WO2022131596A1 - 굽힘성 및 성형성이 우수한 고강도 강판 및 이의 제조방법 - Google Patents
굽힘성 및 성형성이 우수한 고강도 강판 및 이의 제조방법 Download PDFInfo
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- WO2022131596A1 WO2022131596A1 PCT/KR2021/017156 KR2021017156W WO2022131596A1 WO 2022131596 A1 WO2022131596 A1 WO 2022131596A1 KR 2021017156 W KR2021017156 W KR 2021017156W WO 2022131596 A1 WO2022131596 A1 WO 2022131596A1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 127
- 239000010959 steel Substances 0.000 title claims abstract description 127
- 238000000034 method Methods 0.000 title claims abstract description 43
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 34
- 238000001816 cooling Methods 0.000 claims description 70
- 238000000137 annealing Methods 0.000 claims description 42
- 229910000859 α-Fe Inorganic materials 0.000 claims description 42
- 238000005097 cold rolling Methods 0.000 claims description 31
- 230000009467 reduction Effects 0.000 claims description 21
- 238000010438 heat treatment Methods 0.000 claims description 20
- 229910001566 austenite Inorganic materials 0.000 claims description 19
- 229910000734 martensite Inorganic materials 0.000 claims description 19
- 229910001563 bainite Inorganic materials 0.000 claims description 18
- 239000010960 cold rolled steel Substances 0.000 claims description 17
- 239000011572 manganese Substances 0.000 claims description 17
- 239000010936 titanium Substances 0.000 claims description 16
- 239000011651 chromium Substances 0.000 claims description 15
- 239000010955 niobium Substances 0.000 claims description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 14
- 229910052799 carbon Inorganic materials 0.000 claims description 14
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 12
- 238000005098 hot rolling Methods 0.000 claims description 12
- 238000004804 winding Methods 0.000 claims description 8
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 7
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 7
- 229910052796 boron Inorganic materials 0.000 claims description 7
- 229910052717 sulfur Inorganic materials 0.000 claims description 7
- 239000011593 sulfur Substances 0.000 claims description 7
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 6
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 6
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 6
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 6
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 229910052758 niobium Inorganic materials 0.000 claims description 6
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 6
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 239000011574 phosphorus Substances 0.000 claims description 6
- 238000013001 point bending Methods 0.000 claims description 6
- 229910052710 silicon Inorganic materials 0.000 claims description 6
- 239000010703 silicon Substances 0.000 claims description 6
- 229910052719 titanium Inorganic materials 0.000 claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
- 230000000717 retained effect Effects 0.000 claims description 3
- 239000000463 material Substances 0.000 abstract description 16
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- 229910001562 pearlite Inorganic materials 0.000 description 2
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- 239000000725 suspension Substances 0.000 description 2
- FGRBYDKOBBBPOI-UHFFFAOYSA-N 10,10-dioxo-2-[4-(N-phenylanilino)phenyl]thioxanthen-9-one Chemical compound O=C1c2ccccc2S(=O)(=O)c2ccc(cc12)-c1ccc(cc1)N(c1ccccc1)c1ccccc1 FGRBYDKOBBBPOI-UHFFFAOYSA-N 0.000 description 1
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 1
- 229910000655 Killed steel Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
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- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 description 1
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Images
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
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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
- 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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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/22—Martempering
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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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
- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
Definitions
- the present invention relates to a steel suitable as a material for automobiles, and more particularly, to a high-strength steel sheet having excellent bendability and formability, and a method for manufacturing the same.
- high-strength steel with excellent strength is employed as a material for structural members such as members, seat rails, and pillars to improve the impact resistance of the vehicle body. have.
- These automobile parts have a complex shape according to stability and design, and are mainly manufactured by molding with a press mold, so high strength and high formability are required.
- high-strength steels used as automotive materials are typically dual phase steel (DP steel), transformation induced plasticity steel (TRIP steel), and complex phase steel (CP steel). steel), and ferrite-bainite steel (Ferrite Bainite steel, FB steel).
- DP steel an ultra-high tensile steel, has a low yield ratio of about 0.5 to 0.6, so it is easy to process and has the advantage of having the highest elongation after TRIP steel. Accordingly, it is mainly applied to door outers, seat rails, seat belts, suspensions, arms, wheel disks, and the like.
- TRIP steel has a characteristic of exhibiting excellent formability (high ductility) by having a yield ratio in the range of 0.57 to 0.67, and is therefore suitable for parts requiring high formability such as members, roofs, seat belts, bumper rails, etc.
- CP steel is applied to side panels and underbody reinforcing materials due to its high elongation and bending workability as well as resistance yield ratio
- FB steel is mainly applied to suspension lower arms and wheel disks because of its excellent hole expandability.
- DP steel is mainly composed of ferrite with excellent ductility and hard phase with high strength (martensite phase, bainite phase), and a trace amount of retained austenite may exist.
- Such DP steel has excellent characteristics such as low yield strength, high tensile strength, low yield ratio (YR), high work hardening rate, high ductility, continuous yield behavior, room temperature aging resistance, and bake hardenability.
- YR low yield strength
- high tensile strength high tensile strength
- low yield ratio YR
- high work hardening rate high ductility
- continuous yield behavior room temperature aging resistance
- bake hardenability it is possible to manufacture high-strength steel with high bendability by controlling the fraction, recrystallization degree, distribution uniformity, and the like of each phase.
- DP steel for automobiles manufactures slabs through steelmaking and casting processes, then [heating-rough rolling-finishing hot rolling] on the slabs to obtain hot-rolled coils and then annealing to produce final products.
- the annealing process is a process mainly performed during the manufacture of cold-rolled steel sheets.
- the hot-rolled coil is pickled to remove surface scale, cold-rolled at a constant reduction rate at room temperature, and then the annealing process and necessary Accordingly, it is manufactured through an additional temper rolling process.
- Cold rolled steel sheet (cold rolled material) obtained by cold rolling itself is in a very hardened state and is not suitable for manufacturing parts requiring workability. can do it
- a steel sheet (cold rolled material) is heated to approximately 650 to 850° C. in a heating furnace and then maintained for a certain period of time, thereby lowering hardness and improving workability through recrystallization and phase transformation.
- a steel sheet that has not been subjected to an annealing process has high hardness, particularly a high surface hardness and poor workability, whereas a steel sheet subjected to an annealing process has a recrystallized structure, and thus hardness, yield point, and tensile strength are lowered, thereby improving workability.
- the ferrite is completely recrystallized in the heating process during continuous annealing to form an equiaxed crystal, so that it becomes an equiaxed crystal when austenite is generated and grown in the subsequent process, so that the grain size is reduced It is advantageous to form a small and uniform austenite phase.
- Patent Document 1 suggests a method according to the refinement of the structure, and specifically, fine precipitation with a particle diameter of 1 to 100 nm inside the structure for a composite steel sheet mainly having a martensitic phase.
- a method of dispersing copper particles is disclosed.
- this technology requires the addition of 2 to 5% Cu in order to obtain good fine precipitated particles, and there is a concern that red heat brittleness may occur due to a large amount of Cu, and there is a problem that the manufacturing cost is excessively increased.
- Patent Document 2 has a structure containing 2 to 10 area % of pearlite by using ferrite as a matrix structure, and increases the strength by strengthening precipitation and refining grains through the addition of carbon-nitride forming elements (ex, Ti, etc.)
- An improved steel sheet is disclosed. While the steel sheet is good in terms of hole expandability, there is a limitation in further increasing the tensile strength, and there is a problem in that cracks occur during fresh forming due to high yield strength and low ductility.
- Patent Document 3 discloses a technology for producing a cold-rolled steel sheet that simultaneously obtains high strength and high ductility using a tempered martensite phase and has an excellent plate shape after continuous annealing, but the carbon (C) content in the steel is 0.2% or more.
- C carbon
- Patent Document 1 Japanese Patent Application Laid-Open No. 2005-264176
- Patent Document 2 Korean Patent Publication No. 2015-0073844
- Patent Document 3 Japanese Patent Application Laid-Open No. 2010-090432
- One aspect of the present invention is to provide a high-strength steel sheet suitable for automotive structural members, etc., having a low yield ratio, high strength, and excellent formability such as bendability through improvement of ductility, and a method of manufacturing the same will be.
- the subject of the present invention is not limited to the above.
- the subject of the present invention will be understood from the overall content of the present specification, and those of ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional subject of the present invention.
- the microstructure includes ferrite having an area fraction of 35 to 50% and bainite of 35 to 45%, and the remainder martensite, and the ferrite is non-recrystallized ferrite having an area fraction of 8 to 15% and recrystallized ferrite of 27 to 35%.
- ferrite having an area fraction of 35 to 50% and bainite of 35 to 45%, and the remainder martensite, and the ferrite is non-recrystallized ferrite having an area fraction of 8 to 15% and recrystallized ferrite of 27 to 35%.
- a high-strength steel sheet having excellent bendability and formability.
- Another aspect of the present invention comprises the steps of preparing a steel slab having the above-described alloy composition; heating the steel slab in a temperature range of 1100 to 1300 °C; manufacturing a hot-rolled steel sheet by hot rolling the heated steel slab; winding the hot-rolled steel sheet in a temperature range of 400 to 700°C; cooling the hot-rolled steel sheet to room temperature after the winding; manufacturing a cold rolled steel sheet by cold rolling the cooled hot rolled steel sheet; continuous annealing of the cold-rolled steel sheet; first cooling at an average cooling rate of 1 to 10° C./s to a temperature range of 650 to 700° C. after the continuous annealing; and secondary cooling at an average cooling rate of 5 to 50 °C/s to a temperature range of 300 to 580 °C after the primary cooling,
- the cold rolling is performed in 7 passes or less, and provides a method of manufacturing a high-strength steel sheet having excellent bendability and formability, characterized in that the total reduction ratio is 55 to 70%.
- the steel sheet of the present invention with improved formability can prevent machining defects such as cracks or wrinkles during press forming, it has an effect of being suitably applied to structural parts that require processing into complex shapes. Furthermore, when a vehicle to which such parts are applied inevitably collides, it is effective to manufacture a material with improved crash resistance so that defects such as cracks are not easily formed.
- FIG. 1 shows a microstructure photograph of an invention steel according to an embodiment of the present invention.
- FIG 3 is a graph showing a change in physical properties according to a rolling reduction during cold rolling according to an embodiment of the present invention.
- FIG. 4 is a graph showing a change in physical properties according to an annealing temperature according to an embodiment of the present invention.
- the inventors of the present invention have studied deeply in order to develop a material having a level of formability suitable for use in parts requiring processing into complex shapes among materials for automobiles.
- the present inventors have confirmed that the target can be achieved by inducing sufficient recrystallization of the soft phase affecting the ductility of steel, and have completed the present invention.
- High-strength steel sheet having excellent bendability and formability is, by weight, carbon (C): 0.05 to 0.12%, manganese (Mn): 2.0 to 3.0%, silicon (Si): 0.5% or less ( 0% or less), Chromium (Cr): 1.0% or less (excluding 0%), Niobium (Nb): 0.1% or less (excluding 0%), Titanium (Ti): 0.1% or less (excluding 0%) , boron (B): 0.0025% or less (excluding 0%), aluminum (sol.Al): 0.02 to 0.05%, phosphorus (P): 0.05% or less (excluding 0%), sulfur (S): 0.01% or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%).
- the content of each element is based on the weight, and the ratio of the tissue is based on the area.
- Carbon (C) is an important element added for solid solution strengthening, and this C is combined with the precipitating elements to form fine precipitates, thereby contributing to the improvement of the strength of steel.
- the C may be included in an amount of 0.05 to 0.12%. More advantageously, it may be included in an amount of 0.06% or more, and may be included in an amount of 0.10% or less.
- Manganese (Mn) is an element advantageous for precipitating sulfur (S) in steel as MnS to prevent hot brittleness caused by the generation of FeS, and for solid solution strengthening of steel.
- the content of Mn is less than 2.0%, the above-described effect cannot be obtained, and there is a difficulty in securing the strength of the target level.
- the content exceeds 3.0% there is a high possibility that problems such as weldability and hot-rollability occur, and at the same time, there is a fear that ductility may be lowered as martensite is more easily formed due to an increase in hardenability.
- Mn-Bands Mn oxide bands
- the Mn may be included in an amount of 2.0 to 3.0%, and more advantageously, it may be included in an amount of 2.2 to 2.8%.
- Silicon (Si) is a ferrite stabilizing element and is advantageous in promoting ferrite transformation to secure a target level of ferrite fraction. In addition, it is effective in increasing the strength of ferrite due to its good solid solution strengthening ability, and is a useful element for securing strength without reducing the ductility of steel.
- the Si may be included in an amount of 0.5% or less, and 0% may be excluded. More advantageously, it may be included in an amount of 0.1% or more.
- Chromium (Cr) is an element that facilitates the formation of a bainite phase, and suppresses the formation of a martensite phase during annealing heat treatment, and is an element that contributes to strength improvement by forming fine carbides.
- the Cr may be included in an amount of 1.0% or less, and 0% may be excluded.
- Niobium is an element that segregates at the austenite grain boundary, suppresses coarsening of austenite grains during annealing heat treatment, and forms fine carbides to improve strength.
- the Nb may be included in an amount of 0.1% or less, and 0% may be excluded.
- Titanium (Ti) is an element that forms fine carbides and contributes to securing yield strength and tensile strength.
- Ti has the effect of suppressing the formation of AlN by Al inevitably present in the steel by precipitating N as TiN in the steel, thereby reducing the possibility of cracks during continuous casting.
- Ti may be included in an amount of 0.1% or less, and 0% may be excluded.
- Boron (B) is an element that delays the transformation of austenite to pearlite in the cooling process after annealing heat treatment, but when its content exceeds 0.0025%, B is excessively concentrated on the surface, which may lead to deterioration of plating adhesion.
- B may be included in an amount of 0.0025% or less, and 0% may be excluded.
- Aluminum (sol.Al) is an element added for the effect of refining the grain size and deoxidation of steel, and if the content is less than 0.02%, it is impossible to manufacture aluminum killed steel in a stable state. On the other hand, when the content exceeds 0.05%, the crystal grains are refined and the strength is improved, but there is a high risk of surface defects of the plated steel sheet due to excessive formation of inclusions during the steel making operation.
- the sol.Al may be included in an amount of 0.02 to 0.05%.
- Phosphorus (P) is a substitution-type element having the greatest solid solution strengthening effect, and is an element advantageous in securing strength while improving in-plane anisotropy and not significantly reducing formability.
- P Phosphorus
- the content of P can be controlled to 0.05% or less, and 0% can be excluded in consideration of the unavoidably added level.
- S Sulfur
- S is an element that is unavoidably added as an impurity element in steel, and it inhibits ductility, so it is desirable to manage its content as low as possible.
- S since S has a problem of increasing the possibility of generating red hot brittleness, it is preferable to control its content to 0.01% or less. However, 0% may be excluded in consideration of the unavoidably added level during the manufacturing process.
- Nitrogen (N) is a solid solution strengthening element, but when its content exceeds 0.01%, the risk of brittleness increases, and there is a risk of impairing the playing quality by combining with Al in steel to precipitate AlN excessively.
- the N may be included in 0.01% or less, and 0% may be excluded in consideration of the unavoidably added level.
- the remaining component of the present invention is iron (Fe).
- Fe iron
- the steel sheet of the present invention having the above-described alloy composition may be composed of ferrite as a microstructure and a bainite phase and a martensite phase, which are hard phases.
- the steel sheet of the present invention may include a ferrite phase in an area fraction of 35 to 50%, and a bainite phase in an amount of 35 to 45%.
- the remainder may include a martensite phase, and in addition to this, may include a trace amount of a residual austenite phase.
- the ferrite phase may include non-recrystallized ferrite and recrystallized ferrite, and the non-recrystallized ferrite may include an area fraction of 8 to 15%, and the recrystallized ferrite may include an area fraction of 27 to 35%.
- the fraction of the non-recrystallized ferrite is less than 8%, the recrystallization proceeds excessively, and there is a risk of being inferior in strength.
- the fraction exceeds 15%, as the stretched hard phase is distributed and distributed in the tissue, the yield strength is excessively increased, making it difficult to secure workability.
- the martensite phase is not specifically limited in terms of its fraction, but it is advantageous to include an area fraction of 20% or less (excluding 0%) in order to secure ultra-high strength of 980 MPa or higher tensile strength. .
- the fraction of the martensite phase exceeds 20%, ductility is lowered, making it difficult to secure a target level of workability.
- the fraction of the retained austenite phase does not exceed 3%, and even if it is 0%, there is no difficulty in securing the intended physical properties.
- the steel sheet of the present invention having the above-described microstructure has a thickness of 0.5 to 2.5 mm, a tensile strength of 980 MPa or more, a yield strength of 550 to 650 MPa, and an elongation (total elongation) of 12% or more.
- the steel sheet may have an excellent effect of bendability (bendability) by having a three-point bending angle of 90 degrees or more.
- the present invention can manufacture a desired steel sheet through the process of [steel slab heating - hot rolling - winding - cold rolling - continuous annealing], and each process will be described in detail below.
- This process is performed in order to smoothly perform the subsequent hot rolling process and sufficiently obtain the target physical properties of the steel sheet.
- the conditions of the heating process there is no particular limitation on the conditions of the heating process, and any normal conditions may be used.
- the heating process may be performed in a temperature range of 1100 to 1300 °C.
- the hot-rolled steel slab heated according to the above can be manufactured into a hot-rolled steel sheet, and in this case, the finish hot-rolling can be performed at an outlet temperature of Ar3 or more and 1000°C or less.
- the finish hot rolling may be performed in a temperature range of 760 to 940 °C.
- the hot-rolled steel sheet manufactured according to the above may be wound in a coil shape.
- the winding may be performed in a temperature range of 400 to 700 °C. If the coiling temperature is less than 400 °C, the martensite or bainite phase is excessively formed, causing an excessive increase in strength of the hot-rolled steel sheet, and problems such as shape defects due to load during subsequent cold rolling may be caused. On the other hand, when the coiling temperature exceeds 700 °C, there is a problem that the surface scale increases and the pickling property deteriorates.
- the wound hot-rolled steel sheet it is preferable to cool the wound hot-rolled steel sheet to room temperature at an average cooling rate of 0.1° C./s or less (excluding 0° C./s).
- the wound hot-rolled steel sheet may be cooled after passing through processes such as transport and stacking, and the process before cooling is not limited thereto.
- the hot-rolled steel sheet wound according to the above can be cold-rolled to manufacture a cold-rolled steel sheet.
- the present invention is characterized by providing a method for manufacturing a cold rolled steel sheet using an ultra-thin cold rolling mill (ZRM) as a method for overcoming the limitations of the above-described cold rolling process.
- ZRM ultra-thin cold rolling mill
- it may be a rolling mill in which a pair of work rolls and a plurality of (eg, about 17 to 19) back rolls are connected to the work roll, and if the rolling load can be reached, it is limited only to this make it clear that it is not
- cold rolling using the ultra-thin cold rolling mill can be performed in 7 passes or less, preferably 5 to 7 passes, and a lower pass compared to the existing continuous rolling mill (8 to 14 passes) It has the characteristic of doing it with
- the 7 or less passes can be set as 1 stand, and the total reduction ratio is 55% or more, preferably, the reduction is possible at 55 to 70%, and there is an economically advantageous effect.
- the total reduction ratio during the cold rolling is less than 55%, ferrite recrystallization is delayed and it is difficult to obtain a fine and uniform austenite phase.
- the total reduction ratio exceeds 70%, the yield strength is excessively increased due to excessive recrystallization and generation of fine grains to cause a decrease in workability, or to inhibit phase transformation while excessive recrystallization and recovery occur during annealing to suppress low temperature The formation of the metamorphic phase becomes difficult, and there is a fear that the target level of strength may not be obtained as a result.
- a reversing rolling mill is a type of rolling mill used for rolling thin materials, and refers to a rolling mill that rolls materials while reciprocating between a pair of rolls. have.
- the present invention can further improve the material uniformity of the cold-rolled steel sheet to be manufactured by performing cold rolling under reduced pressure, and has the effect of securing a thinner thickness compared to the existing cold-rolled steel sheet.
- the cold-rolled steel sheet of the present invention may have a thickness of 0.5 to 2.5 mm.
- the hot-rolled steel sheet may be pickled before the cold rolling, and the pickling process may be performed in a conventional manner.
- the continuous annealing treatment may be performed, for example, in a continuous annealing furnace (CAL).
- CAL continuous annealing furnace
- a continuous annealing furnace may be composed of [heating zone - cracking zone - cooling zone (slow cooling zone and rapid cooling zone) - (excessive aging zone, if necessary)]. After heating, it is heated to a specific temperature in the heating zone, and after reaching the target temperature, it is maintained in the crack zone for a certain period of time.
- the temperature of the heating zone and the cracking zone can be controlled equally during the continuous annealing, which means that the end temperature of the heating zone and the starting temperature of the cracking zone are controlled equally.
- the temperature of the heating zone and the crack zone can be controlled to 770 ⁇ 810 °C. If the temperature is less than 770 ° C, sufficient heat input for recrystallization cannot be applied, whereas when the temperature exceeds 810 ° C, productivity is reduced and an austenite phase is excessively formed, resulting in the hard phase fraction after subsequent cooling This greatly increases, and there is a fear that the ductility of the steel may be inferior.
- the step-by-step cooling may consist of primary cooling - secondary cooling. Specifically, after the continuous annealing, after primary cooling at an average cooling rate of 1 to 10 °C / s to a temperature range of 650 to 700 °C, Secondary cooling can be performed at an average cooling rate of 5 to 50 °C/s up to a temperature range of 300 to 580 °C.
- the primary cooling process may be performed at an average cooling rate of 1°C/s or more.
- rapid cooling may be performed at a cooling rate of a predetermined or higher.
- the secondary cooling end temperature is less than 300 °C, there is a fear that cooling deviation occurs in the width and length directions of the steel plate and deteriorate the plate shape. It can't be done, and the strength can be lowered.
- the average cooling rate during the secondary cooling is less than 5 °C / s, there is a fear that the fraction of the hard phase becomes excessive, whereas when it exceeds 50 °C / s, there is a risk that the hard phase becomes insufficient.
- overaging may be performed.
- the overaging treatment is a process of maintaining the secondary cooling end temperature for a certain period of time, and uniform heat treatment is performed in the width and length directions of the coil, thereby improving the shape quality. To this end, the overaging treatment may be performed for 200 to 800 seconds.
- the temperature may be the same as the secondary cooling end temperature or may be performed within the secondary cooling end temperature range.
- the high-strength steel sheet of the present invention prepared as described above has a microstructure composed of a hard phase and a soft phase, and in particular, by maximizing ferrite recrystallization by an optimized cold rolling and annealing process, bainite is a hard phase in the finally recrystallized ferrite matrix. and the martensite phase may have a uniformly distributed structure.
- the steel sheet of the present invention has a high tensile strength of 980 MPa or more, it is possible to ensure excellent bendability and formability by ensuring a resistance yield ratio and high ductility.
- each steel slab was heated at 1200° C. for 1 hour, and then finish hot rolled at a finish rolling temperature of 880 to 920° C. to prepare a hot-rolled steel sheet.
- the thickness of each hot-rolled steel sheet was 2.1 to 3.5 mm, and in the case of the cold-rolled steel sheets having a thickness of 0.8 mm (see Table 2), the thickness of the hot-rolled steel sheet was 8 mm.
- each hot-rolled steel sheet was wound at 650°C and cooled to room temperature at a cooling rate of 0.1°C/s. Thereafter, the wound hot-rolled steel sheet was subjected to cold rolling and continuous annealing under the conditions shown in Table 2 below, and then subjected to over-aging treatment at 360° C. for 520 seconds after stepwise cooling (1st - 2nd) to prepare a final steel sheet .
- stepwise cooling primary cooling was performed at an average cooling rate of 3°C/s, and secondary cooling was performed at an average cooling rate of 20°C/s.
- a tensile test piece of JIS No. 5 size was taken in the vertical direction of the rolling direction, and then a tensile test was performed at a strain rate of 0.01/s.
- a three-point bending test for evaluation of bendability was performed based on the VDA standard (VDA238-100) prescribed by the German Automobile Manufacturers Association, and the displacement at the maximum load measured in the bending test was performed.
- the bending angle was measured by converting the angle from the VDA standard.
- the specimen dimensions were 60 mm ⁇ 60 mm, the bending roll diameter was 30 mm, the interval between the rolls was 2.9 mm, the punch R value was 0.4 mm, and the punch press-in speed was 20 mm/min.
- bainite and martensite phases corresponding to the hard phases among the tissue phases were observed through SEM at 5000 magnification after nital etching. At this time, the fraction of the observed hard phase was measured. In addition, for the phases, each fraction was measured using SEM and an image analyzer after nital etching. At this time, unrecrystallized ferrite was expressed as the fraction of ferrite in which the deformed structure remained in the total ferrite fraction through an image analyzer.
- the material uniformity of the steel sheet is improved because the fraction of recrystallized ferrite is formed to be 27% or more.
- Recrystallization of steel is a phenomenon in which ferrite atoms are rearranged during annealing. The higher the recrystallization degree, the more austenite transformation occurs in various directions, and the uniform material quality of the entire steel increases, which is advantageous for improving workability.
- Comparative Examples 1 and 2 which had a low cracking temperature and a low cold rolling reduction during continuous annealing during the steel sheet manufacturing process, showed excessively high yield strength and tensile strength due to excessive ferrite phase in which recrystallization did not occur sufficiently, and elongation and 3 points. The bending angle is also low and the machinability is poor.
- Comparative Example 3 also had a low cracking temperature and a low cold rolling reduction during continuous annealing, so that a non-recrystallized ferrite phase was excessively formed and the three-point bending angle was inferior.
- Comparative Example 8 was also a case where the total reduction ratio during cold rolling was less than 55%, but compared to Comparative Examples 6 or 7, the reduction ratio was higher than that of the present invention but inferior in ductility in terms of workability.
- Comparative Examples 4-5 and 10 are cases in which recrystallization proceeds excessively during annealing after cold rolling to suppress austenite reverse transformation, resulting in inferior strength. Austenite reverse transformation does not occur well in recrystallized ferrite. In an environment where the recrystallization driving force is very high, the reverse transformation of austenite can be suppressed. showed results.
- Figure 1 shows the microstructure photos of Inventive Examples 3 and 4
- Figure 2 shows the microstructure photos of Comparative Examples 6 and 7.
- FIG. 3 is a graph showing the change in workability according to the reduction ratio during cold rolling
- FIG. 4 is a graph showing the change in workability according to the annealing temperature.
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Abstract
Description
강번 | 합금조성 (중량%) | ||||||||||
C | Mn | Si | Cr | Nb | Ti | B* | sol.Al | P | S | N* | |
1 | 0.083 | 2.29 | 0.406 | 0.836 | 0.049 | 0.0019 | 24 | 0.034 | 0.0086 | 0.0008 | 52 |
2 | 0.061 | 2.89 | 0.402 | 0.856 | 0.051 | 0.0202 | 22 | 0.036 | 0.0099 | 0.0016 | 45 |
3 | 0.068 | 2.27 | 0.399 | 0.850 | 0.047 | 0.0205 | 22 | 0.039 | 0.0094 | 0.0008 | 52 |
4 | 0.071 | 2.60 | 0.411 | 0.841 | 0.049 | 0.0198 | 23 | 0.037 | 0.0097 | 0.0007 | 44 |
5 | 0.090 | 2.12 | 0.395 | 0.833 | 0.048 | 0.0203 | 21 | 0.032 | 0.0073 | 0.0024 | 33 |
6 | 0.111 | 2.08 | 0.120 | 0.980 | 0.048 | 0.0210 | 23 | 0.026 | 0.0089 | 0.0009 | 55 |
B* 및 N*는 ppm 으로 나타낸 것이다. |
구분 | 미세조직 (면적분율%) | 기계적 물성 | |||||||||
재결정 F |
미재결정 F |
B | M | R-A | YS (MPa) |
TS (MPa) |
항복비 (YS/TS) |
El (%) |
3점 굽힘각 (°) |
Ceq
(%) |
|
비교예 1 |
3.24 | 32.76 | 40 | 23 | 1 | 766 | 1179 | 0.65 | 10.7 | 74 | 0.231 |
비교예 2 |
14.82 | 24.18 | 38 | 22 | 1 | 756 | 1158 | 0.65 | 9.9 | 84 | 0.245 |
비교예 3 |
18 | 22 | 42 | 17 | 1 | 616 | 1081 | 0.57 | 13.6 | 87 | 0.217 |
발명예 1 |
34 | 15 | 38 | 12 | 1 | 553 | 1034 | 0.53 | 12.5 | 90 | 0.237 |
발명예 2 |
33.84 | 13.16 | 38 | 14 | 1 | 598 | 1077 | 0.55 | 13.6 | 99 | 0.233 |
비교예 4 |
46.55 | 2.45 | 34 | 16 | 1 | 605 | 970 | 0.62 | 17.6 | 102 | 0.233 |
비교예 5 |
49.4 | 2.6 | 38 | 9 | 1 | 456 | 888 | 0.51 | 17.2 | 108 | 0.240 |
비교예 6 |
3.85 | 31.15 | 44 | 20 | 1 | 729 | 1151 | 0.63 | 11.1 | 82 | 0.231 |
비교예 7 |
15.2 | 22.8 | 42 | 19 | 1 | 716 | 1137 | 0.63 | 10.4 | 79 | 0.245 |
비교예 8 |
19.27 | 21.73 | 41 | 17 | 1 | 646 | 1078 | 0.60 | 11.5 | 93 | 0.217 |
발명예 3 |
28.8 | 11.2 | 45 | 14 | 1 | 582 | 1040 | 0.56 | 14.5 | 98 | 0.237 |
발명예 4 |
31.92 | 10.08 | 41 | 16 | 1 | 610 | 1070 | 0.57 | 14.3 | 94 | 0.233 |
비교예 9 |
34.2 | 1.8 | 45 | 18 | 1 | 667 | 1055 | 0.63 | 16.2 | 103 | 0.233 |
비교예 10 |
39.9 | 2.1 | 46 | 11 | 1 | 527 | 989 | 0.53 | 16.2 | 107 | 0.240 |
비교예 11 |
4.32 | 31.68 | 43 | 20 | 1 | 730 | 1110 | 0.66 | 9.9 | 96 | 0.231 |
비교예 12 |
15.91 | 21.09 | 44 | 18 | 1 | 704 | 1099 | 0.64 | 10.5 | 92 | 0.245 |
비교예 13 |
19 | 19 | 43 | 18 | 1 | 706 | 1073 | 0.66 | 11.5 | 93 | 0.217 |
발명예 5 |
28.12 | 9.88 | 43 | 18 | 1 | 647 | 1061 | 0.62 | 14.2 | 101 | 0.237 |
발명예 6 |
27.72 | 8.28 | 44 | 19 | 1 | 648 | 1073 | 0.63 | 12.1 | 106 | 0.233 |
비교예 14 |
28.25 | 1.75 | 45 | 24 | 1 | 720 | 1078 | 0.67 | 15.7 | 108 | 0.233 |
비교예 15 |
30.05 | 1.95 | 44 | 23 | 1 | 657 | 1063 | 0.62 | 16.3 | 108 | 0.240 |
F: 페라이트 B: 베이나이트 M: 마르텐사이트 R-A: 잔류 오스테나이트 YS: 항복강도 TS: 인장강도 El: 연신율 |
Claims (12)
- 중량%로, 탄소(C): 0.05~0.12%, 망간(Mn): 2.0~3.0%, 실리콘(Si): 0.5% 이하(0%는 제외), 크롬(Cr): 1.0% 이하(0%는 제외), 니오븀(Nb): 0.1% 이하(0%는 제외), 티타늄(Ti): 0.1% 이하(0%는 제외), 보론(B): 0.0025% 이하(0%는 제외), 알루미늄(sol.Al): 0.02~0.05%, 인(P): 0.05% 이하(0%는 제외), 황(S): 0.01% 이하(0%는 제외), 질소(N): 0.01% 이하(0%는 제외), 철(Fe) 및 기타 불가피한 불순물을 포함하고,미세조직으로 면적분율 35~50%의 페라이트 및 35~45%의 베이나이트와, 잔부 마르텐사이트를 포함하며, 상기 페라이트는 면적분율 8~15%의 미재결정 페라이트 및 27~35%의 재결정 페라이트로 이루어지는 것인 굽힘성 및 성형성이 우수한 고강도 강판.
- 제 1항에 있어서,상기 강판은 마르텐사이트 상을 면적분율 20% 이하(0% 제외)로 포함하는 굽힘성 및 성형성이 우수한 고강도 강판.
- 제 1항에 있어서,상기 강판은 잔류 오스테나이트 상을 면적분율 3% 이하(0% 포함)로 더 포함하는 굽힘성 및 성형성이 우수한 고강도 강판.
- 제 1항에 있어서,상기 강판은 인장강도 980MPa 이상, 항복강도 550~650MPa, 총 연신율 12% 이상인 굽힘성 및 성형성이 우수한 고강도 강판.
- 제 1항에 있어서,상기 강판은 3점 굽힘각이 90도 이상인 굽힘성 및 성형성이 우수한 고강도 강판.
- 제 1항에 있어서,상기 강판은 0.5~2.5mm의 두께를 가지는 굽힘성 및 성형성이 우수한 고강도 강판.
- 중량%로, 탄소(C): 0.05~0.12%, 망간(Mn): 2.0~3.0%, 실리콘(Si): 0.5% 이하(0%는 제외), 크롬(Cr): 1.0% 이하(0%는 제외), 니오븀(Nb): 0.1% 이하(0%는 제외), 티타늄(Ti): 0.1% 이하(0%는 제외), 보론(B): 0.0025% 이하(0%는 제외), 알루미늄(sol.Al): 0.02~0.05%, 인(P): 0.05% 이하(0%는 제외), 황(S): 0.01% 이하(0%는 제외), 질소(N): 0.01% 이하(0%는 제외), 철(Fe) 및 기타 불가피한 불순물을 포함하는 강 슬라브를 준비하는 단계;상기 강 슬라브를 1100~1300℃의 온도범위에서 가열하는 단계;상기 가열된 강 슬라브를 열간압연하여 열연강판을 제조하는 단계;상기 열연강판을 400~700℃의 온도범위에서 권취하는 단계;상기 권취 후 열연강판을 상온까지 냉각하는 단계;상기 냉각된 열연강판을 냉간압연하여 냉연강판을 제조하는 단계;상기 냉연강판을 연속소둔 처리하는 단계;상기 연속소둔 후 650~700℃의 온도범위까지 1~10℃/s의 평균 냉각속도로 1차 냉각하는 단계; 및상기 1차 냉각 후 300~580℃의 온도범위까지 5~50℃/s의 평균 냉각속도로 2차 냉각하는 단계를 포함하고,상기 냉간압연은 7 패스(pass) 이하로 행하며, 총 압하율이 55~70%인 것을 특징으로 하는 굽힘성 및 성형성이 우수한 고강도 강판의 제조방법.
- 제 7항에 있어서,상기 열간압연은 출구측 온도 Ar3 이상~1000℃ 이하에서 마무리 열간압연하는 것인 굽힘성 및 성형성이 우수한 고강도 강판의 제조방법.
- 제 7항에 있어서,상기 권취 후 냉각은 0.1℃/s 이하(0℃/s 제외)의 냉각속도로 행하는 것인 굽힘성 및 성형성이 우수한 고강도 강판의 제조방법.
- 제 7항에 있어서,상기 연속소둔은 가열대, 균열대 및 냉각대가 구비된 설비에서 행하며, 상기 가열대 및 균열대는 770~810℃의 온도범위로 제어되는 굽힘성 및 성형성이 우수한 고강도 강판의 제조방법.
- 제 7항에 있어서,상기 2차 냉각 후 과시효 처리하는 단계를 더 포함하며,상기 과시효 처리는 200~800초간 행하는 것인 굽힘성 및 성형성이 우수한 고강도 강판의 제조방법.
- 제 7항에 있어서,상기 열연강판의 두께가 4mm 이상일 때,상기 냉간압연은 리버싱 밀(reversing mill)을 이용하여 15~20 패스(pass)로 행하는 것인 굽힘성 및 성형성이 우수한 고강도 강판의 제조방법.
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CN202180084341.XA CN116601323A (zh) | 2020-12-14 | 2021-11-22 | 弯曲性和成型性优异的高强度钢板及其制造方法 |
JP2023535638A JP2023553164A (ja) | 2020-12-14 | 2021-11-22 | 曲げ性及び成形性に優れた高強度鋼板及びこの製造方法 |
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