KR101311120B1 - Hot-rolled steel sheet and method of manufacturing the hot-rolled steel sheet - Google Patents
Hot-rolled steel sheet and method of manufacturing the hot-rolled steel sheet Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 64
- 239000010959 steel Substances 0.000 title claims abstract description 64
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 22
- 239000011572 manganese Substances 0.000 claims abstract description 27
- 238000004804 winding Methods 0.000 claims abstract description 27
- 239000011575 calcium Substances 0.000 claims abstract description 23
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 22
- 239000010955 niobium Substances 0.000 claims abstract description 22
- 238000001816 cooling Methods 0.000 claims abstract description 20
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 16
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 16
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 16
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052791 calcium Inorganic materials 0.000 claims abstract description 14
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 13
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims abstract description 13
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 12
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 12
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 12
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 12
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 12
- 239000010703 silicon Substances 0.000 claims abstract description 12
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 12
- 239000011593 sulfur Substances 0.000 claims abstract description 12
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 11
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 10
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 10
- 239000011574 phosphorus Substances 0.000 claims abstract description 10
- 239000012535 impurity Substances 0.000 claims abstract description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 8
- 238000005096 rolling process Methods 0.000 claims abstract description 7
- 238000005098 hot rolling Methods 0.000 claims description 15
- 238000000034 method Methods 0.000 claims description 12
- 238000003303 reheating Methods 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 2
- 230000009466 transformation Effects 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 238000009628 steelmaking Methods 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 229910001567 cementite Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 241000219307 Atriplex rosea Species 0.000 description 1
- 229910000677 High-carbon steel Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000012417 linear regression Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 239000013077 target material Substances 0.000 description 1
- 238000000844 transformation Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
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- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
코일의 좌굴 발생을 억제할 수 있는 열연강판 및 그 제조 방법에 대하여 개시한다.
본 발명에 따른 열연강판 제조 방법은 탄소(C) : 0.2~0.25 중량%, 망간(Mn) : 1.0~1.5 중량%, 실리콘(Si) : 0.03 중량% 이하, 인(P) : 0.02 중량% 이하, 황(S) : 0.01 중량% 이하, 알루미늄(Al) : 0.01~0.05 중량%, 니오븀(Nb) : 0.01~0.03 중량%, 칼슘(Ca) : 0.001~0.005 중량%, 질소(N) : 100ppm 이하 및 나머지 철(Fe)과 불가피한 불순물로 이루어진 슬라브 판재를 열간압연하는 단계; 및 상기 열간압연된 판재를 냉각한 후, 하기 식을 만족하는 권취 온도에서 권취하는 단계;를 포함하는 것을 특징으로 한다.
식 : Da(mm) = 874.8 - 0.23CT(℃), Da ≥ 740 (여기서, Da는 권취 후 코일 단경, CT : 권취 온도) A hot rolled steel sheet capable of suppressing buckling of a coil and a manufacturing method thereof are disclosed.
Method for producing a hot rolled steel sheet according to the present invention is carbon (C): 0.2 ~ 0.25% by weight, manganese (Mn): 1.0 ~ 1.5% by weight, silicon (Si): 0.03% by weight or less, phosphorus (P): 0.02% by weight or less , Sulfur (S): 0.01% by weight or less, aluminum (Al): 0.01-0.05% by weight, niobium (Nb): 0.01-0.03% by weight, calcium (Ca): 0.001-0.005% by weight, nitrogen (N): 100 ppm Hot and rolling the slab plate made of the remaining iron (Fe) and unavoidable impurities; And after cooling the hot rolled sheet, winding at a winding temperature that satisfies the following equation.
Equation: Da (mm) = 874.8-0.23CT (℃), Da ≥ 740 (where Da is coil short diameter after winding, CT: winding temperature)
Description
본 발명은 열연강판 제조 기술에 관한 것으로, 보다 상세하게는 코일의 좌굴 발생을 억제할 수 있는 열연강판 및 그 제조 방법에 관한 것이다.
The present invention relates to a hot rolled steel sheet manufacturing technology, and more particularly, to a hot rolled steel sheet and a method of manufacturing the same that can suppress the buckling of the coil.
일반적으로 강 중에, 탄소, 망간 등 경화형 원소가 많이 첨가되는 경우, 열간압연 후 냉각 중 변태가 지연되고, 대부분의 변태는 권취 후에 발생한다. In general, when a large amount of hardening elements such as carbon and manganese are added to steel, transformation during cooling after hot rolling is delayed, and most transformation occurs after winding.
한편, 변태는 강의 부피 팽창을 수반하는데, 상기 탄소 등이 많이 첨가되는 경우와 같이 대부분의 변태가 권취 후에 이루어질 경우, 코일의 하중으로 인하여 코일이 찌그러지는 현상인 좌굴이 발생한다. 이러한, 좌굴은 언코일링 시의 형상불량, 조관성 저하 등 많은 문제를 야기한다.
On the other hand, the transformation involves the expansion of the volume of the steel, when most transformations are made after winding, such as when the carbon is added a lot, buckling occurs that is a phenomenon that the coil is crushed due to the load of the coil. Such buckling causes many problems such as poor shape during uncoiling, lowering of the coronality.
본 발명의 목적은 탄소 함량이 높은 열연강판을 제조하되, 코일의 좌굴 발생을 억제할 수 있는 열연강판 제조 방법을 제공하는 것이다. An object of the present invention is to produce a hot rolled steel sheet having a high carbon content, to provide a method for producing a hot rolled steel sheet that can suppress the occurrence of buckling of the coil.
본 발명의 다른 목적은 좌굴 발생이 억제되어 형상불량, 조관 생산성 저하를 방지할 수 있는 열연강판을 제공하는 것이다.
It is another object of the present invention to provide a hot rolled steel sheet which can prevent buckling from occurring and can prevent a shape defect and a decrease in tube manufacturing productivity.
상기 하나의 목적을 달성하기 위한 본 발명의 실시예에 따른 열연강판 제조 방법은 탄소(C) : 0.2~0.25 중량%, 망간(Mn) : 1.0~1.5 중량%, 실리콘(Si) : 0.03 중량% 이하, 인(P) : 0.02 중량% 이하, 황(S) : 0.01 중량% 이하, 알루미늄(Al) : 0.01~0.05 중량%, 니오븀(Nb) : 0.01~0.03 중량%, 칼슘(Ca) : 0.001~0.005 중량%, 질소(N) : 100ppm 이하 및 나머지 철(Fe)과 불가피한 불순물로 이루어진 슬라브 판재를 열간압연하는 단계; 및 상기 열간압연된 판재를 냉각한 후, 하기 식을 만족하는 권취 온도에서 권취하는 단계;를 포함하는 것을 특징으로 한다. Hot-rolled steel sheet manufacturing method according to an embodiment of the present invention for achieving the above one object is carbon (C): 0.2 ~ 0.25% by weight, manganese (Mn): 1.0 ~ 1.5% by weight, silicon (Si): 0.03% by weight Phosphorus (P): 0.02 wt% or less, Sulfur (S): 0.01 wt% or less, Aluminum (Al): 0.01-0.05 wt%, Niobium (Nb): 0.01-0.03 wt%, Calcium (Ca): 0.001 Hot rolling a slab plate composed of 0.005% by weight, nitrogen (N): 100 ppm or less, and remaining iron (Fe) and unavoidable impurities; And after cooling the hot rolled sheet, winding at a winding temperature that satisfies the following equation.
식 : Da(mm) = 874.8 - 0.23CT(℃), Da ≥ 740 (여기서, Da는 권취 후 코일 단경, CT : 권취 온도)
Equation: Da (mm) = 874.8-0.23CT (℃), Da ≥ 740 (where Da is coil short diameter after winding, CT: winding temperature)
상기 다른 목적을 달성하기 위한 본 발명의 실시예에 따른 열연강판은 탄소(C) : 0.2~0.25 중량%, 망간(Mn) : 1.0~1.5 중량%, 실리콘(Si) : 0.03 중량% 이하, 인(P) : 0.02 중량% 이하, 황(S) : 0.01 중량% 이하, 알루미늄(Al) : 0.01~0.05 중량%, 니오븀(Nb) : 0.01~0.03 중량%, 칼슘(Ca) : 0.001~0.005 중량%, 질소(N) : 100ppm 이하 및 나머지 철(Fe)과 불가피한 불순물로 이루어지고, Hot-rolled steel sheet according to an embodiment of the present invention for achieving the above another object is carbon (C): 0.2 ~ 0.25% by weight, manganese (Mn): 1.0 ~ 1.5% by weight, silicon (Si): 0.03% by weight or less, phosphorus (P): 0.02 wt% or less, Sulfur (S): 0.01 wt% or less, Aluminum (Al): 0.01-0.05 wt%, Niobium (Nb): 0.01-0.03 wt%, Calcium (Ca): 0.001-0.005 weight %, Nitrogen (N): 100ppm or less and the remaining iron (Fe) and inevitable impurities,
코일의 단경(Da)이 하기 식을 만족하는 것을 특징으로 한다. The short diameter Da of the coil is characterized by satisfying the following equation.
식 : Da(mm) = 874.8 - 0.23CT(℃), Da ≥ 740 (여기서, Da는 권취 후 코일 단경, CT : 권취 온도)
Equation: Da (mm) = 874.8-0.23CT (℃), Da ≥ 740 (where Da is coil short diameter after winding, CT: winding temperature)
본 발명에 따른 열연강판 제조 방법은 권취온도와 코일의 단경의 관계식을 통하여, 열간압연된 판재를 최적의 온도에서 권취함으로써, 고탄소 열연강판 제조시 문제시되는 코일의 좌굴 발생을 억제할 수 있는 효과가 있다. Hot rolled steel sheet manufacturing method according to the present invention through the relationship between the coiling temperature and the short diameter of the coil, by winding the hot-rolled sheet at the optimum temperature, the effect of suppressing the buckling of the coil in question during the production of high carbon hot rolled steel sheet There is.
따라서, 본 발명은 제조된 열연강판의 언코일링시의 형상불량, 조관성 저하 등을 방지할 수 있다.
Therefore, the present invention can prevent shape defects, deterioration in the tube structure, and the like during uncoiling of the manufactured hot rolled steel sheet.
도 1은 본 발명의 실시예에 따른 열연강판 제조 방법을 개략적으로 나타내는 순서도이다.
도 2는 코일의 단경을 개략적으로 나타낸 도면이다.
도 3은 권취 온도에 따른 코일 단경 변화를 나타낸 도면이다. 1 is a flowchart schematically showing a method of manufacturing a hot-rolled steel sheet according to an embodiment of the present invention.
2 is a view schematically showing the short diameter of the coil.
3 is a view showing a coil short diameter change according to the coiling temperature.
본 발명의 이점 및 특징, 그리고 그것들을 달성하는 방법은 첨부되는 도면과 함께 상세하게 후술되어 있는 실시예들을 참조하면 명확해질 것이다. 그러나, 본 발명은 이하에서 개시되는 실시예들에 한정되는 것이 아니라 서로 다른 다양한 형태로 구현될 것이며, 단지 본 실시예들은 본 발명의 개시가 완전하도록 하며, 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자에게 발명의 범주를 완전하게 알려주기 위해 제공되는 것이며, 본 발명은 청구항의 범주에 의해 정의될 뿐이다. 명세서 전체에 걸쳐 동일 참조 부호는 동일 구성요소를 지칭한다.Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.
이하 첨부된 도면을 참조하여 본 발명의 바람직한 실시예에 따른 열연강판 및 그 제조 방법에 관하여 상세히 설명하면 다음과 같다.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a hot-rolled steel sheet according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
열연강판Hot-rolled steel sheet
본 발명에 따른 열연강판은 탄소(C) : 0.2~0.25 중량%, 망간(Mn) : 1.0~1.5 중량%, 실리콘(Si) : 0 중량% 초과 ~ 0.03 중량% 이하, 인(P) : 0 중량% 초과 ~ 0.02 중량% 이하, 황(S) : 0.01 중량% 이하, 알루미늄(Al) : 0.01~0.05 중량%, 니오븀(Nb) : 0.01~0.03 중량%, 칼슘(Ca) : 0.001~0.005 중량% 및 질소(N) : 0.01 중량% 이하를 포함한다.Hot rolled steel sheet according to the present invention is carbon (C): 0.2 ~ 0.25% by weight, manganese (Mn): 1.0 ~ 1.5% by weight, silicon (Si): more than 0% by weight to 0.03% by weight or less, phosphorus (P): 0 More than 0.0% by weight or less, sulfur (S): 0.01% by weight or less, aluminum (Al): 0.01 to 0.05% by weight, niobium (Nb): 0.01 to 0.03% by weight, calcium (Ca): 0.001 to 0.005% by weight % And nitrogen (N): 0.01 wt% or less.
상기 합금 성분들 외 나머지는 철(Fe)과 제강 과정 등에서 불가피하게 포함되는 불순물로 이루어진다. The rest of the alloy components are made of iron (Fe) and impurities which are inevitably included in steelmaking.
이하, 본 발명에 따른 열연강판에 포함되는 각 성분의 역할 및 그 함량에 대하여 설명하면 다음과 같다.
Hereinafter, the role and content of each component included in the hot-rolled steel sheet according to the present invention will be described.
탄소(C)Carbon (C)
본 발명에서 탄소(C)는 강도를 확보하기 위하여 첨가된다. 본 발명에 따른 열연강판은 고탄소강에 속하며, 이를 보증하기 위하여 탄소는 최소 0.2중량% 포함된다. 다만, 탄소 함량이 0.25중량%를 초과하는 경우, 용접성 및 인성이 저하된다.In the present invention, carbon (C) is added in order to secure strength. Hot rolled steel sheet according to the present invention belongs to high carbon steel, carbon is included at least 0.2% by weight to ensure this. However, when the carbon content exceeds 0.25% by weight, weldability and toughness are reduced.
따라서, 상기 탄소는 본 발명에 따른 열연강판 전체 중량의 0.2~0.25 중량%로 첨가되는 것이 바람직하다.
Therefore, the carbon is preferably added in 0.2 ~ 0.25% by weight of the total weight of the hot rolled steel sheet according to the present invention.
망간(Mn)Manganese (Mn)
본 발명에서 망간(Mn)은 고용강화 원소로써 매우 효과적이며, 강의 경화능을 향상시켜서 강도확보에 효과적인 원소이다. 또한 망간은 오스테나이트(austenite) 안정화 원소로써 페라이트, 펄라이트 변태를 지연시킴으로써 페라이트의 결정립 미세화에 기여한다. In the present invention, manganese (Mn) is very effective as an element for solid solution strengthening, and is an element effective for securing strength by improving the hardenability of steel. Manganese also contributes to grain refinement of ferrite by delaying ferrite and pearlite transformation as an austenite stabilizing element.
상기 망간(Mn)은 본 발명에 따른 열연강판 전체 중량의 1.0~1.5 중량%로 첨가되는 것이 바람직하다. 망간의 첨가량이 1.0 중량% 미만인 경우, 그 첨가 효과가 불충분하다. 반대로, 망간의 첨가량이 1.5 중량%를 초과하는 경우, 용접성을 크게 떨어뜨리며 게재물 생성 및 중심편석 등을 유발하는 문제점이 있다.
The manganese (Mn) is preferably added in 1.0 to 1.5% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the amount of manganese added is less than 1.0% by weight, the effect of addition is insufficient. On the contrary, when the amount of manganese exceeds 1.5% by weight, there is a problem that greatly decreases the weldability and causes the formation of the inclusions and the center segregation.
실리콘(Si)Silicon (Si)
본 발명에서 실리콘은 강 중의 산소를 제거하기 위한 탈산제로 첨가되며, 또한 시멘타이트 구상화에 효과적인 원소이다. In the present invention, silicon is added as a deoxidizer to remove oxygen in the steel, and is also an element effective for cementite sphering.
그러나, 본 발명에 따른 열연강판에서 실리콘의 첨가량이 0.03 중량%를 초과하는 경우, 강의 용접성을 떨어뜨리고 슬라브 재가열 및 열간압연 시에 적 스케일을 생성시킴으로써 표면품질에 문제를 줄 수 있으며, 또한 용접 후 도금성을 저해하는 문제점이 발생할 수 있다.However, when the amount of silicon added in the hot rolled steel sheet according to the present invention exceeds 0.03% by weight, the weldability of the steel can be degraded and the red scale is generated during slab reheating and hot rolling, which may cause a problem in the surface quality, and also after welding Problems that inhibit the plating may occur.
따라서, 상기 실리콘은 본 발명에 따른 열연강판 전체 중량의 0 중량% 초과 ~ 0.03 중량% 이하로 첨가되는 것이 바람직하다.
Therefore, the silicon is preferably added in more than 0% to 0.03% by weight of the total weight of the hot rolled steel sheet according to the present invention.
인(P)Phosphorus (P)
인(P)은 제조되는 열연강판의 강도를 증가시키는데 일부 기여하지만, 0.02 중량%를 초과하면 용접성이 악화되는 문제가 있다. Phosphorus (P) contributes in part to increasing the strength of the hot-rolled steel sheet to be manufactured, but if it exceeds 0.02% by weight, weldability deteriorates.
따라서, 본 발명에서는 인의 함량을 본 발명에 따른 열연강판 전체 중량의 0 중량% 초과 ~ 0.02 중량% 이하로 제한하였다.
Therefore, in the present invention, the content of phosphorus was limited to more than 0% by weight to 0.02% by weight or less of the total weight of the hot rolled steel sheet according to the present invention.
황(S)Sulfur (S)
황(S)은 대표적인 불가피한 불순물로서, 0.01 중량%를 초과하면 강의 용접성을 저해하고, MnS 비금속 개재물을 증가시켜 강의 가공 중 크랙을 발생시킨다. Sulfur (S) is a representative unavoidable impurity. When it exceeds 0.01% by weight, the weldability of the steel is inhibited and MnS non-metallic inclusions are increased to generate cracks during processing of the steel.
따라서, 본 발명에서는 황의 함량을 본 발명에 따른 열연강판 전체 중량의 0.01 중량% 이하로 제한하였다.
Therefore, in the present invention, the sulfur content is limited to 0.01% by weight or less of the total weight of the hot rolled steel sheet according to the present invention.
알루미늄(Al)Aluminum (Al)
본 발명에서 알루미늄(Al)은 실리콘(Si)이나 망간(Mn)에 비해 우수한 탈산능을 가짐으로써 제강공정 시 용강 중에 산소 제거에 효과적인 원소이다. In the present invention, aluminum (Al) is an effective element for removing oxygen in molten steel during the steelmaking process by having excellent deoxidation ability compared to silicon (Si) or manganese (Mn).
상기 알루미늄은 본 발명에 따른 열연강판 전체 중량의 0.01 ~ 0.05 중량%로 첨가되는 것이 바람직하다. 알루미늄의 첨가량이 0.01 중량% 미만인 경우 탈산 효과 등이 충분치 못하다. 반대로 알루미늄의 첨가량이 0.05 중량%를 초과하는 경우 펄라이트 변태시 시멘타이트의 구상화를 방해함으로써 절삭성을 저하시키는 문제가 있다.
The aluminum is preferably added in 0.01 to 0.05% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the amount of aluminum added is less than 0.01% by weight, the deoxidation effect is not sufficient. On the contrary, when the addition amount of aluminum exceeds 0.05% by weight, there is a problem of lowering machinability by preventing spheroidization of cementite during pearlite transformation.
니오븀(Nb)Niobium (Nb)
니오븀(Nb)은 석출물 형성원소로서 강의 강도에 가장 큰 영향을 주는 원소 중 하나이며, 강 중에 탄질화물을 석출하거나 Fe 내 고용강화를 통하여 강의 강도를 향상시키는 원소이다. 특히, 니오븀계 석출물들은 1200℃ 정도의 슬라브 재가열 과정에서 고용된 후 열간압연 중 미세하게 석출하여 강의 강도를 효과적으로 증가시킨다. Niobium (Nb) is one of the elements that have the greatest influence on the strength of steel as a precipitate forming element. It is an element that improves the strength of steel by precipitating carbonitride in steel or strengthening solid solution in Fe. Particularly, the niobium precipitates are dissolved in the slab reheating process at a temperature of about 1200 ° C, and then precipitated finely during hot rolling, effectively increasing the strength of the steel.
상기 니오븀은 본 발명에 따른 열연강판 전체 중량의 0.01~0.03 중량%로 첨가되는 것이 바람직하다. 니오븀의 첨가량이 0.01 중량% 미만인 경우 그 첨가 효과가 불충분하다. 반대로, 니오븀의 첨가량이 0.03 중량%를 초과하면 과다한 석출물 형성에 의하여 롤포스(Roll Force)가 증가되어 압연성을 저하시키는 문제점이 있다.
The niobium is preferably added in 0.01 to 0.03% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the addition amount of niobium is less than 0.01% by weight, the addition effect is insufficient. On the contrary, when the addition amount of niobium exceeds 0.03% by weight, roll force is increased due to excessive precipitate formation, thereby degrading rollability.
칼슘(Ca)Calcium (Ca)
칼슘(Ca)은 CaS를 형성시켜 강중의 황의 함량을 낮추고, 압연중에 연신되어 전기저항용접시 훅 크랙(Hook Crack) 등의 결함을 유발하는 MnS 개재물의 생성을 방해한다. 이는 칼슘이 망간에 비하여 황과의 친화도가 높기 때문이다. 따라서, 칼슘의 첨가는 제조되는 강의 전기저항용접 특성 및 충격 특성 향상에 기여한다. Calcium (Ca) forms CaS to lower the content of sulfur in the steel, and stretches during rolling to inhibit the formation of MnS inclusions that cause defects such as hook cracks during electric resistance welding. This is because calcium has a higher affinity with sulfur than manganese. Therefore, the addition of calcium contributes to the improvement of electric resistance welding characteristics and impact properties of the produced steel.
상기 칼슘은 본 발명에 따른 열연강판 전체 중량의 0.001~0.005 중량%로 첨가되는 것이 바람직하다. 칼슘의 첨가량이 0.001 중량% 미만이면 그 첨가 효과가 불충분하다. 반대로, 칼슘의 첨가량이 0.005 중량%를 초과하면 과도한 CaS가 생성되거나, 또는 원하지 않는 CaO가 생성되는 문제점이 있다.
The calcium is preferably added in 0.001 ~ 0.005% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the addition amount of calcium is less than 0.001% by weight, the addition effect is insufficient. On the contrary, when the added amount of calcium exceeds 0.005% by weight, excessive CaS is generated or unwanted CaO is generated.
질소nitrogen
질소(N)는 불가피한 불순물로서, 다량 첨가시 고용 질소가 증가하여 강의 연신율 및 성형성이 떨어뜨리는 문제점이 있다. Nitrogen (N) is an unavoidable impurity, and there is a problem in that solid solution nitrogen increases when a large amount is added, thereby reducing elongation and formability of steel.
따라서, 본 발명에서는 질소의 함량을 본 발명에 따른 열연강판 전체 중량의 0.01 중량% 이하로 제한하였다.
Therefore, in the present invention, the nitrogen content is limited to 0.01% by weight or less of the total weight of the hot rolled steel sheet according to the present invention.
본 발명에 따른 열연강판은 상기의 합금조성 및 후술하는 공정조건 제어에 따라 다양한 물성을 가질 수 있으며, 코일의 단경이 달라질 수 있다.
Hot rolled steel sheet according to the present invention may have a variety of physical properties according to the alloy composition and the control of the process conditions to be described later, the diameter of the coil may vary.
열연강판 제조 방법Hot-rolled steel sheet manufacturing method
도 1은 본 발명의 실시예에 따른 열연강판 제조 방법을 개략적으로 나타내는 순서도이다. 1 is a flow chart schematically showing a method for manufacturing a hot rolled steel sheet according to an embodiment of the present invention.
도 1을 참조하면, 본 발명에 따른 열연강판 제조 방법은 열간압연 단계(S110) 및 냉각/권취 단계(S120)를 포함한다. 또한, 본 발명에 따른 열연강판 제조 방법은 열간압연 단계(S110) 이전에 슬라브 재가열 단계(S105)를 더 포함할 수 있다. Referring to Figure 1, the method for manufacturing a hot rolled steel sheet according to the present invention includes a hot rolling step (S110) and cooling / winding step (S120). In addition, the method for manufacturing a hot rolled steel sheet according to the present invention may further include a slab reheating step S105 before the hot rolling step S110.
본 발명에서 열간압연의 대상이 되는 반제품 상태의 슬라브 판재는 전술한 합금조성, 즉 탄소(C) : 0.2~0.25 중량%, 망간(Mn) : 1.0~1.5 중량%, 실리콘(Si) : 0 중량% 초과 ~ 0.03 중량% 이하, 인(P) : 0 중량% 초과 ~ 0.02 중량% 이하, 황(S) : 0.01 중량% 이하, 알루미늄(Al) : 0.01~0.05 중량%, 니오븀(Nb) : 0.01~0.03 중량%, 칼슘(Ca) : 0.001~0.005 중량%, 질소(N) : 0.01 중량% 이하를 포함하고, 나머지 철(Fe)과 불가피한 불순물로 이루어진다. In the present invention, the slab plate of the semi-finished state to be subjected to hot rolling is the alloy composition described above, that is, carbon (C): 0.2 to 0.25% by weight, manganese (Mn): 1.0 to 1.5% by weight, silicon (Si): 0 weight More than% to 0.03% by weight or less, phosphorus (P): more than 0% to 0.02% by weight, sulfur (S): 0.01% by weight or less, aluminum (Al): 0.01 to 0.05% by weight, niobium (Nb): 0.01 ˜0.03% by weight, calcium (Ca): 0.001 to 0.005% by weight, nitrogen (N): 0.01% by weight or less, and the remaining iron (Fe) and inevitable impurities.
상기 조성을 갖는 슬라브 판재는 제강공정을 통해 용강을 얻은 다음에 연속주조공정을 통해 얻어질 수 있다.
The slab sheet having the above composition can be obtained through a continuous casting process after obtaining molten steel through a steelmaking process.
슬라브 재가열Reheat slab
슬라브 재가열 단계(S105)는 슬라브 판재의 재가열을 통하여, 주조시 편석된 성분을 재고용하기 위하여 실시될 수 있다. Slab reheating step (S105) may be carried out through the reheating of the slab sheet material to re-use segregated components during casting.
이때, 슬라브 재가열은 슬라브 재가열 온도(SRT)는 1150 ~ 1250℃에서, 대략 1~3시간 정도 실시되는 것이 바람직하다. 슬라브 재가열 온도가 1150℃ 미만일 경우, 주조시 편석된 성분이 재고용되지 못하는 문제점이 있다. 반대로, 슬라브 재가열 온도가 1250℃를 초과하는 경우 오스테나이트 결정입도가 증가하여 최종 페라이트 입도가 조대화되면서 강도가 감소하며, 또한 과도한 가열 공정으로 인하여 강의 제조 비용을 증가시킬 수 있다.
In this case, the slab reheating is preferably performed for about 1 to 3 hours at the slab reheating temperature (SRT) at 1150 to 1250 ° C. If the slab reheating temperature is less than 1150 ℃, there is a problem that the segregated components during casting is not reusable. Conversely, when the slab reheating temperature exceeds 1250 ° C., the austenite grain size increases, resulting in coarsening of the final ferrite grain size, which in turn decreases the strength and may increase the steel manufacturing cost due to excessive heating process.
열간 압연Hot rolling
열간압연 단계(S110)에서는 슬라브 판재를 열간압연한다. In the hot rolling step (S110), the slab plate is hot-rolled.
이때, 열간압연은 마무리 압연 온도(FDT)가 800~850 ℃가 되도록 실시되는 것이 바람직하다. 마무리 압연 온도가 800℃ 미만인 경우 이상역 압연에 의한 혼립 조직이 발생하는 등의 문제점이 발생할 수 있다. 반대로, 압연 마무리 온도가 850℃를 초과할 경우 페라이트 결정립 미세화가 충분히 이루어지지 않아, 강도 확보가 어려운 문제점이 있다.
At this time, the hot rolling is preferably carried out so that the finish rolling temperature (FDT) is 800 ~ 850 ℃. If the finish rolling temperature is less than 800 ° C, problems such as generation of a mixed structure due to abnormal reverse rolling may occur. On the contrary, when the rolling finish temperature exceeds 850 ° C., the ferrite grain refining is not sufficiently performed, which makes it difficult to secure the strength.
냉각/권취Cooling / Winding
냉각 단계(S120)에서는 열간압연이 완료된 판재를 냉각한 후 정해진 권취 온도에서 권취(coiling)한다. In the cooling step (S120) after cooling the plate is completed hot rolling (coiling) at a predetermined winding temperature (coiling).
이때, 냉각은 1℃/sec 미만의 평균냉각속도의 경우 생산성이 저하되고, 50℃/sec를 초과하는 평균냉각속도의 경우 충분한 페라이트 형성이 어려운 점 등을 고려할 때 1~50℃/sec의 평균냉각속도로 실시될 수 있다. 그러나, 평균냉각속도가 반드시 이에 제한되는 것은 아니며, 목표로 하는 재질에 따라 다양한 평균냉각속도로 실시될 수 있다.In this case, the cooling is an average of 1 ~ 50 ℃ / sec considering that the productivity is lowered in the case of the average cooling rate of less than 1 ℃ / sec, difficult formation of sufficient ferrite in the case of the average cooling rate of more than 50 ℃ / sec. It can be carried out at a cooling rate. However, the average cooling rate is not necessarily limited thereto, and may be performed at various average cooling rates depending on the target material.
또한, 냉각 방식은 공냉, 수냉, 이들의 혼용 방식 등 다양한 방식으로 실시될 수 있다.In addition, the cooling method may be carried out in a variety of ways, such as air cooling, water cooling, a mixture thereof.
본 발명에서 권취온도는 하기 식에 의하여 정해질 수 있다. Winding temperature in the present invention can be determined by the following formula.
식 : Da(mm) = 874.8 - 0.23CT(℃), Da ≥ 740 (여기서, Da는 권취 후 코일 단경, CT : 권취 온도) Equation: Da (mm) = 874.8-0.23CT (℃), Da ≥ 740 (where Da is coil short diameter after winding, CT: winding temperature)
도 2는 코일의 단경을 개략적으로 나타낸 것으로, 도 2를 참조하면, 코일의 단경(Da)은, 코일(210)의 내경 중 단축방향 직경을 의미한다. FIG. 2 schematically illustrates a short diameter of the coil. Referring to FIG. 2, the short diameter Da of the coil refers to a shorter diameter in the inner diameter of the
코일의 단경(Da)은 코일(210)의 하중에 의하여 발생하며, 통상 코일의 단경이 740mm 미만일 경우 코일의 좌굴이 문제된다. 따라서, 코일의 단경(Da)이 740mm 이상이 되도록 권취하는 것이 바람직하다. The short diameter Da of the coil is generated by the load of the
본 발명의 발명자들은 많은 연구를 거듭한 결과, 코일의 단경(Da, mm)과 권취 온도(CT, ℃)가 일정한 상관 관계를 가지며, 그 상관 관계가 Da = 874.8 - 0.23CT인 것을 알아내었다. As a result of many studies, the inventors of the present invention have found that the coil short diameter (Da, mm) and the coiling temperature (CT, ° C) have a constant correlation, and the correlation is Da = 874.8-0.23CT.
상기 식은 도 3에 도시된 권취 온도에 따른 코일 단경 변화를 나타낸 그래프를 선형회귀분석하여 얻어진 것이다. The above equation is obtained by linear regression analysis of a graph showing a change in coil short diameter according to the winding temperature shown in FIG. 3.
상기 식 및 도 3을 참조하면, 권취 온도가 낮을수록 코일의 단경이 증가하는 것을 볼 수 있다. 또한, 상기 식을 참조하면, 코일의 단경(Da)이 740mm 이상이 되기 위해서는 874.8 - 0.23CT ≥ 740을 만족하여야 하고, 권취온도(CT)가 586℃ 이하가 되어야 하는 것을 알 수 있다.
Referring to the equation and Figure 3, the lower the coiling temperature can be seen that the shorter diameter of the coil increases. In addition, referring to the above equation, in order for the short diameter Da of the coil to be 740 mm or more, 874.8-0.23 CT ≥ 740 must be satisfied and the coiling temperature CT must be 586 ° C or less.
실시예Example
이하, 본 발명의 바람직한 실시예를 통해 본 발명의 구성 및 작용을 더욱 상세히 설명하기로 한다. 다만, 이는 본 발명의 바람직한 예시로 제시된 것이며 어떠한 의미로도 이에 의해 본 발명이 제한되는 것으로 해석될 수는 없다. Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.
여기에 기재되지 않은 내용은 이 기술 분야에서 숙련된 자이면 충분히 기술적으로 유추할 수 있는 것이므로 그 설명을 생략하기로 한다.
Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.
1. 열연강판 코일 제조1. Hot rolled steel coil manufacturing
표 1에 기재된 조성 및 표 2에 기재된 공정 조건으로 실시예 1~2 및 비교예 1~5에 따른 열연강판 코일을 제조하였다. Hot rolled steel coils according to Examples 1 to 2 and Comparative Examples 1 to 5 were manufactured under the compositions shown in Table 1 and the process conditions described in Table 2.
[표 1](단위 : 중량%)[Table 1] (unit:% by weight)
[표 2][Table 2]
2. 코일 단경 및 2. Coil short diameter and 좌굴Bucking 발생여부Occurrence 평가 evaluation
표 2를 참조하면, 실시예 1~2 및 비교예 1~5에 따라 제조된 강판 코일에 대하여 코일 단경을 측정한 결과, Da(mm) = 874.8 - 0.23CT(℃)를 거의 만족함을 알 수 있다. Referring to Table 2, as a result of measuring the coil short diameters of the steel sheet coils manufactured according to Examples 1 to 2 and Comparative Examples 1 to 5, it can be seen that Da (mm) = 874.8-0.23 CT (° C) was almost satisfied. have.
또한, 권취 온도가 코일 단경이 740mm 이상이 될 수 있도록 상대적으로 낮게 설정된 실시예 1~2에 따라 제조된 강판 코일의 경우 코일의 좌굴이 발생하지 않았다. 그러나, 권취 온도가 상대적으로 높은 비교예 1~5에 따라 제조된 강판 코일의 경우 코일의 좌굴이 발생하였다.
In addition, the coil buckling did not occur in the case of the steel sheet coils manufactured according to Examples 1 to 2 where the coiling temperature was set relatively low so that the coil short diameter could be 740 mm or more. However, in the case of steel sheet coils manufactured according to Comparative Examples 1 to 5 where the coiling temperature was relatively high, buckling of the coils occurred.
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.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.
S105 : 슬라브 재가열 단계
S110 : 열간압연 단계
S120 : 냉각/권취 단계S105: Slab reheating step
S110: Hot rolling step
S120: cooling / winding step
Claims (6)
상기 열간압연된 판재를 냉각한 후, 하기 식을 만족하는 권취 온도에서 권취하는 단계;를 포함하는 것을 특징으로 하는 열연강판 제조 방법.
식 : Da(mm) = 874.8 - 0.23CT(℃), Da ≥ 740 (여기서, Da는 권취 후 코일 단경, CT : 권취 온도)
Carbon (C): 0.2-0.25 wt%, Manganese (Mn): 1.0-1.5 wt%, Silicon (Si): More than 0 wt%-0.03 wt% or less, Phosphorus (P): More than 0 wt%-0.02 wt% Or less, sulfur (S): 0.01% by weight or less, aluminum (Al): 0.01-0.05% by weight, niobium (Nb): 0.01-0.03% by weight, calcium (Ca): 0.001-0.005% by weight, nitrogen (N): Hot rolling a slab plate made of 0.01 wt% or less and remaining iron (Fe) and inevitable impurities; And
After cooling the hot-rolled sheet material, winding at a winding temperature that satisfies the following formula; Hot rolled steel sheet manufacturing method comprising a.
Equation: Da (mm) = 874.8-0.23CT (℃), Da ≥ 740 (where Da is coil short diameter after winding, CT: winding temperature)
상기 열간압연 전, 상기 슬라브 판재를 재가열하는 것을 특징으로 하는 열연강판 제조 방법.
The method of claim 1,
The hot rolled steel sheet manufacturing method, characterized in that for reheating the slab plate before the hot rolling.
상기 재가열은
1150~1250℃에서 실시되는 것을 특징으로 하는 열연강판 제조 방법.
The method of claim 2,
The reheat is
Hot rolled steel sheet manufacturing method characterized in that carried out at 1150 ~ 1250 ℃.
상기 열간압연은
800~850℃의 마무리 압연 온도로 실시되는 것을 특징으로 하는 열연강판 제조 방법.
The method of claim 1,
The hot rolling
Hot rolled steel sheet manufacturing method characterized in that carried out at the finish rolling temperature of 800 ~ 850 ℃.
상기 냉각은
1~50℃/sec의 평균냉각속도로 실시되는 것을 특징으로 하는 열연강판 제조 방법.
The method of claim 1,
The cooling
Hot rolled steel sheet manufacturing method characterized in that carried out at an average cooling rate of 1 ~ 50 ℃ / sec.
코일의 단경(Da)이 하기 식을 만족하는 것을 특징으로 하는 열연강판.
식 : Da(mm) = 874.8 - 0.23CT(℃), Da ≥ 740 (여기서, Da는 권취 후 코일 단경, CT : 권취 온도)Carbon (C): 0.2-0.25 wt%, Manganese (Mn): 1.0-1.5 wt%, Silicon (Si): More than 0 wt%-0.03 wt% or less, Phosphorus (P): More than 0 wt%-0.02 wt% Or less, sulfur (S): 0.01% by weight or less, aluminum (Al): 0.01-0.05% by weight, niobium (Nb): 0.01-0.03% by weight, calcium (Ca): 0.001-0.005% by weight, nitrogen (N): 0.01% by weight or less and the remaining iron (Fe) and inevitable impurities,
Hot-rolled steel sheet, characterized in that the short diameter Da of the coil satisfies the following equation.
Equation: Da (mm) = 874.8-0.23CT (℃), Da ≥ 740 (where Da is coil short diameter after winding, CT: winding temperature)
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