KR100470640B1 - A high strength bake-hardenable cold rolled steel sheet, and a method for manufacturing it - Google Patents

A high strength bake-hardenable cold rolled steel sheet, and a method for manufacturing it Download PDF

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KR100470640B1
KR100470640B1 KR10-2000-0070189A KR20000070189A KR100470640B1 KR 100470640 B1 KR100470640 B1 KR 100470640B1 KR 20000070189 A KR20000070189 A KR 20000070189A KR 100470640 B1 KR100470640 B1 KR 100470640B1
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steel sheet
rolled steel
less
cold rolled
hardening
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KR20020040214A (en
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한성호
김성진
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주식회사 포스코
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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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • 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
    • 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)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

본 발명은 자동차의 외판재 등에 사용되는 냉연강판의 제조방법 및 그 방법으로 제조된 냉연강판에 관한 것으로서, 강중 Nb, V을 첨가하고 이를 C와 결합시킴으로써, 소부경화량이 3~6kgf/mm2, 평균r치가 2.0이상이며, 내시효성도 우수한 소부경화형 냉연강판을 제조하는 방법, 및 그 방법으로 제조된 냉연강판을 제공하는 것을 목적으로 한다.The present invention relates to a method for manufacturing a cold rolled steel sheet used in an outer plate material of a vehicle, and a cold rolled steel sheet manufactured by the method. By adding Nb and V in steel and combining it with C, the hardening hardening amount of 3 to 6 kgf / mm 2 , It is an object of the present invention to provide a method for producing a hardened hardened cold rolled steel sheet having an average r value of 2.0 or more and excellent in aging resistance, and a cold rolled steel sheet produced by the method.

상기한 목적을 달성하기 위한 본 발명은,The present invention for achieving the above object,

중량%로, C : 0.0020~0.0030%, Si : 0.02% 이하, Mn : 0.07~0.2%, P : 0.05~0.08%, S : 0.008% 이하, Sol.Al : 0.02~0.06%, N : 0.0035% 이하, Nb : 0.008~0.012%, V: 0.02~0.1%, 기타 불가피한 불순물로 조성되는 강을 1200℃이상에서 균질화 열처리하고 900~950℃의 온도범위에서 마무리 열간압연한 후 700~750℃의 온도범위에서 권취하고, 75~80%의 압하율로 냉간압연한 다음 830~850℃의 온도범위에서 연속소둔하고, 1.3~2.0%의 압하율로 조질압연하는 것을 포함하여 이루어지는 고강도 소부경화형 냉연강판의 제조방법, 및 그 방법으로 제조된 고강도 소부경화형 냉연강판을 기술적 요지로 한다.By weight%, C: 0.0020 ~ 0.0030%, Si: 0.02% or less, Mn: 0.07 ~ 0.2%, P: 0.05 ~ 0.08%, S: 0.008% or less, Sol.Al: 0.02 ~ 0.06%, N: 0.0035% Or less, Nb: 0.008 ~ 0.012%, V: 0.02 ~ 0.1%, homogeneous heat treatment of steel composed of other unavoidable impurities at 1200 ℃ or higher and finishing hot rolling at temperature range of 900 ~ 950 ℃, then temperature of 700 ~ 750 ℃ Of high strength hardened hardened cold rolled steel sheet comprising winding in the range, cold rolling at a reduction ratio of 75 to 80%, continuous annealing at a temperature range of 830 to 850 ° C, and temper rolling at a reduction ratio of 1.3 to 2.0%. The manufacturing method and the high-strength-baking hardened type cold-rolled steel sheet manufactured by the method are the technical summary.

Description

고강도 소부경화형 냉연강판 및 그 제조방법{A HIGH STRENGTH BAKE-HARDENABLE COLD ROLLED STEEL SHEET, AND A METHOD FOR MANUFACTURING IT}High strength hardened hardened cold rolled sheet and its manufacturing method {A HIGH STRENGTH BAKE-HARDENABLE COLD ROLLED STEEL SHEET, AND A METHOD FOR MANUFACTURING IT}

본 발명은 자동차의 외판재 등에 사용되는 냉연강판 및 그 제조방법에 관한 것으로서, 보다 상세하게는 강중 Nb, V을 첨가하고 이를 C와 결합시킴으로써 성형성이 우수하면서 소부경화성도 우수한 냉연강판을 제조할 수 있는 방법 및 성형성이 평균r치 기준으로 2.0이상이고 상온 내시효성도 우수한 냉연강판에 관한 것이다.The present invention relates to a cold rolled steel sheet and a method for manufacturing the same, which are used in automobile exterior materials, and more particularly, by adding Nb and V in steel and combining the same with C to produce a cold rolled steel sheet having excellent moldability and excellent hardening property. The present invention relates to a cold rolled steel sheet having a method and moldability of 2.0 or more based on an average r value and excellent in aging resistance at room temperature.

최근 자동차의 연비향상 및 차체의 경량화를 목적으로, 차체에 고강도강판을 사용하여 판두께를 감소시키고 내덴트성을 향상시키려는 노력이 진행되고 있다. Recently, for the purpose of improving the fuel efficiency of automobiles and reducing the weight of the vehicle body, efforts have been made to reduce the plate thickness and improve the dent resistance by using a high strength steel sheet for the vehicle body.

한편, 자동차용 냉연강판에 요구되는 특성으로는 우수한 항복강도 및 인장강도, 양호한 프레스 성형성, 스폿트(spot) 용접성, 피로특성 등이 있는데, 일반적으로 강도와 가공성은 서로 상반된 특징을 나타내며, 이러한 두가지 특성을 만족할 수 있는 강판이 요구된다. 이와 같은 강판으로는, 크게 복합조직형 냉연강판과 소부경화형 냉연강판을 들 수 있다. On the other hand, the characteristics required for cold rolled steel sheet for automobiles include excellent yield strength and tensile strength, good press formability, spot weldability, fatigue properties, etc. In general, strength and workability show opposite characteristics. There is a need for a steel sheet that can satisfy both characteristics. As such a steel plate, a composite structure type cold rolled steel sheet and a baking hardening type cold rolled steel sheet are mentioned largely.

복합조직형 냉연강판은, 인장강도 40kgf/㎟급 이상에서는 일반적으로 용이하게 제조할 수 있고 자동차용 소재에 있어서 스트레칭성(stretchability)을 나타내는 인자인 연신율은 높지만, 자동차의 프레스 성형성을 나타내는 평균 r치가 낮으며, 망간, 크롬 등 고가의 합금원소가 과다하게 첨가되어 제조원가가 높은 단점이 있다. The composite structured cold rolled steel sheet can be easily produced at a tensile strength of 40kgf / mm2 or more in general, and has a high elongation, which is a factor indicating stretchability in automobile materials, but has an average r showing press formability of automobiles. It is low in value, expensive alloying elements such as manganese, chromium is added excessively has a disadvantage of high manufacturing cost.

그러나, 소부경화형 냉연강판은 인장강도 40kgf/㎟급 이하에서도, 프레스 성형시 연질강판에 가까운 항복강도를 가지므로 연성이 우수하고, 프레스 성형후 도장소부처리시 저절로 항복강도가 상승하기 때문에, 강도가 증가하면 성형성이 악화되는 종래의 냉연강판에 비해 매우 이상적인 강으로 주목 받고 있다.However, because the hardened hardened cold rolled steel sheet has a yield strength close to the soft steel sheet during press molding even at a tensile strength of 40kgf / mm2 or less, the ductility is excellent, and the yield strength naturally increases during the coating treatment after press molding. It is attracting attention as a very ideal steel compared to the conventional cold rolled steel sheet, which increases the moldability.

상기 소부경화는, 강중에 고용된 침입형 원소인 탄소나 질소가 변형과정에서 생성된 전위를 고착하여 발생되는 일종의 변형시효를 이용한 것으로, 고용탄소 및 질소가 증가하면 소부경화량은 증가하나, 고용원소가 많으면 상온시효를 수반하여 성형성의 악화를 초래하므로, 적정한 고용원소의 제어가 매우 중요하다. The hardening hardening is a kind of strain aging that occurs when carbon or nitrogen, which is a solid solution dissolved in steel, adheres to the potential generated during the deformation process, and the hardening hardening amount increases when the solid solution carbon and nitrogen increase. A large number of elements leads to deterioration of formability with aging at room temperature, so proper control of solid solution elements is very important.

한편, 일반적으로 소부경화성을 가지는 냉연강판은, 저탄소 P첨가 Al-killed강을 단지 저온권취(즉. 열연 권취온도가 400~500℃ 온도범위의 권취)하고, 상소둔에 의해 소부경화량을 약 4-5kgf/㎟로 하여 제조하였는데, 이와 같은 상소둔법을 이용하면 성형성 및 소부경화성을 보다 용이하게 얻을 수 있다. 반면, 연속소둔법에 의한 P첨가 Al-Killed강의 경우, 비교적 빠른 냉각속도를 이용하기 때문에 소부경화성 확보는 용이지만, 급속가열, 단시간 소둔에 의해 성형성이 악화되는 문제점이 있어, 가공성이 요구되지 않는 자동차 외판에만 그 사용이 제한되고 있다. On the other hand, in general, a cold rolled steel sheet having a hardening hardenability is obtained by winding a low carbon P-added Al-killed steel only at low temperature (that is, hot-rolling coiling temperature of 400 to 500 ° C), and reducing the hardening hardening amount by ordinary annealing. 4-5 kgf / mm 2, the moldability and the bake hardenability can be more easily obtained by using such an annealing method. On the other hand, in case of P-added Al-Killed steel by continuous annealing method, it is possible to secure the hardening hardening because it uses relatively fast cooling speed. Its use is limited only to the outer shell of the car.

최근에는, 제강기술의 비약적인 발달에 힘입어 강중에 고용원소를 적정량으로 제어하여 성형성이 우수한 소부경화형 냉연강판을 제조하는 것이 가능해졌는데, 특히 Ti 또는 Nb 등의 강력한 탄질화물 형성원소를 첨가한 Al-Killed 강판은, 내덴트성이 필요한 자동차 외판재 용으로 그 사용이 증가되는 추세에 있다.In recent years, thanks to the rapid development of steelmaking technology, it has become possible to manufacture small hardened type cold rolled steel sheets having excellent formability by controlling solid elements in steel in an appropriate amount. Particularly, Al containing strong carbonitride forming elements such as Ti or Nb is added. -Killed steel sheet is increasingly used for automotive exterior materials requiring dent resistance.

일례로, 일본 특공소61-026757호는, C: 0.0005~0.015%, S+N ≤0.05%, Ti, 및 Ti, Nb복합첨가 극저탄소 냉연강판을 개시하고 있고, 일본 특공소57-89437호는 C: 0.010%이하인 Ti첨가 강을 사용하여 소부경화량이 약 4kgf/mm2이상인 강의 제조방법을 개시하고 있는데, 이들은 Ti, Nb의 첨가량 혹은 소둔시 냉각속도를 제어함으로써 강중 고용원소량을 적절히 제어하여 재질의 열화를 방지하면서 소부경화성을 부여하고 있다. 그러나, Ti 또는 Ti, Nb 복합첨가강의 경우, 적정 소부경화량의 확보를 위해서는 제강공정에서 Ti 및 N, S의 엄격한 제어가 필요하게 되므로, 원가상승의 문제가 발생한다. 또한, 상기 Nb첨가강의 경우 고온소둔에 의한 작업성 악화 및 특수 원소첨가에 의한 제조원가 상승이 예상되는 문제도 있다.As an example, Japanese Unexamined Patent Application Publication No. 61-026757 discloses C: 0.0005 to 0.015%, S + N? 0.05%, Ti, Ti, and Nb-complexed ultra low carbon cold rolled steel sheets, and Japanese Unexamined Patent Application No. 57-89437 Discloses a method of producing steel with a hardened amount of about 4kgf / mm 2 or more using Ti-added steel having a C of 0.010% or less.They control the amount of solid solution in the steel by controlling the addition amount of Ti and Nb or the cooling rate during annealing. This prevents deterioration of the material and gives hardening hardening. However, in the case of Ti, Ti, and Nb composite additive steel, strict control of Ti, N, and S is required in the steelmaking process in order to secure an appropriate bake hardening amount, resulting in a problem of cost increase. In addition, in the case of the Nb-added steel, there is also a problem that the deterioration of workability due to high temperature annealing and the increase in manufacturing cost due to the addition of special elements are expected.

또 다른 예로, 미국특허 제5556485호 및 제5656102호(미국 베들레헴 스틸(Bethlehem Steel)에서 제출)에서는, C: 0.0005~0.1%, Mn: 2.5%이하, Al:0.5% 이하, N:0.04% 이하, 그리고 Ti:0.5%이하, V:0.005~0.6%인 Ti-V계 극저탄소강을 이용한 소부경화형 냉연강판을 제조하는 방법에 관하여 소개하고 있다. 일반적으로, V는 Ti나 Nb와 같은 탄질화물원소보다 더욱 안정하여 소둔온도를 낮출 수 있기 때문에, 열간압연중에 V에 의해 생성된 탄화물인 VC 등은 Nb계 보다 낮은 소둔온도에서도 재용해하여 소부경화성이 확보되는 것이다. 그러나, V는 VC와 같은 탄화물을 형성하기는 하지만 재용해 온도가 매우 낮아 실질적으로 성형성 향상에는 큰 도움을 주지 못하기 때문에, 상기 기술에서는 Ti를 약 0.02%이상 첨가하여 성형성을 도모하고 있다. 이에 따라, 제조원가가 상승할 뿐 아니라, 결정립크기가 커서 내시효성측면에서도 다소 불리한 문제점이 있다.As another example, in U.S. Pat.Nos. 5556485 and 5656102 (submitted by Bethlehem Steel, USA), C: 0.0005-0.1%, Mn: 2.5% or less, Al: 0.5% or less, N: 0.04% or less And a method of producing a hardened hardened cold rolled steel sheet using Ti-V based ultra low carbon steel having a Ti of 0.5% or less and a V of 0.005% to 0.6%. In general, V is more stable than carbonitride elements such as Ti and Nb, so that the annealing temperature can be lowered. Thus, VC, which is a carbide produced by V during hot rolling, is re-dissolved at annealing temperatures lower than that of Nb-based so as to harden the hardening. This is to be secured. However, since V forms carbides such as VC, but the remelting temperature is very low, which does not substantially improve moldability, the above technique adds about 0.02% or more of Ti to achieve moldability. . Accordingly, not only the manufacturing cost rises but also the grain size is large, and thus there is a disadvantage in terms of aging resistance.

또한, 일본 특공평9-249936호는, C: 0.001~0.008%, Mn: 1.5%이하, N: 0.005%이하, Nb: 0.003~0.06% 및 V: 0.004~0.14%, 그리고 0.0002 ≤ C-(12/93)Nb ≤ 0.002(wt%) 및 V ≥ 0.55Nb+0.001(wt%)의 식을 만족하도록 Nb 및 V함량을 제어한 소부경화형 냉연강판의 제조방법을 개시하고 있다. 그러나, 상기한 성분계는, 매우 광범위하여 적정한 소부경화성과 더불어 성형성, 특히 평균r치를 개선하는 데에는 다소 문제가 있음을 알 수 있었다. 예를 들어, 상기 기술의 실시예 중 한 발명강의 경우, C: 0.0076%, Nb: 0.0565% 및 V: 0.132를 첨가함에 의해, 소둔온도 830℃에서 소부경화량(BH)이 45MPa, 시효지수(AI)가 11MPa인 소부경화성 및 내시효성이 우수한 냉연강판을 제조할 수 있다고 주장하였으나, 정밀한 실험결과 상기 성분계로는 소부경화성이 거의 발생하지 않음을 확인할 수 있었다. 즉, 상기 기술에서는, 성형성 및 소부경화성을 확보하기 위해서, C를 Nb로 완전히 석출시켜 성형성을 향상시킨 후 고온소둔을 통해 재용해시켜야 하는 것이다. 그러나, 하기 관계식(1)에 의해 NbC석출물의 재용해온도를 계산한 결과, 그 온도가 약 1040℃로 매우 높아서, 830℃에서 연속소둔할 경우 재용해는 거의 일어나지 않음을 예상할 수 있다. In addition, Japanese Patent Application Laid-Open No. 9-249936 discloses C: 0.001-0.008%, Mn: 1.5% or less, N: 0.005% or less, Nb: 0.003-0.06% and V: 0.004-0.14%, and 0.0002 ≦ C- ( 12/93) discloses a method for producing a hardened hardened cold rolled steel sheet in which Nb and V content are controlled to satisfy the formula of Nb ≦ 0.002 (wt%) and V ≧ 0.55 Nb + 0.001 (wt%). However, it has been found that the above-described component system is very wide and somewhat problematic in improving moldability, in particular, an average r value, with appropriate bake hardenability. For example, in the case of one of the embodiments of the above technique, by adding C: 0.0076%, Nb: 0.0565%, and V: 0.132, the baking hardening amount (BH) was 45 MPa at the annealing temperature of 830 ° C., and the aging index ( It is claimed that the cold rolled steel sheet having excellent AI hardening resistance and aging resistance of 11 MPa can be manufactured. However, it was confirmed that hard hardening hardly occurs in the component system. That is, in the above technique, in order to secure moldability and baking hardening property, C must be completely precipitated with Nb to improve moldability and then re-dissolve through high temperature annealing. However, as a result of calculating the re-dissolution temperature of NbC precipitates by the following relation (1), the temperature is very high at about 1040 ° C., and it can be expected that re-dissolution hardly occurs when continuously annealed at 830 ° C.

[관계식 1][Relationship 1]

log[Nb][C] = -8970/T + 3.46 log [Nb] [C] = -8970 / T + 3.46

또한, Nb/C 원자비도 약 0.95로서 열간압연단계에서부터 잔존하는 고용탄소가 매우 낮아, NbC 석출물의 재용해없이 45MPa의 소부경화성을 확보하기가 매우 어렵다는 문제가 있다. 또한, Nb함량이 0.015%인 다른 발명강의 경우에도 소부경화성은 1.6kgf/㎟으로 매우 낮았다. 따라서, 상기 기술에서는, 소부경화성, 상온내시효성 및 성형성, 특히 평균 r치를 동시에 개선시키기 위해, 성분을 엄격하게 관리해야 하는 문제가 있는 것이다.In addition, the Nb / C atomic ratio is about 0.95, and there is a problem that the solid solution carbon remaining from the hot rolling step is very low, and it is very difficult to secure the baking hardness of 45 MPa without re-dissolving NbC precipitates. Also, in the case of other inventive steels having an Nb content of 0.015%, the bake hardenability was very low, 1.6 kgf / mm 2. Therefore, in the above technique, there is a problem in that the components must be strictly managed in order to simultaneously improve baking hardening, room temperature aging resistance, and moldability, especially the average r value.

이에, 본 발명자들은 상기와 같은 문제점을 해결하기 위하여 연구와 실험을 거듭하고 그 결과에 근거하여 본 발명을 제안하게 된 것으로, 본 발명은 강중 Nb, V을 첨가하고 이를 C와 결합시킴으로써, 소부경화량이 3~6kgf/mm2, 평균r치가 2.0이상이며, 내시효성도 우수한 소부경화형 냉연강판 및, 그 제조방법을 제공하는 것을 목적으로 한다.Accordingly, the present inventors have repeatedly studied and experimented to solve the above problems, and proposed the present invention based on the results. The present invention adds Nb and V in steel and combines it with C, which causes hardening It is an object of the present invention to provide a hardened hardened cold rolled steel sheet having an amount of 3 to 6 kgf / mm 2 and an average r value of 2.0 or more and excellent in aging resistance, and a method of manufacturing the same.

상기한 목적을 달성하기 위한 본 발명은,The present invention for achieving the above object,

중량%로, C : 0.0020~0.0030%, Si : 0.02% 이하, Mn : 0.07~0.2%, P : 0.05~0.08%, S : 0.008% 이하, Sol.Al : 0.02~0.06%, N : 0.0035% 이하, Nb : 0.008~0.012%, V: 0.02~0.1%, 기타 불가피한 불순물로 조성되는 강을 1200℃이상에서 균질화 열처리하고 900~950℃의 온도범위에서 마무리 열간압연한 후 700~750℃의 온도범위에서 권취하고, 75~80%의 압하율로 냉간압연한 다음 830~850℃의 온도범위에서 연속소둔하고, 1.3~2.0%의 압하율로 조질압연하는 것을 포함하여 이루어지는 고강도 소부경화형 냉연강판의 제조방법에 관한 것이다.By weight%, C: 0.0020 ~ 0.0030%, Si: 0.02% or less, Mn: 0.07 ~ 0.2%, P: 0.05 ~ 0.08%, S: 0.008% or less, Sol.Al: 0.02 ~ 0.06%, N: 0.0035% Or less, Nb: 0.008 ~ 0.012%, V: 0.02 ~ 0.1%, homogeneous heat treatment of steel composed of other unavoidable impurities at 1200 ℃ or higher and finishing hot rolling at temperature range of 900 ~ 950 ℃, then temperature of 700 ~ 750 ℃ Of high strength hardened hardened cold rolled steel sheet comprising winding in the range, cold rolling at a reduction ratio of 75 to 80%, continuous annealing at a temperature range of 830 to 850 ° C, and temper rolling at a reduction ratio of 1.3 to 2.0%. It relates to a manufacturing method.

또한, 본 발명은, 중량%로, C : 0.0020~0.0030%, Si : 0.02% 이하, Mn : 0.07~0.2%, P : 0.05~0.08%, S : 0.008% 이하, Sol.Al : 0.02~0.06%, N : 0.0035% 이하, Nb : 0.008~0.012%, V: 0.02~0.1%, 기타 불가피한 불순물로 조성되고, 소부경화량이 3~6kgf/mm2, 평균r치가 2.0이상이며, 그리고 100℃에서 1시간 시효처리시 항복점 연신율값이 0.1%이하인 고강도 소부경화형 냉연강판에 관한 것이다.In addition, the present invention is, in weight%, C: 0.0020 to 0.0030%, Si: 0.02% or less, Mn: 0.07 to 0.2%, P: 0.05 to 0.08%, S: 0.008% or less, Sol.Al: 0.02 to 0.06 %, N: 0.0035% or less, Nb: 0.008 ~ 0.012%, V: 0.02 ~ 0.1%, composed of other unavoidable impurities, baking hardening amount of 3 ~ 6kgf / mm 2 , average r value of 2.0 or more, and at 100 ℃ The present invention relates to a high strength hardening hardened cold rolled steel sheet having a yield point elongation of 0.1% or less during 1 hour aging.

이하, 본 발명에 대하여 설명한다.EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

본 발명의 발명자들은, 성형성이 우수하면서 소부경화성도 우수한 냉연강판을 얻기 위해서, V 및 강력한 탄질화물 형성원소인 Nb을 보다 적정수준으로 첨가하여 C와 상호 결합시킴으로써, 소둔후 서냉처리를 행하더라도 적정 소부경화성을 확보할 수 있는 새로운 Nb-V첨가 극저탄소강을 제조하고자 하였다. 본 발명에서는, 성형성을 향상시키기 위해 VC 및 NbC 석출물을 적절히 제어할 뿐 아니라, S, Mn 및 P의 함량도 엄격하게 제어하여, 평균r치가 2.0인 고성형 소부경화형 냉연강판을 제조할 수 있었다. 특히, Nb을 첨가함으로써, Ti을 첨가하는 경우보다 미세한 소둔 결정립을 얻을 수 있게 되어, 내시효특성을 향상시킬 수 있었다.The inventors of the present invention, in order to obtain a cold-rolled steel sheet having excellent moldability and excellent hardening hardenability, by adding V and Nb, which is a strong carbonitride-forming element, at a more suitable level and mutually bonding with C, even after performing annealing after annealing, The new Nb-V-added ultra low carbon steel was obtained to ensure the appropriate baking hardness. In the present invention, not only the VC and NbC precipitates are properly controlled in order to improve the formability, but also the S, Mn and P contents are strictly controlled to produce a high-molded small hardened cold rolled steel sheet having an average r value of 2.0. . In particular, by adding Nb, fine annealing crystal grains can be obtained than when Ti is added, and the aging resistance can be improved.

이하, 본 발명의 강 성분 및 제조조건에 대하여 설명한다.Hereinafter, the steel component and manufacturing conditions of this invention are demonstrated.

C는 고용강화 및 소부경화성을 나타내는 원소로, 그 함량이 0.0020%미만이면 인장강도가 부족하게 되고, 절대 C량이 낮아 충분한 소부경화성이 얻어지지 않는다. 또한, 0.0030%이상이면 830~850℃의 소둔공정에서 NbC석출물로부터 재용해되는 C와, 열연단계에서 NbC로 석출하지 못한 C의 량이 과다하게 되어, 소부경화성이 매우 높고 상온 내시효성도 확보되지 않는다. 이로 인해, 프레스 성형시 스트레쳐 스트레인이 발생하므로 성형성과 연성이 저하되는 문제가 있다. 따라서, 상기 C의 함량은 0.0020~0.0030%로 설정하는 것이 바람직하다.C is an element showing solid solution hardening and baking hardening. If the content is less than 0.0020%, the tensile strength is insufficient, and the absolute C content is low and sufficient baking hardening is not obtained. In addition, if it is more than 0.0030%, the amount of C re-dissolved from the NbC precipitate in the annealing process at 830 ~ 850 ℃, and C not precipitated by the NbC in the hot rolling step is excessive, so the hardening hardenability is very high and room temperature resistance is not secured . For this reason, since a stretcher strain arises at the time of press molding, there exists a problem that moldability and ductility fall. Therefore, the content of C is preferably set to 0.0020 to 0.0030%.

Si은 강도를 증가시키는 원소로서, 첨가량이 증가할수록 강도는 증가하나 연성의 열화가 현저하므로, 그 첨가량을 0.02%이하로 제한하는 것이 바람직하다.Si is an element that increases the strength, the strength increases as the addition amount increases, but the ductility deterioration is remarkable, it is preferable to limit the addition amount to 0.02% or less.

Mn은 연성의 손상없이 입자를 미세화시키고, 강중 S을 완전히 MnS로 석출시켜 FeS의 생성에 의한 열간취성을 방지하는 역할을 하는 원소로서, 이와 같은 효과를 얻기 위해서는 0.07%이상 첨가되는 것이 바람직하다. 그러나, 0.2%이상 첨가될 경우, Mn-C 다이폴(dipole)이 형성되어 성형성이 저하하고, 소부경화성이 감소하여 평균r치 2.0이상의 냉연강판을 제조할 수 없게 되며, 고용강화에 의해 강도가 급격히 증가한다. 따라서, 그 첨가량을 0.07-0.2%로 제한하는 것이 바람직하다.Mn is an element that plays a role of miniaturizing particles without damaging ductility and precipitating S in steel to MnS to prevent hot brittleness due to the formation of FeS. In order to obtain such an effect, Mn is preferably added at least 0.07%. However, when 0.2% or more is added, Mn-C dipoles are formed and moldability is reduced, and baking hardening properties are reduced, so that cold rolled steel sheets having an average r value of 2.0 or more cannot be manufactured. Increase sharply Therefore, it is preferable to limit the addition amount to 0.07-0.2%.

P은 고용강화효과가 가장 큰 치환형 합금원소로서, 면내 이방성을 개선하고 강도를 향상시키며, 열연판 결정립을 미세화시켜 향후 소둔단계에서 평균r치의 향상에 유리한 (111)집합조직의 발달을 조장하는 역할을 한다. 특히, 소부경화성의 영향측면에서, C와의 싸이트경쟁(site competition)효과에 의해, 그 함량이 증가할수록 소부경화성은 증가하는 경향을 나타내기 때문에, 상기 P의 함량은 0.05% 이상 첨가하는 것이 바람직하다. 그러나, 0.08%이상 첨가하는 경우 성형성의 향상에 비해 급격한 강도상승이 발생되며, 또한 P량의 과다첨가로 인해 P가 입계에 편석하여 재료를 취하시키는 등 연성의 현저한 저하가 발생하게 된다. 따라서, 그 첨가량은 0.05~0.08%로 설정하는 것이 바람직하다.P is the substitution type alloy element with the largest solid solution strengthening effect. It improves in-plane anisotropy and improves the strength, and refines the hot-rolled sheet grain to promote the development of the (111) aggregate structure, which is advantageous for improving the average r value in the future annealing step. Play a role. Particularly, in view of the effect of quench hardening, the quench hardening property tends to increase as the content thereof increases due to the site competition effect with C. Therefore, the content of P is preferably added at least 0.05%. . However, the addition of 0.08% or more causes a sharp increase in strength as compared with the improvement of formability, and also due to the excessive addition of P amount, a significant decrease in ductility such as segregation of P at the grain boundaries and withdrawal of the material occurs. Therefore, it is preferable to set the addition amount to 0.05 to 0.08%.

S은 고온에서 MnS의 황화물로 석출되는 원소이나, 그 함량이 과다한 경우 MnS로 석출하고 남은 S가 입계를 취화시켜 열간취성을 야기시킨다. 또한, S의 함량이 MnS석출물을 완전히 석출시키는 양이라 할지라도, S함량이 많으면 과도한 MnS석출물에 의한 재질열화로 인해, 2.0이상의 평균r치를 확보하기가 어려우므로, 그 첨가량을 0.008% 이하로 제한하는 것이 바람직하다.S is an element that precipitates as a sulfide of MnS at high temperature, but when the content is excessive, S precipitates as MnS and the remaining S embrittles grain boundaries, causing hot brittleness. In addition, even if the content of S is the amount to completely precipitate the MnS precipitate, if the S content is large, due to material deterioration due to excessive MnS precipitate, it is difficult to secure an average r value of 2.0 or more, so the addition amount is limited to 0.008% or less It is desirable to.

Sol.Al은 강의 탈산을 위해 첨가되는 원소로, 그 함량이 0.02%미만이면 강중에 산화개재물이 많아져 가공성이 열화되는 등 기계적 성질에 불리하며, 특히 고용질소를 완전히 AlN으로 석출시키지 못하게 되어 고용질소에 의한 시효열화를 유발하게 된다. 또한, 0.06%이상으로 과다하게 첨가되면, 고용질소를 AlN으로 완전히 석출시켜 질소에 의한 시효열화는 방지될 수 있으나, 재질의 경화 및 제조비용의 상승을 초래하게 된다. 따라서, 상기 Sol.Al의 함량은 0.02-0.06%로 제한하는 것이 바람직하다.Sol.Al is an element added for deoxidation of steel, and if its content is less than 0.02%, it has disadvantages in mechanical properties such as oxidative inclusions in steel and deterioration of workability. Especially, Sol.Al cannot be dissolved completely into AlN. Deterioration of aging by nitrogen is caused. In addition, when excessively added at 0.06% or more, the solid solution of nitrogen is completely precipitated with AlN to prevent age degradation due to nitrogen, but causes hardening of the material and an increase in manufacturing cost. Therefore, the content of Sol.Al is preferably limited to 0.02-0.06%.

N는 소둔전 또는 소둔후에 고용상태로 존재하여 강의 성형성을 열화시키며 시효열화가 다른 침입형원소에 비해 매우 크므로, Al에 의해 고정할 필요가 있다. 그러나, 그 함량이 0.0035%이상이면 고용질소를 제거시키기 위한 Al의 함량이 증가하게 되어 재질을 경화시키고 또한 제조비용 상승을 초래하게 되므로, 그 함량을 0.0035%이하로 제한하는 것이 바람직하다.N is present in solid solution before or after annealing to deteriorate the formability of the steel, and the aging deterioration is much greater than that of other invasive elements, so it is necessary to fix it with Al. However, if the content is more than 0.0035%, the content of Al for removing solid solution nitrogen is increased to cure the material and increase the manufacturing cost. Therefore, the content is preferably limited to 0.0035% or less.

Nb는 C와 결합해 NbC석출물을 석출시켜 강도를 증가시키고 성형성을 향상시키는 역활을 한다. 그러나, 그 함량이 0.012%이상이면, 과도한 NbC 석출물의 형성과 더불어 NbC 석출물의 재용해온도가 상승하기 때문에, 830~850℃의 소둔온도에서 NbC 석출물이 재용해되지 못하여 강중에 적정 고용탄소량의 확보가 매우 어렵다. 이 경우, NbC 석출물의 재용해를 통해 적정량의 고용탄소량을 확보하기 위해서는, 소둔온도를 870℃이상으로 증가시켜야 하는데, 소둔온도를 증가시키면 소둔시 버클링(buckling) 등의 작업성 악화를 유발하게 된다. 따라서, 상기 Nb의 함량은 0.012% 이하로 첨가되는 것이 바람직하다. 그러나, 상기 Nb의 함량이 0.008%미만이면, 본 발명에서 제시한 C성분 범위에서는 Nb가 C를 충분히 고정시키지 못하게 되어 열연단계에서부터 강중에 고용탄소를 다량 함유하게 되므로, 특수원소를 첨가하지 않은 일반 극저탄소 Al-Killed강과 같이 소부경화성은 커지지만, 평균r치 2.0이상의 고성형 소부경화강을 제조하기가 어렵다. 또한, 과다한 고용탄소로 인해 상온 내시효성의 확보가 불가능해 진다. 따라서, 상기 Nb의 함량은 0.008~0.012%로 설정하는 것이 바람직하다.Nb combines with C to precipitate NbC precipitates to increase strength and improve formability. However, if the content is more than 0.012%, the NbC precipitates cannot be re-dissolved at the annealing temperature of 830 to 850 ° C because excessive NbC precipitates form together with the formation of excessive NbC precipitates. It is very difficult to secure. In this case, in order to secure an appropriate amount of solid solution carbon through re-dissolution of NbC precipitates, the annealing temperature should be increased to 870 ° C. or higher. If the annealing temperature is increased, workability such as buckling is caused during annealing. Done. Therefore, the content of Nb is preferably added to 0.012% or less. However, if the content of Nb is less than 0.008%, in the C component range proposed in the present invention, Nb does not sufficiently fix C and thus contains a large amount of solid solution carbon in the steel from the hot rolling step, and thus does not add special elements. Like ultralow carbon Al-Killed steel, the hardening hardening is increased, but it is difficult to produce high hardening hardening steel with an average r value of 2.0 or more. In addition, it is impossible to secure room temperature aging due to excessive dissolved carbon. Therefore, the content of Nb is preferably set to 0.008 to 0.012%.

V는 Nb첨가시 생성되는 NbC석출물에 의한 강중 고용원소 제거효과(scavenging effect)와 동일한 작용을 하는 원소이다. 본 발명의 상기 Nb함량은, C를 완전히 NbC로 석출시킬 수 있는 양이 되지 못하기 때문에, 열연중에는 약간의 고용탄소를 잔존시킬 수 있으며, 이로 인해 소둔시 성형성의 저하와 같은 약간의 재질열화를 초래할 가능성이 있다. 따라서, 상기 V는 강중에서 VC등과 같은 탄화물을 형성하여, Nb에 의해서도 충분히 제거되지 못한 강중 고용탄소를 제거시키는 역할을 하는 것이다. 이와 같이, V를 이용하면, 열연단계에서 고용원소가 전혀 없는 IF(Interstitial Free)강와 동일하게 되어 소둔시 성형성의 향상을 극대화시킬 수 있고, 소둔후 다시 재용해하여 고용탄소를 확보함으로써 성형성과 소부경화성을 동시에 확보할 수 있는 것이다. 또한, V는 소둔온도를 낮추는 역할을 하기 때문에, 열간압연중 V에 의해 생성된 탄화물인 VC 등은 NbC보다 낮은 소둔온도에서도 재용해되어 소부경화성을 확보할 수 있다. 그러나, 그 첨가량이 매우 작으면 VC로 형성된 탄화물이 소둔초기에 재용해되어 V첨가에 의한 성형성 향상효과가 전혀 없으며, 또한 그 첨가량이 매우 많을 경우는 VC석출물의 재용해 온도가 증가하여 NbC 석출물의 재용해온도와 동등이상이 되어 850℃이상의 고온소둔을 야기시킬 수 있다. 따라서, 상기 V함량 0.02~0.1%로 설정하는 것이 바람직하다.V is an element having the same effect as the scavenging effect in the steel by NbC precipitates produced when Nb is added. Since the Nb content of the present invention is not an amount capable of completely depositing C into NbC, some solid solution carbon may be left during hot rolling, thereby causing slight material degradation such as deterioration of formability during annealing. It is likely to cause. Therefore, V forms a carbide such as VC in the steel, and serves to remove solid solution carbon in the steel that is not sufficiently removed by Nb. As such, when V is used, it becomes the same as IF (Interstitial Free) steel which has no solid element in the hot rolling step, thereby maximizing the improvement of formability during annealing, and remelting after annealing to secure solid carbon. Curable property can be secured simultaneously. In addition, since V plays a role of lowering the annealing temperature, VC, which is a carbide produced by V during hot rolling, can be re-dissolved at annealing temperature lower than NbC, thereby ensuring hardening hardening. However, if the addition amount is very small, carbides formed from VC are re-dissolved at the early stage of annealing, and there is no effect of improving the formability due to the V addition. If the addition amount is very large, the re-dissolution temperature of the VC precipitate is increased to increase the NbC precipitate. It can be equal to or higher than the remelting temperature of, causing high temperature annealing above 850 ℃. Therefore, the V content is preferably set at 0.02 to 0.1%.

상기와 같이 조성된 강 슬라브는 오스테나이트조직이 충분히 균질화될 수 있는 1200℃이상에서 가열한 후, Ar3온도직상인 900~950℃의 온도범위에서 열간압연을 마무리한다. 상기 슬라브가열온도가 1200℃미만이면, 강의 조직이 균일한 오스테나이트 결정립으로 되지 못하여 혼립이 발생하게 되므로, 재질의 열화가 초래된다. 상기 열연마무리 온도가 900℃미만이면, 열연코일의 상(top), 하(tail)부 및 가장자리가 단상영역으로 되어 면내 이방성의 증가 및 성형성이 열화된다. 또한, 950℃이상이면, 현저한 조대립이 발생하여 가공후 표면에 오렌지 필(orange peel) 등의 결함이 생기기 쉽다.The steel slabs formed as described above are heated at 1200 ° C. or more, where the austenite structure can be sufficiently homogenized, and then finish hot rolling in a temperature range of 900 to 950 ° C., which is directly above the Ar 3 temperature. If the slab heating temperature is less than 1200 ° C., the structure of the steel does not become uniform austenite grains, and thus the mixing occurs, resulting in deterioration of the material. If the hot polishing temperature is less than 900 ° C., the top, tail, and edges of the hot rolled coil become single phase regions, thereby increasing in-plane anisotropy and degrading formability. In addition, when it is 950 degreeC or more, remarkable coarse grains generate | occur | produce and it is easy to produce defects, such as an orange peel, on the surface after processing.

상기 열간압연후 열연판에 잔존하는 고용탄소에 의한 성형성악화를 방지하기 위해, 700~750℃의 온도범위에서 고온권취를 하는데, 그 온도가 750℃를 초과할 경우 이상립 성장이 발생하여 양호한 재질을 얻을 수 없으며, 700℃미만이면 열연조직이 세립화되어 항복강도가 상승하고 성형성이 열화되는 문제가 있다. In order to prevent mold deterioration due to the solid solution carbon remaining on the hot rolled sheet after hot rolling, high temperature winding is performed in a temperature range of 700 to 750 ° C., and when the temperature exceeds 750 ° C., abnormal grain growth occurs and is satisfactory. If the material cannot be obtained and the temperature is less than 700 ° C., the hot rolled structure becomes fine, the yield strength is increased, and the moldability is deteriorated.

그 후, 통상의 방법으로 산세한 다음, 75~80%의 압연율로 냉간압연을 행한다. 즉, 본 발명에서 요구하는 2.0이상의 평균r치를 확보하기 위해서는, 상기 냉간압연율이 75%이상으로 되어야 하는 것이다. 즉, 냉간압연율이 75%미만이면 강중에 평균 r치에 영향을 주는 집합조직의 형성에 필요한 구동력이 작아, 2.0이상의 충분한 성형성 확보가 어렵다. 그러나, 냉간압연율이 80%이상이면, 집합조직을 형성시킬 수 있는 구동력은 증가하나 과도한 압연율에 의해 결정립의 크기가 매우 미세해져 오히려 재질의 경화를 초래하게 되기 때문에, 바람직하지 못하다.Thereafter, the product is pickled in a usual manner and then cold rolled at a rolling rate of 75 to 80%. That is, in order to secure an average r value of 2.0 or more required by the present invention, the cold rolling rate should be 75% or more. That is, if the cold rolling rate is less than 75%, the driving force required for forming the aggregate structure affecting the average r value in the steel is small, and it is difficult to secure sufficient formability of 2.0 or more. However, if the cold rolling rate is 80% or more, the driving force for forming the aggregate structure is increased, but the grain size becomes very fine due to excessive rolling rate, which is not preferable because it causes hardening of the material.

상기 냉간압연이 완료된 강은 830~850℃의 온도범위에서 통상의 방법에 의해 연속소둔하는 것이 바람직하다. 그 이유는, 상기 소둔온도가 830℃미만이면, 재결정 집합조직의 발달이 다소 약해 평균r치를 2.0이상으로 확보하기가 어렵고, 850℃이상이면 평균r치는 향상되지만, 과도한 소둔온도의 증가로 인해 실제 제조시 설비상의 문제, 즉, 고온소둔에 따른 강판의 텐션(tension)부여문제 및 고온버너(burner)의 개발 등의 문제가 발생하기 때문이다. 또한, 소둔온도가 높으면 고온소둔으로 NbC 석출물의 재용해가 매우 활발해져 강중 고용탄소량이 증가하여 소부경화성이 본 발명강에서 제시한 3~6kgf/mm2이상으로 되기 때문에, 내시효성이 열화하는 문제가 발생한다.The cold rolled steel is preferably continuously annealed by a conventional method in the temperature range of 830 ~ 850 ℃. The reason is that if the annealing temperature is less than 830 ° C., the recrystallization texture is slightly weak, so it is difficult to secure an average r value of 2.0 or more. If the annealing temperature is higher than 850 ° C., the average r value is improved. This is because problems in equipment during manufacturing, that is, problems such as tensioning of the steel sheet due to high temperature annealing and development of a high temperature burner occur. In addition, if the annealing temperature is high, the red annealing of NbC precipitates becomes very active due to the high temperature annealing, so that the amount of solid carbon in the steel increases and the hardening hardening becomes 3 to 6 kgf / mm 2 or more suggested by the present invention. Occurs.

이후, 적정 소부경화성과 상온 내시효성을 확보하기 위하여, 조질압연을 행하는데, 상기 조질압연율이 1.3%미만이면, 상온유지시 단시간내에 시효가 발생하여 항복강도가 증가하고 프레스가공에 치명적인 스트레쳐 스트레인(stretcher strain)이 발생하고, 2.0%이상이면 상온 내시효성은 충분히 확보될 수 있으나, 과다한 조질압연에 의한 가공경화가 발생하여 재질이 열화되므로, 우수한 성형성을 가진 연질의 소부경화형 냉연강판을 얻을 수 없다. 따라서, 상기 조질 압연은 1.3~2.0%의 압하율로 실시하는 것이 바람직하다.Afterwards, in order to secure proper baking hardening and aging resistance at room temperature, temper rolling is performed. When the temper rolling rate is less than 1.3%, aging occurs within a short time when maintaining the room temperature, the yield strength is increased, and the stretcher is fatal to press working. If the strain (strain) occurs, the room temperature aging resistance can be sufficiently secured if more than 2.0%, but the material is deteriorated due to the work hardening caused by excessive temper rolling, the soft small hardened cold-rolled steel sheet having excellent formability Can not get Therefore, it is preferable to perform the said temper rolling at the reduction ratio of 1.3 to 2.0%.

한편, 상기 방법으로 제조된 본 발명의 냉연강판은, 소부경화량이 3~6kgf/mm2, 평균r치가 2.0이상이며, 그리고 100℃에서 1시간 시효처리시 항복점 연신율값이 0.1%이하인 고강도 소부경화형 냉연강판으로 된다.On the other hand, the cold-rolled steel sheet of the present invention produced by the above method, the high-hardening hardening hardening type having a hardening hardening amount of 3 ~ 6kgf / mm 2 , the average r value of 2.0 or more, and the yield point elongation value of 0.1% or less during 1 hour aging treatment at 100 ℃ Cold rolled steel sheet.

이하, 실시예를 통해 본 발명을 보다 상세히 설명한다.Hereinafter, the present invention will be described in more detail with reference to Examples.

(실시예)(Example)

하기 표 1과 같이 조성되는 강 슬라브를 열간압연하고 75%의 압하율로 냉간압연한 후, 850℃의 온도에서 연속소둔한 다음, 1.5%의 압하율로 조질압연하였다. 그 후, 기계적 특성 및 r값, 소부경화량, 항복점 연신율을 측정하고, 그 결과를 하기 표 2에 나타내었다.The steel slab formed as shown in Table 1 was hot rolled and cold rolled at a reduction ratio of 75%, and then continuously annealed at a temperature of 850 ° C., and then tempered at a reduction ratio of 1.5%. After that, the mechanical properties and r value, the amount of cure hardening, the yield point elongation were measured, and the results are shown in Table 2 below.

성분ingredient 화학성분(중량%)Chemical composition (% by weight) CC SiSi MnMn PP SS Sol.AlSol.Al NN NbNb TiTi VV 발명예1Inventive Example 1 0.00290.0029 0.0050.005 0.190.19 0.0710.071 0.00520.0052 0.0400.040 0.00320.0032 0.01200.0120 －－ 0.0410.041 발명예2Inventive Example 2 0.00280.0028 0.0070.007 0.190.19 0.0700.070 0.00450.0045 0.0360.036 0.00320.0032 0.00810.0081 0.0750.075 발명예3Inventive Example 3 0.00250.0025 0.0080.008 0.170.17 0.0690.069 0.00530.0053 0.0330.033 0.00280.0028 0.00990.0099 0.0610.061 발명예4Inventive Example 4 0.00240.0024 0.0100.010 0.200.20 0.0650.065 0.00560.0056 0.0450.045 0.00250.0025 0.01100.0110 0.0320.032 비교예1Comparative Example 1 0.00210.0021 0.0100.010 0.140.14 0.0600.060 0.00750.0075 0.0580.058 0.00200.0020 0.00970.0097 0.2100.210 비교예2Comparative Example 2 0.00120.0012 0.0100.010 0.180.18 0.0670.067 0.00800.0080 0.0480.048 0.00190.0019 0.0100.010 0.0510.051 비교예3Comparative Example 3 0.00250.0025 0.0100.010 0.480.48 0.0600.060 0.00540.0054 0.0430.043 0.00230.0023 －－ 0.0150.015 0.0430.043 비교예4Comparative Example 4 0.00400.0040 0.0100.010 0.200.20 0.0570.057 0.00480.0048 0.0440.044 0.00300.0030 0.0100.010 －－ 0.0450.045 비교예5Comparative Example 5 0.00230.0023 0.0100.010 0.250.25 0.0660.066 0.00590.0059 0.0430.043 0.00490.0049 0.0150.015 0.0610.061 비교예6Comparative Example 6 0.00250.0025 0.0100.010 0.560.56 0.0710.071 0.00550.0055 0.0470.047 0.00260.0026 0.0100.010 0.0710.071 비교예7Comparative Example 7 0.00270.0027 0.0100.010 0.170.17 0.0690.069 0.00420.0042 0.0380.038 0.00480.0048 0.0110.011 0.0680.068

구분division 재질실적Material performance 항복강도(kgf/㎟)Yield strength (kgf / ㎡) 인장강도(kgf/㎟)Tensile strength (kgf / ㎡) 연신율(%)Elongation (%) rr 소부경화량(kgf/㎟)Curing hardening rate (kgf / mm2) 100℃,1시간 시효처리후 항복점연신율(%)Yield point elongation (%) after aging treatment at 100 ℃ for 1 hour 발명강1Inventive Steel 1 24.624.6 38.438.4 34.634.6 2.032.03 3.33.3 0.10.1 발명강2Inventive Steel 2 24.824.8 38.738.7 34.634.6 2.002.00 4.54.5 00 발명강3Invention Steel 3 24.224.2 38.638.6 35.635.6 2.082.08 4.04.0 0.020.02 발명강4Inventive Steel 4 23.723.7 37.037.0 37.937.9 2.192.19 3.53.5 0.10.1 비교강1Comparative Steel 1 24.224.2 37.137.1 35.335.3 2.112.11 1.81.8 00 비교강2Comparative Steel 2 23.123.1 35.635.6 36.936.9 2.092.09 00 00 비교강3Comparative Steel 3 24.524.5 37.737.7 36.636.6 1.941.94 3.43.4 0.30.3 비교강4Comparative Steel 4 28.328.3 38.438.4 32.232.2 1.871.87 6.56.5 0.70.7 비교강5Comparative Steel 5 27.727.7 39.839.8 34.034.0 2.092.09 1.61.6 00 비교강6Comparative Steel 6 26.126.1 39.239.2 32.032.0 1.791.79 3.53.5 00 비교강7Comparative Steel 7 26.726.7 38.138.1 33.233.2 1.921.92 4.24.2 0.250.25

상기 표2에 나타난 바와 같이, 본 발명의 강 성분을 만족하는 발명예(1)~(4)는, 소부경화량이 3.3~4.5kgf/mm2, 평균r치 2.0~2.19, 연신율 34%이상, 인장강도 37.0~38.7kgf/mm2, 항복강도 23.7~24.8kgf/mm2 및 상온 내시효성을 나타내는 100℃, 1hr시효처리후 항복점 연신율이 0.1%이하이기 때문에, 우수한 성형성과 더불어 상온 내시효성이 매우 우수한 소부경화형 냉연강판으로 제조되었음을 알 수 있다.As shown in Table 2, Inventive Examples (1) to (4) satisfying the steel component of the present invention, the baking hardening amount is 3.3 ~ 4.5kgf / mm 2 , the average r value 2.0 ~ 2.19, elongation 34% or more, Tensile strength 37.0 ~ 38.7kgf / mm 2 , Yield strength 23.7 ~ 24.8kgf / mm 2 and yield point elongation less than 0.1% after 1hr aging treatment at 100 ° C showing room temperature aging resistance. It can be seen that it is made of an excellent hardening type cold rolled steel sheet.

그러나, 비교예(1)은 V의 함량이 0.021%로서 매우 높아서 과도한 VC 석출물이 형성되었고, 또한 소둔시 VC 석출물의 재용해에 의한 고용원소의 확보가 매우 어려웠기 떼문에, 소부경화량이 1.8로 매우 낮았다.However, in Comparative Example (1), the V content was very high as 0.021%, and excessive VC precipitates were formed, and it was very difficult to secure the employment element by redissolution of VC precipitates during annealing. Very low.

비교예(2)는 C의 함량이 적어서 평균r치는 2.0이상을 확보할 수 있었으나, 강중 고용탄소함량의 부족으로 소부경화성은 전혀 얻어지지 않았다.In Comparative Example (2), the C content was low, so that an average r value of 2.0 or more was obtained.

비교예(3)은 Mn함량이 0.48%로 첨가되어 과도한 MnS에 의한 재질열화가 발생하였고, 또한 Nb대신 Ti가 첨가되어 소둔판 결정립크기가 조대해져 내시효성을 평가하는 100℃에서 1시간 시효처리후 항복점 연신율값이 0.3%로 높았다.In Comparative Example (3), Mn content was added at 0.48% to cause material deterioration due to excessive MnS. In addition, Ti was added instead of Nb to coarse annealing crystal grains to coarse to evaluate aging resistance. The yield point elongation was high as 0.3%.

비교예(4)는 C함량이 많아 강중 고용탄소가 매우 증가하여, 소부경화량이 약 6.4kgf/mm2으로 매우 높았다. 또한, 100℃, 1hr시효처리후 항복점 연신율이 0.7%로 되어 상온 내시효성의 열화가 발생하였다. 또한, 항복강도가 28kgf/mm2수준으로 매우 증가하여 자동차사의 프레스가공시 스프링 백(spring back)과 같은 결함이 발생할 가능성이 있으며, 평균r치도 낮았다.In Comparative Example (4), since the C content was high, the dissolved carbon in the steel was greatly increased, and the baking hardening amount was about 6.4 kgf / mm 2, which was very high. In addition, the yield point elongation was 0.7% after 100 ° C and 1hr aging treatment, resulting in deterioration of aging resistance at room temperature. In addition, the yield strength is greatly increased to 28kgf / mm 2 level, there is a possibility that a defect such as spring back occurs during the press processing of the automobile company, the average r value was low.

비교예(5)는 Nb과 N 함량이 본 발명의 규제범위를 벗어나서, 소부경화성이 낮았으며 연신율도 다소 열화한 수준이었다.In Comparative Example (5), the Nb and N contents were outside the regulatory range of the present invention, and the baking hardness was low and the elongation was somewhat deteriorated.

비교예(6)은, Mn함량이 본 발명강에서 제시한 성분범위를 초과하여 과도한 MnS 석출에 의해 재질이 경화되었으며 또한 MnS 뿐만 아니라 Mn-C 다이폴 등이 형성되어 평균r치가 매우 열화하였다.In Comparative Example (6), the Mn content exceeded the component range suggested in the present invention steel and the material was cured by excessive MnS precipitation, and not only MnS but also Mn-C dipoles were formed, and the average r value was very deteriorated.

비교예(7)은, N의 함량이 0.0048%로서 매우 높아서, 재질을 경화시켜 평균r치가 본 발명의 목표치보다 매우 낮았다. 또한, 강중에 고용질소의 함량을 증가시켜 소부경화성이 증가되었을 뿐 아니라, 상온 내시효성도 열화하였다. 즉, 고용질소의 증가로 인해, 100℃ 1시간 열처리후 평가하는 항복점연신율이 0.25%로서 매우 높아 단시간 유지시에도 시효결함이 발생할 가능성이 매우 큰 것을 알 수 있다. 이러한 고용질소의 영향을 제거하기 위해서는, Al함량을 증가시켜야 하는데, Al함량이 증가하면 제조원가의 상승은 물론 강중 산화개재물의 증가가 예상되므로 바람직하지 못하다.In Comparative Example (7), the content of N was very high as 0.0048%, and the average r value was much lower than the target value of the present invention by curing the material. In addition, by increasing the content of solid solution nitrogen in the steel not only increased the hardening hardening, but also deteriorated room temperature aging resistance. In other words, due to the increase in solid solution nitrogen, the yield point elongation evaluated after heat treatment at 100 ° C. for 1 hour is 0.25%, which is very high. In order to eliminate the effect of solid solution nitrogen, Al content should be increased. However, it is not preferable that the increase of Al content is expected to increase the production cost as well as increase the oxidation inclusions in the steel.

한편, 본 발명예에서 인장강도에 비해 항복강도가 다소 높은 것은, 소부경화형 강판 특유의 문제점인 상온 내시효성의 열화를 방지하기 위해, 통상의 수준보다 다소 높은 약 1.5%의 조질압연율을 적용하였기 때문이다. 또한, 연신율이 통상의 35kgf/mm2급 고강도보다 다소 낮은 것은, 인장강도가 일반적인 35kgf/mm2급 고강도보다 3kgf/mm2이상 높았기 때문이며, 인장강도를 현수준보다 다소 낮출 경우 연신율은 현 수준보다 훨씬 증가할 것으로 예상된다.On the other hand, the yield strength of the present invention is somewhat higher than the tensile strength, in order to prevent degradation of the room temperature aging resistance, which is a problem peculiar to the hardening-type steel sheet, to apply a rough rolling rate of about 1.5% higher than the normal level Because. In addition, it is somewhat lower than the normal 35kgf / mm 2 class high strength elongation, because group tensile strength of general 35kgf / mm 2 class high strength than 3kgf / mm 2 higher than, the elongation is somewhat lower tensile strength than the current level is more than the current level It is expected to increase much.

상기한 바와 같은 본 발명에 의하면, 우수한 성형성 및 상온 내시효성을 갖는 인장강도 35kgf/mm2급 소부경화형 냉연강판을 제조할 수 있는 효과가 있는 것이다.According to the present invention as described above, it is effective to prepare a tensile strength of 35kgf / mm 2 class baking hardening type cold-rolled steel sheet having an excellent formability at room temperature, and Hyosung Nash.

Claims (2)

중량%로, C : 0.0020~0.0030%, Si : 0.02% 이하, Mn : 0.07~0.2%, P : 0.05~0.08%, S : 0.008% 이하, Sol.Al : 0.02~0.06%, N : 0.0035% 이하, Nb : 0.008~0.012%, V: 0.02~0.1%, 기타 불가피한 불순물로 조성되는 강을 1200℃이상에서 균질화 열처리하고 900~950℃의 온도범위에서 마무리 열간압연한 후 700~750℃의 온도범위에서 권취하고, 75~80%의 압연율로 냉간압연한 다음 830~850℃의 온도범위에서 연속소둔하고, 1.3~2.0%의 압하율로 조질압연하는 것을 포함하여 이루어지는 고강도 소부경화형 냉연강판의 제조방법By weight%, C: 0.0020 ~ 0.0030%, Si: 0.02% or less, Mn: 0.07 ~ 0.2%, P: 0.05 ~ 0.08%, S: 0.008% or less, Sol.Al: 0.02 ~ 0.06%, N: 0.0035% Or less, Nb: 0.008 ~ 0.012%, V: 0.02 ~ 0.1%, homogeneous heat treatment of steel composed of other unavoidable impurities at 1200 ℃ or higher and finishing hot rolling at temperature range of 900 ~ 950 ℃, then temperature of 700 ~ 750 ℃ Of high strength hardened hardened cold rolled steel sheet comprising winding in the range, cold rolling at a rolling rate of 75 to 80%, continuous annealing at a temperature range of 830 to 850 ° C, and temper rolling at a rolling reduction rate of 1.3 to 2.0%. Manufacturing method 중량%로, C : 0.0020~0.0030%, Si : 0.02% 이하, Mn : 0.07~0.2%, P : 0.05~0.08%, S : 0.008% 이하, Sol.Al : 0.02~0.06%, N : 0.0035% 이하, Nb : 0.008~0.012%, V: 0.02~0.1%, 기타 불가피한 불순물로 조성되고, 소부경화량이 3~6kgf/mm2, 평균r치가 2.0이상이며, 그리고 100℃에서 1시간 시효처리시 항복점 연신율값이 0.1%이하인 고강도 소부경화형 냉연강판By weight%, C: 0.0020 ~ 0.0030%, Si: 0.02% or less, Mn: 0.07 ~ 0.2%, P: 0.05 ~ 0.08%, S: 0.008% or less, Sol.Al: 0.02 ~ 0.06%, N: 0.0035% Or less, Nb: 0.008 ~ 0.012%, V: 0.02 ~ 0.1%, other inevitable impurities, the hardened amount of baking is 3 ~ 6kgf / mm 2 , the average r value is 2.0 or more, and yield point when aged at 100 ℃ for 1 hour High strength hardened hardened cold rolled steel sheet with elongation value less than 0.1%
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KR100496532B1 (en) * 2000-12-07 2005-06-22 주식회사 포스코 A bake-hardenable cold rolled steel sheet with superior formability, and a method for manufacturing it
KR100946064B1 (en) * 2002-12-18 2010-03-10 주식회사 포스코 Method for manufacturing high strength cold rolled steel sheets with baking hardening property having excellent strain aging resistance at room temperature
KR100946067B1 (en) * 2002-12-27 2010-03-10 주식회사 포스코 Preparing method of baked hardening cold rolled steel sheet for hot dipping having good anti-aging property

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JPH042729A (en) * 1990-04-20 1992-01-07 Sumitomo Metal Ind Ltd Production of high strength cold rolled steel sheet for deep drawing having baking hardenability
JPH05263146A (en) * 1992-03-17 1993-10-12 Nippon Steel Corp Manufacture of cold rolled steel sheet for deep drawing excellent in baking hardenability
JPH06108153A (en) * 1992-09-30 1994-04-19 Nkk Corp Production of baking-hardened type cold-rolled steel sheet excellent in cold aging resistance
KR940014345A (en) * 1992-12-17 1994-07-18 가와무라 요시부미 Biphenyl derivatives, methods for their preparation and their use as therapeutic agents for hypertension and heart disease
JPH09249936A (en) * 1996-03-14 1997-09-22 Nkk Corp Cold rolled steel sheet excellent in balance among baking hardenability, ductility, and natural aging characteristic and its production
KR20000042049A (en) * 1998-12-24 2000-07-15 이구택 Method for producing cold rolled steel sheet for soft-organic coating having excellent molding property

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH042729A (en) * 1990-04-20 1992-01-07 Sumitomo Metal Ind Ltd Production of high strength cold rolled steel sheet for deep drawing having baking hardenability
JPH05263146A (en) * 1992-03-17 1993-10-12 Nippon Steel Corp Manufacture of cold rolled steel sheet for deep drawing excellent in baking hardenability
JPH06108153A (en) * 1992-09-30 1994-04-19 Nkk Corp Production of baking-hardened type cold-rolled steel sheet excellent in cold aging resistance
KR940014345A (en) * 1992-12-17 1994-07-18 가와무라 요시부미 Biphenyl derivatives, methods for their preparation and their use as therapeutic agents for hypertension and heart disease
JPH09249936A (en) * 1996-03-14 1997-09-22 Nkk Corp Cold rolled steel sheet excellent in balance among baking hardenability, ductility, and natural aging characteristic and its production
KR20000042049A (en) * 1998-12-24 2000-07-15 이구택 Method for producing cold rolled steel sheet for soft-organic coating having excellent molding property

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