JP6315159B1 - Martensitic stainless steel seamless pipe for oil well pipe and method for producing the same - Google Patents

Martensitic stainless steel seamless pipe for oil well pipe and method for producing the same Download PDF

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JP6315159B1
JP6315159B1 JP2017567270A JP2017567270A JP6315159B1 JP 6315159 B1 JP6315159 B1 JP 6315159B1 JP 2017567270 A JP2017567270 A JP 2017567270A JP 2017567270 A JP2017567270 A JP 2017567270A JP 6315159 B1 JP6315159 B1 JP 6315159B1
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まみ 遠藤
まみ 遠藤
江口　健一郎
健一郎 江口
正雄 柚賀
正雄 柚賀
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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Abstract

高強度で、かつ、優れた耐硫化物応力腐食割れ性を有する油井管用マルテンサイト系ステンレス継目無鋼管およびその製造方法の提供。質量％で、C：0.035％以下、Si：0.5％以下、Mn：0.05〜0.5％、P：0.03％以下、S：0.005％以下、Cu：2.6％以下、Ni：5.3〜7.3％、Cr：11.8〜14.5％、Al：0.1％以下、Mo：1.8〜3.0％、V：0.2％以下、N：0.1％以下を含有し、かつC、Mn、Cr、Cu、Ni、Mo、W、Nb、N、Tiが所定の関係式を満足し、残部Feおよび不可避的不純物からなる組成を有する油井管用マルテンサイト系ステンレス継目無鋼管。A martensitic stainless steel seamless pipe for oil well pipes having high strength and excellent sulfide stress corrosion cracking resistance, and a method for producing the same. In mass%, C: 0.035% or less, Si: 0.5% or less, Mn: 0.05-0.5%, P: 0.03% or less, S: 0.005% or less, Cu: 2.6% or less, Ni: 5.3-7.3%, Cr: 11.8 to 14.5%, Al: 0.1% or less, Mo: 1.8 to 3.0%, V: 0.2% or less, N: 0.1% or less, and C, Mn, Cr, Cu, Ni, Mo, W, Nb, A martensitic stainless steel seamless pipe for oil country tubular goods having a composition in which N and Ti satisfy a predetermined relational expression and the balance is Fe and inevitable impurities.

Description

本発明は、原油あるいは天然ガスの油井、ガス井（以下、単に油井と称する）に使用される油井管用(oil country tubular goods)マルテンサイト系ステンレス継目無鋼管およびその製造方法に係り、とくに炭酸ガス（CO2）、塩素イオン（Cl−）などを含む、極めて厳しい腐食環境下における耐食性と、硫化水素（H2S）を含む環境における耐硫化物応力腐食割れ性（耐SSC性）の改善に関する。The present invention relates to an oil country tubular goods martensitic stainless steel pipe used for oil or gas wells (hereinafter simply referred to as oil wells) and a method for producing the same. (CO 2 ), chloride ions (Cl − ), etc., including corrosion resistance in extremely severe corrosive environments, and improvement of sulfide stress corrosion cracking resistance (SSC resistance) in environments containing hydrogen sulfide (H 2 S) .

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高深度の油田や、炭酸ガス、塩素イオンや硫化水素を含む厳しい腐食環境の油田やガス油田等の開発が盛んになっている。このような環境下で使用される油井管用鋼管(oil country tubular goods)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 at high depths that were not previously excluded, and severe corrosive environments containing carbon dioxide, chlorine ions, and hydrogen sulfide The development of oil fields and gas fields in the region has become active. Oil country tubular goods used in such an environment are required to have a material having high strength and excellent corrosion resistance.

従来、炭酸ガス、および塩素イオン等を含む環境の油田および、ガス田では、採掘に使用する油井管(oil country tubular goods)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。最近では、硫化水素を含む極めて厳しい腐食環境での油田等の開発が世界規模で行われているため、耐SSC性の要求が高まりつつあり、Cを低減させ、NiやMoを増加させた成分系の改良型13％Crマルテンサイト系ステンレス鋼管の使用も拡大している。
特許文献１では、13％Cr系鋼を基本組成として、Cを従来よりも著しく低減し、さらにNi、Moおよび、Cuを含有させ、Cr＋2Ni＋1.1Mo＋0.7Cu≦32.5を満足し、また、さらにNb：0.20％以下、V：0.20％以下のうち１種または2種をNb＋V≧0.05％の条件を満足するように、それぞれ含有した組成とすることで、降伏強度：965MPa以上の高強度と、−40℃におけるシャルピー吸収エネルギーが50J以上の高靱性を兼備し、かつ良好な耐食性が確保できるとしている。Conventionally, 13% Cr martensitic stainless steel pipes are often used as oil country tubular goods for mining in oil fields and gas fields that contain carbon dioxide and chlorine ions. Recently, development of oil fields, etc. in extremely severe corrosive environments containing hydrogen sulfide has been carried out on a global scale, so the demand for SSC resistance is increasing, and components that have reduced C and increased Ni and Mo The use of improved 13% Cr martensitic stainless steel pipes is also expanding.
In Patent Document 1, 13% Cr-based steel is used as the basic composition, C is remarkably reduced as compared with the prior art, Ni, Mo and Cu are further included, Cr + 2Ni + 1.1Mo + 0.7Cu ≦ 32.5 is satisfied, and Nb is further added. : 0.20% or less, V: A composition containing one or two of 0.20% or less so as to satisfy the condition of Nb + V ≧ 0.05%, yield strength: high strength of 965 MPa or more, − It is said that it has high toughness with Charpy absorbed energy at 40 ° C of 50J or more, and can secure good corrosion resistance.

特許文献２では、0.015％以下の極低C量、および0.03％以上のTiを含有する成分系の13％Cr系マルテンサイト系ステンレス鋼管が記載されており、降伏応力95ksi級（６５５−７５８ＭＰa）の高強度と、ロックウエル硬さHRCで27未満という低硬さを兼備し、優れた耐SSC性を有するとしている。また、特許文献３では、引張応力から降伏応力を差し引いた値と相関関係を有するTi/Cが、6.0≦Ti/C≦10.1を満たすマルテンサイト系ステンレス鋼が記載されている。記載された技術によって、引張応力から降伏応力を引いた値が20.7MPa以上であり、かつ、耐SSC性を低下させる硬度のばらつきを抑えることができるとしている。   Patent Document 2 describes a 13% Cr martensitic stainless steel pipe containing 0.01% or less of an extremely low C content and 0.03% or more of Ti, and has a yield stress of 95 ksi class (655 to 758 MPa). It has both high strength and low hardness of Rockwell hardness HRC of less than 27, and is said to have excellent SSC resistance. Patent Document 3 describes martensitic stainless steel in which Ti / C having a correlation with a value obtained by subtracting yield stress from tensile stress satisfies 6.0 ≦ Ti / C ≦ 10.1. According to the described technique, the value obtained by subtracting the yield stress from the tensile stress is 20.7 MPa or more, and it is possible to suppress variation in hardness that reduces the SSC resistance.

また、特許文献４では、鋼中のMo量をMo≧2.3−0.89Si＋32.2Cで規定し、かつ、金属組織を主として焼戻しマルテンサイト、焼き戻し時に析出した炭化物および焼き戻し時に微細析出したラーベス相やδ相等の金属間化合物から構成されるマルテンサイト系ステンレス鋼が記載されている。記載された技術により、0.2％耐力が860MPa以上の高強度を達成し、優れた耐炭酸ガス腐食性（carbon dioxide-corrosion resistance）および耐硫化物応力腐食割れ性を有することができるとされている。   In Patent Document 4, the amount of Mo in the steel is specified by Mo ≧ 2.3−0.89Si + 32.2C, and the metal structure is mainly tempered martensite, carbides precipitated during tempering, and Laves phase precipitated finely during tempering. And martensitic stainless steel composed of intermetallic compounds such as δ phase and the like. According to the described technology, 0.2% proof stress can achieve high strength of 860MPa or more, and can have excellent carbon dioxide-corrosion resistance and sulfide stress corrosion cracking resistance. .

特開2007-332442号公報JP 2007-332442 A 特開2010-242163号公報JP 2010-242163 A 国際公開2008/023702号International Publication 2008/023702 国際公開2004/057050号International Publication No. 2004/057050

近年の油田やガス田は、CO2、Cl−および、H2Sを含む厳しい腐食環境で開発されている。更に、経年変化によるH2S濃度の増加が懸念されており、使用される油井用鋼管(oil country tubular goods)には、耐炭酸ガス腐食性に加えて、優れた耐硫化物応力腐食割れ性（耐SSC性）が要求されるようになっている。特許文献１に記載された技術では、優れた耐炭酸ガス腐食性を有するとしている。しかしながら、耐硫化物応力腐食割れ性に対する検討は行われておらず、厳しい腐食環境に耐え得る耐食性を有しているとは言えない。Recent oil and gas fields have been developed in severe corrosive environments containing CO 2 , Cl − and H 2 S. Furthermore, there is concern about an increase in H 2 S concentration due to secular change, and the oil country tubular goods used have excellent sulfide stress corrosion cracking resistance in addition to carbon dioxide corrosion resistance. (SSC resistance) is required. The technique described in Patent Document 1 is said to have excellent carbon dioxide gas corrosion resistance. However, the investigation on the resistance to sulfide stress corrosion cracking has not been made, and it cannot be said that it has corrosion resistance that can withstand a severe corrosive environment.

また、特許文献２では、5％NaCl水溶液（H2S：0.10bar）をpH：3.5に調整した雰囲気下において、655MPaの応力を負荷するという条件で耐硫化物応力腐食割れ性が保持できるとされている。特許文献３では、20％NaCl水溶液（H2S：0.03atm、CO2bal.）をpH：4.5に調整した雰囲気下で、耐硫化物応力腐食割れ性を有するとされている。また、特許文献４では、25％NaCl水溶液（H2S：0.003MPa、CO2bal.）をpH：4.0に調整した雰囲気下において、耐硫化物応力腐食割れ性を有するとされている。しかしながら、上記以外の雰囲気下での耐硫化物応力腐食割れ性は検討されておらず、昨今のより厳しい腐食環境に耐え得る、耐硫化物応力腐食割れ性を具備するとは言い難い。Further, in Patent Document 2, the resistance to sulfide stress corrosion cracking can be maintained under the condition that a stress of 655 MPa is applied in an atmosphere in which a 5% NaCl aqueous solution (H 2 S: 0.10 bar) is adjusted to pH 3.5. Has been. In Patent Document 3, it is said that it has resistance to sulfide stress corrosion cracking in an atmosphere in which a 20% NaCl aqueous solution (H 2 S: 0.03 atm, CO 2 bal.) Is adjusted to pH: 4.5. Further, in Patent Document 4, it is said that it has sulfide stress corrosion cracking resistance in an atmosphere in which a 25% NaCl aqueous solution (H 2 S: 0.003 MPa, CO 2 bal.) Is adjusted to pH: 4.0. However, the resistance to sulfide stress corrosion cracking in atmospheres other than those described above has not been studied, and it is difficult to say that it has the resistance to sulfide stress corrosion cracking that can withstand the more severe corrosion environments of recent years.

本発明は、高強度で、かつ、優れた耐硫化物応力腐食割れ性を有する油井管用マルテンサイト系ステンレス継目無鋼管およびその製造方法を提供することを目的とする。
なお、ここでいう「高強度」とは、降伏応力：758MPa（110ksi）以上であるものとする。好ましくは、降伏応力は、896MPa以下である。
また、ここでいう「優れた耐硫化物応力腐食割れ性」とは、試験液：0.165質量％NaCl水溶液（液温：25℃、H2S：1bar、CO2bal）に、酢酸Na＋塩酸を加えてpH：3.5に調整した水溶液中に、試験片を浸漬させ、浸漬時間を720時間として、降伏応力の90％を負荷応力として付加して試験を行い、試験後の試験片に割れが発生しない場合をいうものとする。An object of the present invention is to provide a martensitic stainless steel seamless pipe for oil well pipes having high strength and excellent sulfide stress corrosion cracking resistance, and a method for producing the same.
Here, “high strength” is assumed to be a yield stress of 758 MPa (110 ksi) or more. Preferably, the yield stress is 896 MPa or less.
In addition, “excellent sulfide stress corrosion cracking resistance” as used herein refers to test solution: 0.165% by mass NaCl aqueous solution (liquid temperature: 25 ° C., H 2 S: 1 bar, CO 2 bal), Na acetate and hydrochloric acid. In addition, the test piece is immersed in an aqueous solution adjusted to pH: 3.5, the immersion time is set to 720 hours, 90% of the yield stress is applied as the load stress, and the test piece is cracked after the test. It shall mean the case where it does not.

本発明者らは、上記した目的を達成するために、13％Cr系ステンレス鋼管を基本組成として、CO2、Cl−、更にH2Sを含む腐食環境下における耐硫化物応力腐食割れ性（耐SSC性）に及ぼす各種合金元素の影響について鋭意検討した。その結果、C、Mn、Cr、Cu、Ni、Mo、W、Nb、N、およびTiを適正な関係式及び範囲を満足するように調整して含有する組成で、適正な焼入れ処理および焼戻処理を施すことにより、所望の強度で、かつCO2、Cl−、更にH2Sを含む腐食雰囲気下で、かつ降伏応力近傍の応力が負荷される環境下において優れた耐SSC性を有する油井管用マルテンサイト系ステンレス継目無鋼管とすることができると見出した。In order to achieve the above-mentioned object, the inventors of the present invention have a 13% Cr stainless steel pipe as a basic composition, sulfide stress corrosion cracking resistance in a corrosive environment containing CO 2 , Cl − , and H 2 S ( The effect of various alloying elements on SSC resistance was studied. As a result, proper quenching and tempering with a composition containing C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, and Ti adjusted to satisfy the appropriate relational expression and range. An oil well that has excellent SSC resistance in a corrosive atmosphere containing CO 2 , Cl − , and H 2 S, and in an environment where stress near the yield stress is applied by applying the treatment. It has been found that a martensitic stainless steel seamless pipe for pipes can be obtained.

本発明は、上記した知見に基づき、更に検討を加えて完成させたものである。すなわち、本発明の要旨は次のとおりである。
［１］質量％で、C：0.035％以下、Si：0.5％以下、Mn：0.05〜0.5％、P：0.03％以下、S：0.005％以下、Cu：2.6％以下、Ni：5.3〜7.3％、Cr：11.8〜14.5％、Al：0.1％以下、Mo：1.8〜3.0％、V：0.2％以下、N：0.1％以下を含有し、かつ下記（1）式、（2）式および（3）式が下記（4）を満足し、残部Feおよび不可避的不純物からなる組成を有し、
758MPa以上の降伏応力を有することを特徴とする油井管用マルテンサイト系ステンレス継目無鋼管。
記
−109.37C＋7.307Mn＋6.399Cr＋6.329Cu＋11.343Ni−13.529Mo＋1.276W＋2.925Nb＋196.775N−2.621Ti−120.307 ・・・(1)
−0.0278Mn＋0.0892Cr＋0.00567Ni＋0.153Mo−0.0219W−1.984N＋0.208Ti−1.83 ・・・(2)
−1.324C＋0.0533Mn＋0.0268Cr＋0.0893Cu＋0.00526Ni＋0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 ・・・(3)
ここで、C、Mn、Cr、Cu、Ni、Mo、W、Nb、N、Ti：各元素の含有量（質量％）（但し、含有しない元素は０（零）％とする。）
−10≦(1)式≦45 且つ −0.25≦(2)式≦−0.20 且つ 0.10≦(3)式≦0.20 ・・・(4)
［２］前記組成に加えて更に、質量％で、Ti：0.19％以下、Nb：0.25％以下、W：1.1％以下、Co：0.45％以下のうちから選ばれた1種または2種以上を含有することを特徴とする前記［１］に記載の油井管用マルテンサイト系ステンレス継目無鋼管。
［３］前記［１］または［２］に記載の油井管用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り、鋼管素材を造管し鋼管としたのち、該鋼管にAc3変態点以上に加熱し、続いて100℃以下の冷却停止温度まで0.1℃/ｓ以上の冷却速度で空冷する焼入れ処理と、ついでAc1変態点以下の温度で焼き戻しをする焼戻処理とを施すことを特徴とする油井管用マルテンサイト系ステンレス継目無鋼管の製造方法。The present invention has been completed by further studies based on the above findings. That is, the gist of the present invention is as follows.
[1] By mass%, C: 0.035% or less, Si: 0.5% or less, Mn: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Cu: 2.6% or less, Ni: 5.3 to 7.3% , Cr: 11.8 to 14.5%, Al: 0.1% or less, Mo: 1.8 to 3.0%, V: 0.2% or less, N: 0.1% or less, and the following formulas (1), (2) and (3 ) Formula satisfies the following (4), has a composition consisting of the balance Fe and inevitable impurities,
A martensitic stainless steel seamless pipe for oil well pipes characterized by having a yield stress of 758 MPa or more.
-109.37C + 7.307Mn + 6.399Cr + 6.329Cu + 11.343Ni-13.529Mo + 1.276W + 2.925Nb + 196.775N-2.621Ti-120.307 (1)
−0.0278Mn + 0.0892Cr + 0.00567Ni + 0.153Mo−0.0219W−1.984N + 0.208Ti−1.83 (2)
−1.324C + 0.0533Mn + 0.0268Cr + 0.0893Cu + 0.00526Ni + 0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 (3)
Here, C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, Ti: Content of each element (mass%) (however, elements not contained are 0 (zero)%)
−10 ≦ (1) Formula ≦ 45 and −0.25 ≦ (2) Formula ≦ −0.20 and 0.10 ≦ (3) Formula ≦ 0.20 (4)
[2] In addition to the above composition, one or more selected from the following in terms of mass%: Ti: 0.19% or less, Nb: 0.25% or less, W: 1.1% or less, Co: 0.45% or less The martensitic stainless steel seamless steel pipe for oil country tubular goods according to the above [1], comprising:
[3] A method for producing a martensitic stainless seamless steel pipe for oil country tubular goods according to [1] or [2], wherein a steel pipe material is formed into a steel pipe, and then the steel pipe is heated to an Ac 3 transformation point or higher. Next, a quenching process in which air cooling is performed at a cooling rate of 0.1 ° C./s or higher to a cooling stop temperature of 100 ° C. or lower and a tempering process in which tempering is performed at a temperature lower than the Ac 1 transformation point is performed. To manufacture martensitic stainless steel seamless pipes for oil well pipes.

本発明によれば、CO2、Cl−、更にH2Sを含む腐食環境下において、優れた耐硫化物応力腐食割れ性（耐SSC性）を有し、かつ降伏応力YS：758MPa（110ksi）以上の高強度を有する油井管用マルテンサイト系ステンレス継目無鋼管を得ることができる。According to the present invention, it has excellent sulfide stress corrosion cracking resistance (SSC resistance) in a corrosive environment containing CO 2 , Cl − and H 2 S, and yield stress YS: 758 MPa (110 ksi) A martensitic stainless steel seamless pipe for oil country tubular goods having the above high strength can be obtained.

本発明のステンレス継目無鋼管は、質量％で、C：0.035％以下、Si：0.5％以下、Mn：0.05〜0.5％、P：0.03％以下、S：0.005％以下、Cu：2.6％以下、Ni：5.3〜7.3％、Cr：11.8〜14.5％、Al：0.1％以下、Mo：1.8〜3.0％、V：0.2％以下、N：0.1％以下を含有し、かつ下記（1）式、（2）式および（3）式が下記（4）または（5）または（6）を満足し、残部Feおよび不可避的不純物からなる組成を有し、758MPa以上の降伏応力を有する油井管用マルテンサイト系ステンレス継目無鋼管である。
記
−109.37C＋7.307Mn＋6.399Cr＋6.329Cu＋11.343Ni−13.529Mo＋1.276W＋2.925Nb＋196.775N−2.621Ti−120.307 ・・・(1)
−0.0278Mn＋0.0892Cr＋0.00567Ni＋0.153Mo−0.0219W−1.984N＋0.208Ti−1.83 ・・・(2)
−1.324C＋0.0533Mn＋0.0268Cr＋0.0893Cu＋0.00526Ni＋0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 ・・・(3)
ここで、C、Mn、Cr、Cu、Ni、Mo、W、Nb、N、Ti：各元素の含有量（質量％）（但し、含有しない元素は０（零）％とする。）
−10≦(1)式≦45 且つ −0.25≦(2)式≦−0.20 且つ 0.10≦(3)式≦0.20 ・・・(4)
−10≦(1)式≦5 且つ −0.35≦(2)式≦−0.25 且つ 0.025≦(3)式≦0.10 ・・・(5)
−10≦(1)式≦−5 且つ −0.39≦(2)式≦−0.35 且つ −0.15≦(3)式≦0.025 ・・・(6)The stainless steel seamless pipe of the present invention is in mass%, C: 0.035% or less, Si: 0.5% or less, Mn: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Cu: 2.6% or less, Ni: 5.3-7.3%, Cr: 11.8-14.5%, Al: 0.1% or less, Mo: 1.8-3.0%, V: 0.2% or less, N: 0.1% or less, and the following formula (1), ( 2) and 3) satisfy the following (4), (5) or (6), have a composition consisting of the remaining Fe and inevitable impurities, and have a yield stress of 758 MPa or more. Stainless steel seamless steel pipe.
-109.37C + 7.307Mn + 6.399Cr + 6.329Cu + 11.343Ni-13.529Mo + 1.276W + 2.925Nb + 196.775N-2.621Ti-120.307 (1)
−0.0278Mn + 0.0892Cr + 0.00567Ni + 0.153Mo−0.0219W−1.984N + 0.208Ti−1.83 (2)
−1.324C + 0.0533Mn + 0.0268Cr + 0.0893Cu + 0.00526Ni + 0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 (3)
Here, C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, Ti: Content of each element (mass%) (however, elements not contained are 0 (zero)%)
−10 ≦ (1) Formula ≦ 45 and −0.25 ≦ (2) Formula ≦ −0.20 and 0.10 ≦ (3) Formula ≦ 0.20 (4)
−10 ≦ (1) Formula ≦ 5 and −0.35 ≦ (2) Formula ≦ −0.25 and 0.025 ≦ (3) Formula ≦ 0.10 (5)
−10 ≦ (1) Formula ≦ −5 and −0.39 ≦ (2) Formula ≦ −0.35 and −0.15 ≦ (3) Formula ≦ 0.025 (6)

まず、本発明鋼管の組成限定理由について説明する。以下、とくに断らない限り、質量％は単に％と記す。   First, the reasons for limiting the composition of the steel pipe of the present invention will be described. Hereinafter, unless otherwise specified, mass% is simply referred to as%.

C：0.035％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、強度向上に有効である。しかしながら、0.035％を超える含有量では、硬度が高くなりすぎるため、硫化物応力腐食割れ感受性が増大する。このため、本発明では、C含有量は0.035％以下に限定する。また好ましくは、C含有量は0.015％以下である。より好ましくは、C含有量は0.0090％以下である。さらに好ましくは、含有量は0.0075％以下である。一方、所望の強度を確保するために、C含有量は0.005％以上含有することが望ましい。C: 0.035% or less
C is an important element related to the strength of martensitic stainless steel and is effective in improving the strength. However, if the content exceeds 0.035%, the hardness becomes too high, so that the sensitivity to sulfide stress corrosion cracking increases. For this reason, in the present invention, the C content is limited to 0.035% or less. Preferably, the C content is 0.015% or less. More preferably, the C content is 0.0090% or less. More preferably, the content is 0.0075% or less. On the other hand, in order to ensure a desired strength, the C content is desirably 0.005% or more.

Si：0.5％以下
Siは、脱酸剤として作用するため、0.05％以上Siを含有することが望ましい。一方で、0.5％を超えるSiの含有は、耐炭酸ガス腐食性および熱間加工性を低下させる。このため、Si含有量は0.5％以下に限定する。Si含有量は、下限が好ましくは0.10％以上であり、上限が好ましくは0.30％以下である。Si: 0.5% or less
Since Si acts as a deoxidizer, it is desirable to contain 0.05% or more of Si. On the other hand, the Si content exceeding 0.5% reduces the carbon dioxide gas corrosion resistance and hot workability. For this reason, Si content is limited to 0.5% or less. The lower limit of the Si content is preferably 0.10% or more, and the upper limit is preferably 0.30% or less.

Mn：0.05〜0.5％
Mnは、熱間加工性を向上させる元素であり、0.05％以上Mnを含有する。一方、0.5％を超えてMnを含有しても、その効果が飽和し、かえってコストの高騰を招く。よって、Mn含有量は0.05〜0.5％に限定する。好ましくは、０．４０％以下である。Mn: 0.05-0.5%
Mn is an element that improves hot workability and contains 0.05% or more of Mn. On the other hand, if the content of Mn exceeds 0.5%, the effect is saturated and the cost is increased. Therefore, the Mn content is limited to 0.05 to 0.5%. Preferably, it is 0.40% or less.

P：0.03％以下
Pは、耐炭酸ガス腐食性、耐孔食性および耐硫化物応力腐食割れ性をともに低下させる元素であり、本発明ではできるだけ低減させることが望ましい。しかしながら、極端な低減は製造コストを高騰させる。よって、特性の極端な低下を招かない範囲で、かつ工業的に安価に実施可能な範囲として、P含有量は0.03％以下に限定する。好ましくは、P含有量は0.02％以下である。P: 0.03% or less
P is an element that lowers both carbon dioxide corrosion resistance, pitting corrosion resistance and sulfide stress corrosion cracking resistance, and is desirably reduced as much as possible in the present invention. However, extreme reduction increases manufacturing costs. Therefore, the P content is limited to 0.03% or less as a range that does not cause an extreme deterioration of the characteristics and can be industrially inexpensively implemented. Preferably, the P content is 0.02% or less.

S：0.005％以下
Sは、熱間加工性を著しく低下させる元素であるため、できるだけ低減させることが望ましい。S含有量を0.005％以下に低減することで、通常工程でのパイプ製造が可能となるため、本発明におけるS含有量は0.005％以下に限定する。好ましくは、S含有量は0.003％以下である。S: 0.005% or less
Since S is an element that significantly reduces hot workability, it is desirable to reduce it as much as possible. By reducing the S content to 0.005% or less, pipe production in a normal process becomes possible, so the S content in the present invention is limited to 0.005% or less. Preferably, the S content is 0.003% or less.

Cu：2.6％以下
Cuは、保護被膜を強固にして耐硫化物応力腐食割れ性を向上させる。しかしながら、2.6％を超えるCuの含有は、CuSを析出させて熱間加工性を低下させる。よって、Cu含有量は2.6％以下に限定する。Cu含有量は、下限が好ましくは0.5％以上であり、上限が好ましくは2.0％以下である。Cu: 2.6% or less
Cu strengthens the protective coating and improves the resistance to sulfide stress corrosion cracking. However, if Cu content exceeds 2.6%, CuS is precipitated and hot workability is lowered. Therefore, the Cu content is limited to 2.6% or less. The lower limit of the Cu content is preferably 0.5% or more, and the upper limit is preferably 2.0% or less.

Ni：5.3〜7.3％
Niは、5.3％以上の含有で保護被膜を強固にして耐食性を向上させ、更に固溶することで鋼の強度を増加させる。一方、Ni含有量が7.3％を超えると、マルテンサイト相の安定性が低下して、強度が低下する。よって、Ni含有量は5.3〜7.3％に限定する。好ましくは、５．７％以上、さらに好ましくは、６．０％以上である。Ni: 5.3-7.3%
Ni is contained in an amount of 5.3% or more to strengthen the protective film and improve the corrosion resistance, and further increase the strength of the steel by solid solution. On the other hand, if the Ni content exceeds 7.3%, the stability of the martensite phase decreases and the strength decreases. Therefore, the Ni content is limited to 5.3-7.3%. Preferably, it is 5.7% or more, more preferably 6.0% or more.

Cr：11.8〜14.5％
Crは、保護被膜を形成して耐食性を向上させる元素であり、11.8％以上のCrの含有で油井管用として必要な耐食性を確保できる。一方、Cr含有量が14.5％を超えるとフェライトの生成が容易となるため、マルテンサイト相の安定確保ができなくなる。よって、Cr含有量は11.8〜14.5％に限定する。Cr含有量は、下限が好ましくは12.0％以上であり、上限が好ましくは13.5％以下である。Cr: 11.8 to 14.5%
Cr is an element that improves the corrosion resistance by forming a protective film, and the content of 11.8% or more of Cr can ensure the necessary corrosion resistance for oil well pipes. On the other hand, if the Cr content exceeds 14.5%, the formation of ferrite becomes easy, and it becomes impossible to ensure the stability of the martensite phase. Therefore, the Cr content is limited to 11.8 to 14.5%. The lower limit of the Cr content is preferably 12.0% or more, and the upper limit is preferably 13.5% or less.

Al：0.1％以下
Alは、脱酸剤として作用するため、このような効果を得るためには、0.01％以上のAlの含有が有効である。しかしながら、0.1％を超えるAlの含有は、靱性に悪影響を及ぼすため、本発明におけるAl含有量は0.1％以下に限定する。好ましくは、Al含有量は0.01〜0.03％である。Al: 0.1% or less
Since Al acts as a deoxidizer, it is effective to contain 0.01% or more of Al in order to obtain such an effect. However, since Al content exceeding 0.1% adversely affects toughness, the Al content in the present invention is limited to 0.1% or less. Preferably, the Al content is 0.01 to 0.03%.

Mo：1.8〜3.0％
Moは、Cl−による孔食に対する抵抗性を向上させる元素であり、厳しい腐食環境に必要な耐食性を得るためには、1.8％以上のMoの含有が必要である。一方、3.0％を超えるMoの含有は、上記の効果が飽和する。また、Moは高価な元素であるため、製造コストの高騰を招く。よって、Mo含有量は1.8〜3.0％に限定する。Mo含有量は、好ましくは下限が2.4％以上であり、上限が好ましくは2.9％以下である。Mo: 1.8-3.0%
Mo is an element that improves the resistance to pitting corrosion caused by Cl − , and in order to obtain the corrosion resistance necessary for a severe corrosive environment, it is necessary to contain 1.8% or more of Mo. On the other hand, if the Mo content exceeds 3.0%, the above effect is saturated. In addition, Mo is an expensive element, which causes an increase in manufacturing cost. Therefore, the Mo content is limited to 1.8 to 3.0%. The lower limit of the Mo content is preferably 2.4% or more, and the upper limit is preferably 2.9% or less.

V：0.2％以下
Vは、析出強化によって鋼の強度を向上させ、更に耐硫化物応力腐食割れ性も向上させるため、0.01％以上の含有が望ましい。一方、0.2％を超えるVの含有は、靱性が低下するため、本発明におけるV含有量は0.2％以下に限定する。V含有量は、好ましくは下限が0.01％以上であり、好ましくは上限が0.08％以下である。V: 0.2% or less
V is preferably contained in an amount of 0.01% or more in order to improve the strength of the steel by precipitation strengthening and further improve the resistance to sulfide stress corrosion cracking. On the other hand, if the V content exceeds 0.2%, the toughness decreases, so the V content in the present invention is limited to 0.2% or less. The lower limit of the V content is preferably 0.01% or more, and preferably the upper limit is 0.08% or less.

N：0.1％以下
Nは、耐孔食性を著しく向上させる元素である。しかしながら、N含有量が0.1％超えでは、種々の窒化物を形成して靱性を低下させるため、本発明におけるN含有量は0.1％以下に限定する。好ましくは、N含有量は0.003％以上である。N含有量は、下限はより好ましくは0.004％以上であり、さらに好ましくは0.005％以上である。上限はより好ましくは0.08％以下であり、さらに好ましくは0.05％以下である。N: 0.1% or less
N is an element that significantly improves the pitting corrosion resistance. However, if the N content exceeds 0.1%, various nitrides are formed to reduce toughness, so the N content in the present invention is limited to 0.1% or less. Preferably, the N content is 0.003% or more. The lower limit of the N content is more preferably 0.004% or more, and further preferably 0.005% or more. The upper limit is more preferably 0.08% or less, still more preferably 0.05% or less.

本発明では更に、C、Mn、Cr、Cu、Ni、Mo、W、Nb、N、Tiを、上記の範囲内で含有し、かつ下記の（1）式、（2）式、および（3）式を下記の（4）または（5）または（6）を満足するように、各元素を含有する。(1)式は残留γ量に相関する式であり、（1）式で計算された値を小さくすることで、残留オーステナイトが低減し、硬度が低下して、耐硫化物応力腐食割れ性が向上する。また、(2)式は再不動態化電位に相関する式であり、（1）式で計算された値を（4）または（5）または（6）の範囲を満足するように、C、Mn、Cr、Cu、Ni、Mo、W、Nb、NおよびTiを含有させつつ、（2）式で計算された値も（4）または（5）または（6）の範囲を満足するように、Mn、Cr、Cu、Ni、Mo、W、NおよびTiを含有することで、不動態被膜の再生が容易になり、再不動態化が向上する。更に、(3)式は孔食電位に相関する式であり、（3）式で計算された値を（4）または（5）または（6）の範囲を満足するように、C、Mn、Cr、Cu、Ni、Mo、W、NおよびTiを含有することで、硫化物応力腐食割れの起点となる孔食の発生を抑制し、耐硫化物応力腐食割れ性が顕著に向上する。尚、(1)式で計算された値が(4)の範囲を満足する場合、(1)式で計算された値は10以上で硬度の上昇を招くが、(2)式で計算された値および(3)式で計算された値が(4)の範囲を満足することで、不動態被膜の再生および孔食発生の抑制が顕著に現れ、耐硫化物応力腐食割れ性が向上する。
好ましくは、下記(4)における(1)式で計算された値は、5以上45以下であり、下記(5)における(1)式で計算された値は、-5以上5以下である。
−109.37C＋7.307Mn＋6.399Cr＋6.329Cu＋11.343Ni−13.529Mo＋1.276W＋2.925Nb＋196.775N−2.621Ti−120.307 ・・・(1)
−0.0278Mn＋0.0892Cr＋0.00567Ni＋0.153Mo−0.0219W−1.984N＋0.208Ti−1.83 ・・・(2)
−1.324C＋0.0533Mn＋0.0268Cr＋0.0893Cu＋0.00526Ni＋0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 ・・・(3)
ここで、C、Mn、Cr、Cu、Ni、Mo、W、Nb、N、Ti：各元素の含有量（質量％）（但し、含有しない元素は０（零）％とする。）
−10≦(1)式≦45 且つ −0.25≦(2)式≦−0.20 且つ 0.10≦(3)式≦0.20 ・・・(4)
−10≦(1)式≦5 且つ −0.35≦(2)式≦−0.25 且つ 0.025≦(3)式≦0.10 ・・・(5)
−10≦(1)式≦−5 且つ −0.39≦(2)式≦−0.35 且つ −0.15≦(3)式≦0.025 ・・・(6)The present invention further contains C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, and Ti within the above range, and the following formulas (1), (2), and (3 ) Each element is contained so that the following formula (4) or (5) or (6) is satisfied. Equation (1) correlates with the amount of residual γ. By reducing the value calculated by equation (1), residual austenite is reduced, hardness is reduced, and resistance to sulfide stress corrosion cracking is reduced. improves. Equation (2) is an equation that correlates with the repassivation potential, and the values calculated in Equation (1) are C, Mn so that the range of (4), (5), or (6) is satisfied. , Cr, Cu, Ni, Mo, W, Nb, N and Ti, while the value calculated by the formula (2) also satisfies the range of (4) or (5) or (6) By containing Mn, Cr, Cu, Ni, Mo, W, N and Ti, regeneration of the passive film is facilitated and repassivation is improved. Furthermore, equation (3) is an equation that correlates with the pitting potential, and the value calculated by equation (3) is C, Mn, so as to satisfy the range of (4) or (5) or (6). By containing Cr, Cu, Ni, Mo, W, N, and Ti, the occurrence of pitting corrosion that is the starting point of sulfide stress corrosion cracking is suppressed, and the resistance to sulfide stress corrosion cracking is significantly improved. In addition, when the value calculated by the formula (1) satisfies the range of (4), the value calculated by the formula (1) leads to an increase in hardness at 10 or more, but was calculated by the formula (2). When the value and the value calculated by the expression (3) satisfy the range of (4), regeneration of the passive film and suppression of pitting corrosion appear remarkably, and resistance to sulfide stress corrosion cracking is improved.
Preferably, the value calculated by the expression (1) in the following (4) is 5 or more and 45 or less, and the value calculated by the expression (1) in the following (5) is -5 or more and 5 or less.
−109.37C + 7.307Mn + 6.399Cr + 6.329Cu + 1.343Ni-13.529Mo + 1.276W + 2.925Nb + 196.775N−2.621Ti−120.307 (1)
−0.0278Mn + 0.0892Cr + 0.00567Ni + 0.153Mo−0.0219W−1.984N + 0.208Ti−1.83 (2)
−1.324C + 0.0533Mn + 0.0268Cr + 0.0893Cu + 0.00526Ni + 0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 (3)
Here, C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, Ti: Content of each element (mass%) (however, elements not contained are 0 (zero)%)
−10 ≦ (1) Formula ≦ 45 and −0.25 ≦ (2) Formula ≦ −0.20 and 0.10 ≦ (3) Formula ≦ 0.20 (4)
−10 ≦ (1) Formula ≦ 5 and −0.35 ≦ (2) Formula ≦ −0.25 and 0.025 ≦ (3) Formula ≦ 0.10 (5)
−10 ≦ (1) Formula ≦ −5 and −0.39 ≦ (2) Formula ≦ −0.35 and −0.15 ≦ (3) Formula ≦ 0.025 (6)

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。上述したこれら基本の組成に加えて更に、必要に応じて選択元素として、Ti：0.19％以下、Nb：0.25％以下、W：1.1％以下、Co：0.45％以下のうちから選ばれた1種または2種以上を含有することができる。   The balance other than the components described above consists of Fe and inevitable impurities. In addition to these basic compositions described above, if necessary, one element selected from Ti: 0.19% or less, Nb: 0.25% or less, W: 1.1% or less, Co: 0.45% or less Or it can contain 2 or more types.

TiおよびNbは、炭化物を形成することで、固溶炭素を減少させて、硬度を低減できる。一方、過剰な含有は、靱性を低下させる場合があるため、Tiおよび／またはNbを含有する場合には、Tiは0.19％以下、Nbは0.25％以下に限定する。   Ti and Nb can reduce the solid solution carbon and reduce the hardness by forming carbides. On the other hand, since excessive inclusion may reduce toughness, when Ti and / or Nb is contained, Ti is limited to 0.19% or less, and Nb is limited to 0.25% or less.

WおよびCoは、共に耐孔食性を向上させる元素である。しかしながら、過剰な含有は靱性を低下させる場合があり、更に材料コストを高騰させる。よって、Wおよび／またはCoを含有する場合にはWは1.1％以下、Coは0.45％以下に限定する。   W and Co are both elements that improve pitting corrosion resistance. However, excessive inclusion may reduce toughness and further increase the material cost. Therefore, when W and / or Co is contained, W is limited to 1.1% or less, and Co is limited to 0.45% or less.

つぎに、本発明の油井管用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。
本発明では、上記の組成を有する鋼管素材を用いる。鋼管素材であるステンレス継目無鋼管の製造方法は特に限定する必要はなく、公知の継目無鋼管の製造方法がいずれも適用できる。
上記組成の溶鋼を、転炉等の溶製方法で溶製し、連続鋳造法、造塊−分塊圧延法等の方法でビレット等の鋼管素材とすることが好ましい。続いて、これらの鋼管素材を加熱し、公知の造管方法である、マンネスマン−プラグミル方式、またはマンネスマン−マンドレルミル方式の造管工程にて、熱間加工および造管し、上記組成を有する継目無鋼管とする。Below, the preferable manufacturing method of the martensitic stainless steel seamless pipe for oil country tubular goods of this invention is demonstrated.
In the present invention, a steel pipe material having the above composition is used. The manufacturing method of the stainless steel seamless steel pipe which is a steel pipe raw material does not need to be specifically limited, Any known manufacturing method of a seamless steel pipe can be applied.
It is preferable that the molten steel having the above composition is melted by a melting method such as a converter and used as a steel pipe material such as a billet by a method such as a continuous casting method or an ingot-bundling rolling method. Subsequently, these steel pipe materials are heated, and are hot-worked and piped in a pipe making process of a Mannesmann-plug mill system or a Mannesmann-Mandrel mill system, which is a known pipe making method, and has a composition having the above composition. Steel-free pipe.

このように鋼管素材を造管し鋼管としたのちの処理も、特に限定されない。好ましくは、鋼管をAc3変態点以上に加熱し、続いて100℃以下の冷却停止温度まで0.1℃/ｓ以上の冷却速度で空冷する焼入れ処理と、ついでAc1変態点以下の温度で焼き戻しをする焼戻処理とを施す。Thus, the processing after forming the steel pipe material into a steel pipe is not particularly limited. Preferably, the steel pipe is heated to the Ac 3 transformation point or higher, followed by quenching to air-cool at a cooling rate of 0.1 ° C./s to a cooling stop temperature of 100 ° C. or lower, and then tempered at a temperature below the Ac 1 transformation point. And tempering.

焼入れ処理
本発明では、更に鋼管に、Ac3変態点以上の温度に再加熱し、好ましくは5min以上保持し、続いて100℃以下の冷却停止温度まで空冷する焼入れ処理を施す。これによって、マルテンサイト相の微細化と高靱化が得られる。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ないため、その後の冷却で十分なマルテンサイト組織が得られず、所望の高強度を達成できない。よって、焼入れ加熱温度はAc3変態点以上に限定する。なお、上記の空冷とは、0.1℃/ｓ以上の冷却速度のことを指す。Quenching treatment In the present invention, the steel pipe is further reheated to a temperature above the Ac 3 transformation point, preferably kept for 5 min or more, and then subjected to a quenching treatment for air cooling to a cooling stop temperature of 100 ° C. or less. Thereby, refinement | miniaturization and toughening of a martensite phase are obtained. When the quenching heating temperature is less than the Ac 3 transformation point, heating cannot be performed in the austenite single phase region, and thus sufficient martensite structure cannot be obtained by subsequent cooling, and a desired high strength cannot be achieved. Therefore, the quenching heating temperature is limited to the Ac 3 transformation point or higher. In addition, said air cooling refers to the cooling rate of 0.1 degree-C / s or more.

焼戻処理
続いて、焼入れ処理を施した鋼管に、焼戻処理を施す。焼戻処理は、Ac1変態点以下に加熱し、好ましくは10min以上保持し、空冷する処理である。焼戻温度がAc1変態点より高温になると、焼戻後にマルテンサイト相が析出し、所望の高靱性、および優れた耐食性を確保できない。よって、焼戻温度はAc1変態点以下に限定する。なお、上記のAc3変態点（℃）、Ac1変態点（℃）については、試験片に加熱および冷却の温度履歴を与え、膨張および収縮の微小変位から変態点を検出するフォーマスター試験により測定することができる。Tempering process Subsequently, the steel pipe which has been subjected to the quenching process is subjected to a tempering process. The tempering process is a process of heating below the Ac 1 transformation point, preferably holding for 10 min or more, and air cooling. When the tempering temperature is higher than the Ac 1 transformation point, the martensite phase precipitates after tempering, and the desired high toughness and excellent corrosion resistance cannot be ensured. Therefore, the tempering temperature is limited to the Ac 1 transformation point or lower. For the Ac 3 transformation point (° C) and Ac 1 transformation point (° C) above, a four-master test that gives a temperature history of heating and cooling to the test piece and detects the transformation point from minute displacements of expansion and contraction. Can be measured.

以下、実施例に基づき、さらに本発明について説明する。   Hereinafter, based on an Example, this invention is demonstrated further.

表１に示す成分の溶鋼を転炉にて溶製した後、連続鋳造法でビレット（鋼管素材）に鋳造し、更にモデルシームレス圧延機を用いる熱間加工で造管し、空冷（冷却速度0.5℃／ｓ）後に外径83.8mm×肉厚12.7mmの継目無鋼管とした。   After molten steel having the components shown in Table 1 is melted in a converter, it is cast into a billet (steel pipe material) by a continuous casting method, further piped by hot working using a model seamless rolling mill, and air-cooled (cooling rate 0.5) C./s) After that, a seamless steel pipe having an outer diameter of 83.8 mm and a wall thickness of 12.7 mm was obtained.

得られた継目無鋼管から試験材を切り出し、表２に示す条件で焼入れ及び焼戻し処理を施した。焼入及び焼戻処理を施した試験材から、組織観察用試験片を採取し、研磨した後、残留オーステナイト（γ）量をX線回折法にて測定した。
具体的には、γの（220）面、αの（211）面、の回折Ｘ線積分強度を測定し、次式
γ（体積率）＝100／（１＋（ＩαＲγ／ＩγＲα））
ここで、Ｉα：αの積分強度
Ｒα：αの結晶額的理論計算値
Ｉγ：γの積分強度
Ｒγ：γの結晶額的理論計算値
を用いて換算した。
また、焼入れ及び焼戻し処理を施した試験材から、API弧状引張試験片（strip specimen specified by API standard 5CT）を採取し、APIの規定に準拠して引張試験を実施し、引張特性（降伏応力YS、引張応力TS）を求めた。表２中、Ac3点（℃）およびAc1点（℃）については、焼入れ処理を施した試験材から、4mmφ×10mmの試験片を採取し、フォーマスター試験により測定した。具体的には、試験片を5℃/sで500℃まで加熱し、更に0.25℃/sで920℃まで昇温させて10分間保持した後、2℃/sで室温まで冷却した。この温度履歴に伴う試験片の膨張・収縮を検出することでAc3点（℃）、Ac1点（℃）を得た。A test material was cut out from the obtained seamless steel pipe and subjected to quenching and tempering treatment under the conditions shown in Table 2. A specimen for microstructure observation was collected from the test material subjected to quenching and tempering treatment and polished, and the amount of retained austenite (γ) was measured by X-ray diffraction.
Specifically, the diffraction X-ray integral intensity of the (220) plane of γ and the (211) plane of α is measured, and the following formula γ (volume ratio) = 100 / (1+ (IαRγ / IγRα))
Here, Iα: α integral strength Rα: α crystallographic theoretical calculated value Iγ: γ integral strength Rγ: γ crystallographic theoretical calculated value.
In addition, API specimen specimens by API standard 5CT are collected from specimens that have been quenched and tempered, and subjected to a tensile test in accordance with the API regulations to obtain tensile properties (yield stress YS). , Tensile stress TS). In Table 2, for Ac 3 point (° C.) and Ac 1 point (° C.), a test piece of 4 mmφ × 10 mm was taken from the test material subjected to quenching treatment and measured by a formaster test. Specifically, the test piece was heated to 500 ° C. at 5 ° C./s, further heated to 920 ° C. at 0.25 ° C./s and held for 10 minutes, and then cooled to room temperature at 2 ° C./s. The Ac 3 point (° C.) and Ac 1 point (° C.) were obtained by detecting the expansion and contraction of the test piece accompanying this temperature history.

SSC試験は、NACE TM0177 Method Aに準拠して実施した。試験環境は、試験溶液として0.165質量％NaClに0.41g/L CH3COONa+HClを加えてpH3.5に調整したものを用い、硫化水素分圧を0.1MPaとし、降伏応力の90％を負荷応力として試験を実施した。The SSC test was performed according to NACE TM0177 Method A. The test environment is 0.165% NaCl by adding 0.41 g / L CH 3 COONa + HCl to pH 3.5 and the hydrogen sulfide partial pressure is 0.1 MPa, and 90% of the yield stress is loaded. The test was carried out as stress.

得られた結果を表２に示す。   The obtained results are shown in Table 2.

Figure 0006315159
Figure 0006315159

Figure 0006315159
Figure 0006315159

本発明例はいずれも、降伏応力758MPa以上の高強度と、H2Sを含む環境下で応力が負荷されても割れの発生が無い、優れた耐SSC性を有するマルテンサイト系ステンレス継目無鋼管となっている。一方、本発明の範囲を外れる比較例では、所望の高強度は得られているものの、優れた耐SSC性を確保できていない。All of the examples of the present invention have a high strength of yield stress of 758 MPa or more and martensite stainless steel seamless steel pipe having excellent SSC resistance without cracking even when stress is applied in an environment containing H 2 S. It has become. On the other hand, in the comparative example outside the scope of the present invention, the desired high strength is obtained, but excellent SSC resistance cannot be ensured.

Claims (3)

質量％で、C：0.035％以下、
Si：0.5％以下、
Mn：0.05〜0.5％、
P：0.03％以下、
S：0.005％以下、
Cu：2.6％以下、
Ni：5.3〜7.3％、
Cr：11.8〜14.5％、
Al：0.1％以下、
Mo：1.8〜3.0％、
V：0.2％以下、
N：0.1％以下を含有し、かつ下記（1）式、（2）式および（3）式が下記（4）を満足し、残部Feおよび不可避的不純物からなる組成を有し、
758MPa以上の降伏応力を有することを特徴とする油井管用マルテンサイト系ステンレス継目無鋼管。
記
−109.37C＋7.307Mn＋6.399Cr＋6.329Cu＋11.343Ni−13.529Mo＋1.276W＋2.925Nb＋196.775N−2.621Ti−120.307 ・・・(1)
−0.0278Mn＋0.0892Cr＋0.00567Ni＋0.153Mo−0.0219W−1.984N＋0.208Ti−1.83 ・・・(2)
−1.324C＋0.0533Mn＋0.0268Cr＋0.0893Cu＋0.00526Ni＋0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 ・・・(3)
ここで、C、Mn、Cr、Cu、Ni、Mo、W、Nb、N、Ti：各元素の含有量（質量％）（但し、含有しない元素は０（零）％とする。）
−10≦(1)式≦45 且つ −0.25≦(2)式≦−0.20 且つ 0.10≦(3)式≦0.20 ・・・(4)% By mass, C: 0.035% or less,
Si: 0.5% or less,
Mn: 0.05-0.5%
P: 0.03% or less,
S: 0.005% or less,
Cu: 2.6% or less,
Ni: 5.3-7.3%
Cr: 11.8 to 14.5%,
Al: 0.1% or less,
Mo: 1.8-3.0%,
V: 0.2% or less
N: 0.1% or less, and the following formulas (1), (2) and (3) satisfy the following (4), and have a composition comprising the balance Fe and unavoidable impurities,
A martensitic stainless steel seamless pipe for oil well pipes characterized by having a yield stress of 758 MPa or more.
-109.37C + 7.307Mn + 6.399Cr + 6.329Cu + 11.343Ni-13.529Mo + 1.276W + 2.925Nb + 196.775N-2.621Ti-120.307 (1)
−0.0278Mn + 0.0892Cr + 0.00567Ni + 0.153Mo−0.0219W−1.984N + 0.208Ti−1.83 (2)
−1.324C + 0.0533Mn + 0.0268Cr + 0.0893Cu + 0.00526Ni + 0.0222Mo−0.0132W−0.473N−0.5Ti−0.514 (3)
Here, C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, Ti: Content of each element (mass%) (however, elements not contained are 0 (zero)%)
−10 ≦ (1) Formula ≦ 45 and −0.25 ≦ (2) Formula ≦ −0.20 and 0.10 ≦ (3) Formula ≦ 0.20 (4) 前記組成に加えて更に、質量％で、Ti：0.19％以下、
Nb：0.25％以下、
W：1.1％以下、
Co：0.45％以下のうちから選ばれた1種または2種以上を含有することを特徴とする請求項１に記載の油井管用マルテンサイト系ステンレス継目無鋼管。In addition to the above composition, Ti: 0.19% or less in mass%,
Nb: 0.25% or less,
W: 1.1% or less,
Co: Martensitic stainless steel seamless pipe for oil country tubular goods according to claim 1, characterized by containing one or more selected from 0.45% or less. 請求項１または２に記載の油井管用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り、鋼管素材を造管し鋼管としたのち、該鋼管をAc3変態点以上に加熱し、続いて100℃以下の冷却停止温度まで0.1℃/ｓ以上の冷却速度で空冷する焼入れ処理と、ついでAc1変態点以下の温度で焼き戻しをする焼戻処理とを施すことを特徴とする油井管用マルテンサイト系ステンレス継目無鋼管の製造方法。A process according to claim 1 or 2 in martensitic stainless seamless steel pipe for oil country tubular goods according, after the by pipe-making steel pipe material steel pipe, heating the steel tube over Ac 3 transformation point, followed by 100 ° C. A martensite system for oil well pipes that is subjected to quenching treatment in which air cooling is performed at a cooling rate of 0.1 ° C./s or higher to the following cooling stop temperature, and then tempering treatment in which temperature is tempered at a temperature below the Ac 1 transformation point. Manufacturing method of stainless steel seamless steel pipe.
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