WO2016182098A1 - Ultra-high strength hot-rolled steel sheet having excellent bending workability and method for manufacturing same - Google Patents

Ultra-high strength hot-rolled steel sheet having excellent bending workability and method for manufacturing same 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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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/en
Priority to EP15891914.2A priority patent/EP3296416A1/en
Priority to JP2017558653A priority patent/JP6543732B2/en
Priority to CN201580079982.0A priority patent/CN107532262A/en
Publication of WO2016182098A1 publication Critical patent/WO2016182098A1/en

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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
    • 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
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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
    • C21D8/0247—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
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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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    • C22C38/00—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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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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    • 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
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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
    • 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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Abstract

The present invention relates to an ultra-high strength hot-rolled steel sheet which is mainly used for components requiring high strength and excellent bending workability, such as a bumper reinforcement and a door impact beam that are reinforcements for the body of a car. The present invention provides: an ultra-high strength hot-rolled steel sheet which has high strength and thus is very effective in forming a lightweight material due to the thin thickness of the material according to the high strength thereof, and at the same time has excellent bending workability so that it is easy to ensure the shape freezing property of a component through roll forming; and a method for manufacturing the same.

Description

굽힘 가공성이 우수한 초고강도 열연강판 및 그 제조 방법Ultra-high strength hot rolled steel sheet with excellent bending workability and manufacturing method
본 발명은 주로 자동차 차체 보강재인 범퍼 (bumper) 보강재 및 도어 임팩트빔 (door impact beam) 등 높은 강도와 우수한 굽힘 가공성이 요구되는 부품에 사용되는 초고강도 열연강판 및 그 제조방법에 관한 것으로서, 더 상세하게는, 강도가 높아 고강도화에 따른 박물화로 인한 경량화 효과가 우수한 동시에 굽힘 가공성이 우수하여 롤 포밍을 통한 부품 형상 동결성 확보가 용이한 초고강도 열연강판 및 그 제조방법에 관한 것이다.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. Preferably, 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.
종래의 고강도 열연강판은 높은 강도를 얻기 위하여, 강 중의 불순물을 최소화 시킨 고순도 강에, C, Si, Mn, Ti, Nb, Mo 및 V 등을 첨가함으로써 제조하는 것이 일반적이다.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.
상기 고강도 열연강판을 제조하기 위하여, 종래에는, Ti, Nb, V, Mo 등을 첨가하여 이들 원소의 석출강화를 활용하여 열연강판을 제조하거나 (일본특허출원 제2010-279711호, 일본특허출원 제2003-156473호), Cr 또는 Mn 등을 다량 첨가하여 강도를 확보하거나 (유럽특허출원 제2003-396059호, 대한민국 특허출원 제1996-7005330호), 또는, Mn 및 Cr 첨가강을 템퍼어닐링에 의해 충격강도 및 인장특성을 강화하는 방법 (PCT특허출원 제IB2011-01436호)들이 알려져 있다. In order to manufacture the high strength hot rolled steel sheet, conventionally, 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.
대부분의 자동차 차체 보강재인 범퍼 (bumper) 보강재 및 도어 임팩트빔 (door impact beam) 등에 사용되는 초고강도 열연강판은, 높은 강도와 동시에 롤 포밍 성형을 위한 우수한 굽힘 가공성을 요구한다.Ultra high strength hot rolled steel sheets used in bumper reinforcements, door impact beams, etc., which are most automobile body reinforcements, require high bending strength and excellent bending workability for roll forming molding.
그러나, 상기에 제시한 종래의 고강도 열연강판의 제조에 사용되는, C, Si, Mn, Cr, Mo 및 W 등의 합금성분에 의한 고용강화나 Ti, Nb, Mo등의 합금성분에 의한 석출강화를 통한 고강도화의 경우, 굽힘 가공성을 열위하게 하고, 템퍼어닐링 처리 시 생산성 하락에 의하여 가격 경쟁력이 떨어지는 문제가 있다.However, solid solution strengthening by alloy components such as C, Si, Mn, Cr, Mo, and W and precipitation strengthening by alloy components such as Ti, Nb, and Mo, which are used in the production of the conventional high strength hot rolled steel sheet, In the case of high strength through, inferior to the bending workability, there is a problem that the price competitiveness is lowered by the productivity decrease during the tempering annealing process.
본 발명의 일태양은 고강도이며 굽힘 가공성이 우수한 초고강도 열연강판을 제공하고자 한다. One aspect of the present invention is to provide an ultra-high strength hot rolled steel sheet having high strength and excellent bending workability.
또한, 본 발명의 또 다른 일태양은 고강도이며 굽힘 가공성이 우수한 초고강도 열연강판의 제조방법을 제공하고자 한다. In addition, 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.
본 발명의 일태양은, C: 0.1∼0.25 중량%, Si: 0.01∼0.2 중량%, Mn: 0.5∼2.0 중량%, P: 0.005∼0.02 중량% 및 S: 0.001∼0.01 중량%을 포함하고, 추가적으로, Ti, Nb, Mo, Cr 및 B 로 이루어진 그룹에서 선택된 적어도 하나의 성분을 총 0.001~0.35 중량% 포함하며, 잔부는 철(Fe) 및 기타 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하는 굽힘 가공성이 우수한 초고강도 열연강판을 제공한다.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, In addition, Ti, Nb, Mo, Cr and at least one component selected from the group consisting of 0.001 to 0.35% by weight in total, the balance contains iron (Fe) and other unavoidable impurities, satisfying the following relation Provides a very high strength hot rolled steel sheet excellent in bending workability.
[관계식 1][Relationship 1]
69.2-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]≥ 069.2-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] ≥ 0
(단, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미함.)(However, [C], [Si], [Mn], [Cr], [Ni], [Ti], [B], and [P] refer to the weight percent of each component content.)
또한, 본 발명의 또 다른 일태양은 C: 0.1∼0.25 중량%, Si: 0.01∼0.2 중량%, Mn: 0.5∼2.0 중량%, P: 0.005∼0.02 중량% 및 S: 0.001∼0.01 중량%을 포함하고, 추가적으로, Ti, Nb, Mo, Cr 및 B 로 이루어진 그룹에서 선택된 적어도 하나의 성분을 총 0.001~0.35 중량% 포함하며, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하는 슬라브를 준비하는 단계; 상기 슬라브를 1100~1300℃의 온도에서 재가열하는 단계; 상기 재가열된 슬라브를 850~1000℃의 마무리압연온도로 열간압연하여 열연강판을 얻는 단계; 상기 열연강판을 100~300℃/s의 냉각속도 및 하기 관계식 3을 만족하도록 냉각하는 단계; 및 상기 냉각된 강판을 350℃ 이하의 권취온도에서 권취하는 단계를 포함하는 굽힘 가공성이 우수한 초고강도 열연강판의 제조방법을 제공한다.In still another aspect of the present invention, 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; 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. to obtain a hot rolled steel sheet; Cooling the hot rolled steel sheet to satisfy a cooling rate of 100 to 300 ° C / s and the following relational expression 3; And it provides a method for producing a super high strength hot rolled steel sheet having excellent bending workability comprising the step of winding the cooled steel sheet at a winding temperature of 350 ℃ or less.
[관계식 1][Relationship 1]
69.2-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]≥ 069.2-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] ≥ 0
(단, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미함.)(However, [C], [Si], [Mn], [Cr], [Ni], [Ti], [B], and [P] refer to the weight percent of each component content.)
[관계식 3][Relationship 3]
85.3-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]-6.9[냉각속도]≥ 085.3-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] -6.9 [Cooling rate] ≥ 0
(단, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미하며, 상기 냉각속도의 단위는 ℃/s이고 마무리압연온도에서 권취온도까지의 냉각속도를 의미함)(Wherein [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] and [P] refer to the weight percent of each component content, and the cooling rate The unit of is ° C / s, which means the cooling rate from finishing rolling temperature to winding temperature.)
본 발명에 따라 우수한 강도를 가지면서 굽힘 가공성도 우수한 초고강도 열연강판을 제공할 수 있다.According to the present invention, it is possible to provide an ultra high strength hot rolled steel sheet having excellent strength and excellent bending workability.
도 1은 발명예와 비교예의 TSxT-EL과 굽힘 가공성을 나타내는 관계식 1로 도출된 값을 그래프로 나타낸 것이다. 1 is a graph showing values derived from relational formula 1 showing TSxT-EL and bending workability of the invention example and the comparative example.
본 발명은 강도가 높아 고강도화에 따른 박물화로 인한 경량화 효과가 우수할 뿐만 아니라, 굽힘 가공성이 우수하여 롤 포밍을 통한 부품 형상 동결성 확보가 용이한 초고강도 열연강판 및 그 제조방법에 관한 것이다.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.
본 발명자는 다양한 성분을 갖는 강들의 굽힘 시험 측정값을 통하여 굽힘 가공성을 나타내는 관계식을 도출하였고, 이 관계식을 기초로 하여 인장강도가 1Gpa 이상이면서 인장강도x연신율 (TSxT-EL)이 10000 이상인 굽힘 가공성이 우수한 초고강도 열연강판을 제공할 수 있다.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.
이하, 본 발명의 굽힘 가공성이 우수한 초고강도 열연강판에 관하여 상세히 설명한다.Hereinafter, the ultra-high strength hot rolled steel sheet excellent in the bending workability of the present invention will be described in detail.
본 발명의 굽힘 가공성이 우수한 초고강도 열연강판의 성분 범위는, C: 0.1∼0.25 중량%, Si: 0.01∼0.2 중량%, Mn: 0.5∼2.0 중량%, P: 0.005∼0.02 중량% 및 S: 0.001∼0.01 중량%, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함하며, Ti, Nb, Mo, Cr 및 B 로 이루어진 그룹에서 선택된 적어도 하나의 성분을 총 0.001~0.35 중량% 포함한다.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.
이하, 상기 본 발명의 합금성분범위의 한정이유를 설명한다.Hereinafter, the reason for limitation of the alloy component range of the present invention will be described.
탄소(C): 0.1~Carbon (C): 0.1 ~ 0.25중량%0.25 wt%
C는 강을 강화시키는데 가장 경제적이며 효과적인 원소이다. 상기 탄소의 함량이 0.1중량% 미만인 경우에는 원하는 강도를 확보하기 어렵다. 반면에, 상기 탄소의 함량이 0.25중량%를 초과하는 경우에는 과도한 강도상승으로 굽힘 가공성이 저하되는 문제점이 있다. 따라서, 상기 탄소의 함량은 0.1~0.25중량%로 포함되는 것이 바람직하다.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.
실리콘(silicon( SiSi ): 0.01~): 0.01 ~ 0.2중량%0.2 wt%
Si는 용강을 탈산시키고 고용강화 효과가 있다. 상기 실리콘의 함량이 0.01중량%미만인 경우에는 탈산 효과 및 강도 향상 효과가 불충분하다. 반면에, 상기 실리콘의 함량이 0.2중량%를 초과하면 열간압연시 강판표면에 Si에 의한 붉은색 스케일이 형성되어 강판표면 품질이 매우 나빠질 뿐만 아니라 용접성도 저하되는 문제가 있다. 따라서, 상기 실리콘의 함량은 0.01~0.2중량%로 포함되는 것이 바람직하다. Si deoxidizes molten steel and has a solid solution effect. When the content of the silicon is less than 0.01% by weight, the deoxidation effect and the strength improving effect are insufficient. On the other hand, if 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.
망간(Mn): 0.5~Manganese (Mn): 0.5 ~ 2.0중량%2.0 wt%
Mn은 Si과 마찬가지로 강을 고용 강화시키는데 효과적인 원소이다. 본 발명에서 이러한 효과를 나타내기 위하여 0.5중량% 이상 포함되는 것이 바람직하다. 그러나, 상기 망간의 함량이 2.0중량%를 초과하는 경우에는 연주공정에서 슬라브 주조시 두께중심부에서 편석부가 크게 발달되어 최종제품의 용접성 및 성형성을 해치는 문제점이 있다. 따라서, 상기 Mn의 함량은 0.5~2.0중량%로 포함되는 것이 바람직하다.Mn, like Si, is an effective element to solidify steel. In order to exhibit such an effect in the present invention, it is preferable that 0.5 wt% or more is included. However, when 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.
인(P): 0.005∼Phosphorus (P): 0.005- 0.02중량%0.02% by weight
P는 Si과 마찬가지로 고용강화 및 페라이트 변태 촉진효과가 있다. 상기 인의 함량이 0.005중량% 미만인 경우에는 본 발명이 확보하고자 하는 강도를 얻기에 불충분 하다. 반면에, 상기 인의 함량이 0.02중량%를 초과하는 경우에는 마이크로 편석에 의한 밴드조직화로 인하여 굽힘 가공성이 저하된다. 따라서 상기 P는 0.005~0.02중량%로 포함되는 것이 바람직하다. 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.
황(S): 0.001∼0.01% Sulfur (S): 0.001-0.01%
상기 황은 불가피하게 함유되는 불순물로써, Mn 등과 결합하여 비금속개재물을 형성하며 이에 따라 강의 인성을 크게 떨어뜨리기 때문에 그 함량을 최대한 억제하는 것이 바람직하다. 이론상의 황의 함량은 0중량%로 제한하는 것이 유리하나, 제조공정상 필연적으로 함유될 수 밖에 없다. 따라서, 상한을 관리하는 것이 중요하며, 본 발명에서 상기 황 함량의 상한은 0.01중량%로 한정하는 것이 바람직하다.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.
더불어, 상기한 유리한 성분계에 더하여, 타이타늄(Ti), 니오븀(Nb), 몰리브덴(Mo), 크롬(Cr) 및 보론(B)으로 이루어진 그룹에서 선택된 1종 이상의 원소를 추가적으로 첨가하는 것이 바람직하다. 상기 원소들의 추가적인 첨가에 의하여 높은 인장강도 및 우수한 굽힘 가공성을 얻을 수 있어, 본 발명의 효과를 더욱 향상시킬 수 있다. 보다 바람직하게는, 상기 그룹에서 선택된 1종 이상의 원소를 합하여 0.001~0.35중량%를 포함한다.In addition to the advantageous component system described above, it is preferable to further add one or more elements selected from the group consisting of titanium (Ti), niobium (Nb), molybdenum (Mo), chromium (Cr) and boron (B). By the addition of the above elements can be obtained high tensile strength and excellent bending workability, it is possible to further improve the effect of the present invention. More preferably, the sum of one or more elements selected from the group includes 0.001 to 0.35% by weight.
Ti는 강중에 TiN으로 존재하여 열간압연을 위한 가열과정에서 결정립이 성장되는 것을 억제하는 효과가 있다. 또한, 질소와 반응하고 남은 Ti이 강 중에서 고용강화로 강의 강도를 향상시키는데 유용한 성분이다.Ti is present in the steel as TiN, thereby suppressing the growth of grains during heating for hot rolling. In addition, Ti remaining after reacting with nitrogen is a useful component to enhance the strength of the steel by solid solution strengthening.
Nb는 석출물 형성원소로서 Nb(C.N)과 같은 니오븀계 석출물을 형성한다. 1200℃ 정도의 가열로에서 고용되면, 열간압연 중 미세하게 석출물이 형성되어 강의 강도를 효과적으로 증가시킨다.Nb forms a niobium-based precipitate such as Nb (C.N) as a precipitate forming element. When dissolved in a heating furnace of about 1200 ℃, fine precipitates are formed during hot rolling to effectively increase the strength of the steel.
Mo은 고용강화를 통한 항복강도 강화와 결정립계 강화에 의한 충격인성 및 굽힘 가공성을 향상시키는데 유용한 성분이다.Mo is a useful component to enhance the yield strength through solid solution strengthening and impact toughness and bending workability by strengthening grain boundaries.
Cr은 강을 고용강화시키며 냉각시 베이나이트 상변태를 지연시켜 마르텐사이트 형성을 도와주는 역할을 한다.Cr strengthens the steel and delays the bainite phase transformation during cooling to help form martensite.
B은 Si의 대체원소로서 함유되기도 하며, 극히 미량으로 담금질성을 향상시키고 결정립계를 강화시켜 강도를 향상시킨다.B may be contained as an alternative element of Si, and in very small amounts, improves hardenability and strengthens grain boundaries to improve strength.
본 발명의 나머지 성분은 철(Fe)이다. 다만, 통상의 제조과정에서는 원료 또는 주위 환경으로부터 의도되지 않는 불순물들이 불가피하게 혼입될 수 있으므로, 이를 배제할 수는 없다. 이들 불순물들은 통상의 제조과정의 기술자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 특별히 본 명세서에서 언급하지는 않는다.The remaining component of the present invention is iron (Fe). However, in the conventional manufacturing process, 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.
본 발명의 굽힘 가공성이 우수한 초고강도강은 상기와 같은 합금성분범위를 만족하면서, 본 발명자가 다양한 성분계에서의 굽힘 가공성을 평가하여 얻어진 하기 관계식 1을 만족함으로써, 얻어질 수 있다.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.
[관계식 1][Relationship 1]
85.3-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]-6.9[냉각속도]≥ 085.3-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] -6.9 [Cooling rate] ≥ 0
여기에서, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미한다.Here, [C], [Si], [Mn], [Cr], [Ni], [Ti], [B], and [P] mean weight percent of each component content.
상기 관계식 1은 다양한 성분을 갖는 강들의 굽힘 가공성을 측정한 값들로부터 얻어진 관계식으로서, 상기 관계식 1을 만족함으로써, 충분한 마르텐사이트 미세조직을 확보할 수 있다. 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.
또한, 인장강도 1Gpa 이상인 초고강도강에서는 상기 관계식 1의 값이 0 미만일 경우, 상기 관계식 2의 상온 R/t가 (인장강도x0.00517-2.60345)를 초과하여, 굽힘 가공성이 열위하게 된다.In addition, in ultra high strength steel having a tensile strength of 1 Gpa or more, when the value of the relation 1 is less than 0, the room temperature R / t of the relation 2 exceeds (tensile strength x 0.00517-2.60345), resulting in inferior bending workability.
[관계식 2][Relationship 2]
굽힘가공성(R/t) ≤ (인장강도 x 0.00517 - 2.60345)Bendability (R / t) ≤ (tensile strength x 0.00517-2.60345)
바람직하게는, 상기 관계식 2를 만족함으로써, 인장강도 1Gpa 이상인 초고강도 강의 원활한 부품 성형이 가능하다. 즉, 상기 굽힘가공성(R/t)의 값이 작을수록 원활한 부품 성형이 가능하며, 상기 (인장강도 x 0.00517 - 2.60345)의 값 이하를 가지면, 원활한 롤포밍을 통해 부품 성형이 가능하게 된다.Preferably, by satisfying the relation 2, it is possible to form a smooth part of ultra-high strength steel having a tensile strength of 1Gpa or more. That is, as the value of the bending workability (R / t) is smaller, smooth part molding is possible, and when the value is less than the value of (tensile strength x 0.00517-2.60345), part molding is possible through smooth roll forming.
본 발명이 제공하는 열연강판은 상기 성분조건을 만족함과 동시에 그 미세조직이 페라이트가 95면적%이상이고, 베이나이트, 마르텐사이트 및 세멘타이트와 같은 탄화물로 이루어지는 그룹으로부터 선택된 1종 이상을 포함하는 제 2 상이 5%이하인 것이 바람직하며, 상기와 같은 미세조직을 확보함으로써 충분한 연성을 확보할 수 있다. 상기 제2상의 분율이 5%를 초과하는 경우에는 베이나이트와 조대한 탄질화물이 페라이트계 결정립계 주위에 형성되어, 원하는 강도를 얻지 못하거나, 상간 경도차가 발생할 수 있으므로, 굽힘 가공성 확보에 어려움이 있을 수 있다.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.
또한, 본 발명의 초고강도 열연강판은 인장강도가 1Gpa 이상인 것이 바람직한데, 인장강도가 1Gpa 미만이면 강도 부족으로 박물화에 한계가 있고 부품 경량화 효과가 열위하게 되는 문제점이 있기 때문이다.In addition, 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.
그리고, 본 발명의 초고강도 열연강판은 인장강도x연신율 (TSxT-EL)이 10000 이상인 것이 바람직한데, 이 값이 10000 미만이면, 부품 가공 시 성형성 혹은 형상 동결성이 열위하게 되는 문제점이 있기 때문이다.In addition, 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.
이하, 본 발명의 굽힘 가공성이 우수한 초고강도 열연강판의 제조방법에 관하여 상세히 설명한다.Hereinafter, the manufacturing method of the ultra-high strength hot rolled steel sheet excellent in the bending workability of the present invention will be described in detail.
상기와 같이, 강도가 우수하고 굽힘 가공성이 우수한 본 발명의 초고강도 열연강판을 제조하기 위하여, 우선 상기 본 발명의 합금성분범위와 관계식 1을 만족하는 조성을 갖는 슬라브를 마련한다. 이후, 상기 마련한 슬라브를 1100~1300℃의 온도에서 가열한 후, 상기 가열된 슬라브를 마무리압연온도 850~1000℃에서 열간압연을 행하고, 냉각하여 350℃이하에서 냉각종료 및 권취하여 본 발명의 굽힘 가공성이 우수한 초고강도 열연강판을 완성한다.As described above, in order to manufacture the super-high strength hot rolled steel sheet of the present invention having excellent strength and excellent bending workability, 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 ℃, hot rolled the heated slab at the finish rolling temperature of 850 ~ 1000 ℃, cooled to finish cooling and winding below 350 ℃ bending of the present invention Complete super high strength hot rolled steel sheet with excellent workability.
이하, 각 단계별 상세한 조건에 대하여 설명한다.Hereinafter, detailed conditions of each step will be described.
슬라브 재가열 온도: 1100~1300℃Slab reheating temperature: 1100 ~ 1300 ℃
본 발명의 슬라브의 재가열 온도는 1100℃ 이상으로 하는 것이 바람직한데, 슬라브 판재의 온도를 확보하여 압연 부하를 줄이는 효과가 있다. 다만, 과다하게 높은 온도로 재가열할 경우에는 오스테나이트가 조대화될 우려가 있으므로, 상기 재가열온도는 1300℃ 이하인 것이 바람직하다.The reheating temperature of the slab of the present invention is preferably 1100 ℃ or more, there is an effect of reducing the rolling load by securing the temperature of the slab plate. However, when reheating excessively high temperature, austenite may coarsen, so the reheating temperature is preferably 1300 ° C or lower.
압연종료온도: 850~1000℃Rolling end temperature: 850 ~ 1000 ℃
상기와 같이 재가열된 슬라브에 열간압연을 실시할 수 있다. 이때, 마무리압연은 850~1000℃에서 행하는 것이 바람직하다. 상기 열간 마무리압연 온도가 850℃미만인 경우에는 압연하중이 크게 증가한다. 반면에, 상기 열간마무리 압연온도가 1000℃를 초과하는 경우에는 강판의 조직이 조대화되어 강재가 취약해지며, 스케일이 두꺼워지고, 고온압연성 스케일 결함 등의 표면 품질 저하가 발생한다. 따라서, 상기 열간마무리압연은 850~1000℃로 한정하는 것이 바람직하다. 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 ℃ 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 ℃.
냉각속도: 100~300℃/sCooling rate: 100 ~ 300 ℃ / s
상기와 같이 열간압연된 강판을 냉각하는 것이 바람직하다. 또한, 상기 열간압연된 강판의 상기 마무리 열간압연 온도로부터 냉각종료온도에 도달할 때까지 100~300℃/s의 냉각속도로 냉각 후, 권취하는 것이 바람직하다. 상기 냉각속도가 100℃/s 미만인 경우에는 마르텐사이트를 제외한 제 2 상의 분율이 5%를 상회하여 본 발명이 확보하고자 하는 강도를 확보하는데 어려움이 있다. 반면에, 300℃/s를 초과하는 경우에는 연신율 및 인성이 하락하는 문제가 있다.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. When 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. On the other hand, when it exceeds 300 ℃ / s, there is a problem that the elongation and toughness is reduced.
또한, 상기 열연강판의 냉각은 하기 관계식 3으로 구해지는 냉각속도 범위로 실시된다.In addition, the cooling of the hot rolled steel sheet is carried out in the cooling rate range obtained by the following relational formula (3).
[관계식 3][Relationship 3]
85.3-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]-6.9[냉각속도]≥ 085.3-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] -6.9 [Cooling rate] ≥ 0
여기에서, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미하며, 상기 냉각속도의 단위는 ℃/s이고 마무리압연온도에서 권취온도까지의 냉각속도를 의미한다.Here, [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.
상기 관계식 3은 다양한 성분을 갖는 강들의 굽힘 가공성을 측정한 값들로부터 얻어진 상기 관계식 1에, 충분한 마르텐사이트를 확보할 수 있는 냉각속도의 인자를 추가함으로써, 충분한 마르텐사이트를 확보한 초고강도 열연강판의 제조방법에 적용할 수 있다.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.
권취온도Coiling temperature : 350℃ 이하: 350 ℃ or less
상기 열간압연된 강판의 상기 마무리 열간압연 온도로부터 350℃ 이하의 온도에 도달할 때까지 100~300℃/s의 냉각속도로 냉각 후 권취하는 것이 바람직하다. 냉각이 종료되는 온도가 350℃를 초과하는 경우, 강 중의 미세조직이 대부분 베이나이트를 가짐으로써, 본 발명이 확보하고자 하는 미세조직을 확보할 수 없다. 상기 권취온도는 냉각을 종료하는 온도로서, 350℃ 이하의 온도이면 어떤 온도에서 냉각을 종료하고 권취를 해도 상관이 없다. 그러나, 냉각이 종료되는 온도를 상온인 20℃ 이하로 냉각하기 위해서는 별도의 장치가 필요하므로, 20℃ 아상의 온도에서 냉각을 종료하고 권취하는 것이 바람직하다.It is preferable to wind up after cooling at the cooling rate of 100-300 degreeC / s until reaching the temperature of 350 degrees C or less from the said finishing hot rolling temperature of the said hot rolled sheet steel. When the temperature at which cooling is terminated exceeds 350 ° C., 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 | finishes cooling, and if temperature is 350 degrees C or less, you may wind up after finishing cooling at what temperature. However, in order to cool the temperature which complete | finishes cooling to 20 degrees C or less which is normal temperature, since a separate apparatus is needed, it is preferable to finish cooling and wind up at the temperature of 20 degreeC subphase.
상기 권취된 열연강판은 상온에서 자연냉각한 후에 산세하여 표층부 스케일을 제거하고 도유하는 단계를 추가로 포함함으로써 산세강판을 제조할 수 있다.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.
상기 귄취 또는 산세 후에는 상기 강판을 450~480℃에서 재가열하고, 용융아연도금하여 용융아연도금강판을 제조할 수 있다. 상기 재가열 온도가 450℃미만일 경우에는 도금밀착성이 저하되어 용융아연도금이 이루어지지 않을 수 있다는 단점이 있으며, 480℃를 초과할 경우에는 열처리 효과로 인해 석출물이 조대화되어 석출강화 효과 감소에 따른 강도하락의 위험이 있으며, 또한, 용융아연의 기화로 인한 환경 문제 및 도금품질 열화의 문제점이 발생할 수 있다.After the odor or pickling, the steel sheet may be reheated at 450 to 480 ° C. and hot-dip galvanized to produce a hot-dip galvanized steel sheet. If the reheating temperature is less than 450 ℃ has the disadvantage that the adhesion of the coating may be reduced and the hot dip galvanized may not be achieved, when the reheating temperature is higher than 480 ℃, the precipitate is coarsened due to the heat treatment effect and the strength due to the decrease in the precipitation strengthening effect There is a risk of falling, and also, environmental problems and deterioration of plating quality may occur due to vaporization of molten zinc.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명하고자 한다. 다만, 하기의 실시예는 본 발명을 예시하여 보다 상세하게 설명하기 위한 것일 뿐, 본 발명의 권리범위를 한정하기 위한 것이 아니라는 점에 유의할 필요가 있다. 본 발명의 권리범위는 특허청구범위에 기재된 사항과 이로부터 합리적으로 유추되는 사항에 의해 결정되는 것이기 때문이다.Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.
하기 표 1에 기재된 성분계를 만족하는 강 슬라브를 1150℃로 가열하고 하기 표 2에 기재되어 있는 온도(FDT)에서 열간마무리 압연을 행하였다. 그 후, 표 2에 기재되어 있는 권취온도(CT)까지 200℃/s의 냉각속도로 냉각을 행한 후, 하기 표 2에 기재되어 있는 온도(CT)에서 권취하였다.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.
하기 표 1의 발명예 1 내지 6은 본 발명의 성분범위를 만족하는 슬라브의 조성을 나타내었고, 비교예 1 내지 9는 본 발명의 성분범위를 벗어난 성분 조성을 갖는 슬라브 조성을 중량%의 단위로 나타내었다. 또한, 상기와 같이 제조된 열연강판에 대하여 재질시험을 실시하고, 그 결과를 하기 표 2에 나타내었다. 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%. In addition, a material test was performed on the hot-rolled steel sheet manufactured as described above, and the results are shown in Table 2 below.
표 1
구분 C Mn Si P S Cr Ti Nb B
비교예1 0.14 1.6 0.1 0.015 0.003 0.5 0.015 0.015 0.002
비교예2 0.12 1.7 0.1 0.015 0.003 0 0.015 0.015 0.002
비교예3 0.15 1.5 0.1 0.015 0.003 0 0.015 0.015 0.002
비교예4 0.18 1 0.1 0.015 0.003 0 0.015 0 0.002
비교예5 0.19 1.2 0.1 0.015 0.003 0 0.015 0 0.002
비교예6 0.2 1.2 0.1 0.015 0.003 0.2 0.015 0 0.002
비교예7 0.19 1.4 0.1 0.015 0.003 0.5 0.015 0 0.002
비교예8 0.2 1.2 0.1 0.015 0.003 0.4 0.015 0 0.002
비교예9 0.21 1.1 0.1 0.015 0.003 0.3 0.015 0 0.002
발명예1 0.13 1.4 0.1 0.015 0.003 0 0.015 0.015 0.002
발명예2 0.15 1 0.1 0.015 0.003 0 0.015 0.015 0.002
발명예3 0.14 1.4 0.1 0.015 0.003 0 0.015 0.015 0.002
발명예4 0.19 1.2 0.1 0.015 0.003 0.2 0.015 0 0.002
발명예5 0.19 1 0.1 0.015 0.003 0.2 0.015 0 0.002
발명예6 0.2 0.7 0.1 0.015 0.003 0.2 0.015 0 0.002
Table 1
division C Mn Si P S Cr Ti Nb B
Comparative Example 1 0.14 1.6 0.1 0.015 0.003 0.5 0.015 0.015 0.002
Comparative Example 2 0.12 1.7 0.1 0.015 0.003 0 0.015 0.015 0.002
Comparative Example 3 0.15 1.5 0.1 0.015 0.003 0 0.015 0.015 0.002
Comparative Example 4 0.18 One 0.1 0.015 0.003 0 0.015 0 0.002
Comparative Example 5 0.19 1.2 0.1 0.015 0.003 0 0.015 0 0.002
Comparative Example 6 0.2 1.2 0.1 0.015 0.003 0.2 0.015 0 0.002
Comparative Example 7 0.19 1.4 0.1 0.015 0.003 0.5 0.015 0 0.002
Comparative Example 8 0.2 1.2 0.1 0.015 0.003 0.4 0.015 0 0.002
Comparative Example 9 0.21 1.1 0.1 0.015 0.003 0.3 0.015 0 0.002
Inventive Example 1 0.13 1.4 0.1 0.015 0.003 0 0.015 0.015 0.002
Inventive Example 2 0.15 One 0.1 0.015 0.003 0 0.015 0.015 0.002
Inventive Example 3 0.14 1.4 0.1 0.015 0.003 0 0.015 0.015 0.002
Inventive Example 4 0.19 1.2 0.1 0.015 0.003 0.2 0.015 0 0.002
Inventive Example 5 0.19 One 0.1 0.015 0.003 0.2 0.015 0 0.002
Inventive Example 6 0.2 0.7 0.1 0.015 0.003 0.2 0.015 0 0.002
(단위: 중량%)(Unit: weight%)
하기 표 2에서 FDT와 CT는 각각 열연마무리온도와 권취온도를 의미하며, YS, TS, T-El, TSxT-EL은 각각 항복강도, 인장강도, 연신율, 인장강도x연신율을 의미한다. 또한, YS는 0.2%off-set 항복강도 또는 하부 항복점을 의미하며 항복비는 항복강도와 인장강도의 비율이다. 인장시험은 압연판재의 압연방향에 대하여 90°방향을 기준으로 JIS5호 규격에 의거하여 채취된 시험편으로 하였다.In the following Table 2, 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. In addition, 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.
표 2의 R/t(실측)은 압연판재의 압연방향에 대하여 90°방향을 기준으로 시편을 채취하여 90°굽힘 시험 후 크랙이 발생하지 않는 최소 굽힘반경 R을 소재의 두께 t로 나눈 값으로 측정한 값이며, R/t(한계)는 (인장강도x0.00517-2.60345)로 계산된 값을 나타낸 것이다. R/t(실측)이 R/t(한계)를 초과할 경우 굽힘가공성이 열위한 것으로 평가하였다.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.
표 2
시편 FDT CT 관계식3 마르텐사이트 면적분율(%) YS TS T-EL TSxT-EL R/t(실측) R/t(한계) 굽힘 가공성
비교예1 947 172 14.5 96 1195 1343 6.0 8058 3.5 4.3 o
비교예2 949 170 23.0 99 968 1257 7.0 8799 3.3 3.9 o
비교예3 968 402 14.5 53 730 784 11.4 8938 1.3 1.4 o
비교예4 952 367 7.1 64 877 964 9.0 8676 2.3 2.4 o
비교예5 954 378 3.2 78 916 985 6.2 6107 2.2 2.5 o
비교예6 955 163 -1.0 96 1264 1542 6.6 10174 5.8 5.4 x
비교예7 961 174 -0.2 97 1215 1519 6.6 10027 5.6 5.2 x
비교예8 958 198 -2.0 98 1207 1548 6.5 10061 6.0 5.4 x
비교예9 965 155 -4.2 99 1232 1579 6.4 10103 6.3 5.6 x
발명예1 971 188 21.1 96 1017 1287 8.6 11065 3.3 4.1 o
발명예2 849 195 16.5 97 1094 1350 7.6 10261 3.5 4.4 o
발명예3 905 222 18.0 97 1032 1323 7.9 10450 3.4 4.2 o
발명예4 909 204 2.2 96 1204 1505 7.1 10688 4.1 5.2 o
발명예5 912 221 3.0 96 1186 1501 6.7 10057 4.1 5.2 o
발명예6 915 212 1.0 98 1225 1531 6.7 10255 4.3 5.3 o
TABLE 2
Psalter FDT CT Relationship 3 Martensite area fraction (%) YS TS T-EL TSxT-EL R / t (actually) R / t (limit) Bending workability
Comparative Example 1 947 172 14.5 96 1195 1343 6.0 8058 3.5 4.3 o
Comparative Example 2 949 170 23.0 99 968 1257 7.0 8799 3.3 3.9 o
Comparative Example 3 968 402 14.5 53 730 784 11.4 8938 1.3 1.4 o
Comparative Example 4 952 367 7.1 64 877 964 9.0 8676 2.3 2.4 o
Comparative Example 5 954 378 3.2 78 916 985 6.2 6107 2.2 2.5 o
Comparative Example 6 955 163 -1.0 96 1264 1542 6.6 10174 5.8 5.4 x
Comparative Example 7 961 174 -0.2 97 1215 1519 6.6 10027 5.6 5.2 x
Comparative Example 8 958 198 -2.0 98 1207 1548 6.5 10061 6.0 5.4 x
Comparative Example 9 965 155 -4.2 99 1232 1579 6.4 10103 6.3 5.6 x
Inventive Example 1 971 188 21.1 96 1017 1287 8.6 11065 3.3 4.1 o
Inventive Example 2 849 195 16.5 97 1094 1350 7.6 10261 3.5 4.4 o
Inventive Example 3 905 222 18.0 97 1032 1323 7.9 10450 3.4 4.2 o
Inventive Example 4 909 204 2.2 96 1204 1505 7.1 10688 4.1 5.2 o
Inventive Example 5 912 221 3.0 96 1186 1501 6.7 10057 4.1 5.2 o
Inventive Example 6 915 212 1.0 98 1225 1531 6.7 10255 4.3 5.3 o
공성은 양호하였으나, Mn 편석대에 의한 연신율 미달로 TSxT-EL 값이 본 발명의 범위를 벗어났다.Although the porosity was good, the TSxT-EL value was out of the scope of the present invention because the elongation was lowered by the Mn segregation zone.
비교예 3, 4 및 5는 CT온도가 본 발명의 범위를 벗어나 95% 이상의 마르텐사이트 조직이 아닌 베이나이트 조직 구현으로 인장강도가 1Gpa 미만으로 나타났다.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.
비교예 6, 7, 8 및 9는 모두 관계식 3을 만족하지 않았으며, 굽힘 가공성 평가 결과도 열위하였다.Comparative Examples 6, 7, 8, and 9 did not satisfy the relation 3, and the results of the evaluation of bending workability were also inferior.
도 1에 비교예과 발명예의 TSxT-EL과 관계식 3으로 도출된 값을 그래프로 나타내었다. 네모난 점으로 표시된 부분은 비교예이고, 동그란점으로 표시된 부분은 발명예이다. 본 발명의 발명예에 해당하는 동그란점은 모두 빗금으로 표시한 부분 내에 위치하는 것을 확인할 수 있다.In Figure 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.
또한, 발명예 1 내지 6은 모두 굽힘가공성의 기준을 모두 만족하며, 인장강도 및 연신율 뿐만 아니라 항복강도도 우수한 것을 확인할 수 있다.In addition, 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.
이상 설명한 바와 같이 본 발명의 예시적인 실시예가 도면을 참조하여 설명되었지만, 다양한 변형과 다른 실시예가 본 분야의 숙련된 기술자들에 의해 행해질 수 있을 것이다. 이러한 변형과 다른 실시예들은 첨부된 청구범위에 모두 고려되고 포함되어, 본 발명의 진정한 취지 및 범위를 벗어나지 않는다 할 것이다.While the exemplary embodiment of the present invention has been described with reference to the drawings as described above, various modifications and other embodiments may be made by those skilled in the art. Such modifications and other embodiments are all considered and included in the appended claims, without departing from the true spirit and scope of the invention.

Claims (6)

  1. C: 0.1∼0.25 중량%, Si: 0.01∼0.2 중량%, Mn: 0.5∼2.0 중량%, P: 0.005∼0.02 중량% 및 S: 0.001∼0.01 중량%을 포함하고, 추가적으로, Ti, Nb, Mo, Cr 및 B 로 이루어진 그룹에서 선택된 적어도 하나의 성분을 총 0.001~0.35 중량% 포함하며, 잔부는 철(Fe) 및 기타 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하는 굽힘 가공성이 우수한 초고강도 열연강판.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, and additionally include Ti, Nb, Mo , 0.001 to 0.35% by weight of at least one component selected from the group consisting of Cr and B, the balance includes iron (Fe) and other unavoidable impurities, and superb high strength hot rolled steel having excellent bending workability satisfying the following Equation 1. Grater.
    [관계식 1][Relationship 1]
    69.2-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]≥ 069.2-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] ≥ 0
    (단, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미함.)(However, [C], [Si], [Mn], [Cr], [Ni], [Ti], [B], and [P] refer to the weight percent of each component content.)
  2. 제 1 항에 있어서, 상기 초고강도 열연강판의 인장강도는 1GPa이상이고, 인장강도x연신율 (TSxT-EL)은 10000이상인 굽힘 가공성이 우수한 초고강도 열연강판.The super high strength hot rolled steel sheet having excellent bending workability according to claim 1, wherein the tensile strength of the super high strength hot rolled steel sheet is 1 GPa or more, and the tensile strength x elongation (TSxT-EL) is 10000 or more.
  3. 제 1 항에 있어서, 상기 초고강도 열연강판의 굽힘가공성(R/t)은 하기 관계식 2를 만족하는 굽힘 가공성이 우수한 초고강도 열연강판.The super high strength hot rolled steel sheet according to claim 1, wherein the bending workability (R / t) of the ultra high strength hot rolled steel sheet satisfies the following Equation 2.
    [관계식 2][Relationship 2]
    굽힘가공성(R/t) ≤ (인장강도 x 0.00517 - 2.60345)Bendability (R / t) ≤ (tensile strength x 0.00517-2.60345)
    (식에서, R: 90°굽힘 시험 후 크랙이 발생하지 않는 최소 굽힘반경, t: 강판 두께)(In formula, R: minimum bending radius without crack after 90 ° bending test, t: sheet thickness)
  4. 제 1 항에 있어서, 상기 초고강도 열연강판의 미세조직은, 면적분율로, 마르텐사이트가 95% 이상이고, 제 2 상이 5% 미만인 굽힘 가공성이 우수한 초고강도 열연강판.The ultra-high strength hot rolled steel sheet according to claim 1, wherein the microstructure of the super high strength hot rolled steel sheet has an area fraction of martensite of 95% or more and a second phase of less than 5%.
  5. C: 0.1∼0.25 중량%, Si: 0.01∼0.2 중량%, Mn: 0.5∼2.0 중량%, P: 0.005∼0.02 중량% 및 S: 0.001∼0.01 중량%을 포함하고, 추가적으로, Ti, Nb, Mo, Cr 및 B 로 이루어진 그룹에서 선택된 적어도 하나의 성분을 총 0.001~0.35 중량% 포함하며, 잔부 철(Fe) 및 기타 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하는 슬라브를 준비하는 단계;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, and additionally include Ti, Nb, Mo Preparing a slab comprising 0.001 to 0.35% by weight of a total of at least one component selected from the group consisting of Cr and B, comprising residual iron (Fe) and other unavoidable impurities, and satisfying the following relational formula 1;
    상기 슬라브를 1100~1300℃의 온도에서 재가열하는 단계;Reheating the slab at a temperature of 1100-1300 ° C .;
    상기 재가열된 슬라브를 850~1000℃의 마무리압연온도로 열간압연하여 열연강판을 얻는 단계;Hot rolling the reheated slab to a finish rolling temperature of 850 to 1000 ° C. to obtain a hot rolled steel sheet;
    상기 열연강판을 100~300℃/s의 냉각속도 및 및 하기 관계식 3을 만족하도록 냉각하는 단계; 및Cooling the hot rolled steel sheet to satisfy a cooling rate of 100 to 300 ° C./s and the following relational expression 3; And
    상기 냉각된 강판을 350℃ 이하의 권취온도에서 권취하는 단계를 포함하는 굽힘 가공성이 우수한 초고강도 열연강판의 제조방법.The method of manufacturing a super high strength hot rolled steel sheet having excellent bending workability, comprising: winding the cooled steel sheet at a winding temperature of 350 ° C. or less.
    [관계식 1][Relationship 1]
    69.2-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]≥ 069.2-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] ≥ 0
    (단, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미함.)(However, [C], [Si], [Mn], [Cr], [Ni], [Ti], [B], and [P] refer to the weight percent of each component content.)
    [관계식 3][Relationship 3]
    85.3-311.5[C]-0.1[Si]-4.0[Mn]-5.3[Cr]-2.6[Ni]-6.6[Ti]-660.6[B]-39[P]-6.9[냉각속도]≥ 085.3-311.5 [C] -0.1 [Si] -4.0 [Mn] -5.3 [Cr] -2.6 [Ni] -6.6 [Ti] -660.6 [B] -39 [P] -6.9 [Cooling rate] ≥ 0
    (단, 상기 [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] 및 [P]는 각각의 성분 함량의 중량%를 의미하며, 상기 냉각속도의 단위는 ℃/s이고 마무리압연온도에서 권취온도까지의 냉각속도를 의미함)(Wherein [C], [Si], [Mn], [Cr], [Ni], [Ti], [B] and [P] refer to the weight percent of each component content, and the cooling rate The unit of is ° C / s, which means the cooling rate from finishing rolling temperature to winding temperature.)
  6. 제 5 항에 있어서, 상기 권취된 열연강판을 산세처리 후, 450~480℃의 온도에서 재가열하고, 용융아연도금을 실시하여 표면에 아연도금층을 형성하는 단계를 추가로 포함하는 굽힘 가공성이 우수한 초고강도 열연강판의 제조방법.The ultra-excellent bending workability according to claim 5, further comprising the step of reheating the wound hot-rolled steel sheet at a temperature of 450 to 480 ° C and performing hot dip galvanizing to form a zinc plated layer on the surface. Method for producing high strength hot rolled steel sheet.
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