KR101174970B1 - High strength linepipe steel and method of manufacturing the steel - Google Patents
High strength linepipe steel and method of manufacturing the steel Download PDFInfo
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Abstract
라인파이프용 고강도 강판 및 그 제조 방법에 관한 것으로, 보다 상세하게는 상대적으로 충격특성이 우수한 미세한 베이나이트(Bainite) 조직을 형성시킴으로써 템퍼링 공정을 생략할 수 있는 라이파이프용 고강도 강판 및 그 제조 방법에 관하여 개시한다.
본 발명은 탄소(C) : 0.02 ~ 0.06 중량%, 실리콘(Si) : 0.4 중량% 이하, 망간(Mn) : 1.8 ~ 2.5 중량%, 인(P) : 0.020 중량% 이하, 황(S) : 0.010 중량% 이하, 크롬(Cr) : 0.04 중량% 이하, 니켈(Ni) : 0.2 ~ 1.0 중량%, 몰리브덴(Mo) : 0.2 ~1.0 중량%, 알루미늄(Al) : 0.030 중량% 이하, 구리(Cu) : 0.2 ~ 1.0 중량% 이하, 티타늄(Ti) : 0.01~0.02 중량%, 니오븀(Nb) : 0.02 ~ 0.10 중량%, 바나듐(V) : 0.02 ~ 0.10 중량% 이하, 보론(B) : 0.0005 ~ 0.0050 중량%, 질소(N) : 0.007 중량% 이하, 칼슘 : 0.002 ~ 0.005 중량% 를 포함하고, 나머지는 Fe와 기타 불가피한 불순물로 조성되는 강슬라브를 슬라브재가열온도(SRT) 1100 ~ 1200 ℃로 재가열한 후 열간압연하되, 압연종료온도(FRT) 750~770℃의 범위에 열간압연을 종료하고, 냉각속도 15℃/sec 이하, 냉각종료온도(FCT) 400℃ 이상으로 열처리하여 제조되는 라인파이프용 고강도 강판를 제공한다.The present invention relates to a high-strength steel sheet for line pipes and a method for manufacturing the same, and more particularly, to a high-strength steel sheet for a pipe and a method for manufacturing the same, which can omit a tempering process by forming a fine bainite structure having excellent impact characteristics. Discuss about.
The present invention is carbon (C): 0.02 ~ 0.06% by weight, silicon (Si): 0.4% by weight or less, manganese (Mn): 1.8 to 2.5% by weight, phosphorus (P): 0.020% by weight or less, sulfur (S): 0.010 wt% or less, Chromium (Cr): 0.04 wt% or less, Nickel (Ni): 0.2-1.0 wt%, Molybdenum (Mo): 0.2 ~ 1.0 wt%, Aluminum (Al): 0.030 wt% or less, Copper (Cu ): 0.2 to 1.0 wt% or less, titanium (Ti): 0.01 to 0.02 wt%, niobium (Nb): 0.02 to 0.10 wt%, vanadium (V): 0.02 to 0.10 wt% or less, boron (B): 0.0005 to Reheat the steel slab consisting of 0.0050% by weight, nitrogen (N): 0.007% by weight or less, calcium: 0.002% to 0.005% by weight, and the remainder composed of Fe and other unavoidable impurities to the slab reheating temperature (SRT) 1100-1200 ° C. After the hot rolling, the end of hot rolling in the rolling end temperature (FRT) 750 ~ 770 ℃ range, the line pipe is manufactured by heat treatment at cooling rate 15 ℃ / sec or less, cooling end temperature (FCT) 400 ℃ or more Provide a high strength steel sheet.
Description
본 발명은 라인파이프용 고강도 강판 및 그 제조 방법에 관한 것으로, 보다 상세하게는 상대적으로 충격특성이 우수한 미세한 베이나이트(Bainite) 조직을 형성시킴으로써 템퍼링 공정을 생략할 수 있는 라이파이프용 고강도 강판 및 그 제조 방법에 관한 것이다.
The present invention relates to a high-strength steel sheet for line pipes and a method for manufacturing the same, and more particularly, to a high-strength steel sheet for pipes that can omit the tempering process by forming a fine bainite structure having relatively high impact characteristics. It relates to a manufacturing method.
원유, 천연 가스 등의 장거리 수송 방법으로서 중요한 파이프 라인의 간선에 사용되는 라인 파이프용 강관으로서, 고강도, 고인성의 라인 파이프용 강관이 요구되고 있다. As a line pipe steel pipe used for the trunk line of a pipeline which is important as a long-distance transportation method of crude oil, natural gas, etc., the high strength and high toughness line pipe steel pipe is calculated | required.
특히, 최근 고압화에 의한 수송 효율의 향상이나, 라인 파이프의 외경 및 중량의 저감에 의한 현지 시공 능률의 향상을 위하여 고강도 라인 파이프가 요망되고 있다.In particular, high-strength line pipes are desired in recent years in order to improve transportation efficiency due to high pressure and to improve local construction efficiency by reducing outer diameter and weight of line pipes.
본 발명의 목적은 저온 인성이 우수한 라인파이프용 고강도 강판 및 그 제조방벙을 제공하는 것이다. An object of the present invention is to provide a high-strength steel sheet for line pipe excellent in low temperature toughness and a manufacturing method thereof.
본 발명의 다른 목적은 충격특성이 우수한 미세 베이나이트 조직을 형성시킴으로써 템퍼링 공정을 생략할 수 있는 라인파이프용 고강도 강판 제조방법을 제공하는 것이다.
Another object of the present invention is to provide a method for producing a high strength steel sheet for a line pipe which can omit the tempering process by forming a fine bainite structure having excellent impact characteristics.
본 발명은 탄소(C) : 0.02 ~ 0.06 중량%, 실리콘(Si) : 0.4 중량% 이하, 망간(Mn) : 1.8 ~ 2.5 중량%, 인(P) : 0.020 중량% 이하, 황(S) : 0.010 중량% 이하, 크롬(Cr) : 0.04 중량% 이하, 니켈(Ni) : 0.2 ~ 1.0 중량%, 몰리브덴(Mo) : 0.2 ~1.0 중량%, 알루미늄(Al) : 0.030 중량% 이하, 구리(Cu) : 0.2 ~ 1.0 중량% 이하, 티타늄(Ti) : 0.01~0.02 중량%, 니오븀(Nb) : 0.02 ~ 0.10 중량%, 바나듐(V) : 0.02 ~ 0.10 중량% 이하, 보론(B) : 0.0005 ~ 0.0050 중량%, 질소(N) : 0.007 중량% 이하, 칼슘 : 0.002 ~ 0.005 중량% 를 포함하고, 나머지는 Fe와 기타 불가피한 불순물로 조성되는 강슬라브를 슬라브재가열온도(SRT) 1100 ~ 1200 ℃로 재가열한 후 열간압연하되, 압연종료온도(FRT) 750~770℃의 범위에 열간압연을 종료하고, 냉각속도 15℃/sec 이하, 냉각종료온도(FCT) 400℃ 이상으로 열처리하여 제조되는 라인파이프용 고강도 강판를 제공한다.
The present invention is carbon (C): 0.02 ~ 0.06% by weight, silicon (Si): 0.4% by weight or less, manganese (Mn): 1.8 to 2.5% by weight, phosphorus (P): 0.020% by weight or less, sulfur (S): 0.010 wt% or less, Chromium (Cr): 0.04 wt% or less, Nickel (Ni): 0.2-1.0 wt%, Molybdenum (Mo): 0.2 ~ 1.0 wt%, Aluminum (Al): 0.030 wt% or less, Copper (Cu ): 0.2 to 1.0 wt% or less, titanium (Ti): 0.01 to 0.02 wt%, niobium (Nb): 0.02 to 0.10 wt%, vanadium (V): 0.02 to 0.10 wt% or less, boron (B): 0.0005 to Reheat the steel slab consisting of 0.0050% by weight, nitrogen (N): 0.007% by weight or less, calcium: 0.002% to 0.005% by weight, and the remainder composed of Fe and other unavoidable impurities to the slab reheating temperature (SRT) 1100-1200 ° C. After the hot rolling, the end of hot rolling in the rolling end temperature (FRT) 750 ~ 770 ℃ range, the line pipe is manufactured by heat treatment at cooling rate 15 ℃ / sec or less, cooling end temperature (FCT) 400 ℃ or more Provide a high strength steel sheet.
본 발명은 탄소(Carbon) 함량을 낮게 설계하고, 망간(Mn)량을 높여 탄소함량 감소에 따른 재질확보 및 인성향상을 유도하고, 바나듐(V)함량을 증가시킴으로서 V(C,N) 석출강화효과에 의한 강도 및 인성향상 얻을 수 있는 라인파이프용 고강도 강판 및 그 제조방법을 제공하는 효과를 가져온다.The present invention is designed to lower the carbon content, increase the manganese (Mn) content to induce material acquisition and toughness improvement by reducing the carbon content, and increase the vanadium (V) content to increase the precipitation of V (C, N) The effect of providing a high-strength steel sheet for line pipe and a method of manufacturing the same can be obtained to improve the strength and toughness by the effect.
그리고, 본 발명은 냉각종료온도를 높게 하고 냉각속도를 15℃/s 이하로 하여 상온까지의 냉각시간을 충분히 확보함으로써 V 석출물에 의한 강도 향상 효과를 증가시킬 수 있고, 상대적으로 낮은 냉각속도와 높은 냉각종료온도에 의한 결정립크기 증가를 B을 첨가에 의한 변태강화를 통해 보상할 수 있는 라인파이프용 고강도 강판 제조방법을 제공한다.In addition, the present invention can increase the strength improvement effect by V precipitates by increasing the cooling end temperature and securing a cooling time up to room temperature by lowering the cooling rate to 15 ° C./s or less, and relatively low cooling rate and high It provides a high-strength steel sheet manufacturing method for line pipe that can compensate for the increase in grain size due to the cooling end temperature through the transformation strengthening by the addition of B.
또한, 본 발명은 상대적으로 충격특성이 우수한 미세 베이나이트 조직을 형성시킴으로써 템퍼링(tempering) 공정을 생략할 수 있는 라인파이프용 고강도 강판 제조방법을 제공한다.
In addition, the present invention provides a high-strength steel sheet manufacturing method for line pipe that can omit the tempering (tempering) process by forming a fine bainite structure having relatively excellent impact characteristics.
도 1은 압연종료온도에 따른 각성분계의 미세조직 그레인 맵(Grain map),
도 2는 Nb 함량에 따른 석출물을 나타낸 비교사진,
도 3은 각 성분계별 FRT 조건에 따른 인장강도를 나타낸 그래프,
도 4는 각 성분계별 FRT 조건에 따른 항복강도를 나타낸 그래프,
도 5는 냉각종료온도(FCT)에 따른 1번 성분계의 미세조직사진,
도 6은 냉각종료온도(FCT)에 따른 2번 성분계의 미세조직사진,
도 7은 냉각종료온도(FCT)에 따른 3번 성분계의 미세조직사진,
도 8은 2차 실험의 1번 성분계와 3번 성분계의 석출물을 나타낸 비교사진,
도 9는 2차 실험의 3번 성분계의 석출물의 확대사진,
도 10은 각 성분계별 냉각종료온도(FCT)에 따른 항복강도(YS)와 인장강도(TS)를 나타낸 그래프,
도 11은 시험온도에 따른 임팩트 에너지 측정결과를 나타낸 그래프,
도 12는 -40℃ 및 -80℃ 에서의 각 성분계별 충격에너지를 나타낸 그래프임.1 is a microstructure grain map (Grain map) of the angular component according to the rolling end temperature,
2 is a comparative picture showing the precipitate according to the Nb content,
3 is a graph showing the tensile strength according to the FRT conditions for each component system,
4 is a graph showing the yield strength according to the FRT conditions for each component system,
5 is a microstructure photograph of the
6 is a microstructure photograph of the second component system according to the cooling end temperature (FCT),
7 is a microstructure photograph of the third component system according to the cooling end temperature (FCT),
8 is a comparative photograph showing the precipitates of
9 is an enlarged photograph of precipitates in component 3 of the second experiment,
10 is a graph showing the yield strength (YS) and tensile strength (TS) according to the cooling end temperature (FCT) for each component system,
11 is a graph showing the impact energy measurement results according to the test temperature,
12 is a graph showing the impact energy of each component system at -40 ° C and -80 ° C.
본 발명의 이점 및 특징, 그리고 그것들을 달성하는 방법은 첨부되는 도면과 함께 상세하게 후술되어 있는 실시예들을 참조하면 명확해질 것이다. 그러나, 본 발명은 이하에서 개시되는 실시예들에 한정되는 것이 아니라 서로 다른 다양한 형태로 구현될 것이며, 단지 본 실시예들은 본 발명의 개시가 완전하도록 하며, 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자에게 발명의 범주를 완전하게 알려주기 위해 제공되는 것이며, 본 발명은 청구항의 범주에 의해 정의될 뿐이다. 명세서 전체에 걸쳐 동일 참조 부호는 동일 구성요소를 지칭한다.Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.
이하 첨부된 도면을 참조하여 본 발명의 실시예에 따른 라인파이프용 고강도 강판 및 그 제조 방법에 관하여 상세히 설명하면 다음과 같다.
Hereinafter, a high strength steel sheet for a line pipe and a method of manufacturing the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
라인파이프용 고강도 강판High strength steel sheet for line pipe
본 발명에 따른 라인파이프용 고강판 강판은 탄소(C) : 0.02 ~ 0.06 중량%, 실리콘(Si) : 0.4 중량% 이하, 망간(Mn) : 1.8 ~ 2.5 중량%, 인(P) : 0.020 중량% 이하, 황(S) : 0.010 중량% 이하, 크롬(Cr) : 0.04 중량% 이하, 니켈(Ni) : 0.2 ~ 1.0 중량%, 몰리브덴(Mo) : 0.2 ~1.0 중량%, 알루미늄(Al) : 0.030 중량% 이하, 구리(Cu) : 0.2 ~ 1.0 중량% 이하, 티타늄(Ti) : 0.01~0.02 중량%, 니오븀(Nb) : 0.02 ~ 0.10 중량%, 바나듐(V) : 0.02 ~ 0.10 중량% 이하, 보론(B) : 0.0005 ~ 0.0050 중량%, 질소(N) : 0.007 중량% 이하, 칼슘 : 0.002 ~ 0.005 중량% 를 포함하고, 나머지는 Fe와 기타 불가피한 불순물로 구성된다.
Steel sheet for line pipe according to the present invention is carbon (C): 0.02 ~ 0.06% by weight, silicon (Si): 0.4% by weight or less, manganese (Mn): 1.8 ~ 2.5% by weight, phosphorus (P): 0.020 weight % Or less, sulfur (S): 0.010% by weight or less, chromium (Cr): 0.04% by weight or less, nickel (Ni): 0.2-1.0% by weight, molybdenum (Mo): 0.2-1.0% by weight, aluminum (Al): 0.030 wt% or less, Copper (Cu): 0.2 to 1.0 wt% or less, Titanium (Ti): 0.01 to 0.02 wt%, Niobium (Nb): 0.02 to 0.10 wt%, Vanadium (V): 0.02 to 0.10 wt% or less , Boron (B): 0.0005 ~ 0.0050% by weight, nitrogen (N): 0.007% by weight or less, calcium: 0.002 ~ 0.005% by weight, the remainder is composed of Fe and other unavoidable impurities.
이하, 본 발명에 따른 라인파이프용 고강판 강판에 포함되는 각 성분의 역할 및 그 함량에 대하여 설명하면 다음과 같다.
Hereinafter, the role and content of each component included in the steel sheet for line pipe according to the present invention will be described.
탄소(C)Carbon (C)
본 발명에서 탄소(C)는 강판의 강도를 확보하기 위해 첨가된다. In the present invention, carbon (C) is added to secure the strength of the steel sheet.
상기 탄소(C)는 강판 전체 중량의 0.02 ~ 0.06 중량%의 함량비로 첨가되는 것이 바람직하다. 상기 탄소(C)가 0.02 중량% 미만으로 첨가되면 제2상 조직의 분율이 저하되어 강판의 강도가 낮아지는 문제점이 있으며, 상기 탄소(C)의 함량이 0.06 중량%을 초과하면 강판의 강도는 증가하나 저온 충격인성 및 용접성이 저하되는 문제점이 있다.
The carbon (C) is preferably added in a content ratio of 0.02 to 0.06% by weight of the total weight of the steel sheet. If the carbon (C) is added less than 0.02% by weight, the fraction of the second phase structure is lowered and the strength of the steel sheet is lowered. If the content of the carbon (C) exceeds 0.06% by weight, the strength of the steel sheet is There is a problem that the increase in low-temperature impact toughness and weldability is reduced.
실리콘(Si)Silicon (Si)
본 발명에서 실리콘(Si)은 제강공정에서 강 중의 산소를 제거하기 위한 탈산제로 첨가된다. 또한 실리콘(Si)은 고용강화 효과도 가진다. In the present invention, silicon (Si) is added as a deoxidizer for removing oxygen in the steel in the steelmaking process. Silicon (Si) also has a solid solution strengthening effect.
상기 실리콘(Si)은 강판 전체 중량의 0.4 중량% 이하의 함량비로 첨가되는 것이 바람직하다. 실리콘(Si)의 함량이 0.4 중량%를 초과하면 강판 표면에 산화물을 형성하여 강판의 도금특성을 저해하고 용접성을 저하시키는 문제점이 있다.
The silicon (Si) is preferably added in an amount ratio of 0.4% by weight or less of the total weight of the steel sheet. When the content of silicon (Si) exceeds 0.4% by weight, an oxide is formed on the surface of the steel sheet, thereby inhibiting plating characteristics of the steel sheet and reducing weldability.
망간(Mn)Manganese (Mn)
망간(Mn)은 오스테나이트 안정화 원소로서 본 발명에서 Ar3 온도를 낮추어 제어 압연 영역을 확대시킴으로써 압연에 의한 결정립을 미세화시켜 강도 및 인성을 향상시키는 역할을 한다. Manganese (Mn) is an austenite stabilizing element in the present invention, by lowering the Ar 3 temperature to enlarge the controlled rolling region, thereby miniaturizing grains by rolling to improve strength and toughness.
상기 망간은 강판 전체 중량의 1.8 ~ 2.5 중량%의 함량비로 첨가되는 것이 바람직하다. 상기 망간(Mn)이 1.8 중량% 미만으로 첨가되면 제2상 조직의 형성이 불충분하여 강도 향상에 기여하지 못한다. 또한, 상기 망간(Mn)의 함량이 2.5 중량%를 초과하면 강에 고용된 황을 MnS로 석출하여 저온충격인성을 저하시키는 문제점이 있다.
The manganese is preferably added in a content ratio of 1.8 to 2.5% by weight of the total weight of the steel sheet. When the manganese (Mn) is added in less than 1.8% by weight, the formation of the second phase tissue is insufficient to contribute to the improvement of strength. In addition, when the content of the manganese (Mn) exceeds 2.5% by weight, there is a problem that precipitates sulfur dissolved in steel as MnS to lower the low temperature impact toughness.
인(P), 황(S), 질소(N)Phosphorus (P), sulfur (S), nitrogen (N)
인(P)은 저온충격인성을 저하시키는 대표적인 원소로서 그 함량이 낮으면 낮을수록 좋다. 따라서, 인(P)의 함량은 0.02 중량% 이하로 제한하는 것이 바람직하다. Phosphorus (P) is a representative element for lowering the low temperature impact toughness. The lower the content, the better. Therefore, the content of phosphorus (P) is preferably limited to 0.02% by weight or less.
황(S)은 상기 인(P)과 함께 강의 제조시 불가피하게 함유되는 원소로서, 유화물계 개재물(MnS)을 형성하여 저온충격인성을 저하시킨다. 따라서, 황(S)의 함량은 0.01 중량% 이하로 제한하는 것이 바람직하다. Sulfur (S) is an element that is inevitably contained in the production of steel together with phosphorus (P), and forms an emulsion-based inclusion (MnS) to lower low-temperature impact toughness. Therefore, the content of sulfur (S) is preferably limited to 0.01% by weight or less.
질소(N)는 강 내부에 개재물을 발생시켜 강판의 내부 품질을 저하시키므로, 극저의 함량비로 관리하는 것이 바람직하나, 이를 위해서는 강판의 제조 비용이 증가하고, 또한 질소(N) 관리의 어려움이 있다. 따라서, 본 발명에서는 질소(N)의 함량을 0.007 중량% 이하로 제한한다.
Since nitrogen (N) causes inclusions in the steel to degrade the internal quality of the steel sheet, it is preferable to manage it at an extremely low content ratio, but for this purpose, the manufacturing cost of the steel sheet increases, and there is also difficulty in managing the nitrogen (N). . Therefore, in the present invention, the content of nitrogen (N) is limited to 0.007% by weight or less.
크롬(Cr)Chrome (Cr)
본 발명에서 크롬(Cr)은 담금질성 향상에 유효한 원소지만, 그 함유량이 0.04 중량%를 초과하면 용접성이나 열영향부(HAZ) 인성을 저하하기 때문에, 그 함량을 0.04 중량% 이하로 제한한다.
In the present invention, chromium (Cr) is an effective element for improving hardenability, but if the content exceeds 0.04% by weight, the weldability and the heat affected zone (HAZ) toughness are lowered, so the content is limited to 0.04% by weight or less.
니켈(Ni)Nickel (Ni)
본 발명에서 니켈(Ni)은 결정립을 미세화하고 오스테나이트 및 페라이트에 고용되어 기지를 강화시킨다. 특히 니켈은 저온인성을 향상시키는데 효과적인 원소이다. In the present invention, nickel (Ni) is refined to solid crystals and dissolved in austenite and ferrite to strengthen the matrix. In particular, nickel is an effective element for improving low temperature toughness.
상기 니켈은 강판 전체 중량의 0.2 ~ 1.0 중량%의 함량비로 첨가되는 것이 바람직하다. 니켈(Ni)이 0.2 중량% 미만의 함량비로 첨가되면 상기 니켈 첨가 효과를 제대로 발휘할 수 없다. 또한, 니켈(Ni)의 함량이 1.0 중량%를 초과하면 적열취성을 유발하는 문제점이 있다.
The nickel is preferably added in a content ratio of 0.2 to 1.0% by weight of the total weight of the steel sheet. When nickel (Ni) is added in an amount ratio of less than 0.2% by weight, the nickel addition effect may not be properly exhibited. In addition, when the content of nickel (Ni) exceeds 1.0% by weight, there is a problem of causing red light brittleness.
몰리브덴(Mo)Molybdenum (Mo)
본 발명에서 몰리브덴(Mo)은 담금질성을 높이는 것과 동시에 템퍼링 연화 저항을 높이고, 강도 상승에 유효하지만 그 함유량이 0.2 중량% 미만으로는 그 효과가 충분하지 않고, 1.0 중량%를 초과하면 용접성을 저하시킴과 동시에 탄화물의 석출에 의하여 항복비를 상승시키므로, 그 함량을 0.2 ~ 1.0 중량%한다.
In the present invention, molybdenum (Mo) increases the hardenability and at the same time increase the tempering softening resistance, but effective in increasing the strength, the content is less than 0.2% by weight, the effect is not enough, if the content exceeds 1.0% by weight, weldability is lowered At the same time, the yield ratio is increased by precipitation of carbide, so that the content is 0.2 to 1.0% by weight.
알루미늄(Al)Aluminum (Al)
알루미늄(Al)은 강 중의 산소를 제거하기 위한 탈산제 역할을 한다. Aluminum (Al) serves as a deoxidizer to remove oxygen in the steel.
상기 알루미늄(Al)은 강판 전체 중량의 0.03 중량% 이하의 함량비로 첨가되는 것이 바람직하다. 알루미늄(Al)의 함량이 0.03 중량%를 초과하면 비금속 개재물인 Al2O3를 형성하여 저온충격인성을 저하시키는 문제점이 있다.
The aluminum (Al) is preferably added in an amount ratio of 0.03% by weight or less of the total weight of the steel sheet. When the content of aluminum (Al) exceeds 0.03% by weight, there is a problem in that low-temperature impact toughness is reduced by forming Al 2 O 3 , which is a non-metallic inclusion.
구리(Cu)Copper (Cu)
본 발명에서 구리(Cu)는 강도 상승 및 인성 개선에 유효한 원소지만, 함유량이 0.2 중량% 미만에서는 충분한 효과가 발휘되지 않고, 1.0%를 초과하면 석출경화가 현저하고, 강재 표면에 균열이 발생하기 때문에 그 범위를 0.2 ~ 1.0 중량%로 한다.
In the present invention, copper (Cu) is an effective element for increasing strength and improving toughness, but when the content is less than 0.2% by weight, sufficient effect is not exerted, and when it exceeds 1.0%, precipitation hardening is remarkable, and cracking occurs on the steel surface. Therefore, the range is made into 0.2 to 1.0 weight%.
티타늄(Ti)Titanium (Ti)
상기 티타늄(Ti)은 용접열영향부(HAZ)의 조직 조대화를 억제하고 HAZ 인성에 기여하는 원소로, 강판 전체 중량의 0.01 ~ 0.02 중량%의 함량비로 첨가되는 것이 바람직하다. 티타늄의 함량이 0.01 중량% 미만이면 상기의 티타늄 첨가 효과가 미미하고, 티타늄의 함량이 0.02 중량%를 초과하면 TiN석출물이 조대해져 결정립 성장을 억제하는 효과가 저하된다.
The titanium (Ti) is an element that suppresses the coarsening of the weld heat affected zone (HAZ) and contributes to the HAZ toughness, and is preferably added in an amount ratio of 0.01 to 0.02% by weight of the total weight of the steel sheet. If the content of titanium is less than 0.01% by weight, the effect of adding titanium is insignificant, and if the content of titanium is more than 0.02% by weight, the TiN precipitate is coarsened, thereby reducing the effect of inhibiting grain growth.
니오븀(Nb)Niobium (Nb)
니오븀(Nb)은 탄소(C), 질소(N)와 결합하여 탄화물 또는 질화물을 형성한다. 이는 압연시 결정립 성장을 억제하여 결정립을 미세화시키므로 강도와 저온인성을 향상시킨다. Niobium (Nb) combines with carbon (C) and nitrogen (N) to form carbides or nitrides. This improves the strength and low temperature toughness by suppressing grain growth during rolling to refine grains.
상기 니오븀(Nb)은 강판 전체 중량의 0.02~0.1 중량%의 함량비로 첨가되는 것이 바람직하다. 니오븀(Nb)의 함량이 0.02 중량% 미만일 경우 상기의 니오븀 첨가 효과를 제대로 발휘할 수 없다. 한편, 니오븀(Nb)의 함량이 0.1 중량%를 초과할 경우 강판의 용접성을 저하하며, 또한 니오븀(Nb) 함량 증가에 따른 강도와 저온인성은 더 이상 향상되지 않고 페라이트 내에 고용된 상태로 존재하여 오히려 충격인성을 저하시킬 위험이 있다.
The niobium (Nb) is preferably added in an amount ratio of 0.02 to 0.1% by weight of the total weight of the steel sheet. When the content of niobium (Nb) is less than 0.02% by weight, the above niobium addition effect may not be properly exhibited. On the other hand, when the content of niobium (Nb) exceeds 0.1% by weight, the weldability of the steel sheet is lowered, and also the strength and low temperature toughness due to the increase in niobium (Nb) content is no longer improved and is present in solid solution in ferrite. Rather, there is a risk of deteriorating impact toughness.
보론(B)Boron (B)
보론(B)은 고용되면 켄칭성을 증가시키고, 또한 BN으로서 석출되면 고용 N을 저하시켜서 HAZ의 인성을 향상시키는 원소이다. 강도와 인성의 밸런스를 양호하게 하기 위해서는 첨가량을 0.0005 내지 0.0050％로 하는 것이 바람직하다.
Boron (B) is an element that increases the hardenability when dissolved and increases the toughness of HAZ by decreasing the solid solution N when precipitated as BN. In order to improve the balance between strength and toughness, the amount of addition is preferably 0.0005 to 0.0050%.
칼슘(Ca)Calcium (Ca)
칼슘(Ca)은 유화물계 개재물의 형태 제어에 의한 인성 향상에 유효한 원소이지만, 0.002 중량% 미만으로는 그 효과가 충분하지 않고, 0.005 중량% 초과하면 그 효과가 포화되고, 인성을 저하시키기 때문에, 첨가량을 0.002 ~ 0.005 중량%로 하는 것이 바람직하다.
Calcium (Ca) is an element effective for improving toughness by controlling the shape of an emulsion-based inclusion, but the effect is not sufficient at less than 0.002% by weight, and if it exceeds 0.005% by weight, the effect is saturated and the toughness is lowered. It is preferable to make the addition amount 0.002 to 0.005 weight%.
상기 조성으로 이루어진 강판은 20% 미만의 페라이트와 80% 이상의 베이나이트 미세조직으로 이루어져, 항복강도(YS) 730~750MPa, 인장강도(TS) 820~850MPa 의 고강도를 가지며, -40℃에서 충격에너지 250J 이상으로 저온인성을 만족한다.
Steel plate is composed of less than 20% ferrite and more than 80% bainite microstructure, yield strength (YS) 730 ~ 750MPa, tensile strength (TS) 820 ~ 850MPa high strength, impact energy at -40 ℃ It satisfies low temperature toughness with 250J or more.
이러한 특성은 본 발명의 조성에 있어서 C 함량을 낮게 설계하고, Mn 량을 높여 C 함량 감소에 따른 재질 확보 및 인성 향상을 유도하고, V 함량을 증가시켜 V(C,N) 석출 강화효과에 의한 강도 및 인성 향상에 의한 것이다.
This characteristic is designed to lower the C content in the composition of the present invention, to increase the Mn content to induce the securing of material and toughness by reducing the C content, and to increase the V content by the V (C, N) precipitation strengthening effect It is by improving strength and toughness.
실시예Example
이하, 본 발명의 바람직한 실시예를 통해 본 발명의 구성 및 작용을 더욱 상세히 설명하기로 한다. 다만, 이는 본 발명의 바람직한 예시로 제시된 것이며 어떠한 의미로도 이에 의해 본 발명이 제한되는 것으로 해석될 수는 없다. Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.
여기에 기재되지 않은 내용은 이 기술 분야에서 숙련된 자이면 충분히 기술적으로 유추할 수 있는 것이므로 그 설명을 생략하기로 한다.
Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.
<1차 실험><1st experiment>
1. 강판의 제조1. Manufacture of steel plate
표 1에 기재된 조성 및 표 2에 기재된 공정 조건으로 강판을 제조하였다.
The steel plate was manufactured by the composition of Table 1, and the process conditions of Table 2.
2번을 기본성분계로 하여, 1번은 C함량을 감소한 것이고, 3번은 C함량을 증가한 것이며, 4번은 B를 첨가한 것이고, 5번은 Nb 함량을 증가시킨 것이고, 6번은 V를 첨가한 것이다.
With No. 2 as the basic component system, No. 1 is the decrease of C content, No. 3 is the increase of C content, No. 4 is the addition of B, No. 5 is the increase of Nb content, No. 6 is the addition of V.
2. 미세조직 분석2. Microstructure Analysis
도 1은 압연종료온도에 따른 각성분계의 미세조직 그레인 맵(Grain map)을 나타낸 것이다.Figure 1 shows a microstructure grain map (Grain map) of each component system according to the rolling end temperature.
도 1을 살펴보면 압연종료온도(FRT)가 낮을수록 조직이 미세해지는 경향을 나타냄을 알 수 있다.
Looking at Figure 1 it can be seen that the lower the rolling end temperature (FRT) shows a tendency for the structure becomes fine.
3. Nb 함량에 따른 석출물 비교3. Comparison of precipitates according to Nb content
도 2는 Nb 함량에 따른 석출물을 나타낸 것이다.Figure 2 shows the precipitate according to the Nb content.
도시된 바와 같이 0.04 중량% Nb 첨가시 Ti, Nb(미량) 탄질화물이 석출되고, As shown, when 0.04% by weight of Nb is added, Ti, Nb (trace) carbonitride is precipitated,
0.04 중량% Nb 첨가시 Ti 탄질화물 이외에 구형 형태의 Nb, Ti(미량) 탄질화물도 석출됨을 알 수 있다.
When 0.04% by weight of Nb is added, it can be seen that in addition to Ti carbonitride, spherical forms of Nb and Ti (trace) carbonitride are also precipitated.
4. 인장강도(TS) 및 항복강도(YS)4. Tensile Strength (TS) and Yield Strength (YS)
도 3은 각 성분계별 FRT 조건에 따른 인장강도를 나타낸 것이고,Figure 3 shows the tensile strength according to the FRT conditions for each component system,
도 4는 각 성분계별 FRT 조건에 따른 항복강도를 나타낸 것이다.Figure 4 shows the yield strength according to the FRT conditions for each component system.
도 3을 살펴보면, 인장강도는 1번(0.04wt% C)과 5번(0.08wt% Nb) 성분계를 제외하고, 목표치인 800MPa 이상에 모두 도달했음을 알 수 있다. Looking at Figure 3, it can be seen that the tensile strength has reached all of the target value of 800MPa or more, except for the 1 (0.04wt% C) and 5 (0.08wt% Nb) component system.
보론(B)을 첨가한 경우(4번 성분계) 인장강도가 약 100MPa 상승함을 알 수 있으나, Nb 첨가(5번 성분계)에 따른 인장강도의 상승효과가 미미하고, V 첨가(6번 성분계)에 따른 인장강도의 상승효과 또한 미미하였다.When boron (B) is added (component 4), the tensile strength increases by about 100 MPa, but the synergistic effect of tensile strength due to the addition of Nb (component 5) is minimal, and V is added (component 6). The synergistic effect of tensile strength was also negligible.
또한, FRT가 높을수록 인장강도가 상승하는 결과를 나타냈다.The higher the FRT, the higher the tensile strength.
상기와 같은 1차 실험의 결과로부터 6번 성분계(V : 0.06wt%)의 조성을 3번 공정조건(FRT 720℃)으로 제조하는 경우, 항복강도(YS) 740MPa, 인장강도(TS) 826MPa 으로 가장 우수한 결과값을 가져오는 것을 알 수 있다.
When the composition of component No. 6 (V: 0.06wt%) was manufactured under the process No. 3 (
<2차 실험><2nd experiment>
1. 강판의 제조1. Manufacture of steel plate
표 3에 기재된 조성 및 표 4에 기재된 공정 조건으로 강판을 제조하였다. The steel sheet was manufactured by the composition of Table 3, and the process conditions of Table 4.
1번 성분계는 V를 0.080 중량% 첨가한 것이고, 2번 성분계는 B를 0.001 중량 % 첨가한 것이고, 3번 성분계는 V : 0.060 중량%, B : 0.001 중량% 첨가한 것이다.
Component No. 1 added 0.080% by weight of V, Component No. 2 added 0.001% by weight of B, and Component No. 3 added V: 0.060% by weight and B: 0.001% by weight.
공정조건은 냉각종료온도(FCT)와 냉각속도에 변화를 주어 실험하였다.
Process conditions were tested by varying the cooling end temperature (FCT) and cooling rate.
2. 미세조직 분석2. Microstructure Analysis
도 5는 냉각종료온도(FCT)에 따른 1번 성분계의 미세조직사진을 나타낸 것이고, 도 6은 냉각종료온도(FCT)에 따른 2번 성분계의 미세조직사진을 나타낸 것이고, 도 7은 냉각종료온도(FCT)에 따른 3번 성분계의 미세조직사진을 나타낸 것이다.Figure 5 shows a microstructure photograph of the
V 첨가시 (1번 성분계, 3번 성분계) FCT 가 높은 경우, 그래뉼러 베이나이트(granular bainite) 형태가 보이고, 모든 성분계에서 FCT가 300일 때 침사 페라이트(acicular ferrite) 형태가 나타남을 알 수 있다.
When V is added (
3. 석출물 비교3. Precipitation Comparison
도 8은 1번 성분계와 3번 성분계의 석출물을 나타낸 것이고, 도 9는 3번 성분계의 석출물을 더욱 확대하여 나타낸 것이다.8 shows the precipitates of component No. 1 and component No. 3, and FIG. 9 shows an enlarged view of the precipitates of component No. 3 further.
기지내 석출물은 1차압연과 동일하게 모든 강에서 사각형태의 수십 nm의 Ti, Nb(미량)탄질화물이 존재하며 1번 성분계(Nb : 0.08wt%)에서는 구형태의 100nm 내외 크기의 Nb탄질화물 관찰되었다. 그리고 V 첨가강(1번, 3번 성분계)에서는 20nm~25nm V(C,N) 석출물이 관찰되었다.
In-situ precipitates have Ti and Nb (trace) carbonitrides of several tens of squares in all steels as in primary rolling, and Nb carbonaceous particles of around 100 nm size in spherical form (Nb: 0.08wt%). Cargo was observed. In the V-added steels (
4. 인장강도(TS) 및 항복강도(YS)4. Tensile Strength (TS) and Yield Strength (YS)
도 10은 각 성분계별 냉각종료온도(FCT)에 따른 항복강도(YS)와 인장강도(TS)를 나타낸 것이다.
Figure 10 shows the yield strength (YS) and tensile strength (TS) according to the cooling end temperature (FCT) for each component system.
길이방향 결과임을 생각하면 전체 조건에서 TS는 760Mpa 이상, YS는 3번 성분계(0.06wt% V & 10ppm B)를 제외하고 690Mpa 에 충족되지 않을 것으로 예상된다.
Considering the longitudinal results, it is expected that TS will not meet 690Mpa at all conditions except for 760Mpa and YS in the third component system (0.06wt% V & 10ppm B).
FCT 감소에 따라,As the FCT decreases,
B첨가강은 YS 유지, TS 증가하는 경향을 나타냈으며,Additive steel B tended to maintain YS and increase TS.
V첨가강은 YS 감소, TS 증가하는 경향을 나타냈고,V additive steels tended to decrease YS and increase TS.
V와 B 모두 첨가된 강은 YS 증가, TS 증가하는 경향을 나타냈다.
The added steels of both V and B tended to increase YS and TS.
냉각속도(CR) 감소에 따라,As the cooling rate (CR) decreases,
B첨가강은 YS 유지, TS 감소하는 경향을 나타냈으며,Additive steel B tended to maintain YS and decrease TS.
V첨가강은 YS 유지, TS 유지하는 경향을 나타냈고,V additive steels tended to maintain YS and TS,
V와 B 모두 첨가된 강은 YS 증가, TS 증가하는 경향을 나타냈다.
The added steels of both V and B tended to increase YS and TS.
5. 충격 시험5. Impact test
도 11은 시험온도에 따른 임팩트 에너지 측정결과를 나타낸 그래프이다.11 is a graph showing the impact energy measurement results according to the test temperature.
도 11을 살펴보면, 3번 성분계(0.06wt% V & 10ppm B)의 경우 -80℃까지 250J 이상의 충격에너지를 보인다.Referring to FIG. 11, in the case of component No. 3 (0.06wt% V & 10ppm B), the impact energy of 250J or more is shown up to -80 ° C.
또한, FCT 400℃, CR 10℃/s 의 경우 -80℃까지 250J 이상의 충격에너지를 보인다.In addition, in the case of
V와 B 단독으로 첨가된 강(1번 성분계와 2번 성분계)일 경우 FCT가 동일할 때 CR이 작으면 충격에너지가 더 큰 것을 알 수 있다.
In the case of steels added with V and B alone (
도 12는 -40℃ 및 -80℃ 에서의 각 성분계별 충격에너지를 나타낸 것이다.12 shows the impact energy of each component system at -40 ° C and -80 ° C.
도 12를 살펴보면, -80℃에서는 -40℃보다 충격에너지(Impact Energy)가 20J정도 감소함을 알 수 있다. 다만, 1번 성분계(0.08wt% V)의 경우 FCT 300℃, CR 10℃/s 조건에서 50J 정도 감소하였다.
Looking at Figure 12, it can be seen that the impact energy (Impact Energy) is reduced by about 20J than -40 ℃ at -80 ℃. However, in case of component 1 (0.08wt% V), FJ decreased by about 50J at 300 ℃ and CR 10 ℃ / s.
상기와 같은 결과로부터, 3번 성분계(0.06wt% V & 10ppm B)의 조성에 2번 공정조건(FRT 760℃, FCT 400℃, CR 10℃/s)으로 제조하는 경우, 항복강도(YS) 680MPa, 인장강도(TS) 822MPa, -40℃ 충격에너지 250J 이상의 결과를 가져오는 것을 알 수 있다.
From the above results, yield strength (YS) when manufactured under the composition of No. 2 process conditions (
이상에서는 본 발명의 실시예를 중심으로 설명하였지만, 당업자의 수준에서 다양한 변경이나 변형을 가할 수 있다. 이러한 변경과 변형이 본 발명의 범위를 벗어나지 않는 한 본 발명에 속한다고 할 수 있다. 따라서 본 발명의 권리범위는 이하에 기재되는 청구범위에 의해 판단되어야 할 것이다. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications may belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.
Claims (10)
압연종료온도(FRT) 750~770℃의 범위에 열간압연을 종료하고,
냉각속도 15℃/sec 이하, 냉각종료온도(FCT) 400℃ 이상으로 열처리하는 것을 특징으로 하는 라인파이프용 고강도 강판 제조 방법.
Carbon (C): 0.02 to 0.06 wt%, Silicon (Si): more than 0 and 0.4 wt% or less, manganese (Mn): 1.8 to 2.5 wt%, phosphorus (P): more than 0 and 0.020 wt% or less, sulfur (S) : More than 0 and 0.010 wt% or less, chromium (Cr): more than 0 and 0.04 wt% or less, nickel (Ni): 0.2 to 1.0 wt%, molybdenum (Mo): 0.2 to 1.0 wt%, aluminum (Al): more than 0 0.030 Weight% or less, Copper (Cu): 0.2 to 1.0 weight% or less, Titanium (Ti): 0.01 to 0.02 weight%, Niobium (Nb): 0.02 to 0.10 weight%, Vanadium (V): 0.02 to 0.10 weight%, Boron (B): 0.0005 to 0.0050% by weight, nitrogen (N): more than 0 and 0.007% by weight or less, calcium: 0.002 to 0.005% by weight, the rest of the steel slab composed of Fe and other unavoidable impurities slab reheating temperature ( SRT) After reheating to 1100 ~ 1200 ℃, hot rolling,
Hot rolling is completed in the range of 750-770 degreeC in the rolling end temperature (FRT),
A method of producing a high strength steel sheet for a line pipe, characterized in that the heat treatment is performed at a cooling rate of 15 ° C./sec or less and a cooling end temperature (FCT) of 400 ° C. or more.
냉각시작온도(SCT)는 740~760℃ 인 것을 특징으로 하는 라인파이프용 고강도 강판 제조 방법.
The method of claim 1,
Cooling start temperature (SCT) is a high strength steel sheet manufacturing method for line pipes, characterized in that 740 ~ 760 ℃.
압연시작온도는 1000~1100℃ 인 것을 특징으로 하는 라인파이프용 고강도 강판 제조 방법.
The method of claim 1,
High temperature steel sheet manufacturing method for line pipes, characterized in that the rolling start temperature is 1000 ~ 1100 ℃.
Carbon (C): 0.02 to 0.06 wt%, Silicon (Si): more than 0 and 0.4 wt% or less, manganese (Mn): 1.8 to 2.5 wt%, phosphorus (P): more than 0 and 0.020 wt% or less, sulfur (S) : More than 0 and 0.010 wt% or less, chromium (Cr): more than 0 and 0.04 wt% or less, nickel (Ni): 0.2 to 1.0 wt%, molybdenum (Mo): 0.2 to 1.0 wt%, aluminum (Al): more than 0 0.030 % By weight or less, copper (Cu): 0.2 to 1.0% by weight, titanium (Ti): 0.01 to 0.02% by weight, niobium (Nb): 0.02 to 0.10% by weight, vanadium (V): 0.02 to 0.10% by weight, Boron (B): 0.0005 ~ 0.0050% by weight, nitrogen (N): more than 0 and 0.007% by weight or less, calcium: 0.002 ~ 0.005% by weight, the remainder is a high-strength steel sheet for line pipe composed of Fe and other unavoidable impurities.
상기 탄소(C)는 0.03~0.05 중량%인 것을 특징으로 하는 라인파이프용 고강도 강판.
The method of claim 4, wherein
The carbon (C) is a high strength steel sheet for line pipes, characterized in that 0.03 ~ 0.05% by weight.
상기 바나듐(V)은 0.07~0.09 중량%인 것을 특징으로 하는 라인파이프용 고강도 강판.
The method of claim 5,
The vanadium (V) is a high strength steel sheet for line pipes, characterized in that 0.07 ~ 0.09% by weight.
상기 보론(B)은 0.0005~0.0015 중량%인 것을 특징으로 하는 라인파이프용 고강도 강판.
The method of claim 6,
The boron (B) is a high strength steel sheet for line pipes, characterized in that 0.0005 ~ 0.0015% by weight.
상기 강판은 항복강도(YS) 730~750MPa, 인장강도(TS) 820~850MPa 인 것을 특징으로 하는 라인파이프용 고강도 강판.
The method of claim 4, wherein
The steel sheet is a high strength steel sheet for line pipes, characterized in that the yield strength (YS) 730 ~ 750MPa, tensile strength (TS) 820 ~ 850MPa.
상기 강판은 -40℃ 충격에너지 250J 이상인 것을 특징으로 하는 라인파이프용 고강도 강판.
The method of claim 4, wherein
The steel sheet is a high-strength steel sheet for line pipes, characterized in that -40 ℃ impact energy 250J or more.
상기 강판의 미세조직은 20% 미만의 페라이트와 80% 이상의 베이나이트를 포함하는 것을 특징으로 하는 라인파이프용 고강도 강판.The method of claim 4, wherein
The microstructure of the steel sheet is a high-strength steel sheet for line pipe, characterized in that it comprises less than 20% ferrite and 80% or more bainite.
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| JP2001152248A (en) | 1999-11-24 | 2001-06-05 | Nippon Steel Corp | Method for producing high tensile strength steel plate and steel pipe excellent in low temperature toughness |
| JP2002155343A (en) | 2000-11-15 | 2002-05-31 | Nkk Corp | High tensile strength hot-rolled steel strip for line pipe and its manufacturing method |
| KR100540686B1 (en) | 1997-05-19 | 2006-01-10 | 아메리칸 캐스트 아이언 파이프 컴패니 | Linepipe and structural steel produced by high speed continuous casting |
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| JP2001152248A (en) | 1999-11-24 | 2001-06-05 | Nippon Steel Corp | Method for producing high tensile strength steel plate and steel pipe excellent in low temperature toughness |
| JP2002155343A (en) | 2000-11-15 | 2002-05-31 | Nkk Corp | High tensile strength hot-rolled steel strip for line pipe and its manufacturing method |
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