WO2016190150A1 - Tôle d'acier épaisse et joint soudé - Google Patents

Tôle d'acier épaisse et joint soudé Download PDF

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Publication number
WO2016190150A1
WO2016190150A1 PCT/JP2016/064444 JP2016064444W WO2016190150A1 WO 2016190150 A1 WO2016190150 A1 WO 2016190150A1 JP 2016064444 W JP2016064444 W JP 2016064444W WO 2016190150 A1 WO2016190150 A1 WO 2016190150A1
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amount
steel plate
thick steel
rem
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PCT/JP2016/064444
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English (en)
Japanese (ja)
Inventor
誠 河盛
文雄 湯瀬
秀徳 名古
喜臣 岡崎
朗 伊庭野
潤一郎 衣笠
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株式会社神戸製鋼所
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Priority claimed from JP2016064064A external-priority patent/JP2016216819A/ja
Application filed by 株式会社神戸製鋼所 filed Critical 株式会社神戸製鋼所
Priority to EP16799856.6A priority Critical patent/EP3299486A4/fr
Priority to CN201680028437.3A priority patent/CN107614724A/zh
Priority to KR1020177033268A priority patent/KR20170138505A/ko
Publication of WO2016190150A1 publication Critical patent/WO2016190150A1/fr

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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
    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—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

Definitions

  • the present invention relates to a thick steel plate and a welded joint, and more particularly to a thick steel plate suitable as a material steel plate for energy structural materials such as for line pipes and marine structures, and a welded joint using the thick steel plate. is there.
  • This steel material for energy does not perform its function, and once an accident occurs, the damage is enormous, so high safety is required.
  • One of the energy steels is steel for line pipes, which is used for the transportation of oil and natural gas.
  • This steel has not only characteristics such as strength and toughness as a structural material, but also the inside of the pipe. Resistance to passing oil and natural gas is required.
  • oil and gas wells of oil and natural gas have deteriorated in quality of oil and gas produced, and a lot of H 2 S has been mixed.
  • hydrogen-induced cracking resistance There has been a strong demand for sour resistance typified by HIC resistance.
  • line pipe steel is required to be thinned from the viewpoint of cost reduction during transportation and construction.
  • it is necessary to improve the strength of the steel material, but the improvement of the steel material strength has the disadvantage of deteriorating the hydrogen-induced cracking resistance.
  • T-cross welds that receive two thermal histories, seam welding when processing thick steel plates into pipes, that is, seam welding, and circumferential welding when joining pipes, have a complex thermal history of rapid heating and rapid cooling. Therefore, in the weld heat affected zone: HAZ, the strength, that is, the hardness increases, and cracks called sulfide stress corrosion cracking are likely to occur.
  • the sulfide stress corrosion cracking is also referred to as SSCC: sulfide stress corrosion cracking. Therefore, in order to realize high-strength line pipe steel, the SSCC resistance of the T-cross welded part is also one of the problems.
  • Patent Document 1 discloses an API that reduces the block-like bainite structure, which is considered to have poor HIC resistance, and develops a uniform upper bainite or acicular ferrite structure, while ensuring the HIC resistance of the base material.
  • a technology for realizing a standard X70 grade high strength thick steel sheet is described.
  • Patent Document 2 describes a technology that can achieve high strength of 56 kgf / mm 2 or more in tensile strength by utilizing precipitation strengthening by fine Nb and V carbonitrides.
  • this document does not describe the HIC resistance of the base material, and only the seam-welded HAZ is considered for the SSCC resistance.
  • the test conditions described in the examples are not sufficiently severe so that the immersion time in a solution simulating a sour environment, that is, an environment containing a large amount of H 2 S, is 21 days.
  • Patent Document 3 describes a component system that suppresses an increase in hardness, which is supposed to deteriorate the SSCC resistance of a T-cross weld.
  • the technology described in this document does not evaluate SSCC resistance itself, and does not describe the HIC resistance of the base material.
  • the present invention has been made as a solution to the above-mentioned conventional problems, and an object thereof is to provide a thick steel plate excellent in sour resistance, particularly HIC resistance. Another object of the present invention is to provide a thick steel plate capable of realizing a welded joint excellent in SSCC resistance of a T-cross welded part and a welded joint excellent in SSCC resistance of a T-cross welded part.
  • the thick steel plate of the present invention is in mass%, C: 0.01 to 0.12%, Si: 0.02 to 0.50%, Mn: 0.6 to 2.0%, P: more than 0% 0 0.03% or less, S: more than 0% to 0.004% or less, Al: 0.010 to 0.080%, Cr: 0.10 to 1.50%, Nb: 0.002 to 0.050%, REM : 0.0002-0.05%, Zr: 0.0003-0.01%, Ca: 0.0003-0.006%, N: more than 0% and not more than 0.010%, O: more than 0%.
  • the REM content is 5 to 50%
  • the Al content is 3 to 30%
  • the Ca content is 5 to 60%.
  • the amount of S in the inclusions is preferably more than 0% and 20% or less.
  • the thick steel plate of the present invention preferably has [Cr] / [Nb] of 10 or more.
  • [] indicates mass%.
  • the thick steel plate of the present invention is further in terms of mass%, Mg: more than 0% and 0.005% or less, Ti: 0.003 to 0.030%, Ni: 0.01 to 1.50%, Cu: One or more of 0.01 to 1.50%, Mo: 0.01 to 1.50%, V: 0.003 to 0.08%, and B: 0.0002 to 0.0032% It is preferable that [Cr] + [Mo] + [Ni] + [Cu] is 2.1 or less. However, in the above formula, [] indicates mass%.
  • the thick steel plate of the present invention contains, by mass%, Ni: 0.01 to 1.50%, and 0.25 ⁇ [Cr] + [Ni] is 0.10 to 1.50. preferable. However, in the above formula, [] indicates mass%.
  • the welded joint of the present invention is characterized by including any of the above-described thick steel plates and peripheral weld metals.
  • the immersion potential difference ⁇ E between the thick steel plate and the circumferential weld metal which is obtained by the following formula, is preferably 25 mV or less.
  • ⁇ E Immersion potential after 1 hour of circumferential weld metal (mV)
  • mV thickness of the thick steel plate
  • a thick steel plate having excellent sour resistance can be provided.
  • the welded joint excellent in the SSCC resistance of a T cross weld part can be provided using the thick steel plate of this invention.
  • the present inventors have earnestly studied from the viewpoint of inclusion control in steel, in addition to the composition of steel, which is fundamental for exhibiting the characteristics of thick steel plates. , Repeated examination. As a result, it was found that a thick steel plate excellent in sour resistance can be obtained by maintaining coarse inclusions having a width of 1 ⁇ m or more in a specific component composition, and the present invention has been completed.
  • the inclusions in the present invention mean coarse precipitate grains generated in molten steel or at the time of solidification, and specifically, particles due to oxides, carbides, sulfides, nitrides, etc. of alloy components in steel. means.
  • the intergranular bainite transformation is promoted by dispersing a large number of inclusions that are the starting points of transformation, and the [Cr] / [Nb] is made 10 or more, so that the grain boundary It has been confirmed that Nb segregation to the grain boundaries that increase the nucleation driving force in the steel is reduced, bainite production from the grain boundaries is promoted, and as a result, the amount of martensite produced in the vicinity of the weld metal can be reduced.
  • [] indicates mass%.
  • the strength of the base metal can be improved by adding Cr and Nb to ensure hardenability.
  • % which is a unit for displaying the composition means “% by mass”.
  • C Component composition of thick steel plate
  • C is an indispensable element for ensuring the strength of the thick steel plate and needs to be contained in an amount of 0.01% or more.
  • it is 0.02% or more, More preferably, it is 0.03% or more.
  • the C amount needs to be 0.12% or less.
  • it is 0.10% or less, More preferably, it is 0.08% or less.
  • Si 0.02 to 0.50%
  • Si is effective for deoxidation.
  • the Si content is set to 0.02% or more.
  • it is 0.04% or more, More preferably, it is 0.06% or more.
  • the amount of Si needs to be suppressed to 0.50% or less.
  • it is 0.45% or less, More preferably, it is 0.35% or less.
  • Mn is an element indispensable for securing the strength of the thick steel plate, and it is necessary to contain 0.6% or more. Preferably it is 0.8% or more, More preferably, it is 1.0% or more. However, if the amount of Mn is excessive, MnS is generated and the HIC resistance deteriorates, so the upper limit of the amount of Mn is set to 2.0%. Preferably it is 1.9% or less, more preferably 1.8% or less.
  • P is an element inevitably contained in the steel material, and if its content exceeds 0.030%, it adversely affects HIC resistance and SSCC resistance. Therefore, in the present invention, the amount of P is suppressed to 0.030% or less. Preferably it is 0.020% or less, More preferably, it is 0.010% or less.
  • the upper limit of the amount of S is made 0.004%.
  • it is 0.003% or less, More preferably, it is 0.0025% or less, More preferably, it is 0.0020% or less.
  • Al 0.010 to 0.080%
  • Al is effective in reducing voids with the steel matrix by reducing the thermal expansion coefficient of inclusions and improving the HIC resistance.
  • the inclusion containing an appropriate amount of Al promotes the formation of intragranular bainite, good SSCC resistance can be obtained.
  • it is necessary to contain at least 0.010% or more.
  • the amount of Al is preferably 0.020% or more, and more preferably 0.025% or more.
  • the Al amount needs to be 0.080% or less.
  • the amount of Al is preferably 0.060% or less, more preferably 0.050% or less.
  • Cr 0.10 to 1.50%
  • Cr is an element indispensable for ensuring the strength, and contributes to the improvement of SSCC resistance by suppressing soft ferrite in the T-cross weld. In order to exhibit these effects, it is necessary to contain at least 0.10% or more.
  • the amount of Cr is preferably 0.15% or more, more preferably 0.17% or more, and further preferably 0.20% or more. However, if the amount of Cr is excessive, the hard martensite of the T-cross welded portion is increased and the SSCC resistance is lowered, so the content is made 1.50% or less.
  • the amount of Cr is preferably 1.00% or less, and more preferably 0.80% or less.
  • Nb is an element indispensable for ensuring strength, and also contributes to improvement of SSCC resistance by suppressing soft ferrite in the T-cross weld. In order to exhibit these effects, it is necessary to contain at least 0.002% or more.
  • the Nb amount is preferably 0.005% or more, and more preferably 0.010% or more. However, if the amount of Nb is excessive, the hard martensite of the T-cross welded portion is increased and the SSCC resistance is lowered, so the content is made 0.050% or less.
  • the amount of Nb is preferably 0.033% or less, and more preferably 0.030% or less.
  • REM 0.0002 to 0.05%
  • REM rare earth element
  • the amount of REM is preferably 0.0005% or more, more preferably 0.0010% or more.
  • the upper limit of the REM amount is set to 0.05%.
  • the content is preferably 0.03% or less, more preferably 0.01% or less, and still more preferably 0.005% or less.
  • REM means 15 elements from La to Lu in the periodic table, that is, lanthanoid elements, and Sc and Y.
  • Zr 0.0003 to 0.01%
  • Zr reduces voids with the steel matrix by reducing the thermal expansion coefficient of inclusions, and improves HIC resistance. Moreover, since the inclusion containing an appropriate amount of Zr promotes the formation of intragranular bainite, good SSCC resistance can be obtained. In order to exert these effects, it is necessary to contain 0.0003% or more of Zr.
  • the amount of Zr is preferably 0.0005% or more, more preferably 0.0010% or more.
  • the upper limit of the Zr amount is set to 0.01%.
  • the amount of Zr is preferably 0.007% or less, more preferably 0.005% or less.
  • Ca 0.0003 to 0.006%
  • Ca improves the SSCC resistance by forming CaS, fixing S, and reducing the amount of MnS produced. Moreover, since the inclusion containing an appropriate amount of Ca promotes the formation of intragranular bainite, good SSCC resistance can be obtained. In order to exert these effects, it is necessary to contain 0.0003% or more of Ca.
  • the Ca content is preferably 0.0005% or more, more preferably 0.0010% or more.
  • the upper limit of the Ca content is set to 0.006%.
  • the amount of Ca is preferably 0.005% or less, and more preferably 0.004% or less.
  • N is an unavoidable impurity, but segregates at the grain boundary to lower the grain boundary strength and degrade the SSCC resistance. Therefore, the upper limit of the N amount is 0.010%.
  • the N amount is preferably 0.008% or less, and more preferably 0.006% or less.
  • O oxygen
  • oxygen is an element that forms inclusions, and excessive addition generates a large amount of coarse oxide, which causes hydrogen-induced cracking. Therefore, the upper limit of the O amount is set to 0.0040%.
  • the amount of O is preferably 0.0030% or less, and more preferably 0.0020% or less.
  • the thick steel plate of the present invention preferably satisfies the above component composition and has [Cr] / [Nb] of 10 or more.
  • [] indicates mass%.
  • Nb segregation to the grain boundary that increases the nucleation driving force at the grain boundary is reduced in the T-cross welded portion, and bainite production from the grain boundary is promoted.
  • [Cr] / [Nb] is preferably 10 or more. More preferably, it is 12 or more, More preferably, it is 15 or more.
  • the component composition of the steel material of the steel plate of the present invention is as described above, and the balance is iron and inevitable impurities. Further, in addition to the above elements, by adding at least one or more selected from the group consisting of Mg, Ti, Ni, Cu, Mo, V and B in the following amounts, HIC resistance and resistance The SSCC property can be improved. Hereinafter, these elements will be described.
  • Mg has the effect of improving the SSCC resistance of the base material by forming MgS and finely dispersing sulfides.
  • the upper limit of Mg content is preferably 0.005%. More preferably, it is 0.004% or less, More preferably, it is 0.003% or less.
  • Ti is an element that contributes to improving the strength of the thick steel plate by precipitation strengthening. In order to exhibit this effect, it is preferable to contain 0.003% or more. More preferably it is 0.004% or more, and still more preferably 0.005% or more. On the other hand, if the Ti content is excessive, the hard martensite in the T-cross welded portion is increased and the SSCC resistance is lowered. Therefore, the content is preferably 0.030% or less. More preferably, it is 0.025% or less, More preferably, it is 0.020% or less.
  • Ni is an element that contributes to improving the strength of the thick steel plate. In order to exhibit this effect, it is preferable to contain 0.01% or more. More preferably, it is 0.05% or more, More preferably, it is 0.10% or more. On the other hand, when the Ni content is excessive, the hard martensite in the T-cross welded portion is increased and the SSCC resistance is lowered. Therefore, the Ni content is preferably 1.50% or less. More preferably, it is 1.00% or less, More preferably, it is 0.50% or less.
  • Cu is an element that contributes to improving the strength of the thick steel plate. In order to exhibit this effect, it is preferable to contain 0.01% or more. More preferably, it is 0.05% or more, More preferably, it is 0.10% or more. On the other hand, if the Cu content is excessive, it causes an increase in hard martensite in the T-cross welded portion and lowers the SSCC resistance, so it is preferably made 1.50% or less. More preferably, it is 1.00% or less, More preferably, it is 0.50% or less.
  • Mo is an element that contributes to improving the strength of the thick steel plate. In order to exhibit this effect, it is preferable to contain 0.01% or more. More preferably, it is 0.05% or more, More preferably, it is 0.10% or more. On the other hand, if the Mo content is excessive, hard martensite in the T-cross welded portion is increased and SSCC resistance is lowered. Therefore, the Mo content is preferably 1.50% or less. More preferably, it is 1.00% or less, More preferably, it is 0.50% or less.
  • V is an element that contributes to improving the strength of the thick steel plate. In order to exhibit this effect, it is preferable to contain 0.003% or more. More preferably it is 0.005% or more, and still more preferably 0.010% or more. On the other hand, if the V content is excessive, the hard martensite in the T-cross welded portion is increased and the SSCC resistance is lowered. Therefore, the V content is preferably 0.08% or less. More preferably, it is 0.07% or less, More preferably, it is 0.05% or less.
  • B is an element that contributes to improving the strength of the thick steel plate. In order to exhibit this effect, it is preferable to contain 0.0002% or more. More preferably, it is 0.0005% or more, More preferably, it is 0.0010% or more. On the other hand, if the B content is excessive, the hard martensite in the T-cross welded portion is increased and the SSCC resistance is lowered, so 0.0032% or less is preferable. More preferably, it is 0.0030% or less, More preferably, it is 0.0025% or less.
  • [[Cr] + [Mo] + [Ni] + [Cu] is 2.1 or less]
  • [Cr] + [Mo] + [Ni] + [Cu] is preferably 2.1 or less after satisfying the above component composition.
  • [] indicates mass%.
  • [Cr] + [Mo] + [Ni] + [Cu] is 2.1 or less. More preferably, it is 1.9 or less, More preferably, it is 1.7 or less.
  • the immersion potential difference ⁇ E after 1 hour when immersed in the solution of the thick steel plate and the peripheral weld metal, obtained by the following formula is 25 mV or less. More preferably, it is 20 mV or less, More preferably, it is 15 mV or less.
  • ⁇ E Immersion potential after 1 hour of circumferential weld metal (mV)
  • mV circumferential weld metal
  • mV thick steel plate
  • the electrode potential that appears when a metal is immersed in a solution may be defined as a corrosion potential or a hybrid potential. In the present invention, this is referred to as an “immersion potential”.
  • the thick steel plate of the present invention satisfies the above-described component composition, particularly the condition that the Ni content is 0.10 to 1.50%, and 0.25 ⁇ [Cr] + [Ni] is 0.10. It is preferably ⁇ 1.50.
  • [] indicates mass%. The addition of these elements contributes to the improvement of the SSCC resistance of the T-cross welded portion by improving the potential of the steel plate as a base material and suppressing hydrogen intrusion at the T-cross welded portion due to the dissimilar metal contact effect.
  • the value obtained from 0.25 ⁇ [Cr] + [Ni] is preferably 0.10 or more, more preferably 0.15 or more, and further preferably 0.20 or more.
  • the value obtained from 0.25 ⁇ [Cr] + [Ni] is excessive, the potential of the steel plate is significantly increased from the potential of the weld metal, and the selective corrosion of the weld metal by galvanic corrosion proceeds. SSCC resistance decreases. Therefore, the upper limit of the value obtained from 0.25 ⁇ [Cr] + [Ni] is set to 1.50. The upper limit is more preferably 1.00 or less, and still more preferably 0.70 or less.
  • the metal used for circumferential welding preferably has the following component composition in order to ensure the strength and toughness of the weld metal and improve corrosion resistance. That is, by mass, C: 0.02 to 0.10%, Si: 0.10 to 0.60%, Mn: 0.90 to 2.50%, Ni: 0.20 to 1.00% It is preferable to contain. In addition to the above components, P: 0.015% or less, S: 0.010% or less, Cu: 1.0% or less, Mo: 1.0% or less, Nb: 0.5% or less, V: It is allowable to contain 0.3% or less, Ti: 0.05% or less, and Al: 0.1% or less. Components other than these are desirably iron and inevitable impurities. Hereinafter, the reason for limiting the component composition of the weld metal will be described.
  • C is an element necessary for ensuring the strength of the weld metal.
  • the C content is less than 0.02%, a predetermined strength cannot be obtained.
  • the C content is excessive, coarsening of the grain boundary carbides causes a reduction in toughness, so the content is made 0.10% or less.
  • Si 0.10 to 0.60%
  • Si is an element necessary for ensuring the strength of the weld metal.
  • the Si content is less than 0.10%, a predetermined strength cannot be obtained.
  • the Si content is excessive, it causes a decrease in toughness, so the content is made 0.60% or less.
  • Mn is an element necessary for ensuring the balance between the strength and toughness of the weld metal. In order to obtain such an effect, the Mn content needs to be 0.90% or more. However, if the Mn content is too large, segregation is promoted and the toughness is reduced, so it is necessary to make it 2.50% or less.
  • Ni 0.20 to 1.00%
  • Ni increases the electric potential of the weld metal and exhibits an effect of improving the corrosion resistance. It is also an element effective in enhancing hardenability to ensure strength and improving low temperature toughness. In order to obtain such an effect, the Ni content needs to be 0.20% or more. On the other hand, if the Ni content is excessive, hot cracking may occur, and the potential of the weld metal is excessively increased, causing selective corrosion of the base metal. 00% or less.
  • Zr in inclusions having a width of 1 ⁇ m or more exists mainly as an oxide. Since this Zr oxide has a smaller coefficient of thermal expansion than steel, if the amount of Zr in the inclusion is ensured, voids with the surrounding steel matrix can be reduced and the HIC resistance is improved. Moreover, since the oxide containing an appropriate amount of Zr promotes the formation of intragranular bainite, it can obtain good SSCC resistance. In order to exert such an effect, the amount of Zr in the inclusion is set to 1 to 40%. If the amount of Zr is less than 1% or more than 40%, the HIC resistance of the base material or the SSCC resistance of the T-cross weld becomes insufficient.
  • REM in inclusions having a width of 1 ⁇ m or more exists as oxides or oxysulfides.
  • REM oxide has a smaller coefficient of thermal expansion than steel. Therefore, if the amount of REM in the inclusion is ensured, voids with the surrounding steel matrix can be reduced, and HIC resistance is improved.
  • S can be fixed and the production
  • these REM inclusions promote the formation of intragranular bainite, good SSCC resistance can be obtained.
  • the amount of REM in the inclusion is set to 5 to 50%.
  • the REM amount is less than 5% or more than 50%, the HIC resistance of the base material or the SSCC resistance of the T-cross welded portion becomes insufficient.
  • Al content is 3-30%
  • Al in inclusions having a width of 1 ⁇ m or more exists mainly as Al oxide. Since this Al oxide has a smaller coefficient of thermal expansion than steel, if the amount of Zr in the inclusion is ensured, voids with the surrounding steel matrix can be reduced, which is effective in improving the HIC resistance. Moreover, since the oxide containing an appropriate amount of Al promotes the formation of intragranular bainite, good SSCC resistance can be obtained. In order to exert such an effect, the amount of Al in the inclusion is made 3 to 30%. When the Al content is less than 3% or more than 30%, the HIC resistance of the base material or the SSCC resistance of the T-cross welded portion becomes insufficient.
  • Ca content is 5-60%
  • Ca in inclusions having a width of 1 ⁇ m or more contributes to the refinement of the steel structure in the T-cross weld during welding and promotes the formation of an intragranular bainite structure starting from the inclusions.
  • the steel structure of the T-cross welded portion after welding becomes fine, and good SSCC resistance can be obtained.
  • the Ca content in the inclusion is set to 5 to 60%. If the Ca content is less than 5% or exceeds 60%, the SSCC resistance of the T-cross weld cannot be improved.
  • the amount of S in the inclusions having a width of 1 ⁇ m or more is limited to the above-described component composition with respect to the content of S in the steel sheet and the content of alloy components such as Zr and REM for refining and dispersing sulfide inclusions. Furthermore, it can be reduced by controlling the inclusion composition as described above. If the component composition and the inclusion composition are not properly controlled, the amount of S in the inclusion exceeds 20%, and the coarse sulfide becomes excessive. As a result, the HIC resistance or T-cross of the base material is increased. The SSCC resistance of the welded portion becomes insufficient.
  • the total number of inclusions is not particularly limited as long as the effects of the present invention are not significantly impaired. However, it is preferable that the inclusions are dispersed in an amount of about 500 to 5,000 / cm 2 in the steel sheet. If it is less than 500 pieces / cm 2 , the starting point of intragranular bainite is insufficient, and it is considered that sufficient microstructure refining action cannot be obtained and SSCC resistance is lowered. On the other hand, if it exceeds 5000 / cm 2 , it will act as a starting point of destruction, and both HIC resistance and SSCC resistance may deteriorate.
  • molten steel treatment process In obtaining the thick steel sheet of the present invention having the above structure, in the molten steel treatment step, (A) a desulfurization step in which S is 0.004% or less using slag satisfying Fe: 0.1 to 10%, (B) molten steel Deoxygenation step in which the dissolved oxygen concentration Of of the molten steel is 10 or less in the ratio of S to the molten steel, (C) Al, Zr, REM and Ca are added in the order of Al, Zr, REM and Ca.
  • (A) Desulfurization process In order to ensure HIC resistance, it is important to reduce coarse sulfides, and to achieve this, it is important to control the amount of S.
  • slag satisfying Fe For molten steel melted in a converter or electric furnace so that the molten steel temperature becomes 1550 ° C. or higher, slag satisfying Fe: 0.1 to 10% is used, and S is made 0.004% or lower.
  • the Fe concentration in the slag is set to 0.1% or more.
  • the Fe concentration in the slag is preferably 0.5% or more, more preferably 1.0% or more.
  • the Fe concentration in the slag exceeds 10%, a large amount of oxide is generated, and the oxide becomes a starting point of hydrogen-induced cracking. Therefore, the Fe concentration in the slag is set to 10% or less. Preferably it is 8% or less, More preferably, it is 5% or less.
  • the Fe concentration in the slag is set to 10% or less. Preferably it is 8% or less, More preferably, it is 5% or less.
  • Ca when Ca is added, by sufficiently performing desulfurization with slag to suppress S to 0.004% or less, a large amount of CaS is formed when Ca is added after REM addition, and the composition of inclusions Can be prevented from deviating from a predetermined range, and HIC resistance and SSCC resistance can be secured.
  • the CaO concentration in the slag may be 10% or more.
  • CaO in the slag reacts with the dissolved S in the molten steel and changes to CaS, thereby sufficiently reducing S in the molten steel, that is, desulfurization.
  • the CaO concentration in the slag is preferably 15% or more, more preferably 20% or more.
  • the upper limit is about 80%.
  • (B) Deoxidation process In order to improve the SSCC resistance, oxide control is important. To achieve this, it is important to control the amount of O. In this step, since the amount of S that has an influence on the HIC resistance slightly increases, so-called recovery S occurs, it is important to control the O amount and the S amount simultaneously.
  • the dissolved oxygen concentration Of of the molten steel is set to 10 or less in the ratio of the S concentration of the molten steel: Of / S.
  • REM is added to molten steel, it forms its sulfide and at the same time forms an oxide.
  • the Of / S exceeds 10
  • most of the added REM forms an oxide, and the composition of inclusions deviates from a predetermined range.
  • Of / S is set to 10 or less as described above.
  • Of / S is preferably 5 or less, more preferably 3.5 or less, and even more preferably 2 or less.
  • the lower limit value of Of / S is about 0.1.
  • the Of / S can be reduced to 10 or less by performing at least one of deoxidation using an RH degassing apparatus and deoxidation using a deoxidizing element such as Mn, Si, or Ti. .
  • the order of addition of Al, Zr, REM, and Ca must be Al ⁇ Zr and REM ⁇ Ca.
  • the time from REM addition to Ca addition needs to be 4 minutes or longer.
  • the time from REM addition to Ca addition is preferably 5 minutes or more, more preferably 8 minutes or more. From the viewpoint of productivity, the upper limit of the time from REM addition to Ca addition is about 60 minutes.
  • the deoxidizing power is generally strongest in Ca, Ca>REM> Zr, and Zr is the weakest. Therefore, in order to contain Zr in inclusions, that is, to form ZrO 2 as oxide inclusions, Zr must be added prior to the addition of Ca or REM, which has stronger deoxidizing power than Zr. Don't be. Therefore, the order of addition of Al, Zr, REM and Ca needs to be Al ⁇ Zr ⁇ REM ⁇ Ca. However, since REM has a smaller deoxidizing ability than Ca, Zr can be contained in inclusions even if it is added simultaneously with Zr. Therefore, the order of addition is Al ⁇ Zr and REM ⁇ Ca. It is good.
  • each element added it is sufficient that a steel plate having a desired amount of each element is obtained.
  • Zr is added to a concentration of 3 to 100 ppm in the molten steel, and thereafter or simultaneously, REM is added to the concentration in the molten steel. After 4 minutes or more have passed since the addition of 2 to 500 ppm, Ca is added to a concentration of 3 to 60 ppm in the molten steel.
  • the time from the addition of Ca to the completion of solidification is set within 200 minutes. It is preferably within 180 minutes, more preferably within 160 minutes. The lower limit of the time is about 4 minutes from the viewpoint of homogenizing Ca.
  • the cooling time is important to set the cooling time at the 1300 ° C. to 1200 ° C. slab t / 4 position during casting to 270 to 460 seconds. If the cooling time exceeds the upper limit, composite formation of sulfide-based secondary inclusions on the inclusions is promoted, and the SSCC resistance is deteriorated by the inclusion composition deviating from a predetermined range. End up. On the other hand, if the cooling time falls below the lower limit, the cooling load increases greatly, which is not preferable in practice.
  • the steel plate can be manufactured by hot rolling according to a conventional method.
  • the steel pipe for line pipes can be manufactured by the method generally performed using this steel plate.
  • the process after rolling is not particularly limited.
  • the cast slab is heated to 1100 ° C. or higher and hot-rolled at a reduction rate of 40% or more in the recrystallization temperature range, and this is performed at 780.
  • Accelerated cooling is preferably performed at a cooling rate of 10 to 20 ° C./s from 0 ° C. Subsequent tempering is unnecessary.
  • a welded joint using the thick steel plate of the present invention is provided.
  • the welded joint is made of a thick steel plate and a circumferential weld metal, and is obtained by welding the end of the thick steel plate with the circumferential weld metal.
  • the immersion potential difference ⁇ E between the thick steel plate and the peripheral weld metal which is obtained by the following formula, is preferably 25 mV or less.
  • ⁇ E Immersion potential after 1 hour of circumferential weld metal (mV) ⁇ Immersion potential after 1 hour of thick steel plate (mV)
  • the immersion potential difference ⁇ E becomes 25 mV or less, and a decrease in SSCC resistance in the welded portion can be suppressed.
  • the immersion potential difference ⁇ E is more preferably 20 mV or less, and further preferably 15 mV or less.
  • the above-described weld metal is preferably used.
  • the welding method for forming the welded joint is not particularly limited, and can be performed by a conventionally known method. Examples thereof include arc welding, laser welding, and electron beam welding.
  • the analysis target elements were Al, Mn, Si, Mg, Ca, Ti, Zr, S, REM, and Nb.
  • REM shown here refers to La, Ce, Nd, Dy, and Y.
  • the relationship between the X-ray intensity of each element and the element concentration is obtained in advance using a known substance as a calibration curve, and then the element concentration of the inclusion is determined from the X-ray intensity obtained from the inclusion and the calibration curve. did. And the average value of content of each said element of the inclusion whose width
  • the surface of the welded portion of the welded pipe assembly was subjected to a grinder process, and the excess portion of the bead weld was removed.
  • a test piece of 115 L ⁇ 15 W ⁇ 5 t was sampled from just below the bead welded portion of this pipe assembly so that the longitudinal direction was parallel to the bead weld line.
  • an SSCC resistance evaluation test using a four-point bending test piece was performed based on ASTM G39, NACE TM0177-2005 B method.
  • NACE solution A which gave a deflection corresponding to a load stress of 388 MPa and 437 MPa and was saturated with hydrogen sulfide of 1 atm: after immersion in 720 hours in 5% by mass NaCl-0.5% by mass CH 3 COOH, Presence / absence was determined by observation with an optical microscope at a magnification of 10 times.
  • the sample was immersed in a NACE solution A (5 mass% NaCl-0.5 mass% CH 3 COOH) saturated with 1 atm of hydrogen sulfide, and the potential after 1 hour was measured.
  • a saturated calomel electrode was used as the reference electrode, and a value obtained by subtracting the immersion potential of the thick steel plate from the immersion potential of the peripheral weld metal was calculated as the immersion potential difference ⁇ E.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

La présente invention vise à fournir une tôle d'acier épaisse présentant une excellente résistance aux acides. Ladite tôle d'acier épaisse comprend, en % en masse, 0,01 à 0,12 % de C, 0,02 à 0,50 % de Si, 0,6 à 2,0 % de Mn, une proportion supérieure à 0 % mais inférieure ou égale à 0,030 % de P, une proportion supérieure à 0 % mais inférieure ou égale à 0,004 % de S, 0,010 à 0,080 % d'Al, 0,10 à 1,50 % de Cr, 0,002 à 0,050% de Nb, 0,0002 à 0,05 % de terres rares, 0,0003 à 0,01 % de Zr, 0,0003 à 0,006 % de Ca, une proportion supérieure à 0 % mais inférieure ou égale à 0,0040 % d'O, le reste étant du fer et les inévitables impuretés. En ce qui concerne la composition des inclusions contenues dans l'acier et présentant des largeurs supérieures ou égales à 1 μm, la proportion de Zr dans les inclusions va de 1 à 40 %, la proportion de terres rares dans les inclusions va de 5 à 50 %, la proportion d'Al dans les inclusions va de 3 à 30 % et la proportion de Ca dans les inclusions va de 5 à 60 %.
PCT/JP2016/064444 2015-05-22 2016-05-16 Tôle d'acier épaisse et joint soudé WO2016190150A1 (fr)

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EP16799856.6A EP3299486A4 (fr) 2015-05-22 2016-05-16 Tôle d'acier épaisse et joint soudé
CN201680028437.3A CN107614724A (zh) 2015-05-22 2016-05-16 厚钢板和焊接接头
KR1020177033268A KR20170138505A (ko) 2015-05-22 2016-05-16 후강판 및 용접 이음

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JP2015-104617 2015-05-22
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JP2016064064A JP2016216819A (ja) 2015-05-22 2016-03-28 厚鋼板及び溶接継手

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Cited By (1)

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Publication number Priority date Publication date Assignee Title
JP2018193595A (ja) * 2017-05-19 2018-12-06 新日鐵住金株式会社 炭素鋼鋳片及び炭素鋼鋳片の製造方法

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JPH0941083A (ja) * 1995-07-28 1997-02-10 Nkk Corp 耐ｈｉｃ及び耐ｓｓｃｃ特性に優れた電縫管及びその製造方法
JPH09165648A (ja) * 1995-12-14 1997-06-24 Nkk Corp 耐溝状腐食性に優れた電縫溶接鋼管およびその製造方法
JP2011117057A (ja) * 2009-12-07 2011-06-16 Kobe Steel Ltd 溶接熱影響部の靭性および強度の均一性に優れた厚鋼板
JP2011219797A (ja) * 2010-04-07 2011-11-04 Kobe Steel Ltd 溶接熱影響部の靭性に優れた厚鋼板
JP2013049896A (ja) * 2011-08-31 2013-03-14 Jfe Steel Corp 高一様伸び特性を備えかつ溶接部靱性に優れた高強度溶接鋼管、およびその製造方法
JP2013127108A (ja) * 2011-11-14 2013-06-27 Kobe Steel Ltd 溶接熱影響部の靭性に優れた厚鋼板
JP2014214371A (ja) * 2013-04-30 2014-11-17 株式会社神戸製鋼所 耐サワー性とｈａｚ靭性に優れた鋼板

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0941083A (ja) * 1995-07-28 1997-02-10 Nkk Corp 耐ｈｉｃ及び耐ｓｓｃｃ特性に優れた電縫管及びその製造方法
JPH09165648A (ja) * 1995-12-14 1997-06-24 Nkk Corp 耐溝状腐食性に優れた電縫溶接鋼管およびその製造方法
JP2011117057A (ja) * 2009-12-07 2011-06-16 Kobe Steel Ltd 溶接熱影響部の靭性および強度の均一性に優れた厚鋼板
JP2011219797A (ja) * 2010-04-07 2011-11-04 Kobe Steel Ltd 溶接熱影響部の靭性に優れた厚鋼板
JP2013049896A (ja) * 2011-08-31 2013-03-14 Jfe Steel Corp 高一様伸び特性を備えかつ溶接部靱性に優れた高強度溶接鋼管、およびその製造方法
JP2013127108A (ja) * 2011-11-14 2013-06-27 Kobe Steel Ltd 溶接熱影響部の靭性に優れた厚鋼板
JP2014214371A (ja) * 2013-04-30 2014-11-17 株式会社神戸製鋼所 耐サワー性とｈａｚ靭性に優れた鋼板

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2018193595A (ja) * 2017-05-19 2018-12-06 新日鐵住金株式会社 炭素鋼鋳片及び炭素鋼鋳片の製造方法

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