WO2008069289A1 - 低温靭性に優れた高強度ラインパイプ用溶接鋼管及びその製造方法 - Google Patents
低温靭性に優れた高強度ラインパイプ用溶接鋼管及びその製造方法 Download PDFInfo
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- WO2008069289A1 WO2008069289A1 PCT/JP2007/073622 JP2007073622W WO2008069289A1 WO 2008069289 A1 WO2008069289 A1 WO 2008069289A1 JP 2007073622 W JP2007073622 W JP 2007073622W WO 2008069289 A1 WO2008069289 A1 WO 2008069289A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/18—Submerged-arc welding
- B23K9/186—Submerged-arc welding making use of a consumable electrodes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/02—Seam welding; Backing means; Inserts
- B23K9/025—Seam welding; Backing means; Inserts for rectilinear seams
- B23K9/0253—Seam welding; Backing means; Inserts for rectilinear seams for the longitudinal seam of tubes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/18—Submerged-arc welding
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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
- 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
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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
- 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
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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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
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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
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/04—Tubular or hollow articles
- B23K2101/06—Tubes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
Definitions
- the present invention relates to a welded steel pipe for high-strength line pipes excellent in low-temperature toughness, suitable for line pipes for crude oil and natural gas transportation.
- Steel pipes for high-strength, high-toughness line pipes have been proposed as steel pipes for line pipes that are used in the trunk lines of pipelines that are important for long-distance transportation of crude oil, natural gas, etc. (for example, Patent Document 1) .
- the internal pressure that is, the pressure of crude oil or natural gas
- the internal pressure resistance makes it possible to reduce material costs, transportation costs, and local welding costs compared to increasing the wall thickness. Costs can be saved significantly.
- pipelines are often laid in cold regions, it is essential to have excellent low-temperature toughness.
- excellent on-site weldability is also required.
- steel pipes for X1 20 class line pipes with higher strength than steel pipes for line pipes proposed in JP-A-6 2-4 8 26 have been proposed (for example, JP-A 2 0 0 4-5 5 1 0 4).
- This is a steel pipe for high-strength line pipes whose matrix is mainly composed of a mixture of paynite and martensite.
- For thickening there has been proposed a method of manufacturing a thick steel plate with good strength and toughness by using a controlled microstructure and controlled cooling to make a fine microstructure of the metal structure (for example, JP-A-2 JP 0 0 0-2 5 6 7 7 7, JP 2 0 0 4 7 6 1 0 1, JP 2 0 4 1 4 3 5 0 9).
- Steel pipes for line pipes with high strength and thickness are manufactured by forming thick steel sheets into a tubular shape by UO process, butting the ends together and welding them together.
- toughness and productivity are required, such as steel pipes for high-strength line pipes, submerged arc welding from the inner surface and outer surface is suitable for joint welding.
- the weld heat affected zone Heat Affected Z one, HA Z
- HA Z weld heat affected zone
- the present invention provides a welded steel pipe for a high-strength line pipe that can secure the low temperature toughness of HA Z even if the content of Mo is limited, is inexpensive, and has excellent low temperature toughness, and a method for producing the same. is there.
- a steel plate for high strength line pipes having a plate thickness of 25 mm or more and a tensile strength (TS) of 60 MPa or more, X70 or X80 or more. Prototyped.
- TS tensile strength
- the problems caused by the increase in the thickness of the steel sheet were much more serious than expected.
- the reduction by controlled rolling and the cooling rate by controlled cooling become insufficient, and the toughness is significantly reduced compared to the surface layer of the steel plate.
- the present invention also solves such problems that could not be predicted from the prior art.
- the wall thickness is 25 mm or more, and more preferably 30 mm or less.
- the present invention provides a welded steel pipe for a high-strength line pipe that is capable of limiting the Mo content, is inexpensive, is thick, and has excellent low-temperature toughness, and a method for producing the same.
- the present invention reduces C and A 1 and contains an appropriate amount of T i to promote intragranular transformation, and further adds an appropriate amount of B to improve hardenability, which is a carbon equivalent that is an index of hardenability. Even if the crack sensitivity index P cm, which is an index of C e Q and weldability, is controlled within the optimal range and the Mo content is limited, the base material and HA Z are finely composed mainly of the bainite. Thickening with improved microstructure at low temperature toughness of HAZ, especially by making finer grain size of HAZ by using intragranular bait formed with metal structure and Ti oxide as nucleus This is a high-strength welded steel pipe for line pipes, and its summary is as follows.
- C, Si, Mn, Ni, Cu, Cr, Mo, V, and B are the content [% by mass] of each element.
- the base steel sheet further contains one or both of Cu: 0.05-1.5% and Ni: 0.05-5.0% by mass%.
- the welded steel pipe for high-strength line pipe excellent in low-temperature toughness according to any one of the above (1) to (3).
- the base steel plate is further, in mass%, Cr: 0.02 to 1.50%, V: 0.01 0 to 0.100%, Nb: 0.0 0 1 to 0.20 0%, Zr: 0. 0 0 0 1 to 0.0. 0 5 0 0%, Ta: 0. 0 0 0 1 to 0.0 5 0 0
- the base steel sheet is further in terms of mass%, M g: 0.0 0 0 1 to 0.0 1 0 0%, C a: 0.0 0 0 1 to 0. 0 0 5 0% , R EM
- the weld metal further contains one or both of Ni: 0.2-3.2% and Cr + Mo + V: 0.2-2.5% by mass%.
- the welded steel pipe for high-strength line pipe excellent in low-temperature toughness as described in (7) above.
- the steel sheet is formed into a tubular shape in the UO process, and the butt portion is subjected to submerged arc welding from the inner and outer surfaces using a welding wire and a firing mold or a melt-type flux, and then expanded.
- (9) or (10) The manufacturing method of the welded steel pipe for high-strength line pipe excellent in low-temperature toughness as described in (10) above.
- Figure 1 is a schematic diagram of reheated HA Z. BEST MODE FOR CARRYING OUT THE INVENTION
- the present invention is based on a steel material in which the C content is reduced and the toughness is improved as a low-temperature transformation structure mainly composed of bainite, and a hardenability index is used instead of limiting the Mo content.
- C eq and weldability index P cm are in the optimal range, B is further added to improve hardenability, and intra-grained beanite is utilized.
- the effective crystal grain size of HA Z is refined and low temperature toughness is reduced. This is a welded steel pipe with improved performance.
- the present invention reduces the amount of A 1, controls the amount of oxygen, adds an appropriate amount of T i, disperses fine inclusions that act extremely effectively as nuclei for intragranular transformation of the base steel sheet,
- the base steel plate is also simply called a steel plate
- the welded steel pipe is also simply called a steel pipe.
- the HA Z intragranular bainette is obtained by transforming the intragranular ferrite produced by intragranular transformation at high temperature during cooling with the fine inclusions described above as the formation nucleus.
- the optimum range of the hardenability index C eq and the weldability index P cm is to generate intragranular stain in the HA Z of the steel pipe in which the addition amount of Mo is limited as in the present invention. This is extremely effective.
- the formation of intragranular bainite significantly improves the low temperature toughness of HA Z.
- intragranular bait may contribute to the suppression of HA Z softening. .
- the mechanism for the formation of intra-grain bainites is considered as follows.
- the cation vacancy type oxide can take in a large amount of M n ions, and M n S is likely to be complexly precipitated in the oxide. Therefore, an Mn-depleted layer is formed around oxides and sulfides.
- This Mn-depleted layer acts as a transformation nucleus when the steel is heated and cooled to a high temperature such that the metal structure becomes an austenite phase, and usually petal-like intragranular ferrite ⁇ is generated.
- This intragranular ferrite has a high degree of supercooling when the cooling rate is high or hardenability is high, so it transforms into bait during cooling and becomes intragranular.
- a typical example of the cation vacancy type oxide is a fine oxide composed mainly of Ti, and a petal-like intragranular stain is produced using this as a core.
- fine sulfides containing Mn as a main component may be combined with the fine oxides containing Ti as the main component.
- the oxide contains one or more of A1, Si, Mn, Cr, Mg, Ca, and the sulfide contains Ca, Cu, One or more of Mg may be contained.
- the size of these inclusions, which are the cores of intragranular bait can be measured with a transmission electron microscope (TEM), and the diameter ranges from 0.01 to 5 m. It is preferable.
- TEM transmission electron microscope
- HA Z of the central part of the welded steel pipe for high-strength line pipes (in the vicinity of the 1/2 part of the thickness, called the 1 Z 2 t part).
- coarse MA that exists along the former austenite grain boundaries of reheated HAZ may become the starting point of fracture and impair toughness.
- 1 is reheated HA Z
- 2 is a mixture of martensite and austenite
- 3 is the old austenite grain boundary.
- Reheat HA Z is the part where the weld metal and H A Z near the fusion line of the preceding weld were reheated by subsequent welding.
- HA Z is a part within 10 mm from the melting line, although it differs slightly depending on the heat input during welding. For example, if a notch is provided at a position of 1 mm or 2 mm from the melting line, The Charpy absorbed energy at 40 may be less than 50 J.
- Fine oxides, composite oxides, and composite sulfides with Ti as the main component are effective for generating HA Z intragranular bait, and also for reducing the effective crystal grain size of the base metal. It is valid. This reduces the effective crystal grain size of H A Z
- the effective crystal grain size of the base steel sheet should be 20 m or less. Is possible.
- the carbon equivalent C eq that is an index of hardenability is 0.3 to 0.53 and the crack susceptibility index that is an index of weldability
- P cm is 0.1 to 0.20
- the area ratio of polygonal ferrite of the base steel sheet is 20% or less
- the area ratio of bainite is 80% or more.
- the tensile strength of the welded joint subjected to the seam welded portion is 60 OMPa or more.
- the wall thickness is 25 mm or more, and even 30 mm or more, the toughness of the 1/2 t part of the base steel sheet has been reduced.
- the composite oxide and composite sulfide made it possible to refine the effective crystal grain size of the base steel sheet.
- the reason for this is considered as follows. First, when reduction in the non-recrystallization temperature range is secured, transformation from normal grain boundaries is promoted, so it is difficult to transform intragranularly from oxides, complex oxides, and complex sulfides. . This is thought to be because when the crystal grain size is reduced by securing the reduction, the growth rate of the Painai nucleated from the grain boundary becomes too high compared to the intragranular transformation. That is, it is considered that the transformation from the grain boundary is completed before the intragranular transformation is generated.
- the grain size grows particularly at the center of the plate thickness, so that the growth of the nucleated vane from the grain boundary also slows down. Become. Therefore, it is considered that the effective crystal grain size is refined within the grains due to intragranular transformation from oxides, composite oxides, and composite sulfides mainly composed of Ti. In addition, it is considered that fine oxides acting as pinning particles and suppressing the growth of crystal grains are effective in reducing the effective crystal grain size of the base steel sheet.
- the base steel plate It is possible to make the effective crystal grain size of 20 m or less. Furthermore, by making the area ratio of polygonal ferrules 20% or less and the area ratio of Paynai cocoons 80% or more, the test was taken from the vicinity of the surface layer, that is, from about 2 to 12 mm from the steel surface. Charpy absorption energy at _ 40 ° C of the piece becomes 2 200 J or more, Charpy absorption energy when taken from 1 Z 2 t part, that is, almost from the center of the wall thickness is 10 0 J or more It can be.
- the present invention in order to produce fine oxides, composite oxides, and composite sulfides mainly composed of T i, it is extremely important to control the amount of oxygen in the steelmaking process.
- the oxygen concentration at the time of adding T i is preferably 0.01 to 0.03%.
- the particle size is 0.01 to: L 0 jLi m, and the number per area 1 ⁇ m 2 is 10 to 1 100 0 1 111111 2 1 oxide, specifically, T i 2 0 3 can be dispersed. This promotes the generation of intragranular transformation and refines the effective crystal grain size of the HAZ of the base steel plate and welded steel pipe.
- the rolling ratio from 90 ° C to the end of rolling is 2.5 or more, preferably 3.
- the effective crystal grain size of the base steel sheet can be set to 20 m or less.
- the effective grain size is the value obtained by converting the area of the portion surrounded by the boundary having a crystal orientation difference of 15 ° or more into the equivalent circle diameter using EBSP.
- Polygonal ferrite is observed in a light microscopic structure as a white massive structure that does not contain coarse precipitates such as coarse cementite MA in the grains.
- the martensite and residual austenite are used as the remainder of the polygonal ferrite and the bainite. May include MA and MA.
- bainite is defined as a structure in which carbides are precipitated between the laths or massive ferrites, or a structure in which carbides are precipitated in the laths.
- martensite is a structure in which carbides are not precipitated between the laths or within the laths.
- Residual austenite is austenite in which austenite generated at high temperature remains in the base steel plate or welded steel pipe.
- the toughness at 1 to 2 t part at the lower temperature or the toughness at the meeting part + 1 mm is improved.
- the V-notch Charbi absorption energy at a low temperature of 0 ° C can be set to 50 J or more. Therefore, when used at an extremely low temperature of 140 ° C or lower, the structure that generated the intragranular bait is further heat-treated to mix the intragranular bain ⁇ and cement ⁇ . An organization is preferred.
- HAZ is a heat-affected zone that does not melt during welding
- the components of HAZ are the same as the base metal.
- C is an element that improves the strength of steel. In the present invention, however, the content of C is limited, and a metal structure mainly composed of vanite is obtained to achieve both high strength and high toughness. Yes. If the amount of C is less than 0, 0 10%, the strength is insufficient, and if it exceeds 0.050%, the toughness decreases. Therefore, in the present invention, the optimum amount of C is 0 0 1 0 ⁇ 0. 0 5
- the range is 0%.
- S i is an important deoxidizing element in the present invention, and in order to obtain the effect, it is necessary to contain 0.0 1% or more of S i in the steel. .
- the Si content exceeds 0.50%, the toughness of HA Z decreases, so the upper limit is set to 0.50%.
- M n is an element that generates sulfides such as M n S, which is used as a deoxidizer and is necessary to ensure the strength and toughness of the base steel sheet, and is also effective as a nucleus for intragranular transformation. And is extremely important in the present invention. To obtain these effects, it is necessary to contain 0.50% of Mn, but if the Mn content exceeds 2.00%, the toughness of HAZ is impaired. Therefore, the range of the content of M n is set to 0.5 0 to 2.0%. Since Mn is an inexpensive element, it is preferable to contain 1.0% or more in order to ensure hardenability, and the optimum lower limit is 1.5% or more.
- P is an impurity, and if it contains more than 0.05%, the toughness of the base steel sheet is significantly reduced. Therefore, the upper limit of the P content is set to 0.05%. In order to improve the toughness of HAZ, it is preferable that the P content is not more than 0.010%.
- S is an important element that produces sulfides such as M n S that are effective as nuclei for intragranular transformation. If the S content is less than 0.0 0 0 1%, the amount of sulfide produced decreases and intragranular transformation does not occur remarkably. is there. On the other hand, if the base steel sheet contains more than 0.005% S, coarse sulfides are formed and the toughness is lowered, so the upper limit of the amount of S is not more than 0.000 Below. In order to improve the toughness of HAZ, the upper limit of the amount of S is preferably set to 0.0 0 30% or less.
- a 1 is a deoxidizer, but in the present invention, in order to finely disperse the Ti oxide, the upper limit of the amount of A 1 may be limited to 0.020% or less. Very important. In order to promote the formation of intragranular transformation, the A 1 content is preferably set to 0.0 10% or less. Even better A preferable upper limit is 0.0 0 8% or less.
- T i is an extremely important element in the present invention because it finely disperses the oxide of T i that effectively acts as a nucleus for intragranular transformation.
- Ti is contained excessively, carbonitrides are formed and toughness is impaired. Therefore, in the present invention, it is necessary that the content of Ding 1 be 0.03 to 0.030%.
- T i is a strong deoxidizing agent, so if the amount of oxygen when T i is added is large, a coarse oxide is formed. Therefore, it is necessary to deoxidize with Si and Mn in advance and reduce the oxygen content during steelmaking.
- the oxide of Ti becomes coarser, intragranular transformation is less likely to occur, and the effect of pinning the grain boundary is reduced, so that the HAZ effective crystal grain size of the base steel plate and welded steel pipe may become coarser. is there.
- B is an element that increases hardenability when dissolved in steel. However, if added in excess, coarse BN is produced, and in particular, the toughness of HA Z is reduced. 0 3 0%. In the welded steel pipe of the present invention, 0.003% or more of B, which enhances hardenability, is added, and the carbon equivalent C eq that is an index of hardenability and the crack sensitivity index P cm that is an index of weldability are optimal. The strength and weldability are ensured by controlling within a proper range. Note that the addition of 0.000% or more of B is also effective in suppressing the formation of ferrite from grain boundaries. In addition, if fine BN is generated by the active addition of B, the toughness of HAZ increases with the decrease in solute N, so the B content is preferably more than 0.005%. .
- M o Although M o is a useful element that improves hardenability and promotes the formation of intragranular stains on HA Z, and also improves strength by forming carbonitrides, 0.1. Addition of more than 10% increases alloy cost. Therefore, in the present invention, the content of expensive Mo is limited to less than 0.1%.
- the welded steel pipe of the present invention has a low Mo content.
- the carbon equivalent C eq, which is a hardenability index, and the crack susceptibility index P cm, which is a weldability index, are controlled within the optimum range so that hardenability can be secured even if it is reduced.
- Oxygen is an element inevitably contained in the steel, but in the present invention, it is necessary to limit the amount of O in order to produce an oxide containing Ti.
- the amount of oxygen remaining in the steel at the time of forging that is, the amount of ⁇ in the base steel plate, needs to be in the range of 0.0 0 0 1 to 0.0 0 8 0%. This is because when the amount is less than 0.0 0 0 1%, the number of oxides is not sufficient, and when it exceeds 0.0 0 80%, the amount of coarse oxide increases, and the base metal and HA Z This is because the toughness is impaired.
- the oxide mainly composed of Ti becomes coarser due to the increase in oxygen content, the effective crystal grain size of HAZ in the base steel plate and welded steel pipe may become coarser.
- one or more of Cu, Ni, Cr, V, Nb, Zr, and Ta may be added as elements for improving strength and toughness.
- these elements can be regarded as impurities because they do not have an adverse effect.
- Cu, Ni Cu and Ni are effective elements that increase the strength without losing the toughness.
- the lower limit of the Cu content and Ni content is set to 0.05. % Or more is preferable.
- the upper limit of the Cu content is preferably 1.5% in order to suppress the occurrence of cracks during heating of the steel slab and during welding.
- the upper limit of the Ni content is preferably 5.0% because the weldability is impaired if it is excessively contained.
- Cu and Ni are preferably combined to contain surface flaws. Further, from the viewpoint of cost, it is preferable that the upper limit of 11 and ⁇ 1 is 1.0% or less.
- C r, V, N b, Z r, T a are It is an element that generates carbides and nitrides and improves the strength of steel by precipitation strengthening, and may contain one or more.
- the lower limit of the Cr amount is 0.02%
- the lower limit of the V amount is 0.01 0%
- the lower limit of the Nb amount is 0.0 0 1%
- Zr Both the lower limit of the amount and the amount of Ta are preferably set to 0.0 0 0 1%.
- the upper limit of Cr content is preferably set to 1.50%.
- the upper limit of V content is 0.110%, and the amount of Nb It is preferable that the upper limit is 0.200%, the Zr amount, and the upper limit of Ta are both 0.05% and 0%.
- one or more of Mg, Ca, REMM, Y, Hf, Re, and W may be added.
- the content of these elements is less than the preferred lower limit, they can be regarded as impurities because they do not have any adverse effects.
- Mg is an element that exerts an effect on oxide refinement and sulfide morphology control.
- fine Mg oxide acts as a nucleus for formation of intragranular transformation, and in order to obtain the effect of suppressing the coarsening of the particle size as pinning particles, 0.0 0 0 1% or more Is preferably added.
- Mg in an amount exceeding 0.01 100% is added, coarse oxides may be formed, which may reduce the HAZ toughness of the base steel plate and welded steel pipe. It is preferable to set the upper limit to 0.0.100%.
- C a, R EM: C a and REM are useful for controlling the morphology of sulfides. Suppresses the formation of granulated materials and the formation of M n S elongated in the rolling direction. In particular, an element that improves lamellar resistance is there. In order to obtain this effect, it is preferable that the lower limits of the Ca amount and the REM amount are both 0.001% or more. On the other hand, when the upper limit of the Ca content and the REM content exceeds 0.0 0 50 0%, the oxide increases, the fine Ti-containing oxide decreases, and the formation of intragranular transformation is inhibited. For this reason, the content is preferably set to 0.0 0 50 0% or less.
- Y, H f, R e, W Y, H f, W, Re are also elements that exhibit the same effect as Ca and R EM, and if added excessively, the formation of intragranular transformation is inhibited. Sometimes. Therefore, the preferable ranges of Y amount, H f amount, and Re amount are 0.00 0 1 to 0.0 0 50%, respectively, and the preferable range of W amount is 0.001 to 0.5 0%.
- the HAZ hardenability of the base metal plate and the welded steel pipe is ensured, the area ratio of the base material bait is 80% or more, and intragranular bait is generated in the HAZ. Therefore, the carbon equivalent C eq of the following (formula 1) calculated from the content [mass%] of C, M n, Ni, Cu, Cr, Mo, V is 0.30-0. 5 3
- Equation 2 Note that, since the selectively contained elements Ni, Cu, Cr, and V are impurities when they are less than the preferred lower limit, the above (Equation 1) And in (Equation 2), it is calculated as 0.
- the metal structure of the base steel sheet used as the welded steel pipe the balance between strength and toughness will be good if the area ratio of the Paynai iron is 80% or more and the area ratio of the polygonal ferrite is 20% or less.
- the effective grain size is 20 m or less due to the formation of oxides mainly composed of Ti, the toughness of the base steel sheet will be good.
- Polygonal ferrite is also effective in reducing the effective crystal grain size of the base steel sheet, and the area ratio is preferably 3% or more.
- the thickness of the base steel plate is preferably 25 mm or more, and the tensile strength in the direction corresponding to the circumferential direction of the steel pipe is preferably 60 OMPa or more. This is to prevent breakage due to internal pressure when used as a line pipe. If it is necessary to increase the internal pressure, the thickness of the base steel plate is preferably 30 mm or more. On the other hand, the thickness of the base steel plate is preferably 40 mm or less, and the tensile strength in the direction corresponding to the circumferential direction of the steel pipe is preferably 80 OMPa or less. This is because the load when forming the base steel sheet in the UO process increases due to an increase in wall thickness and an increase in tensile strength. Normally, the direction corresponding to the circumferential direction of the steel pipe is the plate width direction of the base steel plate.
- Forging After melting the steel in the steelmaking process described above, it is forged into billets. Forging may be performed by a conventional method, but continuous forging is preferable from the viewpoint of productivity.
- the billet is heated for hot rolling.
- the heating temperature for hot rolling is 100 ° C. or higher. This is because hot rolling is performed at a temperature at which the steel structure becomes an austenite single phase, that is, in the austenite region, and the crystal grain size of the base steel sheet is made fine. Although the upper limit is not specified, in order to suppress the coarsening of the effective crystal grain size, it is preferable to set the reheating temperature to 1 2 500 or less.
- the starting temperature of hot rolling is not specified. Fine crystal grain size of base steel
- the rolling ratio in the recrystallization region exceeding 900 ° C. is preferably 2.0 or more.
- the reduction ratio in the recrystallization zone is the ratio between the thickness of the steel slab and the thickness at 900 x.
- the rolling ratio in the non-recrystallized region below 900 ° C is set to 2.5 or more, after water cooling, the effective crystal grain size of the base steel plate becomes 20 / xm or less.
- the rolling ratio in the non-recrystallized region below 90 ° C. is a ratio obtained by dividing the plate thickness at 90 ° C. by the plate thickness after the end of rolling.
- the upper limit of the reduction ratio in the non-recrystallized region and the recrystallized region is not specified, but considering the plate thickness of the steel slab before rolling and the thickness of the base steel plate after rolling, it is usually less than 12.0 It is.
- the rolling end temperature is preferably hot rolling at a temperature equal to or higher than the temperature at which the base steel sheet has an austenite single phase. That is, the rolling end temperature, A is preferably to r 3 or more, because a small amount of Porigonarufu Erai Bok during rolling may be generated, A r 3 _ 5 0 may be more ° C. A c 3 and A r 3 are calculated based on the contents (mass%) of C, Si, Mn, P, Cr, Mo, W, Ni, Cu, Al, V, and Ti. can do.
- water cooling is performed after the rolling is completed. If the water cooling stop temperature is set to 600 ° C. or lower, the above-described metal structure can be obtained, and the toughness of the base steel sheet becomes good.
- the lower limit of the water cooling stop temperature is not specified, and it may be cooled to room temperature. Considering productivity and hydrogen defects, it is preferable to set the value to 1550 or higher. Since the steel of the present invention contains B and has a component composition with improved hardenability, it is easy to generate bait even when air-cooled after the end of rolling, but depending on the component composition and heating temperature, the polygonal A ferrite may occur, and the area ratio of the Paynai pass may be less than 80%.
- the forming is preferably performed by a UOE process in which the steel plate is C-pressed, U-pressed, or O-pressed.
- the heat input of submerged arc welding from the inner and outer surfaces may be set to 4.0 to 10 kJ / mm. It is preferable. If the heat input is within this range, the welded steel pipe of the present invention having the above-described composition will cause intragranular baiting in the HAZ, and the HAZ effective crystal grain size will be less than 1550 m. Low temperature toughness is obtained.
- the wire used for welding has the following components in order to keep the component composition of the weld metal within the range described later. That is, in mass%, C: 0.0 1 0 to 0.1 2 0%, S i: 0.0 5 to 0.5 50%, M n: l. 0 to 2.5% N i: 2 A component composition containing 0 to 8.5%, further containing A 1: 0. 1 0 0% or less, T i: 0.0 5 0% or less, the balance being Fe and unavoidable impurities It is. B: 0. 0 0 0 1 to 0. 0 0 5 0% may be included, and one or more of Cr, Mo and V may be included in Cr + Mo + V: 1.0 to 5. You may contain in 0% of range.
- the C is an extremely effective element for improving the strength, and it is preferable to contain 0.010% or more.
- the upper limit of the C content is preferably set to 0.1 00%. In order to improve the toughness of the weld metal, the upper limit is more preferably set to 0.05% or less.
- S i is preferably contained in an amount of 0.1% or more.
- the upper limit is preferably made 0.5% or less.
- the lower limit is preferably 1.0% or more.
- the upper limit may be made 2.0% or less. preferable.
- P and S are impurities, and in order to reduce the low temperature toughness of the weld metal and reduce the low temperature cracking susceptibility, it is preferable to set these upper limits to 0.020% and 0.010% or less. From the viewpoint of low temperature toughness, a more preferable upper limit of P is 0.010%.
- a 1 is an element that is added in order to improve the precision and solidification during the production of the welding wire, and uses a fine Ti-based oxide to increase the grain size of the weld metal. In order to suppress it, it is preferable to contain 0.001% or more of A 1. However, since A 1 is an element that promotes the production of MA, the preferable upper limit of the content is 0.100% or less.
- T i is an element that produces fine oxides that are the nuclei of intragranular transformation and contributes to refinement of the grain size of the weld metal, and is preferably contained at 0.03% or more.
- the upper limit is preferably made 0.05% or less.
- O is an impurity, and the amount of oxygen finally remaining in the weld metal is often 0.001% or more. However, if the amount of O remains exceeding 0.05%, the amount of coarse oxide increases, and the toughness of the weld metal may decrease, so the upper limit is set to 0.05%. The following is preferable.
- the weld metal preferably further contains Ni, Cr, Mo, and V selectively.
- Ni is an element that enhances hardenability to ensure strength, and further improves low-temperature toughness, and is preferably contained at 0.2% or more. On the other hand, if the Ni content is too high, hot cracking may occur, so the upper limit was made 3.2% or less.
- Cr, Mo, and V are all elements that enhance the hardenability. For high strength of the weld metal, one or more of these elements should be included in a total of 0 • 2% or more. Also good. On the other hand, if the total of one or more of Cr, Mo and V exceeds 2.5%, the low temperature toughness may deteriorate, so the upper limit is preferably made 2.5% or less.
- the weld metal may further contain B.
- B is an element that increases the hardenability of the weld metal, and in order to increase the strength, it is preferable to contain 0.001% or more. On the other hand, if the B content exceeds 0.050%, the toughness may be impaired. Therefore, the upper limit is preferably set to 0.050% or less.
- elements other than the above for example, Cu, Nb, Zr, Ta, Mg, Ca, REM, Y, which are selectively added to the base metal by dilution from the base steel plate , Hi, Re, W, etc.
- Contain elements such as Zr, Nb, and Mg added as necessary to improve the precision and solidification of the welding wire There is a case. These are inevitable impurities.
- the pipes may be expanded to improve the roundness of the steel pipe.
- the expansion ratio is preferably set to 0.7% or more.
- the expansion ratio is the percentage of the difference between the outer peripheral length of the steel pipe after the expansion and the outer peripheral length of the steel pipe before the expansion, with the outer peripheral length of the steel pipe before the expansion. If the expansion ratio exceeds 2%, the toughness may decrease due to plastic deformation of both the base metal and the weld. Therefore, the expansion rate is assumed to be 0.7-2.0%. It is preferable.
- the coarse MA formed along the old austenite grain boundaries Decomposes into a cementite and fine cementitious material, improving toughness. If the heating temperature is less than 300 ° C, the coarse MA is not sufficiently decomposed and the effect of improving toughness may not be sufficient. Therefore, the lower limit is preferably set to 300 ° C or more. On the other hand, if the weld is heated to more than 500 ° C, precipitates may be formed and the toughness of the weld metal may be deteriorated. Therefore, the upper limit is preferably set to 500 ° C or less.
- the heat treatment of the welded portion and HAZ may be performed by heating from the outer surface with a burner, and may be performed by high frequency heating.
- the outer surface may be cooled immediately after reaching the heat treatment temperature, it is preferably maintained for 1 to 60 seconds in order to promote the decomposition of MA.
- the holding time is preferably set to 300 s or less.
- the steel piece had a thickness of 240 mm. These steel slabs were heated to the heating temperature shown in Table 2 and hot-rolled in a recrystallization temperature range of 45 ° C. to 160 ° C. over 9500 ° C. Furthermore, the plate thickness shown in Table 2 Up to now, hot rolling was performed at the reduction ratio shown in Table 2 in the non-recrystallized region in the temperature range from 80 ° C to 800 ° C. The end temperature of hot rolling was Ar 3 550 ° C. or higher, water cooling was started at 75 ° C., and water cooling was stopped at various temperatures.
- a V-notch test piece was prepared in which the plate width direction was the longitudinal direction and the notch was provided parallel to the plate thickness direction in accordance with JIS Z 2 2 4 2.
- the sampling position of the Charpy specimen was set at the surface layer, that is, about 2 to 12 mm from the surface and 1/2 t, that is, approximately at the center of the wall thickness.
- the Charbi test was conducted at 140 ° C and the absorbed energy was determined.
- Tensile properties were evaluated using A PI standard test pieces. When a base steel plate with a thickness of 25 to 40 mm is formed into a welded steel pipe, it is confirmed by analysis by the finite element method that the influence of the strain introduced by forming at the center of the plate thickness is small. did.
- TS may increase by about 20 to 30 MPa, and toughness The effect is small in the middle part and the surface part of the thickness.
- the microstructure of the central part of the base steel sheet was observed with an optical microscope, the area ratio of polygonal ferrite and bainite was measured, and the remaining structure was confirmed.
- the effective grain size of the base steel sheet was measured by EBSP
- V is contained in the range of Cr + Mo + V • 1.0 to 5.0%
- B 0.0 0 1 to 0.0 0 50 0% is contained
- the welding heat input is set to 4.0 to 10.
- Welding was performed to produce a welded joint.
- some joints were heat-treated at the temperatures shown in Table 2.
- Samples were taken from the weld metal and analyzed for components.
- the tensile strength of the weld metal was measured according to JISZ 3 1 1 1.
- Table 3 shows the chemical composition and tensile strength of the weld metal. Small pieces were taken from the welded joints, and the effective grain size of HAZ was measured by EBSP.
- base steel sheets are UO process, submerged arc welding, expanded to make steel pipes, and the microstructure and mechanical properties are investigated, which is equivalent to the HAZ Miku mouth structure and mechanical characteristics of the base steel and joints of the steel plates. It was confirmed that.
- the balance is the sum of the area ratios of retained austenite, martensite, and MA.
- the intragranular transformation structure is the area ratio of intragranular bainite.
- Production Nos. 1 to 9 are examples of the present invention.
- the effective crystal grain size of the base steel sheet is 20 m or less, and the effective crystal grain size of HA Z is 1550; m or less.
- the Charpy absorption energy of the base metal and HAZ at 40 ° C exceeds 50 J, and the low temperature toughness is good.
- the fracture position of the joint tensile test is the base steel plate, and the softening of HA Z is not a problem.
- Production No. 9 is an example in which the heat treatment temperature is low, and the effect of improving low-temperature toughness is slightly smaller than when heat treatment is performed at a preferred temperature.
- production No. 10, 11, 14, and 15 are outside the scope of the present invention, and the production No. 12 and 13 are within the scope of the present invention.
- production No. 10 is an example in which the amount of A 1 is large, and production No. 11 has a small amount of Ti, so that intragranular bait is reduced and low temperature toughness of HAZ is also reduced.
- Manufacture No. 12 is an example in which the reduction ratio at 900 ° C. or less is small, the effective crystal grain size of the base steel plate is increased, and the low temperature toughness of the base steel plate is lowered.
- production No. 10 is an example in which the amount of A 1 is large
- production No. 11 has a small amount of Ti, so that intragranular bait is reduced and low temperature toughness of HAZ is also reduced.
- Manufacture No. 12 is an example in which the reduction ratio at 900 ° C. or less is small, the effective crystal grain size of the base steel plate is increased, and the low temperature toughness of the base steel plate is lowered.
- Manufacture No. 13 is an example in which the area ratio of the polygonal ferrite of the base material increases and the strength decreases because it is air-cooled after rolling.
- Manufacture No. 14 is an example of reduced strength due to low Ceq and Pcm.
- Manufacture No. 15 is an example in which the strength is high and the toughness of the base steel sheet is lowered due to the high C e q and P cm. In addition, because the strength of the base steel plate is high, the HAZ fractured as a result of the joint tensile test.
- the present invention it is possible to ensure low temperature toughness of HAZ of welded steel pipes for line pipes even if the content of M 0 is reduced, and an inexpensive weld steel pipe for high-strength line pipes having excellent low temperature toughness and its Providing manufacturing methods Furthermore, according to the present invention, it becomes possible to ensure the low-temperature toughness of the welded steel pipe for a high-strength linepipe having a wall thickness of 25 mm or more, further 30 mm or more, Industrial contribution is remarkable.
Abstract
Description
Claims
Priority Applications (5)
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BRPI0718935A BRPI0718935B1 (pt) | 2006-11-30 | 2007-11-30 | tubos soldados para tubulação de alta resistência superior em tenacidade à baixa temperatura e método de produção dos mesmos. |
KR1020097008164A KR101119240B1 (ko) | 2006-11-30 | 2007-11-30 | 저온 인성이 우수한 고강도 라인 파이프용 용접 강관 및 그 제조 방법 |
EP07859731.7A EP2093302B1 (en) | 2006-11-30 | 2007-11-30 | Weld steel pipe with excellent low-temperature toughness for high-strength line pipe and process for producing the same |
CN2007800439905A CN101541994B (zh) | 2006-11-30 | 2007-11-30 | 低温韧性优异的高强度管线管用焊接钢管及其制造方法 |
US12/312,885 US8039118B2 (en) | 2006-11-30 | 2007-11-30 | Welded steel pipe for high strength line pipe superior in low temperature toughness and method of production of the same |
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JP2007-310457 | 2007-11-30 | ||
JP2007310457A JP5251092B2 (ja) | 2006-11-30 | 2007-11-30 | 低温靱性に優れた高強度ラインパイプ用溶接鋼管及びその製造方法 |
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WO2012036148A1 (ja) | 2010-09-14 | 2012-03-22 | 新日本製鐵株式会社 | 低温靭性に優れた厚肉溶接鋼管および低温靭性に優れた厚肉溶接鋼管の製造方法、厚肉溶接鋼管製造用鋼板 |
WO2013100106A1 (ja) * | 2011-12-28 | 2013-07-04 | 新日鐵住金株式会社 | 変形性能と低温靭性に優れた高強度鋼管、高強度鋼板、および前記鋼板の製造方法 |
CN104204257A (zh) * | 2012-03-28 | 2014-12-10 | 新日铁住金株式会社 | 热锻压用拼焊板和热锻压构件以及它们的制造方法 |
CN108034885A (zh) * | 2017-11-09 | 2018-05-15 | 江阴兴澄特种钢铁有限公司 | 一种低温条件下使用的低裂纹敏感性管件用钢板及其制造方法 |
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EP2801638B1 (en) * | 2012-03-01 | 2021-05-26 | JFE Steel Corporation | Steel material for high-heat-input welding |
JP6008042B2 (ja) | 2013-03-29 | 2016-10-19 | Jfeスチール株式会社 | 厚肉鋼管用鋼板、その製造方法、および厚肉高強度鋼管 |
RU2651069C1 (ru) * | 2017-11-27 | 2018-04-18 | Юлия Алексеевна Щепочкина | Сплав на основе железа |
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KR101410588B1 (ko) | 2010-09-14 | 2014-06-23 | 신닛테츠스미킨 카부시키카이샤 | 저온 인성이 우수한 후육 용접 강관 및 저온 인성이 우수한 후육 용접 강관의 제조 방법, 후육 용접 강관 제조용 강판 |
US8871039B2 (en) | 2010-09-14 | 2014-10-28 | Nippon Steel & Sumitomo Metal Corporation | Thick welded steel pipe excellent in low temperature toughness, manufacturing method of thick welded steel pipe excellent in low temperature toughness, and steel plate for manufacturing thick welded steel pipe |
RU2534566C1 (ru) * | 2010-09-14 | 2014-11-27 | Ниппон Стил Энд Сумитомо Метал Корпорейшн | Толстостенная сварная стальная труба с превосходной низкотемпературной ударной вязкостью, способ изготовления толстостенной сварной стальной трубы с превосходной низкотемпературной ударной вязкостью, и стальная пластина для изготовления толстостенной сварной стальной трубы |
WO2013100106A1 (ja) * | 2011-12-28 | 2013-07-04 | 新日鐵住金株式会社 | 変形性能と低温靭性に優れた高強度鋼管、高強度鋼板、および前記鋼板の製造方法 |
CN104204257A (zh) * | 2012-03-28 | 2014-12-10 | 新日铁住金株式会社 | 热锻压用拼焊板和热锻压构件以及它们的制造方法 |
US9901969B2 (en) | 2012-03-28 | 2018-02-27 | Nippon Steel & Sumitomo Metal Corporation | Tailored blank for hot stamping, hot stamped member, and methods for manufacturing same |
US10807138B2 (en) | 2012-03-28 | 2020-10-20 | Nippon Steel Corporation | Tailored blank for hot stamping, hot stamped member, and methods for manufacturing same |
CN108034885A (zh) * | 2017-11-09 | 2018-05-15 | 江阴兴澄特种钢铁有限公司 | 一种低温条件下使用的低裂纹敏感性管件用钢板及其制造方法 |
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EP2093302A1 (en) | 2009-08-26 |
EP2093302A4 (en) | 2011-07-27 |
EP2093302B1 (en) | 2017-01-25 |
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