WO2021161366A1 - Line pipe-use electric resistance welded steel pipe - Google Patents

Line pipe-use electric resistance welded steel pipe Download PDF

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Publication number
WO2021161366A1
WO2021161366A1 PCT/JP2020/005072 JP2020005072W WO2021161366A1 WO 2021161366 A1 WO2021161366 A1 WO 2021161366A1 JP 2020005072 W JP2020005072 W JP 2020005072W WO 2021161366 A1 WO2021161366 A1 WO 2021161366A1
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Prior art keywords
resistance
electric
less
content
pipe
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PCT/JP2020/005072
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French (fr)
Japanese (ja)
Inventor
原　卓也
坂本　真也
修治 岩本
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日本製鉄株式会社
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Application filed by 日本製鉄株式会社 filed Critical 日本製鉄株式会社
Priority to EP20919182.4A priority Critical patent/EP4066954A4/en
Priority to KR1020227021826A priority patent/KR20220105166A/en
Priority to PCT/JP2020/005072 priority patent/WO2021161366A1/en
Priority to JP2021577721A priority patent/JP7226595B2/en
Publication of WO2021161366A1 publication Critical patent/WO2021161366A1/en

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    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
    • B21C37/06—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
    • B21C37/08—Making tubes with welded or soldered seams
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/085—Cooling or quenching
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • C21D9/505—Cooling thereof
    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/003—Cementite
    • 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
    • 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
    • C21D2211/009—Pearlite

Definitions

  • This disclosure relates to electric resistance sewn steel pipes for line pipes.
  • a pipeline is a system constructed on the ground or the seabed, and is a system for transferring oil and gas.
  • a pipeline is formed by connecting a plurality of line pipes.
  • As the steel pipe for such a line pipe an electrosewn steel pipe may be used.
  • the area where pipelines are constructed has expanded to areas with harsh environments such as the sour environment.
  • the sour environment including H 2 S is a corrosive gas, means acidified environment.
  • the pipeline constructed in the sour environment, the line pipe for forming the pipeline, and the steel pipe for the line pipe have sulfide stress cracking resistance (Sulfide Stress Cracking resistance: hereinafter referred to as SSC resistance). ) Is required.
  • Patent Document 1 Japanese Patent Application Laid-Open No. 6-41684 (Patent Document 1) and Japanese Patent Application Laid-Open No. 6-235405 (Patent Document 2) disclose techniques for improving the SCC resistance of electric resistance welded steel pipes for line pipes. There is.
  • the electrosewn steel pipe disclosed in Patent Document 1 has C: 0.05 to 0.35%, Si: 0.02 to 0.50%, Mn: 0.30 to 2.00%, Ca: 0.0005. It is made of steel containing ⁇ 0.0080%, Al: 0.005 to 0.100%, and the balance is Fe.
  • This electrosewn steel pipe has S, O, and Ca contents satisfying the formula (1.0 ⁇ (% Ca) ⁇ 1-72 (% O) ⁇ / 1.25 (% S) ⁇ 2.5).
  • the deoxidized product is a composite inclusion of (CaO) m (Al 2 O 3 ) n , and the hardness is measured within 30 mm on both sides with m / n ⁇ 1 and the electro-sewing abutment surface as the center.
  • the maximum value is 250 or less in Vickers hardness, and the difference between the maximum value and the minimum value is 30 or less in Vickers hardness.
  • Paragraph 0063 of Patent Document 1 describes that the electric resistance welded steel pipe has high strength and excellent sulfide stress corrosion cracking resistance even in a harsh environment with a low pH.
  • the electrosewn steel pipe disclosed in Patent Document 2 has a weight% of C: 0.05 to 0.35%, Si: 0.02 to 0.50%, Mn: 0.30 to 2.00%, P. : 0.030% or less, S: 0.005% or less, Ca: 0.0005 to 0.0080%, Al: 0.005 to 0.100%, and the content of S, O, Ca is the formula. (1.0 ⁇ (% Ca) ⁇ 1-72 (% O) ⁇ / 1.25 (% S) ⁇ 2.5) is satisfied, and the relationship between the amount of O and the amount of Ca is (% Ca) / (%). O) Satisfies ⁇ 0.55 and is made of steel consisting of the balance Fe and unavoidable impurities.
  • the maximum value of the measured hardness within 30 mm on both sides of the electric resistance joint surface is 250 or less in Vickers hardness, and the difference between the maximum value and the minimum value is 30 in Vickers hardness.
  • Paragraph 0059 of Patent Document 2 describes that the electric resistance welded steel pipe does not deteriorate the SSC characteristics even in a harsh environment with a low pH.
  • Patent Document 1 Japanese Patent Application Laid-Open No. 6-41684
  • Patent Document 2 Japanese Patent Application Laid-Open No. 6-235405
  • SSC sulfide stress cracking
  • SSC stress-dominated hydrogen-induced cracking
  • SOHIC -Oriented Hydrogen Induced Cracking
  • Patent Documents 1 and 2 do not describe SOHIC resistance. Therefore, even if the techniques disclosed in Patent Documents 1 and 2 are applied to the electrosewn steel pipe for line pipes used in a sour environment, excellent SOHIC resistance may not be obtained.
  • An object of the present disclosure is to provide an electrosewn steel pipe for a line pipe having excellent SSC resistance and SOHIC resistance.
  • Means for solving the above problems include the following aspects. ⁇ 1> Including the base metal part and the electric sewing welded part
  • the chemical composition of the base material is mass%. C: 0.030-0.090%, Si: 0.01-0.50%, Mn: 0.50 to 1.50%, P: 0 to 0.020%, S: 0 to 0.0020%, Nb: 0.005 to 0.060%, Ti: 0.005 to 0.030%, Ca: 0.0001 to 0.0040%, Al: 0 to 0.050%, N: 0.0010 to 0.0080%, O: 0 to 0.0030%, Cu: 0 to 0.500%, Ni: 0 to 0.500%, B: 0 to 0.0020%, V: 0 to 0.100%, Cr: 0 to 0.500%, Mo: 0 to 0.500%, W: 0 to 0.500%, Zr: 0-0.0500%, Ta: 0-0.0500%, Mg: 0 to 0.0050%, REM: 0-0.0050%, Hf:
  • the yield strength of the base material portion is 410 MPa or more, and the tensile strength of the base material portion is 515 to 650 MPa.
  • ⁇ YS which is a value obtained by subtracting the yield strength of the electric sewing welded portion from the yield strength of the base metal portion, is 0 to 80 MPa.
  • ⁇ Hv which is a value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded portion from the Vickers hardness of the outer surface layer of the electric sewing welded portion, is 0 to 25 Hv.
  • the chemical composition of the base material is mass%.
  • Cu More than 0% and less than 0.500%
  • Ni More than 0% and less than 0.500%
  • B More than 0% and less than 0.0020%
  • V More than 0% and less than 0.100%
  • Cr More than 0% and less than 0.500%
  • Mo More than 0% and less than 0.500%
  • W More than 0% and less than 0.500%
  • Zr More than 0% and less than 0.0500%
  • Ta More than 0% and less than 0.0500%
  • Mg More than 0% and less than 0.0050%
  • REM More than 0% and less than 0.0050%
  • Hf More than 0% and less than 0.0050%
  • Re Contains one or more selected from the group consisting of more than 0% and 0.0050% or less.
  • ⁇ 3> The electrosewn steel pipe for a line pipe according to ⁇ 1> or ⁇ 2>, which has a wall thickness of 13 mm or more.
  • ⁇ 4> The electric resistance welded steel pipe for a line pipe according to any one of ⁇ 1> to ⁇ 3>, which has an outer diameter of 300 mm to 650 mm.
  • an electrosewn steel pipe for a line pipe having excellent SSC resistance and SOHIC resistance is provided.
  • the numerical range represented by using “-” means a range including the numerical values before and after “-” as the lower limit value and the upper limit value.
  • “%” indicating the content of a component (element) means “mass%”.
  • the content of C (carbon) may be referred to as “C content”.
  • the content of other elements may be described in the same manner.
  • the term “process” is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. Is done.
  • the electrosewn steel pipe for line pipes of the present disclosure (hereinafter, also simply referred to as “the electrosewn steel pipe of the present disclosure”) includes a base material portion and an electrosewn welded portion, and the chemical composition of the base metal portion is C by mass%. : 0.030 to 0.090%, Si: 0.01 to 0.50%, Mn: 0.50 to 1.50%, P: 0 to 0.020%, S: 0 to 0.0020%, Nb: 0.005 to 0.060%, Ti: 0.005 to 0.030%, Ca: 0.0001 to 0.0040%, Al: 0 to 0.050%, N: 0.0010 to 0.
  • the polygonal ferrite content is 80% or more and less than 100%, the balance contains pseudo-pearlite and cementite, and the yield strength of the base material is 410 MPa or more.
  • the tensile strength of the base metal portion is 515 to 650 MPa, and ⁇ YS, which is the value obtained by subtracting the yield strength of the electrosewn welded portion from the yield strength of the base metal portion, is 0 to 80 MPa, and the outer surface layer of the electrosewn welded portion.
  • ⁇ Hv which is the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded portion from the Vickers hardness of the above, is 0 to 25 Hv.
  • the base metal portion refers to a portion of the electric resistance steel pipe other than the electric resistance welded portion and the heat-affected zone.
  • the heat-affected zone (sometimes referred to as "HAZ") refers to a portion in the vicinity of the electric sewing welded zone, which is affected by heat due to electric sewing welding and seam heat treatment. Point.
  • the electrosewn steel pipe of the present disclosure has excellent SSC resistance and SOHIC resistance. Hereinafter, this effect will be described in detail.
  • the present inventors satisfy all the requirements other than the requirements of ⁇ YS and ⁇ Hv (that is, the requirement that ⁇ YS is 0 to 80 MPa and ⁇ Hv is 0 to 25 Hv) in the electric resistance welded steel pipe of the present disclosure (that is, the electric resistance welded steel pipe that satisfies all the requirements.
  • the SSC resistance and SOHIC resistance of (hereinafter referred to as "electric pipe X") were investigated. As a result, it was found that the SSC resistance and / or the SOHIC resistance of the electric resistance welded portion of the electric resistance steel pipe X may be lowered. Therefore, the present inventors first considered the reason why the SSC resistance is lowered as follows.
  • the strength of the electric sewn welded part of the electric sewn steel pipe is generally higher than the strength of the base metal part (that is,). , ⁇ YS is a negative value). If the strength of the electric-sewn welded portion of the electric-sewn steel pipe is too high, SSC is likely to occur in the electric-sewn welded portion of the electric-sewn steel pipe. As a method of suppressing the generation of SSC, it is conceivable to apply a heat treatment (hereinafter, also referred to as "seam heat treatment”) to the electric stitch welded portion to reduce the strength of the electric stitch welded portion.
  • a heat treatment hereinafter, also referred to as "seam heat treatment
  • the electric resistance pipe X that is, the electric resistance pipe satisfying the requirements other than the requirements of ⁇ YS and ⁇ Hv in the present disclosure
  • the electric resistance welded portion It was found that SSC may occur in.
  • the yield strength of the electric resistance welded portion which is considered to be higher than the yield strength of the base metal portion, tends to be lower than the yield strength of the base metal portion (that is, ⁇ YS is high). It also tends to be a positive value). Therefore, the present inventors have examined in more detail the relationship between the SSC in the electric resistance welded portion of the electric resistance pipe X and the ⁇ YS in the electric resistance pipe X.
  • SSC Sulfide Stress Cracking
  • the internal pressure of the electric resistance welded steel pipe increased during use causes plastic strain (that is, strain in the plastic region) to be applied to the electric resistance welded portion.
  • plastic strain that is, strain in the plastic region
  • the plastic strain applied to is increased. As a result, hydrogen is occluded in the plastic strain of the electric stitch welded portion, and SSC is likely to be generated in the electric stitch welded portion. It is considered that SSC having the above mechanism is likely to occur in the electric resistance welded steel pipe X in which ⁇ YS tends to be a positive value.
  • the present inventors do not reduce the yield strength of the electric stitch welded portion too much, and bring the yield strength of the electric stitch welded portion close to the yield strength of the base metal portion, specifically, ⁇ YS is 0. It has been found that the SSC in the electric sewing welded portion can be suppressed (that is, the SSC resistance in the electric sewing welded portion can be improved) by adjusting the value to about 80 MPa.
  • the present inventors investigated the Vickers hardness of the electric resistance welded portion of the electric resistance steel pipe X in which ⁇ YS was 0 to 80 MPa. As a result, when ⁇ Hv, which is the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric stitch welded portion from the Vickers hardness of the outer surface layer of the electric stitch welded portion, exceeds 25 Hv, SOHIC is generated in the electric stitch welded portion. It was found that
  • the present inventors in the case where ⁇ YS is 0 to 80 MPa and ⁇ Hv is 0 to 25 Hv in the welded steel pipe X (that is, when it corresponds to the welded steel pipe of the present disclosure), the electric pipe is electric. It has been found that the SSC resistance and the SOHIC resistance of the sewn welded portion can be improved. That is, the present inventors have found that the above-described electrosewn steel pipe of the present disclosure has excellent SSC resistance and SOHIC resistance.
  • C 0.030-0.090%
  • C (carbon) is an element that enhances the strength of steel materials. If the C content is too low, the above effect may not be obtained. On the other hand, if the C content is too high, C may form carbides with alloying elements in the steel material, which may reduce the SSC resistance and SOHIC resistance of the steel material. Further, if the C content is too high, the strength of the steel material becomes too high, and ⁇ YS and ⁇ Hv become too large, and as a result, the SSC resistance and the SOHIC resistance of the steel material may decrease. Therefore, the C content is 0.030 to 0.090%.
  • the lower limit of the C content is preferably 0.035%, more preferably 0.040%.
  • the upper limit of the C content is preferably 0.080%, more preferably 0.070%.
  • Si 0.01-0.50% Si is an element that deoxidizes steel. If the Si content is too low, the above effect may not be obtained. On the other hand, if the Si content is too high, the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Si content is 0.01 to 0.50%.
  • the lower limit of the Si content is preferably 0.02%, more preferably 0.05%.
  • the upper limit of the Si content is preferably 0.40%, more preferably 0.35%.
  • Mn 0.50 to 1.50%
  • Mn is an element that deoxidizes steel. Mn is also an element that enhances the strength of steel materials. If the Mn content is too low, the above effect may not be obtained. On the other hand, if the Mn content is too high, the strength of the steel material may become too high. In this case, ⁇ YS may be further increased, and ⁇ Hv may be further increased. In these cases, the SSC resistance and SOHIC resistance of the steel material are lowered. Therefore, the Mn content is 0.50 to 1.50%.
  • the lower limit of the Mn content is preferably 0.60%, more preferably 0.80%, and even more preferably 1.00%.
  • the upper limit of the Mn content is preferably 1.40%, more preferably 1.35%.
  • P 0 to 0.020%
  • P (phosphorus) is an impurity.
  • the P content may be 0% or more than 0%.
  • P may segregate at the grain boundaries and reduce the SSC resistance and / or the SOHIC resistance of the steel material. Therefore, the P content is 0 to 0.020%.
  • the upper limit of the P content is preferably 0.015%, more preferably 0.013%.
  • the P content is preferably as low as possible. However, an extreme reduction in P content may significantly increase the manufacturing cost of steel materials. Therefore, when considering industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.005%.
  • S is an impurity.
  • the S content may be 0% or more than 0%.
  • S may segregate at the grain boundaries and reduce the SSC resistance and / or the SOHIC resistance of the steel material. Therefore, the S content is 0 to 0.0020%.
  • the upper limit of the S content is preferably 0.0015%, more preferably 0.0010%, and even more preferably 0.0008%.
  • the S content is preferably as low as possible. However, an extreme reduction in the S content may significantly increase the manufacturing cost of the steel material. Therefore, when considering industrial production, the lower limit of the S content is preferably 0.0001%, more preferably 0.0002%.
  • Nb 0.005 to 0.060%
  • Nb is an element that combines with C (carbon) and / or N (nitrogen) to form carbides, nitrides or carbonitrides (hereinafter referred to as "carbonitrides and the like").
  • the carbonitride and the like refine the substructure of the steel material by the pinning effect, and enhance the SSC resistance and / or the SOHIC resistance of the steel material. If the Nb content is too low, the above effect may not be obtained. On the other hand, if the Nb content is too high, the carbonitride and the like may become coarse, and the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Nb content is 0.005 to 0.060%.
  • the lower limit of the Nb content is preferably 0.008%, more preferably 0.010%.
  • the upper limit of the Nb content is preferably 0.055%, more preferably 0.050%, and even more preferably 0.045%.
  • Ti 0.005 to 0.030%
  • Ti is an element that combines with N (nitrogen) to form a nitride.
  • the nitride refines the crystal grains by the pinning effect. As a result, the SSC resistance and / or the SOHIC resistance of the steel material is enhanced. If the Ti content is too low, the above effect may not be obtained. On the other hand, if the Ti content is too high, the nitride may become coarse and the SSC resistance and / or SOHIC resistance of the steel material may decrease. Therefore, the Ti content is 0.005 to 0.030%.
  • the lower limit of the Ti content is preferably 0.006%, more preferably 0.007%, and even more preferably 0.008%.
  • the upper limit of the Ti content is preferably 0.025%, more preferably 0.020%, and even more preferably 0.017%.
  • Ca 0.0001 to 0.0040%
  • Ca is an element that controls the morphology of sulfides in steel materials and enhances SSC resistance and / or SOHIC resistance of steel materials. If the Ca content is too low, the above effect may not be obtained. On the other hand, if the Ca content is too high, coarse oxide-based inclusions may be formed, and the SSC resistance and / or SOHIC resistance of the steel material may decrease. Therefore, the Ca content is 0.0001 to 0.0040%.
  • the lower limit of the Ca content is preferably 0.0005%, more preferably 0.0010%.
  • the upper limit of the Ca content is preferably 0.0035%, more preferably 0.0030%.
  • Al 0 to 0.050%
  • Al is an arbitrary element. That is, the Al content may be 0% or more than 0%. If the Al content is too high, coarse oxide-based inclusions are formed, and the SSC resistance and / or SOHIC resistance of the steel material is lowered. Therefore, the Al content is 0 to 0.050%.
  • the upper limit of the Al content is preferably 0.045%, more preferably 0.040%.
  • Al is an element that deoxidizes steel. From the viewpoint of obtaining such an effect, the lower limit of the Al content is preferably 0.0005%, more preferably 0.0010%, and further preferably 0.0015%.
  • N is an element that combines with Ti to form fine nitrides to refine the crystal grains of the steel material and enhance the SSC resistance and SOHIC resistance of the steel material. If the N content is too low, the above effect may not be obtained. On the other hand, if the N content is too high, the nitride may become coarse and the SSC resistance and / or SOHIC resistance of the steel material may decrease. Therefore, the N content is 0.0010 to 0.0080%.
  • the lower limit of the N content is preferably 0.0015%, more preferably 0.0020%.
  • the upper limit of the N content is preferably 0.0070%, more preferably 0.0060%, and even more preferably 0.0050%.
  • O is an impurity.
  • the O content may be 0% or more than 0%.
  • O is an element that forms a coarse oxide and lowers the SSC resistance and / or the SOHIC resistance of the steel material. Therefore, the O content is 0.0030% or less.
  • the upper limit of the O content is preferably 0.0028%, more preferably 0.0025%.
  • the O content is preferably as low as possible. However, an extreme reduction in O content significantly increases the manufacturing cost of steel materials. Therefore, when considering industrial production, the lower limit of the O content is preferably 0.0001%, more preferably 0.0003%, still more preferably 0.0010%, still more preferably 0. It is 0015%.
  • Cu 0 to 0.500%
  • the Cu content may be 0% or more than 0%. If the Cu content is too high, the strength of the steel material may become too high, and the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Cu content is 0 to 0.500%.
  • the upper limit of the Cu content is preferably 0.450%, more preferably 0.400%.
  • Cu is an element that dissolves in a steel material to increase the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Cu content is preferably more than 0%, more preferably 0.010%, further preferably 0.020%, still more preferably 0.030%. be.
  • Ni is an optional element. That is, the Ni content may be 0% or more than 0%. If the Ni content is too high, the strength of the steel material may become too high, and the SSC resistance and SOHIC resistance of the steel material may decrease, and further, the electric sewing weldability of the steel material may decrease. Therefore, the Ni content is 0 to 0.500%.
  • the upper limit of the Ni content is preferably 0.450%, more preferably 0.400%.
  • Ni is an element that dissolves in a steel material to increase the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Ni content is preferably more than 0%, more preferably 0.010%, further preferably 0.050%, still more preferably 0.100%. be.
  • B 0 to 0.0020%
  • B (boron) is an optional element. That is, the B content may be 0% or more than 0%. If the B content is too high, coarse nitrides may be formed, which may reduce the SSC resistance and SOHIC resistance of the steel material. Therefore, the B content is 0 to 0.0020%.
  • the upper limit of the B content is preferably 0.0015%, more preferably 0.0012%.
  • B is an element that dissolves in the steel material to increase the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the content of B is preferably more than 0%, more preferably 0.0001%, further preferably 0.0002%, still more preferably 0.0003%. Is.
  • V 0 to 0.100%
  • V vanadium
  • the V content may be 0% or more than 0%. If the V content is too high, the low temperature toughness of the steel material may decrease. Therefore, the V content is 0 to 0.100%.
  • the upper limit of the V content is preferably 0.090%, more preferably 0.080%.
  • V is an element that forms a carbonitride or the like and enhances the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the V content is preferably more than 0%, more preferably 0.001%, still more preferably 0.005%, still more preferably 0.010%. be.
  • Cr 0 to 0.500%
  • Cr is an arbitrary element. That is, the Cr content may be 0% or more than 0%. If the Cr content is too high, the SSC resistance of the steel material may decrease. Therefore, the Cr content is 0 to 0.500%.
  • the upper limit of the Cr content is preferably 0.450%, more preferably 0.400%.
  • Cr is an element that forms carbides to increase the strength of steel materials. From the viewpoint of obtaining such an effect, the lower limit of the Cr content is preferably more than 0%, more preferably 0.010%, further preferably 0.050%, still more preferably 0.100%. be.
  • Mo 0 to 0.500%
  • Mo is an arbitrary element. That is, the Mo content may be 0% or more than 0%. When Mo content is too high, M 2 C type carbides are excessively generated, it may decrease the SSC resistance of the steel. Therefore, the Mo content is 0 to 0.500%.
  • the upper limit of the Mo content is preferably 0.450%, more preferably 0.400%.
  • Mo is an element that forms carbides to increase the strength of steel materials. From the viewpoint of obtaining such an effect, the lower limit of the Mo content is preferably more than 0%, more preferably 0.010%, further preferably 0.050%, still more preferably 0.100%. be.
  • W 0 to 0.500%
  • W is an optional element. That is, the W content may be 0% or more than 0%. If the W content is too high, coarse carbides may be formed in the steel material, which may reduce the SSC resistance of the steel material. Therefore, the W content is 0 to 0.500%.
  • the upper limit of the W content is preferably 0.450%, more preferably 0.400%.
  • W is an element that increases the strength of the steel material. W is also an element that forms a protective corrosive film in a hydrogen sulfide environment, suppresses hydrogen intrusion, and as a result, enhances SSC resistance and SOHIC resistance of steel materials. From the viewpoint of obtaining these effects, the lower limit of the W content is preferably more than 0%, more preferably 0.001%, still more preferably 0.050%, still more preferably 0.100%. Is.
  • Zr 0-0.0500%
  • Zr is an arbitrary element. That is, the Zr content may be 0% or more than 0%. If the Zr content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Zr content is 0-0.0500%.
  • the upper limit of the Zr content is preferably 0.0400%, more preferably 0.0300%.
  • Zr is an element that refines sulfide in the steel material and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Zr content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
  • Ta 0-0.0500%
  • the Ta content may be 0% or more than 0%. If the Ta content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Ta content is 0 to 0.0500%.
  • the upper limit of the Ta content is preferably 0.0400%, more preferably 0.0300%.
  • Ta is an element that refines sulfide in the steel material and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Ta content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
  • Mg 0 to 0.0050%
  • Mg is an optional element. That is, the Mg content may be 0% or more than 0%. If the Mg content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Mg content is 0 to 0.0050%.
  • the upper limit of the Mg content is preferably 0.0045%, more preferably 0.0040%.
  • Mg is an element that detoxifies S in the steel material as a sulfide and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Mg content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
  • REM 0-0.0050% REM is an optional element. That is, the REM content may be 0% or more than 0%.
  • REM is selected from the group consisting of rare earth elements, that is, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It means at least one element to be produced.
  • the REM content means the total content of rare earth elements. If the REM content is too high, the oxide becomes coarse and the SSC resistance and SOHIC resistance of the steel material deteriorate. Therefore, the REM content is 0 to 0.0050%.
  • REM is an element that controls the morphology of sulfide in the steel material to enhance the SSC resistance and SOHIC resistance of the steel material.
  • REM is also an element that binds to P in the steel material and suppresses segregation of P at the grain boundaries, thereby suppressing a decrease in low temperature toughness of the steel material due to segregation of P.
  • the lower limit of the REM content is preferably more than 0%, more preferably 0.0001%, still more preferably 0.0003%, still more preferably 0.0005%. Is.
  • Hf 0 to 0.0050%
  • Hf is an arbitrary element. That is, the Hf content may be 0% or more than 0%. If the Hf content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Hf content is 0 to 0.0050%.
  • the upper limit of the Hf content is preferably 0.0045%, more preferably 0.0040%.
  • Hf is an element that controls the morphology of sulfide in the steel material to enhance the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Hf content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
  • Re 0-0.0050%
  • the Re content may be 0% or more than 0%. If the Re content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease. Therefore, the Re content is 0 to 0.0050%.
  • the upper limit of the Re content is preferably 0.0045%, more preferably 0.0040%.
  • Re is an element that controls the morphology of sulfide in the steel material and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Re content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
  • Remaining part Fe and impurities
  • the balance excluding each element described above is Fe and impurities.
  • the impurity refers to a component contained in a raw material (for example, ore, scrap, etc.) or a component mixed in a manufacturing process and not intentionally contained in steel.
  • Impurities include any element other than the elements described above.
  • the element as an impurity may be only one kind or two or more kinds. Examples of impurities include Sb, Sn, Co, As, Pb, Bi, H (hydrogen) and the like.
  • Sb, Sn, Co, and As are mixed with a content of 0.1% or less
  • Pb and Bi are mixed with a content of 0.005% or less
  • H is mixed with a content of, for example, 0.005% or less.
  • contamination is 0.0004% or less. It is not necessary to control the content of other elements as long as it is within the normal range.
  • the chemical composition of the base metal is Cu: more than 0% and 0.500% or less, Ni: more than 0% and 0.500% or less, and B: more than 0% and 0.0020 from the viewpoint of obtaining the effect of each of the above-mentioned arbitrary elements.
  • V more than 0% and less than 0.100%
  • Cr more than 0% and less than 0.500%
  • Mo more than 0% and less than 0.500%
  • W more than 0% and less than 0.500%
  • Zr 0 % More than 0.0500% or less
  • Ta More than 0% and less than 0.0500%
  • Mg More than 0% and less than 0.0050%
  • REM More than 0% and less than 0.0050%
  • Hf More than 0% and 0.0050% It may contain one or more selected from the group consisting of the following and Re: more than 0% and 0.0050% or less.
  • the preferable ranges of the contents of these arbitrary elements are as described above.
  • the electrosewn steel pipe of the present disclosure has a polygonal ferrite fraction (hereinafter, also referred to as “F fraction”) of 80% or more and less than 100% in the metal structure of the inner surface layer of the base metal portion, and the balance is pseudo pearlite and Contains cementite.
  • the metallographic structure of the inner surface layer of the base metal portion has ⁇ YS and the above-mentioned chemical composition A, and the tensile strength of the base metal portion is in the range of 515 to 650 MPa. It is a metal structure that is a prerequisite for obtaining the effect of sour resistance (specifically, SSC resistance and SOHIC resistance) according to the requirement of ⁇ Hv.
  • the F fraction in the metal structure of the inner surface layer of the base metal portion is less than 80%, the strength of the base metal portion becomes too high and ⁇ YS and ⁇ Hv become too large, and as a result, the SSC resistance and SOHIC resistance of the steel material become too large. Sex may be reduced. Therefore, the F fraction in the metal structure of the inner surface layer of the base metal portion is 80% or more, preferably 83% or more, more preferably 85% or more, and further preferably 90% or more. If the F fraction in the metal structure of the inner surface layer of the base metal portion is 100%, the tensile strength and yield strength of the base metal portion may become too low. Therefore, the F fraction in the metal structure of the inner surface layer of the base metal portion is less than 100%, preferably 98% or less, and more preferably 95% or less.
  • the rest of the metal structure of the inner surface layer of the base metal portion excluding the polygonal ferrite contains pseudo pearlite and cementite.
  • the balance is preferably composed of pseudo-pearlite and cementite.
  • the measurement of the F fraction and the confirmation of the type of the remaining portion in the metal structure of the inner surface layer of the base metal portion are performed as follows.
  • L cross section that is, a cross section parallel to the pipe axial direction and the wall thickness direction of the power sewn steel pipe) at the 180 ° position of the base material in the power sewn steel pipe (that is, the position shifted by 180 ° in the pipe circumferential direction from the power sewn welded portion).
  • a metallographic photograph at a depth of 1 mm from the inner surface of the electrosewn steel pipe in the L cross section after the tital etching is taken with a scanning electron microscope (SEM) at a magnification of 200 times.
  • SEM scanning electron microscope
  • the electrosewn steel pipe of the present disclosure has a tensile strength (TS) of a base material portion of 515 to 650 MPa.
  • TS of the base material portion means the tensile strength in the pipe axis direction.
  • the TS of the base material portion is preferably 520 MPa or more, more preferably 530 MPa or more.
  • the SSC resistance and the SOHIC resistance of the base material portion are improved.
  • the TS of the base metal portion is preferably 640 MPa or less, more preferably 630 MPa or less.
  • the yield strength (YS) of the base metal portion of the electrosewn steel pipe of the present disclosure is 410 MPa or more.
  • YS of the base metal portion means the yield strength in the pipe axis direction.
  • the YS of the base material portion is preferably 430 MPa or more, more preferably 450 MPa or more.
  • the YS of the base material portion is preferably 630 MPa or less.
  • the YS of the base material portion is 630 MPa or less, it is advantageous in terms of SSC resistance and SOHIC resistance of the base material portion. Further, when the YS of the base material portion is 630 MPa or less, it is advantageous in terms of bending deformability or buckling suppression when laying a pipeline formed by using an electrosewn steel pipe for a line pipe.
  • the YS of the base material portion is more preferably 620 MPa or less, further preferably 610 MPa or less, and further preferably 600 MPa or less.
  • the TS of the base material and the YS of the base material are measured by the following method in accordance with ASTM E8 (2013).
  • a round bar test piece having a diameter of 6 mm and a parallel part length of 35 mm is obtained from the center of the wall thickness at the 180 ° position of the base metal of the electric resistance pipe. Collect in the direction parallel to the pipe axis direction.
  • a tensile test (that is, a tube axial tensile test) is carried out in the air at room temperature (25 ° C.) in accordance with ASTM E8 (2013).
  • the maximum stress during uniform elongation in the above tensile test is defined as TS (MPa) of the base metal portion.
  • the 0.2% proof stress in the above tensile test is defined as YS (MPa) of the base material portion.
  • the yield elongation is substantially not observed when the pipe axial tensile test (for example, the above-mentioned tensile test) is performed.
  • the fact that the yield elongation is substantially not observed means that the yield elongation is less than 1%.
  • the fact that the yield elongation is not substantially observed in the pipe axial tensile test of the base metal portion means that the electric pipe is an as-rolled electric pipe.
  • the azurol electric resistance pipe means an electric pipe that has not been subjected to a heat treatment other than the seam heat treatment after the pipe is made.
  • an electrosewn steel pipe that has been subjected to a heat treatment (for example, tempering) other than the seam heat treatment after the pipe is made has a substantial yield elongation (yield elongation of 1% or more) when a tensile test in the pipe axial direction is performed. Is observed.
  • the YR of the base metal portion means the yield ratio in the pipe axis direction.
  • the YR of the base metal portion is preferably 0.97 or less, more preferably 0.97 or less. It is 0.96 or less. Examples of the lower limit of YR of the base material portion include 0.85 and 0.86.
  • ⁇ YS (that is, a value obtained by subtracting the yield strength of the electric resistance welded portion from the yield strength of the base metal portion) is 0 to 80 MPa.
  • ⁇ YS is 0 to 80 MPa, the generation of SSC in the electric sewing welded portion is suppressed (that is, the SSC resistance in the electric sewing welded portion is improved).
  • ⁇ YS is 80 MPa or less, preferably 70 MPa or less.
  • the fact that ⁇ YS is 0 MPa or more contributes to the manufacturing suitability of the electrosewn steel pipe of the present disclosure.
  • the yield strength of the electric stitch welded portion is higher than the yield strength of the base metal portion.
  • the yield strength of the electric resistance welded portion is equal to or lower than the yield strength of the base metal portion (specifically, ⁇ YS is 0 MPa or more). Is).
  • the method for measuring the yield strength (YS) of the base metal portion for calculating ⁇ YS is as described above.
  • the yield strength (YS) of the electric stitch welded portion for calculating ⁇ YS is measured by the following method in accordance with ASTM E8 (2013).
  • a round bar test piece having a diameter of 6 mm and a parallel portion length of 35 mm is obtained from a region including an electrosewn welded portion on the inner surface side of the electrosewn steel pipe. Collect so that it is parallel to the circumferential direction of the pipe. More specifically, the round bar test piece is collected so that the center of the parallel portion in the round bar test piece in the longitudinal direction and the electric stitch welding abuttal line of the electric resistance pipe are substantially aligned with each other.
  • substantially the same means that the center of the parallel portion in the longitudinal direction and the electric resistance welding abuttal line of the electric resistance pipe are completely coincident with each other, or the deviation between the two is within 1 mm. ..
  • a tensile test that is, a tensile test in the circumferential direction of the tube
  • the 0.2% proof stress in the above tensile test is defined as YS (MPa) of the electric stitch welded portion.
  • ⁇ Hv (that is, the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded portion from the Vickers hardness of the outer surface layer of the electric sewing welded portion) is 0 to 25 Hv.
  • ⁇ Hv is 0 to 25 Hv, the generation of SOHIC in the electric stitch welded portion is suppressed (that is, the SOHIC resistance in the electric stitch welded portion is improved).
  • ⁇ YS is 0 to 80 MPa
  • ⁇ Hv is more than 25 Hv, SOHIC may occur in the electric stitch welded portion. Therefore, ⁇ Hv is 25 Hv or less, preferably 20 Hv, more preferably 18 Hv, and even more preferably 15 Hv.
  • ⁇ Hv is 0 Hv or more contributes to the manufacturing suitability of the electrosewn steel pipe of the present disclosure.
  • the Vickers hardness of the outer surface layer of the electrosewn welded portion is determined as follows. In the C cross section of the electric resistance pipe (that is, the cross section perpendicular to the pipe axis direction), it is on a line corresponding to a depth of 1 mm from the outer surface of the electric resistance pipe, and is centered on the electric resistance welding abutment line. Five points with a 0.5 mm pitch within a range of 2 mm in the circumferential direction of the pipe are specified as measurement points. At each of the five measurement points, the Vickers hardness is measured in accordance with JIS Z 2244 (2009) under the condition of a load of 100 gf. The arithmetic mean value of the measured values at the five measurement points is defined as "Vickers hardness of the outer surface layer of the electric stitch welded portion".
  • the Vickers hardness of the inner surface layer of the electrosewn welded portion is determined as follows.
  • the pitch is 0.5 mm on the line corresponding to the position of 1 mm in depth from the inner surface of the electric resistance welded steel pipe and within the range of 2 mm in the circumferential direction of the electric pipe centered on the electric resistance welding abuttal line. 5 points are specified as measurement points.
  • the Vickers hardness is measured in accordance with JIS Z 2244 (2009) under the condition of a load of 100 gf.
  • the arithmetic mean value of the measured values at the five measurement points is defined as "Vickers hardness of the inner surface layer of the electric stitch welded portion".
  • ⁇ Hv is the “Vickers hardness of the inner surface layer of the electric sewing welded portion” obtained as described above from the “Vickers hardness of the outer surface layer of the electric sewing welded portion” obtained as described above. Is calculated by subtracting.
  • ⁇ Thickness of electric resistance pipe> when the wall thickness of the electric pipe X (that is, the electric pipe satisfying the requirements other than the requirements of ⁇ YS and ⁇ Hv in the electric pipe of the present disclosure) is thick (specifically). It was found that when ⁇ YS is 13 mm or more, there is a strong tendency for ⁇ YS to take a large positive value, and there is a strong tendency for SSC to occur in the electric resistance welded portion.
  • the wall thickness of the electrosewn steel pipe of the present disclosure is preferably 13 mm or more, more preferably 14 mm or more, in that the effect of improving the sour resistance due to the requirements of ⁇ YS and ⁇ Hv is large.
  • the wall thickness of the electrosewn steel pipe of the present disclosure is preferably 25 mm or less, more preferably 23 mm or less, and further, from the viewpoint of further suppressing the occurrence of SSC in the electrosewn welded portion due to the thick wall thickness. It is preferably 20 mm or less.
  • the outer diameter of the electrosewn steel pipe of the present disclosure is not particularly limited, but is preferably 300 to 650 mm.
  • the outer diameter is more preferably 330 mm or more, still more preferably 350 mm or more.
  • the outer diameter is 650 mm or less, the manufacturing suitability of the electrosewn steel pipe is excellent.
  • the outer diameter is preferably 630 mm or less, more preferably 610 mm or less.
  • SSC resistance and SOHIC resistance of electrosewn steel pipe can be evaluated by a 4-point bending test. The details will be described below.
  • a mixed aqueous solution NACE solution A
  • a rectangular parallelepiped test piece having a length of 120 mm, a width of 10 mm, and a thickness of 2 mm is collected from a region including an electric stitch welded portion on the inner surface side of the electric resistance pipe.
  • the length direction of the test piece is the pipe circumferential direction of the electric resistance pipe
  • the width direction of the test piece is the pipe axial direction of the electric resistance pipe
  • the thickness direction of the test piece is the electric resistance steel pipe. Collect in the direction of the wall thickness.
  • the center of the rectangular parallelepiped test piece in the longitudinal direction and the electric resistance welding abuttal line of the electric resistance pipe are collected so as to be substantially coincident with each other.
  • substantially coincident means that the center in the longitudinal direction of the rectangular parallelepiped test piece and the electric resistance welding abuttal line of the electric resistance pipe are completely coincident with each other, or the deviation between the two is within 1 mm. Means.
  • a 4-point bending stress is applied to the collected rectangular parallelepiped test piece using a 4-point bending test jig in accordance with ASTM G39-99 (2011).
  • the load of the four-point bending stress is performed with the distance between the support points (that is, the distance between the outer support points) being 100 mm and the distance between the load points (that is, the distance between the inner support points) being 40 mm.
  • the four-point bending stress applied to the test piece is a stress corresponding to 90% of YS in the tube axial direction of the base metal portion.
  • the test piece with the 4-point bending stress applied is sealed in the test container together with the 4-point bending test jig.
  • test bath is injected into this test container leaving the gas phase portion, and the test piece is immersed in the test bath. Subsequently, after degassing the test bath, by stirring the test bath while continuously bubbling H 2 S gas 1 atm, to saturate the H 2 S gas in a test bath. Next, after sealing the test container, the test bath in which the test piece is immersed is held at 24 ° C. for 720 hours, and then the test piece is taken out. The test piece taken out is observed, and the presence or absence of SSC and SOHIC is determined. When neither SSC nor SOHIC is generated, it can be judged that the SSC resistance and the SOHIC resistance are excellent.
  • SSC and SOHIC are distinguished by the shape of the crack. Specifically, a crack extending in both the pipe axis direction and the wall thickness direction is referred to as SOHIC, and a crack extending in the wall thickness direction but not extending in the pipe axis direction is referred to as SSC.
  • manufacturing method A ⁇ Example of manufacturing method of electric resistance steel pipe (manufacturing method A)>
  • manufacturing method A an example of a manufacturing method for manufacturing the electric resistance welded steel pipe of the present disclosure (hereinafter, referred to as “manufacturing method A”) will be described.
  • the following manufacturing method A is a manufacturing method of an electrosewn steel pipe according to an embodiment described later.
  • Manufacturing method A is A slab preparation step for preparing a slab having a chemical composition A (that is, the chemical composition of the base metal portion in the present disclosure), A hot-rolling process in which the prepared slab is hot-rolled under the conditions described below to obtain a hot-rolled steel sheet, A hot-rolled steel sheet water-cooling process in which the hot-rolled steel sheet is water-cooled until the temperature of the outer surface of the hot-rolled steel sheet reaches a winding temperature of 450 to 625 ° C. A winding process for obtaining a hot coil made of a hot-rolled steel sheet by winding the cooled hot-rolled steel sheet at the above-mentioned winding temperature.
  • a hot-rolling process in which the prepared slab is hot-rolled under the conditions described below to obtain a hot-rolled steel sheet
  • a hot-rolled steel sheet water-cooling process in which the hot-rolled steel sheet is water-cooled until the temperature of the outer surface of the hot-rolled steel sheet reaches a winding temperature of 450 to 625 ° C.
  • a hot-rolled steel sheet is unwound from a hot coil, and the unwound hot-rolled steel sheet is roll-formed to form an open pipe, and the abutting portion of the obtained open pipe is electrosewn to form an electrosewn welded portion.
  • the pipe making process to obtain the raw pipe by The electric-sewn welded part of the raw pipe is heated to a heating temperature of 900 to 1000 ° C., soaked at the above heating temperature for 1 second or longer, and then to a cooling stop temperature of 300 to 580 ° C., 5 to 20 ° C./sec.
  • Seam heat treatment process that performs seam heat treatment to cool with water at the cooling rate of including.
  • the raw pipe means an electro-sewn steel pipe before the seam heat treatment is applied to the electro-sewn welded portion.
  • the electrosewn steel pipe of the present disclosure can be manufactured.
  • each step in the manufacturing method A will be described.
  • the slab preparation step in the production method A is a step of preparing a slab having the above-mentioned chemical composition.
  • the step of preparing the slab may be a step of manufacturing the slab, or may be a step of simply preparing the slab that has been manufactured in advance.
  • a molten steel having the above-mentioned chemical composition is produced, and the produced molten steel is used to produce a slab.
  • a slab may be produced by a continuous casting method, or an ingot may be produced using molten steel, and the ingot may be lump-rolled to produce a slab.
  • the hot-rolling step in the manufacturing method A is a step of heating the slab prepared above and hot-rolling the heated slab to obtain a hot-rolled steel sheet.
  • the slab heating temperature when heating the slab is 1100 to 1250 ° C.
  • the heating temperature is 1100 ° C. or higher, the refinement of crystal grains during hot rolling and the precipitation strengthening after hot rolling are more likely to proceed, and as a result, the strength of steel is more likely to be improved.
  • the heating temperature is 1250 ° C. or lower, the coarsening of the austenite grains can be further suppressed, so that the crystal grains can be easily refined, and as a result, the strength of the steel can be further improved.
  • the slab is heated by, for example, a heating furnace.
  • the slab heating temperature means the temperature of the outer surface of the slab.
  • the slab heated above is hot-rolled to obtain a hot-rolled steel sheet.
  • the hot rolling is preferably performed under the condition that the finish rolling end temperature (hereinafter, also referred to as “finish rolling temperature”) is 780 to 930 ° C.
  • Hot rolling is generally performed using a rough rolling mill and a finishing rolling mill. Both the rough rolling mill and the finishing rolling mill generally have a plurality of rolling stands arranged in a row, and each rolling stand has a roll pair.
  • the finish rolling temperature (that is, the finish rolling end temperature) is the surface temperature of the hot-rolled steel sheet on the outlet side of the final stand of the finish rolling machine.
  • the finish rolling temperature is 780 ° C. or higher, the rolling resistance of the steel sheet can be reduced, so that the productivity is improved. Further, when the finish rolling temperature is 780 ° C. or higher, the phenomenon of rolling in the two-phase region of ferrite and austenite is suppressed, and the formation of a layered structure and the deterioration of mechanical properties due to this phenomenon can be suppressed. On the other hand, when the finish rolling temperature is 930 ° C. or lower, the phenomenon that the hot-rolled steel sheet becomes too hard is suppressed, so that the phenomenon that the TS of the base material portion of the obtained electro-sewn steel pipe becomes too high is suppressed.
  • the hot-rolled steel sheet water-cooling step is a step of water-cooling the hot-rolled steel sheet until the temperature of the outer surface of the hot-rolled steel sheet reaches a winding temperature of 450 to 625 ° C.
  • the winding temperature (that is, the cooling end temperature of the outer surface of the hot-rolled steel sheet) is 450 ° C. or higher.
  • the winding temperature is preferably 500 ° C. or higher.
  • the winding temperature is preferably 600 ° C. or lower.
  • a hot-rolled steel sheet is unwound from a hot coil, and the unwound hot-rolled steel sheet is roll-formed to form an open pipe.
  • This is a step of obtaining a raw pipe (that is, an electro-sewn steel pipe before the seam heat treatment is applied to the electro-sewn welded portion) by forming the portion.
  • the seam heat treatment step in the manufacturing method A is a step of performing a seam heat treatment on the electric resistance welded portion of the raw pipe (that is, the electric resistance welded steel pipe before the seam heat treatment is applied to the electric resistance welded portion).
  • the electric sewing welded portion in the raw pipe is heated to a heating temperature of 900 to 1000 ° C., soaked at the above heating temperature for 1 second or more, and then to a cooling stop temperature of 300 to 580 ° C. It is a process of water cooling at a cooling rate of 5 to 20 ° C./sec. After water cooling, air cool until the temperature of the electrosewn weld reaches room temperature.
  • the seam heat treatment in the manufacturing method A is performed by heating and cooling the electric sewing welded portion before the seam heat treatment from the outer surface side of the electric sewing welded portion in this order. More specifically, the seam heat treatment in the production method A is performed as follows. First, the electrosewn welded portion before the seam heat treatment is heated from the outer surface side by induction heating until the temperature of the outer surface reaches a heating temperature in the range of 900 to 1000 ° C., and the temperature of the outer surface is heated in the above range. The heat is equalized by holding the temperature in the state of the temperature for an equalizing time in the range of 1 second or more (preferably 1 second to 5 seconds).
  • the electrosewn welded portion after heat equalization is water-cooled from the outer surface side at a cooling rate in the range of 5 to 20 ° C./sec to a cooling shutdown temperature in the range of 300 to 580 ° C.
  • a cooling rate in the range of 5 to 20 ° C./sec the water-cooled shower is made into a mist, the flow rate of the water-cooled shower is adjusted, and the angle of the water-cooled shower is adjusted. And so on.
  • the heating temperature is the temperature of the outer surface of the electric sewing welded portion
  • the cooling rate is the cooling rate on the outer surface of the electric sewing welded portion.
  • the cooling stop temperature is the reheat temperature after stopping the water cooling, which is measured on the outer surface of the electric sewing welded portion, and is the maximum temperature measured within 1 minute after the water cooling is stopped.
  • the heating temperature in the seam heat treatment step of the production method A is 900 ° C. or higher.
  • the heating temperature in the seam heat treatment step in the production method A is 1000 ° C. or lower.
  • the cooling shutdown temperature in the seam heat treatment step of the production method A is 300 ° C. or higher.
  • the cooling shutdown temperature in the seam heat treatment step when the cooling shutdown temperature is more than 580 ° C., the YS of the electric stitch welded portion tends to be too low, and the ⁇ YS tends to be more than 80 MPa.
  • the cooling shutdown temperature in the seam heat treatment step of the production method A is 580 ° C. or lower.
  • the cooling rate in the seam heat treatment step of the production method A is 5 ° C./sec or more.
  • the cooling rate in the seam heat treatment step of the production method A is 20 ° C./sec or less.
  • the production method A may include other steps other than the above-mentioned steps.
  • Other steps include a step of adjusting the shape of the electrosewn steel pipe with a sizing roll after the seam heat treatment step.
  • Each step in manufacturing method A does not affect the chemical composition of steel. Therefore, by using a molten steel or a slab having a chemical composition A, an electrosewn steel pipe having a chemical composition of the base material portion A is manufactured.
  • the underline in Tables 1 to 3 means that the pipe is out of the range of the electric resistance welded steel pipe of the present disclosure or is out of the range of the manufacturing method A.
  • Test numbers 1 to 22 are examples, and test numbers 23 to 43 are comparative examples.
  • the above slab is heated in a heating furnace, and the heated slab is hot-rolled using a plurality of hot-rolled mills to obtain a hot-rolled steel sheet, and the obtained hot-rolled steel sheet is water-cooled to obtain a water-cooled hot-rolled steel sheet.
  • a hot coil made of hot-rolled steel sheet was obtained.
  • the heating temperature when heating the slab is set to 1200 ° C.
  • the finish rolling temperature in hot rolling is 790 ° C to 930 ° C.
  • the winding temperature was 500 ° C. to 600 ° C.
  • the soaking time in the seam heat treatment was adjusted to be 1 second to 5 seconds.
  • the soaking time was controlled by adjusting the timing of starting the shower from the end of heating.
  • the cooling rate in the seam heat treatment was controlled by making the water-cooled shower mist and adjusting the flow rate and / or the angle of the water-cooled shower.
  • the cooling shutdown temperature in the seam heat treatment was controlled by adjusting the timing at which the shower was stopped.
  • the chemical composition of the base material portion of the obtained electrosewn steel pipe can be regarded as the same as the chemical composition of the molten steel which is the raw material.
  • the chemical composition of the base metal portion is the above-mentioned chemical composition A, and the chemical composition is the above-mentioned chemical composition A.
  • the F fraction is 80% or more and less than 100%, and the balance contains pseudo pearlite and cementite.
  • the YS of the base material is 410 MPa or more, and the TS of the base material is 515 to 650 MPa.
  • ⁇ YS which is the value obtained by subtracting the YS of the electric sewing welded portion from the YS of the base metal portion, is 0 to 80 MPa.
  • ⁇ Hv which is the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric stitch welded portion from the Vickers hardness of the outer surface layer of the electric stitch welded portion, is 0 to 25 Hv.
  • the electric resistance pipes of Examples were excellent in SSC resistance and SOHIC resistance in the electric resistance welded portion.
  • the electric resistance pipe of test number 23 had an appropriate chemical composition of the base material (that is, the above-mentioned chemical composition A), the heating temperature in the seam heat treatment step was too high. As a result, the YS of the electric stitch welded portion became too high, and the ⁇ YS became less than 0 MPa. Further, the Vickers hardness of the outer surface layer of the electric stitch welded portion became too hard, and ⁇ Hv became more than 25 Hv. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
  • the chemical composition of the base metal portion was appropriate (that is, the chemical composition A described above)
  • the heating temperature in the seam heat treatment step was too low.
  • the YS of the electric stitch welded portion became too low, and the ⁇ YS became more than 80 MPa.
  • the Vickers hardness of the inner surface layer of the electric stitch welded portion was insufficient, and ⁇ Hv became more than 25 Hv.
  • SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
  • the electric resistance welded steel pipe of test number 29 had a C content that was too low in the chemical composition of the base material.
  • the YS of the base material portion was less than 410 MPa, and the TS of the base material portion was less than 515 MPa.
  • the electric resistance welded steel pipe of test number 30 had an excessively high C content in the chemical composition of the base material.
  • the F fraction in the metal structure of the inner surface layer of the base material portion was less than 80%, and the TS of the base material portion exceeded 650 MPa.
  • the YS of the base metal portion became too high, and the ⁇ YS became more than 80 MPa.
  • the Vickers hardness of the outer surface layer of the electric stitch welded portion became too hard, and ⁇ Hv became more than 25 Hv.
  • SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
  • the Mn content of the electrosewn steel pipe of test number 31 was too low in the chemical composition of the base metal part.
  • the YS of the base material portion was less than 410 MPa, and the TS of the base material portion was less than 515 MPa.
  • the electric resistance welded steel pipe of test number 32 had an excessively high Mn content in the chemical composition of the base material.
  • the base material TS was more than 650 MPa.
  • the YS of the base metal portion became too high, and the ⁇ YS became more than 80 MPa.
  • the Vickers hardness of the outer surface layer of the electric stitch welded portion became too hard, and ⁇ Hv became more than 25 Hv.
  • SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
  • the electric resistance pipe of test number 33 had an excessively high P content in the chemical composition of the base material. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
  • the electric resistance welded steel pipe of test number 34 had an S content that was too high in the chemical composition of the base metal part. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
  • the electrolytically sewn steel pipe of test number 35 had an excessively high Si content in the chemical composition of the base material. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
  • the Nb content of the electrosewn steel pipe of test number 36 was too low in the chemical composition of the base metal part. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
  • the electric resistance welded steel pipe of test number 37 had an excessively high Nb content in the chemical composition of the base material. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
  • the electric resistance steel pipe of test number 38 had a Ti content that was too low in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
  • the electric resistance pipe of test number 39 had an excessively high Ti content in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
  • the electric resistance steel pipe of test number 40 had an excessively high Ca content in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
  • the electro-sewn steel pipe of test number 41 had an Al content that was too high in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
  • the electric resistance welded steel pipe of test number 42 had an N content too high in the chemical composition of the base metal part. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
  • the electric resistance pipe of test number 43 had an O content too high in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.

Abstract

A line pipe-use electric resistance welded steel pipe comprising a parent material portion and an electric resistance welded portion, wherein the parent material portion has a chemical composition including, in percentages by mass, 0.030 to 0.090% C, 0.01 to 0.50% Si, 0.50 to 1.50% Mn, 0.005 to 0.060% Nb, 0.005 to 0.030% Ti, 0.0001 to 0.0040% Ca, and 0.0010 to 0.0080% N, the remainder including Fe and impurities. The line pipe-use electric resistance welded steel pipe has a ΔYS of 0 to 80 MPa, which is a value obtained by subtracting, from the yield strength of the parent material portion, the yield strength of the electric resistance welded portion, and a ΔHv of 0 to 25 Hv, which is a value obtained by subtracting, from the Vickers hardness of the outer surface layer in the electric resistance welded portion, the Vickers hardness of the inner surface layer in the electric resistance welded portion.

Description

ラインパイプ用電縫鋼管Electric resistance sewn steel pipe for line pipe
　本開示は、ラインパイプ用電縫鋼管に関する。 This disclosure relates to electric resistance sewn steel pipes for line pipes.
　パイプラインは、地上や海底等に建設されるシステムであって、油やガスを移送するシステムである。
　パイプラインは、複数のラインパイプをつなぎ合わせることによって形成される。かかるラインパイプ用の鋼管として、電縫鋼管が用いられる場合がある。 A pipeline is a system constructed on the ground or the seabed, and is a system for transferring oil and gas.
A pipeline is formed by connecting a plurality of line pipes. As the steel pipe for such a line pipe, an electrosewn steel pipe may be used.
　近年、パイプラインが建設される地域は、サワー環境等の厳しい環境を有する地域へと拡大している。
　ここで、サワー環境とは、腐食性ガスであるＨ２Ｓを含む、酸性化された環境を意味する。
　サワー環境に建設されるパイプライン、上記パイプラインを形成するためのラインパイプ、及び、上記ラインパイプ用の鋼管には、耐硫化物応力割れ性（耐Ｓｕｌｆｉｄｅ　Ｓｔｒｅｓｓ　Ｃｒａｃｋｉｎｇ性：以下、耐ＳＳＣ性という）が要求される。 In recent years, the area where pipelines are constructed has expanded to areas with harsh environments such as the sour environment.
Here, the sour environment, including H 2 S is a corrosive gas, means acidified environment.
The pipeline constructed in the sour environment, the line pipe for forming the pipeline, and the steel pipe for the line pipe have sulfide stress cracking resistance (Sulfide Stress Cracking resistance: hereinafter referred to as SSC resistance). ) Is required.
　特開平６－４１６８４号公報（特許文献１）、及び、特開平６－２３５０４５号公報（特許文献２）には、ラインパイプ用の電縫鋼管の耐ＳＣＣ性を高めるための技術が開示されている。 Japanese Patent Application Laid-Open No. 6-41684 (Patent Document 1) and Japanese Patent Application Laid-Open No. 6-235405 (Patent Document 2) disclose techniques for improving the SCC resistance of electric resistance welded steel pipes for line pipes. There is.
　特許文献１に開示された電縫鋼管は、Ｃ：０．０５～０．３５％、Ｓｉ：０．０２～０．５０％、Ｍｎ：０．３０～２．００％、Ｃａ：０．０００５～０．００８０％、Ａｌ：０．００５～０．１００％を含有し、残部がＦｅからなる鋼で製造される。この電縫鋼管は、Ｓ、Ｏ、Ｃａ含有量が式（１．０≦（％Ｃａ）｛１－７２（％Ｏ）｝／１．２５（％Ｓ）≦２．５）を満足し、脱酸生成物を（ＣａＯ）ｍ（Ａｌ２Ｏ３）ｎの複合介在物とし、ｍ／ｎ＜１であり、かつ、電縫衝合面を中心として両側３０ｍｍ以内での硬さ測定値の最大値がビッカース硬さで２５０以下であり、かつ最大値と最小値の差がビッカース硬さで３０以内である。
　特許文献１の段落００６３には、上記電縫鋼管は、ｐＨが低く厳しい環境下においても高強度にして優れた耐硫化物応力腐食割れ特性を有する、と記載されている。 The electrosewn steel pipe disclosed in Patent Document 1 has C: 0.05 to 0.35%, Si: 0.02 to 0.50%, Mn: 0.30 to 2.00%, Ca: 0.0005. It is made of steel containing ~ 0.0080%, Al: 0.005 to 0.100%, and the balance is Fe. This electrosewn steel pipe has S, O, and Ca contents satisfying the formula (1.0 ≦ (% Ca) {1-72 (% O)} / 1.25 (% S) ≦ 2.5). The deoxidized product is a composite inclusion of (CaO) m (Al 2 O 3 ) n , and the hardness is measured within 30 mm on both sides with m / n <1 and the electro-sewing abutment surface as the center. The maximum value is 250 or less in Vickers hardness, and the difference between the maximum value and the minimum value is 30 or less in Vickers hardness.
Paragraph 0063 of Patent Document 1 describes that the electric resistance welded steel pipe has high strength and excellent sulfide stress corrosion cracking resistance even in a harsh environment with a low pH.
　特許文献２に開示された電縫鋼管は、重量％で、Ｃ：０．０５～０．３５％、Ｓｉ：０．０２～０．５０％、Ｍｎ：０．３０～２．００％、Ｐ：０．０３０％以下、Ｓ：０．００５％以下、Ｃａ：０．０００５～０．００８０％、Ａｌ：０．００５～０．１００％を含有し、Ｓ、Ｏ、Ｃａの含有量が式（１．０≦（％Ｃａ）｛１－７２（％Ｏ）｝／１．２５（％Ｓ）≦２．５）を満足し、Ｏ量とＣａ量の関係が（％Ｃａ）／（％Ｏ）≦０．５５を満足し、残部Ｆｅおよび不可避不純物からなる鋼で製造される。この電縫鋼管は、電縫衝合面を中心として両側３０ｍｍ以内での硬さ測定値の最大値がビッカース硬さで２５０以下であり、かつ最大値と最小値の差がビッカース硬さで３０以内である。
　特許文献２の段落００５９には、上記電縫鋼管は、ｐＨが低く厳しい環境においてもＳＳＣ特性を劣化することがない、と記載されている。 The electrosewn steel pipe disclosed in Patent Document 2 has a weight% of C: 0.05 to 0.35%, Si: 0.02 to 0.50%, Mn: 0.30 to 2.00%, P. : 0.030% or less, S: 0.005% or less, Ca: 0.0005 to 0.0080%, Al: 0.005 to 0.100%, and the content of S, O, Ca is the formula. (1.0 ≦ (% Ca) {1-72 (% O)} / 1.25 (% S) ≦ 2.5) is satisfied, and the relationship between the amount of O and the amount of Ca is (% Ca) / (%). O) Satisfies ≦ 0.55 and is made of steel consisting of the balance Fe and unavoidable impurities. In this electric resistance steel pipe, the maximum value of the measured hardness within 30 mm on both sides of the electric resistance joint surface is 250 or less in Vickers hardness, and the difference between the maximum value and the minimum value is 30 in Vickers hardness. Within.
Paragraph 0059 of Patent Document 2 describes that the electric resistance welded steel pipe does not deteriorate the SSC characteristics even in a harsh environment with a low pH.
　特許文献１：特開平６－４１６８４号公報
　特許文献２：特開平６－２３５０４５号公報 Patent Document 1: Japanese Patent Application Laid-Open No. 6-41684 Patent Document 2: Japanese Patent Application Laid-Open No. 6-235405
　しかし、サワー環境で用いられるラインパイプ用電縫鋼管の耐ＳＣＣ性をより向上させることが求められる場合がある。 However, it may be required to further improve the SCC resistance of the electrosewn steel pipe for line pipes used in the sour environment.
　更に、近年、サワー環境で用いられるラインパイプ用電縫鋼管において、硫化物応力割れ（Sulfide Stress Cracking；ＳＳＣ）についての指摘だけでなく、ＳＳＣとは割れの機構が異なる応力支配水素誘起割れ（Stress-Oriented Hydrogen Induced Cracking：ＳＯＨＩＣ）についての指摘がなされてきている。
　ＳＯＨＩＣが発生する機構は、次のとおりであると考えられている。
　サワー環境で用いられるラインパイプ用電縫鋼管では、電縫鋼管表面近傍に「ブリスタ」と称される、電縫鋼管の管軸方向に延びる膨れが発生する場合がある。電縫鋼管に応力が負荷された場合、電縫鋼管中の複数のブリスタ及び微小な内部割れが、電縫鋼管の肉厚方向に連結することによって、ＳＯＨＩＣが発生する。
　特許文献１及び２には、耐ＳＯＨＩＣ性についての記載がない。そのため、サワー環境で用いられるラインパイプ用電縫鋼管に対し、特許文献１及び２に開示された技術を適用しても、優れた耐ＳＯＨＩＣ性が得られない場合がある。 Furthermore, in recent years, in electrosewn steel pipes for line pipes used in sour environments, not only has been pointed out about sulfide stress cracking (SSC), but also stress-dominated hydrogen-induced cracking (SSC), which has a different cracking mechanism from SSC. -Oriented Hydrogen Induced Cracking (SOHIC) has been pointed out.
The mechanism by which SOHIC is generated is considered to be as follows.
In a line pipe electric pipe used in a sour environment, a bulge called "blister" that extends in the pipe axial direction of the electric pipe may occur in the vicinity of the surface of the electric pipe. When stress is applied to the power-stitched steel pipe, SOHIC is generated by connecting a plurality of blister and minute internal cracks in the power-stitched steel pipe in the wall thickness direction of the power-stitched steel pipe.
Patent Documents 1 and 2 do not describe SOHIC resistance. Therefore, even if the techniques disclosed in Patent Documents 1 and 2 are applied to the electrosewn steel pipe for line pipes used in a sour environment, excellent SOHIC resistance may not be obtained.
　本開示の目的は、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性を有するラインパイプ用電縫鋼管を提供することである。 An object of the present disclosure is to provide an electrosewn steel pipe for a line pipe having excellent SSC resistance and SOHIC resistance.
　上記課題を解決するための手段には、以下の態様が含まれる。
＜１＞　母材部及び電縫溶接部を含み、
　前記母材部の化学組成が、質量％で、
Ｃ：０．０３０～０．０９０％、
Ｓｉ：０．０１～０．５０％、
Ｍｎ：０．５０～１．５０％、
Ｐ：０～０．０２０％、
Ｓ：０～０．００２０％、
Ｎｂ：０．００５～０．０６０％、
Ｔｉ：０．００５～０．０３０％、
Ｃａ：０．０００１～０．００４０％、
Ａｌ：０～０．０５０％、
Ｎ：０．００１０～０．００８０％、
Ｏ：０～０．００３０％、
Ｃｕ：０～０．５００％、
Ｎｉ：０～０．５００％、
Ｂ：０～０．００２０％、
Ｖ：０～０．１００％、
Ｃｒ：０～０．５００％、
Ｍｏ：０～０．５００％、
Ｗ：０～０．５００％、
Ｚｒ：０～０．０５００％、
Ｔａ：０～０．０５００％、
Ｍｇ：０～０．００５０％、
ＲＥＭ：０～０．００５０％、
Ｈｆ：０～０．００５０％、
Ｒｅ：０～０．００５０％、及び、
残部：Ｆｅ及び不純物からなり、
　母材部の内表層の金属組織において、ポリゴナルフェライト分率が８０％以上１００％未満であり、残部が疑似パーライト及びセメンタイトを含み、
　前記母材部の降伏強度が４１０ＭＰａ以上であり、前記母材部の引張強度が５１５～６５０ＭＰａであり、
　前記母材部の降伏強度から前記電縫溶接部の降伏強度を差し引いた値であるΔＹＳが、０～８０ＭＰａであり、
　前記電縫溶接部の外表層のビッカース硬さから前記電縫溶接部の内表層のビッカース硬さを差し引いた値であるΔＨｖが、０～２５Ｈｖである、
ラインパイプ用電縫鋼管。
＜２＞　前記母材部の化学組成が、質量％で、
Ｃｕ：０％超０．５００％以下、
Ｎｉ：０％超０．５００％以下、
Ｂ：０％超０．００２０％以下、
Ｖ：０％超０．１００％以下、
Ｃｒ：０％超０．５００％以下、
Ｍｏ：０％超０．５００％以下、
Ｗ：０％超０．５００％以下、
Ｚｒ：０％超０．０５００％以下、
Ｔａ：０％超０．０５００％以下、
Ｍｇ：０％超０．００５０％以下、
ＲＥＭ：０％超０．００５０％以下、
Ｈｆ：０％超０．００５０％以下、及び、
Ｒｅ：０％超０．００５０％以下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、
＜１＞に記載のラインパイプ用電縫鋼管。
＜３＞　肉厚が１３ｍｍ以上である＜１＞又は＜２＞に記載のラインパイプ用電縫鋼管。
＜４＞　外径が３００ｍｍ～６５０ｍｍである＜１＞～＜３＞のいずれか１つに記載のラインパイプ用電縫鋼管。 Means for solving the above problems include the following aspects.
<1> Including the base metal part and the electric sewing welded part
The chemical composition of the base material is mass%.
C: 0.030-0.090%,
Si: 0.01-0.50%,
Mn: 0.50 to 1.50%,
P: 0 to 0.020%,
S: 0 to 0.0020%,
Nb: 0.005 to 0.060%,
Ti: 0.005 to 0.030%,
Ca: 0.0001 to 0.0040%,
Al: 0 to 0.050%,
N: 0.0010 to 0.0080%,
O: 0 to 0.0030%,
Cu: 0 to 0.500%,
Ni: 0 to 0.500%,
B: 0 to 0.0020%,
V: 0 to 0.100%,
Cr: 0 to 0.500%,
Mo: 0 to 0.500%,
W: 0 to 0.500%,
Zr: 0-0.0500%,
Ta: 0-0.0500%,
Mg: 0 to 0.0050%,
REM: 0-0.0050%,
Hf: 0 to 0.0050%,
Re: 0 to 0.0050% and
Remaining: Consists of Fe and impurities
In the metal structure of the inner surface layer of the base metal part, the polygonal ferrite fraction is 80% or more and less than 100%, and the balance contains pseudo pearlite and cementite.
The yield strength of the base material portion is 410 MPa or more, and the tensile strength of the base material portion is 515 to 650 MPa.
ΔYS, which is a value obtained by subtracting the yield strength of the electric sewing welded portion from the yield strength of the base metal portion, is 0 to 80 MPa.
ΔHv, which is a value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded portion from the Vickers hardness of the outer surface layer of the electric sewing welded portion, is 0 to 25 Hv.
Electric resistance sewn steel pipe for line pipes.
<2> The chemical composition of the base material is mass%.
Cu: More than 0% and less than 0.500%,
Ni: More than 0% and less than 0.500%,
B: More than 0% and less than 0.0020%,
V: More than 0% and less than 0.100%,
Cr: More than 0% and less than 0.500%,
Mo: More than 0% and less than 0.500%,
W: More than 0% and less than 0.500%,
Zr: More than 0% and less than 0.0500%,
Ta: More than 0% and less than 0.0500%,
Mg: More than 0% and less than 0.0050%,
REM: More than 0% and less than 0.0050%,
Hf: More than 0% and less than 0.0050%, and
Re: Contains one or more selected from the group consisting of more than 0% and 0.0050% or less.
The electrosewn steel pipe for line pipes according to <1>.
<3> The electrosewn steel pipe for a line pipe according to <1> or <2>, which has a wall thickness of 13 mm or more.
<4> The electric resistance welded steel pipe for a line pipe according to any one of <1> to <3>, which has an outer diameter of 300 mm to 650 mm.
　本開示によれば、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性を有するラインパイプ用電縫鋼管が提供される。 According to the present disclosure, an electrosewn steel pipe for a line pipe having excellent SSC resistance and SOHIC resistance is provided.
　本明細書において、「～」を用いて表される数値範囲は、「～」の前後に記載される数値を下限値及び上限値として含む範囲を意味する。
　本明細書において、成分（元素）の含有量を示す「％」は、「質量％」を意味する。
　本明細書において、Ｃ（炭素）の含有量を、「Ｃ含有量」と表記することがある。他の元素の含有量についても同様に表記することがある。
　本明細書において、「工程」との用語は、独立した工程だけではなく、他の工程と明確に区別できない場合であってもその工程の所期の目的が達成されれば、本用語に含まれる。 In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
In the present specification, "%" indicating the content of a component (element) means "mass%".
In the present specification, the content of C (carbon) may be referred to as "C content". The content of other elements may be described in the same manner.
In the present specification, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. Is done.
　本開示のラインパイプ用電縫鋼管（以下、単に「本開示の電縫鋼管」ともいう）は、母材部及び電縫溶接部を含み、母材部の化学組成が、質量％で、Ｃ：０．０３０～０．０９０％、Ｓｉ：０．０１～０．５０％、Ｍｎ：０．５０～１．５０％、Ｐ：０～０．０２０％、Ｓ：０～０．００２０％、Ｎｂ：０．００５～０．０６０％、Ｔｉ：０．００５～０．０３０％、Ｃａ：０．０００１～０．００４０％、Ａｌ：０～０．０５０％、Ｎ：０．００１０～０．００８０％、Ｏ：０～０．００３０％、Ｃｕ：０～０．５００％、Ｎｉ：０～０．５００％、Ｂ：０～０．００２０％、Ｖ：０～０．１００％、Ｃｒ：０～０．５００％、Ｍｏ：０～０．５００％、Ｗ：０～０．５００％、Ｚｒ：０～０．０５００％、Ｔａ：０～０．０５００％、Ｍｇ：０～０．００５０％、ＲＥＭ：０～０．００５０％、Ｈｆ：０～０．００５０％、Ｒｅ：０～０．００５０％、及び、残部：Ｆｅ及び不純物からなり（以下、この化学組成を「化学組成Ａ」ともいう）、母材部の内表層の金属組織において、ポリゴナルフェライト分率が８０％以上１００％未満であり、残部が疑似パーライト及びセメンタイトを含み、母材部の降伏強度が４１０ＭＰａ以上であり、母材部の引張強度が５１５～６５０ＭＰａであり、母材部の降伏強度から電縫溶接部の降伏強度を差し引いた値であるΔＹＳが、０～８０ＭＰａであり、電縫溶接部の外表層のビッカース硬さから電縫溶接部の内表層のビッカース硬さを差し引いた値であるΔＨｖが、０～２５Ｈｖである。 The electrosewn steel pipe for line pipes of the present disclosure (hereinafter, also simply referred to as “the electrosewn steel pipe of the present disclosure”) includes a base material portion and an electrosewn welded portion, and the chemical composition of the base metal portion is C by mass%. : 0.030 to 0.090%, Si: 0.01 to 0.50%, Mn: 0.50 to 1.50%, P: 0 to 0.020%, S: 0 to 0.0020%, Nb: 0.005 to 0.060%, Ti: 0.005 to 0.030%, Ca: 0.0001 to 0.0040%, Al: 0 to 0.050%, N: 0.0010 to 0. 0080%, O: 0 to 0.0030%, Cu: 0 to 0.500%, Ni: 0 to 0.500%, B: 0 to 0.0020%, V: 0 to 0.100%, Cr: 0 to 0.500%, Mo: 0 to 0.500%, W: 0 to 0.500%, Zr: 0 to 0.0500%, Ta: 0 to 0.0500%, Mg: 0 to 0.0050 %, REM: 0 to 0.0050%, Hf: 0 to 0.0050%, Re: 0 to 0.0050%, and the balance: Fe and impurities (hereinafter, this chemical composition is referred to as "chemical composition A"). In the metal structure of the inner surface layer of the base material, the polygonal ferrite content is 80% or more and less than 100%, the balance contains pseudo-pearlite and cementite, and the yield strength of the base material is 410 MPa or more. The tensile strength of the base metal portion is 515 to 650 MPa, and ΔYS, which is the value obtained by subtracting the yield strength of the electrosewn welded portion from the yield strength of the base metal portion, is 0 to 80 MPa, and the outer surface layer of the electrosewn welded portion. ΔHv, which is the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded portion from the Vickers hardness of the above, is 0 to 25 Hv.
　本開示において、母材部（base metal portion）とは、電縫鋼管における、電縫溶接部及び熱影響部以外の部分を指す。ここで、熱影響部（heat affected zone；「ＨＡＺ」と称されることがある）とは、電縫溶接部の近傍であって、電縫溶接及びシーム熱処理による熱の影響を受けた部分を指す。 In the present disclosure, the base metal portion refers to a portion of the electric resistance steel pipe other than the electric resistance welded portion and the heat-affected zone. Here, the heat-affected zone (sometimes referred to as "HAZ") refers to a portion in the vicinity of the electric sewing welded zone, which is affected by heat due to electric sewing welding and seam heat treatment. Point.
　本開示の電縫鋼管は、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性を有する。
　以下、この効果について、詳細に説明する。 The electrosewn steel pipe of the present disclosure has excellent SSC resistance and SOHIC resistance.
Hereinafter, this effect will be described in detail.
　本発明者らは、本開示の電縫鋼管における、ΔＹＳ及びΔＨｖの要件（即ち、ΔＹＳが０～８０ＭＰａでありΔＨｖが０～２５Ｈｖであるという要件）以外の要件を全て満足する電縫鋼管（以下、「電縫鋼管Ｘ」とする）について、耐ＳＳＣ性と耐ＳＯＨＩＣ性とを調査した。
　その結果、電縫鋼管Ｘでは、電縫溶接部における耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性が低下する場合があることが判明した。
　そこでまず、本発明者らは、耐ＳＳＣ性が低下する理由について、次のように考えた。 The present inventors satisfy all the requirements other than the requirements of ΔYS and ΔHv (that is, the requirement that ΔYS is 0 to 80 MPa and ΔHv is 0 to 25 Hv) in the electric resistance welded steel pipe of the present disclosure (that is, the electric resistance welded steel pipe that satisfies all the requirements. The SSC resistance and SOHIC resistance of (hereinafter referred to as "electric pipe X") were investigated.
As a result, it was found that the SSC resistance and / or the SOHIC resistance of the electric resistance welded portion of the electric resistance steel pipe X may be lowered.
Therefore, the present inventors first considered the reason why the SSC resistance is lowered as follows.
　電縫鋼管の電縫溶接部は電縫溶接時に急加熱及び急冷されるので、一般的には、電縫鋼管の電縫溶接部の強度は、母材部の強度と比較して高い（即ち、ΔＹＳが負の値である）と考えられる。電縫鋼管の電縫溶接部の強度が高すぎる場合、電縫鋼管の電縫溶接部において、ＳＳＣが発生しやすくなる。ＳＳＣの発生を抑制する方法として、この電縫溶接部に熱処理（以下、「シーム熱処理」ともいう）を施し、これにより電縫溶接部の強度を下げることが考えられる。 Since the electric sewn welded part of the electric sewn steel pipe is rapidly heated and rapidly cooled during the electric sewn welding, the strength of the electric sewn welded part of the electric sewn steel pipe is generally higher than the strength of the base metal part (that is,). , ΔYS is a negative value). If the strength of the electric-sewn welded portion of the electric-sewn steel pipe is too high, SSC is likely to occur in the electric-sewn welded portion of the electric-sewn steel pipe. As a method of suppressing the generation of SSC, it is conceivable to apply a heat treatment (hereinafter, also referred to as "seam heat treatment") to the electric stitch welded portion to reduce the strength of the electric stitch welded portion.
　しかしながら、電縫鋼管Ｘ（即ち、本開示におけるΔＹＳ及びΔＨｖの要件以外の要件を満足する電縫鋼管）においては、電縫溶接部に熱処理が施された場合であっても、電縫溶接部でＳＳＣが発生する場合があることが判明した。
　更に、電縫鋼管Ｘでは、母材部の降伏強度よりも高いと考えていた電縫溶接部の降伏強度が、むしろ、母材部の降伏強度よりも低い傾向があること（即ち、ΔＹＳが正の値となる傾向があること）も判明した。
　そこで本発明者らは、電縫鋼管Ｘの電縫溶接部におけるＳＳＣと、電縫鋼管ＸにおけるΔＹＳとの関係について、より詳細に検討した。 However, in the electric resistance pipe X (that is, the electric resistance pipe satisfying the requirements other than the requirements of ΔYS and ΔHv in the present disclosure), even if the electric resistance welded portion is heat-treated, the electric resistance welded portion It was found that SSC may occur in.
Further, in the electric resistance pipe X, the yield strength of the electric resistance welded portion, which is considered to be higher than the yield strength of the base metal portion, tends to be lower than the yield strength of the base metal portion (that is, ΔYS is high). It also tends to be a positive value).
Therefore, the present inventors have examined in more detail the relationship between the SSC in the electric resistance welded portion of the electric resistance pipe X and the ΔYS in the electric resistance pipe X.
　前述のとおり、電縫溶接部の降伏強度が高すぎる場合には電縫溶接部における耐ＳＳＣ性が低下するが、以下の理由により、電縫溶接部の降伏強度が低すぎる場合にも、電縫溶接部における耐ＳＳＣ性が低下すると考えられる。
　電縫鋼管におけるＳＳＣ（硫化物応力割れ）は、サワー環境における使用中に電縫鋼管の内圧が高まり、これにより、電縫鋼管の管周方向に応力が負荷された際に発生し得る割れである。電縫鋼管における電縫溶接部の降伏強度が低すぎる場合には、使用中に高まった電縫鋼管の内圧により、電縫溶接部に塑性歪み（即ち、塑性域の歪み）が付与される。母材部の降伏強度に対する電縫溶接部の降伏強度が低くなる程（即ち、ΔＹＳが大きくなる程）、負荷された応力が電縫溶接部に集中しやすくなり、その結果、電縫溶接部に付与される塑性歪みが大きくなる。その結果、電縫溶接部の塑性歪みに水素が吸蔵され、電縫溶接部にＳＳＣが発生しやすくなる。
　ΔＹＳが正の値となる傾向がある電縫鋼管Ｘでは、以上の機構のＳＳＣが発生しやすいと考えられる。 As described above, if the yield strength of the electric stitch welded portion is too high, the SSC resistance of the electric stitch welded portion decreases, but for the following reasons, even if the yield strength of the electric stitch welded portion is too low, the electric shock It is considered that the SSC resistance in the sewn welded portion is lowered.
SSC (Sulfide Stress Cracking) in an electric pipe is a crack that can occur when the internal pressure of the electric pipe increases during use in a sour environment, and as a result, stress is applied in the circumferential direction of the electric pipe. be. If the yield strength of the electric resistance welded portion of the electric resistance welded steel pipe is too low, the internal pressure of the electric resistance welded steel pipe increased during use causes plastic strain (that is, strain in the plastic region) to be applied to the electric resistance welded portion. The lower the yield strength of the electric stitch welded portion with respect to the yield strength of the base metal portion (that is, the larger ΔYS), the easier it is for the applied stress to concentrate on the electric stitch welded portion, and as a result, the electric stitch welded portion. The plastic strain applied to is increased. As a result, hydrogen is occluded in the plastic strain of the electric stitch welded portion, and SSC is likely to be generated in the electric stitch welded portion.
It is considered that SSC having the above mechanism is likely to occur in the electric resistance welded steel pipe X in which ΔYS tends to be a positive value.
　以上の知見に基づき、本発明者らは、電縫溶接部の降伏強度を低下させすぎず、電縫溶接部の降伏強度を母材部の降伏強度に近づけること、具体的にはΔＹＳが０～８０ＭＰａとなるように調整することにより、電縫溶接部におけるＳＳＣを抑制できること（即ち、電縫溶接部における耐ＳＳＣ性を向上させることができること）を見出した。 Based on the above findings, the present inventors do not reduce the yield strength of the electric stitch welded portion too much, and bring the yield strength of the electric stitch welded portion close to the yield strength of the base metal portion, specifically, ΔYS is 0. It has been found that the SSC in the electric sewing welded portion can be suppressed (that is, the SSC resistance in the electric sewing welded portion can be improved) by adjusting the value to about 80 MPa.
　しかし、電縫鋼管Ｘでは、ΔＹＳが０～８０ＭＰａである場合であっても、電縫溶接部においてＳＯＨＩＣが発生する場合があることが判明した。
　そこで本発明者らは、このＳＯＨＩＣの発生について、電縫鋼管の電縫溶接部に着目し、詳細に検討した。
　その結果、次の知見を得た。 However, it has been found that in the electric resistance steel pipe X, SOHIC may occur in the electric resistance welded portion even when ΔYS is 0 to 80 MPa.
Therefore, the present inventors have focused on the electric-sewn welded portion of the electric-sewn steel pipe and examined in detail the occurrence of this SOHIC.
As a result, the following findings were obtained.
　本発明者らは、ΔＹＳが０～８０ＭＰａである態様の電縫鋼管Ｘについて、電縫溶接部のビッカース硬さを調査した。その結果、電縫溶接部の外表層のビッカース硬さから電縫溶接部の内表層のビッカース硬さを差し引いた値であるΔＨｖが２５Ｈｖ超である場合に、電縫溶接部においてＳＯＨＩＣが発生していることを知見した。 The present inventors investigated the Vickers hardness of the electric resistance welded portion of the electric resistance steel pipe X in which ΔYS was 0 to 80 MPa. As a result, when ΔHv, which is the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric stitch welded portion from the Vickers hardness of the outer surface layer of the electric stitch welded portion, exceeds 25 Hv, SOHIC is generated in the electric stitch welded portion. It was found that
　従来、電縫鋼管では、電縫溶接部の外表層と内表層との硬さの差（即ち、ΔＨｖ）について、着目されてこなかった。
　この点に関し、本発明者らは、ΔＹＳが小さい場合であっても、ΔＨｖが大きすぎる場合には、電縫溶接部における耐ＳＯＨＩＣ性が低下することを見出した。この理由は、ＳＯＨＩＣは、電縫溶接部中の複数のブリスタ及び微小な内部割れが、電縫溶接部の肉厚方向に連結することによって発生する割れであるためと考えられる。
　その結果、本発明者らは、電縫鋼管Ｘにおいて、ΔＹＳが０～８０ＭＰａであり、かつ、ΔＨｖが０～２５Ｈｖである場合（即ち、本開示の電縫鋼管に該当する場合）に、電縫溶接部の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高めることができることを見出した。
　即ち、本発明者らは、上述した本開示の電縫鋼管が、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性を有することを見出した。 Conventionally, in electric pipes, attention has not been paid to the difference in hardness (that is, ΔHv) between the outer surface layer and the inner surface layer of the electric resistance welded portion.
In this regard, the present inventors have found that even when ΔYS is small, when ΔHv is too large, the SOHIC resistance in the electric stitch welded portion is lowered. It is considered that the reason for this is that SOHIC is a crack generated by connecting a plurality of blister and minute internal cracks in the electric stitch welded portion in the wall thickness direction of the electric stitch welded portion.
As a result, the present inventors, in the case where ΔYS is 0 to 80 MPa and ΔHv is 0 to 25 Hv in the welded steel pipe X (that is, when it corresponds to the welded steel pipe of the present disclosure), the electric pipe is electric. It has been found that the SSC resistance and the SOHIC resistance of the sewn welded portion can be improved.
That is, the present inventors have found that the above-described electrosewn steel pipe of the present disclosure has excellent SSC resistance and SOHIC resistance.
＜母材部の化学組成＞
　以下、母材部の化学組成（即ち、化学組成Ａ）について説明する。 <Chemical composition of base material>
Hereinafter, the chemical composition of the base metal portion (that is, the chemical composition A) will be described.
　Ｃ：０．０３０～０．０９０％
　Ｃ（炭素）は、鋼材の強度を高める元素である。
　Ｃ含有量が低すぎると、上記効果が得られない場合がある。
　一方、Ｃ含有量が高すぎると、Ｃが鋼材中の合金元素と炭化物を形成し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を低下させる場合がある。更に、Ｃ含有量が高すぎると、鋼材の強度が高くなりすぎ、ΔＹＳ及びΔＨｖが大きくなりすぎ、その結果、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｃ含有量は０．０３０～０．０９０％である。
　Ｃ含有量の下限は、好ましくは０．０３５％であり、より好ましくは０．０４０％である。
　Ｃ含有量の上限は、好ましくは０．０８０％であり、より好ましくは０．０７０％である。 C: 0.030-0.090%
C (carbon) is an element that enhances the strength of steel materials.
If the C content is too low, the above effect may not be obtained.
On the other hand, if the C content is too high, C may form carbides with alloying elements in the steel material, which may reduce the SSC resistance and SOHIC resistance of the steel material. Further, if the C content is too high, the strength of the steel material becomes too high, and ΔYS and ΔHv become too large, and as a result, the SSC resistance and the SOHIC resistance of the steel material may decrease.
Therefore, the C content is 0.030 to 0.090%.
The lower limit of the C content is preferably 0.035%, more preferably 0.040%.
The upper limit of the C content is preferably 0.080%, more preferably 0.070%.
　Ｓｉ：０．０１～０．５０％
　Ｓｉは、鋼を脱酸する元素である。
　Ｓｉ含有量が低すぎると、上記効果が得られない場合がある。一方、Ｓｉ含有量が高すぎると、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｓｉ含有量は０．０１～０．５０％である。
　Ｓｉ含有量の下限は、好ましくは０．０２％であり、より好ましくは０．０５％である。
　Ｓｉ含有量の上限は、好ましくは０．４０％であり、より好ましくは０．３５％である。 Si: 0.01-0.50%
Si is an element that deoxidizes steel.
If the Si content is too low, the above effect may not be obtained. On the other hand, if the Si content is too high, the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Si content is 0.01 to 0.50%.
The lower limit of the Si content is preferably 0.02%, more preferably 0.05%.
The upper limit of the Si content is preferably 0.40%, more preferably 0.35%.
　Ｍｎ：０．５０～１．５０％
　Ｍｎは、鋼を脱酸する元素である。Ｍｎは更に、鋼材の強度を高める元素でもある。Ｍｎ含有量が低すぎると、上記効果が得られない場合がある。
　一方、Ｍｎ含有量が高すぎると、鋼材の強度が高くなりすぎる場合がある。この場合更に、ΔＹＳが大きくなり、更に、ΔＨｖが大きくなる場合がある。これらの場合、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する。
　従って、Ｍｎ含有量は０．５０～１．５０％である。
　Ｍｎ含有量の下限は、好ましくは０．６０％であり、より好ましくは０．８０％であり、更に好ましくは１．００％である。
　Ｍｎ含有量の上限は、好ましくは１．４０％であり、より好ましくは１．３５％である。 Mn: 0.50 to 1.50%
Mn is an element that deoxidizes steel. Mn is also an element that enhances the strength of steel materials. If the Mn content is too low, the above effect may not be obtained.
On the other hand, if the Mn content is too high, the strength of the steel material may become too high. In this case, ΔYS may be further increased, and ΔHv may be further increased. In these cases, the SSC resistance and SOHIC resistance of the steel material are lowered.
Therefore, the Mn content is 0.50 to 1.50%.
The lower limit of the Mn content is preferably 0.60%, more preferably 0.80%, and even more preferably 1.00%.
The upper limit of the Mn content is preferably 1.40%, more preferably 1.35%.
　Ｐ：０～０．０２０％
　Ｐ（リン）は、不純物である。Ｐ含有量は、０％であってもよいし、０％超であってもよい。
　Ｐは、粒界に偏析し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性を低下させる場合がある。
　従って、Ｐ含有量は、０～０．０２０％である。
　Ｐ含有量の上限は、好ましくは０．０１５％であり、より好ましくは０．０１３％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、鋼材の製造コストを大幅に高める場合がある。従って、工業生産を考慮した場合、Ｐ含有量の下限は、好ましくは０．００１％であり、より好ましくは０．００５％である。 P: 0 to 0.020%
P (phosphorus) is an impurity. The P content may be 0% or more than 0%.
P may segregate at the grain boundaries and reduce the SSC resistance and / or the SOHIC resistance of the steel material.
Therefore, the P content is 0 to 0.020%.
The upper limit of the P content is preferably 0.015%, more preferably 0.013%.
The P content is preferably as low as possible. However, an extreme reduction in P content may significantly increase the manufacturing cost of steel materials. Therefore, when considering industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.005%.
　Ｓ：０～０．００２０％
　Ｓ（硫黄）は、不純物である。Ｓ含有量は、０％であってもよいし、０％超であってもよい。
　Ｓは、粒界に偏析し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性を低下させる場合がある。
　従って、Ｓ含有量は、０～０．００２０％である。
　Ｓ含有量の上限は、好ましくは０．００１５％であり、より好ましくは０．００１０％であり、更に好ましくは０．０００８％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、鋼材の製造コストを大幅に高める場合がある。従って、工業生産を考慮した場合、Ｓ含有量の下限は、好ましくは０．０００１％であり、より好ましくは０．０００２％である。 S: 0 to 0.0020%
S (sulfur) is an impurity. The S content may be 0% or more than 0%.
S may segregate at the grain boundaries and reduce the SSC resistance and / or the SOHIC resistance of the steel material.
Therefore, the S content is 0 to 0.0020%.
The upper limit of the S content is preferably 0.0015%, more preferably 0.0010%, and even more preferably 0.0008%.
The S content is preferably as low as possible. However, an extreme reduction in the S content may significantly increase the manufacturing cost of the steel material. Therefore, when considering industrial production, the lower limit of the S content is preferably 0.0001%, more preferably 0.0002%.
　Ｎｂ：０．００５～０．０６０％
　Ｎｂは、Ｃ（炭素）及び／又はＮ（窒素）と結合し、炭化物、窒化物又は炭窒化物（以下、「炭窒化物等」という）を形成する元素である。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性及び／又は耐ＳＯＨＩＣ性を高める。Ｎｂ含有量が低すぎると、上記効果が得られない場合がある。
　一方、Ｎｂ含有量が高すぎると、炭窒化物等が粗大化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｎｂ含有量は０．００５～０．０６０％である。
　Ｎｂ含有量の下限は、好ましくは０．００８％であり、より好ましくは０．０１０％である。
　Ｎｂ含有量の上限は、好ましくは０．０５５％であり、より好ましくは０．０５０％であり、更に好ましくは０．０４５％である。 Nb: 0.005 to 0.060%
Nb is an element that combines with C (carbon) and / or N (nitrogen) to form carbides, nitrides or carbonitrides (hereinafter referred to as "carbonitrides and the like"). The carbonitride and the like refine the substructure of the steel material by the pinning effect, and enhance the SSC resistance and / or the SOHIC resistance of the steel material. If the Nb content is too low, the above effect may not be obtained.
On the other hand, if the Nb content is too high, the carbonitride and the like may become coarse, and the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Nb content is 0.005 to 0.060%.
The lower limit of the Nb content is preferably 0.008%, more preferably 0.010%.
The upper limit of the Nb content is preferably 0.055%, more preferably 0.050%, and even more preferably 0.045%.
　Ｔｉ：０．００５～０．０３０％
　Ｔｉは、Ｎ（窒素）と結合し、窒化物を形成する元素である。窒化物は、ピンニング効果により、結晶粒を微細化する。その結果、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性が高まる。Ｔｉ含有量が低すぎると、上記効果が得られない場合がある。
　一方、Ｔｉ含有量が高すぎると、窒化物が粗大化し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｔｉ含有量は０．００５～０．０３０％である。
　Ｔｉ含有量の下限は、好ましくは０．００６％であり、より好ましくは０．００７％であり、更に好ましくは０．００８％である。
　Ｔｉ含有量の上限は、好ましくは０．０２５％であり、より好ましくは０．０２０％であり、更に好ましくは０．０１７％である。 Ti: 0.005 to 0.030%
Ti is an element that combines with N (nitrogen) to form a nitride. The nitride refines the crystal grains by the pinning effect. As a result, the SSC resistance and / or the SOHIC resistance of the steel material is enhanced. If the Ti content is too low, the above effect may not be obtained.
On the other hand, if the Ti content is too high, the nitride may become coarse and the SSC resistance and / or SOHIC resistance of the steel material may decrease.
Therefore, the Ti content is 0.005 to 0.030%.
The lower limit of the Ti content is preferably 0.006%, more preferably 0.007%, and even more preferably 0.008%.
The upper limit of the Ti content is preferably 0.025%, more preferably 0.020%, and even more preferably 0.017%.
　Ｃａ：０．０００１～０．００４０％
　Ｃａは、鋼材中の硫化物の形態を制御化し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性を高める元素である。Ｃａ含有量が低すぎると、上記効果が得られない場合がある。
　一方、Ｃａ含有量が高すぎると、粗大な酸化物系介在物が生成し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｃａ含有量は０．０００１～０．００４０％である。
　Ｃａ含有量の下限は、好ましくは０．０００５％であり、より好ましくは０．００１０％である。
　Ｃａ含有量の上限は、好ましくは０．００３５％であり、より好ましくは０．００３０％である。 Ca: 0.0001 to 0.0040%
Ca is an element that controls the morphology of sulfides in steel materials and enhances SSC resistance and / or SOHIC resistance of steel materials. If the Ca content is too low, the above effect may not be obtained.
On the other hand, if the Ca content is too high, coarse oxide-based inclusions may be formed, and the SSC resistance and / or SOHIC resistance of the steel material may decrease.
Therefore, the Ca content is 0.0001 to 0.0040%.
The lower limit of the Ca content is preferably 0.0005%, more preferably 0.0010%.
The upper limit of the Ca content is preferably 0.0035%, more preferably 0.0030%.
　Ａｌ：０～０．０５０％
　Ａｌは、任意元素である。即ち、Ａｌ含有量は、０％であってもよいし、０％超であってもよい。
　Ａｌ含有量が高すぎると、粗大な酸化物系介在物が生成し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性が低下する。
　従って、Ａｌ含有量は０～０．０５０％である。
　Ａｌ含有量の上限は、好ましくは０．０４５％であり、より好ましくは０．０４０％である。
　一方、Ａｌは、鋼を脱酸する元素である。かかる効果を得る観点から、Ａｌ含有量の下限は、好ましくは０．０００５％であり、より好ましくは０．００１０％であり、更に好ましくは０．００１５％である。 Al: 0 to 0.050%
Al is an arbitrary element. That is, the Al content may be 0% or more than 0%.
If the Al content is too high, coarse oxide-based inclusions are formed, and the SSC resistance and / or SOHIC resistance of the steel material is lowered.
Therefore, the Al content is 0 to 0.050%.
The upper limit of the Al content is preferably 0.045%, more preferably 0.040%.
On the other hand, Al is an element that deoxidizes steel. From the viewpoint of obtaining such an effect, the lower limit of the Al content is preferably 0.0005%, more preferably 0.0010%, and further preferably 0.0015%.
　Ｎ：０．００１０～０．００８０％
　Ｎ（窒素）は、Ｔｉと結合し、微細な窒化物を形成して鋼材の結晶粒を微細化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素である。Ｎ含有量が低すぎると、上記効果が得られない場合がある。
　一方、Ｎ含有量が高すぎると、窒化物が粗大化し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｎ含有量は０．００１０～０．００８０％である。
　Ｎ含有量の下限は、好ましくは０．００１５％であり、より好ましくは０．００２０％である。
　Ｎ含有量の上限は、好ましくは０．００７０％であり、より好ましくは０．００６０％であり、更に好ましくは０．００５０％である。 N: 0.0010 to 0.0080%
N (nitrogen) is an element that combines with Ti to form fine nitrides to refine the crystal grains of the steel material and enhance the SSC resistance and SOHIC resistance of the steel material. If the N content is too low, the above effect may not be obtained.
On the other hand, if the N content is too high, the nitride may become coarse and the SSC resistance and / or SOHIC resistance of the steel material may decrease.
Therefore, the N content is 0.0010 to 0.0080%.
The lower limit of the N content is preferably 0.0015%, more preferably 0.0020%.
The upper limit of the N content is preferably 0.0070%, more preferably 0.0060%, and even more preferably 0.0050%.
　Ｏ：０～０．００３０％
　Ｏ（酸素）は不純物である。Ｏ含有量は、０％であってもよいし、０％超であってもよい。
　Ｏは、粗大な酸化物を形成し、鋼材の耐ＳＳＣ性及び／又は耐ＳＯＨＩＣ性を低下させる元素である。
　従って、Ｏ含有量は０．００３０％以下である。
　Ｏ含有量の上限は、好ましくは０．００２８％であり、より好ましくは０．００２５％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、鋼材の製造コストを大幅に高める。従って、工業生産を考慮した場合、Ｏ含有量の下限は、好ましくは０．０００１％であり、より好ましくは０．０００３％であり、更に好ましくは０．００１０％であり、更に好ましくは０．００１５％である。 O: 0 to 0.0030%
O (oxygen) is an impurity. The O content may be 0% or more than 0%.
O is an element that forms a coarse oxide and lowers the SSC resistance and / or the SOHIC resistance of the steel material.
Therefore, the O content is 0.0030% or less.
The upper limit of the O content is preferably 0.0028%, more preferably 0.0025%.
The O content is preferably as low as possible. However, an extreme reduction in O content significantly increases the manufacturing cost of steel materials. Therefore, when considering industrial production, the lower limit of the O content is preferably 0.0001%, more preferably 0.0003%, still more preferably 0.0010%, still more preferably 0. It is 0015%.
　Ｃｕ：０～０．５００％
　Ｃｕは、任意元素である。即ち、Ｃｕ含有量は、０％であってもよいし、０％超であってもよい。
　Ｃｕ含有量が高すぎると、鋼材の強度が高くなりすぎ、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｃｕ含有量は、０～０．５００％である。
　Ｃｕ含有量の上限は、好ましくは０．４５０％であり、より好ましくは０．４００％である。
　一方、Ｃｕは、鋼材に固溶して鋼材の強度を高める元素である。かかる効果を得る観点から、Ｃｕ含有量の下限は、好ましくは０％超であり、より好ましくは０．０１０％であり、更に好ましくは０．０２０％であり、更に好ましくは０．０３０％である。 Cu: 0 to 0.500%
Cu is an optional element. That is, the Cu content may be 0% or more than 0%.
If the Cu content is too high, the strength of the steel material may become too high, and the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Cu content is 0 to 0.500%.
The upper limit of the Cu content is preferably 0.450%, more preferably 0.400%.
On the other hand, Cu is an element that dissolves in a steel material to increase the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Cu content is preferably more than 0%, more preferably 0.010%, further preferably 0.020%, still more preferably 0.030%. be.
　Ｎｉ：０～０．５００％
　Ｎｉは、任意元素である。即ち、Ｎｉ含有量は、０％であってもよいし、０％超であってもよい。
　Ｎｉ含有量が高すぎると、鋼材の強度が高くなりすぎ、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合があり、更に、鋼材の電縫溶接性が低下する場合もある。
　従って、Ｎｉ含有量は、０～０．５００％である。
　Ｎｉ含有量の上限は、好ましくは０．４５０％であり、より好ましくは０．４００％である。
　一方、Ｎｉは、鋼材に固溶して鋼材の強度を高める元素である。かかる効果を得る観点から、Ｎｉ含有量の下限は、好ましくは０％超であり、より好ましくは０．０１０％であり、更に好ましくは０．０５０％であり、更に好ましくは０．１００％である。 Ni: 0 to 0.500%
Ni is an optional element. That is, the Ni content may be 0% or more than 0%.
If the Ni content is too high, the strength of the steel material may become too high, and the SSC resistance and SOHIC resistance of the steel material may decrease, and further, the electric sewing weldability of the steel material may decrease.
Therefore, the Ni content is 0 to 0.500%.
The upper limit of the Ni content is preferably 0.450%, more preferably 0.400%.
On the other hand, Ni is an element that dissolves in a steel material to increase the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Ni content is preferably more than 0%, more preferably 0.010%, further preferably 0.050%, still more preferably 0.100%. be.
　Ｂ：０～０．００２０％
　Ｂ（ホウ素）は、任意元素である。即ち、Ｂ含有量は、０％であってもよいし、０％超であってもよい。
　Ｂ含有量が高すぎると、粗大な窒化物が生成し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｂ含有量は、０～０．００２０％である。
　Ｂ含有量の上限は、好ましくは０．００１５％であり、より好ましくは０．００１２％である。
　一方、Ｂは、鋼材に固溶して鋼材の強度を高める元素である。かかる効果を得る観点から、Ｂの含有量の下限は、好ましくは０％超であり、より好ましくは０．０００１％であり、更に好ましくは０．０００２％であり、更に好ましくは０．０００３％である。 B: 0 to 0.0020%
B (boron) is an optional element. That is, the B content may be 0% or more than 0%.
If the B content is too high, coarse nitrides may be formed, which may reduce the SSC resistance and SOHIC resistance of the steel material.
Therefore, the B content is 0 to 0.0020%.
The upper limit of the B content is preferably 0.0015%, more preferably 0.0012%.
On the other hand, B is an element that dissolves in the steel material to increase the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the content of B is preferably more than 0%, more preferably 0.0001%, further preferably 0.0002%, still more preferably 0.0003%. Is.
　Ｖ：０～０．１００％
　Ｖ（バナジウム）は、任意元素である。即ち、Ｖ含有量は、０％であってもよいし、０％超であってもよい。
　Ｖ含有量が高すぎると、鋼材の低温靭性が低下する場合がある。
　従って、Ｖ含有量は、０～０．１００％である。
　Ｖ含有量の上限は、好ましくは０．０９０％であり、より好ましくは０．０８０％である。
　一方、Ｖは、炭窒化物等を形成し、鋼材の強度を高める元素である。かかる効果を得る観点から、Ｖ含有量の下限は、好ましくは０％超であり、より好ましくは０．００１％であり、更に好ましくは０．００５％であり、更に好ましくは０．０１０％である。 V: 0 to 0.100%
V (vanadium) is an optional element. That is, the V content may be 0% or more than 0%.
If the V content is too high, the low temperature toughness of the steel material may decrease.
Therefore, the V content is 0 to 0.100%.
The upper limit of the V content is preferably 0.090%, more preferably 0.080%.
On the other hand, V is an element that forms a carbonitride or the like and enhances the strength of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the V content is preferably more than 0%, more preferably 0.001%, still more preferably 0.005%, still more preferably 0.010%. be.
　Ｃｒ：０～０．５００％
　Ｃｒは、任意元素である。即ち、Ｃｒ含有量は、０％であってもよいし、０％超であってもよい。
　Ｃｒ含有量が高すぎると、鋼材の耐ＳＳＣ性が低下する場合がある。
　従って、Ｃｒ含有量は、０～０．５００％である。
　Ｃｒ含有量の上限は、好ましくは０．４５０％であり、より好ましくは０．４００％である。
　一方、Ｃｒは、炭化物を形成して鋼材の強度を高める元素である。かかる効果を得る観点から、Ｃｒ含有量の下限は、好ましくは０％超であり、より好ましくは０．０１０％であり、更に好ましくは０．０５０％であり、更に好ましくは０．１００％である。 Cr: 0 to 0.500%
Cr is an arbitrary element. That is, the Cr content may be 0% or more than 0%.
If the Cr content is too high, the SSC resistance of the steel material may decrease.
Therefore, the Cr content is 0 to 0.500%.
The upper limit of the Cr content is preferably 0.450%, more preferably 0.400%.
On the other hand, Cr is an element that forms carbides to increase the strength of steel materials. From the viewpoint of obtaining such an effect, the lower limit of the Cr content is preferably more than 0%, more preferably 0.010%, further preferably 0.050%, still more preferably 0.100%. be.
　Ｍｏ：０～０．５００％
　Ｍｏは、任意元素である。即ち、Ｍｏ含有量は、０％であってもよいし、０％超であってもよい。
　Ｍｏ含有量が高すぎると、Ｍ２Ｃ型炭化物が過剰に生成し、鋼材の耐ＳＳＣ性を低下する場合がある。
　従って、Ｍｏ含有量は、０～０．５００％である。
　Ｍｏ含有量の上限は、好ましくは０．４５０％であり、より好ましくは０．４００％である。
　一方、Ｍｏは、炭化物を形成して鋼材の強度を高める元素である。かかる効果を得る観点から、Ｍｏ含有量の下限は、好ましくは０％超であり、より好ましくは０．０１０％であり、更に好ましくは０．０５０％であり、更に好ましくは０．１００％である。 Mo: 0 to 0.500%
Mo is an arbitrary element. That is, the Mo content may be 0% or more than 0%.
When Mo content is too high, M 2 C type carbides are excessively generated, it may decrease the SSC resistance of the steel.
Therefore, the Mo content is 0 to 0.500%.
The upper limit of the Mo content is preferably 0.450%, more preferably 0.400%.
On the other hand, Mo is an element that forms carbides to increase the strength of steel materials. From the viewpoint of obtaining such an effect, the lower limit of the Mo content is preferably more than 0%, more preferably 0.010%, further preferably 0.050%, still more preferably 0.100%. be.
　Ｗ：０～０．５００％
　Ｗ（タングステン）は、任意元素である。即ち、Ｗ含有量は、０％であってもよいし、０％超であってもよい。
　Ｗ含有量が高すぎると、鋼材中に粗大な炭化物が生成し、鋼材の耐ＳＳＣ性が低下する場合がある。
　従って、Ｗ含有量は、０～０．５００％である。
　Ｗ含有量の上限は、好ましくは０．４５０％であり、より好ましくは０．４００％である。
　一方、Ｗは、鋼材の強度を高める元素である。Ｗは、更に、硫化水素環境中で保護性の腐食被膜を形成し、水素侵入を抑制し、その結果、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素でもある。これらの効果を得る観点から、Ｗ含有量の下限は、好ましくは０％超であり、より好ましくは０．００１％であり、更に好ましくは０．０５０％であり、更に好ましくは０．１００％である。 W: 0 to 0.500%
W (tungsten) is an optional element. That is, the W content may be 0% or more than 0%.
If the W content is too high, coarse carbides may be formed in the steel material, which may reduce the SSC resistance of the steel material.
Therefore, the W content is 0 to 0.500%.
The upper limit of the W content is preferably 0.450%, more preferably 0.400%.
On the other hand, W is an element that increases the strength of the steel material. W is also an element that forms a protective corrosive film in a hydrogen sulfide environment, suppresses hydrogen intrusion, and as a result, enhances SSC resistance and SOHIC resistance of steel materials. From the viewpoint of obtaining these effects, the lower limit of the W content is preferably more than 0%, more preferably 0.001%, still more preferably 0.050%, still more preferably 0.100%. Is.
　Ｚｒ：０～０．０５００％
　Ｚｒは、任意元素である。即ち、Ｚｒ含有量は、０％であってもよいし、０％超であってもよい。
　Ｚｒ含有量が高すぎると、鋼材中の酸化物が粗大化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｚｒ含有量は、０～０．０５００％である。
　Ｚｒ含有量の上限は、好ましくは０．０４００％であり、より好ましくは０．０３００％である。
　一方、Ｚｒは、鋼材中の硫化物を微細化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素である。かかる効果を得る観点から、Ｚｒ含有量の下限は、好ましくは０％超であり、より好ましくは０．０００１％であり、更に好ましくは０．０００３％であり、更に好ましくは０．０００５％である。 Zr: 0-0.0500%
Zr is an arbitrary element. That is, the Zr content may be 0% or more than 0%.
If the Zr content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Zr content is 0-0.0500%.
The upper limit of the Zr content is preferably 0.0400%, more preferably 0.0300%.
On the other hand, Zr is an element that refines sulfide in the steel material and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Zr content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
　Ｔａ：０～０．０５００％
　Ｔａは、任意元素である。即ち、Ｔａ含有量は、０％であってもよいし、０％超であってもよい。
　Ｔａ含有量が高すぎると、鋼材中の酸化物が粗大化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｔａ含有量は、０～０．０５００％である。
　Ｔａ含有量の上限は、好ましくは０．０４００％であり、より好ましくは０．０３００％である。
　一方、Ｔａは、鋼材中の硫化物を微細化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素である。かかる効果を得る観点から、Ｔａ含有量の下限は、好ましくは０％超であり、より好ましくは０．０００１％であり、更に好ましくは０．０００３％であり、更に好ましくは０．０００５％である。 Ta: 0-0.0500%
Ta is an arbitrary element. That is, the Ta content may be 0% or more than 0%.
If the Ta content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Ta content is 0 to 0.0500%.
The upper limit of the Ta content is preferably 0.0400%, more preferably 0.0300%.
On the other hand, Ta is an element that refines sulfide in the steel material and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Ta content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
　Ｍｇ：０～０．００５０％
　Ｍｇは、任意元素である。即ち、Ｍｇ含有量は、０％であってもよいし、０％超であってもよい。
　Ｍｇ含有量が高すぎると、鋼材中の酸化物が粗大化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｍｇ含有量は、０～０．００５０％である。
　Ｍｇ含有量の上限は、好ましくは０．００４５％であり、より好ましくは０．００４０％である。
　一方、Ｍｇは、鋼材中のＳを硫化物として無害化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素である。かかる効果を得る観点から、Ｍｇ含有量の下限は、好ましくは０％超であり、より好ましくは０．０００１％であり、更に好ましくは０．０００３％であり、更に好ましくは０．０００５％である。 Mg: 0 to 0.0050%
Mg is an optional element. That is, the Mg content may be 0% or more than 0%.
If the Mg content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Mg content is 0 to 0.0050%.
The upper limit of the Mg content is preferably 0.0045%, more preferably 0.0040%.
On the other hand, Mg is an element that detoxifies S in the steel material as a sulfide and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Mg content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
　ＲＥＭ：０～０．００５０％
　ＲＥＭは、任意元素である。即ち、ＲＥＭ含有量は、０％であってもよいし、０％超であってもよい。
　ここで、ＲＥＭは、希土類元素、即ち、Ｓｃ、Ｙ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、及びＬｕからなる群から選択される少なくとも１種の元素を意味する。また、ＲＥＭ含有量は、希土類元素の総含有量を意味する。
　ＲＥＭ含有量が高すぎると、酸化物が粗大化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する。
　従って、ＲＥＭ含有量は、０～０．００５０％である。
　一方、ＲＥＭは、鋼材中の硫化物の形態を制御して鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素である。また、ＲＥＭは、鋼材中のＰと結合して結晶粒界におけるＰの偏析を抑制し、これにより、Ｐの偏析に起因する鋼材の低温靭性の低下を抑制する元素でもある。これらの効果を得る観点から、ＲＥＭ含有量の下限は、好ましくは０％超であり、より好ましくは０．０００１％であり、更に好ましくは０．０００３％であり、更に好ましくは０．０００５％である。 REM: 0-0.0050%
REM is an optional element. That is, the REM content may be 0% or more than 0%.
Here, REM is selected from the group consisting of rare earth elements, that is, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It means at least one element to be produced. The REM content means the total content of rare earth elements.
If the REM content is too high, the oxide becomes coarse and the SSC resistance and SOHIC resistance of the steel material deteriorate.
Therefore, the REM content is 0 to 0.0050%.
On the other hand, REM is an element that controls the morphology of sulfide in the steel material to enhance the SSC resistance and SOHIC resistance of the steel material. REM is also an element that binds to P in the steel material and suppresses segregation of P at the grain boundaries, thereby suppressing a decrease in low temperature toughness of the steel material due to segregation of P. From the viewpoint of obtaining these effects, the lower limit of the REM content is preferably more than 0%, more preferably 0.0001%, still more preferably 0.0003%, still more preferably 0.0005%. Is.
　Ｈｆ：０～０．００５０％
　Ｈｆは、任意元素である。即ち、Ｈｆ含有量は、０％であってもよいし、０％超であってもよい。
　Ｈｆ含有量が高すぎると、鋼材中の酸化物が粗大化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｈｆ含有量は、０～０．００５０％である。
　Ｈｆ含有量の上限は、好ましくは０．００４５％であり、より好ましくは０．００４０％である。
　一方、Ｈｆは、鋼材中の硫化物の形態を制御して鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素である。かかる効果を得る観点から、Ｈｆ含有量の下限は、好ましくは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０．０００５％である。 Hf: 0 to 0.0050%
Hf is an arbitrary element. That is, the Hf content may be 0% or more than 0%.
If the Hf content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Hf content is 0 to 0.0050%.
The upper limit of the Hf content is preferably 0.0045%, more preferably 0.0040%.
On the other hand, Hf is an element that controls the morphology of sulfide in the steel material to enhance the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Hf content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
　Ｒｅ：０～０．００５０％
　Ｒｅは、任意元素である。即ち、Ｒｅ含有量は、０％であってもよいし、０％超であってもよい。
　Ｒｅ含有量が高すぎると、鋼材中の酸化物が粗大化し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。
　従って、Ｒｅ含有量は、０～０．００５０％である。
　Ｒｅ含有量の上限は、好ましくは０．００４５％であり、より好ましくは０．００４０％である。
　一方、Ｒｅは、鋼材中の硫化物の形態を制御し、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性を高める元素である。かかる効果を得る観点から、Ｒｅ含有量の下限は、好ましくは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０．０００５％である。 Re: 0-0.0050%
Re is an arbitrary element. That is, the Re content may be 0% or more than 0%.
If the Re content is too high, the oxide in the steel material may become coarse and the SSC resistance and SOHIC resistance of the steel material may decrease.
Therefore, the Re content is 0 to 0.0050%.
The upper limit of the Re content is preferably 0.0045%, more preferably 0.0040%.
On the other hand, Re is an element that controls the morphology of sulfide in the steel material and enhances the SSC resistance and SOHIC resistance of the steel material. From the viewpoint of obtaining such an effect, the lower limit of the Re content is preferably more than 0%, more preferably 0.0001%, further preferably 0.0003%, still more preferably 0.0005%. be.
　残部：Ｆｅ及び不純物
　母材部の化学組成において、上述した各元素を除いた残部は、Ｆｅ及び不純物である。
　ここで、不純物とは、原材料（例えば、鉱石、スクラップ、等）に含まれる成分、または、製造の工程で混入する成分であって、意図的に鋼に含有させたものではない成分を指す。
　不純物としては、上述した元素以外のあらゆる元素が挙げられる。不純物としての元素は、１種のみであっても２種以上であってもよい。
　不純物として、例えば、Ｓｂ、Ｓｎ、Ｃｏ、Ａｓ、Ｐｂ、Ｂｉ、Ｈ（水素）等が挙げられる。
　通常、Ｓｂ、Ｓｎ、Ｃｏ、及びＡｓについては、例えば含有量０．１％以下の混入が、Ｐｂ及びＢｉについては、例えば含有量０．００５％以下の混入が、Ｈについては、例えば含有量０．０００４％以下の混入が、それぞれあり得る。その他の元素の含有量については、通常の範囲であれば、特に制御する必要はない。 Remaining part: Fe and impurities In the chemical composition of the base metal part, the balance excluding each element described above is Fe and impurities.
Here, the impurity refers to a component contained in a raw material (for example, ore, scrap, etc.) or a component mixed in a manufacturing process and not intentionally contained in steel.
Impurities include any element other than the elements described above. The element as an impurity may be only one kind or two or more kinds.
Examples of impurities include Sb, Sn, Co, As, Pb, Bi, H (hydrogen) and the like.
Usually, Sb, Sn, Co, and As are mixed with a content of 0.1% or less, Pb and Bi are mixed with a content of 0.005% or less, and H is mixed with a content of, for example, 0.005% or less. Each possible contamination is 0.0004% or less. It is not necessary to control the content of other elements as long as it is within the normal range.
　母材部の化学組成は、上述した各任意元素による効果を得る観点から、Ｃｕ：０％超０．５００％以下、Ｎｉ：０％超０．５００％以下、Ｂ：０％超０．００２０％以下、Ｖ：０％超０．１００％以下、Ｃｒ：０％超０．５００％以下、Ｍｏ：０％超０．５００％以下、Ｗ：０％超０．５００％以下、Ｚｒ：０％超０．０５００％以下、Ｔａ：０％超０．０５００％以下、Ｍｇ：０％超０．００５０％以下、ＲＥＭ：０％超０．００５０％以下、Ｈｆ：０％超０．００５０％以下、及び、Ｒｅ：０％超０．００５０％以下からなる群から選択される１種又は２種以上を含有してもよい。
　これら任意元素の含有量の好ましい範囲は、それぞれ前述したとおりである。 The chemical composition of the base metal is Cu: more than 0% and 0.500% or less, Ni: more than 0% and 0.500% or less, and B: more than 0% and 0.0020 from the viewpoint of obtaining the effect of each of the above-mentioned arbitrary elements. % Or less, V: more than 0% and less than 0.100%, Cr: more than 0% and less than 0.500%, Mo: more than 0% and less than 0.500%, W: more than 0% and less than 0.500%, Zr: 0 % More than 0.0500% or less, Ta: More than 0% and less than 0.0500%, Mg: More than 0% and less than 0.0050%, REM: More than 0% and less than 0.0050%, Hf: More than 0% and 0.0050% It may contain one or more selected from the group consisting of the following and Re: more than 0% and 0.0050% or less.
The preferable ranges of the contents of these arbitrary elements are as described above.
＜母材部の内表層の金属組織＞
　本開示の電縫鋼管は、母材部の内表層の金属組織において、ポリゴナルフェライト分率（以下、「Ｆ分率」ともいう）が８０％以上１００％未満であり、残部が疑似パーライト及びセメンタイトを含む。
　上記母材部の内表層の金属組織は、母材部の化学組成が前述の化学組成Ａであり、母材部の引張強度が５１５～６５０ＭＰａの範囲内であるという制約の下で、ΔＹＳ及びΔＨｖの要件による耐サワー性（詳細には耐ＳＳＣ性及び耐ＳＯＨＩＣ性）の効果を得るための前提となる金属組織である。 <Metal structure of the inner surface layer of the base material>
The electrosewn steel pipe of the present disclosure has a polygonal ferrite fraction (hereinafter, also referred to as “F fraction”) of 80% or more and less than 100% in the metal structure of the inner surface layer of the base metal portion, and the balance is pseudo pearlite and Contains cementite.
The metallographic structure of the inner surface layer of the base metal portion has ΔYS and the above-mentioned chemical composition A, and the tensile strength of the base metal portion is in the range of 515 to 650 MPa. It is a metal structure that is a prerequisite for obtaining the effect of sour resistance (specifically, SSC resistance and SOHIC resistance) according to the requirement of ΔHv.
　母材部の内表層の金属組織におけるＦ分率が８０％未満であると、母材部の強度が高くなりすぎ、ΔＹＳ及びΔＨｖが大きくなりすぎ、その結果、鋼材の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が低下する場合がある。従って、母材部の内表層の金属組織におけるＦ分率は８０％以上であり、好ましくは８３％以上であり、より好ましくは８５％以上であり、更に好ましくは９０％以上である。
　母材部の内表層の金属組織におけるＦ分率が１００％であると、母材部の引張強度及び降伏強度が低くなりすぎる場合がある。従って、母材部の内表層の金属組織におけるＦ分率は１００％未満であり、好ましくは９８％以下であり、より好ましくは９５％以下である。 When the F fraction in the metal structure of the inner surface layer of the base metal portion is less than 80%, the strength of the base metal portion becomes too high and ΔYS and ΔHv become too large, and as a result, the SSC resistance and SOHIC resistance of the steel material become too large. Sex may be reduced. Therefore, the F fraction in the metal structure of the inner surface layer of the base metal portion is 80% or more, preferably 83% or more, more preferably 85% or more, and further preferably 90% or more.
If the F fraction in the metal structure of the inner surface layer of the base metal portion is 100%, the tensile strength and yield strength of the base metal portion may become too low. Therefore, the F fraction in the metal structure of the inner surface layer of the base metal portion is less than 100%, preferably 98% or less, and more preferably 95% or less.
　本開示において、母材部の内表層の金属組織における、ポリゴナルフェライトを除いた残部は、疑似パーライト及びセメンタイトを含む。これにより、母材部の引張強度が上述の範囲内に調整されやすい。残部は、疑似パーライト及びセメンタイトからなることが好ましい。 In the present disclosure, the rest of the metal structure of the inner surface layer of the base metal portion excluding the polygonal ferrite contains pseudo pearlite and cementite. As a result, the tensile strength of the base metal portion can be easily adjusted within the above range. The balance is preferably composed of pseudo-pearlite and cementite.
　本開示において、母材部の内表層の金属組織における、Ｆ分率の測定及び残部の種類の確認は、以下のようにして行う。
　電縫鋼管における母材１８０°位置（即ち、電縫溶接部から管周方向に１８０°ずれた位置）のＬ断面（即ち、電縫鋼管の管軸方向及び肉厚方向に対して平行な断面）をナイタールエッチングする。
　ナイタールエッチング後のＬ断面における、電縫鋼管の内表面から深さ１ｍｍの位置の金属組織写真を、走査型電子顕微鏡（ＳＥＭ）を用いて２００倍の倍率にて撮影する。
　撮影した金属組織写真を画像処理することにより、Ｆ分率の測定及び残部の種類の確認を行う。
　画像処理は、例えば（株）ニレコ製の小型汎用画像解析装置ＬＵＺＥＸ　ＡＰを用いて行う。 In the present disclosure, the measurement of the F fraction and the confirmation of the type of the remaining portion in the metal structure of the inner surface layer of the base metal portion are performed as follows.
L cross section (that is, a cross section parallel to the pipe axial direction and the wall thickness direction of the power sewn steel pipe) at the 180 ° position of the base material in the power sewn steel pipe (that is, the position shifted by 180 ° in the pipe circumferential direction from the power sewn welded portion). ) Is nightal etched.
A metallographic photograph at a depth of 1 mm from the inner surface of the electrosewn steel pipe in the L cross section after the tital etching is taken with a scanning electron microscope (SEM) at a magnification of 200 times.
By image processing the photographed metallographic structure, the F fraction is measured and the type of the balance is confirmed.
Image processing is performed using, for example, a small general-purpose image analysis device LUZEX AP manufactured by NIRECO CORPORATION.
＜母材部の引張強度（ＴＳ）＞
　本開示の電縫鋼管は、母材部の引張強度（ＴＳ）が５１５～６５０ＭＰａである。
　ここで、母材部のＴＳは、管軸方向の引張強度を意味する。
　母材部のＴＳが５１５ＭＰａ以上であると、ラインパイプ用電縫鋼管として要求される強度をより満足し易い。母材部のＴＳは、好ましくは５２０ＭＰａ以上であり、より好ましくは５３０ＭＰａ以上である。
　母材部のＴＳが６５０ＭＰａ以下であると、母材部の耐ＳＳＣ性及び耐ＳＯＨＩＣ性が向上する。母材部のＴＳは、好ましくは６４０ＭＰａ以下であり、より好ましくは６３０ＭＰａ以下である。 <Tensile strength (TS) of base material>
The electrosewn steel pipe of the present disclosure has a tensile strength (TS) of a base material portion of 515 to 650 MPa.
Here, TS of the base material portion means the tensile strength in the pipe axis direction.
When the TS of the base material portion is 515 MPa or more, it is easier to satisfy the strength required for the electric resistance sewn steel pipe for line pipes. The TS of the base material portion is preferably 520 MPa or more, more preferably 530 MPa or more.
When the TS of the base material portion is 650 MPa or less, the SSC resistance and the SOHIC resistance of the base material portion are improved. The TS of the base metal portion is preferably 640 MPa or less, more preferably 630 MPa or less.
＜母材部の降伏強度（ＹＳ）＞
　本開示の電縫鋼管は、母材部の降伏強度（ＹＳ）が４１０ＭＰａ以上である。
　ここで、母材部のＹＳは、管軸方向の降伏強度を意味する。
　母材部のＹＳが４１０ＭＰａ以上であると、ラインパイプ用電縫鋼管として要求される強度をより満足し易い。母材部のＹＳは、好ましくは４３０ＭＰａ以上であり、より好ましくは４５０ＭＰａ以上である。
　母材部のＹＳは、好ましくは６３０ＭＰａ以下である。母材部のＹＳが６３０ＭＰａ以下である場合には、母材部の耐ＳＳＣ性及び耐ＳＯＨＩＣ性の点で有利である。また、母材部のＹＳが６３０ＭＰａ以下である場合には、ラインパイプ用電縫鋼管を用いて形成されたパイプラインを敷設する際の、曲げ変形性又は座屈抑制の点で有利である。母材部のＹＳは、より好ましくは６２０ＭＰａ以下であり、更に好ましくは６１０ＭＰａ以下であり、更に好ましくは６００ＭＰａ以下である。 <Yield strength of base metal (YS)>
The yield strength (YS) of the base metal portion of the electrosewn steel pipe of the present disclosure is 410 MPa or more.
Here, YS of the base metal portion means the yield strength in the pipe axis direction.
When the YS of the base material portion is 410 MPa or more, it is easier to satisfy the strength required for the electric resistance sewn steel pipe for line pipes. The YS of the base material portion is preferably 430 MPa or more, more preferably 450 MPa or more.
The YS of the base material portion is preferably 630 MPa or less. When the YS of the base material portion is 630 MPa or less, it is advantageous in terms of SSC resistance and SOHIC resistance of the base material portion. Further, when the YS of the base material portion is 630 MPa or less, it is advantageous in terms of bending deformability or buckling suppression when laying a pipeline formed by using an electrosewn steel pipe for a line pipe. The YS of the base material portion is more preferably 620 MPa or less, further preferably 610 MPa or less, and further preferably 600 MPa or less.
　母材部のＴＳ及び母材部のＹＳは、ＡＳＴＭ　Ｅ８（２０１３）に準拠し、以下の方法で測定する。
　電縫鋼管の母材１８０°位置における肉厚中央部から、直径が６ｍｍで平行部長さが３５ｍｍである丸棒試験片を、この丸棒試験片の平行部の長さ方向が電縫鋼管の管軸方向に対して平行となる向きに採取する。
　採取した丸棒試験片を用い、ＡＳＴＭ　Ｅ８（２０１３）に準拠し、常温（２５℃）、大気中で引張試験（即ち、管軸方向引張試験）を実施する。
　上記引張試験における一様伸び中の最大応力を、母材部のＴＳ（ＭＰａ）とする。
　上記引張試験における０．２％耐力を、母材部のＹＳ（ＭＰａ）とする。 The TS of the base material and the YS of the base material are measured by the following method in accordance with ASTM E8 (2013).
A round bar test piece having a diameter of 6 mm and a parallel part length of 35 mm is obtained from the center of the wall thickness at the 180 ° position of the base metal of the electric resistance pipe. Collect in the direction parallel to the pipe axis direction.
Using the collected round bar test piece, a tensile test (that is, a tube axial tensile test) is carried out in the air at room temperature (25 ° C.) in accordance with ASTM E8 (2013).
The maximum stress during uniform elongation in the above tensile test is defined as TS (MPa) of the base metal portion.
The 0.2% proof stress in the above tensile test is defined as YS (MPa) of the base material portion.
　本開示の電縫鋼管の母材部では、管軸方向引張試験（例えば、上記の引張試験）を行った場合に、降伏伸びが実質的に観測されないことが好ましい。
　ここで、降伏伸びが実質的に観測されないとは、降伏伸びが１％未満であることを意味する。
　また、母材部の管軸方向引張試験において降伏伸びが実質的に観測されないことは、電縫鋼管が、アズロール（as-rolled）電縫鋼管であることを意味する。
　ここで、アズロール電縫鋼管とは、造管後、シーム熱処理以外の熱処理が施されていない電縫鋼管を意味する。
　これに対し、造管後、シーム熱処理以外の熱処理（例えば焼戻し）が施された電縫鋼管は、管軸方向引張試験を行った場合に、実質的な降伏伸び（１％以上の降伏伸び）が観測される。 In the base material portion of the electrosewn steel pipe of the present disclosure, it is preferable that the yield elongation is substantially not observed when the pipe axial tensile test (for example, the above-mentioned tensile test) is performed.
Here, the fact that the yield elongation is substantially not observed means that the yield elongation is less than 1%.
Further, the fact that the yield elongation is not substantially observed in the pipe axial tensile test of the base metal portion means that the electric pipe is an as-rolled electric pipe.
Here, the azurol electric resistance pipe means an electric pipe that has not been subjected to a heat treatment other than the seam heat treatment after the pipe is made.
On the other hand, an electrosewn steel pipe that has been subjected to a heat treatment (for example, tempering) other than the seam heat treatment after the pipe is made has a substantial yield elongation (yield elongation of 1% or more) when a tensile test in the pipe axial direction is performed. Is observed.
＜母材部の降伏比（ＹＲ）＞
　本開示の電縫鋼管において、母材部の降伏比（ＹＲ）（＝母材部のＹＳ／母材部のＴＳ）には特に制限はない。
　ここで、母材部のＹＲは、管軸方向の降伏比を意味する。
　ラインパイプ用電縫鋼管を用いて形成されたパイプラインを敷設する際の座屈をより効果的に抑制する観点から、母材部のＹＲは、好ましくは０．９７以下であり、より好ましくは０．９６以下である。
　母材部のＹＲの下限としては、例えば０．８５及び０．８６が挙げられる。 <Yield ratio of base metal (YR)>
In the electrosewn steel pipe of the present disclosure, the yield ratio (YR) of the base material portion (= YS of the base material portion / TS of the base material portion) is not particularly limited.
Here, the YR of the base metal portion means the yield ratio in the pipe axis direction.
From the viewpoint of more effectively suppressing buckling when laying a pipeline formed by using an electrosewn steel pipe for a line pipe, the YR of the base metal portion is preferably 0.97 or less, more preferably 0.97 or less. It is 0.96 or less.
Examples of the lower limit of YR of the base material portion include 0.85 and 0.86.
＜ΔＹＳ＞
　本開示の電縫鋼管において、ΔＹＳ（即ち、母材部の降伏強度から電縫溶接部の降伏強度を差し引いた値）は、０～８０ＭＰａである。
　ΔＹＳが０～８０ＭＰａであることにより、電縫溶接部におけるＳＳＣの発生が抑制される（即ち、電縫溶接部における耐ＳＳＣ性が向上する）。
　前述したとおり、ΔＹＳが８０ＭＰａ超であると、電縫溶接部に負荷された応力が集中し、電縫溶接部のＳＳＣが発生する場合がある。従って、ΔＹＳは、８０ＭＰａ以下であり、好ましくは７０ＭＰａ以下である。 <ΔYS>
In the electric resistance welded steel pipe of the present disclosure, ΔYS (that is, a value obtained by subtracting the yield strength of the electric resistance welded portion from the yield strength of the base metal portion) is 0 to 80 MPa.
When ΔYS is 0 to 80 MPa, the generation of SSC in the electric sewing welded portion is suppressed (that is, the SSC resistance in the electric sewing welded portion is improved).
As described above, when ΔYS is more than 80 MPa, the stress applied to the electric stitch welded portion is concentrated, and SSC of the electric stitch welded portion may occur. Therefore, ΔYS is 80 MPa or less, preferably 70 MPa or less.
　また、ΔＹＳが０ＭＰａ以上であることは、本開示の電縫鋼管の製造適性に寄与している。
　この点について補足すると、前述したとおり、従来、電縫溶接部の降伏強度は、母材部の降伏強度よりも高いと考えられていた。
　しかし、本開示の電縫鋼管では、電縫溶接部の降伏強度が、母材部の降伏強度と同等か、又は、母材部の降伏強度よりも低い（具体的には、ΔＹＳが０ＭＰａ以上である）。
　この現象が生じる理由の詳細は不明であるが、この現象は、母材部の化学組成、母材部の内表層の金属組織、母材部のＴＳ、母材部のＹＳ等の組み合わせによって生じている現象と推測される。 Further, the fact that ΔYS is 0 MPa or more contributes to the manufacturing suitability of the electrosewn steel pipe of the present disclosure.
To supplement this point, as described above, it has been conventionally considered that the yield strength of the electric stitch welded portion is higher than the yield strength of the base metal portion.
However, in the electric resistance welded steel pipe of the present disclosure, the yield strength of the electric resistance welded portion is equal to or lower than the yield strength of the base metal portion (specifically, ΔYS is 0 MPa or more). Is).
The details of the reason why this phenomenon occurs are unknown, but this phenomenon is caused by a combination of the chemical composition of the base material, the metal structure of the inner surface layer of the base material, the TS of the base material, the YS of the base material, and the like. It is presumed that this is a phenomenon.
　ΔＹＳを算出するための、母材部の降伏強度（ＹＳ）の測定方法は前述のとおりである。
　ΔＹＳを算出するための電縫溶接部の降伏強度（ＹＳ）は、ＡＳＴＭ　Ｅ８（２０１３）に準拠し、以下の方法で測定する。
　電縫鋼管の内表面側における電縫溶接部を含む領域から、直径が６ｍｍで平行部長さが３５ｍｍである丸棒試験片を、この丸棒試験片の平行部の長さ方向が電縫鋼管の管周方向に対して平行となるように採取する。より詳細には、上記丸棒試験片は、上記丸棒試験片における平行部の長手方向の中心と、電縫鋼管の電縫溶接衝合線と、が略一致するように採取する。ここで、略一致とは、平行部の長手方向の中心と、電縫鋼管の電縫溶接衝合線と、が完全に一致するか、又は、両者のずれが１ｍｍ以内であることを意味する。
　採取した丸棒試験片を用い、ＡＳＴＭ　Ｅ８（２０１３）に準拠し、常温（２５℃）、大気中で引張試験（即ち、管周方向引張試験）を実施する。
　上記引張試験における０．２％耐力を、電縫溶接部のＹＳ（ＭＰａ）とする。 The method for measuring the yield strength (YS) of the base metal portion for calculating ΔYS is as described above.
The yield strength (YS) of the electric stitch welded portion for calculating ΔYS is measured by the following method in accordance with ASTM E8 (2013).
A round bar test piece having a diameter of 6 mm and a parallel portion length of 35 mm is obtained from a region including an electrosewn welded portion on the inner surface side of the electrosewn steel pipe. Collect so that it is parallel to the circumferential direction of the pipe. More specifically, the round bar test piece is collected so that the center of the parallel portion in the round bar test piece in the longitudinal direction and the electric stitch welding abuttal line of the electric resistance pipe are substantially aligned with each other. Here, substantially the same means that the center of the parallel portion in the longitudinal direction and the electric resistance welding abuttal line of the electric resistance pipe are completely coincident with each other, or the deviation between the two is within 1 mm. ..
Using the collected round bar test piece, a tensile test (that is, a tensile test in the circumferential direction of the tube) is carried out in the air at room temperature (25 ° C.) in accordance with ASTM E8 (2013).
The 0.2% proof stress in the above tensile test is defined as YS (MPa) of the electric stitch welded portion.
＜ΔＨｖ＞
　本開示の電縫鋼管において、ΔＨｖ（即ち、電縫溶接部の外表層のビッカース硬さから電縫溶接部の内表層のビッカース硬さを差し引いた値）は、０～２５Ｈｖである。
　ΔＨｖが０～２５Ｈｖであることにより、電縫溶接部におけるＳＯＨＩＣの発生が抑制される（即ち、電縫溶接部における耐ＳＯＨＩＣ性が向上する）。
　前述したとおり、ΔＹＳが０～８０ＭＰａである場合であっても、ΔＨｖが２５Ｈｖ超である場合には、電縫溶接部においてＳＯＨＩＣが発生する場合がある。従って、ΔＨｖは、２５Ｈｖ以下であり、好ましくは２０Ｈｖであり、さらに好ましくは１８Ｈｖであり、さらに好ましくは１５Ｈｖである。 <ΔHv>
In the electric resistance welded steel pipe of the present disclosure, ΔHv (that is, the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded portion from the Vickers hardness of the outer surface layer of the electric sewing welded portion) is 0 to 25 Hv.
When ΔHv is 0 to 25 Hv, the generation of SOHIC in the electric stitch welded portion is suppressed (that is, the SOHIC resistance in the electric stitch welded portion is improved).
As described above, even when ΔYS is 0 to 80 MPa, when ΔHv is more than 25 Hv, SOHIC may occur in the electric stitch welded portion. Therefore, ΔHv is 25 Hv or less, preferably 20 Hv, more preferably 18 Hv, and even more preferably 15 Hv.
　また、ΔＨｖが０Ｈｖ以上であることは、本開示の電縫鋼管の製造適性に寄与している。
　例えば、電縫溶接部の外表面側からシーム熱処理を施す（即ち、加熱及び冷却をこの順に施す）ことにより、ΔＨｖが０Ｈｖ以上であることが実現されやすい。 Further, the fact that ΔHv is 0 Hv or more contributes to the manufacturing suitability of the electrosewn steel pipe of the present disclosure.
For example, it is easy to realize that ΔHv is 0 Hv or more by performing seam heat treatment (that is, heating and cooling in this order) from the outer surface side of the electric sewing welded portion.
　本開示において、電縫溶接部の外表層のビッカース硬さは、以下のようにして求める。
　電縫鋼管のＣ断面（即ち、管軸方向に対して垂直な断面）中、電縫鋼管の外表面から深さ１ｍｍの位置に相当する線上であって、電縫溶接衝合線を中心とする管周方向２ｍｍの範囲内における０．５ｍｍピッチの５点を、測定点として特定する。５点の測定点の各々において、荷重１００ｇｆの条件にて、ＪＩＳ　Ｚ　２２４４（２００９）に準拠し、ビッカース硬さを測定する。５点の測定点における測定値の算術平均値を、「電縫溶接部の外表層のビッカース硬さ」とする。 In the present disclosure, the Vickers hardness of the outer surface layer of the electrosewn welded portion is determined as follows.
In the C cross section of the electric resistance pipe (that is, the cross section perpendicular to the pipe axis direction), it is on a line corresponding to a depth of 1 mm from the outer surface of the electric resistance pipe, and is centered on the electric resistance welding abutment line. Five points with a 0.5 mm pitch within a range of 2 mm in the circumferential direction of the pipe are specified as measurement points. At each of the five measurement points, the Vickers hardness is measured in accordance with JIS Z 2244 (2009) under the condition of a load of 100 gf. The arithmetic mean value of the measured values at the five measurement points is defined as "Vickers hardness of the outer surface layer of the electric stitch welded portion".
　本開示において、電縫溶接部の内表層のビッカース硬さは、以下のようにして求める。
　電縫鋼管のＣ断面中、電縫鋼管の内表面から深さ１ｍｍの位置に相当する線上であって、電縫溶接衝合線を中心とする管周方向２ｍｍの範囲内における０．５ｍｍピッチの５点を、測定点として特定する。５点の測定点の各々において、荷重１００ｇｆの条件にて、ＪＩＳ　Ｚ　２２４４（２００９）に準拠し、ビッカース硬さを測定する。５点の測定点における測定値の算術平均値を、「電縫溶接部の内表層のビッカース硬さ」とする。 In the present disclosure, the Vickers hardness of the inner surface layer of the electrosewn welded portion is determined as follows.
In the C cross section of the electric resistance welded steel pipe, the pitch is 0.5 mm on the line corresponding to the position of 1 mm in depth from the inner surface of the electric resistance welded steel pipe and within the range of 2 mm in the circumferential direction of the electric pipe centered on the electric resistance welding abuttal line. 5 points are specified as measurement points. At each of the five measurement points, the Vickers hardness is measured in accordance with JIS Z 2244 (2009) under the condition of a load of 100 gf. The arithmetic mean value of the measured values at the five measurement points is defined as "Vickers hardness of the inner surface layer of the electric stitch welded portion".
　本開示において、ΔＨｖは、以上のようにして求められた「電縫溶接部の外表層のビッカース硬さ」から、以上のようにして求められた「電縫溶接部の内表層のビッカース硬さ」を差し引くことによって求める。 In the present disclosure, ΔHv is the “Vickers hardness of the inner surface layer of the electric sewing welded portion” obtained as described above from the “Vickers hardness of the outer surface layer of the electric sewing welded portion” obtained as described above. Is calculated by subtracting.
＜電縫鋼管の肉厚＞
　前述した本発明者らの検討では、特に、電縫鋼管Ｘ（即ち、本開示の電縫鋼管における、ΔＹＳ及びΔＨｖの要件以外の要件を満足する電縫鋼管）の肉厚が厚い場合（具体的には１３ｍｍ以上である場合）に、ΔＹＳが正の大きな値を採る傾向が強いこと、及び、電縫溶接部にＳＳＣが発生しやすい傾向が強いことが判明した。
　しかし、ΔＹＳ及びΔＨｖの要件（即ち、ΔＹＳが０～８０ＭＰａでありΔＨｖが０～２５Ｈｖであるという要件）を満足する本開示の電縫鋼管では、肉厚が１３ｍｍ以上である場合においても、ΔＹＳ及びΔＨｖの要件により、電縫溶接部における優れた耐サワー性（詳細には、耐ＳＳＣ性及び耐ＳＯＨＩＣ性。以下同じ。）が確保される。言い換えれば、肉厚が１３ｍｍ以上である場合には、ΔＹＳ及びΔＨｖの要件による耐サワー性改善の効果が大きい。
　従って、本開示の電縫鋼管の肉厚は、ΔＹＳ及びΔＨｖの要件による耐サワー性改善の効果が大きい点で、好ましくは１３ｍｍ以上であり、より好ましくは１４ｍｍ以上である。
　一方、本開示の電縫鋼管の肉厚は、肉厚が厚いことによる電縫溶接部のＳＳＣの発生をより抑制する観点から、好ましくは２５ｍｍ以下であり、より好ましくは２３ｍｍ以下であり、更に好ましくは２０ｍｍ以下である。 <Thickness of electric resistance pipe>
In the above-mentioned examination by the present inventors, in particular, when the wall thickness of the electric pipe X (that is, the electric pipe satisfying the requirements other than the requirements of ΔYS and ΔHv in the electric pipe of the present disclosure) is thick (specifically). It was found that when ΔYS is 13 mm or more, there is a strong tendency for ΔYS to take a large positive value, and there is a strong tendency for SSC to occur in the electric resistance welded portion.
However, in the welded steel pipe of the present disclosure that satisfies the requirements of ΔYS and ΔHv (that is, the requirement that ΔYS is 0 to 80 MPa and ΔHv is 0 to 25 Hv), even when the wall thickness is 13 mm or more, ΔYS And, according to the requirement of ΔHv, excellent sour resistance (specifically, SSC resistance and SOHIC resistance; the same applies hereinafter) in the electric resistance welded portion is ensured. In other words, when the wall thickness is 13 mm or more, the effect of improving the sour resistance due to the requirements of ΔYS and ΔHv is large.
Therefore, the wall thickness of the electrosewn steel pipe of the present disclosure is preferably 13 mm or more, more preferably 14 mm or more, in that the effect of improving the sour resistance due to the requirements of ΔYS and ΔHv is large.
On the other hand, the wall thickness of the electrosewn steel pipe of the present disclosure is preferably 25 mm or less, more preferably 23 mm or less, and further, from the viewpoint of further suppressing the occurrence of SSC in the electrosewn welded portion due to the thick wall thickness. It is preferably 20 mm or less.
＜電縫鋼管の外径＞
　本開示の電縫鋼管の外径は特に限定されないが、好ましくは３００～６５０ｍｍである。
　外径が３００ｍｍ以上であると、ラインパイプに求められる性能である、油又はガスの移送効率に優れる。外径は、より好ましくは３３０ｍｍ以上であり、更に好ましくは３５０ｍｍ以上である。
　一方、外径が６５０ｍｍ以下であると、電縫鋼管の製造適性に優れる。外径は、好ましくは６３０ｍｍ以下であり、より好ましくは６１０ｍｍ以下である。 <Outer diameter of electric resistance pipe>
The outer diameter of the electrosewn steel pipe of the present disclosure is not particularly limited, but is preferably 300 to 650 mm.
When the outer diameter is 300 mm or more, the oil or gas transfer efficiency, which is the performance required for the line pipe, is excellent. The outer diameter is more preferably 330 mm or more, still more preferably 350 mm or more.
On the other hand, when the outer diameter is 650 mm or less, the manufacturing suitability of the electrosewn steel pipe is excellent. The outer diameter is preferably 630 mm or less, more preferably 610 mm or less.
＜電縫鋼管の耐ＳＳＣ性及び耐ＳＯＨＩＣ性＞
　電縫鋼管の耐ＳＳＣ性及び耐ＳＯＨＩＣ性は、４点曲げ試験によって評価できる。
　以下、詳細を説明する。
　試験浴として、５．０質量％塩化ナトリウムと０．５質量％酢酸との混合水溶液（ＮＡＣＥ　ｓｏｌｕｔｉｏｎ　Ａ）を準備する。
　電縫鋼管の内表面側における電縫溶接部を含む領域から、長さ１２０ｍｍ、幅１０ｍｍ、及び厚さ２ｍｍの直方体の試験片を採取する。上記直方体の試験片は、試験片の長さ方向が電縫鋼管の管周方向であり、試験片の幅方向が電縫鋼管の管軸方向であり、試験片の厚さ方向が電縫鋼管の肉厚方向である向きに採取する。この際、上記直方体の試験片における長手方向の中心と、電縫鋼管の電縫溶接衝合線と、が略一致するように採取する。ここで、略一致とは、上記直方体の試験片における長手方向の中心と、電縫鋼管の電縫溶接衝合線と、が完全に一致するか、又は、両者のずれが１ｍｍ以内であることを意味する。
　採取した直方体の試験片に対し、ＡＳＴＭ　Ｇ３９－９９（２０１１）に準拠し、４点曲げ試験冶具を用い、４点曲げ応力を負荷する。この４点曲げ応力の負荷は、支持点間距離（即ち、外側支持点間距離）を１００ｍｍとし、荷重点間距離（即ち、内側支持点間距離）を４０ｍｍとして行う。試験片に負荷する４点曲げ応力は、母材部の管軸方向のＹＳの９０％に相当する応力とする。
　次に、４点曲げ応力を負荷した状態の試験片を、４点曲げ試験治具ごと試験容器に封入する。この試験容器に、更に、上述の試験浴を、気相部を残して注入し、試験片を試験浴に浸漬させる。続いて、試験浴を脱気した後、１ａｔｍのＨ２Ｓガスを連続的に通気しながら試験浴を撹拌することにより、試験浴にＨ２Ｓガスを飽和させる。次に、試験容器を封じた後、試験片が浸漬された試験浴を２４℃で７２０時間保持し、その後、試験片を取り出す。
　取り出した試験片を観察し、ＳＳＣ及びＳＯＨＩＣの発生の有無を判断する。
　ＳＳＣもＳＯＨＩＣも発生していない場合、耐ＳＳＣ性及び耐ＳＯＨＩＣ性に優れると判断することができる。
　ここで、ＳＳＣ及びＳＯＨＩＣは、割れの形状によって区別する。
　具体的には、管軸方向及び肉厚方向の両方に延びる割れをＳＯＨＩＣとし、肉厚方向に延びるが管軸方向には延びない割れをＳＳＣとする。 <SSC resistance and SOHIC resistance of electrosewn steel pipe>
The SSC resistance and SOHIC resistance of the electrosewn steel pipe can be evaluated by a 4-point bending test.
The details will be described below.
As a test bath, a mixed aqueous solution (NACE solution A) of 5.0% by mass sodium chloride and 0.5% by mass acetic acid is prepared.
A rectangular parallelepiped test piece having a length of 120 mm, a width of 10 mm, and a thickness of 2 mm is collected from a region including an electric stitch welded portion on the inner surface side of the electric resistance pipe. In the rectangular test piece, the length direction of the test piece is the pipe circumferential direction of the electric resistance pipe, the width direction of the test piece is the pipe axial direction of the electric resistance pipe, and the thickness direction of the test piece is the electric resistance steel pipe. Collect in the direction of the wall thickness. At this time, the center of the rectangular parallelepiped test piece in the longitudinal direction and the electric resistance welding abuttal line of the electric resistance pipe are collected so as to be substantially coincident with each other. Here, "substantially coincident" means that the center in the longitudinal direction of the rectangular parallelepiped test piece and the electric resistance welding abuttal line of the electric resistance pipe are completely coincident with each other, or the deviation between the two is within 1 mm. Means.
A 4-point bending stress is applied to the collected rectangular parallelepiped test piece using a 4-point bending test jig in accordance with ASTM G39-99 (2011). The load of the four-point bending stress is performed with the distance between the support points (that is, the distance between the outer support points) being 100 mm and the distance between the load points (that is, the distance between the inner support points) being 40 mm. The four-point bending stress applied to the test piece is a stress corresponding to 90% of YS in the tube axial direction of the base metal portion.
Next, the test piece with the 4-point bending stress applied is sealed in the test container together with the 4-point bending test jig. Further, the above-mentioned test bath is injected into this test container leaving the gas phase portion, and the test piece is immersed in the test bath. Subsequently, after degassing the test bath, by stirring the test bath while continuously bubbling H 2 S gas 1 atm, to saturate the H 2 S gas in a test bath. Next, after sealing the test container, the test bath in which the test piece is immersed is held at 24 ° C. for 720 hours, and then the test piece is taken out.
The test piece taken out is observed, and the presence or absence of SSC and SOHIC is determined.
When neither SSC nor SOHIC is generated, it can be judged that the SSC resistance and the SOHIC resistance are excellent.
Here, SSC and SOHIC are distinguished by the shape of the crack.
Specifically, a crack extending in both the pipe axis direction and the wall thickness direction is referred to as SOHIC, and a crack extending in the wall thickness direction but not extending in the pipe axis direction is referred to as SSC.
＜電縫鋼管の製造方法の一例（製法Ａ）＞
　以下、本開示の電縫鋼管を製造するための製造方法の一例（以下、「製法Ａ」とする）について説明する。
　以下の製法Ａは、後述する実施例の電縫鋼管の製造方法である。 <Example of manufacturing method of electric resistance steel pipe (manufacturing method A)>
Hereinafter, an example of a manufacturing method for manufacturing the electric resistance welded steel pipe of the present disclosure (hereinafter, referred to as “manufacturing method A”) will be described.
The following manufacturing method A is a manufacturing method of an electrosewn steel pipe according to an embodiment described later.
　製法Ａは、
　化学組成Ａ（即ち、本開示における母材部の化学組成）を有するスラブを準備するスラブ準備工程と、
　準備したスラブを、後述する条件で熱間圧延して熱延鋼板を得る熱延工程と、
　熱延鋼板を、熱延鋼板の外表面の温度が４５０～６２５℃の巻取温度となるまで水冷する熱延鋼板水冷工程と、
　冷却された熱延鋼板を、上記巻取温度にて巻取ることにより、熱延鋼板からなるホットコイルを得る巻取り工程と、
　ホットコイルから熱延鋼板を巻き出し、巻き出された熱延鋼板をロール成形することによりオープン管とし、得られたオープン管の衝合部を電縫溶接して電縫溶接部を形成することにより、素管を得る造管工程と、
　素管の電縫溶接部に対し、９００～１０００℃の加熱温度にまで加熱し、上記加熱温度にて１秒以上均熱し、次いで３００～５８０℃の冷却停止温度まで、５～２０℃／秒の冷却速度にて水冷するシーム熱処理を施すシーム熱処理工程と、
を含む。 Manufacturing method A is
A slab preparation step for preparing a slab having a chemical composition A (that is, the chemical composition of the base metal portion in the present disclosure),
A hot-rolling process in which the prepared slab is hot-rolled under the conditions described below to obtain a hot-rolled steel sheet,
A hot-rolled steel sheet water-cooling process in which the hot-rolled steel sheet is water-cooled until the temperature of the outer surface of the hot-rolled steel sheet reaches a winding temperature of 450 to 625 ° C.
A winding process for obtaining a hot coil made of a hot-rolled steel sheet by winding the cooled hot-rolled steel sheet at the above-mentioned winding temperature.
A hot-rolled steel sheet is unwound from a hot coil, and the unwound hot-rolled steel sheet is roll-formed to form an open pipe, and the abutting portion of the obtained open pipe is electrosewn to form an electrosewn welded portion. The pipe making process to obtain the raw pipe by
The electric-sewn welded part of the raw pipe is heated to a heating temperature of 900 to 1000 ° C., soaked at the above heating temperature for 1 second or longer, and then to a cooling stop temperature of 300 to 580 ° C., 5 to 20 ° C./sec. Seam heat treatment process that performs seam heat treatment to cool with water at the cooling rate of
including.
　製法Ａにおいて、素管とは、電縫溶接部に対してシーム熱処理が施される前の電縫鋼管を意味する。
　この製法Ａによれば、本開示の電縫鋼管を製造できる。
　以下、製法Ａにおける各工程について説明する。 In the manufacturing method A, the raw pipe means an electro-sewn steel pipe before the seam heat treatment is applied to the electro-sewn welded portion.
According to this manufacturing method A, the electrosewn steel pipe of the present disclosure can be manufactured.
Hereinafter, each step in the manufacturing method A will be described.
（スラブ準備工程）
　製法Ａにおけるスラブ準備工程は、上述の化学組成を有するスラブを準備する工程である。
　スラブを準備する工程は、スラブを製造する工程であってもよいし、予め製造されていたスラブを単に準備するだけの工程であってもよい。
　スラブを製造する場合、例えば、上述の化学組成を有する溶鋼を製造し、製造した溶鋼を用いて、スラブを製造する。この際、連続鋳造法によりスラブを製造してもよいし、溶鋼を用いてインゴットを製造し、インゴットを分塊圧延してスラブを製造してもよい。 (Slab preparation process)
The slab preparation step in the production method A is a step of preparing a slab having the above-mentioned chemical composition.
The step of preparing the slab may be a step of manufacturing the slab, or may be a step of simply preparing the slab that has been manufactured in advance.
When producing a slab, for example, a molten steel having the above-mentioned chemical composition is produced, and the produced molten steel is used to produce a slab. At this time, a slab may be produced by a continuous casting method, or an ingot may be produced using molten steel, and the ingot may be lump-rolled to produce a slab.
（熱延工程）
　製法Ａにおける熱延工程は、上記で準備したスラブを加熱し、加熱されたスラブを熱間圧延して熱延鋼板を得る工程である。
　スラブを加熱する際のスラブ加熱温度は、１１００～１２５０℃とする。
　加熱温度が１１００℃以上であると、熱間圧延中の結晶粒の微細化及び熱間圧延後の析出強化をより進行させ易く、その結果、鋼の強度をより向上させ易い。
　加熱温度が１２５０℃以下であると、オーステナイト粒の粗大化をより抑制できるので、結晶粒を微細化させ易く、その結果、鋼の強度をより向上させ易い。
　スラブの加熱は、例えば、加熱炉によって行う。
　ここで、スラブ加熱温度は、スラブの外表面の温度を意味する。 (Hot rolling process)
The hot-rolling step in the manufacturing method A is a step of heating the slab prepared above and hot-rolling the heated slab to obtain a hot-rolled steel sheet.
The slab heating temperature when heating the slab is 1100 to 1250 ° C.
When the heating temperature is 1100 ° C. or higher, the refinement of crystal grains during hot rolling and the precipitation strengthening after hot rolling are more likely to proceed, and as a result, the strength of steel is more likely to be improved.
When the heating temperature is 1250 ° C. or lower, the coarsening of the austenite grains can be further suppressed, so that the crystal grains can be easily refined, and as a result, the strength of the steel can be further improved.
The slab is heated by, for example, a heating furnace.
Here, the slab heating temperature means the temperature of the outer surface of the slab.
　熱延工程では、上記で加熱されたスラブを熱間圧延して熱延鋼板を得る。
　熱間圧延は、好ましくは、仕上げ圧延終了温度（以下、「仕上げ圧延温度」ともいう）が７８０～９３０℃である条件で行うことが好ましい。
　熱間圧延は、一般に、粗圧延機及び仕上げ圧延機を用いて行う。粗圧延機及び仕上げ圧延機ともに、一般に、一列に並んだ複数の圧延スタンドを備え、各圧延スタンドはロール対を備える。この場合、仕上げ圧延温度（即ち、仕上げ圧延終了温度）は、仕上げ圧延機の最終スタンドの出側での熱延鋼板の表面温度である。 In the hot-rolling step, the slab heated above is hot-rolled to obtain a hot-rolled steel sheet.
The hot rolling is preferably performed under the condition that the finish rolling end temperature (hereinafter, also referred to as “finish rolling temperature”) is 780 to 930 ° C.
Hot rolling is generally performed using a rough rolling mill and a finishing rolling mill. Both the rough rolling mill and the finishing rolling mill generally have a plurality of rolling stands arranged in a row, and each rolling stand has a roll pair. In this case, the finish rolling temperature (that is, the finish rolling end temperature) is the surface temperature of the hot-rolled steel sheet on the outlet side of the final stand of the finish rolling machine.
　仕上げ圧延温度が７８０℃以上であると、鋼板の圧延抵抗を低減できるので、生産性が向上する。
　また、仕上げ圧延温度が７８０℃以上であると、フェライト及びオーステナイトの二相域で圧延される現象が抑制され、この現象に伴う、層状組織の形成及び機械的性質の低下を抑制できる。
　一方、仕上げ圧延温度が９３０℃以下であると、熱延鋼板が硬くなりすぎる現象が抑制されるので、得られる電縫鋼管の母材部のＴＳが高くなりすぎる現象が抑制される。 When the finish rolling temperature is 780 ° C. or higher, the rolling resistance of the steel sheet can be reduced, so that the productivity is improved.
Further, when the finish rolling temperature is 780 ° C. or higher, the phenomenon of rolling in the two-phase region of ferrite and austenite is suppressed, and the formation of a layered structure and the deterioration of mechanical properties due to this phenomenon can be suppressed.
On the other hand, when the finish rolling temperature is 930 ° C. or lower, the phenomenon that the hot-rolled steel sheet becomes too hard is suppressed, so that the phenomenon that the TS of the base material portion of the obtained electro-sewn steel pipe becomes too high is suppressed.
（熱延鋼板水冷工程）
　熱延鋼板水冷工程は、熱延鋼板を、熱延鋼板の外表面の温度が４５０～６２５℃の巻取温度となるまで水冷する工程である。 (Hot-rolled steel sheet water cooling process)
The hot-rolled steel sheet water-cooling step is a step of water-cooling the hot-rolled steel sheet until the temperature of the outer surface of the hot-rolled steel sheet reaches a winding temperature of 450 to 625 ° C.
　上記巻取り温度（即ち、熱延鋼板の外表面の冷却終了温度）が４５０℃以上であることにより、生産性が確保される。巻き取り温度は、５００℃以上であることが好ましい。
　上記巻取り温度が６２５℃以下であることにより、結晶粒の粗大化をより抑制できるので、熱延鋼板の強度をより向上させることができる。巻き取り温度は、６００℃以下であることが好ましい。 Productivity is ensured when the winding temperature (that is, the cooling end temperature of the outer surface of the hot-rolled steel sheet) is 450 ° C. or higher. The winding temperature is preferably 500 ° C. or higher.
When the winding temperature is 625 ° C. or lower, coarsening of crystal grains can be further suppressed, so that the strength of the hot-rolled steel sheet can be further improved. The winding temperature is preferably 600 ° C. or lower.
（造管工程）
　造管工程は、ホットコイルから熱延鋼板を巻き出し、巻き出された熱延鋼板をロール成形することによりオープン管とし、得られたオープン管の衝合部を電縫溶接して電縫溶接部を形成することにより、素管（即ち、電縫溶接部にシーム熱処理が施される前の電縫鋼管）を得る工程である。 (Pipe making process)
In the pipe making process, a hot-rolled steel sheet is unwound from a hot coil, and the unwound hot-rolled steel sheet is roll-formed to form an open pipe. This is a step of obtaining a raw pipe (that is, an electro-sewn steel pipe before the seam heat treatment is applied to the electro-sewn welded portion) by forming the portion.
（シーム熱処理工程）
　製法Ａにおけるシーム熱処理工程は、素管（即ち、電縫溶接部にシーム熱処理が施される前の電縫鋼管）における電縫溶接部に対し、シーム熱処理を施す工程である。
　製法Ａにおけるシーム熱処理は、素管における電縫溶接部に対し、９００～１０００℃の加熱温度にまで加熱し、上記加熱温度にて１秒以上均熱し、次いで３００～５８０℃の冷却停止温度まで、５～２０℃／秒の冷却速度にて水冷する処理である。
　水冷後、電縫溶接部の温度が室温となるまで空冷する。 (Seam heat treatment process)
The seam heat treatment step in the manufacturing method A is a step of performing a seam heat treatment on the electric resistance welded portion of the raw pipe (that is, the electric resistance welded steel pipe before the seam heat treatment is applied to the electric resistance welded portion).
In the seam heat treatment in the manufacturing method A, the electric sewing welded portion in the raw pipe is heated to a heating temperature of 900 to 1000 ° C., soaked at the above heating temperature for 1 second or more, and then to a cooling stop temperature of 300 to 580 ° C. It is a process of water cooling at a cooling rate of 5 to 20 ° C./sec.
After water cooling, air cool until the temperature of the electrosewn weld reaches room temperature.
　製法Ａにおけるシーム熱処理は、シーム熱処理前の電縫溶接部に対し、電縫溶接部の外表面側から、加熱及び冷却をこの順に施すことによって行う。
　より具体的には、製法Ａにおけるシーム熱処理は、以下のようにして行う。
　まず、シーム熱処理前の電縫溶接部を、外表面側から、誘導加熱により、外表面の温度が９００～１０００℃の範囲の加熱温度となるまで加熱し、外表面の温度が上記範囲の加熱温度である状態のまま１秒以上（好ましくは１秒～５秒）の範囲の均熱時間にて保持することにより均熱する。
　次に、均熱後の電縫溶接部を、外表面側から、５～２０℃／秒の範囲の冷却速度にて、３００～５８０℃の範囲の冷却停止温度まで水冷する。この際、５～２０℃／秒の範囲の冷却速度を達成するための手段としては、水冷シャワーをミスト状にすること、水冷シャワーの流量を調整すること、水冷シャワーの角度を調整すること、等が挙げられる。 The seam heat treatment in the manufacturing method A is performed by heating and cooling the electric sewing welded portion before the seam heat treatment from the outer surface side of the electric sewing welded portion in this order.
More specifically, the seam heat treatment in the production method A is performed as follows.
First, the electrosewn welded portion before the seam heat treatment is heated from the outer surface side by induction heating until the temperature of the outer surface reaches a heating temperature in the range of 900 to 1000 ° C., and the temperature of the outer surface is heated in the above range. The heat is equalized by holding the temperature in the state of the temperature for an equalizing time in the range of 1 second or more (preferably 1 second to 5 seconds).
Next, the electrosewn welded portion after heat equalization is water-cooled from the outer surface side at a cooling rate in the range of 5 to 20 ° C./sec to a cooling shutdown temperature in the range of 300 to 580 ° C. At this time, as means for achieving a cooling rate in the range of 5 to 20 ° C./sec, the water-cooled shower is made into a mist, the flow rate of the water-cooled shower is adjusted, and the angle of the water-cooled shower is adjusted. And so on.
　ここで、加熱温度は、電縫溶接部の外表面の温度であり、冷却速度は、電縫溶接部の外表面における冷却速度である。
　冷却停止温度は、電縫溶接部の外表面で測定される、水冷を停止した後の復熱温度であって、水冷停止後１分以内に測定される最高温度である。 Here, the heating temperature is the temperature of the outer surface of the electric sewing welded portion, and the cooling rate is the cooling rate on the outer surface of the electric sewing welded portion.
The cooling stop temperature is the reheat temperature after stopping the water cooling, which is measured on the outer surface of the electric sewing welded portion, and is the maximum temperature measured within 1 minute after the water cooling is stopped.
　シーム熱処理工程において、加熱温度が９００℃未満である場合には、電縫溶接部の加熱が不足し、電縫溶接部のＹＳが低くなりすぎ、ΔＹＳが８０ＭＰａ超となる傾向がある。この場合、更に、電縫溶接部の内表層の硬さが不足し、ΔＨｖが２５Ｈｖ超となる傾向もある。従って、製法Ａのシーム熱処理工程における加熱温度は、９００℃以上である。
　一方、シーム熱処理工程において、加熱温度が１０００℃超である場合には、電縫溶接部の加熱が過剰となり、電縫溶接部のＹＳが高くなりすぎ、ΔＹＳが０ＭＰａ未満となる傾向がある。この場合、更に、電縫溶接部の外表層の硬さが硬くなりすぎ、ΔＨｖが２５Ｈｖ超となる傾向がある。従って、製法Ａにおけるシーム熱処理工程における加熱温度は、１０００℃以下である。 In the seam heat treatment step, when the heating temperature is less than 900 ° C., the heating of the electric stitch welded portion is insufficient, the YS of the electric stitch welded portion becomes too low, and ΔYS tends to be more than 80 MPa. In this case, the hardness of the inner surface layer of the electrosewn welded portion is further insufficient, and ΔHv tends to exceed 25 Hv. Therefore, the heating temperature in the seam heat treatment step of the production method A is 900 ° C. or higher.
On the other hand, in the seam heat treatment step, when the heating temperature is more than 1000 ° C., the electric sewing welded portion is excessively heated, the YS of the electric sewing welded portion becomes too high, and ΔYS tends to be less than 0 MPa. In this case, the hardness of the outer surface layer of the electric stitch welded portion becomes too hard, and ΔHv tends to exceed 25 Hv. Therefore, the heating temperature in the seam heat treatment step in the production method A is 1000 ° C. or lower.
　シーム熱処理工程において、冷却停止温度が３００℃未満である場合には、電縫溶接部のＹＳが高くなりすぎ、ΔＹＳが０ＭＰａ未満となる傾向がある。この場合、更に、電縫溶接部の外表層の硬さが硬くなりすぎ、ΔＨｖが２５Ｈｖ超となる傾向がある。従って、製法Ａのシーム熱処理工程における冷却停止温度は、３００℃以上である。
　一方、シーム熱処理工程において、冷却停止温度が５８０℃超である場合には、電縫溶接部のＹＳが低くなりすぎ、ΔＹＳが８０ＭＰａ超となる傾向がある。この場合、更に、電縫溶接部の内表層の硬さが不足し、ΔＨｖが２５Ｈｖ超となる傾向がある。従って、製法Ａのシーム熱処理工程における冷却停止温度は、５８０℃以下である。 In the seam heat treatment step, when the cooling shutdown temperature is less than 300 ° C., the YS of the electric stitch welded portion tends to be too high, and the ΔYS tends to be less than 0 MPa. In this case, the hardness of the outer surface layer of the electric stitch welded portion becomes too hard, and ΔHv tends to exceed 25 Hv. Therefore, the cooling shutdown temperature in the seam heat treatment step of the production method A is 300 ° C. or higher.
On the other hand, in the seam heat treatment step, when the cooling shutdown temperature is more than 580 ° C., the YS of the electric stitch welded portion tends to be too low, and the ΔYS tends to be more than 80 MPa. In this case, the hardness of the inner surface layer of the electrosewn welded portion is further insufficient, and ΔHv tends to exceed 25 Hv. Therefore, the cooling shutdown temperature in the seam heat treatment step of the production method A is 580 ° C. or lower.
　シーム熱処理工程において、冷却速度が５℃／秒未満である場合には、電縫溶接部のＹＳが低くなりすぎ、ΔＹＳが８０ＭＰａ超となる傾向がある。この場合、更に、電縫溶接部の内表層の硬さが不足し、ΔＨｖが２５Ｈｖ超となる傾向がある。従って、製法Ａのシーム熱処理工程における冷却速度は、５℃／秒以上である。
　シーム熱処理工程において、冷却速度が２０℃／秒超である場合には、電縫溶接部の外表層の硬さが高くなりすぎ、その結果、ΔＨｖが２５Ｈｖ超となる傾向がある。従って、製法Ａのシーム熱処理工程における冷却速度は、２０℃／秒以下である。 In the seam heat treatment step, when the cooling rate is less than 5 ° C./sec, the YS of the electric stitch welded portion tends to be too low, and the ΔYS tends to be more than 80 MPa. In this case, the hardness of the inner surface layer of the electrosewn welded portion is further insufficient, and ΔHv tends to exceed 25 Hv. Therefore, the cooling rate in the seam heat treatment step of the production method A is 5 ° C./sec or more.
In the seam heat treatment step, when the cooling rate is more than 20 ° C./sec, the hardness of the outer surface layer of the electric stitch welded portion becomes too high, and as a result, ΔHv tends to be more than 25 Hv. Therefore, the cooling rate in the seam heat treatment step of the production method A is 20 ° C./sec or less.
　製法Ａは、上述した工程以外のその他の工程を含んでもよい。
　その他の工程としては、シーム熱処理工程後、サイジングロールによって電縫鋼管の形状を調整する工程、等が挙げられる。 The production method A may include other steps other than the above-mentioned steps.
Other steps include a step of adjusting the shape of the electrosewn steel pipe with a sizing roll after the seam heat treatment step.
　製法Ａにおける各工程は、鋼の化学組成には影響を及ぼさない。
　従って、化学組成Ａを有する溶鋼又はスラブを用いることにより、母材部の化学組成が化学組成Ａである電縫鋼管が製造される。 Each step in manufacturing method A does not affect the chemical composition of steel.
Therefore, by using a molten steel or a slab having a chemical composition A, an electrosewn steel pipe having a chemical composition of the base material portion A is manufactured.
　以下、本開示の実施例を示すが、本開示は以下の実施例には限定されない。
　表１～表３中の下線は、本開示の電縫鋼管の範囲外であること、又は、製法Ａの範囲外であることを意味する。 Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples.
The underline in Tables 1 to 3 means that the pipe is out of the range of the electric resistance welded steel pipe of the present disclosure or is out of the range of the manufacturing method A.
〔試験番号１～４３〕
　前述した製法Ａに従い、各試験番号の電縫鋼管を製造した。
　詳細を以下に示す。
　試験番号１～２２は実施例であり、試験番号２３～４３は比較例である。 [Test numbers 1-43]
According to the above-mentioned manufacturing method A, the electric resistance welded steel pipe of each test number was manufactured.
Details are shown below.
Test numbers 1 to 22 are examples, and test numbers 23 to 43 are comparative examples.
＜スラブ及びホットコイルの製造＞
　表１及び表２に示す化学組成を有する溶鋼を連続鋳造し、厚さ２４０ｍｍのスラブを製造した。
　表１及び表２中、元素の欄に示す数値は、各元素の質量％である。
　各試験番号の化学組成において、表１及び表２に示した元素を除いた残部は、Ｆｅ及び不純物である。
　試験番号１２、１６、及び２８におけるＲＥＭは、いずれもＣｅである。 <Manufacturing of slabs and hot coils>
Molten steel having the chemical compositions shown in Tables 1 and 2 was continuously cast to produce a slab having a thickness of 240 mm.
In Tables 1 and 2, the numerical value shown in the element column is the mass% of each element.
In the chemical composition of each test number, the balance excluding the elements shown in Tables 1 and 2 is Fe and impurities.
The REMs in test numbers 12, 16 and 28 are all Ce.
　上記スラブを加熱炉で加熱し、加熱されたスラブを複数の熱間圧延ミルを用いて熱間圧延して熱延鋼板とし、得られた熱延鋼板を水冷し、水冷された熱延鋼板を巻取ることにより、熱延鋼板からなるホットコイルを得た。
　ここで、スラブを加熱する際の加熱温度は１２００℃とし、
熱間圧延における仕上げ圧延温度は７９０℃～９３０℃とし、
巻取り温度は、５００℃～６００℃とした。 The above slab is heated in a heating furnace, and the heated slab is hot-rolled using a plurality of hot-rolled mills to obtain a hot-rolled steel sheet, and the obtained hot-rolled steel sheet is water-cooled to obtain a water-cooled hot-rolled steel sheet. By winding, a hot coil made of hot-rolled steel sheet was obtained.
Here, the heating temperature when heating the slab is set to 1200 ° C.
The finish rolling temperature in hot rolling is 790 ° C to 930 ° C.
The winding temperature was 500 ° C. to 600 ° C.
＜電縫鋼管の製造＞
　上記ホットコイルから熱延鋼板を巻き出し、巻き出された熱延鋼板をロール成形することによりオープン管とし、得られたオープン管における衝合部を電縫溶接して電縫溶接部を形成し、素管を得た。
　次いで、素管の電縫溶接部に対し、表３に示す条件のシーム熱処理を施し、次いでサイジングロールによって形状を調整することにより、表３に示す肉厚ｔ及び外径Ｄを有する電縫鋼管を得た。 <Manufacturing of electrosewn steel pipe>
A hot-rolled steel sheet is unwound from the hot coil, and the unwound hot-rolled steel sheet is roll-formed to form an open pipe. , I got a raw tube.
Next, the electric resistance welded portion of the raw pipe is subjected to seam heat treatment under the conditions shown in Table 3, and then the shape is adjusted by a sizing roll to obtain an electric resistance steel pipe having a wall thickness t and an outer diameter D shown in Table 3. Got
　表３では記載を省略したが、シーム熱処理における均熱時間は、１秒～５秒となるように調整した。
　均熱時間は、加熱終了からシャワーを開始するタイミングを調整することによって制御した。
　シーム熱処理における冷却速度は、水冷シャワーをミスト状にし、水冷シャワーの流量及び／又は水冷シャワーの角度を調整することによって制御した。
　シーム熱処理における冷却停止温度は、シャワーを止めるタイミングを調整することによって制御した。 Although the description is omitted in Table 3, the soaking time in the seam heat treatment was adjusted to be 1 second to 5 seconds.
The soaking time was controlled by adjusting the timing of starting the shower from the end of heating.
The cooling rate in the seam heat treatment was controlled by making the water-cooled shower mist and adjusting the flow rate and / or the angle of the water-cooled shower.
The cooling shutdown temperature in the seam heat treatment was controlled by adjusting the timing at which the shower was stopped.
　なお、以上の製造工程は、鋼の化学組成に影響を及ぼさない。従って、得られた電縫鋼管の母材部の化学組成は、原料である溶鋼の化学組成と同一とみなせる。 The above manufacturing process does not affect the chemical composition of steel. Therefore, the chemical composition of the base material portion of the obtained electrosewn steel pipe can be regarded as the same as the chemical composition of the molten steel which is the raw material.
＜各測定＞
　得られた電縫鋼管について、前述した方法により、母材部の内表層におけるＦ分率（即ち、ポリゴナルフェライト分率）の測定及び残部の種類の確認を行った。
　更に、上記電縫鋼管について、前述した方法により、
電縫溶接部のＹＳ（ＭＰａ）、
電縫溶接部のＴＳ（ＭＰａ）、
母材部のＹＳ（ＭＰａ）、
母材部のＴＳ（ＭＰａ）、
ΔＹＳ（即ち、母材部のＹＳから電縫溶接部のＹＳを差し引いた値）、並びに、
ΔＨｖ（即ち、電縫溶接部の外表層のビッカース硬さから電縫溶接部の内表層のビッカース硬さを差し引いた値）
を測定した。
　結果を表３に示す。
　表３の残部において、「Ｐ＋Ｃ」とは、疑似パーライト及びセメンタイトを意味する。 <Each measurement>
With respect to the obtained electric resistance welded steel pipe, the F fraction (that is, the polygonal ferrite fraction) in the inner surface layer of the base metal portion was measured and the type of the balance was confirmed by the above-mentioned method.
Further, with respect to the electric resistance welded steel pipe, by the method described above,
YS (MPa) of the electric stitch welded part,
TS (MPa) of the electric stitch welded part,
YS (MPa) of the base material,
TS (MPa) of the base material,
ΔYS (that is, the value obtained by subtracting the YS of the electric sewing welded portion from the YS of the base metal portion), and
ΔHv (that is, the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded part from the Vickers hardness of the outer surface layer of the electric sewing welded part)
Was measured.
The results are shown in Table 3.
In the rest of Table 3, "P + C" means pseudo-pearlite and cementite.
＜電縫溶接部の耐ＳＳＣ性及び耐ＳＯＨＩＣ性の評価；４点曲げ試験＞
　得られた電縫鋼管について、前述した方法により、電縫溶接部の耐ＳＳＣ性及び耐ＳＯＨＩＣ性の評価（即ち、４点曲げ試験後におけるＳＳＣ及びＳＯＨＩＣの有無の確認）を行った。
　結果を表３に示す。
　表３において、
「ＳＳＣ」は、ＳＳＣが発生していたことを意味し、
「ＳＯＨＩＣ」は、ＳＯＨＩＣが発生していたことを意味し、
「ＳＳＣ＋ＳＯＨＩＣ」は、ＳＳＣ及びＳＯＨＩＣが両方発生していたことを意味し、
「Ｎｏ　ＳＳＣ　Ｎｏ　ＳＯＨＩＣ」は、ＳＳＣもＳＯＨＩＣも発生していなかったことを意味する。 <Evaluation of SSC resistance and SOHIC resistance of welded parts; 4-point bending test>
The obtained electric resistance welded steel pipe was evaluated for SSC resistance and SOHIC resistance of the electric resistance welded portion (that is, confirmation of the presence or absence of SSC and SOHIC after the 4-point bending test) by the method described above.
The results are shown in Table 3.
In Table 3,
"SSC" means that SSC was occurring,
"SOHIC" means that SOHIC was occurring,
"SSC + SOHIC" means that both SSC and SOHIC were generated.
“No SSC No SOHIC” means that neither SSC nor SOHIC was generated.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表１～表３に示すように、
　母材部の化学組成が前述した化学組成Ａであり、
　母材部の内表層の金属組織において、Ｆ分率が８０％以上１００％未満であり、残部が疑似パーライト及びセメンタイトを含み、
　母材部のＹＳが４１０ＭＰａ以上であり、母材部のＴＳが５１５～６５０ＭＰａであり、
　母材部のＹＳから電縫溶接部のＹＳを差し引いた値であるΔＹＳが０～８０ＭＰａであり、
　電縫溶接部の外表層のビッカース硬さから電縫溶接部の内表層のビッカース硬さを差し引いた値であるΔＨｖが０～２５Ｈｖである、
実施例（試験番号１～２２）の電縫鋼管は、電縫溶接部における耐ＳＳＣ性及び耐ＳＯＨＩＣ性に優れていた。 As shown in Tables 1 to 3,
The chemical composition of the base metal portion is the above-mentioned chemical composition A, and the chemical composition is the above-mentioned chemical composition A.
In the metal structure of the inner surface layer of the base material, the F fraction is 80% or more and less than 100%, and the balance contains pseudo pearlite and cementite.
The YS of the base material is 410 MPa or more, and the TS of the base material is 515 to 650 MPa.
ΔYS, which is the value obtained by subtracting the YS of the electric sewing welded portion from the YS of the base metal portion, is 0 to 80 MPa.
ΔHv, which is the value obtained by subtracting the Vickers hardness of the inner surface layer of the electric stitch welded portion from the Vickers hardness of the outer surface layer of the electric stitch welded portion, is 0 to 25 Hv.
The electric resistance pipes of Examples (Test Nos. 1 to 22) were excellent in SSC resistance and SOHIC resistance in the electric resistance welded portion.
　これら実施例に対し、比較例（試験番号２３～４３）の結果は、以下のとおりであった。 For these examples, the results of the comparative examples (test numbers 23 to 43) were as follows.
　試験番号２３の電縫鋼管は、母材部の化学組成が適正（即ち、前述した化学組成Ａ）であるものの、シーム熱処理工程における加熱温度が高すぎた。その結果、電縫溶接部のＹＳが高くなりすぎ、ΔＹＳが０ＭＰａ未満となった。更に、電縫溶接部の外表層のビッカース硬さが硬くなりすぎ、ΔＨｖが２５Ｈｖ超となった。これらの結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 Although the electric resistance pipe of test number 23 had an appropriate chemical composition of the base material (that is, the above-mentioned chemical composition A), the heating temperature in the seam heat treatment step was too high. As a result, the YS of the electric stitch welded portion became too high, and the ΔYS became less than 0 MPa. Further, the Vickers hardness of the outer surface layer of the electric stitch welded portion became too hard, and ΔHv became more than 25 Hv. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号２４の電縫鋼管は、母材部の化学組成が適正（即ち、前述した化学組成Ａ）であるものの、シーム熱処理工程における加熱温度が低すぎた。その結果、電縫溶接部のＹＳが低くなりすぎ、ΔＹＳが８０ＭＰａ超となった。更に、電縫溶接部の内表層のビッカース硬さが不足し、ΔＨｖが２５Ｈｖ超となった。これらの結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 In the electrosewn steel pipe of test number 24, although the chemical composition of the base metal portion was appropriate (that is, the chemical composition A described above), the heating temperature in the seam heat treatment step was too low. As a result, the YS of the electric stitch welded portion became too low, and the ΔYS became more than 80 MPa. Further, the Vickers hardness of the inner surface layer of the electric stitch welded portion was insufficient, and ΔHv became more than 25 Hv. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号２５の電縫鋼管は、母材部の化学組成が適正（即ち、前述した化学組成Ａ）であるものの、シーム熱処理工程における冷却速度が速すぎた。その結果、外表層のビッカース硬さが硬くなりすぎ、ΔＨｖが２５Ｈｖ超となった。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 In the electrosewn steel pipe of test number 25, although the chemical composition of the base metal portion was appropriate (that is, the chemical composition A described above), the cooling rate in the seam heat treatment step was too fast. As a result, the Vickers hardness of the outer surface layer became too hard, and ΔHv became more than 25 Hv. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号２６の電縫鋼管は、母材部の化学組成が適正（即ち、前述した化学組成Ａ）であるものの、シーム熱処理工程における冷却速度が遅すぎた。その結果、電縫溶接部のＹＳが低くなりすぎ、ΔＹＳが８０ＭＰａ超となった。更に、電縫溶接部の内表層のビッカース硬さが不足し、ΔＨｖが２５Ｈｖ超となった。これらの結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 In the electrosewn steel pipe of test number 26, although the chemical composition of the base metal portion was appropriate (that is, the chemical composition A described above), the cooling rate in the seam heat treatment step was too slow. As a result, the YS of the electric stitch welded portion became too low, and the ΔYS became more than 80 MPa. Further, the Vickers hardness of the inner surface layer of the electric stitch welded portion was insufficient, and ΔHv became more than 25 Hv. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号２７の電縫鋼管は、母材部の化学組成が適正（即ち、前述した化学組成Ａ）であるものの、シーム熱処理工程における冷却停止温度が高すぎた。その結果、電縫溶接部のＹＳが低くなりすぎ、ΔＹＳが８０ＭＰａ超となった。更に、電縫溶接部の内表層のビッカース硬さが不足し、ΔＨｖが２５Ｈｖ超となった。これらの結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 In the electrosewn steel pipe of test number 27, although the chemical composition of the base metal portion was appropriate (that is, the chemical composition A described above), the cooling shutdown temperature in the seam heat treatment step was too high. As a result, the YS of the electric stitch welded portion became too low, and the ΔYS became more than 80 MPa. Further, the Vickers hardness of the inner surface layer of the electric stitch welded portion was insufficient, and ΔHv became more than 25 Hv. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号２８の電縫鋼管は、母材部の化学組成が適正（即ち、前述した化学組成Ａ）であるものの、シーム熱処理工程における冷却停止温度が低すぎた。その結果、電縫溶接部のＹＳが高くなりすぎ、ΔＹＳが０ＭＰａ未満となった。更に、電縫溶接部の外表層のビッカース硬さが硬くなりすぎ、ΔＨｖが２５Ｈｖ超となった。これらの結果、４点曲げ試験においてＳＳＣが確認された。これらの結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 In the electrosewn steel pipe of test number 28, although the chemical composition of the base metal portion was appropriate (that is, the chemical composition A described above), the cooling shutdown temperature in the seam heat treatment step was too low. As a result, the YS of the electric stitch welded portion became too high, and the ΔYS became less than 0 MPa. Further, the Vickers hardness of the outer surface layer of the electric stitch welded portion became too hard, and ΔHv became more than 25 Hv. As a result, SSC was confirmed in the 4-point bending test. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号２９の電縫鋼管は、母材部の化学組成において、Ｃ含有量が低すぎた。その結果、母材部のＹＳが４１０ＭＰａ未満であり、母材部のＴＳが５１５ＭＰａ未満であった。 The electric resistance welded steel pipe of test number 29 had a C content that was too low in the chemical composition of the base material. As a result, the YS of the base material portion was less than 410 MPa, and the TS of the base material portion was less than 515 MPa.
　試験番号３０の電縫鋼管は、母材部の化学組成において、Ｃ含有量が高すぎた。その結果、母材部の内表層の金属組織におけるＦ分率が８０％未満となり、母材部のＴＳが６５０ＭＰａを超えた。更に、母材部のＹＳが高くなりすぎ、ΔＹＳが８０ＭＰａ超となった。更に、電縫溶接部の外表層のビッカース硬さが硬くなりすぎ、ΔＨｖが２５Ｈｖ超となった。これらの結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 The electric resistance welded steel pipe of test number 30 had an excessively high C content in the chemical composition of the base material. As a result, the F fraction in the metal structure of the inner surface layer of the base material portion was less than 80%, and the TS of the base material portion exceeded 650 MPa. Further, the YS of the base metal portion became too high, and the ΔYS became more than 80 MPa. Further, the Vickers hardness of the outer surface layer of the electric stitch welded portion became too hard, and ΔHv became more than 25 Hv. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号３１の電縫鋼管は、母材部の化学組成において、Ｍｎ含有量が低すぎた。その結果、母材部のＹＳが４１０ＭＰａ未満であり、母材部のＴＳが５１５ＭＰａ未満であった。 The Mn content of the electrosewn steel pipe of test number 31 was too low in the chemical composition of the base metal part. As a result, the YS of the base material portion was less than 410 MPa, and the TS of the base material portion was less than 515 MPa.
　試験番号３２の電縫鋼管は、母材部の化学組成において、Ｍｎ含有量が高すぎた。その結果、母材部ＴＳが６５０ＭＰａ超であった。更に、母材部のＹＳが高くなりすぎ、ΔＹＳが８０ＭＰａ超となった。更に、電縫溶接部の外表層のビッカース硬さが硬くなりすぎ、ΔＨｖが２５Ｈｖ超となった。これらの結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 The electric resistance welded steel pipe of test number 32 had an excessively high Mn content in the chemical composition of the base material. As a result, the base material TS was more than 650 MPa. Further, the YS of the base metal portion became too high, and the ΔYS became more than 80 MPa. Further, the Vickers hardness of the outer surface layer of the electric stitch welded portion became too hard, and ΔHv became more than 25 Hv. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号３３の電縫鋼管は、母材部の化学組成において、Ｐ含有量が高すぎた。その結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 The electric resistance pipe of test number 33 had an excessively high P content in the chemical composition of the base material. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号３４の電縫鋼管は、母材部の化学組成において、Ｓ含有量が高すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The electric resistance welded steel pipe of test number 34 had an S content that was too high in the chemical composition of the base metal part. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号３５の電縫鋼管は、母材部の化学組成において、Ｓｉ含有量が高すぎた。その結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 The electrolytically sewn steel pipe of test number 35 had an excessively high Si content in the chemical composition of the base material. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号３６の電縫鋼管は、母材部の化学組成において、Ｎｂ含有量が低すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The Nb content of the electrosewn steel pipe of test number 36 was too low in the chemical composition of the base metal part. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号３７の電縫鋼管は、母材部の化学組成において、Ｎｂ含有量が高すぎた。その結果、４点曲げ試験においてＳＳＣ及びＳＯＨＩＣが確認された。すなわち、優れた耐ＳＳＣ性及び耐ＳＯＨＩＣ性が得られなかった。 The electric resistance welded steel pipe of test number 37 had an excessively high Nb content in the chemical composition of the base material. As a result, SSC and SOHIC were confirmed in the 4-point bending test. That is, excellent SSC resistance and SOHIC resistance could not be obtained.
　試験番号３８の電縫鋼管は、母材部の化学組成において、Ｔｉ含有量が低すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The electric resistance steel pipe of test number 38 had a Ti content that was too low in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号３９の電縫鋼管は、母材部の化学組成において、Ｔｉ含有量が高すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The electric resistance pipe of test number 39 had an excessively high Ti content in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号４０の電縫鋼管は、母材部の化学組成において、Ｃａ含有量が高すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The electric resistance steel pipe of test number 40 had an excessively high Ca content in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号４１の電縫鋼管は、母材部の化学組成において、Ａｌ含有量が高すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The electro-sewn steel pipe of test number 41 had an Al content that was too high in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号４２の電縫鋼管は、母材部の化学組成において、Ｎ含有量が高すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The electric resistance welded steel pipe of test number 42 had an N content too high in the chemical composition of the base metal part. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.
　試験番号４３の電縫鋼管は、母材部の化学組成において、Ｏ含有量が高すぎた。その結果、４点曲げ試験においてＳＯＨＩＣが確認された。すなわち、優れた耐ＳＯＨＩＣ性が得られなかった。 The electric resistance pipe of test number 43 had an O content too high in the chemical composition of the base material. As a result, SOHIC was confirmed in the 4-point bending test. That is, excellent SOHIC resistance could not be obtained.

Claims (4)

  1. 　母材部及び電縫溶接部を含み、
    　前記母材部の化学組成が、質量％で、
    Ｃ：０．０３０～０．０９０％、
    Ｓｉ：０．０１～０．５０％、
    Ｍｎ：０．５０～１．５０％、
    Ｐ：０～０．０２０％、
    Ｓ：０～０．００２０％、
    Ｎｂ：０．００５～０．０６０％、
    Ｔｉ：０．００５～０．０３０％、
    Ｃａ：０．０００１～０．００４０％、
    Ａｌ：０～０．０５０％、
    Ｎ：０．００１０～０．００８０％、
    Ｏ：０～０．００３０％、
    Ｃｕ：０～０．５００％、
    Ｎｉ：０～０．５００％、
    Ｂ：０～０．００２０％、
    Ｖ：０～０．１００％、
    Ｃｒ：０～０．５００％、
    Ｍｏ：０～０．５００％、
    Ｗ：０～０．５００％、
    Ｚｒ：０～０．０５００％、
    Ｔａ：０～０．０５００％、
    Ｍｇ：０～０．００５０％、
    ＲＥＭ：０～０．００５０％、
    Ｈｆ：０～０．００５０％、
    Ｒｅ：０～０．００５０％、及び、
    残部：Ｆｅ及び不純物からなり、
    　母材部の内表層の金属組織において、ポリゴナルフェライト分率が８０％以上１００％未満であり、残部が疑似パーライト及びセメンタイトを含み、
    　前記母材部の降伏強度が４１０ＭＰａ以上であり、前記母材部の引張強度が５１５～６５０ＭＰａであり、
    　前記母材部の降伏強度から前記電縫溶接部の降伏強度を差し引いた値であるΔＹＳが、０～８０ＭＰａであり、
    　前記電縫溶接部の外表層のビッカース硬さから前記電縫溶接部の内表層のビッカース硬さを差し引いた値であるΔＨｖが、０～２５Ｈｖである、
    ラインパイプ用電縫鋼管。     Including base metal part and electric stitch welded part
    The chemical composition of the base material is mass%.
    C: 0.030-0.090%,
    Si: 0.01-0.50%,
    Mn: 0.50 to 1.50%,
    P: 0 to 0.020%,
    S: 0 to 0.0020%,
    Nb: 0.005 to 0.060%,
    Ti: 0.005 to 0.030%,
    Ca: 0.0001 to 0.0040%,
    Al: 0 to 0.050%,
    N: 0.0010 to 0.0080%,
    O: 0 to 0.0030%,
    Cu: 0 to 0.500%,
    Ni: 0 to 0.500%,
    B: 0 to 0.0020%,
    V: 0 to 0.100%,
    Cr: 0 to 0.500%,
    Mo: 0 to 0.500%,
    W: 0 to 0.500%,
    Zr: 0-0.0500%,
    Ta: 0-0.0500%,
    Mg: 0 to 0.0050%,
    REM: 0-0.0050%,
    Hf: 0 to 0.0050%,
    Re: 0 to 0.0050% and
    Remaining: Consists of Fe and impurities
    In the metal structure of the inner surface layer of the base metal part, the polygonal ferrite fraction is 80% or more and less than 100%, and the balance contains pseudo pearlite and cementite.
    The yield strength of the base material portion is 410 MPa or more, and the tensile strength of the base material portion is 515 to 650 MPa.
    ΔYS, which is a value obtained by subtracting the yield strength of the electric sewing welded portion from the yield strength of the base metal portion, is 0 to 80 MPa.
    ΔHv, which is a value obtained by subtracting the Vickers hardness of the inner surface layer of the electric sewing welded portion from the Vickers hardness of the outer surface layer of the electric sewing welded portion, is 0 to 25 Hv.
    Electric resistance sewn steel pipe for line pipes.
  2. 　前記母材部の化学組成が、質量％で、
    Ｃｕ：０％超０．５００％以下、
    Ｎｉ：０％超０．５００％以下、
    Ｂ：０％超０．００２０％以下、
    Ｖ：０％超０．１００％以下、
    Ｃｒ：０％超０．５００％以下、
    Ｍｏ：０％超０．５００％以下、
    Ｗ：０％超０．５００％以下、
    Ｚｒ：０％超０．０５００％以下、
    Ｔａ：０％超０．０５００％以下、
    Ｍｇ：０％超０．００５０％以下、
    ＲＥＭ：０％超０．００５０％以下、
    Ｈｆ：０％超０．００５０％以下、及び、
    Ｒｅ：０％超０．００５０％以下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、
    請求項１に記載のラインパイプ用電縫鋼管。     The chemical composition of the base material is mass%.
    Cu: More than 0% and less than 0.500%,
    Ni: More than 0% and less than 0.500%,
    B: More than 0% and less than 0.0020%,
    V: More than 0% and less than 0.100%,
    Cr: More than 0% and less than 0.500%,
    Mo: More than 0% and less than 0.500%,
    W: More than 0% and less than 0.500%,
    Zr: More than 0% and less than 0.0500%,
    Ta: More than 0% and less than 0.0500%,
    Mg: More than 0% and less than 0.0050%,
    REM: More than 0% and less than 0.0050%,
    Hf: More than 0% and less than 0.0050%, and
    Re: Contains one or more selected from the group consisting of more than 0% and 0.0050% or less.
    The electric resistance welded steel pipe for a line pipe according to claim 1.
  3. 　肉厚が１３ｍｍ以上である請求項１又は請求項２に記載のラインパイプ用電縫鋼管。 The electrosewn steel pipe for a line pipe according to claim 1 or 2, wherein the wall thickness is 13 mm or more.
  4. 　外径が３００ｍｍ～６５０ｍｍである請求項１～請求項３のいずれか１項に記載のラインパイプ用電縫鋼管。 The electric resistance steel pipe for a line pipe according to any one of claims 1 to 3, which has an outer diameter of 300 mm to 650 mm.
PCT/JP2020/005072 2020-02-10 2020-02-10 Line pipe-use electric resistance welded steel pipe WO2021161366A1 (en)

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EP20919182.4A EP4066954A4 (en) 2020-02-10 2020-02-10 Line pipe-use electric resistance welded steel pipe
KR1020227021826A KR20220105166A (en) 2020-02-10 2020-02-10 Electric resistance welded steel pipe for line pipe
PCT/JP2020/005072 WO2021161366A1 (en) 2020-02-10 2020-02-10 Line pipe-use electric resistance welded steel pipe
JP2021577721A JP7226595B2 (en) 2020-02-10 2020-02-10 Electric resistance welded steel pipes for line pipes

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JPWO2021161366A1 (en) 2021-08-19

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