KR20230030973A - Cold-rolled steel sheet with excellent plastic anisotropy and strength and method of manufacturing the same - Google Patents
Cold-rolled steel sheet with excellent plastic anisotropy and strength and method of manufacturing the same Download PDFInfo
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 53
- 238000004519 manufacturing process Methods 0.000 title claims description 24
- 239000011572 manganese Substances 0.000 claims abstract description 27
- 239000010936 titanium Substances 0.000 claims abstract description 25
- 239000010955 niobium Substances 0.000 claims abstract description 24
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 21
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 21
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 20
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 19
- 239000011574 phosphorus Substances 0.000 claims abstract description 19
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 16
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 15
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 15
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 15
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims abstract description 14
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 14
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052796 boron Inorganic materials 0.000 claims abstract description 14
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 14
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 14
- 239000011593 sulfur Substances 0.000 claims abstract description 14
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims abstract description 13
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- 239000010703 silicon Substances 0.000 claims abstract description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 8
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- 229910000831 Steel Inorganic materials 0.000 claims description 43
- 239000010959 steel Substances 0.000 claims description 43
- 238000000034 method Methods 0.000 claims description 22
- 239000000463 material Substances 0.000 claims description 20
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- 238000005098 hot rolling Methods 0.000 claims description 14
- 230000008569 process Effects 0.000 claims description 14
- 238000005097 cold rolling Methods 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 9
- 229910000859 α-Fe Inorganic materials 0.000 claims description 9
- 230000009467 reduction Effects 0.000 claims description 8
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- 238000005096 rolling process Methods 0.000 claims description 7
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- 230000000052 comparative effect Effects 0.000 description 7
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- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
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- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
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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
- 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
- C21D8/0273—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
- C22C38/02—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
- C22C38/06—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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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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Abstract
Description
본 발명은 냉연 강판 및 그 제조 방법에 관한 것으로서, 보다 상세하게는 소성이방성이 우수한 고강도 냉연 강판 및 그 제조 방법에 관한 것이다. The present invention relates to a cold-rolled steel sheet and a manufacturing method thereof, and more particularly, to a high-strength cold-rolled steel sheet excellent in plastic isotropy and a manufacturing method thereof.
자동차용 강판은 다양한 부품들의 복잡한 구조 특성상 높은 소성이방성을 갖는 강판이 요구된다. 또한 최근 환경문제를 개선하기 위한 자동차의 경량화가 진행 중이며, 이를 위해 고강도 소재 사용이 확대되고 있다. 자동차 부품 중 시트 쿠션 판넬은 난성형품이며, 이로 인해 높은 소성이방성과 고강도의 물성을 동시에 만족시키는 방향으로 연구가 진행되고 있다.Steel sheets for automobiles are required to have high plastic anisotropy due to the complex structural characteristics of various parts. In addition, the weight reduction of automobiles is currently in progress to improve environmental problems, and for this purpose, the use of high-strength materials is expanding. Among automobile parts, the seat cushion panel is a difficult-to-form product, and thus, research is being conducted in a direction that simultaneously satisfies high plastic isotropy and high-strength physical properties.
소성이방성 지수와 강도는 일반적으로 상반되는 물성이며, 동일한 소재에서 동시에 높은 물성을 나타내기는 어렵다. 또한, 고강도화 목적으로 첨가되는 인(P) 성분으로 인해 입계편석이 유발되어 2차 가공 취성문제가 발생된다.Plasticity isotropic index and strength are generally opposite physical properties, and it is difficult to simultaneously exhibit high physical properties in the same material. In addition, due to the phosphorus (P) component added for the purpose of strengthening, grain boundary segregation is induced, resulting in a problem of brittleness in secondary processing.
본 발명이 이루고자 하는 기술적 과제는 소성이방성이 우수하면서 동시에 강도가 높은 냉연 강판과 그 제조 방법을 제공하는 것이다.A technical problem to be achieved by the present invention is to provide a cold-rolled steel sheet having excellent plastic anisotropy and high strength at the same time, and a manufacturing method thereof.
상기 과제를 해결하기 위한 본 발명의 일 실시예에 따른 소성이방성이 우수한 고강도 냉연 강판은 탄소(C): 0.003 ~ 0.01중량%, 규소(Si): 0.05 ~ 0.3중량%, 망간(Mn): 1.0 ~ 2.0중량%, 인(P): 0.08 ~ 0.12중량%, 황(S): 0 초과 0.01중량% 이하, 알루미늄(Al): 0.01 ~ 0.06중량%, 니오븀(Nb): 0.003 ~ 0.02중량%, 티타늄(Ti): 0.04 ~ 0.08중량%, 붕소(B): 0.0005 ~ 0.002중량% 및 나머지 철(Fe)과 기타 불가피한 불순물을 포함하며, 소성이방성계수(r-value)가 1.4 ~ 3.0인 것을 특징으로 한다. A high-strength cold-rolled steel sheet with excellent plastic anisotropy according to an embodiment of the present invention for solving the above problems contains carbon (C): 0.003 to 0.01% by weight, silicon (Si): 0.05 to 0.3% by weight, manganese (Mn): 1.0 ~ 2.0 wt%, phosphorus (P): 0.08 ~ 0.12 wt%, sulfur (S): greater than 0 and less than 0.01 wt%, aluminum (Al): 0.01 ~ 0.06 wt%, niobium (Nb): 0.003 ~ 0.02 wt%, Titanium (Ti): 0.04 ~ 0.08% by weight, boron (B): 0.0005 ~ 0.002% by weight, and the rest iron (Fe) and other unavoidable impurities, characterized in that the plastic isotropy coefficient (r-value) is 1.4 ~ 3.0 to be
상기 소성이방성이 우수한 고강도 냉연 강판은 항복 강도(YS): 250 ~ 350MPa, 인장강도(TS): 445 ~ 600MPa이며, 연신율(El): 30 ~ 40%인 것을 특징으로 한다. The high-strength cold-rolled steel sheet having excellent plastic anisotropy is characterized in that yield strength (YS): 250 ~ 350 MPa, tensile strength (TS): 445 ~ 600 MPa, and elongation (El): 30 ~ 40%.
상기 소성이방성이 우수한 고강도 냉연 강판의 최종 미세 조직은 페라이트로 이루어질 수 있다. The final microstructure of the high-strength cold-rolled steel sheet having excellent plastic anisotropy may be made of ferrite.
상기 과제를 해결하기 위한 본 발명의 일 실시예에 따른 소성이방성이 우수한 고강도 냉연 강판의 제조 방법은 (a) 탄소(C): 0.003 ~ 0.01중량%, 규소(Si): 0.05 ~ 0.3중량%, 망간(Mn): 1.0 ~ 2.0중량%, 인(P): 0.08 ~ 0.12중량%, 황(S): 0 초과 0.01중량% 이하, 알루미늄(Al): 0.01 ~ 0.06중량%, 니오븀(Nb): 0.003 ~ 0.02중량%, 티타늄(Ti): 0.04 ~ 0.08중량%, 붕소(B): 0.0005 ~ 0.002중량% 및 나머지 철(Fe)과 기타 불가피한 불순물로 이루어진 강재를 제공하는 단계; (b) 상기 강재를 열간 압연하는 단계; (c) 상기 열간 압연된 강재에 대하여 냉간 압연하는 단계; 및 (d) 상기 냉간 압연된 강재에 대하여 소둔 및 냉각 공정을 순차적으로 수행하는 단계; 를 포함하며, 상기 냉연 강판의 소성이방성계수(r-value)는 1.4 ~ 3.0인 것을 특징으로 한다. Method for manufacturing a high-strength cold-rolled steel sheet having excellent plastic anisotropy according to an embodiment of the present invention for solving the above problems is (a) carbon (C): 0.003 to 0.01% by weight, silicon (Si): 0.05 to 0.3% by weight, Manganese (Mn): 1.0 to 2.0% by weight, phosphorus (P): 0.08 to 0.12% by weight, sulfur (S): more than 0 and 0.01% by weight or less, aluminum (Al): 0.01 to 0.06% by weight, niobium (Nb): Providing a steel material consisting of 0.003 to 0.02% by weight, titanium (Ti): 0.04 to 0.08% by weight, boron (B): 0.0005 to 0.002% by weight, and the rest iron (Fe) and other unavoidable impurities; (b) hot rolling the steel; (c) cold-rolling the hot-rolled steel material; And (d) sequentially performing an annealing and cooling process on the cold-rolled steel; Including, characterized in that the plastic isotropy coefficient (r-value) of the cold-rolled steel sheet is 1.4 to 3.0.
상기 소성이방성이 우수한 고강도 냉연 강판의 제조 방법에서, 상기 (d) 단계는 상기 강재에 대하여 820 ~ 850℃에서 소둔 열처리하는 단계; 를 포함할 수 있다. In the manufacturing method of the high-strength cold-rolled steel sheet having excellent plastic anisotropy, the step (d) is an annealing heat treatment at 820 to 850 ° C. for the steel; can include
상기 소성이방성이 우수한 고강도 냉연 강판의 제조 방법에서, 상기 (d) 단계는 상기 소둔 열처리된 강재에 대하여 400 ~ 600℃까지 3 ~ 20℃/s로 냉각하는 단계; 를 포함할 수 있다. In the method for manufacturing a high-strength cold-rolled steel sheet having excellent plastic anisotropy, the step (d) includes cooling the annealed steel material to 400 to 600 ° C at a rate of 3 to 20 ° C / s; can include
상기 소성이방성이 우수한 고강도 냉연 강판의 제조 방법에서, 상기 (b) 단계는 상기 강재를 1100 ~ 1300℃에서 재가열하는 단계; 상기 강재를 마무리 압연온도가 800 ~ 1000℃인 조건으로 열간 압연하는 단계; 상기 강재를 580 ~ 700℃에서 권취하는 단계;를 포함할 수 있다. In the method for manufacturing a high-strength cold-rolled steel sheet having excellent plastic anisotropy, the step (b) includes reheating the steel material at 1100 to 1300 ° C; Hot-rolling the steel material at a finish rolling temperature of 800 to 1000° C.; It may include; winding the steel material at 580 ~ 700 ℃.
상기 소성이방성이 우수한 고강도 냉연 강판의 제조 방법에서, 상기 (c) 단계는 상기 강재를 50 ~ 90%의 압하율로 냉간 압연하는 단계를 포함할 수 있다. In the manufacturing method of the high-strength cold-rolled steel sheet having excellent plastic anisotropy, the step (c) may include cold-rolling the steel at a reduction ratio of 50 to 90%.
본 발명의 실시예에 따르면, 소성이방성이 우수하면서 동시에 강도가 높은 냉연 강판과 그 제조 방법을 구현할 수 있다. 물론 이러한 효과에 의해 본 발명의 범위가 한정되는 것은 아니다.According to an embodiment of the present invention, a cold-rolled steel sheet having excellent plastic isotropy and high strength and a method for manufacturing the same can be implemented. Of course, the scope of the present invention is not limited by these effects.
도 1은 본 발명의 일 실시예에 따르는 소성이방성이 우수한 고강도 냉연 강판의 제조 방법을 개략적으로 나타내는 순서도이다.
도 2는 온도에 따른 오스테나이트 분율을 나타낸 그래프이다.
도 3은 본 발명의 실험예로서 소성이방성 관련 특성값의 결과를 나타낸 그래프이다. 1 is a flowchart schematically illustrating a method for manufacturing a high-strength cold-rolled steel sheet having excellent plastic anisotropy according to an embodiment of the present invention.
2 is a graph showing the austenite fraction as a function of temperature.
3 is a graph showing the results of characteristic values related to plastic anisotropy as an experimental example of the present invention.
본 발명의 일 실시예에 따른 냉연 강판 및 그 제조 방법을 상세하게 설명한다. 후술되는 용어들은 본 발명에서의 기능을 고려하여 적절하게 선택된 용어들로서, 이러한 용어들에 대한 정의는 본 명세서 전반에 걸친 내용을 토대로 내려져야 할 것이다. A cold-rolled steel sheet and a manufacturing method thereof according to an embodiment of the present invention will be described in detail. Terms to be described later are terms appropriately selected in consideration of functions in the present invention, and definitions of these terms should be made based on the contents throughout this specification.
이하에서는 소성이방성계수(r-value)가 1.4 ~ 3.0이며, 항복 강도(YS): 250 ~ 350MPa, 인장강도(TS): 445 ~ 600MPa이며, 연신율(El): 30 ~ 40%인 것을 특징으로 하는 소성이방성이 우수한 고강도 냉연 강판 및 그 제조 방법의 구체적인 내용을 제공하고자 한다. Hereinafter, the plastic isotropy coefficient (r-value) is 1.4 to 3.0, yield strength (YS): 250 to 350 MPa, tensile strength (TS): 445 to 600 MPa, and elongation (El): 30 to 40% It is intended to provide specific details of a high-strength cold-rolled steel sheet having excellent plastic anisotropy and a manufacturing method thereof.
강판steel plate
본 발명의 일 실시예에 따르는 냉연 강판은 탄소(C): 0.003 ~ 0.01중량%, 규소(Si): 0.05 ~ 0.3중량%, 망간(Mn): 1.0 ~ 2.0중량%, 인(P): 0.08 ~ 0.12중량%, 황(S): 0 초과 0.01중량% 이하, 알루미늄(Al): 0.01 ~ 0.06중량%, 니오븀(Nb): 0.003 ~ 0.02중량%, 티타늄(Ti): 0.04 ~ 0.08중량%, 붕소(B): 0.0005 ~ 0.002중량% 및 나머지 철(Fe)과 기타 불가피한 불순물로 이루어진다. 이하에서는, 상기 냉연 강판에 포함되는 각 성분의 역할 및 함량에 대하여 설명한다.In the cold-rolled steel sheet according to an embodiment of the present invention, carbon (C): 0.003 to 0.01% by weight, silicon (Si): 0.05 to 0.3% by weight, manganese (Mn): 1.0 to 2.0% by weight, phosphorus (P): 0.08 ~ 0.12% by weight, sulfur (S): greater than 0 and less than 0.01% by weight, aluminum (Al): 0.01 to 0.06% by weight, niobium (Nb): 0.003 to 0.02% by weight, titanium (Ti): 0.04 to 0.08% by weight, Boron (B): 0.0005 to 0.002% by weight and the balance consists of iron (Fe) and other unavoidable impurities. Hereinafter, the role and content of each component included in the cold-rolled steel sheet will be described.
탄소(C)carbon (C)
탄소(C)는 강의 강도를 확보하기 위하여 첨가하며, 탄소 함량이 증가할수록 강도가 증가한다. 한 구체예에서 상기 탄소(C)는 냉연 강판 전체 중량에 대하여 0.003 ~ 0.01중량% 포함된다. 상기 탄소의 첨가량이 0.003중량% 미만인 경우 강도를 확보하기 어렵고, 상기 탄소가 0.01중량% 초과 시 강도는 증가하나, 용접성에 불리하며 가공성 및 굽힘성 등이 크게 저하될 수 있다.Carbon (C) is added to secure strength of steel, and strength increases as the carbon content increases. In one embodiment, the carbon (C) is included in an amount of 0.003 to 0.01% by weight based on the total weight of the cold-rolled steel sheet. When the amount of carbon added is less than 0.003% by weight, it is difficult to secure strength, and when the amount of carbon exceeds 0.01% by weight, strength increases, but weldability is disadvantageous, and workability and bendability may be greatly reduced.
규소(Si)Silicon (Si)
규소(Si)는 페라이트 안정화 원소로서 페라이트 내 탄화물의 형성을 지연시키며, 고용 강화 효과가 있다. 규소는 냉연 강판 전체 중량에 대하여 0.05 ~ 0.3중량%로 첨가되는 것이 바람직하며 0.05중량% 미만일 경우 탄화물 형성 억제 효과를 제대로 발휘할 수 없고 연신율 확보가 어려우며, 0.3중량%를 초과하는 경우 제조 과정에서 Mn2SiO4등 산화물을 형성하여 강판 도금성이 저해되고, 외관 표면이 저하되며, 탄소 당량을 높여 용접성을 저하시킬 수 있다.Silicon (Si), as a ferrite stabilizing element, delays the formation of carbides in ferrite and has a solid solution strengthening effect. Silicon is preferably added in an amount of 0.05 to 0.3% by weight based on the total weight of the cold-rolled steel sheet. If it is less than 0.05% by weight, the effect of inhibiting carbide formation cannot be properly exerted and it is difficult to secure elongation, and if it exceeds 0.3% by weight, Mn 2 By forming oxides such as SiO 4 , plating properties of the steel sheet are impaired, the appearance surface is deteriorated, and weldability may be reduced by increasing the carbon equivalent.
망간(Mn)Manganese (Mn)
망간(Mn)은 고용 강화 효과가 있고 소입성을 증대시켜 강도 향상에 기여 한다. 즉, 망간은 저온 변태상의 형성을 용이하게 하며 고용 강화로 강도를 상승시키는 효과를 제공하는 원소이다. 망간의 일부는 강 속에 고용되며 일부는 강중에 함유된 황과 결합하여 비금속개재물인 MnS를 형성하는데 이 MnS는 연성이 있어서 소성 가공 시 가공 방향으로 길게 연신된다. 그러나 MnS의 형성으로 강 속에 있는 황 성분이 감소하면서 결정립이 취약해지고 저융점화합물인 FeS의 형성을 억제시킨다. 강의 내산성과 내산화성을 저해하지만 펄라이트가 미세해지고 페라이트를 고용 강화시킴으로써 항복 강도를 향상시킨다. 망간은 냉연 강판 전체 중량에 대하여 1.0 ~ 2.0중량%로 첨가되는 것이 바람직하다. 망간의 함량이 1.0중량% 미만일 경우 그 효과가 충분하지 않아 강도 확보가 어려우며, 2.0중량%를 초과하는 경우 연주 슬라브 및 강판의 내외부의 편석대가 형성되며, 크랙의 발생과 전파를 유발하여 가공성이 저하되는 문제점이 나타나며, MnS등 개재물의 형성이나 편석으로 인한 지연 파괴 저항성이 저하되고 탄소 당량을 높여 용접성을 저하시킬 수 있다.Manganese (Mn) has a solid solution strengthening effect and contributes to strength improvement by increasing hardenability. That is, manganese is an element that facilitates the formation of a low-temperature transformation phase and provides an effect of increasing strength through solid solution strengthening. Some of manganese is dissolved in steel and some is combined with sulfur contained in steel to form MnS, which is a non-metallic inclusion. This MnS is ductile and elongates in the processing direction during plastic processing. However, the formation of MnS reduces the sulfur component in the steel, making the crystal grains brittle and suppressing the formation of FeS, a low melting point compound. It inhibits the acid resistance and oxidation resistance of steel, but improves yield strength by making pearlite finer and strengthening ferrite by solid solution. Manganese is preferably added in an amount of 1.0 to 2.0% by weight based on the total weight of the cold-rolled steel sheet. If the content of manganese is less than 1.0% by weight, the effect is not sufficient, making it difficult to secure strength. There is a problem of deterioration, delayed fracture resistance due to formation or segregation of inclusions such as MnS is lowered, and weldability can be reduced by increasing the carbon equivalent.
인(P)Phosphorus (P)
인(P)은 고용 강화에 의해 강도의 강도를 높이며, 탄화물의 형성을 억제하는 기능을 수행할 수 있다. 상기 인은 냉연 강판 전체 중량에 대하여 0.08 ~ 0.12중량%의 함량비로 첨가될 수 있다. 인의 첨가 시에 고용 강화 의해 강도의 향상에 도움을 줄 수는 있지만, 인의 함량이 0.08중량% 미만인 경우 강도 확보가 어려우며, 0.12중량%를 초과하는 경우에는 결정립계 및 상간 입계에 편석되어 용접부가 취화되며 저온취성이 유발되며 프레스 성형성이 저하되고 충격 저항을 저하시키는 문제가 발생할 수 있다. Phosphorus (P) can increase the strength by solid solution strengthening and suppress the formation of carbides. The phosphorus may be added in a content ratio of 0.08 to 0.12% by weight based on the total weight of the cold-rolled steel sheet. When phosphorus is added, it can help improve strength by solid solution strengthening, but if the phosphorus content is less than 0.08% by weight, it is difficult to secure strength, and if it exceeds 0.12% by weight, it is segregated at grain boundaries and interphase grain boundaries, resulting in brittle welds. Low-temperature brittleness may be induced, press formability may be deteriorated, and impact resistance may be deteriorated.
황(S)Sulfur (S)
황(S)은 망간, 티타늄 등과 결합하여 강의 피삭성을 개선시키며 미세 MnS의 석출물을 형성하여 가공성을 향상시킬 수 있으나, 일반적으로 연성 및 용접성을 저해하는 원소이다. 상기 황은 냉연 강판 전체 중량에 대하여 0 초과 0.01중량% 이하의 함량비로 첨가될 수 있다. 황의 함량이 0.01중량%를 초과할 경우, MnS 개재물 수가 증가하여 가공성 및 용접성이 열위되며, 연속 주조 응고 중에 편석되어 고온 크랙이 발생하는 문제점이 발생할 수 있다. Sulfur (S) can combine with manganese, titanium, etc. to improve the machinability of steel and form precipitates of fine MnS to improve workability, but is an element that generally inhibits ductility and weldability. The sulfur may be added in a content ratio of more than 0 and less than 0.01% by weight based on the total weight of the cold-rolled steel sheet. When the sulfur content exceeds 0.01% by weight, the number of MnS inclusions increases, resulting in poor workability and weldability, and segregation during continuous casting solidification may cause high-temperature cracks.
알루미늄(Al)Aluminum (Al)
알루미늄(Al)은 탈산제로 주로 사용하는 원소로서, 페라이트 형성을 촉진하며 연신율을 향상시키며, 탄화물 형성을 억제하고, 오스테나이트 내 탄소 농화량을 증진하여 오스테나이트를 안정화시킨다. 또한, 알루미늄은 열연 코일 내 망간 밴드의 형성을 억제하는데 효과적인 원소이다. 상기 알루미늄(Al)은 냉연 강판 전체 중량에 대하여 0.01 ~ 0.06중량%의 함량비로 첨가되는 것이 바람직하다. 알루미늄(Al)의 함량이 0.01중량% 미만일 경우에는 상술한 알루미늄 첨가 효과를 제대로 발휘할 수 있다. 반대로, 알루미늄(Al)의 함량이 0.06중량%를 초과하여 과다 첨가될 경우에는 알루미늄 개재물이 증가하여 연주성을 저하시키며 강판의 표면에 농화되어 도금성이 저하되고 슬라브 내 AlN을 형성하여 주조 또는 열연 중 크랙을 유발하는 문제점이 있다.Aluminum (Al) is an element mainly used as a deoxidizer, promotes ferrite formation, improves elongation, suppresses carbide formation, and promotes carbon concentration in austenite to stabilize austenite. In addition, aluminum is an element effective in suppressing the formation of manganese bands in hot-rolled coils. The aluminum (Al) is preferably added in a content ratio of 0.01 to 0.06% by weight based on the total weight of the cold-rolled steel sheet. When the content of aluminum (Al) is less than 0.01% by weight, the above-described effect of adding aluminum may be properly exhibited. Conversely, when the content of aluminum (Al) exceeds 0.06% by weight and is excessively added, aluminum inclusions increase, degrading playability, concentrating on the surface of the steel sheet, degrading plating properties, and forming AlN in the slab for casting or hot rolling There is a problem that causes cracks in the middle.
니오븀(Nb)Niobium (Nb)
니오븀(Nb)은 NbC 탄화물을 형성하여 고용탄소를 제거하며, 소성이방성 지수 향상시키는 원소이다. 비시효성 확보 및 성형성 향상을 목적으로 첨가한다. 니오븀은 강력한 탄화물 생성 원소로 강중에 첨가되어 NbC석출물을 석출시켜 고용 상태의 탄소를 석출함으로써 비시효성을 확보한다. 또한 NbC석출물은 소둔중 집합조직을 발달하게 하여 오무림 가공성을 크게 향상하는 효과가 있다. 니오븀의 첨가량이 0.003중량% 미만인 경우 소성이방성 지수 확보가 불가하며 NbC석출물의 석출량이 너무 적어 집합조직의 발달이 적어 오무림 가공성을 개선하는 효과가 거의 없다. 니오븀이 0.02중량%를 초과할 경우 {111} 집합조직 발달이 저하되며 NbC석출물의 양이 너무 많아 오무림가공성 및 연신율이 낮아져 성형성이 크게 저하될 수 있다.Niobium (Nb) is an element that forms NbC carbide to remove solid solution carbon and improve the plastic anisotropy index. It is added for the purpose of securing non-aging properties and improving moldability. Niobium is a strong carbide-generating element that is added to steel to precipitate NbC precipitates to precipitate carbon in solid solution to secure non-aging properties. In addition, the NbC precipitate has the effect of greatly improving the workability of trimming by developing the texture during annealing. If the amount of niobium added is less than 0.003% by weight, it is impossible to secure the plasticity anisotropy index, and the amount of NbC precipitate is too small, so the development of the texture is small, and there is little effect of improving workability. When the amount of niobium exceeds 0.02% by weight, the development of {111} texture is deteriorated, and the amount of NbC precipitates is too large, so that trimming workability and elongation are lowered, resulting in greatly reduced formability.
티타늄(Ti)Titanium (Ti)
티타늄(Ti)은 TiC 탄화물을 형성하여 고용탄소를 제거하며, 소성이방성 지수 향상시키는 원소이다. 비시효성 확보 및 성형성 향상을 목적으로 첨가하는데 티타늄은 강력한 탄화물 생성 원소로 강중에 첨가되어 TiC석출물을 석출시켜 고용 상태의 탄소를 석출하므로써 비시효성을 확보한다. 티타늄의 첨가량이 0.04중량% 미만의 경우 소성이방성 지수 확보가 불가하며 TiC석출물의 석출량이 너무 적어 집합조직의 발달이 적어 오무림 가공성을 개선하는 효과가 거의 없다. 티타늄이 0.08중량%를 초과할 경우 {111} 집합조직 발달이 저하되며 TiC석출물의 크기 너무 커 결정립미세화 효과가 감소되어 면내이방성지수가 높아지며 항복강도도 저하하고 도금특성이 크게 저하한다.Titanium (Ti) is an element that forms TiC carbide to remove solid solution carbon and improve the plastic anisotropy index. It is added for the purpose of ensuring non-aging and improving formability. Titanium is added to steel as a strong carbide generating element to precipitate TiC precipitates to precipitate carbon in a solid solution, thereby securing non-aging. If the addition amount of titanium is less than 0.04% by weight, it is impossible to secure the plastic anisotropy index, and the amount of TiC precipitate is too small, and the development of the texture is small, so there is little effect of improving the rim workability. When titanium exceeds 0.08% by weight, the development of {111} texture is reduced, and the size of TiC precipitates is too large, so the grain refinement effect is reduced, the in-plane anisotropy index is increased, the yield strength is also lowered, and the plating characteristics are greatly deteriorated.
붕소(B)Boron (B)
붕소(B)는 인(P)의 입계편석을 막아 강도를 향상시키는 역할을 한다. 만일, 인(P)의 편석이 발생할 경우에는 2차 가공 취성이 발생할 수 있으므로, 붕소를 첨가하여 인(P)의 편석을 막아 가공 취성에 대한 저항성을 증가시킨다. 상기 붕소는 냉연 강판 전체 중량에 대하여 5 ~ 20ppm(0.0005 ~ 0.002중량%)의 함량비로 첨가되는 것이 바람직하다. 붕소의 함량이 5 ppm 미만일 경우 상술한 효과가 불충분하여 취성억제가 불가하며, 0.003중량%를 초과하여 과다 첨가될 경우에는 인성이 저하되고 용접성이 저하되며 붕소 산화물의 형성으로 강의 표면 품질을 저해하는 문제를 유발할 수 있다.Boron (B) serves to improve strength by preventing grain boundary segregation of phosphorus (P). If segregation of phosphorus (P) occurs, secondary processing brittleness may occur, so boron is added to prevent segregation of phosphorus (P) to increase resistance to processing brittleness. The boron is preferably added in a content ratio of 5 to 20 ppm (0.0005 to 0.002% by weight) based on the total weight of the cold-rolled steel sheet. If the boron content is less than 5 ppm, the above-mentioned effect is insufficient and brittle suppression is not possible, and if it is added in excess of 0.003% by weight, toughness and weldability deteriorate, and boron oxide is formed, which impairs the surface quality of the steel. can cause problems.
상술한 바와 같은, 합금 원소 조성을 가지는 본 발명의 일 실시예에 따른 냉연 강판은 항복 강도 1400MPa 이상, 인장강도 1760MPa 이상, 연신율 5% 이상을 가지며, 90도 굽힘 기준 R/t 2.5 이하의 우수한 굽힘 가공성을 가질 수 있다. 예를 들어, 상기 냉연 강판은 항복 강도(YS): 1400 ~ 1760MPa, 인장강도(TS): 1760 ~ 1900MPa이며, 연신율(El): 5 ~ 8%, 굽힘 가공성(R/t): 1.5 ~ 2.5일 수 있다. As described above, the cold-rolled steel sheet according to one embodiment of the present invention having an alloy element composition has a yield strength of 1400 MPa or more, a tensile strength of 1760 MPa or more, an elongation of 5% or more, and excellent bending workability of R/t 2.5 or less based on 90 degree bending. can have For example, the cold-rolled steel sheet has yield strength (YS): 1400 to 1760 MPa, tensile strength (TS): 1760 to 1900 MPa, elongation (El): 5 to 8%, bending workability (R/t): 1.5 to 2.5 can be
상술한 바와 같은 합금 원소 조성을 가지는 본 발명의 일 실시예에 따른 상기 냉연 강판은 소성이방성계수(r-value)가 1.4 ~ 3.0이며, 동시에, 항복 강도(YS): 250 ~ 350MPa, 인장강도(TS): 445 ~ 600MPa이며, 연신율(El): 30 ~ 40%일 수 있다. The cold-rolled steel sheet according to an embodiment of the present invention having the alloy element composition as described above has a plastic isotropy coefficient (r-value) of 1.4 to 3.0, and at the same time, yield strength (YS): 250 to 350 MPa, tensile strength (TS ): 445 to 600 MPa, and elongation (El): may be 30 to 40%.
상술한 바와 같은 합금 원소 조성을 가지는 본 발명의 일 실시예에 따른 상기 냉연 강판은 최종 미세 조직이 전부 페라이트로 이루어질 수 있다. The cold-rolled steel sheet according to an embodiment of the present invention having the alloy element composition as described above may have a final microstructure made entirely of ferrite.
이하에서는 상술한 조성과 미세 조직을 가지는 본 발명의 일 실시예에 따른 냉연 강판의 제조 방법을 설명한다. Hereinafter, a method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention having the above-described composition and microstructure will be described.
냉연 강판의 제조 방법Manufacturing method of cold-rolled steel sheet
도 1은 본 발명의 일 실시예에 따르는 소성이방성이 우수한 고강도 냉연 강판의 제조 방법을 개략적으로 나타내는 순서도이다.1 is a flowchart schematically illustrating a method for manufacturing a high-strength cold-rolled steel sheet having excellent plastic anisotropy according to an embodiment of the present invention.
도 1을 참조하면, 본 발명의 일 실시예에 따르는 소성이방성이 우수한 고강도 냉연 강판의 제조 방법은 (a) 탄소(C): 0.003 ~ 0.01중량%, 규소(Si): 0.05 ~ 0.3중량%, 망간(Mn): 1.0 ~ 2.0중량%, 인(P): 0.08 ~ 0.12중량%, 황(S): 0 초과 0.01중량% 이하, 알루미늄(Al): 0.01 ~ 0.06중량%, 니오븀(Nb): 0.003 ~ 0.02중량%, 티타늄(Ti): 0.04 ~ 0.08중량%, 붕소(B): 0.0005 ~ 0.002중량% 및 나머지 철(Fe)과 기타 불가피한 불순물로 이루어진 강재를 제공하는 단계(S10); (b) 상기 강재를 열간 압연하는 단계(S20); (c) 상기 열간 압연된 강재에 대하여 냉간 압연하는 단계(S30); 및 (d) 상기 냉간 압연된 강재에 대하여 소둔 및 냉각 공정을 순차적으로 수행하는 단계(S40); 를 포함한다.Referring to FIG. 1, a method for manufacturing a high-strength cold-rolled steel sheet having excellent plastic anisotropy according to an embodiment of the present invention includes (a) carbon (C): 0.003 to 0.01% by weight, silicon (Si): 0.05 to 0.3% by weight, Manganese (Mn): 1.0 to 2.0% by weight, phosphorus (P): 0.08 to 0.12% by weight, sulfur (S): more than 0 and 0.01% by weight or less, aluminum (Al): 0.01 to 0.06% by weight, niobium (Nb): Providing a steel material consisting of 0.003 to 0.02% by weight, titanium (Ti): 0.04 to 0.08% by weight, boron (B): 0.0005 to 0.002% by weight, and the rest iron (Fe) and other unavoidable impurities (S10); (b) hot-rolling the steel material (S20); (c) cold-rolling the hot-rolled steel material (S30); And (d) sequentially performing an annealing and cooling process on the cold-rolled steel material (S40); includes
상기 (b) 단계(S20)는 상기 강재를 1100 ~ 1300℃에서 재가열(Reheating)하는 단계를 포함할 수 있다. 예를 들어, 슬라브는 제강 공정을 통해 얻은 용강을 연속 주조하여 반제품 형태로 제조되고, 재가열 공정을 통하여 주조 공정에서 발생한 성분 편석을 균질화하고, 열간 압연할 수 있는 상태로 만든다. The (b) step (S20) may include a step of reheating (Reheating) the steel at 1100 ~ 1300 ℃. For example, the slab is manufactured in the form of a semi-finished product by continuously casting molten steel obtained through a steelmaking process, homogenizes component segregation generated in the casting process through a reheating process, and makes it into a state that can be hot rolled.
슬라브 재가열 온도(Slab Reheating Temperature, SRT)가 1100℃ 미만이면, 슬라브의 편석이 충분히 재고용 되지 못하는 문제가 있고, 재가열 온도가 낮아 연속주조 중에 생성된 조대한 석출물들이 완전히 용해되지 않은 상태로 남아 있어 열간 압연후에도 조대한 석출물이 많이 남아 있는 문제가 있다. 한편, 재가열 온도가 1300℃를 초과하면 오스테나이트 결정립의 크기가 증가하며, 공정 비용이 상승할 수 있다. If the slab reheating temperature (SRT) is less than 1100 ° C, there is a problem in that the segregation of the slab is not sufficiently re-dissolved, and the coarse precipitates generated during continuous casting remain in a state that is not completely dissolved due to the low reheating temperature. There is a problem that many coarse precipitates remain even after rolling. Meanwhile, when the reheating temperature exceeds 1300° C., the size of austenite grains increases, and process costs may increase.
상기 (b) 단계(S20)는 상기 재가열된 슬라브를 열간 압연(HR)하는 단계를 포함한다. 열간 압연은 800 ~ 1000℃의 마무리 압연온도(Finish Delivery Temperature, FDT)로 열간 압연한다. The step (b) (S20) includes hot rolling (HR) the reheated slab. Hot rolling is hot rolling at a finish delivery temperature (FDT) of 800 ~ 1000 ℃.
마무리 압연온도가 800℃보다 낮아지면 압연 부하가 급격히 증가하여 생산성이 저하되고, 1000℃를 초과하는 경우 결정립의 크기가 증가하여 강도가 감소할 수 있다. 열간 압연은 마무리 압연온도를 Ar3 변태온도 이상의 조건에서 행하는 것이 바람직하다. 마무리 압연온도가 Ar3 변태온도 미만의 경우에는 압연립의 생성으로 가공성이 저하할 뿐만 아니라 강도도 낮아지기 때문이다.When the finish rolling temperature is lower than 800 ° C., the rolling load increases rapidly and productivity decreases, and when it exceeds 1000 ° C., the strength may decrease due to the increase in the size of grains. Hot rolling is preferably carried out under conditions of a finish rolling temperature equal to or higher than the Ar3 transformation temperature. This is because when the finish rolling temperature is lower than the Ar3 transformation temperature, not only workability is lowered due to generation of rolled grains, but also strength is lowered.
열간 압연 후에 10 ~ 100℃/s의 냉각 속도로 580 ~ 700℃의 온도까지 냉각한 후 권취한다. 권취 온도가 580℃ 미만이면 열연 코일의 형상을 불균일하게 하고 냉간 압연 부하가 증가하고, 700℃를 초과하는 경우 강판의 중심부와 엣지부의 냉각 속도 차이에 의한 불균일 미세 조직을 야기하며, 입계 내부가 산화되는 문제점이 발생할 수 있으며, 표면 산화 등으로 후공정에서 불량을 일으킬 수 있다.After hot rolling, it is cooled to a temperature of 580 ~ 700 ℃ at a cooling rate of 10 ~ 100 ℃ / s, and then wound up. If the coiling temperature is less than 580 ° C, the shape of the hot-rolled coil becomes non-uniform and the cold rolling load increases, and if it exceeds 700 ° C, a non-uniform microstructure is caused due to the difference in cooling rate between the center and the edge of the steel sheet, and the inside of the grain boundary is oxidized. problems may occur, and defects may be caused in the subsequent process due to surface oxidation.
본 발명에 따라 높은 소성이방성을 갖기 위해서는 {111}//ND 집합조직을 증가시키는 것이 중요하다. 권취 온도를 상향할수록 높은 소성이방성을 가질 수 있으나, 권취 온도가 700℃를 초과하는 경우에는 석출물이 너무 조대하게 성장하여 강도 확보가 어렵다.In order to have high plastic anisotropy according to the present invention, it is important to increase the {111}//ND texture. As the coiling temperature increases, it may have high plastic anisotropy, but when the coiling temperature exceeds 700° C., the precipitate grows too coarsely, making it difficult to secure strength.
열간 압연 후 강재의 미세 조직은 페라이트로 이루어질 수 있으며, 열간 압연의 압하율은 70% 이상일 수 있다.After hot rolling, the microstructure of the steel material may be made of ferrite, and the reduction ratio of hot rolling may be 70% or more.
상기 (c) 단계(S30)는 상기 열간 압연된 강재에 대하여 냉간 압연(CR)하는 단계를 포함한다. 상기 열연 코일을 산세하여 표면 스케일층을 제거하고, 냉간 압연을 실시한다. 냉간 압연 시 두께 압하율은 대략 50 ~ 90%이다.The step (c) (S30) includes performing cold rolling (CR) on the hot-rolled steel material. The hot-rolled coil is pickled to remove the surface scale layer, and then cold-rolled. The thickness reduction rate during cold rolling is approximately 50 to 90%.
냉간 압연 후 압연 조직은 1차 소둔 과정에서 재결정의 구동력이 된다. 일반적인 IF(Interstitial Free) 극저탄소강에서는 냉간 압하율 증가에 따라 {111 }//ND 집합조직이 발달하고, 이에 따라 소성이방성이 증가한다. 하지만, 냉간 압하율이 90%를 초과하는 경우에는 성형성은 향상되지만 핵생성 양이 너무 많아 소둔 재결정립은 오히려 너무 미세하여 연성이 저하된다. 냉간 압하율이 50% 미만의 경우에는 소둔재결정 핵생성양이 적기 때문에 소둔시 결정립이 너무 크게 성장하여 소둔 재결정립의 조대화로 강도 및 소성이방성이 저하한다. 따라서 냉간 압하율은 50 ~ 90%범위가 바람직하다. After cold rolling, the rolled tissue becomes a driving force for recrystallization in the primary annealing process. In general IF (Interstitial Free) ultra-low carbon steel, {111 }//ND texture develops as the cold reduction ratio increases, and plastic anisotropy increases accordingly. However, when the cold reduction ratio exceeds 90%, formability is improved, but the amount of nucleation is too large, and the annealed recrystallized grains are rather too fine, resulting in reduced ductility. When the cold reduction ratio is less than 50%, since the amount of annealed recrystallized nuclei is small, grains grow too large during annealing, and strength and plasticity are reduced due to coarsening of the annealed recrystallized grains. Therefore, the cold reduction ratio is preferably in the range of 50 to 90%.
상기 (d) 단계(S40)는 상기 냉간 압연된 강재에 대하여 소둔 및 냉각 공정을 순차적으로 수행하는 단계를 포함한다. The step (d) (S40) includes sequentially performing an annealing and cooling process on the cold-rolled steel material.
상기 소둔 공정은 상기 강재에 대하여 820 ~ 850℃에서 소둔 열처리하는 단계; 및 상기 소둔 열처리된 강재에 대하여 400 ~ 600℃까지 3 ~ 20℃/s로 냉각하는 단계; 를 포함할 수 있다. The annealing process comprises the steps of annealing heat treatment at 820 ~ 850 ℃ with respect to the steel; and cooling the annealed steel to 400 to 600 °C at a rate of 3 to 20 °C/s; can include
도 2는 온도에 따른 오스테나이트 분율을 나타낸 그래프이다. 2 is a graph showing the austenite fraction as a function of temperature.
도 2를 함께 참조하면, 본 발명에서 소둔 공정은 강재의 성형성을 확보하는 공정으로 집합조직 발달에 기여하는 공정이다. 본 실시예에서는 820 ~ 850℃의 온도 범위에서 수행하는 것이 바람직하다. 소둔 온도가 820℃ 미만의 경우에는 재결정이 완료되지 않아 목표로 하는 연성 값을 확보할 수 없으며, 소둔 온도가 850℃를 초과하는 경우에는 재결정립의 조대화로 강도가 저하된다. 소둔 시간은 재결정이 완료되도록 유지하는데, 약 10초 이상이면 재결정이 완료된다. 일반적으로 소둔 시간은 10초 ~ 30분의 범위 내로 수행하는 것이 바람직하다.Referring to FIG. 2 together, the annealing process in the present invention is a process contributing to the development of texture as a process for securing the formability of steel. In this embodiment, it is preferable to carry out in the temperature range of 820 ~ 850 ℃. When the annealing temperature is less than 820 ° C., recrystallization is not completed and the target ductility value cannot be secured, and when the annealing temperature exceeds 850 ° C., the strength is reduced due to coarsening of recrystallized grains. The annealing time maintains recrystallization to be completed, and recrystallization is completed if it is about 10 seconds or more. In general, the annealing time is preferably performed within the range of 10 seconds to 30 minutes.
상술한 (a) 단계 내지 (d) 단계를 수행한 결과 구현된 소성이방성이 우수한 고강도 냉연 강판은 소성이방성계수(r-value)가 1.4 ~ 3.0이며, 항복 강도(YS): 250 ~ 350MPa, 인장강도(TS): 445 ~ 600MPa이며, 연신율(El): 30 ~ 40%일 수 있으며, 최종 미세 조직은 페라이트로 이루어진다. The high-strength cold-rolled steel sheet having excellent plastic anisotropy as a result of performing the above steps (a) to (d) has a plastic isotropic coefficient (r-value) of 1.4 to 3.0, yield strength (YS): 250 to 350 MPa, tensile Strength (TS): 445 to 600 MPa, elongation (El): may be 30 to 40%, and the final microstructure is made of ferrite.
소성이방성 지수와 강도는 일반적으로 상반되는 물성이며, 동일한 소재에서 동시에 높은 물성을 나타내기는 어렵다. 또한, 고강도화 목적으로 첨가되는 인(P) 성분으로 인해 입계편석이 유발되어 2차 가공 취성문제가 발생된다.Plasticity isotropic index and strength are generally opposite physical properties, and it is difficult to simultaneously exhibit high physical properties in the same material. In addition, due to the phosphorus (P) component added for the purpose of strengthening, grain boundary segregation is induced, resulting in a problem of brittleness in secondary processing.
본 발명의 일 실시예에 따른 소성이방성이 우수한 고강도 냉연 강판 및 그 제조 방법에 의하면, 극저탄소강에 Nb와 Ti를 첨가함으로서 소성이방성을 확보하고, 동시에 P와 Si 첨가를 통해 고용강화강의 한계에 이르는 인장강도 440MPa급 이상 시트 쿠션 판넬용 고강도 냉연강판 제품을 제공할 수 있다. According to the high-strength cold-rolled steel sheet having excellent plastic anisotropy and its manufacturing method according to an embodiment of the present invention, plastic anisotropy is secured by adding Nb and Ti to ultra-low carbon steel, and at the same time, through the addition of P and Si, the limit of solid-solution tempered steel is reached. It is possible to provide high-strength cold-rolled steel sheet products for seat cushion panels with a tensile strength of up to 440 MPa or higher.
실험예Experimental example
이하 본 발명의 이해를 돕기 위해 바람직한 실험예를 제시한다. 다만, 다음의 실험예는 본 발명의 이해를 돕기 위한 것일 뿐, 본 발명이 다음의 실험예에 의해 한정되는 것은 아니다. Hereinafter, preferred experimental examples are presented to aid understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited by the following experimental examples.
1. 시편의 조성 및 공정 조건1. Composition of specimen and processing conditions
표 1은 본 실험예의 시편들의 합금 원소 조성(단위: 중량%, 단, 붕소(B)의 단위는 ppm)을 나타낸다. 나아가, CT 항목은 권취 온도(℃), SS 항목은 소둔 온도(℃)를 나타낸다. 본 실험예에서 그 외의 공정 조건은 앞에서 설명한 공정 조건 범위 내에서 적용하였다. Table 1 shows the alloy element composition (unit: wt%, but the unit of boron (B) is ppm) of the specimens of this experimental example. Furthermore, the CT item represents the coiling temperature (° C.), and the SS item represents the annealing temperature (° C.). In this experimental example, other process conditions were applied within the process condition range described above.
표 1을 참조하면, 실험예1 내지 실험예3은 본 발명의 실시예로서, 탄소(C): 0.003 ~ 0.01중량%, 규소(Si): 0.05 ~ 0.3중량%, 망간(Mn): 1.0 ~ 2.0중량%, 인(P): 0.08 ~ 0.12중량%, 황(S): 0 초과 0.01중량% 이하, 알루미늄(Al): 0.01 ~ 0.06중량%, 니오븀(Nb): 0.003 ~ 0.02중량%, 티타늄(Ti): 0.04 ~ 0.08중량%, 붕소(B): 0.0005 ~ 0.002중량% 및 나머지 철(Fe)인 조성범위를 만족하며, 권취 온도: 580 ~ 700℃ 및 소둔 온도: 820 ~ 850℃를 모두 만족한다. Referring to Table 1, Experimental Examples 1 to 3 are examples of the present invention, carbon (C): 0.003 to 0.01% by weight, silicon (Si): 0.05 to 0.3% by weight, manganese (Mn): 1.0 to 2.0% by weight, phosphorus (P): 0.08 to 0.12% by weight, sulfur (S): greater than 0 and less than 0.01% by weight, aluminum (Al): 0.01 to 0.06% by weight, niobium (Nb): 0.003 to 0.02% by weight, titanium (Ti): 0.04 ~ 0.08% by weight, boron (B): 0.0005 ~ 0.002% by weight, and the rest iron (Fe) satisfies the composition range, coiling temperature: 580 ~ 700 ℃ and annealing temperature: 820 ~ 850 ℃ both Satisfies.
이에 반하여, 실험예4 및 실험예5는 본 발명의 비교예로서 인(P): 0.08 ~ 0.12중량%의 조성범위를 만족하지 못하고 하회하며, 실험예6은 본 발명의 비교예로서 규소(Si): 0.05 ~ 0.3중량%의 조성범위를 만족하지 못하고 하회하며, 실험예7은 본 발명의 비교예로서 권취 온도: 580 ~ 700℃를 만족하지 못하고 하회한다. On the other hand, Experimental Example 4 and Experimental Example 5 do not satisfy the composition range of phosphorus (P): 0.08 to 0.12% by weight as a comparative example of the present invention, and Experimental Example 6 is a comparative example of the present invention. ): does not satisfy the composition range of 0.05 to 0.3% by weight and falls below, Experimental Example 7 does not satisfy and falls below the coiling temperature: 580 ~ 700 ℃ as a comparative example of the present invention.
2. 시편의 물성2. Physical properties of the specimen
표 2는 본 실험예의 시편들의 강도, 연신율, 소성이방성계수 및 저온취성 온도 등의 물성을 나타낸다. Table 2 shows physical properties such as strength, elongation, plastic anisotropy coefficient, and low temperature brittleness temperature of the specimens of this experimental example.
표 2를 참조하면, 실험예1 내지 실험예3은 본 발명의 실시예로서, 항복 강도(YS): 250 ~ 350MPa, 인장강도(TS): 445 ~ 600MPa이며, 연신율(El): 30 ~ 40%의 범위를 만족하고, 소성이방성계수(r-value): 1.4 ~ 3.0인 범위를 동시에 만족함을 확인할 수 있다. Referring to Table 2, Experimental Examples 1 to 3 are examples of the present invention, yield strength (YS): 250 ~ 350MPa, tensile strength (TS): 445 ~ 600MPa, elongation (El): 30 ~ 40 It can be seen that the range of % is satisfied, and the range of plastic isotropy coefficient (r-value): 1.4 to 3.0 is satisfied at the same time.
이에 반하여, 실험예4는 본 발명의 비교예로서 인장강도(TS): 445 ~ 600MPa의 범위를 만족하지 못하고 하회하며, 실험예5 및 실험예6은 본 발명의 비교예로서 인장강도(TS): 445 ~ 600MPa의 범위를 만족하지 못하고 하회하며, 소성이방성계수(r-value): 1.4 ~ 3.0인 범위를 만족하지 못하고 하회하며, 실험예7은 본 발명의 비교예로서 연신율(El): 30 ~ 40%의 범위를 만족하지 못하고 하회하며, 소성이방성계수(r-value): 1.4 ~ 3.0인 범위를 만족하지 못하고 하회함을 확인할 수 있다. On the other hand, Experimental Example 4 is a comparative example of the present invention, and the tensile strength (TS): does not satisfy the range of 445 to 600 MPa and falls below, and Experimental Example 5 and Experimental Example 6 are comparative examples of the present invention. : does not satisfy the range of 445 to 600 MPa and falls below, plastic isotropy coefficient (r-value): does not satisfy and falls below the range of 1.4 to 3.0, Experimental Example 7 is a comparative example of the present invention, elongation (El): 30 It can be confirmed that it does not satisfy and falls below the range of ~ 40%, and does not satisfy and falls below the range of plastic isotropy coefficient (r-value): 1.4 to 3.0.
도 3은 본 발명의 실험예로서 소성이방성 관련 특성값의 결과를 나타낸 그래프이다. 도 3에서 ri 항목은 방향별(0도, 45도, 90도) 소성이방성 지수를 각각 측정한 것이며, r-bar는 ri 항목의 산술 평균값을 나타낸 것이다. 3 is a graph showing the results of characteristic values related to plastic anisotropy as an experimental example of the present invention. In FIG. 3, the ri item is a measurement of the plastic anisotropy index for each direction (0 degree, 45 degree, 90 degree), and r-bar shows the arithmetic average value of the ri item.
도 3을 참조하면, 실험예6은 본 발명의 비교예로서 소성이방성계수(r-value): 1.4 ~ 3.0인 범위를 만족하지 못하고 하회하지만, 실험예1은 본 발명의 실시예로서 소성이방성계수(r-value): 1.4 ~ 3.0인 범위를 만족함을 확인할 수 있다. Referring to FIG. 3, Experimental Example 6 is a comparative example of the present invention and falls short of the range of r-value: 1.4 to 3.0, but Experimental Example 1 is an example of the present invention. (r-value): It can be confirmed that the range of 1.4 to 3.0 is satisfied.
이상에서는 본 발명의 실시예를 중심으로 설명하였지만, 당업자의 수준에서 다양한 변경이나 변형을 가할 수 있다. 이러한 변경과 변형이 본 발명의 범위를 벗어나지 않는 한 본 발명에 속한다고 할 수 있다. 따라서 본 발명의 권리범위는 이하에 기재되는 청구범위에 의해 판단되어야 할 것이다.Although the above has been described based on the embodiments of the present invention, various changes or modifications may be made at the level of those skilled in the art. As long as these changes and modifications do not depart from the scope of the present invention, it can be said to belong to the present invention. Therefore, the scope of the present invention will be determined by the claims described below.
Claims (8)
소성이방성계수(r-value)가 1.4 ~ 3.0인 것을 특징으로 하는,
소성이방성이 우수한 고강도 냉연 강판.Carbon (C): 0.003 to 0.01% by weight, Silicon (Si): 0.05 to 0.3% by weight, Manganese (Mn): 1.0 to 2.0% by weight, Phosphorus (P): 0.08 to 0.12% by weight, Sulfur (S): 0 More than 0.01% by weight or less, aluminum (Al): 0.01 to 0.06% by weight, niobium (Nb): 0.003 to 0.02% by weight, titanium (Ti): 0.04 to 0.08% by weight, boron (B): 0.0005 to 0.002% by weight, and Contains the remaining iron (Fe) and other unavoidable impurities,
Characterized in that the plastic isotropy coefficient (r-value) is 1.4 to 3.0,
High-strength cold-rolled steel sheet with excellent plastic isotropy.
항복 강도(YS): 250 ~ 350MPa, 인장강도(TS): 445 ~ 600MPa이며, 연신율(El): 30 ~ 40%인 것을 특징으로 하는,
소성이방성이 우수한 고강도 냉연 강판.According to claim 1,
Yield strength (YS): 250 ~ 350MPa, tensile strength (TS): 445 ~ 600MPa, elongation (El): characterized in that 30 ~ 40%,
High-strength cold-rolled steel sheet with excellent plastic isotropy.
상기 냉연 강판의 최종 미세 조직은 페라이트로 이루어진 것을 특징으로 하는,
소성이방성이 우수한 고강도 냉연 강판.According to claim 1,
Characterized in that the final microstructure of the cold-rolled steel sheet is made of ferrite,
High-strength cold-rolled steel sheet with excellent plastic isotropy.
(b) 상기 강재를 열간 압연하는 단계;
(c) 상기 열간 압연된 강재에 대하여 냉간 압연하는 단계; 및
(d) 상기 냉간 압연된 강재에 대하여 소둔 및 냉각 공정을 순차적으로 수행하는 단계; 를 포함하는 냉연 강판의 제조 방법이며,
상기 냉연 강판의 소성이방성계수(r-value)는 1.4 ~ 3.0인 것을 특징으로 하는,
소성이방성이 우수한 고강도 냉연 강판의 제조 방법.(a) Carbon (C): 0.003 to 0.01% by weight, silicon (Si): 0.05 to 0.3% by weight, manganese (Mn): 1.0 to 2.0% by weight, phosphorus (P): 0.08 to 0.12% by weight, sulfur (S ): more than 0 and 0.01% by weight or less, aluminum (Al): 0.01 to 0.06% by weight, niobium (Nb): 0.003 to 0.02% by weight, titanium (Ti): 0.04 to 0.08% by weight, boron (B): 0.0005 to 0.002 Providing a steel material consisting of weight percent and the remaining iron (Fe) and other unavoidable impurities;
(b) hot rolling the steel;
(c) cold-rolling the hot-rolled steel material; and
(d) sequentially performing an annealing and cooling process on the cold-rolled steel; A method for producing a cold-rolled steel sheet comprising a,
Characterized in that the plastic isotropy coefficient (r-value) of the cold-rolled steel sheet is 1.4 to 3.0,
A method for producing a high-strength cold-rolled steel sheet having excellent plastic anisotropy.
상기 (d) 단계는 상기 강재에 대하여 820 ~ 850℃에서 소둔 열처리하는 단계; 를 포함하는,
소성이방성이 우수한 고강도 냉연 강판의 제조 방법.According to claim 4,
Step (d) is annealing heat treatment at 820 ~ 850 ℃ with respect to the steel; including,
A method for producing a high-strength cold-rolled steel sheet having excellent plastic anisotropy.
상기 (d) 단계는 상기 소둔 열처리된 강재에 대하여 400 ~ 600℃까지 3 ~ 20℃/s로 냉각하는 단계; 를 포함하는,
소성이방성이 우수한 고강도 냉연 강판의 제조 방법.According to claim 5,
The step (d) includes cooling the annealed steel to 400 to 600 ° C at a rate of 3 to 20 ° C / s; including,
A method for producing a high-strength cold-rolled steel sheet having excellent plastic anisotropy.
상기 (b) 단계는 상기 강재를 1100 ~ 1300℃에서 재가열하는 단계; 상기 강재를 마무리 압연온도가 800 ~ 1000℃인 조건으로 열간 압연하는 단계; 상기 강재를 580 ~ 700℃에서 권취하는 단계;를 포함하는,
소성이방성이 우수한 고강도 냉연 강판의 제조 방법.According to claim 4,
Step (b) includes reheating the steel at 1100 to 1300 ° C; Hot-rolling the steel material at a finish rolling temperature of 800 to 1000° C.; Including; winding the steel material at 580 ~ 700 ° C.
A method for producing a high-strength cold-rolled steel sheet having excellent plastic anisotropy.
상기 (c) 단계는 상기 강재를 50 ~ 90%의 압하율로 냉간 압연하는 단계를 포함하는,
소성이방성이 우수한 고강도 냉연 강판의 제조 방법.According to claim 4,
Step (c) comprises cold rolling the steel at a reduction ratio of 50 to 90%,
A method for producing a high-strength cold-rolled steel sheet having excellent plastic anisotropy.
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| KR20120060970A (en) * | 2010-09-29 | 2012-06-12 | 현대제철 주식회사 | Extremely low carbon hot-rolled steel for cold rolling with excelent acid-cleaning characteristic and compactibility and method of manufacturing the same |
| KR20130110635A (en) * | 2012-03-29 | 2013-10-10 | 현대제철 주식회사 | Cold-rolled steel sheet and method of manufacturing the same |
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| KR20120060970A (en) * | 2010-09-29 | 2012-06-12 | 현대제철 주식회사 | Extremely low carbon hot-rolled steel for cold rolling with excelent acid-cleaning characteristic and compactibility and method of manufacturing the same |
| KR20130110635A (en) * | 2012-03-29 | 2013-10-10 | 현대제철 주식회사 | Cold-rolled steel sheet and method of manufacturing the same |
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