WO2018139400A1 - 鋼材、及び、鋼材の製造方法 - Google Patents

鋼材、及び、鋼材の製造方法 Download PDF

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WO2018139400A1
WO2018139400A1 PCT/JP2018/001750 JP2018001750W WO2018139400A1 WO 2018139400 A1 WO2018139400 A1 WO 2018139400A1 JP 2018001750 W JP2018001750 W JP 2018001750W WO 2018139400 A1 WO2018139400 A1 WO 2018139400A1
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steel material
steel
content
tempering
ssc resistance
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PCT/JP2018/001750
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English (en)
French (fr)
Japanese (ja)
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晋士 吉田
勇次 荒井
貴志 相馬
裕紀 神谷
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新日鐵住金株式会社
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Priority to EP18745316.2A priority Critical patent/EP3575428A4/de
Priority to MX2019008642A priority patent/MX2019008642A/es
Priority to AU2018213593A priority patent/AU2018213593A1/en
Priority to RU2019126325A priority patent/RU2725389C1/ru
Priority to CA3049859A priority patent/CA3049859A1/en
Priority to US16/476,704 priority patent/US20190376167A1/en
Priority to CN201880007922.1A priority patent/CN110234779A/zh
Priority to BR112019014676A priority patent/BR112019014676A2/pt
Priority to JP2018564551A priority patent/JP6747524B2/ja
Publication of WO2018139400A1 publication Critical patent/WO2018139400A1/ja

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    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • 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
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • 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
    • C21D9/085—Cooling or quenching
    • 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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    • 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
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    • 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
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    • 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
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

Definitions

  • the present invention relates to a steel material and a method for manufacturing the steel material, and more particularly to a steel material suitable for use in a sour environment and a method for manufacturing the steel material.
  • oil wells and gas wells By making deep wells in oil wells and gas wells (hereinafter, oil wells and gas wells are simply referred to as “oil wells”), it is required to increase the strength of steel pipes for oil wells.
  • steel pipes for oil wells of 80 ksi class yield strength is 80 to 95 ksi, that is, 551 to 655 MPa
  • 95 ksi class yield strength is 95 to 110 ksi, that is, 655 to 758 MPa
  • 110 ksi class yield strength is 110 to 125 ksi, ie, 758 to 862 MPa
  • 125 ksi class yield strength is 125 ksi to 140 ksi, ie 862 to 965 MPa
  • 140 ksi class yield strength is 140 ksi to 155 ksi, ie, 965.
  • Steel pipes for oil wells of ⁇ 1069 MPa are beginning to be demanded.
  • SSC resistance resistance to sulfide stress cracking
  • Patent Document 1 JP-A-62-253720
  • Patent Document 2 JP-A-59-232220
  • Patent Document 3 JP-A-8-3115551
  • Patent Document 5 JP-A 2000-256783
  • Patent Document 6 JP-A 2000-297344
  • Patent Document 7 JP2012-519238A
  • Patent Document 9 JP2012-26030A
  • Patent Document 1 proposes a method for improving the SSC resistance of oil well steel by reducing impurities such as Mn and P.
  • Patent Document 2 proposes a method of increasing the SSC resistance of steel by performing quenching twice to refine crystal grains.
  • Patent Document 3 proposes a method of increasing the SSC resistance of 125 ksi-class steel materials by refining the steel structure by induction heat treatment.
  • Patent Document 4 proposes a method of improving the SSC resistance of 110 ksi class to 140 ksi class steel pipes by increasing the hardenability of steel by using a direct quenching method and further increasing the tempering temperature.
  • Patent Document 5 and Patent Document 6 propose a method for improving the SSC resistance of 110 ksi-class to 140 ksi-class low alloy oil country tubular goods by controlling the form of carbides.
  • Patent Document 7 proposes a method of increasing the SSC resistance of a steel material of 125 ksi (862 MPa) class or higher by controlling the dislocation density and the hydrogen diffusion coefficient to desired values.
  • Patent Document 8 discloses a method for improving the SSC resistance of 125 ksi (862 MPa) grade steel by performing multiple quenching on low alloy steel containing 0.3 to 0.5% C. suggest.
  • Patent Document 9 proposes a method of controlling the form and number of carbides by adopting a tempering process of two-stage heat treatment. More specifically, in Patent Document 9, the SSC resistance of 125 ksi (862 MPa) grade steel is improved by suppressing the number density of large M 3 C or M 2 C.
  • An object of the present disclosure is to provide a steel material having a yield strength of 965 to 1069 MPa (140 to 155 ksi, 140 ksi class) and excellent SSC resistance.
  • the steel material according to the present disclosure is, in mass%, C: more than 0.50 to 0.80%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, P: 0.025%
  • the steel material according to the present disclosure further contains 0.010 to 0.060 mass% of
  • the method for manufacturing a steel material according to the present disclosure includes a preparation process, a quenching process, and a tempering process.
  • a preparation step an intermediate steel material having the above-described chemical composition is prepared.
  • the quenching step after the preparation step, the intermediate steel material at 800 to 1000 ° C. is cooled at a cooling rate of 50 ° C./min or more.
  • the tempering step the quenched intermediate steel material is held at 660 ° C. to Ac 1 point for 10 to 90 minutes, and then cooled at an average cooling rate between 600 ° C. and 200 ° C. at 5 to 300 ° C./second.
  • the steel material according to the present disclosure has a yield strength of 965 to 1069 MPa (140 ksi class) and excellent SSC resistance.
  • FIG. 1 is a diagram showing the relationship between the amount of solute C and the fracture toughness value K1SSC .
  • FIG. 2A is a side view and a cross-sectional view of a DCB test piece used in the DCB test of the example.
  • FIG. 2B is a perspective view of a wedge used in the DCB test of the example.
  • the inventors of the present invention have investigated and studied a method for achieving both the yield strength of 965 to 1069 MPa (140 ksi class) and the SSC resistance in steel materials expected to be used in a sour environment, and obtained the following knowledge.
  • the present inventors can obtain excellent SSC resistance while increasing the yield strength to 140 ksi class (965 to 1069 MPa) using dislocation density by adjusting the amount of solute C in the steel material. I found. The reason for this is not clear, but the following reasons are possible.
  • the fixed dislocation formed by the solute C reduces the amount of hydrogen occluded in the steel material than the movable dislocation. Therefore, it is considered that the amount of hydrogen occluded in the steel material is reduced by increasing the density of the stationary dislocation formed by the solute C. As a result, the SSC resistance of the steel material can be improved. With this mechanism, it is considered that excellent SSC resistance can be obtained even with high strength of 140 ksi class.
  • the present inventors thought that the SSC resistance of the steel material can be improved while maintaining the yield strength of 140 ksi class by appropriately adjusting the amount of solute C in the steel material. Therefore, the present inventors have, in mass%, C: more than 0.50 to 0.80%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, P: 0.00.
  • FIG. 1 is a diagram showing the relationship between the amount of dissolved C and the fracture toughness value K1SSC of each test number in the example.
  • FIG. 1 was obtained by the following method. Among the examples to be described later, for steel materials in which conditions other than the solid solution C amount satisfy the range of the present embodiment, the obtained solid solution C amount (mass%) and the fracture toughness value K 1 SSC (MPa ⁇ m) are used.
  • FIG. 1 was created.
  • the yield strength YS (Yield Strength) of the steel shown in FIG. 1 was 965 to 1069 MPa (140 ksi class). The yield strength YS was adjusted by adjusting the tempering temperature. Further, regarding the SSC resistance, when the fracture toughness value K 1 SSC, which is an index of the SSC resistance, is 30.0 MPa ⁇ m or more, it was determined that the SSC resistance was good.
  • the fracture toughness value K 1 SSC is 30.0 MPa ⁇ m or more, and excellent SSC resistance is obtained. Indicated. On the other hand, in the steel material satisfying the above chemical composition, when the solid solution C amount exceeds 0.060 mass%, the fracture toughness value K 1 SSC is less than 30.0 MPa ⁇ m. That is, it was revealed that when the amount of solute C is too high, the SSC resistance deteriorates.
  • the yield strength YS is set to 965 to 1069 MPa (140 ksi class), and the solid solution C amount is set to 0.010 to 0.060% by mass.
  • the toughness value K 1 SSC is 30.0 MPa ⁇ m or more, and excellent SSC resistance can be obtained.
  • the solid solution C amount of the steel material is 0.010 to 0.060 mass%.
  • the microstructure of steel is a structure mainly composed of tempered martensite and tempered bainite.
  • the tempered martensite and the tempered bainite main body mean that the total volume ratio of the tempered martensite and the tempered bainite is 90% or more.
  • the yield strength YS is 965 to 1069 MPa (140 ksi class)
  • the yield ratio YR the yield strength YS with respect to the tensile strength TS (Tensile Strength)
  • the steel material according to the present embodiment completed based on the above knowledge is, in mass%, C: more than 0.50 to 0.80%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.%. 00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.20 to 1.50%, Mo: 0.25 to 1.50 %, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.002 to 0.010%, O: 0.0100% or less, V: 0 to 0.30 %, Nb: 0 to 0.100%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Zr: 0 to 0.0100%, Co: 0 to 0.50%, W: 0 Contains 0.5 to 0.50%, Ni: 0 to 0.50%, and Cu: 0 to 0.50%, with the balance being Fe and impurities. .
  • the steel material according to the present embodiment further
  • the steel material is not particularly limited, and examples thereof include a steel pipe and a steel plate.
  • the chemical composition may contain one or more selected from the group consisting of V: 0.01 to 0.30% and Nb: 0.002 to 0.100%.
  • the chemical composition is one or two selected from the group consisting of Ca: 0.0001 to 0.0100%, Mg: 0.0001 to 0.0100%, and Zr: 0.0001 to 0.0100%. It may contain seeds or more.
  • the chemical composition may contain one or more selected from the group consisting of Co: 0.02 to 0.50% and W: 0.02 to 0.50%.
  • the chemical composition may contain one or more selected from the group consisting of Ni: 0.02 to 0.50% and Cu: 0.01 to 0.50%.
  • the steel material may be an oil well steel pipe.
  • the oil well steel pipe may be a line pipe steel pipe or an oil well pipe.
  • the oil well steel pipe may be a seamless steel pipe or a welded steel pipe.
  • An oil well pipe is, for example, a steel pipe used for casing and tubing applications.
  • the oil well steel pipe according to the present embodiment is preferably a seamless steel pipe. If the oil well steel pipe according to the present embodiment is a seamless steel pipe, it has a yield strength of 965 to 1069 MPa (140 ksi class) and excellent SSC resistance even if the wall thickness is 15 mm or more.
  • the excellent SSC resistance refers to a solution prepared by mixing degassed 5% saline and 4 g / L Na acetate and adjusting the pH to 3.5 with hydrochloric acid, and 10% H 2 S.
  • K 1SSC MPa ⁇ m is 30.0 MPa ⁇ m or more.
  • the said solid solution C amount means the difference from C content of the chemical composition of steel materials of C amount (mass%) in the carbide
  • the amount of C in the carbide in the steel material is the Fe concentration ⁇ Fe> a, Cr concentration ⁇ Cr> a in the carbide (cementite and MC type carbide) obtained as a residue by performing extraction residue analysis on the steel material, Mn concentration ⁇ Mn> a, Mo concentration ⁇ Mo> a, V concentration ⁇ V> a, Nb concentration ⁇ Nb> a, and cementite specified by TEM observation of the replica film obtained by the extraction replica method Using the Fe concentration ⁇ Fe> b, Cr concentration ⁇ Cr> b, Mn concentration ⁇ Mn> b, and Mo concentration ⁇ Mo> b in the cementite obtained by performing point analysis using EDS, the formula (1 ) To formula (5).
  • ⁇ Mo> c ( ⁇ Fe> a + ⁇ Cr> a + ⁇ Mn> a) ⁇ ⁇ Mo> b / ( ⁇ Fe> b + ⁇ Cr> b + ⁇ Mn> b) (1)
  • ⁇ Mo> d ⁇ Mo> a- ⁇ Mo> c (2)
  • ⁇ C> a ( ⁇ Fe> a / 55.85 + ⁇ Cr> a / 52 + ⁇ Mn> a / 53.94 + ⁇ Mo> c / 95.9) / 3 ⁇ 12
  • cementite means the carbide
  • the method for manufacturing a steel material according to the present embodiment includes a preparation process, a quenching process, and a tempering process.
  • a preparation step an intermediate steel material having the above-described chemical composition is prepared.
  • the quenching step the intermediate steel material at 800 to 1000 ° C. is cooled at a cooling rate of 50 ° C./min or more after the preparation step.
  • the tempering step the quenched intermediate steel material is held at 660 ° C. to Ac 1 point for 10 to 90 minutes, and then cooled at an average cooling rate between 600 ° C. and 200 ° C. at 5 to 300 ° C./second.
  • the intermediate steel material corresponds to a raw pipe when the final product is a steel pipe, and corresponds to a plate-shaped steel material when the final product is a steel plate.
  • the preparation process of the manufacturing method may include a material preparation process for preparing a material having the above-described chemical composition and a hot working process for manufacturing an intermediate steel material by hot working the material.
  • Carbon (C) increases the hardenability and increases the strength of the steel material. C further promotes the spheroidization of carbides during tempering during the manufacturing process, and increases the SSC resistance of the steel material. If the carbide is dispersed, the strength of the steel material is further increased. If the C content is too low, these effects cannot be obtained. On the other hand, if the C content is too high, the toughness of the steel material is lowered and fire cracks are likely to occur. Therefore, the C content is more than 0.50 to 0.80%.
  • the minimum with preferable C content is 0.51%.
  • the upper limit with preferable C content is 0.70%, More preferably, it is 0.62%.
  • Si 0.05 to 1.00% Silicon (Si) deoxidizes steel. If the Si content is too low, this effect cannot be obtained. On the other hand, if the Si content is too high, the SSC resistance of the steel material decreases. Therefore, the Si content is 0.05 to 1.00%.
  • the minimum of preferable Si content is 0.15%, More preferably, it is 0.20%.
  • the upper limit of the preferable Si content is 0.85%, more preferably 0.50%.
  • Mn 0.05 to 1.00%
  • Manganese (Mn) deoxidizes steel. Mn further enhances hardenability. If the Mn content is too low, these effects cannot be obtained. On the other hand, if the Mn content is too high, Mn segregates at grain boundaries together with impurities such as P and S. In this case, the SSC resistance of the steel material decreases. Therefore, the Mn content is 0.05 to 1.00%.
  • the minimum of preferable Mn content is 0.25%, More preferably, it is 0.30%.
  • the upper limit of the preferable Mn content is 0.90%, more preferably 0.80%.
  • Phosphorus (P) is an impurity. That is, the P content is more than 0%. P segregates at the grain boundaries and decreases the SSC resistance of the steel material. Therefore, the P content is 0.025% or less.
  • the upper limit with preferable P content is 0.020%, More preferably, it is 0.015%.
  • the P content is preferably as low as possible. However, the extreme reduction of the P content significantly increases the manufacturing cost. Therefore, when industrial production is considered, the minimum with preferable P content is 0.0001%, More preferably, it is 0.0003%, More preferably, it is 0.001%.
  • S 0.0100% or less Sulfur (S) is an impurity. That is, the S content is more than 0%. S segregates at the grain boundaries and decreases the SSC resistance of the steel material. Therefore, the S content is 0.0100% or less.
  • the upper limit with preferable S content is 0.0050%, More preferably, it is 0.0030%.
  • the S content is preferably as low as possible. However, the extreme reduction of the S content greatly increases the manufacturing cost. Therefore, when industrial production is considered, the minimum with preferable S content is 0.0001%, More preferably, it is 0.0002%, More preferably, it is 0.0003%.
  • Al 0.005 to 0.100%
  • Aluminum (Al) deoxidizes steel. If the Al content is too low, this effect cannot be obtained, and the SSC resistance of the steel material decreases. On the other hand, if the Al content is too high, coarse oxide inclusions are generated and the SSC resistance of the steel material is lowered. Therefore, the Al content is 0.005 to 0.100%.
  • the minimum with preferable Al content is 0.015%, More preferably, it is 0.020%.
  • the upper limit with preferable Al content is 0.080%, More preferably, it is 0.060%.
  • Al content means “acid-soluble Al”, that is, the content of “sol. Al”.
  • Chromium (Cr) improves the hardenability of the steel material. Further, Cr increases the temper softening resistance of the steel material and enables high temperature tempering. As a result, the SSC resistance of the steel material is increased. If the Cr content is too low, the above effect cannot be obtained. On the other hand, if the Cr content is too high, the toughness and SSC resistance of the steel material will decrease. Therefore, the Cr content is 0.20 to 1.50%.
  • the minimum with preferable Cr content is 0.25%, More preferably, it is 0.30%.
  • the upper limit with preferable Cr content is 1.30%.
  • Mo 0.25 to 1.50% Molybdenum (Mo) improves the hardenability of the steel material. Mo further generates fine carbides and increases the temper softening resistance of the steel material. As a result, Mo increases the SSC resistance of the steel material by high temperature tempering. If the Mo content is too low, this effect cannot be obtained. On the other hand, if the Mo content is too high, the above effect is saturated. Therefore, the Mo content is 0.25 to 1.50%. The minimum with preferable Mo content is 0.50%, More preferably, it is 0.65%. The upper limit with preferable Mo content is 1.20%, More preferably, it is 1.00%.
  • Titanium (Ti) forms a nitride and refines crystal grains by a pinning effect. Thereby, the intensity
  • the minimum with preferable Ti content is 0.003%, More preferably, it is 0.005%.
  • the upper limit with preferable Ti content is 0.030%, More preferably, it is 0.020%.
  • B 0.0001 to 0.0050% Boron (B) is dissolved in steel to increase the hardenability of the steel material and increase the strength of the steel material. If the B content is too low, this effect cannot be obtained. On the other hand, if the B content is too high, coarse nitrides are generated and the SSC resistance of the steel material is lowered. Therefore, the B content is 0.0001 to 0.0050%.
  • the minimum with preferable B content is 0.0003%, More preferably, it is 0.0007%.
  • the upper limit with preferable B content is 0.0035%, More preferably, it is 0.0025%.
  • N 0.002 to 0.010% Nitrogen (N) is inevitably contained. N combines with Ti to form fine nitrides and refines the crystal grains. On the other hand, if the N content is too high, N forms coarse nitrides and the SSC resistance of the steel material decreases. Therefore, the N content is 0.002 to 0.010%. The upper limit with preferable N content is 0.005%, More preferably, it is 0.004%.
  • Oxygen (O) is an impurity. That is, the O content is over 0%. O forms a coarse oxide and reduces the corrosion resistance of the steel material. Therefore, the O content is 0.0100% or less.
  • the upper limit with preferable O content is 0.0030%, More preferably, it is 0.0020%.
  • the O content is preferably as low as possible. However, the extreme reduction of the O content greatly increases the manufacturing cost. Therefore, when considering industrial production, the preferable lower limit of the O content is 0.0001%, more preferably 0.0002%, and still more preferably 0.0003%.
  • the balance of the chemical composition of the steel material according to the present embodiment is composed of Fe and impurities.
  • the impurities are mixed from ore as a raw material, scrap, or production environment when industrially producing steel materials, and are allowed within a range that does not adversely affect the steel materials according to the present embodiment. Means what will be done.
  • the chemical composition of the steel material described above may further include one or more selected from the group consisting of V and Nb in place of part of Fe. Any of these elements is an arbitrary element and improves the SSC resistance of the steel material.
  • V 0 to 0.30%
  • Vanadium (V) is an optional element and may not be contained. That is, the V content may be 0%.
  • V combines with C or N to form carbide, nitride, carbonitride, etc. (hereinafter referred to as “carbonitride etc.”). These carbonitrides and the like refine the steel substructure by the pinning effect and increase the SSC resistance of the steel material.
  • V further forms fine carbides during tempering. Fine carbide increases the temper softening resistance of the steel material and increases the strength of the steel material. Further, since V becomes a spherical MC type carbide, the formation of acicular M 2 C type carbide is suppressed, and the SSC resistance of the steel material is improved.
  • the V content is 0 to 0.30%.
  • the minimum with preferable V content is more than 0%, More preferably, it is 0.01%, More preferably, it is 0.02%.
  • the upper limit with preferable V content is 0.20%, More preferably, it is 0.15%, More preferably, it is 0.12%.
  • Niobium (Nb) is an optional element and may not be contained. That is, the Nb content may be 0%. When contained, Nb forms carbonitride and the like. These carbonitrides refine the substructure of the steel material by the pinning effect, and improve the SSC resistance of the steel material. Further, since Nb becomes a spherical MC type carbide, the formation of acicular M 2 C type carbide is suppressed, and the SSC resistance of the steel material is improved. If Nb is contained even a little, the above effect can be obtained to some extent. However, if the Nb content is too high, carbonitrides and the like are excessively generated, and the SSC resistance of the steel material is lowered.
  • the Nb content is 0 to 0.100%.
  • the minimum with preferable Nb content is more than 0%, More preferably, it is 0.002%, More preferably, it is 0.003%, More preferably, it is 0.007%.
  • the upper limit with preferable Nb content is 0.025%, More preferably, it is 0.020%.
  • the total content of V and Nb is preferably 0.30% or less, and more preferably 0.20% or less.
  • the chemical composition of the steel material described above may further include one or more selected from the group consisting of Ca, Mg, and Zr instead of part of Fe. Any of these elements is an arbitrary element and improves the SSC resistance of the steel material.
  • Ca 0 to 0.0100% Calcium (Ca) is an optional element and may not be contained. That is, the Ca content may be 0%. When contained, Ca refines sulfides in the steel material and improves the SSC resistance of the steel material. If Ca is contained even a little, the above effect can be obtained to some extent. However, if the Ca content is too high, the oxide in the steel material becomes coarse, and the SSC resistance of the steel material decreases. Therefore, the Ca content is 0 to 0.0100%.
  • the minimum with preferable Ca content is more than 0%, More preferably, it is 0.0001%, More preferably, it is 0.0003%, More preferably, it is 0.0006%.
  • the upper limit with preferable Ca content is 0.0025%, More preferably, it is 0.0020%.
  • Mg 0 to 0.0100%
  • Magnesium (Mg) is an optional element and may not be contained. That is, the Mg content may be 0%. When contained, Mg renders S in the steel material harmless as a sulfide and improves the SSC resistance of the steel material. If Mg is contained even a little, the above effect can be obtained to some extent. However, if the Mg content is too high, the oxide in the steel material becomes coarse, and the SSC resistance of the steel material decreases. Therefore, the Mg content is 0 to 0.0100%.
  • the lower limit of the Mg content is preferably more than 0%, more preferably 0.0001%, still more preferably 0.0003%, still more preferably 0.0006%, and still more preferably 0.0010%. It is.
  • the upper limit with preferable Mg content is 0.0025%, More preferably, it is 0.0020%.
  • Zr Zirconium
  • Zr Zirconium
  • the Zr content may be 0%.
  • Zr refines sulfides in the steel material and improves the SSC resistance of the steel material. If Zr is contained even a little, the above effect can be obtained to some extent. However, if the Zr content is too high, the oxide in the steel material becomes coarse. Therefore, the Zr content is 0 to 0.0100%.
  • the minimum with preferable Zr content is more than 0%, More preferably, it is 0.0001%, More preferably, it is 0.0003%, More preferably, it is 0.0006%.
  • the upper limit with preferable Zr content is 0.0025%, More preferably, it is 0.0020%.
  • the total content when containing two or more selected from the group consisting of Ca, Mg and Zr is preferably 0.0100% or less, and 0.0050% or less. Is more preferable.
  • the chemical composition of the steel material described above may further include one or more selected from the group consisting of Co and W instead of part of Fe. All of these elements are optional elements, and form a protective corrosion film in a hydrogen sulfide environment and suppress hydrogen intrusion. Thereby, these elements increase the SSC resistance of the steel material.
  • Co 0 to 0.50%
  • Co is an optional element and may not be contained. That is, the Co content may be 0%.
  • Co forms a protective corrosion film in a hydrogen sulfide environment and suppresses hydrogen intrusion. Thereby, SSC resistance of steel materials is improved. If Co is contained even a little, the above effect can be obtained to some extent. However, if the Co content is too high, the hardenability of the steel material decreases and the strength of the steel material decreases. Therefore, the Co content is 0 to 0.50%.
  • the minimum with preferable Co content is more than 0%, More preferably, it is 0.02%, More preferably, it is 0.05%.
  • the upper limit with preferable Co content is 0.45%, More preferably, it is 0.40%.
  • W 0 to 0.50%
  • Tungsten (W) is an optional element and may not be contained. That is, the W content may be 0%. When contained, W forms a protective corrosion film in a hydrogen sulfide environment and suppresses hydrogen intrusion. Thereby, SSC resistance of steel materials is improved. If W is contained even a little, the above effect can be obtained to some extent. However, if the W content is too high, coarse carbides are generated in the steel material, and the SSC resistance of the steel material decreases. Therefore, the W content is 0 to 0.50%.
  • the minimum with preferable W content is more than 0%, More preferably, it is 0.02%, More preferably, it is 0.05%.
  • the upper limit with preferable W content is 0.45%, More preferably, it is 0.40%.
  • the chemical composition of the steel material described above may further include one or more selected from the group consisting of Ni and Cu instead of a part of Fe. All of these elements are optional elements and enhance the hardenability of the steel.
  • Nickel (Ni) is an optional element and may not be contained. That is, the Ni content may be 0%. When contained, Ni increases the hardenability of the steel material and increases the strength of the steel material. If Ni is contained even a little, the above effect can be obtained to some extent. However, if the Ni content is too high, local corrosion is promoted and the SSC resistance of the steel material is lowered. Therefore, the Ni content is 0 to 0.50%.
  • the minimum with preferable Ni content is more than 0%, More preferably, it is 0.02%, More preferably, it is 0.05%.
  • the upper limit with preferable Ni content is 0.35%, More preferably, it is 0.25%.
  • Cu 0 to 0.50% Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When contained, Cu increases the hardenability of the steel material and increases the strength of the steel material. If Cu is contained even a little, the above effect can be obtained to some extent. However, if the Cu content is too high, the hardenability of the steel material becomes too high, and the SSC resistance of the steel material decreases. Therefore, the Cu content is 0 to 0.50%.
  • the minimum with preferable Cu content is more than 0%, More preferably, it is 0.01%, More preferably, it is 0.02%, More preferably, it is 0.05%.
  • the upper limit with preferable Cu content is 0.35%, More preferably, it is 0.25%.
  • the steel material according to the present embodiment contains 0.010 to 0.060 mass% of solute C. If the amount of solute C is less than 0.010% by mass, dislocations in the steel material are not sufficiently fixed, and excellent SSC resistance of the steel material cannot be obtained. On the other hand, if the amount of solute C exceeds 0.060% by mass, the SSC resistance of the steel material is lowered. Therefore, the amount of solid solution C is 0.010 to 0.060% by mass.
  • the minimum with the preferable amount of solute C is 0.020 mass%, More preferably, it is 0.030 mass%.
  • the amount of solute C in this range can be obtained, for example, by controlling the tempering holding time and the cooling rate of the tempering process.
  • the reason for this is as follows.
  • the amount of dissolved C is the highest immediately after quenching. Immediately after quenching, C is in solid solution except for a small amount precipitated as a carbide during quenching. Thereafter, in the tempering step, C is partially precipitated as carbides by soaking. As a result, the amount of solute C decreases toward the thermal equilibrium concentration at the tempering temperature. When the holding time for tempering is too short, this effect cannot be obtained and the amount of dissolved C becomes too high. On the other hand, when the holding time of tempering is too long, the amount of solute C approaches the thermal equilibrium concentration and hardly changes. Therefore, in this embodiment, the tempering holding time is 10 to 90 minutes.
  • the cooling after tempering when the cooling rate is slow, the solid solution C re-deposits during the temperature drop.
  • the cooling after tempering is performed by cooling, so that the cooling rate is slow. Therefore, the amount of solute C was almost 0% by mass. Therefore, in the present embodiment, the cooling rate after tempering is increased to obtain a solid solution C amount of 0.010 to 0.060 mass%.
  • the steel material is continuously forcedly cooled from the tempering temperature, and the surface temperature of the steel material is continuously reduced.
  • a continuous cooling treatment for example, there are a method of immersing a steel material in a water tank and cooling, and a method of accelerating cooling of the steel material by shower water cooling, mist cooling or forced air cooling.
  • the cooling rate after tempering is measured at the site that is cooled most slowly in the cross section of the tempered steel material (for example, the central part of the steel material thickness when both surfaces are forcibly cooled).
  • a cooling rate after tempering can be measured by inserting a sheath-type thermocouple in the center of the plate thickness of the steel plate and measuring the temperature.
  • a cooling rate after tempering can be measured by inserting a sheath-type thermocouple in the center of the thickness of the steel pipe and measuring the temperature.
  • the surface temperature of the non-forced cooling side of steel materials can be measured with a non-contact type infrared thermometer.
  • the temperature range between 600 ° C and 200 ° C is a relatively fast temperature range for C diffusion. Therefore, in this embodiment, the average cooling rate between 600 ° C. and 200 ° C. is set to 5 ° C./second or more.
  • the cooling rate after tempering is set to 300 ° C./second or less.
  • the amount of dissolved C can be 0.010 to 0.060% by mass.
  • the amount of solute C in the steel material may be adjusted to 0.010 to 0.060 mass% by other methods.
  • Solid solution C amount means the difference from C content of the chemical composition of steel materials of C amount (mass%) in the carbide
  • the amount of C in the carbide in the steel material is the Fe concentration ⁇ Fe> a, Cr concentration ⁇ Cr> a in the carbide (cementite and MC type carbide) obtained as a residue by performing extraction residue analysis on the steel material, Mn concentration ⁇ Mn> a, Mo concentration ⁇ Mo> a, V concentration ⁇ V> a, Nb concentration ⁇ Nb> a, and cementite specified by TEM observation of the replica film obtained by the extraction replica method Using the Fe concentration ⁇ Fe> b, Cr concentration ⁇ Cr> b, Mn concentration ⁇ Mn> b, and Mo concentration ⁇ Mo> b in the cementite obtained by performing point analysis using EDS, the formula (1 ) To formula (5).
  • ⁇ Mo> c ( ⁇ Fe> a + ⁇ Cr> a + ⁇ Mn> a) ⁇ ⁇ Mo> b / ( ⁇ Fe> b + ⁇ Cr> b + ⁇ Mn> b) (1)
  • ⁇ Mo> d ⁇ Mo> a- ⁇ Mo> c (2)
  • ⁇ C> a ( ⁇ Fe> a / 55.85 + ⁇ Cr> a / 52 + ⁇ Mn> a / 53.94 + ⁇ Mo> c / 95.9) / 3 ⁇ 12
  • cementite means the carbide
  • the amount of precipitated C is calculated by the following procedure 1 to procedure 4. Specifically, extraction residue analysis is performed in Procedure 1. By the extraction replica method using a transmission electron microscope (hereinafter referred to as “TEM”) and the energy dispersive X-ray spectroscopy (hereinafter referred to as “EDS”) in Step 2. Conduct element concentration analysis in cementite (hereinafter referred to as “EDS analysis”). In step 3, the Mo content is adjusted. In step 4, the amount of precipitated C is calculated.
  • TEM transmission electron microscope
  • EDS analysis energy dispersive X-ray spectroscopy
  • a cylindrical test piece having a diameter of 6 mm and a length of 50 mm is collected from the center of the thickness of the steel pipe so that the thickness center is the center of the cross section.
  • the collected specimen surface is polished by about 50 ⁇ m by preliminary electrolytic polishing to obtain a new surface.
  • the electropolished test piece is electrolyzed with an electrolytic solution 10% acetylacetone + 1% tetraammonium + methanol. Residues are captured by passing the electrolytic solution after electrolysis through a 0.2 ⁇ m filter.
  • the obtained residue is acid-decomposed, and the concentrations of Fe, Cr, Mn, Mo, V, and Nb are quantified in units of mass% by ICP (inductively coupled plasma) emission analysis. These concentrations are defined as ⁇ Fe> a, ⁇ Cr> a, ⁇ Mn> a, ⁇ Mo> a, ⁇ V> a, and ⁇ Nb> a, respectively.
  • Procedure 2 Determination of Fe, Cr, Mn, and Mo contents in cementite by extraction replica method and EDS
  • procedure 2 the contents of Fe, Cr, Mn, and Mo in cementite are determined.
  • the specific procedure is as follows. When the steel material is a plate material, a micro test piece is cut out from the central portion of the plate thickness, and when the steel material is a steel pipe, the micro test piece is cut out and finished by mirror polishing. The test piece is immersed in a 3% nital etchant for 10 minutes to corrode the surface. The surface is covered with a carbon vapor deposition film.
  • a test piece whose surface is covered with a vapor deposition film is immersed in a 5% nital corrosive solution, held for 20 minutes, and the vapor deposition film is peeled off.
  • the peeled deposited film is washed with ethanol, then scooped with a sheet mesh and dried.
  • This deposited film (replica film) is observed with a TEM, and 20 cementites are subjected to point analysis by EDS.
  • the Fe, Cr, Mn, and Mo concentrations when the total of alloy elements excluding carbon in cementite is 100% are quantified in units of mass%.
  • the concentration of 20 cementites is quantified, and the arithmetic average value of each element is defined as ⁇ Fe> b, ⁇ Cr> b, ⁇ Mn> b, ⁇ Mo> b.
  • the amount of Mo precipitated as cementite ( ⁇ Mo> c) is calculated by the equation (1).
  • ⁇ Mo> c ( ⁇ Fe> a + ⁇ Cr> a + ⁇ Mn> a) ⁇ ⁇ Mo> b / ( ⁇ Fe> b + ⁇ Cr> b + ⁇ Mn> b) (1)
  • the amount of Mo precipitated as MC type carbide ( ⁇ Mo> d) is calculated in units of mass% according to the formula (2).
  • ⁇ Mo> d ⁇ Mo> a- ⁇ Mo> c (2)
  • the amount of precipitated C is calculated as the sum of the amount of C precipitated as cementite ( ⁇ C> a) and the amount of C precipitated as MC type carbide ( ⁇ C> b).
  • ⁇ C> a and ⁇ C> b are calculated in units of mass% according to formula (3) and formula (4), respectively.
  • Formula (3) is a formula derived from the structure of cementite being M 3 C type (M includes Fe, Cr, Mn, and Mo).
  • ⁇ C> a ( ⁇ Fe> a / 55.85 + ⁇ Cr> a / 52 + ⁇ Mn> a / 53.94 + ⁇ Mo> c / 95.9) / 3 ⁇ 12 (3)
  • ⁇ C> b ( ⁇ V> a / 50.94 + ⁇ Mo> d / 95.9 + ⁇ Nb> a / 92.9) ⁇ 12 (4)
  • the amount of precipitated C is ⁇ C> a + ⁇ C> b.
  • the amount of solid solution C (hereinafter also referred to as ⁇ C> c) is calculated as a difference between the C content ( ⁇ C>) of the steel material and the amount of precipitated C in units of mass% using Equation (5).
  • ⁇ C> c ⁇ C> ⁇ ( ⁇ C> a + ⁇ C> b) (5)
  • the microstructure of the steel material according to the present embodiment is mainly composed of tempered martensite and tempered bainite. More specifically, the microstructure is composed of tempered martensite and / or tempered bainite having a volume ratio of 90% or more. That is, in the microstructure, the total volume ratio of tempered martensite and tempered bainite is 90% or more. The balance of the microstructure is, for example, retained austenite. If the microstructure of the steel material having the above chemical composition contains 90% or more of the total volume ratio of tempered martensite and tempered bainite, the yield strength is 965 to 1069 MPa (140 ksi class), and the yield ratio is 90%. That's it.
  • the microstructure is a sum of the volume ratios of tempered martensite and tempered bainite being 90% or more.
  • the microstructure consists only of tempered martensite and / or tempered bainite.
  • the steel material is a plate material
  • the steel material is a steel pipe
  • the etched observation surface is observed with a scanning electron microscope (SEM: Scanning Electron Microscope) for 10 fields of view with a secondary electron image.
  • the visual field area is 400 ⁇ m 2 (5000 ⁇ magnification).
  • tempered martensite and tempered bainite are identified from the contrast.
  • the total area fraction of the specified tempered martensite and tempered bainite is determined.
  • the arithmetic average value of the total area fractions of tempered martensite and tempered bainite obtained from all the visual fields is defined as the volume ratio of tempered martensite and tempered bainite.
  • the shape of the steel material by this embodiment is not specifically limited.
  • the steel material is, for example, a steel pipe or a steel plate.
  • the steel material is preferably a seamless steel pipe.
  • the preferred thickness is 9 to 60 mm.
  • the steel material according to the present embodiment is particularly suitable for use as a thick oil well steel pipe. More specifically, even if the steel material according to the present embodiment is a steel pipe for oil well with a thickness of 15 mm or more, and further 20 mm or more, excellent strength and SSC resistance are exhibited.
  • the yield strength YS of the steel material according to this embodiment is 965 to 1069 MPa (140 ksi class), and the yield ratio YR is 90% or more.
  • the yield strength YS as used in this specification means the stress at the time of 0.65% elongation obtained by the tensile test. In short, the strength of the steel material according to the present embodiment is 140 ksi class.
  • the steel material according to the present embodiment has excellent SSC resistance by satisfying the above-described chemical composition, solute C amount, and microstructure even with such high strength.
  • the SSC resistance of the steel material according to the present embodiment can be evaluated by a DCB test based on NACE TM0177-2005 Method D.
  • the solution is mixed with degassed 5% saline and 4 g / L Na acetate and adjusted to pH 3.5 with hydrochloric acid.
  • the gas sealed in the autoclave is a mixed gas of 10% H 2 S gas and 90% CO 2 gas with a total pressure of 1 atm.
  • the DCB test piece into which the wedges are driven is sealed in a container, and kept at 24 ° C. for 3 weeks while stirring the solution and continuously blowing the mixed gas.
  • the K 1 SSC (MPa ⁇ m) of the steel material according to the present embodiment obtained under the above conditions is 30.0 MPa ⁇ m or more.
  • the method for manufacturing a steel material according to the present embodiment includes a preparation process, a quenching process, and a tempering process.
  • the preparation process may include a material preparation process and a hot working process.
  • This embodiment demonstrates the manufacturing method of the steel pipe for oil wells as an example of the manufacturing method of steel materials.
  • the manufacturing method of an oil well steel pipe includes a step of preparing a raw pipe (preparation step) and a step of quenching and tempering the raw pipe to obtain a steel pipe for oil well (quenching step and tempering step).
  • an intermediate steel material having the above-described chemical composition is prepared. If intermediate steel has the said chemical composition, a manufacturing method will not be specifically limited.
  • the intermediate steel material here is a plate-shaped steel material when the final product is a steel plate, and is a raw tube when the final product is a steel pipe.
  • the preparation step may include a step of preparing a raw material (raw material preparation step) and a step of hot working the raw material to produce an intermediate steel material (hot working step).
  • raw material preparation step a step of preparing a raw material
  • hot working step a step of hot working the raw material to produce an intermediate steel material
  • the material is manufactured using molten steel having the above-described chemical composition.
  • a slab slab, bloom, or billet
  • the billet may be produced by rolling the slab, bloom or ingot into pieces.
  • the material (slab, bloom, or billet) is manufactured by the above process.
  • the prepared material is hot worked to produce an intermediate steel material.
  • the steel material is a steel pipe
  • the intermediate steel material corresponds to a raw pipe.
  • the heating temperature is not particularly limited, but is, for example, 1100 to 1300 ° C.
  • the billet extracted from the heating furnace is hot-worked to produce a raw pipe (seamless steel pipe).
  • the Mannesmann method is performed as hot working to manufacture a raw tube.
  • the round billet is pierced and rolled by a piercing machine.
  • the piercing ratio is not particularly limited, but is, for example, 1.0 to 4.0.
  • the round billet that has been pierced and rolled is further hot-rolled by a mandrel mill, a reducer, a sizing mill, or the like into a blank tube.
  • the cumulative reduction in area in the hot working process is, for example, 20 to 70%.
  • the blank tube may be manufactured from the billet by other hot working methods.
  • the raw pipe may be manufactured by forging such as the Erhard method.
  • An element pipe is manufactured by the above process.
  • the thickness of the raw tube is not particularly limited, but is 9 to 60 mm, for example.
  • the raw tube manufactured by hot working may be air-cooled (As-Rolled). Steel pipes manufactured by hot working may be directly quenched after hot pipe making without cooling to room temperature, or may be quenched after supplementary heating (reheating) after hot pipe making. . However, when quenching directly after quenching or after supplementary heating, it is preferable to stop cooling during quenching or to perform slow cooling for the purpose of suppressing quench cracking.
  • SR processing stress relief annealing after quenching and before the next heat treatment.
  • intermediate steel materials are prepared in the preparation process.
  • the intermediate steel material may be manufactured by the above-described preferable process, or an intermediate steel material manufactured by a third party, or a factory other than the factory where the quenching process and the tempering process described below are performed, and other establishments. You may prepare the intermediate steel materials manufactured by. Hereinafter, the quenching process will be described in detail.
  • quenching In the quenching step, quenching is performed on the prepared intermediate steel material (element tube).
  • quenching means quenching an intermediate steel material of A 3 points or more.
  • a preferable quenching temperature is 800 to 1000 ° C.
  • the quenching temperature corresponds to the surface temperature of the intermediate steel material measured by a thermometer installed on the outlet side of the apparatus that performs the final hot working when directly quenching is performed after the hot working.
  • the quenching temperature further corresponds to the temperature of the furnace that performs the supplemental heating when the supplemental heating is performed after the hot working and then the quenching is performed.
  • the raw tube is continuously cooled from the quenching start temperature, and the surface temperature of the raw tube is continuously reduced.
  • the method for the continuous cooling treatment is not particularly limited. Examples of the continuous cooling treatment method include a method in which the raw tube is immersed and cooled in a water tank, and a method in which the raw tube is accelerated and cooled by shower water cooling or mist cooling.
  • the intermediate steel material is rapidly cooled during quenching.
  • an average cooling rate in the range where the surface temperature of the intermediate steel material (element tube) during quenching is in the range of 800 to 500 ° C. is defined as a quenching cooling rate CR 800-500 .
  • the quenching cooling rate CR 800-500 is 50 ° C./min or more.
  • the lower limit of the preferred quenching cooling rate CR 800-500 is 100 ° C./min, more preferably 250 ° C./min.
  • the upper limit of the quenching cooling rate CR 800-500 is not particularly limited, but is, for example, 60000 ° C./min.
  • the element tube is heated in the austenite region a plurality of times and then quenched.
  • the SSC resistance of the steel material is increased.
  • heating in the austenite region may be repeated a plurality of times, or by performing a normalization treatment and a quenching treatment, the heating in the austenite region may be repeated a plurality of times.
  • the tempering step will be described in detail.
  • Tempeering process A tempering process is implemented after implementing the above-mentioned hardening process.
  • the tempering temperature is appropriately adjusted according to the chemical composition of the steel material and the yield strength YS to be obtained.
  • the tempering temperature is adjusted for the base tube having the chemical composition of the present embodiment, and the yield strength YS of the steel material is adjusted to 965 to 1069 MPa (140 ksi class), and the YR of the steel material is adjusted to 90% or more.
  • a preferable tempering temperature is 660 ° C. to Ac 1 point.
  • the tempering temperature is 660 ° C. or higher, the carbide is sufficiently spheroidized and the SSC resistance is further improved.
  • tempering time is set to 10 to 90 minutes in order to control the solid solution C amount within an appropriate range.
  • a preferred lower limit of the tempering time is 15 minutes.
  • the upper limit with preferable tempering time is 70 minutes, More preferably, it is 60 minutes.
  • variation of a steel pipe tends to generate
  • the tempering time is preferably 15 to 90 minutes.
  • those skilled in the art can sufficiently make the yield strength YS within the range of 965 to less than 1069 MPa by appropriately adjusting the holding time at the tempering temperature. It is.
  • an average cooling rate in the range where the surface temperature of the intermediate steel material (element tube) after tempering is 600 to 200 ° C. is defined as a post-tempering cooling rate CR 600-200 .
  • the post-tempering cooling rate CR 600-200 is 5 ° C./second or more. Thereby, the amount of solid solution C of this embodiment is obtained.
  • 600 ° C. and 200 ° C. is a temperature range where C diffusion is relatively fast.
  • the cooling rate after tempering is too fast, the C that has been dissolved is hardly precipitated and the amount of dissolved C may be excessive. In this case, the SSC resistance of the steel material decreases. In this case, the low temperature toughness of the steel material may further decrease.
  • the cooling rate CR 600-200 after tempering is 5 to 300 ° C./second .
  • a preferable lower limit of the cooling rate CR 600-200 after tempering is 10 ° C./second , more preferably 15 ° C./second .
  • a preferable upper limit of the cooling rate CR 600-200 after tempering is 100 ° C./second , more preferably 50 ° C./second .
  • the cooling method for setting the cooling rate CR 600-200 after tempering to 5 to 300 ° C./second is not particularly limited, and may be a well-known method.
  • the raw tube is continuously forcedly cooled from the tempering temperature, and the surface temperature of the raw tube is continuously reduced.
  • a continuous cooling process there are, for example, a method of immersing the raw tube in a water tank and cooling, and a method of accelerating cooling of the raw tube by shower water cooling, mist cooling or forced air cooling.
  • the post-tempering cooling rate CR 600-200 is measured at a portion that is cooled most slowly in the cross section of the tempered intermediate steel material (for example, the center portion of the intermediate steel material thickness when both surfaces are forcedly cooled).
  • the steel material according to the present embodiment may be a steel plate or other shapes.
  • An example of a manufacturing method of a steel plate or other shapes also includes, for example, a preparation process, a quenching process, and a tempering process, as in the above-described manufacturing method.
  • the above-described manufacturing method is an example and may be manufactured by other manufacturing methods.
  • An ingot was manufactured using the above molten steel.
  • the ingot was hot-rolled to produce a steel plate having a thickness of 20 mm.
  • the steel plate of each steel number after hot rolling was allowed to cool and the steel plate temperature was room temperature (25 ° C.).
  • the steel plates of each test number were reheated to bring the steel plate temperature to the quenching temperature (920 ° C., which becomes an austenite single phase region), and soaked for 20 minutes. After soaking, the steel plate was immersed in a water bath and quenched. At this time, the quenching cooling rate (CR 800-500 ) was 400 ° C./min. Test number 23 was soaked in an oil bath after soaking at the quenching temperature. At this time, the average cooling rate between 800 ° C. and 500 ° C. was 40 ° C./min.
  • a tempering treatment was performed on the steel plates of each test number.
  • the tempering temperature was adjusted so as to be an API standard 140 ksi class (yield strength was 965 to 1069 MPa).
  • After performing the heat treatment at each tempering temperature it was cooled.
  • controlled cooling of mist water cooling was performed from both sides of the steel plate.
  • a sheath type K thermocouple was inserted in advance in the center of the plate thickness of the steel plate, and the temperature was measured for tempering and subsequent cooling.
  • Table 2 shows the tempering temperature (° C.), the tempering time (min), and the cooling rate after tempering (CR 600-200 ) (° C./second ).
  • the A c1 points of the steel materials of test numbers 1 to 25 were all 750 ° C., and the tempering temperature was set lower than the A c1 point.
  • the stress at 0.65% elongation obtained in the tensile test was defined as YS of each test number.
  • the maximum stress during uniform elongation was defined as TS.
  • the ratio of YS and TS was taken as the yield ratio YR (%).
  • DCB test A DCB test based on NACE TM0177-2005 Method D was performed on the steel plates of each test number, and the SSC resistance was evaluated. Specifically, three DCB test pieces shown in FIG. 2A were collected from the thickness center of each steel plate. The DCB specimen was collected so that the longitudinal direction was parallel to the rolling direction. Further, the wedge shown in FIG. 2B was produced from the steel plate. The wedge thickness t was 3.10 mm.
  • a wedge was driven between the arms of the DCB specimen. Thereafter, the DCB test piece into which the wedge was driven was sealed in a container.
  • a solution prepared by mixing degassed 5% saline and 4 g / L Na acetate and adjusting the pH to 3.5 with hydrochloric acid was poured into the container so that a gas portion remained in the container. Thereafter, a mixed gas of 10% H 2 S gas and 90% CO 2 gas was sealed in the autoclave at a total pressure of 1 atm, the liquid phase was stirred, and this mixed gas was saturated with the solution.
  • the solution was stirred and kept at 24 ° C. for 3 weeks while continuously blowing the mixed gas. Thereafter, the DCB test piece was taken out from the container.
  • a pin was inserted into the hole formed at the arm tip of each DCB test piece taken out, the notch was opened with a tensile tester, and the wedge release stress P was measured. Furthermore, the notch of the DCB test piece was released in liquid nitrogen, and the crack propagation length a during immersion was measured. The crack propagation length a was measured visually using a caliper. Based on the obtained wedge release stress P and the crack propagation length a, the fracture toughness value K 1 SSC (MPa ⁇ m) was determined using Equation (6). Fracture toughness values K 1 SSC (MPa ⁇ m) of three DCB specimens were determined for each steel. The arithmetic average of the three fracture toughness values for each steel was defined as the fracture toughness value K 1 SSC (MPa ⁇ m) for that steel.
  • Equation (6) h is the height (mm) of each arm of the DCB specimen, B is the thickness (mm) of the DCB specimen, and Bn is the web thickness (mm) of the DCB specimen. is there.
  • Table 2 shows the obtained fracture toughness value K 1 SSC for each test number.
  • K 1 SSC value was 30.0 MPa ⁇ m or more, it was judged that the SSC resistance was good.
  • interval of the arm at the time of driving a wedge before being immersed in a test tank influences K1SSC value. Therefore, the distance between the arms was measured with a micrometer, and it was confirmed that it was within the API standard range.
  • the tempering time was too short. Therefore, the amount of solute C exceeded 0.060% by mass. As a result, the fracture toughness value K 1 SSC was less than 30.0 MPa ⁇ m, and excellent SSC resistance was not exhibited.
  • the fracture toughness value K 1 SSC was less than 30.0 MPa ⁇ m, and excellent SSC resistance was not exhibited.
  • the Mo content was too low.
  • the fracture toughness value K 1 SSC was less than 30.0 MPa ⁇ m, and excellent SSC resistance was not exhibited.
  • the Mn content was too high.
  • the fracture toughness value K 1 SSC was less than 30.0 MPa ⁇ m, and excellent SSC resistance was not exhibited.
  • the N content was too high.
  • the fracture toughness value K 1 SSC was less than 30.0 MPa ⁇ m, and excellent SSC resistance was not exhibited.
  • the Si content was too high.
  • the fracture toughness value K 1 SSC was less than 30.0 MPa ⁇ m, and excellent SSC resistance was not exhibited.
  • the cooling rate after tempering was too slow. Therefore, the amount of solute C was less than 0.010% by mass. As a result, the fracture toughness value K 1 SSC was less than 30.0 MPa ⁇ m, and excellent SSC resistance was not exhibited.
  • the steel material according to the present invention is widely applicable to steel materials used in sour environments, preferably used as oil well steel materials used in oil well environments, and more preferably, casings, tubing, line pipes and the like. It can be used as a steel pipe for oil wells.

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JP2019112681A (ja) * 2017-12-25 2019-07-11 日本製鉄株式会社 鋼材、油井用鋼管、及び、鋼材の製造方法
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WO2020209275A1 (ja) 2019-04-11 2020-10-15 日本製鉄株式会社 鋼板及びその製造方法

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