Method for manufacturing high-strength marine steel and use thereof

Abstract

This invention discloses a manufacturing method for high-strength marine steel and its application. A conventional hot-rolling production line method for 35mm thick Grade B marine steel includes the following steps: S1: Primary refining of molten steel is performed in a top-and-bottom blown converter, followed by LF refining and calcium treatment to obtain refined molten steel; S2: The refined molten steel is continuously cast to produce slabs, which are then fed into a heating furnace; S3: The slabs are hot-rolled, with the finishing rolling reduction rate controlled to be no less than 50%, cooled after rolling, and coiled into steel coils; S4: The steel coils are leveled and normalized to obtain high-strength marine steel. The product obtained by this method has an impact energy exceeding 100J at -20℃, inclusions A 0.5, B 1.0, D 1.5, a microstructure of ferrite + pearlite, a core grain size of grade 10.0 or higher, and a surface grain size of grade 11.5, exhibiting excellent ultra-low temperature high toughness.

Description

Technical Field

[0001] This invention relates to the fields of iron and steel metallurgy and materials processing technology, specifically to a method for manufacturing high-strength marine steel and its application. Background Technology

[0002] With the continuous development of marine engineering structures and the ongoing promotion of deep-sea exploration and green, low-carbon concepts, the shipbuilding industry is experiencing rapid growth. The requirements for steel plate thickness, strength, and toughness in ship structural components (such as hull shells and decks) are increasingly stringent. Among these, high-strength marine steel with a thickness of 28-35mm is in high demand and operates in complex environments, demanding stringent standards for material performance: low inclusion content, excellent transverse and longitudinal impact toughness, low internal stress, and good weldability. However, conventional hot-rolled coil production lines in steel mills are generally designed to roll thicknesses not exceeding 25mm. As thickness increases, products are prone to adverse effects on low-temperature toughness and internal stress control, failing to meet the performance requirements of the shipbuilding industry for ultra-thick marine steel plates. Currently, 28-35mm thick marine steel mainly relies on medium-thick plate rolling processes, resulting in a single production line, low production efficiency, poor dimensional accuracy, high manufacturing costs, and long delivery cycles, making it difficult to adapt to the rapidly growing market demand.

[0003] To overcome the limitations of conventional hot-rolled steel production lines in terms of coil thickness and meet the market demand for high-performance, ultra-thick Grade B marine steel in the shipbuilding industry, while simultaneously improving the capacity and overall efficiency of existing hot-rolled production lines, a manufacturing method for a conventional hot-rolled production line producing 35mm thick Grade B marine steel has been developed. This method, through optimization of the entire process technology, enables stable mass production of 28-35mm thick high-quality Grade B marine steel on a conventional hot-rolled production line. This significantly enhances the technological level of shipbuilding steel manufacturing and brings substantial economic and social benefits. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a conventional hot-rolling production line manufacturing method for 35mm thick Grade B marine steel. The product has an impact energy exceeding 100J at -20℃, inclusions of A0.5, B1.0, and D1.5, and a microstructure mainly consisting of ferrite and pearlite, with a core grain size of 10.0 and a surface grain size of 11.5. Therefore, this material exhibits high toughness at ultra-low temperatures.

[0005] To achieve the above objectives, the present invention provides a method for manufacturing high-strength marine steel, comprising the following steps: S1: The molten steel is initially smelted in a top-and-bottom blown converter, then refined by LF and subjected to calcium treatment to obtain refined molten steel; S2: The refined molten steel is continuously cast to produce slabs, and the slabs are then fed into a heating furnace after casting. S3: The slab is hot rolled, and the finishing rolling reduction rate is controlled to be not less than 50%. After rolling, it is cooled and coiled into a steel coil. S4: The steel coil is subjected to leveling and normalizing heat treatment to obtain high-strength marine steel.

[0006] According to an embodiment of the present invention, in step S1, before the initial steelmaking in the top-bottom blown converter, the molten steel is further subjected to KR desulfurization treatment, and the S content of the molten iron entering the top-bottom blown converter is ≤0.005%.

[0007] According to an embodiment of the present invention, in step S1, after the molten steel is desulfurized by KR, it is added to the top and bottom blowing converter for primary refining with a hot metal ratio of ≥75%. When the steel is tapped, the C content is ≥0.04% and the P content is ≤0.015%. The steel is tapped by slag blocking and slag retention to obtain the primary molten steel.

[0008] According to an embodiment of the present invention, the chemical composition of the molten steel includes: C: 0.10wt%~0.15wt%, Si: 0.10wt%~0.30wt%, Mn: 0.80wt%~1.20wt%, P≤0.018wt%, S≤0.005wt%, Als: 0.015wt%~0.0450wt%, Ti≤0.01wt%, and N≤0.0065wt%.

[0009] According to an embodiment of the present invention, in step S1, during LF refining, the slag basicity R2 is controlled at 5 to 7. During calcium treatment, the Ca content in the molten steel is maintained at 15–30 ppm, and the Ca / S ratio is ≥1.0.

[0010] According to an embodiment of the present invention, in step S2, the refined molten steel is continuously cast within 25 to 35 minutes after leaving the station to produce slabs, and the slabs are then placed into a heating furnace after casting.

[0011] According to an embodiment of the present invention, in step S2, the slab is placed into the heating furnace after an interval of more than 12 hours following the completion of casting.

[0012] According to an embodiment of the present invention, in step S2, the refined molten steel is sent to the continuous casting machine for casting within 25-35 minutes after leaving the station. The casting superheat is controlled at 10-20°C and the casting speed is 1.00-1.20 m / min. At the end of solidification, dynamic light reduction of 4.5 mm is adopted and electromagnetic stirring is performed to obtain a 230 mm thick slab. The center segregation and center porosity of the slab do not exceed C1.5. After the slab is cast, it is sent to the heating furnace after an interval of 12 hours.

[0013] According to an embodiment of the present invention, in step S2, the thickness of the slab is 230 mm.

[0014] According to an embodiment of the present invention, in S3, the slab heating temperature is 1150~1200℃, the finishing rolling temperature does not exceed 980℃, the finishing rolling temperature is 830~860℃, and the CT coiling temperature is 600-650℃.

[0015] According to an embodiment of the present invention, in step S3, the slab is fed into a heating furnace and heated to a furnace exit temperature of 1150~1200℃. After descaling, it undergoes primary rolling and finishing rolling. The finishing rolling inlet temperature is controlled to not exceed 980℃ and the finishing rolling end temperature is controlled to be 830℃~860℃. The total reduction rate during the finishing rolling process is not less than 50%. After finishing rolling, it is immediately subjected to ultra-fast cooling + laminar flow cooling, and then rolled to 600-650℃ to obtain a steel coil.

[0016] According to an embodiment of the present invention, in step S4, the uncoiling temperature of the steel coil is ≤60°C.

[0017] According to an embodiment of the present invention, in step S4, after the steel coil is cooled to an uncoiling temperature of ≤60°C, it is cut to length and leveled according to the customer's order requirements to obtain a steel plate; then the steel plate is subjected to normalizing heat treatment at 850°C for 2 × plate thickness minutes, and then naturally cooled to obtain 35mm thick Grade B marine steel.

[0018] The present invention also provides a method for manufacturing high-strength marine steel and the application of the marine steel produced therefrom in shipbuilding.

[0019] According to an embodiment of the present invention, the thickness of the marine steel is 28-35 mm.

[0020] Conventional hot rolling production lines are limited by cooling and coiling capacities, with a maximum rolling thickness generally not exceeding 25mm, making it impossible to stably produce 28-35mm thick Grade B marine steel. However, structural components such as ship hulls and decks require steel plates of this thickness, demanding materials with good anisotropy, low-temperature impact toughness (high impact energy at -20℃), few inclusions, low internal stress, and excellent weldability. While existing medium-thick plate rolling processes can produce this, they suffer from low production efficiency, poor dimensional accuracy, high manufacturing costs, and long delivery cycles, failing to meet the rapid development and green, low-carbon requirements of the shipbuilding industry. To address these technical problems, this invention employs a complete process from top-bottom blown converter to LF refining, continuous casting, TMCP hot rolling, leveling, and normalizing heat treatment. This process overcomes the bottleneck of ultra-thickness production on conventional hot rolling production lines, successfully achieving efficient, high-precision, and low-cost mass production of 28-35mm thick Grade B marine steel.

[0021] Its key technical features include: (1) Strict control of chemical composition (0.10wt%≤C≤0.15wt%, S≤0.005wt%, P≤0.018wt%, appropriate amount of Als etc.) and obtaining ultra-clean molten steel through KR desulfurization + LF white slag calcium treatment (Ca / S≥1, Ca 15-30ppm); (2) Continuous casting adopts dynamic light reduction 4.5mm + electromagnetic stirring to produce 230mm high-quality slabs with segregation ≤C1.5; (3) TMCP hot rolling precisely controls heating temperature 1150-1200℃, finishing rolling temperature 830℃~860℃, total reduction rate ≥50%, ultra-fast cooling + laminar flow cooling and coiling temperature 600-650℃; (4) After the steel coil is leveled, it is subjected to normalizing heat treatment at 850℃ + 2×plate thickness for minutes.

[0022] Through the synergistic effects of the above-mentioned component purification, slab quality control, and TMCP+normalizing, the fine grain strengthening, phase transformation strengthening, and stress relief mechanisms are fully utilized to obtain a uniform and fine ferrite + pearlite structure (core grain size of grade 10.0 or above). At the same time, the inclusion content and residual internal stress are significantly reduced, so that the ultra-thick grade B marine steel produced by conventional hot rolling production line can achieve excellent comprehensive performance with an impact energy of over 100J at -20℃ and inclusion A0.5, B1.0, and D1.5, meeting the safety requirements of ship structural components in complex low-temperature environments.

[0023] This invention provides a method for manufacturing 35mm thick Grade B marine steel using a conventional hot-rolling production line. The product has an impact energy exceeding 100J at -20℃, inclusions of A0.5, B1.0, and D1.5, and a microstructure mainly consisting of ferrite and pearlite, with a core grain size of 10.0 and a surface grain size of 11.5. Therefore, this material exhibits high toughness at ultra-low temperatures.

[0024] In this invention, the synergistic control of normalizing heat treatment and the entire process is not simply about suppressing inclusion formation. Inclusion control primarily relies on preceding smelting stages such as KR desulfurization and LF refining calcium treatment. Specifically, controlling Ca / S ≥ 1.0 transforms elongated, harmful Class A sulfide inclusions into spherical calcium aluminates. Subsequent 850℃ normalizing further spheroidizes and evenly distributes residual inclusions, thus eliminating their harmful role as crack initiation sites. Regarding grain refinement, normalizing and preceding TMCP hot rolling form a dual refinement mechanism. During hot rolling, a reduction rate of at least 50% and ultra-fast cooling processes store deformation energy in the austenite region, reserving fine austenite grains for phase transformation. Normalizing, through re-austenitization, eliminates internal stress and deformed structures from the hot-rolled state, resulting in a uniform equiaxed ferrite + pearlite structure during subsequent cooling. The grain size reaches grade 10.0 or higher in the inner layer and grade 11.5 on the surface, significantly improving the consistency of transverse and longitudinal properties. For the micro-banding structure problem that is prone to occur in thick-gauge marine steel, the continuous casting process uses dynamic light reduction of 4.5mm and electromagnetic stirring to control the central segregation within grade C1.5. In the normalizing process, the alloying elements are fully diffused by holding at 850℃ (2 × plate thickness for minutes), eliminating the banding structure caused by compositional segregation, and finally obtaining a uniform equiaxed ferrite + pearlite structure. The synergistic effect of the above-mentioned inclusion morphology control, double grain refinement and banding structure elimination makes the 28-35mm ultra-thick grade B marine steel produced by conventional hot rolling production line have an impact energy of over 100J at -20℃, small difference in transverse and longitudinal impact toughness, and comprehensive mechanical properties that fully meet the requirements of ship structural components in complex low-temperature environments. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0026] Figure 1 Metallographic structure diagram of Example 1; Figure 2 This is a metallographic diagram of Example 2.

[0027] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0030] Example 1 This embodiment provides a manufacturing method based on a conventional hot-rolling production line for 35mm thick Grade B marine steel. The specific implementation process includes: S1.1 molten steel composition: C: 0.125wt%, Si: 0.213wt%, Mn: 1.35wt%, P: 0.0112wt%, S: 0.0015wt%, Als: 0.0286wt%, Ti: 0.0135wt%, Nb: 0.0415wt%, Ca: 0.0018wt%, N: 0.0045wt%, Ni: 0.25wt%, with the remainder being iron and unavoidable elements.

[0031] S1.2 molten iron undergoes KR desulfurization treatment, with an S content of 0.002% in the molten iron entering the converter; the molten iron temperature in the converter is 1310℃, the molten iron ratio is 83%, and the primary refining is carried out in a top and bottom combined blowing converter. The steel output has C: 0.04% and P: 0.010%, and the slag-blocking and slag-retaining operation is adopted for steel output.

[0032] S1.3 LF refining adopts white slag operation, the slag basicity R2 is controlled at 5.6, calcium treatment is performed to modify inclusions, the Ca content of molten steel is retained at 0.0020%, micro-stirring for 10 minutes, and casting is carried out at the appropriate temperature. S2. The time from the molten steel leaving the station to the start of continuous casting is controlled within 25 minutes, the casting superheat is 15℃, the casting speed is controlled at 1.15m / min, and at the end of solidification, the steel is dynamically lightly reduced by 4.5mm and electromagnetically stirred to obtain a 230mm thick slab with center segregation and central porosity (C1.0). After the slab is cast, it is cold-charged into the heating furnace after an interval of 15 hours. S3. After heating the billet, descaling, primary rolling, finishing rolling and coiling are carried out. The heating temperature is 1175℃, the finishing rolling inlet temperature is 962℃, the finishing rolling end temperature is 855℃, the finishing rolling start speed is 2.0m / min, and after finishing rolling, ultra-fast cooling + laminar flow cooling is carried out at a cooling rate of 25℃ / s and a coiling temperature of 626℃ to obtain a steel coil with a thickness of 32mm. S4. After rolling, the steel coil is air-cooled for 82 hours at a temperature of 42℃. It is straightened by coarse straightening and fine straightening, and then produced by a four-sided cutting and leveling process to produce steel plate materials of the order size. S5. The steel plate material is subjected to normalizing heat treatment at 860±5℃ for 60 minutes, and then naturally cooled after being removed from the furnace.

[0033] Figure 1 This is a metallographic diagram of Example 1 (32mm thick Grade B marine steel). Figure 1 As can be seen, the microstructure of this steel plate is mainly composed of ferrite and pearlite, with a uniform and fine structure. The core grain size reaches grade 11.0, and the surface grain size reaches grade 11.5, while a small amount of Widmanstätten structure (W1.0) is also present. The grain refinement effect is good, with no obvious banded structure and coarse proeutectoid ferrite, indicating that the TMCP hot rolling process and normalizing heat treatment described in this invention effectively control the growth of austenite grains and obtain a uniform and fine ferrite + pearlite structure.

[0034] Example 2 This embodiment provides a manufacturing method based on a conventional hot-rolling production line for 35mm thick Grade B marine steel. The specific implementation process includes: S1.1 molten steel composition: C: 0.140wt%, Si: 0.253wt%, Mn: 1.12wt%, P: 0.012wt%, S: 0.0020wt%, Als: 0.0216wt%, N: 0.0050wt%. The remainder is iron and unavoidable elements; S1.2 The molten iron undergoes KR desulfurization treatment, and the S content of the molten iron entering the converter is 0.002%; the temperature of the molten iron entering the converter is 1300℃, the molten iron ratio is 85%, the primary refining is carried out in a top and bottom blowing converter, and the steel output has C: 0.055% and P: 0.014%, and the slag-blocking and slag-retaining operation is adopted for steel output. S1.3 LF refining adopts white slag operation, slag basicity R2 is controlled at 6.0, the steel composition is adjusted appropriately, calcium treatment is performed to modify inclusions, the Ca content of the steel is retained at 0.0025%, micro-stirring for 10 minutes, and then the steel is poured at the appropriate temperature. S2. The time from the molten steel leaving the station to the start of continuous casting is controlled within 28 minutes. The casting superheat is 10℃, and the casting speed is controlled at 1.20m / min. At the end of solidification, the steel is dynamically lightly reduced by 4.5mm and electromagnetically stirred to obtain a 230mm thick slab with center segregation and central porosity (C1.0). After casting, the slab is cold-charged into the heating furnace after an interval of 13 hours. S3. After heating the billet, descaling, primary rolling, finishing rolling and coiling are carried out. The heating temperature is 1190℃, the starting temperature of finishing rolling is 955℃, the finishing rolling temperature is 840℃, the starting speed of finishing rolling is 2.2m / min, and after finishing rolling, ultra-fast cooling + laminar flow cooling is carried out at a cooling rate of 22℃ / s and a coiling temperature of 635℃ to obtain a steel coil with a thickness of 35mm. S4. After rolling, the steel coil is air-cooled for 85 hours at a temperature of 20°C. It is then straightened by coarse straightening and fine straightening, and produced by a four-sided cutting and leveling process to produce steel plate materials of the order size. S5. The steel plate material is subjected to normalizing heat treatment at 850±5℃ for 70 minutes, and then naturally cooled after being removed from the furnace.

[0035] Figure 2 This is a metallographic diagram of Example 2 (35mm thick Grade B marine steel). From... Figure 2 It can be seen that the microstructure of this steel plate is also ferrite + pearlite (F+P), with a uniform distribution. The core grain size is grade 10.5, the surface grain size is grade 11.0, and the Widmanstätten grade is W1.0. The overall grains are fine and uniform. Compared with Example 1, the 35mm thicker steel plate still maintains a good microstructure refinement effect, indicating that the present invention, through optimizing the continuous casting light reduction, hot rolling cooling regime, and 850℃ normalizing and holding process, can effectively refine the grains even when producing ultra-thick steel plates on a conventional hot rolling production line, providing microstructure guarantee for the excellent low-temperature impact toughness of the steel plate.

[0036] Comparative Example 1 This comparative example uses the exact same process route and parameters as Example 1, except that in step S5, "after finishing rolling, ultra-fast cooling + laminar flow cooling at a cooling rate of 15°C / s" is changed to conventional laminar flow cooling at a cooling rate of 8°C / s, to obtain a 32mm thick steel plate.

[0037] Under the above conditions, the tissue became significantly coarser, and all properties were significantly lower than those in Example 1.

[0038] The above results show that after canceling ultra-fast cooling or significantly reducing the cooling rate, the grain refinement effect of the steel plate deteriorates and the low-temperature impact toughness decreases significantly. This fully demonstrates that the key process parameter of "ultra-fast cooling + laminar flow cooling" in this invention plays a decisive role in the microstructure refinement and performance improvement of ultra-thick grade B marine steel produced by conventional hot rolling production lines.

[0039] Test Example 1 This invention successfully produced 35mm thick Grade B marine steel on a conventional hot rolling production line through precise control of chemical composition, KR desulfurization + converter + LF refining calcium treatment, high-quality continuous casting slabs, TMCP hot rolling process parameter optimization, and subsequent leveling and normalizing heat treatment. To verify the effectiveness of the technical solution of this invention, mechanical properties, metallographic structure, and inclusions of Example 1 (32mm) and Example 2 (35mm) were tested, and the results are shown in Tables 1 to 3.

[0040] Table 1. Strength and Mechanical Properties The mechanical properties of the 32mm and 35mm thick Grade B marine steel produced in the embodiments of this invention are shown in Table 1. As can be seen from the data in Table 1, the yield strength of the steel plates in both embodiments reaches 315~331 MPa, significantly higher than the standard requirement of 235 MPa; the tensile strength is between 432~450 MPa, within the standard range of 400~520 MPa; and the elongation after fracture is between 31.0%~32.5%, far exceeding the standard requirement of 22%. The results indicate that this invention, through reasonable chemical composition control and a process route combining TMCP and normalizing, achieves the production of 35mm ultra-thick specifications while obtaining mechanical properties with a good match between strength and plasticity, fully meeting the requirements for Grade B marine steel.

[0041] Table 2. Impact Energy Performance The low-temperature impact toughness of the steel plates in this invention at -20℃ is shown in Table 2. As can be seen from Table 2, the average longitudinal impact energy of the 32mm thick steel plate is 120J, and the average transverse impact energy is 85J; the average longitudinal impact energy of the 35mm thick steel plate is 119J, and the average transverse impact energy is 86J. The longitudinal impact energy of both embodiments exceeds 100J, and the transverse impact energy is also far higher than the standard requirements for marine grade B steel, with minimal difference in longitudinal and transverse properties, demonstrating good isotropy. This fully demonstrates that this invention, through optimizing the continuous casting, hot rolling cooling regime, and normalizing heat treatment process, effectively refines the grains and reduces residual stress, enabling ultra-thick grade B marine steel produced by conventional hot rolling production lines to still possess excellent low-temperature impact toughness, meeting the safe use requirements of ship structural components in complex low-temperature environments.

[0042] Table 3. Metallographic Structure The metallographic structure and inclusions of the 32mm and 35mm thick Grade B marine steel produced in this embodiment are shown in Table 3. The data in the table show that the microstructure of the steel plates in both embodiments is ferrite + pearlite (F+P), with a small amount of Widmanstätten structure (W1.0). The microstructure is uniform and fine: the core grain size reaches grade 10.5~11.0, and the surface grain size reaches grade 11.0~11.5, indicating good overall grain refinement. The inclusion grade is controlled at B1.0 and D1.5 (Class A inclusions were not detected or were extremely low), indicating high steel plate cleanliness and low non-metallic inclusion content.

[0043] The above results fully demonstrate that the present invention, through the synergistic control of processes such as KR desulfurization, LF calcium treatment of modified inclusions, continuous casting dynamic light reduction + electromagnetic stirring, and TMCP hot rolling + normalizing heat treatment, effectively suppresses the formation and growth of inclusions, while significantly refining the grains to obtain a uniform and fine ferrite + pearlite microstructure. This not only ensures the excellent low-temperature impact toughness of the steel plate, but also improves weldability and overall reliability, fully meeting the metallographic structure and cleanliness requirements of ultra-thick Grade B marine steel for ship structural components.

[0044] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for manufacturing high-strength marine steel, characterized in that, Includes the following steps: S1: The molten steel is initially smelted in a top-and-bottom blown converter, then refined by LF and subjected to calcium treatment to obtain refined molten steel; S2: The refined molten steel is continuously cast to produce slabs, and the slabs are then fed into a heating furnace after casting. S3: The slab is hot rolled, and the finishing rolling reduction rate is controlled to be not less than 50%. After rolling, it is cooled and coiled into a steel coil. S4: The steel coil is subjected to leveling and normalizing heat treatment to obtain high-strength marine steel.

2. The method for manufacturing high-strength marine steel according to claim 1, characterized in that, The chemical composition of the molten steel, by mass percentage, includes: C: 0.10wt%~0.15wt%, Si: 0.10wt%~0.30wt%, Mn: 0.80wt%~1.20wt%, P≤0.018wt%, S≤0.005wt%, Als: 0.015wt%~0.045wt%, Ti≤0.01wt%, and N≤0.0065wt%.

3. The method for manufacturing high-strength marine steel according to claim 1, characterized in that, In step S1, during LF refining, the slag basicity R2 is controlled at 5-7; During calcium treatment, the Ca content in the molten steel is maintained at 15–30 ppm, and the Ca / S ratio is ≥1.

0.

4. The method for manufacturing high-strength marine steel according to claim 1, characterized in that, In step S2, the refined molten steel is continuously cast within 15 to 35 minutes after leaving the station to produce slabs. After the slabs are cast, they are placed into a heating furnace.

5. The method for manufacturing high-strength marine steel according to claim 1, characterized in that, In step S2, the slab is placed in the heating furnace after an interval of more than 12 hours following the completion of casting.

6. The method for manufacturing high-strength marine steel according to claim 1, characterized in that, In S3, the slab heating temperature is 1150-1200℃, the finishing rolling temperature does not exceed 980℃, the finishing rolling temperature is 830-860℃, and the CT curling temperature is 600-650℃.

7. The method for manufacturing high-strength marine steel according to claim 1, characterized in that, In step S4, the uncoiling temperature of the steel coil is ≤60℃.

8. The method for manufacturing high-strength marine steel according to claim 1, characterized in that, In step S2, the thickness of the slab is 230 mm.

9. The application of marine steel manufactured by the manufacturing method of high-strength marine steel as described in any one of claims 1 to 8 in shipbuilding.

10. The application according to claim 9, characterized in that, The thickness of the marine steel is 28-35 mm.

Images