KR20040034982A - Method for hot rolled steel sheet having excellent coiling quality for line pipe - Google Patents

Method for hot rolled steel sheet having excellent coiling quality for line pipe Download PDF

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KR20040034982A
KR20040034982A KR1020020063675A KR20020063675A KR20040034982A KR 20040034982 A KR20040034982 A KR 20040034982A KR 1020020063675 A KR1020020063675 A KR 1020020063675A KR 20020063675 A KR20020063675 A KR 20020063675A KR 20040034982 A KR20040034982 A KR 20040034982A
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rolling
winding
rough
hot
rough rolling
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KR1020020063675A
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Korean (ko)
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KR100482201B1 (en
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최석찬
전금주
김선웅
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주식회사 포스코
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    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/08Ferrous alloys, e.g. steel alloys containing nickel
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/12Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/14Ferrous alloys, e.g. steel alloys containing titanium or zirconium

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

Abstract

PURPOSE: A manufacturing method of hot strip is provided which is capable of securing commercially required coiling quality as securing low temperature toughness and high strength by controlling manufacturing conditions per unit process of the hot rolling process. CONSTITUTION: In a method for manufacturing hot strip by hot rolling the reheated slab and coiling the hot steel bar after reheating a slab comprising 0.04 to 0.07 wt.% of C, 1.50 to 1.70 wt.% of Mn, 0.15 to 0.25 wt.% of Si, 0.010 wt.% or less of P, 0.003 wt.% or less of S, 0.040 to 0.060 wt.% of Nb, 0.040 to 0.060 wt.% of V, 0.010 to 0.025 wt.% of Ti, 0.10 to 0.30 wt.% of Mo, 0.10 to 0.30 wt.% of Ni and a balance of Fe and other inevitable impurities, the manufacturing method of hot strip for line pipes having superior coiling quality comprises the steps of rough rolling the slab by performing air cooling waiting on the rough rolled slab after performing two times of rough rolling before the final rough rolling of the reheated slab; finish rolling the rough rolled steel bar between stands of finishing mill as injecting cooling water onto the rough rolled steel bar; and injecting cooling water onto the outer side of the coil as coiling the finish rolled hot rolled strip to a temperature of 500 to 590 deg.C.

Description

권취 품질이 우수한 라인파이프용 열연강판의 제조방법{Method for hot rolled steel sheet having excellent coiling quality for line pipe}Method for manufacturing hot rolled steel sheet for line pipe with excellent winding quality {Method for hot rolled steel sheet having excellent coiling quality for line pipe}

본 발명은 유전 및 천연가스 수송관의 소재로 사용되는 고인성-고강도 라인 파이프용 열연강재의 제조방법에 관한 것으로, 상세하게는 압연공정과 권취공정에서의 내부응력의 적절한 해소와 굽힘에 의한 응력해소에 의해 권취 품질을 확보할 수 있는 라인파이프용 열연강판의 제조방법에 관한 것이다.The present invention relates to a method for manufacturing hot rolled steel for high toughness-high strength line pipes used as materials for oilfield and natural gas transport pipes. The present invention relates to a method for manufacturing a hot rolled steel sheet for a line pipe that can secure winding quality by elimination.

석유 수송용 강관은 기존의 유정들이 말기로 접어들면서 불순물의 유입에 따른 내환경성이 중요하다. 또한, 새로운 유정들은 열악한 기후의 극지방으로 이동하고있어 저온인성이 중요시 되고 있다. 그리고, 건설비를 절감하기 위해 대구경-고강도화의 추진에 따라 후물의 라인파이프가 요구되고 있다.Steel pipes for petroleum transportation have an important environmental resistance due to the inflow of impurities as the existing oil wells enter into the late stage. In addition, new wells are moving to the polar regions of poor climate, making low-temperature toughness important. In addition, in order to reduce construction costs, a thick pipe line is required in accordance with the promotion of large diameter-high strength.

사용환경이 극한랭지로 이동함에 따라 강재의 요구두께는 두꺼워졌고, 이를 위해 초기에는 15mm이상의 두께의 경우 후판(Plate)을 사용하였다. 그러나 후판을 이용하여 조관하는 경우 코일을 소재로 하여 강관을 만드는데 비하여 비용증가 및 생산성 하락이 발생한다. 따라서, 생산성 및 비용절감을 통한 경쟁력을 확보를 위하여 두께 15mm이상의 경우에도 열연코일의 공급을 요구하게 되었다. 15mm이상의 열연코일에 대해서도 강도뿐만 아니라 저온인성 요구수준 또한 엄격해지고 있다. 이른바 극저온 충격인성 및 고강도 라인 파이프용 열연강재를 요구하고 있고, 이에 대한 제조방법으로 저온압연, 저온인성 방법이 새롭게 개발 되고 있다.As the usage environment moved to the extreme cold, the required thickness of the steel became thicker. For this purpose, in the case of thicker than 15mm, the plate was used. However, in the case of using a thick plate to produce a steel pipe made of a coil material increases the cost and decrease in productivity. Therefore, in order to secure competitiveness through productivity and cost reduction, it is required to supply a hot rolled coil even when the thickness is 15 mm or more. For hot rolled coils of 15 mm or more, the requirements for toughness as well as low temperature toughness are becoming more stringent. So-called cryogenic impact toughness and hot rolled steel for high-strength line pipes are required, and low-temperature rolling and low-temperature toughness methods are newly developed as a manufacturing method thereof.

저온압연, 저온인성 제조방법에 적용되는 강슬라브는, 중량%로 C:0.04~0.07%, Mn:1.50~1.70%, Si:0.15~0.25%, P:0.010%이하, S:0.003%이하, Nb:0.040~0.060%, V:0.040~0.060%, Ti:0.010~0.025%, Mo:0.10~0.30%, Ni:0.10~0.30%를 포함하여 조성되는 강이다. 이 슬라브를 1150℃~1200℃에서 재가열하고, 조압연 최종패스시 10~25%로 압연하고 890~930℃에서 마무리 조압연하여 45~55mm의 조압연바를 얻은 다음, 마무리온도를 790~830℃의 조건으로 사상압연하고, 560~600℃에서 권취하고 있다. 권취된 열연강판은 미세한 침상 페라이트(Acicular Ferrite)의 조직으로서, 라인 파이프용 열연강판으로서 인성 및 강도를 갖추고 있다. 이런 제조 과정중에도 2의 (가)와 (나)부에서의 변태와 재결정에 따른 조직내부의 부피변화에 따른 내부응력이 발생하여 도 3에서 보여주는 대로 저온 변태에 따른 내부응력, 그리고, 도 4(a) 와 같은 권취시 굽힘에 따른 반력 등의 해소를 하지 못하고 있어 코일(Coil) 길이방향, 폭방향 불균일 응력에 의한 권취불량이 발생한다.The steel slab applied to low temperature rolling and low temperature toughness manufacturing method is% by weight of C: 0.04 ~ 0.07%, Mn: 1.50 ~ 1.70%, Si: 0.15 ~ 0.25%, P: 0.010% or less, S: 0.003% or less, Nb: 0.040 to 0.060%, V: 0.040 to 0.060%, Ti: 0.010 to 0.025%, Mo: 0.10 to 0.30%, Ni: 0.10 to 0.30%. The slab is reheated at 1150 ° C to 1200 ° C, rolled to 10-25% in the final pass of the rough rolling and rough rolled at 890-930 ° C to obtain a roughened bar of 45-55 mm, and then the finishing temperature is 790-830 ° C. Rolling is carried out under the conditions of and wound up at 560-600 degreeC. The wound hot rolled steel sheet is a fine acicular ferrite structure and has toughness and strength as a hot rolled steel sheet for line pipe. During this manufacturing process, the internal stress due to the volume change inside the tissue due to transformation and recrystallization in parts (a) and (b) of 2 is generated, and the internal stress due to low temperature transformation, as shown in FIG. When the winding as in the above, the reaction force due to the bending cannot be solved, and the winding failure due to the uneven stress in the longitudinal and width directions of the coil occurs.

즉, 종래의 제조방법으로는 강도 및 인성을 만족 시킬 수 있으나, 도 1과 같이 권취후 권취코일이 풀어지거나 과도한 텔레스코프 (Telescope)가 빈번하게 발생하는 문제점이 있다. 즉, 저온압연에 의한 조직 미세화를 통해서 저온인성-고강도 강을 제조하는 기술은 많은 진척을 보이고 있으나, 후판이 아닌 코일(Coil)로 생산하여 상업적으로 쉽게 이용할 수 있는 기술개발은 미진한 상태이다. 특히, 권취품질을 확보하면서 저온인성과 고강도를 확보할 수 있는 기술은 전무하다.That is, the conventional manufacturing method can satisfy the strength and toughness, but as shown in FIG. 1, there is a problem in that the winding coil is unwinded or excessive telescope occurs frequently. That is, the technology for producing low-temperature toughness-high strength steel through the microstructure of the cold rolling has shown a lot of progress, but the development of technology that can be easily used commercially by producing a coil rather than a thick plate is in a poor state. In particular, there is no technology that can secure low-temperature toughness and high strength while ensuring the winding quality.

따라서, 본 발명에서는 열연공정의 단위공정별로 제조 조건을 제어하여 저온인성 및 고강도를 확보하면서 상업적으로 요구되는 권취품질을 확보할 수 있는 열연강판의 제조방법을 제공하는데, 그 그 목적이 있다.Accordingly, the present invention provides a method for manufacturing a hot rolled steel sheet that can secure the winding quality commercially required while ensuring low temperature toughness and high strength by controlling the manufacturing conditions for each unit process of the hot rolling process, the object thereof.

도 1은 권취품질이 불량한 코일1 is a coil with poor winding quality

도 2는 Fe-C 상태도2 is Fe-C state diagram

도 3은 연속냉각변태 곡선3 is a continuous cooling transformation curve

도 4는 권취시 트랙 스프레이에 의한 응력 변화를 나타내는 그래프4 is a graph showing the change in stress caused by the track spray during winding

도 5는 본 발명예와 비교예에서 텔레스코브 발생정도를 비교한 그래프5 is a graph comparing the degree of generation of telescope in the present invention and the comparative example

상기 목적을 달성하기 위한 본 발명의 라인파이프용 열연강판의 제조방법은, 중량%로 C:0.04~0.07%, Mn:1.50~1.70%, Si:0.15~0.25%, P:0.010%이하, S:0.003%이하, Nb:0.040~0.060%, V:0.040~0.060%, Ti:0.010~0.025%, Mo:0.10~0.30%,Ni:0.10~0.30%, 나머지 Fe 및 기타 불가피한 불순물로 이루어진 슬라브를 재가열하여 열간압연하고 권취하는 방법에 있어서,Method for producing a hot-rolled steel sheet for line pipe of the present invention for achieving the above object, by weight% C: 0.04 ~ 0.07%, Mn: 1.50 ~ 1.70%, Si: 0.15 ~ 0.25%, P: 0.010% or less, S : Slab composed of less than 0.003%, Nb: 0.040 ~ 0.060%, V: 0.040 ~ 0.060%, Ti: 0.010 ~ 0.025%, Mo: 0.10 ~ 0.30%, Ni: 0.10 ~ 0.30%, remaining Fe and other unavoidable impurities In the method of reheating, hot rolling and winding,

상기 재가열된 슬라브의 마지막 조압연 이전의 2회 조압연후에는 각각 공냉대기하여 조압연하는 단계,After the two rough rolling before the last rough rolling of the reheated slab, the step of rough rolling by air-cooling, respectively,

상기 조압연 바를 사상압연기의 스탠드 사이에서 냉각수를 분사하면서 사상압연하는 단계 및Finishing rolling the rough rolling bar while spraying cooling water between the stands of the finishing mill;

상기 사상압연한 열연판을 500~590℃의 온도로 권취하면서 권취코일의 외측에 냉각수를 분사하는 단계를 포함하여 구성된다.It comprises a step of spraying the cooling water on the outside of the coiling coil while winding the hot-rolled hot rolled plate at a temperature of 500 ~ 590 ℃.

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

본 발명에서는 항복강도 530Mpa 이상과 -60℃의 극저온 환경에서 요구되는 충격인성을 가지면서 권취 품질을 확보할 수 있는 라인파이프용 열연강판을 제조하는데 특징이 있다. 본 발명에서는 조압연과정에서 가공에 의한 내부 발열과 상변화에 따른 조직의 부피 변화로 발생된 응력을 해소하기 위하여 마지막 조압연 바로 이전의 2회 압연부터 조압연후에 일정 시간 공냉대기를 한다. 그리고, 사상압연에서는 압연스탠드사이에서 냉각수를 분사하고, 권취공정에서는 굽힘에 따른 반력 등의 해소를 위하여 권취코일의 외측에 냉각수를 분사하는 것이다.In the present invention is characterized in the production of hot-rolled steel sheet for line pipe having a toughness required in the cryogenic environment of the yield strength of 530Mpa or more and -60 ℃. In the present invention, in order to solve the stress generated by the internal heat generated by the processing during the rough rolling process and the volume change of the tissue due to the phase change, air cooling is performed for a predetermined time after the rough rolling from the second rolling just before the last rough rolling. In the rolling, the cooling water is sprayed between the rolling stands, and in the winding process, the cooling water is sprayed on the outer side of the winding coil in order to eliminate reaction forces due to bending.

본 발명의 대상이 되는 강슬라브는, 라인파이프용 소재로서 그 대표적인 예는C:0.04~0.07%, Mn:1.50~1.70%, Si:0.15~0.25%, P:0.010% 이하,S:0.003%이하, Nb:0.040~0.060%, V:0.040~0.060%, Ti:0.010~0.025%, Mo:0.10~0.30%, Ni:0.10~0.30%, 나머지 Fe 및 기타 불가피한 불순물 조성되는 강이다.Steel slab, which is the object of the present invention, is a line pipe material, and representative examples thereof are C: 0.04 to 0.07%, Mn: 1.50 to 1.70%, Si: 0.15 to 0.25%, P: 0.010% or less, and S: 0.003%. Hereinafter, Nb: 0.040 to 0.060%, V: 0.040 to 0.060%, Ti: 0.010 to 0.025%, Mo: 0.10 to 0.30%, Ni: 0.10 to 0.30%, remaining Fe and other unavoidable impurities.

상기한 Nb-V-Ti-Mo-Ni 성분계의 강슬라브는 가열로에서 합금 원소(Nb)의 충분한 고용을 위해 1150~1200℃로 200~300분간 장시간 가열하여 조압연을 행하고 있다.The steel slab of the Nb-V-Ti-Mo-Ni component system described above is subjected to rough rolling by heating for a long time at 1150 to 1200 ° C. for 200 to 300 minutes for sufficient solid solution of the alloying element (Nb) in a heating furnace.

본 발명에서는 이러한 조압연공정에서 가공에 의한 내부 발열과 상변화에 따른 조직의 부피 변화로 발생된 응력을 해소하기 위하여 마지막 조압연(n회 조압연) 바로 이전의 두 번의 압연(n-2, n-1회의 조압연)후에 공냉대기를 행한다.In the present invention, in order to solve the stress caused by the internal heat generated by processing in the rough rolling process and the volume change of the tissue due to the phase change, the two rollings just before the last rough rolling (n times rough rolling) (n-2, Air cooling is performed after n-1 rough rolling).

조압연 공정은 가역식 압연이 이루어진다. 통상 200∼250mm 슬라브(Slab)를 6회 또는 10회의 패스를 실시하여 사상압연에 들어 가기 위한 40∼60mm 조압연 바(Bar)로 만든다. 이러한 조압연 매패스마다 압연에 의한 가공발열이 발생한다. 또한, 조압연에서는 고온산화에 의한 스케일층 제거를 위해 고압의 디스케일링 (Descaling)을 표층에 분사하는데 이 과정에서 온도의 분포 형태가 표층과 내부가 다르게 되는 현상이 생긴다. 표층만이 우선 냉각에 의해 석출영역 온도에 이르게 되는 불균일한 열평형이 나타나게 된다.The rough rolling process is reversible rolling. In general, a 200-250 mm slab is carried out six or ten times to form a 40-60 mm rough-rolled bar for finishing rolling. In each rough rolling pass, processing heat is generated by rolling. In addition, in the rough rolling, high-pressure descaling is sprayed on the surface layer to remove the scale layer by high temperature oxidation. In this process, the temperature distribution form is different from the surface layer. Only the surface layer first shows non-uniform thermal equilibrium which leads to precipitation region temperature by cooling.

본 발명은 이러한 열이력에 따른 조직변화 및 석출거동 변화의 물리야금학적 고유특성을 착안하여 조압연공정에서의 발열과 응력의 불균일 요인을 제거한다. 이를 구체적으로 설명하면, 가열로에서 추출한 슬라브(SLAB)는 매 패스시 마다 디스케일링을 실시하므로 강판의 냉각이 이루어지면서 결정립은 더욱 미세해 지지만 가공에 의한 내부 발열에 따라 표층과 내부의 온도차가 발생한다. 이는 조압연에서 압연 실시후 대기를 할 경우 내부발열에 의한 온도상승이 나타나는 것을 알 수 있다. 이와 같은 내부와 표층의 온도차는 다음 압연시에 응력 불균일을 유발하고, 내부열원은 다음 패스압연이 실시된 후에도 재결정시에 열원으로 작용하면서 조직 조대화를 유발하게 된다.The present invention focuses on the physical metallurgy inherent characteristics of the structure change and precipitation behavior change according to the thermal history to remove the non-uniformity of heat generation and stress in the rough rolling process. Specifically, the slab extracted from the furnace performs descaling every pass, so that the grains become finer as the steel sheet is cooled, but the temperature difference between the surface layer and the inside occurs due to internal heat generated by the processing. do. It can be seen that the temperature rise due to internal heat generation occurs when the atmosphere is performed after rolling in rough rolling. Such a temperature difference between the inside and the surface layer causes stress unevenness during the next rolling, and the internal heat source acts as a heat source during recrystallization even after the next pass rolling, causing tissue coarsening.

이를 해소하면 조직 미세화 및 응력해소가 가능하게 되는데, 그 방안으로 본 발명에서는 n-2, n-1회 조압연후에 공냉대기하는 것이다. 조압연후에 공냉대기하면 충분한 발열이 일어나서 그 후의 압연시에 반력이 줄어드는 동시에 내부응력을 해소할 수 있다. n-2회 조압연후 공냉대기시간은 20~30초가 바람직하며, n-1회 조압연후 공냉대기시간은 10~20초가 바람직하다. n-2패스 압연후의 대기시간은 발열이 충분히 되는 시간이며, n-1패스후의 대기 시간이 지나치면 조압연 공정 통과 시간이 과다하여 생산성 하락이 발생하는 측면을 고려한 것이다.When this is solved, the structure can be miniaturized and the stress can be resolved. As the method, the present invention is air-cooled after roughing n-2 and n-1 times. When air-cooled after rough rolling, sufficient heat will generate and reaction force will be reduced at the time of subsequent rolling, and internal stress can be solved. After n-2 times of rough rolling, the air cooling standby time is preferably 20 to 30 seconds, and the time of n-1 times of rough cooling is preferably 10 to 20 seconds. The waiting time after n-2 pass rolling is time to generate | occur | produce heat sufficiently, and when the waiting time after n-1 pass passes, the pass time of rough rolling process will be excessive, and the fall of productivity takes into consideration.

본 발명에 따라 n-2, n-1회 압연후에 대기냉각을 하면 니오븀(Nb)의 석출 종료온도인 900∼930℃정도에서 압연을 하게 되어 피닝(Pinning: 조직의 경계에 석출물이 존재하면서 조직이 조대화 되려는 것을 저지하는 현상)효과에 의한 미세화된 상태로 사상압연을 할 수 있게 되어 재결정 후에도 미세화된 조직 확보가 가능하게 된다. 이런 조압연 조건은 마지막 패스후의 조압연 마무리온도 870~910℃를 확보하는데 유리하다. 조압연 마무리 온도가 너무 높으면 오스테나이트 입도 조대화로 강도 확보가 곤란하며, 너무 낮으면 사상압연시 설비에 무리를 주기 때문에 바람직하지 않다.According to the present invention, if the air is cooled after rolling n-2 and n-1 times, rolling is carried out at about 900 to 930 ° C., which is the end temperature of niobium (Nb), and pinning occurs. Mapping rolling can be carried out in a micronized state by the effect of preventing the coarsening), and the micronized structure can be secured even after recrystallization. This rough rolling condition is advantageous to secure the rough rolling finish temperature of 870 ~ 910 ℃ after the last pass. If the rough rolling temperature is too high, it is difficult to secure the strength by coarsening the austenite grain size, too low is unfavorable because it imposes pressure on the facility during finishing rolling.

본 발명에 따라 조압연한 조압연바를 사상압연한다.Rough rolling of the rough rolling bar according to the present invention.

통상적으로 사상압연은 누적압하율을 50% 이상되도록 하여 열연강판의 조직을 침상조직 (Bainitic Ferrite)으로 유도하고 있다. 동일한 사상압연 온도 및 권취 온도인 경우 사상압연의 누적 압하율이 클 경우 결정입계의 밀도, 전위밀도 및 변형대(Deformation Band)가 증가하게 되여 변형 기간 중 변형 유기석출(Strain Induced Precipitation)량이 증가하게 되어 결정립은 더욱 미세해지기 때문이다. 사상 압연 마무리 온도는 입도 미세화를 위해 통상적으로 오스테나이트에서 페라이트의 변태점 근처인 750~830℃에서 행하고 있다.In general, filament rolling causes the cumulative rolling rate to be 50% or more to induce the structure of the hot-rolled steel sheet into the basintic tissue (Bainitic Ferrite). In case of the same filament rolling temperature and winding temperature, if the cumulative rolling reduction rate of filament rolling is large, the density, dislocation density and deformation band of grain boundary increase, so that the amount of strain induced precipitation during deformation period increases. This is because the grains become finer. The finishing rolling finish temperature is usually performed at 750 to 830 ° C., which is near the transformation point of ferrite in austenite for finer grain size.

본 발명에서는 상기와 같은 사상압연조건에서 사상압연기의 스탠드 사이에서 냉각수를 분사하는 것이다. 종래에는 사상압연기 스탠드의 일부에서만 냉각수를 분사하고 있었다. 본 발명에 따라 사상압연기의 모든 스탠드사이에서 냉각수를 분사해주면 매 압연시 마다 발생하는 가공발열을 해소하고 페라이트의 변태점 직전에 압연이 끝나게 해 줌으로서 조직 미세화에 의한 강도 및 인성 개선 효과를 극대화 할 수 있다. 또한, 안정한 상(Phase)에서 사상압연이 이루어지게 됨에 따라 사상압연기에서의 부하 변동 감소가 가능하게 된다. 이에 따라 캠버(Camber: 강판이 길이 방향으로 휘어지는 현상) 방지 및 안정된 형상 확보가 되어 권취 품질 향상에 더욱 유리하고 저온 압연으로 인한 판 내부의 열응력 불균일을 해소하면서 동시에 더욱 미세한 조직을 확보 함으로서 인성과 강도 확보에 유리하다. 냉각수는 압연기에 따라 차등 압력으로 분사하며 압하율이 가장 큰 첫 압연기에 가장 큰 압력의 냉각수가 설치되어 있다.In the present invention, the cooling water is injected between the stands of the finishing mill under the finishing rolling conditions as described above. Conventionally, cooling water is sprayed only on a part of a finishing mill stand. According to the present invention, spraying the cooling water between all the stands of the finishing mill eliminates the processing heat generated in every rolling and allows the rolling to be completed just before the transformation point of the ferrite, thereby maximizing the effect of improving the strength and toughness by the microstructure. have. In addition, as the finishing rolling is performed in a stable phase, it is possible to reduce the load fluctuation in the finishing mill. This prevents the camber and ensures a stable shape, which is more advantageous for improving the winding quality, and eliminates thermal stress unevenness due to low temperature rolling while at the same time securing a finer structure. It is advantageous for securing strength. Cooling water is injected at different pressures depending on the rolling mill, and the largest pressure cooling water is installed in the first rolling mill having the largest reduction ratio.

상기와 같이 사상압연한 다음 권취한다.Roll as described above and wind up.

통상적으로 500~590℃의 저온에서 권취하고 있다. 권취온도는 도 3에서 보는 바와 같이, 사상압연 후의 냉각방법을 나타내는 선이 가고자 하는 영역의 범위이다. 이 권취 온도 역에서는 미세한 침상조직(Bainitic Ferrite)이 형성 되므로 강도 및 저온 충격의 인성 확보가 가능하다. 고온으로 권취하면 페라이트 입자가 조대화 되고 너무 낮으면 강도가 높은 조직으로 변태되어 권취불량이 발생하게 되고 제품으로의 기능을 상실하게 된다.Usually, it is wound up at low temperature of 500-590 degreeC. As shown in FIG. 3, the coiling temperature is a range in which a line showing the cooling method after finishing rolling is intended to go. In this winding temperature range, fine needle structure (Bainitic Ferrite) is formed, so it is possible to secure strength and low temperature impact toughness. If the coil is wound at a high temperature, the ferrite particles become coarse, and if it is too low, the ferrite particles are transformed into high-strength tissue, resulting in winding failure and loss of function to the product.

이 권취 온도영역의 확보를 위한 냉각제어를 함에 있어 권취 온도는 일정한 온도를 유지하는 것이 아니라 일정 수준의 편차를 가지고 있다. 폭 방향, 길이 방향의 온도편차는 침상조직(Bainitic Ferrite), 페라이트, 베이나이트의 분율 분포 불균일을 유발하고 하게 되어 비록 강도 및 인성은 확보가 된다고 하더라도 권취 불량을 초래하는 영향으로 작용하므로 권취과정 중에 제거하여야 한다.In performing cooling control to secure this winding temperature range, the winding temperature does not maintain a constant temperature but has a certain level of variation. Temperature deviations in the width direction and the length direction cause uneven distribution of the fractions of the basintic ferrite, ferrite and bainite, so that even if the strength and toughness are secured, it causes the winding failure. Should be removed.

따라서, 본 발명에서는 사상압연기로부터 나오는 코일(Coil)이 권취기에 감겨진 시점(약 3~4바퀴 정도)부터 권취코일의 외측에 냉각수를 분사한다. 냉각수의 분사는 권취가 종료된 후 귄취코일의 외측에 60∼90초 동안 더 분사하는 것이 바람직하다. 분사시간이 과다하면 전체작업시간에 영향을 주게 되어 생산성 하락이 발생될 수 있고, 부족한 경우는 곡률반경이 작은 외권의 응력이 완전히 풀리지 않아 풀어지는 현상이 발생한다. 본 발명에 따라 권취코일의 외측에 냉각수의 분사는 통상의 트랙스프레이(Track Spray) 설비를 통해 행할 수 있다. 트랙 스프레이(Track Spray)는 권취 종료 후 외권부에 물을 분사(종래 10∼30초 정도)하여 외권부를 냉각해주는 설비이다.Therefore, in the present invention, the cooling water is injected to the outside of the winding coil from the time point (about 3 to 4 wheels) of the coil (Coil) coming from the finishing mill is wound on the winder. Spraying of the cooling water is preferably further sprayed for 60 to 90 seconds to the outside of the winding coil after the end of the winding. Excessive injection time affects the overall working time, which may result in a decrease in productivity. In case of insufficient injection time, the stress of the outer space with a small radius of curvature may not be completely solved, causing the phenomenon to be released. According to the present invention, the spraying of the cooling water on the outer side of the coiling coil can be performed through a conventional track spray equipment. Track Spray is a facility that cools the outer wound part by spraying water on the outer wound part (conventionally 10-30 seconds) after the end of winding.

도 4(a)와 같이 귄취코일은 평평한 상태로 돌아가려는 압축과 인장응력을 가진다. 이러한 권취코일의 외측에 트랙 스프레이를 이용해 냉각수를 분사하면 도 4(b)와 같이 판이 가지고 있는 응력이 열응력에 의해 해소 되면서 도 4(c)와 같은 응력의 평형상태를 유지하게 된다. 트랙스프레이를 이용하는 경우 권취 온도가 낮아 권취 불량이 발생될 것으로 예상될 경우에도 사용하면 권취 불량을 방지할 수 있다.As shown in (a) of FIG. 4, the coil has a compressive and tensile stress to return to a flat state. When spraying the cooling water using the track spray on the outer side of the winding coil, the stress of the plate is solved by the thermal stress as shown in FIG. 4 (b) and maintains the equilibrium state of the stress as shown in FIG. 4 (c). In the case of using the track spray, even when the winding temperature is low and the winding failure is expected to be used, the winding failure can be prevented.

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

[실시예]EXAMPLE

표 1의 슬라브를 1250~ 1300℃에서 200~300분 가열하여 표 2의 조건으로 압연과 권취를 하여 열연강판을 제조하였다. 발명예들은 사상압연기 스탠드사이에서 냉각수를 분사하였다. 이 열연강판의 기계적성질과 충격인성 및 텔레스코프를 측정하여 표 3에 나타내었다. 텔레스코프의 측정결과는 도 5에 그래프의 형식으로도 나타내었다.The slabs of Table 1 were heated at 1250 to 1300 ° C. for 200 to 300 minutes, and rolled and wound under the conditions of Table 2 to prepare hot rolled steel sheets. Inventive examples sprayed cooling water between the finishing mill stands. The mechanical properties, impact toughness and telescope of this hot rolled steel sheet were measured and shown in Table 3. The measurement results of the telescope are also shown in the form of a graph in FIG. 5.

강종Steel grade CC MnMn SiSi PP SS NbNb VV TiTi MoMo NiNi AA 0.0450.045 1.581.58 0.240.24 0.0100.010 0.0030.003 0.0560.056 0.0570.057 0.0200.020 0.130.13 0.140.14 BB 0.0510.051 1.551.55 0.210.21 0.0080.008 0.0010.001 0.0520.052 0.0530.053 0.0230.023 0.170.17 0.180.18 CC 0.0530.053 1.631.63 0.210.21 0.0100.010 0.0010.001 0.0490.049 0.0500.050 0.0160.016 0.250.25 0.200.20 DD 0.0590.059 1.481.48 0.170.17 0.0090.009 0.0030.003 0.0590.059 0.0480.048 0.0170.017 0.290.29 0.280.28

구분division 강종Steel grade 조압연후단4패스진입온도(℃)4-pass inlet temperature (℃) after rough rolling 조압연후단3패스후공냉시간(초)Air cooling time (seconds) after 3 pass after rough rolling 조압연후단4패스후공냉시간(초)4-pass after cold rolling (seconds) 조압연마무리온도(℃)Roughing Finishing Temperature (℃) 사상압연냉각수(개)Filament Rolling Coolant (pcs) 마무리온도(℃)Finishing temperature (℃) 권취온도(℃)Winding temperature (℃) 트랙스프레이사용방법How to use track spray 발명예1Inventive Example 1 AA 913913 2525 1010 909909 66 785785 585585 권취중Winding up 발명예2Inventive Example 2 BB 911911 2727 1212 871871 66 784784 571571 권취중Winding up 발명예3Inventive Example 3 CC 917917 3030 1515 895895 66 800800 545545 권취중Winding up 발명예4Inventive Example 4 DD 915915 2626 1515 890890 66 802802 556556 권취중Winding up 비교예1Comparative Example 1 AA 957957 -- -- 910910 33 791791 580580 권취후After winding 비교예2Comparative Example 2 CC 960960 -- -- 900900 33 789789 573573 권취후After winding 비교예3Comparative Example 3 CC 961961 -- -- 891891 22 810810 563563 권취후After winding 비교예4Comparative Example 4 DD 965965 -- -- 895895 22 811811 559559 권취후After winding

구분division 강종Steel grade 기계적 성질(30℃ 방향)Mechanical property (30 ℃ direction) 충격시험(30℃ 방향)Impact test (30 ° C direction) 텔레스코프(mm)Telescope (mm) 항복강도(MPa)Yield strength (MPa) 인장강도(MPa)Tensile Strength (MPa) 연신율(%)Elongation (%) 항복비(%)Yield Ratio (%) -60℃(CVN, Joule)-60 ℃ (CVN, Joule) 발명예1Inventive Example 1 AA 542542 668668 3535 8181 310310 2121 발명예2Inventive Example 2 BB 549549 685685 3636 8080 309309 1515 발명예3Inventive Example 3 CC 552552 674674 3535 8282 315315 1717 발명예4Inventive Example 4 DD 543543 679679 3737 8080 325325 1010 비교예1Comparative Example 1 AA 539539 666666 3535 8181 305305 1313 비교예2Comparative Example 2 BB 550550 685685 3636 8080 285285 2222 비교예3Comparative Example 3 CC 555555 694694 3535 8080 293293 2525 비교예4Comparative Example 4 DD 540540 685685 3737 7979 308308 3535

표에 나타난 바와 같이, 발명재의 경우 비교재에 비하여 강도 및 인성이 동등 수준이면서 권취 형상 또한 우수하였다. 권취 품질을 확인할 수 있는 척도인 텔레스코프의 측정결과는 도 5에서 알 수 있듯이, 발명재의 권취 형상이 우수하였다.As shown in the table, the invention material was superior in strength and toughness and the winding shape was also higher than that of the comparative material. As can be seen from FIG. 5, the measurement result of the telescope, which is a measure of winding quality, was excellent in the winding shape of the invention material.

상술한 바와 같이, 본 발명에 따르면 인성과 강도를 동등 수준이상으로 이상으로 유지하면서 권취 불량을 해소할 수 있는 유용한 효과가 있는 것이다.As described above, according to the present invention, there is a useful effect of eliminating the winding failure while maintaining the toughness and strength above the equivalent level.

Claims (3)

중량%로 C:0.04~0.07%, Mn:1.50~1.70%, Si:0.15~0.25%, P:0.010%이하,S:0.003%이하, Nb:0.040~0.060%, V:0.040~0.060%, Ti:0.010~0.025%, Mo:0.10~0.30%, Ni:0.10~0.30%, 나머지 Fe 및 기타 불가피한 불순물로 이루어진 슬라브를 재가열하여 열간압연하고 권취하는 방법에 있어서,By weight% C: 0.04 ~ 0.07%, Mn: 1.50 ~ 1.70%, Si: 0.15 ~ 0.25%, P: 0.010% or less, S: 0.003% or less, Nb: 0.040 ~ 0.060%, V: 0.040 ~ 0.060%, In the method of reheating, hot rolling and winding a slab composed of Ti: 0.010 to 0.025%, Mo: 0.10 to 0.30%, Ni: 0.10 to 0.30%, and the remaining Fe and other unavoidable impurities, 상기 재가열된 슬라브의 마지막 조압연 이전의 2회 조압연후에는 각각 공냉대기하여 조압연하는 단계,After the two rough rolling before the last rough rolling of the reheated slab, the step of rough rolling by air-cooling, respectively, 상기 조압연 바를 사상압연기의 스탠드 사이에서 냉각수를 분사하면서 사상압연하는 단계 및Finishing rolling the rough rolling bar while spraying cooling water between the stands of the finishing mill; 상기 사상압연한 열연판을 500~590℃의 온도로 권취하면서 권취코일의 외측에 냉각수를 분사하는 단계를 포함하여 이루어지는 권취품질이 우수한 라인파이프용 열연강판의 제조방법.A method of manufacturing a hot rolled steel sheet for excellent line pipe, comprising the step of spraying cooling water on the outside of the winding coil while winding the hot rolled sheet at a temperature of 500 to 590 ° C. 제 1항에 있어서, 상기 조압연은 n회 조압연에서 n-2회의 조압연후에는 20~30초 공냉대기하고, n-1회 조압연후에는 10~20초 공냉대기하고, 조압연마무리 온도는 870~910℃가 되도록 함을 특징으로 하는 권취품질이 우수한 라인파이프용 열연강판의 제조방법.The method of claim 1, wherein the rough rolling is 20-30 seconds air-cooled after n-2 rough rolling in n rough rolling, 10-20 seconds air-cooling after n-1 rough rolling, and rough finishing Method for producing a hot rolled steel sheet for line pipe having excellent winding quality, characterized in that the temperature is 870 ~ 910 ℃. 제 1항에 있어서, 상기 권취는 권취종료후 권취코일의 외권부에 60~90초 동안 추가로 냉각수를 분사하는 것을 특징으로 하는 권취품질이 우수한 라인파이프용 열연강판의 제조방법.The method according to claim 1, wherein the winding further comprises spraying cooling water for 60 to 90 seconds to the outer winding portion of the winding coil after finishing the winding.
KR10-2002-0063675A 2002-10-18 2002-10-18 Method for hot rolled steel sheet having excellent coiling quality for line pipe KR100482201B1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101149121B1 (en) * 2009-07-24 2012-05-25 현대제철 주식회사 High strength hot rolled steel sheet and the method of producing the same
KR101225725B1 (en) * 2010-10-27 2013-01-24 현대제철 주식회사 Method for manufacturing steel sheet

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JPS56139626A (en) * 1980-03-31 1981-10-31 Kobe Steel Ltd Production of hot-rolled steel plate of superior strength-ductility balance
JPS63100126A (en) * 1986-10-14 1988-05-02 Kawasaki Steel Corp Manufacture of hot rolled high tension steel for resistance welded steel pipe having superior workability
JP2001164321A (en) * 1999-12-07 2001-06-19 Nippon Steel Corp Method for producing high tensile strength hot rolled steel plate for working using hot rolling continuous process
KR100481370B1 (en) * 2000-12-23 2005-04-08 주식회사 포스코 Method for manufacturing heavy gauge high strength linepipe steel with superior low temperature toughness

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101149121B1 (en) * 2009-07-24 2012-05-25 현대제철 주식회사 High strength hot rolled steel sheet and the method of producing the same
KR101225725B1 (en) * 2010-10-27 2013-01-24 현대제철 주식회사 Method for manufacturing steel sheet

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