KR100256352B1 - The manufacturing method for high strength steel sheet used line pipe with excellent ultra low temperature impact toughness - Google Patents

The manufacturing method for high strength steel sheet used line pipe with excellent ultra low temperature impact toughness Download PDF

Info

Publication number
KR100256352B1
KR100256352B1 KR1019950049561A KR19950049561A KR100256352B1 KR 100256352 B1 KR100256352 B1 KR 100256352B1 KR 1019950049561 A KR1019950049561 A KR 1019950049561A KR 19950049561 A KR19950049561 A KR 19950049561A KR 100256352 B1 KR100256352 B1 KR 100256352B1
Authority
KR
South Korea
Prior art keywords
impact toughness
steel
rolling
manufacturing
line pipe
Prior art date
Application number
KR1019950049561A
Other languages
Korean (ko)
Other versions
KR970043150A (en
Inventor
박찬엽
소문섭
박종수
Original Assignee
이구택
포항종합제철주식회사
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 이구택, 포항종합제철주식회사 filed Critical 이구택
Priority to KR1019950049561A priority Critical patent/KR100256352B1/en
Publication of KR970043150A publication Critical patent/KR970043150A/en
Application granted granted Critical
Publication of KR100256352B1 publication Critical patent/KR100256352B1/en

Links

Classifications

    • 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
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/085—Cooling or quenching
    • 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

Landscapes

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

Abstract

PURPOSE: A method for manufacturing a high tensile steel product for pipe line is provided, which not only has a high strength and superior weldability but also has superior impact toughness even under the cryogenic temperature environment by properly controlling manufacturing conditions including injection condition of Ca-Si for spheroidizing while appropriately controlling constituents of the steel product. CONSTITUTION: The method comprises the processes of spheroidizing inclusions by injecting some of Ca-Si during powder injecting and the rest of Ca-Si during vacuum degassing into molten steel comprising 0.08 to 0.11 wt.% of C, 0.20 to 0.30 wt.% of Si, 1.50 to 1.60 wt.% of Mn, 0.020 wt.% or less of P, 0.003 wt.% or less of S, 0.035 to 0.045 wt.% of Nb, 0.055 to 0.065 wt.% of V, 0.005 to 0.015 wt.% of Ti, 0.020 to 0.040 wt.% of sol.-Al and a balance of Fe and other inevitable impurities; rough rolling the reheated slab after reheating the spheroidized slab; initiating finish milling the rough rolled steel product to a reduction ratio of 70±5% from the non-recrystallization temperature zone of 870±20 deg.C and finishing finish rolling in the temperature range of 730±20 deg.C; and accelerated cooling the finish rolled steel product to the temperature range of 520±20 deg.C in a cooling rate of 8 to 12 deg.C/sec.

Description

극저온 충격인성이 우수한 라인 파이프용 고장력강재의 제조방법Manufacturing method of high tensile strength steel for line pipe with excellent cryogenic impact toughness

제1도는 종래의 제어 압연 방식을 설명하는 이력곡선도.1 is a hysteresis curve diagram illustrating a conventional controlled rolling method.

제2도는 본 발명에 의한 제어압연방식을 설명하는 이력곡선도.2 is a hysteresis curve diagram illustrating a control rolling method according to the present invention.

제3도는 라인 파이프용 고장력강재의 조직사진.3 is an organization photograph of high tensile steel for line pipe.

(a)는 발명재.(a) is invention material.

(b)는 비교재.(b) the comparative material.

제4도는 발명재와 비교재에 대한 저온인성 변화를 나타내는 그래프.4 is a graph showing the change in low temperature toughness of the invention and the comparative material.

제5도는 발명재와 비교재의 조직을 나타내는 사진임.5 is a photograph showing the organization of the invention and the comparative material.

본 발명은 유전 및 천연가스 수송수단으로 사용되는 라인 파이프용 고장력강재의 제조방법에 관한 것으로서, 특히 극저온환경에서 충격인성이 우수한 라인파이프용 고장력강재의 제조방법에 관한 것이다.The present invention relates to a method for producing high tensile steel for line pipes used as oil and natural gas transportation means, and more particularly, to a method for manufacturing high tensile steel for line pipes having excellent impact toughness in cryogenic environments.

현재까지는 유전 자원개발추세가 개발환경이 좋은 온·열대지역을 중심으로 활발히 추진되어 왔으나, 최근 석유산업발달과 함께 이 지역에서의 자원이 고갈되고 있기 때문에 점차 시베리아, 북극해, 알래스카등 극한지 및 심해저에 대한 유전개발이 진행되고 있다.Up to now, the trend of oilfield resource development has been actively promoted in temperate and tropical regions with good development environment.However, due to the recent development of the oil industry and the depletion of resources in the region, it is gradually increasing in extreme regions such as Siberia, Arctic Ocean, Alaska and deep seabed. Genetic development is underway.

이와관련하여 대형 프로젝트로서 개발된 석유 및 천연가스를 유전지로부터 실 사용지까지 장거리 운반하기 위한 원유수송관용 강재 역시 이들 극한지의 가혹한 사용환경하에서 적용될 수 있는 강재개발이 필요하게 되었다.In this connection, crude oil pipelines for long-distance transportation of oil and natural gas developed from large oil fields to oil fields are also needed to be developed under the harsh conditions of use in these extreme regions.

극한지 환경하에서 사용되는 파이프 강재의 품질특성은 강도는 물론 저온에서 쉽게 발생될 수 있는 취성에 대한 내력을 갖추는 것이 필수요건이다. 그러나, 현재 사용되는 파이프강재의 경우 충격인성에 대한 특별한 기준이 없이 단지 강재의 사용환경에 따라 수요가 요구수준을 만족시키고 있는 실정이다.The quality characteristics of pipe steels used under extreme cold conditions are essential to have strength as well as strength for brittleness that can easily occur at low temperatures. However, in the case of pipe steel currently used, there is no special standard for impact toughness, and the demand satisfies the required level according to the environment of use of the steel only.

이에따라 종래의 파이프 강재의 경우도 저온인성 측면보다는 강도확보에 중점을 두고 있기때문에 강도 확보는 가능하지만 극저온 충격인성이 열위하여 시베리아와 같은 -60℃의 극저온 환경에서는 사용이 불가능하였다. 다시말해, 종래의 파이프 강재는 극저온 인성보증이 아닌 -26℃충격 인성보증만을 만족하고 있는 실정이었다.Accordingly, in the case of the conventional pipe steel, the strength is secured because it focuses on securing strength rather than low temperature toughness, but it is inferior to cryogenic impact toughness, and thus it cannot be used in cryogenic environments such as Siberia. In other words, the conventional pipe steel has satisfied only the -26 ° C impact toughness guarantee, not the cryogenic toughness guarantee.

한편, 이러한 종래의 파이프 강재의 제조방법을 살펴보면, 먼저 강도 확보를 위해 화학성분 설계에 중점을 두어 강도 향상원소인 탄소, 망간, 바나듐(V)성분등을 다량 첨가하고, 인성향상을 위해서는 후판제어 압연중 결정립 미세화 효과가 있는 니오븀(Nb)을 다량 첨가하는 방법을 적용하고 있다. 또한, 통상적으로 제강공정에서 개재물 구상화처리 및 진공탈가스처리를 행하는 것이 강의 내부품질 건전화에 유리하기 때문에 진공탈가스처리를 단독 실시하거나 또는 개재물 구상화처리 및 진공탈가스처리를 실시하였다. 구체적으로 종래에는 제강공정에서 구상화를 위해 Ca-Si를 투입, 처리한 후 진공탈가스처리를 행하였다. 그리고, 후판제어압연시, 제 1도에 도시된 바와같이, 초기 오스테나이트 결정립 미세화를 위헤 약 900℃이상인 재결정역에서 부분적으로 사상압연을 실시하고 결정립 미세화 효과가 큰 미재결정 영역인 890-730℃에서 다시 사상압연을 실시하였다. 그러나, 이와같은 종래의 파이프강재의 제조방법은 많은 문제를 안고 있는데, 이를 구체적으로 살펴보면 다음과같다.On the other hand, in the conventional method of manufacturing pipe steels, first of all, a large amount of carbon, manganese, vanadium (V) components, etc., which are strength enhancing elements, are added, focusing on chemical component design to secure strength, and thick plate control for improving toughness. The method of adding a large amount of niobium (Nb) which has a grain refinement effect during rolling is applied. In addition, since the inclusion spheroidization treatment and vacuum degassing treatment in the steelmaking process are advantageous for the internal quality of steel, the vacuum degassing treatment is performed alone or the inclusion spheroidization treatment and the vacuum degassing treatment have been performed. Specifically, in the prior art, Ca-Si was added and treated for spheroidization in the steelmaking process, followed by vacuum degassing treatment. In the thick plate control rolling process, as shown in FIG. 1, in the recrystallization zone of about 900 ° C. or more for initial austenite grain refining, the finishing is partially performed and the unrecrystallized region having a large grain refining effect is 890-730 ° C. Finish rolling was again performed at. However, such a conventional method for manufacturing pipe steel has many problems, which will be described in detail as follows.

첫째, 종래의 파이프용 강재의 성분은 탄소당량(CEQ)이 높아 강도는 확보하기 용이하나 저온 충격인성이나 수요가 현장 용접성개선에 한계가 있고, 둘째, Ca-Si에 의한 구상화처리 방법에 있어 투입된 Ca이 개재물 구상화를 못하고 산화되어 저온균열발생 및 균열 전파정지특성개선에 큰효과가 없으며 고청정성 확보에도 문제가 있으며, 또한, 종래의 제조방법의 경우 후판제어압연시 부분적으로 재결정영역에서 사상압연을 행하기 때문에 결정립 미세화효과가 크지 못해 극저온에서 충분한 인성확보가 곤란한 문제가 있다.First, the components of conventional steel for pipes have a high carbon equivalent (CEQ), so the strength is easy to secure, but low-temperature impact toughness and demand are limited in improving on-site weldability. Second, in the spheroidization method using Ca-Si, Ca is oxidized due to inclusion spheroidization, which is not effective in improving low temperature crack generation and crack propagation stop characteristics, and also has problems in securing high cleanliness. Because of this effect, the grain refining effect is not so large that it is difficult to secure sufficient toughness at cryogenic temperatures.

따라서, 본 발명은 상기한 종래의 제조상 문제점을 해결하기 위하여 제안된 것으로서, 본 발명은 강재의 성분계를 적절히 제어하는 한편, 구상화를 위한 Ca-Si의 투입조건을 비롯한 제조조건을 적절히 제어하므로서, 고강도는 물론 우수한 용접성외에 극저온 환경하에서도 우수한 충격인성을 갖는 라인 파이프용 고장력 강재의 제조방법을 제공하고자 하는데 그 목적이 있다.Therefore, the present invention has been proposed to solve the above-described conventional manufacturing problems, while the present invention properly controls the component system of the steel, while appropriately controlling the manufacturing conditions, including the input conditions of Ca-Si for spheroidization, Of course, the purpose of the present invention is to provide a method of manufacturing high tensile strength steel for line pipes having excellent impact toughness even under cryogenic environments.

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

본 발명은 라인 파이프용 고장력 강재의 제조방법에 있어서, 중량%로, C:0.08-0.11%, Si:0.20-0.30%, Mn:1.50-1.60%, P:0.020%이하, S:0.003%이하, Nb:0.035-0.045%, V:0.055-0.065%, Ti:0.005-0.015%, Sol.-Al:0.020-0.040%, 나머지 Fe및 기타불가피한 불순물로 이루어진 용강을, 파우더 인젝션처리시 일부의 Ca-Si를 투입하고, 진공탈가스 처리시 나머지 Ca-Si를 투입하여 개재물 구상화처리한 다음, 구상화 처리된 슬라브를 재가열하고, 조압연한 후 조압연된 강재를 잔압하율 70±5% 상태에서 미재결정온도역인 870±20℃의 온도로부터 사상압연을 개시하여 730±20℃의 온도범위에서 마무리 압연을 종료하고 이어서 8-12℃/초의 범위로 520±20℃의 온도범위까지 가속냉각함을 포함하여 구성되는 극저온 충격인성이 우수한 라인 파이프용 고장력 강재의 제조방법에 관한 것이다.The present invention is a method for producing a high tensile strength steel for line pipe, by weight, C: 0.08-0.11%, Si: 0.20-0.30%, Mn: 1.50-1.60%, P: 0.020% or less, S: 0.003% or less , Nb: 0.035-0.045%, V: 0.055-0.065%, Ti: 0.005-0.015%, Sol.-Al: 0.020-0.040%, molten steel consisting of remaining Fe and other unavoidable impurities. -Si is added and the remaining Ca-Si is added to spheroidizing the inclusions during vacuum degassing treatment.Then, the spheroidized slab is reheated, and rough rolling is performed. After finishing finishing in the temperature range of 870 ± 20 ℃, finish finishing rolling in the temperature range of 730 ± 20 ℃, and then accelerate cooling to the temperature range of 520 ± 20 ℃ in the range of 8-12 ℃ / sec. It relates to a method for producing a high-tensile steel for line pipe excellent in cryogenic impact toughness comprising.

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

본 발명에 따른 라인 파이프용 고장력강 중에 함유되는 탄소는 강도를 향상시키는데 가장 크게 기여하는 원소로서, 첨가량의 증가와 함께 강도는 비례적으로 증가하지만 반면에 충격인성을 저해시키는 원소이다. 따라서, 탄소함량이 0.08%미만이면 인장강도 57.5㎏/㎟이상의 고강도 확보와 저온인성의 균형을 유지할수 없고, 연주조업시 탄소함량이 0.11%초과시 연주표면크랙 발생에 민감하므로 탄소함량은 0.08-0.11%로 제어함이 바람직하다.Carbon contained in the high-tensile steel for line pipes according to the present invention is the most contributing element to improving the strength, and the element increases in proportion with the increase in the amount of addition, but is an element that impairs the impact toughness. Therefore, if the carbon content is less than 0.08%, it is impossible to balance high strength and low temperature toughness of 57.5 kg / mm2 or more of tensile strength, and the carbon content is 0.08-0.11 because the carbon content is sensitive to the occurrence of the playing surface crack when the carbon content exceeds 0.11% during the operation. It is preferable to control by%.

규소(Si)는 강도향상에 부분적인 기여를 하지만 주된 첨가목적은 강종의 탈산에 있다. 그러나, 규소함량이 0.2%미만이면 강의 탈산효과가 미흡하며, 0.30%이상 첨가시 규소계 개재물이 증가하여 저온인성을 열화시킬 수 있다.Silicon (Si) makes a partial contribution to strength improvement, but the main purpose of addition is to deoxidize steel grades. However, if the silicon content is less than 0.2%, the deoxidation effect of the steel is inadequate, and when 0.30% or more is added, the silicon-based inclusions may increase, thereby deteriorating low temperature toughness.

망간(Mn)은 강도와 인성을 동시에 향상시킬 수 있는 원소로서 첨가량의 증가와 함께 페라이트 및 제 2 상의 결정립은 미세해진다. 망간함량이 1.60%를 초과하면 도상 마르텐사이트 조직이 생성되어 오히려 충격인성을 해칠 우려가 있고 1.5% 미만이면 고강도 확보가 곤란하다.Manganese (Mn) is an element that can simultaneously improve strength and toughness, and the grains of ferrite and the second phase become fine with the increase of the added amount. When the manganese content exceeds 1.60%, the martensite structure may be formed, and the impact toughness may be impaired. If the manganese content is less than 1.5%, it is difficult to secure high strength.

인(P)은 강재의 충격인성을 크게 저해시키는 불순물로서 연주시 중심편석부에 집적하여 내부품질을 열화시키기 때문에 조업기술이 수반되는 인 함량은 0.020%이하로 제한하는 것이 바람직하다.Phosphorus (P) is an impurity that significantly impairs the impact toughness of the steel material, so it accumulates in the central segregation unit during performance and degrades the internal quality. Therefore, the phosphorus content accompanying the operation technique is preferably limited to 0.020% or less.

황(S)은 상기 인 성분과 동일하게 유해한 원소로서 연주시 표면크랙, 내부크랙 및 중심편석의 유발로 인하여 충격인성을 대폭감소시킬수 있기때문에 S함량은 0.003%이하로 제한하는 것이 바람직하다.Sulfur (S) is the same harmful element as the phosphorus component, the S content is preferably limited to 0.003% or less because it can significantly reduce the impact toughness due to the occurrence of surface cracks, internal cracks and central segregation when playing.

니오븀(Nb)는 그 첨가량이 증가할수록 Nb(C,N)석출물 생성으로 인장강도가 증가하며 후판압연시는 입계에 석출된 Nb(C,N)석출물이 결정립성장을 억제함으로써 결정립 미세화효과에 의한 강도 및 충격인성을 향상시키는 역할을 한다. 그러나, Nb의 함량이 0.035%미만에서는 재질특성 향상이 미흡하며, 0.04%초과함유시는 포화현상을 나타내어 강도및 충격인성 개선효과가 미미할뿐만 아니라 과다함유시 오히려 용접부의 충격인성을 저해시킨다.Niobium (Nb) increases the tensile strength due to the formation of Nb (C, N) precipitates as the amount of niobium (Nb) is increased, and Nb (C, N) precipitates deposited at grain boundaries during grain rolling suppress the grain growth. It serves to improve strength and impact toughness. However, when the Nb content is less than 0.035%, the improvement of the material properties is insufficient. When the content of Nb exceeds 0.04%, the saturation phenomenon is shown, and the effect of improving the strength and impact toughness is insignificant.

바나듐(V)은 V(C,N)석출원소로서, 그 함유량의 증가에 따라 항복강도의 증가보다는 인장강도증가에 크게 기여한다. 따라서, 강도적인 측면외에 인성과의 균형을 고려하면 V의 함량은 0.055-0.065%로 제한함이 바람직한데, V이 0.055%미만으로 함유되거나 0.065%이상으로 다량함유시 탄소당량(Ceq)의 증가와함께 강도확보는 가능하나 모재 및 용접부 충격인성을 크게 저해시킨다.Vanadium (V) is a V (C, N) precipitation element, which contributes significantly to the increase in tensile strength rather than the increase in yield strength as its content increases. Therefore, considering the balance of toughness in addition to the strength aspect, it is preferable to limit the content of V to 0.055-0.065%, the increase in carbon equivalent (Ceq) when V is contained less than 0.055% or in a large amount of more than 0.065% With this, strength can be secured, but the impact toughness of the base metal and the weld is greatly impaired.

티타늄(Ti)함량은 0.005-0.015%로 제한함이 바람직한데, 그 이유는 통상 Ti/N비를 1.0-3.0으로 관리함으로써 슬라브 재가열공정 및 용접부등 고온에서 TiN석출물이 입계에 미세 분산되어 초기 오스테나이트 결정립성장을 억제하고 강도의 부분적인 증가와 함께 인성의 대폭적인 개선을 도모할 수 있기 때문이다.The content of titanium (Ti) is preferably limited to 0.005-0.015%, because the Ti / N ratio is usually controlled at 1.0-3.0, and the TiN precipitate is finely dispersed at the grain boundary at the high temperature such as the slab reheating process and the welded portion. This is because nitrite grain growth can be suppressed and toughness can be greatly improved with a partial increase in strength.

특히, Ti 함량이 0.015%이상으로 다량 첨가되는 경우 용강중의 질소 수준이 통상 50ppm임을 감안할때 산화물계 개재물 형성 또는 과잉 고용Ti이 조대 석출물로 형성되어 인성을 저해시키므로 바람직하지 않다.In particular, when a large amount of Ti is added in an amount of 0.015% or more, since the nitrogen level in the molten steel is usually 50 ppm, the formation of oxide inclusions or excessive solid solution Ti is formed as coarse precipitates, which is not preferable.

이하, 본 발명에 의한 제조방법을 상세히 설명한다.Hereinafter, the manufacturing method according to the present invention will be described in detail.

상기한 조성을 갖는 파이프용 고장력 강재의 내부품질의 건전성 확보를 위해 본 발명에서는 전로조업시 후판압연에서 길게 연신되어 취성파괴의 기점으로 작용하여 크랙전파를 촉진시키는 MnS개재물을 CaS의 구상화 개재물로 형상을 제어하는 것이 필요하다. 이를 위해 본 발명에서는 종래와는 달리, 파우더 인젝션(Powder Injection)시 Ca-Si를 일부 투입후 강교반을 실시하고 진공탈가스 조업말기에 다시 Ca-Si를 투입시켜 환류시키므로써 용강내 잔류[S]의 구상화를 촉진시킨다. 이때, Ca-Si투입은 파우더 인젝션시 Ca-Si전체 투입량의 50%정도, 그리고 진공탈가스 처리시 나머지 50% 정도를 투입함이 보다 바람직하다.In order to ensure the integrity of the internal quality of the high-strength steel for pipes having the above composition, in the present invention, MnS inclusions, which are elongated in thick plate rolling during the converter operation, act as a starting point of brittle fracture and promote crack propagation, are formed into spherical inclusions of CaS. It is necessary to control. To this end, in the present invention, unlike in the prior art, during the powder injection (Cowder Injection), the part of Ca-Si is added and then the steel is agitated, and the Ca-Si is added to the reflux at the end of the vacuum degassing operation to reflux. ] To promote visualization. At this time, Ca-Si injection is more preferably about 50% of the total Ca-Si input amount during powder injection, and the remaining 50% when vacuum degassing treatment.

또한 본 발명에서는 상기와같은 전로조업을 거쳐 연주된 슬라브를 제어압연하는데, 이때 제어압연은 제 2 도와 같은 방식을 이용한다.In addition, in the present invention, the slab played through the converter operation as described above, the control rolling, wherein the control rolling uses the same method as the second degree.

즉, 제 2 도에 도시된 바와같이, 본 발명에 의한 제어압연은 우선 통상의 온도로 재 가열한 다음, 재결정영역에서 조압연을 실시하고 미재결정 구역인 850-890℃의 온도범위에서 사상압연을 개시하고 710-750℃의 온도범위에서 마무리 압연하며, 또한, 사상압연 개시시점에서의 잔 압하율은 65-75%정도로 설정한다.That is, as shown in FIG. 2, the control rolling according to the present invention is first reheated to a normal temperature, followed by rough rolling in a recrystallization zone, and finishing rolling in a temperature range of 850-890 ° C. which is an unrecrystallized zone. And finish-rolling in the temperature range of 710-750 degreeC, and the residual reduction ratio at the time of starting finishing rolling is set to about 65-75%.

이러한 본 발명에 따른 제어압연 방식은 종래의 제어압연과는 달리 약 20℃정도 낮을 뿐만 아니라 사상압연을 미재결정역에서 실시하기 때문에 강재의 결정립이 보다 미세화되어 극저온 취성에 유리하다. 종래방법에서와 같이, 만일 제어압연시 사상압연을 890℃이상으로 조업시에는 부분적인 재결정성장에 의한 결정립 조대화로 충격인성이 열화되며 압연 종료온도가 750℃이상으로 되면 누적 압하효과 감소로 항복강도 저하 및 저온 충격인성의 열화가 발생되어 바람직하지 않다. 또한, 710℃이하의 저온역에서 압연이 종료되면 2상역 압역에 의한 집합조직 형성으로 항복강도 확보는 유리하지만 충격 이방성의 문제점이 있기 때문에 가능한한 710℃이하의 온도에서 마무리 압연을 종료하는 것은 피해야한다.Unlike the conventional control rolling, the control rolling method according to the present invention is not only about 20 ° C. lower, but also performs the finishing rolling in the non-recrystallized zone, so that the grains of the steel are further refined, which is advantageous for cryogenic brittleness. As in the conventional method, if the filament rolling during control rolling is over 890 ° C, impact toughness deteriorates due to grain coarsening due to partial recrystallization growth. The lowering of strength and the deterioration of low-temperature impact toughness occur, which is not preferable. In addition, if the rolling is finished in the low temperature region below 710 ℃, it is advantageous to secure the yield strength by forming the aggregate structure by the two-phase reverse pressure region, but there is a problem of impact anisotropy, so finishing the finish rolling at a temperature below 710 ℃ should be avoided if possible do.

또한, 상기와같이 제어 압연 후 가속냉각을 할때는 8-12℃/초의 범위로 냉각하여 500-540℃의 온도에서 종료시키는 것이 바람직하다. 만일, 가속냉각속도가 8℃/초미만으로 되면 약랭에 의해 오스테나이트→페라이트 변태 미완료로 충격인성 및 인장강도 향상에 적합한 베이나이트 조직확보가 어려우며, 12℃/초를 초과하면 강냉각에 의해 인장강도는 향상되나 형상이 불량해질 우려가 있다.In addition, when the accelerated cooling after the control rolling as described above, it is preferable to cool in the range of 8-12 ℃ / sec and to terminate at a temperature of 500-540 ℃. If the accelerated cooling rate is less than 8 ° C / sec, it is difficult to secure bainite structure suitable for impact toughness and tensile strength due to austenite to ferrite transformation due to weak cooling, and if it exceeds 12 ° C / sec, the tensile strength due to strong cooling Is improved, but there is a fear that the shape is poor.

그리고, 상기한 냉각속도로 냉각시 그 종료온도가 540℃이상에서 이루어지면 역시 오스테나이트→페라이트 변태가 완료되지 않아 밴드(band)조직이 형성되어 충격특성에 악영향을 미치며 500℃미만의 저온에서 냉각이 종료되면 마르텐사이트등 저온 변태조직을 형성하여 항복강도 및 인장강도 확보는 유리하나 충격인성은 저하되어 바람직하지 않다. 결국, 본 발명에 따라 제조되는 파이프용 고장력 강재는 충격인성에 유해한 밴드(집합조직)이 소멸되고 인성향상에 유리한 페라이트-펄라이트-저온 베이나이트 조직을 형성하여 -60℃의 극저온에서 우수한 저온인성을 갖게된다.When the end temperature is higher than 540 ° C., the austenite-ferrite transformation is not completed. Thus, a band structure is formed, which adversely affects the impact characteristics and cools at a low temperature of less than 500 ° C. When this is completed, the low-temperature transformation structure such as martensite is formed to secure yield strength and tensile strength, but impact toughness is lowered, which is undesirable. As a result, the high tensile strength steel for pipes manufactured according to the present invention forms a ferrite-perlite-low-temperature bainite structure, which has a band (assembly structure) harmful to impact toughness and is advantageous for toughness improvement, and has excellent low-temperature toughness at cryogenic temperatures of -60 ° C. Will have

이하, 본 발명을 실시예를 통하여 구체적으로 설명한다.Hereinafter, the present invention will be described in detail through examples.

[실시예 1]Example 1

중량%로, C:0.10%, Si:0.25%, Mn:1.58%, P:0.020%, S:0.002%, Sol-Al:0.025%, Nb:0.042%, V:0.060%, Ti:0.012%,(탄소당량:0.371)를 포함하여 조성되도록 용선예비처리공정에서 밀스케일(mill scale)투입후 교반처리로 1차정련한 후, 노외정련 공정에서 파우더 인젝션시 Ca-Si 210㎏를 투입하고 진공도를 2torr이하로 한 진공탈가스 처리시 조업말기에 Ca-Si 200㎏를 투입하고 5분이상 용강을 환류처리하고, 연주주조시 중심편석 최소화를 위해 전자교반처리를 실시하였다. 이후, 연주공정에서 얻어진 슬라브는 후판공정에서 통상 가열수준인 1230℃로 가열하고, 조압연을 실시한 다음, 잔압하율이 70%인 상태에서 870℃의 온도에서 사상 압연을 개시하여 730℃의 온도에서 압연을 종료하였다.By weight%, C: 0.10%, Si: 0.25%, Mn: 1.58%, P: 0.020%, S: 0.002%, Sol-Al: 0.025%, Nb: 0.042%, V: 0.060%, Ti: 0.012% First, by milling in the molten iron preliminary treatment process to make a composition including, (carbon equivalent: 0.371) In case of vacuum degassing with less than 2torr, 200kg of Ca-Si was added at the end of the operation, reflux treatment of molten steel for more than 5 minutes, and electro-stirring treatment to minimize center segregation during casting. Subsequently, the slab obtained in the casting process was heated to 1230 ° C., which is a normal heating level in the thick plate process, subjected to rough rolling, and then started finishing rolling at a temperature of 870 ° C. with a residual reduction ratio of 70% to a temperature of 730 ° C. The rolling was finished at.

상기 압연판은 바로 8℃/초 냉각속도로 수 냉각하여 520℃의 온도에서 종료하고, 이렇게 냉각이 완료된 후판강재를 발명재로 하였다.The rolled plate was immediately cooled by water at a cooling rate of 8 ° C./second, and finished at a temperature of 520 ° C., and thus, the steel plate obtained by cooling was used as an inventive material.

또한, 비교를 위하여 중량%로, C:0.11%, Si:0.25%, Mn:1.58%, P:0.020%, S:0.002%, Sol-Al:0.025%, Nb:0.050%, V:0.080%, Ti:0.010%,(탄소당량:0.390%)를 포함하여 조성되는 용선을 노외정련에서 Ca-Si를 410㎏ 투입할 것을 제외하고는 발명재의 방법과 동일하게 연주 슬라브를 제조하였다. 이후, 제조된 슬라브를 제어압연시 조압연후의 잔압하율 70%인 상태에서 980℃의 온도에서 1차 사상압연을 개시하고, 2차사상압연을 890℃에서 시작하여 750℃의 온도에서 압연을 종료하고, 압연된 강재를 7℃/초의 냉각속도로 수냉하여 540℃의 온도에서 냉각을 종료하고, 이렇게 냉각이 완료된 후판강재를 비교재로 하였다.Also, for comparison, in weight%, C: 0.11%, Si: 0.25%, Mn: 1.58%, P: 0.020%, S: 0.002%, Sol-Al: 0.025%, Nb: 0.050%, V: 0.080% The molten iron including Ti: 0.010% and (carbon equivalent: 0.390%) was prepared in the same manner as in the invention except that 410 kg of Ca-Si was added to the outside of the refining furnace. Subsequently, the produced slab is started with primary finishing rolling at a temperature of 980 ° C. in the state of 70% of the residual reduction rate after rough rolling in controlled rolling, and secondary rolling is started at 890 ° C. and rolling is performed at a temperature of 750 ° C. After completion, the rolled steel was water-cooled at a cooling rate of 7 ° C./sec to terminate the cooling at a temperature of 540 ° C., and thus the thick steel plate in which the cooling was completed was used as a comparative material.

상기와같이 제조된 발명재와 비교재에 대하여 각각 기계적성질 및 충격인성을 측정하고 그 결과를 하기표 1에 나타내었다.Mechanical properties and impact toughness were measured for the inventive materials and the comparative materials prepared as described above, and the results are shown in Table 1 below.

또한, 발명재와 비교재의 조직을 광학현미경을 이용하여 200배의 비율로 관찰하고, 그 결과를 제 3도에 나타내었다.In addition, the structure of the invention material and the comparative material was observed at a ratio of 200 times using an optical microscope, and the results are shown in FIG.

상기표 1에 나타난 바와같이, 발명재와 비교재의 경우 모두 API-X70강재 규격(항복강도 : 49㎏/㎟이상, 인장강도: 57.7㎏/㎟이상, 연신: 23%이상)을 만족하고 있지만, 발명재의 경우 비교재에 비하여 저온 충격인성이 매우 우수함을 알수 있다. 이러한 원인은 제 3도의 조직사진에서도 알수 있듯이, 발명재의 경우(a) 비교재의 경우(b) 보다도 결정립이 매우 미세화되었기 때문임을 알수 있다.As shown in Table 1, both the invention material and the comparative material satisfy the API-X70 steel standard (yield strength: 49 kg / mm2 or more, tensile strength: 57.7 kg / mm2 or more, elongation: 23% or more). In the case of the invention material it can be seen that the low temperature impact toughness is very excellent compared to the comparative material. As can be seen from the tissue photograph of FIG. 3, it can be seen that the crystal grains of the invention are much finer than those of the comparative material (a).

[실시예 2]Example 2

하기표 2와 같은 조성을 갖도록 실시예 1의 발명재와 동일한 방법으로 파이프용 고장력강판을 제조하고 제조된 각 강판에 대하여 기계적 성질 저온 충격인성 및 조직을 관찰하고, 그 결과를 각각 하기표 3, 제 4및 제 5도에 나타내었다.To produce a high-tensile steel sheet for pipes in the same manner as the invention material of Example 1 to have a composition as shown in Table 2 and to observe the mechanical properties low-temperature impact toughness and structure for each steel sheet produced, the results are shown in Table 3, 4 and 5 are shown.

상기표 2,3에 나타난 바와같이, 본 발명에 따른 화학성분 조성범위를 만족하는 발명재(1)의 경우 비교재(1-3)에 비하여 인장강도가 우수하며 페라이트 및 제 2 상에서 우수한 경도를 나타냄을 알 수 있다.As shown in Tables 2 and 3, the invention material (1) satisfying the chemical composition range according to the present invention has excellent tensile strength and excellent hardness in ferrite and the second phase compared to the comparative material (1-3). It can be seen that.

또한, 제 4도에 나타난 바와같이, 발명재(1)의 경우 비교재(1)(3)에 비하여 저온에서의 충격인성이 매우 우수함을 알 수 있다.In addition, as shown in Figure 4, in the case of the invention material (1) it can be seen that the impact toughness at low temperature is very superior to the comparative material (1) (3).

이러한 사실은 제 5도의 조직에서도 확인되는 바와같이, 발명재(1)의 조직이 비교재(1-3)에 비하여 매우 미세화되었기 때문에 극저온에서의 취성에 큰 내력을 나타내고 있는 것이다.This fact shows that the structure of the invention material 1 is very fine compared to the comparative material 1-3, as confirmed by the structure of FIG.

상술한 바와같이, 본발명은 강재의 성분계 및 구상화조건을 비롯한 제조조건을 적절히 제어하므로서, 강도는 물론 극저온 환경하에서도 우수한 충격인성을 갖는 라인 파이프용 고장력강재가 제공되어 극한지 지역에서도 원유수송관등에 사용시 수명이 연장될수 있는 효과가 있다.As described above, the present invention provides a high-strength steel for line pipes having excellent impact toughness under not only strength but also cryogenic environments, by appropriately controlling the manufacturing system including the component system and spheroidizing conditions of the steel, so that even in the extreme regions There is an effect that the life can be extended in use.

Claims (2)

라인 파이프용 고장력강재의 제조방법에 있어서, 중량%로, C:0.08-0.11%, Si:0.20-0.30%, Mn:1.50-1.60%, P:0.020%이하, S:0.003%이하, Nb:0.035-0.045%, V:0.055-0.065%, Ti:0.005-0.015%, Sol.-Al:0.020-0.040%, 나머지 Fe및 기타불가피한 불순물로 이루어진 용강을, 파우더 인젝션처리시 일부의 Ca-Si를 투입하고, 진공탈가스 처리시 나머지 Ca-Si를 투입하여 개재물 구상화처리한 다음, 구상화 처리된 슬라브를 재가열하고, 조압연한 후 조압연된 강재를 잔압하율 70±5% 상태에서 미재결정온도역인 870±20℃의 온도로부터 사상압연을 개시하여 730±20℃의 온도범위에서 마무리 압연을 종료하고 이어서 8-12℃/초의 범위로 520±20℃의 온도범위까지 가속냉각함을 포함하여 구성되는 것을 특징으로 하는 극저온 충격인성이 우수한 라인 파이프용 고장력 강재의 제조방법.In the manufacturing method of high tensile steel for line pipe, in weight%, C: 0.08-0.11%, Si: 0.20-0.30%, Mn: 1.50-1.60%, P: 0.020% or less, S: 0.003% or less, Nb: 0.035 Magnesium steel composed of -0.045%, V: 0.055-0.065%, Ti: 0.005-0.015%, Sol.-Al: 0.020-0.040%, remaining Fe and other unavoidable impurities. In the vacuum degassing process, the remaining Ca-Si was added to spheroidize the inclusions, the spheroidized slab was reheated, and the rough rolled steel was roughly recrystallized at a residual pressure reduction rate of 70 ± 5%. Starting finishing finishing from a temperature of 870 ± 20 ° C. and finishing finishing rolling in a temperature range of 730 ± 20 ° C., followed by accelerated cooling to a temperature range of 520 ± 20 ° C. in a range of 8-12 ° C./sec. A method for producing a high tensile strength steel for line pipe, which has excellent cryogenic impact toughness. 제1항에 있어서, 상기 구상화처리에 투입되는 Ca-Si는 파우더 인젝션(Powder injection)처리시 전체 Ca-Si투입량의 50%, 진공탈가스 처리시 전체Ca-Si투입량의 50%로 하여 첨가함을 특징으로하는 극저온 충격인성이 우수한 라인파이프용 고장력 강재의 제조방법.The method of claim 1, wherein the Ca-Si added to the spheroidizing treatment is added as 50% of the total Ca-Si input during powder injection treatment and 50% of the total Ca-Si input during vacuum degassing treatment. Method for producing a high-strength steel for line pipe excellent in cryogenic impact toughness.
KR1019950049561A 1995-12-14 1995-12-14 The manufacturing method for high strength steel sheet used line pipe with excellent ultra low temperature impact toughness KR100256352B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
KR1019950049561A KR100256352B1 (en) 1995-12-14 1995-12-14 The manufacturing method for high strength steel sheet used line pipe with excellent ultra low temperature impact toughness

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
KR1019950049561A KR100256352B1 (en) 1995-12-14 1995-12-14 The manufacturing method for high strength steel sheet used line pipe with excellent ultra low temperature impact toughness

Publications (2)

Publication Number Publication Date
KR970043150A KR970043150A (en) 1997-07-26
KR100256352B1 true KR100256352B1 (en) 2000-05-15

Family

ID=19439871

Family Applications (1)

Application Number Title Priority Date Filing Date
KR1019950049561A KR100256352B1 (en) 1995-12-14 1995-12-14 The manufacturing method for high strength steel sheet used line pipe with excellent ultra low temperature impact toughness

Country Status (1)

Country Link
KR (1) KR100256352B1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100435465B1 (en) * 1999-12-20 2004-06-10 주식회사 포스코 A METHOD FOR MANUFACTURING YS 63kgf/㎟ GRADE THICK STEEL SHEET WITH SUPERIOR LOW TEMPERATURE TOUGHNESS

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100435445B1 (en) * 1996-10-22 2004-08-25 주식회사 포스코 Manufacturing method of high tensile strength plate for line pipes characterizing superior impact toughness and resistance to hydrogen induced cracking in ultra-low temperature environment

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07242944A (en) * 1994-03-04 1995-09-19 Nippon Steel Corp Production of sour resistant high strength steel plate having excellent low temperature toughness
JPH07286214A (en) * 1994-04-18 1995-10-31 Nippon Steel Corp Production of high strength thick hot coil excellent in hydrogen induced cracking resistance and dwtt property

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07242944A (en) * 1994-03-04 1995-09-19 Nippon Steel Corp Production of sour resistant high strength steel plate having excellent low temperature toughness
JPH07286214A (en) * 1994-04-18 1995-10-31 Nippon Steel Corp Production of high strength thick hot coil excellent in hydrogen induced cracking resistance and dwtt property

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100435465B1 (en) * 1999-12-20 2004-06-10 주식회사 포스코 A METHOD FOR MANUFACTURING YS 63kgf/㎟ GRADE THICK STEEL SHEET WITH SUPERIOR LOW TEMPERATURE TOUGHNESS

Also Published As

Publication number Publication date
KR970043150A (en) 1997-07-26

Similar Documents

Publication Publication Date Title
JP3846729B2 (en) Hot-rolled steel sheet for line pipe with excellent cryogenic impact toughness and method for producing the same
JP2006336065A (en) Low yield-ratio high tensile-strength steel, and method for producing low yield-ratio high tensile-strength steel
RU2768842C1 (en) High-strength thick steel sheet for pipeline, having excellent low-temperature impact strength and ductility, as well as low ratio of yield strength to ultimate strength, and method of its production
CN108368593B (en) High-strength steel material having excellent low-temperature strain aging impact characteristics and method for producing same
JP2022510214A (en) Ultra-high-strength steel with excellent cold workability and SSC resistance and its manufacturing method
JP2023110068A (en) High strength steel excellent in resistance to sulfide stress corrosion crack and manufacturing method thereof
JPH10306316A (en) Production of low yield ratio high tensile-strength steel excellent in low temperature toughness
JP3244984B2 (en) High strength linepipe steel with low yield ratio and excellent low temperature toughness
JP3981615B2 (en) Non-water-cooled thin low yield ratio high-tensile steel and method for producing the same
KR100435445B1 (en) Manufacturing method of high tensile strength plate for line pipes characterizing superior impact toughness and resistance to hydrogen induced cracking in ultra-low temperature environment
JP2009084598A (en) Method for manufacturing steel sheet superior in deformability and low-temperature toughness for ultrahigh-strength line pipe, and method for manufacturing steel pipe for ultrahigh-strength line pipe
JP4133175B2 (en) Non-water cooled thin low yield ratio high strength steel with excellent toughness and method for producing the same
JP2002173734A (en) Steel having excellent weldability and its production method
JPH0541683B2 (en)
KR100256352B1 (en) The manufacturing method for high strength steel sheet used line pipe with excellent ultra low temperature impact toughness
JPH0413406B2 (en)
KR101786262B1 (en) Hot-rolled thick steel plate having excellent strength and dwtt toughness at low temperature, and method for manufacturing the same
KR102349426B1 (en) Steel having excellent low-temperature fracture toughness and method of manufacturing the same
JPS63210235A (en) Manufacture of steel excellent in toughness at low temperature in welding heat affected zone
JPH08311549A (en) Production of ultrahigh strength steel pipe
JPH07242944A (en) Production of sour resistant high strength steel plate having excellent low temperature toughness
JP2022510929A (en) Steel materials for pressure vessels with excellent hydrogen-induced crack resistance and their manufacturing methods
JP2022510934A (en) Steel materials for pressure vessels with excellent hydrogen-induced crack resistance and their manufacturing methods
JPH08311550A (en) Production of steel sheet for ultrahigh strength steel pipe
JPH08311548A (en) Production of steel sheet for ultrahigh strength steel pipe excellent in toughness in weld zone

Legal Events

Date Code Title Description
A201 Request for examination
E902 Notification of reason for refusal
E701 Decision to grant or registration of patent right
GRNT Written decision to grant
FPAY Annual fee payment

Payment date: 20130213

Year of fee payment: 14

FPAY Annual fee payment

Payment date: 20140221

Year of fee payment: 15

LAPS Lapse due to unpaid annual fee