KR100723165B1 - Cold rolled steel sheet having increased plastic anisotropy and process for producing the same - Google Patents

Cold rolled steel sheet having increased plastic anisotropy and process for producing the same Download PDF

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KR100723165B1
KR100723165B1 KR1020050129235A KR20050129235A KR100723165B1 KR 100723165 B1 KR100723165 B1 KR 100723165B1 KR 1020050129235 A KR1020050129235 A KR 1020050129235A KR 20050129235 A KR20050129235 A KR 20050129235A KR 100723165 B1 KR100723165 B1 KR 100723165B1
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steel sheet
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rolled steel
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KR20060115309A (en
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윤정봉
조뇌하
정진희
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주식회사 포스코
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Priority to TW095115562A priority Critical patent/TWI346141B/en
Priority to PCT/KR2006/001670 priority patent/WO2006118425A1/en
Priority to US11/913,175 priority patent/US20090126837A1/en
Priority to MX2007013676A priority patent/MX2007013676A/en
Priority to EP06732897.1A priority patent/EP1888800B1/en
Priority to JP2008509936A priority patent/JP4954981B2/en
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
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    • 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
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • 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
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    • C22C—ALLOYS
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Abstract

자동차, 가전제품 등의 소재로 사용되는 냉연강판과 그 제조방법이 제공된다. 본 발명의 냉연강판은, 중량%로, C: 0.005%이하, Mn:0.2%이하, Cu:0.01-0.2%, S:0.005-0.08%, Al:0.1%이하 N:0.004%초과-0.02%이하, P:0.2%이하, B:0.0001-0.002%, Nb:0.002~0.04%, Ti:0.005~0.15%, 나머지 Fe 및 기타 불가피한 불순물로 조성되고, Provided are a cold rolled steel sheet used as a material for automobiles and home appliances, and a manufacturing method thereof. Cold rolled steel sheet of the present invention, in weight%, C: 0.005% or less, Mn: 0.2% or less, Cu: 0.01-0.2%, S: 0.005-0.08%, Al: 0.1% or less N: 0.004% or more-0.02% P: 0.2% or less, B: 0.0001-0.002%, Nb: 0.002-0.04%, Ti: 0.005-0.15%, remaining Fe and other inevitable impurities,

Cu+Mn:0.05-0.4, 0.003≤S*≤0.015, 1≤(Mn/55+Cu/63.5)/(S*/32)≤30, 0.8≤(Ti*/48+Nb/93)/(C/12)≤5.0, 0.003≤N*≤0.01, 1≤(Al/27)/(N*/14)≤10,Cu + Mn: 0.05-0.4, 0.003 ≦ S * ≦ 0.015, 1 ≦ (Mn / 55 + Cu / 63.5) / (S * / 32) ≦ 30, 0.8 ≦ (Ti * / 48 + Nb / 93) / ( C / 12) ≤5.0, 0.003≤N * ≤0.01, 1≤ (Al / 27) / (N * / 14) ≤10,

여기서, S*=S-0.8×(Ti-0.8×N(48/14))×(32/48), Ti*=Ti-0.8×S(48/32)-0.8×N(48/14), N*=N-0.8×(Ti-0.8×S×48/32)×14/48Where S * = S-0.8 × (Ti-0.8 × N (48/14)) × (32/48), Ti * = Ti-0.8 × S (48/32) -0.8 × N (48/14) , N * = N-0.8 × (Ti-0.8 × S × 48/32) × 14/48

를 만족하고, (Mn,Cu)S석출물과 AlN석출물의 평균크기가 0.2㎛이하로 이루어진다. The average size of the (Mn, Cu) S precipitates and AlN precipitates is less than 0.2 μm.

본 발명의 냉연강판은 나노싸이즈의 (Mn,Cu)S석출물과 AlN석출물이 분포함에 따라 결정립이 미세해져서 면내이방성지수가 낮아지고, (Mn,Cu)S석출물과 AlN석출물에 의해 항복강도가 증진된다. 따라서, 고강도를 확보하기 위해 첨가되던 P와 Mn의 함량을 대폭 줄일 수 있어 용접성과 도금특성이 개선된다. In the cold rolled steel sheet of the present invention, as the (Mn, Cu) S precipitates and AlN precipitates are distributed, the grain size becomes fine, resulting in low in-plane anisotropy index, and yield strength by (Mn, Cu) S precipitates and AlN precipitates. Promoted. Therefore, the content of P and Mn added to secure high strength can be greatly reduced, thereby improving weldability and plating characteristics.

냉연강판, 비시효, 고강도, 2차가공취성, 소성이방성 지수, 석출물 Cold rolled steel, non-aging, high strength, secondary work brittleness, plastic anisotropy index, precipitate

Description

소성이방성이 우수한 냉연강판과 그 제조방법{COLD ROLLED STEEL SHEET HAVING INCREASED PLASTIC ANISOTROPY AND PROCESS FOR PRODUCING THE SAME}Cold rolled steel sheet with excellent plastic anisotropy and its manufacturing method {COLD ROLLED STEEL SHEET HAVING INCREASED PLASTIC ANISOTROPY AND PROCESS FOR PRODUCING THE SAME}

일본 공개특허공보 소57-0413349호, Japanese Laid-Open Patent Publication No. 57-0413349,

한국 공개특허공보 2003-0052248호, Korean Unexamined Patent Publication No. 2003-0052248,

일본 공개특허공보 평6-057336호Japanese Unexamined Patent Publication No. Hei 6-057336

일본 공개특허공보 평9-227951호Japanese Patent Laid-Open No. 9-227951

일본 공개특허공보 평10-265900호Japanese Patent Laid-Open No. 10-265900

본 발명은 자동차, 가전제품 등의 소재로 사용되는 냉연강판에 관한 것으로, 보다 상세하게는 Nb와 Ti의 복합 첨가 IF강에서 (Mn,Cu)S석출물과 AlN석출물에 의해 항복강도와 소성이방성이 개선되는 냉연강판과 그 제조방법에 관한 것이다. The present invention relates to a cold-rolled steel sheet used as a material for automobiles, home appliances, and more particularly, to yield strength and plastic anisotropy by (Mn, Cu) S precipitates and AlN precipitates in a composite steel of Nb and Ti. It relates to an improved cold rolled steel sheet and a method of manufacturing the same.

자동차, 가전제품에 사용되는 냉연강판에는 강도와 성형성의 확보와 더불어 비시효특성이 요구된다. 시효는 고용원소(C, N)가 전위에 고착함에 따라 경화가 일어나면서 스트레쳐 스트레인(Stretcher Strain)이라는 결함을 유발하는 일종의 변형시효 현상이다. Cold rolled steel sheets used in automobiles and home appliances require strength and formability as well as non-aging characteristics. Aging is a kind of strain aging that causes hardening as the solid elements (C, N) adhere to dislocations, leading to a defect called stretcher strain.

냉연강판의 비시효성은 알루미늄 킬드강의 상소둔에 의해 확보 가능하나, 상소둔은 소둔시간이 길어 생산성이 낮고 부위별로 재질편차가 심하다는 단점이 있다. The non-aging property of the cold rolled steel sheet can be secured by the annealing of the aluminum-kilted steel, but the annealing has the disadvantage that the annealing time is long and the productivity is low and the material deviation is severe for each part.

따라서, Ti, Nb과 같은 강력한 탄, 질화물 형성 원소를 첨가하고 연속소둔을 행하는 IF강(Interstitial Free Steel)을 주로 이용하고 있다. IF강은 고용탄소나 고용질소를 완전히 또는 일부를 제거하여 비시효성을 확보하고 있다.Therefore, IF steel (Interstitial Free Steel) which adds strong carbon and nitride forming elements such as Ti and Nb and performs continuous annealing is mainly used. IF steels have a non-aging effect by removing some or all of the carbon and nitrogen employed.

IF강의 고강도화 방안으로는 P에 의한 고용강화 기술이 있다. 일본 공개특허공보 소57-0413349호는 Ti첨가 IF강에서 P를 0.04~0.12%첨가하여 강도를 확보하고 있다. 극저탄소 성분계의 IF강에서 P는 입계편석에 의한 2차가공취성의 문제를 발생시킨다.The high-strength method of IF steel is the employment strengthening technology by P. Japanese Laid-Open Patent Publication No. 57-0413349 secures strength by adding 0.04 to 0.12% of P in Ti-added IF steel. In the IF steel of the ultra low carbon component system, P causes the problem of secondary processing brittleness due to grain boundary segregation.

따라서, 일본 공개특허공보 평5-078784호에서는 P 대신 고용강화원소인 Mn을 0.05-0.1% 첨가하여 강도를 확보하고 있다. 또한, 한국 공개특허공보 2003-0052248호에서는 P첨가 대신 0.5-2.0%의 Mn과 Al, B 등을 함께 첨가하여 가공성과 2차가공취성을 개선하고 있다. 그러나, 극저탄소강에서 사용하는 Mn은 고품위여서 Mn의 다량 첨가에 의해 제조원가가 상승하고 특히, Mn의 함량이 많아지면 도금특성에도 좋지 않다. Therefore, Japanese Patent Laid-Open No. 5-078784 adds 0.05-0.1% of Mn, which is a solid solution strengthening element, instead of P to secure strength. In addition, Korean Laid-Open Patent Publication No. 2003-0052248 improves processability and secondary processing brittleness by adding 0.5-2.0% of Mn, Al, and B together instead of P addition. However, Mn used in the ultra low carbon steel is of high quality, so that the manufacturing cost increases due to the large amount of Mn added, and in particular, when the Mn content is increased, the plating properties are not good.

일본 공개특허공보 평6-057336호에서는 IF강에서 Cu를 0.5-2.5% 첨가하여 ε-Cu의 석출상을 형성하여 강도를 확보하고 있다. ε-Cu의 석출상에 의해 고강도는 확보되나, 가공특성은 좋지 않다. In JP-A-6-057336, 0.5-2.5% of Cu is added to IF steel to form an ε-Cu precipitated phase to secure strength. The high strength is ensured by the precipitated phase of? -Cu, but the processing characteristics are not good.

이와는 달리 Cu를 탄화물의 석출핵으로 이용하여 탄화물에 의해 가공성 또는 표면결함을 개선하는 기술이 일본 공개특허공보 평9-227951호와 평10-265900호에 제시되어 있다. In contrast, techniques for improving the processability or surface defects by carbides using Cu as precipitation nuclei of carbides are disclosed in Japanese Patent Laid-Open Nos. 9-227951 and 10-265900.

일본 공개특허공보 평9-227951호는 Cu를 0.01-0.05% 첨가하는 IF강의 슬라브를 조압연후 1100-950℃에서 70초 이상 유지하여 CuS를 석출하고 열간압연하여 Cu-Ti-C-S의 석출물을 갖는 열연판을 얻고 이를 냉간압연하여 가공성을 확보하고 있다. Cu-Ti-C-S의 석출물을 갖는 열연판을 냉간압연하면 재결정시 이러한 석출물의 주위에 판면에 평행한 {111}을 형성하는 결정립의 핵이 통상의 석출물 보다 도 증가하여 그 결과 가공성이 개선된다는 것이다. Japanese Patent Application Laid-Open No. 9-227951 discloses a slab of IF steel containing 0.01-0.05% of Cu after rough rolling at 1100-950 ° C. for at least 70 seconds to precipitate CuS and hot roll to obtain a precipitate of Cu-Ti-CS. The hot rolled plate is obtained and cold rolled to secure workability. Cold rolling of a hot rolled sheet having a precipitate of Cu-Ti-CS increases the nuclei of crystal grains which form {111} parallel to the plate surface around these precipitates during recrystallization, resulting in improved workability as a result. .

일본 공개특허공보 평10-265900호는 Cu를 0.005-0.1% 첨가하는 IF강에서 CuS를 석출시키고 이 CuS석출물을 탄화물의 석출핵으로 유효하게 기능시키는 것에 의해 강판중에 고용C를 감소시켜 표면결함을 개선시키는 기술이다. Japanese Patent Laid-Open No. 10-265900 discloses surface defects by reducing the solid solution C in the steel sheet by precipitating CuS in IF steel to which 0.005-0.1% Cu is added and making the CuS precipitate effectively function as precipitation nuclei of carbides. It is a technique to improve.

상기한 일본 공개특허공보 평9-227951호와 평10-265900호에서는 조대한 CuS석출물 을 중간과정에서 이용하고 최종적으로 냉연강판에는 탄화물을 확보하는 기술이므로, Ti, Zr과 같은 유화물 형성원소를 원자량비로 S량 이상으로 첨가하고 있다. 즉, S가 Ti와 대부분 반응하도록 Ti의 첨가량이 원자량비로 S량 보다 많기 때문에 CuS단독의 석출물을 활용하고 있지 않는 것이다. In Japanese Patent Laid-Open Nos. 9-227951 and 10-265900, the coarse CuS precipitates are used in the intermediate process, and finally, the cold rolled steel sheet secures carbides. It is adding more than S amount by ratio. That is, since the amount of Ti added is larger than the amount of S in atomic ratio so that S reacts most with Ti, the precipitate of CuS alone is not utilized.

본 발명은 미세한 (Mn,Cu)S석출물과 AlN석출물에 의해 항복강도를 증진하면서 소성이방성을 낮출 수 있는 냉연강판과 그 제조방법을 제공하는데 그 목적이 있다. An object of the present invention is to provide a cold rolled steel sheet capable of lowering plastic anisotropy while improving yield strength by fine (Mn, Cu) S precipitates and AlN precipitates and a method of manufacturing the same.

상기 목적을 달성하기 위한 본 발명의 냉연강판은, 중량%로, C: 0.005%이하, Mn:0.2%이하, Cu:0.01-0.2%, S:0.005-0.08%, Al:0.1%이하 N:0.004%초과-0.02%이하, P:0.2%이하, B:0.0001-0.002%, Nb:0.002~0.04%, Ti:0.005~0.15%, 나머지 Fe 및 기타 불가피한 불순물로 조성되고, Cold rolled steel sheet of the present invention for achieving the above object, in weight%, C: 0.005% or less, Mn: 0.2% or less, Cu: 0.01-0.2%, S: 0.005-0.08%, Al: 0.1% or less More than 0.004% -0.02% or less, P: 0.2% or less, B: 0.0001-0.002%, Nb: 0.002 ~ 0.04%, Ti: 0.005 ~ 0.15%, remaining Fe and other unavoidable impurities,

Cu+Mn:0.05-0.4, 0.003≤S*≤0.015, 1≤(Mn/55+Cu/63.5)/(S*/32)≤30, 0.8≤(Ti*/48+Nb/93)/(C/12)≤5.0, 0.003≤N*≤0.01, 1≤(Al/27)/(N*/14)≤10,Cu + Mn: 0.05-0.4, 0.003 ≦ S * ≦ 0.015, 1 ≦ (Mn / 55 + Cu / 63.5) / (S * / 32) ≦ 30, 0.8 ≦ (Ti * / 48 + Nb / 93) / ( C / 12) ≤5.0, 0.003≤N * ≤0.01, 1≤ (Al / 27) / (N * / 14) ≤10,

여기서, S*=S-0.8×(Ti-0.8×N(48/14))×(32/48), Ti*=Ti-0.8×S(48/32)-0.8×N(48/14), N*=N-0.8×(Ti-0.8×S×48/32)×14/48Where S * = S-0.8 × (Ti-0.8 × N (48/14)) × (32/48), Ti * = Ti-0.8 × S (48/32) -0.8 × N (48/14) , N * = N-0.8 × (Ti-0.8 × S × 48/32) × 14/48

를 만족하고, (Mn,Cu)S석출물과 AlN석출물의 평균크기가 0.2㎛이하로 이루어진다. The average size of the (Mn, Cu) S precipitates and AlN precipitates is less than 0.2 μm.

본 발명에서 상기 미세한 석출물은 1X106개/mm2 이상이 바람직하다. In the present invention, the fine precipitate is preferably 1 × 10 6 / mm 2 or more.

본 발명에서 상기 C의 함량은 0.0005-0.003%가 바람직하다. 상기 Cu는 0.03-2.0%가 바람직하다. In the present invention, the content of C is preferably 0.0005-0.003%. As for said Cu, 0.03-2.0% is preferable.

본 발명의 냉연강판은 성분설계에 따라 280MPa급의 연질냉연강판과 340MPa이상의 고강도 냉연강판의 특성을 갖는다. The cold rolled steel sheet of the present invention has the characteristics of a soft cold rolled steel sheet of 280MPa grade and high strength cold rolled steel sheet of 340MPa or more according to the component design.

상기한 성분계에서 P의 함량은 0.015%이하로 하면 280MPa급의 연질냉연강판이 얻어진다. 이 냉연강판에다 고용강화원소인 P, Si, Cr의 1종 또는 2종이 추가로 함유되면 340MPa이상의 고강도 특성이 확보된다. P가 단독으로 함유되는 경우에는 P의 함량은 0.03~0.2%가 바람직하다. Si의 경우에는 0.1-0.8%, Cr의 경우에는 0.2-1.2%가 바람직하다. Si과 Cr의 1종이상 함유되는 경우에 P의 함량은 0.2%이하의 범위에서 다양하게 설계될 수 있다. When the content of P in the above component system is 0.015% or less, a soft cold rolled steel sheet of 280 MPa grade is obtained. When the cold rolled steel sheet further contains one or two of P, Si and Cr as solid solution strengthening elements, high strength characteristics of 340 MPa or more are secured. When P is contained alone, the content of P is preferably 0.03 to 0.2%. 0.1-0.8% for Si and 0.2-1.2% for Cr are preferred. In the case of containing at least one of Si and Cr, the content of P may be variously designed in the range of 0.2% or less.

본 발명의 냉연강판에서 가공성을 보다 개선하고자 한다면 Mo을 0.01~0.2%추가로 포함할 수 있다. If you want to improve the workability in the cold rolled steel sheet of the present invention may further comprise Mo 0.01 ~ 0.2%.

상기한 냉연강판의 제조방법은, 본 발명의 성분계를 만족하는 슬라브를 1100℃이상의 온도로 재가열한 후 마무리 압연온도를 Ar3변태점 이상으로 하여 열간압연하고 300℃/min이상의 속도로 냉각하고 700℃이하의 온도에서 권취한 다음, 냉간 압연하고, 연속소둔하는 것이다. In the method for producing a cold rolled steel sheet, the slab that satisfies the component system of the present invention is reheated to a temperature of 1100 ° C. or higher, and then hot-rolled at a finish rolling temperature of Ar 3 or higher and cooled at a speed of 300 ° C./min or higher, and 700 ° C. After winding up at the following temperature, it cold-rolls and continuously anneales.

이하, 본 발명을 상세히 설명한다. Hereinafter, the present invention will be described in detail.

본 발명에서 (Mn,Cu)S석출물은 Mn단독 유화물, Cu단독 유화물, Mn과 Cu의 복합 유화물을 포함하는 표현이다. In the present invention, the (Mn, Cu) S precipitate is an expression including Mn alone emulsion, Cu alone emulsion, and a complex emulsion of Mn and Cu.

본 발명은 냉연강판에 미세한 (Mn,Cu)S석출물과 AlN석출물이 확보되면 결정립이 미세하게 되어 항복강도가 증진되고 면내이방성지수가 낮아져 가공성이 개선된다는 연구결과에 기초하여 완성된 것이다. The present invention is completed on the basis of the research results that the fine (Mn, Cu) S precipitates and AlN precipitates are secured to the cold rolled steel sheet to improve the yield strength and lower the in-plane anisotropy index to improve workability.

냉연강판에 미세한 (Mn,Cu)S석출물을 확보하기 위해서는 (Mn,Cu)S로 석출되는 S를 확보하여야 한다. Ti는 C, N, S와 석출물을 형성하므로, 이들의 관계를 제어하여 S가 (Mn,Cu)S로 석출될 수 있도록 하는 것이 필요하며, 이를 위해서는 S, Ti, Cu, N, C의 관계를 관리하는 것이 중요하다. In order to secure fine (Mn, Cu) S precipitates on the cold rolled steel sheet, it is necessary to secure S precipitated as (Mn, Cu) S. Since Ti forms precipitates with C, N, and S, it is necessary to control their relationship so that S can be precipitated as (Mn, Cu) S, and for this, the relationship between S, Ti, Cu, N, and C. It is important to manage it.

또한, 본 발명에서는 미세한 AlN의 석출물을 적극적으로 확보하여 결정립 미세화와 석출강화효과를 구현한다. 지금까지 N은 불순물로서 Ti나 Al에 의해 TiN이나 AlN으로 고정하는 관점에서 관리하고 있다(일본 공개특허공보 9-227951). 이러한 기술들은 미세한 AlN석출물이 다량 분포할 때 강에 긍정적인 영향에 대한 인식이 부족한 것이다. 결국, N을 최대한 낮추려고 노력하거나 또는 N을 석출하여 고정 하나 이는 조대한 석출물로 분포하게 되는 것이다. In addition, in the present invention by actively securing a fine precipitate of AlN implements the effect of grain refinement and precipitation strengthening. Until now, N has been managed from the viewpoint of fixing to TiN or AlN by Ti or Al as impurities (Japanese Patent Laid-Open No. 9-227951). These techniques lack awareness of the positive effects on the steel when large amounts of fine AlN precipitates are distributed. Eventually, try to lower N as much as possible, or precipitate N and fix it, but it will be distributed as a coarse precipitate.

본 발명에 따라 미세한 (Mn,Cu)S석출물과 AlN석출물에 의해 결정립이 미세화 되면 고용탄소는 결정립내 보다 결정립계에 더 많이 존재하게 되어 상온 비시효특성이 확보된다. 결정립내에 잔존하는 고용탄소는 이동이 비교적 자유롭기 때문에 가동전위와 결합하여 상온시효특성에 영향을 미치지 않는다. According to the present invention, when the grains are refined by the fine (Mn, Cu) S precipitates and AlN precipitates, the solid solution carbon is more present in the grain boundary than in the grains, thereby ensuring room temperature non-aging characteristics. The dissolved carbon remaining in the grain is relatively free to move, so it does not affect the room temperature aging characteristics in combination with the operating potential.

또한, 본 발명에 따라 미세하게 분포하는 (Mn,Cu)S, AlN석출물들은 석출강화에 의한 항복강도의 상승과 강도-연성 밸런스 특성의 개선 그리고, 면내이방성 지수에도 긍정적인 영향을 미친다. 이를 위해서는 (Mn,Cu)S석출물이 미세하게 분포하여야 하면, 이는 Ti, Cu, C, N, S의 함량과 이들의 성분비 조건 그리고, 열간압연이 끝난 후 냉각속도가 영향을 미친다. In addition, the finely distributed (Mn, Cu) S, AlN precipitates according to the present invention has a positive effect on the increase in yield strength and the strength-ductility balance characteristics and the in-plane anisotropy index. For this purpose, if the (Mn, Cu) S precipitates should be finely distributed, this may affect the content of Ti, Cu, C, N, S and their component ratios, and the cooling rate after the hot rolling.

본 발명의 냉연강판은 항복강도가 높아 강판의 두께를 줄일 수 있어 경량화 효과가 있다. 또한, 면내이방성이 낮아 가공시 주름 발생이 적으며 가공후에는 귀(ear) 발생이 적은 장점이 있다. 이러한 본 발명의 냉연강판과 그 제조방법을 이하에서 구체적으로 설명한다. Cold rolled steel sheet of the present invention has a high yield strength can reduce the thickness of the steel sheet has a light weight effect. In addition, the in-plane anisotropy has the advantage of less wrinkles generated during processing and less ear generation after processing. The cold rolled steel sheet of the present invention and a manufacturing method thereof will be described in detail below.

먼저, 기본성분이 되는 C, Mn, Cu, S, Al, P, N, B, Nb, Ti에 대해 설명한다. First, C, Mn, Cu, S, Al, P, N, B, Nb, and Ti, which are basic components, will be described.

탄소(C)의 함량은 0.005%이하가 바람직하다.The content of carbon (C) is preferably 0.005% or less.

탄소(C)의 함량이 0.005%초과할 경우 시효성 및 소성이방성을 크게 악화시키 는 고용 탄소를 제거 하기 위해 고가의 Ti를 많이 첨가해야 한다. 이 경우 제조원가가 상승하며, 재결정온도가 높아진다. 따라서, 소둔온도를 높여야 하며 그렇지 않을 경우 소둔판의 결정립이 미세하게 되어 연성이 크게 낮아지며, 도금시 도금특성도 낮아진다. 보다 바람직한 탄소 (C)의 함량은 0.003%이하이다. If the content of carbon (C) is more than 0.005%, a large amount of expensive Ti must be added to remove solid solution carbon which greatly degrades aging and plastic anisotropy. In this case, the manufacturing cost rises and the recrystallization temperature increases. Therefore, the annealing temperature should be increased, otherwise the crystal grains of the annealing plate become fine and the ductility is greatly lowered, and the plating property is also lowered during plating. More preferable content of carbon (C) is 0.003% or less.

바람직하게는 탄소(C)함량의 하한을 0.0005%로 하는 것이다. 탄소(C)의 함량이 0.0005%미만의 경우에는 열연판의 결정립이 조대하여 강도가 낮아지고 면내이방성이 높아진다. Preferably, the lower limit of the content of carbon (C) is made 0.0005%. If the content of carbon (C) is less than 0.0005%, the grains of the hot rolled sheet are coarse to lower the strength and to increase the in-plane anisotropy.

망간(Mn)의 함량은 0.2%이하, 바람직하게는 0.01-0.2%의 범위이다. The content of manganese (Mn) is less than 0.2%, preferably in the range of 0.01-0.2%.

망간은 강중 고용상태의 황을 MnS로 석출하여 고용 황에 의한 적열취성(Hot shortness)을 방지하거나 고용강화원소로 알려져 있다. 이러한 기술적 관점에서는 망간의 함량을 높게 첨가하는 것이 일반적이다. 그러나, 본 발명에서는 망간의 함량을 낮추면서 황의 함량을 적절해지는 경우에 MnS가 매우 미세하게 석출되어 결정립 미세화에 의해 소성이방성, 면내이방성의 특성을 개선하고 석출강화에 의해 항복강도의 특성을 개선한다는 연구결과에 기초하여 망간의 함량을 0.2%이하로 한다. 이러한 특성을 확보하기 위해서는 망간의 함량이 0.01%이상이 되는 것이 보다 바람직하다. 망간의 함량이 0.2% 초과의 경우에는 망간의 함량이 높아 조대한 MnS석출물이 생성되어 강도확보가 곤란해 진다.Manganese is known as MnS to prevent hot shortness caused by solid sulfur by precipitating sulfur in solid state in steel. From this technical point of view, it is common to add a high content of manganese. However, in the present invention, when the sulfur content is appropriate while lowering the content of manganese, MnS precipitates very finely, thereby improving the properties of plastic anisotropy and in-plane anisotropy by grain refinement and improving the yield strength characteristics by precipitation strengthening. Based on the results of the study, the content of manganese should be less than 0.2%. In order to secure these characteristics, the content of manganese is more preferably 0.01% or more. When the content of manganese is more than 0.2%, the content of manganese is high, making coarse MnS precipitates, making it difficult to secure strength.

구리(Cu)의 함량은 0.01~0.2%가 바람직하다.The content of copper (Cu) is preferably 0.01 to 0.2%.

Cu는 미세한 CuS석출물을 형성하여 결정립을 미세하게 하여 면내이방성 지수를 낮추고 석출강화에 의해 항복강도를 증진시킨다. 이를 위해서는 Cu의 함량이 0.01%이상 되어야 미세하게 석출할 수 있고 0.2%초과하면 조대하게 석출한다. 바람직한 Cu의 함량은 0.03-0.2%로 하는 것이다. Cu forms fine CuS precipitates to finer grains, lowering the in-plane anisotropy index and enhancing yield strength by precipitation strengthening. For this purpose, the Cu content must be 0.01% or more to precipitate finely, and when it exceeds 0.2%, it precipitates coarsely. Preferable Cu content is 0.03-0.2%.

황(S)의 함량은 0.005-0.08%가 바람직하다.The content of sulfur (S) is preferably 0.005-0.08%.

황(S)은 Cu와 반응하여 미세한 (Mn,Cu)S의 석출물을 형성한다. 이러한 S의 함량이 0.005%미만의 경우에는 상기한 석출물의 석출량이 적을 뿐만 아니라 석출되는 석출물의 숫자가 매우 적다. 황의 함량이 0.08% 초과의 경우에는 고용된 황의 함량이 많아 연성 및 성형성이 크게 낮아지며, 적열취성의 우려가 있기 때문이다. 보다 바람직하게는 황(S)의 함량은 0.005-0.02%가 바람직하다.Sulfur (S) reacts with Cu to form fine (Mn, Cu) S precipitates. When the content of S is less than 0.005%, not only the amount of precipitates precipitated is small but also the number of precipitates precipitated is very small. If the content of sulfur is more than 0.08%, the content of the solid solution of sulfur is so high that the ductility and formability is greatly lowered, there is a fear of red brittleness. More preferably, the content of sulfur (S) is preferably 0.005-0.02%.

알루미늄(Al)의 함량은 0.1%이하가 바람직하다.The content of aluminum (Al) is preferably 0.1% or less.

Al은 N과 미세한 AlN석출물을 형성하여 결정립미세화와 더불어 석출강화에 의해 항복강도를 증진시킨다. 이를 위해 0.1%까지 첨가한다. Al의 함량이 0.1%초과되는 경우에는 고용상태의 Al의 함량이 많아 연성이 저하될 우려가 있다. Al forms fine AlN precipitates with N to enhance yield strength by grain refinement and precipitation strengthening. To this end, add up to 0.1%. When the Al content is more than 0.1%, there is a fear that the ductility decreases because the Al content is high in solid solution.

질소(N)의 함량은 0.004%초과-0.02%이하가 바람직하다. 보다 바람직하게는 0.005-0.02%로 하는 것이다. The content of nitrogen (N) is preferably more than 0.004% -0.02% or less. More preferably, it is 0.005-0.02%.

N함량이 0.004%미만의 경우에는 석출되는 AlN의 숫자가 적어 결정립미세화 및 석출강화의 효과가 적으며, 0.02%를 초과할 경우는 고용질소에 의한 시효보증이 곤란하므로 상한값을 0.02%로 하였다.If the N content is less than 0.004%, the number of precipitated AlNs is small, and the effect of grain refinement and precipitation strengthening is small. If the N content exceeds 0.02%, the aging guarantee due to solid nitrogen is difficult, so the upper limit is set to 0.02%.

인(P)의 함량은 0.2%이하가 바람직하다. The content of phosphorus (P) is preferably 0.2% or less.

인은 고용강화효과가 높으면서 r값의 저하가 적은 원소로서 본 발명에 따라 석출물을 제어하는 강에서 고강도를 보증한다. 280Mpa급의 강도가 요구되는 강종에서 P의 함량은 0.015%이하로 하는 것이 좋다. 340Mpa급 이상의 고강도 강에서는 0.016~0.2%로 하는 것이 좋다. 이러한 P의 함량이 0.2% 초과의 경우에는 연성이 저하하여 상한 값을 0.2%로 제한하는 것이 바람직하다. 본 발명에서 Si, Cr이 첨가되는 경우에는 P의 함량을 0.2%이하의 범위로 하면서 다양한 강도 설계가 가능하다. Phosphorus is an element having a high solid solution strengthening effect and a small decrease in r value, and guarantees high strength in steels for controlling precipitates according to the present invention. In steel grades requiring strength of 280 Mpa, the content of P should be less than 0.015%. For high strength steel of 340Mpa or higher, it is recommended to set it as 0.016 ~ 0.2%. If the content of P is more than 0.2%, it is preferable that the ductility is lowered to limit the upper limit to 0.2%. In the present invention, when Si and Cr are added, various strength designs are possible while the content of P is in the range of 0.2% or less.

보론(B)의 함량은 0.0001~0.002%가 바람직하다.The content of boron (B) is preferably 0.0001 to 0.002%.

보론은 2차가공취성을 방지하기 위해 첨가하는데 이를 위해 보론의 함량이 0.0001%이상인 것이 바람직하다. 보론의 함량이 0.002%를 초과하면 오무림 가공성(deep drawing)이 크게 저하될 수 있다. Boron is added to prevent secondary processing brittleness. For this purpose, the boron content is preferably 0.0001% or more. If the boron content exceeds 0.002%, deep drawing may be greatly degraded.

니오븀(Nb)의 함량은 0.002~0.04%가 바람직하다.The content of niobium (Nb) is preferably 0.002 to 0.04%.

Nb은 비시효성 확보 및 성형성 향상을 목적으로 첨가한다. Nb은 강력한 탄화물 생성 원소로 강중에 첨가되어 NbC석출물을 석출시켜 고용 상태의 탄소를 석출함으로써 비시효성을 확보한다. 또한 NbC석출물은 소둔중 집합조직을 발달하여 오무 림 가공성을 크게 향상하는 효과가 있다. Nb의 첨가량이 0.002%이하의 경우 NbC석출물의 석출량이 너무 적어 집합조직의 발달이 적어 오무림 가공성을 개선하는 효과가 거의 없다. Nb가 0.04%초과할 경우 NbC석출물의 양이 너무 많아 오무림가공성 및 연신율이 낮아져 성형성이 크게 저하할 수 있다.Nb is added for the purpose of ensuring inaging and improving moldability. Nb is a strong carbide-generating element, added to steel to precipitate NbC precipitates, thereby securing ineffective age by depositing solid carbon. In addition, NbC precipitates have an effect of greatly improving the processability of rim by developing the aggregated structure during annealing. If the amount of Nb added is less than 0.002%, the amount of precipitation of NbC precipitates is so small that there is little development of aggregates, and thus there is little effect of improving Omrim processability. When Nb exceeds 0.04%, the amount of NbC precipitates is too high, resulting in low rimability and low elongation, which may significantly reduce moldability.

티타늄(Ti)의 함량은 0.005~0.15%, 바람직하게는 0.005-0.1%로 하는 것이다. The content of titanium (Ti) is 0.005 to 0.15%, preferably 0.005-0.1%.

티타늄은 비시효성 확보 및 성형성 향상을 목적으로 첨가하는데 티타늄은 강력한 탄화물 생성 원소로 강중에 첨가되어 TiC석출물을 석출시켜 고용 상태의 탄소를 석출하므로써 비시효성을 확보한다. 티타늄의 첨가량이 0.005%미만의 경우 TiC석출물의 석출량이 너무 적어 집합조직의 발달이 적어 오무림 가공성을 개선하는 효과가 거의 없다. Ti가 0.15%초과할 경우 TiC석출물의 크기 너무 커 결정립미세화 효가가 감소되어 면내이방성지수가 높아지며 항복강도도 저하하고 도금특성이 크게 저하한다. Titanium is added for the purpose of securing inaging and improving moldability. Titanium is a strong carbide-generating element and is added to steel to precipitate TiC precipitates to precipitate insoluble solids. If the addition amount of titanium is less than 0.005%, the precipitation amount of TiC precipitate is too small, and there is little effect of improving the processability of the soil because of less development of the texture. If Ti exceeds 0.15%, the TiC precipitates are too large to reduce the grain refining efficiency, resulting in an increase in in-plane anisotropy, lowering the yield strength and greatly degrading the plating properties.

본 발명에서는 냉연강판에 미세한 (Mn,Cu)S를 확보하기 위한 관점에서 Ti, S, C, N, Cu의 성분비를 제어하는데 특징이 있다. IF강에서 Ti은 TiC, TiN, TiS, Ti(C,N), Ti4C2S2등의 석출물을 석출하는 것으로 알려져 있고, 이러한 석출물을 활용하기 위하여 Ti, S, C, N, Cu의 성분관계를 제어하고 있다. 그러나 본 발명에서는 (Mn,Cu)S석출물을 확보하기 위하여, Ti, S, C, N, Cu의 관계를 다음과 같이 관 리한다. 아래 관계식 1 내지 6에서 Ti, S, C, N, Cu, Mn, Al의 함량은 중량%이다.The present invention is characterized in controlling the component ratios of Ti, S, C, N and Cu from the viewpoint of securing fine (Mn, Cu) S in the cold rolled steel sheet. In IF steel, Ti is known to precipitate precipitates such as TiC, TiN, TiS, Ti (C, N), Ti 4 C 2 S 2 , and in order to utilize these precipitates, Ti, S, C, N, Cu The component relationship is controlled. However, in the present invention, in order to secure (Mn, Cu) S precipitates, the relationship between Ti, S, C, N, and Cu is managed as follows. In the following relations 1 to 6, the contents of Ti, S, C, N, Cu, Mn, and Al are by weight.

[관계식 1][Relationship 1]

Cu+Mn:0.05-0.4Cu + Mn: 0.05-0.4

[관계식 2][Relationship 2]

0.003≤S*≤0.015,0.003≤S * ≤0.015,

여기서, S*=S-0.8×(Ti-0.8×N(48/14))×(32/48)Where S * = S-0.8 × (Ti-0.8 × N (48/14)) × (32/48)

[관계식 3] [Relationship 3]

1≤(Mn/55+Cu/63.5)/(S*/32)≤301≤ (Mn / 55 + Cu / 63.5) / (S * / 32) ≤30

Mn+Cu의 량이 0.05%이상 되어야 (Mn,Cu)S석출물을 확보할 수 있으며, 0.4%초과의 경우에는 석출물이 크기가 커져 내시효특성을 확보하기 어렵다. 바람직하게는 Mn+Cu의 량을 0.3%이하로 하는 것이다.If the amount of Mn + Cu is 0.05% or more, it is possible to secure (Mn, Cu) S precipitates, and in the case of more than 0.4%, it is difficult to secure aging characteristics due to the large size of precipitates. Preferably, the amount of Mn + Cu is made 0.3% or less.

관계식 2에서 S*은 냉연강판에서 총S의 함량에서 Mn, Cu와 반응하는 S의 함량을 나타내는 것이다. S*의 함량이 0.003-0.015중량%가 되어야 충분한 (Mn,Cu)S석출물이 확보될 수 있다. S*의 함량이 0.003%미만의 경우에는 (Mn,Cu)S석출물의 석출량이 너무 적고, S*의 함량이 0.015%초과의 경우에는 고용S의 함량이 많아 연성 및 가공성이 크게 낮아질 우려가 있다. In relation 2, S * represents the content of S reacting with Mn and Cu in the content of total S in the cold rolled steel sheet. Sufficient (Mn, Cu) S precipitates can be obtained when the content of S * is 0.003-0.015% by weight. If the content of S * is less than 0.003%, the amount of precipitation of (Mn, Cu) S precipitates is too small, and if the content of S * is more than 0.015%, there is a possibility that the ductility and workability will be greatly reduced due to the high content of solid solution S. .

관계식 3은 미세한 (Mn,Cu)S석출물을 확보하도록 하기 위한 Mn, Cu와 S의 관계를 관리하는 것으로, 관계식 2의 값이 1이상이 되어야 유효한 (Mn,Cu)S석출물이 석출하게 되며, 30초과의 경우에는 (Mn,Cu)S석출물이 조대하여 가공성과 항복강도의 특성이 좋지 않다. Equation 3 is to manage the relationship between Mn, Cu and S to secure a fine (Mn, Cu) S precipitate, and the effective (Mn, Cu) S precipitates will be precipitated when the value of relation 2 is 1 or more, In the case of more than 30, (Mn, Cu) S precipitates are coarse, resulting in poor workability and yield strength.

또한, 본 발명에서는 관계식 4와 같이, C의 함량과 Ti, Nb의 함량 관계를 조절하여 상온내시효특성을 확보할 수 있다. 물론 관계식 4에 의해 소부경화특성을 갖도록 할 수도 있다. In addition, in the present invention, as shown in Equation 4, by controlling the relationship between the content of C and the content of Ti, Nb can be obtained at room temperature aging characteristics. Of course, it is possible to have the baking hardening characteristic by the relational expression (4).

[관계식 4][Relationship 4]

0.8≤(Ti*/48+Nb/93)/(C/12)≤5.00.8≤ (Ti * /48+Nb/93)/(C/12)≤5.0

여기서, Ti*=Ti-0.8×S(48/32)-0.8×N(48/14)이며, 각 성분의 함량은 중량%이다. Here, Ti * = Ti-0.8xS (48/32) -0.8xN (48/14), and the content of each component is weight%.

관계식 4는 강에서 C가 Nb와 Ti*와 반응하여 고용상태의 C를 NbC와 TiC로 석출되도록 하여 상온내시효특성을 확보하도록 하는 것이다. Ti*는 총Ti의 함량에서 N, S와 반응하고 남은 Ti가 C와 반응하도록 하는 것이다. 관계식 4의 값이 0.8미만의 경우에는 고용상태로 존재하는 C의 함량이 많아 상온내시효 보증이 어렵고 오무 림 가공성도 낮아진다. 관계식 4의 값이 5.0초과의 경우에는 TiC나 NbC석출물이 조대해져서 항복강도가 저하되고 도금특성도 좋지 않다. In relation to equation 4, C reacts with Nb and Ti * in the steel to precipitate solid-state C into NbC and TiC to ensure room temperature aging characteristics. Ti * reacts with N and S in the total Ti content, and causes the remaining Ti to react with C. If the value of relation 4 is less than 0.8, it is difficult to guarantee room temperature aging because of the high content of C present in the solid solution. If the value of the relation 4 is greater than 5.0, TiC or NbC precipitates coarsen and the yield strength is lowered and plating characteristics are not good.

또한, 본 발명에서는 미세한 AlN석출물을 확보하기 위하여 Al, N, Ti, S의 관계를 다음과 같이 관리한다. In addition, in the present invention, in order to secure a fine AlN precipitate, the relationship between Al, N, Ti, and S is managed as follows.

[관계식 5][Relationship 5]

0.003≤N*≤0.01, 0.003≤N * ≤0.01,

여기서, N*=N-0.8×(Ti-0.8×S×48/32)×14/48Where N * = N-0.8 × (Ti-0.8 × S × 48/32) × 14/48

[관계식 6][Relationship 6]

1≤(Al/27)/(N*/14)≤10,1≤ (Al / 27) / (N * / 14) ≤10,

관계식 5에서 N*은 냉연강판에서 총N의 함량에서 Al과 반응하는 S의 함량을 나타내는 것이다. S*의 함량이 0.003-0.01중량%가 되어야 충분한 AlN석출물이 확보될 수 있다. N*의 함량이 0.003%미만의 경우에는 AlN석출물의 석출량이 너무 적고, N*의 함량이 0.01%초과의 경우에는 고용N의 함량이 많아 연성 및 성형성이 크게 낮아질 우려가 있다. In relation 5, N * represents the amount of S reacting with Al in the total N content in the cold rolled steel sheet. The content of S * should be 0.003-0.01% by weight to ensure sufficient AlN precipitate. If the content of N * is less than 0.003%, the amount of precipitation of AlN precipitates is too small, and if the content of N * is more than 0.01%, the content of solid solution N is high, so there is a possibility that the ductility and formability are greatly reduced.

관계식 6은 미세한 AlN석출물을 확보하도록 하기 위한 Al와 N의 관계를 관리하는 것으로, 관계식 6 값이 1이상이 되어야 유효한 AlN석출물이 석출하게 되며, 10초과의 경우에는Equation 6 is to manage the relationship between Al and N in order to secure a fine AlN precipitate, the effective AlN precipitate is precipitated when the relation 6 value is 1 or more, in the case of more than 10

AlN석출물이 조대하여 가공성과 항복강도의 특성이 좋지 않다. AlN precipitates are coarse, resulting in poor workability and yield strength.

본 발명의 성분계에서 석출물은 미세하게 분포할수록 유리한데, 바람직하게는 (Mn,Cu)S석출물과 AlN석출물의 평균크기가 0.2㎛이하이다. 본 발명의 연구결과에 따르면 석출물의 평균크기가 0.2㎛ 초과의 경우에는 특히 강도가 낮아지고, 면내이방성지수가 좋지 않다. In the component system of the present invention, the finer the distribution, the more advantageous. Preferably, the average size of (Mn, Cu) S precipitates and AlN precipitates is 0.2 µm or less. According to the results of the present invention, especially when the average size of the precipitate is more than 0.2㎛, the strength is low, the in-plane anisotropy index is not good.

나아가, 본 발명의 성분계에서 0.2㎛이하의 석출물의 분포수가 mm2당 1X106개 이상일 때 소성이방성지수가 높아지고 오히려 면내이방성지수는 낮아져 가공성이 크게 개선된다. 일반적으로 소성이방성지수가 높아지면 면내이방성지수는 올라가서 가공성 측면에서 소성이방성지수를 높이는데 한계가 있다는 점을 감안할 때, 석출물의 분포수에 따라 소성이방성지수와 면내이방성지수의 특이한 변화는 주목할만 하다. Furthermore, when the distribution number of precipitates of 0.2 μm or less in the component system of the present invention is 1 × 10 6 or more per mm 2, the plastic anisotropy index is increased, and the in-plane anisotropy index is lowered, thereby greatly improving workability. In general, when the plastic anisotropy index increases, the in-plane anisotropy index rises and there is a limit to increasing the plastic anisotropy index in terms of processability. .

본 발명에서는 340MPa급 이상의 고강도 강판으로 적용하는 경우에는 상기 P와 같은 고용강화원소 즉, P, Si, Cr의 1종 또는 2종이상을 첨가할 수 있다. P는 이미 언급하였는 바, 중복기재는 생략한다. In the present invention, when applied to a high-strength steel sheet of 340 MPa grade or more, one or two or more solid solution strengthening elements such as P, that is, P, Si, and Cr may be added. P has already been mentioned, so duplicate descriptions are omitted.

실리콘(Si)의 함량은 0.8%이하, 바람직하게는 0.1-0.8%의 범위를 갖는 것이다. The content of silicon (Si) is 0.8% or less, preferably in the range of 0.1-0.8%.

Si은 고용강화효과가 높으면서 연신율의 저하가 낮은 원소로 본 발명에 따라 석출물을 제어하는 강에서 고강도를 보증한다. Si의 함량이 0.1%이상 되어야 강도를 확보할 수 있으며, 0.8%초과의 경우에는 연성이 저하한다. 보다 바람직하게는 0.5%이하의 범위로 하는 것이다. Si is an element having a high solid solution strengthening effect and a low drop in elongation, which ensures high strength in steels for controlling precipitates according to the present invention. When the content of Si is more than 0.1% to secure the strength, in the case of more than 0.8% ductility is reduced. More preferably, it is 0.5% or less of range.

크롬(Cr)의 함량은 1.2%이하, 바람직하게는 0.2~1.2%의 범위를 갖는 것이다. The content of chromium (Cr) is 1.2% or less, preferably 0.2 to 1.2%.

Cr은 고용강화효과가 높으면서 2차가공취성온도를 낮추며 Cr탄화물에 의해 시효지수를 낮추는 원소로서, 본 발명에 따라 석출물을 제어하는 강에서 고강도를 보증하며 면내이방성 지수도 낮게 한다. Cr의 함량이 0.2%이상 되어야 강도를 확보할 수 있으며, 1.2% 초과의 경우에는 연성이 저하한다. 보다 바람직하게는 0.5%이하로 하는 것이다. Cr is an element that lowers the secondary brittleness temperature and decreases the aging index by Cr carbide while having a high solid-solution strengthening effect, and assures high strength in steels for controlling precipitates according to the present invention and also lowers in-plane anisotropy index. The Cr content is more than 0.2% to secure the strength, in the case of more than 1.2% ductility is reduced. More preferably, it is 0.5% or less.

본 발명의 냉연강판에서 몰리브덴(Mo)이 추가로 첨가될 수 있다. In the cold rolled steel sheet of the present invention, molybdenum (Mo) may be further added.

몰리브덴(Mo)의 함량은 0.2%이하, 바람직하게는 0.01~0.2%의 범위로 하는 것이다. The content of molybdenum (Mo) is 0.2% or less, preferably in the range of 0.01 to 0.2%.

Mo은 소성이방성지수를 높이는 원소로서 첨가되는데, 그 함량이 0.01%이상 되어야 소성이방성지수가 커지며, 0.2%를 초과하면 소성이방성지수는 더 이상 커지지 않고 열간취성을 일으킬 우려가 있다. Mo is added as an element to increase the plastic anisotropy index, the content of the plastic anisotropy index is increased when the content is more than 0.01%, if the content exceeds 0.2%, the plastic anisotropy index is no longer increased and there is a risk of causing hot brittleness.

[냉연강판의 제조방법][Manufacturing method of cold rolled steel sheet]

본 발명은 상기한 강조성을 만족하는 강을 열간압연과 냉간압연을 통해 냉간압연판에 (Mn,Cu)S석출물과 AlN석출물의 평균크기가 0.2㎛ 이하를 만족하도록 하는데 특징이 있다. 냉간압연판에서 (Mn,Cu)S석출물과 AlN석출물의 평균 크기는 첨가량의 조건과 재가열온도, 권취온도 등의 제조공정에 영향을 받으나 특히 열간압연후의 냉각속도에 직접적인 영향을 받는다. The present invention is characterized by satisfying the average size of (Mn, Cu) S precipitates and AlN precipitates in a cold rolled sheet through hot rolling and cold rolling. The average size of (Mn, Cu) S precipitates and AlN precipitates in cold rolled plates is influenced by the manufacturing conditions such as addition amount, reheating temperature and winding temperature, but especially by the cooling rate after hot rolling.

[열간압연조건][Hot Rolling Condition]

본 발명에서는 상기한 강조성을 만족하는 강을 재가열하여 열간압연한다. 재가열온도는 1100℃이상이 바람직하다. 재가열온도가 1100℃미만의 경우에는 재가열온도가 낮아 연속주조중에 생성된 조대한 석출물들이 완전히 용해되지 않은 상태로 남아 있어 열간압연후에도 조대한 석출물이 많이 남아있기 때문이다.In the present invention, the steel that satisfies the above-mentioned emphasis is reheated and hot rolled. The reheating temperature is preferably 1100 ° C or more. This is because when the reheating temperature is lower than 1100 ° C., the coarse precipitates generated during continuous casting remain completely insoluble due to the low reheating temperature, so that many coarse precipitates remain even after hot rolling.

열간압연은 마무리압연온도를 Ar3변태온도 이상의 조건에서 행하는 것이 바람직하다. 마무리압연온도가 Ar3변태온도 미만의 경우에는 압연립의 생성으로 가공성이 저하할 뿐만아니라 강도도 낮아지기 때문이다. Hot rolling is preferably carried out under the conditions of the finish rolling temperature higher than the Ar 3 transformation temperature. This is because when the finish rolling temperature is lower than the Ar 3 transformation temperature, not only the workability is reduced by the formation of the rolled grain but also the strength is lowered.

열간압연후 권취전 냉각속도는 300℃/min 이상으로 하는 것이 바람직하다. 본 발명에 따라 미세한 석출물을 얻기 위하여 그 성분비를 제어하더라도 냉각속도가 300℃/min 미만이면 석출물의 평균크기가 0.2㎛를 초과할 수 있다. 즉, 냉각속도가 빨라질수록 많은 수의 핵이 생성하여 석출물이 미세해지기 때문이다. 냉각속도가 빨라질수록 석출물의 크기가 미세해지므로 냉각속도의 상한을 제한할 필요는 없으나, 냉각속도가 1000℃/min 보다 빨라지더라도 석출물 미세화 효과가 더 이상 커지지 않으므로 냉각속도는 300~1000℃/min이 보다 바람직하다. It is preferable that the cooling rate before winding after hot rolling shall be 300 degreeC / min or more. Even if the component ratio is controlled to obtain a fine precipitate according to the present invention, if the cooling rate is less than 300 ° C / min, the average size of the precipitate may exceed 0.2 ㎛. In other words, as the cooling rate increases, a large number of nuclei are generated and the precipitate becomes fine. The faster the cooling rate, the finer the precipitate is, so it is not necessary to limit the upper limit of the cooling rate.However, even if the cooling rate is faster than 1000 ° C / min, the finer effect of the precipitate is no longer increased, so the cooling rate is 300 to 1000 ° C / min. This is more preferable.

[권취조건][Coiling condition]

상기와 같이 열간압연한 다음에는 권취를 행하는데, 권취온도는 700℃이하가 바람직하다. 권취온도가 700℃초과의 경우에는 석출물이 너무 조대하게 성장하여 강도확보가 곤란하다.Winding is performed after hot rolling as above, but the winding temperature is preferably 700 ° C or lower. If the coiling temperature exceeds 700 ℃, precipitates grow too coarse, making it difficult to secure strength.

[냉간압연조건][Cold rolling condition]

냉간압연은 50~90%의 압하율로 행하는 것이 바람직하다. 냉간압하율이 50%미만의 경우에는 소둔재결정 핵생성양이 적기 때문에 소둔시 결정립이 너무 크게 성장하여 소둔 재결정립의 조대화로 강도 및 성형성이 저하한다. 냉간압하율이 90%초과의 경우에는 성형성은 향상되지만 핵생성 양이 너무 많아 소둔 재결정립은 오히려 너무 미세하여 연성이 저하한다. Cold rolling is preferably performed at a reduction ratio of 50 to 90%. If the cold reduction rate is less than 50%, the amount of nucleation of the annealing recrystallization is small, so that grains grow too large during annealing, resulting in a decrease in strength and formability due to coarsening of the annealing recrystallization grains. If the cold reduction ratio is more than 90%, the moldability is improved, but the nucleation amount is too high, so the annealing recrystallized grain is too fine to decrease the ductility.

[연속소둔][Continuous Annealing]

연속소둔 온도는 제품의 재질을 결정하는 중요한 역할을 한다. 본 발명에서는 700~900℃의 온도범위에서 행하는 것이 바람직하다. 연속소둔 온도가 700℃미만의 경우에는 재결정이 완료되지 않아 목표로 하는 연성 값을 확보할 수 없으며, 소둔온도가 900℃초과의 경우에는 재결정립의 조대화로 강도가 저하된다. 연속소둔시간은 재결정이 완료되도록 유지하는데, 약 10초이상이면 재결정이 완료된다. 바람직하게는 연속소둔시간을 10초~30분의 범위내로 하는 것이다,Continuous annealing temperature plays an important role in determining the material of the product. In this invention, it is preferable to carry out in the temperature range of 700-900 degreeC. If the continuous annealing temperature is less than 700 ° C., recrystallization is not completed and the target ductility value cannot be secured. If the annealing temperature is more than 900 ° C., the strength decreases due to coarsening of the recrystallized grains. The continuous annealing time keeps the recrystallization complete. If it is about 10 seconds or more, the recrystallization is completed. Preferably the continuous annealing time is in the range of 10 seconds to 30 minutes,

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

[실시예 1]Example 1

표 1의 강슬라브를 재가열하여 마무리열간압연하고 400℃/min 의 속도로 냉각하여 650℃에서 권취한 다음, 75%의 압하율로 냉간압연과 연속소둔처리하였다. 이때의 마무리압연온도는 Ar3변태점이상인 910℃이며, 연속소둔은 10℃/초의 속도로 830℃로 40초 동안 가열하여 행하였다. The steel slabs of Table 1 were reheated, hot rolled to finish, cooled to 400 ° C./min, wound up at 650 ° C., and then cold rolled and continuously annealed at a reduction rate of 75%. The finish rolling temperature of not less than Ar 3 transformation point is 910 ℃, continuous annealing was performed by heating for 40 seconds to 830 ℃ to 10 ℃ / second.

얻어진 소둔판은 기계적 특성을 조사하기 위해 ASTM규격(ASTM E-8 standard)에 의한 표준시편으로 가공하였다. 시편은 인장시험기(INSTRON사, Model 6025)를 이용하여 항복강도, 인장강도, 연신율, 소성이방성 지수(rm값), 면내이방성 지수(△r값) 및 시효평가지수를 측정하였다. 여기서 rm=(r0+2r45+r90)/4, △r=(r0-2r45+r90)/2이며, 시효평가지수는 소둔후 1.0% skin Pass압연한 시편을 100 ℃ X 2hr. 열처리후 측정된 항복점연신(Yield Point Elongation)율이다.The obtained annealing plate was processed into a standard specimen according to ASTM E-8 standard to investigate the mechanical properties. The specimen was measured for yield strength, tensile strength, elongation, plastic anisotropy index (r m value), in-plane anisotropy index (Δr value) and aging evaluation index using a tensile tester (INSTRON, Model 6025). Where r m = (r 0 + 2r 45 + r 90 ) / 4, △ r = (r 0 -2r 45 + r 90 ) / 2, and the aging evaluation index is 1.0 ° C after passing annealing. X 2hr. Yield point elongation rate measured after heat treatment.

구분 division 화학성분(중량%)Chemical composition (% by weight) CC MnMn CuCu SS AlAl NN PP BB NbNb TiTi 기타Etc A1A1 0.00080.0008 0.070.07 0.150.15 0.0090.009 0.0250.025 0.00890.0089 0.0450.045 0.00090.0009 0.0180.018 0.030.03 Si:0.03Si: 0.03 A2A2 0.00150.0015 0.150.15 0.120.12 0.0140.014 0.0340.034 0.0110.011 0.0820.082 0.0010.001 0.0390.039 0.0390.039 Si:0.12Si: 0.12 A3A3 0.00280.0028 0.120.12 0.160.16 0.0110.011 0.0290.029 0.01090.0109 0.1180.118 0.0070.007 0.030.03 0.0380.038 Si:0.09Si: 0.09 A4A4 0.00120.0012 0.150.15 0.10.1 0.020.02 0.030.03 0.0130.013 0.0350.035 0.00110.0011 0.0120.012 0.0630.063 Si:0.12 Mo:0.09Si: 0.12 Mo: 0.09 A5A5 0.00190.0019 0.130.13 0.140.14 0.0170.017 0.0530.053 0.01320.0132 0.0340.034 0.00080.0008 0.0450.045 0.050.05 Si:0.09 Cr:0.22Si: 0.09 Cr: 0.22 A6A6 0.00340.0034 0.450.45 0.10.1 0.00830.0083 0.0380.038 0.00150.0015 0.0480.048 0.0050.005 00 00 A7A7 0.00380.0038 0.070.07 00 0.0120.012 0.0350.035 0.00240.0024 0.130.13 0.0050.005 00 0.170.17 Si:0.08Si: 0.08

구분division Cu+MnCu + Mn S* S * (Mn/55+Cu/63.5)/(S*/32)(Mn / 55 + Cu / 63.5) / (S * / 32) (Ti*/48+Nb/93)/ (C/12)(Ti * / 48 + Nb / 93) / (C / 12) N* N * (Al/27)/ (N*14)(Al / 27) / (N * 14) 석출물의 평균크기(㎛)Average size of precipitate (㎛) 석출물 수 (개/㎟)Number of precipitates (pcs / mm2) A1A1 0.220.22 0.0060.006 19.32419.324 1.271.27 0.00440.0044 2.932.93 0.040.04 9.4X107 9.4X10 7 A2A2 0.270.27 0.00930.0093 15.90115.901 2.032.03 0.00580.0058 3.033.03 0.030.03 9.0X107 9.0X10 7 A3A3 0.280.28 0.00670.0067 22.52722.527 0.930.93 0.00510.0051 2.942.94 0.040.04 8.2X107 8.2X10 7 A4A4 0.250.25 0.00540.0054 25.41325.413 1.991.99 0.00390.0039 3.993.99 0.040.04 7.9X107 7.9 X 10 7 A5A5 0.270.27 0.00960.0096 15.1615.16 2.192.19 0.00630.0063 4.374.37 0.030.03 9.6X107 9.6 X 10 7 A6A6 0.550.55 0.01050.0105 29.75129.751 -1-One 0.00380.0038 5.155.15 0.250.25 1.5X104 1.5X10 4 A7A7 0.070.07 00 00 9.89.8 00 00 0.040.04 3.5X105 3.5 X 10 5 S*=S-0.8×(Ti-0.8×N(48/14))×(32/48) Ti*=Ti-0.8×S(48/32)-0.8×N(48/14) N*=N-0.8(Ti-0.8×S×48/32)×14/48S * = S-0.8 × (Ti-0.8 × N (48/14)) × (32/48) Ti * = Ti-0.8 × S (48/32) -0.8 × N (48/14) N * = N-0.8 (Ti-0.8 × S × 48/32) × 14/48

구분 division 기계적 성질Mechanical properties 비고Remarks 항복강도 (MPa)Yield strength (MPa) 인장강도 (MPa)Tensile Strength (MPa) 연신율 (%)Elongation (%) 소성이방성 지수(rm)Plastic Anisotropy Index (r m ) 면내이방성 지수(Δr)In-plane anisotropy index (Δr) 시효평가지수(%)Aging Evaluation Index (%) 2차가공취성 (DBTT-℃)2nd processing brittleness (DBTT- ℃) A1A1 222222 357357 4343 2.222.22 0.090.09 00 -70-70 발명강Invention steel A2A2 260260 409409 3535 1.931.93 0.060.06 00 -60-60 발명강Invention steel A3A3 332332 453453 3434 1.731.73 0.060.06 00 -60-60 발명강Invention steel A4A4 229229 367367 4040 2.182.18 0.080.08 00 -60-60 발명강Invention steel A5A5 231231 359359 4545 1.891.89 0.070.07 00 -50-50 발명강Invention steel A6A6 202202 355355 3838 1.591.59 0.390.39 00 -60-60 비교강Comparative steel A7A7 338338 458458 2424 1.311.31 0.580.58 0.550.55 -70-70 비교강Comparative steel

본 발명에서 상기 실시형태는 하나의 예시로서, 본 발명이 여기에 한정되는 것은 아니다. 본 발명의 특허청구범위에 기재된 기술적 사상과 실질적으로 동일한 구성을 갖고 동일한 작용효과를 이루는 것은 어떠한 것이어도 본 발명의 기술적 범위에 포함된다. In the present invention, the above embodiment is only one example, and the present invention is not limited thereto. Anything that has substantially the same configuration as the technical idea described in the claims of the present invention and achieves the same operation and effect is included in the technical scope of the present invention.

상술한 바와 같이, 본 발명은 IF강에서 Cu를 ε-Cu의 석출상으로 이용하는 기술 또는 Cu를 (Mn,Cu)S로 석출하여 탄화물의 석출핵으로 이용하는 기술과는 달리, 나노싸이즈의 (Mn,Cu)S석출물과 AlN석출물을 냉연강판에 분포시키는 것에 의해 결정립을 미세화시키고 이에 따라 면내이방성지수를 낮추고 또한, (Mn,Cu)S와 AlN의 석출강화에 의해 항복강도를 증진시키는 것이다.As described above, the present invention is different from the technique of using Cu as a precipitated phase of ε-Cu in IF steel or the technique of using Cu as (Mn, Cu) S as a precipitation nucleus of carbides. By distributing, Cu) S precipitates and AlN precipitates on the cold rolled steel sheet, the grains are refined, thereby lowering the in-plane anisotropy index and enhancing the yield strength by strengthening the precipitation of (Mn, Cu) S and AlN.

Claims (16)

중량%로, C: 0.005%이하, Mn:0.2%이하, Cu:0.01-0.2%, S:0.005-0.08%, Al:0.1%이하 N:0.004%초과-0.02%이하, P:0.2%이하, B:0.0001-0.002%, Nb:0.002~0.04%, Ti:0.005~0.15%, 나머지 Fe 및 기타 불가피한 불순물로 조성되고, By weight%, C: 0.005% or less, Mn: 0.2% or less, Cu: 0.01-0.2%, S: 0.005-0.08%, Al: 0.1% or less N: 0.004% or more-0.02% or less, P: 0.2% or less , B: 0.0001-0.002%, Nb: 0.002 ~ 0.04%, Ti: 0.005 ~ 0.15%, remaining Fe and other inevitable impurities, Cu+Mn:0.05-0.4, 0.003≤S*≤0.015, 1≤(Mn/55+Cu/63.5)/(S*/32)≤30, 0.8≤(Ti*/48+Nb/93)/(C/12)≤5.0, 0.003≤N*≤0.01, 1≤(Al/27)/(N*/14)≤10,Cu + Mn: 0.05-0.4, 0.003 ≦ S * ≦ 0.015, 1 ≦ (Mn / 55 + Cu / 63.5) / (S * / 32) ≦ 30, 0.8 ≦ (Ti * / 48 + Nb / 93) / ( C / 12) ≤5.0, 0.003≤N * ≤0.01, 1≤ (Al / 27) / (N * / 14) ≤10, 여기서, S*=S-0.8×(Ti-0.8×N(48/14))×(32/48), Ti*=Ti-0.8×S(48/32)-0.8×N(48/14), N*=N-0.8×(Ti-0.8×S×48/32)×14/48Where S * = S-0.8 × (Ti-0.8 × N (48/14)) × (32/48), Ti * = Ti-0.8 × S (48/32) -0.8 × N (48/14) , N * = N-0.8 × (Ti-0.8 × S × 48/32) × 14/48 를 만족하고, (Mn,Cu)S석출물과 AlN석출물의 평균크기가 0.2㎛이하로 이루어지는 소성이방성이 우수한 냉연강판. A cold rolled steel sheet having excellent plastic anisotropy, which satisfies and has an average size of (Mn, Cu) S precipitates and AlN precipitates of 0.2 µm or less. 제 1항에 있어서, 상기 석출물수는 1X106개/mm2이상임을 특징으로 하는 소성이방성이 우수한 냉연강판. The cold rolled steel sheet having excellent plastic anisotropy according to claim 1, wherein the precipitate water is 1 × 10 6 / mm 2 or more. 제 1항에 있어서, 상기 C의 함량은 0.0005-0.003%임을 특징으로 하는 소성이방성이 우수한 냉연강판. The cold rolled steel sheet having excellent plastic anisotropy according to claim 1, wherein the C content is 0.0005-0.003%. 제 1항에 있어서, 상기 Cu는 0.03-0.2%임을 특징으로 하는 소성이방성이 우수한 냉연강판.The cold rolled steel sheet having excellent plastic anisotropy according to claim 1, wherein the Cu is 0.03-0.2%. 제 1항 내지 제 4항중 어느 한 항에 있어서, 상기 P의 함량은 0.015%이하임을 특징으로 하는 소성이방성이 우수한 냉연강판.The cold rolled steel sheet having excellent plastic anisotropy according to any one of claims 1 to 4, wherein the content of P is 0.015% or less. 제 1항 내지 제 4항중 어느 한 항에 있어서, 상기 P의 함량은 0.03~0.2%임을 특징으로 하는 소성이방성이 우수한 냉연강판.The cold rolled steel sheet having excellent plastic anisotropy according to any one of claims 1 to 4, wherein the content of P is 0.03 to 0.2%. 제 1항 내지 제 4항중 어느 한 항에 있어서, 상기 냉연강판에는 Si:0.8%이하, Cr:1.2%이하의 1종 또는 2종이 추가로 포함되는 것을 특징으로 하는 소성이방성이 우수한 냉연강판.The cold rolled steel sheet having excellent plastic anisotropy according to any one of claims 1 to 4, wherein the cold rolled steel sheet further includes one or two kinds of Si: 0.8% or less and Cr: 1.2% or less. 제 1항 내지 제 4항중 어느 한 항에 있어서, 상기 냉연강판에는 Mo이 추가로 0.2%이하 포함되는 것을 특징으로 하는 소성이방성이 우수한 냉연강판.The cold rolled steel sheet having excellent plastic anisotropy according to any one of claims 1 to 4, wherein Mo is further included in the cold rolled steel sheet at 0.2% or less. 중량%로, C: 0.005%이하, Mn:0.2%이하, Cu:0.01-0.2%, S:0.005-0.08%, Al:0.1%이하 N:0.004%초과-0.02%이하, P:0.2%이하, B:0.0001-0.002%, Nb:0.002~0.04%, Ti:0.005~0.15%, 나머지 Fe 및 기타 불가피한 불순물로 조성되고, By weight%, C: 0.005% or less, Mn: 0.2% or less, Cu: 0.01-0.2%, S: 0.005-0.08%, Al: 0.1% or less N: 0.004% or more-0.02% or less, P: 0.2% or less , B: 0.0001-0.002%, Nb: 0.002 ~ 0.04%, Ti: 0.005 ~ 0.15%, remaining Fe and other inevitable impurities, Cu+Mn:0.05-0.4, 0.003≤S*≤0.015, 1≤(Mn/55+Cu/63.5)/(S*/32)≤30, 0.8≤(Ti*/48+Nb/93)/(C/12)≤5.0, 0.003≤N*≤0.01, 1≤(Al/27)/(N*/14)≤10,Cu + Mn: 0.05-0.4, 0.003 ≦ S * ≦ 0.015, 1 ≦ (Mn / 55 + Cu / 63.5) / (S * / 32) ≦ 30, 0.8 ≦ (Ti * / 48 + Nb / 93) / ( C / 12) ≤5.0, 0.003≤N * ≤0.01, 1≤ (Al / 27) / (N * / 14) ≤10, 여기서, S*=S-0.8×(Ti-0.8×N(48/14))×(32/48), Ti*=Ti-0.8×S(48/32)-0.8×N(48/14), N*=N-0.8×(Ti-0.8×S×48/32)×14/48Where S * = S-0.8 × (Ti-0.8 × N (48/14)) × (32/48), Ti * = Ti-0.8 × S (48/32) -0.8 × N (48/14) , N * = N-0.8 × (Ti-0.8 × S × 48/32) × 14/48 를 만족하는 슬라브를 1100℃이상의 온도로 재가열한 후 마무리 압연온도를 Ar3변태점 이상으로 하여 열간압연하고 300℃/min이상의 속도로 냉각하고 700℃이하의 온도에서 권취한 다음, 50-90%의 압하율로 냉간 압연하고, 700-900℃의 온도로 연속소둔하여 평균크기가 0.2㎛이하의 AlN석출물과 (Mn,Cu)S석출물이 분포하는 소성이방성이 우수한 냉연강판의 제조방법.After reheating the slab satisfying the temperature above 1100 ℃ and hot rolling with the finish rolling temperature above the Ar 3 transformation point, cooling it at a speed above 300 ℃ / min, winding it at a temperature below 700 ℃, and then 50-90% Cold rolling at a reduction ratio, continuous annealing at a temperature of 700-900 ℃ to produce a cold rolled steel sheet having excellent plastic anisotropy in which AlN precipitate and (Mn, Cu) S precipitate having an average size of 0.2㎛ or less is distributed. 제 9항에 있어서, 상기 석출물수는 1X106개/mm2이상임을 특징으로 하는 소성이방성이 우수한 냉연강판의 제조방법. 10. The method of claim 9, wherein the precipitate water is 1 × 10 6 / mm 2 or more. 제 9항에 있어서, 상기 C의 함량은 0.0005-0.003%임을 특징으로 하는 소성이방성이 우수한 냉연강판의 제조방법. 10. The method of claim 9, wherein the C content is 0.0005-0.003%. 제 9항에 있어서, 상기 Cu는 0.03-0.2%임을 특징으로 하는 소성이방성이 우수한 냉연강판의 제조방법.10. The method of claim 9, wherein the Cu is 0.03-0.2%. 제 9항 내지 제 12항중 어느 한 항에 있어서, 상기 P의 함량은 0.015%이하임을 특징으로 하는 소성이방성이 우수한 냉연강판의 제조방법.The method of manufacturing a cold rolled steel sheet having excellent plastic anisotropy according to any one of claims 9 to 12, wherein the content of P is 0.015% or less. 제 9항 내지 제 12항중 어느 한 항에 있어서, 상기 P의 함량은 0.03~0.2%임을 특징으로 하는 소성이방성이 우수한 냉연강판의 제조방법.The method of manufacturing a cold rolled steel sheet having excellent plastic anisotropy according to any one of claims 9 to 12, wherein the content of P is 0.03 to 0.2%. 제 9항 내지 제 12항중 어느 한 항에 있어서, 상기 냉연강판에는 Si:0.8%이하, Cr:1.2%이하의 1종 또는 2종이 추가로 포함되는 것을 특징으로 하는 소성이방성이 우수한 냉연강판의 제조방법.The cold rolled steel sheet according to any one of claims 9 to 12, wherein the cold rolled steel sheet further includes one or two of Si: 0.8% or less and Cr: 1.2% or less. Way. 제 9항 내지 제 12항중 어느 한 항에 있어서, 상기 냉연강판에는 Mo이 추가로 0.2%이하 포함되는 것을 특징으로 하는 소성이방성이 우수한 냉연강판의 제조방법.The method of claim 9, wherein the cold rolled steel sheet further comprises 0.2% or less of Mo.
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