WO2019077725A1 - 耐サワーラインパイプ用高強度鋼板およびこれを用いた高強度鋼管 - Google Patents
耐サワーラインパイプ用高強度鋼板およびこれを用いた高強度鋼管 Download PDFInfo
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- 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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- 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
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- 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
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- 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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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
Definitions
- the present invention relates to a high strength steel plate for use in sour-line pipes, which is used in the field of sour-line pipes and is excellent in material uniformity in steel plates, particularly HIC characteristics, and a high-strength steel pipe using the same. is there.
- a line pipe is manufactured by forming a steel plate manufactured by a thick plate mill or a hot rolling mill into a steel pipe by UOE forming, press bend forming, roll forming or the like.
- the line pipe used to transport crude oil and natural gas containing hydrogen sulfide also has resistance to hydrogen-induced cracking (resistance to hydrogen induced cracking (HIC)) and resistance to sulfide.
- HIC hydrogen-induced cracking
- So-called sour resistance is required such as stress corrosion cracking resistance (SUSC resistance (Sulfide Stress Corrosion Cracking resistance)).
- SUSC resistance Stress corrosion cracking resistance
- HIC adsorbs hydrogen ions by corrosion reaction on the steel surface, penetrates into the steel as atomic hydrogen, and diffuses and accumulates around non-metallic inclusions such as MnS in the steel and the hard second phase structure It becomes molecular hydrogen and the internal pressure causes cracking.
- Patent Documents 1 and 2 While controlling the morphology of sulfide inclusions by low S and Ca addition to a high strength steel plate, central segregation is suppressed by lowering C and Mn, and the strength is reduced accordingly.
- a method has been proposed which compensates for Cr by addition of Cr, Mo, Ni, etc. and accelerated cooling.
- TMCP Thermo-Mechanical Control Process
- Patent Documents 3 and 4 use a high-frequency induction heating device to heat the steel sheet surface after accelerated cooling to a higher temperature than the inside, thereby reducing the hardness of the surface layer.
- a method of manufacturing steel plate for pipe is disclosed.
- Patent Literatures 5 and 6 disclose a method of improving the shape of a steel sheet by performing descaling just before cooling to reduce cooling unevenness caused by scale thickness unevenness.
- JP-A-5-271766 Japanese Patent Application Laid-Open No. 7-173536 JP 2002-327212
- a Patent 371896 Japanese Patent Application Laid-Open No. 9-57327 Patent No. 3796133 gazette
- Patent Documents 1 to 4 are all directed to the central segregation portion, no consideration is given to the uniformity of the HIC resistance characteristics in the sheet width direction. There is a problem that the variation in center segregation in the plate width direction at the slab stage affects the variation in HIC resistance characteristics in the plate width direction of the rolled steel sheet.
- the present invention is to provide a high strength steel plate for a sour line pipe and a high strength steel pipe using the same, which is excellent in the HIC resistance and suppresses the variation in the HIC resistance in the sheet width direction. With the goal.
- the present inventors prevent HIC generation from a center segregation part, and control variation of HIC-proof characteristic of board width direction.
- the component composition, the microstructure, and the manufacturing method of the steel material were examined earnestly.
- the present invention has been completed on the finding that variation in central segregation can be suppressed.
- the gist configuration of the present invention is as follows. [1] by mass%, C: 0.02 to 0.08%, Si: 0.01 to 0.50%, Mn: 0.50 to 1.80%, P: 0.001 to 0.015% , S: 0.0002 to 0.0015%, Al: 0.01 to 0.08% and Ca: 0.0005 to 0.005%, and the balance has a component composition consisting of Fe and unavoidable impurities
- the number of Mn-concentrated spots exceeding 1.5 mm in major axis length approximate to an elliptical shape in the measurement region of ⁇ 5 mm from the thickness center to the thickness direction Less than 3 per 100 mm of length,
- the plate width is W
- the HIC characteristic is 10% or less in CAR at the position of W / 4, the position of W / 2, and the position of 3 W / 4 from one end of the steel plate in the plate width direction
- the above-mentioned component composition is further selected by mass% from Cu: 0.50% or less, Ni: 0.50% or less, Cr: 0.50% or less and Mo: 0.50% or less.
- the above-mentioned component composition further includes, by mass%, Nb: 0.005 to 0.1%, V: 0.005 to 0.1%, and Ti: from 0.005 to 0.1%.
- Nb 0.005 to 0.1%
- V 0.005 to 0.1%
- Ti from 0.005 to 0.1%.
- the high strength steel plate for the sour line pipe of the present invention is excellent in the HIC resistance characteristic, and further, the variation in the HIC resistance characteristic in the sheet width direction is suppressed. Therefore, the high strength steel pipe of the present invention using this high strength steel plate is excellent in the HIC resistance characteristics, and moreover, the variation in the HIC resistance resistance in the circumferential direction of the pipe is suppressed.
- FIG. 1 It is a schematic diagram of the steel plate C cross section explaining the position of the EMPA analysis area in an Example. It is a schematic diagram of the steel plate C cross section explaining the position of the extraction part of the HIC test piece in an Example. It is a figure explaining the secondary cooling method of the slab in continuous casting for manufacturing the high strength steel plate of this embodiment, (A) is a cooling when the cooling water is injected from one two fluid spray nozzle It is a schematic diagram which shows the injection range and water volume density distribution of water, (B) is the injection range, water volume density distribution of the cooling water when the cooling water is injected from two two fluid spray nozzles, and the wrap cost of the injection range FIG.
- C 0.02 to 0.08% C effectively contributes to the improvement of strength, but if the content is less than 0.02%, sufficient strength can not be secured, while if it exceeds 0.08%, the hardness of the surface layer part increases at the time of accelerated cooling Therefore, the HIC resistance is degraded. In addition, the toughness also deteriorates. For this reason, the amount of C is limited to the range of 0.02 to 0.08%.
- Si 0.01 to 0.50% Si is added for deoxidation, but if the content is less than 0.01%, the deoxidizing effect is not sufficient, while if it exceeds 0.50%, the toughness and weldability are degraded, so the amount of Si is 0. 0. It is limited to the range of 01 to 0.50%.
- Mn 0.50 to 1.80% Mn effectively contributes to the improvement of strength and toughness, but if its content is less than 0.50%, its addition effect is scarce, while if it exceeds 1.80%, the hardness of the surface layer increases at the time of accelerated cooling. HIC resistance is degraded. In addition, the weldability also deteriorates. Therefore, the amount of Mn is limited to the range of 0.50 to 1.80%.
- P 0.001 to 0.015%
- P is an unavoidable impurity element and degrades the weldability, and increases the hardness of the central segregation portion to degrade the HIC resistance. Since the tendency becomes remarkable when it exceeds 0.015%, the upper limit is specified as 0.015%. Preferably it is 0.008% or less. The lower the content, the better, but the content is made 0.001% or more from the viewpoint of the refining cost.
- S 0.0002 to 0.0015%
- S is an unavoidable impurity element, and is preferably small because it becomes MnS inclusions and degrades the HIC resistance in steel, but it is acceptable up to 0.0015%.
- Al 0.01 to 0.08% Al is added as a deoxidizing agent, but if less than 0.01%, there is no addition effect, while if it exceeds 0.08%, the cleanliness of the steel is reduced and the toughness is deteriorated. It is limited to the range of 01 to 0.08%.
- Ca 0.0005 to 0.005% Ca is an element effective for improving the HIC resistance by controlling the form of sulfide inclusions, but if it is less than 0.0005%, its addition effect is not sufficient. On the other hand, if it exceeds 0.005%, the effect not only saturates but also the HIC resistance is deteriorated due to the reduction of the cleanliness of the steel, so the amount of Ca is limited to the range of 0.0005 to 0.005% .
- component composition of the present disclosure is one or more selected from Cu, Ni, Cr, and Mo to further improve the strength and toughness of the steel sheet. Can be optionally contained in the following range.
- Cu 0.50% or less Cu is an element effective for improvement of toughness and increase in strength, and it is preferable to contain 0.05% or more to obtain this effect, but if the content is too large, welding is performed In the case of adding Cu, the upper limit is set to 0.50% because the property is deteriorated.
- Ni 0.50% or less
- Ni is an element effective for improvement in toughness and increase in strength, and it is preferable to contain 0.05% or more to obtain this effect, but if the content is too high, the economy Not only disadvantageously, but also the toughness of the weld heat affected zone is deteriorated. Therefore, when adding Ni, the upper limit is made 0.50%.
- Cr 0.50% or less Cr, like Mn, is an element effective to obtain sufficient strength even at low C, and it is preferable to contain 0.05% or more to obtain this effect, If the amount is too large, the weldability deteriorates, so when adding Cr, the upper limit is made 0.50%.
- Mo 0.50% or less Mo is an element effective for improvement in toughness and increase in strength, and it is preferable to contain 0.05% or more to obtain this effect, but if the content is too large, welding is performed In the case where Mo is added, the upper limit is set to 0.50% because the property is deteriorated.
- the component composition of the present disclosure may further optionally contain one or more selected from Nb, V and Ti in the following range.
- Nb 0.005 to 0.1%
- V 0.005 to 0.1%
- Ti 0.005 to 0.1%
- Nb, V and Ti are Both are elements that can be optionally added to enhance the strength and toughness of the steel sheet. If the content of each element is less than 0.005%, the effect of addition is poor, while if it exceeds 0.1%, the toughness of the welded portion is deteriorated. It is preferable to set the range of
- the balance other than the above-described elements consists of Fe and unavoidable impurities. However, as long as the effects of the present invention are not impaired, the content of other trace elements is not hindered.
- [Mn enrichment spot] In the high strength steel plate for a sour line pipe according to the present disclosure, in a cross section perpendicular to the rolling direction (plate length direction) of the steel plate, a length approximating an elliptical shape in a measurement region of ⁇ 5 mm from the thickness center to the plate thickness direction It is important that the number of Mn-concentrated spots exceeding 1.5 mm in axial length be 3 or less per 100 mm in the sheet width direction.
- Mn-concentrated spot means a portion where the Mn concentration is higher than the addition amount (Mn content in the steel sheet) due to segregation, and specifically, the Mn content in the steel sheet is 1 .50% or less, the Mn concentration is specified as a portion of 1.60% or more, and when the Mn content in the steel plate is more than 1.50% and 1.80% or less, the Mn concentration is in the steel plate Is identified as a portion 0.10% or more higher than the Mn content of
- HIC cracks are easily generated from the location of the Mn-concentrated spot having a major axis length of more than 1.5 mm, and It was found that when the number of Mn-concentrated spots exceeding 1.5 mm in axial length is more than 3 per 100 mm in the sheet width direction, HIC cracking occurs. Therefore, in the present disclosure, the number of Mn-concentrated spots exceeding the major axis length of 1.5 mm is 3 or less per 100 mm in the sheet width direction.
- the number of Mn-concentrated spots exceeding the major axis length of 1.5 mm per 100 mm in the sheet width direction is measured by the following method. First, a sample for analysis is cut out from a steel plate and sample preparation is carried out by polishing. At this time, the surface of the sample is made to have a cross section (C cross section) perpendicular to the plate length direction of the steel plate. Then, as shown in FIG.
- the plate width is W, from one end of the steel plate in the plate width direction, the position of W / 4, the position of W / 2, and the position of 3W / 4 (hereinafter referred to as Three points which are the thickness center (t / 2 position; t is the thickness) of the steel plate at “W / 4 position”, “W / 2 position” and “3W / 4 position” simply Mapping of the Mn concentration is carried out with an electron probe microanalyzer (EMPA) for three regions with ⁇ 5 mm (thickness 10 mm) in the thickness direction and ⁇ 200 mm (width 400 mm) in the width direction centering on the center.
- EMPA electron probe microanalyzer
- the above three regions may overlap to become one region.
- the mapping is performed using an electron probe with a diameter of 0.15 mm at an acceleration voltage of 25 kV.
- this EPMA analysis area (10 mm thick ⁇ 400 mm wide), the number of Mn-concentrated spots exceeding the major axis length of 1.5 mm is counted and converted to the number per 100 mm in the sheet width direction.
- the steel structure of the high strength steel plate for a sour line pipe preferably has a bainite structure in order to achieve high strength with a tensile strength of 520 MPa or more.
- the bainite structure includes a structure called bainitic ferrite or granular ferrite which is transformed during or after accelerated cooling which contributes to transformation strengthening. If different structures such as ferrite, martensite, pearlite, island martensite, retained austenite, etc. are mixed in the bainite structure, a decrease in strength, toughness, a rise in surface hardness and the like occur, so that a structure other than the bainite phase The smaller the fraction, the better.
- the HIC resistance is 10% or less in CAR at W / 4 position, W / 2 position, and 3 W / 4 position, and It is important that the variation in the HIC resistance characteristic be 5% or less in 3 ⁇ , where ⁇ is the standard deviation of CAR. This means that the HIC resistance characteristics are excellent and the variation in the HIC resistance characteristics in the sheet width direction is suppressed.
- the HIC resistant properties of the W / 4 position, W / 2 position and 3 W / 4 position are preferably less than 5% in CAR.
- HIC resistance characteristics at W / 4 position, W / 2 position, and 3 W / 4 position are evaluated by the following method. As shown in FIG. 2, in the C cross section of the steel plate, thickness 20 mm ⁇ width centering on the thickness center (3 points in total) in the sheet width direction at W / 4 position, W / 2 position, and 3 W / 4 position. Take test pieces of dimensions 20 mm. Three samples are taken from each of the three test pieces thus obtained, and HIC (hydrogen induced cracking) characteristic examination is performed on a total of nine samples.
- the method is performed in a method A environment, and a crack generation area ratio (CAR) is determined as a hydrogen induced crack determination criterion.
- CAR crack generation area ratio
- the nine CARs thus obtained are all 10% or less, preferably 5% or less.
- the high-strength steel plate of the present disclosure is a steel plate for steel pipe having a strength of X60 grade or more of API 5L, and thus has a tensile strength of 520 MPa or more.
- the manufacturing method of the present disclosure continuously casts a steel having the above-described component composition into slabs, heats the slab, hot rolling it into steel sheets, and then performing controlled cooling on the steel sheets. .
- secondary cooling in continuous casting is performed under specific conditions, and slab heating and controlled cooling are performed under specific conditions, so that the HIC resistance is excellent and the variation in the HIC resistance in the sheet width direction is suppressed. It is possible to manufacture a high strength steel plate for sour line pipes.
- cooling water is sprayed in a mist form from a plurality of two-fluid spray nozzles 10A and 10B disposed at predetermined intervals in the width direction of the slab 20, and the slab 20 is formed.
- the position where the ratio to the water density immediately below the two-fluid spray nozzle 10 is 50% is the cooling water in the width direction of the slab 20 Using a distance S (mm) from both ends of the injection range of the above, and a wrap amount of the injection range of the cooling water injected from the adjacent two-fluid spray nozzles 10A and 10B is 1.6S or more and 2.4S or less.
- the secondary cooling method of the cast slab characterized by having a range is used.
- FIG. 3 schematically illustrates the injection range and the water density distribution of the cooling water jetted from the two-fluid spray nozzle, and in FIG. 3A, the water amount relative to the water density directly below the two-fluid spray nozzle 10 The distance S from both ends of the injection range where the density ratio is 50% is shown, and in FIG. 3 (B), the wrap amount of the injection range of the cooling water injected from the two dual fluid spray nozzles 10A and 10B is shown. It is shown.
- Distance S from the both ends of the injection range of the cooling water injected from two fluid spray nozzle 10 can be calculated by the following method. First, the water density distribution in the width direction of the slab of the cooling water jetted from the two-fluid spray nozzle 10 is measured. In the water volume density distribution, the two-fluid spray nozzle 10 is disposed above the metering weir groups divided in multiples in the width direction of the slab 1 and the cooling water jetted from the two-fluid spray nozzle 10 is metered for each weighing weir It can be measured by
- the reason why the wrap cost is in the range of 1.6S to 2.4S is as follows. That is, in the case of arranging a plurality of two-fluid spray nozzles and performing secondary cooling of the slab, even if the water density of the cooling water injected from each two-fluid spray nozzle is uniform over the width direction of the slab Even if this is the case, since the collision pressure is low at both ends of the injection range of the cooling water, the cooling capacity of the slab is low, and the slab can not be uniformly cooled in the width direction. However, if the lap cost is in the range of 1.6 S or more and 2.4 S or less, in addition to the water density distribution in the width direction of the slab, the slab is uniformly cooled in the width direction, considering also the collision pressure distribution.
- mist nozzle provided with the supply pipe of cooling water and air, mixing piping, and a nozzle tip can be used, for example, it is not limited to this.
- slab heating temperature 1000 to 1300 ° C If the slab heating temperature is less than 1000 ° C., the solid solution of carbides is insufficient and the necessary strength can not be obtained. On the other hand, if the slab heating temperature exceeds 1300 ° C., the toughness is deteriorated, so the slab heating temperature is set to 1000 to 1300 ° C. This temperature is the temperature in the furnace of the heating furnace, and the slab is heated to this temperature to the center.
- Ar 3 (° C.) 910-310 [% C] -80 [% Mn] -20 [% Cu] -15 [% Cr] -55 [% Ni] -80 [% Mo]
- [% X] indicates the content (mass%) of the element X in steel.
- Cooling start temperature steel plate surface temperature (Ar 3 -10 ° C) or more
- the amount of ferrite formation before controlled cooling increases, especially the temperature drop from the Ar 3 transformation point is 10 If it exceeds ° C, ferrite exceeding 5% in volume fraction will be generated, and the strength reduction will increase and the HIC resistance will deteriorate, so the steel sheet surface temperature at the start of cooling should be (Ar 3 -10 ° C) or higher .
- Cooling stop temperature 250 to 550 ° C at steel plate average temperature
- the bainite phase is generated by quenching to a temperature range of 250 to 550 ° C. which is a temperature range of bainite transformation by controlled cooling.
- the cooling stop temperature exceeds 550 ° C.
- bainite transformation is incomplete and sufficient strength can not be obtained.
- the cooling stop temperature is less than 250 ° C.
- the hardness increase of the surface layer portion becomes remarkable.
- it is 350 to 500 ° C.
- steel plate average temperature can not be measured directly physically, based on the surface temperature at the start of cooling measured by a radiation thermometer and the surface temperature at the time of target cooling stop, for example, a process computer
- the temperature distribution in the plate thickness section can be determined in real time by difference calculation. Let the average value of the temperature of the plate thickness direction in the said temperature distribution be "steel plate average temperature" in this specification.
- High-strength steel pipe The high-strength steel plate of the present disclosure is formed into a tubular shape by press bending, roll forming, UOE forming and the like, and then the butted portion is welded to achieve excellent material uniformity in the steel plate suitable for transporting crude oil and natural gas.
- the high strength steel pipe (UOE steel pipe, ERW steel pipe, spiral steel pipe, etc.) for the sour line pipe can be manufactured.
- UOE steel pipe is edge-processed at the end of steel plate and formed into a steel pipe shape by C press, U press, O press, then seam welded the butt portion by inner surface welding and outer surface welding, and further as required Manufactured through an expansion process.
- the welding method may be any method as long as sufficient joint strength and joint toughness can be obtained, but it is preferable to use submerged arc welding from the viewpoint of excellent welding quality and manufacturing efficiency.
- the steels (Steels A to M) having the component compositions shown in Table 1 were made into slabs having a slab width of 1600 mm by a continuous casting method.
- the wrap amount of the injection range of the cooling water sprayed in the form of mist from the three two-fluid spray nozzles arranged at predetermined intervals in the width direction was secondarily cooled as a value shown in Table 2.
- the slab thus obtained was heated to a temperature shown in Table 2, and then hot rolled at a rolling end temperature and a rolling reduction shown in Table 2 to obtain a steel plate having a thickness shown in Table 2. Thereafter, the steel plate was subjected to controlled cooling using a water-cooled controlled cooling device under the conditions shown in Table 2.
- Examples 1 to 13 are invention examples, and the component composition is in the range of the present invention, and the production method is within the range of suitable conditions for obtaining the steel plate of the present invention.
- the yield strength is 450 MPa or more
- the tensile strength is 520 MPa or more
- the 85% SATT in the DWTT test is -50 ° C. or less
- the variation in the widthwise direction of the HIC resistance is small.
- no. 14 to 22 are comparative examples, and the component composition is within the scope of the present invention, but the production method is outside the range of the suitable conditions for obtaining the steel sheet of the present invention.
- the slab heating temperature was low, and the homogenization of the microstructure and the solid solution of the carbide were insufficient, and the strength was low.
- the cooling start temperature was low, and ferrite was precipitated too much, so the strength was low and the HIC resistance was inferior.
- No. 16 and No. No. 18 had low strength and poor HIC resistance characteristics because pearlite precipitated too much at the center of the plate thickness as a microstructure when the controlled cooling conditions were outside the range of preferable conditions. No. No. No.
- the high strength steel plate for the sour line pipe of the present invention is excellent in the HIC resistance characteristic, and further, the variation in the HIC resistance characteristic in the sheet width direction is suppressed. Therefore, a steel pipe (an ERW steel pipe, a spiral steel pipe, a UOE steel pipe, etc.) manufactured by cold-forming this steel sheet can be suitably used for transportation of crude oil and natural gas containing hydrogen sulfide requiring sour resistance. .
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Abstract
Description
[1]質量%で、C:0.02~0.08%、Si:0.01~0.50%、Mn:0.50~1.80%、P:0.001~0.015%、S:0.0002~0.0015%、Al:0.01~0.08%およびCa:0.0005~0.005%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
鋼板の圧延方向に垂直な断面において、板厚中心から板厚方向に±5mmの測定領域に、楕円形状と近似した長軸長さ1.5mm超えのMn濃化スポットの数が、板幅方向の長さ100mm当たりに3個以下であり、
板幅をWとして、鋼板の板幅方向の片端から、W/4の位置、W/2の位置、および3W/4の位置において、耐HIC特性がCARで10%以下であり、
板幅方向の耐HIC特性のばらつきが、CARの標準偏差をσとしたときに3σで5%以下であり、
520MPa以上の引張強さを有する
ことを特徴とする耐サワーラインパイプ用高強度鋼板。
まず、本開示による高強度鋼板の成分組成とその限定理由について説明する。以下の説明において%で示す単位は全て質量%である。
Cは、強度の向上に有効に寄与するが、含有量が0.02%未満では十分な強度が確保できず、一方0.08%を超えると、加速冷却時に表層部の硬さが上昇するため、耐HIC特性が劣化する。また、靭性も劣化する。このため、C量は0.02~0.08%の範囲に限定する。
Siは、脱酸のため添加するが、含有量が0.01%未満では脱酸効果が十分でなく、一方0.50%を超えると靭性や溶接性を劣化させるため、Si量は0.01~0.50%の範囲に限定する。
Mnは、強度、靭性の向上に有効に寄与するが、含有量が0.50%未満ではその添加効果に乏しく、一方1.80%を超えると加速冷却時に表層部の硬さが上昇するため、耐HIC特性が劣化する。また、溶接性も劣化する。このため、Mn量は0.50~1.80%の範囲に限定する。
Pは、不可避不純物元素であり、溶接性を劣化させるとともに、中心偏析部の硬さを上昇させることで耐HIC性を劣化させる。0.015%を超えるとその傾向が顕著となるため、上限を0.015%に規定する。好ましくは0.008%以下である。含有量は低いほどよいが、精錬コストの観点から0.001%以上とする。
Sは、不可避不純物元素であり、鋼中においてはMnS介在物となり耐HIC性を劣化させるため少ないことが好ましいが、0.0015%までは許容される。含有量は低いほどよいが、精錬コストの観点から0.0002%以上とする。
Alは、脱酸剤として添加するが、0.01%未満では添加効果がなく、一方、0.08%を超えると鋼の清浄度が低下し、靱性が劣化するため、Al量は0.01~0.08%の範囲に限定する。
Caは、硫化物系介在物の形態制御による耐HIC特性向上に有効な元素であるが、0.0005%未満ではその添加効果が十分でない。一方、0.005%を超えた場合、効果が飽和するだけでなく、鋼の清浄度の低下により耐HIC特性を劣化させるので、Ca量は0.0005~0.005%の範囲に限定する。
Cuは、靭性の改善と強度の上昇に有効な元素であり、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると溶接性が劣化するため、Cuを添加する場合は0.50%を上限とする。
Niは、靭性の改善と強度の上昇に有効な元素であり、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると経済的に不利なだけでなく、溶接熱影響部の靱性が劣化するため、Niを添加する場合は0.50%を上限とする。
Crは、Mnと同様、低Cでも十分な強度を得るために有効な元素であり、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると溶接性が劣化するため、Crを添加する場合は0.50%を上限とする。
Moは、靭性の改善と強度の上昇に有効な元素であり、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると溶接性が劣化するため、Moを添加する場合は0.50%を上限とする。
Nb,VおよびTiはいずれも、鋼板の強度および靭性を高めるために任意に添加することができる元素である。各元素とも、含有量が0.005%未満ではその添加効果に乏しく、一方0.1%を超えると溶接部の靭性が劣化するので、添加する場合はいずれも0.005~0.1%の範囲とするのが好ましい。
本開示の耐サワーラインパイプ用高強度鋼板においては、鋼板の圧延方向(板長方向)に垂直な断面において、板厚中心から板厚方向に±5mmの測定領域に、楕円形状と近似した長軸長さ1.5mm超えのMn濃化スポットの数が、板幅方向の長さ100mm当たりに3個以下であることが肝要である。
本開示の耐サワーラインパイプ用高強度鋼板においては、W/4位置、W/2位置、および3W/4位置において、耐HIC特性がCARで10%以下であること、並びに、板幅方向の耐HIC特性のばらつきが、CARの標準偏差をσとしたときに3σで5%以下であることが肝要である。これは、耐HIC特性に優れ、しかも板幅方向における耐HIC特性のばらつきが抑制されていることを意味する。W/4位置、W/2位置、および3W/4位置の耐HIC特性は、好ましくはCARで5%以下である。
本開示の高強度鋼板は、API 5LのX60グレード以上の強度を有する鋼管用の鋼板であるので、520MPa以上の引張強さを有するものとする。
以下、上記耐サワーラインパイプ用高強度鋼板を製造するための製造方法および製造条件について、具体的に説明する。本開示の製造方法は、上記成分組成を有する鋼を連続鋳造して鋳片(スラブ)とし、このスラブの加熱したのち、熱間圧延して鋼板とし、その後当該鋼板に対して制御冷却を行う。このとき、連続鋳造における2次冷却を特定の条件で行い、かつ、スラブ加熱および制御冷却を特定の条件で行うことにより、耐HIC特性に優れ、しかも板幅方向における耐HIC特性のばらつきを抑制した耐サワーラインパイプ用高強度鋼板を製造することができる。
図3(A),(B)に示すように、鋳片20の幅方向に所定の間隔で配置した複数の二流体スプレーノズル10A,10Bから冷却水をミスト状に噴射し、鋳片20をその長手方向に送りながら冷却する方法であって、二流体スプレーノズル10として、二流体スプレーノズル10直下の水量密度に対する比率が50%となる位置が、前記鋳片20の幅方向における前記冷却水の噴射範囲の両端から距離S(mm)であるものを用い、かつ隣り合う二流体スプレーノズル10A,10Bから噴射される前記冷却水の噴射範囲のラップ代が1.6S以上2.4S以下の範囲となるようにすることを特徴とする鋳片の2次冷却方法を用いる。
スラブ加熱温度:1000~1300℃
スラブ加熱温度が1000℃未満では、炭化物の固溶が不十分で必要な強度が得られず、一方1300℃を超えると靭性が劣化するため、スラブ加熱温度は1000~1300℃とする。なお、この温度は加熱炉の炉内温度であり、スラブは中心部までこの温度に加熱されるものとする。
熱間圧延工程において、高い母材靱性を得るには、圧延終了温度は低いほどよいが、その反面、圧延能率が低下するため、鋼板表面温度における圧延終了温度は、必要な母材靱性と圧延能率を勘案して設定する必要がある。強度および耐HIC特性を向上させる観点からは、圧延終了温度を、鋼板表面温度でAr3変態点以上とすることが好ましい。ここで、Ar3変態点とは、冷却中におけるフェライト変態開始温度を意味し、例えば、鋼の成分から以下の式で求めることができる。また、高い母材靱性を得るためにはオーステナイト未再結晶温度域に相当する950℃以下の温度域での圧下率を60%以上とすることが望ましい。なお、鋼板の表面温度は放射温度計等で測定することができる。
Ar3(℃)=910-310[%C]-80[%Mn]-20[%Cu]-15[%Cr]-55[%Ni]-80[%Mo]
ただし、[%X]はX元素の鋼中含有量(質量%)を示す。
冷却開始温度:鋼板表面温度で(Ar3-10℃)以上
冷却開始時の鋼板表面温度が低いと、制御冷却前のフェライト生成量が多くなり、特にAr3変態点からの温度降下量が10℃を超えると体積分率で5%を超えるフェライトが生成して、強度低下が大きくなると共に耐HIC特性が劣化するため、冷却開始時の鋼板表面温度は(Ar3-10℃)以上とする。
鋼板平均温度で750℃から550℃までの平均冷却速度:15℃/s以上
鋼板平均温度で750℃から550℃までの平均冷却速度が15℃/s未満では、ベイナイト組織が得られずに強度低下や耐HIC特性の劣化が生じる。このため、鋼板平均温度での冷却速度は15℃/s以上とする。鋼板強度と硬さのばらつきの観点からは、鋼板平均の冷却速度は20℃/s以上とすることが好ましい。当該平均冷却速度の上限は特に限定されないが、低温変態生成物が過剰に生成しないように、80℃/s以下とすることが好ましい。
冷却停止温度:鋼板平均温度で250~550℃
圧延終了後、制御冷却でベイナイト変態の温度域である250~550℃まで急冷することにより、ベイナイト相を生成させる。冷却停止温度が550℃を超えると、ベイナイト変態が不完全であり、十分な強度が得られない。また、冷却停止温度が250℃未満では、表層部の硬さ上昇が著しくなる。好ましくは、350~500℃である。
本開示の高強度鋼板を、プレスベンド成形、ロール成形、UOE成形等で管状に成形した後、突き合わせ部を溶接することにより、原油や天然ガスの輸送に好適な鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼管(UOE鋼管、電縫鋼管、スパイラル鋼管等)を製造することができる。
得られた鋼板のミクロ組織を、光学顕微鏡および走査型電子顕微鏡により観察した。鋼板の板厚中央(t/2位置)での組織を、表3に示す。
各水準において得られた鋼板から圧延直角方向の全厚試験片(API5L規格)を採取して、これを引張試験片として引張試験を行い、降伏強度(0.5%耐力)および引張強度を測定した。降伏強度450MPa以上、引張強度520MPa以上が目標範囲である。結果を表3に示す。
既述の方法で、W/4位置、W/2位置、および3W/4位置から各々3個のサンプルを採取し、CARを測定した。こうして得た9個の測定値のうちの最大値を表3の「耐HIC特性」の欄に示す。また、9個のCARの標準偏差をσとして求めたときの3σも表3に示す。最大値は10%以下、3σは5%以下が目標範囲である。
既述の方法で板幅方向の長さ100mm当たりの、長軸長さ1.5mm超えのMn濃化スポットの数を測定した。3個以下が目標範囲である。結果を表3に示す。
各水準において得られた鋼板からAPI-5Lに準拠したDWTT試験片を採取し、0~-80℃の試験温度で試験を行い、SA値(Shear Area:延性破面率)が85%となる遷移温度を求めた。遷移温度は-50℃以下が目標範囲である。結果を表3に示す。
No.15は、冷却開始温度が低く、フェライトが析出しすぎたため、低強度であり、且つ耐HIC特性が劣っていた。
No.16およびNo.18は、制御冷却条件が好適な条件の範囲外で、ミクロ組織として板厚中心部でパーライトが析出しすぎたため、低強度であり、且つ耐HIC特性が劣っていた。
No.17は、冷却停止温度が低く、マルテンサイトや島状マルテンサイト(MA)の硬質相が生成したため、DWTT特性と耐HIC特性が劣っていた。
No.19~No.22は、いずれもスラブ段階の2次冷却条件が好適な条件の範囲外で、中心偏析部のMn濃化が多く、鋼板板幅方向の耐HIC特性ばらつきが大きく、HIC特性が劣っていた。
No.23~No.27は、成分組成が本発明の範囲外であり、中心偏析部のMn濃化が多く、鋼板板幅方向のHIC特性ばらつきが大きく、HIC特性が劣っていた。
20 鋳片
Claims (4)
- 質量%で、C:0.02~0.08%、Si:0.01~0.50%、Mn:0.50~1.80%、P:0.001~0.015%、S:0.0002~0.0015%、Al:0.01~0.08%およびCa:0.0005~0.005%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
鋼板の圧延方向に垂直な断面において、板厚中心から板厚方向に±5mmの測定領域に、楕円形状と近似した長軸長さ1.5mm超えのMn濃化スポットの数が、板幅方向の長さ100mm当たりに3個以下であり、
板幅をWとして、鋼板の板幅方向の片端から、W/4の位置、W/2の位置、および3W/4の位置において、耐HIC特性がCARで10%以下であり、
板幅方向の耐HIC特性のばらつきが、CARの標準偏差をσとしたときに3σで5%以下であり、
520MPa以上の引張強さを有する
ことを特徴とする耐サワーラインパイプ用高強度鋼板。 - 前記成分組成が、さらに、質量%で、Cu:0.50%以下、Ni:0.50%以下、Cr:0.50%以下およびMo:0.50%以下のうちから選んだ1種又は2種以上を含有する、請求項1に記載の耐サワーラインパイプ用高強度鋼板。
- 前記成分組成が、さらに、質量%で、Nb:0.005~0.1%、V:0.005~0.1%、およびTi:0.005~0.1%のうちから選んだ1種又は2種以上を含有する、請求項1または2に記載の耐サワーラインパイプ用高強度鋼板。
- 請求項1~3のいずれか一項に記載の耐サワーラインパイプ用高強度鋼板を用いた高強度鋼管。
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- 2017-10-19 BR BR112020007057-2A patent/BR112020007057B1/pt active IP Right Grant
- 2017-10-19 KR KR1020207011797A patent/KR102497363B1/ko active IP Right Grant
- 2017-10-19 EP EP17929314.7A patent/EP3674433A4/en active Pending
- 2017-10-19 WO PCT/JP2017/037891 patent/WO2019077725A1/ja unknown
- 2017-10-19 JP JP2018564993A patent/JP6798565B2/ja active Active
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Also Published As
Publication number | Publication date |
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BR112020007057A2 (pt) | 2020-10-06 |
KR20200058490A (ko) | 2020-05-27 |
EP3674433A1 (en) | 2020-07-01 |
KR102497363B1 (ko) | 2023-02-08 |
JP6798565B2 (ja) | 2020-12-09 |
CN111247261A (zh) | 2020-06-05 |
JPWO2019077725A1 (ja) | 2019-11-14 |
EP3674433A4 (en) | 2020-07-29 |
BR112020007057B1 (pt) | 2022-07-12 |
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