JP4499949B2 - Low alloy steel and line pipe excellent in carbon dioxide corrosion resistance and weld toughness, and method for producing the same - Google Patents
Low alloy steel and line pipe excellent in carbon dioxide corrosion resistance and weld toughness, and method for producing the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、エネルギー分野で使用されるガス・石油等の輸送用のラインパイプに関し、特に、炭酸ガスを含有するガス・石油等の環境下で使用する際に、良好な耐炭酸ガス腐食性及び溶接部靭性を確保できる低合金鋼及びこの低合金鋼を用いて、低合金ラインパイプ及びそのラインパイプの製造方法に関するものである。
【０００２】
【従来の技術】
石油・ガス等の産出・輸送用の油井管やラインパイプ等では、通常、炭素鋼、低合金鋼の材料が用いられている。しかし、炭酸ガスを多く含む石油・ガス等では、通常の中性湿潤環境下での腐食や大気腐食に比べて腐食速度が非常に速くなるため、このような炭酸ガス腐食性の高い石油・ガスの産出・輸送用の油井管やラインパイプ等に対しては、油に腐食抑制剤などを添加したり、材料として耐炭酸ガス腐食性に優れた１３％Ｃｒ鋼などのステンレス鋼材が用いられてきた。しかしながら、油への腐食抑制剤の使用は、環境保全の点から好ましくなく、ラインパイプ等へのステンレス鋼の適用は素材費が高く、使用期間が限られていたり、その腐食条件が余り過酷ではない環境への適用には、費用対効果の点でオーバースペックとなる。
【０００３】
これらに対し、特開昭５６−９３８５６号公報には、炭酸ガスによる全面腐食とともに溶接部の局部腐食を向上させるためにＣｒを３〜１２％含有し、Ｃを０．１％以下に規制したラインパイプ用鋼が開示されている。しかしながら、この公報に記載の発明は、溶接部の靭性が低く、Ｃを０．０１％以下に低減した発明鋼を用いた場合の溶接部靭性は、０℃でのＶノッチシャルピー吸収エネルギーで１６kg／mm2 以下（約１６０Ｊ以下）という低い性能に留まっている。
【０００４】
従って、炭酸ガスを多く含む石油・ガス等の炭酸ガス腐食性環境で使用される素材として、耐炭酸ガス腐食性とともに溶接部の低温靭性に優れ、かつ低廉な低合金鋼及びそれを用いた低合金ラインパイプの開発が望まれていた。
【０００５】
【発明が解決しようとする課題】
本発明は、エネルギー分野で使用され、特に炭酸ガスを含有するガス・石油等の産出・輸送用の油井管やラインパイプ、あるいはプラント用の素材として適用した際に良好な耐炭酸ガス腐食性が得られるとともに溶接部の靭性が良好である低合金鋼及びそれを用いた低合金ラインパイプならびにこのラインパイプの製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、耐炭酸ガス腐食性を向上させるためにＣｒを適量含有するとともに、溶接部の靭性を向上させるためにＣ及びＳｉの含有量を抑制し、さらにＣ量とＭｎ量或いはＣ量、Ｍｎ量及びＭｏ量を特定の式によりバランスしてそれぞれの含有量を規制した低合金鋼およびそれを用いた低合金ラインパイプならびにそのラインパイプの製造方法であり、その要旨は以下の通りである。
【０００７】
（１）化学成分として、質量％で、Ｃ：０．００３５〜０．０２％、Ｃｒ：３．０を超え〜５．０％未満、Ｓｉ：０．１％未満、Ｍｎ：０．６〜２．０％、Ａｌ：０．００１〜０．２０％以下、Ｎ：０．０１５％以下、Ｔｉ：０．００１〜０．２％、Ｎｂ：０．０１〜０．５％を含有し、かつそのＭｎ量〔Ｔ．Ｍｎ〕、Ｃ量〔Ｔ．Ｃ〕が、〔Ｔ．Ｍｎ〕×〔Ｔ．Ｃ〕：０．００７以上、０．０３以下とし、残部鉄及び不可避不純物からなる耐炭酸ガス腐食性及び溶接部靭性に優れた低合金鋼。
【０００８】
（２）質量％で、さらに、Ｃｕ，Ｎｉの１種あるいは２種以上をそれぞれ０．０１％以上１％以下含有することを特徴とする上記（１）記載の耐炭酸ガス腐食性及び溶接部靭性に優れた低合金鋼。
【０００９】
（３）質量％で、さらに、Ｍｏ：０．０１％以上１％以下含有し、Ｍｏ量〔Ｔ．Ｍｏ〕をＭｎ量〔Ｔ．Ｍｎ〕、Ｃ量〔Ｔ．Ｃ〕と表示した場合に、（〔Ｔ．Ｍｎ〕＋〔Ｔ．Ｍｏ〕）×〔Ｔ．Ｃ〕：０．００７以上、０．０３以下の範囲で、含有することを特徴とする上記（１）または（２）記載の耐炭酸ガス腐食性及び溶接部靭性に優れた低合金鋼。
【００１０】
（４）上記（１）〜（３）の何れかに記載の低合金鋼から製造されたことを特徴とする耐炭酸ガス腐食性及び溶接部靭性に優れた低合金鋼ラインパイプ。
（５）上記（４）記載の低合金鋼ラインパイプの製造において、鋼片を下記の工程で順次鋼管として製造することを特徴とする耐炭酸ガス腐食性及び溶接部靭性に優れた低合金鋼電縫ラインパイプの製造方法。
【００１１】
１）鋼片を１０５０℃〜１３００℃の温度に加熱した後に、熱間圧延し、引続き９５０℃以下、Ａｒ3 変態点以上の温度域で圧下率５０％以上で熱間圧延を終了し、次いで２０℃／ｓ以上の冷却速度で５００℃以下まで冷却した後にホットコイルとして巻き取る工程。
２）上記ホットコイルを所定の幅の鋼帯に切断した後、連続的に円筒状に成形しつつ鋼帯両端を電気抵抗溶接して電縫鋼管として造管する工程。
【００１２】
【発明の実施の形態】
以下に、本発明鋼の成分の限定理由について説明する。なお、以下に示す％は、質量％である。
Ｃ：Ｃは鋼の強度向上のために有効な元素であるが、本発明では、Ｃ含有量が増すと溶接部の低温靭性や炭酸ガス耐食性が低下する。特に、Ｃ含有量が０．０２％を超えると鋼材の焼き戻し過程で粒界に多量の炭化物が析出して溶接部の低温靭性が劣化し、また炭酸ガス耐食性も低下するため、Ｃ含有量の上限を０．０２％とする。またＭｎ量〔Ｔ．Ｍｎ〕との関係で、発明者らはＣ量を低減させた時に、それに応じてある一定量以上のＭｎを含有させると良好な溶接部の低温靭性を得られることを見出しており、最低Ｃ量はＭｎ量に応じて決められるが、Ｍｎ自体の添加量にも靭性劣化のために制限があるため、Ｃ量の下限を０．００３５％とした。
【００１３】
Ｃｒ：Ｃｒは炭酸ガス腐食を抑制させるために有効な元素であり、特に、本発明が対象とする腐食環境である、温度８０℃、圧力０．１MPa 以上の条件において、十分な耐炭酸ガス腐食性を得るには、Ｃｒ含有量を３％以上とする必要がある。一方、Ｃｒ含有量が５％以上では、特に酸素の混入した場合に局部腐食発生の恐れがある。
【００１４】
Ｓｉ：Ｓｉは、ＡｌやＴｉと同じ脱酸作用を有する元素であり少量であれば添加しても良いが、特に溶接部の低温靭性向上を図った本発明鋼では、Ｓｉ含有量が０．１％を超えると溶接部の低温靭性向上に悪影響を及ぼすため、その含有量の上限を０．１％とする。
Ｍｎ：Ｍｎは低温靭性を向上させる作用を有する元素であり、適切な量を添加する必要がある。特に溶接部の低温靭性向上を図った本発明鋼では、その効果を十分得るために、Ｍｎ含有量を最低でも０．６％以上とする必要があるが、一方、その含有量が２％を越えると逆に靭性が低下する。従って、Ｍｎの含有量は０．６〜２％とする。さらにその効果は、Ｃ量と相関があることを本発明者らは見出し、Ｃ量が低い場合にはＭｎ量を高めに、Ｃ量が高い場合にはＭｎ量を低めにすることでより良好な溶接部低温靭性を得られることから、０．００７≦〔Ｔ．Ｍｎ〕×〔Ｔ．Ｃ〕≦０．０３の式で示すように、Ｃ量〔Ｔ．Ｃ〕とＭｎ量〔Ｔ．Ｍｎ〕を質量％で表した数の乗数を０．００７以上、０．０３以下に制限することとする。
【００１５】
図１は、良好な溶接部低温靭性を得るための３％Ｃｒ鋼をベースにＣ含有量とＭｎ含有量との関係を示したものである。評価試験は、２．６kJ／mmの入熱量でＭＩＧ溶接を実施後、ノッチの中央が溶融ラインとなるようにとった２mmV ノッチシャルピー試験片を採取しシャルピー衝撃試験を行った。−２０℃のシャルピー衝撃試験での吸収エネルギーが３０Ｊ以上を低温靭性が良好と見なし○で示し、３０Ｊ未満の吸収エネルギーのものを×で示した。矩形の領域が発明鋼の基本的な成分範囲で、その中でさらにふたつの曲線により挟まれた領域が本発明鋼の正確な成分範囲である。矩形外の成分では靭性が不良で、矩形内でも曲線領域外ではやはり靭性不良となるが、本発明成分領域では不良な靭性を示した。
【００１６】
さらに本発明においては耐食性あるいは溶接部靭性を向上させるために以下の成分を含有することが出来る。
Ａｌ：Ａｌは、ＳｉやＴｉと同様に脱酸作用を有する元素であり、その効果を十分得るためには、Ａｌ含有量を０．００１％以上とする必要があり、一方、その含有量が０．２％を超えると、鋼の清浄度を下げ低温靭性劣化の原因となる。従って、Ａｌを添加する場合の含有量は、０．００１％〜０．２％とする。
【００１７】
Ｎ：Ｎは不可避的不純物として鋼中に残存する元素である。低温靭性の向上のためには、低い方が好ましく、特にＮ含有量が０．０１５％を超えると低温靭性が著しく劣化するため、その含有量の上限を０．０１５％とした。
Ｔｉ，Ｎｂ：ＴｉおよびＮｂは母材の強度を向上するために有効であるとともに、溶接熱影響部において微細な（Ｔｉ，Ｎｂ）炭化物を形成することにより、オーステナイト粒の成長を抑制し溶接部靭性を高めるために有効な元素である。これらの効果を十分に得るためには、Ｔｉ含有量の下限を０．００１％とし、かつＮｂ含有量の下限を０．０１％とする必要があり、一方、Ｔｉ含有量で０．２％を超え、Ｎｂ含有量で０．５％を超えるような過剰な添加は靭性を劣化させる。従って、ＴｉおよびＮｂは、Ｔｉ含有量を０．００１〜０．２％とし、Ｎｂ含有量を０．０１〜０．５％の範囲とする。
【００１８】
さらに、Ｃｕ，Ｎｉ，Ｍｏの１種あるいは２種以上を１％以下含有させることによりＣｒ添加により安定化した耐食性皮膜の安定性をさらに増すことが出来る。これらの元素は単独添加した場合と複合添加した場合の差はないので、必要な耐食性に応じて１種あるいは２種以上添加することが出来る。ただし、いずれも０．０１％以下ではその効果がないので、最低量を０．０１％とした。また、Ｍｏについては、Ｍｎと同様にＣ量と相関して溶接熱影響部の低温靭性に影響を与えるため、添加する場合にはＣ量及びＭｎ量に応じて、
（〔Ｔ．Ｍｎ〕＋〔Ｔ．Ｍｏ〕）×〔Ｔ．Ｃ〕：０．００７以上、０．０３以下となるように制限する。
【００１９】
以上の本発明鋼は、制御圧延または焼き入れ焼き戻しなどの熱処理により金属組織を調整して必要な強度・低温靭性バランスを得ることが可能である。
また、以上の本発明鋼を用いて鋼管を製造する方法は、特に限定する必要はなく、シームレス圧延による造管方法、鋼板を成型後、溶接により造管する方法等の何れの方法も用いることができる。これらの方法によって製造された鋼管は、耐炭酸ガス腐食性に優れるとともにガス溶接における溶接部靭性に優れるという特長が得られるが、さらにシーム溶接部を有する鋼管ではそのシーム溶接部靭性にも優れるという効果が得られる。この時のシーム溶接には電縫溶接・レーザービーム溶接の他、比較的大入熱でのサブマージアーク溶接も適用可能である。
【００２０】
ただし、本発明鋼の目的では低廉な材料が求められるので、これらの内でも特に、以下に述べるような、制御圧延を施し、電縫管として製造したものが最も発明の効果が発揮できる。
その制御圧延−電縫管製造方法とは、以下に示す工程を順次取るものである。
１）鋼片を１０５０℃〜１３００℃の温度に加熱した後に、熱間圧延し、引続き９５０℃以下、Ａｒ3 変態点以上の温度域で圧下率５０％以上で熱間圧延を終了し、その後２０℃／ｓ以上の冷却速度で５００℃以下まで冷却した後にホットコイルとして巻き取る工程。
【００２１】
２）上記ホットコイルを所定の幅の鋼帯に切断した後、連続的に円筒状に成形しつつ鋼帯両端を電気抵抗溶接して電縫鋼管として造管する工程。
上記の耐炭酸ガス腐食性と強度・低温靭性に優れた本発明鋼は、耐炭酸ガス腐食性を要求される様々な用途に使用可能である。特に、耐炭酸ガス腐食性とともに溶接部の低温靭性が要求されるラインパイプあるいはフローラインとして使用され、従来材に比較して廉価な材料で寿命を向上できるという顕著な効果が得られる。
【００２２】
【実施例】
表１に本発明鋼および比較鋼の化学組成とともに、耐食性試験及び溶接部低温靭性の試験結果を示す。
なお、耐食性試験は、温度８０℃、炭酸ガス圧力０．４MPa で、塩素濃度５％の地層水模擬溶液中における２週間の浸漬試験を実施した。１）として溶存酸素濃度が１０ppb 以下に脱気し、２）として溶存酸素濃度を１００ppb として実験を行った。
【００２３】
表１に示す耐炭酸ガス腐食性の評価結果は、Ｃｒ含有量０．０１％以下の炭素鋼の腐食量を１として、腐食量が０．２以下のものを◎、腐食量が０．５以下のものを○とした。耐食性が良好でも局部腐食の生じたものは黒丸で示した。
また、溶接部の低温靭性の評価試験は、２．６kJ／mmの入熱量でＭＩＧ溶接を実施後、ノッチの中央が溶融ラインとなるようにとった２mmV ノッチシャルピー試験片を採取しシャルピー衝撃試験を行った。表１の溶接部の低温靭性の評価結果は、−２０℃のシャルピー衝撃試験での吸収エネルギーを測定した結果、吸収エネルギー値が２００Ｊ以上のものを低温靭性が非常に優れたものとし◎で示し、吸収エネルギーが３０Ｊ未満のものを低温靭性が劣っているものと見なし×で示し、その中間を○で示した。
【００２４】
番号１〜１８の鋼は化学成分が本発明で規定した範囲にある本発明鋼であり、番号１９〜２３番の鋼は、化学成分が本発明で規定した範囲外である比較鋼である。
本発明鋼はいずれも良好な耐食性を示し、且つ、溶接熱影響部の低温靭性が良好であった。
【００２５】
一方、比較鋼は、番号１９〜２２においては全て溶接熱影響部の低温靭性が不十分であり、番号２３においては溶接熱影響部の低温靭性は良好だが、耐食性が不十分で、本発明鋼の優位性が明らかである。
さらに、表１の番号７の化学成分の厚み１５０mmの鋼片を１２５０℃に加熱し、１１００℃の温度で１６mmまで熱延し、そのまま９００℃になるまで放冷してさらに８mm厚まで圧延し、直ちに３０℃／秒で５００℃まで水冷し、ホットコイルとして巻き取った。このホットコイルを冷間で成形後、高周波溶接により電縫溶接管とし、ＡＰＩ規格におけるＸ６５グレードのラインパイプを製造した。このラインパイプをガース溶接し、その溶接線近傍からシャルピー試験片を採取して溶接熱影響部の低温靭性を測定した結果、溶接線から何れの位置においても、−２０℃の吸収エネルギーで２００Ｊ以上という非常に高い値を示し、溶接熱影響部の低温靭性の非常に高いラインパイプを製造することが出来た。
【００２６】
【表１】
【発明の効果】
本発明により、耐炭酸ガス腐食性に優れ、かつ強度・低温靭性のバランスにも良好で、溶接部の低温靭性も良好な低合金鋼が得られ、効率的なエネルギー産業の機器装置設計に寄与するところ大である。
【図面の簡単な説明】
【図１】３％Ｃｒ鋼におけるＣ含有量とＭｎ含有量の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a line pipe for transportation of gas, petroleum, etc. used in the energy field, and in particular, when used in an environment of carbon dioxide-containing gas, petroleum, etc., has good carbon dioxide gas corrosion resistance and The present invention relates to a low alloy steel that can secure weld zone toughness, and a low alloy line pipe and a method for producing the line pipe using the low alloy steel.
[0002]
[Prior art]
Carbon oil and low alloy steel materials are usually used in oil well pipes and line pipes for producing and transporting oil and gas. However, oil and gas containing a large amount of carbon dioxide gas has a much faster corrosion rate than corrosion under normal neutral and humid environments and atmospheric corrosion. For oil well pipes and line pipes for production / transportation of oil, stainless steel materials such as 13% Cr steel with excellent corrosion resistance to carbon dioxide gas have been used as materials, and corrosion inhibitors have been added to the oil. It was. However, the use of corrosion inhibitors in oil is not desirable from the viewpoint of environmental protection, and the application of stainless steel to line pipes is expensive, and the usage period is limited or the corrosion conditions are not so severe. It is over-spec in terms of cost-effectiveness for application to a new environment.
[0003]
On the other hand, Japanese Patent Application Laid-Open No. 56-93856 contains 3 to 12% of Cr and restricts C to 0.1% or less in order to improve the local corrosion of the welded portion as well as the overall corrosion by carbon dioxide gas. Steel for line pipes is disclosed. However, according to the invention described in this publication, the toughness of the welded portion is low, and the toughness of the welded portion using the invention steel with C reduced to 0.01% or less is 16 kg in terms of V notch Charpy absorbed energy at 0 ° C. / Mm 2 or less (about 160 J or less).
[0004]
Therefore, as a material used in a carbon dioxide corrosive environment such as oil and gas containing a large amount of carbon dioxide, low-alloy steels that are excellent in low temperature toughness of welded parts as well as carbon dioxide corrosive resistance and low in cost. The development of an alloy line pipe has been desired.
[0005]
[Problems to be solved by the invention]
INDUSTRIAL APPLICABILITY The present invention is used in the energy field, and particularly has good carbon dioxide gas corrosion resistance when applied as oil well pipes and line pipes for production and transportation of carbon-containing gas and oil, etc., or plant materials. It is an object of the present invention to provide a low alloy steel which is obtained and has a good toughness of a welded portion, a low alloy line pipe using the same, and a method for producing the line pipe.
[0006]
[Means for Solving the Problems]
The present invention contains an appropriate amount of Cr in order to improve the carbon dioxide corrosion resistance, suppresses the contents of C and Si in order to improve the toughness of the welded portion, and further, the amount of C and Mn or C, A low alloy steel in which the contents of Mn and Mo are balanced by a specific formula and the respective contents are regulated, a low alloy line pipe using the steel, and a method for manufacturing the line pipe, the summary of which is as follows .
[0007]
(1) As chemical components, in mass%, C: 0.0035 to 0.02%, Cr: more than 3.0 to less than 5.0%, Si: less than 0.1%, Mn: 0.6 to 2.0% , Al: 0.001 to 0.20% or less, N: 0.015% or less, Ti: 0.001 to 0.2%, Nb: 0.01 to 0.5% , And the amount of Mn [T. Mn], C amount [T. C] [T. Mn] × [T. C]: Low alloy steel with 0.007 or more and 0.03 or less and excellent in carbon dioxide gas corrosion resistance and weld zone toughness composed of remaining iron and inevitable impurities.
[0008]
(2) in mass%, further, Cu, 1 kind or above characterized by containing two or more than 1% 0.01%, respectively (1) Symbol placement耐炭acid gas corrosion resistance and the Ni Low alloy steel with excellent weld toughness.
[0009]
( 3 )% by mass, Mo: 0.01% or more and 1% or less, and Mo content [T. Mo] is changed to Mn content [T. Mn], C amount [T. C], ([T.Mn] + [T.Mo]) × [T. C]: A low alloy steel excellent in carbon dioxide gas corrosion resistance and weld toughness as described in (1) or (2) above, which is contained in the range of 0.007 or more and 0.03 or less.
[0010]
( 4 ) A low alloy steel line pipe excellent in carbon dioxide corrosion resistance and weld toughness, characterized by being produced from the low alloy steel according to any one of (1) to ( 3 ) above.
( 5 ) Low alloy steel excellent in carbon dioxide gas corrosion resistance and weld toughness, wherein steel slabs are sequentially manufactured as steel pipes in the following steps in the production of the low alloy steel line pipe described in ( 4 ) above A method for manufacturing electric seam line pipes.
[0011]
1) The steel slab was heated to a temperature of 1050 ° C. to 1300 ° C., and then hot-rolled, and subsequently the hot rolling was finished at a temperature range of 950 ° C. or lower and the Ar 3 transformation point or higher at a reduction rate of 50% or higher. A step of winding as a hot coil after cooling to 500 ° C. or lower at a cooling rate of 20 ° C./s or higher.
2) A step of cutting the hot coil into a steel strip having a predetermined width, and then forming both ends of the steel strip as an electric resistance steel pipe by electric resistance welding while continuously forming a cylindrical shape.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Below, the reason for limitation of the component of this invention steel is demonstrated. In addition,% shown below is the mass%.
C: C is an effective element for improving the strength of steel. However, in the present invention, when the C content increases, the low temperature toughness and carbon dioxide corrosion resistance of the welded portion decrease. In particular, if the C content exceeds 0.02%, a large amount of carbide precipitates at the grain boundaries during the tempering process of the steel material, so that the low temperature toughness of the welded portion deteriorates and the corrosion resistance of carbon dioxide gas also decreases. Is set to 0.02%. Further, the amount of Mn [T. In relation to Mn], the inventors have found that when the amount of C is reduced, if a certain amount or more of Mn is contained accordingly, good low temperature toughness of the weld can be obtained. Although the amount is determined according to the amount of Mn, the amount of Mn itself is limited due to toughness deterioration, so the lower limit of the amount of C is set to 0.0035%.
[0013]
Cr: Cr is an element effective for suppressing carbon dioxide corrosion, and particularly, sufficient corrosion gas corrosion resistance in the corrosive environment targeted by the present invention, at a temperature of 80 ° C. and a pressure of 0.1 MPa or more. In order to obtain the properties, the Cr content needs to be 3% or more. On the other hand, when the Cr content is 5% or more, local corrosion may occur particularly when oxygen is mixed.
[0014]
Si: Si is an element having the same deoxidizing action as Al and Ti, and may be added in a small amount. However, in the steel of the present invention which is intended to improve the low temperature toughness of the welded portion, the Si content is preferably 0.00. If it exceeds 1%, the low temperature toughness of the weld zone will be adversely affected, so the upper limit of its content is made 0.1%.
Mn: Mn is an element having an effect of improving low temperature toughness, and an appropriate amount needs to be added. In particular, in the steel according to the present invention which aims at improving the low temperature toughness of the welded portion, in order to sufficiently obtain the effect, the Mn content needs to be at least 0.6%. On the contrary, the toughness decreases. Therefore, the Mn content is set to 0.6 to 2%. Furthermore, the present inventors have found that the effect is correlated with the C amount, and when the C amount is low, the Mn amount is increased, and when the C amount is high, the Mn amount is decreased. Therefore, 0.007 ≦ [T. Mn] × [T. C] ≦ 0.03, the amount of C [T. C] and the amount of Mn [T. The multiplier of the number of Mn] expressed in mass% is limited to 0.007 or more and 0.03 or less.
[0015]
FIG. 1 shows the relationship between the C content and the Mn content based on 3% Cr steel for obtaining good weld low temperature toughness. In the evaluation test, after performing MIG welding with a heat input of 2.6 kJ / mm, a 2 mm V notch Charpy test piece was taken so that the center of the notch was a melting line, and a Charpy impact test was performed. The absorption energy in the Charpy impact test at −20 ° C. was 30 J or more and the low temperature toughness was considered good, and indicated by ○, and the absorption energy less than 30 J was indicated by ×. The rectangular region is the basic component range of the invention steel, and the region sandwiched by two curves is the exact component range of the invention steel. The toughness is poor in the component outside the rectangle, and the toughness is also inferior in the rectangle outside the curved region, but the toughness is poor in the component region of the present invention.
[0016]
Furthermore, in this invention, in order to improve corrosion resistance or welded part toughness, the following components can be contained.
Al: Al is an element having a deoxidizing action similar to Si and Ti, and in order to obtain the effect sufficiently, the Al content needs to be 0.001% or more, while the content is If it exceeds 0.2%, the cleanliness of the steel is lowered and low temperature toughness is deteriorated. Therefore, the content when Al is added is set to 0.001% to 0.2%.
[0017]
N: N is an element remaining in steel as an inevitable impurity. In order to improve the low temperature toughness, the lower one is preferable. Particularly, when the N content exceeds 0.015%, the low temperature toughness deteriorates remarkably, so the upper limit of the content is set to 0.015%.
Ti, Nb: Ti and Nb are effective for improving the strength of the base metal, and by forming fine (Ti, Nb) carbides in the weld heat affected zone, the growth of austenite grains is suppressed and the weld zone It is an effective element for increasing toughness. In order to sufficiently obtain these effects, the lower limit of the Ti content needs to be 0.001% and the lower limit of the Nb content needs to be 0.01%, while the Ti content is 0.2%. Excessive addition exceeding 0.5% and Nb content exceeding 0.5% deteriorates toughness. Therefore, Ti and Nb have a Ti content of 0.001 to 0.2% and an Nb content of 0.01 to 0.5%.
[0018]
Furthermore, the stability of the corrosion-resistant film stabilized by addition of Cr can be further increased by containing 1% or less of one or more of Cu, Ni, and Mo. Since there is no difference between the case where these elements are added alone and the case where they are added in combination, one or more kinds can be added depending on the required corrosion resistance. However, since the effect is not obtained at 0.01% or less, the minimum amount is set to 0.01%. Further, for Mo, similarly to Mn, it correlates with the amount of C and affects the low temperature toughness of the weld heat affected zone, so when added, depending on the amount of C and the amount of Mn,
([T.Mn] + [T.Mo]) × [T. C]: Restricted to 0.007 or more and 0.03 or less.
[0019]
The above steel of the present invention can obtain the necessary strength / low temperature toughness balance by adjusting the metal structure by heat treatment such as controlled rolling or quenching and tempering.
In addition, the method for producing a steel pipe using the above steel of the present invention is not particularly limited, and any method such as a pipe making method by seamless rolling, a method of forming a steel plate by welding, and the like can be used. Can do. Steel pipes manufactured by these methods have excellent carbon dioxide corrosion resistance and excellent weld joint toughness in gas welding, but steel pipes with seam welds also have excellent seam weld toughness. An effect is obtained. For seam welding at this time, submerged arc welding with relatively large heat input can be applied in addition to electric seam welding and laser beam welding.
[0020]
However, since inexpensive steel is required for the purpose of the steel of the present invention, the effect of the invention can be exerted most particularly among those manufactured by performing controlled rolling as described below and manufacturing as an electric resistance welded tube.
The controlled rolling-electric welded tube manufacturing method sequentially takes the steps shown below.
1) The steel slab was heated to a temperature of 1050 ° C. to 1300 ° C., and then hot-rolled, followed by finishing the hot rolling at a reduction rate of 50% or more in a temperature range of 950 ° C. or lower and the Ar 3 transformation point or higher. A step of winding as a hot coil after cooling to 500 ° C. or lower at a cooling rate of 20 ° C./s or higher.
[0021]
2) A step of cutting the hot coil into a steel strip having a predetermined width, and then forming both ends of the steel strip as an electric resistance steel pipe by electric resistance welding while continuously forming a cylindrical shape.
The steel of the present invention having excellent carbon dioxide corrosion resistance and strength / low temperature toughness can be used in various applications that require carbon dioxide gas corrosion resistance. In particular, it is used as a line pipe or a flow line that requires low temperature toughness of the welded part together with carbon dioxide corrosion resistance, and a remarkable effect that the life can be improved with an inexpensive material as compared with the conventional material is obtained.
[0022]
【Example】
Table 1 shows the test results of the corrosion resistance test and the low temperature toughness of the weld zone together with the chemical compositions of the steels of the present invention and the comparative steel.
The corrosion resistance test was a two-week immersion test in a simulated formation water with a chlorine concentration of 5% at a temperature of 80 ° C. and a carbon dioxide gas pressure of 0.4 MPa. As 1), the dissolved oxygen concentration was degassed to 10 ppb or less. As 2), the dissolved oxygen concentration was 100 ppb.
[0023]
The evaluation results of carbon dioxide corrosion resistance shown in Table 1 show that the corrosion amount of carbon steel having a Cr content of 0.01% or less is 1, the corrosion amount is 0.2 or less, and the corrosion amount is 0.5. The following were marked with ○. Even if the corrosion resistance is good, those with local corrosion are indicated by black circles.
In addition, the low temperature toughness evaluation test of the welded part was performed by MIG welding with a heat input of 2.6 kJ / mm, and then a 2 mm V notch Charpy test piece taken so that the center of the notch was a melting line was collected and a Charpy impact test was performed. Went. The results of the evaluation of the low temperature toughness of the welds in Table 1 are indicated by ◎, as a result of measuring the absorbed energy in a Charpy impact test at −20 ° C. A sample having an absorbed energy of less than 30 J was regarded as being poor in low-temperature toughness, and indicated by “x”, and the middle was indicated by “◯”.
[0024]
The steels of Nos. 1 to 18 are the steels of the present invention whose chemical components are in the range specified in the present invention, and the steels of Nos. 19 to 23 are comparative steels whose chemical components are outside the ranges specified in the present invention.
All of the steels of the present invention exhibited good corrosion resistance and good low temperature toughness in the weld heat affected zone.
[0025]
On the other hand, all of the comparative steels Nos. 19 to 22 have insufficient low temperature toughness of the weld heat affected zone, and No. 23 has good low temperature toughness of the weld heat affected zone but insufficient corrosion resistance. The advantage of is clear.
Furthermore, a 150 mm thick steel slab having the chemical composition number 7 in Table 1 is heated to 1250 ° C., hot rolled to 16 mm at a temperature of 1100 ° C., allowed to cool to 900 ° C., and then rolled to a thickness of 8 mm. Immediately, it was cooled to 500 ° C. at 30 ° C./second and wound up as a hot coil. This hot coil was cold-formed and then made into an electric-welded pipe by high-frequency welding to produce an X65 grade line pipe according to the API standard. This line pipe was girth welded, and Charpy specimens were collected from the vicinity of the weld line, and the low temperature toughness of the heat affected zone was measured. It was possible to manufacture a line pipe with a very high low temperature toughness in the heat affected zone.
[0026]
[Table 1]
【The invention's effect】
The present invention provides low alloy steel with excellent carbon dioxide corrosion resistance, good balance between strength and low temperature toughness, and good low temperature toughness of welds, contributing to efficient equipment design in the energy industry. It ’s big.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between C content and Mn content in 3% Cr steel.
Claims (5)
Ｃ ：０．００３５〜０．０２％、
Ｃｒ：３．０を超え〜５．０％未満、
Ｓｉ：０．１％未満、
Ｍｎ：０．６〜２．０％、
Ａｌ：０．００１〜０．２０％以下、
Ｎ ：０．０１５％以下、
Ｔｉ：０．００１〜０．２％、
Ｎｂ：０．０１〜０．５％
を含有し、かつＭｎ量〔Ｔ．Ｍｎ〕とＣ量〔Ｔ．Ｃ〕が、〔Ｔ．Ｍｎ〕×〔Ｔ．Ｃ〕：０．００７以上、０．０３以下とし残部鉄及び不可避不純物からなることを特徴とする耐炭酸ガス腐食性及び溶接部靭性に優れた低合金鋼。As a chemical component, C: 0.0035 to 0.02% by mass%,
Cr: more than 3.0 to less than 5.0%,
Si: less than 0.1%,
Mn: 0.6 to 2.0%,
Al: 0.001 to 0.20% or less,
N: 0.015% or less,
Ti: 0.001 to 0.2%,
Nb: 0.01 to 0.5%
And the amount of Mn [T. Mn] and C content [T. C] [T. Mn] × [T. C]: A low alloy steel excellent in carbon dioxide gas corrosion resistance and weld zone toughness, characterized by comprising 0.007 or more and 0.03 or less and remaining iron and inevitable impurities.
（１）鋼片を１０５０℃〜１３００℃の温度に加熱した後に、熱間圧延し、引続き９５０℃以下、Ａｒ３変態点以上の温度域で圧下率５０％以上で熱間圧延を終了し、次いで２０℃／ｓ以上の冷却速度で５００℃以下まで冷却した後にホットコイルとして巻き取る工程。
（２）上記ホットコイルを所定の幅の鋼帯に切断した後、連続的に円筒状に成形しつつ鋼帯両端を電気抵抗溶接して電縫鋼管として造管する工程。The low alloy steel line pipe according to claim 4, wherein the steel slabs are sequentially manufactured as a steel pipe in the following steps, and are excellent in carbon dioxide corrosion resistance and weld toughness. Manufacturing method.
(1) After the steel slab was heated to a temperature of 1050 ° C. to 1300 ° C., it was hot-rolled, followed by 950 ° C. or less and finishing the hot rolling at a reduction rate of 50% or more in the temperature range of the Ar 3 transformation point or more, Next, a step of winding as a hot coil after cooling to 500 ° C. or lower at a cooling rate of 20 ° C./s or higher.
(2) A step of cutting the hot coil into a steel strip having a predetermined width, and then forming both ends of the steel strip as an electric resistance steel pipe by electric resistance welding while continuously forming a cylindrical shape.
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| JP2001090970A JP4499949B2 (en) | 2001-03-27 | 2001-03-27 | Low alloy steel and line pipe excellent in carbon dioxide corrosion resistance and weld toughness, and method for producing the same |
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| JP5629279B2 (en) * | 2005-08-08 | 2014-11-19 | 株式会社神戸製鋼所 | Welded joints and welded structures with excellent corrosion resistance |
| CN106676424B (en) * | 2015-11-06 | 2019-04-02 | 攀钢集团攀枝花钢铁研究院有限公司 | Atmosphere corrosion resistance structural steel molten steel and the atmosphere corrosion resistance structural steel of niobium containing vanadium and its production method |
| CN106676402B (en) * | 2015-11-06 | 2019-03-15 | 攀钢集团攀枝花钢铁研究院有限公司 | The atmosphere corrosion resistance structural steel molten steel of titanium containing chromium and atmosphere corrosion resistance structural steel and its production method |
| CN106676425B (en) * | 2015-11-06 | 2019-04-02 | 攀钢集团攀枝花钢铁研究院有限公司 | The atmosphere corrosion resistance structural steel molten steel of niobium containing chromium and atmosphere corrosion resistance structural steel and its production method |
| CN106676413B (en) * | 2015-11-06 | 2019-03-15 | 攀钢集团攀枝花钢铁研究院有限公司 | Atmosphere corrosion resistance structural steel molten steel and containing chrome and nitrogen atmosphere corrosion resistance structural steel and its production method |
| CN106676422B (en) * | 2015-11-06 | 2019-04-02 | 攀钢集团攀枝花钢铁研究院有限公司 | Atmosphere corrosion resistance structural steel molten steel and the atmosphere corrosion resistance structural steel of niobium containing chromium and its production method |
| CN106676421B (en) * | 2015-11-06 | 2019-03-29 | 攀钢集团攀枝花钢铁研究院有限公司 | Atmosphere corrosion resistance structural steel molten steel and titaniferous nitrogen atmosphere corrosion resistance structural steel and its production method |
| CN106011666A (en) * | 2016-06-03 | 2016-10-12 | 深圳市樊溪电子有限公司 | Low alloy steel, steel pipe and manufacturing method of steel pipe |
| CN105861948A (en) * | 2016-06-13 | 2016-08-17 | 苏州双金实业有限公司 | Steel capable of resisting fire effectively |
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| JPH06293915A (en) * | 1993-04-07 | 1994-10-21 | Nippon Steel Corp | Production of low alloy steel plate for line pipe excellent in co2 corrosion resistance and sour resistance |
| JPH07278664A (en) * | 1994-04-13 | 1995-10-24 | Nippon Steel Corp | Manufacture of low alloy steel for line pipe excellent in co2 corrosion resistance and sour resistance |
| WO1999041422A1 (en) * | 1998-02-13 | 1999-08-19 | Nippon Steel Corporation | Corrosion resisting steel and corrosion resisting oil well pipe having high corrosion resistance to carbon dioxide gas |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH06293915A (en) * | 1993-04-07 | 1994-10-21 | Nippon Steel Corp | Production of low alloy steel plate for line pipe excellent in co2 corrosion resistance and sour resistance |
| JPH07278664A (en) * | 1994-04-13 | 1995-10-24 | Nippon Steel Corp | Manufacture of low alloy steel for line pipe excellent in co2 corrosion resistance and sour resistance |
| WO1999041422A1 (en) * | 1998-02-13 | 1999-08-19 | Nippon Steel Corporation | Corrosion resisting steel and corrosion resisting oil well pipe having high corrosion resistance to carbon dioxide gas |
| JPH11293384A (en) * | 1998-02-13 | 1999-10-26 | Nippon Steel Corp | Corrosion resistant steel excellent in gaseous carbon dioxide corrosion resistance, and corrosion resistant oil well pipe |
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