JP5413537B2 - High strength steel plate and high strength steel pipe excellent in deformation performance and low temperature toughness, and methods for producing them - Google Patents
High strength steel plate and high strength steel pipe excellent in deformation performance and low temperature toughness, and methods for producing them Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
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- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- 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
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- C21D2201/05—Grain orientation
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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Description
本発明は、天然ガス、原油等の輸送用ラインパイプとして好適に用いられ、特に、地盤変動等に対する変形許容度が大きい変形性能及び低温靭性に優れた高強度鋼板及び高強度鋼管とこれらの製造方法に関する。 The present invention is suitably used as a line pipe for transportation of natural gas, crude oil and the like, and in particular, a high-strength steel plate and a high-strength steel pipe excellent in deformation performance and low-temperature toughness with a large deformation tolerance against ground fluctuation and the like, and production thereof Regarding the method.
近年、天然ガス、原油の長距離輸送方法としてラインパイプの重要性がますます高まっている。ラインパイプは、敷設される環境が多様化しており、たとえば、凍土地帯での夏と冬とでの地盤変動、海底での海流による外圧、地震による地層変動等が生じる環境に敷設される。このような環境の下では、地盤変動等によりラインパイプに曲がり、変位が生じることがあるので、ラインパイプが変形した場合でも座屈等が生じにくい変形性能に優れた鋼管が要望されている。 In recent years, line pipes have become increasingly important as a long-distance transportation method for natural gas and crude oil. Line pipes are laid in various environments. For example, ground pipes are frozen in summer and winter in frozen land belts, are subject to external pressure due to ocean currents on the seabed, and are subject to ground deformation due to earthquakes. Under such an environment, the line pipe may bend and displace due to ground fluctuation or the like, and therefore, a steel pipe excellent in deformation performance that hardly causes buckling or the like even when the line pipe is deformed is desired.
従来、変形性能に優れた鋼管として、特許文献1に開示されているような、加工硬化指数(n値)に着目してその改善を図った鋼管や、特許文献2に開示されているような、引張強度に対する降伏強度の比である降伏比に着目してその改善を図った鋼管が提案されている。 Conventionally, as steel pipes excellent in deformation performance, steel pipes that have been improved by paying attention to the work hardening index (n value) as disclosed in Patent Document 1, and those disclosed in Patent Document 2 Steel pipes have been proposed in which the yield ratio, which is the ratio of the yield strength to the tensile strength, is focused on and improved.
従来から提案されている技術は、ラインパイプ等に用いられる鋼板、鋼管について、変形性能の改善を図るうえで加工硬化指数や降伏比に着目してその改善を図った技術である。 Conventionally proposed techniques are techniques for improving steel sheet and steel pipes used for line pipes and the like by focusing on work hardening index and yield ratio in order to improve deformation performance.
しかしながら、特に、凍土地帯等の寒冷地に用いられるラインパイプは、低温靭性に優れたものであることが要求されるが、変形性能とともに低温靭性に優れた鋼板、鋼管を得るための技術については十分な検討がなされていなかった。 However, in particular, line pipes used in cold regions such as frozen land zones are required to have excellent low-temperature toughness, but for technology to obtain steel plates and steel pipes that are excellent in deformation performance and low-temperature toughness. Sufficient consideration has not been made.
本発明は、上記の問題点に鑑みて案出されたものであり、変形時の肉厚の減少量を抑えることができる変形性能及び低温靭性に優れた高強度鋼板及び高強度鋼管とこれらの製造方法の提供を課題とする。 The present invention has been devised in view of the above-described problems, and is capable of suppressing the amount of reduction in thickness during deformation, a high-strength steel plate and a high-strength steel pipe excellent in deformation performance and low-temperature toughness, and these It is an object to provide a manufacturing method.
本発明者らは、前記の課題を解決するために、鋭意検討した。その結果、ランクフォード値に着目することにより、パイプライン等に用いられる鋼板、鋼管の変形性能の向上を図ることが可能であることを見出した。 The present inventors have intensively studied to solve the above problems. As a result, it has been found that the deformation performance of steel plates and steel pipes used in pipelines and the like can be improved by paying attention to the Rankford value.
従来、ラインパイプ等に用いられる鋼板、鋼管について、地盤変動等による変形時の肉厚の減少量に着目した検討はなされていなかった。変形時の肉厚の減少量を評価する指標値として、自動車用鋼板等の分野ではランクフォード値が知られている。パイプライン等に用いられる鋼板、鋼管について、ランクフォード値に着目して変形性能の向上を図ることを目的とした技術は提案されていなかった。 Conventionally, studies have not been made on steel sheets and steel pipes used for line pipes, etc., focusing on the amount of reduction in wall thickness when deformed due to ground fluctuation or the like. As an index value for evaluating the amount of reduction in thickness at the time of deformation, the Rankford value is known in the field of automobile steel sheets and the like. For steel plates and steel pipes used in pipelines, no technology has been proposed that aims to improve deformation performance by focusing on the Rankford value.
本発明者らは、変形性能及び低温靭性に優れた高強度鋼板及び高強度鋼管を得るために鋭意検討を行った。その結果、変形性能及び低温靭性に優れた高強度鋼板及び高強度鋼管を得るうえで、所定の結晶方位を有する集合組織の量を適正化しつつ、有効結晶粒径の大きさを適正化することが特に有効であることを知見した。本発明者らは、さらに検討をすすめ、所定の結晶方位を有する集合組織の量を適正化するうえで、熱間圧延時において圧下率をはじめとした種々の製造条件を制御することが特に有効であり、特に、再結晶温度以上の温度域における圧延の1パスあたりの圧下率が非常に重要であることを知見した。 The present inventors have intensively studied to obtain a high-strength steel plate and a high-strength steel pipe excellent in deformation performance and low-temperature toughness. As a result, in order to obtain a high-strength steel sheet and a high-strength steel pipe excellent in deformation performance and low-temperature toughness, the size of the effective crystal grain size should be optimized while optimizing the amount of texture having a predetermined crystal orientation. Was found to be particularly effective. The present inventors have further studied, and in order to optimize the amount of texture having a predetermined crystal orientation, it is particularly effective to control various production conditions including the reduction ratio during hot rolling. In particular, it has been found that the rolling reduction per rolling pass in the temperature range above the recrystallization temperature is very important.
本発明は、上記の知見に基づく検討の結果なされたものであり、その要旨は以下のとおりである。 This invention was made | formed as a result of examination based on said knowledge, The summary is as follows.
(1)質量%で、C:0.03〜0.08%、Si:0.01〜0.50%、Mn:1.50〜2.50%、P:0.015%以下、S:0.0050%以下、Al:0.001〜0.080%、N:0.0010〜0.0060%、Ti:0.005〜0.030%、Nb:0.010〜0.050%を含有し、残部がFe及び不可避的不純物からなり、下記式(A)により表されるCeqが0.35〜0.50%であり、下記式(B)により表されるPcmが0.15〜0.25%であり、フェライトと、ベイナイト又はマルテンサイトのいずれか1種又は2種との複合組織からなり、肉厚中心部における有効結晶粒径が20μm以下であり、肉厚中心部において板面と平行な{111}面のX線ランダム強度比が0.5〜5.0、{554}面のX線ランダム強度比が1.0〜3.0、{100}面のX線ランダム強度比が3.0以下、{112}面及び{223}面それぞれのX線ランダム強度比が0.5〜4.0であり、肉厚が25mm以上であり、引張強度が565MPa以上であることを特徴とする変形性能及び低温靭性に優れた高強度鋼板。 (1) By mass%, C: 0.03 to 0.08%, Si: 0.01 to 0.50%, Mn: 1.50 to 2.50%, P: 0.015% or less, S: 0.0050% or less, Al: 0.001 to 0.080%, N: 0.0010 to 0.0060%, Ti: 0.005 to 0.030%, Nb: 0.010 to 0.050% And the balance consists of Fe and inevitable impurities, Ceq represented by the following formula (A) is 0.35 to 0.50%, and Pcm represented by the following formula (B) is 0.15 to 0.25%, composed of a composite structure of ferrite and either one or two of bainite and martensite, the effective crystal grain size at the center of thickness being 20 μm or less, and a plate at the center of thickness X-ray random intensity ratio of {111} plane parallel to the plane is 0.5 to 5.0, {5 4} plane X-ray random intensity ratio is 1.0 to 3.0, {100} plane X-ray random intensity ratio is 3.0 or less, and each of {112} plane and {223} plane X-ray random intensity ratio Is a high-strength steel sheet excellent in deformation performance and low-temperature toughness, characterized by having a thickness of 25 mm or more and a tensile strength of 565 MPa or more.
Ceq=C+Mn/6+(Ni+Cu)/15+(Cr+Mo+V)/5 …(A) Ceq = C + Mn / 6 + (Ni + Cu) / 15 + (Cr + Mo + V) / 5 (A)
Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15
+V/10+5B …(B)Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15
+ V / 10 + 5B (B)
ここで、C、Mn、Ni、Cu、Cr、Mo、V、Si、Bは、各元素の質量%での含有量である。 Here, C, Mn, Ni, Cu, Cr, Mo, V, Si, and B are contents in mass% of each element.
(2)鋼板の圧延方向に対して45°方向のランクフォード値rD、板幅方向のランクフォード値rCがそれぞれ1.0以上であることを特徴とする前記(1)の変形性能及び低温靭性に優れた高強度鋼板。 (2) The deformation performance and low temperature toughness of (1) above, wherein the Rankford value rD in the 45 ° direction and the Rankford value rC in the sheet width direction are 1.0 or more with respect to the rolling direction of the steel sheet, respectively. Excellent high strength steel plate.
(3)さらに、質量%で、V:0.010〜0.100%、Ni:1.0%以下、Cu:1.0%以下、Cr:1.0%以下、Mo:1.0%以下、B:0.0001〜0.0020%、Ca:0.0040%以下、Mg:0.0017%以下、REM:0.005%以下のうちから選ばれた1種又は2種以上の元素を含有することを特徴とする前記(1)の変形性能及び低温靭性に優れた高強度鋼板。 (3) Further, in mass%, V: 0.010 to 0.100%, Ni: 1.0% or less, Cu: 1.0% or less, Cr: 1.0% or less, Mo: 1.0% Hereinafter, one or more elements selected from B: 0.0001 to 0.0020%, Ca: 0.0040% or less, Mg: 0.0017 % or less, REM: 0.005% or less A high-strength steel sheet excellent in deformation performance and low-temperature toughness as described in (1) above.
(4)前記(1)〜(3)のいずれかの鋼板からなることを特徴とする変形性能及び低温靭性に優れた高強度鋼管。 (4) A high-strength steel pipe excellent in deformation performance and low-temperature toughness, comprising the steel plate of any one of (1) to (3).
(5)質量%で、C:0.03〜0.08%、Si:0.01〜0.50%、Mn:1.50〜2.50%、P:0.015%以下、S:0.0050%以下、Al:0.001〜0.080%、N:0.0010〜0.0060%、Ti:0.005〜0.030%、Nb:0.010〜0.050%、を含有し、残部がFe及び不可避的不純物からなり、下記式(A)により表されるCeqが0.35〜0.50%であり、下記式(B)により表されるPcmが0.15〜0.25%である鋼片を加熱温度1000〜1150℃で加熱し、続いて、再結晶温度以上の温度域において、1パスあたりの圧下率を、前記加熱温度が1000℃以上1050℃未満の時は5〜10%、前記加熱温度が1050℃以上1150℃以下のときは10〜15%とし、さらに、累積圧下率を35%以上として圧延し、次いで、Ar3変態点以上再結晶温度未満の温度域において累積圧下率を70〜80%として圧延し、続いて、Ar3変態点−50℃以上Ar3変態点未満の温度域を冷却開始温度とし、200〜500℃の温度域を冷却終了温度として水冷することを特徴とする変形性能及び低温靭性に優れた高強度鋼板の製造方法。(5) By mass%, C: 0.03 to 0.08%, Si: 0.01 to 0.50%, Mn: 1.50 to 2.50%, P: 0.015% or less, S: 0.0050% or less, Al: 0.001 to 0.080%, N: 0.0010 to 0.0060%, Ti: 0.005 to 0.030%, Nb: 0.010 to 0.050%, The balance consists of Fe and inevitable impurities, Ceq represented by the following formula (A) is 0.35 to 0.50%, and Pcm represented by the following formula (B) is 0.15. The steel slab of ˜0.25% is heated at a heating temperature of 1000 to 1150 ° C., and then the reduction rate per pass in the temperature range above the recrystallization temperature, the heating temperature is 1000 ° C. or more and less than 1050 ° C. When the heating temperature is 1050 ° C. or more and 1150 ° C. or less, the heating temperature is 10%. And 15%, further rolling a cumulative reduction ratio as 35% or more, then rolling a cumulative reduction ratio as 70% to 80% in a temperature range of less than the Ar 3 transformation point recrystallization temperature, followed, Ar 3 transformation A high-strength steel sheet excellent in deformation performance and low-temperature toughness characterized by being water-cooled with a temperature range from −50 ° C. to less than the Ar 3 transformation point as a cooling start temperature and a temperature range of 200 to 500 ° C. as a cooling end temperature. Production method.
Ceq=C+Mn/6+(Ni+Cu)/15+(Cr+Mo+V)/5 …(A) Ceq = C + Mn / 6 + (Ni + Cu) / 15 + (Cr + Mo + V) / 5 (A)
Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15
+V/10+5B …(B)Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15
+ V / 10 + 5B (B)
ここで、C、Mn、Ni、Cu、Cr、Mo、V、Si、Bは、各元素の質量%での含有量である。 Here, C, Mn, Ni, Cu, Cr, Mo, V, Si, and B are contents in mass% of each element.
(6)前記鋼片が、さらに、質量%で、V:0.010〜0.100%、Ni:1.0%以下、Cu:1.0%以下、Cr:1.0%以下、Mo:1.0%以下、B:0.0001〜0.0020%、Ca:0.0040%以下、Mg:0.0017%以下、REM:0.005%、以下のうちから選ばれた1種又は2種以上の元素を含有することを特徴とする前記(6)の変形性能及び低温靭性に優れた高強度鋼板の製造方法。 (6) The steel slab is further in mass%, V: 0.010 to 0.100%, Ni: 1.0% or less, Cu: 1.0% or less, Cr: 1.0% or less, Mo : 1.0% or less, B: 0.0001 to 0.0020%, Ca: 0.0040% or less, Mg: 0.0017 % or less, REM: 0.005%, one selected from the following Or the manufacturing method of the high strength steel plate excellent in the deformation | transformation performance and low-temperature toughness of said (6) characterized by containing 2 or more types of elements.
(7)前記(5)又は(6)の製造方法により得られた鋼板を管状に成形し、突き合わせ部を溶接することを特徴とする変形性能及び低温靭性に優れた高強度鋼管の製造方法。 (7) A method for producing a high-strength steel pipe excellent in deformation performance and low-temperature toughness, characterized in that the steel plate obtained by the production method of (5) or (6) is formed into a tubular shape and the butt portion is welded.
本発明によれば、変形時の肉厚の減少量を抑えることができる変形性能及び低温靭性に優れた高強度鋼板及び高強度鋼管を得ることができる。 According to the present invention, it is possible to obtain a high-strength steel plate and a high-strength steel pipe excellent in deformation performance and low-temperature toughness that can suppress a reduction in thickness during deformation.
はじめに、本発明に係る鋼板及び鋼管の組成の数値範囲を限定した理由について説明する。なお、以下、「%」は「質量%」を表すものとする。 First, the reason for limiting the numerical range of the composition of the steel plate and steel pipe according to the present invention will be described. In the following, “%” represents “mass%”.
Cは、鋼の強度を確保するために必要な元素である。C量が0.03%未満であると最終製品の強度が不足する。C量が0.08%超であると、母材、HAZの低温靭性が著しく低下する。したがって、C量は0.03〜0.08%とする。 C is an element necessary for ensuring the strength of steel. If the C content is less than 0.03%, the strength of the final product is insufficient. When the C content is more than 0.08%, the low temperature toughness of the base material and HAZ is remarkably lowered. Therefore, the C content is 0.03 to 0.08%.
Siは、脱酸剤として作用し、さらに、強度の向上に寄与する元素である。Si量が0.01%未満であると最終製品の強度が不足するおそれがある。Si量が0.50%超であると、HAZ靭性が著しく低下する。したがって、Si量は、0.01〜0.50%とする。 Si is an element that acts as a deoxidizing agent and contributes to improvement in strength. If the Si content is less than 0.01%, the strength of the final product may be insufficient. If the Si amount is more than 0.50%, the HAZ toughness is remarkably lowered. Therefore, the Si amount is set to 0.01 to 0.50%.
Mnは、鋼の強度の向上に寄与する元素である。Mn量が1.50%未満であると最終製品の強度が不足するおそれがある。Mn量が2.50%超であると、母材及びHAZの低温靭性が著しく低下する。したがって、Mn量は1.50〜2.50%とする。好ましくは、1.50〜2.00%である。 Mn is an element that contributes to improving the strength of steel. If the Mn content is less than 1.50%, the strength of the final product may be insufficient. When the amount of Mn exceeds 2.50%, the low temperature toughness of the base material and the HAZ is remarkably lowered. Therefore, the Mn content is 1.50 to 2.50%. Preferably, it is 1.50 to 2.00%.
Alは、脱酸元素とし、さらに、金属組織の微細化に寄与する元素である。Al量が0.001%未満であると、この効果が十分に得られない。Al量が0.080%超であると、鋼中にAl系非金属介在物が増加して鋼の洗浄度が劣化する。したがって、Al量は0.080%以下に制限する。好ましい範囲は、0.001〜0.050%以下である。 Al is an element that serves as a deoxidizing element and contributes to the refinement of the metal structure. If the Al content is less than 0.001%, this effect cannot be sufficiently obtained. If the Al content exceeds 0.080%, Al-based non-metallic inclusions increase in the steel and the cleanliness of the steel deteriorates. Therefore, the amount of Al is limited to 0.080% or less. A preferable range is 0.001 to 0.050% or less.
Tiは、鋼中にTiNとして析出することにより、スラブ再加熱時及びHAZのオーステナイト粒の粗大化を抑制して金属組織を微細化し、母材及びHAZの低温靭性を向上させる元素である。しかしながら、Ti量が0.005%未満であると、この効果が十分に得られない。また、Ti量が0.030%超であるとTiNの粗大化やTiCによる析出硬化によりかえって低温靭性が劣化する。したがって、Ti量は0.005〜0.030%とする。 Ti is an element that precipitates as TiN in the steel to suppress the coarsening of the austenite grains of the HAZ during reheating of the slab and to refine the metal structure and improve the low temperature toughness of the base material and the HAZ. However, if the Ti content is less than 0.005%, this effect cannot be sufficiently obtained. On the other hand, if the Ti content exceeds 0.030%, the low temperature toughness deteriorates due to the coarsening of TiN and precipitation hardening by TiC. Therefore, the Ti content is 0.005 to 0.030%.
Nbは、熱間圧延時においてオーステナイトの再結晶を抑制して組織を微細化し、母材及びHAZの低温靭性を改善する効果があるが、Nb量が0.010%未満であると、この効果が十分に得られない。また、Nb量が0.050%超であると、かえってHAZの靭性や現地溶接性に悪影響を及ぼす。したがって、Nb量は0.010〜0.050%とする。 Nb has the effect of suppressing the recrystallization of austenite during hot rolling to refine the structure and improving the low temperature toughness of the base material and HAZ, but this effect is achieved when the Nb content is less than 0.010%. Is not enough. On the other hand, if the Nb content exceeds 0.050%, the HAZ toughness and on-site weldability are adversely affected. Therefore, the amount of Nb is made 0.010 to 0.050%.
Pは、鋼中に不可避的に含有される不純物であり、粒界偏析や中心偏析を起こすことにより、母材及びHAZの低温靭性が劣化するが、P量が0.015%以下であれば低温靭性について許容できる範囲となる。したがって、P量は0.015%以下に制限する。 P is an impurity inevitably contained in the steel, and the low temperature toughness of the base metal and HAZ deteriorates by causing grain boundary segregation and center segregation, but if the amount of P is 0.015% or less This is an acceptable range for low temperature toughness. Therefore, the P content is limited to 0.015% or less.
Sは、鋼中に不可避的に含有される不純物であり、熱間圧延により延伸化する硫化物を鋼中に生成することにより延性及び靭性が低下するが、S量が0.0050%以下であれば延性及び靭性について許容できる範囲となる。したがって、S量は0.0050%以下に制限する。 S is an impurity inevitably contained in the steel, and the ductility and toughness are reduced by producing a sulfide that is stretched by hot rolling in the steel, but the amount of S is 0.0050% or less. If it exists, it becomes an allowable range for ductility and toughness. Therefore, the amount of S is limited to 0.0050% or less.
Nは、鋼中にTiNとして析出することにより、スラブ再加熱時及びHAZのオーステナイト粒の粗大化を抑制して、母材及びHAZの低温靭性を向上させる元素である。N量が0.0010%未満であると、この効果が十分に得られない。N量が0.0060%超であると、固溶N量の増大により靭性が低下する。したがって、N量は0.0010〜0.0060%とする。 N is an element that improves the low temperature toughness of the base material and HAZ by precipitating as TiN in the steel, thereby suppressing the coarsening of the austenite grains of the HAZ during reheating of the slab. If the N content is less than 0.0010%, this effect cannot be sufficiently obtained. If the N content exceeds 0.0060%, the toughness decreases due to an increase in the solid solution N content. Therefore, the N content is 0.0010 to 0.0060%.
また、本発明においては、C、Mn、Ni、Cu、Cr、Mo、Vの質量%での含有量から算出される、下記数式(A)により表される炭素当量Ceqを0.35〜0.50%とする。炭素当量Ceqは焼入れ性の指標となる値である。 Moreover, in this invention, the carbon equivalent Ceq represented by the following numerical formula (A) computed from content in the mass% of C, Mn, Ni, Cu, Cr, Mo, V is 0.35-0. .50%. The carbon equivalent Ceq is a value that serves as an index of hardenability.
Ceq値が0.35%未満であると、目標とする565MPa以上の引張強度が得られない。また、Ceq値が0.50%超であると、靭性を劣化させるMA(Martensite−Austenite Constituent:マルテンサイトとオーステナイトとの混成物)の生成が顕著となり、靭性が劣化する。なお、下記数式(A)において、鋼中に含有しない元素は0として計算する。 If the Ceq value is less than 0.35%, the target tensile strength of 565 MPa or more cannot be obtained. In addition, when the Ceq value is more than 0.50%, MA (Martensite-Austenite Constituent: a mixture of martensite and austenite) that deteriorates toughness becomes remarkable, and the toughness deteriorates. In addition, in the following numerical formula (A), the element not contained in the steel is calculated as 0.
Ceq=C+Mn/6+(Ni+Cu)/15+(Cr+Mo+V)/5 …(A) Ceq = C + Mn / 6 + (Ni + Cu) / 15 + (Cr + Mo + V) / 5 (A)
また、本発明においては、C、Si、Mn、Cu、Cr、Ni、Mo、V、Bの質量%での含有量から算出される、下記数式(B)により表されるPcmを0.15〜0.25%とする。Pcmは溶接性の指標となる値である。 Moreover, in this invention, Pcm represented by the following numerical formula (B) calculated from the content in the mass% of C, Si, Mn, Cu, Cr, Ni, Mo, V, and B is 0.15. -0.25%. Pcm is a value that serves as an index of weldability.
Pcmが0.25%超であると、母材及びHAZの低温靭性が劣化する。Pcmが0.15%未満であると、母材及びHAZの低温靭性の劣化は抑えられるが、目標とする引張強度が得られなくなる。なお、下記数式(B)において、鋼中に含有しない元素は0として計算する。 When the Pcm is more than 0.25%, the low temperature toughness of the base material and the HAZ deteriorates. When the Pcm is less than 0.15%, deterioration of the low temperature toughness of the base material and the HAZ can be suppressed, but the target tensile strength cannot be obtained. In addition, in the following numerical formula (B), the element not contained in the steel is calculated as 0.
Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15
+V/10+5B …(B)Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15
+ V / 10 + 5B (B)
以上が本発明に係る鋼板及び鋼管の基本元素の限定理由である。本発明に係る鋼板及び鋼管は、この基本元素の他に、残部がFe及び不可避的不純物からなる。 The above is the reason for limiting the basic elements of the steel plate and steel pipe according to the present invention. In addition to this basic element, the balance of the steel sheet and steel pipe according to the present invention is composed of Fe and inevitable impurities.
また、本発明に係る鋼板及び鋼管は、必要に応じて、V、Ni、Cu、Cr、Mo、B、Ca、Mg、REMのうちから選ばれた1種又は2種以上の元素を、以下に説明するような数値範囲で、さらに含有していてもよい。これらの元素を以下の範囲で含有しても、鋼板、鋼管におけるX線ランダム強度比、ランクフォード値は、本発明で規定する範囲となる。 Moreover, the steel plate and the steel pipe according to the present invention include one or more elements selected from V, Ni, Cu, Cr, Mo, B, Ca, Mg, and REM, as necessary. It may be further contained in a numerical range as described in (1). Even if these elements are contained in the following ranges, the X-ray random intensity ratio and the Rankford value in the steel plate and steel pipe are within the ranges specified in the present invention.
Vは、Nbとほぼ同様の効果を有するが、その効果はNbと比較して弱い。また、溶接部の軟化を抑制する効果も有する。V量が0.010%未満であると、母材及びHAZの低温靭性の改善や溶接部の軟化抑制の効果が不十分となる。V量が0.100%超であると、かえってHAZの靭性や現地溶接性に悪影響を及ぼす。したがって、V量は0.010〜0.100%とする。 V has almost the same effect as Nb, but the effect is weaker than Nb. Moreover, it has the effect which suppresses softening of a welding part. If the amount of V is less than 0.010%, the effect of improving the low temperature toughness of the base metal and HAZ and suppressing the softening of the welded portion will be insufficient. If the amount of V exceeds 0.100%, it adversely affects the toughness of HAZ and on-site weldability. Therefore, the V amount is set to 0.010 to 0.100%.
Ni、Cu、Cr、Moは焼入れ性を高め、鋼の高強度化に寄与する元素である。しかしながら、含有量が多すぎると、経済性の低下に加え、HAZの靭性や現地溶接性が低下する。したがって、Ni、Cu、Cr、Moはそれぞれ1.0%以下の含有量とする。 Ni, Cu, Cr, and Mo are elements that increase the hardenability and contribute to increasing the strength of steel. However, when the content is too large, the toughness of the HAZ and the field weldability are lowered in addition to the reduction in economic efficiency. Therefore, Ni, Cu, Cr, and Mo each have a content of 1.0% or less.
Bは、焼入れ性を高め、鋼の高強度化に寄与する元素である。B量が0.0001%未満であると、この効果が十分に得られない。B量が0.0020%超であると、HAZの靭性や現地溶接性が低下する。したがって、B量は0.0001〜0.0020%とする。 B is an element that enhances hardenability and contributes to increasing the strength of steel. If the amount of B is less than 0.0001%, this effect cannot be sufficiently obtained. If the amount of B exceeds 0.0020%, the toughness of HAZ and on-site weldability will deteriorate. Therefore, the B amount is set to 0.0001 to 0.0020%.
Ca、REMは、硫化物の形態を制御し、低温靭性の向上に寄与する元素である。Ca量が0.0040%超、REM量が0.005%超であると、CaO−CaSやREM−CaSが大量に析出して大型クラスター、大型介在物となり、鋼の洗浄度を害し、さらに、現地溶接性にも悪影響を及ぼすおそれがある。したがって、Ca量は0.0040%以下、REM量は0.005%以下とする。 Ca and REM are elements that control the form of sulfide and contribute to the improvement of low temperature toughness. If the Ca content exceeds 0.0040% and the REM content exceeds 0.005%, a large amount of CaO-CaS and REM-CaS precipitate to form large clusters and large inclusions, which impairs the cleanliness of the steel. Also, there is a risk of adversely affecting on-site weldability. Therefore, the Ca content is 0.0040% or less, and the REM content is 0.005% or less.
Mgは、微細な酸化物として分散して析出し、HAZの粒径粗大化を抑制して低温靭性の向上に寄与する元素である。Mg量が0.0017%超であると、酸化物が粗大化することにより靭性が劣化する。したがって、Mg量は0.0017%以下とする。 Mg is an element that is dispersed and precipitated as a fine oxide and contributes to the improvement of low temperature toughness by suppressing the coarsening of the HAZ grain size. If the Mg content exceeds 0.0017 %, the toughness deteriorates due to the coarsening of the oxide. Therefore, the Mg content is 0.0017 % or less.
次に、本発明に係る鋼板、鋼管の金属組織、集合組織、肉厚、引張強度、ランクフォード値(r値)の限定理由について説明する。 Next, the reasons for limiting the metal structure, texture, thickness, tensile strength, and Rankford value (r value) of the steel sheet and steel pipe according to the present invention will be described.
金属組織は、加工硬化特性を向上させるため、軟質のフェライトと、硬質のベイナイト又はマルテンサイトのいずれか1種又は2種との複合組織からなる必要がある。 The metal structure needs to be composed of a composite structure of soft ferrite and either one or two of hard bainite and martensite in order to improve work hardening characteristics.
また、金属組織は、肉厚中心部における有効結晶粒径が20μm以下である必要がある。有効結晶粒径が20μm超であると低温靭性が劣化するためである。有効結晶粒径とは、EBSP(Electron Backscatter Diffraction Pattern:電子線後方散乱パターン)法により測定される、方位差15°以下の組織の境界で囲まれる部分の円相当径での結晶粒径のことを意味する。 Further, the metal structure needs to have an effective crystal grain size of 20 μm or less at the thickness center portion. This is because the low temperature toughness deteriorates when the effective crystal grain size exceeds 20 μm. The effective crystal grain size is a crystal grain size at a circle-equivalent diameter measured by an EBSP (Electron Backscatter Diffraction Pattern) method at a portion surrounded by a boundary of a structure having an orientation difference of 15 ° or less. Means.
集合組織は、鋼板及び鋼管について好ましいランクフォード値を得るために、X線ランダム強度比が以下に説明するような条件を満足する必要がある。本発明においては、鋼板の圧延方向に対して45°方向のランクフォード値rDと、板幅方向のランクフォード値rCに注目する。ランクフォード値を大きくすることにより、鋼板、鋼管の変形性能が高まめることができる。 The texture needs to satisfy the conditions as described below for the X-ray random intensity ratio in order to obtain a preferable Rankford value for the steel plate and the steel pipe. In the present invention, attention is paid to the Rankford value rD in the 45 ° direction with respect to the rolling direction of the steel sheet and the Rankford value rC in the sheet width direction. By increasing the Rankford value, the deformation performance of the steel plate and the steel pipe can be enhanced.
以下において説明する結晶方位は、すべて板面と平行な面に関するもののことを意味する。X線ランダム強度比は、各方位を有する結晶面の集積度を表す数値であり、集合組織のないランダムな標準試料に対する各方位を有する結晶面のX回折強度での比を示す。 The crystal orientations to be described below all relate to a plane parallel to the plate surface. The X-ray random intensity ratio is a numerical value representing the degree of integration of crystal planes having respective orientations, and indicates the ratio of X diffraction intensities of crystal planes having respective orientations to a random standard sample having no texture.
{111}面の結晶方位を有する集合組織は、発達しているほどrC、rDを大きくすることができるので、極力発達していることが好ましい。好ましいrC、rDを得る観点からは、その{111}面のX線ランダム強度比を0.5以上にする必要がある。{111}面のX線ランダム強度比を5.0超にすると、他の結晶方位のX線ランダム強度比について目的とする値が得られなくなるおそれがあるので、{111}面のX線ランダム強度比は5.0以下とする。 Since the texture having the {111} plane crystal orientation can increase rC and rD as it develops, it is preferably developed as much as possible. From the viewpoint of obtaining preferable rC and rD, the X-ray random intensity ratio of the {111} plane needs to be 0.5 or more. If the X-ray random intensity ratio of the {111} plane exceeds 5.0, the target value may not be obtained for the X-ray random intensity ratio of other crystal orientations. The intensity ratio is 5.0 or less.
{554}面の結晶方位を有する集合組織は、発達しているほどrCを上げることができるので、極力発達していることが好ましい。好ましいrCを得る観点からは、その{554}面のX線ランダム強度比を1.0以上にする必要がある。また、{554}面のX線ランダム強度比を3.0超にすると、他の結晶方位のX線ランダム強度比について目的とする値が得られなくなるおそれがあるため、{554}面のX線ランダム強度比は3.0以下とする。 Since the texture having the {554} plane crystal orientation can increase rC as it develops, it is preferably developed as much as possible. From the viewpoint of obtaining preferable rC, the X-ray random intensity ratio of the {554} plane needs to be 1.0 or more. Further, if the X-ray random intensity ratio of the {554} plane is more than 3.0, a target value may not be obtained for the X-ray random intensity ratio of other crystal orientations. The line random intensity ratio is 3.0 or less.
{100}面の結晶方位を有する集合組織は、発達しているほどrC、rDを下げる原因となるので、極力発達が抑えられていることが好ましい。好ましいrCを得る観点からは、その{100}面のX線ランダム強度比を3.0以下にする必要がある。 A texture having a {100} plane crystal orientation causes rC and rD to decrease as it grows, so it is preferable that development is suppressed as much as possible. From the viewpoint of obtaining preferable rC, the X-ray random intensity ratio of the {100} plane needs to be 3.0 or less.
{112}面及び{223}面の結晶方位を有する集合組織は、発達しているほどrDを上げることができるため、極力発達していることが好ましい。好ましいrDを得る観点からは、その{112}面及び{223}面それぞれのX線ランダム強度比を0.5以上にする必要がある。{112}面及び{223}面それぞれのX線ランダム強度比を4.0超にすると、他の結晶方位のX線ランダム強度比について目的とする値が得られなくなるおそれがあるため、{112}面及び{223}面のX線ランダム強度比は4.0以下とする。 The texture having the {112} plane and {223} plane crystallographic orientation is preferably developed as much as possible because rD can be increased as it grows. From the viewpoint of obtaining a preferable rD, the X-ray random intensity ratio of each of the {112} plane and the {223} plane needs to be 0.5 or more. If the X-ray random intensity ratio of each of the {112} plane and the {223} plane exceeds 4.0, the target value may not be obtained for the X-ray random intensity ratio of other crystal orientations. } The X-ray random intensity ratio between the {223} plane and the {223} plane is 4.0 or less.
本発明のX線ランダム強度比には、肉厚中心部においてX線回折により測定した測定値を用る。これは、{111}面等のrC、rDを上げることのできる集合組織は、肉厚表層部において発達しやすく、肉厚中心部において発達しにくいので、肉厚中心部におけるX線ランダム強度比を評価対象とすることにより、肉厚方向全体で一定以上の変形性能を発揮し得るようにしたものである。 For the X-ray random intensity ratio of the present invention, a measurement value measured by X-ray diffraction at the center of thickness is used. This is because the texture that can increase the rC and rD of the {111} plane, etc. is easy to develop in the thick surface layer part and difficult to develop in the central thickness part, so the X-ray random intensity ratio in the thick central part By making the evaluation object, it is possible to exhibit a deformation performance of a certain level or more in the entire thickness direction.
鋼板は、最終製品として必要となる強度を確保しつつ、ラインパイプとして使用する際に内圧による破断を防止する観点から、その肉厚を25mm以上、引張強度を565MPa以上(API規格でX70以上のグレード)とする必要がある。 The steel sheet has a thickness of 25 mm or more and a tensile strength of 565 MPa or more (API standard of X70 or more from the viewpoint of preventing breakage due to internal pressure when used as a line pipe while ensuring the strength required as a final product. Grade).
本発明において、鋼板の圧延方向に対して45°方向のランクフォード値rDと、板幅方向のランクフォード値rCは、大きいほど変形性能が向上する。鋼板、鋼管の変形時に肉厚の減少により座屈等が発生するおそれを小さくするためには、rD、rCは1.0以上であることが好ましく、1.1以上であればより好ましい。 In the present invention, the deformation performance improves as the Rankford value rD in the 45 ° direction and the Rankford value rC in the sheet width direction increase with respect to the rolling direction of the steel sheet. In order to reduce the risk of buckling or the like due to a decrease in thickness when the steel plate or steel pipe is deformed, rD and rC are preferably 1.0 or more, more preferably 1.1 or more.
次に、本発明に係る鋼板の製造方法について説明する。 Next, the manufacturing method of the steel plate which concerns on this invention is demonstrated.
まず、転炉等を用いた公知の溶製方法により上述の組成の溶鋼を溶製した後、連続鋳造等の公知の鋳造方法により得られた溶鋼から鋼片を得る。 First, after melting molten steel having the above-described composition by a known melting method using a converter or the like, a steel piece is obtained from molten steel obtained by a known casting method such as continuous casting.
続いて、得られた鋼片を1000〜1150℃の温度に加熱する。加熱温度が1000℃未満であると、オーステナイトの十分な再結晶化が図れず、十分高い低温靭性が得られない。加熱温度が1150℃超であると、オーステナイト粒が粗大化することにより有効結晶粒径が増大し、低温靭性が低下する。 Subsequently, the obtained steel slab is heated to a temperature of 1000 to 1150 ° C. If the heating temperature is less than 1000 ° C., sufficient recrystallization of austenite cannot be achieved, and sufficiently high low temperature toughness cannot be obtained. When the heating temperature is higher than 1150 ° C., the austenite grains are coarsened, the effective crystal grain size is increased, and the low temperature toughness is lowered.
続いて、再結晶温度以上の温度域において、1パスあたりの圧下率、すなわち累積圧下率/パス数の値を、前記加熱温度が1000℃以上1050℃未満の時は5〜10%、前記加熱温度が1050℃以上1150℃以下のときは10〜15%とし、さらに、累積圧下率を35%以上として圧延を行う。累積圧下率が35%未満であると、再結晶によるオーステナイト粒径の微細化が十分達成できず、有効結晶粒径が増大し、低温靭性が低下する。 Subsequently, in the temperature range above the recrystallization temperature, the reduction rate per pass, that is, the value of the cumulative reduction rate / pass number is 5 to 10% when the heating temperature is 1000 ° C. or more and less than 1050 ° C., and the heating When the temperature is 1050 ° C. or higher and 1150 ° C. or lower, the rolling is performed at 10 to 15%, and the cumulative rolling reduction is 35% or more. If the cumulative rolling reduction is less than 35%, the austenite grain size cannot be sufficiently reduced by recrystallization, the effective crystal grain size increases, and the low temperature toughness decreases.
1パスあたりの圧下率は、目的とする結晶方位の集合組織を得るうえで特に重要である。従来、設備の制約等から、1パスあたりの圧下率を大きくすることはなかった。しかし、本発明の鋼板、鋼管において目的とする組織を得るためには、1パス当たりの圧下率が上記の範囲である必要がある。1パスあたりの圧下率が上記の範囲を外れると、目的とする集合組織の分布が得られなくなる。 The rolling reduction per pass is particularly important in obtaining the target texture of the crystal orientation. Conventionally, the rolling reduction per pass has not been increased due to equipment restrictions and the like. However, in order to obtain the target structure in the steel plate and steel pipe of the present invention, the rolling reduction per pass needs to be in the above range. If the rolling reduction per pass is out of the above range, the target texture distribution cannot be obtained.
個別のパスの圧下率は、パススケジュールの都合等で上記の範囲を外れる場合があってもかまわないが、パス数の半分以上のパスにおいて、圧下率が上記の範囲であることが好ましく、すべてのパスにおいて上記の範囲であることが、より好ましい。 The reduction rate of individual paths may be outside the above range due to reasons such as the pass schedule, but it is preferable that the reduction rate is in the above range in passes that are more than half of the number of passes. It is more preferable that the above range be in the pass.
続いて、Ar3変態点以上再結晶温度未満の温度域において、累積圧下率を70%以上として圧延を行う。累積圧下率が70%未満であると、{554}面の集合組織の発達が抑えられ、X線ランダム強度比について目標とするものが得られなくなり、rC値が低下する。Subsequently, rolling is performed at a cumulative rolling reduction of 70% or more in a temperature range not lower than the Ar 3 transformation point and lower than the recrystallization temperature. If the cumulative rolling reduction is less than 70%, the development of the texture of the {554} plane is suppressed, the target X-ray random intensity ratio cannot be obtained, and the rC value decreases.
続いて、Ar3変態点−50℃以上Ar3変態点未満の温度域を冷却開始温度、200〜500℃の温度域を冷却終了温度として水冷する。冷却開始温度がAr3変態点−50℃未満であると、フェライトの生成が促進し、目標とする強度が得られなくなる。冷却開始温度がAr3変態点以上であると、{112}面及び{223}面のそれぞれの集合組織の発達が抑えられ、X線ランダム強度比について目標とするものが得られなくなり、rD値が低下する。Subsequently, water cooling is performed with an Ar 3 transformation point of −50 ° C. or more and less than the Ar 3 transformation point as a cooling start temperature and a temperature range of 200 to 500 ° C. as a cooling end temperature. When the cooling start temperature is less than Ar 3 transformation point −50 ° C., the formation of ferrite is promoted and the target strength cannot be obtained. When the cooling start temperature is equal to or higher than the Ar 3 transformation point, the development of the texture of each of the {112} plane and the {223} plane is suppressed, and the target X-ray random intensity ratio cannot be obtained. Decreases.
冷却終了温度が200℃未満であると、生産性低下や水素性欠陥の原因となる。冷却終了温度が500℃超であると、目標とする強度が得られなくなる。冷却速度は、特に限定するものではないが、1〜10℃/s程度である。 When the cooling end temperature is less than 200 ° C., it causes a decrease in productivity and a hydrogen defect. If the cooling end temperature exceeds 500 ° C., the target strength cannot be obtained. The cooling rate is not particularly limited, but is about 1 to 10 ° C./s.
Ar3変態点は、下記の数式(C)から求められる。下記数式(C)におけるC、Si等は、それぞれ鋼中における質量%での各元素の含有量を意味する。The Ar 3 transformation point is obtained from the following mathematical formula (C). C, Si, etc. in the following mathematical formula (C) mean the content of each element in mass% in steel.
Ar3=868−396×C+24.6×Si−69.1×Mn−36.1
×Ni−20.7×Cu−24.8×Cr+29.6×Mo …(C)Ar 3 = 868-396 × C + 24.6 × Si-69.1 × Mn-36.1
× Ni-20.7 × Cu-24.8 × Cr + 29.6 × Mo (C)
このように製造された鋼板を、さらに、管状に成形し、突き合わせ部を接合することにより鋼管を得る。鋼板から管状に成形する造管方法は、公知のUOE法、ベンディングロール法等が用いられ、突き合わせ部の溶接方法は、アーク溶接、レーザー溶接等が用いられる。 The steel plate thus manufactured is further formed into a tubular shape, and a steel pipe is obtained by joining the butted portions. A known UOE method, a bending roll method, or the like is used as a tube forming method for forming the steel sheet into a tubular shape, and arc welding, laser welding, or the like is used as a welding method for the butt portion.
以上、本発明の実施形態の例について詳細に説明したが、上記の実施形態は、本発明を実施するにあたっての具体化の例を示したものにすぎず、これらによって本発明の技術的範囲が限定的に解釈されてはならない。 As mentioned above, although the example of embodiment of this invention was demonstrated in detail, said embodiment is only what showed the example of actualization in implementing this invention, and the technical scope of this invention is by these. It should not be interpreted in a limited way.
以下、本発明の効果を、実施例により説明する。 Hereinafter, the effects of the present invention will be described with reference to examples.
下記の表1に示す各鋼種A〜Fの組成の溶鋼を転炉で溶製し、連続鋳造により鋼片とした。得られた鋼片は、下記の表2に示す条件の下で熱間圧延、冷却を施し、No.1〜5及び8〜15の鋼板、並びに、鋼板を管状に成形し、突き合わせ部を接合したNo.6〜7の鋼管を得た。No.6〜7の鋼管の直径は、48インチ(1219.2mm)である。 Molten steel having the composition of each steel type A to F shown in Table 1 below was melted in a converter and made into a steel piece by continuous casting. The obtained steel slab was hot-rolled and cooled under the conditions shown in Table 2 below. No. 1-5 and 8-15 steel plates, and No. 1 in which the steel plates were formed into a tubular shape and the butted portions were joined. 6-7 steel pipes were obtained. No. The diameter of the 6-7 steel pipe is 48 inches (1219.2 mm).
得られた鋼板及び鋼管について、以下に説明するような引張強度等を測定した。この結果を表3に示す。 About the obtained steel plate and steel pipe, the tensile strength etc. which are demonstrated below were measured. The results are shown in Table 3.
引張強度は、得られた鋼板から長手方向が圧延方向と平行なJIS5号板状試験片を切り出し、この試験片を用いてJISZ2241号に記載の方法に準拠した引張試験を行うことにより測定した。また、引張強度はAPI規格でのグレードについても併せて求めた。鋼管については、引張強度はAPI規格に基づき、鋼管長手方向の全厚試験片で測定した。 The tensile strength was measured by cutting out a JIS No. 5 plate-like test piece whose longitudinal direction was parallel to the rolling direction from the obtained steel plate and performing a tensile test based on the method described in JIS Z2241 using this test piece. Further, the tensile strength was also obtained for the grades in the API standard. For the steel pipe, the tensile strength was measured with a full thickness test piece in the longitudinal direction of the steel pipe based on the API standard.
金属組織は、光学顕微鏡により観察した。有効結晶粒径は、EBSP法により測定し、15°以上の方位差を有する組織の境界を粒界とみなし、ひとつの結晶内部の面積を求め、その面積を円相当径に換算したものを有効結晶粒径として評価した。 The metal structure was observed with an optical microscope. Effective crystal grain size is measured by the EBSP method, the boundary of the structure having an orientation difference of 15 ° or more is regarded as a grain boundary, the area inside one crystal is obtained, and the area converted to the equivalent circle diameter is effective. The crystal grain size was evaluated.
X線ランダム強度比は、得られた鋼板から圧延方向10mm×板幅方向10mmの試験片を切り出し、試験片を機械研磨により肉厚中心部付近まで研磨し、バフ研磨により鏡面に研磨した後、電解研磨等によりひずみを除去すると同時に肉厚中心層が測定面となるように調整し、X線回折により各結晶方位の回折強度を測定することにより評価した。 The X-ray random strength ratio was obtained by cutting a test piece of 10 mm in the rolling direction × 10 mm in the plate width direction from the obtained steel plate, polishing the test piece to the vicinity of the thickness center by mechanical polishing, and polishing it to a mirror surface by buffing, The strain was removed by electrolytic polishing or the like, and at the same time, the thickness center layer was adjusted to be a measurement surface, and evaluation was performed by measuring the diffraction intensity of each crystal orientation by X-ray diffraction.
ランクフォード値は、得られた鋼板からJIS5号板状試験片を切り出すことにより、長手方向が圧延方向と平行な試験片、圧延方向に対して45°方向と平行な試験片、板幅方向と平行な試験片を製作し、これら試験片を用いてJISZ2241号に記載の方法に準拠した引張試験を行い、試験片に3%の単軸引張歪を与えたときの各試験片の幅ひずみ及び板厚ひずみの比から各ランクフォード値rC、rD、rLを測定することにより評価した。rLは、圧延方向のランクフォード値である。 The Rankford value is obtained by cutting out a JIS No. 5 plate-shaped test piece from the obtained steel plate, a test piece whose longitudinal direction is parallel to the rolling direction, a test piece parallel to the 45 ° direction with respect to the rolling direction, and the plate width direction. Parallel test specimens were manufactured, and tensile tests based on the method described in JISZ2241 were performed using these test specimens. When the specimen was given a uniaxial tensile strain of 3%, the width strain of each test specimen and Each rankford value rC, rD, rL was evaluated from the thickness strain ratio. rL is the Rankford value in the rolling direction.
シャルピー衝撃試験は、得られた鋼板から肉厚方向1/4位置からVノッチシャルピー試験片を製作し、JISZ2242に記載されている方法に準じ、試験温度が−40℃のときのシャルピー吸収エネルギーを測定することにより評価した。 In the Charpy impact test, a V-notch Charpy test piece is produced from the obtained steel plate from a 1/4 position in the thickness direction, and the Charpy absorbed energy when the test temperature is −40 ° C. according to the method described in JISZ2242. Evaluation was made by measuring.
各例では、引張強度については565MPa以上である例を合格とし、低温靭性についてはシャルピー吸収エネルギーが200J以上である例を合格とした。なお、各表において下線は発明の範囲外であることを示す。 In each example, an example in which the tensile strength was 565 MPa or more was accepted, and an example in which the Charpy absorbed energy was 200 J or more was accepted for low-temperature toughness. In each table, the underline indicates that it is outside the scope of the invention.
製造No.1〜7は発明例であり、No.1〜5は鋼板、No.6〜7は鋼管の実施例である。これらはいずれも、その組成、金属組織、有効結晶粒径、X線ランダム強度比、肉厚、引張強度が本発明の条件を満足しており、rD値が1.0以上、rC値が1.0以上、シャルピー吸収エネルギーが200J以上と、低温靭性に優れた高強度鋼板が得られている。 Production No. Nos. 1 to 7 are invention examples. Nos. 1 to 5 are steel plates, no. 6 to 7 are examples of steel pipes. In all of these, the composition, metal structure, effective crystal grain size, X-ray random strength ratio, wall thickness, and tensile strength satisfy the conditions of the present invention, the rD value is 1.0 or more, and the rC value is 1. A high-strength steel sheet excellent in low-temperature toughness with a Charpy absorbed energy of 200 J or more is obtained.
また、これらはいずれも、その組成、肉厚、製造方法が本発明の条件を満足しているため、金属組織、有効結晶粒径、X線ランダム強度比、引張強度が本発明の条件を満足したものが得られている。 In addition, since the composition, thickness, and manufacturing method of these all satisfy the conditions of the present invention, the metal structure, effective crystal grain size, X-ray random strength ratio, and tensile strength satisfy the conditions of the present invention. What has been obtained.
図1に、発明例の鋼板の肉厚中心部における組織写真の一例を示す。図1の写真は、製造No.2のものである。組織写真中、白く内部に微細な組織構造が無い部分がフェライトであり、フェライト以外の部分で、全体として灰色で内部に微細構造がある部分がベイナイトやマルテンサイトである。 In FIG. 1, an example of the structure | tissue photograph in the thickness center part of the steel plate of the example of an invention is shown. The photograph in FIG. Two. In the structure photograph, a white portion having no fine structure inside is ferrite, and a portion other than ferrite, which is gray as a whole and has a fine structure inside, is bainite or martensite.
製造No.8〜15は比較例である。製造No.8は、加熱温度が高いため有効結晶粒径が大きくなっており、低温靭性が劣化した例である。 Production No. 8 to 15 are comparative examples. Production No. No. 8 is an example in which the effective crystal grain size is large because the heating temperature is high, and the low temperature toughness is deteriorated.
製造No.9は、再結晶温度以上の温度域での1パスあたりの圧下率が低いため、目的とする集合組織の分布が得られておらず、変形特性の指標であるrD値、rC値が劣化した例である。 Production No. No. 9 has a low rolling reduction per pass in a temperature range equal to or higher than the recrystallization temperature, so the target texture distribution was not obtained, and the rD and rC values, which are indicators of deformation characteristics, deteriorated. It is an example.
製造No.10は、再結晶温度以上の温度域での累積圧下率が低いため、再結晶によるオーステナイト粒径の微細化が十分達成できず、有効結晶粒径の増大を招き、低温靭性が劣化した例である。 Production No. No. 10 is an example in which the cumulative reduction rate in the temperature range above the recrystallization temperature is low, so that the austenite grain size cannot be sufficiently reduced by recrystallization, the effective crystal grain size is increased, and the low temperature toughness is deteriorated. is there.
製造No.11は、Ar3変態点以上再結晶温度未満の温度域での累積圧下率が低いため、{554}面の集合組織の発達が抑えられ、rC値が劣化した例である。Production No. No. 11 is an example in which the development of the texture of the {554} plane is suppressed and the rC value is deteriorated because the cumulative rolling reduction in the temperature range from the Ar 3 transformation point to the recrystallization temperature is low.
製造No.12は、冷却開始温度が高いため、{112}面及び{223}面のそれぞれの集合組織の発達が抑えられ、rD値が劣化した例である。 Production No. No. 12 is an example in which, since the cooling start temperature is high, the development of the texture of each of the {112} plane and the {223} plane is suppressed, and the rD value is deteriorated.
製造No.13は、冷却終了温度が高いため、強度が低下した例である。 Production No. No. 13 is an example in which the strength is lowered because the cooling end temperature is high.
製造No.14は、Ceq、Pcmがともに低いことと、再結晶温度以上の温度域での1パスあたりの圧下率が低いため、強度及びrD値、rC値が劣化した例である。 Production No. No. 14 is an example in which the strength, the rD value, and the rC value are deteriorated because both Ceq and Pcm are low and the rolling reduction per pass in the temperature range equal to or higher than the recrystallization temperature is low.
製造No.15は、Ceq、Pcmがともに高く、加熱温度が高いため有効結晶粒径が大きく、さらに強度が上昇することによって、靭性が低下した例である。 Production No. No. 15 is an example in which both Ceq and Pcm are high, the effective crystal grain size is large because the heating temperature is high, and the toughness is lowered by increasing the strength.
Claims (7)
C :0.03〜0.08%、
Si:0.01〜0.50%、
Mn:1.50〜2.50%、
P :0.015%以下、
S :0.0050%以下、
Al:0.001〜0.080%、
N :0.0010〜0.0060%
Ti:0.005〜0.030%、
Nb:0.010〜0.050%、
を含有し、残部がFe及び不可避的不純物からなり、
下記式(A)により表されるCeqが0.35〜0.50%であり、
下記式(B)により表されるPcmが0.15〜0.25%であり、
フェライトと、ベイナイト又はマルテンサイトのいずれか1種又は2種との複合組織からなり、
肉厚中心部における有効結晶粒径が20μ以下であり、
肉厚中心部において板面と平行な{111}面のX線ランダム強度比が0.5〜5.0、{554}面のX線ランダム強度比が1.0〜3.0、{100}面のX線ランダム強度比が3.0以下、{112}面及び{223}面それぞれのX線ランダム強度比が0.5〜4.0であり、
肉厚が25mm以上であり、
引張強度が565MPa以上である
ことを特徴とする変形性能及び低温靭性に優れた高強度鋼板。
Ceq=C+Mn/6+(Ni+Cu)/15+(Cr+Mo+V)/5 (A)
Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15
+V/10+5B (B)
ここで、C、Mn、Ni、Cu、Cr、Mo、V、Si、Bは、各元素の質量%での含有量である。% By mass
C: 0.03-0.08%,
Si: 0.01 to 0.50%,
Mn: 1.50 to 2.50%,
P: 0.015% or less,
S: 0.0050% or less,
Al: 0.001 to 0.080%,
N: 0.0010 to 0.0060%
Ti: 0.005 to 0.030%,
Nb: 0.010 to 0.050%
And the balance consists of Fe and inevitable impurities,
Ceq represented by the following formula (A) is 0.35 to 0.50%,
Pcm represented by the following formula (B) is 0.15 to 0.25%,
Composed of a composite structure of ferrite and one or two of bainite or martensite,
The effective crystal grain size at the center of the wall thickness is 20 μm or less,
In the thickness center portion, the X-ray random intensity ratio of the {111} plane parallel to the plate surface is 0.5 to 5.0, the X-ray random intensity ratio of the {554} plane is 1.0 to 3.0, {100 } The X-ray random intensity ratio of the plane is 3.0 or less, and the X-ray random intensity ratio of each of the {112} plane and the {223} plane is 0.5 to 4.0,
The wall thickness is 25 mm or more,
A high-strength steel sheet excellent in deformation performance and low-temperature toughness, characterized by having a tensile strength of 565 MPa or more.
Ceq = C + Mn / 6 + (Ni + Cu) / 15 + (Cr + Mo + V) / 5 (A)
Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15
+ V / 10 + 5B (B)
Here, C, Mn, Ni, Cu, Cr, Mo, V, Si, and B are contents in mass% of each element.
V :0.010〜0.100%
Ni:1.0%以下、
Cu:1.0%以下、
Cr:1.0%以下、
Mo:1.0%以下
B :0.0001〜0.0020%
Ca:0.0040%以下、
Mg:0.0017%以下、
REM:0.005%以下
のうちから選ばれた1種又は2種以上の元素を含有することを特徴とする請求項1に記載の変形性能及び低温靭性に優れた高強度鋼板。 Furthermore, in mass%,
V: 0.010-0.100%
Ni: 1.0% or less,
Cu: 1.0% or less,
Cr: 1.0% or less,
Mo: 1.0% or less B: 0.0001 to 0.0020%
Ca: 0.0040% or less,
Mg: 0.0017 % or less,
REM: 1 type or 2 or more types of elements chosen from 0.005% or less are contained, The high strength steel plate excellent in the deformation performance and low-temperature toughness of Claim 1 characterized by the above-mentioned.
C :0.03〜0.08%、
Si:0.01〜0.50%、
Mn:1.50〜2.50%、
P :0.015%以下、
S :0.0050%以下、
Al:0.001〜0.080%、
N :0.0010〜0.0060%
Ti:0.005〜0.030%、
Nb:0.010〜0.050%、
を含有し、残部がFe及び不可避的不純物からなり、
下記式(A)により表されるCeqが0.35〜0.50%であり、
下記式(B)により表されるPcmが0.15〜0.25%である鋼片を加熱温度1000〜1150℃で加熱し、
続いて、再結晶温度以上の温度域において、1パスあたりの圧下率を、上記加熱温度が1000℃以上1050℃未満の時は5〜10%、上記加熱温度が1050℃以上1150℃以下のときは10〜15%とし、さらに、累積圧下率を35%以上として圧延し、
次いで、Ar3変態点以上再結晶温度未満の温度域において累積圧下率を70〜80%として圧延し、
続いて、Ar3変態点−50℃以上Ar3変態点未満の温度域を冷却開始温度とし、200〜500℃の温度域を冷却終了温度として水冷する
ことを特徴とする変形性能及び低温靭性に優れた高強度鋼板の製造方法。
Ceq=C+Mn/6+(Ni+Cu)/15+(Cr+Mo+V)/5 (A)
Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15
+V/10+5B (B)
ここで、C、Mn、Ni、Cu、Cr、Mo、V、Si、Bは、各元素の質量%での含有量である。% By mass
C: 0.03-0.08%,
Si: 0.01 to 0.50%,
Mn: 1.50 to 2.50%,
P: 0.015% or less,
S: 0.0050% or less,
Al: 0.001 to 0.080%,
N: 0.0010 to 0.0060%
Ti: 0.005 to 0.030%,
Nb: 0.010 to 0.050%
And the balance consists of Fe and inevitable impurities,
Ceq represented by the following formula (A) is 0.35 to 0.50%,
A steel slab having a Pcm of 0.15 to 0.25% represented by the following formula (B) is heated at a heating temperature of 1000 to 1150 ° C,
Subsequently, in the temperature range above the recrystallization temperature, the reduction rate per pass is 5 to 10% when the heating temperature is 1000 ° C. or higher and lower than 1050 ° C., and the heating temperature is 1050 ° C. or higher and 1150 ° C. or lower. Is 10 to 15%, and further rolled with a cumulative rolling reduction of 35% or more,
Next, rolling is performed at a cumulative reduction ratio of 70 to 80% in a temperature range of not less than the Ar 3 transformation point and less than the recrystallization temperature,
Subsequently, the deformation performance and the low temperature toughness are characterized in that the temperature range from Ar 3 transformation point −50 ° C. to less than Ar 3 transformation point is the cooling start temperature, and the water temperature is 200 to 500 ° C. as the cooling end temperature. A method for producing excellent high-strength steel sheets.
Ceq = C + Mn / 6 + (Ni + Cu) / 15 + (Cr + Mo + V) / 5 (A)
Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15
+ V / 10 + 5B (B)
Here, C, Mn, Ni, Cu, Cr, Mo, V, Si, and B are contents in mass% of each element.
V :0.010〜0.100%
Ni:1.0%以下、
Cu:1.0%以下、
Cr:1.0%以下、
Mo:1.0%以下
B :0.0001〜0.0020%
Ca:0.0040%以下、
Mg:0.0017%以下、
REM:0.005%以下
のうちから選ばれた1種又は2種以上の元素を含有することを特徴とする請求項5に記載の変形性能及び低温靭性に優れた高強度鋼板の製造方法。 The billet is further in mass%,
V: 0.010-0.100%
Ni: 1.0% or less,
Cu: 1.0% or less,
Cr: 1.0% or less,
Mo: 1.0% or less B: 0.0001 to 0.0020%
Ca: 0.0040% or less,
Mg: 0.0017 % or less,
REM: The manufacturing method of the high strength steel plate excellent in the deformation | transformation performance and low-temperature toughness of Claim 5 characterized by including 1 type, or 2 or more types of elements chosen from 0.005% or less.
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