WO2016182098A1 - 굽힘 가공성이 우수한 초고강도 열연강판 및 그 제조 방법 - Google Patents

굽힘 가공성이 우수한 초고강도 열연강판 및 그 제조 방법 Download PDF

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WO2016182098A1
WO2016182098A1 PCT/KR2015/004766 KR2015004766W WO2016182098A1 WO 2016182098 A1 WO2016182098 A1 WO 2016182098A1 KR 2015004766 W KR2015004766 W KR 2015004766W WO 2016182098 A1 WO2016182098 A1 WO 2016182098A1
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steel sheet
rolled steel
weight
high strength
hot rolled
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PCT/KR2015/004766
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English (en)
French (fr)
Korean (ko)
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김용우
서석종
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주식회사 포스코
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Priority to US15/572,367 priority Critical patent/US20180112286A1/en
Priority to PCT/KR2015/004766 priority patent/WO2016182098A1/ko
Priority to JP2017558653A priority patent/JP6543732B2/ja
Priority to CN201580079982.0A priority patent/CN107532262A/zh
Priority to EP15891914.2A priority patent/EP3296416A1/en
Publication of WO2016182098A1 publication Critical patent/WO2016182098A1/ko

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
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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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
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    • C21D6/00—Heat treatment of ferrous alloys
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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
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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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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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
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
    • C21D8/0284—Application of a separating or insulating coating
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • 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

Definitions

  • the present invention relates to an ultra-high strength hot rolled steel sheet and a method for manufacturing the same, which are mainly used for parts requiring high strength and excellent bending workability, such as bumper reinforcements and door impact beams, which are automobile body reinforcements.
  • the present invention relates to an ultra-high strength hot rolled steel sheet and a method of manufacturing the same, which are excellent in lightening effect due to thinning due to high strength and excellent bending workability, thereby ensuring freezing of part shape through roll forming.
  • Conventional high strength hot rolled steel sheets are generally manufactured by adding C, Si, Mn, Ti, Nb, Mo, and V to high purity steels in which impurities in the steel are minimized in order to obtain high strength.
  • a hot rolled steel sheet is manufactured by adding Ti, Nb, V, Mo, etc. and utilizing precipitation strengthening of these elements (Japanese Patent Application No. 2010-279711, Japanese Patent Application No. 2003-156473), to secure the strength by adding a large amount of Cr or Mn (European Patent Application No. 2003-396059, Korean Patent Application No. 1996-7005330), or Mn and Cr addition steel by tempering annealing Methods for enhancing impact strength and tensile properties (PCT Patent Application No. IB2011-01436) are known.
  • One aspect of the present invention is to provide an ultra-high strength hot rolled steel sheet having high strength and excellent bending workability.
  • another aspect of the present invention is to provide a method of manufacturing a super high strength hot rolled steel sheet having high strength and excellent bending workability.
  • One aspect of the present invention includes C: 0.1 to 0.25% by weight, Si: 0.01 to 0.2% by weight, Mn: 0.5 to 2.0% by weight, P: 0.005 to 0.02% by weight, and S: 0.001 to 0.01% by weight,
  • C 0.1 to 0.25 wt%, Si: 0.01 to 0.2 wt%, Mn: 0.5 to 2.0 wt%, P: 0.005 to 0.02 wt% and S: 0.001 to 0.01 wt% And, in addition, at least one component selected from the group consisting of Ti, Nb, Mo, Cr, and B, in an amount of 0.001 to 0.35% by weight, and including balance iron (Fe) and other unavoidable impurities.
  • Preparing a satisfying slab Preparing a satisfying slab; Reheating the slab at a temperature of 1100-1300 ° C .; Hot rolling the reheated slab to a finish rolling temperature of 850 to 1000 ° C.
  • the present invention relates to an ultra-high strength hot rolled steel sheet and a method of manufacturing the same, which are excellent in weight reduction effect due to thinning due to high strength and high bending strength, and easy to secure part shape freezing through roll forming.
  • the present inventor derived a relation indicating bending workability through the bending test measurement values of steels having various components, and based on this relation, bending workability with a tensile strength of 1 Gpa or more and a tensile strength x elongation (TSxT-EL) of 10000 or more This excellent ultra high strength hot rolled steel sheet can be provided.
  • the component range of the ultra-high strength hot rolled steel sheet excellent in the bending workability of the present invention is C: 0.1 to 0.25% by weight, Si: 0.01 to 0.2% by weight, Mn: 0.5 to 2.0% by weight, P: 0.005 to 0.02% by weight, and S: 0.001 to 0.01 weight percent, balance iron (Fe) and other unavoidable impurities, and 0.001 to 0.35 weight percent of at least one component selected from the group consisting of Ti, Nb, Mo, Cr and B.
  • C is the most economical and effective element for strengthening steel. If the content of carbon is less than 0.1% by weight, it is difficult to secure the desired strength. On the other hand, if the carbon content exceeds 0.25% by weight, there is a problem in that bending workability is lowered due to excessive increase in strength. Therefore, the content of carbon is preferably contained in 0.1 to 0.25% by weight.
  • Si deoxidizes molten steel and has a solid solution effect.
  • the content of the silicon is less than 0.01% by weight, the deoxidation effect and the strength improving effect are insufficient.
  • the silicon content exceeds 0.2% by weight, the red scale by Si is formed on the surface of the steel sheet during hot rolling, so that the quality of the steel sheet surface is very bad and the weldability is also degraded. Therefore, the content of the silicon is preferably contained in 0.01 to 0.2% by weight.
  • Mn is an effective element to solidify steel.
  • the content of the manganese exceeds 2.0% by weight, the segregation part is greatly developed at the center of thickness during slab casting in the playing process, thereby deteriorating the weldability and formability of the final product. Therefore, the content of Mn is preferably contained in 0.5 to 2.0% by weight.
  • P like Si, has the effect of strengthening solid solution and promoting ferrite transformation. If the content of phosphorus is less than 0.005% by weight is insufficient to obtain the strength to be secured by the present invention. On the other hand, when the content of the phosphorus exceeds 0.02% by weight, bending workability is lowered due to band structure due to micro segregation. Therefore, the P is preferably contained in 0.005 ⁇ 0.02% by weight.
  • Sulfur is inevitably contained as an impurity, and combines with Mn to form a non-metallic inclusion, thereby greatly reducing the toughness of the steel.
  • the theoretical sulfur content is advantageously limited to 0% by weight, but inevitably contained in the manufacturing process. Therefore, it is important to manage the upper limit, the upper limit of the sulfur content in the present invention is preferably limited to 0.01% by weight.
  • the sum of one or more elements selected from the group includes 0.001 to 0.35% by weight.
  • Ti is present in the steel as TiN, thereby suppressing the growth of grains during heating for hot rolling.
  • Ti remaining after reacting with nitrogen is a useful component to enhance the strength of the steel by solid solution strengthening.
  • Nb forms a niobium-based precipitate such as Nb (C.N) as a precipitate forming element.
  • Nb C.N
  • fine precipitates are formed during hot rolling to effectively increase the strength of the steel.
  • Mo is a useful component to enhance the yield strength through solid solution strengthening and impact toughness and bending workability by strengthening grain boundaries.
  • B may be contained as an alternative element of Si, and in very small amounts, improves hardenability and strengthens grain boundaries to improve strength.
  • the remaining component of the present invention is iron (Fe).
  • impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, all of them are not specifically mentioned in the present specification.
  • the ultra-high strength steel excellent in the bending workability of the present invention can be obtained by satisfying the following relational formula 1 obtained by the present inventor evaluating bending workability in various component systems while satisfying the alloy component range as described above.
  • [C], [Si], [Mn], [Cr], [Ni], [Ti], [B], and [P] mean weight percent of each component content.
  • the relational expression 1 is a relational expression obtained from values for measuring bending workability of steels having various components, and by satisfying the relational expression 1, sufficient martensite microstructure can be secured.
  • the hot-rolled steel sheet provided by the present invention satisfies the above conditions and at least one microstructure has a ferrite content of at least 95 area% and includes at least one member selected from the group consisting of carbides such as bainite, martensite and cementite. It is preferable that two phases are 5% or less, and sufficient ductility can be ensured by ensuring the microstructure as mentioned above. When the fraction of the second phase exceeds 5%, bainite and coarse carbonitride are formed around the ferritic grain boundary, so that the desired strength may not be obtained or hardness difference between phases may occur, thereby making it difficult to secure bending workability. Can be.
  • the ultra-high strength hot-rolled steel sheet of the present invention is preferably a tensile strength of 1Gpa or more, because if the tensile strength is less than 1Gpa there is a problem in that there is a limitation in thinning due to lack of strength and inferior parts light weight effect.
  • the ultra-high strength hot rolled steel sheet of the present invention preferably has a tensile strength x elongation (TSxT-EL) of 10000 or more, but if this value is less than 10000, there is a problem in that moldability or shape freezing property is inferior when processing parts. to be.
  • TxT-EL tensile strength x elongation
  • a slab having a composition satisfying the alloy composition range and relation 1 of the present invention is first prepared. Thereafter, the prepared slab is heated at a temperature of 1100 ⁇ 1300 °C, hot rolled the heated slab at the finish rolling temperature of 850 ⁇ 1000 °C, cooled to finish cooling and winding below 350 °C bending of the present invention Complete super high strength hot rolled steel sheet with excellent workability.
  • the reheating temperature of the slab of the present invention is preferably 1100 °C or more, there is an effect of reducing the rolling load by securing the temperature of the slab plate.
  • austenite may coarsen, so the reheating temperature is preferably 1300 ° C or lower.
  • Hot rolling may be performed on the slab reheated as described above. At this time, it is preferable to perform finish rolling at 850-1000 degreeC. If the hot finish rolling temperature is less than 850 °C rolling load is greatly increased. On the other hand, when the hot finishing rolling temperature exceeds 1000 ° C., the structure of the steel sheet becomes coarse and the steel becomes brittle, the scale becomes thick, and surface quality deterioration such as hot rolling scale defect occurs. Therefore, the hot finish rolling is preferably limited to 850 ⁇ 1000 °C.
  • Cooling rate 100 ⁇ 300 °C / s
  • the hot rolled steel sheet it is preferable to cool the hot rolled steel sheet as described above. In addition, it is preferable to wind up after cooling at a cooling rate of 100 ⁇ 300 ° C / s from the finishing hot rolling temperature of the hot rolled steel sheet to reaching the cooling end temperature.
  • the cooling rate is less than 100 ° C / s, the fraction of the second phase excluding martensite is more than 5%, it is difficult to secure the strength to be secured by the present invention.
  • it exceeds 300 °C / s there is a problem that the elongation and toughness is reduced.
  • the cooling of the hot rolled steel sheet is carried out in the cooling rate range obtained by the following relational formula (3).
  • [C], [Si], [Mn], [Cr], [Ni], [Ti], [B], and [P] mean the weight percent of each component content, and the cooling rate
  • the unit of is ° C / s and means the cooling rate from finishing rolling temperature to winding temperature.
  • Equation 3 is obtained by measuring the bending workability of steels having various components by adding a factor of cooling rate to secure sufficient martensite, thereby obtaining an ultra high strength hot rolled steel sheet having sufficient martensite. It can be applied to the manufacturing method.
  • Coiling temperature 350 °C or less
  • the microstructure in the steel has mostly bainite, and thus the microstructure to be secured by the present invention cannot be secured.
  • the said winding temperature is temperature which complete
  • the wound hot rolled steel sheet may be prepared by naturally pickling after cooling at room temperature to remove the surface layer scale and carry out oiling.
  • the steel sheet may be reheated at 450 to 480 ° C. and hot-dip galvanized to produce a hot-dip galvanized steel sheet.
  • the reheating temperature is less than 450 °C has the disadvantage that the adhesion of the coating may be reduced and the hot dip galvanized may not be achieved
  • the reheating temperature is higher than 480 °C, the precipitate is coarsened due to the heat treatment effect and the strength due to the decrease in the precipitation strengthening effect
  • the steel slab which satisfies the component system of following Table 1 was heated at 1150 degreeC, and hot-finish rolling was performed at the temperature (FDT) described in the following Table 2. Thereafter, cooling was performed at a cooling rate of 200 ° C./s to the winding temperature (CT) described in Table 2, and then wound up at the temperature (CT) described in Table 2 below.
  • Inventive Examples 1 to 6 of Table 1 show the composition of the slab that satisfies the component range of the present invention
  • Comparative Examples 1 to 9 represent the slab composition having a component composition outside the component range of the present invention in units of weight%.
  • a material test was performed on the hot-rolled steel sheet manufactured as described above, and the results are shown in Table 2 below.
  • FDT and CT mean hot polishing temperature and coiling temperature, respectively
  • YS, TS, T-El, TSxT-EL means yield strength, tensile strength, elongation, tensile strength x elongation, respectively.
  • YS means 0.2% off-set yield strength or lower yield point and yield ratio is the ratio of yield strength and tensile strength.
  • the tensile test was taken as the test piece collected based on JIS5 standard based on 90 degree direction with respect to the rolling direction of a rolled sheet material.
  • R / t in Table 2 is the value obtained by dividing the specimen in the 90 ° direction with respect to the rolling direction of the rolled sheet and dividing the minimum bending radius R without cracking after the 90 ° bending test by the material thickness t. It is the measured value, and R / t (limit) shows the value calculated by (tensile strength x 0.00517-2.60345). When R / t (measured) exceeds R / t (limit), bendability was evaluated as inferior.
  • the TSxT-EL value was out of the scope of the present invention because the elongation was lowered by the Mn segregation zone.
  • Comparative Examples 3, 4 and 5 showed a tensile strength of less than 1 Gpa in the implementation of the bainite structure rather than the martensite structure of more than 95% CT temperature outside the scope of the present invention.
  • FIG. 1 the TSxT-EL of Comparative Examples and Inventive Examples and the values derived by the relational expression 3 are shown graphically.
  • the part shown by a square point is a comparative example, and the part shown by a round point is an example of invention. It can be confirmed that all round points corresponding to the inventive examples of the present invention are located within the portions indicated by the hatched lines.
  • Inventive Examples 1 to 6 all satisfy the criterability of bending, and it can be confirmed that the tensile strength and the elongation as well as the yield strength are excellent.

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PCT/KR2015/004766 2015-05-12 2015-05-12 굽힘 가공성이 우수한 초고강도 열연강판 및 그 제조 방법 WO2016182098A1 (ko)

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US15/572,367 US20180112286A1 (en) 2015-05-12 2015-05-12 Ultra-high strength hot-rolled steel sheet having excellent bending workability and method for manufacturing same
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JP2017558653A JP6543732B2 (ja) 2015-05-12 2015-05-12 曲げ加工性に優れた超高強度熱延鋼板及びその製造方法
CN201580079982.0A CN107532262A (zh) 2015-05-12 2015-05-12 弯曲加工性优异的超高强度热轧钢板及其制造方法
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