JP5640762B2 - High strength martensitic stainless steel seamless pipe for oil wells - Google Patents
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- 229910001105 martensitic stainless steel Inorganic materials 0.000 title claims description 35
- 239000003129 oil well Substances 0.000 title claims description 26
- 230000007797 corrosion Effects 0.000 claims description 79
- 238000005260 corrosion Methods 0.000 claims description 79
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 46
- 229910000831 Steel Inorganic materials 0.000 claims description 46
- 239000010959 steel Substances 0.000 claims description 46
- 239000000203 mixture Substances 0.000 claims description 31
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims description 29
- 238000005336 cracking Methods 0.000 claims description 28
- 239000001569 carbon dioxide Substances 0.000 claims description 23
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 23
- 229910000734 martensite Inorganic materials 0.000 claims description 18
- 229910052804 chromium Inorganic materials 0.000 claims description 10
- 229910052726 zirconium Inorganic materials 0.000 claims description 9
- 229910001566 austenite Inorganic materials 0.000 claims description 6
- 229910052750 molybdenum Inorganic materials 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 229910000859 α-Fe Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims 1
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- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 5
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- 230000007423 decrease Effects 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
- 238000012937 correction Methods 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 239000003921 oil Substances 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 230000002411 adverse Effects 0.000 description 3
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- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 239000010779 crude oil Substances 0.000 description 2
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Description
本発明は、原油あるいは天然ガスの油井、ガス井で使用される油井管用として好適な、マルテンサイト系ステンレス継目無鋼管に係り、とくに、YSが95ksi（655MPa）以上の高強度を有し、かつ耐炭酸ガス腐食性と耐硫化物応力腐食割れ性とを兼備する油井用継目無鋼管に関する。 The present invention relates to a martensitic stainless steel seamless pipe suitable for oil wells used in crude oil or natural gas oil wells, in particular, YS has a high strength of 95 ksi (655 MPa) or more, and The present invention relates to a seamless steel pipe for oil wells having both carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance.
近年、原油価格の高騰や、近い将来に予想される石油資源の枯渇という観点から、従来、省みられなかったような深度が深い油田や、炭酸ガス、塩素イオン等を含む厳しい腐食環境の油田やガス田等の開発が盛んになっている。このような油田、ガス田は一般に深度が極めて深く、またその雰囲気は高温でかつ炭酸ガス、塩素イオン、硫化水素等を含む厳しい環境となっており、このような環境下で使用される油井用鋼管等には、高強度で、かつ優れた耐食性を兼ね備えた材質を有することが要求される。 In recent years, from the viewpoint of soaring crude oil prices and the depletion of petroleum resources expected in the near future, oil fields with deeper depths that were not previously excluded, and oil fields with severe corrosive environments including carbon dioxide, chloride ions, etc. Development of gas fields and so on is thriving. Such oil fields and gas fields are generally extremely deep, and the atmosphere is high temperature and is a harsh environment containing carbon dioxide, chlorine ions, hydrogen sulfide, etc. For oil wells used in such an environment Steel pipes and the like are required to have a material having high strength and excellent corrosion resistance.
従来から、炭酸ガスCO２、塩素イオンCl−等を含む環境の油田、ガス田では、採掘に使用する油井管として13％Crマルテンサイト系ステンレス鋼管が多く使用されている。さらに、最近では13Crマルテンサイト系ステンレス鋼のＣを低減し，Ni，Mo等を増加させた成分系の改良型13Crマルテンサイト系ステンレス鋼の使用も拡大している。
例えば、特許文献１〜特許文献５には、13％Crマルテンサイト系ステンレス鋼 (鋼管）の耐食性を改善した、改良型マルテンサイト系ステンレス鋼 (鋼管)が提案されている。
Conventionally, 13% Cr martensitic stainless steel pipes are often used as oil well pipes used for mining in environmental oil fields and gas fields containing carbon dioxide CO 2 , chlorine ions Cl − and the like. Furthermore, recently, the use of improved 13Cr martensitic stainless steels with a reduced content of 13Cr martensitic stainless steel and increased Ni, Mo, etc. has been expanded.
For example, Patent Documents 1 to 5 propose improved martensitic stainless steel (steel pipe) in which the corrosion resistance of 13% Cr martensitic stainless steel (steel pipe) is improved.
例えば、特許文献１に記載された技術は、13％Crマルテンサイト系ステンレス鋼管の組成で、Ｃを0.005 〜0.05％と制限し、Ni：2.4〜６％とCu：0.2〜４％とを複合添加し、さらにMoを0.5〜３％添加し、さらにNieqを10.5以上に調整した組成とし、熱間加工後に空冷以上の速度で冷却したのち、あるいはさらに（Ａc３変態点＋10℃）〜（Ａc３変態点＋200 ℃）の温度に加熱し、あるいはさらにＡc１変態点〜Ａc３変態点の温度に加熱し、続いて室温まで空冷以上の冷却速度で冷却し、焼戻しする、耐食性に優れたマルテンサイト系ステンレス継目無鋼管の製造方法である。特許文献１に記載された技術によれば、ＡＰＩ−Ｃ95級以上の高強度と、180 ℃以上のCO２を含む環境における耐食性と、耐ＳＣＣ性とを兼ね備えたマルテンサイト系ステンレス継目無鋼管となるとしている。 For example, the technology described in Patent Document 1 is a composition of 13% Cr martensitic stainless steel pipe, C is limited to 0.005 to 0.05%, and Ni: 2.4 to 6% and Cu: 0.2 to 4% are combined. Then, Mo is added at 0.5 to 3%, and Nieq is adjusted to 10.5 or more. After hot working, the composition is cooled at a rate higher than air cooling, or (Ac 3 transformation point + 10 ° C.) to (Ac 3 transformation point + 200 ° C), or further heating to a temperature of Ac 1 transformation point to Ac 3 transformation point, followed by cooling to room temperature at a cooling rate higher than air cooling and tempering, martens having excellent corrosion resistance This is a method for producing a site-based stainless steel seamless steel pipe. According to the technique described in Patent Document 1, a martensitic stainless steel seamless steel pipe having high strength of API-C95 grade or higher, corrosion resistance in an environment containing CO 2 of 180 ° C. or higher, and SCC resistance; It is going to be.
また、特許文献２に記載された技術は、Ｃ：0.005〜0.05％、Ｎ：0.005〜0.1％を含み、Ni：3.0〜6.0％、Cu：0.5〜３％、Mo：0.5〜３％に調整した組成の13％Crマルテンサイト系ステンレス鋼を熱間加工し室温まで自然放冷したのち、（Ａc１点＋10℃）〜（Ａc１点＋40℃）に加熱し30〜60分間保持しＭs点以下の温度まで冷却し、Ａc１点以下の温度で焼戻し、組織を焼戻しマルテンサイトと20体積％以上のγ相とが混在した組織とする耐硫化物応力腐食割れ性に優れたマルテンサイト系ステンレス鋼の製造方法である。特許文献２に記載された技術によれば、γ相を20体積％以上含む焼戻しマルテンサイト組織とすることにより耐硫化物応力腐食割れ性が顕著に向上するとしている。 The technique described in Patent Document 2 includes C: 0.005 to 0.05%, N: 0.005 to 0.1%, Ni: 3.0 to 6.0%, Cu: 0.5 to 3%, and Mo: 0.5 to 3%. 13% Cr martensitic stainless steel with the above composition is hot-worked and allowed to cool naturally to room temperature, then heated to (Ac 1 point + 10 ° C) to (Ac 1 point + 40 ° C) and held for 30 to 60 minutes. Martensitic stainless steel with excellent resistance to sulfide stress corrosion cracking by cooling to the following temperature and tempering at a temperature of Ac 1 point or less to make the structure a mixture of tempered martensite and 20% by volume or more of γ phase. It is a manufacturing method of steel. According to the technique described in Patent Document 2, the resistance to sulfide stress corrosion cracking is remarkably improved by forming a tempered martensite structure containing 20% by volume or more of the γ phase.
また、特許文献３に記載された技術は、10〜15％Crを含有するマルテンサイト系ステンレス鋼の組成で、Ｃを0.005〜0.05％と制限し、Ni：4.0％以上、Cu：0.5〜３％を複合添加し、さらにMoを1.0〜3.0％添加し、さらにNieqを−10以上に調整した組成とし、 組織を焼戻しマルテンサイト相、マルテンサイト相、残留オーステナイト相からなり、焼戻しマルテンサイト相、マルテンサイト相の合計の分率が60〜90％である、耐食性、耐硫化物応力腐食割れ性に優れたマルテンサイト系ステンレス鋼である。これにより、湿潤炭酸ガス環境および湿潤硫化水素環境における耐食性と耐硫化物応力腐食割れ性が向上するとしている。 The technique described in Patent Document 3 is a martensitic stainless steel composition containing 10 to 15% Cr, C is limited to 0.005 to 0.05%, Ni: 4.0% or more, Cu: 0.5 to 3 The composition is composed of a tempered martensite phase, a martensite phase, and a retained austenite phase. This is a martensitic stainless steel having a total fraction of the martensite phase of 60 to 90% and excellent in corrosion resistance and sulfide stress corrosion cracking resistance. As a result, the corrosion resistance and sulfide stress corrosion cracking resistance in a wet carbon dioxide environment and a wet hydrogen sulfide environment are improved.
また、特許文献４に記載された技術は、15％超19％以下のCrを含有し、Ｃ：0.05％以下、Ｎ：0.1％以下、Ni：3.5〜8.0％を含み、さらにMo：0.1〜4.0％を含有し、30Cr＋36Mo＋14Si−28Ni≦455 （％）、21Cr＋25Mo＋17Si＋35Ni≦731（％）を同時に満足する鋼組成とする硫化物応力割れ性に優れた油井用マルテンサイト系ステンレス鋼材であり、これにより、塩化物イオン、炭酸ガスと微量の硫化水素ガスが存在する苛酷な油井環境中でも優れた耐食性を有する鋼材となるとしている。 Moreover, the technique described in Patent Document 4 contains Cr of more than 15% and 19% or less, including C: 0.05% or less, N: 0.1% or less, Ni: 3.5 to 8.0%, and Mo: 0.1 to It is a martensitic stainless steel material for oil wells with excellent sulfide stress cracking properties that contains 4.0% and has a steel composition that simultaneously satisfies 30Cr + 36Mo + 14Si−28Ni ≦ 455 (%) and 21Cr + 25Mo + 17Si + 35Ni ≦ 731 (%). It is said that the steel material has excellent corrosion resistance even in a harsh oil well environment in which chloride ions, carbon dioxide gas and a small amount of hydrogen sulfide gas exist.
また、特許文献５に記載された技術は、10.0〜17％のCrを含有し、Ｃ：0.08％以下、Ｎ：0.015％以下、Ni：6.0〜10.0％、Cu：0.5〜2.0％を含み、さらにMo：0.5〜3.0％を含有する鋼組成とし、35％以上の冷間加工と焼鈍により、平均結晶粒径が25μｍ以下、マトリックスに析出した粒径５×10−２μｍ以上の析出物を６×10６個／mm２以下に抑えられた組織を有する強度および靭性に優れた析出硬化型マルテンサイト系ステンレス鋼であり、微細な結晶粒と析出物の少ない組織とすることにより、高強度で靭性低下を引き起こさない析出硬化型マルテンサイト系ステンレス鋼を提供できるとしている。 Moreover, the technique described in patent document 5 contains 10.0 to 17% of Cr, C: 0.08% or less, N: 0.015% or less, Ni: 6.0 to 10.0%, Cu: 0.5 to 2.0%, Furthermore, a steel composition containing Mo: 0.5 to 3.0% is formed, and a precipitate having an average crystal grain size of 25 μm or less and a grain size of 5 × 10 −2 μm or more precipitated in the matrix by cold working and annealing of 35% or more. Precipitation hardening type martensitic stainless steel with excellent strength and toughness with a structure suppressed to 6 × 10 6 pieces / mm 2 or less. By making the structure with fine crystal grains and few precipitates, high strength It is said that precipitation hardening martensitic stainless steel that does not cause toughness reduction can be provided.
しかしながら、特許文献１〜特許文献５に記載された各技術で製造された改良型13％Crマルテンサイト系ステンレス鋼管は、CO２、Cl− 等を含み、180 ℃を超える高温の苛酷な腐食環境下では、安定して所望の耐食性を示さないという問題があった。改良型13％Crマルテンサイト系ステンレス鋼の使用可能温度は、高圧炭酸ガスを含む環境では、高々165℃程度までであり、それ以上の温度では十分な耐食性を示さない。さらに、硫化水素H２Ｓを含む環境下においては、硫化物応力腐食割れを起こしやすいという問題があった。 However, the improved 13% Cr martensitic stainless steel pipe manufactured by each technique described in Patent Documents 1 to 5 contains CO 2 , Cl − and the like, and is a severe corrosive environment at a high temperature exceeding 180 ° C. Below, there was a problem that the desired corrosion resistance was not stably exhibited. The usable temperature of the improved 13% Cr martensitic stainless steel is up to about 165 ° C in an environment containing high-pressure carbon dioxide gas, and does not exhibit sufficient corrosion resistance at temperatures higher than that. Furthermore, in an environment containing hydrogen sulfide H 2 S, there is a problem that sulfide stress corrosion cracking is likely to occur.
本発明は、かかる従来技術の問題を有利に解決し、降伏強さ655MPa以上の高強度を有し、かつ、炭酸ガスCO２、塩素イオンCl−等を含み、さらに硫化水素H２Ｓを含む、170℃以上の苛酷な環境下においても、優れた耐食性（耐炭酸ガス腐食性および耐硫化物応力腐食割れ性）を兼備する油井用高強度マルテンサイト系ステンレス継目無鋼管を提供することを目的とする。 The present invention advantageously solves such problems of the prior art, has a high yield strength of 655 MPa or more, contains carbon dioxide CO 2 , chlorine ions Cl − and the like, and further contains hydrogen sulfide H 2 S. The purpose is to provide a high strength martensitic stainless steel seamless steel pipe for oil wells that has excellent corrosion resistance (carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance) even in harsh environments of 170 ° C or higher. And
本発明者らは、上記した目的を達成するために、代表的なマルテンサイト系ステンレス鋼である13Cr鋼をベースとして、CO２、Cl−等を含み、さらにH２Ｓを含む、170℃以上の苛酷な環境下における耐炭酸ガス腐食性および耐硫化物応力腐食割れ性に及ぼす各種合金元素の影響について調査した。その結果、Ｃを0.01質量％以下に低減し、Crを15.5質量％超え17質量％以下に設定し、Ni、Moを適正範囲に調整したうえで、さらに、適正量のCu、Ｖ、あるいはさらに適正量のＷを含有させることにより、所望の降伏強さYS：655MPa以上の高強度を有しながら、耐炭酸ガス腐食性および耐硫化物応力腐食割れ性が顕著に向上することを知見した。とくに、Ｃを0.01％以下に低減することにより、降伏強さYS：655MPa以上の所望の高強度を確保しながら、降伏比が90％以上と引張強さの増加（硬さの増加）を少なくでき、所望の耐食性を確保できることを知見した。また、Ｗの含有は、pHの低い苛酷な環境下においても、安定して耐食性を顕著に向上させることができることを知見した。また、Ｗは、Mo等にくらべても大きな耐食性向上効果を有することも知見した。 In order to achieve the above-mentioned object, the inventors of the present invention based on 13Cr steel, which is a typical martensitic stainless steel, contains CO 2 , Cl −, etc., and further contains H 2 S, 170 ° C. or higher. The effects of various alloying elements on carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance in harsh environments were investigated. As a result, C is reduced to 0.01% by mass or less, Cr is set to more than 15.5% by mass and 17% by mass or less, Ni and Mo are adjusted to an appropriate range, and an appropriate amount of Cu, V, or further It has been found that by containing an appropriate amount of W, the carbon dioxide corrosion resistance and the sulfide stress corrosion cracking resistance are remarkably improved while having a desired yield strength YS: 655 MPa or more. In particular, by reducing C to 0.01% or less, yield strength YS: While ensuring the desired high strength of 655 MPa or more, the yield ratio is 90% or more and the increase in tensile strength (increased hardness) is small. It was found that the desired corrosion resistance can be secured. Further, it has been found that the inclusion of W can stably improve the corrosion resistance even in a severe environment with a low pH. It was also found that W has a large effect of improving corrosion resistance compared to Mo and the like.
本発明は、上記した知見に基づき、さらに検討を重ねて完成されたものである。すなわち、本発明の要旨は次のとおりである。
（１）質量％で、Ｃ：0.01％以下、Si：0.5％以下、Mn：0.1〜2.0％、Ｐ：0.03％以下、Ｓ：0.005％以下、Cr：15.5％超え17.5％以下、Ni：2.5〜5.5％、Mo：1.8〜3.5％、Cu：0.3〜3.5％、Ｖ：0.20％以下、Al：0.05％以下、Ｎ：0.06％以下を含み、残部Feおよび不可避的不純物からなる組成を有し、体積率で15％以上のフェライト相と25％以下の残留オーステナイト相を含み、50％以上の焼戻マルテンサイト相からなる組織を有し、降伏強さ：655〜862MPaの強度と降伏比：0.90以上を有し、耐炭酸ガス腐食性および耐硫化物応力腐食割れ性に優れることを特徴とする油井用高強度マルテンサイト系ステンレス継目無鋼管。
（２）（１）において、前記組成に加えてさらに、質量％で、Ｗ：0.25〜2.0％を含有する組成とすることを特徴とする油井用高強度マルテンサイト系ステンレス継目無鋼管。
（３）（１）または（２）において、前記組成に加えてさらに、質量％で、Nb：0.20％以下を含有する組成とすることを特徴とする油井用高強度マルテンサイト系ステンレス継目無鋼管。
（４）（１）ないし（３）のいずれかにおいて、前記組成に加えてさらに、質量％で、Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.0005〜0.01％のうちから選ばれた１種または２種以上を含有する組成とすることを特徴とする油井用高強度マルテンサイト系ステンレス継目無鋼管。
（５）（１）ないし（４）のいずれかにおいて、前記組成に加えてさらに、質量％で、Ca：0.0005〜0.01％を含有する組成とすることを特徴とする油井用高強度マルテンサイト系ステンレス継目無鋼管。
The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) By mass%, C: 0.01% or less, Si: 0.5% or less, Mn: 0.1 to 2.0%, P: 0.03% or less, S: 0.005% or less, Cr: more than 15.5%, 17.5% or less, Ni: 2.5 -5.5%, Mo: 1.8-3.5%, Cu: 0.3-3.5%, V: 0.20% or less, Al: 0.05% or less, N: 0.06% or less, and having a composition comprising the balance Fe and inevitable impurities , Having a structure comprising a ferrite phase of 15% or more by volume and a residual austenite phase of 25% or less and a tempered martensite phase of 50% or more, yield strength: strength of 655 to 862 MPa and yield ratio: A high-strength martensitic stainless steel seamless pipe for oil wells that has 0.90 or more and is excellent in carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance.
(2) A high-strength martensitic stainless steel seamless steel pipe for oil wells characterized in that, in addition to the above-described composition, the composition further comprises W: 0.25 to 2.0% in mass%.
(3) A high-strength martensitic stainless steel seamless pipe for oil wells characterized in that, in addition to the above-described composition, Nb: 0.20% or less in addition to the above composition .
(4) In any one of (1) to (3), in addition to the above composition, it is further selected by mass% from Ti: 0.3% or less, Zr: 0.2% or less, and B: 0.0005 to 0.01%. A high-strength martensitic stainless steel seamless pipe for oil wells, characterized in that the composition contains one or more.
(5) In any one of (1) to (4), in addition to the above-mentioned composition, the composition further contains Ca: 0.0005 to 0.01% by mass%, and is a high-strength martensite system for oil wells Stainless steel seamless steel pipe .
本発明によれば、降伏強さYS：655MPa以上の高強度を有し、かつCO２、Cl−等を含み、さらにH２Ｓを含む、170℃以上の苛酷な環境下においても、優れた耐炭酸ガス腐食性および耐硫化物応力腐食割れ性を有する、油井管用として好適な、高強度マルテンサイト系ステンレス継目無鋼管を安価にしかも安定して製造でき、産業上格段の効果を奏する。 According to the present invention, yield strength YS: have more high strength 655 MPa, and CO 2, Cl - include such further comprises H 2 S, even in harsh environments above 170 ° C., excellent A high-strength martensitic stainless steel seamless pipe having carbon dioxide gas corrosion resistance and sulfide stress corrosion cracking resistance, suitable for oil well pipes, can be manufactured at low cost and stably, and has a remarkable industrial effect.
まず、本発明の油井用高強度マルテンサイト系ステンレス継目無鋼管の組成限定の理由について説明する。なお、以下、とくに断らないかぎり質量％は単に％と記す。
Ｃ：0.01％以下
Ｃは、マルテンサイト系ステンレス鋼の強度に関係する重要な元素であり、所望の高強度を確保するためには、0.003％以上含有することが望ましいが、0.01％を超える含有は、Cr炭化物を形成しやすくなり、耐食性が低下しやすくなる。このため、本発明では、Ｃは0.01％以下に限定した。なお、好ましくは、所望の高強度を確保するという観点から0.005％以上である。
First, the reason for the composition limitation of the high-strength martensitic stainless steel seamless steel pipe for oil wells of the present invention will be described. Hereinafter, unless otherwise specified, mass% is simply referred to as%.
C: 0.01% or less C is an important element related to the strength of martensitic stainless steel, and in order to ensure the desired high strength, it is desirable to contain 0.003% or more, but more than 0.01% Makes it easy to form Cr carbide, and corrosion resistance tends to decrease. For this reason, in the present invention, C is limited to 0.01% or less. In addition, Preferably, it is 0.005% or more from a viewpoint of ensuring desired high intensity | strength.
Si：0.5％以下
Siは、脱酸剤として作用する元素であるとともに、固溶して鋼の強度を増加させる。このような効果を得るためには、0.05％以上含有することが望ましいが、0.5％を超える含有は、熱間加工性を低下させる。このため、Siは0.5％以下に限定した。なお、好ましくは0.15〜0.4％である。
Si: 0.5% or less
Si is an element that acts as a deoxidizing agent, and dissolves to increase the strength of the steel. In order to acquire such an effect, it is desirable to contain 0.05% or more, but inclusion exceeding 0.5% lowers hot workability. For this reason, Si was limited to 0.5% or less. In addition, Preferably it is 0.15-0.4%.
Mn：0.1〜2.0％
Mnは、固溶強化あるいは焼入れ性向上を介して、鋼管の強度を増加させる元素であり、所望の鋼管強度を確保するために0.1％以上の含有を必要とするが、2.0％を超える多量の含有は、靭性に悪影響を及ぼす。このため、Mnは0.1〜2.0％の範囲に限定した。なお、好ましくは、0.3〜0.8％である。
Mn: 0.1-2.0%
Mn is an element that increases the strength of the steel pipe through solid solution strengthening or hardenability improvement. It needs to be contained in an amount of 0.1% or more in order to ensure the desired steel pipe strength, but a large amount exceeding 2.0% Inclusion adversely affects toughness. For this reason, Mn was limited to the range of 0.1 to 2.0%. In addition, Preferably, it is 0.3 to 0.8%.
Ｐ：0.03％以下
Ｐは、熱間加工性、耐硫化物応力腐食割れ性をともに劣化させる元素であり、本発明では可及的に低減することが望ましいが、極端な低減は製造コストの上昇を招く。工業的に比較的安価に実施可能でかつ熱間加工性、耐硫化物応力腐食割れ性をともに劣化させない範囲として、Ｐは0.03％以下に限定した。なお、好ましくは0.01％以下である。
P: 0.03% or less P is an element that degrades both hot workability and resistance to sulfide stress corrosion cracking. In the present invention, it is desirable to reduce as much as possible, but extreme reduction increases the manufacturing cost. Invite. P is limited to 0.03% or less as a range that can be implemented relatively inexpensively industrially and does not deteriorate both hot workability and sulfide stress corrosion cracking resistance. In addition, Preferably it is 0.01% or less.
Ｓ：0.005％以下
Ｓは、パイプ製造過程において熱間加工性を著しく劣化させる元素であり、可及的に少ないことが望ましいが、0.005％以下に低減すれば通常工程によるパイプ製造が可能となることから、Ｓは0.005％以下に限定した。なお、好ましくは0.003％以下である。
Cr：15.5％超え17.5％以下
Crは、保護被膜を形成して耐食性を向上させる元素で、とくに所望の耐炭酸ガス腐食性、耐硫化物応力腐食割れ性の保持に有効に寄与する元素である。とくに、高温においても所望の優れた耐食性を維持するために、Crは15.5％超え含有することにした。一方、17.5％を超える含有は、熱間加工性を低下させる。このため、Crは15.5％超え17.5％以下の範囲に限定した。なお、好ましくは、組織安定性という観点から16.0〜17.0％である。
S: 0.005% or less S is an element that significantly deteriorates hot workability in the pipe manufacturing process, and is preferably as small as possible. However, if it is reduced to 0.005% or less, pipe manufacturing by a normal process becomes possible. Therefore, S is limited to 0.005% or less. In addition, Preferably it is 0.003% or less.
Cr: Over 15.5% and below 17.5%
Cr is an element that improves the corrosion resistance by forming a protective film, and is an element that contributes effectively to maintaining the desired carbon dioxide gas corrosion resistance and sulfide stress corrosion cracking resistance. In particular, in order to maintain the desired excellent corrosion resistance even at high temperatures, the Cr content is determined to exceed 15.5%. On the other hand, the content exceeding 17.5% decreases the hot workability. For this reason, Cr was limited to the range of more than 15.5% and less than 17.5%. In addition, Preferably it is 16.0 to 17.0% from a viewpoint of structure | tissue stability.
Ni：2.5〜5.5％
Niは、保護被膜を強固にする作用を有し、耐炭酸ガス腐食性、耐硫化物応力腐食割れ性等の耐食性を高める元素である。本発明が対象としている厳しい腐食環境下でこのような効果を得るためには、2.5％以上の含有が必要になる。一方、5.5％を超えて含有しても、耐食性向上効果が飽和するとともに、強度が低下する場合もあり、含有量に見合う効果が期待できなくなり、経済的に不利となる。このため、Niは2.5〜5.5％の範囲に限定した。なお、好ましくは3.0〜5.0％である。
Ni: 2.5-5.5%
Ni is an element that has a function of strengthening the protective coating and enhances corrosion resistance such as carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance. In order to obtain such an effect under the severe corrosive environment targeted by the present invention, a content of 2.5% or more is necessary. On the other hand, even if the content exceeds 5.5%, the effect of improving the corrosion resistance is saturated and the strength may be lowered, and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, Ni was limited to the range of 2.5 to 5.5%. In addition, Preferably it is 3.0 to 5.0%.
Mo：1.8〜3.5％
Moは、不動態皮膜を安定化させるとともに、Cl−による孔食に対する抵抗性を増加させる作用を有し、耐炭酸ガス腐食性、耐硫化物応力腐食割れ性の両方の向上に寄与する元素である。このような効果を得るためには、1.8％以上の含有を必要とするが、3.5％を超える含有は、熱間加工性を低下させるとともに、材料コストを高騰させる。このため、Moは1.8〜3.5％の範囲に限定した。なお、好ましくは2.0〜3.0％である。
Mo: 1.8-3.5%
Mo, along with stabilizing the passive film, Cl - by having the effect of increasing the resistance to pitting,耐炭acid gas corrosion resistance, in element contributing to the improvement of both the resistance to sulfide stress corrosion cracking is there. In order to obtain such an effect, the content of 1.8% or more is required, but the content exceeding 3.5% lowers the hot workability and raises the material cost. For this reason, Mo was limited to the range of 1.8 to 3.5%. In addition, Preferably it is 2.0 to 3.0%.
Cu：0.3〜3.5％
Cuは、保護皮膜を強固にして、耐炭酸ガス腐食性、耐硫化物応力腐食割れ性の向上に寄与するとともに、耐孔食性を向上させる作用を有する元素であり、このような効果を得るためには、0.3％以上の含有を必要とする。一方、3.5％を超えて含有すると、CuSが高温で粒界析出し、熱間加工性が低下する。このため、Cuは、0.3〜3.5％の範囲に限定した。なお、好ましくは0.7〜2.5％である。
Cu: 0.3-3.5%
Cu is an element that strengthens the protective film and contributes to the improvement of carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance, and also has the effect of improving pitting corrosion resistance. Needs to contain 0.3% or more. On the other hand, if the content exceeds 3.5%, CuS precipitates at grain boundaries at high temperatures, and hot workability is reduced. For this reason, Cu was limited to the range of 0.3 to 3.5%. In addition, Preferably it is 0.7 to 2.5%.
Ｖ：0.20％以下
Ｖは、炭化物（析出物）を形成し、析出強化を介して、強度の増加に寄与するとともに、耐硫化物応力腐食割れ性を向上させる元素である。このような効果を得るためには、0.01％以上の含有を必要とする。一方、0.20％を超える含有は、靭性を低下させる。このため、Ｖは0.20％以下に限定した。なお、好ましくは0.03〜0.08％である。
V: 0.20% or less V is an element that forms a carbide (precipitate) and contributes to an increase in strength through precipitation strengthening and improves resistance to sulfide stress corrosion cracking. In order to acquire such an effect, 0.01% or more of content is required. On the other hand, the content exceeding 0.20% lowers toughness. For this reason, V was limited to 0.20% or less. In addition, Preferably it is 0.03-0.08%.
Al：0.05％以下
Alは、強力な脱酸作用を有する元素であり、このような効果を得るためには、0.001％以上含有することが望ましいが、0.05％を超える含有は、靭性に悪影響を及ぼす。このため、Alは0.05％以下に限定した。なお、好ましくは0.03％以下である。
Ｎ：0.06％以下
Ｎは、耐孔食性を著しく向上させる元素であり、このような効果は、0.01％以上の含有で顕著となる。一方、0.06％を超える含有は、種々の窒化物を形成して靭性を低下させる。このため、Ｎは0.06％以下に限定した。なお、好ましくは0.01〜0.03％である。
Al: 0.05% or less
Al is an element having a strong deoxidizing action, and in order to obtain such an effect, it is desirable to contain 0.001% or more, but inclusion exceeding 0.05% adversely affects toughness. For this reason, Al was limited to 0.05% or less. In addition, Preferably it is 0.03% or less.
N: 0.06% or less N is an element that remarkably improves the pitting corrosion resistance. Such an effect becomes remarkable when the content is 0.01% or more. On the other hand, the content exceeding 0.06% forms various nitrides and lowers the toughness. For this reason, N was limited to 0.06% or less. In addition, Preferably it is 0.01 to 0.03%.
上記した成分が基本の成分であるが、本発明では、このような基本の組成に加えてさらに、選択元素として、Ｗ：0.25〜2.0％、および／または、Nb：0.20％以下、および／または、Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.0005〜0.01％のうちから選ばれた１種または２種以上、および／または、Ca：0.0005〜0.01％、を必要に応じて、選択して含有してもよい。 The above-described components are basic components. In the present invention, in addition to the basic composition, W: 0.25 to 2.0% and / or Nb: 0.20% or less and / or , Ti: 0.3% or less, Zr: 0.2% or less, B: One or more selected from 0.0005 to 0.01%, and / or Ca: 0.0005 to 0.01%, as necessary And may be contained.
Ｗ：0.25〜2.0％
Ｗは、Moと同様に、不動態皮膜を安定化させるとともに、Cl−による孔食に対する抵抗性を増加させる作用を有し、耐炭酸ガス腐食性、耐硫化物応力腐食割れ性の両方の向上に寄与する元素である。とくに、Ｗは、腐食環境下で溶け出して、Ｗ酸化物を形成して、腐食の進行を安定して遅延させる。このような効果を得るためには、0.25％以上含有する必要があるが、2.0％を超える多量の含有は、熱間加工性を低下させる。このため、含有する場合には、Ｗは0.25〜2.0％の範囲に限定することが好ましい。なお、より好ましくは0.5〜1.5％である。
W: 0.25-2.0%
W, like Mo, has the effect of stabilizing the passive film and increasing the resistance to pitting corrosion caused by Cl − , improving both carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance. Is an element that contributes to In particular, W dissolves in a corrosive environment to form W oxide, which stably delays the progress of corrosion. In order to acquire such an effect, it is necessary to contain 0.25% or more, but when it contains more than 2.0%, hot workability will fall. For this reason, when contained, W is preferably limited to a range of 0.25 to 2.0%. In addition, More preferably, it is 0.5 to 1.5%.
Nb：0.20％以下
Nbは、析出物として析出し、強度増加に寄与するとともに、γ未再結晶温度域を拡大して、熱間圧延による結晶粒の微細化を介して靭性の向上に寄与する元素であり、必要に応じて含有できる。このような効果を得るためには、0.01％以上含有することが望ましいが、0.20％を超える含有は、靭性に悪影響を及ぼす。このため、含有する場合には、Nbは0.20％以下に限定することが好ましい。より好ましくは0.15％以下である。
Nb: 0.20% or less
Nb is an element that precipitates as a precipitate and contributes to increase in strength, and also contributes to improvement in toughness through refinement of crystal grains by hot rolling by expanding the γ non-recrystallization temperature range. Depending on the content. In order to acquire such an effect, it is desirable to contain 0.01% or more, but inclusion exceeding 0.20% adversely affects toughness. For this reason, when it contains, it is preferable to limit Nb to 0.20% or less. More preferably, it is 0.15% or less.
Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.0005〜0.01％のうちから選ばれた１種または２種以上
Ti、Zr、Ｂはいずれも、強度を増加させるとともに、耐硫化物応力腐食割れ性を向上させる作用を有する元素であり、必要に応じて選択して１種または２種以上含有できる。このような効果を得るためには、Ti：0.01％、Zr：0.01％、Ｂ：0.0005％以上、それぞれ含有することが望ましいが、Ti：0.3％、Zr：0.2％、Ｂ：0.01％をそれぞれ超える含有は、靭性が低下する。このため、含有する場合には、Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.0005〜0.01％にそれぞれ限定することが好ましい。なお、より好ましくはTi：0.2％以下、Zr：0.1％以下、Ｂ：0.005％以下である。
One or more selected from Ti: 0.3% or less, Zr: 0.2% or less, B: 0.0005 to 0.01%
Ti, Zr, and B are all elements that have the effect of increasing the strength and improving the resistance to sulfide stress corrosion cracking, and can be selected as needed and contained in one or more. In order to obtain such effects, it is desirable to contain Ti: 0.01%, Zr: 0.01%, B: 0.0005% or more, but Ti: 0.3%, Zr: 0.2%, B: 0.01%, respectively. If it exceeds, the toughness decreases. For this reason, when it contains, it is preferable to limit to Ti: 0.3% or less, Zr: 0.2% or less, and B: 0.0005-0.01%, respectively. More preferably, Ti is 0.2% or less, Zr: 0.1% or less, and B: 0.005% or less.
Ca：0.0005〜0.01％
Ca は、ＳをCaS として固定し、硫化物系介在物を球状化する作用を有し、これにより介在物周囲のマトリックスの格子歪を小さくして、介在物の水素トラップ能を低下させる効果を有する。このような効果は、0.0005％以上の含有で顕著となるが、0.01％を超える含有は、CaO の増加を招き、耐炭酸ガス腐食性、耐孔食性が低下する。このため、Caは0.0005〜0.01％の範囲に限定することが好ましい。
Ca: 0.0005 to 0.01%
Ca has the effect of fixing S as CaS and spheroidizing sulfide inclusions, thereby reducing the lattice strain of the matrix around the inclusions and reducing the hydrogen trapping ability of the inclusions. Have. Such an effect becomes remarkable when the content is 0.0005% or more. However, if the content exceeds 0.01%, CaO is increased, and the carbon dioxide corrosion resistance and pitting corrosion resistance are lowered. For this reason, it is preferable to limit Ca to 0.0005 to 0.01% of range.
上記した成分以外の残部は、Feおよび不可避的不純物からなる。不可避的不純物としては、Ｏ：0.006％以下が許容できる。
つぎに、本発明の油井用高強度マルテンサイト系ステンレス継目無鋼管の好ましい組織について説明する。
本発明の油井用高強度マルテンサイト系ステンレス継目無鋼管は、焼戻マルテンサイト相を主体とする。ここでいう「主体」とは、当該相が、体積率で50％以上を有する場合をいうものとする。主体となる相以外の第二相として、25％以下の残留オーステナイト（γ）と15％以上のフェライト相（α）を含む。フェライト相（α）が、15％未満と少量の析出では、熱間加工性が低下する。とくに、高Cr鋼でその傾向が強い。
また、残留γは、体積率で25％以下と、できるだけ低減する。残留γの存在は、降伏強さを低下させるため、所望強度の確保を困難とする。
The balance other than the components described above consists of Fe and inevitable impurities. As an inevitable impurity, O: 0.006% or less is acceptable.
Next, a preferable structure of the high-strength martensitic stainless steel seamless steel pipe for oil wells of the present invention will be described.
The high-strength martensitic stainless steel seamless pipe for oil wells of the present invention is mainly composed of a tempered martensite phase. The “main body” here means a case where the phase has a volume ratio of 50% or more. As the second phase other than the phase composed mainly, including the following residual austenite 25% (gamma) 15% or more of ferrite phase (alpha). When the ferrite phase (α) is precipitated in a small amount of less than 15%, the hot workability is lowered. This tendency is particularly strong with high Cr steel.
Further, the residual γ is 25% or less by volume, reduced as much as possible. The presence of the residual γ reduces the yield strength, making it difficult to ensure the desired strength.
つぎに、本発明の油井用高強度マルテンサイト系ステンレス継目無鋼管の好ましい製造方法について説明する。上記した組成を有するステンレス継目無鋼管を出発素材として、焼入れ処理と焼戻処理とを施す。さらに、必要に応じて、鋼管形状の不良を矯正するために矯正処理を施しても良い。
なお、本発明では、上記した組成を有する出発素材の製造方法はとくに限定する必要はないが、上記した組成を有する溶鋼を、転炉、電気炉、真空溶解炉等の通常公知の溶製方法で溶製し、連続鋳造法、造塊−分塊圧延法等、通常の方法でビレット等の鋼管素材とすることが好ましい。ついで、これら鋼管素材を加熱し、通常のマンネスマン−プラグミル方式、あるいはマンネスマン−マンドレルミル方式の製造工程を用いて熱間加工し造管して、所望寸法の継目無鋼管とし、出発素材とすることが好ましい。なお、プレス方式による熱間押出で継目無鋼管を製造してもよい。また、造管後、継目無鋼管は、空冷以上の冷却速度で室温まで冷却することが好ましい。
Below, the preferable manufacturing method of the high intensity | strength martensitic stainless steel seamless pipe for oil wells of this invention is demonstrated. A stainless steel seamless steel pipe having the above composition is used as a starting material for quenching and tempering. Furthermore, you may perform a correction process in order to correct the defect of a steel pipe shape as needed.
In the present invention, the production method of the starting material having the above-described composition is not particularly limited. However, the molten steel having the above-described composition is usually converted into a known melting method such as a converter, an electric furnace, or a vacuum melting furnace. It is preferable to use a steel pipe material such as billet by a usual method such as continuous casting and ingot-splitting rolling. Next, these steel pipe materials are heated and hot-worked and piped using a normal Mannesmann-plug mill method or Mannesmann-Mandrel mill manufacturing process to produce seamless steel pipes of the desired dimensions, and used as starting materials. Is preferred. In addition, you may manufacture a seamless steel pipe by the hot extrusion by a press system. Moreover, it is preferable that a seamless steel pipe is cooled to room temperature at a cooling rate equal to or higher than air cooling after pipe making.
出発素材（継目無鋼管）は、まず、焼入れ処理を施される。
本発明における焼入れ処理は、Ａc3変態点以上、好ましくは800〜1050℃の範囲の焼入れ温度に再加熱したのち、該焼入れ温度から空冷以上の冷却速度で100℃以下の温度域まで冷却する処理とする。これにより、微細なマルテンサイト組織とすることができる。焼入れ加熱温度が、Ａc3変態点未満では、オーステナイト単相域に加熱することができず、その後の冷却で十分なマルテンサイト組織とすることができないため、所望の強度を確保できなくなる。このため、焼入れ処理の加熱温度はＡc3変態点以上に限定した。なお、好ましくは930℃以上である。
The starting material (seamless steel pipe) is first quenched.
The quenching treatment in the present invention is a treatment of reheating to a quenching temperature not lower than the Ac 3 transformation point, preferably in the range of 800 to 1050 ° C., and then cooling from the quenching temperature to a temperature range of 100 ° C. or lower at a cooling rate higher than air cooling. And Thereby, it can be set as a fine martensitic structure. If the quenching heating temperature is less than the Ac 3 transformation point, the austenite single-phase region cannot be heated, and a sufficient martensite structure cannot be obtained by subsequent cooling, so that a desired strength cannot be ensured. For this reason, the heating temperature of the quenching process is limited to the Ac 3 transformation point or higher. In addition, Preferably it is 930 degreeC or more.
また、焼入れ加熱温度からの冷却は、空冷またはそれ以上の冷却速度で100℃以下の温度域まで行う。本発明における出発素材は焼入れ性が高いため、空冷程度の冷却速度で100℃以下の温度域まで冷却すれば、十分な焼入れ組織（マルテンサイト組織）を得ることができる。また、焼入れ温度における保持時間は、10min以上とすることが均熱の観点から好ましい。 Cooling from the quenching heating temperature is performed to a temperature range of 100 ° C. or lower at an air cooling or higher cooling rate. Since the starting material in the present invention has high hardenability, a sufficient quenched structure (martensitic structure) can be obtained by cooling to a temperature range of 100 ° C. or lower at a cooling rate of about air cooling. The holding time at the quenching temperature is preferably 10 min or more from the viewpoint of soaking.
なお、本発明における出発素材は焼入れ性が高いため、熱間加工により造管した後に、空冷以上の冷却速度で100℃以下まで冷却すれば、十分なマルテンサイト組織とすることができる。このため、再加熱して焼入れる焼入れ処理を省略し、焼戻処理を行うことができる。
焼入れ処理を施された継目無鋼管は、引続き、焼戻処理を施される。
In addition, since the starting material in this invention has high hardenability, if it cools to 100 degrees C or less with the cooling rate more than air cooling after pipe-forming by hot processing, it can be set as sufficient martensitic structure. For this reason, the quenching process which reheats and quenches can be omitted, and the tempering process can be performed.
The seamless steel pipe that has been subjected to the quenching process is subsequently subjected to a tempering process.
本発明では焼戻処理は、優れた低温靭性を確保するうえで重要な処理である。本発明における焼戻処理は、530℃以上好ましくはＡc1変態点以下の焼戻温度に加熱し、好ましくは５min以上保持したのち、好ましくは空冷以上の冷却速度で、好ましくは室温まで冷却する処理とする。これにより、YS：655MPa以上862MPa以下の高強度と降伏比：0.90以上の引張特性を有する継目無鋼管となる。 In the present invention, the tempering process is an important process for securing excellent low temperature toughness. The tempering treatment in the present invention is a treatment of heating to a tempering temperature of 530 ° C. or more, preferably the Ac 1 transformation point or less, preferably holding for 5 min or more, and then preferably cooling to room temperature at a cooling rate of air cooling or more. And As a result, a seamless steel pipe having a high strength of YS: 655 MPa or more and 862 MPa or less and a tensile property of yield ratio: 0.90 or more is obtained.
なお、焼戻温度が530℃未満では、その後の矯正温度を焼戻温度以下に低くせざるを得ないため、降伏強さＹＳのばらつきが生じやすい。一方、焼戻温度がＡc1変態点超えでは、オーステナイト相が生成し、冷却時に焼入れマルテンサイトに変態する。焼入れマルテンサイトは多くの可動転位を有しているため、焼入れマルテンサイトが生成すると、降伏強さYSが低下する。また、焼戻温度からの冷却は、空冷またはそれ以上の冷却速度とすることが、十分なマルテンサイトを得る観点から好ましい。 If the tempering temperature is less than 530 ° C., the subsequent correction temperature must be lowered to the tempering temperature or less, and therefore, the yield strength YS tends to vary. On the other hand, when the tempering temperature exceeds the Ac 1 transformation point, an austenite phase is generated and transformed into quenched martensite during cooling. Since the quenched martensite has many movable dislocations, the yield strength YS decreases when the quenched martensite is generated. The cooling from the tempering temperature is preferably air cooling or a cooling rate higher than that from the viewpoint of obtaining sufficient martensite.
また、本発明では、必要に応じて、焼戻処理に引続き、鋼管形状の不良を矯正するために矯正処理を施しても良い。矯正処理は、450℃以上の温度域で行うことが好ましい。矯正処理の温度が450℃未満では、矯正処理時に鋼管に局所的に加工歪が付加され、機械的特性、とくに降伏強さYSのばらつき、が生じやすい。このため、矯正処理を行う場合には、450℃以上の温度域で行うことが好ましい。 Moreover, in this invention, you may perform a correction process in order to correct the defect of a steel pipe shape following a tempering process as needed. The straightening treatment is preferably performed in a temperature range of 450 ° C. or higher. When the temperature of the straightening treatment is less than 450 ° C., processing strain is locally added to the steel pipe during the straightening treatment, and mechanical characteristics, in particular, yield strength YS, are likely to vary. For this reason, when performing a correction process, it is preferable to carry out in the temperature range of 450 degreeC or more.
上記した製造方法で製造される、継目無鋼管は、上記した組成と上記した組織を有し、降伏強さYS：655MPa以上862MPa以下と降伏比：0.90以上を有する高強度と、さらに油井管として十分な耐食性をも兼備するマルテンサイト系ステンレス継目無鋼管となる。なお、上記した降伏強さを有して、降伏比が0.90未満では、引張強さが高くなり、耐硫化物応力腐食割れ性が低下するため、所望の耐硫化物応力腐食割れ性を確保するためには、所望の範囲の引張特性を確保することが重要となる。YSが655MPa未満では、油井管用として所望の強度を満足できなくなり、一方、YSが862MPaを超えると、耐硫化物応力腐食割れ性が低下する。 Produced by the production method described above, seamless steel pipe has a structure that describes the upper and the above-described composition, yield strength YS: 655 MPa or more 862MPa or less and the yield ratio: high strength with 0.90 or more, more OCTG As a martensitic stainless steel seamless pipe that also has sufficient corrosion resistance. If the yield ratio is less than 0.90, the tensile strength is increased and the sulfide stress corrosion cracking resistance is reduced, so that the desired sulfide stress corrosion cracking resistance is ensured. For this purpose, it is important to ensure a desired range of tensile properties. If YS is less than 655 MPa, the desired strength for oil well pipes cannot be satisfied. On the other hand, if YS exceeds 862 MPa, the resistance to sulfide stress corrosion cracking decreases.
表１に示す組成の溶鋼を十分に脱ガス後、100キロ鋼塊とし、鋼管素材とした。これら鋼管素材を加熱し、研究用モデルシームレス圧延機により、造管したのち、空冷して、継目無鋼管（外径3.3”（83.8mm）φ×肉厚0.5”（12.7mm））とした。
得られた継目無鋼管から、試験材（鋼管）を採取し、該試験材（鋼管）に表２に示す条件で焼入れ処理、焼戻処理を施した。
The molten steel having the composition shown in Table 1 was sufficiently degassed, and then made into a 100 kg steel ingot to obtain a steel pipe material. These steel pipe materials were heated, piped using a research model seamless rolling mill, and then air-cooled to obtain seamless steel pipes (outer diameter 3.3 ”(83.8 mm) φ × thickness 0.5” (12.7 mm)).
A test material (steel pipe) was collected from the obtained seamless steel pipe, and the test material (steel pipe) was quenched and tempered under the conditions shown in Table 2.
焼入れ処理および焼戻処理を施された試験材（鋼管）から、API弧状引張試験片を採取し、引張試験を実施し引張特性（降伏強さYS、引張強さTS）を求めた。
また、焼入れ処理および焼戻処理を施された試験材から、厚さ３mm×幅30mm×長さ40mmの腐食試験片を機械加工によって作製し、炭酸ガス応力腐食試験を、また試験材から、NACE-TM0177のMethod Ａの規定に準拠して丸棒引張試験片を採取し、硫化物応力腐食割れ試験を実施した。
From the specimens (steel pipes) that had been quenched and tempered, API arc-shaped tensile specimens were collected and subjected to tensile tests to determine tensile properties (yield strength YS, tensile strength TS).
In addition, corrosion test specimens of thickness 3mm x width 30mm x length 40mm are made by machining from test materials that have been subjected to quenching and tempering treatments. -A round bar tensile test specimen was taken in accordance with the method A of TM0177 and a sulfide stress corrosion cracking test was conducted.
炭酸ガス応力腐食試験は、オートクレーブ中に保持された試験液：20％NaCl水溶液（液温：230℃、CO２ガス分圧：３MPaのCO２ガス雰囲気）中に、腐食試験片を浸漬し、浸漬期間を２週間（336 ｈr）として実施した。腐食試験後の試験片について、重量を測定し、腐食試験前後の重量減から、腐食速度を算出した。また、腐食試験後の試験片について、10倍のルーペで孔食の有無を観察し、孔食なしを○、孔食ありを×とした。腐食速度：0.1mm/y以下で、かつ孔食なしの場合を、耐炭酸ガス応力腐食性に優れるとして○と評価した。それ以外を、耐炭酸ガス応力腐食性が劣るとして、×と評価した。 The carbon dioxide stress corrosion test is performed by immersing a corrosion test piece in a test solution retained in an autoclave: 20% NaCl aqueous solution (liquid temperature: 230 ° C., CO 2 gas partial pressure: 3 MPa CO 2 gas atmosphere) The immersion period was 2 weeks (336 hr). The test piece after the corrosion test was weighed, and the corrosion rate was calculated from the weight loss before and after the corrosion test. Moreover, about the test piece after a corrosion test, the presence or absence of pitting corrosion was observed with the magnifier 10 times, and it was set as (circle) and pitting corrosion with x. Corrosion rate: 0.1 mm / y or less and no pitting corrosion were evaluated as “good” as being excellent in carbon dioxide stress corrosion resistance. Other than that, it was evaluated as x because the carbon dioxide stress corrosion resistance was poor.
硫化物応力腐食割れ試験は、オートクレーブ中に保持された試験液中に丸棒引張試験片を浸漬し、NACE-TM0177のMethod Ａの規定に準拠して、YSの90％の応力を負荷し、720hr間保持する試験を実施した。720hr経過後に破断していない場合を、耐硫化物応力腐食割れ性に優れるとして○と評価した。それ以外は×とした。なお、使用した試験液は、20％NaCl水溶液（液温：25℃）を用い、0.3％酢酸（CH３COOH）とCH３COONaを添加して、pH：3.5に調整したものを用い、試験は、質量％で、10％H２Sを含み90％CO２のガスを流す環境下（圧力：１気圧）で行った。 The sulfide stress corrosion cracking test is performed by immersing a round bar tensile test piece in a test solution held in an autoclave and applying a stress of 90% of YS in accordance with the method A of NACE-TM0177. A test was held for 720 hours. The case where it did not break after 720 hours passed was evaluated as “good” as being excellent in resistance to sulfide stress corrosion cracking. Otherwise, it was set as “x”. The test solution used was a 20% NaCl aqueous solution (solution temperature: 25 ° C), 0.3% acetic acid (CH 3 COOH) and CH 3 COONa were added, and the pH was adjusted to 3.5. Was carried out in an environment (pressure: 1 atm) containing 10% H 2 S and flowing 90% CO 2 gas.
得られた結果を表３に示す。 The obtained results are shown in Table 3.
本発明例はいずれも、油井管として十分な、強度と、優れた耐食性を有する継目無鋼管となっており、高温、高圧の炭酸ガス雰囲気中においても十分、使用可能であることがわかる。一方、本発明の範囲から外れる比較例は、強度が不足するか、所望の優れた耐食性を確保できていない。 Each of the examples of the present invention is a seamless steel pipe having sufficient strength and excellent corrosion resistance as an oil well pipe, and it can be seen that it can be used sufficiently even in a high-temperature, high-pressure carbon dioxide atmosphere. On the other hand, comparative examples that are out of the scope of the present invention do not have sufficient strength or have not secured the desired excellent corrosion resistance.
Claims (5)
Ｃ：0.01％以下、 Si：0.5％以下、
Mn：0.1〜2.0％、 Ｐ：0.03％以下、
Ｓ：0.005％以下、 Cr：15.5％超17.5％以下、
Ni：2.5〜5.5％、 Mo：1.8〜3.5％、
Cu：0.3〜3.5％、 Ｖ：0.20％以下、
Al：0.05％以下、 Ｎ：0.06％以下
を含み、残部Feおよび不可避的不純物からなる組成を有し、体積率で15％以上のフェライト相と25％以下の残留オーステナイト相を含み、50％以上の焼戻マルテンサイト相からなる組織を有し、降伏強さ：655〜862MPaの強度と降伏比：0.90以上を有し、耐炭酸ガス腐食性および耐硫化物応力腐食割れ性に優れることを特徴とする油井用高強度マルテンサイト系ステンレス継目無鋼管。 % By mass
C: 0.01% or less, Si: 0.5% or less,
Mn: 0.1 to 2.0%, P: 0.03% or less,
S: 0.005% or less, Cr: more than 15.5%, 17.5% or less,
Ni: 2.5-5.5%, Mo: 1.8-3.5%,
Cu: 0.3 to 3.5%, V: 0.20% or less,
Al: 0.05% or less, N: 0.06% or less, with the balance consisting of Fe and inevitable impurities , including 15% or more ferrite phase by volume and 25% or less residual austenite phase, 50% or more It has a structure consisting of a tempered martensite phase, has a yield strength of 655 to 862 MPa and a yield ratio of 0.90 or more, and is excellent in carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance. High strength martensitic stainless steel seamless pipe for oil wells.
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