JP4701874B2 - Manufacturing method of steel pipe for oil well with excellent resistance to sulfide stress cracking - Google Patents

Manufacturing method of steel pipe for oil well with excellent resistance to sulfide stress cracking Download PDF

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JP4701874B2
JP4701874B2 JP2005189183A JP2005189183A JP4701874B2 JP 4701874 B2 JP4701874 B2 JP 4701874B2 JP 2005189183 A JP2005189183 A JP 2005189183A JP 2005189183 A JP2005189183 A JP 2005189183A JP 4701874 B2 JP4701874 B2 JP 4701874B2
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steel pipe
stress cracking
sulfide stress
oil well
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JP2007009249A (en
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尊人 伊藤
秀樹 高部
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Sumitomo Metal Industries Ltd
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本発明は、耐硫化物応力割れ性に優れた油井用鋼管の製造方法に関し、詳しくは、深さが大きく、しかも、硫化水素(H2S)を含む油井やガス井で使用されるケーシング、チュービング及びドリルパイプなどとして好適な、耐硫化物応力割れ性に優れた低合金油井用鋼管を製造する方法に関する。 The present invention relates to a method for producing a steel pipe for an oil well excellent in resistance to sulfide stress cracking. Specifically, the casing has a large depth and is used in an oil well or a gas well containing hydrogen sulfide (H 2 S). The present invention relates to a method for producing a low alloy oil well steel pipe excellent in sulfide stress cracking resistance, which is suitable as a tubing and a drill pipe.

なお、本明細書における「油井用鋼管は上述の「油井やガス井で使用されるケーシング、チュービング及びドリルパイプ」を指す。 Incidentally, refer to "casing used in oil wells and gas wells, tubing and drill pipe" and "oil well steel pipe" described above in this specification.

近年、石油や天然ガスを採取するための井戸が深くなる傾向にあり、油井用鋼管には高強度化が要求されている。   In recent years, wells for extracting oil and natural gas tend to be deeper, and high strength steel pipes are required for oil wells.

一方、近年開発される深井戸の環境は、腐食性を有する硫化水素を含む場合が多く、このような環境では高強度鋼は硫化物応力割れ(以下、硫化物応力割れを「SSC」ということがある。)と呼ばれる一種の水素脆化を起こして油井用鋼管が破壊に至ることがある。 On the other hand, the environment of deep wells developed in recent years often contains corrosive hydrogen sulfide, and in such an environment, high-strength steel has sulfide stress cracking (hereinafter referred to as “SSC”). is.) causing a kind of hydrogen embrittlement called sometimes oil well steel pipe reaches fracture.

このため、SSCを克服することが深井戸に用いられる油井用鋼管の最大の課題となり、降伏強度(YS)の幅を15ksi(約103MPa)に狭めた80ksi級(YSの範囲が552〜655MPa)や95ksi級(YSの範囲が655〜758MPa)の耐SSC性に優れた油井用鋼管が広く用いられ、強度を一層高めた110ksi級(YSの範囲が758〜862MPa)の油井用鋼管を使用することも多くなっている。更に近年では、これまで適用されていなかった125ksi級(YSの範囲が862〜965MPa)という高い強度レベルの耐SSC性に優れた油井用鋼管の検討も開始されている。   Therefore, overcoming SSC is the biggest challenge for oil well steel pipes used in deep wells, and the 80 ksi class (YS range is 552 to 655 MPa) with the yield strength (YS) narrowed to 15 ksi (about 103 MPa). And 95 ksi class (YS range 655 to 758 MPa) oil well steel pipe excellent in SSC resistance is widely used, and 110 ksi class (YS range 758 to 862 MPa) oil well steel pipe having higher strength is used. There are many things. Furthermore, in recent years, studies have been started on oil well steel pipes that have not been applied so far and have a high strength level of 125 ksi class (YS range of 862 to 965 MPa) and excellent SSC resistance.

なお、SSCは鋼の強度が高くなるほど生じやすい。このため、125ksi級の耐SSC性に優れた油井用鋼管を得るためには、95ksi級や110ksi級の油井用鋼管に比べてなお一層の技術改善が必要となる。   SSC is more likely to occur as the strength of the steel increases. For this reason, in order to obtain an oil well steel pipe excellent in SSC resistance of 125 ksi class, further technical improvement is required as compared with a 95 ksi class or 110 ksi class oil well steel pipe.

特許文献1及び特許文献2に、95〜110ksi級の油井用鋼管の耐SSC性を改善する技術が開示され、また、特許文献3には、125ksi級以上の油井用鋼管の耐SSC性を改善する技術が開示されている。   Patent Document 1 and Patent Document 2 disclose a technique for improving the SSC resistance of a 95 to 110 ksi class oil well steel pipe, and Patent Document 3 improves the SSC resistance of an oil well steel pipe of 125 ksi class or higher. Techniques to do this are disclosed.

すなわち、特許文献1には、特定の組み合わせでMn、P及びMoを含有させて粒界破面が現出しないようにして耐SSC性を改善する「硫化物応力割れ抵抗性に優れた低合金高張力油井用鋼の製造方法」が提案されている。   That is, Patent Document 1 discloses that a low alloy excellent in sulfide stress cracking resistance improves SSC resistance by containing Mn, P and Mo in a specific combination so that no grain boundary fracture surface appears. A method for producing steel for high-strength wells has been proposed.

また、特許文献2には、2回の焼入れ処理によって、特定の化学組成の鋼の結晶粒を微細化して耐SSC性を改善する「耐硫化物腐食割れ性に優れた高強度鋼の製法」が提案されている。   Patent Document 2 discloses that a method of producing a high-strength steel excellent in resistance to sulfide corrosion cracking that improves SSC resistance by refining crystal grains of a steel having a specific chemical composition by two quenching treatments. Has been proposed.

更に、特許文献3には、急速加熱焼入れによって、特定の化学組成の鋼の組織を微細化して耐SSC性を改善する「耐硫化物応力割れ抵抗性に優れた高強度鋼およびその製造方法」が提案されている。   Furthermore, Patent Document 3 discloses that “high-strength steel excellent in resistance to sulfide stress cracking and a method for producing the same” improve the SSC resistance by refining the structure of a steel having a specific chemical composition by rapid heating and quenching. Has been proposed.

特開昭62−253720号公報JP-A-62-253720 特開昭59−232220号公報JP 59-232220 A 特開平6−322478号公報JP-A-6-322478

本発明の目的は、優れた耐SSC性を有し、硫化水素を含む深い油井やガス井で使用されるケーシング、チュービング及びドリルパイプなどの用途に好適な、耐硫化物応力割れ性に優れた油井用鋼管の製造方法を提供することである。また、そのなかでも降伏強度(YS)が758MPa以上965MPa以下である110ksi級〜125ksi級の耐硫化物応力割れ性に優れた油井用鋼管の製造方法を提供することである。   The object of the present invention is excellent in resistance to sulfide stress cracking, having excellent SSC resistance, suitable for applications such as casings, tubing and drill pipes used in deep oil wells and gas wells containing hydrogen sulfide. It is providing the manufacturing method of the steel pipe for oil wells. Moreover, it is providing the manufacturing method of the steel pipe for oil wells which was excellent in the 110 ksi class-125 ksi class sulfide stress cracking resistance whose yield strength (YS) is 758 Mpa or more and 965 Mpa or less.

前述の特許文献1〜3で開示された技術によって得られる油井用鋼管は、必ずしも安定して良好な耐SSC性を確保できるものではない。   The oil well steel pipes obtained by the techniques disclosed in the above-mentioned Patent Documents 1 to 3 do not always ensure stable and good SSC resistance.

このため、本発明者らは、鋼の化学組成、製管時の加工度及び焼入れの加熱温度を種々変えて、高強度の油井用鋼管に安定して優れた耐SSC性を確保させるための検討を行った。その結果、先ず、下記(a)〜(c)の知見を得た。   For this reason, the inventors have variously changed the chemical composition of steel, the degree of processing at the time of pipe making, and the heating temperature for quenching to ensure stable and excellent SSC resistance in high strength steel pipes for oil wells. Study was carried out. As a result, first, the following findings (a) to (c) were obtained.

(a)ピアサーより後の加工での総加工度(以下、「ピアサーで穿孔した後の加工度」ともいう。)が高いほど圧延時の加工歪みが大きくなり、製品鋼管つまり、焼入れ−焼戻しを行った油井用鋼管に残留する加工歪みが増えるので転位密度が増加する。一方、ピアサーで穿孔した後の加工度が低いほど製品鋼管である焼入れ−焼戻しを行った油井用鋼管に残留する加工歪みが少なくなって転位密度も減少するが、結晶粒が粗大になる。   (A) The higher the total degree of processing in processing after the piercer (hereinafter also referred to as “degree of processing after drilling with piercer”), the greater the processing distortion during rolling, and the product steel pipe, that is, quenching and tempering. The dislocation density increases because the processing strain remaining in the oil well steel pipe is increased. On the other hand, the lower the degree of work after piercing with a piercer, the less the work strain remaining in the well-tempered steel pipe, which is the product steel pipe, and the dislocation density also decreases, but the crystal grains become coarse.

(b)転位密度が高い場合、耐SSC性を低下させる拡散性水素は転位に多く吸蔵される。このため、転位密度が高いほどSSCが発生しやすい。しかしながら、加工度が高い場合でも、SSCの発生を抑止できる場合がある。   (B) When the dislocation density is high, a large amount of diffusible hydrogen that lowers the SSC resistance is stored in the dislocation. For this reason, SSC is more likely to occur as the dislocation density is higher. However, even when the degree of processing is high, the occurrence of SSC may be suppressed.

(c)製品鋼管に残留する加工歪みが少なく転位密度が低い場合、耐SSC性を低下させる拡散性水素は主に結晶粒界に吸蔵される。この場合、結晶粒が大きいほどその表面積が小さくなるため、単位面積当たりに吸蔵される拡散性水素の量が多くなって、SSCが発生しやすくなる。しかしながら、加工度が低いために粗粒になった場合でも、SSCの発生を抑止できる場合がある。   (C) When the processing strain remaining in the product steel pipe is small and the dislocation density is low, the diffusible hydrogen that lowers the SSC resistance is mainly stored in the crystal grain boundaries. In this case, the larger the crystal grain, the smaller the surface area. Therefore, the amount of diffusible hydrogen stored per unit area increases, and SSC is likely to occur. However, there are cases where the occurrence of SSC can be suppressed even when the particles become coarse due to the low degree of processing.

そこで、SSCの発生を抑止できた場合について、更に詳細な検討を行った。その結果、下記(d)〜(f)の知見を得た。   Therefore, a more detailed study was conducted on the case where the occurrence of SSC could be suppressed. As a result, the following findings (d) to (f) were obtained.

(d)製品鋼管の素材鋼が特定の化学組成からなるものであれば、ピアサーで穿孔した後の加工度が高い場合であっても、その加工度で決定される特定の温度域へ加熱して焼入れし、次いで、特定の温度域で焼戻しすれば、良好な耐SSC性を確保することができる。   (D) If the material steel of the product steel pipe is of a specific chemical composition, even if the degree of work after piercing with a piercer is high, it is heated to a specific temperature range determined by the degree of work. By quenching and then tempering in a specific temperature range, good SSC resistance can be ensured.

(e)製品鋼管の素材鋼が特定の化学組成からなるものであれば、ピアサーで穿孔した後の加工度が低く結晶粒が粗大になった場合でも、特定の温度域へ加熱して焼入れし、次いで、特定の温度域で焼戻しすれば、炭化物が微細に析出し、この微細に析出した炭化物に拡散性水素がトラップされ、結果的に鋼中の拡散性水素の量が減ることになって、良好な耐SSC性を確保することができる。   (E) If the material steel of the product steel pipe has a specific chemical composition, even if the degree of processing after drilling with a piercer is low and the crystal grains become coarse, they are heated to a specific temperature range and quenched. Then, if tempering is performed in a specific temperature range, carbides are finely precipitated, and diffusible hydrogen is trapped in the finely precipitated carbides, resulting in a decrease in the amount of diffusible hydrogen in the steel. Good SSC resistance can be ensured.

(f)素材鋼の化学組成を適正化したうえで、ピアサーで穿孔した後の加工度に応じた適正な温度域へ加熱して焼入れし、次いで、適正な温度域で焼戻しすることにより、耐硫化物応力割れ性に優れた油井用鋼管、なかでも降伏強度(YS)が758MPa以上965MPa以下である110ksi級〜125ksi級の高強度油井用鋼管を得ることができる。   (F) After optimizing the chemical composition of the material steel, it is quenched by heating to an appropriate temperature range according to the degree of processing after piercing with a piercer, and then tempering at an appropriate temperature range. An oil well steel pipe excellent in sulfide stress cracking property, in particular, a 110 ksi class to 125 ksi class high strength steel well steel pipe having a yield strength (YS) of 758 MPa or more and 965 MPa or less can be obtained.

本発明は、上記の知見に基づいて完成されたものである。   The present invention has been completed based on the above findings.

本発明の要旨は、下記(1)〜(9)に示す耐硫化物応力割れ性に優れた油井用鋼管の製造方法にある。   The gist of the present invention resides in a method for producing an oil well steel pipe excellent in sulfide stress cracking resistance shown in the following (1) to (9).

(1)質量%で、C:0.2〜0.35%、Si:0.05〜0.5%、Mn:0.05〜1.0%、P:0.025%以下、S:0.01%以下、Al:0.005〜0.10%、Cr:0.1〜1.0%、Mo:0.5〜1.0%、Ti:0.002〜0.05%、V:0.05〜0.3%、B:0.0001〜0.005%、N:0.01%以下及びO(酸素):0.01%以下を含有し、残部はFe及び不純物からなる化学組成の鋼管を、40%未満の加工度で加工した後895℃以上の温度に加熱して焼入れするか或いは、40%以上の加工度で加工した後下記の(1)式を満たす温度に加熱して焼入れし、次いで、Ac1点以下の温度で焼戻しすることを特徴とする耐硫化物応力割れ性に優れた油井用鋼管の製造方法。
加熱温度(℃)≧0.625×加工度(%)+870・・・(1)、
但し、加工度は、ピアサーより後の加工での総加工度を表し、下記の(2)式に基づく値とする。
加工度(%)={(「ピアサー加工後の鋼管の断面積」−「焼戻し後の鋼管の断面積」)/「ピアサー加工後の鋼管の断面積」}×100・・・(2)。
(1) By mass%, C: 0.2 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.05 to 1.0%, P: 0.025% or less, S: 0.01% or less, Al: 0.005-0.10%, Cr: 0.1-1.0%, Mo: 0.5-1.0%, Ti: 0.002-0.05%, V: 0.05 to 0.3%, B: 0.0001 to 0.005%, N: 0.01% or less and O (oxygen): 0.01% or less, with the balance being Fe and impurities The steel pipe having the chemical composition is processed at a workability of less than 40% and then heated to a temperature of 895 ° C. or higher and quenched, or processed at a workability of 40% or more and a temperature satisfying the following formula (1): A method for producing a steel pipe for oil wells having excellent resistance to sulfide stress cracking, characterized by heating to tempering and then tempering at a temperature of Ac 1 point or less.
Heating temperature (° C.) ≧ 0.625 × working degree (%) + 870 (1),
However, the processing degree represents the total processing degree in processing after the piercer, and is a value based on the following equation (2).
Degree of work (%) = {(“cross-sectional area of steel pipe after piercer processing” − “cross-sectional area of steel pipe after tempering”) / “cross-sectional area of steel pipe after piercing”} × 100 (2).

(2)鋼管の化学組成が上記(1)に記載のFeの一部に代えて、Nb:0.002〜0.1を含有するものであり、加熱温度が940℃以下であ上記(1)に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。 (2) the chemical composition of the steel pipe is in place of part of Fe according to the above (1), Nb: 0.002 to 0.1 all SANYO containing, Ru der heating temperature is 940 ° C. or less, The manufacturing method of the steel pipe for oil wells excellent in sulfide stress cracking resistance as described in said (1).

(3)鋼管の化学組成が上記(1)に記載のFeの一部に代えて、Ca:0.0001〜0.01%を含有するものである上記(1)に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   (3) The chemical composition of the steel pipe is replaced with a part of Fe described in (1) above, and contains Ca: 0.0001 to 0.01%. A method for manufacturing steel pipes for oil wells with excellent cracking properties.

(4)鋼管の化学組成が上記(1)に記載のFeの一部に代えて、Zr:0.002〜0.1%を含有するものである上記(1)に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   (4) Sulfide stress resistance according to (1) above, wherein the chemical composition of the steel pipe contains Zr: 0.002 to 0.1% instead of part of Fe described in (1) above. A method for manufacturing steel pipes for oil wells with excellent cracking properties.

(5)鋼管の化学組成が上記(1)に記載のFeの一部に代えて、Nb:0.002〜0.1及びCa:0.0001〜0.01%を含有するものであり、加熱温度が940℃以下であ上記(1)に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。 (5) Chemical composition of the steel pipe is in place of part of Fe according to the above (1), Nb: 0.002 to 0.1, and Ca: all SANYO containing 0.0001 to 0.01% , Ru der heating temperature is 940 ° C. or less, the production method of an oil well steel pipe having excellent sulfide stress cracking resistance according to (1).

(6)鋼管の化学組成が上記(1)に記載のFeの一部に代えて、Nb:0.002〜0.1及びZr:0.002〜0.1%を含有するものである上記(1)に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   (6) The above-mentioned chemical composition of the steel pipe contains Nb: 0.002-0.1 and Zr: 0.002-0.1% instead of a part of Fe described in (1) above. The manufacturing method of the steel pipe for oil wells excellent in sulfide stress cracking resistance as described in (1).

(7)鋼管の化学組成が上記(1)に記載のFeの一部に代えて、Ca:0.0001〜0.01%及びZr:0.002〜0.1%を含有するものである上記(1)に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   (7) The chemical composition of the steel pipe contains Ca: 0.0001 to 0.01% and Zr: 0.002 to 0.1% in place of part of Fe described in (1) above. The manufacturing method of the steel pipe for oil wells which was excellent in the sulfide stress cracking resistance as described in said (1).

(8)鋼管の化学組成が上記(1)に記載のFeの一部に代えて、Nb:0.002〜0.1、Ca:0.0001〜0.01%及びZr:0.002〜0.1%を含有するものである上記(1)に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   (8) The chemical composition of the steel pipe is replaced with a part of Fe described in the above (1), Nb: 0.002-0.1, Ca: 0.0001-0.01%, and Zr: 0.002- The manufacturing method of the steel pipe for oil wells which is excellent in the sulfide stress cracking resistance as described in said (1) which contains 0.1%.

(9)焼戻し後の鋼管の降伏強度が758〜965MPaである上記(1)から(8)までのいずれかに記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   (9) The method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to any one of the above (1) to (8), wherein the yield strength of the steel pipe after tempering is 758 to 965 MPa.

以下、上記 (1)〜(9)の「耐硫化物応力割れ性に優れた油井用鋼管の製造方法」に係る発明を、それぞれ、「本発明(1)」〜「本発明(9)」という。また、総称して「本発明」ということがある。   Hereinafter, the inventions according to the above-mentioned (1) to (9) “method for producing oil well steel pipe excellent in sulfide stress cracking resistance” are referred to as “present invention (1)” to “present invention (9)”, respectively. That's it. Also, it may be collectively referred to as “the present invention”.

本発明の耐硫化物応力割れ性に優れた油井用鋼管の製造方法によれば、深さが大きく、しかも、硫化水素を含む油井やガス井で使用されるケーシング、チュービング及びドリルパイプなどとして好適な、耐硫化物応力割れ性に優れた油井用鋼管、なかでも降伏強度(YS)が758MPa以上965MPa以下である110ksi級〜125ksi級の耐硫化物応力割れ性に優れた油井用鋼管を容易に製造することができる。   According to the method for manufacturing a steel pipe for oil wells having excellent resistance to sulfide stress cracking according to the present invention, the depth is large, and it is suitable as a casing, tubing and drill pipe used in oil wells and gas wells containing hydrogen sulfide. In addition, oil well steel pipes excellent in sulfide stress cracking resistance, particularly steel pipes for oil wells excellent in sulfide stress cracking resistance of 110 ksi class to 125 ksi class having a yield strength (YS) of 758 MPa to 965 MPa. Can be manufactured.

以下、本発明の各要件について詳しく説明する。なお、化学成分の含有量の「%」は「質量%」を意味する。   Hereinafter, each requirement of the present invention will be described in detail. In addition, “%” of the content of the chemical component means “mass%”.

(A)鋼管の化学組成
C:0.2〜0.35%
Cは、焼入れ性を高めて強度を向上させるのに有効な元素である。しかしながら、その含有量が0.2%未満では、焼入れ性向上効果が低いため十分な強度が得られない。一方、Cの含有量が0.35%を超えると焼割れに対する感受性が増大する。したがって、Cの含有量を0.2〜0.35%とした。なお、C含有量の下限は0.25%とすることが好ましく、上限は0.30%とすることが好ましい。
(A) Chemical composition of steel pipe C: 0.2 to 0.35%
C is an element effective for improving the hardenability and improving the strength. However, if the content is less than 0.2%, the effect of improving the hardenability is low, so that sufficient strength cannot be obtained. On the other hand, when the content of C exceeds 0.35%, sensitivity to fire cracking increases. Therefore, the content of C is set to 0.2 to 0.35%. The lower limit of the C content is preferably 0.25%, and the upper limit is preferably 0.30%.

Si:0.05〜0.5%
Siは、鋼の脱酸に有効な元素であり、焼戻し軟化抵抗を高める効果も有する。上記のうち特に脱酸効果を得るためには、Siの含有量を0.05%以上とする必要がある。一方、その含有量が0.5%を超えると、軟化相であるフェライト相の析出を促進し靱性や耐SSC性を低下させる。したがって、Siの含有量を0.05〜0.5%とした。なお、Si含有量の上限は0.3%とすることが好ましい。
Si: 0.05-0.5%
Si is an element effective for deoxidation of steel, and has an effect of increasing temper softening resistance. In order to obtain the deoxidation effect among the above, it is necessary to make the Si content 0.05% or more. On the other hand, when the content exceeds 0.5%, precipitation of a ferrite phase which is a softening phase is promoted, and toughness and SSC resistance are lowered. Therefore, the Si content is set to 0.05 to 0.5%. In addition, it is preferable that the upper limit of Si content shall be 0.3%.

Mn:0.05〜1.0%
Mnは、鋼の焼入れ性を確保するのに有効な元素であり、この目的からは、Mnの含有量を0.05%以上とする必要がある。しかしながら、Mnを1.0%を超えて含有させると、P、S等の不純物元素とともに粒界に偏析し、靱性や耐SSC性を低下させる。したがって、Mnの含有量を0.05〜1.0%とした。なお、Mn含有量の下限は0.1%とすることが望ましく、上限は0.6%とすることが望ましい。
Mn: 0.05 to 1.0%
Mn is an element effective for ensuring the hardenability of steel. For this purpose, the Mn content needs to be 0.05% or more. However, if Mn is contained in excess of 1.0%, it segregates at grain boundaries together with impurity elements such as P and S, and lowers toughness and SSC resistance. Therefore, the Mn content is set to 0.05 to 1.0%. The lower limit of the Mn content is preferably 0.1%, and the upper limit is preferably 0.6%.

P:0.025%以下
Pは粒界に偏析し、靱性及び耐SSC性を低下させる。特に、その含有量が0.025%を超えると、靱性及び耐SSC性の低下が著しくなる。したがって、Pの含有量を0.025%以下とした。P含有量の上限は0.015%とすることが好ましい。なお、Pの含有量は可及的に少なくすることが望ましい。
P: 0.025% or less P segregates at the grain boundaries and lowers toughness and SSC resistance. In particular, when the content exceeds 0.025%, the toughness and SSC resistance are significantly lowered. Therefore, the content of P is set to 0.025% or less. The upper limit of the P content is preferably 0.015%. It is desirable to reduce the P content as much as possible.

S:0.01%以下
SもPと同様に粒界に偏析し、靱性及び耐SSC性を低下させる。特に、その含有量が0.01%を超えると、靱性及び耐SSC性の低下が著しくなる。したがって、Sの含有量を0.01%以下とした。S含有量の上限は0.003%とすることが好ましい。なお、Sの含有量は可及的に少なくすることが望ましい。
S: 0.01% or less S, like P, segregates at the grain boundaries and lowers toughness and SSC resistance. In particular, when the content exceeds 0.01%, the toughness and SSC resistance are significantly lowered. Therefore, the S content is set to 0.01% or less. The upper limit of the S content is preferably 0.003%. It is desirable to reduce the S content as much as possible.

Al:0.005〜0.10%
Alは、鋼の脱酸に有効な元素である。しかしながら、その含有量が0.005%未満の場合には前記の効果が得られない。一方、Alの含有量が0.10%を超えるとアルミナ系介在物を生成し、靱性を劣化させる。したがって、Alの含有量を0.005〜0.10%とした。なお、本発明におけるAlは、酸可溶Al(いわゆる「sol.Al」)のことを指す。
Al: 0.005-0.10%
Al is an element effective for deoxidation of steel. However, when the content is less than 0.005%, the above effect cannot be obtained. On the other hand, if the Al content exceeds 0.10%, alumina inclusions are generated and the toughness is deteriorated. Therefore, the content of Al is set to 0.005 to 0.10%. In the present invention, Al refers to acid-soluble Al (so-called “sol.Al”).

Cr:0.1〜1.0%
Crは,鋼の焼入れ性を高めるのに有効な元素であり、この効果を得るためには0.1%以上の含有量とする必要がある。しかしながら、その含有量が1.0%を超えると鋼の転位密度が増加して、耐SSC性の低下を招く。したがって、Crの含有量を0.1〜1.0%とした。なお、Cr含有量の上限は0.6%とすることが望ましい。
Cr: 0.1 to 1.0%
Cr is an effective element for enhancing the hardenability of steel. In order to obtain this effect, it is necessary to make the content 0.1% or more. However, if its content exceeds 1.0%, the dislocation density of the steel increases, leading to a decrease in SSC resistance. Therefore, the content of Cr is set to 0.1 to 1.0%. The upper limit of the Cr content is desirably 0.6%.

Mo:0.5〜1.0%
Moは、本発明において重要な元素であり、鋼の焼入れ性を高めるとともに、焼戻し時に微細炭化物を形成し、水素の拡散係数を低減させて耐SSC性を高める作用を有する。前記の効果を得るためには、Moの含有量を0.5%以上とする必要がある。しかしながら、Moの含有量が1.0%を超えても前記の効果は飽和し、コストが嵩むばかりである。したがって、Moの含有量を0.5〜1.0%とした。なお、Mo含有量の下限は0.6%とすることが望ましく、上限は0.8%とすることが望ましい。
Mo: 0.5 to 1.0%
Mo is an important element in the present invention, and has the effect of increasing the hardenability of steel, forming fine carbides during tempering, reducing the diffusion coefficient of hydrogen, and improving SSC resistance. In order to acquire the said effect, it is necessary to make content of Mo 0.5% or more. However, even if the Mo content exceeds 1.0%, the above effect is saturated and the cost is increased. Therefore, the Mo content is set to 0.5 to 1.0%. Note that the lower limit of the Mo content is desirably 0.6%, and the upper limit is desirably 0.8%.

Ti:0.002〜0.05%
Tiは、鋼中の不純物であるNを窒化物として固定する作用を有する。Nの固定は、焼入れ性向上のため添加するBがBNとなるのを抑制し、Bを固溶状態に維持して十分な焼入れ性を確保するために必要である。更に、前記のN固定に必要な量よりも多いTiを含む場合、余ったTiが炭化物として微細に析出し、ピン止め作用によって結晶粒を微細化する作用を有する。これらの効果を得るためには、Tiの含有量を0.002%以上とする必要がある。しかしながら、Tiを0.05%を超えて含有させても結晶粒を微細化する効果が飽和してコストが嵩むばかりである。また、靱性の低下もきたす。したがって、Tiの含有量を0.002〜0.05%とした。なお、Ti含有量の下限は0.005%とすることが望ましく、上限は0.03%とすることが望ましい。Ti含有量の下限は0.01%とすることが一層望ましく、上限は0.02%とすることが一層望ましい。
Ti: 0.002 to 0.05%
Ti has an action of fixing N, which is an impurity in steel, as a nitride. Fixing N is necessary to suppress B added to improve hardenability to become BN and maintain B in a solid solution state to ensure sufficient hardenability. Furthermore, when Ti more than the amount necessary for the N fixation is included, excess Ti precipitates finely as carbides, and has an effect of refining crystal grains by a pinning action. In order to obtain these effects, the Ti content needs to be 0.002% or more. However, even if Ti is contained in excess of 0.05%, the effect of refining crystal grains is saturated and the cost is increased. In addition, the toughness is reduced. Therefore, the Ti content is set to 0.002 to 0.05%. The lower limit of the Ti content is preferably 0.005%, and the upper limit is preferably 0.03%. The lower limit of the Ti content is more preferably 0.01%, and the upper limit is more preferably 0.02%.

V:0.05〜0.3%
Vは、本発明において重要な元素であり、Moと同様に焼戻し時に微細な炭化物として析出し、水素の拡散係数を低減させて耐SSC性を向上させる作用を有する。前記の効果を得るためには、Vの含有量を0.05%以上とする必要がある。しかしながら、Vの含有量が0.3%を超えても前記の効果は飽和し、コストが嵩むばかりである。したがって、Vの含有量を0.05〜0.3%とした。なお、V含有量の上限は0.2%とすることが望ましい。
V: 0.05-0.3%
V is an important element in the present invention and, like Mo, precipitates as fine carbides during tempering, and has the effect of reducing the diffusion coefficient of hydrogen and improving SSC resistance. In order to acquire the said effect, it is necessary to make content of V 0.05% or more. However, even if the content of V exceeds 0.3%, the above effect is saturated and the cost is increased. Therefore, the content of V is set to 0.05 to 0.3%. Note that the upper limit of the V content is preferably 0.2%.

B:0.0001〜0.005%
Bは、鋼の焼入れ性を高める作用を有する。しかしながら、その含有量が0.0001%未満では十分な効果が得られない。一方、Bを0.005%を超えて含有させても前記の焼入れ性向上効果は飽和する。更に、粒界に粗大な炭化物であるCr23(C、B)6を形成して、耐SSC性の低下を招く。したがって、Bの含有量を0.0001〜0.005%とした。B含有量の下限は0.0002%とすることが望ましく、上限は0.002%とすることが望ましい。
B: 0.0001 to 0.005%
B has the effect | action which improves the hardenability of steel. However, if the content is less than 0.0001%, a sufficient effect cannot be obtained. On the other hand, even if B is contained in excess of 0.005%, the effect of improving hardenability is saturated. Furthermore, Cr 23 (C, B) 6 , which is a coarse carbide, is formed at the grain boundary, leading to a decrease in SSC resistance. Therefore, the content of B is set to 0.0001 to 0.005%. The lower limit of the B content is preferably 0.0002%, and the upper limit is preferably 0.002%.

N:0.01%以下
Nは不純物として鋼中に存在し、粒界に偏析して耐SSC性を低下させる。Nの含有量が多くなって、特に、0.01%を超えると、Tiを添加、或いは、Tiに加えて更にZrを添加しても、Nを完全には固定できなくなって、フリーのNが存在することとなり、このNが粒界に偏析すると耐SSC性が低下するし、また、Bと結合してBNを形成すればBの焼入れ向上作用が十分には得られないので、耐SSC性や靱性が低下する。したがって、Nの含有量を0.01%以下とした。N含有量の上限は0.007%とすることが好ましい。なお、Nの含有量は可及的に少なくすることが望ましい。
N: 0.01% or less N is present in the steel as an impurity and segregates at the grain boundary to lower the SSC resistance. When the content of N increases, especially when it exceeds 0.01%, even if Ti is added, or Zr is further added in addition to Ti, N cannot be completely fixed, and free N When this N segregates at the grain boundary, the SSC resistance decreases, and if it is combined with B to form BN, the effect of improving the quenching of B cannot be sufficiently obtained. The strength and toughness are reduced. Therefore, the N content is set to 0.01% or less. The upper limit of the N content is preferably 0.007%. It is desirable to reduce the N content as much as possible.

O(酸素):0.01%以下
OもNと同様に不純物として鋼中に存在し、その含有量が多くなると粗大な酸化物を形成して靱性や耐SSC性の低下を招く。特に、その含有量が0.01%を超えると、靱性や耐SSC性の低下が著しくなる。したがって、Oの含有量を0.01%以下とした。O含有量の上限は0.005%とすることが好ましい。なお、Oの含有量は可及的に少なくすることが望ましい。
O (oxygen): 0.01% or less O, as well as N, is present as an impurity in steel, and when its content is increased, a coarse oxide is formed, leading to a decrease in toughness and SSC resistance. In particular, when the content exceeds 0.01%, the toughness and SSC resistance are significantly lowered. Therefore, the O content is set to 0.01% or less. The upper limit of the O content is preferably 0.005%. It is desirable to reduce the O content as much as possible.

上記の理由から、本発明(1)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、上述した範囲のCからOまでの元素を含み、残部はFe及び不純物からなることと規定した。   For the above reasons, the chemical composition of the steel pipe produced by the method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (1) includes elements from C to O in the above-described range, The remainder was defined as consisting of Fe and impurities.

なお、本発明に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、必要に応じて、Feの一部に代えて、後述する第1群〜第3群のうちの少なくとも1群から選んだ元素を任意添加元素として添加し、含有させてもよい。   In addition, the chemical composition of the steel pipe manufactured by the method for manufacturing a steel pipe for oil wells excellent in sulfide stress cracking resistance according to the present invention is replaced with a part of Fe, if necessary, in the first group to be described later. An element selected from at least one of the third groups may be added as an optional additive element and contained.

以下、任意添加元素に関して説明する。   Hereinafter, the optional additive element will be described.

第1群:Nb:0.002〜0.1%
Nbは、Cと結合して炭化物を形成し、ピン止め作用によって結晶粒を微細化するのに有効な元素である。しかしながら、その含有量が0.002%未満では、前記の効果が不十分である。一方、Nbを0.1%を超えて含有させても前記の効果が飽和し、NbC析出物が増加して耐食性を劣化させる。したがって、添加する場合のNbの含有量を0.002〜0.1%とした。なお、添加する場合のNb含有量の下限は0.005%とすることが望ましく、上限は0.03%とすることが望ましい。
First group: Nb: 0.002 to 0.1%
Nb is an element effective for bonding with C to form carbides and refining crystal grains by a pinning action. However, if the content is less than 0.002%, the above effect is insufficient. On the other hand, even if Nb is contained in an amount exceeding 0.1%, the above effect is saturated, NbC precipitates are increased, and the corrosion resistance is deteriorated. Therefore, the content of Nb when added is set to 0.002 to 0.1%. In addition, when adding, it is desirable that the lower limit of Nb content is 0.005%, and the upper limit is 0.03%.

第2群:Ca:0.0001〜0.01%
Caは、鋼中のSと結合して硫化物を形成することで介在物の形状を改善し、耐SSC性を高めるのに有効な元素である。しかしながら、その含有量が0.0001%未満では前記の効果が得られない。一方、Caを0.01%を超えて含有させても前記の効果が飽和するばかりか、粗大なCa系介在物が生成するので却って耐SSC性が低下し、また、靱性も低下する。したがって、添加する場合のCaの含有量を0.0001〜0.01%とした。なお、添加する場合のCa含有量の下限は0.0003%とすることが望ましく、上限は0.003%とすることが望ましい。
Second group: Ca: 0.0001 to 0.01%
Ca is an element effective for improving the SSC resistance by improving the shape of inclusions by combining with S in steel to form a sulfide. However, if the content is less than 0.0001%, the above effect cannot be obtained. On the other hand, even if Ca is contained in excess of 0.01%, not only the above effects are saturated, but also coarse Ca-based inclusions are produced, so that the SSC resistance is lowered and the toughness is also lowered. Therefore, when Ca is added, the content of Ca is set to 0.0001 to 0.01%. In addition, when adding, the lower limit of the Ca content is desirably 0.0003%, and the upper limit is desirably 0.003%.

第3群:Zr:0.002〜0.1%
Zrは、鋼中の不純物であるNを窒化物として固定するのに有効な元素である。Nを固定することによって、焼入れ性向上のため添加するBがBNとなるのを抑制し、Bを固溶状態に維持して十分な焼入れ性を確保することができる。なお、前記N固定に関与する以外の残りのZrは、炭化物として微細に析出し、ピン止め作用によって結晶粒を微細化するのに有効である。しかしながら、Zrの含有量が0.002%未満では前記の効果が得られない。一方、Zrを0.1%を超えて含有させても結晶粒を微細化する効果が飽和してコストが嵩むばかりである。また、靱性の低下も招く。したがって、添加する場合のZrの含有量を0.002〜0.1%とした。なお、添加する場合のZr含有量の下限は0.005%とすることが望ましく、上限は0.06%とすることが望ましい。添加する場合のZr含有量の下限は0.01%とすることが一層望ましく、上限は0.04%とすることが一層望ましい。
Third group: Zr: 0.002 to 0.1%
Zr is an element effective for fixing N, which is an impurity in steel, as a nitride. By fixing N, B added for improving hardenability can be suppressed from becoming BN, and B can be maintained in a solid solution state to ensure sufficient hardenability. The remaining Zr other than that involved in the N fixation precipitates finely as carbides, and is effective for refining crystal grains by a pinning action. However, if the Zr content is less than 0.002%, the above effect cannot be obtained. On the other hand, even if Zr is contained in an amount exceeding 0.1%, the effect of refining the crystal grains is saturated and the cost is increased. In addition, the toughness is reduced. Therefore, the content of Zr when added is set to 0.002 to 0.1%. When added, the lower limit of the Zr content is preferably 0.005%, and the upper limit is preferably 0.06%. When added, the lower limit of the Zr content is more preferably 0.01%, and the upper limit is more preferably 0.04%.

上記の理由から、本発明(2)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、本発明(1)に係る鋼管のFeの一部に代えて、Nb:0.002〜0.1を含有することと規定した。   For the above reasons, the chemical composition of the steel pipe produced by the method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (2) is a part of Fe of the steel pipe according to the present invention (1). Instead of Nb: 0.002 to 0.1.

本発明(3)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、本発明(1)に係る鋼管のFeの一部に代えて、Ca:0.0001〜0.01%を含有することと規定した。   The chemical composition of the steel pipe produced by the method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (3) is Ca instead of a part of Fe of the steel pipe according to the present invention (1). : It was defined to contain 0.0001 to 0.01%.

本発明(4)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、本発明(1)に係る鋼管のFeの一部に代えて、Zr:0.002〜0.1%を含有することと規定した。   The chemical composition of the steel pipe manufactured by the method for manufacturing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (4) is Zr instead of a part of Fe of the steel pipe according to the present invention (1). : 0.002 to 0.1%.

本発明(5)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、本発明(1)に係る鋼管のFeの一部に代えて、Nb:0.002〜0.1及びCa:0.0001〜0.01%を含有することと規定した。   The chemical composition of the steel pipe manufactured by the method for manufacturing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (5) is Nb instead of a part of Fe of the steel pipe according to the present invention (1). : 0.002-0.1 and Ca: 0.0001-0.01%.

本発明(6)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、本発明(1)に係る鋼管のFeの一部に代えて、Nb:0.002〜0.1及びZr:0.002〜0.1%を含有することと規定した。   The chemical composition of the steel pipe manufactured by the method for manufacturing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (6) is Nb instead of a part of Fe of the steel pipe according to the present invention (1). : 0.002 to 0.1 and Zr: 0.002 to 0.1%.

本発明(7)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、本発明(1)に係る鋼管のFeの一部に代えて、Ca:0.0001〜0.01%及びZr:0.002〜0.1%を含有することと規定した。   The chemical composition of the steel pipe produced by the method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (7) is replaced with a part of Fe of the steel pipe according to the present invention (1). : 0.0001 to 0.01% and Zr: 0.002 to 0.1%.

本発明(8)に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法によって製造される鋼管の化学組成は、本発明(1)に係る鋼管のFeの一部に代えて、Nb:0.002〜0.1、Ca:0.0001〜0.01%及びZr:0.002〜0.1%を含有することと規定した。   The chemical composition of the steel pipe manufactured by the method for manufacturing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention (8) is Nb instead of a part of Fe of the steel pipe according to the present invention (1). : 0.002 to 0.1, Ca: 0.0001 to 0.01%, and Zr: 0.002 to 0.1%.

(B)熱処理
前記(A)項に記載の化学組成を有する鋼管は、その鋼管を40%未満の加工度で加工した後895℃以上の温度に加熱して焼入れするか或いは、40%以上の加工度で加工した後下記の(1)式を満たす温度に加熱して焼入れし、次いで、Ac1点以下の温度で焼戻しすることによって、良好な耐SSC性を発揮することができる。
(B) Heat treatment The steel pipe having the chemical composition described in the item (A) is processed at a workability of less than 40% and then heated to a temperature of 895 ° C. or higher, or quenched. Good SSC resistance can be exhibited by heating at a temperature satisfying the following formula (1) after quenching and then tempering at a temperature of Ac 1 point or less.

加熱温度(℃)≧0.625×加工度(%)+870・・・(1)、
但し、本発明における加工度は、ピアサーより後の加工での総加工度を表し、下記の(2)式に基づく値とする。
加工度(%)={(「ピアサー加工後の鋼管の断面積」−「焼戻し後の鋼管の断面積」)/「ピアサー加工後の鋼管の断面積」}×100・・・(2)。
Heating temperature (° C.) ≧ 0.625 × working degree (%) + 870 (1),
However, the degree of processing in the present invention represents the total degree of processing in processing after the piercer, and is a value based on the following equation (2).
Degree of work (%) = {(“cross-sectional area of steel pipe after piercer processing” − “cross-sectional area of steel pipe after tempering”) / “cross-sectional area of steel pipe after piercing”} × 100 (2).

以下、上記の事柄に関して詳しく説明する。   Hereinafter, the above matters will be described in detail.

本発明者らは、表1に示す化学組成を有する鋼aの9本のビレットを用いて、ピアサーで穿孔した後の加工度が種々変わるようにマンネスマン−マンドレル製管法によって、継目無製管した。なお、ピアサーより後の加工での総加工度は表2に示すとおりである。   The inventors of the present invention made seamless pipes by Mannesmann-Mandrel pipe making method using nine billets of steel a having the chemical composition shown in Table 1 so that the degree of processing after drilling with a piercer varied. did. In addition, the total processing degree in processing after the piercer is as shown in Table 2.

このようにして得た各継目無鋼管を、それぞれ、表2に示す温度で5分均熱してから焼入れし、次いで、650〜710℃の温度で30分均熱の焼戻し処理を施し、降伏強度(YS)を調整した。   Each seamless steel pipe thus obtained was soaked after being soaked for 5 minutes at the temperature shown in Table 2, and then subjected to tempering treatment for 30 minutes at a temperature of 650 to 710 ° C., yield strength. (YS) was adjusted.

Figure 0004701874
Figure 0004701874

Figure 0004701874
上記焼戻し後の継目無鋼管の肉厚中央部から、圧延方向(長手方向)に直径が6mmで平行部長さが40mmの丸棒引張試験片を採取し、常温で引張試験を実施して降伏強度(YS)を測定した。
Figure 0004701874
A round bar tensile test piece having a diameter of 6 mm in the rolling direction (longitudinal direction) and a parallel part length of 40 mm is collected from the center of the thickness of the seamless steel pipe after tempering, and yield strength is obtained by conducting a tensile test at room temperature. (YS) was measured.

また、上記焼戻し後の継目無鋼管の肉厚中央部から、圧延方向(長手方向)に直径が6.35mmで平行部長さが25.4mmの丸棒引張試験片を採取し、NACEのTM0177−96に規定されるA法に基づいて定荷重タイプのSSC試験を行った。   In addition, a round bar tensile test piece having a diameter of 6.35 mm in the rolling direction (longitudinal direction) and a parallel portion length of 25.4 mm was sampled from the thickness center of the seamless steel pipe after tempering, and NACE TM0177- A constant load type SSC test was performed based on the A method defined in 96.

すなわち、10132.5Pa(0.1atm)の硫化水素ガス(残部:炭酸ガス)を飽和させた24℃の5質量%食塩+0.5質量%酢酸水溶液(以下、「A浴」という。)の環境中で、先に測定した降伏強度(YS)の90%を負荷応力とした定荷重タイプのSSC試験を720時間行い、試験片の破断の有無を調査した。なお、720時間のSSC試験で破断しなかった場合に耐SSC性が良好と判断した。   That is, an environment of 5 mass% sodium chloride + 0.5 mass% acetic acid aqueous solution (hereinafter referred to as “A bath”) at 24 ° C. saturated with 10132.5 Pa (0.1 atm) of hydrogen sulfide gas (remainder: carbon dioxide gas). In particular, a constant load type SSC test with 90% of the previously measured yield strength (YS) as the load stress was performed for 720 hours, and the presence or absence of breakage of the test piece was investigated. In addition, when it did not fracture in the SSC test for 720 hours, it was judged that the SSC resistance was good.

表2に、各鋼管の降伏強度(YS)及び上記A浴環境中でのSSC試験結果を併せて示す。SSC試験結果は、試験片が破断せず耐SSC性が良好であったものを「○」で、また、試験片が破断して耐SSC性が劣るものを「×」で示した。   Table 2 also shows the yield strength (YS) of each steel pipe and the SSC test results in the A bath environment. The results of the SSC test were indicated by “◯” when the test piece did not break and had good SSC resistance, and by “x” when the test piece was broken and had poor SSC resistance.

なお、図1に、上記A浴環境中での定荷重タイプのSSC試験結果を整理し、焼入れ前の加熱温度と、ピアサーより後の加工での総加工度、つまり、本発明でいう「加工度」とが、耐SSC性に及ぼす影響を示した。なお、上記の「加工度」を図1では「ピアサー加工後の加工度」と表記した。   In FIG. 1, the SSC test results of the constant load type in the above-described A bath environment are arranged, and the heating temperature before quenching and the total processing degree after processing after the piercer, that is, “processing” in the present invention. "Degree" showed the influence which it has on SSC resistance. In addition, said "working degree" was described with "the working degree after a piercer processing" in FIG.

図1及び表2から、40%未満の加工度で加工した後895℃以上の温度に加熱して焼入れするか或いは、40%以上の加工度で加工した後前記の(1)式を満たす温度に加熱して焼入れすれば、焼戻し後の強度が降伏強度(YS)で869〜952MPaという高強度であっても、良好な耐SSC性が得られることが明らかである。   From FIG. 1 and Table 2, after processing at a working degree of less than 40%, the steel is heated and quenched to a temperature of 895 ° C. or higher, or after processing at a working degree of 40% or more, the temperature that satisfies the above formula (1) It is clear that good SSC resistance can be obtained even if the strength after tempering is as high as 869 to 952 MPa in terms of yield strength (YS).

したがって、本発明に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法においては、前記(A)項に記載の化学組成を有する鋼管を、40%未満の加工度で加工した後895℃以上の温度に加熱して焼入れするか或いは、40%以上の加工度で加工した後前記の(1)式を満たす温度に加熱して焼入れすることと規定した。但し、焼入れ前の加熱温度の上限は、結晶粒の極端な粗大化の抑止やスケールロスを防止して歩留りを高めるために940℃とするのがよい。 Therefore, in the method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention, after the steel pipe having the chemical composition described in the item (A) is processed at a workability of less than 40%, 895 is obtained. It was specified that the material was quenched by heating to a temperature equal to or higher than ° C., or was heated to a temperature satisfying the above-described formula (1) after being processed at a working degree of 40% or more. However, the upper limit of the heating temperature before quenching is preferably set to 940 ° C. in order to prevent excessive coarsening of crystal grains and to prevent scale loss and increase the yield.

なお、高温での焼戻しは、焼入れによって生成したマルテンサイトの内部応力を除去して、耐SSC性の向上をもたらすが、焼戻し温度がAc1点を超える場合には、焼戻し後の冷却時にベイナイトやマルテンサイトといった低温での変態相が生じて却って耐SSC性が低下する。 Tempering at high temperature removes the internal stress of martensite generated by quenching and improves SSC resistance. However, when the tempering temperature exceeds the Ac 1 point, bainite or A transformation phase at a low temperature such as martensite is generated, and the SSC resistance is lowered.

したがって、本発明に係る耐硫化物応力割れ性に優れた油井用鋼管の製造方法においては、上述の焼入れを行い、次いで、Ac1点以下の温度で焼戻しすることと規定した。 Therefore, in the method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to the present invention, it is specified that the above-described quenching is performed and then tempering is performed at a temperature of Ac 1 point or less.

なお、製管に際して、前記(2)式で表される加工度の下限値及び上限値は、素材であるビレットと製品のサイズを変えることで任意に決定可能であるが、設備的制約という点からは、加工度の下限値は現実的には3%とするのがよく、加工度の上限値は現実的には70%とするのがよい。   In addition, in pipe making, the lower limit and upper limit of the degree of processing represented by the above formula (2) can be arbitrarily determined by changing the billet and the product size as materials, but the point of equipment restrictions Therefore, the lower limit value of the working degree is practically 3%, and the upper limit value of the working degree is practically 70%.

また、前述のとおり、焼入れ前の加熱温度の上限は、結晶粒の極端な粗大化の抑止やスケールロスを防止して歩留りを高めるために940℃とするのがよい。 In addition, as described above, the upper limit of the heating temperature before quenching is preferably 940 ° C. in order to prevent excessive coarsening of crystal grains and to prevent scale loss and increase the yield.

更に、焼戻し温度の下限は、耐SSC性の向上を図るという意味から650℃とするのがよい。   Furthermore, the lower limit of the tempering temperature is preferably 650 ° C. from the viewpoint of improving the SSC resistance.

(C)鋼管の強度
SSCは鋼の強度が高くなるほど生じやすい。しかし、前記(B)項で述べたように、(A)項に記載の化学組成を有する鋼管を、40%未満の加工度で加工した後895℃以上の温度に加熱して焼入れするか或いは、40%以上の加工度で加工した後前記の(1)式を満たす温度に加熱して焼入れし(但し、焼入れ前の加熱温度は、940℃以下とするのがよい。)、次いで、Ac1点以下の温度で焼戻しすることによって製造した場合には、降伏強度(YS)が869〜952MPaという高強度であっても、良好な耐SSC性が得られる。
(C) Steel pipe strength SSC is more likely to occur as the strength of steel increases. However, as described in the above section (B), the steel pipe having the chemical composition described in the section (A) is processed at a processing degree of less than 40% and then heated to a temperature of 895 ° C. or higher and quenched. , After being processed at a working degree of 40% or more, it is heated to a temperature satisfying the above-mentioned formula (1) and quenched (however, the heating temperature before quenching is preferably 940 ° C. or less) , and then Ac. When manufactured by tempering at a temperature of 1 point or less, good SSC resistance can be obtained even if the yield strength (YS) is as high as 869 to 952 MPa.

したがって、本発明(9)においては、耐硫化物応力割れ性に優れた油井用鋼管の焼戻し後の強度としての降伏強度を、特に、110ksi級〜125ksi級の降伏強度である758MPa以上(110ksi以上)965MPa以下(140ksi以下)と規定した。   Therefore, in the present invention (9), the yield strength as the strength after tempering of the oil well steel pipe excellent in sulfide stress cracking resistance is 758 MPa or more (110 ksi or more), particularly the yield strength of the 110 ksi class to 125 ksi class. ) 965 MPa or less (140 ksi or less).

以下、実施例により本発明を更に詳しく説明する。   Hereinafter, the present invention will be described in more detail with reference to examples.

表3に示す化学組成を有する24種類の鋼種からなる外径225〜360mmのビレットを1250℃に加熱した後、マンネスマン−マンドレル製管法によって、種々の寸法の継目無鋼管に成形した。   Billets having an outer diameter of 225 to 360 mm made of 24 types of steels having chemical compositions shown in Table 3 were heated to 1250 ° C., and then formed into seamless steel pipes of various dimensions by the Mannesmann-Mandrel pipe manufacturing method.

表3に示した鋼のうち、鋼A〜Uは化学組成が本発明で規定する範囲内にある本発明例に係る鋼であり、一方、鋼V〜Xは本発明で規定する条件から外れた比較例に係る鋼である。   Among the steels shown in Table 3, steels A to U are steels according to examples of the present invention whose chemical compositions are within the range defined by the present invention, while steels V to X are out of the conditions defined by the present invention. The steel according to the comparative example.

表4に、製管製管条件としてのピアサーより後の加工での総加工度を示す。   Table 4 shows the total degree of processing in the processing after the piercer as the pipe making condition.

Figure 0004701874
Figure 0004701874

Figure 0004701874
上記のようにして得た各継目無鋼管を、5分均熱してから焼入れし、次いで、30分均熱して焼戻しを行った。なお、各継目無鋼管に対する焼入れ前の加熱温度及び焼戻しの温度の詳細を表4に併せて示した。また、ピアサーより後の加工での総加工度、つまり本発明でいう「加工度」が40%以上である場合のみ、表4の備考欄に、「0.625×加工度(%)+870」の値を記載した。
Figure 0004701874
Each seamless steel pipe obtained as described above was soaked for 5 minutes and then quenched, and then tempered by soaking for 30 minutes. The details of the heating temperature and the tempering temperature before quenching for each seamless steel pipe are also shown in Table 4. In addition, only when the total degree of machining after the piercer, that is, the “degree of machining” in the present invention is 40% or more, “0.625 × degree of machining (%) + 870” is entered in the remarks column of Table 4. The value of was described.

焼戻し後の各継目無鋼管の肉厚中央部から、圧延方向(長手方向)に直径が6mmで平行部長さが40mmの丸棒引張試験片を採取し、常温で引張試験を実施して降伏強度(YS)を測定した。   A round bar tensile test piece with a diameter of 6 mm in the rolling direction (longitudinal direction) and a parallel part length of 40 mm is taken from the center of the wall thickness of each seamless steel pipe after tempering, and a tensile test is performed at room temperature to yield strength. (YS) was measured.

また、焼戻し後の各継目無鋼管の肉厚中央部から、圧延方向(長手方向)に直径が6.35mmで平行部長さが25.4mmの丸棒引張試験片を採取し、NACEのTM0177−96に規定されるA法に基づいて定荷重タイプのSSC試験を行った。   Further, a round bar tensile test piece having a diameter of 6.35 mm in the rolling direction (longitudinal direction) and a parallel part length of 25.4 mm was collected from the thickness center of each seamless steel pipe after tempering, and NACE TM0177- A constant load type SSC test was performed based on the A method defined in 96.

すなわち、既に述べたA浴環境中(10132.5Pa(0.1atm)の硫化水素ガス(残部:炭酸ガス)を飽和させた24℃の5質量%食塩+0.5質量%酢酸水溶液の環境中)で、先に測定した降伏強度(YS)の90%を負荷応力とした定荷重タイプのSSC試験を720時間行い、破断の有無を調査した。なお、720時間のSSC試験で破断しなかった場合に耐SSC性が良好と判断した。   That is, in the already described bath A environment (in an environment of 5 mass% sodium chloride +0.5 mass% acetic acid aqueous solution at 24 ° C. saturated with hydrogen sulfide gas (remaining: carbon dioxide gas) of 10132.5 Pa (0.1 atm)) Then, a constant load type SSC test with 90% of the previously measured yield strength (YS) as a load stress was conducted for 720 hours to investigate the presence or absence of fracture. In addition, when it did not fracture in the SSC test for 720 hours, it was judged that the SSC resistance was good.

表4に、各継目無鋼管の降伏強度(YS)及び上記A浴環境中でのSSC試験結果を併せて示す。なお、SSC試験結果は、試験片が破断せず耐SSC性が良好であったものを「○」で、また、試験片が破断して耐SSC性が劣るものを「×」で示した。   Table 4 also shows the yield strength (YS) of each seamless steel pipe and the SSC test results in the above-described A bath environment. The SSC test results were indicated by “◯” when the test piece was not broken and had good SSC resistance, and “X” when the test piece was broken and had poor SSC resistance.

表4から、本発明の方法で製造された試験番号1〜13の鋼管の場合、すなわち、化学組成が本発明で規定する範囲内にある鋼A〜Mを素材鋼とし、本発明で規定する条件で焼入れ−焼戻しを行った鋼管の場合、降伏強度(YS)で765〜965MPaという高強度であっても、A浴環境中でのSSC試験で破断せず、良好な耐SSC性を有していることが明らかである。   From Table 4, in the case of the steel pipes of test numbers 1 to 13 manufactured by the method of the present invention, that is, the steels A to M whose chemical composition is within the range defined by the present invention are used as the raw steel, and are defined by the present invention. In the case of a steel pipe that has been quenched and tempered under the conditions, even if the yield strength (YS) is as high as 765 to 965 MPa, it does not break in the SSC test in the A bath environment and has good SSC resistance. It is clear that

これに対して、試験番号14〜24の鋼管は、SSC試験で破断しており、耐SSC性に劣ることが明らかである。   On the other hand, the steel pipes with test numbers 14 to 24 are broken in the SSC test and are clearly inferior in SSC resistance.

すなわち、素材鋼である鋼N〜Uの化学組成は本発明で規定する範囲内であっても、焼入れの加熱条件が本発明で規定する条件から外れた試験番号14〜21の鋼管の場合には、降伏強度(YS)で793〜965MPaという高強度ではA浴環境中でのSSC試験で破断を生じ、耐SSC性に劣っている。   That is, even when the chemical composition of the steels N to U, which is the raw steel, is within the range specified by the present invention, the steel pipes of test numbers 14 to 21 whose quenching heating conditions deviate from the conditions specified by the present invention When the yield strength (YS) is as high as 793 to 965 MPa, fracture occurs in the SSC test in the A bath environment, and the SSC resistance is poor.

試験番号22の鋼管は、素材鋼である鋼VのCr含有量が本発明で規定する上限を超えたものであるため、A浴環境中でのSSC試験で破断を生じ、耐SSC性に劣っている。   The steel pipe of test No. 22 has a Cr content of steel V, which is a material steel, exceeding the upper limit specified in the present invention, and therefore, the SSC test in the A bath environment is broken and inferior in SSC resistance. ing.

試験番号23の鋼管は、素材鋼である鋼WのMo含有量が本発明で規定する下限を下回ったものであるため、A浴環境中でのSSC試験で破断を生じ、耐SSC性に劣っている。   In the steel pipe of test number 23, the Mo content of the steel W, which is a raw material steel, is lower than the lower limit specified in the present invention. Therefore, the steel pipe breaks in the SSC test in the A bath environment and has poor SSC resistance. ing.

試験番号24の鋼管は、素材鋼である鋼XのV含有量が本発明で規定する下限を下回ったものであるため、A浴環境中でのSSC試験で破断を生じ、耐SSC性に劣っている。   In the steel pipe of test number 24, the V content of steel X, which is a raw material steel, is lower than the lower limit specified in the present invention. ing.

本発明の耐硫化物応力割れ性に優れた油井用鋼管の製造方法によれば、深さが大きく、しかも、硫化水素を含む油井やガス井で使用されるケーシング、チュービング及びドリルパイプなどとして好適な、耐硫化物応力割れ性に優れた油井用鋼管、なかでも降伏強度(YS)が758MPa以上965MPa以下である110ksi級〜125ksi級の耐硫化物応力割れ性に優れた油井用鋼管を容易に製造することができる。   According to the method for manufacturing a steel pipe for oil wells having excellent resistance to sulfide stress cracking according to the present invention, the depth is large, and it is suitable as a casing, tubing and drill pipe used in oil wells and gas wells containing hydrogen sulfide. In addition, oil well steel pipes excellent in sulfide stress cracking resistance, particularly steel pipes for oil wells excellent in sulfide stress cracking resistance of 110 ksi class to 125 ksi class having a yield strength (YS) of 758 MPa to 965 MPa. Can be manufactured.

A浴環境中(10132.5Pa(0.1atm)の硫化水素ガス(残部:炭酸ガス)を飽和させた24℃の5質量%食塩+0.5質量%酢酸水溶液環境中)での焼入れ前の加熱温度とピアサーより後の加工での総加工度(図では、「ピアサー加工後の加工度」と表記した。)が耐SSC性に及ぼす影響を示す図である。Heating before quenching in bath A environment (10132.5 Pa (0.1 atm) hydrogen sulfide gas (remainder: carbon dioxide gas) saturated at 24 ° C. in a 5 mass% salt + 0.5 mass% acetic acid aqueous solution environment) It is a figure which shows the influence which temperature and the total processing degree in the process after a piercer (it described with the "working degree after a piercer process" in a figure) have on SSC resistance.

Claims (9)

質量%で、C:0.2〜0.35%、Si:0.05〜0.5%、Mn:0.05〜1.0%、P:0.025%以下、S:0.01%以下、Al:0.005〜0.10%、Cr:0.1〜1.0%、Mo:0.5〜1.0%、Ti:0.002〜0.05%、V:0.05〜0.3%、B:0.0001〜0.005%、N:0.01%以下及びO(酸素):0.01%以下を含有し、残部はFe及び不純物からなる化学組成の鋼管を、40%未満の加工度で加工した後895℃以上の温度に加熱して焼入れするか或いは、40%以上の加工度で加工した後下記の(1)式を満たす温度に加熱して焼入れし、次いで、Ac1点以下の温度で焼戻しすることを特徴とする耐硫化物応力割れ性に優れた油井用鋼管の製造方法。
加熱温度(℃)≧0.625×加工度(%)+870・・・(1)
但し、加工度は、ピアサーより後の加工での総加工度を表し、下記の(2)式に基づく値とする。
加工度(%)={(「ピアサー加工後の鋼管の断面積」−「焼戻し後の鋼管の断面積」)/「ピアサー加工後の鋼管の断面積」}×100・・・(2)
In mass%, C: 0.2 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.05 to 1.0%, P: 0.025% or less, S: 0.01 %: Al: 0.005 to 0.10%, Cr: 0.1 to 1.0%, Mo: 0.5 to 1.0%, Ti: 0.002 to 0.05%, V: 0 0.05 to 0.3%, B: 0.0001 to 0.005%, N: 0.01% or less and O (oxygen): 0.01% or less, with the balance being Fe and impurities. The steel pipe is processed at a working degree of less than 40% and then heated to a temperature of 895 ° C. or higher and quenched, or processed at a working degree of 40% or higher and heated to a temperature satisfying the following formula (1). A method for producing an oil well steel pipe excellent in sulfide stress cracking resistance, characterized by quenching and then tempering at a temperature of Ac 1 point or less.
Heating temperature (° C.) ≧ 0.625 × working degree (%) + 870 (1)
However, the processing degree represents the total processing degree in processing after the piercer, and is a value based on the following equation (2).
Degree of processing (%) = {("Cross sectional area of steel pipe after piercing"-"Cross sectional area of steel pipe after tempering) /" Cross sectional area of steel pipe after piercing "} × 100 (2)
鋼管の化学組成が請求項1に記載のFeの一部に代えて、Nb:0.002〜0.1を含有するものであり、加熱温度が940℃以下であ請求項1に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。 Chemical composition of the steel pipe is in place of part of Fe of claim 1, Nb: 0.002 to 0.1 all SANYO containing, Ru der heating temperature is 940 ° C. or less, in claim 1 The manufacturing method of the steel pipe for oil wells which was excellent in sulfide stress cracking resistance of description. 鋼管の化学組成が請求項1に記載のFeの一部に代えて、Ca:0.0001〜0.01%を含有するものである請求項1に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   The chemical composition of the steel pipe is replaced with a part of Fe described in claim 1 and contains Ca: 0.0001 to 0.01%. Manufacturing method of steel pipe for oil well. 鋼管の化学組成が請求項1に記載のFeの一部に代えて、Zr:0.002〜0.1%を含有するものである請求項1に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   The chemical composition of the steel pipe is Zr: 0.002 to 0.1% in place of a part of Fe according to claim 1, and excellent in resistance to sulfide stress cracking according to claim 1. Manufacturing method of steel pipe for oil well. 鋼管の化学組成が請求項1に記載のFeの一部に代えて、Nb:0.002〜0.1及びCa:0.0001〜0.01%を含有するものであり、加熱温度が940℃以下であ請求項1に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。 Chemical composition of the steel pipe is in place of part of Fe of claim 1, Nb: 0.002 to 0.1, and Ca: all SANYO containing 0.0001 to 0.01%, the heating temperature is 940 ° C. Ru der a method for fabricating an oil well steel pipe having excellent sulfide stress cracking resistance according to claim 1. 鋼管の化学組成が請求項1に記載のFeの一部に代えて、Nb:0.002〜0.1及びZr:0.002〜0.1%を含有するものである請求項1に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   The chemical composition of a steel pipe is replaced with a part of Fe described in claim 1 and contains Nb: 0.002-0.1 and Zr: 0.002-0.1%. A method for producing steel pipes for oil wells with excellent resistance to sulfide stress cracking. 鋼管の化学組成が請求項1に記載のFeの一部に代えて、Ca:0.0001〜0.01%及びZr:0.002〜0.1%を含有するものである請求項1に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   The chemical composition of the steel pipe contains Ca: 0.0001 to 0.01% and Zr: 0.002 to 0.1% in place of a part of Fe described in claim 1. The manufacturing method of the steel pipe for oil wells which was excellent in sulfide stress cracking resistance of description. 鋼管の化学組成が請求項1に記載のFeの一部に代えて、Nb:0.002〜0.1、Ca:0.0001〜0.01%及びZr:0.002〜0.1%を含有するものである請求項1に記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   The chemical composition of the steel pipe is Nb: 0.002-0.1, Ca: 0.0001-0.01% and Zr: 0.002-0.1% in place of a part of Fe according to claim 1 The method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to claim 1. 焼戻し後の鋼管の降伏強度が758〜965MPaである請求項1から8までのいずれかに記載の耐硫化物応力割れ性に優れた油井用鋼管の製造方法。   The method for producing an oil well steel pipe excellent in sulfide stress cracking resistance according to any one of claims 1 to 8, wherein the yield strength of the steel pipe after tempering is 758 to 965 MPa.
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