WO2018139400A1 - Steel material, and steel material manufacturing method - Google Patents
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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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- 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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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
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- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- 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
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- 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
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- 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
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- 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
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- 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- 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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Abstract
Description
図1は、実施例の各試験番号の固溶C量と破壊靭性値K1SSCとの関係を示す図である。図1は次の方法で得られた。後述する実施例のうち、固溶C量以外の条件が本実施形態の範囲を満たす鋼材について、得られた固溶C量(質量%)及び破壊靭性値K1SSC(MPa√m)を用いて、図1を作成した。 [Relationship between the amount of solute C and SSC resistance]
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.
<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 (3)
<C>b=(<V>a/50.94+<Mo>d/95.9+<Nb>a/92.9)×12 (4)
(固溶C量)=<C>-(<C>a+<C>b) (5)
なお、本明細書において、セメンタイトとは、Fe含有量が50質量%以上の炭化物を意味する。 Moreover, 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 | carbonized_material in steel materials. 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 (3)
<C> b = (<V> a / 50.94 + <Mo> d / 95.9 + <Nb> a / 92.9) × 12 (4)
(Solution C amount) = <C> − (<C> a + <C> b) (5)
In addition, in this specification, cementite means the carbide | carbonized_material whose Fe content is 50 mass% or more.
本実施形態による鋼材の化学組成は、次の元素を含有する。 [Chemical composition]
The chemical composition of the steel material according to the present embodiment contains the following elements.
炭素(C)は、焼入れ性を高め、鋼材の強度を高める。Cはさらに、製造工程中の焼戻し時において、炭化物の球状化を促進し、鋼材の耐SSC性を高める。炭化物が分散されればさらに、鋼材の強度が高まる。C含有量が低すぎれば、これらの効果が得られない。一方、C含有量が高すぎれば、鋼材の靭性が低下し、焼割れが発生しやすくなる。したがって、C含有量は0.50超~0.80%である。C含有量の好ましい下限は0.51%である。C含有量の好ましい上限は0.70%であり、より好ましくは0.62%である。 C: Over 0.50 to 0.80%
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%.
シリコン(Si)は、鋼を脱酸する。Si含有量が低すぎれば、この効果が得られない。一方、Si含有量が高すぎれば、鋼材の耐SSC性が低下する。したがって、Si含有量は、0.05~1.00%である。好ましいSi含有量の下限は、0.15%であり、より好ましくは0.20%である。好ましいSi含有量の上限は、0.85%であり、より好ましくは0.50%である。 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%.
マンガン(Mn)は、鋼を脱酸する。Mnはさらに、焼入れ性を高める。Mn含有量が低すぎれば、これらの効果が得られない。一方、Mn含有量が高すぎれば、Mnは、P及びS等の不純物とともに、粒界に偏析する。この場合、鋼材の耐SSC性が低下する。したがって、Mn含有量は、0.05~1.00%である。好ましいMn含有量の下限は、0.25%であり、より好ましくは0.30%である。好ましいMn含有量の上限は、0.90%であり、より好ましくは0.80%である。 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%.
燐(P)は不純物である。すなわち、P含有量は0%超である。Pは、粒界に偏析して鋼材の耐SSC性を低下する。したがって、P含有量は、0.025%以下である。P含有量の好ましい上限は0.020%であり、より好ましくは0.015%である。P含有量はなるべく低い方が好ましい。ただし、P含有量の極端な低減は、製造コストを大幅に高める。したがって、工業生産を考慮した場合、P含有量の好ましい下限は0.0001%であり、より好ましくは0.0003%であり、さらに好ましくは0.001%である。 P: 0.025% or less 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%.
硫黄(S)は不純物である。すなわち、S含有量は0%超である。Sは、粒界に偏析して鋼材の耐SSC性を低下する。したがって、S含有量は0.0100%以下である。S含有量の好ましい上限は0.0050%であり、より好ましくは0.0030%である。S含有量はなるべく低い方が好ましい。ただし、S含有量の極端な低減は、製造コストを大幅に高める。したがって、工業生産を考慮した場合、S含有量の好ましい下限は0.0001%であり、より好ましくは0.0002%であり、さらに好ましくは0.0003%である。 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%.
アルミニウム(Al)は、鋼を脱酸する。Al含有量が低すぎれば、この効果が得られず、鋼材の耐SSC性が低下する。一方、Al含有量が高すぎれば、粗大な酸化物系介在物が生成して鋼材の耐SSC性が低下する。したがって、Al含有量は0.005~0.100%である。Al含有量の好ましい下限は0.015%であり、より好ましくは0.020%である。Al含有量の好ましい上限は0.080%であり、より好ましくは0.060%である。本明細書にいう「Al」含有量は「酸可溶Al」、つまり、「sol.Al」の含有量を意味する。 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%. As used herein, “Al” content means “acid-soluble Al”, that is, the content of “sol. Al”.
クロム(Cr)は、鋼材の焼入れ性を高める。Crはさらに、鋼材の焼戻し軟化抵抗を高め、高温焼戻しを可能にする。その結果、鋼材の耐SSC性を高める。Cr含有量が低すぎれば、上記効果が得られない。一方、Cr含有量が高すぎれば、鋼材の靭性及び耐SSC性が低下する。したがって、Cr含有量は0.20~1.50%である。Cr含有量の好ましい下限は0.25%であり、より好ましくは0.30%である。Cr含有量の好ましい上限は1.30%である。 Cr: 0.20 to 1.50%
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%.
モリブデン(Mo)は、鋼材の焼入れ性を高める。Moはさらに、微細な炭化物を生成し、鋼材の焼戻し軟化抵抗を高める。その結果、Moは、高温焼戻しにより鋼材の耐SSC性を高める。Mo含有量が低すぎれば、この効果が得られない。一方、Mo含有量が高すぎれば、上記効果が飽和する。したがって、Mo含有量は0.25~1.50%である。Mo含有量の好ましい下限は0.50%であり、より好ましくは0.65%である。Mo含有量の好ましい上限は1.20%であり、より好ましくは1.00%である。 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%.
チタン(Ti)は窒化物を形成し、ピンニング効果により、結晶粒を微細化する。これにより、鋼材の強度が高まる。Ti含有量が低すぎれば、この効果が得られない。一方、Ti含有量が高すぎれば、Ti窒化物が粗大化して鋼材の耐SSC性が低下する。したがって、Ti含有量は0.002~0.050%である。Ti含有量の好ましい下限は0.003%であり、より好ましくは0.005%である。Ti含有量の好ましい上限は0.030%であり、より好ましくは0.020%である。 Ti: 0.002 to 0.050%
Titanium (Ti) forms a nitride and refines crystal grains by a pinning effect. Thereby, the intensity | strength of steel materials increases. If the Ti content is too low, this effect cannot be obtained. On the other hand, if the Ti content is too high, the Ti nitride becomes coarse and the SSC resistance of the steel material decreases. Therefore, the Ti content is 0.002 to 0.050%. 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%.
ボロン(B)は鋼に固溶して鋼材の焼入れ性を高め、鋼材の強度を高める。B含有量が低すぎれば、この効果が得られない。一方、B含有量が高すぎれば、粗大な窒化物が生成して鋼材の耐SSC性が低下する。したがって、B含有量は0.0001~0.0050%である。B含有量の好ましい下限は0.0003%であり、より好ましくは0.0007%である。B含有量の好ましい上限は0.0035%であり、より好ましくは0.0025%である。 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%.
窒素(N)は不可避に含有される。NはTiと結合して微細窒化物を形成し、結晶粒を微細化する。一方、N含有量が高すぎれば、Nは粗大な窒化物を形成して、鋼材の耐SSC性が低下する。したがって、N含有量は、0.002~0.010%である。N含有量の好ましい上限は0.005%であり、より好ましくは0.004%である。 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%.
酸素(O)は不純物である。すなわち、O含有量は0%超である。Oは粗大な酸化物を形成し、鋼材の耐食性を低下する。したがって、O含有量は0.0100%以下である。O含有量の好ましい上限は0.0030%であり、より好ましくは0.0020%である。O含有量はなるべく低い方が好ましい。ただし、O含有量の極端な低減は、製造コストを大幅に高める。したがって、工業生産を考慮した場合、O含有量の好ましい下限は0.0001%であり、より好ましくは0.0002%であり、さらに好ましくは0.0003%である。 O: 0.0100% or less 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%.
上述の鋼材の化学組成はさらに、Feの一部に代えて、V及びNbからなる群から選択される1種以上を含有してもよい。これらの元素はいずれも任意元素であり、鋼材の耐SSC性を高める。 [Arbitrary elements]
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.
バナジウム(V)は任意元素であり、含有されなくてもよい。すなわち、V含有量は0%であってもよい。含有される場合、VはC又はNと結合して炭化物、窒化物又は炭窒化物等(以下、「炭窒化物等」という)を形成する。これらの炭窒化物等は、ピンニング効果により鋼材のサブ組織を微細化し、鋼材の耐SSC性を高める。Vはさらに、焼戻し時に微細な炭化物を形成する。微細な炭化物は鋼材の焼戻し軟化抵抗を高め、鋼材の強度を高める。Vはさらに、球状のMC型炭化物となるため、針状のM2C型炭化物の生成を抑制して、鋼材の耐SSC性を高める。Vが少しでも含有されれば、上記効果がある程度得られる。しかしながら、V含有量が高すぎれば、鋼材の靭性が低下する。したがって、V含有量は0~0.30%である。V含有量の好ましい下限は0%超であり、より好ましくは0.01%であり、さらに好ましくは0.02%である。V含有量の好ましい上限は0.20%であり、より好ましくは0.15%であり、さらに好ましくは0.12%である。 V: 0 to 0.30%
Vanadium (V) is an optional element and may not be contained. That is, the V content may be 0%. When contained, 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. If V is contained even a little, the above effect can be obtained to some extent. However, if the V content is too high, the toughness of the steel material decreases. Therefore, 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%.
ニオブ(Nb)は任意元素であり、含有されなくてもよい。すなわち、Nb含有量は0%であってもよい。含有される場合、Nbは炭窒化物等を形成する。これらの炭窒化物等はピンニング効果により鋼材のサブ組織を微細化し、鋼材の耐SSC性を高める。Nbはさらに、球状のMC型炭化物となるため、針状のM2C型炭化物の生成を抑制して、鋼材の耐SSC性を高める。Nbが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Nb含有量が高すぎれば、炭窒化物等が過剰に生成して、鋼材の耐SSC性が低下する。したがって、Nb含有量は0~0.100%である。Nb含有量の好ましい下限は0%超であり、より好ましくは0.002%であり、さらに好ましくは0.003%であり、さらに好ましくは0.007%である。Nb含有量の好ましい上限は0.025%であり、より好ましくは0.020%である。 Nb: 0 to 0.100%
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. Therefore, 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%.
カルシウム(Ca)は任意元素であり、含有されなくてもよい。すなわち、Ca含有量は0%であってもよい。含有される場合、Caは、鋼材中の硫化物を微細化し、鋼材の耐SSC性を高める。Caが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Ca含有量が高すぎれば、鋼材中の酸化物が粗大化して、鋼材の耐SSC性が低下する。したがって、Ca含有量は0~0.0100%である。Ca含有量の好ましい下限は0%超であり、より好ましくは0.0001%であり、さらに好ましくは0.0003%であり、さらに好ましくは0.0006%である。Ca含有量の好ましい上限は0.0025%であり、より好ましくは0.0020%である。 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%.
マグネシウム(Mg)は任意元素であり、含有されなくてもよい。すなわち、Mg含有量は0%であってもよい。含有される場合、Mgは、鋼材中のSを硫化物として無害化し、鋼材の耐SSC性を高める。Mgが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Mg含有量が高すぎれば、鋼材中の酸化物が粗大化して、鋼材の耐SSC性が低下する。したがって、Mg含有量は0~0.0100%である。Mg含有量の好ましい下限は0%超であり、より好ましくは0.0001%であり、さらに好ましくは0.0003%であり、さらに好ましくは0.0006%であり、さらに好ましくは0.0010%である。Mg含有量の好ましい上限は0.0025%であり、より好ましくは0.0020%である。 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%.
ジルコニウム(Zr)は任意元素であり、含有されなくてもよい。すなわち、Zr含有量は0%であってもよい。含有される場合、Zrは鋼材中の硫化物を微細化し、鋼材の耐SSC性を高める。Zrが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Zr含有量が高すぎれば、鋼材中の酸化物が粗大化する。したがって、Zr含有量は0~0.0100%である。Zr含有量の好ましい下限は0%超であり、より好ましくは0.0001%であり、さらに好ましくは0.0003%であり、さらに好ましくは0.0006%である。Zr含有量の好ましい上限は0.0025%であり、より好ましくは0.0020%である。 Zr: 0 to 0.0100%
Zirconium (Zr) is an optional element and may not be contained. That is, the Zr content may be 0%. When contained, 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%.
コバルト(Co)は任意元素であり、含有されなくてもよい。すなわち、Co含有量は0%であってもよい。含有される場合、Coは硫化水素環境中で保護性の腐食被膜を形成し、水素侵入を抑制する。これにより、鋼材の耐SSC性を高める。Coが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Co含有量が高すぎれば、鋼材の焼入れ性が低下して、鋼材の強度が低下する。したがって、Co含有量は0~0.50%である。Co含有量の好ましい下限は0%超であり、より好ましくは0.02%であり、さらに好ましくは0.05%である。Co含有量の好ましい上限は0.45%であり、より好ましくは0.40%である。 Co: 0 to 0.50%
Cobalt (Co) is an optional element and may not be contained. That is, the Co content may be 0%. When contained, 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%.
タングステン(W)は任意元素であり、含有されなくてもよい。すなわち、W含有量は0%であってもよい。含有される場合、Wは硫化水素環境中で保護性の腐食被膜を形成し、水素侵入を抑制する。これにより、鋼材の耐SSC性を高める。Wが少しでも含有されれば、上記効果がある程度得られる。しかしながら、W含有量が高すぎれば、鋼材中に粗大な炭化物が生成して、鋼材の耐SSC性が低下する。したがって、W含有量は0~0.50%である。W含有量の好ましい下限は0%超であり、より好ましくは0.02%であり、さらに好ましくは0.05%である。W含有量の好ましい上限は0.45%であり、より好ましくは0.40%である。 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%.
ニッケル(Ni)は任意元素であり、含有されなくてもよい。すなわち、Ni含有量は0%であってもよい。含有される場合、Niは鋼材の焼入れ性を高め、鋼材の強度を高める。Niが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Ni含有量が高すぎれば、局部的な腐食を促進させ、鋼材の耐SSC性が低下する。したがって、Ni含有量は0~0.50%である。Ni含有量の好ましい下限は0%超であり、より好ましくは0.02%であり、さらに好ましくは0.05%である。Ni含有量の好ましい上限は0.35%であり、より好ましくは0.25%である。 Ni: 0 to 0.50%
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%.
銅(Cu)は任意元素であり、含有されなくてもよい。すなわち、Cu含有量は0%であってもよい。含有される場合、Cuは鋼材の焼入れ性を高め、鋼材の強度を高める。Cuが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Cu含有量が高すぎれば、鋼材の焼入れ性が高くなりすぎ、鋼材の耐SSC性が低下する。したがって、Cu含有量は0~0.50%である。Cu含有量の好ましい下限は0%超であり、より好ましくは0.01%であり、さらに好ましくは0.02%であり、さらに好ましくは0.05%である。Cu含有量の好ましい上限は0.35%であり、より好ましくは0.25%である。 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%.
本実施形態による鋼材は、固溶Cを0.010~0.060質量%含有する。固溶C量が0.010質量%未満であれば、鋼材中の転位の固定が十分でなく、優れた鋼材の耐SSC性が得られない。一方、固溶C量が0.060質量%を超えれば、かえって鋼材の耐SSC性が低下する。したがって、固溶C量は0.010~0.060質量%である。固溶C量の好ましい下限は0.020質量%であり、より好ましくは0.030質量%である。 [Solution C amount]
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%.
固溶C量は、鋼材中の炭化物中のC量(質量%)の、鋼材の化学組成のC含有量からの差分を意味する。鋼材中の炭化物中のC量は、鋼材に対して抽出残渣分析を実施して残渣として得られた炭化物(セメンタイト及びMC型炭化物)中のFe濃度<Fe>a、Cr濃度<Cr>a、Mn濃度<Mn>a、Mo濃度<Mo>a、V濃度<V>a、Nb濃度<Nb>aと、抽出レプリカ法により得られたレプリカ膜をTEM観察することにより特定されたセメンタイトに対してEDSによる点分析を実施して得られたセメンタイト中のFe濃度<Fe>b、Cr濃度<Cr>b、Mn濃度<Mn>b、Mo濃度<Mo>bとを用いて、式(1)~式(5)により求める。
<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 (3)
<C>b=(<V>a/50.94+<Mo>d/95.9+<Nb>a/92.9)×12 (4)
(固溶C量)=<C>-(<C>a+<C>b) (5)
なお、本明細書において、セメンタイトとは、Fe含有量が50質量%以上の炭化物を意味する。以下、固溶C量の算出方法を詳しく示す。 [Calculation method of solid solution C amount]
Solid solution C amount means the difference from C content of the chemical composition of steel materials of C amount (mass%) in the carbide | carbonized_material in steel materials. 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 (3)
<C> b = (<V> a / 50.94 + <Mo> d / 95.9 + <Nb> a / 92.9) × 12 (4)
(Solution C amount) = <C> − (<C> a + <C> b) (5)
In addition, in this specification, cementite means the carbide | carbonized_material whose Fe content is 50 mass% or more. Hereinafter, the calculation method of the solid solution C amount will be described in detail.
鋼材が板材である場合、板厚中央部から、鋼材が管材である場合、肉厚中央部から、切粉状の分析サンプルを採取する。酸素気流中燃焼-赤外線吸収法により、C含有量(質量%)を分析する。これを鋼材のC含有量(<C>)とする。 [Quantification of C content of steel]
When the steel material is a plate material, a chip-like analysis sample is collected from the plate thickness center portion, and when the steel material is a tube material, the chip-shaped analysis sample is collected from the thickness center portion. The C content (mass%) is analyzed by combustion in an oxygen stream-infrared absorption method. This is the C content (<C>) of the steel material.
析出C量は、次の手順1~手順4により算出する。具体的には、手順1で抽出残渣分析を実施する。手順2で透過電子顕微鏡(Transmission Electron Microscope:以下、「TEM」という)を用いた抽出レプリカ法、及び、エネルギー分散型X線分析法(Energy Dispersive X-ray Spectrometry:以下、「EDS」という)によりセメンタイト中の元素濃度分析(以下「EDS分析」という)を実施する。手順3でMo含有量を調整する。手順4で析出C量を算出する。 [Calculation of C amount precipitated as carbide (precipitation C amount)]
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.
手順1では、鋼材中の炭化物を残渣として捕捉し、残渣中のFe、Cr、Mn、Mo、V、及び、Nb含有量を決定する。ここで、「炭化物」とは、セメンタイト(M3C型炭化物)及びMC型炭化物の総称である。具体的な手順は以下のとおりである。鋼材が板材である場合、板厚中央部から、6mm径で長さ50mmの円柱状試験片を採取する。鋼材が鋼管である場合、鋼管の肉厚中央部から、肉厚中心が横断面の中心になるように、6mm径で長さ50mmの円柱状試験片を採取する。採取した試験片表面を予備の電解研磨にて50μm程度研磨して新生面を得る。電解研磨した試験片を電解液10%アセチルアセトン+1%テトラアンモニウム+メタノールで電解する。電解後の電解液を0.2μmのフィルターを通して残渣を捕捉する。得られた残渣を酸分解し、ICP(誘導結合プラズマ)発光分析にてFe、Cr、Mn、Mo、V、Nb濃度を質量%単位で定量する。この濃度をそれぞれ<Fe>a、<Cr>a、<Mn>a、<Mo>a、<V>a、<Nb>aと定義する。 [Procedure 1. Determination of Fe, Cr, Mn, Mo, V and Nb residue amounts by extraction residue analysis]
In the procedure 1, the carbides in the steel material are captured as a residue, and the Fe, Cr, Mn, Mo, V, and Nb contents in the residue are determined. Here, “carbide” is a general term for cementite (M3C type carbide) and MC type carbide. The specific procedure is as follows. When the steel material is a plate material, a columnar test piece having a diameter of 6 mm and a length of 50 mm is collected from the central portion of the plate thickness. When the steel material is a steel pipe, 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 μm 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 μm 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.
手順2では、セメンタイト中のFe、Cr、Mn、及び、Mo含有量を決定する。具体的な手順は以下のとおりである。鋼材が板材である場合板厚中央部から、鋼材が鋼管である場合肉厚中央部から、ミクロ試験片を切り出し、鏡面研磨にて表面を仕上げる。試験片を3%ナイタール腐食液に10分浸漬し、表面を腐食する。その表面をカーボン蒸着膜で覆う。蒸着膜で表面を覆った試験片を5%ナイタール腐食液に浸漬し、20分保持し、蒸着膜を剥離させる。剥離した蒸着膜をエタノールで洗浄した後、シートメッシュですくい取り、乾燥させる。この蒸着膜(レプリカ膜)を、TEMで観察し、20個のセメンタイトについてEDSによる点分析を行う。セメンタイト中の炭素を除く合金元素の合計を100%とした場合の、Fe、Cr、Mn、及びMo濃度を質量%単位で定量する。20個のセメンタイトについて濃度を定量し、それぞれの元素の算術平均値を<Fe>b、<Cr>b、<Mn>b、<Mo>bと定義する。 [Procedure 2. Determination of Fe, Cr, Mn, and Mo contents in cementite by extraction replica method and EDS]
In 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.
続いて、炭化物中のMo濃度を求める。ここで、Fe、Cr、Mn、及び、Moはセメンタイトに濃化する。一方、V、Nb、及び、MoはMC型炭化物に濃化する。すなわち、Moは、焼戻しによりセメンタイト及びMC型炭化物の両方に濃化する。したがって、Mo量については、セメンタイト及びMC型炭化物について個別に算出する。なお、Vはセメンタイトにもその一部が濃化する場合がある。しかしながら、Vのセメンタイトへの濃化量は、MC型炭化物への濃化量と比較して無視できるほど小さい。したがって、固溶C量を求める上で、VはMC型炭化物のみに濃化するとみなす。 [Procedure 3. Adjustment of Mo amount]
Subsequently, the Mo concentration in the carbide is determined. Here, Fe, Cr, Mn, and Mo are concentrated to cementite. On the other hand, V, Nb, and Mo are concentrated in MC type carbides. That is, Mo is concentrated to both cementite and MC type carbide by tempering. Therefore, about Mo amount, it calculates separately about cementite and MC type carbide. A part of V may also concentrate in cementite. However, the amount of V enriched in cementite is negligibly small compared to the amount of enriched MC type carbide. Therefore, in obtaining the amount of dissolved C, V is considered to be concentrated only in MC type carbides.
<Mo>c=(<Fe>a+<Cr>a+<Mn>a)×<Mo>b/(<Fe>b+<Cr>b+<Mn>b) (1) Specifically, 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)
<Mo>d=<Mo>a-<Mo>c (2) On the other hand, 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)
析出C量は、セメンタイトとして析出するC量(<C>a)とMC型炭化物として析出するC量(<C>b)の合計として、算出される。<C>a及び<C>bはそれぞれ、式(3)及び式(4)により、質量%単位で算出される。なお、式(3)は、セメンタイトの構造がM3C型(MはFe、Cr、Mn、Moを含む)であることから導かれた式である。
<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) [Procedure 4. Calculation of amount of precipitated C]
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. In addition, 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)
固溶C量(以下、<C>cともいう)は、鋼材のC含有量(<C>)と、析出C量との差として、式(5)により質量%単位で算出する。
<C>c=<C>-(<C>a+<C>b) (5) [Calculation of solute C content]
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)
本実施形態による鋼材のミクロ組織は、主として焼戻しマルテンサイト及び焼戻しベイナイトからなる。より具体的には、ミクロ組織は体積率で90%以上の焼戻しマルテンサイト及び/又は焼戻しベイナイトからなる。すなわち、ミクロ組織は、焼戻しマルテンサイト及び焼戻しベイナイトの体積率の合計が90%以上である。ミクロ組織の残部はたとえば、残留オーステナイト等である。上述の化学組成を有する鋼材のミクロ組織が、焼戻しマルテンサイト及び焼戻しベイナイトの体積率の合計が90%以上を含有すれば、降伏強度が965~1069MPa(140ksi級)、及び、降伏比が90%以上となる。 [Microstructure]
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.
本実施形態による鋼材の形状は、特に限定されない。鋼材はたとえば鋼管、鋼板である。鋼材が油井用鋼管である場合、好ましくは、鋼材は継目無鋼管である。この場合さらに、好ましい肉厚は9~60mmである。本実施形態による鋼材は特に、厚肉の油井用鋼管としての使用に適する。より具体的には、本実施形態による鋼材が15mm以上、さらに、20mm以上の厚肉の油井用鋼管であっても、優れた強度及び耐SSC性を示す。 [Shape of steel]
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. When the steel material is an oil well steel pipe, the steel material is preferably a seamless steel pipe. In this case, 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.
本実施形態による鋼材の降伏強度YSは965~1069MPa(140ksi級)であり、降伏比YRは90%以上である。本明細書でいう降伏強度YSは、引張り試験で得られた0.65%伸び時の応力を意味する。要するに、本実施形態による鋼材の強度は140ksi級である。本実施形態による鋼材は、このような高強度であっても、上述の化学組成、固溶C量、及びミクロ組織を満たすことで優れた耐SSC性を有する。 [Yield strength YS and yield ratio YR of steel]
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.
本実施形態による鋼材の耐SSC性は、NACE TM0177-2005 Method Dに準拠したDCB試験によって評価できる。溶液は脱気した5%食塩水と4g/Lの酢酸Naとを混合させて、かつ塩酸にてpH3.5に調整する。オートクレーブ内に封入する気体は、10%のH2Sガスと90%のCO2ガスの混合ガスを全圧1atmとする。その後、クサビを打ち込んだDCB試験片を容器内に封入し、溶液を攪拌させながら、かつ前記混合ガスを連続的に吹き込みながら、24℃で3週間保持する。以上の条件で求めた、本実施形態による鋼材のK1SSC(MPa√m)は、30.0MPa√m以上である。 [SSC resistance of steel]
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. Thereafter, 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.
本実施形態による鋼材の製造方法は、準備工程と、焼入れ工程と、焼戻し工程とを備える。準備工程は素材準備工程と、熱間加工工程とを含んでもよい。本実施形態では、鋼材の製造方法の一例として、油井用鋼管の製造方法を説明する。油井用鋼管の製造方法は、素管を準備する工程(準備工程)と、素管に対して焼入れ及び焼戻しを実施して、油井用鋼管とする工程(焼入れ工程及び焼戻し工程)とを備える。以下、各工程について詳述する。 [Production method]
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). Hereinafter, each process is explained in full detail.
準備工程は、上述の化学組成を有する中間鋼材を準備する。中間鋼材は、上記化学組成を有していれば、製造方法は特に限定されない。ここでいう中間鋼材は、最終製品が鋼板の場合は、板状の鋼材であり、最終製品が鋼管の場合は素管である。 [Preparation process]
In the preparation 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.
素材準備工程では、上述の化学組成を有する溶鋼を用いて素材を製造する。具体的には、溶鋼を用いて連続鋳造法により鋳片(スラブ、ブルーム、又は、ビレット)を製造する。溶鋼を用いて造塊法によりインゴットを製造してもよい。必要に応じて、スラブ、ブルーム又はインゴットを分塊圧延して、ビレットを製造してもよい。以上の工程により素材(スラブ、ブルーム、又は、ビレット)を製造する。 [Material preparation process]
In the material preparation step, the material is manufactured using molten steel having the above-described chemical composition. Specifically, a slab (slab, bloom, or billet) is manufactured by continuous casting using molten steel. You may manufacture an ingot by the ingot-making method using molten steel. If necessary, 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.
熱間加工工程では、準備された素材を熱間加工して中間鋼材を製造する。鋼材が鋼管である場合、中間鋼材は素管に相当する。始めに、ビレットを加熱炉で加熱する。加熱温度は特に限定されないが、たとえば、1100~1300℃である。加熱炉から抽出されたビレットに対して熱間加工を実施して、素管(継目無鋼管)を製造する。たとえば、熱間加工としてマンネスマン法を実施し、素管を製造する。この場合、穿孔機により丸ビレットを穿孔圧延する。穿孔圧延する場合、穿孔比は特に限定されないが、たとえば、1.0~4.0である。穿孔圧延された丸ビレットをさらに、マンドレルミル、レデューサ、サイジングミル等により熱間圧延して素管にする。熱間加工工程での累積の減面率はたとえば、20~70%である。 [Hot working process]
In the hot working process, the prepared material is hot worked to produce an intermediate steel material. When the steel material is a steel pipe, the intermediate steel material corresponds to a raw pipe. First, the billet is heated in a heating furnace. 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). For example, the Mannesmann method is performed as hot working to manufacture a raw tube. In this case, the round billet is pierced and rolled by a piercing machine. In the case of piercing and rolling, 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%.
焼入れ工程は、準備された中間鋼材(素管)に対して、焼入れを実施する。本明細書において、「焼入れ」とは、A3点以上の中間鋼材を急冷することを意味する。好ましい焼入れ温度は800~1000℃である。焼入れ温度とは、熱間加工後に直接焼入れを実施する場合、最終の熱間加工を実施する装置の出側に設置した測温計で測温された中間鋼材の表面温度に相当する。焼入れ温度とはさらに、熱間加工後に補熱した後、焼入れを実施する場合、補熱を実施する炉の温度に相当する。 [Quenching process]
In the quenching step, quenching is performed on the prepared intermediate steel material (element tube). In the present specification, “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.
上述の焼入れ処理を実施した後、焼戻し処理を実施する。焼戻し温度は、鋼材の化学組成、及び得ようとする降伏強度YSに応じて適宜調整する。つまり、本実施形態の化学組成を有する素管に対して、焼戻し温度を調整して、鋼材の降伏強度YSを965~1069MPa(140ksi級)、及び鋼材のYRを90%以上に調整する。 [Tempering 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. In other words, 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.
焼戻し後の冷却は、従来は制御されていなかった。しかしながら、焼戻し後(つまり、上記焼き戻し温度で上記保持時間保持した後)の鋼材の冷却速度が遅ければ、固溶していたCのほとんどが、温度低下中に再析出してくる。つまり固溶C量が、ほぼ0質量%になる。そこで本実施形態においては、焼戻し後の中間鋼材(素管)を急冷する。 [Quick cooling after tempering]
The cooling after tempering has not been controlled in the past. However, if the cooling rate of the steel material after tempering (that is, after holding the holding time at the tempering temperature) is slow, most of the solid solution C is reprecipitated during the temperature drop. That is, the amount of dissolved C is almost 0% by mass. Therefore, in the present embodiment, the intermediate steel material (element tube) after tempering is rapidly cooled.
[YS及びTS試験]
引張試験はASTM E8に準拠して行った。上記の焼入れ及び焼戻し処理後の各試験番号の鋼板の板厚中央から、直径6.35mm、平行部長さ35mmの丸棒引張試験片を作製した。引張試験片の軸方向は、鋼板の圧延方向と平行であった。各丸棒試験片を用いて、常温(25℃)、大気中にて引張試験を実施して、各位置における降伏強度YS(MPa)及び引張強度TS(MPa)を得た。なお、本実施例では、引張試験で得られた0.65%伸び時の応力を、各試験番号のYSと定義した。また一様伸び中の最大応力をTSとした。このYSとTSの比を降伏比YR(%)とした。 [Evaluation test]
[YS and TS test]
The tensile test was performed according to ASTM E8. A round bar tensile test piece having a diameter of 6.35 mm and a parallel part length of 35 mm was produced from the center of the thickness of the steel plate of each test number after the above quenching and tempering treatment. The axial direction of the tensile specimen was parallel to the rolling direction of the steel plate. Using each round bar test piece, a tensile test was carried out at room temperature (25 ° C.) and in the atmosphere to obtain a yield strength YS (MPa) and a tensile strength TS (MPa) at each position. In this example, 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 (%).
各試験番号の鋼板のミクロ組織について、試験番号23及び25以外は、YSが965~1069MPa(140ksi級)、及びYRが90%以上であったため、焼戻しマルテンサイト及び焼戻しベイナイトの体積率の合計は90%以上であると判断した。試験番号23では、フェライトが生成したものと考えられる。 [Microstructure judgment test]
Regarding the microstructure of the steel plates of each test number, except for
各試験番号の鋼板について、上述の測定方法により、固溶C量(質量%)を測定及び算出した。なお、TEMは日本電子(株)製JEM-2010で、加速電圧は200kVとし、EDS点分析は照射電流2.56nA、各点で60秒の計測を行った。TEMによる観察領域は8μm×8μmとし、任意の10視野で観察した。固溶C量の計算において用いる、各元素の残渣量及びセメンタイト中の濃度は表3のとおりであった。 [Solution C content measurement test]
About the steel plate of each test number, the amount of solid solution C (mass%) was measured and computed by the above-mentioned measuring method. The TEM was JEM-2010 manufactured by JEOL Ltd., the acceleration voltage was 200 kV, and the EDS point analysis was performed with an irradiation current of 2.56 nA and measurement at each point for 60 seconds. The observation area | region by TEM was 8 micrometers x 8 micrometers, and observed by arbitrary 10 visual fields. Table 3 shows the residual amount of each element and the concentration in cementite used in the calculation of the solid solution C amount.
各試験番号の鋼板について、NACE TM0177-2005 Method Dに準拠したDCB試験を実施し、耐SSC性を評価した。具体的には、各鋼板の肉厚中央部から、図2Aに示すDCB試験片を3本ずつ採取した。DCB試験片の長手方向が圧延方向と平行となるよう採取した。鋼板からさらに、図2Bに示すクサビを作製した。クサビの厚さtは3.10mmであった。 [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.
表2に試験結果を示す。 [Test results]
Table 2 shows the test results.
Claims (8)
- 質量%で、
C:0.50超~0.80%、
Si:0.05~1.00%、
Mn:0.05~1.00%、
P:0.025%以下、
S:0.0100%以下、
Al:0.005~0.100%、
Cr:0.20~1.50%、
Mo:0.25~1.50%、
Ti:0.002~0.050%、
B:0.0001~0.0050%、
N:0.002~0.010%、
O:0.0100%以下、
V:0~0.30%、
Nb:0~0.100%、
Ca:0~0.0100%、
Mg:0~0.0100%、
Zr:0~0.0100%、
Co:0~0.50%、
W:0~0.50%、
Ni:0~0.50%、及び、
Cu:0~0.50%を含有し、残部がFe及び不純物からなる化学組成を有し、
固溶Cを0.010~0.060質量%含有し、
降伏強度が965~1069MPaであり、降伏比が90%以上である、鋼材。 % By 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 to 0.50%,
Ni: 0 to 0.50%, and
Cu: 0 to 0.50% contained, the balance having a chemical composition consisting of Fe and impurities,
Containing 0.010 to 0.060 mass% of solid solution C,
A steel material having a yield strength of 965 to 1069 MPa and a yield ratio of 90% or more. - 請求項1に記載の鋼材であって、
前記化学組成は、
V:0.01~0.30%、及び、
Nb:0.002~0.100%からなる群から選択される1種以上を含有する、鋼材。 The steel material according to claim 1,
The chemical composition is
V: 0.01 to 0.30%, and
Nb: a steel material containing at least one selected from the group consisting of 0.002 to 0.100%. - 請求項1又は請求項2に記載の鋼材であって、
前記化学組成は、
Ca:0.0001~0.0100%、
Mg:0.0001~0.0100%、及び、
Zr:0.0001~0.0100%からなる群から選択される1種又は2種以上を含有する、鋼材。 The steel material according to claim 1 or claim 2,
The chemical composition is
Ca: 0.0001 to 0.0100%,
Mg: 0.0001 to 0.0100%, and
Zr: a steel material containing one or more selected from the group consisting of 0.0001 to 0.0100%. - 請求項1~請求項3のいずれか1項に記載の鋼材であって、
前記化学組成は、
Co:0.02~0.50%、及び、
W:0.02~0.50%からなる群から選択される1種以上を含有する、鋼材。 The steel material according to any one of claims 1 to 3,
The chemical composition is
Co: 0.02 to 0.50%, and
W: a steel material containing at least one selected from the group consisting of 0.02 to 0.50%. - 請求項1~請求項4のいずれか1項に記載の鋼材であって、
前記化学組成は、
Ni:0.02~0.50%、及び、
Cu:0.01~0.50%からなる群から選択される1種以上を含有する、鋼材。 The steel material according to any one of claims 1 to 4,
The chemical composition is
Ni: 0.02 to 0.50%, and
Cu: A steel material containing at least one selected from the group consisting of 0.01 to 0.50%. - 請求項1~請求項5のいずれか1項に記載の鋼材であって、油井用鋼管である、鋼材。 The steel material according to any one of claims 1 to 5, wherein the steel material is an oil well steel pipe.
- 請求項1~請求項5のいずれか1項に記載の化学組成を有する中間鋼材を準備する準備工程と、
準備工程後、800~1000℃の前記中間鋼材を、50℃/分以上の冷却速度で冷却する焼入れ工程と、
焼入れ後の前記中間鋼材を、660℃~Ac1点で10~90分保持した後、600℃から200℃の間の平均冷却速度を5~300℃/秒で冷却する焼戻し工程とを備える、鋼材の製造方法。 A preparation step of preparing an intermediate steel material having the chemical composition according to any one of claims 1 to 5;
A quenching step of cooling the intermediate steel material at 800 to 1000 ° C. at a cooling rate of 50 ° C./min or more after the preparation step;
A tempering step in which the intermediate steel material after quenching 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./sec. Steel manufacturing method. - 請求項7に記載の鋼材の製造方法であって、
前記準備工程は、請求項1~請求項5のいずれか1項に記載の化学組成を有する素材を準備する素材準備工程と、
前記素材を熱間加工して中間鋼材を製造する熱間加工工程とを含む、鋼材の製造方法。 It is a manufacturing method of the steel materials according to claim 7,
The preparation step includes a material preparation step of preparing a material having the chemical composition according to any one of claims 1 to 5.
And a hot working process for producing an intermediate steel material by hot working the material.
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US20190376167A1 (en) | 2019-12-12 |
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