355MPa-grade extra-thick maritime work steel capable of resisting Bauschinger effect and manufacturing method of 355MPa-grade extra-thick maritime work steel

Abstract

The invention relates to the field of preparation of steel and iron materials, in particular to 355MPa-grade extra-thick maritime work steel capable of resisting the Bauschinger effect and a manufacturing method of the 355MPa-grade extra-thick maritime work steel. The high-strength steel is composed of the following chemical components in percentage by weight: 0.05%-0.085% of C, 0.12%-0.25% of Si, 1.05%-1.45% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, 0.03%-0.05% of Als, 0.2%-0.7% of Ni, 0.2%-0.4% of Cr, 0.05%-0.3% of Mo, 0.1%-0.4% of Co, 0.01%-0.05% of Nb, 0.01%-0.05% of V, 0.005%-0.01% of Ti, 0.004%-0.008% of N, 0.05%-0.3% of Zr, 0.05%-0.15% of Sb and the balance of Fe and inevitable impurities. The thickness of the finished steel plate can reach 120 mm, the mechanical property and the high service safety performance of the steel plate can meet the service conditions of extremely cold ocean engineering equipment, and the steel plate has an excellent Bauschinger-resistant effect.

Description

Technical Field

[0001] This invention relates to the field of steel material preparation, specifically to a 355MPa grade extra-thick marine steel resistant to the Bauschinger effect and its manufacturing method. Background Technology

[0002] Since the beginning of the 21st century, the rapid development of shipbuilding and marine engineering, coupled with increased demand for cold-region and Arctic shipping routes, has driven the demand for high-performance marine engineering steels that are resistant to low temperatures, corrosion, and the Bauschinger effect. While the Arctic has enormous potential for resource development, it also faces environmental challenges.

[0003] The development of new marine engineering steels focuses on microalloying, controlled rolling and cooling, and optimized heat treatment processes to improve freeze resistance, corrosion resistance, and resistance to the Bauschinger effect. Microalloying enhances steel plate performance by adding trace elements, while innovative rolling and heat treatment processes optimize microstructure, improving low-temperature toughness and fatigue resistance. Resistance to the Bauschinger effect can significantly improve the reliability and safety of equipment, and requires the use of methods such as material pre-stretch testing to meet high service safety requirements.

[0004] Currently, marine engineering steels can meet most needs, but special steels with ultra-low ductile-brittle transition temperatures, excellent resistance to the Bauschinger effect, and corrosion resistance remain a global research focus. However, the production cost of these high-end steels is high and the processes are complex, requiring a balance between performance, cost, and feasibility. In addition, new technologies such as ultrasonic surface modification are being explored to further improve material properties.

[0005] Chinese patent application CN202210834931.6, entitled "A High-Strength, Low-Carbon Equivalent Extra-Thick Steel Plate with Good Low-Temperature Toughness and Its Manufacturing Method," proposes a high-C, low-Mn alloy normalized extra-thick steel plate. Its high C and Mn content, combined with a normalizing + tempering process, results in a normalized steel alloy composition system. The high carbon equivalent leads to a high dislocation density during deformation, preventing the plate from achieving excellent resistance to the Bauschinger effect while maintaining low-temperature toughness at -60℃. Chinese patent application CN202311405045.2, entitled "A Production Method of Steel for Large Single Heavy Thick-Spec Offshore Wind Turbine Pipe Piles," proposes a normalized steel plate for use in environments up to -20℃. It employs a high-C, high-Mn, low-Ni alloy composition design combined with conventional normalizing heat treatment. This method can only produce steel plates suitable for room-temperature service, and the composition system and production process determine that this invention lacks resistance to the Bauschinger effect. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a 355MPa grade extra-thick marine engineering steel with resistance to Bauschinger effect and its manufacturing method. The finished steel plate thickness can reach 120mm, the steel plate core has a low temperature impact energy of -60℃ ≥150J, the yield strength of the steel plate decreases by ≤10% when the residual strain is 2%, it has excellent resistance to Bauschinger effect, and the uniform elongation is ≥12%.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A 355MPa grade extra-thick marine steel resistant to the Bauschinger effect is composed of the following chemical composition by weight percentage:

[0009] C: 0.05%~0.085%, Si: 0.12%~0.25%, Mn: 1.05%~1.45%, P≤0.02%, S≤0.01%, Als: 0.03%~0.05%, Ni: 0.2%~0.7%, Cr: 0.2%~0.4%, Mo: 0.05%~0.3%, Co: 0.1%~0.4%, Nb: 0.01%~0.05%, V: 0.01%~0.05%, Ti: 0.005%~0.01%, N: 0.004%~0.008%, Zr: 0.05%~0.3%, Sb: 0.05%~0.15%, with the remainder being Fe and unavoidable impurities.

[0010] The effect of selecting the above alloying elements and their contents:

[0011] 1. Carbon (C) is a fundamental strengthening element in steel, improving the strength and hardness of steel plates. Too low a C content leads to a decrease in C solid solution content and carbide content, reducing the fine-grain strengthening effect, resulting in insufficient steel plate strength and reduced resistance to the Bauschinger effect. Too high a C content will produce a hardened structure, reducing the low-temperature toughness of the steel plate. Therefore, precise control of the C content is crucial. This invention precisely controls the C content between 0.05% and 0.085%.

[0012] 2. Si can improve the strength and resistance to the Bouschinger effect of steel plates. Appropriate addition of Si can improve the strength and fatigue life of steel. Simultaneously, Si can reduce the oxygen content. When the Si content is below 0.12%, the deoxidation effect is not significant, and when the Si content is above 0.25%, it leads to a decrease in low-temperature toughness. Therefore, this invention precisely controls the Si content between 0.12% and 0.25%.

[0013] 3. Mn can dissolve extensively in the Fe matrix, increasing the strength of the steel plate. When the Mn content is below 1.05%, its contribution to the strength of thick steel plates is relatively small. This patent utilizes a continuous casting heavy-pressure process to appropriately increase the Mn content, thereby improving the steel plate's resistance to the Bouschinger effect and its low-temperature toughness. However, when the Mn mass percentage exceeds 1.45%, segregation leads to poor low-temperature toughness in the core of the thick plate. Therefore, this invention precisely controls the Mn content between 1.05% and 1.45%.

[0014] 4. P and S elements have no benefit to the mechanical properties of steel plates, especially elongation. P should be controlled to ≤0.02% and S to ≤0.01%.

[0015] 5. Al is the main deoxidizing element in steel. When the Al content is too low, microalloying elements such as V and Ti are oxidized and cannot achieve the purpose of refining grains. For thicker steel plates that require resistance to the Bauschinger effect, the Al content in the steel needs to be appropriately increased. Conversely, if the Al content is too high, large inclusions will form. Therefore, this invention precisely controls the Al content at 0.03%~0.05%.

[0016] 6. The role of Ni is to improve the toughness and hot workability of steel plates. Adding a large amount can achieve a lower ductile-brittle transition temperature, improve the toughness and plasticity of the steel plate, and Ni has a certain resistance to pitting corrosion, improving the resistance of the steel plate to the Bauschinger effect under marine service conditions. Therefore, this invention precisely controls the Ni content to 0.2%~0.7%.

[0017] 7. Cr can effectively improve the strength and stiffness of steel plates; appropriately increasing the Cr content can improve the uniform deformation ability of steel plates, but excessive Cr content will reduce the impact toughness of steel plates. Therefore, this invention precisely controls the Cr content to 0.2%~0.4%.

[0018] 8. Mo can form fine carbides in steel, effectively improving the yield strength of steel plates. Furthermore, adding an appropriate amount of Mo to heat-treated steel plates can enhance their low-temperature toughness. Therefore, this invention precisely controls the Mo content to 0.05%~0.3%.

[0019] 9. Co can improve the strength and hardness of steel plates, thereby enhancing their fatigue resistance. Co can work synergistically with microalloying elements such as Nb and V to refine grain structure, improve dislocation density, and enhance the steel plate's resistance to the Bauschinger effect. However, adding excessive Co alone can lead to twinning defects in the steel plate, reducing its low-temperature toughness. Therefore, this invention precisely controls the Co content to 0.1%~0.4%.

[0020] 10. Nb is the main additive element in this invention, improving the strength and toughness of the steel plate while enhancing its fatigue resistance. During heating, undissolved Nb C and N compound particles are distributed on the austenite grain boundaries, hindering austenite grain growth during heating, refining the grain size, and improving low-temperature toughness. During controlled cooling of the steel plate, a large amount of Nb (CN) precipitates, reacting with Co to further promote dislocation entanglement, refine the grain size, and resist the Bauschinger effect. Therefore, this invention precisely controls the Nb content to 0.01%~0.05%.

[0021] 11. V can form V(C,N) particles in the matrix, which can refine the grain size. The addition of V can improve the low-temperature impact toughness and resistance to the Bauschinger effect of tempered steel plates. Therefore, the V content in this invention is precisely controlled at 0.01%~0.05%.

[0022] 12. The addition of Ti is to form TiN with Ti and N, preventing grain growth in the billet during heating and rolling, and to improve the overall performance of the steel plate by interacting with elements such as Co. When Ti is below 0.005%, its effect on strengthening and toughening the steel is not significant; when it exceeds 0.01%, it will deteriorate the toughness of the steel. Therefore, this invention precisely controls the Ti content to be between 0.005% and 0.01%.

[0023] 13. Nitrogen (N) can combine with Nb, Ti, and V to form fine, dispersed nitrogen oxide precipitates, which can effectively promote the nucleation and growth of ferrite within the grains and effectively control the growth of the original austenite grains. Increased N content leads to an increase in TiN in the steel. However, when the dissolved N content is too high, the toughness of the steel plate decreases, and numerous microcracks easily appear on the surface. Therefore, this invention precisely controls the N content to be between 0.004% and 0.008%.

[0024] 14. Zr has a strong degassing effect, capable of removing harmful elements such as H and O from steel, purifying the steel, and thus improving its purity and quality. Zr can refine the grain size of steel, improving its mechanical properties. Grain refinement increases the strength and toughness of steel, and also helps improve its impact toughness and low-temperature performance. Therefore, this invention precisely controls the Zr content to be between 0.05% and 0.3%.

[0025] 15. Sb can effectively improve the tensile strength, hardness, and stiffness of steel plates, thereby enhancing their resistance to the Boussinger effect. Simultaneously, an appropriate amount of Sb can also improve the low-temperature toughness and microstructural stability of steel plates during hot working, which is beneficial for grain refinement and toughening during the rolling process. Adding an appropriate amount of Sb to steel helps reduce core segregation in extra-thick steel plates, improving the low-temperature toughness of the core. Sb can also improve the corrosion resistance of steel plates. Therefore, this invention precisely controls the Sb content to 0.05%~0.15%.

[0026] The aforementioned 355MPa grade extra-thick marine steel with resistance to the Bauschinger effect has a yield strength ≥355MPa, tensile strength 490~630MPa, transverse elongation ≥30%, and Charpy impact energy of the steel plate core at -60℃ ≥150J. At 2% residual strain, the yield strength decreases by ≤10%, exhibiting excellent resistance to the Bauschinger effect, uniform elongation ≥12%, and a carbon equivalent (Ceq) of 0.37~0.45. The maximum thickness of the finished steel plate is 120mm.

[0027] The microstructure of the steel plate is ferrite (grain size ≥ 10) + pearlite, and the carbonitride size is 5~12nm.

[0028] The manufacturing method of the aforementioned 355MPa grade extra-thick marine steel resistant to the Bauschinger effect specifically includes the following steps:

[0029] 1) Steel refining:

[0030] Molten steel is refined in a converter, LF furnace, RH or VD furnace to further reduce the content of P, S and non-metallic inclusions.

[0031] 2) Continuous casting:

[0032] The entire casting process is protected, with the molten steel in the tundish superheated to 15~25℃. During the casting process, two sets of compression rollers are selected at the solidification two-phase zone of the core of the continuously cast billet to apply heavy pressure, with the compression amount of the two sets of compression rollers ≥10mm.

[0033] 3) Rolling:

[0034] The billet is placed into the heating furnace at a temperature of 600-800℃ and held for 30-90 minutes. This is to ensure a consistent temperature along the thickness of the billet during the low-temperature stage, preventing uneven heating of Co, Mn, and Zr elements that could lead to internal defects. During subsequent heating, the billet's heating rate is controlled at 6-8℃ / min to avoid excessive internal and external stresses that could cause cracks. The heating section temperature is 1050-1120℃, the homogenization temperature is 1020-1100℃, and the homogenization holding time is 60-90 minutes. This low-temperature homogenization holding aims to ensure sufficient dissolution of microalloyed C / N compounds while preventing abnormal growth of the as-cast structure and avoiding internal defects caused by high Co and Zr content in the billet.

[0035] The first-stage rolling temperature is 1000~1080℃, and the intermediate billet thickness is 1.5~2.5 times the thickness of the finished steel plate. The purpose of the first-stage rolling is to increase the core deformation while ensuring a high core temperature in the high-temperature stage of the billet, while minimizing the first-stage rolling temperature to avoid recrystallization after rolling, significant surface hardening due to low surface temperature, large reduction rolling, destruction of the columnar structure in the core, and increased core deformation. The second-stage rolling temperature is 800~850℃, with an average reduction of 10~14mm per pass, and a final rolling temperature of 750~800℃. The purpose of the second-stage low-temperature rolling is to utilize the significant decrease in surface temperature to increase the core deformation of the steel plate, improve the core grain size, and promote the flattening and refinement of austenite grains. The combined action of elements such as Co and Zr with microalloying elements such as Nb and V in steel can improve grain refinement, dislocation density, yield strength and elastic deformation uniformity of steel plates. The single-pass reduction rate and rolling temperature are the most important factors for grain refinement and uniform precipitation of C / N compounds.

[0036] 4) Cooling control:

[0037] The controlled cooling temperature after rolling is 630~730℃, the red-hot temperature is 450~500℃, and the surface cooling rate of the steel plate is 4~7℃ / s. The purpose of controlled cooling after rolling is to utilize the deformation energy accumulated during low-temperature rolling, combined with a relatively large supercooling temperature, to promote the fine and dispersed distribution of a large number of carbonitrides pinning grain boundaries, further refine the ferrite structure and nucleation, inhibit its growth, and control the grain size to level 10 or above, forming a uniform, fine, and dispersed large-angle grain boundary microstructure, ensuring the low-temperature toughness and resistance to the Bauschinger effect of thick steel plates. Too slow a cooling rate will lead to the growth of ferrite and pearlite structures, while too fast a cooling rate will result in a large amount of hardened structures in the steel plate, affecting the low-temperature toughness and resistance to the Bauschinger effect.

[0038] 5) Tempering:

[0039] The water temperature for controlled cooling after rolling is 630~730℃, the red-hot temperature is 450~500℃, and the surface cooling rate of the steel plate is 4~7℃ / s.

[0040] The purpose of quenching is to utilize the deformation energy accumulated during low-temperature rolling, combined with a relatively large supercooling temperature, to promote the fine and dispersed distribution of a large number of carbonitrides pinning the grain boundaries, to further refine the nucleation of ferrite, to inhibit its growth, to control the grain size to level 10 or above, and to form a uniform, fine, and dispersed large-angle grain boundary microstructure, thus ensuring the low-temperature toughness and resistance to the Bauschinger effect of thick steel plates.

[0041] The tempering temperature is 450~550℃, and the tempering time is 1.5~2 min / mm. The purpose of tempering heat treatment is to further optimize the microstructure of the steel plate by controlling the size and distribution of dispersed carbonitrides in the steel. This strengthens the steel plate by replacing dislocation strengthening with fine grain strengthening and solid solution strengthening, thereby mitigating the decrease in strength and toughness caused by dislocation migration after the steel plate has undergone plastic deformation.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] 1. This invention employs a compositional design combining C, Mn, Ni, Cr, Mo, Co, Nb, V, Ti, Zr, and Sb elements to ensure the steel plate achieves excellent strength, toughness, and resistance to the Bauschinger effect. At 2% residual strain, the yield strength decreases by ≤10%. Ni element provides some resistance to pitting corrosion, improving the steel plate's resistance to the Bauschinger effect under marine service conditions. Adding Cr element effectively improves the strength and stiffness of the steel plate. Adding an appropriate amount of Mo element enhances the low-temperature toughness of the steel plate, effectively increasing its yield strength. Co element increases the strength and hardness of the steel plate, thereby improving its fatigue resistance; Co element, in conjunction with microalloying elements such as Nb and V, plays a role in grain refinement, improving dislocation density and enhancing the steel plate's resistance to the Bauschinger effect. The addition of Ti element is to form TiN with Ti and N, preventing grain growth during heating and rolling of the billet, and interacting with elements such as Co to improve the overall performance of the steel plate. Zr has a strong degassing effect, removing harmful elements such as H and O from steel, purifying the steel, and thus improving its purity and quality. Sb can effectively improve the tensile strength, hardness, and stiffness of steel plates, thereby enhancing their resistance to the Boushinger effect.

[0044] 2. The innovative alloy composition system adopted in this invention can ensure that the steel plate has a yield strength ≥355MPa, tensile strength 490~630MPa, elongation ≥30%, core Charpy impact energy ≥150J at -60℃, uniform elongation ≥12%, and carbon equivalent Ceq of 0.37~0.45.

[0045] 3. This invention employs key production technologies for preparing high-quality, heavy-pressure continuously cast billets and extra-thick marine engineering steel plates resistant to the Bauschinger effect, using a combination of C, Mn, Ni, Cr, Mo, Co, Nb, V, Ti, Zr, and Sb elements. This enables the production of high-strength, low-temperature marine engineering steel with a maximum thickness of 120mm. The use of efficient temperature-controlled rolling and tempering heat treatment ensures excellent resistance to the Bauschinger effect while maintaining high steel plate production efficiency.

[0046] 4. The microstructure of the steel plate of the present invention is ferrite (grain size ≥ 10) and pearlite, with carbonitride size of 5~12nm, and it has good mechanical properties.

[0047] 5. The present invention uses post-rolling controlled cooling to utilize the deformation energy stored during low-temperature rolling, combined with a large supercooling temperature, to promote the fine and dispersed distribution of a large number of carbonitrides pinning grain boundaries, further refine the nucleation of ferrite structure, inhibit its growth, control the grain size to level 10 or above, and form a uniform, fine, dispersed large-angle grain boundary microstructure, ensuring the low-temperature toughness and resistance to the Bauschinger effect of thick steel plates.

[0048] 6. This invention further optimizes the microstructure of steel plates by controlling the size and distribution of dispersed carbonitrides in steel through tempering. It replaces the strengthening effect of dislocation strengthening on steel plates by fine grain strengthening and solid solution strengthening, thereby weakening the problem of strength and toughness reduction caused by dislocation migration after the steel plate has undergone plastic deformation in advance. Attached Figure Description

[0049] Figure 1 This is a metallographic diagram of Embodiment 1 of the present invention.

[0050] Figure 2 This is a carbon replica diagram of Embodiment 1 of the present invention. Detailed Implementation

[0051] This invention discloses a 355MPa grade extra-thick marine engineering steel resistant to the Bauschinger effect and its manufacturing method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0052] To address the compositional and performance requirements of high-strength marine engineering steel in the extremely cold and deep-sea marine environment, this invention utilizes a compositional design combining C, Si, Mn, Co, Zr with microalloying elements V, Nb, and Ti, and key production technologies for extra-thick marine engineering steel plates to resist the Bauschinger effect. To achieve the objectives of this invention, extensive and systematic experimental research was conducted in several aspects, including alloy element screening and proportioning, high-purity control of the continuous casting core under heavy pressure, and optimization and parameter selection of efficient rolling processes. Ultimately, the alloy element proportions and production processes that meet the objectives of this invention were determined. The chemical composition of the steel in this invention embodiment is shown in Table 1, the continuous casting process in this invention embodiment is shown in Table 2, the rolling process in this invention embodiment is shown in Table 3, the controlled cooling and tempering process in this invention embodiment is shown in Table 4, and the mechanical properties of the steel plate in this invention embodiment are shown in Table 5.

[0053] Table 1. Chemical composition (wt%) of steel in the embodiments of the present invention

[0054]

[0055] Table 2 Continuous casting process of embodiments of the present invention

[0056]

[0057] Table 3 Rolling process of embodiments of the present invention

[0058]

[0059] Table 4 Controlled cooling tempering process in embodiments of the present invention

[0060]

[0061] Table 5 Mechanical properties of steel plates in embodiments of the present invention

[0062]

[0063] like Figure 1 , Figure 2 As shown, the metallographic structure of Example 1 is ferrite (grain size ≥ 10) and pearlite at 1 / 2 and 1 / 4 of the thickness of the steel plate, with an average carbonitride size of 5~12nm and good mechanical properties.

[0064] As shown in Table 5, this invention is a 355MPa grade extra-thick marine engineering steel resistant to the Bauschinger effect, with a yield strength ≥355MPa, tensile strength 490~630MPa, elongation ≥30%, and Charpy impact energy of the steel plate core at -60℃ ≥150J. At 2% residual strain, the yield strength decreases by ≤10%, exhibiting excellent resistance to the Bauschinger effect, uniform elongation ≥12%, carbon equivalent Ceq of 0.37~0.45, and the finished steel plate thickness can reach 120mm.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A 355MPa grade extra-thick marine steel resistant to the Bauschinger effect, characterized in that, Composed of the following chemical components in weight percentage composition: C: 0.05%~0.085%, Si: 0.12%~0.25%, Mn: 1.05%~1.45%, P≤0.02%, S≤0.01%, Als: 0.03%~0.05%, Ni: 0.2%~0.7%, Cr: 0.2%~0.4%, Mo: 0.05%~0.3%, Co: 0.1%~0.4%, Nb: 0.01%~0.05%, V: 0.01%~0.05%, Ti: 0.005%~0.01%, N: 0.004%~0.008%, Zr: 0.05%~0.3%, Sb: 0.05%~0.15%, with the remainder being Fe and unavoidable impurities.

2. The 355MPa grade extra-thick marine steel with resistance to the Bauschinger effect according to claim 1, characterized in that, Its yield strength is ≥355MPa, tensile strength is 490~630MPa, elongation is ≥30%, Charpy impact energy of the steel plate core at -60℃ is ≥150J, yield strength decreases by ≤10% when the steel plate has 2% residual strain, uniform elongation is ≥12%, and carbon equivalent Ceq is 0.37~0.

45.

3. The 355MPa grade extra-thick marine steel resistant to the Bauschinger effect according to claim 1, characterized in that, The maximum thickness of the finished steel plate is 120mm.

4. The 355MPa grade extra-thick marine steel resistant to the Bauschinger effect according to claim 1, characterized in that, The microstructure of the steel plate is ferrite + pearlite, with ferrite grain size ≥ 10 and carbonitride size 5~12nm.

5. A method for manufacturing 355MPa grade extra-thick marine steel resistant to the Bauschinger effect as described in any one of claims 1 to 4, characterized in that, The manufacturing method specifically includes the following steps: 1) Steel refining; 2) Continuous casting: The casting process is protected throughout. The molten steel in the tundish is superheated to 15~25℃. Two sets of compression rollers at the solidification solid-liquid two-phase zone of the core of the continuously cast billet are subjected to heavy pressure. 3) Two-stage controlled rolling: The first-stage rolling temperature is 1000~1080℃, and the thickness of the intermediate billet is 1.5~2.5 times the thickness of the finished steel plate; The initial rolling temperature in the second stage is 800~850℃, the average reduction rate of a single pass in the second stage is 10~14mm, and the final rolling temperature is 750~800℃. 4) Cooling control: After rolling, the cooling water temperature is controlled at 630~730℃, and the reddening temperature is 450~500℃; 5) Tempering: Tempering temperature 450~550℃, tempering time 1.5~2min / mm.

6. The method for manufacturing 355MPa grade extra-thick marine steel resistant to the Bauschinger effect according to claim 5, characterized in that, In step 1), molten steel is refined through a converter, LF furnace, RH or VD furnace.

7. The method for manufacturing 355MPa grade extra-thick marine steel resistant to the Bauschinger effect according to claim 5, characterized in that, 2) In this case, the compression amount of the two sets of compression rollers is ≥10mm.

8. The method for manufacturing 355MPa grade extra-thick marine steel resistant to the Bauschinger effect according to claim 5, characterized in that, 3) In this process, the billet is loaded into the heating furnace at a furnace temperature of 600~800℃ and held for 30~90 minutes; The heating temperature is 1050~1120℃, the heating rate is controlled at 6~8℃ / min, the heat spread temperature is 1020~1100℃, and the heat spread holding time is 60~90min.

9. The method for manufacturing 355MPa grade extra-thick marine steel resistant to the Bauschinger effect according to claim 5, characterized in that, 4) The surface cooling rate of the steel plate is 4~7℃ / s.

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