JP5660285B2 - Manufacturing method of welded steel pipe for oil well with excellent pipe expandability and low temperature toughness, and welded steel pipe - Google Patents

Manufacturing method of welded steel pipe for oil well with excellent pipe expandability and low temperature toughness, and welded steel pipe Download PDF

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JP5660285B2
JP5660285B2 JP2010123749A JP2010123749A JP5660285B2 JP 5660285 B2 JP5660285 B2 JP 5660285B2 JP 2010123749 A JP2010123749 A JP 2010123749A JP 2010123749 A JP2010123749 A JP 2010123749A JP 5660285 B2 JP5660285 B2 JP 5660285B2
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俊介 豊田
俊介 豊田
岡部 能知
能知 岡部
木村 光男
光男 木村
松岡 才二
才二 松岡
田中 全人
全人 田中
河端 良和
良和 河端
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JFE Steel Corp
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本発明は、原油あるいは天然ガスの油井、ガス井(以下、これらを総称して単に油井という)内に埋設されて使用される油井用溶接鋼管に係り、とくに拡管性と低温靭性に優れた油井用溶接鋼管の製造方法および溶接鋼管に関する。   The present invention relates to oil well welded steel pipes embedded in crude oil or natural gas oil wells and gas wells (hereinafter simply referred to as oil wells) and used particularly for oil wells excellent in pipe expandability and low temperature toughness. The present invention relates to a welded steel pipe manufacturing method and a welded steel pipe.

地表から地下まで油井管を敷設するには、まず地表から所定の深さまで掘削し、その中にケーシングと呼ばれる鋼管を埋設し壁の崩壊を防止する。その後、ケーシングの先端からさらに地下を掘削してより深い井戸とし、先に埋設したケーシング内を通して新たなケーシングを埋設する。この作業を繰り返して、最終的に油田あるいは天然ガス田に到達する油井管(チュービング)が敷設される。深度の深い井戸を掘削する場合には、直径の異なる多種類のケーシングを必要とする。原油や天然ガスを通す油井管(チュービング)の径は定められているため、深度の深い井戸を掘削する場合には、径方向における掘削面積を広くする必要があるが、この掘削面積を必要最小限にすることが強く要望されている。   In order to lay an oil well pipe from the ground surface to the underground, first, excavation from the ground surface to a predetermined depth is carried out, and a steel pipe called a casing is buried therein to prevent the collapse of the wall. Thereafter, the basement is further excavated from the tip of the casing to form a deeper well, and a new casing is buried through the previously buried casing. By repeating this operation, an oil well pipe (tubing) that finally reaches the oil field or natural gas field is laid. When excavating deep wells, many types of casings with different diameters are required. The diameter of the oil well pipe (tubing) through which crude oil and natural gas are passed is fixed, so when drilling deep wells, it is necessary to increase the drilling area in the radial direction, but this drilling area is the minimum necessary There is a strong demand to limit.

このような要望に対し、例えば特許文献1、特許文献2には、井戸内でケーシング(鋼管)を、押拡げ加工等により拡管する方法が記載されている。特許文献1、特許文献2に記載された技術によれば、井戸内でケーシング(鋼管)を半径方向に膨張させることにより、多段構造になったケーシング毎の直径を小さく抑えることができ、井戸上部のケーシングサイズを小さく抑えて、油井の掘削費を低減することが可能となるとしている。   In response to such a request, for example, Patent Literature 1 and Patent Literature 2 describe a method of expanding a casing (steel pipe) in a well by means of expansion or the like. According to the techniques described in Patent Document 1 and Patent Document 2, the diameter of each casing having a multistage structure can be kept small by expanding the casing (steel pipe) in the radial direction in the well. It is said that it becomes possible to reduce the drilling cost of the oil well by suppressing the casing size of the oil well.

特許文献3には質量%でC:0.05〜0.30%、Si:0.2〜2%、Mn:0.7〜4.0%、P:0.03%以下、S:0.015%以下、N:0.007%以下、O:0.005%以下を含有し、あるいはさらにAl,Cr,Ni,Cu,Nb,V,Ti,Mo,B,Caの1種または2種以上を規定量だけ含有し、残部Feおよび不可避的不純物からなり、相分率5体積%以上の残留γ相を有する、引張強度(TS)600MPa以上の高強度でありながら、拡管率30%超の拡管加工に対し優れた拡管性を示す、拡管性に優れる油井用継目無鋼管が記載されている。   In Patent Document 3, C: 0.05 to 0.30%, Si: 0.2 to 2%, Mn: 0.7 to 4.0%, P: 0.03% or less, S: 0% by mass 0.15% or less, N: 0.007% or less, O: 0.005% or less, or one or two of Al, Cr, Ni, Cu, Nb, V, Ti, Mo, B, and Ca Contains a specified amount of seeds or more, consists of the remainder Fe and inevitable impurities, has a residual γ phase with a phase fraction of 5% by volume or more, and has a high tensile strength (TS) of 600 MPa or more, and a tube expansion rate of 30% An oil well seamless steel pipe having excellent pipe expandability and excellent pipe expandability with respect to super pipe expansion processing is described.

特許文献4には質量%で、C:0.01〜0.3%、Si:0.01〜0.7%、Mn:0.5〜2.0%、Nb:0.005〜0.1%、Ti:0.005〜0.05%、Al:0.002〜0.1%、Ca:0.0005〜0.008%を含有し、P:0.10%以下、S:0.005%以下、O:0.0040%以下に制限し、Si/Mn:0.005〜1.5を満足し、残部がFe及び不可避的不純物からなることを特徴とする拡管性能及び耐食性に優れた拡管油井用電縫鋼管が記載されている。   In Patent Document 4, the mass% is C: 0.01 to 0.3%, Si: 0.01 to 0.7%, Mn: 0.5 to 2.0%, Nb: 0.005 to 0.00. 1%, Ti: 0.005-0.05%, Al: 0.002-0.1%, Ca: 0.0005-0.008%, P: 0.10% or less, S: 0 0.005% or less, O: 0.0040% or less, Si / Mn: 0.005 to 1.5 is satisfied, and the balance is composed of Fe and inevitable impurities. An excellent ERW steel pipe for expanded oil wells is described.

特表平7−507610号公報JP 7-507610 A 国際公開W098/00626号公報International Publication No. W098 / 00626 特許第4367259号公報Japanese Patent No. 4367259 特開2008−202128号公報JP 2008-202128 A

しかし、特許文献3に記載された技術では、ビレットを穿孔圧延して製造される継目無鋼管であるため、肉厚精度が所望の値(±10%)を満たすのが困難である。また、特許文献4に記載された技術では、記載された拡管性能を得るために、電縫鋼管全体に対してAc1変態点からAc3変態点の間への加熱‐冷却熱処理を必要とするため熱処理費用が嵩み、その割には拡管加工可能な拡管率は高々28%以下と低レベルであった。なお、拡管加工可能な拡管率範囲の上限を、以下、限界拡管率という。すなわち、従来の油井用溶接鋼管に関する技術では、肉厚精度が不十分であるか、または、拡管性に優れたものが得られないという課題があった。   However, since the technique described in Patent Document 3 is a seamless steel pipe manufactured by piercing and rolling a billet, it is difficult for the wall thickness accuracy to satisfy a desired value (± 10%). Moreover, in the technique described in Patent Document 4, in order to obtain the described tube expansion performance, the entire ERW steel pipe requires a heating-cooling heat treatment from the Ac1 transformation point to the Ac3 transformation point, so that the heat treatment is performed. Expenses increased, and the expansion rate that allowed tube expansion was low, at most 28% or less. In addition, the upper limit of the expansion rate range that can be expanded is hereinafter referred to as a limit expansion rate. That is, the conventional technique related to the welded steel pipe for oil wells has a problem that the wall thickness accuracy is insufficient or an excellent pipe expandability cannot be obtained.

本発明は、上述の課題を解決し、引張強度が490MPa以上、降伏比(=降伏強度/引張強度)が0.74〜0.92の範囲において、肉厚精度が所望の値(±10%)を満たしながら、優れた拡管性と低温靭性を達成しうる手段を提供することを目的とする。
ここにいう「優れた拡管性」とは、次の円錐拡管試験で求められる限界拡管率が46%以上であることとする。
(円錐拡管試験:)溶接鋼管から外径の2倍長さの鋼管を切り出し、両管端を平行に▽▽▽仕上げ(Ra:1.6a相当仕上げ、日本機械学会編「機械工学便覧」新版第6刷、1993.7.30丸善発行、B1-22頁参照)した後、齧りを防ぐためプレス油を塗布後、頂角60°の円錐をプレス機で鋼管に押込んで管端を押し拡げる。管端に亀裂が生じたところで押込みを止め、除荷した後の押し拡げ側の管端外径Dbを測定し、原管の外径Doから拡管率(=(Db−Do)/Do×100(%))を求める。これを3回繰り返し、得られた3つの拡管率データの平均を限界拡管率とする。
The present invention solves the above-mentioned problems, and in the range where the tensile strength is 490 MPa or more and the yield ratio (= yield strength / tensile strength) is 0.74 to 0.92, the thickness accuracy is a desired value (± 10% It is an object of the present invention to provide means capable of achieving excellent pipe expansion and low temperature toughness while satisfying
Here, “excellent tube expandability” means that the limit tube expansion ratio obtained in the next cone tube expansion test is 46% or more.
(Cone expansion test :) Cut out a steel pipe twice as long as the outer diameter from the welded steel pipe and make both pipe ends parallel ▽ ▽ ▽ Finish (Ra: 1.6a equivalent finish, Japan Society of Mechanical Engineers, "Mechanical Engineering Handbook" new edition No. 6), Maruzen issued on July 30, 1993, see page B1-22), and after applying press oil to prevent warping, the cone with a top angle of 60 ° is pushed into the steel pipe with a press to widen the end of the pipe. When the pipe end is cracked, the indentation is stopped, the pipe end outer diameter Db on the side of the expansion after unloading is measured, and the tube expansion ratio (= (Db−Do) / Do × 100) is calculated from the outer diameter Do of the original pipe. (%)). This is repeated three times, and the average of the obtained three tube expansion rate data is defined as the limit tube expansion rate.

また「優れた低温靭性」とは、次の低温衝撃試験により求められる−20が100J/cm以上であることとする。
(低温衝撃試験:)2mmVノッチシャルピー試験(JIS Z 2242規定に準拠)において、ノッチ深さ方向を管円周方向及び肉厚方向に直交させた試験片(JIS Z 2202の規定に準拠)を用い、−20℃で試験して、衝撃値(試験片ノッチ位置のノッチ深さ方向断面の単位面積1cm当たりの吸収エネルギー)を求め、これを−20とする。
The term "excellent low-temperature toughness", and that V E -20 obtained by the following low temperature impact test is 100 J / cm 2 or more.
(Low-temperature impact test :) In a 2 mm V notch Charpy test (conforming to JIS Z 2242), a test piece (conforming to JIS Z 2202) in which the notch depth direction is orthogonal to the pipe circumferential direction and wall thickness direction is used. The impact value (absorbed energy per unit area 1 cm 2 of the cross section in the notch depth direction at the notch position of the test piece) is obtained by testing at −20 ° C., and this is designated as V E −20 .

本発明者らは上記目的を達成するために、電縫鋼管について造管ままでの限界拡管率と低温靭性に及ぼす熱延素材の組成、製造条件、ミクロ組織の影響を系統的に鋭意研究した。さらに、溶接によって硬化する溶接部についても、所望の拡管性と低温靭性を得るための適正なオンライン熱処理条件、ミクロ組織条件を系統的に鋭意研究した。その結果、特定組成を有する素材スラブを、特定温度・加工条件で熱間圧延し、得られた熱延鋼板を電縫鋼管製造工程により溶接鋼管となし、溶接部に特定温度条件でオンライン熱処理を加えることで優れた拡管性と低温靭性を有する油井用溶接鋼管が得られることを見出した。   In order to achieve the above-mentioned object, the present inventors systematically studied the effects of the composition of the hot-rolled material, the manufacturing conditions, and the microstructure on the limit expansion rate and low-temperature toughness of the ERW steel pipe as it is. . In addition, we have systematically researched appropriate online heat treatment conditions and microstructure conditions to obtain the desired tube expansion and low temperature toughness for welds that harden by welding. As a result, a material slab having a specific composition is hot-rolled at a specific temperature and processing conditions. It was found that a welded steel pipe for oil wells having excellent pipe expandability and low temperature toughness can be obtained by adding.

本発明は上記知見に基づいて完成されたものであり、その要旨構成は以下のとおりである。
(1) 質量%で、C:0.05〜0.25%、Si:0.001〜2.00%、Mn:0.50〜2.50%、Al:0.010〜0.100%を含有し、P:0.019%以下、Sn:0.10%以下、S:0.005%以下、N:0.0049%以下、O:0.0030%以下で、かつ、30*C+100*(P+Sn)+1000*(S+N+O)が16.0%未満であり、残部Fe及び不可避的不純物からなる組成を有する鋼スラブを、1150〜1300℃に加熱して30分以上均熱保持し、全圧下率93.0〜98.0%で熱間圧延を施し、750℃以上で仕上げ圧延を終え、750〜600℃間の冷却時間を4s以上とし、300℃超600℃未満の巻取温度で巻き取って熱延鋼帯となし、該熱延鋼帯をスリットし、連続ロール成形によって円弧状断面とし、該円弧状断面の両端を溶接し、該溶接してなる溶接部のみを750〜1000℃に加熱後500℃以下まで5℃/s以上の冷却速度で冷却することを特徴とする、円錐拡管試験で求められる限界拡管率が46%以上であり、かつ−20℃における2mmVノッチシャルピー試験で求められる衝撃値 −20 が100J/cm 以上である拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。
(2) 質量%で、Cu:0.001〜1.00%、Ni:0.001〜1.00%のうちから選ばれた1種又は2種を含有することを特徴とする(1)に記載の拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。
(3) 質量%で、Cr:0.001〜1.50%、Mo:0.001〜0.49%、Nb:0.0001〜0.14%、V:0.0001〜0.14%、Ti:0.0001〜0.14%、W:0.0001〜0.14%、B:0.0001〜0.0030%、Ca:0.0001〜0.0030%、REM:0.0001〜0.10%うちから選ばれた1種又は2種以上を含有することを特徴とする(1)又は(2)に記載の拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。
(4) (1)〜(3)のいずれか1つにおいて、該溶接してなる溶接部のみを、に替えて、該溶接してなる溶接鋼管全体を、としたことを特徴とする拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。
(5) (1)〜(4)のいずれか1つにおいて、最後の冷却の後に、溶接鋼管全体を200〜650℃の範囲で焼戻し熱処理することを特徴とする拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。
(6) 質量%で、C:0.05〜0.25%、Si:0.001〜2.00%、Mn:0.50〜2.50%、Al:0.010〜0.100%を含有し、P:0.019%以下、Sn:0.10%以下、S:0.005%以下、N:0.0049%以下、O:0.0030%以下で、かつ、30*C+100*(P+Sn)+1000*(S+N+O)が16.0%未満であり、あるいはさらに下記A群及び/又はB群を含有し、残部Fe及び不可避的不純物からなる組成を有し、かつ母材部及び溶接部の微視組織中にCが0.4質量%以上に濃化した第2相を0.1〜12面積%含むことを特徴とする、円錐拡管試験で求められる限界拡管率が46%以上であり、かつ−20℃における2mmVノッチシャルピー試験で求められる衝撃値 −20 が100J/cm 以上である拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管。

A群:質量%で、Cu:0.001〜1.00%、Ni:0.001〜1.00%のうちから選ばれた1種又は2種
B群:質量%で、Cr:0.001〜1.50%、Mo:0.001〜0.49%、Nb:0.0001〜0.14%、V:0.0001〜0.14%、Ti:0.0001〜0.14%、W:0.0001〜0.14%、B:0.0001〜0.0030%、Ca:0.0001〜0.0030%、REM:0.0001〜0.10%のうちから選ばれた1種又は2種以上
The present invention has been completed based on the above findings, and the gist of the present invention is as follows.
(1) By mass%, C: 0.05 to 0.25%, Si: 0.001 to 2.00%, Mn: 0.50 to 2.50%, Al: 0.010 to 0.100% P: 0.019% or less, Sn: 0.10% or less, S: 0.005% or less, N: 0.0049% or less, O: 0.0030% or less, and 30 * C + 100 * (P + Sn) + 1000 * (S + N + O) is less than 16.0%, and a steel slab having a composition composed of the balance Fe and inevitable impurities is heated to 1150 to 1300 ° C. and kept soaked for 30 minutes or more. Hot rolling is performed at a reduction rate of 93.0 to 98.0%, finish rolling is finished at 750 ° C. or higher, cooling time between 750 to 600 ° C. is set to 4 s or longer, and the coiling temperature is higher than 300 ° C. and lower than 600 ° C. Winding and forming a hot-rolled steel strip, slitting the hot-rolled steel strip, forming a continuous roll The arc-shaped cross-section is formed according to the shape, both ends of the arc-shaped cross-section are welded, and only the welded portion formed by welding is heated to 750 to 1000 ° C. and then cooled to 500 ° C. or less at a cooling rate of 5 ° C./s or more. Characteristic tube expandability and low temperature where the critical tube expansion ratio obtained in the conical tube expansion test is 46% or more and the impact value V E- 20 obtained in the 2 mmV notch Charpy test at −20 ° C. is 100 J / cm 2 or more. A method for producing a welded steel pipe for oil wells having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92 excellent in toughness.
(2) By mass%, it contains one or two selected from Cu: 0.001 to 1.00%, Ni: 0.001 to 1.00% (1) A method for producing a welded steel pipe for oil wells having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92 excellent in pipe expandability and low temperature toughness.
(3) By mass%, Cr: 0.001-1.50%, Mo: 0.001-0.49%, Nb: 0.0001-0.14%, V: 0.0001-0.14% , Ti: 0.0001 to 0.14%, W: 0.0001 to 0.14%, B: 0.0001 to 0.0003%, Ca: 0.0001 to 0.0003%, REM: 0.0001 The tensile strength is 490 MPa or more excellent in tube expandability and low-temperature toughness according to (1) or (2), and the yield ratio is 0. A method of manufacturing a welded steel pipe for oil wells of .74 to 0.92.
(4) The expandability according to any one of (1) to (3), wherein only the welded portion formed by welding is replaced with the entire welded steel tube formed by welding. And a method for producing a welded steel pipe for oil wells having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92 excellent in low temperature toughness.
(5) In any one of (1) to (4), after the last cooling, the entire welded steel pipe is tempered in the range of 200 to 650 ° C. and has excellent pipe expandability and low temperature toughness. A method for producing a welded steel pipe for an oil well having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92.
(6) By mass%, C: 0.05 to 0.25%, Si: 0.001 to 2.00%, Mn: 0.50 to 2.50%, Al: 0.010 to 0.100% P: 0.019% or less, Sn: 0.10% or less, S: 0.005 % or less, N: 0.0049% or less, O: 0.0030% or less, and 30 * C + 100 * (P + Sn) + 1000 * (S + N + O) is less than 16.0%, or further contains the following group A and / or group B, and has a composition comprising the balance Fe and inevitable impurities, and the base material part and 46% of the limit expansion rate required in the conical tube expansion test is characterized by including 0.1 to 12 area% of the second phase in which C is concentrated to 0.4% by mass or more in the microstructure of the weld. above, and the and the impact value V obtained by 2mmV notch Charpy test at -20 ° C. -20 is 100 J / cm 2 or more at a pipe expansion and low-temperature toughness excellent tensile strength 490MPa or more, for oil wells welded steel pipe yield ratio from 0.74 to 0.92.
Group A:% by mass, Cu: 0.001 to 1.00%, Ni: 0.001 to 1.00% selected from Group 1 or Group B:% by mass, Cr: 0 0.001 to 1.50%, Mo: 0.001 to 0.49%, Nb: 0.0001 to 0.14%, V: 0.0001 to 0.14%, Ti: 0.0001 to 0.14 %, W: 0.0001-0.14%, B: 0.0001-0.0030%, Ca: 0.0001-0.0030%, REM: 0.0001-0.10% One or more

本発明によれば、肉厚精度が±10%以内で、円錐拡管試験での限界拡管率が46%以上になる優れた拡管性と、−20が100J/cm以上になる優れた低温靭性を有する引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管が得られる。 According to the present invention, the wall thickness accuracy is within ± 10%, the excellent tube expandability is 46% or more in the conical tube expansion test, and the V E- 20 is 100 J / cm 2 or more. An oil well welded steel pipe having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92 having low temperature toughness is obtained.

微視組織中に占める、Cが0.4質量%以上に濃化した第2相の面積率と、限界拡管率、−20、YRの関係を示すグラフMicroscopic occupied in the tissue, the graph showing the second phase area ratio of C is concentrated in the least 0.4 wt%, the limit pipe expansion ratio, V E -20, the relationship YR

まず、本発明において組成を上記のとおり限定した理由について説明する。以下、成分含有量は質量%を単位とし、%と略記する。また、TSは引張強度を、YSは降伏強度を、ELは伸びを、YRは降伏比(=YS/TS)を、それぞれ意味する。
C:0.05〜0.25%
Cは所望の原管強度(TS、YS)を確保させ、かつ母材部並びに溶接部の微視組織中に所望の第2相(Cが0.4%以上に濃化した第2相)を所望の面積率(0.1〜12面積%)だけ形成させ、良好な拡管性を得させる元素である。0.05%未満ではこの、所望の原管強度と第2相を得ることができない。一方、0.25%を超えると鋼管の低温靭性が低下するためこれを上限とする。なお、好ましくは0.06〜0.13%である。
First, the reason why the composition is limited as described above in the present invention will be described. Hereinafter, the component content is abbreviated as% in units of mass%. Also, TS means tensile strength, YS means yield strength, EL means elongation, and YR means yield ratio (= YS / TS).
C: 0.05-0.25%
C ensures the desired original pipe strength (TS, YS), and the desired second phase (second phase in which C is concentrated to 0.4% or more) in the microstructure of the base metal part and the welded part. Is an element that forms a desired area ratio (0.1 to 12 area%) and obtains good tube expansion. If it is less than 0.05%, this desired tube strength and the second phase cannot be obtained. On the other hand, if it exceeds 0.25%, the low temperature toughness of the steel pipe is lowered, so this is the upper limit. In addition, Preferably it is 0.06 to 0.13%.

Si:0.001〜2.00%
Siは熱延工程でのフェライト変態を促進する元素であり、必要な拡管性を確保するための元素である。0.001%未満では拡管性が不足する。一方、2.00%を超える場合は酸化物が残存し、溶接部の低温靭性が劣化する。従ってSiは0.001〜2.00%に限定した。なお、好ましくは0.81〜1.45%である。
Si: 0.001 to 2.00%
Si is an element that promotes ferrite transformation in the hot rolling process, and is an element for ensuring necessary tube expansion. If it is less than 0.001%, the tube expandability is insufficient. On the other hand, when it exceeds 2.00%, oxides remain and the low temperature toughness of the welded portion deteriorates. Therefore, Si was limited to 0.001 to 2.00%. In addition, Preferably it is 0.81-1.45%.

Mn:0.50〜2.50%
Mnは所望の原管強度(引張強度TS,降伏強度YS)を確保させ、かつ母材部並びに溶接部の微視組織中に所望の第2相(Cが0.4%以上に濃化した第2相)を所望の面積率(0.1〜1.2面積%)だけ形成させ、良好な拡管性を得させる元素である。0.50%未満ではこの、所望の原管強度と第2相を得ることができない。一方、2.50%を超えると鋼管の低温靭性が低下するためこれを上限とする。なお、好ましくは0.84〜1.25%である。
Mn: 0.50 to 2.50%
Mn ensures the desired original pipe strength (tensile strength TS, yield strength YS), and the desired second phase (C is concentrated to 0.4% or more) in the microstructure of the base metal part and the welded part. The second phase is an element that forms a desired area ratio (0.1 to 1.2 area%) and obtains good tube expandability. If it is less than 0.50%, the desired original tube strength and the second phase cannot be obtained. On the other hand, if it exceeds 2.50%, the low temperature toughness of the steel pipe is lowered, so this is the upper limit. In addition, Preferably it is 0.84-1.25%.

Al:0.010〜0.100%
Alは製鋼時の脱酸元素であるとともに、熱間圧延工程でのオーステナイト粒の成長を抑制し、結晶粒を微細とし、良好な拡管性を得させる元素である。0.010%未満ではこれらの効果が得られず、一方、0.10%を超えると効果は飽和し、酸化物系介在物の増大により拡管性が低下するために0.10%を上限とする。なお、好ましくは0.030〜0.080%である。
Al: 0.010 to 0.100%
Al is a deoxidizing element at the time of steelmaking, and is an element that suppresses the growth of austenite grains in the hot rolling process, makes the crystal grains fine, and obtains good tube expandability. If the content is less than 0.010%, these effects cannot be obtained. On the other hand, if the content exceeds 0.10%, the effect is saturated. To do. In addition, Preferably it is 0.030-0.080%.

P:0.019%以下
PはMnとの凝固共偏析を介し、低温靭性を低下させるとともに、拡管性を低下させる。0.019%を超えるとこの悪影響が顕著となるため、0.019%を上限とする。なお、好ましくは0.009%以下である。
Sn:0.10%以下
Snは低融点固溶元素として鋼中に存在し、拡管性を劣化させる。0.10%を超えると悪影響が顕著となるため、0.10%を上限とする。なお、好ましくは0.05%以下である。
P: 0.019% or less P lowers the low temperature toughness and lowers the pipe expandability through solidification co-segregation with Mn. If the content exceeds 0.019%, this adverse effect becomes significant, so 0.019% is made the upper limit. In addition, Preferably it is 0.009% or less.
Sn: 0.10% or less Sn is present in the steel as a low melting point solid solution element, and deteriorates the pipe expandability. If it exceeds 0.10%, the adverse effect becomes remarkable, so 0.10% is made the upper limit. In addition, Preferably it is 0.05% or less.

S:0.005%以下
SはMnSなどとして鋼中介在物として存在し、拡管性を低下させる。0.005%を超えるとこの悪影響が顕著となるため、0.005%を上限とする。なお、好ましくは0.003%以下である。
N:0.0049%以下
Nは固溶Nとして残存すると拡管性を低下させる。0.0049%を超えるとこの悪影響が顕著となるため、0.0049%を上限とする。なお、好ましくは0.0040%以下である。
S: 0.005% or less S is present as an inclusion in steel as MnS or the like, and lowers the pipe expandability. If this amount exceeds 0.005%, this adverse effect becomes significant, so 0.005% is made the upper limit. In addition, Preferably it is 0.003% or less.
N: 0.0049% or less When N remains as a solid solution N, tube expandability is reduced. If this amount exceeds 0.0049%, this adverse effect becomes remarkable, so 0.0049% is made the upper limit. In addition, Preferably it is 0.0040% or less.

O:0.0030%以下
Oは酸化物系介在物として存在し、拡管性、低温靭性を低下させる。0.0030%を超えるとこの悪影響が顕著となるため、0.0030%を上限とする。なお、好ましくは0.0020%以下である。
30*C+100*(P+Sn)+1000*(S+N+O):16.0%未満
Cは炭化物や硬質第2相の面積率上昇を通して、PとSはメタルフロー部への偏析を通して、Snは低融点固溶元素として、Nは時効硬化を通して、Oは溶接部の酸化物系介在物として、いずれも拡管性と低温靭性を相乗的に低下させる。所望の拡管性と低温靭性を確保するためには、これら元素の成分含有量範囲を個別に規定するだけでは不十分で、各元素の影響を勘案した30*C+100*(P+Sn)+1000*(S+N+O)値を特定の閾値未満に抑える必要がある。30*C+100*(P+Sn)+1000*(S+N+O)値が16.0%以上となると、拡管性と低温靭性の低下が大きくなるため、16.0%未満とする。なお、好ましくは13.0%未満である。
O: 0.0030% or less O exists as oxide inclusions, and lowers the pipe expandability and low temperature toughness. If this content exceeds 0.0030%, this adverse effect becomes significant, so 0.0030% is made the upper limit. In addition, Preferably it is 0.0020% or less.
30 * C + 100 * (P + Sn) + 1000 * (S + N + O): less than 16.0% C is an increase in the area ratio of carbide and hard second phase, P and S are segregated into the metal flow part, and Sn is a low melting solid solution As an element, N is age-hardened, and O is an oxide inclusion in the welded portion, both of which synergistically lower tube expandability and low temperature toughness. In order to ensure the desired tube expandability and low temperature toughness, it is not sufficient to individually define the component content ranges of these elements, and 30 * C + 100 * (P + Sn) + 1000 * (S + N + O) taking into account the influence of each element ) The value should be kept below a certain threshold. If the value of 30 * C + 100 * (P + Sn) + 1000 * (S + N + O) is 16.0% or more, the decrease in tube expandability and low temperature toughness increases, so the content is made less than 16.0%. In addition, Preferably it is less than 13.0%.

上記の成分が基本組成をなすが、本発明では、この基本組成に加えて、さらに前記A群及び/又はB群を含有できる。
A群:質量%で、Cu:0.001〜1.00%、Ni:0.001〜1.00%のうちから選ばれた1種又は2種
Cu:0.001〜1.00%
Cuは腐食保護皮膜を形成し、これを強固にすることで鋼中への水素の侵入を抑制し、耐硫化物応力腐食割れ特性を向上させるとともに、溶接時に再固溶した鋼中SをCuサルファイドとして捕捉し、溶接部の選択腐食を抑制する効果がある。これら効果は0.001%以上の含有で発現するが、1.00%を超える含有は拡管性を低下させ、また、素材の熱間圧延時にCuが液相となり、熱間割れや、表面疵の要因となるために1.00%を上限とする。なお、好ましくは0.001〜0.049%である。
The above components form a basic composition. In the present invention, in addition to the basic composition, the group A and / or the group B can be further contained.
Group A:% by mass, Cu: 0.001 to 1.00%, Ni: 0.001 to 1.00% selected from 1 type or 2 types Cu: 0.001 to 1.00%
Cu forms a corrosion protection film, and by strengthening this, the penetration of hydrogen into the steel is suppressed, and the resistance to sulfide stress corrosion cracking is improved. Captures as sulfide and has the effect of suppressing selective corrosion of welds. These effects are manifested with a content of 0.001% or more. However, when the content exceeds 1.00%, the pipe expandability is lowered, and when the raw material is hot-rolled, Cu becomes a liquid phase, causing hot cracking and surface defects. Therefore, the upper limit is 1.00%. In addition, Preferably it is 0.001 to 0.049%.

Ni:0.001〜1.00%
NiはCuと同様鋼中への水素の侵入を抑制し、耐硫化物応力腐食割れ特性を向上させる効果がある。さらに、母材部及び溶接部の低温靭性を向上させる効果がある。これらの効果は0.001%以上の含有で発現するが、1.00%を超える含有は拡管性を低下させるために1.00%を上限とする。なお、好ましくは0.001〜0.049%である。
B群:質量%で、Cr:0.001〜1.50%、Mo:0.001〜0.49%、Nb:0.0001〜0.14%、V:0.0001〜0.14%、Ti:0.0001〜0.14%、W:0.0001〜0.14%、B:0.0001〜0.0030%、Ca:0.0001〜0.0030%、REM:0.0001〜0.10%のうちから選ばれた1種又は2種以上
Cr:0.001〜1.50%
Crは耐炭酸ガス腐食性、耐炭酸ガス応力腐食割れ性等の耐食性を向上させる元素である。さらに、熱延或いは溶接後の溶接部熱処理時のオーステナイト相からの冷却過程において、組織の2相分離を促進し、母材部並びに溶接部の微視組織中に所望の第2相(Cが0.4%以上に濃化した第2相)を所望の面積率(0.1〜12面積%)だけ形成させるのに有効な元素である。これらの効果は0.001%以上の含有で発現するが、1.50%を超える含有は、溶接部に酸化物が残存して、拡管性並びに溶接部の低温靭性を低下させるために1.50%を上限とする。なお、好ましくは0.01〜0.49%である。
Ni: 0.001 to 1.00%
Ni, like Cu, has the effect of suppressing the penetration of hydrogen into the steel and improving the resistance to sulfide stress corrosion cracking. Furthermore, there is an effect of improving the low temperature toughness of the base metal part and the welded part. These effects are manifested with a content of 0.001% or more. However, the content exceeding 1.00% has an upper limit of 1.00% in order to reduce tube expandability. In addition, Preferably it is 0.001-0.049%.
Group B:% by mass, Cr: 0.001 to 1.50%, Mo: 0.001 to 0.49%, Nb: 0.0001 to 0.14%, V: 0.0001 to 0.14% , Ti: 0.0001 to 0.14%, W: 0.0001 to 0.14%, B: 0.0001 to 0.0003%, Ca: 0.0001 to 0.0003%, REM: 0.0001 One or more selected from ˜0.10% Cr: 0.001 to 1.50%
Cr is an element that improves corrosion resistance such as carbon dioxide corrosion resistance and carbon dioxide stress corrosion cracking resistance. Furthermore, in the cooling process from the austenite phase during the heat treatment of the welded part after hot rolling or welding, the two-phase separation of the structure is promoted, and the desired second phase (C is contained in the microstructure of the base material part and the welded part). It is an element effective for forming a desired second phase ratio (0.1 to 12 area%) of the second phase concentrated to 0.4% or more. These effects are manifested when the content is 0.001% or more. However, when the content exceeds 1.50%, an oxide remains in the welded portion, so that the pipe expandability and the low temperature toughness of the welded portion are lowered. The upper limit is 50%. In addition, Preferably it is 0.01 to 0.49%.

Mo:0.001〜0.49%
Moは硫化水素が存在する環境下での耐硫化物応力腐食割れ性を向上させる元素であり、さらに、熱延或いは溶接後の溶接部熱処理時のオーステナイト相からの冷却過程において、組織の2相分離を促進し、母材部並びに溶接部の微視組織中に所望の第2相(Cが0.4%以上に濃化した第2相)を所望の面積率(0.1〜12面積%)だけ形成させるのに有効な元素である。これらの効果は0.001%以上の含有で発現するが、0.49%を超えると拡管性を低下させるために0.49%を上限とする。なお、好ましくは0.01〜0.09%である。
Mo: 0.001 to 0.49%
Mo is an element that improves the resistance to sulfide stress corrosion cracking in an environment where hydrogen sulfide is present. Further, in the cooling process from the austenite phase during hot rolling or heat treatment of the welded portion after welding, two phases of the structure are formed. Separation is promoted, and a desired second phase (second phase in which C is concentrated to 0.4% or more) is added to a desired area ratio (0.1 to 12 area) in the microstructure of the base material part and the welded part. %) Is an effective element. These effects are manifested with a content of 0.001% or more, but if it exceeds 0.49%, the upper limit is 0.49% in order to reduce tube expandability. In addition, Preferably it is 0.01 to 0.09%.

Nb:0.0001〜0.14%
Nbは結晶粒の微細化を通して、低温靭性の向上に寄与する。0.0001%未満ではこの効果が得られない。一方、0.14%を超えると拡管性低下が顕著となるため0.14%を上限とする。なお、好ましくは0.022〜0.080%である。
V:0.0001〜0.14%
Vは焼入れ性の向上を通して、母材部並びに溶接部の微視組織中に所望の第2相(Cが0.4%以上に濃化した第2相)を所望の面積率(0.1〜12面積%)だけ形成させるのに有効な元素である。0.0001%未満ではこの効果が得られない。一方、0.14%を超えると拡管性低下が顕著となるため0.14%を上限とする。なお、好ましくは0.011〜0.080%である。
Nb: 0.0001 to 0.14%
Nb contributes to improvement of low temperature toughness through refinement of crystal grains. If it is less than 0.0001%, this effect cannot be obtained. On the other hand, if it exceeds 0.14%, the pipe expandability is significantly reduced, so 0.14% is made the upper limit. In addition, Preferably it is 0.022 to 0.080%.
V: 0.0001 to 0.14%
V improves the hardenability, and converts the desired second phase (second phase in which C is concentrated to 0.4% or more) into a desired area ratio (0.1%) in the microstructure of the base metal part and the welded part. (About 12% by area) is an effective element. If it is less than 0.0001%, this effect cannot be obtained. On the other hand, if it exceeds 0.14%, the pipe expandability is significantly reduced, so 0.14% is made the upper limit. In addition, Preferably it is 0.011-0.080%.

Ti:0.0001〜0.14%
Tiは拡管性に悪影響を及ぼす固溶NをTiNとして固定し、拡管性の向上に有効な元素である。0.0001%未満ではこの効果が得られない。一方、0.14%を超えると析出炭化物による拡管性低下が顕著となるため0.14%を上限とする。なお、好ましくは0.0001〜0.0049%である。
Ti: 0.0001 to 0.14%
Ti is an effective element for improving the tube expandability by fixing solid solution N which adversely affects the tube expandability as TiN. If it is less than 0.0001%, this effect cannot be obtained. On the other hand, if it exceeds 0.14%, the pipe expandability decreases due to the precipitated carbide, so 0.14% is made the upper limit. In addition, Preferably it is 0.0001 to 0.0049%.

W:0.0001〜0.14%
Wは炭化物として析出し、強度確保に有効な元素である。この効果は0.0001%以上の含有で発現するが、0.14%を超える含有では拡管性が低下するために0.14%を上限とする。なお、好ましくは0.0001〜0.06%である。
B:0.0001〜0.0030%
Bは焼入れ性の向上を通して、強度確保に有効な元素である。この効果は0.0001%以上の含有で発現するが、0.0030%を超える含有は拡管性を低下させるために0.0030%を上限とする。なお、好ましくは0.0001〜0.0005%である。
W: 0.0001 to 0.14%
W precipitates as a carbide and is an element effective for securing strength. This effect is manifested at a content of 0.0001% or more. However, if the content exceeds 0.14%, the tube expandability decreases, so 0.14% is made the upper limit. In addition, Preferably it is 0.0001 to 0.06%.
B: 0.0001 to 0.0030%
B is an element effective for securing the strength through improvement of hardenability. This effect is manifested at a content of 0.0001% or more, but a content exceeding 0.0030% lowers the tube expandability, so 0.0030% is made the upper limit. In addition, Preferably it is 0.0001 to 0.0005%.

Ca:0.0001〜0.0030%
Caは展伸したMnSを粒状のCa(Al)S(O)とする所謂形態制御効果があり、特に拡管成形時の溶接部近傍メタルフロー立上がり部での割れを抑制し、拡管性の向上に有効な元素である。この効果は0.0001%以上の含有で発現するが、0.0030%を超える含有では、非金属介在物の増大によってかえって拡管性が低下するために0.0030%を上限とする。なお、好ましくは0.0001〜0.0019%である。
Ca: 0.0001 to 0.0003%
Ca has a so-called form control effect in which expanded MnS is granular Ca (Al) S (O), and particularly suppresses cracking at the rise of the metal flow near the weld during pipe expansion, thereby improving pipe expandability. It is an effective element. This effect is manifested at a content of 0.0001% or more. However, when the content exceeds 0.0030%, the tube expandability is lowered due to an increase in nonmetallic inclusions, so 0.0030% is made the upper limit. In addition, Preferably it is 0.0001 to 0.0019%.

REM:0.0001〜0.10%
REMはCaと同様、展伸したMnSを粒状とする所謂形態制御効果があり、特に拡管成形時の溶接部近傍メタルフロー立上がり部での割れを抑制し、拡管性の向上に有効な元素である。この効果は0.0001%以上の含有で発現するが、0.10%を超える含有では拡管性が低下するために0.10%を上限とする。なお、好ましくは0.01〜0.05%である。
REM: 0.0001 to 0.10%
REM, like Ca, has a so-called form control effect that makes expanded MnS granular, and is an effective element for improving pipe expandability by suppressing cracking at the metal flow rising part in the vicinity of the weld, especially during pipe expansion forming. . This effect is manifested at a content of 0.0001% or more, but if the content exceeds 0.10%, the tube expandability is reduced, so the upper limit is made 0.10%. In addition, Preferably it is 0.01 to 0.05%.

上記した成分以外の残部はFe及び不可避的不純物である。
母材部及び溶接部の微視組織中の、Cが0.4%以上に濃化した第2相:0.1〜12面積%
本発明の溶接鋼管は、溶接部を除き、基本的に熱延鋼帯を管状に成形したままで適正なYR(0.74〜0.92)を有し、かつ、溶接部を含む管において所望の拡管性を有すべく、母材部及び溶接部の微視組織中に、Cが0.4%以上に濃化した第2相を0.1〜12面積%だけ含むものとする。当該第2相は、熱延或いは溶接後の溶接部熱処理時のオーステナイト相からの冷却過程において変態時に周囲の軟質相に可動転位を生起せしめ、成形ままでYRが高くなりすぎなくする効果がある。さらに、冷却過程以降、例えば拡管成形時に変態することにより、拡管成形時の応力を緩和し、拡管性を大きく向上させる効果がある。これらの効果は微視組織中の第2相分率が0.1面積%以上で発現し、一方、12面積%を超えると反対に拡管性が低下するためにこれを上限とする。なお、好ましくは2.0〜10.0面積%である。
The balance other than the above components is Fe and inevitable impurities.
Second phase in which C is concentrated to 0.4% or more in the microstructure of the base metal part and the welded part: 0.1 to 12 area%
The welded steel pipe of the present invention has a suitable YR (0.74 to 0.92) with the hot-rolled steel strip basically formed into a tubular shape except for the welded part, and includes a welded part. In order to have a desired tube expansion property, 0.1 to 12 area% of the second phase in which C is concentrated to 0.4% or more is included in the microstructure of the base material portion and the welded portion. The second phase has the effect of causing movable dislocations in the surrounding soft phase during transformation in the process of cooling from the austenite phase during hot rolling or heat treatment of the welded portion after welding, and preventing YR from becoming too high as it is formed. . Furthermore, after the cooling process, for example, transformation during tube expansion molding has an effect of relieving stress during tube expansion molding and greatly improving tube expansion. These effects are manifested when the second phase fraction in the microscopic tissue is 0.1 area% or more. On the other hand, when the area exceeds 12 area%, the tube expandability is decreased, so this is the upper limit. In addition, Preferably it is 2.0-10.0 area%.

ここで、Cが0.4%以上に濃化した第2相の面積率を求めるにあたっては、次の第2相分率測定方法を用いた。
(第2相分率測定方法:)研磨した円周方向断面領域400μm×400μmを測定面積とし電子ビーム寸法2μm×2μmでEMPA面分析を行い、C濃度(鋼中含有量)が0.4%以上となっているC濃化領域を特定してその合計面積を求め、これを前記測定面積に対する百分率で表して前記第2相の面積率とする。
Here, in determining the area ratio of the second phase in which C was concentrated to 0.4% or more, the following second phase fraction measurement method was used.
(Second phase fraction measurement method) EMPA surface analysis was performed with a polished circumferential cross-sectional area of 400 μm × 400 μm as the measurement area and an electron beam size of 2 μm × 2 μm, and the C concentration (content in steel) was 0.4%. The C-enriched region as described above is specified to determine the total area, and this is expressed as a percentage of the measured area as the area ratio of the second phase.

なお、微視組織の残部は、ポリゴナルフェライト、アシキュラーフェライト、ウィッドマンステッテンフェライト(これらをフェライトと総称する)のいずれか1種又は2種以上である第1相:75面積%以上、及び、カーバイド、微細パーライト、ベイナイトなど炭化物と鉄の混合組織である第3相:0.0〜15.1面積%、で構成される。
図1は、微視組織中に占める、Cが0.4%以上に濃化した第2相の面積率と、限界拡管率、−20、YRの関係を示すグラフであり、同図に示されるように、当該第2相の面積率が0.1〜12面積%の範囲において、限界拡管率:46%以上、−20:100J/cm以上、YR:0.74〜0.92が達成される。
The remainder of the microstructure is the first phase that is any one or more of polygonal ferrite, acicular ferrite, and Widmanstatten ferrite (collectively referred to as ferrite): 75 area% or more, And the 3rd phase which is a mixed structure of carbide and iron such as carbide, fine pearlite, bainite, etc .: 0.0 to 15.1 area%.
Figure 1 is occupied tissue microscopic is a graph showing the second phase area ratio of C is concentrated in the 0.4% or more, the limit pipe expansion ratio, V E -20, the relationship YR, drawing as shown in, the area ratio of the second phase is in the range of 0.1 to 12 area%, the limit pipe expansion ratio: 46% or more, V E -20: 100J / cm 2 or more, YR: 0.74~ 0.92 is achieved.

次に、前述の所望の微視組織を得るための素材鋼スラブの好ましい熱間圧延条件について説明する。
スラブ加熱温度及びスラブ均熱時間:1150〜1300℃、30分以上
熱間圧延工程におけるスラブ加熱条件はオーステナイト粒径を通して、鋼管の低温靭性に、含有元素の固溶分散状態を通して拡管性に影響を及ぼす。スラブ加熱温度が1150〜1300℃、かつスラブ均熱時間が30分以上の場合に、−20:100J/cm以上かつ限界拡管率:46%以上が得られる。スラブ加熱温度が1300℃を超えるとオーステナイト粒径が極端に粗大化し、−20が100J/cmを下回る。一方、スラブ加熱温度が1150℃を下回るか、スラブ均熱時間が30分を下回ると、含有元素の固溶分散状態が不均一となり、拡管成形時の変形が局所に集中し、限界拡管率が46%を下回る。このため、スラブ加熱温度は1150〜1300℃、スラブ均熱時間は30分以上とすることが好ましい。
Next, preferable hot rolling conditions for the raw steel slab for obtaining the desired microstructure described above will be described.
Slab heating temperature and slab soaking time: 1150-1300 ° C, 30 minutes or more Slab heating conditions in the hot rolling process affect the low temperature toughness of the steel pipe through the austenite grain size, and the pipe expandability through the solid solution dispersion state of the contained elements. Effect. Slab heating temperature is 1150 to 1300 ° C., and when the slab soaking time is more than 30 minutes, V E -20: 100J / cm 2 or more and critical expansion ratio: 46% or more is obtained. Austenite grain size when the slab heating temperature exceeds 1300 ° C. is extremely coarse, V E -20 is below 100 J / cm 2. On the other hand, if the slab heating temperature is below 1150 ° C. or the slab soaking time is less than 30 minutes, the solid solution dispersion state of the contained elements becomes non-uniform, deformation at the time of pipe expansion molding is concentrated locally, and the limit pipe expansion rate is Below 46%. For this reason, it is preferable that slab heating temperature shall be 1150-1300 degreeC and slab soaking time shall be 30 minutes or more.

全圧下率:93.0〜98.0%
スラブ厚Hから熱延仕上げ板厚hまでの全圧下率(=(H−h)/H×100(%))は変態前のオーステナイトの粒径を通して、鋼管の低温靭性とYRに影響を及ぼす。全圧下率が93.0〜98.0%の場合に−20は100J/cm以上、YRは0.74〜0.92が得られる。全圧下率が93.0%を下回ると、変態前のオーステナイト粒径が大きくなり、−20が100J/cmを下回る。また、YSが低下し、造管後のYRが0.74を下回る。一方、全圧下率が98.0%を上回るとYRが0.92を上回る。以上から全圧下率は93.0〜98.0%とした。なお、好ましくは95.0〜97.6%である。
Total rolling reduction: 93.0-98.0%
The total reduction ratio (= (H−h) / H × 100 (%)) from the slab thickness H to the hot-rolled finished sheet thickness h affects the low temperature toughness and YR of the steel pipe through the austenite grain size before transformation. . When the total rolling reduction is 93.0 to 98.0%, V E- 20 is 100 J / cm 2 or more, and YR is 0.74 to 0.92. When total reduction ratio is lower than 93.0% austenite grain size before transformation increases, V E -20 is below 100 J / cm 2. Moreover, YS falls and YR after pipe making is less than 0.74. On the other hand, when the total rolling reduction exceeds 98.0%, YR exceeds 0.92. From the above, the total rolling reduction was set to 93.0 to 98.0%. In addition, Preferably it is 95.0 to 97.6%.

仕上げ圧延終了温度:750℃以上
熱間圧延工程における仕上げ圧延終了温度は、鋼管の低温靭性、YR、拡管性に影響を及ぼす。仕上げ圧延終了温度が750℃以上で、−20は100J/cm以上、YRは0.92以下、限界拡管率は46%以上が得られる。仕上げ圧延終了温度が750℃を下回ると、圧延歪みが残存するため−20が100J/cmを下回り、YRが0.92を超え、また表層部に粗大粒が形成されるため、限界拡管率が46%を下回る。ここで、仕上げ圧延終了温度の上限は特に定めないが、表面性状を良好に保つという観点から950℃以下であることが好ましい。さらにまた表面性状確保の観点からは、仕上げ圧延前に150kgf/cm以上の水圧でのデスケーリングを行うことが好ましい。
Finish rolling end temperature: 750 ° C. or higher The finish rolling end temperature in the hot rolling process affects the low temperature toughness, YR, and tube expandability of the steel pipe. In the finish rolling end temperature is 750 ° C. or higher, V E -20 is 100 J / cm 2 or more, YR is 0.92, the critical expansion ratio is more than 46% is obtained. Below the finish rolling end temperature of 750 ° C., since the rolling strain is V E -20 for remaining below the 100 J / cm 2, YR exceeds 0.92, also coarse grains in the surface layer portion is formed, the limit The expansion rate is below 46%. Here, the upper limit of the finish rolling finish temperature is not particularly defined, but is preferably 950 ° C. or less from the viewpoint of maintaining good surface properties. Furthermore, from the viewpoint of securing surface properties, it is preferable to perform descaling at a water pressure of 150 kgf / cm 2 or more before finish rolling.

750〜600℃間の冷却時間:4s以上
熱間圧延終了後、ランナウトでの冷却条件は、フェライトの析出有無/量、2相分離状態に影響を及ぼし、微視組織形成を通して、鋼管の低温靭性、YR、拡管性に影響を及ぼす。鋼材のフェライトノーズ温度域に相当する750〜600℃間において冷却時間を4s以上確保することにより、フェライトが75面積%以上生成され、2相分離が進行し、Cが0.4%以上に濃化した第2相が0.1〜12面積%を占有する微視組織が形成されて、−20は100J/cm以上、YRは0.92以下、限界拡管率は46%以上が得られる。750〜600℃間の冷却時間が4sを下回ると、前記第2相の面積率が12面積%を超え、−20が100J/cmを下回り、YRが0.92を超え、限界拡管率が46%を下回る。なお、好ましくは、750〜600℃間の冷却時間が6s以上である。
Cooling time between 750 and 600 ° C .: 4 s or more After the hot rolling is completed, the runout cooling conditions affect the presence / amount of ferrite precipitation and the state of two-phase separation. Through microstructural formation, the low temperature toughness of the steel pipe , YR, affects tube expandability. By securing a cooling time of 4 s or more between 750 and 600 ° C. corresponding to the ferrite nose temperature range of steel, ferrite is generated by 75 area% or more, two-phase separation proceeds, and C is concentrated to 0.4% or more. phased second phase is formed microstructure occupying 0.1 to 12 area%, V E -20 is 100 J / cm 2 or more, YR is 0.92, the critical expansion ratio is not less than 46% can get. If the cooling time between seven hundred and fifty to six hundred ° C. is below 4s, the area ratio of the second phase exceeds 12 area%, V E -20 is below 100 J / cm 2, YR exceeds 0.92, the limit pipe expansion The rate is below 46%. In addition, Preferably, the cooling time between 750-600 degreeC is 6 s or more.

巻取温度:300℃超600℃未満
熱延ランナウトでの冷却によってオーステナイト/フェライト2相分離した微視組織のうちオーステナイト相は巻取(コイリング)後、300℃超600℃未満の温度で、一部ベイナイト変態し、オーステナイト相へのCの濃化が進み、最終的にCが0.4%以上に濃化した第2相が形成される。巻取温度が300℃以下であると、オーステナイト相へのCの濃化が不十分となり、前記第2相の面積率が0.1面積%を下回り、YRが0.92を超え、限界拡管率が46%を下回る。一方、巻取温度が600℃以上であると、Cがパーライトとして析出してしまい、Cの濃化が進行せず、YRが0.92を超える。以上から、巻取温度は300℃超600℃未満とした。なお、好ましくは350〜550℃である。
Winding temperature: More than 300 ° C. and less than 600 ° C. Of the microstructure that has been separated into two phases of austenite / ferrite by cooling in a hot-rolled runout, the austenite phase is coiled and then at a temperature of more than 300 ° C. and less than 600 ° C. Partial bainite transformation, C concentration in the austenite phase proceeds, and finally a second phase in which C is concentrated to 0.4% or more is formed. When the coiling temperature is 300 ° C. or lower, the concentration of C in the austenite phase is insufficient, the area ratio of the second phase is less than 0.1 area%, the YR exceeds 0.92, and the limit tube expansion The rate is below 46%. On the other hand, when the coiling temperature is 600 ° C. or higher, C precipitates as pearlite, C concentration does not progress, and YR exceeds 0.92. From the above, the coiling temperature was set to be higher than 300 ° C and lower than 600 ° C. In addition, Preferably it is 350-550 degreeC.

次に、好ましい溶接鋼管製造方法について説明する。
上記熱延要件を満たして製造された熱延鋼板は、黒皮まま(=酸化スケール付着のまま)、或いは酸洗やショットブラストによって酸化スケールを除去後、スリットし、連続ロール成形によって円弧状断面とし、該円弧状断面の両端を高周波誘導加熱等によって加熱、溶接(衝合・圧接)する。なお、溶接は大気中で行ってもよいが、溶接部の酸化物等の介在物を減少させる目的で不活性ガスの噴きつけ、或いはシールディング等により酸素濃度を低下させて(例えば100ppm以下)溶接してもよい。また、溶接は、高周波誘導加熱に替えて、抵抗溶接、レーザ溶接、アーク溶接、プラズマ溶接等で、あるいはこれらを組み合わせて行うこともできる。
Next, a preferred welded steel pipe manufacturing method will be described.
The hot-rolled steel sheet manufactured to satisfy the above hot-rolling requirements is either blackened (= with oxidized scale attached), or after removing the oxidized scale by pickling or shot blasting, slitting, and arc-shaped cross section by continuous roll forming Then, both ends of the arc-shaped cross section are heated and welded (abutting / pressure welding) by high frequency induction heating or the like. In addition, although welding may be performed in the atmosphere, the oxygen concentration is reduced (for example, 100 ppm or less) by spraying inert gas or shielding for the purpose of reducing inclusions such as oxides in the welded portion. You may weld. In addition, welding can be performed by resistance welding, laser welding, arc welding, plasma welding, or the like, or a combination thereof, instead of high-frequency induction heating.

溶接部のオンライン熱処理条件:溶接部のみを750〜1000℃に加熱後500℃以下まで5℃/s以上の冷却速度で冷却
溶接後急冷された溶接部は、硬度が高く、−20が100J/cmを下回る。これをオンラインで750〜1000℃に加熱した後、500℃以下まで5℃/s以上の冷却速度で冷却することで、Cが0.4%以上に濃化した第2相を0.1〜12面積%だけ含む微視組織が形成され、−20は100J/cmを確保することができる。加熱温度が1000℃を超えると、粒径が大きくなり低温靭性が低下する。一方、加熱温度が750℃を下回ると硬度低下が不十分で低温靭性が低下する。オンライン加熱後、500℃以下まで5℃/s未満の冷却速度で冷却された溶接部は、硬度が低くTS490MPa以上が確保できない。さらに冷却途中でパーライト組織が生成し、−20が100J/cmを下回る。なお、前記オンライン加熱後500℃以下までの冷却速度は、これが速すぎると前記第2相の面積率が12面積%以下となり難いため、好ましくは5〜300℃/sであり、より好ましくは5〜200℃/sである。
Weld line heat treatment condition: weld only the 750 to 1000 ° C. welds rapidly cooled welding at a cooling rate of 500 ℃ 5 ℃ / s or higher to less after heating, the high hardness, V E -20 is less than 100J / cm 2. After heating this to 750-1000 degreeC on-line, by cooling with the cooling rate of 5 degrees C / s or more to 500 degrees C or less, the 2nd phase which C concentrated to 0.4% or more is 0.1 12 microstructure containing only area% is formed, V E -20 can secure 100 J / cm 2. When heating temperature exceeds 1000 degreeC, a particle size will become large and low temperature toughness will fall. On the other hand, when the heating temperature is lower than 750 ° C., the hardness is not sufficiently lowered and the low temperature toughness is lowered. After online heating, the welded portion cooled at a cooling rate of less than 5 ° C./s to 500 ° C. or less has low hardness and cannot secure TS490 MPa or more. Further cooling the way pearlite generates, V E -20 is below 100 J / cm 2. The cooling rate to 500 ° C. or less after the online heating is preferably 5 to 300 ° C./s, more preferably 5 because the area ratio of the second phase is less than 12% by area if this is too fast. ~ 200 ° C / s.

なお、溶接部のオンライン熱処理に替えて、溶接鋼管全体を750〜1000℃に加熱後、500℃以下まで5℃/s以上、好ましくは5〜300℃/s、より好ましくは5〜200℃/s、の冷却速度で冷却すること(全管熱処理と称す)によっても、拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管が得られる。   In addition, it replaces with online heat processing of a welding part, and after heating the whole welded steel pipe to 750-1000 degreeC, it is 5 degreeC / s or more to 500 degreeC or less, Preferably it is 5-300 degreeC / s, More preferably, it is 5-200 degreeC / s. Cooling at a cooling rate of s (referred to as all-tube heat treatment) can also provide a welded steel pipe for oil wells having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92 excellent in pipe expandability and low temperature toughness.

また、特性の均質安定化のために、前記溶接部のオンライン熱処理の後に、或いは前記全管熱処理の後に、溶接鋼管全体を200〜650℃の範囲で焼戻し熱処理することができる。   Further, for uniform stabilization of the characteristics, the entire welded steel pipe can be tempered in the range of 200 to 650 ° C. after the online heat treatment of the weld or after the whole pipe heat treatment.

(実施例1)
表1に示す組成の鋼スラブを約1240℃に加熱し約60分均熱後抽出し、全圧下率約96.8%の熱間圧延を施し、約840℃で仕上げ圧延を終了し、熱延ランナウトで約700℃を挟んだ温度域で空冷を行い、750〜600℃間の冷却時間8sを確保し、約450℃で巻き取って熱延鋼帯(板厚約8mm)とした。次いでこれらの熱延鋼帯を所定の幅寸法にスリット加工し、連続ロール成形してオープン管となし、該オープン管の円弧状断面の両端を高周波抵抗溶接により電縫溶接して管となし、引き続き連続的にオンラインシーム熱処理を、加熱温度約900℃、200℃までの冷却速度30℃/s(ミスト冷却による)の条件で行い、外径φ203.2mm、肉厚約8mmの溶接鋼管を得た。
Example 1
A steel slab having the composition shown in Table 1 was heated to about 1240 ° C., soaked for about 60 minutes, extracted, subjected to hot rolling with a total rolling reduction of about 96.8%, finished at about 840 ° C., and finished with rolling. Air cooling was performed in a temperature range between about 700 ° C. with a rolled runout, a cooling time of 750 to 600 ° C. was secured for 8 s, and the steel was wound at about 450 ° C. to obtain a hot-rolled steel strip (plate thickness of about 8 mm). Next, slitting these hot-rolled steel strips to a predetermined width dimension, continuous roll forming to make an open pipe, both ends of the arc-shaped cross section of the open pipe are electro-welded by high frequency resistance welding to make a pipe, Continuously, on-line seam heat treatment is performed under the conditions of a heating temperature of about 900 ° C. and a cooling rate of 30 ° C./s (by mist cooling) to 200 ° C. to obtain a welded steel pipe having an outer diameter of φ203.2 mm and a wall thickness of about 8 mm. It was.

これらの溶接鋼管から試験片を採取し、組織観察試験、拡管試験、引張試験、低温靭性試験を行った。
(1)組織観察試験
溶接鋼管の円周方向断面が観察面となる組織観察試験片を母材部及び溶接部よりそれぞれ採取し、研磨、ナイタール腐食して走査型電子顕微鏡(3000倍)で組織を観察、撮像し、画像解析装置を用いて、フェライトの面積率を測定した。さらに、前述の第2相分率測定方法により、Cが0.4%以上に濃化した第2相の面積率を求めた。
(2)引張試験
溶接鋼管のL方向(管長さ方向)が引張方向となるように、ASTMのA−370の規定に準拠して母材部から弧状試験片を切り出し、同規定に準拠して引張試験を実施し、引張特性(TS,YS,EL,YR)を求めた。
(3)拡管試験
前述の円錐拡管試験を実施し、限界拡管率を求めた。
(4)低温靭性試験
前述の低温衝撃試験において、試験片として溶接鋼管の母材部及び溶接部より採取した1/2サイズのものを用いた試験により、−20を求めた。
Test pieces were collected from these welded steel pipes and subjected to a structure observation test, a pipe expansion test, a tensile test, and a low temperature toughness test.
(1) Microstructure observation test Microstructure observation specimens with the circumferential cross-section of the welded steel pipe serving as the observation surface were sampled from the base metal part and the welded part, polished, and subjected to nital corrosion, and then subjected to a microstructure with a scanning electron microscope (3000 times). Were observed and imaged, and the area ratio of ferrite was measured using an image analyzer. Furthermore, the area ratio of the second phase in which C was concentrated to 0.4% or more was determined by the above-described second phase fraction measurement method.
(2) Tensile test An arc-shaped test piece is cut out from the base metal part in accordance with ASTM A-370 so that the L direction (pipe length direction) of the welded steel pipe is the tensile direction. A tensile test was performed to determine tensile properties (TS, YS, EL, YR).
(3) Tube expansion test The conical tube expansion test was carried out to determine the limit tube expansion rate.
(4) In the low-temperature impact test of the low-temperature toughness test described above, the test used was a 1/2 size taken from the base metal and the weld of the welded steel pipe as the test piece was determined V E -20.

得られた結果を表2に示す。同表より、本発明例は、いずれも本発明規定の鋼組成要件及び製造方法要件を満たし、得られた溶接鋼管は本発明規定の第2相面積率要件を満たし、拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の特性を有するものとなっている。
これに対し、比較例は、いずれも本発明規定の鋼組成要件及び製造方法要件の少なくともいずれか1つを満たさず、得られた溶接鋼管は本発明規定の第2相面積率要件を満たさず、拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の特性を有するものとはなっていない。
(実施例2)
表1中の鋼B,Cの組成を有する鋼スラブに表3に示す条件(鋼帯の熱間圧延製造条件)で熱間圧延を施し熱延鋼帯とした。次いでこれらの熱延鋼帯を所定の幅寸法にスリット加工し、連続ロール成形してオープン管となし、該オープン管の円弧状断面の両端を高周波抵抗溶接により電縫溶接して管となし、引き続き連続的にオンラインシーム熱処理を、表3に示す条件(溶接部のオンライン熱処理条件。ここでの冷却:空冷又はミスト冷却)で行い、表3に示す外径、肉厚の溶接鋼管を得た。また、表3に示すとおり、電縫溶接後の管のうちいくつかの管には、オンラインシーム熱処理に替えて全管熱処理を施し、あるいはオンラインシーム熱処理もしくは全管熱処理の後に焼戻し熱処理を施した。
The obtained results are shown in Table 2. From the table, all the inventive examples satisfy the steel composition requirements and manufacturing method requirements stipulated by the present invention, and the obtained welded steel pipes satisfy the second phase area ratio requirements stipulated by the present invention. It has excellent tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92.
On the other hand, none of the comparative examples satisfy at least one of the steel composition requirement and the manufacturing method requirement defined in the present invention, and the obtained welded steel pipe does not satisfy the second phase area ratio requirement defined in the present invention. The tensile strength is not less than 490 MPa and the yield ratio is 0.74 to 0.92, which is excellent in tube expandability and low temperature toughness.
(Example 2)
The steel slab having the composition of steels B and C in Table 1 was hot-rolled under the conditions shown in Table 3 (hot rolling production conditions for the steel strip) to form a hot-rolled steel strip. Next, slitting these hot-rolled steel strips to a predetermined width dimension, continuous roll forming to make an open pipe, both ends of the arc-shaped cross section of the open pipe are electro-welded by high frequency resistance welding to make a pipe, Continuously, on-line seam heat treatment was continuously performed under the conditions shown in Table 3 (on-line heat treatment conditions for the welded portion. Cooling here: air cooling or mist cooling) to obtain a welded steel pipe having an outer diameter and a wall thickness shown in Table 3. . In addition, as shown in Table 3, some of the pipes after ERW welding were subjected to whole pipe heat treatment instead of online seam heat treatment, or subjected to tempering heat treatment after online seam heat treatment or whole pipe heat treatment. .

これらの溶接鋼管から実施例1と同様に試験片を採取し、実施例1と同様に組織観察試験、拡管試験、引張試験、低温靭性試験を行った。
得られた結果を表4に示す。同表より、本発明例は、いずれも本発明規定の鋼組成要件及び製造方法要件を満たし、得られた溶接鋼管は本発明規定の第2相面積率要件を満たし、拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の特性を有するものとなっている。
Test specimens were collected from these welded steel pipes in the same manner as in Example 1, and subjected to a structure observation test, a pipe expansion test, a tensile test, and a low temperature toughness test in the same manner as in Example 1.
Table 4 shows the obtained results. From the table, all the inventive examples satisfy the steel composition requirements and manufacturing method requirements stipulated by the present invention, and the obtained welded steel pipes satisfy the second phase area ratio requirements stipulated by the present invention. It has excellent tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92.

これに対し、比較例は、いずれも本発明規定の鋼組成要件及び製造方法要件の少なくともいずれか1つを満たさず、得られた溶接鋼管は本発明規定の第2相面積率要件を満たさず、拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の特性を有するものとはなっていない。
(実施例3)
実施例3では、実施例2のNo.34においてオープン管から管への溶接を、高周波抵抗溶接による電縫溶接に替えてレーザ溶接、TIG溶接の二通りで実施し、それ以外は同様として溶接鋼管を製造し、これらをそれぞれ表3に示す本発明例No.59、60とし、これらについて、実施例2と同様に試験した。その結果を表4に示す。同表より、実施例3においても、得られた溶接鋼管は、実施例2と同様、本発明規定の第2相面積率要件を満たし、拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の特性を有するものとなっている。
On the other hand, none of the comparative examples satisfy at least one of the steel composition requirement and the manufacturing method requirement defined in the present invention, and the obtained welded steel pipe does not satisfy the second phase area ratio requirement defined in the present invention. The tensile strength is not less than 490 MPa and the yield ratio is 0.74 to 0.92, which is excellent in tube expandability and low temperature toughness.
Example 3
In Example 3, welding from an open pipe to a pipe in No. 34 of Example 2 was carried out in two ways: laser welding and TIG welding instead of electric resistance welding by high-frequency resistance welding. Steel pipes were manufactured, and these were designated as Invention Examples Nos. 59 and 60 shown in Table 3, respectively, and these were tested in the same manner as in Example 2. The results are shown in Table 4. From the same table, also in Example 3, the obtained welded steel pipe, like Example 2, satisfies the second phase area ratio requirement of the present invention, and has a tensile strength of 490 MPa or more, excellent in pipe expandability and low temperature toughness, yield. It has the characteristic of ratio 0.74-0.92.

Claims (6)

質量%で、C:0.05〜0.25%、Si:0.001〜2.00%、Mn:0.50〜2.50%、Al:0.010〜0.100%を含有し、P:0.019%以下、Sn:0.10%以下、S:0.005%以下、N:0.0049%以下、O:0.0030%以下で、かつ、30*C+100*(P+Sn)+1000*(S+N+O)が16.0%未満であり、残部Fe及び不可避的不純物からなる組成を有する鋼スラブを、1150〜1300℃に加熱して30分以上均熱保持し、全圧下率93.0〜98.0%で熱間圧延を施し、750℃以上で仕上げ圧延を終え、750〜600℃間の冷却時間を4s以上とし、300℃超600℃未満の巻取温度で巻き取って熱延鋼帯となし、該熱延鋼帯をスリットし、連続ロール成形によって円弧状断面とし、該円弧状断面の両端を溶接し、該溶接してなる溶接部のみを750〜1000℃に加熱後500℃以下まで5℃/s以上の冷却速度で冷却することを特徴とする、円錐拡管試験で求められる限界拡管率が46%以上であり、かつ−20℃における2mmVノッチシャルピー試験で求められる衝撃値 −20 が100J/cm 以上である拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。 In mass%, C: 0.05 to 0.25%, Si: 0.001 to 2.00%, Mn: 0.50 to 2.50%, Al: 0.010 to 0.100% , P: 0.019% or less, Sn: 0.10% or less, S: 0.005% or less, N: 0.0049% or less, O: 0.0030% or less, and 30 * C + 100 * (P + Sn ) + 1000 * (S + N + O) is less than 16.0%, and the steel slab having the composition of the balance Fe and inevitable impurities is heated to 1150 to 1300 ° C. and kept soaked for 30 minutes or more, and the total reduction ratio is 93 Hot rolling is performed at 0.0 to 98.0%, finish rolling is finished at 750 ° C. or higher, cooling time between 750 to 600 ° C. is set to 4 s or longer, and winding is performed at a winding temperature of more than 300 ° C. and lower than 600 ° C. A hot-rolled steel strip, slitting the hot-rolled steel strip, and continuous roll forming Therefore, the arc-shaped cross section is formed, both ends of the arc-shaped cross section are welded, and only the welded portion formed by the welding is heated to 750 to 1000 ° C. and then cooled to 500 ° C. or less at a cooling rate of 5 ° C./s or more. Expandability and low temperature toughness with a critical tube expansion ratio determined by a conical tube expansion test of 46% or more and an impact value V E -20 calculated by a 2 mmV notch Charpy test at −20 ° C. of 100 J / cm 2 or more . A method for producing a welded steel pipe for an oil well having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92. 質量%で、Cu:0.001〜1.00%、Ni:0.001〜1.00%のうちから選ばれた1種又は2種を含有することを特徴とする請求項1に記載の拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。   It contains 1 type or 2 types chosen from Cu: 0.001-1.00% and Ni: 0.001-1.00% by mass%. A method for producing a welded steel pipe for oil wells having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92 excellent in pipe expandability and low temperature toughness. 質量%で、Cr:0.001〜1.50%、Mo:0.001〜0.49%、Nb:0.0001〜0.14%、V:0.0001〜0.14%、Ti:0.0001〜0.14%、W:0.0001〜0.14%、B:0.0001〜0.0030%、Ca:0.0001〜0.0030%、REM:0.0001〜0.10%うちから選ばれた1種又は2種以上を含有することを特徴とする請求項1又は2に記載の拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。   In mass%, Cr: 0.001-1.50%, Mo: 0.001-0.49%, Nb: 0.0001-0.14%, V: 0.0001-0.14%, Ti: 0.0001-0.14%, W: 0.0001-0.14%, B: 0.0001-0.0030%, Ca: 0.0001-0.0030%, REM: 0.0001-0. The tensile strength of 490 MPa or more excellent in tube-expandability and low-temperature toughness according to claim 1 or 2, characterized by containing at least one selected from 10%. 92. Manufacturing method of welded steel pipe for oil well of 92. 請求項1〜3のいずれか1つにおいて、該溶接してなる溶接部のみを、に替えて、該溶接してなる溶接鋼管全体を、としたことを特徴とする拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。   The excellent weldability and low temperature toughness according to any one of claims 1 to 3, wherein only the welded portion formed by welding is replaced with the entire welded steel pipe formed by welding. A method for producing a welded steel pipe for an oil well having a tensile strength of 490 MPa or more and a yield ratio of 0.74 to 0.92. 請求項1〜4のいずれか1つにおいて、最後の冷却の後に、溶接鋼管全体を200〜650℃の範囲で焼戻し熱処理することを特徴とする拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管の製造方法。   In any one of Claims 1-4, after the last cooling, the tensile strength 490 Mpa or more excellent in the pipe expandability and low-temperature toughness characterized by carrying out the tempering heat processing in the range of 200-650 degreeC of the whole welded steel pipe, A method for producing a welded steel pipe for an oil well having a yield ratio of 0.74 to 0.92. 質量%で、C:0.05〜0.25%、Si:0.001〜2.00%、Mn:0.50〜2.50%、Al:0.010〜0.100%を含有し、P:0.019%以下、Sn:0.10%以下、S:0.005%以下、N:0.0049%以下、O:0.0030%以下で、かつ、30*C+100*(P+Sn)+1000*(S+N+O)が16.0%未満であり、あるいはさらに下記A群及び/又はB群を含有し、残部Fe及び不可避的不純物からなる組成を有し、かつ母材部及び溶接部の微視組織中にCが0.4質量%以上に濃化した第2相を0.1〜12面積%含むことを特徴とする、円錐拡管試験で求められる限界拡管率が46%以上であり、かつ−20℃における2mmVノッチシャルピー試験で求められる衝撃値 −20 が100J/cm 以上である拡管性と低温靭性に優れた引張強度490MPa以上、降伏比0.74〜0.92の油井用溶接鋼管。

A群:質量%で、Cu:0.001〜1.00%、Ni:0.001〜1.00%のうちから選ばれた1種又は2種
B群:質量%で、Cr:0.001〜1.50%、Mo:0.001〜0.49%、Nb:0.0001〜0.14%、V:0.0001〜0.14%、Ti:0.0001〜0.14%、W:0.0001〜0.14%、B:0.0001〜0.0030%、Ca:0.0001〜0.0030%、REM:0.0001〜0.10%のうちから選ばれた1種又は2種以上
In mass%, C: 0.05 to 0.25%, Si: 0.001 to 2.00%, Mn: 0.50 to 2.50%, Al: 0.010 to 0.100% , P: 0.019% or less, Sn: 0.10% or less, S: 0.005 % or less, N: 0.0049% or less, O: 0.0030% or less, and 30 * C + 100 * (P + Sn ) + 1000 * (S + N + O) is less than 16.0%, or further contains the following group A and / or group B, and has a composition comprising the balance Fe and inevitable impurities, and the base material part and the welded part The critical tube expansion ratio obtained by the cone tube expansion test is 46% or more, characterized by containing 0.1 to 12 area% of the second phase in which C is concentrated to 0.4% by mass or more in the microscopic tissue . and impact value V E sought 2mmV notch Charpy test at -20 ° C. 20 100 J / cm 2 or more at a pipe expansion and low-temperature toughness excellent tensile strength 490MPa or more, for oil wells welded steel pipe yield ratio from 0.74 to 0.92.
Group A:% by mass, Cu: 0.001 to 1.00%, Ni: 0.001 to 1.00% selected from Group 1 or Group B:% by mass, Cr: 0 0.001 to 1.50%, Mo: 0.001 to 0.49%, Nb: 0.0001 to 0.14%, V: 0.0001 to 0.14%, Ti: 0.0001 to 0.14 %, W: 0.0001-0.14%, B: 0.0001-0.0030%, Ca: 0.0001-0.0030%, REM: 0.0001-0.10% One or more
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