WO2014057519A1 - 形状凍結性に優れた冷延鋼板およびその製造方法 - Google Patents

形状凍結性に優れた冷延鋼板およびその製造方法 Download PDF

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WO2014057519A1
WO2014057519A1 PCT/JP2012/006532 JP2012006532W WO2014057519A1 WO 2014057519 A1 WO2014057519 A1 WO 2014057519A1 JP 2012006532 W JP2012006532 W JP 2012006532W WO 2014057519 A1 WO2014057519 A1 WO 2014057519A1
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cold
less
steel sheet
rolled steel
sheet according
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PCT/JP2012/006532
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English (en)
French (fr)
Japanese (ja)
Inventor
太郎 木津
藤田　耕一郎
秀晴 古賀
容任 森川
健司 田原
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Ｊｆｅスチール株式会社
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Priority to CN201280076329.5A priority Critical patent/CN104870678A/zh
Priority to PCT/JP2012/006532 priority patent/WO2014057519A1/ja
Priority to US14/433,869 priority patent/US20150252456A1/en
Priority to IN599KON2015 priority patent/IN2015KN00599A/en
Priority to KR1020157011022A priority patent/KR20150060957A/ko
Priority to EP12886281.0A priority patent/EP2907887B1/de
Priority to JP2014540643A priority patent/JPWO2014057519A1/ja
Publication of WO2014057519A1 publication Critical patent/WO2014057519A1/ja

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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
    • 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
    • C21D1/26—Methods of annealing
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • 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
    • 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
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to a cold-rolled steel sheet excellent in formability and suitable for use as a member for parts having severe shape accuracy in the fields of electrical machinery, automobiles, building materials, and the like, and in particular, has a shape-fixability. Regarding improvement.
  • Patent Document 1 describes a ferritic thin steel sheet having excellent shape freezing properties.
  • C 0.0001 to 0.05%
  • Si 0.01 to 1.0%
  • Mn 0.01 to 2.0%
  • P 0.15% or less
  • S 0.03% or less
  • Al 0.01 %
  • N 0.01% or less
  • O 0.007% or less of steel composition with hot rolling at 950 ° C or less Ar 3 transformation point or more total rolling reduction of 25% or more and 950 ° C or less
  • the hot rolling is finished at the Ar 3 transformation point or higher so that the friction coefficient in the steel is 0.2 or less, and after cooling, it is wound up at a temperature below a predetermined critical temperature, and thus ⁇ 100 ⁇ parallel to the plate surface
  • a thin steel sheet having a ratio of the plane to the ⁇ 111 ⁇ plane of 1.0 or more can be obtained.
  • the slip system during bending can be controlled, and spring back can be suppress
  • Patent Document 2 describes a press molding method with excellent dimensional accuracy of a molded product.
  • a steel plate having a ratio of ⁇ 100 ⁇ plane and ⁇ 111 ⁇ plane parallel to the plate surface of 1.0 or more is used, and a material tensile strength of 40 is applied to the vertical wall portion of the hat-shaped member.
  • a press molding method that performs molding while applying a tensile stress of ⁇ 100% and has excellent dimensional accuracy of a molded product.
  • a hat bending workability is remarkably improved, a springback amount is small, and a member excellent in shape freezing property can be provided.
  • An object of the present invention is to solve such problems of the prior art, and particularly to provide a cold-rolled steel sheet having excellent shape freezing property and a manufacturing method thereof, in which no significant distortion occurs in a flat part after forming.
  • the present inventors diligently studied the factors affecting the shape freezing property, in particular, the distortion of the flat part after molding.
  • the deformation of the flat part after forming is greatly influenced by the proportional limit of the steel sheet used.
  • the proportional limit exceeds 100 MPa
  • the proportional limit exceeds 100 MPa
  • the ratio of B content to C content, B / C Found that it is necessary to adjust to satisfy 0.5 or more.
  • a JIS No. 5 test piece was sampled so that the tensile direction was the rolling direction, and the proportional limit was obtained.
  • a strain gauge with a length of 5 mm is attached to the parallel part of the tensile test piece, a tensile test is performed at a tensile speed of 1 mm / min, and the stress at which the slope of the stress-strain curve begins to decrease is proportionally limited. It was.
  • a test material (size: 120 ⁇ 120 mm) was sampled from the obtained cold-rolled annealed plate and subjected to stretch forming.
  • the overhang forming was press forming in which a central portion of the test material was overlaid by 8 mm with a ball head punch having a diameter of 20 mm.
  • the stretch forming as shown in FIG. 1, the region (hatched portion) having a diameter of 28 to 54 mm was pressed with a load of 100 kN.
  • the molded test material was placed on a surface plate, and the maximum distortion height of the flange portion was measured.
  • tissue was observed about the obtained cold-rolled annealing board, all the cold-rolling annealing boards were the structures
  • FIG. 3 shows the relationship between the maximum distortion height of the flange portion and the proportional limit
  • FIG. 4 shows the relationship between the proportional limit and B / C.
  • FIG. 3 shows that when the proportional limit increases beyond 100 MPa, the maximum distortion height of the flange increases rapidly.
  • FIG. 4 also shows that B / C needs to be 0.5 or more in order to set the proportional limit to 100 MPa or less.
  • the coarse precipitates of B that are dispersed and precipitated moderately fix dislocations during pressing, and concentrate strain around the precipitates, preventing dislocations from concentrating on the grain boundaries. It is considered that the dislocations are prevented from being entangled with each other, which greatly reduces the springback, lowers the proportional limit, and remarkably improves the shape freezing property.
  • the present invention has been completed based on such findings and further investigations. That is, the gist of the present invention is as follows. (1) In mass%, C: 0.0010 to 0.0030%, Si: 0.05% or less, Mn: 0.1 to 0.5%, P: 0.05% or less, S: 0.02% or less, Al: 0.10% or less, N: 0.0050% or less, Ti: 0.021 to 0.060%, B: Containing 0.0005 to 0.0050%, and containing B and C so that B / C satisfies 0.5 or more, mainly composed of Fe and unavoidable impurities, and ferrite having an average particle size of 10 to 30 ⁇ m A cold-rolled steel sheet having an excellent shape freezing property and having a proportional limit of 100 MPa or less.
  • the structure mainly composed of ferrite is a structure containing 95% or more of ferrite by area ratio.
  • the steel material in mass%, C: 0.0010 to 0.0030%, Si: 0.05% or less, Mn: 0.1 to 0.5%, P: 0.05% or less, S: 0.02% or less, Al: 0.10% or less, N: 0.0050% or less, Ti: 0.021 to 0.060%, B: 0.0005-0.0050% And B and C are contained so that B / C satisfies 0.5 or more, and a steel material having a composition composed of the balance Fe and inevitable impurities
  • the hot rolling process is a process in which the steel material is heated and subjected to rough rolling and finish rolling to a finish rolling finish temperature of 870 to 950 ° C., and winding at a winding temperature of 450 to 630 ° C.
  • the cold rolling step is a step of performing cold rolling with
  • a method for producing a cold-rolled steel sheet having excellent shape freezing properties (13) The method for producing a cold-rolled steel sheet according to (12), further containing Nb: 0.009% or less in mass% in addition to the composition. (14) The method for producing a cold-rolled steel sheet according to (12), further containing, in addition to the above composition, Cr: 0.06% or less by mass%. (15) The method for producing a cold-rolled steel sheet according to (12), further containing Nb: 0.009% or less and Cr: 0.06% or less in mass% in addition to the composition.
  • C 0.0010-0.0030%
  • C is an element that dissolves and promotes the formation of coarse precipitates of B and contributes to the reduction of the proportional limit. Such an effect becomes remarkable when the content is 0.0010% or more.
  • a large content exceeding 0.0030% increases the solid solution C and carbide, increases the strength too much, and causes a decrease in ductility.
  • C is limited to the range of 0.0010 to 0.0030%.
  • Preferably it is 0.0020% or less.
  • Si 0.05% or less
  • workability deteriorates due to hardening, or Si oxide is generated during annealing, thereby inhibiting the plateability.
  • the austenite ( ⁇ ) ⁇ ferrite ( ⁇ ) transformation point is set to a high temperature, so that it is difficult to finish rolling in the ⁇ region during hot rolling. For this reason, Si was limited to 0.05% or less.
  • Mn 0.1-0.5% Mn combines with the harmful S in steel, which significantly reduces the hot ductility, forms MnS, contributes to detoxification of S, and hardens the steel. In order to obtain such an effect, a content of 0.1% or more is required. On the other hand, a large content exceeding 0.5% suppresses deterioration of ductility due to hardening and recrystallization of ferrite during annealing. Therefore, Mn is limited to the range of 0.1 to 0.5%. In addition, Preferably it is 0.3% or less, More preferably, it is 0.2% or less.
  • P 0.05% or less
  • P has a function of segregating at grain boundaries and reducing ductility. Therefore, P is preferably reduced as much as possible in the present invention, but up to 0.05% is acceptable. Therefore, P is limited to 0.05% or less. In addition, Preferably it is 0.03% or less, More preferably, it is 0.02% or less.
  • S 0.02% or less It is desirable to reduce S as an impurity element as much as possible. S has a detrimental effect on hot ductility, induces hot cracking and significantly deteriorates the surface properties, and S hardly contributes to strength and forms coarse MnS to form ductility. Reduce. Such a phenomenon becomes remarkable when it exceeds 0.02%, so in the present invention, S is limited to 0.02% or less. In addition, Preferably it is 0.01% or less.
  • Al 0.10% or less
  • Al is an element that acts as a deoxidizer, and in order to obtain such an effect, it is desirable to contain 0.02% or more.
  • Al has the effect of increasing the ⁇ ⁇ ⁇ transformation point of steel, so a large content exceeding 0.10% makes it difficult to finish rolling in the ⁇ region during hot rolling. For this reason, Al was limited to 0.10% or less.
  • N is an element that combines with a nitride-forming element to form nitride and harden the steel by precipitation strengthening.
  • a large content exceeding 0.0050% only reduces ductility.
  • slab cracking may occur during hot rolling, and surface defects may occur frequently. For this reason, N was limited to 0.0050% or less.
  • Ti 0.021 to 0.060%
  • Ti is an element having an action of fixing N as nitride and suppressing hardening and aging deterioration due to solute N. In order to obtain such an effect, a content of 0.021% or more is required. On the other hand, a large content exceeding 0.060% promotes the precipitation of carbides and reduces the solid solution C, and therefore suppresses the formation of coarse precipitates of B containing C and Fe. Can not be achieved.
  • Ti is limited to the range of 0.021 to 0.060%. In addition, Preferably, it is 0.050% or less.
  • B 0.0005-0.0050%
  • B is an important element in the present invention, and contributes to the reduction of the proportional limit by forming coarse B precipitates. In order to acquire such an effect, 0.0005% or more needs to be contained. On the other hand, a large content exceeding 0.0050% causes slab cracking. For this reason, B is limited to the range of 0.0005 to 0.0050%. In addition, Preferably it is 0.0010% or more, More preferably, it is 0.0020% or more, More preferably, it is 0.0030% or more.
  • B / C 0.5 or more
  • the C and B contents are adjusted so as to include C and B in the above range, and further, the ratio of B content to C content, and B / C to satisfy 0.5 or more.
  • B / C was limited to 0.5 or more.
  • Nb 0.009% or less and / or Cr: 0.06% or less may be further included as a selection element as necessary. it can.
  • Nb 0.009% or less Nb, like Ti, binds with N to form a nitride, fixes N, suppresses hardening and aging deterioration due to solute N, and contributes to improvement of shape freezing property And can be contained as needed. In order to acquire such an effect, it is desirable to contain 0.001% or more. However, if it contains more than 0.009%, crystal grains become finer. For this reason, when it contains, it is preferable to limit Nb to 0.009% or less.
  • Cr 0.06% or less
  • Cr is an element that destabilizes C in a solid solution state and promotes the formation of coarse precipitates of B containing C, and can be contained as necessary. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, a large amount of Cr exceeding 0.06% inhibits the formation of coarse precipitates of B containing C. For this reason, when contained, Cr is preferably limited to 0.06% or less.
  • the balance other than the components described above consists of Fe and inevitable impurities.
  • the cold-rolled steel sheet of the present invention has a structure mainly composed of ferrite having an average particle diameter of 10 to 30 ⁇ m.
  • the structure mainly composed of ferrite refers to a structure in which ferrite (polygonal ferrite) occupies 95% or more, preferably 100% in area ratio.
  • the second phase other than ferrite is preferably cementite or bainite. Further, by setting the average grain size of ferrite to 10 ⁇ m or more, it is possible to suppress the concentration of strain on the grain boundary during molding, to concentrate the strain around the precipitate, and to reduce the proportional limit.
  • the average grain size of ferrite exceeds 30 ⁇ m, surface patterns such as rough skin become apparent during press working. For this reason, the average grain size of ferrite is limited to the range of 10 to 30 ⁇ m.
  • the thickness is preferably 15 to 25 ⁇ m.
  • the starting material is a steel material (slab) having the above composition.
  • the method for producing the steel material is not particularly limited, but after melting the molten steel having the above composition in a conventional converter, electric furnace, etc., the conventional continuous casting method or the ingot-bundling method is used. It is preferable to use a slab (steel material). If the slab is made of continuous casting, if it has heat that can be hot-rolled after casting, it is kept in the heating furnace as it is or without being cooled to room temperature. After that, it is preferable that after cooling to room temperature, it is charged into a heating furnace and reheated to a temperature preferably in the range of 1100 to 1250 ° C. and then hot rolled.
  • the hot steel material is then subjected to a hot rolling process.
  • hot rolling including rough rolling and finish rolling is performed and then wound.
  • the sheet bar is subjected to finish rolling to form a hot-rolled sheet.
  • Finish rolling is rolling with a finish rolling finishing temperature of 870 to 950 ° C.
  • the finish rolling finish temperature is lower than 870 ° C.
  • the structure changes from austenite to ferrite during rolling, and the load control of the rolling mill becomes difficult, which increases the risk of breakage or the like in the plate. .
  • the load during rolling increases.
  • the finish rolling finish temperature exceeds 950 ° C.
  • the ferrite grain size of the hot-rolled sheet increases. For this reason, the ferrite grain size of the cold-rolled annealed plate is too large.
  • the finish rolling finishing temperature is limited to a temperature in the range of 870 to 950 ° C. After finishing rolling, the hot rolled sheet is wound up. In addition, although it does not specifically limit cooling after finishing rolling, although it is sufficient if there is a cooling rate more than air cooling, even if it performs rapid cooling of 100 degrees C / s or more as needed, a problem is especially problematic. Absent.
  • the coiling temperature after finish rolling is in the range of 450 to 630 ° C.
  • the coiling temperature is less than 450 ° C.
  • acicular ferrite is generated, the steel plate becomes hard, the load of subsequent cold rolling becomes high, and hot rolling operation is difficult.
  • the coiling temperature is higher than 630 ° C., the precipitation of carbide is promoted, the solid solution C amount is lowered, and a desired solid solution C amount cannot be secured in the hot rolling stage. For this reason, the coiling temperature is limited to a temperature range of 450 to 630 ° C.
  • the wound hot-rolled sheet is then subjected to a normal pickling process, followed by a cold rolling process to form a cold-rolled sheet.
  • cold rolling with a cold rolling reduction ratio of 90% or less is performed to obtain a cold rolled sheet.
  • the cold rolling reduction ratio exceeds 90%, the recrystallized ferrite grains after annealing become finer, but at the same time, the cold rolling load increases, resulting in cold rolling operation difficulties. For this reason, the cold rolling reduction ratio is limited to 90% or less. In addition, Preferably it is 80% or less. On the other hand, the lower limit of the cold rolling reduction ratio is not particularly specified, but when the cold rolling reduction ratio is small, it is necessary to reduce the thickness of the hot rolled sheet relative to the determined product thickness. Therefore, the cold rolling reduction ratio is preferably 50% or more.
  • the cold-rolled sheet is then subjected to an annealing process to become a cold-rolled annealed sheet.
  • the temperature range of 600 ° C. or higher was heated to a soaking temperature in the range of 700 to 850 ° C. at a heating rate of 1 to 30 ° C./s on average, and held at the soaking temperature for 30 to 200 s. Then, it is set as the process of cooling to 600 degrees C or less with the cooling rate of 3 degrees C / s or more.
  • the cold-rolled processed ferrite is recrystallized to obtain a ferrite having a desired average grain size, and coarse B precipitates containing C and Fe are dispersed and precipitated in the grain boundaries and grains.
  • Heating rate 1-30 ° C / s If the average heating rate in the temperature range from 600 ° C. to the soaking temperature is less than 1 ° C./s, the ferrite grains grow remarkably, and it becomes impossible to obtain a ferrite having a desired average grain size. On the other hand, when the heating rate is higher than 30 ° C./s, TiC precipitates instead of forming B precipitates during heating, and it becomes difficult to form desired B coarse precipitates. For this reason, the heating rate in the temperature range of 600 ° C. or higher was limited to the range of 1 to 30 ° C./s on average. In addition, Preferably it is 5 degrees C / s or more, More preferably, it is 10 degrees C / s or more.
  • Soaking temperature 700-850 ° C
  • the soaking temperature is 700 ° C. or higher.
  • the soaking temperature was limited to 700 to 850 ° C.
  • Soaking time 30-200s
  • the soaking time is set to 30 seconds or more.
  • the soaking time is short, recrystallization is not completed or ferrite grains remain fine.
  • the soaking time is longer than 200 s, the ferrite grains grow too much. For this reason, the soaking time was limited to 30 to 200 s.
  • Cooling rate 3 ° C./s or more If the cooling rate after soaking is small, the growth of ferrite grains is promoted. For this reason, the average cooling rate in the temperature range from the soaking temperature to 600 ° C. is limited to 3 ° C./s or more.
  • the upper limit of the cooling rate is not particularly limited, and is determined depending on the capacity of the cooling facility. If it is a normal cooling facility, the upper limit of the cooling rate is about 30 ° C./s.
  • the cooling conditions of 600 ° C. or lower are not particularly limited, and there is no particular problem with arbitrary cooling.
  • hot dip galvanization in the vicinity of 480 degreeC as needed.
  • the hot dip galvanization may be alloyed by reheating to 500 ° C. or higher. Further, a heat history such as holding during cooling may be applied. Further, if necessary, temper rolling of about 0.5 to 2% may be performed. Further, when plating is not performed, electrogalvanization or the like may be performed in order to improve corrosion resistance. Further, a film may be formed on the cold-rolled steel plate or the plated steel plate by chemical conversion treatment or the like.
  • a steel material (slab) having the composition shown in Table 1 was used as a starting material. After these slabs were heated to 1200 ° C., a hot rolling process, a pickling process, a cold rolling process, and an annealing process were sequentially performed on the slab to obtain a cold-rolled annealed sheet.
  • the hot rolling step the steel material is subjected to rough rolling to form a sheet bar, and then the sheet bar is subjected to finish rolling at which the finish rolling finish temperature (FT) is shown in Table 2, and the winding temperature shown in Table 2 is applied. It was wound up with (CT) to obtain a hot-rolled sheet having a thickness shown in Table 2.
  • CT finish rolling finish temperature
  • the hot-rolled sheet was subjected to a pickling process, and then cold-rolled at the cold rolling reduction shown in Table 2 to obtain cold-rolled sheets having the thickness shown in Table 2.
  • the cold-rolled sheet was subjected to an annealing process to obtain a cold-rolled sheet.
  • annealing was performed at the heating rate, the soaking temperature, the soaking time, and the cooling rate shown in Table 2. In addition, about 600 degrees C or less, it cooled to room temperature with the same cooling rate.
  • temper rolling with a rolling reduction of 1.0% was performed.
  • the obtained cold-rolled annealed plate (cold-rolled steel plate) was subjected to a structure observation, a tensile test, and a stretch forming test.
  • the test method was as follows. (1) Structure observation From the obtained cold-rolled annealed plate, a structure observation specimen is collected, the rolling direction cross section (L cross section) is polished and corroded, and an optical microscope (magnification: 100 times) and scanning electron microscope are used. Using (magnification: 1000 times), the structure was observed, imaged, and the average particle diameter of ferrite, the fraction of ferrite, the type and fraction of the second phase were measured by image analysis.
  • a strain gauge was attached to the parallel part of the tensile test piece, and a tensile test was performed at a tensile rate of 1 mm / min to obtain tensile properties (proportional limit, tensile strength, elongation).
  • the proportional limit is a stress at which the slope of the stress-strain curve starts to decrease.
  • Stretching test A test material (size: 120 ⁇ 120 mm) was sampled from the obtained cold-rolled annealed plate and stretched. The overhang forming was press forming in which a central portion of the test material was overlaid by 8 mm with a ball head punch having a diameter of 20 mm. In the stretch forming, as shown in FIG.
  • the examples of the present invention all have a low proportional limit of 100 MPa or less, the flat part maximum distortion height of the stretch-formed member is 0.8 mm or less, and is a cold-rolled steel sheet excellent in shape freezing property.
  • the proportional limit exceeds 100 MPa, or the maximum distortion height exceeds 0.8 mm, and the shape freezing property is reduced.

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PCT/JP2012/006532 2012-10-11 2012-10-11 形状凍結性に優れた冷延鋼板およびその製造方法 WO2014057519A1 (ja)

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CN201280076329.5A CN104870678A (zh) 2012-10-11 2012-10-11 形状冻结性优异的冷轧钢板及其制造方法
PCT/JP2012/006532 WO2014057519A1 (ja) 2012-10-11 2012-10-11 形状凍結性に優れた冷延鋼板およびその製造方法
US14/433,869 US20150252456A1 (en) 2012-10-11 2012-10-11 Cold-rolled steel sheet with excellent shape fixability and method of manufacturing the same
IN599KON2015 IN2015KN00599A (de) 2012-10-11 2012-10-11
KR1020157011022A KR20150060957A (ko) 2012-10-11 2012-10-11 형상 동결성이 우수한 냉연 강판 및 그의 제조 방법
EP12886281.0A EP2907887B1 (de) 2012-10-11 2012-10-11 Kaltgewalztes stahlblech mit überlegener formfestigkeit und herstellungsverfahren dafür
JP2014540643A JPWO2014057519A1 (ja) 2012-10-11 2012-10-11 形状凍結性に優れた冷延鋼板およびその製造方法

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WO2018117228A1 (ja) * 2016-12-21 2018-06-28 新日鐵住金株式会社 Ｈ形鋼及びその製造方法
KR20210079460A (ko) * 2019-12-19 2021-06-30 주식회사 포스코 경도와 가공성이 우수한 구조부용 냉연강판 및 그 제조방법

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US20150252456A1 (en) 2015-09-10
EP2907887A4 (de) 2015-12-02
JPWO2014057519A1 (ja) 2016-08-25
EP2907887B1 (de) 2018-12-05
IN2015KN00599A (de) 2015-07-17

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