EP3375900A1 - Tube en acier soudé par résistance électrique pour canalisation - Google Patents

Tube en acier soudé par résistance électrique pour canalisation Download PDF

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Publication number
EP3375900A1
EP3375900A1 EP17770030.9A EP17770030A EP3375900A1 EP 3375900 A1 EP3375900 A1 EP 3375900A1 EP 17770030 A EP17770030 A EP 17770030A EP 3375900 A1 EP3375900 A1 EP 3375900A1
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EP
European Patent Office
Prior art keywords
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electric resistance
resistance welded
steel pipe
pipe
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.)
Withdrawn
Application number
EP17770030.9A
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German (de)
English (en)
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EP3375900A4 (fr
Inventor
Kensuke Nagai
Masakazu Ozaki
Noboru Hasegawa
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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Publication of EP3375900A1 publication Critical patent/EP3375900A1/fr
Publication of EP3375900A4 publication Critical patent/EP3375900A4/fr
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C22C38/02—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
    • C22C38/06—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
    • C22C38/12—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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present disclosure relates to an electric resistance welded steel pipe for a line pipe.
  • Electric resistance welded steel pipes used as line pipes may be required to have lower yield ratios in the pipe axis directions of the electric resistance welded steel pipes.
  • Patent Document 1 discloses a technology in which the yield ratio of an obtained electric resistance welded steel pipe in a pipe axis direction is decreased by repeatedly applying a strain to an uncoiled steel sheet which is a raw material, for example, by bending-unbending processing, before pipe-making forming, thereby inducing a Bauschinger effect.
  • Patent Document 2 proposes a technology in which the yield ratio of an electric resistance welded steel pipe in a pipe axis direction is decreased by allowing the metallographic microstructure of a hot-rolled steel sheet for producing an electric resistance welded steel pipe to be a microstructure consisting of martensite having an areal ratio of from 1 to 20% and ferrite.
  • Patent Document 3 proposes a method of producing an electric resistance welded steel pipe using a slab in which the amount of Nb is from 0.003% to less than 0.02%, as a method of producing an electric resistance welded steel pipe in which a rise in yield ratio due to heating is suppressed, and a deformation property is improved, and which has excellent strain aging resistance.
  • a work strain introduced in pipe-making causes the precipitation of Nb carbide to proceed, thereby increasing a yield strength and a tensile strength. Such precipitation strengthening was found to particularly cause a yield strength to be greatly increased, thereby resulting in an increase in yield ratio.” is described.
  • An object of the present disclosure is to provide an electric resistance welded steel pipe for a line pipe, which has a certain amount of tensile strength and yield strength, which has a decreased yield ratio, and a base metal portion and an electric resistance welded portion thereof having excellent toughness.
  • Means for solving the problem described above includes the following aspects.
  • an electric resistance welded steel pipe for a line pipe which has a certain amount of tensile strength and yield strength, which has a decreased yield ratio, and a base metal portion and an electric resistance welded portion thereof having excellent toughness can be provided.
  • Fig. 1 is a scanning electron micrograph showing an example of the metallographic microstructure of a base metal portion in the present disclosure.
  • a numerical range expressed by "x to y" herein includes the values of x and y in the range as the minimum and maximum values, respectively.
  • the content of a component (element) expressed by “%” herein means “% by mass”.
  • C carbon
  • C content The content of another element may be expressed similarly.
  • step herein encompasses not only an independent step but also a step of which the desired object is achieved even in a case in which the step is incapable of being definitely distinguished from another step.
  • An electric resistance welded steel pipe for a line pipe of the present disclosure (hereinafter also simply referred to as “electric resistance welded steel pipe”) includes a base metal portion and an electric resistance welded portion, wherein the chemical composition of the base metal portion consists of, in terms of % by mass: 0.080 to 0.120% of C, 0.30 to 1.00% of Mn, 0.005 to 0.050% of Ti, 0.010 to 0.100% of Nb, 0.001 to 0.020% of N, 0.010 to 0.450% of Si, 0.001 to 0.100% of Al, 0 to 0.030% of P, 0 to 0.0100% of S, 0 to 0.50% of Mo, 0 to 1.00% of Cu, 0 to 1.00% of Ni, 0 to 1.00% of Cr, 0 to 0.100% of V, 0 to 0.0100% of Ca, 0 to 0.0100% of Mg, 0 to 0.0100% of REM, and the balance being Fe and impurities, wherein: CMeq
  • the electric resistance welded steel pipe of the present disclosure includes the base metal portion and the electric resistance welded portion.
  • an electric resistance welded steel pipe is produced by forming a hot-rolled steel sheet into a pipe shape (hereinafter also referred to as "roll forming") to thereby make an open pipe, subjecting abutting portions of the obtained open pipe to electric resistance welding to form an electric resistance welded portion, and then, if necessary, subjecting the electric resistance welded portion to seam heat treatment.
  • the base metal portion refers to a portion other than the electric resistance welded portion and a heat affected zone.
  • the heat affected zone (hereinafter also referred to as "HAZ”) refers to a portion affected by heat caused by electric resistance welding (affected by heat caused by the electric resistance welding and seam heat treatment in a case in which the seam heat treatment is performed after the electric resistance welding).
  • the electric resistance welded portion may be simply referred to as "welded portion”.
  • the electric resistance welded steel pipe of the present disclosure has a certain amount of YS and TS (i.e., YS and TS in the ranges described above), has YR decreased to 90% or less, and has the excellent toughness of the base metal portion and the electric resistance welded portion.
  • the excellent toughness means that a Charpy absorbed energy (J) in the circumferential direction of the pipe at 0°C (hereinafter also referred to as "vE") is high.
  • the electric resistance welded steel pipe of the present disclosure has a vE of 100 J or more in the base metal portion and a vE of 80 J or more in the electric resistance welded portion.
  • the electric resistance welded steel pipe of the present disclosure has low YR, and is therefore expected to exhibit the effect of being capable of suppressing the buckling of the electric resistance welded steel pipe.
  • Examples of a case in which the suppression of the buckling of a steel pipe is demanded include a case in which a steel pipe for a subsea pipeline is laid by reel-lay.
  • the steel pipe is produced on land in advance, and the produced steel pipe is spooled on the spool of a barge.
  • the spooled steel pipe is laid on a sea bottom while being unspooled at sea.
  • plastic bending is applied to the steel pipe at the time of the spooling or unspooling of the steel pipe, and therefore, the steel pipe may be buckled.
  • the occurrence of the buckling of the steel pipe unavoidably results in the stopping of a laying operation, and the damage caused by the stopping is enormous.
  • the buckling of the steel pipe can be suppressed by reducing the YR of the steel pipe.
  • the electric resistance welded steel pipe of the present disclosure is expected to exhibit the effect of being capable of suppressing buckling at the time of reel-lay, for example, in the case of being used as an electric resistance welded steel pipe for a subsea pipeline.
  • the electric resistance welded steel pipe of the present disclosure has the excellent toughness of the base metal portion and the electric resistance welded portion, and is therefore expected to exhibit the effect of having the excellent property of arresting crack propagation at the time of burst in the case of being used as an electric resistance welded steel pipe for a line pipe.
  • YS, TS, YR, the vE of the base metal portion, and the vE of the electric resistance welded portion as described above are achieved by a combination of the chemical composition (including CMeq, a Mn/Si ratio, and LR) and the metallographic microstructure in the electric resistance welded steel pipe.
  • each component in the chemical composition will be first described below, and CMeq, a Mn/Si ratio, and LR will be subsequently described.
  • C is an element necessary for forming a second phase.
  • a C amount of 0.080% or more facilitates achievement of a ferrite fraction of 98% or less and achievement of an LR of 0.210 or more. As a result, achievement of a YR of 90% or less is facilitated. Accordingly, the amount of C is 0.080% or more. The amount of C is preferably 0.085% or more.
  • a C amount of 0.120% or less facilitates achievement of a ferrite fraction of 60% or more. As a result, achievement of a YR of 90% or less is facilitated. Accordingly, the amount of C in the present disclosure is 0.120% or less.
  • the amount of C is preferably 0.115% or less, and more preferably 0.110% or less.
  • Mn is an element that enhances the hardenability of steel.
  • Mn is an essential element for detoxification of S.
  • a Mn amount of less than 0.30% may result in embrittlement due to S and in the deterioration of the toughness of the base metal and the electric resistance welded portion. Accordingly, the amount of Mn is 0.30% or more.
  • the amount of Mn is preferably 0.40% or more, and more preferably 0.50% or more.
  • a Mn amount of more than 1.00% may result in generation of coarse MnS in the central portion of the sheet thickness, thereby degrading the toughness of the base metal and the electric resistance welded portion.
  • a Mn amount of more than 1.00% may make it impossible to achieve an LR of 0.210 or more, thereby consequently making it impossible to achieve a YR of 90% or less.
  • the amount of Mn is 1.00% or less.
  • the amount of Mn is preferably 0.90% or less, and more preferably 0.85% or less.
  • Ti is an element forming a carbonitride and contributing to crystal grain refining.
  • the amount of Ti is 0.005% or more from the viewpoint of securing the toughness of the base metal and the electric resistance welded portion.
  • a Ti amount of more than 0.050% may result in generation of coarse TiN, thereby deteriorating the toughness of the base metal and the electric resistance welded portion. Accordingly, the amount of Ti is 0.050% or less.
  • the amount of Ti is preferably 0.040% or less, still more preferably 0.030 or less, and particularly preferably 0.025%.
  • Nb is an element contributing to improvement in toughness and a reduction in YR.
  • the amount of Nb is 0.010% or more for improvement in toughness due to rolling in the region of unrecrystallization temperature.
  • the amount of Nb is preferably 0.020% or more.
  • the amount of Nb is 0.100% or less.
  • the amount of Nb is preferably 0.090% or less.
  • N is an element that forms a nitride, thereby suppressing the coarsening of crystal grains and consequently improving the toughness of the base metal portion and the electric resistance welded portion. From the viewpoint of such an effect, the amount of N is 0.001% or more. The amount of N is preferably 0.003% or more.
  • the amount of N is 0.020% or less.
  • the amount of N is preferably 0.015% or less, more preferably 0.010% or less, and particularly preferably 0.008% or less.
  • Si is an element that functions as a deoxidizer for steel. More specifically, a Si amount of 0.010% or more results in suppression of generation of a coarse oxide in the base metal portion and the electric resistance welded portion, thereby resulting in improvement in the toughness of the base metal portion and the electric resistance welded portion. Accordingly, the amount of Si is 0.010% or more. The amount of Si is preferably 0.015% or more, and more preferably 0.020% or more.
  • a Si amount of more than 0.450% may result in generation of an inclusion in the electric resistance welded portion, thereby decreasing a Charpy absorbed energy and deteriorating toughness. Accordingly, the amount of Si is 0.450% or less.
  • the amount of Si is preferably 0.400% or less, more preferably 0.350% or less, and particularly preferably 0.300% or less.
  • Al is an element that functions as a deoxidizer, similar to Si. More specifically, an Al amount of 0.001% or more results in suppression of generation of a coarse oxide in the base metal portion and the electric resistance welded portion, thereby resulting in improvement in the toughness of the base metal portion and the electric resistance welded portion. Accordingly, the amount of Al is 0.001% or more.
  • the amount of Al is preferably 0.010% or more, and more preferably 0.015% or more.
  • an Al amount of more than 0.100% may result in generation of an Al-based oxide during electric resistance welding, thereby deteriorating the toughness of a welded portion. Accordingly, the amount of Al is 0.100% or less.
  • the amount of Al is preferably 0.090% or less.
  • P is an impurity element.
  • a P amount of more than 0.030% may result in segregation in a grain boundary, thereby degrading toughness. Accordingly, the amount of P is 0.030% or less.
  • the amount of P is preferably 0.025% or less, more preferably 0.020% or less, still more preferably 0.015% or less, and more preferably 0.010% or less.
  • the amount of P may be 0%. From the viewpoint of reducing a dephosphorization cost, the amount of P may be more than 0%, and may be 0.001% or more.
  • S is an impurity element.
  • a S amount of more than 0.0100% may result in degradation in toughness. Accordingly, the amount of S is 0.0100% or less.
  • the amount of S is preferably 0.0070 or less, more preferably 0.0050% or less, and more preferably 0.0030% or less.
  • the amount of S may be 0%. From the viewpoint of reducing a desulfurization cost, the amount of S may be more than 0%, may be 0.0001% or more, and may be 0.0003% or more.
  • Mo is an optional element. Accordingly, the amount of Mo may be 0%.
  • Mo is an element improving the hardenability of a steel and contributing to the high strength of the steel. From the viewpoint of such an effect, the amount of Mo may be more than 0%, may be 0.01% or more, and may be 0.03% or more.
  • a Mo amount of more than 0.50% may result in generation of a Mo carbonitride, thereby deteriorating toughness. Accordingly, the amount of Mo is 0.50% or less.
  • the amount of Mo is preferably 0.40% or less, more preferably 0.30% or less, still more preferably 0.20% or less, and particularly preferably 0.10% or less.
  • Cu is an optional element. Accordingly, the amount of Cu may be 0%.
  • Cu is an element that is effective for improving the strength of a base metal. From the viewpoint of such an effect, the amount of Cu may be more than 0%, may be 0.01% or more, and may be 0.03% or more.
  • the amount of Cu is 1.00% or less.
  • the amount of Cu is preferably 0.80% or less, more preferably 0.70% or less, still more preferably 0.60% or less, and particularly preferably 0.50% or less.
  • Ni is an optional element. Accordingly, the amount of Ni may be 0%.
  • Ni is an element that contributes to improvement in strength and toughness. From the viewpoint of such an effect, the amount of Ni may be more than 0%, may be 0.01% or more, and may be 0.05% or more.
  • the amount of Ni is 1.00% or less.
  • the amount of Ni is preferably 0.80% or less, more preferably 0.70% or less, and still more preferably 0.60% or less.
  • the amount of Cr is an optional element. Accordingly, the amount of Cr may be 0%.
  • the amount of Cr is an element that improves hardenability. From the viewpoint of such an effect, the amount of Cr may be more than 0%, may be 0.01% or more, and may be 0.05% or more.
  • a Cr amount of more than 1.00% may result in the deterioration of the toughness of the welded portion due to Cr-based inclusions generated in the electric resistance welded portion. Accordingly, the amount of Cr is 1.00% or less.
  • the amount of Cr is preferably 0.80% or less, more preferably 0.70% or less, still more preferably 0.50% or less, and particularly preferably 0.30% or less.
  • V is an optional element. Accordingly, the amount of V may be 0%.
  • V is an element that contributes to improvement in toughness and a reduction in YR. From the viewpoint of such an effect, the amount of V may be more than 0%, may be 0.005% or more, and may be 0.010% or more.
  • a V amount of more than 0.100% may result in the deterioration of toughness due to a V carbonitride. Accordingly, the amount of V is 0.100% or less.
  • the amount of V is preferably 0.080% or less, more preferably 0.070% or less, still more preferably 0.050% or less, and particularly preferably 0.030% or less.
  • Ca is an optional element. Accordingly, the amount of Ca may be 0%.
  • Ca is an element controlling a shape of a sulfide-based inclusion and improving low-temperature toughness. From the viewpoint of such an effect, the amount of Ca may be more than 0%, may be 0.0001% or more, may be 0.0010% or more, may be 0.0030% or more, and may be 0.0050% or more.
  • a Ca amount of more than 0.0100% may result in generation of a large-sized cluster or large-sized inclusion including CaO-CaS, thereby adversely affecting toughness. Accordingly, the amount of Ca is 0.0100% or less.
  • the amount of Ca is preferably 0.0090% or less, more preferably 0.0080% or less, and particularly preferably 0.0060% or less.
  • Mg is an optional element. Accordingly, the amount of Mg may be 0%.
  • Mg is an element that is effective as a deoxidizer and a desulfurization agent and that particularly forms a fine oxide, thereby contributing to improvement in the toughness of an HAZ (heat affected zone).
  • the amount of Mg may be more than 0%, may be 0.0001% or more, may be 0.0010% or more, may be 0.0020% or more, may be 0.0030% or more, and may be 0.0050% or more.
  • a Mg amount of more than 0.0100% is prone to cause an oxide to be aggregated or coarsened, thereby resulting in the deterioration of HIC resistance (hydrogen-induced cracking resistance) or the deterioration of the toughness of the base metal or the HAZ. Accordingly, the amount of Mg is 0.0100% or less. The amount of Mg is preferably 0.0060% or less.
  • the amount of REM is an optional element. Accordingly, the amount of REM may be 0%.
  • REM refers to a rare earth element, i.e., at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
  • REM is an element effective as a deoxidizer or a desulfurization agent. From the viewpoint of such an effect, the amount of REM may be more than 0%, may be 0.0001% or more, and may be 0.0010% or more.
  • an REM amount of more than 0.0100% may result in generation of a coarse oxide, thereby resulting in the deterioration of HIC resistance or in the deterioration of the toughness of a base metal or HAZ. Accordingly, the amount of REM is 0.0100% or less.
  • the amount of REM is preferably 0.0070% or less, and more preferably 0.0050% or less.
  • the chemical composition of the base metal portion may contain one or more of: more than 0% but equal to or less than 0.50% of Mo, more than 0% but equal to or less than 1.00% of Cu, more than 0% but equal to or less than 1.00% of Ni, more than 0% but equal to or less than 1.00% of Cr, more than 0% but equal to or less than 0.100% of V, more than 0% but equal to or less than 0.0100% of Ca, more than 0% but equal to or less than 0.0100% of Mg, and more than 0% but equal to or less than 0.0100% of REM.
  • the balance excluding each element described above is Fe and impurities.
  • the impurities refer to components which are contained in a raw material or mixed into in a production step, and which are not intentionally incorporated into a steel.
  • impurities examples include any elements other than the elements described above. Elements as the impurities may be only one kind, or may be two or more kinds.
  • impurities examples include O, B, Sb, Sn, W, Co, As, Pb, Bi, and H.
  • O is preferably controlled to have a content of 0.006% or less.
  • Sb, Sn, W, Co, or As may be included in a content of 0.1% or less
  • Pb or Bi may be included in a content of 0.005% or less
  • B may be included in a content of 0.0003% or less
  • H may be included in a content of 0.0004% or less
  • the contents of the other elements need not particularly be controlled as long as being in a usual range.
  • CMeq expressed by the following Formula (1) is from 0.170 to 0.300.
  • CMeq C + Mn / 6 + Cr / 5 + Ni + Cu / 15 + Nb + Mo / 3 + V
  • CMeq has a positive correlation with a yield strength.
  • CMeq is 0.170 or more from the viewpoint of facilitating achievement of a yield strength of 390 MPa or more.
  • CMeq is preferably 0.180 or more, more preferably 0.200 or more, and still more preferably 0.230 or more.
  • CMeq is 0.300 or less from the viewpoint of facilitating achievement of a yield strength of 562 MPa or less.
  • CMeq is preferably 0.290 or less, and more preferably 0.275 or less.
  • LR expressed by the following Formula (2) is 0.210 or more.
  • an LR of 0.210 or more may result in achievement of a YR of 90% or less.
  • An LR of less than 0.210 may result in a YR of more than 90%.
  • the reason thereof can be considered to be because the amount of precipitate in a steel is decreased, and work hardenability is deteriorated (i.e., TS is decreased).
  • LR 2.1 ⁇ C + Nb / Mn
  • the reason why the amounts of C and Nb are arranged in the numerator in Formula (2) can be considered to be that C and Nb form precipitates, thereby improving the work hardenability of a steel (i.e., increasing TS) and consequently decreasing the YR of the steel.
  • the reason why the amount of Mn is arranged in the denominator in Formula (2) is because, although the inclusion of Mn enables a steel to be transformed at relatively low temperature, the inclusion of Mn causes the work hardenability in itself of the steel to be deteriorated (i.e., causes TS to be decreased), thereby increasing the YR of the steel.
  • LR has a positive correlation with the amounts of Nb and C, and has a negative correlation with the amount of Mn.
  • LR may be allowed to be 0.210 or more depending on the amounts of C and Mn by allowing LR to satisfy 0.210 or more. In this case, a YR of 90% or less can be achieved.
  • a YR of 90% or less can also be achieved by allowing LR to be 0.210 or more and allowing conditions other than LR to be satisfied, in a case in which the amount of Nb is less than 0.02%.
  • LR is preferably 0.230 or more, and more preferably 0.270 or more.
  • LR is not particularly restricted. From the viewpoint of the production suitability of the electric resistance welded steel pipe, LR is preferably 0.500 or less, more preferably 0.450 or less, and particularly preferably 0.400 or less.
  • a Mn/Si ratio (i.e., a Mn/Si ratio which is a ratio of % by mass of Mn to % by mass of Si) is 2.0 or more.
  • a Mn/Si ratio of 2.0 or more results in improvement in the toughness of the electric resistance welded portion, thereby allowing vE in the electric resistance welded portion (i.e., a Charpy absorbed energy in the circumferential direction of the pipe at 0°C) to be 80 J or more.
  • vE may be less than 80 J.
  • the reason thereof can be considered to be because in a case in which the Mn/Si ratio is less than 2.0, a MnSi-based inclusion initiates brittle fracture in the electric resistance welded portion, whereby toughness is deteriorated.
  • the Mn/Si ratio is preferably 2.1 or more from the viewpoint of further improving the toughness of the electric resistance welded portion.
  • the upper limit of the Mn/Si ratio is not particularly restricted. From the viewpoint of further improving the toughness of the electric resistance welded portion and the toughness of the base metal portion, the Mn/Si ratio is preferably 50 or less, more preferably 40 or less, and particularly preferably 30 or less.
  • the metallographic microstructure of the base metal portion has a ferrite fraction (i.e., an areal ratio of a first phase that is ferrite) of from 60 to 98% and includes a second phase, which is a balance, including at least either tempered bainite or pearlite in a case in which the metallographic microstructure is observed using a scanning electron microscope at a magnification of 1,000 times.
  • a ferrite fraction i.e., an areal ratio of a first phase that is ferrite
  • a second phase which is a balance, including at least either tempered bainite or pearlite in a case in which the metallographic microstructure is observed using a scanning electron microscope at a magnification of 1,000 times.
  • a YR of 90% or less can be achieved by allowing a ferrite fraction to be 60% or more.
  • the ferrite fraction is preferably 65% or more, and more preferably 70% or more.
  • a ferrite fraction of 98% or less as described above enables a TS of 520 MPa or more to be achieved.
  • the ferrite fraction is preferably 95% or less, and more preferably 92% or less.
  • the second phase which is the balance includes tempered bainite.
  • the inclusion of tempered bainite in the second phase means that the electric resistance welded steel pipe of the present disclosure is an electric resistance welded steel pipe tempered after pipe-making (i.e., after electric resistance welding (after seam heat treatment in the case of performing the seam heat treatment after the electric resistance welding)).
  • the electric resistance welded steel pipe of the present disclosure is an electric resistance welded steel pipe tempered after pipe-making, whereby a YR of 90% or less can be achieved.
  • the reason thereof can be considered to be because YR is decreased by the tempering after the pipe-making.
  • the reason why YR is decreased by the tempering after the pipe-making can be considered to be because YS is decreased by decreasing a dislocation density, and cementites are precipitated on a dislocation, thereby increasing work hardening (i.e., increasing TS).
  • tempered bainite is distinguished from bainite which is not tempered bainite, in view of including granular cementites in the structure of the tempered bainite.
  • bainite herein includes bainitic ferrite, granular bainite, upper bainite, and lower bainite.
  • the second phase may include tempered bainite, may be a phase consisting of tempered bainite, or may include a structure other than tempered bainite.
  • tempered bainite examples include pearlite.
  • pearlite herein also includes pseudo-pearlite.
  • the measurement of the ferrite fraction and the identification of the second phase in the metallographic microstructure of the base metal portion are performed by nital-etching a metallographic microstructure at the 1/4 position of a wall thickness in an L cross-section at a base metal 90° position, and observing micrographs of the nital-etched metallographic microstructure (hereinafter also referred to as "metallographic micrographs") with a scanning electron microscope (SEM) at a magnification of 1,000 times.
  • SEM scanning electron microscope
  • Metallographic micrographs corresponding to ten 1,000-times visual fields (corresponding to an actual cross-sectional area of 0.12 mm 2 ) are taken.
  • the measurement of the ferrite fraction and the identification of the second phase are performed by performing image processing of the metallographic micrographs that were taken. The image processing is performed using, for example, a small-sized general-purpose image analysis apparatus LUZEX AP manufactured by NIRECO CORPORATION.
  • base metal 90° position refers to a position deviating at 90° in the circumferential direction of the pipe from an electric resistance welded portion
  • L cross-section refers to a cross section parallel to a pipe axis direction and a wall thickness direction
  • 1/4 position of wall thickness refers to a position to which a distance from the outer surface of the electric resistance welded steel pipe is 1/4 of a wall thickness.
  • the pipe axis direction may be referred to as "L-direction”.
  • Fig. 1 is a scanning electron micrograph (SEM micrograph; a magnification of 1,000 times) showing an example of the metallographic microstructure of a base metal portion in the present disclosure.
  • the SEM micrograph in Fig. 1 is one (one visual field) of SEM micrographs used in the measurement of a ferrite fraction and the identification of a second phase in Example 17 described later.
  • a first phase that is ferrite and a second phase including tempered bainite can be confirmed.
  • the presence of white points (cementites) reveals that the second phase includes tempered bainite.
  • the metallographic microstructure of the base metal portion preferably has an areal ratio (hereinafter also referred to as “specific precipitate areal ratio”) of precipitates having an equivalent circle diameter of 100 nm or less (hereinafter also referred to as “specific precipitates”) of from 0.10 to 1.00% in a case in which the metallographic microstructure is observed using a transmission electron microscope at a magnification of 100,000 times.
  • specific precipitate areal ratio an areal ratio of precipitates having an equivalent circle diameter of 100 nm or less
  • the specific precipitate areal ratio of 0.10% or more further facilitates achievement of a YR of 90% or less.
  • the reason thereof can be considered to be because the specific precipitates (i.e., precipitates having an equivalent circle diameter of 100 nm or less) contribute to improvement in work hardening characteristic (i.e., an increase in TS), thereby resulting in a decrease in YR.
  • the specific precipitate areal ratio of 1.00% or less results in suppression of brittle fracture (i.e., excellent toughness of the base metal portion).
  • the specific precipitate areal ratio is preferably 0.80% or less, and more preferably 0.70% or less.
  • the specific precipitate areal ratio of from 0.10 to 1.00% can be achieved by performing tempering at a temperature of from 400°C to an Ac1 point after pipe-making.
  • the precipitate areal ratio (i.e., the areal ratio of precipitates having an equivalent circle diameter of 100 nm or less) is measured by observing a metallographic microstructure at a position of 1/4 of a wall thickness in an L cross-section at a base metal 90° position with a transmission electron microscope (TEM) at a magnification of 100,000 times.
  • TEM transmission electron microscope
  • a replica for TEM observation is produced by SPEED method using an electrolytic solution including 10% by volume of acetylacetone, 1% by volume of tetramethylammonium chloride, and 89% by volume of methyl alcohol. Then, by observing the obtained replica for TEM observation with TEM at a magnification of 100,000 times, TEM images with a field size of 1 ⁇ m square, corresponding to ten visual fields, are obtained.
  • the areal ratio of precipitates having an equivalent circle diameter of 100 nm or less with respect to the total area of the obtained TEM image is calculated, and the obtained result is regarded as the specific precipitate areal ratio (%).
  • the condition of etching in the SPEED method is set at a condition in which a charge of 10 coulombs is applied at a voltage of -200 mV with respect to a surface area of about 80 square millimeters with the use of a saturated calomel electrode as a reference electrode.
  • the specific precipitates can be specifically considered to be at least one selected from the group consisting of carbides of metals other than Fe, nitrides of metals other than Fe, and carbonitrides of metals other than Fe.
  • Conceivable examples of the metals other than Fe include Ti and Nb.
  • the chemical composition contains at least one of V, Mo, or Cr
  • conceivable examples of the metals other than Fe include at least one of V, Mo, or Cr.
  • the electric resistance welded steel pipe of the present disclosure has a yield strength in a pipe axis direction (YS) of from 390 to 562 MPa.
  • YS in the pipe axis direction is preferably 430 MPa or more, more preferably 450 MPa or more, more preferably 470 MPa or more, and particularly preferably 500 MPa or more.
  • YS in the pipe axis direction is preferably 550 MPa or less, more preferably 540 MPa or less, and particularly preferably 530 MPa or less.
  • a YS in the pipe axis direction of 562 MPa or less can be achieved by performing tempering after pipe-making.
  • the reason thereof can be considered to be because the tempering after pipe-making results in a decrease in pipe-making strain, and a dislocation density.
  • the electric resistance welded steel pipe of the present disclosure has a tensile strength in a pipe axis direction (TS) of from 520 to 690 MPa.
  • TS in the pipe axis direction is preferably 550 MPa or more, and more preferably 580 MPa or more.
  • TS in the pipe axis direction is preferably 680 MPa or less, more preferably 660 MPa or less, and particularly preferably 650 MPa or less.
  • a YR in the pipe axis direction of 90% or less can be achieved by performing tempering after pipe-making.
  • the reason thereof can be considered to be because YS is decreased by decreasing a dislocation density, and because work hardening is increased (i.e., TS is increased) by finely precipitating cementites on a dislocation.
  • the wall thickness of the electric resistance welded steel pipe of the present disclosure is preferably from 10 to 25 mm.
  • a wall thickness of 10 mm or more is advantageous in view of facilitating a decrease in YR by using a strain caused by forming a hot-rolled steel sheet into a pipe shape.
  • the wall thickness is more preferably 12 mm or more.
  • a wall thickness of 25 mm or less is advantageous in view of the production suitability of the electric resistance welded steel pipe (specifically, formability in formation of a hot-rolled steel sheet into a pipe shape).
  • the wall thickness is more preferably 20 mm or less.
  • the outer diameter of the electric resistance welded steel pipe of the present disclosure is preferably from 114.3 to 609.6 mm (i.e., from 4.5 to 24 inches).
  • An outer diameter of 114.3 mm or more is more preferred as the electric resistance welded steel pipe for a line pipe.
  • the outer diameter is preferably 139.7 mm (i.e., 5.5 inches) or more, and more preferably 177.8 mm (i.e., 7 inches) or more.
  • An outer diameter of 609.6 mm or less is advantageous in view of facilitating a decrease in YR by using a strain caused by forming a hot-rolled steel sheet into a pipe shape.
  • the outer diameter is preferably 406.4 mm (i.e., 16 inches) or less, and more preferably 304.8 mm (i.e., 12 inches) or less.
  • One example of a method of producing an electric resistance welded steel pipe of the present disclosure is the following production method A.
  • the production method A includes:
  • the inclusion of the tempering step facilitates the production of an electric resistance welded steel pipe having a YR of 90% or less by the reasons described above.
  • a tempering temperature (i.e., a retention temperature in the tempering) is preferably from 400°C to an Ac1 point.
  • a tempering temperature of 400°C or more further facilitates precipitation of cementite and a specific precipitate (precipitate having an equivalent circle diameter of 100 nm or less), and therefore further facilitates achievement of a YR of 90% or less.
  • the tempering temperature is more preferably 420°C or more.
  • tempering temperature of an Ac1 point or less enables a precipitate to be further inhibited from being coarse.
  • tempering temperature depends on the Ac1 point of a steel, it is also preferably 720°C or less, also preferably 710°C or less, and also preferably 700°C or less.
  • the Ac1 point means a temperature at which transformation to austenite is started in the case of increasing the temperature of a steel.
  • C, Si, Mn, Ni, Cu, Cr, Mo, V, Ti, Nb, and Al represent % by mass of the respective elements, respectively.
  • Ni, Cu, Cr, Mo, and V are optional elements.
  • an element that is not contained in a slab is set at 0% by mass, and the Ac1 point is calculated.
  • a tempering time (i.e., a retention time at the tempering temperature) in the tempering step is preferably 5 minutes or more in view of facilitating a more decrease in YR.
  • the as-rolled electric resistance welded steel pipe refers to an electric resistance welded steel pipe which is produced by roll-forming (i.e., forming into a pipe shape) a hot-rolled steel sheet, and which is not subjected to heat treatment other than seam heat treatment after the roll-forming.
  • the production method A preferably includes a sizer step of adjusting the shape of the as-rolled electric resistance welded steel pipe by a sizer under a condition in which the change in ovality before and after adjustment (hereinafter also referred to as "change in ovality (%) by sizer step”) is 1.0% or more, between the step of producing an as-rolled electric resistance welded steel pipe and the tempering step.
  • the electric resistance welded steel pipe having the specific precipitate areal ratio of from 0.10 to 1.00% described above can be more easily produced.
  • the reason thereof can be considered to be because a dislocation of which the amount is equal to or more than a certain amount is introduced into the as-rolled electric resistance welded steel pipe by the sizer step under the condition in which the change in ovality by sizer step is 1.0% or more, and the as-rolled electric resistance welded steel pipe is then tempered at a temperature of from 400°C to an Ac1 point, thereby facilitating precipitation of fine specific precipitates on the dislocation.
  • ovality of the as-rolled electric resistance welded steel pipe is determined as described below.
  • the change in ovality (%) by sizer step is determined by the following Formula on the basis of the ovality of the as-rolled electric resistance welded steel pipe before the adjustment of the shape by the sizer and the ovality of the as-rolled electric resistance welded steel pipe after the adjustment of the shape by the sizer.
  • Change in ovality % by sizer step (
  • the step of producing an as-rolled electric resistance welded steel pipe in the production method A preferably includes:
  • the electric resistance welded portion may be subjected to seam heat treatment after the electric resistance welding, if necessary.
  • the slab having the chemical composition described above is preferably heated to a temperature of from 1150°C to 1350°C.
  • the toughness of the base metal portion of the electric resistance welded steel pipe can be further improved.
  • the reason thereof can be considered to be because generation of an insoluble Nb carbide can be suppressed in a case in which the temperature to which the slab is heated is 1150°C or more.
  • the toughness of the base metal portion of the electric resistance welded steel pipe can be further improved.
  • the reason thereof can be considered to be because coarsening of a metallographic microstructure can be suppressed in a case in which the temperature to which the slab is heated is 1350°C or less.
  • the slab heated, for example, to a temperature of 1150°C to 1350°C is preferably hot-rolled at a temperature that is equal to or more than Ar3 point + 100°C.
  • the hardenability of the hot-rolled steel sheet can be improved.
  • C, Mn, Ni, Cu, Cr, and Mo represent % by mass of the respective elements, respectively.
  • Ni, Cu, Cr, and Mo are optional elements.
  • an element that is not contained in the slab is set at 0% by mass, and the Ar3 point is calculated.
  • the hot-rolled steel sheet obtained in the hot-rolling step is preferably cooled at a cooling start temperature set at the Ar3 point or more.
  • a cooling start temperature set at the Ar3 point or more.
  • the hot-rolled steel sheet obtained in the hot-rolling step is preferably cooled at a cooling rate of from 5°C/s to 80°C/s.
  • the cooling rate is 5°C/s or more
  • the degradation of the toughness of the base metal portion is further suppressed.
  • the reason thereof can be considered to be because generation of coarse ferrite is suppressed by setting the cooling rate in the cooling step at 5°C/s or more.
  • the cooling rate is 80°C/s or less
  • the degradation of the toughness of the base metal portion is suppressed.
  • the reason thereof can be considered to be because an excessive second phase fraction (i.e., a ferrite fraction of less than 60%) is suppressed by setting the cooling rate in the cooling step at 80°C/s or less.
  • the hot-rolled steel sheet cooled in the cooling step is preferably coiled at a coiling temperature of from 450 to 650°C.
  • a coiling temperature of 450°C or more results in suppression of the degradation of the toughness of the base metal portion.
  • the reason thereof can be considered to be because a coiling temperature of 450°C or more results in suppression of generation of martensite.
  • a coiling temperature of 650°C or less may result in suppression of an increase in YR.
  • the reason thereof can be considered to be because a coiling temperature of 650°C or less results in suppression of excessive generation of a Nb carbonitride, thereby resulting in suppression of an increase in YS.
  • Each of slabs having chemical compositions set forth in Table 1 and Table 2 was heated to a temperature of 1250°C, the heated slab was hot-rolled to obtain a hot-rolled steel sheet, the obtained hot-rolled steel sheet was cooled at a cooling start temperature set at 820°C and a cooling rate of 50°C/s, and the cooled hot-rolled steel sheet was coiled at a coiling temperature of 550°C, whereby a hot coil consisting of the hot-rolled steel sheet was obtained.
  • REM in Example 11 is Ce
  • REM in Example 16 is Nd
  • REM in Example 17 is La.
  • a hot-rolled steel sheet was uncoiled from the hot coil, the uncoiled hot-rolled steel sheet was roll-formed to thereby make an open pipe, abutting portions of the obtained open pipe was subjected to electric resistance welding to form an electric resistance welded portion (hereinafter also referred to as "welded portion"), and the welded portion was then subjected to seam heat treatment, thereby obtaining an as-rolled electric resistance welded steel pipe.
  • welded portion electric resistance welded portion
  • the shape of the as-rolled electric resistance welded steel pipe was adjusted by a sizer under conditions achieving each of changes in ovality (%) by sizer step set forth in Table 3.
  • the as-rolled electric resistance welded steel pipe of which the shape had been adjusted was tempered at each tempering temperature and for each tempering time set forth in in Table 3, thereby obtaining an electric resistance welded steel pipe.
  • the outer diameter of the obtained electric resistance welded steel pipe was 219 mm, and the wall thickness of this electric resistance welded steel pipe was 15.9 mm.
  • the above production step does not affect the chemical composition of a steel. Accordingly, the chemical composition of the base metal portion of the obtained electric resistance welded steel pipe can be considered to be the same as the chemical composition of the slab which is a raw material.
  • the ferrite fraction (F fraction" in Table 3) was measured, and the kind of a second phase was confirmed.
  • TB tempered bainite
  • P pearlite
  • MA martensite island
  • a specimen for a tensile test was sampled in a direction where the test direction (tensile direction) in a tensile test corresponds to the pipe axis direction (hereinafter also referred to as "L-direction") of the electric resistance welded steel pipe from the base metal 90° position of the electric resistance welded steel pipe.
  • the shape of the specimen was allowed to be a flat plate shape conforming to an American Petroleum Institute standard API 5L (hereinafter simply referred to as "API 5L").
  • a tensile test in which a test direction was the L-direction of the electric resistance welded steel pipe was conducted using the sampled specimen in conformity with API 5L at room temperature, and TS in the L-direction of the electric resistance welded steel pipe and YS in the L-direction of the electric resistance welded steel pipe were measured.
  • YR (%) in the L-direction of the electric resistance welded steel pipe was determined based on a calculation formula "(YS/TS) ⁇ 100".
  • a full-size specimen with a V-notch (a specimen for a Charpy impact test) was sampled from the base metal 90°C position of the electric resistance welded steel pipe.
  • the full-size specimen with a V-notch was sampled so that a test direction was the circumferential direction of the pipe (C-direction).
  • the sampled full-size specimen with a V-notch was subjected to a Charpy impact test in conformity with API 5L under a temperature condition of 0°C to measure vE (J).
  • the specific precipitate areal ratio (i.e., the areal ratio of precipitates having an equivalent circle diameter of 100 nm or less, simply referred to as "precipitate areal ratio (%)"in Table 3) was measured by the method described above.
  • [Table 1] Component (% by mass) C Mn Ti Nb N Si Al P S
  • Example 1 0.097 0.73 0.010 0.032 0.010 0.318 0.041 0.019 0.0019
  • Example 2 0.092 0.64 0.016 0.021 0.005 0.200 0.019 0.008 0.0044
  • Example 3 0.088 0.64 0.007 0.047 0.003 0.026 0.071 0.018 0.0050
  • Example 4 0.080 0.50 0.006 0.030 0.009 0.100 0.048 0.013 0.0026
  • Example 5 0.098 0.66 0.007 0.036 0.004 0.179 0.084 0.017 0.0020
  • Example 6 0.103 0.61 0.017 0.026 0.011 0.243 0.099
  • the electric resistance welded steel pipe of each Example satisfied TS, YS, YR, vE (base metal portion), and vE (welded portion) in the present disclosure.
  • the electric resistance welded steel pipe of each Example had a certain amount of tensile strength and yield strength, which had a decreased yield ratio, and had the excellent toughness of a base metal portion and a welded portion.
  • Comparative Example 2 in which the amount of Si was more than the upper limit resulted in the deterioration of the toughness of a welded portion.
  • Comparative Example 3 in which the amount of Si was less than the lower limit resulted in the deterioration of the toughness of a base metal portion and a welded portion. The reason thereof can be considered to be because deoxidization became insufficient, thereby generating a coarse oxide.
  • Comparative Example 4 in which the amount of Mn was less than the lower limit resulted in the deterioration of the toughness of a base metal portion and a welded portion. The reason thereof can be considered to be because embrittlement due to S occurred.
  • Comparative Example 5 in which the amount of Mn was more than the upper limit resulted in the deterioration of the toughness of a base metal portion and a welded portion. The reason thereof can be considered to be because cracking due to MnS was facilitated.
  • Comparative Example 7 in which Ti was more than the upper limit resulted in the deterioration of the toughness of a base metal portion and a welded portion. The reason thereof can be considered to be because coarse TiN was generated.
  • Comparative Example 9 in which Nb was more than the upper limit resulted in the deterioration of the toughness of a base metal portion and a welded portion. The reason thereof can be considered to be because a coarse Nb carbonitride was generated.
  • Comparative Example 14 in which LR was less than 0.210 resulted in a yield ratio of more than 90%.
  • YS and YR were more than the upper limits. The reason thereof can be considered to be because a tempering temperature was too low, thereby resulting in the insufficient effect of reducing a pipe-making strain by tempering (i.e., the effect of reducing a dislocation density by tempering) and in insufficient precipitation on a dislocation.
  • YR was more than 90%. The reason thereof can be considered to be because a change in ovality by sizer step was small, and therefore, the introduction of a dislocation and the precipitation on the dislocation were insufficient.
  • Comparative Example 19 in which the amount of N was less than the lower limit resulted in the deterioration of the toughness of a base metal portion and a welded portion. The reason thereof can be considered to be because crystal grains became coarse.
  • Comparative Example 20 in which the amount of N was more than the upper limit resulted in the deterioration of the toughness of a base metal portion and a welded portion. The reason thereof can be considered to be because a carbide became coarse.
  • YR was more than 90%. The reason thereof can be considered to be because a change in ovality by sizer step was small, and therefore, the introduction of a dislocation and the precipitation on the dislocation were insufficient.

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WO2011052095A1 (fr) * 2009-10-28 2011-05-05 新日本製鐵株式会社 Tôle d'acier pour des tubes de canalisation présentant une excellente résistance et une excellente ductilité et procédé de fabrication de cette dernière
WO2012133558A1 (fr) 2011-03-30 2012-10-04 新日本製鐵株式会社 Tuyau d'acier électrosoudé longitudinalement et son procédé de production
CA2832021C (fr) * 2011-08-23 2014-11-18 Nippon Steel & Sumitomo Metal Corporation Tube d'acier soude par resistance electrique a paroi epaisse et procede de fabrication de ce dernier
CN103014554B (zh) * 2011-09-26 2014-12-03 宝山钢铁股份有限公司 一种低屈强比高韧性钢板及其制造方法
JP2014189808A (ja) * 2013-03-26 2014-10-06 Kobe Steel Ltd 耐水素誘起割れ性と曲げ性に優れた低降伏比型高強度鋼板
JP5708723B2 (ja) * 2013-07-09 2015-04-30 Ｊｆｅスチール株式会社 低温破壊靭性に優れたラインパイプ用厚肉電縫鋼管およびその製造方法
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JP2016056858A (ja) 2014-09-08 2016-04-21 株式会社テイエルブイ スチームトラップ

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Publication number Priority date Publication date Assignee Title
TWI738246B (zh) * 2019-03-29 2021-09-01 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
EP3960891A4 (fr) * 2019-08-23 2022-07-27 Nippon Steel Corporation Tuyau en acier soudé par résistance électrique destiné à des tuyaux de canalisation
WO2021133343A1 (fr) * 2019-12-24 2021-07-01 Ti̇rsan Kardan Sanayi̇ Ve Ti̇caret Anoni̇m Şi̇rketi̇ Composition d'acier faiblement allié à haute résistance
EP4066954A4 (fr) * 2020-02-10 2023-07-05 Nippon Steel Corporation Tube en acier soudé par résistance électrique à usage de tube de canalisation
WO2023014330A1 (fr) * 2021-08-04 2023-02-09 Ti̇rsan Kardan Sanayi̇ Ve Ti̇caret Anoni̇m Şi̇rketi̇ Nouvel acier micro-allié

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KR20180077259A (ko) 2018-07-06
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EP3375900A4 (fr) 2019-07-17
WO2017163987A1 (fr) 2017-09-28

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