A high-toughness S420KT-50 extra-thick steel plate for marine oil and gas platforms with full cross-section and its manufacturing method.

Abstract

This invention discloses a full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms and its manufacturing method, belonging to the field of iron and steel metallurgical production technology. The chemical composition of the steel plate, by mass percentage, is: C: 0.025–0.065%, Si: 0.10–0.40%, Mn: 1.35–1.60%, P≤0.012%, S≤0.003%, Nb: 0.025–0.040%, Ni: 0.20–0.50%, N≤60ppm, H≤2ppm, As≤0.030%, S… The composition is as follows: b≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, with the balance being Fe and unavoidable impurity elements. The sum of all the above components is 100%. A manufacturing method is also designed. This manufacturing method, through low-C design and low-temperature heating + low-temperature rolling technology, achieves an impact toughness of ≥150J, yield strength ≥420MPa, tensile strength: 500~690MPa, and elongation ≥19% at -50℃ for the entire cross-section of the steel plate near the surface and 1 / 2 of the plate thickness.

Description

Technical Field

[0001] This invention relates to an extra-thick steel plate and its manufacturing method, specifically to an S420KT-50 extra-thick steel plate with high toughness across the entire cross section for offshore oil and gas platforms and its manufacturing method, belonging to the field of iron and steel metallurgical production technology. Background Technology

[0002] With the continuous development of global marine resources, the use of marine engineering steel plates for oil and gas platforms, wind power piles, and substations has rapidly developed. Currently, major steel companies produce S420 grade steel plates with a thickness of 60-120mm using TMCP. As marine engineering projects gradually move towards deep-water, low-temperature areas, higher requirements are being placed on the thickness and low-temperature toughness of marine engineering steel.

[0003] Currently, patent CN103695769B describes a high-strength FH40 marine engineering steel plate and its production method, employing processes such as converter smelting (C: 0.12-0.15%), LF refining, VD vacuum refining, slow cooling of the cast billet, casting, heating of the cast billet, rolling, and normalizing heat treatment. However, the normalizing heat treatment increases the production cycle, and the thickness is only 60-100mm, which cannot meet the requirements for thicknesses above 100mm. Patent CN114032466B describes an extra-thick marine engineering steel and its preparation method, employing processes such as normalizing or quenching + tempering heat treatment (C: 0.10-0.18%). However, the heat treatment also increases the production cycle, and the thickness is only 60-100mm. The 100mm thickness cannot meet the requirements for thicknesses greater than 100mm, and the yield strength ≥355MPa cannot meet the requirement of a yield strength ≥420MPa; furthermore, the impact temperature is -40℃, which cannot meet the requirement of -50℃. Patent CN112458355A describes an EW460 extra-thick marine engineering steel plate and its manufacturing method, with a composition containing V: 0.020~0.040% and Cu: 0.25~0.35%, but its cost is relatively high, and the maximum thickness is only 100mm, which cannot meet the requirements for thicknesses greater than 100mm. The above existing technologies mainly target thicknesses ≤100mm and do not cover specifications with thicknesses greater than 100mm.

[0004] Therefore, the development of a 100-120mm thick, full-section, high-toughness S420KT-50 extra-thick steel plate for marine oil and gas platforms and its manufacturing method has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention addresses the aforementioned technical problems and overcomes the shortcomings of existing technologies by providing a full-section high-toughness S420KT-50 extra-thick steel plate for marine oil and gas platforms and its manufacturing method. This manufacturing method, through low-C design and low-temperature heating + low-temperature rolling technology, achieves a full-section impact toughness of ≥150J at -50℃ near the surface and half the plate thickness, yield strength ≥420MPa, tensile strength: 500~690MPa, elongation ≥19%, and the thickness of the manufactured steel plate is greater than 100mm and does not exceed 120mm.

[0006] To address the above technical problems, this invention provides a full-section high-toughness S420KT-50 extra-thick steel plate for marine oil and gas platforms. The chemical composition of this steel plate, by mass percentage, is: C: 0.025–0.065%, Si: 0.10–0.40%, Mn: 1.35–1.60%, P≤0.012%, S≤0.003%, Nb: 0.025–0.040%, Ni: 0.20–0.50%, excluding Mo, N≤60ppm, H≤2ppm, As≤0.030%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, with the balance being Fe and unavoidable impurities. The sum of all components is 100%.

[0007] The technical solution further defined in this invention is:

[0008] Furthermore, in the aforementioned S420KT-50 extra-thick steel plate for high-toughness marine oil and gas platforms across the entire cross-section, the chemical composition of the steel plate, by mass percentage, is: C: 0.035%, Si: 0.25%, Mn: 1.58%, P: 0.010%, S: 0.001%, Nb: 0.035%, Ni: 0.42%, N≤60ppm, H≤2ppm, As≤0.030%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, with the balance being Fe and unavoidable impurity elements, and the sum of all the above components is 100%.

[0009] The aforementioned S420KT-50 extra-thick steel plate for high-toughness marine oil and gas platforms has the following chemical composition by mass percentage: C: 0.055%, Si: 0.30%, Mn: 1.4%, P: 0.012%, S: 0.002%, Nb: 0.030%, Ni: 0.35%, N≤60ppm, H≤2ppm, As≤0.03%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, with the balance being Fe and unavoidable impurity elements. The sum of all the above components is 100%.

[0010] In the aforementioned S420KT-50 extra-thick steel plate for high-toughness marine oil and gas platforms with full cross-section, the thickness of the steel plate is greater than 100mm but not more than 120mm.

[0011] This invention also designs a method for manufacturing S420KT-50 extra-thick steel plates with high toughness across the entire cross-section for offshore oil and gas platforms. The manufacturing process includes converter smelting, refining, continuous casting, billet heating, rolling, and cooling, wherein:

[0012] (1) Heating process: 370mm cross section billet is used, the billet heating temperature is 1060~1150℃, and the heating time is 400~460min;

[0013] (2) Rolling process: The initial rolling temperature of the steel plate in the second stage is 720-780℃, and the water immersion temperature is 720-760℃;

[0014] (3) Cooling process: The red temperature of the steel plate is limited to 300-450℃, and the cooling rate is 5-9℃ / s.

[0015] In the aforementioned manufacturing method of S420KT-50 extra-thick steel plate for full-section high-toughness marine oil and gas platforms, the steel plate produced has a yield strength ≥420MPa, tensile strength 500-690MPa, elongation ≥19%, impact strength at -50℃ ≥150J, yield strength ratio ≤0.89, and aging impact performance with 5% deformation ≥150J.

[0016] The beneficial effects of this invention are:

[0017] The present invention heats the billet to 1060℃~1150℃ to ensure alloy solid solution while avoiding grain coarsening on the billet surface and ensuring relatively uniform grains in the thickness direction of the billet.

[0018] The low-temperature heating process of this invention involves two-stage rolling of the steel plate at a temperature of 720℃~780℃ and immersion in water at a temperature of 720℃~760℃. Through two-stage low-temperature rolling, the deformation of the steel billet penetrates to the core, while forming more distortion zones, providing more nucleation points for microstructure transformation.

[0019] This invention features a controlled cooling process: the steel plate's red-hot temperature is limited to 300–450°C, and the cooling rate is 5–9°C / s. This appropriate cooling rate avoids the formation of martensitic hard structures on the surface while achieving uniform microstructure across the entire cross-section of the steel plate. This invention provides a method for manufacturing S420KT-50 extra-thick steel plates for marine oil and gas platforms with high toughness across the entire cross-section. Through low-carbon composition design, low-temperature heating, low-temperature controlled rolling, and controlled cooling processes, the steel plate achieves uniform microstructure and good low-temperature toughness across its entire cross-section, meeting the requirements for extra-thick marine engineering steel in low-temperature sea areas. Attached Figure Description

[0020] Figure 1 This is a metallographic image of the near-surface area of ​​the steel plate in Embodiment 2 of the present invention;

[0021] Figure 2 This is a metallographic diagram of the steel plate at 1 / 4 thickness in Embodiment 2 of the present invention;

[0022] Figure 3 This is a metallographic diagram of the steel plate at 1 / 2 thickness in Embodiment 2 of the present invention. Detailed Implementation

[0023] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates an S420KT-50 extra-thick steel plate with high toughness across the entire cross section for marine oil and gas platforms and its manufacturing method. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention. Example 1

[0024] This embodiment provides an S420KT-50 extra-thick steel plate with high toughness across the entire cross section for use on marine oil and gas platforms. The chemical composition of the steel plate by mass percentage is shown in Table 1.

[0025] In this embodiment, LF and RH refining technologies are used during smelting to ensure that the steel plate composition meets the characteristic requirements, while ensuring that the gas H content of the steel plate is ≤2ppm and the N content is ≤60ppm.

[0026] This embodiment also provides a method for manufacturing the aforementioned full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms. The manufacturing process includes converter smelting, refining, continuous casting, billet heating, rolling, and cooling, wherein:

[0027] (1) Heating process: 370mm cross section billet is used, the billet heating temperature is 1100~1140℃, and the heating time is 400min;

[0028] (2) Rolling process: The initial rolling temperature of the steel plate in the second stage is 760-780℃, and the water immersion temperature is 740-760℃;

[0029] (3) Cooling process: The temperature of the steel plate is limited to 420-450℃ and the cooling rate is 8℃ / s.

[0030] The mechanical properties of the 110mm thick S420KT-50 extra-thick steel plate for offshore oil and gas platforms manufactured in this embodiment are shown in Table 2. Example 2

[0031] This embodiment provides an S420KT-50 extra-thick steel plate with high toughness across the entire cross section for marine oil and gas platforms. The thickness is 120mm. The chemical composition of the steel plate by mass percentage is shown in Table 1.

[0032] In this embodiment, LF and RH refining technologies are used during smelting to ensure that the gas H content of the steel plate is ≤2ppm and the N content is ≤60ppm.

[0033] This embodiment provides a method for manufacturing the aforementioned high-toughness S420KT-50 extra-thick steel plate for marine oil and gas platforms. The manufacturing process includes converter smelting, refining, continuous casting, billet heating, rolling, and cooling, wherein:

[0034] (1) Heating process: Use 460mm cross section casting billet, billet heating temperature 1080~1120℃, heating time 460min;

[0035] (2) Rolling process: The initial rolling temperature of the steel plate in the second stage is 730-750℃, and the water immersion temperature is 720-740℃;

[0036] (3) Cooling process: The red temperature of the steel plate is limited to 300-330℃, and the cooling rate is 5℃ / s.

[0037] The mechanical properties of the 120mm thick S420KT-50 extra-thick steel plate for offshore oil and gas platforms obtained in this implementation are shown in Table 2.

[0038] Table 1 Chemical composition of steel plates from Examples 1-2 (wt%)

[0039]

[0040] In Table 1, the following values ​​are specified: As ≤ 0.030%, Sb ≤ 0.010%, Sn ≤ 0.020%, Pb ≤ 0.010%, Bi ≤ 0.010%, Ca ≤ 0.0050%, and B ≤ 0.0005%.

[0041] Table 2 Mechanical property data of steel plates in Examples 1-2

[0042]

[0043] As shown in Table 2, a production method for S420KT-50 extra-thick steel plates with a thickness of >100-120mm is proposed. Through low-C design and low-temperature heating + low-temperature rolling technology, the steel plate achieves an impact toughness of ≥150J, yield strength of ≥420MPa, tensile strength of 500-690MPa, and elongation of ≥19% at -50℃ across the entire cross-section near the surface and half the plate thickness. This allows for increased thickness while ensuring performance through TMCP rolling technology, meeting the requirements for thicknesses above 100mm. This method is of great significance for the gradual development of marine engineering projects towards deep-water, low-temperature sea areas.

[0044] Microstructure images of the near-surface, 1 / 4 thickness, and 1 / 2 thickness of the produced extra-thick steel plate are shown below. Figure 1-3 As shown, the near-surface microstructure of the steel plate is bainite + a small amount of ferrite, with a grain size of grade 10; the microstructure at 1 / 4 of the plate thickness is bainite + ferrite, with a grain size of grade 9; and the microstructure at 1 / 2 of the plate thickness is ferrite + bainite, with a grain size of grade 10. The grain size is uniform and fine throughout the thickness direction, and the microstructure difference is small, which ensures the stability of tensile and impact properties.

[0045] This invention relates to an S420KT-50 extra-thick steel plate with high toughness across the entire cross section for offshore oil and gas platforms and its manufacturing method. Its main purpose is to improve the purity of the steel through ultra-low carbon composition design, and to achieve uniform control of the microstructure of the entire cross section of the 100-120mm thick S420KT-50 extra-thick plate through low-temperature heating and low-temperature high-reduction rolling technology, thereby improving the low-temperature toughness of the steel plate in an environment of -50℃.

[0046] With the global energy green transformation, the construction of offshore wind power pipe piles, booster stations, offshore floating platforms, and offshore oil and gas platforms is increasing, leading to a growing demand for ultra-thick and high-toughness marine engineering steel. The development of this type of steel has significant economic value and practical significance.

[0047] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for manufacturing a full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, characterized in that: The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.055%, Si: 0.30%, Mn: 1.40%, P: 0.012%, S: 0.002%, Nb: 0.030%, Ni: 0.35%, N: 0.0050%, H: 0.00015%, As≤0.030%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, with the balance being Fe and unavoidable impurities. The sum of all the above components is 100%. The manufacturing method of S420KT-50 extra-thick steel plates for this full-section high-toughness offshore oil and gas platform involves converter smelting, refining, continuous casting, billet heating, rolling, and cooling, among which: (1) Heating process: 370mm cross section billet is used, the billet heating temperature is 1100~1140℃, and the heating time is 400min; (2) Rolling process: The initial rolling temperature of the steel plate in the second stage is 760-780℃, and the water immersion temperature is 740-760℃; (3) Cooling process: The red-hot temperature of the steel plate is limited to 420-450℃, and the cooling rate is 8℃ / s; For manufacturing 110mm thick steel plates, the near-surface properties are: yield strength 459MPa, tensile strength 588MPa, elongation 24.5%, yield-to-tensile ratio 0.78, and impact energy at -50℃ is 315J, 319J, and 317J, with an average of 317J. At 5% deformation, the impact energy at -50℃ is 270J, 200J, and 212J, with an average of 227.3J. At 1 / 4 of the plate thickness, the yield strength is 448MPa, tensile strength 567MPa, elongation 28.5%, yield-to-tensile ratio 0.79, and impact energy at -50℃ is 405J, 297J, and 363J, with an average of 355J. At 1 / 2 of the plate thickness, the yield strength is 439MPa, tensile strength 546MPa, elongation 26.6%, yield-to-tensile ratio 0.80, and impact energy at -50℃ is 394J. 397J, 391J, with an average of 394J.

2. A method for manufacturing a full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, characterized in that: The chemical composition of this steel plate, by mass percentage, is C: 0.035%, Si: 0.25%, Mn: 1.58%, P: 0.010%, S: 0.001%, Nb: 0.035%, Ni: 0.42%, N: 0.0039%, H: 0.00010%, As≤0.030%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, with the balance being Fe and unavoidable impurity elements; the sum of all the above components is 100%. The manufacturing method of S420KT-50 extra-thick steel plates for this full-section high-toughness offshore oil and gas platform involves converter smelting, refining, continuous casting, billet heating, rolling, and cooling, among which: (1) Heating process: Use 460mm cross section casting billet, billet heating temperature 1080~1120℃, heating time 460min; (2) Rolling process: The initial rolling temperature of the steel plate in the second stage is 730-750℃, and the water immersion temperature is 720-740℃; (3) Cooling process: The reddening temperature of the steel plate is limited to 300-330℃, and the cooling rate is 5℃ / s; For manufacturing 120mm thick steel plates, the near-surface properties are: yield strength 484MPa, tensile strength 590MPa, elongation 24.5%, yield-to-tensile ratio 0.82, and impact energy at -50℃ is 332J, 325J, and 324J, with an average of 327J; with 5% deformation, the impact energy at -50℃ is 299J, 201J, and 220J, with an average of 240J. At 1 / 4 of the plate thickness, the yield strength is 440MPa, tensile strength 572MPa, elongation 25.0%, yield-to-tensile ratio 0.78, and impact energy at -50℃ is 312J, 335J, and 328J, with an average of 325J. At 1 / 2 of the plate thickness, the yield strength is 442MPa, tensile strength 543MPa, elongation 26.6%, yield-to-tensile ratio 0.81, and impact energy at -50℃ is 319J. 317J, 351J, with an average of 329J.

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