WO2018008194A1 - ラインパイプ用電縫鋼管 - Google Patents

ラインパイプ用電縫鋼管 Download PDF

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WO2018008194A1
WO2018008194A1 PCT/JP2017/010024 JP2017010024W WO2018008194A1 WO 2018008194 A1 WO2018008194 A1 WO 2018008194A1 JP 2017010024 W JP2017010024 W JP 2017010024W WO 2018008194 A1 WO2018008194 A1 WO 2018008194A1
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steel pipe
pipe
amount
base material
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PCT/JP2017/010024
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English (en)
French (fr)
Japanese (ja)
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健介 長井
雅和 尾▲崎▼
長谷川　昇
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新日鐵住金株式会社
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Priority to JP2017535721A priority Critical patent/JP6213702B1/ja
Priority to CN201780023247.7A priority patent/CN109072379B/zh
Priority to EP17823802.8A priority patent/EP3428299B1/en
Priority to KR1020187029059A priority patent/KR102129296B1/ko
Publication of WO2018008194A1 publication Critical patent/WO2018008194A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to an ERW steel pipe for a line pipe.
  • Patent Document 1 proposes a hot-rolled steel sheet for sour-resistant, high-strength ERW steel pipes having a bainitic ferrite content in the steel structure of 95 vol% or more.
  • Patent Document 2 before forming a pipe, yielding in the axial direction of the obtained ERW steel pipe by inducing a Bausinger effect by applying repeated strain by, for example, bending and unbending treatment to the material steel strip. Techniques for lowering the ratio are disclosed.
  • Nb amount is 0.003% or more and 0.02
  • a method for manufacturing an ERW steel pipe using a steel slab of less than% is proposed.
  • precipitation of Nb carbide proceeds due to processing strain introduced at the time of pipe making, and yield strength and tensile strength increase. It has been clarified that the yield strength is significantly increased by the strong precipitation strengthening, and as a result, the yield ratio is increased.
  • Patent Document 1 Japanese Patent No. 4305216 Patent Document 2: Japanese Patent No. 4466320 Patent Document 3: International Publication No. 2012/133558
  • Patent Document 1 may not be able to reduce the yield ratio.
  • the steel structure is mainly composed of bainitic ferrite.
  • the technique of patent document 2 since the process of giving a distortion to a strip steel is required, the number of processes increases, As a result, the manufacturing cost of a steel pipe may increase.
  • An object of the present disclosure is to provide an ERW steel pipe for a line pipe having excellent sour resistance, a certain degree of tensile strength and yield strength, a reduced yield ratio, and excellent toughness of a base material portion and an ERW weld portion. It is to be.
  • Means for solving the above problems include the following aspects. ⁇ 1> Including the base metal part and the ERW welded part, The chemical composition of the base material part is mass%, C: 0.030% or more and less than 0.080%, Mn: 0.30 to 1.00% Ti: 0.005 to 0.050%, Nb: 0.010 to 0.100%, N: 0.001 to 0.020%, Si: 0.010 to 0.450%, Al: 0.0010 to 0.1000%, P: 0 to 0.030%, S: 0 to 0.0010%, Mo: 0 to 0.50%, Cu: 0 to 1.00%, Ni: 0 to 1.00%, Cr: 0 to 1.00%, V: 0 to 0.100%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, REM: 0 to 0.0100% and the balance: Fe and impurities, CNeq represented by the following formula (1) is 0.190 to 0.320, The ratio of mass% of Mn to mass% of Si is 2.0
  • Yield strength in the tube axis direction is 390 to 562 MPa, The tensile strength in the tube axis direction is 520 to 690 MPa, The yield ratio in the tube axis direction is 93% or less,
  • the Charpy absorbed energy in the pipe circumferential direction in the base material part is 100 J or more at 0 ° C.
  • the chemical composition of the base material part is mass%, Mo: more than 0% and 0.50% or less, Cu: more than 0% and 1.00% or less, Ni: more than 0% and 1.00% or less, Cr: more than 0% and 1.00% or less, V: more than 0% and 0.100% or less, Ca: more than 0% and 0.0100% or less,
  • the electric-welded steel pipe for line pipes according to ⁇ 1> which contains one or more of Mg: more than 0% and not more than 0.0100% and REM: more than 0% and not more than 0.0100%.
  • ⁇ 3> When the metal structure of the base material portion is observed at a magnification of 100,000 using a transmission electron microscope, the area ratio of precipitates having an equivalent circle diameter of 100 nm or less is 0.100 to 1.000%.
  • ⁇ 4> The ERW steel pipe for line pipes according to any one of ⁇ 1> to ⁇ 3>, wherein the Nb content in the chemical composition of the base material part is 0.020% or more by mass%.
  • ⁇ 5> The electric-welded steel pipe for line pipes according to any one of ⁇ 1> to ⁇ 4>, wherein the wall thickness is 10 to 25 mm and the outer diameter is 114.3 to 609.6 mm.
  • CLR When a hydrogen-induced crack test is performed on a test piece collected from the base material part, CLR, which is a percentage of the total length of cracks with respect to the length of the test piece, is 8% or less.
  • CLR An electric resistance welded steel pipe for line pipes according to any one of the above.
  • an ERW steel pipe for a line pipe that is excellent in sour resistance, has a certain degree of tensile strength and yield strength, has a reduced yield ratio, and is excellent in toughness of a base material portion and an ERW weld portion. Is done.
  • a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
  • “%” indicating the content of a component (element) means “% by mass”.
  • the content of C (carbon) may be expressed as “C amount”.
  • the content of other elements may be expressed in the same manner.
  • the term “process” is not limited to an independent process, and is included in this term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes. It is.
  • the ERW steel pipe for line pipes of the present disclosure (hereinafter, also simply referred to as “ERW steel pipe”) includes a base metal part and an ERW weld part, and the base metal part has a chemical composition of mass%, C: 0.00. 030% or more and less than 0.080%, Mn: 0.30 to 1.00%, Ti: 0.005 to 0.050%, Nb: 0.010 to 0.100%, N: 0.001 to 0.00.
  • TS is 520 to 690 MPa
  • the yield ratio in the tube axis direction (hereinafter also referred to as “YR”) is 93% or less
  • the Charpy absorbed energy in the tube circumferential direction in the base metal part is 0 100 J or more at °C
  • Circumferential direction of the pipe of the Charpy absorbed energy at sewing welds is 80J or more at 0 ° C..
  • the electric resistance steel pipe of this indication contains a base material part and an electric resistance welding part.
  • ERW steel pipes are generally made into open pipes by forming hot-rolled steel sheets into tubes (hereinafter also referred to as “roll forming”). It is manufactured by forming an electric resistance welded portion and then, if necessary, seam heat treating the electro-welded weld.
  • the base metal portion refers to a portion other than the ERW weld and the heat affected zone.
  • the heat affected zone (hereinafter also referred to as “HAZ”) is the effect of heat by electric resistance welding (when seam heat treatment is performed after electric resistance welding, heat generated by electric resistance welding and seam heat treatment).
  • the electric resistance welded portion may be simply referred to as a “welded portion”.
  • the electric resistance welded steel pipe of the present disclosure is excellent in sour resistance, has a certain amount of YS and TS (that is, YS and TS in the above-described range), YR is reduced to 93% or less, and the base metal portion and the electric resistance welded portion.
  • Excellent toughness In the present disclosure, being excellent in toughness means that Charpy absorbed energy (J) (hereinafter also referred to as “vE”) in the pipe circumferential direction at 0 ° C. is large.
  • J Charpy absorbed energy
  • vE Charpy absorbed energy
  • the vE in the base metal part is 100 J or more
  • the vE in the ERW weld part is 80 J or more.
  • excellent sour resistance means excellent resistance to hydrogen-induced cracking (HIC) (hereinafter also referred to as “HIC resistance”).
  • HIC resistance is evaluated by CLR (that is, Crack to Length Ratio) when a hydrogen-induced cracking test (hereinafter also referred to as “HIC test”) is performed on a test piece collected from the base metal part.
  • CLR means the percentage of the total length of cracks relative to the length of the test piece, that is, a value obtained by the following formula.
  • CLR (%) (total length of cracks / test piece length) ⁇ 100 (%)
  • the HIC test is performed according to NACE-TM0284. Specifically, the test piece collected from the base material part is immersed in Solution A (5 mass% NaCl + 0.5 mass% glacial acetic acid aqueous solution) saturated with 100% H 2 S gas for 96 hours. After the immersion, the above-mentioned CLR (%) is obtained by an ultrasonic flaw detection test.
  • Solution A 5 mass% NaCl + 0.5 mass% glacial acetic acid aqueous solution
  • H 2 S gas 100% H 2 S gas
  • CLR means that the lower the value, the better the HIC resistance (ie, sour resistance). CLR is preferably 8% or less.
  • the ERW steel pipe of this indication has low YR, the effect which can control buckling of an ERW steel pipe is expected.
  • buckling suppression of a steel pipe there is a case where a steel pipe for a submarine line pipe is laid by reeling.
  • steel pipes are manufactured in advance on land, and the manufactured steel pipes are wound on a barge ship spool.
  • the rolled steel pipe is laid on the seabed while unwinding at sea.
  • the steel pipe may be buckled because plastic bending is applied to the steel pipe at the time of winding or unwinding the steel pipe.
  • the buckling of the steel pipe occurs, the laying work must be stopped and the damage is enormous.
  • the buckling of the steel pipe can be suppressed by reducing the YR of the steel pipe. Therefore, according to the ERW steel pipe of the present disclosure, for example, it is expected that the buckling at the time of laying laying when used as an ERW steel pipe for a submarine line pipe can be suppressed.
  • the electric resistance welded steel pipe of the present disclosure is excellent in the toughness of the base metal part and the electric resistance welded part, it is expected that the electric resistance steel pipe is excellent in the stop property of crack propagation at the time of burst.
  • the above-mentioned sour resistance (ie, CLR), YS, TS, YR, vE of the base metal part, and vE of the electric resistance welded part are the above chemical compositions (CNeq, Mn / Si ratio, and (Including LR) and the above metal structure.
  • C 0.030% or more and less than 0.080% C is an element necessary for improving the work hardening ability of the steel and achieving a low YR of the ERW steel pipe. From the viewpoint of this effect, the C content is 0.030% or more.
  • the amount of C is preferably 0.033% or more, and more preferably 0.035% or more.
  • the amount of C is less than 0.080%.
  • the amount of C is preferably 0.077% or less, and more preferably 0.070% or less.
  • Mn 0.30 to 1.00%
  • Mn is an element that enhances the hardenability of steel.
  • Mn is an essential element for detoxification of S.
  • the amount of Mn is preferably 0.40% or more, more preferably 0.50% or more.
  • the amount of Mn exceeds 1.00%, coarse MnS is generated in the central portion of the thickness, and the hardness of the central portion of the thickness is increased, so that the sour resistance may be impaired.
  • the amount of Mn exceeds 1.00%, LR0.210 or more may not be achieved, and as a result, YR90% or less may not be achieved. Therefore, the amount of Mn is 1.00% or less.
  • the amount of Mn is preferably 0.90% or less, more preferably 0.85% or less.
  • Ti 0.005 to 0.050%
  • Ti is an element that forms carbonitrides and contributes to refinement of the crystal grain size. From the viewpoint of ensuring the toughness of the base metal part and the ERW weld, the Ti content is 0.005% or more. On the other hand, if the Ti amount exceeds 0.050%, coarse TiN is generated, and the toughness of the base metal part and the ERW welded part may deteriorate. Therefore, the Ti amount is 0.050% or less.
  • the amount of Ti is preferably 0.040% or less, more preferably 0.030 or less, and particularly preferably 0.025%.
  • Nb 0.010 to 0.100%
  • Nb is an element that contributes to improving the toughness of the base material.
  • the Nb content is 0.010% or more.
  • the Nb amount is preferably 0.015% or more, and more preferably 0.020% or more.
  • the amount of Nb is 0.100% or less.
  • the Nb amount is preferably 0.095% or less, more preferably 0.090% or less.
  • N 0.001 to 0.020%
  • N is an element that suppresses the coarsening of crystal grains by forming nitrides, and as a result, improves the toughness of the base metal part and the ERW weld part.
  • the N content is 0.001% or more.
  • the amount of N is preferably 0.003% or more.
  • the N amount is 0.020% or less.
  • the amount of N is preferably 0.008% or less.
  • Si 0.010 to 0.450% Si is an element that functions as a deoxidizer for steel. More specifically, when the Si amount is 0.010% or more, generation of coarse oxides in the base material and the welded portion is suppressed, and as a result, the toughness of the base material and the welded portion is improved. Therefore, the amount of Si is 0.010% or more.
  • the amount of Si is preferably 0.015% or more, and more preferably 0.020% or more.
  • the amount of Si exceeds 0.450%, inclusions are generated in the ERW weld, and Charpy absorbed energy may be reduced and toughness may be deteriorated. Therefore, the amount of Si is 0.450% or less.
  • the amount of Si is preferably 0.400% or less, more preferably 0.350% or less, and particularly preferably 0.300% or less.
  • Al 0.001 to 0.100%
  • Al is an element that functions as a deoxidizer. More specifically, when the Al content is 0.001% or more, generation of coarse oxides in the base material and the welded portion is suppressed, and as a result, the toughness of the base material and the welded portion is improved. Therefore, the Al content is 0.001% or more.
  • the amount of Al is preferably 0.010% or more, and more preferably 0.015% or more. On the other hand, if the Al content exceeds 0.100%, the toughness of the welded portion may deteriorate with the generation of the Al-based oxide during ERW welding. Therefore, the Al content is 0.100% or less.
  • the amount of Al is preferably 0.090% or less.
  • P 0 to 0.030%
  • P is an impurity element.
  • the amount of P is preferably 0.025% or less, more preferably 0.020% or less, and still more preferably 0.010% or less.
  • the amount of P may be 0%. From the viewpoint of reducing the dephosphorization cost, the amount of P may be more than 0% or 0.001% or more.
  • S 0 to 0.0010%
  • S is an impurity element. If the amount of S exceeds 0.0010%, the sour resistance may be impaired. Therefore, the amount of S is 0.0010% or less.
  • the amount of S is preferably 0.0008% or less.
  • the amount of S may be 0%. From the viewpoint of reducing the desulfurization cost, the S amount may be more than 0%, may be 0.0001% or more, and may be 0.0003% or more.
  • Mo 0 to 0.50% Mo is an arbitrary element. Therefore, the Mo amount may be 0%. Mo is an element that improves the hardenability of the steel material and contributes to the high strength of the steel material. From the viewpoint of this effect, the Mo amount may be more than 0%, 0.01% or more, or 0.03% or more. On the other hand, if the amount of Mo exceeds 0.50%, the toughness may be reduced due to the formation of Mo carbonitride. Therefore, the Mo amount is 0.50% or less. The amount of Mo is preferably 0.40% or less, more preferably 0.30% or less, still more preferably 0.20% or less, and particularly preferably 0.10% or less.
  • Cu 0 to 1.00% Cu is an arbitrary element. Therefore, the amount of Cu may be 0%. Cu is an element effective for improving the strength of the base material. From the viewpoint of this effect, the amount of Cu may be more than 0%, 0.01% or more, or 0.03% or more. On the other hand, when the amount of Cu exceeds 1.00%, fine Cu particles are generated, and the toughness may be remarkably deteriorated. Therefore, the amount of Cu is 1.00% or less.
  • the amount of Cu is preferably 0.80% or less, more preferably 0.70% or less, still more preferably 0.60% or less, and particularly preferably 0.50% or less.
  • Ni 0 to 1.00%
  • Ni is an arbitrary element. Therefore, the Ni amount may be 0%.
  • Ni is an element that contributes to improvement in strength and toughness. From the viewpoint of this effect, the Ni content may be greater than 0%, 0.01% or more, or 0.05% or more. On the other hand, if the Ni content exceeds 1.00%, the strength may be too high. Therefore, the Ni content is 1.00% or less.
  • the amount of Ni is preferably 0.80% or less, more preferably 0.70% or less, and still more preferably 0.60% or less.
  • Cr 0 to 1.00% Cr is an arbitrary element. Therefore, the Cr amount may be 0%. Cr is an element that improves hardenability. From the viewpoint of this effect, the Cr content may be more than 0%, 0.01% or more, or 0.05% or more. On the other hand, if the Cr content exceeds 1.00%, the toughness of the welded portion may be deteriorated by the Cr-based inclusions generated in the ERW welded portion. Therefore, the Cr content is 1.00% or less.
  • the amount of Cr is preferably 0.80% or less, more preferably 0.70% or less, still more preferably 0.50% or less, and particularly preferably 0.30% or less.
  • V 0 to 0.100%
  • V is an arbitrary element. Therefore, the V amount may be 0%.
  • V is an element contributing to improvement of toughness. From the viewpoint of this effect, the V amount may be greater than 0%, may be 0.005% or more, and may be 0.010% or more. On the other hand, if the amount of V exceeds 0.100%, the toughness may be deteriorated by the V carbonitride. Therefore, the V amount is 0.100% or less.
  • the amount of V is preferably 0.080% or less, more preferably 0.070% or less, still more preferably 0.050% or less, and particularly preferably 0.030% or less.
  • Ca 0 to 0.0100% Ca is an arbitrary element. Therefore, the Ca content may be 0%. Ca is an element that controls the form of sulfide inclusions and improves low-temperature toughness. From the viewpoint of such an effect, the Ca content may be greater than 0%, may be 0.0001% or more, may be 0.0010% or more, or may be 0.0030% or more. It may be 0.0050% or more. On the other hand, if the Ca content exceeds 0.0100%, large clusters or large inclusions made of CaO—CaS are generated, which may adversely affect toughness. Therefore, the Ca content is 0.0100% or less. The Ca content is preferably 0.0090% or less, more preferably 0.0080% or less, and particularly preferably 0.0060% or less.
  • Mg 0 to 0.0100% Mg is an arbitrary element. Therefore, the amount of Mg may be 0%. Mg is an effective element as a deoxidizing agent and a desulfurizing agent. In particular, Mg is an element that generates fine oxides and contributes to improvement in toughness of HAZ (Heat affected zone). From the viewpoint of such an effect, the amount of Mg may be more than 0%, may be 0.0001% or more, may be 0.0010% or more, or may be 0.0020% or more. Good.
  • the amount of Mg exceeds 0.0100%, the oxide tends to agglomerate or coarsen, resulting in a decrease in HIC resistance (Hydrogen-Induced Cracking Resistance) or a decrease in the toughness of the base material or HAZ. There is a risk. Therefore, the amount of Mg is 0.0100% or less. The amount of Mg is preferably 0.0080% or less.
  • REM 0 to 0.0100% REM is an arbitrary element. Therefore, the REM amount may be 0%.
  • “REM” is a rare earth element, that is, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It refers to at least one element selected.
  • REM is an element effective as a deoxidizer and a desulfurizer. From the viewpoint of this effect, the amount of REM may be greater than 0%, may be 0.0001% or more, and may be 0.0010% or more.
  • the amount of REM exceeds 0.0100%, a coarse oxide is formed, and as a result, there is a possibility that the HIC resistance is lowered or the toughness of the base material or HAZ is lowered. Therefore, the amount of REM is 0.0100% or less.
  • the amount of REM is preferably 0.0070% or less, and more preferably 0.0050% or less.
  • the chemical composition of the base metal part is Mo: more than 0% to 0.50% or less, Cu: more than 0% to 1.00% or less, Ni: more than 0% to 1.00, from the viewpoint of obtaining the effect of any element described above.
  • the more preferable amount of each arbitrary element is as described above.
  • the remainder excluding the above-described elements is Fe and impurities.
  • the impurity refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally contained in the steel.
  • impurities include all elements other than the elements described above.
  • the element as the impurity may be only one type or two or more types.
  • the impurities include O, B, Sb, Sn, W, Co, As, Pb, Bi, and H.
  • O is preferably controlled so that the content is 0.006% or less.
  • Sb, Sn, W, Co, and As are usually mixed with a content of 0.1% or less, and Pb and Bi are mixed with a content of 0.005% or less.
  • Pb and Bi are mixed with a content of 0.005% or less.
  • CNeq 0.190 to 0.320
  • CNeq C + Mn / 6 + Cr / 5 + (Ni + Cu) / 15 + Nb + Mo + V
  • CNeq C + Mn / 6 + Cr / 5 + (Ni + Cu) / 15 + Nb + Mo + V
  • C, Mn, Cr, Ni, Cu, Nb, Mo, and V represent the mass% of each element, respectively.
  • CNeq has a positive correlation with the yield strength. From the viewpoint of easily achieving a yield strength of 390 MPa or more, CNeq is 0.190 or more. CNeq is preferably 0.200 or more, and more preferably 0.210 or more. On the other hand, from the viewpoint of easily achieving a yield strength of 562 MPa or less, CNeq is 0.320 or less. CNeq is preferably 0.310 or less, more preferably 0.300 or less.
  • LR 0.210 or more
  • LR represented by the following formula (2) is 0.210 or more.
  • YR 93% or less
  • YR may exceed 93%. The reason for this is considered to be that the amount of precipitates in the steel is reduced and the work hardening ability is lowered (ie, TS is lowered).
  • formula (2) The technical meaning of formula (2) is as follows.
  • the reason why the C amount and the Nb amount are arranged in the molecule is that C and Nb form precipitates, thereby improving the work hardening ability of the steel (that is, TS increases), and as a result. This is because YR of steel is considered to be reduced.
  • the reason for multiplying the amount of C by “2.1” is that the effect of improving the work hardening ability due to the above-described precipitate formation is considered to be about 2.1 times the effect of containing Cb compared to the effect of containing Nb. It is.
  • the reason for arranging the amount of Mn in the denominator is that although the steel can be transformed at a relatively low temperature by the inclusion of Mn, the work hardening ability of the steel itself is impaired by the inclusion of Mn (that is, , TS decreases), and as a result, the YR of steel increases.
  • LR has a positive correlation with the Nb amount and the C amount, and has a negative correlation with the Mn amount.
  • the Nb amount 0.210 or more depending on the amount of C and the amount of Mn.
  • YR of 93% or less can be achieved.
  • YR of 93% or less is achieved by satisfying conditions other than LR of LR of 0.210 or more. obtain.
  • LR is preferably 0.220 or more, and more preferably 0.230 or more. There is no particular limitation on the upper limit of LR. LR is preferably 0.600 or less from the viewpoint of the suitability for manufacturing an ERW steel pipe.
  • the Mn / Si ratio (that is, the ratio Mn / Si ratio of Mn to Si mass%) is 2.0 or more.
  • the toughness of the welded portion is improved, and vE at the welded portion (that is, Charpy absorbed energy in the pipe circumferential direction at 0 ° C.) is 80 J. That's it.
  • vE may be less than 80J.
  • the reason for this is considered that when the Mn / Si ratio is less than 2.0, the toughness deteriorates due to the MnSi inclusions being the starting point of brittle fracture in the weld zone.
  • the Mn / Si ratio is preferably 2.1 or more from the viewpoint of further improving the toughness of the welded portion. There is no restriction
  • the Mn / Si ratio is preferably 50 or less from the viewpoint of further improving the toughness of the welded portion and the toughness of the base metal portion.
  • the metal structure of the base metal part is a ferrite fraction (that is, the first phase composed of ferrite) when the metal structure is observed at a magnification of 1000 times using a scanning electron microscope. Area ratio) is 40 to 80%, and the remaining second phase contains tempered bainite.
  • YR of 93% or less can be achieved when the ferrite fraction is 40% or more. From the viewpoint of further reducing YR, the ferrite fraction is preferably 45% or more, and more preferably 50% or more. In the ERW steel pipe of the present disclosure, the ferrite fraction is 80% or less, so that the sour resistance is improved. From the viewpoint of improving sour resistance, the ferrite fraction is preferably 75% or less.
  • the remaining second phase includes tempered bainite.
  • the fact that the second phase contains tempered bainite means that the ERW steel pipe of the present disclosure is tempered after pipe forming (that is, after ERW welding (after seam heat treatment if seam heat treatment is applied after ERW welding)).
  • tempered bainite means that the ERW steel pipe of the present disclosure is tempered after pipe forming (that is, after ERW welding (after seam heat treatment if seam heat treatment is applied after ERW welding)).
  • the ERW steel pipe of the present disclosure is an ERW steel pipe that has been tempered after pipe making, whereby YR of 93% or less can be achieved.
  • YR is lowered by tempering after pipe making.
  • the reason why YR decreases due to tempering after pipe forming is that YS decreases as the dislocation density decreases, and that work hardening increases due to precipitation of cementite on the dislocations (ie, TS increases). Conceivable.
  • tempered bainite is distinguished from bainite that is not tempered bainite in that it contains granular cementite in its structure.
  • the concept of “bainite” in this specification includes bainitic ferrite, granular bainite, upper bainite, and lower bainite.
  • the second phase only needs to contain tempered bainite, may be a phase composed only of tempered bainite, or may contain a structure other than tempered bainite.
  • Examples of the structure other than tempered bainite include pearlite.
  • the concept of “perlite” includes pseudo pearlite.
  • the ferrite fraction measurement and the identification of the second phase are performed by performing a nital etching on the metal structure at the thickness 1/4 position in the L cross section of the base material 90 ° position, and after the nital etching.
  • a metal structure photograph (hereinafter, also referred to as “metal structure photograph”) is observed by observing at a magnification of 1000 times using a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • the metal structure photograph is taken for 10 fields of view at a magnification of 1000 times (0.12 mm 2 minutes as the actual area of the cross section).
  • Image processing is performed on the photographed metal structure photograph to measure the ferrite fraction and identify the second phase.
  • the image processing is performed using, for example, a small general-purpose image analyzer LUZEX AP manufactured by Nireco Corporation.
  • the “base material 90 ° position” refers to a position that is shifted 90 ° from the welded portion in the pipe circumferential direction
  • the “L cross section” is a cross section parallel to the pipe axis direction and the wall thickness direction.
  • the “wall thickness 1/4 position” refers to a position where the distance from the outer peripheral surface of the ERW steel pipe is 1/4 of the wall thickness.
  • the tube axis direction may be referred to as the “L direction”.
  • FIG. 1 is a scanning electron micrograph (SEM photograph; magnification 1000 times) showing an example of the metal structure of the base material part in the present disclosure.
  • the SEM photograph of FIG. 1 is one (one field of view) of the SEM photographs used for the measurement of the ferrite fraction and the identification of the second phase in Example 1 described later.
  • a first phase composed of ferrite and a second phase containing tempered bainite can be confirmed.
  • the presence of white spots (cementite) indicates that the second phase contains tempered bainite.
  • the metal structure of the base metal part is the area of a precipitate having an equivalent circle diameter of 100 nm or less (hereinafter also referred to as “specific precipitate”) when the metal structure is observed at a magnification of 100,000 using a transmission electron microscope.
  • the rate (hereinafter also referred to as “specific precipitate area ratio”) is preferably 0.100 to 1.000%.
  • the specific precipitate area ratio is 0.100% or more, it is easier to achieve that YR is 93% or less.
  • the reason for this is considered to be that the specific precipitate (that is, the precipitate having an equivalent circle diameter of 100 nm or less) contributes to the improvement of work-hardening properties (that is, the increase in TS), and as a result, YR decreases.
  • the specific precipitate area ratio is 1.000% or less, brittle fracture is suppressed (that is, the toughness of the base material portion is excellent).
  • the specific precipitate area ratio is preferably 0.900% or less, and more preferably 0.800% or less.
  • the specific precipitate area ratio of 0.100 to 1.000% can be achieved by tempering at a temperature of 400 ° C. or higher and Ac1 point or lower after pipe forming.
  • the area ratio of precipitates (that is, the area ratio of precipitates having a circle-equivalent diameter of 100 nm or less) is determined by using a transmission electron microscope (TEM) and observing at a magnification of 100,000 times. More specifically, based on a sample taken from a thickness 1/4 position in the L cross section of the base material at 90 °, it is composed of 10% by volume of acetylacetone, 1% by volume of tetramethylammonium chloride, and 89% by volume of methyl alcohol. A replica for TEM observation is produced by the SPEED method using an electrolytic solution.
  • TEM transmission electron microscope
  • the obtained TEM observation replica is observed at a magnification of 100000 times using a TEM, thereby acquiring 10 TEM images of a 1 ⁇ m square field size.
  • the area ratio of precipitates having an equivalent circle diameter of 100 nm or less with respect to the total area of the acquired TEM image is calculated, and the obtained result is defined as a specific precipitate area ratio (%).
  • the etching conditions in the SPEED method are such that a saturated gypsum electrode is used as a reference electrode and a charge of 10 coulomb is applied at a voltage of ⁇ 200 mV to a surface area of about 80 square millimeters.
  • the specific precipitate (that is, the precipitate having an equivalent circle diameter of 100 nm or less) is specifically composed of a carbide of a metal other than Fe, a nitride of a metal other than Fe, and a carbonitride of a metal other than Fe. It is considered to be at least one selected from the group. Ti and Nb can be considered as metals other than Fe here. Moreover, when a chemical composition contains at least 1 sort (s) of V, Mo, and Cr, at least 1 sort (s) of V, Mo, and Cr is also considered as metals other than the said Fe.
  • Yield strength in the pipe axis direction (YS)
  • the electric resistance welded steel pipe of the present disclosure has a yield strength (YS) in the pipe axis direction of 390 to 562 MPa.
  • YS in the tube axis direction is preferably 410 MPa or more, more preferably 450 MPa or more, still more preferably 470 MPa or more, and particularly preferably 500 MPa or more.
  • YS in the tube axis direction is preferably 550 MPa or less, more preferably 540 MPa or less, and particularly preferably 530 MPa or less.
  • the fact that the YS in the pipe axis direction is 562 MPa or less can be achieved by tempering after pipe making.
  • the reason for this is considered to be that the tempering after pipe making relaxes the pipe making strain and lowers the dislocation density.
  • the electric resistance welded steel pipe of the present disclosure has a tensile strength (TS) in the pipe axis direction of 520 to 690 MPa.
  • TS in the tube axis direction is preferably 550 MPa or more, and more preferably 580 MPa or more.
  • TS in the tube axis direction is preferably 680 MPa or less, more preferably 660 MPa or less, and particularly preferably 650 MPa or less.
  • the YR in the tube axis direction being 93% or less can be achieved by tempering after pipe forming. This is presumably because YS decreases as the dislocation density decreases and work hardening increases (ie, TS increases) due to precipitation of cementite on the dislocations.
  • the wall thickness of the electric resistance welded steel pipe of the present disclosure is preferably 10 to 25 mm.
  • the wall thickness is more preferably 12 mm or more. If the wall thickness is 25 mm or less, it is advantageous in terms of the suitability for producing an electric resistance steel pipe (specifically, the formability when forming a hot-rolled steel sheet into a tubular shape).
  • the wall thickness is more preferably 20 mm or less.
  • the outer diameter of the electric resistance welded steel pipe of the present disclosure is preferably 114.3 to 609.6 mm (ie, 4.5 to 24 inches). When the outer diameter is 114.3 mm or more, it is more suitable as an ERW steel pipe for line pipes.
  • the outer diameter is preferably 139.7 mm (ie 5.5 inches) or more, more preferably 177.8 mm (ie 7 inches) or more.
  • the outer diameter is 609.6 mm or less, it is advantageous in that the YR can be easily reduced by utilizing strain when the hot-rolled steel sheet is formed into a tubular shape.
  • the outer diameter is preferably 406.4 mm (ie 16 inches) or less, more preferably 304.8 mm (ie 12 inches) or less.
  • Process A is A step of producing an azurol ERW pipe using the hot-rolled steel sheet having the chemical composition described above; A tempering step of obtaining an ERW steel pipe by tempering the as-roll ERW steel pipe, Have
  • the tempering temperature (that is, the holding temperature in tempering) is preferably 400 ° C. or higher and Ac1 point or lower. When the tempering temperature is 400 ° C. or higher, cementite and specific precipitates (precipitates having a circle-equivalent diameter of 100 nm or less) are more likely to be precipitated.
  • the tempering temperature is more preferably 420 ° C. or higher. When the tempering temperature is at most Ac1 point, the coarsening of the metal structure is suppressed, and as a result, the toughness is improved.
  • the tempering temperature is also preferably 720 ° C. or lower, preferably 710 ° C. or lower, and preferably 700 ° C. or lower, although it depends on the Ac1 point of the steel.
  • Ac1 point means the temperature at which transformation to austenite is started when the temperature of the steel is raised.
  • the Ac1 point is calculated by the following formula.
  • Ac1 point (° C) 750.8-26.6C + 17.6Si-11.6Mn-22.9Cu-23Ni + 24.1Cr + 22.5Mo-39.7V-5.7Ti + 232.4Nb-169.4Al
  • C, Si, Mn, Ni, Cu, Cr, Mo, V, Ti, Nb, and Al are mass% of each element, respectively.
  • Ni, Cu, Cr, Mo, and V are arbitrary elements, and among these optional elements, the Ac1 point is calculated as 0% by mass for an element that is not contained in the steel slab.
  • the tempering time in the tempering step (that is, the holding time at the tempering temperature) is preferably 5 minutes or more from the viewpoint of easily reducing YR due to precipitation of cementite and specific precipitates.
  • an as-roll electric-welded steel pipe is an electric-welded steel pipe manufactured by roll-forming (that is, tubular forming) a hot-rolled steel sheet, and is not subjected to heat treatment other than seam heat treatment after roll-forming.
  • ERW steel pipe The preferable aspect of the process of manufacturing the as-roll electric resistance welded steel pipe in the manufacturing method A is mentioned later.
  • the amount of change in roundness before and after adjustment by the sizer (hereinafter, “sizer roundness”) It is preferable to have a sizer process that is adjusted under the condition that the amount of change (also referred to as “change amount (%)” is 1.0% or more.
  • the manufacturing method A has a sizer process, it is easier to manufacture the ERW steel pipe having the above-described specific precipitate area ratio of 0.100 to 1.000%.
  • the reason for this is that the sizer roundness change amount of 1.0% or more introduces a certain amount or more of dislocations into the inside of the as-rolled electric-welded steel pipe, and then into the as-rolled electric-welded steel pipe.
  • fine specific precipitates are easily deposited on dislocations by tempering at a temperature of 400 ° C. or more and Ac1 point or less.
  • the change in size (%) of the sizer roundness is based on the roundness of the as-rolled ERW pipe before shape adjustment by the sizer and the roundness of the Azuroll-ERW pipe after shape adjustment by the sizer.
  • Ask. Amount of change in roundness before and after sizer (%) (
  • the process for producing an as-roll ERW steel pipe in production method A is as follows: A hot-rolling step of obtaining a hot-rolled steel sheet by heating a steel slab (slab) having the above-described chemical composition and hot-rolling the heated steel slab, A cooling step for cooling the hot-rolled steel sheet obtained in the hot rolling step; By winding the hot rolled steel sheet cooled in the cooling process, a winding process for obtaining a hot coil made of the hot rolled steel sheet, By unwinding the hot-rolled steel sheet from the hot coil, roll-forming the unrolled hot-rolled steel sheet to form an open pipe, and forming the ERW welded part by electro-welding the butt portion of the obtained open pipe
  • a pipe making process for obtaining an as-roll ERW steel pipe It is preferable to have. In the pipe making process, seam heat treatment may be applied to the ERW welded portion as necessary after ERW welding.
  • a steel slab (slab) having the above-described chemical composition it is preferable to heat a steel slab (slab) having the above-described chemical composition to a temperature of 1150 ° C to 1350 ° C.
  • the toughness of the base material part of an electric-resistance-welded steel pipe can be improved more as the temperature which heats a steel piece is 1150 degreeC or more. The reason for this is considered to be that when the temperature at which the steel slab is heated is 1150 ° C. or higher, the formation of undissolved Nb carbide can be suppressed.
  • the toughness of the base material part of an ERW steel pipe can be improved more as the temperature which a steel piece heats is 1350 degrees C or less. The reason for this is considered that the coarsening of the metal structure can be suppressed when the heating temperature of the steel slab is 1350 ° C. or less.
  • a steel slab heated to a temperature of 1150 ° C. to 1350 ° C. is preferably hot rolled at a temperature of Ar 3 point + 100 ° C. or higher.
  • the hardenability of a hot-rolled steel sheet can be improved.
  • the sour resistance of the finally obtained electric resistance welded pipe that is, the tempered electric resistance welded pipe
  • the Ar3 point is determined by the following formula from the chemical composition of the base material part.
  • Ar3 (° C.) 910-310C-80Mn-55Ni-20Cu-15Cr-80Mo
  • C, Mn, Ni, Cu, Cr, and Mo are the mass% of each element, respectively.
  • Ni, Cu, Cr, and Mo are arbitrary elements, and among these optional elements, an Ar3 point is calculated as 0% by mass for an element that is not contained in the steel slab.
  • the cooling step is a step of cooling the hot-rolled steel sheet obtained in the hot rolling step.
  • it is preferable to cool the hot-rolled steel sheet obtained in the hot rolling step with a cooling start temperature of Ar3 point or higher.
  • a cooling start temperature of Ar3 point or higher thereby, the intensity
  • the reason for this is considered to be that the formation of coarse ferrite is suppressed by setting the cooling start temperature to the Ar3 point or higher.
  • Cooling in the cooling step is preferably started within 10 seconds after completion of rolling in the hot rolling step (that is, after completion of final rolling in the hot rolling step). Thereby, it is easy to adjust the ferrite fraction of the finally obtained ERW steel pipe to 80% or less.
  • the hot-rolled steel sheet obtained in the hot rolling step is cooled at a cooling rate of 5 ° C./s to 80 ° C./s.
  • the cooling rate is 5 ° C./s or more
  • the toughness deterioration of the base material portion is further suppressed.
  • the reason for this is considered to be that the formation of coarse ferrite is suppressed when the cooling rate in the cooling step is 5 ° C./s or more.
  • the cooling rate is 80 ° C./s or less
  • the toughness deterioration of the base material portion is suppressed. This is because, when the cooling rate in the cooling step is 80 ° C./s or less, the second phase fraction is suppressed from being excessive (that is, the ferrite fraction is less than 40%). Conceivable.
  • the hot-rolled steel sheet cooled in the cooling process it is preferable to wind the hot-rolled steel sheet cooled in the cooling process at a winding temperature of 450 to 650 ° C.
  • the winding temperature is 450 ° C. or higher, the toughness deterioration of the base material portion is suppressed.
  • the reason for this is considered to be that when the winding temperature is 450 ° C. or higher, the formation of martensite is suppressed.
  • the winding temperature is 650 ° C. or lower, the increase in YR can be suppressed.
  • the reason for this is considered to be that when the winding temperature is 650 ° C. or lower, excessive generation of Nb carbonitride is suppressed, and as a result, an increase in YS is suppressed.
  • Examples 1 to 26, Comparative Examples 1 to 31 ⁇ Manufacture of hot coils> Steel pieces having chemical compositions shown in Tables 1 and 2 were prepared.
  • the steel slab of Comparative Example 28 (S: 0.0015%) was produced under normal conditions.
  • a technique for optimizing the composition of slag used during refining, and a technique for replacing slag during refining Utilized the amount of S in the steel slab was controlled to be 0.0010% or less.
  • the steel slab is heated to 1250 ° C., the heated steel slab is hot-rolled to form a hot-rolled steel sheet, the obtained hot-rolled steel sheet is cooled at a cooling rate of 50 ° C./s, and the cooled hot-rolled steel sheet is cooled.
  • a hot coil made of a hot-rolled steel sheet was obtained by winding the steel sheet at a winding temperature of 550 ° C.
  • the time from the end of the final rolling in the hot rolling to the start of cooling was the time shown in Table 3.
  • each example and each comparative example the remainder excluding the elements shown in Tables 1 and 2 is Fe and impurities.
  • REM in Examples 18 and 19 is Ce
  • REM in Examples 23 and 24 is Nd
  • REM in Example 25 is La.
  • the numbers underlined are values outside the scope of the present disclosure.
  • the ferrite fraction was measured by the method described above, and the type of the second phase was confirmed.
  • TB means tempered bainite
  • P means pearlite.
  • test piece for the tensile test is oriented so that the test direction (tensile direction) of the tensile test is the pipe axis direction of the ERW steel pipe (hereinafter also referred to as “L direction”). Collected.
  • the shape of the test piece was a flat plate conforming to the American Petroleum Institute Standard API 5L (hereinafter simply referred to as “API 5L”).
  • a tensile test is performed in which the test direction is the L direction of the ERW steel pipe, the L direction TS of the ERW steel pipe, and the L direction of the ERW steel pipe YS of each was measured. Further, the YR (%) in the L direction of the ERW steel pipe was obtained by the calculation formula “(YS / TS) ⁇ 100”.
  • the specific precipitate area ratio (that is, the area ratio of precipitates having an equivalent circle diameter of 100 nm or less; simply expressed as “precipitate area ratio (%)” in Table 3) was measured by the method described above.
  • CLR (%) of HIC test (sour resistance)
  • the HIC test was performed according to NACE-TM0284.
  • a full-thickness test piece for the HIC test was collected from the base metal position of the ERW steel pipe at 90 ° C., and the collected full-thickness test piece was added to Solution A solution (5 mass% NaCl + 0.5 mass% glacial acetic acid aqueous solution) with 100% H 2. It was immersed for 96 hours in a test solution saturated with S gas. About the test piece after 96-hour immersion, the presence or absence of generation
  • production of HIC was measured with the ultrasonic flaw detector. Based on this measurement result, CLR (%) was calculated by the following formula. The smaller the CLR, the better the sour resistance. CLR (%) (total length of cracks / test piece length) ⁇ 100 (%)
  • the ERW steel pipe of each example has excellent sour resistance, a certain degree of tensile strength and yield strength, yield ratio is reduced, and the toughness of the base metal part and the welded part. It turns out that it is excellent.
  • Comparative Example 5 in which the amount of Mn was lower than the lower limit, the toughness of the base metal part and the welded part was lowered. The reason is considered to be that embrittlement due to S occurred.
  • Comparative Example 6 in which the amount of Mn exceeded the upper limit, the toughness of the base metal part and the welded part was lowered, and sour resistance was lowered. The reason for this is considered to be that a crack caused by MnS occurred.
  • Comparative Example 7 in which the Ti amount was below the lower limit, the toughness of the base material portion was lowered. The reason for this is considered to be that the crystal grains became coarse.
  • Comparative Example 8 in which the Ti amount exceeded the upper limit, the toughness of the base metal part and the welded part decreased.

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PCT/JP2017/010024 2016-07-06 2017-03-13 ラインパイプ用電縫鋼管 WO2018008194A1 (ja)

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