JP2010024504A - Seamless steel pipe for line pipe and method for producing the same - Google Patents
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本発明は、海底フローライン用鋼管、ライザー用鋼管などに使用するのに適したラインパイプ用継目無鋼管およびその製造方法に係り、より詳しくは、ＡＰＩ（米国石油協会）規格に規定されるＸ８０、即ち、降伏強度５５１〜６５５ＭＰａ（８０〜９５ｋｓｉ）またはそれを上回る高強度を有するとともに、良好な母材および溶接熱影響部の耐水素割れ性を有するラインパイプ用継目無鋼管およびその製造方法に関する。 The present invention relates to a seamless steel pipe for a line pipe suitable for use in a steel pipe for a submarine flow line, a steel pipe for a riser, and the like, and more specifically, X80 defined in API (American Petroleum Institute) standard. That is, the present invention relates to a seamless steel pipe for a line pipe having a high strength at a yield strength of 551 to 655 MPa (80 to 95 ksi) or higher, and having a good base metal and hydrogen cracking resistance of a weld heat affected zone, and a method for producing the same. .
陸上または水深ほぼ５００メートルまでのいわゆる浅海に位置する油田の石油、天然ガス資源は近年枯渇しつつあり、例えば、海面下１０００〜３０００メートルといういわゆる深海の海底油田の開発が活発になっている。深海油田では、海底に設置された油井、天然ガス井の坑口から洋上のプラットホームまでの間、フローラインまたはライザーと呼ばれる鋼管を用いて原油および天然ガスを輸送する必要がある。深海に敷設されたフローラインを構成する鋼管の内部には、深い地層圧が加わった高圧の内部流耐圧がかかり、また、鋼管は波浪による繰り返し歪みと、操業停止時には深海の海水圧の影響を受ける。 Oil and natural gas resources in oil fields located on land or in shallow water up to approximately 500 meters in depth have been depleted in recent years. For example, so-called deep-sea submarine oil fields of 1000 to 3000 meters below sea level are being actively developed. In the deep-sea oil field, it is necessary to transport crude oil and natural gas by using a steel pipe called a flow line or riser from the well of the oil well and natural gas well installed on the seabed to the offshore platform. The inside of the steel pipe that constitutes the flow line laid in the deep sea is subjected to high internal flow pressure with deep formation pressure, and the steel pipe is subject to repeated distortion due to waves and the influence of sea water pressure in the deep sea when operation is stopped. receive.
ここに、フローラインとは、地上または海底面の地勢に沿って敷設された輸送用鋼管であり、また、ライザーとは、海底面から地上のプラットホームまで立ち上がった輸送用鋼管であり、深海油田で用いる場合には、その肉厚は、通常３０ｍｍ以上必要と言われており、それだけ苛酷な条件で使用される部材である。 Here, the flow line is a steel pipe for transportation laid along the terrain on the ground or the bottom of the sea, and the riser is a steel pipe for transportation rising from the bottom of the sea to the platform on the ground. When used, it is said that the wall thickness is usually required to be 30 mm or more, and the member is used under such severe conditions.
一方、近年開発される深井やガス井は腐食性を有する硫化水素を含む場合が多く、このような環境では高強度鋼は、水素誘起割れ（Ｈｙｄｒｏｇｅｎ Ｉｎｄｕｃｅｄ Ｃｒａｃｋｉｎｇ、以下、「ＨＩＣ」という。）または硫化物応力割れ（Ｓｕｌｆｉｄｅ Ｓｔｒｅｓｓ Ｃｒａｃｋｉｎｇ、以下、「ＳＳＣ」という。）と呼ばれる水素脆化を起こし破壊に至る。材料強度が上がるほどＨＩＣまたはＳＳＣの感受性が高くなるため、高強度鋼における耐水素割れ性の確保は、大変困難な課題である。また、とりわけ周溶接による熱影響部では、熱が入った後に急冷されるために材料強度が上がりＨＩＣおよびＳＳＣの感受性が増大することが多い。 On the other hand, the deep wells and gas wells that have been developed in recent years often contain corrosive hydrogen sulfide, and in such an environment, high-strength steel has hydrogen induced cracking (hereinafter referred to as “HIC”) or. Hydrogen embrittlement called sulfide stress cracking (hereinafter referred to as “SSC”) occurs, leading to fracture. Since the sensitivity of HIC or SSC increases as the material strength increases, it is very difficult to ensure hydrogen cracking resistance in high-strength steel. In particular, in a heat-affected zone due to circumferential welding, since the material is rapidly cooled after heat is applied, the material strength is increased and the sensitivity of HIC and SSC is often increased.
ＨＩＣは、腐食反応により生成した水素が鋼中に侵入し、ＭｎＳなどの介在物または硬い第２相組織のまわりに拡散・集積することで発生するといわれている。 HIC is said to occur when hydrogen generated by a corrosion reaction penetrates into steel and diffuses and accumulates around inclusions such as MnS or hard second phase structure.
耐ＨＩＣ性を向上させる方法として、例えば、特許文献１には、鋼中のＳ量を低減するとともに、Ｃａを適量添加することにより伸延状のＭｎＳの生成を抑制して、ＨＩＣの発生を抑える技術が開示されている。また、溶接鋼管については、例えば、特許文献２には、割れの伝播経路となりやすい硬化組織の生成を抑制するために、Ｃ、Ｍｎ、Ｐなどの偏析しやすい元素の含有量を低減する技術が、特許文献３には、さらに圧延後の冷却時の変態途中でＣの拡散による硬化組織の生成を防ぐために加速冷却を施す技術が開示されている。継目無鋼管においても、ＭｎＳ等の介在物析出を制限し、偏析元素を低減することでＡＰＩ規格のＸ６５グレードあるいはＸ７０グレードまで安定製造されるようになった。 As a method for improving the HIC resistance, for example, in Patent Document 1, while reducing the amount of S in steel and adding an appropriate amount of Ca, the generation of distracted MnS is suppressed and the generation of HIC is suppressed. Technology is disclosed. As for welded steel pipes, for example, Patent Document 2 discloses a technique for reducing the content of elements that are easily segregated, such as C, Mn, and P, in order to suppress the formation of a hardened structure that tends to be a propagation path of cracks. Further, Patent Document 3 discloses a technique for performing accelerated cooling in order to prevent generation of a hardened structure due to diffusion of C during the transformation at the time of cooling after rolling. Seamless steel pipes are also stably manufactured to API standard X65 grade or X70 grade by limiting the precipitation of inclusions such as MnS and reducing segregation elements.
従来、ラインパイプ用鋼における耐食性の確保は、全般的に、耐ＨＩＣ性の改善に重点がおかれている。また、例えば、特許文献４、特許文献５などに開示されているように、Ｘ８０グレードまたはそれを上回る高強度耐食性鋼管においては、耐ＨＩＣ性に関する研究が盛んに行われてきたが、耐ＳＳＣ性に関する検討はほとんどされていない。 Conventionally, ensuring corrosion resistance in steel for line pipes has generally focused on improving HIC resistance. In addition, as disclosed in, for example, Patent Document 4, Patent Document 5, and the like, in the high-strength corrosion-resistant steel pipe of X80 grade or higher, research on HIC resistance has been actively conducted. Little consideration has been given to this.
Ｘ８０グレードまたはそれを上回る高強度鋼材になると、ＨＩＣ感受性が高まり、例えば、特許文献１〜３に開示される技術では、ＨＩＣの発生を抑制することが困難となる。特に、従来の鋼材では溶接熱影響部において母材よりも強度が上昇するために、更にＨＩＣ感受性高まるという問題がある。また、Ｘ８０グレードまたはそれを上回る高強度鋼材では、これより低強度の鋼材に比べてＳＳＣ感受性が高まるため、耐ＨＩＣ性だけでなく耐ＳＳＣ性にも優れた鋼材が求められる。 When it becomes X80 grade or a high-strength steel material exceeding it, HIC sensitivity increases, for example, it becomes difficult to suppress generation | occurrence | production of HIC with the technique disclosed by patent documents 1-3. In particular, the conventional steel material has a problem that the HIC sensitivity is further increased because the strength is higher than that of the base material in the weld heat affected zone. Further, high strength steel materials of X80 grade or higher are more susceptible to SSC than steel materials of lower strength than this, and therefore steel materials that are excellent not only in HIC resistance but also in SSC resistance are required.
本発明は、上記の問題を解決するためになされたものであり、母材および溶接熱影響部の両方において高強度で、かつ耐水素割れ性（耐ＨＩＣ性および耐ＳＳＣ性）に優れたラインパイプ用継目無鋼管およびその製造方法を提供することを目的とする。 The present invention has been made in order to solve the above problems, and has a high strength and excellent hydrogen cracking resistance (HIC resistance and SSC resistance) in both the base material and the weld heat affected zone. It aims at providing the seamless steel pipe for pipes, and its manufacturing method.
本発明者らは、母材および溶接熱影響部における耐水素割れ性を確保するため、溶接熱影響部での硬さの上昇を防ぎ、かつ母材の耐水素割れ性能を確保することができる化学組成および組織について検討した。耐水素割れ性を改善する方法としては、従来、焼戻し温度を上昇させて強度を低減する方法、焼入れ性を高めて均一組織を形成し、局所的な強度上昇を抑制する方法などが知られているが、これらの方法では、溶接熱影響部における耐水素割れ性を改善することはできない。 In order to ensure hydrogen cracking resistance in the base material and the weld heat affected zone, the present inventors can prevent an increase in hardness in the weld heat affected zone and secure the hydrogen crack resistance performance of the base material. The chemical composition and structure were studied. Conventionally known methods for improving hydrogen cracking resistance include a method for increasing the tempering temperature to reduce the strength, a method for increasing the hardenability to form a uniform structure, and suppressing a local strength increase. However, these methods cannot improve the hydrogen cracking resistance in the weld heat affected zone.
そこで、本発明者らは、継目無鋼管の組織を焼戻し組織として、母材における強度および耐水素割れ性を高めるとともに、溶接熱影響部における強度上昇を防ぐべく、焼き戻し軟化抵抗を高めて、焼戻し時の強度低下を低減するのが有効であると考え、化学組成の影響を調査した。 Therefore, the present inventors made the structure of the seamless steel pipe a tempered structure, increased the strength and hydrogen cracking resistance in the base material, and increased the temper softening resistance in order to prevent an increase in strength in the weld heat affected zone, We considered it effective to reduce the strength reduction during tempering, and investigated the effect of chemical composition.
即ち、本発明者らは、まず、表１に示す化学組成を有する鋼を各々５０ｋｇ真空溶製し、１２５０℃に加熱した後、熱間鍛造によりブロックを作製し、これらのブロックを１２５０℃に加熱した後、熱間圧延により得られた３０ｍｍ厚さの板材を９５０℃で１０分保持した後、水冷して（冷却速度は３０℃／ｓ）焼入れし、その後、６５０℃で３０分保持した後、放冷して焼戻した。このようにして得た鋼材の降伏強度（ＹＳ）および耐ＳＳＣ性について調査した結果を図１に示す。 That is, the inventors first prepared 50 kg of each of the steels having the chemical compositions shown in Table 1 by vacuum melting and heated to 1250 ° C., and then produced blocks by hot forging. After heating, the 30 mm-thick plate material obtained by hot rolling was held at 950 ° C. for 10 minutes, then cooled with water (cooling rate was 30 ° C./s) and quenched, and then held at 650 ° C. for 30 minutes. Then, it was left to cool and tempered. The results of investigating the yield strength (YS) and SSC resistance of the steel material thus obtained are shown in FIG.
なお、耐ＳＳＣ性は、ＮＡＣＥ（Ｎａｔｉｏｎａｌ Ａｓｓｏｃｉａｔｉｏｎ ｏｆ Ｃｏｒｒｏｓｉｏｎ Ｅｎｇｉｎｅｅｒｓ）ＴＭ０１７７−２００５ ｍｅｔｈｏｄ Ｄに従ってＤＣＢ試験を行い、評価した。即ち、鋼材から厚さ１０ｍｍ、幅２５ｍｍ、長さ１００ｍｍのＤＣＢ（Ｄｏｕｂｌｅ Ｃａｎｔｉｌｅｖｅｒ Ｂｅｎｔ Ｂｅａｍ）試験片を採取し、採取した試験片を１ａｔｍの硫化水素ガスを飽和させた常温の５％食塩＋０．５％酢酸水溶液に３３６時間浸漬し、亀裂進展長さａおよび楔開放応力Ｐ（楔厚さ：３．４ｍｍ）から、下記式により応力拡大係数ＫISSCを導出した。
Ｐ：楔開放応力（Ｎ）
ａ：亀裂進展長さ（ｍｍ）
ｈ：ＤＣＢ試験片アーム部高さ（ｍｍ）＝１２．７ｍｍ
Ｂ：ＤＣＢ試験片厚み（ｍｍ）＝９．５３ｍｍ
Ｂｎ：ＤＣＢ試験片溝部厚み（ｍｍ）＝５．７２ｍｍ
The SSC resistance was evaluated by performing a DCB test according to NACE (National Association of Corrosion Engineers) TM0177-2005 method D. That is, a DCB (Double Cantilever Bent Beam) test piece having a thickness of 10 mm, a width of 25 mm, and a length of 100 mm was collected from a steel material, and the collected test piece was saturated with 1 atm hydrogen sulfide gas at room temperature 5% sodium chloride + 0.5 A stress intensity factor K ISSC was derived from the following equation from the crack growth length a and the wedge opening stress P (wedge thickness: 3.4 mm).
P: wedge opening stress (N)
a: Crack growth length (mm)
h: DCB test piece arm height (mm) = 12.7 mm
B: DCB specimen thickness (mm) = 9.53 mm
Bn: DCB test piece groove part thickness (mm) = 5.72 mm
図１は、得られた焼入れ焼戻し後の鋼材の降伏強度（ＹＳ）をＭｏおよびＭｎの含有量について整理した図である。図１に示すように、降伏強度は、Ｍｏ含有量が多いほど高くなるものの、いずれの例でもほぼ一定となった。 FIG. 1 is a diagram in which the yield strength (YS) of the obtained steel material after quenching and tempering is arranged with respect to the contents of Mo and Mn. As shown in FIG. 1, the yield strength increases as the Mo content increases, but is almost constant in all examples.
図２は、得られた焼入れ焼戻し後の鋼材の応力拡大係数（ＫISSC）をＭｏおよびＭｎの含有量について整理した図である。図２に示すように、ＫISSCは、Ｍｎ含有量の減少、Ｍｏ含有量の増加に伴い、向上することが確認された。 FIG. 2 is a diagram in which the stress intensity factor (K ISSC ) of the obtained steel material after quenching and tempering is arranged with respect to the contents of Mo and Mn. As shown in FIG. 2, K ISSC was confirmed to improve as the Mn content decreased and the Mo content increased.
本発明者らは、次に、表２に示す化学組成を有する鋼を各々５０ｋｇ真空溶製し、１２５０℃に加熱した後、熱間鍛造によりブロックを作製し、これらのブロックを１２５０℃に加熱した後、熱間圧延により得られた２０ｍｍ厚さの板材を９５０℃で１０分保持した後、水冷して（冷却速度は４５℃／ｓ）焼入れし、一部の鋼材については、６５０℃で３０分保持した後、放冷して焼戻した。表３に、これらの焼入れままの鋼材および焼戻し鋼材についての引張強度（ＴＳ）、硬さ（Ｈｖ）および耐ＨＩＣ性を示す。 Next, the inventors made 50 kg of steel having the chemical composition shown in Table 2 by vacuum melting and heated to 1250 ° C., then produced blocks by hot forging, and heated these blocks to 1250 ° C. Then, the 20 mm-thick plate material obtained by hot rolling is held at 950 ° C. for 10 minutes, and then water-cooled (cooling rate is 45 ° C./s) and quenched, with some steel materials at 650 ° C. After holding for 30 minutes, it was allowed to cool and tempered. Table 3 shows the tensile strength (TS), hardness (Hv), and HIC resistance of these as-quenched steel materials and tempered steel materials.
なお、表３では、耐ＨＩＣ性として「ＨＩＣ割れ面積率」を評価している。ＨＩＣ割れ面積率は、以下の方法によって得られる。即ち、ＮＡＣＥ（Ｎａｔｉｏｎａｌ Ａｓｓｏｃｉａｔｉｏｎ ｏｆ Ｃｏｒｒｏｓｉｏｎ Ｅｎｇｉｎｅｅｒｓ）ＴＭ００２８４−２００３に従い、鋼材から厚さ２０ｍｍ、幅２０ｍｍ、長さ１００ｍｍの試験片を採取し、採取した試験片を１ａｔｍの硫化水素ガスを飽和させた常温の５％食塩＋０．５％酢酸水溶液に９６時間浸漬し、その後、超音波探傷試験によって試験片中の割れ面積率を求める。 In Table 3, “HIC crack area ratio” is evaluated as HIC resistance. The HIC crack area ratio is obtained by the following method. That is, according to NACE (National Association of Corrosion Engineers) TM00284-2003, a test piece having a thickness of 20 mm, a width of 20 mm, and a length of 100 mm was collected from a steel material, and the collected test piece was saturated with hydrogen sulfide gas of 1 atm. It is immersed for 96 hours in a 5% sodium chloride + 0.5% acetic acid aqueous solution, and then the crack area ratio in the test piece is determined by an ultrasonic flaw detection test.
表３に示すように、Ｍｎ含有量が高い鋼材４およびＣ含有量が高い鋼材５では、焼戻しによる強度低下が大きいことから、焼入れまま鋼材では強度が高く、ＨＩＣ割れ面積率が高い値となった。一方、ＣおよびＭｎの含有量が低く、Ｍｏの含有量が高い鋼材６では、焼戻しによる強度低下がほとんどないことから、焼入れまま鋼材でも強度を低く抑えられ、ＨＩＣは発生しなかった。 As shown in Table 3, in the steel material 4 with a high Mn content and the steel material 5 with a high C content, the strength decrease due to tempering is large. Therefore, the as-quenched steel material has high strength and a high HIC crack area ratio. It was. On the other hand, in the steel 6 having a low content of C and Mn and a high content of Mo, there was almost no decrease in strength due to tempering. Therefore, the strength was kept low even in the as-quenched steel, and no HIC was generated.
ここで、溶接熱影響部では溶接の入熱後急冷されるため、強度・硬さは焼入れまま材に準ずると考えられる。従って、溶接熱影響部の耐水素割れ性を確保するためには、ＣおよびＭｎの含有量を低減し、かつ焼き戻し軟化抵抗の強い鋼となるような合金設計が必要である。 Here, since the welding heat affected zone is rapidly cooled after the heat input of welding, it is considered that the strength and hardness are similar to those of the quenched material. Therefore, in order to ensure the hydrogen cracking resistance of the weld heat-affected zone, it is necessary to design an alloy that reduces the C and Mn contents and provides a steel with strong temper softening resistance.
本発明は、このような知見に基づきなされたものであり、下記の（１）〜（６）に示すラインパイプ用継目無鋼管および下記の（７）に示すラインパイプ用継目無鋼管の製造方法を要旨としている。 This invention is made | formed based on such knowledge, The manufacturing method of the seamless steel pipe for line pipes shown to following (1)-(6), and the seamless steel pipe for line pipes shown to the following (7) Is the gist.
（１）質量％で、
Ｃ ： ０．０３〜０．０８％、
Ｓｉ： ０．０５〜０．５％、
Ｍｎ： ０．２〜１．６％、
Ｐ ： ０．０５％以下、
Ｓ ： ０．０１％以下、
Ｍｏ： ０．５〜３．０％、
Ａｌ： ０．００５〜０．１００％、
Ｎ ： ０．０１％以下、
Ｏ ： ０．０１％以下および
Ｃａ： ０．００１〜０．００５％
を含有し、残部Ｆｅおよび不純物からなることを特徴とするラインパイプ用継目無鋼管。
(1) In mass%,
C: 0.03-0.08%,
Si: 0.05-0.5%
Mn: 0.2 to 1.6%
P: 0.05% or less,
S: 0.01% or less,
Mo: 0.5-3.0%,
Al: 0.005 to 0.100%,
N: 0.01% or less,
O: 0.01% or less and Ca: 0.001 to 0.005%
A seamless steel pipe for a line pipe, characterized by comprising a balance Fe and impurities.
（２）更に、質量％で、
Ｃｒ ： １．５％以下、
Ｎｂ ： ０．１％以下、
Ｔｉ ： ０．１％以下、
Ｚｒ ： ０．１％以下、
Ｎｉ ： １．５％以下、
Ｃｕ： １．０％以下、
Ｖ ： ０．２％以下および
Ｂ ： ０．００５％以下
のうちから選択された１種以上を含有することを特徴とする上記（１）に記載のラインパイプ用継目無鋼管。
(2) Furthermore, in mass%,
Cr: 1.5% or less,
Nb: 0.1% or less,
Ti: 0.1% or less,
Zr: 0.1% or less,
Ni: 1.5% or less,
Cu: 1.0% or less,
The seamless steel pipe for line pipes according to (1) above, which contains one or more selected from V: 0.2% or less and B: 0.005% or less.
（３）降伏強度（ＹＳ）が５５１ＭＰａ以上であることを特徴とする上記（１）または（２）に記載のラインパイプ用継目無鋼管。 (3) The seamless steel pipe for line pipes according to (1) or (2) above, wherein the yield strength (YS) is 551 MPa or more.
（４）降伏強度（ＹＳ）が６２１ＭＰａ以上であることを特徴とする上記（１）または（２）に記載のラインパイプ用継目無鋼管。 (4) The seamless steel pipe for a line pipe according to the above (1) or (2), wherein the yield strength (YS) is 621 MPa or more.
（５）８００〜１１００℃の温度域から２０℃／ｓ以上の冷却速度で冷却して焼入れた後、６００〜７００℃の温度に加熱して焼戻して得た継目無鋼管であることを特徴とする上記（１）〜（４）のいずれかに記載のラインパイプ用継目無鋼管。 (5) A seamless steel pipe obtained by cooling at a cooling rate of 20 ° C./s or more from a temperature range of 800 to 1100 ° C. and then tempering by heating to a temperature of 600 to 700 ° C. The seamless steel pipe for line pipes according to any one of (1) to (4) above.
（６）上記（１）または（２）に記載の化学組成を有する継目無鋼管を８００〜１１００℃の温度域から２０℃／ｓ以上の冷却速度で冷却して焼入れた後、６００〜７００℃の温度に加熱して焼戻すことを特徴とするラインパイプ用継目無鋼管の製造方法。 (6) After cooling and quenching the seamless steel pipe having the chemical composition described in the above (1) or (2) at a cooling rate of 20 ° C./s or more from a temperature range of 800 to 1100 ° C., 600 to 700 ° C. A method for producing a seamless steel pipe for a line pipe, characterized in that the steel pipe is tempered by heating to a temperature of.
本発明によれば、降伏応力（ＹＳ）が５５１ＭＰａ（８０ｋｓｉ）またはそれを上回る高強度の継目無鋼管に母材および溶接熱影響部の全域に渡って良好な耐水素割れ性を付与することができる。 According to the present invention, a high strength seamless steel pipe having a yield stress (YS) of 551 MPa (80 ksi) or higher can be provided with good hydrogen cracking resistance over the entire area of the base metal and the weld heat affected zone. it can.
以下、本発明の継目無鋼管の化学組成の範囲およびその限定理由について説明する。なお、各元素の含有量についての「％」は、「質量％」を意味する。 Hereinafter, the range of the chemical composition of the seamless steel pipe of the present invention and the reason for the limitation will be described. “%” For the content of each element means “mass%”.
Ｃ：０．０３〜０．０８％
Ｃは、焼入れ性を高めて鋼の強度を確保するのに有効な元素であり、０．０３％以上含有させる必要がある。しかし、Ｃ含有量が０．０８％を超えると、溶接熱影響部での強度が上昇し過ぎて、耐水素割れ性が低下する。従って、Ｃの含有量を０．０３〜０．０８％とした。
C: 0.03-0.08%
C is an element effective for enhancing the hardenability and ensuring the strength of the steel, and needs to be contained by 0.03% or more. However, if the C content exceeds 0.08%, the strength at the weld heat affected zone is excessively increased, and the hydrogen cracking resistance is deteriorated. Therefore, the content of C is set to 0.03 to 0.08%.
Ｓｉ：０．０５〜０．５％
Ｓｉは、鋼の脱酸に有効な元素である。脱散剤としての効果を得るためには、０．０５％以上含有させる必要がある。しかし、Ｓｉが過剰な場合には、溶接熱影響部の靭性を大幅に低下させるとともに、軟化相のフェライト層の析出を促進し、耐水素割れ性を低下させる。従って、Ｓｉの含有量を０．０５〜０．５％とした。好ましい上限は０．３％である。
Si: 0.05-0.5%
Si is an element effective for deoxidation of steel. In order to acquire the effect as a desorbing agent, it is necessary to make it contain 0.05% or more. However, when Si is excessive, the toughness of the weld heat-affected zone is greatly reduced, and the precipitation of the ferrite layer in the softened phase is promoted to reduce the hydrogen cracking resistance. Therefore, the Si content is set to 0.05 to 0.5%. A preferable upper limit is 0.3%.
Ｍｎ：０．２〜１．６％
Ｍｎは、焼入れ性を高めて強度向上させるのに有効であり、また、靭性を確保するためにもある程度の含有させる必要がある。これらの効果を得るためには０．２％以上含有させる必要がある。しかし、Ｍｎ含有量が過剰な場合、焼入れ性が上昇し、溶接熱影響部の強度を高めすぎて、耐水素割れ性を低下させる。従って、Ｍｎの含有量を０．２〜１．６％とした。好ましい下限は、０．４％である。
Mn: 0.2 to 1.6%
Mn is effective for enhancing the hardenability and improving the strength, and also needs to be contained to some extent in order to ensure toughness. In order to acquire these effects, it is necessary to contain 0.2% or more. However, when the Mn content is excessive, the hardenability is increased, the strength of the weld heat affected zone is excessively increased, and the hydrogen cracking resistance is decreased. Therefore, the Mn content is set to 0.2 to 1.6%. A preferred lower limit is 0.4%.
Ｐ：０．０５％以下
Ｐは、粒界に偏析し、耐水素割れ性を低下させる元素である。その含有量が０．０５％を超えるとその影響が顕著となる。従って、Ｐの含有量を０．０５％以下に制限することとした。但し、Ｐの含有量は極力低いのがよく、上限は０．０２５％とするのが好ましい。
P: 0.05% or less P is an element that segregates at grain boundaries and reduces hydrogen cracking resistance. If the content exceeds 0.05%, the influence becomes significant. Therefore, the P content is limited to 0.05% or less. However, the P content should be as low as possible, and the upper limit is preferably 0.025%.
Ｓ：０．０１％以下
ＳもＰと同様に粒界に偏析し、耐水素割れ性を低下させる元素である。その含有量が０．０１％を超えるとその影響が顕著になる。従って、Ｓの含有量を０．０１％以下とした。なお、Ｓの含有量は極力低い方が望ましい。
S: 0.01% or less S, like P, is an element that segregates at grain boundaries and reduces hydrogen cracking resistance. If the content exceeds 0.01%, the effect becomes significant. Therefore, the S content is set to 0.01% or less. The S content is desirably as low as possible.
Ｍｏ：０．５〜３．０％
Ｍｏは、焼入れ性を高めて鋼の強度を向上させるとともに、焼戻し軟化抵抗を高めることで焼き戻し組織に比べ、溶接熱影響部における強度上昇を抑えるのに有効な元素である。これらの効果を得るには、０．５％以上含有させる必要がある。しかし、Ｍｏは高価な元素であり、あまりに多量に含有させても上記の効果が飽和する。従って、Ｍｏの含有量を０．５〜３．０％とした。耐水素割れ性を更に向上させるには０．７％以上含有させるのが望ましい。
Mo: 0.5-3.0%
Mo is an element effective in suppressing the increase in strength in the weld heat affected zone as compared with the tempered structure by increasing the hardenability and improving the strength of the steel and increasing the temper softening resistance. In order to obtain these effects, it is necessary to contain 0.5% or more. However, Mo is an expensive element, and the above effect is saturated even if it is contained in an excessive amount. Therefore, the Mo content is set to 0.5 to 3.0%. In order to further improve the hydrogen cracking resistance, it is desirable to contain 0.7% or more.
Ａｌ：０．００５〜０．１００％
Ａｌは、鋼の脱酸に有効な元素であり、０．００５％以上含有させる必要がある。しかし、０．１００％を越えて含有させてもその効果は飽和する。従って、Ａｌの含有量を０．００５〜０．１００％とした。Ａｌ含有量の好ましい下限は０．０１％であり、好ましい上限は０．０５％である。本発明のＡｌ含有量とは、酸可溶Ａｌ（所謂「ｓｏｌ．Ａｌ」）を指す。
Al: 0.005 to 0.100%
Al is an element effective for deoxidation of steel and needs to be contained by 0.005% or more. However, even if the content exceeds 0.100%, the effect is saturated. Therefore, the Al content is set to 0.005 to 0.100%. The minimum with preferable Al content is 0.01%, and a preferable upper limit is 0.05%. The Al content of the present invention refers to acid-soluble Al (so-called “sol.Al”).
Ｎ：０．０１％以下
Ｎ（窒素）は、不純物として鋼中に存在し、その含有量が０．０１％を超えると粗大な窒化物を形成して、靭性および耐ＳＳＣ性を低下させる。従って、Ｎを０．０１％以下に制限することとした。Ｎの含有量は、極力低減することが望ましい。
N: 0.01% or less N (nitrogen) is present in the steel as an impurity, and when its content exceeds 0.01%, coarse nitrides are formed, and toughness and SSC resistance are lowered. Therefore, N is limited to 0.01% or less. It is desirable to reduce the N content as much as possible.
Ｏ：０．０１％以下
Ｏ（酸素）は、不純物として鋼中に存在し、その含有量が０．０１％を超えると粗大な酸化物を形成して、靭性および耐ＳＳＣ性を低下させる。従って、Ｏの含有量を０．０１％以下に制限することとした。Ｏの含有量は、極力低減することが望ましい。
O: 0.01% or less O (oxygen) is present in the steel as an impurity, and when its content exceeds 0.01%, a coarse oxide is formed, and toughness and SSC resistance are lowered. Therefore, the O content is limited to 0.01% or less. It is desirable to reduce the content of O as much as possible.
Ｃａ：０．００１〜０．００５％
Ｃａは、介在物の形態制御により靭性および耐食性を向上させるのに有効であり、かつ、鋳込み時のノズル詰まりを抑制して鋳込み特性を改善するのにも有効な元素である。これらの効果を得るためには、Ｃａを０．００１％以上含有させる必要がある。一方、過剰に含有させると介在物がクラスター化しやすくなり、逆に靭性および耐食性を低下させる。従って、Ｃａの含有量を０．００１〜０．００５％とした。
Ca: 0.001 to 0.005%
Ca is an element effective for improving toughness and corrosion resistance by controlling the form of inclusions, and also effective for improving casting characteristics by suppressing nozzle clogging during casting. In order to obtain these effects, it is necessary to contain 0.001% or more of Ca. On the other hand, when it is contained excessively, inclusions are easily clustered, and conversely, toughness and corrosion resistance are lowered. Therefore, the content of Ca is set to 0.001 to 0.005%.
本発明に係るラインパイプ用継目無鋼管は、上記の化学組成を有し、その残部は、例えば、Ｆｅおよび不純物からなるものであるが、強度を高める目的で、以下に示す元素の１種以上を含有させてもよい。 The seamless steel pipe for line pipes according to the present invention has the above-described chemical composition, and the remainder is composed of, for example, Fe and impurities. For the purpose of increasing the strength, one or more of the following elements are included. May be included.
Ｃｒ：１．５％以下
Ｃｒは、添加すれば、焼入れ性を高めて、鋼の強度を向上させるのに有効な元素である。しかし、その含有量が過剰となると、耐水素割れ性が低下するおそれがあるため、Ｃｒを含有させる場合には、その含有量を１．５％以下とするのが望ましい。Ｃｒ含有量の下限には制限はないが、焼入れ性を向上させるためには、０．０２％以上含有させるのが好ましい。より好ましい下限は０．１％である。
Cr: 1.5% or less When added, Cr is an element effective for enhancing the hardenability and improving the strength of the steel. However, if the content is excessive, hydrogen cracking resistance may be lowered. Therefore, when Cr is contained, the content is desirably 1.5% or less. Although there is no restriction | limiting in the minimum of Cr content, In order to improve hardenability, it is preferable to make it contain 0.02% or more. A more preferred lower limit is 0.1%.
Ｎｂ：０．１％以下
Ｔｉ：０．１％以下
Ｚｒ：０．１％以下
Ｎｂ、ＴｉおよびＺｒは、添加すれば、いずれもＣおよびＮと結びつき炭窒化物を形成し、ピニング効果により細粒化に有効に働き、靭性等の機械的特性を改善する元素である。いずれの元素も０．１％を越えて含有させても効果が飽和する。従って、これらの元素を含有させる場合には、その含有量をそれぞれ０．１％以下とするのが望ましい。上記の効果が顕著となるのは、それぞれ０．００２％以上含有させた場合である。これらの元素の含有量の好ましい下限はいずれも０．０１％であり、好ましい上限はいずれも０．０５％である。
Nb: 0.1% or less Ti: 0.1% or less Zr: 0.1% or less If Nb, Ti and Zr are added, they all combine with C and N to form carbonitrides, which are fine due to the pinning effect. It is an element that works effectively in granulation and improves mechanical properties such as toughness. Even if any element exceeds 0.1%, the effect is saturated. Therefore, when these elements are contained, the content is preferably 0.1% or less. The above effect becomes remarkable when the content is 0.002% or more. The preferable lower limit of the content of these elements is 0.01%, and the preferable upper limit is 0.05%.
Ｎｉ：１．５％以下
Ｎｉは、添加すれば、焼入れ性を向上させて、鋼の強度を向上させるとともに、靭性を向上させるのに有効な元素である。しかし、Ｎｉは、高価な元素であり、過剰に含有させてもその効果が飽和し、材料コストを上昇させるだけである。従って、Ｎｉを含有させる場合には、その含有量を１．５％以下とするのが望ましい。下限には特に制限はないが、０．０２％以上含有させるのが好ましい。
Ni: 1.5% or less Ni, when added, is an element effective in improving hardenability, improving steel strength, and improving toughness. However, Ni is an expensive element, and even if it is excessively contained, the effect is saturated and only the material cost is increased. Therefore, when Ni is contained, the content is desirably 1.5% or less. Although there is no restriction | limiting in particular in a minimum, It is preferable to make it contain 0.02% or more.
Ｃｕ：１．０％以下
Ｃｕは、添加すれば、焼入れ性を向上させて、鋼の強度を向上させるのに有効な元素である。しかし、過剰に含有させてもその効果が飽和する。従って、Ｃｕを含有させる場合には、その含有量を１．０％以下とするのが望ましい。下限には特に制限はないが、０．０２％以上含有させるのが好ましい。
Cu: 1.0% or less Cu, if added, is an element effective in improving hardenability and improving the strength of steel. However, the effect is saturated even if it contains excessively. Therefore, when Cu is contained, the content is desirably 1.0% or less. Although there is no restriction | limiting in particular in a minimum, It is preferable to make it contain 0.02% or more.
Ｖ：０．２％以下
ＶもＭｏと同様に焼入れ性を高めて鋼の強度を向上させるのに有効であり、しかも、焼戻し軟化抵抗を高めることで焼き戻し組織に比べ、溶接熱影響部での強度上昇を抑えることができる元素である。また、Ｖを含有させると、Ｍｏと共に微細炭化物であるＭＣ（ＭはＶおよびＭｏ）を生成し、Ｍｏ含有量が１％を超えたときに生成する針状Ｍｏ2Ｃ（ＳＳＣの起点となる）の生成を抑制する。これらの観点からは、Ｖの含有量を、０．０５％以上の含有させるのが好ましい。しかし、Ｖの含有量が過剰な場合、焼入れ時に固溶するＶは飽和し、焼戻し温度を高める効果が飽和する。従って、Ｖを含有させる場合には、その含有量を０．２％以下とするのが望ましい。
V: 0.2% or less V, like Mo, is effective in improving the hardenability and improving the strength of the steel, and by increasing the resistance to softening by tempering, compared with the tempering structure, It is an element that can suppress an increase in strength. Moreover, when V is contained, MC (M is V and Mo) which is fine carbide together with Mo is generated, and acicular Mo 2 C generated when the Mo content exceeds 1% (begins of SSC). ) Is suppressed. From these viewpoints, the V content is preferably 0.05% or more. However, when the content of V is excessive, V that dissolves during quenching is saturated, and the effect of increasing the tempering temperature is saturated. Therefore, when V is contained, the content is desirably 0.2% or less.
Ｂ：０．００５％以下
Ｂは、高強度鋼材においては粒界粗大炭化物Ｍ23Ｃ6（ＭはＦｅ、Ｃｒ、Ｍｏ）の生成を促進し、耐ＳＳＣ性を低下させるが、同時に焼入れ性を向上させる効果を有する。従って、Ｂを含有させる場合には、耐ＳＳＣ性に影響が少なく、焼入れ性の向上が見込める適度な範囲で含有させるのがよく、その含有量を０．００５％以下とするのが望ましい。Ｂの望ましい下限は、０．０００１％である。
B: 0.005% or less B increases the grain boundary coarse carbide M 23 C 6 (M is Fe, Cr, Mo) in a high-strength steel material and lowers the SSC resistance, but at the same time hardenability. Has the effect of improving. Therefore, when B is contained, it is preferable that it be contained in an appropriate range in which the SSC resistance is not affected and the hardenability can be improved, and the content is preferably 0.005% or less. A desirable lower limit of B is 0.0001%.
次に、本発明に係る継目無鋼管の製造方法について説明する。
継目無鋼管の製造方法としては、マンネスマン・ピルガミル・プロセス、マンネスマン・プラグミル・プロセス、マンネスマン・マンドレルミル・プロセスなどの通常知られている方法を採用することができる。例えば、マンネスマン・マンドレルミル・プロセスにおいては、加熱したビレットをピアサによって穿孔して中空素管を得たのち、この中空素管にマンドレルバーを挿入し、中空素管をマンドレルバーと共にマンドレルミルに通して圧延して継目無鋼管が製造される。
Next, the manufacturing method of the seamless steel pipe which concerns on this invention is demonstrated.
As a method for producing the seamless steel pipe, a generally known method such as a Mannesmann-Pirgamil process, a Mannesmann plug mill process, a Mannesmann mandrel mill process, or the like can be employed. For example, in the Mannesmann mandrel mill process, a heated billet is pierced by a piercer to obtain a hollow shell, a mandrel bar is inserted into the hollow shell, and the hollow shell is passed through the mandrel mill together with the mandrel bar. And rolled to produce a seamless steel pipe.
本発明に係る継目無鋼管の製造に当たっては、上記の通常の方法によって得た継目無鋼管に、焼入れ焼戻し処理を実施するのが有効である。 In producing the seamless steel pipe according to the present invention, it is effective to carry out a quenching and tempering treatment on the seamless steel pipe obtained by the above-described ordinary method.
焼入れ処理としては、８００〜１１００℃の温度域から２０℃／ｓ以上の冷却速度で冷却するのがよい。ここで、焼入れ温度が８００℃未満では、フェライト組織となり、強度、耐食性といった性能が劣化するおそれがある。一方、焼入れ温度が１１００℃を超えると、粒径が大きくなり、強度、耐食性といった性能が劣化するおそれがある。なお、焼入れ時の冷却速度は、遅すぎると十分な強度を確保できなくなるおそれがあるため、２０℃／ｓ以上とするのが望ましい。ただし、冷却速度の上限には、特に制限はない。 As the quenching treatment, it is preferable to cool from a temperature range of 800 to 1100 ° C. at a cooling rate of 20 ° C./s or more. Here, when the quenching temperature is less than 800 ° C., a ferrite structure is formed, and the performance such as strength and corrosion resistance may be deteriorated. On the other hand, when the quenching temperature exceeds 1100 ° C., the particle size increases, and the performance such as strength and corrosion resistance may be deteriorated. In addition, since the cooling rate at the time of quenching may not be able to ensure sufficient strength if it is too slow, it is desirable to set it at 20 ° C./s or more. However, the upper limit of the cooling rate is not particularly limited.
焼戻し処理としては、６００〜７００℃の温度に加熱した後、放冷するのがよい。ここで、焼戻し温度が６００℃未満では十分な耐食性を確保するのが困難となる場合がある。一方、７００℃を超えると、材料表面で脱炭が起こり、強度が低下するおそれがある。放冷時の冷却速度は、３℃／ｓとするのが望ましい。 As a tempering process, it is good to cool after heating to the temperature of 600-700 degreeC. Here, if the tempering temperature is less than 600 ° C., it may be difficult to ensure sufficient corrosion resistance. On the other hand, when it exceeds 700 ° C., decarburization occurs on the material surface, and the strength may decrease. The cooling rate during cooling is preferably 3 ° C./s.
表４に示す化学組成を有する鋼を各々５０ｋｇ真空溶製し、１２５０℃に加熱した後、熱間鍛造によりブロックを作製し、これらのブロックを１２５０℃に加熱した後、熱間圧延により得られた２０〜４０ｍｍ厚さの板材を９５０℃で１０〜１５分保持した後、水冷して（冷却速度は２０〜４５℃／ｓ）焼入れし、一部の鋼材については、６５０℃で３０分保持した後、放冷して焼戻した。表５には、製造条件、材料強度および耐ＳＳＣ性を示す。 Each steel having the chemical composition shown in Table 4 was vacuum-melted in 50 kg, heated to 1250 ° C., then produced by hot forging, and after these blocks were heated to 1250 ° C., they were obtained by hot rolling. A 20-40 mm thick plate material is held at 950 ° C. for 10-15 minutes, then cooled with water (cooling rate is 20-45 ° C./s), and some steel materials are held at 650 ° C. for 30 minutes. Then, it was left to cool and tempered. Table 5 shows manufacturing conditions, material strength, and SSC resistance.
耐ＳＳＣ性は、ＮＡＣＥ（Ｎａｔｉｏｎａｌ Ａｓｓｏｃｉａｔｉｏｎ ｏｆ Ｃｏｒｒｏｓｉｏｎ Ｅｎｇｉｎｅｅｒｓ）ＴＭ０１７７−２００５ ｍｅｔｈｏｄ Ｄに従ってＤＣＢ試験を行い、評価した。即ち。鋼材から厚さ１０ｍｍ、幅２５ｍｍ、長さ１００ｍｍのＤＣＢ（Ｄｏｕｂｌｅ Ｃａｎｔｉｌｅｖｅｒ Ｂｅｎｔ Ｂｅａｍ）試験片を採取し、採取した試験片を１ａｔｍの硫化水素ガスを飽和させた常温の５％食塩＋０．５％酢酸水溶液に３３６時間浸漬し、亀裂進展長さａおよび楔開放応力Ｐ（楔厚さ：３．４ｍｍ）から、下記式により応力拡大係数ＫISSCを導出した。
但し、上記式中の各記号の意味は、下記の通りである。
Ｐ：楔開放応力（Ｎ）
ａ：亀裂進展長さ（ｍｍ）
ｈ：ＤＣＢ試験片アーム部高さ（ｍｍ）＝１２．７ｍｍ
Ｂ：ＤＣＢ試験片厚み（ｍｍ）＝９．５３ｍｍ
Ｂｎ：ＤＣＢ試験片溝部厚み（ｍｍ）＝５．７２ｍｍ
The SSC resistance was evaluated by performing a DCB test according to NACE (National Association of Corrosion Engineers) TM0177-2005 method D. That is. A DCB (Double Cantilever Bent Beam) test piece having a thickness of 10 mm, a width of 25 mm, and a length of 100 mm was taken from a steel material, and the collected test piece was saturated with 1 atm hydrogen sulfide gas at room temperature 5% sodium chloride + 0.5% acetic acid. It was immersed in an aqueous solution for 336 hours, and a stress intensity factor K ISSC was derived from the crack growth length a and wedge opening stress P (wedge thickness: 3.4 mm) by the following equation.
However, the meaning of each symbol in the above formula is as follows.
P: wedge opening stress (N)
a: Crack growth length (mm)
h: DCB test piece arm height (mm) = 12.7 mm
B: DCB specimen thickness (mm) = 9.53 mm
Bn: DCB test piece groove part thickness (mm) = 5.72 mm
なお、一般にＫISSC値は、材料強度の上昇に伴い低下し、材料に関わらず引張強度が１ｋｓｉ（≒６．８９ＭＰａ）上がるのに対して０．９±０．２ｋｓｉ√ｉｎ．程度の低下が見込まれる。よって材料間の耐ＳＳＣ性比較のためにＴＳが１００ｋｓｉの値に規格化をして評価を行い、そのＫISSC値の換算値で３６ ｋｓｉ√ｉｎ．以上となる試材を耐ＳＳＣ性が良好と判断した。 In general, the K ISSC value decreases as the material strength increases, and the tensile strength increases by 1 ksi (≈6.89 MPa) regardless of the material, whereas 0.9 ± 0.2 ksi√in. A decrease in the degree is expected. Therefore, for comparison of SSC resistance between materials, TS is normalized to a value of 100 ksi and evaluated, and the converted value of K ISSC value is 36 ksi√in. It was judged that the above-described sample material had good SSC resistance.
表５に示すように、Ｍｎ含有量が高く、しかもＭｏ含有量が低いＯ鋼、Ｐ鋼およびＱ鋼を用いた比較例１〜６では、ＫISSC値は低かった。また、Ｍｎ含有量が高いＲ鋼を用いた比較例７でもＫISSC値が低い結果となった。一方、Ｍｎ含有量が１．６％以下であり、かつＭｏ含有量が０．５％以上のＡ鋼〜Ｎ鋼を用いた本発明例１〜１７では、いずれも良好なＫISSC値を示した。 As shown in Table 5, in Comparative Examples 1 to 6 using O steel, P steel and Q steel having a high Mn content and a low Mo content, the K ISSC value was low. Further, Comparative Example 7 using R steel having a high Mn content also resulted in a low K ISSC value. On the other hand, in Invention Examples 1 to 17 using A steel to N steel having a Mn content of 1.6% or less and a Mo content of 0.5% or more, all show good K ISSC values. It was.
本発明によれば、降伏応力（ＹＳ）が５５１ＭＰａ（８０ｋｓｉ）またはそれを上回る高強度の継目無鋼管に母材および溶接熱影響部の全域に渡って良好な耐水素割れ性を付与することができる。従って、深海油田で用いられる海底フローライン用鋼管、ライザー用鋼管などに使用するのに適した継目無鋼管を提供することができる。 According to the present invention, a high strength seamless steel pipe having a yield stress (YS) of 551 MPa (80 ksi) or higher can be provided with good hydrogen cracking resistance over the entire area of the base metal and the weld heat affected zone. it can. Therefore, it is possible to provide a seamless steel pipe suitable for use in a submarine flow line steel pipe, a riser steel pipe or the like used in a deep sea oil field.
Claims (6)
Ｃ ：０．０３〜０．０８％、
Ｓｉ：０．０５〜０．５％、
Ｍｎ：０．２〜１．６％、
Ｐ ：０．０５％以下、
Ｓ ：０．０１％以下、
Ｍｏ：０．５〜３．０％、
Ａｌ：０．００５〜０．１００％、
Ｎ ：０．０１％以下、
Ｏ ：０．０１％以下および
Ｃａ：０．００１〜０．００５％
を含有し、残部Ｆｅおよび不純物からなることを特徴とするラインパイプ用継目無鋼管。 % By mass
C: 0.03-0.08%,
Si: 0.05 to 0.5%,
Mn: 0.2 to 1.6%,
P: 0.05% or less,
S: 0.01% or less,
Mo: 0.5 to 3.0%,
Al: 0.005 to 0.100%,
N: 0.01% or less,
O: 0.01% or less and Ca: 0.001-0.005%
A seamless steel pipe for a line pipe, characterized by comprising a balance Fe and impurities.
Ｃｒ：１．５％以下、
Ｎｂ：０．１％以下、
Ｔｉ：０．１％以下、
Ｚｒ：０．１％以下、
Ｎｉ：１．５％以下、
Ｃｕ：１．０％以下、
Ｖ ：０．２％以下および
Ｂ ：０．００５％以下
のうちから選択された１種以上を含有することを特徴とする請求項１に記載のラインパイプ用継目無鋼管。 Furthermore, in mass%,
Cr: 1.5% or less,
Nb: 0.1% or less,
Ti: 0.1% or less,
Zr: 0.1% or less,
Ni: 1.5% or less,
Cu: 1.0% or less,
The seamless steel pipe for a line pipe according to claim 1, comprising one or more selected from V: 0.2% or less and B: 0.005% or less.
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| JP2012197508A (en) * | 2011-02-07 | 2012-10-18 | Dalmine Spa | Heavy wall steel pipe with excellent toughness at low temperature and sulfide stress corrosion cracking resistance |
| JP2012197507A (en) * | 2011-02-07 | 2012-10-18 | Dalmine Spa | High-strength steel pipe having excellent toughness at low temperature and sulfide stress corrosion cracking resistance |
| CN103032635A (en) * | 2011-09-30 | 2013-04-10 | 北京隆盛泰科石油管科技有限公司 | Method of manufacturing mineral slurry delivery pipeline which is anti-erosion and anti-wear |
| WO2013105396A1 (en) | 2012-01-12 | 2013-07-18 | 新日鐵住金株式会社 | Low alloy steel |
| WO2013105395A1 (en) | 2012-01-12 | 2013-07-18 | 新日鐵住金株式会社 | Low alloy steel |
| WO2014034737A1 (en) * | 2012-08-29 | 2014-03-06 | 新日鐵住金株式会社 | Seamless steel pipe and method for producing same |
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| JP2012197508A (en) * | 2011-02-07 | 2012-10-18 | Dalmine Spa | Heavy wall steel pipe with excellent toughness at low temperature and sulfide stress corrosion cracking resistance |
| JP2012197507A (en) * | 2011-02-07 | 2012-10-18 | Dalmine Spa | High-strength steel pipe having excellent toughness at low temperature and sulfide stress corrosion cracking resistance |
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