KR20020034484A - Heat hardenable hot rolled steel sheet having superior formability and producing method thereof - Google Patents

Heat hardenable hot rolled steel sheet having superior formability and producing method thereof Download PDF

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KR20020034484A
KR20020034484A KR1020000064812A KR20000064812A KR20020034484A KR 20020034484 A KR20020034484 A KR 20020034484A KR 1020000064812 A KR1020000064812 A KR 1020000064812A KR 20000064812 A KR20000064812 A KR 20000064812A KR 20020034484 A KR20020034484 A KR 20020034484A
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steel sheet
rolled steel
less
hot rolled
hot
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KR1020000064812A
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Korean (ko)
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조열래
이승복
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이구택
주식회사 포스코
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    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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 Sheet Steel (AREA)

Abstract

PURPOSE: A heat hardenable hot rolled steel sheet that is suitable for use as components requiring superior fatigue property is provided, which has mechanical characteristics of tensile strength higher than 450MPa, elongation higher than 30wt.%. CONSTITUTION: The method includes the steps of (i) finish hot rolling a steel slab comprising C 0.03-0.05 wt.%, Si 0.1 wt.% or less, Mn 0.2-0.4 wt.%, P 0.015 wt.% or less, S 0.01 wt.% or less, Al 0.010-0.050 wt.%, Cu 1.0-1.5 wt.%, Ni 0.5-1.0 wt.%, N50ppm or less, balance of Fe, and other inevitable impurities at higher than Ar3 transformation temperature; (ii) coiling it in the temperature range of 400 to 450°C. In the steel slab, the ratio of Ni/Cu is between 0.6 and 1.

Description

냉간가공성이 우수한 가열경화형 열연강판과 그 제조방법{Heat hardenable hot rolled steel sheet having superior formability and producing method thereof}Heat hardenable hot rolled steel sheet having superior formability and producing method

본 발명은 자동차 프레스 성형부품, 스핀들 등의 구동계 부품, 기어류 등 고강도와 우수한 피로특성이 요구되는 부품의 소재로 사용하기에 적합한 가열 경화형 열연강판에 관한 것이다. 상세하게는 열연강판상태에서는 냉간가공성이 우수하고, 시효열처리에 의하여 고강도와 고피로특성 및 고인성을 가지는 가열 경화형 열연강판 및 그 제조방법에 관한 것이다.The present invention relates to a heat-curable hot rolled steel sheet suitable for use as a material for parts requiring high strength and excellent fatigue characteristics such as automobile press molded parts, drive system parts such as spindles, and gears. Specifically, the present invention relates to a heat-curable hot rolled steel sheet having excellent cold workability in a hot rolled steel sheet, having high strength, high fatigue characteristics, and high toughness by aging heat treatment, and a method of manufacturing the same.

열연강판은 자동차나 산업기기의 부품 혹은 강도부재로 다양하게 사용되고 있다. 최근, 자동차 이산화탄소 배출량에 대한 규제가 가시화되면서 자동차 연비향상을 위한 차체 경량화에 대한 관심이 높아지고 있다. 이를 위해서는 사용강재의 두께를 감소시킴과 동시에 강도를 높일 필요가 있는 것으로 인식되고 있다. 그러나, 강판의 강도가 상승하면 가공성이 저하되는 것이 일반적이기 때문에 강도와 가공성을 동시에 얻기가 용이하지 않다. 또한, 자동차 구동 전달부품과 같이 강도와 피로특성, 인성 등을 요구하는 부품은 통상 주물재를 이용하거나 아니면 고탄소강을 절삭 가공한 후 열처리를 행하여 제조하게 되는데, 이 경우 프레스 성형에 의한 부품 제조에 비하여 제조비용이 높아진다는 단점이 있다.Hot rolled steel sheet is widely used as a component or strength member of automobiles and industrial devices. Recently, as regulations on automobile carbon dioxide emissions become visible, interest in weight reduction of automobiles for improving fuel efficiency of automobiles is increasing. To this end, it is recognized that it is necessary to reduce the thickness of the steel used and to increase the strength at the same time. However, when the strength of the steel sheet rises, workability generally decreases, so it is not easy to obtain strength and workability simultaneously. In addition, parts requiring strength, fatigue characteristics, toughness, and the like, such as automotive drive transmission parts, are usually manufactured by using casting materials or by cutting heat treatment of high carbon steel and then heat-treating them. There is a disadvantage that the manufacturing cost is higher than.

강도와 가공성을 동시에 충족시키기 위하여 구리(Cu)의 시효경화 특성을 이용하여 열연강판을 제조하는 기술이 알려져 있다. 즉, 열연강판 혹은 산세 열연강판상태에서의 성형단계에서는 가공성이 우수하여 가공 불량 방지, 성형 가압력 및 금형의 마모를 감소시키면서 성형 후에는 시효열처리에 의하여 강도특성을 향상시키는 기술이다. 그 대표적인 기술로 일본 공개특허공보 평3-287719호와 소64-79347호를 예로 들 수 있다.In order to simultaneously meet the strength and workability, a technique for manufacturing a hot rolled steel sheet using the age hardening property of copper (Cu) is known. That is, in the forming step in the hot-rolled steel sheet or pickled hot-rolled steel sheet state, the workability is excellent, thereby preventing the machining defect, reducing the pressing force and the wear of the mold, and improving the strength characteristics by aging heat treatment after molding. As the representative techniques, Japanese Patent Laid-Open Nos. 3-287719 and 64-79347 are exemplified.

일본 특허 공개공보 평3-287719호는 0.005%C이하의 극저탄소강에 Cu를 1.0~2.3% 범위로 첨가하고, B(보론)을 3~30ppm 첨가하여 조성되는 강슬라브를 열간압연하고 300℃ 이하에서 권취하여 인장강도 300Mpa정도의 열연강판을 제조하는 방법으로, 이 방법으로 제공된 열연강판은 시효 열처리 후 인장강도가 150~200Mpa 증가된다고 밝히고 있다.Japanese Patent Application Laid-Open No. 3-287719 discloses a steel slab formed by adding Cu in an amount of 1.0 to 2.3% and adding 3 to 30 ppm of B (boron) to an ultra low carbon steel of 0.005% or less, and hot rolling a steel slab at 300 ° C. As a method of manufacturing a hot rolled steel sheet having a tensile strength of about 300Mpa by winding below, it is revealed that the hot rolled steel sheet provided by this method increases the tensile strength by 150 to 200Mpa after aging treatment.

일본 특허 공개공보 소64-79347호도 역시 극저탄소강에 Nb나 Ti을 소량 첨가한 강슬라브를 열간압연하고 500℃ 이하에서 권취하여 열연강판을 제조한후 시효 열처리를 행하면 600Mpa급의 강판이 얻어진다고 밝히고 있다.Japanese Patent Application Laid-Open No. 64-79347 also shows that a 600 Mpa grade steel sheet is obtained by hot-rolling a steel slab containing a small amount of Nb or Ti in ultra low carbon steel, winding it at 500 ° C or below, and manufacturing a hot rolled steel sheet. It is revealed.

그러나, 상기한 두 선행기술에서와 같이 극저탄소강을 이용할 경우 제강공정에서의 취련 비용이 증가할 뿐만 아니라, 열간압연 마무리온도를 확보하기 어려운 단점을 가지고 있다. 특히 특개평 3-287719호에서 제안하는 권취온도 수준은 지나치게 낮기 때문에 열연강판의 형상 제어 측면에서 문제가 있다.However, in the case of using the ultra low carbon steel as in the two prior arts described above, the cost of blowing in the steelmaking process is increased, and it is difficult to secure a hot rolling finish temperature. In particular, since the winding temperature level proposed in Japanese Patent Laid-Open No. 3-287719 is too low, there is a problem in terms of shape control of the hot rolled steel sheet.

본 발명은 저탄소강을 기본 성분계로 하면서도 열연강판상태에서는 성형성이 우수하고 성형 후에는 시효열처리에 의하여 인장강도 600MPa 이상의 강도와 우수한 인성 및 피로특성을 갖는 가열 경화형 열연강판 및 그 제조방법을 제공하는데, 그 목적이 있다.The present invention provides a heat-hardened hot rolled steel sheet having a high tensile strength of 600 MPa or more and excellent toughness and fatigue characteristics by low temperature steel as a basic component but having excellent formability in a hot rolled steel sheet, and after molding, by aging heat treatment. , Its purpose is.

상기 목적을 달성하기 위한 본 발명의 열연강판은, C: 0.03∼0.05중량%(이하, 단지 '%'라 한다), Si:0.1% 이하, Mn: 0.2∼0.4%, P: 0.015% 이하, S: 0.01%이하, Al:0.010∼0.050%, Cu:1.0∼1.5%, Ni: 0.5∼1.0%, N: 50ppm 이하, 나머지 Fe 및 기타 불가피한 불순물을 조성되고, 상기 Cu는 고용상태로 존재하는 것을 포함하여 구성된다.Hot-rolled steel sheet of the present invention for achieving the above object, C: 0.03-0.05% by weight (hereinafter referred to as only '%'), Si: 0.1% or less, Mn: 0.2-0.4%, P: 0.015% or less, S: 0.01% or less, Al: 0.010 to 0.050%, Cu: 1.0 to 1.5%, Ni: 0.5 to 1.0%, N: 50 ppm or less, remaining Fe and other unavoidable impurities are formed, and Cu is present in solid solution It is configured to include.

또한, 본 발명의 열연강판 제조방법은, 중량%로 C: 0.03∼0.05%, Si:0.1% 이하,Mn: 0.2∼0.4%, P: 0.015% 이하, S: 0.01%이하, Al:0.010∼0.050%, Cu:1.0∼1.5%, Ni: 0.5∼1.0%, N: 50ppm 이하, 나머지 Fe 및 기타 불가피한 불순물을 조성되는 Ar3 이상의 마무리압연온도조건으로 열간압연하여 400∼450℃에서 권취하는 것을 포함하여 구성된다.Further, the method for producing a hot rolled steel sheet according to the present invention is C: 0.03 to 0.05%, Si: 0.1% or less, Mn: 0.2 to 0.4%, P: 0.015% or less, S: 0.01% or less, and Al: 0.010 to 0.050%, Cu: 1.0-1.5%, Ni: 0.5-1.0%, N: 50ppm or less, the remaining Fe and other unavoidable impurities are hot-rolled at a finish rolling temperature condition of Ar3 or higher, and wound at 400-450 ° C. It is configured by.

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

본 발명자들은 제강공정에서의 취련이 용이하고 열간압연 마무리 압연온도를 쉽게 확보하기 위해서는 저탄소를 기본성분계로 해야 한다는 전제하에, 저탄소강에서도 성형성이 확보되면서 시효열처리후에 인장강도 600 MPa급의 가공용 열연강판을 제조하기 위한 연구과정에서 본 발명을 완성한 것이다.The present inventors made it easy to blow in the steelmaking process, and to make it easy to secure hot rolling finish rolling temperature, low carbon should be the basic component system. The present invention was completed in the course of research for manufacturing a steel sheet.

본 발명에서는 저탄소강을 기본 성분계로 하여 가공성의 저하를 개선하기 위하여 적정량의 탄소, 망간, 구리(Cu) 및 니켈(Ni)이 유기적인 관련성에 입각하여 그 첨가량을 조정한 것이다. 또한, 이러한 저탄소강의 가열경화형 열연강판이 냉간 성형 단계에서의 가공성을 확보하고, 성형후 열처리에 의하여 강도를 향상시킬 수 있도록 강성분계에 적합한 열간압연조건과 권취조건을 도출하는데, 특히 권취온도의 경우에는 지나치게 저온화되는 것을 방지하여 열연강판의 형상제어에 별다른 문제가 생기지 않도록 하는 것에도 그 특징이 있다. 이러한 본 발명을 열연강판과 그 제조방법으로 구분하여 설명한다.In the present invention, in order to improve the workability deterioration using low carbon steel as a basic component system, an appropriate amount of carbon, manganese, copper (Cu) and nickel (Ni) is adjusted based on the organic relationship. In addition, such a low carbon steel heat-curable hot rolled steel sheet derives hot rolling conditions and winding conditions suitable for a steel component system so as to secure workability in the cold forming step and improve strength by heat treatment after molding, particularly in the case of winding temperature. The present invention is also characterized in that it is prevented from becoming too low to prevent any problems in shape control of the hot rolled steel sheet. This invention will be described by dividing the hot-rolled steel sheet and its manufacturing method.

[열연강판][Hot rolled steel sheet]

본 발명의 열연강판은 저탄소강에 Si, Mn, P, S, Al, Cu, Ni, N의 함유량을 조절하면서, 상기 Cu의 경우 거의 대부분 고용상태로 존재하도록 한다.In the hot-rolled steel sheet of the present invention, while controlling the content of Si, Mn, P, S, Al, Cu, Ni, and N in the low carbon steel, almost all of Cu is present in solid solution.

·탄소(C)는 0.03-0.05% 함유되는 것이 바람직하다.Carbon (C) is preferably contained 0.03-0.05%.

C는 열연강판의 강도를 얻는데 기본적으로 필요한 원소나 냉간 가공성 측면에서는 그 함유량이 가능한 적은 것이 유리하다. 그러나, 탄소함량이 0.03%미만으로 적으면 강판의 에지부 등에 혼립조직이 형성되어 강판의 가공성이 저하되고, 반대로 탄소함량이 0.05% 초과하면 역시 가공성이 저하된다.C is advantageously as small as possible in terms of the elements necessary for obtaining the strength of the hot rolled steel sheet and the cold workability. However, when the carbon content is less than 0.03%, a mixed structure is formed on the edge portion of the steel sheet, and the workability of the steel sheet is deteriorated. On the contrary, when the carbon content exceeds 0.05%, the workability is also deteriorated.

·망간(Mn)은 0.2-0.4% 함유되는 것이 바람직하다.Manganese (Mn) is preferably contained 0.2-0.4%.

Mn은 고용강화에 유효한 원소로서 강도의 향상에 기여한다. 본 발명과 관련한 기초실험 결과에 의하면 0.2% 미만에서는 고용 유황의 증가로 열간압연 강판의 표면, 특히 에지부에 표면결함의 발생 가능성이 높아진다. 한편, 함유량이 0.4%초과하면 Mn편석 등으로 냉간가공성이 저하된다.Mn is an effective element for solid solution strengthening and contributes to the improvement of strength. According to the results of the basic experiments related to the present invention, less than 0.2% increases the solubility of sulfur to increase the possibility of surface defects on the surface of the hot rolled steel sheet, especially the edge portion. On the other hand, when content exceeds 0.4%, cold workability will fall by Mn segregation etc ..

· 실리콘(Si)은 0.1%이하 함유되는 것이 바람직하다.Silicon (Si) is preferably contained 0.1% or less.

Si은 기본적으로 고용강화에 기여하며, 강도 상승에 비하여 연신율의 저하에 비교적 작은 영향을 미치는 원소이다. 그러나 첨가량이 0.1%초과할 정도로 많으면, 적스케일의 발생에 의하여 표면품질이 나빠진다.Si is basically an element that contributes to solid solution strengthening and has a relatively small effect on the lowering of the elongation compared to the increase in strength. However, if the added amount is more than 0.1%, the surface quality deteriorates due to the generation of red scale.

·인(P)은 0.015%이하 관리하는 것이 바람직하다.Phosphorus (P) is preferably managed at 0.015% or less.

P은 강판의 강도 상승에 유효한 원소이지만, 그 첨가량이 0.015% 초과할 정도로 증가하면 슬라브 중심편석을 유발시키고, 냉간가공에서의 가공 취화를 유발시킨다.P is an effective element for increasing the strength of the steel sheet, but when the amount thereof is increased to more than 0.015%, it causes the slab central segregation and causes the work embrittlement in cold working.

·유황(S)은 0.01%이하로 관리하는 것이 바람직하다.Sulfur (S) is preferably managed at 0.01% or less.

S은 열간압연 단계에서 고용S의 입계편석에 의한 취화를 방지하기 위해서는 그 함유량을 극소화시키는 것이 중요하다. 그래서 유향의 함유량은 0.01% 이하로 규제한다.It is important to minimize the content of S in order to prevent embrittlement due to grain boundary segregation of the solid solution S in the hot rolling step. Therefore, the content of frankincense is regulated to 0.01% or less.

· 질소(N)는 50ppm이하로 관리하는 것이 바람직하다.Nitrogen (N) is preferably managed at 50 ppm or less.

N은 주로 고용된 상태로 존재하게 되나, 그 함유량이 많으면 변형시효를 유발시키고 탄소와 마찬가지로 가공성을 저하시키기 때문에 50ppm 이하로 제한한다.N is mainly in a solid solution, but if the content is large, it causes strain aging and, like carbon, reduces workability, so it is limited to 50 ppm or less.

· 구리(Cu)는 1.0-1.5% 함유되는 것이 바람직하다.Copper (Cu) is preferably contained 1.0-1.5%.

Cu는 본 발명강에 있어 중요한 원소로, 열연강판에서는 고용상태로 존재하다가 시효열처리 과정에서 구리 석출물로 석출되면서 기지를 강화시키기 때문에 강도 및 피로강도의 향상에 대단히 유용한 원소이다. 그러나, 함유량이 1.0% 미만이면 시효 경화능이 감소하여 강도 상승이 불충분하고, 1.5% 초과하면 열간압연 과정에서 균열이 발생될 가능성이 높아진다.Cu is an important element in the steel of the present invention, and is present in a solid solution state in hot-rolled steel sheet, but is a very useful element for improving strength and fatigue strength because it precipitates as a copper precipitate during aging heat treatment. However, if the content is less than 1.0%, the aging hardenability decreases and the strength increase is insufficient. If the content exceeds 1.5%, the possibility of cracking during hot rolling increases.

·니켈(Ni)은 0.5-1.0% 함유되는 것이 바람직하다.Nickel (Ni) is preferably contained 0.5-1.0%.

Ni은 Cu와 함께 본 발명에서 중요한 원소로서, Cu 첨가강의 열간취성을 억제하는데 유효하다. 그 함유량이 0.5%미만이면 열간취성을 억제하는데 충분하지 않고, 1.0%를 초과하면 억제효과가 포화될 뿐만 아니라 비경제적이다.Ni, together with Cu, is an important element in the present invention and is effective for suppressing hot brittleness of Cu-added steel. If the content is less than 0.5%, it is not sufficient to suppress hot brittleness, and if the content exceeds 1.0%, the inhibitory effect is not only saturated but also uneconomical.

·알루미늄(Al)은 0.010-0.050% 함유되는 것이 바람직하다.Aluminum (Al) is preferably contained 0.010-0.050%.

Al은 강의 탈산에 필요한 원소로서 0.01%미만이면 탈산이 부족하며, 0.05%를 초과하면 잉여Al의 존재하여 비경제적이다. 가장 바람직하게는 Al은 0.03%로 하는 것이다.Al is an element necessary for deoxidation of steel, and if it is less than 0.01%, deoxidation is insufficient. If Al exceeds 0.05%, excess Al is present and it is uneconomical. Most preferably, Al is made into 0.03%.

·Ni/Cu의 비Ni / Cu ratio

Cu의 첨가량이 증가함에 따라 열연강판상태 뿐 아니라 시효열처리한 강판상태에서도 강도는 증가하지만 열간압연 과정동안 Cu취성에 의하여 강판 에지부에 균열이 발생될 가능성은 높아지게 된다. 본 발명에서는 이러한 Cu 첨가강에서 Ni의 첨가에 따른 균열의 발생억제를 확인한 결과, Ni/Cu의 비가 0.6이상일 때 열연강판에서 균열의 발생이 완전히 방지하는 것을 확인하였다.As the amount of Cu increases, the strength increases not only in the hot rolled steel sheet but also in the aged heat-treated steel sheet, but the possibility of cracking at the edge of the steel sheet is increased due to the brittleness of Cu during the hot rolling process. In the present invention, as a result of checking the occurrence of cracks due to the addition of Ni in such Cu-added steel, it was confirmed that the occurrence of cracks in the hot-rolled steel sheet completely prevented when the Ni / Cu ratio is 0.6 or more.

본 발명에 따라 저탄소강에 합금원소의 첨가량을 조절하고 Cu를 고용상태로 한 열연강판은 인장강도 450MPa이상, 연신율 30% 이상의 기계적성질을 갖으면서, 시효 열처리를 행할 경우 인장강도 600Mpa이상, 연신율 20% 이상, 인장강도×연신율이10000 MPa·% 이상을 만족한다.According to the present invention, the hot rolled steel sheet in which the alloying element is added to the low carbon steel and Cu is dissolved in solid state has a mechanical strength of 450 MPa or more and an elongation of 30% or more, and when aging heat treatment is performed, the tensile strength is 600 Mpa or more and elongation 20 % Or more and tensile strength x elongation satisfy | fills 10000 MPa *% or more.

[열연강판의 제조방법][Method of manufacturing hot rolled steel sheet]

본 발명의 열연강판 제조방법에서는 상기와 같이 조성되는 강이 가열경화형 특성을 발현하는데, 최적의 제조조건을 도출하는데, 특징이 있다. 이러한 제조조건에서 권취온도는 열연강판의 형상제어측면에서 가능한 저온화를 막으면서 Cu의 석출을 방지한다는데 기술적인 의미가 있다.In the method for manufacturing a hot rolled steel sheet of the present invention, the steel formed as described above exhibits heat-curable properties, and thus, there is a feature for deriving an optimal manufacturing condition. In these manufacturing conditions, the coiling temperature has a technical meaning in preventing the precipitation of Cu while preventing possible low temperature from the shape control side of the hot rolled steel sheet.

상기와 같이 조성되는 강슬라브는 통상 직송압연 혹은 재가열압연을 행한 다음에 권취하여 열연강판으로 제조된다.The steel slab formed as described above is usually manufactured by hot rolled steel sheet after winding or reheat rolling.

·열간압연공정Hot rolling process

상기와 같이 조성되는 강슬라브는 직송압연 혹은 재가열압연에 관계없이 마무리압연온도를 Ar3이상으로 하는 조건으로 열간압연한다. 마무리압연온도가 Ar3미만의 경우에는 혼립조직이 형성되어 강판의 가공성이 저하되므로 바람직하지 않다.The steel slab formed as described above is hot rolled under the condition that the finish rolling temperature is Ar 3 or more, regardless of the direct rolling or reheat rolling. When the finish rolling temperature is less than Ar 3 , it is not preferable because a mixed structure is formed and workability of the steel sheet is lowered.

·권취공정Winding process

상기와 같이 열간압연하고 런 아웃트 테이블의 수냉대에서 수냉각하여400-450℃의 온도에서 권취한다. 구리가 고용상태로 존재할 수 있도록 가능한 저온에서 권취하는 것이 유리하나, 권취온도가 지나치게 낮으면 구리와 니켈의 첨가에 따른 경화능 증가로 강판의 가공성이 저하되는 문제가 있고, 열간압연 후 강판의 온도가 급격하게 낮아지면 판 형상이 불량해지기 때문에 하한을 400℃로 제한하는 것이다. 또한, 권취온도가450℃ 보다 높으면 구리가 석출되어 시효열처리에 의한 강도 상승량이 저하된다. 상기한 권취온도는 열간압연후에 수냉각하여 조절하는데, 이때의 수냉각은 통상의40-80℃/s의 냉각조건을 부여하면 본 발명에서 관리하는 권취온도로 제어가 가능하다.Hot rolled as described above, water cooled in the water chiller of the run out table and wound up at a temperature of 400-450 ° C. It is advantageous to wind at low temperature as possible so that copper can exist in solid solution, but if the winding temperature is too low, there is a problem that the workability of the steel sheet is deteriorated due to the increase in hardenability due to the addition of copper and nickel, and the temperature of the steel sheet after hot rolling. If the abruptly lowered plate shape becomes poor, the lower limit is limited to 400 ° C. In addition, when the coiling temperature is higher than 450 ° C., copper precipitates and the amount of increase in strength due to aging heat treatment is lowered. The coiling temperature is adjusted by water cooling after hot rolling, and the water cooling at this time can be controlled by the coiling temperature managed by the present invention if given a cooling condition of the usual 40-80 ℃ / s.

·열연강판의 후처리Post-treatment of hot rolled steel

상기 제조조건으로 권취된 열연강판은 필요에 따라 산세를 행하여 표면 흑피를 제거한후 도유를 행한 산세강판으로 제조할 수도 있다. 이렇게 제조하더라도 가열경화형의 특징을 갖는다.The hot rolled steel sheet wound up under the above manufacturing conditions may be manufactured as a pickled steel sheet subjected to oiling after removing the surface black skin by pickling as necessary. Even if it is manufactured in this way, it has the characteristic of heat-hardening type.

상기 제조조건으로 제조된 열연강판 또는 산세강판은 구리가 고용상태로 존재하고 있어 냉간 성형이 용이한 인장강도 440Mpa이상의 기계적성질을 갖으며, 성형 후 시효열처리를 행하면 구리의 시효석출에 의하여 600Mpa이상의 인장강도를 얻을 수 있다. 아울러 냉간성형에서 도입된 가공경화 조직은 시효 열처리과정에서 회복되기 때문에 연성 역시 향상되어 강도와 인성, 피로강도가 동시에 향상되는 특징을 가지고 있다.The hot rolled steel sheet or pickled steel sheet manufactured under the above manufacturing conditions has a mechanical property of 440 Mpa or more, which is easy to be cold formed because copper is present in solid solution, and after aging heat treatment after molding, tensile strength of 600 Mpa or more may be obtained by aging precipitation of copper. Strength can be obtained. In addition, since the work hardened structure introduced in cold forming is recovered during the aging heat treatment, the ductility is also improved, and the strength, toughness, and fatigue strength are simultaneously improved.

이하 실시예를 통하여 본 발명을 보다 구체적으로 설명한다Hereinafter, the present invention will be described in more detail with reference to the following examples.

[실시예 1]Example 1

아래 표 1의 발명강(강 F, H)과 비교강(강A∼E, G, I)을 용해하여 슬라브를 제조한 후 열간압연을 행하였다. 열연압연에서의 마무리 온도는 850℃ 이며, 열간압연 후 수냉대(ROT)상에서의 수냉하여 권취온도가 400∼600℃ 온도범위가 되도록 제어하여 두께 3.0mm의 열간압연 강판을 제조하였다.Inventive steels (steels F and H) and comparative steels (steels A to E, G and I) shown in Table 1 below were melted to prepare slabs, and then hot rolled. In hot rolling, the finishing temperature was 850 ° C., and after the hot rolling, the resultant was cooled on a water chiller (ROT) to control the winding temperature to be in the 400 to 600 ° C. temperature range, thereby manufacturing a hot rolled steel sheet having a thickness of 3.0 mm.

이 강판을 이용하여 압연방향에 평행한 방향으로 인장시험(JIS5호)과 피로시험을 행하였다.Using this steel sheet, a tensile test (JIS No. 5) and a fatigue test were conducted in a direction parallel to the rolling direction.

또한, 열간압연강판의 시효열처리는 550℃에서 최대 360분 동안 유지한 후 공냉처리하여 역시 인장성질과 피로강도를 측정하였다.In addition, the aging heat treatment of the hot rolled steel sheet was maintained at 550 ℃ for up to 360 minutes and then air cooled to measure the tensile properties and fatigue strength.

표 2에서 알 수 있듯이, 비교예(1~4)의 경우 구리의 증가에 따라 열연 및 시효열처리 강판의 강도는 증가하며, 이중에서 비교예(3, 4)의 경우 열연상태에서 440Mpa의 인장강도와 시효 열처리 후 600Mpa 이상의 인장강도가 얻어졌다. 그러나, 이들 비교예(1-4)의 경우 열연강판의 양 에지부에 열간균열이 발생하여 본 발명의 범위를 충족시키지 못하였다.As can be seen from Table 2, in the case of Comparative Examples (1 to 4), the strength of the hot rolled and aged heat-treated steel sheet increases with the increase of copper, and among the Comparative Examples (3 and 4), the tensile strength of 440 Mpa in the hot rolled state. Tensile strength of 600 Mpa or more was obtained after the aging treatment. However, in these comparative examples (1-4), hot cracks were generated at both edge portions of the hot rolled steel sheet, which did not satisfy the scope of the present invention.

이와 같은 열연강판의 균열 발생은 니켈의 첨가 특히, 구리함량의 1/2이상의 니켈 첨가(Ni/Cu≥0.5)에서 완전하게 방지할 수 있음을 표 1, 2에서 확인할 수 있었다(비교예8, 10, 13, 발명예9, 11-12).It can be seen from Tables 1 and 2 that crack formation of such a hot-rolled steel sheet can be completely prevented from the addition of nickel, in particular, nickel addition (Ni / Cu≥0.5) of 1/2 or more of copper (Comparative Example 8, 10, 13, Inventive Example 9, 11-12).

한편, 비교강 E와 발명강F를 이용하여 시효강도의 권취온도 의존성을 조사한 결과, 고온에서 권취된 열연강판에서는 시효강도의 상승을 기대할 수 없고(비교예5, 8), 권취온도가 430℃ 이하로 되어도 시효강도는 그다지 상승되지 않았다(비교예7,10). 그러나, 본 발명법의 권취온도 범위를 만족하는 발명예(9, 11-12)에서는 시효 열처리후의 강도가 열연강판 대비 130Mpa이상 상승하여 본 발명법의 기계적성질 범위인 600Mpa 이상을 충분히 만족시키고 있다. 아울러 본 발명강의 특징중 하나인 피로강도의 경우, 열연강판의 그것과 비교하여 평균 75Mpa 상승되는 결과가 얻어져 높은 강도와 피로강도를 동시에 구비하고 있다On the other hand, as a result of examining the dependence of the winding temperature on the aging strength by using the comparative steel E and the invention steel F, the increase in the aging strength cannot be expected in the hot rolled steel sheet wound at high temperature (Comparative Examples 5 and 8), and the coiling temperature is 430 ° C. The aging strength did not increase so much even if it was below (Comparative Examples 7, 10). However, in Invention Examples (9, 11-12) satisfying the winding temperature range of the present invention method, the strength after aging heat treatment increased by 130 Mpa or more relative to the hot rolled steel sheet to sufficiently satisfy the 600 Mpa or more, which is the mechanical property range of the present invention method. In addition, the fatigue strength, which is one of the characteristics of the present invention steel, has a result of increasing the average of 75Mpa compared with that of the hot rolled steel sheet, and has both high strength and fatigue strength at the same time.

[실시예 2]Example 2

본 발명법의 강 F와 비교강인 강 A, C이용하여 냉간성형에 의한 변형이 부여되었을 때의 시효 열처리 전후 기계적성질 변화를 표 3에 정리하였다.Table 3 shows the changes in mechanical properties before and after aging heat treatment when the deformation by cold forming is applied using steels F and comparative steels A and C of the present invention.

표 3에서 알 수 있듯이, 비교강(C)의 경우 본 발명에서 목적하는 기계적 성질범위에 근접하나 앞서 표 2에 나타난 바와 같이, 열간압연 강판의 에지부에 균열이발생되어 본 발명의 목적을 충족시키지 못하는 경우이다.As can be seen from Table 3, in the case of the comparative steel (C) is close to the desired mechanical properties range in the present invention, as shown in Table 2, the crack is generated in the edge portion of the hot-rolled steel sheet to meet the object of the present invention This is the case.

또한, 비교강 A는 구리가 첨가되지 않은 경우이며, 발명강F는 본 발명을 충족시키는 조건에 해당하는 것이다. 구리 첨가강의 경우 냉간 변형량이 증가됨에 따라 시효 열처리후의 인장강도 역시 증가하나(비교예15~16, 19~20), 30%의 변형량에서는 열처리에 의한 가공조직의 연화량이 시효석출 강화량 보다 커 최종 강도는 가공경화된 상태 보다 약간 감소하게 된다(17, 21).In addition, comparative steel A is a case where copper is not added and invention steel F corresponds to the conditions which satisfy | fill this invention. In case of copper-added steel, the tensile strength after aging treatment also increases as the cold deformation increases (Comparative Examples 15 ~ 16, 19 ~ 20), but at 30% strain, the softening of the processed structure by heat treatment is greater than the aging precipitation reinforcement. The strength is slightly reduced than the work hardened state (17, 21).

그러나, 구리를 첨가하지 않은 강A의 경우 20% 가공경화된 상태에서 시효 열처리를 행하면 연신율은 증가하나, 인장강도는 냉간가공된 상태와 비교하여 약 95Mpa 감소하게 된다(비교예 23). 다시 말하면, 본 발명의 가열 경화형 열연강판을 이용하여 냉간성형을 실시한 후 시효열처리를 행하면 강도와 연신율이 동시에 향상되고, 강도×연신율 발란스는 냉간 성형 직후의 가공경화된 강판이 갖는 6900~7600MPa·% 수준에서 11000~12100 MPa·% 수준으로 대폭 향상(발명예19~21) 되는데 반하여 구리가 첨가되지 않은 강 A에서는 냉간가공 직후에 비하여 약간 증간된다는 것과 큰 차이가 있다(비교예23).However, in the case of steel A without copper, the aging treatment is performed at 20% work hardening, but the elongation is increased, but the tensile strength is reduced by about 95 Mpa as compared with the cold working (Comparative Example 23). In other words, when cold forming is performed using the heat-curable hot rolled steel sheet of the present invention and then aging heat treatment is performed, the strength and elongation are simultaneously improved, and the strength × elongation balance is 6900 to 7700 MPa ·% of the work hardened steel sheet immediately after cold forming. The level is greatly improved from the level of 11000 to 12100 MPa ·% (Inventive Examples 19 to 21), whereas the steel A without copper is slightly increased compared to immediately after cold working (Comparative Example 23).

상술한 바와 같이, 본 발명에 따르면As mentioned above, according to the present invention

첫째, 본 발명에서는 저탄소강을 기본 성분계로 하기 때문에 제강공정에서 취련비용이 감소되며, 열간압연 마무리온도를 쉽게 확보할 수 있으며,First, in the present invention, since low carbon steel is the basic component system, the blowing cost is reduced in the steelmaking process, and hot rolling finish temperature can be easily secured.

둘째, 본 발명의 열연강판을(고강도 열연강판 혹은 산세 열연강판) 프레스 부품으로 제조할 경우 성형단계에서의 가공불량방지, 성형 가압력 및 금형의 마모를 감소시킬 수 있으면서 성형후에는 열처리에 의하여 강도와 인성이 개선되는 유용한 효과가 있는 것이다.Second, when the hot rolled steel sheet of the present invention (high strength hot rolled steel sheet or pickled hot rolled steel sheet) is manufactured from press parts, it is possible to prevent processing defects during the forming step, reduce the pressing force and wear of the mold while forming the strength and heat by heat treatment after molding. There is a useful effect of improving toughness.

Claims (6)

중량%로 C: 0.03∼0.05%, Si:0.1% 이하, Mn: 0.2∼0.4%, P: 0.015% 이하, S: 0.01%이하, Al:0.010∼0.050%, Cu:1.0∼1.5%, Ni: 0.5∼1.0%, N: 50ppm 이하, 나머지 Fe 및 기타 불가피한 불순물을 조성되고, 상기 Cu는 고용상태로 존재하는 냉간가공성이 우수한 가열경화형 열연강판.By weight% C: 0.03-0.05%, Si: 0.1% or less, Mn: 0.2-0.4%, P: 0.015% or less, S: 0.01% or less, Al: 0.010-0.050%, Cu: 1.0-1.5%, Ni : 0.5 to 1.0%, N: 50ppm or less, the remaining Fe and other unavoidable impurities are formed, the Cu is a heat-hardening hot rolled steel sheet having excellent cold workability in the solid state. 제 1항에 있어서, 상기 Ni/Cu의 비는 0.6-1임을 특징으로 하는 냉간가공성이 우수한 가열경화형 열연강판.The hot hardened hot rolled steel sheet having excellent cold workability according to claim 1, wherein the Ni / Cu ratio is 0.6-1. 제 1항 또는 제 2항에 있어서, 상기 열연강판은 인장강도 450MPa이상, 연신율 30% 이상의 기계적성질을 갖으면서, 시효 열처리를 행할 경우 인장강도 600Mpa이상, 연신율 20% 이상, 인장강도×연신율이 10000 MPa·% 이상을 만족함을 특징으로 하는 냉간가공성이 우수한 가열경화형 열연강판.According to claim 1 or 2, wherein the hot-rolled steel sheet has a mechanical property of 450MPa or more of tensile strength, elongation 30% or more, when aging heat treatment, tensile strength of 600Mpa or more, elongation 20% or more, tensile strength x elongation of 10000 Heat hardening hot rolled steel sheet with excellent cold workability, characterized by satisfying MPa ·% or more. 중량%로 C: 0.03∼0.05%, Si:0.1% 이하, Mn: 0.2∼0.4%, P: 0.015% 이하, S: 0.01%이하, Al:0.010∼0.050%, Cu:1.0∼1.5%, Ni: 0.5∼1.0%, N: 50ppm 이하, 나머지 Fe 및 기타 불가피한 불순물을 조성되는 Ar3이상의 마무리압연온도조건으로 열간압연하여 400∼450℃에서 권취하는 냉간가공성이 우수한 가열경화형 열연강판의 제조방법.By weight% C: 0.03-0.05%, Si: 0.1% or less, Mn: 0.2-0.4%, P: 0.015% or less, S: 0.01% or less, Al: 0.010-0.050%, Cu: 1.0-1.5%, Ni : 0.5 to 1.0%, N: 50ppm or less, a method of producing a hot hardened hot rolled steel sheet having a cold workability which is hot rolled at 400 to 450 ° C. by hot rolling under a finish rolling temperature of Ar 3 or more to form remaining Fe and other unavoidable impurities. 제 4항에 있어서, 상기 강슬라브의 Ni/Cu의 비는 0.6-1임을 특징으로 하는 냉간가공성이 우수한 가열경화형 열연강판의 제조방법.The method of claim 4, wherein the ratio of Ni / Cu of the steel slab is 0.6-1. 제 4항 또는 제 5항에 있어서, 상기 열연강판은 산세를 행하여 표면흑피를 제거한 후 도유하여 산세강판으로 제조함을 특징으로 하는 가열경화형 열연강판의 제조방법.The method according to claim 4 or 5, wherein the hot rolled steel sheet is pickled to remove surface black skin and then oiled to produce a pickled steel sheet.
KR1020000064812A 2000-11-02 2000-11-02 Heat hardenable hot rolled steel sheet having superior formability and producing method thereof KR20020034484A (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57181332A (en) * 1981-04-30 1982-11-08 Sumitomo Metal Ind Ltd Manufacture of high-strength steel plate with superior cold and heat hardenability
JPH0215145A (en) * 1988-07-04 1990-01-18 Sumitomo Metal Ind Ltd Working and heating hardened hot rolled steel plate
JPH0344424A (en) * 1989-07-12 1991-02-26 Sumitomo Metal Ind Ltd Manufacture of hot rolled steel sheet for working having excellent low temperature heating hardenability

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57181332A (en) * 1981-04-30 1982-11-08 Sumitomo Metal Ind Ltd Manufacture of high-strength steel plate with superior cold and heat hardenability
JPH0215145A (en) * 1988-07-04 1990-01-18 Sumitomo Metal Ind Ltd Working and heating hardened hot rolled steel plate
JPH0344424A (en) * 1989-07-12 1991-02-26 Sumitomo Metal Ind Ltd Manufacture of hot rolled steel sheet for working having excellent low temperature heating hardenability

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