KR100481366B1 - A hot rolled trip steel sheet with excellent ductility, and a method for manufacturing it - Google Patents

A hot rolled trip steel sheet with excellent ductility, and a method for manufacturing it Download PDF

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KR100481366B1
KR100481366B1 KR10-2000-0074583A KR20000074583A KR100481366B1 KR 100481366 B1 KR100481366 B1 KR 100481366B1 KR 20000074583 A KR20000074583 A KR 20000074583A KR 100481366 B1 KR100481366 B1 KR 100481366B1
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steel
strength
hot rolled
elongation
temperature range
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KR20020045212A (en
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박성호
백승철
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주식회사 포스코
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

본 발명은 자동차 부품등과 같은 가공용 고장력강에 적용되는 열연 변태유기소성강판 및 그 제조방법에 관한 것으로, 강 성분중 N을 첨가해 AlN의 석출에 의한 고강도 및 고연성을 확보함으로써, 제조공정 중 기타의 열처리공정없이도 인장강도 80kg/mm2 이상이고 연신율 30% 이상인 열연 변태유기소성강판, 및 그 제조방법을 제공하고자 하는데, 그 목적이 있다.The present invention relates to a hot rolled metamorphic organic plastic sheet applied to high tensile strength steel for processing such as automobile parts and the like, and to a method of manufacturing the same, by adding N in the steel component and securing high strength and high ductility due to the precipitation of AlN. To provide a hot rolled transformation organic plastic sheet having a tensile strength of 80kg / mm 2 or more and an elongation of 30% or more, and a method of manufacturing the same, without a heat treatment process.

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

중량%로, C: 0.15~0.30%, Si: 1.5~2.5%, Mn: 1.4~1.8%, Al: 0.02~0.10%, N: 0.0080~0.0120%, 잔부 Fe 및 기타 불가피한 불순물로 조성되는 강을 재가열한 후 850~900℃의 온도범위에서 마무리압연한 다음, 670~710℃의 온도범위에서 수냉을 개시하여 420~540℃의 온도범위에서 종료한 후, 서냉하는 것을 포함하여 이루어지는 열연 변태유기소성강판의 제조방법, 및 상기와 같이 조성되고, 인장강도가 80kg/mm2이상이면서 연신율이 30%이상인 연성이 우수한 열연 변태유기소성 강판을 그 기술적 요지로 한다.By weight%, C: 0.15 to 0.30%, Si: 1.5 to 2.5%, Mn: 1.4 to 1.8%, Al: 0.02 to 0.10%, N: 0.0080 to 0.0120%, remainder Fe and other inevitable impurities After reheating, finish rolling at a temperature range of 850 to 900 ° C., and then start water cooling at a temperature range of 670 to 710 ° C. and finish at a temperature range of 420 to 540 ° C., followed by slow cooling. The technical gist of the method for producing a steel sheet and a hot rolled metamorphic organic plastic sheet having a tensile strength of 80 kg / mm 2 or more and excellent elongation of 30% or more in elongation is set as the technical gist.

Description

연성이 우수한 열연 변태유기소성강판 및 그 제조방법{A HOT ROLLED TRIP STEEL SHEET WITH EXCELLENT DUCTILITY, AND A METHOD FOR MANUFACTURING IT}Hot-rolled ductile organic plastic sheet with excellent ductility and its manufacturing method {A HOT ROLLED TRIP STEEL SHEET WITH EXCELLENT DUCTILITY, AND A METHOD FOR MANUFACTURING IT}

본 발명은 자동차 부품등과 같은 가공용 고장력강에 적용되는 열연 변태유기소성강판 및 그 제조방법에 관한 것으로, 보다 상세하게는 강중 N을 첨가함으로써 고강도와 더불어 연성의 향상도 이룰 수 있는 열연 변태유기소성강판 및 그 제조방법에 관한 것이다.The present invention relates to a hot rolled modified organic plastic sheet applied to high tensile strength steel such as automobile parts and the like, and more particularly to a hot rolled modified organic plastic sheet which can achieve high strength and ductility by adding N in steel. And to a method for producing the same.

변태유기소성강(TRIP강, 즉 TRansformation Induced Plasticity강의 약어임)은, 기본적으로 Si-Mn형 강재로서 스크랩재활용중 미량잔류원소(tramp element)의 영향이 없으므로 환경친화적이다. 또한, 일반적인 압연강재에 비해 훨씬 높은 범위의 고강도와 더불어 고연성을 보이므로, 가공용 고장력강의 용도로 많이 활용되고 있고, 차세대 강재로 주목 받고 있다. 특히, 최근 들어 자동차의 배기가스에 대한 환경오염 문제가 크게 대두되면서 연비향상은 자동차업계의 가장 중요한 기술개발 방향이 되었다. 이러한 연비향상을 위해서는 고강도 소재를 채용하여 자동차 경량화를 이루는 것이 매우 중요한데, 이와 같은 고강도 소재를 사용하여 경량 자동차 부품을 개발하기 위해서는, 강도뿐만 아니라 부품의 가공을 성공적으로 행할 수 있는 소재가공성이 요구된다. Metamorphic organic plastic steel (TRIP, ie TRansformation Induced Plasticity steel) is basically Si-Mn type steel, which is environmentally friendly because it does not affect the trace element during scrap recycling. In addition, since it exhibits high strength and high ductility in a much higher range than general rolled steels, it is widely used as a high tension steel for processing and attracts attention as a next generation steel. In particular, as the environmental pollution problem of automobile exhaust gas has recently emerged, fuel efficiency improvement has become the most important technology development direction of the automobile industry. In order to improve fuel efficiency, it is very important to reduce the weight of automobiles by using high-strength materials. To develop lightweight automobile parts using such high-strength materials, not only the strength but also the material processing ability to successfully process the components are required. .

한편, 고강도 고연성 열연강판은 상당히 많은 종류의 제조방법이 개발되어 실제 제품화에 응용되어 왔다. 기존의 고강도 고연성강의 개발은, 80년대에 듀얼 페이즈(dual phase)강(페라이트와 마르텐사이트의 복합조직), 트리페이즈(triphase강)(페라이트, 베이나이트 및 마르텐사이트의 복합조직), 페라이트-베이나이트 복합조직강 등에 대하여 주로 행해졌다. 이러한 강재는 인장강도가 약 60kg/mm2에 이르고 있으며, 연신율이 약 30%로 고강도와 더불어 고연성을 보이는 특성이 있다. 90년대에 들어 TRIP강이 개발되어 현재에는 상용화를 위해 노력하고 있는데, 인장강도가 약 80kg/mm2에 이르고 있으며, 고연성을 나타내는 것이다.On the other hand, high strength high ductility hot rolled steel sheet has been developed in a considerable number of manufacturing methods have been applied to the actual commercialization. The development of existing high strength, high ductility steels, dual phase steel (composite structure of ferrite and martensite), triphase steel (composite structure of ferrite, bainite and martensite), ferrite in the 80s Primarily for bainite composite steels and the like. These steels have a tensile strength of about 60kg / mm 2 , an elongation of about 30%, and high strength and high ductility. TRIP steel has been developed in the 90's and is currently working to commercialize. Tensile strength is about 80kg / mm 2 and shows high ductility.

이와 같이 TRIP강에서 고강도와 고연성을 얻기 위한 관련기술로서, 일본특개평6-1458920호에서는, 06-0.22%C, 0.05-1.0%SI, 0.5-2.0%Mn과 0.25-1.5%Al을 함유한 강에 필요에 따라 0.03-0.30%Mo을 첨가하여 잔류오스테나이트를 3-20% 함유시킴에 따라 50kg/mm2이상의 고강도와 35%이상의 연신율을 갖는 프레스가공성과 심가공성 및 굽힘성이 우수한 강을 제안하고 있다. 또한, 일본특개평6-145788호에서는, Al양을 0.6%Si≤%Al ≤3-12.5x%C의 범위로 조정하고, 2상영역에서 열처리(650-900℃에서 10초 내지 3분간 유지후 350-600℃의 온도범위까지 4-200℃/sec로 냉각후 여기에서 5초 내지 10분간 유지한 다음 5℃/sec이상의 냉각속도로 250℃이하의 온도로 냉각하는 방법)함으로써 가공성이 우수한 강재를 생산하는 제조법을 제안하고 있다.As a related art for obtaining high strength and high ductility in TRIP steel, Japanese Patent Laid-Open No. 6-1458920 contains 06-0.22% C, 0.05-1.0% SI, 0.5-2.0% Mn and 0.25-1.5% Al. Steel with excellent press workability, deep workability and bendability with high strength of 50kg / mm 2 and elongation of 35% by adding 0.03-0.30% Mo to 3-20% of residual austenite as needed Is proposing. In Japanese Patent Laid-Open No. 6-145788, the amount of Al is adjusted in the range of 0.6% Si≤% Al≤3-12.5x% C, and the heat treatment in the two-phase region is maintained for 10 seconds to 3 minutes at 650-900 ° C. After cooling to 4-200 ℃ / sec to a temperature range of 350-600 ℃ and then maintained for 5 seconds to 10 minutes and then cooled to a temperature below 250 ℃ at a cooling rate of 5 ℃ / sec or more) We propose a production method for producing steel.

또한, 일본특개평5-179396호에서는, 0.18%이하의 C, 0.5-2.5%Si, 0.5-2.5%Mn, 0.05%이하의 P, 0.02%이하의 S, 0.01-0.1%Al의 강에 0.02-0.5%Ti과 0.03-1.0%Nb를 단독 또는 복합적으로 첨가하며 (이때 C, Nb와 Ti의 첨가량은 %C>(%Ti/4)+(%Nb/8)의 범위내로 조정함), 사상압연온도를 820℃이상에서 마친 다음 820-720℃의 온도구간에서 10초이상을 유지하고 이후 10℃/sec이상의 냉각속도로 냉각하여 500℃이하의 온도에서 권취하는 방법을 제출한 바 있다. 상기 기술에 의하면 70kg/mm2이상의 인장강도, 우수한 스팟용접성 및 피로특성 등을 제공할 수 있고 프레스가공후 스프링 백이 많아 생기는 문제를 해결할 수 있으며, 우수한 연신 플랜지성을 제공할 수 있다고 한다.In Japanese Patent Laid-Open No. 5-179396, 0.02 or less C, 0.5-2.5% Si, 0.5-2.5% Mn, 0.05% or less P, 0.02% or less S, 0.01-0.1% Al steel, 0.02 -0.5% Ti and 0.03-1.0% Nb are added alone or in combination (wherein C, Nb and Ti are added in the range of% C> (% Ti / 4) + (% Nb / 8)), After finishing the finishing rolling temperature at 820 ℃ and above, the method maintains more than 10 seconds in the temperature range of 820-720 ℃, and then cools it with cooling rate of 10 ℃ / sec or more and winds it up at the temperature below 500 ℃. According to the above technique, it is possible to provide a tensile strength of 70 kg / mm 2 or more, excellent spot weldability and fatigue characteristics, to solve the problem of a large number of spring back after press working, and to provide excellent stretch flangeability.

또한, 일본특개평5-112846호에서는, 0.05-0.25%C, 0.05-1.0%Si, 0.8-2.5%Mn, 0.8-2.5%Al을 함유하는 강에 Nb, Ti 및 V 등의 석출강화 원소를 첨가한 강을 780-840℃의 온도범위에서 압연을 종료한 다음 10℃/sec이상의 냉각속도로 600-700℃의 온도까지 냉각한후 2-10초의 공냉을 거친후 220℃/sec의 냉각속도로 300-450℃의 온도에서 가속냉각을 마침으로서 5%이상의 잔류오스테나이트를 함유시킨 강으로 제조하는 방법에 대한 특허도 제출하였다. 이 기술은, Si양이 많은 경우 경질의 마르텐사이트의 양이 늘어나 연신 플랜지성이 나빠지므로, 석출한 폴리고날 페라이트내 고용강화하는데 필요한 양인 1.0%이하로 Si을 제한한 것을 특징으로 한다.In addition, Japanese Patent Laid-Open No. 5-112846 discloses precipitation-reinforcing elements such as Nb, Ti, and V in steels containing 0.05-0.25% C, 0.05-1.0% Si, 0.8-2.5% Mn, and 0.8-2.5% Al. After finishing rolling the added steel in the temperature range of 780-840 ℃ and cooling it to the temperature of 600-700 ℃ at the cooling rate of 10 ℃ / sec or more, after 2-10 seconds of air cooling, the cooling rate of 220 ℃ / sec A patent was also filed for a method of making steel with 5% or more residual austenite by finishing accelerated cooling at a temperature of 300-450 ° C. This technique is characterized by limiting Si to 1.0% or less, which is an amount required for solid solution strengthening in precipitated polygonal ferrite because the amount of hard martensite increases due to a large amount of Si, resulting in poor stretch flangeability.

그러나, 상기한 기술들은, 특정 합금원소를 첨가하거나 공정의 제어가 수반되어야 하며, 또한 인장강도를 80kg/mm2 이상으로 하면서 연신율도 30%이상으로 확보하는 데는 한계가 있었다.However, the above-described techniques have to be accompanied by the addition of specific alloying elements or control of the process, and also have a limit in securing an elongation of 30% or more while the tensile strength is 80 kg / mm 2 or more.

이에 본 발명자들은, 상기한 종래 방법들의 문제점을 개선하기 위해 연구 및 실험을 행하고, 그 결과에 근거하여 본 발명을 제안하게 된 것으로, 본 발명은 강 성분중 N을 첨가해 AlN의 석출에 의한 고강도 및 고연성을 확보함으로써, 제조공정 중 기타의 열처리공정없이도 인장강도 80kg/mm2 이상이고 연신율 30% 이상인 열연 변태유기소성강판, 및 그 제조방법을 제공하고자 하는데, 그 목적이 있다.Accordingly, the present inventors conducted research and experiments to improve the problems of the conventional methods described above, and proposed the present invention based on the results, and the present invention provides a high strength due to the precipitation of AlN by adding N in the steel component. And by securing a high ductility, to provide a hot-rolled transformation organic plastic sheet having a tensile strength of 80kg / mm 2 or more and an elongation of 30% or more, and a method of manufacturing the same, without any other heat treatment step in the manufacturing process.

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

중량%로, C: 0.15~0.30%, Si: 1.5~2.5%, Mn: 1.4~1.8%, Al: 0.02~0.10%, N: 0.0080~0.0120%, 잔부 Fe 및 기타 불가피한 불순물로 조성되는 강을 재가열한 후 850~900℃의 온도범위에서 마무리압연한 다음, 670~710℃의 온도범위에서 수냉을 개시하여 420~540℃의 온도범위에서 종료한 후, 서냉하는 것을 포함하여 이루어지는 연성이 우수한 열연 변태유기소성강판의 제조방법에 관한 것이다.By weight%, C: 0.15 to 0.30%, Si: 1.5 to 2.5%, Mn: 1.4 to 1.8%, Al: 0.02 to 0.10%, N: 0.0080 to 0.0120%, remainder Fe and other inevitable impurities After reheating, finish rolling at a temperature range of 850 to 900 ° C., then start water cooling at a temperature range of 670 to 710 ° C. and finish at a temperature range of 420 to 540 ° C., followed by slow cooling. It relates to a method for producing a metamorphic organic plastic steel sheet.

또한, 본 발명은, 상기와 같이 조성되고, 인장강도가 80kg/mm2이상이면서 연신율이 30%이상인 것을 특징으로 하는 연성이 우수한 열연 변태유기소성 강판에 관한 것이다.In addition, the present invention relates to a hot rolled metamorphic organic steel sheet having excellent ductility, characterized in that the composition is as described above, the tensile strength is 80kg / mm 2 or more and the elongation is 30% or more.

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

본 발명의 발명자들은, TRIP강에서 고강도 및 고연성을 동시에 얻기 위한 방법에 대하여 보다 새로운 관점에서 연구하던 중, N첨가에 의한 AlN 석출물을 이용하면 인장강도 80kg/mm2이상을 확보하면서, 연신율도 30%이상으로 할 수 있다는 점에 착안하여, 본 발명을 완성시킨 것이다.The inventors of the present invention, while studying from a new perspective on a method for obtaining high strength and high ductility at the same time in the TRIP steel, when using the AlN precipitates by the addition of N while securing a tensile strength of 80kg / mm 2 or more, The present invention has been accomplished by focusing on the fact that it can be 30% or more.

이하, 강 성분 및 제조조건에 대하여 설명한다.Hereinafter, a steel component and manufacturing conditions are demonstrated.

C는 강의 소입성을 증가시키는 원소로서, 그 함량이 0.15% 미만이면 냉각중 잔류오스테나이트내 C의 농축을 충분히 이룰 수가 없으므로 잔류오스테나이트의 안정화를 이룰 수 없다. 또한, 0.30%이상 첨가되면 강도의 향상은 두드러지나 연성의 저하가 매우 크므로, 그 함량범위는 0.15~0.30%의 범위로 설정하는 것이 바람직하다.C is an element that increases the hardenability of steel. If the content is less than 0.15%, the concentration of C in the residual austenite cannot be sufficiently achieved during cooling, and thus the residual austenite cannot be stabilized. In addition, when 0.30% or more is added, the improvement in strength is remarkable, but the ductility decrease is very large. Therefore, the content range is preferably set in the range of 0.15 to 0.30%.

Si은 탈산에 주로 사용되는 원소로서, C의 활성도를 높이므로 고온에서 페라이트의 형성을 용이하게 한다. 또한, 고온에서 페라이트형성시 남아 있는 오스테나이트로 C의 농축을 조장하므로 변태유기소성강에서는 Si의 첨가가 필수적이다. 그러나, 상기 Si가 과잉 첨가되면 표면에 붉은형 스케일(scale)을 생성하여 표면을 열화시킬 뿐만 아니라 용접중 산화물의 생성이 쉬워 용접부의 결함이 (penetration등) 발생되기 쉬워진다. 따라서, 상기 Si의 함량은, 잔류오스테나이트를 충분히 형성시키는데 필요한 양인 1.5~2.5%로 제한하는 것이 바람직하다. Si is an element mainly used for deoxidation and increases the activity of C, thereby facilitating the formation of ferrite at a high temperature. In addition, the addition of Si is essential in the metamorphic organic-plastic steel because it promotes the concentration of C as austenite remaining during ferrite formation at a high temperature. However, when the Si is excessively added, a red scale is formed on the surface to deteriorate the surface, and oxides are easily generated during welding, and defects in the weld portion (penetration, etc.) are likely to occur. Therefore, the content of Si is preferably limited to 1.5 to 2.5%, which is an amount necessary to sufficiently form residual austenite.

Mn은 강의 강도 및 인성을 증가시키고 오스테나이트를 안정화시켜서 Ms온도(마르텐사이트 개시온도)를 낮추며 강의 소입성을 증가시키는 원소로서, 그 함량이 많은 경우에는 저온변태 생성물의 양을 증가시키므로 강도에는 유리하나 연성의 확보가 어렵다. 또한, 비금속개재물의 양을 증가시키고 편석도를 증가시켜 불리하다. 그러나, 그 함량이 낮은 경우, 페라이트 변태후 남아 있는 미변태 오스테나이트가 유효하게 베이나이트를 형성하기가 어려우므로 잔류오스테나이트를 형성하기 어렵고, 고온에서 펄라이트의 생성이 쉽게 하므로 강도-연성이 저하되기 쉽다. 본 발명에서는 잔류오스테나이트를 효과적으로 형성시키기 위해, 그 함량을 1.4~1.8%로 제한하는 것이 바람직하다.Mn is an element that increases the strength and toughness of steel, stabilizes austenite, lowers Ms temperature (martensite initiation temperature), and increases the hardenability of steel.In the case of high content, Mn increases the amount of low-temperature transformation products. However, securing ductility is difficult. It is also disadvantageous by increasing the amount of nonmetallic inclusions and increasing segregation. However, if the content is low, the unmodified austenite remaining after ferrite transformation is difficult to form bainite effectively, and thus it is difficult to form residual austenite, and it is easy to form pearlite at a high temperature, thereby reducing the strength-ductility. easy. In the present invention, in order to effectively form residual austenite, it is preferable to limit the content to 1.4 to 1.8%.

P은 페라이트의 형성을 조장하는 원소로서, 강의 강도를 해치지 않고 연성을 증가시킬 수 있으나, 일반적으로 강재의 제조시 편석이 극심한 원소로서 중심편석의 형성등으로 재질을 열화시키므로, 그 함량은 0.025% 이하로 관리하는 것이 바람직하다.P is an element that promotes the formation of ferrite and can increase the ductility without harming the strength of steel, but generally, segregation is extremely element when steel is manufactured, which degrades the material due to the formation of central segregation. It is preferable to manage as follows.

S는 MnS로 대표되는 비금속 개재물을 형성하여 강의 가공성을 크게 열화시키는데, 이러한 비금속 개재물은 압연중 길게 연신되어 가공중 크랙발생 등의 치명적인 결함을 발생시키기 쉽다. 따라서, S는 0.01% 이하로 가능한 한 낮게 관리하는 것이 바람직하다. S forms a non-metallic inclusion represented by MnS, which greatly degrades the workability of the steel. The non-metallic inclusion is elongated during rolling and is likely to cause fatal defects such as cracking during processing. Therefore, it is preferable to manage S as low as possible at 0.01% or less.

이를 위해서, 본 발명에서는 강중 20~40ppm의 Ca을 추가로 첨가하여 S를 낮게 관리함으로써, 가공성을 보다 향상시킬 수 있다.To this end, in the present invention, by further adding 20-40 ppm Ca in steel and managing S low, workability can be further improved.

Al은 탈산을 위하여 첨가되는 원소로서, 페라이트의 형성을 도우므로 가공성 향상측면에서 유리하지만 인장강도가 저하하므로, 목표로 하는 재질을 얻기 위해서는 Al의 함량을 적절히 제어해야 한다. 즉, 탈산을 위해서는 최소 0.02%이상 첨가해야 하지만, 과잉 첨가되면 강도를 낮추고 구조재에 있어서 용접시 산화물을 형성하여 용접결함을 생성시키므로, 그 상한은 0.10%로 제한하는 것이 바람직하다.Al is an element added for deoxidation, which is advantageous in terms of processability improvement because it helps the formation of ferrite, but the tensile strength is lowered. Therefore, in order to obtain a target material, the content of Al must be properly controlled. In other words, at least 0.02% or more should be added for deoxidation. However, when excessively added, the strength is lowered and an oxide is formed during welding in the structural material to produce weld defects. Therefore, the upper limit is preferably limited to 0.10%.

N는 본 발명의 특징적인 원소로서, AlN의 석출을 활성화시켜 열간변형중 오스테나이트의 결정립을 미세화하고, 또한 이어서 페라이트의 생성을 촉진시켜 잔류오스테나이트의 형성에 도움이 된다. 이로 인하여, 잔류오스테나이트를 함유시키는 열연 변태유기소성강의 제조에 적극 활용할 수 있다. 또한, 상기 N의 적절한 첨가는 강도와 더불어 연성의 향상에도 효과적이다. 이와 같은 효과를 얻기 위해서는 0.008% 이상 첨가되어야 하지만, 과잉 첨가되면 AlN의 석출물을 크게 하므로 결정립의 미세화 효과보다는 개재물로서의 작용이 조장되어 석출물의 긍정적인 효과를 저감시키게 된다. 즉, 일반적인 석출물은 석출원소의 조성비가 1:1로 되는데 반하여, AlN의 석출에 있어서 조성비가 1:1까지 증가되면 석출물량이 증가되는 긍정적인 영향에 비해 석출물의 크기가 커지므로 석출물의 효과를 떨어뜨리게 된다. 특히, AlN과 같은 비정형의 석출물의 경우는 특히 그 크기가 증가됨에 따라 결정립 미세화나 석출강화의 효과가 크게 저하되므로 석출상의 엄밀한 제어가 필요하다. 따라서, 본 발명에서는 상기 N의 함량을 0.0080~0.0120%로 제한하는 것이 바람직하다N is a characteristic element of the present invention, which activates the precipitation of AlN to refine the grains of austenite during hot deformation, and further promotes the formation of ferrite, thereby contributing to the formation of residual austenite. For this reason, it can utilize actively in manufacture of the hot-rolled transformation organic plastic steel containing residual austenite. In addition, the appropriate addition of N is effective for improving ductility as well as strength. In order to obtain such an effect, it should be added 0.008% or more, but when excessively added, the precipitate of AlN is increased, so that it acts as an inclusion rather than the effect of refining grains, thereby reducing the positive effect of the precipitate. That is, in general precipitates, the composition ratio of the precipitation element is 1: 1, whereas when the composition ratio is increased to 1: 1 in the deposition of AlN, the size of the precipitates is larger than the positive effect of increasing the amount of precipitates. Dropped. In particular, in the case of amorphous precipitates such as AlN, as the size thereof is increased, the effect of grain refinement or precipitation strengthening is greatly reduced, so precise control of the precipitation phase is required. Therefore, in the present invention, it is preferable to limit the content of N to 0.0080 to 0.0120%.

상기와 같이 조성된 강을 재가열한 후 열간압연하고, 이어서 냉각한 다음 권취 및 소둔하는데, 열간압연재의 우수한 강도 및 연성을 확보하기 위해서는 미세조직의 제어가 필수적이며, 따라서 압연 마무리온도, 수냉각개시 및 수냉각 종료온도를 제어하는 것이 중요하다. After reheating the steel formed as described above, it is hot rolled, and then cooled and then wound and annealed. In order to secure the excellent strength and ductility of the hot rolled material, it is essential to control the microstructure, and thus the rolling finish temperature and water cooling. It is important to control the start and end temperature of the water cooling.

상기 압연 마무리온도가 너무 높으면 압연후 오스테나이트의 결정립이 증대되어 소입성이 증가되고, 압연후 마르텐사이트나 베이나이트 등의 저온 변태조직의 양이 크게 증가되므로, 결과적으로 압연후 강의 재질을 강화시키고 연성이 떨어뜨린다. 반면에, 상기 온도가 너무 낮은 경우에는 국부적으로 소재의 온도편차가 발생하여 미세조직 및 재질편차가 크게 발생한다. 따라서, 본 발명에서는 상기 압연 마무리온도를 850~900℃로 설정하는 것이 바람직하다. If the rolling finish temperature is too high, the grain size of the austenite after rolling is increased to increase the hardenability, and the amount of low-temperature transformation structure such as martensite or bainite is greatly increased after rolling, resulting in strengthening the material of the steel after rolling. Ductility falls On the other hand, if the temperature is too low, the temperature deviation of the material is generated locally, the microstructure and material deviation is large. Therefore, in this invention, it is preferable to set the said rolling finishing temperature to 850-900 degreeC.

이후, 수냉각 후 서냉하는데, 상기 수냉각은 페라이트를 충분히 형성시킨 다음에 실시하는 것이 바람직한데, 그 개시온도는 670~710℃로 설정하는 것이 바람직하다. 그 이유는, 상기 온도가 670℃ 미만이면 펄라이트가 생성되고 710℃ 이상으로 수냉각개시 온도가 너무 높으면 충분한 페라이트가 형성되지 않아 냉각후 제2상의 분율이 크게 증가되어 강도는 증가되나 연성이 저하되기 때문이다. 또한, 수냉각 정지온도는 재질을 결정하는데 가장 중요한 요소로서, 이후 서냉에 의해서도 세멘타이트가 생성되지 않고 강도가 크게 저하되지 않도록 그 상한은 베이나이트가 형성될 수 있는 온도를 고려하여 540℃로 설정하는 것이 바람직하고, 그 하한은 연성의 큰 저하가 발생되지 않도록 420℃로 설정하는 것이 바람직하다.Thereafter, after the water cooling is slowly cooled, the water cooling is preferably performed after the ferrite is sufficiently formed, the start temperature is preferably set to 670 ~ 710 ℃. The reason is that if the temperature is less than 670 ° C, pearlite is formed, and if the temperature of the water cooling start above 710 ° C is too high, sufficient ferrite is not formed and the fraction of the second phase is greatly increased after cooling, thereby increasing the strength but decreasing ductility Because. In addition, the water cooling stop temperature is the most important factor in determining the material, and the upper limit is set to 540 ° C in consideration of the temperature at which bainite can be formed so that cementite is not produced even by slow cooling and the strength is not significantly reduced. It is preferable to set it, and it is preferable to set the minimum to 420 degreeC so that a big fall of ductility may not occur.

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

(실시예)(Example)

하기 표1과 같이 조성되는 강 슬라브를 1200℃에서 재가열한 후 열간압연을 행하여 최종두께가 3.0mm인 열연강판으로 제조하고, 열간압연종료 후 롤 소입(roll quenching)에 의해 급냉한 후 일정시간 동안 수냉각 개시온도까지 공냉각시켰다. 다음 수냉각 시뮬레이터로 이송시켜 수냉각 정지온도까지 수냉각한 후, 이후 노냉을 실시함에 의해 열연권취 코일로 제조하였다. 이 때, 열간압연 마무리온도(FRT), 수냉각 개시온도(CS), 및 수냉각 종료온도(CF, 열간압연시의 권취온도에 해당됨)는 하기 표 2와 같이 변화시켰다. The steel slab formed as shown in Table 1 was reheated at 1200 ° C., followed by hot rolling to manufacture a hot rolled steel sheet having a final thickness of 3.0 mm, and after quenching by roll quenching after the end of hot rolling, for a predetermined time. Air-cooled to the water cooling start temperature. Next, the resultant was transferred to a water cooling simulator, cooled to a water cooling stop temperature, and then manufactured by a hot rolled coil by carrying out a furnace cooling. At this time, the hot rolling finish temperature (FRT), the water cooling start temperature (CS), and the water cooling end temperature (CF, corresponding to the winding temperature at the time of hot rolling) were changed as shown in Table 2 below.

이후, 상기한 방법에 의해 제조된 열연강판의 인장특성을 측정하고, 그 결과를 하기 표 2에 나타내었다.Then, the tensile properties of the hot rolled steel sheet produced by the above method was measured, and the results are shown in Table 2 below.

강종Steel grade CC SiSi MnMn PP SS AlAl NN 비교강1Comparative Steel 1 0.390.39 1.981.98 1.471.47 0.0140.014 0.0040.004 0.0510.051 0.00320.0032 종래강Conventional Steel 0.190.19 2.012.01 1.531.53 0.0170.017 0.0040.004 0.0400.040 0.00290.0029 비교강2Comparative Steel 2 0.200.20 1.431.43 1.451.45 0.0170.017 0.0040.004 0.0200.020 0.00290.0029 비교강3Comparative Steel 3 0.200.20 1.961.96 1.971.97 0.0160.016 0.0040.004 0.0400.040 0.00360.0036 발명강Invention steel 0.190.19 1.561.56 1.591.59 0.0120.012 0.0050.005 0.0470.047 0.00960.0096 비교강4Comparative Steel 4 0.200.20 1.611.61 1.491.49 0.0150.015 0.0030.003 0.0370.037 0.01400.0140 비교강5Comparative Steel 5 0.140.14 2.012.01 1.501.50 0.0150.015 0.0050.005 0.0400.040 0.00350.0035

사용강종Steel grade used 구분division 제조조건(℃)Manufacturing condition (℃) 인장특성Tensile Properties FRTFRT CSCS CFCF 항복강도(kg/㎟)Yield strength (kg / ㎡) 인장강도(kg/㎟)Tensile Strength (kg / ㎡) 연신율(%)Elongation (%) 비교강1Comparative Steel 1 비교재1Comparative Material 1 862862 692692 356356 108.7108.7 153.0153.0 3.63.6 비교재2Comparative Material 2 807807 676676 307307 93.393.3 135.0135.0 5.05.0 종래강Conventional Steel 종래재1Conventional Materials 1 866866 726726 563563 61.461.4 76.176.1 24.924.9 종래재2Conventional material 2 859859 718718 447447 55.655.6 82.582.5 29.829.8 비교강2Comparative Steel 2 비교재3Comparative Material 3 860860 714714 420420 62.762.7 74.374.3 22.722.7 비교재4Comparative Material 4 857857 712712 450450 58.958.9 74.574.5 27.327.3 비교강3Comparative Steel 3 비교재5Comparative Material 5 901901 739739 305305 89.789.7 111.8111.8 6.06.0 비교재6Comparative Material 6 867867 721721 376376 71.771.7 105.4105.4 19.719.7 발명강Invention steel 발명재Invention 870870 680680 450450 56.256.2 80.280.2 32.032.0 비교재7Comparative Material7 895895 690690 405405 66.266.2 84.084.0 25.325.3 비교강4Comparative Steel 4 비교재8Comparative Material 8 800800 670670 440440 58.158.1 75.875.8 27.427.4 비교재9Comparative Material 9 830830 660660 450450 57.357.3 74.674.6 28.628.6 비교강5Comparative Steel 5 비교재10Comparative Material 10 862862 717717 420420 61.161.1 75.975.9 23.923.9 비교재11Comparative Material 11 870870 719719 395395 59.459.4 86.786.7 21.021.0

상기 표 2에 나타난 바와 같이, C가 다량 함유된 비교강(1)로 제조된 비교재(1),(2)는 인장강도는 130kg/mm2 이상으로 매우 높으나, 연신율이 5%이하가 되어 가공용 강재로서는 충분한 가공성을 확보하기 어려움을 알 수 있다.As shown in Table 2, the comparative material (1), (2) made of comparative steel (1) containing a large amount of C is very high tensile strength of 130kg / mm 2 or more, but the elongation is less than 5% It can be seen that it is difficult to secure sufficient workability as a steel for processing.

일반적으로 알려져 있는 변태유기소성강의 성분계를 가지고 있는 종래강을 이용한 종래재(2)는 인장강도는 우수하나 연신율이 본 발명의 목표치에 도달하지 못하였고, 수냉각정지 온도가 높게 제조된 종래재(2)은 펄라이트가 혼재하여 인장강도도 76.1kg/mm2로 낮아지고 연신율도 24.9%로 저하되는 경향을 관찰할 수 있다.Conventional material (2) using a conventional steel having a component system of metamorphic organic plastic steel generally known is excellent in tensile strength but the elongation did not reach the target value of the present invention, the conventional material manufactured with high water cooling stop temperature ( 2) can be observed that the pearlite is mixed to lower the tensile strength to 76.1kg / mm 2 and the elongation to 24.9%.

Si양을 감소시킨 비교강(2)를 이용하여 제조된 비교재(3),(4)는 강도 및 연신율이 약간씩 저하된 경향을 보이고 있다. Comparative materials (3) and (4) manufactured by using the comparative steel (2) in which the amount of Si was reduced show a tendency for the strength and elongation to decrease slightly.

Mn양을 증량시킨 비교강(3)강으로 제조된 비교재(5),(6)의 경우, 강도는 100kg/mm2를 넘어서는 고강도를 보이고 있으나, 연성의 저하가 두드러지게 나타나고 있어 가공용강재로 활용되기 어려운 특성을 보이고 있다.In the case of the comparative materials (5) and (6) made of the comparative steel (3) steel with an increased amount of Mn, the strength showed a high strength exceeding 100 kg / mm 2 , but the ductility was deteriorated markedly. It is difficult to utilize.

N양을 더욱 증가시킨 비교강(4)를 이용한 비교재(8),(9)의 경우에는 강도와 연성이 모두 약간씩 저하되는 경향이 관찰되고 있고, C양을 감소시킨 비교강(5)로 제조된 비교재(10),(11)의 경우에도 강도와 연성이 발명강에 비해 떨어지는 결과를 관찰할 수 있다.In the case of the comparative materials (8) and (9) using the comparative steel (4) which further increased the amount of N, both the strength and the ductility tended to decrease slightly, and the comparative steel (5) which reduced the amount of C In the case of the comparative materials 10 and 11 manufactured as described above, the result that the strength and the ductility are lower than those of the inventive steel can be observed.

이에 반하여, 본 발명강으로 제조된 발명재의 경우는, 인장강도 80kg/mm2 이상, 그리고 연신율도 30%를 넘어서 고강도와 더불어 고연성의 특성을 나타내는 것을 알 수 있다. 그러나, 본 발명강을 이용하였으나, 재질에 가장 큰 영향을 미치는 수냉각 종료온도(CF)가 낮게 제조된 비교재(7)은, 마르텐사이트가 형성되어 고강도는 얻어졌으나 연성의 확보가 매우 어려웠다. ,On the contrary, in the case of the invention material manufactured from the present invention steel, it can be seen that the tensile strength is 80kg / mm 2 or more, and the elongation is more than 30%, indicating high ductility and high ductility characteristics. However, although the inventive steel was used, the comparative material 7 produced with a low water cooling end temperature CF having the greatest influence on the material had martensite formed and high strength was obtained, but securing ductility was very difficult. ,

한편, 도 1(a),(b),(c)에는 본 발명의 특징적인 원소인 N 첨가량에 따른 인장특성의 변화를 나타내었다. 도 1(b),(c)에 나타난 바와 같이, N의 함량이 본 발명범위인 0.008~0.012%인 경우에는 인장강도 및 연신율이 최대가 되는 경향을 알 수 있다. 이 때, 도 1(a)에 나타난 바와 같이, 항복강도는 약간 저하되는데, 이러한 경향은 TRIP강에서 자주 관찰되는 현상으로, 잔류오스테나이트를 적정량 함유하는 경우 항목강도는 낮지만 가공중 잔류오스테나이트가 마르텐사이트로 가공유기변태를 하면서 가공경화가 빠르게 진행되어 균일연신율과 총연신율을 증가시키게 된다. On the other hand, Figure 1 (a), (b), (c) shows the change in tensile properties according to the amount of N added as a characteristic element of the present invention. As shown in Figure 1 (b), (c), when the content of N is 0.008 ~ 0.012% of the present invention it can be seen that the tendency to the maximum tensile strength and elongation. At this time, as shown in Fig. 1 (a), the yield strength is slightly reduced, this tendency is often observed in TRIP steel, when the item strength is low when the residual amount of austenite is contained, the residual austenite during processing As the process organic transformation into martensite, the work hardening proceeds rapidly, increasing the uniform elongation and total elongation.

상기한 바와 같은 본 발명에 의하면, 인장강도가 80kg/mm2 이상이면서 연신율이 30%이상이 되는 강도-연성의 조합이 우수한 강재를 제조할 수 있어 가공용도로 사용될 수 있는 효과가 있는 것이다.According to the present invention as described above, the tensile strength is 80kg / mm 2 or more, and the strength-ductility combination of 30% or more elongation can be produced excellent steel material can be used for processing purposes.

도 1(a),(b),(c)는 N첨가량에 따른 항복강도, 인장강도 및 연신율의 변화를 나타내는 그래프1 (a), (b), (c) is a graph showing the change in yield strength, tensile strength and elongation according to N addition amount

Claims (4)

중량%로, C: 0.15~0.30%, Si: 1.5~2.5%, Mn: 1.4~1.8%, Al: 0.02~0.10%, N: 0.0080~0.0120%, 잔부 Fe 및 기타 불가피한 불순물로 조성되는 강을 재가열한 후 850~900℃의 온도범위에서 마무리압연한 다음, 670~710℃의 온도범위에서 수냉을 개시하여 420~540℃의 온도범위에서 종료한 후, 서냉하는 것을 포함하여 이루어지는 연성이 우수한 열연 변태유기소성강판의 제조방법By weight%, C: 0.15 to 0.30%, Si: 1.5 to 2.5%, Mn: 1.4 to 1.8%, Al: 0.02 to 0.10%, N: 0.0080 to 0.0120%, remainder Fe and other inevitable impurities After reheating, finish rolling at a temperature range of 850 to 900 ° C., then start water cooling at a temperature range of 670 to 710 ° C. and finish at a temperature range of 420 to 540 ° C., followed by slow cooling. Manufacturing method of metamorphic organic plastic sheet 제 1항에 있어서, 상기 강이 20~40ppm의 Ca을 추가로 함유하는 것을 특징으로 하는 연성이 우수한 열연 변태유기소성 강판의 제조방법The method according to claim 1, wherein the steel further contains 20 to 40 ppm of Ca. 중량%로, C: 0.15~0.30%, Si: 1.5~2.5%, Mn: 1.4~1.8%, Al: 0.02~0.10%, N: 0.0080~0.0120%, 잔부 Fe 및 기타 불가피한 불순물로 조성되고, 인장강도가 80kg/mm2이상이면서 연신율이 30%이상인 것을 특징으로 하는 연성이 우수한 열연 변태유기소성 강판In weight percent, C: 0.15-0.30%, Si: 1.5-2.5%, Mn: 1.4-1.8%, Al: 0.02-0.10%, N: 0.0080-0.0120%, remainder Fe and other unavoidable impurities, tensile Hot-rolled ductile organic steel sheet having excellent ductility, characterized in that the strength is 80 kg / mm 2 or more and the elongation is 30% or more. 제 3항에 있어서, Ca이 20~40ppm 추가로 함유되는 것을 특징으로 하는 연성이 우수한 열연 변태유기소성 강판The hot rolled transformation organic plastic sheet having excellent ductility according to claim 3, wherein 20 to 40 ppm of Ca is further contained.
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