WO2017149571A1 - Low-alloy, high-strength seamless steel pipe for oil well - Google Patents

Low-alloy, high-strength seamless steel pipe for oil well Download PDF

Info

Publication number
WO2017149571A1
WO2017149571A1 PCT/JP2016/004915 JP2016004915W WO2017149571A1 WO 2017149571 A1 WO2017149571 A1 WO 2017149571A1 JP 2016004915 W JP2016004915 W JP 2016004915W WO 2017149571 A1 WO2017149571 A1 WO 2017149571A1
Authority
WO
WIPO (PCT)
Prior art keywords
less
steel pipe
stress
steel
mpa
Prior art date
Application number
PCT/JP2016/004915
Other languages
French (fr)
Japanese (ja)
Inventor
岡津　光浩
正雄 柚賀
石黒　康英
太田　裕樹
Original Assignee
Ｊｆｅスチール株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to US16/078,924 priority Critical patent/US20190048444A1/en
Priority to MX2018010363A priority patent/MX2018010363A/en
Priority to EP16892416.5A priority patent/EP3425076B1/en
Priority to JP2017513268A priority patent/JP6152929B1/en
Priority to NZ74466816A priority patent/NZ744668A/en
Priority to BR112018017250-2A priority patent/BR112018017250B1/en
Publication of WO2017149571A1 publication Critical patent/WO2017149571A1/en

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/02—Hardening by precipitation
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies

Definitions

  • the present invention relates to a high-strength seamless steel pipe excellent in sulfide stress corrosion cracking resistance (SSC resistance) for oil wells and gas wells, particularly in a sour environment containing hydrogen sulfide.
  • SSC resistance stress corrosion cracking resistance
  • high strength refers to the case where the yield strength is 861 MPa or more (125 ksi or more).
  • Patent Document 1 discloses that, in weight%, C: 0.2 to 0.35%, Cr: 0.2 to 0.7%, Mo: 0.1 to 0.5 %, V: Low well steel containing 0.1 to 0.3%, which defines the total amount of precipitated carbides and the proportion of MC type carbides in them. Steel for use is disclosed.
  • Patent Document 2 by mass, C: 0.15 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.10 to 1.0%, P: 0.025 %: S: 0.005% or less, Cr: 0.1-1.5%, Mo: 0.1-1.0%, Al: 0.003-0.08%, N: 0.008%
  • B 0.0005 to 0.010%
  • Nb 0.05% or less
  • Zr 0.0.
  • V For steel inclusions containing one or more selected from 0.30% or less, the maximum length of continuous non-metallic inclusions and the number of particles having a particle size of 20 ⁇ m or more An oil well steel material excellent in sulfide stress corrosion cracking resistance is disclosed.
  • Patent Document 3 in mass%, C: 0.15 to 0.35%, Si: 0.1 to 1.5%, Mn: 0.1 to 2.5%, P: 0.025%
  • An oil well steel having excellent resistance to sulfide stress corrosion cracking in which the hardness of the composite oxide and the steel is defined by HRC is disclosed.
  • the resistance to sulfide stress corrosion cracking of steels of the techniques disclosed in these Patent Documents 1 to 3 refers to a round bar tensile test piece defined in NACE (abbreviation of National Association of Corrosion Engineering) TM0177 method A. This means the presence or absence of SSC when immersed for 720 hours in a test bath described in NACE TM0177 under constant stress.
  • NACE abbreviation of National Association of Corrosion Engineering
  • K stress intensity factor K under a hydrogen sulfide corrosion environment obtained by performing a DCB (Double Cantilever Beam) test prescribed in NACE TM0177 method D for the purpose of ensuring further safety of steel pipes for oil wells. It is being demanded that the ISSC value satisfies a specified value or more.
  • the above prior art does not disclose a specific measure for improving such a K ISSC value.
  • Patent Document 4 by mass, C: 0.2 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.05 to 1.0%, P: 0.025 %: S: 0.01% or less, Al: 0.005 to 0.10%, Cr: 0.1 to 1.0%, Mo: 0.5 to 1.0%, Ti: 0.002 to [211] of steel containing 0.05%, V: 0.05 to 0.3%, B: 0.0001 to 0.005%, N: 0.01% or less, O: 0.01% or less
  • a steel for low alloy oil country tubular goods having a yield strength of 861 MPa or more and excellent in resistance to sulfide stress corrosion cracking is disclosed by defining a formula consisting of a half width of a crystal plane and a hydrogen diffusion coefficient to a predetermined value.
  • K ISSC values are also described.
  • B bath 0.5 mass% acetic acid aqueous solution
  • resistance to sulfide stress corrosion cracking resistance increases as the hydrogen sulfide gas saturation partial pressure increases.
  • the present invention has been made in view of such problems, and has a high strength of a yield strength of 861 MPa or more and a higher hydrogen sulfide gas saturation environment, specifically, a hydrogen sulfide gas partial pressure of 0.02 MPa.
  • An object of the present invention is to provide a low-strength, high-strength seamless steel pipe for oil wells exhibiting excellent sulfide stress corrosion cracking resistance (SSC resistance) under the following sour environment, in particular, a stable and high KISSC value.
  • the present inventors first made a seamless steel pipe having various chemical compositions and microstructures of steel with a yield strength of 861 MPa or more based on NACE TM0177 method D, with a thickness of 10 mm, Three or more DCB test pieces each having a width of 25 mm and a length of 100 mm were sampled and subjected to a DCB test.
  • the test bath for the DCB test was a mixed aqueous solution of 0.5 mass% CH 3 COOH + CH 3 COONa at 24 ° C. saturated with 0.2 atm (0.02 MPa) hydrogen sulfide gas.
  • FIG. 1 is a schematic diagram of a DCB test piece.
  • h is the height of each arm of the DCB test piece
  • B is the thickness of the DCB test piece
  • Bn is the web thickness of the DCB test piece.
  • the target of the K ISSC value was set to 26.4 MPa ⁇ m or more (24 ksi ⁇ inch or more) based on the assumed maximum notch defect of the oil well pipe and the load weighting condition.
  • FIG. 2 shows a graph in which the obtained K ISSC values are arranged by the average hardness (Rockwell C scale hardness) of the seamless steel pipe provided with the test piece.
  • the K ISSC value obtained in the DCB test tended to decrease as the hardness of the seamless steel pipe increased, but it was found that the numerical values varied greatly even at the same hardness.
  • FIG. 3 shows an example of a stress-strain curve.
  • the stress-strain curves (solid line A and broken line B) of the two steel pipes shown in FIG. 3 do not change the stress value of 0.5 to 0.7% strain corresponding to the yield stress, but one (broken line B) is continuous. Yield is occurring, and the other (solid line A) has an upper yield point. It was also found that the steel exhibiting a continuous yield type stress-strain curve (broken line B) has a larger variation in KISSC values.
  • the inventors of the present invention conducted further research and found that the variation in the K ISSC value was determined by comparing the stress at the time of 0.7% strain with respect to the stress at the time of 0.4% strain ( ⁇ 0.4 ) of the stress-strain curve. (sigma 0.7) performs organized by the value ( ⁇ 0.7 / ⁇ 0.4) of the ratio of, as shown in FIG. 4, the ⁇ 0.7 / ⁇ 0.4 of seamless steel pipe 1.02 It has been found that the variation in K ISSC value can be reduced to about half by setting the following as compared with the case of exceeding 1.02.
  • the fact that is about half the variation in K ISSC value means that the hardness of the steel as a lower limit of the variation in hardness -K ISSC value K ISSC values in the correlation extends to high hardness side.
  • the Rockwell C scale hardness is as low as 30.2.
  • the stress-strain curve should not be a continuous yield type.
  • the precipitation Mo which precipitated before hardening is made into a primary precipitate, and it melts at the time of hardening, and Mo which precipitated after tempering is made into a secondary precipitate.
  • the quenching temperature is lower.
  • DQ is hot At the end of rolling, it indicates that quenching is performed immediately from a state where the steel pipe temperature is still high.
  • the present invention has been completed based on these findings and comprises the following gist.
  • C 0.25 to 0.31%, Si: 0.01 to 0.35%, Mn: 0.45 to 0.70%, P: 0.010% or less, S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.8 to 1.5%, Mo: 1.1 to 1.6%, V: 0.01 to 0.06%, Nb: 0.005 to 0.015%, B: 0.0015 to 0.0030%, Ti: 0.005 to 0.020%, N: 0.005% or less, Containing
  • Ti 0.005 to 0.020%, N: 0.005% or less, Containing
  • the value of the ratio of Ti content to N content (Ti / N) is 3.0 to 4.0, Having a composition consisting of the balance Fe and inevitable impurities, In the stress-strain curve, the ratio of the stress at 0.7% strain to the stress at 0.4% strain ( ⁇
  • a low-alloy high-strength seamless steel pipe for oil wells [2] In addition to the above composition, W: 0.1-0.2% Zr: 0.005 to 0.03% The low-alloy high-strength seamless steel pipe for oil wells according to [1], containing one or two selected from among the above. [3] In addition to the above composition, Ca: 0.0005 to 0.0030% In addition, the number of non-metallic inclusions in the oxide-based steel composed of Ca and Al having a major axis of 5 ⁇ m or more and satisfying the following formula (1) in mass% is 20 or less per 100 mm 2 The low alloy high-strength seamless steel pipe for oil wells according to [1] or [2]. (CaO) / (Al 2 O 3 ) ⁇ 4.0 (1)
  • high strength means that the yield strength is 861 MPa or more (125 ksi or more).
  • the upper limit of yield strength is not particularly limited, but is preferably 960 MPa.
  • the low-alloy high-strength seamless steel pipe for oil wells of the present invention is excellent in sulfide stress corrosion cracking resistance (SSC resistance), and is excellent in sulfide stress corrosion cracking resistance based on NACE TM0177 methodD.
  • SSC resistance sulfide stress corrosion cracking resistance
  • NACE TM0177 methodD sulfide stress corrosion cracking resistance
  • an excellent sulfide stress resistance in a high hydrogen sulfide gas saturation environment specifically, a sour environment with a hydrogen sulfide gas partial pressure of 0.02 MPa or more while having a high yield strength of 861 MPa or more. It is possible to provide a low-alloy high-strength seamless steel pipe exhibiting corrosion cracking resistance (SSC resistance), in particular, a stable high KISSC value.
  • SSC resistance corrosion cracking resistance
  • K is a diagram showing stress-strain curves of steel pipes with different variations in ISSC value. It is a figure which shows that the dispersion
  • the steel pipe of the present invention is, in mass%, C: 0.25 to 0.31%, Si: 0.01 to 0.35%, Mn: 0.45 to 0.70%, P: 0.010% or less S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.8 to 1.5%, Mo: 1.1 to 1.6%, V: 0.01 to 0.06%, Nb: 0.005 to 0.015%, B: 0.0015 to 0.0030%, Ti: 0.005 to 0.020%, N: 0.005% or less, the ratio of Ti content to N content (Ti / N) is 3.0 to 4.0, the balance Fe and inevitable impurities having a composition consisting of, stress - the ratio of the value of 0.7% strain when the stress to 0.4% strain at the stress at strain curve ( ⁇ 0.7 / ⁇ 0.4) is 1.02 or less , And the yield strength is low alloy high strength seamless steel pipe for oil well is at least 861MPa.
  • C 0.25 to 0.31%
  • C is an element that has an effect of increasing the strength of steel and is important for ensuring a desired high strength, and in order to achieve a high yield strength of 861 MPa or more, it is 0.25% or more.
  • C content is required.
  • the content of C exceeding 0.31% causes a significant increase in ⁇ 0.7 / ⁇ 0.4 and increases the variation of the K ISSC value. Therefore, C is set to 0.25 to 0.31%.
  • C is 0.27% or more.
  • C is 0.30% or less.
  • Si 0.01 to 0.35%
  • Si is an element that acts as a deoxidizer and has a function of increasing the strength of the steel by dissolving in steel and suppressing rapid softening during tempering. In order to obtain such an effect, it is necessary to contain 0.01% or more of Si. On the other hand, the inclusion of Si exceeding 0.35% forms coarse oxide inclusions and increases the variation of the K ISSC value. For this reason, Si is made 0.01 to 0.35%. Preferably, Si is 0.01 to 0.04%.
  • Mn 0.45 to 0.70%
  • Mn is an element that has the effect of increasing the strength of steel through the improvement of hardenability and binding to S to fix S as MnS, thereby preventing grain boundary embrittlement due to S.
  • the content of Mn exceeding 0.70% causes a significant increase in ⁇ 0.7 / ⁇ 0.4 and increases the variation of the K ISSC value. Therefore, Mn is set to 0.45 to 0.70%.
  • Mn is 0.50% or more.
  • Mn is 0.65% or less.
  • P 0.010% or less
  • P has a tendency to segregate at grain boundaries in the solid solution state and cause grain boundary embrittlement cracks, etc., and is desirably reduced as much as possible in the present invention. acceptable. Therefore, P is set to 0.010% or less.
  • S 0.001% or less S is mostly present as sulfide inclusions in steel, and lowers corrosion resistance such as ductility, toughness, and resistance to sulfide stress corrosion cracking.
  • a part of S may exist in a solid solution state, but in this case, it segregates at the grain boundaries and tends to cause grain boundary embrittlement cracks. For this reason, it is desirable to reduce S as much as possible in the present invention. However, excessive reduction increases the refining cost. For this reason, in the present invention, S is set to 0.001% or less where the adverse effect is acceptable.
  • O (oxygen) 0.0015% or less
  • O (oxygen) is present as an inevitable impurity in the steel as an oxide such as Al or Si.
  • O (oxygen) is made 0.0015% or less to which the adverse effect is allowable.
  • O (oxygen) is 0.0010% or less.
  • Al acts as a deoxidizer and combines with N to form AlN and contribute to the reduction of solid solution N. In order to acquire such an effect, Al needs to contain 0.015% or more. On the other hand, when Al is contained exceeding 0.080%, oxide inclusions increase and the variation in K ISSC value increases. For this reason, Al is made 0.015 to 0.080%. Preferably, Al is 0.05% or more. Preferably, Al is 0.07% or less.
  • Cu 0.02 to 0.09%
  • Cu is an element that has the effect of improving corrosion resistance. When added in a trace amount, a dense corrosion product is formed, and the formation and growth of pits starting from SSC is suppressed, and the resistance to sulfide stress corrosion cracking. In the present invention, it is necessary to contain 0.02% or more of Cu. On the other hand, when it contains Cu exceeding 0.09%, the hot workability at the time of the manufacturing process of a seamless steel pipe will fall. For this reason, Cu is made 0.02 to 0.09%.
  • Cu is 0.03% or more.
  • Cu is 0.05% or less.
  • Cr 0.8 to 1.5% Cr is an element that contributes to an increase in the strength of steel through an increase in hardenability and improves the corrosion resistance. Also, Cr combines with C during tempering to form carbides such as M 3 C, M 7 C 3 and M 23 C 6 systems, and especially M 3 C carbides improve temper softening resistance. Reduces strength change due to tempering and contributes to improved yield strength. In order to achieve a yield strength of 861 MPa or more, it is necessary to contain 0.8% or more of Cr. On the other hand, even if Cr is contained exceeding 1.5%, the effect is saturated, which is economically disadvantageous. Therefore, Cr is set to 0.8 to 1.5%. Preferably, Cr is 0.9% or more. Preferably, Cr is 1.1% or less.
  • Mo 1.1-1.6%
  • Mo is an element that contributes to an increase in the strength of steel through an increase in hardenability and improves the corrosion resistance.
  • the present inventors particularly focused on the point of forming M 2 C-based carbides.
  • Mo 2 C carbides that are secondarily precipitated after tempering improve resistance to temper softening, reduce strength change due to tempering, contribute to improvement of yield strength, and change the stress-strain curve of steel from a continuous yield type. The present inventors have found that a yield type shape can be obtained.
  • a specific amount of Mo is effective for achieving both high yield strength and K ISSC value in a sour environment with a hydrogen sulfide gas partial pressure of 0.2 atm (0.02 MPa) or more as described above.
  • Mo is set to 1.1 to 1.6%.
  • Mo is 1.2% or more.
  • Mo is 1.5% or less.
  • V 0.01 to 0.06%
  • V is an element that forms carbides or nitrides and contributes to the strengthening of steel. In order to obtain such an effect, the V content of 0.01% or more is required. On the other hand, when V is contained exceeding 0.06%, the V-based carbide becomes coarse and becomes the starting point of sulfide stress corrosion cracking, rather, the K ISSC value decreases. Therefore, V is set to 0.01 to 0.06%.
  • V is 0.03% or more.
  • V is 0.05% or less.
  • Nb 0.005 to 0.015%
  • Nb delays recrystallization in the austenite ( ⁇ ) temperature range, contributes to the refinement of ⁇ grains, and acts extremely effectively on the refinement of the substructure (eg, packets, blocks, lath) of steel immediately after quenching. Element. In order to obtain such an effect, it is necessary to contain 0.005% or more of Nb. On the other hand, the effect is saturated even if it contains Nb exceeding 0.015%. For this reason, Nb is made 0.005 to 0.015%.
  • a packet is defined as a region composed of a group of laths having the same crystal habit plane arranged in parallel, and a block is composed of a group of laths parallel and in the same orientation.
  • Nb is 0.009% or more.
  • B 0.0015 to 0.0030%
  • B is an element that contributes to improving the hardenability when contained in a very small amount.
  • B needs to contain 0.0015% or more of B.
  • the effect is saturated or the formation of Fe boride (Fe-B) makes it impossible to expect the desired effect, which is economically disadvantageous. .
  • B is made 0.0015 to 0.0030%.
  • B is 0.0020 to 0.0030%.
  • Ti forms a nitride and reduces the surplus N in the steel to make the effect of B described above effective.
  • Ti is an element that contributes to prevention of coarsening due to the pinning effect of austenite grains during steel quenching. In order to obtain such an effect, it is necessary to contain 0.005% or more of Ti.
  • the Ti content exceeding 0.020% promotes the formation of coarse MC-type nitride (TiN) during casting, and causes coarsening of austenite grains during quenching. For this reason, Ti is made 0.005 to 0.020%.
  • Ti is 0.008% or more.
  • Ti is 0.015% or less.
  • N 0.005% or less N is an unavoidable impurity in steel and forms MN-type precipitates by combining with nitride-forming elements such as Ti, Nb, and Al. Further, the remaining surplus N that forms these nitrides combines with B to form BN precipitates. At this time, since the effect of improving hardenability due to the addition of B is lost, it is preferable to reduce surplus N as much as possible, and N is set to 0.005% or less.
  • Ti / N Value of ratio of Ti content to N content (Ti / N): 3.0 to 4.0
  • Ti / N is defined.
  • surplus N is generated, and as a result of the formation of BN, the solid solution B at the time of quenching is insufficient, so that the microstructure at the end of quenching is martensite and bainite, or martensite and ferrite.
  • Ti / N is set to 3.0 to 4.0.
  • the balance other than the above components is Fe and inevitable impurities.
  • W 0.1-0.2%
  • Zr 0.005-0
  • One or two selected from 0.03% may be selected and contained.
  • from Ca and Al containing 0.0005 to 0.0030% Ca, mass%, composition ratio (CaO) / (Al 2 O 3 ) ⁇ 4.0, and having a major axis of 5 ⁇ m or more.
  • the number of non-metallic inclusions in the oxide-based steel may be 20 or less per 100 mm 2 .
  • W 0.1-0.2% W, like Mo, forms carbides and contributes to an increase in strength by precipitation hardening, and also forms a solid solution, segregates at the prior austenite grain boundaries, and contributes to an improvement in resistance to sulfide stress corrosion cracking.
  • Zr 0.005 to 0.03%
  • Zr is effective in suppressing austenite grain growth during quenching by forming a nitride and pinning the same as Ti.
  • Zr is set to 0.005 to 0.03%.
  • Ca 0.0005 to 0.0030%
  • Ca is effective in preventing nozzle clogging during continuous casting, and in order to obtain a necessary effect, it is desirable to contain 0.0005% or more of Ca.
  • Ca forms oxide-based non-metallic inclusions complexed with Al.
  • Ca exceeds 0.0030%, a large number of coarse substances exist, and resistance to sulfide stress corrosion cracking is present. Reduce.
  • the major axis has a particularly adverse effect, so that the major axis is 5 ⁇ m or more.
  • the number of inclusions satisfying the expression (1) is 20 or less per 100 mm 2 .
  • the number of inclusions is obtained by taking a sample for a scanning electron microscope (SEM) having a cross section orthogonal to the longitudinal direction of the pipe from an arbitrary circumferential position on the end of the steel pipe. At least the outer surface of the pipe, the center of the wall, It can be calculated from the SEM observation of inclusions at three locations on the surface and the analysis result of the chemical composition with the characteristic X-ray analyzer attached to the SEM. Therefore, when Ca is contained, the Ca content is set to 0.0005 to 0.0030%.
  • the number of non-metallic inclusions in the oxide-based steel composed of Ca and Al having a major axis of 5 ⁇ m or more satisfying the following formula (1) in mass% is 20 or less per 100 mm 2.
  • Ca is 0.0010% or more.
  • Ca is 0.0016% or less.
  • the number of inclusions described above is to control the amount of Al input during Al deoxidation treatment after decarburization refining and to add an amount of Ca according to the analytical values of Al, O, and Ca in the molten steel before Ca addition. Can be controlled.
  • the manufacturing method of the steel pipe material having the above composition is not particularly limited, but the molten steel having the above composition is melted by a generally known melting method such as a converter, an electric furnace or a vacuum melting furnace. It is preferable to produce a steel pipe material such as billet by a conventional method such as continuous casting or ingot-splitting rolling.
  • the steel pipe material is formed into a seamless steel pipe by hot forming.
  • hot forming method after piercer drilling, after forming to a predetermined thickness using any one of mandrel mill rolling and plug mill rolling, hot rolling is performed until appropriate diameter reduction rolling. In order to stabilize ⁇ 0.7 / ⁇ 0.4 to 1.02 or less, it is desirable to perform direct quenching (DQ) after hot rolling.
  • DQ direct quenching
  • the microstructure at the end of DQ becomes a composite structure such as martensite and bainite or martensite and ferrite, the crystal grain size of steel after the quenching and tempering heat treatment, 2 It is necessary to prevent the next precipitation amount from becoming heterogeneous and the value of ⁇ 0.7 / ⁇ 0.4 from exceeding 1.02. Therefore, it is preferable that completion
  • the temperature of the steel pipe at the end of DQ is preferably 200 ° C. or lower.
  • the steel pipe is quenched (Q) and tempered (T) in order to achieve a target yield strength of 861 MPa or more.
  • the quenching temperature at this time is preferably 930 ° C. or lower from the viewpoint of crystal grain refinement.
  • the quenching temperature is preferably 860 to 930 ° C.
  • the tempering temperature In order to avoid austenite retransformation, the tempering temperature needs to be Ac 1 temperature or less, but if it is less than 600 ° C., the secondary precipitation amount of Mo or the like cannot be secured. For this reason, the tempering temperature is preferably at least 600 ° C. or higher.
  • the value ( ⁇ 0.7 / ⁇ 0.4 ) of the ratio of the stress at the time of 0.7% strain ( ⁇ 0.7 ) to the stress at the time of 0.4% strain ( ⁇ 0.4 ) in the stress-strain curve is 1.02 or less
  • the variation of the K ISSC value varies greatly depending on the shape of the stress-strain curve of the steel.
  • the value ( ⁇ 0 ) of the ratio of the stress at the time of 0.7% strain ( ⁇ 0.7 ) to the stress at the time of 0.4% strain ( ⁇ 0.4 ) .7 / ⁇ 0.4 ) was found to be approximately halved in variation in K ISSC value when 1.02 or less.
  • ⁇ 0.7 / ⁇ 0.4 is set to 1.02 or less.
  • the yield strength, the stress at 0.4% strain ( ⁇ 0.4 ), and the stress at 0.7% strain ( ⁇ 0.7 ) are measured by a tensile test based on JIS Z2241. be able to.
  • microstructure of the present invention is not particularly limited, but the main phase is martensite, and the other remaining structures are one type or two types or more of ferrite, retained austenite, pearlite, bainite, etc. And if it is 5% or less, the objective of this invention can be achieved.
  • the bloom slab was formed into a billet with a round cross section by hot rolling. Furthermore, using this billet as a raw material, after heating to the billet heating temperature shown in Table 2, Mannesmann piercing-plug mill rolling-reducing rolling was performed hot, and rolling was completed at the rolling end temperatures shown in Table 2 and Table 3. And formed into a seamless steel pipe.
  • the steel pipe is cooled to the room temperature (below 35 ° C.) by direct quenching (DQ) or air cooling (0.2 to 0.5 ° C./s), and then the steel pipe heat treatment conditions (Q1 temperature) shown in Table 2 and Table 3 1st quenching temperature, T1 temperature: 1st tempering temperature, Q2 temperature: 2nd quenching temperature, T2 temperature: 2nd tempering temperature).
  • Q1 temperature 1st quenching temperature
  • T1 temperature 1st tempering temperature
  • Q2 temperature 2nd quenching temperature
  • T2 temperature 2nd tempering temperature
  • the DCB test was implemented based on NACETM0177 methodD using the extract
  • the test bath for the DCB test was a mixed aqueous solution of 0.5 mass% CH 3 COOH + CH 3 COONa at 24 ° C. saturated with 0.2 atm (0.02 MPa) hydrogen sulfide gas. After immersing the DCB test piece in which the wedge was introduced into this test bath under predetermined conditions for 336 hours, the length a of the crack generated in the DCB test piece during the immersion and the wedge opening stress P were measured, and the following equation (2 ) To calculate K ISSC (MPa ⁇ m).
  • h is the height of each arm of the DCB test piece
  • B is the thickness of the DCB test piece
  • Bn is the web thickness of the DCB test piece.
  • Steel pipes 1 to 7 whose chemical composition and ⁇ 0.7 / ⁇ 0.4 were within the scope of the present invention were all hydrogen sulfide having a yield strength of 861 MPa or more and a DCB test bath of 0.2 atm (0.02 MPa).
  • a DCB test bath 0.2 atm (0.02 MPa).
  • the K ISSC value obtained in each of the three DCB tests does not vary greatly, and the target is 26.4 MPa. Satisfied all over ⁇ m.
  • Comparative Example 8 (steel No. G) in which C of the chemical composition was below the lower limit of the scope of the present invention
  • Comparative Example 9 (steel No. H) in which Mn was below the lower limit of the scope of the present invention, and Cr was within the scope of the present invention
  • Comparative Example 10 (steel No. I), which was less than the lower limit, could not achieve the target yield strength of 861 MPa or more.
  • Comparative Example 11 (steel No. J) in which Mo of the chemical composition was below the lower limit of the range of the present invention and Comparative Example 12 (steel No. K) in which the upper limit was exceeded were all in the three DCB tests. Neither book satisfied the target of 26.4 MPa ⁇ m or more.
  • Comparative Example 13 (steel No. L) in which Nb of the chemical composition was below the lower limit of the range of the present invention
  • Comparative Example 14 (steel No. M) in which B was lower than the lower limit of the range of the present invention were ⁇ 0.7
  • the K ISSC values varied greatly, and two of the three DCB tests did not satisfy the target of 26.4 MPa ⁇ m or more.
  • Comparative Example 16 (steel No. O) in which the Ti / N ratio exceeded the upper limit of the range of the present invention also has a large K ISSC value as a result of ⁇ 0.7 / ⁇ 0.4 being out of the range of the present invention. Variations did not satisfy the target of 26.4 MPa ⁇ m or more, one of the three DCB tests.
  • Comparative Example 17 which had a low final tempering temperature, showed that ⁇ 0.7 / ⁇ 0.4 was outside the scope of the present invention. The target of 26.4 MPa ⁇ m or more was not satisfied. Similarly, in Comparative Example 18 in which the quenching temperature before the final tempering was low, ⁇ 0.7 / ⁇ 0.4 was out of the range of the present invention. As a result, the K ISSC value varied greatly, and three DCB tests Two of them did not satisfy the target of 26.4 MPa ⁇ m or more.
  • the bloom slab was formed into a billet with a round cross section by hot rolling. Further, using this billet as a raw material, after heating to the billet heating temperature shown in Table 5, hot Mannesmann piercing-plug mill rolling-reducing rolling was performed, and rolling was completed at the rolling completion temperature shown in Table 5 and seamlessly performed. Molded into a steel pipe.
  • the steel pipe is cooled to the room temperature (below 35 ° C.) by direct quenching (DQ) or air cooling (0.2 to 0.5 ° C./s), and then the heat treatment conditions (Q1 temperature: first time) shown in Table 5 , T1 temperature: first tempering temperature, Q2 temperature: second quenching temperature, T2 temperature: second tempering temperature).
  • DQ direct quenching
  • T1 temperature first tempering temperature
  • Q2 temperature second quenching temperature
  • T2 temperature second tempering temperature
  • the DCB test was implemented based on NACETM0177 methodD using the extract
  • the test bath for the DCB test was a mixed aqueous solution of 0.5 mass% CH 3 COOH + CH 3 COONa at 24 ° C. saturated with 0.2 atm (0.02 MPa) hydrogen sulfide gas. After immersing the DCB test piece into which the wedge was introduced into this test bath under predetermined conditions for 336 hours, the length a of the crack generated in the DCB test piece during the immersion and the wedge opening stress P were measured. K ISSC (MPa ⁇ m) was calculated.
  • the steel pipes 2-1 to 2-4 whose chemical composition, number of inclusions and ⁇ 0.7 / ⁇ 0.4 were within the range of the present invention, all had a yield strength of 861 MPa or more, and were obtained by three DCB tests. All of the obtained K ISSC values satisfied the target of 26.4 MPa ⁇ m without greatly varying.
  • Comparative Example 2-5 (steel No. T) in which the upper limit of Ca exceeded the upper limit of the range of the present invention, the K ISSC value greatly varied, and one of the three DCB tests was targeted at 26.4 MPa. ⁇ m was not satisfied.
  • Comparative Example 2-6 (steel No. U), considering that the amount of Ca in the molten steel before addition of Ca is high due to impurities Ca contained in the alloy iron of other elements added during secondary refining.
  • Ca was within the scope of the present invention because Ca was added, but the number of non-metallic inclusions in the oxide-based steel composed of Ca and Al with a major axis of 5 ⁇ m or more and satisfying formula (1) was The upper limit of the invention range was exceeded, the K ISSC value varied greatly, and one of the three DCB tests did not satisfy the target of 26.4 MPa ⁇ m.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Mining & Mineral Resources (AREA)
  • Manufacturing & Machinery (AREA)
  • Environmental & Geological Engineering (AREA)
  • Fluid Mechanics (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatment Of Steel (AREA)
  • Rigid Pipes And Flexible Pipes (AREA)

Abstract

A low-alloy, high-strength seamless steel pipe for an oil well is provided which has excellent SSC resistance. This steel pipe has a composition which contains, in mass%, C: 0.25-0.31%, Si: 0.01-0.35%, Mn: 0.45-0.70%, P: 0.010% or less, S: 0.001% or less, O: 0.0015% or less, Al: 0.015-0.080%, Cu: 0.02-0.09%, Cr: 0.8-1.5%, Mo: 1.1-1.6%, V: 0.01-0.06%, Nb: 0.005-0.015%, B: 0.0015-0.0030%, Ti: 0.005-0.020%, and N: 0.005% or less, wherein the value of the ratio (Ti/N) of the Ti content to the N content is 3.0-4.0, and the remainder is Fe and unavoidable impurities, and the value of the ratio (σ0.7/σ0.4) of the stress at 0.7% strain to the stress at 0.4% strain on the stress-strain curve is 1.02 or less, and the yield strength is 861 MPa or greater.

Description

油井用低合金高強度継目無鋼管Low alloy high strength seamless steel pipe for oil wells
　本発明は、油井やガス井用の、特に硫化水素を含むサワー環境下における耐硫化物応力腐食割れ性（耐ＳＳＣ性）に優れた高強度継目無鋼管に関する。なお、ここでいう「高強度」とは、降伏強度が８６１ＭＰａ以上（１２５ｋｓｉ以上）の強度を有する場合をいうものとする。 The present invention relates to a high-strength seamless steel pipe excellent in sulfide stress corrosion cracking resistance (SSC resistance) for oil wells and gas wells, particularly in a sour environment containing hydrogen sulfide. Here, “high strength” refers to the case where the yield strength is 861 MPa or more (125 ksi or more).
　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、硫化水素等を含む、いわゆるサワー環境下にある厳しい腐食環境の油田やガス田等の開発が盛んになっている。このような環境下で使用される油井用鋼管には、高強度で、かつ優れた耐食性（耐サワー性）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 oil resources expected in the near future, the so-called sour environment including deep oil fields, hydrogen sulfide, etc. that have not been previously excluded The development of oil fields and gas fields in corrosive environments has become active. The oil well steel pipe used in such an environment is required to have a material having high strength and excellent corrosion resistance (sour resistance).
　このような要求に対し、例えば、特許文献１には、重量％で、Ｃ：０．２～０．３５％、Ｃｒ：０．２～０．７％、Ｍｏ：０．１～０．５％、Ｖ：０．１～０．３％を含む低合金鋼からなり、析出している炭化物の総量とその内のＭＣ型炭化物の割合を規定した、耐硫化物応力腐食割れ性に優れる油井用鋼が開示されている。 In response to such a demand, for example, Patent Document 1 discloses that, in weight%, C: 0.2 to 0.35%, Cr: 0.2 to 0.7%, Mo: 0.1 to 0.5 %, V: Low well steel containing 0.1 to 0.3%, which defines the total amount of precipitated carbides and the proportion of MC type carbides in them. Steel for use is disclosed.
　また、特許文献２には、質量％で、Ｃ：０．１５～０．３０％、Ｓｉ：０．０５～１．０％、Ｍｎ：０．１０～１．０％、Ｐ：０．０２５％以下、Ｓ：０．００５％以下、Ｃｒ：０．１～１．５％、Ｍｏ：０．１～１．０％、Ａｌ：０．００３～０．０８％、Ｎ：０．００８％以下、Ｂ：０．０００５～０．０１０％、Ｃａ＋Ｏ（酸素）：０．００８％以下を含み、さらにＴｉ：０．００５～０．０５％、Ｎｂ：０．０５％以下、Ｚｒ：０．０５％以下、Ｖ：０．３０％以下から選択される１種または２種以上を含有する鋼の鋼中介在物性状について、連続した非金属介在物の最大長さおよび粒径２０μｍ以上の個数を規定した、耐硫化物応力腐食割れ性に優れた油井用鋼材が開示されている。 Further, in Patent Document 2, by mass, C: 0.15 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.10 to 1.0%, P: 0.025 %: S: 0.005% or less, Cr: 0.1-1.5%, Mo: 0.1-1.0%, Al: 0.003-0.08%, N: 0.008% In the following, B: 0.0005 to 0.010%, Ca + O (oxygen): 0.008% or less, Ti: 0.005 to 0.05%, Nb: 0.05% or less, Zr: 0.0. 05% or less, V: For steel inclusions containing one or more selected from 0.30% or less, the maximum length of continuous non-metallic inclusions and the number of particles having a particle size of 20 μm or more An oil well steel material excellent in sulfide stress corrosion cracking resistance is disclosed.
　また、特許文献３に、質量％で、Ｃ：０．１５～０．３５％、Ｓｉ：０．１～１．５％、Ｍｎ：０．１～２．５％、Ｐ：０．０２５％以下、Ｓ：０．００４％以下、sol.Ａｌ：０．００1～０．1％、Ｃａ：０．０００５～０．００５％を含有する鋼のＣａ系非金属介在物組成、ＣａとＡｌの複合酸化物および鋼の硬さをＨＲＣで規定した、耐硫化物応力腐食割れ性に優れた油井用鋼が開示されている。 Further, in Patent Document 3, in mass%, C: 0.15 to 0.35%, Si: 0.1 to 1.5%, Mn: 0.1 to 2.5%, P: 0.025% Hereinafter, a Ca-based non-metallic inclusion composition of steel containing S: 0.004% or less, sol.Al: 0.001 to 0.1%, Ca: 0.0005 to 0.005%, of Ca and Al An oil well steel having excellent resistance to sulfide stress corrosion cracking in which the hardness of the composite oxide and the steel is defined by HRC is disclosed.
　これらの特許文献１～３に開示された技術の鋼の耐硫化物応力腐食割れ性とは、ＮＡＣＥ（Ｎａｔｉｏｎａｌ　Ａｓｓｏｃｉａｔｉｏｎ　ｏｆ　Ｃｏｒｒｏｓｉｏｎ　Ｅｎｇｉｎｅｅｒｉｎｇの略）ＴＭ０１７７　ｍｅｔｈｏｄ　Ａに規定されている、丸棒引張試験片をＮＡＣＥ　ＴＭ０１７７記載の試験浴中で一定応力を負荷したまま７２０時間浸漬した際のＳＳＣ発生の有無を意味している。一方、近年、油井用鋼管のさらなる安全確保を目的に、ＮＡＣＥ　ＴＭ０１７７　ｍｅｔｈｏｄ　Ｄに規定されている、ＤＣＢ（Ｄｏｕｂｌｅ　Ｃａｎｔｉｌｅｖｅｒ　Ｂｅａｍ）試験を実施することにより得られる硫化水素腐食環境下での応力拡大係数ＫＩＳＳＣ値が規定値以上を満足することが求められるようになりつつある。上記先行技術にはこのようなＫＩＳＳＣ値を向上させる具体的な対策は開示されていない。 The resistance to sulfide stress corrosion cracking of steels of the techniques disclosed in these Patent Documents 1 to 3 refers to a round bar tensile test piece defined in NACE (abbreviation of National Association of Corrosion Engineering) TM0177 method A. This means the presence or absence of SSC when immersed for 720 hours in a test bath described in NACE TM0177 under constant stress. On the other hand, in recent years, the stress intensity factor K under a hydrogen sulfide corrosion environment obtained by performing a DCB (Double Cantilever Beam) test prescribed in NACE TM0177 method D for the purpose of ensuring further safety of steel pipes for oil wells. It is being demanded that the ISSC value satisfies a specified value or more. The above prior art does not disclose a specific measure for improving such a K ISSC value.
　一方、特許文献４には、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、Ｏ：０．０１％以下を含有する鋼の［２１１］結晶面の半価幅と水素拡散係数からなる式を所定の値に規定することで、耐硫化物応力腐食割れ性に優れた、降伏強度８６１ＭＰａ以上の低合金油井管用鋼が開示されている。この文献の実施例には、上述のＫＩＳＳＣ値も記載されている。 On the other hand, in Patent Document 4, by mass, C: 0.2 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.05 to 1.0%, P: 0.025 %: S: 0.01% or less, Al: 0.005 to 0.10%, Cr: 0.1 to 1.0%, Mo: 0.5 to 1.0%, Ti: 0.002 to [211] of steel containing 0.05%, V: 0.05 to 0.3%, B: 0.0001 to 0.005%, N: 0.01% or less, O: 0.01% or less A steel for low alloy oil country tubular goods having a yield strength of 861 MPa or more and excellent in resistance to sulfide stress corrosion cracking is disclosed by defining a formula consisting of a half width of a crystal plane and a hydrogen diffusion coefficient to a predetermined value. In the examples of this document, the above-mentioned K ISSC values are also described.
特開２０００－１７８６８２号公報JP 2000-178682 A 特開２００１－１７２７３９号公報JP 2001-172739 A 特開２００２－６０８９３号公報JP 2002-60893 A 特開２００５－３５０７５４号公報JP 2005-350754 A
　しかしながら、特許文献４の実施例におけるＫＩＳＳＣ値は、０．１ａｔｍ（＝０．０１ＭＰａ）の硫化水素ガスを飽和させた５質量％食塩＋０．５質量％酢酸水溶液（「Ａ浴」と記載）のものがほとんどで、降伏強度が８６１ＭＰａ超えのもので１ａｔｍ（＝０．１ＭＰａ）の硫化水素ガスを飽和させた５質量％食塩＋０．５質量％酢酸水溶液（「Ｂ浴」と記載）での実施例は記載されていない。一般に、耐硫化物応力腐食割れ性は硫化水素ガス飽和分圧が大きいほど感受性が高くなることが知られており、今後開発がなされる、高い硫化水素ガス飽和条件の井戸環境にて、上述の降伏強度８６１ＭＰａ以上の油井用低合金鋼管として使用するにはまだ不安がある。 However, the K ISSC value in the example of Patent Document 4 is 5% by mass sodium chloride + 0.5% by mass acetic acid aqueous solution (described as “A bath”) in which 0.1 atm (= 0.01 MPa) of hydrogen sulfide gas is saturated. Of 5 mass% salt + 0.5 mass% acetic acid aqueous solution (described as “B bath”) with a yield strength exceeding 861 MPa and saturated with 1 atm (= 0.1 MPa) hydrogen sulfide gas. Examples are not described. In general, it is known that resistance to sulfide stress corrosion cracking resistance increases as the hydrogen sulfide gas saturation partial pressure increases. In the well environment under high hydrogen sulfide gas saturation conditions, which will be developed in the future, There is still concern about using it as a low alloy steel pipe for oil wells with a yield strength of 861 MPa or more.
　本発明は、このような問題点に鑑みてなされたものであり、降伏強度８６１ＭＰａ以上の高強度を有しつつ、さらに高い硫化水素ガス飽和環境、具体的には硫化水素ガス分圧０．０２ＭＰａ以下のサワー環境下における優れた耐硫化物応力腐食割れ性（耐ＳＳＣ性）、特に、安定して高いＫＩＳＳＣ値を示す油井用低合金高強度継目無鋼管を提供することを目的としている。 The present invention has been made in view of such problems, and has a high strength of a yield strength of 861 MPa or more and a higher hydrogen sulfide gas saturation environment, specifically, a hydrogen sulfide gas partial pressure of 0.02 MPa. An object of the present invention is to provide a low-strength, high-strength seamless steel pipe for oil wells exhibiting excellent sulfide stress corrosion cracking resistance (SSC resistance) under the following sour environment, in particular, a stable and high KISSC value.
　本発明者等は、上述の課題を解決するため、最初に種々の化学組成および鋼のミクロ組織を有する降伏強度が８６１ＭＰａ以上の継目無鋼管から、ＮＡＣＥ　ＴＭ０１７７　ｍｅｔｈｏｄ　Ｄにもとづいて、厚さ１０ｍｍ、幅２５ｍｍ、長さ１００ｍｍのＤＣＢ試験片を各３本以上ずつ採取し、ＤＣＢ試験に供した。ＤＣＢ試験の試験浴は、０．２気圧（０．０２ＭＰａ）の硫化水素ガスを飽和させた２４℃の０．５質量％ＣＨ３ＣＯＯＨ＋ＣＨ３ＣＯＯＮａ混合水溶液とした。この試験浴に所定条件で楔を導入したＤＣＢ試験片を３３６時間浸漬した後、浸漬中にＤＣＢ試験片に発生した亀裂の長さａと、楔開放応力Ｐを測定し、下記式（２）によってＫＩＳＳＣ（ＭＰａ√ｍ）を算出した。 In order to solve the above-mentioned problems, the present inventors first made a seamless steel pipe having various chemical compositions and microstructures of steel with a yield strength of 861 MPa or more based on NACE TM0177 method D, with a thickness of 10 mm, Three or more DCB test pieces each having a width of 25 mm and a length of 100 mm were sampled and subjected to a DCB test. The test bath for the DCB test was a mixed aqueous solution of 0.5 mass% CH 3 COOH + CH 3 COONa at 24 ° C. saturated with 0.2 atm (0.02 MPa) hydrogen sulfide gas. After immersing the DCB test piece into which the wedge was introduced into the test bath under predetermined conditions for 336 hours, the length a of the crack generated in the DCB test piece during the immersion and the wedge opening stress P were measured, and the following formula (2) Was used to calculate K ISSC (MPa√m).
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　ここで、図１は、ＤＣＢ試験片の模式図である。図１に示すように、ｈはＤＣＢ試験片の各アーム高さ（ｈｅｉｇｈｔ　ｏｆ　ｅａｃｈ　ａｒｍ）、ＢはＤＣＢ試験片の厚さ、ＢｎはＤＣＢ試験片のウェブ厚さ（ｗｅｂ　ｔｈｉｃｋｎｅｓｓ）である。これらは、ＮＡＣＥ　ＴＭ０１７７　ｍｅｔｈｏｄ　Ｄに規定された数値を用いた。なお、ＫＩＳＳＣ値の目標は、油井管の想定最大切欠欠陥と負荷加重条件から２６．４ＭＰａ√ｍ以上（２４ｋｓｉ√ｉｎｃｈ以上）とした。得られたＫＩＳＳＣ値を、試験片を供した継目無鋼管の平均硬さ（ロックウェルＣスケール硬さ）で整理したグラフを図２に示す。ＤＣＢ試験で得られたＫＩＳＳＣ値は、継目無鋼管の硬さの増加に伴い低下する傾向にあるが、同じ硬さでも数値が大きくばらつくことがわかった。 Here, FIG. 1 is a schematic diagram of a DCB test piece. As shown in FIG. 1, h is the height of each arm of the DCB test piece, B is the thickness of the DCB test piece, and Bn is the web thickness of the DCB test piece. For these, the values defined in NACE TM0177 method D were used. The target of the K ISSC value was set to 26.4 MPa√m or more (24 ksi√inch or more) based on the assumed maximum notch defect of the oil well pipe and the load weighting condition. FIG. 2 shows a graph in which the obtained K ISSC values are arranged by the average hardness (Rockwell C scale hardness) of the seamless steel pipe provided with the test piece. The K ISSC value obtained in the DCB test tended to decrease as the hardness of the seamless steel pipe increased, but it was found that the numerical values varied greatly even at the same hardness.
　さらに、鋼の化学組成に着目すると、同じ硬さでもＭｏ含有量が１．１％以上の鋼種は、ＫＩＳＳＣ値が高めの値を示していることがわかった。しかしながら、Ｍｏ含有量が１．１％以上のものであっても、まだばらつきの最小値は目標とする２６．４ＭＰａ√ｍ以上を満足しないものがあった。 Furthermore, when paying attention to the chemical composition of the steel, it was found that a steel type having a Mo content of 1.1% or more shows a higher KISSC value even at the same hardness. However, even when the Mo content is 1.1% or more, there are still cases where the minimum value of variation does not satisfy the target of 26.4 MPa√m or more.
　このばらつきの原因を鋭意調査した結果、そのばらつき具合が、鋼管の降伏強度を測定した際に得られた応力－歪曲線によって異なることをつきとめた。図３に応力－歪曲線の例を示す。図３に示す２つの鋼管の応力－歪曲線（実線Ａと破線Ｂ）は、降伏応力に相当する０．５～０．７％歪の応力値は変わらないが、片方（破線Ｂ）は連続降伏をしており、もう片方（実線Ａ）は上降伏点が現出している。そして、連続降伏型の応力－歪曲線（破線Ｂ）を呈した鋼の方がＫＩＳＳＣ値のばらつきが大きいことを見出した。本発明者らは、さらに鋭意研究を行い、ＫＩＳＳＣ値のばらつきの大小を、この応力－歪曲線の０．４％歪時の応力（σ０．４）に対する０．７％歪時の応力（σ０．７）の比の値（σ０．７／σ０．４）によって整理を行い、図４に示すように、継目無鋼管のσ０．７／σ０．４を１．０２以下とすることで、１．０２超えの場合にくらべてＫＩＳＳＣ値のばらつきを約半分にできしうることを見出した。 As a result of earnest investigation of the cause of this variation, it was found that the variation varies depending on the stress-strain curve obtained when the yield strength of the steel pipe was measured. FIG. 3 shows an example of a stress-strain curve. The stress-strain curves (solid line A and broken line B) of the two steel pipes shown in FIG. 3 do not change the stress value of 0.5 to 0.7% strain corresponding to the yield stress, but one (broken line B) is continuous. Yield is occurring, and the other (solid line A) has an upper yield point. It was also found that the steel exhibiting a continuous yield type stress-strain curve (broken line B) has a larger variation in KISSC values. The inventors of the present invention conducted further research and found that the variation in the K ISSC value was determined by comparing the stress at the time of 0.7% strain with respect to the stress at the time of 0.4% strain (σ 0.4 ) of the stress-strain curve. (sigma 0.7) performs organized by the value (σ 0.7 / σ 0.4) of the ratio of, as shown in FIG. 4, the σ 0.7 / σ 0.4 of seamless steel pipe 1.02 It has been found that the variation in K ISSC value can be reduced to about half by setting the following as compared with the case of exceeding 1.02.
　ここで、ＫＩＳＳＣ値のばらつきを約半分にするということは、硬さ－ＫＩＳＳＣ値相関においてＫＩＳＳＣ値のばらつきの下限となる鋼の硬さが高硬度側まで広がることを意味する。具体的には、図４において、鋼管のσ０．７／σ０．４が１．０２を超える場合（図中、白丸参照）は、ロックウェルＣスケール硬さが３０．２という低い値であっても、ＫＩＳＳＣ値の目標とした２６．４ＭＰａ√ｍを下回る値が発生するのに対し、鋼管のσ０．７／σ０．４が１．０２以下の場合（図中、黒丸参照）は、ロックウェルＣスケール硬さが３１．２という高い値であっても、２６．４ＭＰａ√ｍ以上を満足しうる。すなわち、高強度化しても安定して高いＫＩＳＳＣ値を得ることができる。 Here, the fact that is about half the variation in K ISSC value means that the hardness of the steel as a lower limit of the variation in hardness -K ISSC value K ISSC values in the correlation extends to high hardness side. Specifically, in FIG. 4, when σ 0.7 / σ 0.4 of the steel pipe exceeds 1.02 (see the white circle in the figure), the Rockwell C scale hardness is as low as 30.2. Even when the value is lower than the target value of K ISSC value of 26.4 MPa√m, σ 0.7 / σ 0.4 of the steel pipe is 1.02 or less (see the black circle in the figure) ) Can satisfy 26.4 MPa√m or more even if the Rockwell C scale hardness is as high as 31.2. That is, a high K ISSC value can be stably obtained even when the strength is increased.
　以上より、硫化水素を含むサワー環境下で使用する継目無鋼管を高強度化しつつ、安定して高いＫＩＳＳＣ値を得ることができるという知見が得られた。なお、継目無鋼管の応力－歪曲線における０．４％歪時の応力（σ０．４）に対する０．７％歪時の応力（σ０．７）の比の値が低いことによって安定して高いＫＩＳＳＣ値を得ることができる理由として、以下の理由が考えられる。ＤＣＢ試験のような初期切欠が存在する状態で応力が付与された際、その切欠先端で塑性変形が起こる可能性があり、塑性変形が起こった場合は硫化物応力腐食割れ感受性が増大する。一方で、図２に示すような、σ０．７／σ０．４が高い、すなわち０．４～０．７％歪領域ではまだ連続降伏をしない引張特性を有する鋼の場合は、切欠先端の塑性変形が抑制できるため、硫化物応力腐食割れ感受性が変化せず、安定して高いＫＩＳＳＣ値が得られる。 From the above, it has been found that a high K ISSC value can be stably obtained while increasing the strength of a seamless steel pipe used in a sour environment containing hydrogen sulfide. The stress-strain curve of the seamless steel pipe is stabilized by the low value of the ratio of 0.7% strain stress (σ 0.7 ) to 0.4% strain stress (σ 0.4 ). The following reasons can be considered as the reason why a high K ISSC value can be obtained. When stress is applied in the presence of an initial notch as in the DCB test, plastic deformation may occur at the notch tip, and when plastic deformation occurs, the sensitivity to sulfide stress corrosion cracking increases. On the other hand, in the case of a steel having a tensile property that is high in σ 0.7 / σ 0.4 as shown in FIG. Therefore, the sulfide stress corrosion cracking susceptibility does not change, and a stable high K ISSC value can be obtained.
　継目無鋼管のσ０．７／σ０．４を安定して１．０２以下にするためには、後述する鋼の化学組成の限定に加え、応力－歪曲線を連続降伏型にしないように鋼のミクロ組織をマルテンサイトとし、かつマルテンサイト以外のミクロ組織の生成を極力抑制し、さらにＭｏの２次析出量を増加させるために、焼入れ時に焼入れ温度を高めてＭｏを極力固溶させる必要がある。なお、上記の２次析出量について、焼入れ前に析出していた析出Ｍｏを１次析出物とし、焼入れ時には固溶していて、焼戻し後に析出したＭｏを２次析出物とする。 In order to stabilize σ 0.7 / σ 0.4 of seamless steel pipes to 1.02 or less, in addition to limiting the chemical composition of the steel described later, the stress-strain curve should not be a continuous yield type. In order to make the steel microstructure martensite and to suppress the formation of microstructures other than martensite as much as possible, and to further increase the amount of secondary precipitation of Mo, it is necessary to raise the quenching temperature during quenching and to dissolve Mo as much as possible. There is. In addition, about said secondary precipitation amount, the precipitation Mo which precipitated before hardening is made into a primary precipitate, and it melts at the time of hardening, and Mo which precipitated after tempering is made into a secondary precipitate.
　一方、σ０．４値を高くするには結晶粒の細粒化が必要で、逆に焼入れ温度が低い方が好ましい。これらを両立するために、継目無鋼管の製造において、まず鋼管成形のための熱間圧延時の圧延終了温度を高くし、圧延終了後、直接焼入（ＤＱとも記す。ＤＱとは、熱間圧延終了段階において、まだ鋼管温度が高い状態からただちに焼入れを行うことを指す。）を施す。すなわち、圧延終了温度を高くして、一旦Ｍｏを極力固溶させ、その後鋼管の焼入および焼戻し熱処理時の焼入れ温度を低くすることで、上述したＭｏの２次析出量の増加とミクロ組織の細粒化が両立し、σ０．７／σ０．４を安定して１．０２以下にすることができる。また、鋼管の熱間圧延後にＤＱを適用できない場合は、焼入および焼戻し熱処理を複数回行い、特に初回の焼入れ温度を１０００℃以上に高温化することでＤＱの効果を代替することができる。 On the other hand, in order to increase the σ 0.4 value, it is necessary to make crystal grains finer. Conversely, it is preferable that the quenching temperature is lower. In order to achieve both of these, in the production of seamless steel pipes, firstly, the rolling end temperature at the time of hot rolling for forming the steel pipe is increased, and after the end of rolling, it is directly quenched (also referred to as DQ. DQ is hot At the end of rolling, it indicates that quenching is performed immediately from a state where the steel pipe temperature is still high. That is, by increasing the rolling end temperature, once dissolving Mo as much as possible, and then lowering the quenching temperature during quenching and tempering heat treatment of the steel pipe, the increase in the amount of secondary precipitation of Mo and the microstructure Fine graining is compatible, and σ 0.7 / σ 0.4 can be stably reduced to 1.02 or less. Moreover, when DQ cannot be applied after hot rolling of a steel pipe, the effect of DQ can be substituted by performing quenching and tempering heat treatment a plurality of times, and in particular raising the initial quenching temperature to 1000 ° C. or higher.
　本発明は、これらの知見に基づいて完成されたものであり、下記の要旨からなる。
［１］質量％で、
Ｃ：０．２５～０．３１％、
Ｓｉ：０．０１～０．３５％、
Ｍｎ：０．４５～０．７０％、
Ｐ：０．０１０％以下、
Ｓ：０．００１％以下、
Ｏ：０．００１５％以下、
Ａｌ：０．０１５～０．０８０％、
Ｃｕ：０．０２～０．０９％、
Ｃｒ：０．８～１．５％、
Ｍｏ：１．１～１．６％、
Ｖ：０．０１～０．０６％、
Ｎｂ：０．００５～０．０１５％、
Ｂ：０．００１５～０．００３０％、
Ｔｉ：０．００５～０．０２０％、
Ｎ：０．００５％以下、
を含有し、
Ｎ含有量に対するＴｉ含有量の比の値（Ｔｉ／Ｎ）が３.０～４．０であり、
残部Ｆｅおよび不可避的不純物からなる組成を有し、
応力－歪曲線における０．４％歪時の応力に対する０．７％歪時の応力の比の値（σ０．７／σ０．４）が１．０２以下である降伏強度が８６１ＭＰａ以上である油井用低合金高強度継目無鋼管。
［２］前記組成に加えてさらに、質量％で、
Ｗ：０．１～０．２％、
Ｚｒ：０．００５～０．０３％
のうちから選ばれた１種または２種を含有する［１］に記載の油井用低合金高強度継目無鋼管。
［３］前記組成に加えてさらに、質量％で、
Ｃａ：０．０００５～０．００３０％
を含有し、さらに、質量％で、組成比が下記（１）式を満足する長径５μｍ以上のＣａとＡｌとからなる酸化物系の鋼中非金属介在物の個数が１００ｍｍ２当り２０個以下である［１］または［２］に記載の油井用低合金高強度継目無鋼管。
　（ＣａＯ）／（Ａｌ２Ｏ３）≧４．０　　　　　　　（１） The present invention has been completed based on these findings and comprises the following gist.
[1] By mass%
C: 0.25 to 0.31%,
Si: 0.01 to 0.35%,
Mn: 0.45 to 0.70%,
P: 0.010% or less,
S: 0.001% or less,
O: 0.0015% or less,
Al: 0.015 to 0.080%,
Cu: 0.02 to 0.09%,
Cr: 0.8 to 1.5%,
Mo: 1.1 to 1.6%,
V: 0.01 to 0.06%,
Nb: 0.005 to 0.015%,
B: 0.0015 to 0.0030%,
Ti: 0.005 to 0.020%,
N: 0.005% or less,
Containing
The value of the ratio of Ti content to N content (Ti / N) is 3.0 to 4.0,
Having a composition consisting of the balance Fe and inevitable impurities,
In the stress-strain curve, the ratio of the stress at 0.7% strain to the stress at 0.4% strain (σ 0.7 / σ 0.4 ) is 1.02 or less and the yield strength is 861 MPa or more. A low-alloy high-strength seamless steel pipe for oil wells.
[2] In addition to the above composition,
W: 0.1-0.2%
Zr: 0.005 to 0.03%
The low-alloy high-strength seamless steel pipe for oil wells according to [1], containing one or two selected from among the above.
[3] In addition to the above composition,
Ca: 0.0005 to 0.0030%
In addition, the number of non-metallic inclusions in the oxide-based steel composed of Ca and Al having a major axis of 5 μm or more and satisfying the following formula (1) in mass% is 20 or less per 100 mm 2 The low alloy high-strength seamless steel pipe for oil wells according to [1] or [2].
(CaO) / (Al 2 O 3 ) ≧ 4.0 (1)
　なお、ここでいう「高強度」とは、降伏強度が８６１ＭＰａ以上（１２５ｋｓｉ以上）の強度を有することを指す。なお、降伏強度の上限値は、特に限定されないが、９６０ＭＰａであることが好ましい。 Note that “high strength” as used herein means that the yield strength is 861 MPa or more (125 ksi or more). The upper limit of yield strength is not particularly limited, but is preferably 960 MPa.
　また、本発明の油井用低合金高強度継目無鋼管は、耐硫化物応力腐食割れ性（耐ＳＳＣ性）に優れており、耐硫化物応力腐食割れ性に優れるとは、ＮＡＣＥ　ＴＭ０１７７　ｍｅｔｈｏｄＤにもとづくＤＣＢ試験であって、０．２気圧（０．０２ＭＰａ）の硫化水素ガスを飽和させた２４℃の０．５質量％ＣＨ３ＣＯＯＨとＣＨ３ＣＯＯＮａとの混合水溶液を試験浴としたＤＣＢ試験を３回行った場合に３回全てにおいて、上記の式（２）から得られるＫＩＳＳＣが安定して２６．４ＭＰａ√ｍ以上であることを指す。 The low-alloy high-strength seamless steel pipe for oil wells of the present invention is excellent in sulfide stress corrosion cracking resistance (SSC resistance), and is excellent in sulfide stress corrosion cracking resistance based on NACE TM0177 methodD. A DCB test using a mixed aqueous solution of 0.5 mass% CH 3 COOH and CH 3 COONa at 24 ° C. saturated with 0.2 atm (0.02 MPa) hydrogen sulfide gas as a test bath. in all three when performing three times, K ISSC obtained from the above equation (2) refers to is stable 26.4MPa√m or by.
　本発明によれば、降伏強度８６１ＭＰａ以上の高強度を有しつつ、さらに高い硫化水素ガス飽和環境、具体的には硫化水素ガス分圧０．０２ＭＰａ以上のサワー環境下における優れた耐硫化物応力腐食割れ性（耐ＳＳＣ性）、特に、安定して高いＫＩＳＳＣ値を示す低合金高強度継目無鋼管を提供することができる。 According to the present invention, an excellent sulfide stress resistance in a high hydrogen sulfide gas saturation environment, specifically, a sour environment with a hydrogen sulfide gas partial pressure of 0.02 MPa or more while having a high yield strength of 861 MPa or more. It is possible to provide a low-alloy high-strength seamless steel pipe exhibiting corrosion cracking resistance (SSC resistance), in particular, a stable high KISSC value.
ＤＣＢ試験片の模式図である。It is a schematic diagram of a DCB test piece. 鋼管の硬さとＫＩＳＳＣ値の関係を示す図である。It is a figure which shows the relationship between the hardness of a steel pipe, and a KISSC value. ＫＩＳＳＣ値のばらつき方が異なる鋼管の応力－歪曲線を示す図である。K is a diagram showing stress-strain curves of steel pipes with different variations in ISSC value. 鋼管の応力－歪曲線図から得られるσ０．７／σ０．４を１．０２以下とすることでＫＩＳＳＣ値のばらつきが低減することを示す図である。It is a figure which shows that the dispersion | variation in K ISSC value reduces by making (sigma) 0.7 / (sigma) 0.4 obtained from the stress-strain curve figure of a steel pipe into 1.02.
　本発明の鋼管は、質量％で、Ｃ：０．２５～０．３１％、Ｓｉ：０．０１～０．３５％、Ｍｎ：０．４５～０．７０％、Ｐ：０．０１０％以下、Ｓ：０．００１％以下、Ｏ：０．００１５％以下、Ａｌ：０．０１５～０．０８０％、Ｃｕ：０．０２～０．０９％、Ｃｒ：０．８～１．５％、Ｍｏ：１．１～１．６％、Ｖ：０．０１～０．０６％、Ｎｂ：０．００５～０．０１５％、Ｂ：０．００１５～０．００３０％、Ｔｉ：０．００５～０．０２０％、Ｎ：０．００５％以下、を含有し、Ｎ含有量に対するＴｉ含有量の比の値（Ｔｉ／Ｎ）が３．０～４．０であり、残部Ｆｅおよび不可避的不純物からなる組成を有し、応力－歪曲線における０．４％歪時の応力に対する０．７％歪時の応力の比の値（σ０．７／σ０．４）が１．０２以下であり、降伏強度が８６１ＭＰａ以上である油井用低合金高強度継目無鋼管である。 The steel pipe of the present invention is, in mass%, C: 0.25 to 0.31%, Si: 0.01 to 0.35%, Mn: 0.45 to 0.70%, P: 0.010% or less S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.8 to 1.5%, Mo: 1.1 to 1.6%, V: 0.01 to 0.06%, Nb: 0.005 to 0.015%, B: 0.0015 to 0.0030%, Ti: 0.005 to 0.020%, N: 0.005% or less, the ratio of Ti content to N content (Ti / N) is 3.0 to 4.0, the balance Fe and inevitable impurities having a composition consisting of, stress - the ratio of the value of 0.7% strain when the stress to 0.4% strain at the stress at strain curve (σ 0.7 / σ 0.4) is 1.02 or less , And the yield strength is low alloy high strength seamless steel pipe for oil well is at least 861MPa.
　まず、本発明の鋼管の化学組成の限定理由について説明する。以下、特に断わらないかぎり質量％は単に％で記す。 First, the reason for limiting the chemical composition of the steel pipe of the present invention will be described. Hereinafter, unless otherwise specified, mass% is simply expressed as%.
　Ｃ：０．２５～０．３１％
　Ｃは、鋼の強度を増加させる作用を有し所望の高強度を確保するために重要な元素であり、降伏強度が８６１ＭＰａ以上の高強度化を実現するためには、０．２５％以上のＣの含有を必要とする。一方、０．３１％を超えるＣの含有は、σ０．７／σ０．４の著しい上昇を引き起こし、ＫＩＳＳＣ値のばらつきを大きくする。このため、Ｃは０．２５～０．３１％とする。好ましくは、Ｃは０．２７％以上である。好ましくは、Ｃは０．３０％以下である。 C: 0.25 to 0.31%
C is an element that has an effect of increasing the strength of steel and is important for ensuring a desired high strength, and in order to achieve a high yield strength of 861 MPa or more, it is 0.25% or more. C content is required. On the other hand, the content of C exceeding 0.31% causes a significant increase in σ 0.7 / σ 0.4 and increases the variation of the K ISSC value. Therefore, C is set to 0.25 to 0.31%. Preferably, C is 0.27% or more. Preferably, C is 0.30% or less.
　Ｓｉ：０．０１～０．３５％
　Ｓｉは、脱酸剤として作用するとともに、鋼中に固溶して鋼の強度を増加させ、焼戻時の急激な軟化を抑制する作用を有する元素である。このような効果を得るためには、０．０１％以上のＳｉの含有を必要とする。一方、０．３５％を超えるＳｉの含有は、粗大な酸化物系介在物を形成し、ＫＩＳＳＣ値のばらつきを大きくする。このため、Ｓｉは０．０１～０．３５％とする。好ましくは、Ｓｉは０．０１～０．０４％である。 Si: 0.01 to 0.35%
Si is an element that acts as a deoxidizer and has a function of increasing the strength of the steel by dissolving in steel and suppressing rapid softening during tempering. In order to obtain such an effect, it is necessary to contain 0.01% or more of Si. On the other hand, the inclusion of Si exceeding 0.35% forms coarse oxide inclusions and increases the variation of the K ISSC value. For this reason, Si is made 0.01 to 0.35%. Preferably, Si is 0.01 to 0.04%.
　Ｍｎ：０．４５～０．７０％
　Ｍｎは、焼入れ性の向上を介して、鋼の強度を増加させるとともに、Ｓと結合しＭｎＳとしてＳを固定して、Ｓによる粒界脆化を防止する作用を有する元素であり、本発明では０．４５％以上のＭｎの含有を必要とする。一方、０．７０％を超えるＭｎの含有は、σ０．７／σ０．４の著しい上昇を引き起こし、ＫＩＳＳＣ値のばらつきを大きくする。このため、Ｍｎは０．４５～０．７０％とする。好ましくは、Ｍｎは０．５０％以上である。好ましくは、Ｍｎは０．６５％以下である。 Mn: 0.45 to 0.70%
Mn is an element that has the effect of increasing the strength of steel through the improvement of hardenability and binding to S to fix S as MnS, thereby preventing grain boundary embrittlement due to S. In the present invention, It is necessary to contain 0.45% or more of Mn. On the other hand, the content of Mn exceeding 0.70% causes a significant increase in σ 0.7 / σ 0.4 and increases the variation of the K ISSC value. Therefore, Mn is set to 0.45 to 0.70%. Preferably, Mn is 0.50% or more. Preferably, Mn is 0.65% or less.
　Ｐ：０．０１０％以下
　Ｐは、固溶状態では粒界等に偏析し、粒界脆化割れ等を引き起こす傾向を示し、本発明ではできるだけ低減することが望ましいが、０．０１０％までは許容できる。このようなことから、Ｐは０．０１０％以下とする。 P: 0.010% or less P has a tendency to segregate at grain boundaries in the solid solution state and cause grain boundary embrittlement cracks, etc., and is desirably reduced as much as possible in the present invention. acceptable. Therefore, P is set to 0.010% or less.
　Ｓ：０．００１％以下
　Ｓは、鋼中ではほとんどが硫化物系介在物として存在し、延性、靭性や、耐硫化物応力腐食割れ性等の耐食性を低下させる。Ｓの一部は固溶状態で存在する場合があるが、その場合には粒界等に偏析し、粒界脆化割れ等を引き起こす傾向を示す。このため、Ｓは、本発明ではできるだけ低減することが望ましいが、過剰な低減は精錬コストを高騰させる。このようなことから、本発明では、Ｓは、その悪影響が許容できる０．００１％以下とする。 S: 0.001% or less S is mostly present as sulfide inclusions in steel, and lowers corrosion resistance such as ductility, toughness, and resistance to sulfide stress corrosion cracking. A part of S may exist in a solid solution state, but in this case, it segregates at the grain boundaries and tends to cause grain boundary embrittlement cracks. For this reason, it is desirable to reduce S as much as possible in the present invention. However, excessive reduction increases the refining cost. For this reason, in the present invention, S is set to 0.001% or less where the adverse effect is acceptable.
　Ｏ（酸素）：０．００１５％以下
　Ｏ（酸素）は不可避的不純物として、ＡｌやＳｉ等の酸化物として鋼中に存在する。特に、その粗大な酸化物の数が多いと、ＫＩＳＳＣ値のばらつきを大きくする要因となる。このため、Ｏ（酸素）は、その悪影響が許容できる０．００１５％以下とする。好ましくは、Ｏ（酸素）は０．００１０％以下である。 O (oxygen): 0.0015% or less O (oxygen) is present as an inevitable impurity in the steel as an oxide such as Al or Si. In particular, when the number of coarse oxides is large, it becomes a factor that increases the variation of the KISSC value. For this reason, O (oxygen) is made 0.0015% or less to which the adverse effect is allowable. Preferably, O (oxygen) is 0.0010% or less.
　Ａｌ：０．０１５～０．０８０％
　Ａｌは、脱酸剤として作用するとともに、Ｎと結合しＡｌＮを形成して固溶Ｎの低減に寄与する。このような効果を得るために、Ａｌは０．０１５％以上の含有を必要とする。一方、０．０８０％を超えてＡｌを含有すると、酸化物系介在物が増加しＫＩＳＳＣ値のばらつきを大きくする。このため、Ａｌは０．０１５～０．０８０％とする。好ましくは、Ａｌは０．０５％以上である。好ましくは、Ａｌは０．０７％以下である。 Al: 0.015 to 0.080%
Al acts as a deoxidizer and combines with N to form AlN and contribute to the reduction of solid solution N. In order to acquire such an effect, Al needs to contain 0.015% or more. On the other hand, when Al is contained exceeding 0.080%, oxide inclusions increase and the variation in K ISSC value increases. For this reason, Al is made 0.015 to 0.080%. Preferably, Al is 0.05% or more. Preferably, Al is 0.07% or less.
　Ｃｕ：０．０２～０．０９％
　Ｃｕは、耐食性を向上させる作用を有する元素であり、微量添加した場合、緻密な腐食生成物が形成され、ＳＳＣの起点となるピットの生成・成長が抑制されて、耐硫化物応力腐食割れ性が顕著に向上するため、本発明では、０．０２％以上のＣｕの含有を必要とする。一方、０．０９％を超えてＣｕを含有すると、継目無鋼管の製造プロセス時の熱間加工性が低下する。このため、Ｃｕは０．０２～０．０９％とする。好ましくは、Ｃｕは０．０３％以上である。好ましくは、Ｃｕは０．０５％以下である。 Cu: 0.02 to 0.09%
Cu is an element that has the effect of improving corrosion resistance. When added in a trace amount, a dense corrosion product is formed, and the formation and growth of pits starting from SSC is suppressed, and the resistance to sulfide stress corrosion cracking. In the present invention, it is necessary to contain 0.02% or more of Cu. On the other hand, when it contains Cu exceeding 0.09%, the hot workability at the time of the manufacturing process of a seamless steel pipe will fall. For this reason, Cu is made 0.02 to 0.09%. Preferably, Cu is 0.03% or more. Preferably, Cu is 0.05% or less.
　Ｃｒ：０．８～１．５％
　Ｃｒは、焼入れ性の増加を介して、鋼の強度の増加に寄与するとともに、耐食性を向上させる元素である。また、Ｃｒは、焼戻時にＣと結合し、Ｍ３Ｃ系、Ｍ７Ｃ３系、Ｍ２３Ｃ６系等の炭化物を形成し、とくにＭ３Ｃ系炭化物は焼戻軟化抵抗を向上させ、焼戻しによる強度変化を少なくして、降伏強度の向上に寄与する。８６１ＭＰａ以上の降伏強度の達成には、０．８％以上のＣｒの含有を必要とする。一方、１．５％を超えてＣｒを含有しても、効果が飽和するため、経済的に不利となる。このため、Ｃｒは０．８～１．５％とする。好ましくは、Ｃｒは０．９％以上である。好ましくは、Ｃｒは１．１％以下である。 Cr: 0.8 to 1.5%
Cr is an element that contributes to an increase in the strength of steel through an increase in hardenability and improves the corrosion resistance. Also, Cr combines with C during tempering to form carbides such as M 3 C, M 7 C 3 and M 23 C 6 systems, and especially M 3 C carbides improve temper softening resistance. Reduces strength change due to tempering and contributes to improved yield strength. In order to achieve a yield strength of 861 MPa or more, it is necessary to contain 0.8% or more of Cr. On the other hand, even if Cr is contained exceeding 1.5%, the effect is saturated, which is economically disadvantageous. Therefore, Cr is set to 0.8 to 1.5%. Preferably, Cr is 0.9% or more. Preferably, Cr is 1.1% or less.
　Ｍｏ：１．１～１．６％
　Ｍｏは、焼入れ性の増加を介して、鋼の強度の増加に寄与するとともに、耐食性を向上させる元素である。このＭｏについては、本発明者らは特に、Ｍ２Ｃ系の炭化物を形成する点に着目した。そして、焼戻し後に２次析出するＭｏ２Ｃ炭化物は焼戻軟化抵抗を向上させ、焼戻による強度変化を少なくして、降伏強度の向上に寄与し、鋼の応力－歪曲線を連続降伏型から降伏型の形状にさせることを、本発明者らは知見した。特に、本発明では、特定量のＭｏが、上述のように硫化水素ガス分圧０．２気圧（０．０２ＭＰａ）以上のサワー環境で、高い降伏強度とＫＩＳＳＣ値の両立に有効であることが、本発明者らの鋭意研究の成果としてわかった。このような効果を得るためには、１．１％以上のＭｏの含有を必要とする。一方、１．６％を超えてＭｏを含有すると、Ｍｏ２Ｃ炭化物が粗大化し、硫化物応力腐食割れの起点となってむしろＫＩＳＳＣ値が低下する原因となる。このため、Ｍｏは１．１～１．６％とする。好ましくは、Ｍｏは１．２％以上である。好ましくは、Ｍｏは１．５％以下である。 Mo: 1.1-1.6%
Mo is an element that contributes to an increase in the strength of steel through an increase in hardenability and improves the corrosion resistance. Regarding this Mo, the present inventors particularly focused on the point of forming M 2 C-based carbides. And, Mo 2 C carbides that are secondarily precipitated after tempering improve resistance to temper softening, reduce strength change due to tempering, contribute to improvement of yield strength, and change the stress-strain curve of steel from a continuous yield type. The present inventors have found that a yield type shape can be obtained. In particular, in the present invention, a specific amount of Mo is effective for achieving both high yield strength and K ISSC value in a sour environment with a hydrogen sulfide gas partial pressure of 0.2 atm (0.02 MPa) or more as described above. However, it became clear as a result of the present inventors' earnest research. In order to obtain such an effect, it is necessary to contain 1.1% or more of Mo. On the other hand, if the Mo content exceeds 1.6%, the Mo 2 C carbide is coarsened, which becomes the starting point of sulfide stress corrosion cracking and rather causes the K ISSC value to decrease. Therefore, Mo is set to 1.1 to 1.6%. Preferably, Mo is 1.2% or more. Preferably, Mo is 1.5% or less.
　Ｖ：０．０１～０．０６％
　Ｖは、炭化物あるいは窒化物を形成し、鋼の強化に寄与する元素である。このような効果を得るためには、０．０１％以上のＶの含有を必要とする。一方、０．０６％を超えてＶを含有すると、Ｖ系炭化物が粗大化して硫化物応力腐食割れの起点となり、むしろＫＩＳＳＣ値が低下する。このため、Ｖは０．０１～０．０６％とする。好ましくは、Ｖは０．０３％以上である。好ましくは、Ｖは０．０５％以下である。 V: 0.01 to 0.06%
V is an element that forms carbides or nitrides and contributes to the strengthening of steel. In order to obtain such an effect, the V content of 0.01% or more is required. On the other hand, when V is contained exceeding 0.06%, the V-based carbide becomes coarse and becomes the starting point of sulfide stress corrosion cracking, rather, the K ISSC value decreases. Therefore, V is set to 0.01 to 0.06%. Preferably, V is 0.03% or more. Preferably, V is 0.05% or less.
　Ｎｂ：０．００５～０．０１５％
　Ｎｂは、オーステナイト（γ）温度域での再結晶を遅延させ、γ粒の微細化に寄与し、焼入直後の鋼の下部組織（例えばパケット、ブロック、ラス）の微細化に極めて有効に作用する元素である。このような効果を得るためには、０．００５％以上のＮｂの含有を必要とする。一方、０．０１５％を超えてＮｂを含有しても効果が飽和する。このため、Ｎｂは０．００５～０．０１５％とする。ここで、パケットとは、平行に並んだ同じ晶癖面を持つラスの集団から成る領域と定義され、ブロックは、平行でかつ同じ方位のラスの集団から成る。好ましくは、Ｎｂは０．００９％以上である。 Nb: 0.005 to 0.015%
Nb delays recrystallization in the austenite (γ) temperature range, contributes to the refinement of γ grains, and acts extremely effectively on the refinement of the substructure (eg, packets, blocks, lath) of steel immediately after quenching. Element. In order to obtain such an effect, it is necessary to contain 0.005% or more of Nb. On the other hand, the effect is saturated even if it contains Nb exceeding 0.015%. For this reason, Nb is made 0.005 to 0.015%. Here, a packet is defined as a region composed of a group of laths having the same crystal habit plane arranged in parallel, and a block is composed of a group of laths parallel and in the same orientation. Preferably, Nb is 0.009% or more.
　Ｂ：０．００１５～０．００３０％
　Ｂは、微量の含有で焼入れ性向上に寄与する元素であり、本発明では０．００１５％以上のＢの含有を必要とする。一方、０．００３０％を超えてＢを含有しても、効果が飽和するかあるいはＦｅ硼化物（Ｆｅ－Ｂ）の形成により、逆に所望の効果が期待できなくなり、経済的に不利となる。このため、Ｂは０．００１５～０．００３０％とする。好ましくは、Ｂは０．００２０～０．００３０％である。 B: 0.0015 to 0.0030%
B is an element that contributes to improving the hardenability when contained in a very small amount. In the present invention, B needs to contain 0.0015% or more of B. On the other hand, even if the content of B exceeds 0.0030%, the effect is saturated or the formation of Fe boride (Fe-B) makes it impossible to expect the desired effect, which is economically disadvantageous. . For this reason, B is made 0.0015 to 0.0030%. Preferably, B is 0.0020 to 0.0030%.
　Ｔｉ：０．００５～０．０２０％
　Ｔｉは、窒化物を形成し、鋼中の余剰Ｎを低減させて上述のＢの効果を有効にする。また、Ｔｉは、鋼の焼入れ時においてオーステナイト粒のピン止め効果による粗大化の防止に寄与する元素である。このような効果を得るためには、０．００５％以上のＴｉを含有することを必要とする。一方、０．０２０％を超えるＴｉの含有は、鋳造時に粗大なＭＣ型窒化物（ＴｉＮ）の形成が促進され、かえって焼入れ時のオーステナイト粒の粗大化を招く。このため、Ｔｉは０．００５～０．０２０％とする。好ましくは、Ｔｉは０．００８％以上である。好ましくは、Ｔｉは０．０１５％以下である。 Ti: 0.005 to 0.020%
Ti forms a nitride and reduces the surplus N in the steel to make the effect of B described above effective. Ti is an element that contributes to prevention of coarsening due to the pinning effect of austenite grains during steel quenching. In order to obtain such an effect, it is necessary to contain 0.005% or more of Ti. On the other hand, the Ti content exceeding 0.020% promotes the formation of coarse MC-type nitride (TiN) during casting, and causes coarsening of austenite grains during quenching. For this reason, Ti is made 0.005 to 0.020%. Preferably, Ti is 0.008% or more. Preferably, Ti is 0.015% or less.
　Ｎ：０．００５％以下
　Ｎは、鋼中不可避的不純物であり、Ｔｉ、Ｎｂ、Ａｌ等の窒化物形成元素と結合しＭＮ型の析出物を形成する。さらに、これらの窒化物を形成した残りの余剰Ｎは、Ｂと結合してＢＮ析出物も形成する。この際、Ｂ添加による焼入れ性向上効果が失われるため、余剰Ｎはできるだけ低減することが好ましく、Ｎは０．００５％以下とする。 N: 0.005% or less N is an unavoidable impurity in steel and forms MN-type precipitates by combining with nitride-forming elements such as Ti, Nb, and Al. Further, the remaining surplus N that forms these nitrides combines with B to form BN precipitates. At this time, since the effect of improving hardenability due to the addition of B is lost, it is preferable to reduce surplus N as much as possible, and N is set to 0.005% or less.
　Ｎ含有量に対するＴｉ含有量の比の値（Ｔｉ／Ｎ）：３．０～４．０
　Ｔｉ含有によるＴｉＮ窒化物形成でのオーステナイト粒ピン止め効果、および余剰Ｎ抑制によるＢＮ形成防止を通じたＢ含有による焼入れ性向上効果を両立させるために、Ｔｉ／Ｎを規定する。Ｔｉ／Ｎが３．０を下回る場合、余剰Ｎが発生し、ＢＮ形成することで焼入れ時の固溶Ｂが不足する結果、焼入れ終了時のミクロ組織がマルテンサイトとベイナイト、あるいはマルテンサイトとフェライトの複合組織となり、このような複合組織を焼戻した後の応力－歪曲線が連続降伏型となって、σ０．７／σ０．４の値が上昇する。一方、Ｔｉ／Ｎが４．０を超える場合、ＴｉＮの粗大化によってオーステナイト粒ピン止め効果が低減し、必要とする細粒組織が得られない。このため、Ｔｉ／Ｎは３．０～４．０とする。 Value of ratio of Ti content to N content (Ti / N): 3.0 to 4.0
In order to achieve both the austenite grain pinning effect in the formation of TiN nitride due to the Ti content and the effect of improving the hardenability due to the B content by preventing the BN formation by suppressing the excess N, Ti / N is defined. When Ti / N is less than 3.0, surplus N is generated, and as a result of the formation of BN, the solid solution B at the time of quenching is insufficient, so that the microstructure at the end of quenching is martensite and bainite, or martensite and ferrite. The stress-strain curve after tempering such a composite structure becomes a continuous yield type, and the value of σ 0.7 / σ 0.4 increases. On the other hand, when Ti / N exceeds 4.0, the austenite grain pinning effect is reduced by the coarsening of TiN, and the required fine grain structure cannot be obtained. Therefore, Ti / N is set to 3.0 to 4.0.
　上記した成分以外の残部は、Ｆｅおよび不可避的不純物であるが、上記の基本の組成に加えてさらに、必要に応じて、Ｗ：０．１～０．２％、Ｚｒ：０．００５～０．０３％のうちから選ばれた１種または２種を選択して含有してもよい。加えて、Ｃａを０．０００５～０．００３０％含有し、質量％で、組成比が（ＣａＯ）／（Ａｌ２Ｏ３）≧４．０であり、長径が５μｍ以上のＣａとＡｌとからなる酸化物系の鋼中非金属介在物の個数が１００ｍｍ２当り２０個以下であってもよい。 The balance other than the above components is Fe and inevitable impurities. In addition to the above basic composition, W: 0.1-0.2%, Zr: 0.005-0 One or two selected from 0.03% may be selected and contained. In addition, from Ca and Al containing 0.0005 to 0.0030% Ca, mass%, composition ratio (CaO) / (Al 2 O 3 ) ≧ 4.0, and having a major axis of 5 μm or more. The number of non-metallic inclusions in the oxide-based steel may be 20 or less per 100 mm 2 .
　Ｗ：０．１～０．２％
　Ｗは、Ｍｏと同様に、炭化物を形成し析出硬化により強度の増加に寄与するとともに、固溶して、旧オーステナイト粒界に偏析して耐硫化物応力腐食割れ性の向上に寄与する。このような効果を得るためには、０．１％以上のＷを含有することが望ましいが、０.２％を超えるＷの含有は、耐硫化物応力腐食割れ性を低下させる。このため、Ｗを含有する場合、Ｗは０．１～０．２％とする。 W: 0.1-0.2%
W, like Mo, forms carbides and contributes to an increase in strength by precipitation hardening, and also forms a solid solution, segregates at the prior austenite grain boundaries, and contributes to an improvement in resistance to sulfide stress corrosion cracking. In order to acquire such an effect, it is desirable to contain 0.1% or more of W, but inclusion of W exceeding 0.2% lowers the resistance to sulfide stress corrosion cracking. Therefore, when W is contained, the W is made 0.1 to 0.2%.
　Ｚｒ：０．００５～０．０３％
　ＺｒはＴｉと同様に、窒化物を形成しピン止め効果によって、焼入れ時のオーステナイト粒成長抑制に有効である。必要な効果を得るためには、０．００５％以上のＺｒを含有することが望ましい。一方、０．０３％を超えてＺｒを含有しても効果が飽和する。このため、Ｚｒを含有する場合、Ｚｒは０．００５～０．０３％とする。 Zr: 0.005 to 0.03%
Zr is effective in suppressing austenite grain growth during quenching by forming a nitride and pinning the same as Ti. In order to obtain a necessary effect, it is desirable to contain 0.005% or more of Zr. On the other hand, even if it contains Zr exceeding 0.03%, the effect is saturated. Therefore, when Zr is contained, Zr is set to 0.005 to 0.03%.
　Ｃａ：０．０００５～０．００３０％
　Ｃａは、連続鋳造時のノズル詰まり防止に有効で、必要な効果を得るためには０．０００５％以上のＣａを含有することが望ましい。一方、Ｃａは、Ａｌと複合した酸化物系非金属介在物を形成し、特に０．００３０％を超えてＣａを含有した場合、粗大なものが多数存在し、耐硫化物応力腐食割れ性を低下させる。具体的には、Ｃａ酸化物（ＣａＯ）とＡｌ酸化物（Ａｌ２Ｏ３）との組成比が、質量％で（１）式を満たす介在物が特に悪影響を及ぼすことから、長径が５μｍ以上かつ（１）式を満たす介在物の個数を１００ｍｍ２当り２０個以下とすることが望ましい。なお、この介在物の個数は、鋼管管端の周方向任意１箇所より管長手直交断面の走査型電子顕微鏡（ＳＥＭ）用試料を採取し、該試料について、少なくとも管外面、肉厚中央、管内面の３か所について介在物のＳＥＭ観察、およびＳＥＭに付随する特性Ｘ線分析装置での化学組成の分析結果によって算出することができる。このため、Ｃａを含有する場合、Ｃａは０．０００５～０．００３０％とする。また、この場合、質量％で、組成比が下記（１）式を満足する長径５μｍ以上のＣａとＡｌとからなる酸化物系の鋼中非金属介在物の個数が１００ｍｍ２当り２０個以下であるようにする。好ましくは、Ｃａは０．００１０％以上である。好ましくは、Ｃａは０．００１６％以下である。
（ＣａＯ）／（Ａｌ２Ｏ３）≧４．０　　　　　　　（１）
　上記の介在物の個数は、脱炭精錬終了後に行うＡｌ脱酸処理時のＡｌ投入量の管理、およびＣａ添加前の溶鋼中Ａｌ、Ｏ、Ｃａ分析値に応じた量のＣａを添加することにより制御することができる。 Ca: 0.0005 to 0.0030%
Ca is effective in preventing nozzle clogging during continuous casting, and in order to obtain a necessary effect, it is desirable to contain 0.0005% or more of Ca. On the other hand, Ca forms oxide-based non-metallic inclusions complexed with Al. In particular, when Ca exceeds 0.0030%, a large number of coarse substances exist, and resistance to sulfide stress corrosion cracking is present. Reduce. Specifically, since the composition ratio of Ca oxide (CaO) and Al oxide (Al 2 O 3 ) satisfies the formula (1) in mass%, the major axis has a particularly adverse effect, so that the major axis is 5 μm or more. In addition, it is desirable that the number of inclusions satisfying the expression (1) is 20 or less per 100 mm 2 . The number of inclusions is obtained by taking a sample for a scanning electron microscope (SEM) having a cross section orthogonal to the longitudinal direction of the pipe from an arbitrary circumferential position on the end of the steel pipe. At least the outer surface of the pipe, the center of the wall, It can be calculated from the SEM observation of inclusions at three locations on the surface and the analysis result of the chemical composition with the characteristic X-ray analyzer attached to the SEM. Therefore, when Ca is contained, the Ca content is set to 0.0005 to 0.0030%. In this case, the number of non-metallic inclusions in the oxide-based steel composed of Ca and Al having a major axis of 5 μm or more satisfying the following formula (1) in mass% is 20 or less per 100 mm 2. To be. Preferably, Ca is 0.0010% or more. Preferably, Ca is 0.0016% or less.
(CaO) / (Al 2 O 3 ) ≧ 4.0 (1)
The number of inclusions described above is to control the amount of Al input during Al deoxidation treatment after decarburization refining and to add an amount of Ca according to the analytical values of Al, O, and Ca in the molten steel before Ca addition. Can be controlled.
　本発明では、上記した組成を有する鋼管素材の製造方法はとくに限定する必要はないが、上記した組成を有する溶鋼を、転炉、電気炉または真空溶解炉等の通常公知の溶製方法で溶製し、連続鋳造法または造塊－分塊圧延法等、通常の方法でビレット等の鋼管素材とすることが好ましい。鋼管素材は、熱間成形により継目無鋼管に成形される。熱間成形方法はピアサー穿孔の後、マンドレルミル圧延、プラグミル圧延のいずれかの方法を用いて所定の肉厚に成形後、適切な縮径圧延までを熱間で行われる。σ０．７／σ０．４を安定して１．０２以下とするために、熱間圧延後に直接焼入れ（ＤＱ）を実施することが望ましい。さらに、このＤＱ終了時点のミクロ組織がマルテンサイトとベイナイト、あるいはマルテンサイトとフェライトといった複合組織になることで、その後焼入および焼戻熱処理を行った後の鋼の結晶粒径やＭｏ等の２次析出量が不均質となってσ０．７／σ０．４の値が１．０２を超えることを防ぐ必要がある。そのために、ＤＱ開始をオーステナイト単相域から行えるように、熱間圧延の終了は９５０℃以上であることが好ましい。一方、ＤＱ終了時点の鋼管の温度は２００℃以下であることが好ましい。継目無鋼管成形後、目標とする降伏強度８６１ＭＰａ以上を達成するために、鋼管の、焼入れ（Ｑ）および焼戻し（Ｔ）を実施する。このときの焼入れ温度は結晶粒の細粒化の観点から９３０℃以下とすることが好ましい。一方、焼入れ温度が８６０℃未満の場合は、Ｍｏ等の固溶が不十分でその後の焼戻し終了時の２次析出量が確保できない。このため、焼入れ温度は８６０～９３０℃とすることが好ましい。焼戻し温度は、オーステナイト再変態を避けるため、Ａｃ１温度以下とする必要があるが、６００℃未満だとＭｏ等の２次析出量が確保できない。このため、焼戻し温度は、少なくとも６００℃以上とすることが好ましい。 In the present invention, the manufacturing method of the steel pipe material having the above composition is not particularly limited, but the molten steel having the above composition is melted by a generally known melting method such as a converter, an electric furnace or a vacuum melting furnace. It is preferable to produce a steel pipe material such as billet by a conventional method such as continuous casting or ingot-splitting rolling. The steel pipe material is formed into a seamless steel pipe by hot forming. In the hot forming method, after piercer drilling, after forming to a predetermined thickness using any one of mandrel mill rolling and plug mill rolling, hot rolling is performed until appropriate diameter reduction rolling. In order to stabilize σ 0.7 / σ 0.4 to 1.02 or less, it is desirable to perform direct quenching (DQ) after hot rolling. Furthermore, since the microstructure at the end of DQ becomes a composite structure such as martensite and bainite or martensite and ferrite, the crystal grain size of steel after the quenching and tempering heat treatment, 2 It is necessary to prevent the next precipitation amount from becoming heterogeneous and the value of σ 0.7 / σ 0.4 from exceeding 1.02. Therefore, it is preferable that completion | finish of hot rolling is 950 degreeC or more so that DQ start can be performed from an austenite single phase area | region. On the other hand, the temperature of the steel pipe at the end of DQ is preferably 200 ° C. or lower. After the seamless steel pipe is formed, the steel pipe is quenched (Q) and tempered (T) in order to achieve a target yield strength of 861 MPa or more. The quenching temperature at this time is preferably 930 ° C. or lower from the viewpoint of crystal grain refinement. On the other hand, when the quenching temperature is less than 860 ° C., the solid solution of Mo or the like is insufficient, and the amount of secondary precipitation at the end of the subsequent tempering cannot be ensured. Therefore, the quenching temperature is preferably 860 to 930 ° C. In order to avoid austenite retransformation, the tempering temperature needs to be Ac 1 temperature or less, but if it is less than 600 ° C., the secondary precipitation amount of Mo or the like cannot be secured. For this reason, the tempering temperature is preferably at least 600 ° C. or higher.
　熱間圧延後にＤＱを適用できない場合は、複数回焼入れおよび焼戻しを行い、特に初回の焼入れ温度を９５０℃以上としてＤＱの効果を代替することができる。 When DQ cannot be applied after hot rolling, quenching and tempering are performed multiple times, and the effect of DQ can be replaced by setting the initial quenching temperature to 950 ° C. or more.
　次に、本発明鋼管の機械的性質の限定理由について説明する。 Next, the reason for limiting the mechanical properties of the steel pipe of the present invention will be described.
　応力－歪曲線における０．４％歪時の応力（σ０．４）に対する０．７％歪時の応力（σ０．７）の比の値（σ０．７／σ０．４）が１．０２以下
　前述したように、ＫＩＳＳＣ値のばらつきは鋼の応力－歪曲線の形状によって大きく異なる。この点について、本発明者等が鋭意研究した結果、０．４％歪時の応力（σ０．４）に対する０．７％歪時の応力（σ０．７）の比の値（σ０．７／σ０．４）が１．０２以下の場合に、ＫＩＳＳＣ値のばらつきがほぼ半減することを知見した。このため、本発明では、σ０．７／σ０．４は１．０２以下とする。 The value (σ 0.7 / σ 0.4 ) of the ratio of the stress at the time of 0.7% strain (σ 0.7 ) to the stress at the time of 0.4% strain (σ 0.4 ) in the stress-strain curve is 1.02 or less As described above, the variation of the K ISSC value varies greatly depending on the shape of the stress-strain curve of the steel. As a result of intensive studies by the present inventors on this point, the value (σ 0 ) of the ratio of the stress at the time of 0.7% strain (σ 0.7 ) to the stress at the time of 0.4% strain (σ 0.4 ) .7 / σ 0.4 ) was found to be approximately halved in variation in K ISSC value when 1.02 or less. For this reason, in the present invention, σ 0.7 / σ 0.4 is set to 1.02 or less.
　なお、本発明では、ＪＩＳ　Ｚ２２４１に基づく引張試験により、降伏強度、０．４％歪時の応力（σ０．４）、および０．７％歪時の応力（σ０．７）を測定することができる。 In the present invention, the yield strength, the stress at 0.4% strain (σ 0.4 ), and the stress at 0.7% strain (σ 0.7 ) are measured by a tensile test based on JIS Z2241. be able to.
　また、本発明のミクロ組織は、特に限定されないが、主相をマルテンサイトとし、その他の残部の組織としては、フェライト、残留オーステナイト、パーライト、ベイナイト等の１種、２種以上の組織が面積率で、５％以下であれば、本願発明の目的を達成できる。 Further, the microstructure of the present invention is not particularly limited, but the main phase is martensite, and the other remaining structures are one type or two types or more of ferrite, retained austenite, pearlite, bainite, etc. And if it is 5% or less, the objective of this invention can be achieved.
　以下、実施例に基づいてさらに本発明を詳細に説明する。 Hereinafter, the present invention will be described in more detail based on examples.
　表１に示す組成の鋼を転炉法で溶製後、連続鋳造法でブルーム鋳片とした。このブルーム鋳片を熱間圧延にて丸断面のビレットに成形した。さらに、このビレットを素材として、表２に示すビレット加熱温度に加熱後、熱間でマンネスマン穿孔－プラグミル圧延－縮径圧延を実施し、表２および表３に示す圧延終了温度で圧延を終了して継目無鋼管に成形した。鋼管は直接焼入れ（ＤＱ）、あるいは空冷（０．２～０．５℃／ｓ）で室温度（３５℃以下）まで冷却し、その後、表２および表３に示す鋼管の熱処理条件（Ｑ１温度：１回目の焼入れ温度、Ｔ１温度：１回目の焼戻し温度、Ｑ２温度：２回目の焼入れ温度、Ｔ２温度：２回目の焼戻し温度）で熱処理を実施した。最終焼戻し終了段階で管端の周方向任意１箇所より引張試験片および、ＤＣＢ試験片をそれぞれ採取した。なお、ＤＣＢ試験片は各鋼管より３本以上ずつ採取した。 After melting the steel having the composition shown in Table 1 by the converter method, it was made into a bloom slab by the continuous casting method. The bloom slab was formed into a billet with a round cross section by hot rolling. Furthermore, using this billet as a raw material, after heating to the billet heating temperature shown in Table 2, Mannesmann piercing-plug mill rolling-reducing rolling was performed hot, and rolling was completed at the rolling end temperatures shown in Table 2 and Table 3. And formed into a seamless steel pipe. The steel pipe is cooled to the room temperature (below 35 ° C.) by direct quenching (DQ) or air cooling (0.2 to 0.5 ° C./s), and then the steel pipe heat treatment conditions (Q1 temperature) shown in Table 2 and Table 3 1st quenching temperature, T1 temperature: 1st tempering temperature, Q2 temperature: 2nd quenching temperature, T2 temperature: 2nd tempering temperature). At the end of final tempering, a tensile test piece and a DCB test piece were collected from any one place in the circumferential direction of the pipe end. Three or more DCB test pieces were collected from each steel pipe.
　採取した引張試験片を用いて、ＪＩＳ　Ｚ２２４１の引張試験を行い、降伏強度、０．４％歪時の応力（σ０．４）、および０．７％歪時の応力（σ０．７）を測定した。 Using the collected tensile test pieces, a tensile test of JIS Z2241 was performed, yield strength, stress at 0.4% strain (σ 0.4 ), and stress at 0.7% strain (σ 0.7 ). Was measured.
　また、採取したＤＣＢ試験片を用いて、ＮＡＣＥ　ＴＭ０１７７　ｍｅｔｈｏｄＤにもとづき、ＤＣＢ試験を実施した。ＤＣＢ試験の試験浴は、０．２気圧（０．０２ＭＰａ）の硫化水素ガスを飽和させた２４℃の０．５質量％ＣＨ３ＣＯＯＨ＋ＣＨ３ＣＯＯＮａ混合水溶液とした。この試験浴に所定条件で楔を導入したＤＣＢ試験片を３３６時間浸漬した後、浸漬中にＤＣＢ試験片に発生した亀裂の長さａと、楔開放応力Ｐを測定し、以下の式（２）によってＫＩＳＳＣ（ＭＰａ√ｍ）を算出した。 Moreover, the DCB test was implemented based on NACETM0177 methodD using the extract | collected DCB test piece. The test bath for the DCB test was a mixed aqueous solution of 0.5 mass% CH 3 COOH + CH 3 COONa at 24 ° C. saturated with 0.2 atm (0.02 MPa) hydrogen sulfide gas. After immersing the DCB test piece in which the wedge was introduced into this test bath under predetermined conditions for 336 hours, the length a of the crack generated in the DCB test piece during the immersion and the wedge opening stress P were measured, and the following equation (2 ) To calculate K ISSC (MPa√m).
　降伏強度については、８６１ＭＰａ以上であるものを合格とした。また、ＫＩＳＳＣ値については、３本全てで２６．４ＭＰａ√ｍ以上のものを合格とした。 About yield strength, what was 861 Mpa or more was considered as the pass. As for the K ISSC value, it was passed more than 26.4MPa√m at three all.
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　ここで、ｈはＤＣＢ試験片の各アーム高さ（ｈｅｉｇｈｔ　ｏｆ　ｅａｃｈ　ａｒｍ）、ＢはＤＣＢ試験片の厚さ、ＢｎはＤＣＢ試験片のウェブ厚さ（ｗｅｂ　ｔｈｉｃｋｎｅｓｓ）である。これらは、ＮＡＣＥ　ＴＭ０１７７　ｍｅｔｈｏｄ　Ｄに規定された数値を用いた（図１参照）。 Here, h is the height of each arm of the DCB test piece, B is the thickness of the DCB test piece, and Bn is the web thickness of the DCB test piece. The numerical values defined in NACE TM0177 method D were used (see FIG. 1).
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
  
Figure JPOXMLDOC01-appb-T000003
  
　化学組成とσ０．７／σ０．４が本発明範囲内であった鋼管１～７は、いずれも降伏強度８６１ＭＰａ以上で、ＤＣＢ試験浴が０．２気圧（０．０２ＭＰａ）の硫化水素ガスを飽和させた２４℃の０．５質量％ＣＨ３ＣＯＯＨ＋ＣＨ３ＣＯＯＮａ混合水溶液であれば、各３本のＤＣＢ試験で得られたＫＩＳＳＣ値はいずれも大きくばらつくことなく目標とする２６．４ＭＰａ√ｍ以上を全て満足した。 Steel pipes 1 to 7 whose chemical composition and σ 0.7 / σ 0.4 were within the scope of the present invention were all hydrogen sulfide having a yield strength of 861 MPa or more and a DCB test bath of 0.2 atm (0.02 MPa). In the case of a 0.5 mass% CH 3 COOH + CH 3 COONa mixed aqueous solution saturated with gas at 24 ° C., the K ISSC value obtained in each of the three DCB tests does not vary greatly, and the target is 26.4 MPa. Satisfied all over √m.
　一方、化学組成のＣが本発明範囲の下限を下回った比較例８（鋼Ｎｏ．Ｇ）、Ｍｎが本発明範囲の下限を下回った比較例９（鋼Ｎｏ．Ｈ）、Ｃｒが本発明範囲の下限を下回った比較例１０（鋼Ｎｏ．Ｉ）は、目標とする降伏強度８６１ＭＰａ以上を達成できなかった。 On the other hand, Comparative Example 8 (steel No. G) in which C of the chemical composition was below the lower limit of the scope of the present invention, Comparative Example 9 (steel No. H) in which Mn was below the lower limit of the scope of the present invention, and Cr was within the scope of the present invention. Comparative Example 10 (steel No. I), which was less than the lower limit, could not achieve the target yield strength of 861 MPa or more.
　化学組成のＭｏが本発明範囲の下限を下回った比較例１１（鋼Ｎｏ．Ｊ）、および逆に上限を上回った比較例１２（鋼Ｎｏ．Ｋ）は、いずれも３本のＤＣＢ試験中３本とも目標とする２６．４ＭＰａ√ｍ以上を満足しなかった。 Comparative Example 11 (steel No. J) in which Mo of the chemical composition was below the lower limit of the range of the present invention and Comparative Example 12 (steel No. K) in which the upper limit was exceeded were all in the three DCB tests. Neither book satisfied the target of 26.4 MPa√m or more.
　また、化学組成のＮｂが本発明範囲の下限を下回った比較例１３（鋼Ｎｏ．Ｌ）、Ｂが本発明範囲の下限を下回った比較例１４（鋼Ｎｏ．Ｍ）は、σ０．７／σ０．４が本発明範囲外となった結果、ＫＩＳＳＣ値が大きくばらついて、３本のＤＣＢ試験中２本が目標とする２６．４ＭＰａ√ｍ以上を満足しなかった。 Further, Comparative Example 13 (steel No. L) in which Nb of the chemical composition was below the lower limit of the range of the present invention, and Comparative Example 14 (steel No. M) in which B was lower than the lower limit of the range of the present invention were σ 0.7 As a result of / σ 0.4 being out of the range of the present invention, the K ISSC values varied greatly, and two of the three DCB tests did not satisfy the target of 26.4 MPa√m or more.
　Ｔｉ／Ｎ比が本発明範囲の下限を下回った比較例１５（鋼Ｎｏ．Ｎ）は、σ０．７／σ０．４が本発明範囲外となった結果、ＫＩＳＳＣ値が大きくばらついて、３本のＤＣＢ試験中２本が目標とする２６．４ＭＰａ√ｍ以上を満足しなかった。 In Comparative Example 15 (steel No. N) in which the Ti / N ratio was below the lower limit of the range of the present invention, σ 0.7 / σ 0.4 was outside the range of the present invention, and as a result, the K ISSC value varied greatly. Two of the three DCB tests did not satisfy the target of 26.4 MPa√m or more.
　一方、Ｔｉ／Ｎ比が本発明範囲の上限を超えた比較例１６（鋼Ｎｏ．Ｏ）も、σ０．７/σ０．４が本発明範囲外となった結果、ＫＩＳＳＣ値が大きくばらついて、３本のＤＣＢ試験中１本が目標とする２６．４ＭＰａ√ｍ以上を満足しなかった。 On the other hand, Comparative Example 16 (steel No. O) in which the Ti / N ratio exceeded the upper limit of the range of the present invention also has a large K ISSC value as a result of σ 0.7 / σ 0.4 being out of the range of the present invention. Variations did not satisfy the target of 26.4 MPa√m or more, one of the three DCB tests.
　化学組成は本発明範囲に適合したものの、最終焼戻し温度が低かった比較例１７は、σ０．７／σ０．４が本発明範囲外となった結果、３本のＤＣＢ試験中３本とも目標とする２６．４ＭＰａ√ｍ以上を満足しなかった。また、同様に最終焼戻し前の焼入れ温度が低かった比較例１８は、σ０．７／σ０．４が本発明範囲外となった結果、ＫＩＳＳＣ値が大きくばらついて、３本のＤＣＢ試験中各２本が目標とする２６．４ＭＰａ√ｍ以上を満足しなかった。直接焼入れ（ＤＱ）を行わず、かつ、鋼管の焼入および焼戻し熱処理を１回しか行わなかった比較例１９は、σ０.７／σ０．４が本発明範囲外となった結果、ＫＩＳＳＣ値が大きくばらついて、３本のＤＣＢ試験中１本が目標とする２６．４ＭＰａ√ｍ以上を満足しなかった。 Although the chemical composition conformed to the scope of the present invention, Comparative Example 17, which had a low final tempering temperature, showed that σ 0.7 / σ 0.4 was outside the scope of the present invention. The target of 26.4 MPa√m or more was not satisfied. Similarly, in Comparative Example 18 in which the quenching temperature before the final tempering was low, σ 0.7 / σ 0.4 was out of the range of the present invention. As a result, the K ISSC value varied greatly, and three DCB tests Two of them did not satisfy the target of 26.4 MPa√m or more. In Comparative Example 19 in which direct quenching (DQ) was not performed and the steel pipe was quenched and tempered only once, σ 0.7 / σ 0.4 was out of the range of the present invention. The ISSC values varied widely, and one of the three DCB tests did not satisfy the target of 26.4 MPa√m or more.
　表４に示す組成の鋼を転炉法で溶製後、連続鋳造法でブルーム鋳片とした。このブルーム鋳片を熱間圧延にて丸断面のビレットに成形した。さらに、このビレットを素材として、表５に示すビレット加熱温度に加熱後、熱間でマンネスマン穿孔―プラグミル圧延―縮径圧延を実施し、表５に示す圧延終了温度で圧延を終了して継目無鋼管に成形した。鋼管は直接焼入れ（ＤＱ）、あるいは空冷（０．２～０．５℃／ｓ）で室温度（３５℃以下）まで冷却し、その後、表５に示す鋼管の熱処理条件（Ｑ１温度：１回目の焼入れ温度、Ｔ１温度：１回目の焼戻し温度、Ｑ２温度：２回目の焼入れ温度、Ｔ２温度：２回目の焼戻し温度）で熱処理を実施した。最終焼戻し終了段階で管端の周方向任意１箇所より管長手直交断面のＳＥＭ用試料、引張試験片、およびＤＣＢ試験片をそれぞれ採取した。なお、ＤＣＢ試験片は各鋼管より３本以上ずつ採取した。 After melting the steel having the composition shown in Table 4 by the converter method, it was made into a bloom slab by the continuous casting method. The bloom slab was formed into a billet with a round cross section by hot rolling. Further, using this billet as a raw material, after heating to the billet heating temperature shown in Table 5, hot Mannesmann piercing-plug mill rolling-reducing rolling was performed, and rolling was completed at the rolling completion temperature shown in Table 5 and seamlessly performed. Molded into a steel pipe. The steel pipe is cooled to the room temperature (below 35 ° C.) by direct quenching (DQ) or air cooling (0.2 to 0.5 ° C./s), and then the heat treatment conditions (Q1 temperature: first time) shown in Table 5 , T1 temperature: first tempering temperature, Q2 temperature: second quenching temperature, T2 temperature: second tempering temperature). At the end of final tempering, a sample for SEM, a tensile test piece, and a DCB test piece having a cross section perpendicular to the longitudinal direction of the pipe were sampled from any one location in the circumferential direction of the pipe end. Three or more DCB test pieces were collected from each steel pipe.
　採取したＳＥＭ用試料の管外面、肉厚中央および管内面の３か所について介在物のＳＥＭ観察とＳＥＭに付随する特性Ｘ線分析装置での化学組成の分析を行い、長径が５μｍ以上かつ（１）式を満たすＣａとＡｌからなる酸化物系の鋼中の非金属介在物の個数（個／ｍｍ２）を算出した。
（ＣａＯ）／（Ａｌ２Ｏ３）≧４．０　　　　　　　（１）
　また、採取した引張試験片を用いて、ＪＩＳ　Ｚ２２４１にて引張試験を行い、降伏強度、０．４％歪時の応力（σ０．４）、および０．７％歪時の応力（σ０．７）を測定した。 The SEM observation of the inclusions and the chemical composition analysis with a characteristic X-ray analyzer attached to the SEM sample at three locations on the outer surface of the tube, the center of the wall thickness, and the inner surface of the tube, and the major axis is 5 μm or more ( 1) The number of nonmetallic inclusions (pieces / mm 2 ) in the oxide-based steel composed of Ca and Al satisfying the formula was calculated.
(CaO) / (Al 2 O 3 ) ≧ 4.0 (1)
Further, using the collected tensile test piece, a tensile test was conducted according to JIS Z2241, and yield strength, stress at 0.4% strain (σ 0.4 ), and stress at 0.7% strain (σ 0 .7 ) was measured.
　また、採取したＤＣＢ試験片を用いて、ＮＡＣＥ　ＴＭ０１７７　ｍｅｔｈｏｄＤにもとづき、ＤＣＢ試験を実施した。ＤＣＢ試験の試験浴は、０．２気圧（０．０２ＭＰａ）の硫化水素ガスを飽和させた２４℃の０．５質量％ＣＨ３ＣＯＯＨ＋ＣＨ３ＣＯＯＮａ混合水溶液とした。この試験浴に所定条件で楔を導入したＤＣＢ試験片を３３６時間浸漬した後、浸漬中にＤＣＢ試験片に発生した亀裂の長さａと、楔開放応力Ｐを測定し、式（２）によってＫＩＳＳＣ（ＭＰａ√ｍ）を算出した。 Moreover, the DCB test was implemented based on NACETM0177 methodD using the extract | collected DCB test piece. The test bath for the DCB test was a mixed aqueous solution of 0.5 mass% CH 3 COOH + CH 3 COONa at 24 ° C. saturated with 0.2 atm (0.02 MPa) hydrogen sulfide gas. After immersing the DCB test piece into which the wedge was introduced into this test bath under predetermined conditions for 336 hours, the length a of the crack generated in the DCB test piece during the immersion and the wedge opening stress P were measured. K ISSC (MPa√m) was calculated.
　降伏強度については、８６１ＭＰａ以上であるものを合格とした。また、ＫＩＳＳＣ値については、３本全てで２６．４ＭＰａ√ｍ以上のものを合格とした。 About yield strength, what was 861 Mpa or more was considered as the pass. As for the K ISSC value, it was passed more than 26.4MPa√m at three all.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000005
  
Figure JPOXMLDOC01-appb-T000005
  
　化学組成、介在物個数およびσ０．７／σ０．４が本発明範囲内であった鋼管２－１～２－４は、いずれも降伏強度８６１ＭＰａ以上で、各３本のＤＣＢ試験で得られたＫＩＳＳＣ値はいずれも大きくばらつくことなく目標とする２６．４ＭＰａ√ｍを全て満足した。 The steel pipes 2-1 to 2-4, whose chemical composition, number of inclusions and σ 0.7 / σ 0.4 were within the range of the present invention, all had a yield strength of 861 MPa or more, and were obtained by three DCB tests. All of the obtained K ISSC values satisfied the target of 26.4 MPa√m without greatly varying.
　一方、Ｃａの上限が本発明範囲の上限を上回った比較例２－５（鋼Ｎｏ．Ｔ）は、ＫＩＳＳＣ値が大きくばらついて、３本のＤＣＢ試験中１本が目標とする２６．４ＭＰａ√ｍを満足しなかった。また、比較例２－６（鋼Ｎｏ．Ｕ）は、二次精錬時に添加された他元素の合金鉄に含まれる不純物ＣａによってＣａ添加前の溶鋼中Ｃａ量が高い状態であることを考慮せずにＣａ添加を行ったため、Ｃａは本発明範囲内であったが、長径が５μｍ以上かつ（１）式を満たすＣａとＡｌからなる酸化物系の鋼中の非金属介在物の個数が本発明範囲の上限を上回り、ＫＩＳＳＣ値が大きくばらついて、３本のＤＣＢ試験中１本が目標とする２６．４ＭＰａ√ｍを満足しなかった。 On the other hand, in Comparative Example 2-5 (steel No. T) in which the upper limit of Ca exceeded the upper limit of the range of the present invention, the K ISSC value greatly varied, and one of the three DCB tests was targeted at 26.4 MPa. √m was not satisfied. Further, in Comparative Example 2-6 (steel No. U), considering that the amount of Ca in the molten steel before addition of Ca is high due to impurities Ca contained in the alloy iron of other elements added during secondary refining. Ca was within the scope of the present invention because Ca was added, but the number of non-metallic inclusions in the oxide-based steel composed of Ca and Al with a major axis of 5 μm or more and satisfying formula (1) was The upper limit of the invention range was exceeded, the K ISSC value varied greatly, and one of the three DCB tests did not satisfy the target of 26.4 MPa√m.

Claims (3)

  1. 　質量％で、
    Ｃ：０．２５～０．３１％、
    Ｓｉ：０．０１～０．３５％、
    Ｍｎ：０．４５～０．７０％、
    Ｐ：０．０１０％以下、
    Ｓ：０．００１％以下、
    Ｏ：０．００１５％以下、
    Ａｌ：０．０１５～０．０８０％、
    Ｃｕ：０．０２～０．０９％、
    Ｃｒ：０．８～１．５％、
    Ｍｏ：１．１～１．６％、
    Ｖ：０．０１～０．０６％、
    Ｎｂ：０．００５～０．０１５％、
    Ｂ：０．００１５～０．００３０％、
    Ｔｉ：０．００５～０．０２０％、
    Ｎ：０．００５％以下、
    を含有し、
    Ｎ含有量に対するＴｉ含有量の比の値（Ｔｉ／Ｎ）が３.０～４．０であり、
    残部Ｆｅおよび不可避的不純物からなる組成を有し、
    応力－歪曲線における０．４％歪時の応力に対する０．７％歪時の応力の比の値（σ０．７／σ０．４）が１．０２以下である降伏強度が８６１ＭＰａ以上である油井用低合金高強度継目無鋼管。     % By mass
    C: 0.25 to 0.31%,
    Si: 0.01 to 0.35%,
    Mn: 0.45 to 0.70%,
    P: 0.010% or less,
    S: 0.001% or less,
    O: 0.0015% or less,
    Al: 0.015 to 0.080%,
    Cu: 0.02 to 0.09%,
    Cr: 0.8 to 1.5%,
    Mo: 1.1 to 1.6%,
    V: 0.01 to 0.06%,
    Nb: 0.005 to 0.015%,
    B: 0.0015 to 0.0030%,
    Ti: 0.005 to 0.020%,
    N: 0.005% or less,
    Containing
    The value of the ratio of Ti content to N content (Ti / N) is 3.0 to 4.0,
    Having a composition consisting of the balance Fe and inevitable impurities,
    In the stress-strain curve, the ratio of the stress at 0.7% strain to the stress at 0.4% strain (σ 0.7 / σ 0.4 ) is 1.02 or less and the yield strength is 861 MPa or more. A low-alloy high-strength seamless steel pipe for oil wells.
  2. 　前記組成に加えてさらに、質量％で、
    Ｗ：０．１～０．２％、
    Ｚｒ：０．００５～０．０３％
    のうちから選ばれた１種または２種を含有する請求項１に記載の油井用低合金高強度継目無鋼管。     In addition to the above composition,
    W: 0.1-0.2%
    Zr: 0.005 to 0.03%
    The low-alloy high-strength seamless steel pipe for oil wells according to claim 1, comprising one or two selected from among them.
  3. 　前記組成に加えてさらに、質量％で、
    Ｃａ：０．０００５～０．００３０％
    を含有し、さらに、質量％で、組成比が下記（１）式を満足する長径５μｍ以上のＣａとＡｌとからなる酸化物系の鋼中非金属介在物の個数が１００ｍｍ２当り２０個以下である請求項１または２に記載の油井用低合金高強度継目無鋼管。
    　（ＣａＯ）／（Ａｌ２Ｏ３）≧４．０　　　　　　　（１）
          In addition to the above composition,
    Ca: 0.0005 to 0.0030%
    In addition, the number of non-metallic inclusions in the oxide-based steel composed of Ca and Al having a major axis of 5 μm or more satisfying the following formula (1) by mass% and not more than 20 per 100 mm 2 The low-alloy high-strength seamless steel pipe for oil wells according to claim 1 or 2.
    (CaO) / (Al 2 O 3 ) ≧ 4.0 (1)
PCT/JP2016/004915 2016-02-29 2016-11-18 Low-alloy, high-strength seamless steel pipe for oil well WO2017149571A1 (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US16/078,924 US20190048444A1 (en) 2016-02-29 2016-11-18 Low alloy high strength seamless steel pipe for oil country tubular goods
MX2018010363A MX2018010363A (en) 2016-02-29 2016-11-18 Low-alloy, high-strength seamless steel pipe for oil well.
EP16892416.5A EP3425076B1 (en) 2016-02-29 2016-11-18 Low-alloy, high-strength seamless steel pipe for oil country tubular goods
JP2017513268A JP6152929B1 (en) 2016-02-29 2016-11-18 Low alloy high strength seamless steel pipe for oil wells
NZ74466816A NZ744668A (en) 2016-02-29 2016-11-18 Low alloy high strength seamless steel pipe for oil country tubular goods
BR112018017250-2A BR112018017250B1 (en) 2016-02-29 2016-11-18 LOW ALLOY HIGH STRENGTH SEAMLESS STEEL PIPE FOR OIL PIPELINE PRODUCTS

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2016036575 2016-02-29
JP2016-036575 2016-02-29

Publications (1)

Publication Number Publication Date
WO2017149571A1 true WO2017149571A1 (en) 2017-09-08

Family

ID=59743630

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2016/004915 WO2017149571A1 (en) 2016-02-29 2016-11-18 Low-alloy, high-strength seamless steel pipe for oil well

Country Status (7)

Country Link
US (1) US20190048444A1 (en)
EP (1) EP3425076B1 (en)
AR (1) AR107720A1 (en)
BR (1) BR112018017250B1 (en)
MX (1) MX2018010363A (en)
NZ (1) NZ744668A (en)
WO (1) WO2017149571A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019198459A1 (en) * 2018-04-09 2019-10-17 日本製鉄株式会社 Steel pipe and method for producing steel pipe

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10844453B2 (en) 2014-12-24 2020-11-24 Jfe Steel Corporation High-strength seamless steel pipe for oil country tubular goods and method of producing the same
MX2017008360A (en) 2014-12-24 2017-10-24 Jfe Steel Corp High-strength seamless steel pipe for oil wells, and production method for high-strength seamless steel pipe for oil wells.
BR112018069480B1 (en) * 2016-02-29 2021-10-05 Jfe Steel Corporation THICK WALL-SEAM STEEL PIPE WITH HIGH RESISTANCE OF LOW ALLOY FOR PETROLEUM PIPE PRODUCTS
MX2018010366A (en) 2016-02-29 2018-12-06 Jfe Steel Corp Low-alloy, high-strength seamless steel pipe for oil well.
US11313007B2 (en) 2016-10-17 2022-04-26 Jfe Steel Corporation High-strength seamless steel pipe for oil country tubular goods, and method for producing the same

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000178682A (en) 1998-12-09 2000-06-27 Sumitomo Metal Ind Ltd Steel for oil well excellent in sulfide stress corrosion cracking resistance
JP2001172739A (en) 1999-12-15 2001-06-26 Sumitomo Metal Ind Ltd Steel for oil well use excellent in sulfide stress corrosion cracking resistance and method for producing steel pipe using same
JP2002060893A (en) 2000-08-18 2002-02-28 Sumitomo Metal Ind Ltd Oil-well steel having excellent sulfide stress corrosion cracking resistance, and its manufacturing method
JP2005350754A (en) 2004-06-14 2005-12-22 Sumitomo Metal Ind Ltd Low alloy steel for oil well tube having excellent sulfide stress cracking resistance
WO2008123425A1 (en) * 2007-03-30 2008-10-16 Sumitomo Metal Industries, Ltd. Low alloy steel for the pipe for oil well use and seamless steel pipe
CN101928889A (en) * 2009-06-23 2010-12-29 宝山钢铁股份有限公司 Steel for resisting sulfide corrosion and manufacturing method thereof
CN102409241A (en) * 2010-09-25 2012-04-11 宝山钢铁股份有限公司 Steel for oil casing pipe, oil casing pipe and manufacturing methods thereof
CN102409240A (en) * 2010-09-21 2012-04-11 宝山钢铁股份有限公司 Hydrogen sulfide corrosion-resistant steel for petroleum drill rod and manufacturing method for hydrogen sulfide corrosion-resistant steel

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06220536A (en) * 1993-01-22 1994-08-09 Nkk Corp Production of high strength steel pipe excellent in sulfide stress corrosion cracking resistance
JP4135691B2 (en) * 2004-07-20 2008-08-20 住友金属工業株式会社 Nitride inclusion control steel
JP2013129879A (en) * 2011-12-22 2013-07-04 Jfe Steel Corp High-strength seamless steel tube for oil well with superior sulfide stress cracking resistance, and method for producing the same
CN104039989B (en) * 2012-03-07 2015-11-25 新日铁住金株式会社 The manufacture method of the High Strength Steel of sulfide stress cracking (SSC) patience excellence
JP5958450B2 (en) * 2012-11-27 2016-08-02 Ｊｆｅスチール株式会社 Low-alloy high-strength seamless steel pipe with excellent resistance to sulfide stress corrosion cracking and its manufacturing method
MX2016009009A (en) * 2014-06-09 2017-01-16 Nippon Steel & Sumitomo Metal Corp Low alloy steel pipe for oil well.

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000178682A (en) 1998-12-09 2000-06-27 Sumitomo Metal Ind Ltd Steel for oil well excellent in sulfide stress corrosion cracking resistance
JP2001172739A (en) 1999-12-15 2001-06-26 Sumitomo Metal Ind Ltd Steel for oil well use excellent in sulfide stress corrosion cracking resistance and method for producing steel pipe using same
JP2002060893A (en) 2000-08-18 2002-02-28 Sumitomo Metal Ind Ltd Oil-well steel having excellent sulfide stress corrosion cracking resistance, and its manufacturing method
JP2005350754A (en) 2004-06-14 2005-12-22 Sumitomo Metal Ind Ltd Low alloy steel for oil well tube having excellent sulfide stress cracking resistance
WO2008123425A1 (en) * 2007-03-30 2008-10-16 Sumitomo Metal Industries, Ltd. Low alloy steel for the pipe for oil well use and seamless steel pipe
CN101928889A (en) * 2009-06-23 2010-12-29 宝山钢铁股份有限公司 Steel for resisting sulfide corrosion and manufacturing method thereof
CN102409240A (en) * 2010-09-21 2012-04-11 宝山钢铁股份有限公司 Hydrogen sulfide corrosion-resistant steel for petroleum drill rod and manufacturing method for hydrogen sulfide corrosion-resistant steel
CN102409241A (en) * 2010-09-25 2012-04-11 宝山钢铁股份有限公司 Steel for oil casing pipe, oil casing pipe and manufacturing methods thereof

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP3425076A4

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019198459A1 (en) * 2018-04-09 2019-10-17 日本製鉄株式会社 Steel pipe and method for producing steel pipe
JPWO2019198459A1 (en) * 2018-04-09 2021-01-14 日本製鉄株式会社 Steel pipe and manufacturing method of steel pipe

Also Published As

Publication number Publication date
BR112018017250A2 (en) 2019-05-14
EP3425076B1 (en) 2021-11-10
NZ744668A (en) 2019-11-29
AR107720A1 (en) 2018-05-23
MX2018010363A (en) 2018-12-06
US20190048444A1 (en) 2019-02-14
BR112018017250B1 (en) 2021-10-05
EP3425076A4 (en) 2019-04-24
EP3425076A1 (en) 2019-01-09

Similar Documents

Publication Publication Date Title
JP6064955B2 (en) Manufacturing method of high strength seamless steel pipe for oil wells with excellent resistance to sulfide stress cracking
WO2017149570A1 (en) Low-alloy, high-strength seamless steel pipe for oil well
US9708681B2 (en) High-strength seamless steel pipe for oil well use having excellent resistance to sulfide stress cracking
JP5487689B2 (en) Manufacturing method of martensitic stainless steel seamless pipe for oil well pipe
US11186885B2 (en) High-strength seamless steel pipe for oil country tubular goods, and production method for high-strength seamless steel pipe for oil country tubular goods
JP5958450B2 (en) Low-alloy high-strength seamless steel pipe with excellent resistance to sulfide stress corrosion cracking and its manufacturing method
JP6107437B2 (en) Manufacturing method of low-alloy high-strength seamless steel pipe for oil wells with excellent resistance to sulfide stress corrosion cracking
JP5679114B2 (en) Low yield ratio high strength hot rolled steel sheet with excellent low temperature toughness and method for producing the same
WO2017149571A1 (en) Low-alloy, high-strength seamless steel pipe for oil well
WO2017149572A1 (en) Low-alloy, high-strength thick-walled seamless steel pipe for oil well
JP2016079431A (en) Electroseamed steel pipe for oil well and manufacturing method therefor
JP6131890B2 (en) Manufacturing method and selection method of low-alloy high-strength seamless steel pipe for oil well with excellent resistance to sulfide stress corrosion cracking
JP6468302B2 (en) Material for steel pipe for high strength oil well and method for producing steel pipe for high strength oil well using the material
CA3094517C (en) A steel composition in accordance with api 5l psl-2 specification for x-65 grade having enhanced hydrogen induced cracking (hic) resistance, and method of manufacturing the steel thereof
JP6551632B1 (en) Low alloy high strength seamless steel pipe for oil well
JP6152930B1 (en) Low alloy high strength thick wall seamless steel pipe for oil wells
JP2002309349A (en) Martensitic stainless steel with excellent strength stability
JP6152929B1 (en) Low alloy high strength seamless steel pipe for oil wells
JP6152928B1 (en) Low alloy high strength seamless steel pipe for oil wells
JP6551631B1 (en) Low alloy high strength seamless steel pipe for oil well
US11505842B2 (en) Low-alloy high-strength seamless steel pipe for oil country tubular goods

Legal Events

Date Code Title Description
ENP Entry into the national phase

Ref document number: 2017513268

Country of ref document: JP

Kind code of ref document: A

WWE Wipo information: entry into national phase

Ref document number: MX/A/2018/010363

Country of ref document: MX

NENP Non-entry into the national phase

Ref country code: DE

REG Reference to national code

Ref country code: BR

Ref legal event code: B01A

Ref document number: 112018017250

Country of ref document: BR

WWE Wipo information: entry into national phase

Ref document number: 2016892416

Country of ref document: EP

ENP Entry into the national phase

Ref document number: 2016892416

Country of ref document: EP

Effective date: 20181001

121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 16892416

Country of ref document: EP

Kind code of ref document: A1

ENP Entry into the national phase

Ref document number: 112018017250

Country of ref document: BR

Kind code of ref document: A2

Effective date: 20180822