WO2014024234A1 - Tôle d'acier pour un tuyau d'acier à résistance élevée et tuyau d'acier à résistance élevée - Google Patents

Tôle d'acier pour un tuyau d'acier à résistance élevée et tuyau d'acier à résistance élevée Download PDF

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WO2014024234A1
WO2014024234A1 PCT/JP2012/005117 JP2012005117W WO2014024234A1 WO 2014024234 A1 WO2014024234 A1 WO 2014024234A1 JP 2012005117 W JP2012005117 W JP 2012005117W WO 2014024234 A1 WO2014024234 A1 WO 2014024234A1
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content
steel pipe
steel
high strength
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PCT/JP2012/005117
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English (en)
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Izuru Minato
Nobuaki Takahashi
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Nippon Steel & Sumitomo Metal Corporation
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Priority to PCT/JP2012/005117 priority Critical patent/WO2014024234A1/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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel

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  • the present invention relates to a steel plate for a high strength steel pipe and a high strength steel pipe, particularly to a steel plate for a high strength steel pipe and a high strength steel pipe excellent in hydrogen-induced cracking resistance.
  • H 2 S humid hydrogen sulfide
  • Hydrogen sulfide causes hydrogen-induced cracking (hereinafter referred to as "HIC") in a pipeline for transporting crude oil or natural gas that has been drilled. Therefore, HIC resistance is required in a steel pipe for a pipeline.
  • HIC HIC causes high stress in steel so as to generate HIC.
  • Patent Document 1 JP54-110119A
  • Patent Document 2 JP61-60866A
  • Patent Document 3 JP09-57410A
  • Patent Document 4 JP06-220577A
  • Patent Document 5 JP09-209037A
  • Patent Document 6 JP2003-226922A
  • Patent Document 1 discloses a producing method of containing Ce and Ca in molten steel. The patent document describes that, in this method, MnS-based inclusions in the steel become spheroidized, thereby enhancing HIC resistance.
  • Patent Document 2 discloses steel materials for a pipeline containing Ni, Cr and/or Mo. The patent document describes that, in this method, hydrogen is prevented from intruding into steel, thereby enhancing HIC resistance.
  • Patent Document 3 discloses a producing method of performing rolling reduction of a slab by 20mm or more by using reduction rolls in the vicinity before the solidification completion point when the slab is produced in a continuous casting process. The patent document describes that this method reduces central segregation causing HIC.
  • Patent Document 4 discloses a producing method of producing a high tension steel plate whose ratio of the Mn content in a segregation portion of the steel relative to the average Mn content in the steel is 1.20 or less. The patent document describes that this method enhances HIC resistance.
  • Patent Document 5 discloses a producing method in which steel has the Cu content of 0.05% or less and contains appropriate amount of Ni and Mo. The patent document describes that this method prevents hydrogen from intruding into the steel, thereby enhancing HIC resistance.
  • Patent Document 6 discloses a producing method of forming steel in a ferrite structure, which contains appropriate Mo, Ti, Nb and V contents relative to C content.
  • the patent document describes that the ferrite structure enhances HIC resistance and high strength can be attained due to Mo, Ti, Nb and V.
  • Patent Documents cannot provide a high strength steel pipe having high strength and excellent HIC resistance in some cases. For example, it is possible to obtain HIC resistance to some extent by reducing C content and Mn content in steel so as to reduce C segregation and Mn segregation, but it is hard to obtain high strength.
  • An Object of the present invention is to provide a steel plate for a high strength steel pipe and a high strength steel pipe excellent in HIC resistance.
  • the high strength steel pipe according to the present invention contains, by mass%, C: 0.020 to 0.070%; Si: 0.05 to 0.50%; Mn: 1.10 to 1.60%; P: 0.008% or less; S: 0.0006% or less; Cu: 0.05 to 0.50%; Cr: 0.05 to 0.50%; Ni: 0.05 to 1.00%; Mo: 0.50% or less; Nb: 0.005 to 0.080%; V: 0.005 to 0.080%; Ti: 0.005 to 0.030%; N: 0.0015 to 0.0070%; Al: 0.005 to 0.060%; and Ca: 0.0005 to 0.0060%, the balance being Fe and impurities, and satisfying the formula (1): 0.6 ⁇ Cu + Cr + Ni + Mo ⁇ 1.5 (1) where the content (mass%) of each element is substituted in a symbol of each element in the formula (1).
  • the steel plate for a high strength steel pipe according to the present invention has excellent HIC resistance.
  • the high strength steel pipe according to the present invention comprises base metal made of the steel plate for a high strength steel pipe as described above formed in a tube shape, and weld metal.
  • the weld metal contains, by mass%, C: 0.010 to 0.150%; Si: 0.02 to 0.60%; Mn: 0.60 to 3.00%; Ni: 0.10 to 2.00%; Ti: 0.003 to 0.030%; and Al: 0.004 to 0.080%.
  • the corrosion potential of the weld metal is electropositive relative to the base metal.
  • Wall thickness of the base metal is preferably 30.00 mm or more, and a tensile strength in a circumferential direction of the base metal is preferably 570 MPa or more.
  • the high strength steel pipe has excellent HIC resistance in spite of having a thick wall.
  • Figure 1 illustrates the relation between the P content and the cracking area ratio.
  • Figure 2 illustrates the relation between the S content and the cracking area ratio.
  • Figure 3 shows the relation between a difference in the Ni content between the weld metal and the base metal and a difference in the corrosion potential between the weld metal and the base metal.
  • the present inventors considered that, in order to produce a steel pipe excellent in HIC resistance and having a thick wall, not only the C content and the Mn content should be reduced so as to reduce the C segregation and the Mn segregation, but also the P content and the S content should be reduced so as to reduce the P segregation and the S segregation.
  • Figure 1 illustrates the relation between the P content in steel and the cracking area ratio CAR
  • Figure 2 illustrates the relation between the S content in steel and the cracking area ratio CAR.
  • the cracking area ratio CAR (%) is defined by the formula (A). In general, the smaller the cracking area ratio CAR is, the more excellent the HIC resistance becomes.
  • Cracking area ratio CAR area of HIC generated in specimen / area of specimen (A)
  • Figure 1 was resulted from the following testing method.
  • a plurality of sample materials were produced whose chemical compositions except for P were within the range of the chemical composition of the steel plate of the present invention as described above and whose P contents were different.
  • Each sample material had the substantially same chemical composition except for the P content.
  • Steel plates were produced by using various sample materials in the following producing method.
  • a specimen with a size of 10 mm thickness, 20 mm width and 100 mm length was prepared from each steel plate.
  • the prepared specimens were used to carry out the HIC test.
  • Acetic acid aqueous solution at 25 deg C was prepared as a testing liquid, which contains saline solution with pH of 4.0 and concentration of 5% and was saturated with gas whose H 2 S partial pressure was 0.01 x 10 5 Pa (the balance was nitrogen).
  • the specimens were immersed in the prepared testing liquid for 96 hours. After the immersion, HIC generated in each specimen was measured in the ultrasonic testing method, and the cracking area ratio CAR was found based on the formula (A).
  • the area of each specimen in the formula (A) was 20 mm x 100 mm.
  • the P content and the cracking area ratio CAR obtained based on the Formula (A) of each specimen was plot in the graph of Figure 1.
  • Figure 2 was resulted from the following testing method.
  • a plurality of sample materials were produced whose chemical compositions except for S were within the chemical composition of the steel plate of the present invention as described above and whose S contents were different.
  • Each sample material had the substantially same chemical composition except for the S content.
  • Steel plates were produced by using the various sample materials under the same condition as that of the test method of Figure 1 and a plurality of specimens were prepared from each steel plates. The specimens were used to carry out the HIC test. The S content and the cracking area ratio CAR obtained based on the formula (A) of each specimen was plot in the graph of Figure 2.
  • the cracking area ratio CAR significantly decreased. More specifically, along with decrease of the P content, the cracking area ratio CAR significantly decreased until the P content decreased to 0.008%.
  • the cracking area ratio CAR decreased to 5.0% or less along with the decrease of the P content, but the decrease of the cracking area ratio CAR was not so significant.
  • the cracking area ratio CAR significantly decreased until the S content decreased to 0.0006%.
  • the cracking area ratio CAR decreased to 5.0 % or less.
  • the P content of 0.008% or less and the S content of 0.0006% or less can significantly enhance the HIC resistance. This is because the P segregation and the S segregation can be significantly reduced by reducing the P content and the S content to the above range. Accordingly, the present inventors considered that, if the P content is 0.008% or less and the S content is 0.0006% or less, excellent HIC resistance can be attained even in a thick wall steel pipe in which segregation is likely to be caused during the manufacturing process of the pipe.
  • the present inventors further considered that strength of the steel should be enhanced using elements other than C and Mn having less influence on the HIC resistance in order to increase the tensile strength in the circumferential direction of a steel pipe at or above X70 grade (570 MPa or more) specified by the API standards. Based on the various studies, the present inventors have found that, by satisfying the formula (1), it is possible to attain the tensile strength in the circumferential direction of a steel pipe to be 570 MPa or more, and achieve the excellent HIC resistance of the steel pipe, and also attain both the high strength and the excellent HIC resistance even if the steel pipe has a thickness of 30.00 mm or more.
  • the present inventors have accomplished the steel plate for a high strength steel pipe and the high strength steel pipe according to the present invention.
  • detailed description will be provided on the steel plate for a high strength steel pipe and the high strength steel pipe according to the present invention.
  • the steel plate for a high strength steel pipe according to the present invention has the following chemical composition. As described above, the symbol % for content of an element denotes mass%, hereinafter.
  • C 0.020 to 0.070%
  • Carbon (C) enhances strength of steel. If the C content is 0.020% or more, it is possible to attain sufficient strength required in a steel pipe for a pipeline. To the contrary, excessive C content in the steel is likely to generate macrosegregation at the center portion of wall thickness of a slab produced in the continuous casting process. Such macrosegregation serves as a starting point of generating HIC. Hence, the C content is 0.020 to 0.070%.
  • the preferable C content is more than 0.020% and less than 0.070%.
  • the preferable lower limit of the C content is 0.030%, and the more preferable lower limit thereof is 0.040%.
  • the preferable upper limit of the C content is 0.065% and the more preferable upper limit thereof is 0.060%.
  • Si 0.05 to 0.50% Silicon (Si) deoxidizes steel. Si also enhances strength of the steel. To the contrary, excessive Si content in the steel produces stripe-shaped martensite, so that the HAZ toughness is deteriorated. Furthermore, excessive Si content in the steel is likely to produce TiN. Produced TiN serves as a nucleus so as to be likely to produce Nb carbo-nitride. Specifically, if excessive amount of Si is contained in the steel, the HIC resistance decreases. Hence, the Si content is 0.05 to 0.50%. The preferable Si content is more than 0.05% and less than 0.50%. The preferable lower limit of the Si content is 0.010%. The preferable upper limit thereof is 0.40%.
  • Mn 1.10 to 1.60% Mn enhances strength of steel. To the contrary, if excessive amount of Mn is contained in the steel, Mn is likely to be concentrated at the central segregation portion in the steel, thus the HIC resistance of the steel decreases. Therefore, the Mn content is 1.10 to 1.60%.
  • the Mn content is preferably more than 1.10% and less than 1.60%.
  • the preferable lower limit of the Mn content is 1.15%, and the more preferable lower limit thereof is 1.20%.
  • the preferable upper limit of the Mn content is 1.50%, and the more preferable upper limit thereof is 1.40%.
  • P 0.008% or less Phosphorus (P) is impurity.
  • P is impurity.
  • the P content is preferably as small as possible, thus the P content is 0.008% or less.
  • the preferable P content is less than 0.008%, the more preferable P content is 0.007% or less, the further more preferable P content is 0.006% or less, and the further more preferable P content is 0.005% or less.
  • S 0.0006% or less Sulfur is impurity.
  • S is likely to be concentrated at the central segregation of steel.
  • S also produces MnS at the central segregation portion of the steel. MnS serves as a starting point of generating HIC.
  • the S content is preferably as small as possible, thus the S content is 0.0006% or less.
  • the preferable S content is less than 0.0006%, the more preferable S content is 0.0005% or less, and the further more preferable S content is 0.0004% or less.
  • Cu 0.05 to 0.50% Copper (Cu) enhances hardenability of steel, and enhances strength of the steel, as well. To the contrary, excessive Cu content deteriorates the hot workability or machinability of the steel. If excessive amount of Cu is contained, a slab becomes fragile on its surface during the continuous casting process. Therefore, the Cu content is 0.05 to 0.50%.
  • the preferable Cu content is more than 0.05% and less than 0.50%.
  • the preferable lower limit of the Cu content is 0.10%, and the more preferable Cu content is 0.15%.
  • the preferable upper limit of the Cu content is 0.45%, and the more preferable upper limit thereof is 0.40%.
  • Chromium (Cr) significantly enhances strength of steel. Cr also enhances toughness in the steel. On the other hand, excessive Cr content deteriorates welderbility and often causes weld cracking. Therefore, the Cr content is 0.05 to 0.50%.
  • the preferable Cr content is more than 0.05% and less than 0.50%.
  • the preferable lower limit of the Cr content is 0.10%, and the more preferable lower limit thereof is 0.15%.
  • the preferable upper limit of the Cr content is 0.45% and the more preferable upper limit thereof is 0.40%.
  • Ni 0.05 to 1.00%
  • Nickel (Ni) enhances strength of steel through solid-solution strengthening. Ni also enhances toughness in the steel. On the other hand, excessive Ni content saturates effect thereof, and more excessive Ni content deteriorates weldability of the steel. Therefore, the Ni content is 0.05% to 1.00%.
  • the preferable Ni content is more than 0.05% and less than 1.00%.
  • the preferable lower limit of the Ni content is 0.10%, and the more preferable lower limit thereof is 0.15%.
  • the preferable upper limit of the Ni content is 0.80%, and the more preferable upper limit thereof is 0.60%.
  • Mo Molybdenum
  • Mo is an optional element. Mo improves hardenability of steel and enhances strength of the steel. Furthermore, the microsegregation of Mo is hard to be generated, so that Mo reduces generation of HIC resulted from the central segregation. On the other hand, Mo is expensive, which increases the production cost. Therefore, the content of Mo is 0.50% or less.
  • the preferable content of Mo is less than 0.05%.
  • the preferable lower limit of the Mo content is 0.02%.
  • the preferable upper limit of the Mo content is 0.30% or less.
  • Niobium (Nb) forms carbo-nitride in steel.
  • Nb carbo-nitride enhances strength and toughness of the steel. Particularly Nb controls microstructure of a steel plate.
  • the Nb content is 0.005 to 0.080%.
  • the preferable Nb content is more than 0.005% and less than 0.080%.
  • the preferable lower limit of the Nb content is 0.010%, the more preferable lower limit thereof is 0.020%.
  • the preferable upper limit of the Nb content is 0.060%, and the more preferable upper limit thereof is 0.050%.
  • V 0.005 to 0.080% Vanadium (V) is dissolved in steel or forms carbo-nitride, thereby enhancing strength of the steel.
  • V content is 0.005 to 0.080%.
  • the preferable V content is more than 0.005% and less than 0.080%.
  • the preferable lower limit of the V content is 0.010%, and the more preferable lower limit thereof is 0.020%.
  • the preferable upper limit of the V content is 0.060% and the more preferable upper limit thereof is 0.050%.
  • Titanium (Ti) enhances strength of steel. Ti combines with nitrogen (N) to form TiN as well. TiN reduces production of NbN or AlN. NbN or AlN dynamically precipitates in the g grain boundary during the continuous casting process and causes surface cracking to a slab, and Ti reduces surface cracking of the slab due to NbN and AlN. On the other hand, excessive Ti content deteriorates welding toughness. If excessive amount of Ti is contained and TiN is produced excessively, the produced TiN serves as a nucleus so as to produce coarse Nb carbo-nitride, which deteriorates the HIC resistance. Furthermore, excessive Ti content forms excessive Ti carbo-nitride.
  • Ti carbo-nitride deteriorates the HIC resistance as similar to Nb carbo-nitride. Therefore, the Ti content is 0.005% to 0.030%.
  • the preferable Ti content is more than 0.005% and less than 0.030%.
  • the preferable lower limit of the Ti content is 0.008%.
  • the preferable upper limit of the Ti content is 0.025%.
  • N 0.0015 to 0.0070%
  • Nitrogen (N) is inevitably contained in steel when nitrogen is melted in the atmosphere using a converter or the like. N combines with Al or Ti to form nitride. Nitride refines grains during hot working. On the other hand, excessive N content forms coarse Nb nitride or Nb carbo-nitride, so as to deteriorate the HIC resistance. As described above, if excessive amount of N is contained, Nb nitride or Al nitride dynamically precipitates in the g grain boundary excessively during the continuous casting process, so as to cause surface cracking of a cast piece. Therefore, the N content is 0.0015 to 0.0070%.
  • the preferable N content is more than 0.0015% and less than 0.0070%.
  • the preferable lower limit of the N content is 0.0020%, and the more preferable lower limit thereof is 0.0025%.
  • the preferable upper limit of the N content is 0.0050% and the more preferable upper limit thereof is 0.0040%.
  • Al 0.005 to 0.060%
  • Aluminum (Al) deoxidizes steel. Al also enhances the yield rate of the Ca content in the steel during the casting, so as to enhance the HIC resistance of the steel. Too small Al content cannot deoxidize the steel sufficiently, so as to deteriorate the yield rate of the Ca content in the steel. If the yield rate of the Ca content in the steel decreases, sulfide is likely to be produced, or segregation of S is likely to be caused. Sulfide and S segregation deteriorate the HIC resistance. On the other hand, excessive Al content produces excessive alumina that is produced by deoxidization, and the excessive alumina serves as a starting point of generating the HIC. Therefore, the Al content is 0.005% to 0.060%.
  • the preferable Al content is more than 0.005% and less than 0.060%.
  • the preferable lower limit of the Al content is 0.010%, and the more preferable lower limit thereof is 0.015%.
  • the preferable upper limit of the Al content is 0.050%, and the more preferable upper limit thereof is 0.045%.
  • the Al content in the present embodiment denotes the content of sol. Al (acid-soluble Al).
  • Ca 0.0005% to 0.0060%
  • Calcium (Ca) controls MnS serving as a starting point of generating HIC to be in a spherical shape, so as to reduce generation of HIC.
  • Ca also forms CaS, so as to reduce production of MnS.
  • excessive Ca content saturates effect thereof, resulting in increase in the production cost. Therefore, the Ca content is 0.0005% to 0.0060%.
  • the preferable Ca content is more than 0.0005% and less than 0.0060%.
  • the preferable lower limit of the Ca content is 0.0010%.
  • the preferable upper limit of the Ca content is 0.0040%.
  • the balance of the chemical composition of the high strength steel pipe according to the present embodiment is Fe and impurities.
  • the impurities herein are referred to as ore and scraps that are used as steel materials, or elements mixed in an environment of the production process.
  • the chemical composition of the high strength steel pipe according to the present embodiment satisfies the formula (1), as well: 0.6 ⁇ Cu + Cr + Ni + Mo ⁇ 1.5 (1) where the content (mass%) of each element is substituted in the symbol of each element in the formula (1).
  • F1 Cu + Cr + Ni + Mo is defined. If the value F1 is 0.6% or less, the yield strength in the circumferential direction of the steel pipe made of a steel plate formed into a tube shape becomes less than 570 MPa. On the other hand, if the value F1 is 1.5% or more, the strength of the steel plate becomes excessively high, resulting in deteriorating the HIC resistance.
  • the yield strength in the circumferential direction of the steel pipe becomes 570 MPa or more even if the plate thickness of the steel pipe is 30 mm or more. Furthermore, influence of Cu, Cr, Ni and Mo on the HIC resistance is smaller than other alloying elements, thereby attaining excellent HIC resistance.
  • the structure of the steel plate for a high strength steel pipe according to the present invention is a bainitic ferrite single phase.
  • the single phase herein contains bainitic ferrite and inclusions and/or precipitates.
  • the structure of the steel plate for a high strength steel pipe according to the present invention does not contain low temperature transformation structure such as martensite. Therefore, generation of central segregations of C, Mn, P and S can be reduced.
  • the high strength steel pipe according to the present invention is a welded tube.
  • the high strength steel pipe includes base metal made of the above described steel plate for a high strength steel pipe formed into a tube shape, and a weld zone.
  • the weld zone may be in a straight shape extending in the longitudinal direction of the steel pipe, or in a spiral shape relative to the steel pipe.
  • the weld zone includes a heat affected zone (HAZ) and weld metal.
  • HZ heat affected zone
  • the high strength steel pipe of the present invention includes base metal and weld metal. Detailed description will be provided on the weld metal as follows.
  • Chemical composition of weld metal The chemical composition of the weld metal of the high strength steel pipe contains the following elements.
  • Carbon (C) enhances strength of the weld metal.
  • excessive C content deteriorates toughness in the weld metal. Therefore, the C content is 0.010 to 0.150%.
  • Si 0.02 to 0.60% Silicon (Si) deoxidizes the weld metal. If the Si content is too small, air is mixed into the weld metal, so as to form defects. On the other hand, excessive Si content deteriorates toughness in the weld metal. Therefore, the Si content is 0.02 to 0.60%.
  • Mn 0.60 to 3.00%
  • Manganese (Mn) enhances strength and toughness of the weld metal. Mn also forms complex oxide serving as a precipitation nucleus of ferrite. If Mn forms complex oxide, ferrite is formed so as to enhance toughness in the steel. On the other hand, excessive Mn content deteriorates toughness in the weld metal. Therefore, the Mn content is 0.60 to 3.00%.
  • Ni 0.10 to 2.00%
  • Nickel (Ni) enhances strength and toughness of the weld metal.
  • the Ni content is 0.10 to 2.00%.
  • the Ni content of the weld metal is preferably higher than the Ni content of the base metal.
  • the Ni content of the weld metal is more preferably at least 0.2% higher than the Ni content of the base metal. In this case, the corrosion potential of the weld metal is higher than the corrosion potential of the base metal, thereby reducing corrosion of the weld metal.
  • Titanium (Ti) enhances toughness in the weld metal. Specifically, Ti forms complex oxide. The complex oxide serves as a precipitation nucleus of ferrite. If complex oxide is formed by Ti, ferrite is formed, so as to enhance toughness in the weld metal. On the other hand, excessive Ti content deteriorates toughness in the weld metal. Therefore, the Ti content is 0.003 to 0.030%.
  • Al 0.004 to 0.080%
  • Aluminum (Al) forms complex oxide as similar to Ti, thus Al enhances toughness in weld metal.
  • excessive Al content deteriorates toughness in the weld metal. Therefore, the Al content is 0.004 to 0.080%.
  • the balance of the chemical composition of the weld metal is Fe and impurities.
  • the chemical composition of the weld metal may include elements other than the above described elements.
  • elements included in the chemical composition of the above described steel plate for a high strength steel pipe that is the base metal may be contained in the above range.
  • the chemical composition of the weld metal may also contain boron (B) with appropriate amount.
  • the corrosion potential of the weld metal is electropositive relative to the base metal (the steel plate for a high strength steel pipe).
  • the weld metal In a welded steel pipe, the weld metal has the surface area significantly smaller than the surface area of the base metal.
  • the metal having a smaller surface area is more likely to be corroded (galvanic corrosion). Therefore, in a welded steel pipe, weld metal is more likely to be corroded than base metal.
  • the corrosion potential of the weld metal is electropositive relative to the base metal, that is, the corrosion potential of the weld metal is higher than the corrosion potential of the base metal, the weld metal is hard to be corroded.
  • the corrosion potential of the weld metal is at least 0.005 V higher than the corrosion potential of the base metal. In this case, the weld metal is hard to be corroded, thereby enhancing the HIC resistance of the weld metal.
  • Figure 3 shows the relation between a difference in the Ni content between the weld metal and the base metal and a difference in the corrosion potential between the weld metal and the base metal.
  • Figure 3 was resulted from the following testing method.
  • the base metal was prepared, which satisfied the chemical composition of the steel plate for a high strength steel pipe of the present invention.
  • three kinds of welded metal materials each of which satisfied the chemical composition of the weld metal of the present invention, but only whose Ni contents were different from one another.
  • Specimens were prepared from the base metal and the welded metal materials, respectively.
  • the specimens were used to measure corrosion potentials thereof.
  • a well-known electrolytic apparatus was employed, which included a test chamber, a potentiostat, counter electrodes and a reference electrode. The specimens were immersed in the test chamber, so as to measure corrosion potential of each specimen.
  • Figure 3 was resulted from the measured potentials of three kinds of the welded metal materials and the measured potentials of the base metal.
  • the corrosion potential of the weld metal was at least 0.005 V higher than the corrosion potential of the base metal, so as to be sufficiently electropositive relative to the base metal. Accordingly, as one example, if the Ni content of the weld metal is at least 0.2% higher than the Ni content of the base metal, it is possible to reduce galvanic corrosion of the weld metal, thereby enhancing the HIC resistance of the weld metal.
  • the Ni content of the weld metal was higher than the Ni content of the base metal, thereby allow the weld metal to be electropositive relative to the base metal.
  • the weld metal may be electropositive relative to the base metal by increasing content of any alloying element other than Ni.
  • the reason why the present embodiment employs Ni is that Ni allows the weld metal to be electropositive without deteriorating the toughness and the HIC resistance of the weld metal.
  • Manufacturing method The manufacturing method of the steel plate for a high strength steel pipe and the high strength steel pipe according to the present embodiment will be described as follows. Molten steel that satisfies the chemical composition of the steel plate for a high strength steel pipe according to the present invention is produced into a slab through the continuous casting process (continuous casting process). The slab is rolled into the steel plate for a high strength steel pipe (rolling process). The steel plate for a high strength steel pipe is produced into a pipe so as to be the high strength steel pipe (pipe production process). Detailed description will be provided on each step as follows.
  • the molten steel refined by a well-known method is produced into a slab through the continuous casting process.
  • unsolidified molten steel in the slab during the continuous casting process may be electromagnetically stirred, and the slab may be rolled around the final stage of the solidification. In this case, the P segregation and the S segregation are more reduced.
  • Rolling process The slab produced in the continuous casting process is heated in a heating furnace (heating step).
  • the heated slab is rolled into a steel plate by using a rolling mill (working step).
  • the steel plate is cooled immediately after being rolled (cooling step). After being cooled, the steel plate is tempered if necessary (tempering step).
  • the rolling process is performed based on the heating step, the working step, the cooling step and the tempering step described as below, so as to allow the steel plate for a high strength steel pipe to have the above described structure.
  • Heating step The heating temperature of the slab in the heating furnace is set at 1000 to 1250 deg C. Too high heating temperature coarsens austenite grains so that the grains cannot be refined. Conversely, if the heating temperature of the slab is too low, it is impossible to dissolve Nb which contributes to refinement of grains during the rolling and precipitation strengthening after the rolling. Specifically, if the heating temperature is 1000 to 1250 deg C, it is possible to reduce coarsening of austenite grains and dissolve Nb.
  • the heating temperature T (deg C) preferably satisfies the following formula (2): where the content (mass%) of each element is substituted in the symbol of each element in the formula (2).
  • the preferable soaking temperature is 1000 to 1300 deg C, and the preferable soaking time is 20 to 50 hours. In this case, each segregation of C, Mn, P, S and others is reduced.
  • the temperature of a workpiece during the rolling is set in an austenite non-recrystallization temperature range.
  • the austenite non-recrystallization temperature is a temperature range where high density dislocation introduced by the working such as rolling disappears drastically accompanying interface movement, and specifically is a temperature range of A r3 - 60 deg C to A r3 .
  • the steel plate thickness (mm) after the finishing rolling is completed is substituted in the symbol t.
  • the rolling reduction rate (%) is not limited to a specific value.
  • the rolling reduction rate is generally 50% or more.
  • the rolling reduction rate is defined by the following formula (4).
  • Rolling reduction rate ⁇ cross sectional area of slab (thickness x width) ⁇ / ⁇ cross sectional area of steel plate after final rolling is completed (thickness x width) ⁇ - 1 ⁇ x 100 (4)
  • Cooling step After the completion of the finishing rolling, the steel plate is quickly cooled, that is, accelerated cooling is performed.
  • the cooling speed after the rolling is preferably 10 to 50 deg C / sec. If the cooling speed is too slow, the structure of the steel plate is hard to become a bainitic ferrite single phase. On the other hand, if the cooling speed is too fast, the surface hardness becomes high excessively. Water cooling may be used as the cooling method, for example.
  • the cooling at the above mentioned cooling speed is stopped, and thereafter the steel plate is cooled in air. Toughness in the steel plate is more enhanced by the tempering effect while being cooled in air, so as to reduce generation of hydrogen-related defects.
  • Tempering step After cooling, tempering at a temperature less than the A c1 point is performed if necessary. For example, tempering is performed if surface hardness or toughness should be adjusted. Tempering is not an essential step, thus the tempering step may be omitted.
  • Pipe production step The steel plate produced through the rolling process described above is formed into an open pipe by the U press, O press or the like. Following this operation, the weld zone including the above described weld metal was formed on both end faces in the longitudinal direction of the open pipe by a well-known welding method such as Submerged arc welding method.
  • the high strength steel pipe that is a welded steel pipe is produced through the above described steps.
  • the high strength steel pipe having the weld zone is quenched, and may also be tempered if necessary.
  • the high strength steel pipe may be produced by a method other than the above described pipe producing step.
  • the steel plate may be formed in a spiral shape and be welded so as to produce the steel pipe.
  • the molten steel as shown in Table 1 was continuously casted to produce the slab.
  • the chemical compositions of the steel in the test numbers 1 to 3 were within the range of the present invention and each value F1 satisfied the formula (1). To the contrary, the chemical compositions of the steel in the test numbers 4 and 5 were within the range of the present invention, but each value F1 was less than the lower limit of Formula (1).
  • the content of any of the elements in the chemical composition exceeded the scope of the present invention.
  • the C content, the Mn content and the P content exceeded the upper limit of the present invention.
  • the Cu content and the Ni content were less than the lower limit of the present invention.
  • the Mn content exceeded the upper limit of the present invention.
  • the Cr content was less than the lower limit of the present invention.
  • the P content and the S content exceeded the upper limit of the present invention.
  • the Cr content and the Ca content thereof were less than the lower limit of the present invention.
  • the Mn content was less than the lower limit of the present invention.
  • the P content exceeded the upper limit of the present invention.
  • the S content exceeded the upper limit of the present invention.
  • the chemical composition of the steel in the test number 12 was within the range of the chemical composition of the present invention, but the value F1 exceeded the upper limit of Formula (1).
  • the produced slab in each test number had the thickness of 250 to 300 mm, and the width of 1300 to 2300 mm.
  • the casting speed in each test number was 0.6 to 1.0 m / min.
  • Each produced slab was heated in the heating furnace at the temperature of 1200 deg C for 300 minutes. After being heated, the slab was hot-rolled to be produced into a steel plate.
  • the roll reduction rate was 70% or more.
  • the steel plate was cooled by water cooling at the cooling speed of 10 to 40 deg C / sec. When the temperature of the steel plate reached 400 to 600 deg C, the cooling at this cooling speed was stopped, and thereafter the steel plate was cooled in air to the normal temperature.
  • the produced steel plate was formed into a tube form.
  • the weld zone containing the weld metal was formed by the Submerged arc welding method, so as to produce a welded steel pipe (hereinafter referred to as simply a "steel pipe").
  • the weld zone was configured to linearly extend in the axial direction of the steel pipe.
  • the chemical composition of the weld zone of the steel pipe in each test number was within the range of the present invention.
  • the chemical compositions of the weld metal in the test numbers 1, 2 and 6 were shown in Table 2.
  • the chemical composition of the weld metal in each test number C, Si, Mn, Ni, Ti and Al were within the range of the chemical composition of the weld metal of the present invention.
  • the chemical composition of the weld metal in each test number further contains P, S, Cu, Cr, Mo, Nb, V, N, B and Ca, the balance being Fe and impurities.
  • the chemical compositions of the weld metal in the other test numbers than the test numbers 1, 2 and 6 were within the range of the present invention.
  • Measurements of wall thickness were carried out on the produced steel pipe in each test number. Specifically, the wall thickness was measured at three points: at the both sides of the weld zone and at a position turned 180 deg around the central axis of the steel pipe from the weld metal, viewed in the axial direction of the steel pipe. An average of the measured wall thicknesses was defined as the wall thickness WT (mm) of the steel pipe in the test number.
  • the wall thickness WT (mm) in each test number was shown in Table 1.
  • the wall thickness of the steel pipe corresponded to the thickness of the steel plate for a high strength steel pipe that was the base metal.
  • Tensile specimens in compliance with JIS Z 2201 were prepared from the produced steel pipes.
  • the tensile specimens were prepared from the center of wall thickness of the steel pipe in the vertical direction relative to the axial direction of the steel pipe (circumferential direction of the steel pipe).
  • the tensile specimens were used to carry out the tensile test at normal temperature so as to measure the tensile strength (MPa) of the circumferential direction of each steel pipe.
  • P segregation degree and S segregation degree The P segregation degree of the steel pipe in each test number was found by the following method. A sample including the center of wall thickness of the steel pipe was prepared from the cross section of each steel pipe (cross section in the vertical direction relative to the axial direction of the steel pipe). A macro-etch test was carried out on each of the samples, so as to observe the segregation line at the center of wall thickness thereof. At any five points on the segregation line, the linear analysis was carried out by the EPMA, and an arithmetic mean value of peak values of the P segregation at the five points was defined as P (t/2) .
  • a sample was prepared from the cross section of each steel pipe such that the sample includes a portion of 1/4 wall thickness of the steel pipe (at a position of 1/4 wall thickness inward from the outer surface of the steel pipe).
  • a product analysis in compliance with JIS G 0321 was carried out on each of the samples, so as to find the P concentration thereof.
  • the found P concentration corresponded to the P concentration at a portion having substantially no segregation among the steel pipe.
  • the found P concentration was defined as P (t/4) .
  • P segregation degree P (t/2) / P (t/4) (5)
  • the specimen (thickness: 10 mm, width: 20 mm, length: 100 mm) was prepared from the steel pipe in each test number. The specimens were used to carry out the HIC test. Acetic acid aqueous solution at 25 deg C was prepared, which contained saline solution with a pH of 4.0 and concentration of 5% and was saturated with gas whose H 2 S partial pressure was 0.01 x 10 5 Pa (the balance is nitrogen) as a testing liquid. The specimens were immersed in the prepared testing liquid for 96 hours. After the immersion, the area of HIC generated in each specimen was measured by the ultrasonic testing method, and the cracking area ratio CAR was found based on the formula (A). The area of each specimen in the formula (A) was 20 mm x 100 mm.
  • Test results The test results are shown in Table 1.
  • the P segregation degree and the S segregation degree were shown in the column “Segregation Degree” in Table 1.
  • the tensile strength (MPa) was shown in the column “Tensile Strength.”
  • the cracking area ratio CAR (%) resulted from the HIC test was shown in the column “CAR.”
  • each steel pipe in the test numbers 1 to 3 was within the range of the present invention, and the value F1 satisfied the formula (1).
  • the wall thickness was 30.00 mm or more
  • the tensile strength was 570 MPa or more
  • the P segregation degree and the S segregation degree were less than 1.15, respectively
  • the CAR was 5% or less (0%).
  • the chemical compositions of the steel pipes in the test numbers 4 and 5 were within the range of the present invention, but the value F1 was less than the lower limit of formula (1).
  • the thickness of the steel pipe in the test number 4 was 30.00 mm or more, so that the tensile strength thereof was less than 570 MPa.
  • the C content, the Mn content and the P content exceeded the upper limit of the present invention.
  • the P segregation degree was 1.15 or more.
  • the S segregation degree was also 1.15 or more.
  • the CAR exceeded 5%. Since the C content and the Mn content were higher, macrosegregation was generated at the center of the steel, thus it is estimated that P and S were concentrated at the macrosegregation, and the HIC resistance became low.
  • the P content and the S content exceeded the upper limit of the present invention.
  • the P segregation degree and the S segregation degree were 1.15 or more, and the CAR exceeded 5%.
  • the value F1 was less than the lower limit of the present invention, so that the tensile strength was less than 570 MPa.
  • the Mn content was less than the lower limit of the present invention.
  • the tensile strength was less than 570 MPa.
  • the P content exceeded the upper limit of the present invention.
  • the P segregation degree was 1.15 or more and the CAR exceeded 5%.
  • the S content exceeded the upper limit of the present invention.
  • the S segregation degree was 1.15 or more and the CAR exceeded 5%.
  • the chemical composition of the steel pipe in the test number 12 was within the range of the present invention, but the value F1 exceeded the upper limit of the formula (1). Accordingly, the CAR exceeded 5%.

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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

L'invention concerne une tôle d'acier pour un tuyau d'acier à résistance élevée et le tuyau d'acier à résistance élevée ayant une excellente résistance à la fissuration induite par l'hydrogène (HIC). Le tuyau d'acier à résistance élevée contient, en % en masse, C : 0,020 à 0,070 % ; Si : 0,05 à 0,50 % ; Mn : 1,10 à 1,60 % ; P : 0,008 % ou moins ; S : 0,0006 % ou moins ; Cu : 0,05 à 0,50 % ; Cr : 0,05 à 0,50 % ; Ni : 0,05 à 1,00 % ; Mo : 0,50 % ou moins ; Nb : 0,005 à 0,080 % ; V : 0,005 à 0,080 % ; Ti : 0,005 à 0,030 % ; N : 0,0015 à 0,0070 % ; Al : 0,005 à 0,060 % ; et Ca : 0,0005 à 0,0060 %, le reste étant Fe et des impuretés, et satisfaisant la formule (1) : 0,6 < Cu + Cr + Ni + Mo < 1,5 (1) où la teneur (% en masse) de chaque élément est substituée par un symbole de chaque élément dans la formule (1).
PCT/JP2012/005117 2012-08-10 2012-08-10 Tôle d'acier pour un tuyau d'acier à résistance élevée et tuyau d'acier à résistance élevée WO2014024234A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109957721A (zh) * 2019-03-28 2019-07-02 南京钢铁股份有限公司 一种具有止裂性能的深海管线钢板及轧制工艺
CN110295320A (zh) * 2019-06-20 2019-10-01 江阴兴澄特种钢铁有限公司 一种lf-rh精炼工艺生产的大壁厚x52ms抗酸管线钢板及其制造方法

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JPS54110119A (en) 1978-02-16 1979-08-29 Sumitomo Metal Ind Ltd Manufacture of line pipe steel with superior hydrogen induced cracking resistance
JPS6160866A (ja) 1984-08-31 1986-03-28 Kawasaki Steel Corp 耐サワ−性に優れたラインパイプ用鋼材
JPH02263918A (ja) * 1989-04-03 1990-10-26 Nippon Steel Corp 耐ｈｉｃ性および耐ｓｓｃ性に優れた高張力鋼板の製造法
JPH06220577A (ja) 1993-01-26 1994-08-09 Kawasaki Steel Corp 耐ｈｉｃ特性に優れた高張力鋼及びその製造方法
JPH07173536A (ja) * 1993-12-16 1995-07-11 Nippon Steel Corp 耐サワー性の優れた高強度ラインパイプ用鋼板の製造法
JPH0957410A (ja) 1995-08-18 1997-03-04 Sumitomo Metal Ind Ltd 連続鋳造方法
JPH09209037A (ja) 1996-01-31 1997-08-12 Nkk Corp 耐ｈｉｃ性に優れた高強度ラインパイプ用鋼板の製造方法
JP2003226922A (ja) 2001-11-29 2003-08-15 Jfe Steel Kk 耐ｈｉｃ特性に優れた高強度鋼板の製造方法
JP2005264217A (ja) * 2004-03-17 2005-09-29 Jfe Steel Kk 耐ｈｉｃ性に優れた厚手熱延鋼板とその製造方法
JP2006063351A (ja) * 2004-08-24 2006-03-09 Sumitomo Metal Ind Ltd 耐水素誘起割れ性に優れた高強度鋼板および製造方法、並びにラインパイプ用鋼管
EP2224028A1 (fr) * 2007-11-07 2010-09-01 JFE Steel Corporation Plaques d'acier pour pipelines et tubes d'acier
EP2407570A1 (fr) * 2009-03-12 2012-01-18 Sumitomo Metal Industries, Ltd. Feuille d'acier épais résistant de hic et tuyau en acier fabriqué selon le procédé uoe

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS54110119A (en) 1978-02-16 1979-08-29 Sumitomo Metal Ind Ltd Manufacture of line pipe steel with superior hydrogen induced cracking resistance
JPS6160866A (ja) 1984-08-31 1986-03-28 Kawasaki Steel Corp 耐サワ−性に優れたラインパイプ用鋼材
JPH02263918A (ja) * 1989-04-03 1990-10-26 Nippon Steel Corp 耐ｈｉｃ性および耐ｓｓｃ性に優れた高張力鋼板の製造法
JPH06220577A (ja) 1993-01-26 1994-08-09 Kawasaki Steel Corp 耐ｈｉｃ特性に優れた高張力鋼及びその製造方法
JPH07173536A (ja) * 1993-12-16 1995-07-11 Nippon Steel Corp 耐サワー性の優れた高強度ラインパイプ用鋼板の製造法
JPH0957410A (ja) 1995-08-18 1997-03-04 Sumitomo Metal Ind Ltd 連続鋳造方法
JPH09209037A (ja) 1996-01-31 1997-08-12 Nkk Corp 耐ｈｉｃ性に優れた高強度ラインパイプ用鋼板の製造方法
JP2003226922A (ja) 2001-11-29 2003-08-15 Jfe Steel Kk 耐ｈｉｃ特性に優れた高強度鋼板の製造方法
JP2005264217A (ja) * 2004-03-17 2005-09-29 Jfe Steel Kk 耐ｈｉｃ性に優れた厚手熱延鋼板とその製造方法
JP2006063351A (ja) * 2004-08-24 2006-03-09 Sumitomo Metal Ind Ltd 耐水素誘起割れ性に優れた高強度鋼板および製造方法、並びにラインパイプ用鋼管
EP2224028A1 (fr) * 2007-11-07 2010-09-01 JFE Steel Corporation Plaques d'acier pour pipelines et tubes d'acier
EP2407570A1 (fr) * 2009-03-12 2012-01-18 Sumitomo Metal Industries, Ltd. Feuille d'acier épais résistant de hic et tuyau en acier fabriqué selon le procédé uoe

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109957721A (zh) * 2019-03-28 2019-07-02 南京钢铁股份有限公司 一种具有止裂性能的深海管线钢板及轧制工艺
CN110295320A (zh) * 2019-06-20 2019-10-01 江阴兴澄特种钢铁有限公司 一种lf-rh精炼工艺生产的大壁厚x52ms抗酸管线钢板及其制造方法

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