EH40 extra-thick maritime work steel resistant to tropical marine climate corrosion and manufacturing method of EH40 extra-thick maritime work steel

Abstract

The invention relates to the technical field of extra-thick maritime work steel resistant to tropical marine climate corrosion, in particular to EH40 extra-thick maritime work steel resistant to tropical marine climate corrosion and a manufacturing method of the EH40 extra-thick maritime work steel resistant to tropical marine climate corrosion. The high-strength steel is composed of the following chemical components in percentage by weight: 0.065%-0.08% of C, 0.15%-0.3% of Si, 1.5%-1.7% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, 0.015%-0.03% of Als, 0.4%-0.8% of Ni, 0.1%-0.2% of Cu, 0.1%-0.15% of Co, 0.05%-0.15% of Sn, 0.01%-0.03% of V, 0.01%-0.015% of Ti, 0.002%-0.004% of N and the balance of Fe and inevitable impurities. The thickness of the finished steel plate can reach 100 mm, and the corrosion resistance of the steel plate in the tropical marine climate environment is remarkably improved while EH40-grade high strength, high toughness and excellent weldability are kept.

Description

Technical Field

[0001] This invention relates to the field of extra-thick marine steel resistant to tropical marine climate corrosion, specifically to an EH40 extra-thick marine steel resistant to tropical marine climate corrosion and its manufacturing method. Background Technology

[0002] Tropical marine climates, characterized by year-round high temperatures, extreme humidity, high salt spray deposition, intense ultraviolet radiation, and frequent and intense cycles of wet and dry conditions, constitute one of the most severe atmospheric corrosion environments for engineering metal materials. This environment drastically accelerates the electrochemical corrosion process of steel, inducing severe uniform corrosion, pitting corrosion, crevice corrosion, and even stress corrosion cracking (SCC). This leads to rapid failure of critical load-bearing components in marine structures (such as large ships, deep-sea platforms, cross-sea bridges, and port machinery), significantly shortening their service life and creating substantial safety hazards and high maintenance costs. With the deepening expansion of marine resource development and shipping activities into tropical waters, the demand for high-performance marine structural steel capable of long-term, reliable service in such harsh environments has become unprecedentedly urgent.

[0003] Among numerous marine engineering structural materials, EH40 grade marine steel has become the preferred material for key components of large ships (such as ultra-large container ships and liquefied gas carriers) such as decks, sides, hatch coamings, as well as offshore platform legs and jackets, due to its excellent strength (yield strength ≥ 400 MPa), good low-temperature toughness, and acceptable weldability. Meanwhile, to meet the design requirements of larger structures, deeper waters, and extreme loads, these critical load-bearing components often require extra-thick steel plates (typically ≥ 80 mm or even 100 mm thick).

[0004] However, when standard EH40 steel is applied to extra-thick specifications in tropical marine environments, its inherent limitations are exposed: (1) The chemical composition system of standard EH40 steel is mainly designed to meet the requirements of strength, toughness and basic weldability, and lacks effective protective elements or optimized combinations for the high-salt and high-humidity corrosion environment of tropical marine environments. The rust layer formed is loose and porous with poor protection, resulting in a corrosion rate in tropical marine atmosphere and splash zone environment that is much higher than in ordinary atmospheric environment, making it very easy to cause early corrosion, thinning, and even local perforation failure. (2) The cooling center of extra-thick plates is slow during rolling and cooling, which easily forms coarse or undesirable structures (such as ferrite-pearlite). This structural inhomogeneity not only affects the strength and toughness matching, but also significantly reduces the overall corrosion resistance (coarse / undesirable phases are more prone to corrosion) and exacerbates the risk of hydrogen-induced delayed cracking (HIC) in the core. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides an EH40 extra-thick marine steel resistant to tropical marine climate corrosion and its manufacturing method. The finished steel plate thickness can reach 100mm. While maintaining the high strength, high toughness and excellent weldability of EH40 grade, it significantly improves its corrosion resistance in tropical marine climate environments.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] An EH40 extra-thick marine steel resistant to tropical marine climate corrosion is composed of the following chemical composition by weight percentage:

[0008] C: 0.065%~0.08%, Si: 0.15%~0.3%, Mn: 1.5%~1.7%, P≤0.02%, S≤0.01%, Als: 0.015%~0.03%, Ni: 0.4%~0.8%, Cu: 0.1%~0.2%, Co: 0.1%~0.15%, Sn: 0.05%~0.15%, V: 0.01%~0.03%, Ti: 0.01%~0.015%, N: 0.002%~0.004%, with the remainder being Fe and unavoidable impurities.

[0009] The effect of selecting the above alloying elements and their contents:

[0010] 1. Carbon (C) can effectively improve 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 dislocation strengthening and grain refinement effects, resulting in insufficient steel plate strength. Too high a C content will produce a large amount of hardened structure, reducing impact toughness. Simultaneously, excessive C in steel will decrease the corrosion resistance of the steel plate. Therefore, the C content in steel should be precisely controlled. Thus, this invention precisely controls the C content to 0.065%~0.08%.

[0011] 2. Si can improve the strength and hardness of steel plates and refine the grain size, thereby improving the elastic limit, yield strength, and fatigue resistance of the steel plates. Simultaneously, Si acts as a deoxidizer, reducing the oxygen content; however, the deoxidation effect is not significant when the Si content is below 0.15%. Si can form a surface film with oxygen, thus providing some resistance to atmospheric corrosion; the amount of Si can be appropriately increased. Therefore, this invention precisely controls the Si content between 0.15% and 0.3%.

[0012] 3. Mn has a similar atomic radius to Fe and can dissolve extensively in the Fe matrix, improving the strength, wear resistance, and hot workability of steel plates. Simultaneously, Mn can increase the heat transfer capacity of extra-thick steel plates. However, when the mass percentage of Mn exceeds 1.7%, Mn segregation can lead to poor low-temperature toughness in the core of thick plates. Therefore, this invention precisely controls the Mn content between 1.5% and 1.7%.

[0013] 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%.

[0014] 5. Al is the main deoxidizing element in steel. When the Al content is too low, the deoxidation effect is poor, and microalloying elements such as Ti cannot refine the grains due to oxidation. For ultra-high strength steel plates with large thickness, 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 0.015%~0.03%.

[0015] 6. The role of Ni is to improve the toughness of steel plates. Ni can strengthen ferrite and refine and increase pearlite, thereby improving the strength of steel. Adding a large amount can achieve a lower ductile-brittle transition temperature, improving the low-temperature toughness of the steel plate. Adding a certain amount of Ni to steel can refine ferrite grains and prevent intergranular corrosion. The carbon content of Ni-containing steel can be appropriately reduced, thus improving toughness and plasticity. Simultaneously, the addition of Ni can reduce the hot cracking tendency of Cu in steel. Therefore, this invention precisely controls the Ni content to 0.4%~0.8%.

[0016] 7. Cu (Cu) can improve the strength and hardness of steel, especially low-carbon steel. By promoting the formation of grain boundary hindrance and dispersed precipitates, it enhances the cold work hardening ability and tempering stability of steel, thereby increasing its tensile strength, yield strength, and hardness while maintaining good plasticity and toughness. Cu compounds in steel exhibit high resistance to oxidation and sulfide corrosion, particularly in corrosive media containing seawater. Cu can also reduce the tendency of steel to intergranular corrosion and stress corrosion cracking. Cu can work synergistically with Ni (Ni) to lower the ductile-brittle transition temperature of steel plates and improve low-temperature toughness. However, adding excessive Cu alone can lead to a decrease in low-temperature toughness and cause hot brittleness. Therefore, this invention precisely controls the Cu content to 0.1%~0.2%.

[0017] 8. Co can work synergistically with Mn to significantly enhance solid solution strengthening, thereby improving the strength and hardness of the steel plate. However, excessive addition will reduce the low-temperature toughness of the steel plate. Co can also improve the oxidation resistance of the steel plate. Therefore, this invention precisely controls the Co content to 0.1%~0.15%.

[0018] 9. The main functions of Sn in steel include improving its strength and corrosion resistance, as well as its processing and weldability. Sn can form a solid solution with iron atoms in steel, thereby increasing its hardness and strength, and inhibiting intergranular corrosion, thus enhancing its corrosion resistance. Therefore, this invention precisely controls the Sn content to be between 0.05% and 0.15%.

[0019] 10. V is an important additive element in this invention. V can form fine compounds with C and N, improving the strength and hardness of the steel plate. The C and N compound particles of V are distributed on the austenite grain boundaries, which can hinder the growth of austenite grains during heating, effectively inhibiting the recrystallization of deformed austenite, preventing austenite grain growth, increasing the austenite recrystallization temperature, refining the grains, and improving the fatigue resistance of the steel. At the same time, V can promote the formation of a passivation film, slow down the oxidation reaction on the steel surface, and enhance its corrosion resistance. Therefore, the V content in this invention is precisely controlled at 0.01%~0.03%.

[0020] 11. The addition of Ti is to enable Ti and N to form TiN, which inhibits grain growth and improves the toughness of the steel plate. A certain content of Ti can improve the steel's resistance to intergranular corrosion. Therefore, this invention precisely controls the Ti content to 0.01%~0.015%.

[0021] 12. Nitrogen (N) can combine with v and titanyl chloride (Ti) to form fine, dispersed nitric oxide (CN) compounds, increasing the number of ferrite nucleation sites within the grains and thus refining the grain size. Increased N content leads to increased TiN content in the steel. However, excessive dissolved N content reduces the toughness of the steel plate. Therefore, this invention precisely controls the N content to 0.002%~0.004%.

[0022] The aforementioned EH40 extra-thick marine steel, resistant to tropical marine climate corrosion, has a maximum finished plate thickness of 100mm. Its yield strength is ≥420MPa, tensile strength is 600~680MPa, transverse elongation is ≥26%, and the Charpy impact energy of the steel plate core at 20℃ is ≥200J, and the Charpy impact energy of the steel plate core at -40℃ is ≥200J. The seawater corrosion resistance rate of the steel plate is less than 40% of that of conventional 40MPa grade marine steel, and the marine atmospheric corrosion resistance rate is less than 50% of that of conventional 40MPa grade marine steel.

[0023] The microstructure at 1 / 2 thickness of the steel plate consists of 30%~40% polygonal ferrite and 60%~70% acicular ferrite, with a grain size of 10~12.

[0024] The manufacturing method of the aforementioned EH40 extra-thick marine steel resistant to tropical marine climate corrosion employs a high-purity alloying smelting + casting machine heavy pressure reduction + electroslag remelting + two-stage low-temperature controlled rolling + low-temperature tempering process. The specific steps of this manufacturing method are as follows:

[0025] 1. Steel refining:

[0026] 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.

[0027] 2. Continuous casting:

[0028] The entire casting process is protected, with molten steel superheated by 3~10℃. The total reduction under heavy casting pressure is ≥8mm; the equiaxed crystal ratio in the core of the continuously cast billet is ≥90%, and the center segregation rating is ≤C1.0. The purpose of heavy casting pressure is to improve the quality and performance of the billet by applying greater pressure during continuous casting. This pressure-based technology utilizes the large deformation reduction applied at the end of solidification in the continuous casting machine, fully leveraging the temperature difference in billet thickness to achieve efficient transfer of reduction to the core. This significantly improves problems such as segregation, porosity, and shrinkage cavities in the billet, and enhances its density and chemical composition uniformity.

[0029] 3. Electroslag remelting:

[0030] A Si-Al-Ca ternary slag system is used, with a slag formation time of 75-100 minutes. Argon gas is started 30-40 minutes in advance, and argon gas protection is maintained throughout the process. The inner cavity of the crystallizer is cubic with a thickness of 450-800 mm. The cooling water flow rate of the crystallizer is 35-50 m³ / h. 3 / h; Compensation time ≥3h, slow cooling time 36~72h.

[0031] Electroslag remelting (ESR) has shown significant effectiveness in reducing alloy segregation in steel plates, improving corrosion resistance, and enhancing the core mechanical properties of extra-thick steel plates. By utilizing protective slag, argon protection, and deoxidizers, it can precisely control the chemical composition, inhibit the intrusion of harmful gases, and reduce alloy oxidation. This process's precise and uniform control of alloy composition effectively reduces the internal alloy potential difference in the steel plate, enhances its corrosion resistance, and further optimizes the core mechanical properties of extra-thick steel plates.

[0032] 4. Two-stage controlled rolling:

[0033] The billet is placed in the heating furnace at 600~700℃ and held for 60~75 minutes. The heating temperature is 1150~1250℃, and the holding time after reaching the temperature is 60~90 minutes.

[0034] The purpose of ensuring the heating and holding time is to allow the core of the thick billet to reach the target temperature. Avoiding excessively high heating temperatures and controlling the heating and holding time aims to prevent abnormal growth of the billet structure, which could affect the core strength and low-temperature toughness of the rolled steel plate.

[0035] The first-stage rolling temperature is 1140~1220℃, and the total deformation in the first stage is ≥55%. The intermediate billet cooling rate is 5~8℃ / s, the second-stage initial rolling temperature is 770~830℃, the reduction in the last three passes is ≥10mm, and the final rolling temperature is 700~750℃.

[0036] The purpose of two-stage controlled rolling is to maximize the reduction rate per pass under relatively low hardness conditions at high temperatures, further break up the as-cast grains, increase the deformation energy storage and grain nucleation sites in the billet, and improve the low-temperature toughness of the core of extra-thick plates. During low-temperature controlled rolling, the transformation of austenite to bainite is inhibited or delayed due to the lower temperature, thus avoiding the increase in strength but decrease in low-temperature toughness caused by the high-temperature transformation of austenite to bainite.

[0037] 5. Tempering:

[0038] Tempering temperature is 420~500℃, and tempering time is 3~4.5min / mm. The purpose of tempering heat treatment is to ensure that the steel plate has a uniform and fine precipitate structure through reasonable temperature and time settings, thereby improving the low-temperature toughness of the steel plate. At the same time, the tempering homogenization of the steel microstructure and the elimination of internal stress can also greatly improve the corrosion resistance of the steel plate in marine environments.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. This invention employs a composition design combining elements such as C, Mn, Ni, Cu, Co, and Sn, with microalloying elements such as V and Ti. Adding Mn improves the strength, wear resistance, and hot workability of the steel plate, and also increases the heat transfer capacity of extra-thick steel plates. Adding Ni and Cu strengthens ferrite and refines and increases pearlite, improving the steel's strength. Large additions result in a lower ductile-brittle transition temperature, improving the low-temperature toughness of the steel plate, refining ferrite grains, and preventing intergranular corrosion. Adding Co provides significant solid solution strengthening, increasing the strength and hardness of the steel plate. Adding Sn improves the steel's strength and corrosion resistance, and enhances its processing and welding properties. V is a crucial additive element in this invention; V forms fine compounds with C and N, increasing the strength and hardness of the steel plate, effectively inhibiting the recrystallization of deformed austenite, refining grains, and improving the steel's fatigue resistance. Simultaneously, V promotes the formation of a passivation film, slowing down the oxidation reaction on the steel surface and enhancing its corrosion resistance.

[0041] 2. The purpose of this invention in employing heavy pressure reduction in the casting machine is to improve the quality and performance of the cast billet by applying greater pressure during the continuous casting process. This heavy pressure reduction technology utilizes the temperature difference in billet thickness by applying large deformation reduction at the solidification end of the continuous casting machine, achieving efficient transfer of reduction to the core. This significantly improves problems such as segregation, porosity, and shrinkage cavities in the cast billet, and enhances its density and uniform chemical composition.

[0042] 3. This invention employs an electroslag remelting process, which achieves significant results in reducing alloy segregation in steel plates, improving corrosion resistance, and enhancing the core mechanical properties of extra-thick steel plates. By utilizing protective slag, argon protection, and deoxidizers, the chemical composition can be precisely controlled, inhibiting the intrusion of harmful gases and reducing alloy oxidation. This process's precise and uniform control of alloy composition effectively reduces the internal alloy potential difference in the steel plate, enhances its corrosion resistance, and further optimizes the core mechanical properties of extra-thick steel plates.

[0043] 4. This invention employs a two-stage controlled rolling process. The purpose of this process is to maximize the reduction rate per pass under relatively low hardness conditions in high-temperature steel plates, further breaking down as-cast grains, increasing the deformation energy storage of the billet and the number of grain nucleation sites, and improving the low-temperature toughness of the core of extra-thick plates. During the low-temperature controlled rolling process, the transformation of austenite to bainite is inhibited or delayed due to the lower temperature, thus avoiding the reduction in low-temperature toughness caused by the transformation of austenite to bainite under high-temperature conditions.

[0044] 5. The present invention employs tempering heat treatment. The purpose of tempering heat treatment is to ensure that the steel plate has a uniform and fine precipitated phase structure through reasonable temperature and time settings, thereby improving the low-temperature toughness of the steel plate. At the same time, the tempering homogenizes the microstructure of the steel and eliminates internal stress, thereby improving the corrosion resistance of the steel plate in the marine environment.

[0045] In summary, this invention utilizes a compositional design combining C, Mn, Ni, Cu, Co, Sn elements and microalloying phases such as V and Ti, along with continuous casting, electroslag remelting, two-stage rolling, and tempering processes, to develop ultra-high-strength EH40 marine steel with a maximum thickness of 100 mm. While maintaining the high strength, high toughness, and excellent weldability of EH40 grade steel, its corrosion resistance in tropical marine climates is significantly improved.

[0046] The steel plate of this invention has a yield strength ≥400MPa, a tensile strength of 600~680MPa, a transverse elongation ≥26%, a Charpy impact energy of the steel plate core at 20℃ ≥200J, and a Charpy impact energy of the steel plate core at -40℃ ≥200J. The steel plate's seawater corrosion resistance rate is less than 40% of that of conventional 40MPa grade marine engineering steel, and its marine atmospheric corrosion resistance rate is less than 50% of that of conventional 40MPa grade marine engineering steel. Attached Figure Description

[0047] Figure 1 This is a metallographic diagram of Embodiment 1 of the present invention. Detailed Implementation

[0048] This invention discloses an EH40 extra-thick marine steel resistant to tropical marine climate corrosion 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 clearly modify or appropriately change and combine 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.

[0049] The chemical composition of the steel in the embodiments of the present invention is shown in Table 1; the continuous casting and electroslag remelting process in the embodiments of the present invention is shown in Table 2; the rolling and tempering process in the embodiments of the present invention is shown in Table 3; the mechanical properties of the steel plate in the embodiments of the present invention are shown in Table 4; and the corrosion resistance of the embodiments of the present invention and the comparative examples to marine environments is shown in Table 5.

[0050] Table 1. Chemical composition (wt%) of steel in the embodiments of the present invention

[0051]

[0052] Table 2 Continuous casting and electroslag remelting processes in embodiments of the present invention

[0053]

[0054] Table 3 Rolling and tempering processes in embodiments of the present invention

[0055]

[0056] Table 4 Mechanical properties of steel plates in embodiments of the present invention

[0057]

[0058] Table 5. Resistance to marine corrosion in the embodiments and comparative examples of the present invention

[0059]

[0060] Note: The full immersion test reference standard JBT 7901, and the salt spray test reference standard GBT 10125. The comparison steel composition is 0.06C-0.3Si-1.50Mn-0.3Ni-0.2Cr-0.02Nb-0.02V-0.01Ti.

[0061] like Figure 1 As shown, the metallographic structure of Example 1 has 30%~40% polygonal ferrite and 60%~70% acicular ferrite at 1 / 2 thickness of the steel plate, with a grain size of 10~12 and good mechanical properties.

[0062] As shown in Table 5, this invention is an extra-thick EH40 marine engineering steel resistant to tropical marine climate corrosion. The finished steel plate thickness can reach 100mm, with a yield strength ≥400MPa, tensile strength 600~680MPa, transverse elongation ≥26%, Charpy impact energy of the steel plate core at 20℃ ≥200J, and Charpy impact energy of the steel plate core at -40℃ ≥200J. The seawater corrosion resistance rate of the steel plate is less than 40% of that of conventional 40MPa grade marine engineering steel, and the marine atmospheric corrosion resistance rate is less than 50% of that of conventional 40MPa grade marine engineering steel. This invention significantly improves its corrosion resistance in tropical marine climates while maintaining the high strength, high toughness, and excellent weldability of EH40 grade steel.

[0063] 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. An EH40 extra-thick marine steel resistant to tropical marine climate corrosion, characterized in that, It is composed of the following chemical components in weight percentage: C: 0.065%~0.08%, Si: 0.15%~0.3%, Mn: 1.5%~1.7%, P≤0.02%, S≤0.01%, Als: 0.015%~0.03%, Ni: 0.4%~0.8%, Cu: 0.1%~0.2%, Co: 0.1%~0.15%, Sn: 0.05%~0.15%, V: 0.01%~0.03%, Ti: 0.01%~0.015%, N: 0.002%~0.004%, with the remainder being Fe and unavoidable impurities.

2. The EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 1, characterized in that, The maximum thickness of the finished steel plate is 100mm, with a yield strength ≥420MPa, tensile strength 600~680MPa, transverse elongation ≥26%, Charpy impact energy of the steel plate core at 20℃ ≥200J, and Charpy impact energy of the steel plate core at -40℃ ≥200J.

3. The EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 1, characterized in that, The microstructure at 1 / 2 thickness of the steel plate consists of 30%~40% polygonal ferrite and 60%~70% acicular ferrite, with a grain size of 10~12.

4. A method for manufacturing EH40 extra-thick marine steel resistant to tropical marine climate corrosion as described in any one of claims 1 to 3, characterized in that, The manufacturing method specifically includes the following steps: 1) Steel refining; 2) Continuous casting: The entire casting process is protected, the molten steel is superheated by 3~10℃, and the total reduction under the heavy pressure of the casting machine is ≥8mm; 3) Electroslag remelting: The Si-Al-Ca ternary slag system is adopted, the slag formation time is 75~100min, argon gas is turned on 30~40min in advance, and argon gas is used for protection throughout the process; The crystallizer's inner cavity is cubic with a thickness of 450-800 mm; the crystallizer's cooling water flow rate is 35-50 m³ / h. 3 / h; 4) Two-stage controlled rolling: The first-stage rolling temperature is 1140~1220℃; The intermediate billet cooling rate is 5~8℃ / s, the second-stage rolling temperature is 770~830℃, and the final rolling temperature is 700~750℃. 5) Tempering: Tempering temperature 420~500℃, tempering time 3~4.5min / mm.

5. The method for manufacturing EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 4, characterized in that, In step 1), molten steel is refined through a converter, LF furnace, RH or VD furnace.

6. The method for manufacturing EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 4, characterized in that, 2) In the continuous casting billet, the proportion of equiaxed crystals in the core is ≥90%, and the center segregation rating is ≤C1.

0.

7. The method for manufacturing EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 4, characterized in that, 3) The compensation time is ≥3h, and the slow cooling time is 36~72h.

8. The method for manufacturing EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 4, characterized in that, 4) The billet is loaded into the heating furnace at 600~700℃ and held for 60~75 minutes. The heating temperature is 1150~1250℃ and held for 60~90 minutes after reaching the temperature.

9. The method for manufacturing EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 4, characterized in that, 4) In the first stage, the total deformation is ≥55%.

10. The method for manufacturing EH40 extra-thick marine steel resistant to tropical marine climate corrosion according to claim 4, characterized in that, 4) In the second stage, the reduction amount of the last three passes is ≥10mm.

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