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WO2019058420A1 - Tube en acier et plaque d'acier - Google Patents

Tube en acier et plaque d'acier Download PDF

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Publication number
WO2019058420A1
WO2019058420A1 PCT/JP2017/033706 JP2017033706W WO2019058420A1 WO 2019058420 A1 WO2019058420 A1 WO 2019058420A1 JP 2017033706 W JP2017033706 W JP 2017033706W WO 2019058420 A1 WO2019058420 A1 WO 2019058420A1
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WIPO (PCT)
Prior art keywords
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steel plate
steel
metallographic structure
surface layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/JP2017/033706
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English (en)
Japanese (ja)
Inventor
篠原　康浩
原　卓也
潔 海老原
一輝 筒井
服部　豊
晃 橋本
望 阿部
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel and Sumitomo Metal Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel and Sumitomo Metal Corp filed Critical Nippon Steel and Sumitomo Metal Corp
Priority to JP2018502833A priority Critical patent/JP6319539B1/ja
Priority to CN201780094849.1A priority patent/CN111094608B/zh
Priority to KR1020207006880A priority patent/KR102364255B1/ko
Priority to PCT/JP2017/033706 priority patent/WO2019058420A1/fr
Priority to EP17926174.8A priority patent/EP3686305B1/fr
Publication of WO2019058420A1 publication Critical patent/WO2019058420A1/fr
Anticipated expiration legal-status Critical
Ceased 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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/085—Cooling or quenching
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—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
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/26—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
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted 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
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling

Definitions

  • the present invention relates to a steel pipe and a steel plate.
  • steel pipes for line pipes are required to have high strength in order to save materials by thinning and to reduce the weight of products.
  • the amount of addition of alloying elements is increased or the amount of heat input is increased for high efficiency welding for the purpose of increasing the strength, the low temperature toughness of the heat affected zone (HAZ) of the welding heat decreases.
  • steel pipes having HIC resistance have high purification of steel, reduction of inclusions, shape control of sulfide inclusions by Ca addition, light reduction and acceleration during casting, and the like. It has been manufactured using technology such as suppression of center segregation by cooling.
  • the present invention is a steel pipe suitable for use as a line pipe, having a strength of X 52 to 70 in the API standard and excellent in SSC resistance and HIC resistance, and a steel plate used for a base material of this steel pipe. Intended to be provided.
  • the present invention has been made in view of the above problems, and the summary thereof is as follows.
  • a steel pipe according to an aspect of the present invention has a base material portion made of a cylindrical steel plate, and a welded portion provided in a butt portion of the steel plate and extending in the longitudinal direction of the steel plate,
  • the above steel sheet has a chemical composition, C: 0.030 to 0.070%, Si: 0.005 to 0.50%, Mn: 1.05 to 1.65%, Al: 0.010 by mass%.
  • the surface layer metal structure which is a metal structure in the range of up to 0 mm includes polygonal ferrite and granular bainite, and the area ratio of the polygonal ferrite in the surface layer metal structure is 0 to 70%, and the polygonal ferrite
  • the total area ratio with the granular bainite is 50% or more, the maximum hardness in the surface layer metal structure is 270 Hv or less, and the plate thickness is more than 1.0 mm in the depth direction from the surface of the base material portion
  • the chemical composition is, by mass%, Ni: 0.05 to 0.50%, Mo: 0.05 to 0.50%, Cr: 0.05 to 0.50%, Cu: 0.05 to 0.50%, V: 0.010 to 0.100%, Mg: 0.0001 to 0.0100%, REM: 0.0001 to 0.0100% It may contain species or two or more species.
  • the remaining part of the surface layer metal structure is made of one or two of bainite and pseudo-perlite, and the remaining part of the internal metal structure is granular bainite, It may consist of one or more of bainite and pseudo-perlite.
  • the steel plate according to another aspect of the present invention is used for the base material portion of the steel pipe according to any one of the above (1) to (3).
  • a steel plate suitable for use as a line pipe having a strength of X 52 to 70 according to API standard and excellent in SSC resistance and HIC resistance, and the steel plate as a base material It is possible to provide a steel pipe excellent in SSC resistance and HIC resistance. Specifically, it is possible to provide a steel pipe excellent in SSC resistance (sulfide resistance to stress corrosion cracking) and HIC resistance (hydrogen-induced cracking resistance) and a steel plate used as a base material of the steel pipe.
  • a steel pipe excellent in sour resistance (SSC resistance and HIC resistance) is suitable as a line pipe for transporting petroleum, natural gas and the like.
  • the weld of a steel pipe is at the 0 o'clock position, it is a figure showing the result of measuring the hardness (load 100 g) of the surface layer metal structure from 0.1 to 1.0 mm from the surface at the position corresponding to 3 o'clock.
  • the weld of a steel pipe is at the 0 o'clock position, it is a figure showing the result of measuring the hardness (load 100 g) of the surface layer metal structure from 0.1 to 1.0 mm from the surface at the position corresponding to 6 o'clock.
  • the hardness (load 100 g) of the surface layer metal structure 0.1 to 1.0 mm from the surface at the position corresponding to 9 o'clock is measured. It is a figure which shows an example of the SEM photograph of surface layer metal structure. It is a figure which shows an example of the SEM photograph of internal metallographic structure.
  • a steel pipe according to an embodiment of the present invention (hereinafter referred to as a steel pipe according to the present embodiment) is It has a base material part which consists of a cylindrical steel plate, and a welding part which is provided in a butt of the steel plate and extends in the longitudinal direction of the steel plate,
  • the above steel sheet has a chemical composition, C: 0.030 to 0.070%, Si: 0.005 to 0.50%, Mn: 1.05 to 1.65%, Al: 0.010 by mass%.
  • the surface layer metallographic structure which is a metallographic structure ranging from the surface of the base metal portion in the depth direction to 1.0 mm includes polygonal ferrite and granular bainite, and the area of the polygonal ferrite in the surface layer metallographic structure Rate is 0 to 70%, the area ratio of the total of the polygonal ferrite and the granular bainite is 50% or more, and the balance may include bainite (including tempered bainite),
  • the maximum hardness is 270 Hv or less, preferably 250 Hv or less
  • the internal metallographic structure which is a metallographic structure ranging from more than 1.0 mm in the depth direction to the thickness center of the base material portion, includes polygonal ferrite having an area ratio of 40% or less and the remaining portion is granular bainite May contain bainite, pseudo-perlite or mixtures thereof
  • the maximum hardness is 248 Hv or less and the average hardness is 150 to 220 Hv.
  • a steel plate according to an embodiment of the present invention (hereinafter, referred to as a steel plate according to the present embodiment) is a steel plate used for the base material portion of the steel pipe.
  • the base material portion of the steel pipe according to the present embodiment (that is, the steel plate according to the present embodiment) will be described.
  • Chemical composition The reason for limitation of the chemical composition of the base material portion (the steel plate according to the present embodiment) of the steel pipe according to the present embodiment will be described.
  • % related to the chemical composition means mass%.
  • C 0.030% to 0.070%
  • C is an element necessary to improve the strength of the steel. If the C content is less than 0.030%, the strength improvement effect can not be sufficiently obtained. Therefore, the C content is 0.030% or more. Preferably it is 0.040% or more.
  • the C content exceeds 0.070%, while the strength of the steel increases too much, the surface layer metal structure and the internal metal structure, in particular, the hardness of the central segregation portion exceeds 248 Hv, SSC resistance, resistance to HIC property decreases. Therefore, the C content is set to 0.070% or less.
  • the content of C is preferably 0.050% or less from the viewpoint of suppressing a decrease in weldability, toughness and the like.
  • Si 0.005 to 0.50%
  • Si is an element that functions as a deoxidizer during steel making. In addition, it is an element that is inevitably mixed in the steelmaking stage. The said effect is not fully acquired as Si content is less than 0.005%. Therefore, the Si content is 0.005% or more. It is preferable to make it 0.050% or more in the point which fully acquires the deoxidation effect.
  • the Si content exceeds 0.50%, the toughness of the weld heat affected zone (HAZ) decreases. Therefore, the Si content is 0.50% or less. Preferably it is 0.35% or less.
  • Mn 1.05 to 1.65%
  • Mn is an element which contributes to the improvement of the strength and toughness of steel. If the Mn content is less than 1.05%, the effect of improving strength and toughness can not be sufficiently obtained. Therefore, the Mn content is 1.05% or more. Preferably it is 1.15% or more.
  • the Mn content exceeds 1.65%, a large amount of MnS which degrades the HIC resistance is generated, and the hardness of the internal metal structure, particularly the center segregation portion exceeds 248 Hv, and the HIC resistance decreases Do. Therefore, the Mn content is 1.65% or less. Preferably it is 1.50% or less.
  • Al 0.010% to 0.070%
  • Al is an element added for deoxidation. The said effect is not fully acquired as Al content is less than 0.010%. Therefore, the Al content is made 0.010% or more. Preferably it is 0.020% or more.
  • the Al content exceeds 0.070%, Al oxides are accumulated to form clusters, and the HIC resistance is lowered. Therefore, the Al content is set to 0.070% or less. Preferably it is 0.045% or less.
  • Ti 0.005 to 0.020%
  • Ti is an element which combines with N to form a nitride. This nitride contributes to the refinement of crystal grains. The said effect is not fully acquired as Ti content is less than 0.005%. Therefore, the Ti content is 0.005% or more. Preferably it is 0.008% or more.
  • the Ti content exceeds 0.020%, coarse nitrides are formed and the HIC resistance is lowered. Therefore, the Ti content is 0.020% or less. Preferably it is 0.015% or less.
  • Nb 0.005 to 0.045%
  • Nb is an element which contributes to the improvement of the strength of steel by forming carbides and nitrides as well as enlarging the non-recrystallization temperature range to make crystal grains finer.
  • the said effect is not fully acquired as Nb content is less than 0.005%. Therefore, the Nb content is made 0.005% or more. Preferably, it is 0.010% or more.
  • the Nb content exceeds 0.045%, coarse carbides and nitrides are formed, and the HIC resistance decreases. Therefore, the Nb content is 0.045% or less. Preferably it is 0.035% or less.
  • Ca 0.0010 to 0.0050%
  • Ca is an element that contributes to the improvement of the HIC resistance by combining with S to form CaS and suppressing the formation of MnS that elongates in the rolling direction. If the Ca content is less than 0.0010%, the above effect can not be sufficiently obtained. Therefore, the Ca content is 0.0010% or more. Preferably it is 0.0020% or more. On the other hand, when the Ca content exceeds 0.0050%, Ca oxides accumulate and the HIC resistance decreases. Therefore, the Ca content is made 0.0050% or less. Preferably it is 0.0040% or less.
  • N 0.0015 to 0.0070%
  • N is an element that forms a nitride and contributes to the suppression of coarsening of austenite grains during heating. The said effect is not fully acquired as N content is less than 0.0015%. Therefore, the N content is 0.0015% or more. Preferably it is 0.0020% or more.
  • the N content is made 0.0070% or less. Preferably it is 0.0050% or less.
  • the chemical composition of the base material portion (the steel plate according to the present embodiment) of the steel pipe according to the present embodiment includes the characteristics of the steel plate according to the present embodiment in order to improve the strength, toughness, and other characteristics besides the above elements. In the range which does not reduce, it may replace with a part of Fe, and may contain 1 type, or 2 or more types selected from Ni, Mo, Cr, Cu, V, Mg, and REM in the range mentioned later. These elements are optional elements and may not be contained. That is, the lower limit of the content of these elements is 0%.
  • Ni is an element that contributes to the improvement of the toughness and strength of the steel and the improvement of the corrosion resistance.
  • the Ni content is preferably 0.05% or more. More preferably, it is 0.10% or more.
  • the Ni content is 0.50% or less. Preferably it is 0.35% or less.
  • Mo 0 to 0.50%
  • Mo is an element which contributes to the improvement of the hardenability of steel.
  • the Mo content is preferably 0.05% or more. More preferably, it is 0.10% or more.
  • the Mo content exceeds 0.50%, the strength is excessively increased and the toughness is reduced. Therefore, even when it is contained, the Mo content is 0.50% or less. Preferably it is 0.35% or less.
  • Cr 0 to 0.50% Cr is an element that contributes to the improvement of the strength of the steel.
  • the Cr content is preferably 0.05% or more. More preferably, it is 0.10% or more.
  • the Cr content is made 0.50% or less. Preferably it is 0.35% or less.
  • Cu 0 to 0.50%
  • Cu is an element that contributes to the improvement of the strength of the steel and the improvement of the corrosion resistance.
  • the Cu content is preferably 0.05% or more. More preferably, it is 0.10% or more.
  • the Cu content exceeds 0.50%, the strength is excessively increased and the toughness is reduced. Therefore, even when it is contained, the Cu content is 0.50% or less. Preferably it is 0.35% or less.
  • V 0 to 0.100%
  • V is an element that contributes to the improvement of the strength of the steel by forming carbides and / or nitrides.
  • the V content is preferably 0.010% or more. More preferably, it is 0.030% or more.
  • the V content exceeds 0.100%, the toughness decreases. Therefore, even when it is contained, the V content is 0.100% or less. Preferably it is 0.080% or less.
  • Mg 0 to 0.0100%
  • Mg is an element which contributes to the improvement of the toughness of steel by forming a fine oxide and suppressing the coarsening of crystal grains.
  • the Mg content is preferably made 0.0001% or more. More preferably, it is 0.0010% or more.
  • the Mg content exceeds 0.0100%, the oxides are coagulated and coarsened, and the HIC resistance and the toughness decrease. Therefore, even when it is contained, the Mg content is made 0.0100% or less. Preferably it is 0.0050% or less.
  • REM 0 to 0.0100% REM is an element that contributes to the improvement of SSC resistance, HIC resistance and toughness by controlling the form of sulfide inclusions.
  • the REM content is preferably made 0.0001% or more. More preferably, it is 0.0010% or more.
  • the REM content exceeds 0.0100%, oxides are formed to lower the cleanliness of the steel, and as a result, the HIC resistance and the toughness decrease. Therefore, even when it is contained, the REM content is made 0.0100% or less. Preferably it is 0.0060% or less.
  • REM means a rare earth element and is a generic name of 17 elements of Sc, Y and lanthanoid, and the REM content indicates the total content of these 17 elements.
  • the base material portion of the steel pipe according to the present embodiment is based on the chemical composition containing the above essential elements and the balance containing Fe and impurities.
  • the chemical composition may optionally contain the above optional elements, with the balance being Fe and impurities.
  • Impurities are components that are mixed in from industrial sources such as ore or scrap, or from various environments in the manufacturing process when manufacturing steel products industrially, and are acceptable insofar as they do not adversely affect steel. I mean one.
  • impurities P, S, O, Sb, Sn, Co, As, Pb, Bi, and H are preferably controlled in the range described later.
  • P 0.015% or less
  • P is an impurity element, and the smaller its content, the more preferable element.
  • the P content exceeds 0.015%, the HIC resistance is significantly reduced. Therefore, the P content is 0.015% or less.
  • the lower limit includes 0%.
  • the P content is reduced to less than 0.003%, the manufacturing cost is significantly increased, so 0.003% is a practical lower limit of the P content in practical steel plates.
  • S 0.0015% or less
  • S is an element forming MnS which is stretched in the rolling direction during hot rolling. This stretched MnS lowers the HIC resistance.
  • the S content exceeds 0.0015%, the HIC resistance is significantly reduced. Therefore, the S content is 0.0015% or less. Preferably it is 0.0010% or less.
  • the manufacturing cost is significantly increased, so 0.0001% is a practical upper limit of the S content in practical steel plates.
  • O 0.0040% or less
  • O is an element which inevitably remains after deoxidation, and the smaller its content, the more preferable.
  • the O content exceeds 0.0040%, a large amount of oxides are formed, and the HIC resistance is significantly reduced. Therefore, the O content is made 0.0040% or less. Preferably it is 0.0030% or less.
  • the lower the O content the lower the 0 content.
  • 0.0010% is a practical lower limit of the O content in practical steel plates.
  • Sb, Sn, Co, As are each 0.10% or less, Pb and Bi are each 0.005% or less, H is 0.0005% or less. It is preferable to do.
  • Ceq 0.300 to 0.400
  • the chemical composition of the steel plate used for the base material portion of the steel pipe is not only the content of each element but also the following formula (1 Ceq (carbon equivalent weight) defined by) shall be 0.400 or less.
  • Ceq [C] + [Mn] / 6 + ([Ni] + [Cu]) / 15 + ([Cr] + [Mo] + [V]) / 5 (1)
  • [C], [Mn], [Ni], [Cu], [Cr], [Mo], and [V] in the formulas are C, Mn, Ni, Cu, Cr, Mo, and V contents (mass %).
  • Ceq When the Ceq exceeds 0.400, the hardenability becomes too high, and the maximum hardness of the surface layer metal structure of the base material portion (steel plate) to be described later exceeds 270 Hv, and as a result, the SSC resistance decreases. In addition, the maximum hardness of the internal metal structure exceeds 248 Hv, and the HIC resistance decreases. Therefore, Ceq should be 0.400 or less. Preferably it is 0.350 or less. The lower limit of Ceq is 0.300 or more in order to secure a predetermined strength.
  • the surface layer portion of the steel plate is quenched more rapidly than the inside of the steel plate.
  • the surface layer portion of the steel plate is higher in hardness than the inside.
  • the inventors of the present invention have found that the steel sheet and steel pipe having such a structure have inferior SSC resistance in the (surface layer portion) ranging from the surface to 1.0 mm in the depth direction (plate thickness direction). Found out.
  • the inventors of the present invention can control the metallographic structure of the surface layer of the steel sheet and the metallographic structure of the inside of the steel sheet by controlling the cooling of the steel sheet. As a result, the hardness of the surface layer of the steel sheet is increased. Was found to be able to suppress
  • the metallographic structure of the steel plate of the base material portion is (i) 1 from the surface of the steel plate in the depth direction (thickness direction) Divided into structures in the range of up to .0 mm (surface layer metal structure) and (ii) structures in the range from more than 1.0 mm in the depth direction from the surface of the steel plate to the center of thickness (internal metal structure),
  • the type and fraction (area ratio) of the contained structure and the hardness are defined.
  • the surface layer portion (hereinafter, may be simply referred to as a “steel plate surface layer portion”) up to 1.0 mm in the depth direction from the surface of the steel plate of the base material portion.
  • the hardness in the range from the surface to a depth of 1.0 mm is high, so the surface layer metallographic structure is a structure ranging from a surface of the steel sheet to a depth of 1.0 mm.
  • the area ratio of polygonal ferrite is 0 to 70%, polygonal ferrite and granular bainite
  • the area ratio of polygonal ferrite exceeds 70% in the surface layer portion where the total area ratio is 50% or more and the maximum hardness is 270 Hv or less, a high concentration of C is accumulated in the remaining portion to form a hardened region. , SSC resistance is degraded. Therefore, the area ratio of polygonal ferrite is 70% or less. Preferably it is 50% or less.
  • the total area ratio of polygonal ferrite and granular bainite is set to 50% or more.
  • the balance of the surface layer metal structure is preferably made of one or two of bainite and pseudo-perlite. However, the remainder may not be included. That is, the total area ratio of polygonal ferrite and granular bainite may be 100%.
  • the maximum hardness of the surface layer metal structure exceeds 270 Hv, the SSC resistance decreases. Therefore, the maximum hardness of the surface layer metal structure is set to 270 Hv or less. Preferably it is 250 Hv. Although there is no need to set the lower limit from the viewpoint of SSC resistance, it is substantially 160 Hv or more.
  • the measurement of the area ratio of each tissue is obtained by observing the metal structure with a scanning electron microscope (SEM) at a magnification of, for example, 1000 ⁇ .
  • the surface layer metallographic structure is obtained by observing the positions of 0.1 mm, 0.2 mm and 0.5 mm from the surface of the steel plate and averaging the area ratio at each position.
  • polygonal ferrite is a structure observed as a massive structure that does not contain coarse precipitates such as coarse cementite and MA in the grains.
  • Bainite is a structure in which a prior austenite grain boundary is clear, a fine lath structure is developed in the grain, and fine carbides and austenite-martensitic hybrids are interspersed in the lath and between the laths.
  • bainite also includes tempered bainite.
  • Granular bainite is an acicular ferrite in which former austenite grain boundaries are unclear and intra-granular acicular ferrite (with neither carbide nor austenite-martensitic composite) forming with random crystal orientation And, at a transformation temperature intermediate to that of bainite, the former austenite grain boundaries are partially visible, a coarse lath structure exists in the grains, and fine carbides and austenite-martensitic hybrids are interspersed within and between laths. And the austenite grain boundaries are unclear and a needle-like or irregular-shaped ferrite part is mixed.
  • Pseudo pearlite is pearlite in which cementite is arranged in a line.
  • FIG. 4 shows an example of a metal structure of 0.5 mm from the surface of the steel plate (image taken with a scanning electron microscope: 1000 ⁇ magnification).
  • a portion surrounded by a smooth curve and having a smooth inside is polygonal ferrite, and a portion where white dots exist inside is granular bainite.
  • the measurement of the maximum hardness of the surface part metallographic structure is performed as follows. First, positions of 1/4, 1/2 and 3/4 of the width of the steel plate in the width direction of the steel plate from the end in the width direction of the steel plate (corresponding to a butt joint in the case of steel pipe) Steel plates of 300 mm square are cut out by gas cutting from positions of 3 o'clock, 6 o'clock and 9 o'clock respectively when welds are at 0 o'clock, and block test pieces of 20 mm in length and 20 mm in width from the center of the cut steel plates Are collected by mechanical cutting and polished by mechanical polishing.
  • FIGS. 3A to 3C show the results of measurement of the hardness of the surface layer metal structure at three locations corresponding to 3:00, 6:00 and 9:00 when the welded portion of the steel pipe is at the 0 o'clock position.
  • the hardness of the surface layer metallographic structure was measured using a Vickers hardness tester at an interval of 0.1 mm from the surface layer to a depth of 0.1 mm to a depth of 1.0 mm at a load of 100 g at the same depth of 10 points.
  • the maximum hardness is 270 Hv or less at any point, and it can be seen that the SSC resistance is excellent.
  • Metallographic structure ranging from more than 1.0 mm in the depth direction from the surface of the steel plate of the base metal part to the thickness direction (internal metal structure): Polygonal ferrite area ratio 40% or less, maximum hardness 248 Hv or less, average Hardness 150 to 220 Hv
  • the area ratio of polygonal ferrite is 40% or less. Preferably it is 30% or less, more preferably 25% or less.
  • the remainder of the internal metallographic structure consists of one or more of granular bainite, bainite and pseudo-perlite.
  • the maximum hardness of the internal metal structure exceeds 248 Hv
  • the HIC resistance decreases. Therefore, the maximum hardness is set to 248 Hv or less.
  • the average hardness is 150 Hv or more. Preferably it is 160 Hv or more.
  • the average hardness exceeds 220 Hv
  • the HIC resistance and the toughness decrease. Therefore, the average hardness is set to 220 Hv or less. Preferably it is 210 Hv or less.
  • the structure fraction (area ratio) of the internal metallographic structure is observed, for example, at a magnification of 1000 times the position of 1/4 (t / 4) of the plate thickness from the surface of the steel plate using a scanning electron microscope (SEM) It is obtained by The observation position is set to the position of t / 4 because the tissue at the position of t / 4 indicates a typical tissue of the internal metallographic structure.
  • FIG. 5 shows an example of a metal structure at a position of t / 4 (imaging with a scanning electron microscope: magnification of 1000).
  • a portion surrounded by a smooth curve and having a smooth inside is polygonal ferrite.
  • a portion in which white dots or lines are visible inside is granular bainite or pseudo-perlite, and it is bainite surrounded by white lines of jaggedness and in which a thin pattern is visible inside.
  • the maximum hardness and the average hardness of the internal metal structure can be measured by the following method. Positions of 1/4, 1/2 and 3/4 in the width direction of the steel plate from the end in the width direction of the steel plate (corresponding to a butt joint in the case of steel pipe) Cut out a steel plate of 300 mm square from the positions of 3 o'clock, 6 o'clock and 9 o'clock respectively by gas cutting, and block test pieces of 20 mm long and 20 mm wide from the center of the cut steel plate by mechanical cutting Polish by mechanical polishing.
  • a Vickers hardness tester (load: 1 kg) starts at a depth position of 1.2 mm from the surface, 0.2 mm intervals in the thickness direction, and 1.0 mm width direction for the same depth Measure the hardness at 10 points at intervals.
  • a high hardness value (abnormal value) may appear locally. However, even if such an abnormal value appears, the HIC resistance can be secured.
  • the HIC resistance is lowered, which is not acceptable. Therefore, in the present embodiment, even if one measurement point exceeding 248 Hv is present, if two or more points appear continuously in the thickness direction, that point is not adopted as an abnormal point, and the next highest value is obtained. Is the maximum hardness. On the other hand, when there are two or more measurement points exceeding 248 Hv continuously in the thickness direction, the highest value of them is adopted as the maximum hardness. Also, the average hardness is calculated by averaging the hardness of all the measurement points.
  • the steel pipe according to the present embodiment is obtained by processing the steel plate according to the present embodiment into a cylindrical shape, butting both ends of the cylindrical steel plate (the ends in the width direction of the steel plate) and welding. Therefore, as shown in FIG. 1, the steel pipe 1 according to the present embodiment is provided at the butt portion of the steel plate 2 and has a welded portion 3 extending in the longitudinal direction of the steel plate.
  • the weld 3 is usually provided continuously from the longitudinal end of the steel plate 2 to the other end.
  • the welded portion is constructed so as to be thicker than the base material portion.
  • the weld metal is a higher alloy than the base metal and has high corrosion resistance. As a result, welds are seldom the starting point of failure. Therefore, the welded portion of the steel pipe according to the present embodiment is not particularly limited as long as it is obtained by SAW welding or the like under normal conditions.
  • the steel pipe according to the present embodiment preferably has a strength satisfying X52 to X70 defined in API 5L, in consideration of application to a line pipe.
  • the steel pipe according to the present embodiment has the above-described configuration regardless of the manufacturing method, its effects can be obtained, but can be stably obtained, for example, according to the manufacturing method including the following steps. So preferred. That is, the steel plate according to the present embodiment is (I) A hot rolling process in which a steel piece having a predetermined chemical composition is heated to 1050 to 1250 ° C. and subjected to hot rolling, and the hot rolling is finished at 830 to 1000 ° C. (Ii) The surface temperature of the steel plate after completion of hot rolling is from a temperature range of 750 to 950 ° C. to a temperature range of 400 to 650 ° C., with an average cooling rate of 15 to 100 ° C./sec.
  • the rise is 5 to 65 ° C, Obtained by the manufacturing method including Moreover, in addition to said (i) and (ii), the steel pipe which concerns on this embodiment is (Iii) a forming step of forming the steel plate according to the present embodiment obtained by the above into a cylindrical shape; (Iv) A welding process in which both ends of a cylindrical steel plate are butted and welded, Are obtained by the manufacturing method further including Hereinafter, preferable conditions for each step will be described.
  • Steel billet heating temperature 1050 to 1250 ° C
  • Steel slabs produced by casting a molten steel having the same chemical composition as the base material of the steel pipe according to the present embodiment are heated to 1050 to 1250 ° C. and subjected to hot rolling.
  • Casting of molten steel and production of billet prior to hot rolling may be performed according to a conventional method.
  • the billet heating temperature is less than 1050 ° C., undissolved coarse carbonitrides of Nb and Ti are formed, and the HIC resistance is lowered. Therefore, it is preferable to make steel slab heating temperature into 1050 degreeC or more. More preferably, it is 1100 ° C. or higher.
  • the billet heating temperature exceeds 1250 ° C.
  • the crystal grain size increases and the low temperature toughness decreases.
  • austenite grain size becomes coarse and the hardenability becomes excessively high, a hardened phase is formed in the surface layer metal structure and the internal metal structure, and the SSC resistance and the HIC resistance decrease. Therefore, it is preferable to make steel slab heating temperature into 1250 degrees C or less. More preferably, it is 1200 ° C. or less.
  • the plate thickness may be set according to the required thickness of the line pipe, and is not particularly limited.
  • the rolling finish temperature (finishing temperature) is set to 830 to 1000 ° C. in order to obtain a predetermined surface layer metal structure and an internal metal structure by accelerated cooling after finish rolling. Since it is difficult to obtain the surface layer metallographic structure and the internal metallographic structure when the rolling end temperature is less than 830 ° C., the finish rolling temperature is preferably 830 ° C. or higher. More preferably, it is 850 ° C. or higher. On the other hand, when the rolling finish temperature exceeds 1000 ° C., the crystal grains become coarse and the low temperature toughness decreases. Therefore, the rolling end temperature is preferably set to 1000 ° C. or less. More preferably, it is 900 ° C. or less.
  • Cooling start temperature Ts 750 to 950 ° C.
  • Cooling stop temperature Tf 400 to 650 ° C
  • Average cooling rate Vc 15 to 100 ° C / sec Number of times of recuperation: 2 times or more
  • Temperature rise due to recuperation 5 to 65 ° C (excluding the recuperation after the last water cooling stop)
  • the surface temperature of the steel plate after the end of hot rolling is from the temperature range of 750 to 950 ° C. to the temperature range of 400 to 650 ° C., and the average cooling rate is 15 to 100 ° C./sec. Accelerated cooling so as to include two or more recuperations in which the temperature rise is 5 to 65 ° C.
  • Accelerated cooling sandwiching the heat recovery on the way adjusts the water volume of the cooling water injected to the steel plate for each cooling zone in the cooling facility where the cooling zone is divided into multiple parts in the longitudinal direction (conveyance direction) of the steel plate Can be done.
  • FIG. 1 An example of the cooling curve of a steel plate is shown in FIG. From the top, the four cooling curves are the cooling curve at the center of the plate thickness (1/2 plate thickness), the cooling curve at the position 1 ⁇ 4 of the plate thickness from the surface (t / 4 portion), and the depth 1 from the surface It is a cooling curve of the part of 0 mm, and a cooling curve of a steel plate surface.
  • the entire steel plate is accelerated and cooled so as to include three recuperations on the way from 830 ° C. of the cooling start temperature (Ts) to about 620 ° C. in about 10 seconds.
  • the cooling start temperature Ts and the cooling stop temperature Tf are the points shown, and the average cooling rate Vc is the temperature change ⁇ T (cooling start temperature Ts-cooling stop temperature Tf) and the cooling time ⁇ t (water cooling is performed It is obtained by dividing it by
  • the cooling start temperature Ts is less than 750 ° C.
  • coarse ferrite is formed after rolling in the surface layer metallographic structure, and a high hardness structure such as martensite is generated as the remaining portion.
  • SSC resistance deteriorates.
  • the cooling start temperature Ts is less than 750 ° C.
  • the ferrite fraction in the internal metallographic structure becomes excessive, and the hardness of the hardened phase also becomes high. Therefore, it is preferable to set the cooling start temperature Ts to 750 ° C. or higher. More preferably, it is 780 ° C. or higher.
  • the cooling start temperature Ts exceeds 950 ° C.
  • the maximum hardness of the surface layer metal structure exceeds 270 Hv and the SSC resistance is lowered even if the heat recovery is performed twice or more. Therefore, it is preferable to set the cooling start temperature Ts to 950 ° C. or less. More preferably, it is 880 ° C. or less.
  • the cooling stop temperature Tf is preferably 400 ° C. or more. More preferably, it is 480 degreeC or more.
  • the cooling stop temperature Tf exceeds 650 ° C.
  • the average hardness of the internal metallographic structure may be less than 150 Hv, and the predetermined strength may not be satisfied.
  • a locally hard tissue is formed, which may lower the SSC resistance and the HIC resistance. Therefore, the cooling stop temperature Tf is preferably set to 650 ° C. or less. More preferably, it is 580 ° C. or less.
  • the average cooling rate Vc is less than 15 ° C./sec, polygonal ferrite having an area ratio of more than 70% is formed in the surface layer metallographic structure. In addition, in the internal metallographic structure, polygonal ferrite having an area ratio of more than 40% is formed. In that case, since the strength as a line pipe can not be secured, the average cooling rate Vc is preferably 15 ° C./second or more. More preferably, it is 25 ° C./second or more. On the other hand, when the average cooling rate Vc exceeds 100 ° C./sec, martensitic transformation occurs, the hardness of the surface layer metal structure exceeds 270 Hv, and the SSC resistance decreases.
  • the average cooling rate Vc is preferably 100 ° C./second or less. More preferably, it is 80 ° C./second or less.
  • the hardness of the surface layer metal structure exceeds 270 Hv and the SSC resistance decreases when the number of times of recuperation where the recuperation temperature during accelerated cooling is within the predetermined range is one or less. Therefore, the number of heat recovery is two or more.
  • count of 3 times of heat recovery was shown in FIG. 2, the frequency
  • cooling in a film boiling state is performed to generate a predetermined structure.
  • cooling is performed so as not to completely reheat during water cooling during the water cooling so that the temperature rise due to the heat recovery is 65 ° C. or less. If the temperature rise due to recuperation is over 65 ° C., coarse ferrite will be formed, and a predetermined structure can not be obtained. On the other hand, if the temperature rise due to recuperation is less than 5 ° C., the recuperation effect can not be obtained. Therefore, it is preferable to set the temperature rise width by recuperation to 5 to 65 ° C. More preferably, it is 10 to 65 ° C. However, it is not necessary to set the temperature rise width to 5 to 65 ° C. for the final recuperation after stopping the water cooling.
  • the first heat recovery When the heat recovery is performed twice or more at 5 to 65 ° C., it is preferable to perform the first heat recovery so that the steel sheet surface temperature after the heat recovery becomes 500 ° C. or more. Even if the steel sheet surface after the first heat recovery is less than 500 ° C., it is possible to secure the surface layer metal structure having excellent SSC resistance and the internal metal structure having excellent HIC resistance, but it is excellent. In order to stably secure the surface layer metal structure having SSC resistance and the internal metal structure having excellent HIC resistance, the first recuperation is performed, and the steel sheet surface temperature after recuperation is 500 ° C. or higher. It is preferable to do so.
  • the temperature difference between the surface layer portion (surface temperature) of the steel sheet and the inside (center temperature) of the steel sheet disappears at about 620 ° C., and the steel sheet temperature is stabilized.
  • the forming of the steel pipe according to the present embodiment is not limited to a specific forming. Although warm working can also be used, cold working is preferred in terms of dimensional accuracy.
  • both ends of the cylindrically shaped steel plate are butted and welded.
  • the welds are also not limited to a particular weld, but submerged arc welding (SAW) is preferred.
  • SAW submerged arc welding
  • the welding conditions may be performed under known conditions in accordance with the plate thickness and the like.
  • the welded portion may be subjected to a heat treatment (seam heat treatment) so as not to generate a structure (ferrite and pearlite exceeding 10% in area ratio) that reduces the toughness of the welded portion.
  • the heat treatment temperature may be a normal temperature range, but a range of 300 to Ac 1 point is preferable.
  • the metal structure of the base material portion is the same as the metal structure of the steel plate according to the present embodiment.
  • the base material portion of the steel pipe according to the present embodiment receives the metallographic structure of the steel plate according to the present embodiment, and has mechanical characteristics for line pipe and excellent on-site weldability.
  • the weldability of the steel pipe concerning this embodiment is excellent in the weldability of the steel plate concerning this embodiment, it is a weld part excellent in mechanical characteristics. Therefore, the steel pipe according to the present embodiment is a steel pipe suitable as a steel pipe for line pipe.
  • Example 1 A steel sheet having a chemical composition and Ceq shown in Table 1 was hot-rolled and cooled under the conditions shown in Table 2 to produce a steel plate.
  • the number of times of recuperation is the number of times of recuperation where a temperature rise of 5 ° C. or more occurred.
  • the maximum recuperation temperature range is the temperature rise width in recuperation where the temperature rise width was the largest.
  • Test specimens are collected from the manufactured steel plate, and the surface layer metal structure (0.1 mm, 0.2 mm, 0.5 mm position) and internal metal structure (t / 4 position) are magnified by 1000 times using SEM.
  • the polygonal ferrite, granular bainite, and the fraction (area ratio) of the remaining portion were calculated.
  • the remaining portion of the surface layer metal structure was bainite and / or pseudo-perlite, and the remaining portion of the internal metal structure was both granular bainite, bainite and / or pseudo-perlite.
  • JIS No. 5 tensile test pieces were prepared, and a tensile test prescribed in JIS Z 2241 was performed to measure the yield strength and the tensile strength.
  • the hardness was also measured using a Vickers hardness tester.
  • depths of 0.1 to 1.0 mm were measured from the surface layer at intervals of 0.1 mm with a load of 100 g at the same depth of 10 points.
  • a depth of 1.2 mm from the surface layer and a thickness center of 0.2 mm were measured at a load of 1 kg at the same depth of 10 points. From this result, the maximum hardness was obtained for the surface layer metal structure, and the maximum hardness and the average hardness were obtained for the internal metal structure.
  • test piece was extract
  • HIC resistance A test based on TM0284 of NACE (National Association of Corrosion and Engineer) is performed to observe the occurrence of HIC (hydrogen induced cracking), and if the HIC area ratio is 5% or less, the HIC resistance When it was superior (OK) and more than 5%, it was evaluated as inferior to HIC resistance (NG).
  • the NACE test saturates hydrogen sulfide gas in a solution of 5% NaCl solution + 0.5% acetic acid, pH 2.7, immerses the steel plate in the solution, and observes whether cracking occurs after 96 hours It is a test.
  • test piece to which a stress equivalent to 90% of 0.2% proof stress derived from a tensile test was applied in a four-point bending test was added with 5% sodium chloride + 0.m at room temperature (24 ° C.) saturated with 1 atm hydrogen sulfide gas.
  • the test piece was immersed in an aqueous solution of 5% acetic acid, pH 2.7 for 720 hours, and the surface of the test piece was observed at a magnification of 10 times in order to determine the presence or absence of generation of SSC.
  • Example 2 The steel plates shown in Table 3 were formed into a tubular shape by C press, U press, and O press, and the end faces were tack welded, main welding was performed from the inner and outer surfaces, and after pipe expansion, a steel pipe for line pipe was made. Submerged arc welding was applied to this welding.
  • Steel plate manufacturing No. And No. of steel pipe manufacture. Are related, for example, manufacture no. T1 steel pipe is manufactured by No. Manufactured using the steel plate of S1, manufacture No. T2 steel pipe is manufactured by No. It shows that it manufactured using the steel plate of S2.
  • Test specimens are collected from the manufactured steel plate, and the surface layer metal structure (0.1 mm, 0.2 mm, 0.5 mm position) and internal metal structure (t / 4 position) are magnified using a scanning electron microscope. It observed by 1000 times and calculated the percentage (area ratio) of polygonal ferrite, granular bainite, and the remainder. Further, JIS No. 5 tensile test pieces were prepared, and a tensile test prescribed in JIS Z 2241 was performed to measure the yield strength and the tensile strength.
  • the hardness was also measured with a Vickers hardness tester.
  • the surface layer metallographic structure was measured at a depth of 0.1 to 1.0 mm from the surface layer at intervals of 0.1 mm, 10 points at the same depth, and a load of 100 g.
  • the internal metallographic structure it was measured at a load of 1 kg with 10 points at the same depth at an interval of 0.2 mm from the surface to a depth of 1.2 mm and the plate thickness center.
  • test piece was extract
  • HIC resistance A test based on TM0284 of NACE (National Association of Corrosion and Engineer) was conducted to observe the occurrence of HIC (hydrogen induced cracking), HIC area ratio not more than 5%, HIC resistance Excellent (OK) and more than 5% were evaluated as inferior to HIC resistance (NG).
  • the NACE test saturates hydrogen sulfide gas in a solution of 5% NaCl solution + 0.5% acetic acid, pH 2.7, immerses the steel plate in the solution, and observes whether cracking occurs after 96 hours It is a test.
  • test piece to which a stress equivalent to 90% of 0.2% proof stress derived from a tensile test was applied in a four-point bending test was added with 5% sodium chloride + 0.m at room temperature (24 ° C.) saturated with 1 atm hydrogen sulfide gas.
  • the test piece was immersed in an aqueous solution of 5% acetic acid, pH 2.7 for 720 hours, and the surface of the test piece was observed at a magnification of 10 times in order to determine the presence or absence of generation of SSC. Those that did not generate SSC were passed (OK), and those that generated SSC were rejected (NG).
  • Table 4 The results are shown in Table 4.
  • a steel plate for line pipe having a strength of X52 to 70 according to API standard and excellent in SSC resistance and HIC resistance, and SSC resistance and HIC resistance using the steel plate as a base material It is possible to provide a steel pipe for line pipe which is excellent in the properties. Therefore, the present invention has high availability in the steel plate manufacturing industry and the energy industry.

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Abstract

Le tube en acier selon la présente invention comprend une partie de matériau de base composée d'un tube formé d'une plaque d'acier ayant une composition chimique prédéterminée, et une partie de soudure qui est disposée sur une partie aboutée de la plaque d'acier et s'étend dans le sens longitudinal de la plaque d'acier. Une structure métallographique de partie de surface, qui est la structure métallographique de la partie de matériau de base dans une plage allant de la surface à 1,0 mm dans le sens de la profondeur, contient de la ferrite polygonale et de la bainite granulaire ; le rapport surfacique de la ferrite polygonale dans la structure métallographique de la partie de surface va de 0 à 70 % ; le rapport surfacique total de la ferrite polygonale et de la bainite granulaire est supérieur ou égal à 50 % ; et la dureté maximale dans la structure métallographique de section de surface est inférieure ou égale à 270 Hv. Une structure métallographique interne, qui est la structure métallographique de la partie de matériau de base dans une plage allant de plus de 1,0 mm dans le sens de la profondeur depuis la surface jusqu'au milieu de l'épaisseur de la plaque, contient de la ferrite polygonale à un rapport surfacique inférieur ou égal à 40 % ; la dureté maximale dans la structure métallographique interne est de 248 Hv ou moins ; et la dureté moyenne est de 150 à 220 Hv.
PCT/JP2017/033706 2017-09-19 2017-09-19 Tube en acier et plaque d'acier Ceased WO2019058420A1 (fr)

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JP2018502833A JP6319539B1 (ja) 2017-09-19 2017-09-19 鋼管及び鋼板
CN201780094849.1A CN111094608B (zh) 2017-09-19 2017-09-19 钢管和钢板
KR1020207006880A KR102364255B1 (ko) 2017-09-19 2017-09-19 강관 및 강판
PCT/JP2017/033706 WO2019058420A1 (fr) 2017-09-19 2017-09-19 Tube en acier et plaque d'acier
EP17926174.8A EP3686305B1 (fr) 2017-09-19 2017-09-19 Tuyau en acier et plaque d'acier

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Cited By (3)

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TWI762881B (zh) * 2019-03-29 2022-05-01 日商Ｊｆｅ鋼鐵股份有限公司 電焊鋼管及其製造方法以及鋼管樁
WO2021144953A1 (fr) 2020-01-17 2021-07-22 日本製鉄株式会社 Tôle d'acier et tuyau en acier
JPWO2021144953A1 (fr) * 2020-01-17 2021-07-22
KR20220098786A (ko) 2020-01-17 2022-07-12 닛폰세이테츠 가부시키가이샤 강판 및 강관
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CN114846163B (zh) * 2020-01-17 2023-10-24 日本制铁株式会社 钢板和钢管
KR20220131992A (ko) * 2020-03-04 2022-09-29 닛폰세이테츠 가부시키가이샤 강관 및 강판
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KR102792300B1 (ko) 2020-03-04 2025-04-08 닛폰세이테츠 가부시키가이샤 강관 및 강판

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EP3686305B1 (fr) 2024-12-25
JPWO2019058420A1 (ja) 2019-11-07
JP6319539B1 (ja) 2018-05-09
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