KR100311786B1 - Method for manufacturing steel strip(50kg) with superior strength and yield ratio - Google Patents
Method for manufacturing steel strip(50kg) with superior strength and yield ratio Download PDFInfo
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- KR100311786B1 KR100311786B1 KR1019970024397A KR19970024397A KR100311786B1 KR 100311786 B1 KR100311786 B1 KR 100311786B1 KR 1019970024397 A KR1019970024397 A KR 1019970024397A KR 19970024397 A KR19970024397 A KR 19970024397A KR 100311786 B1 KR100311786 B1 KR 100311786B1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 60
- 239000010959 steel Substances 0.000 title claims abstract description 60
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 10
- 238000000034 method Methods 0.000 title abstract description 9
- 238000005096 rolling process Methods 0.000 claims abstract description 24
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 7
- 229910014458 Ca-Si Inorganic materials 0.000 claims abstract description 4
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 4
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 4
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 4
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 10
- 238000005266 casting Methods 0.000 claims 1
- 238000001816 cooling Methods 0.000 abstract description 20
- 238000009749 continuous casting Methods 0.000 abstract description 3
- 230000009466 transformation Effects 0.000 abstract description 3
- 239000007788 liquid Substances 0.000 abstract 2
- 238000002347 injection Methods 0.000 abstract 1
- 239000007924 injection Substances 0.000 abstract 1
- 239000000463 material Substances 0.000 description 14
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 4
- 235000012255 calcium oxide Nutrition 0.000 description 4
- 239000000292 calcium oxide Substances 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 238000001953 recrystallisation Methods 0.000 description 4
- 239000011593 sulfur Substances 0.000 description 4
- 210000001519 tissue Anatomy 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 3
- 239000011572 manganese Substances 0.000 description 3
- 239000010955 niobium Substances 0.000 description 3
- 239000010936 titanium Substances 0.000 description 3
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 239000011574 phosphorus Substances 0.000 description 2
- 230000000704 physical effect Effects 0.000 description 2
- 238000010079 rubber tapping Methods 0.000 description 2
- 239000002893 slag Substances 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- -1 carbon Chemical compound 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000011863 silicon-based powder Substances 0.000 description 1
- 210000004872 soft tissue Anatomy 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
- B21B3/02—Rolling special iron alloys, e.g. stainless steel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
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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
- C22C38/002—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
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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
-
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2261/00—Product parameters
- B21B2261/20—Temperature
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
Description
본 발명은 강도 및 항복비가 우수한 50kg급 강판의 제조방법에 관한 것으로 특히 철골 건축물에 적합한 강판의 제조방법에 관한 것이다.The present invention relates to a method for producing a 50kg steel sheet excellent in strength and yield ratio, and more particularly, to a method for manufacturing a steel sheet suitable for steel structures.
최근, 한정된 토지를 효율적으로 이용하기 위해 건물이 대형화되는 동시에 초고층화 되어 가는 추세에 있다. 이에 따라 철골구조물에 이용되는 강판의 두께가 두꺼워지는 한편, 건물의 안전을 위해 강판의 강도와 인성의 확보는 물론 용접성 및 내지진성이 강판의 중요한 성질로 대두되고 있다. 특히, 상기 내지진성은 근래에 지진에 의한 건물 붕괴사고가 자주 일어나면서 크게 관심을 일으키고 있는 것으로 강판의 항복비를 기준으로 평가하고 있다.In recent years, in order to efficiently use limited land, buildings are becoming larger and becoming taller. As a result, the thickness of the steel sheet used for the steel structure is increased, while the strength and toughness of the steel sheet, as well as weldability and anti-vibration have emerged as an important property of the steel sheet for building safety. In particular, the tojinjin is evaluated as a basis of the yield ratio of the steel sheet to the interest of the building collapse caused by the earthquake frequently in recent years.
즉, 강판의 항복비라는 것은 외부에서 어떤 자연적인 혹은 인위적인 외력을 받았을 때 강판 내부에서 외력에 대응하는 능력을 말하는 것으로 강판의 항복강도 (YP)와 인장강도(YS)의 비로서 나타내며, 이 항복비(YP/TS)가 80%이하의 것을 사용하도록 규제하고 있다.That is, the yield ratio of the steel sheet refers to the ability to respond to the external force inside the steel sheet when a natural or artificial external force is received from the outside, and is expressed as the ratio of the yield strength (YP) and the tensile strength (YS) of the steel sheet. YP / TS is regulated to use less than 80%.
한편, 건축철골용 강판은 일반적으로 슬라브를 일반압연하여 제조하거나 또는 일반압연된 강판을 소준열처리하여 제조하고 있다. 이중 상기 일반압연방법은 강재의 재결정온도구간에서 압연을 마무리하는 것으로서, 압연은 단지 강판의 두께 및 형상을 결정하게 되므로 인성이 열악해지는 문제가 있다. 이러한 인성의 개선을 위해 소준(노말라이징) 열처리를 적용하는 방법이 현재 널리 이용되고 있다.On the other hand, steel sheet for building steel is generally manufactured by rolling the slab in general or by heat-treating the general rolled steel sheet. The general rolling method is to finish the rolling in the recrystallization temperature section of the steel, the rolling only determines the thickness and shape of the steel sheet has a problem of poor toughness. In order to improve such toughness, a method of applying a roughing (normalizing) heat treatment is currently widely used.
상기 일반압연재에 소준(노말라이징) 열처리를 적용하면 강의 인성을 향상 시킬 수는 있지만, 반대로 강도가 하락할 수 있기 때문에 탄소등 강도상승에 유효한 원소를 다량으로 첨가하게 되어 탄소당량이 높아져 강판의 용접성이 열악해 지는 문제가 있다.Applying an annealing (normalizing) heat treatment to the general rolled material can improve the toughness of the steel, but on the contrary, the strength may decrease, so that a large amount of elements effective for increasing the strength of carbon, such as carbon, is added to increase the carbon equivalent and weldability of the steel sheet. There is a problem of this deterioration.
본 발명자는 건축철골용 강판의 강도와 강인성은 물론 용접성 및 내지진성을 확보하기 위한 연구 결과, 제어압연한 후 가속냉각하는 조건들을 적절히 제어하면 탄소당량의 상승없이도 강의 강도 및 강인성을 확보할 수 있다는 것을 확인하고 본 발명을 제안하게 이르렀다.The present inventors found that the strength and toughness of the steel plate for building steel, as well as the weldability and anti-tearness, as a result of the appropriate control of accelerated cooling conditions after control rolling can ensure the strength and toughness of the steel without increasing the carbon equivalent It was confirmed that the present invention was proposed.
즉, 본 발명은 강성분계를 조절하고, 제어압연시 마무리 압연온도 및 가속냉각조건을 제어함으로써 강의 강도, 인성 특히, 용접성 및 내지진성을 확보할 수 있는 50㎏급 강판의 제조방법을 제공하고자 하는데, 그 목적이 있다.That is, the present invention is to provide a method of manufacturing a 50kg steel sheet that can ensure the strength, toughness, particularly weldability and anti-vibration of the steel by controlling the steel component system, and control the finish rolling temperature and accelerated cooling conditions during the control rolling , Its purpose is.
제 1도는 본 발명재와 비교재 및 종래재의 미세조직사진이다.1 is a microstructure photograph of the present invention, the comparative material and the conventional material.
상기 목적을 달성하기 위한 본 발명은 50kg 강판의 제조방법에 있어서, 중량%로, C:0.09-0.17%, Si:0.10-0.40%, Mn:1.00-1.60%, p:0.025%이하, S:0.010%이하, Nb:0.008-0.02%, Ti:0.008-0.02%, 및 잔부 Fe 와 기타 불가피한 불순물로 이루어지고, 탄소당량이 0.40%이하를 만족하는 용강에 Ca-Si을 0.6-1kg/ton을 투입하여 MnS개재물을 구상화처리하고, 구상화 처리된 용강을 연속주조하여 슬라브를 제조한 다음, 900-800℃의 마무리 압연온도 조건으로 제어압연한 후 Ar3직상의 850-750℃의 온도에서 3-7℃/sec의 속도로 470-650℃까지 냉각한 후 공냉함을 포함하여 구성된다.The present invention for achieving the above object in the method of manufacturing a 50kg steel sheet, in weight%, C: 0.09-0.17%, Si: 0.10-0.40%, Mn: 1.00-1.60%, p: 0.025% or less, S: Ca-Si is 0.6-1kg / ton in molten steel with 0.010% or less, Nb: 0.008-0.02%, Ti: 0.008-0.02%, balance Fe and other unavoidable impurities, and carbon equivalents below 0.40%. in the spheroidization process and the MnS inclusions and spheroidizing the continuous casting process the molten steel to prepare a slab, and then, after controlled rolling, finishing temperature of 900-800 ℃ rolling at a temperature of 850-750 ℃ 3 immediately above the Ar 3 After cooling to 470-650 ℃ at a rate of 7 ℃ / sec is configured to include an air cooling.
이하, 본 발명에 대하여 상세히 설명한다.EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.
상기 탄소(C)는 소입성 향상원소로서 열처리시 강의 경도 및 강도를 증가시키는데, 그 함량이 0.17중량%(이하,'%'라 함)를 초과하여 첨가하면 인성 및 용접성에 유해하며, 0.09%미만으로 소량 첨가되면 소입성이 낮아 경도를 보증할 수 없으므로 0.09-0.17%의 범위로 첨가하는 것이 바람직하다.The carbon (C) increases the hardness and strength of the steel during heat treatment as an element for improving hardenability, and if the content exceeds 0.17% by weight (hereinafter, referred to as '%'), it is harmful to toughness and weldability, and 0.09% If it is added in a small amount, it is preferable to add in a range of 0.09-0.17% because the quenchability is low to ensure the hardness.
상기 규소(Si)는 탄화물을 형성하며 Fe중에 고용되어 탄성한계 인장력을 높이는 원소로서 그 함량이 0.10% 미만에서는 상기 효과가 미흡하고, 0.40% 초과하면 페라이트조직 저하 및 비금속개재물(silicate)을 형성하여 인성을 해치므로 0.10-0.40%의 범위로 첨가하는 것이 바람직하다.The silicon (Si) forms a carbide and is an element that is solid-solution in Fe to increase the elastic limit tensile strength, the content is less than 0.10%, the effect is insufficient, if the content exceeds 0.40% to form a ferrite structure degradation and non-metallic inclusions (silicate) Since toughness is impaired, it is preferable to add in the range of 0.10-0.40%.
상기 망간(Mn)은 소입성 향상원소로 열처리시 경도를 향상시킬 수 있는 유효한 성분으로서, 그 함량이 1.60%초과하면 용접성을 해치고, 1.0%미만이면 소입성 저하로 경도확보가 불안정하므로 1.0-1.60%의 범위로 첨가하는 것이 바람직하다.The manganese (Mn) is an effective component capable of improving hardness when heat-treated as an element for improving hardenability. If the content exceeds 1.60%, the weldability is deteriorated, and if it is less than 1.0%, hardness is unstable due to the decrease in hardenability. It is preferable to add in the range of%.
상기 인(P)은 강판의 저온 충격인정을 저해시키는 가장 큰 불순물로서 내부 품질을 열화시키므로 그 함량은 0.025%이하로 제한한다.The phosphorus (P) is the largest impurity that inhibits the low temperature impact recognition of the steel sheet, so the internal quality is degraded, the content is limited to 0.025% or less.
상기 황(S)은 인(P)성분과 동일한 유해원소로서 후판 제품에 있어서 저온충격인성 열화의 원인 및 용접성을 해치므로 0.010%이하로 제한한다.The sulfur (S) is the same harmful element as the phosphorus (P) component is limited to 0.010% or less because it causes the deterioration of low-temperature impact toughness and weldability in the thick plate product.
상기 니오븀(Nb)은 강조직상 오스테나이트 내에 고용되어 오스테나이트 경화능을 증대시키고, 또한 페라이트 변태온도를 낮추어 페라이트 입도를 미세하게 하는 효과와 함께 석출강화에 의해 인장강도 및 항복강도를 증가시키며 특히, 항복 강도 증가에 유효한 성분으로 상술한 효과를 나타내기 위해서는 0.008%이상 첨가하여야 하며 0.020% 초과하면 소려취성을 유발하고, 용접부인성 열화에 유해하므로 그 함유하는 양은 0.008-0.020%로 하는 것이 바람직하다.The niobium (Nb) is dissolved in the stressed austenite to increase the austenite hardenability, and also increase the tensile strength and yield strength by precipitation strengthening, with the effect of lowering the ferrite transformation temperature to make the ferrite grain size fine. In order to exhibit the above-mentioned effect as an effective ingredient for increasing the yield strength, it should be added at least 0.008%, and if exceeding 0.020%, it causes brittle brittleness and is harmful to deterioration of weld toughness, so the amount thereof is preferably 0.008-0.020%.
상기 티타늄(Ti)은 모재 및 용접부의 저온인성 향상에 유효한 원소이나 다량 첨가시 효과가 포화되므로 0,008-0.020%로 한정하는 것이 바람직하다.The titanium (Ti) is preferably limited to 0,008-0.020% because the effect is saturated when an element or a large amount is added to improve the low temperature toughness of the base metal and the welded part.
상기와 같은 성분으로 이루어진 강의 용접성을 확보하기 위해서는 하기와 같이 표시되는 탄소당량이 0.4%이하를 만족하여야 한다.In order to ensure the weldability of the steel composed of the above components, the carbon equivalent represented as follows should satisfy 0.4% or less.
상기 조건을 만족하는 용강은 통상, 전로에서 정련하고, 출강한 후 용강에 생석회(CaO)를 투입하여 염기도(CaO/Sio2)를 적정치로 하여 황의 흡수능이 우수한 슬래그를 형성하고 이후 불활성 개스(Gas)를 강하게 불어 넣어 교반시켜 용강과 슬래그(Slag)간의 반응 기회를 확대시킴으로써 용강중의 황(S)을 효과적으로 포집, 부상 시켜 제거하도록 하고 있다.In general, molten steel that satisfies the above conditions is refined in a converter, and after tapping, quicklime (CaO) is added to molten steel to form slag excellent in sulfur absorption ability by using basicity (CaO / Sio2) as an appropriate value, and then inert gas (Gas). ) By blowing strongly and expanding the reaction opportunities between molten steel and slag to effectively capture and float the sulfur (S) in the molten steel.
그러나, 이러한 작용으로 S이 완전히 제거되지 않고, 일부 MnS 개재물이 형성되어 열간압연시 압연방향으로 길게 연신되며, 여기서 수소가 집적되어 크랙이 발생되는 문제가 있다. 특히, 이러한 크랙이 내재되어 있는 강판을 초고층의 건축용 강판에 적용하는 경우 대형사고의 위험성이 존재하게 되므로 이를 제거할 필요가 있다.However, S is not completely removed by this action, and some MnS inclusions are formed and elongated in the rolling direction during hot rolling, where hydrogen is accumulated and cracks are generated. In particular, when the steel sheet is embedded in such a crack is applied to the high-rise building steel sheet there is a risk of large accidents need to be removed.
본 발명에 의하면, 상기 크랙이 원인이 되는 MnS개재물을 구상화시키면 압연시 길게 연신되지 않고 크랙발생이 억제되었는데, 그 구체적인 수단은 Ca계 구상화 제인 Ca-Si를 0.6-1㎏/ton 투입하면 MnS개재물을 구상화 시킬 수 있었다.According to the present invention, when the MnS inclusions caused by the cracks are spheroidized, the elongation of the MnS inclusions is not elongated at the time of rolling and cracking is suppressed. Could be envisioned.
본 발명에서, 구상화제의 투입량을 상기와 같이 제한 하는 이유는 투입량이 너무 적은 경우에는 투입효과가 없고, 너무 많은 경우에는 오히려 산화물계 개재물의 양이 증가되기 때문이다.In the present invention, the reason for limiting the amount of the spheroidizing agent as described above is that when the amount is too small, there is no effect of adding, and when too much, the amount of the oxide inclusions is increased.
상기와 같이 구상화처리된 용강은 통상의 방법으로 연속주조하여 슬라브를 제조한 다음 제어압연을 하는데, 그 방법은 마무리 압연온도조건을 제외하고, 나머지 조건은 통상의 방법으로 하면 되므로 특별히 한정하지 않는다.The spheroidized molten steel as described above is continuously cast in a conventional manner to produce a slab, and then subjected to controlled rolling. The method is not particularly limited since the remaining conditions may be a conventional method except for finish rolling temperature conditions.
즉, 강슬라브를 재결정역에서 조압연을 하고, 이후 미재결정역에서 1차 사상압연을 한다음, 900-80℃의 온도에서 마무리 압연하면 되는데, 상기 마무리 압연온도가 900℃ 초과하는 경우 혼립조직이 생성되어 충격인성이 저하되며, 800℃ 미만의 경우 이상역 알연(Two Phase Rolled)시 조직상에 밴드 스트럭처가 생성되어 부분 재결정 압연에서 처럼 충격치가 낮아지고 두께방향 물성치가 불량하게 된다.That is, the steel slab is roughly rolled in the recrystallization station, and then the first finishing rolling in the non-recrystallization station, and finish rolling at a temperature of 900-80 ℃, if the finish rolling temperature exceeds 900 ℃ mixed structure In this case, the impact toughness is lowered, and when the temperature is lower than 800 ° C., a band structure is formed on the structure at the time of two phase rolled, so that the impact value is lowered as in partial recrystallization rolling, and the thickness direction physical properties are poor.
상기와 같이 마무리 압연한후 Ar3직상의 온도인 850-750℃에서 가속냉각을 실시하는데, 이때의 냉각속도는 3-7℃/sec로 하는 것이 좋다. 그 이유는 냉각속도가 3℃/sec미만의 경우 생성되는 페라이트 입도가 조대해져 제2차상의 생성이 적어 적정강도 확보가 어렵고, 7℃/sec 초과하는 경우 제 2차상의 양이 많아져 강도의 급격한 증가에 따른 항복비 상승으로 이어져 소성변형 능력저하로 항복비가 80%를 초과하게 되기 때문이다.After the finish rolling as described above, accelerated cooling is performed at 850-750 ° C., which is directly above Ar 3 , and the cooling rate at this time is preferably 3-7 ° C./sec. The reason for this is that the ferrite particle size generated when the cooling rate is lower than 3 ° C / sec is coarse, so that the formation of the secondary phase is small, so that it is difficult to secure the appropriate strength. This is because the yield ratio will rise due to a sharp increase, and the yield ratio will exceed 80% due to the deterioration of plastic deformation capacity.
상기와 같이 냉각하는데, 이때 냉각종료온도는 470-650℃로 하는 것이 바람직한데, 그 이유는 470℃미만의 경우 강판 내외부의 열전달계수의 차이에 의해 내부응력 발생과다로 강판의 형상이 불량하게 되며, 650℃ 초과하는 경우 조직상 연한조직인 퍼얼라이트로 변태되어 강도가 물성치를 만족하지 못하게 되기 때문이다.As described above, the cooling end temperature is preferably 470-650 ℃, the reason is less than 470 ℃ due to the difference in the heat transfer coefficient of the inside and outside of the steel sheet due to excessive internal stress caused the shape of the steel sheet is poor If the temperature exceeds 650 ° C, it is transformed into soft light, which is a soft tissue, and the strength does not satisfy the physical properties.
상기와 같이 가속냉각을 완료한 후, 공냉하면 본 발명이 완성되며, 이와같이 제조된 50㎏급 강판은 강도 및 인성이 우수하고, 특히 용접성 및 내지진성이 확보되어 철골건축용 강판에 적합하나, 본 발명은 이에 한정하지 않고 상기한 특성이 요구되는 곳에는 그 적용이 가능하다.After the completion of the accelerated cooling as described above, the present invention is completed by air cooling, the 50kg steel sheet thus prepared is excellent in strength and toughness, in particular, weldability and anti-vibration is secured, but suitable for steel plate construction, but the present invention The present invention is not limited thereto, and the above properties can be applied where required.
이하 실시예를 통하여 본 발명을 구체적으로 설명한다.Hereinafter, the present invention will be described in detail through examples.
실시예Example
하기 표1은 발명강 및 종래강을 나타낸 것으로서, 통상의 방법으로 출강된 용강에 생석회를 투입하여 황을 부상 분리 시킨 다음, 이후 Ca-Si분말을 용강톤당 0.6∼1kg 투입하여 MnS개재물의 구상화를 처리한 강 성분이다. 상기와 같이 조성된 강을 연속주조한 다음 980-990℃의 온도에서 조압연하고, 이후 840-970℃의 온도에서 잔압하량 40-70%로 1차사상압연하고, 하기표 2의 조건으로 마무리 압연, 냉각하여 강판을 제조하였다. 상기와 같이 제조된 강판의 기계적특성을 평가한 다음, 그 결과를 하기표 2에 나타내었다.Table 1 shows the invention steel and the conventional steel, the quick lime is added to the molten steel tapping in the usual way to separate the sulfur, and then 0.6 to 1kg per ton of Ca-Si powder to spheroidized MnS inclusions Treated steel component. Continuous casting of the steel composition as described above and then rough-rolled at a temperature of 980-990 ℃, after the primary sequential rolling to a residual load 40-70% at a temperature of 840-970 ℃, under the conditions of Table 2 Finish rolling and cooling were carried out to prepare a steel sheet. After evaluating the mechanical properties of the steel sheet manufactured as described above, the results are shown in Table 2 below.
[표 1]TABLE 1
[표 2]TABLE 2
상기 표 1과 2에 나타난바와 같이, 본 발명의 조성 및 제조조건 범위를 만족하는 발명재(1-9)의 경우 종래재와 비교하여 탄소당량이 낮으므로 용접성이 우수함을 간접적으로 알 수 있으며, 특히 탄소당량이 낮음에도 불구하고, 강도 및 인성 그리고 항복비가 종래재 대비 동등 이상임을 알 수 있었다.As shown in Tables 1 and 2, in the case of the invention material (1-9) that satisfies the composition and the range of manufacturing conditions of the present invention can be indirectly known that the weldability is excellent because the carbon equivalent is lower than that of the conventional material. In particular, despite the low carbon equivalent, the strength, toughness and yield ratio were found to be equal to or higher than those of conventional materials.
반면, 비교재(1-2)의 경우 고온의 마무리 압연온도에 의하여 규격치에 못미치는 인장강도가 나타났다. 또한, 비교재(3-4)의 경우 본 발명의 냉각속도 및 냉각종료온도를 벗어나기 때문에 저온조직인 베이나이트의 분율증가로 강도상승 및 항복비가 초과함을 알 수 있었다. 또한, 비교재(5-6)의 경우 본 발명의 냉각속도보다 늦기 때문에 공냉재와 같은 조직(페라이트+펄라이트)으로 인해 강도가 미달 되었다. 또한, 비교재(7)의 경우 본 발명보다 저온에서 냉각이 종료되고, 냉각속도가 빠르기 때문에 연속항복정 현상이 발생하여 항복강도가 규격치에 못미치는 결과가 나타났다. 이는 조직중에 제2상인 저온변태 조직의 다량발생으로 인해 인장강도는 급격히 상승하지만 항복강도는 미끄럼현상이 일어나 상 ·하항복점 현상이 유실되는 조직적인 문제인 것이다.On the other hand, in the case of the comparative material (1-2), the tensile strength was less than the standard value by the high temperature finish rolling temperature. In addition, in the case of the comparative material 3-4, the strength increase and yield ratio exceeded due to the increase in the fraction of bainite, which is a low-temperature structure, because the cooling rate and the cooling end temperature of the present invention were exceeded. In addition, in the case of the comparative material (5-6) is slower than the cooling rate of the present invention, the strength was insufficient due to the structure (ferrite + pearlite) such as the air-cooling material. In addition, in the case of the comparative material 7, the cooling is terminated at a lower temperature than the present invention, and the cooling rate is faster, so that the yield yield phenomenon occurs and the yield strength is less than the standard value. This is due to the occurrence of a large amount of low-temperature transformation tissue in the second phase of the tissue, the tensile strength rises rapidly, but the yield strength is a sliding problem occurs, the upper and lower yield point phenomenon is lost.
이와같이 발명재, 비교재 및 종래재의 기계적 특성차이는 그 미세조직을 나타낸 도 1를 보면 더욱 확연히 알 수 있다.As such, the difference in mechanical properties between the invention, the comparative material, and the conventional material can be more clearly seen in FIG. 1 showing the microstructure.
즉, 비교재(4,7)의 미세조직사진(도 1의 (c,d))을 보면 저온조직이 발생하여 기계적 특성이 열악함을 알 수 있고, 또한, 종래재(1-2)의 미세조직사진(도 1의 (e,1))을 보면 퍼얼라이트 밴드가 나타나 있는 반면, 발명재(1,4)의 미세조직사진(도 1의 (a,b))을 보면 이방성이 향상되고, 조직이 미세화 되었음을 알 수 있었다.That is, when looking at the microstructure photograph ((c, d) of FIG. 1) of the comparative materials (4, 7), it can be seen that low temperature tissue is generated and the mechanical properties are poor. In the microstructured photograph ((e, 1) of FIG. 1), the pearlite band is shown, while in the microstructured photograph ((a, b) of FIG. 1), the anisotropy is improved. , The tissue was micronized.
상술한 바와 같이, 본 발명은 종래재의 50㎏급 강판에 비교하여 강도 및 인성 그리고 항복비 특성이 우수하고, 특히 용접성이 크게 향상되어 용접구조물에 적용될 수 있는 유용한 효과가 있는 것이다.As described above, the present invention is excellent in strength, toughness and yield ratio characteristics compared to the conventional 50 kg steel sheet, and particularly has a useful effect that can be applied to the weld structure is greatly improved weldability.
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