S420KT-50 extra-thick steel plate with high toughness of total cross section for offshore oil and gas platform and manufacturing method of S420KT-50 extra-thick steel plate

Abstract

The invention discloses a total cross-section high-toughness S420KT-50 extra-thick steel plate for an offshore oil and gas platform and a manufacturing method of the steel plate, and belongs to the technical field of ferrous metallurgy production, the steel plate comprises the following chemical components in percentage by mass: 0.025-0.065% of C, 0.10-0.40% of Si, 1.35-1.60% of Mn, less than or equal to 0.012% of P, less than or equal to 0.003% of S, 0.025-0.040% of Nb, 0.20-0.50% of Ni, less than or equal to 60ppm of N, less than or equal to 2ppm of H, less than or equal to 0.030% of As, less than or equal to 0.010% of Sb, less than or equal to 0.020% of Sn, less than or equal to 0.010% of Pb, less than or According to the manufacturing method, through low-C design and low-temperature heating and low-temperature rolling technologies, the impact toughness at-50 DEG C of the total cross section at the position, close to the surface and 1 / 2 of the plate thickness, of the steel plate is larger than or equal to 150 J, the yield strength is larger than or equal to 420 MPa, the tensile strength ranges from 500 MPa to 690 MPa, and the ductility is larger than or equal to 19%.

Description

Technical Field

[0001] The invention relates to an extra-thick steel plate and a manufacturing method thereof, in particular to an S420KT-50 extra-thick steel plate with high toughness in the entire cross section for use on an offshore oil and gas platform and a manufacturing method thereof, and belongs to the technical field of steel metallurgy production. Background Art

[0002] With the continuous development of global marine resources, offshore engineering steel plates such as oil and gas platforms, wind power piles, and booster stations have developed rapidly. At present, the thickness of S420 produced by TMCP of major steel companies is mainly 60-120mm. Offshore engineering projects are gradually developing towards deep-water low-temperature sea areas, which puts forward higher requirements on the thickness and low-temperature toughness of offshore steel. At present, patent CN103695769B discloses a high-strength FH40 marine engineering steel plate and its production method, which is produced by processes such as C: 0.12-0.15% converter smelting, LF refining, VD vacuum refining, slow cooling of ingot, pouring, heating of ingot, rolling, normalizing heat treatment, etc. However, its normalizing heat treatment increases the production cycle, and the thickness is only 60-100mm, which cannot meet the thickness specification requirements of more than 100mm; patent CN114032466B discloses a super-thick marine engineering steel and its preparation method, which is produced by processes such as C: 0.10-0.18%, normalizing or quenching + tempering heat treatment, etc. However, its heat treatment increases the production cycle, and the thickness is only 60- 100mm, which cannot meet the thickness specification requirements of more than 100mm, and the yield strength is ≥355MPa, which cannot meet the yield strength ≥420MPa requirements; the impact temperature is -40℃, which cannot meet the -50℃ requirements; Patent CN112458355A discloses an EW460 extra-thick marine steel plate and its manufacturing method, which contains V: 0.020-0.040%, Cu: 0.25-0.35%, but its cost is high, and the maximum thickness is only 100mm, which cannot meet the thickness specification requirements of more than 100mm; the above existing technologies are mainly for all thicknesses of ≤100mm, and do not involve specifications with a thickness greater than 100mm; Therefore, developing a 100-120 mm thick full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms and a manufacturing method thereof has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the invention

[0003] In view of the above technical problems, the present invention overcomes the shortcomings of the prior art and provides a S420KT-50 extra-thick steel plate for offshore oil and gas platforms with high toughness in the entire cross-section and a manufacturing method thereof. The manufacturing method achieves the full-section impact toughness of the steel plate near the surface + 1 / 2 of the plate thickness at -50°C ≥150J, the yield strength ≥420MPa, the tensile strength: 500-690MPa, the elongation ≥19% through low C design, low temperature heating + low temperature rolling technology. The thickness of the manufactured steel plate is greater than 100mm and does not exceed 120mm.

[0004] In order to solve the above technical problems, the present invention provides a full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms. The chemical composition of the steel plate 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%, and the remainder is Fe and unavoidable impurity elements, and the sum of the above components is 100%.

[0005] The technical solution further defined in the present invention is: Furthermore, in the aforementioned full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, the chemical composition of the steel plate 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%, and the remainder is Fe and unavoidable impurity elements, and the sum of the above components is 100%.

[0006] In the aforementioned full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, the chemical composition of the steel plate is 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%, and the remainder is Fe and unavoidable impurity elements, and the sum of the above components is 100%.

[0007] In the aforementioned full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, the thickness of the steel plate is greater than 100mm and not more than 120mm.

[0008] The present invention also provides a method for manufacturing a full-section high-toughness S420KT-50 extra-thick steel plate for an offshore oil and gas platform, the manufacturing process of which is converter smelting, refining, continuous casting, billet heating, rolling and cooling, wherein: (1) Heating process: using 370mm cross-section billet, billet heating temperature 1060 ~ 1150 ℃, heating time 400 ~ 460min; (2) Rolling process: The second-stage rolling temperature of the steel plate is 720-780°C, and the water entry temperature is 720-760°C; (3) Cooling process: The steel plate red-return temperature is limited to 300-450°C, and the cooling rate is 5-9°C / s.

[0009] In the manufacturing method of the aforementioned full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, the steel plate obtained has a yield strength ≥420Mpa, a tensile strength of 500-690Mpa, an elongation ≥19%, an impact strength of -50°C ≥150J, a yield strength ratio ≤0.89, and an aging impact performance of 5% deformation ≥150J.

[0010] The beneficial effects of the present invention are: The heating temperature of the steel billet of the present invention is 1060° C. to 1150° C., which ensures the solid solution of the alloy, avoids the coarsening of the grains on the surface of the steel billet, and ensures that the grains in the thickness direction of the steel billet are relatively uniform.

[0011] The low-temperature heating process of the present invention: the temperature of the steel plate in the second-stage rolling is 720°C-780°C, and the water entry is 720°C-760°C. The second-stage low-temperature rolling is used to achieve deformation and penetration of the steel billet into the core, while forming more distortion bands, providing more nucleation points for organizational transformation.

[0012] The controlled cooling process of the present invention: the red-return temperature of the steel plate is limited to 300-450°C, and the cooling rate is 5-9°C / s. Through the appropriate cooling rate, the formation of martensitic hard structure on the surface is avoided, and the uniformity of the structure of the entire cross-section of the steel plate is achieved. The present invention provides a method for manufacturing a S420KT-50 extra-thick steel plate with high toughness in the entire cross-section for an offshore oil and gas platform. Through low C component design, low-temperature heating, low-temperature controlled rolling, and controlled cooling processes, the entire cross-section of the steel plate is uniformly organized, and the low-temperature toughness is good, meeting the demand for extra-thickness marine engineering steel in low-temperature sea areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a metallographic structure diagram of the steel plate near the surface in Example 2 of the present invention; Figure 2 This is the metallographic structure diagram of the steel plate at 1 / 4 thickness in Example 2 of the present invention; Figure 3 This is the metallographic structure diagram of the steel plate at 1 / 2 thickness in Example 2 of the present invention. DETAILED DESCRIPTION

[0014] To make the present invention more clear, the following further describes a full-section high-toughness S420KT-50 extra-thick steel plate for marine oil and gas platforms and its manufacturing method in conjunction with the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0015] This embodiment provides a full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms. The chemical composition of the steel plate is shown in Table 1 in terms of mass percentage.

[0016] In this embodiment, LF and RH refining technologies are used during smelting to ensure that the composition of the steel plate meets the characteristic requirements and that the gas H content of the steel plate is ≤2ppm and the N content is ≤60ppm.

[0017] This embodiment also provides a method for manufacturing the above-mentioned full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, the manufacturing process of which is converter smelting, refining, continuous casting, billet heating, rolling and cooling, wherein: (1) Heating process: 370 mm cross-section billet is used, the billet heating temperature is 1100-1140°C, and the heating time is 400 min; (2) Rolling process: The second-stage rolling temperature of the steel plate is 760-780°C, and the water entry temperature is 740-760°C; (3) Cooling process: The steel plate red-hot temperature is limited to 420-450°C, and the cooling rate is 8°C / s.

[0018] The mechanical properties of the 110 mm thick S420KT-50 extra thick steel plate for offshore oil and gas platforms manufactured in this embodiment are shown in Table 2. Example 2

[0019] This embodiment provides a full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms, with a thickness of 120 mm. The chemical composition of the steel plate is shown in Table 1 in terms of mass percentage.

[0020] 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.

[0021] This embodiment provides a method for manufacturing the above-mentioned S420KT-50 extra-thick steel plate with high toughness in the entire cross section for use in offshore oil and gas platforms. The manufacturing process includes converter smelting, refining, continuous casting, heating of the ingot, rolling and cooling, wherein: (1) Heating process: 460 mm cross-section billet is used, the billet heating temperature is 1080-1120°C, and the heating time is 460 min; (2) Rolling process: The second-stage rolling temperature of the steel plate is 730-750°C, and the water entry temperature is 720-740°C; (3) Cooling process: The steel plate red-return temperature is limited to 300-330°C, and the cooling rate is 5°C / s.

[0022] The mechanical properties of the 120 mm thick S420KT-50 extra thick steel plate for offshore oil and gas platforms obtained in this embodiment are shown in Table 2.

[0023] Table 1 Chemical composition of steel plates of Examples 1-2 (wt%)

[0024] In Table 1, As≤0.030%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%.

[0025] Table 2 Mechanical properties of steel plates of Examples 1-2

[0026] As can be seen from Table 2, a production method of S420KT-50 extra-thick steel plate with an ultra-thickness specification of >100-120mm is proposed. Through low C design, low temperature heating + low temperature rolling technology, the full-section impact toughness of the steel plate near the surface + 1 / 2 of the plate thickness at -50℃ is ≥150J, the yield strength is ≥420MPa, the tensile strength is: 500-690MPa, and the elongation is ≥19%. The thickness is increased while the performance is guaranteed through the TMCP rolling process to meet the thickness requirement of more than 100mm, which is of great significance for the gradual development of marine engineering projects towards deep-water low-temperature sea areas.

[0027] The microstructure images of the produced extra-thick steel plate near the surface, 1 / 4 thickness, and 1 / 2 thickness are shown as follows: Figure 1-3 As shown, the near-surface structure of the steel plate is bainite + a small amount of ferrite, with a grain size of level 10; the structure at 1 / 4 of the plate thickness is bainite + ferrite, with a grain size of level 9; the structure at 1 / 2 of the plate thickness is ferrite + bainite, with a grain size of level 10. The grain size is uniform and small in the entire thickness direction, and the organizational difference is small, which ensures the stability of tensile and impact properties.

[0028] The present invention relates to a S420KT-50 extra-thick steel plate for an offshore oil and gas platform with high toughness in the entire cross section and a manufacturing method thereof. The main purpose is to improve the purity of the steel through an ultra-low carbon component design, and to achieve the structural homogenization control of the entire cross section of the 100-120 mm thick S420KT-50 extra-thick plate through low-temperature heating and low-temperature large-reduction rolling technology, thereby improving the low-temperature toughness of the steel plate in a -50°C environment.

[0029] With the global energy green transformation, the construction of offshore wind power piles, booster stations, offshore floating platforms, and offshore oil and gas platforms is increasing, and the demand for extra-thick and high-toughness marine engineering steel is increasing. The development of this steel has important economic value and practical significance.

[0030] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. 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 is as follows by mass percentage: 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%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, and the remainder is Fe and unavoidable impurity elements. The sum of the above components is 100%.

2. The S420KT-50 extra thick steel plate for offshore oil and gas platforms with full cross-section high toughness according to claim 1 is characterized by: The chemical composition of the steel plate 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%, the remainder is Fe and unavoidable impurity elements, and the sum of the above components is 100%.

3. The S420KT-50 extra thick steel plate for offshore oil and gas platforms with full cross-section high toughness according to claim 1 is characterized by: The chemical composition of the steel plate is 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≤0.030%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, B≤0.0005%, the remainder is Fe and unavoidable impurity elements, and the sum of the above components is 100%.

4. The S420KT-50 extra thick steel plate for offshore oil and gas platforms with full cross-section high toughness according to claim 1 is characterized by: The thickness of the steel plate is greater than 100 mm and does not exceed 120 mm.

5. A method for manufacturing the S420KT-50 extra thick steel plate with high toughness in the whole section for offshore oil and gas platforms as claimed in any one of claims 1 to 4, characterized in that: The manufacturing process includes 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 1060-1150℃, and the heating time is 400-460min; (2) Rolling process: The second-stage rolling temperature of the steel plate is 720-780°C, and the water entry temperature is 720-760°C; (3) Cooling process: The steel plate red-return temperature is limited to 300-450°C, and the cooling rate is 5-9°C / s.

6. The method for manufacturing the full-section high-toughness S420KT-50 extra-thick steel plate for offshore oil and gas platforms according to claim 1, characterized in that: The manufactured steel plate has a yield strength of ≥420Mpa, a tensile strength of 500-690Mpa, an elongation of ≥19%, an impact of -50°C of ≥150J, a yield strength ratio of ≤0.89, and an aging impact performance of 5% deformation of ≥150J.

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