JP2008223134A - High strength electric resistance welded line pipe - Google Patents
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本発明は石油や天然ガスなどの輸送に使用されるAPI X80グレード以上の薄肉電縫ラインパイプに関する。 The present invention relates to a thin electric seam line pipe of API X80 grade or higher used for transportation of oil or natural gas.
石油や天然ガスを輸送するパイプラインでは、高圧操業による輸送効率の向上や、薄肉化による鋼材重量の低減、溶接能率の向上のため、高強度化が進められている。パイプラインの幹線には主として大径のUO鋼管やスパイラル鋼管が用いられるが、その枝となる支線や小規模なパイプラインの幹線には生産性に優れて安価な電縫鋼管が用いられる場合が多い。電縫鋼管はホットコイルを冷間成型して製造されるため、高強度の電縫ラインパイプには高強度のホットコイルが必要である。 Pipelines for transporting oil and natural gas are being strengthened to improve transport efficiency through high-pressure operations, to reduce the weight of steel materials through thinning, and to improve welding efficiency. Large-diameter UO steel pipes and spiral steel pipes are mainly used for the trunk lines of pipelines. However, highly efficient and inexpensive ERW steel pipes may be used for branch lines and small-scale pipeline trunk lines. Many. Since an electric resistance steel pipe is manufactured by cold forming a hot coil, a high-strength electric resistance line pipe requires a high-strength hot coil.
特許文献1にはAPI X70グレードの強度を満足し高靱性のホットコイルおよびその製造方法が開示されている。
特許文献2にはAPI X65グレード以上の強度と耐HIC性を有するホットコイルおよびその製造方法が開示されている。
特許文献3にはAPI X80グレードの強度を有するホットコイルおよびその製造方法が開示されている。
特許文献4にはAPI X100グレードの強度を有する厚肉鋼管の製造方法が開示されている。
特許文献5にはAPI X65〜80グレードの強度を有する電縫鋼管の製造方法が開示されている。
電縫鋼管の高強度化に際しては高圧操業よりは薄肉化のニーズが高く、t/Dの小さい高強度電縫鋼管が求められている。しかしながら電縫鋼管の製造工程では電縫溶接、シーム熱処理の工程の後にサイザーによって円周方向に圧縮加工が加わるために、バウシンガー効果により円周方向の耐力は大幅に減少する。t/Dが大きい鋼管の場合には鋼管成型時の加工硬化の影響により耐力の減少は抑制されるが、t/Dが小さくなるほど円周方向の耐力の低下は大きくなる。ラインパイプの規格強度は主として円周方向の耐力で規定されるためにこの影響は極めて重大である。 In order to increase the strength of an electric resistance welded pipe, there is a high need for thinning rather than a high pressure operation, and a high strength electric resistance welded pipe with a small t / D is required. However, in the manufacturing process of the ERW steel pipe, the compressive processing is applied in the circumferential direction by the sizer after the ERW welding and seam heat treatment processes, so the yield strength in the circumferential direction is greatly reduced by the Bauschinger effect. In the case of a steel pipe having a large t / D, the decrease in yield strength is suppressed by the influence of work hardening at the time of forming the steel pipe, but the decrease in the yield strength in the circumferential direction increases as t / D decreases. This effect is extremely serious because the standard strength of line pipes is mainly defined by the yield strength in the circumferential direction.
特許文献1〜3では鋼管素材であるホットコイルの高強度化にとどまり、t/Dが低い場合の造管後の大幅な耐力低下が何ら考慮されておらず、このホットコイルを用いても実質的にはAPI X80グレード以上の薄肉の高強度電縫鋼管を製造することができない。
In
特許文献4ではAPI X80グレードの電縫鋼管が開示されているが、肉厚が15mmの厚肉鋼管であることからサイザーによる耐力の低下代が小さいため製造が容易であり、しかも高価なNi、Mo添加量が高く経済性に乏しい。
特許文献5ではAPI X80グレードでt/D=1.6%の薄肉高強度電縫鋼管が開示されているが、高価なMoの添加量が高く経済性に乏しい。
本発明は上記問題点に鑑み、API X80グレードの強度を有するt/Dが2%以下の薄肉高強度電縫ラインパイプを低価格で提供することを課題とする。 In view of the above problems, an object of the present invention is to provide a thin high-strength ERW line pipe having a strength of API X80 grade and having a t / D of 2% or less at a low price.
本発明者らは上記の課題を解決するために鋭意検討を重ね、鋼の引張強度、組織、化学成分を適正化することによりt/Dが2%以下でも耐力が高い電縫鋼管が得られた。その要旨とするところは以下のとおりである。
(1)板厚4mm以上12mm以下のホットコイルから、冷間でのロール成形、電縫溶接、シーム熱処理、サイザーの工程を経て製造された、外径200mm以上610mm以下、肉厚/外径比(t/D)が2%以下の電縫鋼管であって、金属組織が平均結晶粒径5μm以下のアシキュラーフェライト組織であり、扁平後の周方向の引張強度が700N/mm2以上、0.5%耐力が550N/mm2以上、電縫溶接衝合部の酸化物占有面積率が0.1%以下であることを特徴とする、高強度電縫ラインパイプ。
(2)質量%で
C:0.04超〜0.08%
Si:0.1〜0.3%
Mn:1.6超〜2.0%
P:0.02%以下
S:0.003%以下
Nb:0.04〜0.08%
V:0.05〜0.1%
Ni:0.1〜0.5%
Cu:0.1〜0.5%
Mo:0.05〜0.20%
Ti:0.01〜0.03%
Al:0.05%以下
N:0.005%以下
であり、かつ、Ni,Cu,Mo含有量が下記<1>式を満足し、残部がFeおよび不可避的不純物よりなる、(1)に記載の高強度電縫ラインパイプ。
1.0>3Mo+Ni+Cu>0.8 <1>
(3)質量%で、さらに、
S:0.0020%以下
Ca:0.001〜0.003%
であることを特徴とする(2)に記載の高強度電縫ラインパイプ。
The inventors of the present invention have made extensive studies in order to solve the above problems, and by optimizing the tensile strength, structure and chemical composition of the steel, an ERW steel pipe having a high yield strength can be obtained even when t / D is 2% or less. It was. The gist is as follows.
(1) Outer diameter 200 mm or more and 610 mm or less, thickness / outer diameter ratio manufactured from hot coil with thickness of 4 mm or more and 12 mm or less through cold roll forming, electro-sealing welding, seam heat treatment, sizer process (T / D) is an electric resistance welded steel pipe of 2% or less, the metal structure is an acicular ferrite structure having an average crystal grain size of 5 μm or less, and the tensile strength in the circumferential direction after flattening is 700 N / mm 2 or more, 0 A high-strength electric resistance line pipe characterized by having a 5% proof stress of 550 N / mm 2 or more and an oxide occupying area ratio of an electric resistance welding contact portion of 0.1% or less.
(2) By mass% C: more than 0.04 to 0.08%
Si: 0.1 to 0.3%
Mn: more than 1.6 to 2.0%
P: 0.02% or less S: 0.003% or less Nb: 0.04 to 0.08%
V: 0.05-0.1%
Ni: 0.1 to 0.5%
Cu: 0.1 to 0.5%
Mo: 0.05-0.20%
Ti: 0.01-0.03%
Al: 0.05% or less, N: 0.005% or less, and the content of Ni, Cu, Mo satisfies the following <1> formula, and the balance is Fe and inevitable impurities. High strength ERW line pipe as described.
1.0> 3Mo + Ni + Cu> 0.8 <1>
(3) In mass%,
S: 0.0020% or less Ca: 0.001 to 0.003%
The high-strength ERW linepipe according to (2), characterized in that:
本発明の高強度電縫ラインパイプは、低t/Dで且つ肉厚が薄いのにもかかわらず、引張強さ、耐力が高いため、既存のラインパイプをさらに薄肉化することができ、鋼材使用重量を大幅に低減できる。金属組織が微細であるため靱性に優れる。電縫溶接衝合部の酸化物面積率が低く、さらにシーム熱処理が施されているため、電縫溶接部が母材並みの健全性を有する。また、高価な合金元素の使用を極力抑制した化学成分で且つ、生産性の高い電縫管であるため、同等な強度レベルのUO鋼管、スパイラル鋼管、シームレス鋼管に比べて製造コストが大幅に低い。 The high-strength ERW line pipe of the present invention has low tensile strength and proof stress despite its low t / D and thin wall thickness. Therefore, the existing line pipe can be made thinner, Use weight can be greatly reduced. Excellent toughness due to its fine metal structure. Since the area ratio of the oxide in the ERW weld abutting portion is low and seam heat treatment is performed, the ERW weld portion has the same level of soundness as the base material. In addition, it is a highly productive ERW pipe with a chemical component that suppresses the use of expensive alloying elements as much as possible. Therefore, the manufacturing cost is significantly lower than UO steel pipe, spiral steel pipe, and seamless steel pipe of the same strength level. .
発明者らは電縫鋼管でAPI X80グレード以上の強度を有するt/Dが2%以下の薄肉高強度鋼管を得るべく検討を重ねた。t/Dが2%以下になると、サイザーでの圧縮応力に起因するバウシンガー効果により円周方向の耐力が大幅に低下する。膨大な製造実績の調査の結果、t/DとYR(耐力と引張強さとの比)の関係は図1に示すようなデータバンドで示され、t/Dが2%以下になるとYRは0.79〜0.73まで低下することが明らかになった。従って、t/Dが2%以下でAPI X80グレードの耐力の下限である550N/mm2を確保するためには鋼管の引張強さは700N/mm2以上でなくてはならないことが判明した。より好ましくは750N/mm2以上である。 The inventors have repeatedly studied to obtain a thin-walled high-strength steel pipe having a strength equal to or higher than API X80 grade and having a t / D of 2% or less. When t / D is 2% or less, the yield strength in the circumferential direction is significantly reduced due to the Bauschinger effect caused by the compressive stress in the sizer. As a result of investigation of a huge production record, the relationship between t / D and YR (ratio between yield strength and tensile strength) is shown by a data band as shown in FIG. 1, and when t / D becomes 2% or less, YR is 0. It became clear that it fell to .79-0.73. Therefore, it was found that the tensile strength of the steel pipe must be 700 N / mm 2 or more in order to secure 550 N / mm 2 which is the lower limit of the proof stress of API X80 grade when t / D is 2% or less. More preferably, it is 750 N / mm 2 or more.
このような高強度の電縫鋼管用ホットコイルを得るには、後に説明するように化学成分範囲を厳密に規定し、熱延条件として高強度鋼板を得るために用いられる通常の条件を適用することにより得ることができる。 In order to obtain such a hot coil for high-strength ERW steel pipe, the chemical component range is strictly defined as described later, and normal conditions used for obtaining a high-strength steel sheet are applied as hot rolling conditions. Can be obtained.
その際に重要なのは金属組織を平均結晶粒径5μm以下のアシキュラーフェライトにすることである。これは、高い引張強度を得ながらも必要最低限の靱性を確保するために必要な条件である。ここでいうアシキュラーフェライトとは、パーライトのような層状組織を有さず炭化物が均一に分散し、ベイナイトとは異なり旧オーステナイト粒界の痕跡を残さない組織のことである。このようなアシキュラーフェライトは、パーライトよりも低温側でフェライト変態して転位密度が高いという性質を有する。本発明では、金属組織中のアシキュラーフェライトが面積率で90%以上を占めていれば、アシキュラーフェライト組織であるとみなす。ここで必要最低限の靱性とは、API X80グレードであれば、−20℃の吸収エネルギーがJIS Z 2202 Vノッチ試験片で100J以上(1/2サブサイズ試験片で50J以上)、vTrsが−50℃以下の条件が好ましい条件である。また、金属組織を平均結晶粒径5μm以下のアシキュラーフェライトにするためには、細粒組織を得るための通常の圧延方法を採用することにより実現することができる。 In this case, it is important to make the metal structure an acicular ferrite having an average crystal grain size of 5 μm or less. This is a necessary condition for ensuring the necessary minimum toughness while obtaining high tensile strength. Acicular ferrite here is a structure that does not have a layered structure like pearlite, and in which carbides are uniformly dispersed, and unlike bainite, does not leave traces of prior austenite grain boundaries. Such acicular ferrite has the property that the ferrite transformation occurs at a lower temperature than pearlite and the dislocation density is high. In the present invention, if the acicular ferrite in the metal structure occupies 90% or more in area ratio, it is regarded as an acicular ferrite structure. Here, the minimum toughness is API X80 grade, the absorbed energy at −20 ° C. is 100 J or more in the JIS Z 2202 V notch test piece (50 J or more in the 1/2 subsize test piece), and vTrs is − A condition of 50 ° C. or lower is a preferable condition. Moreover, in order to make the metal structure an acicular ferrite having an average crystal grain size of 5 μm or less, it can be realized by adopting a normal rolling method for obtaining a fine grain structure.
電縫鋼管では電縫溶接部が母材並みの強度、靱性を確保していることが求められるが、本発明では電縫衝合部の酸化物占有面積率を0.1%以下、より好ましくは0.05%以下に規定し、さらに電縫溶接後にシーム熱処理が施されることを必須としたことにより、母材並みの強度、靱性を確保することができた。ここで、酸化物占有面積率は、電縫衝合部にノッチを入れたシャルピー試験片にて160℃でシャルピー試験を行い、試験後の試験片破面の光学顕微鏡観察にて測定される。また、シーム熱処理とは、電縫溶接後に、例えば誘導加熱方式により電縫溶接部近傍のみを熱処理することであるが、その方法は、Ac3点以上に加熱し急冷する、あるいは、Ac3点以上に加熱し急冷後、Ac1点以下に加熱することにより実施する。より望ましくは後者の方法である。電縫衝合部の酸化物占有面積率を0.1%以下とするためには、例えば溶接速度と溶接入力との関係を、酸化物占有面積率が0.1%以下となる第2種溶接現象領域に設定して溶接することにより実現することができる(例えば「鉄と鋼、70(1984)、S1162(図1)」参照)。あるいは、溶接部の周囲をシールドボックスで囲い、アルゴンガス雰囲気中で溶接することにより、電縫衝合部の酸化物占有面積率を0.1%以下とすることができる。 In an ERW steel pipe, it is required that the ERW welded portion has the same strength and toughness as the base metal. However, in the present invention, the oxide occupation area ratio of the ERW abutting portion is preferably 0.1% or less. Is specified to be 0.05% or less, and it is essential to perform seam heat treatment after ERW welding, so that the same strength and toughness as the base metal can be secured. Here, the oxide occupation area ratio is measured by performing a Charpy test at 160 ° C. with a Charpy test piece having a notch in the electro-welding joint, and observing the fracture surface of the test piece after the test with an optical microscope. In addition, seam heat treatment refers to heat-treating only the vicinity of the ERW welded part by, for example, induction heating after ERW welding. After heating and quenching, heating is performed to Ac1 point or less. The latter method is more desirable. In order to set the oxide occupation area ratio of the electric stitching contact portion to 0.1% or less, for example, the relationship between the welding speed and the welding input is the second type in which the oxide occupation area ratio is 0.1% or less. This can be realized by setting the welding phenomenon region and welding (see, for example, “Iron and Steel, 70 (1984), S1162 (FIG. 1)”). Alternatively, the area occupied by the oxide in the electro-welding abutting portion can be reduced to 0.1% or less by surrounding the welded portion with a shield box and welding in an argon gas atmosphere.
板厚4mm以上12mm以下のホットコイルに制限した理由は、肉厚15mm以上のAPI X80グレードの厚肉電縫鋼管は公知であり、また、板厚4mm未満になると冷間成形が困難になるためである。より望ましい肉厚は6〜10mmである。 The reason for limiting to hot coils with a plate thickness of 4 mm or more and 12 mm or less is that API X80 grade thick ERW steel pipes with a wall thickness of 15 mm or more are known, and if the plate thickness is less than 4 mm, cold forming becomes difficult. It is. A more desirable wall thickness is 6 to 10 mm.
外径200mm以上610mm以下に規定した理由は、上述の板厚の制限範囲内で、従来存在しなかったt/D≦2%が実現できる外径範囲だからである。より望ましくは350〜550mmである。 The reason why the outer diameter is specified to be 200 mm or more and 610 mm or less is that the outer diameter range in which t / D ≦ 2%, which did not exist in the past, can be realized within the above-described limit range of the plate thickness. More desirably, the thickness is 350 to 550 mm.
以下に本発明の高強度電縫ラインパイプの化学成分について説明する。 The chemical components of the high-strength ERW line pipe of the present invention will be described below.
Cの下限0.04%超は、母材および溶接部の強度、低温靱性の確保ならびにNb、V添加による析出強化、再結晶の抑制、結晶粒の微細化効果を発揮させるための最小量である。しかし、C量が多過ぎると低温靱性や現地溶接性の劣化を招くので、上限を0.08%とした。 The lower limit of C exceeds 0.04%, which is the minimum amount for ensuring the strength of the base metal and the welded portion, low temperature toughness, precipitation strengthening by adding Nb and V, suppression of recrystallization, and effect of grain refinement. is there. However, if the amount of C is too much, low temperature toughness and on-site weldability are deteriorated, so the upper limit was made 0.08%.
Siは脱酸や強度向上のために添加する元素であり、その効果を得るためには0.1%以上含有することが必要である。一方、多量に添加すると靱性、溶接性を劣化させるので、含有量を0.1〜0.3%に制限した。 Si is an element added for deoxidation and strength improvement. In order to obtain the effect, it is necessary to contain 0.1% or more. On the other hand, if added in a large amount, the toughness and weldability deteriorate, so the content was limited to 0.1 to 0.3%.
Mnはアシキュラーフェライト組織を得て強度、靱性を確保する上で不可欠な元素であり、その下限は1.6%超である。しかし、Mnが多過ぎると鋼の焼入性が増加して現地溶接性を劣化させるだけでなく、連続鋳造鋼片の中心偏析を助長し、靱性も劣化させるので、上限を2.0%とした。 Mn is an element essential for obtaining an acicular ferrite structure and ensuring strength and toughness, and its lower limit is over 1.6%. However, too much Mn not only increases the hardenability of the steel and deteriorates the local weldability, but also promotes the center segregation of continuously cast steel pieces and deteriorates the toughness, so the upper limit is 2.0%. did.
P、Sは靱性に悪影響を及ぼす元素であるため、Pは0.02%以下、Sは0.003%以下、より望ましくは、Sは0.002%以下に限定する。 Since P and S are elements that adversely affect toughness, P is 0.02% or less, S is 0.003% or less, and more preferably, S is limited to 0.002% or less.
Nbは結晶粒の微細化や析出強化に寄与し、鋼を強靱化する作用を有する。本発明で規定される強度を得るためには0.04%以上含有することが必要である。しかし、Nbを0.08%超添加してもさらなる強度向上効果は得られないだけでなく、溶接性や靱性に悪影響をもたらすので、含有量を0.04〜0.08%に規定した。 Nb contributes to refinement of crystal grains and precipitation strengthening, and has an effect of strengthening steel. In order to obtain the strength defined by the present invention, it is necessary to contain 0.04% or more. However, even if Nb is added in excess of 0.08%, not only a further strength improvement effect can be obtained, but also the weldability and toughness are adversely affected. Therefore, the content is specified to be 0.04 to 0.08%.
Vはホットコイル巻き取り後の徐冷時に炭化物として析出し、強化に寄与する。本発明で規定される強度を得るためには0.05%以上含有することが必要である。しかし、Vを0.10%超添加してもさらなる強度向上効果は得られないだけでなく、溶接性や靱性に悪影響をもたらすので、含有量を0.05〜0.10%に規定した。 V precipitates as a carbide during the slow cooling after hot coil winding, and contributes to strengthening. In order to obtain the strength defined by the present invention, it is necessary to contain 0.05% or more. However, even if V is added in excess of 0.10%, not only a further strength improvement effect is not obtained, but also the weldability and toughness are adversely affected, so the content was specified to be 0.05 to 0.10%.
Ni、Cuは焼き入れ性を向上させアシキュラーフェライト組織を確保するために必要な元素である。その効果を得るためには、0.1%以上の添加が必要であるが、高価な元素であることと、多量な添加は溶接性を劣化させるために、含有量を0.1〜0.5%に規定した。 Ni and Cu are elements necessary for improving the hardenability and securing an acicular ferrite structure. In order to obtain the effect, addition of 0.1% or more is necessary. However, since it is an expensive element and a large amount of addition deteriorates weldability, the content is 0.1 to 0. It was defined as 5%.
Moは焼き入れ性を向上させアシキュラーフェライト組織を確保するために必要な元素であるとともに、ホットコイル巻き取り後の徐冷時に炭化物として析出し、強化に寄与する。その効果を得るためには、0.05%以上の添加が必要であるが、高価な元素であることと、多量な添加は溶接性を劣化させるために、含有量を0.05〜0.20%に規定した。 Mo is an element necessary for improving the hardenability and securing an acicular ferrite structure, and precipitates as a carbide during slow cooling after winding of the hot coil and contributes to strengthening. In order to obtain the effect, addition of 0.05% or more is necessary. However, since it is an expensive element and a large amount of addition deteriorates weldability, the content is 0.05 to 0.00%. It was defined as 20%.
Tiは微細なTiNを形成し、スラブ再加熱時および溶接HAZのオーステナイト粒の粗大化を抑制してミクロ組織を微細化し、母材およびHAZの靱性を向上させる。このようなTiNの効果を発揮させるためには、最低0.01%のTi添加が必要である。しかし、Ti量が多過ぎると、TiNの粗大化やTiCによる析出硬化が生じ、靱性が劣化するので、含有量を0.01〜0.03%に規定した。 Ti forms fine TiN, suppresses coarsening of austenite grains in the slab reheating and welded HAZ, refines the microstructure, and improves the toughness of the base material and the HAZ. In order to exhibit such an effect of TiN, it is necessary to add at least 0.01% Ti. However, if the amount of Ti is too large, TiN coarsening and precipitation hardening due to TiC occur and the toughness deteriorates, so the content was specified to be 0.01 to 0.03%.
Alは、通常脱酸剤として鋼に含まれる元素であり、組織の微細化にも効果を有する。しかし、Al量が0.05%を超えるとAl系非金属介在物が増加して鋼の清浄度を害するので、上限を0.05%とした。 Al is an element usually contained in steel as a deoxidizer, and has an effect on the refinement of the structure. However, if the Al content exceeds 0.05%, Al-based non-metallic inclusions increase to impair the cleanliness of the steel, so the upper limit was made 0.05%.
NはTiNを形成してスラブ再加熱時および溶接HAZのオーステナイト粒の粗大化を抑制して母材、HAZの低温靱性を向上させる。しかし、N量が多過ぎるとスラブ表面疵や固溶NによるHAZ靱性の劣化の原因となるので、その上限は0.005%とした。 N forms TiN and suppresses the coarsening of austenite grains during slab reheating and welding HAZ, thereby improving the low temperature toughness of the base material and HAZ. However, if the amount of N is too large, it will cause deterioration of the HAZ toughness due to slab surface defects or solute N, so the upper limit was made 0.005%.
Caは鋼中でCaSを形成することにより鋼中Sを固定し、靱性や熱間加工性を改善させる効果がある。その効果を得るためには0.001%以上の添加が必要であるが、添加しすぎるとCaOを形成してかえって靱性が低下するために、含有量を0.001〜0.003%に規定した。なお、Caを積極的に添加しない場合、鋼中のCa含有量は0.0001〜0.0002質量%程度である。 Ca has the effect of fixing Ca in steel by forming CaS in steel and improving toughness and hot workability. In order to obtain the effect, addition of 0.001% or more is necessary, but if added too much, CaO is formed and the toughness is lowered, so the content is specified to be 0.001 to 0.003%. did. In addition, when not adding Ca positively, Ca content in steel is about 0.0001-0.0002 mass%.
本発明では上記に加えて、Ni,Cu,Moの添加量を<1>式を満足するように添加することを好ましい条件として規定した。これは、アシキュラーフェライト組織を確実に確保するためのものであり、0.8以下になるとフェライト+パーライトが、1.0以上になるとベイナイトが主体となるからである。
1.0>3Mo+Ni+Cu>0.8 <1>
In the present invention, in addition to the above, addition of Ni, Cu, and Mo so as to satisfy the <1> formula is defined as a preferable condition. This is to ensure an acicular ferrite structure, and when it is 0.8 or less, ferrite + pearlite is mainly, and when it is 1.0 or more, bainite is the main component.
1.0> 3Mo + Ni + Cu> 0.8 <1>
本発明においてホットコイルの圧延条件は、金属組織、強度が本発明を満足するものを任意に採用することが可能である。 In the present invention, the hot coil rolling conditions can be arbitrarily selected such that the metal structure and strength satisfy the present invention.
本発明における電縫鋼管には、通電加熱方式と誘導加熱方式の両者が含まれる。 The electric resistance welded steel pipe in the present invention includes both an electric heating method and an induction heating method.
(実施例1)
表1に化学成分を示した成分記号1の連続鋳造スラブを、抽出温度1230℃で、仕上げ全圧下率、仕上げ圧延終了温度、巻き取るまでの冷却速度、巻き取り温度を変化させて、板厚7mmのホットコイルに圧延した後、外径406.4mmの管に造管した。その際の、ホットコイル(板)の板幅方向の強度、扁平した管の円周方向の強度、金属組織、結晶粒径、1/2サブサイズ試験片でのシャルピー試験結果を表2に示す。なお、いずれも電縫溶接衝合部の酸化物占有面積率は0.1%以下であった。
(Example 1)
Thickness of the continuous cast slab with
管記号a〜cは、管の引張強度、耐力がAPI X80グレードを満足し、−20℃の吸収エネルギーが50J以上、vTrsが−50℃以下と靱性も良好な本発明例である。 Tube symbols a to c are examples of the present invention in which the tensile strength and proof stress of the tube satisfy the API X80 grade, the absorbed energy at −20 ° C. is 50 J or more, the vTrs is −50 ° C. or less and the toughness is also good.
それに対し、管記号dは巻き取り温度が低かったために、Nb、V、Moの析出強化が十分に発揮されず、ホットコイルの強度はAPI X80グレード並みであったが、造管後の耐力の低下によって、API X80グレードが満足できなかった例である。 On the other hand, because the coil symbol d was low in coiling temperature, the precipitation strengthening of Nb, V, and Mo was not sufficiently exhibited, and the strength of the hot coil was similar to the API X80 grade. This is an example in which the API X80 grade could not be satisfied due to the decrease.
管記号eは、平均結晶粒径が大きかったために、−20℃の吸収エネルギーが50J以下、vTrsが−50℃以上と、靱性に乏しかった例である。 The tube symbol e is an example in which the average crystal grain size is large, the absorbed energy at −20 ° C. is 50 J or less, and the vTrs is −50 ° C. or more, resulting in poor toughness.
管記号fは、未再結晶域圧延により扁平した旧γ粒界が明瞭に残るベイナイト組織で、強度は十分であったが、旧γ粒の短径が本発明である5μmを大きく越えたためにvTrsが高かった例である。 The tube symbol f is a bainite structure in which the old γ grain boundaries flattened by non-recrystallization zone rolling remain clearly, and the strength was sufficient, but the minor axis of the old γ grains greatly exceeded 5 μm of the present invention. This is an example in which vTrs was high.
管記号gは、フェライト+パーライト組織で、強度が低かったのに加えて、平均粒径が大きかったために靱性にも乏しかった例である。 The pipe symbol g is an example of a ferrite + pearlite structure, in which the strength was low and the toughness was poor because the average particle size was large.
(実施例2)
表2の管記号aの鋼管を電縫溶接する際に、入熱条件を変化させて、意図的に電縫溶接衝合部の酸化物占有面積率が高い部分を作り、焼き入れ焼き戻しによるシーム熱処理を行った。溶接部がノッチ位置となるような1/2サブサイズ試験片を用いての−20℃でのシャルピー試験結果を表3に示す。管記号a−1、a−2は母材と同等以上の吸収エネルギーを有する本発明例である。
(Example 2)
When the steel pipe of the pipe symbol a in Table 2 is electro-welded, the heat input condition is changed to intentionally create a portion with a high oxide occupation area ratio in the electro-resist welding joint, and quenching and tempering Seam heat treatment was performed. Table 3 shows the Charpy test results at −20 ° C. using a ½ sub-size test piece in which the weld is located at the notch position. Tube symbols a-1 and a-2 are examples of the present invention having absorbed energy equivalent to or higher than that of the base material.
管記号a−3,a−4は酸化物占有面積率が高すぎて、吸収エネルギーが50J以下に低下した例である。 Tube symbols a-3 and a-4 are examples in which the oxide occupation area ratio is too high and the absorbed energy is reduced to 50 J or less.
(実施例3)
表1の化学成分の連続鋳造スラブを、抽出温度1230℃、仕上げ全圧下率80%、仕上げ圧延終了温度860℃、冷却速度10℃/s、巻き取り温度570℃で、各々の板厚、板幅に圧延し、造管した。その際の、扁平した管の円周方向の強度、金属組織、結晶粒径、1/2サブサイズ試験片でのシャルピー試験結果を表4に示す。
(Example 3)
Continuous casting slabs having the chemical components shown in Table 1 were extracted at a temperature of 1230 ° C., a final rolling reduction of 80%, a finish rolling finish temperature of 860 ° C., a cooling rate of 10 ° C./s, and a winding temperature of 570 ° C. Rolled to width and piped. Table 4 shows the strength in the circumferential direction of the flattened tube, the metal structure, the crystal grain size, and the Charpy test results with a ½ subsize test piece.
管記号A〜H、Pは、管の引張強度、耐力がAPI X80グレードを満足し、−20℃の吸収エネルギーが50J以上、vTrsが−50℃以下と靱性も良好な本発明例である。 Pipe symbols A to H and P are examples of the present invention in which the tensile strength and proof stress of the pipe satisfy API X80 grade, the absorbed energy at −20 ° C. is 50 J or more, the vTrs is −50 ° C. or less and the toughness is also good.
それに対し、管記号Iは、t/Dが大きすぎたために造管による耐力低下は小さかったが、肉厚が厚すぎたために結晶粒の微細化が十分でなく、靱性が低めであった例である。 On the other hand, the pipe symbol I was an example in which the t / D was too large and the yield reduction due to the pipe making was small, but the wall thickness was too thick and the crystal grains were not sufficiently refined and the toughness was low. It is.
管記号JはC量が多すぎたために強度がAPI X80グレードを越えるほど高くなり、靱性が低かった例である。 The pipe symbol J is an example in which the amount of C was too high, so that the strength exceeded the API X80 grade and the toughness was low.
管記号KはC量が少なすぎたために十分な強度が得られなかった例である。 The tube symbol K is an example in which sufficient strength cannot be obtained because the amount of C is too small.
管記号LはMn量が多すぎたためにベイナイトとアシキュラーフェライトの混合組織となり、靱性が低かった例である。 The pipe symbol L is an example in which the amount of Mn is too large, resulting in a mixed structure of bainite and acicular ferrite and low toughness.
管記号MはMn量が少なすぎたためにフェライト+パーライトとアシキュラーフェライトの混合組織となり、強度と靱性が低かった例である。 The tube symbol M is an example in which the amount of Mn is too small, so that a mixed structure of ferrite + pearlite and acicular ferrite is formed, and the strength and toughness are low.
管記号Nは<1>式が0.8以下のためにフェライト+パーライトとアシキュラーフェライトの混合組織となり、強度と靱性が低かった例である。 The pipe symbol N is an example in which since the <1> formula is 0.8 or less, a mixed structure of ferrite + pearlite and acicular ferrite is formed, and the strength and toughness are low.
管記号Oは<1>式が1.0以上のためにベイナイトとアシキュラーフェライトの混合組織となり、靱性が低かった例である。 The pipe symbol O is an example in which the toughness is low because the <1> formula has a mixed structure of bainite and acicular ferrite because the formula is 1.0 or more.
Claims (3)
C:0.04超〜0.08%
Si:0.1〜0.3%
Mn:1.6超〜2.0%
P:0.02%以下
S:0.003%以下
Nb:0.04〜0.08%
V:0.05〜0.1%
Ni:0.1〜0.5%
Cu:0.1〜0.5%
Mo:0.05〜0.20%
Ti:0.01〜0.03%
Al:0.05%以下
N:0.005%以下
であり、かつ、Ni,Cu,Mo含有量が下記<1>式を満足し、残部がFeおよび不可避的不純物よりなる、請求項1に記載の高強度電縫ラインパイプ。
1.0>3Mo+Ni+Cu>0.8 <1> In mass% C: more than 0.04 to 0.08%
Si: 0.1 to 0.3%
Mn: more than 1.6 to 2.0%
P: 0.02% or less S: 0.003% or less Nb: 0.04 to 0.08%
V: 0.05-0.1%
Ni: 0.1 to 0.5%
Cu: 0.1 to 0.5%
Mo: 0.05-0.20%
Ti: 0.01-0.03%
Al: 0.05% or less N: 0.005% or less, and the content of Ni, Cu, and Mo satisfies the following <1> formula, and the balance is made of Fe and inevitable impurities. High strength ERW line pipe as described.
1.0> 3Mo + Ni + Cu> 0.8 <1>
S:0.0020%以下
Ca:0.001〜0.003%
であることを特徴とする請求項2に記載の高強度電縫ラインパイプ。 In mass%,
S: 0.0020% or less Ca: 0.001 to 0.003%
The high-strength ERW line pipe according to claim 2, wherein:
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CN110546289A (en) * | 2017-06-22 | 2019-12-06 | 日本制铁株式会社 | Rolled electric resistance welded steel pipe for line pipe and hot-rolled steel plate |
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