KR20140129316A - High-strength cold-rolled steel sheet, high-strength galvanized steel sheet and high-strength galvannealed steel sheet, having excellent formability and shape fixability, and processes for manufacturing same - Google Patents

High-strength cold-rolled steel sheet, high-strength galvanized steel sheet and high-strength galvannealed steel sheet, having excellent formability and shape fixability, and processes for manufacturing same Download PDF

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KR20140129316A
KR20140129316A KR1020147027124A KR20147027124A KR20140129316A KR 20140129316 A KR20140129316 A KR 20140129316A KR 1020147027124 A KR1020147027124 A KR 1020147027124A KR 20147027124 A KR20147027124 A KR 20147027124A KR 20140129316 A KR20140129316 A KR 20140129316A
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steel sheet
strength
less
cooled
cold
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고지 가스야
유이치 후타무라
유키히로 우츠미
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가부시키가이샤 고베 세이코쇼
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • C21D1/18—Hardening; Quenching with or without subsequent tempering
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Abstract

고강도 냉연 강판은, 규정의 성분 조성을 갖고, 강 조직이, 베이니틱 페라이트(BF)+템퍼링 마르텐사이트(TM): 65%(면적%의 의미. 강 조직에 대하여 이하 동일) 이상, 프레쉬 마르텐사이트(M): 3∼18%, 잔류 오스테나이트(잔류 γ): 5% 이상, 및 폴리고널 페라이트(F): 5% 이하를 만족시키고, 또한, 규정의 평균 KAM<1.00°: 0.50° 이상을 만족시키고, 또한 인장 강도가 980MPa 이상이다. 고강도 냉연 강판은, 성형성 및 형상 동결성이 우수하다. The high-strength cold-rolled steel sheet has a specified composition and the steel structure has a composition of 65% (mean of area%, the same shall apply hereinafter) of steel with bainitic ferrite (BF) + tempering martensite (TM) (Residual γ): 5% or more, and the polygonal ferrite (F): 5% or less, and satisfies the specified average KAM <1.00 ° : 0.50 ° or more And a tensile strength of 980 MPa or more. The high-strength cold-rolled steel sheet is excellent in moldability and shape crystallinity.

Description

성형성 및 형상 동결성이 우수한, 고강도 냉연 강판, 고강도 용융 아연도금 강판 및 고강도 합금화 용융 아연도금 강판, 및 그들의 제조 방법{HIGH-STRENGTH COLD-ROLLED STEEL SHEET, HIGH-STRENGTH GALVANIZED STEEL SHEET AND HIGH-STRENGTH GALVANNEALED STEEL SHEET, HAVING EXCELLENT FORMABILITY AND SHAPE FIXABILITY, AND PROCESSES FOR MANUFACTURING SAME}TECHNICAL FIELD [0001] The present invention relates to a high-strength cold-rolled steel sheet, a high-strength hot-dip galvanized steel sheet and a high-strength galvannealed steel sheet excellent in moldability and shape durability and a method of manufacturing the same. BACKGROUND OF THE INVENTION GALVANNEALED STEEL SHEET, HAVING EXCELLENT FORMABILITY AND SHAPE FIXABILITY, AND PROCESSES FOR MANUFACTURING SAME}

본 발명은, 성형성 및 형상 동결성이 우수한, 고강도 냉연 강판, 고강도 용융 아연도금 강판 및 고강도 합금화 용융 아연도금 강판, 및 그들의 제조 방법에 관한 것이다. The present invention relates to a high-strength cold-rolled steel sheet, a high-strength hot-dip galvanized steel sheet and a high-strength galvannealed steel sheet excellent in moldability and shape durability, and a method of manufacturing the same.

최근, 자동차에 있어서는, 환경에 대한 배려에서 연비의 향상이 요망되고 있고, 그를 위해 차체의 경량화가 진행되고 있다. 또한, 차체를 경량화해도 안전성을 유지할 수 있도록, 차체를 구성하는 다양한 강 부재에 있어서, 종래보다도 강도가 높은(인장 강도가 980MPa 이상인) 강판의 수요가 높아지고 있다. 그러나, 강도가 높아지면 성형성의 저하 및 형상 동결성의 저하가 일어나기 쉽기 때문에, 강도가 높고, 또한 형상 동결성 및 성형성(연성, 구멍 확장성)이 양호한 강판이 필요해지고 있다. BACKGROUND ART [0002] In recent years, in automobiles, improvement in fuel efficiency has been demanded in consideration of the environment, and the weight of the vehicle body is progressing for the improvement. Further, in order to maintain the safety even when the vehicle body is made lightweight, the demand for steel sheets having higher strengths (tensile strengths of 980 MPa or more) is higher in various steel members constituting the vehicle body. However, when the strength is increased, the formability is lowered and the shape freezing property is liable to be lowered. Therefore, a steel sheet having high strength and good shape-moldability and moldability (ductility, hole expandability) is required.

지금까지도, 상기 특성을 향상시키기 위해, 다양한 제안이 이루어지고 있다. 예컨대 특허문헌 1에는, 조직 분율, 잔류 오스테나이트 중의 C 농도, 제2상 조직 사이의 거리, 제2상 조직의 입경을 제어하는 것에 의해, TS×EL 균형과 형상 동결성을 개선할 수 있었다는 취지가 개시되어 있다. 그러나, 강도 레벨이 보다 높은 강판을 대상으로 상기 특성을 확보한 것은 아니다. To date, various proposals have been made to improve the above characteristics. For example, Patent Document 1 discloses that TS 占 EL balance and shape dynamics can be improved by controlling the structure fraction, the C concentration in the retained austenite, the distance between the second phase structures, and the grain size of the second phase structure . However, the above characteristics are not secured for steel plates having a higher strength level.

또한 특허문헌 2에는, 성분을 적정 범위로 제어(특히 Cr과 Mn의 합계량을 규정 범위로 제어)함으로써, 조직과 석출물 형태를 제어하여, 굽힘 가공성과 형상 동결성을 개선하는 기술이 개시되어 있다. 본 기술에서는, 조직과 석출물의 제어를 위해 Cr을 다량으로 함유시키고 있지만, 보다 높은 성형성을 확보하는 데 있어서는, 성분 설계의 더한 검토가 필요하다고 생각된다. Patent Document 2 discloses a technique for controlling bending workability and shape durability by controlling the components in an appropriate range (particularly, controlling the total amount of Cr and Mn in a prescribed range) to control the structure and precipitate shape. In the present technology, a large amount of Cr is contained in order to control the texture and the precipitate. However, in order to secure higher moldability, it is considered necessary to further study the component design.

특허문헌 3에는, 강도와 가공성의 균형이 우수한 고강도 냉연 강판과 도금 강판을 얻기 위해, 조직을 제어, 특히, α철의 (200)면에서의 X선 회절 피크의 반가폭을 0.220° 이하로 제어하고 있다. 이 조직의 제어는, 조직(베이니틱 페라이트) 내의 전위 밀도를 저감하는 것을 의미하고 있다. 그러나 고강도 영역에서, 연성과 구멍 확장성의 양 특성을 높이기 위해서는, 별도의 수단을 검토할 필요가 있다고 생각된다. Patent Document 3 discloses a technique for controlling the structure, particularly controlling the half width of the X-ray diffraction peak on the (200) plane of iron to be 0.220 or less in order to obtain a high strength cold-rolled steel sheet and a coated steel sheet excellent in balance of strength and workability . Control of this structure means reduction of the dislocation density in the structure (bainitic ferrite). However, in order to improve both the ductility and the hole expandability in the high-strength region, it is considered that another means should be considered.

특허문헌 4에는, 연성 및 신장 플랜지성이 우수하고, 더구나 인장 강도가 980MPa 이상인 고강도 강판을 얻기 위해, 템퍼링 마르텐사이트와 상부 베이나이트(후술하는 KAM값이 낮다고 생각된다)를 소정량 존재시키고 있다. 또한 특허문헌 5도, 상기 특허문헌 4와 마찬가지로, 상부 베이나이트를 소정량 존재시키는 것에 의해 성형성을 확보한 기술이다. In Patent Document 4, there is a predetermined amount of tempering martensite and upper bainite (which is considered to have a low KAM value, which will be described later) in order to obtain a high strength steel sheet excellent in softness and elongation flangeability and having a tensile strength of 980 MPa or more. Also, Patent Document 5 is a technique in which moldability is secured by allowing a predetermined amount of upper bainite to exist in the same manner as in Patent Document 4.

특허문헌 6에는, 가공성이 우수하고, 또한 인장 강도가 980MPa 이상인 고강도 강판을 얻기 위해, 마르텐사이트(프레쉬 마르텐사이트 및 템퍼링 마르텐사이트)를 주체로 하는 것이 개시되어 있다. 또한 특허문헌 7은, 내수소취성이 우수한 초고강도 박강판을 얻는 것으로, 조직을 베이니틱 페라이트 및 마르텐사이트로 함과 함께, 잔류 오스테나이트 결정립의 형태를 제어하고 있다. Patent Document 6 discloses that mainly a martensite (fresh martensite and tempered martensite) is used in order to obtain a high strength steel sheet having excellent workability and a tensile strength of 980 MPa or more. Patent Document 7 is to obtain an ultra-high strength thin steel sheet excellent in hydrogen embrittlement resistance and to control the shape of the retained austenite grains while using bainitic ferrite and martensite as the structure.

일본 특허공개 2010-236066호 공보Japanese Patent Application Laid-Open No. 2010-236066 일본 특허공개 2010-222688호 공보Japanese Patent Application Laid-Open No. 2010-222688 일본 특허공개 2006-274417호 공보Japanese Patent Application Laid-Open No. 2006-274417 일본 특허공개 2010-090475호 공보Japanese Patent Application Laid-Open No. 2010-090475 일본 특허공개 2010-065273호 공보Japanese Patent Application Laid-Open No. 2010-065273 일본 특허공개 2011-047034호 공보Japanese Patent Application Laid-Open No. 2011-047034 일본 특허공개 2011-190474호 공보Japanese Patent Application Laid-Open No. 11-147474

본 발명도, 980MPa 이상이고, 성형성 및 형상 동결성이 우수한 고강도 냉연 강판, 용융 아연도금 강판, 합금화 용융 아연도금 강판을 얻기 위해 이루어진 것으로, 그 목적은, 상기 종래 기술과 달리, 제조 공정에 있어서의 풀림[燒鈍]에서의 오스템퍼 처리를 저온 단시간으로 하여, 소정의 조직을 갖는 신규한 상기 강판을 제조하는 것에 있다. The present invention is also intended to obtain a high-strength cold-rolled steel sheet, a hot-dip galvanized steel sheet and a galvannealed hot-dip galvanized steel sheet excellent in formability and shape durability, which is not less than 980 MPa. In which austenitizing treatment is carried out at a low temperature for a short period of time to produce a novel steel sheet having a predetermined structure.

상기 과제를 해결할 수 있었던 본 발명의 성형성 및 형상 동결성이 우수한 고강도 냉연 강판은, The high-strength cold-rolled steel sheet excellent in moldability and shape durability of the present invention, which has solved the above problems,

C: 0.1∼0.3%(질량%의 의미. 화학 성분에 대하여 이하 동일), C: 0.1 to 0.3% (meaning% by mass, the same applies hereinafter for chemical components),

Si: 1.0∼3.0%, Si: 1.0 to 3.0%

Mn: 0.5∼3.0%, Mn: 0.5 to 3.0%

P: 0.1% 이하, P: not more than 0.1%

S: 0.03% 이하, S: 0.03% or less,

Al: 0.01∼1.0%, 및 N: 0.01% 이하를 만족시키고, 0.01 to 1.0% of Al, and 0.01% or less of N,

잔부가 철 및 불가피 불순물로 이루어지며, The balance being iron and inevitable impurities,

강 조직이, However,

베이니틱 페라이트(BF)+템퍼링 마르텐사이트(TM): 65%(면적%의 의미. 강 조직에 대하여 이하 동일) 이상, Bainitic ferrite (BF) + tempering martensite (TM): 65% (meaning% of area, hereinafter the same for steel structure)

프레쉬 마르텐사이트(M): 3∼18%, Fresh martensite (M): 3 to 18%,

잔류 오스테나이트(잔류 γ): 5% 이상, 및 Residual austenite (residual?): 5% or more, and

폴리고널 페라이트(F): 5% 이하를 만족시키고, 또한, Polyorganosilicate ferrite (F): 5% or less,

평균 KAM<1.00°: 0.50° 이상Average KAM <1.00 ° : Over 0.5 °

[단, 상기 「평균 KAM<1.00°」은, 복수 개소의 KAM(방위차, Kernel Average Misorientation, 단위는 「°」)값의 1.00° 미만에서의 평균값을 나타낸다.] The average KAM < 1.00 DEG &quot; represents an average value at less than 1.00 DEG of KAM (Kernel Average Misorientation, unit is &quot;

을 만족시키고, 또한 인장 강도가 980MPa 이상인 점에 특징을 갖는다. And a tensile strength of 980 MPa or more.

상기 고강도 냉연 강판은, 추가로, The high-strength cold-rolled steel sheet may further comprise:

(a) Ti: 0.01∼0.1%, Nb: 0.01∼0.1%, 및 V: 0.01∼0.1%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소나, (a) at least one kind of element selected from the group consisting of Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, and V: 0.01 to 0.1%

(b) Cr: 0.01∼1%, Mo: 0.01∼1%, 및 B: 0.0001∼0.005%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소, (b) at least one element selected from the group consisting of 0.01 to 1% of Cr, 0.01 to 1% of Mo, and 0.0001 to 0.005% of B,

(c) Cu: 0.01∼1%, 및 Ni: 0.01∼1%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소, (c) at least one element selected from the group consisting of Cu: 0.01 to 1%, and Ni: 0.01 to 1%

(d) Ca: 0.0005∼0.005%, 및 Mg: 0.0005∼0.005%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소(d) at least one element selected from the group consisting of 0.0005 to 0.005% of Ca, and 0.0005 to 0.005% of Mg

를 포함하고 있어도 좋다. .

본 발명에는, 상기 고강도 냉연 강판의 표면에, 용융 아연도금층이 형성되어 있는 데에 특징을 갖는 성형성 및 형상 동결성이 우수한 고강도 용융 아연도금 강판도 포함된다. The present invention also includes a high-strength hot-dip galvanized steel sheet characterized by having a hot-dip galvanized layer formed on the surface of the high-strength cold-rolled steel sheet and excellent in moldability and shape-formability.

또한 본 발명에는, 상기 고강도 냉연 강판의 표면에, 합금화 용융 아연도금층이 형성되어 있는 데에 특징을 갖는 성형성 및 형상 동결성이 우수한 고강도 합금화 용융 아연도금 강판도 포함된다. The present invention also encompasses a high strength alloyed hot-dip galvanized steel sheet excellent in moldability and shape durability characterized by having a galvannealing layer formed on the surface of the high-strength cold-rolled steel sheet.

또한 본 발명에는, 상기 고강도 냉연 강판을 제조하는 방법으로서, According to the present invention, there is also provided a method of producing the high-strength cold-

상기 성분 조성을 갖는 냉연 강판을, Ac3∼960℃의 온도역(T1)으로 가열한 후, 해당 온도역(T1)으로부터 500℃까지를 평균 냉각 속도(CR1) 5℃/s 이상으로 냉각하고, 500℃로부터 (Ms-200)∼420℃의 온도역(T2)까지를 평균 냉각 속도(CR2) 10℃/s 이상으로 냉각하고, 이어서 해당 온도역(T2)에서 10∼70초(t2) 유지하는 데에 특징을 갖는 성형성 및 형상 동결성이 우수한 고강도 냉연 강판의 제조 방법도 포함된다. The cold-rolled steel sheet having the composition described above is heated to a temperature range (T1) of Ac 3 to 960 ° C and cooled from the temperature range (T1) to 500 ° C at an average cooling rate (CR1) of 5 ° C / (T2) from 500 ° C to (Ms-200) to 420 ° C is cooled to an average cooling rate (CR2) of 10 ° C / s or higher and then maintained for 10 to 70 seconds (t2) Strength cold-rolled steel sheet excellent in moldability and shape-shape crystallinity, which is characterized in that the steel sheet has excellent characteristics.

또한, 상기 고강도 용융 아연도금 강판을 제조하는 방법으로서, 상기 성분 조성을 갖는 냉연 강판을, Ac3∼960℃의 온도역(T1)으로 가열한 후, 해당 온도역(T1)으로부터 500℃까지를 평균 냉각 속도(CR1) 5℃/s 이상으로 냉각하고, 500℃로부터 (Ms-200)∼420℃의 온도역(T2)까지를 평균 냉각 속도(CR2) 10℃/s 이상으로 냉각하고, 이어서 해당 온도역(T2)에서 10∼70초(t2) 유지한 후, 아연욕에 침지하는 데에 특징을 갖는 성형성 및 형상 동결성이 우수한 고강도 용융 아연도금 강판의 제조 방법도 포함된다. As a method of producing the high-strength hot-dip galvanized steel sheet, the cold-rolled steel sheet having the above composition is heated to a temperature range (T1) from Ac 3 to 960 ° C, Cooling to a cooling rate (CR1) of 5 占 폚 / s or more and cooling from 500 占 폚 to a temperature range T2 of (Ms-200) to 420 占 폚 at an average cooling rate (CR2) of 10 占 폚 / s or more, A method of manufacturing a high strength hot-dip galvanized steel sheet excellent in moldability and shape fixability which is characterized in that it is maintained in the temperature range T2 for 10 to 70 seconds (t2) and then immersed in a zinc bath.

또, 상기 고강도 합금화 용융 아연도금 강판을 제조하는 방법으로서, 상기 성분 조성을 갖는 냉연 강판을, Ac3∼960℃의 온도역(T1)으로 가열한 후, 해당 온도역(T1)으로부터 500℃까지를 평균 냉각 속도(CR1) 5℃/s 이상으로 냉각하고, 500℃로부터 (Ms-200)∼420℃의 온도역(T2)까지를 평균 냉각 속도(CR2) 10℃/s 이상으로 냉각하고, 이어서 해당 온도역(T2)에서 10∼70초(t2) 유지한 후, 아연욕에 침지하고, 추가로 450∼560℃의 합금화 처리 온도(T3)로 합금화 처리를 하는 데에 특징을 갖는 성형성 및 형상 동결성이 우수한 고강도 합금화 용융 아연도금 강판의 제조 방법도 포함된다. As a method of producing the high strength alloyed hot-dip galvanized steel sheet, the cold-rolled steel sheet having the above-mentioned composition is heated to a temperature range (T1) from Ac 3 to 960 ° C, Cooled to an average cooling rate (CR1) of 5 占 폚 / s or more and cooled from 500 占 폚 to a temperature range T2 of (Ms-200) to 420 占 폚 at an average cooling rate (CR2) of 10 占 폚 / s or more, (T2) of 10 to 70 seconds (t2), then immersed in a zinc bath, and further subjected to alloying treatment at an alloying treatment temperature (T3) of 450 to 560 deg. A method of manufacturing a high strength alloyed hot dip galvanized steel sheet excellent in shape fixability is also included.

본 발명에 의하면, 규정의 조직으로 조정되어, 자동차용 부품에 적합한, 성형성과 형상 동결성이 우수한, 고강도(980MPa 이상) 냉연 강판, 고강도 용융 아연도금 강판 및 고강도 합금화 용융 아연도금 강판(이하, 이들을 「강판」이라고 총칭하는 경우가 있다)을 제공할 수 있다. 한편, 본 발명에 있어서, 「성형성이 우수하다(고성형성)」란, 980MPa 이상의 인장 강도에 있어서, 인장 강도와 신도의 균형(TS×EL 균형), 및 인장 강도와 구멍 확장성의 균형(TS×λ 균형)이 우수하다는 것을 말한다. 또한, 「형상 동결성이 우수하다」란, 항복비(YR)가 낮다는 것을 말한다. According to the present invention, cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet (hereinafter referred to as &quot;Quot; steel plate &quot;) may be provided. In the present invention, in the present invention, "excellent formability (formation of solid form)" means a balance between tensile strength and elongation (TS 占 EL balance) and tensile strength and hole expandability (TS X lambda balance). The term "excellent in shape crystallinity" means that the yield ratio (YR) is low.

도 1은 본 발명의 제조 방법에 있어서의 풀림 공정을 설명하기 위한 히트 패턴을 나타내는 개략도이다.
도 2는 실시예에 있어서의 풀림 공정의 히트 패턴의 개략도이다.
도 3은 실시예에서 측정한 KAM값의 분포의 일례(본 발명예)이다.
도 4는 실시예에서 측정한 KAM값의 분포의 일례(비교예)이다. Fig. 1 is a schematic view showing a heat pattern for explaining the annealing step in the manufacturing method of the present invention. Fig.
2 is a schematic view of a heat pattern in the annealing step in the embodiment.
3 is an example of the distribution of the KAM values measured in the embodiment (the present invention).
4 is an example (comparative example) of the distribution of KAM values measured in the embodiment.

본 발명자들은, 상기 과제를 해결하기 위해서 예의 연구를 거듭한 결과, TS×EL 균형 및 TS×λ 균형의 향상(고성형성), 및 저YR화(고형상동결성)를 동시에 달성하기 위해서는, 강 조직의 모상을 베이니틱 페라이트+템퍼링 마르텐사이트로 한 후에, 잔류 오스테나이트 및 프레쉬 마르텐사이트를 소정량 존재시키고, 또한 폴리고널 페라이트는 극력 존재시키지 않도록 하는 것이 유효하다는 것을 알았다. 또한, 상기 조직을 얻기 위해서는, 특히 Si량을 1.0% 이상으로 함과 함께, 제조 공정에 있어서의 풀림으로, γ 단상역에서 균열(均熱) 후, 비교적 저온역까지 소정의 냉각 속도로 냉각하고, 상기 저온역에서 단시간 유지하는 것이 필요하다는 것을 알아내어, 본 발명을 완성했다. The inventors of the present invention have conducted intensive studies in order to solve the above problems. As a result, it has been found that in order to simultaneously achieve the improvement of the TS 占 EL balance and the TS 占 balance (high solid formation) and the low YR (solid homogenization) It was found that it is effective to make the parent phase of bainitic ferrite + tempering martensite exist in a predetermined amount of residual austenite and fresh martensite, and to prevent the presence of polygonal ferrite as much as possible. Further, in order to obtain the above-mentioned structure, the Si content is set to not less than 1.0%, and the steel is cooled at a predetermined cooling rate from a relatively low temperature region after cracking (uniform heating) , It is necessary to keep the temperature at the low temperature for a short time, and thus the present invention has been completed.

우선, 본 발명에서 조직을 규정한 이유에 대하여 기술한다. First, the reason for defining the organization in the present invention will be described.

[강 조직][Steel organization]

본 발명의 강판은, 모상 조직을 베이니틱 페라이트(BF)+템퍼링 마르텐사이트(TM)(이하, 이들을 통틀어 「BF+TM」이라고 나타낸다)로 한다. BF+TM은, 신도(EL) 및 구멍 확장성(λ)을 손상시키지 않고 고강도화를 도모하는 데 유효한 조직이다. 따라서, BF+TM은 65%(면적%) 이상 차지하도록 한다. (BF+TM)량은, 바람직하게는 70% 이상이고, 보다 바람직하게는 75% 이상이다. 한편, BF와 TM이 재료 특성에 미치는 영향은 유사하기 때문에, 이들을 구별할 필요는 없다. 즉, BF+TM에서의 각각의 조직의 비율을 규정할 필요는 없고, 본 발명에서는, BF+TM의 합계량으로 규정한다. In the steel sheet of the present invention, the parent structure is bainitic ferrite (BF) + tempering martensite (TM) (hereinafter, these are collectively referred to as "BF + TM"). BF + TM is an effective structure for achieving high strength without deteriorating elongation (EL) and hole expandability (?). Therefore, BF + TM should occupy more than 65% (area%). (BF + TM) is preferably 70% or more, and more preferably 75% or more. On the other hand, since the influence of BF and TM on the material properties is similar, it is not necessary to distinguish between them. That is, it is not necessary to define the ratio of each structure in BF + TM, and in the present invention, the total amount of BF + TM is specified.

또한, BF+TM은 라스상의 조직을 갖고 있지만, 본 발명자들은, 이 라스 사이즈의 미세화와, 결정립 내의 전위 밀도의 상승에 의해, 구멍 확장성을 손상시키지 않고 더한 고강도화를 도모할 수 있다는 것을 발견했다. Further, BF + TM has a lath-like structure. However, the inventors of the present invention have found that by increasing the fineness of the lase size and the dislocation density in the crystal grains, the strength can be further increased without impairing hole expandability .

상기 BF+TM의 라스 사이즈와 결정립 내의 전위 밀도는, KAM(Kernel Average Misorientation)값에 의해서 평가할 수 있다. The rasa size of the BF + TM and the dislocation density in the crystal grain can be evaluated by a Kernel Average Misorientation (KAM) value.

KAM값이란, 대상이 되는 측정점과 그 주위의 측정점 사이에서의 결정 회전량(결정 방위차)의 평균값이며, 이 값이 클수록, 결정 중에 변형이 많이 존재하는 것을 의미하고 있다(측정 방법의 상세는 실시예에 나타낸다). 본 발명자들은, 상기 KAM값과 강 조직의 관계에 대하여 조사한 바, KAM값이 1.00° 미만인 영역이 BF+TM에 대응한다는 것을 확인했다(KAM값이 1.00° 이상인 영역은, 주로 M 및 입계에 대응한다). The KAM value is an average value of the amount of crystal rotation (crystal orientation difference) between the measurement point of interest and the measurement point around the measurement point, and the larger the value, the more deformation is present in the crystal. Shown in the examples). The present inventors have examined the relationship between the KAM value and the steel structure, and confirmed that a region having a KAM value of less than 1.00 DEG corresponds to BF + TM (a region having a KAM value of 1.00 DEG or more corresponds mainly to M and grain boundaries do).

따라서, KAM값이 1.00° 미만인 영역을 대상으로, 전술한 라스 사이즈의 미세화와 결정립 내의 전위 밀도를 높여, 구멍 확장성을 손상시키지 않고 더한 고강도화를 도모하기 위한 수단(즉, 양호한 TS×λ 균형을 얻기 위한 수단)에 대하여 검토했다. 그 결과, KAM값이 1.00° 미만인 영역에서의, KAM값의 평균값(이하, 이것을 「평균 KAM<1.00°」이라고 나타낸다)이 0.50° 이상(즉, 복수 측정점의 KAM값의 분포에 있어서, 1.00° 미만의 영역의 KAM값이 높은 측에 많이 존재하고 있는 상태)이면, 양호한 TS×λ 균형이 얻어진다는 것을 발견했다. Therefore, in order to increase the fineness of the lase size and the dislocation density in the crystal grains and to improve the strength of the hole without damaging the hole expandability (i.e., a good TS x lambda balance (Means for obtaining a sample). As a result, the average value of the KAM values (hereinafter referred to as &quot; average KAM &lt; 1.00 ° &quot;) in the region where the KAM value is less than 1.00 ° is 0.50 or more (I.e., a state in which a large number of KAM values are present on the higher side), a good TS 占 balance can be obtained.

한편, KAM값이 1.00° 미만인 영역에는, 폴리고널 페라이트(F) 영역도 포함되지만, 본 발명에서는, F량이 작기(5% 이하이기) 때문에 무시할 수 있다. 따라서, 평균 KAM<1.00°은, BF+TM 영역의 평균 KAM값을 의미한다고 할 수 있다. On the other hand, the region where the KAM value is less than 1.00 DEG includes the polygonal ferrite (F) region, but in the present invention, since the F amount is small (less than 5%), it can be ignored. Therefore, the average KAM < 1.00 can be said to mean the average KAM value of the BF + TM region.

상기 평균 KAM<1.00°은, 바람직하게는 0.52°이상, 보다 바람직하게는 0.54° 이상이다. 한편, 상한은 TS×EL 균형의 관점에서, 0.7° 정도로 된다. The average KAM < 1.00 DEG is preferably 0.52 DEG or more, more preferably 0.54 DEG or more. On the other hand, the upper limit is about 0.7 DEG from the viewpoint of TS 占 EL balance.

한편, KAM값의 해석에서는, CI(Confidence Index)≤0.1의 측정점은 신뢰성이 결여된다고 생각되어, 해석으로부터 제외했다. 상기 CI란, 각 측정점에서 검출된 전자선 후방 산란 회절상이, 지정된 결정계(철의 경우는 bcc 또는 fcc)의 데이터베이스값과 얼마만큼 일치하는가의 지표로, 데이터의 신뢰도를 나타내는 것이다. On the other hand, in the analysis of the KAM value, it was considered that the measurement point of CI (Confidence Index)? 0.1 lacked reliability and was excluded from the analysis. The CI is an index of how much the electron beam backscattering diffraction pattern detected at each measurement point coincides with the database value of the specified crystal system (bcc or fcc in the case of iron), indicating the reliability of the data.

전술한 바와 같이, BF+TM을 65% 이상으로 하고, 또한 평균 KAM<1.00°을 0.50° 이상으로 하는 것에 의해, 고강도를 달성할 수 있지만, 고강도화를 이들만으로 달성하면, 고YR로 되어, 형상 동결성이 악화된다. 그래서 본 발명에서는, 프레쉬 마르텐사이트(M)도 존재시킨다. 이 M도 고강도화에 유효하고, 또한 M 중의 가동 전위는 YR을 낮추는 데 유효하다. 본 발명에서는, 평균 KAM<1.00°이 0.50° 이상을 만족시키는 BF+TM 중에, M을 3% 이상 존재시키는 것에 의해, 고강도화, 저YR화 및 고성형성을 동시에 달성할 수 있다. M량은, 바람직하게는 5% 이상, 보다 바람직하게는 6% 이상이다. 단 M이 지나치게 많으면, 성형성(TS×EL 균형이나 TS×λ 균형)의 열화를 초래하기 때문에, M량은 18% 이하로 한다. M량은, 바람직하게는 14% 이하, 보다 바람직하게는 10% 이하이다. As described above, high strength can be achieved by setting the BF + TM to 65% or more and the average KAM < 1.00 DEG to 0.50 or more. However, when the high strength is achieved by these alone, The cohesiveness deteriorates. Thus, in the present invention, fresh martensite (M) is also present. This M is effective for high strength, and the movable potential in M is effective for lowering YR. In the present invention, high strength, low YR, and high solidity can be achieved at the same time by allowing M to be present at 3% or more in BF + TM satisfying an average KAM < 1.00 DEG of 0.50 or more. The amount of M is preferably 5% or more, and more preferably 6% or more. If M is excessively large, the moldability (TS 占 EL balance or TS 占 balance) deteriorates, so that the amount of M is 18% or less. The amount of M is preferably 14% or less, and more preferably 10% or less.

또한 본 발명에서는, 잔류 오스테나이트(잔류 γ)를 존재시키는 것에 의해, TS×EL 균형을 향상시킨다. 따라서, 잔류 γ량은 5% 이상으로 한다. 잔류 γ량은, 바람직하게는 6% 이상이고, 보다 바람직하게는 7% 이상이다. 한편, 잔류 γ량의 상한은, 대략 20% 정도이다. Further, in the present invention, the presence of residual austenite (residual?) Improves the TS 占 EL balance. Therefore, the residual? Amount is at least 5%. The residual? Amount is preferably 6% or more, and more preferably 7% or more. On the other hand, the upper limit of the residual? Amount is about 20%.

한편, 본 발명에서는, 폴리고널 페라이트(F)가 혼재하면, TS×λ 균형의 저하를 초래하기 때문에, F는 극력 저감시키는 것이 좋고, 본 발명에서는 F량을 5% 이하로 한다. F량은, 바람직하게는 3% 이하이고, 가장 바람직하게는 0%이다. On the other hand, in the present invention, when the polyorganolithium (F) is mixed, it causes reduction of the TS x lambda balance. Therefore, F is preferably reduced as much as possible. The F amount is preferably 3% or less, and most preferably 0%.

다음으로, 상기 조직을 확보함과 함께, 강판의 더한 성형성 향상 등을 위한 성분 조성과 제조 조건에 대하여 설명한다. Next, the composition and the manufacturing conditions for ensuring the above-mentioned structure and for improving the formability of the steel sheet are described.

우선, 성분 조성에 대하여 설명한다. First, the composition of the components will be described.

[성분 조성] [Composition of ingredients]

〔C: 0.1∼0.3%〕 [C: 0.1 to 0.3%]

C는, 강의 강화능이 높은 원소이며, 또한, 오스테나이트를 안정화시켜 잔류 γ를 확보하기 위해서도 중요한 원소이다. 또한 C는, 고온으로부터의 냉각 중에 폴리고널 페라이트의 생성을 억제하는 효과도 갖고 있다. 이러한 작용을 발휘시키기 위해, 0.1% 이상, 바람직하게는 0.15% 이상, 보다 바람직하게는 0.17% 이상 함유시킨다. 그러나, 0.3%를 초과하여 함유시키면 용접성이 열화되기 때문에, C량의 상한을 0.3%로 한다. C량은, 바람직하게는 0.25% 이하이며, 보다 바람직하게는 0.2% 이하이다. C is an element having a high steel strengthening ability and is also an important element for stabilizing austenite to secure residual?. C also has the effect of suppressing the generation of polygonal ferrite during cooling from a high temperature. In order to exhibit such action, it is contained in an amount of 0.1% or more, preferably 0.15% or more, and more preferably 0.17% or more. However, if the content exceeds 0.3%, the weldability deteriorates, so the upper limit of the C content is set to 0.3%. The amount of C is preferably 0.25% or less, and more preferably 0.2% or less.

〔Si: 1.0∼3.0%〕[Si: 1.0 to 3.0%]

Si는, 고용 강화 원소로서 강의 고강도화에 기여하는 원소이다. 또한, 탄화물의 생성을 억제하는 효과를 갖고 있고, 오스테나이트 중에 C를 응축시켜 안정화시켜, 잔류 γ의 확보에 중요한 원소이기도 하다. 이러한 작용을 발휘시키기 위해, Si를 1.0% 이상, 바람직하게는 1.2% 이상, 보다 바람직하게는 1.4% 이상 함유시킨다. 그러나 Si를 3.0%를 초과하여 함유시키면, 열간 압연 시에 현저한 스케일이 형성되어, 강판 표면에 스케일 적자(跡疵)가 붙어 표면 성상이 악화되기 때문에, Si량의 상한을 3.0%로 한다. Si량은, 바람직하게는 2.5% 이하, 보다 바람직하게는 2.0% 이하이다. Si is an element contributing to the strengthening of steel as a solid solution strengthening element. In addition, it has an effect of suppressing the formation of carbide, and is an important element for securing residual γ by condensing and stabilizing C in austenite. In order to exert such action, Si is contained in an amount of 1.0% or more, preferably 1.2% or more, more preferably 1.4% or more. However, when Si is contained in an amount exceeding 3.0%, a significant scale is formed at the time of hot rolling, and scale defects adhere to the surface of the steel sheet to deteriorate the surface properties. Therefore, the upper limit of the amount of Si is set to 3.0%. The amount of Si is preferably 2.5% or less, more preferably 2.0% or less.

〔Mn: 0.5∼3.0%〕 [Mn: 0.5 to 3.0%]

Mn은, 강의 강도를 높일 뿐만 아니라, 오스테나이트의 안정화에 직접 작용하는 중요한 원소이다. 또한, 담금질성 향상 원소이기도 하고, 폴리고널 페라이트의 생성 억제의 효과도 갖는 원소이다. 이러한 작용을 발휘시키기 위해, Mn을 0.5% 이상, 바람직하게는 1.0% 이상, 보다 바람직하게는 2.0% 이상 함유시킨다. 그러나 Mn을 3.0%를 초과하여 함유시키면, 주편(鑄片) 균열이 생기는 등의 악영향을 야기하기 때문에, 상한을 3.0%로 했다. Mn량은, 바람직하게는 2.8% 이하, 보다 바람직하게는 2.5% 이하이다. Mn is an important element that not only increases the strength of steel but also directly acts to stabilize austenite. It is also an element that improves hardenability and also has an effect of inhibiting the production of polygonal ferrite. In order to exhibit such action, Mn is contained at 0.5% or more, preferably 1.0% or more, and more preferably 2.0% or more. However, if Mn is added in an amount of more than 3.0%, it causes an adverse effect such as cracking of cast slab, and the upper limit is set to 3.0%. The Mn content is preferably not more than 2.8%, more preferably not more than 2.5%.

〔P: 0.1% 이하〕 [P: not more than 0.1%]

P는, 입계 편석에 의한 입계 취화를 조장하여 성형성을 열화시키는 원소이다. 따라서 P는 적은 편이 좋고, 본 발명에서는 P량의 상한을 0.1%로 한다. 바람직하게는 0.08% 이하이며, 보다 바람직하게는 0.05% 이하이다. P is an element which promotes grain boundary embrittlement due to grain boundary segregation and deteriorates moldability. Therefore, P is preferably small, and in the present invention, the upper limit of P amount is set to 0.1%. Preferably 0.08% or less, and more preferably 0.05% or less.

〔S: 0.03% 이하〕[S: 0.03% or less]

S는, MnS 등의 황화물계 개재물을 형성하여, 이것이 균열의 기점이 되어 성형성을 열화시키는 원소이다. 따라서 S는 적은 편이 좋고, 본 발명에서는 S량의 상한을 0.03%로 한다. 바람직하게는 0.02% 이하이며, 보다 바람직하게는 0.01% 이하이다. S is an element that forms sulfide inclusions such as MnS, which becomes a starting point of cracking and deteriorates moldability. Therefore, S is preferably small, and in the present invention, the upper limit of the amount of S is set to 0.03%. , Preferably not more than 0.02%, and more preferably not more than 0.01%.

〔Al: 0.01∼1.0%〕 [Al: 0.01 to 1.0%]

Al은, 탈산재로서 작용하는 원소이며, 이러한 작용을 발휘시키기 위해, Al을 0.01% 이상, 바람직하게는 0.02% 이상, 보다 바람직하게는 0.03% 이상 함유시킨다. 그러나 Al을 1.0%를 초과하여 함유시키면, 강판 중에 알루미나 등의 개재물이 많이 생성되어, 성형성이 열화되기 때문에, Al량의 상한을 1.0%로 한다. Al량은, 바람직하게는 0.5% 이하, 보다 바람직하게는 0.1% 이하이다. Al is an element serving as a de-oxidizing material. In order to exert such action, Al is contained at 0.01% or more, preferably 0.02% or more, and more preferably 0.03% or more. However, when Al is contained in an amount exceeding 1.0%, inclusions such as alumina are generated in the steel sheet to deteriorate the formability. Therefore, the upper limit of the amount of Al is set to 1.0%. The amount of Al is preferably 0.5% or less, more preferably 0.1% or less.

〔N: 0.01% 이하〕[N: 0.01% or less]

N은, 질화물을 형성하여, 이 질화물이 균열의 기점이 되어 성형성을 열화시키는 원소이다. 따라서, N은 적은 편이 좋고, 본 발명에서는 N량의 상한을 0.01%로 한다. 바람직하게는 0.008% 이하이며, 보다 바람직하게는 0.006% 이하이다. N is an element that forms a nitride and causes the nitride to become a starting point of cracking and deteriorates moldability. Therefore, N is preferably as small as possible, and in the present invention, the upper limit of the amount of N is set to 0.01%. It is preferably not more than 0.008%, more preferably not more than 0.006%.

본 발명의 강판의 성분은, 상기와 같으며, 잔부는 철 및 불가피 불순물로 이루어지는 것이다. 또한, 상기 원소에 더하여 추가로, 하기 원소를 적량 함유시키는 것에 의해, 더한 강도의 향상이나 인성, 내식성 등의 향상을 도모할 수 있다. 이하, 이들 원소에 대하여 상술한다. The components of the steel sheet of the present invention are as described above, and the remainder is composed of iron and unavoidable impurities. In addition to the above elements, by further containing the following elements in an appropriate amount, it is possible to further improve the strength, toughness, and corrosion resistance. These elements will be described in detail below.

〔Ti: 0.01∼0.1%, Nb: 0.01∼0.1%, 및 V: 0.01∼0.1%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소〕 At least one element selected from the group consisting of [Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, and V: 0.01 to 0.1%

Ti, Nb, V는, 모두 조직을 미세화하여 강판의 강도와 인성의 향상에 작용하는 원소이며, 필요에 따라 첨가해도 좋다. 이러한 작용을 발휘시키기 위해서는, 어느 쪽의 원소이더라도, 0.01% 이상 함유시키는 것이 바람직하다. 보다 바람직하게는 0.015% 이상이며, 더욱 바람직하게는 0.02% 이상이다. 그러나, 어느 쪽의 원소도 0.1%를 초과하여 함유시키면, 상기 효과가 포화될 뿐만 아니라, 항복비가 상승하여 형상 동결성이 열화되기 때문에, 각각의 원소의 상한을 0.1%로 했다. 바람직하게는, 각각 0.08% 이하이며, 보다 바람직하게는 각각 0.06% 이하이다. Ti, Nb 및 V는, 각각 단독으로 함유시켜도 좋고, 임의로 선택되는 2종 이상을 함유시켜도 좋다. Ti, Nb, and V are elements that improve the strength and toughness of the steel sheet by making the structure finer, and may be added as needed. In order to exhibit such an action, it is preferable to contain 0.01% or more of any element. More preferably, it is 0.015% or more, and more preferably 0.02% or more. However, when either of the elements is contained in an amount exceeding 0.1%, not only the above effect is saturated but also the yield ratio is increased and the shape durability is deteriorated. Therefore, the upper limit of each element is set to 0.1%. Preferably, each is 0.08% or less, and more preferably 0.06% or less. Ti, Nb and V may be contained singly or two or more kinds may be arbitrarily selected.

〔Cr: 0.01∼1%, Mo: 0.01∼1%, 및 B: 0.0001∼0.005%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소〕[At least one element selected from the group consisting of Cr: 0.01 to 1%, Mo: 0.01 to 1%, and B: 0.0001 to 0.005%

Cr, Mo, B는, 모두 고온으로부터의 냉각 중에 폴리고널 페라이트가 생성되는 것을 억제하는 원소이며, 필요에 따라 첨가해도 좋다. 이러한 작용을 발휘시키기 위해, Cr, Mo에 대해서는, 각각 0.01% 이상 함유시키는 것이 바람직하고, 보다 바람직하게는 0.05% 이상, 더욱 바람직하게는 0.1% 이상이다. 또한 B에 대해서는, 0.0001% 이상 함유시키는 것이 바람직하고, 보다 바람직하게는 0.0005% 이상, 더욱 바람직하게는 0.001% 이상이다. 그러나, 어느 쪽의 원소도 과잉으로 함유시키면, 효과가 포화될 뿐만 아니라, 성형성이 열화되기 때문에, Cr, Mo에 대해서는, 상한을 1%로 하는 것이 바람직하고, 보다 바람직하게는 0.8% 이하, 더욱 바람직하게는 0.6% 이하이다. 또한 B량의 상한은 0.005%로 하는 것이 바람직하고, 보다 바람직하게는 0.004% 이하, 더욱 바람직하게는 0.003% 이하이다. Cr, Mo 및 B는, 각각 단독으로 함유시켜도 좋고, 임의로 선택되는 2종 이상을 함유시켜도 좋다. Cr, Mo, and B are all elements that inhibit the generation of polygonal ferrite during cooling from a high temperature, and may be added as needed. In order to exert such action, Cr and Mo are each preferably contained in an amount of 0.01% or more, more preferably 0.05% or more, and still more preferably 0.1% or more. Further, the content of B is preferably 0.0001% or more, more preferably 0.0005% or more, and still more preferably 0.001% or more. However, if either element is contained excessively, the effect becomes saturated and the formability deteriorates. Therefore, the upper limit of Cr and Mo is preferably 1%, more preferably 0.8% or less, More preferably, it is 0.6% or less. The upper limit of the amount of B is preferably 0.005%, more preferably 0.004% or less, still more preferably 0.003% or less. Each of Cr, Mo and B may be contained singly or two or more kinds may be arbitrarily selected.

〔Cu: 0.01∼1%, 및 Ni: 0.01∼1%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소〕[At least one element selected from the group consisting of Cu: 0.01 to 1%, and Ni: 0.01 to 1%]

Cu, Ni는, 모두 강판의 내식성 향상에 유효한 원소이며, 필요에 따라 첨가해도 좋다. 이러한 작용을 발휘시키기 위해, 어느 쪽의 원소이더라도, 0.01% 이상 함유시키는 것이 바람직하다. 보다 바람직하게는 0.05% 이상이며, 더욱 바람직하게는 0.1% 이상이다. 그러나, 어느 쪽의 원소도 1%를 초과하여 함유시키면, 상기 효과가 포화될 뿐만 아니라, 성형성이 열화되기 때문에, 각각의 상한을 1%로 했다. 바람직하게는, 각각 0.8% 이하이며, 보다 바람직하게는 각각 0.6% 이하이다. Cu 및 Ni는, 각각 단독으로 함유시켜도 좋고, 병용하여 함유시켜도 좋다. Cu and Ni are all effective elements for improving the corrosion resistance of the steel sheet, and may be added as needed. In order to exert such action, it is preferable that the content of the element is 0.01% or more. More preferably, it is 0.05% or more, and more preferably 0.1% or more. However, if either element is contained in an amount exceeding 1%, not only the effect is saturated but also the moldability is deteriorated, so that the upper limit of each element is set to 1%. Preferably, they are each 0.8% or less, more preferably 0.6% or less. Cu and Ni may be contained singly or in combination.

〔Ca: 0.0005∼0.005%, 및 Mg: 0.0005∼0.005%로 이루어지는 군으로부터 선택되는 적어도 1종의 원소〕[Ca: at least one element selected from the group consisting of 0.0005 to 0.005%, and Mg: 0.0005 to 0.005%]

Ca, Mg은, Cu, Ni와 같이 강판의 내식성을 향상시키는 데 작용하는 원소이며, 필요에 따라 첨가해도 좋다. 이러한 작용을 발휘시키기 위해, 어느 쪽의 원소이더라도, 0.0005% 이상 함유시키는 것이 바람직하다. 보다 바람직하게는 0.001% 이상이며, 더욱 바람직하게는 0.003% 이상이다. 그러나, 어느 쪽의 원소도 과잉으로 함유시키면 성형성이 나빠지기 때문에, 각각 상한을 0.005%로 했다. 바람직하게는 각각 0.0045% 이하, 보다 바람직하게는 각각 0.0040% 이하이다. Ca and Mg are elements that act to improve the corrosion resistance of the steel sheet, such as Cu and Ni, and may be added as needed. In order to exhibit such an action, it is preferable that the content of both elements is 0.0005% or more. It is more preferably 0.001% or more, and still more preferably 0.003% or more. However, if either element is contained excessively, the moldability is deteriorated. Therefore, the upper limit is set to 0.005%. Preferably not more than 0.0045%, more preferably not more than 0.0040%, respectively.

[제조 방법][Manufacturing method]

제조 공정으로서, 열간 압연, 산세(酸洗), 냉간 압연을 순차적으로 행하여 얻어진 상기 성분 조성을 갖는 냉연 강판을, 풀림, 추가로 필요에 따라 도금 처리, 합금화 처리를 하는 데에 있어서, 상기 규정의 조직을 얻기 위해서는, 특히 상기 풀림의 조건(고강도 합금화 용융 아연도금 강판은, 추가로 합금화 처리의 조건)을 하기와 같이 한다. 그 밖의 공정에 대해서는, 일반적으로 행해지고 있는 조건을 채용하면 된다. 한편, 본 발명에서는, 풀림 직전의 강판을 「냉연 강판」이라고 하고, 냉연 강판에 대하여 규정의 풀림을 실시한 것을 「고강도 냉연 강판」이라고 나타내어 구별한다. As a manufacturing process, the cold-rolled steel sheet having the above composition obtained by sequentially performing hot rolling, pickling (pickling), and cold rolling is subjected to annealing, further plating and alloying treatment as required, The annealing conditions (the conditions of the alloying treatment for the high-strength alloyed hot-dip galvanized steel sheet) are as follows. As for other processes, conditions generally used may be employed. On the other hand, in the present invention, the steel sheet immediately before unwinding is referred to as &quot; cold-rolled steel sheet &quot;

이하에서는, 풀림(열처리) 공정에 대하여 도 1을 이용하여 설명한다. 이 도 1은, 본 발명의 제조 방법에 있어서의 풀림 공정을 예시한 개략 설명도이며, 하기에 설명하는 T1, t1, CR1, CR2, T2, t2, T3, t3, CR3, CR3' 및 CR3''는, 도 1 중의 이들 기호와 대응하고 있다. Hereinafter, the annealing (annealing) step will be described with reference to Fig. 1 is a schematic explanatory view illustrating the annealing process in the manufacturing method of the present invention. In FIG. 1, T1, t1, CR1, CR2, T2, t2, T3, t3, CR3, CR3 ' Correspond to those symbols in Fig.

〔풀림 공정에서의 가열 온도(T1): Ac3∼960℃〕[Heating temperature (T1) in the annealing step: Ac 3 to 960 ° C]

풀림 공정에서, 우선 γ 단상역까지 가열하는 것이 필요하다. 가열 온도가 2상역의 낮은 온도에서는 F가 많아져, TS×λ 균형이 저하되기 때문이다. 또한 상기 F의 혼입에 의해, 미변태 γ 중에 C가 농화되어, 오스템퍼 중의 BF 변태가 억제되기 때문에, 소망량의 BF+TM을 확보하기 어렵게 됨과 함께, 과잉의 M이 생성되어, TS×EL 균형과 TS×λ 균형이 저하된다. 따라서 본 발명에서는, 풀림 공정에서의 가열 온도(T1)를 Ac3 이상으로 한다. T1은, 바람직하게는 Ac3+30℃ 이상, 보다 바람직하게 Ac3+50℃ 이상이다. In the annealing step, it is first necessary to heat up to the? -Phase phase. F is increased at a heating temperature lower than the temperature of the two-phase region, and the TS 占 balance is lowered. Further, by the incorporation of F, C is concentrated in the unconverted gamma, and BF transformation in the ostremer is suppressed, so that it becomes difficult to secure a desired amount of BF + TM, and excess M is generated, Balance and TS x lambda balance are degraded. Therefore, in the present invention, the heating temperature (T1) in the annealing step is set to Ac 3 or more. T1 is preferably Ac 3 + 30 ° C or higher, and more preferably Ac 3 + 50 ° C or higher.

한편, T1이 지나치게 높으면 조직이 조대화되어 인장 강도가 저하된다. 따라서, T1은 960℃ 이하로 한다. 바람직하게는 940℃ 이하, 보다 바람직하게는 920℃ 이하이다. On the other hand, if T1 is too high, the structure becomes coarse and the tensile strength is lowered. Therefore, T1 is set to 960 DEG C or less. Preferably 940 占 폚 or lower, more preferably 920 占 폚 or lower.

한편, T1에서의 유지 시간(t1)은, 10∼1000초(s)인 것이 바람직하다. 10초를 하회하면, 충분히 γ 단상역까지 가열하는 것이 어렵고, 또한, 1000초를 초과하면, 조직이 조대화되어, 성형성이 악화되기 쉽기 때문이다. On the other hand, the holding time t1 at T1 is preferably 10 to 1000 seconds (s). If the time is shorter than 10 seconds, it is difficult to sufficiently heat to the? -Phase phase, and if it exceeds 1000 seconds, the structure becomes coarse and the moldability tends to deteriorate.

〔가열 온도(T1)로부터 500℃까지의 평균 냉각 속도(CR1): 5℃/s 이상〕[Average cooling rate (CR1) from heating temperature (T1) to 500 占 폚: 5 占 폚 / s or more]

〔500℃로부터 (Ms-200)∼420℃의 온도역(T2)까지의 평균 냉각 속도(CR2): 10℃/s 이상〕[Average cooling rate (CR2) from 500 占 폚 to temperature range T2 of (Ms-200) to 420 占 폚: 10 占 폚 / s or more]

가열 온도(T1)로부터 500℃까지의 평균 냉각 속도(CR1)가 느리면, F가 생성되어 TS×λ 균형이 저하된다. 따라서 본 발명에서는, CR1을 5℃/s 이상으로 한다. 바람직하게는 10℃/s 이상, 보다 바람직하게는 15℃/s 이상이다. 한편, CR1의 상한은, 대략 500℃/s 정도이다. If the average cooling rate (CR1) from the heating temperature (T1) to 500 占 폚 is slow, F is generated and the TS 占 balance is lowered. Therefore, in the present invention, CR1 is set to 5 DEG C / s or more. Preferably 10 DEG C / s or higher, and more preferably 15 DEG C / s or higher. On the other hand, the upper limit of CR1 is about 500 DEG C / s.

또한 500℃로부터 (Ms-200)∼420℃의 온도역(오스템퍼 온도역)(T2)까지의 평균 냉각 속도(CR2)가 느리면, KAM값이 낮은(전위 밀도가 낮은) BF가 생성되어(즉, 평균 KAM<1.00°이 0.50°를 하회하여), TS×λ 균형이 저하된다. 따라서 본 발명에서는, CR2를 10℃/s 이상으로 한다. CR2는, 바람직하게는 15℃/s 이상이다. 한편, CR2의 상한은, 실 조업 상 500℃/s 정도이다. Further, if the average cooling rate CR2 from 500 ° C to the temperature range (Ms-200) to 420 ° C in the temperature range (the austemper temperature range) T2 is low, BF having a low KAM value (low dislocation density) That is, the average KAM < 1.00 DEG is less than 0.50 DEG) and the TS x lambda balance is lowered. Therefore, in the present invention, CR2 is set to 10 DEG C / s or more. CR2 is preferably 15 DEG C / s or more. On the other hand, the upper limit of CR2 is about 500 deg. C / s in practical operation.

한편, 상기 도 1에서는, T1로부터의 냉각 중 500℃에서 냉각 속도를 변화시키고 있지만, 이것에 한정되지 않고, 상기 CR1과 CR2의 조건을 만족시키면, 500℃에서 냉각 속도를 바꾸지 않고, 가열 온도(T1)로부터 (Ms-200)∼420℃의 온도역(T2)까지의 평균 냉각 속도를 일정하게, 즉, CR1=CR2로 해도 좋다. On the other hand, in Fig. 1, the cooling rate is changed at 500 deg. C during the cooling from T1. However, the present invention is not limited to this, and if the conditions of CR1 and CR2 are satisfied, T1 to the temperature range T2 of (Ms-200) to 420 占 폚 may be constant, that is, CR1 = CR2.

본 발명에 있어서의 「평균 냉각 속도」란, (냉각 개시 온도-냉각 정지 온도)/(냉각에 요한 시간)이다. 하기의 CR3, CR3' 및 CR3''에 대해서도 동일하다. The "average cooling rate" in the present invention is (cooling start temperature - cooling stop temperature) / (time required for cooling). The same applies to the following CR3, CR3 'and CR3' '.

한편, 500℃로부터 평균 냉각 속도(CR2) 10℃/s 이상으로 냉각하는 경우의 냉각 정지 온도가 Ms 이하인 경우는, 일부에 M이 형성되지만, 이 M은, 하기 온도역 T2에서 유지되는 것에 의해 TM으로 된다. On the other hand, when the cooling stop temperature is 500 ° C or more and the cooling rate is at least 10 ° C / s, the M is formed in a part of M, TM.

〔(Ms-200)∼420℃의 온도역(오스템퍼 온도, T2)에서 10∼70초(s)(t2) 유지〕[10 to 70 seconds (s) (t2) maintained in the temperature range (Ms-200) to 420 占 폚 in the temperature range (Austemper temperature, T2)

이 공정은, BF+TM과 잔류 γ를 생성시키기 위해서 중요한 공정이다. 상세하게는, M은 TM으로 되고, 또한 미변태 γ로부터 BF가 생성되는 공정이다. 또한, 미변태 γ에의 C 농화가 촉진되어, 원하는 잔류 γ 확보에도 필요한 공정이다. This process is an important step for producing BF + TM and residual?. Specifically, M is a step in which TM is formed and BF is generated from unconverted?. Further, C enrichment to the unconverted gamma is promoted, and this is also a step necessary for securing a desired residual gamma.

T2가 (Ms-200)℃를 하회하면, 냉각 정지 시점에서의 미변태 γ가 적기 때문에, 충분한 잔류 γ를 확보할 수 없게 되어, 그 결과 TS×EL이 저하된다. 또한, M이 감소하여, 고YR화되기 때문에 바람직하지 않다. T2는, 바람직하게는 (Ms-150)℃ 이상이며, 보다 바람직하게는 (Ms-100)℃ 이상이다. If T2 is less than (Ms-200) 占 폚, since the unconverted? At the time of stopping the cooling is small, sufficient residual? Can not be ensured, and as a result, TS 占 EL decreases. In addition, M is reduced, resulting in a high YR. T2 is preferably (Ms-150) DEG C or more, and more preferably (Ms-100) DEG C or more.

한편, T2가 420℃를 초과하면, BF+TM 중의 전위 밀도가 작아지고 평균 KAM<1.00°이 낮아져, TS×λ 균형이 저하된다. 또한, 최종 조직에 M이 많아지기 쉬워진다. 따라서 T2는 420℃ 이하로 한다. T2는, 바람직하게는 400℃ 이하, 보다 바람직하게는 380℃ 이하이다. On the other hand, if T2 exceeds 420 占 폚, the dislocation density in BF + 占 becomes smaller, the average KAM < 1.00 占 becomes lower, and the TS 占 balance is lowered. In addition, M is likely to become large in the final structure. Therefore, T2 is set to 420 DEG C or less. T2 is preferably 400 占 폚 or lower, and more preferably 380 占 폚 or lower.

한편, 전술한 온도 범위 내이면, 유지 온도는 일정할 필요는 없고, 소정의 온도 범위 내에서 변동하더라도 본 발명의 취지를 손상시키지 않는다. On the other hand, if the temperature is within the above-mentioned range, the holding temperature need not be constant and even if fluctuated within a predetermined temperature range, the object of the present invention is not impaired.

또한, 상기 T2에서의 유지 시간(t2)이 10초를 하회하면, γ에의 C 농화가 진행되지 않아 충분한 잔류 γ를 확보할 수 없기 때문에, TS×EL 균형이 저하된다. 또한, BF 변태가 충분히 진행되지 않고서 M량이 증가하여, TS×EL 균형과 TS×λ 균형이 저하된다. 따라서 t2는 10초 이상으로 한다. 바람직하게는 20초 이상, 보다 바람직하게는 30초 이상이다. Further, if the holding time t2 at T2 is less than 10 seconds, the C enrichment to? Does not proceed and sufficient residual? Can not be ensured, so that the TS 占 EL balance declines. Further, the BF transformation does not proceed sufficiently and the amount of M increases, and the TS 占 EL balance and the TS 占 balance are lowered. Therefore, t2 should be 10 seconds or more. Preferably 20 seconds or more, and more preferably 30 seconds or more.

한편, t2가 70초를 초과하면, 평균 KAM<1.00°이 작아져, TS×λ가 저하된다. 또한 t2가 지나치게 길면, BF 변태가 지나치게 진행되어, 최종 조직의 M이 감소하고, 그 결과, 고YR로 되기 때문에 바람직하지 않다. 게다가, 장시간이기 때문에, 생산성도 나빠진다. 따라서, t2는 70초 이하로 한다. 바람직하게는 60초 이하이다. On the other hand, if t2 exceeds 70 seconds, the average KAM < 1.00 decreases and TS 占 becomes lower. When t2 is too long, the BF transformation is excessively advanced, and the M of the final structure decreases, resulting in a high YR, which is not preferable. In addition, since it is a long time, productivity also deteriorates. Therefore, t2 is set to 70 seconds or less. Preferably 60 seconds or less.

본 발명은, 이렇게 T2를 비교적 저온역으로 하고, 또한 이 T2에서 단시간 유지하는 것인 점에서, 전술한 특허문헌 3∼7과는 상이하다. 즉, 특허문헌 3에서는, 480∼350℃의 온도역까지 냉각하고, 해당 온도역에서 100∼400초간 유지 또는 완 냉각하는 것이 나타내어져 있어, 유지 시간이 길다. 또한 특허문헌 4에서는, 오스테나이트 단상역에서 가열 후, 일단, 저온역(50∼300℃)까지 냉각하고, 그 다음에 350∼490℃의 온도역으로 승온시킨다고 하는 본 발명과는 다른 공정을 채용하고 있다. 또한 특허문헌 5에서는, 제 1 온도역+제 2 온도역의 합계 유지 시간이 220초 이상으로 길다. 또한 특허문헌 6에서는, 100℃로부터 (Ms-10℃)의 온도역에서 80초 이상으로 길게 유지하고 있다. 또한, 특허문헌 7에서 실시되고 있는 (Ms-20℃)∼Bs의 유지 시간은 240초로 길게 되어 있어, 마르텐사이트의 확보와 높은 평균 KAM<1.00의 확보가 곤란하다고 생각된다. 상기와 같이, 이들 기술에서는 유지 시간이 길기 때문에, 본 발명에서 규정하는 평균 KAM<1.00°이 작아, 0.50° 이상을 달성할 수 없다고 생각된다. The present invention is different from the above-described Patent Documents 3 to 7 in that T2 is set at a relatively low temperature in this way, and the T2 is held for a short time at T2. That is, in Patent Document 3, it is shown that cooling is carried out to a temperature range of 480 to 350 캜, and that the temperature is maintained or completely cooled for 100 to 400 seconds in the temperature range, and the holding time is long. Patent Document 4 adopts a process different from that of the present invention in which after heating in a single phase of austenite, the temperature is once cooled to a low temperature range (50 to 300 ° C) and then raised to a temperature range of 350 to 490 ° C . In Patent Document 5, the total holding time of the first temperature range + the second temperature range is 220 seconds or longer. Also, in Patent Document 6, the temperature is maintained at a temperature range of 100 ° C to (Ms-10 ° C) for 80 seconds or longer. In addition, since the holding time of (Bs-20), which is carried out in Patent Document 7, is prolonged to 240 seconds, it is considered that it is difficult to secure martensite and secure a high average KAM of 1.00 . As described above, in these techniques, since the holding time is long, it is considered that the average KAM < 1.00 defined in the present invention is small and 0.50 or more can not be achieved.

고강도 냉연 강판을 얻는 경우, 상기 풀림 후, 실온까지의 평균 냉각 속도(CR3)는, 1℃/s 이상으로 냉각하는 것을 들 수 있다. 이 냉각으로, 미변태 γ의 일부는 M이 되고, 일부는 잔류 γ로서 남는다. 평균 냉각 속도(CR3)를 1℃/s 이상으로 하는 것에 의해, 냉각 중에 미변태 γ가 분해되는 것을 억제하여, 충분한 양의 잔류 γ를 확보할 수 있다. 한편, 평균 냉각 속도(CR3)의 상한은, 500℃/s 정도이다. In the case of obtaining a high-strength cold-rolled steel sheet, the average cooling rate (CR3) to the room temperature after the annealing is 1 ° C / s or more. With this cooling, a part of the unconverted gamma becomes M, and a part remains as a residual gamma. By setting the average cooling rate (CR3) to 1 DEG C / s or more, decomposition of unmodified gamma during cooling can be suppressed, and a sufficient amount of residual gamma can be ensured. On the other hand, the upper limit of the average cooling rate CR3 is about 500 DEG C / s.

〔도금 처리〕[Plating Treatment]

상기 열처리 후에 도금을 실시해도 좋다. 욕에의 침지는, 재료 특성에 영향을 주는 것은 아니다. 도금 처리 자체는, 일반적으로 행해지고 있는 방법을 채용하면 되고, 예컨대, 일반적으로 이용되고 있는 용융 아연도금욕의 온도를, 400∼500℃ 정도로 제어하는 것을 들 수 있다. 또한, (편면당의) 도금 부착량도 특별히 한정되지 않고, 예컨대 20∼100g/m2의 범위로 하는 것을 들 수 있다. Plating may be performed after the heat treatment. The immersion in the bath does not affect the material properties. The plating treatment itself may be carried out by a commonly used method, for example, controlling the temperature of a commonly used hot-dip galvanizing bath to about 400 to 500 캜. The plating adhesion amount (per one side) is not particularly limited, and may be, for example, in the range of 20 to 100 g / m 2 .

고강도 용융 아연도금 강판을 얻는 경우, 상기 도금 처리 후, 실온까지의 평균 냉각 속도(CR3')는, 1∼500℃/s로 하는 것을 들 수 있다. 그 이유는, 상기 CR3과 동일하다. In the case of obtaining a high-strength hot-dip galvanized steel sheet, the average cooling rate (CR3 ') to room temperature after the plating treatment is 1 to 500 DEG C / s. The reason is the same as CR3.

〔합금화 처리 온도(T3): 450∼560℃〕[Alloying treatment temperature (T3): 450 to 560 DEG C]

합금화 처리 온도(T3)가 560℃를 초과하면, 미변태 γ가 분해되어, 충분한 잔류 γ를 확보할 수 없게 된다. 그 결과, TS×EL 균형이 저하된다. 또한, 평균 KAM<1.00°도 작아져 TS×λ 균형이 저하된다. 게다가, 탄화물의 석출에 의해, 고YR화됨과 함께, TS×EL 균형과 TS×λ 균형이 저하된다. 따라서 본 발명에서는, T3을 560℃ 이하로 한다. T3은, 바람직하게는 540℃ 이하, 보다 바람직하게는 520℃ 이하이다. 한편, 합금화 처리 온도가 450℃를 하회하면, 합금화가 진행되지 않기 때문에, T3은 450℃ 이상으로 한다. T3은 바람직하게는 480℃ 이상이다. If the alloying treatment temperature T3 exceeds 560 deg. C, the unconverted gamma is decomposed and a sufficient residual gamma can not be ensured. As a result, the TS 占 EL balance is degraded. Also, the average KAM < 1.00 deg . Decreases and the TS 占 balance is lowered. In addition, due to the precipitation of carbide, the high YR is formed and the TS 占 EL balance and the TS 占 balance are lowered. Therefore, in the present invention, T3 is set to 560 DEG C or lower. T3 is preferably 540 DEG C or lower, more preferably 520 DEG C or lower. On the other hand, if the alloying treatment temperature is lower than 450 캜, the alloying does not proceed, so T 3 is set to 450 캜 or higher. T3 is preferably 480 DEG C or higher.

한편, 합금화 처리 시간(t3)은, 일반적인 조건을 채용할 수 있고, 예컨대 5∼60초 정도로 할 수 있다. On the other hand, the alloying treatment time t3 can employ general conditions and can be, for example, about 5 to 60 seconds.

고강도 합금화 용융 아연도금 강판을 얻는 경우, 상기 합금화 처리 후, 실온까지의 평균 냉각 속도(CR3'')는, 1∼500℃/s로 하는 것을 들 수 있다. 그 이유는, 상기 CR3과 동일하다. In the case of obtaining a high strength alloyed hot-dip galvanized steel sheet, the average cooling rate (CR 3 ") to room temperature after the alloying treatment is 1 to 500 ° C / s. The reason is the same as CR3.

실시예Example

이하, 실시예를 들어 본 발명을 보다 구체적으로 설명하지만, 본 발명은 물론 하기 실시예에 의해 제한을 받는 것은 아니고, 전·후기의 취지에 적합할 수 있는 범위에서 적당히 변경을 가하여 실시하는 것도 물론 가능하며, 그들은 모두 본 발명의 기술적 범위에 포함된다. Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is of course not limited by the following Examples, and it is of course possible to carry out the present invention by appropriately modifying it within the range suitable for the purposes of the preceding and latter parts All of which are included in the technical scope of the present invention.

실제 기계를 시뮬레이션하여, 표 1에 나타내는 화학 성분 조성의 강괴를 진공 용제로 제작한 후, 1250℃로 가열하고 나서 열간 압연을 행하고, 마무리 압연 온도: 880℃에서 열간 압연을 종료한 후, 권취 온도: 600℃까지 냉각하고, 상기 온도에서 30min 유지하고 나서 노냉하여 열연 강판을 얻었다. 또한, 산세에 의해 표면의 스케일을 제거하고, 그 후 46∼62%의 냉연율로 냉간 압연을 행하여, 1.4mm의 냉연 강판을 얻었다. 그리고 다음에 나타내는 바와 같이 풀림(열처리)을 행했다. 즉, 도 2 및 하기 표 2에 나타내는 바와 같이, 균열 온도 T1(℃)에서 90초 유지하고, T1로부터 500℃까지를 평균 냉각 속도 CR1(℃/s)로, 또한 500℃로부터 T2(℃)까지를 평균 냉각 속도 CR2(℃/s)로 냉각한 후, 당해 온도역(T2)에서 t2(초) 유지했다. The actual machine was simulated to produce a steel ingot having the chemical composition shown in Table 1 in a vacuum solvent and then heated to 1250 占 폚, followed by hot rolling, finish hot rolling at a finish rolling temperature of 880 占 폚, : The steel sheet was cooled to 600 占 폚, maintained at the above temperature for 30 minutes, and then cooled to obtain a hot-rolled steel sheet. Further, the surface scale was removed by pickling, and then cold rolling was performed at a cold rolling rate of 46 to 62% to obtain a cold rolled steel sheet having a thickness of 1.4 mm. Then, annealing (heat treatment) was performed as shown below. That is, as shown in Fig. 2 and the following Table 2, the cracking temperature T1 (占 폚) is maintained for 90 seconds, the T1 to 500 占 폚 is changed to the average cooling rate CR1 (占 폚 / Was cooled to the average cooling rate CR2 (占 폚 / s) and maintained at t2 (sec) in the temperature range T2.

고강도 냉연 강판(CR)은, 상기 풀림 후, 평균 냉각 속도(CR3) 15℃/s로 실온까지 냉각하여 얻었다. 고강도 용융 아연도금 강판(GI)은, 상기 열처리 후, 460℃의 아연 도금욕에 침지하여 도금 처리를 실시한 후, 평균 냉각 속도(CR3') 15℃/s로 실온까지 냉각하여 얻었다. 또 고강도 합금화 용융 아연도금 강판(GA)은, 아연 도금욕에 침지 후, 추가로 표 2에 나타내는 합금화 처리 온도 T3(℃)에서 35초간의 합금화 처리를 행하고 나서, 평균 냉각 속도(CR3'') 15℃/s로 실온까지 냉각하여 얻었다. The high-strength cold-rolled steel sheet CR was obtained by cooling to room temperature at an average cooling rate (CR3) of 15 DEG C / s after the above-mentioned annealing. The high-strength hot-dip galvanized steel sheet (GI) was obtained by dipping it in a galvanizing bath at 460 DEG C after the above-mentioned heat treatment and plating and then cooling it to room temperature at an average cooling rate (CR3 ') of 15 DEG C / s. Further, the high-strength alloyed hot-dip galvanized steel sheet (GA) was subjected to alloying treatment for 35 seconds at the alloying treatment temperature T3 (占 폚) shown in Table 2 after immersion in a zinc plating bath, Lt; 0 &gt; C / s to room temperature.

편면당의 도금 부착량은 40g/m2였다. The coating amount of plating on one side was 40 g / m 2 .

한편, Ac3 및 Ms는, 「레슬리 철강재료과학」(마루젠주식회사, 1985년 5월 31일 발행, p. 273 및 p. 231)에 기재되어 있는 하기 식에 의해 산출했다(하기 식에 있어서, [원소]는, 강판에 포함되는 각 원소의 함유량(질량%)을 나타낸다). 하기 식에 있어서, 강판에 포함되지 않는 원소의 함유량은 0%로 하여 계산했다. On the other hand, Ac 3 and Ms were calculated by the following equation described in &quot; Leslie steel material science &quot; (Maruzen Co., Ltd., May 31, 1985, p.273 and p.231) , And [element] indicates the content (mass%) of each element contained in the steel sheet. In the following formula, the content of the elements not contained in the steel sheet was calculated to be 0%.

Figure pct00001
Figure pct00001

Figure pct00002
Figure pct00002

Figure pct00003
Figure pct00003

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Figure pct00004

얻어진 각 강판을 이용하여, 조직 분율의 측정, 평균 KAM<1.00°의 측정, 및 기계 특성의 평가를 하기와 같이 행했다. Using each steel sheet thus obtained, the measurement of the texture fraction, the measurement of the average KAM < 1.00 , and the evaluation of the mechanical properties were carried out as follows.

[조직 분율의 측정] [Measurement of tissue fraction]

(잔류 γ)(Residual γ)

잔류 γ는, BF의 라스 사이 등에 많이 존재하고 있어, 조직 관찰로 양을 측정하는 것은 곤란하기 때문에, X선 회절을 사용하여 잔류 γ량을 측정했다. Since residual γ exists in large amounts in the laths of BF and the like, and it is difficult to measure the amount by the observation of the structure, residual γ amount was measured using X-ray diffraction.

즉, 강판을 t/4까지 연삭한 후, 화학 연마하고 나서 X선 회절 강도 측정에 의해 구했다. 입사 X선에는 Co-Kα을 이용하고, 페라이트(폴리고널 페라이트나 베이니틱 페라이트를 포함하는, 광의의 페라이트)의 (200), (211), (220) 각 면의 회절 강도에 대한 오스테나이트의 (200), (220), (311) 각 면의 강도비로부터 잔류 γ량을 계산했다. 한편, 상기 X선 회절로 구해지는 잔류 γ량은, 체적률로서 산출되지만, 이 체적률의 값은 그대로 면적률로 고쳐 읽을 수 있다. 따라서 본 발명에서는, 잔류 γ량의 단위를 면적률이라고 간주하여 취급한다. That is, the steel sheet was ground to t / 4, chemically polished, and then measured by X-ray diffraction intensity measurement. Co-K alpha is used for the incident X-rays, and the diffraction intensity of the (200), (211), and (220) planes of the ferrite (optical ferrite containing polygonal ferrite and bainitic ferrite) The residual gamma amount was calculated from the intensity ratios of the respective faces of (200), (220), and (311). On the other hand, the residual? Amount obtained by the X-ray diffraction is calculated as the volume ratio, but the value of the volume ratio can be rewritten to the area ratio as it is. Therefore, in the present invention, the unit of the residual? Amount is treated as the area ratio.

(폴리고널 페라이트, 베이니틱 페라이트+템퍼링 마르텐사이트, 프레쉬 마르텐사이트)(Polygonal ferrite, bainitic ferrite + tempering martensite, fresh martensite)

판 폭방향에 수직한 단면의 t/4 위치를 관찰할 수 있도록 시험편을 채취하고, 기계 연마 후에, 나이탈 부식을 실시하여, 주사형 전자 현미경(SEM; Scanning Electron Microscope)을 사용하여 3000배로 관찰했다. 그리고, 화상 해석에 의해, F(폴리고널 페라이트), M(프레쉬 마르텐사이트)의 각각의 면적률을 측정했다. 이 측정을 3시야에서 행하여, 3시야의 평균값을 구했다. The specimen was sampled so as to observe the t / 4 position of the cross section perpendicular to the plate width direction. After mechanical polishing, the specimen was subjected to ablation corrosion and observed at a magnification of 3000 times using a Scanning Electron Microscope (SEM) did. Then, the area ratios of F (polygonal ferrite) and M (fresh martensite) were measured by image analysis. This measurement was performed in the third field of view to obtain an average value of the three fields of view.

또한, BF+TM의 면적률은 조직 관찰에 의해 측정 가능하지만, 본 실험 범위 내에서는, 조직이 F, BF+TM, M 및 잔류 γ만으로 구성되기 때문에, BF+TM(면적%)은 [100(면적%)-F(면적%)-M(면적%)-잔류 γ(면적%)]로부터 구했다. The area ratio of BF + TM can be measured by observation of the structure, but BF + TM (area%) is [100 (%)) because the structure is composed of F, BF + TM, (Area%) - F (area%) - M (area%) - residual gamma (area%).

[평균 KAM<1.00°의 측정] [Average KAM &lt; Measurement of 1.00 DEG ]

판 두께 t/4까지 연삭한 후에 기계 연마를 실시한 시료를 70° 경사시킨 상태로, SEM에서, 1step: 0.125μm로, 50μm×50μm의 영역의 전자선 후방 산란 회절상을 측정하고, 이 측정 결과로부터, 해석 소프트웨어(테크셈라보라토리즈사제 OIM 시스템)를 이용하여, 각 측정점에서의 KAM값을 구했다. The electron beam backscattering diffraction image in the area of 50 탆 x 50 탆 at the 1step: 0.125 탆 was measured in the SEM in a state in which the sample subjected to the mechanical polishing after the grinding to the plate thickness t / 4 was inclined at 70 째, The KAM value at each measurement point was obtained by using analysis software (OIM system manufactured by Techemal Laboratories).

각 측정점의 KAM값을 측정한 결과(분포)의 일례를 도 3 및 도 4에 나타낸다. 도 3은, No. 26(본 발명예)의 KAM값의 분포를 나타낸 그래프이며, 도 4는, No. 12(비교예)의 KAM값의 분포를 나타낸 그래프이다. 본 발명에서는, 1.00° 미만의 KAM값을 대상으로 삼는 것으로, 도 3 및 도 4에 있어서 흑색으로 나타내어진 부분이 이것에 상당한다. 이 흑색 부분의 KAM값의 평균값이 평균 KAM<1.00°이다. 도 3과 도 4를 대비하면 육안으로는 분포의 차이가 거의 보이지 않는다고 생각되지만, 상기 해석 결과에서는, No. 26(도 3)의 평균 KAM<1.00이 0.52이며, No. 12(도 4)의 평균 KAM<1.00이 0.49로 상이하다. 본 발명에서는, 이 평균 KAM<1.00의 약간의 차이가, 후술하는 바와 같이 특성에 크게 영향을 준다. Figs. 3 and 4 show examples of the results (distribution) of measuring the KAM values of the respective measurement points. Fig. FIG. 4 is a graph showing the distribution of KAM values of 26 (the present invention). FIG. 12 (Comparative Example). Fig. In the present invention, a KAM value of less than 1.00 DEG is targeted, and a portion indicated by black in FIGS. 3 and 4 corresponds to this. The average value of the KAM values of the black portions is an average KAM < 1.00 DEG . In contrast to Figs. 3 and 4, it is considered that the difference in distribution is hardly visible to the naked eye. The average KAM < 1.00 of 26 (Fig. 3) is 0.52, and the average KAM &lt; The average KAM < 1.00 of 12 (Fig. 4) is 0.49. In the present invention, this slight difference in average KAM &lt; 1.00 greatly affects the characteristics as described later.

한편, 본 실시예에 있어서의 그 밖의 예도, 상기 도 3이나 도 4와 같이 측정하여 평균 KAM<1.00°을 구했다. On the other hand, the other examples in this embodiment were also measured as shown in Figs. 3 and 4, and an average KAM < 1.00 was obtained.

[기계 특성의 평가] [Evaluation of Mechanical Characteristics]

(인장 시험)(Tensile test)

JIS 5호 시험편(평점 거리 50mm, 평행부 폭 25mm)을, 강판의 압연 방향에 대하여 수직한 방향이 긴 방향이 되도록 채취하여, JIS Z2241에 따라서, YS, TS, EL(전체 신도)을 측정했다. 한편, 변형 속도는 10mm/min으로 했다. A test piece of JIS No. 5 (a rated distance of 50 mm and a parallel portion width of 25 mm) was sampled so that the direction perpendicular to the rolling direction of the steel sheet was long, and YS, TS and EL (total elongation) were measured in accordance with JIS Z2241 . On the other hand, the strain rate was 10 mm / min.

(구멍 확장 시험)(Hole extension test)

철강연맹규격 JFST 1001에 근거하여 평가했다. 구체적으로는, 강판에 φ 10mm의 구멍을 펀치로 타발한 후, 60° 원추 펀치를 이용하여 버(burr)를 위로 하여 구멍 확장 가공을 행하여, 균열 관통 시점에서의 구멍 확장률 λ을 측정했다. Steel Federation Standard JFST 1001. Specifically, after drilling a hole of 10 mm in diameter with a punch, the steel plate was subjected to a hole expanding process by using a 60 ° cone punch to raise the burr, and the hole expanding rate? At the crack penetration point was measured.

그리고, TS가 980MPa 이상인 경우를 고강도라고 평가하여, 이 TS 980MPa 이상에 있어서, TS×EL≥16(GPa·%) 및 TS×λ≥30(GPa·%)을 만족시키는 경우를 성형성이 우수하다고 평가하고, 또한 YR(=100×YS/TS)≤80(%)을 만족시키는 경우를 형상 동결성이 우수하다고 평가했다. When the TS is 980 MPa or more, it is evaluated as high strength. When the TS is 980 MPa or more, satisfying TS EL ≧ 16 (GPa 揃%) and TS × 了 30 (GPa 揃% And YR (= 100 x YS / TS) 80 (%) was evaluated as superior in shape mobility.

이들의 결과를 표 3에 나타낸다. The results are shown in Table 3.

Figure pct00005
Figure pct00005

표 1∼3으로부터 다음과 같이 고찰할 수 있다(이하, 「No.」는 실험 No.를 나타낸다). 즉, No. 1∼3, 13∼16 및 18∼40은, 본 발명에서 규정하는 방법으로 제조하여, 성분 조성 및 조직이 규정의 범위 내에 있기 때문에, 인장 강도가 980MPa 이상이고, 성형성 및 형상 동결성이 우수한, 냉연 강판, 용융 아연도금 강판 또는 합금화 용융 아연도금 강판이 얻어지고 있다. The following can be considered from Tables 1 to 3 (hereinafter, &quot; No. &quot; indicates Experiment No.). That is, No. 1 to 3, 13 to 16 and 18 to 40 are produced by the method defined in the present invention and have a tensile strength of 980 MPa or more and excellent moldability and shape durability , A cold-rolled steel sheet, a hot-dip galvanized steel sheet, or an alloyed hot-dip galvanized steel sheet.

이에 반하여, No. 4∼12 및 17은, 성분 조성, 제조 조건의 어느 것인가가 규정의 요건을 벗어나기 때문에, 원하는 조직이 얻어지지 않고, 어느 것인가의 특성이 뒤떨어지는 결과로 되었다. On the contrary, 4 to 12 and 17, since any of the component composition and the production conditions deviates from the prescribed requirements, a desired structure can not be obtained, and the result is that any one of the properties is poor.

즉, No. 4는, T1이 낮게 2상역에서 가열한 결과, F가 많아져, TS×λ 균형이 저하되었다. 또한, F의 혼입에 의해 미변태 γ 중에 C가 농화되고, 그 결과, 오스템퍼 중의 BF 변태가 지연되어 M이 많아져, TS×EL 균형 및 TS×λ 균형이 저하되었다. That is, No. 4, as a result of heating at a low temperature in a two-phase region of T1, F was increased and TS 占 balance was lowered. Further, C is concentrated in the unconverted gamma by the incorporation of F, and as a result, the BF transformation in the ostemper is delayed to increase M, and the TS 占 EL balance and the TS 占 balance are lowered.

No. 5는, CR1이 지나치게 작기 때문에, 냉각 중에 F가 생성되어, TS×λ 균형이 저하되었다. No. 5, since CR1 is too small, F is generated during cooling and the TS 占 balance is lowered.

No. 6은, CR2가 지나치게 작기 때문에, 냉각 중에 저KAM값의 BF가 생성되어 평균 KAM<1.00°이 작아져, TS×λ 균형이 저하되었다. No. 6, since CR2 is too small, BF of a low KAM value is generated during cooling, the average KAM < 1.00 deg. Is small, and the TS 占 balance is lowered.

No. 7은, T2가 지나치게 낮기 때문에 충분한 잔류 γ를 확보할 수 없어, TS×EL 균형이 저하되었다. 또한, M이 감소하여, YR이 높아졌다. No. 7, since T2 is too low, sufficient residual? Can not be ensured and the TS 占 EL balance is degraded. Also, M decreased and YR increased.

No. 8은, T2가 지나치게 높기 때문에, 평균 KAM<1.00°이 작아져, TS×λ 균형이 저하되었다. No. 8, since T2 is too high, the average KAM < 1.00 占 becomes smaller, and the TS 占 balance is lowered.

No. 9는, t2가 지나치게 짧기 때문에, 소망량의 BF+TM과 잔류 γ를 확보할 수 없고, M량이 과잉이 되며, 그 결과, TS×EL 균형과 TS×λ 균형이 저하되었다. No. 9, since t2 is too short, the desired amount of BF + TM and residual gamma can not be secured, and the amount of M becomes excessive. As a result, the TS EL balance and the TS L balance are lowered.

No. 10은, t2가 지나치게 길기 때문에, 평균 KAM<1.00°이 작아져, TS×λ 균형이 저하되었다. No. 10, since t2 is excessively long, the average KAM < 1.00 DEG decreases, and the TS 占 balance is lowered.

No. 11은, t2가 더욱 길기 때문에, M을 확보할 수 없어, YR이 높아졌다. 또한, 평균 KAM<1.00°이 작아져, TS×λ 균형이 저하되었다. No. 11, since t2 is longer, M can not be secured, and YR is increased. In addition, the average KAM < 1.00 DEG decreased, and the TS x lambda balance dropped.

No. 12는, T3이 지나치게 높기 때문에, 소망량의 잔류 γ를 확보할 수 없고, 또한 평균 KAM<1.00°이 작아지고, 게다가 탄화물 석출의 영향 등에 의해, TS×λ 균형과 TS× EL 균형이 저하되었다. No. 12, since the T3 is too high, a desired amount of residual? Can not be ensured and the average KAM < 1.00 占 becomes smaller, and furthermore the TS 占 balance and the TS 占 EL balance are lowered due to the influence of carbide precipitation .

No. 17은, Si량이 지나치게 적기 때문에, 충분한 양의 잔류 γ를 확보할 수 없어, TS×EL 균형이 저하되었다.
No. 17, since the amount of Si is excessively small, a sufficient amount of residual? Can not be ensured and the TS 占 EL balance is lowered.

Claims (10)

C: 0.1∼0.3%(질량%의 의미. 화학 성분에 대하여 이하 동일),
Si: 1.0∼3.0%,
Mn: 0.5∼3.0%,
P: 0.1% 이하,
S: 0.03% 이하,
Al: 0.01∼1.0%, 및
N: 0.01% 이하를 만족시키고,
잔부가 철 및 불가피 불순물로 이루어지며,
강 조직이,
베이니틱 페라이트(BF)+템퍼링 마르텐사이트(TM): 65%(면적%의 의미. 강 조직에 대하여 이하 동일) 이상,
프레쉬 마르텐사이트(M): 3∼18%,
잔류 오스테나이트(잔류 γ): 5% 이상, 및
폴리고널 페라이트(F): 5% 이하를 만족시키고, 또한,
평균 KAM<1.00°: 0.50° 이상
[단, 상기 「평균 KAM<1.00°」은, 복수 개소의 KAM(방위차, Kernel Average Misorientation, 단위는 「°」)값의 1.00° 미만에서의 평균값을 나타낸다.]
을 만족시키고, 또한 인장 강도가 980MPa 이상인 것을 특징으로 하는 성형성 및 형상 동결성이 우수한 고강도 냉연 강판. C: 0.1 to 0.3% (meaning% by mass, the same applies hereinafter for chemical components),
Si: 1.0 to 3.0%
Mn: 0.5 to 3.0%
P: not more than 0.1%
S: 0.03% or less,
Al: 0.01 to 1.0%, and
N: 0.01% or less,
The balance being iron and inevitable impurities,
However,
Bainitic ferrite (BF) + tempering martensite (TM): 65% (meaning% of area, hereinafter the same for steel structure)
Fresh martensite (M): 3 to 18%,
Residual austenite (residual?): 5% or more, and
Polyorganosilicate ferrite (F): 5% or less,
Average KAM <1.00 ° : Over 0.5 °
The average KAM < 1.00 DEG &quot; represents an average value at less than 1.00 DEG of KAM (Kernel Average Misorientation, unit is &quot;
And a tensile strength of 980 MPa or more. The high strength cold rolled steel sheet excellent in moldability and shape-formability. 제 1 항에 있어서,
추가로,
Ti: 0.01∼0.1%,
Nb: 0.01∼0.1%, 및
V: 0.01∼0.1%
로 이루어지는 군으로부터 선택되는 적어도 1종의 원소를 함유하는 고강도 냉연 강판. The method according to claim 1,
Add to,
Ti: 0.01 to 0.1%
Nb: 0.01 to 0.1%, and
V: 0.01 to 0.1%
And at least one kind of element selected from the group consisting of iron and iron. 제 1 항에 있어서,
추가로,
Cr: 0.01∼1%,
Mo: 0.01∼1%, 및
B: 0.0001∼0.005%
로 이루어지는 군으로부터 선택되는 적어도 1종의 원소를 함유하는 고강도 냉연 강판. The method according to claim 1,
Add to,
Cr: 0.01 to 1%
Mo: 0.01 to 1%, and
B: 0.0001 to 0.005%
And at least one kind of element selected from the group consisting of iron and iron. 제 1 항에 있어서,
추가로,
Cu: 0.01∼1%, 및
Ni: 0.01∼1%
로 이루어지는 군으로부터 선택되는 적어도 1종의 원소를 함유하는 고강도 냉연 강판. The method according to claim 1,
Add to,
Cu: 0.01 to 1%, and
Ni: 0.01 to 1%
And at least one kind of element selected from the group consisting of iron and iron. 제 1 항에 있어서,
추가로,
Ca: 0.0005∼0.005%, 및
Mg: 0.0005∼0.005%
로 이루어지는 군으로부터 선택되는 적어도 1종의 원소를 함유하는 고강도 냉연 강판. The method according to claim 1,
Add to,
Ca: 0.0005 to 0.005%, and
Mg: 0.0005 to 0.005%
And at least one kind of element selected from the group consisting of iron and iron. 제 1 항 내지 제 5 항 중 어느 한 항에 기재된 고강도 냉연 강판의 표면에, 용융 아연도금층이 형성되어 있는 것을 특징으로 하는 성형성 및 형상 동결성이 우수한 고강도 용융 아연도금 강판. A high strength hot-dip galvanized steel sheet characterized by having a hot-dip galvanized layer formed on the surface of the high-strength cold-rolled steel sheet according to any one of claims 1 to 5, wherein the hot-dip galvanized steel sheet has excellent moldability and shape fixability. 제 1 항 내지 제 5 항 중 어느 한 항에 기재된 고강도 냉연 강판의 표면에, 합금화 용융 아연도금층이 형성되어 있는 것을 특징으로 하는 성형성 및 형상 동결성이 우수한 고강도 합금화 용융 아연도금 강판. A high strength alloyed hot-dip galvanized steel sheet characterized by having a galvannealing layer formed on the surface of the high-strength cold-rolled steel sheet according to any one of claims 1 to 5. 제 1 항 내지 제 5 항 중 어느 한 항에 기재된 고강도 냉연 강판을 제조하는 방법으로서,
제 1 항 내지 제 5 항 중 어느 한 항에 기재된 성분 조성을 갖는 냉연 강판을, Ac3∼960℃의 온도역(T1)으로 가열한 후, 해당 온도역(T1)으로부터 500℃까지를 평균 냉각 속도(CR1) 5℃/s 이상으로 냉각하고, 500℃로부터 (Ms-200)∼420℃의 온도역(T2)까지를 평균 냉각 속도(CR2) 10℃/s 이상으로 냉각하고, 이어서 해당 온도역(T2)에서 10∼70초(t2) 유지하는 것을 특징으로 하는 성형성 및 형상 동결성이 우수한 고강도 냉연 강판의 제조 방법. A method of producing the high-strength cold-rolled steel sheet according to any one of claims 1 to 5,
A cold-rolled steel sheet having a composition according to any one of claims 1 to 5 is heated to a temperature range (T1) of Ac 3 to 960 ° C and then cooled to an average cooling rate (CR1) is cooled to not less than 5 占 폚 / s and cooled from 500 占 폚 to a temperature range T2 of (Ms-200) to 420 占 폚 at an average cooling rate (CR2) of not less than 10 占 폚 / s, (T2) for 10 to 70 seconds (T2). 제 6 항에 기재된 고강도 용융 아연도금 강판을 제조하는 방법으로서,
제 1 항 내지 제 5 항 중 어느 한 항에 기재된 성분 조성을 갖는 냉연 강판을, Ac3∼960℃의 온도역(T1)으로 가열한 후, 해당 온도역(T1)으로부터 500℃까지를 평균 냉각 속도(CR1) 5℃/s 이상으로 냉각하고, 500℃로부터 (Ms-200)∼420℃의 온도역(T2)까지를 평균 냉각 속도(CR2) 10℃/s 이상으로 냉각하고, 이어서 해당 온도역(T2)에서 10∼70초(t2) 유지한 후, 아연욕에 침지하는 것을 특징으로 하는 성형성 및 형상 동결성이 우수한 고강도 용융 아연도금 강판의 제조 방법. A method for producing the high-strength hot-dip galvanized steel sheet according to claim 6,
A cold-rolled steel sheet having a composition according to any one of claims 1 to 5 is heated to a temperature range (T1) of Ac 3 to 960 ° C and then cooled to an average cooling rate (CR1) is cooled to not less than 5 占 폚 / s and cooled from 500 占 폚 to a temperature range T2 of (Ms-200) to 420 占 폚 at an average cooling rate (CR2) of not less than 10 占 폚 / s, (T2) for 10 to 70 seconds (t2), and then immersed in a zinc bath, characterized in that the hot-dip galvanized steel sheet is excellent in moldability and shape crystallinity. 제 7 항에 기재된 고강도 합금화 용융 아연도금 강판을 제조하는 방법으로서,
제 1 항 내지 제 5 항 중 어느 한 항에 기재된 성분 조성을 갖는 냉연 강판을, Ac3∼960℃의 온도역(T1)으로 가열한 후, 해당 온도역(T1)으로부터 500℃까지를 평균 냉각 속도(CR1) 5℃/s 이상으로 냉각하고, 500℃로부터 (Ms-200)∼420℃의 온도역(T2)까지를 평균 냉각 속도(CR2) 10℃/s 이상으로 냉각하고, 이어서 해당 온도역(T2)에서 10∼70초(t2) 유지한 후, 아연욕에 침지하고, 추가로 450∼560℃의 합금화 처리 온도(T3)에서 합금화 처리를 행하는 것을 특징으로 하는 성형성 및 형상 동결성이 우수한 고강도 합금화 용융 아연도금 강판의 제조 방법.
A method for producing the high strength alloyed hot-dip galvanized steel sheet according to claim 7,
A cold-rolled steel sheet having a composition according to any one of claims 1 to 5 is heated to a temperature range (T1) of Ac 3 to 960 ° C and then cooled to an average cooling rate (CR1) is cooled to not less than 5 占 폚 / s and cooled from 500 占 폚 to a temperature range T2 of (Ms-200) to 420 占 폚 at an average cooling rate (CR2) of not less than 10 占 폚 / s, (T2) for 10 to 70 seconds (t2), then immersed in a zinc bath, and further subjected to alloying treatment at an alloying treatment temperature (T3) of 450 to 560 deg. (JP) METHOD FOR PREPARING GOOD STRENGTH ALLOYED HOT - ZINC PLATED.
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