High-toughness and high-strength ship plate steel capable of resisting crack propagation in 420MPa-grade ultralow-temperature environment and manufacturing method of high-toughness and high-strength ship plate steel

Abstract

The invention discloses high-toughness and high-strength ship plate steel capable of resisting crack propagation in a 420 MPa ultralow-temperature environment and a manufacturing method of the high-toughness and high-strength ship plate steel, and relates to the technical field of steel production, and the high-toughness and high-strength ship plate steel comprises the following chemical components in percentage by mass: 0.03-0.07% of C, 0.10-0.30% of Si, 1.25-1.40% 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, 0.20-0.35% of Ni, 0.020-0.050% of Alt, less than or equal to 0.05% of Mo, less than or equal to 60ppm of N, less than or equal to 2ppm of H, less than or equal to 0.0050% of Ca, less than or equal to 0.005 The method comprises the steps of low-C component design, low-temperature heating, TMCP controlled rolling and controlled cooling. The structure of the whole full-thickness section of the steel plate is uniform, grains are ultra-refined, the low-temperature toughness is good, the low-temperature crack propagation resistance is high, and the requirements of steel for large ships in special low-temperature sea areas are met.

Description

Technical Field

[0001] The present invention relates to the technical field of steel production, and in particular to a 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments and a manufacturing method thereof. Background Art

[0002] With the continuous development of polar resources and waterways, the development of high-strength ships for ultra-low temperature environments in polar regions has become particularly urgent. At present, the low-temperature toughness of 420-level ultra-low temperature environment high-strength ship steel produced by major steel companies is mainly at -60°C, without the requirement for crack growth resistance, and cannot meet the demand for low-temperature toughness and crack growth resistance of ship steel in special environments. Therefore, it is particularly important to develop a 420MPa ultra-low temperature environment resistant high-strength ship plate steel plate.

[0003] Relevant patents were searched. Patent 1 201910365883.9 discloses a low-temperature high-toughness cerium composite treated FH40 ship plate steel and its preparation method. The yield strength of the invented steel plate is ≥435MPa, the tensile strength is ≥530MPa, the elongation is ≥22.4%, and the impact energy at -60℃ is ≥244J; it cannot meet the requirements of -80℃ low-temperature impact and -60℃ CTOD, and the thickness is only 16-26mm, which cannot meet the requirements of large thickness specifications. Patent 2 201310730193.1 discloses a high-strength FH40 marine engineering steel plate and its production method. The yield strength of the invented steel plate is 420-440MPa, the tensile strength is 530-580MPa, and the elongation is only 22-24%; the V-type impact energy at -60℃ is only 180-240J; it cannot meet the requirements of -80℃ low-temperature impact and -60℃ CTOD. Patent 3 202110392459.0 discloses a thick FH40 shipbuilding steel plate with good aging impact toughness and a manufacturing method thereof. The yield strength of the invention steel plate is ≥400MPa, the tensile strength is ≥550MPa, the Z-direction performance is ≥70%, and the aging impact energy at -60℃ is ≥160J; it cannot meet the requirements of -80℃ low-temperature impact and -60℃ CTOD value, and cannot meet the needs of ultra-low environment ship steel. Patent 4 201710086846.5 discloses a steel plate for polar ships and a manufacturing method thereof. The steel plate has an impact of ≥200J in a low-temperature environment of -60℃ to -80℃, a CTOD fracture toughness value of ≥0.25mm at -60℃, a yield strength of ≥315MPa, and a tensile strength of ≥510MPa. The yield strength of the patent cannot meet the needs of 420MPa high-strength ship plates, and the CTOD value at -60℃ is low, which cannot meet the ability to resist crack growth in special environments. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments and a manufacturing method thereof.

[0005] In order to solve the above technical problems, the technical solution of the present invention is as follows: A 420MPa grade steel for ship plates with high toughness and high strength and resistant to crack propagation in ultra-low temperature environments, the chemical composition and mass percentage of which are as follows: C: 0.03-0.07%, Si: 0.10-0.30%, Mn: 1.25-1.40%, P≤0.012%, S≤0.003%, Nb: 0.025-0.040%, Ni: 0.20-0.35%, Alt: 0.020-0.050%, Mo≤0.05%, N≤60ppm, H≤2ppm, impurity elements: Ca≤0.0050%, B≤0.005%, and the rest are Fe and unavoidable impurities.

[0006] The present invention also provides a method for manufacturing 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments, which comprises the following steps in sequence: low-temperature heating, TMCP controlled rolling, and controlled cooling.

[0007] As a preferred embodiment of the method for manufacturing the 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments according to the present invention, in the low-temperature heating process, the heating temperature of the steel billet is 1130°C to 1180°C.

[0008] As a preferred embodiment of the method for manufacturing the 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments described in the present invention, in which: in the TMCP controlled rolling process, the cumulative reduction rate of the last three passes of rough rolling of the steel plate is ≥30%, the thickness of the second-stage drying steel is ≥2h, where h is the thickness of the finished steel plate, the starting rolling temperature is 780℃~830℃, the reduction rate of the single pass before the first three passes of finishing rolling is ≥10%, and the water entry temperature is 760℃~810℃.

[0009] As a preferred embodiment of the method for manufacturing the 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments, in the controlled rolling process, the steel plate red-returning temperature is 450-620°C, and the cooling rate is 5-8°C / s.

[0010] As a preferred scheme for the manufacturing method of the 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments described in the present invention, the yield strength of the prepared steel plate is ≥420Mpa, the tensile strength is 520-680Mpa, the elongation is ≥25%, the -80℃ impact is ≥200J, the yield strength ratio is ≤0.85, and the CTOD value in a -60℃ environment is ≥0.60mm.

[0011] As a preferred solution of the method for manufacturing the 420MPa grade high-toughness and high-strength ship plate steel that is resistant to crack propagation in ultra-low temperature environments according to the present invention, the thickness of the manufactured steel plate is 20-70mm.

[0012] The beneficial effects of the present invention are: The present invention achieves uniform structure of the entire thickness section of the steel plate, ultra-fine grains, good low-temperature toughness, and strong low-temperature crack growth resistance through low-C component design, low-temperature heating, TMCP controlled rolling, and controlled cooling processes, meeting the needs of large-scale ship steel in special low-temperature sea areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0014] Figure 1 Schematic diagram of the metallographic structure near the surface of the 420MPa grade ultra-low temperature environment resistant crack propagation high-strength shipbuilding steel prepared in Example 3; Figure 2 Schematic diagram of the metallographic structure of the 420MPa grade ultra-low temperature environment resistant crack propagation high-strength shipbuilding steel prepared in Example 3 at 1 / 4 of the thickness; Figure 3 This is a schematic diagram of the metallographic structure at 1 / 2 of the thickness of the 420MPa grade high-strength shipbuilding steel that is resistant to crack propagation in ultra-low temperature environments prepared in Example 3. DETAILED DESCRIPTION

[0015] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation modes and in combination with the accompanying drawings.

[0016] Example 1: This example provides a 420MPa grade high-strength shipbuilding steel that is resistant to crack propagation in ultra-low temperature environments, with a thickness of 20mm. Its chemical composition and mass percentage are shown in Table 1.

[0017] This embodiment also provides a method for manufacturing 420MPa grade ultra-low temperature environment resistant high-strength shipbuilding steel, wherein LF and RH refining technologies are used during smelting to ensure that the gas H content of the steel plate is 1.2ppm and the N content is 50ppm.

[0018] In addition, the manufacturing method of the 420MPa grade ultra-low temperature environment resistant high-strength shipbuilding steel provided in this embodiment includes low-temperature heating, TMCP controlled rolling, and controlled cooling processes, and the specific process steps are as follows: (1) Low temperature heating process: 260 mm cross-section ingot is used, the ingot heating temperature is 1180 °C, and the heating time is 300 min to ensure alloy solid solution, while avoiding the grain length of the ingot and ensuring that the grain of the entire ingot is relatively uniform.

[0019] (2) TMCP controlled rolling process: The cumulative thickness of the last three passes of rough rolling of steel plates is 35%; the thickness of the second-stage air-drying steel is 60 mm, the start rolling temperature is 830°C, the reduction rates of the first three passes are 12%, 12%, and 10%, and the water entry temperature is 810°C. The large reduction rate of the last three passes of rough rolling allows the steel billet to be deformed and penetrated into the core. By increasing the thickness of the air-drying steel and accurately controlling the start rolling temperature and single-pass reduction rate of the finishing rolling, more distortion bands are formed, providing more nucleation points for structural transformation.

[0020] (3) Controlled cooling process: The red-return temperature of the steel plate is limited to 620°C, and the cooling rate is 3°C / s. Through the appropriate cooling rate, the formation of martensitic hard structure on the surface is avoided, and the full-thickness structure and performance of the steel plate can be accurately controlled.

[0021] The mechanical properties of the 20 mm thick 420 MPa grade high-strength shipbuilding steel plate resistant to crack propagation in ultra-low temperature environments obtained in this embodiment are shown in Table 2.

[0022] Example 2: This example provides a 420MPa grade high-strength shipbuilding steel that is resistant to crack propagation in ultra-low temperature environments, with a thickness of 40mm. Its chemical composition and mass percentage are shown in Table 1.

[0023] This embodiment also provides a method for manufacturing 420MPa grade ultra-low temperature environment resistant high-strength shipbuilding steel, wherein LF and RH refining technologies are used during smelting to ensure that the gas H content of the steel plate is 1.0ppm and the N content is 40ppm.

[0024] In addition, the method for manufacturing a 420MPa ultra-low temperature environment resistant high-strength shipbuilding steel plate provided in this embodiment includes low-temperature heating, TMCP controlled rolling, and controlled cooling processes, and the specific process steps are as follows: (1) Low-temperature heating process: 370 mm cross-section ingot is used, the ingot heating temperature is 1150 °C, and the heating time is 400 min to ensure alloy solid solution, while avoiding the grain length of the ingot and ensuring that the grains of the entire ingot are relatively uniform.

[0025] (2) Rolling process: TMCP controlled rolling process: The final three passes of rough rolling of steel plates have a cumulative total of 32%; the thickness of the second-stage air-drying steel is 90 mm, the start rolling temperature is 810°C, the reduction ratios of the first three passes are 13%, 12%, and 11%, and the water entry temperature is 800°C. The large reduction ratios of the final three passes of rough rolling allow the steel billet to be deformed and penetrated into the core. By increasing the thickness of the air-drying steel and accurately controlling the start rolling temperature and single-pass reduction ratio of the finishing rolling, more distortion bands are formed, providing more nucleation points for structural transformation.

[0026] (3) Controlled cooling process: The red-return temperature of the steel plate is limited to 580°C, and the cooling rate is 4°C / s. Through the appropriate cooling rate, the formation of martensitic hard structure on the surface is avoided, and the full-thickness structure and performance of the steel plate can be accurately controlled.

[0027] The mechanical properties of the 40 mm thick 420 MPa grade high-strength shipbuilding steel plate resistant to crack propagation in ultra-low temperature environments obtained in this embodiment are shown in Table 2.

[0028] Example 3: This example provides a 420MPa grade high-strength shipbuilding steel that is resistant to crack propagation in ultra-low temperature environments, with a thickness of 70mm. Its chemical composition and mass percentage are shown in Table 1.

[0029] This embodiment also provides a method for manufacturing 420MPa grade ultra-low temperature environment resistant high-strength shipbuilding steel, wherein LF and RH refining technologies are used during smelting to ensure that the gas H content of the steel plate is 0.8ppm and the N content is 38ppm.

[0030] In addition, the present embodiment provides a method for manufacturing a 420MPa grade ultra-low temperature environment resistant high-strength shipbuilding steel plate, including heating, TMCP controlled rolling, and controlled cooling processes, and the specific process steps are as follows: (1) Heating process: 370 mm cross-section ingot was used, the ingot heating temperature was 1130 °C, and the heating time was 420 min.

[0031] (2) Rolling process: TMCP controlled rolling process: The final three passes of rough rolling of steel plates have a cumulative reduction of 35%; the thickness of the second-stage air-drying steel is 150 mm, the start rolling temperature is 770 °C, the reduction rates of the first three passes are 12%, 12%, and 10%, and the water entry temperature is 760 °C.

[0032] (3) Controlled cooling process: The steel plate red-hot temperature is limited to 450°C and the cooling rate is 6°C / s.

[0033] The mechanical properties of the 70 mm thick 420 MPa grade high-strength shipbuilding steel plate resistant to crack propagation in ultra-low temperature environments obtained in this embodiment are shown in Table 2.

[0034] Table 1 Chemical composition of steel plates of Examples 1-3 (wt%)

[0035] Table 2 Mechanical properties of steel plates of Examples 1-3 It should be noted that the 20mm and 40m thick steel plate tensile specimens are full-thickness rectangular tensile specimens.

[0036] Therefore, the technical solution of this application achieves uniform structure of the entire thickness section of the steel plate, ultra-fine grains, good low-temperature toughness, and strong low-temperature crack growth resistance through low-C component design, low-temperature heating, TMCP controlled rolling, and controlled cooling processes, meeting the needs of large-scale ship steel in special low-temperature sea areas.

[0037] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A 420MPa grade high toughness and high strength ship plate steel with crack propagation resistance in ultra-low temperature environment, characterized by: Its chemical composition and mass percentage are: C: 0.03-0.07%, Si: 0.10-0.30%, Mn: 1.25-1.40%, P≤0.012%, S≤0.003%, Nb: 0.025-0.040%, Ni: 0.20-0.35%, Alt: 0.020-0.050%, Mo≤0.05%, N≤60ppm, H≤2ppm, impurity elements: Ca≤0.0050%, B≤0.005%, and the rest are Fe and unavoidable impurities.

2. A method for manufacturing the 420MPa grade high-toughness and high-strength ship plate steel with crack propagation resistance in ultra-low temperature environment according to claim 1, characterized in that: The process includes the following steps in sequence: low temperature heating, TMCP controlled rolling, and controlled cooling.

3. The method for manufacturing the 420MPa grade high-toughness and high-strength ship plate steel with crack propagation resistance in ultra-low temperature environment according to claim 2, characterized in that: In the low temperature heating process, the billet is heated to a temperature of 1130°C to 1180°C.

4. The method for manufacturing the 420MPa grade high-toughness and high-strength ship plate steel with crack propagation resistance in ultra-low temperature environment according to claim 2, characterized in that: In the TMCP controlled rolling process, the cumulative reduction rate of the last three passes of rough rolling of the steel plate is ≥30%, the thickness of the second stage drying steel is ≥2h, where h is the thickness of the finished steel plate, the starting rolling temperature is 780℃~830℃, the single pass reduction rate of the first three passes of finishing rolling is ≥10%, and the water entry temperature is 760℃~810℃.

5. The method for manufacturing 420MPa grade high toughness and high strength ship plate steel with crack propagation resistance in ultra-low temperature environment according to claim 2, characterized in that: In the controlled rolling process, the steel plate red-returning temperature is 450-620° C., and the cooling rate is 5-8° C. / s.

6. The method for manufacturing the 420MPa grade high toughness and high strength ship plate steel with crack propagation resistance in ultra-low temperature environment according to claim 2, characterized in that: The yield strength of the steel plate obtained is ≥420Mpa, the tensile strength is 520-680Mpa, the elongation is ≥25%, the -80°C impact is ≥200J, the yield strength ratio is ≤0.85, and the CTOD value in a -60°C environment is ≥0.60mm.

7. The method for manufacturing 420MPa grade high toughness and high strength ship plate steel with crack propagation resistance in ultra-low temperature environment according to claim 2, characterized in that: The thickness of the produced steel plate is 20~70mm.

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