EP4116453A1 - Tube en acier, et plaque en acier - Google Patents

Tube en acier, et plaque en acier Download PDF

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Publication number
EP4116453A1
EP4116453A1 EP20923002.8A EP20923002A EP4116453A1 EP 4116453 A1 EP4116453 A1 EP 4116453A1 EP 20923002 A EP20923002 A EP 20923002A EP 4116453 A1 EP4116453 A1 EP 4116453A1
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EP
European Patent Office
Prior art keywords
less
crack
steel pipe
base material
steel
Prior art date
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Pending
Application number
EP20923002.8A
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German (de)
English (en)
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EP4116453A4 (fr
Inventor
Takuya Hara
Yasuhiro Shinohara
Taishi Fujishiro
Kiyoshi Ebihara
Eiji Tsuru
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Nippon Steel Corp
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Nippon Steel Corp
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Publication of EP4116453A1 publication Critical patent/EP4116453A1/fr
Publication of EP4116453A4 publication Critical patent/EP4116453A4/fr
Pending legal-status Critical Current

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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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C22C38/04—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
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—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
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
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    • 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
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/78—Combined heat-treatments not provided for above
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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

Definitions

  • the present invention relates to a steel pipe and a steel plate.
  • the present invention particularly relates to a welded steel pipe for a line pipe and a steel plate suitable as a material thereof.
  • a system that is installed on the ground or on the seabed and transfers oil or gas is referred to as a pipeline.
  • a steel pipe for a pipeline that constitutes such a pipeline is referred to as a line pipe.
  • a straight seam arc welded steel pipe (hereinafter, referred to as an arc welded steel pipe, a welded steel pipe, or a steel pipe) is widely used for a large-diameter line pipe having a pipe diameter of 508 mm or more, which constitutes a long-range pipeline.
  • the straight seam arc welded steel pipe is a steel pipe manufactured by forming a thick steel plate into a tubular open pipe and welding a butt portion (seam portion) by an arc welding method such as a submerged arc welding method.
  • the pipe may be called a UOE steel pipe or a JCOE steel pipe.
  • the sour environment means an acidified wet hydrogen sulfide environment containing H 2 S which is a corrosive gas. It is known that in a case where the line pipe is exposed to a sour environment, hydrogen-induced crack (HIC) may occur.
  • HIC hydrogen-induced crack
  • SSC sulfide stress crack
  • SSC may occur in an oil country tubular goods having higher strength than a line pipe.
  • SSC may occur in a case where a hydrogen sulfide partial pressure becomes high or the stress becomes high.
  • the line pipe (sour resistant line pipe) used in a harsh sour environment is required to have SSC resistant properties in addition to HIC resistant properties.
  • Patent Document 1 and Non-Patent Document 2 suggest a welded steel pipe or a steel plate for a steel pipe having excellent sour resistant properties, in which the hardness of a base material portion and a welded portion is defined as 220 Hv or less based on the finding that the hardness affects the sour resistant properties.
  • Patent Document 3 suggests a high-strength steel plate for a sour resistant line pipe having excellent material uniformity in a steel plate, in which the metallographic structure is a bainite structure, the hardness unevenness in a plate thickness direction is ⁇ Hv 10 25 or less, the hardness unevenness in a plate width direction is ⁇ Hv 10 25 or less, and the maximum hardness of a surface layer area of the steel plate is Hv 10 220 or less.
  • Patent Document 4 suggests a heat treated steel plate having excellent hydrogen-induced crack resistance, in which a metallographic structure in a range of 1 mm from a steel plate surface in a plate thickness direction consists of one or both of tempered martensite and tempered bainite, in the metallographic structure in a range of ⁇ 1 mm from a plate thickness center portion in the plate thickness direction, a primary phase consisting of one or both of tempered martensite and tempered bainite is 80% or more in area ratio, the remainder other than the primary phase consists of one or more selected from ferrite, pearlite, cementite, and residual austenite, and the hardness at a position of 1 mm from a steel plate surface in the plate thickness direction is 250 HV or less in Vickers hardness, and the hardness difference between the position of 1 mm from the steel plate surface and the plate thickness center portion is 60 HV or less in Vickers hardness.
  • Patent Documents 1 to 4 and Non-Patent Document 2 sour resistant properties are satisfied in an environment where the hydrogen sulfide partial pressure is 0.1 MPa (1 bar) or less and a load stress is 90% or less of the yield stress.
  • a usage environment of the oil country tubular goods or the line pipe has become more severe recently, and the required level for sour resistant properties of the welded steel pipe for a line pipe has become higher.
  • sour resistant properties were required in an environment of the hydrogen sulfide partial pressure of 0.1 MPa (1 bar) or less, but recently, a material design capable of withstanding a high-pressure hydrogen sulfide environment of more than 0.1 MPa has been required.
  • the load stress was 90% or less of the yield stress, but recently, a material design capable of withstanding a high-pressure hydrogen sulfide environment of the load stress of more than 90% of the yield stress.
  • the steel plates of Patent Documents 1 to 4 and the steel plates of Non-Patent Document 2 did not have sufficient sour resistant properties in an environment in which the hydrogen sulfide partial pressure exceeds 0.1 MPa (1 bar) and exceeds 90% of the yield stress.
  • Patent Document 5 discloses a steel pipe having excellent SSC resistant properties, having HIC resistant properties equal to or higher than those of the steel in the related art, and having a yield strength of 350 MPa or more, in which crack does not occur even in a case where a stress of 90% or more of the yield strength is loaded in an environment of 30°C or lower containing hydrogen sulfide of a hydrogen sulfide partial pressure of more than 0.1 MPa.
  • Patent Document 5 shows that SSC resistant properties are excellent in the sulfide stress corrosion crack test in a case where a load stress is 90% of the yield stress, but does not show those in a case where the load stress is more than 90% of the yield stress.
  • an object of the present invention is to provide a welded steel pipe capable of being used in a harsh high-pressure hydrogen sulfide environment and having excellent sour resistant properties, particularly a straight seam arc welded steel pipe, and a steel plate (particularly a thick steel plate) as a material thereof.
  • the object of the present invention is to provide a steel pipe having a HIC resistant properties equal to or higher than those of steel in the related art, having a yield stress of 350 MPa or more, and having excellent SSC resistant properties, in which crack does not occur even in a case where a stress of more than 90% of the yield stress, specifically a stress of 95% of the yield stress, is loaded in an environment of 30°C or lower containing hydrogen sulfide of more than 0.1 MPa, and a steel plate as a material thereof.
  • the present invention has been made to achieve the above objects, and the following steel pipe and steel plate are the gist of the present invention.
  • a steel pipe having excellent SSC resistant properties in which crack does not occur even in a case where a stress of more than 90% of a yield stress is loaded in an environment of 30°C or lower containing hydrogen sulfide of more than 0.1 MPa, and a steel plate capable of being used as a material thereof.
  • the present inventors observed fracture surfaces of a base material portion and a welded portion, structures, and the like of the steel pipe cracked in a high-pressure hydrogen sulfide environment of more than 0.1 MPa (for example, in an H 2 S saturated solution containing 5% salt and acetic acid) in a test in which the load stress is more than 90%.
  • the stress-strain curve of the steel pipe was also examined. As a result, the following findings were obtained.
  • the present invention has been made based on the above findings.
  • the steel pipe according to the present embodiment is a welded steel pipe including a base material portion and a welded portion.
  • the base material portion is cylindrical, and the welded portion extends in a direction parallel to an axial direction of the steel pipe.
  • the welded portion includes a weld metal portion, which is a metal portion that melts and solidifies during welding, and a welded heat-affected zone, which is a region that did not melt during welding but caused changes in the structure and the like due to heat input by welding and subsequent cooling.
  • the steel plate according to the present embodiment is used for the base material portion of the steel pipe. That is, as will be described later, the steel pipe is obtained by forming the steel plate into a tubular shape and butt welding both end portions of the steel plate. Therefore, the chemical composition, metallographic structure, and mechanical properties of the steel plate are the same as those of the base material portion of the steel pipe. Therefore, hereinafter, the description of the base material portion of the steel pipe according to the present embodiment is also applied to the steel plate according to the present embodiment.
  • the C is an element that increases the strength of steel. In a case where the C content is less than 0.030%, the strength increase effect cannot be sufficiently obtained. Therefore, the C content is 0.030% or more. It is preferably 0.035% or more.
  • the C content is set to 0.100% or less.
  • the C content is preferably 0.070% or less, and more preferably 0.060% or less.
  • the Si content is set to 0.50% or less. It is preferably 0.35% or less, and more preferably 0.30% or less.
  • the lower limit of the Si content includes 0%.
  • Si is inevitably mixed from a steel raw material and/or in a steelmaking process, 0.01% is a substantial lower limit of the Si content in practical steel.
  • Si may be added for deoxidation, and in this case, the lower limit of the Si content may be 0.10%.
  • Mn is an element that improves the strength and toughness of steel. In a case where the Mn content is less than 0.80%, these effects cannot be sufficiently obtained. Therefore, the Mn content is set to 0.80% or more.
  • the Mn content is preferably 0.90% or more, and more preferably 1.00% or more.
  • the Mn content is set to 1.60% or less. It is preferably 1.50% or less.
  • the P content is an element that is inevitably included as impurities.
  • the P content is more than 0.020%, the HIC resistant properties are lowered and the toughness of the welded portion is lowered. Therefore, the P content is 0.020% or less. It is preferably 0.015% or less, and more preferably 0.010% or less.
  • the P content is preferably low, and the lower limit includes 0%. However, in a case where the P content is lowered to less than 0.001%, a manufacturing cost significantly increases, and thus 0.001% is the substantial lower limit of the P content in practical steel.
  • S is an element that is inevitably included as impurities.
  • S is an element that forms MnS that stretches in a rolling direction during hot rolling and lowers the HIC resistant properties.
  • the S content is set to 0.0030% or less. It is preferably 0.0020% or less, and more preferably 0.0010% or less.
  • the lower limit includes 0%, but in a case where the S content is reduced to less than 0.0001%, the manufacturing cost increases significantly, and thus 0.0001% is a substantial lower limit on a practical steel plate.
  • the Al content is 0.060% or less. It is preferably 0.050% or less, more preferably 0.035% or less, and further more preferably 0.030% or less. It is preferable that the Al content is low, and the lower limit of the Al content includes 0%.
  • Al is inevitably mixed from the steel raw material and/or in the steelmaking process, 0.001 % is a substantial lower limit of the Al content in practical steel.
  • Al may be added for deoxidation, and in this case, the lower limit of the Al content may be 0.010%.
  • Ti is an element that forms carbonitrides and contributes to the refinement of crystal grains. In a case where the Ti content is less than 0.001%, this effect cannot be sufficiently obtained. Therefore, the Ti content is set to 0.001% or more. It is preferably 0.008% or more, and more preferably 0.010% or more.
  • the Ti content is 0.030% or less. It is preferably 0.025% or less, and more preferably 0.020% or less.
  • Nb is an element that forms carbides and/or nitrides and contributes to the increase of strength. In a case where the Nb content is less than 0.006%, these effects cannot be sufficiently obtained. Therefore, the Nb content is set to 0.006% or more. It is preferably 0.008% or more, and more preferably 0.010% or more. In particular, in a case of ensuring the hardness of the welded heat-affected zone, the Nb content is preferably 0.010% or more, more preferably 0.015% or more, and further more preferably 0.017% or more.
  • the Nb content is set to 0.100% or less. It is preferably 0.080% or less, and more preferably 0.060% or less.
  • the Nb content is preferably 0.040% or less, more preferably 0.035% or less, and further more preferably 0.033% or less.
  • N is an element that bonds with Ti and/or Nb to form a nitride and contributes to the refinement of the austenite grain size during heating.
  • the N content is set to 0.0010% or more. It is preferably 0.0020% or more.
  • the N content is set to 0.0080% or less. It is preferably 0.0060% or less, and more preferably 0.0050% or less.
  • Ca is an element that suppresses the formation of MnS that extends in the rolling direction by forming CaS in steel, and as a result, contributes to the improvement of HIC resistant properties.
  • the Ca content is set to 0.0005% or more. It is preferably 0.0010% or more, and more preferably 0.0015% or more.
  • the Ca content is set to 0.0050% or less. It is preferably 0.0045% or less, and more preferably 0.0040% or less.
  • O is an element that inevitably remains.
  • the O content is set to 0.0050% or less.
  • 0.0040% or less is preferable, and 0.0030% or less is more preferable.
  • the O content is preferably low, and may be 0%.
  • the O content may be 0.0001% or more. From a viewpoint of manufacturing cost, 0.0005% or more is preferable.
  • the amounts of Cr, Ni, and Cu each are more than 1.00%, or the Mo content is more than 0.50%, or the V content is more than 0.10%, the hardness increases and the sour resistant properties are lowered. Therefore, the contents of Cr, Ni, and Cu are all 1.00% or less, the Mo content is 0.50% or less, and the V content is 0.10% or less.
  • Cr 0.50% or less
  • Mo 0.40% or less
  • Cu 0.50% or less
  • V 0.06% or less.
  • the amounts of Mg and REM are both 0.0100% or less. It is preferably 0.0050% or less.
  • REM is a rare earth element and is a collective term for 16 elements of Sc and lanthanoid, and the REM content means the total amount of these elements.
  • the remainder is Fe and impurities.
  • impurities means a component mixed due to raw materials such as ore and scrap and various factors in the manufacturing step when steel is industrially manufactured, and is acceptable in a range not imparting an adverse effect to the present invention.
  • the amount of each is preferably controlled within the range described later.
  • These elements may be mixed from the steel raw material as impurities or inevitable mixing elements, but within the range, the properties of the steel pipe according to the present embodiment are not impaired. Therefore, the total amount of these elements is limited to 0.10% or less.
  • the values of ESSP and Ceq calculated from the amount of the components are required to satisfy predetermined conditions, as shown below.
  • ESSP is a value that is an index showing whether or not there is an amount of effective Ca commensurate with the S content, assuming that the residual Ca (effective Ca) obtained by subtracting Ca bound to oxygen is bound to S in an atomic weight ratio, and is represented by the following Formula (i).
  • the value of ESSP is required to be in a range of 1.5 to 3.0 in order to ensure the HIC resistant properties equal to or higher than those of steel in the related art.
  • ESSP Ca ⁇ 1 ⁇ 124 ⁇ O / 1.25 ⁇ S
  • each element symbol in the formula represents the amount (mass%) of each element included in steel, and is zero in a case where no element is included.
  • the ESSP is set to 1.5 or more. It is preferably 1.6 or more, and more preferably 1.7 or more.
  • the ESSP is set to 3.0 or less. It is preferably 2.8 or less, and more preferably 2.6 or less.
  • the amount of effective Ca is equal to or more than the minimum required amount for controlling the morphology of MnS, and is adjusted to equal to or less than the critical amount at which cluster-like inclusions are not generated, and thus excellent HIC resistant properties can be obtained.
  • Ceq is a value that is an index of hardenability, which means carbon equivalent, and is represented by the following Formula (ii).
  • Formula (ii) an index of hardenability, which means carbon equivalent, and is represented by the following Formula (ii).
  • a structure consisting of one or more selected from polygonal ferrite, granular bainite, acicular ferrite, and bainite, and preferably a metallographic structure consisting of one or more selected from granular bainite, acicular ferrite, and bainite, in total of more than 80% in the surface layer area
  • Ceq C + Mn / 6 + Cu + Ni / 15 + Cr + Mo + V / 5
  • each element symbol in the formula represents the amount (mass%) of one element included in steel, and is zero in a case where no element is included.
  • Ceq is set to 0.20 or more. It is preferably 0.25 or more.
  • Ceq is set to 0.50 or less. It is preferably 0.45 or less.
  • the welded heat-affected zone is a portion where the base material portion is not melted by welding. Therefore, the chemical composition is the same as that of the base material portion, and the reason for limitation is also the same.
  • the chemical composition of the weld metal portion in the welded portion is not particularly limited. However, in order to increase the strength of the weld metal portion to the same level as or higher than the strength of the base material portion, the chemical composition of the weld metal portion is preferably in the following range.
  • the chemical composition of the weld metal portion in the welded portion is, by mass%, preferably C: 0.02% to 0.20%, Si: 0.01% to 1.00%, Mn: 0.1% to 2.0%, P: 0.015% or less, S: 0.0050% or less, Cu: 1.0% or less, Ni: 1.0% or less, Mo: 1.0% or less, Cr: 0.1% or less, Nb: 0.5% or less, V: 0.3% or less, Ti: 0.05% or less, Al: 0.005% to 0.100%, O: 0.010% to 0.070%, Cr: 0% to 1.00%, Ni: 0% to 1.00%, Cu: 0% to 1.00%, Mo: 0% to 0.50%, V: 0% to 0.10%, Mg: 0% to 0.01%, REM: 0% to 0.01%, a remainder: Fe and impurities.
  • the chemical composition of the weld metal portion is determined by an inflow ratio of the base material and the welding material during welding.
  • the welding material a commercially available material may be used, and for example, Y-D, Y-DM, Y-DMH wire, and a flux of NF5000B or NF2000 can be used.
  • a flux of NF5000B or NF2000 can be used.
  • the metallographic structure in the surface layer area of the base material portion is a structure consisting of one or more selected from polygonal ferrite, granular bainite, acicular ferrite, and bainite.
  • the surface layer area means a range up to 1.0 mm from the surface of the base material portion.
  • the metallographic structure in the surface layer area is a structure consisting of one or more selected from polygonal ferrite, granular bainite, acicular ferrite, and bainite.
  • a total area ratio of one or more selected from granular bainite, acicular ferrite, and bainite is more than 80%. In a case where the total area ratio is more than 80%, the strength and sour resistant properties are further improved. More preferably, it is 85% or more.
  • the measurement of the area ratio of each structure is performed by observing the metallographic structure etched with a mixed solution of 3% nitric acid and 97% ethanol with a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • the structure of the surface layer area may be measured at a position of 0.5 mm from the surface of the steel plate as a representative.
  • the metallographic structure of the surface layer area in the base material portion refers to the metallographic structure of the base material portion that is not affected by welding.
  • the steel pipe according to the present embodiment refers to the metallographic structure of the surface layer area at positions of 90°, 180°, and 270° in a circumferential direction of the steel pipe from a butt portion (corresponding to the seam portion and the end portion of the steel plate in a width direction).
  • the position corresponds to the metallographic structure of the surface layer area at positions of 1/4, 1/2, and 3/4 of the steel plate in a width direction in the steel plate.
  • the polygonal ferrite is a structure observed as a massive structure containing no coarse cementite or coarse precipitates such as MA inside the grain, and acicular ferrite is a structure in which prior austenite grain boundary is unclear, and inside the grain, needle-like ferrite (carbide and austenite/martensite mixture do not exist) is generated in random crystal orientation.
  • the worked ferrite is a ferrite subjected to working, and grains flattened in the rolling direction are observed by an optical microscope or SEM observation.
  • Flattening means that an aspect ratio (ferrite length in the rolling direction with respect to the ferrite length in the plate thickness direction) is 2.0 or more.
  • pearlite is a structure in which ferrite and cementite are layered, and among pearlite, a structure in which the cementite forming a layer is cut off in the middle is pseudo-pearlite.
  • the one appeared in white by a modified LePera solution is determined as residual austenite.
  • Granular bainite is generated at an intermediate transformation temperature between that of acicular ferrite and bainite and has intermediate structural properties.
  • Granular bainite is a structure in which prior austenite grain boundaries are partially visible, coarse lath structures are present in the grains, and a portion in which fine carbides and austenite-martensite constituent are scattered in and between the laths, and a portion of needle-like or amorphous ferrite in which the prior austenite grain boundaries are unclear are mixedly present.
  • Bainite and martensite are structures in which the prior austenite grain boundaries are clear and fine lath structures are developed in the grains. Bainite and martensite cannot be easily distinguished by SEM observation, but in the present embodiment, are structures in which the prior austenite grain boundaries are clear, and the inside the grain, a fine lath structure is developed, a structure having a hardness of 250 Hv or more is martensite, and a structure in which prior austenite grain boundaries are clear, a fine lath structure is developed inside the grain, and the hardness is less than 250 Hv is bainite.
  • Whether the hardness is 250 Hv or more or less than 250 Hv is determined by measuring 10 points of the target structure with Micro Vickers with a load of 100 gf and determining whether the maximum value is 250 Hv or less than 250 Hv. All structures are tempered during double heating and heat treatment with steel pipes, but there is no particular distinction between the presence or absence of tempering.
  • the structure other than the surface layer area is not particularly limited.
  • the structure other than the surface layer area for example, the structure of a wall thickness center portion (thickness middle portion of the steel plate) does not contain worked ferrite, or pearlite (containing pseudo-pearlite), and martensite, mainly contains acicular ferrite and bainite, and preferably has a maximum hardness of 250 Hv or less.
  • the metallographic structure of the surface layer area in the welded heat-affected zone preferably contains one or both of bainite and acicular ferrite.
  • the metallographic structure of the surface layer area in the welded heat-affected zone is preferably a uniform structure, that is, a structure consisting of bainite and/or acicular ferrite.
  • the weld metal portion is preferably a structure consisting of acicular ferrite.
  • the following conditions are desirable as the welding conditions in order to control the welded heat-affected zone to the above metallographic structure.
  • the heat input during welding is preferably in a range of 2.0 kJ/ mm to 10 kJ/mm depending on the plate thickness.
  • a test piece including the weld metal portion is cut out from the welded portion of the steel pipe to prepare a sample for microstructure observation. Then, observation is performed in the same method as the base material portion.
  • SSC is caused by micro defects or micro cracks on the surface of the steel plate
  • the metallographic structure and hardness of the surface layer area that is a source of the micro defects and micro cracks are important.
  • the metallographic structure of the surface layer area of the base material portion is controlled as described above, and the maximum hardness of the surface layer area of the base material portion is 250 HV or less.
  • the maximum hardness of the surface layer area is preferably 245 HV or less, and more preferably 240 HV or less.
  • the maximum hardness of the surface layer area is measured by the following method. First, a test piece having an axial length of 20 mm and a circumferential length of 20 mm is collected by mechanical cutting from positions 90°, 180°, and 270° away from the welded portion in the circumferential direction of the steel pipe. In a case of the steel plate, a test piece having a length of 20 mm and a width of 20 mm is collected from positions of 1/4, 1/2, and 3/4 of the steel plate in a width direction from an end portion in the width direction.
  • test piece is polished by mechanical polishing.
  • test force 100 gf
  • 10 points at 0.1 mm intervals in the plate thickness direction 10 points at 1 mm intervals in the width direction for the same depth, and a total of 100 points are measured.
  • the maximum hardness of the surface layer area is 250 HV or less.
  • a high value may appear locally due to inclusions or the like.
  • inclusions do not cause crack, SSC resistant properties can be ensured even if such an abnormal value appears.
  • two or more measurement points of more than 250 HV are continuously present in the plate thickness direction, it is not acceptable since it is not caused by inclusions and the SSC resistant properties are lowered.
  • the point is not adopted as an abnormal point, and the next highest value is denoted as the maximum hardness.
  • the hardness is denoted as the maximum hardness.
  • the present inventors performed examination on SSC resistant properties in a harsher environment. As a result, it was found that in a case where the proportional limit in the stress-strain curve is 90% or more of the yield stress, SSC does not occur even in a case where the load stress is more than 90% of the yield stress (for example, 95%).
  • the proportional limit is less than 90% of the yield stress
  • the load stress in the sulfide stress corrosion crack test is 90% of actual yield stress
  • dislocations proliferate due to plastic deformation.
  • the hydrogen that intruded during the sulfide stress corrosion test is trapped by the proliferated dislocations, and the amount of hydrogen increases, and crack occurs.
  • the proportional limit is 90% or more of the yield stress
  • plastic deformation does not occur even if the yield stress is more than 90%. Therefore, the proliferated dislocations do not increase, and hydrogen is not concentrated there. As a result, it becomes possible to prevent cracking.
  • the proportional limit is 90% or more of the yield stress
  • the proportional limit is more preferably 95% or more of the yield stress.
  • the proportional limit is measured by the following procedure.
  • a round bar tensile test piece is collected at a right angle (C direction) to the longitudinal direction of the steel pipe, and a tensile test is performed.
  • the tensile test is performed under stroke control (tensile speed: 1 mm/min), the test force and displacement are measured at intervals of 0.05 s, and the stress and strain for each measurement time are obtained based thereon.
  • the yield stress (YS) is obtained from the obtained stress-strain curve. In a case where the yield point is not clearly recognized, 0.20% proof stress is adopted as YS.
  • the stress and strain values are subjected to smoothing treatment in consideration of the measurement error. Specifically, an average value of the measurement time ⁇ 2.50 s is calculated for each measurement time, and the value is used as the result at each measurement time. For example, as the stress and strain values at 2.50 s, the average value of 101 measurement values between 0 and 5.00 s is adopted.
  • an inclination of the stress-strain curve after the smoothing treatment in a straight line portion is obtained.
  • the inclination of the straight line portion is calculated by the least squares method using a value between 0.2 YS and 0.4 YS as a representative value.
  • the inclination of the stress-strain curve at each measurement time is calculated. Specifically, for each measurement time, the inclination is calculated by the least squares method from the value between the measurement time ⁇ 0.50 s. For example, the inclination of the stress-strain curve at 60.00 s is calculated by the least squares method using 21 measurement values between 59.50 and 60.50 s.
  • a value of one before the stress in which the inclination of the stress-strain curve continues to be less than 0.95 times the inclination of the straight line portion is set as the proportional limit. Even if the inclination of the stress-strain curve falls below 0.95 times the inclination of the straight line portion due to the influence of measurement error, in a case where the inclination of the stress-strain curve is more than 0.95 times the inclination of the straight line portion again, the value will not be adopted.
  • the yield stress of the base material portion of the steel pipe according to the present embodiment is 415 MPa or more in order to ensure the required strength in the steel pipe according to the present embodiment. It is preferably 430 MPa or more.
  • an upper limit of the yield stress about 630 MPa defined in X70 of API 5L is a substantial upper limit, from a viewpoint of workability. From the viewpoint of workability, the yield stress is preferably 600 MPa or less.
  • the tensile strength of the base material portion of the steel pipe according to the present embodiment is preferably 530 MPa or more in order to ensure the required strength in the steel pipe according to the present embodiment. More preferably, it is 550 MPa or more.
  • An upper limit of the tensile stress is not particularly limited, but from the viewpoint of workability, 690 MPa defined in X70 of API 5L is a substantial upper limit. From the viewpoint of workability, 650 MPa or less is preferable.
  • the maximum hardness of the surface layer area in the welded heat-affected zone is 250 HV or less.
  • the maximum hardness of the surface layer area is more preferably 245 HV or less, and further more preferably 240 HV or less.
  • the maximum hardness of the surface layer area in the welded heat-affected zone is 150 HV or more.
  • the maximum hardness of the surface layer area is more preferably 160 HV or more, and further preferably 170 HV or more.
  • the maximum hardness of the surface layer area in the welded heat-affected zone is a maximum hardness measured in a region from the surface to a depth position of 0.9 mm in the wall thickness direction.
  • the maximum hardness of the surface layer area in the welded heat-affected zone 40 points at 0.5 mm pitch at positions of 0.3 mm, 0.6 mm, and 0.9 mm from the surface, a total of 120 points, on a base material portion side from the welded toe (the boundary between the weld metal portion and the base material portion) by cutting out the sample as shown in Fig. 2 , are measured to measure the maximum hardness.
  • the maximum hardness of the surface layer area in the welded heat-affected zone is 150 to 250 HV.
  • the reason for measuring the hardness in this way is the same as the reason for measuring the maximum hardness of the surface layer area in the above-mentioned base material portion.
  • the plate thickness is 10 to 40 mm, and the pipe diameter (outer diameter) is 508 mm or more.
  • An upper limit of the pipe diameter is not particularly limited, but 1,422.4 mm (56 inches) or less is a substantial upper limit.
  • the angle of the weld toe portion is an angle as shown in Fig. 1 . That is, the angle of the weld toe portion is an angle of an excess weld tip end portion of the weld metal portion, that is, an angle formed by a tangential direction of the weld metal and the surface of the base material portion. It can also be referred to as a so-called flank angle.
  • the angle of the weld toe portion on an inner side of the steel pipe is preferably in a range of 130° to 180°.
  • the angle of the weld toe portion is less than 130° and the angle is sharper, strain is piled up in the welded heat-affected zone, hydrogen intrusion is promoted, and crack easily occurs.
  • Fig. 1 it is described that only a lower left angle is measured, but in the present embodiment, the left and right angles are measured, and the smaller angle is the angle of the weld toe portion (toe angle).
  • a preferable manufacturing method for manufacturing a steel pipe according to the present embodiment and a steel plate as a material thereof will be described.
  • the steel pipe according to the present embodiment can obtain the effect as long as the steel pipe has the above-mentioned configuration, but the steel pipe is preferable since it can be stably obtained by the following manufacturing method, for example.
  • the steel pipe according to the present embodiment is obtained by further performing, in addition to steps of (A) to (C):
  • Steel piece manufactured by casting molten steel having the same chemical composition as that of the base material portion of the steel pipe according to the present embodiment is heated to 1,000°C to 1,250°C for hot rolling. Casting of molten steel and manufacturing of a steel piece prior to hot rolling may be performed according to a general method.
  • the heating temperature is set to 1,000°C or higher. It is preferably 1,100°C or higher.
  • the heating temperature is set to 1,250°C or lower. It is preferably 1,210°C or lower.
  • the heated steel piece is hot-rolled in a temperature range of Ar 3 points or higher to form a steel plate, and hot rolling is completed at Ar 3 points or higher.
  • the hot rolling finish temperature is set to Ar 3 points or higher.
  • Accelerated cooling is started from the temperature of Ar 3 points or higher on the steel plate for which hot rolling has been completed.
  • multi-stage accelerated cooling is performed, in which water cooling is performed twice or more such that the water-cooling stop temperature is 500°C or lower and the maximum attainment temperature due to recure-heating after stopping water cooling is higher than 500°C, at the surface temperature. It is preferably performed 3 times or more.
  • the temperature difference between the surface and the inner side can be adjusted by changing the sprayed water density, collision pressure, and the like in water cooling.
  • the maximum attainment temperature by recure-heating is 500°C or lower
  • the hardness of the steel plate, particularly the maximum hardness of the surface layer area from the surface to a depth of 1 mm cannot be reduced to 250 HV or less.
  • the maximum hardness of the surface layer area cannot be reduced to 250 HV or less. Therefore, accelerated cooling is performed such that the recure-heating by which the maximum attainment temperature becomes higher than 500°C is performed three times or more.
  • Each water-cooling stop temperature in the multi-stage cooling is preferably a temperature higher than the Ms point since the temperature does not generate a hard phase.
  • the water-cooling stop temperature before recure-heating is higher than 500°C, a predetermined structure cannot be obtained, and the water-cooling stop temperature is set to 500°C or lower.
  • the water-cooling stop temperature is preferably 500°C or lower.
  • the maximum hardness HVmax of the surface layer area from the surface of the steel plate to the depth of 1 mm is lowered to 250 HV or less. Since the number of recure-heating is the number of times until the maximum hardness HVmax of the surface layer area reaches 250 HV or less, it is not required to define the upper limit of the number of recure-heating.
  • the first cooling step after the completion of water cooling and recure-heating three times or more, cooling is performed at an average cooling rate of 0.2°C/s or more to a temperature of 500°C or lower.
  • the cooling rate becomes slow by performing coiling or the like, and thereby the average cooling rate up to 500°C is less than 0.2°C/s, the hardness unevenness becomes small but the structure and/or hardness of above-mentioned surface layer area cannot be obtained.
  • the forming of the steel plate according to the present embodiment into a steel pipe is not limited to a specific forming method.
  • warm working also can be used, but cold working is preferable from a viewpoint of dimensional accuracy.
  • both end portions of the steel plate are butted and arc welded (seam welding).
  • Arc welding is not limited to specific welding, but submerged arc welding is preferable.
  • the welding conditions may be known conditions. For example, it is preferable to perform welding with 3 electrodes or 4 electrodes in a heat input range of 2.0 to 10 kJ/mm depending on the plate thickness.
  • it is preferable to carry out inner surface welding and outer surface welding and it is preferable to carry out submerged arc welding on the inner surface 3 electrodes and the outer surface 4 electrodes.
  • the steel pipe is heat-treated under the conditions that the temperature range is 100°C to 300°C and the retention time is 1 minute or more.
  • the upper limit is not particularly limited, but is, for example, 60 minutes or less.
  • seam heat treatment may be performed by heating the welded portion to Ac 1 point or lower and tempering thereof such that a structure harmful to sour resistant properties (ferrite-pearlite of more than 20% in area ratio) is not generated on the welded portion. This heat treatment may be performed immediately after seam welding.
  • the steel pipe according to the present embodiment Since the base material portion of the steel pipe according to the present embodiment is not heat-treated at a temperature of more than the Ac 1 point, the metallographic structure of the base material portion is the same as the metallographic structure of the steel plate according to the present embodiment. Therefore, the steel pipe according to the present embodiment has excellent SSC resistant properties in addition to HIC resistant properties equal to or higher than that of the steel in the related art in both the base material portion and the welded portion.
  • the molten steel having the chemical composition shown in Tables 1-1 and 1-2 was continuously cast to manufacture a steel slab having a thickness of 240 mm, and the steel plate was manufactured under the manufacturing conditions (heating temperature, finish rolling temperature, maximum attainment temperature by recure-heating after the first water-cooling stop in the multi-stage cooling, and number of times of recure-heating of higher than 500°C) shown in Tables 2-1 to 2-3.
  • Tables 2-1 to 2-3 in the column of water-cooling stop temperature, OK means an example in which the water-cooling stop temperature was 500°C or lower after each water cooling of multi-stage accelerated cooling, and NG means an example in which there is a case where the cooling stop temperature is higher than 500°C.
  • a round bar tensile test piece was collected from the obtained steel plate according to API 5L, and the tensile strength was measured.
  • the maximum hardness of the surface layer area from the surface to a depth of 1 mm was measured, and the metallographic structure was observed by SEM.
  • the structure at a position 5 mm away from the surface and the structure at a position of 1/2 (1/2 portion) of the plate thickness from the surface were also observed.
  • a 300 mm square steel plate was cut out by gas cutting from positions of 1/4, 1/2, and 3/4 of the steel plate in a width direction from an end portion of the steel plate in the width direction, a block test piece having a length of 20 mm and a width of 20 mm was collected from a center of the cut-out steel plate by mechanical cutting, and polished by mechanical polishing.
  • a test piece obtained by polishing a sample collected such that positions of 0.5 mm from the surface (surface layer area), 5 mm from the surface, and 1/2 of the plate thickness from the surface can be observed was immersed in a mixed solution of 3% nitric acid and 97% ethanol for several seconds to several tens of seconds and etched, the metallographic structure was exposed and observed by SEM, and bainite and martensite were classified by micro Vickers hardness.
  • the results are shown in Tables 3-1 to 3-3.
  • a modified LePera solution was also used depending on the necessity to observe the metallographic structure. [Table 3-1] Test No.
  • Metallographic structure # of surface layer area of steel plate Total area ratio ## of GB + AF + B (%) Area ratio other than GB + AF + B (%) Metallographic structure at position of 5 mm from surface Metallographic structure of 1/2 portion Maximum hardness of surface layer area (HV)
  • each steel plate was cold-worked into a tubular shape, both end portions of the tubular steel plate were butted against each other, and a steel pipe was manufactured by submerged arc welding (SAW) in which heat input was under a condition in a range of 2.0 kJ/mm to 10 kJ/mm depending on the plate thickness with 3 electrodes or 4 electrodes.
  • SAW submerged arc welding
  • Y-D, Y-DM, Y-D wire and a flux of NF-5000B were used on the inner surface side
  • Y-DM, Y-DMH, Y-DM, Y-DM and a flux of NF-5000 were used on the outer surface side.
  • 3 electrodes were used on the inner surface and 4 electrodes were used on the outer surface, and the heat input during welding was adjusted in a range of 2.0 kJ/mm to 10 kJ/mm depending on the plate thickness.
  • Heat treatment was performed on the obtained steel pipe, and on the base material portion for some of the steel plates, under the conditions as shown Tables 2-1 to 2-3. In addition, heat treatment of heating to 400°C to Ac 1 point was performed on the welded portion regarding some of the steel pipes (Test No. 58).
  • test pieces having an axial length of 20 mm and a circumferential length of 20 mm were collected by mechanical cutting from positions 90°, 180°, and 270° away from the welded portion in the circumferential direction of the steel pipe. Then, using the test pieces, the maximum hardness of the surface layer area of the steel pipe was obtained by the same method as described above. Since it is considered that the metallographic structure after the pipe was made into a steel pipe is the same as the metallographic structure of the steel plate, the measurement results were used as they were.
  • a 4-point bending test piece having a width of 15 mm, a length of 115 mm, and a thickness of 5 mm was collected from an inner surface of the base material portion of the steel pipe so as to remain the inner surface, and the presence or absence of crack in a solution environment of pH 3.5 with various hydrogen sulfide partial pressures was examined in accordance with NACE TM 0316-2016.
  • the load stress during the 4-point bending test was 90% and 95% of the actual yield stress.
  • HIC test a hydrogen-induced crack test
  • NACE TM0284 a test piece having a length of 100 mm and a width of 20 mm with a curvature along an inner surface, collected from the base material portion, was immersed in a test solution obtained by saturating 100% H 2 S gas in Solution A (5 mass% NaCl + 0.5 mass% glacial acetic acid aqueous solution) for 96 hours. After that, the area ratio (CAR) at which crack occurred was measured for the surface layer area and the center portion. In a case where the CAR is 5% or less, it was determined that the HIC resistant properties were excellent.
  • CAR area ratio
  • Test Nos. 1 to 22 and 60 to 65 (steel pipe of the present invention) had HIC resistant properties equal to or higher than that of the steel pipe in the related art, and were excellent in SSC resistant properties.
  • the chemical composition of the weld metal portion was obtained from Steel pipe No. 1.
  • the chemical composition of the weld metal was C: 0.07%, Si: 0.41%, Mn: 1.45%, P: 0.010%, S: 0.0030%, Cu: 0.04%, Ni: 0.12%, Cr: 0.16%, Mo: 0.24%, Nb: 0.02, Ti: 0.02%, Al: 0.02%, O: 0.045%, and a remainder of Fe and impurities.
  • an angle of the excess weld tip end portion of the weld metal portion that is, an angle between the tangential direction of the weld metal and the surface of the base material portion on both sides, and use the smaller angle as the angle of the weld toe portion.
  • a 4-point bending test piece having a width of 15 mm, a length of 115 mm, and a thickness of 5 mm was collected from an inner surface of the steel pipe so as to remain the inner surface such that the weld toe portion is disposed in a center portion of the test piece in a longitudinal direction, and the presence or absence of crack in a solution environment of pH 3.5 with various hydrogen sulfide partial pressures was examined in accordance with NACE TM 0316-2016.
  • the load stress during the 4-point bending test was 90% and 95% of the actual yield stress.
  • the hardness of the surface layer area in the welded heat-affected zone was measured.
  • the hardness was measured in the surface layer area from the center portion in the circumferential direction and the longitudinal direction of the steel pipe to a depth position of 1.0 mm or 0.9 mm from the surface.
  • a method of cutting out the test piece for the hardness test of the welded heat-affected zone is as described above.
  • the metallographic structure in the surface layer area of the welded heat-affected zone was observed, and the area ratio was also measured.
  • the metallographic structure of the surface layer area is a metallographic structure at a depth position of 0.5 mm in the wall thickness direction from the surface. The results are summarized in Table 5. [Table 5] Test No. Test No.
  • Test Nos. 2, 2', 11, and 11' were excellent in SSC resistant properties including the welded portion. On the other hand, in Test Nos. 2" and 11", SSC occurred from the weld toe portion.
  • the steel pipe according to the present invention is suitable for a steel pipe used in a highpressure hydrogen sulfide environment such as a steel pipe for excavation of petroleum or natural gas or a steel pipe for transportation.

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EP20923002.8A 2020-03-04 2020-03-04 Tube en acier, et plaque en acier Pending EP4116453A4 (fr)

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JP (1) JP7360075B2 (fr)
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CN116288065B (zh) * 2022-12-14 2024-11-29 鞍钢股份有限公司 一种轻量化桩体用涂装用钢板及其生产方法
JP2025110367A (ja) * 2024-01-15 2025-07-28 日本製鉄株式会社 鋼板及び鋼管並びに鋼板の製造方法
CN118207478B (zh) * 2024-03-06 2025-09-30 鞍钢股份有限公司 一种x70级管束外承载管用钢及其生产方法
CN121065586B (zh) * 2025-11-04 2026-02-24 鞍钢股份有限公司 一种高性能耐蚀海工用钢板及其制造方法

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JP4631193B2 (ja) * 2001-03-29 2011-02-16 Ｊｆｅスチール株式会社 塗覆装鋼管の製造方法
JP4072009B2 (ja) * 2002-07-01 2008-04-02 新日本製鐵株式会社 圧潰強度の高いｕｏｅ鋼管の製造方法
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JP5672916B2 (ja) 2010-09-30 2015-02-18 Ｊｆｅスチール株式会社 耐サワーラインパイプ用高強度鋼板およびその製造方法並びに耐サワーラインパイプ用高強度鋼板を用いた高強度鋼管
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EP3546610B1 (fr) * 2017-03-29 2021-06-16 Nippon Steel Corporation Tuyau en acier soudé par résistance électrique tel que laminé pour tuyaux de canalisation
KR20190129957A (ko) * 2017-03-30 2019-11-20 제이에프이 스틸 가부시키가이샤 내사우어 라인 파이프용 고강도 강판 및 그의 제조 방법 그리고 내사우어 라인 파이프용 고강도 강판을 이용한 고강도 강관
WO2019058422A1 (fr) * 2017-09-19 2019-03-28 新日鐵住金株式会社 Tube en acier et tôle en acier
JP6319539B1 (ja) * 2017-09-19 2018-05-09 新日鐵住金株式会社 鋼管及び鋼板
EP3686303B1 (fr) * 2017-09-19 2021-12-29 Nippon Steel Corporation Tuyau d' acier et plaque d'acier
EP3677698A4 (fr) * 2017-09-28 2020-07-08 JFE Steel Corporation Plaque d'acier à haute résistance pour tuyau de canalisation résistant à l'acidité, son procédé de fabrication, et tuyau en acier à haute résistance utilisant une plaque d'acier à haute résistance pour tuyau de conduite résistant à l'acidité

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KR20220131992A (ko) 2022-09-29
BR112022013767A2 (pt) 2022-10-11
JP7360075B2 (ja) 2023-10-12
EP4116453A4 (fr) 2023-03-22
WO2021176590A1 (fr) 2021-09-10
KR102792300B1 (ko) 2025-04-08
JPWO2021176590A1 (fr) 2021-09-10
CN115210396A (zh) 2022-10-18

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