a steel sheet for hot stamping.
  • Non-Patent Document 1 proposes improving the balance between strength and toughness of a steel sheet by refining old austenite grains after hot stamping.
  • the cooling rate inside the steel sheet may decrease due to an increase in the mold temperature and the clearance between the mold and the steel sheet.
  • the cooling rate of the steel sheet is equal to or lower than the critical cooling rate, a soft phase such as ferrite and bainite precipitates, and the hardness of the steel sheet is reduced.
  • the autotemper is promoted by a decrease in the cooling rate below the Ms point, which causes a decrease in the hardness of the steel sheet.
  • Non-Patent Document 2 discusses the change in cooling rate when the clearance between the mold and the steel plate is changed. When this clearance is 0.4 mm, the cooling rate is up to about 15 ° C./s. It has been shown to decline.
  • Non-Patent Document 1 there is a method of refining the crystal grains of steel as a general structure design technique for hot stamping steel plates, thereby obtaining a steel plate with an excellent balance between strength and toughness. it can.
  • a method of refining crystal grains there is a method of adding an element such as Nb, Ni, Ti, etc. In this case, the economic efficiency of the steel sheet is deteriorated. Moreover, since the hardenability deteriorates, the steel plate which refined the crystal grain lacks hardness stability.
  • the conventional hot stamping steel plate has a problem that it is difficult to obtain a member (molded product) having an excellent balance between strength and toughness and excellent hardness stability without increasing labor and cost.
  • An object of the present invention is to provide a steel sheet for hot stamping capable of obtaining a molded product excellent in hardness stability in addition to a balance between strength and toughness while suppressing an increase in labor and cost in the hot stamping process. It is.
  • the steel sheet for hot stamping is % By mass C: 0.25% or more, 0.4% or less, Si: 1.05% or more, 1.4% or less, Mn: 0% or more, 1.4% or less, Cr: 0.6% or more, 3.0% or less, P: 0% or more, 0.03% or less, S: 0% or more, 0.02% or less, Al: 0.01% or more, 1% or less, N: 0% or more, 0.01% or less, B: 0.0005% or more and 0.005% or less, and Ti: 0.005% or more and 0.1% or less, with the balance being iron and inevitable impurities.
  • This hot stamping steel sheet has the following relational expression (1) when the C content is [C], the Si content is [Si], the Mn content is [Mn], and the Cr content is [Cr].
  • a hot stamping steel plate capable of obtaining a molded product having excellent hardness stability in addition to a balance between strength and toughness while suppressing an increase in labor and cost in the hot stamping process. Can do.
  • the steel sheet for hot stamping is % By mass C: 0.25% or more, 0.4% or less, Si: 1.05% or more, 1.4% or less, Mn: 0% or more, 1.4% or less, Cr: 0.6% or more, 3.0% or less, P: 0% or more, 0.03% or less, S: 0% or more, 0.02% or less, Al: 0.01% or more, 1% or less, N: 0% or more, 0.01% or less, B: 0.0005% or more and 0.005% or less, and Ti: 0.005% or more and 0.1% or less, with the balance being iron and inevitable impurities.
  • This hot stamping steel sheet has the following relational expression (1) when the C content is [C], the Si content is [Si], the Mn content is [Mn], and the Cr content is [Cr].
  • Non-Patent Document 2 in the hot stamping process, the normal member is cooled in the range of 30 ° C./s to 10 ° C./s due to the clearance between the die and the steel plate and the rise of the die temperature. Speed fluctuations were expected to occur. For this reason, in addition to the balance between strength and toughness, the present inventors have focused on suppressing variation in hardness even if fluctuations in the cooling rate occur, and details on the component system of the steel sheet to achieve this The examination was done.
  • the present inventors adjust the balance of the contents of C, Si, Mn and Cr so that each component composition in the steel sheet satisfies the above range and the relational expression (1) is satisfied.
  • the inventors have newly found that it is possible to achieve both a balance between strength and toughness and hardness stability, and have arrived at the present invention.
  • C content determines the intensity
  • the C content is 0.25% by mass or more, preferably 0.255% by mass or more, and more preferably 0.260% by mass or more.
  • C content is 0.4 mass% or less, it is preferable that it is 0.38 mass% or less, and it is more preferable that it is 0.36 mass% or less.
  • Si silicon: 1.05 mass% or more, 1.4 mass% or less
  • Si contributes to the hardness stability of the steel sheet by increasing the temper softening resistance.
  • Si also has an effect of preventing scale peeling after cooling the mold when the surface of the steel sheet is not plated. In order to exert these effects, the Si content is 1.05% by mass or more.
  • Si facilitates the formation of retained austenite ( ⁇ ) and promotes a decrease in yield strength (YS) and segregation of Mn.
  • Si content is 1.4 mass% or less, and it is preferable that it is 1.35 mass% or less.
  • Mn manganese: 0% by mass or more and 1.4% by mass or less
  • Mn is one of the important elements contained in the steel sheet for hot stamping according to the present embodiment, and contributes to increasing the strength of the steel sheet after cooling the mold by enhancing the hardenability of the steel sheet.
  • the Mn content is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and further preferably 0.8% by mass or more. .
  • Mn content is 1.4 mass% or less, it is preferable that it is 1.35 mass% or less, and it is more preferable that it is 1.30 mass% or less.
  • Cr Cr (chromium): 0.6 mass% or more, 3.0 mass% or less
  • Cr is one of important elements in the hot stamping steel plate according to the present embodiment.
  • Cr contributes to securing hardness at a low cooling rate (for example, 10 ° C./s) and precipitates coarse carbides during mold cooling. It was confirmed that brittle fracture was suppressed when impact stress was applied in a low-temperature environment.
  • the Cr content is 0.6% by mass or more, preferably 0.8% by mass or more, and more preferably 1.05% by mass or more.
  • Cr content is 3.0 mass% or less, and it is preferable that it is 2.5 mass% or less.
  • P phosphorus: 0 mass% or more, 0.03 mass% or less
  • P needs to prescribe
  • S sulfur: 0 mass% or more, 0.02 mass% or less
  • S produces MnS, thereby lowering the uniformity of the Mn concentration distribution and degrading the weldability of the steel sheet. For this reason, S content is 0.02 mass% or less, it is preferable that it is 0.018 mass% or less, and it is more preferable that it is 0.015 mass% or less.
  • Al is an element that acts as a deoxidizer. In order to exhibit this effect, the Al content is 0.01% by mass or more, and preferably 0.015% by mass or more.
  • Al content is 1 mass% or less, it is preferable that it is 0.8 mass% or less, and it is more preferable that it is 0.1 mass% or less.
  • Al content here means content of Al (sol.Al) of a solid solution state.
  • N nitrogen: 0% by mass or more and 0.01% by mass or less
  • N is an element inevitably mixed in the steel sheet. If N is excessively contained in the steel sheet, N forms boride, thereby reducing the amount of solute B in the steel sheet, resulting in deterioration of hardenability. For this reason, N content is 0.01 mass% or less, it is preferable that it is 0.008 mass% or less, and it is more preferable that it is 0.005 mass% or less.
  • B (boron): 0.0005 mass% or more, 0.005 mass% or less]
  • B is an important element for improving the hardenability of the steel sheet.
  • the B content is 0.0005% by mass or more, preferably 0.0010% by mass or more, and more preferably 0.0015% by mass or more.
  • B content is 0.0050 mass% or less, it is preferable that it is 0.0045 mass% or less, and it is more preferable that it is 0.0030 mass% or less.
  • Ti titanium (titanium): 0.005 mass% or more, 0.1 mass% or less] Ti reduces the amount of BN produced in the steel sheet by producing TiN. Thereby, the quantity of the solid solution B in a steel plate increases, and the effect of the hardenability improvement by B can be heightened. In order to exert this effect, the Ti content is 0.0050% by mass or more, preferably 0.010% by mass or more, and more preferably 0.015% by mass or more.
  • Ti content is 0.1 mass% or less, it is preferable that it is 0.08 mass% or less, and it is more preferable that it is 0.06 mass% or less.
  • the steel sheet for hot stamping according to this embodiment may further contain one or more selected from the group consisting of Mo, Nb and V in addition to the above component composition, or from the group consisting of Cu and Ni. One or more selected may further be contained. The range of these component compositions will be described below. These elements are not essential elements in the hot stamping steel sheet of the present invention, and may not be added.
  • Mo molybdenum: 0% by mass or more and 1.0% by mass or less
  • Mo is an element that contributes to improving the hardenability of the steel sheet.
  • the Mo content is preferably 0.01% by mass or more.
  • the Mo content is preferably 1.0% by mass or less.
  • Nb and V have the effect of forming fine carbides and refining the steel structure by the pinning effect. V also has the effect of secondary curing by precipitating during tempering. In order to exert these effects, the Nb and V contents are each preferably 0.0008% by mass or more.
  • the Nb and V contents are each preferably 0.1% by mass or less, more preferably 0.08% by mass or less, and further preferably 0.07% by mass or less.
  • Cu and Ni are preferably added when it is necessary to improve the delayed fracture characteristics of the member.
  • Cu and Ni are excessively contained in the steel plate, it may cause wrinkles on the surface of the steel plate, and finally on the surface of the member.
  • each content of Cu and Ni is 0.5 mass% or less, and it is more preferable that the total content is 0.5 mass% or less.
  • the steel sheet for hot stamping according to this embodiment is excellent in hardness stability in addition to the balance of strength and toughness by satisfying the relational expression (1) below by adjusting the balance of the contents of C, Si, Mn and Cr. It has become.
  • [C] represents the C content (mass%) of the hot stamping steel plate.
  • [Si] indicates the Si content (mass%) of the steel sheet for hot stamping.
  • [Mn] indicates the Mn content (% by mass) of the steel sheet for hot stamping.
  • Cr] indicates the Cr content (mass%) of the steel sheet for hot stamping.
  • the steel sheet for hot stamping according to the present embodiment has an excellent balance between strength after quenching by mold cooling and low temperature toughness. In addition to being a steel plate, it has excellent hardness stability. Specifically, the absorbed energy in a Charpy impact test at ⁇ 40 ° C. when quenching a flat plate using a mold is A (J / cm 2 ), and the steel sheet for hot stamping is heated to the austenite region and then 10 ° C./s.
  • the above relational expression (2) is an index of the balance between strength and toughness of the steel plate newly devised by the present inventors, and is an important concept in considering the balance between strength and toughness of the steel plate for hot stamping. is there.
  • the present inventors paid attention to the hardness when the cooling rate was 10 ° C./s and the toughness after cooling the flat plate.
  • Flat plate mold cooling takes into account ideal cooling conditions in which no clearance is generated between the mold and the steel plate in the hot stamping process.
  • the graph of FIG. 1 shows the absorbed energy A in a Charpy impact test at ⁇ 40 ° C. when a flat plate is quenched using a mold (horizontal axis) and the hardness B of the steel plate when quenched at a cooling rate of 10 ° C./s. (Vertical axis), and the straight line (1) in the graph corresponds to the relational expression (2).
  • the horizontal axis (A) in the graph of FIG. 1 assumes the toughness of the most brittle part in the member after mold cooling. That is, when the flat plate is die-cooled, the die and the steel plate come into contact with each other in an ideal state, so that the cooling rate is increased. For this reason, the strength after cooling increases, but on the other hand it becomes very brittle. That is, this horizontal axis has a meaning as toughness in the most brittle part when the hot stamping steel plate is formed into a member (molded product).
  • the vertical axis (B) of the graph of FIG. 1 assumes the hardness of the most softened portion of the member after cooling the mold.
  • the member after mold cooling has a portion with low hardness (strength) cooled at a low cooling rate.
  • the minimum cooling rate during mold cooling is assumed to be about 10 ° C./s. Therefore, this vertical axis has the meaning as the hardness (strength) at the most softened portion of the member (molded product) after cooling the mold. Therefore, by using these two axes, the toughness of the weakest part when impact stress is applied to the molded member and the strength of the weakest part when static stress is applied to the member Can be evaluated.
  • the strength and toughness of the steel sheet are in a trade-off relationship, and therefore the toughness tends to deteriorate when the strength of the steel sheet is improved. That is, it is difficult to improve both the strength and toughness of the steel sheet, and it is normal that the A / B distribution exists in the region below the straight line (1) in the graph of FIG.
  • the straight line (2) is one index indicating hardness stability.
  • the temperature of the mold rises and there may be a clearance between the mold and the steel plate. Due to these factors, the cooling rate of the steel plate during quenching decreases, and the hardness of the steel plate after quenching decreases as the cooling rate decreases.
  • the hardness range of 516 Hv or higher when quenched in a low cooling rate region (10 ° C./s). . Therefore, even in a steel sheet in which the balance between strength and toughness is improved by refining crystal grains, it is normal that the distribution of A and B exists in the region below the straight line (2) in FIG. .
  • the hot stamping steel plate according to this embodiment has excellent hardness stability in addition to the balance between strength and toughness. That is, this hot stamping steel sheet has an excellent balance between strength and toughness satisfying the above relational expression (2), and has a certain hardness or more even when cooled at a cooling rate of 10 ° C./s. It is feasible.
  • the above relational expression (4) is an index of hardness stability of another steel plate.
  • the cooling rate of the steel sheet may decrease, and the hardness of the steel sheet after quenching may become unstable. Further, as described above, since the hardness stability decreases when the crystal grains are refined, it is usually difficult to satisfy the relational expression (4).
  • the steel sheet for hot stamping satisfying the relational expression (1) and satisfying the component ranges of the claims has a cooling rate of 10 ° C./s. It was clarified that hardness after quenching exceeding 516 Hv can be obtained even in the low cooling rate region, and the hardness difference between the cooling rate of 30 ° C./s and 10 ° C./s can be suppressed to 35 Hv or less. . 30 ° C./s is an ideal cooling rate at the time of mold cooling confirmed by experiments and the like, while 10 ° C./s is the minimum cooling rate expected as described above.
  • the relational expression (4) is an index indicating that the hardness difference (variation) after quenching is small between the upper and lower limits of the cooling rate assumed in the hot stamp.
  • the hardness of the steel sheet after quenching to the extent that the above relational expression (4) is satisfied regardless of the temperature rise of the mold and the occurrence of clearance between the mold and the steel sheet. Can be stabilized.
  • the steel sheet for hot stamping of the present invention may be a base steel sheet that has not been subjected to plating treatment, or a plated steel sheet that has been subjected to plating treatment.
  • the slab manufacturing process is performed.
  • a slab is obtained by melting steel according to a conventional method, pouring molten steel into a mold and continuously casting the steel.
  • the component composition of the steel is adjusted during melting so that each component composition contained in the slab satisfies the above range and the contents of C, Si, Mn, and Cr satisfy the relational expression (1).
  • a hot rolling process is performed.
  • the slab obtained in the above step is placed in a heating furnace, heated to a predetermined temperature (eg, 1200 ° C.), and held at the heating temperature for a predetermined time (eg, 30 minutes).
  • a predetermined temperature eg, 1200 ° C.
  • the heated slab is placed upstream of the hot rolling line. And the said slab is rolled into the steel plate which has predetermined
  • a cold rolling process is performed.
  • the scale (iron oxide) generated on the surface of the steel plate in the hot rolling step is washed off with acid (pickling), and then the hot-rolled steel plate is further rolled so that the plate thickness is further reduced.
  • the hot-rolled steel sheet after pickling is passed between rolls of a rolling stand so that the hot-rolled steel sheet is further thinned.
  • the cold-rolled steel sheet obtained by the above process is the hot stamping steel sheet according to the present embodiment.
  • the hot stamp using the steel plate manufactured by the said process is demonstrated with reference to FIG.
  • the hot stamping steel plate 1 manufactured by the above process is heated in the predetermined heating furnace 2 to the austenite transformation temperature or higher.
  • the heated hot stamping steel plate 1 is placed between the dies 3 and 4, and the hot stamping steel plate 1 is press-formed into a desired shape by the dies 3 and 4.
  • the hot stamping steel plate 1 is cooled by coming into contact with the molds 3 and 4, and quenching is performed simultaneously with the forming.
  • the steel plate after hardening is taken out from the metal mold
  • the molded product 5 has the same component composition as the hot stamping steel plate 1 according to this embodiment described above, and the balance of the contents of C, Si, Mn and Cr is adjusted so as to satisfy the relational expression (1). It has been done. Therefore, the molded product 5 is excellent in hardness stability in addition to the balance between strength and toughness, and can be used for various applications including automobile members.
  • the steel sheet for hot stamping according to the above embodiment is % By mass C: 0.25% or more, 0.4% or less, Si: 1.05% or more, 1.4% or less, Mn: 0% or more, 1.4% or less, Cr: 0.6% or more, 3.0% or less, P: 0% or more, 0.03% or less, S: 0% or more, 0.02% or less, Al: 0.01% or more, 1% or less, N: 0% or more, 0.01% or less, B: 0.0005% or more and 0.005% or less, and Ti: 0.005% or more and 0.1% or less, with the balance being iron and inevitable impurities.
  • This hot stamping steel sheet has the following relational expression (1) when the C content is [C], the Si content is [Si], the Mn content is [Mn], and the Cr content is [Cr].
  • Test piece height h1 10 mm ⁇ 0.05 mm
  • Test piece length L 55 mm ⁇ 0.6 mm
  • Test piece width b 1.4 mm ⁇ 0.05 mm
  • Notch shape V notch Notch angle: 45 ° ⁇ 2 °
  • Notch bottom radius 0.25 mm ⁇ 0.025 mm
  • Notch height h2 8mm ⁇ 0.05mm
  • Angle between adjacent surfaces to remove fracture surface 90 ° ⁇ 2 °
  • test piece having the above dimensions was placed in liquid nitrogen adjusted to a temperature of ⁇ 40 ° C. ⁇ 1 ° C. and held for at least 10 minutes. Thereafter, the test piece was taken out of the liquid nitrogen and placed on a support table, and an impact was applied to the test piece. At this time, after putting a test piece on a support stand, time until giving an impact was made into 5 seconds or less.
  • JIS Charpy impact tester 300J was used as a tester, and an impact blade having a radius of 2 mm was used. The number of test pieces was two, and evaluation was performed using the average value of the two measured values.
  • Rate of temperature rise when austenitizing 10 ° C / s
  • High temperature hold hold at 900 ° C. for 100 seconds
  • Cooling rate constant cooling from 900 ° C. to room temperature at 10 ° C./s or 30 ° C./s
  • the hardness test based on the “Vickers hardness test method” defined in JIS Z 2244 was performed using the specimen after quenching. In this test, five-point measurement was performed at a test load of 9.8 N at a position 1/4 of the plate thickness from the surface of the test piece, and the average value thereof was used for evaluation.
  • Tables 1 and 2 below show No. For each of the steel plates 1 to 17, the composition (mass%), the absorbed energy A (J / cm 2 ) in the Charpy impact test at ⁇ 40 ° C., and the Vickers hardness B (Hv when the cooling rate is 10 ° C./s) ), Vickers hardness C (Hv) when the cooling rate is 30 ° C./s, hardness difference (Hv) when the cooling rate is 10 ° C./s and 30 ° C./s, and the above relational expression ( The value of the left side of 1), the value when the right side is subtracted from the left side of the relational expression (2), and the evaluation of scale adhesion are shown.
  • No. 1 to 9 and 14 to 17 are the contents of C, Si, Mn, Cr, P, S, Al, N, B and Ti in the steel sheet satisfy the scope of the present invention, respectively, and C, Si, Mn and The Cr content satisfied the relational expression (1).
  • the value of “B + 4A ⁇ 627” was a positive value and satisfied the relational expression (2), so that the steel sheet had an excellent balance between strength and toughness.
  • no. In 1 to 9 and 14 to 17, “B ⁇ 516” and “CB ⁇ 35” were satisfied, and the above relational expressions (3) and (4) were satisfied, so that the steel sheet was excellent in hardness stability. This is because in the graph of FIG. It is clear from the fact that the data (black circles) 1 to 9 and 14 to 17 are present in the region above the straight lines (1) and (2). In addition, all the evaluations of scale adhesion were “ ⁇ ”.
  • the Si content is less than 1.05% by mass, and the value of [[C] +2/9 [Si] +7/9 [Mn] +8/9 [Cr] ⁇ 7/4] is a negative value. Therefore, the value of “B + 4A ⁇ 627” became a negative value, and the balance between strength and toughness was inferior.
  • the hardness B when the cooling rate is 10 ° C./s is less than 516 Hv, and the difference in hardness between the cooling rate of 10 ° C./s and 30 ° C./s exceeds 35 Hv, which also improves the hardness stability. inferior.
  • the evaluation of scale adhesion was also “x”.
  • the Cr content is less than 0.6% by mass, and the value of “[C] +2/9 [Si] +7/9 [Mn] +8/9 [Cr] ⁇ 7/4” is negative. Therefore, the value of “B + 4A ⁇ 627” was a negative value, and the balance between strength and toughness was inferior.
  • the hardness B when the cooling rate is 10 ° C./s is less than 516 Hv, and the difference in hardness between the cooling rate of 10 ° C./s and 30 ° C./s exceeds 35 Hv, which also improves the hardness stability. inferior.

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PCT/JP2019/011606 2018-03-27 2019-03-19 ホットスタンプ用鋼板 WO2019188622A1 (ja)

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US17/041,223 US20210054488A1 (en) 2018-03-27 2019-03-19 Steel plate for hot stamping
MX2020009944A MX2020009944A (es) 2018-03-27 2019-03-19 Placa de acero para estampado en caliente.
BR112020019522-7A BR112020019522A2 (pt) 2018-03-27 2019-03-19 Chapa de aço para estampagem a quente
CN202211151222.4A CN115404409A (zh) 2018-03-27 2019-03-19 热冲压用钢板
KR1020207030386A KR102409015B1 (ko) 2018-03-27 2019-03-19 핫 스탬핑용 강판
CA3094926A CA3094926C (en) 2018-03-27 2019-03-19 Steel plate for hot stamping
EP19775683.6A EP3760755A4 (en) 2018-03-27 2019-03-19 HOT STAMPED STEEL SHEET
RU2020134949A RU2766947C1 (ru) 2018-03-27 2019-03-19 Стальной лист для горячей штамповки
CN201980021455.2A CN111902558A (zh) 2018-03-27 2019-03-19 热冲压用钢板

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