KR101100550B1 - High-strength cold-rolled steel sheet having good galvanizing property, and method for producing the same - Google Patents
High-strength cold-rolled steel sheet having good galvanizing property, and method for producing the same Download PDFInfo
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Abstract
본 발명은 인장강도 980MPa 이상의 강도를 가지며 도금 특성이 우수한 고강도 냉연강판 및 그 제조방법에 관한 것이다.The present invention relates to a high strength cold rolled steel sheet having a strength of 980 MPa or more and excellent in plating property and a method of manufacturing the same.
본 발명은 중량%로, C: 0.10~0.15%, Si: 0.01~0.25%이하, Mn: 2.4~2.8%, S: 0초과 0.005%이하, P: 0초과 0.01% 이하, Al: 0초과 0.05% 이하, Cr: 0.25~0.5%, Cu: 0.10~0.30%, Ni: 0.05~0.20%, Nb: 0.04~0.06%, B:0.0005~0.0015%, Sb:0.02~0.05%, N: 0초과 0.006%이하를 함유하고, 나머지 잔부가 Fe 및 불가피적으로 포함되는 불순물로 이루어진 강슬라브를 1200℃ 이상의 온도로 재가열하고, Ac3+30℃ 이상의 온도에서 열간 마무리압연을 행한 후 580-640℃에서 강판 코일 형태로 권취한다.The present invention is in weight%, C: 0.10 to 0.15%, Si: 0.01 to 0.25% or less, Mn: 2.4 to 2.8%, S: greater than 0 and less than 0.005%, P: greater than 0 and 0.01% or less, Al: greater than 0 and 0.05 % Or less, Cr: 0.25-0.5%, Cu: 0.10-0.30%, Ni: 0.05-0.20%, Nb: 0.04-0.06%, B: 0.0005-0.0015%, Sb: 0.02-0.05%, N: more than 0.006 Steel slab containing less than% and the remainder of Fe and inevitably contained impurities is reheated to a temperature of 1200 ° C or higher, hot-rolled at an temperature of Ac3 + 30 ° C or higher, and then coiled at 580-640 ° C. Wind up in form.
이후, 냉간압연을 실시하고, 냉간압연된 강판 코일을 소둔 처리하고, 용융아연도금처리를 실시하고 용융아연도금피막의 합금화를 실시한 후 급냉처리한다. Thereafter, cold rolling is performed, the cold rolled steel sheet coil is annealed, hot dip galvanized and alloyed with the hot dip galvanized film, followed by quenching.
이에 따르면 본 발명은 합금 원소 및 제조 시의 열처리 조건을 조절하여 우수한 연신율 및 도금 특성을 가짐과 아울러 고강도 특성을 만족함으로써, 원가를 절감할 수 있으며 제품의 품질을 대폭 향상시킬 수 있는 유용한 효과를 갖는다.According to the present invention, the present invention has excellent elongation and plating characteristics by controlling alloying elements and heat treatment conditions at the time of manufacture, and satisfies high strength characteristics, thereby reducing costs and significantly improving product quality. .
인장강도, 980MPa, 냉연강판, 도금 Tensile Strength, 980 MPa, Cold Rolled Steel Sheets, Plating
Description
본 발명은 고강도 냉연강판의 제조방법에 관한 것으로, 특히 인장강도 980MPa 이상의 강도 및 우수한 연신율을 갖도록 함과 아울러 도금 특성이 우수한 고강도 냉연강판을 제조할 수 있도록 한 고강도 냉연강판의 제조방법에 관한 것이다.The present invention relates to a method for manufacturing a high strength cold rolled steel sheet, and more particularly, to a method of manufacturing a high strength cold rolled steel sheet, which has a strength and excellent elongation of 980 MPa or more, as well as an excellent high strength cold rolled steel sheet.
일반적으로 기존 자동차 산업은 경쟁이 심화됨에 따라 자동차 품질에 대한 고급화, 다양화 요구가 높아지고 있으며, 강화되고 있는 안전 및 환경규제에 대한 법규를 만족시키기 위해 자체 강성을 증대시키고 연비 효율을 향상시키기 위한 노력을 하고 있다.In general, as the competition intensifies in the existing automobile industry, there is an increasing demand for higher quality and diversification of automobile quality, and efforts to increase self-stiffness and improve fuel efficiency to satisfy the regulations on safety and environmental regulations that are being strengthened. Doing
최근 철강업계 및 자동차 업계의 연구관심은 환경오염과 고강도, 경량화에 집중되고 있으며, 자동차 디자인이 복잡해지고 소비자의 욕구가 다양화됨에 따라 자동차 업계에서는 고강도이면서 가공성과 성형성이 우수한 강을 요구하고 있다.Recently, the research interests of the steel industry and the automotive industry are focused on environmental pollution, high strength, and light weight, and as the automobile design is complicated and the needs of consumers are diversified, the automotive industry demands steel having high strength and excellent workability and formability. .
복합조직을 이용한 고강도강판의 개발 방향은 마르텐사이트와 페라이트의 2상 조직강(DP, dual phase), 페라이트+베이나이트+잔류 오스테나이트의 TRIP 강(TRansformation Induced Plasticity), 그리고 더 복잡한 다상 조직강 (CP, complex phase) 등으로 나눌 수 있다. The direction of development of high strength steel sheet using composite tissues is dual phase (DP) of martensite and ferrite, TRIP steel of ferrite + bainite + residual austenite, and more complex multiphase steel ( CP, complex phase).
2상 조직강은 오스테나이트와 페라이트 2상 영역에서 급냉하여 마르텐사이트를 약 10~30%(부피분율) 정도 생성시킨 것으로, 석출강화강에 비하여 연성 및 장출가공성이 우수하며, 충돌에너지 흡수능이 크기 때문에 멤버, 범퍼 등에 적용된다.Two-phase tissue steels quench in the austenite and ferrite two-phase regions to produce martensite by about 10-30% (volume fraction), and have superior ductility and elongation processability and high impact energy absorption capacity compared to precipitation-reinforced steels. Because it is applied to members, bumpers and so on.
3상 조직을 기본으로 하는 TRIP강은 현재 개발이 활발히 진행되고 있으며 일부 적용이 시도되고 있다. 대체로 1.5%(중량%) 정도의 Si, Mn을 첨가하는 TRIP강은 미세조직 내에 약 5~20% 정도 생성된 연성이 뛰어난 잔류 오스테나이트가 가공 중에 마르텐사이트로 변태하면서 강도 향상되는 현상을 이용한다.TRIP steel, which is based on three-phase organization, is currently being actively developed and some applications have been attempted. In general, TRIP steel containing 1.5% (wt.%) Of Si and Mn utilizes a phenomenon in which ductile residual austenite, which is formed by about 5 to 20% in the microstructure, is transformed into martensite during processing, thereby improving strength.
강판의 강도와 가공성을 높이기 위해 Mn, Si, Nb, Al 등을 첨가하여 요구특성을 만족하는 강판을 제조하지만 위와 같은 원소들은 Fe보다 산소 친화력이 우수하여 냉연과정 중에 강판 표면에 농화 현상이 발생하여 도금 특성이 떨어지는 단점을 내포하고 있다. 이런 문제가 발생할 경우 미도금(bare spot) 등의 도금 품질을 저하시키고 미소 덴트 등의 결함을 발생시킨다.In order to increase the strength and workability of the steel sheet, Mn, Si, Nb, Al, etc. are added to produce a steel sheet that satisfies the required characteristics, but the above elements have higher oxygen affinity than Fe, so that the surface of the steel sheet is thickened during the cold rolling process. It has the disadvantage of poor plating properties. When this problem occurs, the plating quality of the bare spots is degraded and defects such as micro dents are generated.
본 발명은 상기한 제반 문제점을 감안하여 이를 해결하고자 제안된 것으로, 그 목적은 강의 합금성분 및 제조 조건을 조절하여 가공성 및 도금특성이 우수한 고강도 냉연 도금강판을 제공하는 데 있다.The present invention has been proposed to solve the above problems in consideration of the above-mentioned problems, and an object thereof is to provide a high strength cold rolled steel sheet excellent in workability and plating characteristics by adjusting alloy components and manufacturing conditions of steel.
상기한 목적을 달성하기 위한 본 발명은 중량 %로, C: 0.10~0.15%, Si: 0.01~0.25%, Mn: 2.4~2.8%, S: 0초과 0.005% 이하, P: 0초과 0.01% 이하, Al: 0초과 0.05%이하, Cr: 0.25~0.5%, Cu: 0.10~0.3%, Ni: 0.05~0.2%, Nb: 0.04~0.06%, B:0.0005~0.0015%, Sb:0.02~0.05%, N:0초과 0.006%이하를 함유하고, 나머지 잔부가 Fe 및 불가피적으로 포함되는 불순물로 이루어진 강슬라브를,The present invention for achieving the above object by weight%, C: 0.10 to 0.15%, Si: 0.01 to 0.25%, Mn: 2.4 to 2.8%, S: more than 0 and 0.005% or less, P: more than 0 and 0.01% or less , Al: greater than 0 and less than 0.05%, Cr: 0.25 to 0.5%, Cu: 0.10 to 0.3%, Ni: 0.05 to 0.2%, Nb: 0.04 to 0.06%, B: 0.0005 to 0.0015%, Sb: 0.02 to 0.05% , A steel slab containing more than N: 0 and less than 0.006%, the remainder being made of Fe and impurities which are inevitably included,
균질화를 위한 온도로 재가열하고, Ac3+30℃ 이상의 온도에서 열간 마무리압연을 행한 후 580-640℃에서 강판 코일로 권취하며,Reheat to the temperature for homogenization, hot finish rolling at a temperature of Ac3 + 30 ℃ or higher, and then wound into a steel coil at 580-640 ℃,
권취된 강판 코일을 산세처리한 후에 냉간압연을 행하고,After the pickled steel sheet coil is pickled, cold rolling is performed.
냉간압연된 강판을 냉각 처리하는 단계를 거친 후 용융아연도금처리를 실시하고 합금화를 위해 460-510℃의 온도영역으로 재가열한 후에 급냉처리하는 것을 특징으로 한다.After the cold-rolled steel sheet is subjected to a cold treatment step, the hot dip galvanizing treatment is performed, and after the reheating to a temperature range of 460-510 ℃ for alloying is characterized in that the quenching.
상기 냉간압연된 강판을 냉각 처리하는 단계는, 상기 냉간압연된 강판을 780-820℃ 영역에서 5-120초간 유지한 후, 5℃/s 속도로 480℃이하 온도까지 냉각하는 것이 바람직하다.In the step of cooling the cold rolled steel sheet, the cold rolled steel sheet is maintained at 780-820 ° C. for 5-120 seconds, and then cooled to a temperature of 480 ° C. or less at a rate of 5 ° C./s.
상기 냉간압연된 강판을 냉각 처리하는 단계에서 페라이트와 마르텐사이트의 이상 조직을 갖도록 하되,In the step of cooling the cold rolled steel sheet to have an abnormal structure of ferrite and martensite,
상기 페라이트와 마르텐사이트의 체적분율은, 페라이트 60~70%, 마르텐사이트 30~40%의 분율을 갖는다.The volume fraction of the ferrite and martensite has a fraction of ferrite 60 to 70% and martensite 30 to 40%.
본 발명의 다른 특징적인 요소로는, 중량 %로, C: 0.10~0.15%, Si: 0.01~0.25%, Mn: 2.4~2.8%, S: 0초과 0.005% 이하, P: 0초과 0.01% 이하, Al: 0초과 0.05% 이하, Cr: 0.25~0.5%, Cu: 0.10~0.3%, Ni: 0.05~0.2%, Nb: 0.04~0.06%, B:0.0005~0.0015%, Sb:0.02~0.05%, N:0초과 0.006%이하를 함유하고, 나머지 잔부가 Fe 및 불가피적으로 포함되는 불순물로 이루어진 강슬라브를,As another characteristic element of the present invention, in weight%, C: 0.10 to 0.15%, Si: 0.01 to 0.25%, Mn: 2.4 to 2.8%, S: greater than 0 and less than 0.005%, P: greater than 0 and 0.01% or less , Al: more than 0 and 0.05% or less, Cr: 0.25 to 0.5%, Cu: 0.10 to 0.3%, Ni: 0.05 to 0.2%, Nb: 0.04 to 0.06%, B: 0.0005 to 0.0015%, Sb: 0.02 to 0.05% , A steel slab containing more than N: 0 and less than 0.006%, the remainder being made of Fe and impurities which are inevitably included,
균질화를 위한 온도로 재가열하고, Ac3+30℃ 이상의 온도에서 열간 마무리압연을 행한 후 580-640℃에서 강판 코일로 권취하며,Reheat to the temperature for homogenization, hot finish rolling at a temperature of Ac3 + 30 ℃ or higher, and then wound into a steel coil at 580-640 ℃,
권취된 강판 코일을 산세처리한 후에 냉간압연을 행하고,After the pickled steel sheet coil is pickled, cold rolling is performed.
냉간압연된 강판을 780-820℃ 영역에서 5-120초간 유지한 후, 5℃/s 속도로 480℃이하 온도까지 냉각한 후 용융아연도금처리를 실시하고, 460-510℃의 온도영역으로 재가열하여 용융아연도금피막의 합금화를 실시한 후에 20℃/s 이상의 냉각속도로 300℃까지 급냉처리하는 것을 특징으로 한다.The cold rolled steel sheet is maintained at 780-820 ° C. for 5-120 seconds, cooled to a temperature below 480 ° C. at a rate of 5 ° C./s, and subjected to hot dip galvanizing, and reheated to a temperature range of 460-510 ° C. After the alloying of the hot-dip galvanized film is characterized in that the quenching treatment to 300 ℃ at a cooling rate of 20 ℃ / s or more.
본 발명의 또 다른 특징적인 요소인 고강도 냉연강판은, 중량 %로, C: 0.10~0.15%, Si: 0.01~0.25%, Mn: 2.4~2.8%, S: 0초과 0.005% 이하, P: 0초과 0.01% 이하, Al: 0초과 0.05% 이하, Cr: 0.25~0.5%, Cu: 0.10~0.3%, Ni: 0.05~0.2%, Nb: 0.04~0.06%, B:0.0005~0.0015%, Sb:0.02~0.05%, N:0초과 0.006%이 하를 함유하고, 나머지 잔부가 Fe 및 불가피적으로 포함되는 불순물로 이루어진 조성을 가지며,Another characteristic element of the present invention is a high strength cold rolled steel sheet, in weight%, C: 0.10 to 0.15%, Si: 0.01 to 0.25%, Mn: 2.4 to 2.8%, S: greater than 0 and 0.005% or less, P: 0 More than 0.01% or less, Al: greater than 0 and 0.05% or less, Cr: 0.25 to 0.5%, Cu: 0.10 to 0.3%, Ni: 0.05 to 0.2%, Nb: 0.04 to 0.06%, B: 0.0005 to 0.0015%, Sb: 0.02% to 0.05%, more than N: 0 and less than 0.006%, and the remainder has a composition composed of Fe and impurities inevitably included,
미세조직이 페라이트 60~70%, 마르텐사이트 30~40%의 체적 분율을 갖는 것을 특징으로 한다.The microstructure is characterized by having a volume fraction of ferrite 60 ~ 70%, martensite 30 ~ 40%.
본 발명은 인장강도 980MPa 이상의 강도를 가지며 도금 특성이 우수한 고강도 냉연강판 및 그 제조방법에 관한 것인 바, 이에 따르면 본 발명은 합금 원소 및 제조 시의 열처리 조건을 조절하여 우수한 연신율 및 도금 특성을 가짐과 아울러 고강도 특성을 만족함으로써, 원가를 절감할 수 있으며 제품의 품질을 대폭 향상시킬 수 있는 유용한 효과를 갖는다.The present invention relates to a high-strength cold-rolled steel sheet having a strength of 980 MPa or more and excellent in plating properties and a method of manufacturing the same. According to the present invention, the present invention has excellent elongation and plating properties by controlling an alloying element and heat treatment conditions during manufacturing. In addition, by satisfying the high strength characteristics, it is possible to reduce the cost and have a useful effect to significantly improve the quality of the product.
본 발명에서는 강의 주요성분인 탄소함량을 줄이고 대신에 부족한 강도를 향상시키기 위해 망간, 실리콘, 알루미늄을 증가시켜 인장강도와 연신율을 만족시키고, 또한 뛰어난 도금특성을 확보하기 위해 구리, 니켈, 안티몬을 첨가시켜 도금성을 향상시키고 동시에 소입성을 향상시키기 위해 몰리브덴에 비해 상대적으로 값이 싼 크롬을 첨가함으로써 베이나이트나 펄라이트변태를 일어나지 않게 설계하였고 보론을 소량 첨가하여 결정립을 미세화하고 재질 편차를 줄이고자 한 것이다. In the present invention, in order to reduce the carbon content, which is the main component of the steel, and to improve the insufficient strength, instead of increasing the manganese, silicon, aluminum to satisfy the tensile strength and elongation, and also to add copper, nickel, antimony to secure excellent plating properties In order to improve the plating property and at the same time to improve the hardenability, chromium, which is relatively inexpensive than molybdenum, is added to prevent bainite or pearlite transformation, and a small amount of boron is added to refine grains and reduce material variation. will be.
이때 미세조직은 평균입계사이즈가 5-10㎛인 페라이트가 60-70%로 상이 형성되고 제 2상(마르텐사이트 포함)이 30-40%로 구성하여 강도와 연성의 균형을 맞추고자 하였다.At this time, the microstructure of the ferrite having an average grain size of 5-10㎛ was formed in 60-70% phase and the second phase (including martensite) composed of 30-40% to balance the strength and ductility.
본 발명은 중량%로, C: 0.10~0.15%, Si: 0.01~0.25%이하, Mn: 2.4~2.8%, S: 0초과 0.005%이하, P: 0초과 0.01% 이하, Al: 0초과 0.05% 이하, Cr: 0.25~0.5%, Cu: 0.10~0.30%, Ni: 0.05~0.20%, Nb: 0.04~0.06%, B:0.0005~0.0015%, Sb:0.02~0.05%, N: 0초과 0.006%이하를 함유하고, 나머지 잔부가 Fe 및 불가피적으로 포함되는 불순물로 이루어진 강슬라브를 균질화 요구온도인 1200℃ 이상의 온도로 재가열하여 2-3시간 유지하고, Ac3+30℃ 이상의 온도에서 열간 마무리압연을 행한 후 580-640℃에서 강판 코일 형태로 권취한다.The present invention is in weight%, C: 0.10 to 0.15%, Si: 0.01 to 0.25% or less, Mn: 2.4 to 2.8%, S: greater than 0 and less than 0.005%, P: greater than 0 and 0.01% or less, Al: greater than 0 and 0.05 % Or less, Cr: 0.25-0.5%, Cu: 0.10-0.30%, Ni: 0.05-0.20%, Nb: 0.04-0.06%, B: 0.0005-0.0015%, Sb: 0.02-0.05%, N: more than 0.006 The steel slab containing less than% and the remainder of Fe and inevitably contained impurities is reheated to a temperature equal to or higher than 1200 ° C. for a homogenization temperature, and maintained for 2-3 hours, and hot-rolled at a temperature of Ac 3 + 30 ° C. or higher. After winding, it is wound in the form of a steel sheet coil at 580-640 ° C.
열간압연 처리된 강판 코일을 산세처리하여 50%이상의 압하율로 냉간압연을 실시한다. The hot rolled steel coils are pickled and cold rolled at a rolling reduction of 50% or more.
냉간압연된 강판 코일을 780-820℃ 영역에서 5-120초간 유지하여 소둔 처리한 후, 5℃/s 속도로 480℃이하 온도까지 냉각처리한다. The cold rolled steel coil is maintained at 780-820 ° C. for 5 to 120 seconds, followed by annealing, and then cooled to a temperature of 480 ° C. or lower at a rate of 5 ° C./s.
그런 과정을 거친 후 용융아연도금처리를 실시하고 460-510℃의 온도영역으로 재가열하여 용융아연도금피막의 합금화를 실시한 후 20℃/s 이상의 냉각속도로 300℃까지 급냉처리한다. After such a process, the hot dip galvanizing treatment is performed and reheated to a temperature range of 460-510 DEG C to alloy the hot dip galvanized coating, and then quenched to 300 DEG C at a cooling rate of 20 DEG C / s or more.
입계사이즈가 5-10㎛인 페라이트가 60-70%로 형성되어 있고 제 2상으로 마르텐사이트를 포함한 상이 30-40%로 형성되어 프레스 가공성과 도금성이 우수한 인장강도 980MPa이상 고강도 냉연강판의 제조방법에 관한 것이다.Manufactured high strength cold rolled steel sheet with a tensile strength of 980 MPa or more with excellent press formability and plating property by forming 60-70% ferrite with grain size of 5-10㎛ and 30-40% with martensite as second phase It is about a method.
이하에서는 본 발명 강판을 구성하는 합금원소에 대해 설명한다.Hereinafter, the alloying elements constituting the steel sheet of the present invention will be described.
탄소[C]: 0.10~0.15 wt%Carbon [C]: 0.10 ~ 0.15 wt%
탄소(C)원소는 강판의 강도를 증가시키기 위해 필수적으로 첨가하는 원소로써 소망하는 강도를 얻기위해 0.10% 이상 첨가한다. 단, 0.15%를 초과하면 스폿용접성이 저하되고 용접성 및 인성이 저하될 수 있으므로 그 상한치를 0.15%로 한다. Carbon (C) element is an essential element to increase the strength of the steel sheet, 0.10% or more to obtain the desired strength. However, if it exceeds 0.15%, the spot weldability may be lowered and the weldability and toughness may be lowered, so the upper limit thereof is made 0.15%.
실리콘[Si]: 0.01~0.25 wt%Silicon [Si]: 0.01 ~ 0.25 wt%
실리콘은 강판의 연성을 저하시키지 않으면서 강도를 향상시킬 수 있는 유용한 원소이다. 페라이트에 고용되는 페라이트 안정화 원소로 강도에 기여하며 미변태 오스테나이트로의 탄소 농화를 조장하므로써 마르텐사이트 형성을 촉진시킨다. 그러나 본 발명에서는 과잉으로 첨가하면 도금특성을 떨어뜨리는 작용을 하기 때문에 되도록 적게 첨가하는 것이 바람직하다. 따라서 그 상한치를 0.25%로 한다. 또한 0.01% 미만인 경우 페라이트의 강도가 감소하고 탄화물 억제효과가 감소하므로 0.01% 이상 첨가한다.Silicon is a useful element that can improve the strength without lowering the ductility of the steel sheet. Ferrite stabilizing element employed in ferrite contributes to strength and promotes martensite formation by encouraging carbon enrichment with unmodified austenite. However, in the present invention, it is preferable to add as little as possible because excessively acts to degrade the plating properties. Therefore, the upper limit is made into 0.25%. In addition, if less than 0.01%, the strength of the ferrite is reduced and the carbide inhibiting effect is reduced, so 0.01% or more is added.
망간[Mn]: 2.4~2.8 wt%Manganese [Mn]: 2.4 ~ 2.8 wt%
망간은 고용강화와 소입성을 개선하는 효과를 통해 강도를 증가시키는 원소로 오스테나이트 안정화 원소이다. Mn의 저감화가 아니고 그 대신 C의 저감화에 의해 스폿용접성을 향상시키고자 하는 것으로, 본 발명에서는 C 함량을 줄여서 우수한 스폿용접성과 재료안정성을 얻도록 한다.. Manganese is an austenite stabilizing element that increases strength through the effect of strengthening solid solution and improving hardenability. In order to improve spot weldability by reducing C instead of reducing Mn, the present invention reduces C content to obtain excellent spot weldability and material stability.
이러한 사항들을 감안하여 Mn 함유량은 특히 바람직하게는 가급적 2.4% 이상 첨가하고 과도하게 많이 첨가되는 경우 용접성, 도금성이 저하되고, 개재물 형성에 의해 수소유기 취성을 야기하며, 열간압연 시 판재 중앙에 편석대를 형성하므로 최대 2.8 wt% 이하로 제한한다.In view of these considerations, the Mn content is particularly preferably added in an amount of 2.4% or more and excessively high, and thus the weldability and plating property are deteriorated, and hydrogen organic embrittlement is caused by inclusion formation. As it forms a stone slab it is limited to a maximum of 2.8 wt% or less.
황[S]: 0초과 0.005 wt% 이하Sulfur [S]: greater than 0 and less than 0.005 wt%
황[S]이 0.01 wt%를 초과할 경우 유화물계 개재물을 형성하고, 크랙 등의 발생원인이 되며, 또한 본 발명에서는 Mn을 다량첨가하고 있으므로 S량은 더욱 적은 것이 좋기 때문에, 그 상한치를 0.005%로 한다.When sulfur [S] exceeds 0.01 wt%, it forms an emulsion-based inclusion and causes cracks, etc. In addition, in the present invention, since Mn is added in a large amount, the amount of S is better, so the upper limit is 0.005. %.
인[P]: 0초과 0.01 wt% 이하Phosphorus [P]: greater than 0 and less than 0.01 wt%
P는 재료의 강도확보에 유용한 원소이며, 그러나 다량으로 첨가하면 가공성이 저하할 뿐 아니라 용접성도 저하되므로 그 상한치를 0.01%로 한다.P is an element useful for securing the strength of the material. However, if a large amount is added, not only the workability is lowered but also the weldability is lowered, so the upper limit thereof is made 0.01%.
알루미늄[Al]: 0초과 0.05 wt% 이하Aluminum [Al]: greater than 0 and 0.05 wt% or less
Al는 탈산제로서 유용한 원소이고 연신율을 개선하는 효과가 있지만 다량 첨가하면 탈산제로서의 작용이 포화되여 경제적으로 효용이 없고 도금 불량을 유발하지 않고 페라이트 형과 오스테나이트상 중의 C확산을 촉진하므로 0.05%이하로 첨가하여야 한다. Al is a useful element as a deoxidizer and has an effect of improving elongation.However, when a large amount is added, the action as a deoxidizer is saturated, so it is economically ineffective and promotes C diffusion in ferrite type and austenite phase without causing plating defects. Must be added.
크롬[Cr]: 0.25~0.5 wt% Chromium [Cr]: 0.25-0.5 wt%
Cr은 페라이트 형성원소로서 오스테나이트를 펄라이트나 베이나이트로 변태하는 것을 지연하여 이상역 소둔 후 오스테나이트가 상온에서 마르텐사이트로 변태시키는 효과가 있고 강도를 향상시키는 역할을 한다. 0.25% 미만으로 첨가 되면 충분한 강도를 얻기 힘들고 0.5%를 초과하여 첨가할 때는 강도와 연성의 균형이 깨지는 문제가 발생한다.Cr is a ferrite forming element that delays the transformation of austenite into pearlite or bainite, and has an effect of transforming austenite into martensite at room temperature after annealing in an anomaly manner and improves strength. If it is added below 0.25%, it is difficult to obtain sufficient strength, and when it is added above 0.5%, there is a problem that the balance between strength and ductility is broken.
구리[Cu]: 0.1~0.3 wt%Copper [Cu]: 0.1-0.3 wt%
Cu는 강도향상 효과가 있지만 열간취성을 유발할 수 있는 문제점이 있기 때문에 적정량을 첨가하여야 하고 0.3%를 초과하여 함유할 경우 고가의 Ni를 1:1 비율로 첨가하여야 하기 때문에 경제성이 저하되므로 0.15~0.3%로 한정하는 것이 바람직하다. 또한 Mn, Si 등이 다량 함유된 강종에 Ni과 복합 첨가할 경우 Mn, Si 등의 산화물이 도금표면으로 산화되는 것을 억제하고 내부산화를 일으켜 도금특성을 개선하는 효과가 있다.Cu has the effect of improving strength, but there is a problem that can cause hot brittleness, so it is necessary to add an appropriate amount, and if it contains more than 0.3%, expensive Ni must be added in a ratio of 1: 1, and thus economic efficiency is deteriorated. It is preferable to limit to%. In addition, when a composite addition with Ni is applied to steel grades containing a large amount of Mn and Si, oxides such as Mn and Si are prevented from being oxidized to the plating surface, and internal oxidation is caused to improve plating characteristics.
니켈(Ni): 0.05~0.2 wt%Nickel (Ni): 0.05-0.2 wt%
니켈은 강도 증가 및 내식성 향상을 위해 Cu 첨가시 발생되는 적열취성을 막기 위한 원소로서 첨가된다. 보통 Cu : Ni = 1 : 1~2 의 비율로 첨가시 효과가 좋다고 알려져 있다. 또한 Cu와 적절히 첨가시 도금성이 개선된다. 0.05wt%이하로 첨가되면 소기의 목적을 발성하기 힘들고 0.2wt%를 초과하여 첨가할 경우는 경제적 측면에서 불리하기 때문에 Cu 첨가량에 맞춰 적정량을 첨가하는 것이 중요하다.Nickel is added as an element to prevent the heat brittleness generated when Cu is added to increase strength and improve corrosion resistance. Usually, it is known that the effect is good when added in the ratio of Cu: Ni = 1: 1-2. In addition, when properly added with Cu, the plating property is improved. If it is added below 0.05wt%, it is difficult to achieve the desired purpose, and when it exceeds 0.2wt%, it is important to add an appropriate amount in accordance with the Cu addition amount because it is disadvantageous in terms of economics.
안티몬[Sb]:0.02~0.05 wt%Antimony [Sb]: 0.02 ~ 0.05 wt%
Sb는 고온에서 원소 자체가 산화피막을 형성하지는 않지만 표면 및 결정립 계면에 농화되어 강중 Mn, Si이 표면에 확산되는 것을 억제시켜 산화물 형성을 조절할 수 있는 기능을 가지고 있다. 소둔공정 중 산화물 생성을 억제하여 도금 특성을 개선시키며 도금재 표면에 덴트 결함을 억제하는데 효과적이다. 하지만 너무 많이 첨가하였을 경우 재질 특성이 열화되는 경향이 있기 때문에 적절히 첨가하는 것이 바람직하다. 안티몬 함량을 0.02wt% 미만으로 첨가할 경우 상기한 효과를 발휘하기 힘들고 0.05wt%를 초과하여 첨가할 경우 연성이 저하되어 재질이 열화되는 경향이 있어 제한하여야 한다.Sb does not form an oxide film itself at high temperature, but is concentrated on the surface and grain interface, and has a function of controlling oxide formation by suppressing diffusion of Mn and Si in the surface. It is effective in suppressing dent defects on the surface of plating material by improving oxide plating by suppressing oxide generation during annealing process. However, when added too much, the material properties tend to deteriorate. If the antimony content is added less than 0.02wt%, it is difficult to achieve the above effects, and if it is added exceeding 0.05wt%, the ductility is lowered and the material tends to be deteriorated.
니오븀[Nb]:0.04-0.06wt%Niobium [Nb]: 0.04-0.06 wt%
Nb는 Nb(CN)과 NbC 석출물을 형성하여 열간압연과 이상역소둔 시 입계성장을 가로막아 미세한 입계사이즈를 형성한다. 고용원소로 Nb는 강도향상 역할을 하고 오스테나이트가 펄라이트나 베이나이트로 변태하는 것을 막아준다. 0.06%를 초과하여 첨가할 경우 연성을 감소시키는 문제가 있고 0.04% 미만으로 첨가할 경우에는 강화효과를 발휘할 수 없다.Nb forms Nb (CN) and NbC precipitates to prevent grain boundary growth during hot rolling and annealing annealing to form fine grain size. As an employment element, Nb acts as a strength enhancer and prevents austenite from transforming to pearlite or bainite. When added in excess of 0.06%, there is a problem of reducing ductility, and when added in less than 0.04%, the strengthening effect cannot be exerted.
보론[B]: 0.0005-0.0015wt%Boron [B]: 0.0005-0.0015wt%
B는 입계강화원소로서 점용점부의 피로특성을 향상시키고 입계취성을 방지 하는 효과가 있다. 또한 Al 및 Si 함량이 높은 강종을 제조할 때 고온연성을 향상시키는 효과가 있다. 또한 소둔 중 냉각하는 과정에서 오스테나이트가 펄라이트로 변태를 지연시키는 기능을 수행하는데 0.0005%이상 첨가하여야 효과를 볼 수 있으며, 0.0015%를 초과하여 첨가할 경우 도금특성이 현저히 감소하는 경향이 있다. B is a grain boundary strengthening element, and has an effect of improving fatigue characteristics of the spot spot and preventing grain brittleness. In addition, there is an effect of improving the high-temperature ductility when manufacturing a high steel content of Al and Si. In addition, in the cooling process during annealing, the austenite may be added to 0.0005% or more to perform the function of delaying transformation into pearlite, and when added in excess of 0.0015%, the plating property tends to be significantly reduced.
질소[N]:0초과 0.006%이하Nitrogen [N]: more than 0 and less than 0.006%
N은 연성에 악영향을 주는 원소로써 가급적 낮게 유지하는 것이 유리하고 단, N가 과잉으로 존재하면, 질화물이 다량으로 석출하고, 연성의 열화를 일으키기 쉬우므로 N량은 0.0060% 이하로 억제하는 것이 바람직하다.N is an element which adversely affects ductility, and it is advantageous to keep it as low as possible. However, when N is present in excess, it is preferable to deposit a large amount of nitride and cause ductility deterioration, so that N amount is preferably controlled to 0.0060% or less. Do.
본 발명상의 강판은 상기 성분을 함유하고, 잔부는 실질적으로 철(Fe) 및 불가피불순물이며, 원료, 자재, 제조설비 등의 상황에 따라, 들어가는 원소로서 0.01% 이하의 산소(O) 등 불가피한 불순물의 혼입도 허용된다.The steel sheet of the present invention contains the above components, and the balance is substantially iron (Fe) and unavoidable impurities, and inevitable impurities such as oxygen (O) of 0.01% or less as elements to be entered depending on the situation of raw materials, materials, manufacturing facilities, and the like. Incorporation of is also allowed.
본 발명상의 제조되는 강판의 미세조직은 페라이트와 마르텐사이트(베이나이트)를 포함한 제 2상으로 구성된다. 입계사이즈가 5-10㎛인 페라이트상이 60%이하로 구성되면 연성과 프레스가공성을 낮아지는 문제가 발생되고 페라이트가 70%이상 형성되면 강도 확보가 곤란하기 때문에 페라이트 상분율을 60-70%로 한정한다.The microstructure of the steel sheet produced according to the present invention is composed of a second phase including ferrite and martensite (bainite). If ferrite phase with grain size of 5-10㎛ is less than 60%, ductility and press workability will be lowered. If ferrite is formed more than 70%, it is difficult to secure strength, so the ferrite phase fraction is limited to 60-70%. do.
상기와 같이 조성을 갖는 슬라브는 용강을 용제하고 통상적인 공지의 방법으로 주조하여 통상적인 공지의 방법으로 열간압연하고 다시 냉간압연하여 소둔, 도 금 처리하여 강판을 제조한다. The slabs having the composition as described above are molten steel, cast in a conventional known method, hot rolled by a conventional known method, cold rolled again, annealing, plating to produce a steel sheet.
아래에서는 각 공정들에 대해 구체적으로 설명하기로 한다.Hereinafter, each process will be described in detail.
가열로 공정Furnace process
슬라브를 가열하는 공정은 주조시 편석된 성분을 재고용하기 위한 것으로, 재가열온도가 낮은 경우 편석된 성분이 재고용되지 못하며, 과도하게 높게 하면, 오스테나이트 결정입도가 증가하여 페라이트 입도가 조대화되면서 강도가 감소하게 된다. The slab heating process is for reusing the segregated components during casting. If the reheating temperature is low, the segregated components cannot be reclaimed. When the slab is excessively high, the austenite grain size increases and the ferrite grain size is coarsened to increase the strength. Will decrease.
또한 슬라브 두께에 따라 재가열 온도 유지시간을 조절할 필요가 있어 두께가 두꺼워질수록 재가열시간을 길게 유지하고 두께가 얇아질수록 유지시간을 짧게 할 필요가 있다. In addition, it is necessary to adjust the reheating temperature holding time according to the slab thickness, so that the thicker the thickness, the longer the reheating time and the thinner the thickness, the shorter the holding time.
적정유지시간은 2-3시간 정도 유지하는 것이 바람직하고 그 이상 유지할 경우 경제적으로 손해를 볼 수가 있고 너무 짧으면 재질의 균질화 정도가 떨어져 품질이 나빠지는 문제가 발생할 수 있다.It is preferable to maintain the proper holding time for 2-3 hours, and if it is kept longer, economic loss may occur, and if it is too short, the quality of the material may be degraded due to the homogenization of the material.
열간/냉간 압연 공정Hot / cold rolling process
상기와 같이 제조되는 슬라브는 Ac3+30℃에서 열간압연을 마무리하는 것이 좋다. ESlab prepared as described above is good to finish hot rolling at Ac3 + 30 ℃. E
이는, Ac3+30℃ 이하에서 압연할 경우 과도한 전위가 페라이트 내에 도입되어 냉각 혹은 권취 중에 성장하여 표면에 조대한 결정립을 형성하기 때문이다. This is because when rolling at Ac 3 + 30 ° C. or lower, excessive dislocations are introduced into the ferrite and grow during cooling or winding to form coarse grains on the surface.
그러나 930℃ 이상의 온도에서 마무리 압연할 경우에는 페라이트 결정입도가 증가하여 강도가 감소할 우려가 있다. However, when the finish rolling at a temperature of 930 ℃ or more there is a fear that the ferrite grain size increases and the strength decreases.
권취 공정은 640℃ 이하 580℃ 이상온도에서 행해지는 것이 좋다. The winding step is preferably performed at a temperature of 640 ° C or lower and 580 ° C or higher.
권취온도가 너무 높을 경우, 다량 함유된 Mn, Si, Cr가 편석을 발생시킬 수 있고 원하는 강도와 가공성을 얻기 힘든 단점이 있다. If the coiling temperature is too high, a large amount of Mn, Si, Cr may cause segregation and it is difficult to obtain desired strength and workability.
열간압연 후 산세처리 후 압하율 50%이상으로 냉간압연을 실시한다After hot rolling, pickling is performed and cold rolling is performed with a reduction ratio of 50% or more.
연속 소둔조건Continuous Annealing Condition
강도와 연성의 균형을 맞추기 위해 페라이트와 마르텐사이트(베이나이트)의 분율을 제어한다. The proportion of ferrite and martensite (bainite) is controlled to balance strength and ductility.
본 발명의 냉연판은 강도와 연신율이 동시에 확보되어야 하므로, 강도는 마르텐사이트의 분율로 제어하고, 연신율은 주로 페라이트 분율로 제어하는 것이 바람직하다. In the cold rolled sheet of the present invention, strength and elongation must be secured at the same time, the strength is preferably controlled by the fraction of martensite and the elongation is mainly controlled by the ferrite fraction.
합금화용융아연도금강판을 제조할 경우 790-830℃ 영역에서 5-120초간 유지한 후 5℃/s 이상의 냉각속도로 480℃ 온도까지 냉각한다. When manufacturing hot-dip galvanized steel sheet is maintained for 5 to 120 seconds in the 790-830 ℃ area and then cooled to a temperature of 480 ℃ at a cooling rate of 5 ℃ / s or more.
이 공정 중에 이상영역에서 생성된 오스테나이트 상이 펄라이트나 베이나트 상으로 변태하지 못하게 충분한 냉각속도로 냉각하는 것이 중요하다. During this process, it is important to cool the austenite phase produced in the abnormal region at a sufficient cooling rate to prevent transformation into a pearlite or bainite phase.
790-830℃ 영역에서 5초 이상 유지하는 것은 가열 중 오스테나이트 상이 충분히 형성되지 않기 때문에 적정량의 마르텐사이트 분율을 얻을 수 없고 120초 이상 초과할 경우에는 생산성이 떨어지는 문제점이 있다. 480℃ 이하까지 냉각한 코 일을 460℃에서 도금 처리 후 480-520℃ 영역까지 재가열하여 합금화처리한 후 300℃이하 까지 20℃/s 이상의 냉각속도로 냉각하여 강판을 제조한다.Maintaining at least 5 seconds in the region of 790-830 ℃ can not obtain the appropriate amount of martensite fraction because the austenite phase is not sufficiently formed during heating, there is a problem that the productivity is lowered if it exceeds 120 seconds. Coils cooled to 480 ° C. or lower are then reheated to 480-520 ° C. after alloying at 460 ° C., and then alloyed, and cooled to 300 ° C. or lower at a cooling rate of 20 ° C./s or more to produce steel sheets.
표 1은 본 발명의 발명강과 비교강의 화학 성분을 나타낸 것이다.Table 1 shows the chemical components of the inventive steel and the comparative steel of the present invention.
여기서 본 발명의 발명강은 실시 번호 1,3,7에 해당되며, 번호 2,4,5,6,8,9의 비교강은 각각 합금원소의 비율을 달리하여 실험한 것이다.Here, the inventive steel of the present invention corresponds to the practice numbers 1, 3, and 7, and the comparative steels of the numbers 2, 4, 5, 6, 8, and 9 are tested by varying the ratio of alloying elements, respectively.
이러한 조성을 갖는 발명강과 비교강의 잉곳을 1250 ℃에서 2시간 가열하여 마무리 열간 압연한 다음에, 590~620℃로 급냉하고 약 1시간 유지하여 노냉하여 열간 압연을 행한 후에, 산세 처리하고 50% 압하율로 냉간압연을 실시한다.Ingots of the inventive steels and the comparative steels having such a composition were heated at 1250 ° C. for 2 hours to finish hot rolling, and then quenched at 590 to 620 ° C. for about 1 hour to be quenched and hot rolled, followed by pickling treatment and 50% reduction ratio. Cold rolling is carried out with
이어서, 790~830℃에서 소둔 처리한 후에 460℃까지 급냉 처리하고, 도금욕에 담근 후에 490~510℃에서 합금 처리한 후에 기계적 성질을 측정하였다.Subsequently, after annealing at 790-830 degreeC, it quenched to 460 degreeC, immersed in the plating bath, and after alloying at 490-510 degreeC, the mechanical property was measured.
그 측정 결과는 아래의 표 2에서와 같다.The measurement results are shown in Table 2 below.
도금성 : 양호(○), 보통(◆), 불량(×)Plating property: Good (○), Normal (◆), Poor (×)
즉, 본 발명의 발명강은 강도를 확보하기 위한 탄소의 함량을 줄이고 대신 망간, 실리콘, 알루미늄의 합금 원소 비율을 증가시키고, 이에 구리(Cu), 니켈(Ni), 안티몬(Sb)의 원소를 첨가하여 도금 특성을 향상시키며, 보론을 소량 첨가시켜 결정립을 미세하화함과 아울러, 소입성을 향상시키기 위해 크롬을 첨가하여 베이나이트나 펄라이트 변태를 억제시킨 것이다.That is, the invention steel of the present invention reduces the content of carbon to secure the strength, and instead increases the ratio of alloying elements of manganese, silicon, and aluminum, thereby reducing the elements of copper (Cu), nickel (Ni), and antimony (Sb). It is added to improve the plating properties, and a small amount of boron is added to reduce the crystal grains, and chromium is added to improve the hardenability to suppress bainite or pearlite transformation.
이에 반해, 비교강은 표 2에서와 같이, 주성분인 탄소의 함량을 줄인 번호 2,6 비교강의 경우 강도가 매우 저하되고, 그외 다른 비교강도 발명강에 비해 강도 및 연신율이 저하되고, 특히 구리, 니켈, 안티몬의 원소가 투입되지 않은 5,8 비교강의 경우 도금성이 불량한 것을 알 수 있다.On the contrary, the comparative steels, as shown in Table 2, have a very low strength in the case of No. 2 and 6 comparative steels in which the content of carbon as the main component is reduced, and the strength and elongation of the comparative steels are lower than those of the other comparative strength steels. It can be seen that the plating properties are poor in the case of 5,8 comparative steels in which nickel and antimony elements are not added.
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