KR910006027B1 - Making process for steel plate for oil well - Google Patents
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- KR910006027B1 KR910006027B1 KR1019880017916A KR880017916A KR910006027B1 KR 910006027 B1 KR910006027 B1 KR 910006027B1 KR 1019880017916 A KR1019880017916 A KR 1019880017916A KR 880017916 A KR880017916 A KR 880017916A KR 910006027 B1 KR910006027 B1 KR 910006027B1
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Abstract
Description
본 발명은 고인성 고강도를 갖는 유정용 강관강재를 제조하는 방법에 관한 것이다.The present invention relates to a method for producing a steel pipe steel for oil wells having high toughness.
유정용으로 쓰이는 캐이징(casing) 또는 튜빙(tubing pipe)용 API-55 강관은 항복강도에 비하여 높은 인장강도를 요구하기 때문에 합금 성분으로 탄소함량이 약 0.3% 정도 첨가되는데, 이러한 고탄소함유량 때문에 인성과 가공성이 전반적으로 불량하여 파이프제조를 위하여 열연코일(coil)재의 전단(slitting) 작업 또는 굽힘(bending) 작업시 미소 크랙이 자주 발생되는 품질상의 단점이 있다.API-55 steel pipes for casing or tubing pipes used in oil wells require high tensile strength compared to yield strength, so about 0.3% of carbon is added as an alloying element. Due to overall poor workability, there is a disadvantage in quality that micro cracks are frequently generated during the slitting or bending of the hot rolled coil material for the manufacture of pipes.
따라서, 탄소함유량이 높아 인성 및 용접성이 불량한 단점을 개설하기 위한 방법으로서, 중탄소강에 미량의 합금원소 Nb를 첨가하여 제조하거나 또는 중탄소인 C-Mn 강의 저온권취하는 방법등이 제안되어 있다.Therefore, as a method for addressing the disadvantage of high carbon content and poor toughness and weldability, a method of manufacturing by adding a small amount of alloying element Nb to medium carbon steel or winding a low temperature of medium carbon C-Mn steel has been proposed.
API K-55 유정용강관의 생산 강종의 중탄소 Nb 강의 경우는 탄소량이 많음으로 인하여 충격치가 낮은데, 이러한 충격치는 페라이트량과 입도 그리고 펄라이트 조직형성에 따라 크게 좌우되므로, 오스테나이트의 입도 미세화를 위한 제어압연과 오스테나이트 변태시 후물재의 경우 판두께와 같이 방향에 따라 적정변태 조건을 유지시키가 상당히 여려움이 있고 권취온도에 따라 기계적 성질의 변화가 큰 단점이 있다. 또한, 미량합금원소인 Nb, V, Ti이 첨가되지 않는 C-Mn 강을 저온권취하는 방법은 사상압연후 냉각속도로 15℃/sec 이상으로 하여 권취온도를 500℃ 정도로하여 저온권취하기 때문에 제조가격이 낮고 양호한 품질 특성을 얻을 수는 있지만, 런아우트테이블(Run out table)의 냉각능이 큰 설비가 기본적으로 요구된다.The production of API K-55 oil refined steel pipe has low impact value due to the high carbon content, and the impact value is largely dependent on the amount of ferrite, particle size, and pearlite structure. In the case of the material material during rolling and austenite transformation, there is a considerable difficulty in maintaining proper transformation conditions depending on the direction, such as plate thickness, and the mechanical properties change largely depending on the winding temperature. In addition, the low temperature winding method of C-Mn steel without the addition of trace alloy elements Nb, V, and Ti is carried out at a low cooling rate of 15 ° C./sec at a cooling rate after finishing rolling, so that the low temperature winding is performed at about 500 ° C. Although the price is low and good quality characteristics can be obtained, a large cooling capacity of the run out table is basically required.
본 발명은 상기 문제점을 해결하기 위하여 적정합금성분으로 미량인 Nb 및 Ti 원소를 복합첨가하고 적정온도에서 권취하므로서 고인성 고강도 유정용 강관강재를 제조하고자 하는 것으로서 이를 상세히 설명하면 다음과 같다.The present invention is to prepare a high toughness high strength steel pipe steel material by adding a small amount of Nb and Ti as a suitable alloy component and wound at an appropriate temperature in order to solve the above problems as described in detail as follows.
본 발명은 중량%로 C : 0.20%-0.30%, N : 0.003-0.009%, Si : 0.1-0.4%, Mn : 1.0-1.5%, P 및 S : 각각 0.01% 이하, Al : 0.01-0.1%, Nb : 0.02-0.05%, Ti : 0.01-0.03% 및 잔부 Fe로 조성된 슬라브를 1200-1300℃로 가열한 후 마무리 압연온도가 900-950℃범위가 되도록 열간압연을 행한 다음 10℃/sec의 냉각속도로 냉각하여 550-600℃에서 권취시킴을 구성의 특징으로 한다.In the present invention, C: 0.20% -0.30%, N: 0.003-0.009%, Si: 0.1-0.4%, Mn: 1.0-1.5%, P and S: 0.01% or less, Al: 0.01-0.1% , Slab composed of Nb: 0.02-0.05%, Ti: 0.01-0.03% and balance Fe was heated to 1200-1300 ℃ and hot rolled to finish rolling temperature in the range of 900-950 ℃, then 10 ℃ / sec It is characterized by the configuration of winding at 550-600 ℃ by cooling at a cooling rate of.
이하, 본 발명에 대하여 상세히 설명한다.EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.
중탄소 미량합금상에서 탄질화물 형성원소인 Nb와 Ti을 첨가하는 것은 열간압연공정인 가열로에서 Ti은 질소와 반응하여 TiN을 형성하므로서 오스테나이트입의 성장을 억제하는 반면 Nb는 탄소 및 질소와 반응하여 Nb 탄질화물이 열간압연시 석출되도록하여 재결정과입성장을 억제하여 미세한 오스테나이트입을 만듦으로서, 변태후 미세한 페라이트와 펄라이트를 생성시켜 강도와 인성이 우수한 기계적 성질을 얻기 위함인데, 이를 위하여 Nb와 Ti를 각각 0.02-0.05%, 0.01-0.03% 첨가하는 것이 바람직하다.The addition of Nb and Ti, the carbonitride-forming elements, on the medium carbon microalloy suppresses the growth of austenite grains while Ti reacts with nitrogen to form TiN in a hot rolling furnace, while Nb reacts with carbon and nitrogen. Nb carbonitride is precipitated during hot rolling to suppress recrystallization grain growth to create fine austenite grains, and to produce fine ferrite and pearlite after transformation to obtain mechanical properties with excellent strength and toughness. It is preferable to add 0.02-0.05% and 0.01-0.03% of Ti, respectively.
또한, 상기 가열온도는 통상적인 중탄소강의 재가열온도를 행하면되나 1200℃ 이하일 경우에는 Nb, Ti 등의 석출물이 충분히 용해되지 않아 균일한 고용체를 얻기가 어렵고 1300℃ 이상에서는 결정입계에 액상화가 일어나 최종 제품에 고온취화가 발생되기 때문에 그 온도를 1200-1300℃로 하는 것이 바람직하다.In addition, the heating temperature is a reheating temperature of the conventional medium carbon steel, but if it is 1200 ℃ or less, precipitates such as Nb and Ti are not sufficiently dissolved, so that it is difficult to obtain a uniform solid solution. Since high temperature embrittlement occurs in a product, it is preferable to make the temperature into 1200-1300 degreeC.
상기 권취온도가 600℃ 이상인 경우, 페라이트입도가 조대해지고 변태조직의 제2상의 미세한 페라이트 또는 베이나이트상에서 조대한 페라이트로 되어서 강도와 인성이 저하되므로, 550-600℃가 바람직하다. 압연시 오스테나이트 입도는 압연온도와 압하량에 의존되는데 압연 온도가 낮고 압하량이 클수록 미세한 오스테나이트 결정립이 얻어져 오스테나이트 변태시 미세한 펄라이트가 생성되어 충격치(Impact properties)는 향상된다. 따라서, Ar3변태온도 전의 직상에서 마무리 압연을 행해주면 양호한 페라이트 결정립미세화가 일어나게 되나, 더욱 구체적으로는 이 마무리 압연 온도를 900-950℃로 하는 것이 바람직하다.When the coiling temperature is 600 ° C. or higher, the ferrite grain size becomes coarse and the coarse ferrite is reduced on the fine ferrite or bainite phase of the second phase of the metamorphic structure, and thus the strength and toughness are lowered. Therefore, 550-600 ° C. is preferable. The austenite grain size during rolling depends on the rolling temperature and the rolling reduction. The lower the rolling temperature and the larger the rolling reduction, the finer austenite grains are obtained. Thus, Ar 3 haejumyeon row immediately above the finish rolling in the pre-transformation temperature is to occur, but the preferred ferrite grain refinement, and more specifically, it is preferable that the finish rolling temperature to 900-950 ℃.
한편, 냉각시 오스테나이트 변태와 변태시 석출반응조건은 미량합금강(microalloyed steel)의 기계적 성질에 미치는 중요한 요인이 된다. 이때, 상기 기계적 성질중 항복강도 또는 제품의 두께가 증가할수록 적정 변태조건을 유지시키는 것이 상당히 어려우므로 적당한 원소를 첨가하여 변태온도를 낮추거나 혹은 적정냉각조건으로 설비보완을 행하고 있다. 즉, 냉각속도가 빠를수록 페라이트 입도는 작아지고 펄라이트량도 감소되면서 일부는 베이나이트 또는 마르텐사이트 조직으로 변태하므로서 항복강도, 인장강도 값도 증가된다.On the other hand, austenite transformation during cooling and precipitation reaction during transformation are important factors affecting the mechanical properties of microalloyed steel. At this time, as the yield strength or the thickness of the product increases among the mechanical properties, it is very difficult to maintain the proper transformation conditions. Therefore, by adding an appropriate element, the transformation temperature is lowered or the equipment is supplemented with the appropriate cooling conditions. In other words, the faster the cooling rate, the smaller the ferrite grain size and the lower the amount of pearlite, the more the yield strength and tensile strength value are increased as some transform to bainite or martensite structure.
그러나, 상기 냉각속도가 빠를수록 런아우트테이블의 냉각능이 큰 설비가 요구되어 제조비용이 증가되기 때문에 이같은 경제적 측면을 고려하여 냉각속도를 10℃/sec 정도로 하는 것이 바람직하다.However, the higher the cooling rate, the higher the cooling capacity of the runout table is required, and thus the manufacturing cost is increased. Therefore, the cooling rate is preferably about 10 ° C / sec in consideration of such economic aspects.
이하, 실시예를 통하여 본 발명을 상세히 설명한다.Hereinafter, the present invention will be described in detail through examples.
[실시예]EXAMPLE
중탄소선재를 용해하고 필요한 원소를 첨가하여 하기 표1과 같은 조성을 갖는 C-Mn 강, Nb-첨가강, V-첨가강 및 Nb+Ti 첨가강을 제조하였다. 주조된 각 강괴를 1250℃로 가열하여 가열로에서 합금원소 석출물이 완전히 용해되록 일정시간 유지시킨후 마무리 압연을 통상적이 제어압연으로 Ar3변태온도 직상에서 행하였다.The C-Mn steel, the Nb-added steel, the V-added steel, and the Nb + Ti-added steel having the composition shown in Table 1 were prepared by dissolving the medium carbon wire and adding necessary elements. Each cast ingot was heated to 1250 ° C. and maintained for a certain period of time to completely dissolve the alloying element precipitate in the heating furnace, and then finish rolling was usually performed directly under Ar 3 transformation temperature by controlled rolling.
마무리 압연후 런아우트테이블에서 냉각속도를 10℃/sec으로 변환시키고 권취온도를 200-700℃ 범위로 변화실시한후 각각의 권취온도범위에서 권치한 시험소재를 채취하여 인장강도, 항복강도, 충격치 및 연신율을 측정하여 하기 표 2에 나타내었다.After finishing rolling, the run-out table converts the cooling rate into 10 ℃ / sec and changes the winding temperature to 200-700 ℃, and then collects test materials wound in each winding temperature range to obtain tensile strength, yield strength, impact value and Elongation was measured and shown in Table 2 below.
[표 1]TABLE 1
[표 2]TABLE 2
상기 표 2에 나타난 바와같이, 본 발명재(14, 15, 16)는 비교재(1-13)과는 달리 API K-55 품질요구 특성을 만족하는 항복강도, 인장강도 및 연신율을 갖는 다는 것을 알 수 있다.As shown in Table 2, the present invention (14, 15, 16) has a yield strength, tensile strength and elongation that satisfies the API K-55 quality requirements, unlike the comparative material (1-13) Able to know.
이러한 기계적 성질은 가열로에서의 TiN 석출물에 의한 결정립미세화, 압연중 Nb(C, N) 또는 (Nb, Ti)(C, N)의 석출물에 의한 결정립미세화, 변태시 석출강화 및 미세한 펄라이트 또는 일부 베이나이트에 의한 변태강화 효과에 의해서 달성되는 것이다.These mechanical properties are characterized by grain refinement by TiN precipitates in a furnace, grain refinement by precipitates of Nb (C, N) or (Nb, Ti) (C, N) during rolling, precipitation strengthening during transformation and fine pearlite or part It is achieved by the transformation strengthening effect by bainite.
상술한 바와같이, 본 발명은 Nb 및 Ti를 복합 첨가하므로서, 권취온도 또는 냉각속도에 따라 기게적 성질이 크게 영향을 받지 않을 뿐만 아니라 특히, Ti 첨가에 의해 TiN 석출물이 오스테나이트의 입도를 미세화시킴으로서 오스테나이트 변태시 펄라이트의 층상(lamellar) 간격이 좁아져 강에 비하여 우수한 충격치를 갖는 고강도 고인성 유정용 강관강재를 제조할 수 있는 것으로서, 냉각조건을 엄격히 관리할 필요가 없으며, 냉각능력이 적은 설비를 갖는 열연공정에서도 응용될 수 있는 효과가 있는 것이다.As described above, the present invention not only does not significantly affect the mechanical properties depending on the coiling temperature or the cooling rate by adding Nb and Ti in combination, and in particular, by adding Ti, the TiN precipitate refines the particle size of the austenite. When the austenite transformation, the lamellar spacing of pearlite is narrowed, so it is possible to manufacture high-strength, high-toughness oil pipe steel with excellent impact value compared to steel, and it is not necessary to strictly control the cooling conditions, and to install facilities with low cooling ability. There is an effect that can be applied in the hot rolling process.
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KR100431754B1 (en) * | 2001-01-26 | 2004-05-17 | 현대하이스코 주식회사 | Process for producing non-heat treated slurry-type pipe which hardness is guaranteed |
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US20050000601A1 (en) * | 2003-05-21 | 2005-01-06 | Yuji Arai | Steel pipe for an airbag system and a method for its manufacture |
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KR100431754B1 (en) * | 2001-01-26 | 2004-05-17 | 현대하이스코 주식회사 | Process for producing non-heat treated slurry-type pipe which hardness is guaranteed |
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